Free-radical scavenging and mechanism study of flavonoids extracted from the radix of Scutellaria baicalensis Georgi

Free-radical scavenging activities of baicalein, baicalin, wogonin and wogo noside, the four major flavonoids in a traditional Chinese herb medicine, t he radix of Scutellaria baicalensis Georgi, were examined by electron param agnetic resonance (EPR). The results showed that baicalein and baicalin sca venged hydroxyl radical, superoxide anion, 2,2-diphenyl-1-picrylhydrazyl ra dical and alkyl radical in a dose-dependent manner, while wogonin and wogon oside showed subtle or no effect on these radicals. Baicalein was the most effective free-radical scavenger among the four tested compounds. When 10 m mol/l tested flavonoids dissolved in alkaline solution, only baicalein and baicalin form stable free radicals which can be detected by EPR technique, it was found that the signal came from their o-di-hydroxyl structure in rin g A. To our knowledge, it was the first time demonstrated that flavonoids w ith o-di-hydroxyl structure in ring A could also form stable semiquinone fr ee radicals. These results demonstrated that flavonoids in radix of Scutell aria baicalensis with o-di-hydroxyl group in ring A such as baicalein and b aicalin are good free-radical scavengers and might contribute to some of th eir pharmaceutical effects.