Pro-oxidative versus antioxidative reactions between Trolox and Cr(VI): The role of H2O2

The effect of the Vitamin E model compound Trolox in reactions with Cr(VI) in the presence or absence of hydrogen peroxide was investigated. The aim of this study was to establish and discuss potential Trolox-mediated pro-oxidative reactions. The importance of the Trolox:Cr(VI) ratio in the Cr(VI) reduction process was determined from the EPR spectra and DNA cleavage reactions. In the absence of hydrogen peroxide, reduction of Cr(VI) occurred with concomitant oxidation of Trolox to the phenoxyl radical. In the presence of hydrogen peroxide, Cr(V), produced by the reduction of Cr(VI), reduced hydrogen peroxide to the hydroxyl radical. The latter was detected by spin-trapping the methyl radical following reaction with N-methyl sulfoxide. During Cr(VI) reduction with Trolox, DNA single- or double-strand breaks due to Trolox radical formation were not observed. Relaxed DNA appeared only when H2O2 was added to Trolox/Cr(VI) mixtures most probably due to hydroxyl radical formation during the redox cycling of Cr(V/IV)-species. Fenton-like reactions do not play a significant role in the Trolox/Cr(VI) system in the absence of added H2O2.