Thrombin-induced platelet aggregation -effect of dabigatran using automated platelet aggregometry.

Dabigatran, a direct oral thrombin inhibitor, has two therapeutic effects: anticoagulation; and antiplatelet activity. In the clinical field, evaluation of the effect of dabigatran on thrombin-induced platelet aggregation is difficult because of fibrin clot formation and platelet aggregation. The aim of this study was to establish a new platelet aggregation method and to investigate the effects of dabigatran on thrombin-induced platelet aggregation. Platelet aggregation with thrombin was performed with automated light transmission aggregometry (CS2400; Sysmex, Kobe, Japan) in 40 healthy subjects. Thrombin-induced platelet aggregation was performed using thrombin and platelet-rich plasma (PRP), and thrombin-induced fibrin polymerization was inhibited by adding the peptide Gly-Pro-Arg-Pro (GPRP). The effect of dabigatran was then evaluated using the above method. Thrombin at < 0.2 U/mL did not induce platelet aggregation in most normal subjects. Median maximum aggregation percent (MA%) (25th-75th percentile) with 0.5 and 1.0 U/mL of thrombin was 87.0% (79.3-90.8%), and 90.2% (86.5-92.2%), respectively. The anti-platelet effects of dabigatran were then evaluated with these concentrations of thrombin. Dabigatran (final concentration, 2.5-1000 nM) inhibited platelet aggregation by 0.2-1.0 U/mL of thrombin in a concentration-dependent manner in vitro. Dabigatran showed potent inhibitory effects against platelet aggregation induced by 0.5 and 1.0 U/mL thrombin with half maximal inhibitory concentrations of 10.5 and 40.4 nM, respectively. A standard for thrombin-induced platelet aggregation was developed using the CS2400 in healthy subjects, and dabigatran was confirmed to inhibit thrombin-induced platelet aggregation in vitro with PRP.