title: Role of CYP3A4 in the regulation of the aryl hydrocarbon receptor by omeprazole sulphide.
abstract: Cross-talk between nuclear receptors involved in the control of drug metabolism is being increasingly recognised as a source of drug side effects. Omeprazole is a well known activator of the aryl hydrocarbon receptor (AhR). We investigated the regulation of AhR by omeprazole-sulphide, a degradation metabolite of omeprazole, using CYP1A mRNA induction, reporter gene assay, receptor DNA binding, ligand binding, nuclear translocation, trypsin digests, and drug metabolism analysis in mouse Hepa-1c1c7, human HepG2 cells and primary human hepatocytes. Omeprazole-sulphide is a pure antagonist of AhR in Hepa-1c1c7 and HepG2 hepatoma cell lines. In Hepa-1c1c7 cells, omeprazole-sulphide is a ligand of AhR, inhibits AhR activation to a DNA-binding form, induces a specific pattern of AhR trypsin digestion and inhibits AhR nuclear translocation and subsequent degradation in response to 2,3,7,8-tetrachlorodibenzo-p-dioxin. However, in highly differentiated primary human hepatocytes treated with rifampicin an agonist of the pregnane X receptor (PXR), omeprazole-sulphide behaves as an agonist of AhR. Inhibition of drug metabolizing enzymes by ketoconazole restores the antagonist effect of omeprazole-sulphide. Metabolic LC/MS analysis reveals that omeprazole-sulphide (AhR antagonist) is efficiently converted to omeprazole (AhR activator) by cytochrome P450 CYP3A4, a target gene of PXR, in primary human hepatocytes but not in hepatoma cells in which PXR is not expressed. This report provides the first evidence for a cross-talk between PXR/CYP3A4 and AhR. In addition, it clearly shows that conclusions drawn from experiments carried out in cell lines may lead to erroneous in vivo predictions in man.
authors.affiliation: Inserm, U632, 1919 Route de Mende, Montpellier, F-34293 France.
authors.forename: Sabine
authors.initials: S
authors.lastname: Gerbal-Chaloin
authors.forename: Lydiane
authors.initials: L
authors.lastname: Pichard-Garcia
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Fabre
authors.forename: Antonio
authors.initials: A
authors.lastname: Sa-Cunha
authors.forename: Lorenz
authors.initials: L
authors.lastname: Poellinger
authors.forename: Patrick
authors.initials: P
authors.lastname: Maurel
authors.forename: Martine
authors.initials: M
authors.lastname: Daujat-Chavanieu
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000818:Animals; D006528:Carcinoma, Hepatocellular; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D017930:Genes, Reporter; D022781:Hepatocytes / Q000166:cytology / Q000378:metabolism; D006801:Humans; D008113:Liver Neoplasms; D051379:Mice; D009853:Omeprazole / Q000031:analogs & derivatives* / Q000378:metabolism; D000072317:Polychlorinated Dibenzodioxins / Q000378:metabolism; D000077297:Pregnane X Receptor; D012333:RNA, Messenger / Q000378:metabolism; D018336:Receptors, Aryl Hydrocarbon / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D011987:Receptors, Steroid / Q000378:metabolism
chemical_list: D000072317:Polychlorinated Dibenzodioxins; D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; C040449:omeprazole sulfide; D003577:Cytochrome P-450 Enzyme System; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D009853:Omeprazole