title: Activation of the AMP-activated kinase by antidiabetes drug metformin stimulates nitric oxide synthesis in vivo by promoting the association of heat shock protein 90 and endothelial nitric oxide synthase.
abstract: Metformin, one of most commonly used drugs for the treatment of type 2 diabetes, improves vascular endothelial functions and reduces cardiovascular events in patients with type 2 diabetes, although its mechanisms remain unknown. The current study aimed to elucidate how metformin improves endothelial functions. Exposure of cultured bovine aortic endothelial cells (BAECs) to clinically relevant concentrations of metformin (50-500 micromol/l) dose-dependently increased serine-1179 (Ser1179) phosphorylation (equal to human Ser1179) of endothelial nitric oxide (NO) synthase (eNOS) as well as its association with heat shock protein (hsp)-90, resulting in increased activation of eNOS and NO bioactivity (cyclic GMP). These effects of metformin were mimicked or completely abrogated by adenoviral overexpression of a constitutively active 5'-AMP-activated kinase (AMPK) mutant or a kinase-inactive AMPK-alpha, respectively. Furthermore, administration of metformin as well as 5-aminoimidazole-4-carboxamide ribonucleoside, an AMPK agonist, significantly increased eNOS Ser1179 phosphorylation, NO bioactivity, and coimmunoprecipitation of eNOS with hsp90 in wild-type C57BL6 mice but not in AMPK-alpha1 knockout mice, suggesting that AMPK is required for metformin-enhanced eNOS activation in vivo. Finally, incubation of BAECs with clinically relevant concentrations of metformin dramatically attenuated high-glucose (30 mmol/l)-induced reduction in the association of hsp90 with eNOS, which resulted in increased NO bioactivity with a reduction in overexpression of adhesion molecules and endothelial apoptosis caused by high-glucose exposure. Taken together, our results indicate that metformin might improve vascular endothelial functions in diabetes by increasing AMPK-dependent, hsp90-mediated eNOS activation.
authors.affiliation: Vascular Research Laboratory, Department of Surgery, Graduate School of Medicine, University of Tennessee, Knoxville, USA.
authors.forename: Bradley J
authors.initials: BJ
authors.lastname: Davis
authors.forename: Zhonglin
authors.initials: Z
authors.lastname: Xie
authors.forename: Benoit
authors.initials: B
authors.lastname: Viollet
authors.forename: Ming-Hui
authors.initials: MH
authors.lastname: Zou
mesh_terms: D055372:AMP-Activated Protein Kinases; D000818:Animals; D002417:Cattle; D042783:Endothelial Cells / Q000378:metabolism; D004730:Endothelium, Vascular / Q000166:cytology; D004789:Enzyme Activation; D015971:Gene Expression Regulation, Enzymologic; D005947:Glucose / Q000378:metabolism; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D007004:Hypoglycemic Agents / Q000494:pharmacology; D008297:Male; D008687:Metformin / Q000494:pharmacology*; D051379:Mice; D018345:Mice, Knockout; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism*; D009569:Nitric Oxide / Q000096:biosynthesis*; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism
chemical_list: D055372:AMP-Activated Protein Kinases; D005947:Glucose; D018841:HSP90 Heat-Shock Proteins; D007004:Hypoglycemic Agents; D008687:Metformin; D009097:Multienzyme Complexes; D009569:Nitric Oxide; D052250:Nitric Oxide Synthase Type III; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; C526180:PRKAA1 protein, human