Oxidation of N-hydroxy-l-arginine by hypochlorous acid to form nitroxyl (HNO)

Abstract

Recent research has shown that nitroxyl (HNO) has important and unique biological activity, especially as a potential alternative to current treatments of cardiac failure. HNO is a reactive molecule that undergoes efficient dimerization and subsequent dehydration to form nitrous oxide (N2O), making its detection in solution or biologically relevant preparations difficult. Due to this limitation, HNO has not yet been observed in vivo, though several pathways for its endogenous generation have been postulated. Here, we investigate the oxidation of N-hydroxy-l-arginine (NOHA) by hypochlorous acid (HOCl), which is generated in vivo from hydrogen peroxide and chloride by the heme enzyme, myeloperoxidase. NOHA is an intermediate in the enzymatic production of nitric oxide (NO) by NO synthases, and has been shown previously to be chemically oxidized to either HNO or NO, depending on the oxidant employed. Using membrane inlet mass spectrometry and standard N2O analysis by gas chromatography, we find that NOHA is oxidized by excess HOCl to form HNO-derived N2O. In addition, we also observe the analogous production of HNO from the HOCl oxidation of hydroxylamine, hydroxyurea, and (to a lesser extent) acetohydroxamic acid.