New Toxicity Mechanism of Silver Nanoparticles: Promoting Apoptosis and Inhibiting Proliferation

Abstract

Silver nanoparticles are increasingly recognized for their utility in biological applications, especially antibacterial effects. Herein, we confirmed the antibacterial effect of silver nanoparticles on Escherichia coli using the conventional optical density (OD) and colony-forming units (CFU) method and used flow cytometry (FC), TEM and BrdU ELISA to investigate the mechanisms of this effect. From the results, we conclude that AgNPs can simultaneously induce apoptosis and inhibit new DNA synthesis in the cells in a positive concentration-dependent manner. This study presents the first induction of apoptosis in these bacteria by AgNPs in this field. Our findings may provide a new strategy for the use of silver nanoparticles in antibacterial applications.

Minimum bactericidal concentration of chemically synthesized silver nanoparticles against pathogenic Salmonella and Shigella strains isolated from layer poultry farms

“…On the other hand, when AgNPs enter the bacterial cell, they form a low molecular weight region which begin to attack the respiratory chain, so consequently, the cellular signaling pathways will be changed by dephosphorylating assumed key peptide substrates on tyrosine residues (Sondi and Salopek-Sondi, 2004;Mulley et al, 2014;Su et al, 2017b). Moreover, the Ag+ metal ions that released from AgNPs (Feng et al, 2000;Swarnavalli et al, 2017) were found to have obstructing behavior to the bacterial signal transduction pathways (Devi et al, 2017) and moreover they could react with thiol groups present in the bacterial vital enzymes and proteins (Matsumura et al, 2003;Swarnavalli et al, 2017;Su et al, 2017b;Gopinath et al, 2016) and furthermore, they could react with phosphorus-containing compounds like DNA leading to inhibition of bacterial DNA replication, and so the bacterial cell death will be the final result (Jiao et al, 2014;Bao et al, 2015;Su et al, 2017b;Devi et al, 2017). On the other hand, the production of intracellular reactive oxygen species (ROS) by AgNPs occurred via the reaction between the AgNPs with the thiol-containing enzymes of the bacterial respiratory chain (Matsumura et al, 2003;Ahmad et al, 2017).…”

Antimicrobial Activity of Biosynthesized Silver Nanoparticles against E. coli and B. subtilis

“…On the contrary, it is well documented that the size and shape of AgNPs cause microbial inhibition [13,26]. Ivask et al [26] proved that the decrease in particle nano size will increase the toxicity of Ag NPs.…”

“…Previously, heavy metal ions including silver ions were used for their microbial toxicity via reduction of the metal ions or formation of metal sulfides [12]. After the development in AgNPs production, the nanoparticles were used instead of the metal ion owing to their powerful toxicity effect [10,13,14]. The increase in the use of AgNPs in different sectors raised a concern due to their occasional release the environment [9].…”

“…Lots of studies proven that AgNPs penetrate different living cells [13,14]. Therefore, the action of those NPs is inside the cells and not at cellular surface.…”

“…McShan et al [15] showed one of the toxicity mechanism which is oxidative stress via reactive oxygen species (ROS) generation, damaging cell membrane and other cell components including DNA, depleting antioxidant molecules (e.g., glutathione), disabling proteins, lowering reductase activity, reducing protein expression and depressing the activity of some membranous enzymes. Another study showed that apoptosis of E. coli increased with the increase in AgNPs concentrations (5 or 10 μg/ml) of 5-10 nm size [13] in addition to the interaction of both silver ionic and AgNPs form with sulfurcontaining macromolecules such as proteins, due to the strong affinity of silver for sulfur [15].…”