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Abstract
The free radical scavenging activities and inhibitory effect of lipid peroxidation
of a delphinidin derivative in eggplant were investigated. Delphinidin-3-(p-coumaroylrutinoside)-5-glucoside
(nasunin), an anthocyanin, was isolated as purple colored crystals from eggplant peels.
Using electron spin resonance spectrometry and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO),
hydroxyl radicals (OH) or superoxide anion radicals (O(2)(-)) generated by the Fenton
reaction or the hypoxanthine-xanthine oxidase system were measured as DMPO-OH or DMPO-OOH
spin adducts. L-Ascorbic acid 2-[3, 4-dihydro-2,5,7,8-tetramethyl-2-(4,8, 12-trimethyltridecyl)-2H-1-benzopyran-6yl-hydrogen
phosphate] potassium salt (EPC-K1) and bovine erythrocyte superoxide dismutase (SOD)
were used as standards for OH and O(2)(-) scavengers, respectively. Nasunin showed
potent O(2)(-) scavenging (143+/-8 SOD-equivalent U/mg) and OH scavenging (0. 65+/-0.07
EPC-K1-equivalent micromol/mg) activities. Then, by changing the concentration of
DMPO to vary the trapping rate of OH, the presence of a competitive reaction between
nasunin and OH was studied. The 50% inhibition dose (ID(50)) obtained from the inhibition
curve did not change, indicating OH scavenging of nasunin is not due to direct scavenging
but inhibition of OH generating system by chelating ferrous ion. Nasunin protection
against H(2)O(2)-induced lipid peroxidation in rat brain homogenate was measured at
586 nm using the indicator of malonaldehyde and 4-hydroxyalkenals. Nasunin (<50 microM)
protected against lipid peroxidation of brain homogenates. The findings suggest that
nasunin is a potent O(2)(-) scavenger and has protective activity against lipid peroxidation.