Beta 2 adrenoceptor polymorphisms: are they clinically important?

Association between the Ile164 β2 Adrenergic Receptor Polymorphism and Fatigue in Patients with Rheumatoid Arthritis

INTRODUCTION

In the present work, the frequency of inherited polymorphisms of the beta 2 adrenergic receptor (β2AR) gene and their association with fatigue in patients with rheumatoid arthritis (RA) was examined.

METHODS

An allele-specific polymerase chain reaction was used to determine the common variants of the β2AR at position 16, 27, and 164 in 92 German RA outpatients. Health Assessment Questionnaire (HAQ-DI), Beck Depression Inventory (BDI), Perceived Stress Questionnaire (PSQ-30), Multidimensional Fatigue Inventory (MFI-20) were utilized.

RESULTS

34.7% of German RA patients were diagnosed with associated fatigue. Fatigued patients were more likely to carry the Ile allele at position 164 (OR 7.33, 95% CI 1.09-59.8, p = 0.049). Comparing these risk factors' contribution to different fatigue dimensions revealed that Ile164 carriers only had significantly higher MFI-20 mean values for general fatigue (p = 0.014) while the clinical difference among other MFI subscales was the largest for mental fatigue (carrier: 8.23, SD: 4.22, noncarrier: 5.67, SD: 1.56, p = 0.089, Cohen's d = 0.629). Disease activity, perceived stress, and depression were also associated with fatigue with higher mean values for DAS28CRP (p = 0.038), PSQ (p < 0.001), and BDI-II (p < 0.001) in fatigued patients. Physical fatigue was correlated with disease activity (p = 0.009) and depression (p = 0.001) while mental fatigue showed associations with depression (p = 0.001) and perceived stress (p = 0.028).

CONCLUSION

The discovery study indicates that the Ile164 polymorphism might in contrast to other β2AR polymorphisms affect fatigue levels in RA patients. This association was observed especially with mental fatigue. Further replication studies are warranted to determine further role of β2AR polymorphisms in RA patients.

The Relationship Between Glutathione S-Transferase-P1 and Beta-2 Adrenoreceptor Genotypes with Asthmatic Patients in the Turkish Population

BACKGROUND

Individual differences in the activity of enzymes that metabolize xenobiotics can impact health and disease. Beta-2 adrenoreceptor (ADRB2) is a functional G-coupled protein expressed in the vascular endothelium of lungs, alveolar walls, and the ganglions of cholinergic nerves which induces bronchodilation in response to catecholamines. Glutathione S-Transferase-P1 (GSTP1) is a candidate pi class GST gene, which controls pi class glutathione S-transferase activity.

AIMS

In this study we determined the relationship between the ADRB2 Arg16Gly polymorphism and GSTP1 polymorphisms, involved in bronchodilator response and oxidative stress, respectively, with susceptibility to asthma.

METHODS

In this study, 129 asthmatic patients and 127 healthy control cases were recruited to determine ADRB2 and GSTP1 genotypes by allele-specific polymerase chain reaction and restriction fragment length polymorphism assays, respectively.

RESULTS

The ADRB2 genotype frequencies of the patients and control cases were found to be 10.9% (Arg16Arg), 48.8% (Arg16Gly), and 40.3% (Gly16Gly) and 24.4% (Arg16Arg), 36.2% (Arg16Gly), and 39.4% (Gly16Gly), respectively. GSTP1 genotype frequencies of patients and control cases were found to be 55% (Ile105Ile), 43.4% (Ile105Val), and 1.6% (Val105Val) and 75.6% (Ile105Ile), 22% (Ile105Val), and 2.4% (Val105Val), respectively. In the case of the GSTP1 gene, we found statistically significant differences in the genotype frequency of Ile105Val and the allele frequency of Val105 in the asthmatic group compared with the controls. Moreover, we observed a relationship between allele frequencies and clinical phenotypes including atopia nocturnal dyspnea, and steroid dependency in the asthmatic patients.

CONCLUSION

Our results suggest that the GSTP1 Ile105Val polymorphism may be linked to the severeness of airway dysfunction.

beta2 adrenoceptor (ADRB2) pharmacogenetics and cardiovascular phenotypes during laryngoscopy and tracheal intubation

Pharmacogenetics is the study of genetic variations that cause a variable drug response characterized by alteration in drug metabolism or in pharmacodynamics. The polymorphisms in genes encoding receptors relevant to treatment cause variation in sensitivity to many drugs. beta2 Adrenoceptor genetic variation contributes to regulation of blood pressure and hemodynamic changes by mediating peripheral vasodilatation. Laryngoscopy and tracheal intubation associated with hemodynamic changes. Although there are four nonsynomic single-nucleotide polymorphisms (SNPs) of beta2 adrenoceptor gene, codon 16 (Arg16Gly) and codon 27 (Gln27Glu) SNPs are both common and functionally important. In this paper, the authors investigated the beta2 adrenoceptor Gly16 and Glu27 SNPs in response to drugs relevant to anesthesia and how these SNPs impacted upon the cardiovascular phenotypes. The authors measured arterial systolic and diastolic blood pressure, heart rate, and rate-pressure product before induction of anesthesia and 1 min following laryngoscopy and tracheal intubation. Genomic DNA was amplified and genotyped using allele-specific polymerase chain reaction (ASPCR) and restriction fragment length polymorphism (RFLP) assays, respectively. When the authors compared hemodynamic results according to genotypes, the patients with Gln homozygote allele at codon 27 exhibited significant increase of heart rate than patients with Glu allele after laryngoscope and tracheal intubation.

Variable therapeutic response in asthma: a genetic perspective

Asthma is a complex clinical syndrome with multiple genetic and environmental factors contributing to its phenotypic expression. This etiological heterogeneity adds to the complexity when addressing variation in the response to antiasthma treatment. There is regular progress in the field of asthma pharmacogenetics in determining the efficacy and potential for adverse effects of the asthma medication from a patient's genetic background. This reveals that a clinically relevant variability in response to the asthma medications may be due to genetic determinants, and refers to the polymorphisms in the genes encoding either the drug targets, or the molecular component of the downstream signal transduction pathways responsible for drug actions. The major classes of asthma therapy, β-agonists, leukotriene antagonists and inhaled corticosteroids, demonstrate wide interindividual variability. The statistical issues, such as population stratification, sample size and statistical power, are crucial factors for the identification of significant biological marker(s) for patient's response. The aim of this review is to discuss the scientific rationale and outline the genetic impact on the variability in response to different asthma medications. In conclusion, despite of new developments and recent studies in asthma pharmacogenetics, significant gaps in knowledge still remain, and several replicate studies are needed in different populations to derive firm conclusions that may help to bring pharmacotyping into clinical practice.

Cytokine release and adhesion molecule expression by stimulated human bronchial epithelial cells are downregulated by salmeterol

Summary beta2-adrenoreceptor agonists are able to modulate various aspects of airway cell functions involved in the inflammatory and repair processes characterizing a variety of respiratory disorders. Human bronchial epithelial cells (HBECs), which can act as immune effector cells and express beta2-adrenoreceptors, were used to test the effects of different concentrations (0.1-100.0 nM) of salmeterol (Salm) on adhesion molecule expression and chemokine/cytokine release. HBECs, freshly isolated from resected bronchi at the time of surgery in ex-smokers with lung cancer, constitutively expressed over 3 times more ICAM-1 than VCAM-1 (P<0.05) and secreted greater amounts of IL-8 than of GM-CSF or RANTES (P<0.001). Stimulation of HBECs with IL-4, TNF-alpha or IL-4 plus TNF-alpha-upregulated ICAM-1 expression (P<0.05) and increased GM-CSF and IL-8 secretion (P<0.05). Similarly, VCAM-1 expression was significantly increased by IL-4 plus TNF-alpha, while RANTES release was significantly enhanced by IL-4 or by IL-4 plus TNF-alpha (P<0.05), but not by TNF-alpha alone (P>0.05). Dose-response curves showed that Salm, at concentration >1.0 nM, was effective in inhibiting adhesion molecule expression and cytokine release by HBECs (P<0.05). At a Salm concentration of 10 nM the degree of inhibition observed was similar for ICAM-1 and VCAM-1 expression (37.2 +/- 9.3% and 32.9 +/- 9.6%, respectively; P>0.05), but higher for RANTES (88.4 +/- 4.4%), as compared to IL-8 (21.8 +/- 7.0%) or GM-CSF (30.1 +/- 6.6%; P<0.05, each comparison). Thus, adhesion molecules and cytokines may be expressed/released at very different levels by unstimulated or stimulated HBECs and those activities appear to be modulated by Salm.

Basal fat oxidation and after a peak oxygen consumption test in obese women with a beta2 adrenoceptor gene polymorphism

The Glu27Glu genotype in the beta2-adrenergic receptor (ADRB2) has been linked to a higher fat deposition and obesity in females. Also, in our population, it has been described that physically active women carrying the Glu allele had a higher BMI as compared to non-carriers performing the same level of activity. Since exercise may counterbalance a gene predisposition to obesity, we tested the hypothesis of a potential different metabolic response among ADRB2 Gln27Gln versus Glu27Glu obese women when submitted to a peak oxygen consumption test on a treadmill. In our study, 10 obese women with the Gln27Gln genotype were compared to 9 matched obese women bearing the Glu27Glu genotype. The ADRB2 polymorphism was identified by PCR-RFLP, fat oxidation was determined by indirect calorimetry and blood measurements were carried out following conventional procedures. The ADRB2 Glu27Glu subjects had lower plasma glycerol levels (P = 0.026), while plasma triglycerides (P <0.001) and the insulin:glucose ratio were higher (P = 0.046) as compared to the Gln27Gln group along the peak oxygen consumption trial intervention. There was a significantly lower fat oxidation (P = 0.024) in the Glu27Glu obese women during the recovery compared to Gln27Gln obese individuals. These data suggest that exercise would not benefit equally the two ADRB2 polymorphism homozygous groups, since both lipolysis and fat oxidation promoted by a peak oxygen consumption test appear to be blunted in the polymorphic Glu27Glu obese group.

Clinical importance of beta-adrenoceptor polymorphisms in cardiovascular disease

beta-Adrenoceptor antagonists play an important role in the treatment of cardiovascular disease and have been used for three decades in the treatment of hypertension and ischemic heart disease. More recently they have been demonstrated to improve survival in patients with mild to moderate congestive heart failure. The beneficial effects of beta-adrenoceptor antagonists stems from their ability to limit the deleterious effects of adrenergic stimulation, which in the cardiovascular system is primarily transmitted through two subclasses of receptor, beta(1) and beta(2). The advances of the Human Genome Project have led to an increased appreciation that variations in genetic background may underlie a substantial portion of the clinical heterogeneity apparent in cardiovascular disease. This review examines the molecular, functional, and clinical significance of the most common polymorphisms of the beta(1 and beta(2)-adrenoceptors. Initial research in adrenoceptor variation focused on the beta(2)-adrenoceptor. Three common polymorphisms appear to influence receptor function: Arg16-->Gly, Glu(27)-->Gln, and Thr(164)-->Ile. In in vitro studies of agonist stimulation, Gly(16) receptors demonstrate enhanced downregulation, while Glu(27) variants are resistant to downregulation. There is much controversy and conflict among various clinical studies regarding the effect of these variants on vasoreactivity and hypertensive risk. The Ile(164) variant demonstrates decreased responsiveness to agonist activity both in vitro and in animal models. In studies of patients with congestive heart failure, this variant has been associated with poor functional capacity and decreased survival. More recent investigations have focused on the two common polymorphisms of the beta(1)-adrenoceptor: Ser(49)-->Gly, and Arg(389)-->Gly. In vitro studies of Arg(389) receptors demonstrate a gain of function, as agonist stimulation results in significantly higher intracellular levels of cyclic adenosine monophosphate when compared with the Gly(389) variant. Consistent with the in vitro data, clinical studies demonstrate increased responsiveness to beta-agonist stimulation, and an increased risk of hypertension among Arg(389) homozygotes. Further investigation of the clinical implications of these common variants of beta(1)- and beta2)-adrenoceptors are needed. Importantly, the pharmacogenetic impact of these variants on the effectiveness of beta-adrenergic blockade remains unknown.

Gln27Glu polymorphism in the beta2 adrenergic receptor gene and lipid metabolism during exercise in obese women

BACKGROUND

The Glu27Glu genotype in the beta-2-adrenergic receptor (ADRB2) is associated with fat mass, body mass index and obesity in females. In our population, we previously found an association of higher body mass index (BMI) among women who reported more physical activity and carried the Glu27 allele as compared to non carriers with the same level of activity.

OBJECTIVE

To examine the lipid metabolism differences, both at rest and during submaximal exercise in ADRB2 Glu27Glu vs Gln27Gln obese women.

SUBJECTS

Eight obese women with the Glu27Glu genotype (age, 43+/-5 y; body mass index (BMI), 31.7+/-0.9 kg/m(2); percentage fat mass, 42.0+/-1.3; WHR, 0.83+/-0.02; and VO(2max), 21.6+/-0.9 ml/kg/min) were compared with seven obese women with the Gln27Gln genotype (age, 43+/-5 y; BMI, 33.9+/-1.3 kg/m(2); percentage fat mass, 41.6+/-1.2; WHR, 0.83+/-0.02; and VO(2max), 20.6+/-0.8 ml/kg/min).

MEASUREMENTS

The ADRB2 polymorphism was identified by PCR-RFLP. Respiratory quotient was determined by indirect calorimetry at baseline, during 1 h of walking on a treadmill and 1 h after the exercise. Plasma triglycerides, glycerol, FFA, hydroxybutyrate, glucose and lactate were assayed by spectrophotometric methods. Insulin, leptin and progesterone were measured by radioimmunoassay. Adrenaline and noradrenaline were quantified by high performance liquid chromatography.

RESULTS

The ADRB2 Glu27Glu subjects had lower plasma glycerol (P=0.047) and lower hydroxybutyrate (P=0.001) throughout the study than the Gln27Gln group. Plasma triglycerides (P=0.001), lactate (P<0.05) and serum insulin (P<0.05) remained higher in the Glu27Glu group vs the Gln27Gln group. The respiratory quotient (RQ) was higher in the Glu27Glu obese women along the study (P=0.046), and fat oxidation was significantly lower in this group during the recovery (P=0.048). The other variables did not differ statistically between groups.

CONCLUSION

These data suggest that both lipolysis and fat oxidation promoted by an acute submaximal exercise intervention could be blunted in the polymorphic ADRB2 Glu27Glu group of our female obese population.

Pharmacogenomics: the future of drug therapy

Pharmacogenomics aims to optimize patient management by customizing and synthesizing drugs based on genetic variations in drug response. Polymorphisms affecting metabolism, receptors, and absorption can influence drug sensitivity, toxicity, and dosing. The Human Genome Project, DNA chips, and bioinformatics advance the practice of this field by, respectively, identifying polymorphisms related to drug response, determining an individual's profile of polymorphisms, and integrating data to facilitate clinical decision making. Potential benefits of pharmacogenomics include increasing efficacy and preventing adverse drug reactions, thus improving patient care and decreasing costs. These factors imply that a thorough understanding of the principles and applications of pharmacogenomics will be an indispensable part of the future of drug therapy in clinical medicine.

The pathophysiology of asthma

Asthma is a chronic disorder of the airways that is characterized by reversible airflow obstruction and airway inflammation, persistent airway hyperreactivity, and airway remodeling. The etiology of asthma is complex and multifactorial. Recent advances have demonstrated the importance of genetics in the development of asthma, particularly atopic asthma. Environmental stimuli, particularly early childhood infections, have also been associated with the development of asthma. Most current data seem to suggest that these factors drive the development of a Th-2 lymphocyte-predominant immune response, which has been associated with atopy and IgE-mediated inflammation. The concept of reversible airflow obstruction has also recently been challenged. It is now clear that chronic airway changes occur, which may contribute to progressive airflow obstruction. We discuss the important influence of genetic and environmental factors on the emergence of the asthmatic phenotype. The significance of Th-1 and Th-2 lymphocyte-mediated immunity are discussed, and the inflammatory processes leading to chronic airway inflammation are detailed.

The impact of acute dynamic exercise on intraocular pressure: role of the beta 2-adrenergic receptor polymorphism

Effects of mutations in the beta 2-adrenergic receptor (beta 2AR) gene on intraocular pressure (IOP), in response to acute dynamic exercise, were investigated in 19 healthy males (age 22.6 +/- 2.8 years). Intraocular pressures were measured pre- and post-exercise. Weight, height, body mass index, and maximal oxygen (VO2max) uptake were recorded and subjects were genotyped for Arg16Gly, Gln27Glu and Thr164Ile mutations of the beta 2AR gene. Post-exercise, reductions in mean IOP values were found in 16 subjects with the Gly16Gly and Arg16Gly genotypes, but these values remained low in the eight patients with the Gly16Gly genotype 3 h post-exercise, whereas they returned to baseline within 1 h in the eight subjects with the Arg16Gly genotype. beta 2AR stimulation during exercise could be an important regulator of IOP response and determining beta 2AR polymorphisms may improve understanding of pathogenesis and treatment selection in ophthalmic diseases, e.g. glaucoma.

Polymorphism of the beta(2)-adrenoceptor in COPD in Chinese subjects

STUDY OBJECTIVES

To assess the frequencies of three polymorphisms at amino acid positions 16, 27, and 164 of the beta(2)-adrenoceptor (beta(2)-AR) gene and their effects on COPD patients.

DESIGN

Prospective, case-control study

PATIENTS

Sixty-five patients with COPD and 41 healthy subjects were included.

MEASUREMENTS

Polymorphisms of the beta(2)-AR coding block were delineated using an allele-specific polymerase chain reaction (PCR) approach. The allele-specific PCR technique was verified by direct dideoxy sequencing of PCR products. Pulmonary function tests were performed in all patients.

RESULTS

The Arg16 beta(2)-AR polymorphism was less prevalent in COPD patients than in healthy populations (p = 0.01). A significant correlation (p < 0.018) between the Gln27 beta(2)-AR polymorphism and FEV(1) percent predicted value was found. Patients with the Gln27 polymorphism had a higher percentage of low FEV(1) percent predicted than did patients with the GlnGlu and GluGlu variants.

CONCLUSIONS

The polymorphism of Gly16 may increase the patient's susceptibility to the development of COPD. The Gln27 beta(2)-AR polymorphism may be associated with the severity of COPD in a Chinese population.

Risk of myocardial ischaemia and beta-adrenoceptor agonists

Modern therapy for both cardiovascular disease and obstructive lung disease involves diametrically opposed manipulations of the beta-adrenoceptor. Beta-agonists reduce airflow limitation and improve symptoms among patients with obstructive lung disease while beta-blockers reduce symptoms, recurrent myocardial ischaemia and all-cause mortality among patients with ischaemic heart disease. There is biological plausibility for beta-agonists leading to adverse cardiovascular outcomes, and observational trials have raised concern about the safety of beta-agonists among patients with cardiovascular disease. Although there are many potential causal and noncausal explanations for these observational findings, the implications from these studies are the same. Physicians should be careful when prescribing beta-agonists for patients at risk for ischaemic heart disease. Furthermore, careful consideration should be given to distinguish symptoms caused by cardiovascular versus respiratory aetiologies.

Mutation screening of the muscarinic M(2) and M(3) receptor genes in normal and asthmatic subjects

1. Muscarinic receptors are important in the development of airway hyperresponsiveness, and dysfunction of these receptors has been suggested to be present in asthma. 2. The human muscarinic M(2) and M(3) receptor genes were screened for polymorphic variation using single-stranded conformation polymorphism (SSCP) analysis, complemented by direct fluorescent sequencing. Forty-six random DNA samples and 46 respiratory physician diagnosed asthmatic samples were used as a template for analysis. 3. Within the muscarinic M(2) receptor gene, we identified two degenerate single base substitutions (1197T-->C, Thr-->Thr and 976A-->C, Arg-->Arg) in one random and one asthmatic sample respectively. Analysis of the 3' UTR region revealed an additional 'A' at bp 1793 (c.f. ATG). This was present in all of 49 samples analysed by sequencing or BsmI digest, suggesting that the published sequence (GenBank Accession NO: M16404) is incorrect. A common 3' UTR polymorphism (T-->A) was found at bp 1696 (c.f. ATG) (allelic frequency=65%, n=60), but this does not alter transcription factor recognition sites. 4. We were unable to identify any polymorphic variation within the muscarinic M(3) coding region or the flanking regions investigated, using the methods described. 5. The coding regions for the human muscarinic M(2) and M(3) receptor genes are both highly conserved. These data suggest that polymorphic variation within these coding sequences is unlikely to account for inter-individual variability in response to methacholine or anticholinergic therapy. The potential functional significance of the muscarinic M(2) receptor 3' UTR polymorphism (bp 1696) remains to be determined.

Beta2-adrenoceptors: mechanisms of action of beta2-agonists

The human beta2-adrenoceptor is a member of the 7 transmembrane family of receptors. It is encoded by a gene on chromosome 5 and is widely distributed in the respiratory tract. Following beta2-adrenoceptor activation, intracellular signalling is mainly produced by inducing cyclic AMP. This produces airway relaxation through phosphorylation of muscle regulatory proteins and modification of cellular Ca2+concentrations. Beta2-agonists have been characterised into those which directly activate the receptor (salbutamol/terbutaline), those which are taken up into a membrane depot (formoterol) and those which interact with a receptor-specific, auxiliary binding site (salmeterol). These differences in mechanism of action are reflected in the kinetics of airway smooth muscle relaxation and bronchodilation in asthmatic patients. Beta-adrenoceptor desensitisation is associated with beta2-agonist activation and differs depending on the cell type. It is reflected in the different profiles of clinical tolerance to chronic beta2-agonist therapy. A number of polymorphisms of the beta2-receptor have been described which appear to alter the behaviour of the receptor, including the degree of downregulation and response to beta2-agonists.

Pharmacogenomics: a clinician's primer on emerging technologies for improved patient care

Pharmacogenomics is a term recently coined to embody the concept of individualized and rational drug selection based on the genotype of a particular patient. Customization of drug therapy offers the potential for optimal safety and efficacy in an individual patient. Such a process contrasts current prescribing practices, which use medications shown to be safe and effective in patient populations or based on anecdotal experiences. Within patient populations, medications vary in their efficacy among individual patients. More importantly, a medication that is safe and effective in one patient may be ineffective or even harmful in another. Underlying many of these phenotypic differences are genotypic variants (polymorphisms) of key enzymes and proteins that affect the safety and efficacy of a drug in an individual patient. An understanding of these polymorphisms has the potential to enhance patient care by allowing physicians to customize the selection of medication to meet individual patient needs. Pharmacogenomics may also lead to improved compliance and shorter time to optimal disease management, thereby reducing morbidity and mortality. Significant cost savings could result from reductions in polypharmacy as well as from fewer physician encounters and hospitalizations for exacerbations of underlying illness and because of adverse drug reactions.

Effect of M2 and M3 muscarinic receptors on airway responsiveness to carbachol in bronchial-hypersensitive (BHS) and bronchial-hyposensitive (BHR) guinea pigs

The expression balance of M2 and M3 muscarinic receptor subtypes on the pathogenesis of airway hyperresponsiveness was investigated by using two congenitally related strains of guinea pigs, bronchial-hypersensitive (BHS) and bronchial-hyposensitive (BHR). CCh-induced airway responses in vivo and in vitro were investigated by comparing the effects of muscarinic receptor subtype antagonists, and the relative amounts of M2 and M3 muscarinic receptor mRNA in tracheal smooth muscle and lung tissue were investigated. After treatment with muscarinic receptor subtype antagonists, the ventilatory mechanics (VT, Raw, and Cdyn) of response to CCh aerosol inhalation were measured by the bodyplethysmograph method. The effects of these antagonists on CCh-induced tracheal smooth muscle contraction were also investigated. The effects of M2 muscarinic receptor blockade were less but the effects of M3 muscarinic receptors blockade on the airway contractile responses were greater in BHS than in BHR. In M3 muscarinic receptor blockades, CCh-induced tracheal contractions in BHS were significantly greater than those in BHR. In tracheal smooth muscle from BHS, the relative amount of M2 muscarinic receptors mRNA was less but that of M3 muscarinic receptor mRNA was more than those in BHR. These results suggest that the high ACh level as a consequence of dysfunction of M2 muscarinic autoreceptors and the excessive effect of M3 muscarinic receptors on the airway smooth muscle may play an important role in the pathogenesis of airway hyperresponsiveness.

Asthma exacerbations during long term beta agonist use: influence of beta(2) adrenoceptor polymorphism

BACKGROUND

Polymorphisms of the beta(2) adrenoceptor influence receptor function in vitro and asthma phenotypes in vivo. However, their importance in determining responses to inhaled beta agonist treatment has not been clearly defined.

METHODS

In a retrospective analysis of previously published data we have examined relationships between polymorphisms at codons 16 and 27 of the beta(2) adrenoceptor and clinical outcomes in a randomised, placebo controlled, crossover trial of regularly scheduled salbutamol and salmeterol in 115 patients with mild to moderate asthma. Genotyping was obtained for positions 16 and 27 in 108 and 107 patients, respectively. For position 16, 17 patients (16%) were homozygous Arg-Arg, 40 (37%) were heterozygous Arg-Gly, and 51 (47%) were homozygous Gly-Gly.

RESULTS

Within the homozygous Arg-16 group major exacerbations were more frequent during salbutamol treatment than with placebo (1.91 (95% CI 1.07 to 3.12) per year versus 0.81 (95% CI 0.28 to 1.66) per year; p = 0.005). No significant treatment related differences occurred for heterozygous Arg-Gly patients (salbutamol 0.11 (95% CI 0.01 to 0.40), placebo 0.54 (95% CI 0.26 to 1.00) exacerbations per year) or homozygous Gly-16 patients (salbutamol 0.38 (95% CI 0.17 to 0.73), placebo 0.30 (95% CI 0.12 to 0.61) exacerbations per year). No adverse changes occurred for any position 16 subgroup with salmeterol. There was no significant relationship between position 27 genotypes and treatment related outcomes.

CONCLUSION

Homozygous Arg-16 patients are susceptible to clinically important increases in asthma exacerbations during chronic dosing with the short acting beta(2) agonist salbutamol.

The Q/E27 polymorphism in the beta2-adrenoceptor gene is associated with increased body weight and dyslipoproteinaemia involving triglyceride-rich lipoproteins

OBJECTIVES

To investigate whether a substitution of glutamine by glutamic acid at amino acid position 27 (Q/E27) and an arginine to glycine transition at amino acid 16 (R/G16) in the beta2-adrenoceptor gene are associated with lipid and lipoprotein disturbances and/or increased body weight in men.

DESIGN

Population-based study.

SETTING

Department of medicine at a university hospital.

SUBJECTS

A total of 180 healthy men, aged 30-45 years, were recruited at random from a register containing all permanent residents in Stockholm County (response rate of 70%).

MAIN OUTCOME MEASURES

Frequency of beta2-adrenoceptor genotypes and alleles in relation to plasma lipid and lipoprotein levels and body mass index.

RESULTS

Individuals carrying the E27 allele and/or the G16 allele had significantly higher body mass index (BMI). Furthermore, carriers of the E27 allele had significantly higher plasma concentrations of cholesterol, triglycerides, VLDL cholesterol and VLDL triglycerides than did subjects homozygous for the Q allele.

CONCLUSION

The E27 allele of the beta2-adrenoceptor gene is associated with slightly to moderately elevated BMI and dyslipoproteinaemia involving triglyceride-rich lipoproteins in healthy younger and middle-aged men.

Inhibitory activity of fenoterol on Dermatophagoides-, Parietaria-, tetanus-toxoid-, and Candida albicans-stimulated blood mononuclear cells: differences in beta2-adrenoreceptor stimulation but not in cell apoptosis

beta2-adrenoreceptor agonists have the ability to downregulate in vitro the proliferative response of peripheral blood mononuclear cells (BMCs). This activity could be related to a variety of beta2-adrenoreceptor-mediated functions, including induction of cell apoptosis in activated T-cells. To test this hypothesis, BMCs from atopic subjects, sensitized to house dust mites (Dermatophagoides [Der p]) and/or to Parietaria were incubated with fenoterol (10(-8)-10(-5) M) in the presence of (a) purified allergen extracts (Der p [5 microg/mL] or Parietaria [5 microg/mL]) or (b) antigens (tetanus toxoid [1 microg/mL] or Candida albicans [5 x 10(5) bodies/mL]). The BMC proliferation was assessed by [3H] thymidine incorporation and cell apoptosis was assessed by evaluating DNA fragmentation by a fluorescence technique, using propidium iodide. In cultures stimulated with Der p or with Parietaria, fenoterol induced a dose-dependent inhibition of BMC proliferation, significant also at the lowest concentration tested (10(-8) M) (p < 0.05, each comparison). In contrast, the inhibitory activity of the drug on tetanus-toxoid-stimulated BMCs was significant only at the highest dose tested (10(-5)M) (p < 0.05), whereas no effect was seen when BMCs were stimulated with C. albicans extract (p > 0.05). The different inhibitory efficacy of fenoterol appeared to be related to the degree of activation of beta2-adrenoreceptors on the different BMC populations that responded to the different stimuli. Indeed, in the presence of fenoterol (10(-6) and 10(-5)M), a significant increase in cyclic adenosine monophosphate (cAMP) levels was seen in Der p- or Parietaria-stimulated cells (p < 0.05; each comparison), but not in cell cultures stimulated with tetanus toxoid or with C. albicans extracts (p > 0.05; each comparison). Finally, the percentage of cells with fragmented DNA was lower in cultures stimulated with Der p or Parietaria than in those stimulated with tetanus toxoid or C. albicans, and the presence of fenoterol did not modify cell apoptosis (p > 0.05; each comparison). Thus, the different inhibitory activity of fenoterol on BMCs activated by allergens (Der p or Parietaria) or by antigens (tetanus toxoid or C. albicans) seems to be related to differences in beta2-adrenoreceptor expression and/or function in the different antigen-specific T-cell subsets, but it is not influenced by changes in cell apoptosis.

Association analysis of beta2 adrenoceptor polymorphisms with hypertension in a Black African population

OBJECTIVE

To determine whether or not beta2 adrenoceptor polymorphism is a risk factor for the development of hypertension in a Black South African population.

BACKGROUND

Attenuated vasodilator responses to endogenous catecholamines may contribute to the aetiology of hypertension. Downregulation of beta2 adrenoreceptors (beta2AR) following stimulation with agonists is determined in part by variation at the beta2AR gene locus. The Glu27 beta2AR genotype results in attenuated downregulation compared with the wild-type Gln27 receptor, whereas Gly16 exhibits enhanced down-regulation compared to Arg16. Possible racial differences in the prevalence of the beta2AR polymorphisms may be an explanation for the blunted responses to isoprenaline and the increased prevalence of hypertension in Black African populations.

METHODS

One hundred and ninety-two unrelated hypertensives and 123 normotensives of Black South African origin were studied. Hypertensives were recruited from hospital hypertension clinics in the province of Gauteng and if on treatment, had a 2-4 week washout period before 24-h ambulatory blood pressure assessment Normotensive controls were recruited from the same community.

RESULTS

There was no significant association between either the Arg-Gly16 polymorphism or the Gln-Glu27 polymorphism and hypertension status. Furthermore, in the hypertensives, no significant association was seen between beta2AR genotype at either site and clinical blood pressure, 24-h blood pressure or left ventricular mass. A significant association was seen between Arg16 homozygotes and lower body mass index in hypertensives (P = 0.007) although this was not a primary end point. Interestingly, the Glu27 polymorphism was much rarer in this population (allelic frequency 17%) compared to a Caucasian population.

CONCLUSION

These data suggest that beta2AR polymorphism is not a risk factor for hypertension per se in this defined population. The possibility that the decreased prevalence of Glu27 in black South African populations explains blunted vasodilator responses to isoprenaline requires further study.

The alliance of genes and environment in asthma and allergy

The diseases of asthma, eczema and hay fever are typified by reactions to common allergens, which are mediated by immunoglobulin E. These allergic diseases are increasing in prevalence, and are now a major source of disability throughout the developed world. They are the result of complex interactions between largely unknown genetic and environmental mechanisms. The identification of the environmental factors offers the real possibility of prevention of disease, and unravelling the genetics of allergic illnesses is likely to change their classification and treatment. Early life seems particularly important, when the initiation of allergic disease may result from genetic and environmental modification of the immune interaction between mother and child.

Novel polymorphism of the 5-lipoxygenase activating protein (FLAP) promoter gene associated with asthma

The human 5-lipoxygenase activating protein (FLAP) gene is one of the key genes involved in the production of the cysteinyl-leukotrienes. We studied novel polymorphism of the FLAP promoter gene and attempted to clarify the relationship between this polymorphism and asthma. We sequenced the FLAP promoter region, containing the -170 to +46-bp sequence from the translational start codon, and found two homozygotes of novel alleles in the polyadenyl region which showed 21 A repeats and 18 A repeats, respectively. The frequency of the 21 A repeats was 52/71 (73.2%) in asthmatics and 39/71 (54.9%) in control subjects. The difference between these frequencies was statistically significant (P = 0.035). This is the first report of FLAP promoter gene polymorphism associated with asthma. Our data suggest that FLAP promoter gene polymorphism might play a crucial role in the pathogenesis of asthma.

In vivo effect of albuterol on methacholine-contracted bronchi in conjunction with salmeterol and formoterol

BACKGROUND

It has been shown in vitro that prior treatment with salmeterol and formoterol antagonizes the relaxant effect of albuterol in carbachol-contracted human bronchi.

OBJECTIVES

The primary aim of this study was to evaluate whether there is a potential in vivo interaction between long- and short-acting beta2-agonists in the presence of increased airway tone induced by methacholine. In addition, a post hoc analysis was made to evaluate the effects of beta2-adrenoceptor polymorphisms.

METHODS

Sixteen asthmatic subjects (mean age [+/-SD], 39 [13] years; FEV1, 81% [17%] of predicted value), all taking inhaled corticosteroids and having methacholine PD20 values of less than 500 micrograms, were randomized in double-blind, double-dummy, cross-over fashion to receive single doses of inhaled placebo, inhaled formoterol 12 micrograms, or inhaled salmeterol 50 micrograms followed 12 hours later by a single dose of inhaled albuterol 400 micrograms (low dose) or 1600 micrograms (high dose). Methacholine challenges were performed on each of 6 separate occasions 1 hour after albuterol.

RESULTS

There was a greater numerical difference in geometric mean PD20 values between low- and high-dose albuterol after placebo dosing (671 micrograms vs 1080 micrograms, a 1.61-fold difference; P <.05) compared with low- and high-dose albuterol after formoterol dosing (660 micrograms vs 799 micrograms, a 1. 21-fold difference; P =.4), or after salmeterol dosing (568 micrograms vs 847 micrograms, a 1.49-fold difference; P =.055). PD20 values with high-dose albuterol in combination with formoterol or salmeterol were numerically lower than those found with high-dose albuterol in combination with placebo, but they were not significantly different. There was a significant difference between PD20 values with low-dose albuterol after dosing with formoterol (PD20 = 660 micrograms, a 1. 6-fold difference; P <.05) or with salmeterol (PD20 = 568 micrograms, a 1.9-fold difference; P <.05) compared with PD20 with high-dose albuterol after placebo dosing (PD20 = 1080 micrograms). Post hoc polymorphism analysis for pooled pretreatment with formoterol and salmeterol (excluding placebo pretreatment) showed significantly (P <.05) lower PD20 values with homozygous glycine-16 compared with heterozygous glycine/arginine-16 and significantly (P <.05) lower PD20 values with homozygous glutamate-27 compared with either heterozygous glutamate/glutamine-27 or homozygous glutamine-27.

CONCLUSION

Compared with placebo, both salmeterol and formoterol caused a significant degree of antagonism of albuterol-induced bronchorelaxation in methacholine-contracted bronchi in vivo. This interaction could be caused by prolonged occupancy of airway beta2-adrenoceptors by long-acting beta2-agonists or by early tachyphylaxis 12 hours after a single-dose exposure. The degree of albuterol protection was also related to beta2-adrenoceptor polymorphism.

The beta-adrenoceptor

The human beta-adrenoceptor is a member of the seven-transmembrane family of receptors, encoded by a gene on chromosome 5. beta-Adrenoceptors have been classified into beta1, beta2, and beta3 subgroups, with beta2-receptors being widely distributed in the respiratory tract, particularly in airway smooth muscle. Intracellular signaling following beta2-adrenoceptor activation is largely affected through a trimeric Gs protein coupled to adenylate cyclase. Cyclic AMP (cAMP) induces airway relaxation through phosphorylation of muscle regulatory proteins and attenuation of cellular Ca2+ concentrations. Alternative cAMP-independent pathways involving activation of membrane maxi-K+ channels and coupling through Gi to the MAP kinase system have also been described. Site-directed mutagenesis has identified Asp 113 and Ser 204/207 within the third and fourth membrane domains as the active site of the beta2-receptor, critical for beta2-agonist binding and activity. beta2-Agonists have been characterized as those that directly activate the receptor (albuterol), those that are taken up into a membrane depot (formoterol), and those that interact with a receptor-specific auxiliary binding site (salmeterol). These differences in mechanism of action are reflected in the kinetics of airway smooth muscle relaxation and bronchodilation in patients with asthma. beta-Adrenoceptor desensitization associated with beta2-agonist activation is a consequence of phosphorylation by beta-ARK and uncoupling of the receptor from Gs following beta-arrestin binding, of internalization and recycling of the receptor through processes of sequestration and resensitization and downregulation, modulated by an effect on receptor gene expression. The degree of receptor desensitization appears to differ, depending on the cell or tissue type, and is reflected in the different profiles of clinical tolerance to chronic beta2-agonist therapy. A number of polymorphisms of the beta2-receptor have been described that appear to alter the behavior of the receptor following agonist exposure. These include Arg-Gly 16, Glu-Gln 27, and Thr-lle 164. The Gly 16 receptor downregulates to a greater extent and is associated with increased airway hyperreactivity, nocturnal symptoms, and more severe asthma. The Glu 27 form appears to protect against downregulation and is associated with less reactive airways. An individual can be homozygous or heterozygous for given polymorphisms, and large populations will have to be studied to determine their importance to the asthma phenotype.

Association between beta 2-adrenoceptor polymorphism and susceptibility to bronchodilator desensitisation in moderately severe stable asthmatics

BACKGROUND

In-vitro studies have suggested that polymorphisms of the beta 2-adrenoceptor may influence the desensitisation induced by beta 2-agonists. We investigated the influence of beta 2-AR polymorphism on the development of bronchodilator desensitisation in asthma patients.

METHODS

We carried out an analysis of 22 moderately severe stable asthmatics, mean age 38 years, FEV1 63% of predicted and FEF25-75 38% of predicted, who received a median inhaled corticosteroid dose of 1000 micrograms/day. Patients were randomly assigned inhaled placebo or inhaled formoterol 24 micrograms bid for 4 weeks each in a crossover study. Bronchodilator dose-response curves were made at the end of each treatment period by use of cumulative doses of formoterol (6-108 micrograms) with FEV1 and FEF25-75 measured 30 min after each dose, and up to 6 h after the last dose. We calculated the degree of bronchodilator desensitisation by comparing the dose-response (for maximum and 6 h) after placebo with that after formoterol, and expressed this degree as a percentage of placebo response. Patients were divided into groups according to genotype at codon 16: homozygous Arg 16 (n = 4), heterozygous Arg 16/Gly 16 (n = 8), and homozygous Gly 16 (n = 10). At codon 27: homozygous Gln 27 (n = 5), heterozygous Gln 27/Glu 27 (n = 11), and homozygous Glu 27 (n = 6).

FINDINGS

We found a significantly (p < 0.05) greater degree of bronchodilator desensitisation with homozygous Gly 16 than with homozygous Arg 16 for maximal FEV1 response: -8% (Arg 16) vs 46% (Gly 16); and for maximal FEF25-75 response: -32% (Arg 16) vs 74% (Gly 16; 95% CI 15-92% and 49-164%, respectively). Bronchodilator responses at 6 h were also significantly (p < 0.05) different for FEV1 and FEF25-75 when Arg 16 and Gly 16 were compared and values for heterozygous Arg 16/Gly 16 were intermediate. There was significantly greater desensitisation with Glu 27 than with Gln 27 for maximal FEF25-75 response: -7% (Gln 27) vs 68% (Glu 27), p = 0.05; and for 6 h FEF25-75 response: 43% (Gln 27) vs 93% (Glu 27), p < 0.05 (95% CI 2-147% and 5-94%, respectively). All patients who were homozygous Glu 27 were also homozygous Gly 16.

INTERPRETATION

We have found preliminary evidence that beta 2-adrenoceptor polymorphism is associated with altered beta 2-adrenoceptor expression in asthma patients. The homozygous Gly-16 form was significantly more prone to bronchodilator desensitisation than Arg 16, with the influence of Gly 16 dominating over any putative protective effects of Glu 27.

Airway subsensitivity with long-acting beta 2-agonists. Is there cause for concern?

Regular treatment with both long- and short-acting beta 2-agonists results in tolerance to their bronchoprotective effects, although the relevance of this phenomenon in terms of long term asthma control remains unclear. However, there appears to be no appreciable difference between the 2 long-active beta 2-agonists, salmeterol and formoterol, in their propensity to induce beta 2-adrenoceptor down-regulation and subsensitivity. The degree of subsensitivity appears to be somewhat greater with indirect stimuli such as exercise and allergen challenge, compared with direct stimuli such as histamine and methacholine. This loss of functional antagonism with long-acting beta 2-agonist therapy is partial and is not prevented by concomitant inhaled corticosteroid therapy. However, the protective effects of inhaled corticosteroids on their own appear to be additive to those of long-acting beta 2-agonists when both drugs are concomitantly administered in the long term. The subsensitivity to bronchoprotection may be of clinical relevance in terms of patients who are inadvertently exposed to indirect bronchoconstrictor stimuli such as allergens or exercise, suggesting that long-acting beta 2-agonists should not be taken on a regular basis for this particular indication. There is a greater tendency for bronchodilator subsensitivity to develop with longer-acting, than with shorter-acting beta 2-agonists, and this may reflect the longer duration of beta 2-adrenoceptor occupancy and consequent downregulation. As with the bronchoprotective effects of long-acting beta 2-agonists, the development of bronchodilator subsensitivity is only partial and occurs regardless of whether patients are taking concomitant inhaled corticosteroid therapy. The long-term bronchodilator action of the long-acting beta 2-agonist itself is maintained within the twice daily administration interval. However, subsensitivity occurs in relation to a blunted response to repeated doses of short-acting beta 2-agonists, as in the setting of an acute asthma attack. There is considerable inter-individual variability in the propensity for downregulation and subsensitivity, which is determined by genetic polymorphism of the beta 2-adrenoceptor. Current international asthma management guidelines suggest that long-acting beta 2-agonists should be used on a regular basis in patients who ware inadequately controlled on inhaled corticosteroid therapy, so the addition of long-acting beta 2-agonist therapy is an alternative to using higher doses of inhaled corticosteroids. There are, however, concerns that regular long-acting beta 2-agonists might result in masking of inadequately treated inflammation in patients receiving suboptimal inhaled corticosteroid therapy. Physicians should be aware of the airway subsensitivity that develops with long-acting beta 2-agonist therapy, and patients should be warned that they may have to use higher than conventional dosages of short-acting beta 2-agonists to relieve acute bronchoconstriction in order to overcome this effect. In patients receiving an optimised maintenance dose of inhaled corticosteroid, if long-acting beta 2-agonists are to be used on an as required basis, it would seem rational to use formoterol for this purpose, due to its faster onset of action than salmeterol.