Green Synthesis of Gold Nano-bioconjugates from Onion Peel Extract and Evaluation of Their Antioxidant, Anti-inflammatory, and Cytotoxic Studies

Abstract

Plant secondary metabolites such as flavonoids demonstrate high degrees of antioxidant, anti-inflammatory, and anticancer activities. Among flavonoids, quercetin plays an important role in inflammation by downregulating the level of various cytokines. Thereby, in this work, onion (Allium cepa) peel was successfully utilized for the synthesis of gold nano-bioconjugates acting as a natural therapeutic drug. In this process, crude onion peel extract was first divided into different fractionates, namely, ethyl acetate, butanol, methanol, and water, and they were subjected to various preliminary studies of antioxidant activities. The ethyl acetate fractionate shows high antioxidant activities in all the assays. The bioactive components were identified and found to contain a high amount of quercetin as confirmed by liquid chromatography with tandem mass spectrometry and high-performance liquid chromatogrpahy. Three gold nano-bioconjugates were prepared with different concentrations of the ethyl acetate fractionate. Various biochemical anti-inflammatory assays were carried out and compared with the active ethyl acetate fraction of the onion peel drug (OPD). The cytotoxicity of the nano-bioconjugate system and the OPD was checked in the myoblast L6 cell line from skeletal muscle tissues to evaluate the toxicity. All the three nano-bioconjugates A, B, and E demonstrated high percentages of cell viability, viz., 73.07, 72.3, and 69.15%, respectively, at their highest concentration of 200 μg/mL. The OPD also showed 88.56% cell viability with no toxic effects in the myoblast L6 cell line from skeletal muscle tissues. The reactive oxygen species reduction of nano-bioconjugate B showed a marked reduction of 76.77% at a maximum concentration of 200 μg/mL, whereas the OPD showed 68.17%. Hence, through this work, a cheap source of nano-bioconjugates is developed, which can act as a potent antioxidant and anti-inflammatory agent and are more active in comparison to the OPD alone.

Insights into Anti-Inflammatory Activity and Internalization Pathway of Onion Peel-Derived Gold Nano Bioconjugates in RAW 264.7 Macrophages

“…The prepared GNBC exhibits a ruby red color, characteristic of Au nanoparticles which is due to surface plasmon resonance at 540 nm. 20 As shown in the UV−vis spectra Figure 1D a distinct surface plasmon peak at 540 nm has been observed. The zeta potential of GNBC was found to be ζ = −21.2 mV.…”

“…The GNBCs which has been prepared from EA fraction of onion peels adopted from earlier protocol were characterized by UV–visible absorption spectroscopy, zeta potential analyzer, dynamic light scattering (DLS) technique, and transmission electron microscopy (TEM). The prepared GNBC exhibits a ruby red color, characteristic of Au nanoparticles which is due to surface plasmon resonance at 540 nm . As shown in the UV–vis spectra Figure D a distinct surface plasmon peak at 540 nm has been observed.…”

“…The preparation of GNBC was following by our earlier method where 2 mL (1 mg/mL) EA fraction of the onion peel extract was added in 10 mL of 1 mM concentration of gold chloride solution (gold chloride dissolved in sterile Milli-Q-water) for 10 min. During the period, the solution was placed at 33 °C on a magnetic stir and stirred vigorously until any color change appears.…”

“…16,17 The onion peel, although a waste, it contains many-fold quercetin as compared to onion flesh. 18 Instead of using commercially available quercetin as a capping agent for gold nanoparticle (gold NP) synthesis, 19 in our earlier report, 20 the onion peel was used as a cheap source of quercetin which can act as a strong reducing agent and capping agent that also checked the synergistic antioxidant and anti-inflammatory activities in L6 skeletal muscle cell line. The whole onion peel crude extract was purified into four fractionates which are as follows ethyl acetate (EA), butanol, methanol, and water.…”

In vitro Anti-inflammatory Activity and Acute Oral Toxicity Study of Gold Nanoparticles Generated from Stem Extract of Tinospora cordifolia

“…Green synthesis of GNPs using plant extract is recommended as an eco-friendly alternative to biological and chemical methods that reduces the maintenance of septic environment and eliminates the generation of toxic byproducts. 3 Herbal gold nanoparticles synthesized from different plant extracts have been tested for various activities like in vitro antioxidant, 5 in vitro cytotoxicity, 4 anti-cancer 5 and antimicrobial activities. 6 Tinospora cordifolia, which belongs to Menispermaceae family is a large, deciduous, climbing shrub found throughout India and also in Sri Lanka, Bangladesh, and China.…”