Mechanisms of cancer prevention by tea polyphenols based on inhibition of TNF‐α expression

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Abstract
Among various biochemical and biological activities of tea polyphenols, we believe inhibition of the expression and release of tumor necrosis factor‐α (TNF‐α) is crucial, since our study with TNF‐α‐deficient mice has revealed that TNF‐α is an essential factor in tumor promotion. We found that EGCG dose‐dependently inhibited AP‐1 and NF‐κB activation in BALB/3T3 cells treated with okadaic acid, resulting in inhibition of TNF‐α gene expression. Furthermore, treatment with 0.1% gene expression as well as TNF‐α protein level in the lung of TNF‐α transgenic mice; and IL‐1β and IL‐10 gene expression in the lung was also inhibited by treatment with green tea extract, indicating that green tea inhibits both TNF‐α and the cytokines induced by TNF‐α in organs. We recently found synergistic effects of EGCG and cancer preventive agents such as tamoxifen and sulindac, on cancer preventive activity. Taken together, the results show that green tea is efficacious as a non‐toxic cancer preventive for humans.