Fig. 3.

Spitting cobra venom causes dermonecrosis in vivo via CTx and PLA₂ toxin potentiation, and inhibition of PLA₂ toxins with varespladib reduces dermonecrosis severity. Groups of mice (n ≥ 4) were intradermally injected with either East African (Tanzania) N. nigricollis venom or purified venom constituents (CTx, PLA₂, or a combination of CTx + PLA₂) at doses reflecting their relative abundance in crude venom, with or without the PLA₂-inhibiting small molecule drug varespladib (19 μg). At 72 h postinjection, lesions were excised and examined macroscopically and histopathologically. (A) A combination of venom CTx and PLA₂ was required to recapitulate the dermonecrotic activity of crude N. nigricollis venom, as CTx and PLA₂ toxins alone did not cause extensive dermonecrosis, as quantified via (A) caliper-measurements of lesion height and width, and (B) the lesion severity measuring AI tool, VIDAL. (C) Histopathological analysis of excised lesions showed similar results, except for a more severe dermonecrotic effect of the PLA₂ alone. Preincubation with the PLA₂ inhibitor varespladib reduced dermonecrotic lesion severity caused by East African N. nigricollis venom with similar trends for CTx + PLA₂ and PLA₂, as quantified with (D) calipers, (E) VIDAL, and (F) histopathological analysis. For damage scores of individual skin layers, see SI Appendix, Fig. S10. For panels A and D, the data shown represent mean lesion areas and corresponding SDs. Panels B and E show the mean lesion severity, as determined by VIDAL. Panels C and F show mean dermonecrosis severity scores and corresponding SDs calculated from those of the individual skin layers (SI Appendix, Fig. S10). Statistically significant differences were determined by one-way ANOVAs followed by Tukey's multiple comparisons post hoc tests and are denoted by asterisks: *P < 0.05, **P < 0.01. Error bars represent SDs.