Antioxidant activity and mechanism of Rhizoma Cimicifugae

BACKGROUND: As a typical Chinese herbal medicine, rhizoma Cimicifugae (RC, 升麻 in Chinese) possesses various pharmacological effects involved in antioxidant activity. However, its antioxidant activity has not been reported so far. The aim of the present study was to systematically evaluate the antioxidant ability of RC in vitro, then discuss the mechanism. METHODS: Firstly, five RC extracts (i.e. petroleum ether extract PERC, ethyl acetate extract EARC, absolute ethanol extract AERC, 95% ethanol extract 95ERC, and water extract WRC) were prepared and determined by various antioxidant methods, including anti-lipidperoxidation, protection against DNA damage, ·OH scavenging, ·O(2)(-) scavenging, DPPH· (1,1-diphenyl-2-picryl-hydrazl radical) scavenging, ABTS(+)· (2,2’-azino-bis (3-ethylbenzo- thiazoline-6-sulfonic acid radical ion) scavenging, Cu(2+)-chelating, and Fe(3+) reducing assays. Subsequently, we measured the chemical contents of five RC extracts, including total phenolics, total saponins, total sugars, caffeic acid, ferulic acid and isoferulic acid. Finally, we quantitatively analyzed the correlations between antioxidant levels (1/IC(50) values) and chemical contents. RESULTS: In the study, the antioxidant levels and chemical contents (including total phenolics, total saponins, total sugars, caffeic acid, ferulic acid and isoferulic acid) of five RC extracts were determined by various methods. In all antioxidant assays, five RC extracts increased the antioxidant levels in a dose-dependent manner. However, their antioxidant levels (IC(50) values) and chemical contents significantly differed from each other. Quantitative analysis of the correlation showed that total phenolic was of significant positive correlations (average R value was 0.56) with antioxidant levels; In contrast, total sugars and total saponins had no positive correlation with antioxidant (the average R values were −0.20 and −0.26, for total sugars and total saponins, respectively); Among total phenolics, three phenolic acids (caffeic acid, ferulic acid and isoferulic acid) also displayed positive correlations (the average R values were 0.51, 0.50, and 0.51, for caffeic acid, ferulic acid and isoferulic acid, respectively). CONCLUSIONS: As an effective antioxidant, Rhizoma Cimicifugae can protect DNA and lipids against oxidative damage. Its antioxidant ability can be responsible for its various pharmacological effects and may be mainly attributed to the existence of total phenolics, among which caffeic acid, ferulic acid and isoferulic acid are regarded as main bioactive components. Rhizoma Cimicifugae exerts its antioxidant effect through metal-chelating, and radical-scavenging which is via donating hydrogen atom (H·) and donating electron (e).