Although Silver Nanoparticles Research Articles

Biocompatible sodium alginate–silk fibroin antibacterial microspheres from a microfluidic platform for infected wound repair

Micro/nano drug delivery systems can provide ideal controlled drug release. Microfluidic chip technology plays an important role in the preparation of microspheres. Sodium alginate (SA) has been used to prepare microspheres as drug carriers owing to its good biosafety and easy preparation. However, these microspheres lack antimicrobial activity and drug loading efficiency, which prevent their application for infected wound repair. Although silver nanoparticles (AgNPs) possess broad-spectrum antibiotic activity, liquid mixtures of AgNPs and SA are too unstable to fabricate drug-loaded microspheres using microfluidic chip technology. In this study, AgNPs were coated with silk fibroin (SF) and then dispersed in SA solution to fabricate antibacterial microspheres (denoted SA-SF-Ag) using microfluidic chip technology. SA-SF-Ag effectively inhibited the growth of microorganisms and gradually released AgNPs. Moreover, in vivo results showed that SA-SF-Ag promoted infected wound healing and angiogenesis by killing Pseudomonas aeruginosa on the surface of infected skin wounds of mouse models. This study offers a new method to integrate AgNPs into organic polymeric microspheres for the treatment of infected wounds.

Role of bioactive magnetic nanoparticles in the prevention of wound pathogenic biofilm formation using smart nanocomposites

BackgroundBiofilm formation and its resistance to various antibiotics is a serious health problem in the treatment of wound infections. An ideal wound dressing should have characteristics such as protection of wound from microbial infection, suitable porosity (to absorb wound exudates), proper permeability (to maintain wound moisture), nontoxicity, and biocompatibility. Although silver nanoparticles (AgNPs) have been investigated as antimicrobial agents, their limitations in penetrating into the biofilm, affecting their efficiency, have consistently been an area for further research.ResultsConsequently, in this study, the optimal amounts of natural and synthetic polymers combination, along with AgNPs, accompanied by iron oxide nanoparticles (IONPs), were utilized to fabricate a smart bionanocomposite that meets all the requirements of an ideal wound dressing. Superparamagnetic IONPs (with the average size of 11.8 nm) were synthesized through co-precipitation method using oleic acid to improve their stability. It was found that the addition of IONPs to bionanocomposites had a synergistic effect on their antibacterial and antibiofilm properties. Cytotoxicity assay results showed that nanoparticles does not considerably affect eukaryotic cells compared to prokaryotic cells. Based on the images obtained by confocal laser scanning microscopy (CLSM), significant AgNPs release was observed when an external magnetic field (EMF) was applied to the bionanocomposites loaded with IONPs, which increased the antibacterial activity and inhibited the formation of biofilm significantly.ConclusionThese finding indicated that the nanocomposite recommended can have an efficient properties for the management of wounds through prevention and treatment of antibiotic-resistant biofilm.Graphical

How green and simple can nontoxic antimicrobial nanoparticles be obtained? Deposition of AgNPs on the TiO2 surface in a neutral aqueous media by using the flavonoid quercetin

Although silver nanoparticles (AgNPs) are excellent antimicrobial agents, they are considered hazardous materials due to their cytotoxic effects. In this research, AgNPs were deposited on TiO2 using a natural flavonoid under neutral conditions (pH 7) to obtain antibacterial nanomaterials without cytotoxicity. First, AgNPs were synthesized using two types of quercetin as a reducing agent, reactive grade and dietary supplement, to confirm the formation of AgNPs under this green approach. Later, the deposition of AgNPs on TiO2 was carried out again at pH 7 using reactive grade quercetin (sTiO2‐Ag(R)) and dietary supplement (sTiO2‐Ag(S)). They were analyzed by scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), Z potential, and colloidal stability. The results showed that the deposition with dietary supplement is more efficient and safer, while the process carried out with reactive grade is inadequate since it causes nitrates bound to the TiO2 surface. The antipathogenic activity was studied against the main bacteria in raw food (Escherichia coli) and a major human pathogen (Staphylococcus aureus). The disk diffusion method confirmed higher inhibition when the deposition used the dietary supplement. Furthermore, sTiO2‐Ag(S) was analyzed by single‐plate serial dilution method to obtain minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). For S. aureus, the MIC was 31.2 μg/ml, and MBC was 1 mg/ml; for E. coli, the MIC was 7.8 μg/ml, and MBC was 1 mg/ml. Finally, cytotoxicity was evaluated by seeding peripheral blood mononuclear cells, showing that the sTiO2‐Ag(S) is nontoxic up to 100 ppm. These findings open the possibility of using these nanomaterials in numerous applications.

Anti-Adherence and Antimicrobial Activities of Silver Nanoparticles against Serotypes C and K of Streptococcus mutans on Orthodontic Appliances.

Background and Objectives: Streptococcus mutans (S. mutans) is the main microorganism associated with the presence of dental caries and specific serotypes of this bacteria have been related to several systemic diseases limiting general health. In orthodontics, white spot lesions (WSL), represent a great challenge for clinicians due to the great fluctuation of their prevalence and incidence during conventional orthodontic treatments. Although silver nanoparticles (AgNP) have been demonstrated to have great antimicrobial properties in several microorganisms, including S. mutans bacteria, there is no available information about anti adherence and antimicrobial properties of AgNP exposed to two of the most relevant serotypes of S. mutans adhered on orthodontic materials used for conventional therapeutics. The objective of this study was to determine anti-adherence and antimicrobial levels of AgNP against serotypes c and k of S. mutans on conventional orthodontic appliances. Materials and Methods: An AgNP solution was prepared and characterized using dispersion light scattering (DLS) and transmission electron microscopy (TEM). Antimicrobial and anti-adherence activities of AgNP were determined using minimal inhibitory concentrations (MIC) and bacterial adherence testing against serotypes c and k of S. mutans clinically isolated and confirmed by PCR assay. Results: The prepared AgNP had spherical shapes with a good size distribution (29.3 ± 0.7 nm) with negative and well-defined electrical charges (−36.5 ± 5.7 mV). AgNP had good bacterial growth (55.7 ± 19.3 µg/mL for serotype c, and 111.4 ± 38.6 µg/mL for serotype k) and adherence inhibitions for all bacterial strains and orthodontic wires (p < 0.05). The serotype k showed statistically the highest microbial adherence (p < 0.05). The SS wires promoted more bacterial adhesion (149.0 ± 253.6 UFC/mL × 104) than CuNiTi (3.3 ± 6.0 UFC/mL × 104) and NiTi (101.1 ± 108.5 UFC/mL × 104) arches. SEM analysis suggests CuNiTi wires demonstrated better topographical conditions for bacterial adherence while AFM evaluation determined cell wall irregularities in bacterial cells exposed to AgNP. Conclusions: This study suggests the widespread use of AgNP as a potential anti-adherent and antimicrobial agent for the prevention of WSL during conventional orthodontic therapies and, collaterally, other systemic diseases.

Lignin as a multi-functional agent for the synthesis of Ag nanoparticles and its application in antibacterial coatings

Although silver nanoparticles (AgNPs) possess broad-spectrum antimicrobial activity, their intended use may adversely affect the ecosystem. In this study, alkali lignin (AL) was modified via quaternization to synthesize amphoteric lignin (AML), which was further used as a reducing and stabilizing agent for the synthesis of amphoteric lignin@nanosilver (AML@AgNPs) composites under microwave irradiation. The AML@AgNPs were characterized via X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy measurements. The results showed that the average particle size of AgNPs was 24.7 nm. The positively charged AML@AgNPs had excellent antibacterial activity against Escherichia coli and Staphylococcus aureus, with a minimum inhibitory concentration of 30 ppm. The results of quartz crystal microbalance with dissipation monitoring and optical microscopy tests showed that the positively charged AML could effectively capture bacteria, which promoted the adhesion of the AML@AgNPs to bacteria. Furthermore, the AML@AgNPs had good compatibility with polyurethane, and when the AML@AgNPs content in the WPU–AML@AgNPs blend was 0.5 wt.% of the waterborne polyurethane (WPU), the prepared polyurethane film could completely inhibit bacteria growth.

Immobilized Ag-nanoparticles (iNPs) for environmental applications: Elucidation of immobilized silver-induced inhibition mechanism of Escherichia coli

Although silver nanoparticles (AgNPs) appear to be promising for certain medical/pharmaceutical applications, they present significant disadvantages when it comes to environmental applications due to the need for recovery of the metal (Ag) which is considered hazardous for the environment. The present study examines the antimicrobial properties and mechanism of action of immobilized (on Al2O3) silver nanoparticles’ (1 wt% Ag-iNPs) regarding the treatment of E. coli microbial solutions. Antimicrobial experiments were conducted in semi-batch mode using a three-phase continuous flow stirred tank reactor. Every treated sample was taken from the outlet of the reactor for the time intervals of 0, 5 and 25 min. To ensure that the bactericidal property of Ag-iNPs is not attributed to the dissolution of surface silver (as free Ag+), a suitable Ag+ scavenger was used as already described in our earlier studies. Regarding the molecular analysis performed under this study, the regulation of key enzymes involved in bactericidal activity of E. coli, was examined, after their treatment either with immobilized silver nanoparticles (Ag-iNPs) or AgNO3. Specifically, 50 mL sample for each case was centrifuged (10 min at 10,000 rpm) and the pellet (≈109 cells) was immediately subjected to total RNA extraction. For real-time RT-qPCR analyses, 1 μg of total RNA was converted into cDNA. It was found that PldA gene, which encodes outer membrane’s phospholipase A (OMPLA), was up-regulated after 5 and 25 min of treatment with Ag-iNPs. OMPLA’s activation appears to be the initial step of Ag-iNPs bactericidal mechanism that ultimately leads to the creation of holes on the outer membrane (OM), irreversibly disturbing the cells’ respiration cycle. In addition, after treatment with Ag-iNPs, Blue copper oxidase CueO (encoded by cueO gene) was found to be over-produced and appears to play a key-role in the oxidative transfer of silver from the surface of Ag-iNPs to the cell. This leads to the Ag-induced displacement of copper from its native protein sites such as CusS/CusR, a fact that causes the release of labile copper and ROS inside the cell. In addition, TEM analysis of bacteria treated with Ag-iNPs revealed severe morphological changes (“holes”) on bacterial outer membrane, indicating that there is an intermediate step in the proposed antimicrobial mechanism which takes place on the surface of Ag-iNPs.

Antimicrobial Activity of Silver Nanoparticles against Clinical Biofilms from Patients with and without Dental Caries

Dental caries is an infectious oral disease originated by the presence of different microorganisms from well-defined biofilms. Many treatments for dental caries have been demonstrated to be successful protocols; however, incidence and prevalence remain still high. Although silver nanoparticles (AgNPs) have shown excellent antimicrobial properties, even against different oral bacteria, there is no available scientific information that has evaluated the antimicrobial activity of AgNPs against oral biofilms from subjects with active dental caries. The objective of this research was to evaluate the inhibitory effect of AgNPs in dental biofilms from subjects with and without dental caries. Two sizes of AgNPs were prepared and characterized. Dental plaque samples were collected from 30 subjects with dental caries and 30 subjects with no dental caries. Microbiological analysis was determined by the minimum inhibitory concentration (MIC) of nanoparticles, and the presence and distribution of microbial strains were identified by polymerase chain reaction (PCR) assay. AgNPs had significant antimicrobial effects against all samples of dental plaque; however, the physical properties of AgNPs, as well as specific sociodemographic and clinical conditions from patients, were also associated with bacterial growth inhibition of Ag particles ( p &lt; 0.05 ). PCR confirmed the presence of oral bacteria associated with dental caries, such as S. mutans and S. sobrinus strains, principally. The AgNPs exhibited great potential to be used as an antimicrobial therapy for the control and prevention of dental caries.

Toxicity of silver nanoparticles on different tissues in adult Danio rerio.

Although silver nanoparticles (AgNP) are among the most studied nanomaterials by virtue of their broad application in many areas, little is known about their overall toxicity to aquatic organisms after their contamination of the water environment. This study aimed to analyze the effect of the exposure (96 h) to different AgNP concentrations on Danio rerio (zebrafish) tissues. AgNP were synthesized and characterized by transmission electron microscopy (TEM), showing spherical AgNP of 30.00 ± 16.80 nm size. The effects of different AgNP concentrations (1, 3, and 5 μg L-1) on brain, muscle, gill, and liver tissues of zebrafish were investigated. The results show a significant decrease in brain and muscle acetylcholinesterase (AChE) activity. Liver and gill catalase (CAT) activity also decreased significantly. At the highest exposure concentration, muscle AChE was more inhibited (37.3%) than brain AChE (26.4%) and gill CAT was more inhibited (67.4%) than liver CAT (51.2%). D. rerio also showed gill morphological changes such as fusion of secondary lamellae, curvature, dilated marginal channel, and epithelial lifting. This study indicates that gill CAT together with morphological studies are potential biomarkers for AgNP.

Silver nanoparticles induce abnormal touch responses by damaging neural circuits in zebrafish embryos

Although silver nanoparticles (AgNPs) are used in various commercial products, the biological effects of AgNPs on fish embryogenesis and the underlying molecular mechanisms are still poorly understood. In this study, both touch responses and neuron membrane potential were found to be abnormal in AgNPs-stressed embryos. Moreover, neurogenesis genes were unveiled to be down-regulated and were enriched in ligand-gated ion channel activity, dopamine receptor signaling pathway, etc. in AgNPs-stressed embryos by microarray assays. Additionally, the down-regulated expression of otpa/sncgb - gad1b/gad2 dopaminergic neurotransmitter genes, robo2 - vim and glrbb synaptic transmission genes, and motor neuron genes isl1 &isl2a was further identified in both AgNPs- and Ag+-stressed embryos by qPCR, whole-mount in situ hybridization (WISH), and by using specific promoter-derived GFP fluorescence transgenic zebrafish. Moreover, the reduced expression of gad1b, gad2, and isl1 could be recovered by adding Ag+ chelating compound l-cysteine in AgNPs stressed embryos. Our results reveal for the first time that it is through damaging the formation of neural circuits, including dopaminergic neurotransmitter, synaptic transmission, and motor activities, that AgNPs induce abnormal electrical membrane properties, leading to dysfunctional touch responses and locomotor escape responses mostly via their released Ag+ during embryogenesis.

Review of the effects of silver nanoparticle exposure on gut bacteria.

Gut bacteria are involved in regulating several important physiological functions in the host, and intestinal dysbacteriosis plays an important role in several human diseases, including intestinal, metabolic and autoimmune disorders. Although silver nanoparticles (AgNPs) are increasingly being incorporated into medical and consumer products due to their unique physicochemical properties, studies have indicated their potential to affect adversely the gut bacteria. In this review, we focus on the biotoxicological effects of AgNPs entering the gastrointestinal tract and the relationship of these effects with important nanoscale properties. We discuss in detail the mechanisms underlying the bactericidal toxicity effects of AgNPs and explore the relationships between AgNPs, gut bacteria and disease. Finally, we highlight the need to focus on the negative effects of AgNPs usage to facilitate appropriate development of these particles.

Antiadherence and Antimicrobial Properties of Silver Nanoparticles against Streptococcus mutans on Brackets and Wires Used for Orthodontic Treatments

White spot lesions (WSLs) are very frequent alterations during orthodontic treatments causing demineralization of the dental enamel. Various dental treatments have been developed to prevent WSLs; the prevalence and incidence of these lesions remain significantly high. Although silver nanoparticles (AgNPs) have demonstrated good inhibitory effects against several microorganisms, more studies about antiadherence activity on different orthodontic appliance surfaces are necessary. To determine the inhibitory effect and antiadherence activity of AgNPs on the adhesion of S. mutans on surfaces of brackets and wires for orthodontic therapies, two sizes of AgNPs were prepared and characterized. The evaluation of S. mutans adhesion was performed with microbiological assays on surfaces of brackets and orthodontic modules in triplicate. Topographic characteristics of orthodontic brackets and wires were made by scanning electron and atomic force microscopies. All AgNP samples inhibited S. mutans adhesion; however, the smaller AgNPs had better inhibition than the larger ones. The presence of the module influenced the adhesion of S. mutans but not in the activity of AgNPs. The AgNPs used in this study showed to have good antimicrobial and antiadherence properties against S. mutans bacteria determining its high potential use for the control of WSLs in orthodontic treatments.

Photodynamic inactivation assisted by localized surface plasmon resonance of silver nanoparticles: In vitro evaluation on Escherichia coli and Streptococcus mutans.

Localized surface plasmon resonance (LSPR) of gold nanoparticles has been reported to increase the antimicrobial effect of the photodynamic therapy. Although silver nanoparticles (AgNPs) are an efficient growth inhibitor of microorganisms, no studies exploring LSPR of AgNPs to enhance the photodynamic inactivation (PDI) have been related. In this work, we described the LSPR phenomenon of AgNP sand investigated its interaction with riboflavin, a natural photosensitizer. We evaluated the use of AgNPs coated with pectin (p-AgNP) in riboflavin (Rb)-mediated PDI of Escherichia coli (Gram- bacteria) and Streptococcus mutans (Gram + bacteria) using a blue light-emitting diode (λ = 455 ± 20 nm) of optical power 200 mW. Irradiance was 90 mW/cm2 and radiant exposure varied according to the time exposure. Uptake of Rb and p-AgNP by the cells was evaluated by measuring the supernatant absorption spectra of the samples. We observed that LSPR of p-AgNPs was able to enhance the riboflavin photodynamic action on S. mutans but not on E. coli, probably due to the lower uptake of Rb by E. coli. Taken together, our results provide insights to explore the use of the LPRS promoted by silver nanostructures to optimize antimicrobial PDI protocols.

Silver nanoparticles induce lysosomal-autophagic defects and decreased expression of transcription factor EB in A549 human lung adenocarcinoma cells

Although silver nanoparticles (AgNPs) are widely used in consumer and medical products, the mechanism by which AgNPs cause pulmonary damage is unclear. AgNPs are incorporated into cells and processed via the autophagy pathway. We examined the effects of AgNP exposure on autophagic flux and expression of transcription factor EB (TFEB) in A549 lung adenocarcinoma cells. In cells exposed to citrate-coated 60-nm AgNPs, confocal laser microscopic examination showed a decrease in the LysoTracker fluorescence signal and an increase in that of Cyto-ID, indicating lysosomal pH alkalization and autophagosome formation, respectively. The proteins p62 and microtubule-associated protein light chain 3B-II (LC3B-II) are both degraded by autophagy, and their levels increased depending on AgNP dose. Furthermore, AgNP-induced increase in LC3B-II was not enhanced by treatment with the autophagic inhibitor bafilomycin A1. TFEB mRNA levels, and protein levels in cytosolic and nuclear fractions, were suppressed by exposure to AgNPs, suggesting transcriptional inhibition of TFEB expression. Overexpression of TFEB did not suppress AgNP-induced LC3B-II accumulation and cellular damage, indicating that impairment of autophagic flux and cellular damage by AgNPs might not be primarily caused by reduced TFEB expression. The present study suggests that AgNP-induced lysosomal dysfunction plays a principal role in the autophagic flux defect.

Developmental toxicity and DNA damaging properties of silver nanoparticles in the catfish (Clarias gariepinus)

Although, silver nanoparticles (AgNPs) are used in many different products, little information is known about their toxicity in tropical fish embryos. Therefore, this study evaluated the developmental toxicity of waterborne silver nanoparticles in embryos of Clarias gariepinus. Embryos were treated with (0, 25, 50, 75ng/L silver nanoparticles) in water up to 144h postfertilization stage (PFS). Results revealed various morphological malformations including notochord curvature and edema. The mortality rate, malformations, and DNA fragmentation in embryos exposed to silver nanoparticles increased in a dose- and embryonic stage-dependent manner. The total antioxidant capacity and the activity of catalase in embryos exposed to 25ng/L silver nanoparticles were decreased significantly while the total antioxidant capacity and the activity of catalase were insignificantly increased with increasing concentrations in the embryos from 24 to 144 h-PFS exposed to 50 and 75ng/L silver nanoparticles. Lipid peroxidation values showed fluctuations with doses of silver nanoparticles. Histopathological lesions including severely distorted and wrinkled notochord were observed. The current data propose that the toxicity of silver nanoparticles in C. gariepinus embryos is caused by oxidative stress and genotoxicity.

From the Cover: Metabolism Modulation in Different Organs by Silver Nanoparticles: An NMR Metabolomics Study of a Mouse Model.

Although silver nanoparticles (AgNPs) are widely disseminated and show great potential in the biomedical field, there is a recognized need to better understand their action at the metabolic and functional levels. In this work, we have used NMR metabolomics, together with conventional clinical chemistry and histological examination, to characterize multi-organ and systemic metabolic responses to AgNPs intravenously administered to mice at 8 mg/kg body weight (a dose not eliciting overt toxicity). The major target organs of AgNPs accumulation, liver and spleen, showed the greatest metabolic changes, in a clear 2-stage response. In particular, the liver of dosed mice was found to switch from glycogenolysis and lipid storage, at 6 h postinjection, to glycogenesis and lipolysis, at subsequent times up to 48 h. Moreover, metabolites related to antioxidative defense, immunoregulation and detoxification seemed to play a crucial role in avoiding major hepatic damage. The spleen showed several early changes, including depletion of several amino acids, possibly reflecting impairment of hemoglobin recycling, while only a few differences remained at 48 h postinjection. In the heart, the metabolic shift towards TCA cycle intensification and increased ATP production possibly reflected a beneficial adaptation to the presence of AgNPs. On the other hand, the TCA cycle appeared to be down regulated in the lungs of injected mice, which showed signs of inflammation. Thekidneys showed the mildest metabolic response to AgNPs. Overall, this study has shown that NMR metabolomics is a powerful tool to monitor invivo metabolic responses to nanoparticles, revealing unforeseen effects.

Effects of Silver Nanoparticles on Heterotrophic Bacterial Community Inhabiting the Anoxic Paddy Soil of Flooded Rice Microcosms

Although silver nanoparticles (AgNPs) have been applied more in our daily life. They are well known for their antimicrobial activities against a wide range of organisms but more concerns on the negative effects of AgNP products contaminated to the environment especially on most microorganism niches related to nutrient cycling in ecosystem. In the study, research was done to in understand the effects of AgNPs on heterotrophic bacterial populations in rice paddy soil. Both culturable N2-fixing bacteria and common heterotrophic bacteria could adapt themselves to AgNPs at low concentration (less than 50 ppm). However, more distinct reduction in N2-fixing bacteria against AgNPs were detected than heterotrophic bacterial niches at least 100 ppm AgNPs . These evidences indicated AgNPs at high concentration had significant adverse effects on the diverse microbial consortiums as well as rice seedlings.

Not all silver nanoparticles are equal: Effect of functionalization on K homeostasis in human red blood cells

Although silver nanoparticles (AgNPs) are one of the most frequently used nanomaterials (NMs) in industrial and biomedical applications, their toxicity and interaction with blood components, such as erythrocytes, has been insufficiently investigated. Here, we report on the effect of AgNPs at the level of cellular function, and particularly on ion transport in human red blood cells (HRBCs). These AgNPs were size‐selected, concentrated and purified by tangential flow filtration before HRBC exposure. Two methods of synthesis were used for the functionalization of AgNPs, Creighton and Lee‐Meisel. HRBCs were obtained from adult donors at a blood bank, expired or fresh or further stored refrigerated in the laboratory for variable lengths of time, and from fresh or stored refrigerated cord blood. Rubidium, used as a K congener to measure K influx, and the K concentration were determined in the presence and absence of several concentrations (0–150 μg/mL) of negatively charged, spherical 10 nm AgNPs at different time points (0–60 min). Our findings indicate that Creighton AgNPs, independently of the source and in a time‐ and dose‐dependent manner, inhibited Rb influx by ~ 80 % (p &lt; 0.001, n=7) and depleted the cells of K by more than 90 % (p &lt; 0.0001, n = 7), although interindividual differences were observed. In comparison to the Creighton, Lee‐Meisel AgNPs caused a maximum Rb inhibition of ~ 50 % and K loss of ~ 15 % with larger interindividual variability than Creighton AgNPs, albeit in a small sample. The loss of K from HRBCs was entirely accounted for by an increase in K concentration in the extracellular medium. These findings indicate that functionalization of AgNPs has a significant effect on HRBC K homeostasis. Further studies are required to identify the mechanisms underlying the observed changes in HRBC ionic composition.Support or Funding InformationFunded by NSF

Sublethal Concentrations of Silver Nanoparticles Stimulate Biofilm Development

Although silver nanoparticles (AgNPs) are used as antimicrobial agents in a wide variety of commercial products, sublethal exposure can counterproductively promote the development of biofilms. We observed by fluorescence microscopy denser biofilm growth with mixed cultures from a wastewater treatment plant after exposure to 21.6 μg/L 10 nm AgNPs. To further understand biofilm promotion mechanisms, experiments were conducted with a pure culture of Pseudomonas aeruginosa PAO1. Sublethal exposure of PAO1 to AgNPs (10.8 and 21.6 μg/L) also enhanced biofilm development and upregulated quorum sensing, lipopolysaccharide biosynthesis, and antibiotic resistance (efflux pump) genes. An increase in the sugar and protein contents of the PAO1 biofilm matrix (by 55 ± 3 and 114 ± 32%, respectively, relative to unexposed controls) corroborated the transcriptional upregulation of PAO1 biofilm-related genes. Enhanced biofilm development by exposure to low AgNP concentrations might accelerate biofouling and biocorrosion an...

Serum albumin reduces the antibacterial and cytotoxic effects of hydrogel-embedded colloidal silver nanoparticles

Although silver nanoparticles (AgNPs) are widely used as ion-releasing antimicrobial additives in medical devices, recent reports indicate the suppression of effectiveness in the presence of blood serum proteins. Bovine serum albumin (BSA) is known to bind silver and silver ions, so that the presence of proteins may change the antibacterial or cytotoxic properties of AgNPs even when they are embedded in a solid agar hydrogel matrix. We produced ligand-free AgNPs by laser ablation in water resulting in aqueous silver mass concentrations of 0.5 to 7.1%. The AgNPs were immersed into agar in concentrations of 5–70 μg ml−1 medium. We examined the influence of 1% BSA within the hydrogel matrix on the nanoparticles’ antibacterial effect on four clinically relevant bacteria strains and the cytotoxicity of colloidal AgNP was tested on fibroblasts with or without 1% BSA. The hydrogel-immobilized AgNPs showed a significant reduction of antibacterial activity in the presence of BSA. Cytotoxicity started at a colloidal AgNP concentration of 35 μg ml−1, and addition of BSA significantly reduced the effect on cell morphology and viability. Overall, in the presence of BSA, both antibacterial and cytotoxic effects of AgNPs were markedly reduced. Notably, a therapeutic AgNP window, requiring a dose at which pathogenic bacteria growth is inhibited while fibroblast viability is not affected, could only be observed in the absence of BSA. Addition of BSA reduces the antibacterial activity of AgNP to a point without significant growth inhibition of S. aureus but still observable cytotoxic effects on HGFib. Hence, the presence of a major blood serum protein significantly decreases the antimicrobial effects of AgNPs on a range of pathogenic bacteria even when the NPs are immobilized within an agar hydrogel model.

Endoplasmic reticulum stress signaling is involved in silver nanoparticles-induced apoptosis

Although silver nanoparticles (AgNPs) have been reported to exert strong acute toxic effects on various cultured cells by inducing oxidative stress, the molecular mechanisms by which AgNPs-damaged cells are unknown. Because the endoplasmic reticulum (ER) may play an important role in the response to oxidative stress-induced damage and is quite sensitive to oxidative damage, we hypothesized that AgNPs may exert cytotoxic effects on cells by modulating ER stress. In our study, AgNPs resulted in cytotoxicity and apoptotic cell death when analyzing cell viability, DNA fragmentation and the apoptotic sub-G1 population. Flow cytometry and confocal microscopy indicated that the cells were sensitive to AgNPs with respect to the induction of mitochondrial Ca2+ overloading and enhancement of ER stress. AgNPs induced a number of signature ER stress markers, including phosphorylation of RNA-dependent protein kinase-like ER kinase (PERK) and its downstream eukaryotic initiation factor 2α, phosphorylation of inositol-requiring protein 1 (IRE1), splicing of ER stress-specific X-box transcription factor-1, cleavage of activating transcription factor 6 (ATF6) and up-regulation of glucose-regulated protein-78 and CCAAT/enhancer-binding protein–homologous protein (CHOP/GADD153). Down-regulation of PERK, IRE1 and ATF6 expression using siRNA significantly decreased AgNPs-induced the enhancement of ER stress. In addition, down-regulation of CHOP expression with siRNA CHOP attenuated AgNPs-induced apoptosis. Taken together, the present study supports an important role for the ER stress response in mediating AgNPs-induced apoptosis.