Silver ions induce oxidative stress and intracellular zinc release in human skin fibroblasts

A Kinetic Approach to Synergize Bactericidal Efficacy and Biocompatibility in Silver-Based Sol-Gel Coatings

Silver ions are antimicrobial agents with powerful action against bacteria. Applications in surface treatments, as Ag+-functionalized sol-gel coatings, are expected in the biomedical field to prevent contaminations and infections. The potential cytotoxicity of Ag+ cations toward human cells is well known though. However, few studies consider both the bactericidal activity and the biocompatibility of the Ag+-functionalized sol-gels. Here, we demonstrate that the cytotoxicity of Ag+ cations is circumvented, thanks to the ability of Ag+ cations to kill Escherichia coli (E. coli) much faster than normal human dermal fibroblasts (NHDFs). This phenomenon was investigated in the case of two silver nitrate-loaded sol-gel coatings: one with 0.5 w/w% Ag+ cations and the second with 2.5 w/w%. The maximal amount of released Ag+ ions over time (0.25 mg/L) was ten times lower than the minimal inhibition (MIC) and minimal bactericidal (MBC) concentrations (respectively, 2.5 and 16 mg/L) for E. coli and twice lower to the minimal cytotoxic concentration (0.5 mg/L) observed in NHDFs. E. coli were killed 8-18 times, respectively, faster than NHDFs by silver-loaded sol-gel coatings. This original approach, based on the kinetic control of the biological activity of Ag+ cations instead of a concentration effect, ensures the bactericidal protection while maintaining the biocompatibility of the Ag+ cation-functionalized sol-gels. This opens promising applications of silver-loaded sol-gel coatings for biomedical tools in short-term or indirect contacts with the skin.

Mitochondrial Oxidative Stress Is the General Reason for Apoptosis Induced by Different-Valence Heavy Metals in Cells and Mitochondria

This review analyzes the causes and consequences of apoptosis resulting from oxidative stress that occurs in mitochondria and cells exposed to the toxic effects of different-valence heavy metals (Ag+, Tl+, Hg2+, Cd2+, Pb2+, Al3+, Ga3+, In3+, As3+, Sb3+, Cr6+, and U6+). The problems of the relationship between the integration of these toxic metals into molecular mechanisms with the subsequent development of pathophysiological processes and the appearance of diseases caused by the accumulation of these metals in the body are also addressed in this review. Such apoptosis is characterized by a reduction in cell viability, the activation of caspase-3 and caspase-9, the expression of pro-apoptotic genes (Bax and Bcl-2), and the activation of protein kinases (ERK, JNK, p53, and p38) by mitogens. Moreover, the oxidative stress manifests as the mitochondrial permeability transition pore (MPTP) opening, mitochondrial swelling, an increase in the production of reactive oxygen species (ROS) and H2O2, lipid peroxidation, cytochrome c release, a decline in the inner mitochondrial membrane potential (ΔΨmito), a decrease in ATP synthesis, and reduced glutathione and oxygen consumption as well as cytoplasm and matrix calcium overload due to Ca2+ release from the endoplasmic reticulum (ER). The apoptosis and respiratory dysfunction induced by these metals are discussed regarding their interaction with cellular and mitochondrial thiol groups and Fe2+ metabolism disturbance. Similarities and differences in the toxic effects of Tl+ from those of other heavy metals under review are discussed. Similarities may be due to the increase in the cytoplasmic calcium concentration induced by Tl+ and these metals. One difference discussed is the failure to decrease Tl+ toxicity through metallothionein-dependent mechanisms. Another difference could be the decrease in reduced glutathione in the matrix due to the reversible oxidation of Tl+ to Tl3+ near the centers of ROS generation in the respiratory chain. The latter may explain why thallium toxicity to humans turned out to be higher than the toxicity of mercury, lead, cadmium, copper, and zinc.

Self-Sanitizing Polycaprolactone Electrospun Nanofiber Membrane with Ag Nanoparticles

The objective of this research was to develop an environment-friendly and scalable method for the production of self-sanitizing electrospun nanofibers. This was achieved by immobilizing silver nanoparticles (Ag NPs) onto plasma-treated surfaces of biodegradable polycaprolactone (PCL) nanofibers. The plasma deposited polymer layer containing carboxyl groups played a critical role in providing a uniform distribution of Ag NPs on the nanofiber surface. Ag ions were absorbed by electrostatic interaction and then reduced under the action of UV-light. The concentration and release of Ag ions were analyzed using the EDXS/XPS and ICP AES methods, respectively. Although high levels of Ag ions were detected after 3 h of immersion in water, the material retained a sufficient amount of silver nanoparticles on the surface (~2.3 vs. 3.5 at.% as determined by XPS), and the release rate subsequently decreased over the next 69 h. The antipathogenic properties of PCL-Ag were tested against gram-negative and gram-positive bacteria, fungi, and biofilm formation. The results showed that the PCL-Ag nanofibers exhibit significant antimicrobial activity against a wide range of microorganisms, including those that cause human infections. The incorporation of Ag NPs into PCL nanofibers resulted in a self-sanitizing material that can be used in variety of applications, including wound dressings, water treatment, and air filtration. The development of a simple, scalable, and environmentally friendly method for the fabrication of these nanofibers is essential to ensure their widespread use in various industries. The ability to control the concentration and release rate of Ag ions in the PCL nanofibers will be critical to optimize their efficacy while minimizing their potential toxicity to human cells and the environment.

Prenatal exposure to silver is associated with an elevated risk for neural tube defects: a case-control study

Exposure to copper, silver, and titanium has been reported to be associated with a variety of adverse effects on humans, but it is little focused on the fetus. We investigated the associations between prenatal exposure to the three metals (copper, silver, and titanium) and risk for fetal neural tube defects (NTDs). Placental samples from 408 women with pregnancies affected by NTDs and 593 women with normal pregnancies were collected from 2003 to 2016 in Pingding, Xiyang, Shouyang, Taigu, and Zezhou counties of China. Multilevel mixed-effects logistic regression and Bayesian kernel machine regression (BKMR) were used to evaluate the single and joint effects of the metals on NTDs. Silver was associated with an increased risk for NTDs in a dose-response fashion in single-metal logistic regression, with adjusted odds ratios (95% confidence intervals) of 1.78 (1.04-3.06) and 1.92 (1.11-3.32) in the second and third tertiles, respectively, compared to the lowest tertile. BKMR revealed toxic effects of silver on NTDs and the association appeared to be linear. No interaction of silver with any of the other two metals was observed. Besides, silver concentration was positively correlated with maternal certain dietary intakes. Placental high silver concentrations are associated with an elevated risk for NTDs. Maternal diet may be a source of silver exposure.

Silver Ions Incorporation into Nanofibers for Enhanced hMSC Viability

Antimicrobial properties of silver have been known for a long time, but there is also cytotoxicity of high concentrations of silver. Therefore, it is important to select the concentration and shape of silver depending on the goals. The ideal wound dressing should ensure that the wound remains optimally moist, protected from infections, has no toxic compounds, and stimulates regeneration. In the present work, we obtained a series of polycaprolactone-based nanomaterials fabricated by electrospinning and incorporated with silver ions (up to 0.6 at.%). By adjusting the magnetron current (0.3 A) and implanter voltage (5 kV), the deposition of TiO2 and Ag+ implantation into PCL/PEO nanofibers was optimized to achieve implantation of Ag+ without damaging the nanofibrous structure of the biodegradable nanofibers. The obtained results allow us to predict significant protection properties of the developed material not only from mechanical influence but also thanks to the antimicrobial effect due to silver ions, which is important for chronic wounds and injuries with a large area of damage and can activate host cells proliferation.

Impact of Ag Nanoparticles (AgNPs) and Multimicrobial Preparation (EM) on the Carcass, Mineral, and Fatty Acid Composition of Cornu aspersum aspersum Snails

The hygienic practices on farms should reduce pathogenic microorganisms while simultaneously not harming the animals themselves; they must also not degrade the products' quality. We assessed the effect of covering feed tables with paint containing silver nanoparticles (AgNPs) and the periodic spraying of effective microorganisms (EM) on production indicators and basic chemical composition, mineral content and fatty acid profiles in the bodies of Cornu aspersum aspersum snails. The animals were divided into four groups: (1) control, (2) with feed tables covered with AgNPs paint, (3) with EM spray applied and (4) with both factors-AgNP paint and EM spray. The highest increase in Ag, Zn, Fe and Ca retention, and the remodelling of the fatty acid profile in the carcasses of snails was found to be in the group of animals in contact with the feed tables covered with AgNP paint. In the group of animals exposed to the action of EM, an increased retention of Fe, Cu, P, Mg and Zn was found.

Impact of multigenerational exposure to AgNO3 or NM300K Ag NPs on antioxidant defense and oxidative stress in Caenorhabditis elegans

Adaptation of the nematode Caenorhabditis elegans towards NM300K silver nanoparticles (Ag NPs) has previously been demonstrated. In the current study, the sensitivity to a range of secondary stressors (CeO2 NP, Ce3+, Cu2+, Cd2+, and Paraquat) following the multigenerational exposure to silver nanoparticles (Ag NPs NM300K) or AgNO3 was investigated. This revealed improved tolerance to the ROS inducer Paraquat with higher fecundity after pre-exposure to Ag NP, indicating an involvement of reactive oxygen species (ROS) metabolism in the adaptive response to NM300K. The potential contribution of the antioxidant defenses related to adaptive responses was investigated across six generations of exposure using the sod-1::GFP reporter (GA508), and the Grx1-roGFP2 (GRX) biosensor strains. Results showed an increase in sod-1 expression by the F3 generation, accompanied by a reduction of GSSG/GSH ratios, from both AgNO3 and Ag NP exposures. Continuous exposure to AgNO3 and Ag NP until the F6 generation resulted in a decreased sod-1 expression, with a concomitant increase in GSSG/GSH ratios. The results thus show that despite an initial enhancement, the continuous exposure to Ag caused a severe impairment of the antioxidant defense capacity in C. elegans.

Effects of electrical biostimulation and silver ions on porcine fibroblast cells

The medical applications of electrical biostimulation and silver ions have been evaluated in laboratory experiments and clinical studies for more than two decades. Their effects on preventing infection and promoting wound healing have been described. However, little is known about the role of electrical biostimulation and/or silver ion on changes in cellular transcriptome dynamics. To our knowledge, few studies have been conducted to investigate the potential of electrical biostimulation and silver ions in cell reprogramming. Besides, it is essential to assess any possible adverse effects or potential benefits of the silver ions on mammalian cells to address its safety concerns and to improve silver medical products. In this study, we investigated transcriptomic changes in porcine fibroblast cells in response to electrical biostimulation in the presence of silver ions. Exposed cells presented distinct morphological changes after treatment, which was mainly due to the exposure of silver ions rather than the electrical current itself. Gene expression analyses suggested that electrical biostimulation and silver ions did not increase the expression of pluripotency genes. Interestingly, a set of genes related to cellular metabolic processes were differentially expressed after cells were exposed to electrically generated silver ions for 21 hours. We found that 2.00 mg/L of electrically generated silver ion caused an increase of ATP generation and an increase of the total pool of NAD⁺ and NADH, while ROS production did not change. Aside from toxic effects, the results reported herein demonstrate the alternative effects of silver ions on mammalian cells, especially an oxidative phosphorylation burst. To our knowledge, this response of mammalian cells to silver ions has not been described previously. Although the function of this burst is not understood, it may lead to alterations in cellular activities such as metabolic remodeling and cell reprogramming, and/or serve an as-yet unknown function in neutralization or detoxification of the silver ions within the cells.

All That Glitters Is Not Silver-A New Look at Microbiological and Medical Applications of Silver Nanoparticles

Silver and its nanoparticles (AgNPs) have different faces, providing different applications. In recent years, the number of positive nanosilver applications has increased substantially. It has been proven that AgNPs inhibit the growth and survival of bacteria, including human and animal pathogens, as well as fungi, protozoa and arthropods. Silver nanoparticles are known from their antiviral and anti-cancer properties; however, they are also very popular in medical and pharmaceutical nanoengineering as carriers for precise delivery of therapeutic compounds, in the diagnostics of different diseases and in optics and chemistry, where they act as sensors, conductors and substrates for various syntheses. The activity of AgNPs has not been fully discovered; therefore, we need interdisciplinary research to fulfil this knowledge. New forms of products with silver will certainly find application in the future treatment of many complicated and difficult to treat diseases. There is still a lack of appropriate and precise legal condition regarding the circulation of nanomaterials and the rules governing their safety use. The relatively low toxicity, relative biocompatibility and selectivity of nanoparticle interaction combined with the unusual biological properties allow their use in animal production as well as in bioengineering and medicine. Despite a quite big knowledge on this topic, there is still a need to organize the data on AgNPs in relation to specific microorganisms such as bacteria, viruses or fungi. We decided to put this knowledge together and try to show positive and negative effects on prokaryotic and eukaryotic cells.

Identification of mesenchymal stromal cell survival responses to antimicrobial silver ion concentrations released from orthopaedic implants

Antimicrobial silver (Ag⁺) coatings on orthopaedic implants may reduce infection rates, but should not be to the detriment of regenerative cell populations, primarily mesenchymal stem/stromal cells (MSCs). We determined intramedullary silver release profiles in vivo, which were used to test relevant Ag⁺ concentrations on MSC function in vitro. We measured a rapid elution of Ag⁺ from intramedullary pins in a rat femoral implantation model, delivering a maximum potential concentration of 7.8 µM, which was below toxic levels determined for MSCs in vitro (EC₅₀, 33 µM). Additionally, we present in vitro data of the reduced colonisation of implants by Staphylococcus aureus. MSCs exposed to Ag⁺ prior to/during osteogenic differentiation were not statistically affected. Notably, at clonal density, the colony-forming capacity of MSCs was significantly reduced in the presence of 10 µM Ag⁺, suggesting that a subpopulation of clonal MSCs was sensitive to Ag⁺ exposure. At a molecular level, surviving colony-forming MSCs treated with Ag⁺ demonstrated a significant upregulation of components of the peroxiredoxin/thioredoxin pathway and processes involved in glutathione metabolism compared to untreated controls. Inhibition of glutathione synthesis using l-buthionine sulfoxamine eliminated MSC clonogenicity in the presence of Ag⁺, which was rescued by exogenous glutathione.

Silver Nanoparticles Agglomerate Intracellularly Depending on the Stabilizing Agent: Implications for Nanomedicine Efficacy

Engineered nanoparticles are utilized as drug delivery carriers in modern medicine due to their high surface area and tailorable surface functionality. After in vivo administration, nanoparticles distribute and interact with biomolecules, such as polar proteins in serum, lipid membranes in cells, and high ionic conditions during digestion. Electrostatic forces and steric hindrances in a nanoparticle population are disturbed and particles agglomerate in biological fluids. Little is known about the stability of nanoparticles in relation to particle surface charge. Here, we compared three different surface-stabilized silver nanoparticles (50 nm) for intracellular agglomeration in human hepatocellular carcinoma cells (HepG2). Nanoparticles stabilized with branched polyethyleneimine conferred a positive surface charge, particles stabilized with lipoic acid conferred a negative surface charge, and particles stabilized with polyethylene glycol conferred a neutral surface charge. Particles were incubated in fetal bovine serum, simulated lung surfactant fluid, and simulated stomach digestion fluid. Each nanoparticle system was characterized via microscopic (transmission electron, fluorescence, and enhanced darkfield) and spectroscopic (hyperspectral, dynamic light scattering, and ultraviolet-visible absorption) techniques. Results showed that nanoparticle transformation included cellular internalization, agglomeration, and degradation and that these changes were dependent upon surface charge and incubation matrix. Hyperspectral analyses showed that positively charged silver nanoparticles red-shifted in spectral analysis after transformations, whereas negatively charged silver nanoparticles blue-shifted. Neutrally charged silver nanoparticles did not demonstrate significant spectral shifts. Spectral shifting indicates de-stabilization in particle suspension, which directly affects agglomeration intracellularly. These characteristics are translatable to critical quality attributes and can be exploited when developing nano-carriers for nanomedicine.

Toxicity of Ag+ on microstructure, biochemical activities and genic material of Trifolium pratense L. seedlings with special reference to phytoremediation

The objective of this research was to evaluate Ag⁺ toxicity in Trifolium pratense L. seedlings subjected to increasing doses of Ag⁺ by determining photosynthetic pigment and malondialdehyde (MDA) contents, microstructure and hereditary substance alterations, changes in activities of antioxidase-superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) as well as the content of total Ag absorbed in vivo with evaluation of root growth. Doses of approximately 80 mg L^-1 Ag⁺ severely affected photosynthetic efficiency in Trifolium pratense L. seedlings promoted by damages in photosynthetic apparatus evidenced by downward trend in photosynthetic pigment contents and obvious chlorosis. Alterations in enzymatic activity, lipid peroxidation, genic material damage and the presence of Ag⁺in vivo had impacted on photosynthetic machinery as well. A hormesis effect was observed at 60 mg L^-1 Ag⁺ for the photosynthetic pigments and antioxidase for Trifolium pratense L. seedlings. Tissue changes (i.e., roots, stems and leaves) observed in fluorescence microscope with obvious chlorosis, roots blackening and formation of agglomerated black particles, were related to the lesion promoted by excessive ROS in vivo. Asynchronous change of antioxidase activity corresponded to the alteration in the MDA content, indicating the synchronization in the elimination of ROS. The changes occurred in RAPD profiles of treated samples following Ag⁺ toxicity containing loss of normal bands, appearance of new bands and variation in band intensity compared to the normal plants with a dose-dependent effect. On average, the roots of Trifolium pratense L. immobilized 92.20% of the total Ag absorbed as a metal exclusion response. Root growth was significantly sensitive to Ag⁺ stress with obvious hormesis, which corresponded to the changes in Ag uptake, demonstrating the functional alterations in plants. To sum up, we suggest that modulating the genotype of Trifolium pratense L. seedlings to bear higher proportion of pollutants is conducive to contamination site treatment.

Pxr- and Nrf2- mediated induction of ABC transporters by heavy metal ions in zebrafish embryos

Transcription factors including pregnane X receptor (Pxr) and nuclear factor-erythroid 2-related factor-2 (Nrf2) are important modulators of Adenosine triphosphate-binding cassette (ABC) transporters in mammalian cells. However, whether such modulation is conserved in zebrafish embryos remains largely unknown. In this manuscript, pxr- and nrf2-deficient models were constructed with CRISPR/Cas9 system, to evaluate the individual function of Pxr and Nrf2 in the regulation of ABC transporters and detoxification of heavy metal ions like Cd²⁺ and Ag⁺. As a result, both Cd²⁺ and Ag⁺ conferred extensive interactions with ABC transporters in wild type (WT) embryos: their accumulation and toxicity were affected by the activity of ABC transporters, and they significantly induced the mRNA expressions of ABC transporters. These induction effects were reduced by the mutation of pxr and nrf2, but elevations in the basal expression of ABC transporters compensated for the loss of their inducibility. This could be an explanation for remaining transporter function in both mutant models as well as the unaltered toxicity of metal ions in pxr-deficient embryos. However, mutation of nrf2 disrupted the production of glutathione (GSH), resulting in the enhanced toxicity of Cd²⁺/Ag⁺ in zebrafish embryos. In addition, elevated expressions of other transcription factors like aryl hydrocarbon receptor (ahr) 1b, peroxisome proliferator-activated receptor (ppar)-β, and nrf2 were found in pxr-deficient models without any treatment, while enhanced induction of ahr1b, ppar-β and pxr could only be seen in nrf2-deficient embryos after the treatment of metal ions, indicating different compensation phenomena for the absence of transcription factors. After all, pxr-deficient and nrf2-deficient zebrafish embryos are useful tools in the functional investigation of Pxr and Nrf2 in the early life stages of aquatic organisms. However, the compensatory mechanisms should be taken into consideration when interpreting the results and need in-depth investigations.

Real-time monitoring of the Trojan-horse effect of silver nanoparticles by using a genetically encoded fluorescent cell sensor

Silver nanoparticles (AgNPs) are widely incorporated into commercial products due to their antimicrobial properties. As a consequence, concerns about the adverse effects induced by AgNPs to humans and the environment need to be carefully examined. The existing literature reveals that AgNPs exhibit certain toxic effects, but it remains to be proved whether AgNPs or the ionic silver (Ag+) released from AgNPs are the main toxic species. Here, a genetically encoded fluorescent protein sensor with high affinity to Ag+ was developed. The resulting sensor, MT2a-FRET, was found to be ratiometric, sensitive and selective toward only Ag+ but inert against AgNPs. This makes this sensor a potential useful tool for monitoring the real-time intracellular dissolutions of AgNPs. Our data supported that AgNPs display the "Trojan-horse" mechanism, where AgNPs are internalized by cells and undergo dissolution intracellularly. We further found that cells exhibited a detoxification ability to remove active Ag+ from cells in 48 hours.

Fabrication of transparent quaternized PVA/silver nanocomposite hydrogel and its evaluation as an antimicrobial patch for wound care systems

Grafting of quaternary nitrogen atoms into the backbone of polymer is an efficient way of developing new generation antimicrobial polymeric wound dressing. In this study, an elastic, non-adhesive and antimicrobial transparent hydrogel based dressing has been designed, which might be helpful for routine observation of wound area without removing the dressing material along with maintaining a sterile environment for a longer period of time. Green synthesized silver nanoparticles have been loaded into the quaternized PVA hydrogel matrix to improve its antimicrobial property. Silver nanoparticles loaded quaternized PVA hydrogel showed enhanced mechanical and swelling properties compared to native quaternized PVA hydrogel. Release kinetics evaluated by atomic absorption spectroscopy revealed that the release mechanism of silver nanoparticles from the hydrogel follows Fickian diffusion. Antimicrobial efficacy of the hydrogels was evaluated by disk diffusion test on Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli. After 96 h of release in phosphate buffer, the growth inhibition zone created by silver nanoparticless loaded quaternized PVA hydrogel is comparable to that created by ampicillin. These observations assert that the silver nanoparticles loaded quaternized PVA hydrogel acts as a reservoir of silver nanoparticles, which helps in maintaining a sterile environment for longer time duration by releasing Ag nanocrystallite in sustained manner.

Evaluation of Some Biochemical Parameters and Brain Oxidative Stress in Experimental Rats Exposed Chronically to Silver Nitrate and the Protective Role of Vitamin E and Selenium

Due to undesirable hazardous interactions with biological systems, this investigation was undertaken to evaluate the effect of chronic exposure to silver on certain biochemical and some oxidative stress parameters with histopathological examination of brain, as well as the possible protective role of selenium and/or vitamin E as nutritional supplements. Thirty six male rats were divided into six groups of six each: the first group used as a control group. Group II given both vitamin E (400 mg/kg) of diet and selenium (Se) (1 mg/L) in their drinking water. Group III given silver as silver nitrate (AgNO₃) (20 mg/L). Group IV given vitamin E and AgNO₃. Group V given both AgNO₃ and selenium. Group VI given AgNO₃, vitamin E and Se. The animals were in the same exposure conditions for 3 months. According to the results which have been obtained; there was an increase in serum lactate dehydrogenase (LDH), lipase activities and cholesterol level, a decrease in serum total protein, calcium and alkaline phosphatase (ALP) activity in Ag-intoxicated rats. Moreover, the findings showed that Ag⁺ ions affected antioxidant defense system by decreasing superoxide dismutase (SOD) activity and increasing vitamin E concentration with a high level of malondialdehyde (MDA) in brain tissue. The histological examination also exhibited some nervous tissue alterations including hemorrhage and cytoplasm vacuolization. However, the co-administration of selenium and/or vitamin E ameliorated the biochemical parameters and restored the histological alterations. In conclusion, this study indicated that silver could cause harmful effects in animal body and these effects can be more toxic in high concentrations or prolonged time exposure to this metal. However, selenium and vitamin E act as powerful antioxidants which may exercise adverse effect against the toxicity of this metal.

Effects of developmental exposure to silver in ionic and nanoparticle form: A study in rats

Background

Evaluations of silver in both nanoparticle (Ag-NPs) and ionic forms indicate some adverse effects on living organisms, but little is known about their potential for developmental toxicity. In this study, developmental toxicity of Ag-NPs (from 0.2 to 20 mg/kg/day) and ionic Ag (AgNO₃, 20 mg Ag/kg/day) were investigated in rats.

Methods

Animals were dosed by gavage from gestation day 7 − 20. The day after parturition, dams and pups were sacrificed and Ag level assessed in several maternal and pup organs. In addition, hepatotoxicity and oxidative stress parameters and histopathology were evaluated.

Results

No treatment related effects were found for gestational parameters including pregnancy length, maternal weight gain, implantations, birth weight and litter size at any dose level of Ag-NPs. Maternal weight gain was lower in dams receiving AgNO₃ compared to the other groups, suggesting that the ionic form may exert a higher degree of toxicity compared to the NP form. Tissue contents of Ag were higher in all treated groups compared to control dams and pups, indicating transfer of Ag across the placenta. The findings furthermore suggest that Ag may induce oxidative stress in dams and their offspring, although significant induction was only observed after dosing with AgNO₃. Histopathological examination of brain tissue revealed a high incidence of hippocampal sclerosis in dams treated with nanoparticle as well as ionic Ag.

Conclusion

The difference in offspring deposition patterns between ionic and NP Ag and the observations in dam brain tissue, requires scrutiny, and, if corroborated, indicate that ionic and NP forms maybe need separate risk assessments and that the hazard ratings of silver in both ionic and nanoparticle forms should be increased, respectively.

Trial registration

Not applicable.

Graphical abstract

Developmental Toxicity of Ag-NPs.

Impact of pulmonary exposure to gold core silver nanoparticles of different size and capping agents on cardiovascular injury

BACKGROUND

The uses of engineered nanomaterials have expanded in biomedical technology and consumer manufacturing. Furthermore, pulmonary exposure to various engineered nanomaterials has, likewise, demonstrated the ability to exacerbate cardiac ischemia reperfusion (I/R) injury. However, the influence of particle size or capping agent remains unclear. In an effort to address these influences we explored response to 2 different size gold core nanosilver particles (AgNP) with two different capping agents at 2 different time points. We hypothesized that a pulmonary exposure to AgNP induces cardiovascular toxicity influenced by inflammation and vascular dysfunction resulting in expansion of cardiac I/R Injury that is sensitive to particle size and the capping agent.

METHODS

Male Sprague-Dawley rats were exposed to 200 μg of 20 or 110 nm polyvinylprryolidone (PVP) or citrate capped AgNP. One and 7 days following intratracheal instillation serum was analyzed for concentrations of selected cytokines; cardiac I/R injury and isolated coronary artery and aorta segment were assessed for constrictor responses and endothelial dependent relaxation and endothelial independent nitric oxide dependent relaxation.

RESULTS

AgNP instillation resulted in modest increase in selected serum cytokines with elevations in IL-2, IL-18, and IL-6. Instillation resulted in a derangement of vascular responses to constrictors serotonin or phenylephrine, as well as endothelial dependent relaxations with acetylcholine or endothelial independent relaxations by sodium nitroprusside in a capping and size dependent manner. Exposure to both 20 and 110 nm AgNP resulted in exacerbation cardiac I/R injury 1 day following IT instillation independent of capping agent with 20 nm AgNP inducing marginally greater injury. Seven days following IT instillation the expansion of I/R injury persisted but the greatest injury was associated with exposure to 110 nm PVP capped AgNP resulted in nearly a two-fold larger infarct size compared to naïve.

CONCLUSIONS

Exposure to AgNP may result in vascular dysfunction, a potentially maladaptive sensitization of the immune system to respond to a secondary insult (e.g., cardiac I/R) which may drive expansion of I/R injury at 1 and 7 days following IT instillation where the extent of injury could be correlated with capping agents and AgNP size.

Silver nanoparticles induced neurotoxicity through oxidative stress in rat cerebral astrocytes is distinct from the effects of silver ions

The rapid development of silver nanoparticles (AgNPs) based products has raised increasing concerns in view of their potential hazardous risks to the environment and human health. The roles of the released silver ions in AgNPs induced cytotoxicities are being hotly debated. Using rat cerebral astrocytes, the neurotoxicological effects of AgNPs and silver ions were investigated. Acute toxicity based on Alamar Blue assay showed that silver ions were considerably more toxic than AgNPs. Comparative studies indicated that AgNPs increased caspase activities and induced cell apoptosis under cytotoxic level of exposures, while silver ions compromised cell membrane integrity and dominantly caused cell necrosis. Cellular internalization of silver provided the basis for the cytotoxicities of these two silver species. In contrast to silver ions, intracellular reactive oxygen species (ROS) generation occurred in time- and concentration-dependent manners in astrocytes upon AgNPs stimulation, which caused subsequent c-Jun N-terminal kinases (JNK) phosphorylation and promoted the programmed cell death. Non-cytotoxic level of AgNPs exposure increased multiple cytokines secretion from the astrocytes, indicating that AgNPs were potentially involved in neuroinflammation. This effect was independent of silver ions as well. The distinct toxicological effects caused by AgNPs and silver ions provided the solid proofs for the particle-specific effects which should be concerned regarding the accurate assessment of AgNPs exposure risks.

Prenatal Exposure to Silver Nanoparticles Causes Depression Like Responses in Mice

Despite increasing studies on silver nanoparticles, their mechanism of action is not so clear, especially their probable toxicity on reproduction procedure, developmental process and offspring behavior. Therefore in the present study the effect of silver nanoparticles exposure during gestational period on offspring's depression behavior was assessed. Thirty virgin female mice were divided into three groups (n=10 for each group) including: one control and two experimental groups, which received an equal volume (0.2 ml) of suspension containing 0, 0.2 and 2 mg/kg of silver nanoparticles, respectively. After mating, the suspension was injected and repeated every 3 days till accouchement. Depression behaviors were assessed by tail suspension test and forced swimming test, in 45-day-old male and female progenies (6 groups, n=10). In males, both dose of silver nanoparticles (0.2 and 2 mg/kg) decreased mobility and increased immobility time in forced swimming test (P<0.05), but in female no effects were observed in mobility and immobility time. In tail suspension test, 2 mg/kg of silver nanoparticles lead to decrease of mobility time (P<0.05) and increase of immobility time (P<0.05) in female offspring but in males no significant effect was observed on mobility and immobility time. We may concluded that the prenatal exposure to silver nanoparticles probably cause gender-specific depression like behaviors in offspring, possibly through neurotoxic effect during neuronal development.

A metabolomic study on the responses of daphnia magna exposed to silver nitrate and coated silver nanoparticles

We examined the short-term toxicity of AgNPs and AgNO3 to Daphnia magna at sublethal levels using (1)H NMR-based metabolomics. Two sizes of polyvinylpyrrolidone-coated AgNPs (10 and 40nm) were synthesized and characterized and their Ag(+) release was studied using centrifugal ultrafiltration and inductively coupled plasma mass spectrometry. Multivariate statistical analysis of the (1)H NMR spectra showed significant changes in the D. magna metabolic profiles following 48h exposure to both AgNP particle sizes and Ag(+) exposure. Most of the metabolic biomarkers for AgNP exposure, including 3-hydroxybutyrate, arginine, lysine and phosphocholine, were identical to those of the Ag(+)-exposed groups, suggesting that the dominant effects of both AgNPs were due to released Ag(+). The observed metabolic changes implied that the released Ag(+) induced disturbance in energy metabolism and oxidative stress, a proposed mechanism of AgNP toxicity. Elevated levels of lactate in all AgNP-treated but not in Ag(+)-treated groups provided evidence for Ag-NP enhanced anaerobic metabolism. These findings show that (1)H NMR-based metabolomics provides a sensitive measure of D. magna response to AgNPs and that further targeted assays are needed to elucidate mechanisms of action of nanoparticle-induced toxicity.

Mammalian Cells Exhibit a Range of Sensitivities to Silver Nanoparticles that are Partially Explicable by Variations in Antioxidant Defense and Metallothionein Expression

While it is well known that there are interspecies differences in Ag sensitivity, differences in the cytotoxic responses of mammalian cells to silver nanoparticles (Ag NPs) are also observed. In order to explore these response outcomes, six cell lines, including epithelial cells (Caco-2, NHBE, RLE-6TN, and BEAS-2B) and macrophages (RAW 264.7 and THP-1) of human and rodent origin, are exposed to 20 nm citrate- and PVP-coated Ag NPs with Au cores, as well as 20 nm citrate-coated particles without cores. An MTS assay shows that while Caco-2 and NHBE cells are resistant to particles over a 0.1-50 μg mL(-1) dose range, RAW 264.7, THP-1, RLE-6TN, and BEAS-2B cells are more susceptible. While there are small differences in dissolution rates, there are no major differences in the cytotoxic potential of the different particles. However, differences in anti-oxidant defense and metallothionein expression among different cell types are observed, which can partially explain differential Ag NP sensitivity. So, it is important to consider these differences in understanding the potential heterogeneous effects of nano Ag on mammalian biological systems.

Silver from polyurethane dressing is delivered by gradient to exudate, tissue, and serum of patients undergoing negative-pressure wound treatment

OBJECTIVE

This study aimed to evaluate the distribution and concentration of silver eluted from silver-coated polyurethane dressing (V.A.C. GranuFoam Silver Dressing; KCI, San Antonio, Texas) in vitro and in patients undergoing negative-pressure wound therapy (NPWT).

DESIGN

This was a descriptive study of the effect of silver-coated polyurethane dressing in patients undergoing NPWT.

PARTICIPANTS

Six patients with infected wounds undergoing NPWT using silver-coated polyurethane dressing.

INTERVENTIONS

To evaluate silver release in vitro, the authors soaked dressing fragments in water and human serum for different lengths of time and performed atomic absorption spectroscopy. For patient evaluation, the authors obtained exudate, serum, and wound tissue at different time points from 6 patients undergoing NPWT and measured silver levels by atomic absorption and dispersed x-ray spectroscopy.

MAIN RESULTS

Silver from the dressing was immediately released in vitro at a rate 3 times greater in serum than in water. In vivo, silver was delivered to wound exudate at rates 102 to 104 times greater than in corresponding serum. Few surface silver deposits were detected in treated tissue.

CONCLUSION

The high concentration of silver found in wound exudate reflects not only the affinity for silver in serum components and wound fluids, but also that most silver ions are not distributed systemically in the patient; instead, they are transported by the vacuum created by therapy.

Advances in skin regeneration: application of electrospun scaffolds

The paucity of cellular and molecular signals essential for normal wound healing makes severe dermatological ulcers stubborn to heal. The novel strategies of skin regenerative treatments are focused on the development of biologically responsive scaffolds accompanied by cells and multiple biomolecules resembling structural and biochemical cues of the natural extracellular matrix (ECM). Electrospun nanofibrous scaffolds provide similar architecture to the ECM leading to enhancement of cell adhesion, proliferation, migration and neo tissue formation. This Review surveys the application of biocompatible natural, synthetic and composite polymers to fabricate electrospun scaffolds as skin substitutes and wound dressings. Furthermore, the application of biomolecules and therapeutic agents in the nanofibrous scaffolds viz growth factors, genes, antibiotics, silver nanoparticles, and natural medicines with the aim of ameliorating cellular behavior, wound healing, and skin regeneration are discussed.

Evaluating the toxicity of silver nanoparticles by detecting phosphorylation of histone H3 in combination with flow cytometry side-scattered light

Post-translational modification of histones is linked to a variety of biological processes and disease states. This paper focuses on phosphorylation of histone H3 at serine 10 (p-H3S10), induced by silver nanoparticles (AgNPs) and discusses the usefulness of p-H3S10 as a marker to evaluate the toxicity of AgNPs. Cultured human cells showed remarkable p-H3S10 immediately after treatment with AgNPs but not with Ag microparticles. p-H3S10 lasts up to 24 h and strongly depends upon the cellular uptake of AgNPs. Removal of Ag ions suppressed p-H3S10, while adding an excess of Ag ions augmented p-H3S10. We expected that p-H3S10 requires two events: cellular uptake of AgNPs and continuous release of Ag ions from intracellular AgNPs. AgNPs enhanced the expression of the proto-oncogene c-jun, and p-H3S10 increased in the promoter sites of the gene, indicating that p-H3S10 might indicate a biological reaction related to carcinogenesis. We previously showed that side-scattered light from flow cytometry could be used to measure the uptake potential of nanoparticles [ Suzuki , H. ; Toyooka , T. ; Ibuki , Y. Simple and easy method to evaluate uptake potential of nanoparticles in mammalian cells using a flow cytometric light scatter analysis . Environ. Sci. Technol. 2007 , 41 ( 8 ), 3018 - 3024 ]. Our current findings suggest that p-H3S10 can be used to evaluate the toxicity of AgNPs and Ag ion release in combination with detection of side-scattered light from flow cytometry.

Increased DNA damage and oxidative stress among silver jewelry workers

Silver has long been valued as a precious metal, and it is used to make ornaments, jewelry, high-value tableware, utensils, and currency coins. Human exposures to silver and silver compounds can occur oral, dermal, or by inhalation. In this study, we investigated genotoxic and oxidative effects of silver exposure among silver jewelry workers. DNA damage in peripheral mononuclear leukocytes was measured by using the comet assay. Serum total antioxidative status (TAS), total oxidative status (TOS), total thiol contents, and ceruloplasmin levels were measured by using colorimetric methods among silver jewelry workers. Moreover, oxidative stress index (OSI) was calculated. Results were compared with non-exposed healthy subjects. The mean values of mononuclear leukocyte DNA damage were significantly higher than control subjects (p < 0.001). Serum TOS, OSI, and ceruloplasmin levels were also found to be higher in silver particles exposed group than those of non-exposed group (p < 0.001, p < 0.001, p < 0.01, respectively). However, serum TAS levels and total thiol contents of silver exposed group were found significantly lower (p < 0.05, p < 0.001, respectively). Exposure to silver particles among silver jewelry workers caused oxidative stress and accumulation of severe DNA damage.

Predicting the environmental impact of nanosilver

Silver nanoparticles (AgNPs) are incorporated into many consumer and medical products due to their antimicrobial properties; however, the potential environmental risks of AgNPs are yet to be fully understood. This mini-review aims to predict the environmental impact of AgNPs, thus supplementing previous reviews on this topic. To this end, the AgNP production, environmental release and fate, predicted environmental concentrations in surface water, sediment, and sludge-activated soil, as well as reported toxicity and proposed toxic mechanisms are discussed, focusing primarily on fish. Furthermore, knowledge gaps and recommendations for future research are addressed.

Metal-PAH mixtures in the aquatic environment: a review of co-toxic mechanisms leading to more-than-additive outcomes

Mixtures of metals and polycyclic aromatic hydrocarbons (PAHs) occur ubiquitously in aquatic environments, yet relatively little is known regarding their combined toxicities. Emerging reports investigating the additive mortality in metal-PAH mixtures have indicated that more-than-additive effects are equally as common as strictly-additive effects, raising concern for ecological risk assessment typically based on the summation of individual toxicities. Moreover, the current separation of focus between in vivo and in vitro studies, and fine- and coarse-scale endpoints, creates uncertainty regarding the mechanisms of co-toxicity involved in more-than-additive effects on whole organisms. Drawing from literature on metal and PAH toxicity in bacteria, protozoa, invertebrates, fish, and mammalian models, this review outlines several key mechanistic interactions likely to promote more-than-additive toxicity in metal-PAH mixtures. Namely, the deleterious effects of PAHs on membrane integrity and permeability to metals, the potential for metal-PAH complexation, the inhibitory nature of metals to the detoxification of PAHs via the cytochrome P450 pathway, the inhibitory nature of PAHs towards the detoxification of metals via metallothionein, and the potentiated production of reactive oxygenated species (ROS) in certain metal (e.g. Cu) and PAH (e.g., phenanthrenequinone) mixtures. Moreover, the mutual inhibition of detoxification suggests the possibility of positive feedback among these mechanisms. The individual toxicities and interactive aspects of contaminant transport, detoxification, and the production of ROS are herein discussed.

Silver and gold nanoparticles exposure to in vitro cultured retina--studies on nanoparticle internalization, apoptosis, oxidative stress, glial- and microglial activity

The complex network of neuronal cells in the retina makes it a potential target of neuronal toxicity – a risk factor for visual loss. With growing use of nanoparticles (NPs) in commercial and medical applications, including ophthalmology, there is a need for reliable models for early prediction of NP toxicity in the eye and retina. Metal NPs, such as gold and silver, gain much of attention in the ophthalmology community due to their potential to cross the barriers of the eye. Here, NP uptake and signs of toxicity were investigated after exposure to 20 and 80 nm Ag- and AuNPs, using an in vitro tissue culture model of the mouse retina. The model offers long-term preservation of retinal cell types, numbers and morphology and is a controlled system for delivery of NPs, using serum-free defined culture medium. AgNO₃-treatment was used as control for toxicity caused by silver ions. These end-points were studied; gross morphological organization, glial activity, microglial activity, level of apoptosis and oxidative stress, which are all well described as signs of insult to neural tissue. TEM analysis demonstrated cellular- and nuclear uptake of all NP types in all neuronal layers of the retina. Htx-eosin staining showed morphological disruption of the normal complex layered retinal structure, vacuole formation and pyknotic cells after exposure to all Ag- and AuNPs. Significantly higher numbers of apoptotic cells as well as an increased number of oxidative stressed cells demonstrated NP-related neuronal toxicity. NPs also caused increased glial staining and microglial cell activation, typical hallmarks of neural tissue insult. This study demonstrates that low concentrations of 20 and 80 nm sized Ag- and AuNPs have adverse effects on the retina, using an organotypic retina culture model. Our results motivate careful assessment of candidate NP, metallic or-non-metallic, to be used in neural systems for therapeutic approaches.

Synthesis of TiO2 nanotubes with ZnO nanoparticles to achieve antibacterial properties and stem cell compatibility

To endow titanium (Ti) with antibacterial properties, different concentrations of zinc oxide (ZnO) nanoparticles were decorated on anodized titanium dioxide (TiO2) nanotubes by a simple hydrothermal treatment method. The particle sizes of ZnO, which were evenly distributed and tightly adherent to the walls of the Ti nanotubes, ranged from 20-50 nm. Results from this study showed that Zn was released from the TiO2 nanotubes in a constant, slow, and biologically inspired manner. Importantly, the results showed that the ZnO decorated TiO2 nanotubular samples inhibited Streptococcus mutants and Porphyromonas gingivalis growth compared to control unmodified Ti samples. Specifically, S. mutants and P. gingivalis growth were both reduced 45-85% on the ZnO decorated Ti samples compared to Ti controls after 7 days of culture. When examining the mechanism of action, it has been further found for the first time that the ZnO decorated Ti samples inhibited the expression of Streptococcus mutans bacterial adhesion genes. Lastly, the results showed that the same samples which decreased bacterial growth the most (0.015 M precursor Zn(NO3)2 samples) did not inhibit mesenchymal stem cell growth compared to Ti controls for up to 7 days. In summary, results from this study showed that compared to plain TiO2 nanotubes, TiO2 decorated with 0.015 M ZnO provided unprecedented antibacterial properties while maintaining the stem cell proliferation capacity necessary for enhancing the use of Ti in numerous medical applications, particularly in dentistry.

Silver ions enhance UVB-induced phosphorylation of histone H2AX

Silver (Ag) is used in a wide range of industries including healthcare, food, cosmetics, and environmental industries due to its antibacterial properties. The rapidly expanding use of Ag has raised issues concerning its toxicity in humans. However, studies investigating the effects of Ag on humans are very limited, and the combined effects of Ag and other environmental factors have not yet been determined. Ultraviolet (UV) radiation in sunlight is the most prominent and ubiquitous physical stressor in our natural environment. In this study, we investigated the genotoxic potential of combined exposure to Ag(+) (AgNO3) and UVB in the human keratinocyte cell line, HaCaT, by measuring the generation of phosphorylated histone H2AX, which is currently attracting attention as a biomarker for the detection of genotoxic insults. We found that the generation of γ-H2AX was synergistically enhanced when cells were coexposed to Ag(+) and UVB. Furthermore, we showed that the enhanced generation of γ-H2AX could be attributed to the increased formation of UVB-induced cyclobutane pyrimidine dimers and (6-4) photoproducts. These lesions, if not repaired properly, are the major causal factor for skin carcinogenesis. Our results provide an important insight into influence of Ag on the genotoxic potency of sunlight.

Differential effects and potential adverse outcomes of ionic silver and silver nanoparticles in vivo and in vitro

Nanoparticles are of concern because of widespread use, but it is unclear if metal nanoparticles cause effects directly or indirectly. We explored whether polyvinylpyrrolidone-coated silver nanoparticles (PVP-AgNPs) cause effects through intact nanoparticles or dissolved silver. Females of the model species fathead minnow (Pimephales promelas) were exposed to either 4.8 μg/L of AgNO3 or 61.4 μg/L of PVP-AgNPs for 96h. Microarray analyses were used to identify impacted receptors and toxicity pathways in liver and brain tissues that were confirmed using in vitro mammalian assays. AgNO3 and PVP-AgNP exposed fish had common and distinct effects consistent with both intact nanoparticles and dissolved silver causing effects. PVP-AgNPs and AgNO3 both affected pathways involved in Na(+), K(+), and H(+) homeostasis and oxidative stress but different neurotoxicity pathways. In vivo effects were supported by PVP-AgNP activation of five in vitro nuclear receptor assays and inhibition of ligand binding to the dopamine receptor. AgNO3 inhibited ligand binding to adrenergic receptors α1 and α2 and cannabinoid receptor CB1, but had no effect in nuclear receptor assays. PVP-AgNPs have the potential to cause effects both through intact nanoparticles and metal ions, each interacting with different initiating events. Since the in vitro and in vivo assays examined here are commonly used in human and ecological hazard screening, this work suggests that environmental health assessments should consider effects of intact nanoparticles in addition to dissolved metals.

Inactivation of the antibacterial and cytotoxic properties of silver ions by biologically relevant compounds

There has been a recent surge in the use of silver as an antimicrobial agent in a wide range of domestic and clinical products, intended to prevent or treat bacterial infections and reduce bacterial colonization of surfaces. It has been reported that the antibacterial and cytotoxic properties of silver are affected by the assay conditions, particularly the type of growth media used in vitro. The toxicity of Ag⁺ to bacterial cells is comparable to that of human cells. We demonstrate that biologically relevant compounds such as glutathione, cysteine and human blood components significantly reduce the toxicity of silver ions to clinically relevant pathogenic bacteria and primary human dermal fibroblasts (skin cells). Bacteria are able to grow normally in the presence of silver nitrate at >20-fold the minimum inhibitory concentration (MIC) if Ag⁺ and thiols are added in a 1∶1 ratio because the reaction of Ag⁺ with extracellular thiols prevents silver ions from interacting with cells. Extracellular thiols and human serum also significantly reduce the antimicrobial activity of silver wound dressings Aquacel-Ag (Convatec) and Acticoat (Smith & Nephew) to Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli in vitro. These results have important implications for the deployment of silver as an antimicrobial agent in environments exposed to biological tissue or secretions. Significant amounts of money and effort have been directed at the development of silver-coated medical devices (e.g. dressings, catheters, implants). We believe our findings are essential for the effective design and testing of antimicrobial silver coatings.

In vitro toxicity assessment of silver nanoparticles in the presence of phenolic compounds--preventive agents against the harmful effect?

The increasing commercial use of silver nanoparticles (Ag-NPs) will inevitably lead to elevated silver exposure and thus to potential human health complications. In this study the acute toxicity of Ag-NPs <20 nm alone and upon co-administration with food matrix component phenolic compounds (PCs) on the cell-based models of the gastrointestinal tract was investigated. An improved co-culture model of Caco-2 and RajiB cells was applied for more precise in vitro simulation of the gastrointestinal tract. The involvement of two major factors contributing to the toxicity of Ag-NPs, i.e. the release of Ag(+) and the induction of oxidative stress, was investigated. Ag-NPs were cytotoxic for Caco-2 cells with an EC50 of ca. 40 µg/ml. Ag-NPs led to oxidative stress starting from ca. 45 µg/ml. The epithelial barrier integrity disruption by Ag-NPs on Caco-2 cell mono- and co-cultures was established by decreased transepithelial electrical resistances and increased passages of Lucifer Yellow, a paracellular marker. Immunofluorescence staining demonstrated that Ag-NPs affect occludin and zonula occludens 1 distributions, suggesting the opening of tight junctions. Ag(+), corresponding to the release from Ag-NPs, demonstrated a partial contribution in the toxic parameters, induced by Ag-NPs. Two PCs, quercetin and kaempferol, partially protected the Caco-2 cells from Ag-NP-induced toxicity and maintained the epithelial barrier integrity, disrupted by NPs. No protective effect was observed for resveratrol. The protective effect could be beneficial and decrease the potential toxicity of ingested Ag-NPs. However, the precise mechanisms of barrier-integrity-destabilising action of Ag-NPs/Ag(+) and protective effect of PCs still require further elucidation.

Gold- and silver nanoparticles affect the growth characteristics of human embryonic neural precursor cells

Rapid development of nanotechnologies and their applications in clinical research have raised concerns about the adverse effects of nanoparticles (NPs) on human health and environment. NPs can be directly taken up by organs exposed, but also translocated to secondary organs, such as the central nervous system (CNS) after systemic- or subcutaneous administration, or via the olfactory system. The CNS is particularly vulnerable during development and recent reports describe transport of NPs across the placenta and even into brain tissue using in vitro and in vivo experimental systems. Here, we investigated whether well-characterized commercial 20 and 80 nm Au- and AgNPs have an effect on human embryonic neural precursor cell (HNPC) growth. After two weeks of NP exposure, uptake of NPs, morphological features and the amount of viable and dead cells, proliferative cells (Ki67 immunostaining) and apoptotic cells (TUNEL assay), respectively, were studied. We demonstrate uptake of both 20 and 80 nm Au- and AgNPs respectively, by HNPCs during proliferation. A significant effect on the sphere size- and morphology was found for all cultures exposed to Au- and AgNPs. AgNPs of both sizes caused a significant increase in numbers of proliferating and apoptotic HNPCs. In contrast, only the highest dose of 20 nm AuNPs significantly affected proliferation, whereas no effect was seen on apoptotic cell death. Our data demonstrates that both Au- and AgNPs interfere with the growth profile of HNPCs, indicating the need of further detailed studies on the adverse effects of NPs on the developing CNS.

Use of silver in the prevention and treatment of infections: silver review

BACKGROUND

The use of silver for the treatment of various maladies or to prevent the transmission of infection dates back to at least 4000 b.c.e. Medical applications are documented in the literature throughout the 17th and 18th centuries. The bactericidal activity of silver is well established. Silver nitrate was used topically throughout the 1800 s for the treatment of burns, ulcerations, and infected wounds, and although its use declined after World War II and the advent of antibiotics, Fox revitalized its use in the form of silver sulfadiazine in 1968.

METHOD

Review of the pertinent English-language literature.

RESULTS

Since Fox's work, the use of topical silver to reduce bacterial burden and promote healing has been investigated in the setting of chronic wounds and ulcers, post-operative incision dressings, blood and urinary catheter designs, endotracheal tubes, orthopedic devices, vascular prostheses, and the sewing ring of prosthetic heart valves. The beneficial effects of silver in reducing or preventing infection have been seen in the topical treatment of burns and chronic wounds and in its use as a coating for many medical devices. However, silver has been unsuccessful in certain applications, such as the Silzone heart valve. In other settings, such as orthopedic hardware coatings, its benefit remains unproved.

CONCLUSION

Silver remains a reasonable addition to the armamentarium against infection and has relatively few side effects. However, one should weigh the benefits of silver-containing products against the known side effects and the other options available for the intended purpose when selecting the most appropriate therapy.

Circulating microparticles carry a functional endothelial nitric oxide synthase that is decreased in patients with endothelial dysfunction

Background

Microparticles (MPs) are circulating membrane particles of less than a micrometer in diameter shed from endothelial and blood cells. Recent literature suggests that MPs are not just functionally inert cell debris but may possess biological functions and mediate the communication between vascular cells. As a significant proportion of MPs originate from platelets and endothelial cells, we hypothesized that MPs may harbor functional enzymes including an endothelial NO synthase (eNOS).

Methods and Results

Using immunoprecipitation and Western blot analysis, we found that human circulating MPs carry an eNOS. Ca²⁺ and l‐arginine‐dependent NOS activity of crude enzyme extract from MPs was determined by measuring the conversion of [³H]‐L‐arginine to [³H]‐citrulline and NOS‐dependent nitrite production. NOS‐dependent NO production in intact MPs was assessed by the NO‐specific fluorescent probe MNIP‐Cu. In patients with cardiovascular disease, endothelial dysfunction was associated with an increase in the total number of circulating MPs as well as a significant decrease in the expression and activity of eNOS in MPs. No difference in reactive oxygen species was noted in MPs isolated from either group.

Conclusions

Our data further support the concept that circulating MPs may not only retain phenotypic markers but also preserve the functionality of enzymes of the cells they originate from, including eNOS.

A multilevel analytical approach for detection and visualization of intracellular NO production and nitrosation events using diaminofluoresceins

Diaminofluoresceins are widely used probes for detection and intracellular localization of NO formation in cultured/isolated cells and intact tissues. The fluorinated derivative 4-amino-5-methylamino-2',7'-difluorofluorescein (DAF-FM) has gained increasing popularity in recent years because of its improved NO sensitivity, pH stability, and resistance to photobleaching compared to the first-generation compound, DAF-2. Detection of NO production by either reagent relies on conversion of the parent compound into a fluorescent triazole, DAF-FM-T and DAF-2-T, respectively. Although this reaction is specific for NO and/or reactive nitrosating species, it is also affected by the presence of oxidants/antioxidants. Moreover, the reaction with other molecules can lead to the formation of fluorescent products other than the expected triazole. Thus additional controls and structural confirmation of the reaction products are essential. Using human red blood cells as an exemplary cellular system we here describe robust protocols for the analysis of intracellular DAF-FM-T formation using an array of fluorescence-based methods (laser-scanning fluorescence microscopy, flow cytometry, and fluorimetry) and analytical separation techniques (reversed-phase HPLC and LC-MS/MS). When used in combination, these assays afford unequivocal identification of the fluorescent signal as being derived from NO and are applicable to most other cellular systems without or with only minor modifications.

The antibacterial effects of silver, titanium dioxide and silica dioxide nanoparticles compared to the dental disinfectant chlorhexidine on Streptococcus mutans using a suite of bioassays

Metal-containing nanomaterials have the potential to be used in dentistry for infection control, but little is known about their antibacterial properties. This study investigated the toxicity of silver (Ag), titanium dioxide and silica nanoparticles (NPs) against the oral pathogenic species of Streptococcus mutans, compared to the routine disinfectant, chlorhexidine. The bacteria were assessed using the minimum inhibitory concentration assay for growth, fluorescent staining for live/dead cells, and measurements of lactate. All the assays showed that Ag NPs had the strongest antibacterial activity of the NPs tested, with bacterial growth also being 25-fold lower than that in chlorhexidine. The survival rate of bacteria under the effect of 100 mg l⁻¹ Ag NPs in the media was 2% compared to 60% with chlorhexidine, while the lactate concentration was 0.6 and 4.0 mM, respectively. Silica and titanium dioxide NPs had limited effects. Dialysis experiments showed negligible silver dissolution. Overall, Ag NPs were the best disinfectant and performed better than chlorhexidine. Improvements to the MIC assay are suggested.