Association between bronchodilating response to short-acting beta-agonist and non-synonymous single-nucleotide polymorphisms of beta-adrenoceptor gene

ADRB2 and ADCY9 Sequence Variations in Brazilian Asthmatic Patients

Asthma is a chronic inflammatory respiratory condition, characterized by variable airflow limitation, leading to clinical symptoms such as dyspnea and chest tightness. These symptoms result from an underlying inflammatory process. The β2 agonists are bronchodilators prescribed for the relief of the disease. Nevertheless, their efficacy exhibits substantial interindividual variability. Currently, there is widespread recognition of the association between specific genetic variants, predominantly located within the ADRB2 and ADCY9 genes and their efficacy. This association, usually represented by the presence of non-synonymous single nucleotide polymorphisms (SNPs) have a strong impact in the protein functionality. The prevalence of these mutations varies based on the ethnic composition of the population and thus understanding the profiles of variability in different populations would contribute significantly to standardizing the use of these medications. In this study, we conducted a sequence-based genotyping of the relevant SNPs within the ADRB2 and ADCY9 genes in patients undergoing treatment with bronchodilators and/or corticosteroids at two healthcare facilities in the state of Rio de Janeiro, Brazil. We investigated the presence of c.46A>G, c.79C>G, c.252G>A, and c.491C>T SNPs within the ADRB2, and c.1320018 A>G within the ADCY9. Our results were in line with existing literature data with both for individuals in Brazil and Latin American.

Role of THRB, ARG1, and ADRB2 Genetic Variants on Bronchodilators Response in Asthmatic Children

Background: An interindividual variability in response to short-acting bronchodilator drugs (short-acting inhaled β2-agonists, SABA) exists and this is linked in part to genetic factors. The aim of this study was to verify the influence of single nucleotide polymorphisms (SNPs) of a previously studied gene (ADRB2) and of new candidate genes (THRB and ARG1) on the acute response to SABA in children with asthma. Methods: One hundred asthmatic children (mean age 9.6 ± 3.0 years, 77 boys) underwent allergological and lung function evaluations. Spirometry was performed before and after bronchodilation test (BD test). The ADRB2 region containing the Arg16Gly (rs1042713) and Gln27Glu (rs1042714) variants were amplified by polymerase chain reaction, whereas ARG1 rs2781659 (A>G) and THRB rs892940 (G>A) SNPs were genotyped by high-resolution melting (HRM) analysis. Results: Seventy-seven percent of children developed asthma in the first 6 years of life. Allergic sensitization was observed in 92% (total immunoglobulin G: 529.8 ± 477. kU/L). All patients exhibited respiratory allergy: 43% has multiple respiratory, 22% to single respiratory, and 27% multiple respiratory and food allergies. Fifty four percent children showed positive BD response (forced expiratory volume in 1 second [FEV1] > 12%). Presence of Arg/Gly or Gly/Gly genotypes in position 16 of ADRB2 was significantly associated to a worse BD response (post-BD FEV1: 108.68% ± 15.62% in Arg/Arg vs. 101.86% ± 14.03% in Arg/Gly or Gly/Gly patients, p = 0.02). No significant association was found between spirometric parameters before and after BD for the other three examined SNPs. Conclusion: The influence of genetic variability on responsiveness to drugs could become a key parameter to optimize a tailored therapy for young patients with asthma, especially if drug-resistance occurs.

ADRB2 Gene Polymorphisms and Salbutamol Responsiveness in Serbian Children with Asthma

Inhaled β2 adrenergic receptor (β2-AR) agonists are the mainstay of asthma therapy. The β2-AR protein is encoded by the ADRB2 gene and variants within this gene can have significant consequences for modulating the response to asthma therapy. This cross-sectional study performed at the University Children’s Hospital in Belgrade, included 54 children with asthma. The subjects were genotyped for ADRB2 +46A>G (Arg16Gly, rs1042713) and +79C>G (Gln27Glu, rs 1042714) polymorphisms and the association with asthma severity and response to inhaled salbutamol was examined. In Serbian asthmatic children, allele +46A was detected with a frequency of 41.7% and allele +79G was detected with a frequency of 23.1%. Allele +46G was found to be associated with a better response to inhaled salbutamol (p <0.05) and with mild form of asthma (p <0.05). Polymorphism ADRB2 +46A>G may be a determinant of asthma severity and response to salbutamol in children with asthma. We did not find any association of +79C>G polymorphisms with the asthma severity and bronchodilator response to inhaled salbutamol. The results of this study can be potentially useful for personalization of asthma treatment.

Pharmacogenetic and pharmacogenomic considerations of asthma treatment

INTRODUCTION

Pharmacogenetic and pharmacogenomic approaches are already utilized in some areas, such as oncology and cardiovascular disease, for selecting appropriate patients and/or establishing treatment and dosing guidelines. This is not true in asthma although many patients have different responses to drug treatment due to genetic factors. Areas covered: Several genetic factors that affect the pharmacotherapeutic responses to asthma medications, such as β₂-AR agonists, corticosteroids, and leukotriene modifiers and could contribute to significant between-person variability in response are described. Expert opinion: An expanding number of genetic loci have been associated with therapeutic responses to asthma drugs but the individual effect of one single-nucleotide polymorphism is partial. In fact, epigenetic changes can modify genetic effects in time-, environment-, and tissue-specific manners, genes interact together in networks, and nongenetic components such as environmental exposures, gender, nutrients, and lifestyle can significantly interact with genetics to determine the response to therapy. Therefore, well-designed randomized controlled trials or observational studies are now mandatory to define if response to asthma medications in individual patients can be improved by using pharmacogenetic predictors of treatment response. Meanwhile, routine implementation of pharmacogenetics and pharmacogenomics into clinical practice remains a futuristic, far-off challenge for many clinical practices.

ADRB2 Polymorphism and Salbutamol Responsiveness in Northern Indian Children with Mild to Moderate Exacerbation of Asthma

OBJECTIVE

The primary objective was to determine the association between beta-2 adrenergic receptor (ADRB2) gene polymorphism (rs1042713, c.46A>G, p.Arg16Gly) and the response to inhaled salbutamol in North Indian children aged 5 to 15 years, with mild to moderate exacerbation of asthma.

METHODS

This cross-sectional study was done at a tertiary-care hospital in Northern India from June 2011 to May 2013. 120 children with asthma with mild to moderate exacerbation underwent spirometry at baseline and after administration of three doses of salbutamol. An increase in FEV1 =15% was considered as positive response. Blood samples from these children were analysed for ADRB2 polymorphism (p.Arg16Gly). 94 non-asthmatic adult controls were also studied to determine the prevalence of ADRB2 polymorphism.

RESULTS

In asthmatic children, the frequency of AA, GG, AG genotypes were 24.2%, 24.2% and 51.7% compared to 20.2%, 20.2% and 59.6%, respectively in the non-asthmatic adults. Salbutamol responsiveness showed no correlation with the studied ADRB2 polymorphism (p= 0.55). A trend towards greater bronchodilator responsiveness amongst AA genotype, compared to GG genotype was observed (Median change in percent predicted FEV1 14.5% and 7.5%, respectively).

CONCLUSION

No correlation was found between salbutamol responsiveness and ADRB2 genotype in Northern Indian children with asthma with mild-to moderate exacerbation.

Candidate gene analysis of asthma in a population of Arab descent: a case-control study in Jordan

AIM

To evaluate whether SNPs (n = 15) in ten candidate genes (ADRB2, ADH5, ARGI, CRHR1, STIP1, LTA4H, LTC4S, ALOX5, ABCC1 and OATP2B1) are associated with asthma in Jordanian population of Arab descent.

METHODS

A case-control study included 245 adult asthmatics and 249 controls.

RESULTS

Significant genetic association was identified at the rs2236647 (T/C) SNP in STIP1 and risk of asthma (p < 0.001). The C allele and CC genotype of this SNP were significantly higher in asthmatics compared with controls. The rs1141370 SNP (Val34Met) in ADRB2 is not polymorphic in our cohort.

CONCLUSION

The rs2236647 SNP could act as a reliable tool to identify individuals at risk of developing asthma and provision of early intervention in population of Arab descent.

Diagnostic properties of the methacholine and mannitol bronchial challenge tests: a comparison study

BACKGROUND AND OBJECTIVE

Airway hyperresponsiveness is a common feature of asthma. Methacholine and mannitol are two representative agonists for bronchial challenge. They have theoretically different mechanisms of action, and may have different diagnostic properties. However, their difference has not been directly evaluated among Korean adults. In this study, we compare the diagnostic properties of methacholine and mannitol bronchial provocation tests.

METHODS

Asthmatic patients and non-asthmatic controls were recruited prospectively from four referral hospitals in Korea. Participants were challenged with each of methacholine and mannitol inhalation on different days. Their diagnostic utility was evaluated by calculating their sensitivity and specificity for asthma diagnosis. Response-dose ratio was also compared.

RESULTS

A total of 50 asthmatic adults and 54 controls were enrolled (mean age 43.8 years). The sensitivity and specificity of mannitol challenge (defined by a PD15 of <635 mg) were 48.0% and 92.6%, respectively, whereas those of methacholine (defined by a PC20 of <16 mg/mL) were 42.0% and 98.1%, respectively. Twenty asthmatic participants (24%) showed positive response to a single agonist only. In the receiver operating curve analyses using response-dose ratio values, area under the curve was 0.77 (95% confidence interval (CI): 0.68-0.86) for mannitol, and 0.89 (95% CI: 0.83-0.95) for methacholine. The correlations between log- transformed mannitol and methacholine response-dose ratios were significant but moderate (r = 0.683, P < 0.001).

CONCLUSIONS

The present study demonstrated overall similar diagnostic properties of two diagnostic tests, but also suggested their intercomplementary roles for asthma. The clinical trial registration number at ClinicalTrial.gov is NCT02104284.

Pharmacogenetics: implications of race and ethnicity on defining genetic profiles for personalized medicine

Pharmacogenetics is being used to develop personalized therapies specific to subjects from different ethnic or racial groups. To date, pharmacogenetic studies have been primarily performed in trial cohorts consisting of non-Hispanic white subjects of European descent. A "bottleneck" or collapse of genetic diversity associated with the first human colonization of Europe during the Upper Paleolithic period, followed by the recent mixing of African, European, and Native American ancestries, has resulted in different ethnic groups with varying degrees of genetic diversity. Differences in genetic ancestry might introduce genetic variation, which has the potential to alter the therapeutic efficacy of commonly used asthma therapies, such as β2-adrenergic receptor agonists (β-agonists). Pharmacogenetic studies of admixed ethnic groups have been limited to small candidate gene association studies, of which the best example is the gene coding for the receptor target of β-agonist therapy, the β2-adrenergic receptor (ADRB2). Large consortium-based sequencing studies are using next-generation whole-genome sequencing to provide a diverse genome map of different admixed populations, which can be used for future pharmacogenetic studies. These studies will include candidate gene studies, genome-wide association studies, and whole-genome admixture-based approaches that account for ancestral genetic structure, complex haplotypes, gene-gene interactions, and rare variants to detect and replicate novel pharmacogenetic loci.

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.

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.

Pharmacogenetics of β2 adrenergic receptor gene polymorphisms, long-acting β-agonists and asthma

Adrenergic β2 receptor (ADRβ2) agonists are widely used in asthma. Approximately 10% of patients have severe, poorly controlled disease despite extensive use of ADRβ2 agonists. Variations in responses to ADRβ2 agonists can, in part, be attributed to genetic variation, with 49 different polymorphisms having been identified for the ADRβ2 gene. Although clear associations exist between ADRβ2 gene polymorphisms, such as +46G>A, and patient response, the importance of these polymorphisms remains controversial. Patient selection, the number of polymorphisms analysed, differences in the type/dose of ADRβ2 agonist, use of inhaled corticosteroids and population sizes have all varied. Most studies were limited to mild or moderate asthmatics using ADRβ2 agonists sparingly. It is difficult to extrapolate from these studies to individual patients who have severe asthma, use a variety of ADRβ2 agonists and do so frequently. The extent to which ADRβ2 gene polymorphisms are relevant to asthma management needs further review, both clinically and at the molecular level. In vitro studies have helped to define the functional changes induced by specific ADRβ2 gene polymorphisms, including 3'-untranslated region poly-C repeat. The resulting ADRβ2 gene haplotypes (rather than genotypes), the interactions among ADRβ2 gene haplotypes and variations in the chemistry of different agonists deserve more detailed assessment. Responses to ADRβ2 agonists depend on effective downstream signalling following ADRβ2 activation and also on receptor regulation. Studies on other regulators of ADRβ2 receptor signalling and trafficking may be equally important in understanding the functional role of ADRβ2 gene polymorphisms. The role of ADRβ2 gene polymorphisms in the pathogenesis and management of severe asthma cannot be clearly defined until more specific and targeted research studies are performed.

Association of β₂-adrenergic receptor polymorphism with work-related symptoms in workers exposed to wheat flour

PURPOSE

Our previous study indicated that the presence of wheat-specific IgG1 and IgG4 antibodies was associated with work-related symptoms in workers exposed to wheat flour. We performed this study to investigate the genetic polymorphisms of β₂-adrenergic receptors and wheat-specific antibodies in association with the clinical parameters of baker's asthma.

MATERIALS AND METHODS

In total, 379 subjects working in a single industrial bakery were enrolled in this study. The skin prick test was performed with common inhalant allergens and wheat flour extract. The presence of serum- specific IgE, IgG1, and IgG4 antibodies to wheat flour were determined by ELISA. Whole blood samples were obtained for genotype analysis. Subjects were genotyped with regard to five candidate single nucleotide polymorphisms (SNPs) of the β₂-adrenergic receptor gene (ADRB2; -47 T>C, 46 A>G, 79 C>G, 252 G>A, and 523 C>A) using a single-base extension method.

RESULTS

No significant associations were observed between the genotype/allele frequencies of any of the SNPs tested and any clinical parameters. The haplotype of ADRB2 (GAA composed of 46 A>G, 252 G>A, and 523 C>A) was significantly associated with work-related symptoms (p<0.05). Moreover, in subjects with the AG or GG genotype at 46 A>G and haplotype [GAA] of ADRB2, the prevalence rates of wheat-specific IgG1 antibodies and lower respiratory symptoms increased significantly with exposure intensity (both p<0.05).

CONCLUSION

The findings of the present study suggest that ADRB2 genetic polymorphism may contribute to the development of work-related symptoms in workers exposed to wheat flour, which can lead to baker's asthma.

Probable role of Beta 2-adrenergic receptor gene haplotype in toluene diisocyanate-induced asthma

PURPOSE

A genetic polymorphism of the beta 2-adrenergic receptor is a major factor associated with the asthmatic phenotype. The association of this polymorphism with toluene diisocyanate (TDI)-induced asthma has not been investigated. We examined 103 TDI-induced asthma patients (TDI-OA), 60 asymptomatic exposed controls (AEC), and 263 unexposed healthy controls (NC) in order to identify beta 2-adrenergic receptor gene (ADRB2) polymorphisms and the possible association with TDI-induced asthma.

METHODS

Single nucleotide polymorphisms (SNPs) of ADRB2 were genotyped by direct sequencing. Serum-specific IgE and IgG levels were measured using an enzyme-linked immunosorbent assay. Phenotypes and clinical patient parameters were compared.

RESULTS

SNPs were identified (-47 T>C, -20 T>C, Arg16Gly A>G, Gln27Glu C>G, Leu134Leu G>A, Arg175Arg C>A) during ADRB2 screening (from -231 to 793 bp). No significant differences in allelic and genotypic frequencies were noted for any of the six ADRB2 SNPs. The Arg16Gly A>G, Leu134Leu G>A, and Arg175Arg C>A SNPs and haplotype 1 [TTACGC] were significantly associated with specific IgE antibodies to the TDI-human serum albumin (HSA) conjugate in TDI-exposed subjects (P<0.05). Exposed workers with the ADRB2 ht1/ht1 homozygote had a significantly higher TDI-HSA conjugate-specific IgE sensitization rate than did those with the null ht1 haplotype (odds ratio, 15.40; 95% confidence interval, 1.81-131.06).

CONCLUSIONS

ADRB2 polymorphisms may affect IgE-specific sensitization to TDI-HSA conjugate in TDI-exposed workers.

Past, present, and future of allergy in Korea

Korean allergology has made great progress in keeping pace with global scientific advances in spite of a short history. Outstanding academic and scientific researches have been performed in a variety of allergy fields in Korea. Epidemiologic studies revealed increasing prevalence of asthma and allergic diseases and considerable morbidity and mortality in Korea. Novel inhalant allergens such as citrus red mite and two-spotted spider mite as causes of asthma and allergic rhinitis have been discovered and reported in Korea. Bidirectional translational researches have been performed and are underway to elucidate the pathogenesis of asthma and allergy, mechanisms of airway inflammation and remodeling, and new therapeutic modalities for asthma and allergic diseases. Experimental asthma models of different phenotypes according to exposed levels of lipopolysaccharide or double-stranded RNA suggested the crucial role of the innate immunity in the development of allergic airway inflammation and a new insight for asthma pathogenesis, in which both Th1 and Th2 inflammation are involved. In the field of genetic researches, numerous genetic associations with asthma and asthma-related phenotypes, such as atopy, IgE production, and airway hyperresponsiveness, have been demonstrated in Korean population. The Easy Asthma Management (EAM) program, a computer-assisted asthma management program, is anticipated to facilitate the achievement of more successful clinical outcomes by filling the gaps between guidelines and actual practices. The Integration of these multi-disciplinary allergy research resources and translation of scientific achievements to the bedside and society will lead to better allergy and asthma control in Korea.

Pharmacogenomic approaches to asthma treatment

Major classes of medication in asthma management include bronchodilating beta2-agonists, anti-inflammatory inhaled corticosteroids, leukotriene modifiers and theophyllines. However, all asthmatics do not respond to the same extent to a given medication. Available data suggest that a substantial range of individual variability, as much as 70%, may be due to genetic characteristics of each patient. Pharmacogenomics offers the potential to optimize medications for individual asthmatics by using genetic information to improve efficacy or avoid adverse effects. The best-studied case of the potential contribution of pharmacogenomics to treatment response in asthma comes from studies on human beta2 adrenergic receptors. In addition, genetic variation in beta2-adrenergic receptor (Arg16Gly) may predict response to anticholinergics for the treatment of asthma. In case of inhaled corticosteroids, a recent investigation using a traditional SNP-based approach identified a gene for corticotropin releasing hormone receptor 1 as a potential marker of response. Another major pathway that has been investigated is the pathway underlying response to cysteinyl leukotriene receptor antagonist. It is likely that in the near future, pharmacogenomic approaches based on individual genetic information will be introduced into an asthma treatment guideline and this guideline will allow us to identify those who have the best chance to respond to a specific medication.

Polymorphism of the ADRB2 gene and response to inhaled beta- agonists in children with asthma: a meta-analysis

BACKGROUND

About 9% of children have asthma, corresponding to almost 6.8 million children in the USA and 1.1 million in the UK. Asthma exacerbations are the leading cause of pediatric emergency room visits and impose a large burden on the individual, family, and society. There is mounting evidence that therapeutic failure of inhaled beta-agonists is associated with polymorphisms of the beta(2)-adrenergic receptor gene (ADRB2); specifically, mutations leading to amino acid changes at positions 16 and 27, which alter down-regulation of the beta(2)-adrenergic receptor (beta(2)AR), induce resistance to the smooth-muscle relaxing effect of beta(2)-adrenergic agonists.

METHODS

We conducted a meta-analysis to examine the association between ADRB2 polymorphisms and the response to inhaled beta(2)-adrenergic agonists in children with asthma. We included all published studies until November 2008, in which asthmatic children underwent testing for acute bronchodilator response, defined as > or = 15% improvement in forced expiratory volume in 1 second (FEV(1)) and single nucleotide polymorphism (SNP) genotyping for positions 16 and/or 27 of the beta(2)AR. Individual and summary odds ratios were calculated using a random effects model.

RESULTS

We identified three case-control or family-based studies involving 960 asthmatic children (692 children with negative beta(2)-bronchodilator response, defined as < 15% improvement in FEV(1) and 268 children with positive bronchodilator response). We found a significant association between favorable therapeutic response to inhaled beta(2)-adrenergic agonists in asthmatic children and the Arg/Arg phenotype at position 16 of the beta(2)AR [OR = 1.77; 95% CI (1.01; 3.1); p = 0.029], compared with the Arg/Gly or Gly/Gly phenotypes. The beneficial effect of Arg at position 16 of the beta(2)AR was most pronounced in African-American asthmatic children [OR = 3.54; 95% CI (1.37, 9.13)]. There was no association between clinical response to beta(2)-agonists and polymorphism at amino acid position 27 of the beta(2)AR (OR = 1.04; 95% CI [0.76,1.42]).

CONCLUSIONS

Failure of bronchodilator response to inhaled beta-agonists in asthmatic children is associated with the Gly allele (Arg/Gly and Gly/Gly genotypes) at position 16 of the beta(2)-adrenergic receptor. Genetic typing for beta(2)AR polymorphism may help identify children with drug-resistant asthma.

Beta2-receptor polymorphisms in patients receiving salmeterol with or without fluticasone propionate

RATIONALE

Retrospective pharmacogenetic studies have questioned whether patients with asthma who are arginine homozygous at the beta(2-)adrenergic receptor (position 16) should use long-acting beta-agonists.

OBJECTIVES

To examine whether the response to salmeterol alone or in combination with an inhaled corticosteroid is influenced by beta- receptor polymorphisms.

METHODS

Subjects using only as-needed albuterol were screened and completed two sequential open-label run-in periods (8 wk on as-needed albuterol; 8 wk on as-needed ipratropium). Five hundred forty-four subjects were randomized by Arg16Gly genotype to salmeterol alone or with fluticasone propionate for 16 weeks. Change from baseline in morning peak expiratory flow was the primary endpoint.

MEASUREMENTS AND MAIN RESULTS

Lung function responses were sustained over treatment and no statistically significant changes from baseline between genotypes within treatments were observed. Overall mean changes in morning peak flow for salmeterol with fluticasone propionate were 32.6 L/min (Arg/Arg vs. Gly/Gly, 95% confidence interval [CI], -6.3, 22.1), 25.9 L/min (Arg/Arg vs. Arg/Gly, 95% CI, -7.1, 21.3), and 24.9 L/min (Arg/Gly vs. Gly/Gly, 95% CI, -13.0, 14.6), and for salmeterol alone were 19.4 L/min (Arg/Arg vs. Gly/Gly, 95% CI, -1.7, 21.4), 24.6 L/min (Arg/Arg vs. Arg/Gly, 95% CI, -13.0, 10.6), and 12.4 L/min (Arg/Gly vs. Gly/Gly, 95% CI, -0.2, 22.3) for Arg/Arg, Arg/Gly, and Gly/Gly genotypes, respectively. Other measures of asthma control showed similar responses.

CONCLUSIONS

The results showed no evidence of a pharmacogenetic effect of beta-receptor variation on salmeterol response. Clinical trial registered with www.clinicaltrials.gov (NCT 00102882).

Pharmacogenetics and functional genomics in asthma

Asthma is a complex phenotype caused by a combination of genetic and environmental factors that remain poorly understood. The common variants involved in the pathogenesis of asthma have proved difficult to identify by candidate gene association studies. As a result, few genetic variants influencing clinical response to asthma and allergy medications have been uncovered. Recently, genome-wide association, which is more robust in identifying common predisposition variants, has been applied to disorders such as asthma. As genome-wide associations are hypothesis-free, they raise the possibility of identifying novel biological pathways that could be translated to the future benefit of patients through improved diagnostic and therapeutic measures in the form of personalized medicine. This review addresses both recent advances in the genetics of asthma and their potential in transforming the treatment of the disorder into more individualized care in the near future.

Systems biology in pharmacogenomic research: the way to personalized prescribing?

Response to pharmacotherapy can be highly variable amongst individuals. Pharmacogenomics may explain the interindividual variability in drug response due to genetic variation. However, besides genetics, many other factors can play a role in the response to pharmacotherapy, including disease severity, co-morbidity, environmental factors, therapy adherence and co-medication use. Better understanding of these factors and inter-relationships should bring about a much more effective approach to disease management. Systems biology that studies organisms as integrated and interacting networks of genes, proteins and biochemical reactions can contribute to this. Organisms are no longer studied part by part, but in a more integral manner. Integration of the genetic data with intermediate and end point phenotypic characterization may prove essential to define the inherent nature of drug effects. Therefore, in the future, a multidisciplinary systems-based approach will be necessary to deal with the bulk of the biological data that is available and, ultimately, to reach the goal of personalized prescribing.

Effect of beta2-adrenergic receptor polymorphism in asthma control of patients receiving combination treatment

PURPOSE

Combination treatment of inhaled corticosteroid (ICS) plus long-acting beta2-agonist (LABA) is widely used as a maintenance regimen for the management of asthma. This study evaluated the effect of the beta2-adrenergic receptor (ADRB2) polymorphism on lung function and asthma control with regular use of combination treatment of an inhaled ICS plus LABA.

MATERIALS AND METHODS

43 Korean asthmatics who were symptomatic despite regular ICS use for at least 3 months were enrolled. For a 2-week run-in period, they received ICS (budesonide 800 microg/day) plus terbutaline (5 microg prn). as needed. During the 24-week active treatment period, they received budesonide 160 microg and formoterol 4.5 microg b.i.d. as maintenance and rescue medication. Pulmonary function and quality of life scores were monitored every 8 weeks; morning/evening peak expiratory flow meter (PEFR) was recorded daily. Patients were genotyped for ADRB2 Arg16Gly using single base extension methodology.

RESULTS

During the run-in period, there were no significant between-group differences in lung function; after 8 weeks of active treatment, Arg/Arg patients had significantly higher forced expiratory volume in 1 secord (FEV(1)) and maximal mid-expiratory flow (MMEF) (p = 0.023 and p = 0.021, respectively), and better asthma control and quality of life after 24 weeks (p = 0.016 and p = 0.028, respectively). During treatment, there was a greater improvement in morning/evening PEFR in Arg/Arg patients.

CONCLUSION

Asthmatic patients with the Arg/Arg genotype at codon 16 of ADRB2 achieve better asthma control with long-term regular use of combined budesonide and formoterol treatment, suggesting that the ADRB2 genotype may dictate choice of treatment strategy.

Acute and chronic lung function responses to salmeterol and salmeterol plus fluticasone propionate in relation to Arg16Gly beta(2)-adrenergic polymorphisms

OBJECTIVE

There is conflicting clinical evidence describing the response to long-acting beta-agonist (LABA) bronchodilators for patients with Arg16Gly beta(2)-adrenergic receptor (ADRB2 ) genotype differences. Furthermore, the role of inhaled corticosteroids (ICS) in modulating Arg16Gly clinical responses is not well understood. The objective of this study was to investigate the effects of Arg16Gly polymorphism on the 12 hour post-dose bronchodilator response to the LABA salmeterol (SAL) or SAL plus fluticasone propionate (FSC) on first administration and following 12 weeks of treatment.

RESEARCH DESIGN AND METHODS

Genotyping was retrospectively performed in patients with persistent asthma randomized to SAL or FSC who were participating in three similar double-blind clinical trials of 12 week duration. The primary outcome was area under the curve (AUC) for 12 hour serial FEV(1) by treatment and Arg16Gly genotype, recorded on Day 1 and Week 12. In addition, other single nucleotide polymorphisms (SNPs) associated with asthma outcomes we assessed at positions -47, +79 and +491 as well as common ADRB2 haplotypes.

RESULTS

No statistically significant associations between Arg16Gly genotypes and serial FEV(1) clinical responses to SAL and FSC were observed following acute assessment. In addition, the FEV(1) response was preserved following 12 weeks of treatment with SAL and FSC and was not altered by Arg16Gly genotypes analyzed. These results may not be generalizable to other ethnic groups since they are derived predominantly from Caucasians.

CONCLUSIONS

In subjects with persistent asthma, the ADRB2 Arg16Gly polymorphism does not alter lung function responses to SAL or FSC over the 12 hour dosing interval following acute and chronic dosing.

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.

Lung function response to 12-week treatment with combined inhalation of long-acting beta2 agonist and glucocorticoid according to ADRB2 polymorphism in patients with chronic obstructive pulmonary disease

Recent reports suggest that beta(2)-adrenergic receptor (ADRB2) genotypes are associated with therapeutic responses to beta(2) agonists in asthmatics. However, few studies have investigated therapeutic responses to beta(2) agonists in chronic obstructive pulmonary disease (COPD) patients. This study investigated immediate bronchodilator response and lung function responses following a 12-week treatment with a long-acting beta(2) agonist combined with a steroid inhaler in patients with COPD with various ADRB2 genotypes. One hundred four patients with chronic obstruction were genotyped for codon 16 and 27 polymorphisms of the ADRB2 gene. The immediate bronchodilator response to beta(2)-agonist treatment was evaluated after inhalation of 400 microg salbutamol. In addition, long-term response was evaluated using observed change in spirometric values before and after the treatment with salmeterol (50 microg) combined with fluticasone propionate (500 microg) inhalation twice daily for 12 weeks. In terms of codon 16 variants, the immediate bronchodilator response to salbutamol was 6.4 +/- 0.8% (% predicted value) in Arg/Arg patients, 4.9 +/- 0.7% in Arg/Gly patients, and 5.8 +/- 1.2% in Gly/Gly patients (p = 0.418). The FEV(1) changes following the 12-week treatment were 7.0 +/- 1.2% in Arg/Arg patients, 3.0 +/- 1.5% in Arg/Gly patients, and 7.2 +/- 1.2% in Gly/Gly patients (p = 0.229). Similarly, there was no difference between codon 27 variants in terms of immediate bronchodilator response or FEV1 changes after 12 weeks of treatment. We were unable to demonstrate an association between ADRB2 genotype and the effect on lung function of 12-week treatment with combined long-acting beta(2) agonist and glucocorticoid inhalation or on the immediate bronchodilator response to a short-acting beta(2) agonist in patients with COPD.

Race, ethnicity and social class and the complex etiologies of asthma

Asthma is a common but complex respiratory disease caused by the interaction of genetic and environmental factors. Significant racial and ethnic disparities in prevalence, mortality and drug response have been described. These disparities may be explained by racial and ethnic-specific variation in genetic, environmental, social and psychological risk factors. In addition, race, ethnicity and social class are important proxies for unmeasured factors that influence health outcomes. Herein, we review salient differences in the etiologies of asthma by race, ethnicity and social class, and argue for their continued use as variables in asthma research.

Pharmacogenetics of asthma

Asthma is a common disease characterized by airway inflammation and bronchorestriction. There are several common categories of medications for treating asthma; however, not all asthmatics have the same response to these medications, some of which are adverse responses that are potentially life threatening. Because interindividual responses to asthma medications can vary considerably, the potential for genetic contributions to variable drug responses is significant. This chapter reviews the most common biological pathways targeted by asthma therapy and briefly discusses the genetic contribution to varied responses to asthma therapy for four common types of asthma medications: beta-agonists, anticholinergics, leukotriene modifiers, and corticosteroids.

Three generations of ongoing controversies concerning the use of short acting beta-agonist therapy in asthma: a review

An increase in asthma mortality in 1960s noted by British authors stirred a debate about the use of beta-adrenergic therapy that has persisted in the medical literature. The cause appears to be isoproterenol and fenoterol overuse. A second debate evolved around the possible deleterious, pro-inflammatory effects, of the albuterol distomer. Most clinical studies showed improved bronchodilatation, but limited benefits from using levalbuterol. Recently, genotyping has uncovered a single nucleotide polymorphism at codon 16 that appears to affect the long term response to both regular and as needed use of albuterol, calling for a new genotype based therapeutic approach in asthma.

Pharmacogenetics of the response to beta 2 agonist drugs: a systematic overview of the field

The response to beta2-agonist treatment shows large repeatability within individuals and may thus be determined by genetic influences. Here we present a systematic overview of the available genetic association and linkage data for beta2-agonist treatment response. Systematic searches identified 66 eligible articles, as of March 2007, pertaining either to B2AR gene polymorphisms and short-acting or long-acting beta2-agonists or to another 29 different genes. We systematize these study results according to gene, agent and type of outcomes addressed. The systematic review highlights major challenges in the field, including extreme multiplicity of analyses; lack of consensus for main phenotypes of interest; typically small sample sizes; and poor replicability of the proposed genetic variants. Future studies will benefit from standardization of analyses and outcomes, hypothesis-free genome-wide association testing platforms, potentially additional fine mapping around new discovered variants, and large-scale collaborative studies with prospective plans for replication among several teams, with transparent public recording of all data.

Pharmacogenetics of the beta 2-adrenergic receptor gene

Asthma is a complex genetic disease with multiple genetic and environmental determinants contributing to the observed variability in response to common antiasthma therapies. One focus of asthma pharmacogenetic research has been the beta2-adrenergic receptor gene (ADR beta 2) and its effect on individual responses to beta agonist therapy. Knowledge about the effects of ADR beta 2 variation on therapeutic responses is evolving and should not alter current Asthma Guideline approaches, which consist of the use of short-acting beta agonists (SABAs) for as-needed symptom-based therapy and the use of a regular long-acting beta agonist (LABA) in combination with inhaled corticosteroid therapy for those asthmatics whose symptoms are not controlled by inhaled corticosteroid alone. These approaches are based upon studies showing a consistent pharmacogenetic response to regular use of SABAs and less consistent findings in studies evaluating LABAs. The emerging pharmacogenetic studies are provocative and should lead to functional studies. Meanwhile, the conflicting data concerning LABAs may be caused by such factors as small sample sizes of study populations and differences in experimental design.

Recent development in pharmacogenomics: from candidate genes to genome-wide association studies

Genetic diversity, most notably through single nucleotide polymorphisms and copy-number variation, together with specific environmental exposures, contributes to both disease susceptibility and drug response variability. It has proved difficult to isolate disease genes that confer susceptibility to complex disorders, and as a consequence, even fewer genetic variants that influence clinical drug responsiveness have been uncovered. As such, the candidate gene approach has largely failed to deliver and, although the family-based linkage approach has certain theoretical advantages in dealing with common/complex disorders, progress has been slower than was hoped. More recently, genome-wide association studies have gained increasing popularity, as they enable scientists to robustly associate specific variants with the predisposition for complex disease, such as age-related macular degeneration, Type 2 diabetes, inflammatory bowel disease, obesity, autism and leukemia. This relatively new methodology has stirred new hope for the mapping of genes that regulate drug response related to these conditions. Collectively, these studies support the notion that modern high-throughput single nucleotide polymorphism genotyping technologies, when applied to large and comprehensively phenotyped patient cohorts, will readily reveal the most clinically relevant disease-modifying and drug response genes. This review addresses both recent advances in the genotyping field and highlights from genome-wide association studies, which have conclusively uncovered variants that underlie disease susceptibility and/or variability in drug response in common disorders.

Nebulized racemic epinephrine used in the treatment of severe asthmatic exacerbation: a case report and literature review

Acute asthma is a common emergency department (ED) problem that is typically treated with bronchodilators and anti-inflammatories. Nebulized selective, short-acting beta-agonists, such as salbutamol, are the bronchodilators of choice in most Canadian EDs. Other important treatments in moderate-to-severe cases include systemic corticosteroids and in severe cases may include the addition of ipratropium bromide and magnesium sulfate. Despite aggressive management, some patients do not respond adequately to nebulized salbutamol. Treatment options in these patients are limited to interventions such as parenteral epinephrine, and non-invasive and mechanical ventilation (or both). Both parenteral epinephrine and mechanical ventilation have associated risks, so alternative treatments with a lower risk profile would be useful for the treatment of life-threatening asthma. The following case report describes a patient in whom nebulized racemic epinephrine was used successfully to treat severe acute asthma following failure of standard first-line therapies.

Pharmacogenomics of beta2-agonist: key focus on signaling pathways

Asthma is one of the most common respiratory diseases, where inhalation and exhalation are obstructed due to narrowing of the airways by broncho-constriction or by inflammation. Among all the available anti-asthma therapies, beta2-agonists are the most effective bronchodilators available, and give rapid relief of asthma symptoms. Evidence suggests that the degree of beta2-agonist response varies greatly between patients and genetic factors have a major role in it. Despite several studies on the beta2-agonist pharmacogenetics, significant gaps in knowledge still remain and need to be resolved before the pharmacotyping of beta2-agonist responsiveness comes to clinical practice. As we know, beta2-agonists show their influence by targeting beta2-adrenergic receptors, leading to the activation of beta2-adrenergic receptors and its downstream cascade. Signaling through beta2-adrenergic receptors mediates numerous airway functions by regulating broncho-constriction and dilation pathways. Therefore, it is an important prerequisite to understand these pathways, which will assist in defining the variability in therapeutic responses for beta2-agonists. Owing to the complexity of the action of a beta2-agonist and its therapeutic response, a broader genomics approach will help in optimizing therapy for the individual patient. This might be achieved by considering and focusing on receptor/s at which the drug binds directly, signal transduction cascades or downstream proteins and proteins involved in the relaxation and constriction of the airway smooth muscle. Considering that a drug response may involve a large number of proteins, it seems unlikely that a single polymorphism or haplotype in a single gene would explain a high degree of drug response variability in a consistent fashion. Thus, it shows that a polygenic approach will be more appropriate. In order to follow this, the mode of action of the beta2-agonist and its downstream signaling cascade should essentially be assessed to resolve the beta2-agonist enigma.

Determinants of the bronchodilation response to salbutamol on histamine-induced bronchoconstriction

Assessment of the bronchodilation response to short-acting beta2-adrenoreceptor agonists on pharmacologically induced bronchoconstriction has often been used to investigate airway smooth muscle beta2-adrenoreceptor function. However, little is known about factors affecting this response. In the present study, the bronchodilation response to 0.2 mg of salbutamol on histamine-induced bronchoconstriction was assessed in 101 steroid-naïve asthmatic subjects. The associations of the response with a wide range of challenge procedure-related variables, clinical asthma severity indicators, and blood markers of airway inflammation were investigated. The response was re-assessed after 6 and 12 weeks' therapy with inhaled budesonide. Baseline FEV1, final histamine concentration, and the maximal fall in FEV1 explained 35-59% of the total variation in the response to salbutamol, depending on the index chosen to express the response. Serum concentration of myeloperoxidase, an index of neutrophilic inflammation, was associated with a poor response. The preceding week daily PEF variation, rescue bronchodilator use, severity of asthmatic symptoms, blood eosinophil count, and serum eosinophilic cationic protein and eosinophilic protein X concentrations were not associated with the response. The salbutamol response seemed to diminish during budesonide treatment but when adjusted by the challenge procedure-related variables the treatment effect vanished. In conclusion, the bronchodilation response to salbutamol on histamine-induced bronchoconstriction is largely determined by challenge procedure-related variables. It seems to be unrelated to the clinical severity of asthma and is not affected by treatment with inhaled corticosteroids. Neutrophilic airway inflammation may be associated with a poor response.