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Clinical Studies
References
Green tea may be helpful to improve cognitive performance as well as to treat stomach disorders, vomiting, diarrhea and headaches. It is used as a diuretic and in combination products for weight loss. Green tea may be beneficial in solid tumor cancers and to reduce the risk of breast cancer, prostate cancer, colon cancer and gastric cancer. It may be beneficial to maintain remission in people with Crohn's disease, to prevent Parkinson's disease and to protect against heart disease, dental caries and kidney stones.
Green tea is also used to prevent skin damage and cancer related to ultraviolet (UV) radiation (e.g. sunburn) and other environmental causes. Green tea is different than black teas because it is not fermented. Polyphenols such as gallic acid and catechins such as epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG) and epicatechin (EC), are abundant in green tea and are thought to be responsible for many of its proposed benefits.
Green tea also contains 2-4% caffeine or 10-80mg caffeine per cup. The caffeine in green tea acts as a central nervous system (CNS) stimulant; increases blood pressure, heart rate and contractility; inhibits platelet aggregation; stimulates gastric acid secretion; and causes diuresis. Caffeine content is also thought to be responsible for green tea's ability to improve cognitive performance.
Some preliminary studies show that flavonoids found in green tea might reduce lipoprotein oxidation. In vitro tests indicate that catechins in green tea reduce proliferation of vascular smooth muscle that occurs with high concentrations of low-density lipoproteins (LDL). There is some evidence that an unidentified compound in green tea and caffeine suppresses thromboxane formation during blood clotting by inhibiting the release of arachidonic acid from platelets. However, when used in humans green tea does not consistently exhibit useful effects on cardiovascular risk factors.
It is unclear exactly how green tea might reduce the risk of some cancers, but preliminary research suggests EGCG might prevent new blood vessel growth (angiogenesis) in tumors or inhibit tumor cell proliferation, causing cell cycle arrest or apoptosis. Green tea may also reduce oxidative DNA damage, lipid peroxidation and free radical generation, and might reduce mutagenic activity in smokers. Green tea is thought to be beneficial for preventing skin damage and cancer from ultraviolet (UV) radiation due to the antioxidant effects of polyphenols in green tea.
Green tea is also used for weight loss. Early evidence indicates that a green tea extract rich in EGCG can increase calorie and fat metabolism. Research has shown that green tea reduces the risk of developing stomach cancer by 50% and esophageal cancer by 6%.
Published Clinical Studiesclin
Anti-Trypanosoma cruzi activity of green tea (Camellia sinensis) catechins.1
Paveto C, Guida MC, Esteva MI, Martino V, Coussio J, Flawia MM, Torres HN.
Instituto de Investigaciones en Ingenieria Genetica y Biologia Molecular y Facultad de Ciencias Exactas y Naturales (CONICET-UBA), 1428 Buenos Aires, Argentina. cpaveto@dna.uba.ar
The trypanocidal action of green tea catechins against two different developmental stages of Trypanosoma cruzi is reported for the first time. This activity was assayed with the nonproliferative bloodstream trypomastigote and with the intracellular replicative amastigote parasite forms. An ethyl acetate fraction from Camellia sinensis green tea leaves, which contains most of the polyphenolic compounds and the maximal trypanocidal activity, was obtained by fractionation of the aqueous extract with organic solvents. The active compounds present in this extract were further purified by LH-20 column chromatography and were identified by high-performance liquid chromatography analysis with a photo diode array detector and gas chromatography coupled to mass spectroscopy. The following flavan-3-ols derivatives, known as catechins, were identified: catechin, epicatechin, gallocatechin, epigallocatechin, catechin gallate, epicatechin gallate, gallocatechin gallate, and epigallocatechin gallate. The purified compounds lysed more than 50% of the parasites present in the blood of infected BALB/c mice at concentrations as low as 0.12 to 85 pM. The most active compounds were gallocatechin gallate and epigallocatechin gallate, with minimal bactericidal concentrations that inhibited 50% of isolates tested of 0.12 and 0.53 pM, respectively. The number of amastigotes in infected Vero cells decreased by 50% in the presence of each of these compounds at 100 nM. The effects of the catechins on the recombinant T. cruzi arginine kinase, a key enzyme in the energy metabolism of the parasite, were assayed. The activity of this enzyme was inhibited by about 50% by nanomolar concentrations of catechin gallate or gallocatechin gallate, whereas the other members of the group were less effective. On the basis of these results, we suggest that these compounds could be used to sterilize blood and, eventually, as therapeutic agents for Chagas' disease.
PMID: 14693520 [PubMed - in process]
Induction of apoptosis by EGCG in selected tumour cell lines in vitro.2
Borska S, Gebarowska E, Wysocka T, Drag-Zalesinska M, Zabel M.
Department of Histology and Embryology, University Medical School, Wroclaw, Poland. borska@hist.am.wroc.pl
One of the best recognised polyphenols of plant origin, epigallocatechin-3-gallate (EGCG) is contained mainly in green tea and in grapes. Studies performed in vivo and in vitro have demonstrated high probability of anti-neoplastic potential of the compound, due to its capacity to induce programmed cell death. The present studies were aimed at evaluation of apoptosis induction in cells of three selected tumour cell lines, subjected to action of various concentrations of EGCG. The experiment was performed on cultures of HEp-2 laryngeal carcinoma cells, LoVo colon carcinoma cells, HeLa cervical carcinoma cells and on normal myoepithelial cell line, HS. EGCG was found to induce apoptosis in cells of the examined neoplastic lines in a dose-related manner. Moreover, effect of EGCG on normal cells of HS line was found to be much less pronounced as compared to effects exerted on sensitive neoplastic cells.
PMID: 14677763 [PubMed - in process]
4
Protective effects of green tea polyphenol against reactive oxygen species-induced oxidative stress in cultured rat calvarial osteoblast.
Park YH, Han DW, Suh H, Ryu GH, Hyon SH, Cho BK, Park JC.
Department of Medical Engineering, Cardiovascular Research Institute, Yonsei University College of Medicine Seoul, Korea.
The injurious effects of reactive oxygen species on osteoblasts and the potential protective role played by green tea polyphenols (GtPP) were investigated using primarily cultured rat calvarial osteoblasts. Oxidative stress was induced in cultured osteoblasts, either by adding 100 mmol/L H2O2 or by the action of 40 U/L xanthine oxidase (XO) in the presence of xanthine (250 micromol/L). After incubation, the cellular viability, function and morphology were evaluated. Both treatments produced a significant reduction in osteoblast viability, as assessed by a two-colored fluorescence staining method combined with flow cytometric analysis and MTT assay. A significant reduction in the alkaline phosphatase activity was observed after H2O2 addition, whereas XO did not have the same effect. On the microscopic observations, the morphological changes and intracellular ultrastructural damages were remarkably induced by both treatments. The H2O2-induced alterations were prevented by pre-incubating the osteoblasts with 200 microg/ml GtPP for 1 h. When the oxidative stress was induced by XO, the cellular viability and morphology was also maintained at the same polyphenol concentration. These results demonstrate that GtPP can act as a biological antioxidant in a cell culture experimental model and protect cells from oxidative stress-induced toxicity.
PMID: 14703119 [PubMed - in process]
5
Preservation of Human Saphenous Vein against Reactive Oxygen Species-induced Oxidative Stress by Green Tea Polyphenol Pretreatment.
Han DW, Suh H, Park YH, Cho BK, Hyon SH, Park JC.
Department of Medical Engineering and Cardiovascular Research Institute, Yonsei University College of Medicine, Seoul, Korea; and Institute for Frontier Medical Sciences, Kyoto University, Sakyo-ku, Kyoto, Japan.
The injurious effects of reactive oxygen species on venous tissues and the potential protective role played by green tea polyphenol (GTPP) on human saphenous veins were investigated. Oxidative stress was induced exogenously in the vein segments, either by adding 0.8 or 1.6 M of H2O2, or by using 80 or 160 U/L of xanthine oxidase in the presence of xanthine (0.5 mM). After incubation, the viability of the endothelial cells dissociated from veins and the histology of the veins were evaluated. Due to both types of treatment, a significant decrease in cellular viability, severe morphological changes in the veins, and extracellular structural damage were induced. The H2O2-induced alterations were prevented by preincubating the veins with either 0.5 or 1.0 mg/ml of GTPP for 1 h. When the oxidative stress was induced by xanthine oxidase, cellular viability and venous structure were preserved at the same polyphenol concentrations. These results demonstrate that GTPP can act as a biological antioxidant and protect veins from oxidative stress-induced toxicity.
PMID: 14678430 [PubMed - in process]
6
Radiation induced-tubulogenesis in endothelial cells is antagonized by the antiangiogenic properties of green tea polyphenol (-) epigallocatechin-3-gallate.
Annabi B, Lee YT, Martel C, Pilorget A, Bahary JP, Beliveau R.
Laboratoire de Medecine Moleculaire, Centre de Cancerologie Charles-Bruneau, Hopital Sainte-Justine and Universite du Quebec a Montreal, Montreal, Quebec, Canada; Department of Radiology, Hopital Notre-Dame-CHUM; Montreal, Quebec, Canada.
Radiation therapy is a widely-used option for the treatment of a variety of solid tumors. Although effective, ionizing radiation (IR) may give rise to various side effects, including secondary tumors. In agreement with this, recent reports have demonstrated increased invasive potential in different tumor-derived cell lines following radiation treatment. Many of the molecular effects of IR specifically on the endothelial cells involved in tumor neo-vascularization remain unknown. In this study, we found that low sublethal single doses of IR applied to human umbilical vein endothelial cells stimulated cell migration and in vitro tubulogenesis. This correlated with an increase in membrane type-1 matrix metalloproteinase (MT1-MMP) protein expression, a crucial enzyme that promotes endothelial cell migration and tube formation, and of caveolin-1, a protein that regulates tube formation. Cell adhesion was also promoted by IR, reflected in increased gene expression levels of cell surface beta(3) integrin. Pretreatment of the cells with epigallocatechin-3-gallate (EGCg), a green tea catechin that possesses anti-angiogenic properties, prevented most of the IR-induced cellular and molecular events. These observations suggest that current protocols involving radiation therapy for the treatment of cancer can paradoxically promote angiogenesis, but can be improved by combination with anti-angiogenic molecules such as EGCg to target those tumor-derived endothelial cells that escaped IR-induced apoptosis.
PMID: 14688468 [PubMed - in process]
7
Cancer prevention by tea polyphenols is linked to their direct inhibition of antiapoptotic Bcl-2-family proteins.
Leone M, Zhai D, Sareth S, Kitada S, Reed JC, Pellecchia M.
The Burnham Institute, La Jolla, California 92037, USA.
Epidemiological data and in vitro studies on cancer chemoprevention by tea polyphenols have gained attention recently from the scientific community, nutritionists, the pharmaceutical industry, and the public. Despite the several efforts made recently to elucidate the molecular basis for the anticancer activity of these natural products, little correlation has been found thus far between the putative protein targets of compounds found in tea extracts and levels found in plasma after tea consumption. Here, by using a combination of nuclear magnetic resonance binding assays, fluorescence polarization assay, and computational docking studies, we found that certain green tea catechins and black tea theaflavins are very potent inhibitors (K(i) in the nanomolar range) of the antiapoptotic Bcl-2-family proteins, Bcl-x(L) and Bcl-2. These data suggest a strong link between the anticancer activities of these tea polyphenols and their inhibition of a crucial antiapoptotic pathway, which is implicated in the development of many human malignancies.
PMID: 14678963 [PubMed - in process]
8
Multiple effects of green tea catechin on the antifungal activity of antimycotics against Candida albicans.
Hirasawa M, Takada K.
Department of Microbiology, Nihon University School of Dentistry at Matsudo, 2-870-1 Sakaecho-nishi, Matsudo City, Chiba 271-8587, Japan.
OBJECTIVES: The susceptibility of Candida albicans to catechin under varying pH conditions and the synergism of the combination of catechin and antimycotics were evaluated. Method: Antifungal activity was determined by broth dilution and calculation of cfu. RESULTS: The antifungal activity of catechin was pH dependent. The concentration of epigallocatechin gallate (EGCg) causing 90% growth inhibition of tested strains of C. albicans was 2000 mg/L at pH 6.0, 500-1000 mg/L at pH 6.5 and 15.6-250 mg/L at pH 7.0. Among catechins, pyrogallol catechin showed stronger antifungal activity against C. albicans than catechol catechin. The addition of 6.25-25 or 3.12-12.5 mg/L EGCg to amphotericin B 0.125 or 0.25 mg/L (below MIC) at pH 7.0 resulted in enhancement, respectively, of the antifungal effect of amphotericin B against amphotericin B-susceptible or -resistant C. albicans. Combined treatment with 3.12-12.5 mg/L EGCg plus amphotericin B 0.5 mg/L (below MIC) markedly decreased the growth of amphotericin B-resistant C. albicans. When fluconazole-susceptible C. albicans was treated with 25-50 mg/L EGCg and fluconazole 0.125-0.25 mg/L (below MIC), its growth was inhibited by 93.0%-99.4% compared with its growth in the presence of fluconazole alone. The combined use of 12.5 mg/L EGCg and fluconazole 10-50 mg/L (below MIC) inhibited the growth of fluconazole-resistant C. albicans by 98.5%-99.7%. CONCLUSIONS: These results indicate that EGCg enhances the antifungal effect of amphotericin B or fluconazole against antimycotic-susceptible and -resistant C. albicans. Combined treatment with catechin allows the use of lower doses of antimycotics and induces multiple antifungal effects. It is hoped that this may help to avoid the side effects of antimycotics.
PMID: 14688042 [PubMed - as supplied by publisher]
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