compound in grapes may fight diabetes/cancer
Date: Posted 5/22/2002
Compound Identified In Grapes May Fight Cancer And
Diabetes
Researchers with the U.S. Department of Agriculture
have identified another compound in grapes that they
believe shows promise in fighting cancer. The
compound, pterostilbene, is similar to resveratrol, an
antioxidant recently found in grapes and red wine that
has also been linked to cancer-prevention, they say.
Previous studies by others have demonstrated that
pterostilbene also has antidiabetic properties. The
current study is the first to identify it as a
cancer-preventive agent, the researchers report. Their
study is tentatively scheduled to appear in the June
19 issue of the Journal of Agricultural and Food
Chemistry, a peer-reviewed publication of the American
Chemical Society, the world’s largest scientific
society. It was published on the Web version of the
journal on May 10.
“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, two of the major medical problems in this
country, says Rimando. However, 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
well-understood.
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, she says. Earlier
studies by the researcher showed that the compound is
toxic to a human breast cancer cell line.
The conclusion: It appears that pterostilbene is equal
in potency to resveratrol as a cancer-preventive
agent, as both have shown similar anticancer activity
in lab tests, says Rimando. Their similar effect is
likely due to the high antioxidant activity of these
compounds, she says. 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.
“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,” said Rimando. “The compound has always been in
grapes, but no one has paid much attention to it.”
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 about one to two parts pterostilbene. The
relationship between the two similar compounds and
their unequal content in plants is unclear, but
remains the subject of ongoing studies, the researcher
says.
Resveratrol has been found in many fruits, including
blueberries and cranberries, but it is perhaps best
known for its presence in grapes and red wine.
Pterostilbene has so far been identified in grapes and
in a relatively unknown medicinal plant, according to
Rimando.
Dark-skinned grapes (such as red and blue-black) are
likely to contain the most pterostilbene, while green
grapes (also called white grapes) probably contain
less, she says.
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, she
says.
The researcher is currently investigating other fruits
and fruit juices to determine whether they contain
pterostilbene, but results are not yet available.
The USDA and the University of Illinois at Chicago,
through a grant from the National Cancer Institute,
provided funding for this study.
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Note: This story has been adapted from a news release
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