title: Inhibition of heme oxygenase-1 partially reverses the arsenite-mediated decrease of CYP1A1, CYP1A2, CYP3A23, and CYP3A2 catalytic activity in isolated rat hepatocytes.
abstract: Heme oxygenase (HO-1), the rate-limiting enzyme in the physiological breakdown of heme, is ubiquitous, and its expression can be increased by arsenite [As(III)], and similar other stimuli that induce cellular oxidative stress. Interestingly, it has been shown that the As(III)-induced HO-1 is inversely correlated with a decrease in cytochromes P450 (P450s) activity; however, the direct role for HO-1 in the inhibition of P450 enzymes remains unknown. Our results showed that As(III) at a concentration of 5 μM decreased the constitutive and inducible expression of CYP1A1, CYP1A2, CYP3A23, and CYP3A2 at the mRNA, protein, and catalytic activity levels. Moreover, As(III) decreased the nuclear accumulation of aryl hydrocarbon receptor (AhR) and pregnane X receptor without increasing their degradation. As(III) also increased the binding of cytosolic AhR to heat shock protein 90 and hepatitis B virus X-associated protein 2. In the presence of 2,3,7,8-tetrachlorodibenzo-p-dioxin as an inducer for CYP1A and rifampin as an inducer for CYP3A, As(III) decreased the enzymatic activity of the four P450s more than it decreased their mRNA or protein expression levels. It is noteworthy that treatment with the competitive HO-1 inhibitor, tin-mesoporphyrin, or supplementing external heme partially reversed the As(III)-mediated decrease in activities of the four P450s. In conclusion, the current study provides the first evidence that As(III) decreases CYP1A1, CYP1A2, CYP3A23, and CYP3A2 expression in freshly isolated rat primary hepatocytes. Furthermore, inhibiting the As(III)-mediated induction of HO-1 partially restores the enzymatic activity of these P450s that was initially decreased by As(III), confirming the direct role of HO-1 in the inhibition of P450s.
authors.affiliation: Faculty of Pharmacy and Pharmaceutical Sciences, 3126 Dentistry/Pharmacy Centre, University of Alberta, Edmonton, Alberta, Canada T6G 2N8.
authors.forename: Anwar
authors.initials: A
authors.lastname: Anwar-Mohamed
authors.forename: Lars-Oliver
authors.initials: LO
authors.lastname: Klotz
authors.forename: Ayman O S
authors.initials: AO
authors.lastname: El-Kadi
mesh_terms: D000818:Animals; D018053:Arsenites / Q000494:pharmacology*; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics / Q000378:metabolism; D019388:Cytochrome P-450 CYP1A2; D051544:Cytochrome P-450 CYP3A / Q000235:genetics / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D003580:Cytochromes / Q000235:genetics / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism; D006418:Heme / Q000378:metabolism; D006419:Heme Oxygenase (Decyclizing) / Q000037:antagonists & inhibitors* / Q000378:metabolism; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008665:Metalloporphyrins / Q000494:pharmacology; D000072317:Polychlorinated Dibenzodioxins / Q000031:analogs & derivatives / Q000494:pharmacology; D000077297:Pregnane X Receptor; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism; D011987:Receptors, Steroid / Q000378:metabolism; D012293:Rifampin / Q000494:pharmacology; D015534:Trans-Activators / Q000378:metabolism; D054334:Viral Regulatory and Accessory Proteins
chemical_list: D018053:Arsenites; D003580:Cytochromes; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D008665:Metalloporphyrins; D000072317:Polychlorinated Dibenzodioxins; D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; D011987:Receptors, Steroid; D015534:Trans-Activators; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein; C055421:tin mesoporphyrin; D006418:Heme; C445379:1,2,7,8-tetrachlorodibenzo-p-dioxin; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C017170:Cyp1a2 protein, rat; C465260:Cyp3a2 protein, rat; C465138:Cyp3a23-3a1 protein, rat; D019363:Cytochrome P-450 CYP1A1; D019388:Cytochrome P-450 CYP1A2; D051544:Cytochrome P-450 CYP3A; D006419:Heme Oxygenase (Decyclizing); C491523:Hmox1 protein, rat; C015001:arsenite; D012293:Rifampin