Unexpected increased thiabendazole tolerance in Haemonchus contortus resistant to anthelmintics by modulation of glutathione activity.

The effect of several modulators of the synthesis or activity of glutathione (GSH) on the susceptibility of Haemonchus contortus eggs susceptible or resistant to anthelmintics was investigated using in vitro egg-hatch assays. Diethylmaleate, D,L-buthionine-[S,R]-sulfoximine, and patulin induced an unexpected decrease in the susceptibility of resistant eggs to thiabendazole, which was chosen as a reference for resistance to benzimidazole compounds. The results demonstrate that the level of GSH or SH analog plays an important role in the toxicity of thiabendazole to nematode eggs. Comparison with changes observed in the cytotoxicity of antitumor or antiprotozoal drugs after GSH modulation suggests that in H. contortus eggs this increased thiabendazole tolerance might depend on different factors, whether associated or not, including the ability of thiabendazole to conjugate with parasitic GSH or analog, the potential toxicity of such conjugates, their cellular distribution, and their role in the expression of glutathione S-transferase activities, and, perhaps, in the regulation of apoptosis.