Breaking muscle: neurotoxic and myotoxic effects of Central American snake venoms and the relative efficacies of antivenom and varespladib.

Background: The snake genera Atropoides, Cerrophidion, and Metlapilcoatlus form a clade of neotropical pit vipers distributed across Mexico and Central America. This study evaluated the myotoxic and neurotoxic effects of nine species of Atropoides, Cerrophidion, and Metlapilcoatlus, and the neutralising efficacy of the ICP antivenom from Costa Rica against these effects, in the chick biventer cervicis nerve-muscle preparation. Given the prominence of PLA₂s within the venom proteomes of these species, we also aimed to determine the neutralising potency of the PLA₂ inhibitor, varespladib.

Results: All venoms showed myotoxic and potential neurotoxic effects, with differential intra-genera and inter-genera potency. This variation was also seen in the antivenom ability to neutralise the muscle damaging pathophysiological effects observed. Variation was also seen in the relative response to the PLA₂ inhibitor varespladib. While the myotoxic effects of M. mexicanus and M. nummifer venoms were effectively neutralised by varespladib, indicating myotoxicity is PLA₂ mediated, those of C. godmani and M. olmec venoms were not, revealing that the myotoxicity is driven by non-PLA₂ toxin types.

Conclusions: This study characterises the myotoxic and neurotoxic venom activity, as well as neutralisation of venom effects from the Atropoides, Cerrophidion, and Metlapilcoatlus clade of American crotalids. Our findings contribute significant clinical and evolutionary knowledge to a clade of poorly researched snakes. In addition, these results provide a platform for future research into the reciprocal interaction between ecological niche specialisation and venom evolution, as well as highlighting the need to test purified toxins to accurately evaluate the potential effects observed in these venoms.