Phyto-mediated synthesis of silver nanoparticles using Erythrina variegata L. leaf extract and evaluation of their anti-bacterial, anti-Alzheimer, antioxidant and cytotoxic activities

Abstract

Background

Owing to their growing prevalence, multi-drug-resistant bacterial infections, Alzheimer’s disease and cancer has emerged as a global health concern. To combat this real threat to humankind, biogenic silver nanoparticles (AgNPs) are considered as a prime strategy due to its wide-range of medical applications.

Objectives

The current study was aimed to investigate the green synthesis of silver nanoparticles using aqueous leaf extract of Erythrina variegata and evaluation of anti-Alzheimer, antioxidant and anti-cancer efficacies.

Method

The aqueous extract was prepared and initially assessed for its phytochemical composition. Then silver nanoparticles (AgNPs) were synthesized by reducing aqueous AgNO₃ with aqueous leaf extract at nonphotomediated conditions, without any catalyst, template or surfactant. The Ev-AgNPs were characterized by ultraviolet-visible (UV–VIS) & Fourier-transform infrared (FTIR) spectroscopy, zeta sizer, scanning electron microscopy (SEM), energy-dispersive X-ray (EDXA) and X-ray diffraction (XRD) analysis. The bio-activities of extract and Ev-AgNPs including antibacterial, anti-oxidant, anti-Alzheimer’s and anticancer activities were evaluated using well diffusion, ABTS & DPPH radical scavenging, Ellman’s and MTT assays, respectively.

Results

Phytochemical analysis revealed the leaf extract of E. variegata as rich source of flavonoids and phenolics. Physicochemical and morphological characterization inferred that Ev-AgNPs were spherical in shape, small in size (59.5–90.2 nm), crystalline in nature with high stability (−38.8 mV) and associated with capping agents. In biological evaluation, extract of E. variegata disclosed good activities, however, better potencies were noticed with Ev-AgNPs. Biogenic Ev-AgNPs exhibited high ABTS and DPPH radical scavenging abilities with IC₅₀ values of 38.47 and 17.73 µg/mL, respectively. Ev-AgNPs had highest antibacterial activity against Escherichia coli and Pseudomonas aeruginosa, good activity with Bacillus subtilis and Staphylococcus aureus, while least inhibition zone against Pseudomonas syringae. Ev-AgNPs displayed remarkable cytotoxicity against human breast cancer cell line MCF–7 with 53.11 % inhibition at a concentration of 0.5 µg/mL. Ev-AgNPs were found to be non-haemolytic in nature. In Elmann assay, Ev-AgNPs excelled high inhibitory efficiencies against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with IC₅₀ values of 15.18 and 56.21 µg/mL, respectively with mixed mode of inhibition.

Conclusion

Based on these findings, it appears that Ev-AgNPs have promise as multi target directed ligand effective against bacterial infections, breast cancer, Alzheimer’s disease and also oxidative stress mediated illnesses.