Isorhapontigenin, a resveratrol analogue selectively inhibits ADP-stimulated platelet activation

Isorhapontigenin is a polyphenolic compound found in Chinese herbs and grapes. It is a methoxylated analogue of a stilbenoid, resveratrol, which is well-known for its various beneficial effects including anti-platelet activity. Isorhapontigenin possesses greater oral bioavailability than resveratrol and has also been identified to possess anti-cancer and anti-inflammatory properties. However, its effects on platelet function have not been reported previously. In this study, we report the effects of isorhapontigenin on the modulation of platelet function. Isorhapontigenin was found to selectively inhibit ADP-induced platelet aggregation with an IC50 of 1.85 mu M although it displayed marginal inhibition on platelet aggregation induced by other platelet agonists at 100 mu M. However, resveratrol exhibited weaker inhibition on ADP-induced platelet aggregation (IC50 > 100 mu M) but inhibited collagen induced platelet aggregation at 50 mu M and 100 mu M. Isorhapontigenin also inhibited integrin anbf33 mediated inside-out and outside-in signalling and dense granule secretion in ADP-induced platelet activation but interestingly, no effect was observed on a-granule secretion. Isorhapontigenin did not exert any cytotoxicity on platelets at the concentrations of up to 100 mu M. Furthermore, it did not affect haemostasis in mice at the IC50 concentration (1.85 mu M). In addition, the mechanistic studies demonstrated that isorhapontigenin increased CAMP levels and VASP phosphorylation at Ser157 and decreased Akt phosphorylation. This suggests that isorhapontigenin may interfere with cAMP and PI3K signalling pathways that are associated with the P2Y(12) receptor. Molecular docking studies emphasised that isorhapontigenin has greater binding affinity to P2Y(12) receptor than resveratrol. Our results demonstrate that isorhapontigenin has selective inhibitory effects on ADP-stimulated platelet activation possibly via P2Y(12) receptor.