Safe use of long-acting β-agonists: what have we learnt?

Do genetic polymorphisms alter patient response to inhaled bronchodilators?

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Long-acting beta2-adrenergic agonist in pediatric and adolescent asthma patients, 2003-2011

OBJECTIVES

To evaluate changes in the dispensing patterns of long-acting beta2-adrenergic agonist (LABA) in pediatric and adolescent asthma patients in relation to multiple Food and Drug Administration (FDA) regulatory activities from 2003 to 2011.

METHODS

We estimated LABA dispensing to pediatric asthma patients across three periods: 2003-2004 (after the first labeling change), 2005-2009 (after regulatory activities in 2005 and before 2010 LABA labeling change) and 2010-2011 (after 2010 LABA labeling change), using the IMS Health Plan Claims database. We estimated dispensing patterns over time for single-ingredient (SI) LABA and fixed-dose combination (FDC) of inhaled corticosteroid (ICS) and LABA (FDC-ICS/LABA). We also evaluated prior use of non-LABA asthma-control medication (ACM) before LABA initiation.

RESULTS

Of the 147 862 pediatric and adolescent asthma patients who initiated a LABA during the entire study period, the majority (96%) were FDC-ICS/LABA initiators. The proportion of SI-LABA among any LABA initiators was small and declined (9%, 4% and 2%, trend test p < 0.001) for the three periods. Among the patients who initiated, the proportions with prior use of an ACM (1-90 days prior) were 35%, 36% and 39% for the three periods.

CONCLUSIONS

The significant decline in the proportion of SI-LABA initiation over these years is consistent with FDA's recommendations. However, the favorable trend cannot be solely attributed to FDA activities as changes to clinical practice guidelines, and media publicity may have played a role. Investigating the reasons for the low ACM use before LABA initiation may inform approaches to further improve appropriate use of LABA in young asthma patients.

Are inhaled longacting β2 agonists detrimental to asthma?

Possible adverse effects of adrenergic bronchodilators in asthma have been the subject of discussion for more than half a century, with recent intense debate about the safety of longacting β agonists (LABAs). In this Debate, we consider the issues of bronchodilator and bronchoprotective tolerance resulting from the frequent use of bronchodilators, which is noted particularly with shortacting drugs, but has also been shown to occur quicker and to a greater extent with LABAs. Increased allergen responsiveness and masking allowing inflammation to increase, while symptoms and lung function remain apparently controlled, have also been observed. Studies in which LABAs were used as monotherapy were associated with increased mortality. However, several studies have shown the benefits of adding LABAs to inhaled corticosteroids (ICS). Meta-analyses of asthma clinical trials involving LABAs showed that, when given with mandatory ICS, LABAs were not associated with an increased risk of death, intubations, or hospital admission for exacerbations when compared with use of the same dose of ICS only. Withdrawal of LABA therapy once symptom control is achieved is often associated with subsequent loss of symptom control. When used for appropriate indications, LABAs should be combined with ICS in one inhaler so that monotherapy is not possible.

Multiple facets of cAMP signalling and physiological impact: cAMP compartmentalization in the lung

Therapies involving elevation of the endogenous suppressor cyclic AMP (cAMP) are currently used in the treatment of several chronic inflammatory disorders, including chronic obstructive pulmonary disease (COPD). Characteristics of COPD are airway obstruction, airway inflammation and airway remodelling, processes encompassed by increased airway smooth muscle mass, epithelial changes, goblet cell and submucosal gland hyperplasia. In addition to inflammatory cells, airway smooth muscle cells and (myo)fibroblasts, epithelial cells underpin a variety of key responses in the airways such as inflammatory cytokine release, airway remodelling, mucus hypersecretion and airway barrier function. Cigarette smoke, being next to environmental pollution the main cause of COPD, is believed to cause epithelial hyperpermeability by disrupting the barrier function. Here we will focus on the most recent progress on compartmentalized signalling by cAMP. In addition to G protein-coupled receptors, adenylyl cyclases, cAMP-specific phospho-diesterases (PDEs) maintain compartmentalized cAMP signalling. Intriguingly, spatially discrete cAMP-sensing signalling complexes seem also to involve distinct members of the A-kinase anchoring (AKAP) superfamily and IQ motif containing GTPase activating protein (IQGAPs). In this review, we will highlight the interaction between cAMP and the epithelial barrier to retain proper lung function and to alleviate COPD symptoms and focus on the possible molecular mechanisms involved in this process. Future studies should include the development of cAMP-sensing multiprotein complex specific disruptors and/or stabilizers to orchestrate cellular functions. Compartmentalized cAMP signalling regulates important cellular processes in the lung and may serve as a therapeutic target.

Distinct PKA and Epac compartmentalization in airway function and plasticity

Asthma and chronic obstructive pulmonary disease (COPD) are obstructive lung diseases characterized by airway obstruction, airway inflammation and airway remodelling. Next to inflammatory cells and airway epithelial cells, airway mesenchymal cells, including airway smooth muscle cells and (myo)fibroblasts, substantially contribute to disease features by the release of inflammatory mediators, smooth muscle contraction, extracellular matrix deposition and structural changes in the airways. Current pharmacological treatment of both diseases intends to target the dynamic features of the endogenous intracellular suppressor cyclic AMP (cAMP). This review will summarize our current knowledge on cAMP and will emphasize on key discoveries and paradigm shifts reflecting the complex spatio-temporal nature of compartmentalized cAMP signalling networks in health and disease. As airway fibroblasts and airway smooth muscle cells are recognized as central players in the development and progression of asthma and COPD, we will focus on the role of cAMP signalling in their function in relation to airway function and plasticity. We will recapture on the recent identification of cAMP-sensing multi-protein complexes maintained by cAMP effectors, including A-kinase anchoring proteins (AKAPs), proteins kinase A (PKA), exchange protein directly activated by cAMP (Epac), cAMP-elevating seven-transmembrane (7TM) receptors and phosphodiesterases (PDEs) and we will report on findings indicating that the pertubation of compartmentalized cAMP signalling correlates with the pathopysiology of obstructive lung diseases. Future challenges include studies on cAMP dynamics and compartmentalization in the lung and the development of novel drugs targeting these systems for therapeutic interventions in chronic obstructive inflammatory diseases.

Novel cAMP signalling paradigms: therapeutic implications for airway disease

Since its discovery over 50 years ago, cAMP has been the archetypal second messenger introducing students to the concept of cell signalling at the simplest level. As explored in this review, however, there are many more facets to cAMP signalling than the path from Gs-coupled receptor to adenylyl cyclase (AC) to cAMP to PKA to biological effect. After a brief description of this canonical cAMP signalling pathway, a snapshot is provided of the novel paradigms of cAMP signalling. As in the airway the cAMP pathway relays the major bronchorelaxant signal and as such is the target for frontline therapy for asthma and COPD, particular emphasis is given to airway disease and therapy. Areas discussed include biased agonism, continued signalling following internalization, modulation of cAMP by AC, control of cAMP degradation, cAMP and calcium crosstalk, Epac-mediated signalling and finally the implications of altered genotypes will be considered. LINKED ARTICLES This article is part of a themed section on Novel cAMP Signalling Paradigms. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.166.issue-2.

Emerging airway smooth muscle targets to treat asthma

Asthma is characterized in part by variable airflow obstruction and non-specific hyperresponsiveness to a variety of bronchoconstrictors, both of which are mediated by the airway smooth muscle (ASM). The ASM is also involved in the airway inflammation and airway wall remodeling observed in asthma. For all these reasons, the ASM provides an important target for the treatment of asthma. Several classes of drugs were developed decades ago which targeted the ASM - including β-agonists, anti-cholinergics, anti-histamines and anti-leukotrienes - but no substantially new class of drug has appeared recently. In this review, we summarize the on-going work of several laboratories aimed at producing novel targets and/or tools for the treatment of asthma. These range from receptors and ion channels on the ASM plasmalemma, to intracellular effectors (particularly those related to cyclic nucleotide signaling, calcium-homeostasis and phosphorylation cascades), to anti-IgE therapy and outright destruction of the ASM itself.

Key observations from the NHLBI Asthma Clinical Research Network

The National Heart, Lung and Blood Institute (NHLBI) Asthma Clinical Research Network (ACRN) recently completed its work after 20 years of collaboration as a multicentre clinical trial network. When formed, its stated mission was to perform multiple controlled clinical trials for treating patients with asthma by dispassionately examining new and existing therapies, and to rapidly communicate its findings to the medical community. The ACRN conducted 15 major clinical trials. In addition, clinical data, manual of operations, protocols and template informed consents from all ACRN trials are available via NHLBI BioLINCC (https://biolincc.nhlbi.nih.gov/studies/). This network contributed major insights into the use of inhaled corticosteroids, short-acting and long-acting ß-adrenergic agonists, leukotriene receptor antagonists, and novel agents (tiotropium, colchicine and macrolide antibiotics). They also pioneered studies of the variability in drug response, predictors of treatment response and pharmacogenetics. This review highlights the major research observations from the ACRN that have impacted the current management of asthma.

Long-acting beta-agonists and the risk of intensive care unit admission in children

OBJECTIVE

A possible association between long-acting beta-agonists (LABA) and severe asthma exacerbations including death remains controversial. We examined whether LABA in the setting of combination therapy with inhaled corticosteroids (ICS) increase the risk of near-fatal asthma in children using a case-control study design.

METHODS

Medical records from admissions for asthma exacerbations in children 4-18 years of age during the 2005 calendar year at Children's Hospital of Pittsburgh of UPMC were reviewed. Cases and controls were determined by pediatric intensive care unit (PICU) and floor admission, respectively. Exposure was defined by LABA use in combination with ICS versus ICS alone.

RESULTS

Records from 85 PICU and 96 pediatric floor admissions were reviewed. LABA use in combination with ICS did not increase the risk of PICU admission (odds ratio 1.07, 95% CI 0.46-2.52) compared to ICS only without LABA. After adjusting for demographics, asthma severity, history of PICU admissions, and concurrent infection, LABA/ICS use still did not increase the risk of PICU admission (adjusted odds ratio 0.84, 95% CI 0.26-2.76) compared to ICS alone. There were no deaths and five intubations within the study period.

CONCLUSIONS

The combination of LABA and ICS did not appear to increase the risk of near-fatal asthma in children.

Long-acting β-agonists in asthma management: what is the current status?

Large surveillance studies or phase IV clinical studies of long-acting β-agonists (LABA) compared with placebo in asthma patients using variable (from nil to regular) doses of inhaled corticosteroids (ICS) have raised the issue of mortality risk in patients with asthma taking regular LABA. There have been a number of meta-analyses and systematic reviews that have examined the risk of LABA in asthma patients, and the general conclusion is that LABA added to ICS reduces asthma-related hospitalizations compared with ICS alone and there is no statistical increase in mortality. However, LABA without ICS do increase mortality risk in asthma. All reviews and analyses show a greater number of LABA deaths, but not all are statistically significant. A recent meta-analysis found LABA with concomitant ICS had a higher mortality rate in asthma than ICS alone. The flaw in the study is the higher doses of ICS in the control arms, but the implicit message remains: the essential need for enough ICS to control airway inflammation. We suggest that the pragmatic solution is to have LABA only available in the same device as ICS for asthma treatment. We do not think that a study comparing the safety of LABA plus ICS versus ICS alone in asthma is necessary. If such a study is conducted, the measurement of morbidity from increased doses of ICS is an essential design consideration. Furthermore, the critical focus in asthma management should not be forgotten - education of health professionals and the community of the critical role of ICS, and the need for good communication between health professionals and the asthma patient to facilitate good asthma control. The same arguments apply to the asthma-with-chronic obstructive pulmonary disease overlap syndrome in older patients. There is an urgent need to provide medical practitioners with the capability to diagnose the overlap syndrome.