Genotoxic and mutagenic properties of Ni and NiO nanoparticles investigated by comet assay, γ-H2AX staining, Hprt mutation assay and ToxTracker reporter cell lines

Modeling of local and systemic exposure to metals and metalloids after inhalation exposure: Recommended update to the USEPA metals framework

The USEPA issued the "Framework for Metal Risk Assessment" in 2007, recognizing that human and environmental exposure to metals and metalloids (MMEs) poses challenges risk assessment. Inhalation of aerosols containing MMEs is a primary pathway for exposure in the occupational setting, for consumer exposure, and to general population exposure associated with point-source emissions or ambient sources. The impacts of inhalation can be at the point of deposition (local exposure) or may manifest after uptake into the body (systemic exposure). Both local and systemic exposure can vary with factors that determine the regional deposition of MME-containing aerosols. Aerosol characteristics such as particle size combine with species-specific characteristics of airway morphology and lung function to modulate the deposition and clearance of MME particulates. In contrast to oral exposure, often monitored by measuring MME levels in blood or urine, inhalation exposure can produce local pulmonary impacts in the absence of significant systemic distribution. Exposure assessment for nutritionally essential MMEs can be further complicated by homeostatic controls that regulate systemic MME levels. Predictions of local exposure can be facilitated by computer models that estimate regional patterns of aerosol deposition, permitting calculation of exposure intensity in different regions of the respiratory tract. The utility of deposition modeling has been demonstrated in assessments of nutritionally essential MMEs regulated by homeostatic controls and in the comparison of results from inhalation studies in experimental animals. This facilitates extrapolation from animal data to humans and comparisons of exposures possessing mechanistic linkages to pulmonary toxicity and carcinogenesis. Pulmonary deposition models have significantly advanced and have been applied by USEPA in evaluations of particulate matter. However, regional deposition modeling has yet to be incorporated into the general guidance offered by the agency for evaluating inhalation exposure. Integr Environ Assess Manag 2023;00:1-13. © 2023 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Health hazards of particles in additive manufacturing: a cross-disciplinary study on reactivity, toxicity and occupational exposure to two nickel-based alloys

The increasing use of additive manufacturing (AM) techniques (e.g., 3D-printing) offers many advantages but at the same time presents some challenges. One concern is the possible exposure and health risk related to metal containing particles of different sizes. Using the nickel-based alloys Hastelloy X (HX) and Inconel 939 (IN939) as a case, the aim of this cross-disciplinary study was to increase the understanding on possible health hazards and exposure. This was done by performing in-depth characterization of virgin, reused and condensate powders, testing in vitro toxicity (cytotoxicity, genotoxicity, oxidative stress), and measuring occupational airborne exposure. The results showed limited metal release from both HX and IN939, and slightly different surface composition of reused compared to virgin powders. No or small effects on the cultured lung cells were observed when tested up to 100 µg/mL. Particle background levels in the printing facilities were generally low, but high transient peaks were observed in relation to sieving. Furthermore, during post processing with grinding, high levels of nanoparticles (> 100,000 particles/cm3) were noted. Urine metal levels in AM operators did not exceed biomonitoring action limits. Future studies should focus on understanding the toxicity of the nanoparticles formed during printing and post-processing.

Txnrd3 knockout enhancement of lung injury induced by Ni exposure via the VEGF-VEGFR-2 axis and alleviation of this effect by melatonin

Ni exposure leads to respiratory diseases in mice. Txnrd3 has been shown to have a protective effect on the body, but there is a paucity of empirical research focusing specifically on lung tissue. Melatonin possesses potent antioxidant, anti-inflammatory, and anti-fibrotic effects. By regulating inflammation-related factors, melatonin can activate the VEGF signaling pathway, ultimately alleviating lung injuries caused by Ni exposure. One hundred and sixty 8-week-old C57BL/6N mice, that were wild-type or Txnrd3-/- mice and 25-30 g in weight, were randomly divided into eight groups, including the NC group, Ni group, melatonin-treated group, and Ni plus melatonin group. Ni (10 mg/kg) was gavaged, and melatonin (2 mg/kg) was administered for 21 days. Inflammatory cells were found in the bronchioles of Txnrd3-/- mice under Ni exposure. Ultrastructural examination revealed that the homozygous-Ni group had a high amount of collagen fibers. The antioxidant capacity studies also revealed that mice lungs underwent oxidative stress. The results of qRT-PCR and WB showed that Ni induced an inflammatory response, which was also aggravated in Txnrd3-/- mice. Melatonin can effectively reduce the above symptoms. In conclusion, Ni causes lung injury by activating the VEGF-VEGFR-2 pathway and Txnrd3 knockout aggravates injury after Ni exposure.

Nickel nanoparticles exert cytotoxic effects on trophoblast HTR-8/SVneo cells possibly via Nrf2/MAPK/caspase 3 pathway

Nickel nanoparticles are widely used in the industry and may affect the reproductive system. The potential molecular mechanism of exposing the first-trimester trophoblast cell line (HTR-8/SVneo) to nickel nanoparticles remains unclear. Hence, the aim of this study was to investigate the in vitro cytotoxicity of Ni NPs on HTR-8/SVneo cells. HTR-8/SVneo cells were subjected to various concentrations (0, 2.5, 5, 7.5, 10, and 12.5 μg/cm²) of Ni NPs. The toxicity of the Ni NPs was evaluated in HTR-8/SVneo cells by measuring cell viability. The underlying mechanism of nickel nanoparticles toxicity to HTR-8/SVneo cells was determined by measuring the content of intracellular reactive oxygen species, mitochondrial membrane potential, and the rate of cell apoptosis and cell cycle, by measuring adenosine triphosphate levels, intracellular lipid peroxidation malondialdehyde, total superoxide dismutase, and CuZn/Mn-SOD activities, and by determining proteins related to Nrf2, MAPK, and Cytochrome c. Our results showed that the nickel nanoparticles treatment reduced the viability of HTR-8/SVneo cells, while it increased their oxidative stress and lowered their mitochondrial respiratory capacity. Additionally, the nickel nanoparticles treatment induced cell S-phase arrest and apoptosis. These molecular events may be linked to the oxidative stress-Nrf2 pathway/MAPK/Caspase 3 cascade. Thus, nickel nanoparticles exert cytotoxic effects on HTR-8/SVneo cells, which could affect the function of the placenta in human.

Peroral Toxicological Assessment of Two-Dimensional Forms of Nickel Nanoparticles Sized between 20 and 120 nm

Nickel (Ni) nanoparticles (NPs) are used as technological aids-catalysts in the oil and fat industry, in pharmaceuticals, and in the production of cosmetics and pesticides. The acute and subchronic oral toxicity of metallic Ni in the nanoform is not well understood. The study aimed to investigate the acute and subchronic oral toxicity of Ni NPs to rats. We used two NP preparations (Ni NP1 and Ni NP2) with spherical particles and an average diameter of 53.7 and 70.9 nm according to the electron microscopy data. In the study of acute toxicity, both kinds of Ni NPs were administered to male and female Wistar rats aged 8 weeks as a single dose of 2000 mg/kg b.w. through a gastric gavage. In the subchronic experiment, male Wistar rats initially aged 7 weeks received for 92 days Ni NP1 and Ni NP2 as well as the "traditional" soluble salt form of Ni (Ni basic carbonate) at doses of 0.1, 1, and 10 mg/kg body weight (mg/kg b.w.) in terms of Ni content as a part of the diet consumed. As a result, in an acute study, the oral LD₅₀ for Ni NP2 in male and female rats was about 1600 mg/kg b.w. (IV hazard class). The oral dose of Ni NP1 equal to 2000 mg/kg b.w. exceeded LD₁₀₀ for males and corresponded to LD₉₀ for females. In the subchronic study, the bioaccumulation of both Ni NPs as well as Ni salt was observed in the kidney but not in the liver and spleen. Ni NP1 decreased body weight only at a dose of 1 mg/kg b.w.; affected the relative weight of the spleen at 0.1 mg/kg, the brain at 1.0 mg/kg, and the thymus at 10 mg/kg; and decreased locomotor activity at 0.1 and 10 mg/kg. Thus, for Ni NP1, in such cases where a monotonic dose-response relationship could be traced, LOEL could be stated at 10 mg/kg b.w./day for 92 days of oral intake. However, for some endpoints where such a monotonic relationship could be absent, significant toxic effects were observed even at a dose 0.1 mg/kg. In the case of Ni NP2, changes in the relative weight of the liver, thymus, and brain were recorded starting from 0.1 mg/kg b.w.; locomotor activity decreased starting from 0.1 mg/kg. Other effects, including basophiles count and platelet system indexes, were observed at a dose of 1 mg/kg or higher. Thus, the LOEL value for Ni NP2 can be fixed at 0.1 mg/kg. The critical organs affected by both Ni NPs were the brain and immune system. Most of the toxic effects exhibited by metallic Ni NPs were absent or had an opposite orientation upon administration of equivalent doses of Ni in the salt form which indicates the signs of "nanotoxicity" in metallic Ni NPs. In conclusion, the data obtained show that there may be some additional health risks caused by the intake of Ni in a nanoform compared to soluble ionized forms of this element at equivalent doses.

Genotoxicity of Graphene-Based Materials

Graphene-based materials (GBMs) are a broad family of novel carbon-based nanomaterials with many nanotechnology applications. The increasing market of GBMs raises concerns on their possible impact on human health. Here, we review the existing literature on the genotoxic potential of GBMs over the last ten years. A total of 50 articles including in vitro, in vivo, in silico, and human biomonitoring studies were selected. Graphene oxides were the most analyzed materials, followed by reduced graphene oxides. Most of the evaluations were performed in vitro using the comet assay (detecting DNA damage). The micronucleus assay (detecting chromosome damage) was the most used validated assay, whereas only two publications reported results on mammalian gene mutations. The same material was rarely assessed with more than one assay. Despite inhalation being the main exposure route in occupational settings, only one in vivo study used intratracheal instillation, and another one reported human biomonitoring data. Based on the studies, some GBMs have the potential to induce genetic damage, although the type of damage depends on the material. The broad variability of GBMs, cellular systems and methods used in the studies precludes the identification of physico-chemical properties that could drive the genotoxicity response to GBMs.

A review on properties of magnesium-based alloys for biomedical applications

With changing lifestyles, the demand for bone implantation has been increasing day by day. The deficiency of nutritious elements within the human body results in certain diseases like osteoporosis, rickets, and other skeletal disorders; lack of physical activities; and the increasing number of accidents are the primary reasons for bone damage/fracture. Metallic implants made up of chrome steel, cobalt-based alloys, and titanium-based alloys are being majorly used worldwide owing to their high strength and high corrosion resistance which makes them permanent orthopedic bioimplant materials, however, they display a stress-shielding effect and it also requires an implant removal surgery. Thus, these problems can be addressed through the employment of biodegradable materials. Among the available biodegradable metallic materials, Mg alloys have been identified as a prospective orthopedic implant material. These alloys are biodegradable as well as biocompatible, however, they experience a relatively higher rate of degradation limiting their usability as implant material. This study attempts to comprehensively assess the effects of various alloying elements such as Ca, Zn, Sn, Mn, Sr and Rare earth elements (REEs) on the mechanical and degradation behavior (bothin vivoandin vitro) of Mg alloys. Since the microstructure, mechanical properties and degradation response of the Mg alloys are dependent on the processing route, hence detailed processing- property database of different Mg alloys is provided in this paper.

Unveiling the Toxicity of Fine and Nano-Sized Airborne Particles Generated from Industrial Thermal Spraying Processes in Human Alveolar Epithelial Cells

High-energy industrial processes have been associated with particle release into workplace air that can adversely affect workers’ health. The present study assessed the toxicity of incidental fine (PGFP) and nanoparticles (PGNP) emitted from atmospheric plasma (APS) and high-velocity oxy-fuel (HVOF) thermal spraying. Lactate dehydrogenase (LDH) release, 2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate (WST-1) metabolisation, intracellular reactive oxygen species (ROS) levels, cell cycle changes, histone H2AX phosphorylation (γ-H2AX) and DNA damage were evaluated in human alveolar epithelial cells at 24 h after exposure. Overall, HVOF particles were the most cytotoxic to human alveolar cells, with cell viability half-maximal inhibitory concentration (IC₅₀) values of 20.18 µg/cm² and 1.79 µg/cm² for PGFP and PGNP, respectively. Only the highest tested concentration of APS-PGFP caused a slight decrease in cell viability. Particle uptake, cell cycle arrest at S + G₂/M and γ-H2AX augmentation were observed after exposure to all tested particles. However, higher levels of γ-H2AX were found in cells exposed to APS-derived particles (~16%), while cells exposed to HVOF particles exhibited increased levels of oxidative damage (~17% tail intensity) and ROS (~184%). Accordingly, APS and HVOF particles seem to exert their genotoxic effects by different mechanisms, highlighting that the health risks of these process-generated particles at industrial settings should not be underestimated.

Application of ToxTracker for the toxicological assessment of tobacco and nicotine delivery products

Consumer demands and innovation have led to an increasingly diverse range of nicotine delivery systems, driven by a desire to reduce risk associated with traditional combustible cigarettes. This speed of change provides a mandate for rapid new product assessment. We have used the validated technology ToxTracker®, to assess biomarkers of DNA damage, protein misfolding, oxidative and cellular stress, across the categories of cigarette (1R6F), tobacco heating product (THP 1.4) and electronic cigarette (ePen 3). In addition, we compared the commonly used test matrices for tobacco and nicotine products; whole aerosol aqueous extracts (AqE) and gas vapour phase (GVP), determining their suitability across the product categories. We demonstrated a significant reduction in oxidative stress and cytotoxicity for THP 1.4 over cigarette, further reduced for ePen 3, when assessed by both dilution and nicotine dosimetry. We also identified that while the extraction matrices AqE and GVP from combustible products were equivalent in the induced responses, this was not true of the other category examples, moreover THP 1.4 GVP demonstrates a >50 % reduction in both toxicity and cytotoxicity endpoints over AqE. This indicates that unlike cigarette, the active components or toxicants for THP and electronic cigarette are associated with the aerosol fraction of these categories.

Nickel nanoparticles affect the migration and invasion of HTR-8/SVneo cells by downregulating MMP2 through the PI3K/AKT pathway

Proper migration and invasion of extravillous trophoblast cells into the endometrium in early gestation is essential for successful embryo implantation. The development of nanotechnology has led to the emergence of nickel nanoparticles (Ni NPs), for which attendant health concerns are widespread. Ni NPs are known to affect reproduction and be embryotoxic, but whether they affect the migration and invasion functions of trophoblast cells is unclear. We investigated the effects of Ni NPs on the migration and invasion of HTR-8/SVneo in extravillous trophoblast cells and explored the possible role of the PI3K/AKT/MMP2 signaling pathway in this regard. Results showed that the migration and invasion of cells was significantly inhibited by the exposure of Ni NPs. The protein and mRNA levels of PI3K/AKT/MMP2 signaling pathway were significantly reduced with the increase in Ni NPs concentration. The presence of the PI3K activator 740Y-P partially attenuated the inhibition of cell migration and invasion by Ni NPs, confirming the involvement of this pathway. Thus, Ni NPs inhibit migration and invasion of human trophoblast HTR-8/SVneo cells by downregulating the PI3K/AKT/MMP2 signaling pathway. This study is important for the development of safety evaluation criteria for Ni NPs.

Study of the mechanism of mitochondrial division and mitochondrial autophagy in the male reproductive toxicity induced by nickel nanoparticles

Male reproductive health is deteriorating, and fertility is largely affected by environmental factors. This study aims to investigate the potential mechanism underlying mitochondrial division and mitochondrial autophagy in the male reproductive toxicity of nickel nanoparticles (Ni NPs). An in vivo mouse (BALB/c) model was constructed to calculate testicular organ coefficients and sperm abnormality rates, and detect serum reproductive hormones, testicular pathological morphology, and the expression of Drp1, Pink1, and Parkin proteins. Furthermore, mouse spermatogonia (GC-1 cells) were used as an in vitro model to detect cell viability, apoptosis, intracellular reactive oxygen species (ROS), mitochondrial membrane potential (MMP), ATP and protein expression. After treatment with an additional inhibitor, Mdivi-1, such influences were further detected to explore the possible mechanism of male reproductive toxicity induced by Ni NPs. The in vivo studies showed that compared with the control group, exposure to Ni NPs reduced the serum levels of testosterone, follicle stimulating hormone and luteinizing hormone, increased the sperm abnormality rate, widened the gaps in the seminiferous tubules of the testes, decreased the sperm count, and increased the expression of Drp1, Pink1 and Parkin proteins (all P < 0.05). The in vitro studies further confirmed that compared with the control group, Ni NPs can lead to decreased cell viability, increased apoptosis, accumulation of ROS, decreased MMP and ATP, increased expression of Drp1, Pink1, Parkin, Bax, caspase-9 and caspase-3 proteins, and decreased expression of Bcl-2, resulting in an increased value of Bax/Bcl-2. It is worth noting that such influences induced by Ni NPs were significantly reversed by the additional Mdivi-1. In conclusion, Drp1-mediated mitochondrial division and Pink1/Parkin-mediated mitochondrial autophagy play an important role in the male reproductive toxicity of Ni NPs, during which both of them form an interaction cycle and accelerate the occurrence of cell apoptosis.

Toxicity evaluation of particles formed during 3D-printing: Cytotoxic, genotoxic, and inflammatory response in lung and macrophage models

Additive manufacturing (AM) or "3D-printing" is a ground-breaking technology that enables the production of complex 3D parts. Its rapid growth calls for immediate toxicological investigations of possible human exposures in order to estimate occupational health risks. Several laser-based powder bed fusion AM techniques are available of which many use metal powder in the micrometer range as feedstock. Large energy input from the laser on metal powders generates several by-products, like spatter and condensate particles. Due to often altered physicochemical properties and composition, spatter and condensate particles can result in different toxicological responses compared to the original powder particles. The toxicity of such particles has, however, not yet been investigated. The aim of the present study was to investigate the toxicity of condensate/spatter particles formed and collected upon selective laser melting (SLM) printing of metal alloy powders, including a nickel-chromium-based superalloy (IN939), a nickel-based alloy (Hastelloy X, HX), a high-strength maraging steel (18Ni300), a stainless steel (316L), and a titanium alloy (Ti6Al4V). Toxicological endpoints investigated included cytotoxicity, generation of reactive oxygen species (ROS), genotoxicity (comet and micronucleus formation), and inflammatory response (cytokine/chemokine profiling) following exposure of human bronchial epithelial cells (HBEC) or monocytes/macrophages (THP-1). The results showed no or minor cytotoxicity in the doses tested (10-100 μg/mL). Furthermore, no ROS generation or formation of micronucleus was observed in the HBEC cells. However, an increase in DNA strand breaks (detected by comet assay) was noted in cells exposed to HX, IN939, and Ti6Al4V, whereas no evident release of pro-inflammatory cytokine was observed from macrophages. Particle and surface characterization showed agglomeration in solution and different surface oxide compositions compared to the nominal bulk content. The extent of released nickel was small and related to the nickel content of the surface oxides, which was largely different from the bulk content. This may explain the limited toxicity found despite the high Ni bulk content of several powders. Taken together, this study suggests relatively low acute toxicity of condensates/spatter particles formed during SLM-printing using IN939, HX, 18Ni300, 316L, and Ti6Al4V as original metal powders.

Genotoxicity evaluation of medical devices: A regulatory perspective

This review critically evaluates our current regulatory understanding of genotoxicity testing and risk assessment of medical devices. Genotoxicity risk assessment of these devices begins with the evaluation of materials of construction, manufacturing additives and all residual materials for potential to induce DNA damage. This is followed by extractable and/or leachable (E&L) studies to understand the worst case and/or clinical exposures, coupled with risk assessment of extractables or leachables. The TTC (Threshold of Toxicological Concern) approach is used to define acceptable levels of genotoxic chemicals, when identified. Where appropriate, in silico predictions may be used to evaluate the genotoxic potentials of identifiable chemicals with limited toxicological data and above the levels defined by TTC. Devices that could not be supported by E&L studies are evaluated by in vitro genotoxicity studies conducted in accordance with ISO10993-3 and 33. Certain endpoints such as 'site of contact genotoxicity' that are specific for certain classes of medical devices are currently not addressed in the current standards. The review also illustrates the potential uses of recent advances to achieve the goal of robust genotoxicity assessment of medical devices which are being increasingly used for health benefits. The review also highlights the gaps for genotoxicity risk assessment of medical devices and suggests possible approaches to address them taking into consideration the recent advances in genotoxicity testing including their potential uses in biocompatibility assessment.

Nickel nanoparticle-induced cell transformation: involvement of DNA damage and DNA repair defect through HIF-1α/miR-210/Rad52 pathway

Background

Nickel nanoparticles (Nano-Ni) are increasingly used in industry and biomedicine with the development of nanotechnology. However, the genotoxic and carcinogenic effects of Nano-Ni and the underlying mechanisms are still unclear.

Methods

At first, dose–response (0, 10, 20, and 30 μg/mL) and time-response (0, 3, 6, 12, and 24 h) studies were performed in immortalized normal human bronchial epithelial cells BEAS-2B to observe the effects of Nano-Ni on DNA damage response (DDR)-associated proteins and the HIF-1α/miR-210/Rad52 pathway by real-time PCR or Western blot. Then, a Hsp90 inhibitor (1 µM of 17-AAG, an indirect HIF-1α inhibitor), HIF-1α knock-out (KO) cells, and a miR-210 inhibitor (20 nM) were used to determine whether Nano-Ni-induced Rad52 down-regulation was through HIF-1α nuclear accumulation and miR-210 up-regulation. In the long-term experiments, cells were treated with 0.25 and 0.5 µg/mL of Nano-Ni for 21 cycles (~ 150 days), and the level of anchorage-independent growth was determined by plating the cells in soft agar. Transduction of lentiviral particles containing human Rad52 ORF into BEAS-2B cells was used to observe the role of Rad52 in Nano-Ni-induced cell transformation. Nano-Ni-induced DNA damage and dysregulation of HIF-1α/miR-210/Rad52 pathway were also investigated in vivo by intratracheal instillation of 50 µg per mouse of Nano-Ni. gpt delta transgenic mice were used to analyze mutant frequency and mutation spectrum in mouse lungs after Nano-Ni exposure.

Results

Nano-Ni exposure caused DNA damage at both in vitro and in vivo settings, which was reflected by increased phosphorylation of DDR-associated proteins such as ATM at Ser1981, p53 at Ser15, and H2AX. Nano-Ni exposure also induced HIF-1α nuclear accumulation, miR-210 up-regulation, and down-regulation of homologous recombination repair (HRR) gene Rad52. Inhibition of or knocking-out HIF-1α or miR-210 ameliorated Nano-Ni-induced Rad52 down-regulation. Long-term low-dose Nano-Ni exposure led to cell malignant transformation, and augmentation of Rad52 expression significantly reduced Nano-Ni-induced cell transformation. In addition, increased immunostaining of cell proliferation markers, Ki-67 and PCNA, was observed in bronchiolar epithelial cells and hyperplastic pneumocytes in mouse lungs at day 7 and day 42 after Nano-Ni exposure. Finally, using gpt delta transgenic mice revealed that Nano-Ni exposure did not cause increased gpt mutant frequency and certain DNA mutations, such as base substitution and small base insertions/deletions, are not the main types of Nano-Ni-induced DNA damage.

Conclusions

This study unraveled the mechanisms underlying Nano-Ni-induced cell malignant transformation; the combined effects of Nano-Ni-induced DNA damage and DNA repair defects through HIF-1α/miR-210/Rad52 pathway likely contribute to Nano-Ni-induced genomic instability and ultimately cell transformation. Our findings will provide information to further elucidate the molecular mechanisms of Nano-Ni-induced genotoxicity and carcinogenicity.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01117-7.

Recent advances in γH2AX biomarker-based genotoxicity assays: A marker of DNA damage and repair

The phosphorylation of histone variant H2AX and formation of γH2AX is a primary response to the DNA double-strand breaks (DSBs). Detection of γH2AX is a robust and sensitive tool for diagnosis of DNA damage and repair in pre-clinical drug discovery investigations. In addition, the replication stress also leads to the formation of γH2AX and cell death and so γH2AX can serve as a surrogate marker of drug-induced cytotoxicity. Recent advances in genomic research offer an opportunity to detect γH2AX as a specific biomarker for quantitative analysis of DNA damages and repair using high content screening technology and quantitative imaging analysis. The proposed approaches identify a wide range of genetic disorders and are applied in combination with other assays in drug discovery and also for the evaluation of the efficacy of various developmental drugs. In the current review, we provide recent insights into the potential of γH2AX biomarker as a powerful tool in genotoxicity analyses for the monitoring and managing of cancer diseases.

Adverse Outcome Pathway Development for Assessment of Lung Carcinogenicity by Nanoparticles

Lung cancer, one of the most common and deadly forms of cancer, is in some cases associated with exposure to certain types of particles. With the rise of nanotechnology, there is concern that some engineered nanoparticles may be among such particles. In the absence of epidemiological evidence, assessment of nanoparticle carcinogenicity is currently performed on a time-consuming case-by-case basis, relying mainly on animal experiments. Non-animal alternatives exist, including a few validated cell-based methods accepted for regulatory risk assessment of nanoparticles. Furthermore, new approach methodologies (NAMs), focused on carcinogenic mechanisms and capable of handling the increasing numbers of nanoparticles, have been developed. However, such alternative methods are mainly applied as weight-of-evidence linked to generally required animal data, since challenges remain regarding interpretation of the results. These challenges may be more easily overcome by the novel Adverse Outcome Pathway (AOP) framework, which provides a basis for validation and uptake of alternative mechanism-focused methods in risk assessment. Here, we propose an AOP for lung cancer induced by nanosized foreign matter, anchored to a selection of 18 standardized methods and NAMs for in silico- and in vitro-based integrated assessment of lung carcinogenicity. The potential for further refinement of the AOP and its components is discussed in relation to available nanosafety knowledge and data. Overall, this perspective provides a basis for development of AOP-aligned alternative methods-based integrated testing strategies for assessment of nanoparticle-induced lung cancer.

Review and Evaluation of the Potential Health Effects of Oxidic Nickel Nanoparticles

The exceptional physical and chemical properties of nickel nanomaterials have been exploited in a range of applications such as electrical conductors, batteries, and biomaterials. However, it has been suggested that these unique properties may allow for increased bioavailability, bio-reactivity, and potential adverse health effects. Thus, the purpose of this review was to critically evaluate data regarding the toxicity of oxidic nickel nanoparticles (nickel oxide (NiO) and nickel hydroxide (Ni(OH)2) nanoparticles) with respect to: (1) physico-chemistry properties; (2) nanomaterial characterization in the defined delivery media; (3) appropriateness of model system and translation to potential human effects; (4) biodistribution, retention, and clearance; (5) routes and relevance of exposure; and (6) current research data gaps and likely directions of future research. Inhalation studies were prioritized for review as this represents a potential exposure route in humans. Oxidic nickel particle size ranged from 5 to 100 nm in the 60 studies that were identified. Inflammatory responses induced by exposure of oxidic nickel nanoparticles via inhalation in rodent studies was characterized as acute in nature and only displayed chronic effects after relatively large (high concentration and long duration) exposures. Furthermore, there is no evidence, thus far, to suggest that the effects induced by oxidic nickel nanoparticles are related to preneoplastic events. There are some data to suggest that nano- and micron-sized NiO particles follow a similar dose response when normalized to surface area. However, future experiments need to be conducted to better characterize the exposure-dose-response relationship according to specific surface area and reactivity as a dose metric, which drives particle dissolution and potential biological responses.

Research progress on the carcinogenicity of metal nanomaterials

With the rapid development of nanotechnology, new nanomaterials with enormous potentials continue to emerge, especially metal nanomaterials. Metal nanomaterials possess the characteristics of metals and nanomaterials, so they are widely used in many fields. But at the same time, whether the use or release of metal nan4omaterials into the environment is toxic to human beings and animals has now attained widespread attention at home and abroad. Currently, it is an indisputable fact that cancer ranks among the top causes of death among residents worldwide. The properties of causing DNA damage and mutations possessed by these metal nanomaterials make them unpredictable influences in the body, subsequently leading to genotoxicity and carcinogenicity. Due to the increasing evidence of their roles in carcinogenicity, this article reviews the toxicological and carcinogenic effects of metal nanomaterials, including nano-metal elements (nickel nanoparticles, silver nanoparticles, and cobalt nanoparticles) and nano-metal oxides (titanium dioxide nanoparticles, silica nanoparticles, zinc oxide nanoparticles, and alumina nanoparticles). This article provides a reference for the researchers and policymakers to use metal nanomaterials rationally in modern industries and biomedicine.

Nickel carcinogenesis mechanism: cell cycle dysregulation

Nickel (Ni) is a widely distributed metal in the environment and an important pollutant due to its widespread industrial applications. Ni has various toxicity in humans and experimental animals, including carcinogenicity. However, the carcinogenic effects of Ni remain troublesome. Cell cycle dysregulation may be an important carcinogenic mechanism and is also a potential molecular mechanism for Ni complexes anti-cancerous effects. Therefore, we conducted a literature review to summarize the effects of Ni on cell cycle. Up to now, there were three different reports on Ni-induced cell cycle arrest: (i) Ni can induce cell cycle arrest in G0/G1 phase, phosphorylation and degradation of IkappaB kinase-alpha (IKKα)-dependent cyclin D1 and phosphoinositide-3-kinase (PI3K)/serine-threonine kinase (Akt) pathway-mediated down-regulation of expressions of cyclin-dependent kinases 4 (CDK4) play important role in it; (ii) Ni can induce cell cycle arrest in S phase, but the molecular mechanism is not known; (iii) G2/M phase is the target of Ni toxicity, and Ni compounds cause G2/M cell cycle phase arrest by reducing cyclinB1/Cdc2 interaction through the activation of the ataxia telangiectasia mutated (ATM)-p53-p21 and ATM-checkpoint kinase inhibitor 1 (Chk1)/Chk2-cell division cycle 25 (Cdc25) pathways. Revealing the mechanisms of cell cycle dysregulation associated with Ni exposure may help in the prevention and treatment of Ni-related carcinogenicity and toxicology.

DNA damage and ovarian ultrastructural lesions induced by nickel oxide nano-particles in Blaps polycresta (Coleoptera: Tenebrionidae)

Nickel oxide nanoparticles (NiO-NPs) have extensively used in industrial and consumer products. The present study conducted to gain more knowledge about the safe use of NiO-NPs and also to understand their impact on the environment and biological systems. Herein, we examined the genotoxic and ultra-structural effects of a sublethal dose of NiO-NPs (0.03 mg/g) on the ovarian tissues of the ground beetle, Blaps polycresta. The mean diameter of NiO-NPs was 24.49 ± 3.88 nm, as obtained through transmission electron microscopy (TEM). In terms of DNA damage levels, the frequency of micronucleus (MN) formation was highly significant in the NiO-NPs treated group versus the controls. Besides, NiO-NPs treatment resulted in a significant increase in the tail length of comets. Further, electron microscopy revealed a progressive increase in chromatin condensation of the ovarian nurse and follicular cells, in addition to the accumulation of lysosomes and endo-lysosomes in their cytoplasm. In conclusion, NiO-NPs are capable of gaining access to the ovary of B. polycresta and causing DNA damage and a high degree of cellular toxicity in the ovarian cells. The present study highlights, for the first time, the adverse effects of these NPs to female gonads of insects and raised the concern of its genotoxic potential. It would be of interest to investigate NiO-NPs mediated intracellular ROS generation in future studies.

Looking for the LOAEL or NOAEL Concentration of Nickel-Oxide Nanoparticles in a Long-Term Inhalation Exposure of Rats

Rats were exposed to nickel oxide nano-aerosol at a concentration of 2.4 ± 0.4 µg/m³ in a “nose only” inhalation setup for 4 h at a time, 5 times a week, during an overall period of 2 weeks to 6 months. Based on the majority of the effects assessed, this kind of exposure may be considered as close to LOAEL (lowest observed adverse effect level), or even to NOAEL (no observed adverse effect level). At the same time, the experiment revealed genotoxic and allergic effects as early as in the first weeks of exposure, suggesting that these effects may have no threshold at all.

miR-21 mediates nickel nanoparticle-induced pulmonary injury and fibrosis

We and other groups have demonstrated that exposure to nickel nanoparticles (Nano-Ni) results in severe and persistent lung inflammation and fibrosis, but the underlying mechanisms remain unclear. Here, we propose that miR-21 may play an important role in Nano-Ni-induced lung inflammation, injury, and fibrosis. Our dose- and time-response studies demonstrated that exposure of C57BL/6J (WT) mice to Nano-Ni resulted in upregulation of miR-21, proinflammatory cytokines, and profibrotic mediators. Histologically, exposure to Nano-Ni caused severe pulmonary inflammation and fibrosis. Based on the dose- and time-response studies, we chose a dose of 50 µg of Nano-Ni per mouse to compare the effects of Nano-Ni on WT with those on miR-21 KO mouse lungs. At day 3 post-exposure, Nano-Ni caused severe acute lung inflammation and injury that were reflected by increased neutrophil count, CXCL1/KC level, LDH activity, total protein concentration, MMP-2/9 protein levels and activities, and proinflammatory cytokines in the BALF or lung tissues from WT mice, which were confirmed histologically. Although Nano-Ni had similar effects on miR-21 KO mice, the above-mentioned levels were significantly lower than those in WT mice. Histologically, lungs from WT mice exposed to Nano-Ni had infiltration of a large number of polymorphonuclear (PMN) cells and macrophages in the alveolar space and interstitial tissues. However, exposure of miR-21 KO mice to Nano-Ni only caused mild acute lung inflammation and injury. At day 42 post-exposure, Nano-Ni caused extensive pulmonary fibrosis and chronic inflammation in the WT mouse lungs. However, exposure of miR-21 KO mice to Nano-Ni only caused mild lung fibrosis and chronic lung inflammation. Our results also showed that exposure to Nano-Ni caused upregulation of TGF-β1, phospho-Smad2, COL1A1, and COL3A1 in both WT and miR-21 KO mouse lungs. However, levels were significantly lower in miR-21 KO mice than in WT mice, except TGF-β1, which was similar in both kinds of mice. Decreased expression of Smad7 was observed in WT mouse lungs, but not in miR-21 KO mice. Our results demonstrated that knocking out miR-21 ameliorated Nano-Ni-induced pulmonary inflammation, injury, and fibrosis, suggesting the important role of miR-21 in Nano-Ni-induced pulmonary toxicity.

Immunotoxicity of nickel: Pathological and toxicological effects

Nickel (Ni) is a widely distributed metal in the environment and an important pollutant because of its many industrial applications. With increasing incidences of Ni contamination, Ni toxicity has become a global public health concern and recent evidence suggests that Ni adversely affects the immune system. Hence, this paper reviews the literature on immune-related effects of Ni exposure, the immunotoxicological effects of Ni, and the underlying mechanism of Ni immunotoxicity. The main focus was on the effect of Ni on the development of organs of immune system, lymphocyte subpopulations, cytokines, immunoglobulins, natural killer (NK) cells, and macrophages. Moreover, Ni toxicity also induces inflammation and several studies demonstrated that Ni could induce immunotoxicity. Excessive Ni exposure can inhibit the development of immune organs by excessively inducing apoptosis and inhibiting proliferation. Furthermore, Ni can decrease T and B lymphocytes, the specific mechanism of which requires further research. The effects of Ni on immunoglobulin A (IgA), IgG, and IgM remain unknown and while Ni inhibited IgA, IgG, and IgM levels in an animal experiment, the opposite result was found in research on humans. Ni inhibits the production of cytokines in non-inflammatory responses. Cytokine levels increased in Ni-induced inflammation responses, and Ni activates inflammation through toll like (TL)4-mediated nuclear factor-κB (NF-κB) and signal transduction cascades mitogen-activated protein kinase (MAPK) pathways. Ni has been indicated to inactivate NK cells and macrophages both in vitro and in vivo. Identifying the mechanisms underlying the Ni-induced immunotoxicity may help to explain the growing risk of infections and cancers in human populations that have been exposed to Ni for a long time. Such knowledge may also help to prevent and treat Ni-related carcinogenicity and toxicology.

Cytotoxic, Genotoxic, and Apoptotic Effects of Nickel Oxide Nanoparticles in Intestinal Epithelial Cells

Objectives

The superior properties of nickel oxide-nanoparticles (NiO-NPs) have led to their wide use in various fields. However, there is little comprehensive knowledge about their toxicity, especially after oral exposure. The toxic effect of NiO-NPs of mean size 15.0 nm was investigated in Caco-2 (human intestinal epithelial) cells as no study has been performed on their intestinal toxicity.

Materials and Methods

Following identification of their particle size distribution and cellular uptake potential, the risk of exposure to NiO-NPs was evaluated by cellular morphologic changes, cyto- and genotoxic potentials, oxidative damage, and apoptotic induction.

Results

NiO-NPs induced a 50% reduction in cell viability at 351.6 μg/mL and caused DNA damage and oxidative damage at 30-150 μg/mL. It appears that apoptosis might be a main cell death mechanism in NiO-NP-exposed intestinal cells.

Conclusion

NiO-NPs might be hazardous to the gastrointestinal system. The results should raise concerns about using NiO-NPs in food-contact appliances and about NiO-NP-containing wastes. Further in vivo and in vitro research should be conducted to explain the specific toxicity mechanism of these particles and reduce their risk to humans.

Toxicity of iron nanoparticles towards primary cultures of human bronchial epithelial cells

Air pollution is a public health issue and the toxicity of ambient particulate matter (PM) is well-recognized. Although it does not mostly contribute to the total mass of PM, increasing evidence indicates that the ultrafine fraction has generally a greater toxicity than the others do. A better knowledge of the underlying mechanisms involved in the pathological disorders related to nanoparticles (NPs) remains essential. Hence, the goal of this study was to determine better whether the exposure to a relatively low dose of well-characterized iron-rich NPs (Fe-NPs) might alter some critical toxicological endpoints in a relevant primary culture model of human bronchial epithelial cells (HBECs). We sought to use Fe-NPs representative of those frequently found in the industrial smokes of metallurgical industries. After having noticed the effective internalization of Fe-NPs, oxidative, inflammatory, DNA repair, and apoptotic endpoints were investigated within HBECs, mainly through transcriptional screening. Taken together, these results revealed that, despite it only produced relatively low levels of reactive oxygen species without any significant oxidative damage, low-dose Fe-NPs quickly significantly deregulated the transcription of some target genes closely involved in the proinflammatory response. Although this inflammatory process seemed to stay under control over time in case of this acute scenario of exposure, the future study of its evolution after a scenario of repeated exposure could be very interesting to evaluate the toxicity of Fe-NPs better.

Advance on toxicity of metal nickel nanoparticles

As a kind of conventional metal nanomaterial, nickel nanoparticles (Ni NPs) have broad application prospects in the fields of magnetism, energy technology and biomedicine and have quickly attracted great interest. The potential negative effects of Ni NPs have also attracted wide attention from some researchers. Studies have shown that Ni NPs cause a variety of toxic effects on cells, animals and humans and have toxic effects of multiple systems such as respiratory system, cardiovascular system and reproductive system. Ni NPs can lead to oxidative stress, apoptosis, DNA damage and inflammation and induce the increase of intracellular reactive oxygen species. The toxicity of Ni NPs is also found to be related to the mitogen-activated protein kinase pathway and the hypoxia inducible factor-1α pathway. Therefore, the toxicity and mechanism of Ni NPs are reviewed in this paper, and the future researches in this field are also proposed.

Similar polycyclic aromatic hydrocarbon and genotoxicity profiles of atmospheric particulate matter from cities on three different continents

The extractable organic material (EOM) from atmospheric total suspended particles (TSP) contains several organic compounds including non-substituted polycyclic aromatic hydrocarbons (PAHs), alkyl-PAHs, and nitro-PAHs. These chemicals seem to be among the key drivers of TSP genotoxicity. We have shown previously that the mutagenic potencies of the EOM from Limeira, Stockholm, and Kyoto, cities with markedly different meteorological conditions and pollution sources are similar. Here we compare the profiles of non-substituted PAHs (27 congeners), alkyl-PAHs (15 congeners), and nitro-PAHs (7 congeners) from the same EOM samples from these cities. We also compared the genotoxicity profiles using comet and micronucleus assays in human bronchial epithelial cells. The profiles of PAHs, as well as the cytotoxic and genotoxic potencies when expressed in EOM, were quite similar among the studied cities. It seems that despite the differences in meteorological conditions and pollution sources of the cities, removal, mixing, and different atmospheric transformation processes may be contributing to the similarity of the PAHs composition and genotoxicity profiles. More studies are required to verify if this would be a general rule applicable to other cities. Although these profiles were similar for all three cities, the EOM concentration in the atmospheres is markedly different. Thus, the population of Limeira (∼10-fold more EOM/m³ than Stockholm and ∼6-fold more than Kyoto) is exposed to higher concentrations of genotoxic pollutants, and Kyoto's population is 1.5-fold more exposed than Stockholm's. Therefore, to reduce the risk of human exposure to TSP genotoxins, the volume of emissions needs to be reduced.

The damage of the Watson-Crick base pairs by nickel nanoparticles: A first-principles molecular dynamics study

The nickel nanoparticles are harmful atmospheric pollutants, and the damage caused by them in humans has become a topic of great relevance. In this study we investigate the interaction of the Ni2 and Ni3 clusters with the AT and GC Watson-Crick base pairs in an aqueous medium. Molecular dynamics in combination with density functional theory are employed. A novel method is implemented to create realistic thermodynamic conditions (NVT) in the simulations. The energies, the charges of the interacting compounds, the temperature changes, and the geometric rearrangements are reported. The results show the formation of stable organometallic compounds of the nickel nanoparticles with the DNA nucleic acid bases. In this respect, the biological processes where the DNA is implicated may be altered by the formation of such super-structures.

Transcriptome Profiling and Toxicity Following Long-Term, Low Dose Exposure of Human Lung Cells to Ni and NiO Nanoparticles-Comparison with NiCl2

Production of nickel (Ni) and nickel oxide (NiO) nanoparticles (NPs) leads to a risk of exposure and subsequent health effects. Understanding the toxicological effects and underlying mechanisms using relevant in vitro methods is, therefore, needed. The aim of this study is to explore changes in gene expression using RNA sequencing following long term (six weeks) low dose (0.5 µg Ni/mL) exposure of human lung cells (BEAS-2B) to Ni and NiO NPs as well as soluble NiCl₂. Genotoxicity and cell transformation as well as cellular dose of Ni are also analyzed. Exposure to NiCl₂ resulted in the largest number of differentially expressed genes (197), despite limited uptake, suggesting a major role of extracellular receptors and downstream signaling. Gene expression changes for all Ni exposures included genes coding for calcium-binding proteins (S100A14 and S100A2) as well as TIMP3, CCND2, EPCAM, IL4R and DDIT4. Several top enriched pathways for NiCl₂ were defined by upregulation of, e.g., interleukin-1A and -1B, as well as Vascular Endothelial Growth Factor A (VEGFA). All Ni exposures caused DNA strand breaks (comet assay), whereas no induction of micronuclei was observed. Taken together, this study provides an insight into Ni-induced toxicity and mechanisms occurring at lower and more realistic exposure levels.

Effects of Titanium Dioxide Nanoparticles on the Hprt Gene Mutations in V79 Hamster Cells

The genotoxicity of anatase/rutile TiO₂ nanoparticles (TiO₂ NPs, NM105 at 3, 15 and 75 µg/cm²) was assessed with the mammalian in-vitro Hypoxanthine guanine phosphoribosyl transferase (Hprt) gene mutation test in Chinese hamster lung (V79) fibroblasts after 24 h exposure. Two dispersion procedures giving different size distribution and dispersion stability were used to investigate whether the effects of TiO₂ NPs depend on the state of agglomeration. TiO₂ NPs were fully characterised in the previous European FP7 projects NanoTEST and NanoREG2. Uptake of TiO₂ NPs was measured by transmission electron microscopy (TEM). TiO₂ NPs were found in cytoplasmic vesicles, as well as close to the nucleus. The internalisation of TiO₂ NPs did not depend on the state of agglomeration and dispersion used. The cytotoxicity of TiO₂ NPs was measured by determining both the relative growth activity (RGA) and the plating efficiency (PE). There were no substantial effects of exposure time (24, 48 and 72 h), although a tendency to lower RGA at longer exposure was observed. No significant difference in PE values and no increases in the Hprt gene mutant frequency were found in exposed relative to unexposed cultures in spite of evidence of uptake of NPs by cells.

ToxTracker Reporter Cell Lines as a Tool for Mechanism-Based (geno)Toxicity Screening of Nanoparticles-Metals, Oxides and Quantum Dots

The increased use of nanoparticles (NPs) requires efficient testing of their potential toxic effects. A promising approach is to use reporter cell lines to quickly assess the activation of cellular stress response pathways. This study aimed to use the ToxTracker reporter cell lines to investigate (geno)toxicity of various metal- or metal oxide NPs and draw general conclusions on NP-induced effects, in combination with our previous findings. The NPs tested in this study (n = 18) also included quantum dots (QDs) in different sizes. The results showed a large variation in cytotoxicity of the NPs tested. Furthermore, whereas many induced oxidative stress only few activated reporters related to DNA damage. NPs of manganese (Mn and Mn₃O₄) induced the most remarkable ToxTracker response with activation of reporters for oxidative stress, DNA damage, protein unfolding and p53-related stress. The QDs (CdTe) were highly toxic showing clearly size-dependent effects and calculations suggest surface area as the most relevant dose metric. Of all NPs investigated in this and previous studies the following induce the DNA damage reporter; CuO, Co, CoO, CdTe QDs, Mn, Mn₃O₄, V₂O₅, and welding NPs. We suggest that these NPs are of particular concern when considering genotoxicity induced by metal- and metal oxide NPs.

Gene (HPRT) and chromosomal (MN) mutations of nickel metal powder in V79 Chinese hamster cells

Nickel metal is a naturally occurring element used in many industrial and consumer applications. Human epidemiological data and animal cancer bioassays indicate that nickel metal is not likely to be a human carcinogen. Yet, nickel metal is classified as a suspected human carcinogen (CLP) and possibly carcinogenic to humans (IARC). There are no reliable studies on the potential for nickel metal to induce gene and micronucleus (MN) mutations. To fill these datagaps and increase our understanding of the mechanisms underlying the lack of nickel metal carcinogenicity, gene and micronucleus mutation studies were conducted with nickel metal powder (N36F) in V79 Chinese Hamster cells following OECD 476 and 487 guidelines, respectively, under GLP. Gene mutation at the hprt locus was tested, with and without metabolic activation, after 4-h treatment with 0.05-2.5 mM nickel metal powder. Cytokinesis-block MN frequency following exposure to 0.25-1.5 mM nickel metal was tested after 4-h treatment, with and without metabolic activation, followed by a 24-h treatment without metabolic activation. In the gene mutation assay, there were modest increases in hprt mutants observed at some test concentrations, not exceeding 2.2-fold, which were either within the historical control values and/or showed no concentration-response trend. The positive controls showed increases of at least 7-fold. Likewise, no increases in the MN frequency exceeding 1.5-fold were observed with nickel metal, with no concentration-response trends. Taking these results together, it can be concluded that nickel metal is non-mutagenic and does not cause gene nor chromosomal mutations.

Nickel Carcinogenesis Mechanism: DNA Damage

Nickel (Ni) is known to be a major carcinogenic heavy metal. Occupational and environmental exposure to Ni has been implicated in human lung and nasal cancers. Currently, the molecular mechanisms of Ni carcinogenicity remain unclear, but studies have shown that Ni-caused DNA damage is an important carcinogenic mechanism. Therefore, we conducted a literature search of DNA damage associated with Ni exposure and summarized known Ni-caused DNA damage effects. In vitro and vivo studies demonstrated that Ni can induce DNA damage through direct DNA binding and reactive oxygen species (ROS) stimulation. Ni can also repress the DNA damage repair systems, including direct reversal, nucleotide repair (NER), base excision repair (BER), mismatch repair (MMR), homologous-recombination repair (HR), and nonhomologous end-joining (NHEJ) repair pathways. The repression of DNA repair is through direct enzyme inhibition and the downregulation of DNA repair molecule expression. Up to now, the exact mechanisms of DNA damage caused by Ni and Ni compounds remain unclear. Revealing the mechanisms of DNA damage from Ni exposure may contribute to the development of preventive strategies in Ni carcinogenicity.

Redox interactions and genotoxicity of metal-based nanoparticles: A comprehensive review

Nanotechnology is a growing science that may provide several new applications for medicine, food preservation, diagnostic technologies, and sanitation. Despite its beneficial applications, there are several questions related to the safety of nanomaterials for human use. The development of nanotechnology is associated with some concerns because of the increased risk of carcinogenesis following exposure to nanomaterials. The increased levels of reactive oxygen species (ROS) that are due to exposure to nanoparticles (NPs) are primarily responsible for the genotoxicity of metal NPs. Not all, but most metal NPs are able to directly produce free radicals through the release of metal ions and through interactions with water molecules. Furthermore, the increased production of free radicals and the cell death caused by metal NPs can stimulate reduction/oxidation (redox) reactions, leading to the continuous endogenous production of ROS in a positive feedback loop. The overexpression of inflammatory mediators, such as NF-kB and STATs, the mitochondrial malfunction and the increased intracellular calcium levels mediate the chronic oxidative stress that occurs after exposure to metal NPs. In this paper, we review the genotoxicity of different types of metal NPs and the redox mechanisms that amplify the toxicity of these NPs.

High variability in toxicity of welding fume nanoparticles from stainless steel in lung cells and reporter cell lines: the role of particle reactivity and solubility

Millions of people in the world perform welding as their primary occupation resulting in exposure to metal-containing nanoparticles in the fumes generated. Even though health effects including airway diseases are well-known, there is currently a lack of studies investigating how different welding set-ups and conditions affect the toxicity of generated nanoparticles of the welding fume. The aim of this study was to investigate the toxicity of nine types of welding fume particles generated via active gas shielded metal arc welding (GMAW) of chromium-containing stainless steel under different conditions and, furthermore, to correlate the toxicity to the particle characteristics. Toxicological endpoints investigated were generation of reactive oxygen species (ROS), cytotoxicity, genotoxicity and activation of ToxTracker reporter cell lines. The results clearly underline that the choice of filler material has a large influence on the toxic potential. Fume particles generated by welding with the tested flux-cored wire (FCW) were found to be more cytotoxic compared to particles generated by welding with solid wire or metal-cored wire (MCW). FCW fume particles were also the most potent in causing ROS and DNA damage and they furthermore activated reporters related to DNA double- strand breaks and p53 signaling. Interestingly, the FCW fume particles were the most soluble in PBS, releasing more chromium in the hexavalent form and manganese compared to the other fumes. These results emphasize the importance of solubility of different metal constituents of the fume particles, rather than the total metal content, for their acute toxic potential.

Inflammation and (secondary) genotoxicity of Ni and NiO nanoparticles

Nanoparticle-induced genotoxicity can arise through different mechanisms, and generally, primary and secondary genotoxicity can be distinguished where the secondary is driven by an inflammatory response. It is, however, yet unclear how a secondary genotoxicity can be detected using in vitro methods. The aim of this study was to investigate inflammation and genotoxicity caused by agglomerated nickel (Ni) and nickel oxide (NiO) nanoparticles and, furthermore, to explore the possibility to test secondary (inflammation-driven) genotoxicity in vitro. As a benchmark particle to compare with, we used crystalline silica (quartz). A proteome profiler antibody array was used to screen for changes in release of 105 different cytokines and the results showed an increased secretion of various cytokines including vascular endothelial growth factor (VEGF) following exposure of macrophages (differentiated THP-1 cells). Both Ni and NiO caused DNA damage (comet assay) following exposure of human bronchial epithelial cells (HBEC) and interestingly conditioned media (CM) from exposed macrophages also resulted in DNA damage (2- and 3-fold increase for Ni and NiO, respectively). Similar results were also found when using a co-culture system of macrophages and epithelial cells. In conclusion, this study shows that it is possible to detect a secondary genotoxicity in lung epithelial cells by using in vitro methods based on conditioned media or co-cultures. Further investigation is needed in order to find out what factors that are causing this secondary genotoxicity and whether such effects are caused by numerous nanoparticles.

Concise Review of Nickel Human Health Toxicology and Ecotoxicology

Nickel (Ni) metal and Ni compounds are widely used in applications like stainless steel, alloys, and batteries. Nickel is a naturally occurring element in water, soil, air, and living organisms, and is essential to microorganisms and plants. Thus, human and environmental nickel exposures are ubiquitous. Production and use of nickel and its compounds can, however, result in additional exposures to humans and the environment. Notable human health toxicity effects identified from human and/or animal studies include respiratory cancer, non-cancer toxicity effects following inhalation, dermatitis, and reproductive effects. These effects have thresholds, with indirect genotoxic and epigenetic events underlying the threshold mode of action for nickel carcinogenicity. Differences in human toxicity potencies/potentials of different nickel chemical forms are correlated with the bioavailability of the Ni2+ ion at target sites. Likewise, Ni2+ has been demonstrated to be the toxic chemical species in the environment, and models have been developed that account for the influence of abiotic factors on the bioavailability and toxicity of Ni2+ in different habitats. Emerging issues regarding the toxicity of nickel nanoforms and metal mixtures are briefly discussed. This review is unique in its covering of both human and environmental nickel toxicity data.

The mechanism-based toxicity screening of particles with use in the food and nutrition sector via the ToxTracker reporter system

The rapid expansion of the incorporation of nano-sized materials in consumer products overlaps with the necessity for high-throughput reliable screening tools for the identification of the potential hazardous properties of the nanomaterials. The ToxTracker assay (mechanism-based reporter assay based on embryonic stem cells that uses GFP-tagged biomarkers for detection of DNA damage, oxidative stress and general cellular stress) is one such tool, which could prove useful in the field of particle toxicology allowing for high throughput screening. Here, ToxTracker was utilised to evaluate the potential hazardous properties of two particulates currently used in the food industry (vegetable carbon (E153) and food-grade TiO₂ (E171)). Due to the fact that ToxTracker is based on a stem cell format, it is crucial that the data generated is assessed for its suitability and comparability to more conventionally used relevant source of cells - in this case cells from the gastrointestinal tract and the liver. Therefore, the cell reporter findings were compared to data from traditional assays (cytotoxicity, anti-oxidant depletion and DNA damage) and tissue relevant cell types. The data showed E171 to be the most cytotoxic, decreased intracellular glutathione and the most significant with regards to genotoxic effects. The ToxTracker data showed comparability to conventional toxicity and oxidative stress assays; however, some discrepancies were evident between the findings from ToxTracker and the comet assay.

In vitro toxicity assessment of zinc and nickel ferrite nanoparticles in human erythrocytes and peripheral blood mononuclear cell

Ferrite nanoparticles (NPs) have gained attention in biomedicine due to their many potential applications, such as targeted drug delivery, their use as contrast agents for magnetic resonance imaging and oncological treatments. The information about the risk effects of ferrite NPs in human blood cells is, however, scarce. To assess their potential toxicity, in vitro studies were carried out with magnetite and zinc, nickel and nickel‑zinc ferrites NPs at different concentrations (50, 100 and 200 μg·ml^-1). The toxicity of the ferrite NPs was evaluated in humans by determining red blood hemolysis, by measuring the content of total proteins, and by assaying catalase and glutathione-S-transferase activities. Our results show that nickel‑zinc ferrite lead to hemolysis, and that magnetite, zinc and nickel‑zinc ferrites increase glutathione-S-transferase activity. No significant changes in human peripheral blood mononuclear cells viability were observed after the treatment with the four different ferrite NPs in vitro.

High-throughput transcriptomics: Insights into the pathways involved in (nano) nickel toxicity in a key invertebrate test species

Nickel nanoparticles (NiNPs) have an estimated production of ca. 20 tons per year in the US. Nickel has been risk-assessed for long in Europe, but not NiNPs, hence the concern for the environment. In the present study, we focused on investigating the mechanisms of toxicity of NiNPs and the comparison to NiNO₃. The high-throughput microarray for the soil ecotox model Enchytraeus crypticus (Oligochaeta) was used. To anchor gene to phenotype effect level, organisms were exposed to reproduction effect concentrations EC20 and EC50, for 3 and 7 days. Results showed commonly affected pathways between NiNPs and NiNO₃, including increase in proteolysis, apoptosis and inflammatory response, and interference with the nervous system. Mechanisms unique to NiNO₃ were also observed (e.g. glutathione synthesis). No specific mechanisms for NiNPs were found, which could indicate that longer exposure period (>7 days) is required to capture the peak response to NiNPs. A mechanisms scheme is assembled, showing both common and unique mechanisms to NiNO₃ and NiNPs, providing an important framework for further, more targeted, studies.

Comparative mouse lung injury by nickel nanoparticles with differential surface modification

BACKGROUND

Previous studies have demonstrated that exposure to nickel nanoparticles (Nano-Ni) causes oxidative stress and severe, persistent lung inflammation, which are strongly associated with pulmonary toxicity. However, few studies have investigated whether surface modification of Nano-Ni could alter Nano-Ni-induced lung injury, inflammation, and fibrosis in vivo. Here, we propose that alteration of physicochemical properties of Nano-Ni through modification of Nano-Ni surface may change Nano-Ni-induced lung injury, inflammation, and fibrosis.

METHODS

At first, dose-response and time-response studies were performed to observe lung inflammation and injury caused by Nano-Ni. In the dose-response studies, mice were intratracheally instilled with 0, 10, 20, 50, and 100 μg per mouse of Nano-Ni and sacrificed at day 3 post-exposure. In the time-response studies, mice were intratracheally instilled with 50 µg per mouse of Nano-Ni and sacrificed at days 1, 3, 7, 14, 28, and 42 post-instillation. At the end of the experiment, mice were bronchoalveolar lavaged (BAL) and the neutrophil count, CXCL1/KC level, LDH activity, and concentration of total protein in the BAL fluid (BALF) were determined. In the comparative studies, mice were intratracheally instilled with 50 μg per mouse of Nano-Ni or with the same molar concentration of Ni as Nano-Ni of either partially [O]-passivated Nano-Ni (Nano-Ni-P) or carbon-coated Nano-Ni (Nano-Ni-C). At day 3 post-exposure, BAL was performed and the above cellular and biochemical parameters in the BALF were analyzed. The MMP-2/9 protein levels and activities in the BALF and mouse lung tissues were also determined. Mouse lung tissues were also collected for H&E staining, and measurement of thiobarbituric acid reactive substances (TBARS) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) in the genomic DNA. At day 42 post-exposure, mouse right lung tissues were collected for H&E and Trichrome stainings, and left lung tissues were collected to determine the hydroxyproline content.

RESULTS

Exposure of mice to Nano-Ni resulted in a dose-response increase in acute lung inflammation and injury reflected by increased neutrophil count, CXCL1/KC level, LDH activity, and concentration of total protein in the BALF. The time-response study showed that Nano-Ni-induced acute lung inflammation and injury appeared as early as day 1, peaked at day 3, and attenuated at day 7 post-instillation. Although the neutrophil count, CXCL1/KC level, LDH activity, and concentration of total protein in the BALF dramatically decreased over the time, their levels were still higher than those of the controls even at day 42 post-exposure. Based on the results of the dose- and time-response studies, we chose a dose of 50 µg per mouse of Nano-Ni, and day 3 post-exposure as short-term and day 42 post-exposure as long-term to compare the effects of Nano-Ni, Nano-Ni-P, and Nano-Ni-C on mouse lungs. At day 3 post-exposure, 50 μg per mouse of Nano-Ni caused acute lung inflammation and injury that were reflected by increased neutrophil count, CXCL1/KC level, LDH activity, concentration of total protein, and MMP-2/9 protein levels and activities in the BALF. Nano-Ni exposure also caused increased MMP-2/9 activities in the mouse lung tissues. Histologically, infiltration of large numbers of neutrophils and macrophages in the alveolar space and interstitial tissues was observed in mouse lungs exposed to Nano-Ni. Nano-Ni-P exposure caused similar acute lung inflammation and injury as Nano-Ni. However, exposure to Nano-Ni-C only caused mild acute lung inflammation and injury. At day 42 post-exposure, Nano-Ni caused extensive interstitial fibrosis and proliferation of interstitial cells with inflammatory cells infiltrating the alveolar septa and alveolar space. Lung fibrosis was also observed in Nano-Ni-P-exposed lungs, but to a much lesser degree. Only slight or no lung fibrosis was observed in Nano-Ni-C-exposed lungs. Nano-Ni and Nano-Ni-P, but not Nano-Ni-C, caused significantly elevated levels of TBARS in mouse lung tissues and 8-OHdG in mouse lung tissue genomic DNA, suggesting that Nano-Ni and Nano-Ni-P induce lipid peroxidation and oxidative DNA damage in mouse lung tissues, while Nano-Ni-C does not.

CONCLUSION

Our results demonstrate that short-term Nano-Ni exposure causes acute lung inflammation and injury, while long-term Nano-Ni exposure causes chronic lung inflammation and fibrosis. Surface modification of Nano-Ni alleviates Nano-Ni-induced pulmonary effects; partially passivated Nano-Ni causes similar effects as Nano-Ni, but the chronic inflammation and fibrosis were at a much lesser degree. Carbon coating significantly alleviates Nano-Ni-induced acute and chronic lung inflammation and injury.

Determination of Phosphorylated Histone H2AX in Nanoparticle-Induced Genotoxic Studies

DNA double-strand breaks (DSBs), one of the most severe lesions of DNA damage triggered by various genotoxic insults, can lead to chromosome change, genomic instability, and even tumorigenesis if not repaired efficiently. In response to DNA damage, histone H2AX molecules are rapidly phosphorylated at serine 139 near the site of DNA DSBs and form γ-H2AX foci. As an early important cellular event linked to DNA damage and repair, γ-H2AX is a highly sensitive biomarker for "monitoring" DNA damage and consequently is a useful tool in genetic toxicology screen. We and other researchers have used γ-H2AX as a marker to assess the potential genotoxic effects of some nanoparticles in vitro and in vivo. In this chapter, we describe several useful methods for γ-H2AX detection, which can be used to evaluate the potential genotoxic effects of nanoparticles.

Calcium-dependent cyto- and genotoxicity of nickel metal and nickel oxide nanoparticles in human lung cells

Background

Genotoxicity is an important toxicological endpoint due to the link to diseases such as cancer. Therefore, an increased understanding regarding genotoxicity and underlying mechanisms is needed for assessing the risk with exposure to nanoparticles (NPs). The aim of this study was to perform an in-depth investigation regarding the genotoxicity of well-characterized Ni and NiO NPs in human bronchial epithelial BEAS-2B cells and to discern possible mechanisms. Comparisons were made with NiCl₂ in order to elucidate effects of ionic Ni.

Methods

BEAS-2B cells were exposed to Ni and NiO NPs, as well as NiCl₂, and uptake and cellular dose were investigated by transmission electron microscopy (TEM) and inductively coupled plasma mass spectrometry (ICP-MS). The NPs were characterized in terms of surface composition (X-ray photoelectron spectroscopy), agglomeration (photon cross correlation spectroscopy) and nickel release in cell medium (ICP-MS). Cell death (necrosis/apoptosis) was investigated by Annexin V-FITC/PI staining and genotoxicity by cytokinesis-block micronucleus (cytome) assay (OECD 487), chromosomal aberration (OECD 473) and comet assay. The involvement of intracellular reactive oxygen species (ROS) and calcium was explored using the fluorescent probes, DCFH-DA and Fluo-4.

Results

NPs were efficiently taken up by the BEAS-2B cells. In contrast, no or minor uptake was observed for ionic Ni from NiCl₂. Despite differences in uptake, all exposures (NiO, Ni NPs and NiCl₂) caused chromosomal damage. Furthermore, NiO NPs were most potent in causing DNA strand breaks and generating intracellular ROS. An increase in intracellular calcium was observed and modulation of intracellular calcium by using inhibitors and chelators clearly prevented the chromosomal damage. Chelation of iron also protected against induced damage, particularly for NiO and NiCl₂.

Conclusions

This study has revealed chromosomal damage by Ni and NiO NPs as well as Ni ionic species and provides novel evidence for a calcium-dependent mechanism of cyto- and genotoxicity.

Electronic supplementary material

The online version of this article (10.1186/s12989-018-0268-y) contains supplementary material, which is available to authorized users.