Isolation and partial characterization of a myotoxin from the venom of the snake Bothrops nummifer

A myotoxin from the venom of the snake Bothrops nummifer was purified to homogeneity by ion-exchange chromatography on CM-Sephadex. The toxin is a basic dimer with a subunit molecular weight of 16,000, as estimated by SDS-polyacrylamide gel electrophoresis. The toxin lacks phospholipase A2 activity when tested on egg yolk lecithin and skeletal muscle homogenates. It induces skeletal muscle damage both in vivo and in vitro. When injected i.m. it promotes a drastic increase in serum creatine kinase levels; the isozyme CK-MM is responsible for this increment. A rapid release of creatine kinase was observed when mouse gastrocnemius muscle was incubated with the toxin, suggesting that it induces the formation of relatively large 'lesions' in the plasma membrane of muscle cells. Moreover, analysis of the dose-response data indicated that the myotoxin affects muscle sarcolemma by a 'one hit' mechanism. Skeletal muscle cells are affected by the toxin when calcium is eliminated from the medium. The myotoxin has an i.v. LD50 of 3.9 mg/kg body weight in mice, and induces edema when injected in the foot pad. On the other hand, it is not directly hemolytic, anticoagulant, hemorrhagic nor cytotoxic for lymphocytes. The myotoxin shows partial immunologic identity with a myotoxic phospholipase A2 isolated from Bothrops asper venom. The polyvalent antivenom produced in Costa Rica forms a precipitation arc against B. nummifer myotoxin on immunoelectrophoresis.