Combined Dabigatran and Antiplatelet Agents Assessed by the Novel Microchip-Based Flow Chamber System

Abstract 1167

Evaluation of the overall antithrombotic activity of dabigatran in combination with antiplatelet agents is difficult because plasma-based clotting for dabigatran, and platelet aggregometry in anticoagulated blood are two separate tests which do not reflect physiological interactions between soluble factors and platelets. The use of a flow chamber could be more suitable in evaluating a flow-dependent platelet activation and coagulation responses.

The aim of the current study was to comparatively evaluate antithrombotic effects of dabigatran in combination with dual antiplatelet therapy (aspirin plus P₂Y₁₂ blockade) using the microchip-based flow chamber (T-TAS, Fujimori Kogyo, Japan)(1), and thrombin generation (TG) assay (Thrombinoscope, Maastricht, the Netherlands)(2). After the local ethics committee approval, blood samples were obtained from consented 5 healthy volunteers in the tubes containing 3.2% sodium citrate. Whole blood samples were mixed with dabigatran (250, 500, 1000 nM), aspirin (100 nM) plus ARC-66096 (P2Y₁₂ inhibitor, 1000 nM) at 25¡C for 10 min. Corn trypsin inhibitor (50 μg/ml) was used to prevent contact activation. The whole blood sample was perfused in the capillary pre-coated with collagen and thromboplastin at the shear rate of 240 or 600 s⁻¹. The process of thrombus formation was monitored by flow pressure increases inside the capillary; (i) lag time before it reaches 10 kPa (T₁₀), (ii) occlusion time (OT) is the lag time before it reaches 80 kPa as thrombus completely occludes the capillary, and (iii) AUC₃₀ is an area under the flow pressure curve (under 80 kPa) after 30 min of perfusion. For TG assay, platelet-rich plasma (platelet count 150 × 10³/μl) was prepared from citrated whole blood. TG was triggered by adding 20 μl of CaCl₂-fluorogenic substrate buffer to 80 μl of the sample mixed with tissue factor (1 pM) in each well. The lag time (min), and peak thrombin concentration (nM) were evaluated.

In the flow chamber, dabigatran inhibited white thrombus formation in a concentration dependent manner at shear rates of 240 and 600 s⁻¹(Fig. 1). At 500 nM of dabigatran, OT was prolonged by ∼2-fold from the (non-treated) control at both shear rates. The combination of aspirin and AR-C66096 only weakly suppressed thrombus formation, but it enhanced the antithrombotic efficacy of dabigatran at both shear rates (Fig. 1). In TG measurements using platelet-rich plasma, dabigatran at 500 nM prolonged the by 3.17-fold, and reduced the peak by 57.6% compared to the untreated control (Table 1). Aspirin and AR-C66096 weakly prolonged the lag time without affecting the peak height. There were relatively small changes in these parameters when antiplatelet agents were combined with dabigatran (Table 1).

Our results suggest that combined antithrombotic effects of dabigatran, aspirin, and P2Y₁₂inhibition can be demonstrated in the whole blood using the flow chamber system compared without additional plasma preparation required for TG assay.

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The re-calcified whole blood was perfused at the shear rate of 240 s⁻¹ or 600 s⁻¹. Asp/AR-C=aspirin and AR-C66096