Time-dependent subcellular distribution and effects of carbon nanotubes in lungs of mice

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.

High aspect ratio nanomaterial-induced macrophage polarization is mediated by changes in miRNA levels

Introduction

Inhalation of nanomaterials may induce inflammation in the lung which if left unresolved can manifest in pulmonary fibrosis. In these processes, alveolar macrophages have an essential role and timely modulation of the macrophage phenotype is imperative in the onset and resolution of inflammatory responses. This study aimed to investigate, the immunomodulating properties of two industrially relevant high aspect ratio nanomaterials, namely nanocellulose and multiwalled carbon nanotubes (MWCNT), in an alveolar macrophage model.

Methods

MH-S alveolar macrophages were exposed at air-liquid interface to cellulose nanocrystals (CNC), cellulose nanofibers (CNF) and two MWCNT (NM-400 and NM-401). Following exposure, changes in macrophage polarization markers and secretion of inflammatory cytokines were analyzed. Furthermore, the potential contribution of epigenetic regulation in nanomaterial-induced macrophage polarization was investigated by assessing changes in epigenetic regulatory enzymes, miRNAs, and rRNA modifications.

Results

Our data illustrate that the investigated nanomaterials trigger phenotypic changes in alveolar macrophages, where CNF exposure leads to enhanced M1 phenotype and MWCNT promotes M2 phenotype. Furthermore, MWCNT exposure induced more prominent epigenetic regulatory events with changes in the expression of histone modification and DNA methylation enzymes as well as in miRNA transcript levels. MWCNT-enhanced changes in the macrophage phenotype were correlated with prominent downregulation of the histone methyltransferases Kmt2a and Smyd5 and histone deacetylases Hdac4, Hdac9 and Sirt1 indicating that both histone methylation and acetylation events may be critical in the Th2 responses to MWCNT. Furthermore, MWCNT as well as CNF exposure led to altered miRNA levels, where miR-155-5p, miR-16-1-3p, miR-25-3p, and miR-27a-5p were significantly regulated by both materials. PANTHER pathway analysis of the identified miRNA targets showed that both materials affected growth factor (PDGF, EGF and FGF), Ras/MAPKs, CCKR, GnRH-R, integrin, and endothelin signaling pathways. These pathways are important in inflammation or in the activation, polarization, migration, and regulation of phagocytic capacity of macrophages. In addition, pathways involved in interleukin, WNT and TGFB signaling were highly enriched following MWCNT exposure.

Conclusion

Together, these data support the importance of macrophage phenotypic changes in the onset and resolution of inflammation and identify epigenetic patterns in macrophages which may be critical in nanomaterial-induced inflammation and fibrosis.

Grouping MWCNTs based on their similar potential to cause pulmonary hazard after inhalation: a case-study

BACKGROUND

The EU-project GRACIOUS developed an Integrated Approach to Testing and Assessment (IATA) to support grouping high aspect ratio nanomaterials (HARNs) presenting a similar inhalation hazard. Application of grouping reduces the need to assess toxicity on a case-by-case basis and supports read-across of hazard data from substances that have the data required for risk assessment (source) to those that lack such data (target). The HARN IATA, based on the fibre paradigm for pathogenic fibres, facilitates structured data gathering to propose groups of similar HARN and to support read-across by prompting users to address relevant questions regarding HARN morphology, biopersistence and inflammatory potential. The IATA is structured in tiers, allowing grouping decisions to be made using simple in vitro or in silico methods in Tier1 progressing to in vivo approaches at the highest Tier3. Here we present a case-study testing the applicability of GRACIOUS IATA to form an evidence-based group of multiwalled carbon nanotubes (MWCNT) posing a similar predicted fibre-hazard, to support read-across and reduce the burden of toxicity testing.

RESULTS

The case-study uses data on 15 different MWCNT, obtained from the published literature. By following the IATA, a group of 2 MWCNT was identified (NRCWE006 and NM-401) based on a high degree of similarity. A pairwise similarity assessment was subsequently conducted between the grouped MWCNT to evaluate the potential to conduct read-across and fill data gaps required for regulatory hazard assessment. The similarity assessment, based on expert judgement of Tier 1 assay results, predicts both MWCNT are likely to cause a similar acute in vivo hazard. This result supports the possibility for read-across of sub-chronic and chronic hazard endpoint data for lung fibrosis and carcinogenicity between the 2 grouped MWCNT. The implications of accepting the similarity assessment based on expert judgement of the MWCNT group are considered to stimulate future discussion on the level of similarity between group members considered sufficient to allow regulatory acceptance of a read-across argument.

CONCLUSION

This proof-of-concept case-study demonstrates how a grouping hypothesis and IATA may be used to support a nuanced and evidence-based grouping of 'similar' MWCNT and the subsequent interpolation of data between group members to streamline the hazard assessment process.

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.

Innate but Not Adaptive Immunity Regulates Lung Recovery from Chronic Exposure to Graphene Oxide Nanosheets

Graphene has drawn a lot of interest in the material community due to unique physicochemical properties. Owing to a high surface area to volume ratio and free oxygen groups, the oxidized derivative, graphene oxide (GO) has promising potential as a drug delivery system. Here, the lung tolerability of two distinct GO varying in lateral dimensions is investigated, to reveal the most suitable candidate platform for pulmonary drug delivery. Following repeated chronic pulmonary exposure of mice to GO sheet suspensions, the innate and adaptive immune responses are studied. An acute and transient influx of neutrophils and eosinophils in the alveolar space, together with the replacement of alveolar macrophages by interstitial ones and a significant activation toward anti-inflammatory subsets, are found for both GO materials. Micrometric GO give rise to persistent multinucleated macrophages and granulomas. However, neither adaptive immune response nor lung tissue remodeling are induced after exposure to micrometric GO. Concurrently, milder effects and faster tissue recovery, both associated to a faster clearance from the respiratory tract, are found for nanometric GO, suggesting a greater lung tolerability. Taken together, these results highlight the importance of dimensions in the design of biocompatible 2D materials for pulmonary drug delivery system.

Evaluation of TNF Family Gene Expression under the Influence of Single-Walled and Multi-Walled Carboxylated Carbon Nanotubes in Jurkat Cell Line and Rat

Background:

Nanomaterials, e.g.carbon nanotubes (CNTs), have broad usage in medicine for diagnosis, treatment, and drug delivery. Prior to the widespread use of CNTs, any potential toxicity issues must be considered. Apoptosis is an important issue in toxicological studies, and tumor necrosis factor (TNF) family members execute crucial roles in apoptosis and inflammation. We examined the survival of Jurkat cells under the influence of single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNTs) as well as their impacts on the mRNA levels of TNF family transcripts in Jurkat cells and rats.

Objective:

To evaluate the toxicity or safety of a specific concentration and form of CNT on the expression of one of the gene families of the apoptotic pathway.

Materials and Methods:

Jurkat cells were exposed to SWCNTs and MWCNTs in carboxylated form (SWCNTS-COOH and MWCNTs-COOH). MTT assay assessed the cell survival, and using qRT-PCR, the expression levels of TNF, CD40LG, TNFSF10, TNFSF8, CD40, TNFRSF10A, TNFRSF10B, TNFRSF11B, TNFRSF1A, TNFRSF21, TNFRSF25, and TNFRSF9 were examined. The housekeeping genes β-actin and glyceraldehyde 3-phosphate dehydrogenase was utilized for normalization. We also evaluated the expression levels of TNF and TNFRSF10A in rats in vivo 30 and 60 days after being injected with CNTs.

Results:

After 72 h of carboxylated CNTs at 100 µg. mL^-1, no significant change was observed in the survival rate of treated Jurkat cells. The expression of two genes (TNF and TNFRSF10A) changed significantly. Examining the expression profiles of these two genes in rats demonstrated an insignificant change in the expression of any of these genes after 30 and 60 days. The qRT-PCR analysis exhibited the elevated levels of TNF and TNFRSF10A mRNA in the CNT-treated cells, while expression of other TNF family members did not significantly differ from control (untreated) Jurkat cells. There was also no significant change in the gene expression levels of TNF and TNFRSF10A in CNT-treated rats after 30 and 60 days.

Conclusions:

Administration of SWCNTs-COOH and MWCNTs-COOH could result in the up-regulation of TNF and TNFRSF10A but did not initiate apoptosis in Jurkat cells. Carboxylated SWCNTs showed more potent activity than MWCNTs in activating TNF gene expression and probably trigger cell death through external apoptotic pathways.

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.

A 3D-Printed Multi-Chamber Device Allows Culturing Cells On Buckypapers Coated With PAMAM Dendrimer And Obtain Innovative Materials For Biomedical Applications

Background

The advent of 3D printing technology allowed the realization of custom devices that can be used not only in the everyday life but also in the nanotechnology and biomedical fields. In nanotechnology, the use of bi-dimensional nanostructures based on carbon nanotubes, generally referred as buckypapers, have received considerable attention for their versatility and potential application in many biomedical fields. Unfortunately, buckypapers are extremely hydrophobic and cannot be used in aqueous media to culture cells.

Methods

A polymeric device able to accommodate buckypapers and facilitate cell growth was fabricated by using 3D printing technology. We imparted hydrophilicity to buckypapers by coating them with polyamidoamine (PAMAM) dendrimers.

Results

We found that by using novel techniques such as polymer coating the buckypaper hydrophilicity increased, whereas the use of 3D printing technology allowed us to obtain custom devices that have been used to culture cells on buckypapers for many days. We characterized in details the morphology of these structures and studied for the first time the kinetic of cell proliferation. We found that these scaffolds, if properly functionalized, are suitable materials to grow cells for long time and potentially employable in the biomedical field.

Conclusion

Although these materials are cytotoxic under certain circumstances, we have found a suitable coating and specific experimental conditions that encourage using buckypapers as novel scaffolds for cell growth and for potential applications in tissue repair and regeneration.

Effects of physicochemical properties of TiO2 nanomaterials for pulmonary inflammation, acute phase response and alveolar proteinosis in intratracheally exposed mice

Nanomaterial (NM) characteristics may affect the pulmonary toxicity and inflammatory response, including specific surface area, size, shape, crystal phase or other surface characteristics. Grouping of TiO₂ in hazard assessment might be challenging because of variation in physicochemical properties. We exposed C57BL/6 J mice to a single dose of four anatase TiO₂ NMs with various sizes and shapes by intratracheal instillation and assessed the pulmonary toxicity 1, 3, 28, 90 or 180 days post-exposure. The quartz DQ12 was included as benchmark particle. Pulmonary responses were evaluated by histopathology, electron microscopy, bronchoalveolar lavage (BAL) fluid cell composition and acute phase response. Genotoxicity was evaluated by DNA strand break levels in BAL cells, lung and liver in the comet assay. Multiple regression analyses were applied to identify specific TiO₂ NMs properties important for the pulmonary inflammation and acute phase response. The TiO₂ NMs induced similar inflammatory responses when surface area was used as dose metrics, although inflammatory and acute phase response was greatest and more persistent for the TiO₂ tube. Similar histopathological changes were observed for the TiO₂ tube and DQ12 including pulmonary alveolar proteinosis indicating profound effects related to the tube shape. Comparison with previously published data on rutile TiO₂ NMs indicated that rutile TiO₂ NMs were more inflammogenic in terms of neutrophil influx than anatase TiO₂ NMs when normalized to total deposited surface area. Overall, the results suggest that specific surface area, crystal phase and shape of TiO₂ NMs are important predictors for the observed pulmonary effects of TiO₂ NMs.

Advances in Nano Neuroscience: From Nanomaterials to Nanotools

During the last decades, neuroscientists have increasingly exploited a variety of artificial, de-novo synthesized materials with controlled nano-sized features. For instance, a renewed interest in the development of prostheses or neural interfaces was driven by the availability of novel nanomaterials that enabled the fabrication of implantable bioelectronics interfaces with reduced side effects and increased integration with the target biological tissue. The peculiar physical-chemical properties of nanomaterials have also contributed to the engineering of novel imaging devices toward sophisticated experimental settings, to smart fabricated scaffolds and microelectrodes, or other tools ultimately aimed at a better understanding of neural tissue functions. In this review, we focus on nanomaterials and specifically on carbon-based nanomaterials, such as carbon nanotubes (CNTs) and graphene. While these materials raise potential safety concerns, they represent a tremendous technological opportunity for the restoration of neuronal functions. We then describe nanotools such as nanowires and nano-modified MEA for high-performance electrophysiological recording and stimulation of neuronal electrical activity. We finally focus on the fabrication of three-dimensional synthetic nanostructures, used as substrates to interface biological cells and tissues in vitro and in vivo.

Physicochemical predictors of Multi-Walled Carbon Nanotube-induced pulmonary histopathology and toxicity one year after pulmonary deposition of 11 different Multi-Walled Carbon Nanotubes in mice

Multi‐walled carbon nanotubes (MWCNT) are widely used nanomaterials that cause pulmonary toxicity upon inhalation. The physicochemical properties of MWCNT vary greatly, which makes general safety evaluation challenging to conduct. Identification of the toxicity‐inducing physicochemical properties of MWCNT is therefore of great importance. We have evaluated histological changes in lung tissue 1 year after a single intratracheal instillation of 11 well‐characterized MWCNT in female C57BL/6N BomTac mice. Genotoxicity in liver and spleen was evaluated by the comet assay. The dose of 54 μg MWCNT corresponds to three times the estimated dose accumulated during a work life at a NIOSH recommended exposure limit (0.001 mg/m³). Short and thin MWCNT were observed as agglomerates in lung tissue 1 year after exposure, whereas thicker and longer MWCNT were detected as single fibres, suggesting biopersistence of both types of MWCNT. The thin and entangled MWCNT induced varying degree of pulmonary inflammation, in terms of lymphocytic aggregates, granulomas and macrophage infiltration, whereas two thick and straight MWCNT did not. By multiple regression analysis, larger diameter and higher content of iron predicted less histopathological changes, whereas higher cobalt content significantly predicted more histopathological changes. No MWCNT‐related fibrosis or tumours in the lungs or pleura was found. One thin and entangled MWCNT induced increased levels of DNA strand breaks in liver; however, no physicochemical properties could be related to genotoxicity. This study reveals physicochemical‐dependent difference in MWCNT‐induced long‐term, pulmonary histopathological changes. Identification of diameter size and cobalt content as important for MWCNT toxicity provides clues for designing MWCNT, which cause reduced human health effects following pulmonary exposure.

Role of p53 in the chronic pulmonary immune response to tangled or rod-like multi-walled carbon nanotubes

The fiber-like shape of multi-walled carbon nanotubes (MWCNTs) is reminiscent of asbestos, suggesting they pose similar health hazards when inhaled, including pulmonary fibrosis and mesothelioma. Mice deficient in the tumor suppressor p53 are susceptible to carcinogenesis. However, the chronic pathologic effect of MWCNTs delivered to the lungs of p53 heterozygous (p53^+/-) mice has not been investigated. We hypothesized that p53^+/- mice would be susceptible to lung tumor development after exposure to either tangled (t-) or rod-like (r-) MWCNTs. Wild-type (p53^+/+) or p53^+/- mice were exposed to MWCNTs (1 mg/kg) via oropharyngeal aspiration weekly over four consecutive weeks and evaluated for cellular and pathologic outcomes 11-months post-initial exposure. No lung or pleural tumors were observed in p53^+/+ or p53^+/- mice exposed to either t- or rMWCNTs. In comparison to tMWCNTs, the rMWCNTs induced the formation of larger granulomas, a greater number of lymphoid aggregates and greater epithelial cell hyperplasia in terminal bronchioles in both p53^+/- and p53^+/+ mice. A constitutively larger area of CD45R⁺/CD3⁺ lymphoid tissue was observed in p53^+/- mice compared to p53^+/+ mice. Importantly, p53^+/- mice had larger granulomas induced by rMWCNTs as compared to p53^+/+ mice. These findings indicate that a combination of p53 deficiency and physicochemical characteristics including nanotube geometry are factors in susceptibility to MWCNT-induced lymphoid infiltration and granuloma formation.

Biophysical and biological contributions of polyamine-coated carbon nanotubes and bidimensional buckypapers in the delivery of miRNAs to human cells

Recent findings in nanomedicine have revealed that carbon nanotubes (CNTs) can be used as potential drug carriers, therapeutic agents and diagnostics tools. Moreover, due to their ability to cross cellular membranes, their nanosize dimension, high surface area and relatively good biocompatibility, CNTs have also been employed as a novel gene delivery vector system. In our previous work, we functionalized CNTs with two polyamine polymers, polyethyleneimine (PEI) and polyamidoamine dendrimer (PAMAM). These compounds have low cytotoxicity, ability to conjugate microRNAs (such as miR-503) and, at the same time, transfect efficiently endothelial cells. The parameters contributing to the good efficiency of transfection that we observed were not investigated in detail. In fact, the diameter and length of CNTs are important parameters to be taken into account when evaluating the effects on drug delivery efficiency. In order to investigate the biophysical and biological contributions of polymer-coated CNTs in delivery of miRNAs to human cells, we decided to investigate three different preparations, characterized by different dimensions and aspect ratios. In particular, we took into account very small CNTs, a suspension of CNTs starting from the commercial product and a 2D material based on CNTs (ie, buckypapers [BPs]) to examine the transfection efficiency of a rigid scaffold. In conclusion, we extensively investigated the biophysical and biological contributions of polyamine-coated CNTs and bidimensional BPs in the delivery of miRNAs to human cells, in order to optimize the transfection efficiency of these compounds to be employed as efficient drug delivery vectors in biomedical applications.

Biophysical and biological contributions of polyamine-coated carbon nanotubes and bidimensional buckypapers in the delivery of miRNAs to human cells

Recent findings in nanomedicine have revealed that carbon nanotubes (CNTs) can be used as potential drug carriers, therapeutic agents and diagnostics tools. Moreover, due to their ability to cross cellular membranes, their nanosize dimension, high surface area and relatively good biocompatibility, CNTs have also been employed as a novel gene delivery vector system. In our previous work, we functionalized CNTs with two polyamine polymers, polyethyleneimine (PEI) and polyamidoamine dendrimer (PAMAM). These compounds have low cytotoxicity, ability to conjugate microRNAs (such as miR-503) and, at the same time, transfect efficiently endothelial cells. The parameters contributing to the good efficiency of transfection that we observed were not investigated in detail. In fact, the diameter and length of CNTs are important parameters to be taken into account when evaluating the effects on drug delivery efficiency. In order to investigate the biophysical and biological contributions of polymer-coated CNTs in delivery of miRNAs to human cells, we decided to investigate three different preparations, characterized by different dimensions and aspect ratios. In particular, we took into account very small CNTs, a suspension of CNTs starting from the commercial product and a 2D material based on CNTs (ie, buckypapers [BPs]) to examine the transfection efficiency of a rigid scaffold. In conclusion, we extensively investigated the biophysical and biological contributions of polyamine-coated CNTs and bidimensional BPs in the delivery of miRNAs to human cells, in order to optimize the transfection efficiency of these compounds to be employed as efficient drug delivery vectors in biomedical applications.

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.

Multi-walled carbon nanotube-induced genotoxic, inflammatory and pro-fibrotic responses in mice: Investigating the mechanisms of pulmonary carcinogenesis

The International Agency for Research on Cancer has classified one type of multi-walled carbon nanotubes (MWCNTs) as possibly carcinogenic to humans. However, the underlying mechanisms of MWCNT- induced carcinogenicity are not known. In this study, the genotoxic, mutagenic, inflammatory, and fibrotic potential of MWCNTs were investigated. Muta™Mouse adult females were exposed to 36±6 or 109±18μg/mouse of Mitsui-7, or 26±2 or 78±5μg/mouse of NM-401, once a week for four consecutive weeks via intratracheal instillations, alongside vehicle-treated controls. Samples were collected 90days following the first exposure for measurement of DNA strand breaks, lacZ mutant frequency, p53 expression, cell proliferation, lung inflammation, histopathology, and changes in global gene expression. Both MWCNT types persisted in lung tissues 90days post-exposure, and induced lung inflammation and fibrosis to similar extents. However, there was no evidence of DNA damage as measured by the comet assay following Mitsui-7 exposure, or increases in lacZ mutant frequency, for either MWCNTs. Increased p53 expression was observed in the fibrotic foci induced by both MWCNTs. Gene expression analysis revealed perturbations of a number of biological processes associated with cancer including cell death, cell proliferation, free radical scavenging, and others in both groups, with the largest response in NM-401-treated mice. The results suggest that if the two MWCNT types were capable of inducing DNA damage, strong adaptive responses mounted against the damage, resulting in efficient and timely elimination of damaged cells through cell death, may have prevented accumulation of DNA damage and mutations at the post-exposure time point investigated in the study. Thus, MWCNT-induced carcinogenesis may involve ongoing low levels of DNA damage in an environment of persisting fibres, chronic inflammation and tissue irritation, and parallel increases or decreases in the expression of genes involved in several pro-carcinogenic pathways.

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.

Identification of Gene Transcription Start Sites and Enhancers Responding to Pulmonary Carbon Nanotube Exposure in Vivo

Increased use of nanomaterials in industry, medicine, and consumer products has raised concerns over their toxicity. To ensure safe use of nanomaterials, understanding their biological effects at the molecular level is crucial. In particular, the regulatory mechanisms responsible for the cascade of genes activated by nanomaterial exposure are not well-characterized. To this end, we profiled the genome-wide usage of gene transcription start sites and linked active enhancer regions in lungs of C57BL/6 mice 24 h after intratracheal instillation of a single dose of the multiwalled carbon nanotube (MWCNT) Mitsui-7. Our results revealed a massive gene regulatory response, where expression of key inflammatory genes (e.g., Csf3, Il24, and Fgf23) was increased >100-fold 24 h after Mitsui-7 exposure. Many of the Mitsui-7-responsive transcription start sites were alternative transcription start sites for known genes, and the number of alternative transcription start sites used in a given gene was correlated with overall Mitsui-7 response. Strikingly, genes that were up-regulated after Mitsui-7 exposure only through their main annotated transcription start site were linked to inflammatory and defense responses, while genes up-regulated only through alternative transcription start sites were functionally heterogeneous and not inflammation-associated. Furthermore, we identified almost 12 000 active enhancers, many of which were Mitsui-7-responsive, and we identified similarly responding putative target genes. Overall, our study provides the location and activity of Mitsui-7-induced enhancers and transcription start sites, providing a useful resource for targeted experiments elucidating the biological effects of nanomaterials and the identification of biomarkers for early detection of MWCNT-induced inflammation.

Multi-walled carbon nanotube physicochemical properties predict pulmonary inflammation and genotoxicity

Lung deposition of multi-walled carbon nanotubes (MWCNT) induces pulmonary toxicity. Commercial MWCNT vary greatly in physicochemical properties and consequently in biological effects. To identify determinants of MWCNT-induced toxicity, we analyzed the effects of pulmonary exposure to 10 commercial MWCNT (supplied in three groups of different dimensions, with one pristine and two/three surface modified in each group). We characterized morphology, chemical composition, surface area and functionalization levels. MWCNT were deposited in lungs of female C57BL/6J mice by intratracheal instillation of 0, 6, 18 or 54 μg/mouse. Pulmonary inflammation (neutrophil influx in bronchoalveolar lavage (BAL)) and genotoxicity were determined on day 1, 28 or 92. Histopathology of the lungs was performed on day 28 and 92. All MWCNT induced similar histological changes. Lymphocytic aggregates were detected for all MWCNT on day 28 and 92. Using adjusted, multiple regression analyses, inflammation and genotoxicity were related to dose, time and physicochemical properties. The specific surface area (BET) was identified as a positive predictor of pulmonary inflammation on all post-exposure days. In addition, length significantly predicted pulmonary inflammation, whereas surface oxidation (–OH and –COOH) was predictor of lowered inflammation on day 28. BET surface area, and therefore diameter, significantly predicted genotoxicity in BAL fluid cells and lung tissue such that lower BET surface area or correspondingly larger diameter was associated with increased genotoxicity. This study provides information on possible toxicity-driving physicochemical properties of MWCNT. The results may contribute to safe-by-design manufacturing of MWCNT, thereby minimizing adverse effects.

High resolution and dynamic imaging of biopersistence and bioreactivity of extra and intracellular MWNTs exposed to microglial cells

Multi-walled carbon nanotubes (MWNTs) are increasingly being developed both as neuro-therapeutic drug delivery systems to the brain and as neural scaffolds to drive tissue regeneration across lesion sites. MWNTs with different degrees of acid oxidation may have different bioreactivities and propensities to aggregate in the extracellular environment, and both individualised and aggregated MWNTs may be expected to be found in the brain. Before practical application, it is vital to understand how both aggregates and individual MWNTs will interact with local phagocytic immune cells, the microglia, and ultimately to determine their biopersistence in the brain. The processing of extra- and intracellular MWNTs (both pristine and when acid oxidised) by microglia was characterised across multiple length scales by correlating a range of dynamic, quantitative and multi-scale techniques, including: UV-vis spectroscopy, light microscopy, focussed ion beam scanning electron microscopy and transmission electron microscopy. Dynamic, live cell imaging revealed the ability of microglia to break apart and internalise micron-sized extracellular agglomerates of acid oxidised MWNTs, but not pristine MWNTs. The total amount of MWNTs internalised by, or strongly bound to, microglia was quantified as a function of time. Neither the significant uptake of oxidised MWNTs, nor the incomplete uptake of pristine MWNTs affected microglial viability, pro-inflammatory cytokine release or nitric oxide production. However, after 24 h exposure to pristine MWNTs, a significant increase in the production of reactive oxygen species was observed. Small aggregates and individualised oxidised MWNTs were present in the cytoplasm and vesicles, including within multilaminar bodies, after 72 h. Some evidence of morphological damage to oxidised MWNT structure was observed including highly disordered graphitic structures, suggesting possible biodegradation. This work demonstrates the utility of dynamic, quantitative and multi-scale techniques in understanding the different cellular processing routes of functionalised nanomaterials. This correlative approach has wide implications for assessing the biopersistence of MWNT aggregates elsewhere in the body, in particular their interaction with macrophages in the lung.

Changes in cholesterol homeostasis and acute phase response link pulmonary exposure to multi-walled carbon nanotubes to risk of cardiovascular disease

Adverse lung effects following pulmonary exposure to multi-walled carbon nanotubes (MWCNTs) are well documented in rodents. However, systemic effects are less understood. Epidemiological studies have shown increased cardiovascular disease risk after pulmonary exposure to airborne particles, which has led to concerns that inhalation exposure to MWCNTs might pose similar risks. We analyzed parameters related to cardiovascular disease, including plasma acute phase response (APR) proteins and plasma lipids, in female C57BL/6 mice exposed to a single intratracheal instillation of 0, 18, 54 or 162μg/mouse of small, entangled (CNTSmall, 0.8±0.1μm long) or large, thick MWCNTs (CNTLarge, 4±0.4μm long). Liver tissues and plasma were harvested 1, 3 and 28days post-exposure. In addition, global hepatic gene expression, hepatic cholesterol content and liver histology were used to assess hepatic effects. The two MWCNTs induced similar systemic responses despite their different physicochemical properties. APR proteins SAA3 and haptoglobin, plasma total cholesterol and low-density/very low-density lipoprotein were significantly increased following exposure to either MWCNTs. Plasma SAA3 levels correlated strongly with pulmonary Saa3 levels. Analysis of global gene expression revealed perturbation of the same biological processes and pathways in liver, including the HMG-CoA reductase pathway. Both MWCNTs induced similar histological hepatic changes, with a tendency towards greater response following CNTLarge exposure. Overall, we show that pulmonary exposure to two different MWCNTs induces similar systemic and hepatic responses, including changes in plasma APR, lipid composition, hepatic gene expression and liver morphology. The results link pulmonary exposure to MWCNTs with risk of cardiovascular disease.