beta-Adrenergic receptor polymorphisms and response to salmeterol

Treatable traits, combination inhaler therapy and the future of asthma management

The landscape of asthma has considerably changed in the last decade. Effective medications and inhaler devices have been developed and integrated into the asthma pharmacopoeia, but unfortunately, the proportion of uncontrolled patients remains unacceptably high. This is now recognized to be mainly due to the inappropriate use of medications or inhaler devices, heterogeneity of the disease or other factors contributing to the disease. Currently, inhaled corticosteroids (ICS), with or without long-acting beta agonists (LABA), are the cornerstone of asthma management, and recently international guidelines recognized the importance of combination inhaler therapy (ICS/LABA) even in mild asthma. In future, ultra-long-acting personalized medications and smart inhalers will complement combination inhaler therapy in order to effectively addresses issues such as adherence, inhaler technique and polypharmacy (both of drugs and devices). Asthma is now acknowledged as a multifaceted cluster of disorders and the treatment model has evolved from one-size-fits-all to precision medicine approaches such as treatable traits (TTs, defined as measurable and treatable clinically important factors) which encourages the quality use of medications and identification and management of all underlying behavioural and biological treatable risk factors. TT requires research and validation in a clinical context and the implementation strategies and efficacy in various settings (primary/secondary/tertiary care, low-middle income countries) and populations (mild/moderate/severe asthma) are currently evolving. Combination inhaler therapy and the TTs approach are complementary treatment approaches. This review examines the current status of personalized medicine and combination inhaler therapy, and describes futuristic views for these two strategies.

Safety and Effectiveness of As-Needed Formoterol in Asthma Patients Taking Inhaled Corticosteroid (ICS)-Formoterol or ICS-Salmeterol Maintenance Therapy

BACKGROUND

As-needed low-dose inhaled corticosteroid (ICS)-formoterol reliever is recommended in patients with asthma prescribed maintenance ICS-formoterol. Clinicians often ask whether ICS-formoterol reliever can be used with other maintenance ICS-long-acting β2-agonists.

OBJECTIVE

To evaluate the safety and effectiveness of as-needed formoterol in patients taking maintenance ICS-formoterol or ICS-salmeterol from the RELIEF study.

METHODS

RELIEF (SD-037-0699) was a 6-month, open-label study that randomized 18,124 patients with asthma to as-needed formoterol 4.5 μg or salbutamol 200 μg on top of maintenance therapy. This post hoc analysis included patients on maintenance ICS-formoterol or ICS-salmeterol (n = 5436). The primary safety outcome was a composite of serious adverse events (SAEs) and/or adverse events leading to discontinuation (DAEs); the primary effectiveness outcome was time-to-first exacerbation.

RESULTS

For both maintenance groups and both relievers, similar numbers of patients had ≥1 SAE and/or DAE. In patients taking maintenance ICS-salmeterol, but not ICS-formoterol, significantly more non-asthma-related and nonserious DAEs occurred with as-needed formoterol versus as-needed salbutamol (P = .0066 and P = .0034, respectively). In patients taking maintenance ICS-formoterol, there was a significantly lower risk in time-to-first exacerbation with as-needed formoterol versus as-needed salbutamol (hazard ratio [HR]: 0.82, 95% confidence interval [CI]: 0.70, 0.95; P = .007). In patients taking ICS-salmeterol maintenance, time-to-first exacerbation was not significantly different between treatment arms (HR: 0.95, 95% CI: 0.84, 1.06; P = .35).

CONCLUSIONS

As-needed formoterol significantly reduced exacerbation risk compared with as-needed salbutamol when added to maintenance ICS-formoterol, but not to maintenance ICS-salmeterol. More DAEs were seen with ICS-salmeterol maintenance therapy plus as-needed formoterol. Further research is needed to assess whether this is relevant to as-needed combination ICS-formoterol.

The impact of genomic variants on patient response to inhaled bronchodilators: a comprehensive update

INTRODUCTION

The bronchodilator response (BDR) depends on many factors, including genetic ones. Numerous single nucleotide polymorphisms (SNPs) influencing BDR have been identified. However, despite several studies in this field, genetic variations are not currently being utilized to support the use of bronchodilators.

AREAS COVERED

In this narrative review, the possible impact of genetic variants on BDR is discussed.

EXPERT OPINION

Pharmacogenetic studies of β₂-agonists have mainly focused on ADRB2 gene. Three SNPs, A46G, C79G, and C491T, have functional significance. However, other uncommon variants may contribute to individual variability in salbutamol response. SNPs haplotypes in ADRB2 may have a role. Many variants in genes coding for muscarinic ACh receptor (mAChR) have been reported, particularly in the M₂ and, to a lesser degree, M₃ mAChRs, but no consistent evidence for a pharmacological relevance of these SNPs has been reported. Moreover, there is a link between SNPs and ethnic and/or age profiles regarding BDR. Nevertheless, replication of pharmacogenetic results is limited and often, BDR is dissociated from what is expected based on SNP identification. Pharmacogenetic studies on bronchodilators must continue. However, they must integrate data derived from a multi-omics approach with epigenetic factors that may modify BDR.

Pharmacogenomics and Pediatric Asthmatic Medications

Asthma is a respiratory condition often stemming from childhood, characterized by difficulty breathing and/or chest tightness. Current treatment options for both adults and children include beta-2 agonists, inhaled corticosteroids (ICS), and leukotriene modifiers (LTM). Despite recommendations by the Global Initiative for Asthma, a substantial number of patients are unresponsive to treatment and unable to control symptoms. Pharmacogenomics have increasingly become the front line of precision medicine, especially with the recent use of candidate gene and genome- wide association studies (GWAS). Screening patients preemptively could likely decrease adverse events and therapeutic failure. However, research in asthma, specifically in pediatrics, has been low. Although numerous adult trials have evaluated the impact of pharmacogenomics and treatment response, the lack of evidence in children has hindered progress towards clinical application. This review aims to discuss the impact of genetic variability and response to asthmatic medications in the pediatric population.

Genome-wide association studies of exacerbations in children using long-acting beta2-agonists

BACKGROUND

Some children with asthma experience exacerbations despite long-acting beta2-agonist (LABA) treatment. While this variability is partly caused by genetic variation, no genome-wide study until now has investigated which genetic factors associated with risk of exacerbations despite LABA use in children with asthma. We aimed to assess whether genetic variation was associated with exacerbations in children treated with LABA from a global consortium.

METHODS

A meta-analysis of genome-wide association studies (meta-GWAS) was performed in 1,425 children and young adults with asthma (age 6-21 years) with reported regular use of LABA from six studies within the PiCA consortium using a random effects model. The primary outcome of each study was defined as any exacerbation within the past 6 or 12 months, including at least one of the following: 1) hospital admissions for asthma, 2) a course of oral corticosteroids or 3) emergency room visits because of asthma.

RESULTS

Genome-wide association results for a total of 82 996 common single nucleotide polymorphisms (SNPs, MAF ≥1%) with high imputation quality were meta-analysed. Eight independent variants were suggestively (P-value threshold ≤5 × 10^-6 ) associated with exacerbations despite LABA use.

CONCLUSION

No strong effects of single nucleotide polymorphisms (SNPs) on exacerbations during LABA use were identified. We identified two loci (TBX3 and EPHA7) that were previously implicated in the response to short-acting beta2-agonists (SABA). These loci merit further investigation in response to LABA and SABA use.

The role of ADRB2 gene polymorphisms in malignancies

Beta-2-adrenergic receptor is a member of the G protein-coupled receptor superfamily, which is highly expressed in most malignancies. There is increasing evidence showing that beta-2-adrenergic receptors are associated with carcinogenesis, proliferation, immune regulation, invasion, angiogenesis, clinical prognosis and treatment resistance in malignancies. Polymorphisms of the ADRB2 gene have been confirmed to be associated with transcriptional activity, mRNA translation, and beta-2-adrenergic receptor expression and sensitivity. This review discusses clinically relevant examples of single nucleotide polymorphisms of ADRB2 in malignancies and the effects of these polymorphisms on cancer susceptibility, prognosis and treatment response of cancer patients.

Bronchial Asthma: Genetic Factors Contributing to its Pathogenesis

Researching bronchial asthma (BA)-linked gene polymorphisms can help to clarify heterogeneity of the disease and estimate its severity, which, in turn, will aid in developing an appropriate treatment corresponding to the patient’s unique asthma pathogenesis. The aim of presented review is to analyze the published data on the genetic preconditions of BA and the possible role of different genes polymorphisms in its pathogenesis. We have found that despite the fact that numerous genes are involved in the pathogenesis of BA and their polymorphisms are associated with increased risks for BA, it is important to understand that a combination of factors, both genetic and environmental, triggers BA development and determines its progression. On the other hand, the identification of BA susceptibility genes contributing to asthma pathogenesis and treatment response is the first step toward the development of personalized medicine.

Analysis of the polymorphic variants of ADRB2 gene association with the β2-agonists response in patients with a rare theratype of asthma

Standard asthma therapy includes prescription of β2-agonists. Changes in the functional activity of β2-adrenergic receptor are associated with ADRB2 genepolymorphism and related to the low therapeutic response to β2-agonists. Identification of carriers of the clinically significant gene variants will help to avoidineffective treatment and prescribe an alternative therapy. This study aimed to assess clinical significance of the ADRB2 gene polymorphisms (Arg16Gly andGln27Glu) associated with the therapeutic response to β2-agonists in the group of asthma patients. We subjected a small group of adult nonsmoking patients(n = 21) with moderate asthma (III–IV stage of GINA) to clinical and genetic examination. The group included patients with the new theratype, those that poorlyrespond to β2-adrenergic drugs but significantly to M-cholinergic agonists. The first group included patients responding well to both salbutamol and ipratropiumbromide. The second group was comprised of the patients for whom salbutamol was not effective but who tested positive for response to ipratropium bromide. Theanalysis of distribution of polymorphic variants of Arg16Gly and Gln27Glu revealed no significant relationship between alleles and genotypes and the efficacy of β2-agonists(0.52 for the rs1042713 variant, p = 1.0; 1.0 for the rs1042714 variant, p = 0.74, respectively). The genotype of patients that did not respond to salbutamol waseither Arg16Gly or Gly16Gly. Further studies are needed that would involve a larger number of patients and an expanded list of the tested polymorphic variants.

Activation of β2 adrenergic receptor signaling modulates inflammation: a target limiting the progression of kidney diseases

Beta 2 adrenergic receptor (β₂-AR)-agonists, widely used as bronchodilators, have demonstrated wide-spectrum anti-inflammatory properties in both immune and non-immune cells in various tissues. Their anti-inflammatory properties are mediated primarily, but not exclusively, via activation of the canonical β₂-AR signaling pathway (β₂-AR/cAMP/PKA). As non-canonical β₂-AR signaling also occurs, several inconsistent findings on the anti-inflammatory effect of β₂-agonists are notably present. Increasing amounts of evidence have unveiled the alternative mechanisms of the β₂-AR agonists in protecting the tissues against injuries, i.e., by augmenting mitochondria biogenesis and SIRT1 activity, and by attenuating fibrotic signaling. This review mainly covers the basic mechanisms of the anti-inflammatory effects of β₂-AR activation along with its limitations. Specifically, we summarized the role of β₂-AR signaling in regulating kidney function and in mediating the progression of acute and chronic kidney diseases. Given their versatile protective effects, β₂-agonists can be a promising avenue in the treatment of kidney diseases.

How does race and ethnicity effect the precision treatment of asthma?

Introduction

Asthma is a common condition that affects large numbers of children and adults, yet the burden of disease is not equally distributed amongst groups. In the United States, African Americans and Puerto Ricans have higher rates of asthma and its complications when compared with European Americans. However, clinical trials and genetic studies have largely focused on the latter group.

Areas covered

Here we examine what is known regarding differences in asthma treatment response by race-ethnicity. We also review existing genetic studies related to the use of asthma medications, paying special attention to studies that included substantial numbers of non-white population groups. Publicly accessible search engines of the medical literature were queried using combinations of the terms asthma, race, ethnicity, pharmacogenomics, and pharmacogenetics, as well as the names of individual asthma medication classes. The list of articles reviewed was supplemented by bibliographies and expert knowledge.

Expert opinion

A substantial and coordinated effort is still needed to both identify and validate genetic biomarkers of asthma medication response, as currently there are no clinically actionable genetic markers available for this purpose. The path to identifying such markers in non-white populations is even more formidable, since these groups are underrepresented in existing data.

Association of genetic variants with level of asthma control in the Arab population

Background

Rates of asthma in Jordan have been doubled in the past decade, but this increased prevalence was not met with improved asthma control protocols. The aim of the present study was to assess whether there was any significant association between the level of asthma control and certain single-nucleotide polymorphisms (SNPs) in five genes: (ADRB2; rs1042713 and rs1042714), (CRHR1; rs1876828, rs242939, and rs242941), (STIP1; rs2236647), (ADH5, rs1154400), and (ARG1; rs2781659). These SNPs were selected based on their involvement in enzymes and receptors that are related to asthma pathways and subsequent response to medication and based on a high degree of linkage disequilibrium.

Patients and methods

A cross-sectional genetic association study was conducted from June 2016 to June 2017 in the two major hospitals in Jordan. The present study involved sampling from adult asthmatic patients of Arab descent who were selected from two phenotypic groups, ie, controlled and uncontrolled asthma. The blood samples and medical data were collected from the participants. DNA samples were extracted, quantified, and genotyped according to standard operating procedure. Allelic and haplotypic analyses were performed using the Haploview^®.

Results

A total of 245 Arab asthmatic patients were enrolled in this study. Genotyping analysis revealed that the two SNPs (rs1042713 and rs1042714) in ADRB2 gene, along with their related haplotypes, were nominally significantly associated with asthma control in the Jordanian population. The A-allele of rs1042713 and the C-allele of rs1042714 were more common in the uncontrolled asthma group than in the controlled asthma group (P=0.048 and P=0.017, respectively).

Conclusion

This was the first study that identified the nominal significant association between the level of asthma control and genetic variants in ADRB2 gene in Arab population. Further studies in other Arab region with larger sample size are recommended to confirm the relationship.

Impact of Genetic Polymorphism in the β2-Receptor Gene on Risk of Severe Hypoglycemia in Patients With Type 1 Diabetes

CONTEXT

Severe hypoglycemic events are unevenly distributed in people with type 1 diabetes, making a genetic influence probable. Of the common adrenoceptor β-2 receptor gene (ADRB2) polymorphisms, the Arg16 allele is associated with receptor downregulation and reduced agonist-mediated endogenous glucose production.

OBJECTIVE

We tested the hypothesis that the Arg16 variant is associated with severe hypoglycemia.

METHOD

A cohort of 311 patients with type 1 diabetes reported severe hypoglycemic events retrospectively in a validated questionnaire. The patients were characterized by diabetes history, state of hypoglycemia awareness, C-peptide status, HbA1c, and ADRB2 genotype.

RESULTS

The ADRB2 Gly16Arg genotype distribution was in Hardy-Weinberg equilibrium. The rate of severe hypoglycemia differed among all genotypes (P = 0.01). Patients homozygous for the Arg16 genotype (AA; n = 60) had a relative rate (RR) of severe hypoglycemia of 2.2 (95% CI, 1.3 to 3.6) compared with patients homozygous for the Gly16 genotype (GG; n = 116; P = 0.002). Among patients with impaired awareness or unawareness (n = 175), those with the AA genotype (n = 33) had an RR of severe hypoglycemia of 3.2 (95% CI, 1.7 to 6.0) compared with patients with the GG genotype (n = 58; P < 0.000). Genotype was not associated with state of hypoglycemia awareness per se, as assessed by any of three classification methods. The difference was not explained by other risk factors.

CONCLUSION

Genetic polymorphism in ADRB2 is associated with risk of severe hypoglycemia in individuals with type 1 diabetes, especially in those with impaired hypoglycemia awareness.

B2 adrenergic receptor gene polymorphism effect on childhood asthma severity and response to treatment

BackgroundAlterations of B2 adrenergic receptor (β₂AR) can modulate the severity of asthma and the response to treatment. Therefore, we aimed to evaluate β₂AR gene polymorphism at codons 16 and 27 and their effect on asthma severity and response to treatment in asthmatic children.MethodsCase-control study was conducted on 156 children; 104 of them had bronchial asthma and 52 were healthy children (control group). Subjects of the study underwent history taking, clinical examination, pulmonary function tests, serum IgE level assessment, and identification of β₂AR-16 A46G and β₂AR-27 C79G polymorphism using PCR-Restriction Fragment length polymorphisms (RFLP) test.ResultsThere was a higher frequency of Arg-Gly genotypes (odds ratio (OR)=6.57; confidence interval (CI): 2.42-18.81, P<0.001) and lower frequency of Arg-Arg (OR=4.7; CI: 2.05-10.95, P<0.001) among asthmatic children compared with that among controls at codon 16. The presence or absence of Gly16 or Glu27 either homozygous or heterozygous for both correlated with the grade of asthma severity. The presence of heterozygous Arg-Gly and Gln-Glu gives a better response to drug therapy than the presence of Gly-Gly and Glu-Glu genotypes at codons 16 and 27.ConclusionPolymorphism of β₂AR at codons 16 and 27 correlates with asthma severity and response to treatment in asthmatic children.

Monitoring individual cell-signaling activity using combined metal-clad waveguide and surface-enhanced fluorescence imaging

Validation of a combined metal-clad waveguide and surface enhanced fluorescence imaging platform for live cell imaging.

Review on Pharmacogenetics and Pharmacogenomics Applied to the Study of Asthma

Nearly one-half of asthmatic patients do not respond to the most common therapies. Evidence suggests that genetic factors may be involved in the heterogeneity in therapeutic response and adverse events to asthma therapies. We focus on the three major classes of asthma medication: β-adrenergic receptor agonist, inhaled corticosteroids, and leukotriene modifiers. Pharmacogenetics and pharmacogenomics studies have identified several candidate genes associated with drug response.In this chapter, the main pharmacogenetic and pharmacogenomic studies in addition to the future perspectives in personalized medicine will be reviewed. The ideal treatment of asthma would be a tailored approach to health care in which adverse effects are minimized and the therapeutic benefit for an individual asthmatic is maximized leading to a more cost-effective care.

Predicting treatable traits for long-acting bronchodilators in patients with stable COPD

Purpose

There is currently no measure to predict a treatability of long-acting β-2 agonist (LABA) or long-acting muscarinic antagonist (LAMA) in patients with chronic obstructive pulmonary disease (COPD). We aimed to build prediction models for the treatment response to these bronchodilators, in order to determine the most responsive medication for patients with COPD.

Methods

We performed a prospective open-label crossover study, in which each long-acting bronchodilator was given in a random order to 65 patients with stable COPD for 4 weeks, with a 4-week washout period in between. We analyzed 14 baseline clinical traits, expression profiles of 31,426 gene transcripts, and damaged-gene scores of 6,464 genes acquired from leukocytes. The gene expression profiles were measured by RNA microarray and the damaged-gene scores were obtained after DNA exome sequencing. Linear regression analyses were performed to build prediction models after using factor and correlation analyses.

Results

Using a prediction model for a LABA, traits found associated with the treatment response were post-bronchodilator forced expiratory volume in 1 second, bronchodilator reversibility (BDR) to salbutamol, expression of three genes (CLN8, PCSK5, and SKP2), and damage scores of four genes (EPG5, FNBP4, SCN10A, and SPTBN5) (R²=0.512, p<0.001). Traits associated with the treatment response to a LAMA were COPD assessment test score, BDR, expression of four genes (C1orf115, KIAA1618, PRKX, and RHOQ) and damage scores of three genes (FBN3, FDFT1, and ZBED6) (R²=0.575, p<0.001). The prediction models consisting only of clinical traits appeared too weak to predict the treatment response, with R²=0.231 for the LABA model and R²=0.121 for the LAMA model.

Conclusion

Adding the expressions of genes and damaged-gene scores to the clinical traits may improve the predictability of treatment response to long-acting bronchodilators.

Pharmacogenetics and interstitial lung disease

PURPOSE OF REVIEW

Interstitial lung disease (ILD) is comprised of a heterogeneous group of disorders with highly variable natural histories and response to therapies. Pharmacogenetics focuses on the variability in drug response because of the presence of genetic factors that influence drug metabolism or disease activity. In this article, we review relevant drug-specific and disease-specific polymorphisms that may influence therapeutic response, and then highlight a recently identified drug-gene interaction in patients with idiopathic pulmonary fibrosis (IPF).

RECENT FINDINGS

The emergence of high-throughput genomic technology has allowed for identification of gene polymorphisms associated with susceptibility to specific disease states, including IPF and several connective tissue diseases known to cause ILD. IPF risk loci span a diverse group of genes, while most associated with connective tissue disease are critical to immune signaling. A recent pharmacogenetic analysis of patients enrolled in an IPF clinical trial identified a variant within TOLLIP to be associated with differential response to N-acetylcysteine therapy.

SUMMARY

Though few pharmacogenetic investigations have been conducted in patients with ILD to date, ample opportunities for pharmacogenetic exploration exist in this patient population. Such exploration will advance our understanding of specific ILDs and help usher in an era of personalized medicine.

ADRB2 gene polymorphism and emphysema heterogeneity can modulate bronchodilator response in patients with emphysema

BACKGROUND

Genetic variation in the β₂-adrenergic receptor (ADRB2) gene has been thought to have an important role in the differential response to β₂-agonist therapy for asthma. However, previous studies have shown little evidence for an association between these ADRB2 variants and the bronchial dilator response (BDR) in chronic obstructive pulmonary disease (COPD) patients. This discrepancy could be explained by differences in the distribution and heterogeneity of pulmonary emphysema in COPD patients, since emphysema distribution and heterogeneity are thought to have a role in pulmonary function in COPD patients. We hypothesized that differences in emphysema distribution and heterogeneity may have masked significant alterations of the bronchodilator response among ADRB2 genotypes in COPD patients in previous studies.

METHODS

The BDR (induced by 20 μg of procaterol) was measured in 211 patients who had a smoking history of more than 10 pack/years and had undergone chest high resolution computed tomography examination. A low attenuations area (<960 Hounsfield Units) was identified and the emphysema heterogeneity index (EHI%) was calculated with a range in value from -100% to 100%. ADRB2 Arg16Gly genotyping was performed using polymerase chain reaction-restriction fragment length polymorphism analysis.

RESULTS

The BDR was augmented in patients with homogenous emphysema compared with those with upper-dominant emphysema. In patients carrying the AA genotype of ADRB2, the BDR was significantly increased in patients with upper-dominant emphysema, but not in patients with lower-dominant emphysema.

CONCLUSION

Combination analysis of ADRB2 Arg16Gly polymorphism and EHI% may predict the effectiveness of β₂-adrenergic receptor agonist treatment in patients with COPD and emphysema.

β2 Agonists

History suggests β agonists, the cognate ligand of the β₂ adrenoceptor, have been used as bronchodilators for around 5,000 years, and β agonists remain today the frontline treatment for asthma and chronic obstructive pulmonary disease (COPD). The β agonists used clinically today are the products of significant expenditure and over 100 year's intensive research aimed at minimizing side effects and enhancing therapeutic usefulness. The respiratory physician now has a therapeutic toolbox of long acting β agonists to prophylactically manage bronchoconstriction, and short acting β agonists to relieve acute exacerbations. Despite constituting the cornerstone of asthma and COPD therapy, these drugs are not perfect; significant safety issues have led to a black box warning advising that long acting β agonists should not be used alone in patients with asthma. In addition there are a significant proportion of patients whose asthma remains uncontrolled. In this chapter we discuss the evolution of β agonist use and how the understanding of β agonist actions on their principal target tissue, airway smooth muscle, has led to greater understanding of how these drugs can be further modified and improved in the future. Research into the genetics of the β₂ adrenoceptor will also be discussed, as will the implications of individual DNA profiles on the clinical outcomes of β agonist use (pharmacogenetics). Finally we comment on what the future may hold for the use of β agonists in respiratory disease.

Effects of indacaterol versus tiotropium on exercise tolerance in patients with moderate COPD: a pilot randomized crossover study

Objective:

To compare a once-daily long-acting β₂ agonist (indacaterol 150 µg) with a once-daily long-acting anticholinergic (tiotropium 5 µg) in terms of their effects on exercise endurance (limit of tolerance, Tlim) in patients with moderate COPD. Secondary endpoints were their effects on lung hyperinflation, exercise-related dyspnea, and daily-life dyspnea.

Methods:

This was a randomized, single-blind, crossover pilot study involving 20 patients (mean age, 60.9 ± 10.0 years; mean FEV₁, 69 ± 7% of predicted). Spirometric parameters, Transition Dyspnea Index scores, Tlim, and exertional dyspnea were compared after three weeks of each treatment (with a one-week washout period between treatments).

Results:

Nineteen patients completed the study (one having been excluded because of COPD exacerbation). Improvement in Tlim from baseline tended to be greater after treatment with tiotropium than after treatment with indacaterol (96 ± 163 s vs. 8 ± 82 s; p = 0.06). Tlim significantly improved from baseline after treatment with tiotropium (having increased from 396 ± 319 s to 493 ± 347 s; p = 0.010) but not after treatment with indacaterol (having increased from 393 ± 246 to 401 ± 254 s; p = 0.678). There were no differences between the two treatments regarding improvements in Borg dyspnea scores and lung hyperinflation at "isotime" and peak exercise. There were also no significant differences between treatments regarding Transition Dyspnea Index scores (1.5 ± 2.1 vs. 0.9 ± 2.3; p = 0.39).

Conclusions:

In patients with moderate COPD, tiotropium tends to improve Tlim in comparison with indacaterol. No significant differences were observed between the two treatments regarding their effects on lung hyperinflation, exercise-related dyspnea, and daily-life dyspnea. Future studies, including a larger number of patients, are required in order to confirm our findings and explore mechanistic explanations. (ClinicalTrials.gov identifier: NCT01693003 [http://www.clinicaltrials.gov/])

Beta-2-adrenoreceptor polymorphism at position 16 determines the clinical severity of chronic obstructive pulmonary disease

The Arg/Arg homozygosity at codon 16 of the beta-2-adrenoreceptor (ADRB2) gene has been thought to predispose asthma patients to a poorer therapeutic response to beta-2-mimetics, or to worse control of the disease. In contrast, the results of the studies analysing the effect of ADRB2 polymorphisms on the response to beta-2-adrenoreceptor agonists in chronic obstructive pulmonary disease (COPD) patients are sparse and inconclusive. The aim of this research was to verify if p.Arg16Gly (c.46A > G) and p.Gly27Glu (c.79G > C) single nucleotide polymorphisms (SNPs) exert a negative effect on the selected clinical indicators of COPD. The SNPs of the ADRB2 were identified by multiplex allele-specific PCR on DNA isolated from the venous blood leukocytes of 92 patients with stable grade COPD. In addition, all of the patients were asked about the course of COPD during the 12 months preceding the study, including the frequency of exacerbations requiring hospitalisation, the number of antibiotic therapy courses given due to the lower respiratory tract infection, and the number of courses of systemic corticosteroid therapy administered due to the exacerbation of COPD. Arg/Arg homozygotes at codon 16 required at least two courses of antibiotic therapy administered as a result of a lower respiratory tract infection significantly more frequently than carriers of other polymorphic variants of the ADRB2. Moreover, they were the only ones who required three or more courses of corticosteroid therapy due to COPD exacerbation. No significant relationships were observed between the polymorphism at codon 27 and the analysed clinical indicators of COPD severity. These data suggested that Arg/Arg homozygosity at codon 16 of the ADRB2 gene predisposes patients to a clinically more severe course of COPD.

Polymorphisms in Beta-2 Adrenergic Receptor Gene and Association with Tuberculosis

PURPOSE

Genetic susceptibility for tuberculosis in human has been previously demonstrated. Polymorphisms in genes involved in immune responses may alter the susceptibility of individuals to tuberculosis. Polymorphisms of beta-2 adrenergic receptor (ADRB2) gene can be possibly an important risk factor in tuberculosis. In this study, the association between rs1042713 (Arg16Gly +46A>G) and rs1042714 (Gln27Glu +79C>G) polymorphisms in ADRB2 gene and tuberculosis was evaluated.

METHODS

Genotype distributions of the rs1042713 (Arg16Gly +46A>G) and rs1042714 (Gln27Glu +79C>G) polymorphisms in ADRB2 gene in 106 patients with pulmonary tuberculosis and 88 healthy subjects were studied by PCR-RFLP method in an Iranian population.

RESULTS

The frequency of rs1042713*G and rs1042714*G alleles in ADRB2 gene in tuberculosis patients was significantly different from healthy controls [odds ratio (OR) 0.176, 95% confidence interval (CI) 0.065-0.48, P value <0.001 and OR 0.45, 95% CI 0.247-0.825, P value = 0.009, respectively]. There were no significant differences in haplotype analysis between the patients and control subjects.

CONCLUSION

The association was reported between rs1042713 and rs1042714 polymorphisms in ADRB2 gene and tuberculosis for the first time. rs1042713*G and rs1042714*G polymorphisms in ADRB2 gene makes people more susceptible to develop the disease.

Impact of the Arg 16 allele of the B2AR gene on the effect of withdrawal of LABA in patients with moderate to severe asthma

INTRODUCTION

Long-acting beta agonists (LABAs) are effective for controlling asthma, however questions about their safety have led to concerns over use. Genetic polymorphisms at the 16 amino acid position of the beta-2 adrenergic receptor gene (B2AR) may be associated with increased risk.

METHODS

A randomized, double blind study was conducted in patients with moderate to severe asthma being treated with combined inhaled corticosteroids/LABA (ICS/LABA), comparing the effect of LABA continuation versus withdrawal on asthma outcomes among patients stratified by B2AR genotype (Arg/Arg vs. Gly/Gly at the 16th amino acid position).

RESULTS

67 participants (31 Arg/Arg, 36 Gly/Gly) were randomized to receive fluticasone alone (F) or continue combined fluticasone/salmeterol (F/S) after a run-in period on F/S. Among Gly/Gly subjects, those in the F/S treatment group showed improvement in AM PEFR (+ 8.4 L/s) whereas those receiving F alone experienced a reduction in AM PEFR over the study period (-14.4 L/s), (p = 0.06). There was no significant difference in morning peak expiratory flow rate (AM PEFR) in Arg/Arg participants randomized to receive F/S (-15.7L) vs F alone (-5.6 L/s) (p = 0.61). There was no significant difference in exacerbations in the Arg/Arg subjects treated with F/S compared with those treated with F (p = 0.65).

CONCLUSIONS

Withdrawal of LABA therapy in asthmatics with the Arg/Arg genotype at the 16th amino acid position of B2AR did not lead to significant improvement in AM PEFR. LABA withdrawal in the Gly/Gly genotype however led to a borderline significant decline in AM PEFR.

Individualized Household Allergen Intervention Lowers Allergen Level But Not Asthma Medication Use: A Randomized Controlled Trial

BACKGROUND

Environmental exposures to indoor allergens are major contributors to asthma symptoms, particularly in inner cities. The effectiveness of household allergen reduction as an adjunct to National Asthma Education Prevention Program guideline-based pharmacologic therapy in asthma has not been prospectively studied.

OBJECTIVE

To study the effect of individualized allergen reduction on ability to reduce asthma pharmacologic therapy over 40 weeks.

METHODS

We performed a randomized controlled trial to determine the effect of multifaceted indoor allergen avoidance measures on the ability to reduce asthma controller therapy in adults and children residing in New York City who were both sensitized and exposed to at least 1 indoor allergen. Asthma treatment and control were optimized in all subjects before randomization.

RESULTS

A total of 125 subjects were randomized to receive individualized household allergen reduction and 122 received a sham intervention. Subjects in the intervention group significantly reduced all measured allergen levels (cat, dog, dust mite allergens in the bedroom, cockroach and mouse allergens in the kitchen and bedroom); those in the control group reduced only dust mite and mouse allergens in the bedroom and cockroach allergen in the kitchen. Participants in the intervention arm reduced National Asthma Education Prevention Program-based therapy from step 4.4 at randomization to 3.50 postintervention (range, 0-6); participants in the control arm reduced medication from step 4.4 to 3.4 (P = .76). There were no differences in other measured asthma outcomes.

CONCLUSIONS

Targeted allergen avoidance measures do not allow for reduction in asthma pharmacologic therapy compared with usual care in patients already receiving optimal controller therapy.

A Physiologic Approach to the Pharmacogenomics of Hypertension

Hypertension is a multifactorial condition with diverse physiological systems contributing to its pathogenesis. Individuals exhibit significant variation in their response to antihypertensive agents. Traditional markers, such as age, gender, diet, plasma renin level, and ethnicity, aid in drug selection. However, this review explores the contribution of genetics to facilitate antihypertensive agent selection and predict treatment efficacy. The findings, reproducibility, and limitations of published studies are examined, with emphasis placed on candidate genetic variants affecting drug metabolism, the renin-angiotensin system, adrenergic signalling, and renal sodium reabsorption. Single-nucleotide polymorphisms identified and replicated in unbiased genome-wide association studies of hypertension treatment are reviewed to illustrate the evolving understanding of the disease's complex and polygenic pathophysiology. Implementation efforts at academic centers seek to overcome barriers to the broad adoption of pharmacogenomics in the treatment of hypertension. The level of evidence required to support the implementation of pharmacogenomics in clinical practice is considered.

Pharmacogenomics of long-acting β2-agonists

INTRODUCTION

Long-acting β2-agonists are an effective class of drugs, when combined with inhaled corticosteroids, for reducing symptoms and exacerbations in patients with asthma that is not adequately controlled by inhaled corticosteroids alone. However, because this class of drugs has been associated with severe adverse events, including hospitalization and death in small numbers of patients, efforts to identify a pharmacogenetic profile for patients at risk has been diligently investigated.

AREAS COVERED

The PubMed search engine of the National Library of Medicine was used to identify English-language and non-English language articles published from 1947 to March 2015 pertinent to asthma, pharmacogenomics, and long-acting β2-agonists. Keywords and topics included: asthma, asthma control, long-acting β2-agonists, salmeterol, formoterol, pharmacogenetics, and pharmacogenomics. This strategy was also used for the Cochrane Library Database and CINAHL. Reference types were randomized controlled trials, reviews, and editorials. Additional publications were culled from reference lists. The publications were reviewed by the authors and those most relevant were used to support the topics covered in this review.

EXPERT OPINION

Children, who carry the ADRB2 Arg16Arg genotype, may be at greater risk than adults for severe adverse events. Rare ADRB2 variants appear to provide better clues for identifying the at-risk population of asthmatics.

Role of single nucleotide polymorphisms in pharmacogenomics and their association with human diseases

Global statistical data shed light on an alarming trend that every year thousands of people die due to adverse drug reactions as each individual responds in a different way to the same drug. Pharmacogenomics has come up as a promising field in drug development and clinical medication in the past few decades. It has emerged as a ray of hope in preventing patients from developing potentially fatal complications due to adverse drug reactions. Pharmacogenomics also minimizes the exposure to drugs that are less/non-effective and sometimes even found toxic for patients. It is well reported that drugs elicit different responses in different individuals due to variations in the nucleotide sequences of genes encoding for biologically important molecules (drug-metabolizing enzymes, drug targets and drug transporters). Single nucleotide polymorphisms (SNPs), the most common type of polymorphism found in the human genome is believed to be the main reason behind 90% of all types of genetic variations among the individuals. Therefore, pharmacogenomics may be helpful in answering the question as to how inherited differences in a single gene have a profound effect on the mobilization and biological action of a drug. In the present review, we have discussed clinically relevant examples of SNP in associated diseases that can be utilized as markers for "better management of complex diseases" and attempted to correlate the drug response with genetic variations. Attention is also given towards the therapeutic consequences of inherited differences at the chromosomal level and how associated drug disposition and/or drug targets differ in various diseases as well as among the individuals.

Asthma pharmacogenetics and the development of genetic profiles for personalized medicine

Human genetics research will be critical to the development of genetic profiles for personalized or precision medicine in asthma. Genetic profiles will consist of gene variants that predict individual disease susceptibility and risk for progression, predict which pharmacologic therapies will result in a maximal therapeutic benefit, and predict whether a therapy will result in an adverse response and should be avoided in a given individual. Pharmacogenetic studies of the glucocorticoid, leukotriene, and β₂-adrenergic receptor pathways have focused on candidate genes within these pathways and, in addition to a small number of genome-wide association studies, have identified genetic loci associated with therapeutic responsiveness. This review summarizes these pharmacogenetic discoveries and the future of genetic profiles for personalized medicine in asthma. The benefit of a personalized, tailored approach to health care delivery is needed in the development of expensive biologic drugs directed at a specific biologic pathway. Prior pharmacogenetic discoveries, in combination with additional variants identified in future studies, will form the basis for future genetic profiles for personalized tailored approaches to maximize therapeutic benefit for an individual asthmatic while minimizing the risk for adverse events.

Genetics of allergic diseases

Genome-wide association studies (GWAS) have been employed in the field of allergic disease, and significant associations have been published for nearly 100 asthma genes/loci. An outcome of GWAS in allergic disease has been the formation of national and international collaborations leading to consortia meta-analyses, and an appreciation for the specificity of genetic associations to sub-phenotypes of allergic disease. Molecular genetics has undergone a technological revolution, leading to next-generation sequencing strategies that are increasingly employed to hone in on the causal variants associated with allergic diseases. Unmet needs include the inclusion of diverse cohorts and strategies for managing big data.

UGT1A1*28 is associated with greater decrease in serum K⁺ levels following oral intake of procaterol

BACKGROUND AND OBJECTIVE

Procaterol is a potent β2-agonist frequently used for the management of asthma and chronic obstructive pulmonary disease. The efficacy and adverse effects of β2-agonists are heterogeneous in individual patients, which may be partly caused by genetic variations in metabolizing enzymes and receptor molecules. The present study was designed to analyze the relationship between gene polymorphisms and physiological effects of procaterol in healthy subjects.

METHODS

Ninety-two non-smoking healthy volunteers were given 1 µg/kg body weight (max 50 µg) of procaterol as a dry syrup preparation, and the serum concentrations of procaterol, serum K(+), and the physical responses were monitored for 240 min. We genotyped β2-adrenergic receptor (ADRB2) (Arg16Gly and Gln27Glu), cytochrome P450 3A4 (rs2246709, rs4646437), and uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) (rs4148323 [allele A, *6], rs12479045, rs4148328, rs4663971, rs12052787, rs4148329, A (TA)6/7 TAA [seven-repeat allele, *28]). Procaterol concentrations in serum were measured by liquid chromatography-tandem mass spectrometry.

RESULTS

No gene polymorphisms affected serum procaterol concentrations. Meanwhile, overall serum K(+) level changes were significantly lower in carriers of UGT1A1*28 than in non-carriers after correcting for strong effects of serum procaterol concentrations and baseline K(+) levels. No other polymorphisms were associated with serum K(+) levels. None of polymorphisms of ADRB2 were associated with any physical responses.

CONCLUSION

The present study indicates that significant hypokalemia may occur in carriers of UGT1A1*28 by systemic administration of procaterol and potentially by other β2-agonists metabolized in the liver.

Do genetic polymorphisms alter patient response to inhaled bronchodilators?

INTRODUCTION

Short- and long-acting β agonists (SABA and LABA) are bronchodilators for treating asthma. Bronchodilator response (BDR) is quantified by measuring air expired in the first second during a forced expiratory maneuver, prior to and following inhalation of SABA. BDR has been associated with a significant degree of heterogeneity, in part attributable to genetic variation. Heritability, the proportion of phenotypic variability accounted for by genetic variation is estimated to account for 50% of pulmonary function and 28.5% for BDR.

AREAS COVERED

A MEDLINE search for English articles published from January 1990 to June 2014 was completed using the terms: bronchodilator, bronchodilator response, short-acting bronchodilator, long-acting bronchodilator, β2 adrenergic receptor gene (ADRB2), asthma and pharmacogenomics. The effects of ADRB2 variants on BDR and the safety of SABA and LABA + inhaled corticosteroids have been studied with equivocal results. Single and candidate gene studies have identified variants in other genes that alter response to bronchodilators. Associations were recently observed between hospital admission rates and two rare ADRB2 polymorphisms: Thr164Ile and a 25 base pair insertion-deletion at nucleotide -376. This was the first report of life-threatening events associated with LABA being linked to rare ADRB2 variants.

EXPERT OPINION

Pharmacogenomic studies over the last two decades clearly demonstrate that polymorphisms alter patient response to bronchodilators in patients with asthma.

Effect of β2 -adrenergic receptor gene Arg16Gly polymorphisms on response to long-acting β2-agonist in Chinese Han asthmatic patients

Background

To evaluate the effect of variation of the Arg16Gly polymorphism of the β₂-adrenergic receptor gene on clinical response to salmeterol administered with fluticasone propionate in Chinese Han asthmatic patients.

Methods

Moderate persistent asthmatic patients (n = 62) currently receiving short-acting β₂-agonists were administered twice-daily therapy with salmeterol/fluticasone propionate 50/250 μg in a single inhaler for 12 weeks, followed by a 2-to-4-day run-out period. Using direct DNA sequencing, five single nucleotide polymorphisms (SNPs) in the promoter and coding block regions of β₂-adrenergic receptor gene were determined in 62 subjects and haplotypes were combined.

Results

There was sustained and significant improvement (p < 0.001) over baseline in all measures of asthma control in subjects receiving salmeterol and fluticasone, regardless of Arg16Gly genotype. However, there was no significant difference in the improvement among three genotypes (p > 0.05). Responses to salmeterol did not appear to be modified by haplotype pairs (p > 0.05). During the run-out period, all subjects had similar decreases in measures of asthma control, with no differences between genotypes (p > 0.05).

Conclusions

Response to salmeterol does not vary with Arg16Gly polymorphisms after chronic dosing with inhaled corticosteroids in Chinese Han asthmatic patients.

Pharmacogenetics of beta2 adrenergic receptor agonists in asthma management

Beta2 (β2) adrenergic receptor agonists (beta agonists) are a commonly prescribed treatment for asthma despite the small increase in risk for life-threatening adverse responses associated with long-acting beta agonist (LABA). The concern for life-threatening adverse effects associated with LABA and the inter-individual variability of therapeutic responsiveness to LABA-containing combination therapies provide the rationale for pharmacogenetic studies of beta agonists. These studies primarily evaluated genes within the β2-adrenergic receptor and related pathways; however, recent genome-wide studies have identified novel loci for beta agonist response. Recent studies have identified a role for rare genetic variants in determining beta agonist response and, potentially, the risk for rare, adverse responses to LABA. Before genomics research can be applied to the development of genetic profiles for personalized medicine, it will be necessary to continue adapting to the analysis of an increasing volume of genetic data in larger cohorts with a combination of analytical methods and in vitro studies.

Beta2 adrenergic receptor (ADRβ2) haplotype pair (2/4) is associated with severe asthma

Background

β2 adrenergic receptor (ADRβ2) polymorphisms including ADRβ2+46G>A have been reported to cause adverse outcomes in mild asthmatics. The extent to which ADRβ2 polymorphisms and in particular their haplotypes contribute to severe asthma is unknown.

Objective

To determine the association of ADRβ2 polymorphisms and haplotypes with asthma severity.

Methods

Caucasians (n = 2979) were genotyped for 11 ADRβ2 polymorphisms. The cohort (mean age 39.6, 60% female) included 2296 non-asthmatics, 386 mild asthmatics, 172 moderate asthmatics and 125 severe asthmatics. Haplotype frequency and haplotype pair for each subject was determined using the PHASE algorithm.

Results

The three asthmatic cohorts were comparable in age and gender but were distinguishable from each other in terms of symptoms, spirometry, medication use and health care utilisation (p <0.001). None of the polymorphisms showed a genotypic or allelic association with asthma diagnosis or severity. Nine haplotypes were identified and no association was found with asthma diagnosis or severity per se. Haplotype pair 2/4 was associated with asthma severity (Trend Test, OR 1.42, p = 0.0008) but not with asthma per se. Prevalence of haplotype pair 2/2 appeared to decrease with asthma severity (Trend Test, OR 0.78, p = 0.067). Two new haplotypes were identified, occurring exclusively in asthmatics at a frequency of ≥ 1%. In addition, a positive association between carriage of ADRβ2 +523*C and increased risk of atopy was discovered.

Conclusions

ADRβ2 haplotype pair 2/4 is associated with severe asthma and is consistent with findings of poor bronchodilator response in mild asthmatics who are also haplotype 2/4.

Pharmacogenetics of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a complex genetic disease that develops as a result of the interaction of multiple susceptibility genes and environmental factors. Major therapeutic approaches include smoking cessation, treatment with bronchodilators and corticosteroid therapy. The goal of understanding the genetic defects in patients with COPD will be not only to redefine the disease phenotypes based on the genetic information, but also to alternatively approach patients based on the understanding of COPD pathogenesis, which will lead to improved clinical outcomes. Although there is no single ideal phenotype for COPD pharmacogenetic studies, thus far, most pharmacogenetics studies have focused on the role of variants in the β2-adrenergic receptor gene on bronchodilator response. The inconclusive results yielded by these studies highlight many of the difficulties researchers face in assessing the influence of genetic variants and in translating this to clinically relevant outcomes.

Designing clinical trials to address the needs of childhood and adult asthma: the National Heart, Lung, and Blood Institute's AsthmaNet

In 2008, the National Heart, Lung, and Blood Institute announced its intent to support a new asthma network known as AsthmaNet. This clinical trials consortium, now in its fifth year, has been charged with developing and executing clinical trials to address the most important asthma management questions and identify new treatment approaches in pediatric and adult patients. This review will discuss the organization of AsthmaNet and the scientific context in which the network was developed and began its work, report the results of an internal priority-setting exercise designed to guide the network's scientific strategy, and highlight the portfolio of clinical trials, proof-of-concept studies, and mechanistic studies planned for the 7-year period of the network to update the global asthma community regarding the progress and processes of the network.

Loss of salmeterol bronchoprotection against exercise in relation to ADRB2 Arg16Gly polymorphism and exhaled nitric oxide

RATIONALE

β2-Agonists are the treatment of choice for exercise-induced bronchoconstriction (EIB) and act through specific receptors (ADRB2). Arg16Gly polymorphisms have been shown to affect responses to regular use of β2-agonists.

OBJECTIVES

To evaluate the influence of the Arg16Gly receptor polymorphism on salmeterol bronchoprotection in EIB and assess predictors of bronchoprotection.

METHODS

A prospective, genotype-blinded, randomized trial was performed in 26 subjects (12 Arg16Arg and 14 Gly16Gly) with EIB who were not on controller therapy. Subjects were administered salmeterol, 50 μg twice a day for 2 weeks, and underwent an exercise challenge 9 hours after the first and last drug dose. In addition to genotype, FEV1, response to salmeterol, degree of EIB, and exhaled nitric oxide (FE(NO)) at baseline were examined for their association with loss of bronchoprotection (LOB).

MEASUREMENTS AND MAIN RESULTS

The maximum exercise-induced FEV1 fall was 27.9 ± 1.4% during the run-in period, 8.1 ± 1.2% (70.3 ± 4.1% bronchoprotection) after the first salmeterol dose, and 22.8 ± 3.2% (18.9 ± 11.5% bronchoprotection) after 2 weeks of salmeterol (P = 0.0001). The Arg16Gly polymorphisms were not associated with the LOB in response to salmeterol. FeNO values at baseline were significantly related to the LOB (r = 0.47; P = 0.01). Mean change was a 74 ± 13% LOB in subjects with FE(NO) levels greater than 50 ppb and a 7 ± 16% gain in bronchoprotection in those with FE(NO) levels less than 25 ppb (P = 0.01).

CONCLUSIONS

The LOB that occurs with chronic long-acting β2-agonists use is not affected by ADRB2 Arg16Gly polymorphisms. High FE(NO) was associated with marked LOB. Use of long-acting β2-agonists before achieving a reduction in FeNO may need to be avoided. Clinical trial registered with www.clinicaltrials.gov (NCT 00595361).

Pharmacogenetics and the development of personalized approaches for combination therapy in asthma

Asthma is a common, chronic disease of the airways that is treated with a combination of different therapies. The combination of LABA and ICS therapy results in a synergistic interaction that is efficacious in improving asthma symptom control; however, genetic variation has the potential to alter therapeutic efficacy. Both agents mediate complex molecular pathways consisting of gene variation that has been investigated with the analysis of candidate genes in the β2-adrenergic receptor and glucocorticoid pathway. These pharmacogenetic studies have been limited to retrospective analyses of clinical trial cohorts and a small number of prospective, genotype-stratified trials. More recently, genome-wide association studies in combination with replication in additional cohorts and in vitro cell-based models have been used to identify novel pathway-related pharmacogenetic variations. This review of the pharmacogenetics of the β2-adrenergic receptor and glucocorticoid pathways highlights the genotypic effects of variation in multiple genes from interacting pathways which may contribute to differential responses to inhaled beta agonists and glucocorticoids. As our understanding of these genetic mechanisms improves, panels of biomarkers may be developed to determine which combination therapies are the most effective with the least risk to an individual asthma patient. Before we can usher in an era of personalized medicine for asthma, it is first important to improve our ability to analyze large volumes of genetic data in large clinical trial cohorts using a combination of study designs, analytical methods, and in vitro functional studies.

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.

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.

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

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.

Effects of the β-agonist, isoprenaline, on the down-regulation, functional responsiveness and trafficking of β2-adrenergic receptors with N-terminal polymorphisms

The β2-AR (β2-adrenergic receptor) is an important target for respiratory and CVD (cardiovascular disease) medications. Clinical studies suggest that N-terminal polymorphisms of β2-AR may act as disease modifiers. We hypothesized that polymorphisms at amino acids 16 and 27 result in differential trafficking and down-regulation of β2-AR variants following β-agonist exposure. The functional consequences of the four possible combinations of these polymorphisms in the human β2-AR (designated β2-AR-RE, β2-AR-GE, β2-AR-RQ and β2-AR-GQ) were studied using site-directed mutagenesis and recombinant expression in HEK-293 cells (human embryonic kidney cells). Ligand-binding assays demonstrated that after 24 h exposure to 1 μM isoprenaline, isoforms with Arg16 (β2-AR-RE and β2-AR-RQ) underwent increased down-regulation compared with isoforms with Gly16 (β2-AR-GE and β2-AR-GQ). Consistent with these differences in down-regulation between isoforms, prolonged isoprenaline treatment resulted in diminished cAMP response to subsequent isoprenaline challenge in β2-AR-RE relative to β2-AR-GE. Confocal microscopy revealed that the receptor isoforms had similar co-localization with the early endosomal marker EEA1 following isoprenaline treatment, suggesting that they had similar patterns of internalization. None of the isoforms exhibited significant co-localization with the recycling endosome marker Rab11 in response to isoprenaline treatment. Furthermore, we found that prolonged isoprenaline treatment led to a higher degree of co-localization of β2-AR-RE with the lysosomal marker LAMP1 (lysosome-associated membrane protein 1) compared with that of β2-AR-GE. Taken together, these results indicate that a mechanism responsible for differential responses of these receptor isoforms to the β-agonist involves differences in the efficiency with which agonist-activated receptors are trafficked to the lysosomes for degradation, or differences in degradation in the lysosomes.

Airway smooth muscle in the pathophysiology and treatment of asthma

Airway smooth muscle (ASM) plays an integral part in the pathophysiology of asthma. It is responsible for acute bronchoconstriction, which is potentiated by constrictor hyperresponsiveness, impaired relaxation and length adaptation. ASM also contributes to airway remodeling and inflammation in asthma. In light of this, ASM is an important target in the treatment of asthma.