Generation of Nitric Oxide from Spin-trapping Agents under Oxidative Conditions

Nitric oxide (NO) generation from the spin-trapping agents, phenyl-tert-butylnitrone (PBN), α-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN) and 5,5-dimethyl-1-pyrroline N-oxide (DMPO), under UV irradiation in the presence of dissolved oxygen and by oxidation with the Fenton reagent was examined by using ESR spin-trapping and spectrophotometric methods. A triplet signal at g=2.041 was observed after the ferrous complex of dithiocarbamate [Fe(MGD)2] had been added to a solution of these trapping agents treated with UV irradiation and the Fenton reagent, showing that NO was trapped with Fe(MGD)2. The concentration of nitrite induced from NO was determined via the Griess reaction to increase with the time of the treatment. It is speculated by reference to the ESR signal observed at the position around g=2.006 that the C=N double bond might have been cleaved by oxidation, resulting in the formation of a nitroso compound, and that NO was then generated by the fission of the C-N bond of the nitroso compound. NO generated in this way activated guanylate cyclase, from which it can be expected that a spin-trapping agent acts as an NO generator in vivo as well as a free radical scavenger.