title: Competing Mechanistic Hypotheses of Acetaminophen-Induced Hepatotoxicity Challenged by Virtual Experiments.
abstract: Acetaminophen-induced liver injury in mice is a model for drug-induced liver injury in humans. A precondition for improved strategies to disrupt and/or reverse the damage is a credible explanatory mechanism for how toxicity phenomena emerge and converge to cause hepatic necrosis. The Target Phenomenon in mice is that necrosis begins adjacent to the lobule's central vein (CV) and progresses outward. An explanatory mechanism remains elusive. Evidence supports that location dependent differences in NAPQI (the reactive metabolite) formation within hepatic lobules (NAPQI zonation) are necessary and sufficient prerequisites to account for that phenomenon. We call that the NZ-mechanism hypothesis. Challenging that hypothesis in mice is infeasible because 1) influential variables cannot be controlled, and 2) it would require sequential intracellular measurements at different lobular locations within the same mouse. Virtual hepatocytes use independently configured periportal-to-CV gradients to exhibit lobule-location dependent behaviors. Employing NZ-mechanism achieved quantitative validation targets for acetaminophen clearance and metabolism but failed to achieve the Target Phenomenon. We posited that, in order to do so, at least one additional feature must exhibit zonation by decreasing in the CV direction. We instantiated and explored two alternatives: 1) a glutathione depletion threshold diminishes in the CV direction; and 2) ability to repair mitochondrial damage diminishes in the CV direction. Inclusion of one or the other feature into NZ-mechanism failed to achieve the Target Phenomenon. However, inclusion of both features enabled successfully achieving the Target Phenomenon. The merged mechanism provides a multilevel, multiscale causal explanation of key temporal features of acetaminophen hepatotoxicity in mice. We discovered that variants of the merged mechanism provide plausible quantitative explanations for the considerable variation in 24-hour necrosis scores among 37 genetically diverse mouse strains following a single toxic acetaminophen dose.
authors.affiliation: Bioengineering and Therapeutic Sciences, University of California, San Francisco, San Francisco, CA, United States of America.
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Smith
authors.affiliation: UCSF/UCB Joint Graduate Group in Bioengineering, University of California, Berkeley, Berkeley, CA, United States of America.
authors.forename: Brenden K
authors.identifier: 0000-0002-1841-3888
authors.initials: BK
authors.lastname: Petersen
authors.affiliation: Tempus Dictum, Inc., Milwaukie, OR, United States of America.
authors.forename: Glen E P
authors.initials: GE
authors.lastname: Ropella
authors.affiliation: Bioengineering and Therapeutic Sciences, University of California, San Francisco, San Francisco, CA, United States of America.
authors.forename: Ryan C
authors.initials: RC
authors.lastname: Kennedy
authors.affiliation: Division of Gastrointestinal and Liver Diseases, Department of Medicine, Keck School of Medicine, University of Southern California, Los Angeles, CA, United States of America.
authors.forename: Neil
authors.initials: N
authors.lastname: Kaplowitz
authors.affiliation: Division of Gastrointestinal and Liver Diseases, Department of Medicine, Keck School of Medicine, University of Southern California, Los Angeles, CA, United States of America.
authors.forename: Murad
authors.initials: M
authors.lastname: Ookhtens
authors.affiliation: Bioengineering and Therapeutic Sciences, University of California, San Francisco, San Francisco, CA, United States of America.
authors.forename: C Anthony
authors.identifier: 0000-0001-9372-6860
authors.initials: CA
authors.lastname: Hunt
mesh_terms: D000082:Acetaminophen / Q000633:toxicity*; D000818:Animals; D056486:Chemical and Drug Induced Liver Injury / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D019295:Computational Biology; D003198:Computer Simulation; D008099:Liver / Q000187:drug effects / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D051379:Mice; D008954:Models, Biological
chemical_list: D000082:Acetaminophen