Amplified and distinctive genotoxicity of titanium dioxide nanoparticles in transformed yeast reporters with human cytochrome P450 (CYP) genes

Titanium dioxide nanoparticles (nTiO2) have been considered a possible carcinogen to humans, but most existing studies have overlooked the role of human enzymes in assessing the genotoxicity of nTiO2. Here, a toxicogenomics-based in vitro genotoxicity assay using a GFP-fused yeast reporter library was employed to elucidate the genotoxic potential and mechanisms of nTiO2. Moreover, two new GFP-fused yeast reporter libraries containing either human CYP1A1 or CYP1A2 genes were constructed by transformation to investigate the potential modulation of nTiO2 genotoxicity in the presence of human CYP enzymes. This study found a lack of appreciable nTiO2 genotoxicity as indicated by the yeast reporter library in the absence of CYP expression but a significantly elevated indication of genotoxicity in either CYP1A1- or CYP1A2-expressing yeast. The intracellular reactive oxygen species (ROS) measurement indicated significantly higher ROS in yeast expressing either enzyme. The detected mitochondrial DNA damage suggested mitochondria as one of the target sites for oxidative damage by nTiO2 in the presence of either one of the CYP enzymes. The results thus indicated that the genotoxicity of nTiO2 was enhanced by human CYP1A1 or CYP1A2 enzyme and was associated with elevated oxidative stress, which suggested that the similar mechanisms could occur in human cells.

Systematic review of mechanistic evidence for TiO2 nanoparticle-induced lung carcinogenicity

Nano-sized titanium dioxide particles (TiO2 NPs) are a high-production volume nanomaterial widely used in the paints, cosmetics, food and photovoltaics industry. However, the potential carcinogenic effects of TiO2 NPs in the lung are still unclear despite the vast number of in vitro and in vivo studies investigating TiO2 NPs. Here, we systematically reviewed the existing in vitro and in vivo mechanistic evidence of TiO2 NP lung carcinogenicity using the ten key characteristics of carcinogens for identifying and classifying carcinogens. A total of 346 studies qualified for the quality and reliability assessment, of which 206 were considered good quality. Using a weight-of-evidence approach, these studies provided mainly moderate to high confidence for the biological endpoints regarding genotoxicity, oxidative stress and chronic inflammation. A limited number of studies investigated other endpoints important to carcinogenesis, relating to proliferation and transformation, epigenetic alterations and receptor-mediated effects. In summary, TiO2 NPs might possess the ability to induce chronic inflammation and oxidative stress, but it was challenging to compare the findings in the studies due to the wide variety of TiO2 NPs differing in their physicochemical characteristics, formulation, exposure scenarios/test systems, and experimental protocols. Given the limited number of high-quality and high-reliability studies identified within this review, there is a lack of good enough mechanistic evidence for TiO2 NP lung carcinogenicity. Future toxicology/carcinogenicity research must consider including positive controls, endotoxin testing (where necessary), statistical power analysis, and relevant biological endpoints, to improve the study quality and provide reliable data for evaluating TiO2 NP-induced lung carcinogenicity.

Cytotoxicity prediction of nano metal oxides on different lung cells via Nano-QSAR

In recent years, nanomaterials have found extensive applications across diverse domains owing to their distinctive physical and chemical characteristics. It is of great importance in theoretical and practical terms to carry out the relationship between structural characteristics of nanomaterials and different cytotoxicity and to achieve practical assessment and prediction of cytotoxicity. This study investigated the intrinsic quantitative constitutive relationships between the cytotoxicity of nano-metal oxides on human normal lung epithelial cells and human lung adenocarcinoma cells. We first employed quasi-SMILES-based nanostructural descriptors by selecting the five physicochemical properties that are most closely related to the cytotoxicity of nanometal oxides, then established SMILES-based descriptors that can effectively describe and characterize the molecular structure of nanometal oxides, and then built the corresponding Nano-Quantitative Structure-Activity Relationship (Nano-QSAR) prediction models, finally, combined with the theory of reactive oxygen species (ROS) biotoxicity, to reveal the mechanism of toxicity and differences between the two cell types. The established model can efficiently and accurately predict the properties of targets, reveal the corresponding toxicity mechanisms, and guide the safe design, synthesis, and application of nanometal oxides.

Multigenerational inheritance of breathing deficits following perinatal exposure to titanium dioxide nanoparticles in the offspring of mice

BACKGROUND

The utilization of titanium dioxide nanoparticles (TIO2NPs) has experienced a significant surge in recent decades, and these particles are now commonly found in various everyday consumer products. Due to their small size, TIO2NPs can penetrate biological barriers and elicit adverse interactions with biological tissues. Notably, exposure of pregnant females to TIO2NPs during the perinatal period has been shown to disrupt the growth of offspring. Furthermore, this exposure induces epigenetic modifications in the DNA of newborns, suggesting the possibility of multigenerational effects. Thus, perinatal exposure to TIO2NPs may induce immediate metabolic impairments in neonates, which could be transmitted to subsequent generations in the long term.

RESULTS

In this study, we utilized perinatal exposure of female mice to TIO2NPs through voluntary food intake and observed impaired metabolism in newborn male and female F1 offspring. The exposed newborn mice exhibited reduced body weight gain and a slower breathing rate compared to non-exposed animals. Additionally, a higher proportion of exposed F1 newborns experienced apneas. Similar observations were made when the exposure was limited to the postnatal period, highlighting lactation as a critical period for the adverse effects of TIO2NPs on postnatal metabolism. Importantly, the breathing deficits induced by TIO2NPs were transmitted from F1 females to the subsequent F2 generation. Moreover, re-exposure of adult F1 females to TIO2NPs exacerbated the breathing deficits in newborn F2 males.

CONCLUSIONS

Our findings demonstrate that perinatal exposure to TIO2NPs disrupts postnatal body weight gain and respiration in the offspring, and these deficits are transmissible to future generations.

Perinatal foodborne titanium dioxide exposure-mediated dysbiosis predisposes mice to develop colitis through life

BACKGROUND

Perinatal exposure to titanium dioxide (TiO2), as a foodborne particle, may influence the intestinal barrier function and the susceptibility to develop inflammatory bowel disease (IBD) later in life. Here, we investigate the impact of perinatal foodborne TiO2 exposure on the intestinal mucosal function and the susceptibility to develop IBD-associated colitis. Pregnant and lactating mother mice were exposed to TiO2 until pups weaning and the gut microbiota and intestinal barrier function of their offspring was assessed at day 30 post-birth (weaning) and at adult age (50 days). Epigenetic marks was studied by DNA methylation profile measuring the level of 5-methyl-2'-deoxycytosine (5-Me-dC) in DNA from colic epithelial cells. The susceptibility to develop IBD has been monitored using dextran-sulfate sodium (DSS)-induced colitis model. Germ-free mice were used to define whether microbial transfer influence the mucosal homeostasis and subsequent exacerbation of DSS-induced colitis.

RESULTS

In pregnant and lactating mice, foodborne TiO2 was able to translocate across the host barriers including gut, placenta and mammary gland to reach embryos and pups, respectively. This passage modified the chemical element composition of foetus, and spleen and liver of mothers and their offspring. We showed that perinatal exposure to TiO2 early in life alters the gut microbiota composition, increases the intestinal epithelial permeability and enhances the colonic cytokines and myosin light chain kinase expression. Moreover, perinatal exposure to TiO2 also modifies the abilities of intestinal stem cells to survive, grow and generate a functional epithelium. Maternal TiO2 exposure increases the susceptibility of offspring mice to develop severe DSS-induced colitis later in life. Finally, transfer of TiO2-induced microbiota dysbiosis to pregnant germ-free mice affects the homeostasis of the intestinal mucosal barrier early in life and confers an increased susceptibility to develop colitis in adult offspring.

CONCLUSIONS

Our findings indicate that foodborne TiO2 consumption during the perinatal period has negative long-lasting consequences on the development of the intestinal mucosal barrier toward higher colitis susceptibility. This demonstrates to which extent environmental factors influence the microbial-host interplay and impact the long-term mucosal homeostasis.

Nanomaterial genotoxicity evaluation using the high-throughput p53-binding protein 1 (53BP1) assay

Toxicity evaluation of engineered nanomaterials is challenging due to the ever increasing number of materials and because nanomaterials (NMs) frequently interfere with commonly used assays. Hence, there is a need for robust, high-throughput assays with which to assess their hazard potential. The present study aimed at evaluating the applicability of a genotoxicity assay based on the immunostaining and foci counting of the DNA repair protein 53BP1 (p53-binding protein 1), in a high-throughput format, for NM genotoxicity assessment. For benchmarking purposes, we first applied the assay to a set of eight known genotoxic agents, as well as X-ray irradiation (1 Gy). Then, a panel of NMs and nanobiomaterials (NBMs) was evaluated with respect to their impact on cell viability and genotoxicity, and to their potential to induce reactive oxygen species (ROS) production. The genotoxicity recorded using the 53BP1 assay was confirmed using the micronucleus assay, also scored via automated (high-throughput) microscopy. The 53BP1 assay successfully identified genotoxic compounds on the HCT116 human intestinal cell line. None of the tested NMs showed any genotoxicity using the 53BP1 assay, except the positive control consisting in (CoO)(NiO) NMs, while only TiO2 NMs showed positive outcome in the micronucleus assay. Only Fe3O4 NMs caused significant elevation of ROS, not correlated to DNA damage. Therefore, owing to its adequate predictivity of the genotoxicity of most of the tested benchmark substance and its ease of implementation in a high throughput format, the 53BP1 assay could be proposed as a complementary high-throughput screening genotoxicity assay, in the context of the development of New Approach Methodologies.

The Effect of Nanomaterials on DNA Methylation: A Review

DNA methylation is an epigenetic mechanism that involves the addition of a methyl group to a cytosine residue in CpG dinucleotides, which are particularly abundant in gene promoter regions. Several studies have highlighted the role that modifications of DNA methylation may have on the adverse health effects caused by exposure to environmental toxicants. One group of xenobiotics that is increasingly present in our daily lives are nanomaterials, whose unique physicochemical properties make them interesting for a large number of industrial and biomedical applications. Their widespread use has raised concerns about human exposure, and several toxicological studies have been performed, although the studies focusing on nanomaterials' effect on DNA methylation are still limited. The aim of this review is to investigate the possible impact of nanomaterials on DNA methylation. From the 70 studies found eligible for data analysis, the majority were in vitro, with about half using cell models related to the lungs. Among the in vivo studies, several animal models were used, but most were mice models. Only two studies were performed on human exposed populations. Global DNA methylation analyses was the most frequently applied approach. Although no trend towards hypo- or hyper-methylation could be observed, the importance of this epigenetic mechanism in the molecular response to nanomaterials is evident. Furthermore, methylation analysis of target genes and, particularly, the application of comprehensive DNA methylation analysis techniques, such as genome-wide sequencing, allowed identifying differentially methylated genes after nanomaterial exposure and affected molecular pathways, contributing to the understanding of their possible adverse health effects.

Titanium-Based Nanoarchitectures for Sonodynamic Therapy-Involved Multimodal Treatments

Sonodynamic therapy (SDT) has considerably revolutionized the healthcare sector as a viable noninvasive therapeutic procedure. It employs a combination of low-intensity ultrasound and chemical entities, known as a sonosensitizer, to produce cytotoxic reactive oxygen species (ROS) for cancer and antimicrobial therapies. With nanotechnology, several unique nanoplatforms are introduced as a sonosensitizers, including, titanium-based nanomaterials, thanks to their high biocompatibility, catalytic efficiency, and customizable physicochemical features. Additionally, developing titanium-based sonosensitizers facilitates the integration of SDT with other treatment modalities (for example, chemotherapy, chemodynamic therapy, photodynamic therapy, photothermal therapy, and immunotherapy), hence increasing overall therapeutic results. This review summarizes the most recent developments in cancer therapy and tissue engineering using titanium nanoplatforms mediated SDT. The synthesis strategies and biosafety aspects of Titanium-based nanoplatforms for SDT are also discussed. Finally, various challenges and prospects for its further development and potential clinical translation are highlighted.

Titanium Dioxide Nanoparticles Altered the lncRNA Expression Profile in Human Lung Cells

Respiration is considered to be the main occupational or environmental exposure pathway of titanium dioxide nanoparticles (TiO2 NPs), and the lung is considered to be the target organ of respiratory exposure; however, the mechanism of respiratory toxicity is not fully understood. In this study, the effect of TiO2 NPs on the expression profile of long non-coding RNA (lncRNA) in bronchial epithelial cells (BEAS-2B) was investigated to understand their potential toxic mechanism. BEAS-2B cells were treated with 100 μg/mL TiO2 NPs for 48 h, then RNA sequencing was performed to screen the differential lncRNAs compared with the control group, and the enrichment pathways of the differentially expressed lncRNAs were further analyzed using the Kyoto Encyclopedia of Genes and Genomes (KEGG). The results identified a total of 45,769 lncRNAs, and 277 different lncRNAs were screened. KEGG pathway analysis showed that the targeted mRNAs of these different lncRNAs were enriched in the pyrimidine metabolism pathway. This work demonstrates that TiO2 NPs could alter the lncRNA expression profile in BEAS-2B cells, and epigenetics may play a role in the mechanism of respiratory toxicity induced by TiO2 NPs.

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.

Evaluating the Use of TiO2 Nanoparticles for Toxicity Testing in Pulmonary A549 Cells

Purpose

Titanium dioxide nanoparticles, 25 nm in size of crystallites (TiO₂ P25), are among the most produced nanomaterials worldwide. The broad use of TiO₂ P25 in material science has implied a request to evaluate their biological effects, especially in the lungs. Hence, the pulmonary A549 cell line has been used to estimate the effects of TiO₂ P25. However, the reports have provided dissimilar results on caused toxicity. Surprisingly, the physicochemical factors influencing TiO₂ P25 action in biological models have not been evaluated in most reports. Thus, the objective of the present study is to characterize the preparation of TiO₂ P25 for biological testing in A549 cells and to evaluate their biological effects.

Methods

We determined the size and crystallinity of TiO₂ P25. We used four techniques for TiO₂ P25 dispersion. We estimated the colloid stability of TiO₂ P25 in distilled water, isotonic NaCl solution, and cell culture medium. We applied the optimal dispersion conditions for testing the biological effects of TiO₂ P25 (0–100 µg.mL⁻¹) in A549 cells using biochemical assays (dehydrogenase activity, glutathione levels) and microscopy.

Results

We found that the use of fetal bovine serum in culture medium is essential to maintain sufficient colloid stability of dispersed TiO₂ P25. Under these conditions, TiO₂ P25 were unable to induce a significant impairment of A549 cells according to the results of biochemical and microscopy evaluations. When the defined parameters for the use of TiO₂ P25 in A549 cells were met, similar results on the biological effects of TiO₂ P25 were obtained in two independent cell laboratories.

Conclusion

We optimized the experimental conditions of TiO₂ P25 preparation for toxicity testing in A549 cells. The results presented here on TiO₂ P25-induced cellular effects are reproducible. Therefore, our results can be helpful for other researchers using TiO₂ P25 as a reference material.

Industrial-relevant TiO2 types do not promote cytotoxicity in the A549 or TK6 cell lines regardless of cell specific interaction

Due to the expansive application of TiO₂ and its variance in physico-chemical characteristics, the toxicological profile of TiO₂, in all its various forms, requires evaluation. This study aimed to assess the hazard of five TiO₂ particle-types in relation to their cytotoxic profile correlated to their cellular interaction, specifically in human lymphoblast (TK6) and type-II alveolar epithelial (A549) cells. Treatment with the test materials was undertaken at a concentration range of 1-100 μg/cm² over 24 and 72 h exposure. TiO₂ interaction with both cell types was visualised by transmission electron microscopy, supported by energy-dispersive X-ray. None of the TiO₂ materials tested promoted cytotoxicity in either cell type over the concentration and time range studied. All materials were observed to interact with the A549 cells and were further noted to be internalised following 24 h exposure. In contrast, only the pigmentary rutile was internalised by TK6 lymphoblasts after 24 h exposure. Where uptake was observed there was no evidence, as determined by 2D microscopy techniques, of particle localisation within the nucleus of either cell type. This study indicates that industrially relevant TiO₂ particles demonstrate cell interactions that are cell-type dependent and do not induce cytotoxicity at the applied dose range.

On the Cellular Uptake and Exocytosis of Carbon Dots─Significant Cell Type Dependence and Effects of Cell Division

Understanding the cellular uptake and exocytosis processes of nanoparticles (NPs) is essential for developing the nanomedicines and assessing the health risk of nanomaterials. Considerable efforts have been made to reveal how physicochemical properties of NPs influence these processes. However, little attention has been paid to how cell type impacts these processes, especially exocytosis. Herein, the uptake and exocytosis of the carbon dots (CDs) obtained from the carbonization of citric acid with polyethylenimine (PEI) oligomers (CDs-PEI) in five human cell lines (HeLa, A549, BEAS-2B, A431, and MDA-MB-468) are analyzed to understand how cell type influences the fate of CDs in cells. The cell division is taken into account by the correction of cell number for accurate quantification of the uptake and exocytosis of CDs-PEI. The results indicate that the cell type significantly affects the cellular uptake, trafficking, and exocytosis of CDs-PEI. Among the cell types investigated, MDA-MB-468 cells have the greatest capacity for both uptake and exocytosis, and HeLa cells have the least capacity. The kinetics of the exocytosis largely follows a single exponential decay function, with the remaining CDs-PEI in cells reaching plateaus within 24 h. The kinetic parameters are cell-dependent but insensitive to the initial intracellular CDs-PEI content. Generally, the Golgi apparatus pathways are more important in exocytosis than the lysosomal pathway, and the locations of CDs-PEI in the beginning of exocytosis are not correlated with their exocytosis pathways. The findings on the cell type-dependent cellular uptake and exocytosis reported here may be valuable to the future design of high-performance and safe CDs and related nanomaterials in general.

DNA Oxidative Damage as a Sensitive Genetic Endpoint to Detect the Genotoxicity Induced by Titanium Dioxide Nanoparticles

The genotoxicity of nanomaterials has attracted great attention in recent years. As a possible occupational carcinogen, the genotoxic effects and underlying mechanisms of titanium dioxide nanoparticles (TiO2 NPs) have been of particular concern. In this study, the effect of TiO2 NPs (0, 25, 50 and 100 µg/mL) on DNA damage and the role of oxidative stress were investigated using human bronchial epithelial cells (BEAS-2B) as an in vitro model. After detailed characterization, the cytotoxicity of TiO2 NPs was detected. Through transmission electron microscopy (TEM), we found that TiO2 NPs entered the cytoplasm but did not penetrate deep into the nucleus of cells. The intracellular levels of reactive oxygen species (ROS) significantly increased in a dose-dependent manner and the ratios of GSH/GSSG also significantly decreased. The results of the normal comet assay were negative, while the Fpg-modified comet assay that specifically detected DNA oxidative damage was positive. Meanwhile, N-acetyl-L-cysteine (NAC) intervention inhibited the oxidative stress and genotoxicity induced by TiO2 NPs. Therefore, it was suggested that TiO2 NPs could induce cytotoxicity, oxidative stress and DNA oxidative damage in BEAS-2B cells. DNA oxidative damage may be a more sensitive genetic endpoint to detect the genotoxicity of TiO2 NPs.

Nanosafety: An Evolving Concept to Bring the Safest Possible Nanomaterials to Society and Environment

The use of nanomaterials has been increasing in recent times, and they are widely used in industries such as cosmetics, drugs, food, water treatment, and agriculture. The rapid development of new nanomaterials demands a set of approaches to evaluate the potential toxicity and risks related to them. In this regard, nanosafety has been using and adapting already existing methods (toxicological approach), but the unique characteristics of nanomaterials demand new approaches (nanotoxicology) to fully understand the potential toxicity, immunotoxicity, and (epi)genotoxicity. In addition, new technologies, such as organs-on-chips and sophisticated sensors, are under development and/or adaptation. All the information generated is used to develop new in silico approaches trying to predict the potential effects of newly developed materials. The overall evaluation of nanomaterials from their production to their final disposal chain is completed using the life cycle assessment (LCA), which is becoming an important element of nanosafety considering sustainability and environmental impact. In this review, we give an overview of all these elements of nanosafety.

The safety of nanomaterials in food production and packaging

Nanotechnology involves developing, characterising, and applying structures ranging in size from 1 to 100 nm. As a key advanced technology, it has contributed to a substantial impact across engineering, medicine, agriculture and food. With regards to their application in food, nanomaterials posses the ability to lead the quantitative and qualitative development of high-quality, healthier, and safer foods by outperforming traditional food processing technologies for increasing shelf life and preventing contaminations. Although rapid progress has been made in nanotechnology in food products, the toxicity of nanoparticles and nanomaterials is not very well known. As a result, nanomaterials are potentially toxic, therefore, considering the constantly increasing employment in food science, they need to be further characterised, and their use must be better regulated. We may face a crisis of nanotoxicity if the molecular mechanisms by which nanoparticles and nanomaterials interact with food and within living organisms is not fully understood. Food safety can be guaranteed only if we are thoroughly aware of nanomaterial properties and potential toxicity. Therefore, it is urgently necessary to have in the food sector a regulatory system capable of managing nanofood risks and nanotechnology, considering the health effects of food processing techniques based on nanotechnology. This present review discusses the impact and role nanotechnology play in food science. The specific application of Nanomaterials in food science, their advantages and disadvantages, the potential risk for human health and the analysis to detect nanocomponents are also highlighted.

Cytotoxicity of 2D engineered nanomaterials in pulmonary and corneal epithelium

Two-dimensional (2D) engineered nanomaterials are widely used in consumer and industrial goods due to their unique chemical and physical characteristics. Engineered nanomaterials are incredibly small and capable of being aerosolized during manufacturing, with the potential for biological interaction at first-contact sites such as the eye and lung. The unique properties of 2D nanomaterials that make them of interest to many industries may also cause toxicity towards epithelial cells. Using murine and human respiratory epithelial cell culture models, we tested the cytotoxicity of eight 2D engineered nanomaterials: graphene (110 nm), graphene oxide (2 um), graphene oxide (400 nm), reduced graphene oxide (2 um), reduced graphene oxide (400 nm), partially reduced graphene oxide (400 nm), molybdenum disulfide (400 nm), and hexagonal boron nitride (150 nm). Non-graphene nanomaterials were also tested in human corneal epithelial cells for ocular epithelial cytotoxicity. Hexagonal boron nitride was found to be cytotoxic in mouse tracheal, human alveolar, and human corneal epithelial cells. Hexagonal boron nitride was also tested for inhibition of wound healing in alveolar epithelial cells; no inhibition was seen at sub-cytotoxic doses. Nanomaterials should be considered with care before use, due to specific regional cytotoxicity that also varies by cell type. Supported by U01ES027288 and T32HL007013 and T32ES007059.

Advances in genotoxicity of titanium dioxide nanoparticles in vivo and in vitro

Titanium dioxide nanoparticles (TiO₂ NPs) are currently one of the most widely used nanomaterials. Due to an increasing scope of applications, the exposure of humans to TiO₂ NP is inevitable, such as entering the body through the mouth with food additives or drugs, invading the damaged skin with cosmetics, and entering the body through the respiratory tract during the process of production and handling. Compared with TiO₂ coarse particles, TiO₂ NPs have stronger conductivity, reaction activity, photocatalysis, and permeability, which may lead to greater toxicity to organisms. Given that TiO₂ was classified as a category 2B carcinogen (possibly carcinogenic to humans), the genotoxicity of TiO₂ NPs has become the focus of attention. There have been a series of previous studies investigating the potential genotoxicity of TiO₂ NPs, but the existing research results are still controversial and difficult to conclude. More than half of studies have shown that TiO₂ NPs can cause genotoxicity, suggesting that TiO₂ NPs are likely to be genotoxic to humans. And the genotoxicity of TiO₂ NPs is closely related to the exposure concentration, mode and time, and experimental cells/animals as well as its physicochemical properties (crystal type, size, and shape). This review summarized the latest research progress of related genotoxic effects through in vivo studies and in vitro cell tests, hoping to provide ideas for the evaluation of TiO₂ NPs genotoxicity.

Current approaches for the exploration of antimicrobial activities of nanoparticles

Infectious diseases of bacterial and viral origins contribute to substantial mortality worldwide. Collaborative efforts have been underway between academia and the industry to develop technologies for a more effective treatment for such diseases. Due to their utility in various industrial applications, nanoparticles (NPs) offer promising potential as antimicrobial agents against bacterial and viral infections. NPs have been established to possess potent antimicrobial activities against various types of pathogens due to their unique characteristics and cell-damaging ability through several mechanisms. The recently accepted antimicrobial mechanisms possessed by NPs include metal ion release, oxidative stress induction, and non-oxidative mechanisms. Another merit of NPs lies in the low likelihood of the development of microbial tolerance towards NPs, given the multiple simultaneous mechanisms of action against the pathogens targeting numerous gene mutations in these pathogens. Moreover, NPs provide a fascinating opportunity to curb microbial growth before infections: this outstanding feature has led to their utilization as active antimicrobial agents in different industrial applications, e.g. the coating of medical devices, incorporation in food packaging, promoting wound healing and encapsulation with other potential materials for wastewater treatment. This review discusses the progress and achievements in the antimicrobial applications of NPs, factors contributing to their actions, mechanisms underlying their efficiency, and risks of their applications, including the antimicrobial action of metal nanoclusters (NCs). The review concludes with a discussion of the restrictions on present studies and future prospects of nanotechnology-based NPs development.

Differential response of immobile (pneumocytes) and mobile (monocytes) barriers against 2 types of metal oxide nanoparticles

BACKGROUND

Inhaled nanoparticles (NPs) challenges mobile and immobile barriers in the respiratory tract, which can be represented by type II pneumocytes (immobile) and monocytes (mobile) but what is more important for biological effects, the cell linage, or the type of nanoparticle? Here, we addressed these questions and we demonstrated that the type of NPs exerts a higher influence on biological effects, but cell linages also respond differently against similar type of NPs.

DESIGN

Type II pneumocytes and monocytes were exposed to tin dioxide (SnO₂) NPs and titanium dioxide (TiO₂) NPs (1, 10 and 50 μg/cm²) for 24 h and cell viability, ultrastructure, cell granularity, molecular spectra of lipids, proteins and nucleic acids and cytoskeleton architecture were evaluated.

RESULTS

SnO₂ NPs and TiO₂ NPs are metal oxides with similar physicochemical properties. However, in the absence of cytotoxicity, SnO₂ NPs uptake was low in monocytes and higher in type II pneumocytes, while TiO₂ NPs were highly internalized by both types of cells. Monocytes exposed to both types of NPs displayed higher number of alterations in the molecular patterns of proteins and nuclei acids analyzed by Fourier-transform infrared spectroscopy (FTIR) than type II pneumocytes. In addition, cells exposed to TiO₂ NPs showed more displacements in FTIR spectra of biomolecules than cells exposed to SnO₂ NPs. Regarding cell architecture, microtubules were stable in type II pneumocytes exposed to both types of NPs but actin filaments displayed a higher number of alterations in type II pneumocytes and monocytes exposed to SnO₂ NPs and TiO₂ NPs. NPs exposure induced the formation of large vacuoles only in monocytes, which were not seen in type II pneumocytes.

CONCLUSIONS

Most of the cellular effects are influenced by the NPs exposure rather than by the cell type. However, mobile, and immobile barriers in the respiratory tract displayed differential response against SnO₂ NPs and TiO₂ NPs in absence of cytotoxicity, in which monocytes were more susceptible than type II pneumocytes to NPs exposure.

Cytotoxicity and genotoxicity of low-dose vanadium dioxide nanoparticles to lung cells following long-term exposure

Vanadium dioxide nanoparticles (VO₂ NPs) have been massively produced and widely applied due to their excellent metal-insulator transition property, making it extremely urgent to evaluate their safety, especially for low-dose long-term respiratory occupational exposure. Here, we report a comprehensive cytotoxicity and genotoxicity study on VO₂ NPs to lung cell lines A549 and BEAS-2B following a long-term exposure. A commercial VO₂ NP, S-VO₂, was used to treat BEAS-2B (0.15-0.6 μg/mL) and A549 (0.3-1.2 μg/mL) cells for four exposure cycles, and each exposure cycle lasted for 4 consecutive days; then various bioassays were performed after each cycle. Significant proliferation inhibition was observed in both cell lines after long-term exposure of S-VO₂ at low doses that did not cause apparent acute cytotoxicity; however, the genotoxicity of S-VO₂, characterized by DNA damage and micronuclei, was only observed in A549 cells. These adverse effects of S-VO₂ were exposure time-, dose- and cell-dependent, and closely related to the solubility of S-VO₂. The oxidative stress in cells, i.e., enhanced reactive oxygen species (ROS) generation and suppressed reduced glutathione, was the main toxicity mechanism of S-VO₂. The ROS-associated mitochondrial damage and DNA damage led to the genotoxicity, and cell proliferation retard, resulting in the cellular viability loss. Our results highlight the importance and urgent necessity of the investigation on the long-term toxicity of VO₂ NPs.

How can exposure to engineered nanomaterials influence our epigenetic code? A review of the mechanisms and molecular targets

Evidence suggests that engineered nanomaterials (ENM) can induce epigenetic modifications. In this review, we provide an overview of the epigenetic modulation of gene expression induced by ENM used in a variety of applications: titanium dioxide (TiO₂), silver (Ag), gold (Au), silica (SiO₂) nanoparticles and carbon-based nanomaterials (CNM). Exposure to these ENM can trigger alterations in cell patterns of DNA methylation, post-transcriptional histone modifications and expression of non-coding RNA. Such effects are dependent on ENM dose and physicochemical properties including size, shape and surface chemistry, as well as on the cell/organism sensitivity. The genes affected are mostly involved in the regulation of the epigenetic machinery itself, as well as in apoptosis, cell cycle, DNA repair and inflammation related pathways, whose long-term alterations might lead to the onset or progression of certain pathologies. In addition, some DNA methylation patterns may be retained as a form of epigenetic memory. Prenatal exposure to ENM may impair the normal development of the offspring by transplacental effects and/or putative transmission of epimutations in imprinting genes. Thus, understanding the impact of ENM on the epigenome is of paramount importance and epigenetic evaluation must be considered when assessing the risk of ENM to human health.

Safety assessment of titanium dioxide (E171) as a food additive

The present opinion deals with an updated safety assessment of the food additive titanium dioxide (E 171) based on new relevant scientific evidence considered by the Panel to be reliable, including data obtained with TiO2 nanoparticles (NPs) and data from an extended one-generation reproductive toxicity (EOGRT) study. Less than 50% of constituent particles by number in E 171 have a minimum external dimension < 100 nm. In addition, the Panel noted that constituent particles < 30 nm amounted to less than 1% of particles by number. The Panel therefore considered that studies with TiO2 NPs < 30 nm were of limited relevance to the safety assessment of E 171. The Panel concluded that although gastrointestinal absorption of TiO2 particles is low, they may accumulate in the body. Studies on general and organ toxicity did not indicate adverse effects with either E 171 up to a dose of 1,000 mg/kg body weight (bw) per day or with TiO2 NPs (> 30 nm) up to the highest dose tested of 100 mg/kg bw per day. No effects on reproductive and developmental toxicity were observed up to a dose of 1,000 mg E 171/kg bw per day, the highest dose tested in the EOGRT study. However, observations of potential immunotoxicity and inflammation with E 171 and potential neurotoxicity with TiO2 NPs, together with the potential induction of aberrant crypt foci with E 171, may indicate adverse effects. With respect to genotoxicity, the Panel concluded that TiO2 particles have the potential to induce DNA strand breaks and chromosomal damage, but not gene mutations. No clear correlation was observed between the physico-chemical properties of TiO2 particles and the outcome of either in vitro or in vivo genotoxicity assays. A concern for genotoxicity of TiO2 particles that may be present in E 171 could therefore not be ruled out. Several modes of action for the genotoxicity may operate in parallel and the relative contributions of different molecular mechanisms elicited by TiO2 particles are not known. There was uncertainty as to whether a threshold mode of action could be assumed. In addition, a cut-off value for TiO2 particle size with respect to genotoxicity could not be identified. No appropriately designed study was available to investigate the potential carcinogenic effects of TiO2 NPs. Based on all the evidence available, a concern for genotoxicity could not be ruled out, and given the many uncertainties, the Panel concluded that E 171 can no longer be considered as safe when used as a food additive.

High-Throughput Screening Platform for Nanoparticle-Mediated Alterations of DNA Repair Capacity

The potential genotoxic effects of engineered nanomaterials (ENMs) may occur through the induction of DNA damage or the disruption of DNA repair processes. Inefficient DNA repair may lead to the accumulation of DNA lesions and has been linked to various diseases, including cancer. Most studies so far have focused on understanding the nanogenotoxicity of ENM-induced damages to DNA, whereas the effects on DNA repair have been widely overlooked. The recently developed fluorescence multiplex-host-cell reactivation (FM-HCR) assay allows for the direct quantification of multiple DNA repair pathways in living cells and offers a great opportunity to address this methodological gap. Herein an FM-HCR-based method is developed to screen the impact of ENMs on six major DNA repair pathways using suspended or adherent cells. The sensitivity and efficiency of this DNA repair screening method were demonstrated in case studies using primary human small airway epithelial cells and TK6 cells exposed to various model ENMs (CuO, ZnO, and Ga2O3) at subcytotoxic doses. It was shown that ENMs may inhibit nucleotide-excision repair, base-excision repair, and the repair of oxidative damage by DNA glycosylases in TK6 cells, even in the absence of significant genomic DNA damage. It is of note that the DNA repair capacity was increased by some ENMs, whereas it was suppressed by others. Overall, this method can be part of a multitier, in vitro hazard assessment of ENMs as a functional, high-throughput platform that provides insights into the interplay of the properties of ENMs, the DNA repair efficiency, and the genomic stability.

Genotoxicity and Immunotoxicity of Titanium Dioxide-Embedded Mesoporous Silica Nanoparticles (TiO2@MSN) in Primary Peripheral Human Blood Mononuclear Cells (PBMC)

Background: TiO₂ nanoparticles (TiO₂ NPs) are the nanomaterial most produced as an ultraviolet (UV) filter. However, TiO₂ is a semiconductor and, in nanoparticle size, is a strong photocatalyst, raising concerns about photomutagenesis. Mesoporous silica nanoparticles (MSN) were synthetized incorporating TiO₂ NPs (TiO₂@MSN) to develop a cosmetic UV filter. The aim of this study was to assess the toxicity of TiO₂@MSN, compared with bare MSN and commercial TiO₂ NPs, based on several biomarkers. Materials and Methods: Human peripheral blood mononuclear cells (PBMC) were exposed to TiO₂@MSN, bare MSN (network) or commercial TiO₂ NPs for comparison. Exposed PBMC were characterized for cell viability/apoptosis, reactive oxygen species (ROS), nuclear morphology, and cytokines secretion. Results: All the nanoparticles induced apoptosis, but only TiO₂ NPs (alone or assembled into MSN) led to ROS and micronuclei. However, TiO₂@MSN showed lower ROS and cytotoxicity with respect to the P25. Exposure to TiO₂@MSN induced Th2-skewed and pro-fibrotic responses. Conclusions: Geno-cytotoxicity data indicate that TiO₂@MSN are safer than P25 and MSN. Cytokine responses induced by TiO₂@MSN are imputable to both the TiO₂ NPs and MSN, and, therefore, considered of low immunotoxicological relevance. This analytical assessment might provide hints for NPs modification and deep purification to reduce the risk of health effects in the settings of their large-scale manufacturing and everyday usage by consumers.

Insights on the biological role of ultrafine particles of size PM<0.25: A prospective study from New Delhi

When the total ambient PM_2.5 levels are several-fold higher than the recommended limit, it may be important to study the distributions of different sizes of particulate matter (PM). Here, we assess the distributions of various sizes of total PM_2.5 for 12 months (on a monthly basis) in New Delhi, India. Importantly, we found that ultrafine particles (i.e., particles <0.5 μm) contribute significantly to total PM_2.5. PM_<0.25 were the most cytotoxic particles to human lung epithelial cells in all the 12 months. In addition, PM_<0.25 were associated with significantly higher cytotoxicity per unit mass compared to other size fractions constituting PM_2.5. For any given size of PM, the amount of reactive oxygen species (ROS) generated per unit mass is higher for the month of March as compared to that for the rest of the months in the year. The higher ROS generations for all sizes of PM collected in the month of March was not explained by differences in their metal content values. Our data suggests the lack of correlation between total PM_2.5 levels and the highly cytotoxic PM_<0.25. In summary, this work establishes the need for policy changes to routinely monitor PM_<0.25 and the necessity to establish exposure limits for PM_<0.25, especially when the total PM_2.5 levels are breached.

Air-Liquid Interface Exposure of Lung Epithelial Cells to Low Doses of Nanoparticles to Assess Pulmonary Adverse Effects

Reliable and predictive in vitro assays for hazard assessments of manufactured nanomaterials (MNMs) are still limited. Specifically, exposure systems which more realistically recapitulate the physiological conditions in the lung are needed to predict pulmonary toxicity. To this end, air-liquid interface (ALI) systems have been developed in recent years which might be better suited than conventional submerged exposure assays. However, there is still a need for rigorous side-by-side comparisons of the results obtained with the two different exposure methods considering numerous parameters, such as different MNMs, cell culture models and read outs. In this study, human A549 lung epithelial cells and differentiated THP-1 macrophages were exposed under submerged conditions to two abundant types of MNMs i.e., ceria and titania nanoparticles (NPs). Membrane integrity, metabolic activity as well as pro-inflammatory responses were recorded. For comparison, A549 monocultures were also exposed at the ALI to the same MNMs. In the case of titania NPs, genotoxicity was also investigated. In general, cells were more sensitive at the ALI compared to under classical submerged conditions. Whereas ceria NPs triggered only moderate effects, titania NPs clearly initiated cytotoxicity, pro-inflammatory gene expression and genotoxicity. Interestingly, low doses of NPs deposited at the ALI were sufficient to drive adverse outcomes, as also documented in rodent experiments. Therefore, further development of ALI systems seems promising to refine, reduce or even replace acute pulmonary toxicity studies in animals.

Time-Resolved Single-Cell Assay for Measuring Intracellular Reactive Oxygen Species upon Exposure to Ambient Particulate Matter

Health risks associated with exposure to ambient particulate matter (PM) are a major concern around the world. Adverse PM health effects have been proposed to be linked to oxidative stress through the generation of reactive oxygen species (ROS). In vitro cellular assays can provide insights into components or characteristics of PM that best account for its toxicity at a cellular level. However, most current assays report cell population averages and are mostly time endpoint measurements and thus provide no temporal information. This poses limitations on our understanding of PM health effects. In this study, we developed a microfluidic assay that can measure cellular ROS responses at the single-cell level and evaluate temporal dynamic behavior of single cells. We first established a protocol that enables culturing cells in our microfluidic platform and that can provide reproducible ROS readouts. We further examined the heterogeneous ROS responses of cell populations and tracked the dynamics of individual cellular responses upon exposure to different concentrations of PM extracts. Our results show that in an alveolar macrophage cell line, cellular ROS responses are highly heterogeneous. ROS responses from different cells can vary over an order of magnitude, and large coefficients of variation at each timepoint measurement indicate a high variability. The dynamic behavior of single-cell responses is strongly dependent on PM concentrations. Our work serves as a proof-of-principle demonstration of the capability of our microfluidic technology to study time-resolved single-cell responses upon PM exposure. We envision applying this high-resolution, high-content assay to investigate a wide array of single-cell responses (beyond ROS) upon exposure to different types of PM in the future.

Titanium dioxide nanoparticle genotoxicity: A review of recent in vivo and in vitro studies

Titanium dioxide nanoparticles (TiO2 NPs, size <100 nm) find applications in a wide range of products including food and cosmetics. Studies have found that exposure to TiO2 NPs can cause inflammation, cytotoxicity, genotoxicity and cell apoptosis. In this article, we have reviewed the recent literature on the potential of TiO2 NPs to cause genotoxicity and summarized the results of two standard genotoxicity assays, the comet and micronucleus (MN) assays. Analysis of these peer-reviewed publications shows that the comet assay is the most common genotoxicity test, followed by MN, Ames, and chromosome aberration tests. These assays have reported positive as well as negative results, although there is inconsistency in some results that need to be confirmed further by well-designed experiments. We also discuss the possible mechanisms of TiO2 NP genotoxicity and point out areas that warrant further research.

TiO2 genotoxicity: An update of the results published over the last six years

TiO₂ particles are broadly used in daily products, including cosmetics for their UV-absorbing property, food for their white colouring property, water and air purification systems, self-cleaning surfaces and photoconversion electrical devices for their photocatalytic properties. The toxicity of TiO₂ nano- and microparticles has been studied for decades, and part of this investigation has been dedicated to the identification of their potential impact on DNA, i.e., their genotoxicity. This review summarizes data retrieved from their genotoxicity testing during the past 6 years, encompassing both in vitro and in vivo studies, mostly performed on lung and intestinal models. It shows that TiO₂ particles, both nano- and micro-sized, produce genotoxic damage to a variety of cell types, even at low, realistic doses.

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.

Toxicity and Gene Expression Profiling of Copper- and Titanium-Based Nanoparticles Using Air-Liquid Interface Exposure

To assess the toxicity of nanomaterials, most in vitro studies have been performed under submerged conditions, which do not reflect physiological conditions upon inhalation. An air-liquid interface (ALI) exposure may provide more reliable data on dosimetry and prevent interactions with cell culture media components. Therefore, an ALI exposure was combined with a high-throughput RT-qPCR approach to evaluate the toxicological potential of CuO and TiO₂ nanoparticles (NP) in A549 cells. While TiO₂ NP did not show any cytotoxicity or other effects compromising genomic stability up to 25.8 μg/cm², CuO NP revealed a dose-dependent cytotoxicity, starting at 4.9 μg/cm². Furthermore, CuO NP altered distinct gene expression patterns indicative for disturbed metal homeostasis, stress response, and DNA damage induction. Thus, induction of metal homeostasis associated genes (MT1X, MT2A) at 0.4 μg/cm² and higher suggested uptake and intracellular dissolution of CuO NP, which was verified by a dose-dependent increase in intracellular copper concentration. Starting at 4.9 μg/cm², oxidative stress markers (HMOX1, HSPA1A) were induced dose-dependently, supported by elevated ROS levels. Furthermore, a dose-dependent induction of genes associated with DNA damage response (DDIT3, GADD45A) was observed, in concordance with an increase in DNA strand breaks. Finally, transcriptional data suggested the induction of apoptosis at high doses, while flow cytometric analysis revealed increased numbers of either late apoptotic or necrotic cells and clearly necrotic cells at the highest concentrations. Thus, an ALI cell culture system was successfully combined with a comprehensive high-throughput RT-qPCR system, allowing the quantification of NP deposition and their impact on genomic stability. For CuO NP, in principle the data confirm observations made under submerged conditions with respect to intracellular copper ion release, as well as oxidative and genotoxic stress response. However, the results derived from ALI exposure allow the assessment of dose-response-relationships as well as the comparison of relative toxic potencies of different NP.

Genotoxicity of TiO2 Nanoparticles in Four Different Human Cell Lines (A549, HEPG2, A172 and SH-SY5Y)

Titanium dioxide nanoparticles (TiO2 NPs) have a wide variety of applications in many consumer products, including as food additives, increasing the concern about the possible hazards that TiO2 NPs may pose to human health. Although most previous studies have focused on the respiratory system, ingestion must also be considered as an important exposure route. Furthermore, after inhalation or ingestion, TiO2 NPs can reach several organs, such as the liver, brain or lungs. Taking this into consideration, the present study focuses on the uptake and potential genotoxicity (micronuclei induction) of TiO2 NPs on four human cell lines of diverse origin: lung cells (A549), liver cells (HepG2), glial cells (A172) and neurons (SH-SY5Y), using flow cytometry methods. Results showed a concentration-, time- and cell-type- dependent increase in TiO2 NPs uptake but no significant induction of micronuclei in any of the tested conditions. Data obtained reinforce the importance of cell model and testing protocols choice for toxicity assessment. However, some questions remain to be answered, namely on the role of cell culture media components on the agglomeration state and mitigation of TiO2 NPs toxic effects.

Titanium Dioxide Nanoparticles Alter the Cellular Phosphoproteome in A549 Cells

TiO₂ nanoparticles (NPs) are one of the most produced NPs worldwide and are used in many consumer products. Their impact on human health, especially through inhalation, has been studied for more than two decades. TiO₂ is known for its strong affinity towards phosphates, and consequently interaction with cellular phosphates may be one of the mechanisms driving its toxicity. In the present study, we used a phosphoproteomics approach to document the interaction of TiO₂-NP with phosphoproteins from A549 human pulmonary alveolar epithelial cells. Cells were exposed to 21 nm anatase/rutile TiO₂-NPs, then their phosphopeptides were extracted and analyzed using shotgun proteomics. By comparing the phosphoprotein content, phosphorylation status and phosphorylation sites of exposed cells with that of control cells, our results show that by affecting the phosphoproteome, TiO₂-NPs affect cellular processes such as apoptosis, linked with cell cycle and the DNA damage response, TP53 being central to these pathways. Other pathways including inflammation and molecular transport are also affected. These molecular mechanisms of TiO₂-NP toxicity have been reported previously, our study shows for the first time that they may derive from phosphoproteome modulation, which could be one of their upstream regulators.

Insights into Theranostic Properties of Titanium Dioxide for Nanomedicine

Titanium dioxide (TiO2) nanostructures exhibit a broad range of theranostic properties that make them attractive for biomedical applications. TiO2 nanostructures promise to improve current theranostic strategies by leveraging the enhanced quantum confinement, thermal conversion, specific surface area, and surface activity. This review highlights certain important aspects of fabrication strategies, which are employed to generate multifunctional TiO2 nanostructures, while outlining post-fabrication techniques with an emphasis on their suitability for nanomedicine. The biodistribution, toxicity, biocompatibility, cellular adhesion, and endocytosis of these nanostructures, when exposed to biological microenvironments, are examined in regard to their geometry, size, and surface chemistry. The final section focuses on recent biomedical applications of TiO2 nanostructures, specifically evaluating therapeutic delivery, photodynamic and sonodynamic therapy, bioimaging, biosensing, tissue regeneration, as well as chronic wound healing.

Insights into the epigenetic effects of nanomaterials on cells

With the development of nanotechnology, nanomaterials are increasingly being applied in health fields, such as biomedicine, pharmaceuticals, and cosmetics. Concerns have therefore been raised over their toxicity and numerous studies have been carried out to assess their safety. Most studies on the toxicity and therapeutic mechanisms of nanomaterials have revealed the effects of nanomaterials on cells at the transcriptome and proteome levels. However, epigenetic modifications, for example DNA methylation, histone modification, and noncoding RNA expression induced by nanomaterials, which play an important role in the regulation of gene expression, have not received sufficient attention. In this review, we therefore state the importance of studying epigenetic effects induced by nanomaterials; then we review the progress of nanomaterial epigenetic research in the assessment of toxicity, therapeutic, and other mechanisms. We also clarify the possible study directions for future nanomaterial epigenetic research. Finally, we discuss the future development and challenges of nanomaterial epigenetics that must still be addressed. We hope to understand the potential toxicity of nanomaterials and clearly understand the therapeutic mechanism through a thorough investigation of nanomaterial epigenetics.

The size-dependent genotoxic potentials of titanium dioxide nanoparticles to endothelial cells

Despite intensive research activities, there are still many major knowledge gaps over the potential adverse effects of titanium dioxide nanoparticles (TiO₂ -NPs), one of the most widely produced and used nanoparticles, on human cardiovascular health and the underlying mechanisms. In the present study, alkaline comet assay and cytokinesis-block micronucleus test were employed to determine the genotoxic potentials of four sizes (100, 50, 30, and 10 nm) of anatase TiO₂ -NPs to human umbilical vein endothelial cells (HUVECs) in culture. Also, the intracellular redox statuses were explored through the measurement of the levels of reactive oxygen species (ROS) and reduced glutathione (GSH) with kits, respectively. Meanwhile, the protein levels of nuclear factor erythroid 2-related factor 2 (Nrf2) were also detected by western blot. The results showed that at the exposed levels (1, 5, and 25 μg/mL), all the four sizes of TiO₂ -NPs could elicit an increase of both DNA damage and MN frequency in HUVECs in culture, with a positive dose-dependent and negative size-dependent effect relationship (T100 < T50 < T30 < T10). Also, increased levels of intracellular ROS, but decreased levels of GSH, were found in all the TiO₂ -NP-treated groups. Intriguingly, a very similar manner of dose-dependent and size-dependent effect relationship was observed between the ROS test and both comet assay and MN test, but contrary to that of GSH assay. Correspondingly, the levels of Nrf2 protein were also elevated in the TiO₂ -NP-exposed HUVECs, with an inversely size-dependent effect relationship. These findings indicated that induction of oxidative stress and subsequent genotoxicity might be an important biological mechanism by which TiO₂ -NP exposure would cause detrimental effects to human cardiovascular health.

Mechanoregulation of titanium dioxide nanoparticles in cancer therapy

Titanium dioxide (TiO₂) nanoparticles (NPs), first developed in the 1990s, have been applied in numerous biomedical fields such as tissue engineering and therapeutic drug development. In recent years, TiO₂-based drug delivery systems have demonstrated the ability to decrease the risk of tumorigenesis and improve cancer therapy. There is increasing research on the origin and effects of pristine and doped TiO₂-based nanotherapeutic drugs. However, the detailed molecular mechanisms by which drug delivery to cancer cells alters sensing of gene mutations, protein degradation, and metabolite changes as well as its associated cumulative effects that determine the microenvironmental mechanosensitive metabolism have not yet been clearly elucidated. This review focuses on the microenvironmental influence of TiO₂-NPs induced various mechanical stimuli on tumor cells. The differential expression of genome, proteome, and metabolome after treatment with TiO₂-NPs is summarized and discussed. In the tumor microenvironment, mechanosensitive DNA mutations, gene delivery, protein degradation, inflammatory responses, and cell viability affected by the mechanical stimuli of TiO₂-NPs are also examined.

The Comet Assay as a Tool to Detect the Genotoxic Potential of Nanomaterials

The interesting physicochemical characteristics of nanomaterials (NMs) has brought about their increasing use and, consequently, their increasing presence in the environment. As emergent contaminants, there is an urgent need for new data about their potential side-effects on human health. Among their potential effects, the potential for DNA damage is of paramount relevance. Thus, in the context of the EU project NANoREG, the establishment of common robust protocols for detecting genotoxicity of NMs became an important aim. One of the developed protocols refers to the use of the comet assay, as a tool to detect the induction of DNA strand breaks. In this study, eight different NMs—TiO₂NP (2), SiO₂NP (2), ZnONP, CeO₂NP, AgNP, and multi-walled carbon nanotubes (MWCNT)—were tested using two different human lung epithelial cell lines (A549 and BEAS-2B). The comet assay was carried out with and without the use of the formamidopyrimidine glycosylase (FPG) enzyme to detect the induction of oxidatively damaged DNA bases. As a high throughput approach, we have used GelBond films (GBF) instead of glass slides, allowing the fitting of 48 microgels on the same GBF. The results confirmed the suitability of the comet assay as a powerful tool to detect the genotoxic potential of NMs. Specifically, our results indicate that most of the selected nanomaterials showed mild to significant genotoxic effects, at least in the A549 cell line, reflecting the relevance of the cell line used to determine the genotoxic ability of a defined NM.

Tangeretin-Assisted Platinum Nanoparticles Enhance the Apoptotic Properties of Doxorubicin: Combination Therapy for Osteosarcoma Treatment

Osteosarcoma (OS) is the most common type of cancer and the most frequent malignant bone tumor in childhood and adolescence. Nanomedicine has become an indispensable field in biomedical and clinical research, with nanoparticles (NPs) promising to increase the therapeutic efficacy of anticancer drugs. Doxorubicin (DOX) is a commonly used chemotherapeutic drug against OS; however, it causes severe side effects that restrict its clinical applications. Here, we investigated whether combining platinum NPs (PtNPs) and DOX could increase their anticancer activity in human bone OS epithelial cells (U2OS). PtNPs with nontoxic, effective, thermally stable, and thermoplasmonic properties were synthesized and characterized using tangeretin. We examined the combined effects of PtNPs and DOX on cell viability, proliferation, and morphology, reactive oxygen species (ROS) generation, lipid peroxidation, nitric oxide, protein carbonyl content, antioxidants, mitochondrial membrane potential (MMP), adenosine tri phosphate (ATP) level, apoptotic and antiapoptotic gene expression, oxidative stress-induced DNA damage, and DNA repair genes. PtNPs and DOX significantly inhibited U2OS viability and proliferation in a dose-dependent manner, increasing lactate dehydrogenase leakage, ROS generation, and malondialdehyde, nitric oxide, and carbonylated protein levels. Mitochondrial dysfunction was confirmed by reduced MMP, decreased ATP levels, and upregulated apoptotic/downregulated antiapoptotic gene expression. Oxidative stress was a major cause of cytotoxicity and genotoxicity, confirmed by decreased levels of various antioxidants. Furthermore, PtNPs and DOX increased 8-oxo-dG and 8-oxo-G levels and induced DNA damage and repair gene expression. Combination of cisplatin and DOX potentially induce apoptosis comparable to PtNPs and DOX. To the best of our knowledge, this is the first report to describe the combined effects of PtNPs and DOX in OS.

The Effects of Apigenin-Biosynthesized Ultra-Small Platinum Nanoparticles on the Human Monocytic THP-1 Cell Line

Generally, platinum nanoparticles (PtNPs) are considered non-toxic; however, toxicity depends on the size, dose, and physico-chemical properties of materials. Owing to unique physico-chemical properties, PtNPs have emerged as a material of interest for several biomedical applications, particularly therapeutics. The adverse effect of PtNPs on the human monocytic cell line (THP-1) is not well-established and remains elusive. Exposure to PtNPs may trigger oxidative stress and eventually lead to inflammation. To further understand the toxicological properties of PtNPs, we studied the effect of biologically synthesized ultra-small PtNPs on cytotoxicity, genotoxicity, and proinflammatory responses in the human monocytic cell line (THP-1). Our observations clearly indicated that PtNPs induce cytotoxicity in a dose-dependent manner by reducing cell viability and proliferation. The cytotoxicity of THP-1 cells correlated with an increase in the leakage of lactate dehydrogenase, generation of reactive oxygen species, and production of malondialdehyde, nitric oxide, and carbonylated proteins. The involvement of mitochondria in cytotoxicity and genotoxicity was confirmed by loss of mitochondrial membrane potential, lower ATP level, and upregulation of proapoptotic and downregulation of antiapoptotic genes. Decreases in the levels of antioxidants such as reduced glutathione (GSH), oxidized glutathione (GSH: GSSG), glutathione peroxidase (GPx), superoxide dismutase (SOD), catalase (CAT), and thioredoxin (TRX) were indicative of oxidative stress. Apoptosis was confirmed with the significant upregulation of key apoptosis-regulating genes. Oxidative DNA damage was confirmed by the increase in the levels of 8-oxodG and 8-oxoG and upregulation of DNA damage and repair genes. Finally, the proinflammatory responses to PtNPs was determined by assessing the levels of multiple cytokines such as interleukin-1β (IL-1β), IL-6, IL-8, tumor necrosis factor-α (TNF-α), granulocyte-macrophage colony-stimulating factor (GM-CSF), and monocyte chemoattractant protein 1 (MCP-1). All the cytokines were significantly upregulated in a dose-dependent manner. Collectively, these observations suggest that THP-1 cells were vulnerable to biologically synthesized ultra-small PtNPs.

The size-dependent apoptotic effect of titanium dioxide nanoparticles on endothelial cells by the intracellular pathway

Concerns over the health risk of the widely distributed, commonly used titanium dioxide nanoparticles (nano-TiO₂ ) are increasing worldwide. Yet, up-to-now, our understanding in their potential effects on the cardiovascular system is very limited and the toxicological mechanisms are still unclear. In the present study, the CCK-8 assay was performed to determine the cytotoxicity of four sizes (10, 30, 50, and 100 nm) of anatase nano-TiO₂ on human umbilical vein endothelial cells (HUVECs) in culture, and the flow cytometry was employed to investigate the potential of these nano-TiO₂ to induce the apoptosis of HUVECs. The apoptotic pathway was also probed through the determination of the protein expression and activation of p53, Bax, Bcl-2, caspases-9, -7, -3, and PARP by western blot. The results showed that at the administrative levels (1, 5, 25 μg/mL), all the four sizes of nano-TiO₂ could significantly inhibit the viability of HUVECs and elicit significant apoptosis in them, compared with the negative control (P < .05, P < .01). Moreover, the apoptotic rates of HUVECs were increased respectively with the elevating levels and decreasing sizes of the administrative nano-TiO₂ , showing a clear dose- and size-dependent effect relationships. Interestingly, the increasing phosphorylation of p53, decreasing ratio of Bcl-2/Bax, and enhancing activation of the downstream proteins caspase-9, -7, -3, and PARP, were also observed with the decreasing sizes of the administrative nano-TiO₂ in the western blot, indicating that the intracellular approach of apoptosis, the p53-caspase pathway, is the major way of the nano-TiO₂ -mediated apoptosis in HUVECs in culture and that the size is an important parameter that may determine the potential of nano-TiO₂ to induce cellular response. In conclusion, these results suggested that high levels of nano-TiO₂ exposure may pose potential risks to human cardiovascular health by inducing cardiovascular EC apoptosis.

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.