Processing of pro-tumor necrosis factor-alpha by venom metalloproteinases: a hypothesis explaining local tissue damage following snake bite.

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-alpha fusion protein (GST-TNF-alpha) substrate to form biologically active TNF-alpha which was shown to be neutralized by ovine TNF-alpha 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-alpha-sensitive cell culture assay and electrophoresis. These observations demonstrate the possible importance of TNF-alpha 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-alpha. 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-alpha. The results indicate that inhibition or neutralization of endogenous TNF-alpha 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.