Abstract

Recognition of the role of hepatic drug transporters in elimination of xenobiotics continues to grow. Hepatic uptake transporters, such as hepatic isoforms of the organic anion-transporting polypeptide (Oatp) family as well as the bile acid transporter Na⁺-taurocholate cotransporting polypeptide (Ntcp) have been studied extensively both at the mRNA and protein expression levels in adults. However, in pediatric/juvenile populations, there continues to be a knowledge gap about the functional activity of these transporters. Therefore, the aim of this study was to examine the functional maturation of Ntcp and Oatp isoforms as major hepatic transporters. Hepatocytes were freshly isolated from rats aged between birth and 8 weeks. Transporter activities were assessed by measuring the initial uptake rates of known substrates: taurocholate (TCA) for Ntcp and sodium fluorescein (NaFluo) for Oatp. Relative to adult values, uptake clearance of TCA in hepatocytes from rats aged 0, 1, 2, 3, and 4 weeks reached 19, 43, 22, 46, and 63%, respectively. In contrast, Oatp-mediated NaFluo uptake showed a considerably slower developmental pattern: uptake clearance of NaFluo in hepatocytes from rats aged 0, 1, 2, 3, 4, and 6 weeks were 24, 20, 19, 8, 19, and 64%, respectively. Maturation of NaFluo uptake activity correlated with the previously reported ontogeny of Oatp1b2 mRNA expression, confirming the role of Oatp1b2 for NaFluo uptake in rat liver. The outcome of this project will help in understanding and predicting age-dependent drug exposure in juvenile animals and will eventually support safe and more effective drug therapies for children.