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

Bridging the gap: Innovative human-based in vitro approaches for nanomaterials hazard assessment and their role in safe and sustainable by design, risk assessment, and life cycle assessment

The application of nanomaterials in industry and consumer products is growing exponentially, which has pressed the development and use of predictive human in vitro models in pre-clinical analysis to closely extrapolate potential toxic effects in vivo. The conventional cytotoxicity investigation of nanomaterials using cell lines from cancer origin and culturing them two-dimensionally in a monolayer without mimicking the proper pathophysiological microenvironment may affect a precise prediction of in vitro effects at in vivo level. In recent years, complex in vitro models (also belonging to the new approach methodologies, NAMs) have been established in unicellular to multicellular cultures either by using cell lines, primary cells or induced pluripotent stem cells (iPSCs), and reconstituted into relevant biological dimensions mimicking in vivo conditions. These advanced in vitro models retain physiologically reliant exposure scenarios particularly appropriate for oral, dermal, respiratory, and intravenous administration of nanomaterials, which have the potential to improve the in vivo predictability and lead to reliable outcomes. In this perspective, we discuss recent developments and breakthroughs in using advanced human in vitro models for hazard assessment of nanomaterials. We identified fit-for-purpose requirements and remaining challenges for the successful implementation of in vitro data into nanomaterials Safe and Sustainable by Design (SSbD), Risk Assessment (RA), and Life Cycle Assessment (LCA). By addressing the gap between in vitro data generation and the utility of in vitro data for nanomaterial safety assessments, a prerequisite for SSbD approaches, we outlined potential key areas for future development.

Manganese dioxide nanoparticles provoke inflammatory damage in BV2 microglial cells via increasing reactive oxygen species to activate the p38 MAPK pathway

With the widespread use of manganese dioxide nanoparticles (nano MnO2), health hazards have also emerged. The inflammatory damage of brain tissues could result from nano MnO2, in which the underlying mechanism is still unclear. During this study, we aimed to investigate the role of ROS-mediated p38 MAPK pathway in nano MnO2-induced inflammatory response in BV2 microglial cells. The inflammatory injury model was established by treating BV2 cells with 2.5, 5.0, and 10.0 μg/mL nano MnO2 suspensions for 12 h. Then, the reactive oxygen species (ROS) scavenger (20 nM N-acetylcysteine, NAC) and the p38 MAPK pathway inhibitor (10 μM SB203580) were used to clarify the role of ROS and the p38 MAPK pathway in nano MnO2-induced inflammatory lesions in BV2 cells. The results indicated that nano MnO2 enhanced the expression of pro-inflammatory cytokines IL-1β and TNF-α, elevated intracellular ROS levels and activated the p38 MAPK pathway in BV2 cells. Controlling intracellular ROS levels with NAC inhibited p38 MAPK pathway activation and attenuated the inflammatory response induced by nano MnO2. Furthermore, inhibition of the p38 MAPK pathway with SB203580 led to a decrease in the production of inflammatory factors (IL-1β and TNF-α) in BV2 cells. In summary, nano MnO2 can induce inflammatory damage by increasing intracellular ROS levels and further activating the p38 MAPK pathway in BV2 microglial cells.

Unravelling the Mechanistic Understanding of Metal Nanoparticle-Induced Reactive Oxygen Species Formation: Insights from a Cu Nanoparticle Study

Humans can be exposed to engineered and nonintentionally formed metal and metal oxide nanoparticles (Me NPs) in occupational settings, in public transportation areas, or by means of contact with different consumer products. A critical factor in the toxic potency of Me NPs is their ability to induce oxidative stress. It is thus essential to assess the potential reactive oxygen species (ROS) formation properties of Me NPs. A common way to assess the relative extent of ROS formation in vitro is to use fluorescence spectroscopy with the DCFH-DA (2',7'-dichlorofluorescein diacetate) probe, with and without HRP (horseradish peroxidase). However, this method does not provide any information about specific ROS species or reaction mechanisms. This study investigated the possibility of using complementary techniques to obtain more specific information about formed ROS species, both the type and reaction mechanisms. Cu NPs in PBS (phosphate buffered saline) were chosen as a test system to have the simplest (least interference from other components) aqueous solution with a physiologically relevant pH. ROS formation was assessed using fluorescence by means of the DCFH-DA method (information on relative amounts of oxygen radicals without selectivity), the Ghormley's triiodide method using UV-vis spectrophotometry (concentrations of H2O2), and electron paramagnetic resonance with DMPO as the spin-trap agent (information on specific oxygen radicals). This approach elucidates that Cu NPs undergo ROS-generating corrosion reactions, which previously have not been assessed in situ. In the presence of H2O2, and based on the type of oxygen radical formed, it was concluded that released copper participates in Haber-Weiss and/or Fenton reactions rather than in Fenton-like reactions. The new combination of techniques used to determine ROS induced by Me NPs provides a way forward to gain a mechanistic understanding of Me NP-induced ROS formation, which is important for gaining crucial insight into their ability to induce oxidative stress.

An update on the biological effects of quantum dots: From environmental fate to risk assessment based on multiple biological models

Quantum dots (QDs) are zero-dimension nanomaterials with excellent physical and chemical properties, which have been widely used in environmental science and biomedicine. Therefore, QDs are potential to cause toxicity to the environment and enter organisms through migration and bioenrichment effects. This review aims to provide a comprehensive and systematic analysis on the adverse effects of QDs in different organisms based on recently available data. Following PRISMA guidelines, this study searched PubMed database according to the pre-set keywords, and included 206 studies according to the inclusion and elimination criteria. CiteSpace software was firstly used to analyze the keywords of included literatures, search for breaking points of former studies, and summarize the classification, characterization and dosage of QDs. The environment fate of QDs in the ecosystems were then analyzed, followed with comprehensively summarized toxicity outcomes at individual, system, cell, subcellular and molecular levels. After migration and degradation in the environment, aquatic plants, bacteria, fungi as well as invertebrates and vertebrates have been found to be suffered from toxic effects caused by QDs. Aside from systemic effects, toxicity of intrinsic QDs targeting to specific organs, including respiratory system, cardiovascular system, hepatorenal system, nervous system and immune system were confirmed in multiple animal models. Moreover, QDs could be taken up by cells and disturb the organelles, which resulted in cellular inflammation and cell death, including autophagy, apoptosis, necrosis, pyroptosis and ferroptosis. Recently, several innovative technologies, like organoids have been applied in the risk assessment of QDs to promote the surgical interventions of preventing QDs' toxicity. This review not only aimed at updating the research progress on the biological effects of QDs from environmental fate to risk assessment, but also overcame the limitations of available reviews on basic toxicity of nanomaterials by interdisciplinarity and provided new insights for better applications of QDs.

A Novel Nanosafety Approach Using Cell Painting, Metabolomics, and Lipidomics Captures the Cellular and Molecular Phenotypes Induced by the Unintentionally Formed Metal-Based (Nano)Particles

Additive manufacturing (AM) or industrial 3D printing uses cutting-edge technologies and materials to produce a variety of complex products. However, the effects of the unintentionally emitted AM (nano)particles (AMPs) on human cells following inhalation, require further investigations. The physicochemical characterization of the AMPs, extracted from the filter of a Laser Powder Bed Fusion (L-PBF) 3D printer of iron-based materials, disclosed their complexity, in terms of size, shape, and chemistry. Cell Painting, a high-content screening (HCS) assay, was used to detect the subtle morphological changes elicited by the AMPs at the single cell resolution. The profiling of the cell morphological phenotypes, disclosed prominent concentration-dependent effects on the cytoskeleton, mitochondria, and the membranous structures of the cell. Furthermore, lipidomics confirmed that the AMPs induced the extensive membrane remodeling in the lung epithelial and macrophage co-culture cell model. To further elucidate the biological mechanisms of action, the targeted metabolomics unveiled several inflammation-related metabolites regulating the cell response to the AMP exposure. Overall, the AMP exposure led to the internalization, oxidative stress, cytoskeleton disruption, mitochondrial activation, membrane remodeling, and metabolic reprogramming of the lung epithelial cells and macrophages. We propose the approach of integrating Cell Painting with metabolomics and lipidomics, as an advanced nanosafety methodology, increasing the ability to capture the cellular and molecular phenotypes and the relevant biological mechanisms to the (nano)particle exposure.

High-throughput screening paradigms in ecotoxicity testing: Emerging prospects and ongoing challenges

The rapidly increasing number of new production chemicals coupled with stringent implementation of global chemical management programs necessities a paradigm shift towards boarder uses of low-cost and high-throughput ecotoxicity testing strategies as well as deeper understanding of cellular and sub-cellular mechanisms of ecotoxicity that can be used in effective risk assessment. The latter will require automated acquisition of biological data, new capabilities for big data analysis as well as computational simulations capable of translating new data into in vivo relevance. However, very few efforts have been so far devoted into the development of automated bioanalytical systems in ecotoxicology. This is in stark contrast to standardized and high-throughput chemical screening and prioritization routines found in modern drug discovery pipelines. As a result, the high-throughput and high-content data acquisition in ecotoxicology is still in its infancy with limited examples focused on cell-free and cell-based assays. In this work we outline recent developments and emerging prospects of high-throughput bioanalytical approaches in ecotoxicology that reach beyond in vitro biotests. We discuss future importance of automated quantitative data acquisition for cell-free, cell-based as well as developments in phytotoxicity and in vivo biotests utilizing small aquatic model organisms. We also discuss recent innovations such as organs-on-a-chip technologies and existing challenges for emerging high-throughput ecotoxicity testing strategies. Lastly, we provide seminal examples of the small number of successful high-throughput implementations that have been employed in prioritization of chemicals and accelerated environmental risk assessment.

Evaluation of behavioural, chemical, toxicological and clinical studies of a tobacco heated product glo™ and the potential for bridging from a foundational dataset to new product iterations

Background

Tobacco Heating Products (THPs) are tobacco products that heat rather than burn tobacco with temperatures less than 350 °C. Because of this operating principle, they produce substantially fewer and lower levels of tobacco smoke toxicants than combustible cigarette smoke produced when tobacco is burnt, which occurs at much higher temperatures of around 900 °C. This paper analyses data on a THP, glo™, and assesses whether its use would result in reduced health risks compared to the health risks of smoking cigarettes. It also looks at the possibility of bridging datasets across the different variants of the glo™ product.

Methods

The approach is to consider whether datasets from behavioural, chemical, toxicological and clinical studies provide consistent findings of reductions in toxicant exposure with glo™ use by subjects who switch completely from smoking cigarettes to using glo™ and whether these reductions are similar to those who stop smoking cigarettes without switching to glo™ or any other tobacco or nicotine product. We also examine the similarities and differences of different versions of the glo™ product and benchmark it against a THP from another manufacturer.

Results

The studies indicate that the use of the glo™ results in substantial and prolonged reductions in toxicant exposure for smokers who switch to glo™ completely. A long-term clinical study shows substantial reductions in toxicant exposure over a period of time, similar to reduction of some biomarkers of exposure found following smoking cessation without switching to glo™ or any other tobacco product, and biomarkers of potential harm trending in a favourable manner for both groups that switch to glo™ and that quit all tobacco and nicotine use. Data suggests that all iterations of glo™ result in substantial reductions in toxicant exposure compared to smoking cigarettes and that bridging across datasets is feasible.

Conclusions

Given the accumulated scientific data summarised in this paper, and particularly the findings from a long-term clinical study, the data demonstrate that glo™ is a reduced exposure product compared to combustible cigarettes and is reasonably deemed to reduce the risk of smoking-related diseases and supports the conclusion that smokers who would have otherwise continued to smoke and instead switch entirely to THP glo™ use, will reduce their relative risk of developing smoking-related diseases as compared to continued smoking. The extent of reduction in risk compared to continuing to smoke is likely to vary by smoking-related disease and by an individuals' smoking history, other risk factors and an individual's susceptibility to disease. Use of the THP will present some level of increased health risk as compared to cessation of tobacco and nicotine products and will cause dependence. As long as the principles of heat-not-burn are maintained, THP use will result in substantially reduced exposure to smoke toxicants as compared to continued conventional cigarette smoking. It is possible to use bridging or read across to apply these conclusions to new iterations of the glo™ product, extending the utility and validity of the evidence generated through study of prior iterations.

Reactive Oxygen Species Formed by Metal and Metal Oxide Nanoparticles in Physiological Media—A Review of Reactions of Importance to Nanotoxicity and Proposal for Categorization

Diffusely dispersed metal and metal oxide nanoparticles (NPs) can adversely affect living organisms through various mechanisms and exposure routes. One mechanism behind their toxic potency is their ability to generate reactive oxygen species (ROS) directly or indirectly to an extent that depends on the dose, metal speciation, and exposure route. This review provides an overview of the mechanisms of ROS formation associated with metal and metal oxide NPs and proposes a possible way forward for their future categorization. Metal and metal oxide NPs can form ROS via processes related to corrosion, photochemistry, and surface defects, as well as via Fenton, Fenton-like, and Haber–Weiss reactions. Regular ligands such as biomolecules can interact with metallic NP surfaces and influence their properties and thus their capabilities of generating ROS by changing characteristics such as surface charge, surface composition, dissolution behavior, and colloidal stability. Interactions between metallic NPs and cells and their organelles can indirectly induce ROS formation via different biological responses. H₂O₂ can also be generated by a cell due to inflammation, induced by interactions with metallic NPs or released metal species that can initiate Fenton(-like) and Haber–Weiss reactions forming various radicals. This review discusses these different pathways and, in addition, nano-specific aspects such as shifts in the band gaps of metal oxides and how these shifts at biologically relevant energies (similar to activation energies of biological reactions) can be linked to ROS production and indicate which radical species forms. The influences of kinetic aspects, interactions with biomolecules, solution chemistry (e.g., Cl⁻ and pH), and NP characteristics (e.g., size and surface defects) on ROS mechanisms and formation are discussed. Categorization via four tiers is suggested as a way forward to group metal and metal oxide NPs based on the ROS reaction pathways that they may undergo, an approach that does not include kinetics or environmental variations. The criteria for the four tiers are based on the ability of the metallic NPs to induce Fenton(-like) and Haber–Weiss reactions, corrode, and interact with biomolecules and their surface catalytic properties. The importance of considering kinetic data to improve the proposed categorization is highlighted.

Influence of natural organic matter on the transformation of metal and metal oxide nanoparticles and their ecotoxic potency in vitro

Increased use and production of engineered nanoparticles (NPs) lead to an elevated risk of their diffuse dispersion into the aquatic environment and increased concern on unknown effects induced by their release into the aquatic ecosystem. An improved understanding of the environmental transformation processes of NPs of various surface characteristics is hence imperative for risk assessment and management. This study presents results on effects of natural organic matter (NOM) on the environmental transformation and dissolution of metal and metal oxide NPs of different surface and solubility properties in synthetic freshwater (FW) with and without NOM. Adsorption of NOM was evident on most of the studied NPs, except Sb and Sb₂O₃, which resulted in the formation of negatively charged colloids of higher stability and smaller size distribution compared with the same NPs in FW only. The dissolution rate of the NPs in the presence of NOM correlated with the strength of interactions between the carboxylate group of NOM and the particle surface, and resulted in either no (Mn, Sb, ZnO NPs), increased (Co, Sn NPs) and decreased (Ni, NiO, Sb₂O₃, Y₂O₃ NPs) levels of dissolution. One type of metal NP from each group (Mn, Ni, Sn) were investigated to assess whether observed differences in adsorption of NOM and dissolution would influence their ecotoxic potency. The results showed Mn, Ni, and Sn NPs to generate intracellular reactive oxygen species (ROS) in a time and dose-dependent manner. The extent of ROS generation in FW was similar for both Mn and Ni NPs but higher for Sn NPs. These findings are possibly related to interactions and infiltration of the NPs with the cells, which lead to redox imbalances which could induce oxidative stress and cell damage. At the same time, the presence of NOM generally reduced the intracellular ROS generation by 20-40% for the investigated NPs and also reduced cytotoxicity of Sn NPs, which can be attributed to the stronger interaction of carboxylate groups of NOM with the surface of the NPs.

Toxicity of stainless and mild steel particles generated from gas-metal arc welding in primary human small airway epithelial cells

Welding fumes induce lung toxicity and are carcinogenic to humans but the molecular mechanisms have yet to be clarified. The aim of this study was to evaluate the toxicity of stainless and mild steel particles generated via gas-metal arc welding using primary human small airway epithelial cells (hSAEC) and ToxTracker reporter murine stem cells, which track activation of six cancer-related pathways. Metal content (Fe, Mn, Ni, Cr) of the particles was relatively homogenous across particle size. The particles were not cytotoxic in reporter stem cells but stainless steel particles activated the Nrf2-dependent oxidative stress pathway. In hSAEC, both particle types induced time- and dose-dependent cytotoxicity, and stainless steel particles also increased generation of reactive oxygen species. The cellular metal content was higher for hSAEC compared to the reporter stem cells exposed to the same nominal dose. This was, in part, related to differences in particle agglomeration/sedimentation in the different cell media. Overall, our study showed differences in cytotoxicity and activation of cancer-related pathways between stainless and mild steel welding particles. Moreover, our data emphasizes the need for careful assessment of the cellular dose when comparing studies using different in vitro models.

The in vitro ToxTracker and Aneugen Clastogen Evaluation extension assay as a tool in the assessment of relative genotoxic potential of e-liquids and their aerosols

In vitro (geno)toxicity assessment of electronic vapour products (EVPs), relative to conventional cigarette, currently uses assays, including the micronucleus and Ames tests. Whilst informative on induction of a finite endpoint and relative risk posed by test articles, such assays could benefit from mechanistic supplementation. The ToxTracker and Aneugen Clastogen Evaluation analysis can indicate the activation of reporters associated with (geno)toxicity, including DNA damage, oxidative stress, the p53-related stress response and protein damage. Here, we tested for the different effects of a selection of neat e-liquids, EVP aerosols and Kentucky reference 1R6F cigarette smoke samples in the ToxTracker assay. The assay was initially validated to assess whether a mixture of e-liquid base components, propylene glycol (PG) and vegetable glycerine (VG) had interfering effects within the system. This was achieved by spiking three positive controls into the system with neat PG/VG or phosphate-buffered saline bubbled (bPBS) PG/VG aerosol (nicotine and flavour free). PG/VG did not greatly affect responses induced by the compounds. Next, when compared to cigarette smoke samples, neat e-liquids and bPBS aerosols (tobacco flavour; 1.6% freebase nicotine, 1.6% nicotine salt or 0% nicotine) exhibited reduced and less complex responses. Tested up to a 10% concentration, EVP aerosol bPBS did not induce any ToxTracker reporters. Neat e-liquids, tested up to 1%, induced oxidative stress reporters, thought to be due to their effects on osmolarity in vitro. E-liquid nicotine content did not affect responses induced. Additionally, spiking nicotine alone only induced an oxidative stress response at a supraphysiological level. In conclusion, the ToxTracker assay is a quick, informative screen for genotoxic potential and mechanisms of a variety of (compositionally complex) samples, derived from cigarettes and EVPs. This assay has the potential for future application in the assessment battery for next-generation (smoking alternative) products, including EVPs.

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.

From Basic Research to New Tools and Challenges for the Genotoxicity Testing of Nanomaterials

Genotoxicity is one of the key endpoints investigated as early as possible before marketing a product [...].

Cytotoxic effects of manganese oxide nanoparticles in combination with microbial components on intestinal epithelial cells

Background: Manganese oxide has been shown to cause toxicity and is associated with occupational-related disease (e.g., welders). With the goal to improve several biomedical areas, manganese oxide nanoparticles (MnO NP) are being considered for use in drug delivery and magnetic resonance imaging (MRI) to obtain high resolution anatomical images of tumors and gastrointestinal (GI) inflammation. Regardless of whether it is intentional or unintentional ingestion, the GI tract has been shown to be the primary route of entry for metal nanoparticles including MnO NP. However, studies assessing toxicity of MnO NP for intestinal epithelial cells (IECs) are virtually nonexistent. Methods: Given the proximity to the GI lumen, assessing the effects of nanoparticles on IECs in the presence of bacterial components presents a more holistic model of exposure. Therefore, we examined the effects of MnO NP alone and MnO NP in combination with Escherichia coli LF82 bacterial lysate on selected functions of MODE-K cells, a murine intestinal epithelial cell line. Data were analyzed using one-way ANOVA. Differences with p < 0.05 were considered significant. Results: Results showed MnO NP plus E. coli LF82 lysate added to MODE-K cells severely inhibited monolayer scratch wound healing, enhanced the secretion of interleukin 6 (IL-6), and induced mitochondrial dysfunction. Conclusions: Overall, our findings show that toxicity of MnO NP deleteriously affected MODE-K cells and demonstrated the necessity to integrate other environmental factors, such as microbial components and/or inflammatory cytokines, into studies assessing effects of nanoparticles on mucosal epithelia.