title: Alpha-lipoic acid activates eNOS through activation of PI3-kinase/Akt signaling pathway.
abstract: BACKGROUND
  Lipoic acid (LA) exerts therapeutic effects on cardiovascular diseases. However, the mechanisms underlying these therapeutic effects remain elusive. Endothelial nitric oxide synthase (eNOS) plays a critical role in cardiovascular homeostasis. LA was shown to potently activate PI3-kinase/Akt pathway, and the latter is critical in the regulation of eNOS activity. In the present study, we test the hypothesis that LA improves endothelial function through PI3-kinase/Akt-mediated eNOS activation.
  
  
  RESULTS
  Western blot analysis showed that LA time- and dose-dependently induced phosphorylation of Akt and eNOS in human umbilical vein endothelial cells (HUVECs). Both PI3-kinase and Akt inhibitors abolished LA-induced eNOS phosphorylation, indicating that LA induces eNOS phosphorylation through the PI3-kinase/Akt pathway. This increase in eNOS phosphorylation was paralleled by an increase in NO release by HUVECs, supporting its relevance in eNOS activity regulation. Myograph analysis revealed that LA relaxed phenylephrine-induced contraction. Endothelium removal and NOS inhibition by L-NAME abolished this vasodilator action of LA, and Akt but not AMPK inhibition significantly reduced the vasodilator action of LA, indicating that it is mediated by PI3-kinase/Akt pathway-dependent activation of eNOS. Consistent with in vitro results, intraperitoneal injection with LA significantly increased plasma nitrite and nitrate levels in C57Bl/6j mice.
  
  
  CONCLUSIONS
  LA activates eNOS through a PI3-kinase/Akt signaling pathway-dependent mechanism, offering a potential molecular basis for the therapeutic effects of LA on cardiovascular diseases.
authors.affiliation: Department of Cardiology, East Hospital, Tongji University School of Medicine, Shanghai 200120, PR China; Department of Medicine Cardiology Division, University of Maryland School of Medicine, Baltimore, MD 21201, USA. Electronic address: yingzhekang@hotmail.com.
authors.forename: Zhekang
authors.initials: Z
authors.lastname: Ying
authors.affiliation: Division of Geriatric Medicine, Tongji Hospital, Tongji University School of Medicine, Shanghai 200065, PR China.
authors.forename: Xiaoyun
authors.initials: X
authors.lastname: Xie
authors.affiliation: Department of Cardiology, East Hospital, Tongji University School of Medicine, Shanghai 200120, PR China; Department of Medicine Cardiology Division, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
authors.forename: Minjie
authors.initials: M
authors.lastname: Chen
authors.affiliation: Department of Medicine Cardiology Division, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
authors.forename: Kevin
authors.initials: K
authors.lastname: Yi
authors.affiliation: Department of Medicine Cardiology Division, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
authors.forename: Sanjay
authors.initials: S
authors.lastname: Rajagopalan
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D061307:Human Umbilical Vein Endothelial Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D008063:Thioctic Acid / Q000494:pharmacology*
chemical_list: D008063:Thioctic Acid; C496314:NOS3 protein, human; D052250:Nitric Oxide Synthase Type III; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt
keywords: Akt; Endothelium; Lipoic acid; Phosphorylation; eNOS