Single- and multi-wall carbon nanotubes versus asbestos: are the carbon nanotubes a new health risk to humans?

Safety evaluation of engineered nanomaterials for health risk assessment: an experimental tiered testing approach using pristine and functionalized carbon nanotubes

Increasing application of engineered nanomaterials within occupational, environmental, and consumer settings has raised the levels of public concern regarding possible adverse effects on human health. We applied a tiered testing strategy including (i) a first in vitro stage to investigate general toxicity endpoints, followed by (ii) a focused in vivo experiment. Cytotoxicity of laboratory-made functionalized multiwalled carbon nanotubes (CNTs) (i.e., MW-COOH and MW-NH2), compared to pristine MWCNTs, carbon black, and silica, has been assessed in human A549 pneumocytes by MTT assay and calcein/propidium iodide (PI) staining. Purity and physicochemical properties of the test nanomaterials were also determined. Subsequently, pulmonary toxic effects were assessed in rats, 16 days after MWCNTs i.t. administration (1 mg/kg b.w.), investigating lung histopathology and monitoring several markers of lung toxicity, inflammation, and fibrosis. In vitro data: calcein/PI test indicated no cell viability loss after all CNTs treatment; MTT assay showed false positive cytotoxic response, occurring not dose dependently at exceedingly low CNT concentrations (1 μg/mL). In vivo results demonstrated a general pulmonary toxicity coupled with inflammatory response, without overt signs of fibrosis and granuloma formation, irrespective of nanotube functionalization. This multitiered approach contributed to clarifying the CNT toxicity mechanisms improving the overall understanding of the possible adverse outcomes resulting from CNT exposure.

ROS evaluation for a series of CNTs and their derivatives using an ESR method with DMPO

Carbon nanotubes (CNTs) are important materials in advanced industries. It is a concern that pulmonary exposure to CNTs may induce carcinogenic responses. It has been recently reported that CNTs scavenge ROS though non-carbon fibers generate ROS. A comprehensive evaluation of ROS scavenging using various kinds of CNTs has not been demonstrated well. The present work specifically investigates ROS scavenging capabilities with a series of CNTs and their derivatives that were physically treated, and with the number of commercially available CNTs. CNT concentrations were controlled at 0.2 through 0.6 wt%. The ROS scavenging rate was measured by ESR with DMPO. Interestingly, the ROS scavenging rate was not only influenced by physical treatments, but was also dependent on individual manufacturing methods. Ratio of CNTs to DMPO/ hydrogen peroxide is a key parameter to obtain appropriate ROS quenching results for comparison of CNTs. The present results suggest that dangling bonds are not a sole factor for scavenging, and electron transfer on the CNT surface is not clearly determined to be the sole mechanism to explain ROS scavenging.

Systematic analysis of multiwalled carbon nanotube-induced cellular signaling and gene expression in human small airway epithelial cells

Multiwalled carbon nanotubes (MWCNT) are one of the most commonly produced nanomaterials, and pulmonary exposure during production, use, and disposal is a concern for the developing nanotechnology field. The airway epithelium is the first line of defense against inhaled particles. In a mouse model, MWCNT were reported to reach the alveolar space of the lung after in vivo exposure, penetrate the epithelial lining, and result in inflammation and progressive fibrosis. This study sought to determine the cellular and gene expression changes in small airway epithelial cells (SAEC) after in vitro exposure to MWCNT in an effort to elucidate potential toxicity mechanisms and signaling pathways. A direct interaction between SAEC and MWCNT was confirmed by both internalization of MWCNT and interaction at the cell periphery. Following exposure, SAEC showed time-dependent increases in reactive oxygen species production, total protein phosphotyrosine and phosphothreonine levels, and migratory behavior. Analysis of gene and protein expression suggested altered regulation of multiple biomarkers of lung damage, carcinogenesis, and tumor progression, as well as genes involved in related signaling pathways. These results demonstrate that MWCNT exposure resulted in the activation of SAEC. Gene expression data derived from MWCNT exposure provide information that may be used to elucidate the underlying mode of action of MWCNT in the small airway and suggest potential prognostic gene signatures for risk assessment.

Lung alterations following single or multiple low-dose carbon black nanoparticle aspirations in mice

Carbon black nanoparticle (CBNP) applications in high doses have been shown to be harmful to the lung. It is postulated that even small, environmentally relevant concentrations induce changes on lung homeostasis. The present study determined the impact of low-dose single and multiple CBNP (Printex 90) applications on mouse alveolar cell metabolism, especially inflammatory and oxidative stress parameters. Nanoparticles were administered to mice by a single or 8 oropharyngeal aspirations at wk 1, 2, 3, 5, 7, 9, 11, and 12 using 7 μg Printex 90, 7 μg DQ12 quartz (positive control), with water vehicle and saline as negative controls. After 2 d or 3 mo lung function was analyzed. Further lung histology, bronchoalveolar lavage fluid (BALF) parameters, and mRNA expression of cytokines and antioxidants enzymes in type II pneumocytes were measured on d 3 or after 3 mo. Single low-dose Printex 90 application induced no marked alterations in lung functions or BALF phospholipid levels but significant decrease in superoxide dismutase 2 and numerically elevated glutathione peroxidase 3 mRNA expression levels in type II pneumocytes. Multiple CBNP applications produced reduced lung function, collagen accumulation, elevated phospholipid levels in BALF, and a massive infiltration of macrophages. Type II pneumocyte mRNA expression of antioxidative enzymes remained unchanged throughout the subchronic experiment, but showed a significant decrease in interleukin (IL)-6Rα mRNA expression. This study demonstrates that an environmentally relevant CBNP concentration induced an acute inflammatory response, an effect that is exacerbated throughout the subchronic duration.

The role of iron impurities in the toxic effects exerted by short multiwalled carbon nanotubes (MWCNT) in murine alveolar macrophages

Lung toxicity mediated by multiwalled carbon nanotubes (MWCNT) has been widely demonstrated and recently associated with induction of carcinogenic asbestos-like effects, but the chemical features that drive this toxic effect have still not been well elucidated. The presence of metals as trace contaminants during MWCNT preparation, in particular iron (Fe) impurities, plays an important role in determining a different cellular response to MWCNT. Our goal was to clarify the mechanisms underlying MWCNT-induced toxicity with correlation to the presence of Fe impurities by exposing murine alveolar macrophages to two different MWCNT samples, which differed only in the presence or absence of Fe. Data showed that only Fe-rich MWCNT were significantly cytotoxic and genotoxic and induced a potent cellular oxidative stress, while Fe-free MWCNT did not exert any of these adverse effects. These results confirm that Fe content represents an important key constituent in promoting MWCNT-induced toxicity, and this needs to be taken into consideration when planning new, safer preparation routes.

Pulmonary instillation of multi-walled carbon nanotubes promotes coronary vasoconstriction and exacerbates injury in isolated hearts

The growing use of multi-walled carbon nanotubes (MWCNTs) across industry has increased human exposures. We tested the hypothesis that pulmonary instillation of MWCNTs would exacerbate cardiac ischaemia/reperfusion (I/R) injury. One day following intratracheal instillation of 1, 10 or 100 μg MWCNT in Sprague-Dawley rats, we used a Langendorff isolated heart model to examine cardiac I/R injury. In the 100 μg MWCNT group we report increased premature ventricular contractions at baseline and increased myocardial infarction. This was associated with increased endothelin-1 (ET-1) release and depression of coronary flow during early reperfusion. We also tested if isolated coronary vascular responses were affected by MWCNT instillation and found trends for enhanced coronary tone, which were dependent on ET-1, cyclooxygenase, thromboxane and Rho-kinase. We concluded that instillation of MWCNTs promoted cardiac injury and depressed coronary flow by invoking vasoconstrictive mechanisms involving ET-1, cyclooxygenase, thromboxane and Rho-kinase.

Multi-walled carbon nanotube-induced inflammatory response and oxidative stress in a dynamic cell growth environment

BACKGROUND

Rapid increase in multi-walled carbon nanotube (MWCNT) production for their industrial and biomedical applications has led to concerns over the effects of MWCNTs on human health and the environment. Both animal and in vitro studies have provided important findings about MWCNT-induced effects on the lung cells or tissues. In vitro studies have provided a considerable amount of fundamental information on MWCNT-induced effects on the specific lung cells. However, the cell culture systems used in those studies were limited by the absence of dynamic nature of lung tissues. We hypothesized that MWCNT-induced cellular responses such as proliferation, inflammation, and oxidative stress under dynamic cell growth environment may differ from those under static cell growth environment.

RESULTS

In this study, we used a dynamic cell growth condition to mimic mechanically dynamic environment of the lung and characterized interleukin 8 (IL-8), reactive oxygen species (ROS), glutathione (GSH), and cell proliferation for three days following exposure of MWCNTs at different concentrations (5, 10, and 20 μg/ml) to A549 cell monolayer under both static and dynamic cell growth conditions. Our results demonstrated the distinct differences in the levels of inflammatory response and oxidative stress between static and dynamic cell growth conditions.

CONCLUSIONS

In conclusion, the dynamic cell growth system used in this study provided important changes in cellular responses that were not found in the static cell growth system and were similar to animal studies. The dynamic cell growth system can be considered as a viable alternative to in vivo test system in combination with existing in vitro static cell growth systems to evaluate the effect of MWCNTs on cellular responses in the respiratory system.

Characterization of carbon nanotube protein corona by using quantitative proteomics

The protein corona of a nanomaterial is a complex layer of proteins spontaneously and stably formed when the material is exposed to body fluids or intracellular environments. In this study, we utilised stable isotope labeling by amino acids in cell culture (SILAC)-based quantitative proteomics to characterise the binding of human cellular proteins to two forms of carbon nanoparticles: namely multi-walled carbon nanotubes (MWCNTs) and carbon black (CB). The relative binding efficiency of over 750 proteins to these materials is measured. The data indicate that MWCNTs and CB bind to vastly different sets of proteins. The molecular basis of selectivity in protein binding is investigated. This study is the first large-scale characterisation of protein corona on CNT, providing the biochemical basis for the assessment of the suitability of CNTs as biomedical tools, and as an emerging pollutant.

FROM THE CLINICAL EDITOR

This team of investigators performed the first large-scale characterization of protein corona on carbon nanotubes, studying 750 proteins and assessing the suitability of CNTs as biomedical tools and as an emerging pollutant.

Impairment of coronary arteriolar endothelium-dependent dilation after multi-walled carbon nanotube inhalation: a time-course study

Engineered nanomaterials have been developed for widespread applications due to many highly unique and desirable characteristics. The purpose of this study was to assess pulmonary inflammation and subepicardial arteriolar reactivity in response to multi-walled carbon nanotube (MWCNT) inhalation and evaluate the time course of vascular alterations. Rats were exposed to MWCNT aerosols producing pulmonary deposition. Pulmonary inflammation via bronchoalveolar lavage and MWCNT translocation from the lungs to systemic organs was evident 24 h post-inhalation. Coronary arterioles were evaluated 24-168 h post-exposure to determine microvascular response to changes in transmural pressure, endothelium-dependent and -independent reactivity. Myogenic responsiveness, vascular smooth muscle reactivity to nitric oxide, and α-adrenergic responses all remained intact. However, a severe impact on endothelium-dependent dilation was observed within 24 h after MWCNT inhalation, a condition which improved, but did not fully return to control after 168 h. In conclusion, results indicate that MWCNT inhalation not only leads to pulmonary inflammation and cytotoxicity at low lung burdens, but also a low level of particle translocation to systemic organs. MWCNT inhalation also leads to impairments of endothelium-dependent dilation in the coronary microcirculation within 24 h, a condition which does not fully dissipate within 168 h. The innovations within the field of nanotechnology, while exciting and novel, can only reach their full potential if toxicity is first properly assessed.

Multi-walled carbon nanotubes translocate into the pleural cavity and induce visceral mesothelial proliferation in rats

Multi-walled carbon nanotubes have a fibrous structure similar to asbestos and induce mesothelioma when injected into the peritoneal cavity. In the present study, we investigated whether carbon nanotubes administered into the lung through the trachea induce mesothelial lesions. Male F344 rats were treated with 0.5 mL of 500 μg/mL suspensions of multi-walled carbon nanotubes or crocidolite five times over a 9-day period by intrapulmonary spraying. Pleural cavity lavage fluid, lung and chest wall were then collected. Multi-walled carbon nanotubes and crocidolite were found mainly in alveolar macrophages and mediastinal lymph nodes. Importantly, the fibers were also found in the cell pellets of the pleural cavity lavage, mostly in macrophages. Both multi-walled carbon nanotube and crocidolite treatment induced hyperplastic proliferative lesions of the visceral mesothelium, with their proliferating cell nuclear antigen indices approximately 10-fold that of the vehicle control. The hyperplastic lesions were associated with inflammatory cell infiltration and inflammation-induced fibrotic lesions of the pleural tissues. The fibers were not found in the mesothelial proliferative lesions themselves. In the pleural cavity, abundant inflammatory cell infiltration, mainly composed of macrophages, was observed. Conditioned cell culture media of macrophages treated with multi-walled carbon nanotubes and crocidolite and the supernatants of pleural cavity lavage fluid from the dosed rats increased mesothelial cell proliferation in vitro, suggesting that mesothelial proliferative lesions were induced by inflammatory events in the lung and pleural cavity and likely mediated by macrophages. In conclusion, intrapulmonary administration of multi-walled carbon nanotubes, like asbestos, induced mesothelial proliferation potentially associated with mesothelioma development.

Single-Walled Carbon Nanotubes Induce Fibrogenic Effect by Disturbing Mitochondrial Oxidative Stress and Activating NF-κB Signaling

Single-walled carbon nanotubes (SWCNTs) are newly discovered material of crystalline carbon that forms single-carbon layer cylinders with nanometer diameters and varying lengths. Although SWCNTs are potentially suitable for a range of novel applications, their extremely small size, fiber-like shape, large surface area, and unique surface chemistry raise potential hazard to humans, including lung toxicity and fibrosis. The molecular mechanisms by which SWCNTs cause lung damage remain elusive. Here we show that SWCNTs dose and time-dependently caused toxicity in cultured human bronchial epithelial (BEAS-2B), alveolar epithelial (A549), and lung fibroblast (WI38) cells. At molecular levels, SWCNTs induced significant mitochondrial depolarization and ROS production at subtoxic doses. SWCNTs stimulated the secretion of proinflammatory cytokines and chemokines TNFα, IL-1β, IL-6, IL-10 and MCP1 from macrophages (Raw 264.7), which was attributed to the activation of the canonical signaling pathway of NF-κB by SWCNT. Finally, SWCNTs stimulated profibrogenic growth factors TGFβ1 production and fibroblast-to-myofibroblast-transformation. These results indicate that SWCNTs has a potential to induce human lung damage and fibrosis by damaging mitochondria, generating ROS, and stimulating production of proinflammatory and profibrogenic cytokines and growth factors.

IL-33 mediates multi-walled carbon nanotube (MWCNT)-induced airway hyper-reactivity via the mobilization of innate helper cells in the lung

Allergic asthma is a chronic inflammatory disorder of the airway associated with bronchial obstruction, airway hyper-reactivity (AHR), and mucus production. The epithelium may direct and propagate asthmatic-like responses. Central to this theory is the observation that viruses, air pollution, and allergens promote epithelial damage and trigger the generation of IL-25, IL-33, and TSLP via innate pathways such as TLRs and purinergic receptors. Similarly, engineered nanomaterials promote a Th2-associated pathophysiology. In this study, we tested the hypothesis that instillation of multi-walled carbon nanotubes (MWCNT) impair pulmonary function in C57Bl/6 mice due to the development of IL-33-dependent Th2-associated inflammation. MWCNT exposure resulted in elevated levels of IL-33 in the lavage fluid (likely originating from airway epithelial cells), enhanced AHR, eosinophil recruitment, and production of Th2-associated cytokines and chemokines. Moreover, these events were dependent on IL-13 signaling and the IL-33/ST2 axis, but independent of T and B cells. Finally, MWCNT exposure resulted in the recruitment of innate lymphoid cells. Collectively, our data suggest that MWCNT induce epithelial damage that results in release of IL-33, which in turn promotes innate lymphoid cell recruitment and the development of IL-13-dependent inflammatory response.

Nanoparticles in the environment: assessment using the causal diagram approach

Nanoparticles (NPs) cause concern for health and safety as their impact on the environment and humans is not known. Relatively few studies have investigated the toxicological and environmental effects of exposure to naturally occurring NPs (NNPs) and man-made or engineered NPs (ENPs) that are known to have a wide variety of effects once taken up into an organism. A review of recent knowledge (between 2000-2010) on NP sources, and their behaviour, exposure and effects on the environment and humans was performed. An integrated approach was used to comprise available scientific information within an interdisciplinary logical framework, to identify knowledge gaps and to describe environment and health linkages for NNPs and ENPs. The causal diagram has been developed as a method to handle the complexity of issues on NP safety, from their exposure to the effects on the environment and health. It gives an overview of available scientific information starting with common sources of NPs and their interactions with various environmental processes that may pose threats to both human health and the environment. Effects of NNPs on dust cloud formation and decrease in sunlight intensity were found to be important environmental changes with direct and indirect implication in various human health problems. NNPs and ENPs exposure and their accumulation in biological matrices such as microbiota, plants and humans may result in various adverse effects. The impact of some NPs on human health by ROS generation was found to be one of the major causes to develop various diseases. A proposed cause-effects diagram for NPs is designed considering both NNPs and ENPs. It represents a valuable information package and user-friendly tool for various stakeholders including students, researchers and policy makers, to better understand and communicate on issues related to NPs.

Xenobiotic particle exposure and microvascular endpoints: a call to arms

Xenobiotic particles can be considered in two genres: air pollution particulate matter and engineered nanoparticles. Particle exposures can occur in the greater environment, the workplace, and our homes. The majority of research in this field has, justifiably, focused on pulmonary reactions and outcomes. More recent investigations indicate that cardiovascular effects are capable of correlating with established mortality and morbidity epidemiological data following particle exposures. While the preliminary and general cardiovascular toxicology has been defined, the mechanisms behind these effects, specifically within the microcirculation, are largely unexplored. Therefore, the purpose of this review is several fold: first, a historical background on toxicological aspects of particle research is presented. Second, essential definitions, terminology, and techniques that may be unfamiliar to the microvascular scientist will be discussed. Third, the most current concepts and hypotheses driving cardiovascular research in this field will be reviewed. Lastly, potential future directions for the microvascular scientist will be suggested. Collectively speaking, microvascular research in the particle exposure field represents far more than a "niche." The immediate demand for basic, translational, and clinical studies is high and diverse. Microvascular scientists at all career stages are strongly encouraged to expand their research interests to include investigations associated with particle exposures.

Teratogenicity of multi-wall carbon nanotube (MWCNT) in ICR mice

A possible teratogenicity of multi-wall carbon nanotube (MWCNT) was assessed using ICR mice. MWCNTs were suspended in 2% carboxymethyl cellulose and given intraperitoneally or intra-tracheally to pregnant ICR mice on day 9 of the gestation. All fetuses were removed from the uterus on day 18 of the gestation, and were examined for external and skeletal anomalies. In the intraperitoneal study, various types of malformation were observed in all MWCNT-treated groups (2, 3, 4 and 5 mg/kg body weight, intraperitoneal). In contrast, such malformations were observed in groups given 4 or 5 mg/kg body weight, but not in that treated with 3 mg/kg in the intratracheal study. In either study, the number of litters having fetuses with external malformation and that of litters having fetuses with skeletal malformations were both increased in proportion to the doses of MWCNT. The present results are the first to report that MWCNT possesses the teratogenicity at least under the present experimental conditions. Mechanism(s) to result such malformations is yet unclear and further experiment is necessary.

Surface reactivity and cell responses to chrysotile asbestos nanofibers

High aspect-ratio nanomaterials (HARNs) have recently attracted great attention from nanotoxicologists because of their similarity to asbestos. However, the actual risk associated with the exposure to nanosized asbestos, which escapes most regulations worldwide, is still unknown. Nanometric fibers of chrysotile asbestos have been prepared from two natural sources to investigate whether nanosize may modulate asbestos toxicity and gain insight on the hazard posed by naturally occurring asbestos, which may be defined as HARNs because of their dimensions. Power ultrasound was used to obtain nanofibers from two different chrysotile specimens, one from the dismissed asbestos mine in Balangero (Italian Western Alps) and the other from a serpentine outcrop in the Italian Central Alps. Electron microscopy, X-ray diffraction, and fluorescence spectroscopy revealed that the procedure does not affect mineralogical and chemical composition. Surface reactions related to oxidative stress, free radical generation, bioavailability of iron, and antioxidant depletion, revealed a consistent reduction in reactivity upon reduction in size. When tested on A549 human epithelial cells, the pristine but not the nanosized fibers proved cytotoxic (LDH release), induced NO production, and caused lipid peroxidation. However, nanofibers still induced some toxicity relevant oxidative stress activity (ROS production) in a dose-dependent fashion. The reduction in length and a lack of poorly coordinated bioavailable iron in nanochrysotile may explain this behavior. The present study provides a one-step procedure for the preparation of a homogeneous batch of natural asbestos nanofibers and shows how a well-known toxic material might not necessarily become more toxic than its micrometric counterpart when reduced to the nanoscale.

Nitrative DNA damage induced by multi-walled carbon nanotube via endocytosis in human lung epithelial cells

Carbon nanotube (CNT) has a promising usage in the field of material science for industrial purposes because of its unique physicochemical property. However, intraperitoneal administration of CNT was reported to cause mesothelioma in experimental animals. Chronic inflammation may contribute to carcinogenesis induced by fibrous materials. 8-Nitroguanine is a mutagenic DNA lesion formed during inflammation and may play a role in CNT-induced carcinogenesis. In this study, we examined 8-nitroguanine formation in A549 human lung alveolar epithelial cells treated with multi-walled CNT (MWCNT) by fluorescent immunocytochemistry. Both MWCNTs with diameter of 20-30 nm (CNT20) and 40-70 nm (CNT40) significantly induced 8-nitroguanine formation at 5 and 10 μg/ml (p<0.05), which persisted for 24h, although there was no significant difference in DNA-damaging abilities of these MWCNTs. MWCNTs significantly induced the expression of inducible nitric oxide synthase (iNOS) for 24 h (p<0.05). MWCNTs also significantly increased the level of nitrite, a hydrolysis product of oxidized NO, in the culture supernatant at 4 and 8 h (p<0.05). MWCNT-induced 8-nitroguanine formation and iNOS expression were largely suppressed by inhibitors of iNOS (1400 W), nuclear factor-κB (Bay11-7082), actin polymerization (cytochalasin D), caveolae-mediated endocytosis (methyl-β-cyclodextrin, MBCD) and clathrin-mediated endocytosis (monodansylcadaverine, MDC). Electron microscopy revealed that MWCNT was mainly located in vesicular structures in the cytoplasm, and its cellular internalization was reduced by MBCD and MDC. These results suggest that MWCNT is internalized into cells via clathrin- and caveolae-mediated endocytosis, leading to inflammatory reactions including iNOS expression and resulting nitrative DNA damage, which may contribute to carcinogenesis.

Multiwalled carbon nanotube-induced gene signatures in the mouse lung: potential predictive value for human lung cancer risk and prognosis

Concerns over the potential for multiwalled carbon nanotubes (MWCNT) to induce lung carcinogenesis have emerged. This study sought to (1) identify gene expression signatures in the mouse lungs following pharyngeal aspiration of well-dispersed MWCNT and (2) determine if these genes were associated with human lung cancer risk and progression. Genome-wide mRNA expression profiles were analyzed in mouse lungs (n = 160) exposed to 0, 10, 20, 40, or 80 μg of MWCNT by pharyngeal aspiration at 1, 7, 28, and 56 d postexposure. By using pairwise statistical analysis of microarray (SAM) and linear modeling, 24 genes were selected, which have significant changes in at least two time points, have a more than 1.5-fold change at all doses, and are significant in the linear model for the dose or the interaction of time and dose. Additionally, a 38-gene set was identified as related to cancer from 330 genes differentially expressed at d 56 postexposure in functional pathway analysis. Using the expression profiles of the cancer-related gene set in 8 mice at d 56 postexposure to 10 μg of MWCNT, a nearest centroid classification accurately predicts human lung cancer survival with a significant hazard ratio in training set (n = 256) and test set (n = 186). Furthermore, both gene signatures were associated with human lung cancer risk (n = 164) with significant odds ratios. These results may lead to development of a surveillance approach for early detection of lung cancer and prognosis associated with MWCNT in the workplace.

New perspectives for in vitro risk assessment of multiwalled carbon nanotubes: application of coculture and bioinformatics

Nanotechnology is a rapidly expanding field with wide application for industrial and medical use; therefore, understanding the toxicity of engineered nanomaterials is critical for their commercialization. While short-term in vivo studies have been performed to understand the toxicity profile of various nanomaterials, there is a current effort to shift toxicological testing from in vivo observational models to predictive and high-throughput in vitro models. However, conventional monoculture results of nanoparticle exposure are often disparate and not predictive of in vivo toxic effects. A coculture system of multiple cell types allows for cross-talk between cells and better mimics the in vivo environment. This review proposes that advanced coculture models, combined with integrated analysis of genome-wide in vivo and in vitro toxicogenomic data, may lead to development of predictive multigene expression-based models to better determine toxicity profiles of nanomaterials and consequent potential human health risk due to exposure to these compounds.

Cell permeability, migration, and reactive oxygen species induced by multiwalled carbon nanotubes in human microvascular endothelial cells

Multiwalled carbon nanotubes (MWCNT) have elicited great interest in biomedical applications due to their extraordinary physical, chemical, and optical properties. Intravenous administration of MWCNT-based medical imaging agents and drugs in animal models was utilized. However, the potential harmful health effects of MWCNT administration in humans have not yet been elucidated. Furthermore, to date, there are no apparent reports regarding the precise mechanisms of translocation of MWCNT into target tissues and organs from blood circulation. This study demonstrates that exposure to MWCNT leads to an increase in cell permeability in human microvascular endothelial cells (HMVEC). The results obtained from this study also showed that the MWCNT-induced rise in endothelial permeability is mediated by reactive oxygen species (ROS) production and actin filament remodeling. In addition, it was found that MWCNT promoted cell migration in HMVEC. Mechanistically, MWCNT exposure elevated the levels of monocyte chemoattractant protein-1 (MCP-1) and intercellular adhesion molecule 1 (ICAM-1) in HMVEC. Taken together, these results provide new insights into the bioreactivity of MWCNT, which may have implications in the biomedical application of MWCNT in vascular targeting, imaging, and drug delivery. The results generated from this study also elucidate the potential adverse effects of MWCNT exposure on humans at the cellular level.

Cell permeability, migration, and reactive oxygen species induced by multiwalled carbon nanotubes in human microvascular endothelial cells

Multiwalled carbon nanotubes (MWCNT) have elicited great interest in biomedical applications due to their extraordinary physical, chemical, and optical properties. Intravenous administration of MWCNT-based medical imaging agents and drugs in animal models was utilized. However, the potential harmful health effects of MWCNT administration in humans have not yet been elucidated. Furthermore, to date, there are no apparent reports regarding the precise mechanisms of translocation of MWCNT into target tissues and organs from blood circulation. This study demonstrates that exposure to MWCNT leads to an increase in cell permeability in human microvascular endothelial cells (HMVEC). The results obtained from this study also showed that the MWCNT-induced rise in endothelial permeability is mediated by reactive oxygen species (ROS) production and actin filament remodeling. In addition, it was found that MWCNT promoted cell migration in HMVEC. Mechanistically, MWCNT exposure elevated the levels of monocyte chemoattractant protein-1 (MCP-1) and intercellular adhesion molecule 1 (ICAM-1) in HMVEC. Taken together, these results provide new insights into the bioreactivity of MWCNT, which may have implications in the biomedical application of MWCNT in vascular targeting, imaging, and drug delivery. The results generated from this study also elucidate the potential adverse effects of MWCNT exposure on humans at the cellular level.

Imaging methods for determining uptake and toxicity of carbon nanotubes in vitro and in vivo

Demand for carbon nanotubes (CNTs) is increasing rapidly in electrical, mechanical, and health and medical applications due to their thermal, electrical conductive and other properties. The continued commercial up-scaling of CNT production and application needs to be accompanied by an understanding of the occupational health, public safety and environmental implications of these materials. An increasing volume of literature on the toxicity of CNTs is being published; however, the results of these studies are frequently inconclusive. Due to the enormous number of permutations of nanoparticle shape, dimensions, composition and surface chemistry, only a fundamental understanding of the processes by which CNTs interact with cells will allow a realistic, practical assessment of the risks of the wide range of possible products. Alternatively, by understanding how the physicochemical properties of CNTs relate to their interaction with cells, it will be possible to design 'medical grade' CNTs, which can be used as diagnostic agents or as vectors to deliver therapeutic agents to cell and tissue targets. This article discusses the challenges associated with characterizing the toxicity of CNTs and the need for complimentary nanometrology techniques to relate their physicochemical properties to their toxicity.

Effect of chemical composition and state of the surface on the toxic response to high aspect ratio nanomaterials

Nanomaterials often act as a double sword. On the one hand they offer exceptional new properties, but on the other hand show signs of toxicity. High aspect ratio nanomaterials (HARNs) cause more concern than isometric nanoparticles owing to their physical similarity with asbestos. Many compounds may be prepared in fibrous shape with nano-sized diameter differing one from the other in various ways. This article reports a comparative picture of the chemical features and related toxic responses to a variety of HARNs, namely carbon nanotubes, asbestos, carbon nanofibers, oxide and metal wires and rods. In spite of similarities in form, durability and several biological responses elicited in vitro and in vivo, carbon nanotubes - opposite to asbestos - quench radicals, are hydrophobic and may be fully purified from metal impurities. Most of the other HARNs produced so far are metal or metal oxide compounds, less biopersistent than carbon nanotubes.

DJ-1 as a potential biomarker for the development of biocompatible multiwalled carbon nanotubes

BACKGROUND

In the present study, we investigated whether DJ-1 could serve as a biomarker for assessing the biocompatibility of multiwalled carbon nanotubes (MWCNTs), using the highly purified carbon nanotube, HTT2800.

METHODS

Using Western blot analysis, we determined DJ-1 protein levels in two different types of cells (one capable and the other incapable of HTT2800 endocytosis). Using quantitative real-time polymerase chain reaction, we also investigated the ability of purified nanotubes to alter DJ-1 mRNA levels.

RESULTS

We demonstrated that the DJ-1 protein concentration was reduced, regardless of the cytotoxic activity of intracellular HTT2800. Furthermore, HTT2800 decreased the DJ-1 mRNA levels in a dose-dependent manner. This decrease in DJ-1 mRNA levels was not observed in the case of Sumi black or cup-stacked carbon nanotubes.

CONCLUSION

These data indicate that modification of DJ-1 expression is caused by the cell response to MWCNTs. We conclude that DJ-1 is a promising candidate biomarker for the development of biocompatible MWCNTs.

A strategy for assessing workplace exposures to nanomaterials

This article describes a highly tailorable exposure assessment strategy for nanomaterials that enables effective and efficient exposure management (i.e., a strategy that can identify jobs or tasks that have clearly unacceptable exposures), while simultaneously requiring only a modest level of resources to conduct. The strategy is based on strategy general framework from AIHA® that is adapted for nanomaterials and seeks to ensure that the risks to workers handling nanomaterials are being managed properly. The strategy relies on a general framework as the basic foundation while building and elaborating on elements essential to an effective and efficient strategy to arrive at decisions based on collecting and interpreting available information. This article provides useful guidance on conducting workplace characterization; understanding exposure potential to nanomaterials; accounting methods for background aerosols; constructing SEGs; and selecting appropriate instrumentation for monitoring, providing appropriate choice of exposure limits, and describing criteria by which exposure management decisions should be made. The article is intended to be a practical guide for industrial hygienists for managing engineered nanomaterial risks in their workplaces.

Ameliorative effects of dimetylthiourea and N-acetylcysteine on nanoparticles induced cyto-genotoxicity in human lung cancer cells-A549

We study the ameliorative potential of dimetylthiourea (DMTU), an OH^• radical trapper and N-acetylcysteine (NAC), a glutathione precursor/H₂O₂ scavenger against titanium dioxide nanoparticles (TiO₂-NPs) and multi-walled carbon nanotubes (MWCNTs) induced cyto-genotoxicity in cultured human lung cancer cells-A549. Cytogenotoxicity was induced by exposing the cells to selected concentrations (10 and 50 µg/ml) of either of TiO₂-NPs or MWCNTs for 24 h. Anti-cytogenotoxicity effects of DMTU and NAC were studied in two groups, i.e., treatment of 30 minutes prior to toxic insult (short term exposure), while the other group received DMTU and NAC treatment during nanoparticles exposure, i.e., 24 h (long term exposure). Investigations were carried out for cell viability, generation of reactive oxygen species (ROS), micronuclei (MN), and expression of markers of oxidative stress (HSP27, CYP2E1), genotoxicity (P⁵³) and CYP2E1 dependent n- nitrosodimethylamine-demethylase (NDMA-d) activity. In general, the treatment of both DMTU and NAC was found to be effective significantly against TiO₂-NPs and MWCNTs induced cytogenotoxicity in A549 cells. Long-term treatment of DMTU and NAC during toxic insults has shown better prevention than short-term pretreatment. Although, cells responded significantly to both DMTU and NAC, but responses were chemical specific. In part, TiO_2-NPs induced toxic responses were mediated through OH^• radicals generation and reduction in the antioxidant defense system. While in the case of MWCNTs, adverse effects were primarily due to altering/hampering the enzymatic antioxidant system. Data indicate the applicability of human lung cancer cells-A549 as a pre-screening tool to identify the target specific prophylactic and therapeutic potential of drugs candidate molecules against nanoparticles induced cellular damages.

Multi-walled carbon nanotube-induced gene expression in the mouse lung: association with lung pathology

Due to the fibrous shape and durability of multi-walled carbon nanotubes (MWCNT), concerns regarding their potential for producing environmental and human health risks, including carcinogenesis, have been raised. This study sought to investigate how previously identified lung cancer prognostic biomarkers and the related cancer signaling pathways are affected in the mouse lung following pharyngeal aspiration of well-dispersed MWCNT. A total of 63 identified lung cancer prognostic biomarker genes and major signaling biomarker genes were analyzed in mouse lungs (n=80) exposed to 0, 10, 20, 40, or 80μg of MWCNT by pharyngeal aspiration at 7 and 56days post-exposure using quantitative PCR assays. At 7 and 56days post-exposure, a set of 7 genes and a set of 11 genes, respectively, showed differential expression in the lungs of mice exposed to MWCNT vs. the control group. Additionally, these significant genes could separate the control group from the treated group over the time series in a hierarchical gene clustering analysis. Furthermore, 4 genes from these two sets of significant genes, coiled-coil domain containing-99 (Ccdc99), muscle segment homeobox gene-2 (Msx2), nitric oxide synthase-2 (Nos2), and wingless-type inhibitory factor-1 (Wif1), showed significant mRNA expression perturbations at both time points. It was also found that the expression changes of these 4 overlapping genes at 7days post-exposure were attenuated at 56days post-exposure. Ingenuity Pathway Analysis (IPA) found that several carcinogenic-related signaling pathways and carcinogenesis itself were associated with both the 7 and 11 gene signatures. Taken together, this study identifies that MWCNT exposure affects a subset of lung cancer biomarkers in mouse lungs.

Synchrotron soft X-ray imaging and fluorescence microscopy reveal novel features of asbestos body morphology and composition in human lung tissues

Background

Occupational or environmental exposure to asbestos fibres is associated with pleural and parenchymal lung diseases. A histopathologic hallmark of exposure to asbestos is the presence in lung parenchyma of the so-called asbestos bodies. They are the final product of biomineralization processes resulting in deposition of endogenous iron and organic matter (mainly proteins) around the inhaled asbestos fibres. For shedding light on the formation mechanisms of asbestos bodies it is of fundamental importance to characterize at the same length scales not only their structural morphology and chemical composition but also to correlate them to the possible alterations in the local composition of the surrounding tissues. Here we report the first correlative morphological and chemical characterization of untreated paraffinated histological lung tissue samples with asbestos bodies by means of soft X-ray imaging and X-Ray Fluorescence (XRF) microscopy, which reveals new features in the elemental lateral distribution.

Results

The X-ray absorption and phase contrast images and the simultaneously monitored XRF maps of tissue samples have revealed the location, distribution and elemental composition of asbestos bodies and associated nanometric structures. The observed specific morphology and differences in the local Si, Fe, O and Mg content provide distinct fingerprints characteristic for the core asbestos fibre and the ferruginous body. The highest Si content is found in the asbestos fibre, while the shell and ferruginous bodies are characterized by strongly increased content of Mg, Fe and O compared to the adjacent tissue. The XRF and SEM-EDX analyses of the extracted asbestos bodies confirmed an enhanced Mg deposition in the organic asbestos coating.

Conclusions

The present report demonstrates the potential of the advanced synchrotron-based X-ray imaging and microspectroscopy techniques for studying the response of the lung tissue to the presence of asbestos fibres. The new results obtained by simultaneous structural and chemical analysis of tissue specimen have provided clear evidence that Mg, in addition to Fe, is also involved in the formation mechanisms of asbestos bodies. This is the first important step to further thorough investigations that will shed light on the physiopathological role of Mg in tissue response to the asbestos toxicity.

Nanotoxicology--a pathologist's perspective

Advances in chemistry and engineering have created a new technology, nanotechnology, involving the tiniest known manufactured products. These products have a rapidly increasing market share and appear poised to revolutionize engineering, cosmetics, and medicine. Unfortunately, nanotoxicology, the study of nanoparticulate health effects, lags behind advances in nanotechnology. Over the past decade, existing literature on ultrafine particles and respirable durable fibers has been supplemented by studies of first-generation nanotechnology products. These studies suggest that nanosizing increases the toxicity of many particulates. First, as size decreases, surface area increases, thereby speeding up dissolution of soluble particulates and exposing more of the reactive surface of durable but reactive particulates. Second, nanosizing facilitates movement of particulates across cellular and intracellular barriers. Third, nanosizing allows particulates to interact with, and sometimes even hybridize with, subcellular structures, including in some cases microtubules and DNA. Finally, nanosizing of some particulates, increases pathologic and physiologic responses, including inflammation, fibrosis, allergic responses, genotoxicity, and carcinogenicity, and may alter cardiovascular and lymphatic function. Knowing how the size and physiochemical properties of nanoparticulates affect bioactivity is important in assuring that the exciting new products of nanotechnology are used safely. This review provides an introduction to the pathology and toxicology of nanoparticulates.

Carbon nanotubes in neural interfacing applications

Carbon nanotubes (CNT) are remarkable materials with a simple and inert molecular structure that gives rise to a range of potentially valuable physical and electronic properties, including high aspect ratio, high mechanical strength and excellent electrical conductivity. This review summarizes recent research on the application of CNT-based materials to study and control cells of the nervous system. It includes the use of CNT as cell culture substrates, to create patterned surfaces and to study cell-matrix interactions. It also summarizes recent investigations of CNT toxicity, particularly as related to neural cells. The application of CNT-based materials to directing the differentiation of progenitor and stem cells toward neural lineages is also discussed. The emphasis is on how CNT surface chemistry and nanotopography can be altered, and how such changes can affect neural cell function. This knowledge can be applied to creating improved neural interfaces and devices, as well as providing new approaches to neural tissue engineering and regeneration.

Physico-chemical features of engineered nanoparticles relevant to their toxicity

Nanotoxicology studies require investigations of several physico-chemical aspects of the particle/body fluid interaction, here described by reviewing recent literature in the light of new experimental data. Current characterization mostly covers morphology and metric-related characteristics (form, chemical composition, specific surface area, primary particle size and size distribution), and is mandatory in any experimental study. To unveil toxicity mechanisms, several other physico-chemical properties relevant to (geno) toxicity need to be assessed, typically the release or quenching of radical/ROS (Reactive Oxygen Species), the presence of active metal ions, evidence of structural defects. Major tasks for physical chemists working on nanoparticles-induced genotoxicity are described with some examples: (i), Tailored preparation of the same material in different sizes; (ii) particle modification changing a single property at a time; and (iii) identification of appropriate reference materials. Phenomena occurring during the contact between nanoparticles and cellular media or biological fluids (dispersion, agglomeration/aggregation, protein adsorption) are discussed in relation to the surface properties of the nanoparticles considered.

Comparative proteomics and pulmonary toxicity of instilled single-walled carbon nanotubes, crocidolite asbestos, and ultrafine carbon black in mice

Reflecting their exceptional potential to advance a range of biomedical, aeronautic, and other industrial products, carbon nanotube (CNT) production and the potential for human exposure to aerosolized CNTs are increasing. CNTs have toxicologically significant structural and chemical similarities to asbestos (AB) and have repeatedly been shown to cause pulmonary inflammation, granuloma formation, and fibrosis after inhalation/instillation/aspiration exposure in rodents, a pattern of effects similar to those observed following exposure to AB. To determine the degree to which responses to single-walled CNTs (SWCNT) and AB are similar or different, the pulmonary response of C57BL/6 mice to repeated exposures to SWCNTs, crocidolite AB, and ultrafine carbon black (UFCB) were compared using high-throughput global high performance liquid chromatography fourier transform ion cyclotron resonance mass spectrometry (HPLC-FTICR-MS) proteomics, histopathology, and bronchoalveolar lavage cytokine analyses. Mice were exposed to material suspensions (40 micrograms per mouse) twice a week for 3 weeks by pharyngeal aspiration. Histologically, the incidence and severity of inflammatory and fibrotic responses were greatest in mice treated with SWCNTs. SWCNT treatment affected the greatest changes in abundance of identified lung tissue proteins. The trend in number of proteins affected (SWCNT [376] > AB [231] > UFCB [184]) followed the potency of these materials in three biochemical assays of inflammation (cytokines). SWCNT treatment uniquely affected the abundance of 109 proteins, but these proteins largely represent cellular processes affected by AB treatment as well, further evidence of broad similarity in the tissue-level response to AB and SWCNTs. Two high-sensitivity markers of inflammation, one (S100a9) observed in humans exposed to AB, were found and may be promising biomarkers of human response to SWCNT exposure.