Myotoxic components of snake venoms: their biochemical and biological activities

Specific in vitro biological activity of snake venom myotoxins

Some snake venoms contain toxins that are reported to be selective for damaging muscle. This specificity can be used to design experiments intended to eliminate muscle. We studied the small myotoxins and fractions IV and V of Bothrops nummifer venom to evaluate their direct effect on cultured muscle cells, neurons, macrophages, and a fibroblast cell line. The small myotoxins, at 100 micrograms/ml for 2 h, had no effect in vitro, contrary to the in vivo applications. Fractions IV and V were both myotoxic and, at 100 micrograms/ml, destroyed all cell types. However, at 10 micrograms/ml the effects of fraction IV were more selective for muscle. Vacuolation of the sarcoplasmic reticulum and T-tubules was first seen in the poisoned muscles, without initial lesions in the nuclei, sarcolemma, mitochondria, and rough endoplasmic reticulum. Fractions IV and V have different toxic activity in cells other than muscles and are a mixture of two basic proteins (i and ii). Protein ii is predominant in fraction IV and protein i is predominant in fraction V. The toxic effects may be mediated by the formation of nonspecific ionic pores in the sarcolemma and/or T-tubule muscle membrane.

European viper venoms: haemorrhagic and myotoxic activities

Thirty-one venom samples from European vipers (genera Vipera and Daboia) were tested for haemorrhagic and myotoxic activity by intramuscular injection into mice. Most venoms exhibited haemorrhagic activity and fewer had myotoxic activity, both of which are not strictly related.

Effects of myotoxin alpha on fusion and contractile activity in myoblast-myotube cell cultures

Cultured myoblasts and moytubes were used to study the effects of purified myotoxins from rattlesnake venoms. Standard cell culture techniques were used to establish and maintain primary cultures derived from neonatal rat tissue and two clonal cell lines, rat RMo cells and mouse C2 cells. Toxin concentrations, ranging from 0.04 to 1.0 microM, were added to the cultures at various times under distinct, well-defined conditions. Addition of myotoxin alpha to primary myoblast cultures did not appear to affect the fusion process, whereas similar experiments with two clonal cell lines produced larger myotubes when contrasted with untreated control cultures, particularly with RMo cells. The myotubes derived from primary cell cultures twitched spontaneously but the twitching ceased when the medium was replaced with a serum-free chemically defined incubation medium. Addition of myotoxin alpha to the primary myotubes incubated with serum-free defined medium caused the myotubes to twitch again. Derivatives of myotoxin alpha were prepared by reactions with tetranitromethane and with iodoacetic acid, the latter under reducing and non-reducing conditions. The resulting products, purified but not chemically characterized, were nearly devoid of activity when primary cultures were used to test activity.

Neutralization of myotoxic phospholipases A2 from the venom of the snake Bothrops asper by monoclonal antibodies

The neutralization of two myotoxic phospholipases A2 from the venom of Bothrops asper, myotoxins I and II, by two murine monoclonal antibodies is reported. The monoclonal antibodies, MAb-3 and Mab-4, recognize different epitopes of the toxin. Both antibodies completely neutralized myotoxic activity of myotoxin I and crude venom. MAb-3 also completely neutralized myotoxic activity of myotoxin II, a lysine-49 phospholipase A2 isoform, whereas MAb-4 neutralized this toxin only partially. MAb-3 neutralized myotoxin II at a molar ratio of 1:1, showing a higher efficiency than affinity-purified polyclonal antibodies. A dissociation of myotoxic and enzymatic activities of myotoxin I was observed with both monoclonal antibodies.

Neutralization of myotoxic activity of Bothrops venoms by antisera to purified myotoxins and to crude venoms

A phospholipase myotoxin (MOO-1) and a non-phospholipase myotoxin (JSU-5) were studied for their antigenic cross-reactivity and neutralization by different antisera. Antisera against JSU-5 and MOO-1 reacted equally with both myotoxins in ELISA assays. The specificity of these antisera was also similar, recognizing the same 14,000-18,000 mol. wt components in the venoms of Bothrops jararacussu, Bothrops moojeni, Bothrops neuwiedi and Bothrops pradoi. Using creatine kinase assays, JSU-5 myotoxicity was completely neutralized by B. jararacussu antivenom or anti-JSU-5 antibodies and partially neutralized by B. moojeni antivenom or anti-MOO-1 antibodies. MOO-1 myotoxicity was completely neutralized by antisera against JSU-5 and MOO-1 and B. jararacussu antivenom, and only partially neutralized by B. moojeni antivenom. B. jararacussu venom induced high titres of antibodies against purified myotoxins. This antiserum completely inhibited the myotoxicity of the homologous venom and significantly reduced the myotoxicity of the remaining myotoxin-containing venoms. It is suggested that B. jararacussu venom is a good immunogen to induce antibodies against myotoxins present in the venoms of the different species of Bothrops.