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

Dietary fatty acids modulate oxidative stress response to air pollution but not to infection

Anthropogenic changes to the environment expose wildlife to many pollutants. Among these, tropospheric ozone is of global concern and a highly potent pro-oxidant. In addition, human activities include several other implications for wildlife, e.g., changed food availability and changed distribution of pathogens in cities. These co-occurring habitat changes may interact, thereby modulating the physiological responses and costs related to anthropogenic change. For instance, many food items associated with humans (e.g., food waste and feeders for wild birds) contain relatively more ω6-than ω3-polyunsaturated fatty acids (PUFAs). Metabolites derived from ω6-PUFAs can enhance inflammation and oxidative stress towards a stimulus, whereas the opposite response is linked to ω3-derived metabolites. Hence, we hypothesized that differential intake of ω6-and ω3-PUFAs modulates the oxidative stress state of birds and thereby affects the responses towards pro-oxidants. To test this, we manipulated dietary ω6:ω3 ratios and ozone levels in a full-factorial experiment using captive zebra finches (Taeniopygia guttata). Additionally, we simulated an infection, thereby also triggering the immune system's adaptive pro-oxidant release (i.e., oxidative burst), by injecting lipopolysaccharide. Under normal air conditions, the ω3-diet birds had a lower antioxidant ratio (GSH/GSSG ratio) compared to the ω6-diet birds. When exposed to ozone, however, the diet effect disappeared. Instead, ozone exposure overall reduced the total concentration of the key antioxidant glutathione (tGSH). Moreover, the birds on the ω6-rich diet had an overall higher antioxidant capacity (OXY) compared to birds fed a ω3-rich diet. Interestingly, only the immune challenge increased oxidative damage, suggesting the oxidative burst of the immune system overrides the other pro-oxidative processes, including diet. Taken together, our results show that ozone, dietary PUFAs, and infection all affect the redox-system, but in different ways, suggesting that the underlying responses are decoupled despite that they all increase pro-oxidant exposure or generation. Despite lack of apparent cumulative effect in the independent biomarkers, the combined single effects could together reduce overall cellular functioning and efficiency over time in wild birds exposed to pathogens, ozone, and anthropogenic food sources.

Cardiorespiratory Effects of Indoor Ozone Exposure Associated with Changes in Metabolic Profiles among Children: A Repeated-Measure Panel Study

Ozone is one of the major gaseous pollutants associated with short-term adverse cardiopulmonary effects, even at concentrations below the current indoor air quality limits. However, the underlying biological mechanisms of cardiorespiratory changes with exposure to ozone remain unclear. To further explore molecular linkages between indoor ozone exposure and relevant cardiorespiratory effects, a repeated-measure panel study including 46 schoolchildren was conducted and real-time exposure measurements including ozone were performed inside classrooms every weekday during the study period. Repeated health measurements and urine sample collection were conducted in each participant. Ultra-high-performance liquid chromatography/tandem mass spectrometry and meet-in-metabolite approach were used in metabolomics analysis. Methods including mixed-effect models were adopted to identify metabolites associated with ozone exposure or health indices. Nine metabolites were found to be associated with ozone after mixed-effect model analysis, which are mainly involved in amino acid and bile acid metabolism. Boys may have a greater decrease in bile acid and RNA related metabolites. Four of the nine ozone-related metabolites were also associated with cardiorespiratory function indices. Furthermore, 26.67% of the positive association between ozone and heart rate was mediated by cholestane-3,7,12,25-tetrol-3-glucuronide. Exposure to ozone below the current indoor standards was associated with the deteriorated cardiovascular function by disturbing bile acid and endogenous nitric oxide-related oxidation and inflammation, and associated with the exacerbated airway inflammation by reducing GPx-related anti-oxidation. The results provide metabolic evidence of the cardiorespiratory effects of indoor ozone exposure. Indoor ozone pollution should be controlled further, and more attention should be paid to preventing its adverse health effects, especially in children.

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Indoor O₃ exposure far below the indoor air quality limits disturbed amino acid and bile acid metabolism of children

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Exposure to indoor O₃ at low concentrations was associated with the deteriorated HRV, BP by affecting bile acid- and endogenous NO-related oxidation and inflammation

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Exposure to indoor O₃ at low concentrations was associated with the aggravated airway inflammation by reducing GPx-related anti-oxidation

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The cardiorespiratory effects of low-level ozone exposure indoors in children require additional attention

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Indoor ozone pollution should be controlled further and the current indoor ozone standards should be revised

Short-term ozone exposure and asthma severity: Weight-of-evidence analysis

To determine whether evidence indicates that short-term exposure to ambient concentrations of ozone in the United States can affect asthma severity, we systematically reviewed published controlled human exposure, epidemiology, and animal toxicity studies. The strongest evidence for a potential causal relationship came from epidemiology studies reporting increased emergency department visits and hospital admissions for asthma following elevated ambient ozone concentrations. However, while controlled exposure studies reported lung function decrements and increased asthma symptoms following high ozone exposures 160-400 parts per billion [ppb]), epidemiology studies evaluating similar outcomes reported less consistent results. Animal studies showed changes in pulmonary function at high ozone concentrations (> 500ppb), although there is substantial uncertainty regarding the relevance of these animal models to human asthma. Taken together, the weight of evidence indicates that there is at least an equal likelihood that either explanation is true, i.e., the strength of the evidence for a causal relationship between short-term exposure to ambient ozone concentrations and asthma severity is "equipoise and above."

Air Pollution and Climate Change Effects on Allergies in the Anthropocene: Abundance, Interaction, and Modification of Allergens and Adjuvants

Air pollution and climate change are potential drivers for the increasing burden of allergic diseases. The molecular mechanisms by which air pollutants and climate parameters may influence allergic diseases, however, are complex and elusive. This article provides an overview of physical, chemical and biological interactions between air pollution, climate change, allergens, adjuvants and the immune system, addressing how these interactions may promote the development of allergies. We reviewed and synthesized key findings from atmospheric, climate, and biomedical research. The current state of knowledge, open questions, and future research perspectives are outlined and discussed. The Anthropocene, as the present era of globally pervasive anthropogenic influence on planet Earth and, thus, on the human environment, is characterized by a strong increase of carbon dioxide, ozone, nitrogen oxides, and combustion- or traffic-related particulate matter in the atmosphere. These environmental factors can enhance the abundance and induce chemical modifications of allergens, increase oxidative stress in the human body, and skew the immune system toward allergic reactions. In particular, air pollutants can act as adjuvants and alter the immunogenicity of allergenic proteins, while climate change affects the atmospheric abundance and human exposure to bioaerosols and aeroallergens. To fully understand and effectively mitigate the adverse effects of air pollution and climate change on allergic diseases, several challenges remain to be resolved. Among these are the identification and quantification of immunochemical reaction pathways involving allergens and adjuvants under relevant environmental and physiological conditions.

Hydrogen Peroxide and Sodium Transport in the Lung and Kidney

Renal and lung epithelial cells are exposed to some significant concentrations of H2O2. In urine it may reach 100 μM, while in the epithelial lining fluid in the lung it is estimated to be in micromolar to tens-micromolar range. Hydrogen peroxide has a stimulatory action on the epithelial sodium channel (ENaC) single-channel activity. It also increases stability of the channel at the membrane and slows down the transcription of the ENaC subunits. The expression and the activity of the channel may be inhibited in some other, likely higher, oxidative states of the cell. This review discusses the role and the origin of H2O2 in the lung and kidney. Concentration-dependent effects of hydrogen peroxide on ENaC and the mechanisms of its action have been summarized. This review also describes outlooks for future investigations linking oxidative stress, epithelial sodium transport, and lung and kidney function.

Relationship between exposure to fine particulates and ozone and reduced lung function in children

BACKGROUND

A limited number of studies have reported an association between long-term exposure to ambient air pollutants and lung function growth among children, with inconclusive results.

OBJECTIVES

To assess the relationship between air pollutant exposure and lung function growth, and to examine potential sex differences in the susceptibility of lung function growth to air pollution.

METHODS

We conducted a two-year prospective cohort study of Taiwanese children aged 12 at baseline who were followed from October 1, 2007 to November 31, 2009. The study population comprised 2941 non-smoking children who completed pulmonary function tests at both baseline and follow-up surveys. We applied spatial modeling for individual-level exposure assessment to capture relevant exposures and also attempted to eliminate potential community-level confounding. The exposure parameters were annual averages and values calculated from 24-hourly PM2.5 and 8-hourly ozone (O3) concentrations, corresponding to the residential addresses over the study period. The effect estimates were presented as lung function growth deficits per interquartile range (IQR) for PM2.5 and O3.

RESULTS

In a multiple linear mixed effect model, adjusted for confounding, growth deficits in the forced vital capacity (FVC), forced expiration volume in 1s (FEV1), and forced expiratory flow between the 25th and 75th percentiles of the FVC were associated with increased exposure to PM2.5 and O3. For example, greater exposure to PM2.5 (IQR, 17.92μg/m(3)) was associated with an annual deficit in FVC growth of 75mL in boys and 61mL in girls (p for interaction <0.05). Similar associations were found for O3.

CONCLUSIONS

The study provides evidence that long-term exposure to PM2.5 and O3 may have a detrimental effect on the development of lung function in children. The estimated deficits were generally larger in boys, compared to girls.

Associations between inflammatory and immune response genes and adverse respiratory outcomes following exposure to outdoor air pollution: a HuGE systematic review

Variants of inflammatory and immune response genes have been associated with adverse respiratory outcomes following exposure to air pollution. However, the genes involved and their associations are not well characterized, and there has been no systematic review. Thus, we conducted a review following the guidelines of the Human Genome Epidemiology Network. Six observational studies and 2 intervention studies with 14,903 participants were included (2001-2010). Six studies showed at least 1 significant gene-pollutant interaction. Meta-analysis was not possible due to variations in genes, pollutants, exposure estimates, and reported outcomes. The most commonly studied genes were tumor necrosis factor α (TNFA) (n = 6) and toll-like receptor 4 (TLR4) (n = 3). TNFA -308G>A modified the action of ozone and nitrogen dioxide on lung function, asthma risk, and symptoms; however, the direction of association varied between studies. The TLR4 single-nucleotide polymorphisms rs1927911, rs10759931, and rs6478317 modified the association of particulate matter and nitrogen dioxide with asthma. The transforming growth factor β1 (TGFB1) polymorphism -509C>T also modified the association of pollutants with asthma. This review indicates that genes controlling innate immune recognition of foreign material (TLR4) and the subsequent inflammatory response (TGFB1, TLR4) modify the associations of exposure to air pollution with respiratory function. The associations observed have biological plausibility; however, larger studies with improved reporting are needed to confirm these findings.

Glutathione peroxidase-1 as a novel therapeutic target for COPD

Oxidative stress plays a role in a variety of diseases but it is even more pertinent in chronic obstructive pulmonary disease (COPD) given the increased oxidant burden in smokers. The increased oxidant burden results from the fact that cigarette smoke contains over 4700 different chemical compounds and more than 10(15) oxidants/free radicals per puff. Other factors, such as air pollutants, infections, and occupational dusts that may exacerbate COPD, also have the potential to produce oxidative stress. These oxidants give rise to Reactive Oxygen Species (ROS) that are generated enzymatically by inflammatory and epithelial cells within the lung as part of an inflammatory immune response towards a pathogen or irritant. Thus, while ROS are necessary for host defence against invading pathogens, increased levels of ROS have been implicated in initiating inflammatory responses in the lungs through the activation of transcriptional factors, signal transduction pathways, chromatin remodelling and gene expression of pro-inflammatory mediators. However, the normal lung has developed defences to ROS-mediated damage, which include antioxidant enzymes such as superoxide dismutase, catalase, and glutathione peroxidase. In this review we consider the therapeutic potential of the antioxidant enzyme glutathione peroxidase-1 for the treatment of cigarette smoke-induced lung inflammation and damage.

Evaluation of adverse human lung function effects in controlled ozone exposure studies

The US EPA is evaluating controlled human ozone exposure studies to determine the adequacy of the current ozone National Ambient Air Quality Standard of 75 ppb. These studies have shown that ozone exposures of 80 ppb and greater are associated with lung function decrements. Here, we critically review studies with exposures below 80 ppb to determine the lowest ozone concentration at which decrements are causally associated with ozone exposure and could be considered adverse using the Adverse Effects/Causation Framework. Regarding causation, the framework includes consideration of whether exposure-related effects are primary or secondary, statistically significant, isolated or independent, or due to study limitations. Regarding adversity, the framework indicates one should consider whether effects are adaptive, compensatory, precursors to an apical effect, severe, transient and/or reversible. We found that, at exposures below 72 ppb ozone, lung function effects are primary effects, but are isolated, independent and not statistically different compared to effects observed during filtered air exposure, indicating a lack of causation. Up to 72 ppb, lung function effects may be precursors to an apical effect, but are not likely adverse because they are transient, reversible, of low severity, do not interfere with normal activity and do not result in permanent respiratory injury or progressive respiratory dysfunction. Overall, these studies do not demonstrate a causal association between ozone concentrations in the range of the current National Ambient Air Quality Standard and adverse effects on lung function.

Exacerbated airway toxicity of environmental oxidant ozone in mice deficient in Nrf2

Ozone (O3) is a strong oxidant in air pollution that has harmful effects on airways and exacerbates respiratory disorders. The transcription factor Nrf2 protects airways from oxidative stress through antioxidant response element-bearing defense gene induction. The present study was designed to determine the role of Nrf2 in airway toxicity caused by inhaled O3 in mice. For this purpose, Nrf2-deficient (Nrf2(-/-)) and wild-type (Nrf2(+/+)) mice received acute and subacute exposures to O3. Lung injury was determined by bronchoalveolar lavage and histopathologic analyses. Oxidation markers and mucus hypersecretion were determined by ELISA, and Nrf2 and its downstream effectors were determined by RT-PCR and/or Western blotting. Acute and sub-acute O3 exposures heightened pulmonary inflammation, edema, and cell death more severely in Nrf2(-/-) mice than in Nrf2(+/+) mice. O3 caused bronchiolar and terminal bronchiolar proliferation in both genotypes of mice, while the intensity of compensatory epithelial proliferation, bronchial mucous cell hyperplasia, and mucus hypersecretion was greater in Nrf2(-/-) mice than in Nrf2(+/+) mice. Relative to Nrf2(+/+), O3 augmented lung protein and lipid oxidation more highly in Nrf2(-/-) mice. Results suggest that Nrf2 deficiency exacerbates oxidative stress and airway injury caused by the environmental pollutant O3.

Fine particle, ozone exposure, and asthma/wheezing: effect modification by glutathione S-transferase P1 polymorphisms

Background

There are limited studies on the role of interaction between exposure to ambient air pollution and glutathione-S-transferase (GST) P1 on the risk of asthma/wheezing among children, which provided suggestive, but inconclusive results.

Methods

To assess the joint effect of air pollutants and GSTP1 on asthma/wheezing, we conducted a nationwide cross-sectional study of 3,825 children in Taiwan Children Health Study. The studied determinants were three GSTP1 Ile105Val (rs 1695) genotypes (Ile-Ile; Ile-Val and Val-Val) and expoure to ambient air pollutants. We used routine air-pollution monitoring data for ozone (O₃) and particles with an aerodynamic diameter of 2.5 µm or less (PM_2.5). The effect estimates were presented as odds ratios (ORs) per interquartile changes for PM_2.5 and O₃.

Findings

In a two-stage hierarchical model adjusting for confounding, the risk of asthma was negatively associated with PM_2.5 (adjusted odds ratio (OR) 0.60; 95% confidence interval (CI) 0.45, 0.82) and O₃ (OR 0.74; 95% CI 0.60, 0.90) among Ile105 homozygotes, but positively associated with PM_2.5 (OR 1.52; 95% CI 1.01, 2.27) and O₃ (OR 1.19; 95% CI 0.91, 1.57) among those with at least one val105 allele (interaction p value = 0.001 and 0.03, respectively). A similar tendency of effect modification between PM_2.5 and O₃ and GSTP1 on wheezing was found.

Conclusion

Children who carried Ile105 variant allele and exposed to PM_2.5 and O₃ may be less likely to occurrence of asthma/wheezing.

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

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

Modification by antioxidant supplementation of changes in human lung function associated with air pollutant exposure: a systematic review

BACKGROUND

Outdoor air pollution, given its demonstrated negative effects on the respiratory system, is a growing public health concern worldwide, particularly in urban cities. Human exposure to pollutants such as ozone, nitrogen oxides, combustion-related particulate matter and oxides of sulfur is responsible for significant cardiopulmonary morbidity and mortality in both adults and children. Several antioxidants have shown an ability to partially attenuate the negative physiological and functional impacts of air pollutants. This study systematically presents current data on the potential benefits of antioxidant supplementation on lung function outcomes associated with air pollutant exposures in intact humans.

METHODS

Electronic databases (MEDLINE, EMBASE, BIOSIS Previews, Web of Sciences, Environmental Sciences & Pollution Management and TOXNET) were systematically searched for all studies published up to April 2009. Search terms relating to the concepts of respiratory tract diseases, respiratory function tests, air pollution, and antioxidants were used. Data was systematically abstracted from original articles that satisfied selection criteria for inclusion. For inclusion, the studies needed to have evaluated human subjects, given supplemental antioxidants, under conditions of known levels of air pollutants with measured lung function before and after antioxidant administration and/or air pollution exposure. Selected studies were summarized and conclusions presented.

RESULTS

Eight studies investigated the role of antioxidant supplementation on measured lung function outcomes after subject exposure to air pollutants under controlled conditions; 5 of these studies concluded that pollutant-induced airway hyper-responsiveness and diminution in lung function measurements were attenuated by antioxidant supplementation. The remaining five studies took place under ambient (uncontrolled) exposures and unanimously concluded that antioxidant supplementations attenuate the negative effects of urban air pollution on lung function.

CONCLUSIONS

The data evaluating modification of changes in lung function associated with air pollutant exposure by antioxidant supplementation, in intact humans, is limited. Of 13 studies dedicated to this concern, ten demonstrated an attenuation of pollution-associated decrements. There is growing evidence for the benefit of anti-oxidant supplementation in moderating the effects of air pollution on lung function, but more research on human participants is needed to inform this topic.

An alternative form and level of the human health ozone standard

Controlled human laboratory studies have shown that there is a disproportionately greater pulmonary function response from higher hourly average ozone (O3) concentrations than from lower hourly average values and thus, a nonlinear relationship exists between O3 dose and pulmonary function (FEV1) response. The nonlinear dose-response relationship affects the efficacy of the current 8-h O3 standard to describe adequately the observed spirometric response to typical diurnal O3 exposure patterns. We have reanalyzed data from five controlled human response to O3 health laboratory experiments as reported by Hazucha et al. (1992), Adams (2003, 2006a, 2006b), and Schelegle et al. (2009). These investigators exposed subjects to multi-hour variable/stepwise O3 concentration profiles that mimicked typical diurnal patterns of ambient O3 concentrations. Our findings indicate a common response pattern across most of the studies that provides valuable information for the development of a lung function (FEV1)-based alternate form for the O3 standard. Based on our reanalysis of the realistic exposure profiles used in these experiments, we suggest that an alternative form of the human health standard, similar to the proposed secondary (i.e., vegetation) standard form, be considered. The suggested form is an adjusted 5-h cumulative concentration weighted O3 exposure index, which addresses both the delay associated with the onset of response (FEV1 decrement) and the nonlinearity of response (i.e., the greater effect of higher concentrations over the mid- and low-range values) on an hourly basis.

Critical review of the human data on short-term nitrogen dioxide (NO2) exposures: evidence for NO2 no-effect levels

Nitrogen dioxide (NO2) is a ubiquitous atmospheric pollutant due to the widespread prevalence of both natural and anthropogenic sources, and it can be a respiratory irritant when inhaled at elevated concentrations. Evidence for health effects of ambient NO2 derives from three types of studies: observational epidemiology, human clinical exposures, and animal toxicology. Our review focuses on the human clinical studies of adverse health effects of short-term NO2 exposures, given the substantial uncertainties and limitations in interpretation of the other lines of evidence. We examined more than 50 experimental studies of humans inhaling NO2, finding notably that the reporting of statistically significant changes in lung function and bronchial sensitivity did not show a consistent trend with increasing NO2 concentrations. Functional changes were generally mild and transient, the reported effects were not uniformly adverse, and they were not usually accompanied by NO2-dependent increases in symptoms. The available human clinical results do not establish a mechanistic pathway leading to adverse health impacts for short-term NO2 exposures at levels typical of maximum 1-h concentrations in the present-day ambient environment (i.e., below 0.2 ppm). Our review of these data indicates that a health-protective, short-term NO2 guideline level for susceptible (and healthy) populations would reflect a policy choice between 0.2 and 0.6 ppm. EXTENDED ABSTRACT: Nitrogen dioxide (NO2) is a ubiquitous atmospheric pollutant due to the widespread prevalence of both natural and anthropogenic sources, and it can be a respiratory irritant when inhaled at elevated concentrations. Natural NO2 sources include volcanic action, forest fires, lightning, and the stratosphere; man-made NO2 emissions derive from fossil fuel combustion and incineration. The current National Ambient Air Quality Standard (NAAQS) for NO2, initially established in 1971, is 0.053 ppm (annual average). Ambient concentrations monitored in urban areas in the United States are approximately 0.015 ppm, as an annual mean, i.e., below the current NAAQS. Short-term (1-h peak) NO2 concentrations outdoors are not likely to exceed 0.2 ppm, and even 1-h periods exceeding 0.1 ppm are infrequent. Inside homes, 1-h NO2 peaks, typically arising from gas cooking, can range between 0.4 and 1.5 ppm. The health effects evidence of relevance to ambient NO2 derives from three lines of investigation: epidemiology studies, human clinical studies, and animal toxicology studies. The NO2 epidemiology remains inconsistent and uncertain due to the potential for exposure misclassification, residual confounding, and co-pollutant effects, whereas animal toxicology findings using high levels of NO2 exposure require extrapolation to humans exposed at low ambient NO2 levels. Given the limitations and uncertainties in the other lines of health effects evidence, our review thus focused on clinical studies where human volunteers (including asthmatics, children, and elderly) inhaled NO2 at levels from 0.1 to 3.5 ppm during short-term ((1/2)-6-h) exposures, often combined with exercise, and occasionally combined with co-pollutants. We examined the reported biological effects and classified them into (a) lung immune responses and inflammation, (b) lung function changes and airway hyperresponsiveness (AHR), and (c) health effects outside the lungs (extrapulmonary). We examined more than 50 experimental studies of humans inhaling NO2, finding that such clinical data on short-term exposure allowed discrimination of NO2 no-effect levels versus lowest-adverse-effects levels. Our conclusions are summarized by these six points: For lung immune responses and inflammation: (1) healthy subjects exposed to NO2 below 1 ppm do not show pulmonary inflammation; (2) at 2 ppm for 4 h, neutrophils and cytokines in lung-lavage fluid can increase, but these changes do not necessarily correlate with significant or sustained changes in lung function; (3) there is no consistent evidence that NO2 concentrations below 2 ppm increase susceptibility to viral infection; (4) for asthmatics and individuals having chronic obstructive pulmonary disease (COPD), NO2-induced lung inflammation is not expected below 0.6 ppm, although one research group reported enhancement of proinflammatory processes at 0.26 ppm. With regard to NO2-induced AHR: (5) studies of responses to specific or nonspecific airway challenges (e.g., ragweed, methacholine) suggest that asthmatic individuals were not affected by NO2 up to about 0.6 ppm, although some sensitive subsets may respond to levels as low as 0.2 ppm. And finally, for extra-pulmonary effects: (6) such effects (e.g., changes in blood chemistry) generally required NO2 concentrations above 1-2 ppm. Overall, our review of data from experiments with humans indicates that a health-protective, short-term-average NO2 guideline level for susceptible populations (and healthy populations) would reflect a policy choice between 0.2 and 0.6 ppm. The available human clinical results do not establish a mechanistic pathway leading to adverse health impacts for short-term NO2 exposures at levels typical of maximum 1-h concentrations in the present-day ambient environment (i.e., below 0.2 ppm).

Redox control of asthma: molecular mechanisms and therapeutic opportunities

An imbalance in reducing and oxidizing (redox) systems favoring a more oxidative environment is present in asthma and linked to the pathophysiology of the defining symptoms and signs including airflow limitation, hyper-reactivity, and airway remodeling. High levels of hydrogen peroxide, nitric oxide ((*)NO), and 15-F(2t)-isoprostane in exhaled breath, and excessive oxidative protein products in lung epithelial lining fluid, peripheral blood, and urine provide abundant evidence for pathologic oxidizing processes in asthma. Parallel studies document loss of reducing potential by nonenzymatic and enzymatic antioxidants. The essential first line antioxidant enzymes superoxide dismutases (SOD) and catalase are reduced in asthma as compared to healthy individuals, with lowest levels in those patients with the most severe asthma. Loss of SOD and catalase activity is related to oxidative modifications of the enzymes, while other antioxidant gene polymorphisms are linked to susceptibility to develop asthma. Monitoring of exhaled (*)NO has entered clinical practice because it is useful to optimize asthma care, and a wide array of other biochemical oxidative and nitrative biomarkers are currently being evaluated for asthma monitoring and phenotyping. Novel therapeutic strategies that target correction of redox abnormalities show promise for the treatment of asthma.

Effects of nitrogen dioxide on human health: systematic review of experimental and epidemiological studies conducted between 2002 and 2006

In order to assess health effects in humans caused by environmental nitrogen dioxide (NO(2)) a systematic review of studies in humans was conducted. MEDLINE database was searched for epidemiological studies and experiments on adverse effects of NO(2) published between 2002 and 2006. The evidence with regard to NO(2) exposure limits was assessed using the Scottish Intercollegiate Guidelines Network (SIGN) grading system and the modified three star system. Of the 214 articles retrieved 112 fulfilled the inclusion criteria. There was limited evidence that short-term exposure to a 1-h mean value below 200 microg NO(2)/m(3) is associated with adverse health effects provided by only one study on mortality in patients with severe asthma (*2+). The effect remained after adjusting for other air pollutants. There was moderate evidence that short-term exposure below a 24-h mean value of 50 microg NO(2)/m(3) at monitor stations increases hospital admissions and mortality (**2+). Evidence was also moderate when the search was restricted to susceptible populations (children, adolescents, elderly, and asthmatics). There was moderate evidence that long-term exposure to an annual mean below 40 microg NO(2)/m(3) was associated with adverse health effects (respiratory symptoms/diseases, hospital admissions, mortality, and otitis media) provided by generally consistent findings in five well-conducted cohort and case-control studies with some shortcomings in the study quality (**2+). Evidence was also moderate when the search was restricted to studies in susceptible populations (children and adolescents) and for the combination with other air pollutants. The most frequent reasons for decreased study quality were potential misclassification of exposure and selection bias. None of the high-quality observational studies evaluated was informative for the key questions due to the choice of the dose parameter (e.g., 1-week mean) and exposure levels above the limit values. Inclusion of study designs unlisted in the SIGN grading system did not bring additional evidence regarding exposures below the current air quality limit values for NO(2). As several recent studies reported adverse health effects below the current exposure limits for NO(2) particularly among susceptible populations regarding long-term exposure further research is needed. Apart from high-quality epidemiological studies on causality and the interaction of NO(2) with other air pollutants there is a need for double-blinded randomized cross-over studies among susceptible populations for further evaluation of the short-term exposure limits.

Panel discussion review: session four--assessing biological plausibility of epidemiological findings in air pollution research

In December 2006, the U.S. Environmental Protection Agency (EPA) sponsored a 2-day workshop on "Interpretation of Epidemiologic Studies of Multipollutant Exposure and Health Effects" in Chapel Hill, NC. The final session at this workshop was devoted to assessing the biological plausibility of epidemiological findings with regard to criteria air pollutants. The presentations and the panel contributions of this last session primarily focused on controlled exposure studies and led to wide-ranging discussions, some of which were provocative. The panel summary provides some guidance to future evaluations of the biological plausibility of the epidemiological reports on criteria pollutants and is intended to stimulate thinking, without drawing any definitive conclusions. This paper does not approach, nor was it intended to approach, the more formal analytical approach such as that used in EPA's development of its Science Assessment Document for the criteria pollutants.

Time course of ozone-induced changes in breathing pattern in healthy exercising humans

We examined the time course of O3-induced changes in breathing pattern in 97 healthy human subjects (70 men and 27 women). One- to five-minute averages of breathing frequency (fB) and minute ventilation (V̇e) were used to generate plots of cumulative breaths and cumulative exposure volume vs. time and cumulative exposure volume vs. cumulative breaths. Analysis revealed a three-phase response; delay, no response detected; onset, fB began to increase; response, fB stabilized. Regression analysis was used to identify four parameters: time to onset, number of breaths at onset, cumulative inhaled dose of ozone at onset of O3-induced tachypnea, and the percent change in fB. The effect of altering O3 concentration, V̇e, atropine treatment, and indomethacin treatment were examined. We found that the lower the O3 concentration, the greater the number of breaths at onset of tachypnea at a fixed ventilation, whereas number of breaths at onset of tachypnea remains unchanged when V̇e is altered and O3 concentration is fixed. The cumulative inhaled dose of O3 at onset of tachypnea remained constant and showed no relationship with the magnitude of percent change in fB. Atropine did not affect any of the derived parameters, whereas indomethacin did not affect time to onset, number of breaths at onset, or cumulative inhaled dose of O3 at onset of tachypnea but did attenuate percent change in fB. The results are discussed in the context of dose response and intrinsic mechanisms of action.

Oxidant and antioxidant balance in the airways and airway diseases

Although oxygen is a prerequisite to life, at concentrations beyond the physiological limits it may be hazardous to the cells. Since the lungs are directly exposed to very high amounts of oxygen, it is imperative for the organ to possess defences against possible oxidative challenge. The lungs are therefore endowed with an armamentarium of a battery of endogenous agents called antioxidants. The antioxidant species help the lungs ward off the deleterious consequences of a wide variety of oxidants/reactive oxygen species such as superoxide anion, hydroxyl radical, hypohalite radical, hydrogen peroxide and reactive nitrogen species such as nitric oxide, peroxynitrite, nitrite produced endogenously and sometimes accessed through exposure to the environment. The major non-enzymatic antioxidants of the lungs are glutathione, vitamins C and E, beta-carotene, uric acid and the enzymatic antioxidants are superoxide dismutases, catalase and peroxidases. These antioxidants are the first lines of defence against the oxidants and usually act at a gross level. Recent insights into cellular redox chemistry have revealed the presence of certain specialized proteins such as peroxiredoxins, thioredoxins, glutaredoxins, heme oxygenases and reductases, which are involved in cellular adaptation and protection against an oxidative assault. These molecules usually exert their action at a more subtle level of cellular signaling processes. Aberrations in oxidant: antioxidant balance can lead to a variety of airway diseases, such as asthma, chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis which is the topic of discussion in this review.

Chronic Exposure to Ambient Ozone and Lung Function in Young Adults

BACKGROUND

Tropospheric ozone (O3) is an oxidant, outdoor air pollutant. Chronic exposure has been associated with decreased lung function in children and adolescents. This study investigated the effects of long-term exposure to O3 on lung function in college freshmen.

METHODS

We recruited University of California, Berkeley students (n=255) who were lifelong residents of the Los Angeles and San Francisco Bay areas and who never smoked. Lifetime exposures to O3, small particulate matter (PM10), and nitrogen dioxide (NO2) were based on spatial interpolation of compliance monitor measurements to all residences at which students lived. Spirometry was performed between February and May, times when students would not have had recent exposure to increased levels of O3.

RESULTS

Lifetime exposure to O3 was associated with decreased levels of measures of small airways (<2 mm) function (FEF75 and FEF25-75). There was an interaction with the FEF25-75/FVC ratio, a measure of intrinsic airway size. Subjects with a large ratio were less likely to have decreases in FEF75 and FEF25-75 for a given estimated lifetime exposure to O3. This association was not altered by history of chronic respiratory disease, allergy, second-hand exposure to environmental tobacco smoke, exposure to PM10 and NO2, or measurement errors in exposure assessment.

CONCLUSIONS

A history of increased level of lifetime exposure to ambient O3 is associated with decreased function of airways in which O3 deposition in the lungs is the greatest. Adolescents with intrinsically smaller airways appear to be at greatest risk. Any environmental or genetic factors that lead to reduced airway size may lead to increased susceptibility to the adverse effects of ambient ozone.

Determinants of Human Plasma Glutathione Peroxidase (GPx-3) Expression

Plasma glutathione peroxidase (GPx-3) is a selenocysteine-containing protein with antioxidant properties. GPx-3 deficiency has been associated with cardiovascular disease and stroke. The regulation of GPx-3 expression remains largely uncharacterized, however, and we studied its transcriptional and translational determinants in a cultured cell system. In transient transfections of a renal cell line (Caki-2), the published sequence cloned upstream of a luciferase reporter gene produced minimal activity (relative luminescence (RL) = 0.6 +/- 0.4). Rapid amplification of cDNA ends was used to identify a novel transcription start site that is located 233 bp downstream (3') of the published site and that produced a >25-fold increase in transcriptional activity (RL = 16.8 +/- 1.9; p < 0.0001). Analysis of the novel GPx-3 promoter identified Sp-1- and hypoxia-inducible factor-1-binding sites, as well as the redox-sensitive metal response element and antioxidant response element. Hypoxia was identified as a strong transcriptional regulator of GPx-3 expression, in part through the presence of the hypoxia-inducible factor-1-binding site, leading to an almost 3-fold increase in expression levels after 24 h compared with normoxic conditions (normalized RL = 3.5 +/- 0.3 versus 1.2 +/- 0.1; p < 0.001). We also investigated the role of the translational cofactors tRNA(Sec), SECIS-binding protein-2, and SelD (selenophosphate synthetase D) in GPx-3 protein expression. tRNA(Sec) and SelD significantly enhanced GPx-3 expression, whereas SECIS-binding protein-2 showed a trend toward increased expression. These results demonstrate the presence of a novel functional transcription start site for the human GPx-3 gene with a promoter regulated by hypoxia, and identify unique translational determinants of GPx-3 expression.

Nasal epithelial and inflammatory response to ozone exposure: a review of laboratory-based studies published since 1985

This article summarizes biological events in human and animal nasal epithelium after short- and long-term exposure to ozone, the principal agent in photochemical smog. Despite anatomical and histological interspecies differences, ozone exposures resulted in common nasal qualitative alterations with an anterior-posterior gradient of phenomena occurring immediately, and with a lag time postexposure: epithelial disruption and increased permeability, inflammatory cell influx, and proliferative and secretory responses. Described mechanisms of toxicity included a direct effect of ozone on epithelial lining fluid and cellular membranes and the subsequent release of cytokines and cyclooxygenase and lipoxygenase products. An indirect effect of ozone was indicated by a decreased mucociliary clearance, free radicals production interacting with a gene promoting factor, and increased DNA synthesis. Studies highlighted the pivotal role of activated neutrophils and mast cells leading to the release of deleterious enzymes (tryptase, eosinophil cationic protein) and numerous cytokines. Experiments performed with ozone exposure/allergen challenge reported that, besides the intrinsic deleterious properties of ozone, it also had a priming effect on the late-phase response to allergen challenge, providing new insights into the pathophysiology of respiratory allergic diseases.

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.

Isoflavones protect against diesel engine exhaust injury in organotypic culture of lung tissue

The wide range of potential health beneficial effects of isoflavones, including a chemoprentive action, have prompted us to study the potential benefits of genistein and daidzein in an experimental model of environmental pollution impact on lung tissue. A diesel engine placed was used to generate reproducible emissions including both gaseous and particulate matters that are commonly found in urban atmospheres. Isoflavones were added to culture medium of rat lung slices 2 h prior to their exposure to pollutants for 3 h. Intracellular ATP and GSH levels, TNFα production, nucleosome assay and TUNEL labeling were monitored. Isoflavones showed almost total in vitro protection against inflammatory and pro-apoptotic responses in lung slices. Isoflavones 0.3 and 1 μmol/l protected against exhaust induced GSH depletion. Isoflavones 0.3 μmol/l appeared to exert the most beneficial effects. In conclusion, this study points out the potential interest of soy isoflavones consumption in polluted areas. Further studies should be undertaken to verify that similar effects could be obtained after in vivo administration of isoflavones.

Differences in basal airway antioxidant concentrations are not predictive of individual responsiveness to ozone: a comparison of healthy and mild asthmatic subjects

The air pollutant ozone induces both airway inflammation and restrictions in lung function. These responses have been proposed to arise as a consequence of the oxidizing nature of ozone, depleting endogenous antioxidant defenses with ensuing tissue injury. In this study we examined the impact of an environmentally relevant ozone challenge on the antioxidant defenses present at the surface of the lung in two groups known to have profound differences in their antioxidant defense network: healthy control (HC) and mild asthmatic (MA) subjects. We hypothesized that baseline differences in antioxidant concentrations within the respiratory tract lining fluid (RTLF), as well as induced responses, would predict the magnitude of individual responsiveness. We observed a significant loss of ascorbate (ASC) from proximal (-45.1%, p <.01) and distal RTLFs (-11.7%, p <.05) in healthy subjects 6 h after the end of the ozone challenge. This was associated (Rs, -0.71, p <.01) with increased glutathione disulphide (GSSG) in these compartments (p =.01 and p <.05). Corresponding responses were not seen in asthmatics, where basal ASC concentrations were significantly lower (p <.01) and associated with elevated concentrations of GSSG (p <.05). In neither group was any evidence of lipid oxidation seen following ozone. Despite differences in antioxidant levels and response, the magnitude of ozone-induced neutrophilia (+20.6%, p <.01 [HC] vs. +15.2%, p =.01 [MA]) and decrements in FEV(1) (-8.0%, p <.01 [HC] vs. -3.2%, p <.05 [MA]) did not differ between the two groups. These data demonstrate significant differences between the interaction of ozone with RTLF antioxidants in MA and HC subjects. These responses and variations in basal antioxidant defense were not, however, useful predictive markers of group or individual responsiveness to ozone.