Bile acids (BAs) have been established as ubiquitous regulatory molecules implicated in a large variety of healthy and pathological processes. However, the scope of BA heterogeneity is often underrepresented in current literature. This is due in part to inadequate detection methods, which fail to distinguish the individual constituents of the BA pool. Thus, the primary aim of this study was to develop a method that would allow the simultaneous analysis of specific C24 BA species, and to apply that method to biological systems of interest. Herein, we describe the generation and validation of an LC-MS/MS assay for quantification of numerous BAs in a variety of cell systems and relevant biofluids and tissue. These studies included the first baseline level assessment for planar BAs, including allocholic acid, in cell lines, biofluids, and tissue in a nonhuman primate (NHP) laboratory animal, Macaca mulatta, in healthy conditions. These results indicate that immortalized cell lines make poor models for the study of bile acid synthesis and metabolism, whereas human primary hepatocytes represent a promising alternative model system. We also characterized the BA pool of M. mulatta in detail. Our results support the use of NHP models for the study of BA metabolism and pathology in lieu of murine models. Moreover, the method developed here can be applied to the study of common and planar C24 BA species in other systems.

Background: Coronavirus disease 2019 (COVID-19) is a global pandemic that has caused more than 600 million cases and over six million deaths worldwide. Despite the availability of vaccination, COVID-19 cases continue to grow making pharmacological interventions essential. Remdesivir (RDV) is an FDA-approved antiviral drug for treatment of both hospitalized and non-hospitalized COVID-19 patients, albeit with potential for hepatotoxicity. This study characterizes the hepatotoxicity of RDV and its interaction with dexamethasone (DEX), a corticosteroid often co-administered with RDV for inpatient treatment of COVID-19. Methods: Human primary hepatocytes and HepG2 cells were used as in vitro models for toxicity and drug-drug interaction studies. Real-world data from hospitalized COVID-19 patients were analyzed for drug-induced elevation of serum ALT and AST. Results: In cultured hepatocytes, RDV markedly reduced the hepatocyte viability and albumin synthesis, while it increased the cleavage of caspase-8 and caspase-3, phosphorylation of histone H2AX, and release of ALT and AST in a concentration-dependent manner. Importantly, co-treatment with DEX partially reversed RDV-induced cytotoxic responses in human hepatocytes. Moreover, data from COVID-19 patients treated with RDV with and without DEX co-treatment suggested that among 1037 patients matched by propensity score, receiving the drug combination was less likely to result in elevation of serum AST and ALT levels (≥ 3 × ULN) compared to the RDV alone treated patients (OR = 0.44, 95% CI = 0.22–0.92, p = 0.03). Conclusion: Our findings obtained from in vitro cell-based experiments and patient data analysis provide evidence suggesting combination of DEX and RDV holds the potential to reduce the likelihood of RDV-induced liver injury in hospitalized COVID-19 patients.