title: Homocysteine inhibition of endothelium-dependent nitric oxide-mediated dilation of porcine retinal arterioles via enhanced superoxide production.
abstract: OBJECTIVE
  Elevated plasma concentration of homocysteine, a sulfur-containing amino acid, is an emerging risk factor for cardiovascular diseases. Recent epidemiologic studies have confirmed that elevated homocysteine levels are associated with ocular vascular diseases; however, the direct effect of homocysteine on ocular microvascular reactivity remains unknown. We investigated whether homocysteine affects endothelium-dependent nitric oxide (NO)-mediated dilation of retinal arterioles and whether oxidative stress and distinct protein kinase signaling pathways are involved in the homocysteine-mediated effect.
  
  
  METHODS
  Porcine retinal arterioles were isolated, cannulated, and pressurized without flow in vitro. Diameter changes were recorded using videomicroscopy techniques.
  
  
  RESULTS
  Intraluminal treatment with homocysteine (1 mM, 180 minutes) significantly attenuated arteriolar dilation in response to the endothelium-dependent NO-mediated agonists bradykinin and A23187 but not in response to the endothelium-independent NO donor sodium nitroprusside. In the presence of the superoxide scavenger 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL), the nicotinamide adenine dinucleotide phosphate-oxidase (NAD(P)H oxidase inhibitor apocynin, p38 kinase inhibitor SB203580, and peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist pioglitazone, the detrimental effect of homocysteine on bradykinin-induced dilation was prevented; however, neither the xanthine oxidase inhibitor allopurinol, the JNK inhibitor SP600125, or pioglitazone with PPAR-γ inhibitor GW9662 had that effect.
  
  
  CONCLUSIONS
  Homocysteine inhibits endothelium-dependent NO-mediated dilation in the retinal arterioles by producing superoxide from NAD(P)H oxidase, which appears to be linked with p38 kinase. By impairing endothelium-dependent NO-mediated vasoreactivity, homocysteine potentially facilitates development of retinal vascular diseases. In addition, pioglitazone can prevent homocysteine-induced endothelial dysfunction possibly by activating PPAR-γ.
authors: Department of Ophthalmology, Asahikawa Medical University, Asahikawa, Japan.
authors: Tsuneaki
authors: T
authors: Omae
authors: Taiji
authors: T
authors: Nagaoka
authors: Ichiro
authors: I
authors: Tanano
authors: Akitoshi
authors: A
authors: Yoshida
mesh_terms: D000818:Animals; D001160:Arterioles / Q000187:drug effects; D001920:Bradykinin / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D004728:Endothelium, Corneal; D006710:Homocysteine / Q000494:pharmacology*; D007004:Hypoglycemic Agents / Q000494:pharmacology; D019255:NADPH Oxidases / Q000502:physiology; D009569:Nitric Oxide / Q000819:agonists; D047495:PPAR gamma / Q000502:physiology; D000077205:Pioglitazone; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011494:Protein Kinases / Q000502:physiology; D012161:Retinal Artery / Q000187:drug effects* / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism*; D013552:Swine; D045162:Thiazolidinediones / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects*; D014969:Xanthine Oxidase / Q000502:physiology
chemical_list: D007004:Hypoglycemic Agents; D047495:PPAR gamma; D047428:Protein Kinase Inhibitors; D045162:Thiazolidinediones; D006710:Homocysteine; D013481:Superoxides; D009569:Nitric Oxide; D000001:Calcimycin; D014969:Xanthine Oxidase; D019255:NADPH Oxidases; D011494:Protein Kinases; D001920:Bradykinin; D000077205:Pioglitazone