OC 31.5 - Novel Snake Venom Hemocoagulase Reverses Anticoagulant Effect of Factor Xa Inhibitors and Restores Hemostasis in Vitro and in Vivo

Background: Factor Xa (FXa) inhibitors are widely used to treat thromboembolism and prevent stroke. Despite their favorable antithrombotic effects, bleeding events still occur, which require urgent restoration of hemostasis. We recently reported slounase, a novel hemocoagulase containing a snake venom-derived batroxobin (a thrombin-like enzyme that converts fibrinogen to fibrin independent of thrombin) and a Factor X activator, restores hemostatic clot formation in heparin-anticoagulated mice suggesting slounase may circumvent FXa inhibition and restore coagulation.

Aims: Investigate slounase as a novel bypassing agent to reverse anticoagulation by FXa inhibitors in vitro and the restoration of hemostasis in vivo.

Methods: The effect of slounase on clot formation in whole human blood pretreated with apixaban or rivaroxaban was determined by in vitro thromboelastography (TEG). Wild-type mice were pretreated with apixaban or rivaroxaban (via oral gavage). The reversal effect of slounase was determined in vivo with the laser-induced cremaster arteriole thrombosis model and bleeding was assessed with a tail bleeding assay.

Results: Rivaroxaban or apixaban treatment in human whole blood dose-dependently inhibited clot formation in vitro on TEG. Slounase treatment dose-dependently restored clot formation in apixaban and rivaroxaban-treated human blood and restored the rate of clot formation and clot strength to the normal range. Platelet accumulation and fibrin formation in the hemostatic clot was severely impaired in mice pretreated with FXa inhibitors as examined under intravital microscopy. Slounase intervention (1U/kg) reversed the anticoagulant effect of FXa inhibitors in vivo and significantly enhanced platelet-fibrin hemostatic clot formation in response to vascular injury. FXa inhibitors prolonged tail bleeding time, and slounase treatment significantly decreased blood loss and shortened the bleeding time.

Conclusion(s): Slounase treatment reversed the anticoagulant effect of FXa inhibitors rivaroxaban and apixaban in vitro. Our results demonstrate that slounase is a potential bypassing agent for the rapid reversal of anticoagulation by FXa inhibitors to decrease bleeding and blood loss.