Proinflammogenic effects of low-toxicity and metal nanoparticles in vivo and in vitro: highlighting the role of particle surface area and surface reactivity

Bioaccessibility of Metallic Nickel and Nickel Oxide Nanoparticles in Four Simulated Biological Fluids

Bioaccessibility of metals from substances and alloys is increasingly used as part of the assessment to predict potential toxicity. However, data are sparse on the metal bioaccessibility from nanoparticle (NP) size metal substances. This study examines nickel ion release from metallic nickel and nickel oxide micron particles (MPs) and NPs in simulated biological fluids at various timepoints including those relevant for specific routes of exposure. The results suggest that MPs of both metallic nickel and nickel oxide generally released more nickel ions in acidic simulated biological fluids (gastric and lysosomal) than NPs of the same substance, with the largest differences being for nickel oxide. In more neutral pH fluids (interstitial and perspiration), nickel metal NPs released more nickel ions than MPs, with nickel oxide results showing a higher release for MPs in interstitial fluid yet a lower release in perspiration fluid. Various experimental factors related to the particle, fluid, and extraction duration were identified that can have an impact on the particle dissolution and release of nickel ions. Overall, the results suggest that based on nickel release alone, nickel NPs are not inherently more hazardous than nickel MPs. Moreover, analyses should be performed on a case-by-case basis with consideration of various experimental factors and correlation with in vivo data.

Optimizing Wound Healing: Examining the Influence of Biopolymers Through a Comprehensive Review of Nanohydrogel-Embedded Nanoparticles in Advancing Regenerative Medicine

Nanohydrogel wound healing refers to the use of nanotechnology-based hydrogel materials to promote the healing of wounds. Hydrogel dressings are made up of a three-dimensional network of hydrophilic polymers that can absorb and retain large amounts of water or other fluids. Nanohydrogels take this concept further by incorporating nanoscale particles or structures into the hydrogel matrix. These nanoparticles can be made of various materials, such as silver, zinc oxide, or nanoparticles derived from natural substances like chitosan. The inclusion of nanoparticles can provide additional properties and benefits to the hydrogel dressings. Nanohydrogels can be designed to release bioactive substances, such as growth factors or drugs, in a controlled manner. This allows for targeted delivery of therapeutics to the wound site, promoting healing and reducing inflammation. Nanoparticles can reinforce the structure of hydrogels, improving their mechanical strength and stability. Nanohydrogels often incorporate antimicrobial nanoparticles, such as silver or zinc oxide. These nanoparticles have shown effective antimicrobial activity against a wide range of bacteria, fungi, and other pathogens. By incorporating them into hydrogel dressings, nanohydrogels can help prevent or reduce the risk of infection in wounds. Nanohydrogels can be designed to encapsulate and release bioactive substances, such as growth factors, peptides, or drugs, in a controlled and sustained manner. This targeted delivery of therapeutic agents promotes wound healing by facilitating cell proliferation, reducing inflammation, and supporting tissue regeneration. The unique properties of nanohydrogels, including their ability to maintain a moist environment and deliver bioactive agents, can help accelerate the wound healing process. By creating an optimal environment for cell growth and tissue repair, nanohydrogels can promote faster and more efficient healing of wounds.

Size- and oxidative potential-dependent toxicity of environmentally relevant expanded polystyrene styrofoam microplastics to macrophages

Expanded polystyrene (EPS), also known as Styrofoam, is a widespread global pollutant, and its lightweight floating property increases its chances of weathering by abrasion and ultraviolet (UV) irradiation, resulting in microplastics. Herein, we investigated the effects of particle size ((1 µm versus 10 µm), UV irradiation (pristine versus UV oxidation), and origin (secondary versus primary) on the toxicity of Styrofoam microplastics. The target cells used in this study were selected based on human exposure-relevant cell lines: differentiated THP-1 cells for macrophages, Caco-2 for enterocytes, HepG2 for hepatocytes, and A549 for alveolar epithelial cells. In the differentiated THP-1 cells, the levels of cytotoxicity and inflammatory cytokines showed size- (1 µm > 10 µm), UV oxidation- (UV > pristine), and origin- (secondary > primary) dependency. Furthermore, the intrinsic oxidative potential of the test particles was positively correlated with cellular oxidative levels and toxicity endpoints, suggesting that the toxicity of Styrofoam microplastics also follows the oxidative stress paradigm. Additionally, all microplastics induced the activation of the pyrin domain-containing protein 3 (NLRP3) inflammasome and the release of interleukin-1β (IL-1β). These results imply that weathering process can aggravate the toxicity of Styrofoam microplastics due to the increased oxidative potential and decreased particle size.

Kinetic mechanism of wheat straw pellets combustion process with a thermogravimetric analyser

In this study, the combustion characteristics of two wheat straw pellets (WSP) (T1: 100% wheat straw and T5: 70% wheat straw; 10% sawdust, 10% biochar; 10% bentonite clay) were performed at a heating rate 20 °C/min under a temperature from 25 to 1200 °C in air atmosphere. A thermogravimetric analyser (TGA) was used to investigate the activation energy (Eα), pre-exponential factor (A), and thermodynamic parameters. The DTG/TG profile of WSP was evaluated by model-free and model-based methods and found the model-based method was suitable for WSP thermal characterisation. The result demonstrates that the thermal decomposition occurred in four stages, comprising four consecutive reaction steps. A→B→C→D→E→F. Further, the model-based techniques were best fitted with kinetic reaction models like Cn (nth-order reaction with auto-catalyst), Fn (reaction of nth order), F2 (second-order phase interfacial reaction) and D3 (diffusion control). The average Eα for Fn, Cn, D3 and F2 models were 164.723, 189.782, 273.88, and 45.0 kJ/mol, respectively, for the T1 pellets. Alternatively, for T5 pellets, the A was 1.17E+2, 1.76E+16, 5.5E+23, and 1.1E+3 (1/s) for F2, D3, Cn and Fn models. Overall, the thermodynamic properties showed that WSP thermokinetic reactions were complex and multi-point equilibrium, indicating a potentiality as a bioenergy feedstock.

Uncovering the cytotoxic effects of air pollution with multi-modal imaging of in vitro respiratory models

Annually, an estimated seven million deaths are linked to exposure to airborne pollutants. Despite extensive epidemiological evidence supporting clear associations between poor air quality and a range of short- and long-term health effects, there are considerable gaps in our understanding of the specific mechanisms by which pollutant exposure induces adverse biological responses at the cellular and tissue levels. The development of more complex, predictive, in vitro respiratory models, including two- and three-dimensional cell cultures, spheroids, organoids and tissue cultures, along with more realistic aerosol exposure systems, offers new opportunities to investigate the cytotoxic effects of airborne particulates under controlled laboratory conditions. Parallel advances in high-resolution microscopy have resulted in a range of in vitro imaging tools capable of visualizing and analysing biological systems across unprecedented scales of length, time and complexity. This article considers state-of-the-art in vitro respiratory models and aerosol exposure systems and how they can be interrogated using high-resolution microscopy techniques to investigate cell-pollutant interactions, from the uptake and trafficking of particles to structural and functional modification of subcellular organelles and cells. These data can provide a mechanistic basis from which to advance our understanding of the health effects of airborne particulate pollution and develop improved mitigation measures.

Characterizing Nanoparticle Release Patterns of Laser Powder Bed Fusion in Metal Additive Manufacturing: First Step Towards Mitigation Measures

Laser Powder Bed Fusion (L-PBF) is a well-known Additive Manufacturing (AM) technology with a wide range of industrial applications. Potential occupational exposures to metal nanoparticles (NP) as by-products could occur in these processes, and no cogent occupational exposure limits are available. To contribute to this assessment, a monitoring campaign to measure the NP release pattern in two metal L-PBF facilities was carried out in two academic laboratories adopting L-PBF technology for research purposes. The monitored processes deal with two devices and three feedstock types, namely stainless steel (AISI 316L), aluminium-silicon alloy (A357) and pure copper, which are associated with different levels of industrial maturity. Prolonged environmental and personal real-time monitoring of NP concentration and size were performed, temperature and relative humidity were also measured during environmental monitoring. The measurements reveal a controlled NP release of the monitored processes, resulting in an average reduced exposure of the operators during the whole working shift, in compliance with proposed limit values (20 000 n cm-3 for density >6000 kg m-3 or 40 000 n cm-3 for density <6000 kg m-3). Nonetheless, the monitoring results show release events with an increase in NP concentration and a decrease in NP size corresponding with several actions usually performed during warm-up and cleaning, leading to exposures over 40-50 000 n cm-3 during a considerable time interval, especially during the manufacturing of pure copper powder. The results show that the actions of the operators, boundary conditions (relative humidity) and set-up of the L-PBF device have an impact on the amount of NP released and their size. Several release events (significant increase in NP concentration and decrease in NP size) are identified and associated with specific job tasks of the workers as well as building conditions. These results contribute to the definition of NP release benchmarks in AM processes and provide information to improve the operational conditions of L-PBF processes as well as safety guidelines for operators.

Computational Fluid Dynamics Simulations of Aerosol Behavior in a High Speed (Heubach) Rotating Drum Dustiness Tester

Potential exposure from hazardous dusts may be assessed by evaluating the dustiness of the powders being handled. Dustiness is the tendency of a powder to aerosolize with a given input of energy. We have previously used computational fluid dynamics (CFD) to numerically investigate the flow inside the European Standard (EN15051) Rotating Drum dustiness tester during its operation. The present work extends those CFD studies to the widely used Heubach Rotating Drum. Air flow characteristics are investigated within the Abe-Kondoh-Nagano k-epsilon turbulence model; the aerosol is incorporated via a Euler-Lagrangian multiphase approach. The air flow inside these drums consists of a well-defined axial jet penetrating relatively quiescent air. The spreading of the Heubach jet results in a fraction of the jet recirculating as back-flow along the drum walls; at high rotation rates, the axial jet becomes unstable. This flow behavior qualitatively differs from the stable EN15051 flow pattern. The aerodynamic instability promotes efficient mixing within the Heubach drum, resulting in higher particle capture efficiencies for particle sizes d < 80 μm.

Dynamic Fluid Flow Exacerbates the (Pro-)Inflammatory Effects of Aerosolised Engineered Nanomaterials In Vitro

The majority of in vitro studies focusing upon particle-lung cell interactions use static models at an air-liquid interface (ALI). Advancing the physiological characteristics of such systems allows for closer resemblance of the human lung, in turn promoting 3R strategies. PATROLS (EU Horizon 2020 No. 760813) aimed to use a well-characterised in vitro model of the human alveolar epithelial barrier to determine how fluid-flow dynamics would impact the outputs of the model following particle exposure. Using the QuasiVivo^TM (Kirkstall Ltd., York, UK) system, fluid-flow conditions were applied to an A549 + dTHP-1 cell co-culture model cultured at the ALI. DQ₁₂ and TiO₂ (JRCNM01005a) were used as model particles to assess the in vitro systems' sensitivity. Using a quasi- and aerosol (VitroCell Cloud12, VitroCell Systems, Waldkirch, Germany) exposure approach, cell cultures were exposed over 24 h at IVIVE concentrations of 1 and 10 (DQ₁₂) and 1.4 and 10.4 (TiO₂) µg/cm², respectively. We compared static and fluid flow conditions after both these exposure methods. The co-culture was subsequently assessed for its viability, membrane integrity and (pro-)inflammatory response (IL-8 and IL-6 production). The results suggested that the addition of fluid flow to this alveolar co-culture model can influence the viability, membrane integrity and inflammatory responses dependent on the particle type and exposure.

In vitro evaluation of the inhalation toxicity of the cosmetic ingredient aluminum chlorohydrate

Aluminum chlorohydrate (ACH) is a major aerosol component frequently used as the active ingredient in antiperspirants, and in vivo studies have raised a concern about its inhalation toxicity. Still, few studies have addressed its effects on the human respiratory tract. Therefore, we developed a study on ACH inhalation toxicity using an in vitro human alveolar cell model (A549 cells) with molecular and cellular markers of oxidative stress, immunotoxicity, and epigenetic changes. The chemical characterization of ACH suspensions indicated particle instability and aggregation; however, side-scatter analysis demonstrated significant particle uptake in cells exposed to ACH. Exposure of A549 cells to non-cytotoxic concentrations of ACH (0.25, 0.5, and 1 mg/ml) showed that ACH induced reactive oxygen species. Moreover, ACH upregulated TNF, IL6, IL8, and IL1A genes, but not the lncRNAs NEAT1 and MALAT1. Finally, no alterations on the global DNA methylation pattern (5-methylcytosine and 5-hydroxymethylcytosine) or the phosphorylation of histone H2AX (γ-H2AX) were observed. Our data suggest that ACH may induce oxidative stress and inflammation on alveolar cells, and A549 cells may be useful to identify cellular and molecular events that may be associated with adverse effects on the lungs. Still, further research is needed to ensure the inhalation safety of ACH.

Biomarkers of nanomaterials hazard from multi-layer data

There is an urgent need to apply effective, data-driven approaches to reliably predict engineered nanomaterial (ENM) toxicity. Here we introduce a predictive computational framework based on the molecular and phenotypic effects of a large panel of ENMs across multiple in vitro and in vivo models. Our methodology allows for the grouping of ENMs based on multi-omics approaches combined with robust toxicity tests. Importantly, we identify mRNA-based toxicity markers and extensively replicate them in multiple independent datasets. We find that models based on combinations of omics-derived features and material intrinsic properties display significantly improved predictive accuracy as compared to physicochemical properties alone.

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.

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

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

Developing a Solution for Nasal and Olfactory Transport of Nanomaterials

With advances in nanotechnology, engineered nanomaterial applications are a rapidly growing sector of the economy. Some nanomaterials can reach the brain through nose-to-brain transport. This transport creates concern for potential neurotoxicity of insoluble nanomaterials and a need for toxicity screening tests that detect nose-to-brain transport. Such tests can involve intranasal instillation of aqueous suspensions of nanomaterials in dispersion media that limit particle agglomeration. Unfortunately, protein and some elements in existing dispersion media are suboptimal for potential nose-to-brain transport of nanomaterials because olfactory transport has size- and ion-composition requirements. Therefore, we designed a protein-free dispersion media containing phospholipids and amino acids in an isotonic balanced electrolyte solution, a solution for nasal and olfactory transport (SNOT). SNOT disperses hexagonal boron nitride nanomaterials with a peak particle diameter below 100 nm. In addition, multiwalled carbon nanotubes (MWCNTs) in an established dispersion medium, when diluted with SNOT, maintain dispersion with reduced albumin concentration. Using stereomicroscopy and microscopic examination of plastic sections, dextran dyes dispersed in SNOT are demonstrated in the neuroepithelium of the nose and olfactory bulb of B6;129P2-Omp^tm3Mom/MomJ mice after intranasal instillation in SNOT. These findings support the potential for SNOT to disperse nanomaterials in a manner permitting nose-to-brain transport for neurotoxicity studies.

The influence of exposure approaches to in vitro lung epithelial barrier models to assess engineered nanomaterial hazard

Exposure to engineered nanomaterials (ENM) poses a potential health risk to humans through long-term, repetitive low-dose exposures. Currently, this is not commonplace within in vitro lung cell cultures. Therefore, the purpose of this study was to consider the optimal exposure approach toward determining the stability, sensitivity and validity of using in vitro lung cell mono- and co-cultures to determine ENM hazard. A range of exposure scenarios were conducted with DQ₁₂ (previously established as a positive particle control) (historic and re-activated), TiO₂ (JRC NM-105) and BaSO₄ (JRC NM-220) on both monocultures of A549 cells as well as co-cultures of A549 cells and differentiated THP-1 cells. Cell cultures were exposed to either a single, or a repeated exposure over 24, 48- or 72-hours at in vivo extrapolated concentrations of 0-5.2 µg/cm², 0-6 µg/cm² and 0-1µg/cm². The focus of this study was the pro-inflammatory, cytotoxic and genotoxic response elicited by these ENMs. Exposure to DQ₁₂ caused pro-inflammatory responses after 48 hours repeat exposures, as well as increases in micronucleus frequency. Neither TiO₂ nor BaSO₄ elicited a pro-inflammatory response at this time point. However, there was induction of IL-6 after 24 hours TiO₂ exposure. In conclusion, it is important to consider the appropriateness of the positive control implemented, the cell culture model, the time of exposure as well as the type of exposure (bolus or fractionated) before establishing if an in vitro model is appropriate to determine the level of response to the specific ENM of interest.

Preparation of Mesoporous Silica Nanosphere-Doped Color-Sensitive Materials and Application in Monitoring the TVB-N of Oysters

In this work, a new colorimetric sensor based on mesoporous silica nanosphere-modified color-sensitive materials was established for application in monitoring the total volatile basic nitrogen (TVB-N) of oysters. Firstly, mesoporous silica nanospheres (MSNs) were synthesized based on the improved Stober method, then the color-sensitive materials were doped with MSNs. The “before image” and the “after image” of the colorimetric senor array, which was composed of nanocolorimetric-sensitive materials by a charge-coupled device (CCD) camera were then collected. The different values of the before and after image were analyzed by principal component analysis (PCA). Moreover, the error back-propagation artificial neural network (BP-ANN) was used to quantitatively predict the TVB-N values of the oysters. The correlation coefficient of the colorimetric sensor array after being doped with MSNs was greatly improved; the Rc and Rp of BP-ANN were 0.9971 and 0.9628, respectively when the principal components (PCs) were 10. Finally, a paired sample t-test was used to verify the accuracy and applicability of the BP-ANN model. The result shows that the colorimetric-sensitive materials doped with MSNs could improve the sensitivity of the colorimetric sensor array, and this research provides a fast and accurate method to detect the TVB-N values in oysters.

Contribution of Physical and Chemical Properties to Dithiothreitol-Measured Oxidative Potentials of Atmospheric Aerosol Particles at Urban and Rural Sites in Japan

Dithiothreitol-measured oxidative potential (OPDTT) can chemically quantify the adverse health effects of atmospheric aerosols. Some chemical species are characterized with DTT activities, and the particle diameter and surface area control DTT oxidizability; however, the physical contribution to OPDTT by atmospheric aerosols is controversial. Therefore, we performed field observations and aerosol sampling at urban and rural sites in Japan to investigate the effect of both physical and chemical properties on the variation in OPDTT of atmospheric aerosols. The shifting degree of the representative diameter to the ultrafine range (i.e., the predominance degree of ultrafine particles) was retrieved from the ratio between the lung-deposited surface area and mass concentrations. The chemical components and OPDTT were also elucidated. We discerned strong positive correlations of K, Mn, Pb, NH4+, SO42−, and pyrolyzable organic carbon with OPDTT. Hence, anthropogenic combustion, the iron–steel industry, and secondary organic aerosols were the major emission sources governing OPDTT variations. The increased specific surface area did not lead to the increase in the OPDTT of atmospheric aerosols, despite the existing relevance of the surface area of water-insoluble particles to DTT oxidizability. Overall, the OPDTT of atmospheric aerosols can be estimated by the mass of chemical components related to OPDTT variation, owing to numerous factors controlling DTT oxidizability (e.g., strong contribution of water-soluble particles). Our findings can be used to estimate OPDTT via several physicochemical parameters without its direct measurement.

Evaluation of Antioxidant Activity and Histopathological Changes Occurred by the Oral Ingestion of CuO Nanoparticles in Monosodium Urate Crystal-Induced Hyperuricemic BALB/c Mice

Nanotechnology is an intensive branch of science due to the unique features of nano range particles (1-100 nm). Their nano size results in a high surface area of absorption when orally administered. Monosodium urate crystal excessive deposition causes a commonly known inflammatory disease called gout into the synovial joints. Previously it has been observed that copper oxide nanoparticles (CuONPs) had a significant effect in reducing the serum uric acid levels in BALB/c mice as well as reducing the inflammation in the ankles of mice. This study was made to investigate the antioxidant and histopathological changes in hyperuricemic BALB/c mice upon the oral administration of copper oxide nanoparticles. Different concentrations of copper oxide nanoparticles 5, 10, and 20 ppm were given orally to gouty mice. To investigate the antioxidant activity of CuONPs, various antioxidant protocols were applied. It was noted that the nanoparticle-treated group of 20 ppm showed no significant changes in superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), thiobarbituric acid reactive substances (TBARS), and ROS values while the protein estimation values of the negative control group exhibited a significant increase (0.001). When compared to negative control, no significant effect was shown on the interpretation of histopathological changes of muscles, kidney, and liver tissues.

An in vitro assessment of the toxicity of two-dimensional synthetic and natural layered silicates

Natural Layered Silicates (NLS) and Synthetic Layered Silicates (SLS) are a diverse group of clay minerals that have attracted great interest in various branches of industry. However, despite growing demand for this class of material, their impact on human health has not been fully investigated. Therefore, the aim of this study was to evaluate and compare the potential toxic effects of a wide range of commercially available SLS and NLS of varying physicochemical properties (lithium (Li) or fluoride (F) content and size). Mouse BALB/c monocyte macrophage (J774A.1) and human monocyte-derived macrophages (MDMs) were chosen as in vitro models of alveolar macrophages. Montmorillonite, hectorite, Medium (med) F/High Li and Low F/Med Li particles, were cytotoxic to cells and induced potent pro-inflammatory responses. The remaining particles (No F/Very (V)Low Li, No F/Med Li, No F/Low Li, High F/Med Li and High F/Med Li washed) were non- to relatively low- cytotoxic and inflammogenic, in both type of cells. In an acellular condition none of the tested samples increased reactive oxygen species (ROS), while ROS generation was observed following exposure to sublethal concentrations of Med F/High Li, Low F/Med Li, montmorillonite and hectorite samples, in J774A.1 cells. Based on the results obtained in this study the toxic potency of tested samples was not associated with lithium or fluoride content, but appeared to be dependent on particle size, with the platelets of larger dimension and lower surface area being more potent than the smaller platelet particles with higher surface area. In addition, the increased bioactivity of Med F/High Li and Low F/Med Li was associated with endotoxin contamination. Obtained results demonstrated that layered silicate materials have different toxicological profiles and suggest that toxicological properties of a specific layered silicate should be investigated on an individual basis.

Six-well plate-based colony-forming efficacy assay and Co-Culture application to assess toxicity of metal oxide nanoparticles

The development of a universal, label-free, and reliable in vitro toxicity testing method for nanoparticles is urgent because most nanoparticles can interfere with toxicity assays. In this regard, the colony-forming efficacy (CFE) assay has been suggested as a suitable in vitro toxicity assay for testing nanoparticles without such interference. Recently, the Organisation for Economic Co-operation and Development (OECD) developed a 60 × 15 mm Petri dish-based CFE assay for testing nanoparticles in MDCK-1 cells. However, further investigations are needed, including testing with other cell types, at a smaller scale for greater efficiency, and the application of the co-culture technique. In this study, we selected TiO₂, CuO, CeO₂, and SiO₂ as test nanoparticles and successfully developed a 6-well plate-based CFE assay using HepG2 and A549 cells and a co-culture assay for combinations of HepG2 cells and THP-1 macrophages or A549 cells and THP-1 monocytes. The results suggest that the 6-wellplate-based CFE assay for HepG2 and A549 cells can be applied to nanoparticles, but the co-culture CFE assay has limitations in that it is not different from the single culture study, and it inhibits colony-formation by A549 cells in the presence of macrophages; this warrant further study.

An Integrated Approach to Testing and Assessment to Support Grouping and Read-Across of Nanomaterials After Inhalation Exposure

Introduction: Here, we describe the generation of hypotheses for grouping nanoforms (NFs) after inhalation exposure and the tailored Integrated Approaches to Testing and Assessment (IATA) with which each specific hypothesis can be tested. This is part of a state-of-the-art framework to support the hypothesis-driven grouping and read-across of NFs, as developed by the EU-funded Horizon 2020 project GRACIOUS.

Development of Grouping Hypotheses and IATA: Respirable NFs, depending on their physicochemical properties, may dissolve either in lung lining fluid or in acidic lysosomal fluid after uptake by cells. Alternatively, NFs may also persist in particulate form. Dissolution in the lung is, therefore, a decisive factor for the toxicokinetics of NFs. This has led to the development of four hypotheses, broadly grouping NFs as instantaneous, quickly, gradually, and very slowly dissolving NFs. For instantaneously dissolving NFs, hazard information can be derived by read-across from the ions. For quickly dissolving particles, as accumulation of particles is not expected, ion toxicity will drive the toxic profile. However, the particle aspect influences the location of the ion release. For gradually dissolving and very slowly dissolving NFs, particle-driven toxicity is of concern. These NFs may be grouped by their reactivity and inflammation potency. The hypotheses are substantiated by a tailored IATA, which describes the minimum information and laboratory assessments of NFs under investigation required to justify grouping.

Conclusion: The GRACIOUS hypotheses and tailored IATA for respiratory toxicity of inhaled NFs can be used to support decision making regarding Safe(r)-by-Design product development or adoption of precautionary measures to mitigate potential risks. It can also be used to support read-across of adverse effects such as pulmonary inflammation and subsequent downstream effects such as lung fibrosis and lung tumor formation after long-term exposure.

Microplastics disrupt accurate soil organic carbon measurement based on chemical oxidation method

Microplastics are widespread contaminants in soils and terrestrial ecosystems in many areas worldwide. In this study, we measured soil organic carbon (SOC) and soil organic matter (SOM) in microplastic-treated soils to determine if the presence of microplastics could affect the accuracy of carbon-based soil quality indicator measurements. Six different sizes and types of microplastics were selected, and six soil samples were used to evaluate the impacts. Treating soil with polyethylene and low-density polyethylene significantly increased SOC (p < 0.05) when measured with the modified Walkley & Black method; microplastic addition (0.01%, v/v) increased SOC by >40% compared to control organic carbon-poor soil (<10.0 g kg^-1). We conclude that the microplastics can disrupt the accurate measurement of SOC. Likely, the physicochemical treatment used in the SOC measurement process can cause the organic compounds and/or carbon complexes to be extracted from microplastics, and this can affect the results. Considering that SOC is a main indicator for assessing soil quality and the global carbon cycle, overestimations caused by microplastic contamination should be further discussed to identify appropriate ways to deal with microplastics as a new carbon source in the environment.

Treating colon cancers with a non-conventional yet strategic approach: An overview of various nanoparticulate systems

Regardless of progress in therapy management which are developed for colon cancer (CC), it remains the third most common cause of mortality due to cancers around the world. Conventional medicines pose side effects due to untoward action on non-target cells. Their inability to deliver drugs to the affected regions of the colon locally, in a reproducible manner raises a concern towards the efficacy of therapy. In this regard, nanoparticles emerged as a promising drug delivery system due to their flexibility in designing, drug release modulation and cancer cell targeting. Not only are nanoparticles making their way into colon cancer research in the revolution of conventional onco-therapeutics, but they also offer promising scope in the development of colon cancer vaccines and theranostic tools. However, there are challenges with respect to drug delivery using nanoparticles, which may hamper the delivery of these novel carriers to the colon. The present review addresses recent advents in nanotechnology for colon-specific drug delivery (CDDS) which may help to overcome the existing challenges and intends to recognize futuristic potentials in the treatment of CC with CDDS.

Disinfection mechanism of the photocatalytic activity of SnO2 thin films against Candida albicans, proposed from experimental and simulated perspectives

Nosocomial infections are an important health problem and cause of complications and death in hospitalized patients. This problem should be solved from the preventive angle, avoiding the spread of infections by designing disinfection methods based on the photocatalytic activity of semiconductor materials such as tin oxide (SnO₂). The antimicrobial activity of UV light was tested by using inoculation with Candida albicans ATCC10231 on SnO₂ thin films and counting colony forming units (CFU). The interaction of UV light with SnO₂ was analyzed by density functional theory (DFT) and the extension to the Hubbard model (DFT+U) schemes to predict the electron behavior at the subatomic level. After exposure to UV light, C. albicans showed a reduction of 36.5% in viable cells, and when SnO₂ was included, cell viability was reduced by 60.2%. Measurements of the electronic structure obtained by the first-principle calculations under the DFT and DFT+U schemes showed that the O-p orbitals mediate the oxidation process in the bulk semiconductor. By including the surface effects when cleaving the (1 0 0) plane, the three orbitals O-p, Sn-p, and Sn-s are the mediators. SnO₂ films are promising antimicrobial coatings because UV light has a synergic activity with thin films, resulting in faster disinfection.

Understanding nano-engineered particle-cell interactions: biological insights from mathematical models

Understanding the interactions between nano-engineered particles and cells is necessary for the rational design of particles for therapeutic, diagnostic and imaging purposes. In particular, the informed design of particles relies on the quantification of the relationship between the physicochemical properties of the particles and the rate at which cells interact with, and subsequently internalise, particles. Quantitative models, both mathematical and computational, provide a powerful tool for elucidating this relationship, as well as for understanding the mechanisms governing the intertwined processes of interaction and internalisation. Here we review the different types of mathematical and computational models that have been used to examine particle-cell interactions and particle internalisation. We detail the mathematical methodology for each type of model, the benefits and limitations associated with the different types of models, and highlight the advances in understanding gleaned from the application of these models to experimental observations of particle internalisation. We discuss the recent proposal and ongoing community adoption of standardised experimental reporting, and how this adoption is an important step toward unlocking the full potential of modelling approaches. Finally, we consider future directions in quantitative models of particle-cell interactions and highlight the need for hybrid experimental and theoretical investigations to address hitherto unanswered questions.

Non-Animal Strategies for Toxicity Assessment of Nanoscale Materials: Role of Adverse Outcome Pathways in the Selection of Endpoints

Faster, cheaper, sensitive, and mechanisms-based animal alternatives are needed to address the safety assessment needs of the growing number of nanomaterials (NM) and their sophisticated property variants. Specifically, strategies that help identify and prioritize alternative schemes involving individual test models, toxicity endpoints, and assays for the assessment of adverse outcomes, as well as strategies that enable validation and refinement of these schemes for the regulatory acceptance are needed. In this review, two strategies 1) the current nanotoxicology literature review and 2) the adverse outcome pathways (AOPs) framework, a systematic process that allows the assembly of available mechanistic information concerning a toxicological response in a simple modular format, are presented. The review highlights 1) the most frequently assessed and reported ad hoc in vivo and in vitro toxicity measurements in the literature, 2) various AOPs of relevance to inhalation toxicity of NM that are presently under development, and 3) their applicability in identifying key events of toxicity for targeted in vitro assay development. Finally, using an existing AOP for lung fibrosis, the specific combinations of cell types, exposure and test systems, and assays that are experimentally supported and thus, can be used for assessing NM-induced lung fibrosis, are proposed.

Combination effect of nanoparticles on the acute pulmonary inflammogenic potential: additive effect and antagonistic effect

The combination effect of co-exposed different types of nanomaterials is little known although humans are generally exposed to a mixture of nanomaterials from urban ultrafine particles or industrial nanomaterials. Herein, we evaluated the combined effect of nanoparticles (NPs) using three types of NPs in different inflammogenic categories: carbon black (CB), nickel oxide (NiO), and copper oxide (CuO). A single type of NPs or NPs in combination was intratracheally instilled into the lungs of rats and the bronchoalveolar lavage fluid (BALF) was analyzed at 24 h after instillation to evaluate the acute inflammogenic potential. The percentage of neutrophils in BALF was selected as a toxicity endpoint and the potential for reactive oxygen species (ROS) generation, dose-response of the combined effect, sequential treatment of CB and NiO, and uptake of NiO to alveolar macrophages after combined treatment of CB and NiO were evaluated for the mechanism of the combined effect. Co-exposure of CuO and NiO showed an additive effect on the percentage of neutrophils and ROS generation potential, which implies that the physicochemical properties of each NP are not influenced by the other type. While CB exerted an antagonistic effect on the percentage of neutrophils in combined treatment with CuO or NiO. The antagonistic effect of CB was due to the scavenging activity of the ROS generated by the CuO and NiO rather than the competition in cellular uptake to target cells (i.e. alveolar macrophages), which highlight the importance of the combined effect of NPs in the risk assessment.

Investigations of acute effects of polystyrene and polyvinyl chloride micro- and nanoplastics in an advanced in vitro triple culture model of the healthy and inflamed intestine

The continuous degradation of plastic waste in the environment leads to the generation of micro- and nanoplastic fragments and particles. Due to the ubiquitous presence of plastic particles in natural habitats as well as in food, beverages and tap water, oral exposure of the human population with plastic particles occurs worldwide. We investigated acute toxicological effects of polystyrene (PS) and polyvinyl chloride (PVC) micro- and nanoparticles in an advanced in vitro triple culture model (Caco-2/HT29-MTX-E12/THP-1) mimicking the healthy and inflamed human intestine to study the effect of inflammatory processes on plastic particle toxicity. We monitored barrier integrity, cytotoxicity, cell layer integrity, DNA damage, the release of pro-inflammatory cytokines (IL-1β, IL-6, IL-8 and TNF-α) and mucus distribution after 24 h of particle exposure. In addition, we investigated cytotoxicity, DNA damage and IL-1β release in monocultures of the three cell lines. Amine-modified polystyrene nanoparticles (PS-NH₂) served as a positive control for particle-induced toxicity. No acute effects in the investigated endpoints were observed in the model of the healthy intestine after PS or PVC exposure. However, during active inflammatory processes, exposure to PVC particles was found to augment the release of IL-1β and to cause a loss of epithelial cells. Our results suggest that prevalent intestinal inflammation might be an important factor to consider when assessing the hazard of ingested micro- and nanoplastic particles.

Nanotechnology shaping stem cell therapy: Recent advances, application, challenges, and future outlook

Currently, stem cell nanotechnology is one of the novel and exciting fields. Certain experimental studies conducted on the interaction of stem cells with nanostructures or nanomaterials have made significant progress. The significance of nanostructures, nanotechnology, and nanomaterials in the development of stem cell-based therapies for degenerative diseases and injuries has been well established. Specifically, the structure and properties of nanomaterials affecting the propagation and differentiation of stem cells have become a new interdisciplinary frontier in material science and regeneration medicines. In the current review, we highlight the recent major progress in this field, explore the application prospects, and discuss the issues, approaches, and challenges, to improve the applications of nanotechnology in the research and development of stem cells.

Rationale and decision rules behind the ECETOC NanoApp to support registration of sets of similar nanoforms within REACH

New registration requirements for nanomaterials under REACH consider the possibility to form 'sets of similar nanoforms' for a joined human health and environmental hazard, exposure and risk assessment. We developed a tool to create and justify sets of similar nanoforms and to ensure that each of the nanoforms is sufficiently similar to all other nanoforms. The decision logic is following the ECHA guidance in a transparent and evidence-based manner. For each two nanoforms the properties under consideration are compared and corresponding thresholds for maximal differences are proposed. In tier1, similarity is assessed based on intrinsic properties that mostly correspond to those required for nanoform identification under REACH: composition, impurities/additives, size, crystallinity, shape and surface treatment. Moreover, potential differences in the agglomeration/aggregation state resulting from different production processes are considered. If nanoforms were not sufficiently similar based on tier1 criteria, additional data from functional assays are required in tier2. In rare cases, additional short-term in vivo rodent data could be required in a third tier. Data required by tier 2 are triggered by the intrinsic properties in the first tier that did not match the similarity criteria. Most often this will be data on dissolution and surface reactivity followed by in vitro toxicity, dispersion stability, dustiness. Out of several nanoforms given by the user, the tool concludes which nanoforms could be justified to be in the same set and which nanoforms are outside. It defines the boundaries of sets of similar nanoforms and generates a justification for the REACH registration.

Use of Superparamagnetic Iron Oxide Nanoparticles (SPIONs) via Multiple Imaging Modalities and Modifications to Reduce Cytotoxicity: An Educational Review

The aim of the present educational review on superparamagnetic iron oxide nanoparticles (SPIONs) is to inform and guide young scientists and students about the potential use and challenges associated with SPIONs. The present review discusses the basic concepts of magnetic resonance imaging (MRI), basic construct of SPIONs, cytotoxic challenges associated with SPIONs, shape and sizes of SPIONs, site-specific accumulation of SPIONs, various methodologies applied to reduce cytotoxicity including coatings with various materials, and application of SPIONs in targeted delivery of chemotherapeutics (Doxorubicin), biotherapeutics (DNA, siRNA), and positron emission tomography (PET) imaging applications.

The REACH registration process: A case study of metallic aluminium, aluminium oxide and aluminium hydroxide

The European Union's REACH Regulation requires determination of potential health and environmental effects of chemicals in commerce. The present case study examines the application of REACH guidance for health hazard assessments of three high production volume (HPV) aluminium (Al) substances: metallic aluminium, aluminium oxide, and aluminium hydroxide. Among the potential adverse health consequences of aluminium exposure, neurotoxicity is one of the most sensitive targets of Al toxicity and the most critical endpoint. This case study illustrates integration of data from multiple lines of evidence into REACH weight of evidence evaluations. This case study then explains how those results support regulatory decisions on classification and labelling. Challenges in the REACH appraisal of Al compounds include speciation, solubility and bioavailability, application of assessment factors, read-across rationale and differences with existing regulatory standards. Lessons learned from the present case study relate to identification and evaluation of toxicologic and epidemiologic data; assessing data relevance and reliability; development of derived no-effect levels (DNELs); addressing data gaps and preparation of chemical safety reports.

Exposure, assessment and health hazards of particulate matter in metal additive manufacturing: A review

Metal additive manufacturing (AM), also known as metal three-dimensional (3D) printing, is a new technology offering design freedom to create complex structures that has found increasing applications in industrial processes. However, due to the fine metal powders and high temperatures involved, the printing process is likely to generate particulate matter (PM) that has a detrimental impact on the environment and human health. Therefore, comprehensive assessement of the exposure and health hazards of PM pollution related to this technique is urgently required. This review provides general knowledge of metal AM and its possible particle release. The health issues of metal PM are described considering the exposure routes, adverse human health outcomes and influencing factors. Methods of evaluating PM exposure and risk assessment techniques are also summarized. Lastly, future research needs are suggested. The information and knowledge presented in this review will contribute to the understanding, assessment, and control of possible risks in metal AM and benefit the wider metal 3D printing community, which includes machine operators, consumers, R&D scientists, and policymakers.

The sp3/sp2 carbon ratio as a modulator of in vivo and in vitro toxicity of the chemically purified detonation-synthesized nanodiamond via the reactive oxygen species generation

Nanodiamonds have been suggested as biocompatible materials and are suitable for various biomedical applications, but little is known about how to synthesize safer nanodiamonds. Herein, seven different detonation-synthesized nanodiamonds (DNDs) with sequential sp³/sp² carbon ratios were assembled by controlling the chemical purification parameters and the role of sp³/sp² carbon ratio on the toxicity of DNDs was investigated. Carbon black and nickel oxide nanoparticles were used as reference particles. The intrinsic reactive oxygen species (ROS) generation potential of DNDs was estimated by a 2'7'-dichlorofluorescein diacetate (DCFH-DA) assay, and these values showed a good negative correlation with the sp³/sp² carbon ratios, which implies that ROS generation increased as the sp³/sp² carbon ratio decreased. As a model to investigate inflammogenic potential of DND samples, a rat intratracheal instillation model was used as the lung is very sensitive to nanoparticle exposures. The sp³/sp² carbon ratios or the estimated values of ROS generation potential showed excellent linear correlations with the number of neutrophils and pro-inflammatory cytokines in bronchoalveolar lavage fluid at 24 h after instillation. Treatment of DND samples to THP-1 derived macrophages also showed that the sp³/sp² carbon ratios or the estimated values of ROS generation potential were closely related with the toxicity endpoints such as cell viability and pro-inflammatory cytokines. Taken together, these data demonstrate that the sp³/sp² carbon ratio is the key determinant for the toxicity of DNDs, which can be a useful tool for the safer-by-design approach of DNDs and the safety assessment of carbon nanoparticles.

Determination of total and lung-deposited particle surface area concentrations, in central Athens, Greece

Numerous health studies have linked the exposure to particulate matter with adverse health effects, while there is an increasing scientific interest in the particle metrics of surface area (SA) and lung-deposited SA (LDSA) concentration. In the present study, two integrated SA estimation methods, both based on widely used instrumentation, were applied at an urban traffic environment in Athens for a 6-month period. The first estimation method used the size distribution by number to estimate SA (average SA₁ 669.3 ± 229.0 μm² cm^-3), while the second method used a simple inversion scheme that incorporates number and mass concentrations (average SA₂ 1627.9 ± 562.8 μm² cm^-3). In pairwise comparisons, SA₂ levels were found two times greater than the corresponding SA₁, but exhibited a strong correlation (r = 0.73). SA₁ and SA₂ concentrations correlated well with the traffic-related pollutants NO_x (r = 0.64 and 0.78) and equivalent black carbon (r = 0.53 and 0.51). The diurnal variation of SA₁ concentrations by size range indicated traffic as a major controlling factor. Estimated LDSA (53.9 μm² cm^-3 on average) concentrations were also clearly affected by anthropogenic emissions with more pronounced associations in the 0.01-0.4 μm range (r = 0.66 with NO_x and r = 0.65 with equivalent black carbon). Validating estimated LDSA through simultaneous measurements with a reference instrument revealed that the estimation method underestimates LDSA by a factor between 2 and 3, exhibiting, however, a high correlation (r = 0.79). Overall, the performance of estimation methods appear satisfactory and indicate that a trustworthy assessment of the temporal variability of SA and LDSA concentration metrics can be provided in real time, on the basis of relatively lower-cost instrumentation, especially in view of recent advances in particle sensing technologies.

A concise review of metallic nanoparticles encapsulation methods and their potential use in anticancer therapy and medicine

Interest in the use of metallic nanoparticles (NPs) in medicine is constantly increasing. The key challenge to the introduction of NPs into anticancer treatment is to limit the contact of their surface with healthy cells and to enable specific targeting of certain tissues, for example, cancerous cells. These aspects have raised a question whether the recent methods of drug delivery allow restricting the contact of NPs with healthy and/or nontarget cells. NPs can be restricted by encapsulation, which involves entrapping them into organic layers. This review is the first to present the different approaches for the encapsulation of metallic NPs, using liposomes, dendrimers, and proteins. The types and methods of entrapping are shown in an accessible way, enriched with graphics, and the pros and cons of these methods are disputable. Furthermore, the potential uses of NP complexes in medicine are described.

Segregation of respirable dust for chemical and toxicological analyses

Respirable dust can pass beyond ciliated airways of the respiratory tract and influence adverse health effects. Health effects can be studied using samples generated from bulk dust segregation. Because previous segregation methods diverge from size-selection criteria of the international convention for respirable particles (ICRP), a method was developed to approximate the ICRP. The method was compared to an ideal sampler by measuring the sample collection bias. The comparison shows that the uncertainty due to the bias was 0.10 based on European Standard EN13205:2014 criteria, which indicates that the segregator effectively follows the ICRP. Respirable particle size distributions were confirmed by an aerodynamic particle sizer and by computer-controlled scanning electron microscopy. Consequently, a systematic way to generate respirable powders for health effects studies and chemical analyses was developed.

Inflammation, oxidative stress and genotoxicity responses to biodiesel emissions in cultured mammalian cells and animals

Biodiesel fuels are alternatives to petrodiesel, especially in the transport sector where they have lower carbon footprint. Notwithstanding the environmental benefit, biodiesel fuels may have other toxicological properties than petrodiesel. Particulate matter (PM) from petrodiesel causes cancer in the lung as a consequence of delivery of genotoxic polycyclic aromatic hydrocarbons, oxidative stress and inflammation. We have reviewed articles from 2002 to 2019 (50% of the articles since 2015) that have described toxicological effects in terms of genotoxicity, oxidative stress and inflammation of biodiesel exhaust exposure in humans, animals and cell cultures. The studies have assessed first generation biodiesel from different feedstock (e.g. rapeseed and soy), certain second generation fuels (e.g. waste oil), and hydrogenated vegetable oil. It is not possible to rank the potency of toxicological effects of specific biodiesel fuels. However, exposure to biodiesel exhaust causes oxidative stress, inflammation and genotoxicity in cell cultures. Three studies in animals have not indicated genotoxicity in lung tissue. The database on oxidative stress and inflammation in animal studies is larger (13 studies); ten studies have reported increased levels of oxidative stress biomarkers or inflammation, although the effects have been modest in most studies. The cell culture and animal studies have not consistently shown a different potency in effect between biodiesel and petrodiesel exhausts. Both increased and decreased potency have been reported, which might be due to differences in feedstock or combustion conditions. In conclusion, combustion products from biodiesel and petrodiesel fuel may evoke similar toxicological effects on genotoxicity, oxidative stress and inflammation.

Organomodified nanoclays induce less inflammation, acute phase response, and genotoxicity than pristine nanoclays in mice lungs

Surface modification by different quaternary ammonium compounds (QAC) makes nanoclays more compatible with various polymeric matrices, thereby expanding their potential applications. The growing industrial use of nanoclays could potentially pose a health risk for workers. Here, we assessed how surface modification of nanoclays modulates their pulmonary toxicity. An in vitro screening of the unmodified nanoclay Bentonite (montmorillonite) and four organomodified nanoclays (ONC); coated with various QAC, including benzalkonium chloride (BAC), guided the selection of the materials for the in vivo study. Mice were exposed via a single intratracheal instillation to 18, 54, and 162 µg of unmodified Bentonite or dialkyldimethyl-ammonium-coated ONC (NanofilSE3000), or to 6, 18, and 54 µg of a BAC-coated ONC (Nanofil9), and followed for one, 3, or 28 days. All materials induced dose- and time-dependent responses in the exposed mice. However, all doses of Bentonite induced larger, but reversible, inflammation (BAL neutrophils) and acute phase response (Saa3 gene expression in lung) than the two ONC. Similarly, highest levels of DNA strand breaks were found in BAL cells of mice exposed to Bentonite 1 day post-exposure. A significant increase of DNA strand breaks was detected also for NanofilSE3000, 3 days post-exposure. Only mice exposed to Bentonite showed increased Tgf-β gene expression in lung, biomarker of pro-fibrotic processes and hepatic extravasation, 3 days post-exposure. This study indicates that Bentonite treatment with some QAC changes main physical-chemical properties, including shape and surface area, and may decrease their pulmonary toxicity in exposed mice.

Functionalized Surface-Charged SiO2 Nanoparticles Induce Pro-Inflammatory Responses, but Are Not Lethal to Caco-2 Cells

Nanoparticles (NPs) are widely used in food, and analysis of their potential gastrointestinal toxicity is necessary. The present study was designed to determine the effects of silica dioxide (SiO₂), titanium dioxide (TiO₂), and zinc oxide (ZnO) NPs on cultured THP-1 monocyte-derived macrophages and human epithelial colorectal adenocarcinoma (Caco-2) cells. Exposure to ZnO NPs for 24 h increased the production of redox response species (ROS) and reduced cell viability in a dose-dependent manner in THP-1 macrophages and Caco-2 cells. Although TiO₂ and SiO₂ NPs induced oxidative stress, they showed no apparent cytotoxicity against both cell types. The effects of functionalized SiO₂ NPs on undifferentiated and differentiated Caco-2 cells were investigated using fluorescently labeled SiO₂ NPs with neutral, positive, or negative surface charge. Exposure of both types of cells to the three kinds of SiO₂ NPs significantly increased their interaction in a dose-dependent manner. The largest interaction with both types of cells was noted with exposure to more negatively surface-charged SiO₂ NPs. Exposure to either positively or negatively, but not neutrally, surface-charged SiO₂ NPs increased NO levels in differentiated Caco-2 cells. Exposure of differentiated Caco-2 cells to positively or negatively surface-charged SiO₂ NPs also upregulated interleukin-8 expression. We conclude that functionalized surface-charged SiO₂ NPs can induce pro-inflammatory responses but are noncytotoxic.

Acute Phase Response as a Biological Mechanism-of-Action of (Nano)particle-Induced Cardiovascular Disease

Inhaled nanoparticles constitute a potential health hazard due to their size-dependent lung deposition and large surface to mass ratio. Exposure to high levels contributes to the risk of developing respiratory and cardiovascular diseases, as well as of lung cancer. Particle-induced acute phase response may be an important mechanism of action of particle-induced cardiovascular disease. Here, the authors review new important scientific evidence showing causal relationships between inhalation of particle and nanomaterials, induction of acute phase response, and risk of cardiovascular disease. Particle-induced acute phase response provides a means for risk assessment of particle-induced cardiovascular disease and underscores cardiovascular disease as an occupational disease.

An integrated pathway based on in vitro data for the human hazard assessment of nanomaterials

In line with the 3R concept, nanotoxicology is shifting from a phenomenological to a mechanistic approach based on in vitro and in silico methods, with a consequent reduction in animal testing. Risk Assessment (RA) and Life Cycle Assessment (LCA) methodologies, which traditionally rely on in vivo toxicity studies, will not be able to keep up with the pace of development of new nanomaterials unless they adapt to use this new type of data. While tools and models are already available and show a great potential for future use in RA and LCA, currently none is able alone to quantitatively assess human hazards (i.e. calculate chronic NOAEL or ED₅₀ values). By highlighting which models and approaches can be used in a quantitative way with the available knowledge and data, we propose an integrated pathway for the use of in vitro data in RA and LCA. Starting with the characterization of nanoparticles' properties, the pathway then investigates how to select relevant in vitro human data, and how to bridge in vitro dose-response relationships to in vivo effects. If verified, this approach would allow RA and LCA to stir up the development of nanotoxicology by giving indications about the data and quality requirements needed in risk methodologies.

Toxicity of urban air pollution particulate matter in developing and adult mouse brain: Comparison of total and filter-eluted nanoparticles

Air pollution (AirP) is associated with many neurodevelopmental and neurological disorders in human populations. Rodent models show similar neurotoxic effects of AirP particulate matter (PM) collected by different methods or from various sources. However, controversies continue on the identity of the specific neurotoxic components and mechanisms of neurotoxicity. We collected urban PM by two modes at the same site and time: direct collection as an aqueous slurry (sPM) versus a nano-sized sub-fraction of PM0.2 that was eluted from filters (nPM). The nPM lacks water-insoluble PAHs (polycyclic aromatic hydrocarbons) and is depleted by >50% in bioactive metals (e.g., copper, iron, nickel), inorganic ions, black carbon, and other organic compounds. Three biological models were used: in vivo exposure of adult male mice to re-aerosolized nPM and sPM for 3 weeks, gestational exposure, and glial cell cultures. In contrast to larger inflammatory responses of sPM in vitro, cerebral cortex responses of mice to sPM and nPM largely overlapped for adult and gestational exposures. Adult brain responses included induction of IFNγ and NF-κB. Gestational exposure to nPM and sPM caused equivalent depressive behaviors. Responses to nPM and sPM diverged for cerebral cortex glutamate receptor mRNA, systemic fat gain and insulin resistance. The shared toxic responses of sPM with nPM may arise from shared transition metals and organics. In contrast, gestational exposure to sPM but not nPM, decreased glutamatergic mRNAs, which may be attributed to PAHs. We discuss potential mechanisms in the overlap between nPM and sPM despite major differences in bulk chemical composition.

Silver Nanoparticles Stimulates Spermatogenesis Impairments and Hematological Alterations in Testis and Epididymis of Male Rats

The potential pharmaceutical application of nanoparticles has led to the toxicity within the male reproductive system. In the present study, the effects of silver nanoparticles (Ag-NPs) on hematological parameters, free radical generation, antioxidant system, sperm parameters, and organ histo-morphometry in male rats were investigated. Ag-NPs were produced by the reduction of silver ions, while the formation of which was monitored by UV-visible spectrophotometry. Zeta potential, transmission, and scanning electron microscopies were applied for the characterization of AgNPs. A total of 30 rats were divided into 6 groups and were sub-dermally exposed to Ag-NPs at the dosage of 0 (control), 10, and 50 mg/kg bodyweight (bw) doses for either 7 or 28 days. Ag-NP administration altered hematological indices and caused dose-dependent decreases in sperm motility, velocity, kinematic parameters, concentrations of luteinizing hormone, follicle-stimulating hormone, and testosterone. In the epididymis and testis, the concentrations of malondialdehyde and peroxide increases while superoxide dismutase, catalase, reduced glutathione, and total thiol group decreases. These findings suggest that Ag-NP triggered hormonal imbalance and induce oxidative stress in testis and epididymis; which negatively affect sperm parameters of male rats.

TiO2 Nanomaterials Non-Controlled Contamination Could Be Hazardous for Normal Cells Located in the Field of Radiotherapy

Among nanomaterials (NMs), titanium dioxide (TiO₂) is one of the most manufactured NMs and can be found in many consumers' products such as skin care products, textiles and food (as E171 additive). Moreover, due to its most attractive property, a photoactivation upon non-ionizing UVA radiation, TiO₂ NMs is widely used as a decontaminating agent. Uncontrolled contaminations by TiO₂ NMs during their production (professional exposure) or by using products (consumer exposure) are rather frequent. So far, TiO₂ NMs cytotoxicity is still a matter of controversy depending on biological models, types of TiO₂ NMs, suspension preparation and biological endpoints. TiO₂ NMs photoactivation has been widely described for UV light radiation exposure, it could lead to reactive oxygen species production, known to be both cyto- and genotoxic on human cells. After higher photon energy exposition, such as X-rays used for radiotherapy and for medical imaging, TiO₂ NMs photoactivation still occurs. Importantly, the question of its hazard in the case of body contamination of persons receiving radiotherapy was never addressed, knowing that healthy tissues surrounding the tumor are indeed exposed. The present work focuses on the analysis of human normal bronchiolar cell response after co-exposition TiO₂ NMs (with different coatings) and ionizing radiation. Our results show a clear synergistic effect, in terms of cell viability, cell death and oxidative stress, between TiO₂ NMS and radiation.

Increased surface area of halloysite nanotubes due to surface modification predicts lung inflammation and acute phase response after pulmonary exposure in mice

The toxicological potential of halloysite nanotubes (HNTs) and variants after functional alterations to surface area are not clear. We assessed the toxicological response to HNTs (NaturalNano (NN)) before and after surface etching (NN-etched). Potential cytotoxicity of the two HNTs was screened in vitro in MutaTMMouse lung epithelial cells. Lung inflammation, acute phase response and genotoxicity were assessed 1, 3, and 28 days after a single intratracheal instillation of adult female C57BL/6 J BomTac mice. The doses were 6, 18 or 54 μg of HNTs, compared to vehicle controls and the Carbon black NP (Printex 90) of 162 μg/mouse. The cellular composition of bronchoalveolar lavage (BAL) fluid was determined as a measure of lung inflammation. The pulmonary and hepatic acute phase responses were assessed by Serumamyloida mRNA levels in lung and liver tissue by real-time quantitative PCR. Pulmonary and systemic genotoxicity were analyzed by the alkaline comet assay as DNA strand breaks in BAL cells, lung and liver tissue. The etched HNT (NN-etched) had 4-5 times larger BET surface area than the unmodified HNT (NN). Instillation of NN-etched at the highest dose induced influx of neutrophils into the lungs at all time points and increased Saa3 mRNA levels in lung tissue on day 1 and 3 after exposure. No genotoxicity was observed at any time point. In conclusion, functionalization by etching increased BET surface area of the studied NN and enhanced pulmonary inflammatory toxicity in mice.

The early onset and persistent worsening pulmonary alveolar proteinosis in rats by indium oxide nanoparticles

Workplace inhalation exposure to indium compounds has been reported to produce 'indium lung disease' characterized by pulmonary alveolar proteinosis (PAP), granulomas, and pulmonary fibrosis. However, there is little information about the pulmonary toxicity of nano-sized indium oxide (In₂O₃), which is widely used in various applications such as liquid crystal displays. In this study, we evaluated the time-course and dose-dependent lung injuries by In₂O₃ nanoparticles (NPs) after a single intratracheal instillation to rats. In₂O₃ NPs were instilled to female Wistar rats at 7.5, 30, and 90 cm²/rat and lung injuries were evaluated at day 1, 3, 7, 14, 30, 90, and 180 after a single intratracheal instillation. Treatment of In₂O₃ NPs induced worsening diverse pathological changes including PAP, persistent neutrophilic inflammation, type II cell hyperplasia, foamy macrophages, and granulomas in a time- and dose-dependent manner. PAP was induced from day 3 and worsened throughout the study. The concentrations of interleukin-1β, tumor necrosis factor-α, and monocyte chemoattractant protein-1 in bronchoalveolar lavage fluid (BALF) showed dose- and time-dependent increases and the levels of these inflammatory mediators are consistent with the data of inflammatory cells in BALF and progressive lung damages by In₂O₃ NPs. This study suggests that a single inhalation exposure to In₂O₃ NPs can produce worsening lung damages such as PAP, chronic active inflammation, infiltration of foamy macrophages, and granulomas. The early onset and persistent PAP even at the very low dose (7.5 cm²/rat) implies that the re-evaluation of occupational recommended exposure limit for In₂O₃ NPs is urgently needed to protect workers.

Iron Oxide Nanoparticle-Induced Neoplastic-Like Cell Transformation in Vitro Is Reduced with a Protective Amorphous Silica Coating

Iron oxide nanoparticles (IONP) have recently surged in production and use in a wide variety of biomedical and environmental applications. However, their potential long-term health effects, including carcinogenesis, are unknown. Limited research suggests IONP can induce genotoxicity and neoplastic transformation associated with particle dissolution and release of free iron ions. "Safe by design" strategies involve the modification of particle physicochemical properties to affect subsequent adverse outcomes, such as an amorphous silica coating to reduce IONP dissolution and direct interaction with cells. We hypothesized that long-term exposure to a specific IONP (nFe₂O₃) would induce neoplastic-like cell transformation, which could be prevented with an amorphous silica coating (SiO₂-nFe₂O₃). To test this hypothesis, human bronchial epithelial cells (Beas-2B) were continuously exposed to a 0.6 μg/cm² administered a dose of nFe₂O₃ (∼0.58 μg/cm² delivered dose), SiO₂-nFe₂O₃ (∼0.55 μg/cm² delivered dose), or gas metal arc mild steel welding fumes (GMA-MS, ∼0.58 μg/cm² delivered dose) for 6.5 months. GMA-MS are composed of roughly 80% iron/iron oxide and were recently classified as a total human carcinogen. Our results showed that low-dose/long-term in vitro exposure to nFe₂O₃ induced a time-dependent neoplastic-like cell transformation, as indicated by increased cell proliferation and attachment-independent colony formation, which closely matched that induced by GMA-MS. This transformation was associated with decreases in intracellular iron, minimal changes in reactive oxygen species (ROS) production, and the induction of double-stranded DNA damage. An amorphous silica-coated but otherwise identical particle (SiO₂-nFe₂O₃) did not induce this neoplastic-like phenotype or changes in the parameters mentioned above. Overall, the presented data suggest the carcinogenic potential of long-term nFe₂O₃ exposure and the utility of an amorphous silica coating in a "safe by design" hazard reduction strategy, within the context of a physiologically relevant exposure scenario (low-dose/long-term), with model validation using GMA-MS.

Pulmonary toxicity in rats following inhalation exposure to poorly soluble particles: The issue of impaired clearance and the relevance for human health hazard and risk assessment

Intensive discussions are ongoing about the interpretation of pulmonary effects observed in rats exposed to poorly soluble particles. Alveolar clearance differs between rats and humans and becomes impaired in rats at higher exposure concentrations. Some have doubted the human relevance of toxic effects observed in rats under impaired clearance conditions and have suggested that experimental exposures should stay below concentrations inducing impaired clearance. However, for regulatory purposes, insight in potential health effects at relatively high concentrations is needed to fully understand the hazard. Many aspects of impaired particle clearance remain unclear, hampering human health hazard and risk assessment. For an adequate evaluation of the impact of impaired clearance on pulmonary toxicity, a clear definition of alveolar clearance is needed that enables to quantitatively relate the level of impairment to the induction of adverse pulmonary health effects. Also, information is needed on the mechanism of action and the appropriate dose metric for the pulmonary effects observed. In absence of these data, human hazard and risk assessment can only be performed in a pragmatic way. Unless available data clearly point out otherwise, rat pulmonary toxicity including lung inflammation and tumour formation, needs to be considered relevant for human hazard and risk assessment.