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

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

RATIONALE

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Direct molecular haplotyping by melting curve analysis of hybridization probes: beta 2-adrenergic receptor haplotypes as an example

Direct determination of the association of multiple genetic polymorphisms, or haplotyping, in individual samples is challenging because of chromosome diploidy. Here, we describe the ability of hybridization probes, commonly used as genotyping tools, to establish single nucleotide polymorphism (SNP) haplotypes in a single step. Three haplotypes found in the beta 2-adrenergic receptor (beta2AR) gene and characterized by three different SNPs combinations are presented as examples. Each combination of SNPs has a unique stability, recorded by its melting temperature, even when intervening sequences from the template must loop out during probe hybridization. In the course of this study, two haplotypes in beta2AR not described previously were discovered. This approach provides a tool for molecular haplotyping that should prove useful in clinical molecular genetics diagnostics and pharmacogenetic research where methods for direct haplotyping are needed.

Asthma

There have been four types of drug treatment of asthma that have been used over the past 100 years. Belladonna alkaloids, derived from the thorn-apple plant were used in 1905, and chemically synthesized entities in this class are still in use today. Western medicine began to use adrenergic stimulants approximately 100 years ago, but they were likely used in Asian medicine long before that. Systemic treatment with corticosteroids was introduced into the treatment of asthma in the mid-20th century; inhaled corticosteroids have been in use for over 35 years. The last 40 years have also seen the development of the first targeted asthma treatments: cromones, antileukotrienes, and anti-IgE. As we learn more of the biology of asthma, we anticipate that more effective targeted asthma treatments will be developed.

The genetics of atopic dermatitis: recent findings and future options

Atopic dermatitis (AD) is a chronic pruritic skin disease affecting up to 15% of children in industrialized countries. AD belongs to the group of allergic disorders that include food allergy, allergic rhinitis, and asthma. A multifactorial background for AD has been suggested, with genetic as well as environmental factors influencing disease development. Genome-wide screens for AD have been completed in four different populations to date. Interestingly, the susceptibility regions identified for AD show little overlap with asthma susceptibility regions, suggesting that, at least in part, separate genes might be involved in the pathogenesis of the different atopic disorders. Instead, some of the identified regions overlap with susceptibility regions for psoriasis, another chronic skin disease. Thus, genes expressed in the skin might play an important role in AD pathogenesis, in addition to genes influencing atopic diatheses. Although no veritable "AD gene" has been identified by positional cloning to date, examples from other complex genetic disorders such as asthma show that this goal is likely to be reached in the near future. Candidate gene studies, on the other hand, have identified 19 genes that were shown to be associated with AD in at least one study. The results of genome-wide screens as well as candidate gene studies are evaluated here in detail.

Molecular properties and pharmacogenetics of a polymorphism of adenylyl cyclase type 9 in asthma: interaction between beta-agonist and corticosteroid pathways

In asthma, the response to beta-agonists acting at beta2-adrenergic receptors (beta2AR) displays extensive interindividual variation. One effector for airway beta2AR, adenylyl cyclase type 9 (AC9), was considered a candidate locus for predicting beta-agonist efficacy in the absence and presence of corticosteroid treatment. One non-synonymous AC9 polymorphism has been identified, which results in substitution of Met for Ile at amino acid 772. Under standard culture conditions in stably transfected cells, we found decreased catalytic activity of Met772. However, cells cultured in the presence of glucocorticoid expressing Met772 had a significantly increased albuterol-stimulated adenylyl cyclase response (approximately 80%) when compared with those expressing Ile772 (approximately 20%, P=0.02). An equivalent increase in beta2AR expression was observed in both lines due to glucocorticoid, but AC9 expression was unaffected. The hypothesis that Met772-AC9 is associated with an improved albuterol bronchodilator response in asthmatics was investigated in 436 asthmatic children who were followed for 4 years and randomized to receive placebo or the inhaled corticosteroid budesonide. Met772 carriers on budesonide showed a significant improvement in forced expiratory volume in 1 s (P=0.005). Moreover, a highly significant interaction (P=0.002) was found for budesonide treatment and the AC9 polymorphism. These in vitro and human association studies are consistent with this AC9 polymorphism altering albuterol responsiveness in the context of concomitant inhaled corticosteroid administration, which is a common asthma regimen. The Met772-AC9 polymorphism represents one of most likely several multi-gene polymorphisms along the receptor-relaxation axis, which together may provide for a composite pharmacogenetic index for asthma therapy.

Single-dose agents in the prevention of exercise-induced asthma: a descriptive review

Exercise-induced asthma (EIA) refers to the transient narrowing of the airways that occurs after vigorous exercise in 50-60% of patients with asthma. The need to condition the air inspired during exercise causes water to be lost from the airway surface, and this is thought to cause the release of inflammatory mediators (histamine, leukotrienes, and prostaglandins) from mast cells. EIA is associated with airway inflammation and its severity is markedly reduced following treatment with inhaled corticosteroids. Drugs that inhibit the release of mediators and drugs that inhibit their contractile effects are the most successful in inhibiting EIA. Single doses of short-acting beta(2)-adrenoceptor agonists, given as aerosols immediately before exercise, are very effective in the majority of patients with asthma, providing about 80% protection for up to 2 hours. Long-acting beta(2)-adrenoceptor agonists (LABAs) given in single doses can be effective for up to 12 hours when used intermittently, but tolerance to the protective effect occurs if they are taken daily. Drugs such as cromolyn sodium (sodium cromoglicate) and nedocromil given as aerosols are less effective than beta(2)-adrenoceptor agonists (beta(2)-agonists), providing 50-60% protection for only 1-2 hours, but they have some advantages. They do not induce tolerance, the aerosol dosage can be easily titrated for the individual, and the protective effect is immediate. Because they cause no significant adverse effects, multiple doses can be used in a day. Leukotriene receptor antagonists, such as montelukast and zafirlukast, are also used for the prevention of EIA and provide 50-60% protection for up to 24 hours when given as tablets. Tolerance to the protective effect does not develop with regular use. If breakthrough EIA occurs, a beta(2)-agonist can be used effectively for rescue medication. For those patients with more persistent symptoms, the use of a LABA in combination with an inhaled corticosteroid has raised a number of issues with respect to the choice of prophylactic treatment for EIA. The most important issue is the development of tolerance to the protective effect of a LABA such that extra treatment may be needed in the middle of a treatment period. Recommending extra doses of a beta(2)-agonist to control EIA is not advisable on the basis that multiple doses can enhance the severity of EIA, delay spontaneous recovery from bronchoconstriction, and enhance responses to other contractile stimuli. It is time to take into account the advantages and disadvantages of the different drugs available to prevent EIA and to recognize that there are some myths related to their use in EIA.

What is new with the beta2-agonists: issues in the management of asthma

OBJECTIVE

To review the more recent literature addressing the issue of whether beta2-agonists can worsen asthma and/or increase the risk of severe exacerbations and death from asthma.

DATA SOURCES

PubMed was searched (2001-December 2004), along with the Food and Drug Administration and Cochrane Library Web sites. In addition, the bibliographies of recent reviews of the subject were assessed.

STUDY SELECTION AND DATA EXTRACTION

Randomized clinical trials, retrospective and prospective cohort studies, and meta-analyses published in the past 3 years were reviewed. Studies assessing the potential for beta2-agonists to worsen outcomes in asthma as well as long-term studies assessing asthma outcomes that included an arm with regular administration of short- or long-acting inhaled beta2-agonists (LABAs) were selected. Worsening asthma was defined as a decline in lung function, an increase in bronchial hyperresponsiveness, exacerbations, or death. Studies older than 3 years selected from the bibliographies of the primary articles that addressed background perspective were also included where appropriate.

DATA SYNTHESIS

The studies fell into 3 primary categories with some overlap: those assessing toxicity of the S-enantiomer of albuterol, those evaluating the risk of specific genotypes regarding worsening asthma, and those assessing asthma outcomes with LABA therapy.

CONCLUSIONS

The current data on the use of beta2-agonists continue to support the national and international guidelines for the treatment of asthma. That is, short-acting inhaled beta2-agonists should only be used as needed for symptoms and prevention of exercise-induced bronchospasm, and LABAs should only be used regularly as adjunctive therapy with inhaled corticosteroids in patients whose asthma is not controlled with low to medium doses of the inhaled corticosteroid.

Bronchoalveolar lymphocytosis correlates with human T lymphotropic virus type I (HTLV-I) proviral DNA load in HTLV-I carriers

BACKGROUND

A study was undertaken to investigate the pathogenesis of pulmonary involvement in human T lymphotropic virus type I (HTLV-I) carriers.

METHODS

The bronchoalveolar lavage (BAL) cell profile of 30 HTLV-I carriers (15 asymptomatic HTLV-I carriers (AHCs) and 15 symptomatic HTLV-I carriers (SHCs)) with chronic inflammatory diseases of respiratory tract and eight patients with HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP) was investigated. The HTLV-I proviral deoxyribonucleic acid (DNA) load in peripheral blood mononuclear cells (PBMCs) and BAL fluid from HTLV-I carriers was estimated using the quantitative polymerase chain reaction method and the correlation between the lymphocyte number in BAL fluid and the HTLV-I proviral DNA load in PBMCs and BAL fluid was examined.

RESULTS

The percentage of lymphocytes in BAL fluid was increased (>18%) in 11 of 30 HTLV-I carriers although there was no significant difference compared with control subjects. In HTLV-I carriers the lymphocyte number in BAL fluid correlated well with the copy number of HTLV-I proviral DNA in PBMCs. In addition, the copy number of HTLV-I proviral DNA in BAL fluid correlated well with the number of lymphocytes (both CD4+ and CD8+ cells) in BAL fluid.

CONCLUSIONS

These findings suggest that pulmonary lymphocytosis can occur in a subset of HTLV-I carriers without HAM/TSP and that the increased HTLV-I proviral DNA load may be implicated in the pathogenesis of pulmonary involvement in HTLV-I carriers.