The in vitro study, published in Phytomedicine, confirmed that post-digestion, extracts of the phytochemical rich drink shows protective effects for dementia, and could play an important role in protecting the body against cancer.
The researchers investigated whether the protective properties of green tea – which have previously been shown to be present in the undigested, freshly brewed form of the drink – were still ‘active’ once the drink had been digested.
Lead researcher Dr Ed Okello from Newcastle University, U.K.said that just because a consumed food is generally accepted to contain health-boosting properties; it should not be assumed that such compounds will ever be absorbed in the body.
“What was really exciting about this study was that we found when green tea is digested by enzymes in the gut, the resulting chemicals are actually more effective against key triggers of Alzheimer's development than the undigested form of the tea,” explained Okello
“In addition to this, we also found the digested compounds had anti-cancer properties, significantly slowing down the growth of the tumour cells which we were using in our experiments,” added Okello.
Alzheimer's disease – the most common form of dementia – is a progressive and irreversible neurodegenerative disorder associated with cognitive dysfunction.
The authors noted that “mounting evidence” suggests that beta-amyloid peptides in conjunction with free radical species (such as hydrogen peroxide) in the brain play a significant role in the development and pathogenesis of Alzheimer's.
Many previous studies, have suggested that both black and green teas possess protective properties, which have been mainly attributed to their polyphenol content.
Green tea is high in flavan-3-ols, which are believed to be efficient scavengers of highly reactive free radical species, and have been shown to exhibit anti-carcinogenic; hypocholesterolaemic and neuroprotective properties in previous research.
Okello said that although research has identified certain compounds as beneficial for health, and in many cases has identified foods with high concentrations of such compounds, he explained that “what happens during the digestion process is crucial to whether these foods are actually doing us any good.”
“Flavan-3-ols have been reported to possess properties beneficial to health, [but] they are known to undergo significant metabolism and conjugation in the gastrointestinal tract,” said the researchers.
“It is unknown how such metabolism and conjugation may influence the putative properties of these polyphenols, hence the focus of our study on a digested green tea extract,” they explained.
Green tea extract – from brewed Temple of Heaven, Gunpowder China tea, purchased by the researchers from a local store – was subjected to a simulated gastrointestinal digestion and a ‘colon-available’ extract (CAGTE) was prepared and assessed for its potential protective effects against the damaging effects of hydrogen peroxide and beta-amyloid on neuronal cells in the brain – which are believed to play a role in the development of dementia.
The CAGTE, which represents green tea phytochemicals potentially available after upper gastrointestinal digestion, was found to be depleted in flavan-3-ols when compared to the pre-digested green tea extract; yet was still found to protect cells in a brain neurone model from both hydrogen peroxide and beta-amyloid toxicity.
“At high concentrations, CAGTE exhibited direct anti-proliferative effects, in line with the reputed anti-cancer properties of green tea polyphenols,” wrote the authors.
“The CAGTE, which effectively lacked flavan-3-ols, had a protective effect on beta-amyloid induced toxicity in vitro at 0.03–0.125 μg/ml … This figure is much lower than the 20 μg/ml reported for effective protection in whole green tea extracts,” said the researchers.
“Green tea has been used in Traditional Chinese medicine for centuries and what we have here provides the scientific evidence why it may be effective against some of the key diseases we face today,” said Okello.
He said that the next step in the research is to investigate whether the beneficial compounds found in the digestion model are produced during digestion in human volunteers that consume green tea polyphenols – for which the team has already secured funding from the Biotechnology and Biological Sciences Research Council (BBSRC).
Published online ahead of print, doi: 10.1016/j.phymed.2010.11.004
“In vitro protective effects of colon-available extract of Camellia sinensis (tea) against hydrogen peroxide and beta-amyloid (Aβ(1–42)) induced cytotoxicity in differentiated PC12 cells”
Authors: E.J. Okello, G.J. McDougall, S. Kumar, C.J. Seal