Metabolism of oltipraz and glutathione reductase inhibition

A decrease in glutathione reductase (GR) activity was observed in Schistosoma mansoni isolated from oltipraz(OPZ)-treated mice. Yeast and Schistosoma mansoni GR-activity was inhibited by OPZ derivatives only. These OPZ-derivatives showed in vitro schistosomicidal activity. Using yeast GR and dithiolium salts of OPZ, time-dependent inactivation and gel chromatography experiments revealed irreversible inhibition dependent on the redox state of the enzyme. Binding of radiolabelled ([3H]7-methyl-8-methylthio-pyrrolo[1,2-a]pyrazine disulphide 1b) obtained from OPZ was observed using exclusion chromatography and equilibrium dialysis. These results indicate that GR can be considered as the target of schistosomicidal activity of OPZ. The lack of inhibitory activity of OPZ and dithiole-thione analogues, and the potent activity of the corresponding pyrrolo-pyrazine derivatives, is consistent with the hypothesis that OPZ is a pro-drug.