Obesity is associated with the development of asthma and considerable asthma-related healthcare utilization. To understand the immunological pathways that lead to obesity-associated asthma, we fed mice a high fat diet for 12 weeks, which resulted in obesity and the development of airway hyperreactivity (AHR), a cardinal feature of asthma. This AHR depended on innate immunity, since it occurred in obese Rag−/− mice, and on IL-17A and the NLRP3 inflammasome, since it did not develop in obese Il17−/− or Nlrp3−/− mice. The AHR was also associated with the presence in the lungs of CCR6+ innate lymphoid cells producing IL-17A (ILC3 cells), which could by themselves mediate AHR when adoptively transferred into Rag2−/−
Il2rγ−/− mice. IL-1β played an important role by expanding the ILC3 cells, and treatment to block the function of IL-1β abolished obesity-induced AHR. Since we found ILC3-like cells in the bronchoalveolar lavage fluid of human patients with asthma, we suggest that obesity-associated asthma is facilitated by inflammation mediated by NLRP3, IL-1β and ILC3 cells.
airway hyperreactivity; asthma; obesity; innate lymphoid cells; IL-17; NLRP3; ILC3
To determine whether a disintegrin and a metalloproteinase-8 (Adam8) regulates allergic airway inflammation (AAI) and airway hyper-responsiveness (AHR), we compared AAI and AHR in wild type (WT) versus Adam8−/− mice in different genetic backgrounds sensitized and challenged with ovalbumin (OVA) or house dust mite protein extract (HDM). OVA- and HDM-treated Adam8−/− mice had higher lung leukocyte counts, more airway mucus metaplasia, greater lung levels of some TH2 cytokines, and higher methacholine-induced increases in central airway resistance than allergen-treated WT mice. Studies of OVA-treated Adam8 bone marrow chimeric mice confirmed that leukocyte-derived Adam8 predominantly mediated Adam8’s anti-inflammatory activities in murine airways. Airway eosinophils and macrophages both expressed Adam8 in WT mice with AAI. Adam8 limited AAI and AHR in mice by reducing leukocyte survival because: 1) Adam8−/− mice with AAI had fewer apoptotic eosinophils and macrophages in their airways than WT mice with AAI; and 2) Adam8−/− macrophages and eosinophils had reduced rates of apoptosis compared with WT leukocytes when the intrinsic (but not the extrinsic) apoptosis pathway was triggered in the cells in vitro. ADAM8 was robustly expressed by airway granulocytes in lung sections from human asthma patients but, surprisingly, airway macrophages had less ADAM8 staining than airway eosinophils. Thus, ADAM8 has anti-inflammatory activities during AAI in mice by activating the intrinsic apoptosis pathway in myeloid leukocytes. Strategies that increase ADAM8 levels in myeloid leukocytes may have therapeutic efficacy in asthma.
Genome-wide association studies (GWAS) have emerged as a powerful tool to identify loci that affect drug response or susceptibility to adverse drug reactions. However, current GWAS based on a simple analysis of associations between genotype and phenotype ignores the biochemical reactions of drug response, thus limiting the scope of inference about its genetic architecture. To facilitate the inference of GWAS in pharmacogenomics, we sought to undertake the mathematical integration of the pharmacodynamic process of drug reactions through computational models. By estimating and testing the genetic control of pharmacodynamic and pharmacokinetic parameters, this mechanistic approach does not only enhance the biological and clinical relevance of significant genetic associations, but also improve the statistical power and robustness of gene detection. This report discusses the general principle and development of pharmacodynamics-based GWAS, highlights the practical use of this approach in addressing various pharmacogenomic problems, and suggests that this approach will be an important method to study the genetic architecture of drug responses or reactions.
Rationale: Increasing body mass index (BMI) has been associated with less fractional exhaled nitric oxide (FeNO). This may be explained by an increase in the concentration of asymmetric dimethyl arginine (ADMA) relative to l-arginine, which can lead to greater nitric oxide synthase uncoupling.
Objectives: To compare this mechanism across age of asthma onset groups and determine its association with asthma morbidity and lung function.
Methods: Cross-sectional study of participants from the Severe Asthma Research Program, across early- (<12 yr) and late- (>12 yr) onset asthma phenotypes.
Measurements and Main Results: Subjects with late-onset asthma had a higher median plasma ADMA level (0.48 μM, [interquartile range (IQR), 0.35–0.7] compared with early onset, 0.37 μM [IQR, 0.29–0.59], P = 0.01) and lower median plasma l-arginine (late onset, 52.3 [IQR, 43–61] compared with early onset, 51 μM [IQR 39–66]; P = 0.02). The log of plasma l-arginine/ADMA was inversely correlated with BMI in the late- (r = −0.4, P = 0.0006) in contrast to the early-onset phenotype (r = −0.2, P = 0.07). Although FeNO was inversely associated with BMI in the late-onset phenotype (P = 0.02), the relationship was lost after adjusting for l-arginine/ADMA. Also in this phenotype, a reduced l-arginine/ADMA was associated with less IgE, increased respiratory symptoms, lower lung volumes, and worse asthma quality of life.
Conclusions: In late-onset asthma phenotype, plasma ratios of l-arginine to ADMA may explain the inverse relationship of BMI to FeNO. In addition, these lower l-arginine/ADMA ratios are associated with reduced lung function and increased respiratory symptom frequency, suggesting a role in the pathobiology of the late-onset phenotype.
asthma; obesity; age of asthma onset; ADMA; arginine
Rationale: The function of the P2X7 nucleotide receptor protects against exacerbation in people with mild-intermittent asthma during viral illnesses, but the impact of disease severity and maintenance therapy has not been studied.
Objectives: To evaluate the association between P2X7, asthma exacerbations, and incomplete symptom control in a more diverse population.
Methods: A matched P2RX7 genetic case-control was performed with samples from Asthma Clinical Research Network trial participants enrolled before July 2006, and P2X7 pore activity was determined in whole blood samples as an ancillary study to two trials completed subsequently.
Measurements and Main Results: A total of 187 exacerbations were studied in 742 subjects, and the change in asthma symptom burden was studied in an additional 110 subjects during a trial of inhaled corticosteroids (ICS) dose optimization. African American carriers of the minor G allele of the rs2230911 loss-of-function single nucleotide polymorphism were more likely to have a history of prednisone use in the previous 12 months, with adjustment for ICS and long-acting β2-agonists use (odds ratio, 2.7; 95% confidence interval, 1.2–6.2; P = 0.018). Despite medium-dose ICS, attenuated pore function predicted earlier exacerbations in incompletely controlled patients with moderate asthma (hazard ratio, 3.2; confidence interval, 1.1–9.3; P = 0.033). After establishing control with low-dose ICS in patients with mild asthma, those with attenuated pore function had more asthma symptoms, rescue albuterol use, and FEV1 reversal (P < 0.001, 0.03, and 0.03, respectively) during the ICS adjustment phase.
Conclusions: P2X7 pore function protects against exacerbations of asthma and loss of control, independent of baseline severity and the maintenance therapy.
asthma; P2X7; exacerbation; Asthma Clinical Research Network; corticosteroids
Dietary supplementation with botanical oils that contain n-6 and n-3 eighteen carbon chain (18C)-PUFA such as γ linolenic acid (GLA, 18:3n-6), stearidonic acid (SDA, 18:4n-3) and α linolenic acid (ALA, 18:3n-3) have been shown to impact PUFA metabolism, alter inflammatory processes including arachidonic acid (AA) metabolism and improve inflammatory disorders.
The diet of mild asthmatics patients was supplemented for three weeks with varying doses of two botanical seed oils (borage oil [Borago officinalis, BO] and echium seed oil [Echium plantagineum; EO]) that contain SDA, ALA and GLA. A three week wash out period followed. The impact of these dietary manipulations was evaluated for several biochemical endpoints, including in vivo PUFA metabolism and ex vivo leukotriene generation from stimulated leukocytes.
Supplementation with several EO/BO combinations increased circulating 20–22 carbon (20–22C) PUFAs, including eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA), and dihommo-gammalinolenic acid (DGLA), which have been shown to inhibit AA metabolism and inflammation without impacting circulating AA levels. BO/EO combinations also inhibited ex vivo leukotriene generation with some combinations attenuating cysteinyl leukotriene generation in stimulated basophils by >50% and in stimulated neutrophils by >35%.
This study shows that dietary supplementation with BO/EO alters 20–22C PUFA levels and attenuates leukotriene production in a manner consistent with a reduction in inflammation.
Asthma; Gammalinolenic acid; Stearidonic acid; Inflammation; Leukotrienes; Borage oil; Echium oil
Genome-wide association studies (GWASs) of asthma have consistently implicated the ORM1-like 3 and gasdermin B (ORMDL3-GSDMB), IL33, IL-1 receptor–like 1 and IL-18 receptor 1 (IL1RL1-IL18R1), RAD50-IL13, thymic stromal lymphopoietin and WD repeat domain 36 region (TSLP-WDR36), and HLA-DR/DQ regions.
A GWAS of asthma was performed in a non-Hispanic white population.
A GWAS was performed in 813 Severe Asthma Research Program/Collaborative Studies on the Genetics of Asthma/Chicago Asthma Genetics Study cases and 1564 control subjects. The GWAS results were compared with those of the published GWASs of autoimmune diseases.
Multiple single nucleotide polymorphisms in the TNFAIP3 interacting protein 1 (TNIP1) gene, which interacts with TNFAIP3 and inhibits the TNF-α–induced nuclear factor κB inflammation pathway, were associated with asthma: rs1422673 (P = 3.44 × 10−7) and rs10036748 (P = 1.41 × 10−6, r2 = 0.67). rs1422673 was also associated with asthma in the published GABRIEL (P = .018) and EVE (P = 1.31 × 10−5) studies. The minor allele T of rs20541 in IL13 is the risk allele for asthma but the protective allele for psoriasis. The minor allele T of rs2395185 in HLA-DRA is the risk allele for asthma but the protective allele for ulcerative colitis. The minor allele A of rs2872507 in GSDMB is the protective allele for asthma but the risk allele for rheumatoid arthritis, Crohn disease, and ulcerative colitis. The T allele of rs10036748 in the TNIP1 gene is the minor protective allele for asthma but the minor or major risk allele for systemic lupus erythematosus and systemic sclerosis in non-Hispanic white or Chinese subjects, respectively.
Our study suggests that single nucleotide polymorphisms associated with both asthma and autoimmune diseases might have opposite effects on immunopathogenesis. (J Allergy Clin Immunol 2012;130:861-8.)
Asthma; genetics; genome-wide association study; TNFAIP3 interacting protein 1
No consensus exists for adjusting inhaled corticosteroid therapy in patients with asthma. Approaches include adjustment at outpatient visits guided by physician assessment of asthma control (symptoms, rescue therapy, pulmonary function), based on exhaled nitric oxide, or on a day-to-day basis guided by symptoms.
To determine if adjustment of inhaled corticosteroid therapy based on exhaled nitric oxide or day-to-day symptoms is superior to guideline-informed, physician assessment–based adjustment in preventing treatment failure in adults with mild to moderate asthma.
Design, Setting, and Participants
A randomized, parallel, 3-group, placebo-controlled, multiply-blinded trial of 342 adults with mild to moderate asthma controlled by low-dose inhaled corticosteroid therapy (n=114 assigned to physician assessment–based adjustment [101 completed], n=115 to biomarker-based [exhaled nitric oxide] adjustment [92 completed], and n=113 to symptom-based adjustment [97 completed]), the Best Adjustment Strategy for Asthma in the Long Term (BASALT) trial was conducted by the Asthma Clinical Research Network at 10 academic medical centers in the United States for 9 months between June 2007 and July 2010.
For physician assessment–based adjustment and biomarker-based (exhaled nitric oxide) adjustment, the dose of inhaled corticosteroids was adjusted every 6 weeks; for symptom-based adjustment, inhaled corticosteroids were taken with each albuterol rescue use.
Main Outcome Measure
The primary outcome was time to treatment failure.
There were no significant differences in time to treatment failure. The 9-month Kaplan-Meier failure rates were 22% (97.5% CI, 14%-33%; 24 events) for physician assessment–based adjustment, 20% (97.5% CI, 13%-30%; 21 events) for biomarker-based adjustment, and 15% (97.5% CI, 9%-25%; 16 events) for symptom-based adjustment. The hazard ratio for physician assessment–based adjustment vs biomarker-based adjustment was 1.2 (97.5% CI, 0.6-2.3). The hazard ratio for physician assessment–based adjustment vs symptom-based adjustment was 1.6 (97.5% CI, 0.8-3.3).
Among adults with mild to moderate persistent asthma controlled with low-dose inhaled corticosteroid therapy, the use of either biomarker-based or symptom-based adjustment of inhaled corticosteroids was not superior to physician assessment–based adjustment of inhaled corticosteroids in time to treatment failure.
clinicaltrials.gov Identifier: NCT00495157
Genetic variants that contribute to asthma susceptibility may be present at varying frequencies in different populations, which is an important consideration and advantage for performing genetic association studies in admixed populations.
To identify asthma-associated loci in African Americans.
We compared local African and European ancestry estimated from dense single nucleotide polymorphism (SNP) genotype data in African American adults with asthma and non-asthmatic controls. Allelic tests of association were performed within the candidate regions identified, correcting for local European admixture.
We identified a significant ancestry association peak on chromosomes 6q. Allelic tests for association within this region identified a SNP (rs1361549) on 6q14.1 that was associated with asthma exclusively in African Americans with local European admixture (OR=2.2). The risk allele is common in Europe (42% in the HapMap CEU) but absent in West Africa (0% in the HapMap YRI), suggesting the allele is present in African Americans due to recent European admixture. We replicated our findings in Puerto Ricans and similarly found that the signal of association is largely specific to individuals who are heterozygous for African and non-African ancestry at 6q14.1. However, we found no evidence for association in European Americans or in Puerto Ricans in the absence of local African ancestry, suggesting that the association with asthma at rs1361549 is due to an environmental or genetic interaction.
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.
asthma; population structure; genome-wide association study; admixture mapping; ancestry association testing; admixed populations; African Americans; Puerto Ricans
Airway hyperresponsiveness (AHR), a primary characteristic of asthma, involves increased airway smooth muscle contractility in response to certain exposures. We sought to determine whether common genetic variants were associated with AHR severity.
A genome-wide association study (GWAS) of AHR, quantified as the natural log of the dosage of methacholine causing a 20% drop in FEV1, was performed with 994 non-Hispanic white asthmatic subjects from three drug clinical trials: CAMP, CARE, and ACRN. Genotyping was performed on Affymetrix 6.0 arrays, and imputed data based on HapMap Phase 2, was used to measure the association of SNPs with AHR using a linear regression model. Replication of primary findings was attempted in 650 white subjects from DAG, and 3,354 white subjects from LHS. Evidence that the top SNPs were eQTL of their respective genes was sought using expression data available for 419 white CAMP subjects.
The top primary GWAS associations were in rs848788 (P-value 7.2E-07) and rs6731443 (P-value 2.5E-06), located within the ITGB5 and AGFG1 genes, respectively. The AGFG1 result replicated at a nominally significant level in one independent population (LHS P-value 0.012), and the SNP had a nominally significant unadjusted P-value (0.0067) for being an eQTL of AGFG1.
Based on current knowledge of ITGB5 and AGFG1, our results suggest that variants within these genes may be involved in modulating AHR. Future functional studies are required to confirm that our associations represent true biologically significant findings.
Asthma; Airway hyperresponsiveness; Genome-wide association study; ITGB5; AGFG1
The National Heart, Lung and Blood Institute (NHLBI) Asthma Clinical Research Network (ACRN) recently completed its work after 20 years of collaboration as a multicentre clinical trial network. When formed, its stated mission was to perform multiple controlled clinical trials for treating patients with asthma by dispassionately examining new and existing therapies, and to rapidly communicate its findings to the medical community. The ACRN conducted 15 major clinical trials. In addition, clinical data, manual of operations, protocols and template informed consents from all ACRN trials are available via NHLBI BioLINCC (https://biolincc.nhlbi.nih.gov/studies/). This network contributed major insights into the use of inhaled corticosteroids, short-acting and long-acting ß-adrenergic agonists, leukotriene receptor antagonists, and novel agents (tiotropium, colchicine and macrolide antibiotics). They also pioneered studies of the variability in drug response, predictors of treatment response and pharmacogenetics. This review highlights the major research observations from the ACRN that have impacted the current management of asthma.
Rationale: To date, most studies aimed at discovering genetic factors influencing treatment response in asthma have focused on biologic candidate genes. Genome-wide association studies (GWAS) can rapidly identify novel pharmacogenetic loci.
Objectives: To investigate if GWAS can identify novel pharmacogenetic loci in asthma.
Methods: Using phenotypic and GWAS genotype data available through the NHLBI-funded Single-nucleotide polymorphism Health association-Asthma Resource Project, we analyzed differences in FEV1 in response to inhaled corticosteroids in 418 white subjects with asthma. Of the 444,088 single nucleotide polymorphisms (SNPs) analyzed, the lowest 50 SNPs by P value were genotyped in an independent clinical trial population of 407 subjects with asthma.
Measurements and Main Results: The lowest P value for the GWAS analysis was 2.09 × 10−6. Of the 47 SNPs successfully genotyped in the replication population, three were associated under the same genetic model in the same direction, including two of the top four SNPs ranked by P value. Combined P values for these SNPs were 1.06 × 10−5 for rs3127412 and 6.13 × 10−6 for rs6456042. Although these two were not located within a gene, they were tightly correlated with three variants mapping to potentially functional regions within the T gene. After genotyping, each T gene variant was also associated with lung function response to inhaled corticosteroids in each of the trials associated with rs3127412 and rs6456042 in the initial GWAS analysis. On average, there was a twofold to threefold difference in FEV1 response for those subjects homozygous for the wild-type versus mutant alleles for each T gene SNP.
Conclusions: Genome-wide association has identified the T gene as a novel pharmacogenetic locus for inhaled corticosteroid response in asthma.
polymorphism; genome; pharmacogenomics; glucocorticoid
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
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
Asthma is a common chronic respiratory disease characterized by airway hyperresponsiveness (AHR). The genetics of asthma have been widely studied in mouse and human, and homologous genomic regions have been associated with mouse AHR and human asthma-related phenotypes. Our goal was to identify asthma-related genes by integrating AHR associations in mouse with human genome-wide association study (GWAS) data. We used Efficient Mixed Model Association (EMMA) analysis to conduct a GWAS of baseline AHR measures from males and females of 31 mouse strains. Genes near or containing SNPs with EMMA p-values <0.001 were selected for further study in human GWAS. The results of the previously reported EVE consortium asthma GWAS meta-analysis consisting of 12,958 diverse North American subjects from 9 study centers were used to select a subset of homologous genes with evidence of association with asthma in humans. Following validation attempts in three human asthma GWAS (i.e., Sepracor/LOCCS/LODO/Illumina, GABRIEL, DAG) and two human AHR GWAS (i.e., SHARP, DAG), the Kv channel interacting protein 4 (KCNIP4) gene was identified as nominally associated with both asthma and AHR at a gene- and SNP-level. In EVE, the smallest KCNIP4 association was at rs6833065 (P-value 2.9e-04), while the strongest associations for Sepracor/LOCCS/LODO/Illumina, GABRIEL, DAG were 1.5e-03, 1.0e-03, 3.1e-03 at rs7664617, rs4697177, rs4696975, respectively. At a SNP level, the strongest association across all asthma GWAS was at rs4697177 (P-value 1.1e-04). The smallest P-values for association with AHR were 2.3e-03 at rs11947661 in SHARP and 2.1e-03 at rs402802 in DAG. Functional studies are required to validate the potential involvement of KCNIP4 in modulating asthma susceptibility and/or AHR. Our results suggest that a useful approach to identify genes associated with human asthma is to leverage mouse AHR association data.
asthma genetics; atopy; C11orf30; LRRC32; total serum IgE levels
Rationale: Recent studies suggest that people with asthma of different racial backgrounds may respond differently to various therapies.
Objectives: To use data from well-characterized participants in prior Asthma Clinical Research Network (ACRN) trials to determine whether racial differences affected asthma treatment failures.
Methods: We analyzed baseline phenotypes and treatment failure rates (worsening asthma resulting in systemic corticosteroid use, hospitalization, emergency department visit, prolonged decrease in peak expiratory flow, increase in albuterol use, or safety concerns) in subjects participating in 10 ACRN trials (1993–2003). Self-declared race was reported in each trial and treatment failure rates were stratified by race.
Measurements and Main Results: A total of 1,200 unique subjects (whites = 795 [66%]; African Americans = 233 [19%]; others = 172 [14%]; mean age = 32) were included in the analyses. At baseline, African Americans had fewer asthma symptoms (P < 0.001) and less average daily rescue inhaler use (P = 0.007) than whites. There were no differences in baseline FEV1 (% predicted); asthma quality of life; bronchial hyperreactivity; or exhaled nitric oxide concentrations. A total of 147 treatment failures were observed; a significantly higher proportion of African Americans (19.7%; n = 46) experienced a treatment failure compared with whites (12.7%; n = 101) (odds ratio = 1.7; 95% confidence interval, 1.2–2.5; P = 0.007). When stratified by treatment, African Americans receiving long-acting β-agonists were twice as likely as whites to experience a treatment failure (odds ratio = 2.1; 95% confidence interval, 1.3–3.6; P = 0.004), even when used with other controller therapies.
Conclusions: Despite having fewer asthma symptoms and less rescue β-agonist use, African-Americans with asthma have more treatment failures compared with whites, especially when taking long-acting β-agonists.
asthma; long-acting β-agonist; African Americans; race; treatment failure
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
Bronchodilator response (BDR) is an important asthma phenotype that measures reversibility of airway obstruction by comparing lung function (i.e. FEV1) before and after the administration of a short-acting β2-agonist, the most common rescue medications used for the treatment of asthma. BDR also serves as a test of β2-agonist efficacy. BDR is a complex trait that is partly under genetic control. A genome-wide association study (GWAS) of BDR, quantified as percent change in baseline FEV1 after administration of a β2-agonist, was performed with 1,644 non-Hispanic white asthmatic subjects from six drug clinical trials: CAMP, LOCCS, LODO, a medication trial conducted by Sepracor, CARE, and ACRN. Data for 469,884 single-nucleotide polymorphisms (SNPs) were used to measure the association of SNPs with BDR using a linear regression model, while adjusting for age, sex, and height. Replication of primary P-values was attempted in 501 white subjects from SARP and 550 white subjects from DAG. Experimental evidence supporting the top gene was obtained via siRNA knockdown and Western blotting analyses. The lowest overall combined P-value was 9.7E-07 for SNP rs295137, near the SPATS2L gene. Among subjects in the primary analysis, those with rs295137 TT genotype had a median BDR of 16.0 (IQR = [6.2, 32.4]), while those with CC or TC genotypes had a median BDR of 10.9 (IQR = [5.0, 22.2]). SPATS2L mRNA knockdown resulted in increased β2-adrenergic receptor levels. Our results suggest that SPATS2L may be an important regulator of β2-adrenergic receptor down-regulation and that there is promise in gaining a better understanding of the biological mechanisms of differential response to β2-agonists through GWAS.
Bronchodilator response (BDR) is an important asthma phenotype that measures reversibility of airway obstruction by comparing lung function before and after the administration of short-acting β2-agonists, common medications used for asthma treatment. We performed a genome-wide association study of BDR with 1,644 white asthmatic subjects from six drug clinical trials and attempted to replicate these findings in 1,051 white subjects from two independent cohorts. The most significant associated variant was near the SPATS2L gene. We knocked down SPATS2L mRNA in human airway smooth muscle cells and found that β2-adrenergic receptor levels increased, suggesting that SPATS2L may be a regulator of BDR. Our results highlight the promise of pursuing GWAS results that do not necessarily reach genome-wide significance and are an example of how results from pharmacogenetic GWAS can be studied functionally.
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
Studies of asthma phenotypes have identified obesity as a component of a group characterized by a high proportion of adult-onset asthmatics. However, whether age of asthma onset modifies the association between obesity and asthma is unknown.
From the Severe Asthma Project (SARP), we defined age of asthma onset as early (before 12 years of age) and late-onset (12 and higher). Comparisons of body mass index (BMI) categories were done within age of onset groups and obesity was also compared across these groups. Multivariable logistic regression analysis was done to evaluate the association between BMI categories with healthcare utilization and respiratory symptoms and multivariable linear regression for the association between duration of asthma and weight gain (BMI change/yr). An interaction between obesity and age of asthma onset was included in the multivariable analyses.
The study population consisted on 1,049 subjects of which the median age for asthma onset was 10 years (IQR 4 – 25); 48% were late-onset (≥ 12) and 52% were early-onset (<12). Compared to late-onset obese asthmatics, early-onset obese asthmatics had more airway obstruction, bronchial hyperresponsiveness, and higher OR of ever having 3 or more oral steroid tapers preceding/year or ICU admissions for asthma/preceding year (Interactions between obesity and age of asthma onset were respectively p=0.055 and p=0.02). In early-onset, but not in late-onset asthmatics, there was a significant association between increasing BMI and duration of asthma, after adjusting for confounders. The interaction between asthma duration and age of asthma onset was p < 0.01.
Asthmatics are differentially affected by obesity, based on whether they developed asthma early (<12 years) or later in life. These results highlight the need to understand obesity as a comorbidity that affects specific clinical phenotypes and not all asthma subjects alike.
Severe; asthma; obesity; SARP
In asthma, cysteinyl leukotrienes (CysLTs) play varying roles in the bronchomotor response to multiple provocative stimuli. The contribution of CysLTs on the airway's response to hypertonic saline (HS) inhalation in asthma is unknown. Whether polymorphisms in the leukotriene biosynthetic pathway affect the contribution of CysLTs to this response is also unknown.
In a prospective, randomized, double blind, placebo-controlled cross-over study, mild and moderate asymptomatic asthmatics underwent inhaled 3% HS challenge by doubling the duration of nebulization (0.5, 1, 2, 4, and 8 min) two hours after one dose of montelukast (a CysLT receptor 1 [CysLTR1] antagonist) or placebo, and after three week courses. We examined the effect of the leukotriene C4 synthase (LTC4S) polymorphism (A-444C) on the efficacy of montelukast against HS inhalation in an exploratory manner.
In 37 subjects, two hours after administration of montelukast, the mean provocative dose of HS required to cause a 20% drop in FEV1 (HS-PD20) increased by 59% (9.17 after placebo vs. 14.55 ml after montelukast, p = 0.0154). Three weeks of cysLTR1 antagonism increased the HS-PD20 by 84% (10.97 vs. 20.21 ml, p = 0.0002). Three weeks of CysLTR1 antagonism appeared to produce greater effects on blocking bronchial hyper responsiveness (two hour vs. three week HS-PD20 values 14.55 vs. 20.21 ml respectively, p = 0.0898). We did not observe an effect of the LTC4S polymorphism on the response to CysLTR1 antagonism in this cohort.
A significant proportion of HS-induced bronchoconstriction is mediated by release of leukotrienes as evidenced by substantial acute inhibition with a CysLTR1 antagonist. There was a trend toward greater inhibition of bronchial responsiveness with three weeks of therapy as opposed to acute CysLTR1 antagonism.
Asthma; Leukotriene-C4 synthase; Montelukast; Polymorphism, Single Nucleotide; Saline Solution, Hypertonic