Serotonin enhances platelet procoagulant properties and their activation induced during platelet tissue factor uptake.

AIMS: Circulating tissue factor (TF) has been linked to thrombus propagation. Our group demonstrated that platelets possess mechanisms to capture TF-rich microvesicles (TF-MVs). Serotonin facilitates the development of platelets with increased procoagulant activity. An enhanced platelet serotonin uptake has been identified with increased cardiovascular risk. We have investigated the involvement of serotonergic mechanisms facilitating the interaction of human platelets with TF-MVs. Inhibitory strategies aimed at blocking serotonin and coagulation mechanisms were also studied. METHODS AND
RESULTS: Standard aggregometry, flow cytometry, electron microscopy, and thrombin generation assays were performed. TF-MVs induced platelet aggregation in heparinized platelet-rich plasma (PRP) samples; this aggregation was further accelerated by serotonin. In washed platelets, serotonin enhanced platelet aggregation to TF-MVs with a maximum peak of 55.9 +/- 1.8 vs. 48.7 +/- 2.1% (P < 0.05). Inhibitory strategies with a selective serotonin re-uptake inhibitor and with lepirudin decreased these aggregations. Ultrastructural analysis revealed that serotonin induced platelet pseudopodia formation, thus facilitating the engulfment of TF-MVs. In general, serotonin significantly enhanced (P < 0.05) thrombin generation and the expression of activation markers and procoagulant activity in platelets measured for TF-MVs alone.
CONCLUSION: Serotonin enhances the interaction of platelets with TF-MVs, increases platelet activation, and potentiates their overall procoagulant activity. The present results could have significant implications in thrombus formation and in the thrombogenic profile of pathological situations with increased cardiovascular risk.