Procoagulant and Antifibrinolytic Effects of Bothrops lanceolatus Venom: Differential Interference with Tissue Plasminogen Activator-Mediated Clot Lysis and with Cell-Surface Plasminogen Activation

Bothrops lanceolatus, a viper species endemic to Martinique, is unusual among lancehead pit vipers in producing delayed thrombosis rather than venom-induced consumption coagulopathy. The molecular basis of the thrombotic phenotype of this venom, and the role of impaired fibrinolysis in particular, remains incompletely characterised. Therefore, this study assessed various aspects of the venom’s effects on blood clotting. B. lanceolatus venom was assessed by rotational thromboelastometry, a 96-well halo clot-lysis assay using tissue plasminogen activator (tPA), a cell-surface plasminogen activation assay, and platelet aggregometry. The impact of varespladib (a phospholipase A2 inhibitor), marimastat (a metalloprotease inhibitor), and the Fab antivenom (Crofab) in mitigating venom-induced effects was evaluated. The venom produced concentration-dependent procoagulant activity that was partially reversed by varespladib, marimastat, and Crofab. The venom did not lyse preformed whole-blood clots, but preincubation with tPA significantly impaired tPA-mediated fibrinolysis. In the cell-surface plasminogen activation assay, the venom unexpectedly enhanced rather than inhibited substrate cleavage, an effect attributed in part to non-specific venom protease activity. The venom did not induce platelet aggregation but selectively inhibited collagen-induced aggregation. B. lanceolatus venom impairs fibrinolysis at the level of polymerised fibrin while leaving the cell-surface plasminogen-activation pathway intact. Combined with its procoagulant activity, this fibrinolytic impairment provides a coherent mechanistic basis for the delayed thrombotic complications observed clinically. Small-molecule toxin inhibitors warrant further evaluation as adjuncts to species-specific antivenom.