SAEDC: Development of a technological solution for exploratory data analysis and statistics in cytotoxicity

INTRODUCTION

The intergovernmental organizations Organisation for Economic Co-operation and Development (OECD) and Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM) have developed guidelines for the use of in vitro models for toxicological evaluation of chemicals. However, the presence of manual steps and the requirement of multiple tools for data analysis, apart from being costly and time-consuming, can inadvertently introduce errors by researchers.

OBJECTIVES

We have developed the SAEDC platform (Technological Solution for Exploratory Data Analysis and Statistics for Cytotoxicity, in Portuguese), which enables analysis of cytotoxicity data from assays following OECD Guideline No. 129.

METHODOLOGY

In vitro experimental data were used to compare with the analysis methodology suggested in the Guideline. We analyzed 117 data sets covering chemicals from Category I to Unclassified according to GHS classification.

RESULTS

The four-parameters of non-linear regression (4PL) calculated by the SAEDC platform showed no significant differences compared to standard methodology in any of the data sets (p > 0.05). The coefficient of determination (R-squared) also demonstrated not only a good fit of the 4PL model to the data but also significant similarity to values obtained by the conventional methodology. Finally, the SAEDC platform predicted LD50 values for the chemicals from IC50, using the Registry of Cytotoxicity (RC) regression models.

CONCLUSION

The comparison with the standard data analysis methodology revealed that SAEDC platform fulfills the requirements for cytotoxicity data analysis, generating reliable and accurate results with fewer steps performed by researchers. The use of SAEDC platform for obtaining toxicity values can reduce analysis time compared to the standard methodology proposed by regulatory agencies. Thus, automation of the analysis using the SAEDC platform has the potential to save time and resources for cytotoxicity researchers and laboratories while generating reliable results.

Pro-inflammatory and genotoxic responses by metal oxide nanomaterials in alveolar epithelial cells and macrophages in submerged condition and air-liquid interface: An in vitro-in vivo correlation study

Studies on in vitro-in vivo correlations of inflammatory and genotoxic responses are needed to advance new approach methodologies. Here, we assessed pro-inflammatory and genotoxic responses by 13 nanosized metal oxides (nMeOx) and quartz (DQ12) in alveolar epithelial cells (A549) and macrophages (THP-1a) exposed in submerged conditions, and in A549:THP-1a co-cultures in air-liquid interface (ALI) system. Soluble nMeOx produced the highest IL-8 expression in A549 and THP-1a cells in submerged conditions (≥2-fold, p < 0.05), whereas only CuO caused a strong response in co-cultures exposed in the ALI system (13-fold, p < 0.05). IL-8 expression in A549 cells with concentrations as nMeOx specific surface area (SSA) correlated with neutrophil influx in mice (r = 0.89-0.98, p < 0.05). Similarly, IL-8 expression in THP-1a cell with concentrations as mass and SSA (when excluding soluble nMeOx) correlated with neutrophil influx in mice (r = 0.81-0.84, p < 0.05). DNA strand breaks (SB) was measured by the comet assay. We used a scoring system that categorizes effects in standard deviation units for comparison of genotoxicity in different models. Concordant genotoxicity was observed between SB levels in vitro (A549 and co-culture) and in vivo (broncho-alveolar lavage fluid cells and lung tissue). In conclusion, this study shows in vitro-in vivo correlations of nMeOx-induced inflammatory and genotoxic responses.

Toxicity of airborne nanoparticles: Facts and challenges

Air pollution is one of the most severe environmental healthhazards, and airborne nanoparticles (diameter <100 nm) are considered particularly hazardous to human health. They are produced by various sources such as internal combustion engines, wood and biomass burning, and fuel and natural gas combustion, and their origin, among other parameters, determines their intrinsic toxicity for reasons that are not yet fully understood. Many constituents of the nanoparticles are considered toxic or at least hazardous, including polycyclic aromatic hydrocarbons (PAHs) and heavy metal compounds, in addition to gaseous pollutants present in the aerosol fraction, such as NOx, SO2, and ozone. All these compounds can cause oxidative stress, mitochondrial damage, inflammation in the lungs and other tissues, and cellular organelles. Epidemiological investigations concluded that airborne pollution may affect the respiratory, cardiovascular, and nervous systems. Moreover, particulate matter has been linked to an increased risk of lung cancer, a carcinogenic effect not related to DNA damage, but to the cellular inflammatory response to the pollutants, in which the release of cytokines promotes the proliferation of pre-existing mutated cancer cells. The mechanisms behind toxicity can be investigated experimentally using cell cultures or animal models. Methods for gathering particulate matter have been explored, but standardized protocols are needed to ensure that the samples accurately represent chemical mixtures in the environment. Toxic constituents of nanoparticles can be studied in animal and cellular models, but designing realistic exposure settings is challenging. The air-liquid interface (ALI) system directly exposes cells, mimicking particle inhalation into the lungs. Continuous research and monitoring of nanoparticles and other airborne pollutants is essential for understanding their effects and developing active strategies to mitigate their risks to human and environmental health.

Nanoparticles and Airway Epithelial Cells: Exploring the Impacts and Methodologies in Toxicity Assessment

The production of nanoparticles has recently surged due to their varied applications in the biomedical, pharmaceutical, textile, and electronic sectors. However, this rapid increase in nanoparticle manufacturing has raised concerns about environmental pollution, particularly its potential adverse effects on human health. Among the various concerns, inhalation exposure to nanoparticles poses significant risks, especially affecting the respiratory system. Airway epithelial cells play a crucial role as the primary defense against inhaled particulate matter and pathogens. Studies have shown that nanoparticles can disrupt the airway epithelial barrier, triggering inflammatory responses, generating reactive oxygen species, and compromising cell viability. However, our understanding of how different types of nanoparticles specifically impact the airway epithelial barrier remains limited. Both in vitro cell culture and in vivo murine models are commonly utilized to investigate nanoparticle-induced cellular responses and barrier dysfunction. This review discusses the methodologies frequently employed to assess nanoparticle toxicity and barrier disruption. Furthermore, we analyze and compare the distinct effects of various nanoparticle types on the airway epithelial barrier. By elucidating the diverse responses elicited by different nanoparticles, we aim to provide insights that can guide future research endeavors in assessing and mitigating the potential risks associated with nanoparticle exposure.

The human health effects of unconventional oil and gas (UOG) chemical exposures: a scoping review of the toxicological literature

Many chemicals associated with unconventional oil and natural gas (UOG) are known toxicants, leading to health concerns about the effects of UOG. Our objective was to conduct a scoping review of the toxicological literature to assess the effects of UOG chemical exposures in models relevant to human health. We searched databases for primary research studies published in English or French between January 2000 and June 2023 on UOG-related toxicology studies. Two reviewers independently screened abstracts and full texts to determine inclusion. Seventeen studies met our study inclusion criteria. Nine studies used solely in vitro models, while six conducted their investigation solely in animal models. Two studies incorporated both types of models. Most studies used real water samples impacted by UOG or lab-made mixtures of UOG chemicals to expose their models. Most in vitro models used human cells in monocultures, while all animal studies were conducted in rodents. All studies detected significant deleterious effects associated with exposure to UOG chemicals or samples, including endocrine disruption, carcinogenicity, behavioral changes and metabolic alterations. Given the plausibility of causal relationships between UOG chemicals and adverse health outcomes highlighted in this review, future risk assessment studies should focus on measuring exposure to UOG chemicals in human populations.

Aerosol exposure at air-liquid-interface (AE-ALI) in vitro toxicity system characterisation: Particle deposition and the importance of air control responses

Experimental systems allowing aerosol exposure (AE) of cell cultures at the air-liquid-interface (ALI) are increasingly being used to assess the toxicity of inhaled contaminants as they are more biomimetic than standard methods using submerged cultures, however, they require detailed characterisation before use. An AE-ALI system combining aerosol generation with a CULTEX® exposure chamber was characterised with respect to particle deposition and the cellular effects of filtered air (typical control) exposures. The effect of system parameters (electrostatic precipitator voltage, air flowrate to cells and insert size) on deposition efficiency and spatial distribution were investigated using ICP-MS and laser ablation ICP-MS, for an aerosol of CeO2 nanoparticles. Deposition varied with conditions, but appropriate choice of operating parameters produced broadly uniform deposition at suitable levels. The impact of air exposure duration on alveolar cells (A549) and primary small airway epithelial cells (SAECs) was explored with respect to LDH release and expression of selected genes. Results indicated that air exposures could have a significant impact on cells (e.g., cytotoxicity and expression of genes, including CXCL1, HMOX1, and SPP1) at relatively short durations (from 10 mins) and that SAECs were more sensitive. These findings indicate that detailed system characterisation is essential to ensure meaningful results.

Repeat treatment of organotypic airway cultures with ethyl methanesulfonate causes accumulation of somatic cell mutations without expansion of bronchial-carcinoma-specific cancer driver mutations

The human in vitro organotypic air-liquid-interface (ALI) airway tissue model is structurally and functionally similar to the human large airway epithelium and, as a result, is being used increasingly for studying the toxicity of inhaled substances. Our previous research demonstrated that DNA damage and mutagenesis can be detected in human airway tissue models under conditions used to assess general and respiratory toxicity endpoints. Expanding upon our previous proof-of-principle study, human airway epithelial tissue models were treated with 6.25-100 µg/mL ethyl methanesulfonate (EMS) for 28 days, followed by a 28-day recovery period. Mutagenesis was evaluated by Duplex Sequencing (DS), and clonal expansion of bronchial-cancer-specific cancer-driver mutations (CDMs) was investigated by CarcSeq to determine if both mutation-based endpoints can be assessed in the same system. Additionally, DNA damage and tissue-specific responses were analyzed during the treatment and following the recovery period. EMS exposure led to time-dependent increases in mutagenesis over the 28-day treatment period, without expansion of clones containing CDMs; the mutation frequencies remained elevated following the recovery. EMS also produced an increase in DNA damage measured by the CometChip and MultiFlow assays and the elevated levels of DNA damage were reduced (but not eliminated) following the recovery period. Cytotoxicity and most tissue-function changes induced by EMS treatment recovered to control levels, the exception being reduced proliferating cell frequency. Our results indicate that general, respiratory-tissue-specific and genotoxicity endpoints increased with repeat EMS dosing; expansion of CDM clones, however, was not detected using this repeat treatment protocol. DISCLAIMER: This article reflects the views of its authors and does not necessarily reflect those of the U.S. Food and Drug Administration. Any mention of commercial products is for clarification only and is not intended as approval, endorsement, or recommendation.

Air-liquid interface exposure of A549 human lung cells to characterize the hazard potential of a gaseous bio-hybrid fuel blend

Gaseous and semi-volatile organic compounds emitted by the transport sector contribute to air pollution and have adverse effects on human health. To reduce harmful effects to the environment as well as to humans, renewable and sustainable bio-hybrid fuels are explored and investigated in the cluster of excellence "The Fuel Science Center" at RWTH Aachen University. However, data on the effects of bio-hybrid fuels on human health is scarce, leaving a data gap regarding their hazard potential. To help close this data gap, this study investigates potential toxic effects of a Ketone-Ester-Alcohol-Alkane (KEAA) fuel blend on A549 human lung cells. Experiments were performed using a commercially available air-liquid interface exposure system which was optimized beforehand. Then, cells were exposed at the air-liquid interface to 50-2000 ppm C3.7 of gaseous KEAA for 1 h. After a 24 h recovery period in the incubator, cells treated with 500 ppm C3.7 KEAA showed significant lower metabolic activity and cells treated with 50, 250, 500 and 1000 ppm C3.7 KEAA showed significant higher cytotoxicity compared to controls. Our data support the international occupational exposure limits of the single KEAA constituents. This finding applies only to the exposure scenario tested in this study and is difficult to extrapolate to the complex in vivo situation.

The effects of fine particulate matter (SRM 2786) on three different 3D lung models exposed at the air-liquid interface - A comparative study

3D cell culture models exposed at the air-liquid interface (ALI) represent a potential alternative to animal experiments for hazard and risk assessment of inhaled compounds. This study compares cocultures composed of either Calu-3, A549 or HBEC3-KT lung epithelial cells, cultured together with THP-1-derived macrophages and EA.hy926 endothelial cells, in terms of barrier capacity and responses to a standard reference sample of fine particulate matter (SRM 2786). High-content imaging analysis revealed a similar cellular composition between the different cell models. The 3D cell cultures with Calu-3 cells showed the greatest barrier capacity, as measured by transepithelial electrical resistance and permeability to Na-fluorescein. Mucus production was detected in 3D cell cultures based on Calu-3 and A549 cells. Exposure to SRM 2786 at ALI increased cytokine release and expression of genes associated with inflammation and xenobiotic metabolism. Moreover, the presence of THP-1-derived macrophages was central to the cytokine responses in all cell models. While the different 3D cell culture models produced qualitatively similar responses, more pronounced pro-inflammatory responses were observed in the basolateral compartment of the A549 and HBEC3-KT models compared to the Calu-3 model, likely due to their reduced barrier capacity and lower retention of secreted mediators in the apical compartment.

A novel in vitro high-content imaging assay for the prediction of drug-induced lung toxicity

The development of inhaled drugs for respiratory diseases is frequently impacted by lung pathology in non-clinical safety studies. To enable design of novel candidate drugs with the right safety profile, predictive in vitro lung toxicity assays are required that can be applied during drug discovery for early hazard identification and mitigation. Here, we describe a novel high-content imaging-based screening assay that allows for quantification of the tight junction protein occludin in A549 cells, as a model for lung epithelial barrier integrity. We assessed a set of compounds with a known lung safety profile, defined by clinical safety or non-clinical in vivo toxicology data, and were able to correctly identify 9 of 10 compounds with a respiratory safety risk and 9 of 9 compounds without a respiratory safety risk (90% sensitivity, 100% specificity). The assay was sensitive at relevant compound concentrations to influence medicinal chemistry optimization programs and, with an accessible cell model in a 96-well plate format, short protocol and application of automated imaging analysis algorithms, this assay can be readily integrated in routine discovery safety screening to identify and mitigate respiratory toxicity early during drug discovery. Interestingly, when we applied physiologically-based pharmacokinetic (PBPK) modelling to predict epithelial lining fluid exposures of the respiratory tract after inhalation, we found a robust correlation between in vitro occludin assay data and lung pathology in vivo, suggesting the assay can inform translational risk assessment for inhaled small molecules.

Roles of airway and intestinal epithelia in responding to pathogens and maintaining tissue homeostasis

Epithelial cells form a resilient barrier and orchestrate defensive and reparative mechanisms to maintain tissue stability. This review focuses on gut and airway epithelia, which are positioned where the body interfaces with the outside world. We review the many signaling pathways and mechanisms by which epithelial cells at the interface respond to invading pathogens to mount an innate immune response and initiate adaptive immunity and communicate with other cells, including resident microbiota, to heal damaged tissue and maintain homeostasis. We compare and contrast how airway and gut epithelial cells detect pathogens, release antimicrobial effectors, collaborate with macrophages, Tregs and epithelial stem cells to mount an immune response and orchestrate tissue repair. We also describe advanced research models for studying epithelial communication and behaviors during inflammation, tissue injury and disease.

Impact of Wildfires on Cardiovascular Health

Wildfire smoke (WFS) is a mixture of respirable particulate matter, environmental gases, and other hazardous pollutants that originate from the unplanned burning of arid vegetation during wildfires. The increasing size and frequency of recent wildfires has escalated public and occupational health concerns regarding WFS inhalation, by either individuals living nearby and downstream an active fire or wildland firefighters and other workers that face unavoidable exposure because of their profession. In this review, we first synthesize current evidence from environmental, controlled, and interventional human exposure studies, to highlight positive associations between WFS inhalation and cardiovascular morbidity and mortality. Motivated by these findings, we discuss preventative measures and suggest interventions to mitigate the cardiovascular impact of wildfires. We then review animal and cell exposure studies to call attention on the pathophysiological processes that support the deterioration of cardiovascular tissues and organs in response to WFS inhalation. Acknowledging the challenges of integrating evidence across independent sources, we contextualize laboratory-scale exposure approaches according to the biological processes that they model and offer suggestions for ensuring relevance to the human condition. Noting that wildfires are significant contributors to ambient air pollution, we compare the biological responses triggered by WFS to those of other harmful pollutants. We also review evidence for how WFS inhalation may trigger mechanisms that have been proposed as mediators of adverse cardiovascular effects upon exposure to air pollution. We finally conclude by highlighting research areas that demand further consideration. Overall, we aspire for this work to serve as a catalyst for regulatory initiatives to mitigate the adverse cardiovascular effects of WFS inhalation in the community and alleviate the occupational risk in wildland firefighters.

Pulmonary evaluation of whole-body inhalation exposure of polycarbonate (PC) filament 3D printer emissions in rats

During fused filament fabrication (FFF) 3D printing with polycarbonate (PC) filament, a release of ultrafine particles (UFPs) and volatile organic compounds (VOCs) occurs. This study aimed to determine PC filament printing emission-induced toxicity in rats via whole-body inhalation exposure. Male Sprague Dawley rats were exposed to a single concentration (0.529 mg/m3, 40 nm mean diameter) of the 3D PC filament emissions in a time-course via whole body inhalation for 1, 4, 8, 15, and 30 days (4 hr/day, 4 days/week), and sacrificed 24 hr after the last exposure. Following exposures, rats were assessed for pulmonary and systemic responses. To determine pulmonary injury, total protein and lactate dehydrogenase (LDH) activity, surfactant proteins A and D, total as well as lavage fluid differential cells in bronchoalveolar lavage fluid (BALF) were examined, as well as histopathological analysis of lung and nasal passages was performed. To determine systemic injury, hematological differentials, and blood biomarkers of muscle, metabolic, renal, and hepatic functions were also measured. Results showed that inhalation exposure induced no marked pulmonary or systemic toxicity in rats. In conclusion, inhalation exposure of rats to a low concentration of PC filament emissions produced no significant pulmonary or systemic toxicity.

Use of quantitative in vitro to in vivo extrapolation (QIVIVE) for the assessment of non-combustible next-generation product aerosols

With the use of in vitro new approach methodologies (NAMs) for the assessment of non-combustible next-generation nicotine delivery products, new extrapolation methods will also be required to interpret and contextualize the physiological relevance of these results. Quantitative in vitro to in vivo extrapolation (QIVIVE) can translate in vitro concentrations into in-life exposures with physiologically-based pharmacokinetic (PBPK) modelling and provide estimates of the likelihood of harmful effects from expected exposures. A major challenge for evaluating inhalation toxicology is an accurate assessment of the delivered dose to the surface of the cells and the internalized dose. To estimate this, we ran the multiple-path particle dosimetry (MPPD) model to characterize particle deposition in the respiratory tract and developed a PBPK model for nicotine that was validated with human clinical trial data for cigarettes. Finally, we estimated a Human Equivalent Concentration (HEC) and predicted plasma concentrations based on the minimum effective concentration (MEC) derived after acute exposure of BEAS-2B cells to cigarette smoke (1R6F), or heated tobacco product (HTP) aerosol at the air liquid interface (ALI). The MPPD-PBPK model predicted the in vivo data from clinical studies within a factor of two, indicating good agreement as noted by WHO International Programme on Chemical Safety (2010) guidance. We then used QIVIVE to derive the exposure concentration (HEC) that matched the estimated in vitro deposition point of departure (POD) (MEC cigarette = 0.38 puffs or 11.6 µg nicotine, HTP = 22.9 puffs or 125.6 µg nicotine) and subsequently derived the equivalent human plasma concentrations. Results indicate that for the 1R6F cigarette, inhaling 1/6th of a stick would be required to induce the same effects observed in vitro, in vivo. Whereas, for HTP it would be necessary to consume 3 sticks simultaneously to induce in vivo the effects observed in vitro. This data further demonstrates the reduced physiological potency potential of HTP aerosol compared to cigarette smoke. The QIVIVE approach demonstrates great promise in assisting human health risk assessments, however, further optimization and standardization are required for the substantiation of a meaningful contribution to tobacco harm reduction by alternative nicotine delivery products.

Human in vitro blood barrier models: architectures and applications

Blood barriers serve as key points of transport for essential molecules as well as lines of defense to protect against toxins. In vitro modeling of these barriers is common practice in the study of their physiology and related diseases. This review describes a common method of using an adaptable, low cost, semipermeable, suspended membrane to experimentally model three blood barriers in the human body: the blood-brain barrier (BBB), the gut-blood barrier (GBB), and the air-blood barrier (ABB). The GBB and ABB both protect from the outside environment, while the BBB protects the central nervous system from potential neurotoxic agents in the blood. These barriers share several commonalities, including the formation of tight junctions, polarized cellular monolayers, and circulatory system contact. Cell architectures used to mimic barrier anatomy as well as applications to study function, dysfunction, and response provide an overview of the versatility enabled by these cultural systems.

Modular air-liquid interface aerosol exposure system (MALIES) to study toxicity of nanoparticle aerosols in 3D-cultured A549 cells in vitro

We present a novel lung aerosol exposure system named MALIES (modular air-liquid interface exposure system), which allows three-dimensional cultivation of lung epithelial cells in alveolar-like scaffolds (MatriGrids®) and exposure to nanoparticle aerosols. MALIES consists of multiple modular units for aerosol generation, and can be rapidly assembled and commissioned. The MALIES system was proven for its ability to reliably produce a dose-dependent toxicity in A549 cells using CuSO4 aerosol. Cytotoxic effects of BaSO4- and TiO2-nanoparticles were investigated using MALIES with the human lung tumor cell line A549 cultured at the air-liquid interface. Experiments with concentrations of up to 5.93 × 105 (BaSO4) and 1.49 × 106 (TiO2) particles/cm3, resulting in deposited masses of up to 26.6 and 74.0 µg/cm2 were performed using two identical aerosol exposure systems in two different laboratories. LDH, resazurin reduction and total glutathione were measured. A549 cells grown on MatriGrids® form a ZO-1- and E-Cadherin-positive epithelial barrier and produce mucin and surfactant protein. BaSO4-NP in a deposited mass of up to 26.6 µg/cm2 resulted in mild, reversible damage (~ 10% decrease in viability) to lung epithelium 24 h after exposure. TiO2-NP in a deposited mass of up to 74.0 µg/cm2 did not induce any cytotoxicity in A549 cells 24 h and 72 h after exposure, with the exception of a 1.7 fold increase in the low exposure group in laboratory 1. These results are consistent with previous studies showing no significant damage to lung epithelium by short-term treatment with low concentrations of nanoscale BaSO4 and TiO2 in in vitro experiments.

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

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

Characterization and applicability of a novel physiologically relevant 3D-tetraculture bronchial model for in vitro assessment of respiratory sensitization

Chemical Respiratory Allergy (CRA) is triggered after exposure to Low Molecular Weight (LMW) sensitizers and manifests clinically as asthma and rhinitis. From a risk/toxicity assessment point of view, there are few methods, none of them validated, for evaluating the respiratory sensitization potential of chemicals once the in vivo-based models usually employed for inhalation toxicity addressment do not comprise allergenicity endpoints specifically. Based on that, we developed, characterized, and evaluated the applicability of a 3D-tetraculture airway model reconstructed with bronchial epithelial, fibroblasts, endothelial and monocytic cell lines. Moreover, we exposed the tissue to maleic anhydride (MA) aerosols to challenge the model and subsequently assessed inflammatory and functional aspects of the tissue. The reconstructed tissue presented phenotypic biomarkers compatible with human bronchial epithelium, and MA aerosol exposure triggered an increased IL-8 and IL-6 production, reactive oxygen species (ROS) formation, and apoptosis of epithelial cells. Besides, augmented IL-8 production by monocytic cells was also found, correlating with dendritic cell activation within the co-culture model after MA exposure. Our results demonstrated that the 3D-tetraculture bronchial model presents hallmarks related to human airways' structure and function. Additionally, exposure to a respiratory sensitizer induced inflammatory and functional alterations in the reconstructed tissue, rendering it a valuable tool for exploring the mechanistic framework of chemically induced respiratory sensitization.

Evaluation of Cytotoxicity and Oxidative Stress of Whole Aerosol from Vuse Alto ENDS Products

Assessment of in vitro cytotoxicity is an important component of tobacco product toxicological evaluations. However, current methods of regulatory testing involve exposing monolayer cell cultures to various preparations of aerosols from cigarettes or other emerging products such as electronic nicotine delivery systems (ENDS), which are not representative of human exposure. In the present study, a whole aerosol (WA) system was used to expose lung epithelial cultures (2D and 3D) to determine the potential of six Vuse Alto ENDS products that varied in nicotine content (1.8%, 2.4%, and 5%) and flavors (Golden Tobacco, Rich Tobacco, Menthol, and Mixed Berry), along with a marketed ENDS and a marked cigarette comparator to induce cytotoxicity and oxidative stress. The WA from the Vuse Alto ENDS products was not cytotoxic in the NRU and MTT assays, nor did it activate the Nrf2 reporter gene, a marker of oxidative stress. In summary, Vuse Alto ENDS products did not induce cytotoxic or oxidative stress responses in the in vitro models. The WA exposures used in the 3D in vitro models described herein may be better suited than 2D models for the determination of cytotoxicity and other in vitro functional endpoints and represent alternative models for regulatory evaluation of tobacco products.

Utilizing primary human airway mucociliary tissue cultures to model ramifications of chronic E-cigarette usage

Electronic cigarettes are battery powered devices that use a vape-liquid to produce a vapor that is inhaled. A consequence of the rise in e-cigarette usage was the 2019 emergence of a vaping-induced respiratory disease denoted as 'e-cigarette or vaping use-associated lung injury' (EVALI). One of the suspected causes of EVALI is Vitamin E Acetate (VEA), which was found to be a diluent in certain illicit vape-pens, whereas nicotine is commonly diluted in equal parts propylene glycol and vegetable glycerin (PG:VG). The prevalent use of e-cigarettes and the emergence of a novel illness has made understanding how e-cigarette vapors affect our respiratory tissues a public health concern. We have designed and produced a simple device that can operate e-cigarettes and deliver the vapor to a chamber containing a standard cell culture multi-well plate. Here we utilize our device to model the response of human airway mucociliary tissue after chronic exposure to vapors produced from either PG:VG or VEA. We note several differences between how PG:VG and VEA vapors interact with and alter airway tissue cultures and suggest potential mechanisms for how VEA-vapors can exacerbate EVALI symptoms. Our device combined with primary human airway tissue cultures make an economical and compact model system that allows for animal-free investigations into the acute and chronic consequences of e-cigarette vapors on primary respiratory cells.

How to use an in vitro approach to characterize the toxicity of airborne compounds

As part of the development of new approach methodologies (NAMs), numerous in vitro methods are being developed to characterize the potential toxicity of inhalable xenobiotics (gases, volatile organic compounds, polycyclic aromatic hydrocarbons, particulate matter, nanoparticles). However, the materials and methods employed are extremely diverse, and no single method is currently in use. Method standardization and validation would raise trust in the results and enable them to be compared. This four-part review lists and compares biological models and exposure methodologies before describing measurable biomarkers of exposure or effect. The first section emphasizes the importance of developing alternative methods to reduce, if not replace, animal testing (3R principle). The biological models presented are mostly to cultures of epithelial cells from the respiratory system, as the lungs are the first organ to come into contact with air pollutants. Monocultures or cocultures of primary cells or cell lines, as well as 3D organotypic cultures such as organoids, spheroids and reconstituted tissues, but also the organ(s) model on a chip are examples. The exposure methods for these biological models applicable to airborne compounds are submerged, intermittent, continuous either static or dynamic. Finally, within the restrictions of these models (i.e. relative tiny quantities, adhering cells), the mechanisms of toxicity and the phenotypic markers most commonly examined in models exposed at the air-liquid interface (ALI) are outlined.

Assessment of wood smoke induced pulmonary toxicity in normal- and chronic bronchitis-like bronchial and alveolar lung mucosa models at air-liquid interface

BACKGROUND

Chronic obstructive pulmonary disease (COPD) has the highest increased risk due to household air pollution arising from biomass fuel burning. However, knowledge on COPD patho-mechanisms is mainly limited to tobacco smoke exposure. In this study, a repeated direct wood smoke (WS) exposure was performed using normal- (bro-ALI) and chronic bronchitis-like bronchial (bro-ALI-CB), and alveolar (alv-ALI) lung mucosa models at air-liquid interface (ALI) to assess broad toxicological end points.

METHODS

The bro-ALI and bro-ALI-CB models were developed using human primary bronchial epithelial cells and the alv-ALI model was developed using a representative type-II pneumocyte cell line. The lung models were exposed to WS (10 min/exposure; 5-exposures over 3-days; n = 6-7 independent experiments). Sham exposed samples served as control. WS composition was analyzed following passive sampling. Cytotoxicity, total cellular reactive oxygen species (ROS) and stress responsive NFkB were assessed by flow cytometry. WS exposure induced changes in gene expression were evaluated by RNA-seq (p ≤ 0.01) followed by pathway enrichment analysis. Secreted levels of proinflammatory cytokines were assessed in the basal media. Non-parametric statistical analysis was performed.

RESULTS

147 unique compounds were annotated in WS of which 42 compounds have inhalation toxicity (9 very high). WS exposure resulted in significantly increased ROS in bro-ALI (11.2%) and bro-ALI-CB (25.7%) along with correspondingly increased NFkB levels (bro-ALI: 35.6%; bro-ALI-CB: 18.1%). A total of 1262 (817-up and 445-down), 329 (141-up and 188-down), and 102 (33-up and 69-down) genes were differentially regulated in the WS-exposed bro-ALI, bro-ALI-CB, and alv-ALI models respectively. The enriched pathways included the terms acute phase response, mitochondrial dysfunction, inflammation, oxidative stress, NFkB, ROS, xenobiotic metabolism of AHR, and chronic respiratory disorder. The enrichment of the 'cilium' related genes was predominant in the WS-exposed bro-ALI (180-up and 7-down). The pathways primary ciliary dyskinesia, ciliopathy, and ciliary movement were enriched in both WS-exposed bro-ALI and bro-ALI-CB. Interleukin-6 and tumor necrosis factor-α were reduced (p < 0.05) in WS-exposed bro-ALI and bro-ALI-CB.

CONCLUSION

Findings of this study indicate differential response to WS-exposure in different lung regions and in chronic bronchitis, a condition commonly associated with COPD. Further, the data suggests ciliopathy as a candidate pathway in relation to WS-exposure.

A Fast Scoring of Human Primary Respiratory Epithelia Grown at Air-Liquid Interface (ALI) to Assess Epithelial Morphology in Research and Personalized Medicine Settings

BACKGROUND

In recent years, increasingly complex ALI protocols involving specialized, albeit laboratory-specific media have been established, while at the same time, many studies compile the data of only a few ALI donors in spite of site-, protocol- and donor-specific differentiation.

METHODS

We describe a simple morphology scoring protocol using histology material derived from epithelia grown on ALI inserts in parallel to other, more complex readouts.

RESULTS

Among more than 100 ALI inserts derived from different donors, significant differences in layer score (p = 0.001) and goblet cell score (p = 0.002) were observed when ALI epithelia derived from explanted lung material were compared to trachea-derived ALI cultures. Cortisol withdrawal for the final 2 days of ALI cultures influenced goblet cell density (p = 0.001).

CONCLUSIONS

While the histology score provides less resolution than FACS- or OMICs- based single cell analyses, the use of a subportion of the ALI epithelia grown on inserts makes it feasible to combine morphology assessment and other readouts of the same insert. This allows us to control for basic ALI morphology in research and personalized medicine settings in order to assess and, if desired, control for the impact of ALI culture protocols, site- and donor-specific influences on outcome of studies of ALI-derived epithelia.

An integrated new approach methodology for inhalation risk assessment of safe and sustainable by design nanomaterials

The production and use of nanomaterials (NMs) has increased over the last decades posing relevant questions on their risk after release and exposure of the population or sub-populations. In this context, the safe and sustainable by design (SSbD) approach framework requires to assess the potential hazard connected with intrinsic properties of the material along the whole life cycle of the NM and/or of the nano enabled products. Moreover, in the last years, the use of new advanced methodologies (NAMs) has increasingly gained attention for the use of alternative methods in obtaining relevant information on NMs hazard and risk. Considering the SSbD and the NAMs frameworks, within the ASINA H2020 project, we developed new NAMs devoted at improving the hazard and risk definition of different Ag and TiO2 NPs. The NAMs are developed considering two air liquid interface exposure systems, the Vitrocell Cloud-α and the Cultex Compact module and the relevant steps to obtain reproducible exposures are described. The new NAMs build on the integration of environmental monitoring campaigns at nano-coating production sites, allowing the quantification by the multiple-path particle dosimetry (MPPD) model of the expected lung deposited dose in occupational settings. Starting from this information, laboratory exposures to the aerosolized NPs are performed by using air liquid interface exposure equipment and human alveolar cells (epithelial cells and macrophages), replicating the doses of exposure estimated in workers by MPPD. Preliminary results on cell viability and inflammatory responses are reported. The proposed NAMs may represent possible future reference procedures for assessing the NPs inhalation toxicology, supporting risk assessment at real exposure doses.

The Cytotoxic Effects of Fine Particulate Matter (PM2.5) from Different Sources at the Air-Liquid Interface Exposure on A549 Cells

The health of humans has been negatively impacted by PM2.5 exposure, but the chemical composition and toxicity of PM2.5 might vary depending on its source. To investigate the toxic effects of particulate matter from different sources on lung epithelial cells (A549), PM2.5 samples were collected from residential, industrial, and transportation areas in Nanjing, China. The chemical composition of PM2.5 was analyzed, and toxicological experiments were conducted. The A549 cells were exposed using an air-liquid interface (ALI) exposure system, and the cytotoxic indicators of the cells were detected. The research results indicated that acute exposure to different sources of particulate matter at the air-liquid interface caused damage to the cells, induced the production of ROS, caused apoptosis, inflammatory damage, and DNA damage, with a dose-effect relationship. The content of heavy metals and PAHs in PM2.5 from the traffic source was relatively high, and the toxic effect of the traffic-source samples on the cells was higher than that of the industrial- and residential-source samples. The cytotoxicity of particulate matter was mostly associated with water-soluble ions, carbon components, heavy metals, PAHs, and endotoxin, based on the analysis of the Pearson correlation. Oxidative stress played an important role in PM2.5-induced biological toxicity.

A comprehensive review of micro- and nano-plastics in the atmosphere: Occurrence, fate, toxicity, and strategies for risk reduction

Micro- and nano-plastics (MNPs) have received considerable attention over the past 10 years due to their environmental prevalence and potential toxic effects. With the increase in global plastic production and disposal, MNP pollution has become a topic of emerging concern. In this review, we describe MNPs in the atmospheric environment, and potential toxicological effects of exposure to MNPs. Studies have reported the occurrence of MNPs in outdoor and indoor air at concentrations ranging from 0.0065 items m-3 to 1583 items m-3. Findings have identified plastic fragments, fibers, and films in sizes predominantly <1000 μm with polyamide (PA), polyester (PES), polyethylene terephthalate (PET), polypropylene (PP), rayon, polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), polyacrylonitrile (PAN), and ethyl vinyl acetate (EVA) as the major compounds. Exposure through indoor air and dust is an important pathway for humans. Airborne MNPs pose health risks to plants, animals, and humans. Atmospheric MNPs can enter organism bodies via inhalation and subsequent deposition in the lungs, which triggers inflammation and other adverse health effects. MNPs could be eliminated through source reduction, policy/regulation, environmental awareness and education, biodegradable materials, bioremediation, and efficient air-filtration systems. To achieve a sustainable society, it is crucial to implement effective strategies for reducing the usage of single-use plastics (SUPs). Further, governments play a pivotal role in addressing the pressing issue of MNPs pollution and must establish viable solutions to tackle this significant challenge.

On the path to predicting immune responses in the lung: Modeling the pulmonary innate immune system at the air-liquid interface (ALI)

Chronic respiratory diseases and infections are among the largest contributors to death globally, many of which still have no cure, including chronic obstructive pulmonary disorder, idiopathic pulmonary fibrosis, and respiratory syncytial virus among others. Pulmonary therapeutics afford untapped potential for treating lung infection and disease through direct delivery to the site of action. However, the ability to innovate new therapeutic paradigms for respiratory diseases will rely on modeling the human lung microenvironment and including key cellular interactions that drive disease. One key feature of the lung microenvironment is the air-liquid interface (ALI). ALI interface modeling techniques, using cell-culture inserts, organoids, microfluidics, and precision lung slices (PCLS), are rapidly developing; however, one major component of these models is lacking-innate immune cell populations. Macrophages, neutrophils, and dendritic cells, among others, represent key lung cell populations, acting as the first responders during lung infection or injury. Innate immune cells respond to and modulate stromal cells and bridge the gap between the innate and adaptive immune system, controlling the bodies response to foreign pathogens and debris. In this article, we review the current state of ALI culture systems with a focus on innate immune cells and suggest ways to build on current models to add complexity and relevant immune cell populations.

A bibliometric analysis of the recent achievements in pulmonary safety of nanoparticles

Assessing research activity is an important step for planning future initiatives oriented toward filling the remaining gaps in a field. Therefore, the objective of the current study was to review recently published research on pulmonary toxicity caused by nanomaterials. However, here, instead of reviewing possible toxic effects and discussing their mode of action, the goal was to establish trends considering for example examined so far nanomaterials or used testing strategies. A total of 2316 related articles retrieved from the three most cited databases (PubMed Scopus, Web of Science), selected based on the title and abstract requirements, were used as the source of the review. Based on the bibliometric analysis, the nano-meter metal oxides, and carbon-based nanotubes were identified as the most frequently studied nanomaterials, while quantum dots, which might induce possible harmful effects, were not considered so far. The majority of testing of pulmonary safety is based on in vitro studies with observed growth of the contribution of novel testing strategies, such as 3D lung model, air-liquid interface system, or omic analysis.

N-acetyl cysteine mitigates lung damage and inflammation after chlorine exposure in vivo and ex vivo

The objective of this study was to explore the effects of antioxidant treatments, specifically N-acetylcysteine (NAC) and N-acetylcysteine amide (NACA), in a mouse model of chlorine (Cl2)-induced lung injury. Additionally, the study aimed to investigate the utility of pig precision-cut lung slices (PCLS) as an ex vivo alternative for studying the short-term effects of Cl2 exposure and evaluating antioxidant treatments. The toxicological responses were analyzed in Cl2-exposed mice (inflammation, airway hyperresponsiveness (AHR)) and PCLS (viability, cytotoxicity, inflammatory mediators). Airways contractions were assessed using a small ventilator for mice and electric-field stimulation (EFS) for PCLS. Antioxidant treatments were administered to evaluate their effects. In Cl2-exposed mice, NAC treatment did not alleviate AHR, but it did reduce the number of neutrophils in bronchoalveolar lavage fluid and inflammatory mediators in lung tissue. In PCLS, exposure to Cl2 resulted in concentration-dependent toxicity, impairing the lung tissue's ability to respond to EFS-stimulation. NAC treatment increased viability, mitigated the toxic responses caused by Cl2 exposure, and maintained contractility comparable to unexposed controls. Interestingly, NACA did not provide any additional treatment effect beyond NAC in both models. In conclusion, the establishment of a pig model for Cl2-induced lung damage supports further investigation of NAC as a potential treatment. However, the lack of protective effects on AHR after NAC treatment in mice suggests that NAC alone may not be sufficient as a complete treatment for Cl2 injuries. Optimization of existing medications with a polypharmacy approach may be more successful in addressing the complex sequelae of Cl2-induced lung injury.

Goblet cell interactions reorient bundled mucus strands for efficient airway clearance

The respiratory tract of larger animals is cleared by sweeping bundled strands along the airway surface. These bundled strands can be millimetric in length and consist of MUC5B mucin. They are produced by submucosal glands, and upon emerging from these glands, the long axis of the bundled strands is oriented along the cilia-mediated flow toward the oral cavity. However, after release, the bundled strands are found to have turned orthogonal to the flow, which maximizes their clearance potential. How this unexpected reorientation is accomplished is presently not well understood. Recent experiments suggest that the reorientation process involves bundled strands sticking to MUC5AC mucus threads, which are tethered to the goblet cells. Such goblet cells are present in small numbers throughout the airway epithelium. Here, we develop a minimal model for reorientation of bundled mucus strands through adhesive interactions with surface goblet cells. Our simulations reveal that goblet cell interactions can reorient the bundled strands within 10 mm of release-making reorientation on the length scale of the tracheal tube feasible-and can stabilize the orthogonal orientation. Our model also reproduces other experimental observations such as strong velocity fluctuations and significant slow-down of the bundled strand with respect to the cilia-mediated flow. We further provide insight into the strand turning mechanism by examining the effect of strand shape on the impulse exerted by a single goblet cell. We conclude that goblet cell-mediated reorientation is a viable route for bundled strand reorientation, which should be further validated in future experiment.

Liver organoid culture methods

Organoids, three-dimensional structures cultured in vitro, can recapitulate the microenvironment, complex architecture, and cellular functions of in vivo organs or tissues. In recent decades, liver organoids have been developed rapidly, and their applications in biomedicine, such as drug screening, disease modeling, and regenerative medicine, have been widely recognized. However, the lack of repeatability and consistency, including the lack of standardized culture conditions, has been a major obstacle to the development and clinical application of liver organoids. It is time-consuming for researchers to identify an appropriate medium component scheme, and the usage of some ingredients remains controversial. In this review, we summarized and compared different methods for liver organoid cultivation that have been published in recent years, focusing on controversial medium components and discussing their advantages and drawbacks. We aimed to provide an effective reference for the development and standardization of liver organoid cultivation.

Exposure to urban nanoparticles at low PM[Formula: see text] concentrations as a source of oxidative stress and inflammation

Exposures to fine particulate matter (PM[Formula: see text]) have been associated with health impacts, but the understanding of the PM[Formula: see text] concentration-response (PM[Formula: see text]-CR) relationships, especially at low PM[Formula: see text], remains incomplete. Here, we present novel data using a methodology to mimic lung exposure to ambient air (2[Formula: see text] 60 [Formula: see text]g m[Formula: see text]), with minimized sampling artifacts for nanoparticles. A reference model (Air Liquid Interface cultures of human bronchial epithelial cells, BEAS-2B) was used for aerosol exposure. Non-linearities observed in PM[Formula: see text]-CR curves are interpreted as a result of the interplay between the aerosol total oxidative potential (OP[Formula: see text]) and its distribution across particle size (d[Formula: see text]). A d[Formula: see text]-dependent condensation sink (CS) is assessed together with the distribution with d[Formula: see text] of reactive species . Urban ambient aerosol high in OP[Formula: see text], as indicated by the DTT assay, with (possibly copper-containing) nanoparticles, shows higher pro-inflammatory and oxidative responses, this occurring at lower PM[Formula: see text] concentrations (< 5 [Formula: see text]g m[Formula: see text]). Among the implications of this work, there are recommendations for global efforts to go toward the refinement of actual air quality standards with metrics considering the distribution of OP[Formula: see text] with d[Formula: see text] also at relatively low PM[Formula: see text].

Development of a non-target strategy for evaluation of potential biological effects of inhalable aerosols generated during purposeful room conditioning using an in vitro inhalation model

OBJECTIVES

An integrated in vitro inhalation approach was outlined to estimate potential adverse acute inhalation effects of aerosols from commercial nebulizer applications used for purposeful room conditioning such as disinfection, scenting or others. Aerosol characterization, exposure estimation and evaluation of acute biological effects by in vitro inhalation were included to generate dose-response data, allowing for determination of in vitro lowest observable adverse effect levels (LOAELs). Correlation of these to estimates of human lung deposition was included for quantitative in vitro to in vivo extrapolation approach (QIVIVE) for acute effects during human exposure.

METHODS

To test the proposed approach, a case study was undertaken using two realistic test materials. An acute in vitro inhalation setup with air-liquid interface A549-cells in an optimized exposure situation (P.R.I.T.® ExpoCube®) was used to expose cells and analysis of relevant biological effects (viability, mitochondrial membrane potential, stress, IL-8 release) was carried out.

RESULTS

The observed dose-responsive effects in a sub-toxic dose-range could be attributed to the main component of one test material and its presence in the aerosol phase of the nebulized material. QIVIVE resulted in a factor of at least 256 between the in vitro LOAEL and the estimated acute human lung exposure for this test material.

CONCLUSIONS

The case-study shows the value of the non-target in vitro inhalation testing approach especially in case of a lack of knowledge on complex product composition. It is expected that approaches like this will be of high value for product safety and environmental health in the future.

Key challenges for in vitro testing of tobacco products for regulatory applications: Recommendations for dosimetry

The Institute for In Vitro Sciences (IIVS) is sponsoring a series of workshops to develop recommendations for optimal scientific and technical approaches for conducting in vitro assays to assess potential toxicity within and across tobacco and various next-generation products (NGPs) including heated tobacco products (HTPs) and electronic nicotine delivery systems (ENDSs). This publication was developed by a working group of the workshop members in conjunction with the sixth workshop in that series entitled "Dosimetry for conducting in vitro evaluations" and focuses on aerosol dosimetry for aerosol exposure to combustible cigarettes, HTP, and ENDS aerosolized tobacco products and summarizes the key challenges as well as documenting areas for future research.

Airway epithelial cells mount an early response to mycobacterial infection

Lung epithelial cells represent the first line of host defence against foreign inhaled components, including respiratory pathogens. Their responses to these exposures may direct subsequent immune activation to these pathogens. The epithelial response to mycobacterial infections is not well characterized and may provide clues to why some mycobacterial infections are cleared, while others are persistent and pathogenic. We have utilized an air-liquid interface model of human primary bronchial epithelial cells (ALI-PBEC) to investigate the epithelial response to infection with a variety of mycobacteria: Mycobacterium tuberculosis (Mtb), M. bovis (BCG), M. avium, and M. smegmatis. Airway epithelial cells were found to be infected by all four species, albeit at low frequencies. The proportion of infected epithelial cells was lowest for Mtb and highest for M. avium. Differential gene expression analysis revealed a common epithelial host response to mycobacteria, including upregulation of BIRC3, S100A8 and DEFB4, and downregulation of BPIFB1 at 48 h post infection. Apical secretions contained predominantly pro-inflammatory cytokines, while basal secretions contained tissue growth factors and chemokines. Finally, we show that neutrophils were attracted to both apical and basal secretions of infected ALI-PBEC. Neutrophils were attracted in high numbers to apical secretions from PBEC infected with all mycobacteria, with the exception of secretions from M. avium-infected ALI-PBEC. Taken together, our results show that airway epithelial cells are differentially infected by mycobacteria, and react rapidly by upregulation of antimicrobials, and increased secretion of inflammatory cytokines and chemokines which directly attract neutrophils. Thus, the airway epithelium may be an important immunological component in controlling and regulating mycobacterial infections.

A549 as an In Vitro Model to Evaluate the Impact of Microplastics in the Air

Airborne microplastics raise significant concerns due to their potential health impacts. Having a small size, larger surface area, and penetrative ability into the biological system, makes them hazardous to health. This review article compiles various studies investigating the mechanism of action of polystyrene micro- and nanoplastics affecting lung epithelial cells A549. These inhalable microplastics damage the respiratory system, by triggering a proinflammatory environment, genotoxicity, oxidative stress, morphological changes, and cytotoxic accumulation in A549 cells. PS-NP lung toxicity depends on various factors such as size, surface modifications, concentration, charge, and zeta potential. However, cellular uptake and cytotoxicity mechanisms depend on the cell type. For A549 cells, PS-NPs are responsible for energy imbalance by mitochondrial dysfunction, oxidative stress-mediated cytotoxicity, immunomodulation, and apoptosis. Additionally, PS-NPs have the ability to traverse the placental barrier, posing a risk to offspring. Despite the advancements, the precise mechanisms underlying how prolonged exposure to PS-NPs leads to the development and progression of lung diseases have unclear points, necessitating further investigations to unravel the root cause. This review also sheds light on data gaps, inconsistencies in PS-Nos research, and provides recommendations for further research in this field.

Toxicity and health effects of ultrafine particles: Towards an understanding of the relative impacts of different transport modes

Exposure to particulate matter (PM) has been associated with a wide range of adverse health effects, but it is still unclear how particles from various transport modes differ in terms of toxicity and associations with different human health outcomes. This literature review aims to summarize toxicological and epidemiological studies of the effect of ultrafine particles (UFPs), also called nanoparticles (NPs, <100 nm), from different transport modes with a focus on vehicle exhaust (particularly comparing diesel and biodiesel) and non-exhaust as well as particles from shipping (harbor), aviation (airport) and rail (mainly subway/underground). The review includes both particles collected in laboratory tests and the field (intense traffic environments or collected close to harbor, airport, and in subway). In addition, epidemiological studies on UFPs are reviewed with special attention to studies aimed at distinguishing the effects of different transport modes. Results from toxicological studies indicate that both fossil and biodiesel NPs show toxic effects. Several in vivo studies show that inhalation of NPs collected in traffic environments not only impacts the lung, but also triggers cardiovascular effects as well as negative impacts on the brain, although few studies compared NPs from different sources. Few studies were found on aviation (airport) NPs, but the available results suggest similar toxic effects as traffic-related particles. There is still little data related to the toxic effects linked to several sources (shipping, road and tire wear, subway NPs), but in vitro results highlighted the role of metals in the toxicity of subway and brake wear particles. Finally, the epidemiological studies emphasized the current limited knowledge of the health impacts of source-specific UFPs related to different transport modes. This review discusses the necessity of future research for a better understanding of the relative potencies of NPs from different transport modes and their use in health risk assessment.

High-throughput bioprinting of the nasal epithelium using patient-derived nasal epithelial cells

Progenitor human nasal epithelial cells (hNECs) are an essential cell source for the reconstruction of the respiratory pseudostratified columnar epithelium composed of multiple cell types in the context of infection studies and disease modeling. Hitherto, manual seeding has been the dominant method for creating nasal epithelial tissue models through biofabrication. However, this approach has limitations in terms of achieving the intricate three-dimensional (3D) structure of the natural nasal epithelium. 3D bioprinting has been utilized to reconstruct various epithelial tissue models, such as cutaneous, intestinal, alveolar, and bronchial epithelium, but there has been no attempt to use of 3D bioprinting technologies for reconstruction of the nasal epithelium. In this study, for the first time, we demonstrate the reconstruction of the nasal epithelium with the use of primary hNECs deposited on Transwell inserts via droplet-based bioprinting (DBB), which enabled high-throughput fabrication of the nasal epithelium in Transwell inserts of 24-well plates. DBB of progenitor hNECs ranging from one-tenth to one-half of the cell seeding density employed during the conventional cell seeding approach enabled a high degree of differentiation with the presence of cilia and tight-junctions over a 4 weeks air-liquid interface culture. Single cell RNA sequencing of these cultures identified five major epithelial cells populations, including basal, suprabasal, goblet, club, and ciliated cells. These cultures recapitulated the pseudostratified columnar epithelial architecture present in the native nasal epithelium and were permissive to respiratory virus infection. These results denote the potential of 3D bioprinting for high-throughput fabrication of nasal epithelial tissue models not only for infection studies but also for other purposes, such as disease modeling, immunological studies, and drug screening.

Can the impact of micro- and nanoplastics on human health really be assessed using in vitro models? A review of methodological issues

Because of the many advantages they offer (strength, low cost, durability, lightweight, resistance, etc.), plastics are integral part of our daily life with a production constantly rising. However, their waste management is still inadequate, resulting in their release and accumulation in the environment, representing a main source of pollution. Their degradation results in debris of variable size including microplastics (0.1 μm-5 mm) and even nanoplastics (<0.1 μm), whose potential impact on ecosystems and human health have raised concerns. The potential adverse effects they may cause have been evaluated using both in vitro and in vivo models. However, due to some specific characteristics of micro- and nanoplastics, there are challenging questions about whether conventional in vitro tests are appropriate for evaluating their toxicity. For example, low-density plastics float on the surface of the culture medium and cannot come into contact with cells adhering to the bottom of the culture plates, which prevents proper evaluation of potential adverse effects and leads to misinterpretation of toxicological assays. In this review, we discuss the main issues related to the evaluation of micro- and nanoplastics toxicity using conventional in vitro assays. A literature survey has allowed to propose some solutions to circumvent these issues including the use of mathematical models to accurately determine the dose of particles delivered to cells, advanced 3D models (organoids), inverted cell culture models, cell cultures at the air-liquid interface or under dynamic conditions. Finally, we propose some perspectives and recommendations for further research on the in vitro evaluation of micro- and nanoplastics toxicity, underlining the importance of using standardized protocols for comparison purposes and samples and experimental conditions more representative of real-life exposure.

Protective effects of inhaled antioxidants against air pollution-induced pathological responses

As the public health burden of air pollution continues to increase, new strategies to mitigate harmful health effects are needed. Dietary antioxidants have previously been explored to protect against air pollution-induced lung injury producing inconclusive results. Inhaled (pulmonary or nasal) administration of antioxidants presents a more promising approach as it could directly increase antioxidant levels in the airway surface liquid (ASL), providing protection against oxidative damage from air pollution. Several antioxidants have been shown to exhibit antioxidant, anti-inflammatory, and anti-microbial properties in in vitro and in vivo models of air pollution exposure; however, little work has been done to translate these basic research findings into practice. This narrative review summarizes these findings and data from human studies using inhaled antioxidants in response to air pollution, which have produced positive results, indicating further investigation is warranted. In addition to human studies, cell and murine studies should be conducted using more relevant models of exposure such as air-liquid interface (ALI) cultures of primary cells and non-aqueous apical delivery of antioxidants and pollutants. Inhalation of antioxidants shows promise as a protective intervention to prevent air pollution-induced lung injury and exacerbation of existing lung disease.

Development of a novel air-liquid interface airway tissue equivalent model for in vitro respiratory modeling studies

The human airways are complex structures with important interactions between cells, extracellular matrix (ECM) proteins and the biomechanical microenvironment. A robust, well-differentiated in vitro culture system that accurately models these interactions would provide a useful tool for studying normal and pathological airway biology. Here, we report the development and characterization of a physiologically relevant air-liquid interface (ALI) 3D airway 'organ tissue equivalent' (OTE) model with three novel features: native pulmonary fibroblasts, solubilized lung ECM, and hydrogel substrate with tunable stiffness and porosity. We demonstrate the versatility of the OTE model by evaluating the impact of these features on human bronchial epithelial (HBE) cell phenotype. Variations of this model were analyzed during 28 days of ALI culture by evaluating epithelial confluence, trans-epithelial electrical resistance, and epithelial phenotype via multispectral immuno-histochemistry and next-generation sequencing. Cultures that included both solubilized lung ECM and native pulmonary fibroblasts within the hydrogel substrate formed well-differentiated ALI cultures that maintained a barrier function and expressed mature epithelial markers relating to goblet, club, and ciliated cells. Modulation of hydrogel stiffness did not negatively impact HBE differentiation and could be a valuable variable to alter epithelial phenotype. This study highlights the feasibility and versatility of a 3D airway OTE model to model the multiple components of the human airway 3D microenvironment.

Conditional Cell Reprogramming and Air-Liquid Interface Modeling Life Cycle of Oncogenic Viruses (HPV and EBV) in Epithelial Cells and Virus-Associated Human Carcinomas

Several oncogenic viruses are associated with approximately 20% of human cancers. Experimental models are crucial for studying the pathogenicity and biological aspects of oncogenic viruses and their potential mechanisms in tumorigenesis. Current cell models have considerable limitations such as: their low yield, genetic and epigenetic modification, and reduction in tumor heterogeneity during long propagation. Cancer cell lines are limited and not appropriate for studying the viral life cycle, for example, natural viral life cycles of HPV and EBV, and their persistence and latency in epithelial cells are poorly understood, since these processes are highly related to epithelial differentiation. Therefore, there is an urgent need of reliable human physiological cell models to study viral life cycle and cancer initiation. Conditional cell reprogramming (CCR) is a rapid and robust cell culture system, where the cells can be established from minimally invasive or noninvasive specimens and their lineage functions preserved during the long-term culture. These CR cells retain their ability to differentiate at air-liquid interface (ALI). Here, we recapitulated the applications of CR and ALI approaches in modeling host-virus interactions and viral-mediated tumorigenesis.

Bovine Airway Models: Approaches for Investigating Bovine Respiratory Disease

Bovine respiratory disease (BRD) is a multifactorial condition where different genera of bacteria, such as Mannheimia haemolytica, Histophilus somni, Pasteurella multocida, and Mycoplasma bovis, and viruses, like bovine respiratory syncytial virus, bovine viral diarrhea virus, and bovine herpes virus-1, infect the lower respiratory tract of cattle. These pathogens can co-infect cells in the respiratory system, thereby making specific treatment very difficult. Currently, the most common models for studying BRD include a submerged tissue culture (STC), where monolayers of epithelial cells are typically covered either in cellular or spent biofilm culture medium. Another model is an air-liquid interface (ALI), where epithelial cells are exposed on their apical side and allowed to differentiate. However, limited work has been reported on the study of three-dimensional (3D) bovine models that incorporate multiple cell types to represent the architecture of the respiratory tract. The roles of different defense mechanisms in an infected bovine respiratory system, such as mucin production, tight junction barriers, and the production of antimicrobial peptides in in vitro cultures require further investigation in order to provide a comprehensive understanding of the disease pathogenesis. In this report, we describe the different aspects of BRD, including the most implicated pathogens and the respiratory tract, which are important to incorporate in disease models assembled in vitro. Although current advancements of bovine respiratory cultures have led to knowledge of the disease, 3D multicellular organoids that better recapitulate the in vivo environment exhibit potential for future investigations.

Human disease models in drug development

Biomedical research is undergoing a paradigm shift towards approaches centred on human disease models owing to the notoriously high failure rates of the current drug development process. Major drivers for this transition are the limitations of animal models, which, despite remaining the gold standard in basic and preclinical research, suffer from interspecies differences and poor prediction of human physiological and pathological conditions. To bridge this translational gap, bioengineered human disease models with high clinical mimicry are being developed. In this Review, we discuss preclinical and clinical studies that benefited from these models, focusing on organoids, bioengineered tissue models and organs-on-chips. Furthermore, we provide a high-level design framework to facilitate clinical translation and accelerate drug development using bioengineered human disease models.

RSV-induced expanded ciliated cells contribute to bronchial wall thickening

Viral infection, particularly respiratory syncytial virus (RSV), causes inflammation in the bronchiolar airways (bronchial wall thickening, also known as bronchiolitis). This bronchial wall thickening is a common pathophysiological feature in RSV infection, but it causes more fatalities in infants than in children and adults. However, the molecular mechanism of RSV-induced bronchial wall thickening remains unknown, particularly in healthy adults. Using highly differentiated pseudostratified airway epithelium generated from primary human bronchial epithelial cells, we revealed RSV-infects primarily ciliated cells. The infected ciliated cells expanded substantially without compromising epithelial membrane integrity and ciliary functions and contributed to the increased height of the airway epithelium. Furthermore, we identified multiple factors, e.g., cytoskeletal (ARP2/3-complex-driven actin polymerization), immunological (IP10/CXCL10), and viral (NS2), contributing to RSV-induced uneven epithelium height increase in vitro. Thus, RSV-infected expanded cells contribute to a noncanonical inflammatory phenotype, which contributes to bronchial wall thickening in the airway, and is termed cytoskeletal inflammation.

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.

High-Throughput Bioprinting of the Nasal Epithelium using Patient-derived Nasal Epithelial Cells

Human nasal epithelial cells (hNECs) are an essential cell source for the reconstruction of the respiratory pseudostratified columnar epithelium composed of multiple cell types in the context of infection studies and disease modeling. Hitherto, manual seeding has been the dominant method for creating nasal epithelial tissue models. However, the manual approach is slow, low-throughput and has limitations in terms of achieving the intricate 3D structure of the natural nasal epithelium in a uniform manner. 3D Bioprinting has been utilized to reconstruct various epithelial tissue models, such as cutaneous, intestinal, alveolar, and bronchial epithelium, but there has been no attempt to use of 3D bioprinting technologies for reconstruction of the nasal epithelium. In this study, for the first time, we demonstrate the reconstruction of the nasal epithelium with the use of primary hNECs deposited on Transwell inserts via droplet-based bioprinting (DBB), which enabled high-throughput fabrication of the nasal epithelium in Transwell inserts of 24-well plates. DBB of nasal progenitor cells ranging from one-tenth to one-half of the cell seeding density employed during the conventional cell seeding approach enabled a high degree of differentiation with the presence of cilia and tight-junctions over a 4-week air-liquid interface culture. Single cell RNA sequencing of these cultures identified five major epithelial cells populations, including basal, suprabasal, goblet, club, and ciliated cells. These cultures recapitulated the pseudostratified columnar epithelial architecture present in the native nasal epithelium and were permissive to respiratory virus infection. These results denote the potential of 3D bioprinting for high-throughput fabrication of nasal epithelial tissue models not only for infection studies but also for other purposes such as disease modeling, immunological studies, and drug screening.

The dependence of particle size on cell toxicity for modern mining dust

Progressive massive pulmonary fibrosis among coal miners has unexpectedly increased. It would likely due to the greater generation of smaller rock and coal particles produced by powerful equipment used in modern mines. There is limited understanding of the relationship between micro- or nanoparticles with pulmonary toxicity. This study aims to determine whether the size and chemical characteristics of typical coal-mining dust contribute to cellular toxicity. Size range, surface features, morphology, and elemental composition of coal and rock dust from modern mines were characterized. Human macrophages and bronchial tracheal epithelial cells were exposed to mining dust of three sub- micrometer and micrometer size ranges at varying concentrations, then assessed for cell viability and inflammatory cytokine expression. Coal had smaller hydrodynamic size (180–3000 nm) compared to rock (495–2160 nm) in their separated size fractions, more hydrophobicity, less surface charge, and consisted of more known toxic trace elements (Si, Pt, Fe, Al, Co). Larger particle size had a negative association with in-vitro toxicity in macrophages (p < 0.05). Fine particle fraction, approximately 200 nm for coal and 500 nm for rock particles, explicitly induced stronger inflammatory reactions than their coarser counterparts. Future work will study additional toxicity endpoints to further elucidate the molecular mechanism causing pulmonary toxicity and determine a dose–response curve.

Evaluation of the cytotoxic and genotoxic potential of printer toner particles in a 3D air-liquid interface, primary cell-based nasal tissue model

Printer toner particles (TPs) are a common, potentially hazardous substance, with an unclear toxicological impact on the respiratory mucosa. Most of the airways surface is covered by a ciliated respiratory mucosa, therefore appropriate tissue models of the respiratory epithelium with a high in vivo correlation are necessary for in vitro evaluation of airborne pollutants toxicology and the impact on the functional integrity. The aim of this study is the evaluation of TPs toxicology in a human primary cell-based air-liquid-interface (ALI) model of respiratory mucosa. The TPs were analyzed and characterized by scanning electron microscopy, pyrolysis and X-ray fluorescence spectrometry. ALI models of 10 patients were created using the epithelial cells and fibroblasts derived from nasal mucosa samples. TPs were applied to the ALI models via a modified Vitrocell® cloud and submerged in the dosing 0.89 - 892.96 µg/ cm². Particle exposure and intracellular distribution were evaluated by electron microscopy. The MTT assay and the comet assay were used to investigate cytotoxicity and genotoxicity, respectively. The used TPs showed an average particle size of 3 - 8 µm. Mainly carbon, hydrogen, silicon, nitrogen, tin, benzene and benzene derivates were detected as chemical ingredients. By histomorphology and electron microscopy we observed the development of a highly functional, pseudostratified epithelium with a continuous layer of cilia. Using electron microscopy, TPs could be detected on the cilia surface and also intracellularly. Cytotoxicity was detected from 9 µg/ cm² and higher, but no genotoxicity after ALI and submerged exposure. The ALI with primary nasal cells represents a highly functional model of the respiratory epithelium in terms of histomorphology and mucociliary differentiation. The toxicological results indicate a weak TP-concentration-dependent cytotoxicity. AVAILABILITY OF DATA AND MATERIALS: The datasets used and analysed during the current study are available from the corresponding author on reasonable request.

In vitro human cell-based models to study airway remodeling in asthma

Airway remodeling, as a predominant characteristic of asthma, refers to the structural changes that occurred both in the large and small airways. These pathological changes not only contribute to airway hyperresponsiveness and airway obstruction, but also predict poor outcomes of patients. In vitro models are the alternatives to animal models that facilitate airway remodeling research. Current approaches to mimic airway remodeling in vitro include mono cultures of cell lines and primary cells that are derived from the respiratory tract, and co-culture systems that consist of different cell subpopulations. Moreover, recent advances in microfluid chips and organoids show promise in simulating the complex architecture and functionality of native organs. According, they enable highly physiological-relevant investigations of human diseases in vitro. Here we aim to detail the current human cell-based models regarding their key pros and cons, and to discuss how they may be used to facilitate our understanding of airway remodeling in asthma.