title: Nitrate decreases xanthine oxidoreductase-mediated nitrite reductase activity and attenuates vascular and blood pressure responses to nitrite.
abstract: Nitrite and nitrate restore deficient endogenous nitric oxide (NO) production as they are converted back to NO, and therefore complement the classic enzymatic NO synthesis. Circulating nitrate and nitrite must cross membrane barriers to produce their effects and increased nitrate concentrations may attenuate the nitrite influx into cells, decreasing NO generation from nitrite. Moreover, xanthine oxidoreductase (XOR) mediates NO formation from nitrite and nitrate. However, no study has examined whether nitrate attenuates XOR-mediated NO generation from nitrite. We hypothesized that nitrate attenuates the vascular and blood pressure responses to nitrite either by interfering with nitrite influx into vascular tissue, or by competing with nitrite for XOR, thus inhibiting XOR-mediated NO generation. We used two independent vascular function assays in rats (aortic ring preparations and isolated mesenteric arterial bed perfusion) to examine the effects of sodium nitrate on the concentration-dependent responses to sodium nitrite. Both assays showed that nitrate attenuated the vascular responses to nitrite. Conversely, the aortic responses to the NO donor DETANONOate were not affected by sodium nitrate. Further confirming these results, we found that nitrate attenuated the acute blood pressure lowering effects of increasing doses of nitrite infused intravenously in freely moving rats. The possibility that nitrate could compete with nitrite and decrease nitrite influx into cells was tested by measuring the accumulation of nitrogen-15-labeled nitrite (15N-nitrite) by aortic rings using ultra-performance liquid chromatography tandem mass-spectrometry (UPLC-MS/MS). Nitrate exerted no effect on aortic accumulation of15N-nitrite. Next, we used chemiluminescence-based NO detection to examine whether nitrate attenuates XOR-mediated nitrite reductase activity. Nitrate significantly shifted the Michaelis Menten saturation curve to the right, with a 3-fold increase in the Michaelis constant. Together, our results show that nitrate inhibits XOR-mediated NO production from nitrite, and this mechanism may explain how nitrate attenuates the vascular and blood pressure responses to nitrite.
authors.affiliation: Department of Pharmacology, Faculty of Medical Sciences, State University of Campinas, Campinas, São Paulo, Brazil.
authors.forename: Célio
authors.initials: C
authors.lastname: Damacena-Angelis
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 Chemistry, School of Philosophy, Sciences and Languages, University of São Paulo, Ribeirão Preto, SP, Brazil.
authors.forename: Eduardo J
authors.initials: EJ
authors.lastname: Crevelin
authors.affiliation: Department of Pharmacology, Ribeirao Preto Medical School, University of Sao Paulo, Ribeirao Preto, SP, Brazil.
authors.forename: Rafael L
authors.initials: RL
authors.lastname: Portella
authors.affiliation: Department of Chemistry, School of Philosophy, Sciences and Languages, University of São Paulo, Ribeirão Preto, SP, Brazil.
authors.forename: Luiz Alberto B
authors.initials: LAB
authors.lastname: Moraes
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; D001794:Blood Pressure / Q000187:drug effects; D008297:Male; D008954:Models, Biological; D009566:Nitrates / Q000008:administration & dosage / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism; D009572:Nitrite Reductases / Q000378:metabolism*; D009603:Nitroso Compounds / Q000494:pharmacology; D051381:Rats; D012977:Sodium Nitrite / Q000008:administration & dosage / Q000378:metabolism*; D014968:Xanthine Dehydrogenase / Q000378:metabolism*
chemical_list: D009566:Nitrates; D009603:Nitroso Compounds; C094210:2,2'-(hydroxynitrosohydrazono)bis-ethanamine; D009569:Nitric Oxide; C031618:sodium nitrate; D014968:Xanthine Dehydrogenase; D009572:Nitrite Reductases; D012977:Sodium Nitrite
keywords: Hypertension; Nitrate; Nitric oxide; Nitrite; Xanthine oxidoreductase