Carbon Nanotube- and Asbestos-Induced DNA and RNA Methylation Changes in Bronchial Epithelial Cells

Roles of reactive oxygen species in inflammation and cancer

Reactive oxygen species (ROS) constitute a spectrum of oxygenic metabolites crucial in modulating pathological organism functions. Disruptions in ROS equilibrium span various diseases, and current insights suggest a dual role for ROS in tumorigenesis and the immune response within cancer. This review rigorously examines ROS production and its role in normal cells, elucidating the subsequent regulatory network in inflammation and cancer. Comprehensive synthesis details the documented impacts of ROS on diverse immune cells. Exploring the intricate relationship between ROS and cancer immunity, we highlight its influence on existing immunotherapies, including immune checkpoint blockade, chimeric antigen receptors, and cancer vaccines. Additionally, we underscore the promising prospects of utilizing ROS and targeting ROS modulators as novel immunotherapeutic interventions for cancer. This review discusses the complex interplay between ROS, inflammation, and tumorigenesis, emphasizing the multifaceted functions of ROS in both physiological and pathological conditions. It also underscores the potential implications of ROS in cancer immunotherapy and suggests future research directions, including the development of targeted therapies and precision oncology approaches. In summary, this review emphasizes the significance of understanding ROS-mediated mechanisms for advancing cancer therapy and developing personalized treatments.

Epigenetic regulation of pulmonary inflammation

Pulmonary disease such as chronic obstructive pulmonary disease (COPD), asthma, pulmonary fibrosis and pulmonary hypertension are the leading cause of deaths. More importantly, lung diseases are on the rise and environmental factors induced epigenetic modifications are major players on this increased prevalence. It has been reported that dysregulation of genes involved in epigenetic regulation such as the histone deacetylase (HDACs) and histone acetyltransferase (HATs) play important role in lung health and pulmonary disease pathogenesis. Inflammation is an essential component of respiratory diseases. Injury and inflammation trigger release of extracellular vesicles that can act as epigenetic modifiers through transfer of epigenetic regulators such as microRNAs (miRNAs), long non-coding RNAs (lncRNAs), proteins and lipids, from one cell to another. The immune dysregulations caused by the cargo contents are important contributors of respiratory disease pathogenesis. N6 methylation of RNA is also emerging to be a critical mechanism of epigenetic alteration and upregulation of immune responses to environmental stressors. Epigenetic changes such as DNA methylation are stable and often long term and cause onset of chronic lung conditions. These epigenetic pathways are also being utilized for therapeutic intervention in several lung conditions.

Malignant peritoneal mesotheliomas of rats induced by multiwalled carbon nanotubes and amosite asbestos: transcriptome and epigenetic profiles

BACKGROUND

Malignant mesothelioma is an aggressive cancer that often originates in the pleural and peritoneal mesothelium. Exposure to asbestos is a frequent cause. However, studies in rodents have shown that certain multiwalled carbon nanotubes (MWCNTs) can also induce malignant mesothelioma. The exact mechanisms are still unclear. To gain further insights into molecular pathways leading to carcinogenesis, we analyzed tumors in Wistar rats induced by intraperitoneal application of MWCNTs and amosite asbestos. Using transcriptomic and epigenetic approaches, we compared the tumors by inducer (MWCNTs or amosite asbestos) or by tumor type (sarcomatoid, epithelioid, or biphasic).

RESULTS

Genome-wide transcriptome datasets, whether grouped by inducer or tumor type, showed a high number of significant differentially expressed genes (DEGs) relative to control peritoneal tissues. Bioinformatic evaluations using Ingenuity Pathway Analysis (IPA) revealed that while the transcriptome datasets shared commonalities, they also showed differences in DEGs, regulated canonical pathways, and affected molecular functions. In all datasets, among highly- scoring predicted canonical pathways were Phagosome Formation, IL8 Signaling, Integrin Signaling, RAC Signaling, and TREM1 Signaling. Top-scoring activated molecular functions included cell movement, invasion of cells, migration of cells, cell transformation, and metastasis. Notably, we found many genes associated with malignant mesothelioma in humans, which showed similar expression changes in the rat tumor transcriptome datasets. Furthermore, RT-qPCR revealed downregulation of Hrasls, Nr4a1, Fgfr4, and Ret or upregulation of Rnd3 and Gadd45b in all or most of the 36 tumors analyzed. Bisulfite sequencing of Hrasls, Nr4a1, Fgfr4, and Ret revealed heterogeneity in DNA methylation of promoter regions. However, higher methylation percentages were observed in some tumors compared to control tissues. Lastly, global 5mC DNA, m6A RNA and 5mC RNA methylation levels were also higher in tumors than in control tissues.

CONCLUSIONS

Our findings may help better understand how exposure to MWCNTs can lead to carcinogenesis. This information is valuable for risk assessment and in the development of safe-by-design strategies.

Hypermethylation and low expression of FANCC involved in multi-walled carbon nanotube-induced toxicity on ARPE-19 cells

Multi-walled carbon nanotube (MWCNT) exposure was observed to cause damages on the viability of ocular cells, however, the underlying mechanisms remain not well understood. Epigenetic alterations that regulate gene expression have been identified as a major responsiveness to environmental challenge. Thus, the aim of this study was to screen methylation-regulated genes involved in MWCNT exposure. The Illumina Human Methylation 850 K array was employed to determine the genome-wide DNA methylation profile of human retinal pigment epithelial cell line (ARPE-19) exposed to 50% inhibition concentration of MWCNTs (100 μg/ml) for 24 h or without (n = 3 for each group). Then, the transcriptome data obtained by high-throughput RNA sequencing previously were integrated with DNA methylome to identify the overlapped genes. As a result, the integrative bioinformatics analysis identified that compared with controls, FA complementation group C (FANCC) was hypermethylated and downregulated in MWCNT-exposed ARPE-19 cells. Quantitative real-time polymerase chain reaction analysis confirmed the mRNA expression level of FANCC was significantly decreased following MWCNT treatment and the addition of DNA methylation inhibitor 5-Aza-deoxycytidine (10 μM) reversed this decrease. Pyrosequencing analysis further validated the hypermethylation status at the 5'-untranslated promoter region of FANCC (cg14583550) in MWCNT-exposed ARPE-19 cells. Protein-protein interaction network and function analyses predicted that FANCC may contribute to MWCNT-induced cytotoxicity by interacting with heat shock protein 90 beta family member 1 and then upregulating cytokine interleukin-6 and apoptosis biomarker caspase 3. In conclusion, the present study links the epigenetic modification of FANCC with the pathogenesis of MWCNT-induced retinal toxicity.

METTL3-mediated m6A mRNA modification was involved in cadmium-induced liver injury

Cadmium is an environmental pollutant that has extensive deleterious effects. However, the mechanisms underlying the hepatotoxicity induced by long-term exposure to cadmium remained undefined. In the present study, we explored the role of m6A methylation in the development of cadmium-induced liver disease. We showed a dynamic change of RNA methylation in liver tissue from mice administrated with cadmium chloride (CdCl2) for 3, 6 and 9 months, respectively. Particularly, the METTL3 expression was declined in a time-dependent manner, associated with the degree of liver injury, indicating the involvement of METTL3 in hepatotoxicity induced by CdCl2. Moreover, we established a mouse model with liver-specific over-expression of Mettl3 and administrated these mice with CdCl2 for 6 months. Notably, METTL3 highly expressed in hepatocytes attenuated CdCl2-induced steatosis and liver fibrosis in mice. In vitro assay also showed METTL3 overexpression ameliorated the CdCl2-induced cytotoxicity and activation of primary hepatic stellate cells. Furthermore, transcriptome analysis identified 268 differentially expressed genes both in mice liver tissue treated with CdCl2 for 3 months and 9 months. Among them, 115 genes were predicted to be regulated by METTL3 determined by m6A2Target database. Further analysis revealed the perturbation of metabolic pathway, glycerophospholipid metabolism, ErbB signaling pathway, Hippo signaling pathway, and choline metabolism in cancer, and circadian rhythm, led to hepatotoxicity induced by CdCl2. Collectively, our findings reveal new insight into the crucial role of epigenetic modifications in hepatic diseases caused by long-term exposure to cadmium.

Role of RNA modifications in carcinogenesis and carcinogen damage response

The field of epitranscriptomics encompasses the study of post-transcriptional RNA modifications and their regulatory enzymes. Among the numerous RNA modifications, N6 -methyladenosine (m6 A) has been identified as the most common internal modification of messenger RNA (mRNA). Although m6 A modifications were first discovered in the 1970s, advances in technology have revived interest in this field, driving an abundance of research into the role of RNA modifications in various biological processes, including cancer. As analogs to epigenetic modifications, RNA modifications also play an important role in carcinogenesis by regulating gene expression post-transcriptionally. A growing body of evidence suggests that carcinogens can modulate RNA modifications to alter the expression of oncogenes or tumor suppressors during cellular transformation. Additionally, the expression and activity of the enzymes that regulate RNA modifications can be dysregulated and contribute to carcinogenesis, making these enzymes promising targets of drug discovery. Here we summarize the roles of RNA modifications during carcinogenesis induced by exposure to various environmental carcinogens, with a main focus on the roles of the most widely studied m6 A mRNA methylation.

A review on the epigenetics modifications to nanomaterials in humans and animals: novel epigenetic regulator

In the nanotechnology era, nanotechnology applications have been intensifying their prospects to embrace all the vigorous sectors persuading human health and animal. The safety and concerns regarding the widespread use of engineered nanomaterials (NMA) and their potential effect on human health still require further clarification. Literature elucidated that NMA exhibited significant adverse effects on various molecular and cellular alterations. Epigenetics is a complex process resulting in the interactions between an organism’s environment and genome. The epigenetic modifications, including histone modification and DNA methylation, chromatin structure and DNA accessibility alteration, regulate gene expression patterns. Disturbances of epigenetic markers induced by NMA might promote the sensitivity of humans and animals to several diseases. Also, this paper focus on the epigenetic regulators of some dietary nutrients that have been confirmed to stimulate the epigenome and, more exactly, DNA histone modifications and non-histone proteins modulation by acetylation, and phosphorylation inhibition, which counteracts oxidative stress generations. The present review epitomizes the recent evidence of the potential effects of NMA on histone modifications, in addition to in vivo and in vitro cytosine DNA methylation and its toxicity. Furthermore, the part of epigenetic fluctuations as possible translational biomarkers for uncovering untoward properties of NMA is deliberated.

The critical role of epigenetic mechanisms involved in nanotoxicology

Over the past decades, nanomaterials (NMs) have been widely applied in the cosmetic, food, engineering, and medical fields. Along with the prevalence of NMs, the toxicological characteristics exhibited by these materials on health and the environment have gradually attracted attentions. A growing number of evidences have indicated that epigenetics holds an essential role in the onset and development of various diseases. NMs could cause epigenetic alterations such as DNA methylation, noncoding RNA (ncRNA) expression, and histone modifications. NMs might alternate either global DNA methylation or the methylation of specific genes to affect the biological function. Abnormal upregulation or downregulation of ncRNAs might also be a potential mechanism for the toxic effects caused by NMs. In parallel, the phosphorylation, acetylation, and methylation of histones also take an important part in the process of NMs-induced toxicity. As the adverse effects of NMs continue to be explored, mechanisms such as chromosomal remodeling, genomic imprinting, and m⁶ A modification are also gradually coming into the limelight. Since the epigenetic alterations often occur in the early development of diseases, thus the relevant studies not only provide insight into the pathogenesis of diseases, but also screen for the prospective biomarkers for early diagnosis and prevention. This review summarizes the epigenetic alterations elicited by NMs, hoping to provide a clue for nanotoxicity studies and security evaluation of NMs. This article is categorized under: Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials.

Cancer Targeting and Diagnosis: Recent Trends with Carbon Nanotubes

Cancer belongs to a category of disorders characterized by uncontrolled cell development with the potential to invade other bodily organs, resulting in an estimated 10 million deaths globally in 2020. With advancements in nanotechnology-based systems, biomedical applications of nanomaterials are attracting increasing interest as prospective vehicles for targeted cancer therapy and enhancing treatment results. In this context, carbon nanotubes (CNTs) have recently garnered a great deal of interest in the field of cancer diagnosis and treatment due to various factors such as biocompatibility, thermodynamic properties, and varied functionalization. In the present review, we will discuss recent advancements regarding CNT contributions to cancer diagnosis and therapy. Various sensing strategies like electrochemical, colorimetric, plasmonic, and immunosensing are discussed in detail. In the next section, therapy techniques like photothermal therapy, photodynamic therapy, drug targeting, gene therapy, and immunotherapy are also explained in-depth. The toxicological aspect of CNTs for biomedical application will also be discussed in order to ensure the safe real-life and clinical use of CNTs.

Reactive Oxygen Species Bridge the Gap between Chronic Inflammation and Tumor Development

According to numerous animal studies, adverse environmental stimuli, including physical, chemical, and biological factors, can cause low-grade chronic inflammation and subsequent tumor development. Human epidemiological evidence has confirmed the close relationship between chronic inflammation and tumorigenesis. However, the mechanisms driving the development of persistent inflammation toward tumorigenesis remain unclear. In this study, we assess the potential role of reactive oxygen species (ROS) and associated mechanisms in modulating inflammation-induced tumorigenesis. Recent reports have emphasized the cross-talk between oxidative stress and inflammation in many pathological processes. Exposure to carcinogenic environmental hazards may lead to oxidative damage, which further stimulates the infiltration of various types of inflammatory cells. In turn, increased cytokine and chemokine release from inflammatory cells promotes ROS production in chronic lesions, even in the absence of hazardous stimuli. Moreover, ROS not only cause DNA damage but also participate in cell proliferation, differentiation, and apoptosis by modulating several transcription factors and signaling pathways. We summarize how changes in the redox state can trigger the development of chronic inflammatory lesions into tumors. Generally, cancer cells require an appropriate inflammatory microenvironment to support their growth, spread, and metastasis, and ROS may provide the necessary catalyst for inflammation-driven cancer. In conclusion, ROS bridge the gap between chronic inflammation and tumor development; therefore, targeting ROS and inflammation represents a new avenue for the prevention and treatment of cancer.

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.

Properties and applications of boron nitride nanotubes

Nanomaterials have received increasing attention due to their controllable physical and chemical properties and their improved performance over their bulk structures during the last years. Carbon nanostructures are one of the most widely searched materials for use in different applications ranging from electronic to biomedical because of their exceptional physical and chemical properties. However, BN nanostructures surpassed the attention of the carbon-based nanostructure because of their enhanced thermal and chemical stabilities in addition to structural similarity with the carbon nanomaterials. Among these nanostructures, one dimensional-BN nanostructures are on the verge of development as new materials to fulfill some necessities for different application areas based on their excellent and unique properties including their tunable surface and bandgap, electronic, optical, mechanical, thermal, and chemical stability. Synthesis of high-quality boron nitride nanotubes (BNNTs) in large quantities with novel techniques provided greater access, and increased their potential use in nanocomposites, biomedical fields, and nanodevices as well as hydrogen uptake applications. In this review, properties and applications of one-dimensional BN (1D) nanotubes, nanofibers, and nanorods in hydrogen uptake, biomedical field, and nanodevices are discussed in depth. Additionally, research on native and modified forms of BNNTs and also their composites with different materials to further improve electronic, optical, structural, mechanical, chemical, and biological properties are also reviewed. BNNTs find many applications in different areas, however, they still need to be further studied for improving the synthesis methods and finding new possible future applications.

Assessment of the Carcinogenicity of Carbon Nanotubes in the Respiratory System

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

Carbon Nanotubes: Probabilistic Approach for Occupational Risk Assessment

In this study, the occupational risk assessment of carbon nanotubes (CNTs) was performed by means of a probabilistic approach. Chronic and subchronic inhalation exposure studies were retrieved during the hazard identification phase of the study. These studies were then used to obtain a guidance value (BMC_h, expressed as a lognormal distribution with geometric mean ± geometric standard deviation = 10.0 ± 4.2 µg/m³) for occupational inhalation exposure to CNTs. An exposure scenario was selected from the scientific literature: three different work events (WEs) related to the production of conductive films were considered: (WE1) manufacturing of single walled carbon nanotubes films during normal operation using local exhaust ventilation (LEV); (WE2) manufacturing of SWCNT film without LEV; and (WE3) cleaning of one of the reactors. For each WE, a probability distribution function was applied, considering exposure expressed as mass concentration, as derived from three different measurement techniques. The ratio of the exposure and the BMC_h distributions (i.e., the risk characterization ratio-RCR) was used to calculate the probability of occurrence of a relevant occupational risk. All the considered WEs indicated the presence of a risk (i.e., RCR distributions ≥ 1); however, only WE2 resulted in a statistically significant level of risk.

Epigenetic Effects of Nanomaterials and Nanoparticles

The rise of nanotechnology and widespread use of engineered nanomaterials in everyday human life has led to concerns regarding their potential effect on human health. Adverse effects of nanomaterials and nanoparticles on various molecular and cellular alterations have been well-studied. In contrast, the role of epigenetic alterations in their toxicity remains relatively unexplored. This review summarizes current evidence of alterations in cytosine DNA methylation and histone modifications in response to nanomaterials and nanoparticles exposures in vivo and in vitro. This review also highlights existing knowledge gaps regarding the role of epigenetic alterations in nanomaterials and nanoparticles toxicity. Additionally, the role of epigenetic changes as potential translational biomarkers for detecting adverse effects of nanomaterials and nanoparticles is discussed.

Identification of four methylation-driven genes as candidate biomarkers for monitoring single-walled carbon nanotube-induced malignant transformation of the lung

Long-term exposure to carbon nanotubes (CNTs) has been reported to induce malignant transformation. This study aimed to screen candidate biomarkers for monitoring occupational workers to prevent the development of lung cancer. mRNA (GSE56104) and methylation (GSE153246) profiles of lung epithelial BEAS-2B cells exposed to malignant transformation dose of single-walled CNTs or control medium were downloaded from Gene Expression Omnibus database. A total of 1513 differentially expressed genes (DEGs) and 912 differentially methylated genes (DMGs) were identified using LIMMA method. The weighted correlation network analysis identified blue and turquoise modules were associated with malignant transformation of BEAS-2B cells, 124 DMGs of which were overlapped with DEGs. The mRNA and methylation levels of four methylation-driven DEGs were validated in both lung adenocarcinoma (LUAD) and squamous cell carcinomas (LUSC) of The Cancer Genome Atlas dataset and they were associated with overall survival of LUAD patients. Downregulation of PXMP4 and MCOLN2, while upregulation of MET was confirmed in both LUSC and LUAD via Human Protein Atlas analysis. PXMP4 and MET protein levels were also supported in the proteomic analysis of LUAD. Receiver operating characteristic (ROC) curve analysis showed the combination of four genes may be the optimal biomarker for predicting lung cancer, with the area under ROC curve >0.9. Function analysis revealed BARX2 may interact with CCND1 to regulate cell cycle; MET and PXMP4/MCOLN2 may positively correlate with CCR5/IL-6 or GATA3/HLA-DPB1/HLA-DPA1 to involve immune regulation. In conclusion, these four methylation-driven genes may be candidate prognostic and diagnostic biomarkers for single-walled CNT-related lung cancer.

Engineered nanoparticle-induced epigenetic changes: An important consideration in nanomedicine

Engineered nanoparticles (ENPs) are now being applied across a range of disciplines, and as a result numerous studies have now assessed ENP-related bioeffects. Among them, ENP-induced epigenetic changes including DNA methylation, histone modifications, and miRNA-mediated regulation of gene expression have recently attracted attention. In this review, we describe the diversity of ENP-induced epigenetic changes, focusing on their interplay with related functional biological events, especially oxidative stress, MAPK pathway activation, and inflammation. In doing so, we highlight the underlying mechanisms and biological effects of ENP-induced epigenetic changes. We also summarize how high-throughput technologies have helped to uncover ENP-induced epigenetic changes. Finally, we discuss future perspectives and the challenges related to ENP-induced epigenetic changes that still need to be addressed.

Health and Safety Concerns Related to CNT and Graphene Products, and Related Composites

The use of Carbon Nanotubes (CNT) and Graphene increased in the last decade and it is likely to keep increasing in the near future. The attractiveness of their properties, particularly the possibility to enhance the composites performance using a tailor made methodology, brings new materials, processes and products for highly demanding industrial applications and to the market. However, there are quite a lot of health/safety issues, as well as lack of understanding and standards to evaluate their effects. This paper starts with a general description of materials, processes and products dealing with CNT and graphene. Then, an overview of concerns related to the health and safety when handling, researching, producing and using products that include these materials is presented. It follows a risk management approach with respect to simulation and evaluation tools, and considering the consensual limits already existing for research, industry and consumers. A general discussion integrating the relevant aspects of health and safety with respect to CNT and graphene is also presented. A proactive view is presented with the intention to contribute with some guidelines on installation, maintenance, evaluation, personal protection equipment (PPE) and personnel training to deal with these carbon-based nanomaterials in research, manufacture, and use with composite materials.

Carbon Nanotubes under Scrutiny: Their Toxicity and Utility in Mesothelioma Research

Research on the toxicity of engineered carbon nanotubes (CNT) was initiated by Belgian academic chemists and toxicologists more than 15 years ago. It is now undisputed that some of these attractive nanomaterials induce serious illness such as fibrosis and cancer. The physico-chemical determinants of CNT-induced adverse effects are now elucidated and include shape, nanoscale diameter, and structural defects. Generated in vitro and in vivo data on their inflammogenic and fibrogenic activities were combined and translated in AOP (adverse outcome pathways) available for risk assessment and regulatory policies. The asbestos-like carcinogenic effect of CNT, notably their capacity to induce malignant mesothelioma (MM), remain, however, a cause of concern for public health and strongly curb the craze for CNT in industries. MM still represents a real challenge for clinicians and a highly refractory cancer to existing therapeutic strategies. By comparing mesotheliomagenic CNT (needle-like CNT-N) to non mesotheliomagenic CNT (tangled-like CNT-T), our group generated a relevant animal model that highlights immune pathways specifically associated to the carcinogenic process. Evidence indicates that only CNT-N possess the intrinsic capacity to induce a preferential, rapid, and sustained accumulation of host immunosuppressive cells that subvert immune surveillance and suppress anti-mesothelioma immunity. This new concept offers novel horizons for the clinical management of mesothelioma and represents an additional tool for predicting the mesotheliomagenic activity of newly elaborated CNT or nanoparticles.

Effect of titanium dioxide nanoparticles on DNA methylation in multiple human cell lines

Nanoscale titanium dioxide (TiO2) is manufactured in wide scale, with a range of applications in consumer products. Significant toxicity of TiO2 nanoparticles has, however, been recognized, suggesting considerable risk to human health. To evaluate fully their toxicity, assessment of the epigenetic action of these nanoparticles is critical. However, only few studies are available examining capability of nanoparticles to alter epigenetic integrity. In the present study, the effect of TiO2 nanoparticles exposure on DNA methylation, a major epigenetic mechanism, was investigated in in vitro cellular model systems. A panel of cells relevant to portals of human exposure (Caco-2 (colorectal), HepG2 (liver), NL20 (lung), and A-431 (skin)) was exposed to TiO2 nanoparticles to assess effects on global methylation, gene-specific methylation, and expression levels of DNA methyltransferases, MBD2, and UHRF1. Global methylation was determined by enzyme-linked immunosorbent assay-based immunochemical analysis. Degree of promoter methylation across a defined panel of genes was evaluated using EpiTect Methyl II Signature PCR System Array technology. Expression of DNMT1, DNMT3a, DNMT3b, MBD2, and URHF1 was quantified by qRT-PCR. Decrease in global DNA methylation in cell lines Caco-2, HepG2, and A-431 exposed to TiO2 nanoparticles was shown. Across four cell lines, eight genes (CDKN1A, DNAJC15, GADD45A, GDF15, INSIG1, SCARA3, TP53, and BNIP3) were identified in which promotors were methylated after exposure. Altered expression of these genes is associated with disease etiology. The results also revealed aberrant expression of epigenetic regulatory genes involved in DNA methylation (DNMT1, DNMT3a, DNMT3b, MBD2, and UHRF1) in TiO2 exposed cells, which was cell type dependent. Findings from this study clearly demonstrate the impact of TiO2 nanoparticles exposure on DNA methylation in multiple cell types, supporting potential involvement of this epigenetic mechanism in the toxicity of TiO2 nanoparticles. Hence for complete assessment of potential risk from nanoparticle exposure, epigenetic studies are critical.

Distinct autophagy-apoptosis related pathways activated by Multi-walled (NM 400) and Single-walled carbon nanotubes (NIST-SRM2483) in human bronchial epithelial (16HBE14o-) cells

Given the recent development in the field of particle and fibre toxicology, parallels have been drawn between Carbon nanotubes (CNTs) and asbestos. It is now established that both multi-walled (MWCNTs) and single-walled (SWCNTs) carbon nanotubes might contribute to pulmonary disease. Although multiple mechanisms might be involved in CNT induced pathogenesis, systematic understanding of the relationship between different CNT exposure (MWCNT vs SWCNT) and autophagy/ apoptosis/ necrosis, in human lung epithelial cells remains limited. In this study, we demonstrate that exposure to MWCNT (NM-400), but not SWCNT (NIST-SRM2483), leads to an autophagic response after acute exposure (24 h). MWCNT exposure was characterized by an increase in anti-apoptotic BCL2, downregulation of executor Caspase-3/7 and increase in expression of genes from the autophagy machinery. For SWCNT exposure however, we observed an overexpression of executor Caspase-3/7 and upregulation of pro-apoptotic BAX; enrichment for processes like cornification, apoptotic process, cell differentiation from proteomic analysis. These results clearly indicate a major difference in the pathways initiated by the CNTs, in vitro. While the present study design provides mechanistic understanding after an acute exposure for the tested CNTs, we believe that the information obtained here would have relevance in better understanding of CNT toxicity and pathogenesis in general.

Induction and recovery of CpG site specific methylation changes in human bronchial cells after long-term exposure to carbon nanotubes and asbestos

INTRODUCTION

Inhalation of asbestos induces lung cancer via different cellular mechanisms. Together with the increased production of carbon nanotubes (CNTs) grows the concern about adverse effects on the lungs given the similarities with asbestos. While it has been established that CNT and asbestos induce epigenetic alterations, it is currently not known whether alterations at epigenetic level remain stable after withdrawal of the exposure. Identification of DNA methylation changes after a low dose of CNT and asbestos exposure and recovery can be useful to determine the fibre/particle toxicity and adverse outcome.

METHODS

Human bronchial epithelial cells (16HBE) were treated with a low and non-cytotoxic dose (0.25 µg/ml) of multi-walled carbon nanotubes (MWCNTs-NM400) or single-walled carbon nanotubes (SWCNTs-SRM2483) and 0.05 µg/ml amosite (brown) asbestos for the course of four weeks (sub-chronic exposure). After this treatment, the cells were further incubated (without particle/fibre) for two weeks, allowing recovery from the exposure (recovery period). Nuclear depositions of the CNTs were assessed using femtosecond pulsed laser microscopy in a label-free manner. DNA methylation alterations were analysed using microarrays that assess more than 850 thousand CpG sites in the whole genome.

RESULTS

At non-cytotoxic doses, CNTs were noted to be incorporated with in the nucleus after a four weeks period. Exposure to MWCNTs induced a single hypomethylation at a CpG site and gene promoter region. No change in DNA methylation was observed after the recovery period for MWCNTs. Exposure to SWCNTs or amosite induced hypermethylation at CpG sites after sub-chronic exposure which may involve in 'transcription factor activity' and 'sequence-specific DNA binding' gene ontologies. After the recovery period, hypermethylation and hypomethylation were noted for both SWCNTs and amosite. Hippocalcinlike 1 (HPCAL1), protease serine 3 (PRSS3), kallikrein-related peptidase 3 (KLK3), kruppel like factor 3 (KLF3) genes were hypermethylated at different time points in either SWCNT-exposed or amosite-exposed cells.

CONCLUSION

These results suggest that the specific SWCNT (SRM2483) and amosite fibres studied induce hypo- or hypermethylation on CpG sites in DNA after very low-dose exposure and recovery period. This effect was not seen for the studied MWCNT (NM400).

Toxicity of Carbon Nanotubes as Anti-Tumor Drug Carriers

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