Direct Oxidation and CovalentBinding of Isoniazidto Rodent Liver and Human Hepatic Microsomes: Humans Are More LikeMice than Rats

摘要

Isoniazid (INH) is associated with serious liver injury and autoimmunity. Classic studies in rats indicated that a reactive metabolite of acetylhydrazine is responsible for the covalent binding and toxicity of INH. Studies in rabbits suggested that hydrazine might be the toxic species. However, these models involved acute toxicity with high doses of INH, and INH-induced liver injury in humans has very different features than such animal models. In this study, we demonstrated that a reactive metabolite of INH itself can covalently bind in the liver of mice and also to human liver microsomes. Covalent binding also occurred in rats, but it was much less than that in mice. We were able to trap the reactive metabolite of INH with N-α-acetyl-l-lysine in incubations with human liver microsomes. This suggests that the reactive intermediate of INH that leads to covalent binding is a diazohydroxide rather than a radical or carbocation because those reactive metabolites would be too reactive to trap in this way. Treatment of mice or rats with INH for up to 5 weeks did not produce severe liver injury. The alanine transaminase assay (ALT) is inhibited byINH, and other assays such as glutamate and sorbitol dehydrogenase(SDH) were better biomarkers of INH-induced liver injury. High dosesof INH (200 and 400 mg/kg/day) for one week produced steatosis inrats and an increase in SDH, which suggests that it can cause mitochondrialinjury. However, steatosis was not observed when INH was given atlower doses for longer periods of time to either mice or rats. Wepropose that covalent binding of the parent drug can contribute toINH-induced hepatotoxicity and autoimmunity. We also propose thatthese are immune-mediated reactions, and there are clinical data tosupport these hypotheses.