Green Tea Antioxidant

According to Dr. Tariq M. Haqqi, an expert on Greet Tea and associate professor of medicine at Case Western Reserve University, "many polyphenols in green tea possess much more potent antioxidant activity than well-known antioxidants such as vitamin C and vitamin E." The main antioxidant found in green tea called epigallocatechin gallate, or EGCG is at least 100 times more effective than vitamin C and 25 times better than vitamin E at protecting cells and their genetic material, DNA, from damage believed to be linked to cancer, heart disease and other potentially life-threatening illnesses, according to research conducted at Kansas University. This was believed to be the first research that actually quantify the effectiveness of green tea's disease-fighting capabilities and compared it with other popular antioxidants.

Abstracts of Research proving
Green Tea's Antioxidant Capability

Green tea metabolite EGCG protects membranes against oxidative damage in vitro.

Life Sci. 2004 Feb 6;74(12):1513-8.

Saffari Y, Sadrzadeh SM.

Department of Laboratory Medicine, University of Washington, Harborview Medical Center, 325 9th Avenue, Seattle, WA 98104, USA.

Green tea polyphenols like epigallocatechin gallate (EGCG) have been proposed as a cancer chemopreventative. Several studies have shown that EGCG can act as an antioxidant by trapping proxyl radicals and inhibiting lipid peroxidation. The main propose of this study is to investigate the antioxidant capacity of EGCG using erythrocyte membrane-bound ATPases as a model. The effects of EGCG on t-butylhydroperoxide-induced lipid peroxidation and the activity of membrane-bound ATPases in human erythrocyte membranes were studied. The extent of oxidative damage in membranes was assessed by measuring lipid peroxidation, (TBARS, thiobarbituric acid reactive substances formation) and the activity of ATPases (Na(+)/K(+), Ca(2+), and CaM-activated Ca(2+) pump ATPases). EGCG blocked t-BHP induced lipid peroxidation in erythrocyte membranes, significantly (0.45 +/- 0.02 vs 0.20 +/- 0.01; t-BHP vs t-BHP + EGCG respectively, microm/L TBARS) (p < 0.05). EGCG also protected ATPases against t-BHP induced damage; for Na/K ATPase (2.4 +/- 0.2 vs 1.6 +/- 0.1 vs 2.44 +/- 0.2, nmol Pi/min/mg protein, control vs t-BHP vs t-BHP and EGCG respectively), for Ca ATPase (5.8 +/- 0.4 vs 3.9 +/- 0.3 vs 5.6 +/- 0.34, nmol Pi/min/mg protein, control vs t-BHP vs t-BHP and EGCG respectively) and for CaM-Ca ATPase (14.7 +/- 0.7 vs 7.3 +/- 0.4 vs 11.6 +/- 0.55, nmol Pi/min/mg protein, control vs t-BHP vs t-BHP and EGCG respectively) (p < 0.05). In conclusion our results indicate that EGCG is a powerful antioxidant that is capable protecting erythrocyte membrane-bound ATPases against oxidative stress.

PMID: 14729400 [PubMed - in process]

Green tea metabolite EGCG protects membranes against oxidative damage in vitro.

Life Sci. 2004 Feb 6;74(12):1513-8.

Saffari Y, Sadrzadeh SM.

Department of Laboratory Medicine, University of Washington, Harborview Medical Center, 325 9th Avenue, Seattle, WA 98104, USA.

Green tea polyphenols like epigallocatechin gallate (EGCG) have been proposed as a cancer chemopreventative. Several studies have shown that EGCG can act as an antioxidant by trapping proxyl radicals and inhibiting lipid peroxidation. The main propose of this study is to investigate the antioxidant capacity of EGCG using erythrocyte membrane-bound ATPases as a model. The effects of EGCG on t-butylhydroperoxide-induced lipid peroxidation and the activity of membrane-bound ATPases in human erythrocyte membranes were studied. The extent of oxidative damage in membranes was assessed by measuring lipid peroxidation, (TBARS, thiobarbituric acid reactive substances formation) and the activity of ATPases (Na(+)/K(+), Ca(2+), and CaM-activated Ca(2+) pump ATPases). EGCG blocked t-BHP induced lipid peroxidation in erythrocyte membranes, significantly (0.45 +/- 0.02 vs 0.20 +/- 0.01; t-BHP vs t-BHP + EGCG respectively, microm/L TBARS) (p < 0.05). EGCG also protected ATPases against t-BHP induced damage; for Na/K ATPase (2.4 +/- 0.2 vs 1.6 +/- 0.1 vs 2.44 +/- 0.2, nmol Pi/min/mg protein, control vs t-BHP vs t-BHP and EGCG respectively), for Ca ATPase (5.8 +/- 0.4 vs 3.9 +/- 0.3 vs 5.6 +/- 0.34, nmol Pi/min/mg protein, control vs t-BHP vs t-BHP and EGCG respectively) and for CaM-Ca ATPase (14.7 +/- 0.7 vs 7.3 +/- 0.4 vs 11.6 +/- 0.55, nmol Pi/min/mg protein, control vs t-BHP vs t-BHP and EGCG respectively) (p < 0.05). In conclusion our results indicate that EGCG is a powerful antioxidant that is capable protecting erythrocyte membrane-bound ATPases against oxidative stress.

PMID: 14729400 [PubMed - in process]

Antioxidative activities of volatile extracts from green tea, oolong tea, and black tea.

J Agric Food Chem. 2003 Dec 3;51(25):7396-401.

Yanagimoto K, Ochi H, Lee KG, Shibamoto T.

Department of Environmental Toxicology, University of California, Davis, California 95616.

Antioxidative activities of volatile extracts from six teas (one green tea, one oolong tea, one roasted green tea, and three black teas) were investigated using an aldehyde/carboxylic acid assay and a conjugated diene assay. The samples were tested at levels of 20, 50, 100, and 200 micrograms/mL of dichloromethane. The results obtained from the two assays were consistent. All extracts except roasted green tea exhibited dose-dependent inhibitory activity in the aldehyde/carboxylic acid assay. A volatile extract from green tea exhibited the most potent activity in both assays among the six extracts. It inhibited hexanal oxidation by almost 100% over 40 days at the level of 200 micrograms/mL. The extract from oolong tea inhibited hexanal oxidation by 50% in 15 days. In the case of the extract from roasted green tea, the lowest antioxidative activity was obtained at the level of 200 micrograms/mL, suggesting that the extract from roasted green tea contained some pro-oxidants. The extracts from the three black teas showed slight anti- or proactivities in both assays. The major volatile constituents of green tea and roasted green tea extracts, which exhibited significant antioxidative activities, were analyzed using gas chromatography-mass spectrometry. The major volatile chemicals with possible antioxidative activity identified were alkyl compounds with double bond(s), such as 3,7-dimethyl-1,6-octadien-3-ol (8.04 mg/kg), in the extract from green tea and heterocyclic compounds, such as furfural (7.67 mg/kg), in the extract from roasted green tea. Benzyl alcohol, which was proved to be an antioxidant, was identified both in a green tea extract (4.67 mg/kg) and in a roasted tea extract (1.35 mg/kg).

PMID: 14640590 [PubMed - indexed for MEDLINE]

Antioxidant effects of tea: evidence from human clinical trials.

J Nutr. 2003 Oct;133(10):3285S-3292S.

Rietveld A, Wiseman S.

Unilever Health Institute, Unilever Research and Development, Vlaardingen, The Netherlands. anton.rietveld@unilever.com

Tea remains the most consumed drink in the world after water, well ahead of coffee, beer, wine and carbonated soft drinks. An accumulated number of population studies suggests that consumption of green and black tea beverages may bring positive health effects (1). One hypothesis explaining such effects is that the high levels of flavonoids in tea can protect cells and tissues from oxidative damage by scavenging oxygen-free radicals. Chemically, the flavonoids found in green and black tea are very effective radical scavengers. The tea flavonoids may therefore be active as antioxidants in the digestive tract or in other tissues after uptake. A substantial number of human intervention studies with green and black tea demonstrates a significant increase in plasma antioxidant capacity in humans approximately 1 h after consumption of moderate amounts of tea (1-6 cups/d). There are initial indications that the enhanced blood antioxidant potential leads to reduced oxidative damage to macromolecules such as DNA and lipids. However, the measurement of oxidative damage through biomarkers needs to be further established. In conclusion, tea flavonoids are potent antioxidants that are absorbed from the gut after consumption. Tea consumption consistently leads to a significant increase in the antioxidant capacity of the blood. Beneficial effects of increased antioxidant capacity in the body may be the reduction of oxidative damage to important biomolecules. The scientific support is strongest for the protection of DNA from oxidative damage after black or green tea consumption. However, the quality of the studies now available is insufficient to draw firm conclusions. Therefore, further evidence from human intervention studies is required.

PMID: 14519827 [PubMed - indexed for MEDLINE]

Tea catechins and polyphenols: health effects, metabolism, and antioxidant functions.

Crit Rev Food Sci Nutr. 2003;43(1):89-143.

Higdon JV, Frei B.

Linus Pauling Institute, Oregon State University, Corvallis, OR 97331, USA.

Increasing interest in the health benefits of tea has led to the inclusion of tea extracts in dietary supplements and functional foods. However, epidemiologic evidence regarding the effects of tea consumption on cancer and cardiovascular disease risk is conflicting. While tea contains a number of bioactive chemicals, it is particularly rich in catechins, of which epigallocatechin gallate (EGCG) is the most abundant. Catechins and their derivatives are thought to contribute to the beneficial effects ascribed to tea. Tea catechins and polyphenols are effective scavengers of reactive oxygen species in vitro and may also function indirectly as antioxidants through their effects on transcription factors and enzyme activities. The fact that catechins are rapidly and extensively metabolized emphasizes the importance of demonstrating their antioxidant activity in vivo. In humans, modest transient increases in plasma antioxidant capacity have been demonstrated following the consumption of tea and green tea catechins. The effects of tea and green tea catechins on biomarkers of oxidative stress, especially oxidative DNA damage, appear very promising in animal models, but data on biomarkers of in vivo oxidative stress in humans are limited. Larger human studies examining the effects of tea and tea catechin intake on biomarkers of oxidative damage to lipids, proteins, and DNA are needed.

PMID: 12587987 [PubMed - indexed for MEDLINE]

Protective effect of green tea polyphenol (-)-epigallocatechin gallate and other antioxidants on lipid peroxidation in gerbil brain homogenates.

Phytother Res. 2003 Mar;17(3):206-9.

Lee SR, Im KJ, Suh SI, Jung JG.

Department of Pharmacology, School of Medicine and Brain Research Institute, Keimyung University, Taegu, South Korea. srlee@dsmc.or.kr

The aim of this study was to compare the protective effects of green tea polyphenol (-)-epigallocatechin gallate (EGCG) and other well-known antioxidants on the lipid peroxidation in gerbil brain homogenates. Oxidative stress was induced by H2O2 (10 mM) or ferrous ammonium sulfate (5 microM) and lipid peroxidation was studied. Hydrogen peroxide and ferrous ions are capable of oxidizing a wide range of substrates and causing biological damage. The reaction, referred to as the Fenton process, is complex and can generate both hydroxyl radicals and higher oxidation states of the iron. Thiobarbituric acid-reactive substances (TBA-RS) were used as a marker of lipid peroxidation. EGCG, trolox, lipoic acid, and melatonin reduced H2O2- or ferrous ion-induced lipid peroxidation in a concentration-dependent manner. In reducing the H2O2-induced lipid peroxidation, IC50 values of antioxidants were as follows: EGCG (0.66 microM), trolox (37.08 microM), lipoic acid (7.88 mM), and melatonin (19.11 mM). In reducing the ferrous ion-induced lipid peroxidation, IC50 values of antioxidants were as follows: EGCG (3.32 microM), trolox (75.65 microM), lipoic acid (7.63 mM), and melatonin (15.48 mM). Under the in vitro conditions of this experiment, EGCG was the most potent antioxidant in inhibiting H2O2 or ferrous ion-induced lipid peroxidation in the gerbil brain homogenates. Copyright 2003 John Wiley & Sons, Ltd.

PMID: 12672147 [PubMed - indexed for MEDLINE]

Antioxidant activity of tea polyphenols in vivo: evidence from animal studies.

J Nutr. 2003 Oct;133(10):3275S-84S.

Frei B, Higdon JV.

Linus Pauling Institute, Oregon State University, Corvallis, OR 97331, USA. Balz.Frei@oregonstate.edu

Tea is particularly rich in polyphenols, including catechins, theaflavins and thearubigins, which are thought to contribute to the health benefits of tea. Tea polyphenols act as antioxidants in vitro by scavenging reactive oxygen and nitrogen species and chelating redox-active transition metal ions. They may also function indirectly as antioxidants through 1) inhibition of the redox-sensitive transcription factors, nuclear factor-kappaB and activator protein-1; 2) inhibition of "pro-oxidant" enzymes, such as inducible nitric oxide synthase, lipoxygenases, cyclooxygenases and xanthine oxidase; and 3) induction of phase II and antioxidant enzymes, such as glutathione S-transferases and superoxide dismutases. The fact that catechins are rapidly and extensively metabolized emphasizes the importance of demonstrating their antioxidant activity in vivo. Animal studies offer a unique opportunity to assess the contribution of the antioxidant properties of tea and tea polyphenols to the physiological effects of tea administration in different models of oxidative stress. Most promising are the consistent findings in animal models of skin, lung, colon, liver and pancreatic cancer that tea and tea polyphenol administration inhibit carcinogen-induced increases in the oxidized DNA base, 8-hydroxy-2'-deoxyguanosine. In animal models of atherosclerosis, green and black tea administration has resulted in modest improvements in the resistance of lipoproteins to ex vivo oxidation, although limited data suggest that green tea or green tea catechins inhibit atherogenesis. To determine whether tea polyphenols act as effective antioxidants in vivo, future studies in animals and humans should employ sensitive and specific biomarkers of oxidative damage to lipids, proteins and DNA.

PMID: 14519826 [PubMed - indexed for MEDLINE]