Redox-sensitive mechanism of no scavenging by nitronyl nitroxides

Nitronyl nitroxides, NN*, have been increasingly used in the field of NO-related studies as specific antagonists of NO*. We employed a combination of EPR and NMR spin trapping to study the mechanisms of the reaction of NN* with NO* in reducing environments. EPR allowed observation of NO-induced transformation of the paramagnetic trap, NN*, to the corresponding iminonitroxide, IN*. In a complementary way, corresponding EPR-invisible diamagnetic products (the hydroxylamines NN-H and IN-H) were detected by F-19-NMR using newly synthesized fluorinated traps. Addition of reducing agents to a solution of NN* resulted in fast disappearance of its EPR spectra and appearance of a F-19-NMR peak of the corresponding hydroxylamine, NN-H. Addition of NO* as a bolus, or NO* generated on sodium nitroprusside photolysis, resulted in F-19-NMR-detectable accumulation of the hydroxylamine, IN-H. Upon high rates of NO* generation in ascorbate-containing solutions, partial recovery of NN* was observed, which undergoes further reactions with NO* and ascorbate in a competitive manner. Using 19F-NMR and a fluorinated trap, NO-induced conversion of NN-H into IN-H was also observed in vivo in hypertensive ISIAH rats compared with normotensive WAG rats. The results provide insight into a new potential redox-sensitive mechanism of the antagonistic action of NN* against NO*, which may provide insight into previously unexplained behavior of this category of NO-reacting compounds. (C) 2003 Elsevier Inc. All rights reserved.