Biochemical behaviour of norbixin during in vitro DNA damage induced by reactive oxygen species

Naturally occurring antioxidants such as carotenoids are extensively studie d for their potential in reducing the risk for cancer and other chronic dis eases. In the present study, the radical-scavenger activity of the food add itive norbixin, a water-soluble carotenoid extracted from Bixa orellana see ds and commercialized as annatto, was evaluated under conditions of DNA dam age induced by reactive oxygen species, particularly by hydroxyl radicals. The cell-free scavenger activity of norbixin was evaluated using plasmid DN A as target molecule and Sn2+ or Fe2+ as oxidant. The addition of H2O2 enha nced DNA breakage induced by metal ions, particularly Fe2+. Under these con ditions, norbixin started to protect plasmid DNA against single- and double -strand breakage at a metal:norbixin ratio of 1:1 (Sn2+) and 1:10 (Fe2+). H owever, at lower ratios to Sn2+, norbixin enhanced Sn2+-induced DNA breakag e (P < 0.05). The ability of norbixin to protect genomic DNA against oxidat ive damage was assessed in murine fibroblasts submitted to H2O2-induced oxi dative stress and the results were evaluated by the comet assay. Under low serum conditions (2 % fetal bovine serum (FBS)), a protective effect of nor bixin against H2O2-induced DNA breakage was inversely related to its concen tration, a protection ranging from 41 % (10 <mu>m) to 21 % (50 mum). At hig her concentrations of norbixin, however, oxidative DNA breakage was still e nhanced, even in the presence of a high serum concentration (10 % FBS). Und er normal conditions, norbixin per se has no detectable genotoxic or cytoto xic 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 H2O2. Although plasmid DNA and Ames data indicated that norbixin can pro tect DNA against oxidative damage, it seems to be a risky guardian of genom ic DNA as it can also increase the extent of oxidative damage.