SHU T T ERSTO CK
SCIENCE & TECHNOLOGY
Soon after Sirtris was founded, the link between sirtuins and resveratrol drew additional scrutiny. A set of studies showed that the fluorescent peptide throws off the assay results. Without the fluorophore around, resveratrol can’t activate sirtuin enzymes under the assay conditions (J. Biol. Chem. 2005, 280, 17038 and 17187; Chem. Biol. Drug Des. 2009, 74, 619). “In my mind, the resveratrol claim is an artifact,” says DiStefano, who coauthored one of the studies. The results don’t necessarily mean that the sirtuin result was a red herring, says Matt R. Kaeberlein of the University of Washington, one of DiStefano’s coauthors. Sirtuins remove acetyl groups from a wide variety of substrates, and a given assay might be looking at deacetylation of model peptides for only a couple of those substrates. “It’s really hard to prove that there isn’t some specific substrate” for which resveratrol will activate the sirtuins, More results question molecular link between he says. “Clearly, this fluorescent substrate RED WINE COMPOUND and its antiaging activity works. The question is, ‘Are there biologiCARMEN DRAHL, C&EN WASHINGTON cally relevant substrates?’ ” Resveratrol has also attracted attention because it appears to mimic gene changes A GLASS OF RED WINE might hold a like a lot of natural products, it has mulrelated to caloric restriction, which for certain mystique, but its mystery on a motiple actions,” says Peter DiStefano, chief decades has been known to extend lifelecular level runs far deeper. That’s largely scientific officer at Elixir Pharmaceuticals, spans in animal models (C&EN, Aug. 3, because of resveratrol, a compound in red a company that has expage 36). And genetic wine and many plants. In animal tests, resplored sirtuin pathways. tests that attempt to OH veratrol has shown potential for protecting Biologist David A. deconvolute resveraagainst a number of diseases, from stroke Sinclair and coworktrol’s antiaging activity HO to cancer. But perhaps the most controverers at Harvard Medical still point to some kind sial of its potential benefits comes from its School were the first to of sirtuin connection, effects on longevity in simple animals such link resveratrol and the says molecular biologist OH as fruit flies and worms, and in more comsirtuins. Using a fluoresCynthia Kenyon of the plex animals such as obese mice. cent peptide substrate University of California, Resveratrol It’s been suggested that resveratrol that lights up upon reSan Francisco. “It’s a boosts these animals’ life-spans by actmoval of an acetyl group, story that almost makes ing on a specific family of enzymes called the team detected sirtuin activation in the sense, but not quite,” she says. “Why is it sirtuins that remove acetyl groups from presence of resveratrol (Nature 2003, 425, that you need sirtuins for resveratrol to do proteins. But resveratrol affects a slew of 191). Sinclair later cofounded Sirtris Pharwhat it does, and yet resveratrol doesn’t biochemical pathways, and even after years maceuticals, a company focused on the seem to be activating sirtuins?” of research, it’s not clear how the sirtuins therapeutic potential of the sirtuin pathIt takes more than a single assay to define fit into the antiaging picture, if at all. way. In 2008, GlaxoSmithKline acquired such complex biochemistry, DiStefano “Structurally, resveratrol is simple, but Sirtris for $720 million. says. Elixir isn’t pursuing resveratrol, but DRINK UP?
Resveratrol, a compound in red wine, has antiaging effects in lab animals for reasons that still aren’t clear.
REVISITING RESVERATROL
“There’s a lot of interesting stuff going on with resveratrol and a lot of interesting stuff going on with the sirtuins. How it fits together is the big question.” WWW.CEN-ONLINE.ORG
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the company has developed other ways to measure sirtuin activation, such as a proprietary assay that measures the formation of radioactively labeled nicotinamide (Methods 2005, 36, 346). Sirtuins release one molecule of nicotinamide from a hydrolyzed cofactor for every deacetylation event. Pharmaceutical firm Amgen has also described assays for measuring sirtuin activity (Anal. Biochem. 2008, 378, 53). The first of these assays is based on microfluidics. The assay also employs a fluorescent peptide substrate but is designed to minimize interference from fluorescent compounds. The second Amgen assay couples turnover of the sirtuin enzymes’ cofactor to a lightgenerating process catalyzed by a bacterial luciferase enzyme. “Secondary screens are important and necessary to verify whether or not resveratrol activates the enzyme,” DiStefano says. In addition to finding valid assays, it would be nice to determine what the effects of resveratrol are, if any, in mice that lack individual sirtuins, Kaeberlein says. IN THE END, the resveratrol excitement
is about whether it has antiaging potential in people, which has yet to be evaluated by the Food & Drug Administration. “Whether resveratrol or sirtuin-activating compounds have significant biological effects in humans remains unclear,” Kaeberlein says. Sirtris is testing a proprietary formulation of resveratrol called SRT-501 in cancer patients, but the firm is mainly focused on testing more selective sirtuin activators for treating a variety of diseases, including type 2 diabetes, says biochemist George Vlasuk, president of the company. “We’ve always considered resveratrol to be an interesting compound from a proof-of-concept point of view,” he says. Although several studies indicate a sirtuin dependence, resveratrol’s many activities complicate researchers’ understanding of its mode of action, he adds. Researchers who are interested in understanding resveratrol and the sirtuins will be looking to clinical trials for clues, says Kenyon, a cofounder of Elixir. Even if resveratrol doesn’t directly activate sirtuins, it’s still worth investigating for many other reasons, and the sirtuins are still major metabolic regulators, she adds. “There’s a lot of interesting stuff going on with resveratrol and a lot of interesting stuff going on with the sirtuins,” Kaeberlein says. “How it fits together is the big question.” ■ WWW.CEN-ONLINE.ORG
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