The study reveals the powers of two members of the chemical family known as polyphenols. The polyphenols don't block UV light, but they interfere with a cascade of chemical events, set off by UV light and other carcinogens, that lead to the uncontrolled cell division typical of cancer.
"We asked if polyphenols can block the process that turns a normal cell into a cancer cell," said Dong. "We looked for a target." The researchers studied the effects of polyphenols on "target" proteins known to be important in the chain of events leading to cancer. The proteins belonged to two classes: enzymes that activate other proteins, including other enzymes (protein kinases); and proteins that interact with DNA to influence the expression of genes (transcription factors).
The researchers shined UVB light, the ultraviolet light that causes skin cancer, on the shaven backs of mice. They also applied a substance called TPA, which promotes tumor formation. Mice in the experimental groups were swabbed with solutions containing polyphenols; mice in the control group received no further treatment. When the researchers measured activities of the protein kinases and transcription factors in the epidermis, they found that polyphenols inhibited both targets compared to epidermis from mice in the control group. Working with cultured human and mouse epidermal cells, they found a similar pattern.
The researchers suggested that polyphenols in tea can interfere with signaling pathways inside cells that may "order" cells to divide and multiply. If cells multiply too long or too fast, the result is cancer. UV light can activate such a pathway in the skin. Work led by Allan Conney of Rutgers has already shown that caffeine, a well-known component of tea, blocks ultraviolet light-induced carcinogenesis, said Dong.
"Blocking UV light is the best prevention, but sometimes, people cannot avoid going out in the sun," he said. "We hope to develop a cancer preventive agent for those people." Dong and his colleagues are in the early stages of developing a polyphenol-based cream that could supplement sunscreens currently in use, most of which act by absorbing UV rays.
Citing work by C.S. Yong at Rutgers, Dong said that one would need to drink seven cups a day of strong tea to reach the same levels of tea polyphenols as were applied to mice in these experiments. Dong himself enjoys plenty of regular (nondecaffeinated) black and green tea every day.
Besides Dong, the research team included Ann Bode, Wei-ya Ma, Zhiwei He, Tatiana Zykova, Svetlana Ermakova and Hideya Mizuno of the Hormel Institute. The work was supported by the National Institutes of Health and the Hormel Foundation.
Zigang Dong, Hormel Institute, (507) 437-9640
in New York (9/7 and 9/8/03): (212) 971-0101 (Ramada Inn & Plaza)