Abstract
Objectives: The purpose of this research was to estimate the phenolic content, flavonoid content, antioxidant, antibacterial, and α-amylase inhibitory activity of some selected plants such as Anethum sowa, Trigonella foenum-graecum, Lepidium sativum, Cuscuta reflexa, Eclipta alba, Leucas cephalotes, and Tinospora cordifolia collected from Siraha district of Nepal using in vitro studies.
 Methods: Methanol extracts of these medicinal plants were prepared by cold percolation method. Preliminary phytochemical screening was performed by color differentiation method. Total phenolic and flavonoid content were estimated by Folin-Ciocalteu reagent method and aluminum chloride colorimetric method. Antioxidant potential was evaluated by 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay. Furthermore, the α-amylase enzyme inhibitory activity was studied using starch as a substrate, pancreatic α-amylase as the enzyme, and acarbose as standard.
 Results: Phytochemical screening showed that the plant extracts were found a rich source of secondary metabolites. The phenolic content estimation showed T. foenum-graecum 939.764±0.01, L. sativum 551.63±0.02, A. sowa 306.34±0.06, L. cephalotes 233.19±0.03, T. cordifolia 211.76±0.02, E. alba 202.67±0.02, and C. reflexa Roxb. 145.09±0.09 mg milligram gallic acid equivalent per gram. The flavonoid content estimation showed T. cordifolia 852.07±0.11, L. sativum 553.81±0.05, E. alba 322.13±0.02, A. sowa 329.02±0.05, L. cephalotes 164.93±0.02, and C. reflexa Roxb. 146.37±0.00 mg milligram quercetin equivalent per gram. The antioxidant potential showed by E. alba IC50 33.48±0.82 μg/ml and the values ranged from E. alba 33.48±0.82 to A. sowa 47.62±1.09 μg/ml. The α-amylase inhibitory activity showed by A. sowa 76.78±2.00–E. alba 777.36±9.66 μg/ml. The result of brine shrimp toxicity showed LC50 value >1000 μg/ml. Among the seven plant extracts, only the plant extract of E. alba showed a zone of inhibition 14 mm against Staphylococcus aureus.
 Conclusions: The plant extract of T. foenum-graecum showed the highest phenolic content, and T. cordifolia showed the highest flavonoid content. The highest antioxidant potential exhibited by E. alba and the highest α-amylase inhibition activity showed by A. sowa. The plant extract of E. alba showed moderate antibacterial activity against S. aureus. All plant extracts were found non-toxic against brine shrimp larvae although further study is needed to assess its mechanism of action.
Highlights
Nepal is rich in all the three levels of biodiversity, namely, species diversity, genetic diversity, and habitat diversity
It can be concluded that plant extracts are the good sources of secondary metabolites
Radical scavenging activities of the methanolic extract of the selected plants showed a varied degree of antioxidant property, of which E. alba was found to have high antioxidant properties
Summary
Nepal is rich in all the three levels of biodiversity, namely, species diversity, genetic diversity, and habitat diversity. In Nepal, the use of different parts of several medicinal plants to cure specific diseases has been in vogue since ancient times [1]. Plants used for traditional medicine contain a wide range of substances that can be used to treat chronic as well as infection diseases. Oxidation reaction can produce the free radicals, which starts chain reactions that damage the cells. Antioxidants are natural or synthetic substances that may prevent or delay oxidative cell damage [4]. The antioxidant from natural sources neutralizes the radicals formed in the human body by oxidative stress. Numerous antimicrobial agents exist to treat a wide range of infections. The development of new anticancer and antimicrobial therapeutic agents from natural sources is one of the fundamental goals in medicinal chemistry [8]
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