Cytotoxicity and genotoxicity of silver nanoparticles in human cells

Genotoxicity of metal nanoparticles

Nanotechnology is currently used in industry, medicine, and military applications, as well as in more than 300 commercial products. Yet, the same properties that make these particles exciting for technology also make them daunting public health concerns because their toxicity is unknown and relatively unexplored. Increased attention is being placed on the study of metal particle genotoxicity; however, a lot of unknowns remain about their effects and the mechanisms. In this article, we highlight some metal and metal oxide nanoparticles of interest and discuss the current in vivo and in vitro studies of genotoxic effects. Many metal nanoparticles were found to cause chromosomal aberrations, DNA strand breaks, oxidative DNA damage, and mutations. Inconsistencies are found in the literature, however, thus drawing conclusions is difficult due to a variety of factors. Therefore, the areas requiring further attention are highlighted and recommendations to improve our understanding of the genotoxic potential are addressed.

Aluminum nanoparticle exposure in L1 larvae results in more severe lethality toxicity than in L4 larvae or young adults by strengthening the formation of stress response and intestinal lipofuscin accumulation in nematodes

Toxicity of Al(2)O(3)-NPs, as compared to that of Al(2)O(3), to L1-larval, L4-larval or young adult nematodes was evaluated. When exposure was performed at L1-larval stage, the significant increases of lethality, stress response, and intestinal lipofuscin autofluorescence were observed in 6.3-203.9 mg/L of Al(2)O(3)-NPs exposed nematodes. In contrast, when exposure was performed at L4-larval or young adult stage, the significant increases of lethality and intestinal lipofuscin autofluorescence were observed in 12.7-203.9 mg/L of Al(2)O(3)-NPs exposed nematodes, and the significant inductions of stress response were detected in 25.5-203.9 mg/L of Al(2)O(3)-NPs exposed nematodes. Moreover, the lethality was significantly correlated with the stress response and the intestinal lipofuscin autofluorescence in Al(2)O(3)-NPs exposed nematodes. These data imply that Al(2)O(3)-NPs exposure in L1 larvae causes more severe lethality toxicity than in L4 larvae or young adults by strengthening the formation of stress response and intestinal lipofuscin accumulation in nematodes.

Toxicology of nanomaterials used in nanomedicine

With the development of nanotechnology, nanomaterials are being widely used in many industries as well as in medicine and pharmacology. Despite the many proposed advantages of nanomaterials, increasing concerns have been expressed on their potential adverse human health effects. In recent years, application of nanotechnology in medicine has been defined as nanomedicine. Techniques in nanomedicine make it possible to deliver therapeutic agents into targeted specific cells, cellular compartments, tissues, and organs by using nanoparticulate carriers. Because nanoparticles possess different physicochemical properties than their fine-sized analogues due to their extremely small size and large surface area, they need to be evaluated separately for toxicity and adverse health effects. In addition, in the field of nanomedicine, intravenous and subcutaneous injections of nanoparticulate carriers deliver exogenous nanoparticles directly into the human body without passing through the normal absorption process. These nanoparticulate carriers themselves may be responsible for toxicity and interaction with biological macromolecules within the human body. Second, insoluble nanoparticulate carriers may accumulate in human tissues or organs. Therefore, it is necessary to address the potential health and safety implications of nanomaterials used in nanomedicine. Toxicological studies for biosafety evaluation of these nanomaterials will be important for the continuous development of nanomedical science. This review summarizes the current knowledge on toxicology of nanomaterials, particularly on those used in nanomedicine.

Drug permeation across intestinal epithelial cells using porous silicon nanoparticles

Mesoporous silicon particles hold great potential in improving the solubility of otherwise poorly soluble drugs. To effectively translate this feature into the clinic, especially via oral or parenteral administration, a thorough understanding of the interactions of the micro- and nanosized material with the physiological environment during the delivery process is required. In the present study, the behaviour of thermally oxidized porous silicon particles of different sizes interacting with Caco-2 cells (both non-differentiated and polarized monolayers) was investigated in order to establish their fate in a model of intestinal epithelial cell barrier. Particle interactions and TNF-α were measured in RAW 264.7 macrophages, while cell viabilities, reactive oxygen species and nitric oxide levels, together with transmission electron microscope images of the polarized monolayers, were assessed with both the Caco-2 cells and RAW 264.7 macrophages. The results showed a concentration and size dependent influence on cell viability and ROS-, NO- and TNF-α levels. There was no evidence of the porous nanoparticles crossing the Caco-2 cell monolayers, yet increased permeation of the loaded poorly soluble drug, griseofulvin, was shown.

Effects of cell culture media on the dynamic formation of protein-nanoparticle complexes and influence on the cellular response

The development of appropriate in vitro protocols to assess the potential toxicity of the ever expanding range of nanoparticles represents a challenging issue, because of the rapid changes of their intrinsic physicochemical properties (size, shape, reactivity, surface area, etc.) upon dispersion in biological fluids. Dynamic formation of protein coating around nanoparticles is a key molecular event, which may strongly impact the biological response in nanotoxicological tests. In this work, by using citrate-capped gold nanoparticles (AuNPs) of different sizes as a model, we show, by several spectroscopic techniques (dynamic light scattering, UV-visible, plasmon resonance light scattering), that proteins-NP interactions are differently mediated by two widely used cellular media (i.e., Dulbecco Modified Eagle's medium (DMEM) and Roswell Park Memorial Institute medium (RPMI), supplemented with fetal bovine serum). We found that, while DMEM elicits the formation of a large time-dependent protein corona, RPMI shows different dynamics with reduced protein coating. Characterization of these nanobioentities was also performed by sodium dodecyl sulfate polyacrylamide gel electrophoresis and mass spectroscopy, revealing that the average composition of protein corona does not reflect the relative abundance of serum proteins. To evaluate the biological impact of such hybrid bionanostructures, several comparative viability assays onto two cell lines (HeLa and U937) were carried out in the two media, in the presence of 15 nm AuNPs. We observed that proteins/NP complexes formed in RPMI are more abundantly internalized in cells as compared to DMEM, overall exerting higher cytotoxic effects. These results show that, beyond an in-depth NPs characterization before cellular experiments, a detailed understanding of the effects elicited by cell culture media on NPs is crucial for standardized nanotoxicology tests.

Cytotoxicity of, and innate immune response to, size-controlled polypyrrole nanoparticles in mammalian cells

Monodisperse polypyrrole (PPy) nanoparticles with five different diameters (20, 40, 60, 80, and 100 nm) were fabricated via chemical oxidation polymerization in order to evaluate size-dependent cytotoxicity. The cellular uptake of PPy nanoparticles in human lung fibroblasts (IMR90) and mouse alveolar macrophages (J774A.1) was observed by transmission electron microscopy. The nanoparticles were internalized into the IMR90 via endocytosis. In the J774A.1, the nanoparticles were entered via phagocytosis and endocytosis. Endocytosed nanoparticles were transported to lysosome via endosome-network. The cytotoxicity and innate immune response of PPy-treated cells were systematically investigated by viability assay, oxidative stress, apoptosis/necrosis, and expression of costimulatory molecules. The viability, oxidative stress, and apoptosis/necrosis of PPy-treated cells revealed size- and dose-dependency. Because of phagocytosis, PPy treatment had more adverse effects on the J774A.1 than the IMR90. Innate immune response of PPy-treated macrophages was measured by the expression of costimulatory molecules on surface of the cells. The expression of costimulatory molecules involved in Th1 response (CD40 and CD80) was lightly up-regulated and the other costimulatory molecule related in Th2 response (CD86) was less expressed than a negative control. These findings may provide better nanotoxicological information of polymer nanomaterials, and support the further development of PPy nanoparticles in bioelectronic applications.

Silver nanoparticles induce oxidative cell damage in human liver cells through inhibition of reduced glutathione and induction of mitochondria-involved apoptosis

Silver nanoparticles (AgNPs), which have well-known antimicrobial properties, are extensively used in various medical and general applications. Despite the widespread use of AgNPs, relatively few studies have been undertaken to determine the cytotoxic effects of AgNPs exposure. This study investigates possible molecular mechanisms underlying the cytotoxic effects of AgNPs. Here, we show that AgNPs-induced cytotoxicity was higher compared than that observed when AgNO(3) was used as a silver ion source. AgNPs induced reactive oxygen species (ROS) generation and suppression of reduced glutathione (GSH) in human Chang liver cells. ROS generated by AgNPs resulted in damage to various cellular components, DNA breaks, lipid membrane peroxidation, and protein carbonylation. Upon AgNPs exposure, cell viability decreased due to apoptosis, as demonstrated by the formation of apoptotic bodies, sub-G(1) hypodiploid cells, and DNA fragmentation. AgNPs induced a mitochondria-dependent apoptotic pathway via modulation of Bax and Bcl-2 expressions, resulting in the disruption of mitochondrial membrane potential (Δψ(m)). Loss of Δψ(m) was followed by cytochrome c release from the mitochondria, resulting in the activation of caspases 9 and 3. The apoptotic effect of AgNPs was exerted via the activation of c-Jun NH(2)-terminal kinase (JNK) and was abrogated by the JNK-specific inhibitor, SP600125 and siRNA targeting JNK. In summary, the results suggest that AgNPs cause cytotoxicity by oxidative stress-induced apoptosis and damage to cellular components.

Influence of individual ionic components on the agglomeration kinetics of silver nanoparticles

The precise characteristic of the agglomeration behavior of colloidal suspensions is of paramount interest to many current studies in nanoscience. This work seeks to elucidate the influence that differently charged salts have on the agglomeration state of a Lee-Meisel-type silver colloid. Moreover, we investigate the influence of the chemical nature of individual ions on their potential to induce agglomeration. Raman spectroscopy and surface-enhanced Raman spectroscopy are used to give insights into mechanistic aspects of the agglomeration process and to assess the differences in the influence of different salts on the agglomeration behavior. Finally, we demonstrate the potential of the measurement procedure used in this work to determine the elementary charge on colloidal NPs.

Nano-silver - feasibility and challenges for human health risk assessment based on open literature

This study aims at investigating feasibility and challenges associated with conducting a human health risk assessment for nano-silver based on the open literature by following an approach similar to a classical regulatory risk assessment. Gaps in the available data set, both in relation to exposures and hazard, do not allow reaching any definite conclusions that could be used for regulatory decision making. Results show that repeated inhalation in the workplace and possibly consumer inhalation may cause risks. Also (uncontrolled) nano-silver drug intake and burn treatment of large parts of the body with wound dressings may cause risks. Main future work should focus on generating occupational and consumer exposure data, as well as toxicity data on absorption (are particles or only ions absorbed?), information on genetoxicity, and further information on the toxicity following inhalation exposure to sizes and agglomeration states as uncounted in the workplace.

Metal-based nanoparticles and their toxicity assessment

Nanoparticles (NPs) can potentially cause adverse effects on organ, tissue, cellular, subcellular, and protein levels due to their unusual physicochemical properties (e.g., small size, high surface area to volume ratio, chemical composition, crystallinity, electronic properties, surface structure reactivity and functional groups, inorganic or organic coatings, solubility, shape, and aggregation behavior). Metal NPs, in particular, have received increasing interest due to their widespread medical, consumer, industrial, and military applications. However, as particle size decreases, some metal-based NPs are showing increased toxicity, even if the same material is relatively inert in its bulk form (e.g., Ag, Au, and Cu). NPs also interact with proteins and enzymes within mammalian cells and they can interfere with the antioxidant defense mechanism leading to reactive oxygen species generation, the initiation of an inflammatory response and perturbation and destruction of the mitochondria causing apoptosis or necrosis. As a result, there are many challenges to overcome before we can determine if the benefits outweigh the risks associated with NPs.

Active targeting of cancer cells using folic acid-conjugated platinum nanoparticles

Interaction of nanoparticles with human cells is an interesting topic for understanding toxicity and developing potential drug candidates. Water soluble platinum nanoparticles were synthesized via reduction of hexachloroplatinic acid using sodium borohydride in the presence of capping agents. The bioactivity of folic acid and poly(vinyl pyrrolidone) capped platinum nanoparticles (Pt-nps) has been investigated using commercially available cell lines. In the cell viability experiments, PVP-capped nanoparticles were found to be less toxic (>80% viability), whereas, folic acid-capped platinum nanoparticles showed a reduced viability down to 24% after 72 h of exposure at a concentration of 100 μg ml(-1) for MCF7 breast cancer cells. Such toxicity, combined with the possibility to incorporate functional organic molecules as capping agents, can be used for developing new drug candidates.

Controlled release of biologically active silver from nanosilver surfaces

Major pathways in the antibacterial activity and eukaryotic toxicity of nanosilver involve the silver cation and its soluble complexes, which are well established thiol toxicants. Through these pathways, nanosilver behaves in analogy to a drug delivery system, in which the particle contains a concentrated inventory of an active species, the ion, which is transported to and released near biological target sites. Although the importance of silver ion in the biological response to nanosilver is widely recognized, the drug delivery paradigm has not been well developed for this system, and there is significant potential to improve nanosilver technologies through controlled release formulations. This article applies elements of the drug delivery paradigm to nanosilver dissolution and presents a systematic study of chemical concepts for controlled release. After presenting thermodynamic calculations of silver species partitioning in biological media, the rates of oxidative silver dissolution are measured for nanoparticles and macroscopic foils and used to derive unified area-based release kinetics. A variety of competing chemical approaches are demonstrated for controlling the ion release rate over 4 orders of magnitude. Release can be systematically slowed by thiol and citrate ligand binding, formation of sulfidic coatings, or the scavenging of peroxy-intermediates. Release can be accelerated by preoxidation or particle size reduction, while polymer coatings with complexation sites alter the release profile by storing and releasing inventories of surface-bound silver. Finally, the ability to tune biological activity is demonstrated through a bacterial inhibition zone assay carried out on selected formulations of controlled release nanosilver.

Inorganic nanoparticles in cancer therapy

Nanotechnology is an evolving field with enormous potential for biomedical applications. The growing interest to use inorganic nanoparticles in medicine is due to the unique size- and shape-dependent optoelectronic properties. Herein, we will focus on gold, silver and platinum nanoparticles, discussing recent developments for therapeutic applications with regard to cancer in terms of nanoparticles being used as a delivery vehicle as well as therapeutic agents. We will also discuss some of the key challenges to be addressed in future studies.

Dose-dependent in-vivo toxicity assessment of silver nanoparticle in Wistar rats

This study aims to suggest the limits of silver nanoparticle (AgNP) uses for medicinal purpose and was performed to explore the effect of various doses of silver nanoparticle in rats. Four different doses of AgNP (4, 10, 20, and 40 mg/kg) were injected intravenously. For safety evaluation of injected AgNP, body weight, organ coefficient, whole blood count, and biochemistry panel assay for liver function enzyme (AST, ALT, ALP, and GGTP), comet assay, ROS, and histological parameter were performed; 10-12 week old animals were randomly divided into groups of six individuals each for control, and doses of 40, 20, 10, and 4 mg/kg AgNP injected. Significant changes were observed (p < 0.01) in hematological parameters (WBC count, platelets counts, haemoglobin, and RBC count) in the 40 and 20 mg/kg groups. The changes were non-significant in the other groups (4 and 10 mg/kg group). In the 40 mg/kg group, a significant increase was also found in liver function enzymes like ALT and AST (p < 0.01), ALP (p < 0.01), GGTP (p < 0.01), and bilirubin (p < 0.01). ROS in blood serum increased in the high dose group. Tail migration in single cell gel electrophoresis in the 40, 20, 10, 4 mg/kg, and control groups was 34.9, 29.5, 17.8, 5.8, and 0.0 µm, respectively, which indicated damage in the DNA strand in the high dose group. EDXRF showed a ∼ 10-times increase in silver concentration in the 40 mg/kg group and TEM image also showed particle deposition in the 40 mg/kg group. This study indicates that the AgNP in doses (< 10 mg/kg) is safe for biomedical application and has no side-effects, but its high dose (> 20 mg/kg) is toxic.

p38 MAPK activation, DNA damage, cell cycle arrest and apoptosis as mechanisms of toxicity of silver nanoparticles in Jurkat T cells

To identify potential harmful effects of silver nanoparticles (AgNPs) on human health, a comprehensive toxicity assay was conducted on human Jurkat T cells, using oxidative stress-related endpoint. The effect of Ag ions was also investigated and compared with that of AgNPs, as it is anticipated that Ag ions will be released from AgNPs, which may be responsible for their toxicity. Cell viability tests indicated high sensitivity of Jurkat T cells when exposed to AgNPs compared to Ag ions; however, both AgNPs and Ag ions induce similar levels of cellular reactive oxygen species during the initial exposure period and; after 24 h, they were increased on exposure to AgNPs compared to Ag ions, which suggest that oxidative stress may be an indirect cause of the observed cytotoxicity of AgNPs. AgNPs exposure activates p38 mitogen-activated protein kinase through nuclear factor-E2-related factor-2 and nuclear factor-kappaB signaling pathways, subsequently inducing DNA damage, cell cycle arrest and apoptosis. Selective toxicity of AgNPs on Jurkat T cells suggests that rigorous toxicity evaluation should be conducted using various different cell types and biological systems prior to the widespread use of AgNPs.

Correlating physico-chemical with toxicological properties of nanoparticles: the present and the future

Nanotoxicology is still a new discipline. In this Perspective, both its origins and its future trends are discussed. In particular, we note several issues we consider important for publications in this field.

Induction of oxidative stress and apoptosis by silver nanoparticles in the liver of adult zebrafish

Silver nanoparticles (AgNPs) may induce deleterious effects in aquatic life on environmental release. The hepatotoxicity of AgNPs was assessed in the liver of adult zebrafish, with the aim of studying the roles of oxidative damage and apoptosis. Zebrafish were exposed to an AgNP solution in which free Ag+ ions were absent at the time of treatment. However, the metal-sensitive metallothionein 2 (MT2) mRNA was induced in the liver tissues of AgNP-treated zebrafish, suggesting that Ag+ ions were released from AgNPs after treatment. It is also possible that MT2 mRNA was induced in the liver tissues by AgNP-generated free radicals. A number of cellular alterations including disruption of hepatic cell cords and apoptotic changes were observed in histological analysis of the liver tissues. The levels of malondialdehyde, a byproduct of cellular lipid peroxidation, and total glutathione were increased in the tissues after treatment with AgNPs. The mRNA levels of the oxyradical-scavenging enzymes catalase and glutathione peroxidase 1a were reduced in the tissues. AgNP treatment induced DNA damage, as demonstrated by analysis with the double-strand break marker γ-H2AX and the expression of p53 protein in liver tissues. In addition, the p53-related pro-apoptotic genes Bax, Noxa, and p21 were upregulated after treatment with AgNPs. These data suggest that oxidative stress and apoptosis are associated with AgNP toxicity in the liver of adult zebrafish.

Effects of silver nanoparticles on the development and histopathology biomarkers of Japanese medaka (Oryzias latipes) using the partial-life test

Silver nanoparticles (AgNPs) have emerged as an important class of nanomaterials and are currently used in a wide range of industrial and commercial applications. This has caused increasing concern about their effects on the environment and to human health. Using Japanese medaka (Oryzias latipes) at early-life stages as experimental models, the developmental toxicity of silver nanoparticles was investigated following exposure to 100-1000 μg/L homogeneously dispersed AgNPs for 70 days, and developmental endpoints were evaluated by microscopy during embryonic, larval and juvenile stages of development in medaka. Meanwhile, histopathological changes in the larval eye were evaluated. Retarded development and reduced pigmentation were observed in the treated embryos by AgNPs at high concentrations (≥ 400 μg/L). Maximum width of the optic tectum, as an indicator of midbrain development, decreased significantly in a dose-related manner. Furthermore, silver nanoparticles exposure at all concentrations induced a variety of morphological malformations such as edema, spinal abnormalities, finfold abnormalities, heart malformations and eye defects. Histopathological observations also confirmed the occurrence of abnormal eye development induced by AgNPs. The data showed non-linear or U-shaped dose-response patterns for growth retardation at 5 days of postfertilization, as well as the incidence of abnormalities. Preliminary results suggested that the developmental process of medaka may be affected by exposure to silver nanoparticles. Morphological abnormalities in early-life stages of medaka showed the potential developmental toxicities of silver nanoparticles. Further research should be focused on the mechanisms of developmental toxicity in fish exposed to silver nanoparticles.

Bacterial cytotoxicity of the silver nanoparticle related to physicochemical metrics and agglomeration properties

Silver particles are used in various consumer products due to their positive effects, which include sterilization and antibacterial properties. However, it has been reported that silver nanoparticles (AgNPs) have strongly acute toxic effects on various cells. Therefore, the cytotoxicity of AgNPs was investigated, using Escherichia coli as a model organism, from the standpoint of three key metrics (ionic ratio, size, and agglomeration) that are the most relevant physicochemical properties. The findings indicated that cytotoxicity is depressed by the agglomeration of AgNPs. The order of toxic sensitivity was as follows: total Ag concentration  >  ionic ratio  >  size, the order of which was inversely related to the extent of agglomeration.

Cellular uptake, cytotoxicity, and innate immune response of silica-titania hollow nanoparticles based on size and surface functionality

Silica-titania hollow nanoparticles (HNPs) with uniform diameters of 25, 50, 75, 100, and 125 nm were fabricated by dissolution and redeposition method in order to evaluate size dependent cellular response. Surface-modified HNPs with cationic, anionic, and neutral functional group were prepared by silane treatment. We systematically investigated cellular internalization, toxicity, and innate immune response of HNPs in human breast cancer (SK-BR-3) and mouse alveolar macrophage (J774A.1) cells. Size- and surface functionality-dependent cellular uptake of HNPs was investigated by fluorescence labeling (fluorescein isothiocyanate), inductively coupled plasma-emission spectroscopy, and ultrastructural resolution using transmission electron microscopy. Viability, reactive oxygen species, and apoptosis/necrosis of HNP-treated J774A.1 revealed the size-dependent phenomenon. Innate immune response of HNP-treated macrophages was measured by three cytokines such as interleukin-1, interleukin-6, and tumor necrosis factor α. Among the HNPs of different sizes, 50-nm HNPs demonstrated the highest toxic influence on macrophages. Among the HNPs with surface functionalities, cationic HNPs demonstrated the most toxic effect on J774A.1 and the highest uptake efficiency. The toxicity results of HNP-treated macrophages were consistent with the cellular internalization efficiency. These findings provide size- and surface functionality-dependent nanotoxicity and uptake of HNPs, and lead to HNPs for bioapplications such as drug delivery and imaging probe.

Current studies into the genotoxic effects of nanomaterials

Nanotechnology has created opportunities for engineers to manufacture superior and more efficient devices and products. Nanomaterials (NMs) are now widely used in consumer products as well as for research applications. However, while the lists of known toxic effects of nanomaterials and nanoparticles (NPs) continue to grow, there is still a vast gap in our knowledge about the genotoxicity of NMs. In this paper, we highlight some NMs of interest and discuss the current in vivo and in vitro studies into genotoxic effects of NMs.

Involvement of JNK and P53 activation in G2/M cell cycle arrest and apoptosis induced by titanium dioxide nanoparticles in neuron cells

Despite that applications of titanium dioxide nanoparticles (TiO(2)-NPs) have been developed in the fields of paints, waste water treatment, sterilization, cosmetics, food additive, bio-medical ceramic and implant biomaterials and so on, relatively few studies have been conducted to determine the neurotoxicity of TiO(2)-NPs exposure. In the present study, we investigated the cytotoxicity of TiO(2)-NPs using PC12 cells and intended to clarify the molecular mechanisms underlying the biological effects of TiO(2)-NPs. PC12 cell is a type of cells, which have been used as an in vitro model of dopaminergic neurons for neurodegenerative diseases research. In addition, the roles of the particle size and crystal structure of TiO(2)-NPs to the neurotoxicity were also investigated. The anatase TiO(2)-NPs displayed a dose-dependent behavior on decreasing cell viability, increasing levels of lactate dehydrogenase (LDH), activating oxidative stress, inducing apoptosis, disturbing cell cycle, triggering JNK- and p53-mediated signaling pathway. In comparison to anatase TiO(2)-NPs, the rutile TiO(2)-NPs showed moderately toxic effect on neuron cells. The micron-sized TiO(2) did not exhibit any toxic response. It is suggested from our results that reactive oxygen species (ROS) have a mediation effect to oxidative stress and up-regulation of JNK and P53 phosphorylation involved in mechanistic pathways of TiO(2)-NPs can induce apoptosis and cell cycle arrest in PC12 cells. In addition, both the size and crystal structure of TiO(2)-NPs exposure contributed to the neurotoxicity. Nanoparticles were more toxic than micrometer-sized particles and the anatase form were more toxic than the rutile.

Surface functional polymers by post-polymerization modification using diarylcarbenes: introduction, release and regeneration of hydrogen peroxide and bactericidal activity

Functionalized diarylcarbenes are excellent reactive intermediates suitable for the direct surface modification of organic polymers, and these may be used to introduce urea and thiourea functions onto polystyrene at loading levels of up to 2.3 x 10(13) molecules/cm(2). These functions are capable of the reversible binding and release of peroxide at loading levels of up to 0.6 mmol/g and give polymers that display biocidal activity against a spectrum of gram-positive and gram-negative bacteria.

Iodine-125 radiolabeling of silver nanoparticles for in vivo SPECT imaging

Silver nanoparticles are increasingly finding applications in medicine; however, little is known about their in vivo tissue distribution. Here, we have developed a rapid method for radiolabeling of silver nanoparticles with iodine-125 in order to track in vivo tissue uptake of silver nanoparticles after systemic administration by biodistribution analysis and single-photon emission computerized tomography (SPECT) imaging. Poly(N-vinyl-2 -pyrrolidone)-capped silver nanoparticles with an average size of 12 nm were labeled by chemisorption of iodine-125 with a > 80% yield of radiolabeling efficiency. Radiolabeled silver nanoparticles were intravenously injected in Balb/c mice, and the in vivo distribution pattern of these nanoparticles was evaluated by noninvasive whole-body SPECT imaging, which revealed uptake of the nanoparticles in the liver and spleen. Biodistribution analysis confirmed predominant accumulation of the silver nanoparticles in the spleen (41.5%ID/g) and liver (24.5%ID/g) at 24 h. Extensive uptake in the tissues of the reticuloendothelial system suggests that further investigation of silver nanoparticle interaction with hepatic and splenic tissues at the cellular level is critical for evaluation of the in vivo effects and potential toxicity of silver nanoparticles. This method enables rapid iodine-125 radiolabeling of silver nanoparticles with a specific activity sufficient for in vivo imaging and biodistribution analysis.

Nanoparticle-induced pulmonary toxicity

In recent decades, advances in nanotechnology engineering have given rise to the rapid development of many novel applications in the biomedical field. However, studies into the health and safety of these nanomaterials are still lacking. The main concerns are the adverse effects to health caused by acute or chronic exposure to nanoparticles (NPs), especially in the workplace environment. The lung is one of the main routes of entry for NPs into the body and, hence, a likely site for accumulation of NPs. Once NPs enter the interstitial air spaces and are quickly taken up by alveolar cells, they are likely to induce toxic effects. In this review, we highlight the different aspects of lung toxicity resulting from NP exposure, such as generation of oxidative stress, DNA damage and inflammation leading to fibrosis and pneumoconiosis, and the underlying mechanisms causing pulmonary toxicity.

Toxicity and cellular uptake of gold nanoparticles: what we have learned so far?

Gold nanoparticles have attracted enormous scientific and technological interest due to their ease of synthesis, chemical stability, and unique optical properties. Proof-of-concept studies demonstrate their biomedical applications in chemical sensing, biological imaging, drug delivery, and cancer treatment. Knowledge about their potential toxicity and health impact is essential before these nanomaterials can be used in real clinical settings. Furthermore, the underlying interactions of these nanomaterials with physiological fluids is a key feature of understanding their biological impact, and these interactions can perhaps be exploited to mitigate unwanted toxic effects. In this Perspective we discuss recent results that address the toxicity of gold nanoparticles both in vitro and in vivo, and we provide some experimental recommendations for future research at the interface of nanotechnology and biological systems.

Nanosilver as a new generation of nanoproduct in biomedical applications

Nanosilver (NS), comprising silver nanoparticles, is attracting interest for a range of biomedical applications owing to its potent antibacterial activity. It has recently been demonstrated that NS has useful anti-inflammatory effects and improves wound healing, which could be exploited in developing better dressings for wounds and burns. The key to its broad-acting and potent antibacterial activity is the multifaceted mechanism by which NS acts on microbes. This is utilized in antibacterial coatings on medical devices to reduce nosocomial infection rates. Many new synthesis methods have emerged and are being evaluated for NS production for medical applications. NS toxicity is also critically discussed to reflect on potential concerns before widespread application in the medical field.

Investigation of the cytotoxicity mechanism of silver nanoparticles in vitro

Nowadays, more and more nanotechnology products and nanomaterials are being applied in our lives. Silver nanoparticles (SNPs) are used in infection prevention and treatment due to their antimicrobial activity. However, as a kind of nanomaterial, the toxicology of SNPs has not been completely studied. The mechanism of cytotoxicity of SNPs in vitro to mouse's fibroblast cells (L929) was investigated in this study. As a contrast, silver microparticles (SMPs) were also studied. Propidium iodide (PI) single staining and Annexin-V/PI staining were carried out to unveil the influence of SNPs and SMPs on the cells. A transmission electron microscope (TEM) was used to observe SNPs' distribution in the cells. The results of cell cycle analysis indicated that the cells treated with SNPs were arrested in the G2M phase. Meanwhile, SNPs lead to apoptosis of more cells compared to SMPs at the same dose as a result of apoptosis analysis. Analysis of the cells' ultrastructure showed that SNPs could be phagocytized into the cells while SMPs could not. The mechanism of cytotoxicity of SNPs in vitro to L929 cells may be that SNPs are phagocytized into the cells and they interact with mitochondria or other organelles, even nuclei, which results in cells' apoptosis or necrosis.

Nanofibers offer alternative ways to the treatment of skin infections

Injury to the skin causes a breach in the protective layer surrounding the body. Many pathogens are resistant to antibiotics, rendering conventional treatment less effective. This led to the use of alternative antimicrobial compounds, such as silver ions, in skin treatment. In this review nanofibers, and the incorporation of natural antimicrobial compounds in these scaffolds, are discussed as an alternative way to control skin infections. Electrospinning as a technique to prepare nanofibers is discussed. The possibility of using these structures as drug delivery systems is investigated.

Antistaphylococcal nanocomposite films based on enzyme-nanotube conjugates

Infection with antibiotic-resistant pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) is one of the primary causes of hospitalizations and deaths. To address this issue, we have designed antimicrobial coatings incorporating carbon nanotube-enzyme conjugates that are highly effective against antibiotic-resistant pathogens. Specifically, we incorporated conjugates of carbon nanotubes with lysostaphin, a cell wall degrading enzyme, into films to impart bactericidal properties against Staphylococcus aureus and Staphylococcus epidermidis. We fabricated and characterized nanocomposites containing different conjugate formulations and enzyme loadings. These enzyme-based composites were highly efficient in killing MRSA (>99% within 2 h) without release of the enzyme into solution. Additionally, these films were reusable and stable under dry storage conditions for a month. Such enzyme-based film formulations may be used to prevent growth of pathogenic and antibiotic-resistant microorganisms on various common surfaces in hospital settings. Polymer and paint films containing such antimicrobial conjugates, in particular, could be advantageous to prevent risk of staphylococcal-specific infection and biofouling.