Bioactive compounds and biological activities of some medicinal plants from central Nepal

Abstract

Considerable attempts have been made globally to validate the traditional use of plants in phytomedicine. Phytomedicine can counter the challenge posed by drug resistance and toxicity by continuous search for novel drugs. This study focuses on the estimation of total phenolic content, total flavonoid content, examination of antioxidant activities, GC‐MS identification of bioactive compounds, observation of antimicrobial, cytotoxic, and anticancer effects. Twelve medicinal plants with some history of use as traditional medicine have been selected for the purpose. They include Loxogramme involuta, Hydrocotyle javanica, Phyllanthus emblica, Chrysopogan aciculatus, Rhododendron lepidotum, Geranium wallichianum, Tsuga dumosa, Anemone rivularis, Scurrula elata, Terminalia bellerica, Ranunculus scleratus, and Symplocos lucida. Total phenolic content was determined by the Folin‐Ciocalteu method, total flavonoid content by aluminium chloride colorimetric method. Antioxidant activity was tested by their capacity to scavenge DPPH (2,2‐diphenyl‐1‐picrylhydrazyl) free radicals. GC‐MS analysis was performed to identify the bioactive compounds. The antimicrobial efficacy was tested against Staphylococcus aureus, methicillin‐resistant Staphylococcus aureus, Klebsiella pneumoniae, Salmonella Typhi, Saccharomyces cerevisiae and Pichia sp. by agar well diffusion method. Cytotoxicity was determined by brine shrimp bioassay. Anticancer activity was determined by MTT assay on HeLa and MDCK cell lines. P. emblica (55.66 ± 0.84 mgGAE/g) possessed the highest amount of total phenolic content. Higher amount of TPC was also observed in G. wallichianum (54.99 ± 0.74 mgGAE/g), S. elata (54.71 ± 0.68 mgGAE/g), T. bellerica (54.69 ± 0.77 mgGAE/g), and T. dumosa (54.19 ± 0.93 mgGAE/g). The lowest amount of TPC was observed in R. scleratus (6.74 ± 0.62 mgGAE/g). The highest amount of total flavonoid content was observed in P. emblica (25.65 ± 0.77 mgQE/g). The lowest amount of TFC was observed in T. bellerica (7.51 ± 0.54 mgQE/g). TFC for other plant extracts locate within the short range between these two values. T. dumosa (4.54 ± 0.18 µg/ml) showed the highest antioxidant activity with the lowest IC 50 value – lower than that observed in ascorbic acid (4.57 ± 00 µg/ml). Higher antioxidant activity was also observed in P. emblica (6.64 ± 0.71 µg/ml), G. wallichianum (7.24 ± 0.48 µg/ml), T. bellerica (12.08 ± 0.76 µg/ml), and S. elata (14.20 ± 0.94 µg/ml). R. scleratus (195.55 ± 2.45 µg/ml) showed the lowest antioxidant activity. A significant Pearson’s correlation between TPC and IC 50

of DPPH RSA (r = ‐0.9684) attributed phenolic compounds to be the main contributor of antioxidant activity in plants. GC‐MS analysis showed the presence of a wide range of bioactive compounds such as fatty acids, esters, sugars, steroidal, phenolic, and heterocyclic xiv compounds. Maximum inhibition of S. aureus and MRSA both were shown by T. bellerica. Highest inhibition of S. Typhi was caused by T. dumosa. Minimum number of plants inhibited K. pneumoniae on which L. involuta exerted the highest effect. Ten of the twelve plants inhibited at least three of the six organisms. Eight of them inhibited at least four organisms. G. wallichianum inhibited five of the six organisms. S. elata and T. bellerica both inhibited all of them. Plants showed higher effects on gram positive bacteria. Nine of the twelve plants showed significant toxicity to brine shrimps (LC 50 <500µg/ml) of which three were found to be highly toxic (LC 50 <100 µg/ml) which includes A. rivularis, L. involuta and T. bellerica. Maximum number of plants showed higher inhibition of HeLa cell line than of MDCK. The highest inhibition of HeLa cell was shown by S. lucida (52.22 μg/ml) which precedes other ten with EC 50

value less than 1000 μg/ml. T. bellerica (1048 μg/ml) showed the lowest inhibition. Highest inhibition of MDCK cell was shown by L. involuta (240 μg/ml) followed by T. dumosa (305 μg/ml), A. rivularis (407.7 μg/ml), S. elata (751.1 μg/ml), and P. emblica (925.3 μg/ml). Other showed less inhibition with EC50 value more than 1000 μg/ml. The results provide justification for traditional use of medicinal plants in treatment of various diseases. The biological activities of medicinal plants may have been attributed due to the presence of bioactive compounds identified. These plants can be the candidates as the potential source of high valued phytopharmaceuticals. Further meticulous analysis of plants might lead to isolation, identification and characterization of biologically active substances. Keywords: medicinal plants, phenolic, flavonoid, antioxidant, bioactive compounds, antimicrobial, cytotoxicity, anticancer