About this Author
College chemistry, 1983
The 2002 Model
After 10 years of blogging. . .
Derek Lowe, an Arkansan by birth, got his BA from Hendrix College and his PhD in organic chemistry from Duke before spending time in Germany on a Humboldt Fellowship on his post-doc. He's worked for several major pharmaceutical companies since 1989 on drug discovery projects against schizophrenia, Alzheimer's, diabetes, osteoporosis and other diseases.
To contact Derek email him directly: firstname.lastname@example.org
May 5, 2014
Anti-aging studies, when they make the news, fall into three unequal categories. There's a vast pile of quackery, which mercifully isn't (for the most part) newsworthy. There are studies whose conclusions are misinterpreted by some reporters, or overblown by one party or another. And there's a small cohort of really interesting stuff.
Yesterday's news in the field very much looks like it belongs in that last set. Two papers (here and here) came out early in Science that result from long-running research programs on what happens when young mice and old mice have their circulatory systems joined together, coming from the labs of Amy Wagers and Richard Lee at Brigham and Women's Hospital in Boston, and Lee Rubin's group at Harvard. Wagers herself started on this work as a postdoc at Stanford almost fifteen years ago, and she clearly hit on a project with some real staying power. A third new paper in Nature Medicine, from Tony Wyss-Coray's group at Stanford, also bears on the same topic (see below).
The aged rodents seem to benefit from exposure to substances in the youthful blood, and one of these seems to be a protein called GDF11. Wagers and Lee had already reported that administering this protein alone can ameliorate age-related changes in rodent heart muscle, and these latest papers extend the effects to skeletal muscle (both baseline performance and recovery from injury) and to brain function (specifically olfactory sensing and processing, which mice put a lot of effort into).
So the natural thought is to give aging humans the homolog of GDF11 and see what happens, and it wouldn't surprise me if someone in Boston ponies up the money to try it. You might need a lot of protein, though, and there's no telling how often you'd need infusions of it, but to roll back aging people would presumably put up with quite a bit of inconvenience. Another approach, which is also being pursued, is the dig-into-the-biology route, in an attempt to figure out what GDF11's signaling pathways are and which ones are important for the anti-aging effects. That's when the medicinal chemists will look up from the bench, because there might be some small-molecule targets in there.
That's going to be a long process, though, most likely. GDF11 seems to have a lot of different functions. Interestingly, it's actually known as an inhibitor of neurogenesis, which might be a quick illustration of how much we don't know about it and its roles. It would seem very worthwhile to try to sort these things out, but there are a lot of worthwhile biochemical pathways whose sorting-out is taking a while.
The Wyss-Coray paper goes in the other direction, though. Building on earlier work of their own, they've seen beneficial effects on the hippocampus of older mice after the circulatory connection with younger animals, but were able to reproduce a fair amount of that by just injecting younger blood plasma itself. This makes you wonder if the "teenage transfusion" route might a much more simple way to go - simple enough, in fact, that I'm willing to put down money on the possibility of some experimentally-minded older types trying it out on their own very shortly. Wyss-Coray is apparently planning a clinical trial as we speak, having formed a company called Alkahest for just that purpose. Since blood plasma is given uncounted thousands of times a day in every medical center in the country, this route should have a pretty easy time of it from the FDA. But I'd guess that Alkahest is still going to have to identify specific aging-related disease states for its trials, because aging, just by itself, has no regulatory framework for treatment, since it's not considered a disease per se. The FDA has consistently avoided going into making-normal-people-better territory, not that I can blame them, but they may not be able to dodge the question forever. At least, I hope they won't be able to. You also have to wonder what something like this would do to the current model of blood donation and banking, if it turns out that plasma from an 18-year-old is worth a great deal more than plasma from a fifty-year-old. I hope that the folks at the Red Cross are keeping up with the literature.
Irreverent aside: (Countess Báthory, an apparent pioneer in this field whose dosing protocols were suboptimal, does not seem to be cited in any of the press reports I've seen. Not sure about her publication record, though - maybe she's hard to reference from the primary literature.
+ TrackBacks (0) | Category: Aging and Lifespan | Biological News
March 14, 2014
If you haven't seen it, the Sinclair group and numerous co-workers at the NIH and elsewhere now report that the SIRT1 activator SRT1720 extends the lifespan of mice on a diet of normal chow, and they see a number of good metabolic indicators - increase fat oxidation, decrease fat mass, increased insulin sensitivity, and so on.
There are several things to note about this effect, though. The mice were started on the compound at six months of age, and the compound was supplemented in chow to a dose of 100 mpk, which was maintained from there on out. (I don't have any allometric tables to hand,
but it's safe to say that this would translate to a daily multigram dose in humans Absolutely wrong: it's about 8.8 mpk, a 600mg dose or so. Good thing I'm not a clinician). The lifespan extension was mean lifespan (up 8.8%) - they saw a trend towards extended median lifespan, but it didn't reach significance. (That sounds, at first, like there were some long-lived responders in the treatment group). There was no difference in 90th-percentile survival, which as the authors note, is consistent with the idea of the compound delaying age-related illness. There was also a high-fat-fed group of mice, supplemented in the same fashion, and consistent with earlier reports, these had their mean lifespan extended over 20%.
Blood markers of liver and kidney function seemed to hold up fine. Other than less steatitis (fatty tissue inflammation) in the liver, histology didn't appear to show any major changes (good or bad) in the treated mice compared to controls, especially considering that the treated mice were older when assayed. Gross pathology was also the same, which is worth noting because SIRT1 pathways have been implicated in slowing down some cancer phenotypes but speeding up others. Getting down to DNA microarrays, the most altered genes were found in liver and muscle tissue, and were associated with lower levels of inflammation.
This paper is not going to clear up the sirtuin controversies, but it is interesting and worthwhile. 100mpk, q.d. for life, is a hard and heavy dose, though, and if SRT1720 really is an efficacious sirtuin activator (a point subject to plenty of disagreement in the literature), then it's worth wondering if the pathway is really within range of therapeutic effects in humans. Resveratrol has been studied in a human trial, but resveratrol is polypharmacologic, to the point that in vivo data with it are probably only capable of telling us about the effects of resveratrol itself.
A couple of the authors on this new paper have their affiliations listed as "Sirtris, a GSK company", but there's no such thing any more. When last heard from, GSK was continuing sirtuin work on its own, but if there have been any notable announcements from them, I've missed them. What a selective SIRT1 activator does, long-term in normal humans, no one yet knows. Will anyone, ever?
+ TrackBacks (0) | Category: Aging and Lifespan
January 13, 2014
Here's a paper from a few weeks back that I missed during the holidays: work from the Sinclair labs at Harvard showing a new connection between SIRT1 and aging, this time through a mechanism that no one had appreciated. I'll appreciate, in turn, that that opening sentence is likely to divide its readers into those who will read on and those who will see the words "SIRT1" or "Sinclair" and immediate seek their entertainment elsewhere. I feel for you, but this does look like an interesting paper, and it'll be worthwhile to see what comes of it.
Here's the Harvard press release, which is fairly detailed, in case you don't have access to Cell. The mechanism they're proposing is that as NAD+ levels decline with age, this affects SIRT1 function to the point that it no longer constains HIF-1. Higher levels of HIF-1, in turn, disrupt pathways between the nucleus and the mitochondia, leading to lower levels of mitochondria-derived proteins, impaired energy generation, and cellular signs of aging.
Very interestingly, these effects were reversed (on a cellular/biomarker level) by one-week treatment of aging mice with NMN (nicotine mononucleotide edit: fixed typo), a precursor to NAD. That's kind of a brute-force approach to the problem, but a team from Washington U. recently showed extremely similar effects in aging diabetic rodents supplemented with NMN, done for exactly the same NAD-deficiency reasons. I would guess that the NMN is flying off the shelves down at the supplement stores, although personally I'll wait for some more in vivo work before I start taking it with my orange juice in the mornings.
Now, whatever you think of sirtuins (and of Sinclair's work with them), this work is definitely not crazy talk. Mitochondria function has long been a good place to look for cellular-level aging, and HIF-1 is an interesting connection as well. As many readers will know, that acronym stands for "hypoxia inducible factor" - the protein was originally seen to be upregulated when cells were put under low-oxygen stress. It's a key regulatory switch for a number of metabolic pathways under those conditions, but there's no obvious reason for it to be getting more active just because you're getting older. Some readers may have encountered it as an oncology target - there are a number of tumors that show abnormal HIF activity. That makes sense, on two levels - the interiors of solid tumors are notoriously oxygen-poor, so that would at least be understandable, but switching on HIF under normal conditions is also bad news. It promotes glycolysis as a metabolic pathway, and stimulates growth factors for angiogenesis. Both of those are fine responses for a normal cell that needs more oxygen, but they're also the behavior of a cancer cell showing unrestrained growth. (And those cells have their tradeoffs, too, such as a possible switch between metastasis and angiogenesis, which might also have a role for HIF).
There's long been speculation about a tradeoff between aging and cellular prevention of carcinogenicity. In this case, though, we might have a mechanism where our interests on on the same side: overactive HIF (under non-hypoxic conditions) might be a feature of both cancer cells and "normally" aging ones. I put that word in quotes because (as an arrogant upstart human) I'm not yet prepared to grant that the processes of aging that we undergo are the ones that we have to undergo. My guess is that there's been very little selection pressure on lifespan, and that what we've been dealt is the usual evolutionary hand of cards: it's a system that works well enough to perpetuate the species and beyond that who cares?
Well, we care. Biochemistry is a wonderful, heartbreakingly intricate system whose details we've nowhere near unraveled, and we often mess it up when we try to do anything to it, anyway. But part of what makes us human is the desire (and now the ability) to mess around with things like this when we think we can benefit. Not looking at the mechanisms of aging seems to me like not looking at the mechanisms of, say, diabetes, or like letting yourself die of a bacterial infection when you could take an antibiotic. Just how arrogant that attitude is, I'm not sure yet. I think we'll eventually get the chance to find out. All this recent NAD work suggests that we might get that chance sooner than later. Me, I'm 51. Speed the plow.
+ TrackBacks (0) | Category: Aging and Lifespan | Biological News | Diabetes and Obesity
September 20, 2013
If you haven't heard that Google is now funding research into human aging and lifespan, they'll be very disappointed. There's been plenty of publicity, which I find sort of interesting, considering that there's not too much to announce:
The Time article—and a Google blog post released at the same time—provided scant detail about what the new company, called Calico, will actually do. According to Time, the company, to be based somewhere in the Bay Area, will place long-term bets on unspecified technologies that could help fight the diseases of aging.
Page did tell Time he thinks biomedical researchers may have focused on the wrong problems and that health-care companies don’t think long-term enough. “In some industries it takes 10 or 20 years to go from an idea to something being real. Health care is certainly one of those areas,” Page told Time. “We should shoot for the things that are really, really important, so 10 or 20 years from now we have those things done.”
The company’s initial investors are Google and Arthur Levinson, also chairman of Apple’s board and that of biotech company Genentech. Levinson, a trained biochemist, will be the CEO of Calico, which the The New York Times reported is short for California Life Company.
I'm fine with this. Actually, I'm more than fine - I think it's a good idea, and I also think that it's a good idea for the money coming into it to be long-term, patient money, because it's going to have to be. I think that human life span can probably be extended, although no one's ready to say if that's going to mean thirty extra years of being 40, or thirty extra years of being 90. If you know what Trimalchio says about seeing the Cumaean Sybil in the Satyricon, you'll have come across the problem before. (Trimalchio's an unlikely fount of wisdom, but he seems pretty much on target with that one).
Patience will be needed on several fronts. Biochemically, there are actually a number of ideas to follow up on, and while that's good news in general, it also means that there's a lot of work ahead. Not all of these are going to actually extend lifespan, I think it's safe to say, and sorting them out will be a real job. But that's the sort of problem that a lot of therapeutic areas have. Aging research has several others piled on top of it.
One of them it shares with areas like diabetes and cardiovascular disease: you're looking for a drug or therapy that the patient will be taking for the rest of their lives - their extended lives, if all goes well - so toxicology becomes a huge concern. Tiny safety concerns can become big ones over the decades. And that leads into another big issue, the regulatory one. How would one set up a clinical trial for an anti-aging therapy? How long would it run? How long would you have to work with the FDA to get something together? Keep in mind that the agency doesn't have any framework for making people better than normal. You'll note that despite the possible lifespan enhancement with the sirtuin compounds, GSK never really mentioned this possibility in their takeover of Sirtris. It was all about diabetes and other conditions that have defined clinical endpoints and a regulatory environment already in place.
The answer to that problem, then, is surely to pick some disease of aging and see if you can ameliorate it by attacking the aging process in general. It's a bit like a second derivative: in other therapeutic areas, you pick a biomarker, and you try to get approval based on an effect against it as a surrogate for the long-term benefits against the actual disease. In this case, though, you'd pick an actual medical condition, and hope to get approval using it as a surrogate against the meta-disease of aging itself. Those will not be short trials, nor easy to run, nor will it be easy to obtain statistical significance in them.
And I don't think we'll be seeing one of those for quite some time. Larry Page himself is 40, I believe, so if he's looking for a benefit that he might realize, he's almost certainly out of luck. As am I at 51. Page's ten or twenty year timeline seems very short indeed. If I find a wonder drug in my lab this afternoon, it won't be hitting the pharmacy shelves for about fifteen years itself. I hope I'm wrong about this, but I doubt if anything will be worked out enough to try before either of us are much further into old age, at which point you start to run into that Cumaean Sibyl problem. Unless, of course, you are fortunate enough to come up with something that actually turns the clock back a bit, but that's much less likely. Just slowing it down is enough of a feat already. I realize that this is more of my patented brand of "pessimistic optimism", but I can't make myself come up with any other opinion yet.
I thought seriously about titling this post "Gegen Den Tod Ist Kein Kräutlein Gewachsen", but I figured that would drive my traffic into the basement. That is, I'm told, one of the mottos of the old German herbalists, translating as "Against death does no simple grow". It's safe to assume, though, that anything that really does usefully treat aging will not be simple, so the Germans are probably still in the right.
Update: a reader has sent along more information on that quotation. It actually goes back to Latin (cue various readers holding their heads and moaning). It goes ". . .contra vim mortis non est medicamen in hortis", and is part of the declamations that are more or less Quintilian's work on Roman court cases and rhetoric (thus often ascribed to "pseudo-Quintilian").
+ TrackBacks (0) | Category: Aging and Lifespan
August 29, 2013
As someone who will not be seeing the age of 50 again, I find a good deal of hope in a study out this week from Eric Kandel and co-workers at Columbia. In Science Translational Medicine, they report results from a gene expression study in human brain samples. Looking at the dentate gyrus region of the hippocampus, long known to be crucial in memory formation and retrieval, they found several proteins to have differential expression in younger tissue samples versus older ones. Both sets were from otherwise healthy individuals - no Alzheimer's, for example.
RbAp48 (also known as RBBP4 and NURF55), a protein involved in histone deacetylation and chromatin remodeling, stood out in particular. It was markedly decreased in the samples from older patients, and the same pattern was seen for the homologous mouse protein. Going into mice as a model system, the paper shows that knocking down the protein in younger mice causes them to show memory problems similar to elderly ones (object recognition tests and the good old Morris water maze), while overexpressing it in the older animals brings their performance back to the younger levels. Overall, it's a pretty convincing piece of work.
It should set off a lot of study of the pathways the protein's involved in. My hope is that there's a small-molecule opportunity in there, but it's too early to say. Since it's involved with histone coding, it could well be that this protein has downstream effects on the expression of others that turn out to be crucial players (but whose absolute expression levels weren't changed enough to be picked up in the primary study). Trying to find out what RbAp48 is doing will keep everyone busy, as will the question of how (and/or why) it declines with age. Right now, I think the whole area is wide open.
It is good to hear, though, that age-related memory problems may not be inevitable, and may well be reversible. My own memory seems to be doing well - everyone who knows me well seems convinced that my brain is stuffed full of junk, which detritus gets dragged out into the sunlight with alarming frequency and speed. But, like anyone else, I do get stuck on odd bits of knowledge that I think I should be able to call up quickly, but can't. I wonder if I'm as quick as I was when I was on Jeopardy almost twenty years ago, for example?
(If you don't have access to the journal, here's the news writeup from Science, and here's Sharon Begley at Bloomberg).
+ TrackBacks (0) | Category: Aging and Lifespan | The Central Nervous System
July 26, 2013
A few years ago, there came the interesting news that rapamycin looked as if it prolonged lifespan in mice. That result is robust; it's been replicated. Now a large multicenter effort in Germany has looked closely at this effect, and they have many more details about what's going on.
The big question is: does rapamycin extend lifespan through some general effect on aging, or does it work through a non-aging mechanism (by perhaps suppressing tumor formation)? Now, many people wouldn't find that much of a distinction - would you like a drug that makes you age more slowly, or would you like one that keeps you from getting cancer? The answer would probably be "Yes". But it's a question that very much matters biochemically.
And it turns out that it's the latter. This new paper does a very careful examination of many phenotypes of aging, on both whole-animal and tissue levels, and finds that rapamycin treatment does not really seem to affect age-related changes. What changes they did see on rapamycin treatment were also present in young mice as well as older ones, making them less likely to be an underlying cause of the effect. They now believe that the compound's effect on lifespan is entirely, or almost entirely, due to the lower rate of fatal neoplasms.
+ TrackBacks (0) | Category: Aging and Lifespan
July 23, 2013
I've been meaning to blog about this new paper in PLOS Biology on resveratrol's effects on mitochondria. It's suggesting that the results previously reported in this area cannot be reproduced, namely the idea that resveratrol increases mitochondrial biogenesis and running endurance. In fact, says this new paper, the whole mechanistic story advanced in this field (resveratrol activates SIRT1, which activates the coactivator PGC1, which cranks up the mitochondria) is wrong. SIRT1 has, they say, the opposite effect: it decreases PGC1 activity, and downregulates mitochondria.
That's an interesting dispute, and leads to all kinds of questions about who's wrong (because someone certainly appears to be). But there's another issue peculiar to this new paper. It now says that there are no reader comments, but for a couple of days there was one, which went into detail about how various Western blots appeared to have been performed sloppily and with confusing control lanes. I have no idea how well substantiated these objections were, and I have no idea why they have disappeared from the paper. It's all quite peculiar.
+ TrackBacks (0) | Category: Aging and Lifespan
April 24, 2013
The University of Chicago Press has sent along a copy of a new book by DePaul professor Ted Anton, The Longevity Seekers. It's a history of the last thirty years or so of advances in understanding the biochemical pathways of aging. As you'd imagine, much of it focuses on sirtuins, but many other discoveries get put into context as well. There are also thoughts on what this whole story tells us about medical research, the uses of model animal systems, about the public's reaction to new discoveries, and what would happen if (or when) someone actually succeeds in lengthening human lifespan. (That last part is an under-thought topic among people doing research in the field, in my experience, at least in print).
Readers will be interested to note that Anton uses posts and comments on this blog as source material in some places, when he talks about the reaction in the scientific community to various twists and turns in the story. (You'll be relieved to hear that he's also directly interviewed almost all the major players in the field, as well!) If you're looking for a guide to how the longevity field got to where it is today and how everything fits together so far, this should get you up to speed.
+ TrackBacks (0) | Category: Aging and Lifespan | Book Recommendations
April 9, 2013
And since that last post was about sirtuins, here's a new paper in press at J. Med. Chem. from the Sirtris folks (or the Sirtris folks that were, depending on who's making the move down to PA). They report a number of potent new sirtuin inhibitor compounds, which certainly do look drug-like, and there are several X-ray structures of them bound to SIRT3. It seems that they're mostly SIRT1/2/3 pan-inhibitors; if they have selective compounds, they're not publishing on them yet.
I should also note, after this morning's post, that the activities of these compounds were characterized by a modified mass spec assay! I would expect sirtuin researchers in other labs to gladly take up some of these compounds for their own uses. . .
Note: I should make it clear that these are more compounds produced via the DNA-encoded library technology. Note that these are yet another chemotype from this work.
+ TrackBacks (0) | Category: Aging and Lifespan | Chemical News
March 12, 2013
I've been meaning to write on this paper, from David Sinclair and co-workers, on the mechanism of resveratrol action. The backstory is so long and convoluted that you're going to have to set aside some time to catch up if you're just joining it (paging back through this category archive will give you some play-by-play). But the basics are that resveratrol came on the scene as an activator of the enzyme SIRT1, which connection was later called into question by work that showed a lot of artifacts in the assay conditions used to establish it.
This new paper may well clear some of that up. The fluorescent tagged peptides that were producing the false positive may well be mimicking the natural protein partners, if this analysis is correct. SIRT1, as it turns out, recognizes a hydrophobic domain in the same region of each, which can be the fluorescent tag, or native hydrophobic amino acids themselves.
So it appears that resveratrol (and other synthetic sirtuin activators) are acting allosterically on the protein. This work found a single SIRT1 amino acid mutant (E230K) that doesn't affect SIRT1's catalytic activity, but does completely mess with resveratrol's ability to activate it (the other compounds in this class show the same effect). That makes for a neat story, and it would resolve several questions about the molecular mechanism of action.
But it leaves open the bigger questions: is SIRT1 a human drug target? Do activators exert beneficial effects, and do different ones have different profiles in living systems? There's already plenty of evidence for some of these; the problem is, the evidence points both ways (much of this is summed up and linked to in this post). Resveratrol itself is not, I would say, an appropriate molecule to answer the detailed questions (other than "What does effects does resveratrol itself have?"). It does not have particularly good pharmacokinetic properties, for one thing, and it is known to hit a lot of other things besides SIRT1 (Sinclair himself has referred to it as a "dirty molecule", and I agree).
So it's the follow-on sitruin activators that GSK has that are the real vehicles for answering these very interesting (and potentially important, and potentially lucrative) questions. A quick look at Clinicaltrials.gov shows that work has been done on SRT2104 and SRT2379, but many of these studies have been complete for a year or two now. (Here's the one that's listed as ongoing - it and several others have an anti-inflammatory bent). All we can deduce is that at least two SRT compounds are being (or recently have been) evaluated in the clinic. Fierce Biotech has a bit more from Sirtris CEO George Vlasuk:
About those clinical trials: GSK's massive investment in Sirtris has yet to lead to a drug or a prime-time drug candidate. Sirtris has ended clinical development of multiple synthetic compounds after initial human studies, Vlasuk said. And his team is hunting for the precise mechanism for activating SIRT1 in hopes of creating more potent compounds than resveratrol to treat diseases.
Hmm. I thought that maybe this new Science paper was the precise mechanism. But maybe not? The story continues. . .
+ TrackBacks (0) | Category: Aging and Lifespan
August 29, 2012
Nature is out today with a paper on the results of a calorie-restriction study that began in 1987. This one took place with rhesus monkeys at the National Institute of Aging, and I'll skip right to the big result: no increase in life span.
That's in contrast to a study from 2009 (also in rhesus) that did see an extension - but as this New York Times article details, there are a number of differences between the two studies that confound interpretation. For one thing, a number of monkeys that died in the Wisconsin study were not included in the results, since it was determined that they did not die of age-related causes. The chow mixtures were slightly different, as were the monkeys' genetic background. And a big difference is that the Wisconsin control animals were fed ad libitum, while the NIA animal were controlled to a "normal" level of calorie intake (and were smaller than the Wisconsin controls in the end).
Taken together with this study in mice, which found great variation in response to caloric restriction depending on the strain of mouse used, it seems clear that this is not one of those simple stories. It also complicates a great deal the attempts to link the effect of various small molecules to putative caloric restriction pathways. I used to think that caloric restriction was the bedrock result of the whole aging-and-lifespan research world - so now what? More complications, is what. Some organisms, under some conditions, do seem to show longevity effects. But unraveling what's going on is just getting trickier and trickier as time goes on.
I wanted to take a moment as well to highlight something that caught my eye in the Times article linked above. Here:
. . .Lab test results showed lower levels of cholesterol and blood sugar in the male monkeys that started eating 30 percent fewer calories in old age, but not in the females. Males and females that started dieting when they were old had lower levels of triglycerides, which are linked to heart disease risk. Monkeys put on the diet when they were young or middle-aged did not get the same benefits, though they had less cancer. But the bottom line was that the monkeys that ate less did not live any longer than those that ate normally. . .
Note that line about "benefits". The problem is, as far as I can see (Nature's site is down as I write), the two groups of monkeys appear to have shown the same broad trends in cardiovascular disease. And cardiovascular outcomes are supposed to be the benefits of better triglyceride numbers, aren't they? You don't just lower them to lower them, you lower them to see better health. More on this as I get a chance to see the whole paper. . .
+ TrackBacks (0) | Category: Aging and Lifespan | Cardiovascular Disease | Diabetes and Obesity
June 28, 2012
You'll remember the life-extending fullerenes paper that I blogged about here, and the various problems with it that sharp-eyed readers here spotted. (These drew comments from the lead author here and here). Now the journal has issued a correction that covers some of these issues, along with the following Editor's Note:
It should be noted that one of these errors, referring to the inadvertent duplication of the same image within two panels of Fig 4, was pointed out to the Editor-in-Chief by several readers. The authors contacted the Editor-in-Chief with an explanation of this error and an error in Figure 3 before he requested an explanation from the authors. This paper draws conclusions that appear counter-intuitive. The Editor-in-Chief received two very detailed reports from referees who indicated that the methodology appeared sound and they both recommended acceptance after some revision. Neither referee nor the Editor-in-Chief noticed either error, and the revised paper was published. Due consideration has been given to the potential effect of these errors on the overall results and conclusions drawn, and so it has been decided the conclusions are still valid. The authors have provided explanations of how the errors were made during the preparation of graphics and images.
The big questions remain - can these results be duplicated, and is anyone willing to try?
+ TrackBacks (0) | Category: Aging and Lifespan
May 9, 2012
I've received another e-mail from Prof. Fathi Moussa, lead author of the C60 longevity paper that's been discussed around here. I'd sent a list of the critiques that had shown up in the comments sections, and here's the reply:
An erratum with the right figures 3 and 4 will be published soon in Biomaterials. The right lifespan values after the beginning of the treatment are given in the original text without any change. To sum it up, the extensions of lifespans are twenty months and sixteen months with respect to water-treated controls and olive-oil-treated controls, respectively.
Our original objective was not to study lifespan extension but the toxic effects of C60 at reiterated doses. Lifespan extension by C60 is not really surprising, all the more so as it had already been shown by others that some C60-derivatives can prolong lifespans in several experimental models, albeit moderately.
What is really surprising in our results is that C60 acts at very low doses, which means that the effect is very strong, and that this effect lasts for a long time after the end of the administration. A possible explanation is that some C60 precipitated inside the reticulo-endothelial system and then slowly dissolves and diffuses.
Of course we understand that non C60 specialist readers are incredulous about these results, as it could be expected.
We hope now that others will try and confirm our results. If our results are confirmed by others, which we firmly believe, it will be then necessary to try to reproduce these experiments on bigger samples including other species and of course to optimize the dose and the duration of the treatment.
I share that hope that others will try to confirm the results. It'll be a while, most likely, before we hear about anything in this area, but when something comes up, I'll blog about it.
+ TrackBacks (0) | Category: Aging and Lifespan
May 8, 2012
I've received a reply from Dr. Fathi Moussa at Université Paris-Sud, lead author of the C60 longevity paper that I blogged about here, which turned out to have a duplicated figure. With permission, here are the main points of the e-mail:
Of course, you are right: in the published figure 4 the GAog and GAip panels are identical. These two panels were meant to represent the well-known effect of intra-peritoneally (i.p.) administered CCl4 on rat livers. The mistake was obviously due to the fact that the pretreatment of control animals with water either orally (GAog) or i.p. (GAip) cannot influence the effects of CCl4 on livers. Therefore the effects on liver are identical and the corresponding figures are expected to be closely alike. Anyway we sent to the Editor an erratum that will be published soon.
We are very grateful to you for warning us about this figure. We are very furious against ourselves. We still do not understand how such error could have escaped our notice during the revision process. While this mistake has not any influence on the validity of the results described in the text, this could raise a certain amount of doubt over the work. The extension of the lifespan of rats is real and we fear that our error could delay or even prevent control experiments we are expecting to be made by others.
We have published on C60 toxicity since 1995 and all our results have been confirmed by several independent teams. . .
That point in the second paragraph is an important one: if these results are real, they're quite important and interesting. But, as with any other scientific result, they won't be accepted as real until they've been replicated, and replicating this experiment is already a substantial undertaking. The mistake with the figures doesn't help to get these started. (I should note that I've also called the authors' attention to the other points raised here in the comments).
My hope is that other groups studying longevity effects in rodents (and having already made the commitment that entails) will be able to add a C60 arm to their experiments as a comparison.
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May 2, 2012
There's a new paper out in Cell Metabolism on resveratrol and SIRT1, and the press release from Elsevier (Cell Press) is just a tiny bit optimistic. "Study resolves controversy on life-extending red wine ingredient, restores hope for anti-aging pill", says the headline, but believe me, no one paper is going to do that. (This entry has links back to some of the history of the compound and the target, as covered here, but it's a convoluted story indeed). The EmbargoWatch web site calls it a "truly appalling" press release, and while I can't disagree with that, I don't think it particularly stands out: a lot of press releases are appalling.
And I disagree with them when they say that studies like this "probably don't deserve any coverage at all". It's actually a very interesting paper, even if it's not going to resolve any major controversies all by itself. It's from David Sinclair and co-workers (a large international team), and it presents the results of a long-running effort to see if what resveratrol does in animals that don't have the SIRT1 protein at all. That's a good experiment, which cuts right to the question of whether resveratrol's effects are SIRT1-driven or not. Problem is, the traditional knockout mouse model is almost always embryonic lethal in that case, so it's not so simple that generate such animals. The team was able to develop inducible whole-body conditional knockout adult mice, though, and set about dosing them with resveratrol to see what happened then.
Well, quite a few things did. From what I can see, the marquee items are these: normal mice fed a high-fat regimen showed beneficial effects on their mitochondria when given resveratrol, but the knockouts didn't, so that might be a clear connection to SIRT1. Resveratrol's effects on AMPK appear to be SIRT1-dependent (there are several links in this post about that connection, some of which led to papers that hypothesized a SIRT1-independent effect). But resveratrol treatment had good effects on glucose levels in mice, whether or not they had SIRT1 present, so that part seems to be going through some other pathway.
Sinclair's quoted in this Nature News piece as saying that this reflects the nature of resveratrol as a compound. “Resveratrol is a dirty, dirty molecule, very non-specific", he says. I think that's a very fair characterization, which is one of the reasons why I wouldn't take it myself. (That does shed an interesting light on the 2010 controversy when two former Sirtris executives set up their own reveratrol distribution effort, though, doesn't it?)
It would be quite interesting, for the sheer science of it, to take one of the later (apparently cleaner and more targeted) SIRT1 activating compounds that have come out of the GSK/Sirtris work and run it through the same animal model. You might expect the same sorts of SIRT1-driven effects, and perhaps much less of an effect on blood glucose, if that's really some off-target resveratrol thing. But since we're talking about epigenetic enzymes here, prediction is a chancy business. I wonder if this experiment is being done somewhere?
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April 20, 2012
We have a problem here. The paper I blogged about yesterday, on life extension effects with C60 fullerene ("buckyballs") has a duplicated figure. This was first spotted by commenter "Flatland" yesterday. I was traveling all day, and when I came home in the evening I saw the comment and immediately realized that he was right. I've made the animation below (via Picasion) to illustrate the point:
These are from the part of the paper where they showed protective effects of C60 on animals that were being dosed with (toxic) carbon tetrachloride, and these are supposed to be the water/carbon tet control animal dosed by oral gavage (GAog) and by intraperitoneal injection (GAip). In other words, these are supposed to be separate animals, but as you can see, these are, in fact, the exact same histology slide. I've scaled the GAip image up about 120% and moved the two to correct the offset, but otherwise, I've done no image processing at all. The originals are screen shots from the PDF of the paper, the top two images of Figure 4.
This is, at the very least, very sloppy work, on both the part of the authors and the editorial staff at Biomaterials. I didn't catch this one myself, true - but I wasn't asked to review the paper, either, and I can assure you that I spend more time critically studying the figures in a paper under review than one I'm writing a quick blog entry about. Under normal reading conditions, most of us don't look at histology slides in a paper while constantly asking ourselves "Is this right? Or is this just a duplicate of another image that's supposed to be something else?"
And while this image duplication does not directly bear on the most surprising and interesting results of the paper - life extension in rodents - it does not inspire confidence in those results, either. I'm emailing the editorial staff at Biomaterials and the corresponding author of the paper with this blog entry. We'll see what happens.
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April 18, 2012
I'm really, really not sure what to make of this paper (PDF). It's from a team that was studying the long-term toxicology of C60 (fullerene, "buckyballs") by giving them to rats as a solution in olive oil. The control groups were water and olive oil without C60. The compound has already been shown to have no noticeable short-term toxic effects, so they probably didn't expect anything dramatic in the lower-dose long-term mode.
Wrong. What they found was that the fullerene/olive oil group had their life spans extended by some 90%, which would make this mixture perhaps the most efficacious life-extended treatment ever seen in a rodent model. This is a very odd and interesting result.
There's nothing bizarre about the pharmacokinetics, anyway. A reasonable amount of the C60 is absorbed after an oral dose (they did both oral gavage and intraperitoneal dosing), with a time course consistent with the very high lipophilicity of the compound. Distribution is still being worked out, but a lot of any given dose ends up in the liver and spleen (although it doesn't accumulate with successive q.d. dosing), with detectable amounts even crossing the blood-brain barrier. It has a long half life, consistent with enterohepatic recirculation and elimination through the bile (no C60 was found in the urine).
The most likely mechanism for the life-extension effects is through oxidative stress and free radical scavenging. There have been several reports of C60 as an antioxidant, although there have also been reports that it can be cytotoxic via lipid peroxidation. (One difference was that that report was with aggregates of C60 in water, versus soluble C60 in oil, but there are other reports that hydrated C60 does the opposite: there's clearly a lot that hasn't been cleared up here). In this study, even at very low doses, C60 appears to protect rodents against carbon tetrachloride-induced liver damage, for example, which is known to involve a radical process. Significantly, it does so while showing protection against glutathione depletion, which also suggests that it's directly scavenging reactive intermediates.
These are reasonable (but unproven) hypotheses, and I very much look forward to seeing this work followed up to see some more light shed on them. The whole life-extension result needs to be confirmed as well, and in other species. I congratulate the authors of this work, though, for giving me the most number of raised eyebrows I've had while reading a scientific paper in quite some time.
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April 9, 2012
I've written many times here about sirtuins, and their most famous associated small molecule, resveratrol. And I've been asked more than once by people outside the med-chem field if I take (or would take) resveratrol, given the available evidence. My reply has been the same for several years: no, not yet.
Why so cautious, for a compound that's found in red grapes and other foods, and to which I've presumably been exposed many times? Several reasons - I'll lay them out and let readers decide how valid they are and how they'd weight these factors themselves.
First off, we can dispose of the "it's in food already, and it's natural, so why worry?" line of thinking. Strychnine is all-natural too, as are any number of other hideous molecules that are capable of terrible effects, so that's no defense at all - it never is. And as for being exposed to it already, that's true - but the dose makes the poison, and the dose makes the drug. I've no idea how much resveratrol I've ingested over the years, but it's safe to say that it's been in small amounts and at irregular intervals. Going from that to regular higher dosages is worth some forethought.
So what do we know about what resveratrol does? A lot, and not nearly enough. Its pharmacology is very complex indeed, and the one thing that you can clearly draw from the (large) scientific literature is that its (a) a very biochemically active compound and (b) we haven't figured out many of those actions yet. Not even close. Even if all it did was act as on one or more sirtuins, that would be enough to tell us that we didn't understand it.
That's because the sirtuins, along with many other enzymes, are involved in epigenetic signaling, a catch-all term for everything in the DNA-to-RNA-to-protein sequence that doesn't depend on just the DNA sequence itself. (And as everyone discovered when the number of human genes came in on the low end of the low estimates, these processes are very important indeed). There are a lot of mechanisms, and it's safe to say that we haven't found them all, either, but the sirtuins modify histones, the proteins that DNA is wrapped around, and thus affect how genes are transcribed. All these transcriptional processes are wildly complex, with hundreds and thousands of genes being up- (and down-) regulated in different tissues, at different times, under different conditions. Anyone that tells you that we're close to unraveling those balls of yarn is not keeping up with the literature, or not understanding what they read.
Of course, one of the controversies about resveratrol (and some of the other sirtuin modulators) is whether they act directly on these enzymes or not. Opinion is very much divided on that, but resveratrol seems to have a number of other effects, mediated through processes that (again!) are best described as "unclear". For example, its metabolic effects seem to be at least partially driven by its actions on an enzyme called AMPK, a key enzyme in a number (brace yourself) of important cellular processes. It might well be that AMPK (activated by resveratrol) is what's having an effect on the sirtuins. A very recent paper implicates another step in the process: resveratrol may well be acting on a set of phosphodiesterase (PDE) enzymes, which affect AMPK, which affect sirtuins. But then again, there's another paper from earlier this year that suggests that resveratrol's activity against sphingosine kinase might be the key. So your guess is as good as mine.
One objection to all this is that there's room to wonder about the mechanisms of a number of drugs. Indeed, there have been many that have made it to market (and stayed there for many years) without anyone knowing their mechanisms at all. We're still finding things out about aspirin; how much can one expect? Well, one response to that is that aspirin has been used widely in the human population for quite a long time now, and resveratrol hasn't. So the question is, what do we know about what resveratrol actually does in living creatures? If it has beneficial effects, why not go ahead and take advantage of them?
Unfortunately, the situation is wildly confusing (for an overview, see here). The first thing that brought resveratrol into the spotlight was life extension in animal models, so you'd think that that would be well worked out by now, but boy, would you be wrong. The confusion extends up to mouse models, where some of the conclusions - all from respectable groups in respectable publications - seem to flatly contradict each other. No, the animal-model work on resveratrol is such a bubbling swamp that I don't see how anyone can safely draw conclusions from it.
How about people, then? There have been some clinical trials reported, with this one the most recent, and these are summed up in this open-access paper. The longest reported trials are on the order of weeks, which is useful, but not necessarily indicative of what might happen out in the real world. But there have been some beneficial metabolic effects seen (although not in all trials), and these constitute some of the biggest arguments for taking resveratrol at all.
One of the things that seems to be possible, from both the animal and human studies, is that the compound might exert these beneficial effects mostly in systems that are already under metabolic stress. Does this translate to people as well? If you're healthy already, which does resveratrol do for (or to) you? No one knows yet, and no one knows how much resveratrol you'd have to take to see things happen. Here's another article (PDF) summarizing the known effects, and here's the way the authors sum up:
"It is no exaggeration to say that the literature on resveratrol is contradictory and confusing. The wide range of concentrations and doses used to achieve the various effects reported for resveratrol in both in vitro cell culture and animal studies raises many questions about the concentrations achievable in vivo. . .
The bottom line? Resveratrol is a very interesting compound, and potentially useful. But the details of its actions aren't clear, and neither, honestly, are the actions themselves. Given the importance of the processes we're talking about - cellular metabolism, which is intimately involved with aging and lifespan, which is intimately involved with defenses against cancer - I don't feel that the situation is clear enough yet to make an intelligent decision. So no, I don't take resveratrol. But I'd be willing to if the fog ever clears.
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January 16, 2012
I'm getting all the press releases from Bill Sardi, of Resveratrol Partners, as he does damage control from the Das scandal at UConn. And I have to say, he's putting in the hours getting these together. Problem is, on some key points, he doesn't know what his biggest problems are.
The latest one is titled "World Without Resveratrol: Researcher Falsely Accused", and claims that this may all be a plan to "send a message" to any academic who collaborates with the makers of resveratrol pills. The release goes on about how these are old accusations, which Das has refuted since then, and asks why these ancient concerns are coming up now, eh? The phrase "orchestrated hit job" is used. But that glosses over the times of the whole investigation, which has been a very detailed and involved one, and glosses over the amount of due process involved as well. There are a lot of problems with the publications from the Das lab, as detailed in the report that I linked to the other day, and tying them together has involved a lot of work.
But here comes my favorite part of the latest Sardi release:
". . .I asked Dr. Das directly, did he altered (sic) western blot images, or directed others in his lab to do so. While his initial answer was no, meaning he had not fabricated or altered any scientific finding, altering western blot images are a common practice in laboratories for reasons other than deception. The university chose to present their findings in a derogatory manner. Dr. Das explains that editors at scientific publications commonly request researchers enhance faded images of western blot tests so they can be duplicated in their publications. Western blot tests are frequently altered to remove backgrounds, enhance contrast and increase dots-per-inch resolution so they are suitable for publication. This had been fully explained to university officials long before. . .
No, no, no. The problems with the Das papers have nothing to do with enhancing the contrast on Western blots. They have to do with cutting and pasting sections of them, rearranging them, reusing them, and creating them out of pieces of other experiments. Look at that report. These people appear to have spent a ridiculous amount of time assembling "Western blots" out of miscellaneous digitized chunks. The resulting figures purport, in many cases, to represent particular experiments, but they do no such thing. They represent a bunch of previous bands from other experiments entirely, sliced and diced in a way that would seem to have no other possible motive than to deceive. Come on.
Oh, but there's more. Here, according to the press release, is how a cutting-edge academic lab works these days:
"As I drilled Dr. Das’ former students with questions, I found that lead researchers like Dr. Das do not do any lab bench experiments. Students do all the work and submit their results to him via e-mail or by directly downloading data into his computer. Dr. Das says when he is not traveling his office is open and students can enter and download data directly onto his computer. I had previously visited Dr. Das at the University of Connecticut and noticed his office door was left open and anyone could have access to his computer.
One former student told me that typically lead researchers like Dr. Das write the introduction and conclusion of experiments and the students enter all the data, before publication in scientific journals. Dr. Das, who is busy lecturing all over the globe because of his groundbreaking studies, does not directly oversee tests that are performed, and neither do most other lead researchers. The University of Connecticut report says the university holds Dr. Das responsible for all of the data. Probably most lead researchers in scientific laboratories around the globe are vulnerable to errors or even fabrication of data by their students."
Where to start? What the heck is this "download data directly into his computer" stuff? And what about all the doctored files found on other machines in the group? And yes, while lead authors are indeed vulnerable to errors and fabrication, this sort of thing typically does not involved years of work spread out across dozens of papers in multiple journals. Even the busiest and most distracted principal investigator might be expected to take the time to notice, eventually, that his group's work is a tower of fraud. And yes, the University should hold Dr. Das responsible for the data in his papers. His name is on the grants, his name is on the office door, he's the one with a high-paying tenured position while the students are cranking away under low salaries and stipends, and it's his name with an asterisk next to it on all those papers, as the contact person for any questions about them. Damn right he's responsible. He's responsible for making sure that anything going out into the literature with his name on it is something that he can stand behind.
Ah, but not to worry. It's all being taken care of:
"Dr. Das says many editors at scientific journals don’t believe the University of Connecticut report. They full-well know that editing of western blot tests is common practice and that the tests in question in no way invalidate his work and were only one part of the evidence provided in his papers from which Dr. Das drew conclusions. This is the case of scientific fraud that wasn’t."
That would explain why Dr. Das has been pulled from the co-editor job he had at one of those journals. They must believe him. And that would also shore up all those allegations of prejudice against East Indian researchers, since the editor of that journal is. . .well, he's Indian too, but you know what I mean. (Personally, if I were from India myself, I'd be furious at Das for helping to drag the reputation of my country's scientists through the mudhole, but maybe that's just me.)
No, I hope these press releases keep on coming. So far, we have lots of elaborate reasons why Dr. Das had nothing to do with all these fabricated Western blots, but who cares, right, since they're only a tiny part of his papers, which are great and important work even though he really doesn't write them anyway, and no, he has almost no connection with Longevinex and Resveratrol Partners, which is why the head of the company is spending all this time defending him in this case of minor stuff he never did, all 600 pages of summary and 60,000 pages of investigation material, and that explains why the journals that believe him are ditching him from their mastheads and publishing retractions of those great papers. Because it's all a conspiracy. Yeah. That's it.
+ TrackBacks (0) | Category: Aging and Lifespan | The Dark Side | The Scientific Literature
January 12, 2012
My inbox has exploded with the story that many reports on the effects of resveratrol appear to be fraudulent. Prof. Dipak Das of Connecticut is at the center of what looks like a huge research stink bomb, which is being well covered by Retraction Watch (here and here), among others. The Chronicle of Higher Education has a lot of good info as well.
Here's what's known so far: UConn has a press release saying that Das has been under investigation for the last three years, and that the university (along with the Office of Research Integrity) has uncovered substantial evidence of fraud and misconduct.
An extensive research misconduct investigation has led the University of Connecticut Health Center to send letters of notification to 11 scientific journals that had published studies conducted by a member of its faculty. Dipak K. Das, Ph.D., a professor in the Department of Surgery and director of the Cardiovascular Research Center, was at the center of a far reaching, three-year investigation process that examined more than seven years of activity in Das’ lab. . .
. . .The investigation was sparked by an anonymous allegation of research irregularities in 2008. The comprehensive report, which totals approximately 60,000 pages, concludes that Das is guilty of 145 counts of fabrication and falsification of data. Inquiries are currently underway involving former members of Das’ lab; no findings have been issued to date.
Here are the details, in a long PDF, if you want them. What that report shows are a lot of manipulated Western blots, with obvious copy-and-paste artifacts. Well, they're obvious once you're alerted to them, at any rate - the first thing you think of when you see a gel isn't "Hmmm. . .I wonder if that's been Photoshopped?" At any rate, examination of presentation slides on various hard drives also showed Westerns with various regions - in some cases, every single damn band on the whole thing - which had been moved around with the "Group" and "Ungroup" tools, starting from separate unrelated files. And they've even tracked down the original images which formed the basis for the figures in so many other papers, once they'd been sliced and diced. Classy stuff. Dr. Das, for his part, told the investigators that he had no idea who had prepared any of these figures, a position that (since he's the lead flippin' author on them), strains belief. "Dr. Das has been of no help in this matter", states the report, and I'd say that still overstates his contributions.
UConn has notified the editors of 11 journals where Das and his group had published suspect results - and on three of these journals, according to Retraction Watch, he had editorial or advisory responsibilities. Looking over the list, it's not exactly the most high-profile publication record that you could imagine. Das's papers do seem to have picked up a number of citations, in many cases, but I don't really get the sense that he was driving the field. (That Chronicle link above quotes David Sinclair, of sirtuin fame, as saying that he'd never even heard of Das at all, and for what it's worth, I hadn't either).
Meanwhile, Retraction Watch has received a press release from Das' lawyer, and it looks like he's not going down without firing all his ammo. To wit, Das claims that:
. . .the charges against him involve prejudice within the university against Indian researchers. Six other East Indian researchers were also named as “potential respondents” to charges of scientific fraud, but no researchers of other ethnicities. . .
. . .Another party, a university internal investigator whom Dr. Das accuses of long-standing prejudice against foreign-born researchers, reportedly broke the lock on Dr. Das’ office door, removed computer files and personal items such as bank records and a passport, and could have manipulated data in his computer files. Dr. Das says this university investigator has had a long-standing vendetta against him going back to 1984. . .
There's a lot more in the same vein (and great big steaming heaps of it in Das' official response to the investigation) and it all points to a long, ugly process. The lawyers involved will have plenty to keep themselves occupied.
There's one last big issue: Das appears to have had a business relationship with Longevinex, a well-known supplier of resveratrol supplements. I note that Bill Sardi, the managing partner of the firm that runs Longevinex, has showed up on this site in the comments section before, as have many fans of the product itself. (I know that David Sinclair has heard of those guys, because they were throwing around his name for a while, which seems to have led to talk of possible legal action). And it's worth noting as well that Dr. Das had published work suggesting that Longevinex was superior to garden-variety resveratrol. That paper (and that journal) does not appear to be one of the ones named specifically in the fraud investigation. But one of the authors on it (other than Das) figures prominently in the UConn report. Who feels inclined to trust it?
Now for the last big issue: what does this do to the whole resveratrol/sirtuin field? Not as much as you might think. As mentioned above, Das really doesn't seem to have been that big a figure in it, despite cranking out the publications, and a lot of interesting (although often confusing) work has come from a variety of other labs. The people who did this study in humans, for example, are (to the best of my knowledge) above reproach. But (as that post shows in its various links), there's a lot of conflicting data about resveratrol in animal models. The whole topic is deeply confusing. But this UConn/Das business does not help clear anything up, not at all - it's a big bucket of mud and slop dumped into the tank, which is just what we didn't need.
And as for sirtuins, well, I don't think anyone would disagree with the statement I made here, that resveratrol has so many off-target effects that it's completely unsuitable as a tool to understand sirtuin biology, which is quite difficult enough to understand already, thanks very much. Sirtuins have their own wild complications and (seeming) contradictions, separate from resveratrol - this latest scandal is off to the side of that topic completely, or should be.
But I don't mean to minimize Das' apparent misconduct here, not at all. He's not at the center of his field, but he looks to be at or near the center of something very dishonorable, very dishonest, and very wrong.
+ TrackBacks (0) | Category: Aging and Lifespan | The Dark Side
December 13, 2011
Science has a long article detailing the problems that have developed over the last few years in the whole siturin story. That's a process that I've been following here as well (scrolling through this category archive will give you the tale), but this is a different, more personality-driven take. The mess is big enough to warrant a long look, that 's for sure:
". . .The result is mass confusion over who's right and who's wrong, and a high-stakes effort to protect reputations, research money, and one of the premier theories in the biology of aging. It's also a story of science gone sour: Several principals have dug in their heels, declined to communicate, and bitterly derided one another. . ."
As the article shows, one of the problems is that many of the players in this drama came out of the same lab (Leonard Guarente's at MIT), so there are issues even beyond the usual ones. Mentioned near the end of the article is the part of the story that I've spent more time on here, the founding of Sirtris and its acquisition by GlaxoSmithKline. It's safe to say that the jury is still out on that one - from all that anyone can tell from outside, it could still work out as a big diabetes/metabolism/oncology success story, or it could turn out to have been a costly (and arguably preventable) mistake. There are a lot of very strongly held opinions on both sides.
Overall, since I've been following this field from the beginning, I find the whole thing a good example of how tough it is to make real progress in fundamental biology. Here you have something that is (or at the very least has appeared to be) very interesting and important, studied by some very hard-working and intelligent people all over the world for years now, with expenditure of huge amounts of time, effort, and money. And just look at it. The questions of what sirtuins do, how they do it, and whether they can be the basis of therapies for human disease - and which diseases - are all still the subject of heated argument. Layers upon layers of difficulty and complexity get peeled back, but the onion looks to be as big as it ever was.
I'm going to relate this to my post the other day about the engineer's approach to biology. This sort of tangle, which differs only in degree and not in kind from many others in the field, illustrates better than anything else how far away we are from formalism. Find some people who are eager to apply modern engineering techniques to medical research, and ask them to take a crack at the sirtuins. Or the nuclear receptors. Or autoimmune disease, or schizophrenia therapies. Turn 'em loose on one of those problems, come back in a year, and see what color their remaining hair is.
+ TrackBacks (0) | Category: Aging and Lifespan | Drug Development | Drug Industry History
November 10, 2011
The effects of resveratrol have been controversial, to say the least. Arguments rage about whether (and how) it affects the various sirtuin pathways, what those various sirtuin pathways are and what they do, and what the compound does in animal models at all (whether you care about the mechanism or not). That last topic recently boiled over once more. I've spoken about the compound and these issues many, many times around here, as long-time readers will know - go here and just keep scrolling back if you're interested. GSK halted its development of resveratrol itself (as opposed to follow-up ligands) last year, it appears.
Get ready for more head-scratching. There's a new paper out from researchers in the Netherlands and Switizerland looking at the effects of resveratrol in obese human subjects. They ran a small (11-subject) double-blind crossover trial vs. placebo of 150mg of resveratrol per day, and found. . .well, let me quote the summary, because I can't put it in fewer words myself. If you're not a technical kind of person, that last line (emphasis added) tells the story:
Resveratrol significantly reduced sleeping and resting metabolic rate. In muscle, resveratrol activated AMPK, increased SIRT1 and PGC-1α protein levels, increased citrate synthase activity without change in mitochondrial content, and improved muscle mitochondrial respiration on a fatty acid-derived substrate. Furthermore, resveratrol elevated intramyocellular lipid levels and decreased intrahepatic lipid content, circulating glucose, triglycerides, alanine-aminotransferase, and inflammation markers. Systolic blood pressure dropped and HOMA index improved after resveratrol. In the postprandial state, adipose tissue lipolysis and plasma fatty acid and glycerol decreased. In conclusion, we demonstrate that 30 days of resveratrol supplementation induces metabolic changes in obese humans, mimicking the effects of calorie restriction.
Well, that is interesting. What this (and some of the earlier data) seems to be telling us is that resveratrol may well be beneficial - but particularly so under conditions of metabolic stress, such as in obesity. As for the mechanism, when they looked at muscle tissue samples, they found over 400 genes with altered expression (some up, some down). These seem to have particularly concentrated in metabolic and inflammation pathways, particularly mitochondrial oxidative phosphorylation. These are quite similar results to those seen in obese rodents.
On the other hand, some things were very different indeed in the two species. Mice actually showed an increase in energy expenditure during reservatrol treatment - these humans showed a decrease. The plasma concentration reached in both experiments were similar, but mice needed a 200-fold higher dose of resveratrol to reach that, which has to be one confounding factor. (Another is the duration of treatment; the mice got the compound for several months, which is longer by the calendar but also a much higher percentage of their entire lives).
Still, the effects in the human subjects were quite impressive. Not all the changes were huge, but they all seem to point in the same direction: mimicking the effects of caloric restriction and exercise. This is exactly the sort of thorough, well-controlled study this field has been needing, and it makes all the questions in it take on that much more urgency. What does resveratrol do in humans, on a molecular level? Are sirtuins involved, and to what extent? Can other compounds do the same thing, or even more? What are the long-term effects of such compounds on human morbidity and mortality? Do these effects only manifest themselves in obese subjects? How much would happen in people who are under less metabolic stress to start with? And so on. . .
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September 22, 2011
As promised, today we have a look at a possible bombshell in longevity research and sirtuins. Again. This field is going to make a pretty interesting book at some point, but it's one that I'd wait a while to start writing, because the dust is hanging around pretty thickly.
Some background: in 1999, Sir2 the Guarente lab at MIT reported that Sir2 was a longevity gene in yeast. In 2001, theyextended Sir2 these results to C. elegans nematodes, lengthening their lifespan between 15 and 50% by overexpressing the gene. And in 2004, Stephen Helfand's lab at Brown reported similar results in Drosophila fruit flies. Since then, the sirtuin field has been the subject of more publications than anyone would care to count. The sirtuins are involved, it turns out, in regulating histone acetylation, which regulates gene expression, so there aren't many possible effects they might have that you can rule out. Like many longevity-associated pathways, they seem to be tied up somehow with energy homeostasis and response to nutrients, and one of the main hypotheses has been that they're somehow involved in the (by now irrefutable) life-extending effects of caloric restriction.
As an aside, you may have noticed that almost every news about something that extends life gets tied to caloric restriction somehow. There are two good reasons for that - one is, as stated, that a lot of longevity seems - reasonably enough - to be linked to metabolism, and the other one is that caloric restriction is by far the most solid of all the longevity effects that can be shown in animal models.
I'd say that the whole sirtuin story has split into two huge arguments: (1) arguments about the sirtuin genes and enzymes themselves, and (2) arguments about the compounds used to investigate them, starting with resveratrol and going through the various sirtuin activators reported by Sirtris, both before and after their (costly) acquisition by GlaxoSmithKline. That division gets a bit blurry, since it's often those compounds that have been used to try to unravel the roles of the sirtuin enzymes, but there are ways to separate the controversies.
I've followed the twists and turns of argument #2, and it has had plenty of those. It's not safe to summarize, but if I had to, I'd say that the closest thing to a current consensus is that (1) resveratrol is a completely unsuitable molecule as an example of a clean sirtuin activator, (2) the earlier literature on sirtuin activation assays is now superseded, because of some fundamental problems with the assay techniques, and (3) agreement has not been reached on what compounds are suitable sirtuin activators, and what their effects are in vivo. It's a mess, in other words.
But what about argument #1, the more fundamental one about what sirtuins are in the first place? That's what these latest results address, and boy, do they ever not clear things up. There has been persistent talk in the field that the original model-organism life extension effects were difficult to reproduce, and now two groups (those of David Gems and Linda Partridge) at University College, London (whose labs I most likely walked past last week) have re-examined these. They find, on close inspection, that they cannot reproduce them. The effects in the LG100 strain of C. elegans appear to be due to another background mutation in the dyf family, which is also known to have effects on lifespan. Another mutant strain, NL3909, shows a similar problem: its lifespan decreases on outcrossing, although the Sir2 levels remain high. A third long-lived strain, DR1786, has a duplicated section of its genome that includes Sir2, but knocking that down with RNA interference has no effect on its lifespan. Taken together, the authors say, the correlation of Sir2 with lifespan in nematodes appears to be an artifact.
How about the fruit flies? This latest paper reproduces the lifespan effects, but finds that they seem to be due to the expression system that was used to increase dSir2 levels. When the same system is used to overexpress other genes, lifespan is also increased. They then used another expression vector to crank up the fly Sir2 by over 300%, but those flies did not show an extension in lifespan, even under a range of different feeding conditions. They also went the other way, examining mutants with their sirtuin expression knocked down by a deletion in the gene. Those flies show no different response to caloric restriction, indicating that Sir2 isn't part of that effect, either - in direct contrast to the effects reported in 2004 by Helfand.
It's important to keep in mind that these aren't the first results of this kind. Others had reported problems with sirtuin effects on lifespan (or sirtuin ties to caloric restriction effects) in yeast, and as mentioned, this had been the stuff of talk in the field for some time. But now it's all out on the table, a direct challenge.
So how are the original authors taking it? Guarente, who to his credit has been right out in the spotlight throughout the whole story, has a new paper of his own, published alongside the UCL results. They partially agree, saying that there does indeed appear to be an unlinked mutation in the LG100 strain that's affecting lifespan. But they disagree that sirtuin overexpression has no effect. Instead of their earlier figure of 15 to 50%, they're claiming a 10 to 14% - not as dramatic, for sure, but the key part for the argument is that it's not zero.
And as for the fruit flies, Hefland at Brown is pointing out that in 2009, his group reported a totally different expression system to increase dSir2, which also showed longevity effects (see their Figure 2 in that link). This work, he's noting, is not cited in the new UCL paper, and from his tone in interviews, he's not too happy about that. That's leading to coverage from the "scientific feud!" angle - and it's not that I think that's inaccurate, but it's not the most important part of the story. (Another story with follow-up quotes is here).
So what are the most important parts? I'd nominate these:
1. Are sirtuins involved in lifespan extension, or not? And by that, I mean not only in model organisms, but are they subject to pharmacological intervention in the field of human aging?
2. What are the other effects of sirtuins, outside of aging? Diabetes, cancer, several other important areas touch on this whole metabolic regulation question: what are the effects of sirtuins in these?
3. What is the state of our suite of tools to answer these questions? Resveratrol may or may not do interesting things in humans or other organisms, but it's not a suitable tool compound to unravel the basic mechanisms. Do we have such compounds, from the reported Sirtris chemical matter or from other sources? And on the biology side, how useful are the reported overexpression and deletion strains of the various model organisms, and how confident are we about drawing conclusions from their behavior?
4. Getting more specific to drug discovery, are sirtuin regulator compounds drug candidates or not? Given the disarray in the basic biology, they're at the very least quite speculative. GlaxoSmithKline is the company most immediately concerned with this question, since they spent over $700 million to buy Sirtris, and have been spending money in the clinic ever since evaluating their more advanced chemical matter. And that brings up the last question. . .
5. What does GSK think of that deal now? Did they jump into an area of speculative biology too quickly? Or did they make a bold deal that put them out ahead in an important field?
I do not, of course, have answers to any of these. But the fact that we're still asking these questions ten years after the sirtuin story started tells you that this is both an important and interesting area, and a tricky one to understand.
+ TrackBacks (0) | Category: Aging and Lifespan | Biological News
September 21, 2011
This will be the subject of a longer post tomorrow, but I wanted to alert people to some breaking news in the sirtuin/longevity saga. It now appears that the original 2001 report of longevity effects of Sir2 in the C. elegans model, which was the starting gun of the whole story, is largely incorrect. That would help to explain the conflicting results in this area, wouldn't it? Topics for discussion in tomorrow's post will include, but not be limited to: what else do sirtuins do? Are those results reproducible? What can we now expect to come out of pharma research in the field? And what does GSK now think about its investment in Sirtris?
+ TrackBacks (0) | Category: Aging and Lifespan | Biological News
August 23, 2011
Readers of this blog will be fairly familiar with the long, interesting story of sirtuin activators. Today we will speak of SRT1720, of which we have spoken before. This molecule was described in 2007 as an activator of Sirt1 with beneficial effects in rodent models of diabetes. But both of those statements were called into question by a series of papers which found difficulties with both the in vitro and the in vivo results (summarized here). The GSK/Sirtris team fired back, but that paper also served as a white flag on the in vitro assay questions: there were indeed artifacts due to the fluorescent peptides used. (Another paper has since confirmed these problems and proposed an off-target mechanism).
But that GSK response didn't address the in vivo assay questions at all - we still had a situation where one group said that these compounds (SRT1720 in particular) were beneficial, and another said that it showed no benefit and was toxic at higher doses. Adding to the controversy, another paper appeared late last year that went back to nematodes, and found the SRT1720 did not extend their lives, either. The state of this field can be fairly described, then, as "extremely confused".
Now we have a new paper whose title gets right down to it: "SRT1720 improves survival and healthspan of obese mice". First time I've seen "healthspan" as a word, I might add, and another interesting sidelight is that this appears in Nature Scientific Reports, the publishing group's open-access experiment. But now to the data:
What this (large) team did was place one-year-old male mice on a high-fat diet in the presence of two different doses of SRT1720 in the chow, corresponding to 30 mg/kilo and 100mg/kilo. The effects on lifespan were notable: standard-diet animals had a median lifespan of 125 weeks, and that was shortened to 94 weeks on the high fat diet. But on that diet plus the lower dose of SRT1720, the median lifespan was 103 weeks, and on the higher dose it was 115 weeks. It's interesting, though, that this took place while the animals ate the same number of calories and gained the same amount of (extra) weight as the control group.
Blood work and histopathology revealed many more differences. The high-fat animals (with no SRT1720) showed the expected problems that you see in such studies - fat accumulation in the liver, increased numbers of beta-cells in the pancreas, higher insulin levels, and so on. But the SRT1720-dosed animals showed a good deal of reversal of all these effects. DIgging down to the molecular level, inflammatory markers, indicators of apoptosis and DNA fragmentation were increased in the high-fat animals, and these were also mitigated by SRT1720.
There are many other effects mentioned in the paper, but I'm not going to go into all the details - hey, it's open-access, so if you're really into this stuff you can find it all. Suffice it to say that a long list of deleterious effects of a high-fat diet on rodents seem to be partially to fully reversed on treatment with SRT1720, particularly at the higher dose, without significant evidence of toxicity. But how do we reconcile that with the report that the compound showed no benefit, and toxic effects to boot? I'll let the authors tackle that one:
Our results continue to support the beneficial pharmacological effect of SRT1720 in models of metabolic disease despite a recent report by Pacholec and colleagues to the contrary14 where the authors report 100 mg/kg SRT1720 is not tolerable and increases mortality in mice and that the compound does not elicit beneficial effects in the Lep ob/ob mouse model of diabetes. This conclusion is inconsistent with not only our findings but also several additional studies where SRT1720 has been reported to exert positive effects in multiple models of metabolic disease including Lep ob/ob mice, diet-induced obese mice, MSG-induced hypothalamic obese mice15 and Zucker fa/fa rats. Pacholec and colleagues did report that fasting insulin levels are reduced by SRT1720 administration, which is in agreement with our findings (Fig. 2) and with data reported previously in diet-induced obese mice. The putative toxicity of SRT1720 administered at a 100 mg/kg oral dose to 8 mice over 18 days is inconsistent with a study where the compound exhibited no toxicity at a 5-fold higher dose for 15 weeks12 nor is it consistent with our long-term feeding study involving over 100 mice consuming an equivalent daily dose. In fact, our mice showed increased survival and improvement in multiple physiological parameters in response to SRT1720 treatment and did not display overt signs of toxicity even after more than 80 weeks of treatment.
So yes, there's pretty much a flat contradiction here, and I have no idea of how to resolve it. This paper doesn't reference the failure of SRT1720 to show effects in nematodes, but that's another piece of the puzzle that can't be ignored, either. One possibility is that the doses of the compound need to be rather heroic. Believe me, by the usual pharmacological standards, extended dosing at 100 mpk is pretty heavy-duty (and, I might add, basically unattainable in humans under normal conditions, especially humans on a high-fat diet).
So for now, I have to throw up my hands. This latest paper seems very thorough, and represents a really significant effort on the part of a long list of highly competent people. But there can be no doubt that the SRT1720 story (and the story of sirtuin activators in general) is still very complex and hard to evaluate, because the various problems and complications that have been found can't be dismissed, either. There's something here, all right, and it could well be very important. But what are we looking at?
Side note: this work was the subject of a writeup by Nicholas Wade in the New York Times the other day. It reveals that there's another arm of this study - normal mice, on normal chow, also treated with SRT1720. Those results, out next year, will be very interesting indeed, although I can only think that they're just going to keep the fires burning. I'd also like to note (as one comment on this blog did) the tone of most of the online comments on the Times story. They can, I think, be summed up as "Great, the big evil drug companies have found something so people can just stay big and fat and not die early, and they're going to sell it to us for a zillion dollars while their corporate masters stay thin and healthy and laugh at us all". Read through a few of them and see if I haven't captured their general spirit - and think for a bit about what that tells us, both about the public perception of drug research and (perhaps) about the sort of people who leave comments over at the Times.
+ TrackBacks (0) | Category: Aging and Lifespan | Diabetes and Obesity
August 15, 2011
Caloric restriction increases healthy lifespan. That's true in a range of organisms, and probably in humans. But it's never going to be popular - and what's more, it's not going to be feasible, either, given how clearly people like to eat. So the search has been on for just how it exerts its effects, with a number of interesting clues turning up.
And now there's another one. There's a longevity gene in fruit flies known as INDY (short for, I fear, "I'm Not Dead Yet", and if you don't get that reference, you should probably turn in your geek license. This would be a good time to note, as required by law, that the fruit fly people are a longstanding and apparently endless fountain of weird nomenclature). Reducing INDY expression definitely lengthens lifespan in flies and in the nematode C. elegan.
A recent paper in Cell Metabolism, from a large-multicontinent team involving the Shulman group at Yale and many others, explores the effects of the mammalian homolog, mINDY, in mice. The knockout mice are smaller, although they take in the same number of calories. They are much leaner, though, with remarkable less fat. Their metabolism seems to be ramped up, as you might figure from that situation, and they're especially good at fat oxidation in the liver. Very interestingly, they maintain this phenotype as they age, while normal mice tend to put on more fat. They have lower basal glucose and insulin levels, and are better at clearing glucose, apparently through better uptake in skeletal muscle. They also seem resistant to the bad effects of a high-fat-chow diet, show a much reduced tendency to putting on weight and developing insulin resistance. All in all, this is what you'd call a desirable metabolic phenotype, and it fits in very well with what has been worked out in the fruit flies.
So what does this gene code for? Turns out that it's a citrate transporter, which might not be the most obvious thing at first, but it makes sense. Citrate is converted to acetylCoA, which is the building block for fatty acid synthesis. Cutting down its availability basically starves the liver tissue, which depends on fatty acids for a good part of its energy needs, and causes it to efficiently burn off whatever fatty acids it can acquire. And this effect might just be one of the things that produce the benefits of caloric restriction - in other words, you might not have to deprive your whole body of calories, just the key parts of it. To show that I'm not overinterpreting here, I'll let the authors say it:
These data suggest that mIndy may be a key mediator of the beneﬁcial effects of dietary energy restriction. Since prolonged caloric restriction is very difﬁcult to achieve in humans, our observations raise the tantalizing possibility that modulating the levels or function of mIndy could lead to some of the health-promoting effects of calorie restriction, without requiring severe caloric restriction.
And as they go on to suggest, this makes for a very interesting target for obesity, diabetes, and fatty liver disease. What about extending lifespan? Well, I've dug through the paper several time, and can find no mention of mice older than 8 months, and no numbers on their longevity. I assume that this will be the subject of another paper as the rodents get older - it's too big an issue to ignore, and this paper seems determined not to say a word about it.
+ TrackBacks (0) | Category: Aging and Lifespan | Diabetes and Obesity
April 1, 2011
I'll freely admit to being very interested in research on aging and lifespan. It's a great subject from a scientific (and philosophical) point of view, but perhaps the prospect of turning 50 years old next year has something to do with it, too (not that that age seems anywhere near believable from my end).
Model organisms such as nematodes and fruit flies have already helped identify a number of highly conserved pathways that affect lifespan, many of them having to do with nutrient sensing and various insulin-related pathways. But there are other possibilities. One hallmark of aging at the cellular level is an accumulation of protein defects, chiefly misfolded and chemically modified proteins that apparently are difficult to clear out.
A new paper in Nature takes an alarmingly direct route to investigating potential therapies for this pathway. The researchers looked at small molecules that are known to bind tightly to insoluble protein aggregates and fibrils like amyloid. And what sort of compounds are we sure bind tightly to such things? Why, the sorts of dyes used to selectively stain them for histopathology slides, what else? (See, I told you that this was a rather forceful approach).
But it certainly seems to have paid off. As it turns out, treating nematodes (roundworms, C. elegans) with the dye Thioflavin T (also known as ThT or Basic Yellow 1) extends their lives quite significantly - up around a 60% increase in both median and maximal lifespan. Several other related benzazole compounds were also tried, which produced lifespan extension of up to 40%, and at much lower concentrations.
There are some nematode strains with known defects in protein handling - they produce extra amyloid or polyglutamine proteins, which eventually paralyze them and kill them off. Treating these with the dye had a significant lowering effect on the number of paralyzed nematodes, and the protein aggregrates in their muscle tissue were much lower as well. Similar effects were seen in several other mutant strains that had been used as markers of protein homeostasis.
A number of RNAi and immunological experiments (this is a very data-rich paper, by the way) indicated that ThT's effects depend on several known protein regulators and chaperones. In particular, a strain with a defective heat-shock factor 1 (HSF-1) gene showed no effects with ThT treatment at all, and neither do nematodes with an RNA knockdown of SKN-1 (also known to be implicated in stress responses and longevity). Taken together, these folks really do seem to have found a way to enhance the protein homeostasis functions of living cells, and this seems to have a very beneficial effect on their aging process.
Very interesting work, and very thoroughly followed up on, as it should be. I would be absolutely certain that similar experiments are underway in other species as we speak - I'd go straight to mice, personally, and not neglect some of the mutantmouse strains with protein-handling defects of their own, and compare them to mice that overexpress or underexpress HSF-1 itself. (I can't find any references to SKN-1 mutant mice). Those would be excellent experiments, but I'll bet that I'm not the only one who thinks so. In fact, I'll clean my lab bench off with my tongue if the people who did these studies haven't already thought of them, too.
Oh, and just one more thing: as my wife pointed out to me when I told her about this paper, the FDA was just making headlines the other day by recommending that more study be given to any possible links between food dyes and hyperactivity (though stopping short of recommending any warning at this time, due to lack of convincing evidence). On the basis of this latest work, though, I'm starting to wonder if we're not putting enough dyes in our food. . .
+ TrackBacks (0) | Category: Aging and Lifespan
December 1, 2010
Back in May, GlaxoSmithKline halted a trial of SRT501, which is a formulation of resveratrol, in myeloma. Now the folks at the Myeloma Beacon site are the first with the news that the company has halted all further development:
According to a GlaxoSmithKline spokesperson, an internal analysis of the kidney failure cases has concluded that they “most likely were due to the underlying disease … However, the formulation of SRT501 was not well tolerated, and side effects of nausea / vomiting / diarrhea may have indirectly led to dehydration, which exacerbated the development of the acute [kidney] failure.”
For this reason, the company decided to halt further development of SRT501 in multiple myeloma. The SRT501 formulation of resveratrol “may only offer minimal efficacy,” explained the Glaxo spokesperson, while increasing the chances of kidney failure. . .
. . .In a separate statement to The Myeloma Beacon, a Glaxo spokesperson explained the rationale for the company’s decision to halt all development of SRT501. Ending all work on SRT501, the spokesperson said, will allow Glaxo to focus its resources on the development of drugs that act similarly to SRT501, but have more favorable properties. The spokesperson mentioned, in particular, SRT2104 and SRT2379 as drugs similar to SRT501 that the company is developing.
These compounds are still a bit of a mystery - they've been in the clinical trial registry for a while, and are certainly the subject of active investigation, but we don't know how they fit into the whole activation-of-SIRT1 brouhaha. They haven't been challenged by the critics of the work, nor specifically defended by GSK, so we're just going to have to see how they perform out there in the real world (which was always going to be the final word, anyway).
But this would appear to be it for resveratrol itself in the real world, as far as GSK's concerned. Hey, does this mean that they'll let their two former Sirtris execs start selling it again on the side, now that they have no interest in the parent compound? One doubts it. But why not?
+ TrackBacks (0) | Category: Aging and Lifespan | Cancer | Clinical Trials
October 26, 2010
Get ready for the life-extension folks to jump on this one: there's a report out in PNAS that the longtime treatment for leprosy (Hansen's disease), diaminodiphenylsulfone (DDS or dapsone), also prolongs life in the nematode C. elegans.
We seem to be talking about nematodes a lot around here recently. The authors of the current study (from Korea) got around the dosing problem by feeding DDS to bacteria, and them feeding those to the nematodes. (When you can get away with that, it seems like the most reliable way of getting drugs into the little beasts). The nematodes accumulated the compound up to about 5 mg/kilo body weight - although I have to say, a kilo of nematodes is a rather alarming thought. The treated animals showed a significantly longer lifespan, faster body movements compared to untreated controls, and a delay in accumulating the "aging pigment" lipofuscin.
Now, DDS kills bacteria by inhibiting folate synthesis, but that doesn't seem to have anything to do with lifespan extension. The authors found that one of its key targets might be pyruvate kinase - and this might be the source for the mild anemia that's sometimes seen as a side effect in human patients. Nematodes have two isoforms of the enzyme, one mostly in muscle, and the other mostly in the digestive tract. Further study (with RNAi, etc.) showed that the lifespan extension seems to be working through the former, but not the latter. But it also showed that this probably can't be responsible for the whole lifespan effect, either: mutant nematodes with that isoform deleted live longer than wild type, but treating them with DDS makes them live longer still.
The authors point out that dapsone has been used in humans for a very long time, and that there's a 5% gel that's been shown to be safe for long-term treatment (and which reaches the blood levels that you'd think would be sufficient). They finish up by saying: "We suggest that is is worthwhile to examine whether DDS is effective in enhancing longevity in humans as well." There are enough people interested in these things that I think that this will be tried out very shortly, probably starting this week, albeit in a rather uncontrolled manner. . .
+ TrackBacks (0) | Category: Aging and Lifespan
October 8, 2010
You'll recall that we recently had the flap over two GSK/Sirtris executives running their own sideline business selling resveratrol as a dietary supplement. There's a lot of it out there, understandably, since the publicity around the compound has been intense for several years now. But even if it works, how likely is it that a person could take enough of it to show an effect?
A new paper goes back to the C. elegans nematode model to try to answer that question. The original life-extending results in this organism were done at 100 micromolar concentration, which is way more than any human being is going to be exposed to. Unless you're showering in the stuff, I suppose. The current study dials that back to levels that could be reached in human dosing.
What they saw was no effect on lifespan at 0.5 micromolar, which would be a realistic blood level for humans. When they turned up the concentration to 5 micromolar, there was a slight but apparently real effect of just under 4%. Now, 5 micromolar is a pretty heroic level of resveratrol - I think you could hit that as a peak concentration, but surely not hold it. The medicinal chemists in the audience will appreciate that some drug effects are driven by their Cmax, and others by their AUC, but this still seems to be a likely shortfall.
Oh, and there's another interesting part to this paper. The authors also looked at SRT1720, the resveratrol follow-up from Sirtris that has been the subject of all kinds of arguing in the recent literature. This compound is supposed to be several hundred times more potent than resveratrol itself at SIRT1, although if you've been following the story, you'll know that those numbers are widely believed to be artifacts of the assay conditions. And sure enough, the authors saw no effect on C. elegans lifespan when dosing with physiological concentrations of SRT1720. The authors finish, dryly, with:
Given the above-mentioned and conflicting findings for the efficiency of SRT1720 and the metabolic state in rodents, it is interesting to note that, as shown here, SRT1720 exerts no detectable effects on lifespan of an established model for the analysis of longevity. . .
Indeed it is. Given the recent follow-up work in this area, I can't say I'm surprised, but I am disappointed. And yes, in case anyone's wondering, I do actually hope that the Sirtris work (and other research on sirtuin compounds) leads to something good. It's just that the story is a lot messier than anyone would have liked, so far. All I have to do is look back on what I wrote just four years ago, and wonder if it really had to be this way. Did it?
+ TrackBacks (0) | Category: Aging and Lifespan
August 25, 2010
OK, time (finally) for the latest chapter in the GSK-Sirtris saga. (This is going to get fairly geeky, so feel free to skip ahead if you're not into enzymology). You'll recall from previous installments that Amgen and Pfizer, among others, had disputed whether the reported sirtuin compounds worked the way that had originally been reported. GSK has now published a paper in the Journal of Biological Chemistry to address those questions. How well does this clear things up? Let's take things in order:
Claim 1: Resveratrol is not a direct activator of SIRT1 activity (Amgen). Building on two 2005 papers, the Amgen team said that resveratrol, the prototype SIRT1 ligand, only works in that manner when the fluorescent peptide (Fluor de Lys) was used in the assay. This is due, they found, exclusively to the fluorophore on the peptide - it's an artifact of the assay conditions. Without it, no activation was seen with protein assays in vitro, nor in cell assays. Native substrates (p53-derived peptide and PGC-1alpha) show nothing.
GSK's response: This is true. They too, found that activation of SIRT1 depends on the structure of the substrate. Without the fluorescent label, no activation is seen.
Claim 2: Not only is this true for resveratrol, it's true for SRT1720, SRT2183, and SRT 1460 (Pfizer). The Pfizer team did a similar breakdown of the assay conditions, and found (through several biophysical methods) that the fluorophore is indeed the crucial element in the activity seen in these assays. And again, since that's an artificial tag, the Fluor de Lys-based assays can have nothing to do with real in vivo activity. Native substrates (p53-derived peptide, full-length p53, and acetyl CoA synthase 1) show nothing.
GSK's response: As above, activation of SIRT1 depends on the structure of the substrate. Without the fluorescent label, no activation is seen. SRT1460 and SRT1720 do indeed bind to the fluorescent peptide, but not to the unlabeled versions. Looking over a broader range of structures, some of them interact with the fluorophore, and some don't. There's no correlation between this affinity and a compound's ability to activate SIRT1.
A screen of 5,000 compounds in this class turned up three that actually do work with nonfluorescent peptide substrates (compounds 22, 23, and 24 in the paper). None of these have been previously disclosed. They, however, that even these still don't work when the peptide substrate lacks both the fluorescent tag and a biotin tag.
What's more, when these three compounds are tested on a p53-derived 20-mer peptide substrate, they actually inhibit acetylation, instead of enhancing it. Looking closer at a range of peptide substrates, SRT1460 and other compounds can also inhibit or enhance acetylation, depending on what peptide is being used. An allosteric mechanism could explain these results. It seems more likely that there are at least two specific sites on SIRT1 that can bind these compounds - the active site and an allosteric one. Thus there are several species in equilibrium, depending on whether these sites have substrate or small molecule bound to them, and on how this binding stabilizes or destabilizes particular pathways. In the real cell, this may all be part of various protein-protein interactions.
Claim 3: SRT1720 does not lower glucose in a high-fat-fed mouse model (Pfizer). Even though exposure of the drug was as reported previously, they saw no evidence (at 30 mg/kilo) of glucose lowering or of any increased mitochondrial function. These animals showed increased food intake and weight gain. The 100 mpk dose was not well tolerated, and killed some animals.
GSK's response: not addressed in this paper. It's an enzymology study only.
Claim 4: Resveratrol, SRT 1460, SRT1720, and SRT2183 are not selective (Pfizer). A screen of over 100 targets showed all of these compounds hitting multiple targets, with resvertrol itself showing the closest thing to a clean profile. None of them, say the Pfizer team, are suitable pharmacological tools.
GSK's response: not addressed in this paper. None of the newly disclosed compounds have selectivity data of this sort attached to them, either. I'd be very curious to know how they look, and I'd be very leery of attaching much importance to their behavior in living systems until that's been done.
The take-home: On the enzymology level, this new paper seems to be solid work. But it's the sort of solid work that should have been done around the time that GSK bought Sirtris, and not something appearing in 2010 in response to major attacks in the literature. The first main claim of those attacking papers is, in fact, absolutely true: the original Fluor de Lys assay is worthless for characterizing these compounds. What we learn from this paper is that the assay is worthless for even more complicated reasons than originally thought, and that the whole series of SRT compounds behaves in ways that were not apparent from the published work, to put it lightly.
As to the selectivity and in vivo effects of these compounds, Pfizer's gauntlet is still thrown down right where they left it. The fact that these compounds are so much harder to understand than was originally thought, even in well-controlled enzyme assays, makes me wonder how easy it will be to figure out the rest of the story. . .
+ TrackBacks (0) | Category: Aging and Lifespan | Drug Assays | Drug Development
August 12, 2010
Update - see below for more on this story. GSK has reacted quickly. . .
Now this seems rather odd. According to Xconomy, two former Sirtris higher-ups have formed a nonprofit foundation which is selling resveratrol online.
Michelle Dipp, a Sirtris-turned-Glaxo executive, confirmed that the nonprofit that she and former Sirtris CEO Christoph Westphal co-founded last year has started online sales of resveratrol. Dipp leads the effort on the off hours when she isn’t doing her main job as senior vice president of Glaxo’s Center of Excellence for External Drug Discovery.
While the group is charging $540 for a one-year supply of resveratrol, Dipp says that the nonprofit is selling the supplements for cost and is not profiting from the sales.
And thanks to Hatch-Waxman, since this is being offered as a "dietary supplement", hey, it can go straight into people - people with $540, anyway:
To be clear, this resveratrol operation is a volunteer effort that Dipp and Westphal do on the side. Both are still employees of Glaxo, and they have also started a Boston venture firm called Longwood Founders Fund with fellow Sirtris co-founder Rich Aldrich.
“Our main business is brining new drugs to patients through our work at Longwood and (Glaxo),” says Dipp, who is president of the Healthy Lifespan Institute. “But there was so much demand for (resveratrol).”
I really don't know what to make of this. This formulation of resveratrol would appear to be basically SRT501, which has been involved in a number of clinical trials (and unexpectedly dropped out of one not too long ago). I can't recall another case where an investigational drug has also been sold as a dietary supplement, by some of the same people, who are working both for the company funding the trials and for a nonprofit foundation. I mean, what if GSK/Sirtris find a clinically relevant use for resveratrol? Why buy it from them if you can get it at cost? Or would all that change if SRT501 gets FDA approval? Makes a person's head hurt, it does. . .
Update - GSK has now asked Dipp and Westphal to resign from their institute, saying that they didn't realize that they were selling resveratrol. That didn't take long!
+ TrackBacks (0) | Category: Aging and Lifespan | Clinical Trials
May 17, 2010
I've been meaning to write about this paper from a recent issue of Science. They've been studying the differences between young (3-month) mice and old (16-month) mice - their ability to learn, and to remember. Markers of neuronal plasticity and the like are pretty similar between the groups, although the older mice definitely show some impairments in spatial learning and recall. Looking down at the genetic level, for effects on chromatin handling, didn't seem to show much, either - the young and old mice have similar levels of histone deacetylase and histone acyltransferase enzymes.
But a look at the real levels of acetylated histones showed something different: the older mice seemed to be deficient in one particular type of acetylation, H4K12. That particular lysine residue was acetylated much more readily in the younger animals in response to a fearful event, but the older animals didn't upregulate the process. A broad-based search using microarrays showed that a wide range of genes were regulated by the young mice when learning to avoid a fear stimulus, but were not altered to nearly the same degree in the older ones. And as it turns out, the H4K12 acetylation looks to be one of the common factors in the regulation of these genes.
The authors went so far as to use Vorinostat (SAHA), a marketed histone deacetylase inhibitor, to test this hypothesis. Administering that to the older mice (directly into the brain; it doesn't really cross on its own) led to both H4K12 effects and to beneficial effects on learning.
This is a long way from being a therapy, but it's a very interesting lead towards one. The effects of messing around with histone acylation states could be profound (both in the sense of "profoundly good" as well as "profoundly bad"), so it's going to be quite a while before the dust settles enough for us to know what to do. But I'm encouraged to see things like this coming up. Given that I'm 48, we're going to have to keep moving right along in order to have something ready by the time I'm going to need it!
+ TrackBacks (0) | Category: Aging and Lifespan | Alzheimer's Disease | The Central Nervous System
May 3, 2010
A comment to this post on the Sirtris compound saga just had me checking Clinicaltrials.gov. And indeed the commenter is correct: a trial against myeloma of a combination of Velcade (bortezomib) and SRT501, which I believe is reformulated resveratrol itself, was suspended as of April 22 for "unexpected safety concerns".
There's no way of knowing what those are, and it's worth keeping in mind that a number of other studies have been completed with SRT501. But since there's been (as far as I can tell) no mention of this trial's halt anywhere, I thought it worth noting.
+ TrackBacks (0) | Category: Aging and Lifespan | Cancer | Clinical Trials
April 29, 2010
Here's something I never knew: odors can regulate lifespan. Well, in fruit flies, anyway - a group at Baylor published results in 2007 showing that exposure to food-derived odors (yeast smells, in the case of Drosophila) partially cancels out the longevity-inducing effects of caloric restriction. Normally fed flies showed no effect.
That 2007 paper identified a specific sensory receptor (Or83b) as modulating the effect of odor on lifespan. Now comes a report that another receptor has been tracked down in this case, the G-protein coupled Gr63a. Flies missing this particular olfactory GPCR no longer show the lifespan sensitivity to yeast odors. This narrows things down. Or83b mutations seem to broadly affect sensory response in flies, but this is a much more specific receptor, just one of a great many similar ones:
"Unlike previous reports involving more general olfactory manipulations, extended longevity via loss of Gr63a occurs through a mechanism that is likely independent of dietary restriction. We do, however, find that Gr63a is required for odorants from live yeast to affect longevity, suggesting that with respect to lifespan, CO2 is an active component of this complex odor. Because Gr63a is expressed in a highly specific population of CO2-sensing neurons (the ab1C neurons) that innervate a single glomerulus in the antennal lobe (the V glomerulus), these data implicate a specific sensory cue and its associated neurosensory circuit as having the ability to modulate fly lifespan and alter organismal stress response and physiology. Our results set the stage for the dissection of more complex neurosensory and neuroendocrine circuits that modulate aging in Drosophila. . ."
It's going to be very interesting to follow that neuronal pathway - I've no idea where it will lead, but we're bound to learn something worthwhile. To make a wild generalization straight up to humans, this makes me wonder about people who are practicing caloric restriction on themselves - they're still exposed to food odors all the time, right? Does the same reversal apply? For me, I think that the scent of barbecue and fried catfish might be enough to do it right there, but keep in mind that I'm from Arkansas. Your mileage may vary.
+ TrackBacks (0) | Category: Aging and Lifespan | Biological News
April 28, 2010
Christoph Westphal gave what by all accounts was a very interesting talk at the recent Bio-IT conference. And considering his track record in company formation, he's well worth listening to. But concerning the recent controversy over the compounds and results from his most recent success (Sirtris), I found this part of his speech. . .well, interesting:
"There’s a debate in the academic world,” Westphal acknowledged. “We don’t know the specific molecular mechanism of why you need a specific substrate on the in vitro screen to find Sirt1 activators. Pfizer, Amgen, GSK, Sirtris, everyone in academia agrees on that. Then the question is: Is the mechanism direct on SIRT1 or indirect on SIRT1? Everyone in the field agrees our molecules have beneficial effects in animals, and I hope they will in man soon. The specifics of the mechanism are under debate. This kind of thing will be debated for ten years.”
Emphasis mine. And I emphasize that part because Pfizer specifically tested one of the highlighted Sirtris compounds, SRT1720, and was unable to reproduce the in vivo effects. So no, I wouldn't say that "everyone agrees" on this point. Not quite.
Westphal says that there's another paper in press that might be able to clear things up a bit, so we'll see what that one has to say. And he's right that the clinical results are what will really settle these questions - but we're going to have to wait a while for those. For now, agreement on a lot of key points remains hard to come by. . .
+ TrackBacks (0) | Category: Aging and Lifespan | Business and Markets
April 6, 2010
A reader sends along a note about this patent application from the University of Rochester. The inventor, David Goldfarb, seems to have used an assay (the subject of a previous application) to screen a library of commercially available compounds for potential life-extending properties in model organisms. Here's some detail on the screen from PubChem.
The abstract of the application makes it sound worse than it is: "A method for altering the lifespan of a eukaryotic organism. The method comprises the steps of providing a lifespan altering compound, and administering an effective amount of the compound to a eukaryotic organism, such that the lifespan of the organism is altered. . ." That sounds like one of those "Oh, get real" applications that the patent databases are cluttered with. But when you get to the claims, you find that a list of compounds is specifically given, with more- and most-preferred ones as you go down. And I don't have a problem with that, as far as it goes - the inventor has an assay, has run a bunch of compounds through it, and finds that some of them have utility that apparently no one else has recognized.
The compounds themselves, though. . .well, here are the specifically claimed ones on the list. I don't necessarily see aliphatic triketones extending my life, but perhaps I'm cynical.
+ TrackBacks (0) | Category: Aging and Lifespan | Drug Assays | Patents and IP
April 5, 2010
Last summer a paper was published (PDF) showing rapamycin dosing appeared to lengthen lifespan in mice. (In that second link, I went more into the background of rapamycin and TOR signaling, for those who are interested). Now comes word that it also seems to prevent cognitive deficits in a mouse model of Alzheimer's.
The PDAPP mice have a mutation in their amyloid precursor protein associated with early-onset familiar Alzheimer's in humans, and it's a model that's been used for some years now in the field. It's not perfect, but it's not something you can ignore, either, and the effects of rapamycin treatment do seem to be significant. (The paper uses the same dose that was found to extend lifespan). The hypothesis is that rapamycin allowed increase autophagy (protein digestion) to take place in the brain, helping to clear out amyloid plaques.
What I also found interesting, though, was the rapamycin-fed non-transgenic control animals. In each case, they seem to show a trend for increased performance in the various memory tests, although they don't quite reach significance. This makes me wonder what the effects in humans might be, Alzheimer's or not. After that lifespan report last year, it wouldn't surprise me to find out that some people are taking the stuff anyway, but it's not going to be anywhere near enough of a controlled setting for us to learn anything.
This report is definitely going to start a lot of people thinking about experimenting with rapamycin for Alzheimer's - there are a lot of desperate patients and relatives out there. But together with that lifespan paper, it might also start some people thinking about it whether they're worried about Alzheimer's or not.
+ TrackBacks (0) | Category: Aging and Lifespan | Alzheimer's Disease | Biological News
March 25, 2010
Nature has a review of a new book on the anti-aging field, Eternity Soup by Greg Critser, and I found this part very instructive. The same things apply to several other therapeutic areas where people see fast money to be made:
Critser's methodical portrayal of a host of anti-ageing practitioners reveals some fascinating people who seek to convince others that they can purchase longer and healthier lives like any other commodity. He makes clear that many anti-ageing treatments are based more on faith healing than on science, and that the industry defends them and presents them to the public with evangelical zeal. Scientific gerontologists who point out the lack of empirical evidence behind the claims are shouted down, sued for libel or made fun of as lab technicians or statisticians with no experience in treating patients.
Critser became aware during his research of why the ridiculed scientific gerontologists find the anti-ageing industry so aggravating. The industry closely monitors the field for any advances, and when it spots something that might be turned into a commercial enterprise, the product is repackaged, branded and sold to the public as the next great breakthrough of its own invention. . .
It's interesting, though, that the cancer-cure quacks tend not to ride so much on the current research. A lot of that stuff seems just to be completely made up, without even a connection to something in the scientific literature. Perhaps that's because there are occasional spontaneous remissions from cancer, but none from old age. . .
+ TrackBacks (0) | Category: Aging and Lifespan | Cancer | Snake Oil
March 17, 2010
A small company called BioTime has gotten a lot of attention in the last couple of days after a press release about cellular aging. To give you an idea of the company's language, here's a quote:
"Normal human cells were induced to reverse both the "clock" of differentiation (the process by which an embryonic stem cell becomes the many specialized differentiated cell types of the body), and the "clock" of cellular aging (telomere length)," BioTime reports. "As a result, aged differentiated cells became young stem cells capable of regeneration."
Hey, that sounds good to me. But when I read their paper in the journal Regenerative Medicine, it seems to be interesting work that's a long way from application. Briefly - and since I Am Not a Cell Biologist, it's going to be brief - what they're looking at is telomere length in various stem cell lines. Telomere length is famously correlated with cellular aging - below a certain length, senescence sets in and the cells don't divide any more.
What's become clear is that a number of "induced pluripotent" cell lines have rather short telomeres as compared to their embryonic stem cell counterparts. You can't just wave a wand and get back the whole embryonic phenotype; their odometers still show a lot of wear. The BioTime people induced in such cells a number of genes thought to help extend and maintain telomeres, in an attempt to roll things back. And they did have some success - but only by brute force.
The exact cocktail of genes you'd want to induce is still very much in doubt, for one thing. And in the cell line that they studied, five of their attempts quickly shed telomere length back to the starting levels. One of them, though, for reasons that are completely unclear, maintained a healthy telomere length over many cell divisions. So this, while a very interesting result, is still only that. It took place in one particular cell line, in ways that (so far) can't be controlled or predicted, and the practical differences between this one clone and other similar cells lines still aren't clear (although you'd certainly expect some). It's worthwhile early-stage research, absolutely - but not, to my mind, worth this.
+ TrackBacks (0) | Category: Aging and Lifespan | Biological News | Business and Markets
March 9, 2010
Nature Biotechnology weighs in on the GSK/Sirtris controversy. They have a lot of good information, and I'm not just saying that because someone there has clearly read over the comments that have showed up to my posts on the subject. The short form:
The controversy over Sirtris drugs reached a tipping point in January with a publication by Pfizer researchers led by Kay Ahn showing that resveratrol activates SIRT1 only when linked to a fluorophore. Although Ahn declined to be interviewed by Nature Biotechnology, a statement issued by Pfizer says the group's findings “call into question the mechanism of action of resveratrol and other reported activators of the SIRT1 enzyme.”
Most experts, however, say it's too soon to write off Sirtris' compounds altogether, assuming they're clinically useful by mechanisms that don't involve sirtuin binding. And for its part, GSK won't concede that Sirtris' small molecules don't bind the targets. In an e-mailed statement, Ad Rawcliffe, head of GSK's WorldWide Business Development group, says, “There is nothing that has happened to date, including the publication [by Pfizer,] that suggests otherwise.”
We'll see if GSK and Sirtris have some more publications ready to silence their detractors. But what will really do that, and what we'll all have to wait for, are clinical results.
+ TrackBacks (0) | Category: Aging and Lifespan | Biological News
January 26, 2010
So says GlaxoSmithKline CEO Andrew Witty about the Sirtris controversy - see this Forbes story for more. I hope he's right. I actually would like to see good things come out of sirtuin research - the biology's clearly interesting enough. And I would like to think that GSK didn't blow $720 million, because we could all use that sort of money these days. This story will only be settled for sure in the clinic, with the agents the GSK is developing. Good luck to them. I fear that they might need it, but I hope that they don't.
+ TrackBacks (0) | Category: Aging and Lifespan
January 25, 2010
Nature has a short item on the Pfizer paper that questions the reproducibility of some key sirtuin work (covered here and here). There are some good points to temper the pessimism. Leonard Guarente of MIT, a key pioneer in the field, says:
". . . that the latest findings are neither surprising nor worrisome. The compounds may work only with fluorophore-conjugated peptides in vitro, says Guarente, but the situation is different in cells and in animals. The Nature paper, among others, went beyond the test tube and indicated that SIRT1 was more active in cells and in animals after application of the Sirtris compounds. Furthermore, resveratrol administration made no difference to the lifespan of yeast that did not have Sir23, indicating that the compound's action depends on this gene.
According to a statement from GlaxoSmithKline, Ahn's conclusion "ignores any possibility of direct activation of SIRT1 that may occur in a cellular environment that is not reproduced in vitro".
True, but there's still that problem of the Pfizer group not being able to reproduce the in vivo effects, which to me was perhaps the most worrisome part of the paper. Now, it's worth remembering that animal studies are not the easiest things in the world to do right, since there are so many variables. Small differences in animal strains and the like can sometimes throw things off severely. Even the Pfizer group admits this readily, with Kay Ahn telling Nature that "every in vivo experiment is a little bit different" and that "Under our conditions we didn't see beneficial effects, but we don't want to make a big conclusion out of those results."
That's an honorable way to put things, I have to say. Rather less honorable, though, at least to me, is David Sinclair's response from the Sirtris team. See what you think:
A possible explanation for the discrepancy, says Sinclair, is that Ahn and her colleagues did not provide information on the characterization of the compounds, which they synthesized themselves. So there is no way of knowing how pure they were or whether they're the same as those made by Sirtris. "The fact that mice died indicates that there may be an issue with purity,".
That's. . .not so good. In fact, it comes close to being insulting. Although I say a lot of uncomplimentary things about Pfizer's management, the fact remains that they have a lot of very good scientists there. And I assume that they can reproduce Sirtris's published procedures to make the sirtuin ligands. If they can't, frankly, that's Sirtris's fault. Everyone (well, everyone competent) checks out compounds thoroughly before putting them into an animal study. Asking "Are you sure you made the right stuff?" at this point is really a bit much, and doesn't do anything improve my opinion of Sirtris. (Which opinion actually was pretty good - until recently).
+ TrackBacks (0) | Category: Aging and Lifespan | Drug Assays
January 15, 2010
So, after reading what Pfizer has to say about Sirtris (and by extension, about GlaxoSmithKline's heavy investment in them), let's go over the possibilities. What happened, and what's going on?
We'll start out with the first branch point: either Pfizer (and Amgen) are right that there's trouble with the Sirtris assays and compounds (Reality A, I'll call it), or they're wrong (Reality B). For the rest of this piece, I'm going to assume that they're right, because I think that this is almost certainly the case. At least two separate groups of competent investigators have reported trouble, and that's good enough for me. (We'll discuss the implications of that in a bit).
Now we come to the second branch point: either Glaxo did enough due diligence to be aware of the problems (scenario A1) or they didn't realize them at the time of the deal (scenario A2). If A1 is the case, then we'd have to assume that the most likely consequence (A1a) is that Sirtris had other non-public assets that did check out, and that GSK's management felt that these justified the purchase. (A1b would be the scenario where GSK was well aware of the Sirtris problems, knew also that they didn't have anything else to offer, and bought them anyway, which doesn't make sense). These assets could have been other compounds, and/or a leg up on the complicated biology of this field. The difficulty with that line of thinking is that having found the fundamental assay problems with the Sirtris work, the GSK people would surely have been much more cautious about drawing sweeping conclusions about the rest of the company's intellectual property.
If A2 is the case, then we're looking at sheer fecklessness on the part of GSK's upper management. I'd like to be able to rule this out, but there have been other deals in the history of this industry that make that hard to do. I have witnessed at least one such personally. One problem is that these deals tend to be initiated near the highest levels of a company, and these people are not always the most technically savvy (or up-to-date) members of an organization. Even with a science background, the CEO of a large company does not have the time to be a scientist. (I'm reminded of Peter O'Toole's character in My Favorite Year: "I'm not an actor - I'm a movie star!"
Overall, though, I find it hard to believe that no one would have noticed the reported problems at all, which leads me to favor what I'll call scenario A3: the problems with the Sirtris assays may well have been known/realized at the lower scientific levels of GSK's organization, but these concerns may not have made it to the top in a sufficiently timely or vigorous manner. The deal would have gone through under its own momentum, then, in a flurry of last-minute misgivings which would have been hard to distinguish from the usual butterflies that accompany any large transaction or the preliminary stirrings of buyer's remorse. The sorts of reasons advanced in the A1 paragraph above would have been used to justify pushing ahead. With that in mind, this scenario could be broken down further into A3a, where Sirtris also had some other assets that the rest of us haven't seen, and A3b, where they didn't. I think that A3a is more likely, since that would have provided some of the momentum to get the deal done regardless. A3b is basically A2 with different timing and slightly less cluelessness.
So where do things go from here? That obviously depends on which of those three realities obtains. If A1 (specifically A1a) is the case, then GSK plows ahead with their secret Sirtris assets and compounds, and good luck to all concerned. It's worth keeping in mind that sirtuins are quite interesting and important, and that it's an area worth investigating on its own merits. (Pfizer and Amgen, among others, must think so too; that's the only reason that they would have been trying to replicate the Sirtris work).
If A2 is the real story, well, I'm very sorry to hear it. A lot of people seem ready to believe this one, partly because of anger over the layoffs the company has been going through. The most likely consequence of A2 is that $720 million dollars disappears, never to yield anything that's of use to anyone, so I hope that this isn't what happened.
And if, as I think, A3 is what actually happened, then that sort of depends on whether we're looking at A3a or A3b. If the former, then Glaxo overpaid, but has a fighting chance to redeem itself. If the latter, then Glaxo not only overpaid, but (as with A2) is in danger of losing its whole investment as well. We'll all find out.
But we may not find out very quickly. GSK has (like many other companies) a tendency to be rather close-mouthed about the progress of some of its research. When I worked in the nuclear receptor field, we all were very interested in the fate of a particular Glaxo compound, the first selective PPAR-delta ligand to go into the clinic. The company had talked about some animal and preclinical data, but we knew that they were taking it into humans (after all, it was listed that way in their pipeline updates). But it stayed listed like that. . .and stayed. . .and stayed. . .until, as the months and years passed, it became obvious to even the most optimistic observer that the compound's development was (at the very least) extremely complicated, and (more likely) had actually quietly ceased a good while before, albeit with no change in its public status.
In this case, now that these doubts have come up, GSK has a real interest in pointing out any success it may have. If its sirtuin compounds go into the clinic and just sort of hang there, that will probably be an even worse sign than usual. And if no sirtuin compounds even go into the clinic at all, well, the question has answered itself. I hope that's not what happens.
+ TrackBacks (0) | Category: Aging and Lifespan | Clinical Trials | Diabetes and Obesity | Drug Development
January 12, 2010
As followers of the drug industry know, GlaxoSmithKline famously paid $720 million to buy Sirtris Pharmaceuticals in 2008. Sirtris is the most high-profile shop working on sirtuins and resveratrol-like pharmacology, which subject has received a massive amount of press (some accurate, some scrambled). I've been following the story with interest, since the literature has me convinced that the aging process can indeed be modified in a number of model organisms, which makes me think that it could be in humans as well. And I also feel sure that advances in this area could lead to many profound medical, social, and economic effects. (GSK, though, is going after diabetes first with the Sirtris deal, I should add - among other reasons, the FDA has no regulatory framework whatsoever for an antigeronic, if I can coin a word.)
But whatever the state of the anti-aging field, doubts have crept in about the wisdom of the Sirtris purchase. Last fall, a group at Amgen published a study suggesting that some of the SIRT1/resveratrol connections might be due an an experimental artifact caused by a particular fluorescent peptide. Now a group at Pfizer has piled on in the Journal of Biological Chemistry. They're looking over resveratrol and a series of sirtuin activators described by the Sirtris group in Nature.
And unfortunately, they also find trouble due to fluorogenic peptides. The TAMRA fluorophore on their peptide substrates seems to pervert the assay. While the Sirtris compounds looked like activators initially, switching to the native peptide substrates showed them to be worthless. Further study (calorimetry) showed that the activator compounds bind to a complex of SIRT1 and the fluorescent peptide substrate, but not to SIRT1 itself (or in the presence of native substrate without the fluorogenic group). That's not good.
But worse is to come:
"Despite a lack of evidence for the Sirtris series of compounds as direct SIRT1 activators, we investigated whether the in vivo efficacy demonstrated by SRT1720 in several rodent models diabetes could be validated and attributed to indirect activation of SIRT1. We therefore attempted to reproduce the in vivo efficacy for SRT1720 in mouse models of type 2 diabetes previously shown. . ."
That word "attempted" should tell you what comes next. The reported high dose of the compound (100 mpk) resulted in weight effects and death. The reported low dose (30 mpk) showed no effects at all on any diabetic parameters, but instead seemed to lead to increased feeding and weight gain. To complete the debacle, the Pfizer group screened the Sirtris compounds through a broad panel of assays, and found that all of them hit a number of other targets (and appear significantly worse than resvertarol itself, which is no one's idea of a clean compound to start with).
Basically, these folks have thrown down the gauntlet: they claim that the reported Sirtris compounds do not do what they are claimed to do, neither in vitro nor in vivo, and are worthless as model compounds for anything in this area of study. So what is GSK going to have to say about this? And what, if this paper is at all accurate, did they buy with their $720 million?
+ TrackBacks (0) | Category: Aging and Lifespan | Business and Markets | Drug Assays
December 4, 2009
If there's one thing that study-of-aging researchers can agree on, it's that caloric restriction seems to prolong lifespan in a number of different organisms. The jury is still out on whether this extends all the way up to humans - people are giving it a try, with varying degrees of dedication and experimental rigor, but it takes quite a while for the results to come in.
One thing that stands out from experiments in small organisms is that cutting back on food intake seems to increase lifespan at the expense of fertility. That makes sense in a sort of three-laws-of-robotics way: the first task is to survive. The second task is to reproduce, as long as that doesn't interfere too much with survival. . .so under very tight energy restrictions, the organism doesn't have enough overhead to move on to the reproduction side of things. (On the other hand, under abundant food conditions, it may be that for some organisms reproduction moves up into first place, depending on what kind of ecological niche they're trying to fill).
This usual thinking here has been that it's total availability of food that throws these switches, through pathways that are sensitive to metabolic flux. There's now a paper out in Nature that makes this model harder to stick with. The researchers look at fruit flies, Drosophila, the very pest that I'm trying to evict from my kitchen at home (thanks to a recent contaminated package of plantains). As it turns out, it's known that these flies don't eat fruit so much as they eat yeast, which accounts for their attraction to bread, vinegar, beer, and overripe produce. This paper tries to pin down which nutrients, exactly, in yeast have effects on fecundity and lifespan, and whether they really are mutually exclusive.
A good way to search for those effects is to take a population of calorically-restricted fruit flies and add nutrients back to their diet to see if anything shows up in lifespan or egg-laying behavior. Vitamins, lipids, and carbohydates were soon ruled out as entire classes - none of the ones found in yeast seemed to have much of an effect either way when they were added back to the diet. That's an interesting result right there - the flies were now getting more food, but their lifespans did not decrease, suggesting that it's not just calories per se that have the effect.
That leaves proteins, and their constituent amino acids. And there things started to get interesting. Adding an amino acid mixture recapitulated the effect of full feeding: lifespans went down, and reproduction went back up. After looking for possible general non-nutritional effects of amino acids (effects on pH, osmotic strength of the food solution, and so on - nothing meaningful found), the team then narrowed things down, trying mixtures of the ten amino acids that are known to be essential for Drosophila versus the ten that aren't. (It's pretty much the same list as for humans, actually).
Adding back the non-essential ones slightly decreased lifespan, with no effect on reproduction. Adding back the essential amino acids (EAAs), though, had substantial effects on both. Now things are getting close to the payoff: amino acids seem to be behind basically all of the caloric restriction effect, and the ten essential ones account for almost all of that. What about looking at them one by one? (I really love science, I have to tell you).
I'll take you right to the end, although plenty of experimentation was needed to get there: it comes down to methionine. Tryptophan has some effect, but methionine alone is sufficient to bring reproduction back to the levels seen in full feeding when you start with calorically restricted flies that are getting the other essential amino acids. It works in a dose-dependent manner, too: if you take restricted-nutrient flies and start putting methionine back into their diet, the fecudity comes up in tandem, eventually plateauing out to a level that you can only raise by giving them more of the other essential amino acids (which are presumably now the things in short supply). That makes it seems as if methionine isn't some signal that it's time to lay eggs - its effects depend on the concentration of the other nine essential amino acids.
Now here's the really neat part: adding methionine back to the diet did not decrease lifespan. So lifespan and reproduction are not always coupled. I'll let the authors lay it out (I've stripped out the references to other papers and to figures that are found in the original text):
Adding back each EAA individually did not decrease lifespan, although, again, methionine alone increased fecundity. Adding back all EAAs except methionine restored lifespan to the level corresponding to dietary restriction, whereas omission of tryptophan had no effect. Notably, restriction of methionine alone also increases lifespan in rodents. Methionine thus acts in combination with one or more other EAAs to shorten lifespan with full feeding. Full feeding thus increases fecundity and decreases lifespan through the effects of different nutrients in Drosophila, the fecundity increase through methionine alone and the lifespan decrease through a combination of methionine and other EAAs. There is thus an imbalance in the ratio of amino acids in yeast relative to the ratio the fly requires for the high fecundity from full feeding, and some consequence of this imbalance decreases lifespan. . .
. . .The mechanisms that influence lifespan are conserved over the large evolutionary distances between invertebrates and mammals, and our results hence imply that in mammals also the benefits of dietary restriction for health and lifespan may be obtained without impaired fecundity and without dietary restriction itself, by a suitable balance of nutrients in the diet.
Now that's going to set off the nutrional supplement industry, for sure, although the lack of effect of vitamins and various lipids will put a crimp into some sections of it. But I find this a fascinating result, and believe that it's probably only the beginning of a long, interesting, and important field of study.
+ TrackBacks (0) | Category: Aging and Lifespan
November 5, 2009
Resveratrol's a mighty interesting compound. It seems to extend lifespan in yeast and various lower organisms, and has a wide range of effects in mice. Famously, GlaxoSmithKline has expensively bought out Sirtris, a company whose entire research program started with resveratrol and similar compound that modulate the SIRT1 pathway.
But does it really do that? The picture just got even more complicated. A group at Amgen has published a paper saying that when you look closely, resveratrol doesn't directly affect SIRT1 at all. Interestingly, this conclusion has been reached before (by a group at the University of Washington), and both teams conclude that the problem is the fluorescent peptide substrate commonly used in sirtuin assays. With the fluorescent group attached, everything looks fine - but when you go to the extra trouble of reading things out without the fluorescent tag, you find that resveratrol doesn't seem to make SIRT1 do anything to what are supposed to be its natural substrates.
"The claim of resvertraol being a SIRT1 activator is likely to be an experimental artifact of the SIRT1 assay that employs the Fluor de Lys-SIRT1 peptide as a substrate. However, the beneficial metabolic effects of resveratrol have been clearly demonstrated in diabetic animal models. Our data do not support the notion that these metabolic effects are mediated by direct SIRT1 activation. Rather, they could be mediated by other mechanisms. . ."
They suggest activation of AMPK (an important regulatory kinase that's tied in with SIRT1) as one such mechanism, but admit that they have no idea how resveratrol might activate it. Does that process still require SIRT1 at all? Who knows? One thing I think I do know is that this has something to do with this Amgen paper from 2008 on new high-throughput assays for sirtuin enzymes.
One wonders what assay formats Sirtris has been using to evaluate their new compounds, and one also wonders what they make of all this now at GSK. Does one not? We can be sure, though, that there are plenty of important things that we don't know yet about sirtuins and the compounds that affect them. It's going to be quite a ride as we find them out, too.
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October 5, 2009
As many had expected, a Nobel Prize has been awarded to Elizabeth Blackburn (of UCSF), Carol Greider (of Johns Hopkins), and Jack Szostak (of Harvard Medical School/Howard Hughes Inst.) for their work on telomerase. Blackburn had been studying telomeres since her postdoc days in the late 1970s, and she and Szostak worked together in the field in the early 1980s, collarborating from two different angles. Greider (then a graduate student in Blackburn's lab) discovered the telomerase enzyme in 1984. She's continued to work in the area, as well she might, since it's been an extremely interesting and important one.
Telomeres, as many readers will know, are repeating DNA stretches found on the end of chromosomes. It was realized in the 1970s that something of this kind needed to be there, since otherwise replication of the chromosomes would inevitably clip off a bit from the end each time (the enzymes involved can't go all the way to the ends of the strands). Telomeres are the disposable buffer regions, which distinguish the natural end of a chromosome from a plain double-stranded DNA break.
What became apparent, though was that the telomerase complex often didn't quite compensate for telomere shortening. This provides a mechanism for limiting the number of cell divisions - when the telomeres get below a certain length, further replication is shut down. Telomerase activity is higher in stem cells and a few other specialized lines. This means that the whole area must be a key part of both cellular aging and the biology of cancer. In a later post, I'll talk about telomerase as a drug target, a tricky endeavour that straddles both of those topics.
It's no wonder that this work has attracted the amount of attention it has, and it's no wonder either that it's the subject of a well deserved Nobel. Congratulations to the recipients!
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July 10, 2009
A new paper coming out in Nature is getting a lot of attention, and well it should. This is some of the more dramatic anti-aging news that's been reported to date. (The accompanying editorial is also surely the first time anyone's quoted "Stairway to Heaven" in Nature).
The work hinges on a kinase enzyme called TOR (you often see an "m" in front of it, for "mammalian"). TOR, in accordance with the best gotta-name-it-something traditions of biochemistry, stands for "target of rapamycin", by which you would deduce (correctly) that rapamycin was discovered well before TOR. Rapamycin's a complex natural product first isolated from bacteria in a soil sample from Easter Island (Rapa Nui) - right here, in fact. In the late 1980s and early 1990s it was (along with another macrolide immunosuppresant, FK-506) the subject of a huge amount of research. (Note that FK-506 and rapamycin, though similar, still have some major differences in mechanism - unraveling these was most definitely nontrivial). Both compounds have strong immunosuppressive properties - the hope was that one or the other might prove to be some sort of universal transplant drug, among other things.
Rapamycin isn't that, but it's still useful, particularly in kidney transplants. And since TOR is involved in a lot of important cellular processes (brace yourself), inhibition of it by rapamycin and synthetic molecules has been studied extensively for other actions. The most interesting (well, perhaps until now) has been as an anticancer therapy. That alone illustrates the trickiness of this area, since one problem with any immunosuppressive therapy is a significantly higher risk of cancer. Decoupling these two effects has occupied a lot of time and effort over the years; that last link should give you an idea of the magnitude of the task.
But rapamycin has also shown life-extending properties in simple organisms, and this latest paper extends this effect to mice. The NIH group studying this had their problems, though - just adding the compound to rodent chow wasn't enough to achieve useful blood levels. More formulation work had to be done to produce an encapsulated version that could make it past the upper gut, and by the time that was worked out, the large cohort of mice set aside for the experiment was. . .well, rather more aged than planned.
But they went ahead with the experiment anyway, starting them off at 600 days old, which is roughly a 60-year-old human. Startlingly, the compound still extends life span, by about 14% in the female mice and 9% in the males. At ages where about 5% of the control mice were still alive, some 20% of the treated mice were still going. That's a very significant result, especially considering the late start. All in all, this looks like the most dramatic mid-to-later lifespan intervention that anyone's ever seen in a mammal. (Caloric restriction, for example, has been basically useless if started at the 600 day mark in mice, and no weight losses were seen here). There's a rapamycin study under way with mice in the prime of rodent life (starting at 270 days), and the preliminary results look quite similar (with again a stronger effect in the females).
The causes of death don't seem to have altered. A good sample of animals from both groups were checked by necropsy, and nothing significant was noted. That seems rather surprising, because the blood levels of the compound are (at least from what I can see) rather high. The paper mentions that the mice had 60 to 70 ng/mL rapamycin, and looking around, I find blood levels of 15 ng/mL mentioned as effective in tumor suppression in one mouse model, and the immunosuppressive doses seem to be similar. I'd be glad to hear from anyone who knows more about rapamycin dosing in mice, though; it's definitely outside my range of experience.
Are people going to run out and start taking the stuff? It wouldn't surprise me, although I'd have to say that that's a bad idea at the moment. There's an awful lot that we don't understand about the tradeoffs between aging, cancer, and the immune response, and I'd hate to end up on the wrong side of that bet. Jumping straight to humans is too big a leap for now, but remember - there are a lot of other mTOR inhibitors out there in development (try this paper for starters). If we can narrow down which pathways are important for lifespan (and believe me, there are people thinking hard about this right now, especially after this paper), then there could be some very interesting opportunities
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May 13, 2009
Now, this is an example of an idea being followed through to its logical conclusion. Here’s where we start: the good effects of exercise are well known, and seem to be beyond argument. Among these are marked improvements in insulin resistance (the hallmark of type II diabetes) and glucose uptake. In fact, exercise, combined with losing adipose weight, is absolutely the best therapy for mild cases of adult-onset diabetes, and can truly reverse the condition, an effect no other treatment can match.
So, what actually causes these exercise effects? There has to be a signal (or set of signals) down at the molecular level that tells your cells what’s happening, and initiates changes in their metabolism. One good candidate is the formation of reactive oxygen species (ROS) in the mitochondria. Exercise most certainly increases a person’s use of oxygen, and increases the work load on the mitochondria (since that’s where all the biochemical energy is coming from, anyway). Increased mitochondrial formation of ROS has been well documented, and they have a lot of physiological effects.
Of course, ROS are also implicated in many theories of aging and cellular damage, which is why cells have several systems to try to soak these things up. That’s exactly why people take antioxidants, vitamin C and vitamin E especially. So. . .what if you take those while you’re exercising?
A new paper in PNAS askes that exact question. About forty healthy young male volunteers took part in the study, which involved four weeks of identical exercise programs. Half of the volunteers were already in athletic training, and half weren’t. Both groups were then split again, and half of each cohort took 1000 mg/day of vitamin C and 400 IU/day vitamin E, while the other half took no antioxidants at all. So, we have the effects of exercise, plus and minus previous training, and plus and minus antioxidants.
And as it turns out, antioxidant supplements appear to cancel out many of the beneficial effects of exercise. Soaking up those transient bursts of reactive oxygen species keeps them from signaling. Looked at the other way, oxidative stress could be a key to preventing type II diabetes. Glucose uptake and insulin sensitivity aren't affected by exercise if you're taking supplementary amounts of vitamins C and E, and this effect is seen all the way down to molecular markers such as the PPAR coactivator proteins PGC1 alpha and beta. In fact, this paper seems to constitute strong evidence that ROS are the key mediators for the effects of exercise, and that this process is mediated through PGC1 and PPAR-gamma. (Note that PPAR-gamma is the target of the glitazone class of drugs for type II diabetes, although signaling in this area is notoriously complex).
Interestingly, exercise also increases the body's endogenous antioxidant systems - superoxide dismutase and so on. These are some of the gene targets of PPAR-gamma, suggesting that these are downstream effects. Taking antioxidant supplements kept these from going up, too. All these effects were slightly more pronounced in the group that hadn't been exercising before, but were still very strong across the board.
This confirms the suspicions raised by a paper from a group in Valencia last year, which showed that vitamin C supplementation seemed to decrease the development of endurance capacity during an exercise program. I think that there's enough evidence to go ahead and say it: exercise and antioxidants work against each other. The whole take-antioxidants-for-better-health idea, which has been taking some hits in recent years, has just taken another big one.
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June 6, 2008
Since it’s a favorite topic of mine, I really have to point out this study in PLoS ONE on resveratrol. A large collaboration looked at the gene transcription effects of dosing the compound in mice, compared to a normal diet and to a calorie-restricted one. I can’t do better than the first paragraph of the paper does at setting the scene:
” Caloric restriction (CR) retards several aspects of the aging process in mammals, including age-related mortality, tumorigenesis, physiological decline and the establishment of age-related transcriptional profiles. The wide scope of these actions, and the profound metabolic and hormonal shifts induced by CR has led to efforts at identifying natural or synthetic compounds that mimic the effects of CR in the absence of overt metabolic and endocrine disturbances or reduced caloric intake. Because most age-related diseases are likely to be secondary to the aging process itself, the discovery of such compounds could have a profound public health impact by reducing disease incidence and possibly extending the quality and length of the human lifespan.”
That’s a fine list of things that everyone would like to avoid: cancer, decline, and death. And the last sentence makes a key point, that the age-related diseases are not inevitable, but can be attacked as a group by attacking aging itself. A few years back, that statement might not have made it into a scientific paper at this level, but it can now.
This study had three groups of male mice (in a hybrid strain derived from C57 black): a control group getting 84 kcal/mouse/week of food, a calorie-restricted group getting 25% less chow, and a group getting the first diet plus 4.9 mg/kg of resveratrol, both experimental diets starting at mouse middle age (14 months). This same group had already reported that starting CR at that point in that mouse strain leads to about a 13% increase in lifespan.
As a baseline, they checked the transcriptional changes in young versus old mice on the control diet. There were, for example, about a thousand genes in heart tissue (out of twenty thousand checked) with a highly significant change in their profile. Comparing old heart tissue from the controls to the old tissue from the CR group, 536 genes showed a highly significant difference due to caloric restriction. The resveratrol-treated group, meanwhile, showed the same level of change in 522 genes, from basically the same list.
They also looked at skeletal muscle and brain (neocortex) and found similar but definitely less dramatic effects. In muscle, CR only affected about a quarter of the age-related genes (as opposed to half in the heart), and resveratrol was very similar. In the brain tissue, CR was able to reverse the aging profile in only 19% of age-related genes, and resveratrol lagged with 13%. The take-home message there is that aging can be a different process in different tissues, and attempts to alter it are going to vary across those tissues as well. (Here's the figure covering all these).
Another interesting question is whether CR (or resveratrol) affect other genes that aren’t in the age-related group. The answer is “Oh, yes indeed”, with over seven hundred genes whose profile was altered by CR but are not directly altered by age alone. (Compare that to the thousand age-altered genes, five hundred of which are reversed by CR, and you can see that this could be a source of significant effects). Resveratrol treatment did an extraordinary job of mimicking this profile, affecting 745 of the same 747 genes. The same thing was found in the other tissues – 1164 non-age-related transcription changes were found in skeletal muscle from the CR mice, and resveratrol treatment affected all 1164 of them.
So resveratrol appears to be a pretty close mimic of caloric restriction – but it’s closest in the non-age-related genes, which is interesting. The thing is, there’s no guarantee that all these transcriptional changes are good – presumably a lot of the ones that reverse age-related changes are beneficial (although we don’t know that for sure), but the ones that aren’t involved in aging could be more of a mixed bag. The net effect of CR does seem to be beneficial, but there are a lot of ways to arrive at that end point, and resveratrol could be mimicking the bad as well as the good. Here’s an attempt at figuring out the functions of the various genes involved in each group.
Of course, a much more relevant measure of benefit is how the animals themselves are doing under these treatments. The paper looks at some measures of cardiac function in young and old control mice, as well as in the treatment groups, and find that both CR and resveratrol seem to protect against decline. That chart also shows some other physiological readouts, at least one of which is rather surprising.
There's a huge insulin-signaling component in this whole field of study - the putative target of resveratrol (the sirtuins) are thoroughly tangled up in insulin and insulin-related growth factor (IGF) pathways. Genetic manipulation of several genes in those areas has also shown powerful effects on lifespan and aging in model organisms. So one of the oddities here is that the CR diet showed an effect on IGF-1, but resveratrol didn't. And while both treatment groups showed increased insulin sensitivity, several markers of that (glucose transporters, for example) showed the expected changes in the CR group but not the resveratrol group.
So if resveratrol treatment really does increase lifespan in the same way that caloric restriction does, it could mean that the insulin signaling axis isn't as important in CR as people thought. That's a difficult conclusion to come to, given the other data in the field, so a more reasonable one might be that resveratrol is hitting those same pathways, but not in the same way that CR does. (The similar increase in insulin sensitivity in the two groups argues for that view). Supporting this view, the transcription factor Pgc-1alpha, which is known to be very important for a range of genes in insulin sensitivity, was upregulated in muscle in the CR group but untouched in the resveratrol group.
The weirdest thing about this whole study, though, to my mind was the finding that levels of the prototype sirtuin, SIRT1, were not elevated in either group. That's in direct contrast to results seen in rats and humans under caloric restriction. In fact, in this case SIRT1 levels actually went down in the CR mice. There are several potential conclusions, all of which will keep people busy for a good while: perhaps some (or most?) of the anti-aging benefits of either CR or resveratrol in all species are coming from something else other than the effect on SIRT1. That would sow confusion, for sure. Or perhaps this is only true in mice, but not in rats (or people), and the sirtuin pathway really is the answer in the other species - in that case, you have to wonder what's so special about mice, and just what those different pathways are that kick in with them.
No, this is a very interesting study, and a very hopeful one, but it also points out just how much we don't know. I'm sure many more surprises like this are on the way, both positive and negative ones. But the overall point is made: aging and its effects can be altered. We don't understand quite how it's happening, and there are a lot of things to be worked out, but we can do it. If we can get the details worked out, human history is going to go through the biggest inflection point since fire and agriculture.
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April 25, 2008
I don’t want to say that this is a trend, but I notice that GSK is saying that they’re going to leave Sirtris more or less alone as well (as Takeda has said they’ll do with Millennium). The researchers in both shops should feel good about that, and not only because they’ll be keeping their jobs. They’re getting a vote of confidence in the most meaningful way that a large company can give that to its employees: by paying you money and not messing with you.
Of course, these deals have two sides to them. I don’t know what it’s like in Takeda back in Japan – my contacts inside the Japanese pharmaceutical industry aren’t extensive. But I think that some of the people at GSK (where I do know a lot of people) are wondering just what motivated their company to spend $720 million on Sirtris rather than on them.
It’s a fair question, even though I don’t have a problem myself with the Sirtris deal (as I said yesterday). But the sirtuins themselves are targets that anyone can work on, and you’d assume that a big outfit like GlaxoSmithKline could, if they wanted to, make a big push into the area and find some interesting things. So why didn’t they? The most obvious reason would be Sirtris had already done a good deal of that work, and it was more economical for GSK to buy it than to redo it. Another possibility is that the chemical space for drug-like hits in that area may not be very spacious, and that Sirtris may have already carved out a good piece of that real estate.
There’s also a bit of Glaxo history to deal with. The company had already, about fifteen years ago, decided to make a great big push into a promising new research area: nuclear receptors. They set up a whole research institute and did a huge amount of good science trying to figure out how these things worked, what they were good for, and how to get drugs that affected them. I got interested in the field in the late 1990s, and it became clear to me very quickly that Glaxo’s effort was the most serious of the bunch (and that included some really substantial research going on at Merck, Lilly and some other outfits). The company had teams of people who seemed to do nothing else than study the structures of these things, generate reams of X-ray data, synthesize huge lists of ligand molecules of every kind you could want, and so on. Just run "Glaxo nuclear receptor" through PubMed to see what I mean.
And what did it get them? From what I can see, not much. Avandia (rosiglitazone) is a nuclear receptor ligand (for PPAR-gamma), but its activity had already been discovered, and it was in clinical trials without a known mechanism. Figuring out how it worked was one of the Glaxo team’s early triumphs. But Avandia has turned out to be famously troublesome, and no others have come to market, despite multiple tries in the clinic. The huge amount of time and money the company spent generated a lot of interesting science, but appears (at least to me) to have brought in not one dime of revenue. (No doubt someone from GSK will correct me if I’m wrong).
So you can see how the company might be wary of starting a big internal effort to explore a massive, complex, and risky new field of biology. Politically and psychologically, it’s probably easier for them to structure this in terms of an acquisition.
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April 24, 2008
Well, I’m back from a brief vacation, and catching up with the news. It looks like the big headline is GlaxoSmithKline’s offer for Sirtris: $720 million, which is a hefty premium (84%!) to what the company was trading for previously. Reckless waste of money, or canny deal?
I lean toward the latter, but I’ve long had a place in my heart for sirtuin research and its potential. It’s still a long shot, but it’s one of the most intriguing ones in the history of medicine. Actually, from one perspective, you wonder how long a shot it is: a biochemical pathway that seems to extend healthy life in yeast, roundworms, flies, and mice would seem to have some odds of doing the same thing in man. A lot of drug programs have been started with a lot less backing them up, albeit for rather less earth-shattering indications.
Of course, Sirtris hasn’t officially been targeting life extension drugs, at least not in the near term. A number of these potential life-extending biochemical pathways are tied up with insulin signaling, which makes sirtuin-targeted drugs a natural for diabetic therapy as well. Sirtris has reported encouraging data for just that indication. If a sirtuin-based drug is going to make it to market, that’s a good bet for how it’ll do it. I note, though, that the company has also applied for orphan-drug status for resveratrol itself for a rare muscle disorder. But they don’t own that parent compound, just its use in this case – the diabetes work is being carried on with second- and third-generation analogs that address some of resveratrol’s problems. (It’s not a particularly stable compound, for one thing).
Once one of these drugs is approved, it’ll have the biggest, strangest potential for off-label use that anyone has ever seen. Oh, that’s going to be something to watch. GSK is well aware of this – I’m not saying that it’s part of their business plan, but when you see their head of drug discovery talking to Forbes and tossing the word “transformational” around, you know that they’ve thought beyond a replacement for Avandia. The Wall Street Journal headlines it like it is: “Glaxo to Buy Sirtris in Bet on Antiaging Reseach”.
That’s the truth, all right, and it’s going to be fascinating to watch things develop. As I was saying here the other day, a drug for aging is a perfect example of something the FDA has absolutely no idea of how to approach. Well, it’s not just the FDA, come to think of it: how on earth would you design a Phase II trial for life extension? How long would it take? What’s your clinical endpoint? And further on, how long will you want to monitor your Phase III patients (recall Pfizer’s recent follow-up of Exubera trial participants? How long will it take before you could be sure that some horrible bargain wasn’t struck along the way?
That’s the lurking fear behind all this research, fit to give Leon Kass the shakes. Life extension tends to give some people the same “Things Man Was Not Meant to Know” shivers as (for example) germ-line genetic manipulation. I’m tempted to cue the theramin music in the background, but I can’t really make fun of this attitude, since I understand where the uneasiness is coming from. In all these cases, we’re looking at real alterations of what we think of as human. Personally, I think there’s room for improvement in what we think of as human, but I agree that we should reach for those improvements carefully. And I can see how the very thought could strike some people as coming close to crazy.
But we’re going to find out. That’s the real import of the GSK news: the money is there to find out what’s possible in this field. I’m happy to hear it. But then, I was a bit euphoric back in 2003 when this news started breaking, and I’ve never really lost that feeling. We shall see.
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January 21, 2008
Update: Prof. de Grey responds to Jim Hu's criticisms below
I didn’t note it at the time here, but back in November there was a very interesting paper in Nature that bears on aging and life extension. A group at the Hutchinson Center in Seattle did a survey of compounds, looking for whatever might show up that seemed to extend lifespan. (That’s just the sort of see-what-falls-out screen that C. elegans is good for, since the little beasts are so small, and they only live for about 20 days or so).
They screened 88,000 compounds - by far the largest direct survey ever run for longevity, as far as anyone knows, but (I should point out) still a tiny run by industrial standards. But they came up with a few hits: 1083 compounds made the first cut (roundworms still alive longer than they should be), and 115 of those repeated with statistical significance. 13 compounds increased lifespan by 30 to 60%. Interestingly, I don't think that they list all of them in the paper, but they did note that one of the strong hits looked very much like a known hit set of serotinergic antagonists.
They ran a set of analogs through the assay, and had a high hit rate. All the compounds that worked were 5-HT2 antagonists, such as marketed drug mianserin, although they each have some other activities as well. (It should be noted that the reuptake inhibitors, the Prozac/Zoloft type compounds, had no effect). But the 5-HT2 subtype, particularly 5-HT2c, has long been regarded as important in food intake, so the guess is that these compounds also tie into the whole caloric restriction story for aging. Restricting food intake and giving one of these drugs at the same time didn't add anything, the group found. It may be that these compounds set off metabolic signals that tell the roundworms that they’re short of food, even they they really aren’t, and thus do a sort of fake caloric restriction on them. At any rate, mutant nematodes that can't make serotonin showed no lifespan extension with exposure to these compounds, so one way or another, it seems to be involved.
Now, I wouldn’t advocate running out and trying this on a human being just yet, though, since we’ve come up with several higher brain functions for our serotinergic receptors that roundworms don’t have much call for. There’s also the question of what this strategy would feel like in a higher animal: would you want to live longer, but always feel as if you were starving, for example? I know that the people who are trying CR on themselves say that this isn’t the case, at least after the first few weeks or months (!), but there’s no telling what would happen with a pharmacological approach.
What this study does point out, though, is something that I think that a lot of people haven’t really caught on to yet: first, it’s increasingly clear that there are deep connections between metabolism and lifespan. All sorts of genes related to food intake and insulin signaling affect how long model organisms live, and there’s every reason to expect that the same is true of us.
Second, the settings for our lifespans may not be optimal – or what we’d now consider optimal. There’s every reason to expect that this relationship has been under very heavy selection pressure. Evolutionarily, this would be the balance between reproductive fitness and everything else an organism might do, and evolutionarily, reproductive fitness is going to be the big winner every time. But there’s no reason that we necessarily have to accept whatever tradeoffs were made during the development of our species.
We’re going to have to be very careful, of course. There may be all kinds of catches to extending lifespan – susceptibility to cancer and other diseases being the first one that everyone thinks of. But ever since our brains became large and complex enough for language and culture, and ever since we started growing our own food, we’ve been altering the evolutionary bargains that all other species have had to make – predator/prey relationships, availability of food, and so on. We may yet be able to draw a black line through another paragraph of the contract, and make it stick.
I don’t think that many people realize that this is possible, or that it’s an area of active research. Most of the large drug companies, in fact, seem to be staying away from it for now, content to let the smaller ones take on the (considerable) risks. Some people may not be able to get past Aubrey de Grey’s hair, and may have decided the whole subject is out on the fringe. But, increasingly, I don’t think it is. This stuff could work, eventually, and if it does, it’ll be one of the biggest inflection points in the history of the species.
Update: Jim Hu has more to criticize about de Grey than his hair - see here and here, for starters. Of course, as Jim himself points out in the comments, criticizing de Grey isn't the same as criticizing research on aging. Perhaps de Grey's high profile is doing as much harm as good for the field. . .
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September 24, 2007
It’s been a while since I talked about sirtuins, but the field has not been quiet. The latest data is a paper in Cell which set off a strong move in the stock of Sirtris, the company closely tied to the labs involved.
SIRT1 had already been the focus of a huge amount of attention in the aging/cancer field, but this paper seems to validate two other members of the family, SIRT3 and SIRT4. It’s mostly the story of NAD+, a very fundamental molecule indeed in cellular metabolism. There’s been some evidence (and a lot of speculation) that NAD+ levels are regulated quite differently in the mitochondria as opposed to the rest of the cell, but getting hard data on this pathway hasn’t been easy.
What is known is that apoptosis (programmed cell death) can depend on NAD+ levels. An enzyme called PARP-1 depletes NAD+ levels when it’s activated, and sets off a chain of events leading to apoptosis. Recently it was shown that there’s a PARP-1 fraction inside mitochondria, and given their central role in energy production, this gave room to wonder if an apoptosis signal could be set off from in there as well. On the flip side, NAD+ is synthesized (in mammals, anyway) though a pathway involving the enzyme Nampt. It’s also present in mitochondria, along with another NAD-pathway enzyme called Nnmat, so all the machinery is presumably there to up- and downregulate mitochondrial NAD+.
And so it does. The Cell paper looked at NAD+ levels inside mitrochondria for the first time, and found that they change greatly in response to nutrient levels. Fasted animals (and cells) greatly increased their mitrochondrial NAD+, which makes sense.
At first the authors were puzzled, when they found that although Nampt protected cells from genotoxic stress, it didn’t seem to affect how low the NAD+ levels in the cells went. Overexpression, underexpression – they all went down to the same low levels. It was only when the looked inside the mitochondria that they found where the NAD+ was being maintained.
So mitochondria can hold normal NAD+ levels even after they’ve fallen in other cell compartments. As far as the authors can tell, this is because of local synthesis, although it’s possible that the mitochondria also import all that they can get their hands on under such conditions. But the fact that levels of mitochondrial Nampt also rise along with the NAD+ argues for biosynthesis.
And the protective effects of all this NAD+ work through SIRT3 and SIRT4. Their activity is limited by the amount of NAD+ around, so it makes sense that they get more active under stress, when NAD+ levels are up. siRNA knockdowns of all seven sirtuins showed that only the 3 and 4 subtypes – which are localized in the mitochondria – are the players.
All this makes Nampt look like the yeast gene called PNC-1, which is on the yeast and roundworm pathway to make NAD+. PNC-1 has been shown to be involved in extending lifespan in such creatures, so if the human homolog has been found, the immediate question is whether it has the same effects. Its changes in fasting rats suggest a link with the caloric restriction route to lifespan extension. Overall, you have to think that if we’re not onto the relevant pathways, we’re very close indeed.
Thus the spike in Sirtris stock. It came back down as various analysts make cautious noises today, but until the company gets some Phase II data, publications like this one will be what moves things around. If you’re interested in a wild and speculative ride, they’re worth a look. Don’t expect a dull time, though – there’s an awful lot about this stuff that we don’t know.
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November 1, 2006
Back in 2003, I wrote about the paper that identified the natural product resveratrol as an activator of the sirtuin deacetylase pathway. This may well be the common thread between a host of studies on life-extending genes in model organisms and the much-publicized phenomenon of life extension through caloric restriction. In other words, if you want to live longer, but don't feel like taking in a third fewer calories, it's possible that activating sirtuin might do the job for you, and resveratrol is the prototype activator.
Three years ago, after first pointing out that many companies might want to run screens for sirtuin activators, I went on to speculate:
Second, there is no reason to think that resveratrol itself is an optimized molecule. It's a great starting point, but as a medicinal chemist I can see several things I'd like to do to it immediately. Hey, fellow chemists, let's talk shop here. . .(list of possible structural modifications follows - DBL). . .Believe me, thousands of folks like me are looking at this structure today and having these exact thoughts, and some of them are going to act on them (if someone hasn't already.)
Third, this compound is surely being given to higher animals as we speak. I can see no reason not to start feeding it to mice in a long-term study. Mice live around two years - let's try for three! After all, it's already been given to rodents in other studies. (And those are just papers from the last year or two!) But as far as I can tell, none of these have allowed the mice to age to their full normal lifespan under resveratrol dosing. Time to find out!
Well, in an unusual development for my predictions, all of this is coming true. This summer, David Sinclair (who leads one of the major efforts in this area - another is led by his former boss, Leonard Guarente) published an interesting review of resveratrol's in vivo effects. Now his group reports in Nature that resveratrol does indeed have effects in mice - very powerful effects indeed. When put on a high-fat diet, normal mice gain weight, develop diabetes and liver problems, and die early. But on the same diet along with resveratrol, the mice (although they do put on weight) show improved glucose and insulin levels, better liver function, and significantly increased lifespan. Their activity and motor abilities appear to mimic normal-diet mice, even into their extended old age. (Here's their press release if you don't have a Nature subscription).
And on top of this, Sinclair's company has let it be known that they have developed improved molecules based on resveratrol, and are now taking them into the clinic. The first one is called SRT501, and I'd be very interested to know its structure. But remember that compound code - you're going to be hearing about it again.
These are still early days. There may be penalties to pay for messing around with longevity (increased cancer rates are only the first thing that come to mind). But there may also be a revolution in progress here, something that will make the future quite different from what we've been imagining it will be. G. K. Chesterton would be happy - scroll down here for a discussion of the game of "Cheat The Prophet". Is anyone ready for Cheat the Reaper?
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November 20, 2005
I've written before about the gene known as SIR2. Overexpression of it (or its homologs in different animals) extends lifespan in a range of organisms, and there's been a tremendous amount of research on these over the last few years. A good deal of evidence has linked them to the known life-extending effects of caloric restriction. In mice, for example, Sirt1 is involved in nutrient sensing and fat mobilization.
It suggests a pretty neat package, but the ribbon on it is unraveling. I wrote about Sir2/Sirt1 here a couple of years ago, where I said "An extra copy of the gene lengthens life; deletion shortens it." Well, in yeast cells that appears to be true, when you measure lifespan by how many times the cells can divide before burning out.
But what if you measure lifespan by the amount of time the cells can live when they're not dividing? That's the subject of a new paper in Cell from Valter Longo's group at USC, which they have given the provocative title "Sir2 Blocks Extreme Life-Span Extension." Yep, deleting it actually extends the non-dividing lifespan of the yeast, and combining that with caloric restriction increases it even more. These yeast cells have some problems, though, some of which can be ameliorated by further mutations in the IGF-1 pathway (itself heavily implicated in metabolic rate and lifespan). Yeast with combined Sir2 and IGF mutations, under caloric restriction, live longer by up to sixfold, a startling increase.
So what about higher organisms? Well, there appear to be some very similar findings in mice - maybe. Earlier this year, Frederick Alt's lab at Children's Hospital in Boston deleted Sirt1 in mouse cells and found, quite to their surprise, that the cells were extremely vigorous indeed. Such cell lines start to break down after a certain number of passages (cell divisions), but the Sirt1 knockouts just keep rolling along.
They then tried growing the cells under oxidative stress, but they plowed right through that, too. That led to the thought that Sirt1 might be some sort of checkpoint, which would normally limit cell division under such DNA-damaging conditions. But the Sirt1-deleted cells showed no signs of greater DNA degradation than normal lines. They're quite robust.
This is all extremely interesting, but you may have noticed that I pulled a fast one here. In these mouse cell lines, it appears that replicative life span has increased when Sirt1 is taken out - but with Sir2 deletion in yeast that's not the case at all. There it's replicative life span that takes the hit, and non-replicating (chronological) life span that's increased. How do we reconcile these blatantly contradictory findings? I've no idea, but it's a safe bet that several high-powered labs are currently working overnight shifts to answer that question.
So much for mouse cells - how about whole mice? Well, as hardy as some of their cells may be, the Sirt1 knockout is a pretty hard animal to prepare, because most of the mice don't survive. The ones that do appear fairly normal, but have a complex phenotype, which includes decreased fat mass and body weight. (Alt's group is also trying to interfere with Sirt1 in adult animals, bypassing all the developmental roles that make the standard knockouts so hard to work with).
The big question now, given all these divergent cell findings, is: will these guys live longer, or not? And what happens to them when you put them on a limited-calorie diet? Are they going to act like the replicative-aging models, or the chronological aging ones? (We'll leave the yeast-mouse contradiction out of it for a while). Perhaps the two mechanisms will fight each other to a standstill, leaving the animals with plain ol' normal lifespans, but with some tissues acting much younger than the whole-body age and some acting much older. Mice generally live around two years. I wonder just how many months ago these lifespan studies started. . .
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September 19, 2005
There's been a lot of news in the aging-research area about the Klotho gene (and its associated protein) the last few years. Now there's a recent paper in Science that is bringing it back into the spotlight.
I won't go into all the details - that link and this one will give you some good background - but the short form is that adding an extra Klotho gene extends mouse lifespan by up to 30%. (It was already known that deleting the gene shortened lifespan drastically - the paper we're seeing now is the result of an immediate effort to take the system in the opposite direction. Aging research takes a long time!)
Some of the most interesting anti-aging genes that have turned up in roundworms and flies have to do with insulin (and insulin-related growth factor, IGF) signaling. This team of researchers thought that the Klotho protein might fall into the same category, and they were right: the protein seems to lower insulin sensitivity by affecting signaling through the insulin and IGF receptors.
Here's where my drug-discovery radar started pinging. These receptors are part of a family that carries their own kinase along to phosphorylate themselves, and that's a key even in their signaling cascade. This new work noted that Klotho suppressed autophosphorylation of the receptors, and that makes sense, considering the downstream effects. It's very interesting to note that compounds that affect the IGF receptor kinase are already being developed. They're potential anticancer agents, and a number of companies seem to be working on them.
Now, I'm not aware of anything that's been developed to inhibit the insulin receptor kinase, mainly because no one has seen a market for giving people a sort of quick-acting type II diabetes. But it's certainly possible that such a compound could be discovered, if someone were to look. What would the effects be of lower doses of such kinase inhibitors in normal humans? Could one get the effect of the Klotho hormone through that route, or does it cause other things to happen through its own pathways?
I think someone's going to be tempted to find out. Intense work is doubtless in progress in this area, and there will be many more things to be discovered. But if the insulin/IGF story continues to hold up, I don't see what's going to stop people from trying this out on themselves or on others. It's probably the nearest thing in the whole field to being realized in practice. And if it doesn't happen here, it might take place somewhere else with more. . .relaxed clinical standards. Worth keeping an eye on. . .
UPDATE: ". . .I just wish I understood more than every third word." Well, that was a kind of condensed post, I have to admit. I was a bit short on time, and it's a pretty knotty subject, even for the people who work in it. But I promise that I'll come back to it and try for a from-the-bottom-up backgrounder. And I'll try to get to it before we all need life-extension drugs. What's that? You say we all need them now?
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August 1, 2002
I've written about the idea that aging is related to oxidative damage (most recently on June 3.) There's a lot of support for it, and the documented life-extending properties of caloric restriction are thought by many to be tied into this hypothesis. CR has worked in (for example) fruit flies and rodents, and some slow-moving experiments suggest that it works in larger animals up to primates. The less you eat, the less you metabolize, the fewer reactive oxygen species you generate, and the less damage you do to your cellular machinery. It makes a lot of sense.
Too much sense, I suppose. As is the relentless way of science, the waters have been thoroughly muddied by a report in the July 18 issue of Nature (a summary is here.) [Note added on August 1: these links don't seem to work without a subscription to Nature. I'll see if I can find free ones and post those.] These researchers studied yeast, using the number of divisions a cell can go through as a measure of lifespan. Some of their earlier work supported the CR trend, since they found that yeast grown in reduced-glucose conditions went on dividing for 30% longer.
They were even able to tie this effect to the presence of a particular gene, SIR2. That codes for a histone deacetylase, which would puts it squarely in the gene transcription / regulation area. There's a lot to write about those, of course, but for those who don't follow the field, the short story is that DNA needs to be wound and unwound from histone proteins in order to be transcribed into RNA. Acetylation and deacetylation of the histones is one of the key switches for those processes, although there are others. And there are things that regulate them, and things that regulate the regulators, and things that modulate the effect of the regulation of the thing that cancels the actions of the. . .ah, cell biology. Nothing like it.
But when they looked at things more closely, they found that the calorically-restricted yeast actually have three times the respiration rate! So much for the simple hypothesis. A closer look showed that a key factor is the way that yeast can switch back and forth between respiration (when there's enough oxygen) and fermentation (when there isn't.) Carbon dioxide is the waste product of the first process, which yields more bang for the buck. And as the world well knows, ethanol is the waste product of the second one. Grow yeast under conditions where they do both, and you've got beer. When there's just enough food to survive, it seems, the yeast switch entirely over to respiration for its greater efficiency.
As it turns out, not only do the CR yeast respire faster, but if you mutate them to where they can't respire at all, caloric restriction doesn't increase life span. So what about all the foul free radicals produced by all that respiration? The CR yeast were shown to be more sensitive to free radical sources (which usually means that their existing machinery for detoxifying such things is already stretched near its limit) but these cells showed no increase in the usual suspects (like superoxide dismutatase.)
The free-radical production and protection pathways are clearly more complicated than they seemed. (And, of course, anyone who buys superoxide dismutase tablets at a health food store is clearly a fool, but that's been obvious long before this paper came out.) What would make the story neat and clean is if the SIR2 histone deactylase turned out to be regulating unknown genes that are involved in detoxifying free radicals. That's probably too rational, but it's the first thing to check.
Does any of this apply to larger things than yeast? No one knows yet if mammals on CR diets respire more (although I'll bet that folks are checking as we speak.) SIR2 works the same way in roundworms (C. elegans, the biologist's friend,) and there are homologous genes in higher animals. It's part of some highly conserved metabolic pathway, whatever it is. If we can get our hands on it, there may be hope for an extended life span during which we could actually have a pizza every so often.
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June 3, 2002
Another useful paper (Science 296, 1276) has come out on the mechanisms of aging. Ever since the 1950s, the idea of accumulating free radical damage has been a strong contender, to the point that it's been absorbed into popular culture. All the free radicals needed for this damage to take place are produced by our own metabolism: oxygen is pretty fierce stuff to handle.
There's a good amount of evidence that this theory is at least partially correct (such as the existence of enzymes like superoxide dismutase, SOD, whose only function in life is to get rid of one of those reactive oxygen-derived species.) And now there's more. The latest work involves mice with a mutated form of a particular helicase protein called Xpd. This is an important part of the DNA-RNA transcription machinery, and it's also important for a variety of DNA repair, nucleotide excision. The dual function makes sense; both processes involve unwinding the double helix so enzymes can bind to it directly.
There's a human genetic disease, trichothiodystrophy (TTD) that involves alterations in Xpd function, and the research group was trying to come up with a mouse syndrome that would mimic it. They got it, but the mice also shown signs of accelerating aging (gray hair, osteoporosis, loss of appetite, shorter life span.)
That would seem to be the end of the story: if you can't repair DNA damage, you age quicker. But another experiment has already been done to completely knock out a closely related protein called Xpa, and that knockout completely wipes out the ability to do nucleotide-excision repair. But those knockout mice don't show signs of premature aging! So what's going on?
One way to find out would be to take those Xpa-knockout mice and introduce the Xpd mutation into them. This group tried that experiment, and got the same premature aging, but in much more severe form. What might be happening, then, is that the total effect of DNA damage on gene transcription might be the aging factor. If you can still read off the DNA, damaged or not, then cell activity can still muddle on (as in the Xpa knockouts that don't show premature aging.) If your gene transcription keeps getting stalled out, as in the Xpd mutants, then you're in trouble. The cells involved end up dying (by programmed cellular suicide, apoptosis) or damaged. If you have both mutations at once, the defective DNA that accumulates is unwound and exposed for even longer periods, setting both those processes in motion even faster.
We're getting closer to making a coherent picture out of this - other knockout experiments shed some light on it, and others are no doubt in progress. As for what to do about it, that's a different question. The close association of aging with DNA damage means that there may well be a tradeoff between oncogenesis and aging - you can keep your cells alive for a long time, at the risk of developing cancer, or you can have them kill themselves off at the first sign of trouble, which helps to cause aging. We'll have to tread carefully, but there would still seem to be some wiggle room in there.
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May 14, 2002
There's an interesting article on aging in the latest issue of Current Biology. The researchers used gene-chip assays, which look at over 13,000 genes simultaneously for signs of up- or down-regulation, in populations of aging fruit flies.
Fruit flies share a rather unnerving number of similar genes with other animals (all the way up to us,) and their short live span makes the attractive for this kind of study. What makes this one stand out is the amount of detail it goes into.
The team checked the flies at different time points, in multiple populations, and under conditions of normal aging and caloric restriction. That last technique - basically, living close to starvation - has been shown in increase life span in many species. There are some people trying it as well (you have to be pretty careful with your nutritional balance, and the question always comes up about how wonderful excess life span can be if you can't eat anything. . .)
This study also controlled for how much the various genes tend to vary. You can see some genes tripling in activity, and it means nothing, because they vary naturally even more than that. Others are so steady that almost any change (up or down) is news.
Gene chips have been all the rage for a few years now, and they're getting more powerful all the time. But not too many people control their experiments with them as well as this group did, which often makes it hard to figure out what the data are telling you. In this case, though, they saw about 800 genes that were definitely associated with age-related changes. Half of those changed whether the flies were calorically restricted or not.
Some of them were things that had already been picked up by other studies. But there are quite a few new ones (enzymes and proteins that inhibit them, proteins involved at the cell nucleus, and others) that no one had fingered before. This paper will be a road map for some time to come for those looking at aging.
And many are, or will be. I think that over the next ten to twenty years, this is a field that could really take off. What use is a longer lifespan if you spend your extra ten (or 20, or 30) years as an eighty-year-old? Let's add those extra years to the twenties, thirties, and forties instead.
This is just the sort of research that probably sends Francis Fukuyama up the wall, to judge from his recent book and op-eds. (There's been a huge pile of commentary in the Blogosphere about all this, which I assume people have seen.) It's true that changing the human life span will probably lead to all sorts of disruptions - but we've done it before. The last hundred years has been a huge experiment in lengthening the average life expectancy, but because it was done by improving mortality rates and nutrition, no one had any room to object. In the same way, no one objects to the long, slow genetic engineering that humans have been doing with their crops and domestic animals. It's just when things get more efficient that the alarm bells start to go off. . .
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