Electron spin resonance spin-trapping investigation into the effects of paraquat and desferrioxamine on hydroxyl radical generation during acute iron poisoning

Abstract

We have previously described a secondary radical-trapping technique for the detection of in vivo hydroxyl radical generation during acute iron overload. With this technique, the hydroxyl radical (.OH) reacts with dimethylsulfoxide to form the methyl radical (.CH3), which is then detected by ESR spectroscopy as its adduct with the spin trap phenyl-N-tert-butylnitrone in the bile of treated animals. In this study, we report both the individual and combined effects of the futile-cycling agent paraquat (PQ2+) and the iron-chelating agent desferrioxamine (DFO) on iron-dependent .OH generation. Interactions between iron and the partially reduced oxygen species superoxide and hydrogen peroxide, which are generated during the metabolism of PQ2+, might be expected to stimulate .OH generation to a level above that seen in the presence of the metal ion alone. Although PQ2+ was often found to promote further .OH generation when administered to animals also given iron, the large variation observed between individual animals in response to the reagent meant that the effect was not statistically significant (p < 0.05). DFO was found to abolish iron-dependent .OH generation, both in the presence and in the absence of PQ2+. This is believed to result from the chelation of iron by DFO, to form an essentially redox-inert iron(III) complex that is unable to catalyze .OH radical formation. In addition, it was found that the iron(II) complex of DFO can reduce PQ2+ to its radical cation in vitro, indicating, therefore, that the chelation of iron by DFO may not necessarily prevent its participation in free radical reactions.