Screening of edible Japanese plants for suppressive effects on phorbol ester-induced superoxide generation in differentiated HL-60 cells and AS52 cells

Epithelial xanthine oxidase (XOD) is one of the major enzymes responsible for superoxide (O₂^-) generation, which is involved in oxidative stress. However, there are few known reports of a convenient bioassay to detect cellular XOD activity. We tested several cell lines, and found that AS52, from Chinese hamster ovary cells, produced a significant level of O₂^- in response to 12-O-tetradecanoylphorbol 13-acetate (TPA), and this activity was markedly inhibited by allopurinol, an XOD inhibitor. Using AS52 cells and differentiated HL-60 cells, we conducted screening tests of edible Japanese plant extracts for their inhibitory activities toward TPA-induced O₂^- generation from both reduced nicotinamide adenine dinucleotide oxidase (HL-60) and XOD (AS52). Notably, the extracts from mioga ginger, rape, avocado, carrot, turnip, taro, and shimeji showed potent inhibition of O₂^- generation in both cell lines. These results suggest that several edible Japanese plants carry a significant antioxidative and cancer preventive potential.