Rotenone Increases Isoniazid Toxicity but Does Not Cause Significant Liver Injury: Implications for the Hypothesis that Inhibition of the Mitochondrial Electron Transport Chain Is a Common Mechanism of Idiosyncratic Drug-Induced Liver Injury

Idiosyncratic drug reactions (IDRs) significantly increase the risk of failure in drug development. The major IDR leading to drug candidate failure is idiosyncratic drug-induced liver injury (IDILI). Although most evidence suggests that IDRs are mediated by the immune system, there are other hypotheses, such as mitochondrial dysfunction. Many pharmaceutical companies routinely screen for mitochondrial toxicity in an attempt to "derisk" drug candidates. However, the basic hypothesis has never been rigorously tested. A major assay used for this screening involves measurement of inhibition of the mitochondria] electron transport chain. One study found that the combination of rotenone and isoniazid, which inhibit mitochondrial complex I and II, respectively, were synergistic in causing hepatocyte toxicity in vitro and suggested the combination of another drug that inhibited complex I would increase the risk of isoniazid-induced liver injury in patients. We tested this hypothesis in vivo where wild-type and PD-1-/- mice administered anti-CTLA-4, our impaired immune tolerance mouse model, were given 0.02% (w/v) rotenone in water or 0.1%, 0.05%, and 0.01% (w/w) rotenone alone or in combination with isoniazid in food. The cotreatment led to lethality in 100% of the animals receiving 0.1% rotenone and 0.2% isoniazid and 83% of the animals cotreated with 0.05% rotenone and 0.2% isoniazid in food. Nevertheless, there was no significant increase in GLDH or histological evidence of liver injury. No signs of toxicity were observed in any of the mice given rotenone or isoniazid alone. Even though inhibition of the mitochondrial electron transport chain did not lead to significant liver toxicity, it could provide danger signals that promote immune-mediated liver injury. However, rotenone did not significantly increase the liver injury induced by isoniazid in our impaired immune tolerance model. Overall, we conclude that inhibition of the mitochondrial electron transport chain is not a significant mechanism of IDILI.