Comparative Gas Chromatography-Mass Spectrometric Analysis of Biologically Active Volatile Phytochemical Constituents of Aerial Parts and Roots of Coronopus didymus

Measurement of total phenolic content and antioxidant activity of aerial parts of medicinal plant Coronopus didymus

OBJECTIVE

To evaluate the total phenolic content and compare the antioxidant activity of various solvent extracts and fractions from the aerial parts of Coronopus didymus through various assays.

METHODS

Total phenolic content was determined using the Folin-Ciocalteu assay and the in vitro antioxidant activity of a number of different extracts was investigated in a dose-dependent manner with three different methods: the 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) and ferric reducing antioxidant power (FRAP) assays. A flavone was isolated from the most active ethanolic extract with high antioxidant activity using size exclusion chromatography. IC₅₀ values were calculated for the DPPH and ABTS methods. The FRAP activity was assessed in terms of μM Fe (II) equivalent.

RESULTS

The phenolic content was found to be highest in the ethanol extract (CDA Et; 47.8 mM GAE) and the lowest in the dichloromethane extract (CDA DCM; 3.13 mM GAE). The ethanol extract showed high radical scavenging activity towards DPPH and ABTS radicals with IC₅₀ values of (7.80 × 10²) and (4.32 × 10²) μg/mL, respectively. The most active ethanol extract had a FRAP value of 1921.7 μM Fe (II) equivalent. The isolated flavone F10C (5,7,4'-trihydroxy-3'-methoxy flavone) was far more effective for scavenging free radicals in the DPPH and ABTS assays with IC₅₀ of 43.8 and 0.08 μg/mL, than the standard trolox, with IC₅₀ values of 97.5 and 21.1 μg/mL, respectively. In addition, the flavone F10C and the standard ascorbic acid had FRAP values of 1621.7 and 16 038.0 μM Fe (II) equivalents, respectively.

CONCLUSIONS

The total phenolic content of extracts in decreasing order is ethanol extract (CDA Et) > acetone extract (CDA ACE) > phenolic extract (CDA MW) > n-hexane extract (CDA nHX)> chloroform extract (CDA CHL) > dichloromethane extract (CDA DCM). The ordering of extracts in terms of antioxidant activity from highest to lowest is CDA Et > CDA MW > CDA DCM > CDA CHL > CDA ACE > CDA nHX in DPPH, ABTS and FRAP assays. A significant relationship is found between antioxidant potential and total phenolic content, suggesting that phenolic compounds are the major contributors to the antioxidant activity of C. didymus.

Bioassay-guided isolation of cytotoxic flavonoids from aerial parts of Coronopus didymus

ETHNOPHARMACOLOGICAL RELEVANCE

Coronopus didymus Linn. (Brassicaceae) is a medicinal plant used traditionally as antipyretic, expectorant, to purify blood and for alleviating symptoms of pain, inflammations, malaria, wounds and cancer.

AIM OF THE STUDY

The present study was designed to isolate and identify the cytotoxic compounds responsible for anticancer activity from this traditionally useful medicinal plant.

MATERIALS AND METHODS

Bioassay-guided fractionation of the ethanolic extract of aerial parts of C. didymus allowed the isolation of compounds responsible for anticancer activity. Their structures were elucidated by UV Spectroscopy (with shift reagents), ESI-MS and NMR spectral data. Preliminary anticancer activity of ethanolic extract, different fractions and isolated compounds was assessed through MTT in vitro cytotoxicity assay in a dose dependent manner against human cancer cell lines (HeLa and LN18) and normal 293T cells.

RESULTS

Three flavonoids namely 5,7,4'-trihydroxy-3'-methoxyflavone-4'-O-β-D-glucoside (1), 5,7,4'-trihydroxy-3'-methoxyflavone-4'-O-(6''-acetyl)-β-D-glucoside (2) and 5,7,4'-trihydroxy-3'-methoxy flavone (3), were isolated from aerial parts. Compound 1 was identified for the first time from the genus Coronopus. All the compounds 1-3 showed promising activity against HeLa cells with IC50 values of 43.50, 0.63 and 3.67 µM, respectively. Significant result was also obtained with compound 3 against LN18 cells with IC50 value of 46.63 µM.

CONCLUSION

The cytotoxic activity of the crude extract and fractions which may largely be due to its major isolated constituents, flavonoids 1-3, against both HeLa and LN18 cells provides a scientific basis for the ethnopharmacological use of C. didymus as anticancer agent.