Modulation of ADP-lnduced Platelet Activation by Aspirin and Pravastatin: Role of Lectin-Like Oxidized Low-Density Lipoprotein Receptor-1, Nitric Oxide, Oxidative Stress, and Inside-Out Integrin Signaling

摘要

Lectin-like oxidized low-density lipoprotein (LDL) receptor-1 (LOX-1), a receptor for oxidized-LDL, is up-regulated in activated endothelial cells, and it plays a role in atherothrombosis. However, its role in platelet aggregation is unclear. Both aspirin and HMG CoA reductase inhibitors (statins) reduce LOX-1 expression in endothelial cells. In this study, we investigated the effect of aspirin and pravastatin on LOX-1 expression on platelets. After ADP stimulation, mean fluorescence intensity of LOX-1 expression on platelets increased 1.5- to 2.0-fold. Blocking LOX-1 inhibited ADP-induced platelet aggregation in a concentration- and time-dependent manner. We also established that LOX-1 is important for ADP-stimulated inside-out activation of platelet alpha_(Ilb)beta_3 and alpha_2beta_1 integrins (fibrinogen receptors). The specificity of this interaction was determined by arginine-glycine-aspartate-peptide inhibition. Furthermore, we found that LOX-1 inhibition of integrin activation is mediated by inhibition of protein kinase C activity. In other experiments, treatment with aspirin (1-10 mM) and pravastatin (1-5 mu M) reduced platelet LOX-1 expression, with a synergistic effect of the combination of aspirin and pravastatin. Aspirin and pravastatin both reduced reactive oxygen species (ROS) released by activated platelets measured as malonyldialdehyde (MDA) release and nitrateitrite ratio. Aspirin and pravastatin also enhanced nitric oxide (NO) release measured as nitriteitrite + nitrate (NOx) ratio in platelet supernates. Small concentrations of aspirin and pravastatin had a synergistic effect on the inhibition of MDA release and enhancement of nitrite/NOx. Thus, LOX-1 is important for ADP-mediated platelet integrin activation, possibly through protein kinase C activation. Furthermore, aspirin and pravastatin inhibit LOX-1 expression on platelets in part by favorably affecting ROS and NO release from activated platelets.