Green Tea, Glycine May Slow Tumor Growth
Nov. 2, 2001 -- You've probably read that green tea appears to protect against cancer. You may even know that its anti-cancer properties are attributed to an abundance of chemicals called polyphenols. But new research may explain, for the first time, how those chemicals fight tumors at a molecular level.
Using prostate cancer cell lines, researchers from H. Lee Moffitt Cancer Center in Tampa, Fla., found that polyphenols in green tea, and black and red teas for that matter, target a protein known to protect cancer cells from death. The research, along with several other studies evaluating the anti-tumor properties of food components, was presented this week at an international conference in Miami Beach, Fla.
The amino acid glycine was found to reduce breast tumor growth in rats. Apparently, it blocks the growth of new blood vessels that feed tumors. Glycine is manufactured in the body, but is also commercially available as a dietary supplement.
"These are very preliminary studies, but they are quite interesting," American Association for Cancer Research (AACR) President Waun Ki Hong, MD, tells WebMD. He says that human studies are needed to verify the findings, but this may represent an important contribution to the research. AACR co-sponsored the annual meeting along with the National Cancer Institute and the European Organization for Research and Treatment of Cancer.
In the green tea research, Aslamuzzaman Kazi, PhD, and colleagues found that polyphenols reduced the level of Bcl-XL protein in prostate cancer cell lines. Bcl-XL has been shown to protect cancer cells from death -- known scientifically as apoptosis
"The higher the concentration [of polyphenols] the more apoptosis," Kazi tells WebMD. "Epidemiological studies have shown that tea has anticancer activities. We wanted to try to understand the molecular mechanism of this action."
Studies in humans have, in fact, been inconclusive regarding the role of tea in preventing or slowing cancers. While some have shown a clear protective benefit, others have not. The most recent large study, published last March in The New England Journal of Medicine, found that drinking green tea did not lower the risk of developing stomach cancer in a group of Japanese subjects.
In the glycine study, researcher Zishan Haroon, MD, PhD, and colleagues at Duke University Medical Center, found high levels of glycine reduced breast tumor growth rates by 15% in rats by blocking the growth of new tumor-feeding blood vessels. The special diet also reduced wound-healing by 30%, which, Haroon tells WebMD, explains glycine's effect on tumors.
"Tumors and wounds have one very important thing in common -- they both produce new blood vessels through the same mechanism, known as angiogenesis," he says. If you can block one response, you can block the other, he says.