A predictive, quantitative, mathematical model (DILIsym™) is under development as a public-private initiative based on the physiological processes involved in drug-induced liver injury. The model includes multiple scales, ranging from molecular/cellular interactions to organ-tissue level considerations. Simulated mice, rats, and humans accurately reproduce the hepatotoxic responses to acetaminophen and methapyrilene, providing validation of the DILIsym™ model for reactive metabolite mediated toxicity. Furosemide (FS) hepatotoxicity is also thought to be reactive metabolite mediated, but with some mechanistic differences. FS was also recently included in the DILIsym™ model, simulating the quantitative aspects of drug metabolism, covalent binding, glutathione, and ATP levels that are described in the literature and from unpublished experiments in mice dosed with 400 mg/kg. ALT levels were accurately predicted based on these inputs, and multiple hypotheses for the ATP reductions were tested with additional modeling and simulations. Dose-dependent necrosis and associated increases in ALT levels do not appear to be dependent upon mitochondrial toxicity. Rather, simulations that included substantial (4x) increases in cellular energy expenditure or decreases (75%) in mitochondrial ATP production due to substrate limitations were more consistent with the experimental hepatotoxic responses. Specific laboratory experiments that will test these hypotheses were identified and are currently underway, including providing glycolytic substrate to sustain ATP production and levels in mice treated with FS. Incorporating FS into the DILIsym™ model provided an increased understanding of the mechanisms associated with FS hepatotoxicity, identified gaps in knowledge, and suggested multiple testable hypotheses to close these gaps.
SOT 51st Annual Meeting and ToxExpo, March 11-15, 2012, San Francisco, CA
By Scott Q. Siler, DJ Antoine, Brett A. Howell, Jeff L. Woodhead, BK Park, Paul B. Watkins