Use of regularly scheduled albuterol treatment in asthma: genotype-stratified, randomised, placebo-controlled cross-over trial

Asthma pharmacogenetics: responding to the call for a personalized approach

PURPOSE OF REVIEW

Asthma is a chronic, complex disease that is treated with a combination of different therapies. However, interindividual variability in clinical responses to different therapies complicates asthma management. A personalized approach to asthma management could identify appropriate responders to specific agents or those that might be at an increased risk for adverse responses.

RECENT FINDINGS

Pharmacogenetic studies of genes from the leukotriene, glucocorticoid, and beta2-adrenergic receptor pathways have improved our understanding of how gene variation determines therapeutic responses to different classes of antiasthma therapies. Such studies have previously been limited to retrospective analyses of candidate genes in the leukotriene, glucocorticoid, and beta2-adrenergic receptor pathways in trial cohorts. However, prospective genotype-stratified trials in asthma have recently been done and recent genome-wide association studies have identified novel pharmacogenetic loci.

SUMMARY

It will be important to replicate previous genotypic associations in large clinical trial cohorts as future pharmacogenetic studies continue to focus on genome-wide approaches and the study of novel therapeutic pathways. This review of the pharmacogenetics of asthma highlights the contributions of genomics research to the future of personalized medicine in asthma and draws attention to the role of genetic biomarkers in predicting clinical responses to specific therapies.

A genome-wide association study of bronchodilator response in asthmatics

Reversibility of airway obstruction in response to β2-agonists is highly variable among asthmatics, which is partially attributed to genetic factors. In a genome-wide association study of acute bronchodilator response (BDR) to inhaled albuterol, 534 290 single-nucleotide polymorphisms (SNPs) were tested in 403 white trios from the Childhood Asthma Management Program using five statistical models to determine the most robust genetic associations. The primary replication phase included 1397 polymorphisms in three asthma trials (pooled n=764). The second replication phase tested 13 SNPs in three additional asthma populations (n=241, n=215 and n=592). An intergenic SNP on chromosome 10, rs11252394, proximal to several excellent biological candidates, significantly replicated (P=1.98 × 10(-7)) in the primary replication trials. An intronic SNP (rs6988229) in the collagen (COL22A1) locus also provided strong replication signals (P=8.51 × 10(-6)). This study applied a robust approach for testing the genetic basis of BDR and identified novel loci associated with this drug response in asthmatics.

Effect of rare variants in ADRB2 on risk of severe exacerbations and symptom control during longacting β agonist treatment in a multiethnic asthma population: a genetic study

BACKGROUND

Severe adverse life-threatening events associated with longacting β agonist (LABA) use have caused the US Food and Drug Administration (FDA) to review the safety of these drugs, resulting in a boxed warning and a mandatory safety study in 46 800 patients with asthma. Identification of an at-risk, susceptible subpopulation on the basis of predictive biomarkers is crucial for understanding LABA safety. The β2-adrenergic receptor gene (ADRB2) contains a common, non-synonymous single nucleotide polymorphism, Gly16Arg, that is unlikely to account for the rare, life-threatening events seen with LABA use. We hypothesise that rare ADRB2 variants modulate therapeutic responses to LABA therapy and contribute to rare, severe adverse events.

METHODS

In this genetic study, ADRB2 was sequenced in 197 African American, 191 non-Hispanic white, and 73 Puerto Rican patients. Sequencing identified six rare variants, which were genotyped in 1165 patients with asthma. The primary hypothesis was that severe asthma exacerbations requiring hospital admission were associated with rare ADRB2 variants in patients receiving LABA therapy. This outcome was assessed overall and by ethnic group. Replication was done in 659 non-Hispanic white patients with asthma.

FINDINGS

Patients receiving LABA with a rare ADRB2 variant had increased asthma-related hospital admissions (15 [44%] of 34 patients with rare variant vs 121 [22%] of 553 patients with common ADRB2 alleles admitted to hospital in past 12 months; meta-analysis for all ethnic groups, p=0·0003). Specifically, increases in hospital admission rates were recorded in LABA-treated non-Hispanic white patients with the rare Ile 164 allele compared with non-Hispanic white patients with the common allele (odds ratio [OR] 4·48, 95% CI 1·40-13·96, p=0·01) and African American patients with a 25 bp promoter polynucleotide insertion, -376ins, compared with African American patients with the common allele (OR 13·43, 95% CI 2·02-265·42, p=0·006). The subset of non-Hispanic white and African American patients receiving LABAs with these rare variants had increased exacerbations requiring urgent outpatient health-care visits (non-Hispanic white patients with or without the rare Ile 164 allele, 2·6 [SD 3·5] vs 1·1 [2·1] visits, p<0·0001; and African American patients with or without the rare insertion, 3·7 [4·6] vs 2·4 [3·4] visits, p=0·01), and more frequently were treated with chronic systemic corticosteroids (OR 4·25, 95% CI 1·38-14·41, p=0·01, and 12·83, 1·96-251·93, p=0·006). Non-Hispanic white patients from the primary and replication cohorts with the rare Ile 164 allele were more than twice as likely as Thr 164 homozygotes to have uncontrolled, persistent symptoms during LABA treatment (p=0·008-0·04).

INTERPRETATION

The rare ADRB2 variants Ile164 and -376ins are associated with adverse events during LABA therapy and should be evaluated in large clinical trials including the current FDA-mandated safety study.

FUNDING

US National Institutes of Health.

Genetic influences on response to asthma pharmacotherapy

Asthma is a complex inflammatory disease that affects 300 million people worldwide. Safe and effective drugs control the symptoms but heterogeneity in response is large and attributable, in part, to genetic variation. Polymorphisms in several genes influence response to asthma drugs. The genotype of the ADRB2 Gly16Arg single nucleotide polymorphism (SNP) associates with asthma worsening during continuous therapy with β-agonists. SNPs in four genes influence response to inhaled corticosteroids: CRHR1, ACP, TBX21 and FCER2. Polymorphisms in leukotriene pathway and transporter genes influence response to zileuton and the leukotriene receptor antagonists, including ALOX5, LTA4H, LTC4S, ABCC1 and SLCO2B1. Known sequence variants explain a small fraction of response heterogeneity to asthma drugs. More studies are required to formulate a genetic signature that will lead to the personalization of asthma treatment.

Impact of single nucleotide polymorphism in IL-4, IL-4R genes and systemic concentration of IL-4 on the incidence of glioma in Iraqi patients

Glioma is the most common and believed to be one of the most aggressive tumors of the central nervous system (CNS) in humans. Very little information is available on the etiology and pathogenesis of these tumors to date. A significant gap remains in our current understanding of the molecular pathways involved in the genesis, progression and clinical behavior of these tumors. Recently, several single nucleotide polymorphisms (SNPs) have been identified in cytokine gene sequences, particularly within the promoter region of these genes, and have been shown to be associated with the development of different types of brain tumors. The present study investigates the association of C-33T SNP in the interleukin-4 (IL-4) gene with systemic IL-4 level and the S503P SNP in the IL-4R gene with the incidence of glioma. Blood samples were collected from 100 histologically confirmed adult patients with glioma, and 30 apparently healthy individuals from the same area. DNA was extracted from each blood sample, and the IL-4 and IL-4R genes were amplified using polymerase chain reaction (PCR) with gene-specific primers. Systemic IL-4 concentration was assessed in serum samples from each participant by enzyme-linked immunosorbent assay (ELISA). We observed a negative association between the homozygous genotype (CC) of the SNP C-33T of the IL-4 gene with the incidence of glioma (OR=0.19, 95% CI=0.035-1.02), while the T allele of the SNP demonstrated a significant protective association against glioma. Similarly, the heterozygous (CT) and homozygous mutant (CC) of the SNP S503P of the IL-4R gene demonstrated a significant association with glioma development (OR=0.405, 95% CI=0.17-0.969 and OR=0.147, 95% CI=0.036-0.6 respectively), while the C allele exhibited a highly significant association with protection from glioma formation. These findings suggest that the T allele of the SNP C-33T in the IL-4 gene and the C allele of the SNP S503P in IL-4R may have a protective role against glioma development.

Arg16 ADRB2 genotype increases the risk of asthma exacerbation in children with a reported use of long-acting β2-agonists: results of the pacman cohort

Background: Current evidence suggests that asthma patients with the ADRB2 Arg16 genotype have a poorer response to long-acting β2-agonists (LABA), but the results remain inconsistent. Aim: This study assessed the association between Arg16 variants and treatment outcome in children treated with inhaled corticosteroids (ICS) and LABA. Materials & methods: ADRB2 Arg16 was genotyped in 597 children (4–12 years of age) participating in the PACMAN cohort study. A questionnaire was used to assess asthma control, frequency of asthma-related emergency department visits and use of oral corticosteroids in the past year. Results: Arg/Arg carriers with a reported use of ICS and LABA had an increased risk of oral corticosteroid use (odds ratio: 14.9; 95% CI: 1.59–140.1) and emergency department visits in the past year (odds ratio: 11.9; 95% CI: 1.22–115.8) compared to Gly/Gly carriers. This effect was not observed in Arg/Arg genotype carriers reporting ICS use only. Conclusion: Children who are homozygous for ADRB2 Arg16 have an increased risk of exacerbations when treated with combined LABA and ICS.

Original submitted 4 September 2013; Revision submitted 27 September 2013

Proof-of-concept evaluation of trough airway hyper-responsiveness following regular racemic or levosalbutamol in genotype-stratified steroid-treated persistent asthmatic patients

Asthmatic patients receiving ICSs (inhaled corticosteroids) may take frequent add-on therapy with salbutamol despite on-demand prescription. Frequent salbutamol use can be detrimental in asthma. The isomeric formulation of salbutamol and the B2ADR (β2 adrenoceptor) 16 genotype may also influence this phenomenon. We performed a randomized, double-blind, placebo-controlled, triple crossover, proof of concept trial comparing 2 weeks of regular therapy with inhaled racemic salbutamol [200 μg q.i.d. (four times daily)], levosalbutamol (100 μg q.i.d.) or placebo on trough methacholine PC20 [provocative concentration causing 20% fall in FEV1 (forced expiratory volume in 1 s)] 6 h post-dose (the primary outcome) in 30 persistent asthmatic patients (15 who were Arg16 homozygous and 15 who were Gly16 homozygous) all receiving ICSs. There was no worsening of AHR (airway hyper-responsiveness) at trough to methacholine after 2 weeks regular exposure to either racemic (P=0.53) or levosalbutamol (P=0.84) compared with placebo, nor between genotypes-as dd (doubling dilution) difference in methacholine PC20 from placebo [salbutamol/Arg16=0.36 dd [95% CI (confidence interval), -0.43, 1.15]; salbutamol/Gly16=0.01 dd (95% CI, -0.47, 0.49); levosalbutamol/Arg16=-0.01 dd (95% CI, -0.89, 0.87); and levosalbutamol/Gly16=0.28 dd (95% CI, -0.22, 0.77)]. Both active treatments improved morning PEF (peak expiratory flow) in Gly16 (P=0.04 overall) but not Arg16 (P=0.50 overall) patients, whereas evening PEF improved in both Gly16 (P<0.001 overall) and Arg16 (P=0.006 overall) patients. In conclusion, the regular exposure to either racemic or levosalbutamol for 2 weeks added to ICSs did not cause worsening of AHR at trough compared with placebo; with no difference seen between B2ADR 16 genotypes.

Exploiting functional domains of GRK2/3 to alter the competitive balance of pro- and anticontractile signaling in airway smooth muscle

To clarify the potential utility of targeting GRK2/3-mediated desensitization as a means of manipulating airway smooth muscle (ASM) contractile state, we assessed the specificity of GRK2/3 regulation of procontractile and relaxant G-protein-coupled receptors in ASM. Functional domains of GRK2/3 were stably expressed, or siRNA-mediated GRK2/3 knockdown was performed, in human ASM cultures, and agonist-induced signaling was assessed. Regulation of contraction of murine tracheal rings expressing GRK2 C terminus was also assessed. GRK2/3 knockdown or expression of the GRK2 C terminus caused a significant (∼ 30-90%) increase in maximal β-agonist and histamine [phosphoinositide (PI) hydrolysis] signaling, without affecting the calculated EC50. GRK2 C-terminal expression did not affect signaling by methacholine, thrombin, or LTD4. Expression of the GRK2 N terminus or kinase-dead holo-GRK2 diminished (∼ 30-70%) both PI hydrolysis and Ca(2+) mobilization by every Gq-coupled receptor examined. Under conditions of GRK2 C-terminal expression, β-agonist inhibition of methacholine-stimulated PI hydrolysis was greater. Finally, transgenic expression of the GRK2 C terminus in murine ASM enabled ∼ 30-50% greater β-agonist-mediated relaxation of methacholine-induced contraction. Collectively these data demonstrate the relative selectivity of GRKs for the β2AR in ASM and the ability to exploit GRK2/3 functional domains to render ASM hyporesponsive to contractile agents while increasing responsiveness to bronchodilating β-agonist.

Single nucleotide polymorphisms of ADRB2 gene and their association with susceptibility for Plasmodium falciparum malaria and asthma in an Indian population

The essential route to blood parasitaemia in malaria, erythrocyte invasion is facilitated by activation of the G-protein coupled receptor signaling pathway mediated by the β2-adrenoreceptor as one of the proteins on the surface of red blood cells. The effectiveness of bronchodilators and inhaled corticosteroids in the clinical treatment for asthma patients also depend on polymorphisms in the β2-adrenoreceptor gene (ADRB2). In a case control study, individuals affected by Plasmodium falciparum malaria, asthma and controls were tested for association of six ADRB2 single nucleotide polymorphisms (SNPs) viz. rs1042711, rs1801704, rs1042713, rs1042714, rs1042717 and rs1042718, by direct DNA sequencing. The rs1801704 locus was significantly associated with malaria when compared against controls. The rs1042713 polymorphism was associated with forced expiratory flow between 25% and 75% of the FVC in asthma patients, pre (p=0.048) and post (p=0.038) treatment measurements. Predicted haplotype of the six SNPs computed from genotype data showed T-T-A-C-G-C conferred significant risk of malaria (p=0.02) whereas T-T-A-C-G-A was associated with risk of asthma (p=0.02). The haplotype T-T-G-C-G-C was protective against both malaria (p=0.02) as well as asthma (p=0.026) and C-C-G-G-G-C was protective uniquely for asthma (p=0.04). A significant outcome was that all variant alleles at the SNP loci were part of the haplotype conferring resistance to malaria disease and asthma, except rs1042713 and rs1042718 which showed very high frequency in asthma. The pairwise linkage disequilibrium (LD) estimates showed a distinct LD block of all SNP loci (D'=1 or >0.8) in malaria patients. This characteristic haplotype block was disrupted in the controls due to non-significant pairwise LD of the SNP loci; and a more extensive disruption of the block was noted in asthma patients. The study provides evidence for the proposed role of β2-adrenoreceptor mediated molecular mechanisms in etiology of malaria, as well as asthma disease and drug response, for further clinical and therapeutic application studies.

Tolerance & resistance to β₂-agonist bronchodilators

For the past half-century, β₂-agonists have been the mainstay of treatment of the bronchoconstriction associated with asthma. Although their usefulness in reversing acute bronchospasm remains undiminished, there is increasing evidence that chronic use may lead to development of tolerance and thus, potentially increasing morbidity and even mortality. In addition, genetic studies have shown that certain individuals carrying specific mutations may be prone to developing resistance to β₂-agonists regardless of the duration of treatment. This article reviews the current evidence regarding the underlying mechanisms that cause or contribute to the development of the resistance, as well as the strategies for the evaluation and management of patients who are at risk for or have developed tolerance to β₂-agonists.

Novel therapies in asthma: leukotriene antagonists, biologic agents, and beyond

Asthma is one of the most common conditions seen in clinical practice and carries both a significant disease burden in terms of patient morbidity and a high economic burden in both direct and indirect costs. Despite this, it remains a comparatively poorly understood disease, with only modest advances in treatment over the past decade. Corticosteroids remain the cornerstone of therapy. Both patient compliance with medications and physician adherence to evidence-based guidelines are often poor, and a high percentage of patients continue to have inadequately controlled disease even with optimal therapy. Following a contextual overview of the current treatment guidelines, this review focuses on novel asthma therapies, beginning with the introduction of the leukotriene receptor antagonist zafirlukast in the 1990s, continuing through advanced endoscopic therapy and into cytokine-directed biologic agents currently in development. Along with clinically relevant biochemistry and pharmacology, the evidence supporting the place of these therapies in current guidelines will be highlighted along with data comparing these agents with more conventional treatment. A brief discussion of other drugs, such as those developed for unrelated conditions and subsequently examined as potential asthma therapies, is included.

Integrative systems biology approaches in asthma pharmacogenomics

In order to improve therapeutic outcomes, there is a tremendous need to identify patients who are likely to respond to a given asthma treatment. Pharmacogenomic studies have explained a portion of the variability in drug response and provided an increasing list of candidate genes and SNPs. However, as phenotypic variation arises from a network of complex interactions among genetic and environmental factors, rather than individual genes or SNPs, a multidisciplinary, systems-level approach is required in order to understand the inter-relationships among these factors. Systems biology, which seeks to capture interactions between genetic factors and other variables, offers a promising approach to improved therapeutic outcomes in asthma. This aritcle will review and update progress in the pharmacogenomics of asthma and then discuss the application of systems biology approaches to asthma pharmacogenomics.

Can certain genotypes predispose to poor asthma control in children? A pharmacogenetic study of 9 candidate genes in children with difficult asthma

Objective

We tested the hypothesis that patients with difficult asthma have an increased frequency of certain genotypes that predispose them to asthma exacerbations and poor asthma control.

Methods

A total of 180 Caucasian children with confirmed asthma diagnosis were selected from two phenotypic groups; difficult (n = 112) versus mild/moderate asthma (n = 68) groups. All patients were screened for 19 polymorphisms in 9 candidate genes to evaluate their association with difficult asthma.

Key Results

The results indicated that LTA4H A-9188>G, TNFα G-308>A and IL-4Rα A1727>G polymorphisms were significantly associated with the development of difficult asthma in paediatric patients (p<0.001, p = 0.019 and p = 0.037, respectively). Haplotype analysis also revealed two haplotypes (ATA haplotype of IL-4Rα A1199>C, IL-4Rα T1570>C and IL-4Rα A1727>G and CA haplotype of TNFα C-863>A and TNFα G-308>A polymorphisms) which were significantly associated with difficult asthma in children (p = 0.04 and p = 0.018, respectively).

Conclusions and Clinical Relevance

The study revealed multiple SNPs and haplotypes in LTA4H, TNFα and IL4-Rα genes which constitute risk factors for the development of difficult asthma in children. Of particular interest is the LTA4H A-9188>G polymorphism which has been reported, for the first time, to have strong association with severe asthma in children. Our results suggest that screening for patients with this genetic marker could help characterise the heterogeneity of responses to leukotriene-modifying medications and, hence, facilitate targeting these therapies to the subset of patients who are most likely to gain benefit.

A tailored approach to asthma management: Arg(16) holds the key?

Asthma is heterogeneous with respect to clinical presentation, underlying disease mechanisms and response to existing drugs making tailored therapy desirable. Pharmacogenetics, the study of the influence of genetic polymorphisms on drug efficacy and/or adverse effects, is relatively advanced in asthma with replicated genetic associations identified in the main drug classes. In the present issue of Clinical Science, Lipworth and co-workers report a proof-of-concept study and demonstrate that, in asthmatic children carrying the β(2)-adrenergic receptor gene Arg(16) polymorphism, a combination of corticosteroid plus leukotriene receptor antagonist provides superior asthma control (e.g. quality of life scores) compared with corticosteroid plus a long-acting β(2)-adrenergic receptor agonist as add-on therapy. The basis of these observations is well founded, as it has been demonstrated previously that the Arg(16) polymorphism may confer an increased risk of exacerbation following prolonged β(2)--adrenergic receptor agonist use. These results suggest Gly16Arg genotyping in Caucasian asthma patients may have a role in the clinical management of asthma by influencing the decision of which add-on therapy to prescribe; however, larger studies are required to provide definitive conclusions regarding the clinical utility of this approach.

Intermittent versus daily inhaled corticosteroids for persistent asthma in children and adults

BACKGROUND

Daily inhaled corticosteroids (ICS) are the recommended mainstay of treatment in children and adults with persistent asthma. However, often, ICS are used intermittently by patients or recommended by physicians to be used only at the onset of exacerbations.

OBJECTIVES

The aim of this review was to compare the efficacy and safety of intermittent versus daily ICS in the management of children and adults with persistent asthma and preschool-aged children suspected of persistent asthma.

SEARCH METHODS

We searched the Cochrane Airways Group Specialised Register of trials (CAGR) and the ClinicalTrials.gov web site up to October 2012.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) that compared intermittent ICS versus daily ICS in children and adults with persistent asthma. No co-interventions were permitted other than rescue relievers and oral corticosteroids used during exacerbations.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for inclusion, methodological quality and extracted data. The primary efficacy outcome was the number of patients with one or more exacerbations requiring oral corticosteroids and the primary safety outcome was the number of patients with serious adverse health events. Secondary outcomes included exacerbations, lung function tests, asthma control, adverse effects, withdrawal rates and inflammatory markers. Equivalence was assumed if the risk ratio (RR) estimate and its 95% confidence interval (CI) were between 0.9 and 1.1. Quality of the evidence was assessed using GRADE.

MAIN RESULTS

Six trials (including one trial testing two relevant protocols) met the inclusion criteria for a total of seven group comparisons. The four paediatric trials (two involving preschool children and two school-aged children) and two adult parallel-group trials, lasting 12 to 52 weeks, were of high methodological quality. A total of 1211 patients with confirmed, or suspected, persistent asthma contributed to the meta-analyses. There was no statistically significant group difference in the risk of patients experiencing one or more exacerbations requiring oral corticosteroids (1204 patients; RR 1.07; 95% CI 0.87 to 1.32; the large confidence interval translates into a risk of exacerbations in the intermittent ICS group varying between 17% and 25%, assuming a 19% risk with daily ICS). Age, severity of airway obstruction, step-up protocol used during exacerbations and trial duration did not significantly influence the primary efficacy outcome. No group difference was observed in the risk of patients with serious adverse health events (1055 patients; RR 0.82; 95% CI 0.33 to 2.03). Compared to the daily ICS group, the intermittent ICS group displayed a smaller improvement in change from baseline peak expiratory flow rate (PEFR) by 2.56% (95% CI -4.49% to -0.63%), fewer symptom-free days (standardised mean difference (SMD) -0.15 (95% CI -0.28 to -0.03), fewer asthma control days -9% (95% CI -14% to -4%), more use of rescue β2-agonists by 0.12 puffs/day (95% CI 0 to 0.23) and a greater increase from baseline in exhaled nitric oxide of 16.80 parts per billion (95% CI 11.95 to 21.64). There was no significant group difference in forced expiratory volume in one second (FEV1), quality of life, airway hyper-reactivity, adverse effects, hospitalisations, emergency department visits or withdrawals. In paediatric trials, intermittent ICS (budesonide and beclomethasone) were associated with greater growth by 0.41 cm change from baseline (532 children; 95% CI 0.13 to 0.69) compared to daily treatment.

AUTHORS' CONCLUSIONS

In children and adults with persistent asthma and in preschool children suspected of persistent asthma, there was low quality evidence that intermittent and daily ICS strategies were similarly effective in the use of rescue oral corticosteroids and the rate of severe adverse health events. The strength of the evidence means that we cannot currently assume equivalence between the two options.. Daily ICS was superior to intermittent ICS in several indicators of lung function, airway inflammation, asthma control and reliever use. Both treatments appeared safe, but a modest growth suppression was associated with daily, compared to intermittent, inhaled budesonide and beclomethasone. Clinicians should carefully weigh the potential benefits and harm of each treatment option, taking into account the unknown long-term (> one year) impact of intermittent therapy on lung growth and lung function decline.

The adult asthmatic

Asthma in the adult patient is a complex clinical syndrome. Multiple patient phenotypes and subphenotypes exist that contribute to disease heterogeneity. Whether adult asthma begins in utero, develops in childhood, or manifests for the first time in adulthood is not completely understood, nor are the mechanisms fully delineated. In this chapter, we update definitions that apply to this group, emphasize epidemiologic factors and pathogenic mechanisms, diagnosis, therapeutic options, and controversies regarding drug safety. Finally, we provide a brief discussion of biomarker technologies and novel therapies with the potential to impact adult-onset asthma outcomes.

Chapter 7: Pharmacogenomics

There is great variation in drug-response phenotypes, and a “one size fits all” paradigm for drug delivery is flawed. Pharmacogenomics is the study of how human genetic information impacts drug response, and it aims to improve efficacy and reduced side effects. In this article, we provide an overview of pharmacogenetics, including pharmacokinetics (PK), pharmacodynamics (PD), gene and pathway interactions, and off-target effects. We describe methods for discovering genetic factors in drug response, including genome-wide association studies (GWAS), expression analysis, and other methods such as chemoinformatics and natural language processing (NLP). We cover the practical applications of pharmacogenomics both in the pharmaceutical industry and in a clinical setting. In drug discovery, pharmacogenomics can be used to aid lead identification, anticipate adverse events, and assist in drug repurposing efforts. Moreover, pharmacogenomic discoveries show promise as important elements of physician decision support. Finally, we consider the ethical, regulatory, and reimbursement challenges that remain for the clinical implementation of pharmacogenomics.

Intermittent versus daily inhaled corticosteroids for persistent asthma in children and adults

BACKGROUND

Daily inhaled corticosteroids (ICS) are the recommended mainstay of treatment in children and adults with persistent asthma. Yet often, ICS are used intermittently by patients or recommended by physicians to be used only at the onset of exacerbations.

OBJECTIVES

The aim of this review was to compare the efficacy and safety of intermittent versus daily ICS in the management of children and adults with persistent asthma and preschool-aged children suspected of persistent asthma.

SEARCH METHODS

We searched the Cochrane Airways Group Specialised Register of trials (CAGR) and the ClinicalTrials.gov website up to December 2011.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) that compared intermittent ICS versus daily ICS in children and adults with persistent asthma. No co-interventions were permitted other than rescue relievers and oral corticosteroids used during exacerbations.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for inclusion, methodological quality and extracted data. The primary efficacy outcome was the number of patients with one or more exacerbations requiring oral corticosteroids and the primary safety outcome was the number of patients with serious adverse health events. Secondary outcomes included exacerbations, lung function tests, asthma control, adverse effects, withdrawal rates and inflammatory markers. Equivalence was assumed if the risk ratio (RR) estimate and its 95% confidence interval (CI) were between 0.9 and 1.1.

MAIN RESULTS

Six trials (including one trial testing two relevant protocols) met the inclusion criteria for a total of seven group comparisons. The four paediatric trials (two involving preschool children and two school-aged children) and two adult parallel-group trials, lasting 12 to 52 weeks, were of high methodological quality. A total of 1211 patients with confirmed, or suspected, persistent asthma contributed to the meta-analyses. There was no statistically significant group difference in the risk of patients experiencing one or more exacerbations requiring oral corticosteroids (1204 patients; RR 1.07; 95% CI 0.87 to 1.32). The patients' age, severity of airway obstruction, step-up protocol used during exacerbations and trial duration did not significantly influence the primary efficacy outcome. No group difference was observed in the risk of patients with serious adverse health events (1055 patients; RR 0.82; 95% CI 0.33 to 2.03). Compared to the daily ICS group, the intermittent ICS group displayed a smaller improvement in change from baseline peak expiratory flow rate (PEFR) by 2.56% (95% CI -4.49% to -0.63%), fewer symptom-free days (standardised mean difference (SMD) -0.15 (95% CI -0.28 to -0.03), fewer asthma control days -9% (95% CI -14% to -4%), more use of rescue β(2)-agonists by 0.12 puffs/day (95% CI 0 to 0.23) and a greater increase from baseline in exhaled nitric oxide of 16.80 parts per billion (95% CI 11.95 to 21.64). There was no significant group difference in forced expiratory volume in one second (FEV(1)), quality of life, airway hyper-reactivity, adverse effects, hospitalisations, emergency department visits or withdrawals. In paediatric trials, intermittent ICS (budesonide and beclomethasone) were associated with greater growth by 0.41 cm change from baseline (532 children; 95% CI 0.13 to 0.69) compared to daily treatment.

AUTHORS' CONCLUSIONS

In children and adults with persistent asthma and in preschool children suspected of persistent asthma, intermittent and daily ICS strategies did not significantly differ in the use of rescue oral corticosteroids and the rate of severe adverse health events, neither did they reach equivalence. Daily ICS was superior to intermittent ICS in several indicators of lung function, airway inflammation, asthma control and reliever use. Both treatments appeared safe, but a modest growth suppression was associated with daily, compared to intermittent, inhaled budesonide and beclomethasone. The clinician should carefully weigh the potential benefits and harm of each treatment option, taking into account the unknown long-term (> one year) impact of intermittent therapy on lung growth and lung function decline.

Beta 2 adrenergic receptor polymorphisms, at codons 16 and 27, and bronchodilator responses in adult Venezuelan asthmatic patients

BACKGROUND

One of the gene polymorphisms often studied in asthmatic patients is the β2 adrenergic receptor (ADRβ2). Even though in the Venezuelan Mestizo population there is a high incidence of asthma, there are no direct reports of ADRβ2 gene polymorphism, and treatment response. The aim of this study was to assess, in this population, the gene frequency of ADRβ2 polymorphisms at codons 16 Arg/Gly and 27 Gln/Glu, allergen sensitization, and its relationship to bronchodilator response.

METHODS

Purified genomic DNA was obtained form 105 Mestizo asthmatic and 100 Mestizo healthy individuals from Venezuela. The two polymorphisms were assessed by PCR-RFLP. Patient sensitization to aeroallergens and their response to bronchodilatation were correlated.

RESULTS

Significant differences between patients and controls were recorded in: 1) the prevalence of Arg/Arg at codon 16 (28.6% in patients vs. 47% in controls, P<0.01), 2) the frequency of heterozygotes Arg/Gly (55% in patients vs. 35% in controls, P<0.01). Conversely, no differences in polymorphism frequencies were found at codon 27. The haplotypes Arg/Gly-Gln/Gln were more common in patients than controls (P <0.01), whereas the Arg/Arg-Gln/Glu combination prevailed in the control group (P<0.01). The Arg/Gly and Gln/Glu genotypes were associated with better responses after salbutamol. The asthmatic homozygotes Arg/Arg have higher sensitivity to aeroallergens.

CONCLUSION

The difference in Arg/Arg frequency between groups suggests that this could be a protective genotype although the asthmatic group had a higher sensitivity to aeroallergens. The asthmatic heterozygotes had better bronchodilator responses than the homozygotes.

Asthma and bronchodilator responsiveness are associated with polymorphic markers of ARG1, CRHR2 and chromosome 17q21

OBJECTIVE

Asthma is caused by complex interactions between multiple genes. β2-Agonist is the standard rescue treatment to relieve asthma symptoms and bronchoconstriction. A genetic study for spirometric parameters helps to predict the responses to this antiasthma treatment. This study investigated the relationship between asthma and bronchodilator responsiveness (BDR) and eight asthma genes.

METHODS

Fifteen single-nucleotide polymorphisms in these genes were genotyped in 345 Chinese asthmatics and 464 controls. Gene-gene interactions were analysed by generalized multifactor dimensionality reduction (GMDR).

RESULTS

The diagnosis of asthma was associated with rs7216389 in ORMDL3 [odds ratio (OR) 0.74 and 95% confidence interval (95% CI) 0.56-0.99] and rs3756780 in ARG1 (OR 0.67, 95% CI 0.51-0.89) and BDR with rs2749935 in ARG1. However, none of these associations remained significant at 5% when adjusted for multiple testing by the Bonferroni correction or a false discovery rate. GMDR analyses revealed that rs7216389 in ORMDL3 and rs3756780 in ARG1 might interact for a risk of asthma. Individuals with high-risk genotypes had OR 1.66 (95% CI 1.24-2.23) for asthma when compared with those with low-risk genotypes. GMDR suggested a two-locus model with rs2749935 in ARG1 and rs2190242 in CRHR2 to be associated with BDR. Specifically, reversibility of forced expiratory volume in 1 s was higher in high-risk than that in low-risk patients [mean (95% CI): 10.7 (8.6-12.9) vs. 6.8 (5.9-7.6)%]; with the latter group showing higher forced expiratory volume in 1 s reversibility compared with high-risk controls [2.8 (1.4-4.3)%].

CONCLUSION

ARG1 and ORMDL3 may interact to determine the risk of asthma and ARG1 and CRHR2 to alter BDR in asthmatics. Nonetheless, this study is only hypothesis-generating as none of the single marker comparisons is significant when adjusted for multiple testing. These findings need to be confirmed in independent populations.

β2-adrenergic receptor haplotype linked to intubation and mechanical ventilation in children with asthma

BACKGROUND AND AIMS

Children with asthma and respiratory failure comprise a small but significant subset of children with acute asthma. In addition to clinical and historical factors that have been associated with respiratory failure, there may also be genetic factors that predispose some asthmatic children to intubation and mechanical ventilation. However, this has not previously been assessed in this population. We hypothesized that genetic polymorphisms of the β(2)-adrenergic receptor (ADRβ(2)) are associated with intubation and mechanical ventilation in children with asthma.

MATERIALS AND METHODS

We performed genotyping of the ADRβ(2) in a pooled cohort of 104 children admitted to the intensive care unit (ICU) with a severe asthma exacerbation between 2002 and 2008. Genotype of the ADRβ(2) was compared with intubation for respiratory failure.

RESULTS

At amino acid position 16, 33% (n = 34) of children were homozygous for the glycine allele (Gly16Gly), 15% (n = 16) were homozygous for the arginine allele (Arg16Arg), and 52% (n = 54) were heterozygous (Arg16Gly). At amino acid position 27, 54% (n = 56) of children were homozygous for the glutamine allele (Gln27Gln), 8% (n = 8) were homozygous for the glutamic acid allele (Glu27Glu), and 38% (n = 40) were heterozygous (Gln27Glu). The haplotypes at these positions were Arg16Gly-Gln27Gln (29%, n = 30), Arg16Gly-Gln27Glu (22%, n = 23), Gly16Gly-Gln27Glu (16%, n = 17), Arg16Arg-Gln27Gln (16%, n = 17), Gly16Gly-Gln27Gln (9%, n = 9), and Gly16Gly-Glu27Glu (8%, n = 8). Twelve children in this cohort were intubated for respiratory failure. Intubation was not associated with age, obesity, race/ethnicity, or NHBLI asthma classification. However, children with the Arg16Gly-Gln27Gln haplotype were significantly more likely to be intubated and mechanical ventilated (OR = 4.2; 95% CI = 1.2-14.5; p = .036) than children with other haplotypes of the ADRβ(2). When examining the subset of intubated children, those with the Arg16Gly-Gln27Gln haplotype trended towards longer ICU length of stay (329 ± 270 vs. 124 ± 57 hours; p = .09), but this was not statistically significant.

CONCLUSIONS

Children with the Arg16Gly-Gln27Gln haplotype of the ADRβ(2) were four times more likely to be intubated and mechanically ventilated during severe asthma exacerbations. Genetic factors may influence the development of a more severe asthma phenotype during acute exacerbations.

Novel cAMP signalling paradigms: therapeutic implications for airway disease

Since its discovery over 50 years ago, cAMP has been the archetypal second messenger introducing students to the concept of cell signalling at the simplest level. As explored in this review, however, there are many more facets to cAMP signalling than the path from Gs-coupled receptor to adenylyl cyclase (AC) to cAMP to PKA to biological effect. After a brief description of this canonical cAMP signalling pathway, a snapshot is provided of the novel paradigms of cAMP signalling. As in the airway the cAMP pathway relays the major bronchorelaxant signal and as such is the target for frontline therapy for asthma and COPD, particular emphasis is given to airway disease and therapy. Areas discussed include biased agonism, continued signalling following internalization, modulation of cAMP by AC, control of cAMP degradation, cAMP and calcium crosstalk, Epac-mediated signalling and finally the implications of altered genotypes will be considered. LINKED ARTICLES This article is part of a themed section on Novel cAMP Signalling Paradigms. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.166.issue-2.

β(2) -adrenoreceptor polymorphisms in asthmatic and non-asthmatic schoolchildren from Colombia and their relationship to treatment response

Asthma is a chronic and recurrent disease. Its high prevalence around the world is the result of a complex interaction between genetic and environmental factors. The genetic aspects of susceptibility, severity, and response to treatment in asthma are of great scientific interest. The purpose of the study was to establish the relationship between the Gln27Glu and Arg16Gly alleles of the β(2) -adrenergic receptor (ADRB2) gene with respect to the susceptibility to and severity of asthma, as well as the response to treatment in mestizo schoolchildren. 109 schoolchildren with asthma diagnosis and 137 asymptomatic controls were genotyped for the Arg16Gly and Gln27Glu alleles of the ADRB2 gene by minisequencing. Allele, genotype, and haplotype frequencies of the ADRB2 gene between asthmatic and non-asthmatic as well as demographic, clinical, and spirometric variables among asthmatic patients according to their genotype were compared. ADRB2 gene expression was determined by real-time quantitative PCR. No statistical differences were found in allele, genotype, and haplotype frequencies of the ADRB2 gene between cases and controls. We did not find differences between asthmatic patients classified according to their ADRB2 genotypes and haplotypes when evaluating demographic, clinical, and spirometric variables. The ADRB2 genotype and haplotype are not associated with spirometric responses or ADRB2 gene expression after administration of a β-(2) agonist plus a glucocorticoid. These results suggest that in the group of mestizo schoolchildren studied, the Arg16Gly and Gln27Glu polymorphisms are not markers of susceptibility or severity of asthma and do not affect ADRB2 gene expression during the rescue therapy.

Key observations from the NHLBI Asthma Clinical Research Network

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.

ADRB2 polymorphisms and budesonide/formoterol responses in COPD

BACKGROUND

Effects of β(2)-adrenergic receptor gene (ADRB2) polymorphism on therapeutic responses to long-acting β(2)-adrenergic agonists have not been evaluated in long-term COPD trials. We aimed to investigate the effects of the ADRB2 Gly16Arg polymorphism on response to formoterol alone or in combination with the inhaled corticosteroid budesonide in patients with COPD.

METHODS

Patients ≥ 40 years of age with moderate to very severe COPD from the 12-month trial I (NCT00206167) or the 6-month trial II (NCT00206154) were randomly assigned to bid budesonide/formoterol pressurized metered-dose inhaler (pMDI) 320/9 μg or 160/9 μg, budesonide pMDI 320 μg + formoterol dry powder inhaler 9 μg (trial II), budesonide pMDI 320 μg (trial II), formoterol dry powder inhaler 9 μg, or placebo. The effect of Gly16Arg on predose FEV(1) and 1-h postdose FEV(1), exacerbations, diary variables, and adverse events were analyzed.

RESULTS

No significant interaction between genotype and treatment response was observed for predose (P ≥ .197) or postdose FEV(1) (P ≥ .125) in either pharmacogenetic study (n = 2,866). The number of COPD exacerbations per patient-treatment year was low and similar across genotypes for the active treatment groups (both studies). Percentages of patients with adverse events were similar across Gly16Arg genotype groups for each treatment.

CONCLUSION

Therapeutic response and tolerability to long-term treatment with formoterol alone or in combination with budesonide was not modified by ADRB2 Gly16Arg genotype in two large independent pharmacogenetic studies in patients with moderate to very severe COPD.

Genetics of asthma susceptibility and severity

This article summarizes major findings in genome-wide studies of asthma susceptibility and severity. Two large meta-analyses identified four chromosomal regions which were consistently associated with development of asthma. Genes that are associated with asthma subphenotypes such as lung function, biomarker levels, and asthma therapeutic responses can provide insight into mechanisms of asthma severity and disease progression. Future genetic studies will incorporate sequencing in comprehensively phenotyped asthmatics to lead to the development of personalized therapy.

Genome-wide association analysis in asthma subjects identifies SPATS2L as a novel bronchodilator response gene

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.

Pharmacology and therapeutics of bronchodilators

Bronchodilators are central in the treatment of of airways disorders. They are the mainstay of the current management of chronic obstructive pulmonary disease (COPD) and are critical in the symptomatic management of asthma, although controversies around the use of these drugs remain. Bronchodilators work through their direct relaxation effect on airway smooth muscle cells. at present, three major classes of bronchodilators, β(2)-adrenoceptor (AR) agonists, muscarinic receptor antagonists, and xanthines are available and can be used individually or in combination. The use of the inhaled route is currently preferred to minimize systemic effects. Fast- and short-acting agents are best used for rescue of symptoms, whereas long-acting agents are best used for maintenance therapy. It has proven difficult to discover novel classes of bronchodilator drugs, although potential new targets are emerging. Consequently, the logical approach has been to improve the existing bronchodilators, although several novel broncholytic classes are under development. An important step in simplifying asthma and COPD management and improving adherence with prescribed therapy is to reduce the dose frequency to the minimum necessary to maintain disease control. Therefore, the incorporation of once-daily dose administration is an important strategy to improve adherence. Several once-daily β(2)-AR agonists or ultra-long-acting β(2)-AR-agonists (LABAs), such as indacaterol, olodaterol, and vilanterol, are already in the market or under development for the treatment of COPD and asthma, but current recommendations suggest the use of LABAs only in combination with an inhaled corticosteroid. In addition, some new potentially long-acting antimuscarinic agents, such as glycopyrronium bromide (NVA-237), aclidinium bromide, and umeclidinium bromide (GSK573719), are under development, as well as combinations of several classes of long-acting bronchodilator drugs, in an attempt to simplify treatment regimens as much as possible. This review will describe the pharmacology and therapeutics of old, new, and emerging classes of bronchodilator.

Effect of β2-adrenergic receptor gene (ADRB2) 3' untranslated region polymorphisms on inhaled corticosteroid/long-acting β2-adrenergic agonist response

Background

Evidence suggests that variation in the length of the poly-C repeat in the 3′ untranslated region (3′UTR) of the β₂-adrenergic receptor gene (ADRB2) may contribute to interindividual variation in β-agonist response. However, methodology in previous studies limited the assessment of the effect of sequence variation in the context of poly-C repeat length. The objectives of this study were to design a novel genotyping method to fully characterize sequence variation in the ADRB2 3′UTR poly-C repeat in asthma patients treated with inhaled corticosteroid and long-acting β₂-adrenergic agonist (ICS/LABA) combination therapy, and to analyze the effect of the poly-C repeat polymorphism on clinical response.

Methods

In 2,250 asthma patients randomized to treatment with budesonide/formoterol or fluticasone/salmeterol in a six-month study (AstraZeneca study code: SD-039-0735), sequence diversity in the ADRB2 poly-C repeat region was determined using a novel sequencing-based genotyping method. The relationship between the poly-C repeat polymorphism and the incidence of severe asthma exacerbations, and changes in pulmonary function and asthma symptoms from baseline to the average during the treatment period, were analyzed.

Results

Poly-C repeat genotypes were assigned in 97% (2,192/2,250) of patients. Of the 13 different poly-C repeat alleles identified, six alleles occurred at a frequency of >5% in one or more population in this study. The repeat length of these six common alleles ranged from 10 to 14 nucleotides. Twelve poly-C repeat genotypes were observed at a frequency of >1%. No evidence of an association between poly-C repeat genotype and the incidence of severe asthma exacerbations was observed. Patients’ pulmonary function measurements improved and asthma symptoms declined when treated with ICS/LABA combination therapy regardless of poly-C repeat genotype.

Conclusions

The extensive sequence diversity present in the poly-C repeat region of the ADRB2 3′UTR did not predict therapeutic response to ICS/LABA therapy.

Asthma outcomes: exacerbations

BACKGROUND

The goals of asthma treatment include preventing recurrent exacerbations. Yet there is no consensus about the terminology for describing or defining "exacerbation" or about how to characterize an episode's severity.

OBJECTIVE

National Institutes of Health institutes and other federal agencies convened an expert group to propose how asthma exacerbation should be assessed as a standardized asthma outcome in future asthma clinical research studies.

METHODS

We used comprehensive literature reviews and expert opinion to compile a list of asthma exacerbation outcomes and classified them as either core (required in future studies), supplemental (used according to study aims and standardized), or emerging (requiring validation and standardization). This work was discussed at a National Institutes of Health-organized workshop in March 2010 and finalized in September 2011.

RESULTS

No dominant definition of "exacerbation" was found. The most widely used definitions included 3 components, all related to treatment, rather than symptoms: (1) systemic use of corticosteroids, (2) asthma-specific emergency department visits or hospitalizations, and (3) use of short-acting β-agonists as quick-relief (sometimes referred to as "rescue" or "reliever") medications.

CONCLUSIONS

The working group participants propose that the definition of "asthma exacerbation" be "a worsening of asthma requiring the use of systemic corticosteroids to prevent a serious outcome." As core outcomes, they propose inclusion and separate reporting of several essential variables of an exacerbation. Furthermore, they propose the development of a standardized, component-based definition of "exacerbation" with clear thresholds of severity for each component.

Genome-wide association identifies the T gene as a novel asthma pharmacogenetic locus

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 FEV(1) 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 FEV(1) 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.

New approaches to personalized medicine for asthma: where are we?

Access to an electronic medical record is essential for personalized medicine. Currently, only 40% of US physicians have such access, but this is rapidly changing. It is expected that 100,000 Americans will have their whole genome sequenced in 2012. The cost of such sequencing is rapidly dropping, and is estimated to be $1000 by 2013. These technological advances will make interpretation of whole genome sequence data a major clinical challenge for the foreseeable future. At present, a relatively small number of genes have been identified to determine drug treatment response phenotypes for asthma. It is anticipated that this will dramatically increase over the next 10 years as personalized medicine becomes more of a reality for asthma patients.

Beta-adrenergic receptor polymorphisms associated with length of ICU stay in pediatric status asthmaticus

BACKGROUND

During severe exacerbations, asthmatic children vary significantly in their response to high-dose continuous β(2) -adrenergic receptor (ADRβ(2) ) agonist therapy. Genetic polymorphisms have been identified within the ADRβ(2) that may be functionally relevant, but few studies have been performed in this population. Our hypothesis was that genotypic differences are associated with magnitude of response to ADRβ(2) agonist treatment during severe asthma exacerbations in children.

METHODS

Children aged 2-18 years admitted to the ICU (intensive care unit) with a severe asthma exacerbation between 2006 and 2008 were eligible. Genotyping of the ADRβ(2) was performed.

RESULTS

Eighty-nine children consented and were enrolled. Despite similar clinical asthma scores on admission, children with the Gly(16) Gly genotype at amino acid position 16 had significantly shorter ICU length of stay (LOS) and hospital LOS, compared to children with Arg(16) Arg and Arg(16) Gly genotypes. Children with either the Gln(27) Glu or Glu(27) Glu genotype at amino acid position 27 also had significantly shorter ICU LOS and hospital LOS compared to children with the Gln(27) Gln genotype. The Arg(16) Gly-Gln(27) Gln haplotype was associated with the longest ICU LOS, but this was not statistically different from other haplotypes.

CONCLUSIONS

In this cohort of children with severe asthma exacerbations, ADRβ(2) polymorphisms were associated with responses to therapy. Knowledge of the genetic profile of children with asthma may allow for targeted therapy during acute exacerbations.

Pharmacogenetics of asthma controller treatment

The interpatient variability in response to asthma controllers is significant and associates with pharmacogenomic variability. The goal of the present study was to identify novel variants that associate with response to common asthma controllers: fluticasone, combination of fluticasone + salmeterol and montelukast with single nucleotide polymorphisms (SNPs) in β2-adrenergic receptor, corticosteroid and leukotriene pathway candidate genes. Participants in a large clinical trial of step-down strategies volunteered for this pharmacogenetic study. A total of 169 SNPs in 26 candidate genes were genotyped in 189 Caucasian participants with asthma who took either fluticasone (100 μg bid), fluticasone propionate (100 μg) + salmeterol (50 μg) (FP/Salm) or montelukast (5 or 10 mg) each night for 16 weeks. Primary outcomes were the slopes of plots of Asthma Control Questionnaire (ACQ) scores versus time following randomization; and the percent change in percent predicted FEV1 (ΔFEV1%pred) from enrollment to the end of the study. Associations between SNPs and outcomes were analyzed using general linear models. False discovery rate and Bonferroni corrections were used to correct for multiple comparisons. In all, 16 SNPs in seven genes were significantly associated with outcomes. For FP/Salm, three SNPs in CHRM2 associated with ACQ slope (P=2.8 × 10⁻⁵), and rs1461496 in HSPA8 associated with ΔFEV1%pred. For fluticasone, five SNPs in CRHR1 (P=1.9 × 10⁻⁴), and three SNPs in COL2A1 associated with ACQ slope and ΔFEV1%pred, respectively. For montelukast, four SNPs in CHRM2 associated with ΔFEV1%pred and predicted an opposite effect compared with fluticasone (P=9 × 10⁻³). The present study indentified several novel SNPs that associate with response to common asthma controllers, and support further pharmacogenomic study and the use of genetic variants to personalize asthma treatment.

Relationship between polymorphisms in the 5' leader cistron, positions 16 and 27 of the adrenergic β2 receptor gene and asthma in a Han population from southwest China

BACKGROUND AND OBJECTIVE

Adrenergic β2 receptors (ADRB2) play an important role in regulating pulmonary function. Many previous studies have investigated possible associations between polymorphisms in the ADRB2 gene and asthma, but have yielded conflicting results. Furthermore, little is known regarding the possible role of the Arg19Cys polymorphism in susceptibility to asthma among Chinese.

METHODS

This case-control association study involved 238 patients with asthma and 265 healthy subjects from a Han population in southwest China. For all subjects, the 5' leader cistron Arg19Cys, Arg16Gly and Gln27Glu polymorphisms in the ADRB2 gene were characterized by direct sequencing. Genotype, allele and haplotype frequencies were determined. In addition, to evaluate the association between the ADRB2 polymorphisms and lung function, bronchodilator response to inhaled β2 agonists (400 µg of albuterol) was assessed in the asthmatic patients.

RESULTS

There were no significant differences in genotype or allele frequencies for the three ADRB2 polymorphisms between the two cohorts. The Arg19/Arg16/Gln27 haplotype was more frequent among asthmatic patients than control subjects (odds ratio 2.24, 95% confidence interval (CI): 1.05-4.73, P=0.04). Moreover, the Arg19/Cys19 genotype was associated with a lower FEV₁% (mean difference -4.5, 95% CI: -12.5 to 3.6, P=0.02) and FEV₁/FVC (mean difference 8.9, 95% CI: 8.5-9.4, P=0.01). The bronchodilator response to albuterol was also marginally lower in individuals who were homozygous for the Arg19 genotype (mean difference 4.2, 95% CI: 3.7-4.8, P=0.03).

CONCLUSIONS

The Arg19/Cys19 genotype was an independent risk factor for lower FEV₁% and FEV₁/FVC. Asthmatic patients with the Arg19/Arg19 genotype showed decreased responsiveness to albuterol. Furthermore, the Arg19/Arg16/Gln27 haplotype may contribute to increased susceptibility to asthma in the Chinese population.

Asthma Clinical Research Network: lessons learned

The Asthma Clinical Research Network was created by the National Heart, Lung, and Blood Institute to improve public health by rapidly evaluating novel and existing therapeutic approaches to asthma. The multicenter clinical research network has greatly contributed to the healthcare community's understanding of asthma by conducting clinical trials independent of the pharmaceutical industry. The following manuscript reviews the experimental design and major findings of noteworthy studies performed in this network. All of the network's publications were reviewed, and 19 were selected for summary. As shown in these publications, the research performed by the Asthma Clinical Research Network has produced significant data with important implications that should impact the way the healthcare community treats asthma at the present time.

A polymorphism-specific "memory" mechanism in the β(2)-adrenergic receptor

Signaling through G protein (heterotrimeric guanosine triphosphate-binding protein)-coupled receptors is affected by polymorphisms in receptor-encoding genes. Using fluorescence resonance energy transfer, we found that the β(2)-adrenergic receptor (β(2)AR) responded to repeated activation with altered activation kinetics. Polymorphic variants of the β(2)AR displayed divergent changes of β(2)AR activation kinetics that closely mimicked their different efficacies to generate cyclic adenosine 3',5'-monophosphate. More efficacious variants became faster in their activation kinetics, whereas less efficacious variants became slower, compared to their initial activation. These differences depended on phosphorylation of the receptor by G protein-coupled receptor kinases. Our findings suggest an intrinsic, polymorphism-specific property of the β(2)AR that alters activation kinetics upon continued stimulation and that may account for individual drug responses.

A pharmacogenetic study of ADRB2 polymorphisms and indacaterol response in COPD patients

Genetic variation in the ADRB2 gene has been hypothesized to have a role in differential response to beta-agonist (BA) therapy in asthma. However, study results have been inconsistent and the issue remains controversial. Furthermore, the impact of ADRB2 genetic variation on BA response in chronic obstructive pulmonary disease (COPD) patients has not been thoroughly studied. We carried out a large pharmacogenetic analysis testing for an association between common ADRB2 polymorphisms and indacaterol response in COPD patients. A total of 648 indacaterol-treated patients enrolled in two large randomized phase III studies were genotyped for the most commonly studied polymorphisms in the ADRB2 gene: Gly16Arg, Gln27Glu, Thr164Ile, and a variant in the 5' untranslated region (rs1042711). Our analysis showed little evidence for the association between these ADRB2 variants and indacaterol response, suggesting that ADRB2 genetic variation is unlikely to have a major role in differential response to indacaterol treatment in COPD patients.

Impact of race on asthma treatment failures in the asthma clinical research network

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 FEV(1) (% 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.

Association between body mass index and asthma among Japanese adults: risk within the normal weight range

BACKGROUND

Increasing amounts of data have shown that some Asian populations are more susceptible to increased weight and development of noncommunicable disease than Western populations. However, little is known about the association between increased weight, particularly within the normal range, and the development of asthma among Asian populations.

METHODS

To examine the association between increased body mass index (BMI) and asthma among Japanese adults, data from a nationwide population-based cross-sectional survey of asthma prevalence in Japan were analyzed (n = 22,962; age range 20-79 years). BMIs were classified into 7 categories considering WHO recommendations (cutoff points: 17.00, 18.50, 23.00, 25.00, 27.50 and 30.00), and the association between BMI and the prevalences of asthma as well as asthma symptoms were assessed by multivariate logistic regression.

RESULTS

The prevalences of obesity (BMI ≥ 30.00) in this population were relatively low (males 3.0%, females 2.3%). BMI categories of 25.00 or higher in both genders were significantly associated with an increased risk of asthma compared with the reference category (BMI 18.50-22.99). Even in females with a BMI of 23.00-24.99, the prevalence of asthma significantly increased (adjusted odds ratio 1.49, 95% confidence interval 1.16-1.92) compared with that in the reference category.

CONCLUSIONS

An increase in the prevalence of asthma among Japanese females starts at a BMI of 23.00, which was relatively lower than those reported from Western countries. This finding suggests that the Japanese population is likely to have asthma with a lesser degree of obesity than Western populations.

Controversies regarding long-acting β2-agonists

PURPOSE OF REVIEW

This review examines the literature regarding the efficacy and safety of long-acting β2-agonists as add-on therapy to inhaled corticosteroids.

RECENT FINDINGS

The Global Initiative for Asthma (GINA) 2009 guidelines and the National Heart, Lung, and Blood Institute (NHLBI) 2007 asthma guidelines recommend adding long-acting β2-agonists to patients inadequately controlled on inhaled corticosteroids. These recommendations must be balanced against published data which demonstrate a signal of increased morbidity and mortality with use of long-acting β2-agonists. These conflicting data raise the question of whether or not there may be genotypic or phenotypic discriminators leading to disparate responses to long-acting β2-agonists.

SUMMARY

The combination of long-acting β2-agonists and inhaled corticosteroids demonstrates improvement in asthma control and exacerbation rates; however, long-acting β2-agonists are not recommended for use as monotherapy or without optimization of inhaled corticosteroid dose. Although the majority of asthmatic patients appear to benefit from the addition of long-acting β2-agonists, there are concerns that a small proportion of patients, including steroid-naïve patients and African Americans, may not obtain such benefits. Thus far, studies have not clearly demonstrated genotypic or phenotypic differences explaining the variability in response.

The pharmacogenetics and pharmacogenomics of asthma therapy

Despite the availability of several classes of asthma medications and their overall effectiveness, a significant portion of patients fail to respond to these therapeutic agents. Evidence suggests that genetic factors may partly mediate the heterogeneity in asthma treatment response. This review discusses important findings in asthma pharmacogenetic and pharmacogenomic studies conducted to date, examines limitations of these studies and, finally, proposes future research directions in this field. The focus will be on the three major classes of asthma medications: β-adrenergic receptor agonists, inhaled corticosteroids and leukotriene modifiers. Although many studies are limited by small sample sizes and replication of the findings is needed, several candidate genes have been identified. High-throughput technologies are also allowing for large-scale genetic investigations. Thus, the future is promising for a personalized treatment of asthma, which will improve therapeutic outcomes, minimize side effects and lead to a more cost-effective care.