Epigallocatechins

Chemical Antioxidant Systems. The antioxidant activity of tea extracts and tea polyphenols have been determined using in vitro model systems which are based on hydroxyl-, peroxyl-, superoxide-, hydrogen peroxide-, and oxygen-induced oxidation reactions (109—113). The effectiveness of purified tea polyphenols and cmde tea extracts as antioxidants against the autoxidation of fats has been studied using the standard Rancimat system, an assay based on air oxidation of fats or oils. A direct correlation between the antioxidant index of a tea extract and the concentration of epigallocatechin gallate in the extract was found (107). 

The total antioxidant activity of teas and tea polyphenols in aqueous phase oxidation reactions has been deterrnined using an assay based on oxidation of 2,2 -azinobis-(3-ethylbenzothiazoline-sulfonate) (ABTS) by peroxyl radicals (114—117). Black and green tea extracts (2500 ppm) were found to be 8—12 times more effective antioxidants than a 1-mAf solution of the water-soluble form of vitamin E, Trolox. The most potent antioxidants of the tea flavonoids were found to be epicatechin gallate and epigallocatechin gallate. A 1-mAf solution of these flavanols were found respectively to be 4.9 and 4.8 times more potent than a 1-mAf solution of Trolox in scavenging an ABT radical cation. 

HU G, HAN c and chen j (1995) Inhibition of oncogene expression by green tea and (-)-epigallocatechin gallate in mice Nutrition and Cancer 24, 203-9. 

COPLAND E L, CLIFFORD M N and WILLIAMS c M (1998) Preparation of (-)-epigallocatechin gallate from commercial green tea by caffeine precipitation and solvent partition . Food Chem, 61, 81-7. 

D s (1996) Prevention of photocarcinogenesis by topical administration of pure epigallocatechin gallate isolated from green tea , Nutr Cancer, 26 (3), 325-35. 

KATIYAR s K, MATSUI M s, ELMETS c A and MUKHTAR H (1999) Polyphenolic antioxidant epigallocatechin gallate from green tea reduces UVB-induced inflammatory responses and infiltration of leukocytes in human skin , Photochem Photobiol, 69, 148-53. 

KHAFIF A, SCHANTZ s P, CHOU T c, EDELSTEIN D and SACKS P G (1998) Quantitation of chemopreventive synergism between epigallocatechin gallate and curcumin in normal, premalignant, and malignant oral epithelial cells . Carcinogenesis, 19, 419-24. 

LONG L H, CLEMENT M V and HALLiwELL B (2000) Artifacts in cell-culture rapid generation of hydrogen peroxide on addition of (-)-epigaUocatechin, (-)-epigallocatechin gallate, (-i-)-catechin, and quercetin , Biochem Biophys Res Commun, 273 (1), 50-53. 

PASCHKA A G, BUTLER R and YOUNG c Y (1998) luductiou of apoptosis in prostate cancer cell lines by the green tea component, (-)-epigallocatechin-3-gallate . Cancer Lett, 130, 1-7. 

SUGANUMA M, OKABE s, KAi Y, suEOKA N, suEOKA E and FUJiKi H (1999) Synergistic effects of (-)-epigallocatechin gallate with (-)-epicatechin, sulindac, or tamoxifen on cancer-preventive activity in human lung cancer cell line PC-9 , Cancer Res, 59, 44-7. 

UCHIDA S, OZAKI M, KASHI T, YAMASHITA K, NIWA M and TANIYAMA K (1995) Effects of (-)-epigallocatechin-3-O-gallate (green tea tannin) on the life span of stroke-prone spontaneously hypertensive rats , Clin Exp Pharmacol, 11 (Suppl 1), S302-303. 

UNNO T, KONDO K, iTAKURA H and TAKEO T (1996) Analysis of (-)-epigallocatechin gallate in hiunan serum obtained after ingesting green tea , Biosci Biotech Biochem, 60, 2066-68. 

LP = Low phloem bread, HP = High phloem bread. Sum of epicatechin and epigallocatechin. 

The amount of catechins (i.e. (+)-catechin, (—)-epicatechin, (-)-epigallocatechin) is marked with number 1 in the original phloem sample. 

The chemical characteristics of the proanthocyanidins were elucidated by total oxidation and partial degradation in the presence of phloroglucinol followed by HPLC analysis. The native extract of proanthocyanidins contained (+) gallocatechin, (-) epigallocatechin, (h-) catechin, and (-) epicatechin units. ... 

The catechins are soluble in water, colorless, and possess an astringent taste. They are easily oxidized and form complexes with many other substances including the methylxanthines.44 Epigallocatechin gallate is the... 

The initial oxidation of the flavanol components of fresh leaf to quinone structures through the mediation of tea polyphenol oxidase is the essential driving force in the production of black tea. While each of the catechins is oxidizable by this route, epigallocatechin and its galloyl ester are preferentially oxidized.68 Subsequent reactions of the flavonoid substances are largely nonenzymic. 

Each of the four theaflavins theoretically are derived from the reactions the quinones of epicatechin or its gallate with those of epigallocatechin or its gallate has been identified in black tea and its structure authenticated.50... 

Bisflavanols are the compounds formed by the coupling of the quino-nes produced by the oxidation of epigallocatechin and epigallocatechin gallate.50 The three predicted bisflavanols have been found and characterized in black tea. They are illustrated in Figure 5. They occur only in very small quantities in black tea, presumably because of high reactivity. Re-... 

Hayakawa S, Saeki K, Sazuka M, et al. Apoptosis induction by epigallocatechin gallate involves its binding to Fas. Biochem Biophys Res Commun 2001 285 1102-1106. 

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