Quercetin inhibits collagen-stimulated platelet activation through inhibition of multiple components of the glycoprotein VI signaling pathway


J. M. Gibbins, Cardiovascular Research Group, School of Animal and Microbial Sciences, University of Reading, Whiteknights, Reading, Berks RG6 6AJ, UK.
Tel.: +44 11 8987 5123, ext. 7082; fax +44 11 8931 0180; e-mail: j.m.gibbins@reading.ac.uk


Summary. Background: The regulation of platelet function by pharmacological agents that modulate platelet signaling has proven a successful approach to the prevention of thrombosis. A variety of molecules present in the diet have been shown to inhibit platelet activation, including the antioxidant quercetin. Objectives: In this report we investigate the molecular mechanisms through which quercetin inhibits collagen-stimulated platelet aggregation. Methods: The effect of quercetin on platelet aggregation, intracellular calcium release, whole cell tyrosine phosphorylation and intracellular signaling events including tyrosine phosphorylation and kinase activity of proteins involved in the collagen-stimulated glycoprotein (GP) signaling pathway were investigated. Results: We report that quercetin inhibits collagen-stimulated whole cell protein tyrosine phosphorylation and intracellular mobilization of calcium, in a concentration-dependent manner. Quercetin was also found to inhibit various events in signaling generated by the collagen receptor GPVI. This includes collagen-stimulated tyrosine phosphorylation of the Fc receptor γ-chain, Syk, LAT and phospholipase Cγ2. Inhibition of phosphorylation of the Fc receptor γ-chain suggests that quercetin inhibits early signaling events following stimulation of platelets with collagen. The activity of the kinases that phosphorylate the Fc receptor γ-chain, Fyn and Lyn, as well as the tyrosine kinase Syk and phosphoinositide 3-kinase was also inhibited by quercetin in a concentration-dependent manner, both in whole cells and in isolation. Conclusions: The present results provide a molecular basis for the inhibition by quercetin of collagen-stimulated platelet activation, through inhibition of multiple components of the GPVI signaling pathway, and may begin to explain the proposed health benefits of high quercetin intake.