Nitric oxide inhibits platelet adhesion to platelet-microparticles through reducing integrin αIIbβ3 activation

Increased platelet microparticle (PMP) levels in individuals with risk factors for cardiovascular disease correlate with clinical outcomes in these patient groups. PMPs promote thrombosis through enhancing platelet aggregation and binding to the sub-endothelial matrix following vascular injury. Thus, PMPs behave as soluble ligands and adhesive substrates for platelets, and may drive cardiovascular disease progression. Nitric oxide (NO) is released continually from the endothelium as a potent regulator of platelet activation that is crucial to the balance between haemostasis and thrombosis. However, it is unknown if NO regulates PMP-induced platelet activation. In this study we isolated platelets and PMPs from whole blood and measured their interactions in adhesion assays and by flow cytometry. Platelet activation was analysed by ELISA for ADP and thromboxane-B2; both secondary platelet agonists released by activated platelets which enhance thrombosis. The affinity upregulation of the principal platelet integrin receptor responsible for platelet aggregation, integrin IIb{beta}3, was measured using the antibody PAC-1. Our data show that PMP induced platelet adhesion was associated with, and partially dependent upon, platelet ADP release, TxA2 production and IIb{beta}3 upregulation. Crucially, NO dose-dependently reduced these events through cGMP dependent signalling. This is the first report that NO signalling can regulate PMP induced platelet activation and may open an avenue of exploration for clinically targeting PMP driven cardiovascular disease processes.