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No attention has been paid to anthocyanin pigments from the viewpoint of inhibitors of lipid peroxidation and scavengers of active oxygen radicals; therefore, we investigated the antioxidative, radical scavenging, and inhibitory effects on lipid peroxidation by UV light irradiation of three anthocyanin pigments, pelargonidin 3-O-beta-D-glucoside (P3G), cyanidin 3-O-beta-D-glucoside (C3G), and delphinidin 3-O-beta-D-glucoside (D3G), isolated from the Phaseolus vulgaris L. seed coat, and their aglycons, pelargonidin chloride (Pel), cyanidin chloride (Cy), and delphinidin chloride (Del). All pigments had strong antioxidative activity in a liposomal system and reduced the formation of malondialdehyde by UVB irradiation. On the other hand, the extent of antioxidative activity in a rat liver microsomal system and the scavenging effect of hydroxyl radicals (-OH) and superoxide anion radicals (O2-) were influenced by their own structures.

We examined the inhibitory effects of curcumin and tetrahydrocurcumin (THC), one of the major metabolites of curcumin, on the lipid peroxidation of erythrocyte membrane ghosts induced by tert -butylhydroperoxide. The results demonstrated that THC showed a greater inhibitory effect than curcumin. To investigate the mechanism of antioxidative activity, we examined the effects of several inhibitors, such as antioxidant enzymes, hydroxyl radical scavengers, 1 O 2 quencher, and chelating agents for metal ions. Given that all inhibitors failed to inhibit membrane peroxidation, THC must scavenge radicals such as tert -butoxyl radical and peroxyl radical. To clarify the antioxidative mechanism of THC, in particular the role of the β-diketone moiety, dimethylated THC was incubated with peroxyl radicals generated by thermolysis of 2,2′-azobis(2,4-dimethylvaleronitrile). Four oxidation products were detected, three of which were identified as 3,4-dimethoxybenzoic acid, 3′,4′-dimethoxyacetophenone, and 3-(3,4-dimethoxyphenyl)-propionic acid. The fourth oxidation product seems to be an unstable intermediate, and its detailed structure has not been determined. These results suggest that the β-diketone moiety of THC must exhibit antioxidative activity by cleavage of the CC bond at the active methylene carbon between two carbonyls in the β-diketone moiety. Because THC is one of the major metabolites of curcumin, it may also exhibit the same physiological and pharmacological properties as the active form of curcumin in vivo by means of the β-diketone moiety as well as phenolic hydroxy groups. biochem pharmacol 52;4:519–525, 1996.

The flavonoids quercetin, kaempferol, catechin and taxifolin suppressed cytotoxicity of active oxygen species (O2- and H2O2) on Chinese hamster V79 cells. Cytotoxicity of active oxygen species was assessed with a colony formation assay. The flavonoids prevented the decrease in the number of colonies caused by H2O2 or O2- at concentrations which were not themselves cytotoxic. There was a very substantial difference in the dose-dependency of the protective effects brought about by quercetin and kaempferol in contrast to catechin and taxifolin. The structure-activity relationship revealed that either the o-dihydroxy structure in the B ring or certain structures in the A and C rings of the flavonoids are necessary for the protective activities.