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Green Tea Suppresses Inflammatory Autoimmune Response
A compound found in green tea appears to reduce the inflammatory responses associated with autoimmune diseases, say researchers from the Medical College of Georgia in the journal Autoimmunity.
The researchers have been working with animals modeling primary Sjogren's syndrome (also known as dry mouth), which damages the glands that produce tears and saliva. While around 30 percent of elderly Americans suffer from dry mouth, only around 5 percent of elderly people in China do. Dry mouth is also seen in patients undergoing radiation treatment.
Sjogren's syndrome causes the body to attack itself and produce extra antibodies that mistakenly target the salivary and lacrimal glands. In his study, researcher Stephen Hsu found significantly less salivary gland damage in a group of animals treated with green tea extract.
Hsu explained that the animals treated with green tea had significantly lower levels of autoantibodies, protein "weapons" produced when the immune system attacks itself. "The salivary gland cells treated with EGCG [a component of green tea] had much fewer signs of cell death caused by TNF-alpha [a group of proteins involved in inflammation]," said Hsu. "We don't yet know exactly how EGCG makes that happen. That will require further study. In some ways, this study gives us more questions than answers."
Hsu speculates that the EGCG in green tea can turn on the body's defense system against TNF-alpha. Further study could help determine green tea's protective role in other autoimmune diseases, including lupus, psoriasis, scleroderma and rheumatoid arthritis
New Theory On Green Tea’s Medicinal Properties
Scientists have for some time been puzzled about the lower incidence of cardiovascular disease and cancer in Asian countries where the population smokes heavily. A preventative effect from green tea has been thought to be responsible and now a new study from Yale has found what could be the key chemical component.
"We do not yet have a full explanation for the 'Asian paradox', which refers to the very low incidence of both heart disease and cancer in Asia, even though consumption of cigarettes is greater than in most other countries," said Yale's Bauer Sumpio, "but we now have some theories."
According to Sumpio, writing in the Journal of the American College of Surgeons, the average 1.2 liters of green tea consumed daily by many people in Asia offers the anti-oxidant protective effects of the polyphenolic epigallocatechin-3-gallate (EGCG). Sumpio said that EGCG may prevent LDL oxidation, which has been shown to play a key role in the pathophysiology of arteriosclerosis. EGCG also reduces the amount of platelet aggregation, regulates lipids, and promotes proliferation and migration of smooth muscle cells, which are all factors in reducing cardiovascular disease. Sumpio added that other reports show that EGCG prevents growth of certain tumors.
"More studies are necessary to fully elucidate and better understand green tea's method of action, particularly at the cellular level," Sumpio concluded. "The evidence is strong that green tea consumption is a useful dietary habit to lower the risk for, as well as treat, a number of chronic diseases."
Source: Yale University
How Green Tea Prevents Cancer
Purdue University researchers Dorothy Morre and D. James Morre 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. The findings offer the first scientific evidence to explain precisely how this compound works within a cell to ward off cancer. The results were presented this month at the 38th annual meeting of the American Society for Cell Biology in San Francisco.
"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 at Purdue.
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.
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.
Morre and her husband, who is the Dow Distinguished Professor of Medicinal Chemistry and Molecular Pharmacology at Purdue, show in their 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.
"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.
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.
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.
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," 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."
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.
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.
"This is one of the first studies to directly link the EGCg in green tea to anti-cancer activity," Dorothy Morre says. "In the presence of EGCg, the cancer cells literally failed to grow or enlarge after division. Then, presumably because they did not reach the minimum size needed to divide, they underwent programmed cell death, or apoptosis
by Kate Melville