Antioxidant activity of nasunin, an anthocyanin in eggplant

Delphinidine-3-(p-coumaroylrutinoside)-5-glucoside (nasunin), an anthocyani n was isolated as purple colored crystals from eggplant peels, Solanum melo ngena L. 'Chouja'. Using an electron spin resonance spectrometer and 5,5-di methyl-1-pyrroline-N-oxide (DMPO), spin trapping, hydroxyl (. OH) or supero xide anion radicals (O2(.-)) generated by the Fenton reaction or the hypoxa nthine-xanthine oxidase system were measured as DMPO-OH or DMPO-OOH spin ad ducts. L-Ascorbic acid 2-[3,4-dihydro-2,5,7,8-tetramethyl-2-(4,8,l 2-trimet hyltridecyl)-2H-1-benzopyran-6yl-hydrogen phosphate] potassium salt (EPC-K1 ) and bovine erythrocyte superoxide dismutase (SOD) were used as standards for OH and O2(.-), respectively. Nasunin directly scavenged O2(.-) with a p otency of 143+/-8 SOD-equivalent units/mg), and inhibited formation of DMPO -OH (0.65+/-0.07 EPC-K1 mu mol/mg). A spectrophotometric study showed that nasunin formed an iron complex with a molar ratio of nasunin : Fe3+ of 2 : 1. Therefore, hydroxyl radical scavenging by nasunin is not due to direct r adical scavenging but inhibition of OH generation by chelating iron. Nasuni n (1 mu M) significantly protected against lipid peroxidation of brain homo genates (p<0.001) as measured by malonaldehyde and 4-hydroxyalkenals. These findings demonstrate that nasunin is a potent O2(.-) scavenger and iron ch elator which can protect against lipid peroxidation.