Hepatobiliary Disposition of a Drug/Metabolite Pair: Comprehensive Pharmacokinetic Modeling in Sandwich-Cultured Rat Hepatocytes

Abstract

The hepatobiliary disposition of xenobiotics may involve passive and/or active uptake, metabolism by cytochromes P450, and excretion of the parent compound and/or metabolite(s) into bile. Although in vitro systems have been used to evaluate these individual processes discretely, mechanistic in vitro studies of the sequential processes of uptake, metabolism, and biliary or basolateral excretion are limited. The current studies used sandwichcultured (SC) rat hepatocytes combined with a comprehensive pharmacokinetic modeling approach to investigate the hepatobiliary disposition of terfenadine and fexofenadine, a model drug/ metabolite pair. The metabolism of terfenadine and the biliary excretion of terfenadine and fexofenadine were determined in control and dexamethasone-treated SC rat hepatocytes. Dexamethasone (DEX) treatment increased the formation rates of the terfenadine metabolites azacyclonol and fexofenadine ϳ20-and 2-fold, respectively. The biliary excretion index (BEI) of fexofenadine, when generated by terfenadine metabolism, was not significantly different from the BEI of preformed fexofenadine (15 Ϯ 2% versus 19 Ϯ 2%, respectively). Pharmacokinetic modeling revealed that the rate constant for hepatocyte uptake was faster for terfenadine compared with preformed fexofenadine (2.5 versus 0.08 h Ϫ1 , respectively), whereas the biliary excretion rate constant for preformed fexofenadine exceeded that of terfenadine (0.44 versus 0.039 h Ϫ1 , respectively). Interestingly, the rate constants for basolateral excretion of terfenadine and fexofenadine were comparable (3.2 versus 1.9 h Ϫ1 , respectively) and increased only slightly with DEX treatment. These studies demonstrate the utility of the SC hepatocyte model, coupled with pharmacokinetic modeling, to evaluate the hepatobiliary disposition of generated metabolites.Biliary clearance is a predominant route of elimination for many compounds, including bile salts, organic anions, and organic cations. In recent years, the mechanisms involved in the hepatic uptake, as well as the sinusoidal and canalicular excretion, of many substances have been elucidated. After transport into the hepatocyte, many compounds undergo phase I and/or phase II metabolism before excretion into bile (by canalicular transport proteins) or sinusoidal blood (by basolateral transport proteins). Pang and coworkers have clearly established that, in some cases, the hepatic disposition of an administered preformed metabolite may be very different from a metabolite generated in the intact organ (Pang et al., 1984;Tirona and Pang, 1996). However, differences in disposition of a generated versus preformed metabolite are by no means assured and must be demonstrated on a case-by-case basis.Recent advances in molecular biology have allowed the mechanistic investigation of discrete transport or metabolic processes in isolation through administration of parent drug or metabolite to a variety of transfected, cell-based expression systems (Wrighton et al., 1995;Mizuno et al., 2003). Cummins et al....

Evaluation of Hepatic Disposition of Paroxetine Using Sandwich-Cultured Rat and Human Hepatocytes

“…Metabolic/hepatobiliary transport studies that provide the hepatic disposition of various compounds have been conducted (Lengyel et al, 2005;Turncliff et al, 2006;Lee et al, 2010;Yan et al, 2011). In this study, we evaluated the hepatic disposition of paroxetine and revealed that the species difference of hepatobiliary disposition of M1-glucuronide between rats and humans using the SCH system could be determined.…”

“…For this reason, SCH are superior to double-transfected cells, because they maintain intracellular metabolic activity. Indeed, some researchers have previously conducted metabolic/hepatobiliary transport studies that have proven to be useful to reveal the hepatic disposition of various compounds, such as bilirubin, terfenadine, troglitazone, pafuramidine, and 2,5-bis [5-(N-methoxyamidino)-2-pyridyl] furan (CPD-8068) (Lengyel et al, 2005;Turncliff et al, 2006;Lee et al, 2010;Yan et al, 2011). Moreover, the Food and Drug Administration guidance for the safety testing of drug metabolites and the ICH-M3 (R2) have had a significant impact on drug discovery and development, and further evaluation of circulating metabolite(s) is needed in both nonclinical species and humans.…”

In Vitro Evaluation of Hepatic Transporter-Mediated Clinical Drug-Drug Interactions: Hepatocyte Model Optimization and Retrospective Investigation

“…Turncliff et al (2006) evaluated the hepatobiliary disposition of metabolites of terfenadine generated in sandwich-cultured rat hepatocytes (SCRHs). The advancement of in vitro models for clearance prediction in humans has further reflected an increase in the mechanistic understanding of the hepatic vectorial elimination process (Kotani et al, 2011).…”

Data-Based Mathematical Modeling of Vectorial Transport across Double-Transfected Polarized Cells

“…2. This procedure is in accordance with similar modeling approaches (Liu and Pang, 2006;Turncliff et al, 2006). The rates of BSP uptake into cells may vary somewhat between different sets of experiments depending on the expression level of OATP1B3.…”