Methodological considerations when conductingin vitro, air–liquid interface exposures to engineered nanoparticle aerosols

Review of in vitro studies evaluating respiratory toxicity of aerosols: impact of cell types, chemical composition, and atmospheric processing

In recent decades, several cell-based and acellular methods have been developed to evaluate ambient particulate matter (PM) toxicity. Although cell-based methods provide a more comprehensive assessment of PM toxicity, their results are difficult to comprehend due to the diversity in cellular endpoints, cell types, and assays and the interference of PM chemical components with some of the assays' techniques. In this review, we attempt to clarify some of these issues. We first discuss the morphological and immunological differences among various macrophage and epithelial cells, belonging to the respiratory systems of human and murine species, used in the in vitro studies evaluating PM toxicity. Then, we review the current state of knowledge on the role of different PM chemical components and the relevance of atmospheric processing and aging of aerosols in the respiratory toxicity of PM. Our review demonstrates the need to adopt more physiologically relevant cellular models such as epithelial (or endothelial) cells instead of macrophages for oxidative stress measurement. We suggest limiting macrophages for investigating other cellular responses (e.g., phagocytosis, inflammation, and DNA damage). Unlike monocultures (of macrophages and epithelial cells), which are generally used to study the direct effects of PM on a given cell type, the use of co-culture systems should be encouraged to investigate a more comprehensive effect of PM in the presence of other cells. Our review has identified two major groups of toxic PM chemical species from the existing literature, i.e., metals (Fe, Cu, Mn, Cr, Ni, and Zn) and organic compounds (PAHs, ketones, aliphatic and chlorinated hydrocarbons, and quinones). However, the relative toxicities of these species are still a matter of debate. Finally, the results of the existing studies investigating the effect of aging on PM toxicity are ambiguous, with varying results due to different cell types, different aging conditions, and the presence/absence of specific oxidants. More systematic studies are necessary to understand the role of different SOA precursors, interactions between different PM components, and aging conditions in the overall toxicity of PM. We anticipate that our review will guide future investigations by helping researchers choose appropriate cell models, resulting in a more meaningful interpretation of cell-based assays and thus ultimately leading to a better understanding of the health effects of PM exposure.

The use of a complex tetra-culture alveolar model to study the biological effects induced by gold nanoparticles with different physicochemical properties

A substantial increase in engineered nanoparticles in consumer products has been observed, heightening human and environmental exposure. Inhalation represents the primary route of human exposure, necessitating a focus on lung toxicity studies. However, to avoid ethical concerns the use of in vitro models is an efficient alternative to in vivo models. This study utilized an in vitro human alveolar barrier model at air-liquid-interface with four cell lines, for evaluating the biological effects of different gold nanoparticles. Exposure to PEGylated gold nanospheres, nanorods, and nanostars did not significantly impact viability after 24 h, yet all AuNPs induced cytotoxicity in the form of membrane integrity impairment. Gold quantification revealed cellular uptake and transport. Transcriptomic analysis identified gene expression changes, particularly related to the enhancement of immune cells. Despite limited impact, distinct effects were observed, emphasizing the influence of nanoparticles physicochemical parameters while demonstrating the model's efficacy in investigating particle biological effects.

Development of lung tissue models and their applications

The lungs are important organs that play a critical role in the development of specific diseases, as well as responding to the effects of drugs, chemicals, and environmental pollutants. Due to the ethical concerns around animal testing, alternative methods have been sought which are more time-effective, do not pose ethical issues for animals, do not involve species differences, and provide easy investigation of the pathobiology of lung diseases. Several national and international organizations are working to accelerate the development and implementation of structurally and functionally complex tissue models as alternatives to animal testing, particularly for the lung. Unfortunately, to date, there is no lung tissue model that has been accepted by regulatory agencies for use in inhalation toxicology. This review discusses the challenges involved in developing a relevant lung tissue model derived from human cells such as cell lines, primary cells, and pluripotent stem cells. It also introduces examples of two-dimensional (2D) air-liquid interface and monocultured and co-cultured three-dimensional (3D) culture techniques, particularly organoid culture and 3D bioprinting. Furthermore, it reviews development of the lung-on-a-chip model to mimic the microenvironment and physiological performance. The applications of lung tissue models in various studies, especially disease modeling, viral respiratory infection, and environmental toxicology will be also introduced. The development of a relevant lung tissue model is extremely important for standardizing and validation the in vitro models for inhalation toxicity and other studies in the future.

Assessment of Scanning Mobility Particle Sizer (SMPS) for online monitoring of delivered dose in an in vitro aerosol exposure system

Real-time monitoring of dosimetry is critical to mitigating the constraints of offline measurements. To address this need, the use of the Scanning Mobility Particle Sizer (SMPS) to estimate the dose delivered through the Dosimetric Aerosol in Vitro Inhalation Device (DAVID) was assessed. CuO nanoparticles suspended in ethanol at different concentrations (0.01-10 mg/mL) were aerosolized using a Collison nebulizer and diluted with air at a ratio of either 1:3 (setup 1) or 1:18 (setup 2). From the aerosol volume concentrations measured by the SMPS, density of CuO (6.4 g/cm3), collection time (5-30 min), flow rate (0.5 LPM) and deposition area (0.28 cm2), the mass doses (DoseSMPS) were observed to increase exponentially over time and ranged from 0.02 ± 0.001 to 84.75 ± 3.49 μg/cm2. The doses calculated from the Cu concentrations determined by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) (DoseICP) also increased exponentially over time (0.01 ± 0.01-97.25 ± 1.30 μg/cm2). Regression analysis between DoseICP and DoseSMPS showed R2 ≥ 0.90 for 0.1-10 mg/mL. As demonstrated, the SMPS can be used to monitor the delivered dose in real-time, and controlled delivery of mass doses with a 226-fold range can be attained in ≤30 min in DAVID by adjusting the nebulizer concentration, dilution air and time.

Assessing the in vitro toxicity of airborne (nano)particles to the human respiratory system: from basic to advanced models

Several studies have been conducted to address the potential adverse health risks attributed to exposure to nanoscale materials. While in vivo studies are fundamental for identifying the relationship between dose and occurrence of adverse effects, in vitro model systems provide important information regarding the mechanism(s) of action at the molecular level. With a special focus on exposure to inhaled (nano)particulate material toxicity assessment, this review provides an overview of the available human respiratory models and exposure systems for in vitro testing, advantages, limitations, and existing investigations using models of different complexity. A brief overview of the human respiratory system, pathway and fate of inhaled (nano)particles is also presented.

Cell Cultures at the Air-Liquid Interface and Their Application in Cancer Research

Air-liquid interface (ALI) cell cultures are considered a valid tool for the replacement of animals in biomedical research. By mimicking crucial features of the human in vivo epithelial barriers (e.g., lung, intestine, and skin), ALI cell cultures enable proper structural architectures and differentiated functions of normal and diseased tissue barriers. Thereby, ALI models realistically resemble tissue conditions and provide in vivo-like responses. Since their implementation, they are routinely used in several applications, from toxicity testing to cancer research, receiving an appreciable level of acceptance (in some cases a regulatory acceptance) as attractive testing alternatives to animals. In this chapter, an overview of the ALI cell cultures will be presented together with their application in cancer cell culture, highlighting the potential advantages and disadvantages of the model.

Comparison of biological responses between submerged, pseudo-air-liquid interface, and air-liquid interface exposure of A549 and differentiated THP-1 co-cultures to combustion-derived particles

Air liquid interface (ALI) exposure systems are gaining interest, and studies suggest enhanced response of lung cells exposed to particles at ALI as compared to submerged exposure, although the results have been somewhat inconsistent. Previous studies have used monocultures and measured particle deposition using assumptions including consistent particle deposition, particle density, and shape. This study exposed co-cultures of A549 and differentiated THP-1 cells to flame-generated particles using three exposure methods: ALI, pseudo-ALI, and submerged. The dose at ALI was measured directly, reducing the need for assumptions about particle properties and deposition. For all exposure methods an enhanced pro-inflammatory response (TNFα) and Cytochrome P450 (CYP1A1) gene expression, compared to their corresponding negative controls, was observed. ALI exposure induced a significantly greater TNFα response compared to submerged exposure. The submerged exposures exhibited greater induction of CYP1A1 than other exposure methods, although not statistically significant. Some of the factors behind the observed difference in responses for the three exposure methods include differences in physicochemical properties of particles in suspending media, delivered dose, and potential contribution of gas-phase species to cellular response in ALI exposure. However, given the difficulty and expense of ALI exposures, submerged exposure may still provide relevant information for particulate exposures.

In Vitro Toxicity of Industrially Relevant Engineered Nanoparticles in Human Alveolar Epithelial Cells: Air-Liquid Interface versus Submerged Cultures

Diverse industries have already incorporated within their production processes engineered nanoparticles (ENP), increasing the potential risk of worker inhalation exposure. In vitro models have been widely used to investigate ENP toxicity. Air-liquid interface (ALI) cell cultures have been emerging as a valuable alternative to submerged cultures as they are more representative of the inhalation exposure to airborne nano-sized particles. We compared the in vitro toxicity of four ENP used as raw materials in the advanced ceramics sector in human alveolar epithelial-like cells cultured under submerged or ALI conditions. Submerged cultures were exposed to ENP liquid suspensions or to aerosolised ENP at ALI. Toxicity was assessed by determining LDH release, WST-1 metabolisation and DNA damage. Overall, cells were more sensitive to ENP cytotoxic effects when cultured and exposed under ALI. No significant cytotoxicity was observed after 24 h exposure to ENP liquid suspensions, although aerosolised ENP clearly affected cell viability and LDH release. In general, all ENP increased primary DNA damage regardless of the exposure mode, where an increase in DNA strand-breaks was only detected under submerged conditions. Our data show that at relevant occupational concentrations, the selected ENP exert mild toxicity to alveolar epithelial cells and exposure at ALI might be the most suitable choice when assessing ENP toxicity in respiratory models under realistic exposure conditions.

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.

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.

Estimating Lung Deposition of Fungal Spores Using Actual Airborne Spore Concentrations and Physiological Data

Exposure to bioaerosols has been implicated in adverse respiratory symptoms, infectious diseases, and bioterrorism. Although these particles have been measured within residential and occupational settings in multiple studies, the deposition of bioaerosol particles within the human respiratory system has been only minimally explored. This paper uses real-world environmental measurement data of total fungal spores using Air-o-Cell cassettes in 16 different apartments and residents' physiological data in those apartments to predict respiratory deposition of the spores. The airborne spore concentrations were measured during the spring, summer, and fall. The respiratory deposition of five most prevalent spore genera-Ascospores, Aspergillus, Basidiospores, Cladosporium, and Myxomycetes-was predicted using three empirical models: the Multiple Path Particle Dosimetry model, using both the Yeh and age-specific versions, and the Bioaerosol Adaptation of the International Committee on Radiological Protection's Lung deposition model. The predicted total deposited number of spores was highest for Ascospores and Cladosporium. While the majority of spores deposit were in the extrathoracic region, there is a significant deposition for both Aspergillus and Cladosporium in the alveolar region, potentially leading to the development of aspergillosis or allergic asthma. Although the dose-response relationship is unknown, the estimate of the actual spore deposition could be the first step in determining such a relationship.

Determining real-time mass deposition with a quartz crystal microbalance in an electrostatic, parallel-flow, air-liquid interface exposure system

In vitro studies are the first step toward understanding the biological effects of particulate matter. As a more realistic exposure strategy than submerged culture approaches, air-liquid interface (ALI) in vitro exposure systems are gaining interest. One challenge with ALI systems is determining accurate particle mass deposition. Although a few commercially available ALI systems are equipped with online mass deposition monitoring, most studies use indirect methods to estimate mass doses. These different indirect methods may contribute to inconsistencies in the results from in vitro studies of aerosolized nanoparticles. This study explored the effectiveness of using a commercially available Quartz Crystal Microbalance (QCM) to estimate the real-time, particle-mass deposition inside an electrostatic, parallel-flow, ALI system. The QCM system required minor modifications, including custom-designed and fabricated headers. Three QCM systems were simultaneously placed in three of the six wells in the ALI exposure chamber to evaluate the uniformity of particle deposition. The measurements from fluorescein dosimetry and QCM revealed an uneven deposition between these six wells. The performance of the QCM system was also evaluated using two different methods. First, using fluorescein deposition in one well, depositions in three other wells were estimated, which was then compared to the actual QCM readings. Second, using the QCM measured deposition in one well, the deposition in three other wells was estimated and compared to deposition measured by fluorescein dosimetry. For both methods, the expected and actual deposition yields a linear fit with the slope ~1. This good fit suggests that QCM systems can be used to measure real-time mass deposition in an electrostatic ALI system.

Air-Liquid Interface Exposure of Lung Epithelial Cells to Low Doses of Nanoparticles to Assess Pulmonary Adverse Effects

Reliable and predictive in vitro assays for hazard assessments of manufactured nanomaterials (MNMs) are still limited. Specifically, exposure systems which more realistically recapitulate the physiological conditions in the lung are needed to predict pulmonary toxicity. To this end, air-liquid interface (ALI) systems have been developed in recent years which might be better suited than conventional submerged exposure assays. However, there is still a need for rigorous side-by-side comparisons of the results obtained with the two different exposure methods considering numerous parameters, such as different MNMs, cell culture models and read outs. In this study, human A549 lung epithelial cells and differentiated THP-1 macrophages were exposed under submerged conditions to two abundant types of MNMs i.e., ceria and titania nanoparticles (NPs). Membrane integrity, metabolic activity as well as pro-inflammatory responses were recorded. For comparison, A549 monocultures were also exposed at the ALI to the same MNMs. In the case of titania NPs, genotoxicity was also investigated. In general, cells were more sensitive at the ALI compared to under classical submerged conditions. Whereas ceria NPs triggered only moderate effects, titania NPs clearly initiated cytotoxicity, pro-inflammatory gene expression and genotoxicity. Interestingly, low doses of NPs deposited at the ALI were sufficient to drive adverse outcomes, as also documented in rodent experiments. Therefore, further development of ALI systems seems promising to refine, reduce or even replace acute pulmonary toxicity studies in animals.

Toxicity and Gene Expression Profiling of Copper- and Titanium-Based Nanoparticles Using Air-Liquid Interface Exposure

To assess the toxicity of nanomaterials, most in vitro studies have been performed under submerged conditions, which do not reflect physiological conditions upon inhalation. An air-liquid interface (ALI) exposure may provide more reliable data on dosimetry and prevent interactions with cell culture media components. Therefore, an ALI exposure was combined with a high-throughput RT-qPCR approach to evaluate the toxicological potential of CuO and TiO₂ nanoparticles (NP) in A549 cells. While TiO₂ NP did not show any cytotoxicity or other effects compromising genomic stability up to 25.8 μg/cm², CuO NP revealed a dose-dependent cytotoxicity, starting at 4.9 μg/cm². Furthermore, CuO NP altered distinct gene expression patterns indicative for disturbed metal homeostasis, stress response, and DNA damage induction. Thus, induction of metal homeostasis associated genes (MT1X, MT2A) at 0.4 μg/cm² and higher suggested uptake and intracellular dissolution of CuO NP, which was verified by a dose-dependent increase in intracellular copper concentration. Starting at 4.9 μg/cm², oxidative stress markers (HMOX1, HSPA1A) were induced dose-dependently, supported by elevated ROS levels. Furthermore, a dose-dependent induction of genes associated with DNA damage response (DDIT3, GADD45A) was observed, in concordance with an increase in DNA strand breaks. Finally, transcriptional data suggested the induction of apoptosis at high doses, while flow cytometric analysis revealed increased numbers of either late apoptotic or necrotic cells and clearly necrotic cells at the highest concentrations. Thus, an ALI cell culture system was successfully combined with a comprehensive high-throughput RT-qPCR system, allowing the quantification of NP deposition and their impact on genomic stability. For CuO NP, in principle the data confirm observations made under submerged conditions with respect to intracellular copper ion release, as well as oxidative and genotoxic stress response. However, the results derived from ALI exposure allow the assessment of dose-response-relationships as well as the comparison of relative toxic potencies of different NP.

Pathogenesis of chronic rhinosinusitis with nasal polyps: role of IL-6 in airway epithelial cell dysfunction

Background

Chronic rhinosinusitis with nasal polyps (CRSwNP) is characterized by an alteration in airway epithelial cell functions including barrier function, wound repair mechanisms, mucociliary clearance. The mechanisms leading to epithelial cell dysfunction in nasal polyps (NPs) remain poorly understood. Our hypothesis was that among the inflammatory cytokines involved in NPs, IL-6 could alter epithelial repair mechanisms and mucociliary clearance. The aim of this study was to evaluate the in vitro effects of IL-6 on epithelial repair mechanisms in a wound repair model and on ciliary beating in primary cultures of Human Nasal Epithelial Cells (HNEC).

Methods

Primary cultures of HNEC taken from 38 patients during surgical procedures for CRSwNP were used in an in vitro model of wound healing. Effects of increasing concentrations of IL-6 (1 ng/mL, 10 ng/mL, and 100 ng/mL) and other ILs (IL-5, IL-9, IL-10) on wound closure kinetics were compared to cultures without IL-modulation. After wound closure, the differentiation process was characterized under basal conditions and after IL supplementation using cytokeratin-14, MUC5AC, and β_IV tubulin as immunomarkers of basal, mucus, and ciliated cells, respectively. The ciliated edges of primary cultures were analyzed on IL-6 modulation by digital high-speed video-microscopy to measure: ciliary beating frequency (CBF), ciliary length, relative ciliary density, metachronal wavelength and the ciliary beating efficiency index.

Results

Our results showed that: (i) IL-6 accelerated airway wound repair in vitro, with a dose–response effect whereas no effect was observed after other ILs-stimulation. After 24 h, 79% of wounded wells with IL6-100 were fully repaired, vs 46% in the IL6-10 group, 28% in the IL6-1 group and 15% in the control group; (ii) specific migration analyses of closed wound at late repair stage (Day 12) showed IL-6 had the highest migration compared with other ILs (iii) The study of the IL-6 effect on ciliary function showed that CBF and metachronal wave increased but without significant modifications of ciliary density, length of cilia and efficiency index.

Conclusion

The up-regulated epithelial cell proliferation observed in polyps could be induced by IL-6 in the case of prior epithelial damage. IL-6 could be a major cytokine in NP physiopathology.

New Approach Methods to Evaluate Health Risks of Air Pollutants: Critical Design Considerations for In Vitro Exposure Testing

Air pollution consists of highly variable and complex mixtures recognized as major contributors to morbidity and mortality worldwide. The vast number of chemicals, coupled with limitations surrounding epidemiological and animal studies, has necessitated the development of new approach methods (NAMs) to evaluate air pollution toxicity. These alternative approaches include in vitro (cell-based) models, wherein toxicity of test atmospheres can be evaluated with increased efficiency compared to in vivo studies. In vitro exposure systems have recently been developed with the goal of evaluating air pollutant-induced toxicity; though the specific design parameters implemented in these NAMs-based studies remain in flux. This review aims to outline important design parameters to consider when using in vitro methods to evaluate air pollutant toxicity, with the goal of providing increased accuracy, reproducibility, and effectiveness when incorporating in vitro data into human health evaluations. This review is unique in that experimental considerations and lessons learned are provided, as gathered from first-hand experience developing and testing in vitro models coupled to exposure systems. Reviewed design aspects include cell models, cell exposure conditions, exposure chambers, and toxicity endpoints. Strategies are also discussed to incorporate in vitro findings into the context of in vivo toxicity and overall risk assessment.

State-of-the-art methods and devices for generation, exposure, and collection of aerosols from e-vapor products

E-vapor products (EVP) have become popular alternatives for cigarette smokers who would otherwise continue to smoke. EVP research is challenging and complex, mostly because of the numerous and rapidly evolving technologies and designs as well as the multiplicity of e-liquid flavors and solvents available on the market. There is an urgent need to standardize all stages of EVP assessment, from the production of a reference product to e-vapor generation methods and from physicochemical characterization methods to nonclinical and clinical exposure studies. The objective of this review is to provide a detailed description of selected experimental setups and methods for EVP aerosol generation and collection and exposure systems for their in vitro and in vivo assessment. The focus is on the specificities of the product that constitute challenges and require development of ad hoc assessment frameworks, equipment, and methods. In so doing, this review aims to support further studies, objective evaluation, comparison, and verification of existing evidence, and, ultimately, formulation of standardized methods for testing EVPs.

Development of a Novel Shallow Liquid Interface Exposure System for MWCNT Toxicity Assessment

Increasing applications of multiwalled carbon nanotubes (MWCNT) lead to significant occupational exposure and potential health concerns. Toxicity of MWCNT should be carefully elucidated since the conventional (CON) method with fully immersed condition fails to mimic the air-liquid interface (ALI) in airways. Additionally, quantification of MWCNT in cells was a real challenge. Currently available ALI exposure devices are costly, posing problems to conducting in vitro evaluations for emerging nanomaterials. A novel system, consisting of a shaker fluidized-bed atomizer (SFA) and electrostatic shallow liquid interface (ESLI) exposure chamber, has been developed for investigating nanotoxicity of well-dispersed pristine-MWCNT (pMWCNT) and carboxylized-MWCNT (cMWCNT). After 24-h exposure, LDH, MCP-1, IL-1β, IL-6, and TNF-α releases were determined, and cell uptakes were quantified according to the molybdenum content in cells. Biological responses triggered by SLI exposure are obviously more sensitive compared with those caused by CON exposure at equivalent doses. Exposure dose-dependent release of LDH and IL-6 was highlighted in A549 cells, indicating higher cytotoxicity and inflammatory responses of cMWCNT attributed to its shorter length, smaller size, and higher cell uptake. Cell-associated dose-dependent release of LDH and IL-6 was highlighted in RAW264.7 cells, revealing the higher adverse health risk of pMWCNT due to frustrated phagocytosis and its much higher molybdenum content. These results suggest that inherent characteristics of cells and distinct physicochemical properties of pMWCNT and cMWCNT lead to either exposure dose-dependent or cell-associated dose-dependent responses. Notably, the SLI is superior to the CON exposure method and well suited for nanotoxicity assessment of different MWCNTs.

FcRn-Dependent Transcytosis of Monoclonal Antibody in Human Nasal Epithelial Cells In Vitro: A Prerequisite for a New Delivery Route for Therapy?

Monoclonal antibodies (mAbs) are promising therapies to treat airway chronic inflammatory disease (asthma or nasal polyps). To date, no study has specifically assessed, in vitro, the potential function of neonatal Fc receptor (FcRn) in IgG transcytosis through the human nasal airway epithelium. The objective of this study was to report the in vitro expression and function of FcRn in nasal human epithelium. FcRn expression was studied in an air–liquid interface (ALI) primary culture model of human nasal epithelial cells (HNEC) from polyps. FcRn expression was characterized by quantitative RT-PCR, western blot, and immunolabeling. The ability of HNECs to support mAb transcytosis via FcRn was assessed by transcytosis assay. This study demonstrates the expression of FcRn mRNA and protein in HNEC. We report a high expression of FcRn in the cytosol of ciliated, mucus, and basal cells by immunohistochemistry with a higher level of FcRn proteins in differentiated HNEC. We also proved in vitro transepithelial delivery of an IgG1 therapeutic mAb with a dose–response curve. This is the first time that FcRn expression and mAb transcytosis has been shown in a model of human nasal respiratory epithelium in vitro. This study is a prerequisite for FcRn-dependent nasal administration of mAbs.

Air-Liquid Interface In Vitro Models for Respiratory Toxicology Research: Consensus Workshop and Recommendations

In vitro air-liquid interface (ALI) cell culture models can potentially be used to assess inhalation toxicology endpoints and are usually considered, in terms of relevancy, between classic (i.e., submerged) in vitro models and animal-based models. In some situations that need to be clearly defined, ALI methods may represent a complement or an alternative option to in vivo experimentations or classic in vitro methods. However, it is clear that many different approaches exist and that only very limited validation studies have been carried out to date. This means comparison of data from different methods is difficult and available methods are currently not suitable for use in regulatory assessments. This is despite inhalation toxicology being a priority area for many governmental organizations. In this setting, a 1-day workshop on ALI in vitro models for respiratory toxicology research was organized in Paris in March 2016 to assess the situation and to discuss what might be possible in terms of validation studies. The workshop was attended by major parties in Europe and brought together more than 60 representatives from various academic, commercial, and regulatory organizations. Following plenary, oral, and poster presentations, an expert panel was convened to lead a discussion on possible approaches to validation studies for ALI inhalation models. A series of recommendations were made and the outcomes of the workshop are reported.

Agglomeration of Escherichia coli with Positively Charged Nanoparticles Can Lead to Artifacts in a Standard Caenorhabditis elegans Toxicity Assay

The increased use and incorporation of engineered nanoparticles (ENPs) in consumer products requires a robust assessment of their potential environmental implications. However, a lack of standardized methods for nanotoxicity testing has yielded results that are sometimes contradictory. Standard ecotoxicity assays may work appropriately for some ENPs with minimal modification but produce artifactual results for others. Therefore, understanding the robustness of assays for a range of ENPs is critical. In this study, we evaluated the performance of a standard Caenorhabditis elegans ( C. elegans) toxicity assay containing an Escherichia coli ( E. coli) food supply with silicon, polystyrene, and gold ENPs with different charged coatings and sizes. Of all the ENPs tested, only those with a positively charged coating caused growth inhibition. However, the positively charged ENPs were observed to heteroagglomerate with E. coli cells, suggesting that the ENPs impacted the ability of nematodes to feed, leading to a false positive toxic effect on C. elegans growth and reproduction. When the ENPs were tested in two alternate C. elegans assays that did not contain E. coli, we found greatly reduced toxicity of ENPs. This study illustrates a key unexpected artifact that may occur during nanotoxicity assays.

Evaluating opportunities for advancing the use of alternative methods in risk assessment through the development of fit-for-purpose in vitro assays

An evolving regulatory, scientific, and legislative landscape is driving a fundamental change in how chemical safety decisions are made. As we move to implement changes, regulatory agencies and industry are beginning to adopt tiered approaches, which leverage high-throughput screening technologies for prioritization and read across, followed by interrogation of "hit chemicals" with more rigorous dose-response assessment either in fit-for-purpose human cell-based assays or with traditional in vivo tests. However, to date, suitable in vitro alternatives do not exist for the vast majority of the organ toxicities that form the basis of current regulatory decisions. To successfully support safety decisions, biologically relevant, quantitative, cell-based assays that evaluate dose-response and identify regions of safety for chemical exposure are required. This review evaluates the current state of the science in the development of such assays, identifies key gaps in the current tests, and recommends areas where research efforts may be focused to help move the risk assessment community towards more wide-spread use of in vitro methods. Our analysis suggests that a key shortcoming in the current efforts is the ability to test volatile compounds and to predict pulmonary toxicity. We present a mechanistically-based path forward for the development of a fit-for-purpose lung toxicity assay.

Toxicity of ZnO nanoparticles (NPs) to A549 cells and A549 epithelium in vitro: Interactions with dipalmitoyl phosphatidylcholine (DPPC)

Once inhaled, nanoparticles (NPs) will first interact with lung surfactant system, which may influence the colloidal aspects of NPs and consequently the toxic potential of NPs to pulmonary cells. In this study, we investigated the effects of dipalmitoyl phosphatidylcholine (DPPC), the major component in lung surfactant, on stability and toxicity of ZnO NPs. The presence of DPPC increased the UV-vis spectra, hydrodynamic size, Zeta potential and dissolution rate of ZnO NPs, which indicates that DPPC might interact with NPs and affect the colloidal stability of NPs. Exposure to ZnO NPs induced cytotoxicity associated with increased intracellular Zn ions but not superoxide in A549 cells. In A549 epithelium model, exposure to ZnO NPs induced cytotoxicity and decreased the release of interleukin 6 (IL-6) without a significant effect on epithelial permeability rate. Co-exposure of A549 cells or A549 epithelium model to DPPC and ZnO NPs induced a higher release of lactate dehydrogenase (LDH) and interleukin-6 (IL-6) compared with the exposure of ZnO NPs alone. We concluded that the presence of DPPC could influence the colloidal stability of ZnO NPs and increase the damage of NPs to membrane probably due to the increased positive surface charge.