Metformin suppresses pregnane X receptor (PXR)-regulated transactivation of CYP3A4 gene |
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Authors: | Krausova Lucie Stejskalova Lucie Wang Hongwei Vrzal Radim Dvorak Zdenek Mani Sridhar Pavek Petr |
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Institution: | aDepartment of Pharmacology and Toxicology, Faculty of Pharmacy in Hradec Kralove, Charles University in Prague, Heyrovskeho 1203, Hradec Kralove, CZ-500 05, Czech Republic;bAlbert Einstein Cancer Center, Albert Einstein College of Medicine, 1300 Morris Park Ave, Chanin 302D-1 Bronx, NY 1046, United States;cDepartment of Cell Biology and Genetics, Faculty of Science, Palacky University in Olomouc, Slechtitelu 11, Olomouc, CZ-783 71, Czech Republic |
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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. |
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Keywords: | Metformin Cytochrome P450 Induction PXR AMPK |
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