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.
Mol Pharmacol. 2014 Feb;85(2):249-60. doi: 10.1124/mol.113.089763. Epub 2013 Nov 19.
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.
二甲双胍是目前治疗 2 型糖尿病最常用的药物。从机制上讲，二甲双胍与许多蛋白激酶和转录因子相互作用，改变了许多下游靶基因的表达，这些靶基因控制着脂质代谢、细胞增殖和药物代谢。组成型雄烷受体（CAR，NR1i3），一种已知的外源性传感器，最近被认为是一种新型信号分子，因为其激活除了传统的配体结合外，还可以被蛋白激酶调节。我们表明，二甲双胍可以通过调节 CAR 的磷酸化状态来抑制药物诱导的 CYP2B6（CAR 的典型靶基因）的表达。在人原代肝细胞中，二甲双胍可显著抑制间接（苯巴比妥）和直接 CITCO [6-（4-氯苯基）咪唑[2,1-b]1,3 噻唑-5-甲酰基-O-（3,4-二氯苄基）肟]激活物诱导的 CYP2B6 的表达。机制研究表明，二甲双胍特异性增强了 CAR 第 38 位苏氨酸的磷酸化，从而阻止了 CAR 的核转位和激活。此外，我们表明，二甲双胍对 CAR 的磷酸化主要是 AMP 激活蛋白激酶和细胞外信号调节激酶 1/2 依赖性事件。另外的双杂交和免疫共沉淀实验表明，二甲双胍还可以破坏 CITCO 介导的 CAR 与甾体受体辅激活因子 1 或糖皮质激素受体相互作用蛋白 1 之间的相互作用。我们的结果表明，二甲双胍通过特异性抑制人 CAR 的激活，是一种有效的药物诱导 CYP2B6 表达抑制剂。因此，二甲双胍可能会影响 CYP2B6 底物药物的代谢和清除。
