Analysis of the bile acid composition in a fibroblast growth factor 19-expressing liver-humanized mouse model and its use for CYP3A4-mediated drug-drug interaction studies .

Numerous biomedical applications have been described for liver-humanized mouse models, such as in drug metabolism or drug-drug interaction (DDI) studies. However, the strong enlargement of the bile acid (BA) pool due to lack of recognition of murine intestine-derived fibroblast growth factor-15 (FGF15) by human hepatocytes and a resulting up-regulation in the rate-controlling enzyme for BA synthesis, Cytochrome P450 (CYP) 7A1, may pose a challenge in interpreting the results obtained from such mice. To address this challenge, the human FGF19 gene was inserted into the Fah -/- , Rag2 -/- , Il2rg -/- , NOD (FRGN) mouse model, allowing repopulation with human hepatocytes capable of responding to FGF19. While a decrease in CYP7A1 expression in human hepatocytes from humanized FRGN19 mice (huFRGN19) and a concomitant reduction in BA production was previously shown, a detailed analysis of the BA pool in these animals has not been elucidated. Furthermore, there is sparse data on the use of this model to assess potential clinical DDI. In the present work, the change in BA composition in huFRGN19 compared to huFRGN control animals was systematically evaluated, and the ability of the model to recapitulate a clinically described CYP3A4-mediated DDI was assessed. In addition to a massive reduction in the total amount of BA, FGF19 expression in huFRGN19 mice resulted in significant changes in the profile of various primary, secondary, and sulfated BAs in serum and feces. Moreover, as observed clinically, administration of the pregnane X receptor agonist rifampicin reduced the oral exposure of the CYP3A4 substrate triazolam. Significance Statement Transgenic expression of FGF19 normalizes the unphysiologically high level of bile acids in a chimeric liver humanized mouse model and leads to massive changes in bile acid composition. These adaptations could overcome one of the potential impediments in the use of these mouse models for drug-drug interaction studies.