Particulate nature of inhaled zinc oxide nanoparticles determines systemic effects and mechanisms of pulmonary inflammation in mice

COPD basal cells are primed towards secretory to multiciliated cell imbalance driving increased resilience to environmental stressors

INTRODUCTION

Environmental pollutants injure the mucociliary elevator, thereby provoking disease progression in chronic obstructive pulmonary disease (COPD). Epithelial resilience mechanisms to environmental nanoparticles in health and disease are poorly characterised.

METHODS

We delineated the impact of prevalent pollutants such as carbon and zinc oxide nanoparticles, on cellular function and progeny in primary human bronchial epithelial cells (pHBECs) from end-stage COPD (COPD-IV, n=4), early disease (COPD-II, n=3) and pulmonary healthy individuals (n=4). After nanoparticle exposure of pHBECs at air-liquid interface, cell cultures were characterised by functional assays, transcriptome and protein analysis, complemented by single-cell analysis in serial samples of pHBEC cultures focusing on basal cell differentiation.

RESULTS

COPD-IV was characterised by a prosecretory phenotype (twofold increase in MUC5AC+) at the expense of the multiciliated epithelium (threefold reduction in Ac-Tub+), resulting in an increased resilience towards particle-induced cell damage (fivefold reduction in transepithelial electrical resistance), as exemplified by environmentally abundant doses of zinc oxide nanoparticles. Exposure of COPD-II cultures to cigarette smoke extract provoked the COPD-IV characteristic, prosecretory phenotype. Time-resolved single-cell transcriptomics revealed an underlying COPD-IV unique basal cell state characterised by a twofold increase in KRT5+ (P=0.018) and LAMB3+ (P=0.050) expression, as well as a significant activation of Wnt-specific (P=0.014) and Notch-specific (P=0.021) genes, especially in precursors of suprabasal and secretory cells.

CONCLUSION

We identified COPD stage-specific gene alterations in basal cells that affect the cellular composition of the bronchial elevator and may control disease-specific epithelial resilience mechanisms in response to environmental nanoparticles. The identified phenomena likely inform treatment and prevention strategies.

Immune response to zinc oxide inhalation in metal fume fever, and the possible role of IL-17f

Metal fume fever (MFF) is a work-related disease caused by the inhalation of metal particles, including zinc oxide. Chronic asthma may develop as a long-term consequence of exposure, particularly for welders and metal workers who are most at risk. In this study, we investigated the effects of ZnO fume inhalation on multiple inflammation-related cytokine- and cytokine receptor genes in mice from lung and lymph node samples, to explore the role of these in the pathogenesis of MFF. In our experiments, the animals were treated with a sub-toxic amount of ZnO fume for 4 h a day for 3 consecutive days. Sampling occurred 3 and 12 h post-treatment. We are the first to demonstrate that ZnO inhalation causes extremely increased levels of IL-17f gene expression at both sampling time points, in addition to increased gene expression rates of several other interleukins and cytokines, such as IL-4, IL-13, CXCL5, CSF-3, and IFN-γ. Our animal experiment provides new insights into the immunological processes of early metal fume fever development. IL-17f plays a crucial role in connecting immunological and oxidative stress events. The increased levels of IL-4 and IL-13 cytokines may explain the development of long-term allergic asthma after exposure to ZnO nanoparticles, which is well-known among welders, smelters, and metal workers.

Toxicity dose descriptors from animal inhalation studies of 13 nanomaterials and their bulk and ionic counterparts and variation with primary particle characteristics

This study collects toxicity data from animal inhalation studies of some nanomaterials and their bulk and ionic counterparts. To allow potential grouping and interpretations, we retrieved the primary physicochemical and exposure data to the extent possible for each of the materials. Reviewed materials are compounds (mainly elements, oxides and salts) of carbon (carbon black, carbon nanotubes, and graphene), silver, cerium, cobalt, copper, iron, nickel, silicium (amorphous silica and quartz), titanium (titanium dioxide), and zinc (chemical symbols: Ag, C, Ce, Co, Cu, Fe, Ni, Si, Ti, TiO₂, and Zn). Collected endpoints are: a) pulmonary inflammation, measured as neutrophils in bronchoalveolar lavage (BAL) fluid at 0-24 hours after last exposure; and b) genotoxicity/carcinogenicity. We present the dose descriptors no-observed-adverse-effect concentrations (NOAECs) and lowest-observed-adverse-effect concentrations (LOAECs) for 88 nanomaterial investigations in data-library and graph formats. We also calculate 'the value where 25% of exposed animals develop tumors' (T25) for carcinogenicity studies. We describe how the data may be used for hazard assessment of the materials using carbon black as an example. The collected data also enable hazard comparison between different materials. An important observation for poorly soluble particles is that the NOAEC for neutrophil numbers in general lies around 1 to 2 mg/m³. We further discuss why some materials' dose descriptors deviate from this level, likely reflecting the effects of the ionic form and effects of the fiber-shape. Finally, we discuss that long-term studies, in general, provide the lowest dose descriptors, and dose descriptors are positively correlated with particle size for near-spherical materials.

Metal-oxide inhalation induced fever - Immuntoxicological aspects of welding fumes

Metal fume fever is a well-known occupational disease that arises from prolonged exposure to subtoxic levels of zinc oxide-containing fumes or dust. This review article aims to identify and examine the possible immunotoxicological effects of inhaled zinc oxide nanoparticles. The current most widely accepted pathomechanism for the development of the disease involves the formation of reactive oxygen species following the entry of zinc oxide particles into the alveolus resulting the release of pro-inflammatory cytokines by activation of the Nuclear Factor Kappa B transcriptional signal, thus evoking the symptoms. The role of metallothionein in inducing tolerance is believed to be a key factor in mitigating the development of metal fume fever. The other, poorly proven hypothetical route is that zinc-oxide particles bind to an undefined protein in the body as haptens to form an antigen and act as an allergen. After activation of the immune system, primary antibodies and immune complexes are developed and type 1. hypersensitivity reaction occurs, that can cause asthmatic dyspnoea, urticaria and angioedema. The development of tolerance is explained by the formation of secondary antibodies against primary antibodies. Oxidative stress and immunological processes cannot be completely separated from each other, as they can induce each other.

Transcriptomic Profiling the Effects of Airway Exposure of Zinc Oxide and Silver Nanoparticles in Mouse Lungs

Consumers and manufacturers are exposed to nanosized zinc oxide (nZnO) and silver particles (nAg) via airways, but their biological effects are still not fully elucidated. To understand the immune effects, we exposed mice to 2, 10, or 50 μg of nZnO or nAg by oropharyngeal aspiration and analyzed the global gene expression profiles and immunopathological changes in the lungs after 1, 7, or 28 days. Our results show that the kinetics of responses varied in the lungs. Exposure to nZnO resulted in the highest accumulation of F4/80- and CD3-positive cells, and the largest number of differentially expressed genes (DEGs) were identified after day 1, while exposure to nAg caused peak responses at day 7. Additionally, nZnO mainly activated the innate immune responses leading to acute inflammation, whereas the nAg activated both innate and adaptive immune pathways, with long-lasting effects. This kinetic-profiling study provides an important data source to understand the cellular and molecular processes underlying nZnO- and nAg-induced transcriptomic changes, which lead to the characterization of the corresponding biological and toxicological effects of nZnO and nAg in the lungs. These findings could improve science-based hazard and risk assessment and the development of safe applications of engineered nanomaterials (ENMs), e.g., in biomedical applications.

Disruption of the lung-gut-brain axis is responsible for cortex damage induced by pulmonary exposure to zinc oxide nanoparticles

Increasing evidence shows that gut microbiota is important for host health in response to metal nanomaterials exposure. However, the effect of gut microbiota on the cortex damage caused by pulmonary exposure to zinc oxide nanoparticles (ZnONPs) remains mainly unknown. In this study, a total of 48 adult C57BL/6J mice were intratracheally instilled with 0.6 mg/kg ZnONPs in the presence or absence of antibiotics (ABX) treatment. Besides, 24 mice were treated with or without fecal microbiota transplantation (FMT) after the intraperitoneal administration of ABX. Our results demonstrated for the first time that dysbiosis induced by ABX treatment significantly aggravated cortex damage induced by pulmonary exposure to ZnONPs. Such damage might highly occur through the induction of oxidative stress, manifested by the enhancement of antioxidative enzymes and products of lipid peroxidation. However, ferroptosis was not involved in this process. Interestingly, our data revealed that ABX treatment exacerbated the alterations of gut-brain peptides (including Sst, Sstr2, and Htr4) induced by ZnONPs in both gut and cortex tissues. Moreover, fecal microbiota transplantation (FMT) was able to alleviate cerebral cortex damage, oxidative stress, and alterations of gut-brain peptides induced by pulmonary exposure to ZnONPs. The results together indicate that pulmonary exposure to ZnONPs causes cerebral cortex damage possibly via the disruption of the lung-gut-brain axis. These findings not only propose valuable insights into the mechanism of ZnONPs neurotoxicity but also provide a potential therapeutic method against brain disorders induced by pulmonary exposure to ZnONPs. AVAILABILITY OF DATA AND MATERIALS: The datasets used and/or analyzed during the current study are available from the The corresponding author on reasonable request.

Unchanged pulmonary toxicity of ZnO nanoparticles formulated in a liquid matrix for glass coating

The inclusion of nanoparticles can increase the quality of certain products. One application is the inclusion of Zinc oxide (ZnO) nanoparticles in a glass coating matrix to produce a UV-absorbing coating for glass sheets. Yet, the question is whether the inclusion of ZnO in the matrix induces toxicity at low exposure levels. To test this, mice were given single intratracheal instillation of 1) ZnO powder (ZnO), 2) ZnO in a glass matrix coating in its liquid phase (ZnO-Matrix), and 3) the matrix with no ZnO (Matrix). Doses of ZnO were 0.23, 0.67, and 2 µg ZnO/mouse. ZnO Matrix doses had equal amounts of ZnO, while Matrix was adjusted to have an equal volume of matrix as ZnO Matrix. Post-exposure periods were 1, 3, or 28 d. Endpoints were pulmonary inflammation as bronchoalveolar lavage (BAL) fluid cellularity, genotoxicity in lung and liver, measured by comet assay, histopathology of lung and liver, and global gene expression in lung using microarrays. Neutrophil numbers were increased to a similar extent with ZnO and ZnO-Matrix at 1 and 3 d. Only weak genotoxicity without dose-response effects was observed in the lung. Lung histology showed an earlier onset of inflammation in material-exposed groups as compared to controls. Microarray analysis showed a stronger response in terms of the number of differentially regulated genes in ZnO-Matrix exposed mice as compared to Matrix only. Activated canonical pathways included inflammatory and cardiovascular ones. In conclusion, the pulmonary toxicity of ZnO was not changed by formulation in a liquid matrix for glass coating.

Meta-analysis of in-vitro cytotoxicity evaluation studies of zinc oxide nanoparticles: Paving way for safer innovations

Nano-based products have shown their daunting presence in several sectors. Among them, Zinc Oxide (ZnO) nanoparticles wangled the reputation of providing "next-generation solutions" and are being utilized in plethora of products. Their widespread application has led to increased exposure of these particles, raising concerns regarding toxicological repercussions to the human health and environment. The diversity, complexity, and heterogeneity in the available literature, along with correlation of befitting attributes, makes it challenging to develop one systematic framework to predict this toxicity. The present study aims at developing predictive modelling framework to tap the prospective features responsible for causing cytotoxicity in-vitro on exposure to ZnO nanoparticles. Rigorous approach was used to mine the information from complete body of evidence published to date. The attributes, features and experimental conditions were systematically extracted to unmask the effect of varied features. 1240 data points from 76 publications were obtained, containing 14 qualitative and quantitative attributes, including physiochemical properties of nanoparticles, cell culture and experimental parameters to perform meta-analysis. For the first time, the efforts were made to investigate the degree of significance of attributes accountable for causing cytotoxicity on exposure to ZnO nanoparticles. We show that in-vitro cytotoxicity is closely related with dose concentration of nanoparticles, followed by exposure time, disease state of the cell line and size of these nanoparticles among other attributes.

A New Look at the Effects of Engineered ZnO and TiO2 Nanoparticles: Evidence from Transcriptomics Studies

Titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles (NPs) have attracted a great deal of attention due to their excellent electrical, optical, whitening, UV-adsorbing and bactericidal properties. The extensive production and utilization of these NPs increases their chances of being released into the environment and conferring unintended biological effects upon exposure. With the increasingly prevalent use of the omics technique, new data are burgeoning which provide a global view on the overall changes induced by exposures to NPs. In this review, we provide an account of the biological effects of ZnO and TiO2 NPs arising from transcriptomics in in vivo and in vitro studies. In addition to studies on humans and mice, we also describe findings on ecotoxicology-related species, such as Danio rerio (zebrafish), Caenorhabditis elegans (nematode) or Arabidopsis thaliana (thale cress). Based on evidence from transcriptomics studies, we discuss particle-induced biological effects, including cytotoxicity, developmental alterations and immune responses, that are dependent on both material-intrinsic and acquired/transformed properties. This review seeks to provide a holistic insight into the global changes induced by ZnO and TiO2 NPs pertinent to human and ecotoxicology.

A review: zinc oxide nanoparticles - friends or enemies?

Modern nanotechnology allows obtaining zinc oxide nanomaterials with unique properties that let its use in a wide range of commercial applications. Direct contact with these particles as well as their release into the environment is almost inevitable. This review aims to consider whether the toxicity of zinc oxide nanoparticles found in numerous test models is a real threat to humans and plants. Emerging reports indicated both the risks and benefits associated with the use of zinc oxide nanoparticles in a manner dependent on the concentration and a method of synthesis, as well as the tested object. The amounts needed to achieve the antibacterial activity of ZnO-NPs, and the reported amounts of these nanoparticles in consumer products are sufficient to have a negative impact on living organisms. The most sensitive to their action are human cells, and the mechanism of cytotoxicity is mainly associated with the formation of oxidative stress caused by the action of zinc ions. ZnO-NPs in small concentration can have positive affect to plants, but it poses a threat to more sensitive ones.

Investigation and disinfection of bacteria and fungi in sports fitness center

This study investigated the air quality improvement in terms of bacterial and fungal contamination in an exercise room of a fitness center under normal operating conditions. Environmental conditions including air conditioning, ventilation, moisture, CO₂, particulate matters, and total number of users were also recorded. In addition, fungal and bacterial load were assessed and disinfection on sports equipment surface was also examined. Background bacteria and fungi densities in bioaerosols were in the range of 249 ± 65 to 812 ± 111 CFU/m³ and 226 ± 39 to 837 ± 838 CFU/m³ in the exercise room of the fitness center and 370 ± 86 to 953 ± 136 CFU/m³ and 465 ± 108 to 1734 ± 580 CFU/m³ in the outdoor air, respectively. Chlorine dioxide and weak acid hypochlorous water aerosols could remove both bacteria and fungi much better than water scrubbing. Contact time of 15 min was sufficient to control both bacteria and fungi to comply with the official air quality standards. User density and carbon dioxide deteriorated both bacteria and fungi disinfection performance whereas temperature was only statistically significant on fungi disinfection. Other factors including relative humidity, airflow velocity, and particulate matters did not have any statistically significant effect on microbial inactivation. Apart from bioaerosol disinfection, inactivation of microorganisms on surfaces of sports equipment was also conducted using chlorine dioxide, zinc oxide, weak acid hypochlorous water, and commercial disinfectant. The surfaces of bicycle handle, dumbbell, and sit-up bench were found to be contaminated with bacteria. Overall bacterial load was 390 to 3720 CFU/cm² with Escherichia coli specifically 550 to 1080 CFU/cm². Chlorine dioxide and zinc oxide were noticeably better than weak acid hypochlorous water and commercial disinfectant in terms of bacteria inactivation whereas all tested disinfectants had comparable effectiveness on E. coli disinfection. Targeted microorganisms on the sports equipment surface were sufficiently inactivated within 2 min after the application of disinfectant.

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.

A semi-quantitative risk ranking of potential human exposure to engineered nanoparticles (ENPs) in Europe

Large quantities of engineered nanoparticles (ENPs) have emerged on the European market with the rapid development of nanotechnology, however knowledge of potential health risks to humans remains in its infancy. The ENP safety issue is of pressing concern as their novel physicochemical characteristics have been illustrated compared to other bulk-form counterparts. Therefore, it is critical to carry out a comprehensive risk assessment for ENPs to guide risk management in industrial sectors. Based on current data availability, a risk ranking model is developed in accordance with the European Chemicals Agency (ECHA) advice for ENP risk assessment. In this study a Quantity, Exposure, Hazard (QEH) risk scoring model was adopted for characterizing both quantitative and qualitative data, including potential exposure pathways and hazard information. Scores were assigned to quantities of ENPs used in consumer products, intake likelihoods (oral, inhalation, and dermal intake), and hazard potential. Exposure through environmental routes and through consumer products are regarded as significant potential exposure routes. This model prioritized ENPs used in Europe according to human health risk potential. Nano-titanium dioxide (TiO₂) ranked the highest, resulting from exposure through consumer products. Silver nanoparticles (AgNP), as the second most critical ENP, is of most concern in terms of the risk from environmental sinks. Regarding the compartmentalization of total ENP risks to humans, the consumption of consumer products with nano-ingredients, especially nano-TiO₂, nano-silicon dioxide (SiO₂), and AgNP, constitutes the majority of the QEH risk index. The inadequacy of ENP risk management procedures is highlighted, not only during manufacturing, but also during nanomaterial waste disposal processes from marketplace through to the environment. Current risk assessments are based upon recent knowledge of the ENP class as novel pollutants, highlighting the need for further quantification of underlying risks as data emerges.

Cytotoxicity and DNA damage evaluation of TiO2 and ZnO nanoparticles. Uptake in lung cells in culture

The cytotoxicity and DNA damage of titanium dioxide and zinc oxide nanoparticles (TiO₂ and ZnO NPs) have been studied in a human lung carcinoma cell line (A549) after 24 h exposure. TiO₂ and ZnO NPs had mean diameters of 12.9 ± 2.8 and 24.1 ± 8.0 nm, respectively. ZnO NPs reduced cell viability from 250 μg/mL, increasing reactive oxygen species (ROS) and decreased GSH/GSSG ratio. The comet assay detected DNA damage from 50 μg/mL. TiO₂ NPs induced cytotoxicity and DNA damage from 50 to 100 μg/mL, respectively, along with a decrease of the GSH/GSSG ratio. Both particles were found inside the cells, within membrane-bound vesicles. The internalization mechanism is promoted partially by caveolae-mediated endocytosis and, in the case of TiO₂ NPs, also by macropinocytosis.

Toxicological effects of zinc oxide nanoparticle exposure: an in vitro comparison between dry aerosol air-liquid interface and submerged exposure systems

Engineered nanomaterials (ENMs) are increasingly produced and used today, but health risks due to their occupational airborne exposure are incompletely understood. Traditionally, nanoparticle (NP) toxicity is tested by introducing NPs to cells through suspension in the growth media, but this does not mimic respiratory exposures. Different methods to introduce aerosolized NPs to cells cultured at the air-liquid-interface (ALI) have been developed, but require specialized equipment and are associated with higher cost and time. Therefore, it is important to determine whether aerosolized setups induce different cellular responses to NPs than traditional ones, which could provide new insights into toxicological responses of NP exposure. This study evaluates the response of human alveolar epithelial cells (A549) to zinc oxide (ZnO) NPs after dry aerosol exposure in the Nano Aerosol Chamber for In Vitro Toxicity (NACIVT) system as compared to conventional, suspension-based exposure: cells at ALI or submerged. Similar to other studies using nebulization of ZnO NPs, we found that dry aerosol exposure of ZnO NPs via the NACIVT system induced different cellular responses as compared to conventional methods. ZnO NPs delivered at 1.0 µg/cm² in the NACIVT system, mimicking occupational exposure, induced significant increases in metabolic activity and release of the cytokines IL-8 and MCP-1, but no differences were observed using traditional exposures. While factors associated with the method of exposure, such as differing NP aggregation, may contribute toward the different cellular responses observed, our results further encourage the use of more physiologically realistic exposure systems for evaluating airborne ENM toxicity.

Exposure to Zinc Oxide Nanoparticles Disrupts Endothelial Tight and Adherens Junctions and Induces Pulmonary Inflammatory Cell Infiltration

Zinc oxide nanoparticles (ZnONPs) are frequently encountered nanomaterials in our daily lives. Despite the benefits of ZnONPs in a variety of applications, many studies have shown potential health hazards of exposure to ZnONPs. We have shown that oropharyngeal aspiration of ZnONPs in mice increases lung inflammation. However, the detailed mechanisms underlying pulmonary inflammatory cell infiltration remain to be elucidated. Endothelium functions as a barrier between the blood stream and the blood vessel wall. Endothelial barrier dysfunction may increase infiltration of immune cells into the vessel wall and underlying tissues. This current study examined the effects of ZnONPs exposure on endothelial barriers. ZnONPs exposure increased leukocyte infiltration in the mouse lungs. In endothelial cells, ZnONPs reduced the continuity of tight junction proteins claudin-5 and zonula occludens-1 (ZO-1) at the cell junctions. ZnONPs induced adherens junction protein VE-cadherin internalization from membrane to cytosol and dissociation with β-catenin, leading to reduced and diffused staining of VE-cadherin and β-catenin at cell junctions. Our results demonstrated that ZnONPs disrupted both tight and adherens junctions, compromising the integrity and stability of the junction network, leading to inflammatory cell infiltration. Thus, ZnONPs exposure in many different settings should be carefully evaluated for vascular effects and subsequent health impacts.

Inhalation of ZnO Nanoparticles: Splice Junction Expression and Alternative Splicing in Mice

Despite the wide application of nanomaterials, toxicity studies of nanoparticles (NP) are often limited to in vitro cell models, and the biological impact of NP exposure in mammals has not been thoroughly investigated. Zinc oxide (ZnO) NPs are commonly used in various consumer products. To evaluate the effects of the inhalation of ZnO NP in mice, we studied splice junction expression in the lungs as a proxy to gene expression changes analysis. Female ICR mice were treated with 6.46 × 104 and 1.93 × 106 NP/cm3 for 3 days and 3 months, respectively. An analysis of differential expression and alternative splicing events in 298 targets (splice junctions) of 68 genes involved in the processes relevant to the biological effects of ZnO NP was conducted using next-generation sequencing. Three days of exposure resulted in the upregulation of IL-6 and downregulation of BID, GSR, NF-kB2, PTGS2, SLC11A2, and TXNRD1 splice junction expression; 3 months of exposure increased the expression of splice junctions in ALDH3A1, APAF1, BID, CASP3, DHCR7, GCLC, GCLM, GSR, GSS, EHHADH, FAS, HMOX-1, IFNγ, NF-kB1, NQO-1, PTGS1, PTGS2, RAD51, RIPK2, SRXN1, TRAF6, and TXNRD1. Alternative splicing of TRAF6 and TXNRD1 was induced after 3 days of exposure to 1.93 × 106 NP/cm3. In summary, we observed changes of splice junction expression in genes involved in oxidative stress, apoptosis, immune response, inflammation, and DNA repair, as well as the induction of alternative splicing in genes associated with oxidative stress and inflammation. Our data indicate the potential negative biological effects of ZnO NP inhalation.

Pulmonary toxicity of Fe2O3, ZnFe2O4, NiFe2O4 and NiZnFe4O8 nanomaterials: Inflammation and DNA strand breaks

Exposure to metal oxide nanomaterials potentially occurs at the workplace. We investigated the toxicity of two Fe-oxides: Fe₂O₃ nanoparticles and nanorods; and three MFe₂O₄ spinels: NiZnFe₄O₈, ZnFe₂O₄, and NiFe₂O₄ nanoparticles. Mice were dosed 14, 43 or 128 μg by intratracheal instillation. Recovery periods were 1, 3, or 28 days. Inflammation - neutrophil influx into bronchoalveolar lavage (BAL) fluid - occurred for Fe₂O₃ rods (1 day), ZnFe₂O₄ (1, 3 days), NiFe₂O₄ (1, 3, 28 days), Fe₂O₃ (28 days) and NiZnFe₄O₈ (28 days). Conversion of mass-dose into specific surface-area-dose showed that inflammation correlated with deposited surface area and consequently, all these nanomaterials belong to the so-called low-solubility, low-toxicity class. Increased levels of DNA strand breaks were observed for both Fe₂O₃ particles and rods, in BAL cells three days post-exposure. To our knowledge, this is, besides magnetite (Fe₃O₄), the first study of the pulmonary toxicity of MFe₂O₄ spinel nanomaterials.

Heterozygous Disruption of Beclin 1 Alleviates Zinc Oxide Nanoparticles-Induced Disturbance of Cholesterol Biosynthesis in Mouse Liver

Purpose

Liver is regarded as one of the primary target organs for zinc oxide nanoparticles (ZnONPs) toxicity. Since liver represents the leading site for de novo cholesterol biosynthesis in mammals, the injuries of liver could result in the disruption of cholesterol biosynthesis. In this study, we aimed to investigate whether pulmonary ZnONPs exposure induces disturbance of cholesterol biosynthesis in mouse liver.

Methods and results

Our data demonstrated intratracheally instilled with a single dose of 3, 6, and 12 μg/animal ZnONPs could induce histopathological deterioration in mouse liver in a dose-related manner at 3 days, but remission was observed at 7 days after treatment. Moreover, ZnONPs caused the disturbance of cholesterol biosynthesis by increasing both 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase and sterol regulatory element-binding protein 2 (SREBP2) protein expressions. To further reveal the underlying toxic mechanisms, we detected the biomarkers of autophagy and found that pulmonary ZnONPs exposure led to the elevation of LC3B-II and Beclin 1, suggesting ZnONPs might trigger autophagy in liver tissues. By using both beclin 1^+/+ and beclin 1^+/- mice, we demonstrated that inhibition of autophagy by heterozygous disruption of beclin 1 attenuated the disturbance of cholesterol biosynthesis induced by ZnONPs in liver.

Conclusion

Pulmonary exposure of ZnONPs would induce the cholesterol biosynthesis disturbance in mouse liver through Beclin-1-dependent autophagy activation, suggesting that inhibition of autophagy may contribute to preventing the cholesterol biosynthesis disturbance and its associated pathologies induced by ZnONPs in liver.

Nanoparticles in the lungs of old mice: Pulmonary inflammation and oxidative stress without procoagulant effects

Pulmonary exposure to nanoparticles (NPs) has been shown to induce pulmonary as well as cardiovascular toxicity. These effects might be enhanced in elderly subjects as a result of a compromised immunity and/or declined organ functions. To study the adverse in vivo effects of NPs in a model for the elderly, we exposed 18-month-old C75Bl/6 mice to multi-walled carbon nanotubes (MWCNTs) or ZnO NPs by intratracheal instillation once a week during 5 consecutive weeks. Pulmonary and hemostatic toxicity was determined 24 h (T1) and 8 weeks (T2) after the last administration. Both NP types significantly increased the pulmonary macrophages at both time points. The MWCNTs and ZnO NPs also induced a pulmonary influx of neutrophils, which was even larger at T2 compared to T1. All NPs induced only a modest increase of pulmonary IL-1β, IL-6 and KC levels. Both types of NPs also increased blood neutrophils. Red blood cells were not significantly affected. Both NPs significantly increased coagulation factor VIII levels at both time points. Histological analysis revealed the presence of MWCNTs in the alveolar macrophages up to 8 weeks after the last administration and the ZnO NPs induced a pronounced alveolar inflammation. In these 18-month-old mice, NPs caused pulmonary inflammation (without evidence of oxidative stress) accompanied by large increases in coagulation factor VIII up to 8 weeks after the last NP exposure. The persistence of the MWCNTs in the lungs resulted in translocation from the lungs to the left heart and the ZnO NPs induced a fibrosis-like pathology.

The size of zinc oxide nanoparticles controls its toxicity through impairing autophagic flux in A549 lung epithelial cells

Zinc oxide nanoparticles (ZnONPs) widely used in various products, have been concerned with its impact on human health, in particular, on the risk of pulmonary toxicity. Our previous study indicated that ZnONPs could harness autophagy and impair the autophagic flux, which was positively linked to ZnONPs-induced toxicity. The objective of this study was to investigate whether ZnONPs-induced impairment of autophagic flux and cell death in lung epithelial cells is related to the size of ZnONPs. We demonstrate that ZnONPs with the average size of 50 nm could induce toxic effects in A549 lung epithelial cells, including accumulation of autophagosomes (the elevation of LC3B-II/LC3B-I ratio), impaired autophagic flux (the increase of p62 expression), the release of intracellular zinc ions (the increase of FluoZin-3 signal and ZnT1 mRNA expression), mitochondrial damage (the decrease of TMRE signal), lysosomal dysfunction (the aberrant expression of LAMP-2), oxidative stress (the increase of DCFH-DA signal and HO-1 expression) and cell death. Interestingly, ZnONPs with the average size of 200 nm failed to induce autophagy-mediated toxicity. Taken together, our results indicate that the size of ZnONPs is closely correlated with its toxicity, which is probably mediated by induction of impaired autophagic flux. This finding provides an insight into better understating of ZnONPs-associated toxicity, and mitigating the risk to humans and allowing the safer application.

Mechanistic insight into the impact of nanomaterials on asthma and allergic airway disease

Asthma is a chronic respiratory disease known for its high susceptibility to environmental exposure. Inadvertent inhalation of engineered or incidental nanomaterials is a concern for human health, particularly for those with underlying disease susceptibility. In this review we provide a comprehensive analysis of those studies focussed on safety assessment of different nanomaterials and their unique characteristics on asthma and allergic airway disease. These include in vivo and in vitro approaches as well as human and population studies. The weight of evidence presented supports a modifying role for nanomaterial exposure on established asthma as well as the development of the condition. Due to the variability in modelling approaches, nanomaterial characterisation and endpoints used for assessment in these studies, there is insufficient information for how one may assign relative hazard potential to individual nanoscale properties. New developments including the adoption of standardised models and focussed in vitro and in silico approaches have the potential to more reliably identify properties of concern through comparative analysis across robust and select testing systems. Importantly, key to refinement and choice of the most appropriate testing systems is a more complete understanding of how these materials may influence disease at the cellular and molecular level. Detailed mechanistic insight also brings with it opportunities to build important population and exposure susceptibilities into models. Ultimately, such approaches have the potential to more clearly extrapolate relevant toxicological information, which can be used to improve nanomaterial safety assessment for human disease susceptibility.

Evaluation of LPS-Induced Acute Lung Injury Attenuation in Rats by Aminothiazole-Paeonol Derivatives

Paeonol is a key phenolic compound in the root bark of Moutan Cortex Radicis that has been used in traditional Chinese Medicine to ameliorate inflammation. A series of aminothiazole-paeonol derivatives (APDs) were synthesized in this work and subjected to preliminary evaluation in cells followed by verification in animals. Quantification of monocyte chemotactic protein-1 (MCP-1) and interleukin-6 (IL-6) in culture media of LPS-activated A549 cells, a lung epithelial adenocarcinoma cell line, were used to investigate the anti-inflammatory capability of APDs. ALI-bearing rats were employed to verify therapeutic efficacy of APDs according to observations of total cells, protein amounts, MCP-1 and IL-6 in bronchoalveolar lavage fluid (BALF). Histopathological examinations of lung tissues were consequently applied for validation of APDs. Among these compounds, 2-(2-aminothiazol-4-yl)-5-methoxyphenol (4) had the most potent activity, showing comparable inhibition of MCP-1/IL-6 and superior elimination of neutrophil infiltration and protein exudation in lungs compared to others as well as dexamethasone. This study demonstrated a comprehensive strategy to evaluate APDs through integration of cell-based screening and animal-based verification. In order to fulfill unmet needs of treating acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), APDs introduced in this work could be promising lead compounds to develop high potent anti-inflammation agents.

Zinc oxide nanoparticles harness autophagy to induce cell death in lung epithelial cells

Although zinc oxide nanoparticles (ZnONPs) are widely used, they have raised concerns of toxicity in humans. Previous studies have indicated that reactive oxygen species (ROS) and autophagy are involved in the cytotoxicity of ZnONPs, but the regulatory mechanisms between autophagy and ROS remain to be elucidated. Herein, we comprehensively investigated the regulatory mechanism of autophagy and the link between autophagy and ROS in ZnONPs-treated lung epithelial cells. We demonstrated that ZnONPs could induce autophagy, and this process could enhance the dissolution of ZnONPs in lysosomes to release zinc ions. Sequentially, zinc ions released from ZnONPs were able to damage not only lysosomes, leading to impaired autophagic flux, but also mitochondria. Impaired autophagic flux resulted in the accumulation of damaged mitochondria, which could generate excessive ROS to cause cell death. We further demonstrated that the inhibition of autophagy by either pharmacological inhibitors or small interfering RNA (siRNA)-mediated knockdown of Beclin-1 and AMP-activated protein kinase could ameliorate ZnONPs-induced cell death. Moreover, we found that lysosomal-associated membrane protein 1/2 (LAMP-1/2), which were the most abundant highly glycosylated protein in late endosomes/lysosomes, exhibited aberrant expression pattern upon treatment with ZnONPs. Intriguingly, LAMP-2 knockdown, but not LAMP-1 knockdown, could exacerbate the ROS generation and cell death induced by ZnONPs treatment. Meanwhile, LAMP-2 overexpression alleviated ZnONPs-induced cell death, suggesting that LAMP-2 was linked to this toxic phenotype induced by ZnONPs. Our results indicate that autophagic dysfunction could contribute to excessive ROS generation upon treatment with ZnONPs in lung epithelial cells, suggesting that modulating the autophagy process would minimize ZnONPs-associated toxicity.

Inhalation exposure during spray application and subsequent sanding of a wood sealant containing zinc oxide nanoparticles

Nano-enabled construction products have entered into commerce. There are concerns about the safety of manufactured nanomaterials, and exposure assessments are needed for a more complete understanding of risk. This study assessed potential inhalation exposure to ZnO nanoparticles during spray application and power sanding of a commercially available wood sealant and evaluated the effectiveness of local exhaust ventilation in reducing exposure. A tradesperson performed the spraying and sanding inside an environmentally-controlled chamber. Dust control methods during sanding were compared. Filter-based sampling, electron microscopy, and real-time particle counters provided measures of exposure. Airborne nanoparticles above background levels were detected by particle counters for all exposure scenarios. Nanoparticle number concentrations and particle size distributions were similar for sanding of treated versus untreated wood. Very few unbound nanoparticles were detected in aerosol samples via electron microscopy, rather nano-sized ZnO was contained within, or on the surface of larger airborne particles. Whether the presence of nanoscale ZnO in these aerosols affects toxicity merits further investigation. Mass-based exposure measurements were below the NIOSH Recommended Exposure Limit for Zn, although there are no established exposure limits for nanoscale ZnO. Local exhaust ventilation was effective, reducing airborne nanoparticle number concentrations by up to 92% and reducing personal exposure to total dust by at least 80% in terms of mass. Given the discrepancies between the particle count data and electron microscopy observations, the chemical identity of the airborne nanoparticles detected by the particle counters remains uncertain. Prior studies attributed the main source of nanoparticle emissions during sanding to copper nanoparticles generated from electric sander motors. Potentially contrary results are presented suggesting the sander motor may not have been the primary source of nanoparticle emissions in this study. Further research is needed to understand potential risks faced by construction workers exposed to mixed aerosols containing manufactured nanomaterials. Until these risks are better understood, this study demonstrates that engineering controls can reduce exposure to manufactured nanomaterials; doing so may be prudent for protecting worker health.

Involvement of the cytokine-IDO1-AhR loop in zinc oxide nanoparticle-induced acute pulmonary inflammation

Zinc oxide nanoparticles (ZnONPs) are widely used in our daily life, such as in sunscreens and electronic nanodevices. However, pulmonary exposure to ZnONPs causes acute pulmonary inflammation, which is considered as an initial event for various respiratory diseases. Thus, elucidation of the underlying cellular mechanisms of ZnONPs can help us in predicting their potential effects in respiratory diseases. In this study, we observed that ZnONPs increased proinflammatory cytokines, accompanied with an increased expression of aryl hydrocarbon receptor (AhR) and its downstream target cytochrome P450 1A1 (CYP1A1) in macrophages in vitro and in mouse lung epithelia in vivo. Moreover, zinc nitrate, but not silica or titanium dioxide nanoparticles (NPs), had similar effects on macrophages, indicating that the zinc element or ion released from ZnONPs is likely responsible for the activation of the AhR pathway. Cotreatment with an AhR antagonist or AhR knockout reduced ZnONPs-induced cytokine secretion in macrophages or mice, respectively. Furthermore, kynurenine (KYN), an endogenous AhR agonist and a tryptophan metabolite catalyzed by indoleamine 2,3-dioxygenase (IDO), was increased in the serums of mice that aspirated ZnONPs. Consistently, ZnONPs increased IDO1 expression in lung cells in vitro and in vivo. Finally, AhR knockout reduced ZnONPs-induced pulmonary inflammation, cytokine secretion and KYN production in mice, suggesting that AhR activation is involved in ZnONPs-induced cytokine secretion and pulmonary inflammation. In summary, we demonstrated that the pulmonary exposure of ZnONPs stimulated the cytokine-IDO1-AhR loop in the lungs, which has been implied to play roles in immune dysfunctions.

Generation of protective immunity against Orientia tsutsugamushi infection by immunization with a zinc oxide nanoparticle combined with ScaA antigen

Background

Zinc oxide nanoparticle (ZNP) has been applied in various biomedical fields. Here, we investigated the usage of ZNP as an antigen carrier for vaccine development by combining a high affinity peptide to ZNP.

Results

A novel zinc oxide-binding peptide (ZBP), FPYPGGDA, with high affinity to ZNP (K_a = 2.26 × 10⁶ M⁻¹) was isolated from a random peptide library and fused with a bacterial antigen, ScaA of Orientia tsutsugamushi, the causative agent of scrub typhus. The ZNP/ZBP-ScaA complex was efficiently phagocytosed by a dendritic cell line, DC2.4, in vitro and significantly enhanced anti-ScaA antibody responses in vivo compared to control groups. In addition, immunization with the ZNP/ZBP-ScaA complex promoted the generation of IFN-γ-secreting T cells in an antigen-dependent manner. Finally, we observed that ZNP/ZBP-ScaA immunization provided protective immunity against lethal challenge of O. tsutsugamushi, indicating that ZNP can be used as a potent adjuvant when complexed with ZBP-conjugated antigen.

Conclusions

ZNPs possess good adjuvant potential as a vaccine carrier when combined with an antigen having a high affinity to ZNP. When complexed with ZBP-ScaA antigen, ZNPs could induce strong antibody responses as well as protective immunity against lethal challenges of O. tsutsugamushi. Therefore, application of ZNPs combined with a specific soluble antigen could be a promising strategy as a novel vaccine carrier system.

Airway irritation, inflammation, and toxicity in mice following inhalation of metal oxide nanoparticles

Metal oxide nanoparticles are used in a broad range of industrial processes and workers may be exposed to aerosols of the particles both during production and handling. Despite the widespread use of these particles, relatively few studies have been performed to investigate the toxicological effects in the airways following inhalation. In the present study, the acute (24 h) and persistent (13 weeks) effects in the airways after a single exposure to metal oxide nanoparticles were studied using a murine inhalation model. Mice were exposed 60 min to aerosols of either ZnO, TiO₂, Al₂O₃ or CeO₂ and the deposited doses in the upper and lower respiratory tracts were calculated. Endpoints were acute airway irritation, pulmonary inflammation based on analyses of bronchoalveolar lavage (BAL) cell composition, DNA damage assessed by the comet assay and pulmonary toxicity assessed by protein level in BAL fluid and histology. All studied particles reduced the tidal volume in a concentration-dependent manner accompanied with an increase in the respiratory rate. In addition, ZnO and TiO₂ induced nasal irritation. BAL cell analyses revealed both neutrophilic and lymphocytic inflammation 24-h post-exposure to all particles except TiO₂. The ranking of potency regarding induction of acute lung inflammation was Al₂O₃ = TiO₂<CeO₂ ≪ ZnO. Exposure to CeO₂ gave rise to a more persistent inflammation; both neutrophilic and lymphocytic inflammation was seen 13 weeks after exposure. As the only particles, ZnO caused a significant toxic effect in the airways while TiO₂ gave rise to DNA-strand break as shown by the comet assay.

Biological reactivity of zinc oxide nanoparticles with mammalian test systems: an overview

Zinc oxide nanoparticles (ZnO NPs) have useful physicochemical advantages, and are used extensively. This has raised concerns regarding their potential toxicity. ZnO NP attributes that contribute to cytotoxicity and immune reactivity, however, seem to vary across literature considerably. Largely, dissolution and generation of reactive oxygen species appear to be the most commonly reported paradigms. Moreover, ZnO NP size and shape may also contribute toward their overall nano-bio interactions. Analysis is further complicated by factors such as adsorption of proteins on the NP surface, which may influence their bioreactivity. The main aim of this review is to give a systematic overview of the postulates explaining cytotoxic, inflammatory and genotoxic effects of ZnO NPs when exposed to different types of cells in vitro and in vivo.

Value of phagocyte function screening for immunotoxicity of nanoparticles in vivo

Nanoparticles (NPs) present in the environment and in consumer products can cause immunotoxic effects. The immune system is very complex, and in vivo studies are the gold standard for evaluation. Due to the increased amount of NPs that are being developed, cellular screening assays to decrease the amount of NPs that have to be tested in vivo are highly needed. Effects on the unspecific immune system, such as effects on phagocytes, might be suitable for screening for immunotoxicity because these cells mediate unspecific and specific immune responses. They are present at epithelial barriers, in the blood, and in almost all organs. This review summarizes the effects of carbon, metal, and metal oxide NPs used in consumer and medical applications (gold, silver, titanium dioxide, silica dioxide, zinc oxide, and carbon nanotubes) and polystyrene NPs on the immune system. Effects in animal exposures through different routes are compared to the effects on isolated phagocytes. In addition, general problems in the testing of NPs, such as unknown exposure doses, as well as interference with assays are mentioned. NPs appear to induce a specific immunotoxic pattern consisting of the induction of inflammation in normal animals and aggravation of pathologies in disease models. The evaluation of particle action on several phagocyte functions in vitro may provide an indication on the potency of the particles to induce immunotoxicity in vivo. In combination with information on realistic exposure levels, in vitro studies on phagocytes may provide useful information on the health risks of NPs.

Pulmonary and hemostatic toxicity of multi-walled carbon nanotubes and zinc oxide nanoparticles after pulmonary exposure in Bmal1 knockout mice

BACKGROUND

Pulmonary exposure to nanoparticles (NPs) may affect, in addition to pulmonary toxicity, the cardiovascular system such as procoagulant effects, vascular dysfunction and progression of atherosclerosis. However, only few studies have investigated hemostatic effects after pulmonary exposure.

METHODS

We used Bmal1 (brain and muscle ARNT-like protein-1) knockout (Bmal1(-/-)) mice which have a disturbed circadian rhythm and procoagulant phenotype, to study the pulmonary and hemostatic toxicity of multi-walled carbon nanotubes (MWCNTs) and zinc oxide (ZnO) NPs after subacute pulmonary exposure. Bmal1(-/-) and wild-type (Bmal1(+/+)) mice were exposed via oropharyngeal aspiration, once a week, during 5 consecutive weeks, to a cumulative dose of 32 or 128 μg MWCNTs or 32 or 64 μg ZnO NPs.

RESULTS

MWCNTs caused a pronounced inflammatory response in the lung with increased cell counts in the broncho-alveolar lavage and increased secretion of interleukin-1β and cytokine-induced neutrophil chemo-attractant (KC), oxidative stress (increased ratio of oxidized versus reduced glutathione and decreased total glutathione) as well as anemic and procoagulant effects as evidenced by a decreased prothrombin time with increased fibrinogen concentrations and coagulation factor (F)VII. In contrast, the ZnO NPs seemed to suppress the inflammatory (decreased neutrophils in Bmal1(-/-) mice) and oxidative response (increased total glutathione in Bmal1(-/-) mice), but were also procoagulant with a significant increase of FVIII. The procoagulant effects, as well as the significant correlations between the pulmonary endpoints (inflammation and oxidative stress) and hemostasis parameters were more pronounced in Bmal1(-/-) mice than in Bmal1(+/+) mice.

CONCLUSIONS

The Bmal1(-/-) mouse is a sensitive animal model to study the procoagulant effects of engineered NPs. The MWCNTs and ZnO NPs showed different pulmonary toxicity but both NPs induced procoagulant effects, suggesting different mechanisms of affecting hemostasis. However, the correlation analysis suggests a causal association between the observed pulmonary and procoagulant effects.