Epigallocatechin gallate antioxidant activity

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. 

Classic antioxidants, vitamin E, vitamin C, and others can suppress the activation of apoptosis. For example, ascorbic acid prevented cytochrome c release and caspase activation in human leukemia cells exposed to hydrogen peroxide [128], Pretreatment with A -acctylcystcinc, ascorbate, and vitamin E decreased homocysteine thiolactone-induced apoptosis in human promyelocytic leukemia HL-60 cells [129]. Resveratrol protected rat brain mitochondria from anoxia-reoxygenation damage by the inhibition of cytochrome c release and the reduction of superoxide production [130]. However, it should be mentioned that the proapoptotic effect of ascorbate, gallic acid, or epigallocatechin gallate has been shown in the same human promyelocytic leukemia cells [131]. 

The antioxidant activity of these catechins and the derivatives showed a marked difference depending on the substrate used for evaluation. In bulk corn oil that was oxidized at 50°C epigaUocatechin, epigallocatechin gallate and epicatechin gallate exhibited better antioxidant activity than epicatechin or catechin. These catechins have been very effective in retarding oxidation of polyunsturated fatty acids-rich... 

Hu B, Ting Y, Zeng X, Huang Q. Bioactive peptides/chitosan nanoparticles enhance cellular antioxidant activity of (-)-epigallocatechin-3-gallate. J Agric Food C/icm. janv 30, 2013 61(4) 875—881. 

Na HK, Kim EH, Jung JH, Lee HH, Hyun JW, Surh YJ (2008) (-)-Epigallocatechin gallate induces Nrf2-mediated antioxidant enzyme expression via activation of P13K and ERK in human mammary epithelial cells. Arch Biochem Biophys 476 171-177... 

Takagaki, A., Sh. Otani, and F. Nanjo. 2011. Antioxidative activity of microbial metabolites of (-)-epigallocatechin gallate produced in rat intestines. Biosci. Biotechnol. Biochem. 75 582-585. 

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