Scavenging effect of tea catechins and their epimers on superoxide anion radicals generated by a hypoxanthine anal xanthine oxidase system

Catechins are a major group of polyphenolic compounds contained in abundanc e in green tea. Using electron spin resonance spectroscopy along with a spi n-trapping agent, the scavenging effect of tea catechins and their correspo nding epimers against superoxide anion radicals generated by a hypoxanthine and xanthine oxidase reaction system was evaluated. The presence of 3',4', 5'-trihydroxyl groups attached to the B-ring of the flavan skeleton of tea catechins elevated their radical-scavenging efficiency in comparison to tho se with 3',4'-dihydroxyl groups. There were no significant differences betw een the four dominant tea catechins and their corresponding epimers with re gard to radical-scavenging ability. Under the different spin-trapping agent concentrations, the sigmoid curves of reducing spin-trapping adducts produ ced by tea catechins were shifted leftward, suggesting that a likely possib le action of tea catechins is to scavenge superoxide anion radicals directl y, not to inhibit the function of xanthine oxidase. Although caffeine is al so known as a major ingredient of tea, its superoxide anion radical-scaveng ing effect was much weaker than that of the catechin family. It is conclude d that tea catechins and their epimers serve as powerful antioxidants for d irectly eliminating superoxide anion radicals, and may be useful in the pre vention of diseases relating to in vivo oxidative stress. (C) 2000 Society of Chemical Industry.