Ozone sensitivity in aging WI-38 cells based on acid phosphatase content

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.

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.

An improved system for exposure of cultured mammalian cells to gaseous compounds in the chromosomal aberration assay

A gas exposure system using rotating vessels was improved for exposure of cultured mammalian cells to gaseous compounds in the chromosomal aberration assay. This system was composed of 12 square culture vessels, a device for preparation of air containing test gas, and positive and negative control gases at target concentrations and for supplying these gases to the culture vessels, and a roller apparatus in an incubator. Chinese hamster lung cells (CHL/IU) were grown on one side of the inner surface of the square culture vessel in the MEM medium. Immediately prior to exposure, the medium was changed to the modified MEM. Air in the culture vessel was replaced with air containing test gas, positive or negative control gas. Then, the culture vessels were rotated at 1.0 rpm. The monolayered culture cells were exposed to test gas during about 3/4 rotation at upper positions and alternatively immersed into the culture medium during about 1/4 rotation at lower positions. This system allowed the chromosomal aberration assay simultaneously at least at three different concentrations of a test gas together with positive and negative control gases with and without metabolic activations, and duplicate culture at each exposure concentration. Seven gaseous compounds, 1,3-butadiene, chlorodifluoromethane, ethyl chloride, methyl bromide, methyl chloride, propyne, and vinyl chloride, none of which has been tested to date, were tested on CHL/IU for the chromosomal aberration assay using this gas exposure system. All the compounds except chlorodifluoromethane showed positive responses of the structural chromosomal aberrations, whereas polyploidy was not induced by any of these gases. This improved gas exposure system proved to be useful for detecting chromosomal aberrations of gaseous compounds.

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.

Two in vitro models for gas-phase exposure to volatile compounds

Two experimental models suitable for the screening of volatile compounds were set up. The first consisted of a glass-chamber slide with eight wells, one carrying the test compound, and the others carrying cells in monolayers. In the second model, the cells were cultured in a glass Petri dish, and the test compound was poured onto a filter lying on a glass cover-slip, supported by a metal ring. Four plant volatiles [carvacrol, S-(+)- carvone, thymol and decanal] and one essential oil (caraway oil) were chosen as test compounds. The toxicity rankings obtained with the two models were compared with that obtained in a previous study performed with the same compounds under conventional culture conditions. Differences in the toxicity ranking were observed between the conventional culture conditions and the gas-phase models, confirming the importance of correct exposure conditions for the evaluation of toxicity. Both models have advantages that make them suitable as a preliminary step in the toxicity screening of volatile compounds, or for use in a test battery when combined with conventional approaches.

An in vitro model for evaluation of vaporous toxicity of trichloroethylene and tetrachloroethylene to CHO-K1 cells

Toxicokinetics of trichloroethylene (TCE) and tetrachloroethylene (PER) in culture medium and their toxicity to CHO-K1 cells were investigated by employing an in vitro vapor exposure system. Cells were cultured in a 60 mm petri dish with a 25 mm glass dish glued in the central area. TCE or PER was added to the central glass dish so that it would evaporate and dissolve in the surrounding medium in which cells were growing. The results showed that the concentration of TCE or PER in medium increased significantly within 20 min and then decreased very rapidly with time. After a 24 h incubation, the residual of TCE or PER in the medium was very low, but was displayed in a dose-dependent manner. Treatment of cells with either TCE or PER resulted in a dose- and time-dependent inhibition of cell growth. A significantly increase in the frequency of micronuclei (MN) was also observed with either TCE or PER treatment. Low doses of TCE (5-20 microl) or PER (1-5 microl) significantly enhanced the intracellular glutathione (GSH) level. However, the level of GSH rapidly decreased with higher doses of TCE (40-80 microl) or PER (10-20 microl). Depletion of cellular GSH showed no effect on the sensitivity of cells to TCE or PER treatment. GSH-conjugation has been proposed as an activation mechanism to account for the nephrotoxicity of TCE and PER, however the toxicity of TCE and PER to CHO-K1 cells is probably mediated through a distinct mechanism.

A new approach to evaluate toxicity of gases on mobile cells in culture

A novel technique is described that measures the degree of toxicity of short-term exposure to gaseous pollutants or other chemical compounds on cultured cells, in 30 min. This technique, based on the study of the mobility properties of activated macrophages, consists of an image analysis procedure incorporating a specific exposure chamber (EC). The EC, which is developed from commercial culture flasks (50 ml, 25 cm(2) of culture surface), was first used to maintain cells in culture conditions, overnight, prior to the assay. In order to measure toxicity, it was then connected to the gaseous pollutant or chemical source. After exposing the culture medium and cells to the gas stream for 10 min, fMLP, a chemotactic factor, was added and the mobility of the macrophages measured by superimposing sequential analogue images captured by a CCD camera that were digitised and analysed using a software developed for this purpose. For example, the effect of ozone on macrophage-like cell (THP-1) was investigated. After exposure to 0.1 and 0.5 ppm, cells lost, respectively 79% and 90% of their mobility, compared to the control sample.

A novel apparatus for the exposure of cultured cells to volatile agents

This article presents a novel exposure apparatus that allows the exposure of cultured cells to volatile chemicals, e.g., inhalation anesthetics. The apparatus consists of an exposure chamber and a tightly linked vaporizer unit with pumps and valves allowing adjustable fluxes of mixtures of test chemicals and carrier gas under open and closed-circuit conditions. The exposure chamber uses commercially available cell culture flasks and accommodates up to 12 flasks simultaneously. Both modules fit into a standard culture incubator. The exposure chamber may be mounted onto an oscillating axis to tilt the cultures periodically forth and back, thus allowing direct contact of the cells with test atmosphere. The vaporizer unit is connected to a personal computer which lets the experimenter set the "open" and "close" intervals of individual valves thereby controlling the composition and flow rate of the test gas mixture. The vapor concentration of test chemicals can be monitored at the inlet and outlet using infrared photodetectors or mass spectrometers. Computer-aided processing of exposure protocols allows unattended runs. Exposure protocols can be scripted and stored on disk, thus ensuring interexperimental reproducibility of complex exposure profiles. As an application example, the effect of three volatile anesthetics, halothane, enflurane, and isoflurane, on the viability of three commercially available cell lines (A549--human lung carcinoma, HTC-rat hepatoma, MDCK--Madin-Darby canine kidney) was investigated. After exposure to haloalkyl vapors (3%) for 6 and 24 h, respectively, significantly increased LDH levels versus controls, indicating cellular membrane damage, were detected in A549 and hepatoma cells after exposure for 24 h. Hepatoma cells showed a significant LDH release also after 6 h exposure to isoflurane. On the other hand, LDH release from MDCK cells was not significantly different from controls even after 24 h of continuous exposure to any of the tested anesthetics.

In vitro study of gas effects on alveolar macrophages

To evaluate the biological effects of gas pollutants on alveolar macrophages several in vitro systems have been developed. We described here an original method of cell culture in aerobiosis, which permitted direct contact between the atmosphere and the target cells. We studied the long term (24 h) and short term (30 min) effects of NO2 on alveolar macrophages. Our results demonstrated that exposure of alveolar macrophages to gas pollutants may be responsible for either cell injury or cell activation associated with the release of various bioactive mediators (superoxide anion, neutrophil chemotactic activity). Cell culture in aerobiosis opens new ways for the research on the biological effects of gas pollutants.

Morphologic injury and lipid peroxidation in monolayer cultures of rabbit tracheal epithelium exposed in vitro to ozone

Numerous reports have documented airway epithelial damage and lipid peroxidation in the lungs of animals exposed to ozone. However, the response of isolated tracheal epithelial (TE) cells to ozone has not been extensively studied. To assess ozone-induced injury in cultured TE cells, an in vitro exposure system was developed in which cells were maintained at gas-fluid interface analogous to in vivo conditions. Confluent monolayer cultures of rabbit TE cells were exposed for 30 min to atmospheres of 5% CO2/air containing 0.05, 0.1, 0.5, 1, 2, 4, 6, or 8 ppm ozone. Morphologic injury was assessed by phase-contrast microscopy and by determination of TE cell number and viability (trypan blue dye exclusion) pre- and postexposure, and the lipid peroxide content of TE cells was measured as thiobarbituric acid (TBA) reactive substances. Exposure to 5% CO2/air alone did not affect monolayer morphology, cell number of viability. Cultures exposed to 0.05 or 0.1 ppm ozone demonstrated no consistent light microscopic changes, whereas exposure to 0.5 ppm and higher ozone concentrations caused distortion of monolayer morphology, cytoplasmic vacuolization, and decreased viability. Exposure to 0.5 or 1 ppm resulted primarily in cytoplasmic vacuolization while exposure to 2, 4, 6, or 8 ppm induced more pronounced cellular injury associated with cell necrosis (viability post 8 ppm ozone 75.0 +/- 7.0%, vs. 95.9 +/- 2.6% for 5% CO2/air controls). Ozone exposure also caused changes in cell shape, which on occasion resulted in loss of cell-to-cell contact. Increased production of TBA-reactive substances was detected in TE cells following ozone exposure, including exposure to 0.05 and 0.1 ppm. The morphologic changes induced by in vitro ozone exposure in the cultured TE cells were similar to those described in the tracheal epithelium of ozone-exposed animals and occurred independent of recruited inflammatory cells or extravasated circulating mediators.

Effect of fatty acid profiles on the susceptibility of cultured rabbit tracheal epithelial cells to hyperoxic injury

To investigate the role of cellular fatty acid content on the susceptibility of airway epithelial cells to hyperoxic injury, monolayer cultures of rabbit tracheal epithelial (TE) cells were grown to confluence in serum-free media with or without a commercial mixture of cholesterol esters and phospholipid-rich lipoproteins (Excyte III, Miles-Pentex, Kankakee, IL) in conjunction with arachidonic acid complexed to BSA. Monolayer cultures were then exposed to control (5% CO2/air) or hyperoxic atmospheres (95% oxygen/5% CO2) for 2 h using an in vitro system in which cells were maintained at a gas-liquid interface analogous to in vivo conditions. Hyperoxic injury was assessed by cell viability (trypan blue exclusion) and by the generation of lipid peroxides measured as thiobarbituric acid (TBA) reactive substances. Changes in TE cell and cell culture effluent fatty acid content induced by exposure to control or hyperoxic atmospheres were analyzed by gas chromatography. TE cells grown in lipid-unsupplemented media had fatty acid profiles characteristic of essential fatty acid deficiency, whereas the fatty acid content of lipid-supplemented TE cells more closely resembled those of acutely recovered TE cells. Lipid-unsupplemented cells were more susceptible to hyperoxic injury as demonstrated by decreased viability and increased production of TBA-reactive substances compared to cells maintained in lipid-supplemented media. In both lipid-supplemented and unsupplemented cells, hyperoxic exposure was associated with a decreased relative cellular content of the monounsaturated and polyunsaturated fatty acids (PUFA) and an increased content of saturated fatty acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Superoxide dismutase: its role in xenobiotic detoxification

Since the discovery of superoxide dismutase in 1969, the role of this enzyme in modulating cellular toxicity of superoxide has been well established. Experimentally, cellular damage from compounds or exposures which produce superoxide extracellularly can be prevented or modified by pretreating a cell or organ system with SOD. Likewise, induction of intracellular SOD by exposing the cell system to various types of nonlethal stress will impart resistance or tolerance to further exposures to oxidant and nonoxidant stresses which would normally be toxic. The differences in intracellular SOD activity based on species, age, and organ variability can have a major impact on the interpretation of toxicology data, particularly extrapolation to human toxicology. An awareness of the importance of SOD to the toxicity of xenobiotics which produce superoxide, either directly or indirectly, will enable those conducting toxicology studies to better understand and interpret their results.

In vitro systems for exposure of lung cells to NO2 and O3

In vitro studies of the effects of NO2 and O3 require development of methods for separation and culture of those lung cells that experience in vivo exposure, and also the design and construction of systems for controlled exposure of the cells to known concentrations of the gases. Separation of lung cell types has been accomplished by enzymatic dispersal of lung tissue and centrifugation of the mixed cells on media of various densities in order to separate the cells on the basis of buoyant density or sedimentation rate. The application of centrifugal elutriation has enabled separation of type II alveolar cells and Clara cells with a high degree of purity. Alveolar macrophages and endothelial cells have also been obtained in good yield. Exposure of cultured cells to test atmospheres requires precise control of pollutant levels, close contact of cells and gas without an intervening layer of medium, capability for prolonged exposure, and maintenance of sterile conditions, so that recovered cells can be cultured further or studied for other biological activity. Systems which meet these criteria include roller bottle cultures, petri dish cultures on rocker platforms, cell cultures on cellulose filters fed by perfusion of medium from the side opposite the cells, and cells grown in dishes with gas-permeable film bottoms. Systems that rely on solution of the gases in the overlaying medium do not resemble exposure conditions in vivo, and may not be suitable for studying effects of the poorly soluble oxidant gases. The cell exposure systems have not been used extensively for studies of the effects of pollutants on freshly isolated specific lung cell types. Such studies should be encouraged.

Role of in vitro factors in ozone toxicity for cultured rat lung fibroblasts

Ozone toxicity for cultured rat lung fibroblasts was concentration dependent and was affected by the manner in which ozone was delivered to the cells, i.e. cultures were either rotated with a thin moving overlay of medium or were stationary with a fixed layer of medium between the cells and the gas phase. The influence of culture medium components and culture dish composition on the toxicity of ozone were also investigated. Cell viability, used to measure ozone toxicity, was quantified by the chromium-51 release assay, and by a viability index calculated from the percentage of cells stained with a vital dye combined with the decrease in cell number as determined by DNA measurements. During stationary ozone exposure, toxicity appeared to be mediated primarily by hydrogen peroxide and could be inhibited by catalase or fetal bovine serum when measured by the viability index. During rotated exposure, catalase and fetal bovine serum provided no protection when measured by the viability index, however, when measured by the chromium-51 release assay, fetal bovine serum was partially protective. The effect of ozone on the fibroblasts was not influenced by whether culture dishes were glass or plastic, or whether the culture medium was balanced salt solution or complete chemically-defined medium.