Processing of pro‐tumor necrosis factor‐α by venom metalloproteinases: A hypothesis explaining local tissue damage following snake bite

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Abstract
Venom-induced necrosis is a common local debilitating sequela of bites by many vipers, frequently resulting in severe permanent scarring and deformity. Antivenoms are not effective under these circumstances unless administered within a few minutes of the bite; this is unlikely to occur in the rural tropics where most victims take a long time to reach medical care. We have shown that two venom zinc metalloproteinases (jararhagin from Bothrops jararaca venom and a metalloproteinase from Echis pyramidum leakeyi venom) successfully cleaved the recombinant glutathione-S-transferase – tumor necrosis factor-α fusion protein (GST-TNF-α) substrate to form biologically active TNF-α which was shown to be neutralized by ovine TNF-α Fab antibodies. This resulted in a reduction of venom-induced necrosis in mice when injected intravenously or intradermally both before and after intradermal injections of E.p.leakeyi venom. A peptidomimetic (POL 647) was also found to inhibit the Echis metalloproteinase, thus preventing the processing of the TNF precursor; this was shown using a TNF-α-sensitive cell culture assay and electrophoresis. These observations demonstrate the possible importance of TNF-α in the development of the resulting necrotic lesion and leads to the hypothesis that increased levels of venom metalloproteinases following snake bite release active TNF-α. This cytokine may contribute to the local necrosis and also induce the production of endogenous matrix metalloproteinases, which in turn generate a positive feedback mechanism resulting in continued cleavage of pro-TNF-α. The results indicate that inhibition or neutralization of endogenous TNF-α appears to result in a significant reduction in venom-induced necrosis. This could help to explain the clinical observations that treatment of local necrosis following snake bite by antivenom is only minimally successful.