Research Paper
Subject Category: Pharmacokinetics, drug metabolism, toxicology
British Journal of Pharmacology (2008) 154, 246–255; doi:10.1038/bjp.2008.69; published online 10 March 2008
Rifampin and digoxin induction of MDR1 expression and function in human intestinal (T84) epithelial cells
I S Haslam1, K Jones2, T Coleman2 and N L Simmons1
- 1Epithelial Research Group, Institute for Cell and Molecular Biosciences, University of Newcastle Upon Tyne, Medical School, Newcastle Upon Tyne, UK
- 2AstraZeneca, Discovery DMPK, Cheshire, UK
Correspondence: Professor NL Simmons, Epithelial Research Group, Institute for Cell and Molecular Biosciences, University of Newcastle Upon Tyne, Medical School, Framlington Place, Newcastle Upon Tyne NE2 4HH, UK. E-mail: n.l.simmons@ncl.ac.uk
Received 25 September 2007; Revised 14 December 2007; Accepted 7 January 2008; Published online 10 March 2008.
Abstract
Background and purpose
Oral drug bioavailability is limited by intestinal expression of P-glycoprotein (MDR1, Pgp, ABCB1) whose capacity is regulated via nuclear receptors e.g. the pregnane X receptor (PXR, SXR, NR1I2). In order to study dynamic regulation of MDR1 transport capacity we have identified the T84 epithelial cell-line as a model for human intestine co-expressing MDR1 with PXR. The ability of rifampin, a known PXR agonist and digoxin, a model MDR1 substrate, to regulate MDR1 expression and transport activity has been tested, in these T84 cells.
Experimental approach
Transport was assayed by bi-directional [ 3H] -digoxin transepithelial fluxes across epithelial layers of T84 cells seeded onto permeable filter supports following pre-exposure to rifampin and digoxin. Quantitative real-time PCR, Western blotting and immunocytochemistry were used to correlate induction of MDR1 transcript and protein levels with transport activity.
Key results
Rifampin exposure (10 
M, 72 hours) increased MDR1 transcript levels (3.4 fold), MDR1 total protein levels (4.4 fold), apical MDR1 protein (2.7 fold) and functional activity of MDR1 (1.2 fold). Pre-incubation with digoxin (1 M, 72 hours) potently induced MDR1 transcript levels (92 fold), total protein (7 fold), apical MDR1 protein (4.7 fold) and functional activity (1.75 fold). Whereas PXR expression was increased by rifampin incubation (2 fold), digoxin reduced PXR expression (0.3 fold).
Conclusions and implications
Chronic digoxin pre-treatment markedly upregulates MDR1 expression and secretory capacity of T84 epithelia. Digoxin-induced changes in MDR1 levels are distinct from PXR-mediated changes resulting from rifampin exposure.
Keywords:
digoxin, rifampin, T84 cells, P-glycoprotein, pregnane X receptor, constitutive androstane receptor, induction
Abbreviations:
ABC, ATP-binding cassette; CAR, constitutive androstane receptor; MDR1, multidrug resistance 1; Pgp, P-glycoprotein; PXR, pregnane X receptor
