Effect of superoxide dismutase mimics on radical adduct formation during the reaction between peroxynitrite and thiols - An ESR-spin trapping study

We have reexamined the formation and reactions of radicals formed from peroxynitrite (ONOO-)-mediated oxidation of glutathione (GSH), L-cysteine (Cys), N-acetyl-D,L-penicillamine (NAP), and sodium bisulfite (NaHSO3). Sulfur centered and superoxide anion radicals were trapped using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and the radical adducts were analyzed by electron spin resonance (ESR) spectroscopy, The following sulfur-centered radicals were detected: glutathionyl radical (GS(.)) from GSH, L-cysteinyl radical ((.)Scys) from L-cysteine, N-acetyl-D,L-penicillamine thiyl radical ((.)SNAP) from NAP, and sulfite anion radical (SO3-) from NaHSO3. Additionally the formation of the hydroxyl radical adduct of DMPO (DMPO/(OH)-O-.) was observed, DMPO/(OH)-O-. formation was totally inhibited by low-molecular-weight superoxide dismutase (SOD) mimics, This suggests that DMPO/(OH)-O-. was formed from the decay of the superoxide radical adduct of DMPO, In the presence of SOD mimics, the DMPO-sulfur-centered adducts were more persistent, suggesting that O-2(-) is partially responsible for the instability of DMPO-thiyl adducts, Sulfur-centered radicals formed during oxidation of thiols and sulfite by peroxynitrite react with ammonium formate to form the carbon dioxide anion radical (CO2-), We conclude that sulfur-centered radicals produced from the oxidation of thiols and sulfite by peroxynitrite arise from a hydroxyl-radical-independent mechanism, Biological implications of peroxynitrite-mediated oxidation of thiols as well as the use of SOD mimics in biological spin-trapping are discussed. (C) 1996 Academic Press, Inc.