Nox2-mediated platelet activation by glycoprotein (GP) VI: Effect of rivaroxaban alone and in combination with aspirin.

Factor Xa (FXa) has been reported to activate platelet via interaction with glycoprotein (GP) VI but the underlying mechanism has not been fully elucidated. We investigated if Nox2-derived oxidative stress is implicated in FXa-induced platelet aggregation (PA), and the effect of a FXa inhibitor, namely rivaroxaban, with or without aspirin (ASA), on PA. We performed an in vitro study measuring convulxin-induced PA, thromboxane (Tx) B2 and isoprostanes biosynthesis, soluble Nox2-dp (sNox2-dp), a marker of Nox2 activation, soluble GPVI (sGPVI) and PLA2 activation in platelets from healthy subjects (n = 5) added with and without a Nox2 inhibitor. The same variables were also examined in platelets treated with rivaroxaban (15-60 ng/ml), combined or less with ASA (25 µM). Convulxin-stimulated platelets increased sGPVI, sNox2-dp, H2 O2 , eicosanoid biosynthesis and PLA2 phosphorylation, which were all inhibited by a Nox2 inhibitor. Rivaroxaban alone significantly reduced PA, sGPVI, TxB2 and isoprostanes biosynthesis, concomitantly with Syk, sNox2-dp and PLA2 activation in a dose-dependent fashion; a significant effect was achieved with 30 ng/ml rivaroxaban. Docking simulation analysis showed that rivaroxaban interacts with GPVI. In platelets co-incubated with ASA, rivaroxaban amplified the ASA antiplatelet effect, which was achieved with 30 ng/ml and prevalently attributable to Nox2 inhibition and impaired isoprostane biosynthesis. Here we show that rivaroxaban, at concentrations achievable in human circulation, inhibits PA via GPVI interaction and eventually Nox2-mediated isoprostanes biosynthesis and amplifies the ASA antiplatelet effect.