- WEST LAFAYETTE, Ind. -- Green tea, long associated with good health, has new
scientific evidence to back its claim. Purdue University researchers Dorothy
Morre and D. James Morre (pronounced MORE-aye) found that EGCg, a compound
in green tea, inhibits an enzyme required for cancer cell growth and can
kill cultured cancer cells with no ill effect on healthy cells.
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- The findings offer the first scientific
evidence to explain precisely how this compound works within a cell to
ward off cancer. The results will be presented Monday (12/14) at the 38th
annual meeting of the American Society for Cell Biology in San Francisco.
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- "Our research shows that green tea
leaves are rich in this anti-cancer compound, with concentrations high
enough to induce anti-cancer effects in the body," says Dorothy Morre,
professor of foods and nutrition in Purdue's School of Consumer and Family
Sciences.
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- 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, she says.
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- 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 natural active substances of the leaf.
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- 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 were unsure how the tea produced these effects.
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- Morre and her husband, who is the Dow
Distinguished Professor of Medicinal Chemistry and Molecular Pharmacology
at Purdue, show in their independent study how green tea interacts with
an enzyme on the surface of many types of cancer cells including breast,
prostate, colon and neuroblastoma. 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.
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- "Normal cells express the NOX enzyme
only when they are dividing in response to growth hormone signals,"
Dorothy Morre says. "In contrast, cancer cells have somehow gained
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.
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- After hearing a researcher discuss green
tea's anti-cancer potential on a television show, the couple set out to
investigate whether tea infusions -- made when the compounds of tea leaves
leach into hot water -- would have an effect on tNOX enzyme activity.
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- In studies of cultured cells and isolated
membranes of cells, they found that black tea could inhibit tNOX activity
at dilutions of one part tea to 100 parts of water.
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- 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.
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- "This finding suggested that green
tea leaves are rich in a compound that inhibits tNOX," Dorothy Morre
says. "With concentrations of the active compound at these levels,
drinking several cups of green tea per day might inhibit the growth of
cancer cells in the body."
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- To determine what the active compound
was, Morre and her husband 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.
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- 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.
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- The Morres also found that EGCg inhibits
the growth of, and kills, cancerous human mammary cells in culture, but
does not kill cultured, non-cancerous human mammary cells.
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- "This is one of the first studies
to directly link the EGCg in green tea to anti-cancer activity," Dorothy
Morre says.
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- The Purdue team also determined how the
cancer cells died. "In the presence of EGCg, the cancer cells literally
failed to grow or enlarge after division," Dorothy Morre says. "Then,
presumably because they did not reach the minimum size needed to divide,
they underwent programmed cell death, or apoptosis."
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- Others who worked on the research are
Andrew Bridge, a premed student at Wabash College in Crawfordsville, Ind.;
Peichuan Sun, a graduate student supervised by Dorothy Morre; and Lian-Ying
Wu, a research technologist at Purdue.
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- Dorothy Morre says that further work
is needed to understand how tNOX works in cancer cell growth. "For
now, it is sufficient to know that when tNOX activity is inhibited, the
cancerous cells eventually die," she says.
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- Editor's Note: The original news release
can be found at <http://www.purdue.edu/UNS/html4ever/9901.Morre.greentea.htmlhttp://www.purdu
e. edu/UNS/html4ever/9901.Morre.greentea.html
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