DNA oxidatively damaged by chromium(III) and H2O2 is protected by the antioxidants melatonin, N-1-acetyl-N-2-formyl-5-methoxykynuramine, resveratrol and uric acid

Chromium (Cr) compounds are widely used industrial chemicals and well known carcinogens. Cr(III) was earlier found to induce oxidative damage as docum ented by examining the levels of 8-hydroxydeoxyguanosine (8-OH-dG), an inde x for DNA damage, in isolated calf thymus DNA incubated with CrCl3 and H2O, . In the present in vitro study, we compared the ability of the free radica l scavengers melatonin, N-1-acetyl-N-2-formyl-5-methoxykynuramine (AFMK), r esveratrol and uric acid to reduce DNA damage induced by Cr(III). Each of t hese scavengers markedly reduced the DNA damage in a concentration-dependen t manner. The concentrations that reduced 8-OH-dG formation by 50% (IC50) w ere 0.10 muM for both resveratrol and melatonin, and 0.27 muM for AFMK. How ever, the efficacy of the fourth endogenous antioxidant, i.e. uric acid, in terms of its inhibition of DNA damage in the same in vitro system was abou t 60-150 times less effective than the other scavengers; the IC50 for uric acid was 15.24 muM. These findings suggest that three of the four antioxida nts tested in these studies may have utility in protecting against the envi ronmental pollutant Cr and that the protective effects of these free radica l scavengers against Cr(III)-induced carcinogenesis may relate to their dir ect hydroxyl radical scavenging ability. In the present study, the formatio n of 8-OH-dG was likely due to a Cr(III)-mediated Fenton-type reaction that generates hydroxyl radicals, which in turn damage DNA. Once formed, 8-OH-d G can mutate eventually leading to cancer; thus the implication is that the se antioxidants may reduce the incidence of Cr-related cancers. (C) 2001 Pu blished by Elsevier Science Ltd.