Inhibition of crotoxin phospholipase A(2) activity by manoalide associated with inactivation of crotoxin toxicity and dissociation of the heterodimeric neurotoxic complex.

Crotoxin (CACB complex) is a convulsant heterodimeric neurotoxic phospholipase A(2) (PLA(2)). The role of phospholipid hydrolysis in its epileptogenic properties remains unresolved. We, thus, studied the effect of manoalide (MLD), a PLA(2) inhibitor, on the toxin catalytic activity and its central and peripheral toxicity. Incubation of crotoxin with MLD fully and irreversibly inactivated its enzymatic activity. Interestingly, crotoxin also lost its central neurotoxicity after intracerebroventricular injection and peripheral toxicity after intravenous administration. MLD-treated crotoxin prevented the high affinity binding of [125I]-radiolabeled crotoxin on rat cortex synaptic plasma membranes. Further analysis of MLD-treated crotoxin by non-denaturing PAGE and surface plasmon resonance indicated that the crotoxin complex was dissociated after MLD treatment. Although the loss of MLD-treated crotoxin peripheral neurotoxicity could not be attributed to this dissociation, the presence of free CA subunit might explain the observed competition in binding experiments. In conclusion, the dissociation of the crotoxin complex by MLD, as demonstrated in this study, did not permit to specify the role of the enzymatic activity in crotoxin epileptogenic properties. Other approaches would be required to resolve this question.