Mini-Symposium - Abstracts
9 SUBSTANCES THAT ANTAGONIZE THE MYOTOXIC EFFECT OF CROTALID SNAKE VENOMS
P.A. MELO
Department of Basic and Clinical Pharmacology, Institute of Biomedical Sciences, Center of Health Sciences, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
Crotalid snake venoms contain components that induce hemorrhage, edema and muscle damage in vivo. These effects are due to the presence of various components of the venom that may present or not enzymatic activity. We have been studying the myotoxic effect of crotalid snake venoms by using in vitro and in vivo experimental models and testing many different substances that can neutralize this effect. Some previous results so far obtained indicated that polyanions and extracts or purified constituents of the plant Eclipta prostrata (EP) are effective in the prevention of myotoxicity of crotalid snake venoms. In previous publications, we have shown that heparin inhibits the myotoxic effect of Bothrops venoms by the formation of acid-base complexes between the basic myotoxins of the venoms and the polyanionic heparin. The myotoxicity effect of B. jararacussu venom or Bothropstoxin (BthTx) was inhibited by preincubation with heparin that opposed the increase in plasma creatine kinase (CK) activity induced by a subsequent intramuscular injection of venom or BthTx. Recently, using the same protocol we have observed that the in vivo myotoxicity of some North American crotalid snake venoms and their isolated toxins are inhibited by heparin and also by wedelolactone (W), a component isolated from (EP). In these experiments, we examined the antagonism of the in vivo myotoxicity of the crude snake venoms of Agkistrodon contortrix laticinctus (ACL) and Crotalus viridis viridis (CVV), and their isolated toxins by a low molecular weight heparin and by (W). They were performed in vivo by injecting the myotoxic agent (2.5 mg/g) alone or preincubated with the antagonist into a region of the Extensor digitorum longus muscle of the right limb of mouse in a final volume of 50µl. Myotoxicity was evaluated by the increase of plasma (CK) activity two hours after the venom injection, and also by light microscopy. The injection of ACL or CVV crude venoms increased the basal level of plasma CK activity from 217.70 ± 23.73 U/L, (N= 18) to 2740.0 ± 276.30 U/L, (N=5) and 3742.60 ± 723.0 U/L (N=5), respectively, and induced myonecrosis observed histologically. The isolated toxins also induced an increase in the plasma CK and myonecrosis. Heparin reduced the increase of plasma CK by more than 60% for the ACL crude venom or isolated toxin. However, with CVV crude venom or CVV myotoxin, heparin reduced the increase in plasma CK only 52.3% and 37%, respectively. Wedelolactone was effective against crude venoms and isolated toxins by reducing their effect on more than 70%. Wedelolactone did not antagonize the increase of plasma CK or myonecrosis induced by polylysine, a polycathionic peptide that was completely antagonized by heparin. Also, a phospholipase inhibitor, p-bromophenacylbromide did not inhibit this polypeptide, but completely inhibited the myotoxic effect of the isolated toxins. These data confirm our previous results (Melo et al., Toxicon 31: 285, 1993 and Melo et al., Toxicon 32: 595, 1994) and suggest that heparin antagonizes the myotoxic effect of snake venoms by its polyanion property and wedelolactone by its anti-enzyme activity.
This work was supported by CNPq, FAPERJ and CEPG/UFRJ. Part of this work was completed at Dr. Charlotte L. Ownby's laboratory at Oklahoma State University when Dr. Paulo A. Melo was supported with a Postdoctoral Fellowship from CNPq/Brazil.
CORRESPONDENCE TO:
Dr. Paulo de Assis Melo - UFRJ, ICB, Departamento de Farmacologia Básica e Clínica, Bloco J, Ilha do Fundão, CEP 22295-900, Rio de Janeiro, RJ, Brasil. email: pamelo@acd.ufrj.br
Publication Dates
-
Publication in this collection
08 Jan 1999 -
Date of issue
1997
