Effect of natural antioxidants on reactive oxygen species

Abstract

Superoxide dismutase (SOD)-like activity of natural antioxidants was examined based on the inhibition of the pyrogallol autoxidation catalyzed by the superoxide anion radical ($O_2$). When 22 water-soluble antioxidants were tested using the aqueous assay system containing 0.2 mM pyrogallol at pH 8.20, L-ascorbic acid, L-ascorbic acid-6-palmitate, glutathione (reduced form: GSH), (+)-catechin, and (-)-epicatechin showed the efficacious SOD-like activities. For the analysis of lipophilic antioxidants, optically clear reverse micellar system composed of diethyl ether, dioctyl sulfosuccinate (AOT) and water was newly developed. The pyrogallol autoxidation in this system was also mediated by superoxide anion as in aqueous system, and it was proved that the optimum concentrations of AOT, water and pyrogallol for determining the SOD-like activity were found to be 50 mM, 1.3 M and 40 mM, respectively. Of 24 lipophilic antioxidants examined, cinnamon oil, $\gamma$-oryzanol, ether extract of rosemary leaf, L-$\alpha$-lecithin, and L-$\alpha$-cephalin exhibited the activities. SOD-like compounds were also screened in the extracts of 61 agricultural produces. The activity was high in aqueous extracts of nameko, garlic, broccoli, and oriental lettuce. In studies on activators of human erythrocyte SOD, it was revealed that ethanolic extracts of onion and watermelon could enhance in vitro human SOD activity more than 40\%. In an attempt to extract SOD-like compounds from the mixture of farm produces screened, extraction with hot water ($95^\circ C$) or 80\% ethanol was about twenty times as effective as that of cold water. The biological effect of the natural antioxidants exhibiting the SOD-like activity in in vitro test was examined using fruit flies, Drosophila melanogaster. In Drosophila fed with 5 mM of paraquat as an endogenous source of superoxide radical, their survival was higher in groups of flies previously supplied with glutathione (GSH), (+)-catechin and/or (-)-ep...