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Flavonoids Found in Purple Grape Juice Thought to Increase Nitric Oxide
Levels
While Reducing Free Radical Production
DALLAS, Nov. 10 /PRNewswire/ -- The so-called French Paradox seems a
little less mysterious today as researchers reported that flavonoids
found in purple grape juice, also found in red wine, stimulate platelet
production of nitric oxide -- a chemical which plays a role in
inhibiting platelet aggregation and thrombus formation. Preliminary
studies in both humans and animals have previously reported the effects
of drinking purple grape juice on platelet aggregation. Studies have
reported similar anti-platelet effects for red wine. The mechanisms
behind these potentially beneficial effects, however, are not fully
understood.
In a laboratory study presented today at the 71st Scientific Sessions of
the American Heart Association, Jane E. Freedman, M.D., assistant
professor of medicine and pharmacology at Georgetown University Medical
Center, found that blood platelets bathed in a dilute solution of purple
grape juice released three times more nitric oxide (NO) than those in a
control group.
"The process by which coronary artery disease progresses is
multifactorial and extremely complicated. Nonetheless, these findings
are significant for a number of reasons," Freedman explains. "First,
there is a growing understanding that a reduction in nitric oxide
production, which normally comes from both the platelets and from the
endothelial lining of the blood vessel, contributes to platelet
aggregation and thrombus formation. In patients with coronary artery
disease, for example, their platelet and blood vessel nitric oxide
production appears to be lower than in healthy subjects."
At the same time, Freedman found that platelets bathed in purple grape
juice also released 55% less superoxide -- a free radical -- than
platelets in the control solution.
"We also believe that the release of superoxide contributes to thrombus
formation as well, by rendering the nitric oxide ineffective. Thus, a
patient with coronary artery disease who has low levels of nitric oxide
and high levels of superoxide may be likelier to experience a
potentially dangerous thrombus formation than a person with normal
levels. Seeing the ability of purple grape juice to increase nitric
oxide production combined with its ability to suppress superoxide
production gives us a better understanding of why drinking purple grape
juice may support healthy cardiovascular function."
Finally, Freedman was able to show the beneficial effects of a specific
flavonoid called quercetin, one of many polyphenolic compounds found in
purple grape juice. She found that platelet incubation with quercetin
inhibited PMA-induced stimulation of protein kinase C -- a pathway by
which platelet aggregation is increased.
"There have always been questions about the role of alcohol in the
health benefits of drinking red wine," says Freedman. "However, it
carries with it its own set of problems and concerns. Isolating the
effects of quercetin is important because it suggests that purple grape
juice may be a legitimate, non-alcoholic alternative to red wine."
Freedman's co-authors on the study are Ryan Sauter, B.S., Georgetown
University Medical Center, and John D. Folts, Ph.D., University of
Wisconsin Medical School.
For more information:
Please see AHA Press Release: "The heart-healthy cup runneth over --
with grape juice" at www.amhrt.org. Contact AHA press office at
214-853-8056. Dr. Freedman is also available for interviews on Monday
through that office.
Dr. Freedman's research is being presented as a poster at the AHA. See
poster #1558, November 10, 1998, from 1:30 P.M. -- 5:00 P.M.
Of related interest is AHA abstract #1559 entitled: "a-Tocopherol
Increases Platelet-Derived Nitric Oxide Release."
Editorial usage notes:
1. The research studied the effect of nitric oxide (NO), which is
different from but often confused with nitrous oxide (NO2), the
so-called laughing gas.
2. Research often refers to "red" grape products as a way to
differentiate them from white grape products. This should not be
translated into "red" grape juice. Much of the research in this
field, including Dr. Freedman's, has been conducted using juice made
from Concord grapes, which produces purple grape juice.
ABSTRACT
Purple Grape Juice Inhibits Platelet Function and
Increases Platelet-Derived Nitric Oxide Release
Ryan Sauter, Georgetown University Medical Center, Washington, DC; John
D. Folts, University of Wisconsin Medical School, Madison, WI; Jane E.
Freedman, Georgetown University Medical Center, Washington, DC
Background: Moderate red wine consumption is inversely associated with
coronary ischemia. Red wine and purple grape juice (GJ) contain
flavonoids with antioxidant and anti-platelet properties believed to be
protective against cardiovascular events. Acute cardiac events, caused
by platelet activation and thrombosis, are also associated with
decreased platelet-derived nitric oxide (NO) release. Therefore, we
investigated the effect of GJ on platelet NO release. Methods and
Results: Platelet aggregation was significantly inhibited after
incubation with a 1:1000 dilution of GJ as compared to vehicle control
(58.3% plus/minus 6.0% vs. 88.3% plus/minus 4.4%, P<0.01, n=3).
Platelet-derived NO release was measured with an electrochemical
detector adapted for use in a standard aggregometer. Incubation of human
platelets with a 1:1000 dilution of GJ increased NO release as compared
to control (1.5 plus/minus 0.2 pmol/108 platelets vs. 0.5 plus/minus 0.1
pmol/108 platelets, P=0.01, n=4). Because NO interacts with superoxide,
we measured superoxide release in platelets incubated with GJ. Platelets
incubated with GJ had a 55% decrease in platelet release of superoxide
as compared to control (P<0.01, n=4). In addition, red grape products
are rich in the flavonoid quercetin. Platelet incubation with quercetin
inhibited PMA-induced stimulation of platelet protein kinase C (PKC) as
determined by phosporylation of the 47-kD PKC substrate. Conclusion:
These data indicate that the flavonoids in purple grape juice are a
potent inhibitor of platelet function and increase platelet-derived NO
release through antioxidant- and PKC-dependent mechanisms. These
observations represent a potential mechanism for the beneficial effects
of red grape products in cardiovascular disease.
SOURCE Scientific Sessions of the American Heart Association
------------------------------
Date: Wed, 11 Nov 1998 10:11:58 -0500
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