Antioxidant and antibacterial activities of ethanol extract and flavonoids isolated from Athrixia phylicoides

Abstract

The ethanol extract of A. phylicoides was investigated for its antioxidant activity using the DPPH scavenging method. The extract showed good antioxidant results with a EC50 value of 10.64 ± 0.0842 µ/ml. The extract was also tested for antibacterial activity against microorganisms (Staphylococcus aureus, Enterococus faecalis, Bacillus cereus, Bacillus subtilis, Bacillus pumilus, Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumonia) commonly known to pose a threat in the wellbeing of man. All tested microorganisms were significantly inhibited by the extract with the MIC values ranging from 3.13 µg/ml to 6.25 µg/ml. Folin-Ciocalteu’s reagent method was used to determine total phenolic content of dried and freshly prepared crude extract of A. phylicoides. Higher total phenolic content (28.28 ± 0.019 mg GAC/100g) and antioxidant activity (EC50, 10.64 ± 0.084 µg/ml) was observed in the dried extract compared to the fresh extract with a TPC value of 23.04 ± 0.003 mg GAC/100g and EC50 of 13.97 ± 0.066 µg/ml. Bioassay-guided fractionation of ethanolic extract from aerial parts of Athrixia phylicoides using silica and sephadex column chromatography led to the isolation of four known flavanoids, 5-hydroxy-6,7,8,3’,4’,5’-hexamethoxyflavon-3-ol (1), 3-0- demethyldigicitrin (2), 5,6,7,8,3’,4’-hexamethoxyflavone (3) and Quecertin (4). Due to the low yield, no further tests were done on compound 3. A DPPH-scavenging assay was performed to evaluate the antioxidant activity of the isolated compounds. All the tested compounds showed potent antioxidant activity with EC50 values ranging from 1.27 to 3.41 µg/ml. Compound 4 showed a higher antioxidant activity (EC50, 1.27 µg/ml) than vitamin C (EC50, 2.66 µg/ml) used as a control. The MIC values of the isolated compounds against tested microorganisms varied from 20 to more than 40 µg/ml. All the tested compounds showed no activity against S. aureus, B. pumilus, K. pneumonia and P. aeruginosa at the highest concentration tested (40 µg/ml). These compounds together with the extract were further analyzed by XTT assay on Vero cells. The extract showed a low toxicity effect on the cells at lower concentrations exhibiting EC50 value of 107.8 ± 0.129 µg/ml. Compound 4 showed minimal toxicity effect on the cells with a EC50 value of 81.38±0.331 µg/ml, compared to Compound 1 and 2 which exhibited EC50 values of 27.91 ± 0.181 µg/ml and 28.92 ± 0.118 µg/ml respectively. The results obtained from this study provide a clear rationale for the medicinal uses of Athrixia phylicoides.