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New research shows that green tea may prevent cancer.

Green tea, long associated with good health, has new scientific evidence to back its claim. Purdue University researchers (Department of Foods and Nutrition, Stone Hall, W. Lafayette, IN 47907) have found that EGCg, a compound in green tea, inhibits an enzyme that cancer cells need to grow and can kill cultured cancer cells with no ill effect on healthy cells. The findings offer the first scientific evidence to explain precisely how this compound works within a cell to ward off cancer.

The research shows that green tea leaves are rich in this anticancer compound, with concentrations high enough to induce anticancer effects in the body. The findings suggest that drinking more than four cups of green tea a day could provide enough of the active compound to slow and prevent the growth of cancer cells. Although all teas come from the same botanical source, green tea differs from black tea or other teas because of the way the tea leaves are processed after they are picked. For black tea, freshly-picked leaves are withered indoors and allowed to oxidize. With green tea, the leaves are not oxidized, but are steamed and parched to better preserve the naturally-active substances of the leaf.

Epidemiologists have found that people who drink more than four cups a day of green tea seem to have a lower overall risk of cancer, but scientists have been unsure how the tea produced these effects. Purdue investigators show in their study how green tea interacts with an enzyme on the surface of many types of cancer cells. This enzyme, called quinol oxidase, or NOX, helps carry out several functions on the cell surface and is required for growth in both normal and cancerous cells.

Normal cells express the NOX enzyme only when they are dividing in response to growth hormone signals. In contrast, cancer cells have the ability to express NOX activity at all times. This overactive form of NOX, known as tNOX-for tumor-associated NOX-has long been assumed to be vital for the growth of cancer cells, because drugs that inhibit tNOX activity also block tumor cell growth in culture.

In studies of cultured cells and isolated membranes of cells, researchers found that black tea could inhibit tNOX activity at dilutions of one part tea to 100 parts of water. The green tea infusions, however, were 10 to 100 times more potent, inhibiting the activity of tNOX at dilutions ranging from one part tea per 1,000 to 10,000 parts water. This finding suggested that green tea leaves are rich in a compound that inhibits tNOX.

To determine what the active compound was, investigators tested a number of compounds found in tea, including epigallocatechin gallate, or EGCg, a primary component of green tea that has been linked to anti-cancer effects. Their studies, done with cultured cells and with purified NOX protein in solutions, found that EGCg was capable of inhibiting the tNOX activity of cancer cells at low doses-such as those that could be derived from drinking several cups of green tea per day-but did not inhibit the NOX activity of healthy cells. Further work is needed to understand how tNOX works in cancer cell growth.

Further information. Dorothy Morre; phone: 765-494-8233; fax: 765-494-0674; email: morred@cfs.purdue.edu.
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Comment:New research shows that green tea may prevent cancer.
Publication:Emerging Food R&D Report
Geographic Code:1U3IN
Date:Jan 1, 1999
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