Urinary Nitrotyrosine Content as a Marker of Peroxynitrite-induced Tolerance to Organic Nitrates

Abstract

Background: Anti-ischemic therapy with nitrovasodilators as NO-donors is complicated by the induction of tolerance. When nitrovasodilators are metabolized to release NO there is a considerable coproduction of oxygen-derived radicals leading to a diminished cyclic GMP production and to impaired vasomotory responses. We analyzed in vivo the glyceroltrinitrate- induced generation of strong oxidative/nitrating compounds contributing to development of tolerance. Methods and Results: In 16 patients we studied the urinary nitrotyrosine excretion during either (1) placebo control conditions, (2) 2-day nonintermittent transdermal nitroglycerin administration (0.4 mg/h), (3) 2-day nonintermittent glyceroltrinitrate administration (0.4 mg/h) along with a continuous infusion of vitamin C (55 μg/kg/min) as an antioxidant, or (4) with vitamin C but without glyceroltrinitrate (diminished urinary nitrotyrosine content of 34 ± 18 μg/day observed). Glyceroltrinitrate administration augmented urinary nitrotyrosine from 56 ± 24 (basal) to 186 ± 32 μg/day (glyceroltrinitrate tolerance). Coadministration of vitamin C caused complete elimination of tolerance and a decrease in urinary nitrotyrosine to 130 ± 28 μg/day. Glyceroltrinitrate-induced formation of oxidants was confirmed in vitro comparing glyceroltrinitrate-induced and peroxynitrite-induced tachyphylaxis in isolated perfused rabbit hearts and analyzing tolerance-induced inactivation of soluble guanylyl cyclase in cultured aortic smooth muscle cells. Conclusions: Augmented urinary nitrotyrosine excretion during glyceroltrinitrate adminis tration reflects enhanced formation of peroxynitrite and of nitrotyrosine. Glyceroltrinitrate- induced tolerance is the result of oxidative stress and can be suppressed by additional antiox idant therapy aimed to prevent glyceroltrinitrate-induced formation and/or actions of peroxynitrite.