Repair activity of oxidatively damaged DNA and telomere length in human lung epithelial cells after exposure to multi-walled carbon nanotubes

The dispersion method does not affect the in vitro genotoxicity of multi-walled carbon nanotubes despite inducing surface alterations

Multi-walled carbon nanotubes (MWCNTs) are a desirable class of high aspect ratio nanomaterials (HARNs) owing to their extensive applications. Given their demand, the growing occupational and consumer exposure to these materials has warranted an extensive investigation into potential hazards they may pose towards human health. This study utilised both the in vitro mammalian cell gene mutation and the cytokinesis-blocked micronucleus (CBMN) assays to investigate genotoxicity in human lymphoblastoid (TK6) and 16HBE14o- human lung epithelial cells, following exposure to NM-400 and NM-401 MWCNTs for 24 h. To evaluate the potential for secondary genotoxicity, the CBMN assay was applied on a co-culture of 16HBE14o- with differentiated human monocytic (dTHP-1) cells. In addition, two dispersion methods (NanoGenoTox vs. high shear mixing) were utilised prior to exposures and in acellular experiments to assess the effects on MWCNT oxidative potential, aspect ratio and surface properties. These were characterized in chemico as well as by electron microscopy and Raman spectroscopy. Structural damage of NM-400 was observed following both dispersion approaches; Raman spectra highlighted greater oxidative transformation under probe sonication as opposed to high shear mixing. Despite the changes to the oxidative potential of the MWCNTs, no statistically significant genotoxicity was observed under the conditions applied. There was also no visible signs of cellular internaliation of NM-400 or NM-401 into either cell type under the test conditions, which may support the negative genotoxic response. Whilst these HARNs may have oxidative potential, cells have natural protective mechanisms for repairing transient DNA damage. Therefore, it is crucial to evaluate biological endpoints which measure fixed DNA damage to account for the impact of DNA repair mechanisms.

Recent advances in nanoantibiotics against multidrug-resistant bacteria

Multidrug-resistant (MDR) bacteria-caused infections have been a major threat to human health. The abuse of conventional antibiotics accelerates the generation of MDR bacteria and makes the situation worse. The emergence of nanomaterials holds great promise for solving this tricky problem due to their multiple antibacterial mechanisms, tunable antibacterial spectra, and low probabilities of inducing drug resistance. In this review, we summarize the mechanism of the generation of drug resistance, and introduce the recently developed nanomaterials for dealing with MDR bacteria via various antibacterial mechanisms. Considering that biosafety and mass production are the major bottlenecks hurdling the commercialization of nanoantibiotics, we introduce the related development in these two aspects. We discuss urgent challenges in this field and future perspectives to promote the development and translation of nanoantibiotics as alternatives against MDR pathogens to traditional antibiotics-based approaches.

Effects of nanomaterial exposure on telomere dysfunction, hallmarks of mammalian and zebrafish cell senescence, and zebrafish mortality

Environmental and occupational exposure to hazardous substances accelerates biological aging. However, the toxic effects of nanomaterials on telomere and cellular senescence (major hallmarks of the biological aging) remained controversial. This study was to synthesize all published evidence to explore the effects of nanomaterial exposure on the telomere change, cellular senescence and mortality of model animals. Thirty-five studies were included by searching electronic databases (PubMed, Embase and Web of Science). The pooled analysis by Stata 15.0 software showed that compared with the control, nanomaterial exposure could significantly shorten the telomere length [measured as kbp: standardized mean difference (SMD) = -1.88; 95% confidence interval (CI) = -3.13 - - 0.64; % of control: SMD = -1.26; 95%CI = -2.11- - 0.42; < 3 kbp %: SMD = 5.76; 95%CI = 2.92 - 8.60), increase the telomerase activity (SMD = -1.00; 95%CI = -1.74 to -0.26), senescence-associated β-galactosidase levels in cells (SMD = 8.20; 95%CI = 6.05 - 10.34) and zebrafish embryos (SMD = 7.32; 95%CI = 4.70 - 9.94) as well as the mortality of zebrafish (SMD = 3.83; 95%CI = 2.94 - 4.72)]. The expression levels of telomerase TERT, shelterin components (TRF1, TRF2 and POT1) and senescence biomarkers (p21, p16) were respectively identified to be decreased or increased in subgroup analyses. In conclusion, this meta-analysis demonstrates that nanomaterial exposure is associated with telomere attrition, cell senescence and organismal death.

Long-term cryopreservation of potassium bromate positive assay controls for measurement of oxidatively damaged DNA by the Fpg-modified comet assay: results from the hCOMET ring trial

The formamidopyrimidine DNA glycosylase (Fpg)-modified comet assay is widely used for the measurement of oxidatively generated damage to DNA. However, there has not been a recommended long-term positive control for this version of the comet assay. We have investigated potassium bromate as a positive control for the Fpg-modified comet assay because it generates many Fpg-sensitive sites with a little concurrent generation of DNA strand breaks. Eight laboratories used the same procedure for the treatment of monocytic THP-1 cells with potassium bromate (0, 0.5, 1.5, and 4.5 mM) and subsequent cryopreservation in a freezing medium consisting of 50% foetal bovine serum, 40% RPMI-1640 medium, and 10% dimethyl sulphoxide. The samples were analysed by the Fpg-modified comet assay three times over a 3-year period. All laboratories obtained a positive concentration-response relationship in cryopreserved samples (linear regression coefficients ranging from 0.79 to 0.99). However, there was a wide difference in the levels of Fpg-sensitive sites between the laboratory with the lowest (4.2% Tail DNA) and highest (74% Tail DNA) values in THP-1 cells after exposure to 4.5 mM KBrO3. In an attempt to assess sources of inter-laboratory variation in Fpg-sensitive sites, comet images from one experiment in each laboratory were forwarded to a central laboratory for visual scoring. There was high consistency between measurements of %Tail DNA values in each laboratory and the visual score of the same comets done in the central laboratory (r = 0.98, P < 0.001, linear regression). In conclusion, the results show that potassium bromate is a suitable positive comet assay control.

Genotoxicity of Particles From Grinded Plastic Items in Caco-2 and HepG2 Cells

Large plastic litters degrade in the environment to micro- and nanoplastics, which may then enter the food chain and lead to human exposure by ingestion. The present study explored ways to obtain nanoplastic particles from real-life food containers. The first set of experiments gave rise to polypropylene nanoplastic suspensions with a hydrodynamic particle size range between 100 and 600 nm, whereas the same grinding process of polyethylene terephthalate (PET) produced suspensions of particles with a primary size between 100 and 300 nm. The exposure did not cause cytotoxicity measured by the lactate dehydrogenase (LDH) and water soluble tetrazolium 1 (WST-1) assays in Caco-2 and HepG2 cells. Nanoplastics of transparent PET food containers produced a modest concentration-dependent increase in DNA strand breaks, measured by the alkaline comet assay [net induction of 0.28 lesions/10⁶ bp at the highest concentration (95% CI: 0.04; 0.51 lesions/10⁶ base pair)]. The exposure to nanoplastics from transparent polypropylene food containers was also positively associated with DNA strand breaks [i.e., net induction of 0.10 lesions/10⁶ base pair (95% CI: −0.04; 0.23 lesions/10⁶ base pair)] at the highest concentration. Nanoplastics from grinding of black colored PET food containers demonstrated no effect on HepG2 and Caco-2 cells in terms of cytotoxicity, reactive oxygen species production or changes in cell cycle distribution. The net induction of DNA strand breaks was 0.43 lesions/10⁶ bp (95% CI: 0.09; 0.78 lesions/10⁶ bp) at the highest concentration of nanoplastics from black PET food containers. Collectively, the results indicate that exposure to nanoplastics from real-life consumer products can cause genotoxicity in cell cultures.

Multiwalled Carbon Nanotubes Induce Fibrosis and Telomere Length Alterations

Telomere shortening can result in cellular senescence and in increased level of genome instability, which are key events in numerous of cancer types. Despite this, few studies have focused on the effect of nanomaterial exposure on telomere length as a possible mechanism involved in nanomaterial-induced carcinogenesis. In this study, effects of exposure to multiwalled carbon nanotubes (MWCNT) on telomere length were investigated in mice exposed by intrapleural injection, as well as in human lung epithelial and mesothelial cell lines. In addition, cell cycle, apoptosis, and regulation of genes involved in DNA damage repair were assessed. Exposure to MWCNT led to severe fibrosis, infiltration of inflammatory cells in pleura, and mesothelial cell hyperplasia. These histological alterations were accompanied by deregulation of genes involved in fibrosis and immune cell recruitment, as well as a significant shortening of telomeres in the pleura and the lung. Assessment of key carcinogenic mechanisms in vitro confirmed that long-term exposure to the long MWCNT led to a prominent telomere shortening in epithelial cells, which coincided with G1-phase arrest and enhanced apoptosis. Altogether, our data show that telomere shortening resulting in cell cycle arrest and apoptosis may be an important mechanism in long MWCNT-induced inflammation and fibrosis.

Do Carbon Nanotubes and Asbestos Fibers Exhibit Common Toxicity Mechanisms?

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

Particulate matter causes telomere shortening and increase in cellular senescence markers in human lung epithelial cells

Exposure to particulate matter (PM) has been associated with DNA damage, but the relationships between PM, telomere length and cellular senescence remain unclear. This study aimed to investigate the effects and potential mechanisms of PM on telomere length and cellular senescence in human lung epithelial cells. Human lung epithelial A549 cells were exposed to PM for 24 h. Cell viability and cytotoxicity were measured by the WST-1 assay and the lactate dehydrogenase release, respectively. Cellular uptake of PM was observed using transmission electron microscopy. Telomere length was measured using qPCR and expressed as T/S ratio. Cell cycle progression was analyzed by flow cytometry. Expression of human telomerase reverse transcriptase (hTERT) and cell cycle regulators was measured using mRNA by qPCR and protein levels by Western blot. Cellular senescence was determined by the expression of senescence-associated β-galactosidase (SA-β-Gal) with fluorescent microscopy and flow cytometry. Exposed to PM at the concentration of 200 μg/ml decreased cell viability and increased LDH levels in culture medium. Remarkably increased uptake of PM, shortening of telomere length, induction of G0/G1 phase arrest, and increased expression of senescence hallmarks were observed after exposure to PM in A549 cells. PM exposure induced upregulation of p21 and downregulation of proliferating cell nuclear antigen (PCNA) and hTERT expression, but no significant change in p53 expression, in A549 cells. Overall, exposure to PM may downregulate hTERT and PCNA through p53-independent induction of p21 expression, leading to telomere shortening, G0/G1 arrest and the onset of cellular senescence in human lung epithelial cells.

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.

Multi-Walled Carbon Nanotubes (MWCNTs) Cause Cellular Senescence in TGF-β Stimulated Lung Epithelial Cells

Multi-walled carbon nanotubes are engineered nanomaterials (ENMs) that have a fiber-like structure which may be a concern for the development of cellular senescence. Premature senescence, a state of irreversible cell cycle arrest, is implicated in the pathogenesis of chronic lung diseases such as pulmonary fibrosis (PF). However, the crosstalk between downstream pathways mediating fibrotic and senescent responses of MWCNTs is not well-defined. Here, we exposed human bronchial epithelial cells (BEAS-2B) to MWCNTs for up to 72 h and demonstrate that MWCNTs increase reactive oxygen species (ROS) production accompanied by inhibition of cell proliferation. In addition, MWCNT exposure resulted in the increase of p21 protein abundance and senescence associated β-galactosidase (SA β-gal) activity. We also determined that co-exposure with the cytokine, transforming growth factor-β (TGF-β) exacerbated cellular senescence indicated by increased protein levels of p21, p16, and γH2A.X. Furthermore, the production of fibronectin and plasminogen activator inhibitor (PAI-1) was significantly elevated with the co-exposure compared to MWCNT or TGF-β alone. Together, our study suggests that the cellular senescence potential of MWCNTs may be enhanced by pro-fibrotic mediators, such as TGF-β in the surrounding microenvironment.

Reactive oxygen species production, genotoxicity and telomere length in FE1-Muta™Mouse lung epithelial cells exposed to carbon nanotubes

Carbon nanotubes (CNTs) are fiber-like nanomaterials, which are used in various applications with possible exposure to humans. The genotoxicity and carcinogenic potential of CNTs remain to be fully understood. This study assessed the genotoxicity of three different multi-walled carbon nanotubes (MWCNTs) (MWCNT-7, NM-401 and NM-403) and one single-walled carbon nanotube (SWCNT) (NM-411) in FE1-Muta™Mouse lung epithelial (MML) cells using the alkaline comet assay. With the 2',7'-dichlorodihydrofluorescein diacetate fluorescent probe, we assessed the effect of CNT-exposure on the intracellular production of reactive oxygen species (ROS). We measured the effect of a 10-week CNT exposure on telomere length using quantitative PCR. Two of the included MWCNTs (NM-401 and MWCNT-7) and the SWCNT (NM-411) caused a significant increase in the level of DNA damage at concentrations up to 40 µg/ml (all concentrations pooled, p < 0.05), but no concentration-response relationships were found. All of the CNTs caused an increase in intracellular ROS production compared to unexposed cells (p_trend < 0.05). Results from the long-term exposure showed longer telomere length in cells exposed to MWCNTs compared to unexposed cells (p < 0.01). In conclusion, our results indicated that the included CNTs cause ROS production and DNA strand breaks in FE1-MML cells. Moreover, the MWCNTs, but not the SWCNT, had an impact on telomere length in a long-term exposure scenario.

An optimized comet-based in vitro DNA repair assay to assess base and nucleotide excision repair activity

This optimized protocol (including links to instruction videos) describes a comet-based in vitro DNA repair assay that is relatively simple, versatile, and inexpensive, enabling the detection of base and nucleotide excision repair activity. Protein extracts from samples are incubated with agarose-embedded substrate nucleoids ('naked' supercoiled DNA) containing specifically induced DNA lesions (e.g., resulting from oxidation, UVC radiation or benzo[a]pyrene-diol epoxide treatment). DNA incisions produced during the incubation reaction are quantified as strand breaks after electrophoresis, reflecting the extract's incision activity. The method has been applied in cell culture model systems, human biomonitoring and clinical investigations, and animal studies, using isolated blood cells and various solid tissues. Once extracts and substrates are prepared, the assay can be completed within 2 d.

Telomere length and genotoxicity in the lung of rats following intragastric exposure to food-grade titanium dioxide and vegetable carbon particles

Vegetable carbon (E153) and titanium dioxide (E171) are widely used as black and white food colour additives. The aim of this study was to assess gastrointestinal tight junction and systemic genotoxic effects in rats following exposure to E153 and E171 for 10 weeks by oral gavage once a week. The expression of tight junction proteins was assessed in intestinal tissues. Levels of DNA strand breaks, oxidatively damaged DNA and telomere length were assessed in secondary organs. Hydrodynamic suspensions of E153 and E173 indicated mean particles sizes of 230 and 270 nm, respectively, and only E153 gave rise to intracellular production of reactive oxygen species in colon epithelial (Caco-2) cells. Rats exposed to E153 (6.4 mg/kg/week) or E171 (500 mg/kg/week) had decreased gene expression of the tight junction protein TJP1 (P < 0.05). E153 (6.4 mg/kg/week) also decreased OCLN (P < 0.05) in the colon and occludin protein expression in the small intestine (P < 0.05). Furthermore, E153 or E171 exposed rats had shorter telomeres in the lung (P < 0.05). Plasma from particle-exposed rats also produced telomere shortening in cultured lung epithelial cells. There were unaltered levels of oxidatively damaged DNA in the liver and lung and no changes in the DNA repair activity of oxidatively damaged DNA in the lung. Altogether, these results indicate that intragastric exposure to E153 and E171 is associated with reduced tight junction protein expression in the intestinal barrier and telomere length shortening in the lung in rats.

Effect of combustion-derived particles on genotoxicity and telomere length: A study on human cells and exposed populations

Particulate matter (PM) from combustion processes has been associated with oxidative stress to DNA, whereas effects related to telomere dysfunction are less investigated. We collected air-borne PM from a passenger cabin of a diesel-propelled train and at a training facility for smoke diving exercises. Effects on oxidative stress biomarkers, genotoxicity measured by the comet assay and telomere length in PM-exposed A549 cells were compared with the genotoxicity and telomere length in peripheral blood mononuclear cells (PBMCs) from human volunteers exposed to the same aerosol source. Although elevated levels of DNA strand breaks and oxidatively damaged DNA in terms of Fpg-sensitive sites were observed in PBMCs from exposed humans, the PM collected at same locations did not cause genotoxicity in the comet assay in A549 cells. Nevertheless, A549 cells displayed telomere length shortening after four weeks exposure to PM. This is in line with slightly shorter telomere length in PBMCs from exposed humans, although it was not statistically significant. In conclusion, the results indicate that genotoxic potency measured by the comet assay of PM in A549 cells may not predict genotoxicity in exposed humans, whereas telomere length measurements may be a novel indicator of genotoxic stress in cell cultures and humans.

Pulmonary toxicity of two different multi-walled carbon nanotubes in rat: Comparison between intratracheal instillation and inhalation exposure

Multi-walled carbon nanotubes (MWCNTs), which vary in length, diameter, functionalization and specific surface area, are used in diverse industrial processes. Since these nanomaterials have a high aspect ratio and are biopersistant in the lung, there is a need for a rapid identification of their potential health hazard. We assessed in Sprague-Dawley rats the pulmonary toxicity of two pristine MWCNTs (the "long and thick" NM-401 and the "short and thin" NM-403) following either intratracheal instillation or 4-week inhalation in order to gain insights into the predictability and intercomparability of the two methods. The deposited doses following inhalation were lower than the instilled doses. Both types of carbon nanotube induced pulmonary neutrophil influx using both exposure methods. This influx correlated with deposited surface area across MWCNT types and means of exposure at two different time points, 1-3 days and 28-30 days post-exposure. Increased levels of DNA damage were observed across doses and time points for both exposure methods, but no dose-response relationship was observed. Intratracheal instillation of NM-401 induced fibrosis at the highest dose while lower lung deposited doses obtained by inhalation did not induce such lung pathology. No fibrosis was observed following NM-403 exposure. When the deposited dose was taken into account, sub-acute inhalation and a single instillation of NM-401 and NM-403 produced very similar inflammation and DNA damage responses. Our data suggest that the dose-dependent inflammatory responses observed after intratracheal instillation and inhalation of MWCNTs are similar and were predicted by the deposited surface area.

DNA repair as a human biomonitoring tool: Comet assay approaches

The comet assay offers the opportunity to measure both DNA damage and repair. Various comet assay based methods are available to measure DNA repair activity, but some requirements should be met for their effective use in human biomonitoring studies. These conditions include i) robustness of the assay, ii) sources of inter- and intra-individual variability must be known, iii) DNA repair kinetics should be assessed to optimize sampling timing; and iv) DNA repair in accessible surrogate tissues should reflect repair activity in target tissues prone to carcinogenic effects. DNA repair phenotyping can be performed on frozen and fresh samples, and is a more direct measurement than genomic or transcriptomic approaches. There are mixed reports concerning the regulation of DNA repair by environmental and dietary factors. In general, exposure to genotoxic agents did not change base excision repair (BER) activity, whereas some studies reported that dietary interventions affected BER activity. On the other hand, in vitro and in vivo studies indicated that nucleotide excision repair (NER) can be altered by exposure to genotoxic agents, but studies on other life style related factors, such as diet, are rare. Thus, crucial questions concerning the factors regulating DNA repair and inter-individual variation remain unanswered. Intra-individual variation over a period of days to weeks seems limited, which is favourable for DNA repair phenotyping in biomonitoring studies. Despite this reported low intra-individual variation, timing of sampling remains an issue that needs further investigation. A correlation was reported between the repair activity in easily accessible peripheral blood mononuclear cells (PBMCs) and internal organs for both NER and BER. However, no correlation was found between tumour tissue and blood cells. In conclusion, although comet assay based approaches to measure BER/NER phenotypes are feasible and promising, more work is needed to further optimize their application in human biomonitoring and intervention studies.

The comet assay: ready for 30 more years

During the last 30 years, the comet assay has become widely used for the measurement of DNA damage and repair in cells and tissues. A landmark achievement was reached in 2016 when the Organization for Economic Co-operation and Development adopted a comet assay guideline for in vivo testing of DNA strand breaks in animals. However, the comet assay has much more to offer than being an assay for testing DNA strand breaks in animal organs. The use of repair enzymes increases the range of DNA lesions that can be detected with the assay. It can also be modified to measure DNA repair activity. Still, despite the long-term use of the assay, there is a need for studies that assess the impact of variation in specific steps of the procedure. This is particularly important for the on-going efforts to decrease the variation between experiments and laboratories. The articles in this Special Issue of Mutagenesis cover important technical issues of the comet assay procedure, nanogenotoxicity and ionising radiation sensitivity on plant cells. The included biomonitoring studies have assessed seasonal variation and certain predictors for the basal level of DNA damage in white blood cells. Lastly, the comet assay has been used in studies on genotoxicity of environmental and occupational exposures in human biomonitoring studies and animal models. Overall, the articles in this Special Issue demonstrate the versatility of the comet assay and they hold promise that the assay is ready for the next 30 years.

Establishment of an in vivo simulating co-culture assay platform for genotoxicity of multi-walled carbon nanotubes

Engineered nanomaterials (ENM) are now used in a wide variety of fields, and, thus, their safety should urgently be assessed and secured. It has been suggested that inflammatory responses via the phagocytosis of ENM by macrophages is a key mechanism for their genotoxicity. The present study was conducted to establish a mechanism‐based assay to evaluate the genotoxicity of ENM under conditions simulating an in vivo situation, featuring a co‐culture system of murine lung resident cells (GDL1) and immune cells (RAW264.7). GDL1 were cultured with or without RAW264.7, exposed to a multi‐walled carbon nanotube (MWCNT), and then analyzed for mutagenicity and underlying mechanisms. Mutation frequencies induced in GDL1 by the MWCNT were significantly greater with the co‐existence of RAW264.7 than in its absence. Mutation spectra observed in GDL1 co‐cultured with RAW264.7 were different from those seen in GDL1 cultured alone, but similar to those observed in the lungs of mice exposed to the MWCNT in vivo. Inflammatory cytokines, such as IL‐1β and TNF‐α, were produced from RAW264.7 cells treated with the MWCNT. The generation of reactive oxygen species and the formation of 8‐oxodeoxyguanosine in GDL1 exposed to the MWCNT were greater in the co‐culture conditions than in the single culture conditions. Based on these findings, it is indicated that inflammatory responses are involved in the genotoxicity of MWCNT, and that the presently established, novel in vitro assay featuring a co‐culture system of tissue resident cells with immune cells is suitable to evaluate the genotoxicity of ENM.

Silica inhalation altered telomere length and gene expression of telomere regulatory proteins in lung tissue of rats

Exposure to silica can cause lung fibrosis and cancer. Identification of molecular targets is important for the intervention and/or prevention of silica-induced lung diseases. Telomeres consist of tandem repeats of DNA sequences at the end of chromosomes, preventing chromosomal fusion and degradation. Regulator of telomere length-1 (RTEL1) and telomerase reverse transcriptase (TERT), genes involved in telomere regulation and function, play important roles in maintaining telomere integrity and length. The goal of this study was to assess the effect of silica inhalation on telomere length and the regulation of RTEL1 and TERT. Lung tissues and blood samples were collected from rats at 4, 32, and 44 wk after exposure to 15 mg/m3 of silica × 6 h/d × 5 d. Controls were exposed to air. At all-time points, RTEL1 expression was significantly decreased in lung tissue of the silica-exposed animals compared to controls. Also, significant increases in telomere length and TERT were observed in the silica group at 4 and 32 wk. Telomere length, RTEL1 and TERT expression may serve as potential biomarkers related to silica exposure and may offer insight into the molecular mechanism of silica-induced lung disease and tumorigeneses.

Effects of multi-walled carbon nanotubes with various diameters on bacterial cellular membranes: Cytotoxicity and adaptive mechanisms

The effect of multi-walled carbon nanotubes (MWNTs) with different diameters on the destruction degree toward cellular membranes of bacterial has been explored by investigating the viability of bacteria and the change of composition and surface properties in cellular membranes with the exposure of MWNTs. The atrazine degrading bacteria Acinetobacter lwoffii DNS32 (DNS32) is chosen as the model species and Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) are selected as the comparison specie. Bacterial viability testing shows that MWNTs with smaller diameters generally display stronger toxicity to bacteria and also influenced by many factors including the electrostatic repulsion between MWNTs and bacteria and bacteria types. Interestingly, bacteria can self-regulate as an adaptive response to the toxicity of MWNTs, notably, DNS32 strain presents the adaptive responses when cultivated with MWNT_60-100 through modification of fatty acids in cell membranes, but does not exhibit similar responses when exposed to MWNT_10-20. This result may be related to the interference from MWNT_10-20, which exceeds the cellular ability to self-repair. Transmission electron microscopy (TEM) images and flow cytometric analysis of bacteria exposed to MWNTs reveal that the destruction of cell membrane in the DNS32 strain is more serious than that in the B. subtilis, indicating that electrostatic repulsion between the material and bacteria leading to the decrease of direct contact may be the primary factor that reduces the impacts from MWNTs.

NanoGenotoxicology: present and the future

This Mutagenesis special issue is on the topic of nanogenotoxicology. It unites a collection of reports that provide insight into: (i) the properties of engineered nanomaterials (ENMs) that contribute to genotoxicity, (ii) the genotoxic mechanisms associated with DNA damage observed in both in vitro and in vivo tests and (iii) the future test systems that will provide more accurate prediction of ENM genotoxicity to support regulatory hazard assessment frameworks. The contributions within therefore provide collective oversight of our current understanding, coupled to future perspectives aimed at overcoming technical hurdles and describing novel analytical methods to further advance the field.