Antioxidant and pro-oxidant effects of various tea extracts

The antioxidant and pro-oxidant effects of various tea extracts were investigated. The tea extracts, especially the green, pouchong, and oolong tea extracts, markedly stimulated the oxidation of deoxyribose in the presence of Fe3+ and H2O2. The rate of DNA degradation, induced by bleomycin-Fe3+, was also accelerated by tea extracts (green tea, pouchong tea, and oolong tea) up to 65-fold at the dosage of 0.125 mg, and then decreased at higher dosages. Black. tea exhibited greater stimulatory effects than the other three teas at higher dosage. The systems that contained only tea extracts and 2'-deoxyguanosine (2'-dG) do not induce the oxidation of 2'-dG to 8-hydroxy-2'-deoxyguanosine. Addition of ascorbic acid to the reaction system accelerated the oxidation of deoxyribose, DNA, and DNA bases, however, the oxidation was decreased by a high dosage of tea extracts. Tea extracts showed dual effects in the model system that was dependent on the ability of both reducing iron and scavenging oxy-radicals.