Page last updated: Tuesday, November 18, 2008
Important antioxidant, pterostilben, found in grapes
A further compound identified in grapes may fight cancer and diabetes according to researchers with the U.S. Department of Agriculture.The compound, pterostilbene, is similar to resveratrol.

Previous studies by others have demonstrated that pterostilbene also has anti-diabetic properties. The current study is the first to identify it as a cancer-preventive agent, however.

‘The study adds to the growing health benefits of grapes’ said Agnes M. Rimando, Ph.D., lead investigator for the study and a research chemist with the USDA’s Natural Products Utilization Research Unit in Oxford, Miss.The research, limited to laboratory studies of cells, could lead to more healthful varieties of grapes and the design of better drugs to fight cancer and diabetes. Prompted by the structural similarity of pterostilbene to resveratrol, Rimando decided to test the compound to determine if it had similar anticancer and antioxidant activities. In lab tests using mouse mammary cells, pterostilbene prevented a type of cell damage that is normally induced by cancer-causing agents. . Earlier studies by the researcher showed that the compound is toxic to a human breast cancer cell line. It appears that pterostilbene is equal in potency to resveratrol as a cancer-preventive agent.The similar effect is likely due to their high antioxidant activity. Antioxidants destroy free-radicals, highly reactive molecules whose excess has been linked to cancer.Pterostilbene has another benefit not found in resveratrol. Animal studies by others have shown that the compound can lower blood glucose and may be a potent antidiabetic agent. At least one study showed that it could lower plasma glucose levels in rats with high blood sugar by 42 percent, comparable to at least one known antidiabetic agent (metformin), according to the researcher.

Both pterostilbene and resveratrol belong to a group of chemicals called phytoalexins, which are produced by plants in response to fungal infection, ultraviolet light, and various chemical and physical stressors. While both exhibit strong antifungal activity, pterostilbene appears to be 60 to 100 times more potent as a fungicide, a property that may one day be exploited by farmers in search of a more disease-resistant grape, says Rimando.

In plants that contain these chemicals, their content usually differs dramatically. Quantitative studies have shown that for every 10 parts resveratrol, there’s only 1-2 parts pterostilbene. The relationship between the two similar compounds and their unequal content in plants is unclear, but remains the subject of ongoing studies. Dark-skinned grapes are likely to contain the most pterostilbene. For reasons that are unclear, pterostilbene is not normally found in wine,Rimando says. This may be because it is unstable in light and air, which makes it less likely to survive the wine-making process.

Source: Rimando AM et al. Cancer Chemopreventive and Antioxidant Activitiesof Pterostilbene, a Naturally Occurring Analogue of Resveratrol.

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