DNA oxidatively damaged by chromium(III) and H 2O 2 is protected by the antioxidants melatonin, N1-acetyl- N2-formyl-5-methoxykynuramine, resveratrol and uric acid

Abstract

Chromium (Cr) compounds are widely used industrial chemicals and well known carcinogens. Cr(III) was earlier found to induce oxidative damage as documented by examining the levels of 8-hydroxydeoxyguanosine (8-OH-dG), an index for DNA damage, in isolated calf thymus DNA incubated with CrCl 3 and H 2O 2. In the present in vitro study, we compared the ability of the free radical scavengers melatonin, N 1-acetyl- N 2-formyl-5-methoxykynuramine (AFMK), resveratrol and uric acid to reduce DNA damage induced by Cr(III). Each of these scavengers markedly reduced the DNA damage in a concentration-dependent manner. The concentrations that reduced 8-OH-dG formation by 50% (IC 50) were 0.10 μM for both resveratrol and melatonin, and 0.27 μM for AFMK. However, 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 about 60–150 times less effective than the other scavengers; the IC 50 for uric acid was 15.24 μM. These findings suggest that three of the four antioxidants tested in these studies may have utility in protecting against the environmental pollutant Cr and that the protective effects of these free radical scavengers against Cr(III)-induced carcinogenesis may relate to their direct hydroxyl radical scavenging ability. In the present study, the formation 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-dG can mutate eventually leading to cancer; thus the implication is that these antioxidants may reduce the incidence of Cr-related cancers.