Abstract
The expression of three cytochromes P450 (CYP3A4, CYP2C9, and CYP2B6) was investigated in primary human hepatocyte cultures following treatment with four calcium channel modulators (CCM) of the dihydropyridine family, three antagonists (nifedipine, nicardipine, and isradipine), and one agonist (BK8644). Induction of CYP3A4 was studied by Northern blot, Western blot, and enzymatic activity. Induction began between 1 and 10 microM CCM and was dependent on the presence of dexamethasone (100 nM) in the medium. CYP3A4 mRNA accumulation started only after 16 h of treatment because pregnane X receptor (hPXR) synthesis was needed. Cotransfection experiments showed that the proximal and the distal PXR response elements of the CYP3A4 promoter and hPXR (HepG2 cells) or dexamethasone-induced hPXR (primary hepatocytes) were necessary to obtain full induction. Furthermore, glutathione S-transferase pull-down assays demonstrated that the CCM tested can act as hPXR ligands. In addition, cotransfection experiments in CV1 cells showed that these compounds failed to reverse CAR (constitutively activated receptor) inactivation by androstenol. Finally, 10 microM CCM induced both CYP2C9 and CYP2B6, strengthening the evidence that hPXR is involved in the regulation of these genes. All together, these results widen the field of hPXR activators to a new class of ligand, namely the CCM of the dihydropyridine family.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Aryl Hydrocarbon Hydroxylases*
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Calcium Channels / drug effects
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Calcium Channels / metabolism*
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Cytochrome P-450 CYP2B6
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Cytochrome P-450 CYP2C9
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Cytochrome P-450 CYP3A
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Cytochrome P-450 Enzyme System / biosynthesis*
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Cytochrome P-450 Enzyme System / genetics
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Dihydropyridines / pharmacology*
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Dose-Response Relationship, Drug
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Enzyme Induction / drug effects
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Enzyme Inhibitors / pharmacology
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Hepatocytes / drug effects*
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Hepatocytes / enzymology
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Humans
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Kinetics
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Mixed Function Oxygenases / biosynthesis
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Mixed Function Oxygenases / genetics
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Nifedipine / pharmacology
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Oxidoreductases, N-Demethylating / biosynthesis
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Pregnane X Receptor
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Promoter Regions, Genetic / drug effects
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Promoter Regions, Genetic / physiology
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RNA, Messenger / biosynthesis
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RNA, Messenger / drug effects
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Receptors, Cytoplasmic and Nuclear / metabolism*
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Receptors, Steroid / metabolism*
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Rifampin / pharmacology
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Steroid 16-alpha-Hydroxylase*
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Steroid Hydroxylases / biosynthesis
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Time Factors
Substances
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Calcium Channels
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Dihydropyridines
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Enzyme Inhibitors
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Pregnane X Receptor
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RNA, Messenger
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Receptors, Cytoplasmic and Nuclear
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Receptors, Steroid
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Cytochrome P-450 Enzyme System
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Mixed Function Oxygenases
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Steroid Hydroxylases
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CYP2C9 protein, human
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Cytochrome P-450 CYP2C9
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Aryl Hydrocarbon Hydroxylases
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CYP2B6 protein, human
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CYP3A protein, human
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Cytochrome P-450 CYP2B6
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Cytochrome P-450 CYP3A
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Steroid 16-alpha-Hydroxylase
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CYP3A4 protein, human
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Oxidoreductases, N-Demethylating
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Nifedipine
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Rifampin