Thrombomodulin is required for the antithrombotic activity of thrombin mutant W215A/E217A in a mouse model of arterial thrombosis

Introduction: The thrombin mutant W215A/E217A (WE thrombin) has greatly reduced procoagulant activity, but it activates protein C in the presence of thrombomodulin and inhibits binding of platelet glycoprotein Ib to von Willebrand factor and collagen under flow conditions. Both thrombomodulin- dependent protein C activation and inhibition of platelet adhesion could contribute to the antithrombotic activity of WE thrombin. Materials and methods: To assess the role of thrombomodulin, we administered WE thrombin to thrombomodulin-deficient (TM^Pro/Pro) mice and measured the time to occlusive thrombus formation in the carotid artery after photochemical injury of the endothelium. Results and conclusions: Doses of WE thrombin ≥ 10 μg/kg prolonged the thrombosis time of wild-type mice (> 1.6-fold), while doses ≥ 100 μg/kg only slightly prolonged the thrombosis time of TM ^Pro/Pro mice. We conclude that thrombomodulin plays a predominate role in mediating the antithrombotic effect of WE thrombin in the arterial circulation of mice after endothelial injury. Thrombomodulin-independent effects may occur only when high doses of WE thrombin are administered.