Progressive airflow limitation is a feature of children with severe asthma

Severe pediatric asthma endotypes: current limits and future perspectives

INTRODUCTION

Although rare, pediatric severe therapy-resistant asthma (STRA) is a highly heterogeneous, resource-demanding disease that differs significantly from severe adult asthma and whose pathogenesis is still poorly understood.

AREAS COVERED

This review summarizes the latest 10 years of English-written studies defining pediatric STRA endotypes using lung-specific techniques such as bronchoalveolar lavage and endobronchial biopsy. Results of the studies and limits on the field are discussed, together with some future perspectives.

EXPERT OPINION

Over the years, it has become increasingly clear that 'one size does not fit all" in asthma. However, "Does an extremely tailored size fit more than one?'. Only using multicentric, longitudinal pediatric studies, will we be able to answer. Three issues could be particularly critical for future research. First, to provide, if existing, a distinction between prepuberal STRA and puberal STRA endotypes to understand the transition from pediatric to adult STRA and to design effective, tailored therapies in adolescents, usually suffering from poorer asthma control. Second, design early treatments for pediatric airway remodeling to preserve lifelong good lung function. Finally, to better characterize inflammation before and during biological therapies, to provide clues on whether to stop or change treatments.

T2-"Low" Asthma: Overview and Management Strategies

Although the term "asthma" has been applied to all patients with airway lability and variable chest symptoms for centuries, phenotypes of asthma with distinct clinical and molecular features that may warrant different treatment approaches are well recognized. Patients with type 2 (T2)-"high" asthma are characterized by upregulation of T2 immune pathways (ie, IL-4 and IL-13 gene sets) and eosinophilic airway inflammation, whereas these features are absent in patients with T2-"low" asthma and may contribute to poor responsiveness to corticosteroid treatment. This review details definitions and clinical features of T2-"low" asthma, potential mechanisms and metabolic aspects, pediatric considerations, and potential treatment approaches. Priority research questions for T2-"low" asthma are also discussed.

Are We Meeting the Promise of Endotypes and Precision Medicine in Asthma?

While the term asthma has long been known to describe heterogeneous groupings of patients, only recently have data evolved which enable a molecular understanding of the clinical differences. The evolution of transcriptomics (and other 'omics platforms) and improved statistical analyses in combination with large clinical cohorts opened the door for molecular characterization of pathobiologic processes associated with a range of asthma patients. When linked with data from animal models and clinical trials of targeted biologic therapies, emerging distinctions arose between patients with and without elevations in type 2 immune and inflammatory pathways, leading to the confirmation of a broad categorization of type 2-Hi asthma. Differences in the ratios, sources, and location of type 2 cytokines and their relation to additional immune pathway activation appear to distinguish several different (sub)molecular phenotypes, and perhaps endotypes of type 2-Hi asthma, which respond differently to broad and targeted anti-inflammatory therapies. Asthma in the absence of type 2 inflammation is much less well defined, without clear biomarkers, but is generally linked with poor responses to corticosteroids. Integration of "big data" from large cohorts, over time, using machine learning approaches, combined with validation and iterative learning in animal (and human) model systems is needed to identify the biomarkers and tightly defined molecular phenotypes/endotypes required to fulfill the promise of precision medicine.

Clinical significance of the bronchodilator response in children with severe asthma

BACKGROUND

Our objective was to determine those characteristics associated with reversibility of airflow obstruction and response to maximal bronchodilation in children with severe asthma through the Severe Asthma Research Program (SARP).

METHODS

We performed a cross-sectional analysis evaluating children ages 6 to 17 years with nonsevere asthma (NSA) and severe asthma (SA). Participants underwent spirometry before and after 180 µg of albuterol to determine reversibility (≥12% increase in FEV₁ ). Participants were then given escalating doses up to 720 µg of albuterol to determine their maximum reversibility.

RESULTS

We evaluated 230 children (n = 129 SA, n = 101 NSA) from five centers across the United States in the SARP I and II cohorts. SA (odds ratio [OR], 2.08, 95% confidence interval [CI], 1.05-4.13), second-hand smoke exposure (OR, 2.81, 95%CI, 1.23-6.43), and fractional exhaled nitric oxide (FeNO; OR, 1.97, 95%CI, 1.35-2.87) were associated with increased odds of airway reversibility after maximal bronchodilation, while higher prebronchodilator (BD) FEV₁ % predicted (OR, 0.91, 95%CI, 0.88-0.94) was associated with decreased odds. In an analysis using the SARP III cohort (n = 186), blood neutrophils, immunoglobulin E (IgE), and FEV₁ % predicted were significantly associated with BD reversibility. In addition, children with BD response have greater healthcare utilization. BD reversibility was associated with reduced lung function at enrollment and 1-year follow-up though less decline in lung function over 1 year compared to those without reversibility.

CONCLUSIONS

Lung function, that is FEV₁ % predicted, is a predictor of BD response in children with asthma. Additionally, smoke exposure, higher FeNO or IgE level, and low peripheral blood neutrophils are associated with a greater likelihood of BD reversibility. BD response can identify a phenotype of pediatric asthma associated with low lung function and poor asthma control.

Severe asthma in children: Evaluation and management

Severe asthma in children is associated with significant morbidity. Children with severe asthma are at increased risk for adverse outcomes including medication-related side effects, life-threatening exacerbations, and impaired quality of life. It is important to differentiate between severe therapy resistant asthma and difficult-to-treat asthma due to comorbidities. The most common problems that need to be excluded before a diagnosis of severe asthma can be made are poor medication adherence, poor medication technique or incorrect diagnosis of asthma. Difficult to treat asthma is a much more common reason for persistent symptoms and exacerbations and can be managed if comorbidities are clearly addressed. Children with persistent symptoms and exacerbations despite correct inhaler technique and good medical adherence to standard Step 4 asthma therapies according to the guidelines^1,2, should be referred to an asthma specialist with expertise in severe asthma.

High prevalence of house dust mite sensitization in children with severe asthma living at high altitude in a tropical country

BACKGROUND

Some studies, mainly in Europe, have shown a low level of sensitization to house dust mite (HDM) allergens at high altitude (HA). Differently, some others in tropical countries have shown a higher level. The aim of this study was to evaluate allergens sensitization, including HDM, in children with severe asthma (SA), residents at HA in a tropical middle-income developing country.

METHODS

Observational, analytical, cross-sectional study in children aged 6-15 years old with SA at HA (2640 m). Skin prick tests (SPT), serum IgE, exhaled fraction of nitric oxide (FE_NO ), spirometry, and asthma questionnaire (ACT) were performed. Associations were explored by Pearson or Spearman coefficients.

RESULTS

We included 61 children. Most patients were male (61.3%), median age: 10 years (Interquartile range [IQR]: 8-12), median BMI: 17 kg/m² (IQR: 16-20); Median of positive SPT: 2 (IQR: 2-3). At least one SPT was positive in 88.7% of patients and 87.9% were positive for at least one HDM. Serum IgE: 348 UI/mL (IQR: 154-760) and FE_NO : 22 ppb (IQR: 9-41). Prebronchodilator values were (% predicted): FVC: 109.7% (±15.5%), FEV₁ : 98.4% (±16.3); FEV₁ /FVC: 82% (±8%). SPT were inversely correlated with the FEV₁ /FVC (Rho: -0.34; 95% CI: -0.55 a -0.09; P = 0.008).

CONCLUSIONS

These children with SA living at HA in a tropical middle-income developing country have a high prevalence of HDM sensitization. One explanation for this might be that tropical conditions, such as temperature and humidity, could modify the effect of the altitude on asthma.

Severe Asthma Phenotypes - How Should They Guide Evaluation and Treatment?

Although patients with "severe" asthma tend to be characterized by ongoing symptoms and airway inflammation despite treatment with high doses of inhaled and systemic corticosteroids, there is increasing recognition of marked phenotypic heterogeneity within affected patients. Although "precision medicine" approaches for patients with severe asthma are needed, there are many hurdles that must be overcome in daily practice. The National Heart, Lung and Blood Institute's Severe Asthma Research Program (SARP) has been at the forefront of phenotype discovery in severe asthma for the past decade. SARP, along with other international groups, has described clinical severe asthma phenotypes in both adults and children that can be evaluated in the clinical setting. Although these clinical phenotypes provide a good "starting point" for addressing disease heterogeneity in severe asthma in everyday practice, more efforts are needed to understand how these phenotypes relate to underlying disease mechanisms and pharmacological treatment responses. This review highlights the clinical asthma phenotypes identified to date, their associations with underlying endotypes and potential biomarkers, and remaining knowledge gaps that must be addressed before precision medicine can become a reality for patients with severe asthma.

Severe Asthma in Children

Severe asthma in children is associated with significant morbidity and is a highly heterogeneous disorder with multiple clinical phenotypes. Cluster analyses have been performed in several groups to explain some of the heterogeneity of pediatric severe asthma, which is reviewed in this article. The evaluation of a child with severe asthma includes a detailed diagnostic assessment and excluding other possible diagnoses and addressing poor control due to comorbidities, lack of adherence to asthma controller medications, poor technique, and other psychological and environmental factors. Children with severe asthma require significant resources including regular follow-up appointments with asthma education, written asthma action plan, and care by a multidisciplinary team. Management of pediatric severe asthma now includes emerging phenotypic-directed therapies; however, continued research is still needed to further study the long-term outcomes of pediatric severe asthma and its treatment.

Lung function in severe pediatric asthma: a longitudinal study in children and adolescents in Brazil

Background

In severe asthma, high doses of inhaled corticosteroids (ICS) are used in order to achieve clinical and functional control. This study aimed to evaluate lung function in outpatients (children and adolescents) with severe asthma in Brazil, all of whom were treated with high doses of ICS. We evaluated all spirometry tests together and by ICS dose: 800 and > 800 µg/day.

Methods

This was a 3-year longitudinal study in which we analyzed 384 spirometry tests in 65 severe asthma patients (6–18 years of age), divided into two groups by the dose of ICS (budesonide or equivalent): 800 and > 800 µg/day.

Results

At baseline, the forced expiratory volume in one second (FEV₁) and the FEV₁/forced vital capacity (FVC) ratio were both < 80% of the predicted values in 50.8% of the patients. The median age of the patients was 10.4 years (interquartile range 7.8–13.6 years). In the sample as a whole, there were significant increases in FEV₁% and in the FEV₁/FVC% ratio (p = 0.01 and p < 0.001, respectively) over the course of the study. In the > 800 µg/day group, there were no statistical increases or decreases in FEV₁, the FEV₁/FVC ratio, or forced expiratory flow between 25 and 75% of the FVC (FEF_25–75%), when calculated as percentages of the predicted values. However, the z-score for FEF_25–75% showed a statistically significant reduction, in the sample as a whole and in the > 800 µg/day group. Also in the > 800 µg/day group, there was a significant reduction in the post-bronchodilator FEV₁% (p = 0.004).

Conclusions

The fact that the spirometric parameters (as percentages of the predicted values) remained constant in the > 800 µg/day group, whereas there was a gain in lung function in the sample as a whole, suggests an early plateau phase in the > 800 µg/day group. However, there was some loss of lung function in the > 800 µg/day group, as evidenced by a decrease in the z-score for FEF_25–75%, suggesting irreversible small airway impairment, and by a reduction in the post-bronchodilator FEV₁%, suggesting reduced reversibility of airway obstruction. Among children and adolescents with severe asthma, the use of ICS doses higher than those recommended for age does not appear to improve lung function.

Sputum pentraxin 3 as a candidate to assess airway inflammation and remodeling in childhood asthma

Pentraxin 3 (PTX3) is a soluble pattern recognition receptor and an acute-phase protein. It has gained attention as a new biomarker reflecting tissue inflammation and damage in a variety of diseases. Aim of this study is to investigate the role of PTX3 in childhood asthma.In total, 260 children (140 patients with asthma and 120 controls) were enrolled. PTX3 levels were measured in sputum supernatants using enzyme-linked immunosorbent assay test. We performed spirometry and methacholine challenge tests and measured the total eosinophil count and the serum levels of total IgE and eosinophil cationic protein (ECP) in all subjects.Sputum PTX3 concentration was significantly higher in children with asthma than in control subjects (P < 0.001). Furthermore, sputum PTX3 levels correlated with atopic status and disease severity among patients with asthma. A positive significant correlation was found between sputum PTX3 and the bronchodilator response (r = 0.25, P = 0.013). Sputum PTX3 levels were negatively correlated with forced expiratory volume in 1 second (FEV1) (r = -0.30, P = 0.001), FEV1/forced vital capacity (FVC) (r = -0.27, P = 0.002), and FEF25-75 (r = -0.392, P < 0.001), which are indicators of airway obstruction and inflammation. In addition, the PTX3 concentration in sputum showed negative correlations with post-bronchodilator (BD) FEV1 (r = -0.25, P < 0.001) and post-BD FEV1/FVC (r = -0.25, P < 0.001), which are parameters of persistent airflow limitation reflecting airway remodeling.Sputum PTX3 levels increased in children with asthma, suggesting that PTX3 in sputum could be a candidate molecule to evaluate airway inflammation and remodeling in childhood asthma.

Severe Asthma in Children: Lessons Learned and Future Directions

Severe asthma in children is a complicated and heterogeneous disorder that is extremely challenging to treat. Although most children with asthma derive clinical benefit from daily administration of low-to-medium-dose inhaled corticosteroid (ICS) therapy, a small subset of children with "severe" or "refractory" asthma require high doses of ICS and even systemic corticosteroids to maintain symptom control. These children with severe asthma are at increased risk for adverse outcomes including medication-related side effects and recurrent and life-threatening exacerbations that significantly impair quality of life. This review highlights findings on severe asthma in school-age children (age 6-17 years) from the National Heart, Lung and Blood Institute's Severe Asthma Research Program (SARP) over a 10-year period, between 2001 and 2011. Although SARP has advanced knowledge of the unique clinical, biological, and molecular attributes of severe asthma in children, considerable gaps remain for which additional studies are needed.

Severe asthma in school-age children: evaluation and phenotypic advances

Although the majority of children with asthma have a favorable clinical response to treatment with low to moderate doses of inhaled corticosteroids (ICS), a small subset of children have "severe" asthma characterized by ongoing symptoms and airway inflammation despite treatment with high doses of ICS and even oral corticosteroids. Although there is symptom heterogeneity in the affected children, children with severe asthma share the risk for adverse outcomes, including recurrent and potentially life-threatening exacerbations, which contribute to substantial economic burden. This article reviews current knowledge of severe asthma in school-age children (age 6-17 years) with a focus on recent literature published after January 2012. Clinical management approaches for children with severe asthma are discussed as well as current phenotyping efforts and emerging phenotypic-directed therapies that may be of benefit for subpopulations of children with severe asthma in the future.

Update on the current methods for the diagnosis and treatment of severe childhood asthma

The level of asthma control is the key outcome towards which asthma management is evaluated. The majority of children with asthma can obtain adequate control of symptoms through avoidance of triggering factors and/or with the help of low to moderate doses of current available medications. However, there is still a group of children with poor symptom control despite intensive treatment. The current review will provide an overview of a standardized approach to characterize this heterogeneous group of severely sick children. Factors that attenuate the effect of the prescribed treatment and make asthma difficult to treat are discussed. In addition, the usefulness of current methods of assessing asthma severity, pulmonary function, allergy and airway inflammation is also described. Finally, an overview of therapeutic options for children with severe asthma is provided.

Clinical heterogeneity in the severe asthma research program

The National Heart, Lung, and Blood Institute has sponsored several asthma clinical networks, but the Severe Asthma Research Program (SARP) is unique, because it is not a clinical trials network, and it includes both adults and children. Investigators in SARP have comprehensively characterized 1,644 patients with asthma over the past 10 years, including 583 individuals with severe asthma and 300 children below the age of 18 years. The diversity in clinical characteristics, physiologic measures, and biomarkers in a large number of subjects across the ages provides an ideal cohort in which to investigate asthma heterogeneity. Using both biased and unbiased approaches, multiple asthma phenotypes have been described in SARP. These phenotypic analyses have improved our understanding of heterogeneity in asthma, and may provide a starting point to transform clinical practice through the evidence-based classification of disease severity. Although these new phenotypes strive to make order out of a heterogeneous group of patients, they are limited by that heterogeneity. There may be large groups of patients, especially those with milder asthma, that can be grouped into a clinical phenotype to guide therapy, but there will always be patients on the "edge" of a phenotype who will not fit into these groupings. In the SARP cluster analysis, subjects on the "edge" of a phenotype frequently had lung function that was better or worse than other subjects in the same cluster, despite similar clinical characteristics. This suggests that different pathophysiologic mechanisms may be responsible for decrements in lung function in some subjects. This is extremely important for subjects with severe asthma who may be on the "edge" of two phenotypes that may be driven by different pathobiologic mechanisms that warrant different therapeutic approaches.

Management of severe asthma in childhood--state of the art and novel perspectives

The majority of children with asthma have mild or moderate disease and can obtain adequate control of symptoms through avoidance of triggering factors and/or with the help of medications. There is still a group of children with severe asthma in whom symptom control is poor depending either on identifiable aggravating factors or on true therapy resistance. These children have a poor quality of life and are limited by the severity of their disease. There is a need for a staged approach to the assessment and treatment of this small but vulnerable and resource-consuming group. The current review will provide an overview of a possible standardized approach to characterize this heterogeneous group of severely sick children including some newly developed ways of assessing asthma severity and potentialities of new asthma therapies. Furthermore, the umbrella term 'problematic severe asthma' is described. The term encompasses children whose severe asthma is due to identifiable exacerbating factors, as well as children who are resistant to any conventional therapeutic approach. Characteristics of these two groups of children are described, as are possible biomarkers and current and emerging diagnostic tools for allergy evaluation. Some recent advances and future possibilities for treatment of severe asthma are also presented in this review.

Newer treatments in the management of pediatric asthma

Asthma control remains a significant challenge in the pediatric age range in which ongoing loss of lung function in children with persistent asthma has been reported, despite the use of regular preventer therapy. This has important implications for observed mortality and morbidity during adulthood. Over the past decade, there has been an emergence of other treatment adjuncts, such as anti-Immunoglobulin E (IgE)-directed therapy, low dose theophylline, and the use of macrolide antibiotics, yet their exact role in asthma management remains unclear, despite omalizumab now being incorporated into several international asthma guidelines. As with many aspects of pediatric care, this is driven by a lack of appropriately designed pediatric trials. Extrapolation of data reported in adult studies may be appropriate for adolescent asthma, but is not for younger age groups, in which important pathophysiological differences exist. Novel drugs under development offer potential for benefit in the future, but to date existing data are in most cases limited to adults. Pediatric asthma also offers unique potential to prevent or modify the underlying pathophysiology. Although attempts to do so have been unsuccessful to date, advances may yet come from this approach, as our understanding about the interaction between genetics, environmental factors, and viral illness improve. This review provides an overview of the newer treatment options available for management of pediatric asthma and discusses the merits of other novel therapies in development, as we search to optimize management and improve future outcomes.

Phenotypes and endotypes of severe asthma in children

Severe childhood asthma is a complicated and heterogeneous disorder with distinct phenotypes. Children with severe asthma have more persistent symptoms despite receiving treatment, more atopy, greater airway obstruction, and more air trapping than those with mild-to-moderate asthma. They also have higher morbidity and substantial airflow limitations that persist throughout adulthood. Identification of the phenotype clusters and endotypes of severe asthma can allow further modulation of the natural history of severe asthma and may provide the pathophysiologic rationale for appropriate management strategies.

Difficult childhood asthma: management and future

Diagnosis and management of severe asthma implies the definition of different entities, that is, difficult asthma and refractory severe asthma, but also the different phenotypes included in the term refractory severe asthma. A complete evaluation by a physician expert in asthma is necessary, adapted for each child. Identification of mechanisms involved in different phenotypes in refractory severe asthma may improve the therapeutic approach. The quality of care and monitoring of children with severe asthma is as important as the prescription drug, and is also crucial for differentiating between severe asthma and difficult asthma, whereby expertise is required.

Severe asthma in childhood: recent advances in phenotyping and pathogenesis

PURPOSE OF 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 with 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. Whereas 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.

Residential proximity to a major roadway is associated with features of asthma control in children

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.

Understanding the complexity of IgE-related phenotypes from childhood to young adulthood: a Mechanisms of the Development of Allergy (MeDALL) seminar

Mechanisms of the Development of Allergy (MeDALL), a Seventh Framework Program European Union project, aims to generate novel knowledge on the mechanisms of initiation of allergy. Precise phenotypes of IgE-mediated allergic diseases will be defined in MeDALL. As part of MeDALL, a scientific seminar was held on January 24, 2011, to review current knowledge on the IgE-related phenotypes and to explore how a multidisciplinary effort could result in a new integrative translational approach. This article provides a summary of the meeting. It develops challenges in IgE-related phenotypes and new clinical and epidemiologic approaches to the investigation of allergic phenotypes, including cluster analysis, scale-free models, candidate biomarkers, and IgE microarrays; the particular case of severe asthma was reviewed. Then novel approaches to the IgE-associated phenotypes are reviewed from the individual mechanisms to the systems, including epigenetics, human in vitro immunology, systems biology, and animal models. The last chapter deals with the understanding of the population-based IgE-associated phenotypes in children and adolescents, including age effect in terms of maturation, observed effects of early-life exposures and shift of focus from early life to pregnancy, gene-environment interactions, cohort effects, and time trends in patients with allergic diseases. This review helps to define phenotypes of allergic diseases in MeDALL.

Airway TGF-β1 and oxidant stress in children with severe asthma: association with airflow limitation

BACKGROUND

TGF-β1 is thought to play a role in airway remodeling in asthmatic subjects. TGF-β1 expression might 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 TGF-β1 protein and mRNA gene expression in the airways of children with mild-to-moderate and severe atopic asthma and (2) determine the relationship of airway TGF-β1 concentrations to oxidant burden (ie, lipid peroxidation), T(H)2-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 control subjects. Airway TGF-β1 expression and activation were assessed in relation to airway IL-13, 8-isoprostane, and malondialdehyde concentrations. The relationship of airway TGF-β1 expression to airflow limitation in children with asthma was also assessed.

RESULTS

Children with severe asthma had higher total airway concentrations of TGF-β1 that were associated with increased protein and mRNA expression of TGF-β1 in airway macrophages and an increase in concentrations of the lipid peroxidation biomarkers 8-isoprostanes and malondialdehyde. TGF-β1 activation was also greater in children with severe asthma and was associated with higher airway 8-isoprostane, malondialdehyde, and IL-13 concentrations. Total airway TGF-β1 concentrations were further associated with airflow limitation.

CONCLUSIONS

Children with severe asthma have increased airway TGF-β1 expression and activation associated with an increased airway oxidant burden. Oxidant stress might mediate the effects of TGF-β1 and promote airway remodeling in children with severe asthma.

Severe asthma: lessons learned from the National Heart, Lung, and Blood Institute Severe Asthma Research Program

The National Heart, Lung, and Blood Institute Severe Asthma Research Program (SARP) has characterized over the past 10 years 1,644 patients with asthma, including 583 individuals with severe asthma. SARP collaboration has led to a rapid recruitment of subjects and efficient sharing of samples among participating sites to conduct independent mechanistic investigations of severe asthma. Enrolled SARP subjects underwent detailed clinical, physiologic, genomic, and radiological evaluations. In addition, SARP investigators developed safe procedures for bronchoscopy in participants with asthma, including those with severe disease. SARP studies revealed that severe asthma is a heterogeneous disease with varying molecular, biochemical, and cellular inflammatory features and unique structure-function abnormalities. Priorities for future studies include recruitment of a larger number of subjects with severe asthma, including children, to allow further characterization of anatomic, physiologic, biochemical, and genetic factors related to severe disease in a longitudinal assessment to identify factors that modulate the natural history of severe asthma and provide mechanistic rationale for management strategies.

Thiol redox disturbances in children with severe asthma are associated with posttranslational modification of the transcription factor nuclear factor (erythroid-derived 2)-like 2

BACKGROUND

Airway thiol redox disturbances, including depletion of the antioxidant, glutathione, are differentiating features of severe asthma in children.

OBJECTIVES

Given the role of the transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2) in maintaining glutathione homeostasis and antioxidant defense, we quantified expression and activity of Nrf2 and its downstream targets in the airways and systemic circulation of children with asthma. We hypothesized that Nrf2 activation and function would be impaired in severe asthma, resulting in depletion of thiol pools and insufficient glutathione synthesis and conjugation.

METHODS

PBMCs and airway lavage cells were collected from children 6 to 17 years with severe (n = 51) and mild-to-moderate asthma (n = 38). The thiols glutathione and cysteine 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 glutathione and cysteine 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 glutathione-dependent enzymes, were not different between groups. The duration of asthma was a key factor associated with Nrf2 dysfunction in severe asthma.

CONCLUSION

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 posttranslational modification of Nrf2. We conclude that the Nrf2 pathway is disrupted in severe asthma as a function of chronic oxidative stress, which ultimately inhibits glutathione synthesis and antioxidant defense.