Elucidating Hepatocyte Transporter Alterations in Nonalcoholic Fatty Liver Disease (NAFLD): A Prerequisite for Precision Dosing in Liver Disease

Hepatic transport proteins play a critical role in the disposition of many medications and endogenous compounds such as bile acids (BAs). Approximately one-third of adults worldwide have nonalcoholic fatty liver disease (NAFLD). The impact of previously observed changes in hepatic transporters on medications in patients with NAFLD is poorly understood. This dissertation employed various nonclinical methods to investigate key drug/BA transporters influenced by NAFLD, and to predict changes in hepatic drug disposition in patients with this disease. The hepatocyte transporter organic solute transporter (OST)α/β is upregulated in patients with nonalcoholic steatohepatitis (NASH), the progressive form of NAFLD. However, limited knowledge of OSTα/β protein structure has hampered identification of OSTα/β drug substrates/inhibitors. In Chapter 2, model-identified pore-lining OSTα amino acids were investigated using site-directed mutagenesis in OSTα/β overexpressing cells. Studies revealed OSTα residues (Ser228, Thr229, Gln269, Glu305) that impact OSTα/β cellular abundance/localization and may influence OSTα/β-mediated BA transport. In Chapter 3, a novel technique was developed to estimate transporter functional capacity by quantifying the plasma membrane localization and zonation (membrane-localized zonal abundance [MZA]) of transporters in NAFLD liver biopsies. This study identified changes in bile salt export pump (BSEP)MZA that may explain findings of altered BA homeostasis in NASH, and provided novel MZA data for key hepatocyte drug transporters including sodium-taurocholate cotransporting polypeptide and organic anion transporting polypeptides. In Chapter 4, MZA data were incorporated into a permeability-limited multi-compartment liver framework for physiologically based pharmacokinetic modeling. Statin medications are commonly prescribed in patients with NAFLD, who are often obese. Mathematical models were used to simulate pravastatin, rosuvastatin, and atorvastatin hepatic disposition in Healthy Volunteers, Obese, Morbidly Obese, and NASH virtual populations. Notably, model predictions revealed increased plasma exposure and decreased pericentral intrahepatic exposure to statins in NASH. In Chapter 5, an in vitro NASH model was developed to predict hepatobiliary drug disposition. Lipid-cytokine media supplementation induced NASH-like alterations in the lipidome and hepatocyte transporters. In conclusion, the knowledge and methodological advances described in this dissertation provide new insight and a foundation for future research on NAFLD-mediated alterations in hepatocyte transporter function to help guide medication optimization strategies for this patient population.