Mesothelioma response to carbon nanotubes is associated with an early and selective accumulation of immunosuppressive monocytic cells

Carbon nanotube pathogenicity conforms to a unified theory for mesothelioma causation by elongate materials and fibers

The purpose of this review is to elucidate how dimensional and durability characteristics of high aspect ratio nanomaterials (HARN), including carbon nanotubes (CNT) and metal nanowires (MeNW), contribute to understanding the fiber pathogenicity paradigm (FPP), including by explaining the structure-activity relationships (SAR) of a diverse range of natural and synthetic elongate materials that may or may not contribute to mesothelioma development in the lung. While the FPP was originally developed to explain the critical importance of asbestos and synthetic vitreous fiber length, width, aspect ratio and biopersistence in mesothelioma development, there are a vast number of additional inhalable materials that need to be considered in terms of pathogenic features that may contribute to mesothelioma or lack thereof. Not only does the ability to exert more exact control over the length and biopersistence of HARNs confirm the tenets of the FPP, but could be studied by implementating more appropriate toxicological tools for SAR analysis. This includes experimentation with carefully assembled libraries of CNTs and MeNWs, helping to establish more precise dimensional features for interfering in lymphatic drainage from the parietal pleura, triggering of lysosomal damage, frustrated phagocytosis and generation of chronic inflammation. The evidence includes data that long and rigid, but not short and flexible multi-wall CNTs are capable of generating mesotheliomas in rodents based on an adverse outcome pathway requiring access to pleural cavity, obstruction of pleural stomata, chronic inflammation and transformation of mesothelial cells. In addition to durability and dimensional characteristics, bending stiffness of CNTs is a critical factor in determining the shape and rigidity of pathogenic MWCNTs. While no evidence has been obtained in humans that CNT exposure leads to a mesothelioma outcome, it is important to monitor exposure levels and health effect impacts in workers to prevent adverse health outcomes in humans.

Time-Course of Transcriptomic Change in the Lungs of F344 Rats Repeatedly Exposed to a Multiwalled Carbon Nanotube in a 2-Year Test

Despite intensive toxicological studies of carbon nanotubes (CNTs) over the last two decades, only a few studies have demonstrated their pulmonary carcinogenicities in chronic animal experiments, and the underlying molecular mechanisms are still unclear. To obtain molecular insights into CNT-induced lung carcinogenicity, we performed a transcriptomic analysis using a set of lung tissues collected from rats in a 2-year study, in which lung tumors were induced by repeated intratracheal instillations of a multiwalled carbon nanotube, MWNT-7. The RNA-seq-based transcriptome identified a large number of significantly differentially expressed genes at Year 0.5, Year 1, and Year 2. Ingenuity Pathway Analysis revealed that macrophage-elicited signaling pathways such as phagocytosis, acute phase response, and Toll-like receptor signaling were activated throughout the experimental period. At Year 2, cancer-related pathways including ERBB signaling and some axonal guidance signaling pathways such as EphB4 signaling were perturbed. qRT-PCR and immunohistochemistry indicated that several key molecules such as Osteopontin/Spp1, Hmox1, Mmp12, and ERBB2 were markedly altered and/or localized in the preneoplastic lesions, suggesting their participation in the induction of lung cancer. Our findings support a scenario of inflammation-induced carcinogenesis and contribute to a better understanding of the molecular mechanism of MWCNT carcinogenicity.

Myeloid-derived suppressor cells and pulmonary hypertension

Pulmonary hypertension (PH) is a chronic pulmonary vascular disorder characterized by an increase in pulmonary vascular resistance and pulmonary arterial pressure. The detailed molecular mechanisms remain unclear. In recent decades, increasing evidence shows that altered immune microenvironment, comprised of immune cells, mesenchymal cells, extra-cellular matrix and signaling molecules, might induce the development of PH. Myeloid-derived suppressor cells (MDSCs) have been proposed over 30 years, and the functional importance of MDSCs in the immune system is appreciated recently. MDSCs are a heterogeneous group of cells that expand during cancer, chronic inflammation and infection, which have a remarkable ability to suppress T-cell responses and may exacerbate the development of diseases. Thus, targeting MDSCs has become a novel strategy to overcome immune evasion, especially in tumor immunotherapy. Nowadays, severe PH is accepted as a cancer-like disease, and MDSCs are closely related to the development and prognosis of PH. Here, we review the relationship between MDSCs and PH with respect to immune cells, cytokines, chemokines and metabolism, hoping that the key therapeutic targets of MDSCs can be identified in the treatment of PH, especially in severe PH.

Continuous infiltration of small peritoneal macrophages in the mouse peritoneum through CCR2-dependent and -independent routes during fibrosis and mesothelioma development induced by a multiwalled carbon nanotube, MWNT-7

Although toxicities of multiwalled carbon nanotube (MWCNT) have been found to be related with activities of macrophages phagocytosing the fibers, the exact relationship between macrophage population and pathogenesis of fibrosis and mesotheliomas induced by MWCNTs is largely unknown. CCL2-CCR2 axis, a major monocyte/macrophage infiltration route, is thought to be involved in not only acute inflammation but also the formation of tumor microenvironment. We therefore described a time-course of alteration of macrophage population in an attempt to clarify the contribution of the Ccr2 gene to mesotheliomagenesis. Wild-type (WT) C57BL/6 mice and Ccr2-knockout (KO) mice were intraperitoneally administered with MWNT-7 and were sequentially necropsied at 1, 7, 28, 90, and 245 day(s) after the injection. Peritoneal fibrosis was prominent in all MWCNT-treated mice, with a lower severity in the KO mice. No differences were observed in the incidences of neoplastic lesions of mesothelia between WT and KO mice. A flow cytometric analysis revealed that after gross disappearance of macrophages after MWCNT exposure, small peritoneal macrophages (SPMs) were exclusively refurbished by the CCR2-dependent route at day 1 (as Ly-6C+MHC class II- cells), followed by additional CCR2-independent routes (as Ly-6C-MHC class II- cells); i.e., the only route in KO mice; with a delay of 1-7 days. The SPMs derived from both routes appeared to differentiate into maturated cells as Ly-6C-MHC class II+, whose ratio increased in a time-dependent manner among the total SPM population. Additionally, most macrophages expressed M1-like features, but a small fraction of macrophages exhibited an M1/M2 mixed status in MWCNT-treated animals. Our findings demonstrate a long-persistent activation of the CCL2-CCR2 axis after MWCNT exposure and enable a better understanding of the participation and potential roles of SPMs in fibrous material-induced chronic toxicities.

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.

Single-cell transcriptomics reveals immune dysregulation mediated by IL-17A in initiation of chronic lung injuries upon real-ambient particulate matter exposure

Background

Long-term exposure to fine particulate matter (PM_2.5) increases susceptibility to chronic respiratory diseases, including inflammation and interstitial fibrosis. However, the regulatory mechanisms by which the immune response mediates the initiation of pulmonary fibrosis has yet to be fully characterized. This study aimed to illustrate the interplay between different cell clusters and key pathways in triggering chronic lung injuries in mice following PM exposure.

Results

Six-week-old C57BL/6J male mice were exposed to PM or filtered air for 16 weeks in a real-ambient PM exposure system in Shijiazhuang, China. The transcriptional profiles of whole lung cells following sub-chronic PM exposure were characterized by analysis of single-cell transcriptomics. The IL-17A knockout (IL-17A^−/−) mouse model was utilized to determine whether the IL-17 signaling pathway mediated immune dysregulation in PM-induced chronic lung injuries. After 16-week PM exposure, chronic lung injuries with excessive collagen deposition and increased fibroblasts, neutrophils, and monocytes were noted concurrent with a decreased number of major classes of immune cells. Single-cell analysis showed that activation of the IL-17 signaling pathway was involved in the progression of pulmonary fibrosis upon sub-chronic PM exposure. Depletion of IL-17A led to significant decline in chronic lung injuries, which was mainly triggered by reduced recruitment of myeloid-derived suppressor cells (MDSCs) and downregulation of TGF-β.

Conclusion

These novel findings demonstrate that immunosuppression via the IL-17A pathway plays a critical role in the initiation of chronic lung injuries upon sub-chronic PM exposure.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-022-00483-w.

Two-year intermittent exposure of a multiwalled carbon nanotube by intratracheal instillation induces lung tumors and pleural mesotheliomas in F344 rats

BACKGROUND

A mounting number of studies have been documenting the carcinogenic potential of multiwalled carbon nanotubes (MWCNTs); however, only a few studies have evaluated the pulmonary carcinogenicity of MWCNTs in vivo. A 2-year inhalation study demonstrated that MWNT-7, a widely used MWCNT, was a pulmonary carcinogen in rats. In another 2-year study, rats administered MWNT-7 by intratracheal instillation at the beginning of the experimental period developed pleural mesotheliomas but not lung tumors. To obtain data more comparable with rats exposed to MWNT-7 by inhalation, we administered MWNT-7 to F344 rats by intratracheal instillation once every 4-weeks over the course of 2 years at 0, 0.125, and 0.5 mg/kg body weight, allowing lung burdens of MWNT-7 to increase over the entire experimental period, similar to the inhalation study.

RESULTS

Absolute and relative lung weights were significantly elevated in both MWNT-7-treated groups. Dose- and time-dependent toxic effects in the lung and pleura, such as inflammatory, fibrotic, and hyperplastic lesions, were found in both treated groups. The incidences of lung carcinomas, lung adenomas, and pleural mesotheliomas were significantly increased in the high-dose group compared with the control group. The pleural mesotheliomas developed mainly at the mediastinum. No MWNT-7-related neoplastic lesions were noted in the other organs. Cytological and biochemical parameters of the bronchoalveolar lavage fluid (BALF) were elevated in both treated groups. The lung burden of MWNT-7 was dose- and time-dependent, and at the terminal necropsy, the average value was 0.9 and 3.6 mg/lung in the low-dose and high-dose groups, respectively. The number of fibers in the pleural cavity was also dose- and time-dependent.

CONCLUSIONS

Repeated administration of MWNT-7 by intratracheal instillation over the 2 years indicates that MWNT-7 is carcinogenic to both the lung and pleura of rats, which differs from the results of the 2 carcinogenicity tests by inhalation or intratracheal instillation.

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.

Promotion of trained innate immunity by nanoparticles

The dogma that immunological memory is an exclusive trait of adaptive immunity has been recently challenged by studies showing that priming of innate cells can also result in modified long-term responsiveness to secondary stimuli, once the cells have returned to a non-activated state. This phenomenon is known as 'innate immune memory', 'trained immunity' or 'innate training'. While the main known triggers of trained immunity are microbial-derived molecules such as β-glucan, endogenous particles such as oxidized low-density lipoprotein and monosodium urate crystals can also induce trained phenotypes in innate cells. Whether exogenous particles can induce trained immunity has been overlooked. Our exposure to particulates has dramatically increased in recent decades as a result of the broad medical use of particle-based drug carriers, theragnostics, adjuvants, prosthetics and an increase in environmental pollution. We recently showed that pristine graphene can induce trained immunity in macrophages, enhancing their inflammatory response to TLR agonists, proving that exogenous nanomaterials can affect the long-term response of innate cells. The consequences of trained immunity can be beneficial, for instance, enhancing protection against unrelated pathogens; however, they can also be deleterious if they enhance inflammatory disorders. Therefore, studying the ability of particulates and biomaterials to induce innate trained phenotypes in cells is warranted. Here we analyse the mechanisms whereby particles can induce trained immunity and discuss how physicochemical characteristics of particulates could influence the induction of innate memory. We review the implications of trained immunity in the context of particulate adjuvants, nanocarriers and nanovaccines and their potential applications in medicine. Finally, we reflect on the unanswered questions and the future of the field.

Carbon Nanotubes: A Summary of Beneficial and Dangerous Aspects of an Increasingly Popular Group of Nanomaterials

Carbon nanotubes (CNTs) are nanomaterials with broad applications that are produced on a large scale. Animal experiments have shown that exposure to CNTs, especially one type of multi-walled carbon nanotube, MWCNT-7, can lead to malignant transformation. CNTs have characteristics similar to asbestos (size, shape, and biopersistence) and use the same molecular mechanisms and signaling pathways as those involved in asbestos tumorigenesis. Here, a comprehensive review of the characteristics of carbon nanotubes is provided, as well as insights that may assist in the design and production of safer nanomaterials to limit the hazards of currently used CNTs.

Monocytic Ontogeny of Regenerated Macrophages Characterizes the Mesotheliomagenic Responses to Carbon Nanotubes

Macrophages are not only derived from circulating blood monocytes or embryonic precursors but also expand by proliferation. The origin determines macrophage fate and functions in steady state and pathological conditions. Macrophages predominantly infiltrate fibre-induced mesothelioma tumors and contribute to cancer development. Here, we revealed their ontogeny by comparing the response to needle-like mesotheliomagenic carbon nanotubes (CNT-7) with tangled-like non-mesotheliomagenic CNT-T. In a rat peritoneal cavity model of mesothelioma, both CNT induced a rapid macrophage disappearance reaction (MDR) of MHCII^low resident macrophages generating an empty niche available for macrophage repopulation. Macrophage depletion after mesotheliomagenic CNT-7 was followed by a substantial inflammatory reaction, and macrophage replenishment completed after 7 days. Thirty days after non-mesotheliomagenic CNT-T, macrophage repopulation was still incomplete and accompanied by a limited inflammatory reaction. Cell depletion experiments, flow cytometry and RNA-seq analysis demonstrated that, after mesotheliomagenic CNT-7 exposure, resident macrophages were mainly replaced by an influx of monocytes, which differentiated locally into MHCII^high inflammatory macrophages. In contrast, the low inflammatory response induced by CNT-T was associated by the accumulation of self-renewing MHCII^low macrophages that initially derive from monocytes. In conclusion, the mesotheliomagenic response to CNT specifically relies on macrophage niche recolonization by monocyte-derived inflammatory macrophages. In contrast, the apparent homeostasis after non-mesotheliomagenic CNT treatment involves a macrophage regeneration by proliferation. Macrophage depletion and repopulation are thus decisive events characterizing the carcinogenic activity of particles and fibres.

Inflammatory response, reactive oxygen species production and DNA damage in mice after intrapleural exposure to carbon nanotubes

Carbon nanotubes (CNTs) are speculated to cause mesothelioma by persistent inflammation, oxidative stress, tissue injury and genotoxicity. To investigate pleural response to CNTs, we exposed C57BL/6 mice by intrapleural injection of 0.2 or 5 µg multi-walled CNTs (MWCNT-7, NM-401 and NM-403) or single-walled CNTs (NM-411). Inflammatory response, cellular reactive oxygen species (ROS) production of pleural lavage cells and genotoxicity in cells from the mesothelial surface were assessed at day 1 and 90 after the exposure. Long and rigid types of MWCNTs (MWCNT-7 and NM-401) caused acute inflammation, characterized by influx of macrophages, neutrophils and eosinophils into the pleural cavity. The inflammation was still evident at 90 days after the exposure, although it had reduced dramatically. The cellular ROS production was increased at day 90 after the exposure to MWCNT-7 and NM-401. The short and tangled type of MWCNT (i.e. NM-403) did not cause pleural inflammation or ROS production in pleural fluid cells. The exposure to NM-411 did not cause consistent inflammation responses or cellular ROS production. Levels of DNA strand breaks and DNA oxidation damage were unaltered, except for NM-411-exposed mice that had increased level of DNA strand breaks at 90 days after the exposure. In conclusion, the long and rigid CNTs caused prolonged inflammatory response and increased ROS production in pleural lavage cells, yet it was not reflected in higher levels of DNA damage in pleural tissue.

Histological sequence of the development of rat mesothelioma by MWCNT, with the involvement of apolipoproteins

A rat model of mesothelioma development by peritoneal injection of multiwalled carbon nanotube (MWCNT) has been established and found to be useful to understand the mechanisms underlying fibrous particles‐associated carcinogenesis. Its detailed histological sequence, however, remains largely obscure. We therefore aimed to assess the time‐course of mesothelioma development by MWCNT and evaluate a set of lipoprotein‐related molecules as potential mechanism‐based biomarkers for the phenomenon. Male Fischer 344 rats were injected intraperitoneally (ip) with MWCNT (MWNT‐7) at 1 mg/kg body weight, and necropsied at 8, 16, 24, 32, or 42 wk after injection. For biochemical analyses of the lipoprotein‐related molecules, more samples, including severe mesothelioma cases, were obtained from 2 other carcinogenicity tests. Histologically, in association with chronic inflammation, mesothelial proliferative lesions appeared at c. Wk‐24. Before and at the beginning of the tumor development, a prominent infiltration of CD163‐positive cells was seen near mesothelial cells. The histological pattern of early mesothelioma was not a papillary structure, but was a characteristic structure with a spherical appearance, composed of the mesothelioma cells in the surface area that were underlain by connective tissue‐like cells. Along with the progression, mesotheliomas started to show versatile histological subtypes. Serum levels of apolipoprotein A‐I and A‐IV, and a ratio of HDL cholesterol to total cholesterol were inversely correlated with mesothelioma severity. Overall, the detailed histological sequence of mesotheliomagenesis by MWCNT is demonstrated, and indicated that the altered profile of apolipoproteins may be involved in its underlying mechanisms.

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

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

Assessment of the Carcinogenicity of Carbon Nanotubes in the Respiratory System

In 2014, the International Agency for Research on Cancer (IARC) classified the first type of carbon nanotubes (CNTs) as possibly carcinogenic to humans, while in the case of other CNTs, it was not possible to ascertain their toxicity due to lack of evidence. Moreover, the physicochemical heterogeneity of this group of substances hamper any generalization on their toxicity. Here, we review the recent relevant toxicity studies produced after the IARC meeting in 2014 on an homogeneous group of CNTs, highlighting the molecular alterations that are relevant for the onset of mesothelioma. Methods: The literature was searched on PubMed and Web of Science for the period 2015-2020, using different combinations keywords. Only data on normal cells of the respiratory system after exposure to fully characterized CNTs for their physico-chemical characteristics were included. Recent studies indicate that CNTs induce a sustained inflammatory response, oxidative stress, fibrosis and histological alterations. The development of mesothelial hyperplasia, mesothelioma, and lungs tumors have been also described in vivo. The data support a strong inflammatory potential of CNTs, similar to that of asbestos, and provide evidence that CNTs exposure led to molecular alterations known to have a key role in mesothelioma onset. These evidences call for an urgent improvement of studies on exposed human populations and adequate systems for monitoring the health of workers exposed to this putative carcinogen.

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.

Functional effects of differentially expressed microRNAs in A549 cells exposed to MWCNT-7 or crocidolite

Multi-walled carbon nanotubes (MWCNT) are engineered nanomaterials widely used in industrial and biomedical applications. Yet, MWCNT inhalation may induce pulmonary adverse effects, and the MWCNT-7 (Mitsui-7) has been classified as possibly carcinogenic to humans. However, its molecular mechanisms of action are poorly understood and there are no biomarkers of exposure for occupational monitoring. Several pulmonary diseases, including lung cancer, have been associated with alterations in microRNA expression that are used as biomarkers of disease progression, and differentially-expressed microRNAs (DE miRNAs) can also allow understanding the molecular effects induced by a toxicant. In this study, we identify DE miRNAs in A549 alveolar epithelial cells following 24 h exposure to MWCNT-7 or crocidolite, as well as their enriched cellular functional pathways. These indicate that both materials change cell survival, differentiation and proliferative properties under the influence of AMPK, FoxO, TGF-β and Hippo pathways, and their metabolic activity and cell-to-cell communication. In addition, MWCNT-7 affects the actin cytoskeleton, ubiquitin mediated proteolysis, and ECM-receptor interactions; crocidolite the PI3K-Akt and mTOR pathways, endocytosis, and central carbon metabolism. Since deregulation of these pathways may be related to carcinogenesis, an interaction network of DE miRNAs and corresponding target cancer-related genes was constructed, highlighting the carcinogenic potential of Mitsui-7.

Cytotoxicity and genotoxicity of MWCNT-7 and crocidolite: assessment in alveolar epithelial cells versus their coculture with monocyte-derived macrophages

In the past years, several in vitro studies have addressed the pulmonary toxicity of multi-walled carbon nanotubes (MWCNT) and compared it with that caused by asbestos fibers, but their conclusions have been somewhat inconsistent and difficult to extrapolate to in vivo. Since cell coculture models were proposed to better represent the in vivo conditions than conventional monocultures, this work intended to compare the cytotoxicity and genotoxicity of MWCNT-7 (Mitsui-7) and crocidolite using A549 cells grown in a conventional monoculture or in coculture with THP-1 macrophages. Although a decrease in A549 viability was noted following exposure to a concentration range of MWCNT-7 and crocidolite, no viability change occurred in similarly exposed cocultures. Early events indicating epithelial to mesenchymal transition (EMT) were observed which could explain apoptosis resistance. The comet assay results were similar between the two models, being positive and negative for crocidolite and MWCNT-7, respectively. An increase in the micronucleus frequency was detected in the cocultured A549-treated cells with both materials, but not in the monoculture. On the other hand, exposure of A549 monocultures to MWCNT-7 induced a highly significant increase in nucleoplasmic bridges in which those were found embedded. Our overall results demonstrate that (i) both materials are cytotoxic and genotoxic, (ii) the presence of THP-1 macrophages upholds the viability of A549 cells and increases the aneugenic/clastogenic effects of both materials probably through EMT, and (iii) MWCNT-7 induces the formation of nucleoplasmic bridges in A549 cells.

Toxicity of Carbon Nanotubes as Anti-Tumor Drug Carriers

Nanoparticle drug formulations have enormous application prospects owing to achievement of targeted and sustained release drug delivery, improvement in drug solubility and reduction of adverse drug reactions. Recently, a variety of efficient drug nanometer carriers have been developed, among which carbon nanotubes (CNT) have been increasingly utilized in the field of cancer therapy. However, these nanotubes exert various toxic effects on the body due to their unique physical and chemical properties. CNT-induced toxicity is related to surface modification, degree of aggregation in vivo, and nanoparticle concentration. This review has focused on the potential toxic effects of CNTs utilized as anti-tumor drug carriers. The main modes by which CNTs enter target sites, the toxicity expressive types and the factors affecting toxicity are discussed.

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.

Advances in Carbon Nanotubes for Malignant Melanoma: A Chance for Treatment

Malignant melanoma is an aggressive skin cancer with limited therapeutic options. Cancer is the second largest cause of death in society and one of the most difficult diseases to treat. Advances in biotechnology have enabled the current use of nanotechnology via the application of nanomaterials, especially as drug delivery systems for the transportation of very small particles. In this context, carbon nanotubes, with a potential role in the diagnosis and treatment of melanoma, are still an emerging research field. Their properties have been extensively studied for the use of antineoplastics drugs, as well as for DNA and RNA interference for the treatment of cancer. However, the most important challenge in nanomedicine is to decrease the toxicity and increase the biocompatibility of the nanomaterials used to transport therapeutic molecules. In this sense, this article addresses the recent advances in the use of carbon nanotubes in melanoma therapy and highlights the opportunities and challenges in this area. The advances and challenges involving these topics are essential to the success of nanoconjugate systems, and studies improving the comprehension of these nanosystems contribute to the development of specific antitumor therapies.

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.

P-Glycoprotein-Targeted Photothermal Therapy of Drug-Resistant Cancer Cells Using Antibody-Conjugated Carbon Nanotubes

P-Glycoprotein (Pgp)-medicated multidrug resistance (MDR) remains a formidable challenge to cancer therapy. As conventional approaches using small-molecule inhibitors failed in clinical development because of the lack of cancer specificity, we develop Pgp-targeted carbon nanotubes to achieve highly cancer-specific therapy through combining antibody-based cancer targeting and locoregional tumor ablation with photothermal therapy. Through a dense coating with phospholipid-poly(ethylene glycol), we have engineered multiwalled carbon nanotubes (MWCNTs) which show minimum nonspecific cell interactions and maximum intercellular diffusion. After chemically modifying with an anti-Pgp antibody, these MWCNTs showed highly Pgp-specific cellular uptake. Treatment of the targeted MWCNTs caused dramatic cytotoxicity in MDR cancer cells upon photoirradiation, whereas they did not cause any toxicity in the dark or phototoxicity toward normal cells that do not express Pgp. Because of excellent intratumor diffusion and Pgp-specific cellular uptake, the targeted MWCNTs produced strong phototoxicity in tumor spheroids of MDR cancer cells, a 3-D tumor model for studying tumor penetration and therapy. In conclusion, we have developed highly Pgp-specific MWCNTs that may provide an effective therapy for MDR cancers where other approaches have failed.

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

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

How asbestos drives the tissue towards tumors: YAP activation, macrophage and mesothelial precursor recruitment, RNA editing, and somatic mutations

Chronic exposure to intraperitoneal asbestos triggered a marked response in the mesothelium well before tumor development. Macrophages, mesothelial precursor cells, cytokines, and growth factors accumulated in the peritoneal lavage. Transcriptome profiling revealed YAP/TAZ activation in inflamed mesothelium with further activation in tumors, paralleled by increased levels of cells with nuclear YAP/TAZ. Arg1 was one of the highest upregulated genes in inflamed tissue and tumor. Inflamed tissue showed increased levels of single-nucleotide variations, with an RNA-editing signature, which were even higher in the tumor samples. Subcutaneous injection of asbestos-treated, but tumor-free mice with syngeneic mesothelioma tumor cells resulted in a significantly higher incidence of tumor growth when compared to naïve mice supporting the role of the environment in tumor progression.

Differences in MWCNT- and SWCNT-induced DNA methylation alterations in association with the nuclear deposition

BACKGROUND

Subtle DNA methylation alterations mediated by carbon nanotubes (CNTs) exposure might contribute to pathogenesis and disease susceptibility. It is known that both multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) interact with nucleus. Such, nuclear-CNT interaction may affect the DNA methylation effects. In order to understand the epigenetic toxicity, in particular DNA methylation alterations, of SWCNTs and short MWCNTs, we performed global/genome-wide, gene-specific DNA methylation and RNA-expression analyses after exposing human bronchial epithelial cells (16HBE14o- cell line). In addition, the presence of CNTs on/in the cell nucleus was evaluated in a label-free way using femtosecond pulsed laser microscopy.

RESULTS

Generally, a higher number of SWCNTs, compared to MWCNTs, was deposited at both the cellular and nuclear level after exposure. Nonetheless, both CNT types were in physical contact with the nuclei. While particle type dependency was noticed for the identified genome-wide and gene-specific alterations, no global DNA methylation alteration on 5-methylcytosine (5-mC) sites was observed for both CNTs. After exposure to MWCNTs, 2398 genes were hypomethylated (at gene promoters), and after exposure to SWCNTs, 589 CpG sites (located on 501 genes) were either hypo- (N = 493 CpG sites) or hypermethylated (N = 96 CpG sites). Cells exposed to MWCNTs exhibited a better correlation between gene promoter methylation and gene expression alterations. Differentially methylated and expressed genes induced changes (MWCNTs > SWCNTs) at different cellular pathways, such as p53 signalling, DNA damage repair and cell cycle. On the other hand, SWCNT exposure showed hypermethylation on functionally important genes, such as SKI proto-oncogene (SKI), glutathione S-transferase pi 1 (GTSP1) and shroom family member 2 (SHROOM2) and neurofibromatosis type I (NF1), which the latter is both hypermethylated and downregulated.

CONCLUSION

After exposure to both types of CNTs, epigenetic alterations may contribute to toxic or repair response. Moreover, our results suggest that the observed differences in the epigenetic response depend on particle type and differential CNT-nucleus interactions.

CCR2+ monocytic myeloid-derived suppressor cells (M-MDSCs) inhibit collagen degradation and promote lung fibrosis by producing transforming growth factor-β1

Monocytes infiltrating scar tissue are predominantly viewed as progenitor cells. Here, we show that tissue CCR2⁺ monocytes have specific immunosuppressive and profibrotic functions. CCR2⁺ monocytic cells are acutely recruited to the lung before the onset of silica-induced fibrosis in mice. These tissue monocytes are defined as monocytic myeloid-derived suppressor cells (M-MDSCs) because they significantly suppress T-lymphocyte proliferation in vitro. M-MDSCs collected from silica-treated mice also express transforming growth factor (TGF)-β1, which stimulates lung fibroblasts to release tissue inhibitor of metalloproteinase (TIMP)-1, an inhibitor of metalloproteinase collagenolytic activity. By using LysMCreCCR2^loxP/loxP mice, we show that limiting CCR2⁺ M-MDSC accumulation reduces the pulmonary contents of TGF-β1, TIMP-1 and collagen after silica treatment. M-MDSCs do not differentiate into lung macrophages, granulocytes or fibrocytes during pulmonary fibrogenesis. Collectively, our data indicate that M-MDSCs contribute to lung fibrosis by specifically promoting a non-degrading collagen microenvironment. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.