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DBL%20Hendrix%20small.png College chemistry, 1983

Derek Lowe The 2002 Model

Dbl%20new%20portrait%20B%26W.png 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: Twitter: Dereklowe

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April 1, 2002

Enzymes, Right and Wrong

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Posted by Derek

>A post of mine from February 26 mentioned in passing the side effects of the anti-HIV protease inhibitor drugs. There's nothing inherent in their mechanism that should cause lipid profile changes and insulin resistance, so the hunt has been on for what other target is responsible.

Now a team at Washington University in St. Louis seems to have picked up the scent. They've found that one of the drugs, Crixivan (indinavir) shuts down the action of a protein called Glut4. Metabolism and endocrinology folks will find that connection pretty believable: Glut4 is one of a family of glucose transporter proteins, whose lot in life it is to take glucose out of the blood stream and pump it into cells. They're found everywhere, with different levels of activity, but Glut4 is key one that responds to insulin stimulation - its action is the primary reason why a shot of insulin lowers blood sugar.

Inhibiting it, then, causes some of the most important actions of insulin to be less effective, which is a back-door route into a state much like Type II diabetes. Lipids and glucose are tied together physiologically, since they're the two main circulating fuels available. You can't mess around with one system without the other responding.

I'm not aware of any other molecules that selectively inhibit Glut4 - as you can imagine, doing that hasn't been a priority for anyone. There's not much of a market for a compound that pushes you toward diabetes. Now, if you knew a way to activatethe transporter, or to keep it working longer, then the metabolic-disease researchers would be ringing your phone pretty quickly. No one's been able to do those things, and many of the steps in Glut4 activation aren't well worked out.

And as far as I can tell, the mechanism by which this new inhibition takes place isn't worked out yet, either. The drugs that cause the side effects are structurally rather different, so the best guess is that they're all hitting some other enzyme that's necessary for Glut4 function. It would just be bad luck that this enzyme, whatever it is, looks enough like HIV protease at the molecular level for drugs to shut down both of them.

If we can find the culprit, then we can try to come up with compounds that are more selective, or find some other treatment to compensate. At the same time, figuring out that problem could shed light on some longstanding problems in diabetes research, too. Stay tuned.

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