The Effects of Pregnenolone 16α-Carbonitrile Dosing on Digoxin Pharmacokinetics and Intestinal Absorption in the Rat

The effect of Pgp induction in rats by pregnenolone 16α-carbonitrile (PCN) (3 days, 35 mg/kg/d, p.o.) on digoxin pharmacokinetics and intestinal transport has been assessed. After intravenous or oral digoxin dosing the arterial and hepatic portal vein (oral) AUC(0-24h) were significantly reduced by PCN pre-treatment. Biliary digoxin clearance increased 2-fold following PCN treatment. PCN significantly increased net digoxin secretion (2.05- and 4.5-fold respectively) in ileum and colon but not in duodenum or jejunum. This increased secretion correlated with increased Pgp protein expression in ileum and colon. Both intestinal and biliary excretion therefore contribute to altered digoxin disposition following PCN

Digoxin net secretory transport in bronchial epithelial cell layers is not exclusively mediated by P-glycoprotein/MDR1

Copyright © 2013 The Authors. Published by Elsevier B.V. All rights reserved. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-No Derivative Works License, which permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are creditedThe impact of P-glycoprotein (MDR1, ABCB1) on drug disposition in the lungs as well as its presence and activity in in vitro respiratory drug absorption models remain controversial to date. Hence, we characterised MDR1 expression and the bidirectional transport of the common MDR1 probe 3H-digoxin in air-liquid interfaced (ALI) layers of normal human bronchial epithelial (NHBE) cells and of the Calu-3 bronchial epithelial cell line at different passage numbers. Madin-Darby Canine Kidney (MDCKII) cells transfected with the human MDR1 were used as positive controls. 3H-digoxin efflux ratio (ER) was low and highly variable in NHBE layers. In contrast, ER=11.4 or 3.0 was measured in Calu-3 layers at a low or high passage number, respectively. These were, however, in contradiction with increased MDR1 protein levels observed upon passaging. Furthermore, ATP depletion and the two MDR1 inhibitory antibodies MRK16 and UIC2 had no or only a marginal impact on 3H-digoxin net secretory transport in the cell line. Our data do not support an exclusive role of MDR1 in 3H-digoxin apparent efflux in ALI Calu-3 layers and suggest the participation of an ATP-independent carrier. Identification of this transporter might provide a better understanding of drug distribution in the lungs.Peer reviewe

Resolving the Distribution–Metabolism Interplay of Eight OATP Substrates in the Standard Clearance Assay with Suspended Human Cryopreserved Hepatocytes

Uptake transporters may act to elevate the intrahepatic exposure of drugs, impacting the route and rate of elimination, as well as the drug–drug interaction potential. We have here extended the assessment of metabolic drug stability in a standard human hepatocyte incubation to allow for elucidation of the distribution–metabolism interplay established for substrates of drug transporters. Cellular concentration–time profiles were obtained from incubations of eight known OATP substrates at 1 μM, each for two different 10-donor batches of suspended cryopreserved human hepatocytes. The kinetic data sets were analyzed using a mechanistic mathematical model that allowed for separate estimation of active uptake, bidirectional diffusion, metabolism and nonspecific extracellular and intracellular binding. The range of intrinsic clearances attributed to active uptake, diffusion and metabolism of the test set spanned more than 2 orders of magnitude each, with median values of 18, 5.3, and 0.5 μL/min/10⁶ cells, respectively. This is to be compared with the values for the apparent clearance from the incubations, which only spanned 1 order of magnitude with a median of 2.6 μL/min/10⁶ cells. The parameter estimates of the two pooled 10-donor hepatocyte batches investigated displayed only small differences in contrast to the variability associated with use of cells from individual donors reported in the literature. The active contribution to the total cellular uptake ranged from 55% (glyburide) to 96% (rosuvastatin), with an unbound intra-to-extracellular concentration ratio at steady state of 2.1 and 17, respectively. Principal component analysis showed that the parameter estimates of the investigated compounds were largely influenced by lipophilicity. Active cellular uptake in hepatocytes was furthermore correlated to pure OATP1B1-mediated uptake as measured in a transfected cell system. The presented approach enables the assessment of the key pathways regulating hepatic disposition of transporter and enzyme substrates from one single, reproducible and generally accessible human <i>in vitro</i> system

In Vitro Intrinsic Permeability: A Transporter-Independent Measure of Caco‑2 Cell Permeability in Drug Design and Development

In vitro permeability data have a central place in absorption risk assessments in drug discovery and development. For compounds where active efflux impacts permeability in vitro, the inherent passive membrane permeability (“intrinsic permeability”) gives a concentration-independent measure of the compound’s permeability. This work describes the validation of an in vitro intrinsic permeability assay and application of the data in a predictive in silico model. Apparent intrinsic permeability (P_app) across Caco-2 cell monolayers is determined in the presence of an optimized cocktail of chemical inhibitors toward the three major efflux transporters ABCB1, ABCC2, and ABCG2. The intrinsic P_app value gives an estimate of passive permeability, which is independent of transporter expression levels and not limited by solubility or cell toxicity. An in silico model has been established to predict the Caco-2 intrinsic permeability and shown to consistently identify highly permeable compounds. The new intrinsic permeability assay is useful for early absorption estimates and suitable for absorption risk assessment in DMPK and pharmaceutical development

Utility of in vitro systems and preclinical data for the prediction of human intestinal first-pass metabolism during drug discovery and preclinical development

A growing awareness of the risks associated with extensive intestinal metabolism has triggered an interest in developing robust methods for its quantitative assessment. This study explored the utility of intestinal S9 fractions, human liver microsomes, and recombinant cytochromes P450 to quantify CYP3A-mediated intestinal extraction in humans for a selection of marketed drugs that are predominantly metabolized by CYP3A4. A simple competing rates model is used to estimate the fraction of drug escaping gut wall metabolism (f g ) from in vitro intrinsic clearance in humans. The f g values extrapolated from the three in vitro systems used in this study, together with literature-derived f g from human intestinal microsomes, were validated against f g extracted from human in vivo pharmacokinetic (PK) profiles using a generic whole-body physiologically-based pharmacokinetic (PBPK) model. The utility of the rat as a model for human CYP3A-mediated intestinal meta bolism was also evaluated. Human f g from PBPK compares well with that from the grapefruit juice method, justifying its use for the evaluation of human in vitro systems. Predictive performance of all human in vitro systems was comparable [root mean square error (RMSE) = 0.22-0.27; n = 10]. Rat f g derived from in vivo PK profiles using PBPK has the lowest RMSE (0.19; n = 11) for the prediction of human f g for the selected compounds, most of which have a fraction absorbed close to 1. On the basis of these evaluations, the combined use of f g from human in vitro systems and rats is recommended for the estimation of CYP3A4-mediated intestinal metabolism in lead optimization and preclinical development phases

Expression and functionality of P-glycoprotein in human bronchial epithelial cells in vitro

P-glycoprotein (P-gp) is expressed in normal tissues with barrier functions where it participates in cell defence mechanisms (Huls, M. et al. J Pharm Exp Ther 2009; 328:3-9). Its presence in the bronchial epithelium and role in the lung protection against inhaled toxicants has yet to be elucidated. The human bronchial epithelial cell line Calu-3 and normal human bronchial epithelial (NHBE) cells were cultured at an air-liquid interface on Transwell® inserts for 21 days. P-gp expression was evaluated by quantitative polymerase chain reaction and its functionality was assessed by permeability measurements using the established substrate 3H-digoxin either alone or in the presence of chemical or biomolecular inhibitors. P-gp was absent in NHBE cells and moderately expressed in Calu-3 cells. Net secretory transport of 3H-digoxin was observed in both models. This was reduced at 4°C and in the presence of the selective but non specific P-gp inhibitor PSC833 and the multidrug resistance protein (MRP) inhibitor MK571. The P-gp specific antibody inhibitor UIC2 and the metabolic inhibitors sodium azide and sodium dichloroacetate had no effect on 3H-digoxin transport in Calu-3 cells. The presence of active transport mechanisms in cultures of human bronchial epithelial cells was demonstrated, although they differed between the models tested. P-gp was not detected in NHBE cells, in line with observed low gene expression in human lung tissue (Bleasby, K. et al. Xenobiotica 2006; 36:963-988). The involvement of P-gp could not be confirmed and the transporter(s) responsible for 3H-digoxin asymmetric broncho-epithelial permeability remain(s) to be identified.Peer reviewe