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Orally Administered Green Tea Polyphenols Prevent Ultraviolet Radiation-Induced Skin Cancer in Mice through Activation of Cytotoxic T Cells and Inhibition of Angiogenesis in Tumors

Solar UV radiation is a main cause of melanoma and non-melanoma skin cancers, especially among Caucasians. The incidence of skin cancer will further increase because of the aging of the population and increased exposure to solar UV light and UV radiation from tanning devices. Recently there is an increased interest in the use of phytochemicals for the prevention of UV induced skin cancer. Green tea polyphenols are known for their antioxidant, anti-inflammatory and immune modulating activity. Green tea polyphenols may also prevent the development of skin cancer induced by UV rays. The aim of this study was to investigate the mechanism by which green tea polyphenols prevent UV induced skin cancer in mice. The tests were carried out on young female hairless mice during a period of 24 weeks. They were divided into three groups: the control group, UV radiated group without green tea polyphenol and UV radiated group with green tea polyphenol. The mice from the control group consumed water whereas the green tea polyphenol mice consumed water containing 2 g green tea polyphenol per liter. The skin and tumours were analysed with Western blotting, zymography and immunostaining.

The researchers found that the mice treated with green tea polyphenol reduced the UV induced tumor incidence by 35 percent, tumor multiplicity by 63 percent and tumor size by 55 percent. The anti-carcinogenic effect of green tea polyphenols may be explained by the following changes initiated by green tea polyphenols:
  • Reduced expression of matrix metalloproteinase and increased expression of tissue inhibitor matrix metalloproteinase.
    Analysis of the activity of matrix metalloproteinase-2 with gelatinolytic zymography showed decreased activity. Green tea polyphenols also inhibited the activity and expression of matrix metalloproteinase-9. The inhibition of these proteins reduces tumor growth.
  • Reduced expression of vascular endothelial cell antigen CD31 and vascular endothelial growth factor.
    Green tea polyphenols inhibits the formation of new vessels in tumours, thereby reducing tumour growth.
  • Inhibited expression of proliferating cell nuclear antigen in tumours.
    Administration of green tea polyphenols inhibits the expression of proliferating cell nuclear antigen which is an indicator of tumour growth.
  • Higher frequency of cytotoxic T-cells in tumours.
    Cytotoxic T-cells control the apoptosis of tumour cells and are required to reduce incidence of tumours. It seems that green tea polyphenols stimulates the migration of cytotoxic T-cells to the tumor cells.

The study concluded that green tea polyphenols affect several biomarkers that are involved in UV induced skin cancer, including the inhibition of angiogenic factors and recruitment of cytotoxic T-cells. Green tea polyphenols could prevent UV induced skin cancer formation and could reduce the growth of established skin tumours. The daily consumption of 5 to 6 cups of green tea by humans provides same levels of green tea polyphenols as used in this study. This knowledge could be used to develop medicines with green tea polyphenol that could be used as a complementary or alternative treatment of UV induced skin cancer.


Source: Sudheer K. Mantena, Syed M. Meeran, Craig A. Elmets and Santosh K. Katiyar. Orally Administered Green Tea Polyphenols Prevent Ultraviolet Radiation-Induced Skin Cancer in Mice through Activation of Cytotoxic T Cells and Inhibition of Angiogenesis in Tumors. Journal of Nutrition, 135:2871-2877, December 2005


 
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