trans-Resveratrol inhibits calcium influx in thrombin-stimulated human platelets

1 The phytoestrogenic compound trans-resveratrol (trans-3,5,4'-trihydroxystilbene) is found in appreciable quantities in grape skins and wine. It has been shown that both products rich in trans-resveratrol and pure trans-resveratrol inhibit platelet aggregation both in vivo and in vitro. However the mechanism of this action still remains unknown. 2 An essential component of the aggregation process in platelets is an increase in intracellular free Ca2+ ([Ca2+](i)). Ca2+ must enter the cell from the external media through specific and tightly regulated Ca2+ channels in the plasma membrane. The objective of this study was to characterize what effect trans-resveratrol had on the Ca2+ channels in thrombin stimulated platelets. 3 In this study we showed that trans-resveratrol immediately inhibited Ca2+ influx in thrombin-stimulated platelets with an IC50 of 0.5 mu M. trans-Resveratrol at 0.1, 1.0 and 10.0 mu M produced 20 +/- 6, 37 +/- 6 and 57 +/- 4% inhibition respectively of the effect of thrombin (0.01 u ml(-1)) to increase [Ca2+](i). 4 trans-Resveratrol also inhibited spontaneous Ba2+ entry into Fura-2 loaded platelets, with 0.1, 1.0 and 10.0 mu M trans-resveratrol producing 10 +/- 5, 30 +/- 5 and 50 +/- 7% inhibition respectively. This indicated that trans-resveratrol directly inhibited Ca2+ channel activity in the platelets in the absence of agonist stimulation. 5 trans-Resveratrol also inhibited thapsigargin-mediated Ca2+ influx into platelets. This suggests that the store-operated Ca2+ channels are one of the possible targets of trans-resveratrol. These channels rely on the emptying of the internal Ca2+ stores to initiate influx of Ca2+ into the cell. 6 The phytoestrogens genistein, daidzein, apigenin and genistein-glucoside (genistin) produced inhibitory effects against thrombin similar to those seen with trans-resveratrol. 7 We conclude that trans-resveratrol is an inhibitor of store-operated Ca2+ channels in human platelets. This accounts for the ability of trans-resveratrol to inhibit platelet aggregation induced by thrombin.