Naturally occurring antioxidants such as carotenoids are extensively studied for their potential in reducing the risk for cancer and other chronic diseases. In the present study, the radicalscavenger activity of the food additive norbixin, a water-soluble carotenoid extracted from Bixa orellana seeds and commercialized as annatto, was evaluated under conditions of DNA damage induced by reactive oxygen species, particularly by hydroxyl radicals. The cell-free scavenger activity of norbixin was evaluated using plasmid DNA as target molecule and Sn 2+ or Fe 2+ as oxidant. The addition of H 2 O 2 enhanced DNA breakage induced by metal ions, particularly Fe 2+ . Under these conditions, norbixin started to protect plasmid DNA against single-and double-strand breakage at a metal:norbixin ratio of 1:1 (Sn 2+ ) and 1:10 (Fe 2+ ). However, at lower ratios to Sn 2+ , norbixin enhanced Sn 2+ -induced DNA breakage P , 0´05X The ability of norbixin to protect genomic DNA against oxidative damage was assessed in murine fibroblasts submitted to H 2 O 2 -induced oxidative stress and the results were evaluated by the comet assay. Under low serum conditions (2 % fetal bovine serum (FBS)), a protective effect of norbixin against H 2 O 2 -induced DNA breakage was inversely related to its concentration, a protection ranging from 41 % (10 mM) to 21 % (50 mM). At higher concentrations of norbixin, however, oxidative DNA breakage was still enhanced, even in the presence of a high serum concentration (10 % FBS). Under normal conditions, norbixin per se has no detectable genotoxic or cytotoxic effects on murine fibroblasts. The antimutagenic potential of norbixin against oxidative mutagens was also evaluated by the Salmonella typhimurium assay, with a maximum inhibition of 87 % against the mutagenicity induced by H 2 O 2 . Although plasmid DNA and Ames data indicated that norbixin can protect DNA against oxidative damage, it seems to be a risky guardian of genomic DNA as it can also increase the extent of oxidative damage.

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In an attempt to determine whether electromagnetic field (EMF) exposure might lead to DNA damage, we exposed SnCl2-treated pBR322 plasmids to EMF and analysed the resulting conformational changes using agarose gel electrophoresis. An EMF-dependent potentiation of DNA scission (i.e. the appearance of relaxed plasmids) was observed. In confirmation of this, plasmids pre-exposed to EMF also were less capable of transforming Escherichia coli. The results indicate that EMF, in the presence of a transition metal, is capable of causing DNA damage. These observations support the idea that EMF, probably through secondary generation of reactive oxygen species, can be clastogenic and provide a possible explanation for the observed correlation between EMF exposure and the frequency of certain types of cancers in humans.

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