Sputum eosinophils (Eos) are a strong predictor of airway inflammation, exacerbations, and aid asthma management, whereas sputum neutrophils (Neu) indicate a different severe asthma phenotype, potentially less responsive to TH2-targeted therapy. Variables such as blood Eos, total IgE, fractional exhaled nitric oxide (FeNO) or FEV1% predicted, may predict airway Eos, while age, FEV1%predicted, or blood Neu may predict sputum Neu. Availability and ease of measurement are useful characteristics, but accuracy in predicting airway Eos and Neu, individually or combined, is not established.
To determine whether blood Eos, FeNO, and IgE accurately predict sputum eosinophils, and age, FEV1% predicted, and blood Neu accurately predict sputum neutrophils (Neu).
Subjects in the Wake Forest Severe Asthma Research Program (N=328) were characterized by blood and sputum cells, healthcare utilization, lung function, FeNO, and IgE. Multiple analytical techniques were utilized.
Despite significant association with sputum Eos, blood Eos, FeNO and total IgE did not accurately predict sputum Eos, and combinations of these variables failed to improve prediction. Age, FEV1%predicted and blood Neu were similarly unsatisfactory for prediction of sputum Neu. Factor analysis and stepwise selection found FeNO, IgE and FEV1% predicted, but not blood Eos, correctly predicted 69% of sputum Eos
Despite statistically significant associations FeNO, IgE, blood Eos and Neu, FEV1%predicted, and age are poor surrogates, separately and combined, for accurately predicting sputum eosinophils and neutrophils.
asthma phenotypes; sputum eosinophils and neutrophils; inflammatory biomarker surrogates; TH2 biomarkers; fractional exhaled nitric oxide
While accurate measures of heritability are needed to understand the pharmacogenetic basis of drug treatment response, these are generally not available, since it is unfeasible to give medications to individuals for which treatment is not indicated. Using a polygenic linear mixed modeling approach, we estimated lower-bounds on asthma heritability and the heritability of two related drug-response phenotypes, bronchodilator response and airway hyperreactivity, using genome-wide SNP data from existing asthma cohorts. Our estimate of the heritability for bronchodilator response is 28.5% (se 16%, p = 0.043) and airway hyperresponsiveness is 51.1% (se 34%, p = 0.064), while we estimate asthma genetic liability at 61.5% (se 16%, p < 0.001). Our results agree with previously published estimates of the heritability of these traits, suggesting that the LMM method is useful for computing the heritability of other pharmacogenetic traits. Furthermore, our results indicate that multiple SNP main-effects, including SNPs as yet unidentified by GWAS methods, together explain a sizable portion of the heritability of these traits.
Asthma; Pharmacogenetics; Heritability; Bronchodilator Response; Airway Hyperresponsiveness
This is the first large pharmacogenetic investigation of the inflammatory IL-4/IL-13 pathway in patients with moderate-to-severe asthma. We analyzed genomic DNA from participants in a 12-week placebo-controlled efficacy trial of pitrakinra (1, 3, or 10 mg twice daily), a novel IL-4/IL-13 pathway antagonist (Clinicaltrials.gov NCT00801853).
The primary hypothesis for this analysis is that amino acid changes in the 3′ end of the IL-4 receptor α gene (IL4RA) or closely proximal variants would predict reductions in asthma exacerbations for subjects randomized to pitrakinra therapy.
Nineteen IL4RA single nucleotide polymorphisms (SNPs) were tested in 407 non-Hispanic white subjects for association with the primary clinical end point of asthma exacerbations and changes in secondary end points for asthma symptom scores.
The most consistent pharmacogenetic associations were observed for the correlated tagging SNPs rs8832 and rs1029489 in the IL4RA 3′ untranslated and proximal regions, respectively. Subjects homozygous for the rs8832 common G allele randomized to pitrakinra (placebo group nonsignificant) had decreased asthma exacerbations and decreased nocturnal awakenings and activities limited by asthma. There was also a significant pitrakinra dose-response relationship (placebo/1 mg/3 mg/10 mg) for exacerbations in subjects homozygous for the common allele in rs1029489 (P = .005) and rs8832 (P = .009) and the intronic SNPs rs3024585, rs3024622, and rs4787956 (P = .03).
This study demonstrates a significant pharmacogenetic interaction between anti–IL-4 receptor a therapy and IL4RA gene variation, identifying an asthma subgroup that is more responsive to therapy with this antagonist.
Pharmacogenetics; pitrakinra; IL-4 receptor; asthma therapy; IL-4 receptor antagonist
Inhaled corticosteroids are the most commonly used controller medications prescribed for asthma. Two single-nucleotide polymorphisms (SNPs), rs1876828 in CRHR1 and rs37973 in GLCCI1, have previously been associated with corticosteroid efficacy. We studied data from four existing clinical trials of asthmatics who received inhaled corticosteroids and had lung function measured by forced expiratory volume in one second (FEV1) before and after the period of such treatment. We combined the two SNPs rs37973 and rs1876828 into a predictive test of FEV1 change using a Bayesian model, which identified patients with good or poor steroid response (highest or lowest quartile, respectively) with predictive performance of 65.7% (p = 0.039 vs. random) area under the receiver-operator characteristic curve in the training population and 65.9% (p = 0.025 vs. random) in the test population. These findings show that two genetic variants can be combined into a predictive test that achieves similar accuracy and superior replicability compared with single SNP predictors.
Pharmacogenetics; Asthma; Glucocorticoids; Predictive Modeling
A pro-asthmatic culture milieu and β2-agonist (isoproterenol) were previously shown to regulate the expression of select transcription factors (TFs) within human airway epithelial and smooth muscle cells. This study tests 1116 single nucleotide polymorphisms (SNPs) across 98 of these TF genes for association with bronchodilator response (BDR) in asthma patients. Genotyping was conducted using the Illumina HumanHap550v3 Beadchip in 403 non-Hispanic White asthmatic children and their parents. SNPs were evaluated for association with BDR using family and population-based analyses. Forty-two SNPs providing p values < 0.1 in both analyses were then genotyped in three adult asthma trials. One SNP 5’ of the thyroid hormone receptor beta gene was associated with BDR in the childhood population and two adult populations (p value = 0.0012). This investigation identified a novel locus for inter-individual variability in BDR and represents a translation of a cellular drug-response study to potential personalization of clinical asthma management.
Bronchodilator response; transcription factor; association; thyroid hormone receptor β; asthma; pharmacogenetics
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: 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
Rationale: β2-agonists, the most common treatment for asthma, have a wide interindividual variability in response, which is partially attributed to genetic factors. We previously identified single nucleotide polymorphisms in the arginase 1 (ARG1) gene, which are associated with β2-agonist bronchodilator response (BDR).
Objectives: To identify cis-acting haplotypes in the ARG1 locus that are associated with BDR in patients with asthma and regulate gene expression in vitro.
Methods: We resequenced ARG1 in 96 individuals and identified three common, 5′ haplotypes (denoted 1, 2, and 3). A haplotype-based association analysis of BDR was performed in three independent, adult asthma drug trial populations. Next, each haplotype was cloned into vectors containing a luciferase reporter gene and transfected into human airway epithelial cells (BEAS-2B) to ascertain its effect on gene expression.
Measurements and Main Results: BDR varied by haplotype in each of the three populations with asthma. Individuals with haplotype 1 were more likely to have higher BDR, compared to those with haplotypes 2 and 3, which is supported by odds ratios of 1.25 (95% confidence interval, 1.03–1.71) and 2.18 (95% confidence interval, 1.34–2.52), respectively. Luciferase expression was 50% greater in cells transfected with haplotype 1 compared to haplotypes 2 and 3.
Conclusions: The identified ARG1 haplotypes seem to alter BDR and differentially regulate gene expression with a concordance of decreased BDR and reporter activity from haplotypes 2 and 3. These findings may facilitate pharmacogenetic tests to predict individuals who may benefit from other therapeutic agents in addition to β2-agonists for optimal asthma management.
Clinical trial registered with www.clinicaltrials.gov (NCT00156819, NCT00046644, and NCT00073840).
pharmacogenetics; asthma; β2-agonist
Asthma in children is a heterogeneous disorder with many phenotypes. Although unsupervised cluster analysis is a useful tool for identifying phenotypes, it has not been applied to school-age children with persistent asthma across a wide range of severities.
This study determined how children with severe asthma are distributed across a cluster analysis and how well these clusters conform to current definitions of asthma severity.
Cluster analysis was applied to 12 continuous and composite variables from 161 children at 5 centers enrolled in the Severe Asthma Research Program (SARP).
Four clusters of asthma were identified. Children in Cluster 1 (n = 48) had relatively normal lung function and less atopy, while children in Cluster 2 (n = 52) had slightly lower lung function, more atopy, and increased symptoms and medication usage. Cluster 3 (n = 32) had greater co-morbidity, increased bronchial responsiveness and lower lung function. Cluster 4 (n = 29) had the lowest lung function and the greatest symptoms and medication usage. Predictors of cluster assignment were asthma duration, the number of asthma controller medications, and baseline lung function. Children with severe asthma were present in all clusters, and no cluster corresponded to definitions of asthma severity provided in asthma treatment guidelines.
Severe asthma in children is highly heterogeneous. Unique phenotypic clusters previously identified in adults can also be identified in children, but with important differences. Larger validation and longitudinal studies are needed to determine the baseline and predictive validity of these phenotypic clusters in the larger clinical setting.
Allergic sensitization; Asthma; Severe asthma; Asthma guidelines; Children; Cluster analysis; Lung function; Phenotype
Interleukin 6 (IL6) belongs to a family of cytokines with both pro- and anti-inflammatory properties. The functional relationship between IL6 signaling and airway disease has not be well characterized; however, IL6 expression is increased during lung inflammation and injury. In this study, serum IL6 and soluble IL6R levels were assessed in non-Hispanic whites with asthma from the Severe Asthma Research Program. Correlations between serum IL6 and IL6R levels, lung function, phenotypic asthma clusters, and asthma severity were evaluated.
Serum IL6 and soluble IL6R was measured in 149 subjects with mild to severe asthma. Serum sIL6R levels were measured using the sIL-6R DuoSet (R&D Systems, Minneapolis, MN) ELISA kit and reported as ng/ml. Serum IL6 measurements were determined using the IL-6 ELISA kit (R&D Systems, Minneapolis, MN) and reported as pg/ml. Serum IL6 and sIL6R measurements were transformed to normalize distribution. The continuous variables analyzed included: % predicted FEV1 [ppFEV1], % predicted FVC [ppFVC], and FEV1/FVC. Serum samples were collected at Wake Forest. Phenotypic asthma clusters were derived as previously described (Am J Respir Crit Care Med. 2010;181:315–323).
Elevated serum IL6 was associated with lower ppFEV1 (P = 0.02) and lower ppFVC (P = 0.003), while elevated serum soluble IL6R was associated with lower ppFEV1 (P = 0.02) and lower ppFVC (P = 0.008). Increasing trends in serum IL6 were observed in atopic asthma Clusters 2 and 4 and the later onset fixed airways obstruction Cluster 5. The highest IL6 serum levels were observed in Cluster 3 characterized has having late onset asthma and elevated BMI. Serum IL6 levels were elevated in subjects with severe asthma (log IL6 = 0.33; N = 25) compared to subjects with mild/moderate asthma (log IL6 = 0.16; N = 69).
Serum IL6 and sIL6R levels are elevated in non-Hispanic white asthma subjects with lower lung function. Serum IL6 and sIL6R are potentially important biomarkers that may distinguish between non-severe and severe asthma and between atopic asthma Clusters.
Asthma was the most common comorbidity of patients hospitalized with 2009 H1N1 influenza.
To assess immunogenicity and safety of an unadjuvanted, inactivated 2009 H1N1 vaccine in severe versus mild/moderate asthma.
We conducted an open-label study involving 390 participants (age:12–79y) enrolled in October-November 2009. Severe asthma was defined as need for ≥880mcg/d of inhaled fluticasone equivalent and/or systemic corticosteroids. Within each severity group, participants were randomized to receive intramuscularly 15mcg or 30mcg of 2009 H1N1 vaccine twice, 21 days apart. Immunogenicity endpoints were seroprotection (≥40 titer in hemagglutination inhibition assay) and seroconversion (4-fold or greater titer increase). Safety was assessed through local and systemic reactogenicity, asthma exacerbations and pulmonary function.
In mild/moderate asthma (N=217), the 2009 H1N1 vaccine provided equal seroprotection 21 days after the first immunization at the 15mcg (90.6%,CI:83.5–95.4) and 30mcg (95.3%,CI:89.4–98.5) doses. In severe asthma (N=173), seroprotection 21 days after the first immunization was 77.9% (CI:67.7–86.1) and 94.1% (CI:86.8–98.1) at the 15mcg and 30mcg dose, respectively (p=0.004). The second vaccination did not provide further increases in seroprotection. Participants with severe asthma ≥60y showed the lowest seroprotection (44.4% at Day 21) with the 15mcg dose, but had adequate seroprotection with 30mcg. The two dose groups did not differ in seroconversion rates. There were no safety concerns.
Monovalent inactivated 2009 H1N1 pandemic influenza vaccine was safe and provided overall seroprotection as a surrogate of efficacy. In severe asthma participants over 60y, a 30mcg dose may be more appropriate.
H1N1; asthma; influenza; vaccine; seroprotection; severe asthma
Patients with severe asthma have increased granulocytes in their sputum compared to patients with mild to moderate asthma.
We hypothesized that inflammatory granulocytes in sputum may identify specific asthma severity phenotypes and are associated with different patterns of inflammatory proteins in sputum supernatants.
This hypothesis was tested in 242 asthmatics enrolled in the Severe Asthma Research Program who provided sputum samples for cell count, differential cell determinations, cell lysates for Western blot, and supernatant analyses by inflammatory protein microarrays and ELISAs. ANOVA and multiple linear regression models tested mediator associations.
Stratified by sputum granulocytes, < or ≥2%eosinophils and < or ≥40%neutrophils, subjects with both increased eosinophils and neutrophils had the lowest lung function, increased symptoms and healthcare utilization. Subjects with elevated eosinophils with or without increased neutrophils had significantly increased FeNO, serum eosinophils and greater frequency of daily β-agonist use. Microarray data, stratified by granulocytes revealed 25–28 inflammatory proteins increased >2-fold in sputa with ≥40% neutrophils. Microarray analyses stratified by severity of asthma, identified 6–9 proteins increased >2-fold in sputa in subjects with severe asthma compared to nonsevere asthma. ELISA data, stratified by sputum granulocytes, showed significant increases in BDNF, IL-1β, and MIP-3α/CCL20 for those with ≥40%neutrophils; these mediators demonstrated positive associations with neutrophil counts.
Combined increased sputum eosinophils and neutrophils identified asthmatics with the lowest lung function and worse asthma control, increased symptoms and healthcare requirements. Inflammatory protein analyses of sputum supernatants found novel mediators increased in asthmatics, predominantly associated with increased sputum neutrophils.
asthma phenotypes; protein microarrays; BDNF; CXCL13; TNFSF14; CCL20; CCL18
Long-acting beta-agonist (LABA) therapy improves symptoms in patients whose asthma is poorly controlled by an inhaled glucocorticoid alone. Alternative treatments for adults with uncontrolled asthma are needed.
In a three-way, double-blind, triple-dummy crossover trial involving 210 patients with asthma, we evaluated the addition of tiotropium bromide (a long-acting anticholinergic agent approved for the treatment of chronic obstructive pulmonary disease but not asthma) to an inhaled glucocorticoid, as compared with a doubling of the dose of the inhaled glucocorticoid (primary superiority comparison) or the addition of the LABA salmeterol (secondary noninferiority comparison).
The use of tiotropium resulted in a superior primary outcome, as compared with a doubling of the dose of an inhaled glucocorticoid, as assessed by measuring the morning peak expiratory flow (PEF), with a mean difference of 25.8 liters per minute (P<0.001) and superiority in most secondary outcomes, including evening PEF, with a difference of 35.3 liters per minute (P<0.001); the proportion of asthma-control days, with a difference of 0.079 (P = 0.01); the forced expiratory volume in 1 second (FEV1) before bronchodilation, with a difference of 0.10 liters (P = 0.004); and daily symptom scores, with a difference of −0.11 points (P<0.001). The addition of tiotropium was also noninferior to the addition of salmeterol for all assessed outcomes and increased the prebronchodilator FEV1 more than did salmeterol, with a difference of 0.11 liters (P = 0.003).
When added to an inhaled glucocorticoid, tiotropium improved symptoms and lung function in patients with inadequately controlled asthma. Its effects appeared to be equivalent to those with the addition of salmeterol. (Funded by the National Heart, Lung, and Blood Institute; ClinicalTrials.gov number, NCT00565266.)
Asthma is a heterogeneous disease that is caused by the interaction of genetic susceptibility with environmental influences. Genome-wide association studies (GWAS) represent a powerful approach to investigate the association of DNA variants with disease susceptibility. To date, few GWAS for asthma have been reported.
GWAS was performed on a population of severe or difficult-to-treat asthmatics to identify genes that are involved in the pathogenesis of asthma.
292,443 SNPs were tested for association with asthma in 473 TENOR cases and 1,892 Illumina general population controls. Asthma-related quantitative traits (total serum IgE, FEV1, FVC, and FEV1/FVC) were also tested in identified candidate regions in 473 TENOR cases and 363 phenotyped controls without a history of asthma to further analyze GWAS results. Imputation was performed in identified candidate regions for analysis with denser SNP coverage.
Multiple SNPs in the RAD50-IL13 region on chromosome 5q31.1 were associated with asthma: rs2244012 in intron 2 of RAD50 (P = 3.04E-07). The HLA-DR/DQ region on chromosome 6p21.3 was also associated with asthma: rs1063355 in the 3’ UTR of HLA-DQB1 (P = 9.55E-06). Imputation identified several significant SNPs in the TH2 locus control region (LCR) 3’ of RAD50. Imputation also identified a more significant SNP, rs3998159 (P = 1.45E-06), between HLA-DQB1 and HLA-DQA2.
This GWAS confirmed the important role of TH2 cytokine and antigen presentation genes in asthma at a genome-wide level and the importance of additional investigation of these two regions to delineate their structural complexity and biologic function in the development of asthma.
Asthma; GWAS; RAD50; IL13; HLA-DQB1; TENOR
Combined long-acting β2-agonist and inhaled corticosteroid (LABA/ICS) therapy improves outcomes in many asthmatics. Some studies suggest that patients homozygous for arginine at the 16th amino-acid position of the β2 adrenergic receptor (B16 Arg/Arg) benefit less than those with B16 Gly/Gly.
In an NIH-funded, B16 genotype-stratified, prospective, randomized, double-blind, placebo-controlled, cross-over trial (www.ClinicalTrials.gov registration ID NCT00200967), we compared adding salmeterol or placebo to ICS in patients with moderate asthma, using AM PEF as the primary outcome.
After 18 weeks, Arg/Arg (n=42) and Gly/Gly (n=45) subjects had greater AM PEF with salmeterol than placebo, with no difference in improvement by genotype (Arg/Arg 21.4 (p<0.0001) vs. Gly/Gly 21.5 L/min (p<0.0001); 0.1 L/min difference between genotypes, 95% CI (−14.2, 14.4), p=0.99). In Gly/Gly subjects, methacholine PC20 (a secondary outcome) doubled when salmeterol was added to ICS (p<0.0001), but remained unchanged in Arg/Arg subjects (p=0.87) (1.32 doubling dose difference between genotypes (95%CI 0.43,2.21), p=0.0038). An exploratory posthoc subset analysis of African Americans showed that salmeterol improved the AM and PM PEF for the 8 Gly/Gly subjects (29 L/min, p=0.013 and 45 L/min, p= 0.0005, respectively) but not for the 9 Arg/Arg subjects (−12 L/min, p=0.57 and−2.2 L/min, p=0.92, respectively).
B16 Arg/Arg and Gly/Gly patients experience improved airway function with salmeterol added to moderate-dose ICS. While these data provide reassurance that in the general population these polymorphisms should not alter the use of LABA with moderate-dose ICS, the significance of the genotype-differentiated response in airway reactivity favoring Gly/Gly subjects and the post-hoc analysis in African Americans require further investigation.
Asthma; pharmacogenetics; beta-adrenergic receptor; beta-agonists; salmeterol
The "Th2 hypothesis for asthma" asserts that an increased ratio of Th2:Th1 cytokine production plays an important pathogenic role in asthma. Although widely embraced, the hypothesis has been challenged by various empirical observations and has been described as overly simplistic. We sought to establish whether CD3+CD28-mediated and antigen-independent accumulation of type 1 and type 2 T cells differs significantly between nonasthmatic and asthmatic populations.
An ex vivo system was used to characterize the regulation of IFN-γ-producing (type 1) and IL-13-producing (type 2) T cell accumulation in response to CD3+CD28 and IL-2 stimulation by flow cytometry.
IL-13-producing T cells increased in greater numbers in response to antigen-independent stimulation in peripheral blood lymphocytes from female atopic asthmatic subjects compared with male asthmatics and both male and female atopic non-asthmatic subjects. IFN-γ+ T cells increased in greater numbers in response to either antigen-independent or CD3+CD28-mediated stimulation in peripheral blood lymphocytes from atopic asthmatic subjects compared to non-asthmatic subjects, regardless of gender.
We demonstrate that T cells from asthmatics are programmed for increased accumulation of both type 2 and type 1 T cells. Gender had a profound effect on the regulation of type 2 T cells, thus providing a mechanism for the higher frequency of adult asthma in females.
Genetic association studies have become an important part of our scientific landscape. This commentary discusses some basic scientific issues which should be considered when reporting and evaluating such studies including SNP Discovery, Genotyping and Haplotype Analysis; Population Size, Matching of Cases and Controls, and Population Stratification; Phenotype Definition and Multiple Related Phenotypes; Multiple Testing; Replication; Genome-wide Association Studies (GWAS); and the Role of Functional Studies. All of these elements are important in evaluating such studies and should be carefully considered when these studies are conceived and carried out.
Rationale: Inhaled β-agonists are one of the most widely used classes of drugs for the treatment of asthma. However, a substantial proportion of patients with asthma do not have a favorable response to these drugs, and identifying genetic determinants of drug response may aid in tailoring treatment for individual patients.
Objectives: To screen variants in candidate genes in the steroid and β-adrenergic pathways for association with response to inhaled β-agonists.
Methods: We genotyped 844 single nucleotide polymorphisms (SNPs) in 111 candidate genes in 209 children and their parents participating in the Childhood Asthma Management Program. We screened the association of these SNPs with acute response to inhaled β-agonists (bronchodilator response [BDR]) using a novel algorithm implemented in a family-based association test that ranked SNPs in order of statistical power. Genes that had SNPs with median power in the highest quartile were then taken for replication analyses in three other asthma cohorts.
Measurements and Main Results: We identified 17 genes from the screening algorithm and genotyped 99 SNPs from these genes in a second population of patients with asthma. We then genotyped 63 SNPs from four genes with significant associations with BDR, for replication in a third and fourth population of patients with asthma. Evidence for association from the four asthma cohorts was combined, and SNPs from ARG1 were significantly associated with BDR. SNP rs2781659 survived Bonferroni correction for multiple testing (combined P value = 0.00048, adjusted P value = 0.047).
Conclusions: These findings identify ARG1 as a novel gene for acute BDR in both children and adults with asthma.
pharmacogenetics; asthma; bronchodilator agents
Asthma is a complex genetic disease with multiple genetic and environmental determinants contributing to the observed variability in response to common anti-asthma therapies. Asthma pharmacogenetic research has focused on multiple candidate genes including the β2-adrenergic receptor gene (ADRβ2) and its effect on individual responses to beta agonist therapy. At present, knowledge about the effects of ADRβ2 variation on therapeutic responses is evolving and should not alter current Asthma Guideline approaches consisting of the use of short acting beta agonists for as-needed symptom based therapy and the use of a regular long-acting beta agonist in combination with inhaled corticosteroid therapy for optimal control of asthma symptoms in those asthmatics who are not controlled on inhaled corticosteroid alone. This approach is based upon studies showing a consistent pharmacogenetic response to regular use of short acting beta agonists (SABA) and less consistent findings in studies evaluating long acting beta agonist (LABA). While emerging pharmacogenetic studies are provocative and should lead to functional approaches, conflicting data with responses to LABA therapy may be caused by factors that include small sample sizes of study populations and differences in experimental design that may limit the conclusions that may be drawn from these clinical trials at the present time.
Rationale: Long-acting β-agonists (LABAs) and inhaled corticosteroids administered together appear to be complementary in terms of effects on asthma control. The elements of asthma control achieved by LABAs (improved lung function) and leukotriene receptor antagonists (LTRAs; protection against exacerbations) may be complementary as well.
Objective: We sought to determine whether the combination of the LTRA montelukast and the LABA salmeterol could provide an effective therapeutic strategy for asthma.
Methods and Measurements: In a randomized, placebo-controlled, crossover study of 192 subjects with moderate asthma, we compared the clinical efficacy of regular treatment over 14 weeks with the combination of montelukast and salmeterol to that with the combination of beclomethasone and salmeterol in moderate asthma. The primary efficacy outcome was time to treatment failure.
Main Results: Three months after the randomization of the last subject, the Data and Safety Monitoring Board determined that the primary research question had been answered and terminated the trial. The combination of montelukast and salmeterol was inferior to the combination of beclomethasone and salmeterol as judged by protection against asthma treatment failures (p = 0.0008), lung function (26 L/min difference in a.m. peak expiratory flow rate, p = 0.011), asthma control score (0.22 difference in Asthma Control Questionnaire score, p = 0.038), and markers of inflammation and airway reactivity.
Conclusions: Patients with moderate asthma similar to those we studied should not substitute the combination of an LTRA and an LABA for the combination of inhaled corticosteroid and an LABA.
combination therapy; leukotriene; beta-agonists; inhaled corticosteroids
Rationale: The comprehensive evaluation of gene variation, haplotype structure, and linkage disequilibrium is important in understanding the function of β2-adrenergic receptor gene (ADRβ2) on disease susceptibility, pulmonary function, and therapeutic responses in different ethnic groups with asthma.
Objectives: To identify ADRβ2 polymorphisms and haplotype structure in white and African American subjects and to test for genotype and haplotype association with asthma phenotypes.
Methods: A 5.3-kb region of ADRβ2 was resequenced in 669 individuals from 429 whites and 240 African Americans. A total of 12 polymorphisms, representing an optimal haplotype tagging set, were genotyped in whites (338 patients and 326 control subjects) and African Americans (222 patients and 299 control subjects).
Results: A total of 49 polymorphisms were identified, 21 of which are novel; 31 polymorphisms (frequency > 0.03) were used to identify 24 haplotypes (frequency > 0.01) and assess linkage disequilibrium. Association with ratio (FEV1/FVC)2 for single-nucleotide polymorphism +79 (p < 0.05) was observed in African Americans. Significant haplotype association for (FEV1/FVC)2 was also observed in African Americans.
Conclusions: There are additional genetic variants besides +46 (Gly16Arg) that are important in determining asthma phenotypes. These data suggest that the length of a poly-C repeat (+1269) in the 3′ untranslated region of ADRβ2 may influence lung function, and may be important in delineating variation in β-agonist responses, especially in African Americans.
asthma; β2-adrenergic receptor; β-agonist therapy; DNA polymorphisms; pharmacogenomics
Rationale: Several studies suggest that patients with asthma who are homozygous for arginine at the 16th position of the β2-adrenergic receptor may not benefit from short-acting β-agonists.
Objectives: We investigated whether such genotype-specific effects occur when patients are treated with long-acting β-agonists and whether such effects are modified by concurrent inhaled corticosteroid (ICS) use.
Methods: We compared salmeterol response in patients with asthma homozygous for arginine at B16 (B16Arg/Arg) with those homozygous for glycine at B16 (B16Gly/Gly) in two separate cohorts. In the first, subjects were randomized to regular therapy with salmeterol while simultaneously discontinuing ICS therapy. In the second, subjects were randomized to regular therapy with salmeterol while continuing concomitant ICS.
Results: In both trials, B16Arg/Arg subjects did not benefit compared with B16Gly/Gly subjects after salmeterol was initiated. In the first cohort, compared with placebo, the addition of salmeterol was associated with a 51.4 L/min lower A.M. peak expiratory flow (PEF; p = 0.005) in B16Arg/Arg subjects(salmeterol, n = 12; placebo, n = 5) as compared with B16Gly/Gly subjects (salmeterol, n = 13; placebo, n = 13). In the second cohort, B16Arg/Arg subjects treated with salmeterol and ICS concurrently (n = 8) had a lower A.M. PEF (36.8 L/min difference, p = 0.048) than B16Gly/Gly subjects (n = 22) treated with the same regimen. In addition, B16 Arg/Arg subjects in the second cohort had lower FEV1 (0.42 L, p = 0.003), increased symptom scores (0.2 units, p = 0.034), and increased albuterol rescue use (0.95 puffs/d, p = 0.004) compared with B16Gly/Gly subjects.
Conclusions: Relative to B16Gly/Gly patients with asthma, B16Arg/Arg patients with asthma may have an impaired therapeutic response to salmeterol in either the absence or presence of concurrent ICS use. Investigation of alternate treatment strategies may benefit this group.
asthma; β-adrenergic receptor; β-agonists; pharmacogenetics; salmeterol
Rationale: Basic and clinical research strategies used for many lung diseases have depended on volunteer subjects undergoing bronchoscopy to establish access to the airways to collect biological specimens and tissue, perhaps with added bronchoprovocation in asthma syndromes. These procedures have yielded a wealth of important scientific information. Since the last critical review more than a decade ago, some of the techniques and applications have changed, and untoward events have occurred, raising safety concerns and increasing institutional review scrutiny.
Objectives and Methods: To reappraise these investigational methods in the context of current knowledge, the National Heart, Lung, and Blood Institute and the National Institute of Allergy and Infectious Diseases of the National Institutes of Health convened a working group to review these procedures used for airway disease research, emphasizing asthma and chronic obstructive pulmonary disease.
Main Results: The group reaffirmed the scientific importance of investigative bronchoscopy and bronchoprovocation, even as less invasive technologies evolve. The group also considered the safety of bronchoscopy and bronchoprovocation with methacholine and antigen to be acceptable for volunteer subjects and patients, but stressed the need to monitor this closely and to emphasize proper training of participating medical research personnel. Issues were raised about vulnerable volunteers, especially children who need surrogates for informed consent.
Conclusion: This review of investigative bronchoscopy and bronchoprovocation could serve as the basis for future guidelines for the use of these procedures in the United States.
airway hyperresponsiveness; asthma; bronchoalveolar lavage; chronic obstructive pulmonary disease; lidocaine; methacholine; segmental allergen challenge
OBJECTIVE: Inhaled corticosteroids (ICSs) are the most effective medications available for patients with persistent asthma of all severities and currently are recommended as the preferred asthma controller therapy by the National Heart, Lung and Blood Institute. Nevertheless, lingering concerns about potential adverse systemic effects of ICSs contribute to their underuse. This review discusses the safety of ICSs with respect to potential systemic effects of most concern to physicians and patients. METHODS: Articles reporting on the safety of ICSs in children and adults with persistent asthma were identified from the Medline database from January 1966 through December 2003, reference lists of review articles and international respiratory meetings. RESULTS: Ocular effects of ICSs and ICS effects on bone mineral density and adrenal function are minimal in patients maintained on recommended ICS doses. One-year growth studies in children have shown decreased growth velocity with ICSs, but long-term studies with inhaled budesonide and beclomethasone show no effect on final adult height, suggesting that these effects are transient. In addition, extensive data from the Swedish Medical Birth Registry show no increased risk of adverse perinatal outcomes when inhaled budesonide is administered to pregnant women with asthma. CONCLUSIONS: ICSs have minimal systemic effects in most patients when taken at recommended doses. The benefits of ICS therapy clearly outweigh the risks of uncontrolled asthma, and ICSs should be prescribed routinely as first-line therapy for children and adults with persistent disease.
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