title: Tempol improves xanthine oxidoreductase-mediated vascular responses to nitrite in experimental renovascular hypertension.
abstract: Upregulation of xanthine oxidoreductase (XOR) increases vascular reactive oxygen species (ROS) levels and contributes to nitroso-redox imbalance. However, XOR can generate nitric oxide (NO) from nitrite, and increased superoxide could inactivate NO formed from nitrite. This study tested the hypothesis that XOR contributes to the cardiovascular effects of nitrite in renovascular hypertension, and that treatment with the antioxidant tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl) improves XOR-mediated effects of nitrite. Blood pressure was assessed weekly in two-kidney one-clip (2K1C) and control rats. After six weeks of hypertension, the relaxing responses to nitrite were assessed in aortic rings in the presence of the XOR inhibitor oxypurinol (or vehicle), either in the absence or in the presence of tempol. Moreover, in vivo hypotensive responses to nitrite were also examined in the presence of oxypurinol (or vehicle) and tempol (or vehicle). Aortic XOR activity and expression were evaluated by fluorescence and Western blot, respectively. Vascular ROS production was assessed by the dihydroethidium assay. 2K1C hypertensive rats showed increased aortic XOR activity and vascular ROS production compared with control rats. Oxypurinol shifted the nitrite concentration-response curve to the right in aortic rings from 2K1C rats (but not in controls). Oxypurinol also attenuated the hypotensive responses to nitrite in 2K1C rats (but not in controls). These functional findings agree with increased aortic and plasma XOR activity found in 2K1C rats. Tempol treatment enhanced oxypurinol-induced shift of the nitrite concentration-response curve to the right. However, antioxidant treatment did not affect XOR-mediated hypotensive effects of nitrite. Our results show that XOR is important to the cardiovascular responses to nitrite in 2K1C hypertension, and XOR inhibitors commonly used by patients may cancel this effect. This finding suggests that nitrite treatment may not be effective in patients being treated with XOR inhibitors. Moreover, while tempol may improve the vascular responses to nitrite, antihypertensive responses are not affected.
authors.affiliation: Department of Pharmacology, Ribeirao Preto Medical School, University of Sao Paulo, Ribeirao Preto, SP, Brazil.
authors.forename: Gustavo H
authors.initials: GH
authors.lastname: Oliveira-Paula
authors.affiliation: Department of Pharmacology, Ribeirao Preto Medical School, University of Sao Paulo, Ribeirao Preto, SP, Brazil.
authors.forename: Lucas C
authors.initials: LC
authors.lastname: Pinheiro
authors.affiliation: Department of Pharmacology, Ribeirao Preto Medical School, University of Sao Paulo, Ribeirao Preto, SP, Brazil.
authors.forename: Danielle A
authors.initials: DA
authors.lastname: Guimaraes
authors.affiliation: Department of Pharmacology, Ribeirao Preto Medical School, University of Sao Paulo, Ribeirao Preto, SP, Brazil.
authors.forename: Sandra O Conde
authors.initials: SO
authors.lastname: Tella
authors.affiliation: Department of Pharmacology, Ribeirao Preto Medical School, University of Sao Paulo, Ribeirao Preto, SP, Brazil.
authors.forename: Ana L Furlan
authors.initials: AL
authors.lastname: Blanco
authors.affiliation: Department of Pharmacology, State University of Campinas, Campinas, SP, Brazil.
authors.forename: Celio D
authors.initials: CD
authors.lastname: Angelis
authors.affiliation: Molecular Medicine Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, United States.
authors.forename: Alan N
authors.initials: AN
authors.lastname: Schechter
authors.affiliation: Department of Pharmacology, Ribeirao Preto Medical School, University of Sao Paulo, Ribeirao Preto, SP, Brazil. Electronic address: tanus@fmrp.usp.br.
authors.forename: Jose E
authors.initials: JE
authors.lastname: Tanus-Santos
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000008:administration & dosage*; D001794:Blood Pressure / Q000187:drug effects; D003497:Cyclic N-Oxides / Q000008:administration & dosage*; D004195:Disease Models, Animal; D006801:Humans; D006978:Hypertension, Renovascular / Q000139:chemically induced / Q000188:drug therapy* / Q000473:pathology; D009569:Nitric Oxide / Q000378:metabolism; D009573:Nitrites / Q000633:toxicity; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D013113:Spin Labels; D014968:Xanthine Dehydrogenase / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D000975:Antioxidants; D003497:Cyclic N-Oxides; D009573:Nitrites; D017382:Reactive Oxygen Species; D013113:Spin Labels; D009569:Nitric Oxide; D014968:Xanthine Dehydrogenase; C001803:tempol
keywords: Hypertension; Nitric Oxide; Nitrite; Oxidative stress; Xanthine oxidoreductase