Comparison of the toxic effects of hydrogen peroxide and ozone on cultured human bronchial epithelial cells

Cell death induced by ozone and various non-thermal plasmas: therapeutic perspectives and limitations

Non-thermal plasma has been recognized as a promising tool across a vast variety of biomedical applications, with the potential to create novel therapeutic methods. However, the understanding of the molecular mechanisms behind non-thermal plasma cellular effects remains a significant challenge. In this study, we show how two types of different non-thermal plasmas induce cell death in mammalian cell cultures via the formation of multiple intracellular reactive oxygen/nitrogen species. Our results showed a discrepancy in the superoxide accumulation and lysosomal activity in response to air and helium plasma, suggesting that triggered signalling cascades might be grossly different between different plasmas. In addition, the effects of ozone, a considerable component of non-thermal plasma, have been simultaneously evaluated and have revealed much faster and higher cytotoxic effects. Our findings offer novel insight into plasma-induced cellular responses, and provide a basis for better controlled biomedical applications.

In vivo ozone exposure does not increase DNA single-strand breaks in human peripheral lymphocytes

In this randomized parallel study, we examined whether an acute ozone (O3) exposure leads to increased DNA strand breaks in human lymphocytes. The groups were exposed to 0.21 ppm O3 or filtered air for two hours. 30min and 4.5 h after exposure, DNA damage was determined in isolated lymphocytes using the Fast Micromethod. There was no detectable effect after O3 exposure. We conclude that an acute O3 exposure at the tested concentration does not lead to persistent DNA damage.

Effect of modifying quantum dot surface charge on airway epithelial cell uptake in vitro

The respiratory system is one of the portals of entry into the body, and hence inhalation of engineered nanomaterials is an important route of exposure. The broad range of physicochemical properties that influence biological responses necessitate the systematic study to contribute to understanding occupational exposure. Here, we report on the influence of nanoparticle charge and dose on human airway epithelial cells, and show that this platform can be used to evaluate consequences of exposure to engineered nanomaterials.

Exposure to ozone modulates human airway protease/antiprotease balance contributing to increased influenza A infection

Exposure to oxidant air pollution is associated with increased respiratory morbidities and susceptibility to infections. Ozone is a commonly encountered oxidant air pollutant, yet its effects on influenza infections in humans are not known. The greater Mexico City area was the primary site for the spring 2009 influenza A H1N1 pandemic, which also coincided with high levels of environmental ozone. Proteolytic cleavage of the viral membrane protein hemagglutinin (HA) is essential for influenza virus infectivity. Recent studies suggest that HA cleavage might be cell-associated and facilitated by the type II transmembrane serine proteases (TTSPs) human airway trypsin-like protease (HAT) and transmembrane protease, serine 2 (TMPRSS2), whose activities are regulated by antiproteases, such as secretory leukocyte protease inhibitor (SLPI). Based on these observations, we sought to determine how acute exposure to ozone may modulate cellular protease/antiprotease expression and function, and to define their roles in a viral infection. We utilized our in vitro model of differentiated human nasal epithelial cells (NECs) to determine the effects of ozone on influenza cleavage, entry, and replication. We show that ozone exposure disrupts the protease/antiprotease balance within the airway liquid. We also determined that functional forms of HAT, TMPRSS2, and SLPI are secreted from human airway epithelium, and acute exposure to ozone inversely alters their expression levels. We also show that addition of antioxidants significantly reduces virus replication through the induction of SLPI. In addition, we determined that ozone-induced cleavage of the viral HA protein is not cell-associated and that secreted endogenous proteases are sufficient to activate HA leading to a significant increase in viral replication. Our data indicate that pre-exposure to ozone disrupts the protease/antiprotease balance found in the human airway, leading to increased influenza susceptibility.

GSTM1 modulation of IL-8 expression in human bronchial epithelial cells exposed to ozone

Exposure to the major air pollutant ozone can aggravate asthma and other lung diseases. Our recent study in human volunteers has shown that the glutathione S-transferase Mu 1 (GSTM1)-null genotype is associated with increased airway neutrophilic inflammation induced by inhaled ozone. The aim of this study was to examine the effect of GSTM1 modulation on interleukin 8 (IL-8) production in ozone-exposed human bronchial epithelial cells (BEAS-2B) and the underlying mechanisms. Exposure of BEAS-2B cells to 0.4 ppm ozone for 4 h significantly increased IL-8 release, with a modest reduction in intracellular reduced glutathione (GSH). Ozone exposure induced reactive oxygen species (ROS) production and NF-κB activation. Pharmacological inhibition of NF-κB activation or mutation of the IL-8 promoter at the κB-binding site significantly blocked ozone-induced IL-8 production or IL-8 transcriptional activity, respectively. Knockdown of GSTM1 in BEAS-2B cells enhanced ozone-induced NF-κB activation and IL-8 production. Consistently, an ozone-induced overt increase in IL-8 production was detected in GSTM1-null primary human bronchial epithelial cells. In addition, supplementation with reduced GSH inhibited ozone-induced ROS production, NF-κB activation, and IL-8 production. Taken together, GSTM1 deficiency enhances ozone-induced IL-8 production, which is mediated by generated ROS and subsequent NF-κB activation in human bronchial epithelial cells.

Septin-2 mediates airway epithelial barrier function in physiologic and pathologic conditions

Epithelial cells have the ability to regulate paracellular permeability dynamically in response to extracellular stimuli. With every respiratory effort, airway epithelial cells are exposed to both physiologic as well as pathologic stimuli, and regulation of the epithelial barrier in response to these stimuli is crucial to respiratory function. We report that increased membrane septin-2 localization mediates decreases in paracellular permeability by altering cortical actin arrangement in human airway epithelial cells. This phenomenon occurs in response to both physiologic levels of shear stress and a pathologic stimulus, particular matter exposure. The resulting changes in barrier function in response to septin-2 redistribution have a significant impact on the ability of the apical ligand, epidermal growth factor, to interact with its receptor, epidermal growth factor receptor, which is segregated to the basolateral side in airway epithelial cells. This suggests that the dynamic regulation of the epithelial barrier function is essential in regulating signaling responses to extracellular stimuli. These findings indicate that septin-2 plays a fundamental role in regulating barrier function by altering cortical actin expression.

Lung injury after ozone exposure is iron dependent

We tested the hypothesis that oxidative stress and biological effect after ozone (O3) exposure are dependent on changes in iron homeostasis. After O3 exposure, healthy volunteers demonstrated increased lavage concentrations of iron, transferrin, lactoferrin, and ferritin. In normal rats, alterations of iron metabolism after O3 exposure were immediate and preceded the inflammatory influx. To test for participation of this disruption in iron homeostasis in lung injury following O3 inhalation, we exposed Belgrade rats, which are functionally deficient in divalent metal transporter 1 (DMT1) as a means of iron uptake, and controls to O3. Iron homeostasis was disrupted to a greater extent and the extent of injury was greater in Belgrade rats than in control rats. Nonheme iron and ferritin concentrations were higher in human bronchial epithelial (HBE) cells exposed to O3 than in HBE cells exposed to filtered air. Aldehyde generation and IL-8 release by the HBE cells was also elevated following O3 exposure. Human embryonic kidney (HEK 293) cells with elevated expression of a DMT1 construct were exposed to filtered air and O3. With exposure to O3, elevated DMT1 expression diminished oxidative stress (i.e., aldehyde generation) and IL-8 release. We conclude that iron participates critically in the oxidative stress and biological effects after O3 exposure.

Lung epithelial cells release ATP during ozone exposure: signaling for cell survival

The common air pollutant ozone causes acute toxicity to human airways. In primary and transformed epithelial cells from all levels of human or rat airways, ozone levels relevant to air pollution (50-200 ppb) increased extracellular [ATP] within 7-30 min. A human bronchial epithelial cell line (16HBE14o(-)) that forms electrically resistant polarized monolayers had up to 10-fold greater apical than basolateral surface extracellular [ATP] within 7 min of ozone exposure. Increased extracellular [ATP] appeared due to ATP secretion or release because (1) inhibition of ectonucleotidase (cell surface enzyme(s) which degrade ATP) by ozone did not occur until >120 min of ozone exposure and (2) brefeldin A, a secretory inhibitor, eliminated elevation of extracellular [ATP] without affecting intracellular ATP. Extracellular ATP protected against ozone toxicity in a P2Y receptor-dependent manner as (1) removal of ATP and adenosine by apyrase and adenosine deaminase, respectively, potentiated ozone toxicity, (2) extracellular supplementation with ATP, a poorly hydrolyzable ATP analog ATPgammaS, or UTP inhibited apoptotic and necrotic ozone-mediated cell death, and (3) ATP-mediated protection was eliminated by P2 and P2Y receptor inhibitors suramin and Cibacron blue (reactive blue 2), respectively. The decline in glucose uptake caused by prolonged ozone exposure was prevented by supplemental extracellular ATP, an effect blocked by suramin. Further, Akt and ERK phosphorylation resulted from exposure to supplemental extracellular ATP. Thus, extracellularly released ATP signals to prevent ozone-induced death and supplementation with ATP or its analogs can augment protection, at least in part via Akt and /or ERK signaling pathways and their metabolic effects.

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.

In vitro genotoxicity assay of sidestream smoke using a human bronchial epithelial cell line

Genotoxic effects of air contaminants, such as gaseous or particulate compounds, have been difficult to investigate due to inefficient methods for exposing cell cultures directly to these substances. New cultivation and exposure techniques enable treatment of epithelial cells with sample atmospheres with subsequent in vitro assays, as demonstrated by a new system called CULTEX (CULTEX: patent No. DE 19801763; PCT/EP99/00295), which uses a transwell membrane technique for direct exposure of complex mixtures, for example sidestream cigarette smoke, at the air/liquid interface. The sensitivity and susceptibility of human bronchial epithelial cells to this complex mixture have already been shown for cytotoxic endpoints. In this study, genotoxic effects of sidestream cigarette smoke at different concentrations were assessed using the alkaline comet assay. HFBE 21 cells were exposed for 1 h to clean air, nitrogen dioxide or sidestream smoke. Exposure of the cells to sidestream cigarette smoke induced DNA strand breaks in a dose-dependent manner. The combination of gas phase exposure and the comet assay provides a realistic and efficient model for sensitive detection of DNA strand breaks induced by airborne and inhalable compounds.

Genotoxic effect of ozone in human peripheral blood leukocytes

The genotoxic effect of ozone was studied in human leukocytes in vitro, using the single cell gel electrophoresis (SCGE) assay. Cell treatment for 1 h at 37 degrees C with 0.9-5.3 mM O(3) resulted in a dose-dependent increase of DNA damage, comparable to that induced by 4-40 mM of H(2)O(2), used as a positive control. This effect of ozone was reversed by post-treatment incubation of the cells for 45-90 min at 37 degrees C, and prevented by pre-incubation of the cells with catalase (20 microg/ml). These results demonstrate that O(3) induces DNA-damage in primary human leukocytes. The damage is rapidly repaired, and probably mediated by the formation of H(2)O(2).

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

An exposure system for adherent growing cells to native gaseous compounds was developed using air/liquid culture techniques on the basis of the Cultex system'. In contrast to other exposure systems the reproducible testing of native environmentally relevant gases without changing their physical or chemical properties including heating, CO2- content and humidity is possible. Specially designed systems for medium flow and gas support guarantee the nutrification and humidification as well as the direct gas contact of the exposed cells which are cultivated on microporous membranes (0.4 microm pore size). The system works independently of a cell culture incubator offering the possibility to analyze any relevant gas mixture directly under indoor or outdoor conditions. Several experimental approaches were carried out to characterize the properties of the system. In exploratory experiments without cells, the reproducibility and quality of the gas/membrane contact could be demonstrated. Exposures of human lung fibroblasts (Lk004 cells) and human lung epithelial cells (HFBE-21 cells) to synthetic air, ozone (202 ppb, 510 ppb) and nitrogen dioxide (75 ppb to 1,200 ppb) established that cells could be treated for 120 minutes without significant loss of cellular viability. At the same time, the experiments confirmed that such exposure times are long enough to detect biological effects of environmentally relevant gas mixtures. The analysis of viability (viable cell number, tetrazoliumsalt cleavage) and intracellular end-points (oxidized/reduced glutathione, ATP/ADP) showed that both gases induced relevant cellular changes. In summary, the efficiency and practicability of this newly developed exposure system for adherent human lung cells could be clearly demonstrated.

A method for in vitro analysis of the biological activity of complex mixtures such as sidestream cigarette smoke

Studies of the cytotoxicity of air contaminants such as gaseous or particulate compounds and complex mixtures have traditionally used in animal experiments because of the difficulties in exposing cell cultures directly to these substances. New cultivation and exposure techniques enhance the efficiency of in vitro methods, as demonstrated by a new system called CULTEX* which uses a transwell membrane technique for direct exposure of complex mixtures like sidestream cigarette smoke at the air/liquid interface. The factors influencing the susceptibility of human bronchial epithelial cells (e.g. gas flow rate or duration of exposure) were studied and the cells were finally exposed for one hour to clean air or different concentrations of sidestream smoke. The biological parameters estimated were number of cells, metabolic activity and glutathione concentration. After exposure of the cells to sidestream cigarette smoke, dose-dependent effects were measured. Thus, the introduction of these cultivation and exposure techniques offers new testing strategies for the toxicological evaluation of a broad range of airborne and inhalable compounds.

Detection of ozone-induced DNA single strand breaks in murine bronchoalveolar lavage cells acutely exposed in vivo

Single-strand breaks (SSBs) in DNA have been used a biomarker of oxidative damage. The comet assay, also known as single-cell gel electrophoresis, was used to investigate the ability of ozone (O(3)) to induce DNA SSBs in murine bronchoalveolar lavage (BAL) cells. The comet assay is more sensitive than other techniques currently utilized for detecting SSBs and requires fewer cells. In the present study, 3 mice were exposed for 3 h to 0.25 ppm of O(3), and 3 to 0.5 ppm of O(3) for 3 h. Two air-exposed mice served as negative controls. All mice were euthanized 3 h after exposure, at which time BAL cells were recovered from the lungs and stained with ethidium bromide. BAL cells recovered from an air-exposed mouse were exposed to various concentrations of H(2)O(2) in vitro for 1 h at 4 degrees C. Excluding cells from the H(2)O(2) group (n = 25), 50 randomly selected BAL cells were graded by comet tail length into 1 of 4 categories: no damage (0 mm), low damage (1-10 mm), medium damage (11-30 mm), and high damage (31 + mm). The nonparametric Wilcoxon rank-sum test was used for statistical analysis, and p values lower than .05 were considered significant. The H(2)O(2) and the 0.25 and 0.5 ppm O3 groups showed statistically significant increases in DNA SSBs as compared to air-exposed controls. The results of this study indicate that (1) O(3) induces DNA strand breaks in murine BAL cells at 0.25 and 0.5 ppm, as evidenced by statistically significant increases in the length of comet tails for O(3)-exposed groups, and (2) the comet assay can be used to assess O(3)-induced SSBs for in vivo exposures. Therefore, it has the potential as a biomarker for in vivo oxidant exposures.