Interactions of Antiretroviral Protease Inhibitors with Hepatic Transport Proteins: Mechanisms of Drug-induced Liver Injury

Lopinavir and ritonavir are protease inhibitors available as a coformulation for the management of HIV infection. However, liver enzyme elevations are associated with protease inhibitor use. Inhibition of bile acid transport leading to cellular accumulation of bile acids is one proposed mechanism of drug-induced liver injury (DILI). The global objective of this project was to investigate the influence of coadministered protease inhibitors on the hepatobiliary disposition of bile acids. Canalicular excretion of bile acid transport is facilitated by the bile salt export pump (BSEP). Impaired BSEP activity is a risk factor in the development of DILI. Drugs that decrease BSEP function are considered liver liabilities from a drug development perspective. Potent inhibitory activity of lopinavir and ritonavir in vitro has been demonstrated previously. However, the combined effect of lopinavir and ritonavir on the hepatobiliary disposition of bile acids has not been determined. Experiments were undertaken to determine the consequences of coadministered lopinavir and ritonavir on hepatocellular viability and bile acid transport. Lopinavir, alone and combined with ritonavir, demonstrated minimal toxicity but inhibited the biliary excretion of taurocholate and chenodeoxycholate in sandwich-cultured rat hepatocytes (SCRH). Studies in suspended rat hepatocytes revealed that neither lopinavir nor ritonavir altered the initial uptake of either bile acid. Contrary to expectations, 24-hour exposure to lopinavir and ritonavir significantly decreased measured endogenous bile acid concentrations in SCRH. Lastly a genetic association study was carried out to explore the relationship between genetic variants in genes involved in bile acid transport or metabolism and risk of DILI. A comparison of data from patients in the Drug-induced Liver Injury Network to controls obtained from the British Birth Cohort revealed a significant association between the rs2919351 variant in OST[beta] and susceptibility to cholestatic and mixed liver injury. This work demonstrates that 10-minute lopinavir and ritonavir exposure, alone and combined, significantly impaired the biliary excretion of exogenously administered bile acids. However, 24-hour exposure to lopinavir and ritonavir evoked little toxicity in vitro. The lack of toxicity may be due to protective mechanisms in normal-functioning hepatocytes, such as a decrease in both the synthesis and cellular retention of endogenous bile acids