1. The role of cholangiocytes in the prediction and detection of drug-induced liver injury
- Author
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Howell, L. S.
- Subjects
616.3 - Abstract
Drug-induced liver injury (DILI) is a leading cause of drug attrition throughout all stages of the drug discovery process and is a frequent adverse drug reaction (ADR) with significant clinical burden. Therefore, a concerted effort to predict the onset of DILI before clinical manifestation is paramount. Nevertheless, currently available models to predict DILI are often lacking, due to their poor physiological relevancy to the in vivo hepatic phenotype. Furthermore, the current gold standard biomarkers for diagnosing DILI, such as alkaline phosphatase (ALP), have inadequate sensitivity and specificity. Whilst circulating levels of miR-122 have shown improved clinical utility in diagnosing hepatocellular DILI, miRNAs signatures for other hepatic cell types have not yet been elucidated. Cholangiocytes are epithelial cells that line the hepatic bile ducts and are primarily responsible for altering the composition of canalicular bile. Cholangiocytes are targeted by both mixed and cholestatic DILI, which without proper diagnosis and clinical intervention, can cause bile duct degeneration and destruction. Cholangiocyte DILI is typically diagnosed by elevations in circulating ALP, though it is not known if a panel of cholangiocyte-derived miRNAs could aid a more effective diagnosis. Recent research has identified that cholangiocytes can be reprogrammed in vitro into a biphenotypic hepatic organoids. This novel liver model has demonstrated a degree of Drug-Metabolizing Enzymes and Transporter (DMET) activity, which may make them viable in vitro tools for predicting DILI. However, their proteome remains poorly characterised. Therefore, the aims of this thesis were threefold. 1) To characterise global miRNA expression in murine cholangiocytes and hepatocytes in order to identify novel circulating biomarkers. 2) Induce cell-specific toxicity in vivo to assess the detection of putative circulating biomarkers in pre-clinical models. 3) Characterise the proteome of biliary-derived organoids to assess their phenotype relative to donor-derived liver tissue. In order to identify the global miRNA profiles of hepatocytes and cholangiocytes, both cell types were isolated from CD-1 mice with a purity of =97 % and =94 %, respectively. Global miRNA expression was assessed by microarray, which revealed 93 miRNAs uniquely expressed in cholangiocytes and 178 miRNAs co-expressed between cholangiocytes and hepatocytes. This data was further triaged by SAM statistical analysis and publicly available database searching. Ultimately, 50 uniquely expressed and 13 enriched cholangiocyte miRNAs were identified as candidate miRNA biomarkers of cholangiocyte DILI. Although these 63 miRNAs of interest were all translational into human, their tissue expression is not solely liver specific. The expression of all five members of the miR-200 family (miR-141, -200a, -200b, -200c and -429) were found to be enriched or unique to cholangiocytes. These miRNAs have previously been implemented as circulating biomarkers for various biliary diseases, although their role in cholangiocyte DILI is yet to be assessed. Cholangiocyte injury was therefore induced in CD-1 and C57BL/6J mice and Sprague Dawley rats with a-napthylisothiocyanate (ANIT) and 4,4'-Diaminodiphenylmethane (DAPM). Although these miRNAs were elevated in the serum of hepatotoxin-dosed animals, there was a highly variable degree of liver injury. In ANIT-dosed animals, significant enlargement and toxicity of the stomach was observed, which has not been previously reported. Further work is therefore required to induce a more consistent liver injury and to fully elucidate if the detection of these circulating miRNAs in the serum was caused by hepatic or gastric toxicity. Hepatic organoids are a recent innovation in in vitro modelling. Initial research suggests organoids better recapitulate the liver phenotype in vitro compared to pre-existing proliferative cell models. However, they remain poorly characterised. A global proteomic profiling of undifferentiated and differentiated hepatic organoids and donormatched livers was therefore performed to assess both their similarity to liver tissue and DMET expression. iTRAQ analysis revealed 4,405 proteins commonly detected in all sample types. Differentiation of organoids significantly increased the expression of multiple CYP450s, phase II enzymes, liver biomarkers and some hepatic transporters. While the final phenotype of differentiated organoids is distinct from liver tissue, they contain multiple DMET proteins necessary for liver function and drug metabolism, such as CYP450 3A, GSTA and MDR1A. Further experimentation, optimisation and characterisation of biliary-derived hepatic organoids is needed relative to pre-existing models to fully contextualise their use as a putative in vitro model of DILI. In summary, this work has utilised cholangiocytes as both diagnostic and predictive tools of DILI. A selection of translational candidate miRNAs that could be used as circulating biomarkers of cholangiocyte injury has been identified. In vivo investigation of cholangiocyte injury by ANIT was highly variable and was associated with a previously unidentified stomach toxicity. However, a selection of candidate miRNAs was elevated under certain conditions. This work has also characterised the proteomic profile of biliary-derived organoids, a novel hepatic in vitro model.
- Published
- 2019
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