New research provides more evidence to back green tea's anti-cancer effects in humans. The tea's active agent Epigallocatecin-3-gallate, already thought to lower cholesterol, prevent heart disease, fight bacteria and dental cavities, and possibly aid weight loss, may also slow tumour growth in breast and liver cancers, suggests research presented this week.
"Laboratory studies have suggested that green tea consumption may produce many health benefits, including the prevention of cancer, but the beneficial effects in humans are not clearly known," said Dr CS Yang from Rutgers University, N.J at this week's Frontiers in Cancer Prevention Research meeting in the US.
"Research is now showing how this novel chemopreventive agent might work at the molecular level and in the human population," he added. Green tea polyphenols (GTP), highly effective agents in inhibiting a variety of cancer-induced tumours in different models, may be valuable in preventing and helping the early detection of liver cancer, suggested researchers from the Texas Tech University System. The team reported on recent research showing how GTP reduced the risk factors represented by two biomarkers for liver cancer, aflatoxin markers and urinary excretion of 8-hydroxydeoxyguanosine (8-OHdG).
The study involved 124 people aged 20 to 55, who tested positive for both hepatitis-B surface antigen and aflatoxin-albumin adducts. Aflatoxin is a naturally occurring poisonous substance produced by mold that can be found in blood serum, plasma or urine (albumin).They were randomly divided into three groups and treated daily with either low-dose GTP (500 mg), high-dose GTP (1,000 mg) or placebo for three months.
In the first arm of the study, urine samples were collected at day 0, one month and three months to assess urinary 8-OHdG and GTP biomarkers. After one month, EGC had increased 1.7-fold in both treated groups. EC increased 2.2-fold in the low-dose group and 3.5-fold in the high-dose group. Samples collected at three months showed similar patterns.
Levels of 8-OHdG at baseline were comparable for all three groups and did not show obvious changes at one month. But at three months, 8-OHdG was greatly reduced in GTP-treated groups, as compared to that in the placebo group. The results suggest that urinary EGC and EC are good biomarkers for GTP intake, and GTP treatment reduces urinary excretion of 8-OHdG.
In the second arm of the study, blood and urine samples were collected at day 0, one month and three months to assess AF (aflatoxin) biomarkers. Levels of AF-albumin adduct at baseline were comparable for all three groups. Sample levels collected at one month were significantly decreased in the high-dose group, as compared with the placebo group. At three months, the levels of AF-albumin adduct were significantly decreased in the low-dose and high-dose groups, as compared with the baseline levels.
"These results demonstrate that green tea polyphenol treatment effectively inhibits phase I enzyme activities and enhances the phase II enzyme activities," said Dr Jia-Sheng Wang, lead investigator of the study.
"At the same time, we see the value of green tea polyphenols in reducing excretion of 8-OHdG. All of this is good news for the prevention and early detection of liver cancer," he added.
Further research on green tea revealed at the meeting describes the methods to produce analogs for epigallocatchin-3-gallate (EGCG), the most abundant and active chemopreventive agent in green tea. Although associated with reduced risk of breast, pancreatic, colon, esophageal and lung cancers in humans, EGCG's low oral bioavailability means that individuals would need drink at least seven to eight cups of tea a day, or ingest large amounts of green tea polyphenol extract, to see any benefits.
Researchers from California-based SRI International have successfully synthesised several EGCG analogs that inhibit the in vitro growth of tumour cell lines with potencies equal to or greater than EGCG itself.
The investigators developed a chemical synthesis of cis racemic EGCG that allows them to modify the A-, B- and D-rings of EGCG independently of each other. Using this method, they created several different analogs (a chemical compound structurally similar, but different in composition).
SR 13196, an analog modified in the B- and D-rings, displays significantly more potent growth inhibition of breast cancer cell lines when compared to EGCG. SR 13193, an analog modified in the D-ring, inhibits expression of the potent angiogenic factor VEGF (vascular endothelial growth factor) in breast cancer cells, similar to EGCG.
"These analogs are not only valuable tools to clarify how green tea may fight cancer, but are also potential chemopreventive drug candidates themselves, with perhaps better pharmacokinetic properties than have been seen with EGCG thus far," said SRI's Dr Nurulain Zaveri, lead author of the study.
Researchers from the Arizona Cancer Center in Tucson also discussed their study showing how green tea can help prevent the DNA damage caused by smoking. The research was recently presented at the Third International Scientific Symposium on Tea and Human Health.
While scientists continue to research how green tea can prevent human disease, the continuing stream of good news linked to the beverage has led food makers to include green tea flavours and extracts in a growing number of foods.