Abstract
Patients with hemorrhage after treatment with direct oral anticoagulants (DOACs) are saved from hematoma expansion by administration of Andexanet alfa, a modified factor Xa analog. A recent clinical trial points to incidental prothrombotic effects after Andexanet alfa treatment. We investigated mechanisms explaining the thrombogenic side effect. Calibrated automated thrombin generation was employed to assess the effect of Andexanet alfa on the coagulant potential of DOAC-treated plasma and whole blood. The study examined anticoagulant inhibition pathways involving tissue factor pathway inhibitor (TFPI), antithrombin, and endothelial cell components. Treatment of control plasmas with rivaroxaban, apixaban, or edoxaban resulted in an impaired thrombin generation, exemplified by a prolonged lag time and reduced thrombin peak height. Andexanet alfa over-converted this anticoagulant activity into a procoagulant effect. Plasma treatment with Andexanet alfa similarly increased thrombin generation in the absence of DOACs, even at 8 nM far below the therapeutic dose. The enhancement was abrogated in the absence or by blocking of TFPI. The Andexanet alfa effect was enhanced in the presence of heparin, thereby reversing the antithrombin protection. In the presence of endothelial cells, Andexanet alfa stimulated coagulation via TFPI and heparin inhibition. Andexanet alfa overconverts the anticoagulant effect of rivaroxaban, apixaban, and edoxaban to achieve a hypercoagulable plasma state. The action mechanism involves TFPI inhibition and neutralization of antithrombin-heparin complexes. This may account for the incidence of thrombosis observed in patients treated with Andexanet alfa.