Peroxyl radical scavenging capacity of extracts and isolated components from selected medicinal plants

We determined the ability of extracts and active components isolated from nine medicinal plants, Poncirus trifoliata, Astragalus membranaceus, Magnolia obovata, Salvia miltiorrhiza, Angelica dahurica, Cornus officinalis, Cnidium officinale, Pueraria lobata and Ostericum koreanum, to neutralize peroxyl radicals using the total oxyradical scavenging capacity (TOSC) assay. Peroxyl radicals were generated from thermal homolysis of 2,2'-azobis(2-methylpropionamidine) dihydrochloride, which oxidize alpha-keto-gamma-methiolbutyric acid to yield ethylene, and the TOSC of the substances tested is quantified from their ability to inhibit ethylene formation. Extracts from S. miltiorrhiza, M. obovata and P. lobata were determined to be potent peroxyl radical scavenging agents with a specific TOSC (sTOSC) being at least threefold greater than that of glutathione. Major constituents of the three plants, tanshinone, cryptotanshinone, 15,16-dihydrotanshinone, syringin, honokiol, magnolol, daidzein, puerarin and genistein, were examined for the antioxidant potential toward peroxyl radical. Puerarin and genistein were shown to have microM sTOSCs at least ten-fold greater than sTOSC of glutathione. Daidzein, syringin and honokiol demonstrated the peroxyl radical scavenging capacity comparable to that of glutathione. The implication of peroxyl radical in lipid peroxidation and other cellular damage suggests a possible protective role for the extracts and isolated components in oxidative stress caused by this reactive oxygen species.