Role of hepatic transport proteins in drug disposition and drug-induced liver injury

Transport proteins in the liver play a crucial role in hepatic uptake and biliary excretion of drugs/metabolites. Understanding how altered hepatic transport (due to sex, genetic polymorphisms, disease states, drug interactions) influences systemic and hepatic exposure of drugs/metabolites is important from both a therapeutic and toxicologic standpoint. The objective of this dissertation research was to investigate the role of hepatic transport proteins in the hepatobiliary disposition of drugs/generated metabolites and drug-induced liver injury. Initial studies in perfused livers from male and female wild-type (WT) and breast cancer resistance protein (Bcrp)-deficient mice revealed that acetaminophen sulfate and glucuronide hepatobiliary disposition was influenced by sex-dependent Bcrp expression as well as other factors relating to conjugate formation and basolateral transport. In a second set of studies, sandwich-cultured hepatocytes (SCH), coupled with pharmacokinetic modeling/Monte Carlo simulations, were used to examine the impact of impaired biliary excretion on the hepatobiliary disposition of troglitazone (TGZ) and metabolites. Consistent with in vivo data, TGZ was extensively metabolized to TGZ-sulfate, and to a lesser extent to TGZ-glucuronide and TGZ-quinone, in both rat and human SCH. Modeling/simulation revealed that hepatocyte accumulation of metabolites was extensive when biliary excretion pathways were impaired; medium concentrations (analogous to systemic concentrations in vivo) may not reflect changes in hepatic exposure. Subsequent studies focused on two hepatotoxic drugs (trabectedin and sulindac) and the potential role of altered hepatic transport in drug-induced liver injury. Trabectedin-mediated cytotoxicity was significantly decreased in dexamethasone-pretreated WT rat SCH and in Mrp2-deficient TR- rat SCH, compared to control WT rat SCH. These data emphasize the importance of Mrp2 and Mrp3 in hepato-protection from trabectedin-mediated cytotoxicity. Sulindac and metabolites inhibited multiple hepatic transport proteins in rat and human hepatocytes; potent inhibition of the hepatic transport of bile acids and/or drugs by sulindac sulfide and sulfone may play a previously unrecognized role in sulindac-mediated hepatotoxicity. Collectively, this dissertation research demonstrated the impact of sex-dependent transporter expression on the hepatobiliary disposition of phase II conjugates, illustrated use of an in vitro approach coupled with modeling/simulation to predict altered drug/metabolite hepatobiliary disposition, and defined the involvement of multiple transport proteins in drug-induced liver injury