CAFFEINE AS AN ANTIOXIDANT - INHIBITION OF LIPID-PEROXIDATION INDUCEDBY REACTIVE OXYGEN SPECIES

Caffeine (1,3,7-trimethyl xanthine), an ingredient of coffee, has been investigated for its potential antioxidant activity against oxidative damage to rat liver microsomes. Such damage was induced by three reac tive oxygen species of cardinal importance in causing membrane damage in vivo namely hydroxyl radical ((OH)-O-.), peroxyl radical (ROO(.)) a nd singlet oxygen (O-1(2)). The results obtained showed that caffeine was an effective inhibitor of lipid peroxidation, at millimolar concen trations, against all the three reactive species. The extent of inhibi tion was high against peroxidation induced by (OH)-O-., medium against O-1(2) and low against ROO(.). In general, the antioxidant ability of caffeine was similar to that of the established biological antioxidan t glutathione and significantly higher than ascorbic acid. Investigati ons into the possible mechanisms involved in the observed antioxidant effect reveal that the quenching of these reactive species by caffeine may be one of the possible factor responsible. The rate constant of c affeine with (OH)-O-. was 7.3 . 10(9) M(-1) s(-1) and with O-1(2) it w as 2.9 . 10(7) M(-1) s(-1). Considering their potential for damage, ha lf-life estimates and generation in biological systems, the ability of caffeine to inhibit oxidative damage induced by these reactive specie s in membranes suggest one more positive attribute of caffeine, whose daily intake as coffee may be considerable in most populations.