Rat lung recovery from 3 days of continuous exposure to 0.75 ppm ozone

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.

Ozone and ozonated oils in skin diseases: a review

Although orthodox medicine has provided a variety of topical anti-infective agents, some of them have become scarcely effective owing to antibiotic- and chemotherapeutic-resistant pathogens. For more than a century, ozone has been known to be an excellent disinfectant that nevertheless had to be used with caution for its oxidizing properties. Only during the last decade it has been learned how to tame its great reactivity by precisely dosing its concentration and permanently incorporating the gas into triglycerides where gaseous ozone chemically reacts with unsaturated substrates leading to therapeutically active ozonated derivatives. Today the stability and efficacy of the ozonated oils have been already demonstrated, but owing to a plethora of commercial products, the present paper aims to analyze these derivatives suggesting the strategy to obtain products with the best characteristics.

Acute ozone-induced differential gene expression profiles in rat lung

Ozone is an oxidant gas that can directly induce lung injury. Knowledge of the initial molecular events of the acute O3 response would be useful in developing biomarkers of exposure or response. Toward this goal, we exposed rats to toxic concentrations of O3 (2 and 5 ppm) for 2 hr and the molecular changes were assessed in lung tissue 2 hr postexposure using a rat cDNA expression array containing 588 characterized genes. Gene array analysis indicated differential expression in almost equal numbers of genes for the two exposure groups: 62 at 2 ppm and 57 at 5 ppm. Most of these genes were common to both exposure groups, suggesting common roles in the initial toxicity response. However, we also identified the induction of nine genes specific to 2-ppm (thyroid hormone-beta receptor c-erb-A-beta; and glutathione reductase) or 5-ppm exposure groups (c-jun, induced nitric oxide synthase, macrophage inflammatory protein-2, and heat shock protein 27). Injury markers in bronchoalveolar lavage fluid (BALF) were used to assess immediate toxicity and inflammation in rats similarly exposed. At 2 ppm, injury was marked by significant increases in BALF total protein, N-acetylglucosaminidase, and lavageable ciliated cells. Because infiltration of neutrophils was observed only at the higher 5 ppm concentration, the distinctive genes suggested a potential amplification role for inflammation in the gene profile. Although the specific gene interactions remain unclear, this is the first report indicating a dose-dependent direct and immediate induction of gene expression that may be separate from those genes involved in inflammation after acute O3 exposure.

Induction of stress proteins and MMP-9 by 0.8 ppm of ozone in murine skin

Ozone (O(3)) is among the most reactive environmental oxidant pollutants to which cutaneous tissues are exposed. O(3) exposure has been shown to induce antioxidant depletion as well as the oxidation of lipids and proteins within the outermost skin layer, the stratum corneum. However, relatively little is known regarding the potential effects of O(3) on the cellular constituents of the underlying skin epidermis and dermis. In the present study, hairless mice exposed for 6 h to 0.8 ppm O(3) showed increases in lipid peroxidation, as quantitated by increases in 4-hydroxynonenal-protein adducts. O(3) exposure caused an induction of the stress proteins HSP27 and heme oxygenase-1 (HO-1), starting at 6 h and increasing up to 18 h after O(3) exposure. This was accompanied by an increase in matrix metalloproteinase-9 (MMP-9) mRNA and activity levels, indicative of possible injurious-reparative processes. Collectively, our data demonstrate that skin exposure to O(3) not only affects antioxidant levels and oxidation markers in the outermost stratum corneum layer, but also induces cellular stress responses in the deeper cellular layers of the skin.

Ozone exposure activates oxidative stress responses in murine skin

Ozone (O(3)) is among the most reactive environmental oxidant to which skin is exposed. O(3) exposure has previously been shown to induce antioxidant depletion as well as lipid and protein oxidation in the outermost skin layer, the stratum corneum (SC), but little is known regarding the potential effects of O(3) on the skin epidermis and dermis. To evaluate such skin responses to O(3), SKH-1 hairless mice were exposed for 2 h to 8.0 ppm O(3) or to ambient air. O(3) exposure caused a significant increase in skin carbonyls (28%) compared to the skin of air exposed control animals. An evident increase in 4-hydroxynonenal-protein adducts was detected after O(3) exposure. O(3) exposure caused a rapid up-regulation of HSP27 (20-fold), and more delayed induction of HSP70 (2.8-fold) and heme oxygenase-1 (5-fold). O(3) exposure also led to the induction of nitric oxide synthase (iNOS) 6-12 h following O(3) exposure. We conclude that skin exposure to high levels of O(3) not only affects antioxidant levels and oxidation markers in the SC, but also induces stress responses in the active layers of the skin, most likely by indirect mechanisms, since it is unlikely that O(3) itself penetrates the protective SC layers.

Inflammatory cell availability affects ozone-induced lung damage

Identifying whether or not neutrophils have a role to play in the early stages of acute lung epithelial injury brought about by inhalation of reactive substances continues to be a major area of investigation. In this study, the availability of circulating neutrophils was manipulated by treatment with either cyclophosphamide or rabbit antiserum against rat neutrophils, prior to exposures to air, a single high ozone exposure of 1 or 2 ppm for 3 h, or a continuous exposure to 0.8-1.0 ppm for up to 48 h. Although cyclophosphamide treatment resulted in undetectable levels of neutrophils in the blood, the recovery of tissue marginated-interstitial neutrophils of 1 x 10(6) cells by collagenase tissue digestion was not significantly diminished at the onset of air and ozone exposures. Cyclophosphamide treatment alone did not cause any permeability damage to air-exposed rat lungs, but did ameliorate ozone-induced increases in bronchoalveolar lavage (BAL) neutrophil and albumin recoveries after both short-term and 1 d of continuous ozone exposure. In contrast to cyclophosphamide, antiserum treatment resulted in greater than a 90% decrease in neutrophil recoveries from both blood and lung tissue at the onset of air and ozone exposures. Antiserum treatment also abrogated ozone-induced neutrophil accumulations in lung lavageable spaces following both single and continuous ozone exposures, but did not significantly affect ozone-associated lung permeability damage indicated by unaltered BAL fluid albumin recoveries. These data demonstrated that under experimental conditions when neutrophils remain within lung tissue marginated and interstitial pools, reduction in circulating blood neutrophil availability is associated with a concomitant decrease in ozone-induced lung damage.

H441 pulmonary epithelial cell mitogenic effects and signaling pathways in response to HGF and TGF-alpha

Pulmonary epithelial cells are important in lung growth, development, and injury. H441 pulmonary adenocarcinoma cells may be a useful model for studying pulmonary epithelial cell growth factor responses in vitro. Isolated pulmonary epithelial type II cells proliferate in response to transforming growth factor (TGF)-alpha via the epidermal growth factor (EGF) receptor. Type II cells also proliferate in response to hepatocyte growth factor (HGF). In the present study, H441 cell responses to these growth factors were examined, and compared to type II cells. Both the EGF-R and the c-met proto-oncogene receptor, to which HGF binds, were immunoprecipitated from H441 cells. In H441 cells, addition of TGF-alpha resulted in phosphorylation of the EGF receptor and increased cell number and tritiated thymidine incorporation. Incubation with HGF resulted in phosphorylation of its c-met proto-oncogene receptor in type II and H441 cells, and also increased cell number and tritiated thymidine incorporation. Both HGF and TGF-alpha stimulated phosphorylation of the intracellular signaling molecules p42 and p44 mitogen activated protein kinases in H441 cells. H441 cells exhibited responses to mitogenic growth factors similar to type II cells and may be useful as a model for type II cell growth factor responses and signal transduction.

Potential involvement of 4-hydroxynonenal in the response of human lung cells to ozone

Ozone is a photochemically generated pollutant that can cause acute pulmonary inflammation and induce cellular injury and may contribute to the development or exacerbation of chronic lung diseases. Despite much research, the mechanisms of ozone- and oxidant-induced cellular injury are still uncertain. Ozone and secondary free radicals have been reported to cause the formation of aldehydes in biological fluids. One of the most toxic aldehydes formed during oxidant-induced lipid peroxidation is 4-hydroxynonenal (HNE). HNE reacts primarily with Cys, Lys, and His amino acids, altering protein function and forming protein adducts. The purpose of this study was to determine whether HNE could account for the acute effects of ozone on lung cells. Human subjects were exposed to 0.4 parts/million ozone or air for 1 h with exercise (each subject served as his/her own control). Six hours after ozone exposure, cells obtained by airway lavage were examined for apoptotic cell injury, and cells from bronchoalveolar lavage were examined for apoptosis, presence of HNE adducts, and expression of stress proteins. Significant apoptosis was evident in airway lung cells after ozone exposure. Western analysis demonstrated an increase in a 32-kDa HNE protein adduct and a number of stress proteins, viz., 72-kDa heat shock protein and ferritin, in alveolar macrophages (AM) after ozone exposure. All of these effects could be replicated by in vitro exposure of AM to HNE. Consequently, the in vitro results and demonstration of HNE protein adducts after ozone exposure are consistent with a potential role for HNE in the cellular toxic effects of ozone.

Repeated subacute ozone exposure of inbred mice: airway inflammation and ventilation

The present study was designed to assess the effects of repeated subacute ozone (O3) exposure on pulmonary inflammation and ventilation in two inbred strains of mice differentially susceptible to a single O3 exposure. Susceptible C57BL/6J (B6) and resistant C3H/HeJ (C3) mice were exposed to 0.3 ppm O3 for 48 and 72 h and, after 14 days recovery, both strains were reexposed. Airway inflammation and lung injury were assessed by counting inflammatory cells and measuring total protein content and lactate dehydrogenase (LDH) activity in bronchoalveolar lavage (BAL) returns. Minute ventilation [VE, the product of breathing frequency (f), and tidal volume (VT)] was measured prior to and immediately following each exposure. After the initial exposure, B6 mice developed greater O3-induced increases in total protein, inflammatory cell influx, and LDH activity compared to C3 mice. In normal air, VE was also significantly elevated in B6, but not C3, mice after O3. The hypercapnic f of B6 and hypercapnic VT of C3 mice were significantly altered after O3 exposure. Reexposure to O3 caused a smaller increase in the numbers of macrophages, lymphocytes, epithelial cells, and BAL protein in both strains, and no changes in LDH activity. However, the number of polymorphonuclear leukocytes significantly increased in B6 and C3 mice as compared to the initial O3 exposure. In both strains, the ventilatory responses to normal air or hypercapnia were largely reproducible after O3 reexposure. Results indicated that differential susceptibility to O3-induced inflammation was maintained in B6 and C3 mice with O3 reexposure although the magnitude of the difference was reduced. Results also suggest that the ventilatory responses to O3 in B6 and C3 mice were reproducible with reexposure, and that airway inflammation and ventilation were not codependent.

Messenger RNA levels of lung extracellular matrix proteins during ozone exposure

Continuous exposure of rats to ozone has been shown to result in lung epithelial damage, inflammation, and subsequent increases in collagen content. The main goal of this study was to identify the earliest time point of altered extracellular matrix protein gene expression by utilizing Northern blot analyses of rat lungs continuously exposed to 1.0 ppm ozone for 14 days. An early increase of steady-state fibronectin mRNA levels was observed at 2 days of exposure, prior to the time point of increased type I collagen mRNA, which was seen at 4 days. This increased level of type I collagen mRNA preceded measurable changes in total lung collagen content, observed at 7 days. In addition, peak levels of the growth-related proto-oncogene c-myc mRNA could be correlated with maximal increases of lung DNA content, although the initial increase in c-myc mRNA preceded measurable changes of total lung DNA. The use of specific cDNA probes for measuring altered gene expression can be useful for defining the early cellular and molecular events in ozone-induced lung injury.

Lung mitochondrial function following oxygen exposure and diethyl maleate-induced depletion of glutathione

Diethyl maleate (DEM) pretreatment has previously been shown to result in a transient depletion of lung glutathione and an associated decrease of the time to the onset of rat mortality resulting from exposures to 100% oxygen in vivo. The effects of oxygen exposure on mitochondrial energy metabolism were assessed by measurements of ADP-stimulated rates of O2 utilization by lung homogenates prepared from untreated and DEM-treated rats following 4 and 24 hr of exposure to either air or 100% oxygen. Twenty-four hours of oxygen exposure of untreated rats resulted in significant decreases in lung homogenate ADP-stimulated rates of respiration supported by the substrates, pyruvate, isocitrate, and alpha-ketoglutarate. No changes were observed in succinate-supported respiration, indicating that oxygen exposure appears to adversely affect NAD-linked rather than FAD-linked pathways of mitochondrial energy metabolism. The decreased lung mitochondrial glutathione, observed 4 hr following DEM treatment, returned to normal levels following 24 hr of air and oxygen exposure. No effects of glutathione depletion were observed on ADP-stimulated rates of respiratory activity 4 hr following DEM treatment. The DEM-induced transient depletion of glutathione also did not result in any additional detrimental effects on mitochondrial respiratory activity following 24 hr of oxygen exposure in vivo. These results suggested that transient mitochondrial depletion of glutathione does not accelerate the oxygen-induced impairment of mitochondrial energy metabolism. The onset of mortality associated with DEM-pretreatment might therefore result from a failure of glutathione-dependent cytosolic protective mechanisms, rather than from an increased rate of oxygen-induced mitochondrial damage.

Glutathione and GSH-dependent enzymes in bronchoalveolar lavage fluid cells in response to ozone

The purpose of this study was to determine if in vivo ozone exposure results in elevations in the levels of glutathione and glutathione-dependent enzymes in cells derived from bronchoalveolar lavage fluid (BALF). Our hypothesis was that, as part of a defense mechanism against oxygen toxicity, such cells would have increased levels of glutathione (GSH) in response to an oxidant stress. Female F344/N rats were exposed to 0.8 ppm ozone, 6 hr/day, for 1, 3, or 7 days, after which cells were collected by lung lavage. The GSH and GSH-peroxidase activity per milligram of protein in the cellular fraction, both necessary for reducing cellular peroxides, were elevated after 3 days of ozone exposure. After 7 days of exposure, cellular GSH had returned to control values, but the activity of glutathione reductase, the enzyme that reduces oxidized glutathione to GSH, was increased. Extracellular GSH concentration and glutathione reductase activity in BALF were also increased after 7 days of exposure. The total glutathione equivalents (GSH and GSSG, both cellular and extracellular) in BALF increased throughout the 7-day exposure, with GSH increasing first in the cells, and then in the extracellular fluid. This study demonstrated that the glutathione anti-oxidant system of BALF cells is stimulated by exposure to ozone. This response may serve to protect cells from the toxic effects of oxidant stress.

Species differences in impairment and recovery of alveolar macrophage functions following single and repeated ozone exposures

Effects of single (0.4 ppm for 3, 6, or 12 hr) and repeated (0.4 ppm, 12 hr/day for 3 or 7 days) in vivo ozone exposures on rat and mouse alveolar macrophage functions and cell number were investigated. Single ozone exposure of rats resulted in a small (approximately 15%) decrease in Fc-receptor-mediated phagocytosis and phorbol ester-induced superoxide production by the alveolar macrophages and was followed by recovery above control levels within 12 hr of exposure. Repeated exposures of rats for up to 7 days did not alter alveolar macrophage functions, with the exception of the effects of 3 days of exposure on superoxide production (71 +/- 9% as compared with the controls). In mice, significant changes in alveolar macrophage functions were not observed until 12 hr of exposure (at that timepoint phagocytosis was 74 +/- 2%). Repeated ozone exposures of mice did not cause a further decrease in phagocytosis (at Day 7, 74 +/- 14%). Both after 3 and 7 days of repeated ozone exposure of mice, superoxide production by the alveolar macrophages was inhibited approximately 50%. In rats and mice, repeated ozone exposures led to an increase in the number of alveolar macrophages. In mice, this increase appeared at a later time point (at Day 7 vs Day 3) and was less pronounced (at Day 7, 139 +/- 9% vs 179 +/- 17%) as compared with rats. In summary, our data show that rat and mouse alveolar macrophages have different susceptibilities to both single and repeated in vivo ozone exposures.

Effects of short-term, single and combined exposure to low-level NO2 and O3 on lung tissue enzyme activities in rats

To examine the pulmonary effects of relatively low levels of NO2 and O3, and test for any possible interaction in their effects, we exposed 3-mo-old male Sprague-Dawley rats, free of specific pathogens, to either filtered room air (control) or 1.20 ppm (2256 micrograms/m3) NO2, 0.30 ppm (588 micrograms/m3) O3, or a combination of the two oxidants continuously for 3 d. We studied a series of parameters in the lung, including lung weight, and enzyme activities related to NADPH generation, sulfhydryl metabolism, and cellular detoxification. The results showed that relative to control, exposure to NO2 caused small but nonsignificant changes in all the parameters; O3 caused significant increases in all the parameters except for superoxide dismutase; and a combination of NO2 and O3 caused increases in all the parameters, and the increases were greater than those caused by NO2 or O3 alone. Statistical analysis of the data showed that the effects of combined exposure were synergistic for 6-phosphogluconate dehydrogenase, isocitrate dehydrogenase, glutathione reductase, and superoxide dismutase activities, and additive for glutathione peroxidase and disulfide reductase activities, but indifferent from those of O3 exposure for other enzyme activities.

Oxygen radicals in lung pathology

Pulmonary tissue can be damaged in different ways, for instance by xenobiotics (paraquat, butylated hydroxytoluene, bleomycin), during inflammation, ischemia reperfusion, or exposure to mineral dust or to normobaric pure oxygen levels. Reactive oxygen species are partly responsible for the observed pulmonary tissue damage. Several mechanisms leading to toxicity are described in this review. The reactive oxygen species induce bronchoconstriction, elevate mucus secretion, and cause microvascular leakage, which leads to edema formation. Reactive oxygen species even induce an autonomic imbalance between muscarinic receptor-mediated contraction and the beta-adrenergic-mediated relaxation of the pulmonary smooth muscle. Vitamin E and selenium have a regulatory role in this balance between these two receptor responses. The autonomic imbalance might be involved in the development of bronchial hyperresponsiveness, occurring in lung inflammation. Finally, several antioxidants are discussed which may be beneficial as therapeutics in several lung diseases.

Pretreatment with EDU decreases rat lung cellular responses to ozone

The phenylurea compound EDU (N-[2-(2-oxo-1-imidazolindinyl)ethyl]-N'-phenylurea) has been shown to protect plants from the damaging effects of ozone exposure. Models of rat lung injury, based on acute exposure to 2 ppm ozone for 3 hr and on exposure to 0.85 ppm ozone for 2 days, were used to determine whether EDU pretreatment of rats protected lungs from oxidant injury. Rats were pretreated with 100 mg/kg body wt EDU by ip administration for 2 days prior to and on the days of ozone exposure. No adverse toxicological effects of EDU pretreatment were observed. Lung superoxide dismutase (SOD) and catalase (CAT) activities were significantly enhanced from 636 to 882 U/lung and from 599 to 856 U/lung, respectively. One day following acute exposure (2 ppm for 3 hr), an ozone-induced increase of polymorphonuclear leukocytes (PMNs) from 0.01 to 1.18 million cells/lung was decreased to 0.68 million by EDU pretreatment. No alteration occurred in the degree of lung permeability indicated by increased lavage fluid albumin. EDU pretreatment also significantly decreased ozone-induced increases in PMN recovery after 2 days exposure to 0.85 ppm ozone from 5.54 to 2.12 million cells/lung. However, in this second case, EDU pretreatment reduced the observed ozone damage, indicated by a decrease in lavage fluid albumin and by a decrease in the macrophage and lymphocyte infiltration associated with this length of ozone exposure. The observation that EDU-treated cultured pulmonary arterial endothelial cells increased SOD and CAT activities identified a potential lung site of EDU interaction. These data demonstrated that although EDU pretreatment appears not to prevent initial ozone damage, it does reduce the infiltration of PMNs and might therefore prevent amplification of the injury associated with this cell type.