STUDIES ON PROTECTIVE MECHANISMS OF 4 COMPONENTS OF GREEN TEA POLYPHENOLS AGAINST LIPID-PEROXIDATION IN SYNAPTOSOMES

The comparison of the protective effects of four components of 'green tea polyphenols' (GTP) - (-)-epigallocatechin gallate, EGCG; (-)-epica techin gallate, ECG; (-)epigallocatechin, EGC; and(-)epicatechin, EC - against iron-induced lipid peroxidation in synaptosomes showed that: (1) the inhibitory effects of those compounds on TBA reactive material s from lipid peroxidation decreased in the order of EGCG > ECG > EGC > EC; (2) the scavenging effects of those compounds on lipid free radic als produced by lipid peroxidation could be classified as follows: ECG > EGCG > EC > EGC. Furthermore, we investigated the iron-chelating ac tivity and the free radical scavenging activity of those compounds as their protective mechanisms against lipid peroxidation in synaptosomes . As for the iron-chelating activity, the ratio of EGC, EGCG, ECG or E C to iron(III) was 3:2, 2:1, 2:1 and 3:1, respectively. The hydroxyl r adical (HO.) scavenging activity of those compounds was investigated i n a photolysis of the H2O2 system. It was found that their ability to scavenge hydroxyl radicals decreased in the order of ECG > EC > EGCG m uch greater than EGC. It was also found that they could scavenge lipid free radicals in the lecithin/lipoxidase system and their scavenging activity was classified as follows: ECG > EGCG much greater than EGC > EC. Moreover, we found that their antioxidant active positions were d ifferent from each other and the stability of the semiquinone free rad icals produced by those compounds in NaOH solution decreased in the or der of EGCG > ECG much greater than EC. The results indicated that the ability of those compounds to protect synaptosomes from the damage of lipid peroxidation initiated by Fe2+/Fe3+ was dependent not only on t heir iron-chelating activity and free-radical scavenging activity, but also on the stability of their semiquinone free radicals.