LC-MS/MS detection of peroxynitrite-derived 3-nitrotyrosine in rat microvessels

3-Nitrotyrosine (3NT) is used as a biomarker of nitrative pathology caused by peroxynitrite (PN), myeloperoxidase (MPO)-, and/or eosinophil peroxidase (EPO)- dependent nitrite oxidation. 3NT measurements in biological materia ls are usually based on either antibody staining, HPLC detection, or GC det ection methodologies. In this report, a procedure is described for the meas urement of 3NT and tyrosine (TYR) by LC-MS/MS that is simple, direct, and s ensitive. Though highly specialized in its use as an assay, LC-MS/MS techno logy is available in many research centers in academia and industry. The cr itical assay for 3NT was linear below 100 ng/ml and the limit of detection was below 100 pg/ml. Regarding protein digested samples, we found that MRM was most selective with 133.1 m/z as the daughter ion. In comparison, LC-EC D was 100 times less sensitive. Basal levels of 3NT in extracted digests of rat brain homogenate were easily detected by LC-MS/MS, but were below dete ction by LC-ECD. The LC-MS/MS assay was used to detect 3NT in rat brain hom ogenate that was filtered through a 180 micron nylon mesh. Three fractions were collected and examined by phase contrast microscopy. The mass ratio (3 NT/TYR) of 3NT in fractions of large vessel enrichment, microvessel enrichm ent, and vessel depletion was 0.6 ng/mg, 1.2 ng/mg, and 0.2 ng/mg, respecti vely. Ultimately, we found that the basal 3NT/TYR mass ratio as determined by LC-MS/MS was six times greater in microvessel-enriched brain tissue vs. tissue devoid of microvessels. (C) 2000 Elsevier Science Inc.