Mechanisms of anticarcinogenic and other activity

As strong metal ion chelators due to their catechol structure, tea flavonoids are able to bind and thus decrease the level of free cellular ferric and ferrous ions, which are required for the generation of reactive oxygen radicals via the Fenton reaction (Yang and Wang, 1993). 

As strong antioxidants and scavengers of superoxide, hydroxyl and peroxyl radicals, tea flavonoids can suppress radical chain reactions and terminate lipid peroxidation (Kumamoto and Sonda, 1998, Yang and Wang, 1993). 

As inhibitors of certain enzyme reactions and apoptosis related to the development of cancer (Naasani et al, 1998 Yang et al, 2001), specifically by selective induction or modification of phase I and phase II metabolic enzymes so as to increase the formation and excretion of detoxified metabolites of carcinogens. 

As modifiers of the intestinal microflora by favouring the growth of health promoting bacteria (Weisburger, 1999). 

Therefore depending upon the conditions used to simulate either in vitro or in vivo oxidation, catechins or other phenolic compounds display differences in their antioxidant properties. Catechins also limited the consumption of a-tocopherol, allowing it to act as a scavenger within cell membranes whilst the catechins scavenged aqueous peroxyl radicals near the membrane surface (Pietta and Simonetti, 1998). 

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