Polymeric black tea polyphenols inhibit mouse skin chemical carcinogenesis by decreasing cell proliferation

.  Objectives : The aim of this study was to investigate the antitumour promoting effects and possible mechanisms of action of the most abundant polymeric black tea polyphenols (PBPs 1–5) or thearubigins, in vivo . Materials and methods : Effect of PBP pre‐treatments on 12‐ O ‐tetradecanoylphorbol‐13‐acetate (TPA) promoted skin papillomas was studied in 7,12‐dimethylbenz(a)anthracene initiated mice over 40 weeks. Cell proliferation and apoptosis, in epidermis of the skin, were measured using appropriate immunohistochemical staining. Mitogen‐activated protein kinase signalling studies were conducted with Western blot analysis at 10, 20, 30 and 40 weeks of promotion. Results : Pre‐treatments with PBP fractions differentially altered latency, multiplicity and incidence of skin papillomas as compared to TPA treatments thereby exhibiting antipromoting effects. Most PBP fractions decreased TPA‐induced cell proliferation by decreasing activation of signalling kinases (c‐Jun N‐terminal protein kinase, extracellular signal‐regulated protein kinase, p38 protein kinase and Akt), transcription factors (activator protein‐1 and nuclear factor kappa B) and inflammatory protein (cyclooxygenase 2). TPA‐induced epidermal cell apoptosis was also decreased by pre‐treatment with most PBP fractions. Higher levels of p53 and p21 in skin cells pre‐treated with PBP fractions followed by TPA treatment as compared to only TPA‐treated animals suggested possible activation of a cell cycle checkpoint. Conclusions : PBP‐2 was observed to be the most potent polymeric polyphenol fraction and PBP‐4 and PBP‐5 showed only marginal activity, whereas PBP‐1 and PBP‐3 displayed intermediate efficacies. In conclusion, the protective effects of PBP fractions could be attributed to inhibition of TPA‐induced cellular proliferation.