Mechanisms of pulmonary toxicity and medical applications of carbon nanotubes: Two faces of Janus?

Development of a Mouse Cardiac Sarcoidosis Model Using Carbon Nanotubes

Sarcoidosis, a granulomatous disorder of unknown etiology affecting multiple organs. It is often a benign disease but can have significant morbidity and mortality when the heart is involved (often presenting with clinical manifestations such as conduction irregularities and heart failure). This study addresses a critical gap in cardiac sarcoidosis (CS) research by developing a robust animal model. The absence of a reliable animal model for cardiac sarcoidosis is a significant obstacle in advancing understanding and treatment of this condition. The proposed model utilizes carbon nanotube injection and transverse aortic constriction as stressors. Intramyocardial injection of carbon nanotubes induces histiocytes typical of sarcoid granulomas in the heart but shows limited effects on fibrosis or cardiac function. Priming the immune system with transverse aortic constriction prior to intramyocardial injection of carbon nanotubes enhances cardiac fibrosis, diminishes cardiac function, and impairs cardiac conduction. This novel, easily executable model may serve as a valuable tool for disease profiling, biomarker identification, and therapeutic exploration.

Nanoparticles toxicity: an overview of its mechanism and plausible mitigation strategies

Over the last decade, nanoparticles have found great interest among scientists and researchers working in various fields within the realm of biomedicine including drug delivery, gene delivery, diagnostics, targeted therapy and biomarker mapping. While their physical and chemical properties are impressive, there is growing concern about the toxicological potential of nanoparticles and possible adverse health effects as enhanced exposure of biological systems to nanoparticles may result in toxic effects leading to serious contraindications. Toxicity associated with nanoparticles (nanotoxicity) may include the undesired response of several physiological mechanisms including the distressing of cells by external and internal interaction with nanoparticles. However, comprehensive knowledge of nanotoxicity mechanisms and mitigation strategies may be useful to overcome the hazardous situation while treating diseases with therapeutic nanoparticles. With the same objectives, this review discusses various mechanisms of nanotoxicity and provides an overview of the current state of knowledge on the impact of nanotoxicity on biological control systems and organs including liver, brain, kidneys and lungs. An attempt also been made to present various approaches of scientific research and strategies that could be useful to overcome the effect of nanotoxicity during the development of nanoparticle-based systems including coating, doping, grafting, ligation and addition of antioxidants.

Pulmonary Fibrosis Induced by CdSe Nanorods and the Therapy with Modified Procyanidinere

The CdSe nanorod as a one-dimensional nanostructure has an excellent performance in many fields, such as healthcare, new energy, and environmental protection. Thus, it is crucial to investigate its potential adverse health effects prior to their wide exposure. The lung tissue would be the main target organ after CdSe nanorods enter living systems. Here, we showed that pulmonary instillation of CdSe nanorods could decrease the vitality of T-SOD and T-AOC in lung tissues of a rat, increase MDA and hydroxyproline levels and lipid peroxidation products, induce mitochondrial cristae breakage and vacuolization, cause inflammatory responses, and finally induce pulmonary fibrosis. The oral administration of modified procyanidinere could significantly increase the content of antioxidant enzymes, scavenge free radicals, reduce lipid peroxidation, and have protective effects on CdSe nanorods-induced pulmonary fibrosis. The benefit is not only in the early inflammatory stage but also in the later stages of the CdSe nanorods-induced pulmonary fibrosis.

β-Glucan-Functionalized Nanoparticles Down-Modulate the Proinflammatory Response of Mononuclear Phagocytes Challenged with Candida albicans

Systemic fungal infections are associated with significant morbidity and mortality, and Candida albicans is the most common causative agent. Recognition of yeast cells by immune cell surface receptors can trigger phagocytosis of fungal pathogens and a pro-inflammatory response that may contribute to fungal elimination. Nevertheless, the elicited inflammatory response may be deleterious to the host by causing excessive tissue damage. We developed a nanoparticle-based approach to modulate the host deleterious inflammatory consequences of fungal infection by using β1,3-glucan-functionalized polystyrene (β-Glc-PS) nanoparticles. β-Glc-PS nanoparticles decreased the levels of the proinflammatory cytokines TNF-α, IL-6, IL-1β and IL-12p40 detected in in vitro culture supernatants of bone marrow-derived dendritic cells and macrophage challenged with C. albicans cells. Moreover, β-Glc-PS nanoparticles impaired the production of reactive oxygen species by bone marrow-derived dendritic cells incubated with C. albicans. This immunomodulatory effect was dependent on the nanoparticle size. Overall, β-Glc-PS nanoparticles reduced the proinflammatory response elicited by fungal cells in mononuclear phagocytes, setting the basis for a targeted therapy aimed at protecting the host by lowering the inflammatory cost of infection.

Toxicological Aspects of Carbon Nanotubes, Fullerenes and Graphenes

Nanomedicines exhibit unbelievable capability in overcoming the hurdles faced in biological applications. Carbon nanotubes (CNTs), graphene-family nanomaterials and fullerenes are a class of engineered nanoparticles that have emerged as a new option for possible use in drug/gene delivery for life-threatening diseases. Their adaptability to pharmaceutical applications has opened new vistas for biomedical applications. Successful applications of this family of engineered nanoparticles in various fields may not support their use in medicine due to inconsistent data on toxicity as well as the lack of a centralized toxicity database. Inconsistent toxicological studies and lack of mechanistic understanding have been the reasons for limited understanding of their toxicological aspects. These nanoparticles, when underivatized or pristine, are considered as safe, however less reactive. The derivatized forms or functionalization changes their chemistry significantly to modify their biological effects including toxicity. They can cause acute and long term injuries in tissues by penetration through the the blood-air barrier, blood-alveolus barrier, blood-brain barrier, and blood-placenta barrier. and by accumulating in the lung, liver, and spleen . The toxicological effects are manifested through inflammatory response, DNA damage, apoptosis, autophagy and necrosis. Other factors that largely influence the toxicity of carbon nanotubes, graphenes and fullerenes are the concentration, functionalization, dimensional and surface topographical factors. Thus, a better understanding of the toxicity profile of CNTs, graphene-family nanomaterials and fullerenes in humans, animals and the environment is of significant importance, to improve their biological safety, to facilitate their wide biological application and for the successful commercial application. The exploration of appropriate cell lines to investigate specific receptors and intracellular targets as well as chronic toxicity beyond the proof-of-concept is required.

Occupational Exposure to Carbon Nanotubes and Carbon Nanofibres: More Than a Cobweb

Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are erroneously considered as singular material entities. Instead, they should be regarded as a heterogeneous class of materials bearing different properties eliciting particular biological outcomes both in vitro and in vivo. Given the pace at which the industrial production of CNTs/CNFs is increasing, it is becoming of utmost importance to acquire comprehensive knowledge regarding their biological activity and their hazardous effects in humans. Animal studies carried out by inhalation showed that some CNTs/CNFs species can cause deleterious effects such as inflammation and lung tissue remodeling. Their physico-chemical properties, biological behavior and biopersistence make them similar to asbestos fibers. Human studies suggest some mild effects in workers handling CNTs/CNFs. However, owing to their cross-sectional design, researchers have been as yet unable to firmly demonstrate a causal relationship between such an exposure and the observed effects. Estimation of acceptable exposure levels should warrant a proper risk management. The aim of this review is to challenge the conception of CNTs/CNFs as a single, unified material entity and prompt the establishment of standardized hazard and exposure assessment methodologies able to properly feed risk assessment and management frameworks.

Single-walled carbon nanotubes as a photo-thermo-acoustic cancer theranostic agent: theory and proof of the concept experiment

Theranostics is the emerging field of medicine that uniquely combines diagnostic techniques and active agents to diagnose and treat medical conditions simultaneously or sequentially. Finding a theranostic agent capable to cure the affected cells and being safe for the healthy ones is the key for successful treatment. Here, we demonstrate that agglomerated single-walled carbon nanotubes (SWCNTs) are promising theranostic agent that enables photo-activated ‘cold’ destruction of the cancer cells keeping their environment alive. The absorption of picosecond pulses by SWCNT agglomerates results in the mechanical (due to photoacoustic effect) rather than photothermal cancer cell destruction, which was visualized by micro-Raman and ultrafast near-infrared CARS. The developed theoretical model allows us to distinguish photothermal, photoacoustic, and photothermoacoustic regimes of the cancer cell destruction, and also to optimize SWCNT-based theranostics recipe.

3D-printed scaffolds with carbon nanotubes for bone tissue engineering: Fast and homogeneous one-step functionalization

Three-dimensional (3D) printing is a promising technology for tissue engineering. However, 3D-printing methods are limited in their ability to produce desired microscale features or electrochemical properties in support of robust cell adhesion, proliferation, and differentiation. This study addresses this deficiency by proposing an integrated, one-step, method to increase the cytocompatibility of 3D-printed scaffolds through functionalization leveraging conductive carbon nanotubes (CNTs). To this end, CNTs were first sonicated with water-soluble single-stranded deoxyribonucleic acid (ssDNA) to generate a negatively charged ssDNA@CNT nano-complex. Concomitantly, 3D-printed poly(propylene fumarate) (PPF) scaffolds were ammonolyzed to introduce free amine groups, which can take on a positive surface charge in water. The ssDNA@CNT nano-complex was then applied to 3D-printed scaffolds through a simple one-step coating utilizing electric-static force. This fast and facile functionalization step resulted in a homogenous and non-toxic coating of CNTs to the surface, which significantly improved the adhesion, proliferation, and differentiation of pre-osteoblast cells. In addition, the CNT based conductive coating layer enabled modulation of cell behavior through electrical stimuli (ES) leading to cellular proliferation and osteogenic gene marker expression, including alkaline phosphatase (ALP), osteocalcin (OCN), and osteopontin (OPN). Collectively, these data provide the foundation for a one-step functionalization method for simple, fast, and effective functionalization of 3D printed scaffolds that support enhanced cell adhesion, proliferation, and differentiation, especially when employed in conjunction with ES. STATEMENT OF SIGNIFICANCE: Three-dimensional (3D) printing is a promising technology for tissue engineering. However, 3D-printing methods have limited ability to produce desired features or electrochemical properties in support of robust cell behavior. To address this deficiency, the current study proposed an integrated, one-step method to increase the cytocompatibility of 3D-printed scaffolds through functionalization leveraging conductive carbon nanotubes (CNTs). This fast and facile functionalization resulted in a homogenous and non-toxic coating of CNTs to the surface, which significantly improved the adhesion, proliferation, and differentiation of cells on the 3D-printed scaffolds.

Nanoparticle exposure and hazard in the ceramic industry: an overview of potential sources, toxicity and health effects

The ceramic industry is an industrial sector of great impact in the global economy that has been benefiting from advances in materials and processing technologies. Ceramic manufacturing has a strong potential for airborne particle formation and emission, namely of ultrafine particles (UFP) and nanoparticles (NP), meaning that workers of those industries are at risk of potential exposure to these particles. At present, little is known on the impact of engineered nanoparticles (ENP) on the environment and human health and no established Occupational Exposure Limits (OEL) or specific regulations to airborne nanoparticles (ANP) exposure exist raising concerns about the possible consequences of such exposure. In this paper, we provide an overview of the current knowledge on occupational exposure to NP in the ceramic industry and their impact on human health. Possible sources and exposure scenarios, a summary of the existing methods for evaluation and monitoring of ANP in the workplace environment and proposed Nano Reference Values (NRV) for different classes of NP are presented. Case studies on occupational exposure to ANP generated at different stages of the ceramic manufacturing process are described. Finally, the toxicological potential of intentional and unintentional ANP that have been identified in the ceramic industry workplace environment is discussed based on the existing evidence from in vitro and in vivo inhalation toxicity studies.

Pleural translocation and lesions by pulmonary exposed multi-walled carbon nanotubes

Carbon nanotubes (CNTs) are recently developed tubular nanomaterials, with diameters ranging from a few nanometers to tens of nanometers, and the length reaching up to several micrometers. They can be either single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs). Due to their nano-scaled structure, CNTs have a unique set of mechanical, electrical, and chemical properties that make them useful in information technologies, optoelectronics, energy technologies, material sciences, medical technologies, and other fields. However, with the wide application and increasing production of CNTs, their potential risks have led to concerns regarding their impact on environment and health. The shape of some types of CNTs is similar to asbestos fibers, which suggests that these CNTs may cause characteristic pleural diseases similar to those found in asbestos-exposed humans, such as pleural plaques and malignant mesothelioma. Experimental data indicate that CNTs can induce lung and pleural lesions, inflammation, pleural fibrosis, lung tumors, and malignant mesothelioma upon inhalation in the experimental animals. In this review, we focus on the potential of MWCNTs to induce diseases similar to those by asbestos, molecular and cellular mechanisms associated with these diseases, and we discuss a method for evaluating the pleural toxicity of MWCNTs.

28-Day inhalation toxicity study with evaluation of lung deposition and retention of tangled multi-walled carbon nanotubes

Lung deposition and retention measurements are now required by the newly revised OECD inhalation toxicity testing guidelines 412 and 413 when evaluating the clearance and biopersistence of poorly soluble nanomaterials, such as multi-walled carbon nanotubes (MWCNTs). However, evaluating the lung deposition concentration is challenging with certain nanomaterials, such as carbon-based and iron-based nanomaterials, as it is difficult to differentiate them from endogenous elements. Therefore, the current 28-day inhalation toxicity study investigated the lung retention kinetics of tangled MWCNTs. Male Sprague Dawley rats were exposed to MWCNTs at 0, 0.257, 1.439, and 4.253 mg/m³ for 28 days (6 h/day, 5 days/week, 4 weeks). Thereafter, the rats were sacrificed at day 1, 7, and 28 post-exposure and the pulmonary inflammatory response evaluated by analyzing the bronchoalveolar lavage fluid. Plus, the blood biochemistry, hematology, and histopathology of the lungs were also examined. The lung deposition and retention of MWCNTs were determined based on the elemental carbon content in the lungs after tissue digestion. The number of polymorphonuclear cells and LDH concentration were both found to be significantly higher with the medium and high concentrations (1.439 and 4.253 mg/m³) and dose dependent. The estimated retention half-life for the high concentration (4.253 mg/m³) was about 35 days. The results of this study indicate that tangled MWCNTs seem to have a relatively shorter retention half-life when compared to previous reports on rigid MWCNTs, and the no-observed adverse effect level (NOAEL) for the tested tangled MWCNTs was 0.257 mg/m³ in a previous rat 28-day subacute inhalation toxicity study.

Single-walled carbon nanotubes repress viral-induced defense pathways through oxidative stress

Exposure of lung cells in vitro or mice to single-walled carbon nanotubes (SWCNTs) directly to the respiratory tract leads to a reduced host anti-viral immune response to infection with influenza A virus H1N1 (IAV), resulting in significant increases in viral titers. This suggests that unintended exposure to nanotubes via inhalation may increase susceptibility to notorious respiratory viruses that carry a high social and economic burden globally. However, the molecular mechanisms that contribute to viral susceptibility have not been elucidated. In the present study, we identified the retinoic acid-induced gene I (RIG-I) like receptors (RLRs)/mitochondrial antiviral signaling (MAVS) pathway as a target of SWCNT-induced oxidative stress in small airway epithelial cells (SAEC) that contribute to significantly enhanced influenza viral titers. Exposure of SAEC to SWCNTs increases viral titers while repressing several aspects of the RLR pathway, including mRNA expression of key genes (e.g. IFITs, RIG-I, MDA5, IFNβ1, CCL5). SWCNTs also reduce mitochondrial membrane potential without altering oxygen consumption rates. Our findings also indicate that SWCNTs can impair formation of MAVS prion-like aggregates, which is known to impede downstream activation of the RLR pathway and hence the transcriptional production of interferon-regulated anti-viral genes and cytokines. Furthermore, application of the antioxidant NAC alleviates inhibition of gene expression levels by SWCNTs, as well as MAVS signalosome formation, and increased viral titers. These data provide evidence of targeted impairment of anti-viral signaling networks that are vital to immune defense mechanisms in lung cells, contributing to increased susceptibility to IAV infections by SWCNTs.

Substrate Stiffness-Dependent Carbon Nanotube-Induced Lung Fibrogenesis

Most living tissues exhibit the specific stiffness, which has been known to have profound influence on cell behaviors, yet how the stiffness affects cellular responses to engineered nanomaterials has not been elucidated. Particularly, discrepancies exist between in vitro and in vivo nanotoxicological studies. Here, we investigated the effects of substrate stiffness on the fibrogenic responses of normal human lung fibroblasts (NHLFs) to multiwalled carbon nanotubes (MWCNTs). NHLFs were grown on polyacrylamide (PAAm) hydrogels with the stiffness comparable to that of human normal and fibrotic lung tissues, and treated with MWCNTs for various time. The fibrogenic responses, including cell proliferation, reactive oxygen species production, and collagen I expression, of NHLFs to MWCNTs were observed to be regulated by substrate stiffness in a time-dependent manner. NHLFs generally were rounded on soft hydrogels and required a long treatment time to exhibit fibrogenic responses, while on stiff hydrogels the cells were well-spread with defined stress fibers and short-time MWCNTs treatment sufficiently induced the fibrogenic responses. Mechanistic studies showed that MWCNTs induced fibrogenesis of NHLFs through promoting expression and phosphorylation of focal adhesion kinase (FAK), while attenuating intracellular tension in the cells on stiff gels could increase MWCNTs uptake and thus elevate the induced fibrogenic responses. Moreover, we proposed a time-stiffness superposition principle to describe the equivalent effects of treatment time and substrate stiffness on nanomaterials-induced fibrogenesis, which suggested that increasing substrate stiffness expedited fibrogenesis and shed light on the rational design of in vitro models for nanotoxicological study.

Employing multi-omics to elucidate the hormetic response against oxidative stress exerted by nC60 on Daphnia pulex

This study evaluated hormetic effect of oxidative stress exerted by fullerene crystals (nC₆₀) on Daphnia pulex, employing transcriptomics and metabolomics. D. pulex were exposed to various concentrations of nC₆₀ for 21 days. Hormetic effect of oxidative stress was most evident after 7 days, with markedly increased L-Glutathione (GSH) concentration and Superoxide Dismutase (SOD) activity at low doses of nC₆₀ exposure, and oppositely at high doses. The transcriptomics and metabolomics were used to elucidate the molecular mechanism underlying the hormesis in oxidative stress. There were significant alterations in major pathways involving oxidative stress and energy metabolism in D. pulex. Some important intermediates and the expression of their regulatory genes coincided with each other with first up-regulated and then down-regulated with the concentration increased, consistent with the hormesis description. The nC₆₀ interfered the TCA cycle of D. pulex. The synthesis of L-cysteine and glutamate was directly affected, and further disturbed the synthesis of GSH. This work is of great significance to provide the molecular-level evidence into the hormetic effect in oxidative stress of D. pulex exposed to nC₆₀.

Inhalation exposure to multi-walled carbon nanotubes alters the pulmonary allergic response of mice to house dust mite allergen

Background: Increasing evidence from rodent studies indicates that inhaled multi-walled carbon nanotubes (MWCNTs) have harmful effects on the lungs. In this study, we examined the effects of inhalation exposure to MWCNTs on allergen-induced airway inflammation and fibrosis. We hypothesized that inhalation pre-exposure to MWCNTs would render mice susceptible to developing allergic lung disease induced by house dust mite (HDM) allergen. Methods: Male B6C3F1/N mice were exposed by whole-body inhalation for 6 h a day, 5 d a week, for 30 d to air control or 0.06, 0.2, and 0.6 mg/m³ of MWCNTs. The exposure atmospheres were agglomerates (1.4-1.8 µm) composed of MWCNTs (average diameter 16 nm; average length 2.4 µm; 0.52% Ni). Mice then received 25 µg of HDM extract by intranasal instillation 6 times over 3 weeks. Necropsy was performed at 3 and 30 d after the final HDM dose to collect serum, bronchoalveolar lavage fluid (BALF), and lung tissue for histopathology. Results: MWCNT exposure at the highest dose inhibited HDM-induced serum IgE levels, IL-13 protein levels in BALF, and airway mucus production. However, perivascular and peribronchiolar inflammatory lesions were observed in the lungs of mice at 3 d with MWCNT and HDM, but not MWCNT or HDM alone. Moreover, combined HDM and MWCNT exposure increased airway fibrosis in the lungs of mice. Conclusions: Inhalation pre-exposure to MWCNTs inhibited HDM-induced TH2 immune responses, yet this combined exposure resulted in vascular inflammation and airway fibrosis, indicating that MWCNT pre-exposure alters the immune response to allergens.

Differential gene regulation in human small airway epithelial cells grown in monoculture versus coculture with human microvascular endothelial cells following multiwalled carbon nanotube exposure

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Coculture gene expression may have opposite direction of changes than monoculture.

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Cells grow and treated in monoculture may exaggerate toxicological responses.

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Coculture of cells may provide a more in-depth assessment of toxicological responses.

Concurrent with rising production of carbon-based engineered nanomaterials is a potential increase in respiratory and cardiovascular diseases due to exposure to nanomaterials in the workplace atmosphere. While single-cell models of pulmonary exposure are often used to determine the potential toxicity of nanomaterials in vitro, previous studies have shown that coculture cell models better represent the cellular response and crosstalk that occurs in vivo. This study identified differential gene regulation in human small airway epithelial cells (SAECs) grown either in monoculture or in coculture with human microvascular endothelial cells following exposure of the SAECs to multiwalled carbon nanotubes (MWCNTs). SAEC genes that either changed their regulation direction from upregulated in monoculture to downregulated in coculture (or vice versa) or had a more than a two-fold changed in the same regulation direction were identified. Genes that changed regulation direction were most often involved in the processes of cellular growth and proliferation and cellular immune response and inflammation. Genes that had a more than a two-fold change in regulation in the same direction were most often involved in the inflammatory response. The direction and fold-change of this differential gene regulation suggests that toxicity testing in monoculture may exaggerate cellular responses to MWCNTs, and coculture of cells may provide a more in-depth assessment of toxicological responses.

Sirtuin 6 inhibits MWCNTs-induced epithelial-mesenchymal transition in human bronchial epithelial cells via inactivating TGF-β1/Smad2 signaling pathway

Multi-walled carbon nanotubes (MWCNTs) have been developed with numerous beneficial applications. However, rodent models demonstrate that exposure to MWCNTs via respiratory pathways results in pulmonary fibrosis. Therefore, they could elicit a potential risk of pulmonary fibrosis in humans due to occupational or consumer exposure. Sirtuin 6 (SIRT6), a nicotinamide adenine dinucleotide (NAD)-dependent deacetylase, has been proved to prevent fibrosis in the liver, renal and myocardial tissues. In this present study, we aimed to explore the role of SIRT6 in MWCNTs-induced epithelial-mesenchymal transition (EMT), one of the major contributor of lung fibrogenesis in human bronchial epithelial BEAS-2B cells. We found that the protein level of SIRT6 was elevated after exposure to MWCNTs in BEAS-2B cells. Overexpression of SIRT6 significantly inhibited MWCNTs-induced EMT and EMT-like cell behaviors in BEAS-2B cells. Moreover, wild-type SIRT6 was found to decrease MWCNTs-induced phosphorylation of Smad2, but not mutant SIRT6 (H133Y) without histone deacetylase activity. In conclusion, our study demonstrated that SIRT6 inhibited MWCNTs-induced EMT in BEAS-2B cells through TGF-β1/Smad2 signaling pathway, which depended on its deacetylase activity, and provided evidences that targeting SIRT6 could be a potential novel therapeutic strategy for MWCNTs-induced pulmonary fibrosis.

Culture of dental pulp stem cells on nanoporous alumina substrates modified by carbon nanotubes

PURPOSE

Alumina substrates are one of the commonly used scaffolds applied in cell culture, but in order to prevent formation of biofilm on the alumina substrate, these substrates are modified with carbon nanotube.

METHODS

The alumina substrate was made by a two-step anodization method and was then modified with carbon nanotubes by simple chemical reaction. The substrates were characterized with FTIR, SEM, EDX, 3D laser scanning digital microscope, contact angle (CA) and surface free energy (SFE). To determine how this modification influences the reduction of biofilm, biofilm of two various bacteria, Escherichia coli (E.coli) and Staphylococcus aureus (S. aureus), were investigated.

RESULTS

The biofilm on the modified substrate decreased due to the presence of carbon nanotubes and increased antibacterial properties. Dental pulp stem cells (DPSCs) were cultured onto flat alumina (FA) and nanoporous alumina-multiwalled carbon nanotubes (NAMC) substrates to examine how the chemical modification and surface topography affects growth of DPSCs.

CONCLUSION

Cell attachment and proliferation were investigated with SEM and Presto Blue assay, and the findings show that the NAMC substrates are suitable for cell culture.

Carbon Nanotubes and Graphene as Nanoreinforcements in Metallic Biomaterials: a Review

Current challenges in existing metallic biomaterials encourage undertaking research in the development of novel materials for biomedical applications. This paper critically reviews the potential of carbon nanotubes (CNT) and graphene as nanoreinforcements in metallic biomaterials for bone tissue engineering. Unique and remarkable mechanical, electrical, and biological properties of these carbon nanomaterials allow their use as secondary-phase reinforcements in monolithic biomaterials. The nanoscale dimensions and extraordinarily large surface areas of CNT and graphene make them suitable materials for purposeful reaction with living organisms. However, the cytocompatibility of CNT and graphene is still a controversial issue that impedes advances in utilizing these promising materials in clinical orthopedic applications. The interaction of CNT and graphene with biological systems including proteins, nucleic acids, and human cells is critically reviewed to assess their cytocompatibity in vitro and in vivo. It is revealed that composites reinforced with CNT and graphene show enhanced adhesion of osteoblast cells, which subsequently promotes bone tissue formation in vivo. This potential is expected to pave the way for developing ground-breaking technologies in regenerative medicine and bone tissue engineering. In addition, current progress and future research directions are highlighted for the development of CNT and graphene reinforced implants for bone tissue engineering.

Different aggregation and shape characteristics of carbon materials affect biological responses in RAW264 cells

Introduction

Carbon nanotubes (CNTs) have various shapes, including needle-like shapes and curled shapes, and the cytotoxicity and carcinogenicity of CNTs differ depending on their shapes and surface modifications. However, the biological responses induced by CNTs and related mechanisms according to the dispersion state of CNTs have not been extensively studied.

Materials and methods

We prepared multiwalled CNTs (MWCNTs) showing different dispersions and evaluated these MWCNTs in RAW264 cells to determine cytotoxicity, cellular uptake, and immune responses. Furthermore, RAW264 cells were also used to compare the cellular uptake and cytotoxicity of fibrous MWCNTs and spherical carbon nanohorns (CNHs) exhibiting the same degree of dispersion.

Results

Our analysis showed that the cellular uptake, localization, and inflammatory responses of MWCNTs differed depending on the dispersion state. Moreover, there were differences in uptake between MWCNTs and CNHs, even showing the same degree of dispersion. These findings suggested that receptors related to cytotoxicity and immune responses differed depending on the aggregated state of MWCNTs and surface modification with a dispersant. Furthermore, our results suggested that the receptors recognized by the cells differed depending on the particle shape.

Conclusion

Therefore, to apply MWCNTs as a biomaterial, it is important to determine the carcinogenicity and toxicity of the CNTs and to examine different biological responses induced by varying shapes, dispersion states, and surface modifications of particles.

Crosstalk between DNA Damage and Inflammation in the Multiple Steps of Carcinogenesis

Inflammation can be induced by chronic infection, inflammatory diseases and physicochemical factors. Chronic inflammation is estimated to contribute to approximately 25% of human cancers. Under inflammatory conditions, inflammatory and epithelial cells release reactive oxygen (ROS) and nitrogen species (RNS), which are capable of causing DNA damage, including the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine and 8-nitroguanine. We reported that 8-nitroguanine was clearly formed at the sites of cancer induced by infectious agents including Helicobacter pylori, inflammatory diseases including Barrett's esophagus, and physicochemical factors including asbestos. DNA damage can lead to mutations and genomic instability if not properly repaired. Moreover, DNA damage response can also induce high mobility group box 1-generating inflammatory microenvironment, which is characterized by hypoxia. Hypoxia induces hypoxia-inducible factor and inducible nitric oxide synthase (iNOS), which increases the levels of intracellular RNS and ROS, resulting DNA damage in progression with poor prognosis. Furthermore, tumor-producing inflammation can induce nuclear factor-κB, resulting in iNOS-dependent DNA damage. Therefore, crosstalk between DNA damage and inflammation may play important roles in cancer development. A proposed mechanism for the crosstalk may explain why aspirin decreases the long-term risk of cancer mortality.

Elevated MicroRNA-33 in Sarcoidosis and a Carbon Nanotube Model of Chronic Granulomatous Disease

We established a murine model of multiwall carbon nanotube (MWCNT)-induced chronic granulomatous disease, which resembles human sarcoidosis pathology. At 60 days after oropharyngeal MWCNT instillation, bronchoalveolar lavage (BAL) cells from wild-type mice exhibit an M1 phenotype with elevated proinflammatory cytokines and reduced peroxisome proliferator-activated receptor γ (PPARγ)-characteristics also present in human sarcoidosis. Based upon MWCNT-associated PPARγ deficiency, we hypothesized that the PPARγ target gene, ATP-binding cassette (ABC) G1, a lipid transporter with antiinflammatory properties, might also be repressed. Results after MWCNT instillation indicated significantly repressed ABCG1, but, surprisingly, lipid transporter ABCA1 was also repressed, suggesting a possible second pathway. Exploration of potential regulators revealed that microRNA (miR)-33, a lipid transporter regulator, was strikingly elevated (13.9 fold) in BAL cells from MWCNT-instilled mice but not sham control mice. Elevated miR-33 was also detected in murine granulomatous lung tissue. In vitro studies confirmed that lentivirus-miR-33 overexpression repressed both ABCA1 and ABCG1 (but not PPARγ) in cultured murine alveolar macrophages. BAL cells of patients with sarcoidosis also displayed elevated miR-33 together with reduced ABCA1 and ABCG1 messenger RNA and protein compared with healthy control subjects. Moreover, miR-33 was elevated within sarcoidosis granulomatous tissue. The findings suggest that alveolar macrophage miR-33 is up-regulated by proinflammatory cytokines and may perpetuate chronic inflammatory granulomatous disease by repressing antiinflammatory functions of ABCA1 and ABCG1 lipid transporters. The results also suggest two possible pathways for transporter dysregulation in granulomatous disease-one associated with intrinsic PPARγ status and the other with miR-33 up-regulation triggered by environmental challenges, such as MWCNT.

In vitro experimental models of mesothelioma revisited

Malignant pleural mesothelioma (MPM) is a biologically unusual, highly aggressive cancer that defies current multimodality treatments. Epidemiologic data suggest that this malignancy has not abated despite increasingly strict environmental regulations on asbestos, the putative causative agent for sporadic cases. An incomplete understanding of all the factors mechanistically driving mesothelioma is largely responsible for the current lack of curative treatments. Many approaches have been employed to ascertain the step-by-step molecular events involved in mesothelioma oncogenesis including in vitro, small animal in vivo, and human experimental models; though clearly defined, druggable mechanisms still are elusive. Importantly, the foundation of the latest accepted model of tumor initiation is derived from in vitro systems. A thorough review of in vitro mesothelioma oncogenesis models may suggest further opportunities for discovery.

Current applications and future prospects of nanomaterials in tumor therapy

Tumors are one of the most serious human diseases and cause numerous global deaths per year. In spite of many strategies applied in tumor therapy, such as radiation therapy, chemotherapy, surgery, and a combination of these treatments, tumors are still the foremost killer worldwide among human diseases, due to their specific limitations, such as multidrug resistance and side effects. Therefore, it is urgent and necessary to develop new strategies for tumor therapy. Recently, the fast development of nanoscience has paved the way for designing new strategies to treat tumors. Nanomaterials have shown great potential in tumor therapy, due to their unique properties, including passive targeting, hyperthermia effects, and tumor-specific inhibition. This review summarizes the recent progress using the innate antitumor properties of metallic and nonmetallic nanomaterials to treat tumors, and related challenges and prospects are discussed.

Biological Surface Adsorption Index of Nanomaterials: Modelling Surface Interactions of Nanomaterials with Biomolecules

Quantitative analysis of the interactions between nanomaterials and their surrounding environment is crucial for safety evaluation in the application of nanotechnology as well as its development and standardization. In this chapter, we demonstrate the importance of the adsorption of surrounding molecules onto the surface of nanomaterials by forming biocorona and thus impact the bio-identity and fate of those materials. We illustrate the key factors including various physical forces in determining the interaction happening at bio-nano interfaces. We further discuss the mathematical endeavors in explaining and predicting the adsorption phenomena, and propose a new statistics-based surface adsorption model, the Biological Surface Adsorption Index (BSAI), to quantitatively analyze the interaction profile of surface adsorption of a large group of small organic molecules onto nanomaterials with varying surface physicochemical properties, first employing five descriptors representing the surface energy profile of the nanomaterials, then further incorporating traditional semi-empirical adsorption models to address concentration effects of solutes. These Advancements in surface adsorption modelling showed a promising development in the application of quantitative predictive models in biological applications, nanomedicine, and environmental safety assessment of nanomaterials.

Induction of cancer-associated fibroblast-like cells by carbon nanotubes dictates its tumorigenicity

Tumor microenvironment has been recognized as a key determinant of tumor formation and metastasis, but how tumor microenvironment is affected by nanomaterials is essentially unknown. Here, we investigated whether carbon nanotubes (CNTs), a widely used nanomaterial with known carcinogenic potential, can affect cancer-associated fibroblasts (CAFs), which are a key component of tumor microenvironment that provides necessary support for tumor growth. We show for the first time that single-walled CNT and to a lesser extent multi-walled and its COOH-functionalized form induced CAF-like cells, which are non-tumorigenic in animals, but promote tumor growth of human lung carcinoma and CNT-transformed lung epithelial cells. The mechanism by which CNT-induced CAF-like cells promote tumor growth involved the acquisition of cancer stem cells (CSCs) in cancer population. Gene knockdown experiments showed that an expression of podoplanin on CAF-like cells is essential for their effects, indicating the functional role of CAF-like cells and podoplanin in CNT tumorigenic process. Our findings unveil a novel mechanism of CNT-induced carcinogenesis through the induction of CAF-like cells that support CSCs and drive tumor formation. Our results also suggest the potential utility of podoplanin as a mechanism-based biomarker for rapid screening of carcinogenicity of CNTs and related nanomaterials for their safer design.

Quantum-mechanical parameters for the risk assessment of multi-walled carbon-nanotubes: A study using adsorption of probe compounds and its application to biomolecules

This work forwards new insights into the risk-assessment of multi-walled carbon-nanotubes (MWCNTs) while analysing the role of quantum-mechanical interactions between the electrons in the adsorption of probe compounds and biomolecules by MWCNTs. For this, the quantitative models are developed using quantum-chemical descriptors and their electron-correlation contribution. The major quantum-chemical factors contributing to the adsorption are found to be mean polarizability, electron-correlation energy, and electron-correlation contribution to the absolute electronegativity and LUMO energy. The proposed models, based on only three quantum-chemical factors, are found to be even more robust and predictive than the previously known five or four factors based linear free-energy and solvation-energy relationships. The proposed models are employed to predict the adsorption of biomolecules including steroid hormones and DNA bases. The steroid hormones are predicted to be strongly adsorbed by the MWCNTs, with the order: hydrocortisone > aldosterone > progesterone > ethinyl-oestradiol > testosterone > oestradiol, whereas the DNA bases are found to be relatively less adsorbed but follow the order as: guanine > adenine > thymine > cytosine > uracil. Besides these, the developed electron-correlation based models predict several insecticides, pesticides, herbicides, fungicides, plasticizers and antimicrobial agents in cosmetics, to be strongly adsorbed by the carbon-nanotubes. The present study proposes that the instantaneous inter-electronic interactions may be quite significant in various physico-chemical processes involving MWCNTs, and can be used as a reliable predictor for their risk assessment.

Multi-walled carbon nanotubes directly induce epithelial-mesenchymal transition in human bronchial epithelial cells via the TGF-β-mediated Akt/GSK-3β/SNAIL-1 signalling pathway

Background

Multi-walled carbon nanotubes (MWCNT) are currently under intense toxicological investigation due to concern on their potential health effects. Current in vitro and in vivo data indicate that MWCNT exposure is strongly associated with lung toxicity (inflammation, fibrosis, granuloma, cancer and airway injury) and their effects might be comparable to asbestos-induced carcinogenesis. Although fibrosis is a multi-origin disease, epithelial-mesenchymal transition (EMT) is recently recognized as an important pathway in cell transformation. It is known that MWCNT exposure induces EMT through the activation of the TGF-β/Smad signalling pathway thus promoting pulmonary fibrosis, but the molecular mechanisms involved are not fully understood. In the present work we propose a new mechanism involving a TGF-β-mediated signalling pathway.

Methods

Human bronchial epithelial cells were incubated with two different MWCNT samples at various concentrations for up to 96 h and several markers of EMT were investigated. Quantitative real time PCR, western blot, immunofluorescent staining and gelatin zymographies were performed to detect the marker protein alterations. ELISA was performed to evaluate TGF-β production. Experiments with neutralizing anti-TGF-β antibody, specific inhibitors of GSK-3β and Akt and siRNA were carried out in order to confirm their involvement in MWCNT-induced EMT. In vivo experiments of pharyngeal aspiration in C57BL/6 mice were also performed. Data were analyzed by a one-way ANOVA with Tukey’s post-hoc test.

Results

Fully characterized MWCNT (mean length < 5 μm) are able to induce EMT in an in vitro human model (BEAS-2B cells) after long-term incubation at sub-cytotoxic concentrations. MWCNT stimulate TGF-β secretion, Akt activation and GSK-3β inhibition, which induces nuclear accumulation of SNAIL-1 and its transcriptional activity, thus contributing to switch on the EMT program. Moreover, a significant increment of nuclear β-catenin - due to E-cadherin repression and following translocation to nucleus - likely reinforces signalling for EMT promotion. In vivo results supported the occurrence of pulmonary fibrosis following MWCNT exposure.

Conclusions

We demonstrate a new molecular mechanism of MWCNT-mediated EMT, which is Smad-independent and involves TGF-β and its intracellular effectors Akt/GSK-3β that activate the SNAIL-1 signalling pathway. This finding suggests potential novel targets in the development of therapeutic and preventive approaches.

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-016-0138-4) contains supplementary material, which is available to authorized users.

Carcinogenic Potential of High Aspect Ratio Carbon Nanomaterials

Engineered nanomaterials, including high aspect ratio carbon nanomaterials, are often commercialized without a complete human risk assessment and safety evaluation. A health concern has been raised that high aspect ratio nanomaterials such as carbon nanotubes may cause unintended health consequences, such as asbestos-like lung cancer and mesothelioma, when chronically inhaled. Considering the widespread industrial and clinical applications and the increasing incidence of human exposure to nanomaterials, it is important to address the issue of nanomaterial carcinogenicity in a timely manner. This review summarizes recent advances in nanomaterial genotoxicity and carcinogenicity with a focus on high aspect ratio carbon nanotubes, and discusses current knowledge gaps and future research directions.

Multi-walled carbon nanotube induces nitrative DNA damage in human lung epithelial cells via HMGB1-RAGE interaction and Toll-like receptor 9 activation

Background

Carbon nanotube (CNT) is used for various industrial purposes, but exhibits carcinogenic effects in experimental animals. Chronic inflammation in the respiratory system may participate in CNT-induced carcinogenesis. 8-Nitroguanine (8-nitroG) is a mutagenic DNA lesion formed during inflammation. We have previously reported that multi-walled CNT (MWCNT) induced 8-nitroG formation in lung epithelial cells and this process involved endocytosis. To clarify the mechanism of CNT-induced carcinogenesis, we examined the role of Toll-like receptor (TLR) 9, which resides in endosomes and lysosomes, in 8-nitroG formation in human lung epithelial cell lines.

Methods

We performed immunocytochemistry to examine 8-nitroG formation in A549 and HBEpC cells treated with MWCNT with a length of 1-2 μm (CNT-S) or 5-15 μm (CNT-L) and a diameter of 20-40 nm. We examined inhibitory effects of endocytosis inhibitors, small interfering RNA (siRNA) for TLR9, and antibodies against high-mobility group box-1 (HMGB1) and receptor for advanced glycation end-products (RAGE) on 8-nitroG formation. The release of HMGB1 and double-stranded DNA (dsDNA) into the culture supernatant from MWCNT-treated cells was examined by ELISA and fluorometric analysis, respectively. The association of these molecules was examined by double immunofluorescent staining and co-immunoprecipitation.

Results

CNT-L significantly increased 8-nitroG formation at 0.05 μg/ml in A549 cells and its intensity reached a maximum at 1 μg/ml. CNT-L tended to induce stronger cytotoxicity and 8-nitroG formation than CNT-S. Endocytosis inhibitors, TLR9 siRNA and antibodies against HMGB1 and RAGE largely reduced MWCNT-induced 8-nitroG formation. MWCNT increased the release of HMGB1 and dsDNA from A549 cells into culture supernatant. The culture supernatant of MWCNT-exposed cells induced 8-nitroG formation in fresh A549 cells. Double immunofluorescent staining and co-immunoprecipitation showed that TLR9 was associated with HMGB1 and RAGE in lysosomes of MWCNT-treated cells.

Conclusions

MWCNT induces injury or necrosis of lung epithelial cells, which release HMGB1 and DNA into the extracellular space. The HMGB1-DNA complex binds to RAGE on neighboring cells and then CpG DNA is recognized by TLR9 in lysosomes, leading to generation of nitric oxide and 8-nitroG formation. This is the first study demonstrating that TLR9 and related molecules participate in MWCNT-induced genotoxicity and may contribute to carcinogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-016-0127-7) contains supplementary material, which is available to authorized users.

A designed lipopeptide with a leucine zipper as an imbedded on/off switch for lipid bilayers

Thermo-sensitive drug carriers are receiving increasing attention for use with localized hyperthermia at abnormal tissue sites or to easily implement hyperthermia. In this study, a thermo-sensitive lipopeptide was designed, consisting of a carbon chain and a leucine zipper with an amino acid sequence CH3-(CH2)4-CO-NH-VAQLEVK-VAQLESK-VSKLESK-VSSLESK-COOH. They could form dimers by the hydrophobic force at body temperature and separate into single random coils above the melting temperature (Tm). The lipopeptide was mixed with phospholipids to form a hybrid liposome (Lipo-LPe). The Tm of the free lipopeptide and lipopeptide in Lipo-LPe was found to be 48.0 °C and 42.5 °C from circular dichroism data, respectively. Compared with the pure liposome, the phase-transition temperature (Ttr) of Lipo-LPe, which was obtained by differential scanning calorimetry, was increased by about 5 °C, showing an improvement of thermal stability. The drug release rate of Lipo-LPe was slightly decreased at body temperature but greatly increased at mild hyperthermia in vitro. Drug release under intermittent heating was performed, and the reversibility of thermo-sensitive on/off switch was confirmed. Furthermore, Lipo-LPe achieved the maximum amount of cell death under mild hyperthermia. We concluded that Lipo-LPe, as a novel thermo-sensitive drug carrier, provides a promising opportunity for controlling drug release.

Role of signal transducer and activator of transcription 1 in murine allergen-induced airway remodeling and exacerbation by carbon nanotubes

Asthma is characterized by a T helper type 2 phenotype and by chronic allergen-induced airway inflammation (AAI). Environmental exposure to air pollution ultrafine particles (i.e., nanoparticles) exacerbates AAI, and a concern is possible exacerbation posed by engineered nanoparticles generated by emerging nanotechnologies. Signal transducer and activator of transcription (STAT) 1 is a transcription factor that maintains T helper type 1 cell development. However, the role of STAT1 in regulating AAI or exacerbation by nanoparticles has not been explored. In this study, mice with whole-body knockout of the Stat1 gene (Stat1(-/-)) or wild-type (WT) mice were sensitized to ovalbumin (OVA) allergen and then exposed to multiwalled carbon nanotubes (MWCNTs) by oropharygneal aspiration. In Stat1(-/-) and WT mice, OVA increased eosinophils in bronchoalveolar lavage fluid, whereas MWCNTs increased neutrophils. Interestingly, OVA sensitization prevented MWCNT-induced neutrophilia and caused only eosinophilic inflammation. Stat1(-/-) mice displayed increased IL-13 in bronchoalveolar lavage fluid at 1 day compared with WT mice after treatment with OVA or OVA and MWCNTs. At 21 days, the lungs of OVA-sensitized Stat1(-/-) mice displayed increased eosinophilia, goblet cell hyperplasia, airway fibrosis, and subepithelial apoptosis. MWCNTs further increased OVA-induced goblet cell hyperplasia, airway fibrosis, and apoptosis in Stat1(-/-) mice at 21 days. These changes corresponded to increased levels of profibrogenic mediators (transforming growth factor-β1, TNF-α, osteopontin) but decreased IL-10 in Stat1(-/-) mice. Finally, fibroblasts isolated from the lungs of Stat1(-/-) mice produced significantly more collagen mRNA and protein in response to transforming growth factor-β1 compared with WT lung fibroblasts. Our results support a protective role for STAT1 in chronic AAI and exacerbation of remodeling caused by MWCNTs.

Impact of single-walled carbon nanotubes on the embryo: a brief review

Carbon nanotubes (CNTs) are considered one of the most interesting materials in the 21st century due to their unique physiochemical characteristics and applicability to various industrial products and medical applications. However, in the last few years, questions have been raised regarding the potential toxicity of CNTs to humans and the environment; it is believed that the physiochemical characteristics of these materials are key determinants of CNT interaction with living cells and hence determine their toxicity in humans and other organisms as well as their embryos. Thus, several recent studies, including ours, pointed out that CNTs have cytotoxic effects on human and animal cells, which occur via the alteration of key regulator genes of cell proliferation, apoptosis, survival, cell-cell adhesion, and angiogenesis. Meanwhile, few investigations revealed that CNTs could also be harmful to the normal development of the embryo. In this review, we will discuss the toxic role of single-walled CNTs in the embryo, which was recently explored by several groups including ours.

Functionalized carbon nanotubes and their promising applications in therapeutics and diagnostics

Carbon nanotubes (CNTs) have attracted much attention from researchers worldwide in recent years due to their high aspect ratio, high surface area, and excellent material properties, such as electrical and thermal conductivities and mechanical strength. These rolled-up seamless cylinders of graphene sheets possess nanosized hollow-tube-shaped structures. The CNTs can be single-walled, double-walled or multi-walled, depending upon the number of graphene layers from which a single nanotube is composed. The CNTs, favoring encapsulation of drug molecules or by possible attachment of theranostic agents on the nanotube walls, have enabled their use in controlled drug delivery, and in targeting of drug molecules to specific sites such as the lymphatic system, brain, ocular system, and cancerous tissue. This chapter provides an overview of various types of CNTs, methods utilized for their commercial production, and the functionalization approaches employed in drug-delivery applications. In addition, the chapter also endeavors to provide a thoughtful insight into the toxicity and regulatory concerns that need to be addressed before the CNTs can be launched in the market.

Five years update on relationships between malignant pleural mesothelioma and exposure to asbestos and other elongated mineral particles

Despite the reduction of global asbestos consumption and production due to the ban or restriction of asbestos uses in more than 50 countries since the 1970s, malignant mesothelioma remains a disease of concern. Asbestos is still used, imported, and exported in several countries, and the number of mesothelioma deaths may be expected to increase in the next decades in these countries. Asbestos exposure is the main risk factor for malignant pleural mesothelioma, but other types of exposures are linked to the occurrence of this type of cancer. Although recent treatments improve the quality of life of patients with mesothelioma, malignant pleural mesothelioma remains an aggressive disease. Recent treatments have not resulted in appreciable improvement in survival, and thus development of more efficient therapies is urgently needed. The development of novel therapeutic strategies is dependent on our level of knowledge of the physiopathological and molecular changes that mesothelial cells acquired during the neoplastic process. During the past 5 years, new findings have been published on the etiology, epidemiology, molecular changes, and innovative treatments of malignant pleural mesothelioma. This review aims to update the findings of recent investigations on etiology, epidemiology, and molecular changes with a focus on (1) attributable risk of asbestos exposure in men and women and (2) coexposure to other minerals and other elongated mineral particles or high aspect ratio nanoparticles. Recent data obtained on genomic and gene alterations, pathways deregulations, and predisposing factors are summarized.

Applied Nanotoxicology

Nanomaterials, including nanoparticles and nanoobjects, are being incorporated into everyday products at an increasing rate. These products include consumer products of interest to toxicologists such as pharmaceuticals, cosmetics, food, food packaging, household products, and so on. The manufacturing of products containing or utilizing nanomaterials in their composition may also present potential toxicologic concerns in the workplace. The molecular complexity and composition of these nanomaterials are ever increasing, and the means and methods being applied to characterize and perform useful toxicologic assessments are rapidly advancing. This article includes presentations by experienced toxicologists in the nanotoxicology community who are focused on the applied aspect of the discipline toward supporting state of the art toxicologic assessments for food products and packaging, pharmaceuticals and medical devices, inhaled nanoparticle and gastrointestinal exposures, and addressing occupational safety and health issues and concerns. This symposium overview article summarizes 5 talks that were presented at the 35th Annual meeting of the American College of Toxicology on the subject of "Applied Nanotechnology."

Risk Assessment of the Carbon Nanotube Group

This study assessed the health risks via inhalation and derived the occupational exposure limit (OEL) for the carbon nanotube (CNT) group rather than individual CNT material. We devised two methods: the integration of the intratracheal instillation (IT) data with the inhalation (IH) data, and the "biaxial approach." A four-week IH test and IT test were performed in rats exposed to representative materials to obtain the no observed adverse effect level, based on which the OEL was derived. We used the biaxial approach to conduct a relative toxicity assessment of six types of CNTs. An OEL of 0.03 mg/m(3) was selected as the criterion for the CNT group. We proposed that the OEL be limited to 15 years. We adopted adaptive management, in which the values are reviewed whenever new data are obtained. The toxicity level was found to be correlated with the Brunauer-Emmett-Teller (BET)-specific surface area (BET-SSA) of CNT, suggesting the BET-SSA to have potential for use in toxicity estimation. We used the published exposure data and measurement results of dustiness tests to compute the risk in relation to particle size at the workplace and showed that controlling micron-sized respirable particles was of utmost importance. Our genotoxicity studies indicated that CNT did not directly interact with genetic materials. They supported the concept that, even if CNT is genotoxic, it is secondary genotoxicity mediated via a pathway of genotoxic damage resulting from oxidative DNA attack by free radicals generated during CNT-elicited inflammation. Secondary genotoxicity appears to involve a threshold.

Oxidative injury induced by cadmium sulfide nanoparticles in A549 cells and rat lungs

BACKGROUND

Rod-shaped cadmium sulfide nanoparticles (CdS NPs) are becoming increasingly important in many industrial fields, but their potential hazards remain unknown.

OBJECTIVES

This study aimed to explore the patterns and mechanisms of lung injury induced by CdS NPs.

METHODS

A549 cells and rats were exposed to two types of CdS NPs with a same diameter of 20-30 nm but different lengths, CdS1 (80-100 nm) and CdS2 (110-130 nm). The using doses were included 10 μg/ml and 20 μg/ml two types of CdS NPs for cellular experiments and five times dose of 20 mg/kg body weight for rats' exposure. Methylthiazolyldiphenyl-tetrazolium bromide (MTT) and trypan blue staining were used to detect the A549 cell mortality percentage. The levels of reactive oxygen species (ROS) were determined in A549 cell. The vigor of superoxide dismutase (SOD) and the contents of catalase (CAT) and malondialdehyde (MDA) were detected both in A549 cells and in rats' serum and lung tissues. The cellular morphological changes were observed under transmission electron microscopy (TEM) and the pathological changes were observed in rats' lung tissue.

RESULTS

CdS NPs significantly increased A549 cell mortality percentage. The CdS NPs also increased the levels of ROS and MDA content, whereas they decreased SOD and CAT activities. In parallel, similar changes of the contents of MDA, SOD and CAT were also observed in the sera and lung tissues of CdS NP-treated rats. The cellular TEM detection revealed that two types of CdS nanorods appeared as orderly arranged rounded fat droplets separately and leading to nucleus condensation (CdS1). These cellular and rats' tissues changes in the group treated with CdS1 were more significant than the CdS2 groups. Furthermore, CdS NPs induced many pathological changes, including emphysematous changes in rat lung tissue. Especially visible lung consolidation can be observed in the CdS1 group.

CONCLUSIONS

CdS NPs induce oxidative injury in the respiratory system, and their toxic effects may be related to grain length.

Microglia Determine Brain Region-Specific Neurotoxic Responses to Chemically Functionalized Carbon Nanotubes

Surface tunability and their ability to translocate plasma membranes make chemically functionalized carbon nanotubes (f-CNTs) promising intracellular delivery systems for therapeutic or diagnostic purposes in the central nervous system (CNS). The present study aimed to determine the biological impact of different types of multiwalled CNTs (MWNTs) on primary neuronal and glial cell populations isolated from fetal rat frontal cortex (FCO) and striatum (ST). Neurons from both brain regions were generally not affected by exposure to MWNTs as determined by a modified LDH assay. In contrast, the viability of mixed glia was reduced in ST-derived mixed glial cultures, but not in FCO-derived ones. Cytotoxicity was independent of MWNT type or dose, suggesting an inherent sensitivity to CNTs. Characterization of the cell populations in mixed glial cultures prior to nanotube exposure showed higher number of CD11b/c positive cells in the ST-derived mixed glial cultures. After exposure to MWNTs, CNT were uptaken more effectively by CD11b/c positive cells (microglia), compared to GFAP positive cells (astrocytes). When exposed to conditioned media from microglia enriched cultures exposed to MWNTs, ST-derived glial cultures secreted more NO than FCO-derived cells. These results suggested that the more significant cytotoxic response obtained from ST-derived mixed glia cultures was related to the higher number of microglial cells in this brain region. Our findings emphasize the role that resident macrophages of the CNS play in response to nanomaterials and the need to thoroughly investigate the brain region-specific effects toward designing implantable devices or delivery systems to the CNS.

Respirator Performance against Nanoparticles under Simulated Workplace Activities

Filtering facepiece respirators (FFRs) and elastomeric half-mask respirators (EHRs) are commonly used by workers for protection against potentially hazardous particles, including engineered nanoparticles. The purpose of this study was to evaluate the performance of these types of respirators against 10-400 nm particles using human subjects exposed to NaCl aerosols under simulated workplace activities. Simulated workplace protection factors (SWPFs) were measured for eight combinations of respirator models (2 N95 FFRs, 2 P100 FFRs, 2 N95 EHRs, and 2 P100 EHRs) worn by 25 healthy test subjects (13 females and 12 males) with varying face sizes. Before beginning a SWPF test for a given respirator model, each subject had to pass a quantitative fit test. Each SWPF test was performed using a protocol of six exercises for 3 min each: (i) normal breathing, (ii) deep breathing, (iii) moving head side to side, (iv) moving head up and down, (v) bending at the waist, and (vi) a simulated laboratory-vessel cleaning motion. Two scanning mobility particle sizers were used simultaneously to measure the upstream (outside the respirator) and downstream (inside the respirator) test aerosol; SWPF was then calculated as a ratio of the upstream and downstream particle concentrations. In general, geometric mean SWPF (GM-SWPF) was highest for the P100 EHRs, followed by P100 FFRs, N95 EHRs, and N95 FFRs. This trend holds true for nanoparticles (10-100 nm), larger size particles (100-400 nm), and the 'all size' range (10-400 nm). All respirators provided better or similar performance levels for 10-100 nm particles as compared to larger 100-400 nm particles. This study found that class P100 respirators provided higher SWPFs compared to class N95 respirators (P < 0.05) for both FFR and EHR types. All respirators provided expected performance (i.e. fifth percentile SWPF > 10) against all particle size ranges tested.

Microfluidic gradient device for studying mesothelial cell migration and the effect of chronic carbon nanotube exposure

Cell migration is one of the crucial steps in many physiological and pathological processes, including cancer development. Our recent studies have shown that carbon nanotubes (CNTs), similarly to asbestos, can induce accelerated cell growth and invasiveness that contribute to their mesothelioma pathogenicity. Malignant mesothelioma is a very aggressive tumor that develops from cells of the mesothelium, and is most commonly caused by exposure to asbestos. CNTs have a similar structure and mode of exposure to asbestos. This has raised a concern regarding the potential carcinogenicity of CNTs, especially in the pleural area which is a key target for asbestos-related diseases. In this paper, a static microfluidic gradient device was applied to study the migration of human pleural mesothelial cells which had been through a long-term exposure (4 months) to subcytotoxic concentration (0.02 μg cm-2) of single-walled CNTs (SWCNTs). Multiple migration signatures of these cells were investigated using the microfluidic gradient device for the first time. During the migration study, we observed that cell morphologies changed from flattened shapes to spindle shapes prior to their migration after their sensing of the chemical gradient. The migration of chronically SWCNT-exposed mesothelial cells was evaluated under different fetal bovine serum (FBS) concentration gradients, and the migration speeds and number of migrating cells were extracted and compared. The results showed that chronically SWCNT-exposed mesothelial cells are more sensitive to the gradient compared to non-SWCNT-exposed cells. The method described here allows simultaneous detection of cell morphology and migration under chemical gradient conditions, and also allows for real-time monitoring of cell motility that resembles in vivo cell migration. This platform would be much needed for supporting the development of more physiologically relevant cell models for better assessment and characterization of the mesothelioma hazard posed by nanomaterials.

Tangible nanocomposites with diverse properties for heart valve application

Cardiovascular disease claims millions of lives every year throughout the world. Biomaterials are used widely for the treatment of this fatal disease. With the advent of nanotechnology, the use of nanocomposites has become almost inevitable in the field of biomaterials. The versatile properties of nanocomposites, such as improved durability and biocompatibility, make them an ideal choice for various biomedical applications. Among the various nanocomposites, polyhedral oligomeric silsesquioxane-poly(carbonate-urea)urethane, bacterial cellulose with polyvinyl alcohol, carbon nanotubes, graphene oxide and nano-hydroxyapatite nanocomposites have gained popularity as putative choices for biomaterials in cardiovascular applications owing to their superior properties. In this review, various studies performed utilizing these nanocomposites for improving the mechanical strength, anti-calcification potential and hemocompatibility of heart valves are reviewed and summarized. The primary motive of this work is to shed light on the emerging nanocomposites for heart valve applications. Furthermore, we aim to promote the prospects of these nanocomposites in the campaign against cardiovascular diseases.