Grape expectations

Another antioxidant found in grapes could be used to fight cancer and combat diabetes, according to US scientists.

US Department of Agriculture researcher Agnes Rimando of the Natural Products Utilization Research Unit in Oxford, Mississippi and her colleagues have identified a new compound in grapes, which they say shows promise as an anticancer agent. The compound, pterostilbene, resembles resveratrol, another antioxidant identified in grapes and red wine that has previously been linked with cancer prevention, but pterostilbene also displays antidiabetic properties. "Pterostilbene itself is not a new compound, it's been known in the scientific literature for some time, but in our studies we have discovered new activity as a potential cancer-preventive agent for the first time," says Rimando.

"The study adds to the growing health benefits of grapes," Rimando adds, although her study has so far been limited to cell culture experiments with mouse mammary cells in the laboratory. She cautions that studies will be needed in both animals and humans to evaluate the potential health benefits of pterostilbene, whose biological activities are not yet well understood.

	Agnes Rimando

Nevertheless, pterostilbene prevented a type of cell damage that is normally induced by cancer-causing agents. Moreover, earlier studies had revealed that pterostilbene is toxic to human breast cancer cells.

The researchers say that pterostilbene is equal in potency to resveratrol against cancer cells, which Rimando ascribes to the molecule's potent antioxidant capacity.

Earlier animal studies with the compound have shown that it can also lower blood glucose and may be a potent antidiabetic agent. In at least one study, plasma glucose levels in rats with high blood sugar could be reduced by 42%, which is comparable with another antidiabetic agent, metformin. "My study is saying that there's another compound in grapes with equal cancer-fighting power as resveratrol, but which has antidiabetic properties as well," says Rimando. "The compound has always been in grapes, but no one has paid much attention to it."

The pterostilbene molecule. Click on picture to get molecule in ChemSketch format.

Chemically, pterostilbene and resveratrol are phytoalexins. Plants seem to produce these compounds when they are exposed to ultraviolet light, certain chemical and physicals stresses, and fungal infection. Pterostilbene is about 60 to 100 times stronger an antifungal agent than resveratrol, which farmers may be able to exploit in a natural product fungicide in the future.

Dark-skinned grapes (such as red and blue-black) are likely to contain the most pterostilbene, while green grapes (white grapes) probably contain less, Rimando says, although the compound has been isolated from infected Chardonnay and Gamay grapes. But, unfortunately for those hoping to sample the bacchanalian delights and get a health kick at the same time, pterostilbene is not normally found in wine. It is less stable than resveratrol and exposure to light and air during the winemaking process probably destroys it.

Other fruits and fruit juices are now being investigated.

J. Agric. Food Chem., 2002; 50(12); 3453-3457