Airway inflammation in smokers and nonsmokers with varying responsiveness to ozone

Effects of Ozone on Sickness and Depressive-like Behavioral and Biochemical Phenotypes and Their Regulation by Serum Amyloid A in Mice

Ozone (O₃) is an air pollutant that primarily damages the lungs, but growing evidence supports the idea that O₃ also harms the brain; acute exposure to O₃ has been linked to central nervous system (CNS) symptoms such as depressed mood and sickness behaviors. However, the mechanisms by which O₃ inhalation causes neurobehavioral changes are limited. One hypothesis is that factors in the circulation bridge communication between the lungs and brain following O₃ exposure. In this study, our goals were to characterize neurobehavioral endpoints of O₃ exposure as they relate to markers of systemic and pulmonary inflammation, with a particular focus on serum amyloid A (SAA) and kynurenine as candidate mediators of O₃ behavioral effects. We evaluated O₃-induced dose-, time- and sex-dependent changes in pulmonary inflammation, circulating SAA and kynurenine and its metabolic enzymes, and sickness and depressive-like behaviors in Balb/c and CD-1 mice. We found that 3 parts per million (ppm) O₃, but not 2 or 1 ppm O₃, increased circulating SAA and lung inflammation, which were resolved by 48 h and was worse in females. We also found that indoleamine 2,3-dioxygenase (Ido1) mRNA expression was increased in the brain and spleen 24 h after 3 ppm O₃ and that kynurenine was increased in blood. Sickness and depressive-like behaviors were observed at all O₃ doses (1-3 ppm), suggesting that behavioral responses to O₃ can occur independently of increased SAA or neutrophils in the lungs. Using SAA knockout mice, we found that SAA did not contribute to O₃-induced pulmonary damage or inflammation, systemic increases in kynurenine post-O₃, or depressive-like behavior but did contribute to weight loss. Together, these findings indicate that acute O₃ exposure induces transient symptoms of sickness and depressive-like behaviors that may occur in the presence or absence of overt pulmonary neutrophilia and systemic increases of SAA. SAA does not appear to contribute to pulmonary inflammation induced by O₃, although it may contribute to other aspects of sickness behavior, as reflected by a modest effect on weight loss.

Ozone-induced enhancement of airway hyperreactivity in rhesus macaques: Effects of antioxidant treatment

BACKGROUND

Ozone (O3) inhalation elicits airway inflammation and impairs treatment responsiveness in asthmatic patients. The underlying immune mechanisms have been difficult to study because of the lack of relevant experimental models. Rhesus macaques spontaneously have asthma and have a similar immune system to human subjects.

OBJECTIVES

We sought to investigate mucosal immune changes after O3 inhalation in a clinically relevant nonhuman primate asthma model and to study the effects of an antioxidant synthetic lignan (synthetic secoisolariciresinol diglucoside [LGM2605]).

METHODS

A cohort of macaques (n = 17) previously characterized with airway hyperreactivity (AHR) to methacholine was assessed (day 1). Macaques were treated (orally) with LGM2605 (25 mg/kg) or placebo twice per day for 7 days, exposed to 0.3 ppm O3 or air for 6 hours (on day 7), and studied 12 hours later (day 8). Lung function, blood and bronchoalveolar lavage (BAL) fluid immune cell profile, and bronchial brushing and blood cell mRNA expression were assessed.

RESULTS

O3 induced significant BAL fluid neutrophilia and eosinophilia and increased AHR and expression of IL6 and IL25 mRNA in the airway epithelium together with increased BAL fluid group 2 innate lymphoid cell (ILC2s), CD1c+ myeloid dendritic cell, and CD4+ T-cell counts and diminished surfactant protein D expression. Although LGM2605 attenuated some of the immune and inflammatory changes, it completely abolished O3-induced AHR.

CONCLUSION

ILC2s, CD1c+ myeloid dendritic cells, and CD4+ T cells are selectively involved in O3-induced asthma exacerbation. The inflammatory changes were partially prevented by antioxidant pretreatment with LGM2605, which had an unexpectedly disproportionate protective effect on AHR.

Short-term exposure to ambient ozone and inflammatory biomarkers in cross-sectional studies of children and adolescents: Results of the GINIplus and LISA birth cohorts

BACKGROUND

While exposure to ambient particulate matter (PM) and nitrogen dioxide (NO₂) is thought to be associated with diseases via inflammatory response, the association between exposure to ozone, an oxidative pollutant, and inflammation has been less investigated.

AIM

We analyzed associations between short-term exposure to ozone and three inflammatory biomarkers among children and adolescents.

METHODS

These cross-sectional analyses were based on two follow-ups of the GINIplus and LISA German birth cohorts. We included 1330 10-year-old and 1591 15-year-old participants. Fractional exhaled nitric oxide (FeNO) and high-sensitivity C-reactive protein (hs-CRP) were available for both age groups while interleukin (IL)-6 was measured at 10 years only. Maximum 8-h averages of ozone and daily average concentrations of NO₂ and PM with an aerodynamic diameter <10 μm (PM₁₀) were adopted from two background monitoring stations 0 (same day), 1, 2, 3, 5, 7, 10 and 14 days prior to the FeNO measurement or blood sampling. To assess associations, we utilized linear regression models for FeNO, and logistic regressions for IL-6 and hs-CRP, adjusting for potential covariates and co-pollutants NO₂ and PM₁₀.

RESULTS

We found that short-term ozone exposure was robustly associated with higher FeNO in adolescents at age 15, but not at age 10. No consistent associations were observed between ozone and IL-6 in children aged 10 years. The relationship between hs-CRP levels and ozone was J-shaped. Relatively low ozone concentrations (e.g., <120 μg/m³) were associated with reduced hs-CRP levels, while high concentrations (e.g., ≥120 μg/m³) tended to be associated with elevated levels for both 10- and 15-year-old participants.

CONCLUSIONS

Our study demonstrates significant associations between short-term ozone exposure and FeNO at 15 years of age and a J-shaped relationship between ozone and hs-CRP. The finding indicates that high ozone exposure may favor inflammatory responses in adolescents, especially regarding airway inflammation.

Respiratory Responses to Ozone Exposure. MOSES (The Multicenter Ozone Study in Older Subjects)

RATIONALE

Acute respiratory effects of low-level ozone exposure are not well defined in older adults.

OBJECTIVES

MOSES (The Multicenter Ozone Study in Older Subjects), although primarily focused on acute cardiovascular effects, provided an opportunity to assess respiratory responses to low concentrations of ozone in older healthy adults.

METHODS

We performed a randomized crossover, controlled exposure study of 87 healthy adults (59.9 ± 4.5 yr old; 60% female) to 0, 70, and 120 ppb ozone for 3 hours with intermittent exercise. Outcome measures included spirometry, sputum markers of airway inflammation, and plasma club cell protein-16 (CC16), a marker of airway epithelial injury. The effects of ozone exposure on these outcomes were evaluated with mixed-effect linear models. A P value less than 0.01 was chosen a priori to define statistical significance.

MEASUREMENTS AND MAIN RESULTS

The mean (95% confidence interval) FEV₁ and FVC increased from preexposure values by 2.7% (2.0-3.4) and 2.1% (1.3-2.9), respectively, 15 minutes after exposure to filtered air (0 ppb). Exposure to ozone reduced these increases in a concentration-dependent manner. After 120-ppb exposure, FEV₁ and FVC decreased by 1.7% (1.1-2.3) and 0.8% (0.3-1.3), respectively. A similar concentration-dependent pattern was still discernible 22 hours after exposure. At 4 hours after exposure, plasma CC16 increased from preexposure levels in an ozone concentration-dependent manner. Sputum neutrophils obtained 22 hours after exposure showed a marginally significant increase in a concentration-dependent manner (P = 0.012), but proinflammatory cytokines (IL-6, IL-8, and tumor necrosis factor-α) were not significantly affected.

CONCLUSIONS

Exposure to ozone at near ambient levels induced lung function effects, airway injury, and airway inflammation in older healthy adults. Clinical trial registered with www.clinicaltrials.gov (NCT01487005).

Lung transcriptional profiling: insights into the mechanisms of ozone-induced pulmonary injury in Wistar Kyoto rats

Acute ozone-induced pulmonary injury and inflammation are well characterized in rats; however, mechanistic understanding of the pathways involved is limited. We hypothesized that acute exposure of healthy rats to ozone will cause transcriptional alterations, and comprehensive analysis of these changes will allow us to better understand the mechanism of pulmonary injury and inflammation. Male Wistar Kyoto rats (10-12 week) were exposed to air, or ozone (0.25, 0.5 or 1.0 ppm) for 4 h and pulmonary injury and inflammation were assessed at 0-h or 20-h (n = 8/group). Lung gene expression profiling was assessed at 0-h (air and 1.0 ppm ozone, n = 3-4/group). At 20-h bronchoalveolar lavage, fluid protein and neutrophils increased at 1 ppm ozone. Numerous genes involved in acute inflammatory response were up-regulated along with changes in genes involved in cell adhesion and migration, steroid metabolism, apoptosis, cell cycle control and cell growth. A number of NRF2 target genes were also induced after ozone exposure. Based on expression changes, Rela, SP1 and TP3-mediated signaling were identified to be mediating downstream changes. Remarkable changes in the processes of endocytosis provide the insight that ozone-induced lung injury and inflammation are likely initiated by changes in cell membrane components and receptors likely from oxidatively modified lung lining lipids and proteins. In conclusion, ozone-induced injury and inflammation are preceded by changes in gene targets for cell adhesion/migration, apoptosis, cell cycle control and growth regulated by Rela, SP1 and TP53, likely mediated by the process of endocytosis and altered steroid receptor signaling.

Ozone-induced airway epithelial cell death, the neurokinin-1 receptor pathway, and the postnatal developing lung

Children are uniquely susceptible to ozone because airway and lung growth continue for an extensive period after birth. Early-life exposure of the rhesus monkey to repeated ozone cycles results in region-specific disrupted airway/lung growth, but the mediators and mechanisms are poorly understood. Substance P (SP), neurokinin-1 receptor (NK-1R); and nuclear receptor Nur77 (NR4A1) are signaling pathway components involved in ozone-induced cell death. We hypothesize that acute ozone (AO) exposure during postnatal airway development disrupts SP/NK-1R/Nur77 pathway expression and that these changes correlate with increased ozone-induced cell death. Our objectives were to 1) spatially define the normal development of the SP/NK-1R/Nur77 pathway in conducting airways; 2) compare how postnatal age modulates responses to AO exposure; and 3) determine how concomitant, episodic ozone exposure modifies age-specific acute responses. Male infant rhesus monkeys were assigned at age 1 mo to two age groups, 2 or 6 mo, and then to one of three exposure subgroups: filtered air (FA), FA+AO (AO: 8 h/day × 2 days), or episodic biweekly ozone exposure cycles (EAO: 8 h/day × 5 days/14-day cycle+AO). O3 = 0.5 ppm. We found that 1) ozone increases SP/NK-1R/Nur77 pathway expression in conducting airways, 2) an ozone exposure cycle (5 days/cycle) delivered early at age 2 mo resulted in an airway that was hypersensitive to AO exposure at the end of 2 mo, and 3) continued episodic exposure (11 cycles) resulted in an airway that was hyposensitive to AO exposure at 6 mo. These observations collectively associate with greater overall inflammation and epithelial cell death, particularly in early postnatal (2 mo), distal airways.

Effect of summer ozone concentrations on the lung function of walkers in the Medvednica Mountain Nature Park, Croatia

The study examines the influence of naturally elevated ozone concentrations and some meteorological variables on the lung function of untrained volunteers walking in an unpolluted mountain area. Forty male participants between 18 and 70 years (smokers and nonsmokers) walked at the top of Medvednica Mountain near Zagreb, Croatia, at approximately 1000 m above sea level (a.s.l.) and engaged in other recreational activities for at least 1 hour. Forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV(1)) of the participants were measured at arrival and before they left the mountain. Regression analysis showed a statistically significant influence of environmental variables on lung function tests. However, all variables together explained less than 35% variability of FVC and 41% variability of FEV(1). The results suggest that short-term exposure to ozone may affect lung function tests, but no more than temperature and humidity. FEV(1) was found to be more sensitive to ozone than FVC. Smoking habit also had an important role in subject's sensitivity to ozone.

Ozone exposure enhances mast-cell inflammation in asthmatic airways despite inhaled corticosteroid therapy

Asthmatics are recognised to be more susceptible than healthy individuals to adverse health effects caused by exposure to the common air pollutant ozone. Ozone has been reported to induce airway neutrophilia in mild asthmatics, but little is known about how it affects the airways of asthmatic subjects on inhaled corticosteroids. We hypothesised that ozone exposure would exacerbate the pre-existent asthmatic airway inflammation despite regular inhaled corticosteroid treatment. Therefore, we exposed subjects with persistent asthma on inhaled corticosteroid therapy to 0.2 ppm ozone or filtered air for 2 h, on 2 separate occasions. Lung function was evaluated before and immediately after exposure, while bronchoscopy was performed 18 h post exposure. Compared to filtered air, ozone exposure increased airway resistance. Ozone significantly enhanced neutrophil numbers and myeloperoxidase levels in airway lavages, and induced a fourfold increase in bronchial mucosal mast cell numbers. The present findings indicate that ozone worsened asthmatic airway inflammation and offer a possible biological explanation for the epidemiological findings of increased need for rescue medication and hospitalisation in asthmatic people following exposure to ambient ozone.

Critical considerations in evaluating scientific evidence of health effects of ambient ozone: a conference report

The U.S. Environmental Protection Agency (EPA), under the authority of the Clean Air Act (CAA), is required to promulgate National Ambient Air Quality Standards (NAAQSs) for criteria air pollutants, including ozone. Each NAAQS includes a primary health-based standard and a secondary or welfare-based standard. This paper considers only the science used for revision of the primary standard for ozone in 2008. This paper summarizes deliberations of a small group of scientists who met in June 2007 to review the scientific information informing the EPA Administrator's proposed revision of the 1997 standard. The Panel recognized that there is no scientific methodology that, in the absence of judgment, can define the precise numerical level, related averaging time, and statistical form of the NAAQS. The selection of these elements of the NAAQS involves policy judgments that should be informed by scientific information and analyses. Thus, the Panel members did not feel it appropriate to offer either their individual or collective judgment on the specific numerical level of the NAAQS for ozone. The Panel deliberations focused on the scientific data available on the health effects of exposure to ambient concentrations of ozone, controlled ozone exposure studies with human volunteers, long-term epidemiological studies, time- series epidemiological studies, human panel studies, and toxicological investigations. The deliberations also dealt with the issue of background levels of ozone of nonanthropogenic origin and issues involved with conducting formal risk assessments of the health impacts of current and prospective levels of ambient ozone. The scientific issues that were central to the EPA Administrator's 2008 revision of the NAAQS for ozone will undoubtedly also be critical to the next review of the ozone standard. That review should begin very soon if it is to be completed within the 5-year cycle specified in the CAA. It is hoped that this Report will stimulate discussion of these scientific issues, conduct of additional research, and conduct of new analyses that will provide an improved scientific basis for the policy judgment that will have to be made by a future EPA Administrator in considering potential revision of the ozone standard.

Early suppression of NFkappaB and IL-8 in bronchial epithelium after ozone exposure in healthy human subjects

Exposure to elevated concentrations of ozone, a common air pollutant, has been associated with numerous adverse health effects. We have previously reported the time-course of ozone-induced airway inflammation, demonstrating an early up-regulation of vascular endothelial adhesion molecules in bronchial mucosa at 1.5 hours, followed by a neutrophilic infiltration 6 hours after exposure to 0.2 ppm ozone. We hypothesized that the neutrophilic infiltration in the bronchial mucosa would reflect an early increase in bronchial epithelial expression of redox-sensitive transcription factors and kinases regulating neutrophil chemoattractant expression. To test this hypothesis, endobronchial biopsies were obtained from healthy human subjects (n = 11) 1.5 hours after 0.2 ppm of ozone and filtered air exposures (lasting for 2 hours) and stained for mitogen-activated protein kinases (MAPKs), transcription factors, and neutrophil chemoattractants. Total epithelial staining was quantified, as well as the extent of nuclear translocation. Contrary to expectation, ozone significantly suppressed total and nuclear expression of nuclear factor kappaB (NFkappaB) in bronchial epithelial cells (p = 0.02 and p = 0.003 respectively). Similarly, the total staining for phosphorylated C-jun was suppressed (p = 0.021). Expression of interleukin 8 (IL-8) in the bronchial epithelium was likewise decreased after ozone (p = 0.018), while GRO-alpha, ENA-78, C-fos, p-p38, p-JNK, and p-ERK stainings were unchanged. These data suggest that the redox-sensitive NFkappaB and activator protein 1 (AP-1) pathways within the human bronchial epithelium do not seem to be involved in the early inflammatory cell recruitment pathways in healthy subjects exposed to ozone.

Lower airway disease in asthmatics with and without rhinitis

STUDY OBJECTIVES

The purpose of this study was to determine if asthma with rhinitis and asthma without rhinitis represent distinct forms of disease.

DESIGN

We performed a prospective cross-sectional study.

PARTICIPANTS

The study included healthy controls, participants with asthma without rhinitis, and participants with both asthma and rhinitis. Interventions We compared lung function and airway inflammation between the three groups of participants.

RESULTS

We recruited 32 participants: 12 normals, 8 asthmatics without rhinitis, and 12 with rhinitis. Compared to asthmatics with rhinitis, asthmatics without rhinitis had more severe airflow limitation (FEV(1)/FVC = 60.6% [IQR = 22.8] vs. 74.8% [IQR = 7.8] and fewer induced sputum eosinophils (2.8 [IQR = 5.8] and 9.6 [IQR = 23.8], respectively). Sputum interleukin-6 correlated inversely with lung function measured by postbronchodilator FEV(1) in the study cohort (Spearman correlation coefficient = -0.55, p < 0.01).

CONCLUSIONS

Asthmatics without rhinitis tend to have lower lung function and less eosinophilic inflammation in the lung. This small study suggests that asthmatics without rhinitis represent a distinct phenotype of asthma in which low lung function is dissociated from eosinophilic cellular inflammation, and it suggests that larger studies addressing this phenotype are warrented.

The temporal dynamics of ozone-induced FEV1 changes in humans: an exposure-response model

Although ozone is known to induce reversible decrements in forced expiratory volume in 1 s (FEV1), no exposure-response model has been identified that accurately describes the dynamics of response to the changing concentrations and activity patterns of normal ambient human exposure. The purpose of the current analysis was to identify and evaluate a dynamic model of FEV1 response using a large existing data set (541 volunteers, 864 exposures, 3485 FEV1 measures) with a wide range of exposure conditions (ozone = 0.0 to 0.4 ppm, activity level = rest to heavy exercise, duration = 1 to 7.6 h), including recovery in clean air. A previously described model containing a differential equation and a logistic function was modified to include a new between-subjects variance structure and was fitted to the data. The model described well the mean observed response data across the range of exposure conditions, including the periods of recovery in clean air. Predicted values of individual responses were distributed lognormally and appeared to accurately describe the distribution of observed responses. We observed that responsiveness to ozone decreased with age, that response was weakly related to body size, and that response was marginally more sensitive to changes in ozone concentration than to changes in minute ventilation. In summary, we have identified a dynamic ozone exposure-response model that accurately describes the temporal pattern of FEV1 response to a wide range of changing exposure conditions and that may have utility for predicting population responses to ambient exposures.

Lung injury after ozone exposure is iron dependent

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

Nasal effects of a mixture of volatile organic compounds and their ozone oxidation products

OBJECTIVE

Our objective was to determine if low levels of a mixture of volatile organic compounds (VOCs) and their ozone (O3) oxidation products, similar to what might be found in "sick buildings," cause nasal irritation and inflammation under controlled exposure conditions.

METHODS

Healthy, nonsmoking women (n=130) completed 2-hour controlled exposures to VOCs, VOCs and O3, and a masked air "MA" control in random order at least 1 week apart. VOCs and O3 concentrations were approximately 25 mg/m and approximately 40 ppb, respectively. Nasal symptoms were rated before, during, and after exposure. Nasal lavage fluid was analyzed for polymorphonuclear cells, total protein, interleukin-6, and interleukin-8.

RESULTS

We found no significant differences in symptoms or markers of nasal inflammation between exposure conditions.

CONCLUSIONS

Results suggest that VOCs and their oxidation products may not cause acute nasal effects at low concentrations.

Ozone and PM2.5 exposure and acute pulmonary health effects: a study of hikers in the Great Smoky Mountains National Park

To address the lack of research on the pulmonary health effects of ozone and fine particulate matter (</= 2.5 microm in aerodynamic diameter; PM2.5) on individuals who recreate in the Great Smoky Mountains National Park (USA) and to replicate a study performed at Mt. Washington, New Hampshire (USA) , we conducted an observational study of adult (18-82 years of age) day hikers of the Charlies Bunion trail during 71 days of fall 2002 and summer 2003. Volunteer hikers performed pre- and posthike pulmonary function tests (spirometry), and we continuously monitored ambient O3, PM2.5, temperature, and relative humidity at the trailhead. Of the 817 hikers who participated, 354 (43%) met inclusion criteria (nonsmokers and no use of bronchodilators within 48 hr) and gave acceptable and reproducible spirometry. For these 354 hikers, we calculated the posthike percentage change in forced vital capacity (FVC) , forced expiratory volume in 1 sec (FEV1) , FVC/FEV1, peak expiratory flow, and mean flow rate between 25 and 75% of the FVC and regressed each separately against pollutant (O3 or PM2.5) concentration, adjusting for age, sex, hours hiked, smoking status (former vs. never) , history of asthma or wheeze symptoms, hike load, reaching the summit, and mean daily temperature. O3 and PM2.5 concentrations measured during the study were below the current federal standards, and we found no significant associations of acute changes in pulmonary function with either pollutant. These findings are contrasted with those in the Mt. Washington study to examine the hypothesis that pulmonary health effects are associated with exposure to O3 and PM2.5 in healthy adults engaged in moderate exercise. .

Modulatory effects of ozone on THP-1 cells in response to SP-A stimulation

Ozone (O(3)), a major component of air pollution and a strong oxidizing agent, can lead to lung injury associated with edema, inflammation, and epithelial cell damage. The effects of O(3) on pulmonary immune cells have been studied in various in vivo and in vitro systems. We have shown previously that O(3) exposure of surfactant protein (SP)-A decreases its ability to modulate proinflammatory cytokine production by cells of monocyte/macrophage lineage (THP-1 cells). In this report, we exposed THP-1 cells and/or native SP-A obtained from bronchoalveolar lavage of patients with alveolar proteinosis to O(3) and studied cytokine production and NF-kappaB signaling. The results showed 1) exposure of THP-1 cells to O(3) significantly decreased their ability to express TNF-alpha in response to SP-A; TNF-alpha production, under these conditions, was still significantly higher than basal (unstimulated) levels in filtered air-exposed THP-1 cells; 2) exposure of both THP-1 cells and SP-A to O(3) did not result in any significant differences in TNF-alpha expression compared with basal levels; 3) O(3) exposure of SP-A resulted in a decreased ability of SP-A to activate the NF-kappaB pathway, as assessed by the lack of significant increase and decrease of the nuclear p65 subunit of NF-kappaB and cytoplasmic IkappaBalpha, respectively; and 4) O(3) exposure of THP-1 cells resulted in a decrease in SP-A-mediated THP-1 cell responsiveness, which did not seem to be mediated via the classic NF-kappaB pathway. These findings indicate that O(3) exposure may mediate its effect on macrophage function both directly and indirectly (via SP-A oxidation) and by involving different mechanisms.

Ozone-induced bronchial epithelial cytokine expression differs between healthy and asthmatic subjects

BACKGROUND

Ozone (O3) is a common air pollutant associated with adverse health effects. Asthmatics have been suggested to be a particularly sensitive group.

OBJECTIVE

This study evaluated whether bronchial epithelial cytokine expression would differ between healthy and allergic asthmatics after ozone exposure, representing an explanatory model for differences in susceptibility.

METHODS

Healthy and mild allergic asthmatic subjects (using only inhaled beta2-agonists prn) were exposed for 2 h in blinded and randomized sequence to 0.2 ppm of O3 and filtered air. Bronchoscopy with bronchial mucosal biopsies was performed 6 h after exposure. Biopsies were embedded in GMA and stained with mAbs for epithelial expression of IL-4, IL-5, IL-6, IL-8, IL-10, TNF-alpha, GRO-alpha, granulocyte-macrophage colony-stimulating factor (GM-CSF), fractalkine and ENA-78.

RESULTS

When comparing the two groups at baseline, the asthmatic subjects showed a significantly higher expression of IL-4 and IL-5. After O3 exposure the epithelial expression of IL-5, GM-CSF, ENA-78 and IL-8 increased significantly in asthmatics, as compared to healthy subjects.

CONCLUSION

The present study confirms a difference in epithelial cytokine expression between mild atopic asthmatics and healthy controls, as well as a differential epithelial cytokine response to O3. This O3-induced upregulation of T helper type 2 (Th2)-related cytokines and neutrophil chemoattractants shown in the asthmatic group may contribute to a subsequent worsening of the airway inflammation, and help to explain their differential sensitivity to O3 pollution episodes.

Effects of ozone on lung function and lung diseases

Ozone (O3) is an air pollutant produced by sunlight-driven reactions involving the oxides of nitrogen and volatile organic compounds. The population of many large metropolitan areas in the US is exposed to high levels of O3, particularly in the summer months. Individuals exposed to O3 levels in human experiments at higher than common ambient levels develop reversible reductions in lung function often associated with symptoms, such as airway hyperreactivity and lung inflammation. Animal models have helped characterize potential mechanisms of lung injury from O3 exposure. Defining the adverse effects of chronic exposure to ambient levels of O3 on lung function and disease have been challenging, in part due to the presence of co-pollutants, such as particulate matter. The US Environmental Protection Agency's 1997 revised standard for O3 (0.08 ppm averaged over 8 hours) is designed to provide better protection to susceptible individuals. The revised standard is being implemented following the failure of court challenges.

Ozone exposure increases eosinophilic airway response induced by previous allergen challenge

We investigated whether exposure to ozone (O(3)) 24 hours after an allergen challenge test would increase airway eosinophilia induced by allergen in subjects with mild asthma with late airway response. Twelve subjects with mild atopic asthma participated in a randomized, single-blind study. Subjects underwent allergen challenge 24 hours before a 2 hour exposure to O(3) (0.27 ppm) or filtered air. Pulmonary function was monitored during the allergen challenge and after the exposure to O(3) or air. Six hours later, induced sputum was collected. After 4 weeks, the experiment was repeated with the same subjects. Allergen induced a comparable late airway response in both challenges. O(3) exposure induced a significant decrease in FVC, FEV(1), and vital capacity, and was associated with a significant increase in total symptom score compared with air exposure. The percentage of eosinophils, but not the percentage of neutrophils, in induced sputum was significantly higher after exposure to O(3) than after exposure to air (p = 0.04). These results indicate that O(3) exposure after a late airway response elicited by allergen challenge can potentiate the eosinophilic inflammatory response induced by the allergen challenge itself in subjects with mild atopic asthma. This observation may help explain the synergistic effect of air pollution and allergen exposure in the exacerbation of asthma.

Non-eosinophilic asthma: importance and possible mechanisms

There is increasing evidence that inflammatory mechanisms other than eosinophilic inflammation may be involved in producing the final common pathway of enhanced bronchial reactivity and reversible airflow obstruction that characterises asthma. A review of the literature has shown that, at most, only 50% of asthma cases are attributable to eosinophilic airway inflammation. It is hypothesised that a major proportion of asthma is based on neutrophilic airway inflammation, possibly triggered by environmental exposure to bacterial endotoxin, particulate air pollution, and ozone, as well as viral infections. If there are indeed two (or more) subtypes of asthma, and if non-eosinophilic (neutrophil mediated) asthma is relatively common, this would have major consequences for the treatment and prevention of asthma since most treatment and prevention strategies are now almost entirely focused on allergic/eosinophilic asthma and allergen avoidance measures, respectively. It is therefore important to study the aetiology of asthma further, including the underlying inflammatory profiles.

Nasal lavage as a tool for the assessment of upper-airway inflammation in adults and children

The prevalence of respiratory allergies has increased over the last 20 years, highlighting the need for a simple and noninvasive tool to investigate, in a clinical and epidemiological context, airway-inflammation mechanisms encountered in allergic and inflammatory processes. The nose, as the first region of the respiratory tract to come in contact with airborne pollutants, is easily explored with the use of nasal lavage (NL). We evaluated an NL method for adults and children, along with its reproducibility and capacity to separate different subgroups. NL reproducibility, assessed in 10 healthy, nonsmoking adults on three different occasions, was determined with the use of the intraclass coefficient of correlation for such inflammatory markers as total cell count, albumin, urea, neutrophil elastase, alpha(1)-antitrypsin, interleukin-6, and interleukin-8. Using this NL method, we analyzed nasal markers of 50 healthy adults (smokers and nonsmokers) and 12 healthy children. Our NL method demonstrated high reproducibility with regard to total cell count, albumin, urea, and alpha(1)-antitrypsin (intraclass correlation coefficient > 0.75). Compared with NL results in nonsmokers, NL in heavy smokers revealed significant increased concentrations of total cell counts and interleukin-8 and significant decreased concentrations of interleukin-6. These findings suggest that NL can be used as a tool in the assessment of inflammation because it has the correct reproducibility and can discriminate between heavy smokers and nonsmokers. Moreover, the use of this standardized method in children is feasible.

Ozone-induced lung inflammation and hyperreactivity are mediated via tumor necrosis factor-alpha receptors

This study was designed to investigate the mechanisms through which tumor necrosis factor (Tnf) modulates ozone (O(3))-induced pulmonary injury in susceptible C57BL/6J (B6) mice. B6 [wild-type (wt)] mice and B6 mice with targeted disruption (knockout) of the genes for the p55 TNF receptor [TNFR1(-/-)], the p75 TNF receptor [TNFR2(-/-)], or both receptors [TNFR1/TNFR2(-/-)] were exposed to 0.3 parts/million O(3) for 48 h (subacute), and lung responses were determined by bronchoalveolar lavage. All TNFR(-/-) mice had significantly less O(3)-induced inflammation and epithelial damage but not lung hyperpermeability than wt mice. Compared with air-exposed control mice, O(3) elicited upregulation of lung TNFR1 and TNFR2 mRNAs in wt mice and downregulated TNFR1 and TNFR2 mRNAs in TNFR2(-/-) and TNFR1(-/-) mice, respectively. Airway hyperreactivity induced by acute O(3) exposure (2 parts/million for 3 h) was diminished in knockout mice compared with that in wt mice, although lung inflammation and permeability remained elevated. Results suggested a critical role for TNFR signaling in subacute O(3)-induced pulmonary epithelial injury and inflammation and in acute O(3)-induced airway hyperreactivity.

Bronchial reactivity of healthy subjects: 18-20 h postexposure to ozone

Exposure of humans to ambient levels of ozone (O(3)) causes inflammatory changes within lung tissues. These changes have been reported for the "initial" (1- to 3-h) and "late" (18- to 20-h) postexposure periods. We hypothesized that at the late period, when protein and cellular markers of inflammation at the airway surface remain abnormal and the integrity of the epithelial barrier is compromised, bronchial reactivity would be increased. To test this, we measured airway responsiveness to cumulative doses of methacholine (MCh) aerosol in healthy subjects 19+/-1 h after a single exposure to O(3) (130 min at ambient levels between 120 and 240 parts/billion and alternate periods of rest and moderate exercise) or filtered air. Exposures were conducted at two temperatures: mild (22 degrees C) and moderate (30 degrees C). At the late period, bronchial reactivity to MCh increased, i.e., interpolated dose of MCh leading to a 50% fall in specific airway conductance (PC(50)) was less after O(3) than after filtered air. PC(50) for O(3) at 22 degrees C was 27 mg/ml (20% less than the PC(50) after filtered air), and for O(3) at 30 degrees C it was 19 mg/ml (70% less than the PC(50) after filtered air). The forced expiratory volume in 1 s (FEV(1)) at the late time point after O(3) was slightly but significantly reduced (2.3%) from the preexposure level. There was no relationship found between the functional changes observed early after exposure to O(3) and subsequent changes in bronchial reactivity or FEV(1) at the late time point. These results suggest that bronchial reactivity is significantly altered approximately 1 day after O(3); this injury may contribute to the respiratory morbidity that is observed 1-2 days after an episode of ambient air pollution.

Subacute effects of ozone exposure on cultivated human respiratory mucosa

This study was designed to investigate subacute effects of long-term exposure of both healthy and chronically inflamed human respiratory mucosa to ozone. Functional and metabolic effects on ciliary beat frequency (CBF), release of interleukin 8 (IL-8), interleukin 4 (IL-4), and gamma interferon (g-INF), as well as cellular viability and cytotoxicity, were monitored. Cell cultures of 60 specimens (healthy mucosa: n = 30, inflamed mucosa: n = 30) were exposed to synthetic air and to ozone-enriched synthetic air in different concentrations of 100, 500, and 1000 micrograms/m3. Continuous expositions were performed using an air/liquid interface cell culture technique for a period of 4 weeks. CBF was monitored using video-interference contrast microscopy and cytokine release was quantified by enzyme immunoassays. Cellular viability and cytotoxicity were controlled by measuring lactate dehydrogenase activity, cytosolic activity of esterases, and by staining of nuclear DNA. Synthetic air had no influence on CBF during the 4 weeks of exposure. IL-8 release was continuously diminished in unaffected and in chronically inflamed mucosa. Within the first week of continuous exposure with any ozone concentration neither CBF nor release of IL-8 were affected in healthy or in inflamed mucosa. During the second and the following weeks of exposure CBF and the release of IL-8 were reduced in both tissues. Release of IL-4 or g-INF were not detectable at any time during the 4 weeks of ozone exposure. At higher ozone concentrations of 500 and 1000 micrograms/m3 there was an increase of cytotoxicity which was greater in chronically inflamed than in healthy mucosa. In conclusion, ozone had no measurable effect on those parameters measured in human upper respiratory epithelium after one week of in vitro exposure to different concentrations, but did after longer periods of exposure. Chronically inflamed mucosa had a tendency toward a higher susceptibility to intermediate and high concentrations of ozone that did not reach a level of statistical significance under the conditions used in this study.

Ozone, but not nitrogen dioxide, exposure decreases glutathione peroxidases in epithelial lining fluid of human lung

Antioxidants, such as glutathione peroxidases (GPxs), in epithelial lining fluid (ELF) protect against health effects of oxidant pollutants, which includes O(3) or NO(2). We hypothesized that GPxs concentration in ELF is responsive to O(3) or NO(2) exposure. Subjects underwent two 4-h exposures to O(3) (0.22 ppm) and one to air. In another experiment, subjects underwent 3-h exposures to air and NO(2) (0.6 and 1.5 ppm). Bronchoalveolar lavage (BAL) was performed immediately or 18 h after O(3) exposure and 3.5 h after each NO(2) exposure. GPx activity and extracellular GPx (eGPx) protein concentrations were determined in ELF, and their relationships to markers of lung function, inflammation, and epithelial permeability were examined. Although the total amounts were not changed, basal (air) GPx activity (223.6 +/- 24.4 mU/ml), basal eGPx protein concentration (2.62 +/- 0.25 microg/ml), and basal ELF dilution factor (152.3 +/- 8.4) decreased 40% immediately after O(3) exposure and remained 30% decreased 18 h after exposure (p = 0.0001). No effect of NO(2) exposure on GPxs concentration was detected. There was an inverse correlation between baseline ELF eGPx protein concentration and the change in PMN 18 h after O(3) exposure (p = 0.04). Thus, O(3), a strong oxidant, decreases both GPx activity and eGPx protein in ELF, whereas NO(2), a weaker oxidant, does not. eGPx in ELF may protect against O(3)-induced airway inflammation.

The effect of repeated ozone exposures on inflammatory markers in bronchoalveolar lavage fluid and mucosal biopsies

The aim of this study was to investigate the cellular and biochemical events associated with repeated exposures to ozone. Twenty-three healthy subjects underwent single exposures to 200 ppb ozone and to filtered air (FA), as well as repeated exposures to 200 ppb ozone on 4 consecutive days, each for 4 h of intermittent exercise. Bronchoalveolar lavage was performed and mucosal biopsies were taken 20 h after the single or the last of the repeated exposures. As compared with FA, the single exposure to ozone caused a decrease in FEV(1), an increase in the percentages of neutrophils and lymphocytes, the concentrations of total protein, IL-6, IL-8, reduced glutathione, urate, and ortho-tyrosine in BAL fluid (BALF), but no changes in the cellular composition of biopsy. After the repeated exposure, the effect on lung function was abolished and differential cell counts in BALF were not significantly different from those after FA. However, the concentrations of total protein, IL-6, IL-8, reduced glutathione, and ortho-tyrosine were still increased. IL-10 could only be detected in BALF after repeated ozone exposures. Furthermore, macroscopic scores for bronchitis, erythema, and hypervulnerability of airway mucosa were increased, as well as numbers of neutrophils in bronchial mucosal biopsies. Our data demonstrate that airway inflammation persists after repeated ozone exposure, despite attenuation of some inflammatory markers in BALF and adaptation of lung function.

Effect of inhaled ozone on exhaled nitric oxide, pulmonary function, and induced sputum in normal and asthmatic subjects

BACKGROUND

Nitric oxide (NO) may have a role in the pathophysiology of tissue injury in response to inhaled ozone in animals.

METHODS

A double blind, randomised, placebo controlled, crossover study was undertaken to investigate the effects of inhaled ozone in 10 normal and 10 atopic asthmatic volunteers. Subjects were exposed to 200 ppb ozone or clean air for four hours with intermittent exercise, followed by hourly measurement of spirometric parameters and exhaled NO for four hours. Nasal NO and methacholine reactivity were measured and exhaled breath condensate and induced sputum samples were collected four and 24 hours after exposure.

RESULTS

Exposure to ozone caused a fall in forced expiratory volume in one second (FEV(1)) of 7% in normal subjects (p<0.05) and 9% in asthmatic subjects (p<0.005). There was a 39% increase in sputum neutrophils at four hours in normal subjects (p<0.05) and a 35% increase at four hours in asthmatic subjects, remaining high at 24 hours (p<0.005 and p<0.05, respectively). There were no differences between normal and asthmatic subjects. There were no changes in methacholine reactivity, exhaled or nasal NO, nitrite levels in exhaled breath condensate, or sputum supernatant concentrations of interleukin 8, tumour necrosis factor alpha, or granulocyte-macrophage colony stimulating factor in either group.

CONCLUSIONS

Exposure to 200 ppb ozone leads to a neutrophil inflammatory response in normal and asthmatic subjects but no changes in exhaled NO or nitrite levels.

Ozone-induced inflammation assessed in sputum and bronchial lavage fluid from asthmatics: a new noninvasive tool in epidemiologic studies on air pollution and asthma

We investigated correlations between ozone-induced increases in inflammatory markers in induced sputum and in bronchial lavage fluid. Sixteen volunteers with intermittent asthma participated in a placebo-controlled parallel study with two exposures. Six days before and 16 h after the first exposure to ozone (0.4 ppm during 2 h) sputum was induced with hypertonic saline. This resulted in a significant increase in the sputum levels of eosinophil cationic protein (ECP; 1.8-fold; p = .03), neutrophil elastase (5.0-fold; p = .005) and the total cell number (1.6-fold; p = .02). After 4 weeks, a second exposure was randomized for air or ozone. Six days before and 16 h after the second exposure a bronchial lavage was performed. ECP values in sputum and in bronchial lavage fluid obtained after ozone correlated significantly (Rs = .79; p = .04), as did interleukin-8 (IL-8) values (Rs = .86; p = .01), and the percentage eosinophils (Rs = .89; p = .007). Moreover, the ozone-induced changes in percentage eosinophils observed in sputum and lavage fluid were highly correlated (Rs = .93; p = .003). In conclusion, changes in eosinophils, IL-8, and ECP markers induced by ozone and measured in sputum reflect the inflammatory responses in the lower airways of asthmatics, and may provide a noninvasive tool in epidemiologic studies on air pollution and asthma.

Cigarette smoking and ozone-associated emergency department use for asthma by adults in New York City

The association between ambient ozone (O3) and hospital use for asthma in children and adults is well documented. The question remains of whether there are susceptible subpopulations of asthmatic individuals who are particularly vulnerable to high O3 levels. Because tobacco use was prevalent in our cohort of inner-city adult asthmatic individuals (n = 1,216) in New York City (NYC), we investigated whether cigarette smoking was an effect modifier for asthma morbidity. We examined the relationship between personal tobacco use and O3-associated emergency department (ED) use for asthma in public hospitals in NYC. Three subpopulations were defined: never smokers (0 pack-yr), heavy smokers (>/= 13 pack-yr) and light smokers (< 13 pack-yr). Time-series regression analysis of ED use for asthma and daily O3 levels was done while controlling for temperature, seasonal/long-term trends, and day-of-week effects. Heavy smokers displayed an increased relative risk (RR) of ED visits for asthma in response to increases in 2-d lagged O3 levels (RR per 50 ppb O3 = 1.72; 95% confidence interval: 1.13 to 2.62). Logistic regression analysis confirmed that heavy cigarette use was a predictor of ED use for asthma following days with high O3 levels. Although adverse health effects of ambient O3 have also been documented in asthma populations not using cigarettes (e.g., children), our results suggest that in adult asthmatic individuals, heavy personal tobacco use may be an effect modifier for O3-associated morbidity.

Ozone exposure increases aldehydes in epithelial lining fluid in human lung

We hypothesized that exposure of healthy humans to ozone causes both ozonation and peroxidation of lipids in lung epithelial lining fluid. Twelve smokers and 15 nonsmokers (eight lung function "responders" and seven "nonresponders") were exposed once to air and twice to 0. 22 ppm ozone for 4 h with exercise in an environmental chamber, with each exposure separated by at least 3 wk. Bronchoalveolar lavage (BAL) was performed immediately after one ozone exposure and 18 h after the other ozone exposure. BAL fluid was analyzed for the aldehyde products of ozonation and lipid peroxidation, nonanal (C9) and hexanal (C6), as well as total protein, albumin, and immunoglobulin M as markers of changes in epithelial permeability. Ozone exposure resulted in a significant early increase in C9 (p = 0. 0001), with no statistically significant relationship between increases in C9 and lung function changes, airway inflammation, or changes in epithelial permeability. Increases in C6 levels were not statistically significant (p = 0.16). Both C9 and C6 levels returned to baseline by 18 h after exposure. These studies confirm that exposure to ozone with exercise, at concentrations relevant to urban outdoor air, results in ozonation of lipids in the airway epithelial lining fluid of humans.

Ozone-induced airway inflammatory changes differ between individuals and are reproducible

To study whether the individual inflammatory response to ozone was reproducible, dose-dependent, and time-dependent, we performed two exposures to 250 ppb ozone, one to 125 ppb and one to filtered air, each for 3 h of intermittent exercise and separated by at least 1 wk. Twenty-one healthy and 15 asthmatic subjects participated in the study. One hour after the two exposures to 250 ppb ozone we observed a mean increase in sputum neutrophils of 17.9 and 17.9% in healthy and of 20.3 and 15.2% in asthmatic subjects (p < 0.05 each). Twenty-four hours after exposure, the respective values were 11.9 and 14.8%, and 9.1 and 16.1% (p < 0.05 each). In the whole group of subjects, individual changes in the percentage of neutrophils were significantly correlated between the two exposure days 1 h (r = 0.87, p < 0.001; intraclass correlation coefficient [Ri] = 0.86) as well as 24 h (r = 0.79, p < 0.001; Ri = 0.71) after exposure. The percentages of lymphocytes were increased 24 h after exposures (all subjects combined: p < 0.05). The decrease in FEV1 in both groups (p < 0.01), was also reproducible (r = 0.77, p < 0.001), but there were no correlations between changes in sputum parameters and lung function. Exposure to 125 ppb ozone caused a small increase (p < 0. 05) in the percentage of neutrophils in asthmatic subjects and in the concentrations of interleukin-8 in both groups combined. Our data demonstrate that inflammatory and lung function responses to ozone differ between individuals and are reproducible but not related to each other. Therefore, these responses appear to represent two independent factors underlying the airway response to ozone.

Role of reactive oxygen species in occupational and environmental obstructive pulmonary diseases

Free radicals and their metabolites, also called reactive oxygen species (ROS), have been implicated in the pathogenesis of many diseases. Because of its continuous exposure to toxic pollutants in the ambient air, such as cigarette smoke, air pollution, and mineral dusts, the lung is very vulnerable to ROS-induced injury. In this review, the role of ROS in the pathogenesis of obstructive lung diseases is reviewed. A central theme in this review is the pivotal role of transition metals such as iron, vanadium, and nickel in ROS-induced cell damage, not only in exposure to mineral dusts but also in cigarette smoke and air pollution.