Mechanistic study of idiosyncratic drug-induced hepatitis (DIH) continues to be a challenging problem because of the lack of animal models. The inability to produce this type of hepatotoxicity in animals, and its relative rarity in humans, may be linked to the production of antiinflammatory factors that prevent drug-protein adducts from causing liver injury by immune and nonimmune mechanisms. We tested this hypothesis by using a model of acetaminophen (APAP)-induced liver injury in mice. After APAP treatment, a significant increase was observed in serum levels of interleukin (IL)-4, IL-10, and IL-13, cytokines that regulate inflammatory mediator production and cell-mediated autoimmunity. When IL-10 knockout (KO) mice were treated with APAP, most of these mice died within 24 to 48 hours from liver injury. This increased susceptibility to APAP-induced liver injury appeared to correlate with an elevated expression of liver proinflammatory cytokines, tumor necrosis factor (TNF)-␣, and IL-1, as well as inducible nitric oxide synthase (iNOS). In this regard, mice lacking both IL-10 and iNOS genes were protected from APAP-induced liver injury and lethality when compared with IL-10 KO mice. All strains, including wild-type animals, generated similar amounts of liver APAPprotein adducts, indicating that the increased susceptibility of IL-10 KO mice to APAP hepatotoxicity was not caused by an enhanced formation of APAP-protein adducts. Epidemiologic studies reveal that as many as 25% of fulminant hepatitis cases in intensive care units are caused by DIH. 1 It is also the major reason for removal of new drugs from clinical development and widespread use. 2 Although DIH can be very severe, the incidence for any given drug is usually low. It has been hypothesized that this idiosyncratic nature of DIH is either caused by a metabolic idiosyncrasy, in which patients who develop toxicity metabolize the drug to reactive metabolites to a greater extent than most others, 3 or an immunologic idiosyncrasy (druginduced allergic hepatitis [DIAH]), in which the immune system of patients who develop DIH react against protein adducts of drugs or other neoantigens formed in the liver. 3,4 These 2 mechanisms are not mutually exclusive and might both contribute to the initiation of DIH. 3 However, the demonstration of specific antibodies and sensitized T cells that react with drugs, their metabolites, or specific protein neoantigens and/or autoantigens supports the immunologic basis of DIH. [2][3][4][5][6] The host-dependent, idiosyncratic nature of DIH is poorly understood, but may be related to a variety of factors that in most individuals either fail to promote or, in fact, protect against DIH. For example, genetic polymorphisms in the specific repertoire of major histocompatibility complex class I and II antigens and/or Band T-cell receptors may render the immune cells from most individuals incapable of satisfactorily binding or presenting protein adducts of drugs or their derived peptides and, therefore, unable to lead to immunopatholog...

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A consortium of biopharmaceutical companies previously developed an optimized Zebrafish developmental toxicity assay (ZEDTA) where chorionated embryos were exposed to non-proprietary test compounds from 5 to 6 h post fertilization and assessed for morphological integrity at 5 days post fertilization. With the original 20 test compounds, this achieved an overall predictive value for teratogenicity of 88% of mammalian in vivo outcome [Gustafson, A. L., Stedman, D. B., Ball, J., Hillegass, J. M., Flood, A., Zhang, C. X., Panzica-Kelly, J., Cao, J., Coburn, A., Enright, B. P., et al. (2012). Interlaboratory assessment of a harmonized Zebrafish developmental toxicology assay-Progress report on phase I. Reprod. Toxicol. 33, 155-164]. In the second phase of this project, 38 proprietary pharmaceutical compounds from four consortium members were evaluated in two laboratories using the optimized method using either pond-derived or cultivated-strain wild-type Zebrafish embryos at concentrations up to 100μM. Embryo uptake of all compounds was assessed using liquid chromatography-tandem mass spectrometry. Twenty eight of 38 compounds had a confirmed embryo uptake of >5%, and with these compounds the ZEDTA achieved an overall predictive value of 82% and 65% at the two respective laboratories. When low-uptake compounds (≤ 5%) were retested with logarithmic concentrations up to 1000μM, the overall predictivity across all 38 compounds was 79% and 62% respectively, with the first laboratory achieving 74% sensitivity (teratogen detection) and 82% specificity (non-teratogen detection) and the second laboratory achieving 63% sensitivity (teratogen detection) and 62% specificity (non-teratogen detection). Subsequent data analyses showed that technical differences rather than strain differences were the primary contributor to interlaboratory differences in predictivity. Based on these results, the ZEDTA harmonized methodology is currently being used for compound assessment at lead optimization stage of development by 4/5 of the consortium companies.