Mechanism of induction of binucleated cells by multiwalled carbon nanotubes as revealed by live-cell imaging analysis

Tetraploidy in normal tissues and diseases: mechanisms and consequences

Tetraploidisation plays a crucial role in evolution, development, stress adaptation, and disease, but its beneficial or pathological effects in different tissues remain unclear. This study aims to compare physiological and unphysiological tetraploidy in eight steps: 1) mechanisms of diploidy-to-tetraploidy transition, 2) induction and elimination of unphysiological tetraploidy, 3) tetraploid cell characteristics, 4) stress-induced unphysiological tetraploidy, 5) comparison of physiological vs. unphysiological tetraploidy, 6) consequences of unphysiological stress-induced tetraploidy, 7) nutritional or pharmacological prevention strategies of tetraploidisation, and 8) knowledge gaps and future perspectives. Unphysiological tetraploidy is an adaptive stress response at a given threshold, often involving mitotic slippage. If tetraploid cells evade elimination through apoptosis or immune surveillance, they may re-enter the cell cycle, causing genetic instability, micronuclei formation, aneuploidy, modification of the epigenome and the development of diseases. The potential contributions of unphysiological tetraploidy to neurodegenerative, cardiovascular and diabetes related diseases are summarized in schematic figures and contrasted with its role in cancer development. The mechanisms responsible for the transition from physiological to unphysiological tetraploidy and the tolerance to tetraploidisation in unphysiological tetraploidy are not fully understood. Understanding these mechanisms is of critical importance to allow the development of targeted nutritional and pharmacological prevention strategies and therapies.

Morphological and cellular effects in Boana faber tadpoles (Anura: Hylidae) exposed to atrazine-based herbicide and glyphosate-based herbicide and their mixtures

Atrazine and glyphosate are considered some of the main pollutants for aquatic ecosystems, directly and indirectly affecting non-target organisms, such as amphibians. This study aimed to evaluate the sublethal effects of different concentrations of atrazine-based herbicide (ABH) and glyphosate-based herbicide (GBH) commercial formulations, both individually and in a mixture, through toxicity tests on the larval stage of Boana faber. Tadpoles were exposed to concentrations of ABH (2, 9.33, 10.40, 47.21, and 240 μg L-1) and GBH (65, 144, 280, 500, and 1000 μg L-1), as well as a mixture ABH + GBH, for 7 days. Although survival and swimming activity were not significantly affected by herbicide exposure, tadpoles in all treatments showed damage to the mouth and intestine, changes in size and mass, and an increase in the frequency of micronuclei and other nuclear abnormalities. Despite differences in some variables analyzed, it is not possible to definitively state that there is a difference in the toxicity of these two herbicides, as both caused morphological damage and were cyto-genotoxic. Our findings suggest that exposure to commercial formulations of these herbicides, whether alone or in mixture, can directly impact the quality of life of B. faber tadpoles.

Cellular uptake of multi-walled carbon nanotubes is associated to genotoxic and teratogenic effects towards the freshwater diatom Nitzschia linearis

The increase in industrial production of multi-walled carbon nanotubes (MWCNTs) raises concerns about their potential adverse effects associated to environmental releases, especially in aquatic environments where they are likely to accumulate. This study focuses on the environmental impact of MWCNTs, specifically on a benthic freshwater diatom (Nitzschia linearis), which plays a major role in the primary production of water bodies. The obtained results indicate that exposure to MWCNTs in the presence of natural organic matter (NOM) inhibits diatom's growth in a dose-dependent manner after 72 h of exposure. Interestingly, the photosystem II quantum yield (PSIIQY) in diatoms remains unaffected even after exposure to MWCNTs at 10 mg/L. After 48 h of exposure, MWCNTs are found to bind preferentially to extracellular polymeric substances (EPS) produced by diatoms, which could decrease their toxicity by limiting their interaction with this organism. However, measurement of genotoxicity and teratogenicity in diatoms exposed to MWCNTs revealed that the exposure to MWCNTs increased the occurrence of cells with micronuclei and abnormal frustules. Microscopy analyses including two-photon excitation microscopy (TPEM) revealed the internalization of MWCNTs. Investigations of the diatom's frustule structure using Scanning electron microscopy (SEM) indicated that the presence of pore structures constitutes a pathway allowing MWCNTs uptake. The presence in the diatom's cytoplasm of MWCNTs might possibly induce disturbances of the cellular components, leading to the observed genotoxic and teratogenic effects. In view of previous studies, this work underscores the need for further studies on the interaction between nanomaterials and different diatom species, given the species-specific nature of the interactions.

Hematological and genotoxic biomarkers in a natural population of freshwater turtles Trachemys dorbigni (Duméril & Bibron, 1835) (Testudines: Emydidae) living in an urban area in Southern Brazil

The present study aimed to report the morphometric and hematological indices and genotoxicity of a free-life population of D'Orbigny's slider turtles (Trachemys dorbigni) living in an urban area in Southern Brazil. For that, 16 specimens were randomly captured in an urban canal that receives irregular releases of wastewater. Biometrics and external visual changes were analyzed, such as turtle shell deformities, and the presence of parasites. Blood samples were collected to evaluate the hematological profile and the presence of micronuclei and other erythrocyte nuclear abnormalities as potential mutagenic and genotoxic effects. Water physicochemical parameters were also measured. Organisms with ectoparasites (31.25%) and small carapace deformations (56.25%) were observed, but maximum carapace length and weight were considered normal for the species according to the literature. The blood profile indicated low hemoglobin and hematocrit and a high number of total leukocytes, particularly eosinophils which characterize parasitic infections. A frequency of 0.12% for the micronucleus was considered basal, but the frequency of other erythrocyte abnormalities was evident, mainly of blebbed nuclei (63.79%), indicating chromosomal damage in the early stage. The results of this study suggest that natural populations of chelonian inhabiting urbanized areas are impacted by anthropogenic activities in the surrounding environment. Furthermore, it provides comprehensive data which can serve as a comparative model for environmental monitoring studies involving turtles.

Pleural inflammatory response, mesothelin content and DNA damage in mice at one-year after intra-pleural carbon nanotube administration

Many in vitro and in vivo studies have shown that exposure to carbon nanotubes (CNTs) is associated with inflammation, oxidative stress and genotoxicity, although there is a paucity of studies on these effects in the pleural cavity. In the present study, we investigated adverse outcomes of pleural exposure to multi-walled CNTs (MWCNT-7, NM-401 and NM-403) and single-walled CNTs (NM-411). Female C57BL/6 mice were exposed to 0.2 or 5 µg of CNTs by intra-pleural injection and sacrificed one-year post-exposure. Exposure to long and straight types of MWCNTs (i.e. MWCNT-7 and NM-401) was associated with decreased number of macrophages and increased number of neutrophils and eosinophils in pleural lavage fluid. Increased protein content in the pleural lavage fluid was also observed in mice exposed to MWCNT-7 and NM-401. The concentration of mesothelin was increased in mice exposed to MWCNT-7 and NM-411. Levels of DNA strand breaks and DNA oxidation damage, measured by the comet assay, were unaltered in cells from pleural scrape. Extra-pleural effects were seen in CNT exposed mice, including enlarged and pigmented mediastinal lymph nodes (all four types of CNTs), pericardial plaques (MWCNT-7 and NM-401), macroscopic abnormalities on the liver (MWCNT-7) and ovaries/uterus (NM-411). In conclusion, the results demonstrate that intra-pleural exposure to long and straight MWCNTs is associated with adverse outcomes. Certain observations such as increased content of mesothelin in pleural lavage fluid and ovarian/uterine abnormalities in mice exposed to NM-411 suggests that exposure to SWCNTs may also be associated with some adverse outcomes.

Exposure of Rats to Multi-Walled Carbon Nanotubes: Correlation of Inhalation Exposure to Lung Burden, Bronchoalveolar Lavage Fluid Findings, and Lung Morphology

To evaluate lung toxicity due to inhalation of multi-walled carbon nanotubes (MWCNTs) in rats, we developed a unique MWCNT aerosol generator based on dry aerosolization using the aerodynamic cyclone principle. Rats were exposed to MWNT-7 (also known as Mutsui-7 and MWCNT-7) aerosolized using this device. We report here an analysis of previously published data and additional unpublished data obtained in 1-day, 2-week, 13-week, and 2-year inhalation exposure studies. In one-day studies, it was found that approximately 50% of the deposited MWNT-7 fibers were cleared the day after the end of exposure, but that clearance of the remaining fibers was markedly reduced. This is in agreement with the premise that the rapidly cleared fibers were deposited in the ciliated airways while the slowly cleared fibers were deposited beyond the ciliated airways in the respiratory zone. Macrophage clearance of MWNT-7 fibers from the alveoli was limited. Instead of macrophage clearance from the alveoli, containment of MWNT-7 fibers within induced granulomatous lesions was observed. The earliest changes indicative of pulmonary toxicity were seen in the bronchoalveolar lavage fluid. Macrophage-associated inflammation persisted from the one-day exposure to MWNT-7 to the end of the two-year exposure period. Correlation of lung tumor development with MWNT-7 lung burden required incorporating the concept of area under the curve for the duration of the study; the development of lung tumors induced by MWNT-7 correlated with lung burden and the duration of MWNT-7 residence in the lung.

In vivo genotoxicity assessment of a multiwalled carbon nanotube in a mouse ex vivo culture

Background

Multiwalled carbon nanotubes (MWCNTs) are suspected lung carcinogens because their shape and size are similar to asbestos. Various MWCNT types are manufactured; however, only MWNT-7 is classified into Group 2B by The International Agency for Research on Cancer. MWNT-7’s carcinogenicity is strongly related to inflammatory reactions. On the other hand, inconsistent results on MWNT-7 genotoxicity have been reported. We previously observed no significant differences in both Pig-a (blood) and gpt (lung) mutant frequencies between MWNT-7-intratracheally treated and negative control rats. In this study, to investigate in vivo MWNT-7 genotoxicity on various endpoints, we attempted to develop a lung micronucleus assay through ex vivo culture targeting the cellular fraction of Clara cells and alveolar Type II (AT-II) cells, known as the initiating cells of lung cancer. Using this system, we analyzed the in vivo MWNT-7 genotoxicity induced by both whole-body inhalation exposure and intratracheal instillation. We also conducted an erythrocyte micronucleus assay using the samples obtained from animals under intratracheal instillation to investigate the tissue specificity of MWNT-7 induced genotoxicities.

Results

 We detected a significant increase in the incidence of micronucleated cells derived from the cellular fraction of Clara cells and AT-II cells in both MWNT-7-treated and positive control groups compared to the negative control group under both whole-body inhalation exposures and intratracheal instillation. Additionally, the erythrocyte micronucleus assay detected a significant increase in the incidence of micronucleated reticulocytes only in the positive control group.

Conclusions

Our findings indicated that MWNT-7 was genotoxic in the lungs directly exposed by both the body inhalation and intratracheal instillation but not in the hematopoietic tissue.

Genotoxicity of multi-walled carbon nanotube reference materials in mammalian cells and animals

Carbon nanotubes (CNTs) were the first nanomaterials to be evaluated by the International Agency for Research on Cancer (IARC). The categorization as possibly carcinogenic agent to humans was only applicable to multi-walled carbon nanotubes called MWCNT-7. Other types of CNTs were not classifiable because of missing data and it was not possible to pinpoint unique CNT characteristics that cause cancer. Importantly, the European Commission's Joint Research Centre (JRC) has established a repository of industrially manufactured nanomaterials that encompasses at least four well-characterized MWCNTs called NM-400 to NM-403 (original JRC code). This review summarizes the genotoxic effects of these JRC materials and MWCNT-7. The review consists of 36 publications with results on cell culture experiments (22 publications), animal models (9 publications) or both (5 publications). As compared to the publications in the IARC monograph on CNTs, the current database represents a significant increase as there is only an overlap of 8 publications. However, the results come mainly from cell cultures and/or measurements of DNA strand breaks by the comet assay and the micronucleus assay (82 out of 97 outcomes). A meta-analysis of cell culture studies on DNA strand breaks showed a genotoxic response by MWCNT-7, less consistent effect by NM-400 and NM-402, and least consistent effect by NM-401 and NM-403. Results from other in vitro tests indicate strongest evidence of genotoxicity for MWCNT-7. There are too few observations from animal models and humans to make general conclusions about genotoxicity.

Morphological, behavioral and genotoxic effects of glyphosate and 2,4-D mixture in tadpoles of two native species of South American amphibians

Pesticide contamination is an important factor in the global decline of amphibians. The herbicides glyphosate and 2,4-D are the most applied worldwide. These herbicides are often found in surface waters close to agricultural areas. This study aims at evaluating the chronic effects caused by glyphosate + 2,4-D mixture in Boana faber and Leptodactylus latrans tadpoles. The combined solution of the glyphosate and 2,4-D, in 5 different concentrations, was applied for 168 h. Herbicide mixtures did not affect the survival of the exposed tadpoles but growth and swimming activity were altered; besides causing several damages in the mouth and intestine. The erythrocytes showed micronuclei and other nuclear abnormalities. There is an ecological risk in the exposure of tadpoles of B. faber and L. latrans from the mixture of glyphosate + 2,4-D. Therefore, the approach used in this study provides important information on how commonly used pesticides can affect non-target organisms.

Continuous Long-Term Exposure to Low Concentrations of MWCNTs Induces an Epithelial-Mesenchymal Transition in BEAS-2B Cells

In the field of nanotechnology, the use of multi-walled carbon nanotubes (MWCNTs) is growing. Pulmonary exposure during their production, use, and handling is raising concerns about their potential adverse health effects. The purpose of this study is to assess how the physical characteristics of MWCNTs, such as diameter and/or length, can play a role in cellular toxicity. Our experimental design is based on the treatment of human bronchial epithelial cells (BEAS-2B) for six weeks with low concentrations (0.125-1 µg/cm2) of MWCNTs having opposite characteristics: NM-403 and Mitsui-7. Following treatment with both MWCNTs, we observed an increase in mitotic abnormalities and micronucleus-positive cells. The cytotoxic effect was delayed in cells treated with NM-403 compared to Mitsui-7. After 4-6 weeks of treatment, a clear cellular morphological change from epithelial to fibroblast-like phenotype was noted, together with a change in the cell population composition. BEAS-2B cells underwent a conversion from the epithelial to mesenchymal state as we observed a decrease in the epithelial marker E-cadherin and an increased expression of mesenchymal markers N-cadherin, Vimentin, and Fibronectin. After four weeks of recovery, we showed that the induced epithelial-mesenchymal transition is reversible, and that the degree of reversibility depends on the MWCNT.

Genomic instability in people living with HIV

The increased life expectancy of people living with HIV (PLWH) receiving antiretroviral treatment (ART) has transformed HIV infection into a chronic disease. However, patients may be at risk of accelerated aging and the accumulation of cellular damage, which may trigger the development of cancer. We evaluated genomic instability in HIV-positive individuals with different viral loads receiving antiretroviral treatment (ART) and in HIV ART-naïve individuals. We included 67 participants divided into four groups: group 1 (n = 24) HIV patients receiving reverse-transcriptase inhibitors (tenofovir/ emtricitabine/ efavirenz and abacavir/ lamivudine/ efavirenz), group 2 (n = 22) HIV patients receiving protease inhibitors combined with other antiretroviral drugs (tenofovir/ emtricitabine with ritonavir/ atazanavir or lopinavir/ ritonavir, and darunavir/ ritonavir/ raltegravir), group 3 (n = 13) HIV ART-naïve patients, and group 4 (n = 8) healthy individuals (controls). Nuclear abnormalities in buccal mucosal samples (micronuclei, binucleated cells, nuclear buds, karyorrhexis, karyolysis, and pyknosis) were quantified. Simultaneously, blood samples were taken to quantify CD4+, CD8+, and HIV viral load. There was a significant age difference between HIV ART-naïve patients and receiving ART groups. Infection time was longer in HIV patients with ART than in ART-naïve patients. There were no differences in sex, smoking, alcohol consumption, or number of micronucleated cells between the study groups. We found higher frequencies of binucleated cells and nuclear buds in HIV patients, HIV ART-naïve, and HIV ART patients compared to the control group. We found a positive correlation between nuclear buds and CD4/CD8 ratio in the HIV ART-naïve group. In conclusion, PLWH showed increased genomic instability. The CD4/CD8 ratio affects the numbers of nuclear buds and binucleated cells. These findings are pertinent to mechanisms of damage and possible strategies to mitigate carcinogenesis in PLWH.

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.

Mitsui-7, heat-treated, and nitrogen-doped multi-walled carbon nanotubes elicit genotoxicity in human lung epithelial cells

Background

The unique physicochemical properties of multi-walled carbon nanotubes (MWCNT) have led to many industrial applications. Due to their low density and small size, MWCNT are easily aerosolized in the workplace making respiratory exposures likely in workers. The International Agency for Research on Cancer designated the pristine Mitsui-7 MWCNT (MWCNT-7) as a Group 2B carcinogen, but there was insufficient data to classify all other MWCNT. Previously, MWCNT exposed to high temperature (MWCNT-HT) or synthesized with nitrogen (MWCNT-ND) have been found to elicit attenuated toxicity; however, their genotoxic and carcinogenic potential are not known. Our aim was to measure the genotoxicity of MWCNT-7 compared to these two physicochemically-altered MWCNTs in human lung epithelial cells (BEAS-2B & SAEC).

Results

Dose-dependent partitioning of individual nanotubes in the cell nuclei was observed for each MWCNT material and was greatest for MWCNT-7. Exposure to each MWCNT led to significantly increased mitotic aberrations with multi- and monopolar spindle morphologies and fragmented centrosomes. Quantitative analysis of the spindle pole demonstrated significantly increased centrosome fragmentation from 0.024–2.4 μg/mL of each MWCNT. Significant aneuploidy was measured in a dose-response from each MWCNT-7, HT, and ND; the highest dose of 24 μg/mL produced 67, 61, and 55%, respectively. Chromosome analysis demonstrated significantly increased centromere fragmentation and translocations from each MWCNT at each dose. Following 24 h of exposure to MWCNT-7, ND and/or HT in BEAS-2B a significant arrest in the G1/S phase in the cell cycle occurred, whereas the MWCNT-ND also induced a G2 arrest. Primary SAEC exposed for 24 h to each MWCNT elicited a significantly greater arrest in the G1 and G2 phases. However, SAEC arrested in the G1/S phase after 72 h of exposure. Lastly, a significant increase in clonal growth was observed one month after exposure to 0.024 μg/mL MWCNT-HT & ND.

Conclusions

Although MWCNT-HT & ND cause a lower incidence of genotoxicity, all three MWCNTs cause the same type of mitotic and chromosomal disruptions. Chromosomal fragmentation and translocations have not been observed with other nanomaterials. Because in vitro genotoxicity is correlated with in vivo genotoxic response, these studies in primary human lung cells may predict the genotoxic potency in exposed human populations.

Electronic supplementary material

The online version of this article (10.1186/s12989-019-0318-0) contains supplementary material, which is available to authorized users.

Do Amazon turtles exposed to environmental concentrations of the antineoplastic drug cyclophosphamide present mutagenic damages? If so, would such damages be reversible?

Antineoplastic drugs (AD) have been increasingly used, but the disposal of their wastes in the environment via hospital effluent and domestic sewage has emerged as an environmental issue. The current risks posed to these animals and effects of pollutants on the reptiles' population level remain unknown due to lack of studies on the topic. The aim of the present study was to evaluate the mutagenicity of neonate Podocnemis expansa exposed to environmental concentrations (EC) of cyclophosphamide (Cyc). The adopted doses were EC-I 0.2 μg/L and EC-II 0.5 μg/L Cyc. These doses correspond to 1/10 and ¼ of concentrations previously identified in hospital effluents. Turtles exposed to the CyC recorded larger total number of erythrocyte nuclear abnormalities than the ones in the control group after 48-h exposure. The total number of abnormalities for both groups (EC-I and EC-II) 96 h after the experiment had started was statistically similar to that of animals exposed to high Cyc concentration (positive control 5 × 10⁴ μg/L). This outcome confirms the mutagenic potential of Cyc, even at low concentrations. On the other hand, when the animals were taken to a pollutant-free environment, their mutagenic damages disappeared after 240 h. After such period, their total of abnormalities matched the basal levels recorded for the control group. Therefore, our study is the first evidence of AD mutagenicity in reptiles, even at EC and short-term exposure, as well as of turtles' recovery capability after the exposure to Cyc.

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.

Carcinogenicity of multi-walled carbon nanotubes: challenging issue on hazard assessment

OBJECTIVES

This report reviews the carcinogenicity of multi-walled carbon nanotubes (MWCNTs) in experimental animals, concentrating on MWNT-7, a straight fibrous MWCNT.

METHODS

MWCNTs were administered to mice and rats by intraperitoneal injection, intrascrotal injection, subcutaneous injection, intratracheal instillation and inhalation.

RESULTS

Intraperitoneal injection of MWNT-7 induced peritoneal mesothelioma in mice and rats. Intrascrotal injection induced peritoneal mesothelioma in rats. Intratracheal instillation of MWCNT-N (another straight fibrous MWCNT) induced both lung carcinoma and pleural mesothelioma in rats. In the whole body inhalation studies, in mice MWNT-7 promoted methylcholanthrene-initiated lung carcinogenesis. In rats, inhalation of MWNT-7 induced lung carcinoma and lung burdens of MWNT-7 increased with increasing concentration of airborne MWNT-7 and increasing duration of exposure.

CONCLUSIONS

Straight, fibrous MWCNTs exerted carcinogenicity in experimental animals. Phagocytosis of MWCNT fibers by macrophages was very likely to be a principle factor in MWCNT lung carcinogenesis. Using no-observed-adverse-effect level-based approach, we calculated that the occupational exposure limit (OEL) of MWNT-7 for cancer protection is 0.15 μg/m3 for a human worker. Further studies on the effects of the shape and size of MWCNT fibers and mode of action on the carcinogenicity are required.

Different Cellular Response of Human Mesothelial Cell MeT-5A to Short-Term and Long-Term Multiwalled Carbon Nanotubes Exposure

Despite being a commercially important product, multiwalled carbon nanotubes (MWCNTs) continue to raise concerns over human health due to their structural similarity to asbestos. Indeed, exposure to MWCNT has been shown to induce lung cancer and even mesothelioma, but contradictory results also exist. To clarify the potentially carcinogenic effects of rigid and rod-like MWCNT and to elucidate the underlying mechanisms, the effects of MWCNT on human mesothelial cell MeT-5A were examined throughout 3 months of continuous exposure, including cytotoxicity, genotoxicity, and cell motility. It was found that MWCNT did not affect MeT-5A cell proliferation at 10 μg/cm² within 72 h treatment, but under the same condition, MWCNT induced genotoxicity and perturbed cell motility. In addition, MeT-5A cells demonstrated different cellular responses to MWCNT after short-term and long-term exposure. Taken together, our results indicated a possible carcinogenic potential for MWCNT after long-term treatment, in which Annexin family proteins might be involved.

Absence of in vivo mutagenicity of multi-walled carbon nanotubes in single intratracheal instillation study using F344 gpt delta rats

Introduction

It is known that fibrous particles of micrometer length, such as carbon nanotubes, which have same dimensions as asbestos, are carcinogenic. Carcinogenicity of nanomaterials is strongly related to inflammatory reactions; however, the genotoxicity mechanism(s) is unclear. Indeed, inconsistent results on genotoxicity of multi-walled carbon nanotubes (MWCNTs) have been shown in several reports. Therefore, we analyzed the in vivo genotoxicity induced by an intratracheal instillation of straight MWCNTs in rats using a different test system—the Pig-a gene mutation assay—that can reflect the genotoxicity occurring in the bone marrow. Since lungs were directly exposed to MWCNTs upon intratracheal instillation, we also performed the gpt assay using the lungs.

Findings

We detected no significant differences in Pig-a mutant frequencies (MFs) between the MWCNT-treated and control rats. Additionally, we detected no significant differences in gpt MFs in the lung between the MWCNT-treated and control rats.

Conclusions

Our findings indicated that a single intratracheal instillation of MWCNTs was non-mutagenic to both the bone marrow and lung of rats.

Lung carcinogenicity of inhaled multi-walled carbon nanotube in rats

BACKGROUND

Multi-walled carbon nanotubes (MWCNTs) constitute one of the most promising types of nanomaterials in industry today. With their increasing use, the potential toxicity and carcinogenicity of MWCNT needs to be evaluated in bioassay studies using rodents. Since humans are mainly exposed to MWCNT by inhalation, we performed a 104-week carcinogenicity study using whole-body inhalation exposure chambers with a fibrous straight type of MWCNT at concentrations of 0, 0.02, 0.2, and 2 mg/m3 using male and female F344 rats.

RESULTS

Lung carcinomas, mainly bronchiolo-alveolar carcinoma, and combined carcinomas and adenomas were significantly increased in males exposed to 0.2 and 2 mg/m3 MWNT-7 and in females exposed to 2 mg/m3 MWNT-7 compared to the clean air control group. However, no development of pleural mesothelioma was observed. Concentration-dependent toxic effects in the lung such as epithelial hyperplasia, granulomatous change, localized fibrosis, and alteration in BALF parameters were found in MWNT-7 treatment groups of both sexes. There were no MWNT-7-specific macroscopic findings in the other organs, including the pleura and peritoneum. Absolute and relative lung weights were significantly elevated in male rats exposed to 0.2 and 2 mg/m3 MWNT-7 and in all exposed female groups. The lung burdens of MWNT-7 were clearly increased in a concentration-dependent as well as a duration-dependent manner.

CONCLUSION

There is clear evidence that MWNT-7 is carcinogenic to the lungs of male and female F344 rats, however no plural mesothelioma was observed.

In vitro chromosomal aberrations induced by various shapes of multi-walled carbon nanotubes (MWCNTs)

Objectives:

IARC has classified one type of multi-walled carbon nanotubes (MWCNTs), MWNT-7, as possibly carcinogenic to humans (Group 2B); however, other types of MWCNT were categorized as not classifiable as to their carcinogenicity to humans (Group 3). In vitro chromosomal aberration assays of MWNT-7 showed polyploid formation but not structural abnormalities. This study investigated the influence of the shape and size of MWCNT on in vitro induction of chromosomal aberrations.

Methods:

Microscopic analysis and viable cell counting were used to assay for chromosomal aberrations and cytotoxicity induced in a Chinese hamster lung cell line (CHL/IU) exposed to different MWCNTs.

Results:

Using scanning electron microscopy, seven MWCNTs were classified into three types: straight fibrous, curved fibrous, and tangled. The straight fibrous MWCNTs were the strongest inducers of polyploidy and the most cytotoxic among the three types of MWCNTs. The curved fibrous MWCNTs induced more polyploidy than the tangled MWCNTs, and the cytotoxicity of both types seemed to be a reflection of their induction of polyploidy. None of the seven MWCNTs induced structural chromosomal aberrations.

Conclusion:

The non-clastogenicity of the MWCNTs indicates that the MWCNTs may not interact directly with DNA. Since the straight fibrous MWCNTs, which exhibit a structure similar to asbestos, were the strongest inducers of polyploidy, MWCNT shape may be an important factor in induction of polyploidy. We hypothesize that CHL/IU cells endocytosed MWCNTs and formed endosomes with shapes corresponding to those of the endocytosed MWCNTs, and that the long axis diameter of the endosome is important in the capability of MWCNTs to induce polyploidy.