A Morphologic Study on the Fate of Ultrafine Silver Particles: Distribution Pattern of Phagocytized Metallic Silver in Vitro and in Vivo

The splenocyte proliferative response and cytokine secretion in mice after 28-day oral administration of silver nanocolloid

An increasing number of applications of silver nanoparticles in industry, medicine and everyday life means that the risk of exposure of the human organism to their potential harmful influence is growing. This study has sought to assess the effect of 28-day alimentary administration of different concentrations (0.25, 2.5 and 25 ppm) of a commercial silver nanocolloid on the proliferative activity and synthesis of cytokines by mouse splenocytes. All of the analyzed doses of the colloid had a significant, albeit different, effect on the activity of splenocytes. At the lowest dose, a significant decrease in the proliferation of T cells and more intensive synthesis of pro-inflammatory cytokines, both by non-stimulated and LPS-stimulated cells, was observed. The intermediate dose, on the other hand, stimulated proliferation of B cells while producing a pro-inflammatory effect regarding the synthesis of cytokines. Finally, the highest dose decreased the synthesis of cytokines by non-stimulated cells, but after LPS stimulation, through the strong activation of the IL-10 synthesis, it raised the proliferation of B cells and decreased the synthesis of pro-inflammatory cytokines. The results suggest that silver nanoparticles administered orally have an easy access to the peripheral organs of the immune system, such as the spleen, but the effect of long-term exposure of this organ to the effect of silver nanocolloid depends on several factors, including the dose of nanoparticles, and seems as difficult to predict.

The in vitro effect of commercially available noble metal nanocolloids on the splenocyte proliferative response and cytokine production in mice

Noble metal nanoparticles, currently among the most popular types of nanomaterials, are capable of penetrating through biological barriers once they enter a living organism. There, they can permeate into organs possessing the reticuloendothelial system, such as the spleen. The objective of this study was to determine the effect of commercial nanocolloids of noble metals (silver, gold and copper), recommended by the manufacturer as dietary supplements, on the in vitro viability, proliferative activity and production of cytokines (IL-1β, IL-2, IL-6, IL- 10 and TNF-α) by mouse splenocytes.

All of the analyzed colloids had some effect on the activity of mouse splenocytes. Silver colloid was characterized by high toxicity - concentrations of 1.25 ppm and above substantially depressed the viability of cells as well as their proliferative activity and ability to synthesize cytokines. The other two colloids were far less toxic than nanosilver, although their non-toxic concentrations had a significant effect on the production of cytokines by mitogen activated splenocytes. The colloid of gold decreased the level of IL-2, and the colloid of copper caused an increase in IL-2, IL6 and Il-10. At the same time, copper colloid alone induced the synthesis of IL-1β in mitogen unstimulated cells. The results indicate that colloids of noble metals are capable of affecting the activity of immunocompetent cells in important peripheral organs of the immune system.

Nanosilver induces minimal lung toxicity or inflammation in a subacute murine inhalation model

Background

There is increasing interest in the environmental and health consequences of silver nanoparticles as the use of this material becomes widespread. Although human exposure to nanosilver is increasing, only a few studies address possible toxic effect of inhaled nanosilver. The objective of this study was to determine whether very small commercially available nanosilver induces pulmonary toxicity in mice following inhalation exposure.

Results

In this study, mice were exposed sub-acutely by inhalation to well-characterized nanosilver (3.3 mg/m³, 4 hours/day, 10 days, 5 ± 2 nm primary size). Toxicity was assessed by enumeration of total and differential cells, determination of total protein, lactate dehydrogenase activity and inflammatory cytokines in bronchoalveolar lavage fluid. Lungs were evaluated for histopathologic changes and the presence of silver. In contrast to published in vitro studies, minimal inflammatory response or toxicity was found following exposure to nanosilver in our in vivo study. The median retained dose of nanosilver in the lungs measured by inductively coupled plasma - optical emission spectroscopy (ICP-OES) was 31 μg/g lung (dry weight) immediately after the final exposure, 10 μg/g following exposure and a 3-wk rest period and zero in sham-exposed controls. Dissolution studies showed that nanosilver did not dissolve in solutions mimicking the intracellular or extracellular milieu.

Conclusions

Mice exposed to nanosilver showed minimal pulmonary inflammation or cytotoxicity following sub-acute exposures. However, longer term exposures with higher lung burdens of nanosilver are needed to ensure that there are no chronic effects and to evaluate possible translocation to other organs.

Environmental and human health risks of aerosolized silver nanoparticles

Silver nanoparticles (AgNPs) are gaining attention from the academic and regulatory communities, not only because of their antimicrobial effects and subsequent product applications, but also because of their potential health and environmental risks. Whereas AgNPs in the aqueous phase are under intensive study, those in the atmosphere have been largely overlooked, although it is well established that inhalation of nanoparticles is associated with adverse health effects. This review summarizes the present state of knowledge concerning airborne AgNPs to shed light on the possible environmental exposure scenarios that may accompany the production and popularization of silver nanotechnology consumer products. The current understanding of the toxicity of AgNPs points toward a potential threat via the inhalation exposure route. Nanoparticle size, chemical composition, crystal structure, surface area, and the rate of silver ion release are expected to be important variables in determining toxicity. Possible routes of aerosolization of AgNPs from the production, use, and disposal of existing consumer products are presented. It is estimated that approximately 14% of silver nanotechnology products that have been inventoried could potentially release silver particles into the air during use, whether through spraying, dry powder dispersion, or other methods. In laboratory and industrial settings, six methods of aerosolization have been used to produce airborne AgNPs: spray atomization, liquid-flame spray, thermal evaporation-condensation, chemical vaporization, dry powder dispersion, and manual handling. Fundamental uncertainties remain about the fate of AgNPs in the environment, their short- and long-term health effects, and the specific physical and chemical properties of airborne particles that are responsible for health effects. Thus, to better understand the risks associated with silver nanotechnology, it is vital to understand the conditions under which AgNPs could become airborne.

Nanoparticle-induced cell culture models for degenerative protein aggregation diseases

Protein aggregates and nuclear inclusions containing components of the ubiquitin-proteasome system, expanded polyglutamine (polyQ) proteins, and transcriptional co-activators characterize cellular responses to stress and are hallmarks of neurodegenerative diseases. For instance, in Huntington's disease, an expansion of a polyQ region causes its aggregation into beta-sheet-containing amyloid fibrils. The biological function of polyQ-containing inclusions is unknown. By means of a silica nanoparticle (NP)-based strategy we induced intranuclear protein inclusions that form amyloid-like structures, recapitulating the protein composition and solubility of polyQ-induced nuclear protein aggregates exactly. We showed that global proteasomal proteolysis increases in silica-NP-treated nuclei and, on the local level, a subpopulation of nuclear inclusions overlaps with focal domains of proteasome-dependent protein degradation. The results suggest that inclusions in the nucleus constitute active proteolysis modules that may serve to concentrate and decompose damaged, mal-folded, or misplaced proteins. While nanoparticle-nucleus interactions turn out to be invaluable tools to study the molecular mechanisms of degenerative protein aggregation diseases, one also has to consider the other side of the coin, namely, emerging environmental risks posed by these very interactions.

Distribution pattern of inhaled ultrafine gold particles in the rat lung

The role of alveolar macrophages in the fate of ultrafine particles in the lung was investigated. Male Wistar-Kyoto rats were exposed to ultrafine gold particles, generated by a spark generator, for 6 h at a concentration of 88 microg/m3 (4 x 10(6)/cm3, 16 nm modal mobility diameter). Up to 7 days, the animals were serially sacrificed, and lavaged cells and lung tissues were examined by transmission electron microscopy. The gold concentration/content in the lung, lavage fluid, and blood was estimated by inductively coupled plasma-mass spectrometry. Gold particles used were spherical and electron dense with diameters of 5-8 nm. The particles were individual or slightly agglomerated. By inductively coupled plasma-mass spectrometry analysis of the lung, 1945 +/- 57 ng (mean +/- SD) and 1512 +/- 184 ng of gold were detected on day 0 and on day 7, respectively, indicating that a large portion of the deposited gold particles was retained in the lung tissue. In the lavage fluid, 573 +/- 67 ng and 96 +/- 29 ng were found on day 0 and day 7, respectively, which means that 29% and 6% of the retained gold particles were lavageable on these days. A low but significant increase of gold (0.03 to 0.06% of lung concentration) was found in the blood. Small vesicles containing gold particles were found in the cytoplasm of alveolar macrophages. In the alveolar septum, the gold particles were enclosed in vesicles observed in the cytoplasm of alveolar type I epithelial cells. These results indicate that inhaled ultrafine gold particles in alveolar macrophages and type I epithelial cells are processed by endocytotic pathways, though the uptake of the gold particles by alveolar macrophages is limited. To a low degree, systemic particle translocation took place.

Examination of nonendocytotic bulk transport of nanoparticles across phospholipid membranes

Nonendocytotic transport is believed to play a role in the transmigration of particles less than 100 nm within biological systems. Determining the fundamental mechanism of this transport across cell membranes is essential if nanotechnology is to be utilized in general medical practice and may lead to methods of treating the deleterious internalization of ambient, possibly pollutant, nanoparticles. In order to gain a broader understanding of nonendocytotic transmembrane transport, it becomes essential to devise a method which allows the isolation of fundamental modes of transport such as passive Brownian diffusion through a membrane, as opposed to effusion-like transport of particles through transmembrane channels. The passive Brownian diffusion contribution was investigated using gold nanoparticles and mimetic biomembranes. Specifically, gold nanoparticle dispersions consisting of 7, 10, and 15 nm diameter particles were captured in giant unilamelar vesicles composed of phosphatidylcholine, phosphatidic acid, and cholesterol. Nonendocytotic transmembrane transport was modeled as the time derivative of the appearance of nanoparticles in the phosphate buffer outside the vesicles at 37 degrees C. The results show the transport rate to be zero; hence, a simple diffusive process of transmembrane transport is not supported.

Bioavailability of beryllium oxide particles: an in vitro study in the murine J774A.1 macrophage cell line model

Beryllium metal and its oxide and alloys are materials of industrial significance with recognized adverse effects on worker health. Currently, the degree of risk associated with exposure to these materials in the workplace is assessed through measurement of beryllium aerosol mass concentration. Compliance with the current mass-based occupational exposure limit has proven ineffective at eliminating the occurrence of chronic beryllium disease (CBD). The rationale for this research was to examine the mechanism of beryllium bioavailability, which may be pertinent to risk. The authors tested the hypothesis in vitro that dissolution of particles engulfed by macrophages is greater than dissolution in cellular medium alone. Physicochemical changes were evaluated in vitro for well-characterized high-purity beryllium oxide (BeO) particles in cell-free media alone and engulfed by and retained within murine J774A.1 monocyte-macrophage cells. The BeO particles were from a commercially available powder and consisted of diffuse clusters (aerodynamic diameter range 1.5 to 2.5 microm) of 200-nm diameter primary particles. Following incubation for 124 to 144 hours, particles were recovered and recharacterized. Recovered particles were similar in morphology, chemical composition, and size relative to the original material, confirming the relatively insoluble nature of the BeO particles. Measurable levels of dissolved beryllium, representing 0.3% to 4.8% of the estimated total beryllium mass added, were measured in the recovered intracellular fluid. Dissolved beryllium was not detected in the extracellular media. The BeO chemical dissolution rate constant in the J774A. 1 cells was 2.1 +/- 1.7 x 10(-8)g/(cm2 . day). In contrast, the BeO chemical dissolution rate constant in cell-free media was < 8.1 x 10(-9)g/(cm2 . day). In vivo, beryllium dissolved by macrophages may be released in the pulmonary alveolar environment, in the lymphatic system after transport of beryllium by macrophages, or in the alveolar interstitium after migration and dissolution of beryllium particles in tissue. These findings demonstrate a mechanism of bioavailability for beryllium, are consistent with previously observed results in canine alveolar macrophages, and provide insights into additional research needs to understand and prevent beryllium sensitization and CBD.

Fate and toxic effects of inhaled ultrafine cadmium oxide particles in the rat lung

Female Fischer 344 rats were exposed to ultrafine cadmium oxide particles, generated by spark discharging, for 6 h at a concentration of 70 microg Cd/m(3) (1 x 10(6)/cm(3)) (40 nm modal diameter). Lung morphology and quantification of Cd content/concentration by inductively coupled plasma (ICP)-mass spectrometry were performed on days 0, 1, 4, and 7 after exposure. Cd content in the lung on day 0 was 0.53 +/- 0.12 microg/lung, corresponding to 19% of the estimated total inhaled cumulative dose, and the amount remained constant throughout the study. In the liver no significant increase of Cd content was found up to 4 days. A slight but statistically significant increase was observed in the liver on day 7. We found neither exposure-related morphological changes of lungs nor inflammatory responses in lavaged cells. Another group of rats were exposed to a higher concentration of ultrafine CdO particles (550 microg Cd/m(3) for 6 h, 51 nm modal diameter). The rats were sacrificed immediately and 1 day after exposure. The lavage study performed on day 0 showed an increase in the percentage of neutrophils. Multifocal alveolar inflammation was seen histologically on day 0 and day 1. Although the Cd content in the lung was comparable between day 0 and day 1 (3.9 microg/lung), significant elevation of Cd levels in the liver and kidneys was observed on both days. Two of 4 rats examined on day 0 showed elevation of blood cadmium, indicating systemic translocation of a fraction of deposited Cd from the lung in this group. These results and comparison with reported data using fine CdO particles indicate that inhalation of ultrafine CdO particles results in efficient deposition in the rat lung. With regard to the deposition dose, adverse health effects of ultrafine CdO and fine CdO appear to be comparable. Apparent systemic translocation of Cd took place only in animals exposed to a high concentration that induced lung injury.