In vitro exposure of isolated cells to native gaseous compounds--development and validation of an optimized system for human lung cells

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 Cultivation Modality and Barrier Maturity Modulate the Toxicity of Industrial Zinc Oxide and Titanium Dioxide Nanoparticles on Nasal, Buccal, Bronchial, and Alveolar Mucosa Cell-Derived Barrier Models

As common industrial by-products, airborne engineered nanomaterials are considered important environmental toxins to monitor due to their potential health risks to humans and animals. The main uptake routes of airborne nanoparticles are nasal and/or oral inhalation, which are known to enable the transfer of nanomaterials into the bloodstream resulting in the rapid distribution throughout the human body. Consequently, mucosal barriers present in the nose, buccal, and lung have been identified and intensively studied as the key tissue barrier to nanoparticle translocation. Despite decades of research, surprisingly little is known about the differences among various mucosa tissue types to tolerate nanoparticle exposures. One limitation in comparing nanotoxicological data sets can be linked to a lack of harmonization and standardization of cell-based assays, where (a) different cultivation conditions such as an air-liquid interface or submerged cultures, (b) varying barrier maturity, and (c) diverse media substitutes have been used. The current comparative nanotoxicological study, therefore, aims at analyzing the toxic effects of nanomaterials on four human mucosa barrier models including nasal (RPMI2650), buccal (TR146), alveolar (A549), and bronchial (Calu-3) mucosal cell lines to better understand the modulating effects of tissue maturity, cultivation conditions, and tissue type using standard transwell cultivations at liquid-liquid and air-liquid interfaces. Overall, cell size, confluency, tight junction localization, and cell viability as well as barrier formation using 50% and 100% confluency was monitored using trans-epithelial-electrical resistance (TEER) measurements and resazurin-based Presto Blue assays of immature (e.g., 5 days) and mature (e.g., 22 days) cultures in the presence and absence of corticosteroids such as hydrocortisone. Results of our study show that cellular viability in response to increasing nanoparticle exposure scenarios is highly compound and cell-type specific (TR146 6 ± 0.7% at 2 mM ZnO (ZnO) vs. ~90% at 2 mM TiO2 (TiO2) for 24 h; Calu3 93.9 ± 4.21% at 2 mM ZnO vs. ~100% at 2 mM TiO2). Nanoparticle-induced cytotoxic effects under air-liquid cultivation conditions declined in RPMI2650, A549, TR146, and Calu-3 cells (~0.7 to ~0.2-fold), with increasing 50 to 100% barrier maturity under the influence of ZnO (2 mM). Cell viability in early and late mucosa barriers where hardly influenced by TiO2 as well as most cell types did not fall below 77% viability when added to Individual ALI cultures. Fully maturated bronchial mucosal cell barrier models cultivated under ALI conditions showed less tolerance to acute ZnO nanoparticle exposures (~50% remaining viability at 2 mM ZnO for 24 h) than the similarly treated but more robust nasal (~74%), buccal (~73%), and alveolar (~82%) cell-based models.

Establishing an air-liquid interface exposure system for exposure of lung cells to gases

OBJECTIVE

Growing interest in non-animal-based models has led to the development of devices to expose cells to airborne substances. Cells/tissues grown at the air-liquid interface (ALI) are more representative of lung cells/tissues in vivo compared to submerged cell cultures. Additionally, airborne exposures should allow for closer modeling of human lung toxicity. However, such exposures present technical challenges, including maintaining optimal cell health, and establishing consistent exposure monitoring and control. We aimed to establish a reliable system and procedures for cell exposures to gases at the ALI.

METHODS

We tested and adapted a horizontal-flow ALI-exposure system to verify and optimize temperature, humidity/condensation, and control of atmosphere delivery. We measured temperature and relative humidity (RH) throughout the system, including at the outlet (surrogate measures) and at the well, and evaluated viability of lung epithelial A549 cells under control conditions. Exposure stability, dosimetry, and toxicity were tested using ozone.

RESULTS

Temperatures measured directly above wells vs. outflow differed; using above-well temperature enabled determination of near-well RH. Under optimized conditions, the viability of A549 cells exposed to clean air (2 h) in the ALI system was unchanged from incubator-grown cells. In-well ozone levels, determined through reaction with potassium indigotrisulfonate, confirmed dosing. Cells exposed to 200 ppb ozone at the ALI presented reduced viability, while submerged cells did not.

CONCLUSION

Our results emphasize the importance of monitoring near-well conditions rather than relying on surrogate measures. Rigorous assessment of ALI exposure conditions led to procedures for reproducible exposure of cells to gases.

TUBE Project: Transport-Derived Ultrafines and the Brain Effects

The adverse effects of air pollutants on the respiratory and cardiovascular systems are unquestionable. However, in recent years, indications of effects beyond these organ systems have become more evident. Traffic-related air pollution has been linked with neurological diseases, exacerbated cognitive dysfunction, and Alzheimer's disease. However, the exact air pollutant compositions and exposure scenarios leading to these adverse health effects are not known. Although several components of air pollution may be at play, recent experimental studies point to a key role of ultrafine particles (UFPs). While the importance of UFPs has been recognized, almost nothing is known about the smallest fraction of UFPs, and only >23 nm emissions are regulated in the EU. Moreover, the role of the semivolatile fraction of the emissions has been neglected. The Transport-Derived Ultrafines and the Brain Effects (TUBE) project will increase knowledge on harmful ultrafine air pollutants, as well as semivolatile compounds related to adverse health effects. By including all the major current combustion and emission control technologies, the TUBE project aims to provide new information on the adverse health effects of current traffic, as well as information for decision makers to develop more effective emission legislation. Most importantly, the TUBE project will include adverse health effects beyond the respiratory system; TUBE will assess how air pollution affects the brain and how air pollution particles might be removed from the brain. The purpose of this report is to describe the TUBE project, its background, and its goals.

Pulmonary in vitro instruments for the replacement of animal experiments

Advanced in vitro systems often combine a mechanical-physical instrument with a biological component e.g. cell culture models. For testing of aerosols, it is of advantage to consider aerosol behavior, particle deposition and lung region specific cell lines. Although there are many good reviews on the selection of cell cultures, articles on instruments are rare. This article focuses on the development of in vitro instruments targeting the exposure of aerosols on cell cultures. In this context, guidelines for toxicity investigation are taken into account as the aim of new methods must be the prediction of human relevant data and the replacement of existing animal experiments. We provide an overview on development history of research-based instruments from a pharmaceutical point of view. The standardized commercial devices resulting from the research-based instruments are presented and the future perspectives on pulmonary in vitro devices are discussed.

Development and validation of an open-source, disposable, 3D-printed in vitro environmental exposure system for Transwell culture inserts

Accessible in vitro models recapitulating the human airway that are amenable to study whole cannabis smoke exposure are needed for immunological and toxicological studies that inform public health policy and recreational cannabis use. In the present study, we developed and validated a novel three-dimensional (3D)-printed in vitro exposure system (IVES) that can be directly applied to study the effect of cannabis smoke exposure on primary human bronchial epithelial cells.

Using commercially available design software and a 3D printer, we designed a four-chamber Transwell insert holder for exposures to whole smoke. COMSOL Multiphysics software was used to model gas distribution, concentration gradients, velocity profile and shear stress within IVES. Following simulations, primary human bronchial epithelial cells cultured at the air–liquid interface on Transwell inserts were exposed to whole cannabis smoke using a modified version of the Foltin puff procedure. Following 24 h, outcome measurements included cell morphology, epithelial barrier function, lactate dehydrogenase (LDH) levels, cytokine expression and gene expression.

Whole smoke delivered through IVES possesses velocity profiles consistent with uniform gas distribution across the four chambers and complete mixing. Airflow velocity ranged between 1.0 and 1.5 µm·s⁻¹ and generated low shear stresses (<<1 Pa). Human airway epithelial cells exposed to cannabis smoke using IVES showed changes in cell morphology and disruption of barrier function without significant cytotoxicity. Cannabis smoke elevated interleukin-1 family cytokines and elevated CYP1A1 and CYP1B1 expression relative to control, validating IVES smoke exposure impacts in human airway epithelial cells at a molecular level.

The growing legalisation of cannabis on a global scale must be paired with research related to potential health impacts of lung exposures. IVES represents an accessible, open-source, exposure system that can be used to model varying types of cannabis smoke exposures with human airway epithelial cells grown under air–liquid interface culture conditions.

Development of an open-source, disposable, 3D-printed in vitro environmental exposure system for Transwell culture inserts that can be used for environmental exposures important for lung health, and validation with cannabis smoke exposurehttps://bit.ly/2JjgDrm

Invited review: human air-liquid-interface organotypic airway tissue models derived from primary tracheobronchial epithelial cells-overview and perspectives

The lung is an organ that is directly exposed to the external environment. Given the large surface area and extensive ventilation of the lung, it is prone to exposure to airborne substances, such as pathogens, allergens, chemicals, and particulate matter. Highly elaborate and effective mechanisms have evolved to protect and maintain homeostasis in the lung. Despite these sophisticated defense mechanisms, the respiratory system remains highly susceptible to environmental challenges. Because of the impact of respiratory exposure on human health and disease, there has been considerable interest in developing reliable and predictive in vitro model systems for respiratory toxicology and basic research. Human air-liquid-interface (ALI) organotypic airway tissue models derived from primary tracheobronchial epithelial cells have in vivo–like structure and functions when they are fully differentiated. The presence of the air-facing surface allows conducting in vitro exposures that mimic human respiratory exposures. Exposures can be conducted using particulates, aerosols, gases, vapors generated from volatile and semi-volatile substances, and respiratory pathogens. Toxicity data have been generated using nanomaterials, cigarette smoke, e-cigarette vapors, environmental airborne chemicals, drugs given by inhalation, and respiratory viruses and bacteria. Although toxicity evaluations using human airway ALI models require further standardization and validation, this approach shows promise in supplementing or replacing in vivo animal models for conducting research on respiratory toxicants and pathogens.

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.

Regulating temperature and relative humidity in air-liquid interface in vitro systems eliminates cytotoxicity resulting from control air exposures

VITROCELL^® systems permit cell exposures at the air-liquid interface (ALI); however, there are inconsistent methodologies in the literature for their operation. Some studies find that exposure to air (vehicle control) induced cytotoxicity relative to incubator controls; others do not mention if any cytotoxicity was encountered. We sought to test whether temperature and relative humidity (temp/RH) influence cytotoxicity with an unmodified (conditions A & B) and modified (condition C) VITROCELL^® 6 CF with temp/RH controls to permit conditioning of the sampled air-flow. We exposed BEAS-2B cells for 1 h to air and measured viability (WST-1 cell proliferation assay) and lactate dehydrogenase (LDH) release 6 h post-exposure. Relative to controls, cells exposed to air at (A) 22 °C and 18% RH had a 47.9% ± 3.2% (p < 0.0001) reduction in cell viability and 10.7% ± 2.0% (p < 0.0001) increase in LDH release (B) 22 °C and 55% RH had a 40.3% ± 5.8% (p < 0.0001) reduction in cell viability and 2.6% ± 2.0% (p = 0.2056) increase in LDH release, or (C) 37 °C and >75% RH showed no changes in cell viability and no increase in LDH release. Furthermore, cells exposed to air at 37 °C and >75% RH 24 h post-exposure showed no changes in viability or LDH release relative to incubator controls. Thus, reductions in cell viability were induced under conditions used typically in the literature (conditions A & B). However, our modifications (condition C) overcome this shortcoming by preventing cell desiccation; regulating temp/RH is essential for conducting adequate ALI exposures.

In vitro toxicity testing of cigarette smoke based on the air-liquid interface exposure: A review

Cigarette smoke is a complex aerosol comprising particulate phase and gaseous vapour phase. The air-liquid interface exposure provides a possible technical means to implement whole smoke exposure for the assessment of tobacco products. In this review, the research progress in the in vitro toxicity testing of cigarette smoke based on the air-liquid interface exposure is summarized. The contents presented involve mainly cytotoxicity, genotoxicity, oxidative stress, inflammation, systems toxicology, 3D culture and cigarette smoke dosimetry related to cigarette smoke, as well as the assessment of electronic cigarette aerosol. Prospect of the application of the air-liquid interface exposure method in assessing the biological effects of tobacco smoke is discussed.

In vitro cytotoxicity testing of airborne formaldehyde collected in serum-free culture media

The purpose of this study was to identify a suitable sampling model for on-site toxicity assessment of soluble air contaminants such as formaldehyde, a well known industrial and indoor air contaminant. The in vitro cytotoxicity of formaldehyde, the selected model for soluble air contaminants, was studied using the MTS (tetrazolium salt) assay in two carcinoma cell lines, A549 epithelial lung and HepG2 hepatocarcinoma, and in skin fibroblasts. The cytotoxic effects of airborne formaldehyde were evaluated using test atmospheres in concentrations below 10 ppm (12.3 mg/m3), generated by a dynamic diffusion method and bubbled (0.3 L/min) through serum-free culture media for one or four hours. Human cells were treated with formaldehyde air samples, and cell viability was determined after four hours incubation. In parallel, the concentration of airborne formaldehyde was monitored, using the 3500 NIOSH method. Cell viability of the HepG2 cells exposed to formaldehyde air samples (8.75 ppm-4 h) was reduced to less than 50% (31.69/1.24%). The HepG2 cell lines were found to be more sensitive (IC50=103.799/23.55 mg/L) to formaldehyde than both A549 cell lines (IC50=198.369/9.54 mg/L) and skin fibroblasts (IC50=196.689/36.73 mg/L) (PB/0.01). An average of 96.8% was determined for collection efficiency of formaldehyde in serum-free culture media. The results of this study suggest that absorption of soluble air contaminants, such as formaldehyde, in serum-free culture media can be used as a suitable sampling model for on-site toxicity assessments.

BTEX in vitro exposure tool using human lung cells: trips and gains

Cytotoxicity of benzene, toluene, ethylbenzene and xylenes (BTEX) to human lung cells was explored using three different exposure methods: Method 1 - in normal 96-well plates using DMSO as a carrier vehicle, we exposed (a) human lung carcinoma A549 cells, (b) A549 cells over-expressed with cytochrome P450 2E1 cells, and (c) normal lung fibroblast LL-24 cells to benzene, toluene, ethylbenzene and xylene individually and in a mixture which models car exhaust gases for between 1-88 h. We found that the order of the BTEX potency is benzene<toluene<ethylbenzene=m-xylene with acute BTEX toxicity to A549≈LL-24>CYP2E1 over-expressed A549 cells. A significant difference was found between inter-assay responses for all 24h exposures (P<0.005) suggesting a poor assay repeatability. No sign of potency increase was found from 6 to 72 h exposures. Method 2 - Using sealed vials to expose A549 cells to benzene, toluene and ethylbenzene, we observed a twenty-fold increase in their cytotoxicity, but also with no time-course effect. Method 3 - Using air exposed hanging-drop cell culture, we were able to see both an increase of demonstration of toxicity and a time-course effect from 1 to 12h exposure. We conclude that exposing cells in sealed and unsealed media using DMSO as a carrier vehicle was not suitable for BTEX exposure studies. Hanging-drop air exposure has more potential. It should be noted that if there are any changes in their exposure matrixes, its exposure mass distribution in cells could differ.

Toxicological perspectives of inhaled therapeutics and nanoparticles

INTRODUCTION

The human respiratory system is an important route for the entry of inhaled therapeutics into the body to treat diseases. Inhaled materials may consist of gases, vapours, aerosols and particulates. In all cases, assessing the toxicological effect of inhaled therapeutics has many challenges.

AREAS COVERED

This article provides an overview of in vivo and in vitro models for testing the toxicity of inhaled therapeutics and nanoparticles implemented in drug delivery. Traditionally, inhalation toxicity has been performed on test animals to identify the median lethal concentration of airborne materials. Later maximum tolerable concentration denoted by LC0 has been introduced as a more ethically acceptable end point. More recently, in vitro methods have been developed, allowing the direct exposure of airborne material to cultured human target cells on permeable porous membranes at the air-liquid interface.

EXPERT OPINION

Modifications of current inhalation therapies, new pulmonary medications for respiratory diseases and implementation of the respiratory tract for systemic drug delivery are providing new challenges when conducting well-designed inhalation toxicology studies. In particular, the area of nanoparticles and nanocarriers is of critical toxicological concern. There is a need to develop toxicological test models, which characterise the toxic response and cellular interaction between inhaled particles and the respiratory system.

A review of in vitro cigarette smoke exposure systems

In vitro test methods may be vital in understanding tobacco smoke, the main toxicants responsible for adverse health effects, and elucidating disease mechanisms. There is a variety of 'whole smoke' exposure systems available for the generation, dilution and delivery of tobacco smoke in vitro; these systems can be procured commercially from well-known suppliers or can be bespoke set-ups. These exposure technologies aim to ensure that there are limited changes in the tobacco smoke aerosol from generation to exposure. As the smoke aerosol is freshly generated, interactions in the smoke fractions are captured in any subsequent in vitro analysis. Of the commercially available systems, some have been characterised more than others in terms of published scientific literature and developed biological endpoints. Others are relatively new to the scientific field and are still establishing their presence. In addition, bespoke systems are widely used and offer a more flexible approach to the challenges of tobacco smoke exposure. In this review, the authors present a summary of the major tobacco smoke exposure systems available and critically review their function, set-up and application for in vitro exposure scenarios. All whole smoke exposure systems have benefits and limitations, often making it difficult to make comparisons between set-ups and the data obtained from such diverse systems. This is where exposure and dose measurements can add value and may be able to provide a platform on which comparisons can be made. The measurement of smoke dose, as an emerging field of research, is therefore also discussed and how it may provide valuable and additional data to support existing whole smoke exposure set-ups and aid validation efforts.

Hanging drop: an in vitro air toxic exposure model using human lung cells in 2D and 3D structures

Using benzene as a candidate air toxicant and A549 cells as an in vitro cell model, we have developed and validated a hanging drop (HD) air exposure system that mimics an air liquid interface exposure to the lung for periods of 1h to over 20 days. Dose response curves were highly reproducible for 2D cultures but more variable for 3D cultures. By comparing the HD exposure method with other classically used air exposure systems, we found that the HD exposure method is more sensitive, more reliable and cheaper to run than medium diffusion methods and the CULTEX(®) system. The concentration causing 50% of reduction of cell viability (EC50) for benzene, toluene, p-xylene, m-xylene and o-xylene to A549 cells for 1h exposure in the HD system were similar to previous in vitro static air exposure. Not only cell viability could be assessed but also sub lethal biological endpoints such as DNA damage and interleukin expressions. An advantage of the HD exposure system is that bioavailability and cell concentrations can be derived from published physicochemical properties using a four compartment mass balance model. The modelled cellular effect concentrations EC50cell for 1h exposure were very similar for benzene, toluene and three xylenes and ranged from 5 to 15 mmol/kgdry weight, which corresponds to the intracellular concentration of narcotic chemicals in many aquatic species, confirming the high sensitivity of this exposure method.

Toxicological analysis of limonene reaction products using an in vitro exposure system

Epidemiological investigations suggest a link between exposure to indoor air chemicals and adverse health effects. Consumer products contain reactive chemicals which can form secondary pollutants which may contribute to these effects. The reaction of limonene and ozone is a well characterized example of this type of indoor air chemistry. The studies described here characterize an in vitro model using an epithelial cell line (A549) or differentiated epithelial tissue (MucilAir™). The model is used to investigate adverse effects following exposure to combinations of limonene and ozone. In A549 cells, exposure to both the parent compounds and reaction products resulted in alterations in inflammatory cytokine production. A one hour exposure to limonene+ozone resulted in decreased proliferation when compared to cells exposed to limonene alone. Repeated dose exposures of limonene or limonene+ozone were conducted on MucilAir™ tissue. No change in proliferation was observed but increases in cytokine production were observed for both the parent compounds and reaction products. Factors such as exposure duration, chemical concentration, and sampling time point were identified to influence result outcome. These findings suggest that exposure to reaction products may produce more severe effects compared to the parent compound.

The CULTEX RFS: a comprehensive technical approach for the in vitro exposure of airway epithelial cells to the particulate matter at the air-liquid interface

The EU Regulation on Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) demands the implementation of alternative methods for analyzing the hazardous effects of chemicals including particulate formulations. In the field of inhalation toxicology, a variety of in vitro models have been developed for such studies. To simulate the in vivo situation, an adequate exposure device is necessary for the direct exposure of cultivated lung cells at the air-liquid interface (ALI). The CULTEX RFS fulfills these requirements and has been optimized for the exposure of cells to atomized suspensions, gases, and volatile compounds as well as micro- and nanosized particles. This study provides information on the construction and functional aspects of the exposure device. By using the Computational Fluid Dynamics (CFD) analysis, the technical design was optimized to realize a stable, reproducible, and homogeneous deposition of particles. The efficiency of the exposure procedure is demonstrated by exposing A549 cells dose dependently to lactose monohydrate, copper(II) sulfate, copper(II) oxide, and micro- and nanoparticles. All copper compounds induced cytotoxic effects, most pronounced for soluble copper(II) sulfate. Micro- and nanosized copper(II) oxide also showed a dose-dependent decrease in the cell viability, whereby the nanosized particles decreased the metabolic activity of the cells more severely.

Detection of the cytotoxicity of water-insoluble fraction of cigarette smoke by direct exposure to cultured cells at an air-liquid interface

For the biological evaluation of cigarette smoke in vitro, the particulate phase (PP) and the gas vapor phase (GVP) of mainstream smoke have usually been collected individually and exposed to biological material such as cultured cells. Using this traditional method, the GVP is collected by bubbling in an aqueous solution such as phosphate-buffered saline (PBS). In such a way the water-insoluble GVP fraction is excluded from the GVP, meaning that the toxic potential of the water-insoluble GVP fraction has hardly been investigated so far. In our experiments we used a direct exposure method to expose cells at the air-liquid interface (ALI) to the water-insoluble GVP fraction for demonstrating its toxicological/biological activity. In order to isolate the water-insoluble GVP fraction from mainstream smoke, the GVP was passed through 6 impingers connected in series with PBS. After direct exposure of Chinese hamster ovary cells (CHO-K1) with the water-insoluble GVP fraction in the CULTEX(®) system its cytotoxicity was assayed by using the neutral red uptake assay. The water-insoluble GVP fraction was proven to be less cytotoxic than the water-soluble GVP fraction, but showed a significant effect in a dose-dependent manner. The results of this study showed that the direct exposure of cultivated cells at the air-liquid interface offers the possibility to analyze the biological and toxicological activities of all fractions of cigarette smoke including the water-insoluble GVP fraction.

Investigations on cytotoxic and genotoxic effects of laser printer emissions in human epithelial A549 lung cells using an air/liquid exposure system

Exposure to emissions from laser printers during the printing process is commonplace worldwide, both in the home and workplace environment. In the present study, cytotoxic and genotoxic effects of the emission from five low to medium-throughput laser printers were investigated with respect to the release of ozone (O(3) ), volatile organic compounds (VOC), particulate matter (PM), and submicrometer particles (SMP) during standby and operation. Experiments were conducted in a 1 m(3) emission chamber connected to a Vitrocell® exposure system. Cytotoxicity was determined by the WST-1 assay and genotoxicity by the micronucleus test in human A549 lung cells. The five laser printers emitted varying but generally small amounts of O(3) , VOC, and PM. VOC emissions included 13 compounds with total VOC concentrations ranging from 95 to 280 μg/m(3) (e.g., 2-butanone, hexanal, m,p-xylene, and o-xylene). Mean PM concentrations were below 2.4 μg/m(3). SMP number concentration levels during standby ranged from 9 to 26 particles/cm(3). However, three of the printers generated a 90 to 16 × 10(3) -fold increase of SMP during the printing process (maximum 294,460 particles/cm(3)). Whereas none of the printer emissions were found to cause cytotoxicity, emissions from two printers induced formation of micronuclei (P < 0.001), thus providing evidence for genotoxicity. As yet, differences in biological activity cannot be explained on the basis of the specific emission characteristics of the different printers. Because laser printing technology is widely used, studies with additional cytogenetic endpoints are necessary to confirm the DNA-damaging potency and to identify emission components responsible for genotoxicity.

New exposure system to evaluate the toxicity of (scooter) exhaust emissions in lung cells in vitro

A constantly growing number of scooters produce an increasing amount of potentially harmful emissions. Due to their engine technology, two-stroke scooters emit huge amounts of adverse substances, which can induce adverse pulmonary and cardiovascular health effects. The aim of this study was to develop a system to expose a characterized triple cell coculture model of the human epithelial airway barrier, to freshly produced and characterized total scooter exhaust emissions. In exposure chambers, cell cultures were exposed for 1 and 2 h to 1:100 diluted exhaust emissions and in the reference chamber to filtered ambient air, both controlled at 5% CO(2), 85% relative humidity, and 37 degrees C. The postexposure time was 0-24 h. Cytotoxicity, used to validate the exposure system, was significantly increased in exposed cell cultures after 8 h postexposure time. (Pro-) inflammatory chemo- and cytokine concentrations in the medium of exposed cells were significantly higher at the 12 h postexposure time point. It was shown that the described exposure system (with 2 h exposure duration, 8 and 24 h postexposure time, dilution of 1:100, flow of 2 L/min as optimal exposure conditions) can be used to evaluate the toxic potential of total exhaust emissions.

A dose-controlled system for air-liquid interface cell exposure and application to zinc oxide nanoparticles

BACKGROUND

Engineered nanoparticles are becoming increasingly ubiquitous and their toxicological effects on human health, as well as on the ecosystem, have become a concern. Since initial contact with nanoparticles occurs at the epithelium in the lungs (or skin, or eyes), in vitro cell studies with nanoparticles require dose-controlled systems for delivery of nanoparticles to epithelial cells cultured at the air-liquid interface.

RESULTS

A novel air-liquid interface cell exposure system (ALICE) for nanoparticles in liquids is presented and validated. The ALICE generates a dense cloud of droplets with a vibrating membrane nebulizer and utilizes combined cloud settling and single particle sedimentation for fast (~10 min; entire exposure), repeatable (<12%), low-stress and efficient delivery of nanoparticles, or dissolved substances, to cells cultured at the air-liquid interface. Validation with various types of nanoparticles (Au, ZnO and carbon black nanoparticles) and solutes (such as NaCl) showed that the ALICE provided spatially uniform deposition (<1.6% variability) and had no adverse effect on the viability of a widely used alveolar human epithelial-like cell line (A549). The cell deposited dose can be controlled with a quartz crystal microbalance (QCM) over a dynamic range of at least 0.02-200 mug/cm(2). The cell-specific deposition efficiency is currently limited to 0.072 (7.2% for two commercially available 6-er transwell plates), but a deposition efficiency of up to 0.57 (57%) is possible for better cell coverage of the exposure chamber. Dose-response measurements with ZnO nanoparticles (0.3-8.5 mug/cm(2)) showed significant differences in mRNA expression of pro-inflammatory (IL-8) and oxidative stress (HO-1) markers when comparing submerged and air-liquid interface exposures. Both exposure methods showed no cellular response below 1 mug/cm(2 )ZnO, which indicates that ZnO nanoparticles are not toxic at occupationally allowed exposure levels.

CONCLUSION

The ALICE is a useful tool for dose-controlled nanoparticle (or solute) exposure of cells at the air-liquid interface. Significant differences between cellular response after ZnO nanoparticle exposure under submerged and air-liquid interface conditions suggest that pharmaceutical and toxicological studies with inhaled (nano-)particles should be performed under the more realistic air-liquid interface, rather than submerged cell conditions.

RESPONSES OF DIFFERENTIATED PRIMARY HUMAN LUNG EPITHELIAL CELLS TO EXPOSURE TO DIESEL EXHAUST AT AN AIR-LIQUID INTERFACE

In vitro responses of potential target cell types to air pollutants under physiological conditions may be useful in understanding the health effects of air pollution exposure. The study evaluated responses of human primary airway epithelial cells to diesel exhaust (DE). Cultures of cells from 3 donors, differentiated by culture on membranes with the apical surfaces exposed to the atmosphere, were exposed to filtered air or DE. Some exposure-related effects were similar among donors, whereas others were affected by the donor, consistent with human population heterogeneity. This model may be useful for mechanistic and comparative toxicology studies.

Toxicity Assessment of Industrial Chemicals and Airborne Contaminants: Transition fromIn VivotoIn VitroTest Methods: A Review

Exposure to occupational and environmental contaminants is a major contributor to human health problems. Inhalation of gases, vapors, aerosols, and mixtures of these can cause a wide range of adverse health effects, ranging from simple irritation to systemic diseases. Despite significant achievements in the risk assessment of chemicals, the toxicological database, particularly for industrial chemicals, remains limited. Considering there are approximately 80,000 chemicals in commerce, and an extremely large number of chemical mixtures, in vivo testing of this large number is unachievable from both economical and practical perspectives. While in vitro methods are capable of rapidly providing toxicity information, regulatory agencies in general are still cautious about the replacement of whole-animal methods with new in vitro techniques. Although studying the toxic effects of inhaled chemicals is a complex subject, recent studies demonstrate that in vitro methods may have significant potential for assessing the toxicity of airborne contaminants. In this review, current toxicity test methods for risk evaluation of industrial chemicals and airborne contaminants are presented. To evaluate the potential applications of in vitro methods for studying respiratory toxicity, more recent models developed for toxicity testing of airborne contaminants are discussed.

An optimized method for in vitro exposure of human derived lung cells to volatile chemicals

Volatile organic compounds (VOCs) such as benzene and toluene, and low molecular weight carbonyls like formaldehyde belong to the main air pollutants found in indoor environments. They are suspected to induce acute and chronic adverse health effects like asthma, allergic and cardiovascular diseases, and strongly affect well-being. Our aim was to further develop and optimize an in vitro method to study the exposure of epithelial tumour lung cells (A549) by using a commercial exposure chamber (CULTEX) to assess the biological effects of VOCs and carbonyl compounds at low concentration levels. Exposing the cells to toluene, benzene and formaldehyde at mixing ratios varying from 0.1 to 0.6ppmv in air resulted in reproducible direct effects with the induction of an inflammatory response and a modification of the glutathione redox status.

Comparative in vitro cytotoxicity assessment of selected gaseous compounds in human alveolar epithelial cells

Exposure to airborne contaminants is significantly associated with human health risks, ranging from bronchial reactivity to morbidity and mortality due to acute intense or long term low level repeated exposures. However, the precise mechanisms that derive such effects are not always understood. Although inhalation studies are technologically complicated, correct hazard characterisation is essential for comparable risk assessment of inhaled materials. The aim of this study was to investigate the comparative in vitro cytotoxicity of selected gaseous contaminants in human lung cells. The cytotoxicity of nitrogen dioxide (NO(2)), sulphur dioxide (SO(2)) and ammonia (NH(3)) was investigated in A549- human pulmonary type II-like epithelial cell lines cultured on porous membranes in Snapwell inserts. A dynamic direct exposure method was established by utilizing the horizontal diffusion chamber system (Harvard Apparatus Inc, USA) for delivery of test atmospheres. Test atmospheres were generated using a dynamic direct dilution method and the concentration monitored by appropriate analytical methods. A diversified battery of in vitro assays including the MTS (tetrazolium salt; Promega), NRU (neutral red uptake; Sigma) and ATP (adenosine triphosphate; Promega) assays was implemented. Airborne IC(50) (50% inhibitory concentration) values were calculated based on the most sensitive assay for each test gas including NO(2) (IC(50)=11+/-3.54 ppm; NRU)>SO(2) (IC(50)=48+/-2.83 ppm; ATP)> and NH(3) (IC(50)=199+/-1.41 ppm; MTS). However, all in vitro assays revealed similar toxicity ranking for selected gaseous contaminants. Identical toxicity ranking was achieved using both in vitro and published in vivo data. This comparison suggests that results of in vitro methods are comparable to in vivo data and may provide greater sensitivity for respiratory toxicity studies of gaseous contaminants.

An integrated in vitro approach for toxicity testing of airborne contaminants

While it is possible to establish the chemical composition of air pollutants through conventional air sampling and analytical techniques, such data do not provide direct measures of toxicity and the potential mechanisms that induce adverse effects. The aim of this study was to optimize in vitro methods for toxicity testing of airborne contaminants. An integrated approach was designed in which appropriate exposure techniques were developed. A diversified range of in vitro assays using multiple human cell systems were implemented. Direct exposure of cells to airborne contaminants was developed by culturing cells on porous membranes in conjunction with a horizontal diffusion chamber system. Concentration-response curves were generated allowing the measurement of toxicity endpoints. Regression analysis indicated a significant correlation between in vitro and published in vivo toxicity data for the majority of selected chemical contaminants. Airborne IC50 values were calculated for selected volatile organic compounds (xylene, 5350 +/- 328 ppm > toluene, 10,500 +/- 527 ppm) and gaseous contaminants (NO2, 11 +/- 3.54 ppm > SO2, 48 +/- 2.83 ppm and > NH3, 199 +/- 1.41 ppm). Results of this study indicate the significant potential of in vitro methods as an advanced technology for toxicity assessment of airborne contaminants.

Cellular mechanisms of mainstream cigarette smoke-induced lung epithelial tight junction permeability changes in vitro

Mainstream cigarette smoke increases the permeability of human airways; however, the mechanism for this increased permeability is poorly defined. Tight junctions between adjacent epithelial cells constitute the physiological barrier to fluid and macromolecules in epithelium. These structures are highly regulated by phosphorylation and their association with the cytoskeleton. The goal of these studies was to identify the signal transduction pathways that regulate smoke-induced permeability. Using a physiologically relevant air-liquid interface exposure system, electrically tight monolayers of the human bronchial epithelial cell-line Calu-3 were exposed to fresh, whole mainstream cigarette smoke. This exposure results in a regulated, dose-dependent loss of epithelial barrier function in the lung epithelial monolayers. With cigarette smoke exposure, transepithelial electrical resistance (TER) is decreased and albumin flux is increased, indicating a loss in barrier function to ions and macromolecules, respectively; however, both largely recover in 30 min. Smoke-induced losses of macromolecular barrier function are the result of multicellular junctional reorganization, resulting in increased leak volume rather than leak frequency. Inhibiting Rho kinase (ROCK) significantly reduces the smoke-induced permeability to both ions and macromolecules, while inhibiting protein tyrosine kinases (PTK) only reduces smoke-induced macromolecular permeability. Interestingly, inhibiting myosin light chain kinase (MLCK) exacerbates smoke-induced permeability, indicating that MLCK and ROCK have opposing regulatory roles. Our results demonstrate that the smoke-induced loss of epithelial barrier function in human bronchial epithelium is a regulated process rather than a cytotoxic response. Additionally, our results indicate that activation of PTK and ROCK and inactivation of MLCK contribute to the increased airway permeability caused by mainstream cigarette smoke.

Dose-controlled exposure of A549 epithelial cells at the air-liquid interface to airborne ultrafine carbonaceous particles

The geometry of commercially available perfusion chambers designed for harbouring three membrane-based cell cultures was modified for reliable and dose-controlled air-liquid interface (ALI) exposures. Confluent A549 epithelial cells grown on membranes were integrated in the chamber system and supplied with medium from the chamber bottom. Cell viability was not impaired by the conditions of ALI exposure without particles. Expression of the inflammatory cytokines interleukin 6 and interleukin 8 by A549 cells during ALI exposure to filtered air for 6h and subsequent stimulation with tumor necrosis factor was not altered compared to submersed controls, indicating that the cells maintained their functional integrity. Ultrafine carbonaceous model particles with a count median mobility diameter of about 95+/-5 nm were produced by spark discharge at a stable concentration of about 2 x 10(6) cm(-3) and continuously monitored for accurate determination of the exposure dose. Delivery to the ALI exposure system yielded a homogeneous particle deposition over the membranes with a deposition efficiency of 2%. Mid dose exposure of A549 cells to this aerosol for 6h yielded a total particle deposition of (2.6+/-0.4) x 10(8) cm(-2) corresponding to (87+/-23) ng cm(-2). The 2.7-fold (p < or = 0.05) increased transcription of heme oxygenase-1 indicated a sensitive antioxidant and stress response, while cell viability did not reveal a toxic mechanism.

Effects of ozone exposure on inactivation of intra- and extracellular enterovirus 71

In this study, the potential of ozone in inactivating enterovirus 71 (EV71) free particles was investigated using either various ozone flow rates of 100, 80 or 60 mg/h or a constant flow rate of 80 mg/h, given to culture medium or various pH culture media containing EV71, respectively. Results demonstrated that EV71 inactivation by ozone was related to the kinetics of ozone solubility, approximately 99% inactivation being obtained in the exponential phase of ozone solubility. However, the inactivation rate was dependent on the ozone input flow rate and positively enhanced at acidic pH. Inactivation of intracellular EV71 was also studied. At a constant ozone supply of 60 mg/h, a significant reduction of intracellular virus titer (> or =99%, p < 0.01) was obtained after 45 or 60 min exposure but with low cell viability. Upon 30 min exposure, however, 45% cell viability was retained. The results indicate that the inactivating effect of ozone on intracellular EV71 virus is dependent on exposure duration.

An experimental in vitro model for dynamic direct exposure of human cells to airborne contaminants

The aim of this study was to establish a dynamic in vitro model for direct exposure of human cells to gaseous contaminants to investigate the cellular responses to airborne chemical exposures. Nitrogen dioxide (NO2) was selected as a model gas compound. Standard test atmospheres were generated (2.5-10 ppm), using a dynamic direct dilution method. Human cells including: A549 pulmonary type II-like epithelial cell lines and skin fibroblasts were grown on porous membranes. Human cells on snapwell inserts were placed in horizontal diffusion chambers and exposed to various airborne concentrations of NO2 directly at the air/liquid interface for 1 h at 37 degrees C. Cytotoxicity of the test gas was investigated using the MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium), NRU (neutral red uptake) and ATP (Adenosine triphosphate) assays. Dose-dependent effects of NO2 were observed in human cells tested which resulted in a significant reduction of cell viability at concentrations normally encountered in workplace environments (p<0.05). Our findings suggest that the dynamic direct exposure method can be used for in vitro inhalational and dermal toxicity studies and potentially as an advanced technology for biomonitoring of airborne contaminants in future occupational and environmental toxicity assessments.

Comparative assessment of three in vitro exposure methods for combustion toxicity

A comparative assessment of three approaches for the use of human cells in vitro to investigate combustion toxicity was conducted. These included one indirect and two direct (passive and dynamic) exposure methods. The indirect method used an impinger system in which culture medium was used to trap the toxicants, whilst the direct exposure involved the use of a Horizontal Harvard Navicyte Chamber at the air/liquid interface. The cytotoxic effects of thermal decomposition products were assessed using the MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay (Promega) on a selection of human cells including: HepG2, A549 and skin fibroblasts. A small scale laboratory fire test using a vertical tube furnace was designed for the generation of combustion products. Polymethyl methacrylate (PMMA) was selected as a model polymer to study the cytotoxic effects of combustion products. NOAEC (no observable adverse effect concentration), IC10 (10% inhibitory concentration), IC50 (50% inhibitory concentration) and TLC (total lethal concentration) values were determined from dose response curves. Assessment using the NRU (neutral red uptake) and ATP (adenosine triphosphate) assays on human lung derived cells (A549) was also undertaken. Comparison between in vitro cytotoxicity results against published toxicity data for PMMA combustion and predicted LC50 (50% lethal concentration) values calculated from identified compounds using GCMS (gas chromatography mass spectrometry) was determined. The results suggested that the indirect exposure method did not appear to simulate closely exposure via inhalation, whilst exposure at the air/liquid interface by using the dynamic method proved to be a more representative method of human inhalation. This exposure method may be a potential system for in vitro cytotoxicity testing in combustion toxicity.

A direct nitric oxide gas delivery system for bacterial and mammalian cell cultures

Nitric oxide (NO) is the smallest known gaseous signaling molecule released by mammalian and plant cells. To investigate the pathophysiologic role of exogenous NO gas (gNO) in bacterial and mammalian cell cultures, a validated in vitro delivery method is required. The system should be able to deliver gNO directly to bacterial and/or cell cultures in a continuous, predictable, and reproducible manner over a long period of time (days). To accomplish this, a gas delivery system was designed to provide optimal growth conditions for bacteria and/or mammalian cells. Parameters for cell exposure, such as concentration of gNO, nitrogen dioxide (NO(2)), oxygen (O(2)), temperature, and relative humidity (RH) were continuously monitored and evaluated. Uptake of gNO into various media was monitored by measuring the nitrite concentration using the Griess reagent technique. A selection of standard growth media [saline, tryptic soy broth (TSB), Middlebrook 7H9 (MB 7H9), and Dulbecco's modified Eagle's medium (DMEM)] exposed to various concentrations of gNO revealed a steady and consistent transfer of gNO into the aqueous phase over a 48-h period. Validation of optimal growth conditions within the device, as compared to a conventional incubator, were accomplished by growing and observing viability of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and human fibroblast cultures in the absence of gNO. These results indicate that an optimal growth environment for the above tested cells was accomplished inside the proposed delivery system. Dose-dependent toxicological data revealed a significant bacteriostatic effect on P. aeruginosa and S. aureus with continuous exposure to 80 ppm gNO. No toxic effects were observed on dermal fibroblast proliferation at concentrations up to 400 ppm gNO for 48 h. In conclusion, the designed gNO exposure system is capable of supporting cellular viability for a representative range of prokaryote and eukaryotic cells. The exposure system is also capable of obtaining toxicological data. Therefore, the proposed device can be utilized to continuously expose cells to various levels of gNO for up to 72 h to study the in vitro effects of gNO therapy.

Oxidative stress induction by short time exposure to ozone on THP-1 cells

Ozone is a major component of air pollution mainly formed by photochemical reactions of nitrogen oxides with volatile organic compounds and/or carbon monoxide. Numerous studies have shown the association between ozone exposure with pulmonary injuries. This pollutant is a strong oxidant exerting its biological action either by direct reaction with target molecules or by generating reactive oxygen species which result in its biological effects and its toxicity. In order to study the effects of an induced oxidative stress by ozone on THP-1 cell, a human macrophage-like cell line, we used an in vitro system which has been previously used to study the rapid responses to ozone exposure. Using this system, THP-1 cells were subjected to short time exposure (30 min) followed by different incubation times ranging from 4 to 24 h. Our results show that ozone exposure provokes an alteration of the cell membrane translating an induction of lipid peroxidation resulting in a 3.2-fold increase of thiobarbituric reactive substances (TBARS), an increase by 35% of heme oxygenase-1 (HO-1) expression, and significant modifications of the redox status evaluated by glutathione measurement and of antioxidant enzyme activities in THP-1 cells. Our in vitro model constitutes a very interesting tool for the measurement of ozone effect on rapid modifications induced by this pollutant as well as intracellular modifications due to an oxidative stress.

Direct exposure methods for testing native atmospheres

In vitro studies of adverse cellular effects induced by inhalable substances face a number of problems due to the difficulties in exposing cultured cells of the respiratory tract directly to test atmospheres composed of complex gases and particulate compounds. This paper discusses the characteristics of in vitro work and summarizes the use of different in vitro technologies to determine the adverse effects of inhaled pollutants. The exposure of cells to test atmospheres requires accurate control of the pollutant levels, as well as the close contact of cells and gas without interfering with the medium. Systems which rely on the solution of the gas in the medium overlay do not resemble the exposure conditions in vivo, and may not be suitable for studying, for example, the effects of poorly soluble gases. Exposure to gases or complex mixtures can be performed with roller bottles or flasks on rotating and rocking platforms and, using these techniques, the cells are periodically exposed to the test atmosphere. However, the most promising approach is based on a biphasic cell culture technique, where cells are grown on microporous membranes at an air-liquid interface. Here the cells are nutrified from the basal side of the membrane whilst the apical part with the cultivated cells is in direct contact with the test atmosphere. Based on this culture technique, different exposure systems have been developed and these are described and discussed. Exposure of cells from the respiratory tract to gases or particles is responsible for cell injury or cell activation associated with an overexpression of mRNA and the release of bioactive mediators. Therefore, in vitro studies using such a strategy, in combination with relevant and efficient exposure devices, open up new ways to test native complex gases and aerosols. Furthermore, such an experimental approach is not only suitable for cultivated cells, but it can also be used for exposing bacteria to inhalable test compounds. It is possible to analyze the mutagenic potency of in- and outdoor pollutants and several attempts have been made to determine the induction of revertants in a modified Ames assay after exposure to single gases or complex mixtures.

Exposure of bronchial epithelial cells to whole cigarette smoke: assessment of cellular responses

Cigarette smoke is composed of approximately 5% particulate phase and 95% vapour phase by weight. However, routine in vitro toxicological testing of smoke normally only measures the activity of the particulate phase. This study describes a new system for exposing cells at an air-liquid interface to serial dilutions of gaseous smoke. Confluent monolayers of NCI-H292 human lung epithelial cells on semipermeable membranes were placed in a purpose-designed Perspex chamber at an air-liquid interface. The cells were exposed to dilute whole mainstream cigarette smoke for 30 minutes, followed by a 20-hour recovery period. Firstly, high and low delivery cigarettes were compared, and cytotoxicity was determined by using the neutral red uptake assay. Clear differential cytotoxic responses were observed with the two cigarette types, which correlated positively with the concentrations of components in smoke, and particularly compounds in the vapour phase, such as aldehydes. Secondly, low doses of smoke were found to up-regulate mRNA levels of the secreted mucin, MUC5AC, and to stimulate the production of interleukin (IL)-6, IL-8 and matrix-metalloprotease-1, but had no effect on growth-related oncogene alpha. This system will facilitate further investigations into the toxicological mechanisms of cigarette smoke components, and may be useful for studying other gaseous mixtures or aerosols.

Modification of membrane markers on THP-1 cells after ozone exposure in the presence or absence of fMLP

The impacts of ozone and N-formyl-methionyl-leucyl-phenylalanine (fMLP) on the detection of membrane markers on non-differentiated THP-1 cells were evaluated for in vitro exposures. Several markers, specific for monocytes and macrophages, were identified on the THP-1 cells, allowing their use as a model for alveolar macrophages. Ozone exposure modified not only the detection of membrane markers, especially CD13 and CD14, monocyte and macrophage markers, but also the detection of the specific receptor for fMLP, formyl peptide receptor (FPR). Activation by fMLP also reduced the detection of the CD antigens, and a combined exposure to ozone and fMLP amplified this decrease, probably due to an additive effect of these chemicals. Overall, these results suggest important membrane rearrangements for short-term treatments to ozone and/or fMLP.

Comparative assessment of toxicities of mainstream smoke from commercial cigarettes

Three cigarette types were compared using an experimental approach for quantifying selected toxicological effects of diluted fresh whole cigarette mainstream smoke in vitro. The test procedure involved automatic smoking of cigarettes according to the FTC/ISO standard, online monitoring of generated smoke aerosols with respect to particulate and gas-phase components, and direct exposure of a human type II-like lung cell line (A549) using exposure conditions relevant to human smoking. Test specimens were the K1R4F standard research cigarettes (9.2 mg tar/cigarette) and two commercial European light filter cigarettes (brand 1, brand 2) having the same tar content (7.0 mg/cigarette). As a representative of the toxicological effect of smoke, intracellular reduced glutathione was analyzed directly after exposure of cells. Results revealed statistically significant different quantitative effects with regard to glutathione depletion when comparing whole smoke and filtered smoke from all three cigarettes. ED50 values revealed a depletion of reduced glutathione by brand 1 cigarettes that was more than twice the depletion caused by brand 2 cigarettes on a per cigarette basis. Also, quantitatively different effects were found on a per particle and on a per CO concentration basis using whole or filtered smoke from the cigarettes. We conclude that the methods we employed provide sensitive and reproducible ways of detecting differences in the toxicological action of smoke from various types of cigarettes.

An improved in vitro model for testing the pulmonary toxicity of complex mixtures such as cigarette smoke

Numerous approaches have been employed for testing the biological activity of cigarette smoke in vitro. None of them has managed to expose cultured lung cells in a realistic manner to the complex gaseous and particulate mixture that constitutes cigarette smoke. We have devised a system that makes this possible. The system presented here enables the direct exposure of human lung cells to native, unmodified cigarette mainstream smoke. It consists of a smoking machine, a dilution device for the smoke, analytical devices for online monitoring and a specially adapted exposure module based on the Cultex** cell cultivation system that is equipped with a gas-exposure top. Due to the special design of the exposure device and the optimised exposure conditions, this equipment allows cultured human lung cells to be exposed to freshly generated cigarette mainstream smoke. Exploratory experiments revealed that the smoke could be diluted over a wide concentration range in a reproducible way with respect to gas and particulate phases, and also demonstrated reproducible particle deposition depending on smoke concentration. Furthermore, it was shown that the exposed cells maintained their viability. Native cigarette mainstream smoke induced dose-dependent cellular effects in exposed cells with respect to cellular viability (viable cell number monitored by tetrazolium salt cleavage) and intracellular parameters (ATP and glutathione content). Therefore, fresh, physically and chemically unmodified cigarette mainstream smoke can be tested using this novel system.

Novel approaches for studying pulmonary toxicity in vitro

The in vitro study of adverse cellular effects induced by inhaled pollutants poses a special problem due to the difficulties of exposing cultured cells of the respiratory tract directly to test atmospheres that can include complex gaseous and particulate mixtures. In general, there is no widely accepted in vitro exposure system. However, in vitro methods offer the unique possibility for use of human cells, developed and validated cell culture and exposure device (CULTEX(1)) using the principle of the air/liquid exposure technique. Cells of the respiratory tract are grown on porous membranes in transwell inserts. After removal of the medium, the cells can be treated on their superficial surfaces with the test atmosphere, and at the same time they are supplied with nutrients through the membrane below. In comparison with other experimental approaches, the goal of our studies is to analyze the biological effects of test atmospheres under environmental conditions, i.e. without humidifying the atmosphere or adding additional CO(2). The system used is small and flexible enough independent of a cultivation chamber and thus offers the opportunity for onsite study of indoor and outdoor atmospheres in the field. The efficacy of the exposure device has already been demonstrated in the analysis of dose-dependent cytotoxic and genotoxic effects of exposure of epithelial lung cells to complex mixtures such as native diesel exhaust and side-stream smoke.

A method for the in vitro exposure of human cells to environmental and complex gaseous mixtures: application to various types of atmosphere

The application of in vitro methods to the analysis of the effects of airborne materials is still limited, because there are no generally accepted concepts and technologies for efficiently exposing adherent growing cells to test atmospheres, especially those comprising complex mixtures of gaseous and particulate phases. The introduction of in vitro research into the field of inhalation toxicology offers a unique possibility for using human cells and tissues for pre-screening studies, thus reducing the necessity for animal experiments, and cutting the numbers of animals used in toxicological testing. We therefore developed a novel experimental concept that uses an exposure device based on the cell cultivation system CULTEX (Patent No. DE 198011763; PCT/EP99/00295). This allowed us to investigate environmental atmospheres, which were chemically and physically unmodified, in an in vitro system, by exposing the target cells directly at the air/liquid interface. The exposure device itself is small and flexible enough to be connected to a variety of aerosol-generating systems without the need for an incubator, as it fulfils all the requirements for maintaining cell viability over a defined period. The general applicability and the sensitivity of this in vitro approach for testing various generated atmospheres under the same cell-exposure conditions were demonstrated by studying dose-dependent cytotoxic effects in human lung epithelial cells exposed to air contaminated with single gases or complex mixtures, such as diesel exhaust fumes and side-stream cigarette smoke.