|
Green Teas Cancer-Fighting Allure Becomes More Potent
Aug. 4,
2003 - Green tea's ability to fight cancer is even more potent and
varied than scientists suspected, say researchers who have discovered
that chemicals in green tea shut down one of the key molecules that
tobacco relies upon to cause cancer. It's a find that could help
explain why people who drink green tea are less likely to develop
cancer.
The
finding by scientists at the University of Rochester's Environmental
Health Science Center appears in the July 21 issue of Chemical
Research in Toxicology, published by the American Chemical Society.
Graduate
student Christine Palermo and adviser Thomas Gasiewicz, Ph.D., set out
to measure the effects of the chemicals found in green tea on a
molecule known as the aryl hydrocarbon (AH) receptor, a molecule that
frequently plays a role in turning on genes that are oftentimes
harmful. Gasiewicz has previously shown how both tobacco smoke and
dioxin manipulate the molecule a favorite target of toxic substances
to cause havoc within the body.
The team
isolated the chemicals that make up green tea and found two that
inhibit AH activity. The two substances, epigallocatechingallate (EGCG)
and epigallocatechin (EGC), are close molecular cousins to other
flavonoids found in broccoli, cabbage, grapes and red wine that are
known to help prevent cancer.
While
green tea has been much-ballyhooed for its anti-cancer effects as well
as other purported abilities such as preventing rheumatoid arthritis
and lowering cholesterol, just how the substance works has been a
mystery. Scientists do know that green tea contains chemicals that are
anti-oxidants and quench harmful molecules. But its effects on the AH
receptor have not been thoroughly evaluated until now.
"It's
likely that the compounds in green tea act through many different
pathways," says Gasiewicz, professor and chair of Environmental
Medicine and director of Rochester's Environmental Health Science
Center. "Green tea may work differently than we thought to exert its
anti-cancer activity."
Gasiewicz
and Palermo showed that the chemicals shut down the AH receptor in
cancerous mouse cells, and early results indicate the same is true in
human cells as well.
In the
laboratory the AH-inhibiting effects of green tea become evident when
EGCG and EGC reach levels typical of those found in a cup of green
tea. But the scientists say that how green tea is metabolized by the
body is crucial to its effectiveness, and that results in the
laboratory don't necessarily translate directly to the dinner table.
"Right now
we don't know if drinking the amount of green tea that a person
normally drinks would make a difference, but the work is giving us
insight into how the proteins work," says Palermo, who enjoys cold
green tea herself. "There are a lot of differences between various
kinds of green tea, so a lot more research is needed."
For this
work Palermo received the award for best poster in the chemical
carcinogenesis specialty section at the meeting of the Society of
Toxicology in March. Now she is studying exactly how green tea
inhibits the AH receptor. After she graduates Palermo plans to study
links between environmental agents and childhood leukemia.
In
addition to Palermo and Gasiewicz, other authors are former
post-doctoral associate Jose Martin Hernando and chemist Andrew Kende,
who teased apart the components of green tea extract; and Stephen
Dertinger, a former student who first had the idea to test green tea's
effects on the AH receptor. The work was funded by the National
Institute of Environmental Health Sciences and the American Institute
for Cancer Research.
|
