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Novel bioassay system for evaluating anti-oxidative activities of food items: Use of basolateral media from differentiated Caco-2 cells

Reactive oxygen and nitrogen species, including superoxide and nitric oxide (NO), are known to be mediators of oxidative stress and play pivotal roles in the onset of numerous life style-related diseases. While a number of studies have shown that naturally occurring anti-oxidants may be applicable for prevention and therapy for those diseases, most in vitro anti-oxidation tests reported have not provided significant insight into the absorption efficiency or metabolism of dietary anti-oxidants in the gastrointestinal tract. In the present study, we established a novel assay system by focusing on the bioconversion of food constituents using differentiated Caco-2 cells as a model of human intestinal epithelial cells. Various fresh food preparations [ginger, garlic, shimeji (Hypsizigus marmoreus), onion, carrot] were added to the apical side of differentiated Caco-2 monolayers. After incubation, the medium was recovered and tested for its inhibitory effects on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced generation in differentiated HL-60 cells, and on combined lipopolysaccharide (LPS)- and interferon (IFN)-γ -induced NO generation in RAW 264.7 macrophages. The garlic preparation (25% v/v) basolateral medium abolished generation without any cytotoxicity toward HL-60 cells, though it was cytotoxic to Caco-2 cells. In the NO generation tests, all of the food preparations showed notable inhibitory activity, while the garlic preparation (5% v/v) basolateral medium inhibited NO generation with substantial cytotoxicity toward RAW 264.7 cells. Interestingly, the carrot preparation (1% v/v) basolateral medium inhibited NO generation in both a concentration- and time-dependent manner without any cytotoxicity toward RAW 264.7 or Caco-2 cells, and its activities were higher than those of the carrot preparation alone (1% v/v). Our results indicate that the present assay system is appropriate and reliable for determination of the anti-oxidative efficacy of dietary phytochemicals in vivo.