A Single Aspiration of Rod-like Carbon Nanotubes Induces Asbestos-like Pulmonary Inflammation Mediated in Part by the IL-1 Receptor

Pulmonary toxicity and translocation of gallium phosphide nanowires to secondary organs following pulmonary exposure in mice

BACKGROUND

III-V semiconductor nanowires are envisioned as being integrated in optoelectronic devices in the near future. However, the perspective of mass production of these nanowires raises concern for human safety due to their asbestos- and carbon nanotube-like properties, including their high aspect ratio shape. Indeed, III-V nanowires have similar dimensions as Mitsui-7 multi-walled carbon nanotubes, which induce lung cancer by inhalation in rats. It is therefore urgent to investigate the toxicological effects following lung exposure to III-V nanowires prior to their use in industrial production, which entails risk of human exposure. Here, female C57BL/6J mice were exposed to 2, 6, and 18 µg (0.12, 0.35 and 1.1 mg/kg bw) of gallium phosphide (III-V) nanowires (99 nm diameter, 3.7 μm length) by intratracheal instillation and the toxicity was investigated 1, 3, 28 days and 3 months after exposure. Mitsui-7 multi-walled carbon nanotubes and carbon black Printex 90 nanoparticles were used as benchmark nanomaterials.

RESULTS

Gallium phosphide nanowires induced genotoxicity in bronchoalveolar lavage cells and acute inflammation with eosinophilia observable both in bronchoalveolar lavage and lung tissue (1 and 3 days post-exposure). The inflammatory response was comparable to the response following exposure to Mitsui-7 multi-walled carbon nanotubes at similar dose levels. The nanowires underwent partial dissolution in the lung resulting in thinner nanowires, with an estimated in vivo half-life of 3 months. Despite the partial dissolution, nanowires were detected in lung, liver, spleen, kidney, uterus and brain 3 months after exposure.

CONCLUSION

Pulmonary exposure to gallium phosphide nanowires caused similar toxicological effects as the multi-walled carbon nanotube Mitsui-7.

Toxicogenomics Data for Chemical Safety Assessment and Development of New Approach Methodologies: An Adverse Outcome Pathway-Based Approach

Mechanistic toxicology provides a powerful approach to inform on the safety of chemicals and the development of safe-by-design compounds. Although toxicogenomics supports mechanistic evaluation of chemical exposures, its implementation into the regulatory framework is hindered by uncertainties in the analysis and interpretation of such data. The use of mechanistic evidence through the adverse outcome pathway (AOP) concept is promoted for the development of new approach methodologies (NAMs) that can reduce animal experimentation. However, to unleash the full potential of AOPs and build confidence into toxicogenomics, robust associations between AOPs and patterns of molecular alteration need to be established. Systematic curation of molecular events to AOPs will create the much-needed link between toxicogenomics and systemic mechanisms depicted by the AOPs. This, in turn, will introduce novel ways of benefitting from the AOPs, including predictive models and targeted assays, while also reducing the need for multiple testing strategies. Hence, a multi-step strategy to annotate AOPs is developed, and the resulting associations are applied to successfully highlight relevant adverse outcomes for chemical exposures with strong in vitro and in vivo convergence, supporting chemical grouping and other data-driven approaches. Finally, a panel of AOP-derived in vitro biomarkers for pulmonary fibrosis (PF) is identified and experimentally validated.

Mechanisms of cell injury induced by inhaled molybdenum trioxide nanoparticles in Golden Syrian Hamsters

Molybdenum trioxide nanoparticles (MoO₃ NPs) are extensively used in the biomedical, agricultural, and engineering fields that may increase exposure and adverse health effects to the human population. The purpose of this study is to evaluate a possible molecular mechanism leading to cell damage and death following pulmonary exposure to inhaled MoO₃ NPs. Animals were separated into four groups: two control groups exposed to room air or aerosolized water and two treated groups exposed to aerosolized MoO₃ NPs with a concentration of 5 mg/m³ NPs (4 h/day for eight days) and given a one-day (T-1) or seven-day (T-7) recovery period post exposure. Pulmonary toxicity was evaluated with total and differential cell counts. Increases were seen in total cell numbers, neutrophils, and multinucleated macrophages in the T-1 group, with increases in lymphocytes in the T-7 group (*P < 0.05). To evaluate the mechanism of toxicity, protein levels of Beclin-1, light chain 3 (LC3)-I/II, P-62, cathepsin B, NLRP3, ASC, caspase-1, interleukin (IL)-1β, and tumor necrosis factor-α (TNF-α) were assessed in lung tissue. Immunoblot analyses indicated 1.4- and 1.8-fold increases in Beclin-1 in treated groups (T-1 and T-7, respectively, *P < 0.05), but no change in protein levels of LC3-I/II in either treated group. The levels of cathepsin B were 2.8- and 2.3-fold higher in treated lungs (T-1 and T-7, respectively, *P < 0.05), the levels of NLRP3 had a fold increase of 2.5 and 3.6 (T-1 *P < 0.05, T-7 **P < 0.01, respectively), and the levels of caspase-1 indicated a 3.8- and 3.0-fold increase in treated lungs (T-1 and T-7, respectively, *P < 0.05). Morphological changes were studied using light and electron microscopy showing alterations to airway epithelium and the alveoli, along with particle internalization in macrophages. The results from this study may indicate that inhalation exposure to MoO₃ NPs may interrupt the autophagic flux and induce cytotoxicity and lung injury through pyroptosis cell death and activation of caspase-1.

Skin microbiota of oxazolone-induced contact hypersensitivity mouse model

Contact allergy is a common skin allergy, which can be studied utilising contact hypersensitivity (CHS) animal model. However, it is not clear, whether CHS is a suitable model to investigate skin microbiota interactions. We characterised the effect of contact dermatitis on the skin microbiota and studied the biological effects of oxazolone (OXA) -induced inflammation on skin thickness, immune cell numbers and changes of the microbiota in CHS mouse model (n = 72) for 28 days. Through 16S rRNA gene sequencing we defined the composition of bacterial communities and associations of bacteria with inflammation. We observed that the vehicle solution of acetone and olive oil induced bacterial community changes on day 1, and OXA-induced changes were observed mainly on day 7. Many of the notably enriched bacteria present in the OXA-challenged positive group represented the genus Faecalibaculum which were most likely derived from the cage environment. Additionally, skin inflammation correlated negatively with Streptococcus, which is considered a native skin bacterium, and positively with Muribacter muris, which is typical in oral environment. Skin inflammation favoured colonisation of cage-derived faecal bacteria, and additionally mouse grooming transferred oral bacteria on the skin. Due to the observed changes, we conclude that CHS model could be used for certain skin microbiome-related research set-ups. However, since vehicle exposure can alter the skin microbiome as such, future studies should include considerations such as careful control sampling and statistical tests to account for potential confounding factors.

Effect of Surface Modification on the Pulmonary and Systemic Toxicity of Cellulose Nanofibrils

Cellulose nanofibrils (CNFs) have emerged as sustainable options for a wide range of applications. However, the high aspect ratio and biopersistence of CNFs raise concerns about potential health effects. Here, we evaluated the in vivo pulmonary and systemic toxicity of unmodified (U-CNF), carboxymethylated (C-CNF), and TEMPO (2,2,6,6-tetramethyl-piperidin-1-oxyl)-oxidized (T-CNF) CNFs, fibrillated in the same way and administered to mice by repeated (3×) pharyngeal aspiration (14, 28, and 56 μg/mouse/aspiration). Toxic effects were assessed up to 90 days after the last administration. Some mice were treated with T-CNF samples spiked with lipopolysaccharide (LPS; 0.02-50 ng/mouse/aspiration) to assess the role of endotoxin contamination. The CNFs induced an acute inflammatory reaction that subsided within 90 days, except for T-CNF. At 90 days post-administration, an increased DNA damage was observed in bronchoalveolar lavage and hepatic cells after exposure to T-CNF and C-CNF, respectively. Besides, LPS contamination dose-dependently increased the hepatic genotoxic effects of T-CNF.

Do Carbon Nanotubes and Asbestos Fibers Exhibit Common Toxicity Mechanisms?

During the last two decades several nanoscale materials were engineered for industrial and medical applications. Among them carbon nanotubes (CNTs) are the most exploited nanomaterials with global production of around 1000 tons/year. Besides several commercial benefits of CNTs, the fiber-like structures and their bio-persistency in lung tissues raise serious concerns about the possible adverse human health effects resembling those of asbestos fibers. In this review, we present a comparative analysis between CNTs and asbestos fibers using the following four parameters: (1) fibrous needle-like shape, (2) bio-persistent nature, (3) high surface to volume ratio and (4) capacity to adsorb toxicants/pollutants on the surface. We also compare mechanisms underlying the toxicity caused by certain diameters and lengths of CNTs and asbestos fibers using downstream pathways associated with altered gene expression data from both asbestos and CNT exposure. Our results suggest that indeed certain types of CNTs are emulating asbestos fiber as far as associated toxicity is concerned.

Statins repress needle-like carbon nanotube- or cholesterol crystal-stimulated IL-1β production by inhibiting the uptake of crystals by macrophages

Statins are 3-hydroxy-3-methylglutaryl-CoA reductase inhibitors that lower atherogenic LDL-cholesterol levels. Statins exert clinically relevant anti-inflammatory effects; however, the underlying molecular mechanism remains unclear. Studies have shown that endogenous and exogenous pathogenic crystals, such as cholesterol and monosodium urate (MSU), and needle-like nanomaterials, such as multi-wall carbon nanotubes (MWCNT), induce the production of IL-1β and play a critical role in the development of crystal-associated sterile inflammatory pathologies. In this study, we evaluated the effect of statins on crystal-induced IL-1β production in macrophages. We found that various statins, including pitavastatin, atorvastatin, fluvastatin, and lovastatin, but not squalene synthase inhibitor, repressed IL-1β release upon MWCNT stimulation. In addition, IL-1β production induced by cholesterol crystals and MSU crystals, but not by ATP or nigericin, was diminished. MWCNT-stimulated IL-1β release was dependent on the expression of NLRP3, but not AIM2, NLRC4, or MEFV. Statin-induced repression was accompanied by reduced levels of mature caspase-1 and decreased uptake of MWCNT into cells. Supplementation of mevalonate, geranylgeranyl pyrophosphate, or farnesyl pyrophosphate prevented the reduction in IL-1β release, suggesting a crucial role of protein prenylation, but not cholesterol synthesis. The statin-induced repression of MWCNT-elicited IL-1β release was observed in THP-1-derived and mouse peritoneal macrophages, but not in bone marrow-derived macrophages where statins act in synergy with lipopolysaccharide to enhance the expression of IL-1β precursor protein. In summary, we describe a novel anti-inflammatory mechanism through which statins repress mature IL-1β release induced by pathogenic crystals and nanoneedles by inhibiting the internalization of crystals by macrophages.

Profiling of Sub-Lethal in Vitro Effects of Multi-Walled Carbon Nanotubes Reveals Changes in Chemokines and Chemokine Receptors

Engineered nanomaterials are potentially very useful for a variety of applications, but studies are needed to ascertain whether these materials pose a risk to human health. Here, we studied three benchmark nanomaterials (Ag nanoparticles, TiO2 nanoparticles, and multi-walled carbon nanotubes, MWCNTs) procured from the nanomaterial repository at the Joint Research Centre of the European Commission. Having established a sub-lethal concentration of these materials using two human cell lines representative of the immune system and the lungs, respectively, we performed RNA sequencing of the macrophage-like cell line after exposure for 6, 12, and 24 h. Downstream analysis of the transcriptomics data revealed significant effects on chemokine signaling pathways. CCR2 was identified as the most significantly upregulated gene in MWCNT-exposed cells. Using multiplex assays to evaluate cytokine and chemokine secretion, we could show significant effects of MWCNTs on several chemokines, including CCL2, a ligand of CCR2. The results demonstrate the importance of evaluating sub-lethal concentrations of nanomaterials in relevant target cells.

Signaling Pathways Implicated in Carbon Nanotube-Induced Lung Inflammation

Inflammation is a tissue response to a variety of harmful stimuli, such as pathogens, irritants, and injuries, and can eliminate insults and limit tissue damage. However, dysregulated inflammation is recognized as a cause of many human diseases, exemplified by organ fibrosis and cancer. In this regard, inflammation-promoted fibrosis is commonly observed in human lung diseases, such as idiopathic pulmonary fibrosis and pneumoconiosis. Carbon nanotubes (CNTs) are a type of nanomaterials with unique properties and various industrial and commercial applications. On the other hand, certain forms of CNTs are potent inducers of inflammation and fibrosis in animal lungs. Notably, acute inflammation is a remarkable phenotype elicited by CNTs in the lung during the early acute phase post-exposure; whereas a type 2 immune response is evidently activated and dominates during the late acute and chronic phases, leading to type 2 inflammation and lung fibrosis. Numerous studies demonstrate that these immune responses involve distinct immune cells, various pathologic factors, and specific functions and play crucial roles in the initiation and progression of inflammation and fibrosis in the lung exposed to CNTs. Thus, the mechanistic understanding of the immune responses activated by CNTs has drawn great attention in recent years. This article reviews the major findings on the cell signaling pathways that are activated in immune cells and exert functions in promoting immune responses in CNT-exposed lungs, which would provide new insights into the understanding of CNT-induced lung inflammation and inflammation-driven fibrosis, the application of CNT-induced lung inflammation and fibrosis as a new disease model, and the potential of targeting immune cells as a therapeutic strategy for relevant human lung diseases.

Pulmonary toxicity of synthetic amorphous silica - effects of porosity and copper oxide doping

Materials can be modified for improved functionality. Our aim was to test whether pulmonary toxicity of silica nanomaterials is increased by the introduction of: a) porosity; and b) surface doping with CuO; and whether c) these modifications act synergistically. Mice were exposed by intratracheal instillation and for some doses also oropharyngeal aspiration to: 1) solid silica 100 nm; 2) porous silica 100 nm; 3) porous silica 100 nm with CuO doping; 4) solid silica 300 nm; 5) porous silica 300 nm; 6) solid silica 300 nm with CuO doping; 7) porous silica 300 nm with CuO doping; 8) CuO nanoparticles 9.8 nm; or 9) carbon black Printex 90 as benchmark. Based on a pilot study, dose levels were between 0.5 and 162 µg/mouse (0.2 and 8.1 mg/kg bw). Endpoints included pulmonary inflammation (neutrophil numbers in bronchoalveolar fluid), acute phase response, histopathology, and genotoxicity assessed by the comet assay, micronucleus test, and the gamma-H2AX assay. The porous silica materials induced greater pulmonary inflammation than their solid counterparts. A similar pattern was seen for acute phase response induction and histologic changes. This could be explained by a higher specific surface area per mass unit for the most toxic particles. CuO doping further increased the acute phase response normalized according to the deposited surface area. We identified no consistent evidence of synergism between surface area and CuO doping. In conclusion, porosity and CuO doping each increased the toxicity of silica nanomaterials and there was no indication of synergy when the modifications co-occurred.

Susceptibility Factors in Chronic Lung Inflammatory Responses to Engineered Nanomaterials

Engineered nanomaterials (ENMs) are products of the emerging nanotechnology industry and many different types of ENMs have been shown to cause chronic inflammation in the lungs of rodents after inhalation exposure, suggesting a risk to human health. Due to the increasing demand and use of ENMs in a variety of products, a careful evaluation of the risks to human health is urgently needed. An assessment of the immunotoxicity of ENMs should consider susceptibility factors including sex, pre-existing diseases, deficiency of specific genes encoding proteins involved in the innate or adaptive immune response, and co-exposures to other chemicals. This review will address evidence from experimental animal models that highlights some important issues of susceptibility to chronic lung inflammation and systemic immune dysfunction after pulmonary exposure to ENMs.

SOX2Mediates Carbon Nanotube-Induced Fibrogenesis and Fibroblast Stem Cell Acquisition

Certain nanosized particles like carbon nanotubes (CNTs) are known to induce pulmonary fibrosis, but the underlying mechanisms are unclear, and efforts to prevent this disease are lacking. Fibroblast-associated stem cells (FSCs) have been suggested as a critical driver of fibrosis induced by CNTs by serving as a renewable source of extracellular matrix-producing cells; however, a detailed understanding of this process remains obscure. Here, we demonstrated that single-walled CNTs induced FSC acquisition and fibrogenic responses in primary human lung fibroblasts. This was indicated by increased expression of stem cell markers (e.g., CD44 and ABCG2) and fibrogenic markers (e.g., collagen and α-SMA) in CNT-exposed cells. These cells also showed increased sphere formation, anoikis resistance, and aldehyde dehydrogenase (ALDH) activities, which are characteristics of stem cells. Mechanistic studies revealed sex-determining region Y-box 2 (SOX2), a self-renewal associated transcription factor, as a key driver of FSC acquisition and fibrogenesis. Upregulation and colocalization of SOX2 and COL1 were found in the fibrotic lung tissues of CNT-exposed mice via oropharyngeal aspiration after 56 days. The knockdown of SOX2 by gene silencing abrogated the fibrogenic and FSC-inducing effects of CNTs. Chromatin immunoprecipitation assays identified SOX2-binding sites on COL1A1 and COL1A2, indicating SOX2 as a transcription factor in collagen synthesis. SOX2 was also found to play a critical role in TGF-β-induced fibrogenesis through its collagen- and FSC-inducing effects. Since many nanomaterials are known to induce TGF-β, our findings that SOX2 regulate FSCs and fibrogenesis may have broad implications on the fibrogenic mechanisms and treatment strategies of various nanomaterial-induced fibrotic disorders.

Carbon Nanotubes under Scrutiny: Their Toxicity and Utility in Mesothelioma Research

Research on the toxicity of engineered carbon nanotubes (CNT) was initiated by Belgian academic chemists and toxicologists more than 15 years ago. It is now undisputed that some of these attractive nanomaterials induce serious illness such as fibrosis and cancer. The physico-chemical determinants of CNT-induced adverse effects are now elucidated and include shape, nanoscale diameter, and structural defects. Generated in vitro and in vivo data on their inflammogenic and fibrogenic activities were combined and translated in AOP (adverse outcome pathways) available for risk assessment and regulatory policies. The asbestos-like carcinogenic effect of CNT, notably their capacity to induce malignant mesothelioma (MM), remain, however, a cause of concern for public health and strongly curb the craze for CNT in industries. MM still represents a real challenge for clinicians and a highly refractory cancer to existing therapeutic strategies. By comparing mesotheliomagenic CNT (needle-like CNT-N) to non mesotheliomagenic CNT (tangled-like CNT-T), our group generated a relevant animal model that highlights immune pathways specifically associated to the carcinogenic process. Evidence indicates that only CNT-N possess the intrinsic capacity to induce a preferential, rapid, and sustained accumulation of host immunosuppressive cells that subvert immune surveillance and suppress anti-mesothelioma immunity. This new concept offers novel horizons for the clinical management of mesothelioma and represents an additional tool for predicting the mesotheliomagenic activity of newly elaborated CNT or nanoparticles.

Polarization of Immune Cells in the Pathologic Response to Inhaled Particulates

Polarization of immune cells is commonly observed in host responses associated with microbial immunity, inflammation, tumorigenesis, and tissue repair and fibrosis. In this process, immune cells adopt distinct programs and perform specialized functions in response to specific signals. Accumulating evidence indicates that inhalation of micro- and nano-sized particulates activates barrier immune programs in the lung in a time- and context-dependent manner, including type 1 and type 2 inflammation, and T helper (Th) 17 cell, regulatory T cell (Treg), innate lymphoid cell (ILC), and myeloid-derived suppressor cell (MDSC) responses, which highlight the polarization of several major immune cell types. These responses facilitate the pulmonary clearance and repair under physiological conditions. When exposure persists and overwhelms the clearance capacity, they foster the chronic progression of inflammation and development of progressive disease conditions, such as fibrosis and cancer. The pulmonary response to insoluble particulates thus represents a distinctive disease process wherein non-infectious, persistent exposures stimulate the polarization of immune cells to orchestrate dynamic inflammatory and immune reactions, leading to pulmonary and pleural chronic inflammation, fibrosis, and malignancy. Despite large variations in particles and their associated disease outcomes, the early response to inhaled particles often follows a common path. The initial reactions entail a barrier immune response dominated by type 1 inflammation that features active phagocytosis by M1 macrophages and recruitment of neutrophils, both of which are fueled by Th1 and proinflammatory cytokines. Acute inflammation is immediately followed by resolution and tissue repair mediated through specialized pro-resolving mediators (SPMs) and type 2 cytokines and cells including M2 macrophages and Th2 lymphocytes. As many particles and fibers cannot be digested by phagocytes, resolution is often extended and incomplete, and type 2 inflammation becomes heightened, which promotes interstitial fibrosis, granuloma formation, and tumorigenesis. Recent studies also reveal the involvement of Th17-, Treg-, ILC-, and MDSC-mediated responses in the pathogenesis caused by inhaled particulates. This review synopsizes the progress in understanding the interplay between inhaled particles and the pulmonary immune functions in disease pathogenesis, with focus on particle-induced polarization of immune cells and its role in the development of chronic inflammation, fibrosis, and cancer in the lung.

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.

Carbon Nanomaterials Promote M1/M2 Macrophage Activation

Toxic effects of certain carbon nanomaterials (CNM) have been observed in several exposure scenarios both in vivo and in vitro. However, most of the data currently available has been generated in a high-dose/acute exposure setup, limiting the understanding of their immunomodulatory mechanisms. Here, macrophage-like THP-1 cells, exposed to ten different CNM for 48 h in low-cytotoxic concentration of 10 µg mL^-1 , are characterized by secretion of different cytokines and global transcriptional changes. Subsequently, the relationships between cytokine secretion and transcriptional patterns are modeled, highlighting specific pathways related to alternative macrophage activation. Finally, time- and dose-dependent activation of transcription and secretion of M1 marker genes IL-1β and tumor necrosis factor, and M2 marker genes IL-10 and CSF1 is confirmed among the three most responsive CNM, with concentrations of 5, 10, and 20 µg mL^-1 at 24, 48, and 72 h of exposure. These results underline CNM effects on the formation of cell microenvironment and gene expression leading to specific patterns of macrophage polarization. Taken together, these findings imply that, instead of a high and toxic CNM dose, a sub-lethal dose in controlled exposure setup can be utilized to alter the cell microenvironment and program antigen presenting cells, with fascinating implications for novel therapeutic strategies.

Transcriptomics in Toxicogenomics, Part I: Experimental Design, Technologies, Publicly Available Data, and Regulatory Aspects

The starting point of successful hazard assessment is the generation of unbiased and trustworthy data. Conventional toxicity testing deals with extensive observations of phenotypic endpoints in vivo and complementing in vitro models. The increasing development of novel materials and chemical compounds dictates the need for a better understanding of the molecular changes occurring in exposed biological systems. Transcriptomics enables the exploration of organisms' responses to environmental, chemical, and physical agents by observing the molecular alterations in more detail. Toxicogenomics integrates classical toxicology with omics assays, thus allowing the characterization of the mechanism of action (MOA) of chemical compounds, novel small molecules, and engineered nanomaterials (ENMs). Lack of standardization in data generation and analysis currently hampers the full exploitation of toxicogenomics-based evidence in risk assessment. To fill this gap, TGx methods need to take into account appropriate experimental design and possible pitfalls in the transcriptomic analyses as well as data generation and sharing that adhere to the FAIR (Findable, Accessible, Interoperable, and Reusable) principles. In this review, we summarize the recent advancements in the design and analysis of DNA microarray, RNA sequencing (RNA-Seq), and single-cell RNA-Seq (scRNA-Seq) data. We provide guidelines on exposure time, dose and complex endpoint selection, sample quality considerations and sample randomization. Furthermore, we summarize publicly available data resources and highlight applications of TGx data to understand and predict chemical toxicity potential. Additionally, we discuss the efforts to implement TGx into regulatory decision making to promote alternative methods for risk assessment and to support the 3R (reduction, refinement, and replacement) concept. This review is the first part of a three-article series on Transcriptomics in Toxicogenomics. These initial considerations on Experimental Design, Technologies, Publicly Available Data, Regulatory Aspects, are the starting point for further rigorous and reliable data preprocessing and modeling, described in the second and third part of the review series.

Microenvironmental Alterations in Carbon Nanotube-Induced Lung Inflammation and Fibrosis

Carbon nanotube (CNT)-induced pulmonary inflammation and fibrosis have been intensively observed and characterized in numerous animal studies in the past decade. Remarkably, CNT-induced fibrotic lesions highly resemble some human fibrotic lung diseases, such as IPF and pneumoconiosis, regarding disease development and pathological features. This notion leads to a serious concern over the health impact of CNTs in exposed human populations, considering the rapidly expanding production of CNT materials for diverse industrial and commercial applications, and meanwhile provides the rationale for exploring CNT-induced pathologic effects in the lung. Accumulating mechanistic understanding of CNT lung pathology at the systemic, cellular, and molecular levels has demonstrated the potential of using CNT-exposed animals as a new disease model for the studies on inflammation, fibrosis, and the interactions between these two disease states. Tissue microenvironment plays critical roles in maintaining homeostasis and physiological functions of organ systems. When aberrant microenvironment forms under intrinsic or extrinsic stimulation, tissue abnormality, organ dysfunction, and pathological outcomes are induced, resulting in disease development. In this article, the cellular and molecular alterations that are induced in tissue microenvironment and implicated in the initiation and progression of inflammation and fibrosis in CNT-exposed lungs, including effector cells, soluble mediators, and functional events exemplified by cell differentiation and extracellular matrix (ECM) modification, are summarized and discussed. This analysis would provide new insights into the mechanistic understanding of lung inflammation and fibrosis induced by CNTs, as well as the development of CNT-exposed animals as a new model for human lung diseases.

Real-Time Measurement of Airborne Carbon Nanotubes in Workplace Atmospheres

With growing applications of carbon nanomaterials, there is a concern over health risks presented by inhalation of carbon nanotube (CNT) aerosol in workplace atmospheres. Current methods used for CNT aerosol measurement lack selectivity to specific form of carbonaceous component or allotrope of interest. Moreover, the detection limits of these methods are also inadequate for short-term monitoring. Here, we describe, for the first time, a near real-time, field-portable instrument for selective quantification of airborne CNT concentration. The approach uses an automated cyclical scheme involving collect-analyze-ablate steps to obtain continuous near real-time measurement using Raman spectroscopy. The method achieves significantly lower detection limits by employing corona-assisted particle microconcentration for efficient coupling with laser Raman spectroscopy. A combination of techniques involving (i) use of characteristic Raman peaks, (ii) distinct ratio of disordered and graphitic peaks, and (iii) principal component classification and regression is employed to identify and quantify the specific form of the aerosolized carbonaceous nanomaterial. We show that the approach is capable of selectively quantifying trace single-walled CNT in the presence of interfering agents such as diesel particulate matter. The detection limit of the method for the single-walled CNT studied in this work was 60 ng m^-3, corresponding to a 10 min aerosol collection period, which is significantly lower than that for the NIOSH Method 5040 (∼0.15 μg m^-3 for an 8-h collection on a 25 mm filter at 4 L min^-1), a commonly used method for elemental carbon. We demonstrate the automated real-time capability of this field-portable method by continuously measuring a transient single-walled CNT aerosol.

Integration of inflammation, fibrosis, and cancer induced by carbon nanotubes

Carbon nanotubes (CNTs) are nanomaterials with unique physicochemical properties that are targets of great interest for industrial and commercial applications. Notwithstanding, some characteristics of CNTs are associated with adverse outcomes from exposure to pathogenic particulates, raising concerns over health risks in exposed workers and consumers. Indeed, certain forms of CNTs induce a range of harmful effects in laboratory animals, among which inflammation, fibrosis, and cancer are consistently observed for some CNTs. Inflammation, fibrosis, and malignancy are complex pathological processes that, in summation, underlie a major portion of human disease. Moreover, the functional interrelationship among them in disease pathogenesis has been increasingly recognized. The CNT-induced adverse effects resemble certain human disease conditions, such as pneumoconiosis, idiopathic pulmonary fibrosis (IPF), and mesothelioma, to some extent. Progress has been made in understanding CNT-induced pathologic conditions in recent years, demonstrating a close interconnection among inflammation, fibrosis, and cancer. Mechanistically, a number of mediators, signaling pathways, and cellular processes are identified as major mechanisms that underlie the interplay among inflammation, fibrosis, and malignancy, and serve as pathogenic bases for these disease conditions in CNT-exposed animals. These studies indicate that CNT-induced pathological effects, in particular, inflammation, fibrosis, and cancer, are mechanistically, and in some cases, causatively, interrelated. These findings generate new insights into CNT adverse effects and pathogenesis and provide new targets for exposure monitoring and drug development against inflammation, fibrosis, and cancer caused by inhaled nanomaterials.

Quantification of Carbon Nanotubes by Raman Analysis

The increasing prevalence of carbon nanotubes (CNTs) in manufacturing and research environments, together with the potential exposure risks, necessitates development of reliable and accurate monitoring methods for these materials. We examined quantification of CNTs by two distinct methods based on Raman spectroscopy. First, as measured by the Raman peak intensity of aqueous CNT suspensions, and second, by Raman mapping of air filter surfaces onto which CNTs were collected as aerosols or applied as small-area (0.05 cm2) deposits. Correlation (R2 = 0.97) between CNT concentration and Raman scattering intensity for suspensions in cuvettes was found over a concentration range from about 2 to 10 µg/ml, but measurement variance precludes practical determination of a calibration curve. Raman mapping of aerosol sample filter surfaces shows correlation with CNT mass when the surface density is relatively high (R2 = 0.83 and 0.95 above about 5 µg total mass on filter), while heterogeneity of CNT deposition makes obtaining representative maps of lower density samples difficult. This difficulty can be mitigated by increasing the area mapped relative to the total sample area, improving both precision and the limit of detection (LOD). For small-area deposits, detection of low masses relevant to occupational monitoring can be achieved, with an estimated LOD of about 50 ng.

Cellular Toxicity and Immunological Effects of Carbon-based Nanomaterials

BACKGROUND

Carbon nanomaterials are a growing family of materials featuring unique physicochemical properties, and their widespread application is accompanied by increasing human exposure.

MAIN BODY

Considerable efforts have been made to characterize the potential toxicity of carbon nanomaterials in vitro and in vivo. Many studies have reported various toxicology profiles of carbon nanomaterials. The different results of the cytotoxicity of the carbon-based materials might be related to the differences in the physicochemical properties or structures of carbon nanomaterials, types of target cells and methods of particle dispersion, etc. The reported cytotoxicity effects mainly included reactive oxygen species generation, DNA damage, lysosomal damage, mitochondrial dysfunction and eventual cell death via apoptosis or necrosis. Despite the cellular toxicity, the immunological effects of the carbon-based nanomaterials, such as the pulmonary macrophage activation and inflammation induced by carbon nanomaterials, have been thoroughly studied. The roles of carbon nanomaterials in activating different immune cells or inducing immunosuppression have also been addressed.

CONCLUSION

Here, we provide a review of the latest research findings on the toxicological profiles of carbon-based nanomaterials, highlighting both the cellular toxicities and immunological effects of carbon nanomaterials. This review provides information on the overall status, trends, and research needs for toxicological studies of carbon nanomaterials.

A novel human 3D lung microtissue model for nanoparticle-induced cell-matrix alterations

BACKGROUND

Multi-walled carbon nanotubes (MWCNT) have been shown to elicit the release of inflammatory and pro-fibrotic mediators, as well as histopathological changes in lungs of exposed animals. Current standards for testing MWCNTs and other nanoparticles (NPs) rely on low-throughput in vivo studies to assess acute and chronic toxicity and potential hazard to humans. Several alternative testing approaches utilizing two-dimensional (2D) in vitro assays to screen engineered NPs have reported conflicting results between in vitro and in vivo assays. Compared to conventional 2D in vitro or in vivo animal model systems, three-dimensional (3D) in vitro platforms have been shown to more closely recapitulate human physiology, providing a relevant, more efficient strategy for evaluating acute toxicity and chronic outcomes in a tiered nanomaterial toxicity testing paradigm.

RESULTS

As inhalation is an important route of nanomaterial exposure, human lung fibroblasts and epithelial cells were co-cultured with macrophages to form scaffold-free 3D lung microtissues. Microtissues were exposed to multi-walled carbon nanotubes, M120 carbon black nanoparticles or crocidolite asbestos fibers for 4 or 7 days, then collected for characterization of microtissue viability, tissue morphology, and expression of genes and selected proteins associated with inflammation and extracellular matrix remodeling. Our data demonstrate the utility of 3D microtissues in predicting chronic pulmonary endpoints following exposure to MWCNTs or asbestos fibers. These test nanomaterials were incorporated into 3D human lung microtissues as visualized using light microscopy. Differential expression of genes involved in acute inflammation and extracellular matrix remodeling was detected using PCR arrays and confirmed using qRT-PCR analysis and Luminex assays of selected genes and proteins.

CONCLUSION

3D lung microtissues provide an alternative testing platform for assessing nanomaterial-induced cell-matrix alterations and delineation of toxicity pathways, moving towards a more predictive and physiologically relevant approach for in vitro NP toxicity testing.

Emerging Role of Immunosuppression in Diseases Induced by Micro- and Nano-Particles: Time to Revisit the Exclusive Inflammatory Scenario

Fibrosis, cancer, and autoimmunity developing upon particle exposure have been exclusively linked with uncontrolled inflammatory processes. The critical role of inflammation is now challenged by several contradictory observations indicating that the emergence of these chronic disorders may result from non-inflammatory events. A growing number of studies reveals that micro- and nano-particles can cause exaggerated and persistent immunosuppression characterized by the release of potent anti-inflammatory cytokines (IL-10 and TGF-β), and the recruitment of major regulatory immune cells (M2 macrophages, T and B regs, and MDSC). This persistent immunosuppressive environment is initially established to limit early inflammation but contributes later to fibrosis, cancer, and infection. Immunosuppression promotes fibroblast proliferation and matrix element synthesis and subverts innate and adaptive immune surveillance against tumor cells and microorganisms. This review details the contribution of immunosuppressive cells and their derived immunoregulatory mediators and delineates the mutual role of inflammatory vs. immunosuppressive mechanisms in the pathogenesis of chronic diseases induced by particles. The consideration of these new results explains how particle-related diseases can develop independently of chronic inflammation, enriches current bioassays predicting particle toxicity and suggests new clinical strategies for treating patients affected by particle-associated diseases.

Nanostructures: between natural environment and medical practice

Nanoparticles (NPs) are small structures under 100 nm in dimension. Interrelationships among the morphological parameters and toxicity of NPs have been the focus of several investigations that assessed potential health risk in environmentally-exposed subjects and the realistic uses of NPs in medical practice. In the current review, we provide a summary of the cellular mechanisms of membrane-mediated transport, including old and novel molecules that transport nanostructures across cellular membranes. The effects of geochemical exposure to natural NPs are evaluated through epidemiological data and cancerous pathways activated by Fe2+ NPs. Specifically, we discuss screening for papillary thyroid carcinomas in the inhabitants of the Sicilian volcanic area surrounding Mount Etna to compare the incidence of thyroid carcinoma in this population. Lastly, considering the increased production of carbon nanotubes (CNTs), we examine the toxicity and potential use of these engineered NPs in drug delivery of an extensive amount of therapeutic and imaging molecules (theranosis) that can be conjugated to CNTs.

Fibrous nanocellulose, crystalline nanocellulose, carbon nanotubes, and crocidolite asbestos elicit disparate immune responses upon pharyngeal aspiration in mice

With the rapid development of synthetic alternatives to mineral fibers, their possible effects on the environment and human health have become recognized as important issues worldwide. This study investigated effects of four fibrous materials, i.e. nanofibrillar/nanocrystalline celluloses (NCF and CNC), single-walled carbon nanotubes (CNTs), and crocidolite asbestos (ASB), on pulmonary inflammation and immune responses found in the lungs, as well as the effects on spleen and peripheral blood immune cell subsets. BALB/c mice were given NCF, CNC, CNT, and ASB on Day 1 by oropharyngeal aspiration. At 14 days post-exposure, the animals were evaluated. Total cell number, mononuclear phagocytes, polymorphonuclear leukocytes, lymphocytes, and LDH levels were significantly increased in ASB and CNT-exposed mice. Expression of cytokines and chemokines in bronchoalveolar lavage (BAL) was quite different in mice exposed to four particle types, as well as expression of antigen presentation-related surface proteins on BAL cells. The results revealed that pulmonary exposure to fibrous materials led to discrete local immune cell polarization patterns with a T_H2-like response caused by ASB and T_H1-like immune reaction to NCF, while CNT and CNC caused non-classical or non-uniform responses. These alterations in immune response following pulmonary exposure should be taken into account when testing the applicability of new nanosized materials with fibrous morphology.

Mediation of the single-walled carbon nanotubes induced pulmonary fibrogenic response by osteopontin and TGF-β1

PURPOSE OF THE STUDY

A number of in vivo studies have shown that pulmonary exposure to carbon nanotubes (CNTs) may lead to an acute local inflammatory response, pulmonary fibrosis, and granulomatous lesions. Among the factors that play direct roles in initiation and progression of fibrotic processes are epithelial-mesenchymal transition and myofibroblasts recruitment/differentiation, both mediated by transforming growth factor-β1 (TGF-β1). Yet, other contributors to TGF-β1 associated signaling, such as osteopontin (OPN) has not been fully investigated.

MATERIALS AND METHODS

OPN-knockout female mice (OPN-KO) along with their wild-type (WT) counterparts were exposed to single-walled carbon nanotubes (SWCNT) (40 µg/mouse) via pharyngeal aspiration and fibrotic response was assessed 1, 7, and 28 days post-exposure. Simultaneously, RAW 264.7 and MLE-15 cells were treated with SWCNT (24 hours, 6 µg/cm² to 48 µg/cm²) or bleomycin (0.1 µg/ml) in the presence of OPN-blocking antibody or isotype control, and TGF-β1 was measured in supernatants.

RESULTS AND CONCLUSIONS

Diminished lactate dehydrogenase activity at all time points, along with less pronounced neutrophil influx 24 h post-exposure, were measured in broncho-alveolar lavage (BAL) of OPN-KO mice compared to WT. Pro-inflammatory cytokine release (IL-6, TNF-α, MCP-1) was reduced. A significant two-fold increase of TGF-β1 was found in BAL of WT mice at 7 days, while TGF-β1 levels in OPN-KO animals remained unaltered. Histological examination revealed marked decrease in granuloma formation and less collagen deposition in the lungs of OPN-KO mice compared to WT. RAW 264.7 but not MLE-15 cells exposed to SWCNT and bleomycin had significantly less TGF-β1 released in the presence of OPN-blocking antibody. We believe that OPN is important in initiating the cellular mechanisms that produce an overall pathological response to SWCNT and it may act upstream of TGF-β1. Further investigation to understand the mechanistic details of such interactions is critical to predict outcomes of pulmonary exposure to CNT.

Multi-omics analysis of ten carbon nanomaterials effects highlights cell type specific patterns of molecular regulation and adaptation

New strategies to characterize the effects of engineered nanomaterials (ENMs) based on omics technologies are emerging. However, given the intricate interplay of multiple regulatory layers, the study of a single molecular species in exposed biological systems might not allow the needed granularity to successfully identify the pathways of toxicity (PoT) and, hence, portraying adverse outcome pathways (AOPs). Moreover, the intrinsic diversity of different cell types composing the exposed organs and tissues in living organisms poses a problem when transferring in vivo experimentation into cell-based in vitro systems. To overcome these limitations, we have profiled genome-wide DNA methylation, mRNA and microRNA expression in three human cell lines representative of relevant cell types of the respiratory system, A549, BEAS-2B and THP-1, exposed to a low dose of ten carbon nanomaterials (CNMs) for 48 h. We applied advanced data integration and modelling techniques in order to build comprehensive regulatory and functional maps of the CNM effects in each cell type. We observed that different cell types respond differently to the same CNM exposure even at concentrations exerting similar phenotypic effects. Furthermore, we linked patterns of genomic and epigenomic regulation to intrinsic properties of CNM. Interestingly, DNA methylation and microRNA expression only partially explain the mechanism of action (MOA) of CNMs. Taken together, our results strongly support the implementation of approaches based on multi-omics screenings on multiple tissues/cell types, along with systems biology-based multi-variate data modelling, in order to build more accurate AOPs.

The Secretory Response of Rat Peritoneal Mast Cells on Exposure to Mineral Fibers

BACKGROUND

Exposure to mineral fibers is of substantial relevance to human health. A key event in exposure is the interaction with inflammatory cells and the subsequent generation of pro-inflammatory factors. Mast cells (MCs) have been shown to interact with titanium oxide (TiO₂) and asbestos fibers. In this study, we compared the response of rat peritoneal MCs challenged with the asbestos crocidolite and nanowires of TiO₂ to that induced by wollastonite employed as a control fiber.

METHODS

Rat peritoneal MCs (RPMCs), isolated from peritoneal lavage, were incubated in the presence of mineral fibers. The quantities of secreted enzymes were evaluated together with the activity of fiber-associated enzymes. The ultrastructural morphology of fiber-interacting RPMCs was analyzed with electron microscopy.

RESULTS

Asbestos and TiO₂ stimulate MC secretion. Secreted enzymes bind to fibers and exhibit higher activity. TiO₂ and wollastonite bind and improve enzyme activity, but to a lesser degree than crocidolite.

CONCLUSIONS

(1) Mineral fibers are able to stimulate the mast cell secretory process by both active (during membrane interaction) and/or passive (during membrane penetration) interaction; (2) fibers can be found to be associated with secreted enzymes-this process appears to create long-lasting pro-inflammatory environments and may represent the active contribution of MCs in maintaining the inflammatory process; (3) MCs and their enzymes should be considered as a therapeutic target in the pathogenesis of asbestos-induced lung inflammation; and (4) MCs can contribute to the inflammatory effect associated with selected engineered nanomaterials, such as TiO₂ nanoparticles.

In vitro assessment of neurotoxicity and neuroinflammation of homemade MWCNTs

Multi walled carbon nanotubes (MWCNTs) activate pathways involved in cytotoxicity, genotoxicity and inflammation. Inhaled MWCNTs are translocated to extra pulmonary organs and their hydrophobicity allows them to cross the blood-brain barrier (BBB). Further exposure of central nervous system (CNS) occurs via olfactory neurons. Using differentiated SH-SY5Y, we studied the neurotoxicity and neuroinflammation of pristine and functionalised MWCNTs. ROS overproduction was dose- and time-dependent (P<0.01) and was related to mitochondrial impairment, DNA damage and decreased viability (P<0.05). Transcript levels of TNFα, IL-1β and IL-6 increased, as confirmed by an ELISA test. Raman spectra were acquired to assess MWCNT-cells interactions. The almost superimposable pro-oxidant activity of both CNTs could be imputable to excessive lengths with regard to the pristine MWCNTs and to the eroded surface, causing increased reactivity, with regard to functionalised MWCNTs. Considering the ease with which lightweight MWCNTs aerosolize and the increased production, the results underlined the potential onset of neurodegenerative diseases, due to unintentional MWCNT exposure.

Carbon Nanotube as a Tool for Fighting Cancer

In 2015, cancer was the cause of almost 22% of deaths worldwide. The high frequency of relapsing diseases and metastasis requires the development of new diagnostic and therapeutic approaches, and the use of nanomaterials is a promising tool for fighting cancer. Among the more extensively studied nanomaterials are carbon nanotubes (CNTs), synthesized as graphene sheets, whose spiral shape is varied in length and thickness. Their physicochemical features, such as the resistance to tension, and thermal and electrical conductivity, allow their application in several fields. In this review, we show evidence supporting the applicability of CNTs in biomedical practice as nanocarriers for drugs and immunomodulatory material, emphasizing their potential for use in cancer treatment.

Stat-6 signaling pathway and not Interleukin-1 mediates multi-walled carbon nanotube-induced lung fibrosis in mice: insights from an adverse outcome pathway framework

BACKGROUND

The accumulation of MWCNTs in the lung environment leads to inflammation and the development of disease similar to pulmonary fibrosis in rodents. Adverse Outcome Pathways (AOPs) are a framework for defining and organizing the key events that comprise the biological changes leading to undesirable events. A putative AOP has been developed describing MWCNT-induced pulmonary fibrosis; inflammation and the subsequent healing response induced by inflammatory mechanisms have been implicated in disease progression. The objective of the present study was to address a key data gap in this AOP: empirical data supporting the essentiality of pulmonary inflammation as a key event prior to fibrosis. Specifically, Interleukin-1 Receptor1 (IL-1R1) and Signal Transducer and Activator of Transcription 6 (STAT6) knock-out (KO) mice were employed to target inflammation and the subsequent healing response using MWCNTs as a model pro-fibrotic stressor to determine whether this altered the development of fibrosis.

RESULTS

Wild type (WT) C57BL/6, IL-1R1 (KO) or STAT6 KO mice were exposed to a high dose of Mitsui-7 MWCNT by intratracheal administration. Inflammation was assessed 24 h and 28 days post MWCNT administration, and fibrotic lesion development was assessed 28 days post MWCNT administration. MWCNT-induced acute inflammation was suppressed in IL-1R1 KO mice at the 24 h time point relative to WT mice, but this suppression was not observed 28 days post exposure, and IL-1R1 KO did not alter fibrotic disease development. In contrast, STAT6 KO mice exhibited suppressed acute inflammation and attenuated fibrotic disease in response to MWCNT administration compared to STAT6 WT mice. Whole genome analysis of all post-exposure time points identified a subset of differentially expressed genes associated with fibrosis in both KO mice compared to WT mice.

CONCLUSION

The findings support the essentiality of STAT6-mediated signaling in the development of MWCNT-induced fibrotic disease. The IL-1R1 KO results also highlight the nature of the inflammatory response associated with MWCNT exposure, and indicate a system with multiple redundancies. These data add to the evidence supporting an existing AOP, and will be useful in designing screening strategies that could be used by regulatory agencies to distinguish between MWCNTs of varying toxicity.

The role of the iron catalyst in the toxicity of multi-walled carbon nanotubes (MWCNTs)

This study aimed to investigate the role of iron, used as a catalyst, in the biological response to pristine and functionalized multi-walled carbon nanotubes (p/fMWCNTs) with an iron content of 2.5-2.8%. Preliminarily, we assessed the pro-oxidant activity of MWCNTs-associated iron by an abiotic test. To evaluate iron bioavailability, we measured intracellular redox-active iron in A549 cells exposed to both MWCNT suspensions and to the cell medium preconditioned by MWCNTs, in order to assess the iron dissolution rate under physiological conditions. Moreover, in exposed cells, we detected ROS levels, 8-oxo-dG and mitochondrial function. The results clearly highlighted that MWCNTs- associated iron was not redox-active and that iron leakage did not occur under physiological conditions, including the oxidative burst of specialized cells. Despite this, in MWCNTs exposed cells, higher level of intracellular redox-active iron was measured in comparison to control and a significant time-dependent ROS increase was observed (P<0.01). Higher levels of 8-oxo-dG, a marker of oxidative DNA damage, and decreased mitochondrial function, confirmed the oxidative stress induced by MWCNTs. Based on the results we believe that oxidative damage could be attributable to the release of endogenous redox-active iron. This was due to the damage of acidic vacuolar compartment caused by endocytosis-mediated MWCNT internalization.

Osteopontin enhances multi-walled carbon nanotube-triggered lung fibrosis by promoting TGF-β1 activation and myofibroblast differentiation

BACKGROUND

Carbon nanotubes (CNTs) have been used in a variety of applications because of their unique properties and functions. However, many CNTs have been shown to induce lung fibrosis in experimental animals with some at a potency greater than that of silica, raising concern over possible toxic effects of CNT exposure in humans. Research into the mechanisms by which CNTs induce pulmonary fibrosis is warranted in order to facilitate the understanding, monitoring, and treatment of CNT-induced lung lesions that might occur in exposed populations. The current study focuses on investigating the role of osteopontin (OPN) in the development of lung fibrosis upon exposure to multi-walled carbon nanotubes (MWCNTs).

METHODS

C57BL/6J (WT) and Opn knockout (KO) mice were exposed to MWCNTs by pharyngeal aspiration to examine the acute and chronic effects of MWCNT exposure. The role of OPN and its mode of action in lung fibrosis development were analyzed at the cellular and molecular levels in vivo and in vitro.

RESULTS

OPN was highly and persistently induced in both the acute and chronic phases of the response to MWCNT exposure in mouse lungs. Comparison between WT and Opn KO mice revealed that OPN critically regulated MWCNT-induced lung fibrosis as indicated by reduced fibrotic focus formation and myofibroblast accumulation in Opn KO lungs. At the molecular level, OPN promotes the expression and activation of TGF-β1, stimulates the differentiation of myofibroblasts from fibroblasts, and increases the production of fibrous matrix proteins in lungs and cultured lung cells exposed to MWCNTs.

CONCLUSION

OPN is highly induced in CNT-exposed lungs and plays critical roles in TGF-β1 signaling activation and myofibroblast differentiation to promote fibrosis development from MWCNT exposure. This study reveals an OPN-dependent mechanism to promote MWCNT-induced lung fibrosis. The findings raise the possibility of using OPN as a biomarker to monitor CNT exposure and as a drug target to halt fibrosis development.

Airway exposure to multi-walled carbon nanotubes disrupts the female reproductive cycle without affecting pregnancy outcomes in mice

BACKGROUND

The use of multiwalled carbon nanotubes (MWCNT) is increasing due to a growing use in a variety of products across several industries. Thus, occupational exposure is also of increasing concern, particularly since airway exposure to MWCNTs can induce sustained pulmonary acute phase response and inflammation in experimental animals, which may affect female reproduction. This proof-of-principle study therefore aimed to investigate if lung exposure by intratracheal instillation of the MWCNT NM-400 would affect the estrous cycle and reproductive function in female mice.

RESULTS

Estrous cycle regularity was investigated by comparing vaginal smears before and after exposure to 67 μg of NM-400, whereas reproductive function was analyzed by measuring time to delivery of litters after instillation of 2, 18 or 67 μg of NM-400. Compared to normal estrous cycling determined prior to exposure, exposure to MWCNT significantly prolonged the estrous cycle during which exposure took place, but significantly shortened the estrous cycle immediately after the exposed cycle. No consistent effects were seen on time to delivery of litter or other gestational or litter parameters, such as litter size, sex ratio, implantations and implantation loss.

CONCLUSION

Lung exposure to MWCNT interfered with estrous cycling. Effects caused by MWCNTs depended on the time of exposure: the estrous stage was particularly sensitive to exposure, as animals exposed during this stage showed a higher incidence of irregular cycling after exposure. Our data indicates that MWCNT exposure may interfere with events leading to ovulation.

Network Analysis Reveals Similar Transcriptomic Responses to Intrinsic Properties of Carbon Nanomaterials in Vitro and in Vivo

Understanding the complex molecular alterations related to engineered nanomaterial (ENM) exposure is essential for carrying out toxicity assessment. Current experimental paradigms rely on both in vitro and in vivo exposure setups that often are difficult to compare, resulting in questioning the real efficacy of cell models to mimic more complex exposure scenarios at the organism level. Here, we have systematically investigated transcriptomic responses of the THP-1 macrophage cell line and lung tissues of mice, after exposure to several carbon nanomaterials (CNMs). Under the assumption that the CNM exposure related molecular alterations are mixtures of signals related to their intrinsic properties, we inferred networks of responding genes, whose expression levels are coordinately altered in response to specific CNM intrinsic properties. We observed only a minute overlap between the sets of intrinsic property-correlated genes at different exposure scenarios, suggesting specific transcriptional programs working in different exposure scenarios. However, when the effects of the CNM were investigated at the level of significantly altered molecular functions, a broader picture of substantial commonality emerged. Our results imply that in vitro exposures can efficiently recapitulate the complex molecular functions altered in vivo. In this study, altered molecular pathways in response to specific CNM intrinsic properties have been systematically characterized from transcriptomic data generated from multiple exposure setups. Our computational approach to the analysis of network response modules further revealed similarities between in vitro and in vivo exposures that could not be detected by traditional analysis of transcriptomics data. Our analytical strategy also opens a possibility to look for pathways of toxicity and understanding the molecular and cellular responses identified across predefined biological themes.

Inhalation and Oropharyngeal Aspiration Exposure to Rod-Like Carbon Nanotubes Induce Similar Airway Inflammation and Biological Responses in Mouse Lungs

Carbon nanotubes (CNTs) have the potential to impact technological and industrial progress, but their production and use may, in some cases, cause serious health problems. Certain rod-shaped multiwalled CNTs (rCNTs) can, in fact, induce severe asbestos-like pathogenicity in mice, including granuloma formation, fibrosis, and even cancer. Evaluating the comparability between alternative hazard assessment methods is needed to ensure fast and reliable evaluation of the potentially adverse effects of these materials. To compare two alternative airway exposure methods, C57BL/6 mice were exposed to rCNTs by a state-of-the-art but laborious and expensive inhalation method (6.2-8.2 mg/m³, 4 h/day for 4 days) or by oropharyngeal aspiration (10 or 40 μg/day for 4 days), which is cheaper and easier to perform. In addition to histological and cytological studies, transcriptome analysis was also carried out on the lung tissue samples. Both inhalation and low-dose (10 μg/day) aspiration exposure to rCNTs promoted strong accumulation of eosinophils in the lungs and recruited also a few neutrophils and lymphocytes. In contrast, the aspiration of a high-dose (40 μg/day) rCNT caused only a mild pulmonary eosinophilia but enhanced accumulation of neutrophils in the airways. Inhalation and low-dose aspiration exposure promoted comparable giant cell formation, mucus production, and IL-13 expression in the lungs. Both exposure methods also exacerbated similar expression alterations with 154 (56.4%) differentially expressed, overlapping genes in microarray analyses. Of all differentially expressed genes, up to 80% of the activated biological functions were shared according to pathway enrichment analyses. Inhalation and low-dose aspiration elicited very similar pulmonary inflammation providing evidence that oropharyngeal aspiration is a valid approach and a convenient alternative to the inhalation exposure for the hazard assessment of nanomaterials.

Multiwalled Carbon Nanotube Functionalization with High Molecular Weight Hyaluronan Significantly Reduces Pulmonary Injury

Commercialization of multiwalled carbon nanotubes (MWCNT)-based applications has been hampered by concerns regarding their lung toxicity potential. Hyaluronic acid (HA) is a ubiquitously found polysaccharide, which is anti-inflammatory in its native high molecular weight form. HA-functionalized smart MWCNTs have shown promise as tumor-targeting drug delivery agents and can enhance bone repair and regeneration. However, it is unclear whether HA functionalization could reduce the pulmonary toxicity potential of MWCNTs. Using in vivo and in vitro approaches, we investigated the effectiveness of MWCNT functionalization with HA in increasing nanotube biocompatibility and reducing lung inflammatory and fibrotic effects. We utilized three-dimensional cultures of differentiated primary human bronchial epithelia to translate findings from rodent assays to humans. We found that HA functionalization increased stability and dispersion of MWCNTs and reduced postexposure lung inflammation, fibrosis, and mucus cell metaplasia compared with nonfunctionalized MWCNTs. Cocultures of fully differentiated bronchial epithelial cells (cultivated at air-liquid interface) and human lung fibroblasts (submerged) displayed significant reduction in injury, oxidative stress, as well as pro-inflammatory gene and protein expression after exposure to HA-functionalized MWCNTs compared with MWCNTs alone. In contrast, neither type of nanotubes stimulated cytokine production in primary human alveolar macrophages. In aggregate, our results demonstrate the effectiveness of HA functionalization as a safer design approach to eliminate MWCNT-induced lung injury and suggest that HA functionalization works by reducing MWCNT-induced epithelial injury.

Original Research: Evaluation of pulmonary response to inhaled tungsten (IV) oxide nanoparticles in golden Syrian hamsters

Extensive industrial and military uses of tungsten have raised the possibilities of human occupational and environmental exposure to nanoparticles of this metal, with concomitant health concerns. The goal of this study was to investigate the potential mechanism of pulmonary toxicity associated with inhaled tungsten (IV) oxide nanoparticles (WO₃ NPs) in Golden Syrian Hamsters. Animals exposed to WO₃ NPs via inhalation were divided into three groups - control and two treatment groups exposed to either 5 or 10 mg/m³ of aerosolized WO₃ NPs for 4 h/day for four days. A long-term exposure study (4 h/day for eight days) was also carried out using an additional three groups. Pulmonary toxicity assessed by examining changes in cell numbers, lactate dehydrogenase activity, alkaline phosphatase activity, total protein content, TNF-α, and HMGB1 levels in bronchoalveolar lavage fluids showed a significant difference when compared to control (P < 0.05). The molecular mechanism was established by assessing protein expression of cathepsin B, TXNIP, NLRP3, ASC, IL-1β and caspase-1. Western blot analysis indicated a 1.5 and 1.7 fold changes in NLRP3 in treatment groups (5 mg/m³, P < 0.05 and 10 mg/m³, P < 0.01, respectively), whereas levels of cathepsin B were 1.3 fold higher in lung tissue exposed to WO₃ NPs suggesting activation of inflammasome pathway. Morphological changes studied using light and electron microscopy showed localization of nanoparticles and subsequent perturbation in airway epithelia, macrophages, and interstitial areas of alveolar structures. Results from the current study indicate that inhalation exposure to WO₃ NPs may induce cytotoxicity, morphological changes, and lung injury via pyroptotic cell death pathway caused by activation of caspase-1.

Multiwalled carbon nanotube-induced pulmonary inflammatory and fibrotic responses and genomic changes following aspiration exposure in mice: A 1-year postexposure study

Pulmonary exposure to multiwalled carbon nanotubes (MWCNT) induces an inflammatory and rapid fibrotic response, although the long-term signaling mechanisms are unknown. The aim of this study was to examine the effects of 1, 10, 40, or 80 μg MWCNT administered by pharyngeal aspiration on bronchoalveolar lavage (BAL) fluid for polymorphonuclear cell (PMN) infiltration, lactate dehydrogenase (LDH) activity, and lung histopathology for inflammatory and fibrotic responses in mouse lungs 1 mo, 6 mo, and 1 yr postexposure. Further, a 120-μg crocidolite asbestos group was incorporated as a positive control for comparative purposes. Results showed that MWCNT increased BAL fluid LDH activity and PMN infiltration in a dose-dependent manner at all three postexposure times. Asbestos exposure elevated LDH activity at all 3 postexposure times and PMN infiltration at 1 mo and 6 mo postexposure. Pathological changes in the lung, the presence of MWCNT or asbestos, and fibrosis were noted at 40 and 80 μg MWCNT and in asbestos-exposed mice at 1 yr postexposure. To determine potential signaling pathways involved with MWCNT-associated pathological changes in comparison to asbestos, up- and down-regulated gene expression was determined in lung tissue at 1 yr postexposure. Exposure to MWCNT tended to favor those pathways involved in immune responses, specifically T-cell responses, whereas exposure to asbestos tended to favor pathways involved in oxygen species production, electron transport, and cancer. Data indicate that MWCNT are biopersistent in the lung and induce inflammatory and fibrotic pathological alterations similar to those of crocidolite asbestos, but may reach these endpoints by different mechanisms.

Nano-risk Science: application of toxicogenomics in an adverse outcome pathway framework for risk assessment of multi-walled carbon nanotubes

BACKGROUND

A diverse class of engineered nanomaterials (ENMs) exhibiting a wide array of physical-chemical properties that are associated with toxicological effects in experimental animals is in commercial use. However, an integrated framework for human health risk assessment (HHRA) of ENMs has yet to be established. Rodent 2-year cancer bioassays, clinical chemistry, and histopathological endpoints are still considered the 'gold standard' for detecting substance-induced toxicity in animal models. However, the use of data derived from alternative toxicological tools, such as genome-wide expression profiling and in vitro high-throughput assays, are gaining acceptance by the regulatory community for hazard identification and for understanding the underlying mode-of-action. Here, we conducted a case study to evaluate the application of global gene expression data in deriving pathway-based points of departure (PODs) for multi-walled carbon nanotube (MWCNT)-induced lung fibrosis, a non-cancer endpoint of regulatory importance.

METHODS

Gene expression profiles from the lungs of mice exposed to three individual MWCNTs with different physical-chemical properties were used within the framework of an adverse outcome pathway (AOP) for lung fibrosis to identify key biological events linking MWCNT exposure to lung fibrosis. Significantly perturbed pathways were categorized along the key events described in the AOP. Benchmark doses (BMDs) were calculated for each perturbed pathway and were used to derive transcriptional BMDs for each MWCNT.

RESULTS

Similar biological pathways were perturbed by the different MWCNT types across the doses and post-exposure time points studied. The pathway BMD values showed a time-dependent trend, with lower BMDs for pathways perturbed at the earlier post-exposure time points (24 h, 3d). The transcriptional BMDs were compared to the apical BMDs derived by the National Institute for Occupational Safety and Health (NIOSH) using alveolar septal thickness and fibrotic lesions endpoints. We found that regardless of the type of MWCNT, the BMD values for pathways associated with fibrosis were 14.0-30.4 μg/mouse, which are comparable to the BMDs derived by NIOSH for MWCNT-induced lung fibrotic lesions (21.0-27.1 μg/mouse).

CONCLUSIONS

The results demonstrate that transcriptomic data can be used to as an effective mechanism-based method to derive acceptable levels of exposure to nanomaterials in product development when epidemiological data are unavailable.

Prolongevity hormone FGF21 protects against immune senescence by delaying age-related thymic involution

Age-related thymic degeneration is associated with loss of naïve T cells, restriction of peripheral T-cell diversity, and reduced healthspan due to lower immune competence. The mechanistic basis of age-related thymic demise is unclear, but prior evidence suggests that caloric restriction (CR) can slow thymic aging by maintaining thymic epithelial cell integrity and reducing the generation of intrathymic lipid. Here we show that the prolongevity ketogenic hormone fibroblast growth factor 21 (FGF21), a member of the endocrine FGF subfamily, is expressed in thymic stromal cells along with FGF receptors and its obligate coreceptor, βKlotho. We found that FGF21 expression in thymus declines with age and is induced by CR. Genetic gain of FGF21 function in mice protects against age-related thymic involution with an increase in earliest thymocyte progenitors and cortical thymic epithelial cells. Importantly, FGF21 overexpression reduced intrathymic lipid, increased perithymic brown adipose tissue, and elevated thymic T-cell export and naïve T-cell frequencies in old mice. Conversely, loss of FGF21 function in middle-aged mice accelerated thymic aging, increased lethality, and delayed T-cell reconstitution postirradiation and hematopoietic stem cell transplantation (HSCT). Collectively, FGF21 integrates metabolic and immune systems to prevent thymic injury and may aid in the reestablishment of a diverse T-cell repertoire in cancer patients following HSCT.