Grape-derived antioxidants as inhibitors of murine skin carcinogenesis Free

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A major focus of our work has been the elucidation of mechanism(s) explaining the anticancer actions of chemopreventive, natural source agents, present in commonly consumed foods and beverages. We have selected for the present in vitro and in vivo studies agents rich in anthocyanins and proanthocyanidins, i.e, grape powder (GP) and grape seed extract (GSE), obtained from grapes as important sources of the nature most potent antioxidants. Proanthocyanidins, major free radical scavengers, serve as anti-inflammatory, anti-histamine and anti-allergenic agents. In addition, we have used powerful radical scavengers quercetin (Q) and resveratrol (R), a natural phytoalexin, present in skins of red grapes. Seven-week-old pathogen free, female SENCAR mice were treated topically on the shaved dorsal skin with antioxidants 30 minutes prior to 7,12-dimethylbenz[a]anthracene (DMBA) treatment (25 μg DMBA in 200 μl of acetone). Different doses from 0.5, 1.0, 2.0, to 4.0 mg of test or control antioxidants per mouse were applied topically twice a week for a total of 8 treatments. Control mice were treated in the same manner with DMBA only. The grape-derived antioxidants GP, GSE, Q, and R showed marked inhibitory effects in the above in vivo model as well as in the in vitro assays. Thus, these antioxidants markedly and in a dose-related manner, inhibited autooxidation of linoleic acid in a standard in vitro assay. The inhibitory effects of these test antioxidants were more powerful than those of the control antioxidants such as ?-tocopherol and L-ascorbic acid. The GP, GSE, containing proanthocyanidin B-2-gallate, Q, and R were also found to be potent scavengers of free radicals in salicylate trapping assay, chemiluminescence, and cytochrome c reduction assays. All these test agents strongly and in a dose-related manner inhibited the DMBA-induced hyperplasia and DNA oxidative damage in a standard in vivo model of murine skin tumorigenesis. The extent of the epidermal hyperplasia inhibition (50-70%) caused by the grape-derived antioxidants was similar or better than that of the above control antioxidants. Even more significant inhibition was obtained from simultaneous dietary and topical treatment with different combinations of antioxidants. The occurrence of DMBA-mediated Ha-ras mutations in codon 61 was reduced by up to 50% with topical applications of the mixed antioxidants. Much higher inhibition was observed (up to 90%) in DNA samples obtained from mice treated with different combinations of the test compounds given systemically and topically. The results of the present clearly show impressive synergistic effects of the combined topical and dietary treatments with the selected antioxidants. Supported by CA 102747 and a grant from California Table Grape Commission.