Formation of intracellular free radicals in guinea pig airway epithelium during in vitro exposure to ozone

Optimisation of growth conditions for ovine airway epithelial cell differentiation at an air-liquid interface

Respiratory tract infections are of significant concern in the agriculture industry. There is a requirement for the development of well-characterised in vitro epithelial cell culture models in order to dissect the diverse molecular interactions occurring at the host-pathogen interface in airway epithelia. We have analysed key factors that influence growth and differentiation of ovine tracheal epithelial cells in an air-liquid interface (ALI) culture system. Cellular differentiation was assessed at 21 days post-ALI, a time-point which we have previously shown to be sufficient for differentiation in standard growth conditions. We identified a dose-dependent response to epidermal growth factor (EGF) in terms of both epithelial thickening and ciliation levels. Maximal ciliation levels were observed with 25 ng ml-1 EGF. We identified a strict requirement for retinoic acid (RA) in epithelial differentiation as RA exclusion resulted in the formation of a stratified squamous epithelium, devoid of cilia. The pore-density of the growth substrate also had an influence on differentiation as high pore-density inserts yielded higher levels of ciliation and more uniform cell layers than low pore-density inserts. Differentiation was also improved by culturing the cells in an atmosphere of sub-ambient oxygen concentration. We compared two submerged growth media and observed differences in the rate of proliferation/expansion, barrier formation and also in terminal differentiation. Taken together, these results indicate important differences between the response of ovine tracheal epithelial cells and other previously described airway epithelial models, to a variety of environmental conditions. These data also indicate that the phenotype of ovine tracheal epithelial cells can be tailored in vitro by precise modulation of growth conditions, thereby yielding a customisable, potential infection model.

Investigations of the Biological Effects of Airborne and Inhalable Substances by Cell-Based In Vitro Methods: Fundamental Improvements to the ALI Concept

The state of the art for cell-based in vitro investigations of airborne and inhalable material is “air-liquid interface” (ALI) technology. Cell lines, primary cells, complex 3D models, or precision-cut lung slices (PCLS) are used to represent the lung or skin by way of an in vitro barrier model. These models have been applied in toxicity or pharmacological testing. However, contrasting with a clear demand for alternative methods, there is still no widely accepted procedure for cell-based in vitro testing of inhalable substances. In the light of this, an analysis was undertaken of common drawbacks of current approaches. Hence, the pivotal improvements aimed at were the cellular exposure environment, overall performance and applicability, operability of online investigations during exposure and routine setup. It resulted in an improved device (P.R.I.T. ExpoCube) based on an “all-in-one-plate” concept including all phases of the experiment (cell culture, exposure, and read-out) and all experimental groups (two test gas groups, controls) in one single commercial multiwell plate. Verification of the concept was demonstrated in a first experimental series using reference substances (formaldehyde, ozone, and clean air). The resulting ALI procedure enables the application of inhalable substances and mixtures under highly effective exposure conditions in routine utilization.

Effects of ozone exposure on the ocular surface

Changes in the ocular surface induced by ozone have received limited research attention. Here, we investigate the effects of ozone exposure on the integrity of the ocular surface, the production of inflammatory cytokines in tears, and changes in mucin-secreting cells in a mouse model. In addition, ozone-induced nuclear factor-κB (NF-κB)-mediated inflammatory processes were evaluated in cultured human conjunctival epithelial cells. In vivo, ozone induced the breakdown of corneal epithelial integrity, decreased the number of mucin-secreting cells, and induced the production of inflammatory cytokines, without altering tear volume. In vitro, ozone exposure led to increases in NF-κB nuclear translocation, κB-dependent transcriptional activity, NF-κB inhibitor α (IκBα) proteolysis, and expression of phosphorylated IκBα (p-IκBα), but did not cause cytotoxicity or cellular apoptosis. In addition, ozone induced the expression of inflammatory cytokines, Toll-like receptors, and C-C chemokine receptors, but decreased the expression of mucins. Furthermore, inhibition of NF-κB with pyrrolidine dithiocarbamate before exposure of cultured human conjunctival epithelial cells to ozone prevented changes in IκBα and p-IκBα levels in association with a decrease in the levels of inflammatory cytokines. Therefore, we conclude that ozone exposure interferes with ocular surface integrity and induces inflammation involving NF-κB-mediated processes at the level (and/or upstream) of IκBα. Understanding the role of ozone in the initiation of inflammatory processes on the animal ocular surface and in cultured human conjunctival epithelial cells can help elucidate the pathogenesis of ocular surface damage and suggest protective strategies for preserving a healthy ocular surface against ozone exposure.

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.

Effect of aqueous ozone on the NF-kappaB system

Ozone has been proposed as an alternative oral antiseptic in dentistry, due to its antimicrobial power reported for gaseous and aqueous forms, the latter showing a high biocompatibility with mammalian cells. New therapeutic strategies for the treatment of periodontal disease and apical periodontitis should consider not only antibacterial effects, but also their influence on the host immune response. Therefore, our aim was to investigate the effect of aqueous ozone on the NF-kappaB system, a paradigm for inflammation-associated signaling/transcription. We showed that NF-kappaB activity in oral cells stimulated with TNF, and in periodontal ligament tissue from root surfaces of periodontally damaged teeth, was inhibited following incubation with ozonized medium. Under this treatment, IkappaBalpha proteolysis, cytokine expression, and kappaB-dependent transcription were prevented. Specific ozonized amino acids were shown to represent major inhibitory components of ozonized medium. In summary, our study establishes a condition under which aqueous ozone exerts inhibitory effects on the NF-kappaB system, suggesting that it has an anti-inflammatory capacity.

Ozone-induced cell death mediated with oxidative and calcium signaling pathways in tobacco bel-w3 and bel-B cell suspension cultures

Ozone (O(3))-induced cell death in two suspension-cultured cell lines of tobacco (Nicotiana tabacum L.) derived from Bel-W3 (hyper-sensitive to O(3)) and Bel-B (highly tolerant to O(3)) varieties were studied. By exposing the newly prepared cell lines to the pulse of ozonized air, we could reproduce the conditions demonstrating the difference in O(3) sensitivity as observed in their original plants, depending on the exposure time. Since O(3)-induced acute cell death was observed in the dark, the requirement for photochemical reactions could be eliminated. Addition of several ROS scavengers and chelators inhibited the cell death induced by O(3), indicating that singlet oxygen ((1)O(2)), hydrogen peroxide (H(2)O(2)), hydroxyl radical and redox-active metals such as Fe(2+) play central roles in O(3)-induced acute damages to the cells. As expected, we observed the generation of (1)O(2) and H(2)O(2) in the O(3)-treated cells using chemiluminescent probes. On the other hand, an NADPH oxidase inhibitor, superoxide dismutase (SOD), and some SOD mimics showed no inhibitory effect. Thiols added as antioxidants unexpectedly behaved as prooxidants drastically enhancing the O(3)-induced cell death. It is noteworthy that some ROS scavengers effectively rescued the cells from dying even treated after the pulse of O(3) exposure, confirming the post-ozone progress of ROS-dependent cell death mechanism. Since one of the key differences between Bel-B and Bel-W3 was suggested to be the capacity for ROS detoxification by catalase, the endogenous catalase activities were compared in vivo in two cell lines. As expected, catalase activity in Bel-B cells was ca. 7-fold greater than that in Bel-W3 cells. Interestingly, Ca(2+) chelators added prior to (not after) the pulse of O(3) effectively inhibited the induction of cell death. In addition, increases in cytosolic Ca(2+) concentration sensitive to Ca(2+) chelators, ion channel blockers, and ROS scavengers were observed in the transgenic Bel-W3 cells expressing aequorin, suggesting the action of Ca(2+) as a secondary messenger initiating the oxidative cell death. The O(3)-induced calcium response in Bel-W3 cells was much greater than Bel-B cells. Based on the results, possible pathways for O(3)-dependent generation of the lethal level of ROS and corresponding signaling mechanism for induction of cell death were discussed.

The ortho hydroxy-amino group: another choice for synthesizing novel antioxidants

Four ortho hydroxy-amino derivatives have been designed based on the structures of flavonoids to explore the effect of the ortho hydroxy-amino group on the antioxidant properties of molecules, and their bond dissociation enthalpies (BDE), ionization potentials (IP), the highest occupied molecular orbitals (HOMO), and spin densities have been calculated. The results reveal that the ortho hydroxy-amino group plays an important role in promoting the antioxidant properties of molecules because of its lowering effect on BDE, IP, and spin density. The derivatives with ortho hydroxy-amino group show stronger antioxidant activity than the derivatives with mono hydroxy or ortho dihydroxy group. Thus, the ortho hydroxy-amino group can be used as another potential functional group to synthesize novel antioxidants as guessed.

Hydrogen peroxide-scavenging properties of normal human airway secretions

To examine the antioxidant capacity of normal human airway secretions and to characterize its molecular components, tracheal lavages were obtained from eight patients intubated for elective surgery and free of lung disease. These samples (20 microl, approximately 6.8 microg of protein) scavenged 0.57 +/- 0.09 nmol of added 0.96 nmol hydrogen peroxide (H2O2) within 10 minutes at room temperature (n = 8). The scavenging activity was inhibited 60 +/- 4% by azide (an inhibitor of heme-containing peroxidases and catalase) and 42 +/- 9% by dapsone (an inhibitor of lactoperoxidase). Mercaptosuccinic acid (an inhibitor of glutathione peroxidase) did not significantly inhibit H2O2 scavenging by these secretions. Fourfold diluted secretions showed only nonenzymatic scavenging activity, but the addition of thiocyanate to these samples (0.4 mM; substrate for lactoperoxidase) restored their ability to scavenge H2O2. The addition of reduced glutathione (8 microM) only enhanced nonenzymatic scavenging activity. These data provide evidence that multiple enzymatic and nonenzymatic systems coexist in human airway secretions that contribute to H2O2 scavenging. It appears, however, that H2O2 is mainly consumed by the lactoperoxidase system.

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.

Vanilloid (capsaicin) receptors influence inflammatory sensitivity in response to particulate matter

The signs of airway inflammation and hyperresponsiveness that occur in animals exposed to air pollutants are often strain- and species-specific. To investigate the underlying causes of this phenomenon, BALB/c and C57bl/6 mice were exposed intratracheally to residual oil fly ash (ROFA, 3 mg/kg) and examined after 24 h for signs of airway inflammation. BALB/c showed significantly higher numbers of neutrophils and increased airway hyperresponsiveness in response to methacholine challenge, whereas B6 mice showed no significant change in either inflammatory endpoint. To determine the underlying cause of this strain specificity, cultures of dorsal root ganglion (DRG) sensory neurons, which innervate the upper airways in situ, were explanted from both BALB/c and B6 fetal mice. After 5-7 days in culture, they were exposed to ROFA, other urban and industrial particulate matter (PM; e.g., oil fly ash, woodstove, Mt. St. Helen, St. Louis, Ottawa, coal fly ash) or to prototype irritants (e.g., capsaicin 3-10 microM, pH 5.0 and 6.5). In all instances (except for woodstove), DRG neurons from BALB/c mice released significantly higher levels of the pro-inflammatory cytokine IL-6 into their nutrient media relative to neurons from B6 mice. This cytokine release could be significantly reduced for all PM treated cultures (except woodstove) by pretreatment of cultures with capsazepine (CPZ), a competitive antagonist of vanilloid receptors. DRG neurons, cultured from BALB/c and B6 neonates, were loaded with Fluo-3 AM and exposed to the prototype irritants, acid pH (5.0, 6.5), or capsaicin (3, 10 microM). Analysis of their increases in intracellular calcium showed that significantly higher numbers of BALB/c neurons responded to these prototype irritants, relative to B6 neurons. Morphometric analysis of BALB/c neurons, histochemically stained with cobalt to label neurons bearing capsaicin-sensitive receptors, showed a significantly higher level of stained neurons relative to B6 neurons. Finally, semiquantitative RT-PCR showed a higher expression of VR1 receptor mRNA in DRG and spinal cord taken from neonatal BALB/c mice relative to B6 mice. Taken together, these data suggest that capsaicin and acid-sensitive irritant receptors, located on somatosensory cell bodies and their nerve fiber terminals, subserve PM-induced airway inflammation and are quantitatively different in responsive and nonresponsive mouse strains.

CULTEX--an alternative technique for cultivation and exposure of cells of the respiratory tract to airborne pollutants at the air/liquid interface

The assessment of cytotoxicity of air contaminants such as gaseous or particulate compounds and complex mixtures has traditionally involved animal experiments, due to the difficulties in exposing cell cultures directly to these substances. New cultivation and exposure techniques enhance the efficiency of in vitro studies, as demonstrated by a new experimental system called CULTEX which allows direct exposure of cells at the air/liquid interface. In this case, human bronchial epithelial cells are cultivated on porous transwell membranes in a device allowing intermittent medium supply. The medium is pumped into a special modular culture unit through the transwell membrane supporting the cells. At certain time intervals, the medium is completely removed and the cells can be maintained and exposed at the air/liquid interface until the next medium supply without loss of viability. In comparison to conventional submersed culture conditions, the cells have been grown on transwell membranes using the new pulse submersion technique. There are no deleterious effects on cell viability due to the direct exposure to airborne pollutants. Thus, the introduction of these new cultivation and exposure techniques offers new testing strategies for the toxicological evaluation of inhalable soluble and inert substances as well as complex mixtures.

Effects of low ozone-oxygen concentrations on the acetylcholine release at the mouse neuromuscular junction

The use of a mixture of low concentrations of ozone (O3) with oxygen (O2) have been proved to be useful in different human pathological conditions. Owing to a lack of both pharmacological and epidemiological basic studies, the scientific consideration of this therapeutic potential is still inappropriate. Here, we started, from an electrophysiological point of view, a study on the possible effects of low O3 doses on the acetylcholine (ACh) release at the neuromuscular junction. Indeed, some experimental conditions indicate a positive effect either in maintaining cytosolic calcium (Ca2+) homeostasis or in increasing the efficacy of the intracellular antioxidant systems. Furthermore, a positive action on the kinetics of some antioxidant enzymes must be taken into account as a possible molecular mechanism in the regulation of the function of cellular homeostasis. Our data demonstrate a reduction of evoked ACh release in the mouse neuromuscular junction. O3 affects neither the spontaneous ACh release nor the kinetics of the ACh-receptor-channel complex. The results are compatible with a reduction of intracellular Ca2+ and proved a molecular action of O3.

IL-8 is one of the major chemokines produced by monkey airway epithelium after ozone-induced injury

A rhesus monkey interleukin (IL)-8 cDNA clone with >94% homology to the human IL-8 gene was isolated by differential hybridization from a cDNA library of distal airways after ozone inhalation. In situ hybridization and immunohistochemistry showed increased IL-8 mRNA and protein levels in epithelial cells at 1 h but not at 24 h after inhalation of ozone. The appearance of IL-8 in airway epithelial cells correlated well with neutrophil influx into airway epithelia and lumens. Air-liquid interface cultures of tracheobronchial epithelial cells were exposed to ozone in vitro. We observed a transient increase in IL-8 secretion in culture medium immediately after ozone exposure and a dose-dependent increase in IL-8 secretion and mRNA production. In vitro neutrophil chemotaxis showed a parallel dose and time profile to epithelial cell secretion of IL-8. Treatment with anti-IL-8 neutralizing antibody blocked >80% of the neutrophil chemotaxis in vitro. These results suggest that IL-8 is a key chemokine in acute ozone-induced airway inflammation in primates.