TY - JOUR T1 - Kinetic characterization of Rat Hepatic Uptake of 16 Actively Transported Drugs JF - Drug Metabolism and Disposition JO - Drug Metab Dispos DO - 10.1124/dmd.111.040477 SP - dmd.111.040477 AU - Yoshiyuki Yabe AU - Aleksandra Galetin AU - J Brian Houston Y1 - 2011/07/05 UR - http://dmd.aspetjournals.org/content/early/2011/07/05/dmd.111.040477.abstract N2 - In order to explore the determinants of hepatic uptake, 16 compounds were investigated with different physicochemical and disposition characteristics, including five statins, three sartans, saquinavir, ritonavir, erythromycin, clarithromycin, nateglinide, repaglinide, fexofenadine and bosentan. Freshly isolated rat hepatocytes in suspension were used with the oil-spin method to generate kinetic parameters. Clearances, via passive diffusion (Pdiff) and active uptake (CLactive, characterized by maximum uptake rate and Km), were estimated from the initial uptake rate data over a 0.01-100 μM concentration range. The Km values ranged 15-fold, with 10 of the 16 drugs with Km<10 μM (median 6 μM). Both CLactive and Pdiff ranged over 100-fold (median 188 and 14 µL/min/106 cells). Assessment of the relative contribution of Pdiff and CLactive indicated that at low concentrations (~0.1 μM) the active process contributes >80% to the overall uptake for 13 drugs. Although high Pdiff values were obtained for ritonavir and repaglinide, active process contributed predominantly to uptake; in contrast, high passive permeability dominates over transporter-mediated uptake for saquinavir over the full concentration range. For bosentan and erythromycin, active and passive processes were equally important. Hepatocyte-to-medium unbound concentration ratio was >10 for nine of the 16 drugs, ranging from 2-494 for bosentan and atorvastatin, respectively. Some drugs showed extensive intracellular binding (fraction unbound ranging from 0.01-0.6) which was not correlated with active uptake. LogD7.4 correlated significantly with Pdiff and the extent of intracellular binding but not with active uptake. This study provides systematic assessment of the role of active uptake relative to the passive process; implications of the findings are discussed. ER -