Differential inhibitory effect of cyclosporin A and bosentan on taurocholate uptake in human and rat hepatocytes as a function of culturing time

Bile salt transport across hepatocytes requires a coordinate action of transporters, which is thought to be a target for drug-induced cholestasis. Hepatocytes provide the most competent in vitro model to predict transporter-related toxic drug effects. The aim of this study was to show a correlation between inhibitory potential of drugs and the change of rate, as well as of the active to passive ratio of taurocholate uptake in these cells. In rat hepatocytes, along with a significant decrease of uptake (86.4% by 72 h), and the shift of saturable/unsaturable transport (from 92/8 to 55/45 in a 24-72 h time interval), the efficacy of taurocholate uptake inhibition was highly reduced (IC50 cyclosporin A 3.9 to >100 mu M, and bosentan 9.1-49.8 mu M at 1 and 72 h, respectively). In contrast, 5-day-old human hepatocytes preserved 70% of their taurocholate uptake capacity with a 2-fold higher active than passive transport, which resulted in a more efficient inhibition by drugs (IC50 cyclosporin A, 2.4 to similar to 10 mu M and bosentan 28.9-45.5 mu M at 1 h and 5 days, respectively). Our results support that reliable drug interaction studies might be performed in 5-day-old human hepatocyte cultures, while experiments using rat hepatocytes at more than 24 h after seeding will highly underestimate the probability of drug interaction. (C) 2011 Elsevier Ltd. All rights reserved.