F. Violi, P. Pignatelli and F.M. Pulcinelli

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Synergism Among Flavonoids in Inhibiting Platelet Aggregation and H

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Synergism Among Flavonoids in Inhibiting Platelet
Aggregation and H

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Production

To the Editor:

In vitro and in vivo studies carried out by Freedman et

1

demonstrated that purple grape juice inhibits platelet aggregation
and production of superoxide anion and increases the platelet
formation of nitric oxide. These findings are of potential rele-
vance for explaining the cardioprotective effect of grape juice
and red wine. The authors sought also to investigate the mech-
anism by which grape juice inhibits platelet function and ob-
served a consistent difference in terms of platelet inhibition
among the 5 fractions of grape twice containing flavonoids. We
agree with the authors that flavonoids, which are constituent of
both red wine and grape juice, contribute to inhibiting platelet
activity, but there are some issues that merit consideration.

The first point is to determinate whether one or more fla-

vonoids contribute to the antiplatelet effect of red wine or grape
juice. Assuming that only one flavonoid inhibits platelet function
is not realistic because the concentration of flavonoids in human
circulation is low. Surprisingly, there are no data of flavonoids
concentration in human circulation after assumption of red wine,
but taking into account other sources, such as onions or tea, the
plasma concentration would range from 0.6 to 13

␮mol/L.

2,3

Assuming a similar range of concentration after ingestion of red
wine or grape juice, it is difficult to imagine that one flavonoid
contributes to platelet inhibition. Indeed, Freedman’s study and
others

4

demonstrated in vitro that much higher concentrations,

for instance of quercetin or resveratrol, are necessary for inhib-
iting platelet function.

On the basis of these considerations, we combined in vitro 2

flavonoids, namely quercetin and cathechin, and demonstrated
that they are synergistic in reducing platelet formation of H

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and inhibiting platelet function by interfering with the activation
of phospholipase C pathway.

5

As this effect was observed with

concentrations of quercetin and cathechin (5

␮mol/L and 25

␮mol/L, respectively) close to those potentially achievable in
blood after wine assumption, we believe that the concept of
synergism among the flavonoids could help explain the antiplate-
let activity of red wine and grape juice in vivo. In this regard, it
is crucial that future studies with red wine or grape juice provide
information on flavonoid bioavailability and its relationship with
antioxidant activity and platelet function.

F. Violi

Institute of Clinical Medicine I

University La Sapienza

Rome, Italy

P. Pignatelli

F.M. Pulcinelli

Department of Experimental Medicine and Pathology

University La Sapienza

Rome, Italy

1. Freedman JE, Parker C 3rd, Li L, et al. Select flavonoids and whole juice

from purple grapes inhibit platelet function and enhance nitric oxide
release. Circulation. 2001;103:2792–2798.

2. Janssen PLTMK, Mensink RP, Cox FJJ, et al. Effect of the flavonoids

quercetin and apigenin on hemostasis in healthy volunteers: results from

an in vitro and dietary supplement study. Am J Clin Nutr. 1998;67:
255–262.

3. Pietta P, Simonetti P, Gardana C, et al. Relationship between rate and

extent of catechin absorption and plasma antioxidant status. Biochem Mol
Biol Int. 1998;46:895–903.

4. Pace-Asciak CR, Hahn S, Diamandis EP, et al. The red wine phenolics

trans-resveretrol and quercetin block human platelet aggregation and
eicosanoid synthesis: implications for protection against coronary heart
disease. Clin Chim Acta. 1995;235:207–219.

5. Pignatelli P, Pulcinelli FM, Celestini A, et al. The flavonoids quercetin

and catechin synergistically inhibit platelet function by antagonizing the
intracellular production of hydrogen peroxide. Am J Clin Nutr. 2000;72:
1150 –1155.

Response

The findings from our study

1

are in agreement with the main

comments of Violi and colleagues. A central message of this
study

1

is that one isolated flavonoid is not responsible for the

antioxidant and platelet inhibitory effects that we reported. This
is clear from the failure of any single flavonoid group to cause
the same effects as the purple grape juice either in vitro or ex
vivo. As we were not sure what the relevant flavonoids were, it
was difficult to measure specific flavonoids from the subjects
who drank the juice. However, we do not believe that the
quercetin or resveratrol are the main substances responsible for
the platelet inhibitory or nitric oxide–releasing effects. Although
previous studies have shown that, in vitro, flavonoids including
quercetin, resveratrol, and catechin inhibit platelet aggregation,

2

the physiological relevance of these findings has been questioned
in humans because oral supplementation with quercetin causes
markedly increased plasma levels but does not alter total, LDL,
or HDL cholesterol levels or change thrombogenic markers
including platelet aggregation and platelet thromboxane B

2

production.

3

However, Violi and colleagues are correct that

flavonoid levels would have provided useful information espe-
cially as a point of comparison with the antioxidant levels
measured from the plasma of subjects who consumed purple
grape juice.

Jane E. Freedman, MD

Crawford Parker III, MD

Liqing Li, MS

Jacob A. Perlman

Balz Frei, PhD

Vadim Ivanov, PhD

Leslie R. Deak, BS

Mark D. Iafrati, MD

John D. Folts, PhD

Boston University School of Medicine

Boston, Mass

1. Freedman JE, Parker C 3rd, Li L, et al. Select flavonoids and whole juice

from purple grapes inhibit platelet function and enhance nitric oxide
release. Circulation. 2001;103:2792–2798.

2. Pace-Asciak C, Hahn S, Diamandis E, et al. The red wine phenolics

trans-resveratrol and quercetin block human platelet aggregation and
eicosanoid synthesis: implications for protection against coronary heart
disease. Clin Chim Acta. 1995;235:207–219.

3. Conquer J, Maiani G, Azzini E, et al. Supplementation with quercetin

markedly increases plasma quercetin concentrations without effect on
selected risk factors for heart disease in healthy subjects. J Nutr. 1998;
128:593–597.

1

Correspondence

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