The present study was undertaken to evaluate the in vitro antioxidant activities of aqueous extract of Rhodiola imbricata rhizome. The plant extract was evaluated for DPPH (1,1-diphenyl, 2-picryl hydrazyl) radical scavenging, superoxide anion radical scavenging, hydrogen peroxide scavenging, anti-lipid peroxidation assay, metal chelating activity, reducing power and total flavonoid content. Rhodiola imbricata aqueous extract (RIAE) exhibited more DPPH scavenging potential with IC50 value of 5.56 µg/ml as compared to standard butylated hydroxytoluene (BHT) (IC50 = 5.74 µg/ml). The extract also provided superoxide anion radicals' scavenging (IC50 = 4.68 vs 4.63 µg/ml) and anti-lipid per-oxidation activity (IC50 = 5.06 vs 4.91 µg/ml) and IC50 value was comparable to standard ?-tocopherol. The RIAE showed a decrease in hydrogen peroxide generation with IC50 value of 3.25 µg/ml when compared with standard ?-tocopherol (IC50 value=4.00 µg/ml). IC50 of the extract for chelating activity was 5.33 ?g/ml which was lower than the positive standard quercetin (IC50 = 3.12 ?g/ml) but higher than ?-tocopherol (IC50 = 6.13 ?g/ml). The reducing capability of extract increased in dose dependent manner. Flavonoid content of RIAE determined spectrophotometrically in terms of Quercetin equivalent was 66.7µg/mg. The results obtained in the present study indicated that aqueous extract of root of Rhodiola imbricata is a potent source of natural antioxidant.
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