Quercetin and its methylated metabolites possess anti-thrombotic properties that interact with aspirin to enhance its anti-platelet effects

Quercetin, a dietary flavonoid, has been reported to possess anti-platelet activity. However, its extensive metabolism following ingestion has resulted in difficulty elucidating precise mechanisms of action. In this study, we aimed to characterise the anti-platelet mechanisms of two methylated metabolites of quercetin - isorhamnetin and tamarixetin - and explore potential interactions with aspirin. Isorhamnetin and tamarixetin inhibited human platelet aggregation, and suppressed activatory processes including granule secretion, integrin alphaIIbbeta3 function, calcium mobilisation, and Syk/LAT phosphorylation downstream of GPVI with similar potency to quercetin. All three flavonoids attenuated thrombus formation in an in vitro microfluidic model, and isoquercetin, a 3-O-glucoside of quercetin, inhibited thrombosis in a murine laser injury model. Isorhamnetin, tamarixetin and quercetin enhanced the anti-platelet effects of aspirin more-than-additively in a plate-based aggregometry assay, reducing aspirin IC50 values by an order of magnitude, with this synergy maintained in a whole blood test of platelet function. Our data provide mechanistic evidence for the anti-platelet activity of two quercetin metabolites, isorhamnetin and tamarixetin, and suggest a potential anti-thrombotic role for these flavonoids. In combination with their interactions with aspirin, this may represent a novel avenue of investigation for the development of new anti-thrombotic strategies and management of current therapies