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Study of antioxidant potential, and quantification of major polyphenols in Leonurus sibiricus L. leaves using HPLC

The objectives of this study was to evaluate the possible in vitro antioxidant potential and analysis of the active polyphenols in ethyl acetate and methanol extracts of leaves of Leonurus sibiricus L. Alcoholic extraction of Leonurus sibiricus leaf was carried out in two different solvents (ethyl acetate and methanol) on the basis of their different polarity. The in vitro antioxidant efficacy for both the fractions were evaluated using different free radical scavenging methods such as 1, 1-diphenyl-2-picrylhydrazyl (DPPH), nitric oxide (NO) and hydrogen peroxide. The total phenolic content (TPC) and total tannin content (TTC) were determined using Folin Ciocalteu’s (FC) reagent, whereas the total flavonoid content (TFC) was measured using basic solution of NaNO2 and AlCl3. High-performance liquid chromatography (HPLC) was used to identify and quantify the major phenolic compounds of both the crude extracts. The TPC of ethyl acetate and methanol extracts were found to be 45.7 and 33.2 mg gallic acid equivalent per g of dry mass, the FC were calculated to be 68.3 and 42.2 mg quercetin equivalent per g of dry extract and while TTC were found to be 15.2 and 20.5 mg gallic acid equivalent per g of dry extract respectively. In DPPH scavenging assay, the EC50 values for ethyl acetate and methanol extracts were 17.1 and 27.7 µg/mL respectively. The well recognized H2O2 radical was scavenged strongly by both the fractions and the observed values were 49.2 and 29.8 µg/mL respectively. Both ethyl acetate and methanol extracts were displayed scavenging activity against NO radical and the measured values were 29.2 and 36.6 µg/mL, respectively. In reducing power assay, maximum absorbance of ethyl acetate and methanol extracts were 2.0 and 1.7, respectively. In HPLC analysis, catechin and epi-catechin (higher amount) were detected only in the ethyl acetate extract (14.94 and 248.30 mg per 100 g of dry extract). On the other hand, gallic acid was detected (90.64 mg/100 g of dry weight) only in the methanol extract. Several polyphenols like p-coumaric acid, rutin, ellagic acid and quercetin were detected in both the extracts but rutin and ellagic acid were found in high concentration in methanol extract (102.9, 192.5 mg per 100 g of dry extract). Both the Ethyl acetate and methanol extracts of L. sibiricus have shown significant free radicals scavenging activity in concentration dependent manner as well as the presence of diverse phenolic moieties. Therefore, the results suggest that the plant, L. sibiricus may be a potential source of active therapeutic components which might be proved beneficial for human health as well as development of better novel antioxidant drugs.

Leonurus sibiricus ; Antioxidant activity ; Oxidative stress ; Free radicals ; DPPH ; Folin Ciocalteu ; Gallic acid ; Polyphenols

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