The X Factor: Regional differences in the level of ontogenetic variations in procoagulant venom activity in the Northwestern Neotropical Rattlesnake (Crotalus culminatus)

Rattlesnakes are among the most widespread and medically significant venomous snakes in the Americas. Mexico boasts the highest diversity of these snakes, making it an ideal setting for research on the biology and medical implications of rattlesnake venom. The Northwestern Neotropical rattlesnake ( Crotalus culminatus ), endemic to Mexico, has been previously shown to exhibit an ontogenetic loss of strong Factor X activation procoagulant activity. This pathophysiological activity was poorly neutralized by antivenom but was abolished by a metalloproteinase inhibitor. This toxicological study expands on initial findings to assess ontogenetic venom variation across a broader geographic scale, while also testing the efficacy of three antivenoms and three metalloproteinase inhibitors against C. culminatus coagulotoxicity. Our results reveal a potential geographic influence on ontogenetic loss of FX activation-based procoagulant toxicity, which appears more marked in the state of Morelos than in Guerrero and Michoacán (all within Mexico). Possible evolutionary and ecological explanations for this are discussed. Furthermore, none of the tested antivenoms were able to neutralize procoagulant venom activity. In contrast, the metalloproteinase inhibitors marimastat and prinomastat were effective. However, the metalloproteinase inhibitor DMPS (2,3-Dimercapto-1-propanesulfonic acid) was ineffective even at a 5X higher molarity concentration than prinomastat and marimastat. The results of this study have implications across clinical medicine, toxicology, and evolutionary biology. They highlight the need for improvements in antivenom manufacturing while also providing data supporting the utility of enzyme inhibitors as therapeutic options. The data also lays the foundation for exploring the selection pressures leading to this novel rattlesnake venom phenotype. • Ontogenetic and geographic variation in Crotalus culminates venom was tested. • Ontogenetic loss of procoagulant toxicity in Morelos, not in Guerrero and Michoacán. • Activation of Factor X responsible for true procoagulant activity in neonates. • Three antivenoms failed to neutralize procoagulant neonate venoms. • Two metalloprotease inhibitors successfully neutralized procoagulant neonate venoms.