EPR spin trapping and 2-deoxyribose degradation studies of the effect of pyridoxal isonicotinoyl hydrazone (PIH) on (OH)-O-center dot formation by the Fenton reaction

The search for effective iron chelating agents was primarily driven by the need to treat iron-loading refractory anemias such as beta-thalassemia majo r. However, there is a potential for therapeutic use of iron chelators in n on-iron overload conditions. Iron can, under appropriate conditions, cataly ze the production of toxic oxygen radicals which have been implicated in nu merous pathologies and, hence, iron chelators may be useful as inhibitors o f free radical-mediated tissue damage. We have developed the orally effecti ve iron chelator pyridoxal isonicotinoyl hydrazone (PIH) and demonstrated t hat it inhibits iron-mediated oxyradical formation and their effects (e.g. 2-deoxyribose oxidative degradation, lipid peroxidation and plasmid DNA bre aks). In this study we further characterized the mechanism of the antioxida nt action of PIH and some of its analogs against (OH)-O-. formation from th e Fenton reaction. Using electron paramagnetic resonance (EPR) with 5,5-dim ethyl-1-pyrroline-N-oxide (DMPO) as a spin trap for (OH)-O-. we showed that PIH and salicylaldehyde isonicotinoyl hydrazone (SIH) inhibited Fe(II)-dep endent production of (OH)-O-. from H2O2 Moreover, PIH protected 2-deoxyribo se against oxidative degradation induced by Fe(II) and H2O2 The protective effect of PIH against both DMPO hydroxylation and 2-deoxyribose degradation was inversely proportional to Fe(II) concentration. However, PIH did not c hange the primary products of the Fenton reaction as indicated by EPR exper iments on (OH)-O-.-mediated ethanol radical formation. Furthermore, PIH dra matically enhanced the rate of Fe(II) oxidation to Fe(III) in the presence of oxygen, suggesting that PIH decreases the concentration of Fe(II) availa ble for the Fenton reaction. These results suggest that PIH and SIH deserve further investigation as inhibitors of free-radical mediated tissue damage . (C) 1999 Elsevier Science B.V. All rights reserved.