Effects Of Myotoxins II and III, Isolated From Bothrops asper Venom (Bav), On The Expression Of Cyclooxigenases (COX).

Moreira, V.¹; Zamuner, S.R.^1*; Gutiérrez, J.M.² Teixeira, C.F.P¹.

1 Lab. Farmacologia, Instituto Butantan, São Paulo, Brasil; 1*Lab. Pharmacology, Calgary University, Calgary, Canadá; 2 Instituto Clodomiro Picado, Costa Rica.

Four myotoxins with structure of phospholipase A2 (PLA2) were isolated from Bothrops asper snake venom. Two of them are the myotoxin-III, with catalytic activity and myotoxin II, wich lacks enzymatic activity due to substitution of the amino acid Asp by Lys at position 49. Despite diffrences in enzymatic activity, both display inflammatory effects. Considering that cyclooxigenases (COX) are key enzymes for conversion of arachidonic acid to eicosanoids and that Bav induces the release of these mediators, we evaluated the in vivo effect of Bav, MTX-II and III on expression of cyclooxigenase-1 (COX-1) and cyclooxigenase-2 (COX-2) in peritoneal leukocytes. Myotoxins and Bav 20 and 5 mg/ animal, respectively were injected into peritoneal cavity of male swiss mice (18-20g). After 1, 3, 6 and 12 h, peritoneal leukocytes were collected and COX expression was determined by western blot. Results showed that Bav induced expression of COX-2 from 3 to 12 h and did not affect COX-1 protein. The MTX-II and III induced COX-2 expression from 1 to 12 h and COX-1 remained unchanged. These findings indicate that the that myotoxins and Bav did not affect COX-1 expression but were able to induce COX-2 expression. The effect of toxins on COX-2 expression was earlier and longer than that of Bav suggesting that PLA2s are important components for the crude venom-induced release of arachidonic acid-derived lipid mediators. Moreover, the ability of MTX-II to induce COX-2 expression suggests that the catalytic activity of PLA2s i not relevant for this effect.

Support: Fapesp, CNPq.

Correspondence to: vanessam@usp.br