Are beta2-adrenoceptor polymorphisms important in asthma--an unravelling story

Pharmacotherapy of critical asthma syndrome: current and emerging therapies

The critical asthma syndrome (CAS) encompasses the most severe, persistent, refractory asthma patients for the clinician to manage. Personalized pharmacotherapy is necessary to prevent the next acute severe asthma exacerbation, not just the control of symptoms. The 2007 National Asthma Education and Prevention Program Expert Panel 3 provides guidelines for the treatment of uncontrolled asthma. The patient's response to recommended pharmacotherapy is highly variable which risks poor asthma control leading to frequent exacerbations that can deteriorate into CAS. Controlling asthma symptoms and preventing acute exacerbations may be two separate clinical activities with their own unique demands. Clinicians must be prepared to use the entire spectrum of asthma medications available but must concurrently be aware of potential drug toxicities some of which can paradoxically worsen asthma control. Medications normally prescribed for COPD can potentially be useful in the CAS patient, particularly those with asthma-COPD overlap syndrome. Immunomodulation with drugs like omalizumab in IgE-mediated asthma syndromes is one important approach. New and emerging drugs address unique aspects of airway inflammation and biology but at a significant financial cost. The pharmacology and toxicities of the agents that may be used in the treatment of CAS to control asthma symptoms and prevent severe exacerbations are reviewed.

Recent advance in investigation of gene polymorphisms in Japanese patients with aspirin-exacerbated respiratory disease

Aspirin-exacerbated respiratory disease (AERD) is a complex clinical syndrome characterised by severe asthmatic attack upon treatment with aspirin and/or non-steroidal anti-inflammatory drugs (NSAIDs). Genetic predisposition has been considered as a crucial determinant and candidate genes have concentrated especially on cysteinyl leukotrienes (LTs)-related genes as the inhibitory action of aspirin and NSAIDs on cyclooxygenase activity may cause overproduction of cysteinyl LTs. However, conflicting results have been reported, in parallel with replication studies in different ethnic groups. Thus, future areas of investigations need to focus on comprehensive approaches towards the discovery of other genetic biomarkers. Unfortunately, few papers have been reported about gene polymorphisms in Japanese patients with AERD. Here, we described on our recent genetic investigations on B2ADR, IL-13, IL-17A, CYP2C19, TBXA2R, CRTH2 and HSP70. This review indicates potential genetic biomarkers contributing to the early diagnosis of AERD, which may include CYP2C19 and HSP70 gene polymorphisms, and future validation studies in independent population are required to provide reassurance about our findings.

The emerging role of tiotropium for patients with asthma

OBJECTIVE

To review clinical data on the use of the long-acting anticholinergic agent tiotropium in patients with asthma.

DATA SOURCES

A literature search was performed via EMBASE and MEDLINE (1966-November 2012). The search was limited to human data published in the English language. Search terms included asthma, tiotropium, and long-acting anticholinergics.

STUDY SELECTION AND DATA EXTRACTION

Relevant information related to the use of tiotropium in patients with asthma was reviewed. Randomized controlled trials and open-label trials were included. The references of published articles identified in the search were also examined for additional studies appropriate to include in the review. Data were prioritized if they originated from human studies, especially if derived from randomized, placebo-controlled trials. Trials and case reports involving the use of long-acting anticholinergic tiotropium in asthma patients were included; conversely, trials involving ipratropium were not.

DATA SYNTHESIS

Two large randomized controlled trials support the safety and efficacy of adding tiotropium to the treatment regimen of select patients with poorly controlled asthma already receiving combination high-dose glucocorticosteroid/long-acting β-agonist (LABA) therapy. Pharmacogenomic studies have shown that patients with polymorphisms of the β2-adrenoreceptor (ADRB2; 16 Arg/Arg and 16 Arg/Gly) are particularly responsive to treatment with tiotropium. Smaller studies indicate that the advantages may be most pronounced in patients with a predominance of sputum neutrophils and that tiotropium can assist with decreasing the inhaled corticosteroid (ICS) dose. An increased risk of cardiovascular events was not identified.

CONCLUSIONS

Tiotropium should be considered in patients with asthma who remain symptomatic while receiving high-dose ICS and LABA therapy. Specifically, patients with high sputum neutrophil levels or with 16 Arg/Arg or 16 Arg/Gly polymorphism of the ADRB2 gene appear to respond best.

Arg16Gly β2-adrenergic receptor gene polymorphism in Japanese patients with aspirin-exacerbated respiratory disease

BACKGROUND

There has been no report that investigated β(2)-adrenergic receptor (ADRB2) gene polymorphism in patients with aspirin-exacerbated respiratory disease (AERD).

METHODS

DNA in the specimens in three groups of study subjects classified patients with AERD, patients with aspirin-tolerant asthma (ATA) and normal controls was extracted, and the target DNA sequence of the ADRB2 was amplified using a set of primers to generate an amplicon of 219 bp in length. Allelic discrimination assay for single nucleotide polymorphisms relating to the ADRB2 gene expression was carried out by using a previously described single nucleotide polymorphism detective system, sequence-specific thermal-elution chromatography.

RESULTS

The frequency of the Gly variant allele in patients with AERD was significantly lower than that in patients with ATA (p = 0.007), and the odds ratio (OR) of AERD to ATA associated with wild-type ArgArg homozygote was 3.300. Frequencies of wild-type ArgArg homozygote are significantly higher than those of variant-type ArgGly/GlyGly genotype in patients with AERD compared with those with ATA (p < 0.001, OR = 3.153). In patients with AERD, frequencies of wild-type ArgArg homozygote in both female and male patients are significantly higher than those of variant-type ArgGly/GlyGly genotype in male patients compared with those with ATA (p < 0.001, OR = 5.128 and p = 0.007, OR = 4.367, respectively). Also, in patients with AERD, frequencies of wild-type ArgArg homozygote in female patients are significantly higher than those of variant-type ArgGly/GlyGly genotype in female patients compared with those with ATA (p = 0.002, OR = 2.825).

CONCLUSIONS

We were the first to analyze Arg16Gly ADRB2 gene polymorphism in Japanese patients with AERD, and showed that Arg16Gly ADRB2 gene polymorphism in Japanese patients with AERD is different from that in the patients with ATA.

The pharmacogenetics of asthma treatment

The treatment response to each of the three major classes of asthma medications-beta agonists, leukotriene modifiers, and inhaled corticosteroids-demonstrates substantial interindividual variability. Evidence indicates that this variability is mediated, at least in part, by genetic factors. Pharmacogenetics is the study of the role of heritable factors in the response to pharmacologic therapy. The goal of pharmacogenetics is "predictive medicine," whereby a genetic profile, combined with clinical characteristics, can be used to predict response to medications a priori, allowing for maximal therapeutic response while minimizing side effects. In this review, we discuss the rationale behind conducting asthma pharmacogenetics studies, provide an overview of asthma pharmacogenetic phenotypes, and detail the most important results of asthma pharmacogenetics studies conducted to date. Although no specific predictive tests have been developed thus far, the existing studies serve as strong proof of concept of the applicability of pharmacogenetics in the future management of asthma.

Pharmacogenetic response to albuterol among asthmatics

Pharmacogenetics offers to individualize asthma treatment by identifying genetic variants associated with drug efficacy or adverse events. Several studies have focused on pharmacogenetic associations with albuterol, the most commonly prescribed medication for asthma worldwide. However, pharmacogenetic associations have varied within and between studies and across populations. Herein, we focus on pharmacogenetic associations between genetic variants in the beta(2)-adrenergic receptor gene and bronchodilator response to albuterol among subjects with asthma.

Part IV: Genetic variations in beta2-adrenergic receptors: long-acting and short-acting beta2-agonists and therapeutic response

Inhaled beta2-agonists are the most commonly used treatment for asthma. It has been hypothesized that patients who exhibit functional polymorphic variants of the beta2-adrenergic receptor may be more likely to experience adverse outcomes with the regular use of beta2-agonists, particularly the short-acting beta2-agonist albuterol. This hypothesis has been confirmed in retrospective studies and in a prospective clinical trial. Results from these studies demonstrate that patients with the Arg/Arg phenotype at the 16th amino acid position of the beta2-adrenergic receptor may experience worsening asthma outcomes after regular beta2-agonist use. Data regarding the impact of polymorphic variants of the beta2-adrenergic receptor on response to long-acting beta2-agonists are conflicting. However, recent data indicate that use of long-acting beta2-agonists may be associated with an increased risk of life-threatening asthma or asthma-related deaths, which might be increased among African-Americans and patients who do not use inhaled corticosteroids. Until more data are available, short-acting beta-agonists should only be used on an as-needed basis and to prevent exercise-induced asthma symptoms, and long-acting beta-agonists should only be used as an adjunct to controller therapy with inhaled corticosteroids. Any patient with asthma who requires adjunctive use of a long-acting beta2-agonist in addition to an inhaled corticosteroid should be carefully monitored for possible adverse asthma outcomes.

Beta-2-adrenergic receptor polymorphisms in cystic fibrosis

OBJECTIVES

Cystic fibrosis (CF), an autosomal recessive disease affecting the lung, pancreas, gut, liver, and reproductive tract, is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which encodes a cyclic adenosine 3', 5' monophosphate-regulated chloride channel. The variability of disease progression among patients with CF suggests effects of genetic modifiers of disease. Beta-2 adrenergic receptors (beta2AR), which are abundant in airway epithelial cells, accelerate the formation of cyclic adenosine 3', 5' monophosphate, which can modulate CFTR activity and affect smooth muscle contractility. We tested the hypothesis that genetic variants of the beta2AR gene, which have been shown to influence receptor desensitization, are more frequent in patients than in controls.

METHODS

We genotyped 130 adult CF patients and 1 : 1 age-matched, sex-matched, and ethnicity-matched normal volunteers for GlyArg and GlnGlu beta2AR.

RESULTS

We found that CF patients were more likely than controls to be Gly homozygotes (48 and 32%, respectively) (P<0.01) and Glu homozygotes (29 and 10%, respectively) (P<0.01).

CONCLUSIONS

Our results, showing a higher frequency of Gly and Glu beta2AR alleles in adult CF patients than in the control population, contrast with data from children with CF, who are reported to have lower frequency of Gly and similar frequency of G1u, and with data from young adults with CF, who showed no differences in frequencies of beta2AR variants. The GlyGlu variant of beta2AR may have properties that lead to enhanced beta2AR function, resulting in the upregulation of CFTR activity and the improvement of CF disease.

The influence of the AA 16 beta 2-adrenoceptor polymorphism on systemic and airway responses in asthma

BACKGROUND

The impact of the polymorphic amino acids 16 and 27 of the beta 2-adrenoceptor (beta 2-AR) on the susceptibility to bronchodilator tolerance remains unclear since clinical studies thus far have shown discordant results. Tolerance towards the effects of inhaled beta 2-AR agonists generally is more easily shown for systemic parameters than for airway effects and can be substantial. This study evaluates whether differences exist between position 16 homozygous genotyped asthmatics, in tolerance development towards airway responses and the systemic effect hypokalemia.

METHODS

Twenty patients were genotyped for amino acids 16 and 27 of the beta 2-AR gene. Time-effect curves for FEV1 and serum potassium concentration were constructed after s.c. administration of terbutaline after two-week treatment periods with either terbutaline inhalation or matching placebo in a double-blind, randomised and cross-over design. Statistical analysis was done by a repeated measures multivariate analysis on area under time-effect curve (AUC).

MAIN RESULTS

Pre-treatment with inhaled terbutaline did not influence the improvement in FEV1 in response to s.c. terbutaline and there were no significant differences between Arg-16 and Gly-16 individuals in this respect. Pre-treatment with inhaled terbutaline resulted in an overall increase of baseline plasma potassium before administration of s.c. terbutaline (3.78-3.95 mmol/L, p=0.034). However, this effect appeared to be solely confined to the Arg-16 homozygous individuals, leading to a statistically highly significant difference between the Arg-16 and Gly-16 subjects (p=0.005). However, there was no genotype related difference in the decrease in plasma potassium response to s.c. terbutaline relative to baseline.

CONCLUSION

In patients carrying the Arg-16 genotype the development of hypokalemia by s.c. terbutaline is attenuated after pre-treatment with inhaled terbutaline, be it on the basis of higher baseline values.

Beta2-adrenoceptor polymorphisms and asthma from childhood to middle age in the British 1958 birth cohort: a genetic association study

BACKGROUND

Functionally relevant polymorphisms of the beta2-adrenoceptor gene (ADRB2) are common in white populations, but their contribution to the burden of airways disease in the population is uncertain. We aimed to relate the long-term prevalence of asthma or wheeze to functional coding region polymorphisms in the ADRB2 gene.

METHODS

The British 1958 birth cohort consisted of all people born in Britain during a week in 1958. Asthma, wheezy bronchitis, and wheezing were ascertained by interview at ages 7, 11, 16, 23, 33, and 42 years, and lung function tests at 35 and 45 years. DNA samples from 8018 participants in the 45-year follow-up were genotyped for three coding variants in the ADRB2 gene. We extend the follow-up of this nationwide cohort by a further 10 years and relate asthma prevalence, prognosis, and lung function to functional coding region polymorphisms in the ADRB2 gene in the cohort members who contributed DNA samples. We also compared and combined our findings with those reaching significance in two previous meta-analyses.

FINDINGS

Half the cohort (4105 of 8018) had some history of wheezing illness by age 42 years. Neither lifetime prevalence nor age at onset were related to ADRB2 coding variants. However, the common polymorphisms Arg16Gly (rs1042713, Arg 16 allele frequency 36.3%) and Gln27Glu (rs1042714, Glu 27 allele frequency 44.6%) were significantly associated with persistence of asthmatic symptoms from childhood to middle age. Among homozygotes for the Arg16-Gln27 haplotype at these loci, 19.3% (41 of 212) childhood wheezers had five or more wheezing episodes in the past year at age 42, compared with 11.9% (71 of 599) with no copy of this haplotype. However, only 3% of all frequent adult wheezing was statistically attributable to this haplotype. The less common Thr164Ile polymorphism (rs1800888, Ile allele frequency 1.5%) was not a major predictor of either frequency or prognosis of asthma. Our data do not support the findings of previous meta-analyses when considered in isolation or when combined with their contributory studies.

INTERPRETATION

ADRB2 polymorphisms might predict a small component of the long-term prognosis in childhood asthma, but are not important determinants of asthma incidence or prevalence in the British population.

Pharmacogenomics and the future of drug therapy

With the completion of the human genome project, many investigators are striving to translate the resulting wealth of new information into new and improved clinical practices. Pharmacogenomics represents one of the most promising of these applications for adult- and pediatric-based therapies. This article provides a historical perspective, but most importantly, uses this background to illustrate important principles of the field. The application of pharmacogenomics to asthma therapy is presented as an example of the current status of pharmacogenomics as it is being applied to an important pediatric health problem. Finally, a discussion of future promises and challenges to the application of pharmacogenomics is presented, including economic and ethical issues.

Three major haplotypes of the beta2 adrenergic receptor define psychological profile, blood pressure, and the risk for development of a common musculoskeletal pain disorder

Adrenergic receptor beta(2) (ADRB2) is a primary target for epinephrine. It plays a critical role in mediating physiological and psychological responses to environmental stressors. Thus, functional genetic variants of ADRB2 will be associated with a complex array of psychological and physiological phenotypes. These genetic variants should also interact with environmental factors such as physical or emotional stress to produce a phenotype vulnerable to pathological states. In this study, we determined whether common genetic variants of ADRB2 contribute to the development of a common chronic pain condition that is associated with increased levels of psychological distress and low blood pressure, factors which are strongly influenced by the adrenergic system. We genotyped 202 female subjects and examined the relationships between three major ADRB2 haplotypes and psychological factors, resting blood pressure, and the risk of developing a chronic musculoskeletal pain condition-Temporomandibular Joint Disorder (TMD). We propose that the first haplotype codes for lower levels of ADRB2 expression, the second haplotype codes for higher ADRB2 expression, and the third haplotype codes for higher receptor expression and rapid agonist-induced internalization. Individuals who carried one haplotype coding for high and one coding for low ADRB2 expression displayed the highest positive psychological traits, had higher levels of resting arterial pressure, and were about 10 times less likely to develop TMD. Thus, our data suggest that either positive or negative imbalances in ADRB2 function increase the vulnerability to chronic pain conditions such as TMD through different etiological pathways that imply the need for tailored treatment options.

The significance of beta2-adrenergic receptor polymorphisms in asthma

PURPOSE OF REVIEW

The gene that encodes the beta2-adrenergic receptor (ADRB2) is one of the most studied candidate genes in asthma. This review examines recent articles of the relationship between ADRB2 polymorphisms and asthma.

RECENT FINDINGS

Candidate gene association studies of ADRB2 and asthma have been dominated by analyses of the two common non-synonymous coding single nucleotide polymorphisms, Arg16Gly and Glu27Gly. Published studies have yielded inconsistent results. Three recent meta-analyses on the effects of these two polymorphisms have found no associations with asthma, although there were suggestions of associations with other asthma-related phenotypes, such as nocturnal asthma and asthma severity. Other recent studies have investigated other single nucleotide polymorphisms in this gene (i.e. single nucleotide polymorphisms in the promoter region and other single nucleotide polymorphisms in the coding region). These analyses have investigated the association between these single nucleotide polymorphisms (and haplotypes of these polymorphisms) and asthma-related phenotypes such as lung function, airways hyperresponsiveness, and response to a bronchodilator, and have suggested that certain regions of the gene may be associated with different phenotypes. Results from these studies, however, have also been inconsistent.

SUMMARY

Polymorphisms of ADRB2 are not major risk factors for the development of asthma. These polymorphisms are likely to be important, however, in determining drug response. Future studies need to fully characterize all of the variation in the gene and perform comprehensive association studies. Finally, interactions between ADRB2 and other genes in the beta-agonist pathway are an important and active area of research that will shed more light on inter-individual differences in drug response.

Genetic variation in G-protein-coupled receptors – consequences for G-protein-coupled receptors as drug targets

G-protein-coupled receptors (GPCRs), including 'orphan' GPCRs whose natural ligands are unknown, comprise the largest membrane receptor superfamily and are the most commonly used therapeutic targets. GPCR genetic loci harbour numerous variants, such as DNA insertions or deletions and single nucleotide polymorphisms that alter GPCR expression and function, thereby contributing to inter-individual differences in disease susceptibility/progression and drug responses. In this article, the authors review examples of GPCR genetic variants that influence transcription, translation, receptor folding and expression on cell surface (by affecting receptor trafficking, dimerisation, desensitisation/downregulation), or perturb receptor function (by altering ligand binding, G-protein coupling and receptor constitutive activity). In spite of such effects, assessment for genetic variants is not currently applied to the drug development and approval process or in the clinical use of GPCR drugs. Further insights will, the authors believe, alter drug discovery/development, therapeutics and likely provide new GPCR drug targets.

Bronchodilator response in relation to beta2-adrenoceptor haplotype in patients with asthma

RATIONALE

Genetic variation of the beta2-adrenoceptor (ADRB2) influences receptor function in vitro. There are reports that, in vivo, bronchodilator response is related to ADRB2 genotype, and that clinical outcomes during chronic therapy with beta2-agonist drugs are also influenced by genotype. Whether these features are related to single nucleotide polymorphisms or to combinations (haplotypes) is unclear.

OBJECTIVES

Our aim was to measure bronchodilator response in patients with asthma stratified by ADRB2 haplotype. This was done after eliminating the confounding effect of prior drug treatment with inhaled beta2-agonists and corticosteroids.

METHODS

ADRB2 haplotype was determined in 176 patients with asthma, of whom 161 harbored the six most common combinations. Treatment with inhaled beta2-agonists and inhaled corticosteroids was withheld for appropriate intervals. Spirometric changes 20 minutes after a single dose of albuterol (2.5 mg by nebulizer) were then recorded.

RESULTS

There were no significant differences in bronchodilator response (% improvement in FEV(1)) with respect to any of the major ADRB2 haplotypes or genotypes.

CONCLUSIONS

Genetic variation of the ADRB2 does not influence the immediate response to inhaled beta2-agonist. The confounding effect of tolerance resulting from regular beta2-agonist use must be controlled when assessing the pharmacogenetic influences on clinical outcomes with beta2-agonists.