Use of back-scatter electron signals to visualise cell/nanowires interactions in vitro and in vivo; frustrated phagocytosis of long fibres in macrophages and compartmentalisation in mesothelial cells in vivo

A Network Toxicology Approach for Mechanistic Modelling of Nanomaterial Hazard and Adverse Outcomes

Hazard assessment is the first step in evaluating the potential adverse effects of chemicals. Traditionally, toxicological assessment has focused on the exposure, overlooking the impact of the exposed system on the observed toxicity. However, systems toxicology emphasizes how system properties significantly contribute to the observed response. Hence, systems theory states that interactions store more information than individual elements, leading to the adoption of network based models to represent complex systems in many fields of life sciences. Here, they develop a network-based approach to characterize toxicological responses in the context of a biological system, inferring biological system specific networks. They directly link molecular alterations to the adverse outcome pathway (AOP) framework, establishing direct connections between omics data and toxicologically relevant phenotypic events. They apply this framework to a dataset including 31 engineered nanomaterials with different physicochemical properties in two different in vitro and one in vivo models and demonstrate how the biological system is the driving force of the observed response. This work highlights the potential of network-based methods to significantly improve their understanding of toxicological mechanisms from a systems biology perspective and provides relevant considerations and future data-driven approaches for the hazard assessment of nanomaterials and other advanced materials.

Interplay between oncolytic measles virus, macrophages and cancer cells induces a proinflammatory tumor microenvironment

Attenuated measles virus (MV) exerts its oncolytic activity in malignant pleural mesothelioma (MPM) cells that lack type-I interferon (IFN-I) production or responsiveness. However, other cells in the tumor microenvironment (TME), such as myeloid cells, possess functional antiviral pathways. In this study, we aimed to characterize the interplay between MV and the myeloid cells in human MPM. We cocultured MPM cell lines with monocytes or macrophages and infected them with MV. We analyzed the transcriptome of each cell type and studied their secretion and phenotypes by high-dimensional flow cytometry. We also measured transgene expression using an MV encoding GFP (MV-GFP). We show that MPM cells drive the differentiation of monocytes into M2-like macrophages. These macrophages inhibit GFP expression in tumor cells harboring a defect in IFN-I production and a functional signaling downstream of the IFN-I receptor, while having minimal effects on GFP expression in tumor cells with defect of responsiveness to IFN-I. Interestingly, inhibition of the IFN-I signaling by ruxolitinib restores GFP expression in tumor cells. Upon MV infection, cocultured macrophages express antiviral pro-inflammatory genes and induce the expression of IFN-stimulated genes in tumor cells. MV also increases the expression of HLA and costimulatory molecules on macrophages and their phagocytic activity. Finally, MV induces the secretion of inflammatory cytokines, especially IFN-I, and PD-L1 expression in tumor cells and macrophages. These results show that macrophages reduce viral proteins expression in some MPM cell lines through their IFN-I production and generate a pro-inflammatory interplay that may stimulate the patient's anti-tumor immune response.

Effects of different amosite preparations on macrophages, lung damages, and autoimmunity

The underlying mechanisms of asbestos-related autoimmunity are poorly understood. As the size, surface reactivity, and free radical activity of asbestos particles are considered crucial regarding the health effects, this study aims to compare the effects of exposure to pristine amosite (pAmo) or milled amosite (mAmo) particles on lung damage, autoimmunity, and macrophage phenotype. Four months after lung exposure to 0.1 mg of amosite, BAL levels of lactate dehydrogenase, protein, free DNA, CCL2, TGF-β1, TIMP-1, and immunoglobulin A of pAmo-exposed C57Bl/6 mice were increased when compared to fluids from control- and mAmo-exposed mice. Effects in pAmo-exposed mice were associated with lung fibrosis and autoimmunity including anti-double-strand DNA autoantibody production. mAmo or pAmo at 20 µg/cm2 induced a pro-inflammatory phenotype characterized by a significant increase in TNFα and IL-6 secretion on human monocyte-derived macrophages (MDMs). mAmo and pAmo exposure induced a decrease in the efferocytosis capacities of MDMs, whereas macrophage abilities to phagocyte fluorescent beads were unchanged when compared to control MDMs. mAmo induced IL-6 secretion and reduced the percentage of MDMs expressing MHCII and CD86 markers involved in antigen and T-lymphocyte stimulation. By contrast, pAmo but not mAmo activated the NLRP3 inflammasome, as evaluated through quantification of caspase-1 activity and IL-1β secretion. Our results demonstrated that long-term exposure to pAmo may induce significant lung damage and autoimmune effects, probably through an alteration of macrophage phenotype, supporting in vivo the higher toxicity of entire amosite (pAmo) with respect to grinded amosite. However, considering their impact on efferocytosis and co-stimulation markers, mAmo effects should not be neglected. KEY MESSAGES: Lung fibrosis and autoimmunity induced by amosite particles depend on their physicochemical characteristics (size and surface) Inhalation exposure of mice to pristine amosite fibers is associated with lung fibrosis and autoimmunity Anti-dsDNA antibody is a marker of autoimmunity in mice exposed to pristine amosite fibers Activation of lung mucosa-associated lymphoid tissue, characterized by IgA production, after exposure to pristine amosite fibers Pristine and milled amosite particle exposure reduced the efferocytosis capacity of human-derived macrophages.

Pulmonary Toxicity of Boron Nitride Nanomaterials Is Aspect Ratio Dependent

Boron nitride (BN) nanomaterials have drawn a lot of interest in the material science community. However, extensive research is still needed to thoroughly analyze their safety profiles. Herein, we investigated the pulmonary impact and clearance of two-dimensional hexagonal boron nitride (h-BN) nanosheets and boron nitride nanotubes (BNNTs) in mice. Animals were exposed by single oropharyngeal aspiration to h-BN or BNNTs. On days 1, 7, and 28, bronchoalveolar lavage (BAL) fluids and lungs were collected. On one hand, adverse effects on lungs were evaluated using various approaches (e.g., immune response, histopathology, tissue remodeling, and genotoxicity). On the other hand, material deposition and clearance from the lungs were assessed. Two-dimensional h-BN did not cause any significant immune response or lung damage, although the presence of materials was confirmed by Raman spectroscopy. In addition, the low aspect ratio h-BN nanosheets were internalized rapidly by phagocytic cells present in alveoli, resulting in efficient clearance from the lungs. In contrast, high aspect ratio BNNTs caused a strong and long-lasting inflammatory response, characterized by sustained inflammation up to 28 days after exposure and the activation of both innate and adaptive immunity. Moreover, the presence of granulomatous structures and an indication of ongoing fibrosis as well as DNA damage in the lung parenchyma were evidenced with these materials. Concurrently, BNNTs were identified in lung sections for up to 28 days, suggesting long-term biopersistence, as previously demonstrated for other high aspect ratio nanomaterials with poor lung clearance such as multiwalled carbon nanotubes (MWCNTs). Overall, we reveal the safer toxicological profile of BN-based two-dimensional nanosheets in comparison to their nanotube counterparts. We also report strong similarities between BNNTs and MWCNTs in lung response, emphasizing their high aspect ratio as a major driver of their toxicity.

Distinct Pro-Inflammatory Mechanisms Elicited by Short and Long Amosite Asbestos Fibers in Macrophages

While exposure to long amphibolic asbestos fibers (L > 10 µm) results in the development of severe diseases including inflammation, fibrosis, and mesothelioma, the pathogenic activity associated with short fibers (L < 5 µm) is less clear. By exposing murine macrophages to short (SFA) or long (LFA) fibers of amosite asbestos different in size and surface chemistry, we observed that SFA internalization resulted in pyroptotic-related immunogenic cell death (ICD) characterized by the release of the pro-inflammatory damage signal (DAMP) IL-1α after inflammasome activation and gasdermin D (GSDMD)-pore formation. In contrast, macrophage responses to non-internalizable LFA were associated with tumor necrosis factor alpha (TNF-α) release, caspase-3 and -7 activation, and apoptosis. SFA effects exclusively resulted from Toll-like receptor 4 (TLR4), a pattern-recognition receptor (PRR) recognized for its ability to sense particles, while the response to LFA was elicited by a multifactorial ignition system involving the macrophage receptor with collagenous structure (SR-A6 or MARCO), reactive oxygen species (ROS) cascade, and TLR4. Our findings indicate that asbestos fiber size and surface features play major roles in modulating ICD and inflammatory pathways. They also suggest that SFA are biologically reactive in vitro and, therefore, their inflammatory and toxic effects in vivo should not be underestimated.

Lung Persistence, Biodegradation, and Elimination of Graphene-Based Materials are Predominantly Size-Dependent and Mediated by Alveolar Phagocytes

Graphene-based materials (GBMs) have promising applications in various sectors, including pulmonary nanomedicine. Nevertheless, the influence of GBM physicochemical characteristics on their fate and impact in lung has not been thoroughly addressed. To fill this gap, the biological response, distribution, and bio-persistence of four different GBMs in mouse lungs up to 28 days after single oropharyngeal aspiration are investigated. None of the GBMs, varying in size (large versus small) and carbon to oxygen ratio as well as thickness (few-layers graphene (FLG) versus thin graphene oxide (GO)), induce a strong pulmonary immune response. However, recruited neutrophils internalize nanosheets better and degrade GBMs faster than macrophages, revealing their crucial role in the elimination of small GBMs. In contrast, large GO sheets induce more damages due to a hindered degradation and long-term persistence in macrophages. Overall, small dimensions appear to be a leading feature in the design of safe GBM pulmonary nanovectors due to an enhanced degradation in phagocytes and a faster clearance from the lungs for small GBMs. Thickness also plays an important role, since decreased material loading in alveolar phagocytes and faster elimination are found for FLGs compared to thinner GOs. These results are important for designing safer-by-design GBMs for biomedical application.

Transient, Implantable, Ultrathin Biofuel Cells Enabled by Laser-Induced Graphene and Gold Nanoparticles Composite

Transient power sources with excellent biocompatibility and bioresorablility have attracted significant attention. Here, we report high-performance, transient glucose enzymatic biofuel cells (TEBFCs) based on the laser-induced graphene (LIG)/gold nanoparticles (Au NPs) composite electrodes. Such LIG electrodes can be easily fabricated from polyimide (PI) with an infrared CO₂ laser and exhibit a low impedance (16 Ω). The resulted TEBFC yields a high open circuit potential (OCP) of 0.77 V and a maximum power density of 483.1 μW/cm². The TEBFC not only exhibits a quick response time that enables reaching the maximum OCP within 1 min but also owns a long lifetime over 28 days in vitro. The excellent biocompatibility and transient performance from in vitro and in vivo tests allow long-term implantation of TEBFCs in rats for energy harvesting. The TEBFCs with advanced processing methods provide a promising power solution for transient electronics.

Comparison of Metal-Based Nanoparticles and Nanowires: Solubility, Reactivity, Bioavailability and Cellular Toxicity

While the toxicity of metal-based nanoparticles (NP) has been investigated in an increasing number of studies, little is known about metal-based fibrous materials, so-called nanowires (NWs). Within the present study, the physico-chemical properties of particulate and fibrous nanomaterials based on Cu, CuO, Ni, and Ag as well as TiO₂ and CeO₂ NP were characterized and compared with respect to abiotic metal ion release in different physiologically relevant media as well as acellular reactivity. While none of the materials was soluble at neutral pH in artificial alveolar fluid (AAF), Cu, CuO, and Ni-based materials displayed distinct dissolution under the acidic conditions found in artificial lysosomal fluids (ALF and PSF). Subsequently, four different cell lines were applied to compare cytotoxicity as well as intracellular metal ion release in the cytoplasm and nucleus. Both cytotoxicity and bioavailability reflected the acellular dissolution rates in physiological lysosomal media (pH 4.5); only Ag-based materials showed no or very low acellular solubility, but pronounced intracellular bioavailability and cytotoxicity, leading to particularly high concentrations in the nucleus. In conclusion, in spite of some quantitative differences, the intracellular bioavailability as well as toxicity is mostly driven by the respective metal and is less modulated by the shape of the respective NP or NW.

Recent progress and perspectives on the mechanisms underlying Asbestos toxicity

Most cases of mesothelioma are known to result from exposure to asbestos fibers in the environment or occupational ambient air. The following questions regarding asbestos toxicity remain partially unanswered: (i) why asbestos entering the alveoli during respiration exerts toxicity in the pleura; and (ii) how asbestos causes mesothelioma, even though human mesothelial cells are easily killed upon exposure to asbestos. As for the latter question, it is now thought that the frustrated phagocytosis of asbestos fibers by macrophages prolongs inflammatory responses and gives rise to a “mutagenic microenvironment” around mesothelial cells, resulting in their malignant transformation. Based on epidemiological and genetic studies, a carcinogenic model has been proposed in which BRCA1-associated protein 1 mutations are able to suppress cell death in mesothelial cells and increase genomic instability in the mutagenic microenvironment. This leads to additional mutations, such as CDKN2A [p16], NF2, TP53, LATS2, and SETD2, which are associated with mesothelioma carcinogenesis. Regarding the former question, the receptors involved in the intracellular uptake of asbestos and the mechanism of transfer of inhaled asbestos from the alveoli to the pleura are yet to be elucidated. Further studies using live-cell imaging techniques will be critical to fully understanding the mechanisms underlying asbestos toxicity.

Uptake, intracellular dissolution, and cytotoxicity of silver nanowires in cell models

The uptake, intracellular dissolution, and cytotoxicity of silver nanowires (AgNWs) in two cell models (human keratinocytes - HaCaT cells and murine macrophages) were systemically investigated for the first time. Cellular uptake of AgNWs occurred mainly via pathways of clathrin-dependent endocytosis, caveolae-dependent endocytosis, and phagocytosis. AgNWs could be internalized by two types of cells with numerous lysosomal vesicles detected in close vicinity to AgNWs. Meanwhile, AgNWs exposure caused lysosomal permeabilization and release of cathepsisn B into cytoplasm. Furthermore, for the first time, this study found that AgNWs exposure inhibited the transmembrane ATP binding cassette (ABC) efflux transporter activity, which could make AgNWs as chemosensitizers to increase the toxicity of other xenobiotic pollutants. Toxicity assays evaluating reactive oxygen species production and mitochondrial activity indicated that cytotoxicity differed for different cell types and particles. The intracellular presence of AgNWs with different diameters induced similar toxic events but to different extents. AgNWs were absorbed by macrophages more efficiently than HaCaT cells, while AgNWs exhibited only marginal cytotoxicity towards macrophages compared to HaCaT cells. Using an Ag⁺ fluorescence probe, it was found that a fraction of AgNWs was dissolved inside the lysosomes. A higher amount of released Ag⁺ was detected in HaCaT cells than in macrophages, which might partially contribute to their higher cytotoxicity in HaCaT cells. The toxicity of AgNWs in HaCaT cells and macrophages is due to the high-aspect nature of the nanowires rather than the extracellular release of Ag⁺. This study may be useful for risk assessments of AgNWs in their practical applications in the biomedical field.

An integrated approach to testing and assessment of high aspect ratio nanomaterials and its application for grouping based on a common mesothelioma hazard

Here we describe the development of an Integrated Approach to Testing and Assessment (IATA) to support the grouping of different types (nanoforms; NFs) of High Aspect Ratio Nanomaterials (HARNs), based on their potential to cause mesothelioma. Hazards posed by the inhalation of HARNs are of particular concern as they exhibit physical characteristics similar to pathogenic asbestos fibres. The approach for grouping HARNs presented here is part of a framework to provide guidance and tools to group similar NFs and aims to reduce the need to assess toxicity on a case-by-case basis. The approach to grouping is hypothesis-driven, in which the hypothesis is based on scientific evidence linking critical physicochemical descriptors for NFs to defined fate/toxicokinetic and hazard outcomes. The HARN IATA prompts users to address relevant questions (at decision nodes; DNs) regarding the morphology, biopersistence and inflammatory potential of the HARNs under investigation to provide the necessary evidence to accept or reject the grouping hypothesis. Each DN in the IATA is addressed in a tiered manner, using data from simple in vitro or in silico methods in the lowest tier or from in vivo approaches in the highest tier. For these proposed methods we provide justification for the critical descriptors and thresholds that allow grouping decisions to be made. Application of the IATA allows the user to selectively identify HARNs which may pose a mesothelioma hazard, as demonstrated through a literature-based case study. By promoting the use of alternative, non-rodent approaches such as in silico modelling, in vitro and cell-free tests in the initial tiers, the IATA testing strategy streamlines information gathering at all stages of innovation through to regulatory risk assessment while reducing the ethical, time and economic burden of testing.

Direct Observations of Silver Nanowire-Induced Frustrated Phagocytosis among NR8383 Lung Alveolar Macrophages

The interaction of long nanowires and living cells is directly related to nanowires' nanotoxicity and health impacts. Interactions of silver nanowires (AgNWs) and macrophage cell lines (NR8383) were investigated using laser scanning confocal microscopy and single cell compression (SCC). With high-resolution imaging and mechanics measurement of individual cells, AgNW-induced frustrated phagocytosis was clearly captured in conjunction with structural and property changes of cells. While frustrated phagocytosis is known for long microwires and long carbon nanotubes, this work reports first direct observations of frustrated phagocytosis of AgNWs among living cells in situ. In the case of partial penetration of AgNWs into NR8383 cells, confocal imaging revealed actin participation at the entry sites, whose behavior differs from microwire-induced frustrated phagocytosis. The impacts of frustrated phagocytosis on the cellular membrane and cytoskeleton were also quantified by measuring the mechanical properties using SCC. Taken collectively, this study reveals the structural and property characteristics of nanowire-induced frustrated phagocytosis, which deepens our understanding of nanowire-cell interactions and nanocytotoxicity.

A review on nanotoxicity and nanogenotoxicity of different shapes of nanomaterials

Nanomaterials (NMs) generally display fascinating physical and chemical properties that are not always present in bulk materials; therefore, any modification to their size, shape, or coating tends to cause significant changes in their chemical/physical and biological characteristics. The dramatic increase in efforts to use NMs renders the risk assessment of their toxicity highly crucial due to the possible health perils of this relatively uncharted territory. The different sizes and shapes of the nanoparticles are known to have an impact on organisms and an important place in clinical applications. The shape of nanoparticles, namely, whether they are rods, wires, or spheres, is a particularly critical parameter to affect cell uptake and site-specific drug delivery, representing a significant factor in determining the potency and magnitude of the effect. This review, therefore, intends to offer a picture of research into the toxicity of different shapes (nanorods, nanowires, and nanospheres) of NMs to in vitro and in vivo models, presenting an in-depth analysis of health risks associated with exposure to such nanostructures and benefits achieved by using certain model organisms in genotoxicity testing. Nanotoxicity experiments use various models and tests, such as cell cultures, cores, shells, and coating materials. This review article also attempts to raise awareness about practical applications of NMs in different shapes in biology, to evaluate their potential genotoxicity, and to suggest approaches to explain underlying mechanisms of their toxicity and genotoxicity depending on nanoparticle shape.

Role of inflammation in the malignant transformation of pleural mesothelial cells induced by multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) are one of the most widely used types of novel nano-fiber materials. The aim of this study was to establish an experimental system based on actual exposure dosage and environments and explore the roles and mechanisms of inflammation in the malignant transformation of pleural mesothelial cells induced by MWCNTs after low doses and long-term exposure. Here, we established an in vitro system by co-culturing macrophages and mesothelial cells and exposing these cells to high aspect ratio MWCNTs (0.1 μg/mL) for three months. Results indicated that IL-1β, secreted by macrophages stimulated by MWCNTs, may significantly enhance the release of inflammatory cytokines, such as IL-8, TNF-α, and IL-6, from mesothelial cells. Results obtained from proliferation, migration, invasion, colony formation, and chromosomal aberration studies indicated that MWCNTs may promote malignant transformation of mesothelial cells after long-term and low-dose exposure via inflammation. Furthermore, the obtained results demonstrated that the NF-κB/IL-6/STAT3 pathway was active in the malignant transformation of Met 5A cells, induced by MWCNTs, and played an important role in the process. In conclusion, our results showed that the NF-κB (p65)/IL-6/STAT3 molecular pathway, which was mediated by inflammation, played an important role in the malignant transformation of pleural mesothelial cells induced by MWCNTs. These findings also provide novel ideas and references for the treatment of mesothelioma and offers options for the occupational safety of nanomaterial practitioners.

Adverse outcome pathways as a tool for the design of testing strategies to support the safety assessment of emerging advanced materials at the nanoscale

Toxicity testing and regulation of advanced materials at the nanoscale, i.e. nanosafety, is challenged by the growing number of nanomaterials and their property variants requiring assessment for potential human health impacts. The existing animal-reliant toxicity testing tools are onerous in terms of time and resources and are less and less in line with the international effort to reduce animal experiments. Thus, there is a need for faster, cheaper, sensitive and effective animal alternatives that are supported by mechanistic evidence. More importantly, there is an urgency for developing alternative testing strategies that help justify the strategic prioritization of testing or targeting the most apparent adverse outcomes, selection of specific endpoints and assays and identifying nanomaterials of high concern. The Adverse Outcome Pathway (AOP) framework is a systematic process that uses the available mechanistic information concerning a toxicological response and describes causal or mechanistic linkages between a molecular initiating event, a series of intermediate key events and the adverse outcome. The AOP framework provides pragmatic insights to promote the development of alternative testing strategies. This review will detail a brief overview of the AOP framework and its application to nanotoxicology, tools for developing AOPs and the role of toxicogenomics, and summarize various AOPs of relevance to inhalation toxicity of nanomaterials that are currently under various stages of development. The review also presents a network of AOPs derived from connecting all AOPs, which shows that several adverse outcomes induced by nanomaterials originate from a molecular initiating event that describes the interaction of nanomaterials with lung cells and involve similar intermediate key events. Finally, using the example of an established AOP for lung fibrosis, the review will discuss various in vitro tests available for assessing lung fibrosis and how the information can be used to support a tiered testing strategy for lung fibrosis. The AOPs and AOP network enable deeper understanding of mechanisms involved in inhalation toxicity of nanomaterials and provide a strategy for the development of alternative test methods for hazard and risk assessment of nanomaterials.

Measurement of Flexural Rigidity of Multi-Walled Carbon Nanotubes by Dynamic Scanning Electron Microscopy

In this work the flexural rigidity of individual large diameter multi-walled carbon nanotubes (MWCNTs) was investigated. The bending modulus were obtained by detecting the resonance frequencies of mechanically excited cantilevered carbon nanotubes using the so-called dynamic scanning electron microscopy technique, and applying the Euler–Bernoulli beam theory. For the nanotubes studied, we determined a modulus of up to 160 GPa. This agrees with values reported by other authors for MWCNTs produced by catalytic chemical vapor deposition, however, it is 6-8 times smaller than values reported for single and multi-walled carbon nanotubes produced by arc-discharge synthesis. Toxicological studies with carbon nanotubes have been showing that inhaled airborne nanofibers that reach the deep airways of the respiratory system may lead to serious, asbestos-like lung diseases. These studies suggested that their toxicity critically depends on the fiber flexural rigidity, with high rigidity causing cell lesions. To complement the correlation between observed toxicological effects and fiber rigidities, reliable and routinely applicable measurement techniques for the flexural rigidity of nanofibers are required.

Complex cytotoxicity mechanism of bundles formed from self-organised 1-D anodic TiO2 nanotubes layers

The present study reports on a comprehensive investigation of mechanisms of in vitro cytotoxicity of high aspect ratio (HAR) bundles formed from anodic TiO₂ nanotube (TNT) layers. Comparative cytotoxicity studies were performed using two types of HAR TNTs (diameter of ∼110 nm), differing in initial thickness of the nanotubular layer (∼35 μm for TNTs-1 vs. ∼10 μm for TNTs-2). Using two types of epithelial cell lines (MDA-MB-231, HEK-293), it was found that nanotoxicity is highly cell-type dependent and plausibly associates with higher membrane fluidity and decreased rigidity of cancer cells enabling penetration of TNTs to the cell membrane towards disruption of membrane integrity and reorganization of cytoskeletal network. Upon penetration, TNTs dysregulated redox homeostasis followed by DNA fragmentation and apoptotic/necrotic cell death. Both TNTs exhibited haemolytic activity and rapidly activated polarization of RAW 264.7 macrophages. Throughout the whole study, TNTs-2 possessing a lower aspect ratio manifested significantly higher cytotoxic effects. Taken together, this is the first report comprehensively investigating the mechanisms underlying the nanotoxicity of bundles formed from self-organised 1-D anodic TNT layers. Except for description of nanotoxicity of industrially-interesting nanomaterials, the delineation of the nanotoxicity paradigm in cancer cells could serve as solid basis for future efforts in rational engineering of TNTs towards selective anticancer nanomedicine.

Proinflammatory Effect of Carbon-Based Nanomaterials: In Vitro Study on Stimulation of Inflammasome NLRP3 via Destabilisation of Lysosomes

Carbon-based nanomaterials (C-BNM) have recently attracted an increased attention as the materials with potential applications in industry and medicine. Bioresistance and proinflammatory potential of C-BNM is the main obstacle for their medicinal application which was documented in vivo and in vitro. However, there are still limited data especially on graphene derivatives such as graphene platelets (GP). In this work, we compared multi-walled carbon nanotubes (MWCNT) and two different types of pristine GP in their potential to activate inflammasome NLRP3 (The nod-like receptor family pyrin domain containing 3) in vitro. Our study is focused on exposure of THP-1/THP1-null cells and peripheral blood monocytes to C-BNM as representative models of canonical and alternative pathways, respectively. Although all nanomaterials were extensively accumulated in the cytoplasm, increasing doses of all C-BNM did not lead to cell death. We observed direct activation of NLRP3 via destabilization of lysosomes and release of cathepsin B into cytoplasm only in the case of MWCNTs. Direct activation of NLRP3 by both GP was statistically insignificant but could be induced by synergic action with muramyl dipeptide (MDP), as a representative molecule of the family of pathogen-associated molecular patterns (PAMPs). This study demonstrates a possible proinflammatory potential of GP and MWCNT acting through NLRP3 activation.

Ultralong AgNWs-induced toxicity in A549 cells and the important roles of ROS and autophagy

Safety concerns have been raised with regard to silver nanowires (AgNWs) because of their extensive applications. Recently, ultralong AgNWs have shown physical properties superior to those of short AgNWs. However, little is known about their toxicity and potential risks. In this study, we demonstrated a series of ultralong AgNWs-induced biological effects in human lung cancer epithelial cells (A549). Ultralong AgNWs treatments induced ROS generation, mitochondria-mediated apoptosis, and self-protective autophagy at nonlethal concentrations. In contrast to some previous reports, apoptosis was found not to correlate with the reduction of intracellular ROS. Measuring the processing of ROS generation, apoptosis and autophagy, we demonstrated that ROS not only enhance mitochondrial damage, but also raise protective autophagic flux in ultralong AgNW-treated cells. Moreover, ultralong AgNWs were found to be internalized into the cytoplasm of the epithelial cells. This study not only investigates ultralong AgNWs-induced cytotoxicity but also pinpoints ROS as a key signal in mechanisms of their toxicity.

Length and diameter-dependent phagocytosis and cytotoxicity of long silver nanowires in macrophages

Long silver nanowires (AgNWs, >5 μm) have shown promising applications in next generation biomaterials. However, the toxicity of long AgNWs is not well characterized in terms of their size. In this study, five AgNWs types, including SAgNW30 (length: 5-10 μm; diameter: 30 nm), MAgNW30 (length: 20-30 μm; diameter: 30 nm), LAgNW30 (length: ∼100 μm; diameter: 30 nm), LAgNW50 (length: ∼100 μm; diameter: 50 nm), and LAgNW100 (length: ∼100 μm; diameter: 100 nm), were used to investigate the size-dependent phagocytosis and cytotoxicity in macrophage. It showed that SAgNW30, MAgNW30, LAgNW30 can be fully phagocytosed by macrophages, but LAgNW50 and LAgNW100 frustrated the phagocytosis. It demonstrated that LAgNW30 can be internalized into macrophage in a curly manner. The size-dependent cytotoxicity was observed in cell viability, apoptosis, mitochondrial damage, phenotypic transition, and inflammatory response in AgNWs-treated macrophage. The AgNWs-induced cytotoxicity was depended on their length and diameter, increased gradually in the order of SAgNW30 > MAgNW30 > LAgNW30 > LAgNW50 > LAgNW100. The findings presented here will assist in the evaluation of the size-dependent cytotoxicity mediated by long AgNWs.

Iron-Based Core-Shell Nanowires for Combinatorial Drug Delivery and Photothermal and Magnetic Therapy

Combining different therapies into a single nanomaterial platform is a promising approach for achieving more efficient, less invasive, and personalized treatments. Here, we report on the development of such a platform by utilizing nanowires with an iron core and iron oxide shell as drug carriers and exploiting their optical and magnetic properties. The iron core has a large magnetization, which provides the foundation for low-power magnetic manipulation and magnetomechanical treatment. The iron oxide shell enables functionalization with doxorubicin through a pH-sensitive linker, providing selective intracellular drug delivery. Combined, the core-shell nanostructure features an enhanced light-matter interaction in the near-infrared region, resulting in a high photothermal conversion efficiency of >80% for effective photothermal treatment. Applied to cancer cells, the collective effect of the three modalities results in an extremely efficient treatment with nearly complete cell death (∼90%). In combination with the possibility of guidance and detection, this platform provides powerful tools for the development of advanced treatments.

Surface area- and mass-based comparison of fine and ultrafine nickel oxide lung toxicity and augmentation of allergic response in an ovalbumin asthma model

Background: The correlation of physico-chemical properties with mechanisms of toxicity has been proposed as an approach to predict the toxic potential of the vast number of emerging nanomaterials. Although relationships have been established between properties and the acute pulmonary inflammation induced by nanomaterials, properties' effects on other responses, such as exacerbation of respiratory allergy, have been less frequently explored.Methods: In this study, the role of nickel oxide (NiO) physico-chemical properties in the modulation of ovalbumin (OVA) allergy was examined in a murine model. Results: 181 nm fine (NiO-F) and 42 nm ultrafine (NiO-UF) particles were characterized and incorporated into a time course study where measured markers of pulmonary injury and inflammation were associated with NiO particle surface area. In the OVA model, exposure to NiO, irrespective of any metric was associated with elevated circulating total IgE levels. Serum and lung cytokine levels were similar with respect to NiO surface area. The lower surface area was associated with an enhanced Th2 profile, whereas the higher surface area was associated with a Th1-dominant profile. Surface area-normalized groups also exhibited similar alterations in OVA-specific IgE levels and lung neutrophil number. However, lung eosinophil number and allergen challenge-induced alterations in lung function related more to particle size, wherein NiO-F was associated with an increased enhanced pause response and NiO-UF was associated with increased lung eosinophil burden.Conclusions: Collectively, these findings suggest that although NiO surface area correlates best with acute pulmonary injury and inflammation following respiratory exposure, other physico-chemical properties may contribute to the modulation of immune responses in the lung.

Crumpling of silver nanowires by endolysosomes strongly reduces toxicity

Fibrous particles interact with cells and organisms in complex ways that can lead to cellular dysfunction, cell death, inflammation, and disease. The development of conductive transparent networks (CTNs) composed of metallic silver nanowires (AgNWs) for flexible touchscreen displays raises new possibilities for the intimate contact between novel fibers and human skin. Here, we report that a material property, nanowire-bending stiffness that is a function of diameter, controls the cytotoxicity of AgNWs to nonimmune cells from humans, mice, and fish without deterioration of critical CTN performance parameters: electrical conductivity and optical transparency. Both 30- and 90-nm-diameter AgNWs are readily internalized by cells, but thinner NWs are mechanically crumpled by the forces imposed during or after endocytosis, while thicker nanowires puncture the enclosing membrane and release silver ions and lysosomal contents to the cytoplasm, thereby initiating oxidative stress. This finding extends the fiber pathology paradigm and will enable the manufacture of safer products incorporating AgNWs.

Live-cell imaging of macrophage phagocytosis of asbestos fibers under fluorescence microscopy

Background

Frustrated phagocytosis occurs when an asbestos fiber > 10 μm in length is engulfed imperfectly by a macrophage, and it is believed to be associated with chromosomal instability. Few studies have focused on dynamic cellular imaging to assess the toxicity of hazardous inorganic materials such as asbestos. One reason for this is the relative lack of fluorescent probes available to facilitate experimental visualization of inorganic materials. We recently developed asbestos-specific fluorescent probes based on asbestos-binding proteins, and achieved efficient fluorescent labeling of asbestos.

Results

Live-cell imaging with fluorescent asbestos probes was successfully utilized to dynamically analyze asbestos phagocytosis. The fluorescently labeled asbestos fibers were phagocytosed by RAW 264.7 macrophages. Internalized fibers of < 5 μm in length were visualized clearly via overlaid phase contrast and fluorescence microscopy images, but they were not clearly depicted using phase contrast images alone. Approximately 60% of the cells had phagocytosed asbestos fibers after 2 h, but over 96% of cells remained alive even 24 h after the addition of asbestos fibers. Immediate cell death was only observed when an asbestos fiber was physically pulled from a cell by an external force. Notably, at 24 h after the addition of asbestos fibers an approximately 4-fold increase in the number of binucleated cells was observed. Monitoring of individual cell divisions of cells that had phagocytosed asbestos suggested that binucleated cells were formed via the inhibition of cell separation, by asbestos fibers of > 10 μm in length that were localized in the proximity of the intercellular bridge.

Conclusions

Fluorescently labeled asbestos facilitated visualization of the dynamic biological processes that occur during and after the internalization of asbestos fibers, and indicated that (i) frustrated phagocytosis itself does not lead to immediate cell death unless the asbestos fiber is physically pulled from the cell by an external force, and (ii) macrophages that have phagocytosed asbestos can divide but sometimes the resulting daughter cells fuse, leading to the formation of a binucleated cell. This fusion only seemed to occur when a comparatively long asbestos fiber (> 10 μm) was shared by two daughter cells.

In vitro exposure of a 3D-tetraculture representative for the alveolar barrier at the air-liquid interface to silver particles and nanowires

BACKGROUND

The present study aimed to evaluate the potential differences in the biological effects of two types of spherical silver particles of 20 and 200 nm (Ag20 and Ag200), and of PVP-coated silver nanowires (AgNWs) with a diameter of 50 nm and length up to 50 μm, using a complex 3D model representative for the alveolar barrier cultured at air-liquid interface (ALI). The alveolar model was exposed to 0.05, 0.5 and 5 μg/cm2 of test compounds at ALI using a state-of-the-art exposure system (Vitrocell™Cloud System). Endpoints related to the oxidative stress induction, anti-oxidant defence mechanisms, pro-inflammatory responses and cellular death were selected to evaluate the biocompatibility of silver particles and nanowires (AgNMs) and to further ascribe particular biological effects to the different morphologic properties between the three types of AgNMs evaluated.

RESULTS

Significant cytotoxic effect was observed for all three types of AgNMs at the highest tested doses. The increased mRNA levels of the pro-apoptotic gene CASP7 suggests that apoptosis may occur after exposure to AgNWs. All three types of AgNMs increased the mRNA level of the anti-oxidant enzyme HMOX-1 and of the metal-binding anti-oxidant metallothioneins (MTs), with AgNWs being the most potent inducer. Even though all types of AgNMs induced the nuclear translocation of NF-kB, only AgNWs increased the mRNA level of pro-inflammatory mediators. The pro-inflammatory response elicited by AgNWs was further confirmed by the increased secretion of the 10 evaluated interleukins.

CONCLUSION

In the current study, we demonstrated that the direct exposure of a complex tetra-culture alveolar model to different types of AgNMs at ALI induces shape- and size-specific biological responses. From the three AgNMs tested, AgNWs were the most potent in inducing biological alterations. Starting from 50 ng/cm2, a dose representative for an acute exposure in a high exposure occupational setting, AgNWs induced prominent changes indicative for a pro-inflammatory response. Even though the acute responses towards a dose representative for a full-lifetime exposure were also evaluated, chronic exposure scenarios at low dose are still unquestionably needed to reveal the human health impact of AgNMs during realistic conditions.

Sidewall contact regulating the nanorod packing inside vesicles with relative volumes

Intracellular packing of one-dimensional and rodlike materials plays an important role in many biological processes such as cell mimicking, microtubule protrusion, cell division, frustrated phagocytosis, and pathogenicity. To understand the mechanical interplay between cells/intracellular membranous organelles and encapsulated rodlike materials, we perform theoretical analyses to investigate how the morphologies and mechanical behaviors of lipid vesicles of given relative volumes are regulated by encapsulated rigid nanorods of finite diameters and selected geometries, including a cylindrical nanorod, a nanorod with one widened end, and a cone-shaped nanorod. The contact between the vesicle protrusion and the sidewall of the rod, neglected in most theoretical studies, is shown to play an important role in regulating vesicle tubulation, membrane tension, and axial contact force on the nanorod. As the nanorod length increases, the confining vesicle evolves from a prolate into different shapes, such as a lemon, a conga drum, a cherry, and a bowling pin, depending on the radical size of the nanorod and the relative vesicle volume. The corresponding morphological phase diagrams are determined. Moreover, phase diagrams of the buckling of the encapsulated nanorods are determined based on the classical Euler buckling theory. It is shown that there exists an optimal filament number at which the encapsulated weakly cross-linked filament bundle maintains the largest length in a mechanically stable state. Similarities and differences between the nanorod packing in vesicles at a given pressure difference and a relative volume are discussed. Our results provide valuable insight into the biophysics underlying cell interactions with one-dimensional and rodlike materials.

Mast Cells Respond to Candida albicans Infections and Modulate Macrophages Phagocytosis of the Fungus

Mast cells (MCs) are long-lived immune cells widely distributed at mucosal surfaces and are among the first immune cell type that can get in contact with the external environment. This study aims to unravel the mechanisms of reciprocal influence between mucosal MCs and Candida albicans as commensal/opportunistic pathogen species in humans. Stimulation of bone marrow-derived mast cells (BMMCs) with live forms of C. albicans induced the release of TNF-α, IL-6, IL-13, and IL-4. Quite interestingly, BMMCs were able to engulf C. albicans hyphae, rearranging their α-tubulin cytoskeleton and accumulating LAMP1+ vesicles at the phagocytic synapse with the fungus. Candida-infected MCs increased macrophage crawling ability and promoted their chemotaxis against the infection. On the other side, resting MCs inhibited macrophage phagocytosis of C. albicans in a contact-dependent manner. Taken together, these results indicate that MCs play a key role in the maintenance of the equilibrium between the host and the commensal fungus C. albicans, limiting pathological fungal growth and modulating the response of resident macrophages during infections.

Threshold Rigidity Values for the Asbestos-like Pathogenicity of High-Aspect-Ratio Carbon Nanotubes in a Mouse Pleural Inflammation Model

The qualitative and quantitative evaluation of the physicochemical parameters associated with the pathogenicity of high-aspect-ratio nanomaterials is important for comprehensive regulation efforts and safety-by-design approaches. Here, we report quantitative data on the correlations between the rigidity of these nanomaterials and toxicity endpoints in vitro and in vivo. As measured by new ISO standards published in 2017, rigidity shows a strong positive correlation with inflammogenic potential, as indicated by inflammatory cell counts and IL-1β (a biomarker for frustrated phagocytosis) levels in both the acute and chronic phases. In vitro experiments using differentiated THP-1 cells find that only highly rigid multiwalled carbon nanotubes (MWCNTs) and asbestos fibers lead to piercing and frustrated phagocytosis. Thus, this study suggests a bending ratio of 0.97 and a static bending persistence length of 1.08 as threshold rigidity values for asbestos-like pathogenicity. However, additional research using MWCNTs with rigidity values that lie between those of non-inflammogenic ( D_b = 0.66 and SBPL = 0.87) and inflammogenic fibers ( D_b = 0.97 and SBPL = 1.09) is required to identify more accurate threshold values, which would be useful for comprehensive regulation and safety-by-design approaches based on MWCNTs.

In vitro immunotoxicological assessment of a potent microbicidal nanocomposite based on graphene oxide and silver nanoparticles

Graphene oxide (GO) and silver nanoparticles (AgNPs) can be formed into a hybrid nanomaterial, known as GOAg nanocomposite, which presents high antibacterial activity. The successful translation of this nanomaterial into medical use depends on critical information about its toxicological profile. In keeping with a Safe-by-design approach, we evaluated the immunotoxicity of GOAg using J774 and primary murine macrophages. The interaction between GOAg and macrophages was investigated with a scanning electron microscope (SEM). High-throughput technologies were employed to evaluate cell viability, apoptosis/necrosis, mitochondrial depolarization and lipid peroxidation. The inflammogenicity of nanomaterials was predicted after quantification of the cytokines IL-1β, TNF-α and IL-10 before and after stimulation with interferon-γ (IFN-γ). The ratio between CD80 and CD206 macrophage populations were also estimated. In addition, the production of nitric oxide (NO) was investigated. SEM surveys revealed the potential of GOAg to induce frustrated phagocytosis. GOAg induced a dose-dependent mitochondrial depolarization, apoptosis and lipid peroxidation to J774 macrophages. GOAg toxicity was not modified in an inflammatory microenvironment, but its toxicity was within the range of concentrations used in bacterial inactivation. GOAg did not induce primary macrophages to significantly produce inflammatory cytokines, and previous macrophage stimulation did not enhance GOAg inflammogenicity. Additionally, the pristine nanomaterials and GOAg do not shift macrophages polarization towards M1. Sublethal concentrations of GOAg did not impair macrophages NO production. Finally, we suggest options for improvement of GOAg nanocomposite in ways that may help minimize its possible adverse outcomes to human health.

In Vitro Dermal Safety Assessment of Silver Nanowires after Acute Exposure: Tissue vs. Cell Models

Silver nanowires (AgNW) are attractive materials that are anticipated to be incorporated into numerous consumer products such as textiles, touchscreen display, and medical devices that could be in direct contact with skin. There are very few studies on the cellular toxicity of AgNW and no studies that have specifically evaluated the potential toxicity from dermal exposure. To address this question, we investigated the dermal toxicity after acute exposure of polymer-coated AgNW with two sizes using two models, human primary keratinocytes and human reconstructed epidermis. In keratinocytes, AgNW are rapidly and massively internalized inside cells leading to dose-dependent cytotoxicity that was not due to Ag⁺ release. Analysing our data with different dose metrics, we propose that the number of NW is the most appropriate dose-metric for studies of AgNW toxicity. In reconstructed epidermis, the results of a standard in vitro skin irritation assay classified AgNW as non-irritant to skin and we found no evidence of penetration into the deeper layer of the epidermis. The findings show that healthy and intact epidermis provides an effective barrier for AgNW, although the study does not address potential transport through follicles or injured skin. The combined cell and tissue model approach used here is likely to provide an important methodology for assessing the risks for skin exposure to AgNW from consumer products.

Carbon Nanotubes and Other Engineered Nanoparticles Induced Pathophysiology on Mesothelial Cells and Mesothelial Membranes

Nanoparticles have great potential for numerous applications due to their unique physicochemical properties. However, concerns have been raised that they may induce deleterious effects on biological systems. There is accumulating evidence that, like asbestos, inhaled nanomaterials of >5 μm and high aspect ratio (3:1), particularly rod-like carbon nanotubes, may inflict pleural disease including mesothelioma. Additionally, a recent set of case reports suggests that inhalation of polyacrylate/nanosilica could in part be associated with inflammation and fibrosis of the pleura of factory workers. However, the adverse outcomes of nanoparticle exposure to mesothelial tissues are still largely unexplored. In that context, the present review aims to provide an overview of the relevant pathophysiological implications involving toxicological studies describing effects of engineered nanoparticles on mesothelial cells and membranes. In vitro studies primarily emphasize on simulating cellular uptake and toxicity of nanotubes on benign or malignant cell lines. On the other hand, in vivo studies focus on illustrating endpoints of serosal pathology in rodent animal models. From a molecular aspect, some nanoparticle categories are shown to be cytotoxic and genotoxic after acute treatment, whereas chronic incubation may lead to malignant-like transformation. At an organism level, a number of fibrous shaped nanotubes are related with features of chronic inflammation and MWCNT-7 is the only type to consistently inflict mesothelioma.

Nanoparticle-induced inflammation can increase tumor malignancy

Nanomaterials, such as aluminum oxide, have been regarded with high biomedical promise as potential immune adjuvants in favor of their bulk counterparts. For pathophysiological conditions where elevated immune activity already occurs, the contribution of nanoparticle-activated immune reactions remains unclear. Here, we investigated the effect of spherical and wire-shaped aluminum oxide nanoparticles on primary splenocytes and observed a clear pro-inflammatory effect of both nanoparticles, mainly for the high aspect ratio nanowires. The nanoparticles resulted in a clear activation of NLRP3 inflammasome, and also secreted transforming growth factor β. When cancer cells were exposed to these cytokines, this resulted in an increased level of epithelial-to-mesenchymal-transition, a hallmark for cancer metastasis, which did not occur when the cancer cells were directly exposed to the nanoparticles themselves. Using a syngeneic tumor model, the level of inflammation and degree of lung metastasis were significantly increased when the animals were exposed to the nanoparticles, particularly for the nanowires. This effect could be abrogated by treating the animals with inflammatory inhibitors. Collectively, these data indicate that the interaction of nanoparticles with immune cells can have secondary effects that may aggravate pathophysiological conditions, such as cancer malignancy, and conditions must be carefully selected to finely tune the induced aspecific inflammation into cancer-specific antitumor immunity.

STATEMENT OF SIGNIFICANCE

Many different types of nanoparticles have been shown to possess immunomodulatory properties, depending on their physicochemical parameters. This can potentially be harnessed as a possible antitumor therapy. However, in the current work we show that inflammation elicited by nanomaterials can have grave effects in pathophysiological conditions, where non-specific inflammation was found to increase cancer cell mobility and tumor malignancy. These data show that immunomodulatory properties of nanomaterials must be carefully controlled to avoid any undesired side-effects.

Direct comparison between in vivo and in vitro microsized particle phagocytosis assays in Drosophila melanogaster

The effects of micro and nanoparticles on the innate immune system have been widely investigated and a general lack of agreement between in vivo and in vitro assays has been observed. In order to determine the origin of these discrepancies, there is a need for comparing the results of in vivo and in vitro phagocytosis assays obtained using the same particles and same immune cells. Here, we establish an in vivo polystyrene microsized particle phagocytosis assay in Drosophila melanogaster and compare it with an in vitro assay consisting of exposing the same immune cells in culture to the same particles. The distribution of number of phagocytized beads per cell was shifted to lower numbers of beads per cell in the case of the in vitro assay compared to the in vivo assay, which we suggest is partly due to a reduced amount of membrane available in cultured cells.

Impact of biopersistent fibrous dusts on glycolysis, glutaminolysis and serine metabolism in A549 cells

The conversion rates of different metabolic pathways summarized as a metabolic signature mirror the physiological functions and the general physiological status of a cell. The present study compared the impact of crocidolite and chrysotile asbestos, glass fibers and multi‑walled carbon nanotubes (MWCN) of two different lengths (1‑2 µm and 5‑15 µm) on the conversion rates in glycolysis, glutaminolysis and serine metabolism of A549 cells. The concentration tested was 1 µg/cm2 for all fibers. A concentration of 5 µg/cm2 was additionally used for chrysotile and crocidolite, and 25 µg/cm2 for glass fibers and MWCN. With respect to the inhibitory effect on cell proliferation and the extent of metabolic alterations, the present study revealed the following ranking among the fibers tested: Chrysotile>crocidolite>glass fibers>MWCN 5‑15 µm>MWCN 1‑2 µm. For the asbestos and glass fibers this ranking correlated best with the number of fibers. It appeared that the results observed for MWCN did not match this correlation. However, electron microscopy revealed an agglomeration of MWCN. The agglomeration decreased the toxicologically relevant number of fibers by forming larger particle‑like shapes and explained the smaller effects of MWCN 5‑15 µm and 1‑2 µm on cell proliferation and metabolism.

Silver Nanowire Particle Reactivity with Human Monocyte-Derived Macrophage Cells: Intracellular Availability of Silver Governs Their Cytotoxicity

Silver nanowires (AgNWs) are increasingly being used in the production of optoelectronic devices, with manufacturing processes posing a risk for occupational exposures via inhalation. Although some studies have explored the environmental effects of AgNWs, few data exist on human health effects. Alveolar macrophages are central in the clearance of inhaled fibers from the lungs, with frustrated phagocytosis often stated as a key determinant for the onset of inflammatory reactions. However, the mechanisms through which fully ingested AgNWs interact with, degrade, and transform within primary macrophages over time, and whether the reactivity of the AgNWs arises due to ionic or particulate effects, or both, are poorly understood. Here, a combination of elemental quantification, 3D tomography, analytical transmission electron microscopy (TEM), and confocal microscopy were employed to monitor the uptake, intracellular Ag⁺ availability, and processing of AgNWs of two different lengths (1 and 10 μm) inside human monocyte-derived macrophages (HMMs). Using AgNO₃ and spherical silver nanoparticles (AgNPs) as a comparison, the amount of total bioavailable/intracellular Ag highly correlated to the cytotoxicity of AgNWs. The 10 μm AgNWs were completely internalized in HMMs, with numerous lysosomal vesicles observed in close vicinity to the AgNWs. Following cellular uptake, AgNWs dissolved and transformed intracellularly, with precipitation of AgCl as well as Ag₂S. These transformation processes were likely due to AgNW degradation in the acidic environment of lysosomes, leading to the release of Ag⁺ ions that rapidly react with Cl^- and SH^- species of the cell microenvironment. Our data suggest that, in HMMs, not only frustrated phagocytosis but also the extent of intracellular uptake and dissolution of AgNWs dictates their cytotoxicity.

Effects of silver nanowire length and exposure route on cytotoxicity to earthworms

To accurately evaluate the environmental toxicity of silver nanowires (AgNWs), it is necessary to characterize how the cytotoxicity of these nanomaterials is affected by the route of exposure. However, few studies have addressed the exposure route or mechanism of toxicity of nanomaterials, particularly of nanowires, in living organisms. In this study, we therefore analyzed the main exposure route of AgNWs in vitro, using earthworms (Eisenia andrei) as a model system, via flow cytometry. We subsequently examined the in vivo toxicity of AgNWs to earthworms in soil. These tests revealed that intracellular esterase activity was correlated with adsorption of the nanowires to the surfaces of coelomocytes in vitro, and that in vivo cytotoxicity resulted mainly from oral, rather than dermal, exposure to the nanowires. Overall, shorter AgNWs (10 μm) were more toxic than longer AgNWs (20 μm). To our knowledge, this study is the first report regarding the ecotoxicity of nanowires to earthworms in soil. Our findings provide important information to help assess the risk of toxic AgNW contamination of soil ecosystems.

Inactivation, Clearance, and Functional Effects of Lung-Instilled Short and Long Silver Nanowires in Rats

There is a potential for silver nanowires (AgNWs) to be inhaled, but there is little information on their health effects and their chemical transformation inside the lungs in vivo. We studied the effects of short (S-AgNWs; 1.5 μm) and long (L-AgNWs; 10 μm) nanowires instilled into the lungs of Sprague-Dawley rats. S- and L-AgNWs were phagocytosed and degraded by macrophages; there was no frustrated phagocytosis. Interestingly, both AgNWs were internalized in alveolar epithelial cells, with precipitation of Ag₂S on their surface as secondary Ag₂S nanoparticles. Quantitative serial block face three-dimensional scanning electron microscopy showed a small, but significant, reduction of NW lengths inside alveolar epithelial cells. AgNWs were also present in the lung subpleural space where L-AgNWs exposure resulted in more Ag+ve macrophages situated within the pleura and subpleural alveoli, compared with the S-AgNWs exposure. For both AgNWs, there was lung inflammation at day 1, disappearing by day 21, but in bronchoalveolar lavage fluid (BALF), L-AgNWs caused a delayed neutrophilic and macrophagic inflammation, while S-AgNWs caused only acute transient neutrophilia. Surfactant protein D (SP-D) levels in BALF increased after S- and L-AgNWs exposure at day 7. L-AgNWs induced MIP-1α and S-AgNWs induced IL-18 at day 1. Large airway bronchial responsiveness to acetylcholine increased following L-AgNWs, but not S-AgNWs, exposure. The attenuated response to AgNW instillation may be due to silver inactivation after precipitation of Ag₂S with limited dissolution. Our findings have important consequences for the safety of silver-based technologies to human health.

In vivo toxicological assessment of electrochemically engineered anodic alumina nanotubes: a study of biodistribution, subcutaneous implantation and intravenous injection

Electrochemically engineered anodic alumina nanotubes (AANTs) have recently shown good in vitro biocompatibility. However, in vivo toxicological and pathological studies are required to clarify the bio-safety of this novel nanomaterial. Herein, we present a pioneering pilot toxicity study on AANTs in immune-competent murine models (Balb/c mice, 8 weeks). AANTs were administered by intravenous (IV) injection and subcutaneous (SC) implantation routes considering the future toxicological implications associated with this nanomaterial for potential biomedical applications. AANTs, 736 nm long and 90 nm in outer diameter, were chosen as a nanomaterial model. We demonstrate that IV injected AANTs do not have any effect on the mortality or body weight of these animal models within 28 days at three different doses (20, 50, 100 mg kg^-1). The biodistribution of AANTs characterized by fluorescence imaging and inductively coupled plasma revealed the accumulation of AANTs in the liver and spleen after IV injection. When AANTs were injected intravenously, the highest dose of 100 mg kg^-1 caused moderate hepatotoxicity, identified by histopathological analysis. The implantation of AANTs subcutaneously and directly under the skin leads to an inflammatory response, which is a typical foreign body reaction. Taken together, this work provides new insights into the toxicity patterns of new nanomaterials such as AANTs and establishes a rationale for the design of functional AANTs for future biomedical applications.

Anodically Grown Titania Nanotube Induced Cytotoxicity has Genotoxic Origins

Nanoarchitectures of titania (TiO₂) have been widely investigated for a number of medical applications including implants and drug delivery. Although titania is extensively used in the food, drug and cosmetic industries, biocompatibility of nanoscale titania is still under careful scrutiny due to the conflicting reports on its interaction with cellular matter. For an accurate insight, we performed in vitro studies on the response of human dermal fibroblast cells toward pristine titania nanotubes fabricated by anodic oxidation. The nanotubes at low concentrations were seen to induce toxicity to the cells, whereas at higher concentrations the cell vitality remained on par with controls. Further investigations revealed an increase in the G₀ phase cell population depicting that majority of cells were in the resting rather than active phase. Though the mitochondrial set-up did not exhibit any signs of stress, significantly enhanced reactive oxygen species production in the nuclear compartment was noted. The TiO₂ nanotubes were believed to have gained access to the nuclear machinery and caused increased stress leading to genotoxicity. This interesting property of the nanotubes could be utilized to kill cancer cells, especially if the nanotubes are functionalized for a specific target, thus eliminating the need for any chemotherapeutic agents.

Quantitative analysis of the role of fiber length on phagocytosis and inflammatory response by alveolar macrophages

BACKGROUND

In the lung, macrophages attempt to engulf inhaled high aspect ratio pathogenic materials, secreting inflammatory molecules in the process. The inability of macrophages to remove these materials leads to chronic inflammation and disease. How the biophysical and biochemical mechanisms of these effects are influenced by fiber length remains undetermined. This study evaluates the role of fiber length on phagocytosis and molecular inflammatory responses to non-cytotoxic fibers, enabling development of quantitative length-based models.

METHODS

Murine alveolar macrophages were exposed to short and long populations of JM-100 glass fibers, produced by successive sedimentation and repeated crushing, respectively. Interactions between fibers and macrophages were observed using time-lapse video microscopy, and quantified by flow cytometry. Inflammatory biomolecules (TNF-α, IL-1α, COX-2, PGE2) were measured.

RESULTS

Uptake of short fibers occurred more readily than for long, but long fibers were more potent stimulators of inflammatory molecules. Stimulation resulted in dose-dependent secretion of inflammatory biomolecules but no cytotoxicity or strong ROS production. Linear cytokine dose-response curves evaluated with length-dependent potency models, using measured fiber length distributions, resulted in identification of critical fiber lengths that cause frustrated phagocytosis and increased inflammatory biomolecule production.

CONCLUSION

Short fibers played a minor role in the inflammatory response compared to long fibers. The critical lengths at which frustrated phagocytosis occurs can be quantified by fitting dose-response curves to fiber distribution data.

GENERAL SIGNIFICANCE

The single physical parameter of length can be used to directly assess the contributions of length against other physicochemical fiber properties to disease endpoints.

Cellular uptake and dynamics of unlabeled freestanding silicon nanowires

The ability to seamlessly merge electronic devices with biological systems at the cellular length scale is an exciting prospect for exploring new fundamental cell biology and in designing next-generation therapeutic devices. Semiconductor nanowires are well suited for achieving this goal because of their intrinsic size and wide range of possible configurations. However, current studies have focused primarily on delivering substrate-bound nanowire devices through mechanical abrasion or electroporation, with these bulkier substrates negating many of the inherent benefits of using nanoscale materials. To improve on this, an important next step is learning how to distribute these devices in a drug-like fashion, where cells can naturally uptake and incorporate these electronic components, allowing for truly noninvasive device integration. We show that silicon nanowires (SiNWs) can potentially be used as such a system, demonstrating that label-free SiNWs can be internalized in multiple cell lines (96% uptake rate), undergoing an active "burst-like" transport process. Our results show that, rather than through exogenous manipulation, SiNWs are internalized primarily through an endogenous phagocytosis pathway, allowing cellular integration of these materials. To study this behavior, we have developed a robust set of methodologies for quantitatively examining high-aspect ratio nanowire-cell interactions in a time-dependent manner on both single-cell and ensemble levels. This approach represents one of the first dynamic studies of semiconductor nanowire internalization and offers valuable insight into designing devices for biomolecule delivery, intracellular sensing, and photoresponsive therapies.

Effect of pulmonary surfactant on the dissolution, stability and uptake of zinc oxide nanowires by human respiratory epithelial cells

Inhaled nanoparticles (NPs) have high-deposition rates in the alveolar region of the lung but the effects of pulmonary surfactant (PS) on nanoparticle bioreactivity are unclear. Here, the impact of PS on the stability and dissolution of ZnO nanowires (ZnONWs) was investigated, and linked with their bioreactivity in vitro with human alveolar epithelial type 1-like cells (TT1). Pre-incubation of ZnONWs with Curosurf® (a natural porcine PS) decreased their dissolution at acidic pH, through the formation of a phospholipid corona. Confocal live cell microscopy confirmed that Curosurf® lowered intracellular dissolution, thus delaying the onset of cell death compared to bare ZnONWs. Despite reducing dissolution, Curosurf® significantly increased the uptake of ZnONWs within TT1 cells, ultimately increasing their toxicity after 24 h. Although serum improved ZnONW dispersion in suspension similar to Curosurf®, it had no effect on ZnONW internalization and toxicity, indicating a unique role of PS in promoting particle uptake. In the absence of PS, ZnONW length had no effect on dissolution kinetics or degree of cellular toxicity, indicating a less important role of length in determining ZnONW bioreactivity. This work provides unique findings on the effects of PS on the stability and toxicity of ZnONWs, which could be important in the study of pulmonary toxicity and epithelial-endothelial translocation of nanoparticles in general.

Approaches to Develop Alternative Testing Strategies to Inform Human Health Risk Assessment of Nanomaterials

The development of alternative testing strategies (ATS) for hazard assessment of new and emerging materials is high on the agenda of scientists, funders, and regulators. The relatively large number of nanomaterials on the market and under development means that an increasing emphasis will be placed on the use of reliable, predictive ATS when assessing their safety. We have provided recommendations as to how ATS development for assessment of nanomaterial hazard may be accelerated. Predefined search terms were used to identify the quantity and distribution of peer-reviewed publications for nanomaterial hazard assessment following inhalation, ingestion, or dermal absorption. A summary of knowledge gaps relating to nanomaterial hazard is provided to identify future research priorities and areas in which a rich data set might exist to allow ATS identification. Consultation with stakeholders (e.g., academia, industry, regulators) was critical to ensure that current expert opinion was reflected. The gap analysis revealed an abundance of studies that assessed the local and systemic impacts of inhaled particles, and so ATS are available for immediate use. Development of ATS for assessment of the dermal toxicity of chemicals is already relatively advanced, and these models should be applied to nanomaterials as relatively few studies have assessed the dermal toxicity of nanomaterials to date. Limited studies have investigated the local and systemic impacts of ingested nanomaterials. If the recommendations for research prioritization proposed are adopted, it is envisioned that a comprehensive battery of ATS can be developed to support the risk assessment process for nanomaterials. Some alternative models are available for immediate implementation, while others require more developmental work to become widely adopted. Case studies are included that can be used to inform the selection of alternative models and end points when assessing the pathogenicity of fibers and mode of action of nanomaterial toxicity.

Large Porous Hollow Particles: Lightweight Champions of Pulmonary Drug Delivery

The deep lungs provide an efficient pathway for drugs to transport into the systemic circulation, as the extremely large surface area and thin epithelial membrane enable rapid drug transport to the blood stream. To penetrate into the deep lungs, aerosol particles with aerodynamic diameters of 1-3 µm are optimal. Large porous hollow particles (LPHPs) can achieve this aerodynamic size range through enhanced porosity within the particles (typically < 0.4 g/cm(3)), which aerodynamically balances the large particle size (> 5 µm, up to 30 µm). The physical properties of these particles provide some key advantages compared to their small, nonporous counterparts through enhanced dispersibility, efficient deep lung deposition, and avoidance of phagocytic clearance. This review highlights the potential of LPHPs in pulmonary delivery of systemic drugs, with a focus on their critical attributes and key formulation aspects. In addition, three examples of LPHPs under development are presented to emphasize the potential of this technology to treat systemic diseases.

Fluoro-edenite and carbon nanotubes: The health impact of 'asbestos-like' fibres

Several decades have passed since Wagner et al demonstrated a causal link between asbestos fibre inhalation and the development of pleural mesothelioma in 1960. It was later suggested that pleural plaques are a benign consequence of exposure to these fibres. Most recently, a significant association between exposure to asbestos and cancer diagnosed at various sites, such as the peritoneum, stomach, pharynx, colon and ovaries has been demonstrated. The great concerns about public health that arose from the scientific evidence presented above have led to the banning of asbestos in several countries. Over the years, the suspicion that particles with a high aspect ratio may have asbestos-like pathogenicity has been supported by increasing evidence. Natural occurring minerals, as well as man-made fibres, have proven capable of inducing either chronic inflammation of serous membranes, or, in some cases, the development of peritoneal and pleural mesothelioma. The pathogenic role of both fluoro-edenite and carbon nanotubes, two ‘asbestos-like’ fibres is summarized and discussed in this review. The data presented herein support the notion that occupational exposure to these two types of fibre contributes to the development of different types of cancer.