Airway wall remodelling and inflammation are features of chronic asthma. Transforming growth factor β (TGF‐β) has been implicated in these processes.
To determine the effect of allergen challenge on airway inflammation and remodelling and whether TGF‐β isoforms and the Smad signalling pathways are involved.
Thirteen patients with atopic asthma underwent inhalational challenge with 0.9% saline, followed by allergen 3–4 weeks later. After both challenges, fibreoptic bronchoscopy was undertaken to obtain bronchial biopsies and tissue samples were processed for immunohistochemistry and examined by microscopy.
Forced expiratory volume in 1 s (FEV1) fell after allergen challenge (mean (SE) −28.1 (0.9)% at 30 min with a late response at 7 hours (−23.0 (1.2)%). Allergen challenge caused an increase in neutrophils and eosinophils in the bronchial mucosa compared with saline. Sub‐basement membrane (SBM) thickness did not change after allergen, but tenascin deposition in SBM was increased. Intranuclear (activated) Smad 2/3 and Smad 4 detected by immunohistochemistry were increased after allergen challenge in epithelial and subepithelial cells of bronchial biopsies. No inhibitory Smad (Smad 7) protein was detected. TGF‐β isoforms 1, 2 and 3 were expressed predominantly in bronchial epithelium after saline and allergen challenges, but only TGF‐β2 expression was increased after allergen. Double immunostaining showed an increase in TGF‐β2 positive eosinophils and neutrophils but not in TGF‐β1 positive eosinophils and neutrophils after allergen challenge.
TGF‐β2 may contribute to the remodelling changes in allergic asthma following single allergen exposure.
Airway wall remodelling and inflammation are features of chronic asthma. Transforming growth factor β (TGF-β) has been implicated in these processes.
We determined the effect of allergen challenge on airway inflammation and remodelling and whether TGF-β isoforms and the Smad signalling pathways were involved.
Thirteen atopic asthmatics underwent inhalational challenge with 0.9% saline (SC), followed by allergen (AC) 3-4 weeks later. After both challenges, fiberoptic bronchoscopy was undertaken in order to obtain bronchial biopsies and tissue samples were processed for immunohistochemistry and examined by microscopy.
FEV1 fell after AC (−28.1 % ± 0.92, mean ± SEM, at 30 minutes) with a late response at 7 hours (−23.0% ± 1.23). AC caused an increase in neutrophils (p=0.016) and eosinophils (p=0.01) in the bronchial mucosa when compared with SC. Sub-basement membrane (SBM) thickness did not change after AC, but tenascin deposition in SBM was increased (p=0.02). Intranuclear (activated) Smad 2/3 and Smad 4 detected by immunohistochemistry were increased after AC in epithelial and subepithelial cells of bronchial biopsies. No inhibitory Smad (Smad 7) protein was detected. TGF-β isoforms 1, 2 and 3 were expressed predominantly in bronchial epithelium both after saline or allergen, but only TGF-β2 expression was increased after AC (p=0.03). Using double-immunostaining, an increase in TGF-β2-positive eosinophils (p=0.01) and neutrophils (p=0.04), but not in TGF-β1 positive eosinophils and neutrophils, was also found after AC.
TGF-β2 may contribute to the remodelling changes in allergic asthma following single allergen exposure; further detailed studies will be needed.
Asthma wall remodelling; allergen challenge; transforming growth factor-beta isoforms
Airway wall remodeling processes are present in the small airways of patients with chronic obstructive pulmonary disease, consisting of tissue repair and epithelial metaplasia that contribute to airway wall thickening and airflow obstruction. With increasing disease severity, there is also increased mucous metaplasia and submucosal gland hypertrophy, peribronchial fibrosis, and an increase in airway smooth muscle mass. Apart from its contractile properties, airway smooth muscle produces inflammatory cytokines, proteases, and growth factors, which may contribute to the remodeling process and induce phenotypic changes of the muscle. Airflow limitation responds minimally to β-agonists and corticosteroid therapy, unlike asthma, perhaps because of alterations in β-receptor or glucocorticoid receptor numbers, alterations in receptor signaling, or the constrictive limitation imposed by peribronchial fibrosis. Better response is observed with the combination of inhaled long-acting β-agonists and corticosteroids. This could result from effects at the level of airway smooth muscle. Airway wall remodeling may involve the release of growth factors from inflammatory or resident cells. The influence of smoking cessation or of current therapies on airway wall remodeling is unknown. Specific therapies for airway wall remodeling may be necessary, together with noninvasive methods of imaging small airway wall remodeling to assess responses.
corticosteroids; emphysema; long-acting β-agonists; matrix metalloproteases; transforming growth factor-β
Chronic exposure to high levels of ozone induces emphysema and chronic inflammation in mice. We determined the recovery from ozone-induced injury and whether an antioxidant, N-acetylcysteine (NAC), could prevent or reverse the lung damage.
Mice were exposed to ozone (2.5 ppm, 3 hours/12 exposures, over 6 weeks) and studied 24 hours (24h) or 6 weeks (6W) later. Nac (100 mg/kg, intraperitoneally) was administered either before each exposure (preventive) or after completion of exposure (therapeutic) for 6 weeks.
After ozone exposure, there was an increase in functional residual capacity, total lung volume, and lung compliance, and a reduction in the ratio of forced expiratory volume at 25 and 50 milliseconds to forced vital capacity (FEV25/FVC, FEV50/FVC). Mean linear intercept (Lm) and airway hyperresponsiveness (AHR) to acetylcholine increased, and remained unchanged at 6W after cessation of exposure. Preventive NAC reduced the number of BAL macrophages and airway smooth muscle (ASM) mass. Therapeutic NAC reversed AHR, and reduced ASM mass and apoptotic cells.
Emphysema and lung function changes were irreversible up to 6W after cessation of ozone exposure, and were not reversed by NAC. The beneficial effects of therapeutic NAC may be restricted to the ASM.
The effect of sleep quality on asthma control independent from common comorbidities like gastroesophageal reflux disease (GERD) and obstructive sleep apnea (OSA) is unknown. This study examined the association between sleep quality and asthma control and quality of life after accounting for OSA and GERD in non-severe (NSA) and severe (SA) asthma.
Cross-sectional data from 60 normal controls, 143 with NSA, and 79 with SA participating in the Severe Asthma Research Program was examined. Those who reported using positive airway pressure therapy or were at high risk for OSA were excluded.
Both SA and NSA had poorer sleep quality than controls, with SA reporting the worst sleep quality. All asthmatics with GERD and 92% of those without GERD had poor sleep quality (p =.02). The majority (88%–100%) of NSA and SA participants who did not report nighttime asthma disturbances still reported having poor sleep quality. In both NSA and SA, poor sleep quality was associated with worse asthma control and quality of life after controlling for GERD and other covariates.
These results suggest that poor sleep quality is associated with poor asthma control and quality of life among asthmatics and cannot be explained by comorbid GERD and nighttime asthma disturbances.
Asthma control; Gastroesphogeal reflux disease; Sleep
John Widdicombe has made substantial contributions to respiratory physiology and to the field of cough particularly. He was one of the first to characterise Aδ-myelinated fibres in the airways that could mediate cough and increased breathing. Later on, he initiated the series of international London Cough Symposia that gathered researchers and clinicians on a two-yearly basis to discuss recent results and concepts regarding cough. John Widdicombe was interested in all aspects of cough from the definition to potential new antitussives. This article will focus on his contributions and on his generous personality through reminiscences from three friends.
Patients with severe asthma are less responsive to the beneficial effects of corticosteroid therapy.
We investigated whether corticosteroid insensitivity was present in airway smooth muscle cells (ASMCs) of patients with severe asthma.
ASMCs cultured from bronchial biopsy specimens of nonasthmatic control subjects (n = 12) and patients with nonsevere (n = 10) or severe (n = 10) asthma were compared for the effect of dexamethasone on suppression of TNF-α– and IFN-γ–induced CCL11 (eotaxin), CXCL8 (IL-8), and CX3CL1 (fractalkine) expression. The mechanisms of corticosteroid insensitivity are also determined.
CCL11 release was higher in ASMCs of patients with nonsevere but not severe asthma and nonasthmatic control subjects; CXCL8 and CX3CL1 release were similar in all groups. In patients with severe asthma, dexamethasone caused less suppression of CCL11 and CXCL8 release induced by TNF-α. Dexamethasone potentiated TNF-α– and IFN-γ–induced CX3CL1 release equally in all 3 groups. TNF-α–induced phosphorylated p38 mitogen-activated protein kinase levels were increased in ASMCs from patients with severe asthma compared with those from patients with nonsevere asthma and nonasthmatic subjects, whereas TNF-α–induced phosphorylated c-Jun N-terminal kinase and phosphorylated extracellular signal-related kinase levels were increased in all asthmatic groups. A p38 inhibitor increased the inhibitory effect of dexamethasone.
ASMCs of patients with severe asthma are corticosteroid insensitive; this might be secondary to heightened p38 mitogen-activated protein kinase levels.
Airway smooth muscle; asthma; corticosteroid insensitivity; CX3CL1; CCL11; CXCL8
Hydrogen sulfide (H2S) is synthesized intracellularly by the enzymes cystathionine-γ-lyase and cystathionine-β-synthase (CBS), and is proposed to be a gasotransmitter with effects in modulating inflammation and cellular proliferation. We determined a role of H2S in airway smooth muscle (ASM) function. ASM were removed from resection or transplant donor lungs and were placed in culture. Proliferation of ASM was induced by FCS and the proinflammatory cytokine, IL-1β. Proliferation of ASM and IL-8 release were measured by bromodeoxyuridine incorporation and ELISA, respectively. Exposure of ASM to H2S “donors” inhibited this proliferation and IL-8 release. Methemoglobin, a scavenger of endogenous H2S, increased DNA synthesis induced by FCS and IL-1β. In addition, methemoglobin increased IL-8 release induced by FCS, but not by IL-1β, indicating a role for endogenous H2S in these systems. Inhibition of CBS, but not cystathionine-γ-lyase, reversed the inhibitory effect of H2S on proliferation and IL-8 release, indicating that this is dependent on CBS. CBS mRNA and protein expression were inhibited by H2S donors, and were increased by methemoglobin, indicating that CBS is the main enzyme responsible for endogenous H2S production. Finally, we found that exogenous H2S inhibited the phosphorylation of extracellular signal–regulated kinase–1/2 and p38, which could represent a mechanism by which H2S inhibited cellular proliferation and IL-8 release. In summary, H2S production provides a novel mechanism for regulation of ASM proliferation and IL-8 release. Therefore, regulation of H2S may represent a novel approach to controlling ASM proliferation and cytokine release that is found in patients with asthma.
hydrogen sulfide; airway smooth muscle; cystathionine-γ-lyase; cystathionine-β-synthase; extracellular signal–regulated kinase–1/2
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.
asthma; remodeling; inflammation; bronchoscopy; imaging
Investigative bronchoscopy was performed in a subset of participants in the Severe Asthma Research Program (SARP) to gain insights into the pathobiology of severe disease. We evaluated the safety aspects of this procedure in this cohort with specific focus on patients with severe asthma.
To prospectively evaluate changes in lung function and the frequency of adverse events related to investigative bronchoscopy.
Bronchoscopy was performed using a common Manual of Procedures. A subset of very severe asthma was defined by severe airflow obstruction, chronic oral corticosteroid use and recent asthma exacerbations. Subjects were monitored for changes in lung function and contacted by telephone for 3 days after the procedure.
436 subjects underwent bronchoscopy (97 normal, 196 not severe, 102 severe and 41 very severe asthma). Nine subjects were evaluated in hospital settings after bronchoscopy; seven of these were respiratory related events. Recent Emergency Department visits, chronic oral corticosteroid use and a history of pneumonia were more frequent in subjects who had asthma exacerbations after bronchoscopy. The fall in FEV1 following bronchoscopy was similar in the severe compared to milder asthma group. Pre-bronchodilator FEV1 was the strongest predictor of change in FEV1 after bronchoscopy with larger decreases observed in subjects with better lung function.
Bronchoscopy in severe asthma subjects was well tolerated. Asthma exacerbations were rare and reduction in pulmonary function after the procedure was similar to subjects with less severe asthma. With proper precautions, investigative bronchoscopy can be performed safely in severe asthma.
investigative bronchoscopy; safety; severe asthma; exacerbation
Two recent large meta-analyses of genome-wide association studies of lung function in general populations of European descent identified 11 candidate genes/regions. The importance of these genes in lung function in whites and African Americans with asthma is unknown.
To determine if genes that regulate lung function in general populations are associated with lung function abnormalities in subjects with asthma from different racial groups.
SNPs were tested in five asthma populations (n = 1,441) for association with pulmonary function and meta-analysis was performed across populations. The SNPs with the highest significance were then tested for association with bronchodilator reversibility and bronchial hyperresponsiveness to methacholine (BHR). A joint analysis of consistently replicated SNPs was performed to predict lung function in asthma.
Hedgehog interacting protein (HHIP) on chromosome 4q31 was associated with lung function in all five populations, rs1512288: Pmeta = 9.62E-05 and 3.23E-05 for ppFEV1 and ppFVC, respectively. The SNPs in HHIP were also associated with reversibility (P < 0.05) but not BHR. Because of differences in linkage disequilibrium in the African-American subjects, the most relevant SNPs in HHIP were identified. A subset of normal lung function genes, including HHIP, family with sequence similarity 13, member A (FAM13A), and patched homolog 1 (PTCH1), together predict lung function abnormalities, a measure of severity in whites and African Americans with asthma.
A subset of the genes, including HHIP, which regulate lung function in general populations are associated with abnormal lung function in asthma in non-Hispanic whites and African Americans.
Asthma; Genetics; Asthma severity; Meta-analysis; FEV1; FVC; FEV1/FVC; HHIP; FAM13A; PTCH1
Rationale: Aberrant airway smooth muscle cell (ASMC) function and overexpression of transforming growth factor (TGF)-β, which modulates ASMC proliferative and inflammatory function and induces oxidant release, are features of asthma. Nuclear factor E2-related factor 2 (Nrf2) activates antioxidant genes conferring protection against oxidative stress.
Objectives: To determine the role of Nrf2 in ASMCs and its modulation by TGF-β, and compare Nrf2 activity in ASMCs from subjects with severe and nonsevere asthma and healthy subjects.
Methods: ASMCs were cultured from airways of subjects without asthma, and from airway biopsies from patients with severe and nonsevere asthma. We studied Nrf2 activation on antioxidant gene expression and proliferation, the effect of TGF-β on Nrf2 transcriptional activity, and the impact of Nrf2 activation on TGF-β–mediated proliferation and IL-6 release. Nrf2–antioxidant response elements binding and Nrf2-dependent antioxidant gene expression was determined in asthmatic ASMCs.
Measurements and Main Results: Activation of Nrf2 led to up-regulation of the antioxidant genes heme oxygenase (HO)-1, NAD(P)H:quinone oxidoreductase, and manganese superoxide dismutase, and a reduction in proliferation. TGF-β reduced Nrf2-mediated antioxidant gene transcription through induction of activating transcription factor-3 expression. Nrf2 activation attenuated TGF-β–mediated reduction in HO-1, ASMC proliferation, and IL-6 release. Nrf2–antioxidant response elements binding was reduced in ASMCs from patients with severe asthma compared with ASMCs from patients with nonsevere asthma and normal subjects. HO-1 expression was reduced in ASMCs from patients with both nonsevere and severe asthma compared with healthy subjects.
Conclusions: Nrf2 regulates antioxidant responses and proliferation in ASMCs and is inactivated by TGF-β. Nrf2 reduction may underlie compromised antioxidant protection and aberrant ASM function in asthma.
asthma; airway smooth muscle; nuclear factor E2-related factor 2; transforming growth factor-β; antioxidant
Reactive oxygen species (ROS) are generated as a result of normal cellular metabolism, mainly through the mitochondria and peroxisomes, but their release is enhanced by the activation of oxidant enzymes such as NADPH oxidases or downregulation of endogenous antioxidant enzymes such as manganese-superoxide dismutase (MnSOD) and catalase. Transforming growth factor-β (TGF-β), found to be overexpressed in airway smooth muscle (ASM) from asthmatic and chronic obstructive pulmonary disease patients, may be a pivotal regulator of abnormal ASM cell (ASMC) function in these diseases. An important effect of TGF-β on ASMC inflammatory responses is the induction of IL-6 release. TGF-β also triggers intracellular ROS release in ASMCs by upregulation of NADPH oxidase 4 (Nox4). However, the effect of TGF-β on the expression of key antioxidant enzymes and subsequently on oxidant/antioxidant balance is unknown. Moreover, the role of redox-dependent pathways in the mediation of the proinflammatory effects of TGF-β in ASMCs is unclear. In this study, we show that TGF-β induced the expression of Nox4 while at the same time inhibiting the expression of MnSOD and catalase. This change in oxidant/antioxidant enzymes was accompanied by elevated ROS levels and IL-6 release. Further studies revealed a role for Smad3 and phosphatidyl-inositol kinase-mediated pathways in the induction of oxidant/antioxidant imbalance and IL-6 release. The changes in oxidant/antioxidant enzymes and IL-6 release were reversed by the antioxidants N-acetyl-cysteine (NAC) and ebselen through inhibition of Smad3 phosphorylation, indicating redox-dependent activation of Smad3 by TGF-β. Moreover, these findings suggest a potential role for NAC in preventing TGF-β-mediated pro-oxidant and proinflammatory responses in ASMCs. Knockdown of Nox4 using small interfering RNA partially prevented the inhibition of MnSOD but had no effect on catalase and IL-6 expression. These findings provide novel insights into redox regulation of ASM function by TGF-β.
Smad; phosphatidyl-inositol kinases; reactive oxygen species; N-acetyl cysteine; manganese-superoxide dismutase; transforming growth factor-β; NADPH oxidase 4 (Nox4)
Biologic factors are known to contribute to asthma severity. It is unknown whether these factors differentially contribute to asthma severity in Blacks compared to Whites.
We sought to assess the extent to which racial disparities in severe asthma between Blacks and Whites are attributable to physiologic, immunoinflammatory, and sociodemographic variables.
Black and White asthmatic adults enrolled in a cross-sectional study focused on severe asthma were evaluated. Severe asthma was identified using the American Thoracic Society definition. Following initial univariable analyses, unconditional logistic regression models were used to estimate the probability of having severe asthma for Blacks and Whites.
Differences in severe asthma in Blacks compared to Whites were observed. In univariable analysis, IgE was not associated with severe asthma in Blacks or Whites, while in multivariable analysis IgE was significantly associated with severe asthma for Blacks (p=0.014) but not in Whites. The odds of having severe asthma more than doubled for Blacks with 2 or more family members with asthma (p=0.026), while the odds of severe asthma for White participants with a strong family history of asthma decreased by almost half (p=0.05). Atopy was negatively associated with severe asthma in both races in univariable analysis, but remained significant only in Blacks, while co-morbidities were associated with severe asthma in Whites.
Biologic factors were distinctly associated with severe asthma only in Blacks. Studies which incorporate comprehensive evaluation of biologic factors associated with asthma may lead to the development of therapies which target biologic abnormalities in Blacks.
severe asthma; race; IgE; allergic sensitization; immunoinflammatory
The T lymphocyte-mediated immune response to Mycobacterium tuberculosis infection in the parietal pleura of patients with tuberculous pleurisy is unknown. The aim of this study was to investigate the immune response in the parietal pleura of tuberculous pleurisy compared with nonspecific pleuritis. We have measured the numbers of inflammatory cells particularly T-cell subsets (Th1/Th2/Th17/Treg cells) in biopsies of parietal pleura obtained from 14 subjects with proven tuberculous pleurisy compared with a control group of 12 subjects with nonspecific pleuritis. The number of CD3+, CD4+ and CCR4+ cells and the expression of RORC2 mRNA were significantly increased in the tuberculous pleurisy patients compared with the nonspecific pleuritis subjects. The number of toluidine blue+ cells, tryptase+ cells and GATA-3+ cells was significantly decreased in the parietal pleura of patients with tuberculous pleurisy compared with the control group of nonspecific pleuritis subjects. Logistic regression with receiver operator characteristic (ROC) analysis for the three single markers was performed and showed a better performance for GATA-3 with a sensitivity of 75%, a specificity of 100% and an AUC of 0.88. There was no significant difference between the two groups of subjects in the number of CD8, CD68, neutrophil elastase, interferon (IFN)-γ, STAT4, T-bet, CCR5, CXCR3, CRTH2, STAT6 and FOXP3 positive cells. Elevated CD3, CD4, CCR4 and Th17 cells and decreased mast cells and GATA-3+ cells in the parietal pleura distinguish patients with untreated tuberculous pleurisy from those with nonspecific pleuritis.
We propose an innovative, integrated, cost-effective health system to combat major non-communicable diseases (NCDs), including cardiovascular, chronic respiratory, metabolic, rheumatologic and neurologic disorders and cancers, which together are the predominant health problem of the 21st century. This proposed holistic strategy involves comprehensive patient-centered integrated care and multi-scale, multi-modal and multi-level systems approaches to tackle NCDs as a common group of diseases. Rather than studying each disease individually, it will take into account their intertwined gene-environment, socio-economic interactions and co-morbidities that lead to individual-specific complex phenotypes. It will implement a road map for predictive, preventive, personalized and participatory (P4) medicine based on a robust and extensive knowledge management infrastructure that contains individual patient information. It will be supported by strategic partnerships involving all stakeholders, including general practitioners associated with patient-centered care. This systems medicine strategy, which will take a holistic approach to disease, is designed to allow the results to be used globally, taking into account the needs and specificities of local economies and health systems.
Rationale: Exhaled nitric oxide (FeNO) is a biomarker of airway inflammation in mild to moderate asthma. However, whether FeNO levels are informative regarding airway inflammation in patients with severe asthma, who are refractory to conventional treatment, is unknown. Here, we hypothesized that classification of severe asthma based on airway inflammation as defined by FeNO levels would identify a more reactive, at-risk asthma phenotype.
Methods: FeNO and major features of asthma, including airway inflammation, airflow limitation, hyperinflation, hyperresponsiveness, and atopy, were determined in 446 individuals with various degrees of asthma severity (175 severe, 271 nonsevere) and 49 healthy subjects enrolled in the Severe Asthma Research Program.
Measurements and Main Results: FeNO levels were similar among patients with severe and nonsevere asthma. The proportion of individuals with high FeNO levels (>35 ppb) was the same (40%) among groups despite greater corticosteroid therapy in severe asthma. All patients with asthma and high FeNO had more airway reactivity (maximal reversal in response to bronchodilator administration and by methacholine challenge), more evidence of allergic airway inflammation (sputum eosinophils), more evidence of atopy (positive skin tests, higher serum IgE and blood eosinophils), and more hyperinflation, but decreased awareness of their symptoms. High FeNO identified those patients with severe asthma characterized by the greatest airflow obstruction and hyperinflation and most frequent use of emergency care.
Conclusions: Grouping of asthma by FeNO provides an independent classification of asthma severity, and among patients with severe asthma identifies the most reactive and worrisome asthma phenotype.
nitric oxide; severe asthma; phenotype; airway reactivity; exhaled breath
Rationale: The Severe Asthma Research Program cohort includes subjects with persistent asthma who have undergone detailed phenotypic characterization. Previous univariate methods compared features of mild, moderate, and severe asthma.
Objectives: To identify novel asthma phenotypes using an unsupervised hierarchical cluster analysis.
Methods: Reduction of the initial 628 variables to 34 core variables was achieved by elimination of redundant data and transformation of categorical variables into ranked ordinal composite variables. Cluster analysis was performed on 726 subjects.
Measurements and Main Results: Five groups were identified. Subjects in Cluster 1 (n = 110) have early onset atopic asthma with normal lung function treated with two or fewer controller medications (82%) and minimal health care utilization. Cluster 2 (n = 321) consists of subjects with early-onset atopic asthma and preserved lung function but increased medication requirements (29% on three or more medications) and health care utilization. Cluster 3 (n = 59) is a unique group of mostly older obese women with late-onset nonatopic asthma, moderate reductions in FEV1, and frequent oral corticosteroid use to manage exacerbations. Subjects in Clusters 4 (n = 120) and 5 (n = 116) have severe airflow obstruction with bronchodilator responsiveness but differ in to their ability to attain normal lung function, age of asthma onset, atopic status, and use of oral corticosteroids.
Conclusions: Five distinct clinical phenotypes of asthma have been identified using unsupervised hierarchical cluster analysis. All clusters contain subjects who meet the American Thoracic Society definition of severe asthma, which supports clinical heterogeneity in asthma and the need for new approaches for the classification of disease severity in asthma.
asthma phenotype; definition; cluster analysis; severe asthma
An important problem in realizing personalized medicine is the development of methods for identifying disease subtypes using quantitative proteomics. Recently we found that bronchoalveolar lavage (BAL) cytokine patterns contain information about dynamic lung responsiveness. In this study, we examined physiological data from 1048 subjects enrolled in the US Severe Asthma Research Program (SARP) to identify four largely separable, quantitative intermediate phenotypes. Upper extremes in the study population were identified for eosinophil- or neutrophil- predominant inflammation, bronchodilation in response to albuterol treatment, or methacholine sensitivity. We evaluated four different statistical (“machine”) learning methods to predict each intermediate phenotypes using BAL cytokine measurements on a 76 subject subset. Comparison of these models using area under the ROC curve and overall classification accuracy indicated that logistic regression and multivariate adaptive regression splines produced the most accurate methods to predict intermediate asthma phenotypes. These robust classification methods will aid future translational studies in asthma targeted at specific intermediate phenotypes.
Asthma; logistic regression; multivariate regression splines; quantitative phenotypes; personalized medicine
Chronic obstructive pulmonary disease (COPD) is characterized by an abnormal and chronic inflammatory response in the lung that underlies the chronic airflow obstruction of the small airways, the inexorable decline of lung function, and the severity of the disease. The control of this inflammation remains a key strategy for treating the disease; however, there are no current anti-inflammatory treatments that are effective. Although glucocorticoids (GCs) effectively control inflammation in many diseases such as asthma, they are less effective in COPD. The molecular mechanisms that contribute to the development of this relative GC-insensitive inflammation in the lung of patients with COPD remain unclear. However, recent studies have indicated novel mechanisms and possible therapeutic strategies. One of the major mechanisms proposed is an oxidant-mediated alteration in the signaling pathways in the inflammatory cells in the lung, which may result in the impairment of repressor proteins used by the GC receptor to inhibit the transcription of proinflammatory genes. Although these studies have described mechanisms and targets by which GC function can be restored in cells from patients with COPD, more work is needed to completely elucidate these and other pathways that may be involved in order to allow for more confident therapeutic targeting. Given the relative GC-insensitive nature of the inflammation in COPD, a combination of therapies in addition to a restoration of GC function, including effective alternative anti-inflammatory targets, antioxidants, and proresolving therapeutic strategies, is likely to provide better targeting and improvement in the management of the disease.
inflammation; oxidative stress; histone deacetylase; phosphoinositol 3-kinase; p38 mitogen-activated protein kinase
The panel considered the different types of cough in terms of basic mechanisms and clinical manifestations; both experimentally and clinically cough could occur in single efforts and as ‘bouts’ or ‘epochs’. There were different definitions of cough but, provided the definition used was clear, this did not seem to be a major concern.
The methods available for determining the nature or type of clinical cough were discussed, in particular automated cough counting in the clinic and more sophisticated methods available in the laboratory. With regard to semantics, there has been great variation in the names used; this applies to nervous sensors for cough, to cough reflexes and epochs, to clinical names for cough, and to cough sounds. Some simplification and uniformity of nomenclature seemed desirable although, provided the use of a name was clear, little confusion probably existed. The panel felt that the cough nomenclature would evolve with time and would prove to be useful for investigators, clinicians and coughers.
Cough; Cough reflexes; Cough types; Cough semantics; Cough sounds
The key co-repressor complex components HDAC-2, Mi-2α/β and mSin3a are all critical to the regulation of gene transcription. HDAC-2 function is impaired by oxidative stress in a PI3Kδ dependant manner which may be involved in the chronic glucocorticoid insensitive inflammation in the lungs of COPD patients. However, the impact of cigarette smoke exposure on the expression of mSin3a and Mi2α/β and their role in glucocorticoid responsiveness is unknown.
Wild type, PI3Kγ knock-out (PI3Kγ-/-) and PI3K kinase dead knock-in (PI3KδD910/A910) transgenic mice were exposed to cigarette smoke for 3 days and the expression levels of the co-repressor complex components HDAC-2, mSin3a, Mi-2α and Mi-2β and HDAC-2 activity in the lungs were assessed.
Cigarette smoke exposure impaired glucocorticoid function and reduced HDAC-2 activity which was protected in the PI3KδD910/A910 mice. Both mSin3a and Mi-2α protein expression was reduced in smoke-exposed mice. Budesonide alone protected mSin3a protein expression with no additional effect seen with abrogation of PI3Kγ/δ activity, however Mi-2α, but not Mi-2β, expression was protected in both PI3KδD910/A910 and PI3Kγ-/- budesonide-treated smoke-exposed mice. The restoration of glucocorticoid function coincided with the protection of both HDAC activity and mSin3a and Mi-2α protein expression.
Cigarette smoke exposure induced glucocorticoid insensitivity and alters co-repressor activity and expression which is prevented by blockade of PI3K signaling with glucocorticoid treatment. Inhibition of PI3Kδ signalling in combination with glucocorticoid treatment may therefore provide a therapeutic strategy for restoring oxidant-induced glucocortiocid unresponsiveness.
An imbalance in the generation of pro-inflammatory leukotrienes, and counter-regulatory lipoxins is present in severe asthma. We measured leukotriene B4 (LTB4), and lipoxin A4 (LXA4) production by alveolar macrophages (AMs) and studied the impact of corticosteroids.
AMs obtained by fiberoptic bronchoscopy from 14 non-asthmatics, 12 non-severe and 11 severe asthmatics were stimulated with lipopolysaccharide (LPS,10 μg/ml) with or without dexamethasone (10-6M). LTB4 and LXA4 were measured by enzyme immunoassay.
LXA4 biosynthesis was decreased from severe asthma AMs compared to non-severe (p < 0.05) and normal subjects (p < 0.001). LXA4 induced by LPS was highest in normal subjects and lowest in severe asthmatics (p < 0.01). Basal levels of LTB4 were decreased in severe asthmatics compared to normal subjects (p < 0.05), but not to non-severe asthma. LPS-induced LTB4 was increased in severe asthma compared to non-severe asthma (p < 0.05). Dexamethasone inhibited LPS-induced LTB4 and LXA4, with lesser suppression of LTB4 in severe asthma patients (p < 0.05). There was a significant correlation between LPS-induced LXA4 and FEV1 (% predicted) (rs = 0.60; p < 0.01).
Decreased LXA4 and increased LTB4 generation plus impaired corticosteroid sensitivity of LPS-induced LTB4 but not of LXA4 support a role for AMs in establishing a pro-inflammatory balance in severe asthma.
Severe asthma causes the majority of asthma morbidity. Understanding mechanisms that contribute to the development of severe disease is important.
The goal of the Severe Asthma Research Program is to identify and characterize subjects with severe asthma to understand pathophysiologic mechanisms in severe asthma.
We performed a comprehensive phenotypic characterization (questionnaires, atopy and pulmonary function testing, phlebotomy, exhaled nitric oxide) in subjects with severe and not severe asthma.
A total of 438 subjects with asthma were studied (204 severe, 70 moderate, 164 mild). Severe subjects with asthma were older with longer disease duration (P < .0001), more daily symptoms, intense urgent health care utilization, sinusitis, and pneumonia (P ≤ .0001). Lung function was lower in severe asthma with marked bronchodilator reversibility (P < .001). The severe group had less atopy by skin tests (P = .0007), but blood eosinophils, IgE, and exhaled nitric oxide levels did not differentiate disease severity. A reduced FEV1, history of pneumonia, and fewer positive skin tests were risk factors for severe disease. Early disease onset (age < 12 years) in severe asthma was associated with longer disease duration (P < .0001) and more urgent health care, especially intensive care (P = .002). Later disease onset (age ≥ 12 years) was associated with lower lung function and sinopulmonary infections (P ≤ .02).
Severe asthma is characterized by abnormal lung function that is responsive to bronchodilators, a history of sinopulmonary infections, persistent symptoms, and increased health care utilization.
Lung function abnormalities in severe asthma are reversible in most patients, and pneumonia is a risk factor for the development of severe disease.
Severe asthma; definition; bronchodilator response; pathophysiology; phenotype; pneumonia