title: Metformin represses drug-induced expression of CYP2B6 by modulating the constitutive androstane receptor signaling.
abstract: Metformin is currently the most widely used drug for the treatment of type 2 diabetes. Mechanistically, metformin interacts with many protein kinases and transcription factors that alter the expression of numerous downstream target genes governing lipid metabolism, cell proliferation, and drug metabolism. The constitutive androstane receptor (CAR, NR1i3), a known xenobiotic sensor, has recently been recognized as a novel signaling molecule, in that its activation could be regulated by protein kinases in addition to the traditional ligand binding. We show that metformin could suppress drug-induced expression of CYP2B6 (a typical target gene of CAR) by modulating the phosphorylation status of CAR. In human hepatocytes, metformin robustly suppressed the expression of CYP2B6 induced by both indirect (phenobarbital) and direct CITCO [6-(4-chlorophenyl)imidazo[2,1-b]1,3thiazole-5-carbaldehyde O-(3,4-dichlorobenzyl)oxime] activators of human CAR. Mechanistic investigation revealed that metformin specifically enhanced the phosphorylation of threonine-38 of CAR, which blocks CAR nuclear translocation and activation. Moreover, we showed that phosphorylation of CAR by metformin was primarily an AMP-activated protein kinase- and extracellular signal-regulated kinase 1/2-dependent event. Additional two-hybrid and coimmunoprecipitation assays demonstrated that metformin could also disrupt CITCO-mediated interaction between CAR and the steroid receptor coactivator 1 or the glucocorticoid receptor-interacting protein 1. Our results suggest that metformin is a potent repressor of drug-induced CYP2B6 expression through specific inhibition of human CAR activation. Thus, metformin may affect the metabolism and clearance of drugs that are CYP2B6 substrates.
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, Maryland (H.Y., B.G., P.S., H.W.); and Bioreclamation In Vitro Technologies (S.H., T.M.), Baltimore, Maryland.
authors.forename: Hui
authors.initials: H
authors.lastname: Yang
authors.forename: Brandy
authors.initials: B
authors.lastname: Garzel
authors.forename: Scott
authors.initials: S
authors.lastname: Heyward
authors.forename: Timothy
authors.initials: T
authors.lastname: Moeller
authors.forename: Paul
authors.initials: P
authors.lastname: Shapiro
authors.forename: Hongbing
authors.initials: H
authors.lastname: Wang
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000502:physiology; D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics*; D000090702:Constitutive Androstane Receptor; D065702:Cytochrome P-450 CYP2B6; D004305:Dose-Response Relationship, Drug; D066246:ErbB Receptors / Q000502:physiology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000502:physiology; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D008687:Metformin / Q000494:pharmacology*; D010091:Oximes / Q000494:pharmacology; D010634:Phenobarbital / Q000494:pharmacology; D010766:Phosphorylation; D018160:Receptors, Cytoplasmic and Nuclear / Q000187:drug effects* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013844:Thiazoles / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases / Q000502:physiology
chemical_list: D000090702:Constitutive Androstane Receptor; D007004:Hypoglycemic Agents; C000716327:NR1I3 protein, human; D010091:Oximes; D018160:Receptors, Cytoplasmic and Nuclear; D013844:Thiazoles; D008687:Metformin; C475093:6-(4-chlorophenyl)imidazo(2,1-b)(1,3)thiazole-5-carbaldehyde O-(3,4-dichlorobenzyl)oxime; D001189:Aryl Hydrocarbon Hydroxylases; C585599:CYP2B6 protein, human; D065702:Cytochrome P-450 CYP2B6; D066246:ErbB Receptors; D048049:Extracellular Signal-Regulated MAP Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D055372:AMP-Activated Protein Kinases; D010634:Phenobarbital