Abstract
Nitroxyl (HNO), the protonated one-electron reduction product of NO, remains an enigmatic reactive nitrogen species. Its chemical reactivity and biological activity are still not completely understood. HNO donors show biological effects different from NO donors. Although HNO reactivity with molecular oxygen is described in the literature, the product of this reaction has not yet been unambiguously identified. Here we report that the decomposition of HNO donors under aerobic conditions in aqueous solutions at physiological pH leads to the formation of peroxynitrite (ONOO(-)) as a major intermediate. We have specifically detected and quantified ONOO(-) with the aid of boronate probes, e.g. coumarin-7-boronic acid or 4-boronobenzyl derivative of fluorescein methyl ester. In addition to the major phenolic products, peroxynitrite-specific minor products of oxidation of boronate probes were detected under these conditions. Using the competition kinetics method and a set of HNO scavengers, the value of the second order rate constant of the HNO reaction with oxygen (k = 1.8 × 10(4) m(-1) s(-1)) was determined. The rate constant (k = 2 × 10(4) m(-1) s(-1)) was also determined using kinetic simulations. The kinetic parameters of the reactions of HNO with selected thiols, including cysteine, dithiothreitol, N-acetylcysteine, captopril, bovine and human serum albumins, and hydrogen sulfide, are reported. Biological and cardiovascular implications of nitroxyl reactions are discussed.
Highlights
Nitroxyl (HNO) is a reactive nitrogen species implicated in cardioprotection
We report that the decomposition of HNO donors under aerobic conditions in aqueous solutions at physiological pH leads to the formation of peroxynitrite (ONOO؊) as a major intermediate
We demonstrated that the formation of the products of both major and minor pathways in a specific ratio can be used as a “peroxynitrite fingerprint” and applied this strategy to unambiguously determine the identity of the product of the reaction of HNO with molecular oxygen
Summary
Nitroxyl (HNO) is a reactive nitrogen species implicated in cardioprotection. Results: Nitroxyl reacts with oxygen to form an oxidizing and nitrating species, peroxynitrite. The possibility of peroxynitrite formation from the reaction between HNO and O2 remained skeptical and understudied [42, 44] This is, in part, due to the lack of availability of specific probes that directly react with ONOOϪ to form specific diagnostic products. We present unambiguous evidence for ONOOϪ formation during the reaction between HNO and molecular oxygen using the recently developed assays for specific detection and quantification of peroxynitrite [47, 48]. We demonstrated that the formation of the products of both major and minor pathways in a specific ratio can be used as a “peroxynitrite fingerprint” and applied this strategy to unambiguously determine the identity of the product of the reaction of HNO with molecular oxygen
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