Background information: Bile acids and bile salts (BAs/BSs) contribute in several physiological processes, although high concentration of BAs/BSs intracellularly or in the circulation can lead to cytotoxicity. Assaying the effect of drug candidates with high hepatic clearance on the transport of BAs/BSs is therefore an issue of critical importance. The most commonly used probe substrate in in vitro test systems is taurocholate (TC), although the concentration of taurine-conjugated BSs in human is ~3-fold lower than that of glycine-conjugated species. Hypothesis: Using glycochenodeoxycholate (GCDC), one of the most relevant conjugated BS in human, as probe substrate in in vitro test systems might provide better prediction on the effect on enterohepatic circulation of BSs. Methods: HEK293 cells transduced with OATP1B1 and OATP1B3, as well as NTCP expressing CHO and HEK293 cells were used for proof of concept experiments with radiolabeled TC and unlabeled GCDC, sulfated GCDC and chenodeoxycholate-sulfate. Results and conclusion: All BSs were transported by OATP1B1 and 1B3 in a time- and concentration-dependent manner, while only TC and GCDC were identified as substrates for NTCP. Full transport characterization on OATP1B1, 1B3 and NTCP were conducted with tritiated TC and GCDC as probe substrates. Inhibitory effect of known substrates and inhibitors (atorvastatin, CCK8, diclofenac, pravastatin, telmisartan and troglitazone) on both probes was also tested. Based on the obtained data, the authors suggest replacing TC with GCDC for human in vitro test systems. We have no COI according to this presentation.
