Doxepin inhibits GPVI-dependent platelet Ca2+ signaling and collagen-dependent thrombus formation.

Platelet adhesion, activation, and aggregation are essential for primary hemostasis, but are also critically involved in the development of acute arterial thrombotic occlusion. Stimulation of the collagen receptor glycoprotein VI (GPVI) leads to phospholipase Cγ2-dependent inositol triphosphate (IP3) production with subsequent platelet activation, due to increased intracellular Ca2+ concentration ([Ca2+]i). Although tricyclic antidepressants have been shown to potentially impair platelet activation, nothing is hitherto known about potential effects of the tricyclic antidepressant doxepin on platelet Ca2+ signaling and thrombus formation. As shown in the present study, doxepin significantly diminished the stimulatory effect of GPVI agonist collagen-related peptide (CRP) on intracellular Ca2+ release as well as subsequent extracellular Ca2+ influx. Doxepin was partially effective by impairment of CRP-dependent IP3 production. Moreover, doxepin abrogated CRP-induced platelet degranulation and integrin αIIbβ3 activation and aggregation. Finally, doxepin markedly blunted in vitro platelet adhesion to collagen and thrombus formation under high arterial shear rates (1,700-s). In conclusion, doxepin is a powerful inhibitor of GPVI-dependent platelet Ca2+ signaling, platelet activation, and thrombus formation.