Doxepin inhibits GPVI-dependent platelet Ca 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 (IP) production with subsequent platelet activation, due to increased intracellular Ca concentration ([Ca]). 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 Ca 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 Ca release as well as subsequent extracellular Ca influx. Doxepin was partially effective by impairment of CRP-dependent IP production. Moreover, doxepin abrogated CRP-induced platelet degranulation and integrin αβ activation and aggregation. Finally, doxepin markedly blunted in vitro platelet adhesion to collagen and thrombus formation under high arterial shear rates (1,700). In conclusion, doxepin is a powerful inhibitor of GPVI-dependent platelet Ca signaling, platelet activation, and thrombus formation.