Preparation, characterization, and in vitro dosimetry of dispersed, engineered nanomaterials

Full-cycle study on developing a novel structured micromixer and evaluating the nanoparticle products as mRNA delivery carriers

Achieving precise control of nanoparticle size while maintaining consistency and high uniformity is of paramount importance for improving the efficacy of nanoparticle-based therapies and minimizing potential side effects. Although microfluidic technologies are widely used for reliable nanoparticle synthesis, they face challenges in meeting critical homogeneity requirements, mainly due to imperfect mixing efficiency. Furthermore, channel clogging during continuous operation presents a significant obstacle in terms of quality control, as it progressively impedes the mixing behavior necessary for consistent nanoparticle production for therapeutic delivery and complicates the scaling-up process. This study entailed the development of a 3D-printed novel micromixer embedded with hemispherical baffle microstructures, a dual vortex mixer (DVM), which integrates Dean vortices to generate two symmetrical counter-rotating intensified secondary flows. The DVM with a relatively large mixer volume showed rapid mixing characteristics even at a flow rate of several mL min-1 and produced highly uniform lipids, liposomes, and polymer nanoparticles in a size range (50-130 nm) and polydispersity index (PDI) values below 0.15. For the evaluation of products, SARS-CoV-2 Spike mRNA-loaded lipid nanoparticles were examined to verify protein expression in vitro and in vivo using firefly luciferase (FLuc) mRNA. This showed that the performance of the system is comparable to that of a commercial toroidal mixer. Moreover, the vigorous in-situ dispersion of nanoparticles by harnessing the power of vortex physically minimizes the occurrence of aggregation, ensuring consistent production performance without internal clogging of a half-day operation and facilitating quality control of the nanoparticles at desired scales.

Overview of in vitro-in vivo extrapolation approaches for the risk assessment of nanomaterial toxicity

Nanomaterials are increasingly used in many applications due to their enhanced properties. To ensure their safety for humans and the environment, nanomaterials need to be evaluated for their potential risk. The risk assessment analysis on the nanomaterials based on animal or in vivo studies is accompanied by several concerns, including animal welfare, time and cost needed for the studies. Therefore, incorporating in vitro studies in the risk assessment process is increasingly considered. To be able to analyze the potential risk of nanomaterial to human health, there are factors to take into account. Utilizing in vitro data in the risk assessment analysis requires methods that can be used to translate in vitro data to predict in vivo phenomena (in vitro-in vivo extrapolation (IVIVE) methods) to be incorporated, to obtain a more accurate result. Apart from the experiments and species conversion (for example, translation between the cell culture, animal and human), the challenge also includes the unique properties of nanomaterials that might cause them to behave differently compared to the same materials in a bulk form. This overview presents the IVIVE techniques that are developed to extrapolate pharmacokinetics data or doses. A brief example of the IVIVE methods for chemicals is provided, followed by a more detailed summary of available IVIVE methods applied to nanomaterials. The IVIVE techniques discussed include the comparison between in vitro and in vivo studies, methods to rene the dose metric or the in vitro models, allometric approach, mechanistic modeling, Multiple-Path Particle Dosimetry (MPPD), methods using organ burden data and also approaches that are currently being developed.

Understanding Human Health Impacts Following Microplastic Exposure Necessitates Standardized Protocols

Microplastics (MPs; 1 µm to 5 mm) are a persistent and pervasive environmental pollutant of emergent and increasing concern. Human exposure to MPs through food, water, and air has been documented and thus motivates the need for a better understanding of the biological implications of MP exposure. These impacts are dependent on the properties of MPs, including size, morphology, and chemistry, as well as the dose and route of exposure. This overview offers a perspective on the current methods used to assess the bioactivity of MPs. First, we discuss methods associated with MP bioactivity research with an emphasis on the variety of assays, exposure conditions, and reference MP particles that have been used. Next, we review the challenges presented by common instrumentation and laboratory materials, the lack of standardized reference materials, and the limited understanding of MP dosimetry. Finally, we propose solutions that can help increase the applicability and impact of future studies while reducing redundancy in the field. The excellent protocols published in this issue are intended to contribute toward standardizing the field so that the MP knowledge base grows from a reliable foundation. © 2024 Wiley Periodicals LLC.

Improving the dichloro-dihydro-fluorescein (DCFH) assay for the assessment of intracellular reactive oxygen species formation by nanomaterials

To facilitate Safe and Sustainable by Design (SSbD) strategies during the development of nanomaterials (NMs), quick and easy in vitro assays to test for hazard potential at an early stage of NM development are essential. The formation of reactive oxygen species (ROS) and the induction of oxidative stress are considered important mechanisms that can lead to NM toxicity. In vitro assays measuring oxidative stress are therefore commonly included in NM hazard assessment strategies. The fluorescence-based dichloro-dihydro-fluorescein (DCFH) assay for cellular oxidative stress is a simple and cost-effective assay, making it a good candidate assay for SSbD hazard testing strategies. It is however subject to several pitfalls and caveats. Here, we provide further optimizations to the assay using 5-(6)-Chloromethyl-2',7'-dichlorodihydrofluorescein diacetate acetyl ester (CM-H2DCFDA-AE, referred to as DCFH probe), known for its improved cell retention. We measured the release of metabolic products of the DCFH probe from cells to supernatant, direct reactions of CM-H2DCFDA-AE with positive controls, and compared the commonly used plate reader-based DCFH assay protocol with fluorescence microscopy and flow cytometry-based protocols. After loading cells with DCFH probe, translocation of several metabolic products of the DCFH probe to the supernatant was observed in multiple cell types. Translocated DCFH products are then able to react with test substances including positive controls. Our results also indicate that intracellularly oxidized fluorescent DCF is able to translocate from cells to the supernatant. In either way, this will lead to a fluorescent supernatant, making it difficult to discriminate between intra- and extra-cellular ROS production, risking misinterpretation of possible oxidative stress when measuring fluorescence on a plate reader. The use of flow cytometry instead of plate reader-based measurements resolved these issues, and also improved assay sensitivity. Several optimizations of the flow cytometry-based DCFH ISO standard (ISO/TS 19006:2016) were suggested, including loading cells with DCFH probe before incubation with the test materials, and applying an appropriate gating strategy including live-death staining, which was not included in the ISO standard. In conclusion, flow cytometry- and fluorescence microscopy-based read-outs are preferred over the classical plate reader-based read-out to assess the level of intracellular oxidative stress using the cellular DCFH assay.

Advancements in Nanomaterial Dispersion and Stability and Thermophysical Properties of Nano-Enhanced Phase Change Materials for Biomedical Applications

Phase change materials (PCMs) are materials that exhibit thermal response characteristics, allowing them to be utilized in the biological field for precise and controllable temperature regulation. Due to considerations of biosafety and the spatial limitations within human tissue, the amount of PCMs used in medical applications is relatively small. Therefore, researchers often augment PCMs with various materials to enhance their performance and increase their practical value. The dispersion of nanoparticles to modify the thermophysical properties of PCMs has emerged as a mature concept. This paper aims to elucidate the role of nanomaterials in addressing deficiencies and enhancing the performance of PCMs. Specifically, it discusses the dispersion methods and stabilization mechanisms of nanoparticles within PCMs, as well as their effects on thermophysical properties such as thermal conductivity, latent heat, and specific heat capacity. Furthermore, it explores how various nano-additives contribute to improved thermal conductivity and the mechanisms underlying enhanced latent heat and specific heat. Additionally, the potential applications of PCMs in biomedical fields are proposed. Finally, this paper provides a comprehensive analysis and offers suggestions for future research to maximize the utilization of nanomaterials in enhancing the thermophysical properties of PCMs for biomedical applications.

Applying new approach methodologies to assess next-generation tobacco and nicotine products

In vitro toxicology research has accelerated with the use of in silico, computational approaches and human in vitro tissue systems, facilitating major improvements evaluating the safety and health risks of novel consumer products. Innovation in molecular and cellular biology has shifted testing paradigms, with less reliance on low-throughput animal data and greater use of medium- and high-throughput in vitro cellular screening approaches. These new approach methodologies (NAMs) are being implemented in other industry sectors for chemical testing, screening candidate drugs and prototype consumer products, driven by the need for reliable, human-relevant approaches. Routine toxicological methods are largely unchanged since development over 50 years ago, using high-doses and often employing in vivo testing. Several disadvantages are encountered conducting or extrapolating data from animal studies due to differences in metabolism or exposure. The last decade saw considerable advancement in the development of in vitro tools and capabilities, and the challenges of the next decade will be integrating these platforms into applied product testing and acceptance by regulatory bodies. Governmental and validation agencies have launched and applied frameworks and "roadmaps" to support agile validation and acceptance of NAMs. Next-generation tobacco and nicotine products (NGPs) have the potential to offer reduced risks to smokers compared to cigarettes. These include heated tobacco products (HTPs) that heat but do not burn tobacco; vapor products also termed electronic nicotine delivery systems (ENDS), that heat an e-liquid to produce an inhalable aerosol; oral smokeless tobacco products (e.g., Swedish-style snus) and tobacco-free oral nicotine pouches. With the increased availability of NGPs and the requirement of scientific studies to support regulatory approval, NAMs approaches can supplement the assessment of NGPs. This review explores how NAMs can be applied to assess NGPs, highlighting key considerations, including the use of appropriate in vitro model systems, deploying screening approaches for hazard identification, and the importance of test article characterization. The importance and opportunity for fit-for-purpose testing and method standardization are discussed, highlighting the value of industry and cross-industry collaborations. Supporting the development of methods that are accepted by regulatory bodies could lead to the implementation of NAMs for tobacco and nicotine NGP testing.

Identification and quantification of trace metal(loid)s in water-extractable road dust nanoparticles using SP-ICP-MS

Resuspension of road dust is a major source of airborne particulate matter (PM) in urban environments. Inhalation of ultrafine particles (UFP; < 0.1 μm) represents a health concern due to their ability to reach the alveoli and be translocated into the blood stream. It is therefore important to characterize chemical properties of UFPs associated with vehicle emissions. We investigated the capability of Single-Particle ICP-MS (SP-ICP-MS) to quantify key metal(loid)s in nanoparticles (NPs; < 0.1 μm) isolated from road dust collected in Toronto, Canada. Water extraction was performed to separate the <1-μm fraction from two different road dust samples (local road vs. arterial road) and a multi-element SP-ICP-MS analysis was then conducted on the samples' supernatants. Based on the particle number concentrations obtained for both supernatants, the metal(loid)-containing NPs could be grouped in the following categories: high (Cu and Zn, > 1.3 × 1011 particles/L), medium (V, Cr, Ba, Pb, Sb, Ce, La), low (As, Co, Ni, < 4.6 × 109 particles/L). The limit of detection for particle number concentration was below 5.5 × 106 particles/L for most elements, except for Cu, Co, Ni, Cr, and V (between 0.9 and 7.7 × 107 particles/L). The results demonstrate that road dust contains a wide range of readily mobilizable metal(loid)-bearing NPs and that NP numbers may vary as a function of road type. These findings have important implications for human health risk assessments in urban areas. Further research is needed, however, to comprehensively assess the NP content of road dust as influenced by various factors, including traffic volume and speed, fleet composition, and street sweeping frequency. The described method can quickly characterize multiple isotopes per sample in complex matrices, and offers the advantage of rapid sample scanning for the identification of NPs containing potentially toxic transition metal(loid)s at a low detection limit.

An overview on dispersion procedures and testing methods for the ecotoxicity testing of nanomaterials in the marine environment

Considerable efforts have been devoted to develop or adapt existing guidelines and protocols, to obtain robust and reproducible results from (eco)toxicological assays on engineered nanomaterials (NMs). However, while many studies investigated adverse effects of NMs on freshwater species, less attention was posed to the marine environment, a major sink for these contaminants. This review discusses the procedures used to assess the ecotoxicity of NMs in the marine environment, focusing on the use of protocols and methods for preparing NMs dispersions and on the NMs physicochemical characterization in exposure media. To this purpose, a critical analysis of the literature since 2010 was carried out, based on the publication of the first NMs dispersion protocols. Among the 89 selected studies, only <5 % followed a standardized dispersion protocol combined with NMs characterization in ecotoxicological media, while more than half used a non-standardized dispersion method but performed NMs characterization. In the remaining studies, only partial or no information on dispersion procedures or on physicochemical characterization was provided. This literature review also highlighted that metal oxides NMs were the most studied (42 %), but with an increasing interest in last years towards nanoplastics (14 %) and multicomponent nanomaterials (MCNMs, 7 %), in line with the growing attention on these emerging contaminants. For all these NMs, primary producers as algae and bacteria were the most studied groups of marine species, in addition to mollusca, while organisms at higher trophic levels were less represented, likely due to challenges in evaluating adverse effects on more complex organisms. Thus, despite the wide use of NMs in different applications, standard dispersion protocols are not often used for ecotoxicity testing with marine species. However, the efforts to characterize NMs in ecotoxicological media recognize the importance of following conditions that are as standardized as possible to support the ecological hazard assessment of NMs.

Nanotherapeutic Heterogeneity: Sources, Effects, and Solutions

Nanomaterials have revolutionized medicine by enabling control over drugs' pharmacokinetics, biodistribution, and biocompatibility. However, most nanotherapeutic batches are highly heterogeneous, meaning they comprise nanoparticles that vary in size, shape, charge, composition, and ligand functionalization. Similarly, individual nanotherapeutics often have heterogeneously distributed components, ligands, and charges. This review discusses nanotherapeutic heterogeneity's sources and effects on experimental readouts and therapeutic efficacy. Among other topics, it demonstrates that heterogeneity exists in nearly all nanotherapeutic types, examines how nanotherapeutic heterogeneity arises, and discusses how heterogeneity impacts nanomaterials' in vitro and in vivo behavior. How nanotherapeutic heterogeneity skews experimental readouts and complicates their optimization and clinical translation is also shown. Lastly, strategies for limiting nanotherapeutic heterogeneity are reviewed and recommendations for developing more reproducible and effective nanotherapeutics provided.

Bridging Smart Nanosystems with Clinically Relevant Models and Advanced Imaging for Precision Drug Delivery

Intracellular delivery of nano-drug-carriers (NDC) to specific cells, diseased regions, or solid tumors has entered the era of precision medicine that requires systematic knowledge of nano-biological interactions from multidisciplinary perspectives. To this end, this review first provides an overview of membrane-disruption methods such as electroporation, sonoporation, photoporation, microfluidic delivery, and microinjection with the merits of high-throughput and enhanced efficiency for in vitro NDC delivery. The impact of NDC characteristics including particle size, shape, charge, hydrophobicity, and elasticity on cellular uptake are elaborated and several types of NDC systems aiming for hierarchical targeting and delivery in vivo are reviewed. Emerging in vitro or ex vivo human/animal-derived pathophysiological models are further explored and highly recommended for use in NDC studies since they might mimic in vivo delivery features and fill the translational gaps from animals to humans. The exploration of modern microscopy techniques for precise nanoparticle (NP) tracking at the cellular, organ, and organismal levels informs the tailored development of NDCs for in vivo application and clinical translation. Overall, the review integrates the latest insights into smart nanosystem engineering, physiological models, imaging-based validation tools, all directed towards enhancing the precise and efficient intracellular delivery of NDCs.

Strategies to reduce the risks of mRNA drug and vaccine toxicity

mRNA formulated with lipid nanoparticles is a transformative technology that has enabled the rapid development and administration of billions of coronavirus disease 2019 (COVID-19) vaccine doses worldwide. However, avoiding unacceptable toxicity with mRNA drugs and vaccines presents challenges. Lipid nanoparticle structural components, production methods, route of administration and proteins produced from complexed mRNAs all present toxicity concerns. Here, we discuss these concerns, specifically how cell tropism and tissue distribution of mRNA and lipid nanoparticles can lead to toxicity, and their possible reactogenicity. We focus on adverse events from mRNA applications for protein replacement and gene editing therapies as well as vaccines, tracing common biochemical and cellular pathways. The potential and limitations of existing models and tools used to screen for on-target efficacy and de-risk off-target toxicity, including in vivo and next-generation in vitro models, are also discussed.

Dispersion and Dosimetric Challenges of Hydrophobic Carbon-Based Nanoparticles in In Vitro Cellular Studies

Methodologies across the dispersion preparation, characterization, and cellular dosimetry of hydrophilic nanoparticles (NPs) have been developed and used extensively in the field of nanotoxicology. However, hydrophobic NPs pose a challenge for dispersion in aqueous culture media using conventional methods that include sonication followed by mixing in the culture medium of interest and cellular dosimetry. In this study, a robust methodology for the preparation of stable dispersions of hydrophobic NPs for cellular studies is developed by introducing continuous energy over time via stirring in the culture medium followed by dispersion characterization and cellular dosimetry. The stirring energy and the presence of proteins in the culture medium result in the formation of a protein corona around the NPs, stabilizing their dispersion, which can be used for in vitro cellular studies. The identification of the optimal stirring time is crucial for achieving dispersion and stability. This is assessed through a comprehensive stability testing protocol employing dynamic light scattering to evaluate the particle size distribution stability and polydispersity. Additionally, the effective density of the NPs is obtained for the stable NP dispersions using the volumetric centrifugation method, while cellular dosimetry calculations are done using available cellular computational modeling, mirroring approaches used for hydrophilic NPs. The robustness of the proposed dispersion approach is showcased using a highly hydrophobic NP model (black carbon NPs) and two culture media, RPMI medium and SABM, that are widely used in cellular studies. The proposed approach for the dispersion of hydrophobic NPs results in stable dispersions in both culture media used here. The NP effective density of 1.03-1.07 g/cm3 measured here for black carbon NPs is close to the culture media density, resulting in slow deposition on the cells over time. So, the present methodology for dispersion and dosimetry of hydrophobic NPs is essential for the design of dose-response studies and overcoming the challenges imposed by slow particle deposition.

Combustion conditions influence toxicity of flame-generated soot to ocular (ARPE-19) cells

Soot is a prevalent aerosol found both indoors and outdoors that has several sources, such as natural (e.g., wildfires), civilian (e.g., cooking), or military (e.g., burn pit operation). Additionally, within the sources, factors that influence the physicochemical properties of the soot include combustion temperature, oxygen availability, and fuel type. Being able to reproduce soot in the laboratory and systematically assess its toxicity is important in the pursuit of elucidating pathologies associated with its exposure. Of the organs of interest, we targeted the eye given the scant attention received. Yet, air pollution constituents such as soot have been linked to diseases such as age-related macular degeneration and proliferative vitreoretinopathy. We developed a bench-scale system to synthesize different types of soot, that is, soot with a systematically varied physical attributes or chemical composition. We used common analytical techniques to probe such properties, and used statistical analyses to correlate them with toxicity in vitro using ARPE-19 cells. Within the range of flame conditions studied, we find that soot toxicity increases with increasing oxygen concentration in fuel-rich premixed flames, and weakly increases with decreasing flame temperature. Additionally, soot particles produced in premixed flames are generally smaller in size, exhibit a lesser fractal structure, and are considerably more toxic to ARPE-19 cells than soot particles produced in non-premixed flames.

Effective density of inhaled environmental and engineered nanoparticles and its impact on the lung deposition and dosimetry

BACKGROUND

Airborne environmental and engineered nanoparticles (NPs) are inhaled and deposited in the respiratory system. The inhaled dose of such NPs and their deposition location in the lung determines their impact on health. When calculating NP deposition using particle inhalation models, a common approach is to use the bulk material density, ρb, rather than the effective density, ρeff. This neglects though the porous agglomerate structure of NPs and may result in a significant error of their lung-deposited dose and location.

RESULTS

Here, the deposition of various environmental NPs (aircraft and diesel black carbon, wood smoke) and engineered NPs (silica, zirconia) in the respiratory system of humans and mice is calculated using the Multiple-Path Particle Dosimetry model accounting for their realistic structure and effective density. This is done by measuring the NP ρeff which was found to be up to one order of magnitude smaller than ρb. Accounting for the realistic ρeff of NPs reduces their deposited mass in the pulmonary region of the respiratory system up to a factor of two in both human and mouse models. Neglecting the ρeff of NPs does not alter significantly the distribution of the deposited mass fractions in the human or mouse respiratory tract that are obtained by normalizing the mass deposited at the head, tracheobronchial and pulmonary regions by the total deposited mass. Finally, the total deposited mass fraction derived this way is in excellent agreement with those measured in human studies for diesel black carbon.

CONCLUSIONS

The doses of inhaled NPs are overestimated by inhalation particle deposition models when the ρb is used instead of the real-world effective density which can vary significantly due to the porous agglomerate structure of NPs. So the use of realistic ρeff, which can be measured as described here, is essential to determine the lung deposition and dosimetry of inhaled NPs and their impact on public health.

New methodological developments for testing the in vitro genotoxicity of nanomaterials: Comparison of 2D and 3D HepaRG liver cell models and classical and high throughput comet assay formats

Nanomaterials (NMs) are defined as materials with at least one external dimension below 100 nm. Their small size confers them interesting unique physico-chemical properties, hence NMs are increasingly used in a diversity of applications. However, the specific properties of NMs could also make them more harmful than their bulk counterparts. Therefore, there is a crucial need to deliver efficient NM hazard assessment in order to sustain the responsible development of nanotechnology. This study analysed the genotoxic potential of several NMs: one titanium dioxide (TiO2) and two zinc oxide NMs (ZnO) that were tested up to 100 μg/mL on 2D and 3D hepatic HepaRG models. Genotoxicity analysis was performed comparing the alkaline comet assay in classical and high throughput formats. Moreover, oxidative DNA lesions were investigated with the Fpg-modified comet assay. Results showed that TiO2 NMs were not cytotoxic and not genotoxic in either cell model, although a small increase in the % tail DNA was observed in 3D HepaRG cells at 100 μg/mL in the classical format. The two ZnO NMs (ZnO S. NMs a commercial suspension and NM110 provided by the European Union Joint Research Centre) induced a concentration-dependent increase in cytotoxicity that was more pronounced in the 2D (>20% cytotoxicity was observed for ZnO S. at concentrations greater than 25 μg/mL, and for NM 110 at 50 μg/mL) than in the 3D model (more than 20% cytotoxicity for ZnO S. NMs at 50 μg/mL). While ZnO S. NMs induced DNA damage associated with cytotoxicity (at 25 and 50 μg/mL in 2D and 50 μg/mL in 3D), NM110 showed a clear genotoxic effect at non-cytotoxic concentrations (25 μg/mL in 2D and at 25 and 50 μg/mL in 3D). No major differences could be observed in the comet assay in the presence or absence of the Fpg enzyme. High throughput analysis using CometChip® mostly confirmed the results obtained with the classical format, and even enhanced the detection of genotoxicity in the 3D model. In conclusion, this study demonstrated that new approach methodologies (NAMs), 3D models and the high throughput format for the comet assay, were more efficient in the detection of genotoxic effects, and are therefore promising approaches to improve hazard assessment of NMs.

Structural Color from Cellulose Nanocrystals or Chitin Nanocrystals: Self-Assembly, Optics, and Applications

Widespread concerns over the impact of human activity on the environment have resulted in a desire to replace artificial functional materials with naturally derived alternatives. As such, polysaccharides are drawing increasing attention due to offering a renewable, biodegradable, and biocompatible feedstock for functional nanomaterials. In particular, nanocrystals of cellulose and chitin have emerged as versatile and sustainable building blocks for diverse applications, ranging from mechanical reinforcement to structural coloration. Much of this interest arises from the tendency of these colloidally stable nanoparticles to self-organize in water into a lyotropic cholesteric liquid crystal, which can be readily manipulated in terms of its periodicity, structure, and geometry. Importantly, this helicoidal ordering can be retained into the solid-state, offering an accessible route to complex nanostructured films, coatings, and particles. In this review, the process of forming iridescent, structurally colored films from suspensions of cellulose nanocrystals (CNCs) is summarized and the mechanisms underlying the chemical and physical phenomena at each stage in the process explored. Analogy is then drawn with chitin nanocrystals (ChNCs), allowing for key differences to be critically assessed and strategies toward structural coloration to be presented. Importantly, the progress toward translating this technology from academia to industry is summarized, with unresolved scientific and technical questions put forward as challenges to the community.

Toxicity assessment of CeO₂ and CuO nanoparticles at the air-liquid interface using bioinspired condensational particle growth

CeO2 and CuO nanoparticles (NPs) are used as additives in petrodiesel to enhance engine performance leading to reduced diesel combustion emissions. Despite their benefits, the additive application poses human health concerns by releasing inhalable NPs into the ambient air. In this study, a bioinspired lung cell exposure system, Dosimetric Aerosol in Vitro Inhalation Device (DAVID), was employed for evaluating the toxicity of aerosolized CeO2 and CuO NPs with a short duration of exposure (≤10 min vs. hours in other systems) and without exerting toxicity from non-NP factors. Human epithelial A549 lung cells were cultured and maintained within DAVID at the air-liquid interface (ALI), onto which aerosolized NPs were deposited, and experiments in submerged cells were used for comparison. Exposure of the cells to the CeO2 NPs did not result in detectable IL-8 release, nor did it produce a significant reduction in cell viability based on lactate dehydrogenase (LDH) assay, with a marginal decrease (10%) at the dose of 388 μg/cm2 (273 cm2/cm2). In contrast, exposure to CuO NPs resulted in a concentration dependent reduction in LDH release based on LDH leakage, with 38% reduction in viability at the highest dose of 52 μg/cm2 (28.3 cm2/cm2). Cells exposed to CuO NPs resulted in a dose dependent cellular membrane toxicity and expressed IL-8 secretion at a global dose five times lower than cells exposed under submerged conditions. However, when comparing the ALI results at the local cellular dose of CuO NPs to the submerged results, the IL-8 secretion was similar. In this study, we demonstrated DAVID as a new exposure tool that helps evaluate aerosol toxicity in simulated lung environment. Our results also highlight the necessity in choosing the right assay endpoints for the given exposure scenario, e.g., LDH for ALI and Deep Blue for submerged conditions for cell viability.

The Influence of Liquid Menisci on Nanoparticle Dosimetry in Submerged Cells

Understanding the interaction between cells and nanoparticles (NPs) is vital to understand the hazard associated with nanoparticles. This requires quantifying and interpreting dose-response relationships. Experiments with cells cultured in vitro and exposed to particle dispersions mainly rely on mathematical models that estimate the received nanoparticle dose. However, models need to consider that aqueous cell culture media wets the inner surface of hydrophilic open wells, which results in a curved liquid-air interface called the meniscus. Here the impact of the meniscus on nanoparticle dosimetry is addressed in detail. Experiments and build an advanced mathematical model, to demonstrate that the presence of the meniscus may bring about systematic errors that must be considered to advance reproducibility and harmonization is presented. The script of the model is co-published and can be adapted to any experimental setup. Finally, simple and practical solutions to this problem, such as covering the air-liquid interface with a permeable lid or soft rocking of the cell culture well plate is proposed.

Effect of graphene-based nanomaterials on corneal wound healing in vitro

Graphene-based nanomaterials (GBNs) are widely used due to their chemical and physical properties for multiple commercial and environmental applications. From an occupational health perspective, there is concern regarding the effects of inhalation on the respiratory system, and many studies have been conducted to study inhalation impacts on lung. Similar to the respiratory system, the eyes may also be exposed to GBNs and thus impacted. In this study, immortalized human corneal epithelial (hTCEpi) cells and rabbit corneal fibroblasts (RCFs) were used to investigate the toxicity of eight types of GBN: graphene oxide (GO; 400 nm), GO (1 μm), partially reduced graphene oxide (PRGO; 400 nm), reduced graphene oxide (RGO; 400 nm), RGO (2 μm), graphene (110 nm), graphene (140 nm), and graphene (1 μm). We next examined the effects of these GBNs on hTCEpi cell migration. We also determined whether the expression of α-smooth muscle actin (αSMA), a myofibroblast marker, is altered by the GBNs using RCFs. We found that RGO (400 nm) and RGO (2 μm) were highly toxic to hTCEPi cells and RCFs meanwhile, PRGO (400 nm) was toxic only to hTCEpi cells. In addition, PRGO (400 nm), RGO (400 nm), and RGO (2 μm) inhibited hTCEpi cell migration and significantly increased αSMA mRNA expression. Further study in vivo is required to determine if RGO nanomaterials delay corneal epithelial healing and induce scar formation.

Nano-biotechnology in tumour and cancerous disease: A perspective review

In recent years, drug manufacturers and researchers have begun to consider the nanobiotechnology approach to improve the drug delivery system for tumour and cancer diseases. In this article, we review current strategies to improve tumour and cancer drug delivery, which mainly focuses on sustaining biocompatibility, biodistribution, and active targeting. The conventional therapy using cornerstone drugs such as fludarabine, cisplatin etoposide, and paclitaxel has its own challenges especially not being able to discriminate between tumour versus normal cells which eventually led to toxicity and side effects in the patients. In contrast to the conventional approach, nanoparticle-based drug delivery provides target-specific delivery and controlled release of the drug, which provides a better therapeutic window for treatment options by focusing on the eradication of diseased cells via active targeting and sparing normal cells via passive targeting. Additionally, treatment of tumours associated with the brain is hampered by the impermeability of the blood-brain barriers to the drugs, which eventually led to poor survival in the patients. Nanoparticle-based therapy offers superior delivery of drugs to the target by breaching the blood-brain barriers. Herein, we provide an overview of the properties of nanoparticles that are crucial for nanotechnology applications. We address the potential future applications of nanobiotechnology targeting specific or desired areas. In particular, the use of nanomaterials, biostructures, and drug delivery methods for the targeted treatment of tumours and cancer are explored.

Ingested Polystyrene Nanospheres Translocate to Placenta and Fetal Tissues in Pregnant Rats: Potential Health Implications

Recent studies in experimental animals found that oral exposure to micro- and nano-plastics (MNPs) during pregnancy had multiple adverse effects on outcomes and progeny, although no study has yet identified the translocation of ingested MNPs to the placenta or fetal tissues, which might account for those effects. We therefore assessed the placental and fetal translocation of ingested nanoscale polystyrene MNPs in pregnant rats. Sprague Dawley rats (N = 5) were gavaged on gestational day 19 with 10 mL/kg of 250 µg/mL 25 nm carboxylated polystyrene spheres (PS25C) and sacrificed after 24 h. Hyperspectral imaging of harvested placental and fetal tissues identified abundant PS25C within the placenta and in all fetal tissues examined, including liver, kidney, heart, lung and brain, where they appeared in 10-25 µm clusters. These findings demonstrate that ingested nanoscale polystyrene MNPs can breach the intestinal barrier and subsequently the maternal-fetal barrier of the placenta to access the fetal circulation and all fetal tissues. Further studies are needed to assess the mechanisms of MNP translocation across the intestinal and placental barriers, the effects of MNP polymer, size and other physicochemical properties on translocation, as well as the potential adverse effects of MNP translocation on the developing fetus.

Establishing relationships between particle-induced in vitro and in vivo inflammation endpoints to better extrapolate between in vitro markers and in vivo fibrosis

BACKGROUND

Toxicity assessment for regulatory purposes is starting to move away from traditional in vivo methods and towards new approach methodologies (NAM) such as high-throughput in vitro models and computational tools. For materials with limited hazard information, utilising quantitative Adverse Outcome Pathways (AOPs) in a testing strategy involving NAM can produce information relevant for risk assessment. The aim of this work was to determine the feasibility of linking in vitro endpoints to in vivo events, and moreover to key events associated with the onset of a chosen adverse outcome to aid in the development of NAM testing strategies. To do this, we focussed on the adverse outcome pathway (AOP) relating to the onset of pulmonary fibrosis.

RESULTS

We extracted in vivo and in vitro dose-response information for particles known to induce this pulmonary fibrosis (crystalline silica, specifically α-quartz). To test the in vivo-in vitro extrapolation (IVIVE) determined for crystalline silica, cerium dioxide nanoparticles (nano-CeO₂) were used as a case study allowing us to evaluate our findings with a less studied substance. The IVIVE methodology outlined in this paper is formed of five steps, which can be more generally summarised into two categories (i) aligning the in vivo and in vitro dosimetry, (ii) comparing the dose-response curves and derivation of conversion factors.

CONCLUSION

Our analysis shows promising results with regards to correlation of in vitro cytokine secretion to in vivo acute pulmonary inflammation assessed by polymorphonuclear leukocyte influx, most notable is the potential of using IL-6 and IL-1β cytokine secretion from simple in vitro submerged models as a screening tool to assess the likelihood of lung inflammation at an early stage in product development, hence allowing a more targeted investigation using either a smaller, more targeted in vivo study or in the future a more complex in vitro protocol. This paper also highlights the strengths and limitations as well as the current difficulties in performing IVIVE assessment and suggestions for overcoming these issues.

The State of the Art and Challenges of In Vitro Methods for Human Hazard Assessment of Nanomaterials in the Context of Safe-by-Design

The Safe-by-Design (SbD) concept aims to facilitate the development of safer materials/products, safer production, and safer use and end-of-life by performing timely SbD interventions to reduce hazard, exposure, or both. Early hazard screening is a crucial first step in this process. In this review, for the first time, commonly used in vitro assays are evaluated for their suitability for SbD hazard testing of nanomaterials (NMs). The goal of SbD hazard testing is identifying hazard warnings in the early stages of innovation. For this purpose, assays should be simple, cost-effective, predictive, robust, and compatible. For several toxicological endpoints, there are indications that commonly used in vitro assays are able to predict hazard warnings. In addition to the evaluation of assays, this review provides insights into the effects of the choice of cell type, exposure and dispersion protocol, and the (in)accurate determination of dose delivered to cells on predictivity. Furthermore, compatibility of assays with challenging advanced materials and NMs released from nano-enabled products (NEPs) during the lifecycle is assessed, as these aspects are crucial for SbD hazard testing. To conclude, hazard screening of NMs is complex and joint efforts between innovators, scientists, and regulators are needed to further improve SbD hazard testing.

Physicochemical and toxicological properties of wood smoke particulate matter as a function of wood species and combustion condition

Wood burning is a major source of ambient particulate matter (PM) and has been epidemiologically linked to adverse pulmonary health effects, however the impact of fuel and burning conditions on PM properties has not been investigated systematically. Here, we employed our recently developed integrated methodology to characterize the physicochemical and biological properties of emitted PM as a function of three common hardwoods (oak, cherry, mesquite) and three representative combustion conditions (flaming, smoldering, incomplete). Differences in PM and off-gas emissions (aerosol number/mass concentrations; carbon monoxide; volatile organic compounds) as well as inorganic elemental composition and organic carbon functional content of PM0.1 were noted between wood types and combustion conditions, although the combustion scenario exerted a stronger influence on the emission profile. More importantly, flaming combustion PM0.1 from all hardwoods significantly stimulated the promoter activity of Sterile Alpha Motif (SAM) pointed domain containing ETS (E-twenty-six) Transcription Factor (SPDEF) in human embryonic kidney 293 (HEK-293 T) cells, a biomarker for mucin gene expression associated with mucus production in pulmonary diseases. However, no bioactivity was observed for smoldering and incomplete combustion, which was likely driven by differences in the organic composition of PM0.1. Detailed chemical speciation of organic components of wood smoke is warranted to identify the individual compounds that drive specific biological responses.

Potential Artifacts and Control Experiments in Toxicity Tests of Nanoplastic and Microplastic Particles

To fully understand the potential ecological and human health risks from nanoplastics and microplastics (NMPs) in the environment, it is critical to make accurate measurements. Similar to past research on the toxicology of engineered nanomaterials, a broad range of measurement artifacts and biases are possible when testing their potential toxicity. For example, antimicrobials and surfactants may be present in commercially available NMP dispersions, and these compounds may account for toxicity observed instead of being caused by exposure to the NMP particles. Therefore, control measurements are needed to assess potential artifacts, and revisions to the protocol may be needed to eliminate or reduce the artifacts. In this paper, we comprehensively review and suggest a next generation of control experiments to identify measurement artifacts and biases that can occur while performing NMP toxicity experiments. This review covers the broad range of potential NMP toxicological experiments, such as in vitro studies with a single cell type or complex 3-D tissue constructs, in vivo mammalian studies, and ecotoxicity experiments testing pelagic, sediment, and soil organisms. Incorporation of these control experiments can reduce the likelihood of false positive and false negative results and more accurately elucidate the potential ecological and human health risks of NMPs.

An In Vitro Dosimetry Tool for the Numerical Transport Modeling of Engineered Nanomaterials Powered by the Enalos RiskGONE Cloud Platform

A freely available "in vitro dosimetry" web application is presented enabling users to predict the concentration of nanomaterials reaching the cell surface, and therefore available for attachment and internalization, from initial dispersion concentrations. The web application is based on the distorted grid (DG) model for the dispersion of engineered nanoparticles (NPs) in culture medium used for in vitro cellular experiments, in accordance with previously published protocols for cellular dosimetry determination. A series of in vitro experiments for six different NPs, with Ag and Au cores, are performed to demonstrate the convenience of the web application for calculation of exposure concentrations of NPs. Our results show that the exposure concentrations at the cell surface can be more than 30 times higher compared to the nominal or dispersed concentrations, depending on the NPs' properties and their behavior in the cell culture medium. Therefore, the importance of calculating the exposure concentration at the bottom of the cell culture wells used for in vitro arrays, i.e., the particle concentration at the cell surface, is clearly presented, and the tool introduced here allows users easy access to such calculations. Widespread application of this web tool will increase the reliability of subsequent toxicity data, allowing improved correlation of the real exposure concentration with the observed toxicity, enabling the hazard potentials of different NPs to be compared on a more robust basis.

The miniaturized enzyme-modified comet assay for genotoxicity testing of nanomaterials

The in vitro comet assay is a widely applied method for investigating genotoxicity of chemicals including engineered nanomaterials (NMs). A big challenge in hazard assessment of NMs is possible interference between the NMs and reagents or read-out of the test assay, leading to a risk of biased results. Here, we describe both the standard alkaline version of the in vitro comet assay with 12 mini-gels per slide for detection of DNA strand breaks and the enzyme-modified version that allows detection of oxidized DNA bases by applying lesion-specific endonucleases (e.g., formamidopyrimidine DNA glycosylase or endonuclease III). We highlight critical points that need to be taken into consideration when assessing the genotoxicity of NMs, as well as basic methodological considerations, such as the importance of carrying out physicochemical characterization of the NMs and investigating uptake and cytotoxicity. Also, experimental design-including treatment conditions, cell number, cell culture, format and volume of medium on the plate-is crucial and can have an impact on the results, especially when testing NMs. Toxicity of NMs depends upon physicochemical properties that change depending on the environment. To facilitate testing of numerous NMs with distinct modifications, the higher throughput miniaturized version of the comet assay is essential.

The alamar blue assay in the context of safety testing of nanomaterials

The Alamar Blue (AB) assay is widely used to investigate cytotoxicity, cell proliferation and cellular metabolic activity within different fields of toxicology. The use of the assay with nanomaterials (NMs) entails specific aspects including the potential interference of NMs with the test. The procedure of the AB assay applied for testing NMs is described in detail and step-by-step, from NM preparation, cell exposure, inclusion of interference controls, to the analysis and interpretation of the results. Provided that the proper procedure is followed, and relevant controls are included, the AB assay is a reliable and high throughput test to evaluate the cytotoxicity/proliferation/metabolic response of cells exposed to NMs.

Development of an Integrated Platform to Assess the Physicochemical and Toxicological Properties of Wood Combustion Particulate Matter

Wood burning contributes to indoor and ambient particulate matter (PM) pollution and has been associated with increased morbidity and mortality. Here, we present an integrated methodology that allows to generate, sample, and characterize wood smoke derived from different moisture contents and representative combustion conditions using pine wood as a model. Flaming, smoldering, and incomplete combustion were assessed for low-moisture pine, whereas both low-moisture pine and high-moisture pine were investigated under flaming conditions. Real-time monitoring of carbon monoxide, volatile organic compounds, and aerosol number concentration/size in wood smoke was performed. The PM was size-fractionated, sampled, and characterized for elemental/organic carbon, organic functional groups, and inorganic elements. Bioactivity of PM was assessed by measuring the sterile alpha motif (SAM) pointed domain containing ETS (E-twenty-six) transcription factor (SPDEF) gene promoter activity in human embryonic kidney 293 (HEK-293T) cells, a biomarker for mucin gene expression. Findings showed that moisture content and combustion condition significantly affected the organic and inorganic elemental composition of PM0.1 as well as its bioactivity. Also, for a given moisture and combustion scenario, PM chemistry and bioactivity differed considerably with PM size. Importantly, PM0.1 from flaming combustion of low-moisture pine contained the highest abundance of the oxygenated saturated aliphatic functional group [H-C-O] and was also biologically most potent in stimulating SPDEF promoter activity, suggesting the role of organic compounds such as carbohydrates and sugar alcohols (that contain [H-C-O]) in driving mucus-related respiratory outcomes. Our platform enables further well-controlled parametric studies using a combination of in vitro and in vivo approaches to link wood burning parameters with acute and chronic inhalation health effects of wood smoke.

Cerium Oxide Enhances the Toxicity of Zinc Oxide Nanoparticles in Human Lung Epithelial Cell Cultures

Recently, many approaches have been developed to improve the performance of nanomaterials. Combining more than one nanomaterial is one such approach that achieves superior results. However, during the fabrication of nanomaterials or formulation of end products, materials can be released into the ambient air and be inhaled by workers. The adverse health outcomes of inhaling such compounds are unknown. In this study, we examined such effects in combining two of the most utilized nanomaterials in several industrial sectors: zinc oxide (ZnO) and cerium oxide (CeO₂). These materials can be found together in sunscreens, polyvinyl alcohol (PVA) films, and construction products. The aim of this study was to assess the adverse biological outcomes of CeO₂-ZnO nano-mixtures in human lung epithelial cells. A549 human lung epithelial cells were treated with increasing concentrations of ZnO or CeO₂ NPs alone, or as a mixture of both, under submerged conditions for 24 h. After treatment, cell viability, reactive oxygen species (ROS) formation, cell membrane integrity, and cytokine production were examined. ZnO NPs showed a dose-dependent trend for all endpoints. CeO₂ NPs did not exhibit any toxic effect in any individual concentrations. When higher doses of ZnO were combined with increasing doses of CeO₂, loss of cell viability and an elevation in cell membrane leakage were observed. Interleukin 8 (IL-8) and ROS generation were higher when ZnO NPs were combined with CeO₂ NPs, compared to cells that were treated with ZnO alone. The release of monocyte chemoattractant protein-1 (MCP-1) was reduced in the cells that were treated with higher doses of ZnO and CeO₂. Thus, the presence of CeO₂ enhanced the toxicity of ZnO in A549 cells at non-toxic levels of CeO₂. This suggests an additive toxicity of these two nanomaterials.

Effect of Titanium Dioxide Nanoparticles on Mammalian Cell Cycle In Vitro: A Systematic Review and Meta-Analysis

Although most studies that explore the cytotoxicity of titanium dioxide nanoparticles (nano-TiO₂) have focused on cell viability and oxidative stress, the cell cycle, a basic process of cell life, can also be affected. However, the results on the effects of nano-TiO₂ on mammalian cell cycle are still inconsistent. A systematic review and meta-analysis were therefore performed in this research based on the effects of nano-TiO₂ on the mammalian cell cycle in vitro to explore whether nano-TiO₂ can induce cell cycle arrest. Meanwhile, the impact of physicochemical properties of nano-TiO₂ on the cell cycle in vitro was investigated, and the response of normal cells and cancer cells was compared. A total of 33 articles met the eligibility criteria after screening. We used Review Manager 5.4 and Stata 15.1 for analysis. The results showed an increased percentage of cells in the sub-G1 phase and an upregulation of the p53 gene after being exposed to nano-TiO₂. Nevertheless, nano-TiO₂ had no effect on cell percentage in other phases of the cell cycle. Furthermore, subgroup analysis revealed that the cell percentage in both the sub-G1 phase of normal cells and S phase of cancer cells were significantly increased under anatase-form nano-TiO₂ treatment. Moreover, nano-TiO₂ with a particle size <25 nm or exposure duration of nano-TiO₂ more than 24 h induced an increased percentage of normal cells in the sub-G1 phase. In addition, the cell cycle of cancer cells was arrested in the S phase no matter if the exposure duration of nano-TiO₂ was more than 24 h or the exposure concentration was over 50 μg/mL. In conclusion, this study demonstrated that nano-TiO₂ disrupted the cell cycle in vitro. The cell cycle arrest induced by nano-TiO₂ varies with cell status and physicochemical properties of nano-TiO₂.

Fabrication of Nylon-6 and Nylon-11 Nanoplastics and Evaluation in Mammalian Cells

Microplastics (MPs) and nanoplastics (NPs) exist in certain environments, beverages, and food products. However, the ultimate risk and consequences of MPs and NPs on human health remain largely unknown. Studies involving the biological effects of small-scale plastics have predominantly used commercially available polystyrene beads, which cannot represent the breadth of globally dominant plastics. Nylon is a commodity plastic that is used across various industry sectors with substantial global production. Here, a series of well-characterized nylon-11 and nylon-6 NPs were successfully fabricated with size distributions of approximately 100 nm and 500 nm, respectively. The facile fabrication steps enabled the incorporation of fluorescent tracers in these NPs to aid the intracellular tracking of particles. RAW 264.7 macrophages were exposed to nylon NPs in a dose-dependent manner and cytotoxic concentrations and cellular uptake were determined. These well-characterized nylon NPs support future steps to assess how the composition and physicochemical properties may affect complex biological systems and ultimately human health.

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

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

Toxicity mitigation and biodistribution of albumin corona coated graphene oxide and carbon nanotubes in Caenorhabditis elegans

In this work, the toxicity and biodistribution of graphene oxide (GO) and oxidized multi-walled carbon nanotubes (MWCNT) were investigated in Caenorhabditis elegans. Bovine serum albumin (BSA) was selected as a model protein to evaluate the influence of protein corona formation on materials physicochemical properties, colloidal stability, and toxicity. Biological assays were performed to assess the effects of bare and albumin corona coated materials on survival, oxidative stress, intestinal barrier permeability, growth, reproduction, and fertility. Critical alterations in topography, surface roughness and chemistry of GO and MWCNT were observed due to albumin corona formation. These modifications were associated with changes in colloidal stability of materials and prevention of their aggregation and sedimentation in nematode testing medium. Both GO and MWCNT caused damage to nematode survival, growth, reproduction, and fertility, as well as enhanced oxidative stress and permeability of the intestinal barrier. But GO was more toxic than MWCNT to C. elegans, especially at long-term assays. Albumin corona mitigated 100% of acute and chronic effects of MWCNT. In contrast, the negative effects of GO were not completely mitigated; GO inhibited 16.2% of nematode growth, 86.5% of reproduction, and 32.0% of fertility at the highest concentration evaluated (10 mg L^-1), while corona coated GO mitigated 50% and 100% of fertility and growth, respectively. Confocal Raman spectroscopy imaging was crucial to point out that bare and albumin corona coated GO and MWCNT crossed the C. elegans intestinal barrier reaching its reproductive organs. However, BSA corona protected the nematodes targeted organs from negative effects from MWCNT and blocked its translocation to other tissues, while coated GO was translocated inside the nematode affecting the functionality of crucial organs. In addition, coated MWCNT was excreted after 2 h of food resumption, whereas coated GO still accumulated in the nematode intestine. Our results demonstrate that the materials different translocation and excretion patterns in C. elegans had a relation to the impaired physiological functions of primary and secondary organs. This work is a contribution towards a better understanding of the impacts of protein corona on the toxicity of graphene oxide and carbon nanotubes; essential information for biological applications and nanosafety.

Approach toward In Vitro-Based Human Toxicity Effect Factors for the Life Cycle Impact Assessment of Inhaled Low-Solubility Particles

Today's scarcity of animal toxicological data for nanomaterials could be lifted by substituting in vivo data with in vitro data to calculate nanomaterials' effect factors (EF) for Life Cycle Assessment (LCA). Here, we present a step-by-step procedure to calculate in vitro-to-in vivo extrapolation factors to estimate human Benchmark Doses and subsequently in vitro-based EFs for several inhaled nonsoluble nanomaterials. Based on mouse data, the in vitro-based EF of TiO2 is between 2.76 · 10-4 and 1.10 · 10-3 cases/(m2/g·kg intake), depending on the aerodynamic size of the particle, which is in good agreement with in vivo-based EFs (1.51 · 10-4-5.6 · 10-2 cases/(m2/g·kg intake)). The EF for amorphous silica is in a similar range as for TiO2, but the result is less robust due to only few in vivo data available. The results based on rat data are very different, confirming the importance of selecting animal species representative of human responses. The discrepancy between in vivo and in vitro animal data in terms of availability and quality limits the coverage of further nanomaterials. Systematic testing on human and animal cells is needed to reduce the variability in toxicological response determined by the differences in experimental conditions, thus helping improve the predictivity of in vitro-to-in vivo extrapolation factors.

Physical Characterization and Cellular Toxicity Studies of Commercial NiO Nanoparticles

Nickel oxide (NiO) nanoparticles from several manufacturers with different reported sizes and surface coatings were characterized prior to assessing their cellular toxicity. The physical characterization of these particles revealed that sizes often varied from those reported by the supplier, and that particles were heavily agglomerated when dispersed in water, resulting in a smaller surface area and larger hydrodynamic diameter upon dispersion. Cytotoxicity testing of these materials showed differences between samples; however, correlation of these differences with the physical properties of the materials was not conclusive. Generally, particles with higher surface area and smaller hydrodynamic diameter were more cytotoxic. While all samples produced an increase in reactive oxygen species (ROS), there was no correlation between the magnitude of the increase in ROS and the difference in cytotoxicity between different materials.

In vitro to in vivo extrapolation to support the development of the next generation risk assessment (NGRA) strategy for nanomaterials

There is growing interest in developing novel strategies to support assessment of human health risks due to chemicals. Regulatory and decision-making agencies have recommended that non-animal-based alternatives should be applied whenever possible instead of experimentation on living animals. These alternative methods are beneficial because they are ethical, inexpensive, and rapid. Herein, we review recent activities aimed at developing in vitro to in vivo extrapolation (IVIVE) models as a part of the Next Generation Risk Assessment (NGRA) of nanomaterials. In this context, we show the adverse outcome pathway (AOP)-based methodology for the identification of mechanistically relevant events serving as biomarkers for the targeted selection of in vitro assays. Considered events need to be biologically plausible, regulatory relevant, and crucial for the examination of occurrence of adverse outcomes. The promising advantages of using high-throughout-based omics data are highlighted. Furthermore, the application of 3D in vitro models and nano genome atlases to study nanoparticle toxicity is briefly summarized. Additionally, the challenges related to the extrapolation of in vitro doses into in vivo-relevant responses are presented. We also discuss the limitations of models applied thus far to study the fate of chemicals in the human body, which exist due to the lack of available knowledge regarding transformations of nanomaterials occurring in biological systems.

IVIVE: Facilitating the Use of In Vitro Toxicity Data in Risk Assessment and Decision Making

During the past few decades, the science of toxicology has been undergoing a transformation from observational to predictive science. New approach methodologies (NAMs), including in vitro assays, in silico models, read-across, and in vitro to in vivo extrapolation (IVIVE), are being developed to reduce, refine, or replace whole animal testing, encouraging the judicious use of time and resources. Some of these methods have advanced past the exploratory research stage and are beginning to gain acceptance for the risk assessment of chemicals. A review of the recent literature reveals a burst of IVIVE publications over the past decade. In this review, we propose operational definitions for IVIVE, present literature examples for several common toxicity endpoints, and highlight their implications in decision-making processes across various federal agencies, as well as international organizations, including those in the European Union (EU). The current challenges and future needs are also summarized for IVIVE. In addition to refining and reducing the number of animals in traditional toxicity testing protocols and being used for prioritizing chemical testing, the goal to use IVIVE to facilitate the replacement of animal models can be achieved through their continued evolution and development, including a strategic plan to qualify IVIVE methods for regulatory acceptance.

Cytotoxicity of 2D engineered nanomaterials in pulmonary and corneal epithelium

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

Differential modulation of endothelial cytoplasmic protrusions after exposure to graphene-family nanomaterials

Engineered nanomaterials offer the benefit of having systematically tunable physicochemical characteristics (e.g., size, dimensionality, and surface chemistry) that highly dictate the biological activity of a material. Among the most promising engineered nanomaterials to date are graphene-family nanomaterials (GFNs), which are 2-D nanomaterials (2DNMs) with unique electrical and mechanical properties. Beyond engineering new nanomaterial properties, employing safety-by-design through considering the consequences of cell-material interactions is essential for exploring their applicability in the biomedical realm. In this study, we asked the effect of GFNs on the endothelial barrier function and cellular architecture of vascular endothelial cells. Using micropatterned cell pairs as a reductionist in vitro model of the endothelium, the progression of cytoskeletal reorganization as a function of GFN surface chemistry and time was quantitatively monitored. Here, we show that the surface oxidation of GFNs (graphene, reduced graphene oxide, partially reduced graphene oxide, and graphene oxide) differentially affect the endothelial barrier at multiple scales; from the biochemical pathways that influence the development of cellular protrusions to endothelial barrier integrity. More oxidized GFNs induce higher endothelial permeability and the increased formation of cytoplasmic protrusions such as filopodia. We found that these changes in cytoskeletal organization, along with barrier function, can be potentiated by the effect of GFNs on the Rho/Rho-associated kinase (ROCK) pathway. Specifically, GFNs with higher surface oxidation elicit stronger ROCK2 inhibitory behavior as compared to pristine graphene sheets. Overall, findings from these studies offer a new perspective towards systematically controlling the surface-dependent effects of GFNs on cytoskeletal organization via ROCK2 inhibition, providing insight for implementing safety-by-design principles in GFN manufacturing towards their targeted biomedical applications.

Size- and Oxidation-Dependent Toxicity of Graphene Oxide Nanomaterials in Embryonic Zebrafish

Graphene oxides (GOs) are a popular graphene alternative. The goal of this study was to compare the biocompatibility of a diversity of well-characterized GOs. Our previous work advanced developmental zebrafish as a model to interrogate the interactions and biological responses following exposures to engineered nanomaterials (ENMs). Here, we investigated GO 250 nm × 250 nm (sGO), 400 nm × 400 nm (mGO), and 1 μm × 1 μm (lGO), partially reduced GO (prGO) 400 nm × 400 nm, and reduced GO (rGO) 400 nm × 400 nm and 2 μm × 2 μm, which first underwent extensive characterization under the support of the Nanomaterials Health Implications Research (NHIR) Consortium. GOs were stabilized in water (GOs), while prGO and rGOs were dispersed in sodium cholate. Zebrafish were statically exposed to up to 50 μg/mL of each material from 6 h post-fertilization (hpf) until 120 hpf. Toxicity was dependent on GO properties. mGO was the most toxic material; its effects manifested in the yolk syncytial layer (YSL). Additionally, sodium cholate stabilization significantly increased GO toxicity. The observed effects were size- and oxidation-state-dependent, revealing the importance of identifying the structure-specific toxicity of GOs.

Artificial Digestion of Polydisperse Copper Oxide Nanoparticles: Investigation of Effects on the Human In Vitro Intestinal Co-Culture Model Caco-2/HT29-MTX

Copper oxide nanoparticles (CuO-NP) are increasingly used in consumer-related products, which may result in increased oral ingestion. Digestion of particles can change their physicochemical properties and toxicity. Therefore, our aim was to simulate the gastrointestinal tract using a static in vitro digestion model. Toxic properties of digested and undigested CuO-NP were compared using an epithelial mono-culture (Caco-2) and a mucus-secreting co-culture model (Caco-2/HT29-MTX). Effects on intestinal barrier integrity, permeability, cell viability and apoptosis were analyzed. CuO-NP concentrations of 1, 10 and 100 µg mL−1 were used. Particle characterization by dynamic light scattering and transmission electron microscopy showed similar mean particle sizes before and after digestion, resulting in comparable delivered particle doses in vitro. Only slight effects on barrier integrity and cell viability were detected for 100 µg mL−1 CuO-NP, while the ion control CuCl2 always caused significantly higher adverse effects. The utilized cell models were not significantly different. In summary, undigested and digested CuO-NP show comparable effects on the mono-/co-cultures, which are weaker than those of copper ions. Only in the highest concentration, CuO-NP showed weak effects on barrier integrity and cell viability. Nevertheless, a slightly increased apoptosis rate indicates existing cellular stress, which gives reason for further investigations.

A systematic review on the effects of nanomaterials on gut microbiota

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Nanomaterials have been shown to affect gut microbiota (GM) both in vivo and in vitro.

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The effects have been shown to depend on size, dose, dose duration and functional groups.

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In general, more studies seem to indicate dose-dependent adverse effects of NMs towards GM.

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Standardized protocols are needed for characterization of NMs, dosing, and test systems (both in vitro and in vivo).

Some nanomaterials (NMs) have been shown to possess antimicrobial activity and cause GM dysbiosis. Since NMs are being used widely, a systematic assessment of the effects of NMs on GM is warranted. In this systematic review, a total of 46 in vivo and 22 in vitro studies were retrieved from databases and search engines including Science-Direct, Pubmed and Google scholar. Criteria for assessment of studies included use of in vitro or in vivo studies, characterization of NMs, use of single or multiple doses as well as consistency of results. GM dysbiosis has been studied most widely on TiO₂, Ag, Zn-based NMs. There was moderate evidence for GM dysbiosis caused by Zn- and Cu-based NMs, Cu-loaded chitosan NPs and Ag NMs, and anatase TiO₂ NPs, as well as low evidence for SWCNTs, nanocellulose, SiO₂, Se, nanoplastics, CeO_2, MoO₃ and graphene-based NMs. Most studies indicate adverse effects of NMs towards GM. However, more work is required to elucidate the differences on the reported effects of NM by type and sex of organisms, size, shape and surface properties of NMs as well as effects of exposure to mixtures of NMs. For consistency and better agreement among studies on GM dysbiosis, there is need for internationally agreed protocols on, inter alia, characterization of NMs, dosing (amounts, frequency and duration), use of sonication, test systems (both in vitro and in vivo), including oxygen levels for in vitro models.

Sample preparation for the analysis of nanoparticles in natural waters by single particle ICP-MS

With the significant increase in the production and use of nanoparticles (NP), concern is increasing over their release into their environment. Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) is emerging as one of the best techniques for detecting the very small NP at very low concentrations in natural waters. However, there is no unified protocol for the preparation of natural water samples for SP-ICP-MS analysis. In order to minimize nebulizer blockage, filtration is often used with the expectation that 0.45 μm membranes will not remove significant quantities of 1-100 nm NP. Nonetheless, there are limited data on its effect on the concentrations or size distributions of the NP. To that end, we examined the interactions between six different membrane filters and silver (Ag) and cerium oxide (CeO₂) NP in aqueous samples. For Ag NP, the highest recoveries were observed for polypropylene membranes, where 55% of the pre-filtration NP were found in rainwater and 75% were found in river waters. For CeO₂ NP, recoveries for the polypropylene membrane attained 60% in rainwater and 75% in river water. Recoveries could be increased to over 80% by pre-conditioning the filtration membranes with a multi-element solution. Similar recoveries were obtained when samples were centrifuged at low centrifugal forces (≤1000×g).

Effects of Zinc Oxide Nanoparticles on Model Systems of the Intestinal Barrier

Zinc oxide nanoparticles (ZnO NP) are often used in the food sector, among others, because of their advantageous properties. As part of the human food chain, they are inevitably taken up orally. The debate on the toxicity of orally ingested ZnO NP continues due to incomplete data. Therefore, the aim of our study was to examine the effects of two differently sized ZnO NP (<50 nm and <100 nm primary particle size; 123-614 µmol/L) on two model systems of the intestinal barrier. Differentiated Caco-2 enterocytes were grown on Transwell inserts in monoculture and also in coculture with the mucus-producing goblet cell line HT29-MTX. Although no comprehensive mucus layer was detectable in the coculture, cellular zinc uptake was clearly lower after a 24-h treatment with ZnO NP than in monocultured cells. ZnO NP showed no influence on the permeability, metabolic activity, cytoskeleton and cell nuclei. The transepithelial electrical resistance was significantly increased in the coculture model after treatment with ≥307 µmol/L ZnO NP. Only small zinc amounts (0.07-0.65 µg/mL) reached the basolateral area. Our results reveal that the cells of an intact intestinal barrier interact with ZnO NP but do not suffer serious damage.

Digital research data: from analysis of existing standards to a scientific foundation for a modular metadata schema in nanosafety

BACKGROUND

Assessing the safety of engineered nanomaterials (ENMs) is an interdisciplinary and complex process producing huge amounts of information and data. To make such data and metadata reusable for researchers, manufacturers, and regulatory authorities, there is an urgent need to record and provide this information in a structured, harmonized, and digitized way.

RESULTS

This study aimed to identify appropriate description standards and quality criteria for the special use in nanosafety. There are many existing standards and guidelines designed for collecting data and metadata, ranging from regulatory guidelines to specific databases. Most of them are incomplete or not specifically designed for ENM research. However, by merging the content of several existing standards and guidelines, a basic catalogue of descriptive information and quality criteria was generated. In an iterative process, our interdisciplinary team identified deficits and added missing information into a comprehensive schema. Subsequently, this overview was externally evaluated by a panel of experts during a workshop. This whole process resulted in a minimum information table (MIT), specifying necessary minimum information to be provided along with experimental results on effects of ENMs in the biological context in a flexible and modular manner. The MIT is divided into six modules: general information, material information, biological model information, exposure information, endpoint read out information and analysis and statistics. These modules are further partitioned into module subdivisions serving to include more detailed information. A comparison with existing ontologies, which also aim to electronically collect data and metadata on nanosafety studies, showed that the newly developed MIT exhibits a higher level of detail compared to those existing schemas, making it more usable to prevent gaps in the communication of information.

CONCLUSION

Implementing the requirements of the MIT into e.g., electronic lab notebooks (ELNs) would make the collection of all necessary data and metadata a daily routine and thereby would improve the reproducibility and reusability of experiments. Furthermore, this approach is particularly beneficial regarding the rapidly expanding developments and applications of novel non-animal alternative testing methods.

Printer center nanoparticles alter the DNA repair capacity of human bronchial airway epithelial cells

Nano-enabled, toner-based printing equipment emit nanoparticles during operation. The bioactivity of these nanoparticles as documented in a plethora of published toxicological studies raises concerns about their potential health effects. These include pro-inflammatory effects that can lead to adverse epigenetic alterations and cardiovascular disorders in rats. At the same time, their potential to alter DNA repair pathways at realistic doses remains unclear. In this study, size-fractionated, airborne particles from a printer center in Singapore were sampled and characterized. The PM_0.1 size fraction (particles with an aerodynamic diameter less than 100 nm) of printer center particles (PCP) were then administered to human lung adenocarcinoma (Calu-3) or lymphoblastoid (TK6) cells. We evaluated plasma membrane integrity, mitochondrial activity, and intracellular reactive oxygen species (ROS) generation. Moreover, we quantified DNA damage and alterations in the cells' capacity to repair 6 distinct types of DNA lesions. Results show that PCP altered the ability of Calu-3 cells to repair 8oxoG:C lesions and perform nucleotide excision repair, in the absence of acute cytotoxicity or DNA damage. Alterations in DNA repair capacity have been correlated with the risk of various diseases, including cancer, therefore further genotoxicity studies are needed to assess the potential risks of PCP exposure, at both occupational settings and at the end-consumer level.

Immunotoxicity of nanomaterials in health and disease: Current challenges and emerging approaches for identifying immune modifiers in susceptible populations

Nanosafety assessment has experienced an intense era of research during the past decades driven by a vivid interest of regulators, industry, and society. Toxicological assays based on in vitro cellular models have undergone an evolution from experimentation using nanoparticulate systems on singular epithelial cell models to employing advanced complex models more realistically mimicking the respective body barriers for analyzing their capacity to alter the immune state of exposed individuals. During this phase, a number of lessons were learned. We have thus arrived at a state where the next chapters have to be opened, pursuing the following objectives: (1) to elucidate underlying mechanisms, (2) to address effects on vulnerable groups, (3) to test material mixtures, and (4) to use realistic doses on (5) sophisticated models. Moreover, data reproducibility has become a significant demand. In this context, we studied the emerging concept of adverse outcome pathways (AOPs) from the perspective of immune activation and modulation resulting in pro-inflammatory versus tolerogenic responses. When considering the interaction of nanomaterials with biological systems, protein corona formation represents the relevant molecular initiating event (e.g., by potential alterations of nanomaterial-adsorbed proteins). Using this as an example, we illustrate how integrated experimental-computational workflows combining in vitro assays with in silico models aid in data enrichment and upon comprehensive ontology-annotated (meta)data upload to online repositories assure FAIRness (Findability, Accessibility, Interoperability, Reusability). Such digital twinning may, in future, assist in early-stage decision-making during therapeutic development, and hence, promote safe-by-design innovation in nanomedicine. Moreover, it may, in combination with in silico-based exposure-relevant dose-finding, serve for risk monitoring in particularly loaded areas, for example, workplaces, taking into account pre-existing health conditions. This article is categorized under: Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials.

Cellular and Molecular Mechanisms of Toxicity of Ingested Titanium Dioxide Nanomaterials

An exponential increase in products containing titanium dioxide nanomaterials (TiO2), in agriculture, food and feed industry, lead to increased oral exposure to these nanomaterials (NMs). Thus, the gastrointestinal tract (GIT) emerges as a possible route of exposure that may drive systemic exposure, if the intestinal barrier is surpassed. NMs have been suggested to produce adverse outcomes, such as genotoxic effects, that are associated with increased risk of cancer, leading to a concern for public health. However, to date, the differences in the physicochemical characteristics of the NMs studied and other variables in the test systems have generated contradictory results in the literature. Processes like human digestion may change the NMs characteristics, inducing unexpected toxic effects in the intestine. Using TiO2 as case-study, this chapter provides a review of the works addressing the interactions of NMs with biological systems in the context of intestinal tract and digestion processes, at cellular and molecular level. The knowledge gaps identified suggest that the incorporation of a simulated digestion process for in vitro studies has the potential to improve the model for elucidating key events elicited by these NMs, advancing the nanosafety studies towards the development of an adverse outcome pathway for intestinal effects.