title: Quantification of (15)N-nitrate in urine with gas chromatography combustion isotope ratio mass spectrometry to estimate endogenous NO production.
abstract: The use of stable isotope labeled substrates and subsequent analysis of urinary nitrate, forms a noninvasive test for evaluation of the in vivo NO metabolism. The present paper describes a new method for simultaneous quantification of (15)N-nitrate and total nitrate with gas chromatography combustion isotope ratio mass spectrometry (GC-C-IRMS). Nitrate, isolated from urine with a nitrate selective resin, was reduced to nitrite using copperized cadmium. Subsequently, Sudan I was formed by diazotation. Sudan II was added as internal standard, and both molecules were analyzed with GC-C-IRMS as tert-butyldimethylsilyl derivatives. The accuracy was determined during a recovery study of two different known nitrate concentrations and two (15)N-enrichments. A recovery of 101.6% and 103.9% for total nitrate and 107.6% and 91.2% for (15)N-nitrate was obtained, respectively. The validated method was applied on complete 72 h urine collections after intravenous administration of (15)N-nitrate and (15)N-arginine in humans. On average, 51.8% (47.0-71.0%) of administered (15)N-nitrate was excreted, while 0.68% (0.44-1.17%) of (15)N-arginine was metabolized to nitrate. In conclusion, this method can be used for accurate simultaneous determination of (15)N-nitrate and total nitrate concentrations in urine and can be applied in clinical studies for noninvasive evaluation of NO metabolism in vivo.
authors.affiliation: Department of Gastrointestinal Research, University Hospitals Leuven and Leuven Food Science and Nutrition Research Centre (LFoRCe), Leuven, Belgium.
authors.forename: Els
authors.initials: E
authors.lastname: Houben
authors.forename: Henrike M
authors.initials: HM
authors.lastname: Hamer
authors.forename: Anja
authors.initials: A
authors.lastname: Luypaerts
authors.forename: Vicky
authors.initials: V
authors.lastname: De Preter
authors.forename: Pieter
authors.initials: P
authors.lastname: Evenepoel
authors.forename: Paul
authors.initials: P
authors.lastname: Rutgeerts
authors.forename: Kristin
authors.initials: K
authors.lastname: Verbeke
mesh_terms: D001391:Azo Compounds / Q000737:chemistry; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D009284:Naphthols / Q000737:chemistry; D009566:Nitrates / Q000652:urine*; D009569:Nitric Oxide / Q000378:metabolism*; D009587:Nitrogen Isotopes / Q000737:chemistry
chemical_list: D001391:Azo Compounds; D009284:Naphthols; D009566:Nitrates; D009587:Nitrogen Isotopes; D009569:Nitric Oxide; C024336:1-phenylazo-2-naphthol; C033003:sudan red