Keywords: Phytochemicals, Phenolics, Flavonoids, Antioxidant activity, Antibacterial activity, High resolution liquid chromatography-mass spectrometry (HRLCMS), Medicinal plants
Medicinal plants have been conspicuous source of novel chemicals and bioactive compounds due to illustrious history of use in traditional medicine. Research on Nepalese medicinal plants are still limited to ethnopharmacological studies and qualitative phytochemical screening with a very few studies exploring their biological activities. This study aims to investigate biological activities of these plants and identify bioactive compounds present in each extract. A phytochemical profile of methanolic extracts of selected medicinal plants was established using high resolution (HR)-LCMS. Antioxidant activities were determined using DPPH, ABTS and FRAP assays. Highest DPPH radical scavenging was shown by Padamchal (IC50 = 3.47 ± 0.09), ABTS radical were most efficiently quenched by Pashanbed (IC50 = 3.82 ± 0.63) and the highest reducing potential was shown by Nirbikhi (FRAP = 61.76 ± 2.29 equivalent µg Fe2+/ml). The antioxidant activities of Padamchal and Pashanbed was comparable to that of standard Ascorbic acid and Gallic acid. Further, a significant correlation was found between different antioxidant activities and total phenolic/flavonoid contents of each plant extract. Antibacterial properties against five pathogenic microorganisms was established using agar well diffusion and broth microdilution method. The extracts showed considerable inhibition zones ranging from 10–17.5 mm at maximum concentration of 10 mg/ml. Inhibitory effect was observed against Staphylococcus aureus at MIC 31.25 µg/ml of Padamchal, against Escherichia coli at MIC 125 µg/ml of Ragatsingey, against Bacillus subtilis at MIC 250 µg/ml of Nirbikhi, against Klebsiella pneumoniae at MIC 250 µg/ml of Ragatsingey and against Shigella flexneri at MIC 250 µg/ml of Padamchal. Furthermore, HR-LCMS analysis manifested presence of several compounds of pharmaceutical importance in the plant extracts. These selected medicinal plants contain significant antioxidant and antibacterial activities owing to the presence of prominent bioactive chemicals. The results stipulate a need for further research and bioprospecting of these plants as source of new natural antioxidants and antibacterial agents.
We would like to acknowledge University Grants Commission, Nepal for providing Collaborative Research Grant to conduct this study. We extend our gratitude to Department of Biotechnology, Kathmandu University for facilitating this research. We are truly grateful to Dr. Dhurva Gauchan, Department of Biotechnology and Tirtha Maiya Shrestha, Department of pharmacy for identification and taxonomic confirmation of collected plant samples. We are also grateful to Dr. Bhupal Govind Shrestha, Kathmandu University for providing the microbial samples and Sophisicated Analytical Instrument Facility (SAIF), IIT, Bombay for performing HRLCMS analysis of our samples.