Identification of Eschweilenol C in derivative of Terminalia fagifolia Mart. and green synthesis of bioactive and biocompatible silver nanoparticles

TLDR: In this paper, a green synthetic route was developed to prepare silver nanoparticles (AgNPs) in aqueous solution for biological applications, which showed high levels of antioxidant and considerable antibacterial and antifungal activities.

About: This article is published in Industrial Crops and Products.The article was published on 2019-10-01 and is currently open access. It has received 23 citations till now. The article focuses on the topics: Silver nanoparticle & Haemolysis.

Figures

Fig. 4. Representative size distribution profiles of AgNPs from NTA measurements.

Fig. 5. FTIR spectra of the AgNPs/extracts or fractions. A)AgNPEtE/EtE and B)AgNPAqF/AqF.

Fig. 3. Schematic illustration of the AgNP green synthesis and respective AgNPs colloidal solutions (A); UV–vis spectra of AgNPs solutions (B). (Nanoparticle synthesized with: ethanolic extract - AgNPEtE and aqueous fraction -AgNPAqF).

Table 3 Mean particle size, polydispersity index (PDI), Zeta potential and concentration of AgNPs.

Table 6 Minimal Inhibitory Concentrations (MICs) values of AgNPs, AgNO3 and itraconazole against tested fungi.

Fig. 14. AFM height images of Escherichia coli ATCC 25922. A) E. coli untreated (control); B) E. coli treated at sub-MIC concentration of AgNPEtE and C) E. coli treated at MIC concentration of AgNPEtE.

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "Identification of eschweilenol c in derivative of terminalia fagifolia mart. and green synthesis of bioactive and biocompatible silver nanoparticles" ?

In the green synthesis, the ethanolic extract of T. fagifolia and its aqueous fraction were used to promote silver reduction and nanoparticle stabilization. Gram-positive and Gram-negative bacteria were susceptible to growth inhibition by the nanoparticles, among which the AgNPs formed by the ethanolic extract was the most effective. This work represents the first description of antifungal activity by AgNPs against Fonsecaea pedrosoi, the etiologic agent of chromoblastomycosis. Synthesized nanoparticles presented significant antioxidant activity by sequestration of DPPH and ABTS radicals, in addition to iron reduction ( FRAP assay ) and measurement of antioxidant capacity in ORAC units, in addition, AgNP synthesized with the aqueous fraction also demonstrated antioxidant potential in microglial cells. The data obtained by AFM images suggested that AgNPs could lead to the lysis of bacteria and subsequent death. 

Q2. What is the effect of AgNPs on the cell?

AgNPs might destabilize the outer membrane, collapse the plasma membrane potential, deplete the levels of intracellular ATP and lead to pore formation, culminating in cell lysis (Składanowski et al., 2017). 

Q3. Why is it necessary to develop new therapeutic alternatives?

Increased survival of immunocompromised patients has led to an increase in the incidence of fungal infections; therefore it is necessary to develop new therapeutic alternatives. 

Q4. What was the method used to study the surface morphology and size of the AgNPs?

Transmission electron microscopy - TEM/EDS (using either a Hitachi H7000 TEM at 100 kV or a JEOL JEM 1400 also at 100 kV) was performed to study the surface morphology and size of the AgNPs, and confirm the composition. 

Q5. What is the effect of AgNPs on the bacterial membrane?

Treatment with AgNPs may lead to pore formation in the bacterial membrane, increasing the permeability to Ag cations; however, the intrinsic antibacterial activity does not only depend on it. 

Q6. What was the method used to measure the antioxidant capacity of the AgNPs?

Nanoparticle tracking analysis – NTA (Malvern NanoSight NS300, using NTA 3.2 software) was performed to observe the particle concentration and mean size of the AgNPs using a 542 nm laser. 

Q7. What is the mechanism of action of AgNPs on yeasts?

It is reported in the literature that AgNPs have inhibitory activity on yeasts of the genus Candida sp. by altering the membrane potential, forming pores, and releasing the cytoplasmic content, similar to the mechanism of action for bacteria (Kim et al., 2009). 

Q8. What are the limitations of the DPPH-RSA assay?

The principle of the DPPH-RSA assay is based on the ability of the tested samples to act as donors of hydrogen to the 2,2-diphenyl-1-picrylhydrazyl free radical, this capacity can be attributed to the presence of phenolic compounds and its derivatives, however this assay has some limitations, including greater reactivity in hydrophobic systems: 

Q9. What is the main reason why the fungi are resistant to antifungal agents?

C. krusei yeast, recognized for intrinsic resistance, was the most sensitive strain to the action of AgNPs, however it is important to emphasize that the filamentous fungi used in this study are difficult to treat and have become resistant to antifungal agents used in clinical practice (Tamura et al., 2014; Vandeputte et al., 2012). 

Q10. What is the role of AgNPs in the development of S. aureus?

Besides being an important virulence factor in the establishment and development of infections caused by S. aureus, Methicillin resistance is becoming increasingly prevalent (Garza-González and Dowzicky, 2013). 

Q11. What is the effect of light scattering techniques on the data?

It is also worth mentioning that light scattering techniques, such as DLS and NTA tend to be more sensitive to larger particles, skewing the data somewhat, and increasing PDI values (Eaton et al., 2017). 

Q12. What was the biocompatible nanoparticle among the AgNPs tested?

AgNPEtE was the most biocompatible nanoparticle among the AgNPs tested as it presented lower than 15% of haemolysis at the highest concentration tested, followed by AgNPAqF that presented around 65% of haemolysis at the concentration of 27 μg/mL, while AgNO3 promoted 100% haemolysis at this same concentration. 

Q13. What is the role of AgNPs in the development of the circulatory system?

After demonstrating the antimicrobial and antioxidant potential ofAgNPs, testing for lysis of red blood cells following exposure to silver nanoparticles is relevant because AgNPs may translocate into the circulatory system by several routes (Huang et al., 2016). 

Q14. What is the advantage of a green synthesis method?

A major advantage of a green synthesis method such as that described here, is the lack of toxic by products or reagents in the synthesis medium, reducing the need for further purification. 

Q15. What is the role of the aqueous fraction in the antioxidant capacity of AgNPs?

The antioxidant capacity of AgNPs synthesized with the aqueous fraction (AgNPAqF) was also evaluated in relation to the generation of lipopolysaccharide (LPS)-induced reactive oxygen species (ROS) in microglial cells, which are implicated in neurodegenerative diseases, such as Parkinson's disease and is a suitable cellular model for this type of study (Barbosa et al., 2018). 

Q16. What is the significance of the ORAC assay?

The ORAC assay has a good correlation with in vivo assays and is widely accepted for measuring the total antioxidant capacity of biological samples because it is related to the measurement of a biologically relevant radical (Thaipong et al., 2006). 

Q17. What is the mean particle hydrodynamic size of AgNPs?

The mean particle hydrodynamic size measured by DLS was equal to 66.2 ± 3.6 nm and 81.4 ± 1.6 nm, for AgNPEtE (silver nanoparticle synthesized with the ethanolic extract of T. fagifolia) and AgNPAqF (silver nanoparticle synthesized with the aqueous fraction of ethanolic extract of T. fagifolia), respectively. 

Q18. At what concentrations did the AgNPAqF show the haemolytic?

It is important to emphasize that AgNPEtE was active against all strains of microorganisms used in concentrations below 13.5 μg/mL, and therefore was biocompatible at the effective concentrations. 

Q19. What is the first time that silver nanoparticles have been tested against F. ped?

This is the first time that silver nanoparticles have been tested against F. pedrosoi, the etiologic agent of chromoblastomycosis (Queiroz-Telles et al., 2017), however studies against another filamentous fungus reveals that AgNPs may interfere in the fungal reproduction process and cause structural changes in hyphae (Lamsal et al., 2011). 

Q20. What is the effect of the aqueous fraction on the antioxidant activity of AgNPs?

maintenance of amount of these compounds adsorbed to the surface of the nanoparticles can promote antioxidant activity of AgNPs (Patil and Kumbhar, 2017).