Comparative evaluation on chemical composition, in vitro antioxidant, antidiabetic and antibacterial activities of various solvent extracts of Dregea volubilis leaves

Abstract

• Chemical characterization of leaf extract by GC-MS analysis showed 67 compounds. • DVL extract exhibited excellent in vitro antidiabetic activity. • Leaf extract showed significant free radical scavenging abilities. • Some of the extracts inhibited the growth of selected pathogenic bacteria comparable to the standard. • Hydroalcoholic and methanolic extracts showed promising results. Dregea volubilis is an important folk medicinal plant used as an ingredient in Ayurvedic formulations to treat asthma, piles, urinary tract infections, tumours, leucoderma, piles, inflammations, rheumatic pain, cough, severe cold and fever. The phytochemicals, percentage of extract yield, total phenolics and flavonoids, in vitro antioxidant, antidiabetic and antibacterial activities of six solvent extracts obtained from the leaves of D. volubilis (DVL) were investigated. Chemical composition of DVL extract was analysed using GC-MS, total phenolics and flavonoids by spectrophotometric methods. Antioxidant activity was performed using eight in vitro assays and antidiabetic activity was evaluated by α-amylase and α-glucosidase inhibitory assays. Antibacterial activity was studied against 10 pathogenic bacteria by agar disc diffusion and microdilution method. The extract yield was higher in hydroalcoholic (9.15%) and methanolic extracts (6.8%). A total of 67 compounds were identified from six extracts, of which 17 compounds especially squalene, oleic acid and palmitic acid were prominent constituents. Maximum amount of total phenolics (48.66 ± 4.19 mg GAE/g) and flavonoids (29.58 ± 0.47 mg QE/g) were recorded in methanolic and hydroalcoholic extracts respectively. Hydroalcoholic and methanolic extracts displayed strong inhibition of α-amylase and α-glucosidase with an IC 50 of 60.51 ± 2.78 and 38.58 ± 0.56 µg/mL respectively. Methanol extract showed highest DPPH, nitric oxide and superoxide radical activities with the IC 50 of 39.24 ± 2.56, 13.06 ± 1.40 and 13.71 ± 6.99 µg/mL respectively. While, hydroalcoholic extract exhibited better free radical scavenging ability for ABTS (51.23 ± 8.36 µg/mL), hydroxyl radical scavenging (46.92 ± 14.30 µg/mL), total antioxidant (16.81 ± 1.60 AAE mg/g) and metal chelating ability (49.61 ± 0.96 EDTA E mg/g). The FRAP assay showed better activity in aqueous extract with a value of 258.25 ± 3.31 mM Fe (II) E mg/g. Hydroalcoholic, ethyl acetate and aqueous extracts showed significant antibacterial activity at higher concentrations against P. vulgaris (21.0 ± 1.01 mm), B. subtilis (22.6 ± 0.54 mm) and E. coli (27.8 ± 0.83 mm) respectively. The correlation analysis revealed a strong positive relationship between the amount of total phenolics and flavonoids with antioxidant and antidiabetic activities in a concentration dependent way. The results of present investigation proved that hydroalcoholic extract of DVL could be used as a promising natural antioxidant with potential enzyme inhibitory and antibacterial properties and might be used as a therapeutic agent in pharmaceutical and nutraceutical industries.