Role of heme modulation in inhibition of Atheris, Atractaspis, Causus, Cerastes, Echis, and Macrovipera hemotoxic venom activity

Venomous snake bite and subsequent coagulopathy is a significant source of morbidity and mortality worldwide. The gold standard to treat coagulopathy caused by these venoms is the administration of antivenom; however, despite this therapy, coagulopathy still occurs and recurs. Of interest, our laboratory has demonstrated in vitro and in vivo that coagulopathy-inducing venom exposed to carbon monoxide (CO) is inhibited, potentially by an attached heme. The present investigation sought to determine if venoms derived from snakes of the African genera Atheris, Atractaspis, Causus, Cerastes, Echis, and Macrovipera that have no or limited antivenoms available could be inhibited with CO or with the metheme-inducing agent, O-phenylhydroxylamine (PHA). Assessing changes in coagulation kinetics of human plasma with thrombelastography, venoms were exposed in isolation to CO or PHA. Eight species were found to have procoagulant activity consistent with the generation of human thrombin, while one was likely fibrinogenolytic. All venoms were significantly inhibited by CO/PHA with species-specific variation noted. These data demonstrate indirectly that the heme is likely bound to these disparate venoms as an intermediary modulatory molecule. In conclusion, future investigation is warranted to determine if heme could serve as a potential therapeutic target to be modulated during treatment of envenomation by hemotoxic enzymes.