Interactions of gallic acid, resveratrol, quercetin and aspirin at the platelet cyclooxygenase-1 level. Functional and modelling studies.

While resveratrol and quercetin possess antiplatelet activity, little is known on the effect of gallic acid on platelets. We studied the interactions of these three different polyphenols among themselves and with aspirin, at the level of platelet cyclooxygenase-1 (COX-1). Both functional (in vitro and in vivo) and molecular modelling approaches were used. All three polyphenols showed comparable antioxidant activity (arachidonic acid [AA]-induced intraplatelet ROS production); however, resveratrol and quercetin, but not gallic acid, inhibited AA-induced platelet aggregation. Gallic acid, similarly to salicylic acid, the major aspirin metabolite, prevented inhibition of AA-induced platelet function by aspirin but, at variance with salicylic acid, also prevented inhibition by the other two polyphenols. Molecular modelling studies, performed by in silico docking the polyphenols into the crystal structure of COX-1, suggested that all compounds form stable complexes into the COX-1 channel, with slightly different but functionally relevant interaction geometries. Experiments in mice showed that gallic acid administered before aspirin, resveratrol or quercetin fully prevented their inhibitory effect on serum TxB(2). Finally, a mixture of resveratrol, quercetin and gallic acid, at relative concentrations similar to those contained in most red wines, did not inhibit platelet aggregation, but potentiated sub-inhibitory concentrations of aspirin. Gallic acid interactions with other polyphenols or aspirin at the level of platelet COX-1 might partly explain the complex, and possibly contrasting, effects of wine and other components of the Mediterranean diet on platelets and on the pharmacologic effect of low-dose aspirin.