P104 Inhibition of platelet aggregation in vitro and in vivo by the H2S releasing compound GYY4137

Abstract

Platelets are key modulators of thrombotic events and a major target in the prevention of conditions including myocardial infarction. The role of H 2 S in regulating platelets remains unclear with contradictory reports. The functional modulation of platelets by H 2 S was investigated using light transmission aggregometry of isolated human platelets and in a mouse model for assessing aggregation of radiolabelled platelets in vivo . Additional biochemical assays determined the expression and activity of H 2 S generating enzymes. Western blotting revealed that human platelets express the H 2 S generating enzyme cystathione-beta synthase (CBS). Cystathione-gamma-lysase (CSE) was present at lower or undetectable levels. CBS activity was significantly higher in platelets compared to cell free samples whereas CSE was not active. Platelets were shown to generate H 2 S using a fluorescent probe and H 2 S production was significantly reduced by the CBS antagonist amino-oxyacetic acid. GYY4137 significantly reduced collagen-induced platelet aggregation in vitro and in vivo compared to control compound lacking the H 2 S donating moiety. GYY4137 also enhanced NO-mediated inhibition of platelet aggregation in vitro , an effect that was shown to be mediated via soluble guanylyl cyclase. The ability of GYY4137 to inhibit platelet aggregation in vivo was attenuated in eNOS −/− mice. Platelets therefore generate H 2 S primarily via CBS. H 2 S inhibits platelet aggregation and enhances the inhibitory actions of NO via cGMP-mediated signaling. H 2 S therefore has potential physiological roles in platelets and as a putative therapeutic strategy in the treatment of platelet-driven disorders. We continue to develop and assess the effects of other novel H 2 S donors including AP67 and AP72.