Mechanism for isaxonine hepatitis. II. Protective role of glutathione and toxicological studies in mice.
Coincubation of 0.4 mM [3H]glutathione with 4 mM isaxonine , an NADPH-generating system, glutathione S-transferase and mouse liver microsomes, followed by thin-layer chromatography of the incubation mixture, resulted in the appearance of a 3H-labeled peak with characteristics consistent with a glutathione- isaxonine metabolite adduct: this peak was absent if either isaxonine or the NADPH-generating system was omitted and was decreased if the transferase was omitted. In vivo, the concentrations of hepatic glutathione and glutathione disulfide were markedly decreased 2.5 hr after administration of isaxonine (4 mmol X kg-1 i.p.); this depletion of glutathione was prevented essentially by pretreatment with piperonyl butoxide. In vitro, addition of 4 mM glutathione decreased markedly the amount of [14C] isaxonine metabolite that bound to microsomal proteins during incubation of 1 mM [2-14C] isaxonine with hepatic microsomes and an NADPH-generating system. In vivo, pretreatment with diethylmaleate decreased further hepatic glutathione concentration and markedly increased the amount of [14C] isaxonine metabolite covalently bound to hepatic proteins, 2.5 hr after administration of [2-14C] isaxonine (4 mmol X kg-1 i.p.). Administration of isaxonine (4 mmol X kg-1 i.p.) decreased hepatic cytochrome P-450 concentration, but failed to produce liver cell necrosis, even in mice pretreated with phenobarbital, 3-methylcholanthrene or diethylmaleate, despite high levels of in vivo covalent binding in pretreated animals. We conclude that the reactive metabolite of isaxonine may be conjugated with glutathione or may covalently bind to hepatic proteins. The metabolite, however, has limited hepatotoxic potential in mice.