Effects of cyclo-oxygenase inhibition on ozone-induced respiratory inflammation and lung function changes

Ozone in the Development of Pediatric Asthma and Atopic Disease

Ozone (O3) is a ubiquitous outdoor air pollutant, which may be derived from various primary pollutants such as nitrates, hydrocarbons, and volatile organ compounds through ultraviolet radiation exposure, and has been shown to negatively impact respiratory health. O3 is the most common noninfectious environmental cause of asthma exacerbations among children and adults. Its effects on pediatric respiratory health could be due to multiple physiologic factors that may contribute to enhanced O3 exposure seen in children compared with adults, including differences in lung surface area per unit of body weight and ventilation rates. O3 can reach the distal regions of human lungs due to its low water solubility, resulting in either injury or activation of airway epithelial cells and macrophages. Multiple epidemiologic studies have highlighted a link between exposure to air pollution and the development of asthma. This review article specifically focuses on examining the impact of early life O3 exposure on lung development, lung function, and the risk of developing atopic diseases including asthma, allergic rhinitis, and atopic dermatitis among children.

Desensitization of the Cough Reflex Induced by Corticosteroids in Ovalbumin-Sensitized Rabbits During Artificial Limb Exercise

Introduction

Cough is a major symptom frequently experienced during exercise, mainly in asthmatic patients. Inhaled glucocorticoids represent the keystone treatment in the management of asthma, but little is known about interactions between cough and exercise, especially in controlled patients. During exercise, cough reflex (CR) appears downregulated in healthy animal models whereas a lack of desensitization of CR has been shown in ovalbumin-sensitized animal models, mimicking asthmatic disease.

Aims and Objectives

The goal of our study was to clarify the potential modulation of the CR induced by inhaled corticosteroids (CS) in ovalbumin (OVA) sensitized rabbits during artificial limb exercise.

Materials and Methods

Seventeen OVA sensitized rabbits were studied. Among them, 9 were treated with CS delivered intravenously (OVA-Corticoids). The ventilatory response to direct tracheal stimulation, performed at rest and during exercise, was determined to assess the incidence and the sensitivity of the CR. Broncho-alveolar lavage (BAL) and cell counts were performed to determine the level of airway inflammation. Exercise was mimicked by electrically induced hindlimb muscular contractions (EMC).

Results

Compared to rest values, EMC increased minute ventilation by 28% without any decrease in respiratory resistance (Rsr). Among 322 tracheal stimulations, 172 (53%) were performed at rest and 150 (47%) during exercise. The sensitivity of CR decreased during artificial limb exercise compared to baseline in OVA-Corticoids rabbits (p = 0.0313) while it remained unchanged in OVA rabbits (p = NS).

Conclusion

Corticosteroids appear to restore the desensitization of the CR in OVA sensitized rabbits during artificial limb exercise, suggesting the potential role of airway inflammation in the pathophysiology of cough during exercise in asthmatics.

Exercise-Induced Bronchoconstriction and the Air We Breathe

An association between airway dysfunction and airborne pollutant inhalation exists. Volatilized airborne fluorocarbons in ski wax rooms, particulate matter, and trichloromines in indoor environments are suspect to high prevalence of exercise-induced bronchoconstriction and new-onset asthma in athletes competing in cross-country skiing, ice rink sports, and swimming. Ozone is implicated in acute decreases in lung function and the development of new-onset asthma from exposure during exercise. Mechanisms and genetic links are proposed for pollution-related new-onset asthma. Oxidative stress from airborne pollutant inhalation is a common thread to progression of airway damage. Key pollutants and mechanisms for each are discussed.

Down-Regulation of Cough during Exercise Is Less Frequent in Healthy Children than Adults. Role of the Development and/or Atopy?

Cough is typically associated with physical activity in children with asthma, but the characteristics of the relationship between cough and exercise has not been established under physiological conditions. The aim of the study was to describe the effect of exercise on the reflex cough response elicited by a single breath of capsaicin in non-asthmatic children. A group of non-asthmatic adults was studied as reference. Thirty children and 29 adults were recruited. The cough reflex sensitivity to capsaicin was first determined to establish the dose that provokes 5 cough efforts (C5). The number of coughs elicited by C5 (NC5) was then compared at baseline and during a standardized submaximal treadmill exercise. Data are expressed as median (interquartile range). Children and adults showed a significant decrease in NC5 (respectively from 5.0 (4.0–6.0) to 2.5 (2.0–4.0), p < 0.0005 and from 6.0 (5.0–7.0) to 2.0 (0.0–3.0, p < 0.0005). During exercise, NC5 was observed to decrease in all adult subjects, but in only 24/30 children (80%, p = 0.02). A trend for a higher incidence of personal and familial atopy was observed in children that lacked cough down-regulation during exercise compared with other children. It is concluded that the cough reflex response to capsaicin is down regulated by exercise in both children and adults. The effect however is less consistently observed in the former. The difference may reflect maturation of descending inhibitory pathways of the cough reflex, but may also be associated to atopy. The data stress the importance of assessing the time relationship of cough and exercise in questionnaire studies of asthma.

Linking physiological parameters to perturbations in the human exposome: Environmental exposures modify blood pressure and lung function via inflammatory cytokine pathway

Human biomonitoring is an indispensable tool for evaluating the systemic effects derived from external stressors including environmental pollutants, chemicals from consumer products, and pharmaceuticals. The aim of this study was to explore consequences of environmental exposures to diesel exhaust (DE) and ozone (O₃) and ultimately to interpret these parameters from the perspective of in vitro to in vivo extrapolation. In particular, the objective was to use cytokine expression at the cellular level as a biomarker for physiological systemic responses such as blood pressure and lung function at the systemic level. The values obtained could ultimately link in vivo behavior to simpler in vitro experiments where cytokines are a measured parameter. Human exposures to combinations of DE and O₃ and the response correlations between forced exhaled volume in 1 second (FEV₁), forced vital capacity (FVC), systolic and diastolic blood pressure (SBP and DBP, respectively), and 10 inflammatory cytokines in blood (interleukins 1β, 2, 4, 5, 8, 10, 12p70 and 13, IFN-γ, and TNF-α) were determined in 15 healthy human volunteers. Results across all exposures revealed that certain individuals displayed greater inflammatory responses compared to the group and, generally, there was more between-person variation in the responses. Evidence indicates that individuals are more stable within themselves and are more likely to exhibit responses independent of one another. Data suggest that in vitro findings may ultimately be implemented to elucidate underlying adverse outcome pathways (AOP) for linking high-throughput toxicity tests to physiological in vivo responses. Further, this investigation supports assessing subjects based upon individual responses as a complement to standard longitudinal (pre vs. post) intervention grouping strategies. Ultimately, it may become possible to predict a physiological (systemic) response based upon cellular-level (in vitro) observations.

Mechanisms of the acute effects of inhaled ozone in humans

Ambient air ozone (O3) is generated photochemically from oxides of nitrogen and volatile hydrocarbons. Inhaled O3 causes remarkably reversible acute lung function changes and inflammation. Approximately 80% of inhaled O3 is deposited on the airways. O3 reacts rapidly with CC double bonds in hydrophobic airway and alveolar surfactant-associated phospholipids and cholesterol. Resultant primary ozonides further react to generate bioactive hydrophilic products that also initiate lipid peroxidation leading to eicosanoids and isoprostanes of varying electrophilicity. Airway surface liquid ascorbate and urate also scavenge O3. Thus, inhaled O3 may not interact directly with epithelial cells. Acute O3-induced lung function changes are dominated by involuntary inhibition of inspiration (rather than bronchoconstriction), mediated by stimulation of intraepithelial nociceptive vagal C-fibers via activation of transient receptor potential (TRP) A1 cation channels by electrophile (e.g., 4-oxo-nonenal) adduction of TRPA1 thiolates enhanced by PGE2-stimulated sensitization. Acute O3-induced neutrophilic airways inflammation develops more slowly than the lung function changes. Surface macrophages and epithelial cells are involved in the activation of epithelial NFkB and generation of proinflammatory mediators such as IL-6, IL-8, TNFa, IL-1b, ICAM-1, E-selectin and PGE2. O3-induced partial depolymerization of hyaluronic acid and the release of peroxiredoxin-1 activate macrophage TLR4 while oxidative epithelial cell release of EGFR ligands such as TGFa or EGFR transactivation by activated Src may also be involved. The ability of lipid ozonation to generate potent electrophiles also provides pathways for Nrf2 activation and inhibition of canonical NFkB activation. This article is part of a Special Issue entitled Air Pollution, edited by Wenjun Ding, Andrew J. Ghio and Weidong Wu.

Diesel exhaust modulates ozone-induced lung function decrements in healthy human volunteers

The potential effects of combinations of dilute whole diesel exhaust (DE) and ozone (O₃), each a common component of ambient airborne pollutant mixtures, on lung function were examined. Healthy young human volunteers were exposed for 2 hr to pollutants while exercising (~50 L/min) intermittently on two consecutive days. Day 1 exposures were either to filtered air, DE (300 μg/m³), O₃ (0.300 ppm), or the combination of both pollutants. On Day 2 all exposures were to O₃ (0.300 ppm), and Day 3 served as a followup observation day. Lung function was assessed by spirometry just prior to, immediately after, and up to 4 hr post-exposure on each exposure day. Functional pulmonary responses to the pollutants were also characterized based on stratification by glutathione S-transferase mu 1 (GSTM1) genotype. On Day 1, exposure to air or DE did not change FEV1 or FVC in the subject population (n = 15). The co-exposure to O₃ and DE decreased FEV1 (17.6%) to a greater extent than O₃ alone (9.9%). To test for synergistic exposure effects, i.e., in a greater than additive fashion, FEV1 changes post individual O₃ and DE exposures were summed together and compared to the combined DE and O₃ exposure; the p value was 0.057. On Day 2, subjects who received DE exposure on Day 1 had a larger FEV1 decrement (14.7%) immediately after the O₃ exposure than the individuals' matched response following a Day 1 air exposure (10.9%). GSTM1 genotype did not affect the magnitude of lung function changes in a significant fashion. These data suggest that altered respiratory responses to the combination of O₃ and DE exposure can be observed showing a greater than additive manner. In addition, O₃-induced lung function decrements are greater with a prior exposure to DE compared to a prior exposure to filtered air. Based on the joint occurrence of these pollutants in the ambient environment, the potential exists for interactions in more than an additive fashion affecting lung physiological processes.

Challenge models to assess new therapies in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality. Current therapies confer partial benefits either by incompletely improving airflow limitation or by reducing acute exacerbations, hence new therapies are desirable. In the absence of robust early predictors of clinical efficacy, the potential success of novel therapeutic agents in COPD will not entirely be known until the drugs enter relatively large and costly clinical trials. New predictive models in humans, and new study designs are being sought to allow for confirmation of pharmacodynamic and potentially clinically meaningful effects in early development. This review focuses on human challenge models with lipopolysaccharide endotoxin, ozone, and rhinovirus, in the early clinical development phases of novel therapeutic agents for the treatment and reduction of exacerbations in COPD.

The effect of environmental oxidative stress on airway inflammation

PURPOSE OF REVIEW

Asthma is an inflammatory respiratory condition with significantly associated morbidity and mortality that is increasing in prevalence. Air pollution is an important factor in both the development of asthma and in asthma exacerbations. Oxidative stress as a result of exposure to air pollution and underlying genetic polymorphisms that may play a role in susceptibility to this oxidative stress are the subject of current investigation. This article reviews the data regarding the effects of air pollution on the innate immune response and potential clinical and treatment implications of how genetic polymorphisms affect this response.

RECENT FINDINGS

Recent investigation reveals how pollutant-induced oxidative stress impacts airway inflammatory responses. Work by our study group demonstrates that asthmatic patients have an exaggerated inflammatory response to air pollution-induced oxidative stress. New trials investigating antioxidants as potential therapeutic interventions may target this specific issue.

SUMMARY

Air pollution plays a critical role in asthma and may affect certain patients more than others. Further investigation into the genetic polymorphisms that affect inflammatory responses may help target patient populations at greatest risk for air pollution-induced asthma and may provide new therapeutic options for these patient populations.

Impact of aging on pulmonary responses to acute ozone exposure in mice: role of TNFR1

CONTEXT

Chamber studies in adult humans indicate reduced responses to acute ozone with increasing age. Age-related changes in TNFα have been observed. TNFα induced inflammation is predominantly mediated through TNFR1.

OBJECTIVE

To examine the impact of aging on inflammatory responses to acute ozone exposure in mice and determine the role of TNFR1 in age-related differences.

MATERIALS AND METHODS

Wildtype and TNFR1 deficient (TNFR1(-/-)) mice aged 7 or 39 weeks were exposed to ozone (2 ppm for 3 h). Four hours after exposure, bronchoalveolar lavage (BAL) was performed and BAL cells, cytokines, chemokines, and protein were examined.

RESULTS

Ozone-induced increases in BAL neutrophils and in neutrophil chemotactic factors were lower in 39- versus 7-week-old wildtype, but not (TNFR1(-/-)) mice. There was no effect of TNFR1 genotype in 7-week-old mice, but in 39-week-old mice, BAL neutrophils and BAL concentrations of MCP-1, KC, MIP-2, IL-6 and IP-10 were significantly greater following ozone exposure in TNFR1(-/-) versus wildtype mice. BAL concentrations of the soluble form of the TNFR1 receptor (sTNFR1) were substantially increased in 39-week-old versus 7-week-old mice, regardless of exposure.

DISCUSSION AND CONCLUSION

The data suggest that increased levels of sTNFR1 in the lungs of the 39-week-old mice may neutralize TNFα and protect these older mice against ozone-induced inflammation.

The role of oxidative stress and innate immunity in O(3) and endotoxin-induced human allergic airway disease

Ozone (O(3)) and endotoxin are common environmental contaminants that cause asthma exacerbation. These pollutants have similar phenotype response characteristics, including induction of neutrophilic inflammation, changes in airway macrophage immunophenotypes, and ability to enhance response to inhaled allergen. Evoked phenotyping studies of volunteers exposed to O(3) and endotoxin were used to identify the response characteristics of volunteers to these pollutants. New studies support the hypotheses that similar innate immune and oxidant processes modulate response to these agents. These include TLR4 and inflammasome-mediated signaling and cytokine production. Innate immune responses are also impacted by oxidative stress. It is likely that continued discovery of common molecular processes which modulate response to these pollutants will occur. Understanding the pathways that modulate response to pollutants will also allow for discovery of genetic and epigenetic factors that regulate response to these pollutants and determine risk of disease exacerbation. Additionally, defining the mechanisms of response will allow rational selection of interventions to examine. Interventions focused on inhibition of Toll-like receptor 4 and inflammasome represent promising new approaches to preventing pollutant-induced asthma exacerbations. Such interventions include specific inhibitors of innate immunity and antioxidant therapies designed to counter the effects of pollutants on cell signaling.

20-HETE mediates ozone-induced, neutrophil-independent airway hyper-responsiveness in mice

Background

Ozone, a pollutant known to induce airway hyper-responsiveness (AHR), increases morbidity and mortality in patients with obstructive airway diseases and asthma. We postulate oxidized lipids mediate in vivo ozone-induced AHR in murine airways.

Methodology/Principal Findings

Male BALB/c mice were exposed to ozone (3 or 6 ppm) or filtered air (controls) for 2 h. Precision cut lung slices (PCLS; 250 µm thickness) containing an intrapulmonary airway (∼0.01 mm² lumen area) were prepared immediately after exposure or 16 h later. After 24 h, airways were contracted to carbachol (CCh). Log EC₅₀ and E_max values were then calculated by measuring the airway lumen area with respect to baseline. In parallel studies, dexamethasone (2.5 mg/kg), or 1-aminobenzotriazol (ABT) (50 mg/kg) were given intraperitoneal injection to naïve mice 18 h prior to ozone exposure. Indomethacin (10 mg/kg) was administered 2 h prior. Cell counts, cytokine levels and liquid chromatography-mass spectrometry (LC-MS) for lipid analysis were assessed in bronchoalveolar lavage (BAL) fluid from ozone exposed and control mice. Ozone acutely induced AHR to CCh. Dexamethasone or indomethacin had little effect on the ozone-induced AHR; while, ABT, a cytochrome P450 inhibitor, markedly attenuated airway sensitivity. BAL fluid from ozone exposed animals, which did not contain an increase in neutrophils or interleukin (IL)-6 levels, increased airway sensitivity following in vitro incubation with a naïve PCLS. In parallel, significant increases in oxidized lipids were also identified using LC-MS with increases of 20-HETE that were decreased following ABT treatment.

Conclusions/Significance

These data show that ozone acutely induces AHR to CCh independent of inflammation and is insensitive to steroid treatment or cyclooxygenase (COX) inhibition. BAL fluid from ozone exposed mice mimicked the effects of in vivo ozone exposure that were associated with marked increases in oxidized lipids. 20-HETE plays a pivotal role in mediating acute ozone-induced AHR.

Environmental and occupational allergies

Airborne allergens are the major cause of allergic rhinitis and asthma. Daily exposure comes from indoor sources, chiefly at home but occasionally at schools or offices. Seasonal exposure to outdoor allergens, pollens, and molds is another important source. Exposure to unusual substances at work causes occupational asthma, accounting for about 5% of asthma in adults. Indoor and outdoor air pollutants trigger airway inflammation and increase the severity of asthma. Diesel exhaust particles increase the production of IgE antibodies. Identification and reduction of exposure to allergens is a very important part of the management of respiratory allergic diseases. The first section of this chapter discusses domestic allergens, arthropods (mites and cockroaches), molds, and mammals (pets and mice). Indoor humidity and water damage are important factors in the production of mite and mold allergens, and discarded human food items are important sources of proliferation of cockroaches and mice. Means of identifying and reducing exposure are presented. The second section discusses outdoor allergens: pollens and molds. The particular plants or molds and the amount of exposure to these allergens is determined by the local climate, and local pollen and mold counts are available to determine the time and amount of exposure. Climate change is already having an important effect on the distribution and amount of outdoor allergens. The third section discusses indoor and outdoor air pollution and methods that individuals can take to reduce indoor pollution in addition to eliminating cigarette smoking. The fourth section discusses the diagnosis and management of occupational asthma.

Fluticasone propionate protects against ozone-induced airway inflammation and modified immune cell activation markers in healthy volunteers

BACKGROUND

Ozone exposure induces airway neutrophilia and modifies innate immune monocytic cell-surface phenotypes in healthy individuals. High-dose inhaled corticosteroids can reduce O(3)-induced airway inflammation, but their effect on innate immune activation is unknown.

OBJECTIVES

We used a human O(3) inhalation challenge model to examine the effectiveness of clinically relevant doses of inhaled corticosteroids on airway inflammation and markers of innate immune activation in healthy volunteers.

METHODS

Seventeen O(3)-responsive subjects [>10% increase in the percentage of polymorphonuclear leukocytes (PMNs) in sputum, PMNs per milligram vs. baseline sputum] received placebo, or either a single therapeutic dose (0.5 mg) or a high dose (2 mg) of inhaled fluticasone proprionate (FP) 1 hr before a 3-hr O(3) challenge (0.25 ppm) on three separate occasions at least 2 weeks apart. Lung function, exhaled nitric oxide, sputum, and systemic biomarkers were assessed 1-5 hr after the O(3) challenge. To determine the effect of FP on cellular function, we assessed sputum cells from seven subjects by flow cytometry for cell-surface marker activation.

RESULTS

FP had no effect on O(3)-induced lung function decline. Compared with placebo, 0.5 mg and 2 mg FP reduced O(3)-induced sputum neutrophilia by 18% and 35%, respectively. A similar effect was observed on the airway-specific serum biomarker Clara cell protein 16 (CCP16). Furthermore, FP pretreatment significantly reduced O(3)-induced modification of CD11b, mCD14, CD64, CD16, HLA-DR, and CD86 on sputum monocytes in a dose-dependent manner.

CONCLUSIONS

This study confirmed and extended data demonstrating the protective effect of FP against O(3)-induced airway inflammation and immune cell activation.

Regulation of caveolin-1 expression, nitric oxide production and tissue injury by tumor necrosis factor-alpha following ozone inhalation

Alveolar macrophages (AM) and inflammatory mediators including nitric oxide and peroxynitrite contribute to ozone-induced lung injury. The generation of these mediators is regulated, in part, by the transcription factor NF-kappaB. We previously demonstrated a critical role for NF-kappaB p50 in ozone-induced injury. In the present studies mechanisms regulating NF-kappaB activation in the lung after ozone inhalation were analyzed. Treatment of wild type (WT) mice with ozone (0.8 ppm, 3 h) resulted in a rapid increase in NF-kappaB binding activity in AM, which persisted for at least 12 h. This was not evident in mice lacking TNFalpha which are protected from ozone-induced injury; there was also no evidence of nitric oxide or peroxynitrite production in lungs from these animals. These data demonstrate that TNFalpha plays a role in NF-kappaB activation and toxicity. TNFalpha signaling involves PI-3-kinase (PI3K)/protein kinase B (PKB), and p44/42 MAP kinase (MAPK) which are important in NF-kappaB activation. Ozone Inhalation resulted in rapid and transient increases in p44/42 MAPK and PI3K/PKB in AM from WT mice, which was evident immediately after exposure. Caveolin-1, a transmembrane protein that negatively regulates PI3K/PKB and p44/42 MAPK signaling, was downregulated in AM from WT mice after ozone exposure. In contrast, ozone had no effect on caveolin-1, PI3K/PKB or p44/42 MAPK expression in AM from TNFalpha knockout mice. These data, together with our findings that TNFalpha suppressed caveolin-1 expression in cultured AM, suggest that TNFalpha and downstream signaling mediate activation of NF-kappaB and the regulation of inflammatory genes important in ozone toxicity, and that this process is linked to caveolin-1.

Breath condensate levels of 8-isoprostane and leukotriene B4 after ozone inhalation are greater in sensitive versus nonsensitive subjects

Ozone (O3) inhalation induces pulmonary function decrements and inflammation. The present study was designed to determine if a relationship exists between O3 induced pulmonary function changes and the presence of inflammatory markers as measured in exhaled breath condensates (EBCs) obtained from O3-sensitive and nonsensitive human subjects. Eight healthy adult volunteers (4 males/4 females, age 18 to 30 years) were studied, characterized as to their ozone sensitivity and placed into 2 groups (sensitive and nonsensitive) with each group having 2 males and 2 females. Subjects completed a 20-minute EBC collection and pulmonary function test (PFT) prior to a single 60-minute bout of cycle ergometer exercise (V(E) = 50-55 L/min) while breathing filtered air (FA) or 0.35 ppm O3. Subjective symptom scores (SSSs) were collected at 6, 20, 40, and 60 minutes during exposure. An immediate postexposure PFT was performed followed by an EBC collection. Subjective symptom scores, EBCs, and PFTs were collected at 1, 4 and 8 hours post exposure. EBCs were analyzed for prostaglandin E2 (PGE2), leukotriene B4 (LTB4), 8-isoprostane, and total nitric oxide (NO) metabolites (nitrate + nitrite content). Sensitive subjects, breathing O3, had significantly greater functional decrements in PFTs, increased SSSs, and increased rapid shallow breathing as well as elevated levels of 8-isoprostane and LTB4 in EBCs compared to those breathing FA. In addition, there were significant increases in nitrate + nitrite content in both sensitive and nonsensitive subjects breathing O3 compared to FA. These results indicate that sensitive subjects have elevated arachidonic acid metabolites in EBCs compared to nonsensitive subjects after O3 inhalation.

Type I interleukin-1 receptor is required for pulmonary responses to subacute ozone exposure in mice

Interleukin (IL)-1, a proinflammatory cytokine, is expressed in the lung after ozone (O(3)) exposure. IL-1 mediates its effects through the type I IL-1 receptor (IL-1RI), the only signaling receptor for both IL-1alpha and IL-1beta. The purpose of this study was to determine the role of IL-1RI in pulmonary responses to O(3.) To that end, wild-type, C57BL/6 (IL-1RI(+/+)) mice and IL-1RI-deficient (IL-1RI(-/-)) mice were exposed to O(3) either subacutely (0.3 ppm for 72 h) or acutely (2 ppm for 3 h). Subacute O(3) exposure increased bronchoalveolar lavage fluid (BALF) protein, interferon-gamma-inducible protein (IP)-10, soluble tumor necrosis factor receptor 1 (sTNFR1), and neutrophils in IL-1RI(+/+) and IL-1RI(-/-) mice. With the exception of IP-10, all outcome indicators were reduced in IL-1RI(-/-) mice. Furthermore, subacute O(3) exposure increased IL-6 mRNA expression in IL-1RI(+/+), but not IL-1RI(-/-) mice. Acute (2 ppm) O(3) exposure increased BALF protein, IL-6, eotaxin, KC, macrophage inflammatory protein (MIP)-2, IP-10, monocyte chemotactic protein-1, sTNFR1, neutrophils, and epithelial cells in IL-1RI(+/+) and IL-1RI(-/-) mice. For IL-6, eotaxin, MIP-2, and sTNFR1, there were small but significant reductions of these outcome indicators in IL-1RI(-/-) versus IL-1RI(+/+) mice at 6 hours after exposure, but not at other time points, whereas other outcome indicators were unaffected by IL-1RI deficiency. These results suggest that IL-1RI is required for O(3)-induced pulmonary inflammation during subacute O(3) exposure, but plays a more minor role during acute O(3) exposure. In addition, these results suggest that the induction of IL-6 via IL-1RI may be important in mediating the effects of O(3) during subacute exposure.

Effects of ambient ozone exposure on mail carriers' peak expiratory flow rates

The extent to which occupational exposure to ozone in ambient air can affect lung function remains unclear. We conducted a panel study in 43 mail carriers by measuring their peak expiratory flow rates (PEFRs) twice daily for 6 weeks in 2001. The daily exposure of each mail carrier to O3, particulate matter < 10 microm in aerodynamic diameter (PM10), and nitrogen dioxide was estimated by one air monitoring station in the center of the mail carrier's delivery area. Hourly concentrations of air pollutants during their exposure periods were 6-96 ppb for O3, 11-249 microg/m3 for PM10, and 14-92 ppb for NO2. Linear mixed-effects models were used to estimate the association between air pollution exposures and PEFR after adjusting for subject's sex, age, and disease status and for temperature and humidity. We found that night PEFR and the deviation in night PEFR were significantly decreased in association with 8-hr O3 exposures with a lag 0-2 days and by daily maximum O3 exposures with a lag of 0-1 day in our multipollutant models. By contrast, neither PM10 nor NO2 was associated with a PEFR reduction. Daily 8-hr mean concentrations of O3 had greater reduction effects on PEFR than did daily maximum concentrations. For a 10-ppb increase in the 8-hr average O3 concentration, the night PEFR was decreased by 0.54% for a 0-day lag, 0.69% for a 1-day lag, and 0.52% for a 2-day lag. We found that an acute lung function reduction occurs in mail carriers exposed to O3 concentrations below current ambient air quality standards and occupational exposure limits.

CXCR2 is essential for maximal neutrophil recruitment and methacholine responsiveness after ozone exposure

Ozone (O(3)), a common air pollutant, induces airway inflammation and airway hyperresponsiveness. In mice, the neutrophil chemokines KC and macrophage inflammatory protein-2 (MIP-2) are expressed in the lungs following O(3) exposure. The purpose of this study was to determine whether CXCR2, the receptor for these chemokines, is essential to O(3)-induced neutrophil recruitment, injury to lungs, and increases in respiratory system responsiveness to methacholine (MCh). O(3) exposure (1 ppm for 3 h) increased the number of neutrophils in the bronchoalveolar lavage fluid (BALF) of wild-type (BALB/c) and CXCR2-deficient mice. However, CXCR2-deficient mice had significantly fewer emigrated neutrophils than did wild-type mice. The numbers of neutrophils in the blood and concentrations of BALF KC and MIP-2 did not differ between genotypes. Together, these data suggest CXCR2 is essential for maximal chemokine-directed migration of neutrophils to the air spaces. In wild-type mice, O(3) exposure increased BALF epithelial cell numbers and total protein levels, two indirect measures of lung injury. In contrast, in CXCR2-deficient mice, the number of BALF epithelial cells was not increased by O(3) exposure. Responses to inhaled MCh were measured by whole body plethysmography using enhanced pause as the outcome indicator. O(3) exposure increased responses to inhaled MCh in both wild-type and CXCR2-deficient mice 3 h after O(3) exposure. However, at 24 h after exposure, responses to inhaled MCh were elevated in wild-type but not CXCR2-deficient mice. These results indicate CXCR2 is essential for maximal neutrophil recruitment, epithelial cell sloughing, and persistent increases in MCh responsiveness after an acute O(3) exposure.

Responses to ozone are increased in obese mice

Epidemiological data indicate an increased incidence of asthma in overweight adults and children. Ozone (O3) is a common trigger for asthma. Accordingly, the purpose of this study was to compare O3-induced airway hyperresponsiveness and airway inflammation in lean, wild-type (C57BL/6J) mice and mice that are obese as a consequence of a genetic defect in the gene encoding the satiety hormone leptin (ob/ob mice). The ob/ob mice eat excessively and weighed more than twice as much as age- and gender-matched wild-type mice. Airway responsiveness to intravenous methacholine was measured by forced oscillation. In air-exposed controls, baseline pulmonary resistance was greater, and the dose of methacholine required to double pulmonary resistance was lower in ob/ob than wild-type mice. Exposure to O3 (2 parts/million for 3 h) caused AHR and airway inflammation in both groups of mice, but responses to O3 were enhanced in ob/ob compared with wild-type mice. Administration of exogenous leptin did not reverse the enhanced inflammatory response observed in ob/ob mice, but augmented airway inflammation in wild-type mice. The inhaled dose of O3 per gram of lung tissue was greater in ob/ob than wild-type mice. Our results indicate that O3-induced airway responses are enhanced in ob/ob mice and suggest that inhaled O3 dose may be one factor contributing to this difference, but other aspects of the obese phenotype may also contribute. Our results also indicate that the hormone leptin, which is increased in the obese, has the capacity to increase airway inflammation.

Ozone-induced airway hyperresponsiveness is reduced in immature mice

During ozone (O(3)) exposure, adult mice decrease their minute ventilation (VE). To determine whether there are age-related differences in the ventilatory response to O(3), A/J mice, aged 2, 4, 8, or 12 wk, were exposed to O(3) (0.3-3.0 parts/million for 3 h) in nose-only exposure plethysmographs. Baseline VE normalized for body weight (VE/g) decreased with increasing age, consistent with the higher metabolic rates of younger animals. O(3) caused a concentration-related decrease in VE in mice of all ages, but the response was significantly less in 2-wk-old than in older mice. The increased baseline VE/g and smaller decrements in VE induced by O(3) in immature mice resulted in an inhaled dose of O(3) normalized for body weight that was three to four times higher than in adult mice. O(3) exposure caused a dose-related increase in airway responsiveness in 8- and 12-wk-old mice but did not cause airway hyperresponsiveness at any dose in either 2- or 4-wk-old mice, although higher inhaled doses of O(3) normalized for body weight were delivered to these younger animals. Interleukin-6 and macrophage inflammatory protein-2 levels in bronchoalveolar lavage fluid were also increased in 8-wk-old compared with 2-wk-old mice exposed to O(3). The results suggest that immature mice are less sensitive than adult mice to O(3), at least in terms of the ability of O(3) to induce airway hyperresponsiveness and promote release of certain cytokines.

Effect of antioxidant supplementation on ozone-induced lung injury in human subjects

To determine whether antioxidants can influence human susceptibility to ozone (O(3))-induced changes in lung function and airway inflammation, we placed 31 healthy nonsmoking adults (18 to 35 yr old) on a diet low in ascorbate for 3 wk. At 1 wk, subjects were exposed to filtered air for 2 h while exercising (20 L/min/m(2)), and then underwent bronchoalveolar lavage (BAL) and were randomly assigned to receive either a placebo or 250 mg of vitamin C, 50 IU of alpha-tocopherol, and 12 oz of vegetable cocktail daily for 2 wk. Subjects were then exposed to 0.4 ppm O(3) for 2 h and underwent a second BAL. On the day of the O(3) exposure, supplemented subjects were found to have significantly increased levels of plasma ascorbate, tocopherols, and carotenoids as compared with those of the placebo group. Pulmonary function testing showed that O(3)-induced reductions in FEV(1) and FVC were 30% and 24% smaller, respectively, in the supplemented cohort. In contrast, the inflammatory response to O(3) inhalation, as represented by the percent neutrophils and the concentration of interleukin-6 recovered in the BAL fluid at 1 h after O(3) exposure was not different for the two groups. These data suggest that dietary antioxidants protect against O(3)-induced pulmonary function decrements in humans.

Tumor necrosis factor receptor 2 contributes to ozone-induced airway hyperresponsiveness in mice

The purpose of this study was to determine whether tumor necrosis factor (TNF) contributes to airway hyperresponsiveness (AHR) and migration of polymorphonuclear leukocytes (PMN) into the airways following exposure to ozone (O(3)). Wild-type mice, TNF p55 or p75 receptor knockout mice (p55 TNFR -/- and p75 TNFR -/-), as well as double receptor knockout mice (p55/p75 TNFR -/-), were exposed to O(3). Three hours after cessation of O(3), airway responses to inhaled methacholine were determined by whole body plethysmography using changes in enhanced pause (Penh) as an index of airway narrowing. In wild-type mice, O(3) exposure (0.5 ppm, 3 h) caused a significant increase in airway responsiveness as indicated by a 1.2 log leftward shift in the methacholine dose- response curve. In contrast, in p55/p75 TNFR -/- mice, O(3) caused only a 0.5 log shift in the dose-response curve (p < 0.05 compared with wild-type). Similar results were obtained in p75 TNFR -/- mice. In contrast, O(3)-induced airway hyperresponsiveness was not different in WT and p55 TNFR -/- mice. During O(3) exposure (1 pm, 3 h), minute ventilation (V E) decreased by 64 +/- 4% in wild-type, but only 24 +/- 5% in p55/p75 TNFR -/- mice, indicating that despite their reduced O(3)-induced AHR, the TNFR-deficient mice actually inhaled a greater dose of O(3). Similar results were obtained in p75 -/- mice, whereas changes in V E induced by O(3) were the same in wild-type and p55 -/- mice. PMN numbers in bronchoalveolar lavage fluid recovered 21 h after cessation of exposure to O(3) (2 ppm, 3 h) were significantly increased compared with after air exposure but were not different in wild-type and p55/p75 TNFR -/- mice. Our results indicate that TNF contributes to the AHR but not the PMN emigration induced by acute O(3) exposure.

KEYWORDS

whole body plethysmography; polymorphonuclear leukocytes; minute ventilation; knockout mice; methacholine

Exercise and outdoor ambient air pollution

OBJECTIVES

To establish by literature survey: (a) levels at which air pollutants are considered damaging to human health and to exercisers in particular; (b) the current ambient levels experienced in the United Kingdom; (c) whether athletes are especially at risk.

METHODS

Six major urban air pollutants were examined: carbon monoxide (CO); nitrogen oxides (NO(X)); ozone (O(3)); particulate matter (PM(10)); sulphur dioxide (SO(2)); volatile organic compounds (VOCs).

RESULTS

CO is detrimental to athletic performance. NO(2) is of concern to human health, but outdoor levels are low. O(3) poses a potentially serious risk to exercising athletes. Decrements in lung function result from exposure, and there is evidence that athletic performance may be affected. Detrimental effects may occur at low ambient levels, but there is no scientific consensus on this matter. PM(10) is causing concern in the scientific community. Blood lead accumulation during exercise indicates that personal exposure to toxic compounds associated with PM(10) may be magnified. Generally, outdoor ambient levels of SO(2) are too low to cause a problem to the athlete, except the asthmatic athlete. The few studies on exposure of exercisers to VOCs are reviewed.

CONCLUSIONS

Athletes and exercisers should avoid exercising by the road side even though levels of the more noxious air pollutants have been controlled in the United Kingdom. O(3) is particularly damaging to athletes; it reaches its highest concentrations on hot bright days in rural areas.

Cyclooxygenase metabolites play a different role in ozone-induced pulmonary function decline in asthmatics compared to normals

Indomethacin has been used to demonstrate that cyclooxygenase (COX) metabolites of arachidonic acid play a mechanistic role in ozone-induced spirometric decline in normals (Nm). Since the weight of evidence suggests that asthmatics (Asth) do not differ substantially from Nm subjects in the magnitude of their spirometric response to ozone, we sought to determine whether COX metabolites play a similar role in the asthmatic response to ozone. Thirteen (n = 13) Asth and nine (n = 9) Nm volunteers were pretreated with indomethacin or placebo (3 days, 75 mg/day), then exposed for 2 h to 400 ppb ozone or clean air while performing mild intermittent exercise (Vi(min) = 30 L/min.). Baseline changes in spirometry (FVC, FEV(1), FEF(25), FEF(50), FEF(60p), FEF(75)) and soluble markers of COX metabolism (prostaglandin [PG] F2-alpha) were measured from induced sputum samples. Results showed similar reductions in FVC (Asth = 12%, Nm = 10%) and FEV(1) (Asth = 13%, Nm = 11%) in Asth and Nm following ozone. Variables representing small-airways function demonstrated the greatest ozone-induced decline in Asth (FEF(75) = 25%). Indomethacin pretreatment significantly attenuated ozone-induced decreases in FVC and FEV(1) in Nm, but not in Asth. Marked attenuation of ozone-induced decrements in FEF(75) and FEF(60p) was observed in Asth but not in Nm. PGF2-alpha levels were similar in both groups prior to ozone exposure with indomethacin (Asth = 65 pg/ml, Nm = 59 pg/ml), but postexposure levels in Asth were significantly elevated (118 pg/ml) compared to Nm (54 pg/ml). We conclude that COX metabolites, such as PGF2-alpha, play an important but different role in asthmatics than normals with respect to ozone-induced pulmonary function decline. Specifically, COX metabolites contribute to restrictive-type changes in normals and obstructive-type changes in small airways in asthmatics.

Effect of ozone on diesel exhaust particle toxicity in rat lung

Ambient particulate matter (PM) concentrations have been associated with mortality and morbidity. Diesel exhaust particles (DEP) are present in ambient urban air PM. Coexisting with DEP (and PM) is ozone (O(3)), which has the potential to react with some components of DEP. Some reports have shown increased lung injury in rats coexposed to PM and O(3), but it is unclear whether this increased injury was due to direct interaction between the pollutants or via other mechanisms. To examine whether O(3) can directly react with and affect PM bioactivity, we exposed DEP to O(3) in a cell-free in vitro system and then examined the bioactivity of the resultant DEP in a rat model of lung injury. Standard Reference Material 2975 (diesel exhaust PM) was initially exposed to 0.1 ppm O(3) for 48 h and then instilled intratracheally in Sprague-Dawley rats. Rat lung inflammation and injury was examined 24 h after instillation by lung lavage. The DEP exposed to 0.1 ppm O(3) was more potent in increasing neutrophilia, lavage total protein, and LDH activity compared to unexposed DEP. The increased DEP activity induced by the O(3) exposure was not attributable to alteration by air that was also present during the O(3) exposure. Exposure of DEP to a higher O(3) concentration (1.0 ppm) led to a decreased bioactivity of the particles. In contrast, carbon black particles, low in organic content relative to DEP, did not exhibit an increase in any of the bioactivities examined after exposure to 0.1 ppm O(3). DEP incorporated O(3) (labeled with (18)O) in a linear fashion. These data suggest that ambient concentrations of O(3) can increase the biological potency of DEP. The ozonized DEP may play a role in the induction of lung responses by ambient PM.

Time course of response to ozone exposure in healthy adult females

Ozone exposure causes acute decrements in pulmonary function, increases airway responsiveness, and changes the breathing pattern. We examined these responses in 19 ozone-responsive (DeltaFEV(1) > 5%) young females exposed to both air and 0.35 ppm ozone. The randomized 75-min exposures included two 30-min exercise periods at V(E) approximately 40 L/min. Responses were measured before, during, and after exposure and at 18 and 42 h postexposure. FVC, FEV(1), and FIV(0.5) decreased (p <.01) immediately postexposure by 13.2%, 19.9%, and 20.8%, respectively, and the airway responsiveness was significantly increased. Raw increased (p <.05), while TGV remained essentially unchanged. At 18 h postexposure, the airways were still hyperresponsive and FEV(1) and FIV(0.5) were still 5% below the preexposure levels. There were no residual effects in any of the variables at 42 h postexposure. During exercise in ozone the tidal volume was decreased (-14%) and respiratory frequency increased (+15%). The changes in airway responsiveness were not related to changes in spirometric measurements. We found no significant differences between postair and postozone mouth occlusion pressure (Pm(0.1)) and the hypercapnic response to CO(2) rebreathing. We conclude that ozone induced typical acute changes in airway responsiveness and that ventilatory (exercise), spirometric (inspiratory and expiratory), and plethysmographic pulmonary function may show some residual effects for up to 18 h after exposure. The ozone-induced alteration in breathing pattern during exercise does not appear to be related to a change in ventilatory drive.

Short-term effect of ozone on the pulmonary function of children in primary school

The objective of this study was to evaluate the short-term effect of ambient air pollution on the pulmonary function of schoolchildren. We sampled 941 children in primary school in three communities in Taiwan (Sanchun, Taihsi, and Linyuan). The nearby stations of the Taiwan air quality monitoring network provided the hourly ambient concentrations of sulfur dioxide, carbon monoxide, ozone, particulate matter < or = to 10 microm in aerodynamic diameter, and nitrogen dioxide. Spirometry was performed once for each sampled child. We also obtained the status of indoor air pollution and chronic respiratory disease history by using a structured questionnaire. Multivariate linear model analysis was used to evaluate pulmonary function effects of each pollutant in addition to determinants of indoor air pollution and meteorologic conditions. We found a significantly negative association of peak O(3) concentration on the day before spirometry with individual forced vital capacity and forced expiratory volume in 1 sec. The decrease in children's lung function can occur at peak hourly O(3) concentrations < 80 ppb. The slope of lung function decrease for Taiwanese children is approximately 1 mL/ppb for peak hourly O(3) exposure.

A comparison of biomarkers of ozone exposure in human plasma, nasal lavage, and sputum

We examined ozone-induced upper and lower airway inflammatory responses and the concentrations of hydroxylated salicylate metabolites using nasal lavage fluid and induced sputum, in order to identify noninvasive and sensitive biomarkers for ozone exposure and effects. A time course for plasma concentration of 2, 3-dihydroxybenzoic acid (2,3-DHBA, a salicylate metabolite and an indicator for hydroxyl radical) in response to 0.12 ppm ozone was also studied. Healthy, young, nonsmoking volunteers were given acetylsalicylic acid (ASA, 975 mg) or placebo orally. Subjects were exposed to ozone (0.12 or 0.4 ppm) or filtered air in an environmental chamber for 2 h, while performing intermittent exercise. Blood was collected hourly over a 4-h period. After exposure, nasal lavage fluid was collected, and sputum was induced using hypertonic saline. Results show that in sputum the percentage of neutrophils was significantly higher after the subjects were exposed to 0.4 ppm ozone (p<.05) than after they were exposed to filtered air or 0.12 ppm ozone. The absolute number and the percentage of macrophages were significantly lower at 0.4 ppm ozone than for filtered air control or 0.12 ppm ozone. The percentage of lymphocytes in sputum was also significantly lower at 0.4 ppm ozone than for filtered air control or 0.12 ppm ozone. The sputum cellular responses to ozone were not significantly altered by ASA treatment. In nasal lavage, cell counts and differentials did not change significantly after exposure to ozone in comparison to filtered air control. The cellular data indicate an acute inflammation developed during ozone exposure in the lower respiratory tract. The concentrations of total protein and interleukin-8 and the activity of N-acetyl-beta-D-glucosaminidase (a lysosomal enzyme) in nasal lavage and sputum did not change significantly following exposure to ozone in comparison to filtered air control. Plasma 2,3-DHBA concentration increased significantly following exposure to 0.12 ppm ozone in an exposure-dependent temporal pattern. Salicylate metabolites in nasal lavage fluid and sputum did not increase significantly following exposure to ozone. There was a marked variation of 2,3-DHBA concentrations in airway fluids. Data suggest that plasma 2,3-DHBA is a sensitive marker indicating acute ozone exposure, even at an ozone concentration that causes minimal observable airway effects in healthy subjects.

Antioxidant supplementation and respiratory functions among workers exposed to high levels of ozone

Ozone exposure has been related to adverse respiratory effects, in particular to lung function decrements. Antioxidant vitamins are free-radical scavengers and could have a protective effect against photo-oxidant exposure. To evaluate whether acute effects of ozone on lung functions could be attenuated by antioxidant vitamin supplementation, we conducted a randomized trial using a double-blind crossover design. Street workers (n = 47) of Mexico City were randomly assigned to take daily a supplement (75 mg vitamin E, 650 mg vitamin C, 15 mg beta carotene) or a placebo and were followed from March to August 1996. Pulmonary function tests were done twice a week at the end of the workday. During the follow-up, the mean 1-h maximum ozone level was 123 ppb (SD = 40). During the first phase, ozone levels were inversely associated with FVC (beta = -1.60 ml/ppb), FEV1 (beta = -2.11 ml/ppb), and FEF25-75 (beta = -4.92 ml/ppb) (p < 0.05) in the placebo group but not in the supplement group. The difference between the two groups was significant for FVC, FEV1, and FEF25-75 (p < 0.01). During the second phase, similar results were observed, but the lung function decrements in the placebo group were smaller, suggesting that the supplementation may have had a residual protective effect on the lung. These results need to be confirmed in larger supplementation studies.

In vivo salicylate hydroxylation: a potential biomarker for assessing acute ozone exposure and effects in humans

Ozone is known to yield hydroxyl radical, which may contribute to ozone-mediated lung injury. In the presence of hydroxyl radical, salicylate is hydroxylated to form 2,3-dihydroxybenzoic acid (2,3-DHBA). There is no evidence of enzymatic formation of 2,3-DHBA. We hypothesized that salicylate hydroxylation might be used as a biomarker indicating human exposure to ozone. Healthy, nonsmoking volunteers, 18 to 34 yr of age, were given acetylsalicylic acid (975 mg) or placebo orally 0.5 h before an exposure. Subjects were exposed to ozone (0.12 or 0.4 ppm) or filtered air in an environmental chamber for 2 h, while performing intermittent exercise. Results indicate significant decrements in FVC, FEV1.0, forced expiratory flows at 50% and 75% of FVC, and peak expiratory flow rate, and an increase in airway resistance, after exposure to 0.4 ppm ozone in comparison with air control (p < 0.05). Exposure to 0.4 ppm ozone also resulted in increased symptom numbers and severity (p < 0.05). When subjects were exposed to 0.12 ppm ozone, changes of pulmonary function and symptoms reported were minimal. Plasma concentration of 2,3-DHBA was significantly increased after exposure to 0.12 and 0.4 ppm ozone in comparison with air control (p < 0.05). There was a significant correlation between ozone-induced changes of pulmonary function and normalized salicylate hydroxylation (p < 0.05). The results indicate that exposure to ozone can initiate in vivo production of hydroxyl radical, a potent reactive agent. Salicylate hydroxylation may then serve as a sensitive dosimetric biomarker for ozone exposure, even at subclinical ozone exposure levels.