pitavastatin and fexofenadine

The use of in vitro data for quantitative predictions of transporter-mediated elimination in vivo requires an accurate estimation of the transporter Michaelis-Menten parameters, V(max) and K(m), as a first step. Therefore, the experimental conditions of in vitro studies used to assess hepatic uptake transport were optimized regarding active transport processes, nonspecific binding, and passive diffusion (P(dif)). A mechanistic model was developed to analyze and accurately describe these active and passive processes. This two-compartmental model was parameterized to account for nonspecific binding, bidirectional passive diffusion, and active uptake processes based on the physiology of the cells. The model was used to estimate kinetic parameters of in vitro transport data from organic anion-transporting peptide model substrates (e.g., cholecystokinin octapeptide deltorphin II, fexofenadine, and pitavastatin). Data analysis by this mechanistic model significantly improved the accuracy and precision in all derived parameters [mean coefficient of variations (CVs) for V(max) and K(m) were 19 and 23%, respectively] compared with the conventional kinetic method of transport data analysis (mean CVs were 58 and 115%, respectively, using this method). Furthermore, permeability was found to be highly temperature-dependent in Chinese hamster ovary (CHO) control cells and artificial membranes (parallel artificial membrane permeability assay). Whereas for some compounds (taurocholate, estrone-3-sulfate, and propranolol) the effect was moderate (1.5-6-fold higher permeability at 37 degrees C compared with that at 4 degrees C), for fexofenadine a 16-fold higher passive permeability was seen at 37 degrees C. Therefore, P(dif) was better predicted if it was evaluated under the same experimental conditions as V(max) and K(m), i.e., in a single incubation of CHO overexpressed cells or rat hepatocytes at 37 degrees C, instead of a parallel control evaluation at 4 degrees C.

Topics: Algorithms; Animals; Biological Transport, Active; CHO Cells; Computer Simulation; Cricetinae; Cricetulus; Diffusion; Estrone; Fatty Acids, Monounsaturated; Fluvastatin; Hepatocytes; Indoles; Kinetics; Male; Membranes, Artificial; Models, Biological; Naphthalenes; Oligopeptides; Organic Anion Transporters; Permeability; Pharmaceutical Preparations; Pharmacokinetics; Piperidines; Quinolines; Rats; Rats, Wistar; Sincalide; Temperature; Terfenadine

Fexofenadine (FEX) is mainly eliminated from the liver into bile in unchanged form. We demonstrated previously that organic anion transporting polypeptide (OATP) 1B1 and OATP1B3 are involved in the hepatic uptake of FEX. However, little is known about the mechanisms controlling the hepatic efflux of FEX from the liver to bile and blood. In the present study, the involvement of hepatic efflux transporters in the pharmacokinetics of FEX was investigated in both in vitro and in vivo studies. Vectorial transport of FEX was observed in OATP1B3/human bile salt export pump (hBSEP) double transfectants but not in OATP1B3/human breast cancer resistance protein double transfectants, which indicates the possible contribution of hBSEP to the biliary excretion of FEX in humans. In multidrug resistance-associated protein 2 (Mrp2)(-/-) mice, the biliary excretion clearance based on the plasma concentration and the liver-to-plasma concentration ratio significantly decreased, whereas the biliary excretion clearance based on the liver concentration decreased only with 20%, suggesting the minimum contribution of Mrp2 to its biliary excretion. ATP-dependent transport of FEX was observed in hMRP3-enriched membrane vesicles but not hMRP4. In Mrp3(-/-) mice, the biliary excretion clearance based on both the plasma and liver concentration and the liver-to-plasma concentration ratio increased, suggesting the significant contribution of Mrp3 to its sinusoidal efflux and the up-regulation of its biliary excretion in Mrp3(-/-) mice. On the other hand, pharmacokinetics of FEX remained unchanged in Mrp4(-/-) mice. This information provides a novel insight into the transporters important for FEX disposition.

Topics: Adenosine Triphosphate; Animals; ATP Binding Cassette Transporter, Subfamily B, Member 11; ATP-Binding Cassette Transporters; Bile Acids and Salts; Biological Transport; Cell Line; Dogs; Gene Expression Regulation; Glutathione; Humans; Liver; Male; Membrane Transport Proteins; Mice; Mice, Inbred C57BL; Multidrug Resistance-Associated Protein 2; Multidrug Resistance-Associated Proteins; Quinolines; Recombinant Proteins; Terfenadine