Reactivity of an indolinonic aminoxyl with superoxide anion and hydroxyl radicals

The increasing knowledge on the participation of free radicals in many dive rse clinical and pathological conditions, has consequently expanded the sea rch for new and versatile antioxidants aimed at combating oxidative stress. Our interest in this field concerns aromatic indolinonic aminoxyls (nitrox ides) which efficiently react with alkoxyl, peroxyl, aminyl, arylthiyl and alkyl radicals to give non-paramagnetic species. This prompted us to test t heir antioxidant activity on different biological systems exposed to free r adical-induced oxidative stress and the results obtained so far have been v ery promising. However little is known about their behaviour towards supero xide and hydroxyl radicals. Here, we report on the reactivity of an indolinonic aminoxyl, with the two above mentioned radicals using hypoxanthine/xanthine oxidase and potassium superoxide for generating the former and the Fenton reagent for the latter. Besides performing the deoxyribose assay for studying the reaction of the aminoxyl with hydroxyl radical and monitoring spectral changes of the amino xyl in the presence of superoxide radical, macroscale reactions were perfor med in both cases and the products of the reactions isolated and identified . The EPR technique was used in this study to help elucidate the data obtai ned. The results show that this compound efficiently reacts with both hydro xyl and superoxide radicals and furthermore, it is capable of maintaining i ron ions in its oxidized form. The results thus contribute to increasing th e knowledge on the reactivity of indolinonic aminoxyls towards free radical species and as a consequence, these compounds and/or other aminoxyl deriva tives, may be considered as complementary, and sometimes alternative source s for combating oxidative damage.