Free-radical scavenging actions of natural antioxidants

A dose-dependent inhibitory effect of wheat, alfalfa and ginkgo biloba (EGb) extracts on TEARS production was measured. The half-inhibition concentration (IC50) of the tested antioxidants were 2.7+/-0.2, 1.3+/-0.1, and 0.20+/-0.02 mg/ml for wheat, alfalfa and EGb extracts, respectively. Lipid radicals combined with the spin trap POBN resulted in adducts that gave a characteristic EPR spectrum. The IC50 of the tested antioxidants on lipid radical content, were 12.4+/-0.2, 7.7+/-0.3, and 1.20+/-0.06 mg/ml:for wheat, alfalfa and EGb extracts, respectively. Rat liver microsomes in the presence of DMPO, NADPH and iron-citrate generate an EPR spectra with characteristics of the DMPO-OH spin adduct. The basic system, without the addition of any scavenger showed an area of 3.5 AU/mg protein. The areas in the presence of 1.5 mg/ml EGb, 4 mg/ml wheat or alfalfa, were of 1.7+/-0.2, 3.4 +/-0.3, and 3.6+/-0.2 AU/mg protein, respectively. O-2(-) generation rate by the microsomes exposed to EGb extract was decreased by 40%, as compared to the rate measured in microsomes incubated in the absence of the extract. However, the supplementation of rat liver microsomes with either wheat or alfalfa extracts did not affect microsomal generation of O-2(-). Iron reduction rate was not affected by the addition of any of the tested extracts. The data presented here showed that EGb extracts were able to limit lipid peroxidation and scavenge lipid radicals in rat liver microsomes more efficiently than alfalfa and wheat bran extracts. Moreover, wheat and alfalfa extracts were not able to inhibit O-2(-) and . OH generation by biological membranes, suggesting that their potentiality to be successfully used in human health in the treatment of diseases involving free radical and oxidative damage are not as promising as that for the use of EGb extracts. (C) 1998 Elsevier Science Inc.