Differences in Antioxidative Efficiency of Catechins in Various Metal-Induced Lipid Peroxidations in Cultured Hepatocytes

The effects of tea catechins, including (–)-epicatechin (EC), (–)-epigallocatechin (EGC), (–)-epicatechingallate (ECg) or (–)-epigallocatechingallate (EGCg) on the lipid peroxidation induced by either ferrous (Fe), copper (Cu) or vanadium (V ) ions were examined in normal and α-linolenic acid-loaded (LNA-loaded) cultured rat hepatocytes. The order of antioxidative activity was almost similar and ranked as follows: EGCg > ECg > EGC > EC against the three metal-induced lipid peroxidations in both groups of cultured hepatocytes. However, each catechin displayed a marked variation in its antioxidative potency depending on the added metal ion species, whereas dibutyl hydroxy toluene (BHT), a typical lipid radical scavenger, exhibited a similar antioxidative potency with all metal ions. The half inhibition concentration (IC50) values of the catechins for Fe ion-induced lipid peroxidation were 2 to 3 times and 5 to 14 times higher than those for V ion and Cu ion, respectively in normal hepatocytes. Only in LNA-loaded hepatocytes, was EC antioxidative at 20 μM Fe concentration but it became prooxidative above 50 μM Fe concentration. Catechins such as (+)-catechin, (+)-epicatechin and (±)-catechin also acted as prooxidants at high Fe concentrations in LNA-loaded hepatocytes. The antioxidative efficiency of EGC, ECg or EGCg decreased with the increase in Fe ion concentrations from 20 μM up to 500 μM in LNA-loaded hepatocytes. These findings suggest that the metal-chelating property of catechins may play a major role in determining antioxidative activity in cultured hepatocytes.