title: Endosulfan induces CYP2B6 and CYP3A4 by activating the pregnane X receptor.
abstract: Endosulfan is an organochlorine pesticide commonly used in agriculture. Endosulfan has affects on vertebrate xenobiotic metabolism pathways that may be mediated, in part, by its ability to activate the pregnane X receptor (PXR) and/or the constitutive androstane receptor (CAR) which can elevate expression of cytochrome P450 (CYP) enzymes. This study examined the dose-dependency and receptor specificity of CYP induction in vitro and in vivo. The HepG2 cell line was transiently transfected with CYP2B6- and CYP3A4-luciferase promoter reporter plasmids along with human PXR (hPXR) or hCAR expression vectors. In the presence of hPXR, endosulfan-alpha exposure caused significant induction of CYP2B6 (16-fold) and CYP3A4 (11-fold) promoter activities over control at 10 microM. The metabolite endosulfan sulfate also induced CYP2B6 (12-fold) and CYP3A4 (6-fold) promoter activities over control at 10 microM. In the presence of hCAR-3, endosulfan-alpha induced CYP2B6 (2-fold) promoter activity at 10 microM, but not at lower concentrations. These data indicate that endosulfan-alpha significantly activates hPXR strongly and hCAR weakly. Using western blot analysis of human hepatocytes, the lowest concentrations at which CYP2B6 and CYP3A4 protein levels were found to be significantly elevated by endosulfan-alpha were 1.0 microM and 10 microM, respectively. In mPXR-null/hPXR-transgenic mice, endosulfan-alpha exposure (2.5mg/kg/day) caused a significant reduction of tribromoethanol-induced sleep times by approximately 50%, whereas no significant change in sleep times was observed in PXR-null mice. These data support the role of endosulfan-alpha as a strong activator of PXR and inducer of CYP2B6 and CYP3A4, which may impact metabolism of CYP2B6 or CYP3A4 substrates.
authors.affiliation: Department of Environmental and Molecular Toxicology, Box 7633, North Carolina State University, Raleigh, NC 27695, USA.
authors.forename: Richard C T
authors.initials: RC
authors.lastname: Casabar
authors.forename: Parikshit C
authors.initials: PC
authors.lastname: Das
authors.forename: Gregory K
authors.initials: GK
authors.lastname: Dekrey
authors.forename: Catherine S
authors.initials: CS
authors.lastname: Gardiner
authors.forename: Yan
authors.initials: Y
authors.lastname: Cao
authors.forename: Randy L
authors.initials: RL
authors.lastname: Rose
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Wallace
mesh_terms: D000777:Anesthetics / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001189:Aryl Hydrocarbon Hydroxylases / Q000096:biosynthesis* / Q000235:genetics; D000090702:Constitutive Androstane Receptor; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A / Q000096:biosynthesis* / Q000235:genetics; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D004726:Endosulfan / Q000633:toxicity*; D004790:Enzyme Induction; D000431:Ethanol / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D017930:Genes, Reporter; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000187:drug effects* / Q000201:enzymology; D006801:Humans; D007306:Insecticides / Q000633:toxicity*; D008156:Luciferases / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D010089:Oxidoreductases, N-Demethylating / Q000096:biosynthesis* / Q000235:genetics; D000077297:Pregnane X Receptor; D011401:Promoter Regions, Genetic / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000819:agonists / Q000235:genetics / Q000378:metabolism; D011987:Receptors, Steroid / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D012890:Sleep / Q000187:drug effects; D013997:Time Factors; D014162:Transfection; D008565:Membrane Proteins
chemical_list: D000777:Anesthetics; D001189:Aryl Hydrocarbon Hydroxylases; D000090702:Constitutive Androstane Receptor; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System; D004726:Endosulfan; D000431:Ethanol; D007306:Insecticides; D008156:Luciferases; D010089:Oxidoreductases, N-Demethylating; D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; C062527:tribromoethanol; C585599:CYP2B6 protein, human; C510163:CYP3A4 protein, human; C496508:Cyp3a11 protein, mouse; D008565:Membrane Proteins