title: Metformin suppresses pregnane X receptor (PXR)-regulated transactivation of CYP3A4 gene.
abstract: Metformin is widely used in the treatment of type-2 diabetes. The pleotropic effects of metformin on glucose and lipid metabolism have been proposed to be mediated by the activation of AMP-activated protein kinase (AMPK) and the subsequent up-regulation of small heterodimer partner (SHP). SHP suppresses the functions of several nuclear receptors involved in the regulation of hepatic metabolism, including pregnane X receptor (PXR), which is referred to as a "master regulator" of drug/xenobiotic metabolism. In this study, we hypothesize that metformin suppresses the expression of CYP3A4, a main detoxification enzyme and a target gene of PXR, due to SHP up-regulation. We employed various gene reporter assays in cell lines and qRT-PCR in human hepatocytes and in Pxr(-/-) mice. We show that metformin dramatically suppresses PXR-mediated expression of CYP3A4 in hepatocytes. Consistently, metformin significantly suppressed the up-regulation of Cyp3a11 mRNA in the liver and intestine of wild-type mice, but not in Pxr(-/-) mice. A mechanistic investigation of the phenomenon showed that metformin does not significantly up-regulate SHP in human hepatocytes. We further demonstrate that AMPK activation is not involved in this process. We show that metformin disrupts PXR's interaction with steroid receptor coactivator-1 (SRC1) in a two-hybrid assay independently of the PXR ligand binding pocket. Metformin also inhibited vitamin D receptor-, glucocorticoid receptor- and constitutive androstane receptor (CAR)-mediated induction of CYP3A4 mRNA in human hepatocytes. We show, therefore, a suppressive effect of metformin on PXR and other ligand-activated nuclear receptors in transactivation of the main detoxification enzyme CYP3A4 in human hepatocytes.
authors.affiliation: Department of Pharmacology and Toxicology, Faculty of Pharmacy in Hradec Kralove, Charles University in Prague, Heyrovskeho 1203, Hradec Kralove, CZ-500 05, Czech Republic.
authors.forename: Lucie
authors.initials: L
authors.lastname: Krausova
authors.forename: Lucie
authors.initials: L
authors.lastname: Stejskalova
authors.forename: Hongwei
authors.initials: H
authors.lastname: Wang
authors.forename: Radim
authors.initials: R
authors.lastname: Vrzal
authors.forename: Zdenek
authors.initials: Z
authors.lastname: Dvorak
authors.forename: Sridhar
authors.initials: S
authors.lastname: Mani
authors.forename: Petr
authors.initials: P
authors.lastname: Pavek
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000502:physiology; D000818:Animals; D002478:Cells, Cultured; D000090702:Constitutive Androstane Receptor; D051544:Cytochrome P-450 CYP3A / Q000235:genetics* / Q000378:metabolism; D017930:Genes, Reporter; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D008687:Metformin / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D056918:Nuclear Receptor Coactivators / Q000378:metabolism; D000077297:Pregnane X Receptor; D012333:RNA, Messenger / Q000378:metabolism; D018167:Receptors, Calcitriol / Q000502:physiology; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism / Q000502:physiology; D011965:Receptors, Glucocorticoid / Q000502:physiology; D011987:Receptors, Steroid / Q000235:genetics / Q000502:physiology*; D057897:Reflex, Righting / Q000187:drug effects; D015398:Signal Transduction; D015533:Transcriptional Activation
chemical_list: D000090702:Constitutive Androstane Receptor; D007004:Hypoglycemic Agents; D008565:Membrane Proteins; D056918:Nuclear Receptor Coactivators; D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D018167:Receptors, Calcitriol; D018160:Receptors, Cytoplasmic and Nuclear; D011965:Receptors, Glucocorticoid; D011987:Receptors, Steroid; C099713:nuclear receptor subfamily 0, group B, member 2; D008687:Metformin; C496508:Cyp3a11 protein, mouse; D051544:Cytochrome P-450 CYP3A; D055372:AMP-Activated Protein Kinases