Background While several studies suggest that traffic-related air pollutants are detrimental for respiratory health, few studies have examined relationships between residential proximity to a major roadway and asthma control in children. Furthermore, a major limitation of existing research is reliance on self-reported outcomes. We therefore determined the spatial relationship between the distance from a major roadway and clinical, physiologic and inflammatory features of asthma in a highly characterized sample of asthmatic children 6–17 years of age across a wide range of severities. We hypothesized that a closer residential proximity to a major roadway would be associated with increased respiratory symptoms, altered pulmonary function and a greater magnitude of airway and systemic inflammation. Methodology/Principal Findings 224 children 6–17 years with confirmed asthma completed questionnaires and underwent spirometry, plethysmography, exhaled nitric oxide determination, exhaled breath condensate collection and venipuncture. Residential distance from a major roadway was determined by mapping the geographic coordinates of the residential address in Geographic Information System software. The distance between the home address and the nearest major roadway was calculated according to the shortest distance between the two points (i.e., “as the crow flies”). Asthmatic children living in closer proximity to a major roadway had an increased frequency of wheezing associated with increased medication requirements and more hospitalizations even after controlling for potential confounders. These children also had increased airway resistance, increased airway inflammation reflected by a lower breath condensate pH, and higher plasma EGF concentrations. Conclusions/Significance These findings suggest that closer residential proximity to a major roadway is associated with poorer asthma control in school-age children. Assessment of residential proximity to major roadways may be useful in the clinical evaluation of asthma in children.

Genetic variants that contribute to asthma susceptibility might be present at varying frequencies in different populations, which is an important consideration and advantage for performing genetic association studies in admixed populations. Objective: We sought to identify asthma-associated loci in African American subjects. Methods: We compared local African and European ancestry estimated from dense single nucleotide polymorphism genotype data in African American adults with asthma and nonasthmatic control subjects. Allelic tests of association were performed within the candidate regions identified, correcting for local European admixture. Results: We identified a significant ancestry association peak on chromosome 6q. Allelic tests for association within this region identified a single nucleotide polymorphism (rs1361549) on 6q14.1 that was associated with asthma exclusively in African American subjects with local European admixture (odds ratio, 2.2). The risk allele is common in Europe (42% in the HapMap population of Utah residents with Northern and Western European ancestry from the Centre d'Etude du Polymorphisme Humain collection) but absent in West Africa (0% in the HapMap population of Yorubans in Ibadan, Nigeria), suggesting the allele is present in African American subjects because of recent European admixture. We replicated our findings in Puerto Rican subjects and similarly found that the signal of association is largely specific to subjects who are heterozygous for African and non-African ancestry at 6q14.1. However, we found no evidence for association in European American or Puerto Rican subjects in the absence of local African ancestry, suggesting that the association with asthma at rs1361549 is due to an environmental or genetic interaction. Conclusion: We identified a novel asthma-associated locus that is relevant to admixed populations with African ancestry and highlight the importance of considering local ancestry in genetic association studies of admixed populations.

Background: Diesel exhaust particle (DEP) exposure enhances allergic inflammation and has been linked to the incidence of asthma. Oxidative stress on the thiol molecules cysteine (Cys) and glutathione (GSH) can promote inflammatory host responses. The effect of DEP on the thiol oxidation/reduction (redox) state in the asthmatic lung is unknown. Objective: To determine if DEP exposure alters the Cys or GSH redox state in the asthmatic airway. Methods: Bronchoalveolar lavage fluid was obtained from a house dust mite (HDM) induced murine asthma model exposed to DEP. GSH, glutathione disulfide (GSSG), Cys, cystine (CySS), and s-glutathionylated cysteine (CySSG) were determined by high pressure liquid chromatography. Results: DEP co-administered with HDM, but not DEP or HDM alone, decreased total Cys, increased CySS, and increased CySSG without significantly altering GSH or GSSG. Conclusions: DEP exposure promotes oxidation and S-glutathionylation of cysteine amino acids in the asthmatic airway, suggesting a novel mechanism by which DEP may enhance allergic inflammatory responses. © 2013 Lee et al.

Airway cellular dysfunction is a differentiating feature of severe asthma in children that may be related to an imbalance of the antioxidant, glutathione (GSH). We hypothesized that oxidation of GSH to glutathione disulfide (GSSG) in the epithelial lining fluid (ELF) of children with severe asthma would contribute to altered airway macrophage (AM) GSH homeostasis and AM cellular dysfunction. Bronchoalveolar lavage (BAL) was performed in 64 asthmatic children (severe asthma, n = 43). GSH, GSSG, markers of lipid peroxidation and DNA oxidation, and IL-8 were quantified in the BAL supernatant. GSH, GSSG, activities of histone deacetylase (HDAC) and histone acetyltransferase, apoptosis, and phagocytosis were assessed in isolated AMs. Children with severe asthma had increased GSSG, lipid peroxidation, byproducts of DNA oxidation, and inflammation in the ELF. This imbalance of GSH homeostasis was also noted intracellularly within the AMs and was associated with decreased HDAC activities, increased apoptosis, and impaired phagocytosis. In vitro GSH supplementation inhibited apoptosis and rescued phagocytosis in children with severe asthma. Severe asthma in children is characterized by altered airway and intracellular AM GSH homeostasis that translates to impaired AM function. Interventions to restore airway GSH homeostasis may be warranted in children with severe asthma.

Purpose of the review Children with severe asthma have a high degree of respiratory morbidity despite treatment with high doses of inhaled corticosteroids and are therefore very difficult to treat. This review will discuss phenotypic and pathogenic aspects of severe asthma in childhood, as well as remaining knowledge gaps. Recent findings As a group, children with severe asthma have a number of distinct phenotypic features compared to children with mild-to-moderate asthma. Clinically, children with severe asthma are differentiated by greater allergic sensitization, increased exhaled nitric oxide, and significant airflow limitation and air trapping that worsens as a function of age. These findings are accompanied by structural airway changes and increased and dysregulated airway inflammation and oxidant stress which may explain the differential nature of corticosteroid responsiveness in this population. Because children with severe asthma themselves are a heterogeneous group, current efforts are focused on improved definition and sub-phenotyping of the disorder. While the clinical relevance of phenotyping approaches in severe asthma is not yet clear, they may provide important insight into the mechanisms underlying the disorder. Summary Improved classification of severe asthma through unified definitions, careful phenotypic analyses, and mechanism-focused endotyping approaches may ultimately advance knowledge and personalized treatment.

BACKGROUND Although studies in adults have shown a non-TH2 obese asthma phenotype, whether a similar phenotype exists in children is unclear. OBJECTIVE We hypothesized that asthmatic children with obesity, defined as a body mass index above the 95th percentile for age and sex, would have poorer asthma control as well as decreased quality of life, increased health care utilization, and decreased pulmonary function measures as a function of increased TH1 versus TH2 polarization. METHODS This study involved a post hoc analysis of cross-sectional data from 269 children 6 to 17 years of age enrolled in the National Heart, Lung, and Blood Institute Severe Asthma Research Program. Children answered questionnaires and underwent spirometry, plethysmography, exhaled nitric oxide determination, and venipuncture for TH1/TH2 cytokine determination. Asthma control was defined according to national asthma treatment guidelines that are based on prespecified thresholds for lung function and symptom frequency. RESULTS Fifty-eight children (22%) were overweight and 67 (25%) were obese. Obese children did not have poorer asthma control but were more likely to report nonspecific symptoms such as dyspnea and nocturnal awakenings. Obese children did have decreased asthma-related quality of life and increased health care utilization, but this was not associated with airflow limitation. Instead, obese children had decreased functional residual capacity. A unique pattern of TH1 or TH2 polarization was not observed. CONCLUSIONS Poor asthma control in obese children with asthma may be overestimated because of enhanced perception of nonspecific symptoms such as dyspnea that results from altered mechanical properties of the chest wall. Careful assessment of physiologic as well as symptom-based measures is needed in the evaluation of obese children with respiratory symptoms.

Background Transforming growth factor beta-1 (TGFβ1) is thought to play a role in airway remodeling in asthma. TGFβ1 expression may be mediated by an excessive burden of reactive oxygen species and oxidant stress. Objective Given the profound airway oxidant stress we have previously observed in children with severe asthma, we sought to: 1) quantify TGFβ1 protein and mRNA gene expression in the airways of children with mild-to-moderate and severe atopic asthma; and to 2) determine the relationship of airway TGFβ1 concentrations to oxidant burden (i.e., lipid peroxidation), Th2-mediated eosinophilic inflammation, and airflow limitation. Methods Bronchoalveolar lavage fluid was collected from 68 atopic children with asthma (severe asthma, n = 28) and 12 atopic adult controls. Airway TGFβ1 expression and activation were assessed in relation to airway IL-13, 8-isoprostane, and malondialdehyde concentrations. The relationship of airway TGFβ1 expression to airflow limitation in children with asthma was also assessed. Results Children with severe asthma had higher total airway concentrations of TGFβ1 that were associated with increased protein and mRNA expression of TGFβ1 in airway macrophages and an increase in the lipid peroxidation biomarkers 8-isoprostanes and malondialdehyde. TGFβ1 activation was also greater in children with severe asthma and was associated with higher airway 8-isoprostane, malondialdehyde and IL-13 concentrations. Total airway TGFβ1 concentrations were further associated with airflow limitation. Conclusions Children with severe asthma have increased airway TGFβ1 expression and activation associated with an increased airway oxidant burden. Oxidant stress may mediate the effects of TGFβ1 and promote airway remodeling in children with severe asthma.

Summary Children with moderate-to-severe asthma have decreased expression of acetaminophen metabolizing genes and glutathione that may account for the previously-reported risk of acetaminophen in this vulnerable population.

Rationale Airway thiol redox disturbances, including depletion of the antioxidant, glutathione (GSH), are differentiating features of severe asthma in children. Objectives Given the role of the transcription factor, Nrf2, in maintaining GSH homeostasis and antioxidant defense, we quantified expression and activity of Nrf2 and its downstream targets in the airways and systemic circulation of asthmatic children. We hypothesized that Nrf2 activation and function would be impaired in severe asthma, resulting in depletion of thiol pools and insufficient GSH synthesis and conjugation. Methods Peripheral blood mononuclear cells (PBMCs) and airway lavage cells were collected from children 6–17 years with severe (n=51) and mild-to-moderate asthma (n=38). The thiols GSH and cysteine (CyS) were quantified and expression and activity of Nrf2 and its downstream targets were assessed. Results Children with severe asthma had greater oxidation and lower concentrations of GSH and Cys in the plasma and airway lavage. Although Nrf2 mRNA and protein increased in severe asthma as a function of increased thiol oxidation, the Nrf2 expressed was highly dysfunctional. Nrf2 activation and downstream targets of Nrf2 binding, including GSH-dependent enzymes, were not different between groups. The duration of asthma was a key factor associated with Nrf2 dysfunction in severe asthma. Conclusions Children with severe asthma have a global disruption of thiol redox signaling and control in both the airways and systemic circulation that is associated with post-translational modification of Nrf2. We conclude that the Nrf2 pathway is disrupted in severe asthma as a function of chronic oxidative stress, which ultimately inhibits GSH synthesis and antioxidant defense.

Background Asthma in children is a heterogeneous disorder with many phenotypes. Although unsupervised cluster analysis is a useful tool for identifying phenotypes, it has not been applied to school-age children with persistent asthma across a wide range of severities. Objectives This study determined how children with severe asthma are distributed across a cluster analysis and how well these clusters conform to current definitions of asthma severity. Methods Cluster analysis was applied to 12 continuous and composite variables from 161 children at 5 centers enrolled in the Severe Asthma Research Program (SARP). Results Four clusters of asthma were identified. Children in Cluster 1 (n = 48) had relatively normal lung function and less atopy, while children in Cluster 2 (n = 52) had slightly lower lung function, more atopy, and increased symptoms and medication usage. Cluster 3 (n = 32) had greater co-morbidity, increased bronchial responsiveness and lower lung function. Cluster 4 (n = 29) had the lowest lung function and the greatest symptoms and medication usage. Predictors of cluster assignment were asthma duration, the number of asthma controller medications, and baseline lung function. Children with severe asthma were present in all clusters, and no cluster corresponded to definitions of asthma severity provided in asthma treatment guidelines. Conclusions Severe asthma in children is highly heterogeneous. Unique phenotypic clusters previously identified in adults can also be identified in children, but with important differences. Larger validation and longitudinal studies are needed to determine the baseline and predictive validity of these phenotypic clusters in the larger clinical setting.