How urine analysis reflects oxidative stress--nitrotyrosine as a potential marker

Enhanced oxidant stress involved in the pathogenesis of cardiovascular (heart failure, atherosclerosis, ischemia-reperfusion injury), neurodegenerative (M. Alzheimer), metabolic (hypercholesterolemia, diabetes) and inflammatory disorders is mimicked by non-intermittent therapy with nitrovasodilators. We used this latter therapy model to study urinary 3-nitrotyrosine (n-tyr) excretion as a potential biomarker that may reflect the enhanced generation of reactive oxygen species. Namely, free or protein-bound n-tyr is formed in the organism by nitration of tyrosine (residues) via peroxynitrite (reaction product of NO&z.ccirf; and O(2)(-)&z. ccirf;). Free n-tyr content was analyzed by gas chromatography in urine obtained from healthy human subjects under a nitrite-limited diet during a two-day non-intermittent transdermal administration of glyceroltrinitrate (GTN; 0.4 mg/h) with or without vitamin C (Vit-C; 55 microg/kg/min) as antioxidant. Concomitant with the development of complete vascular tolerance (loss of dilator action), a progressive increase in urinary n-tyr excretion (up to 186+/-9 microg/day) was demonstrated in volunteers given GTN only. In contrast, when Vit-C was added, the GTN-induced increases in urinary n-tyr content were significantly suppressed (up to 130.20+/-6.91 microg/day), whereas Vit-C alone even decreased urinary n-tyr content (down to 34.00+/-5.66 microg/day), which was below control values (56.0+/-3.4 microg/day). Thus, urinary n-tyr may serve as a biomarker to detect changes in oxidant stress and thereby to evaluate the efficacy of therapeutic interventions aimed at reducing oxidant stress under various pathophysiological conditions.