Abstract: Green tea is manufactured from the leaves of the plant Camellia sinensis Theaceae and has been regarded to possess anti-cancer, anti-obesity, anti-atherosclerotic, anti-diabetic, anti-bacterial, and anti-viral effects. Many of the beneficial effects of green tea are related to the activities of (−)-epigallocatechin gallate (EGCG), a major component of green tea catechins. For about 20 years, we have engaged in studies to reveal the biological activities and action mechanisms of green tea and EGCG. This review summarizes several lines of evidence to indicate the health-promoting properties of green tea mainly based on our own experimental findings.
Introduction: Green tea (Camellia sinensis Theaceae) was discovered in China in 3000 BC or earlier and has been known to have various medical effects.1) It was brought to Japan from China by Buddhist priests over a thousand years ago. In 1211, a Japanese Zen priest, Yeisai, published the book “Kitcha-Yojoki” (Tea and Health Promotion) in which the methodology of harvesting tea leaves, production processes for tea, and pharmacological effects were described. Nowadays, scientific evidence indicates that green tea is indeed beneficial to health and many of the components of tea have specific health-promoting effects.1–12) For example, tea catechins, especially (−)-epigallocatechin gallate (EGCG), are considered to be associated with the anti-cancer, anti-obesity, anti-atherosclerotic, anti-diabetic, anti-bacterial, anti-viral, and anti-dental caries effects of tea. Caffeine stimulates wakefulness, decreases the sensation of fatigue, and has a diuretic effect. Theanine and γ-aminobutyric acid act to lower blood pressure and regulate brain and nerve functions. Vitamin C is an anti-scorbutic, prevents cataracts, and strengthens the immune system.
Other effects: It was shown that EGCG suppressed experimental autoimmune encephalomyelitis induced by proteolipid protein 139–151 in mice.94) EGCG reduced clinical severity when given at initiation or after the onset of encephalomyelitis by both limiting brain inflammation and reducing neuronal damage. Mice given EGCG orally showed abrogated proliferation and TNF-α production in encephalitogenic T cells. Proposed models for signal transduction pathways modified by EGCG include: EGCG is capable of inhibiting both catalytic activities of the proteasome, including the activation of NF-κB, and the amount of ROS produced. In lymphocytes, this leads to decreased proliferation and production of TNF-α, while in neurons, it results in less damage. Additionally, the antioxidative effects of EGCG on neurons might involve the NF-κB pathway as well, since an oxidative stress can induce production of NF-κB, which regulates the expression of a variety of factors contributing to cell proliferation, inflammation, and neuronal damage. Thus, a natural green tea constituent may open up a new therapeutic avenue for young disabled adults with inflammatory brain disease by combining, on the one hand, anti-inflammatory and, on the other, neuroprotective capacities.
Theanine and γ-aminobutyric acid are also characteristic components of green tea. Using an in vivobrain microdialysis method, Yamada et al.102) demonstrated that theanine affects the release of neurotransmitters in the rat striatum. Recently, theanine was reported to enhance the synthesis of nerve growth factor and neurotransmitters during a nerve maturing period and promote maturation of the central nervous system.103) Electroencephalograms of volunteers who received 200 mg of theanine revealed the generation of α wave activity suggesting relaxation. γ-Aminobutyric acid is perhaps the most important inhibitory neurotransmitter in the brain, and its intake will affect brain functions. Thus, effects on brain function are a very important target for future investigations of green tea.
Conclusion: Modern scientific techniques have given the basis for the health-promoting effects of green tea, which have been recognized from ancient times. Many of the action mechanisms of green tea and its constituent EGCG are now known. For example, EGCG binds several enzyme proteins to inhibit their activities, induces oxidative stress in cells, and initiate signal transduction by binding to cell surface proteins. Our recent studies revealed that green tea and EGCG may cause changes in the mRNA levels of gluconeogenic and lipogenic enzymes by changing the expression levels of the respective transcription factors, HNFs and SREBFs. However, these findings pose new questions on the mechanism of how green tea and its constituents can induce changes in the level of the transcription factors. In addition, we demonstrated that an EGCG-free fraction of green tea had certain health-promoting effects, but the active entity remains to be determined. Although these and other questions await future investigations, epidemiological studies seem to indicate that ingestion of green tea contributes to human health-promotion. Future clinical intervention studies will provide more convincing evidence for effects of green tea.
Article originally published on March 9th, 2012 by the National Center for Biotechnology Information. To view the full study, conducted by the Proceeding of the Japan Academy, Series B Physical and Biological Sciences, please visit the NCBI site – http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3365247/