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

[Display omitted] ► Total TC uptake activity was better preserved in human than in rat hepatocytes. ► The loss of uptake activity slowed down in sandwich culture of rat hepatocytes. ► Active/passive TC uptake ratio rapidly decreased in rat, but not in human cells. ► Reduced active TC uptake resulted in a decrease of inhibitory potential of drugs. ► A reliable uptake interaction study must perform with rat cells not older than 24h. 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 72h), and the shift of saturable/unsaturable transport (from 92/8 to 55/45 in a 24–72h time interval), the efficacy of taurocholate uptake inhibition was highly reduced (IC50 cyclosporin A 3.9 to >100μM, and bosentan 9.1–49.8μM at 1 and 72h, 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 ∼10μM and bosentan 28.9–45.5μM at 1h and 5days, 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 24h after seeding will highly underestimate the probability of drug interaction.