Ex Vivo Antiplatelet Effects of Oral Anticoagulants

Abstract

Background: The impact of non-vitamin K antagonist oral anticoagulants (NOACs) on platelet function is still unclear. We conducted a comprehensive ex vivo study aimed at assessing the effect of the four currently marketed NOACs on platelet function.

Methods: We incubated blood samples from healthy donors with concentrations of NOACs (50, 150 and 250 ng/mL), in the range of those achieved in the plasma of patients during therapy. We evaluated generation of thrombin; light transmittance platelet aggregation (LTA) in response to adenosine diphosphate (ADP), thrombin receptor-activating peptide (TRAP), human γ-thrombin (THR) and tissue factor (TF); generation of thromboxane (TX)B₂; and expression of protease-activated receptor (PAR)-1 and P-selectin on the platelet surface.

Results: All NOACs concentration-dependently reduced thrombin generation compared with control. THR-induced LTA was suppressed by the addition of dabigatran at any concentration, while TF-induced LTA was reduced by factor-Xa inhibitors. ADP- and TRAP-induced LTA was not modified by NOACs. TXB₂ generation was reduced by all NOACs, particularly at the highest concentrations. We found a concentration-dependent increase in PAR-1 expression after incubation with dabigatran, mainly at the highest concentrations, but not with FXa inhibitors; P-selectin expression was not changed by any drugs.

Conclusions: Treatment with the NOACs is associated with measurable ex vivo changes in platelet function, arguing for antiplatelet effects beyond the well-known anticoagulant activities of these drugs. There are differences, however, among the NOACs, especially between dabigatran and the FXa inhibitors.

Keywords: DOACs; NOACs; antiplatelet effects; direct oral anticoagulants; non-vitamin K antagonist oral anticoagulants; oral anticoagulants; platelets.

Figure 1

Thrombin generation parameters after the addition of increasing concentrations of dabigatran, rivaroxaban, apixaban and edoxaban. Dot plots report all single values of endogenous thrombin potential (ETP, panel (A)) and peak of thrombin generation (panel (B)). The horizontal lines represent the mean values. * p < 0.0001, ° p < 0.001, ^# p < 0.01, ^§ p < 0.05 vs. the corresponding controls. C = control; 50 = 50 ng/mL; 150 = 150 ng/mL; 250 = 250 ng/mL.

Figure 2

Platelet aggregation induced by different agents after the addition of increasing concentrations of dabigatran, rivaroxaban, apixaban and edoxaban. Box and whiskers Tukey plot reporting the median, 25th and 75th percentile and range for values of platelet aggregation in platelet-rich plasma (optical transmittance, in percent of maximum aggregation) induced by ADP (A), thrombin receptor-activating peptide (TRAP) (B), gamma-thrombin (THR) (C) and tissue factor (TF) (D). The asterisk within the bars reports the mean values. * p < 0.0001, ^# p < 0.01, vs. corresponding controls.

Figure 3

Serum TXB₂ generation after the addition of increasing concentrations of dabigatran, rivaroxaban, apixaban and edoxaban. Box and whiskers Tukey plot reporting the median, 25th and 75th percentile and range for values of serum TXB₂. The asterisk within the bars reports the mean values. ^# p < 0.01, ^§ p < 0.05 vs. corresponding control.

Figure 4

Expression of PAR-1 on platelet surface using flow cytometry without and with the addition of increasing concentrations of dabigatran. Box and whiskers Tukey plot reporting the median, 25th and 75th percentile and range for values of mean fluorescence intensity (MFI) ratio. The «+» within the bars indicate the mean values. ° p < 0.001 vs. control; ^§ p < 0.05 vs. control.