triacetoneamine-n-oxyl and 1-hydroxy-2-2-6-6-tetramethyl-4-oxopiperidine

Nitroxyl radicals are important antioxidants that have been used to protect animal tissues from oxidative damage. Their reaction with hydroxyl radical ((*)OH) is generally accepted to be the mechanism of antioxidant function. However, the direct interaction of nitroxyl radicals with (*)OH does not always provide a satisfactory explanation in various pH, because the concentration of hydrogen ion may affect the generation of secondary (*)OH-derived radicals. In the present study, it was confirmed that the reaction between 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPOL) and (*)OH generated TEMPOL-hydroxylamine, 4-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPON) and TEMPON-hydroxylamine using HPLC coupled with electrochemical detection. In the absence of NADH, TEMPOL-H may be generated by the reaction with secondary (*)OH-derived radicals in acidic condition. In the presence of NADH, a large proportion of the non-paramagnetic products was TEMPOL-H. Finally, it was clarified that TEMPOL-H was generated during dopamine metabolism, which is believed to be one of the (*)OH sources in pathological processes such as Parkinson's disease.

Topics: Antioxidants; Chromatography, High Pressure Liquid; Cyclic N-Oxides; Dopamine; Electron Spin Resonance Spectroscopy; Free Radicals; Humans; Hydrogen; Hydrogen-Ion Concentration; Hydroxyl Radical; Hydroxylamines; Nitric Oxide; Piperidines; Spin Labels; Triacetoneamine-N-Oxyl

The reactions of hydroxylamine 1-hydroxy-2,2,6,6-tetramethyl-4-oxo-piperidine hydrochloride (TEMPONE-H) with peroxynitrite, superoxide and peroxyl radicals were studied. It was shown that under these reactions TEMPONE-H is oxidized into a stable nitroxide 1-hydroxy-2,2,6,6-tetramethyl-4-oxo-piperidi-noxyl (TEMPONE). The reactivity of TEMPONE-H towards reactive oxygen species was compared with the spin traps DMPO and TMIO as well as with DMSO and SOD. The rate constants of reactions of TEMPONE-H with peroxynitrite and superoxide radicals were 6 x 10(9) M(-1)s(-1) and 1.2x10(4) M(-1)s(-1), respectively. Using TEMPONE-H the sensitivity in the detection of peroxynitrite or superoxide radical was about 10-fold higher than using the spin traps DMPO or TMIO. Thus, TEMPONE-H may be used as a spin trap in chemical and biological systems to quantify peroxynitrite and superoxide radical formation.

Topics: Amidines; Dimethyl Sulfoxide; Electron Spin Resonance Spectroscopy; Free Radicals; Kinetics; Molsidomine; Nitrates; Peroxides; Piperidines; Reactive Oxygen Species; Spin Labels; Superoxides; Triacetoneamine-N-Oxyl