Human OATP1B1 (SLCO1B1) transports sulfated bile acids and bile salts with particular efficiency.

Human OATP1B1 is highly expressed at the basolateral membrane of the hepatocyte. It plays an important role in the sodium-independent transport of bile acids and bile salts and contributes to the systemic clearance of many drugs. In this study, the interaction of at least one representative of all major chemical classes of bile acids and bile salts, which include the bile acid chenodeoxycholate (CDC), monovalent (amidated) bile salts glycochenodeoxycholate (GCDC), taurochenodeoxycholate (TCDC) and taurocholate (TC), a sulfated bile acid 3-sulfo-chenodeoxycholate (3S-CDC) and a divalent (amidated and sulfated) bile salt 3-sulfo-glycolithocholate (3S-GLC) were tested with OATP1B1 overexpressed in HEK293 cells. All bile acid derivatives except for CDC showed an efficient transport by OATP1B1. 3S-GLC gave the lowest KM (0.708 ±â€¯0.125 µM) and 3S-CDC showed the highest Vmax value (158 ±â€¯87.3 pmol/mg protein/min). The ranking of Clint values (3S-GLC > 3S-CDC > TCDC > GCDC > TC) also showed a preference for sulfated derivatives. In summary, human OATP1B1 transports sulfate esters of bile acids and bile salts more efficiently than monovalent bile salts.

The utility of HepG2 cells to identify direct mitochondrial dysfunction in the absence of cell death.

Drug-induced mitochondrial dysfunction has been hypothesized to be an important determining factor in the onset of drug-induced liver injury. It is essential to develop robust screens with which to identify drug-induced mitochondrial toxicity and to dissect its role in hepatotoxicity. In this study we have characterised a mechanistically refined HepG2 model, using a panel of selected hepatotoxicants and non-hepatotoxicants. We have demonstrated that acute metabolic modification, via glucose-deprivation over a 4 h period immediately prior to compound addition, is sufficient to allow the identification of drugs which induce mitochondrial dysfunction, in the absence of cell death over a short exposure (2-8 h) using a plate-based screen to measure cellular ATP content and cytotoxicity. These effects were verified by measuring changes in cellular respiration, via oxygen consumption and extracellular acidification rates. Overall, these studies demonstrate the utility of HepG2 cells for the identification of mitochondrial toxins which act directly on the electron transport chain and that the dual assessment of ATP content alongside cytotoxicity provides an enhanced mechanistic understanding of the causes of toxicity.