Pulmonary fibrotic response to aspiration of multi-walled carbon nanotubes

Nanoparticles in drinking water: Assessing health risks and regulatory challenges

Nanoparticles (NPs) pose a significant concern in drinking water due to their potential health risks and environmental impact. This review provides a comprehensive analysis of the current understanding of NP sources and contamination in drinking water, focusing on health concerns, mitigation strategies, regulatory frameworks, and future perspectives. This review highlights the importance of nano-specific pathways, fate processes, health risks & toxicity, and the need for realistic toxicity assessments. Different NPs like titanium dioxide, silver, nanoplastics, nanoscale liquid crystal monomers, copper oxide, and others pose potential health risks through ingestion, inhalation, or dermal exposure, impacting organs and potentially leading to oxidative stress, inflammatory responses, DNA damage, cytotoxicity, disrupt intracellular energetic mechanisms, reactive oxygen species generation, respiratory and immune toxicity, and genotoxicity in humans. Utilizing case studies and literature reviews, we investigate the health risks associated with NPs in freshwater environments, emphasizing their relevance to drinking water quality. Various mitigation and treatment strategies, including filtration systems (e.g., reverse osmosis, and ultra/nano-filtration), adsorption processes, coagulation/flocculation, electrocoagulation, advanced oxidation processes, membrane distillation, and ultraviolet treatment, all of which demonstrate high removal efficiencies for NPs from drinking water. Regulatory frameworks and challenges for the production, applications, and disposal of NPs at both national and international levels are discussed, emphasizing the need for tailored regulations to address NP contamination and standardize safety testing and risk assessment practices. Looking ahead, this review underscores the necessity of advancing detection methods and nanomaterial-based treatment technologies while stressing the pivotal role of public awareness and tailored regulatory guidelines in upholding drinking water quality standards. This review emphasizes the urgency of addressing NP contamination in drinking water and provides insights into potential solutions and future research directions. Lastly, this review worth concluded with future recommendations on advanced analytical techniques and sensitive sensors for NP detection for safeguarding public health and policy implementations.

Evaluating the ameliorative effect of nano bis-demethoxy curcumin analog against extrapulmonary toxicity in rat induced by inhaled multi-walled carbon nanotube

Carbon nanotubes (CNTs) exposure in human beings through inhalation may affect pulmonary organs and extrapulmonary organs including liver, kidney, brain, spleen, etc. The toxic effects developed as the result of CNTs exposure made us to explore the beneficial effect of nano bis-demethoxy curcumin analog (NBDMCA) towards multi-walled carbon nanotubes (MWCNTs)-induced toxicity in extrapulmonary organs. The current study described the ameliorative effect of NBDMCA against the toxic effects developed by inhaled MWCNTs in the extrapulmonary organs. The rats are exposed to the fixed aerosol concentration of 5 mg/m3 maintained in inhalation exposure chambers MWCNTs for 15 days as per OECD guidelines. After the exposure with MWCNTs, the animals were treated with NBDMCA (5 mg/kg body weight) with different dose frequencies, i.e., 2 doses per week for 1, 2, and 4 weeks. After treatment duration, the blood was drawn from retro-orbital vein and subjected to biochemical and cytokine analysis. Further the animals were euthanized, and the sample tissues were collected and performed oxidative stress and histopathology. The study results revealed that the intravenous administration of NBDMCA suppresses the extrapulmonary toxicity induced by MWCNTs, i.e., annulling the clinical changes and oxidative stress in various extrapulmonary organs at low doses of NBDMCA, evidenced its antioxidant efficacy. Moreover, use of increased doses provides better reduction in toxic symptoms with negligible side effects confirming the dose-dependent efficacy of NBDMCA. Overall, we suggested that NBDMCA may materialize into an effective compound for the reduction of MWCNTs-induced toxicity.

Effects of multi-walled carbon nanotubes on gene and microRNA expression in human hepatocarcinoma HepG2 cells

The usage of multi-walled carbon nanotubes (MWCNT) has increased exponentially in the past years, but, potential toxicity mechanisms are not clear. We studied the transcriptomic alterations induced by one multi-walled carbon nanotube (MWCNT) and its -OH and -COOH functionalized derivatives in human HepG2 cells. We showed that all three MWCNT treatments induced alterations in stress-related signaling pathways, inflammation-related signaling pathways, cholesterol synthesis pathways, proliferation-related pathways, senescence-related pathways and cancer-related pathways. In stress-related pathways, the acute phase response was induced in all three MWCNTs and all doses treated and ranked high. Other stress-related pathways were also related to the oxidative-induced signaling pathways, such as NRF-2 mediated oxidative stress response, hepatic fibrosis/Stella cell activation, iNOS signaling, and Hif1α signaling. Many inflammation-related pathways were altered, such as IL-8, IL-6, TNFR1, TNFR2, and NF-κB signaling pathways. These results were consistent with our previous results with exposures to the same three multi-walled carbon nanotubes in human lung BEAS-2B and also with results in mice and rats. From the microRNA target filter analysis, TXNIP & miR-128-3p interaction was present in all three MWCNT treatments, and maybe important for the induction of oxidative stress. CXCL-8 & miR-146-5p and Wee1 & miR-128-3p were only present in the cells treated with the parent and the OH-functionalized MWCNTs. These mRNA-miRNA interactions were involved in oxidative stress, inflammation, cell cycle, cholesterol biosynthesis and cancer related pathways. Target filter analysis also showed altered liver hyperplasia/hyperproliferation and hepatic cancer pathways. In short, target filter analysis complemented the transcriptomic analysis and pointed to specific gene/microRNA interactions that can help inform mechanism of action. Moreover, our study showed that the signaling pathways altered in HepG2 cells correlated well with the toxicity and carcinogenicity observed in vivo, indicating that HepG2 may be a good in vitro predictive model for MWCNT toxicity studies.

Immunomodulation of susceptibility to pneumococcal pneumonia infection in mouse lungs exposed to carbon nanoparticles via dysregulation of innate and adaptive immune responses

Carbon nanotubes (CNTs) are emerging pollutants of occupational and environmental health concern. While toxicological mechanisms of CNTs are emerging, there is paucity of information on their modulatory effects on susceptibility to infections. Here, we investigated cellular and molecular events underlying the effect of multi-walled CNT (MWCNT) exposure on susceptibility to Streptococcus pneumoniae infection in our 28-day sub-chronic exposure mouse model. Data indicated reduced phagocytic function in alveolar macrophages (AMs) from MWCNT-exposed lungs evidenced by lower pathogen uptake in 1-h infection assay. At 24-h post-infection, intracellular pathogen count in exposed AMs showed 2.5 times higher net increase (2-fold in vehicle- versus 5-fold in MWCNT-treated), indicating a greater rate of intracellular multiplication and/or survival due to MWCNT exposure. AMs from MWCNT-exposed lungs exhibited downregulation of pathogen-uptake receptors CD163, Phosphatidyl-serine receptor (Ptdsr), and Macrophage scavenger receptors class A type 1 (Msr1) and type 2 (MSr2). In whole lung, MWCNT exposure shifted the macrophage polarization state towards the immunosuppressive phenotype M2b and increased the CD11c+ dendritic cell population required to activate the adaptive immune response. Notably, the MWCNT pre-exposure dysregulated T-cell immunity, evidenced by diminished CD4 and Th17 response, and exacerbated Th1 and Treg responses (skewed Th17/Treg ratio), thereby favoring the pneumococcal infection. Overall, these findings indicated that MWCNT exposure compromises both innate and adaptive immunity leading to diminished host lung defense against pneumonia infection. To our knowledge, this is the first report on an immunomodulatory role of CNT pre-exposure on pneumococcal infection susceptibility due to dysregulation of both innate and adaptive immunity targets.

Potent lung tumor promotion by inhaled MWCNT

In the lung, carcinogenesis is a multi-stage process that includes initiation by a genotoxic agent, promotion that expands the population of cells with damaged DNA to form a tumor, and progression from benign to malignant neoplasms. We have previously shown that Mitsui-7, a long and rigid multi-walled carbon nanotube (MWCNT), promotes pulmonary carcinogenesis in a mouse model. To investigate the potential exposure threshold and dose-response for tumor promotion by this MWCNT, 3-methylcholanthrene (MC) initiated (10 μg/g, i.p., once) or vehicle (corn oil) treated B6C3F1 mice were exposed by inhalation to filtered air or MWCNT (5 mg/m3) for 5 h/day for 0, 2, 5, or 10 days and were followed for 17 months post-exposure for evidence of lung tumors. Pulmonary neoplasia incidence in MC-initiated mice significantly increased with each MWCNT exposure duration. Exposure to either MC or MWCNT alone did not affect pulmonary neoplasia incidence compared with vehicle controls. Lung tumor multiplicity in MC-initiated mice also significantly increased with each MWCNT exposure duration. Thus, a significantly higher lung tumor multiplicity was observed after a 10-day MWCNT exposure than following a 2-day exposure. Both bronchioloalveolar adenoma and bronchioloalveolar adenocarcinoma multiplicity in MC-initiated mice were significantly increased following 5- and 10-day MWCNT exposure, while a 2-day MWCNT exposure in MC-initiated mice significantly increased the multiplicity of adenomas but not adenocarcinomas. In this study, even the lowest MWCNT exposure promoted lung tumors in MC-initiated mice. Our findings indicate that exposure to this MWCNT strongly promotes pulmonary carcinogenesis.

Recycling of fiber reinforced composites: Online mass spectrometric tracing, offline physicochemical speciation and toxicological evaluation of a pilot plant pyrolytic conversion

The increasing demand for lightweight materials with exceptional stability and durability has resulted in a significant rise in fiber-reinforced plastic (FRP) production. These materials find applications in various fields. However, the exceptional properties and diverse compositional range of FRPs pose challenges to conventional recycling strategies. Pyrolysis has emerged as a highly promising approach for separating the fibers from the polymer matrix. In this study, we employed thermal analysis coupled with high-resolution mass spectrometry to investigate the pyrolysis process. Representative FRP showed a starting decomposition temperature of 300 °C and bisphenol A, styrene, alkenes, and phenols could be identified. The identified parameters were used to operate a pilot plant with a capacity of up to 50 kg/h FRP, and reactor products were directly analyzed with soft photoionization mass spectrometry. The findings demonstrated good agreement between the pilot plant results and laboratory experiments, particularly for smaller compounds (m/z<200). The non-condensable fraction showed a range of 17 to 22 MJ/m3 as lower heating value. Analysis of the recovered fibers (diameter between 6.20 and 8.05 μm) revealed residual coke, but no toxic fibers were detected, according to the World Health Organization's definition. Yet, the organic coating of the fibers contained small amounts of potentially harmful PAHs. A toxicological assessment using a multicellular in vitro model confirmed the low hazardous potential of the recovered fibers. The findings contribute to developing sustainable and environmentally friendly recycling strategies for FRP while addressing important aspects related to the safety and toxicological implications of the resulting chemicals and fibers.

Recent advances in tailoring stimuli-responsive hybrid scaffolds for cardiac tissue engineering and allied applications

To recapitulate bio-physical properties and functional behaviour of native heart tissues, recent tissue engineering-based approaches are focused on developing smart/stimuli-responsive materials for interfacing cardiac cells. Overcoming the drawbacks of the traditionally used biomaterials, these smart materials portray outstanding mechanical and conductive properties while promoting cell-cell interaction and cell-matrix transduction cues in such excitable tissues. To date, a large number of stimuli-responsive materials have been employed for interfacing cardiac tissues alone or in combination with natural/synthetic materials for cardiac tissue engineering. However, their comprehensive classification and a comparative analysis of the role played by these materials in regulating cardiac cell behaviour and in vivo metabolism are much less discussed. In an attempt to cover the recent advances in fabricating stimuli-responsive biomaterials for engineering cardiac tissues, this review details the role of these materials in modulating cardiomyocyte behaviour, functionality and surrounding matrix properties. Furthermore, concerns and challenges regarding the clinical translation of these materials and the possibility of using such materials for the fabrication of bio-actuators and bioelectronic devices are discussed.

Effect biomarkers of nanoparticle-exposed workers: A scoping review

The widespread and increasing use of engineered nanomaterials (i.e., particulate materials measuring 1-100 nanometers (nm) in at least one dimension) poses a potential health and safety risk to exposed workers. The unique properties of nanomaterials have made nanomaterials useful in multiple industries. However, their production and use may compromise worker health, presenting an emerging occupational health hazard, the acute and chronic effects of which have not been fully assessed. In this scoping review, we critically assess the literature on biomarkers of effect from nanoparticles and discuss the utility of biomonitoring as a means of assessing the physiological effects of nanoparticle exposure among nanotechnology workers. Multiple databases were queried based on select inclusion and exclusion criteria according to PRISMA guidelines, and articles were independently screened by two topic experts. Of 286 articles initially retrieved, 28 were included after screening and eligibility. The reviewed articles indicated that sensitive effect biomarkers could reflect early health effects of exposure to nanoparticles in the workplace and may be useful for monitoring toxicological effects and associated risks.

Total and regional microfiber transport characterization in a 15th - Generation human respiratory airway

Fiber transport and deposition in the complete respiratory airway is of great significance for human health risk assessment. Thus far, the literature has mainly focused on limited branches of the upper airway and assumes spherical particles by neglecting fiber anisotropy. To fill the gap, this paper utilized an extended realistic respiratory airway from the nasal cavity to the distal bronchial tracts, up to the 15th generation. Fibers with aerodynamic diameters from 2 to 12 μm and aspect ratios of 1, 10, and 50 were released at the inlet of the respiratory airway model, and the coupled translational and rotational motion were computed. Overall and regional fiber deposition fractions, including the nasal cavities, laryngeal airway, and lungs were predicted and compared with earlier numerical results. The study also investigated: 1) secondary flow and distributions of the fibers at the lower respiratory airway entrance; 2) upstream conditions toward fiber deposition efficiencies; 3) fiber deposition patterns and detailed deposition fractions in the five lobes. Utilizing the realistic fiber transport model, the current study found that the upstream airway geometry and the flow condition have a significant impact on the fiber transport and deposition in the downstream airway regions. The fiber depositions in the lower and middle lobes are sensitive to the fiber aerodynamic diameter, but insensitive in the upper lobes. This study expects to generate innovative knowledge on the unique fiber motion characteristics toward potential inhalation health risks.

Biomimetic Human Lung Alveolar Interstitium Chip with Extended Longevity

Determining the mechanistic causes of lung diseases, developing new treatments thereof, and assessing toxicity whether from chemical exposures or engineered nanomaterials would benefit significantly from a preclinical human lung alveolar interstitium model of physiological relevance. The existing preclinical models have limitations because they fail to replicate the key anatomical and physiological characteristics of human alveoli. Thus, a human lung alveolar interstitium chip was developed to imitate key alveolar microenvironmental factors including an electrospun nanofibrous membrane as the analogue of the basement membrane for co-culture of epithelial cells with fibroblasts embedded in 3D collagenous gels, physiologically relevant interstitial matrix stiffness, interstitial fluid flow, and 3D breathing-like mechanical stretch. The biomimetic chip substantially improved the epithelial barrier function compared to transwell models. Moreover, the chip having a gel made of a collagen I-fibrin blend as the interstitial matrix sustained the interstitium integrity and further enhanced the epithelial barrier, resulting in a longevity that extended beyond eight weeks. The assessment of multiwalled carbon nanotube toxicity on the chip was in line with the animal study.

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.

Nanoparticles-induced potential toxicity on human health: Applications, toxicity mechanisms, and evaluation models

Nanoparticles (NPs) have become one of the most popular objects of scientific study during the past decades. However, despite wealth of study reports, still there is a gap, particularly in health toxicology studies, underlying mechanisms, and related evaluation models to deeply understanding the NPs risk effects. In this review, we first present a comprehensive landscape of the applications of NPs on health, especially addressing the role of NPs in medical diagnosis, therapy. Then, the toxicity of NPs on health systems is introduced. We describe in detail the effects of NPs on various systems, including respiratory, nervous, endocrine, immune, and reproductive systems, and the carcinogenicity of NPs. Furthermore, we unravels the underlying mechanisms of NPs including ROS accumulation, mitochondrial damage, inflammatory reaction, apoptosis, DNA damage, cell cycle, and epigenetic regulation. In addition, the classical study models such as cell lines and mice and the emerging models such as 3D organoids used for evaluating the toxicity or scientific study are both introduced. Overall, this review presents a critical summary and evaluation of the state of understanding of NPs, giving readers more better understanding of the NPs toxicology to remedy key gaps in knowledge and techniques.

Needlelike, short and thin multi-walled carbon nanotubes: comparison of effects on wild type and p53+/- rat lungs

Carbon nanotubes (CNTs) are nanomaterials presenting an occupational inhalation risk during production or handling. The International Agency for Research on Cancer classified one CNT, Mitsui-7 (MWNT-7), as 'possibly carcinogenic to humans'. In recognition of their similarities, a proposal has been submitted to the risk assessment committee of ECHA to classify all fibers with 'Fibre Paradigm' (FP)-compatible dimensions as carcinogenic. However, there is a lack of clarity surrounding the toxicity of fibers that do not fit the FP criteria. In this study, we compared the effects of the FP-compatible Mitsui-7, to those of NM-403, a CNT that is too short and thin to fit the paradigm. Female Sprague Dawley rats deficient for p53 (GMO) and wild type (WT) rats were exposed to the two CNTs (0.25 mg/rat/week) by intratracheal instillation. Animals (GMO and WT) were exposed weekly for four consecutive weeks and were sacrificed 3 days or 8 months after the last instillation. Exposure to both CNTs induced acute lung inflammation. However, persistent inflammation at 8 months was only observed in the lungs of rats exposed to NM-403. In addition to the persistent inflammation, NM-403 stimulated hyperplasic changes in rat lungs, and no adenomas or carcinomas were detected. The degree and extent of hyperplasia was significantly more pronounced in GMO rats. These results suggest that CNT not meeting the FP criteria can cause persistent inflammation and hyperplasia. Consequently, their health effects should be carefully assessed.

Comparing species-different responses in pulmonary fibrosis research: Current understanding of in vitro lung cell models and nanomaterials

Pulmonary fibrosis (PF) is a chronic, irreversible lung disease that is typically fatal and characterized by an abnormal fibrotic response. As a result, vast areas of the lungs are gradually affected, and gas exchange is impaired, making it one of the world's leading causes of death. This can be attributed to a lack of understanding of the onset and progression of the disease, as well as a poor understanding of the mechanism of adverse responses to various factors, such as exposure to allergens, nanomaterials, environmental pollutants, etc. So far, the most frequently used preclinical evaluation paradigm for PF is still animal testing. Nonetheless, there is an urgent need to understand the factors that induce PF and find novel therapeutic targets for PF in humans. In this regard, robust and realistic in vitro fibrosis models are required to understand the mechanism of adverse responses. Over the years, several in vitro and ex vivo models have been developed with the goal of mimicking the biological barriers of the lung as closely as possible. This review summarizes recent progress towards the development of experimental models suitable for predicting fibrotic responses, with an emphasis on cell culture methods, nanomaterials, and a comparison of results from studies using cells from various species.

Understanding toxicity associated with boron nitride nanotubes: Review of toxicity studies, exposure assessment at manufacturing facilities, and read-across

Boron nitride nanotubes (BNNT) are produced by many different methods leading to variances in physicochemical characteristics and impurities in the final product. These differences can alter the toxicity profile. The importance of understanding the potential pathological implications of this high aspect ratio nanomaterial is increasing as new approaches to synthesize and purify in large scale are being developed. In this review, we discuss the various factors of BNNT production that can influence its toxicity followed by summarizing the toxicity findings from in vitro and in vivo studies conducted to date, including a review of particle clearance observed with various exposure routes. To understand the risk to workers and interpret relevance of toxicological findings, exposure assessment at manufacturing facilities was discussed. Workplace exposure assessment of BNNT from two manufacturing facilities measured boron concentrations in personal breathing zones from non-detectable to 0.95 μg/m3 and TEM structure counts of 0.0123 ± 0.0094 structures/cm3, concentrations well below what was found with other engineered high aspect ratio nanomaterials like carbon nanotubes and nanofibers. Finally, using a purified BNNT, a "read-across" toxicity assessment was performed to demonstrate how known hazard data and physicochemical characteristics can be utilized to evaluate potential inhalation toxicity concerns.

Future Prospects for Clinical Applications of Nanocarbons Focusing on Carbon Nanotubes

Over the past 15 years, numerous studies have been conducted on the use of nanocarbons as biomaterials towards such applications as drug delivery systems, cancer therapy, and regenerative medicine. However, the clinical use of nanocarbons remains elusive, primarily due to short- and long-term safety concerns. It is essential that the biosafety of each therapeutic modality be demonstrated in logical and well-conducted experiments. Accordingly, the fundamental techniques for assessing nanocarbon biomaterial safety have become more advanced. Optimal controls are being established, nanocarbon dispersal techniques are being refined, the array of biokinetic evaluation methods has increased, and carcinogenicity examinations under strict conditions have been developed. The medical implementation of nanocarbons as a biomaterial is in sight. With a particular focus on carbon nanotubes, these perspectives aim to summarize the contributions to date on nanocarbon applications and biosafety, introduce the recent achievements in evaluation techniques, and clarify the future prospects and systematic introduction of carbon nanomaterials for clinical use through practical yet sophisticated assessment methods.

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.

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.

Histopathology of the broad class of carbon nanotubes and nanofibers used or produced in U.S. facilities in a murine model

BACKGROUND

Multi-walled carbon nanotubes and nanofibers (CNT/F) have been previously investigated for their potential toxicities; however, comparative studies of the broad material class are lacking, especially those with a larger diameter. Additionally, computational modeling correlating physicochemical characteristics and toxicity outcomes have been infrequently employed, and it is unclear if all CNT/F confer similar toxicity, including histopathology changes such as pulmonary fibrosis. Male C57BL/6 mice were exposed to 40 µg of one of nine CNT/F (MW #1-7 and CNF #1-2) commonly found in exposure assessment studies of U.S. facilities with diameters ranging from 6 to 150 nm. Human fibroblasts (0-20 µg/ml) were used to assess the predictive value of in vitro to in vivo modeling systems.

RESULTS

All materials induced histopathology changes, although the types and magnitude of the changes varied. In general, the larger diameter MWs (MW #5-7, including Mitsui-7) and CNF #1 induced greater histopathology changes compared to MW #1 and #3 while MW #4 and CNF #2 were intermediate in effect. Differences in individual alveolar or bronchiolar outcomes and severity correlated with physical dimensions and how the materials agglomerated. Human fibroblast monocultures were found to be insufficient to fully replicate in vivo fibrosis outcomes suggesting in vitro predictive potential depends upon more advanced cell culture in vitro models. Pleural penetrations were observed more consistently in CNT/F with larger lengths and diameters.

CONCLUSION

Physicochemical characteristics, notably nominal CNT/F dimension and agglomerate size, predicted histopathologic changes and enabled grouping of materials by their toxicity profiles. Particles of greater nominal tube length were generally associated with increased severity of histopathology outcomes. Larger particle lengths and agglomerates were associated with more severe bronchi/bronchiolar outcomes. Spherical agglomerated particles of smaller nominal tube dimension were linked to granulomatous inflammation while a mixture of smaller and larger dimensional CNT/F resulted in more severe alveolar injury.

U.S. Federal Agency interests and key considerations for new approach methodologies for nanomaterials

Engineered nanomaterials (ENMs) come in a wide array of shapes, sizes, surface coatings, and compositions, and often possess novel or enhanced properties compared to larger sized particles of the same elemental composition. To ensure the safe commercialization of products containing ENMs, it is important to thoroughly understand their potential risks. Given that ENMs can be created in an almost infinite number of variations, it is not feasible to conduct in vivo testing on each type of ENM. Instead, new approach methodologies (NAMs) such as in vitro or in chemico test methods may be needed, given their capacity for higher throughput testing, lower cost, and ability to provide information on toxicological mechanisms. However, the different behaviors of ENMs compared to dissolved chemicals may challenge safety testing of ENMs using NAMs. In this study, member agencies within the Interagency Coordinating Committee on the Validation of Alternative Methods were queried about what types of ENMs are of agency interest and whether there is agency-specific guidance for ENM toxicity testing. To support the ability of NAMs to provide robust results in ENM testing, two key issues in the usage of NAMs, namely dosimetry and interference/bias controls, are thoroughly discussed.

Mechanical Performance and Applications of CNTs Reinforced Polymer Composites-A Review

Developments in the synthesis and scalable manufacturing of carbon nanomaterials like carbon nanotubes (CNTs) have been widely used in the polymer material industry over the last few decades, resulting in a series of fascinating multifunctional composites used in fields ranging from portable electronic devices, entertainment and sports to the military, aerospace, and automotive sectors. CNTs offer good thermal and electrical properties, as well as a low density and a high Young's modulus, making them suitable nanofillers for polymer composites. As mechanical reinforcements for structural applications CNTs are unique due to their nano-dimensions and size, as well as their incredible strength. Although a large number of studies have been conducted on these novel materials, there have only been a few reviews published on their mechanical performance in polymer composites. As a result, in this review we have covered some of the key application factors as well as the mechanical properties of CNTs-reinforced polymer composites. Finally, the potential uses of CNTs hybridised with polymer composites reinforced with natural fibres such as kenaf fibre, oil palm empty fruit bunch (OPEFB) fibre, bamboo fibre, and sugar palm fibre have been highlighted.

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.

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

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

Nanomaterials and the Serosal Immune System in the Thoracic and Peritoneal Cavities

The thoracic and peritoneal cavities are lined by serous membranes and are home of the serosal immune system. This immune system fuses innate and adaptive immunity, to maintain local homeostasis and repair local tissue damage, and to cooperate closely with the mucosal immune system. Innate lymphoid cells (ILCs) are found abundantly in the thoracic and peritoneal cavities, and they are crucial in first defense against pathogenic viruses and bacteria. Nanomaterials (NMs) can enter the cavities intentionally for medical purposes, or unintentionally following environmental exposure; subsequent serosal inflammation and cancer (mesothelioma) has gained significant interest. However, reports on adverse effects of NM on ILCs and other components of the serosal immune system are scarce or even lacking. As ILCs are crucial in the first defense against pathogenic viruses and bacteria, it is possible that serosal exposure to NM may lead to a reduced resistance against pathogens. Additionally, affected serosal lymphoid tissues and cells may disturb adipose tissue homeostasis. This review aims to provide insight into key effects of NM on the serosal immune system.

Current understanding of nanoparticle toxicity mechanisms and interactions with biological systems

Nanotechnology is an emerging science involving the manipulation of matter on the nanometer scale.

Physicochemical characterization and genotoxicity of the broad class of carbon nanotubes and nanofibers used or produced in U.S. facilities

BACKGROUND

Carbon nanotubes and nanofibers (CNT/F) have known toxicity but simultaneous comparative studies of the broad material class, especially those with a larger diameter, with computational analyses linking toxicity to their fundamental material characteristics was lacking. It was unclear if all CNT/F confer similar toxicity, in particular, genotoxicity. Nine CNT/F (MW #1-7 and CNF #1-2), commonly found in exposure assessment studies of U.S. facilities, were evaluated with reported diameters ranging from 6 to 150 nm. All materials were extensively characterized to include distributions of physical dimensions and prevalence of bundled agglomerates. Human bronchial epithelial cells were exposed to the nine CNT/F (0-24 μg/ml) to determine cell viability, inflammation, cellular oxidative stress, micronuclei formation, and DNA double-strand breakage. Computational modeling was used to understand various permutations of physicochemical characteristics and toxicity outcomes.

RESULTS

Analyses of the CNT/F physicochemical characteristics illustrate that using detailed distributions of physical dimensions provided a more consistent grouping of CNT/F compared to using particle dimension means alone. In fact, analysis of binning of nominal tube physical dimensions alone produced a similar grouping as all characterization parameters together. All materials induced epithelial cell toxicity and micronuclei formation within the dose range tested. Cellular oxidative stress, DNA double strand breaks, and micronuclei formation consistently clustered together and with larger physical CNT/F dimensions and agglomerate characteristics but were distinct from inflammatory protein changes. Larger nominal tube diameters, greater lengths, and bundled agglomerate characteristics were associated with greater severity of effect. The portion of tubes with greater nominal length and larger diameters within a sample was not the majority in number, meaning a smaller percentage of tubes with these characteristics was sufficient to increase toxicity. Many of the traditional physicochemical characteristics including surface area, density, impurities, and dustiness did not cluster with the toxicity outcomes.

CONCLUSION

Distributions of physical dimensions provided more consistent grouping of CNT/F with respect to toxicity outcomes compared to means only. All CNT/F induced some level of genotoxicity in human epithelial cells. The severity of toxicity was dependent on the sample containing a proportion of tubes with greater nominal lengths and diameters.

Pulmonary surfactant inhibition of nanoparticle uptake by alveolar epithelial cells

Pulmonary surfactant forms a sub-micrometer thick fluid layer that covers the surface of alveolar lumen and inhaled nanoparticles therefore come in to contact with surfactant prior to any interaction with epithelial cells. We investigate the role of the surfactant as a protective physical barrier by modeling the interactions using silica-Curosurf-alveolar epithelial cell system in vitro. Electron microscopy displays that the vesicles are preserved in the presence of nanoparticles while nanoparticle-lipid interaction leads to formation of mixed aggregates. Fluorescence microscopy reveals that the surfactant decreases the uptake of nanoparticles by up to two orders of magnitude in two models of alveolar epithelial cells, A549 and NCI-H441, irrespective of immersed culture on glass or air-liquid interface culture on transwell. Confocal microscopy corroborates the results by showing nanoparticle-lipid colocalization interacting with the cells. Our work thus supports the idea that pulmonary surfactant plays a protective role against inhaled nanoparticles. The effect of surfactant should therefore be considered in predictive assessment of nanoparticle toxicity or drug nanocarrier uptake. Models based on the one presented in this work may be used for preclinical tests with engineered nanoparticles.

Hydroxyl functionalized multi-walled carbon nanotubes modulate immune responses without increasing 2009 pandemic influenza A/H1N1 virus titers in infected mice

Growing use of carbon nanotubes (CNTs) have garnered concerns regarding their association with adverse health effects. Few studies have probed how CNTs affect a host's susceptibility to pathogens, particularly respiratory viruses. We reported that exposure of lung cells and mice to pristine single-walled CNTs (SWCNTs) leads to significantly increased influenza virus H1N1 strain A/Mexico/4108/2009 (IAV) titers in concert with repressed antiviral immune responses. In the present study, we investigated if hydroxylated multi-walled CNTs (MWCNTs), would result in similar outcomes. C57BL/6 mice were exposed to 20 μg MWCNTs on day 0 and IAV on day 3 and samples were collected on day 7. We investigated pathological changes, viral titers, immune-related gene expression in lung tissue, and quantified differential cell counts and cytokine and chemokine levels in bronchoalveolar lavage fluid. MWCNTs alone caused mild inflammation with no apparent changes in immune markers whereas IAV alone presented typical infection-associated inflammation, pathology, and titers. The co-exposure (MWCNTs + IAV) did not alter titers or immune cell profiles compared to the IAV only but increased concentrations of IL-1β, TNFα, GM-CSF, KC, MIPs, and RANTES and inhibited mRNA expression of Tlr3, Rig-i, Mda5, and Ifit2. Our findings suggest MWCNTs modulate immune responses to IAV with no effect on the viral titer and modest pulmonary injury, a result different from those reported for SWCNT exposures. This is the first study to show that MWCNTs modify cytokine and chemokine responses that control aspects of host defenses which may play a greater role in mitigating IAV infections.

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.

An In Vitro Lung System to Assess the Proinflammatory Hazard of Carbon Nanotube Aerosols

In vitro three-dimensional (3D) lung cell models have been thoroughly investigated in recent years and provide a reliable tool to assess the hazard associated with nanomaterials (NMs) released into the air. In this study, a 3D lung co-culture model was optimized to assess the hazard potential of multiwalled carbon nanotubes (MWCNTs), which is known to provoke inflammation and fibrosis, critical adverse outcomes linked to acute and prolonged NM exposure. The lung co-cultures were exposed to MWCNTs at the air-liquid interface (ALI) using the VITROCELL^® Cloud system while considering realistic occupational exposure doses. The co-culture model was composed of three human cell lines: alveolar epithelial cells (A549), fibroblasts (MRC-5), and macrophages (differentiated THP-1). The model was exposed to two types of MWCNTs (Mitsui-7 and Nanocyl) at different concentrations (2–10 μg/cm²) to assess the proinflammatory as well as the profibrotic responses after acute (24 h, one exposure) and prolonged (96 h, repeated exposures) exposure cycles. The results showed that acute or prolonged exposure to different concentrations of the tested MWCNTs did not induce cytotoxicity or apparent profibrotic response; however, suggested the onset of proinflammatory response.

Use of EpiAlveolar Lung Model to Predict Fibrotic Potential of Multiwalled Carbon Nanotubes

Expansion in production and commercial use of nanomaterials increases the potential human exposure during the lifecycle of these materials (production, use, and disposal). Inhalation is a primary route of exposure to nanomaterials; therefore it is critical to assess their potential respiratory hazard. Herein, we developed a three-dimensional alveolar model (EpiAlveolar) consisting of human primary alveolar epithelial cells, fibroblasts, and endothelial cells, with or without macrophages for predicting long-term responses to aerosols. Following thorough characterization of the model, proinflammatory and profibrotic responses based on the adverse outcome pathway concept for lung fibrosis were assessed upon repeated subchronic exposures (up to 21 days) to two types of multiwalled carbon nanotubes (MWCNTs) and silica quartz particles. We simulate occupational exposure doses for the MWCNTs (1-30 μg/cm²) using an air-liquid interface exposure device (VITROCELL Cloud) with repeated exposures over 3 weeks. Specific key events leading to lung fibrosis, such as barrier integrity and release of proinflammatory and profibrotic markers, show the responsiveness of the model. Nanocyl induced, in general, a less pronounced reaction than Mitsui-7, and the cultures with human monocyte-derived macrophages (MDMs) showed the proinflammatory response at later time points than those without MDMs. In conclusion, we present a robust alveolar model to predict inflammatory and fibrotic responses upon exposure to MWCNTs.

Lung deposition patterns of MWCNT vary with degree of carboxylation

Functionalization of multi-walled carbon nanotubes (MWCNT) is known to affect the biological response (e.g. toxicity, inflammation) in vitro and in vivo. However, the reasons for these changes in vivo are not well described. This study examined the degree of MWCNT functionalization with regard to in vivo mouse lung distribution, particle retention, and resulting pathology. A commercially available MWCNT (source MWCNT) was functionalized (f-MWCNT) by systematically varying the degree of carboxylation on the particle's surface. Following a pilot study using seven variants, two f-MWCNT variants were chosen and for lung pathology and particle distribution using oropharyngeal aspiration administration of MWCNT in Balb/c mice. Particle distribution in the lung was examined at 7 and 28 days post-instillation by bright-field microscopy, CytoViva hyperspectral dark-field imaging, and Stimulated Raman Scattering (SRS) microscopy. Examination of the lung tissue by bright-field microscopy showed some acute inflammation for all MWCNT that was highest with source MWCNT. Hyperspectral imaging and SRS were employed to assess the changes in particle deposition and retention. Highly functionalized MWCNT had a higher lung burden and were more disperse. They also appeared to be associated more with epithelial cells compared to the source and less functionalized MWCNT that were mostly interacting with alveolar macrophages (AM). These results showing a slightly reduced pathology despite the extended deposition have implications for the engineering of safer MWCNT and may establish a practical use as a targeted delivery system.

Biocompatibility and Carcinogenicity of Carbon Nanotubes as Biomaterials

With the development of nanotechnology in recent years, there have been concerns about the health effects of nanoparticles. Carbon nanotubes (CNTs) are fibrous nanoparticles with a micro-sized length and nano-sized diameter, which exhibit excellent physical properties and are widely studied for their potential application in medicine. However, asbestos has been historically shown to cause pleural malignant mesothelioma and lung cancer by inhalation exposure. Because carbon nanotubes are also fibrous nanotubes, some have raised concerns about its possible carcinogenicity. We have reported that there is no clear evidence of carcinogenicity by local and intravenous administration of multi-walled CNTs to cancer mice models. We firmly believe that CNTs can be a safe, new, and high-performance biomaterials by controlling its type, site of administration, and dosage.

Comparative analysis of lung and blood transcriptomes in mice exposed to multi-walled carbon nanotubes

Pulmonary exposure to multi-walled carbon nanotubes (MWCNT) causes inflammation, fibroproliferation, immunotoxicity, and systemic responses in rodents. However, the search for representative biomarkers of exposure is an ongoing endeavor. Whole blood gene expression profiling is a promising new approach for the identification of novel disease biomarkers. We asked if the whole blood transcriptome reflects pathology-specific changes in lung gene expression caused by MWCNT. To answer this question, we performed mRNA sequencing analysis of the whole blood and lung in mice administered MWCNT or vehicle solution via pharyngeal aspiration and sacrificed 56 days later. The pattern of lung mRNA expression as determined using Ingenuity Pathway Analysis (IPA) was indicative of continued inflammation, immune cell trafficking, phagocytosis, and adaptive immune responses. Simultaneously, innate immunity-related transcripts (Plunc, Bpifb1, Reg3g) and cancer-related pathways were downregulated. IPA analysis of the differentially expressed genes in the whole blood suggested increased hematopoiesis, predicted activation of cancer/tumor development pathways, and atopy. There were several common upregulated genes between whole blood and lungs, important for adaptive immune responses: Cxcr1, Cd72, Sharpin, and Slc11a1. Trim24, important for T_H2 cell effector function, was downregulated in both datasets. Hla-dqa1 mRNA was upregulated in the lungs and downregulated in the blood, as was Lilrb4, which controls the reactivity of immune response. "Cancer" disease category had opposing activation status in the two datasets, while the only commonality was "Hypersensitivity". Transcriptome changes occurring in the lungs did not produce a completely replicable pattern in whole blood; however, specific systemic responses may be shared between transcriptomic profiles.

Quantification of Carbon Nanotube Doses in Adherent Cell Culture Assays Using UV-VIS-NIR Spectroscopy

The overt hazard of carbon nanotubes (CNTs) is often assessed using in vitro methods, but determining a dose–response relationship is still a challenge due to the analytical difficulty of quantifying the dose delivered to cells. An approach to accurately quantify CNT doses for submerged in vitro adherent cell culture systems using UV-VIS-near-infrared (NIR) spectroscopy is provided here. Two types of multi-walled CNTs (MWCNTs), Mitsui-7 and Nanocyl, which are dispersed in protein rich cell culture media, are studied as tested materials. Post 48 h of CNT incubation, the cellular fractions are subjected to microwave-assisted acid digestion/oxidation treatment, which eliminates biological matrix interference and improves CNT colloidal stability. The retrieved oxidized CNTs are analyzed and quantified using UV-VIS-NIR spectroscopy. In vitro imaging and quantification data in the presence of human lung epithelial cells (A549) confirm that up to 85% of Mitsui-7 and 48% for Nanocyl sediment interact (either through internalization or adherence) with cells during the 48 h of incubation. This finding is further confirmed using a sedimentation approach to estimate the delivered dose by measuring the depletion profile of the CNTs.

Mouse pulmonary response to dust from sawing Corian®, a solid-surface composite material

Corian®, a solid-surface composite (SSC), is composed of alumina trihydrate and acrylic polymer. The aim of the present study was to examine the pulmonary toxicity attributed to exposure to SSC sawing dust. Male mice were exposed to either phosphate buffer saline (PBS, control), 62.5, 125, 250, 500, or 1000 µg of SSC dust, or 1000 µg silica (positive control) via oropharyngeal aspiration. Body weights were measured for the duration of the study. Bronchoalveolar lavage fluid (BALF) and tissues were collected for analysis at 1 and 14 days post-exposure. Enhanced-darkfield and histopathologic analysis was performed to assess particle distribution and inflammatory responses. BALF cells and inflammatory cytokines were measured. The geometric mean diameter of SSC sawing dust following suspension in PBS was 1.25 µm. BALF analysis indicated that lactate dehydrogenase (LDH) activity, inflammatory cells, and pro-inflammatory cytokines were significantly elevated in the 500 and 1000 µg SSC exposure groups at days 1 and 14, suggesting that exposure to these concentrations of SSC induced inflammatory responses, in some cases to a greater degree than the silica positive control. Histopathology indicated the presence of acute alveolitis at all doses at day 1, which was largely resolved by day 14. Alveolar particle deposition and granulomatous mass formation were observed in all exposure groups at day 14. The SSC particles were poorly cleared, with 81% remaining at the end of the observation period. These findings demonstrate that SSC sawing dust exposure induces pulmonary inflammation and damage that warrants further investigation. Abbreviations: ANOVA: Analysis of Variance; ATH: Alumina Trihydrate; BALF: Bronchoalveolar Lavage Fluid; D_pg: Geometric Mean Diameter; FE-SEM: Field Emission Scanning Electron Microscopy; IACUC: Institutional Animal Care and Use Committee; IFN-γ: Interferon Gamma; IL-1 Β: Interleukin-1 Beta; IL-10: Interleukin-10; IL-12: Interleukin-12; IL-2: Interleukin-2; IL-4: Interleukin-4; IL-5: Interleukin-5; IL-6: Interleukin-6; KC/GRO: Neutrophil-Activating Protein 3; MMAD: Mass Median Aerodynamic Diameter; PBS: Phosphate-Buffered Saline; PEL: Permissible Exposure Limit; PM: Polymorphonuclear Leukocytes; PNOR: Particles Not Otherwise Regulated; SEM/EDX: Scanning Electron Microscope/Energy-Dispersive X-Ray; SSA: Specific Surface Area; SSC: Solid Surface Composite; TNFα: Tumor Necrosis Factor-Alpha; VOC: Volatile Organic Compounds; σ_g: Geometric Standard Deviation.

Toxicological assessment of dust from sanding micronized copper-treated lumber in vivo

Micronized copper azole (MCA) is a lumber treatment improve longevity. In this study, the in vivo response to PM_2.5 sanding dust generated from MCA-treated lumber was compared to that of untreated yellow pine (UYP) or soluble copper azole-treated (CA-C) lumber to determine if the MCA was more bioactive than CA-C. Mice were exposed to doses (28, 140, or 280 μg/mouse) of UYP, MCA, or CA-C sanding dust using oropharyngeal aspiration. Bronchoalveolar lavage fluid (BALF) lactate dehydrogenase activity was increased at 1 day post-exposure to 280 μg/mouse of MCA and CA-C compared to UYP. BALF polymorphonuclear cells were increased by MCA and CA-C. There were increases in BALF cytokines in MCA and CA-C-exposed groups at 1 day post-exposure. Lung histopathology indicated inflammation with infiltration of neutrophils and macrophages. Pulmonary responses were more severe in MCA and CA-C-exposed groups at 1 day post-exposure. MCA caused more severe inflammatory responses than CA-C at 1 day post-exposure. These findings suggest that the MCA and CA-C sanding dusts are more bioactive than the UYP sanding dust, and, moreover, the MCA sanding dust is more bioactive in comparison to the CA-C sanding dust. No chronic toxic effects were observed among all observed sanding dusts.

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

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

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Cells grow and treated in monoculture may exaggerate toxicological responses.

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

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

Vial sonication and ultrasonic immersion probe sonication to generate stable dispersions of multiwall carbon nanotubes for physico-chemical characterization and biological testing

Nanotechnology is considered to be a key enabling technology and in recent years there has been much growth in the use of nanostructured materials in industrial applications and in consumer products. It is, therefore, important that prior to being commercialized in consumer products, engineered nanomaterials are subjected to a thorough physico-chemical characterization as part of broader risk assessment to evaluate their possible effects on human health and the environment. The proper dispersion of nanomaterials sourced as powders becomes a first crucial step in the characterization process. This paper focuses on the dispersion of multiwall carbon nanotubes - often hydrophobic and tangled - since it may be challenging to re-disperse them effectively in aqueous media prior to characterization. A comparison has been made of non-contact vial sonication and immersion probe sonication using tannic acid as a dispersant. Transmission electron microscopy and UV-Vis spectroscopy were the techniques used to evaluate the dispersions. We used High Content Imaging and Colony Forming Efficiency to perform in vitro cytotoxicity studies on Human Alveolar Epithelial cells. It was found that both sonication treatments produce equivalent stable dispersions. No cytotoxic effects from MWCNTs were observed although some toxicity was observed and attributed to excess of the tannic acid dispersant.

CaCO3 as an Environmentally Friendly Renewable Material for Drug Delivery Systems: Uptake of HSA-CaCO3 Nanocrystals Conjugates in Cancer Cell Lines

Chemical and biochemical functionalization of nanoparticles (NPs) can lead to an active cellular uptake enhancing their efficacy thanks to the targeted localization in tumors. In the present study calcium carbonate nano-crystals (CCNs), stabilized by an alcohol dehydration method, were successfully modified by grafting human serum albumin (HSA) on the surface to obtain a pure protein corona. Two types of CCNs were used: naked CaCO3 and the (3-aminopropyl)triethoxysilane (APTES) modified CaCO3-NH2. The HSA conjugation with naked CCN and amino-functionalized CCN (CCN-NH2) was established through the investigation of modification in size, zeta potential, and morphology by Transmission Electron Microscopy (TEM). The amount of HSA coating on the CCNs surface was assessed by spectrophotometry. Thermogravimetric analysis (TGA) and Differential scanning calorimetry (DSC) confirmed the grafting of APTES to the surface and successive adsorption of HSA. Furthermore, to evaluate the effect of protein complexation of CCNs on cellular behavior, bioavailability, and biological responses, three human model cancer cell lines, breast cancer (MCF7), cervical cancer (HeLa), and colon carcinoma (Caco-2) were selected to characterize the internalization kinetics, localization, and bio-interaction of the protein-enclosed CCNs. To monitor internalization of the various conjugates, chemical modification with fluorescein-isothiocyanate (FITC) was performed, and their stability over time was measured. Confocal microscopy was used to probe the uptake and confirm localization in the perinuclear region of the cancer cells. Flow cytometry assays confirmed that the bio-functionalization influence cellular uptake and the CCNs behavior depends on both cell line and surface features.

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

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

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.

Effect of iron overload from multi walled carbon nanotubes on neutrophil-like differentiated HL-60 cells

Multi walled carbon nanotubes (MWCNTs) are one of the most intensively explored nanomaterials because of their unique physical and chemical properties. Due to the widespread use of MWCNTs, it is important to investigate their effects on human health. The precise mechanism of MWCNT toxicity has not been fully elucidated. The present study was designed to examine the mechanisms of MWCNT toxicity toward human promyelocytic leukemia HL-60 cells. First, we found that MWCNTs decreased the viability of neutrophil-like differentiated HL-60 cells but not undifferentiated HL-60 cells. Because neutrophil-like differentiated HL-60 cells exhibit enhanced phagocytic activity, the cytotoxicity of MWCNTs is dependent on the intracellularly localized MWCNTs. Next, we revealed that the cytotoxicity of MWCNTs is correlated with the intracellular accumulation of iron that is released from the engulfed MWCNTs in an acidic lysosomal environment. The intracellular accumulation of iron was repressed by treatment with cytochalasin D, a phagocytosis inhibitor. In addition, our results indicated that iron overload enhanced the release of interleukin-8 (IL-8), a chemokine that activates neutrophils, and subsequently elevated intracellular calcium concentration ([Ca²⁺]_i). Finally, we found that the sustained [Ca²⁺]_i elevation resulted in the loss of mitochondrial membrane potential and the increase of caspase-3 activity, thereby inducing apoptotic cell death. These findings suggest that the iron overload caused by engulfed MWCNTs results in the increase of IL-8 production and the elevation of [Ca²⁺]_i, thereby activating the mitochondria-mediated apoptotic pathway.

Sample preparation method for visualization of nanoparticulate captured on mixed cellulose ester filter media by enhanced darkfield microscopy and hyperspectral imaging

A significant hurdle in conducting effective health and safety hazard analysis and risk assessment for the nanotechnology workforce is the lack of a rapid method for the direct visualization and analysis of filter media used to sample nanomaterials from work environments that represent potential worker exposure. Current best-known methods include transmission electron microscopy (TEM) coupled with energy dispersive x-ray spectroscopy (EDS) for elemental identification. TEM-EDS is considerably time-, cost-, and resource-intensive, which may prevent timely health and safety recommendations and corrective actions. A rapid screening method is currently being explored using enhanced darkfield microscopy with hyperspectral imaging (EDFM-HSI). For this approach to be effective, rapid, and easy, sample preparation that is amenable to the analytical technique is needed. Here, we compare the sample preparation steps for mixed cellulose ester (MCE) filter media specified in NIOSH Method 7400-Asbestos and Other Fibers by Phase Contrast Microscopy (PCM)-against a new method, which involves saturation of the filter media with acetone. NIOSH Method 7400 was chosen as a starting point since it is an established technique for preparing transparent MCE filters for optical microscopy. Limitations in this method led to the development and comparison of a new method. The new method was faster, easier, and rendered filters more transparent, resulting in improved visualization and analysis of nanomaterials via EDFM-HSI. This new method is suitable for a rapid screening protocol due to its speed, ease of use, and the improvement in image acquisition and analysis.