Ultrastructural localization and chemical binding of silver ions in human organotypic skin cultures

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.

Theoretical Insight into the Phosphate-Targeted Silver's Antibacterial Action: Differentiation between Gram (+) and Gram (-) Bacteria

Although silver is one of the first metals finding broad applications in everyday life, specific key points of the intimate mechanism of its bacteriostatic/bactericidal activity lack explanation. It is widely accepted that the antimicrobial potential of the silver cation depends on the composition and thickness of the bacterial external envelope: the outer membrane in Gram-negative bacteria is more prone to Ag⁺ attack than the cell wall in Gram-positive bacteria. The major cellular components able to interact strongly with Ag⁺ (teichoic acids, phospholipids, and lipopolysaccharides) contain mono/diesterified phosphate moieties. By applying a reliable DFT/SMD methodology, we modeled the reactions between the aforementioned constituents in typical Gram-positive and Gram-negative bacteria and hydrated Ag⁺ species, thus disclosing the factors that govern the process of metal-model ligand complexation. The conducted research indicates thermodynamically possible reactions in all cases but still a greater preference of the Ag⁺ toward the constituents in Gram-negative bacteria in comparison with their counterparts in Gram-positive bacteria. The observed tendencies shed light on the specific interactions of the silver cation with the modeled phosphate-containing units at the atomic level.

Silver Nanoparticles Induce Changes in the Structural and Functional Properties of Human Lymphocytes

Exposure of human lymphocytes to silver nanoparticles (2-12 nm) reduced viability of cells and RNA, reduced activities of lactate dehydrogenase, glutathione reductase, and cytosolic calcium, increased ROS content in cells, affected surface architectonics of cells and changed hydrophobicity and charge of their plasma membranes. Silver nanoparticles triggered the process of cellular death by the mechanism of ETosis that is accompanied by chromatin release into the extracellular environment and formation of extracellular traps.

Growth, serum biochemical, and histopathological responses of broilers administered with silver nanoparticles as a drinking water disinfectant

The supplementation of 50 ppm dosed silver nanoparticles (AgNPs) as a disinfectant in broilers drinking water was investigated to examine their growth performance, blood serum biochemistry, and organ histology in the case group, compared to the control. The growth performance parameters, such as water intake, feed intake, and body weight were recorded 6 times, each in an interval of 7 days, over a period of 42 days. At the end of each 42 days, the blood and major organs of the 1 case boiler out of 75 and 1 control broiler out of 75 were collected in random. The procedure was repeated 3 sets one after another, each consisting 42 day intervening period. The liver enzyme, lipid profile, glucose level, organ histology, and concentration of AgNPs in liver, spleen, heart, and small intestine were determined. The obtained results show that the growth performance of the case broilers was significantly higher than the control section (p < 0.05). However, in all the three sets the changes in lipid profile, liver enzyme, and glucose level of the case broilers were not statistically significantly different compared to the control (p > 0.05). The histology of liver, kidney, heart, spleen, and small intestine of broilers has not shown any damages to the cells as compared to the control samples. In the case samples, the highest concentration of AgNPs was observed in the small intestine (5.44 µg/g) followed by liver (4.32 µg/g), kidney (3.94 µg/g), heart (3.82 µg/g), and spleen (3.49 µg/g). The present study concludes that the administering 50 ppm AgNPs of average 15 nm size in the poultry drinking water was found safe for consumption as well as for growth enhancing, due to better bird comfort.

Toxicity mechanisms and synergies of silver nanoparticles in 2,4-dichlorophenol degradation by Phanerochaete chrysosporium

Mechanisms of silver nanoparticles-mediated toxicity to Phanerochaete chrysosporium and the influence of silver nanoparticles (AgNPs) on the biodegradation of 2,4-dichlorophenol (2,4-DCP) have been systematically investigated. AgNPs at low doses (0-60μM) have greatly enhanced the degradation ability of P. chrysosporium to 2,4-DCP with the maximum degradation rates of more than 94%, exhibiting excellent synergies between AgNPs and P. chrysosporium in the degradation of 2,4-DCP. Meanwhile, removal of total Ag was also at high levels and highly pH dependent. However, significant inhibition was highlighted on 2,4-DCP biodegradation and Ag removal upon treatment with AgNPs at high doses and AgNO₃ at low-level exposure. Results also suggested that AgNPs-induced cytotoxicity could arise from the "Trojan-horse" mechanism executing particle effects, ion effects, or both, ruling out extracellularly released Ag⁺. Moreover, under relatively low concentrations of AgNPs exposure, 2,4-DCP was broken into linear chain organics, and eventually turned into CO₂ and H₂O through reductive dechlorination and reaction with hydroxyl radicals. FTIR analysis showed that amino, carboxyl, carbonyl, and sulfur-containing functional groups played crucial roles in Ag transportation and the reduction of Ag⁺ to Ag⁰.

Comparative proteomic analysis of the response to silver ions and yeast extract in Salvia miltiorrhiza hairy root cultures

Biotic and abiotic stresses can inhibit plant growth, resulting in losses of crop productivity. However, moderate adverse stress can promote the accumulation of valuable natural products in medicinal plants. Elucidating the underlying molecular mechanisms thus might help optimize the variety of available plant medicinal materials and improve their quality. In this study, Salvia miltiorrhiza hairy root cultures were employed as an in vitro model of the Chinese herb Danshen. A comparative proteomic analysis using 2-dimensional gel electrophoresis and MALDI-TOF-MS was performed. By comparing the gel images of groups exposed to the stress of yeast extract (YE) combined with Ag(+) and controls, 64 proteins were identified that showed significant changes in protein abundance for at least one time point after treatment. According to analysis based on the KEGG and related physiological experimental verification, it was found that YE and Ag(+) stress induced a burst of reactive oxygen species and activated the Ca(2+)/calmodulin signaling pathway. Expression of immune-suppressive proteins increased. Epidermal cells underwent programmed cell death. Energy metabolism was enhanced and carbon metabolism shifted to favor the production of secondary metabolites such as lignin, tanshinone and salvianolic acids. The tanshinone and salvianolic acids were deposited on the collapsed epidermal cells forming a physicochemical barrier. The defense proteins and these natural products together enhanced the stress resistance of the plants. Since higher levels of natural products represent good quality in medicinal materials, this study sheds new light on quality formation mechanisms of medicinal plants and will hopefully encourage further research on how the planting environment affects the efficacy of herbal medicines.

Toxicity and bioaccumulation of sediment-associated silver nanoparticles in the estuarine polychaete, Nereis (Hediste) diversicolor

In this study, the toxicities of sediment-associated silver added to sediment as commercially available silver nanoparticles (Ag NPs, 20 and 80 nm) and aqueous Ag (AgNO3) to the estuarine polychaete, Nereis (Hediste) diversicolor, were investigated for both individual and subcellular endpoints after 10 d of exposure. Both Ag NP types were characterized in parallel to the toxicity studies and found to be polydispersed and overlapping in size. Burrowing activity decreased (marginally) with increasing Ag concentration and depended on the form of Ag added to sediment. All worms accumulated Ag regardless of the form in which it was added to the sediment, and worm size (expressed as dry weight) was found to significantly affect bioaccumulation such that smaller worms accumulated more Ag per body weight than larger worms. Lysosomal membrane permeability (neutral red retention time, NRRT) and DNA damage (comet assay tail moment and tail DNA intensity %) of Nereis coelomocytes increased in a concentration-dependent manner in all three Ag treatments. Ag NP treatments were more toxic than aqueous Ag for all toxicity endpoints, even though bioaccumulation did not differ significantly among Ag forms. No significant difference in toxicity was observed between the two Ag NP treatments which was attributed to their overlap in particle size.

The biological fate of silver ions following the use of silver-containing wound care products - a review

Ionic silver has a long history as an antimicrobial in human health care. This article is a review of the published literature on how ionic silver may enter the body from exposure to silver-containing wound care products and its eventual metabolic fates, in an assessment of the safety during normal use of these products in wound care. Following the application to breached skin, there appears to be little evidence of localised or systemic toxicity, and this is borne out by the continuous use of silver sulfadiazine formulations for more than 50 years. Consequently, following normal use, the risk of silver ion toxicity locally and systemically is considered to be low or negligible.

Cellular uptake, intracellular trafficking and cytotoxicity of silver nanoparticles

Silver nanoparticles (Ag NPs) are used in consumer products and wound dressings due to their antimicrobial properties. However, in addition to toxic effects on microbes, Ag NPs can also induce stress responses as well as cytotoxicity in mammalian cells. We observed that Ag NPs are efficiently internalized via scavenger receptor-mediated phagocytosis in murine macrophages. Confocal and electron microscopy analysis revealed that internalized Ag NPs localize in the cytoplasm. Ag NPs cause mitochondrial damage, induce apoptosis and cell death. These effects were abrogated in presence of Ag ion-reactive, thiol-containing compounds suggesting the central of Ag ions in Ag NP toxicity. Quantitative image analysis revealed that intracellular dissolution of Ag NPs occurs about 50 times faster than in water. In conclusion, we demonstrate for the first time that Ag NPs are internalized by scavenger receptors, trafficked to cytoplasm and induce toxicity by releasing Ag ions.

Mechanism of silver nanoparticle toxicity is dependent on dissolved silver and surface coating in Caenorhabditis elegans

The rapidly increasing use of silver nanoparticles (Ag NPs) in consumer products and medical applications has raised ecological and human health concerns. A key question for addressing these concerns is whether Ag NP toxicity is mechanistically unique to nanoparticulate silver, or if it is a result of the release of silver ions. Furthermore, since Ag NPs are produced in a large variety of monomer sizes and coatings, and since their physicochemical behavior depends on the media composition, it is important to understand how these variables modulate toxicity. We found that a lower ionic strength medium resulted in greater toxicity (measured as growth inhibition) of all tested Ag NPs to Caenorhabditis elegans and that both dissolved silver and coating influenced Ag NP toxicity. We found a linear correlation between Ag NP toxicity and dissolved silver, but no correlation between size and toxicity. We used three independent and complementary approaches to investigate the mechanisms of toxicity of differentially coated and sized Ag NPs: pharmacological (rescue with trolox and N-acetylcysteine), genetic (analysis of metal-sensitive and oxidative stress-sensitive mutants), and physicochemical (including analysis of dissolution of Ag NPs). Oxidative dissolution was limited in our experimental conditions (maximally 15% in 24 h) yet was key to the toxicity of most Ag NPs, highlighting a critical role for dissolved silver complexed with thiols in the toxicity of all tested Ag NPs. Some Ag NPs (typically less soluble due to size or coating) also acted via oxidative stress, an effect specific to nanoparticulate silver. However, in no case studied here was the toxicity of a Ag NP greater than would be predicted by complete dissolution of the same mass of silver as silver ions.

Nanomaterial-Based Antibacterial Paper

Antibacterial materials are widely used in everyday life and plays important roles in the public health system. There are a wide range of materials that have been known to prevent attachment and proliferation of microbes on material surfaces. These include antibiotics, metal ions and quaternary ammonium compounds. Given the availability of these various antibacterial materials, concerns about antibiotics-resistance, environmental pollution, relatively complex processing and high cost have been of much recent interest. Antimicrobial properties of nanomaterials have been explored to meet these challenges. Various nanomaterials including silver nanoparticles (AgNPs), titanium oxide nanoparticles and carbon nanotubes (CNTs) have been found to be highly effective bacterial-killing materials. The most well-known examples are silver and silver-based compounds, which were well known to be antiseptic to a spectrum of bacterium even in ancient times. AgNPs have proven to possess high antibacterial activity with minimal perturbation to human cells. Consequently, widespread applications of AgNPs have been found in medical and environmental areas [1]. More recently, carbon nanomaterials have emerged as a type of novel antibacterial nanomaterials, including CNTs and graphene. In this chapter, we aim to provide a review on the fabrication of nanomaterials-based paper-like films and their antibacterial applications.

Polymeric Multilayers that contain Silver Nanoparticles can be Stamped onto Biological Tissues to Provide Antibacterial Activity

We report the design of polyelectrolyte multilayers (PEMs) that can be prefabricated on an elastomeric stamp and mechanically transferred onto biomedically-relevant soft materials, including medical-grade silicone elastomers (E'~450-1500 kPa; E'-elastic modulus) and the dermis of cadaver-skin (E'~200-600 kPa). Whereas initial attempts to stamp PEMs formed from poly(allylamine hydrochloride) and poly(acrylic acid) resulted in minimal transfer onto soft materials, we report that integration of micrometer-sized beads into the PEMs (thicknesses of 6-160 nm) led to their quantitative transfer within 30 seconds of contact at a pressure of ~196 kPa. To demonstrate the utility of this approach, PEMs were impregnated with a range of loadings of silver-nanoparticles and stamped onto the dermis of human cadaver-skin (a wound-simulant) that was subsequently incubated with bacterial cultures. Skin-dermis stamped with PEMs that released 0.25±0.01 μg cm-2 of silver ions caused a 6 log10 reduction in colony forming units of Staphylococcus epidermidis and Pseudomonas aeruginosa within 12 h. Significantly, this level of silver release is below that which is cytotoxic to NIH 3T3 mouse fibroblast cells. Overall, this study describes a general and facile approach for the functionalization of biomaterial surfaces without subjecting them to potentially deleterious processing conditions.

Metallic silver fragments cause massive tissue loss in the mouse brain

Silver is a metal with well-known antibacterial effects. This makes silver an attractive coating material for medical devices for use inside the body, e.g. orthopaedic prostheses and catheters used in neurosurgery as it has been found to reduce the high risk of infections. Lately, the use of nano-silver particles in the industry, e.g. woven into fabrics and furniture has increased, and thus the exposure to silver particles in daily life increases. To study the effect of metallic silver particles on nervous tissue, we injected micron-sized silver particles into the mouse brain by stereotactic procedures. After 7, 14 days and 9 months, the silver-exposed animals had considerable brain damage seen as cavity formation and inflammation adjacent to the injected metallic silver particles. The tissue loss involved both cortical and hippocampal structures and resulted in enlargement of the lateral ventricles. Autometallographic silver enhancement showed silver uptake in lysosomes of glia cells and neurons in the ipsilateral cortex and hippocampus alongside a minor uptake on the contralateral side. Silver was also detected in ependymal cells and the choroid plexus. After 9 months, spreading of silver to the kidneys was seen. Cell counts of immunostained sections showed that metallic silver induced a statistically significant inflammatory response, i.e. increased microgliosis (7 days: p < 0.0001; 14 days: p < 0.01; 9 months: p < 0.0001) and TNF-α expression (7 and 14 days: p < 0.0001; 9 months: p = 0.91). Significant astrogliosis (7, 14 days and 9 months: p < 0.0001) and increased metallothionein (MT I + II) expression (7 and 14 days: p < 0.0001; 9 months: p < 0.001) were also seen in silver-exposed brain tissue. We conclude that metallic silver implants release silver ions causing neuroinflammation and a progressive tissue loss in the brain.

Surfaces modified with nanometer-thick silver-impregnated polymeric films that kill bacteria but support growth of mammalian cells

Silver is widely used as a biocidal agent in ointments and wound dressings. However, it has also been associated with tissue toxicity and impaired healing. In vitro characterization has also revealed that typical loadings of silver employed in ointments and dressings (approximately 100 microg/cm(2)) lead to cytotoxicity. In this paper, we report the results of an initial study that sought to determine if localization of carefully controlled loadings of silver nanoparticles within molecularly thin films immobilized on surfaces can lead to antimicrobial activity without inducing cytotoxicity. Polymeric thin films of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) were prepared by layer-by-layer deposition and loaded with approximately 0.4 microg/cm(2) to approximately 23.6 microg/cm(2) of silver nanoparticles. Bacterial killing efficiencies of the silver-loaded films were investigated against Staphylococcus epidermidis, a gram-positive bacterium, and it was determined that as little as approximately 0.4 microg/cm(2) of silver in the polymeric films caused a reduction of 6log(10)CFU/mL (99.9999%) bacteria in suspensions incubated in contact with the films (water-borne assays). Significantly, whereas the antibacterial films containing high loadings of silver were found to be toxic to a murine fibroblast cell line (NIH-3T3), the polymeric films containing approximately 0.4 microg/cm(2) of silver were not toxic and allowed attachment, and growth of the mammalian cells. Thus, the results of this study go beyond prior reports by identifying silver-impregnated, polymeric thin films that are compatible with in vitro mammalian cell culture yet exhibit antibacterial activity. These results support the hypothesis that localization of carefully controlled loadings of silver nanoparticles within molecularly thin polymeric films can lead to antimicrobial activity without cytotoxicity. More broadly, this strategy of modifying surfaces with minimal loadings of bioactive molecules indicates the basis of approaches that may permit management of microbial burden in wound beds without impairment of wound healing.

State-of-the-art technologies, current opinions and developments, and novel findings: news from the field of histochemistry and cell biology

Investigations of cell and tissue structure and function using innovative methods and approaches have again yielded numerous exciting findings in recent months and have added important data to current knowledge, inspiring new ideas and hypotheses in various fields of modern life sciences. Topics and contents of comprehensive expert reviews covering different aspects in methodological advances, cell biology, tissue function and morphology, and novel findings reported in original papers are summarized in the present review.