title: Metformin attenuates fluctuating glucose-induced endothelial dysfunction through enhancing GTPCH1-mediated eNOS recoupling and inhibiting NADPH oxidase.
abstract: The aim of this study was to investigate whether and how metformin ameliorated endothelial dysfunction induced by fluctuating glucose (FG) in human umbilical vein endothelial cells (HUVECs).
  
  
  
  HUVECs, which were exposed to FG to induce endothelial dysfunction, were incubated with nitric oxide synthase (NOS) inhibitor N-nitro-l-arginine-methyl ester (l-NAME), nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor apocynin, metformin and/or adenosine monophosphate-activated protein kinase (AMPK) inhibitor compound C. The oxidative stress and endothelial NOS (eNOS) coupling were evaluated.
  
  
  
  FG induced endothelial dysfunction as indicated by increased reactive oxygen species (ROS) generation and decreased nitric oxide (NO) production. Although FG increased eNOS phosphorylation, uncoupled eNOS was evidenced by downregulated guanosine 5'-triphosphate cyclohydrolase 1 (GTPCH1) and tetrahydrobiopterin (BH4) levels. FG also upregulated the level of p47-phox, a subunit of NADPH oxidase. Similar to l-NAME and apocynin, metformin ameliorated the FG-induced endothelial dysfunction by decreasing ROS generation. Furthermore, metformin recoupled eNOS through upregulating GTPCH1 and BH4 levels, and attenuated the upregulation of p47-phox in FG-treated HUVECs. Addition of compound C abolished the above effects of metformin.
  
  
  
  Metformin improves the FG-induced endothelial dysfunction in HUVECs. The protective effect of metformin may be mediated through activation of GTPCH1-mediated eNOS recoupling and inhibition of NADPH oxidase via an AMPK-dependent pathway.
authors.affiliation: Department of Endocrinology and Metabolism, Peking University Third Hospital, Beijing, China; Department of Endocrinology, Beijing Chaoyang Hospital, Capital Medical University, Beijing, China.
authors.forename: Huijie
authors.initials: H
authors.lastname: An
authors.affiliation: Department of Endocrinology and Metabolism, Peking University Third Hospital, Beijing, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Wei
authors.affiliation: Department of Endocrinology and Metabolism, Peking University Third Hospital, Beijing, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Ke
authors.affiliation: Department of Endocrinology and Metabolism, Peking University Third Hospital, Beijing, China.
authors.forename: Jin
authors.initials: J
authors.lastname: Yang
authors.affiliation: Department of Endocrinology and Metabolism, Peking University Third Hospital, Beijing, China.
authors.forename: Ye
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Key Laboratory of Molecular Cardiovascular Science of Ministry of Education, Peking University Health Science Center, Beijing, China.
authors.forename: Xian
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Endocrinology and Metabolism, Peking University Third Hospital, Beijing, China; Department of Endocrinology, Beijing Chaoyang Hospital, Capital Medical University, Beijing, China. Electronic address: drwg6688@126.com.
authors.forename: Guang
authors.initials: G
authors.lastname: Wang
authors.affiliation: Department of Endocrinology and Metabolism, Peking University Third Hospital, Beijing, China. Electronic address: tpho66@bjmu.edu.cn.
authors.forename: Tianpei
authors.initials: T
authors.lastname: Hong
mesh_terms: D006136:GTP Cyclohydrolase / Q000378:metabolism*; D005947:Glucose / Q000009:adverse effects*; D061307:Human Umbilical Vein Endothelial Cells / Q000187:drug effects*; D006801:Humans; D008687:Metformin / Q000494:pharmacology*; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors*; D009569:Nitric Oxide / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D017382:Reactive Oxygen Species; D009569:Nitric Oxide; D008687:Metformin; C496314:NOS3 protein, human; D052250:Nitric Oxide Synthase Type III; D019255:NADPH Oxidases; D006136:GTP Cyclohydrolase; D005947:Glucose
keywords: Fluctuating glucose; Guanosine 5′-triphosphate cyclohydrolase 1; Human umbilical vein endothelial cells; Metformin; Type 2 diabetes