sincalide 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 hydrochloride (FEX), a second generation H(1)-receptor antagonist, is mainly eliminated from the liver into bile in unchanged form. Recent studies have shown that FEX can be accepted by human MDR1 (P-glycoprotein), OATP1A2 [organic anion-transporting polypeptide (OATP)-A, and OATP2B1 (OATP-B)] expression systems. However, other transporters responsible for the hepatic uptake of FEX have not yet been identified. In the present study, we evaluated the contribution of OATP family transporters, namely OATP1B1 (OATP2/OATP-C), OATP1B3 (OATP8), and OATP2B1 (OATP-B), to FEX uptake using transporter-expressing HEK293 (human embryonic kidney) cells. The uptake of FEX in OATP1B3-expressing cells was significantly greater than that in vector-transfected cells. On the other hand, OATP1B1- or OATP2B1-mediated uptake of FEX was not statistically significant. OATP1B3-mediated transport could be explained by a one-saturable component with a Michaelis constant (K(m)) of 108 +/- 11 microM. The inhibitory effect of FEX on the uptake of estrone-3-sulfate (E(1)S), cholecystokinin octapeptide (CCK-8), and 17beta-estradiol-17beta-d-glucuronide (E(2)17betaG) was also examined. Both OATP1B1- and OATP1B3-mediated E(2)17betaG uptake was inhibited by FEX. The K(i) values were 148 +/- 61 and 205 +/- 72 microM for OATP1B1 and OATP1B3, respectively. FEX also inhibited OATP1B3-mediated CCK-8 uptake and OATP1B1-mediated E(1)S uptake with a K(i) value of 83.3 +/- 15.3 and 257 +/- 84 microM, respectively, suggesting that FEX could not be used as a specific inhibitor for OATP1B1 and OATP1B3, although FEX was preferentially accepted by OATP1B3. In conclusion, this is, to our knowledge, the first demonstration that OATP1B3 is thought to be a major transporter involved in hepatic uptake of FEX in humans.

Topics: Cell Line; Estradiol; Estrone; Histamine H1 Antagonists; Humans; Liver; Liver-Specific Organic Anion Transporter 1; Organic Anion Transport Protein 1; Sincalide; Terfenadine