Bronchodilator subsensitivity to salbutamol after twice daily salmeterol in asthmatic patients

Molecular mechanism of bitter taste receptor agonist-mediated relaxation of airway smooth muscle

G-protein-coupled receptors (GPCRs) belonging to the type 2 taste receptors (TAS2Rs) family are predominantly present in taste cells to allow the perception of bitter-tasting compounds. TAS2Rs have also been shown to be expressed in human airway smooth muscle (ASM), and TAS2R agonists relax ASM cells and bronchodilate airways despite elevating intracellular calcium. This calcium "paradox" (calcium mediates contraction by pro-contractile Gq-coupled GPCRs) and the mechanisms by which TAS2R agonists relax ASM remain poorly understood. To gain insight into pro-relaxant mechanisms effected by TAS2Rs, we employed an unbiased phosphoproteomic approach involving dual-mass spectrometry to determine differences in the phosphorylation of contractile-related proteins in ASM following the stimulation of cells with TAS2R agonists, histamine (an agonist of the Gq-coupled H1 histamine receptor) or isoproterenol (an agonist of the Gs-coupled β2-adrenoceptor) alone or in combination. Our study identified differential phosphorylation of proteins regulating contraction, including A-kinase anchoring protein (AKAP)2, AKAP12, and RhoA guanine nucleotide exchange factor (ARHGEF)12. Subsequent signaling analyses revealed RhoA and the T853 residue on myosin light chain phosphatase (MYPT)1 as points of mechanistic divergence between TAS2R and Gs-coupled GPCR pathways. Unlike Gs-coupled receptor signaling, which inhibits histamine-induced myosin light chain (MLC)20 phosphorylation via protein kinase A (PKA)-dependent inhibition of intracellular calcium mobilization, HSP20 and ERK1/2 activity, TAS2Rs are shown to inhibit histamine-induced pMLC20 via inhibition of RhoA activity and MYPT1 phosphorylation at the T853 residue. These findings provide insight into the TAS2R signaling in ASM by defining a distinct signaling mechanism modulating inhibition of pMLC20 to relax contracted ASM.

Impact of the cAMP efflux and extracellular cAMP-adenosine pathway on airway smooth muscle relaxation induced by formoterol and phosphodiesterase inhibitors

β2-adrenoceptors agonists and phosphodiesterase (PDE) inhibitors are effective bronchodilators, due to their ability to increase intracellular cyclic AMP (cAMP) levels and induce airway smooth muscle (ASM) relaxation. We have shown that increment of intracellular cAMP induced by β2-adrenoceptors agonist fenoterol is followed by efflux of cAMP, which is converted by ecto-PDE and ecto-5'-nucleotidases (ecto-5'NT) to adenosine, leading to ASM contraction. Here we evaluate whether other classical bronchodilators used to treat asthma and chronic obstructive pulmonary disease (COPD) could induce cAMP efflux and, as consequence, influence the ASM contractility. Our results showed that β2-adrenoceptor agonists formoterol and PDE inhibitors IBMX, aminophylline and roflumilast induced cAMP efflux and a concentration-dependent relaxation of rat trachea precontracted with carbachol. Pretreatment of tracheas with MK-571 (MRP transporter inhibitor), AMP-CP (ecto-5'NT inhibitor) or CGS-15943 (nonselective adenosine receptor antagonist) potentiated the relaxation induced by β2-adrenoceptor agonists but did not change the relaxation induced by PDE inhibitors. These data showed that all bronchodilators tested were able to induce cAMP efflux. However, only β2-adrenoceptor-induced relaxation of tracheal smooth muscle was affected by cAMP efflux and extracellular cAMP-adenosine pathway.

Selective Signal Capture from Multidimensional GPCR Outputs with Biased Agonists: Progress Towards Novel Drug Development

G protein coupled receptors (GPCRs) are a superfamily of transmembrane-spanning receptors that are activated by multiple endogenous ligands and are the most common target for agonist or antagonist therapeutics across a broad spectrum of diseases. Initial characterization within the superfamily suggested that a receptor activated a single intracellular pathway, depending on the G protein to which it coupled. However, it has become apparent that a given receptor can activate multiple different pathways, some being therapeutically desirable, while others are neutral or promote deleterious signaling. The activation of pathways that limit effectiveness of a primary pathway or promote unwanted signals has led to abandonment of some GPCRs as drug targets. However, it is now recognized that the conformation of the receptor in its ligand-bound state can be altered by the structure of the agonist or antagonist to achieve pathway selectivity, a property termed biased signaling. Biased ligands could dramatically expand the number of novel drugs acting at GPCRs for new indications. However, the field struggles with the complexity and uncertainty of these structure-functions relationships. In this review we define the theoretical underpinnings of the biased effect, discuss the methods for measuring bias, and the pitfalls that can lead to incorrect assignments of bias. Using the recent elucidation of a β₂-adrenergic receptor agonist that is biased in favor of Gs coupling over β-arrestin binding, we provide an example of how large libraries of compounds that are impartial to preconceived notions of agonist binding can be utilized to discover pathway-specific agonists. In this case, an agonist that lacks tachyphylaxis for the treatment of obstructive lung diseases was uncovered, with a structure that was distinctly different from other agonists. We show how biased characteristics were ascertained analytically, and how molecular modeling and simulations provide a structural basis for a restricted signaling repertoire.

Biased β-Agonists Favoring Gs over β-Arrestin for Individualized Treatment of Obstructive Lung Disease

Signals from G-protein-coupled receptors (GPCRs) are the most frequently targeted pathways of currently prescribed therapeutics. Rather than being a simple switch, it is now evident that a given receptor can directly initiate multiple signals, and biasing to achieve signal selectivity based on agonist structure is possible. Biased agonists could direct therapeutically favorable pathways while avoiding counterproductive or adverse reaction pathways. For obstructive lung diseases, β2-adrenergic receptor (β2AR) agonists act at these receptors on airway smooth muscle (ASM) cells to open the airways by relaxing ASM, improving airflow and morbidity. However, these receptors signal to the G protein Gs (increasing cAMP and promoting relaxation), but also to β-arrestin (promoting desensitization and a loss of effectiveness). Indeed, β-agonist use is associated with adverse events in asthma pathogenesis and clinical outcomes which are related to desensitization. β-agonists favoring Gs coupling over β-arrestin binding would provide a means of tailoring bronchodilator therapy. In this review, we show how combinatorial methods with a 40 million compound agnostic library led to a new class of biased β-agonists that do not desensitize, providing an opportunity to personalize therapy in patients who experience poor efficacy or adverse effects from traditional balanced agonists.

Identification and characterization of an atypical Gαs-biased β2AR agonist that fails to evoke airway smooth muscle cell tachyphylaxis

We sought β₂AR agonists for treating obstructive lung diseases such as asthma, in which this receptor relaxes airway smooth muscle (ASM) cells and opens airways. Agonists favoring Gs coupling (leads to airway relaxation) compared with activating β-arrestin (limits effectiveness due to receptor desensitization) were pursued in a 40-million-compound screening library. Of several agonists identified, one was apparently biased away from β-arrestin. Agonist–receptor–G protein modeling revealed different receptor interactions compared with other agonists. The favorable effects of the apparent biasing with this agonist were demonstrated in a physiologic system (ASM relaxation). These studies point to a different structural class of β-agonists that might be used to treat obstructive lung diseases without the adverse effects associated with tachyphylaxis.

G protein–coupled receptors display multifunctional signaling, offering the potential for agonist structures to promote conformational selectivity for biased outputs. For β₂-adrenergic receptors (β₂AR), unbiased agonists stabilize conformation(s) that evoke coupling to Gαs (cyclic adenosine monophosphate [cAMP] production/human airway smooth muscle [HASM] cell relaxation) and β-arrestin engagement, the latter acting to quench Gαs signaling, contributing to receptor desensitization/tachyphylaxis. We screened a 40-million-compound scaffold ranking library, revealing unanticipated agonists with dihydroimidazolyl-butyl-cyclic urea scaffolds. The S-stereoisomer of compound C1 shows no detectable β-arrestin engagement/signaling by four methods. However, C1-S retained Gαs signaling—a divergence of the outputs favorable for treating asthma. Functional studies with two models confirmed the biasing: β₂AR-mediated cAMP signaling underwent desensitization to the unbiased agonist albuterol but not to C1-S, and desensitization of HASM cell relaxation was observed with albuterol but not with C1-S. These HASM results indicate biologically pertinent biasing of C1-S, in the context of the relevant physiologic response, in the human cell type of interest. Thus, C1-S was apparently strongly biased away from β-arrestin, in contrast to albuterol and C5-S. C1-S structural modeling and simulations revealed binding differences compared with unbiased epinephrine at transmembrane (TM) segments 3,5,6,7 and ECL2. C1-S (R2 = cyclohexane) was repositioned in the pocket such that it lost a TM6 interaction and gained a TM7 interaction compared with the analogous unbiased C5-S (R2 = benzene group), which appears to contribute to C1-S biasing away from β-arrestin. Thus, an agnostic large chemical-space library identified agonists with receptor interactions that resulted in relevant signal splitting of β₂AR actions favorable for treating obstructive lung disease.

The short third intracellular loop and cytoplasmic tail of bitter taste receptors provide functionally relevant GRK phosphorylation sites in TAS2R14

For most G protein–coupled receptors, the third intracellular loop (IL3) and carboxy-terminal tail (CT) are sites for G protein–coupled receptor kinase (GRK)–mediated phosphorylation, leading to β-arrestin binding and agonist-specific desensitization. These regions of bitter taste receptors (TAS2Rs) are extremely short compared with the superfamily, and their function in desensitization is unknown. TAS2R14 expressed on human airway smooth muscle cells relax the cell, suggesting a novel target for bronchodilators. To assess IL3 and CT in agonist-promoted TAS2R14 desensitization (tachyphylaxis), we generated fusion proteins of both the WT sequence and Ala substituted for Ser/Thr in the IL3 and CT sequences. In vitro, activated GRK2 phosphorylated WT IL3 and WT CT proteins but not Ala-substituted forms. TAS2R14s with mutations in IL3 (IL-5A), CT (CT-5A), and in both regions (IL/CT-10A) were expressed in human embryonic kidney 293T cells. IL/CT-10A and CT-5A failed to undergo desensitization of the intracellular calcium response compared with WT, indicating that functional desensitization by GRK phosphorylation is at residues in the CT. Desensitization of TAS2R14 was blocked by GRK2 knockdown in human airway smooth muscle cells. Receptor:β-arrestin binding was absent in IL/CT-10A and CT-5A and reduced in IL-5A, indicating a role for IL3 phosphorylation in the β-arrestin interaction for this function. Agonist-promoted internalization of IL-5A and CT-5A receptors was impaired, and they failed to colocalize with early endosomes. Thus, agonist-promoted functional desensitization of TAS2R14 occurs by GRK phosphorylation of CT residues and β-arrestin binding. However, β-arrestin function in the internalization and trafficking of the receptor also requires GRK phosphorylation of IL3 residues.

Identification and Characterization of Novel Bronchodilator Agonists Acting at Human Airway Smooth Muscle Cell TAS2R5

Bitter taste receptors (TAS2Rs) are recognized as being expressed on multiple cell types and organs, including human airway smooth muscle (HASM) cells, where agonists promote significant relaxation to constrictive stimuli. Thus, the HASM TAS2Rs have been targeted as novel bronchodilators for the treatment of asthma and other obstructive lung diseases. The TAS2R5 subtype, a dominant receptor on HASM, has few known agonists, all with reported low potency and efficacy. We screened multiple compounds by measuring [Ca²⁺]_i release in HASM (a consequence of receptor-G protein coupling) to establish structure-activity relationships and arrive at a potent agonist for TAS2R5. HASM physiological studies using magnetic twisting cytometry confirmed the relaxation effects of lead compounds. 1,10-Phenanthroline-5,6-dione had the greatest potency (EC₅₀ ≈ 120 nM), amounting to a >1000-fold improvement over the other compounds, and displayed maximal efficacy. These studies revealed critical structural requirements for favorable potencies and efficacies for a potential first-in-class bronchodilator targeting TAS2R5 of the airway.

Hyperinsulinemia promotes heterologous desensitization of β2 adrenergic receptor in airway smooth muscle in obesity

β-Adrenergic receptor (β-AR) agonists are the most common clinical bronchodilators for asthma. Obesity influences asthma severity and may impair response to β-AR agonists. Previous studies show that in obese mice, hyperinsulinemia plays a crucial role in β-AR desensitization in the heart. We therefore investigated whether insulin promotes β-AR desensitization in airway smooth muscle (ASM) and compromises airway relaxation responsiveness to β-AR agonists. We found that human ASM cells and mouse airway tissues exposed to insulin exhibit impaired β₂ AR-induced cAMP accumulation and airway relaxation. This impaired relaxation is associated with insulin-induced phosphorylation and expression of phosphodiesterase 4D (PDE4D) through transactivation of a G protein-coupled receptor kinase 2 (GRK2)-dependent β₂ AR-G_i -ERK1/2 cascade. Both acute and chronic pharmacological inhibition of PDE4 effectively reversed impaired β₂ AR-mediated ASM relaxation in an obesity mouse model induced by a high fat diet. Collectively, these findings reveal that cross talk between insulin and β₂ AR signaling promotes ASM β₂ AR desensitization in obesity through upregulation of PDE4D phosphorylation and expression. Our results identify a novel pathway of asthma pathogenesis in patients with obesity/metabolic syndrome, in which the GRK2-mediated signaling can be a potential therapeutic modality to prevent or treat β₂ AR desensitization in ASM. Moreover, PDE4 inhibitors may be used as efficacious therapeutic agents for asthma in obese and diabetic subjects.

Loss of bronchoprotection with ICS plus LABA treatment, β-receptor dynamics, and the effect of alendronate

BACKGROUND

Loss of bronchoprotection (LOBP) with a regularly used long-acting β2-adrenergic receptor agonist (LABA) is well documented. LOBP has been attributed to β2-adrenergic receptor (B2AR) downregulation, a process requiring farnesylation, which is inhibited by alendronate.

OBJECTIVE

We sought to determine whether alendronate can reduce LABA-associated LOBP in inhaled corticosteroid (ICS)-treated patients.

METHODS

We conducted a randomized, double-blind, placebo-controlled, parallel-design, proof-of-concept trial. Seventy-eight participants with persistent asthma receiving 250 μg of fluticasone twice daily for 2 weeks were randomized to receive alendronate or placebo while initiating salmeterol for 8 weeks. Salmeterol-protected methacholine challenges (SPMChs) and PBMC B2AR numbers (radioligand binding assay) and signaling (cyclic AMP ELISA) were assessed before randomization and after 8 weeks of ICS plus LABA treatment. LOBP was defined as a more than 1 doubling dose reduction in SPMCh PC20 value.

RESULTS

The mean doubling dose reduction in SPMCh PC20 value was 0.50 and 0.27 with alendronate and placebo, respectively (P = .62). Thirty-eight percent of participants receiving alendronate and 33% receiving placebo had LOBP (P = .81). The after/before ICS plus LABA treatment ratio of B2AR number was 1.0 for alendronate (P = .86) and 0.8 for placebo (P = .15; P = .31 for difference between treatments). The B2AR signaling ratio was 0.89 for alendronate (P = .43) and 1.02 for placebo (P = .84; P = .44 for difference). Changes in lung function and B2AR number and signaling were similar between those who did and did not experience LOBP.

CONCLUSION

This study did not find evidence that alendronate reduces LABA-associated LOBP, which relates to the occurrence of LOBP in only one third of participants. LOBP appears to be less common than presumed in concomitant ICS plus LABA-treated asthmatic patients. B2AR downregulation measured in PBMCs does not appear to reflect LOBP.

Bronchoprotective effect of vilanterol against methacholine-induced bronchoconstriction in mild asthmatics: A randomized three-way crossover study

BACKGROUND

Ultra-long-acting β2 agonists (uLABA) are relatively new anti-asthma medications of which there are three different formulations currently available: olodaterol, indacaterol, and vilanterol. The first 2 formulations have been shown to exert bronchoprotective effects; they are able to prevent airway smooth muscle contraction on exposure to constricting stimuli. However, studies have found that these 2 drugs produce different degrees and durations of bronchoprotection against methacholine.

OBJECTIVE

The objective of this study was to investigate the degree of bronchoprotection provided by vilanterol against methacholine-induced bronchoconstriction.

METHODS

Fourteen patients with mild-to-moderate asthma (8 male; baseline percent predicted forced expiratory volume in 1 second [FEV₁] > 65%; provocative concentration of methacholine causing a 20% reduction in FEV₁ [PC20] ≤ 8 mg/mL) completed this randomized, double-blind, 3-way crossover study. Methacholine challenges were performed before treatment administration (placebo, 100 μg fluticasone furoate, or 25 μg vilanterol + 100 μg fluticasone furoate) and at 0.5 and 24 hours posttreatment. Each treatment arm was separated by a minimum 7-day washout period. A combination therapy of vilanterol+fluticasone furoate was used, because vilanterol is not available as a monotherapy.

RESULTS

Significant bronchoprotection was evident after the combination treatment at both 0.5 and 24 hours with doubling dose shifts in methacholine PC20 of 2.0 (P = .0004) and 1.6 (P = .0001), respectively. Clinically significant bronchodilation was only recorded at 24 hours after combination treatment (P < .05).

CONCLUSION

These findings suggest that vilanterol (in combination with fluticasone furoate) provides significant bronchoprotection against methacholine-induced bronchoconstriction for at least 24 hours in patients with mild-to-moderate asthma.

CLINICAL TRIAL REGISTRATION

clinicaltrials.gov (NCT03315000).

A CREB-mediated increase in miRNA let-7f during prolonged β-agonist exposure: a novel mechanism of β2-adrenergic receptor down-regulation in airway smooth muscle

β₂-Adrenergic receptors (β₂ARs) desensitize during continuous agonist activation, which manifests clinically as tachyphylaxis. β-Agonist desensitization of β₂ARs in human airway smooth muscle (HASM) cells is recognized in the treatment of asthma and may be related to poor outcomes. Rapid events in desensitization include receptor phosphorylation and internalization, but mechanisms responsible for the decrease in receptor protein after prolonged agonist exposure (down-regulation) are ill defined. The microRNA (miRNA) let-7f regulates β₂AR expression by translational repression. In cultured HASM cells from nonasthmatic and asthmatic lungs, 18 h of β-agonist exposure increased let-7f by 2-3-fold, concomitant with a ∼90% decrease in β₂ARs. Inhibition of let-7f attenuated this down-regulation response by ∼50%. The let-7f increase was found to be cAMP/PKA-dependent. The mechanism of the let-7f increase was found by chromatin immunoprecipitation to be from activated cAMP response element-binding protein (CREB) binding to the let-7f promoter, thereby increasing let-7f expression. Knockdown of CREB attenuated agonist-promoted β₂AR down-regulation by ∼50%. Thus, β₂AR down-regulation occurs as a result of not only internalized receptor degradation but also a novel cAMP/PKA/CREB-mediated increase in let-7f, which causes enhanced repression of the β₂AR gene, adrenoreceptor β₂ ( ADRB2) translation and represents ∼50% of the net loss of receptors observed after prolonged agonist exposure. This mechanism is apparent in asthmatic HASM cells, indicating relevance in a disease model.-Kim, D., Cho, S., Woo, J. A., Liggett, S. B. A CREB-mediated increase in miRNA let-7f during prolonged β-agonist exposure: a novel mechanism of β₂-adrenergic receptor down-regulation in airway smooth muscle.

β2 Agonists

History suggests β agonists, the cognate ligand of the β₂ adrenoceptor, have been used as bronchodilators for around 5,000 years, and β agonists remain today the frontline treatment for asthma and chronic obstructive pulmonary disease (COPD). The β agonists used clinically today are the products of significant expenditure and over 100 year's intensive research aimed at minimizing side effects and enhancing therapeutic usefulness. The respiratory physician now has a therapeutic toolbox of long acting β agonists to prophylactically manage bronchoconstriction, and short acting β agonists to relieve acute exacerbations. Despite constituting the cornerstone of asthma and COPD therapy, these drugs are not perfect; significant safety issues have led to a black box warning advising that long acting β agonists should not be used alone in patients with asthma. In addition there are a significant proportion of patients whose asthma remains uncontrolled. In this chapter we discuss the evolution of β agonist use and how the understanding of β agonist actions on their principal target tissue, airway smooth muscle, has led to greater understanding of how these drugs can be further modified and improved in the future. Research into the genetics of the β₂ adrenoceptor will also be discussed, as will the implications of individual DNA profiles on the clinical outcomes of β agonist use (pharmacogenetics). Finally we comment on what the future may hold for the use of β agonists in respiratory disease.

Bronchoprotective tolerance with indacaterol is not modified by concomitant tiotropium in persistent asthma

BACKGROUND

Tiotropium is a long acting muscarinic antagonist (LAMA), licensed as triple therapy with inhaled corticosteroid and long-acting beta-agonist (ICS/LABA). There may be a synergistic benefit between LAMA and LABA as a consequence of receptor cross-talk, which in turn could modify beta-2 receptor downregulation and associated tolerance induced by LABA.

OBJECTIVE

We hypothesize this mechanism may result in a reduction of airway hyperresponsiveness (AHR) when using triple therapy.

METHODS

We evaluated 14 non-smoking asthmatics using an open-label, randomized crossover design. ICS with Indacaterol and Tiotropium (IND/TIO) vs ICS with Indacaterol (IND) over 4 weeks with challenge performed after first and last doses at trough.

RESULTS

We found no significant difference in mannitol sensitivity, expressed as the provocative dose of mannitol required to reach a 15% drop in FEV₁ , or mannitol reactivity, expressed as the response dose ratio (RDR: max % fall in FEV₁ /cumulative dose), when comparing ICS/IND/TIO to ICS/IND. Geometric mean fold differences for RDR comparing single and chronic dosing were 3.26-fold (95% CI 1.46-7.29) and 2.51-fold (95% CI 1.32-4.79) for IND and IND/TIO, respectively. Furthermore, salbutamol recovery post-challenge was significantly blunted after chronic compared to single dosing with either ICS/IND (P<.005) or ICS/IND/TIO (P<.05).

CONCLUSION AND CLINICAL RELEVANCE

Our data suggest that concomitant tiotropium does not modify the bronchoprotective tolerance induced by Indacaterol, in turn suggesting that cross-talk may not be clinically relevant when using triple therapy. This study was registered on clinicaltrials.gov as NCT02039011.

Vitamin D Deficiency in Outpatients: - a Scottish Perspective

Vitamin D deficiency is common in older people and increases risk of falls, osteoporosis and fracture. This may be reduced with supplements. Recent Scottish guidelines recommend routine use of vitamin D and calcium for all older housebound, sunlight deprived or institutionalised people. Whilst many outpatients will undoubtedly meet these criteria, others who would benefit may not. We have determined the extent of vitamin D deficiency in older outpatients in our geographical area, to clarify further whether those found to be deficient, would receive supplementation under current guidelines

Methodology

102 new patient referrals to outpatient clinics and day hospital were questioned over their social circumstances and activity levels, and had serum 25 - Hydroxy Vitamin D (25(OH)D) levels measured in wintertime

Results

Mean age was 79.6 (SD 7.3), 31.4% were housebound and 51.0% exposed their skin to sunlight. 72.6% had insufficient vitamin D levels [25(OH)D <50 nmol/l], 27.5% of whom levels were frankly deficient [25(OH)D <25 nmol/l]. Deficiency was significantly more common in females (p=0.002), those attending the falls clinic or day hospital (p=0.021), the housebound (p=0.012) or patients who never exposed their skin to sunlight (p=0.007). However, even in those patients who were outdoors frequently or who did expose their skin to the sun, the mean vitamin D levels remained insufficient [mean 25(OH)D = 45.6 (SD 26.2) nmol/l and 47.9 (SD 26.3) nmol/l respectively].

Conclusions

The prevalence of vitamin D deficiency is high in older outpatients in this geographical area. These patients may benefit from routine vitamin D and calcium, but currently many would not be targeted in recent Scottish Executive recommendations because they are not housebound and sunlight deprived.

Pharmacogenomics of long-acting β2-agonists

INTRODUCTION

Long-acting β2-agonists are an effective class of drugs, when combined with inhaled corticosteroids, for reducing symptoms and exacerbations in patients with asthma that is not adequately controlled by inhaled corticosteroids alone. However, because this class of drugs has been associated with severe adverse events, including hospitalization and death in small numbers of patients, efforts to identify a pharmacogenetic profile for patients at risk has been diligently investigated.

AREAS COVERED

The PubMed search engine of the National Library of Medicine was used to identify English-language and non-English language articles published from 1947 to March 2015 pertinent to asthma, pharmacogenomics, and long-acting β2-agonists. Keywords and topics included: asthma, asthma control, long-acting β2-agonists, salmeterol, formoterol, pharmacogenetics, and pharmacogenomics. This strategy was also used for the Cochrane Library Database and CINAHL. Reference types were randomized controlled trials, reviews, and editorials. Additional publications were culled from reference lists. The publications were reviewed by the authors and those most relevant were used to support the topics covered in this review.

EXPERT OPINION

Children, who carry the ADRB2 Arg16Arg genotype, may be at greater risk than adults for severe adverse events. Rare ADRB2 variants appear to provide better clues for identifying the at-risk population of asthmatics.

Radiological correlates and clinical implications of the paradoxical lung function response to β₂ agonists: an observational study

BACKGROUND

Bronchodilator response has been noted in a significant proportion of patients with chronic obstructive pulmonary disease (COPD). However, there are also reports of a paradoxical response to β₂ agonists resulting in bronchoconstriction. Asymptomatic bronchoconstriction is likely to be far more common than is symptomatic bronchoconstriction with β₂ agonists, but no systematic studies have been done. We assessed the prevalence of paradoxical response in current and former smokers with and without COPD, and its radiological correlates and clinical implications.

METHODS

Non-Hispanic white and African-American patients (aged 45-80 years) from a large multicentre study COPDGene were classified into two groups on the basis of a paradoxical response, defined as at least a 12% and 200 mL reduction in forced expiratory volume in 1 sec (FEV₁) or forced vital capacity (FVC), or both, after administration of a shortacting β₂ agonist (180 μg salbutamol).

FINDINGS

Patients were recruited from January, 2008, to June, 2011. 9986 (96%) of 10,364 patients enrolled in the COPDGene study were included in the analysis population (mean age 59·6 years [SD 9·0]). Paradoxical response was noted in 453 (5%) of 9986 patients and the frequency was similar in patients with COPD (198 [4%] of 4439) and smokers without airflow obstruction (255 [5%] of 5547). Compared with white patients, a paradoxical response was twice as common in African-American patients (227 [7%] of 3282 vs 226 [3%] of 6704; p<0·0001). In the multivariate analyses, African-American ethnic origin (adjusted odds ratio 1·89, 95% CI 1·50-2·39; p<0·0001), less emphysema (0·96, 0·92-0·99; p=0·023), and increased wall-area percentage of the segmental airways (1·04, 1·01-1·08; p=0·023) were independently associated with a paradoxical response. A paradoxical response was independently associated with worse dyspnoea (adjusted β for Modified Medical Research Council Dyspnoea Scale 0·12 [95% CI 0·00 to 0·24]; p=0·05), lower 6 min walk distance (-45·8 [-78·5 to -13·2]; p=0·006), higher Body Mass Index, Airflow Obstruction, Dyspnea, and Exercise Capacity (BODE) index (0·31 [0·19 to 0·43]; p<0·0001), and a greater frequency of severe exacerbations (increased by a factor of 1·35, 1·00-1·81; p=0·048).

INTERPRETATION

Paradoxical response to β₂ agonists is associated with respiratory morbidity and is more common in African-Americans. These findings might have implications for the use of β2agonists in some patients.

FUNDING

National Institutes of Health.

β-Agonist-mediated relaxation of airway smooth muscle is protein kinase A-dependent

Inhaled β-agonists are effective at reversing bronchoconstriction in asthma, but the mechanism by which they exert this effect is unclear and controversial. PKA is the historically accepted effector, although this assumption is made on the basis of associative and not direct evidence. Recent studies have asserted that exchange protein activated by cAMP (Epac), not PKA, mediates the relaxation of airway smooth muscle (ASM) observed with β-agonist treatment. This study aims to clarify the role of PKA in the prorelaxant effects of β-agonists on ASM. Inhibition of PKA activity via expression of the PKI and RevAB peptides results in increased β-agonist-mediated cAMP release, abolishes the inhibitory effect of isoproterenol on histamine-induced intracellular calcium flux, and significantly attenuates histamine-stimulated MLC-20 phosphorylation. Analyses of ASM cell and tissue contraction demonstrate that PKA inhibition eliminates most, if not all, β-agonist-mediated relaxation of contracted smooth muscle. Conversely, Epac knockdown had no effect on the regulation of contraction or procontractile signaling by isoproterenol. These findings suggest that PKA, not Epac, is the predominant and physiologically relevant effector through which β-agonists exert their relaxant effects.

The β-2 agonist debate: is there still a problem?

PURPOSE OF REVIEW

To present an evidence-based review of the US Food and Drug Administration (FDA) recommendations for long-acting β agonist (LABA) use in asthma.

RECENT FINDINGS

The FDA recommendation contraindicating the use of LABAs without a concomitant asthma-controller medication such as an inhaled corticosteroid (ICS) is supported, with the caveat that concomitant use of an asthma-controller medication applies only to ICS therapy and not other asthma controller medications (such as leukotriene receptor antagonist therapy or theophylline). The recommendation that LABA therapy be stopped once asthma control is achieved is restrictive. Although downtitration of therapy should be considered in patients with asthma, who are well controlled, other options such as reducing the dose of ICS may be preferable to stopping LABA therapy. In patients who are at risk of unstable asthma or severe exacerbations, maintaining the ICS/LABA therapy without downtitration may be required. The recommendation against LABA use in patients whose asthma is adequately controlled with a low or medium dose ICS is supported. The recommendation that fixed-dose combination ICS/LABA products should be the only form in which LABAs are prescribed in adolescents and paediatric patients should be extended to all asthma patients.

SUMMARY

The current β agonist debate focuses on the optimal management approaches for the use of LABA therapy to both minimize risk and maximize clinical efficacy.

Beta-blockers: friend or foe in asthma?

BACKGROUND AND AIM

Recently, β-blockers have been suggested as a potential maintenance treatment option for asthma. The aim of this review is to provide an overview of the current knowledge of the potential benefits and risks of β-blocker therapy for asthma.

METHOD

Systematic literature review.

RESULTS

No significant increase in the number of patients requiring rescue oral corticosteroid for an exacerbation of asthma has been observed after initiation of β-blocker treatment. Patients with mild to moderate reactive airway disease, probably both asthma and chronic obstructive pulmonary disease, may have a limited fall in forced expiratory volume in 1 second (FEV1) following single-dose administration of β-blocker, whereas no change in FEV1 has been reported following long-term administration. In a murine model of asthma, long-term administration of β-blockers resulted in a decrease in airway hyperresponsiveness, suggesting an anti-inflammatory effect. In keeping with this, long-term administration of a nonselective β-blocker to steroid-naïve asthma patients has shown a dose-dependent improvement in airway hyperresponsiveness, and either an asymptomatic fall in FEV1 or no significant change in FEV1. Furthermore, available studies show that bronchoconstriction induced by inhaled methacholine is reversed by salbutamol in patients on regular therapy with a β-blocker. On the other hand, a recent placebo-controlled trial of propranolol and tiotropium bromide added to inhaled corticosteroids revealed no effect on airway hyperresponsiveness and a small, not statistically significant, fall in FEV1 in patients classified as having mild to moderate asthma.

CONCLUSION

The available, although limited, evidence suggests that a dose-escalating model of β-blocker therapy to patients with asthma is well tolerated, does not induce acute bronchoconstriction, and, not least, may have beneficial effects on airway inflammation and airway hyperresponsiveness in some patients with asthma. Further studies addressing the potential role of β-blocker therapy for asthma are clearly needed, but careful selection of the target population is warranted.

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.

Assessment of murine lung mechanics outcome measures: alignment with those made in asthmatics

Although asthma is characterized as an inflammatory disease, recent reports highlight the importance of pulmonary physiology outcome measures to the clinical assessment of asthma control and risk of asthma exacerbation. Murine models of allergic inflammatory airway disease have been widely used to gain mechanistic insight into the pathogenesis of asthma; however, several aspects of murine models could benefit from improvement. This review focuses on aligning lung mechanics measures made in mice with those made in humans, with an eye toward improving the translational utility of these measures. A brief description of techniques available to measure murine lung mechanics is provided along with a methodological consideration of their utilization. How murine lung mechanics outcome measures relate to pulmonary physiology measures conducted in humans is discussed and we recommend that, like human studies, outcome measures be standardized for murine models of asthma.

Effects of hydrocortisone on acute β-adrenoceptor blocker and histamine induced bronchoconstriction

AIMS

β-adrenoceptor blockers are avoided in asthma due to concerns of bronchoconstriction. We investigated the safety of acute exposure to propranolol in asthmatics, sequentially challenged with histamine to mimic an asthma exacerbation and evaluated the role of intravenous hydrocortisone in potentiating salbutamol reversibility.

METHODS

Persistent atopic asthmatics, requiring ≤ 1000 µg day(-1) budesonide, performed a randomized double-blind placebo-controlled crossover study. Following 10 mg or 20 mg of oral propranolol, patients received 400 mg intravenous hydrocortisone or placebo, followed by histamine challenge with nebulized salbutamol 5 mg and ipratropium 500 µg recovery.

RESULTS

Thirteen patients completed per protocol. Hydrocortisone did not potentiate salbutamol recovery post propranolol and histamine challenge vs. placebo (mean difference in FEV(1) 0.04 ml, 95% CI -0.07, 0.15, P= 0.417). β-adrenoceptor blocker induced bronchoconstriction was demonstrated by spirometry and impulse oscillometry. For the placebo visit, FEV(1) fell 4.7% 2 hours post propranolol (95% CI 1.8, 7.5, P= 0.008) whilst total airway resistance (R5%) increased 31.3% (95% CI 15.6, 47.0, P= 0.04). On both visits FEV(1) % and R5% returned to baseline after salbutamol post histamine.

CONCLUSION

Nebulized salbutamol and ipratropium produced a full recovery after propranolol and histamine induced bronchoconstriction, independent of hydrocortisone use. Since the greatest risk of β-adrenoceptor blockade is after first dose, our findings offer reassurance to those undertaking further evaluation of chronic β-adrenoceptor blockade as a potential treatment for mild-to-moderate asthma.

Chronic treatment in vivo with β-adrenoceptor agonists induces dysfunction of airway β(2) -adrenoceptors and exacerbates lung inflammation in mice

BACKGROUND AND PURPOSE

Inhalation of a β-adrenoceptor agonist (β-agonist) is first-line asthma therapy, used for both prophylaxis against, and acute relief of, bronchoconstriction. However, repeated clinical use of β-agonists leads to impaired bronchoprotection and, in some cases, adverse patient outcomes. Mechanisms underlying this β(2) -adrenoceptor dysfunction are not well understood, due largely to the lack of a comprehensive animal model and the uncertainty as to whether or not bronchorelaxation in mice is mediated by β(2) -adrenoceptors. Thus, we aimed to develop a mouse model that demonstrated functional β-agonist-induced β(2) -adrenoceptor desensitization in the context of allergic inflammatory airway disease.

EXPERIMENTAL APPROACH

We combined chronic allergen exposure with repeated β-agonist inhalation in allergen-treated BALB/C mice and examined the contribution of β(2) -adrenoceptors to albuterol-induced bronchoprotection using FVB/NJ mice with genetic deletion of β(2) -adrenoceptors (KO). Associated inflammatory changes - cytokines (ELISA), cells in bronchoalevolar lavage and airway remodelling (histology) and β(2) -adrenoceptor density (radioligand binding) - were also measured. KEY RESULTS β(2) -Adrenoceptors mediated albuterol-induced bronchoprotection in mice. Chronic treatment with albuterol induced loss of bronchoprotection, associated with exacerbation of the inflammatory components of the asthma phenotype.

CONCLUSIONS AND IMPLICATIONS

This animal model reproduced salient features of human asthma and linked loss of bronchoprotection with airway pathobiology. Accordingly, the model offers an advanced tool for understanding the mechanisms of the effects of chronic β- agonist treatment on β-adrenoceptor function in asthma. Such information may guide the clinical use of β-agonists and provide insight into development of novel β-adrenoceptor ligands for the treatment of asthma.

Effect of AeroChamber Plus™ on the lung and systemic bioavailability of beclometasone dipropionate/formoterol pMDI

AIM

To assess the effect of AeroChamber Plus™ on lung deposition and systemic exposure to extra-fine beclometasone dipropionate (BDP)/formoterol (100/6 µg) pMDI (Foster®). The lung deposition of the components of the combination given with the pMDI was also evaluated using the charcoal block technique.

METHODS

Twelve healthy male volunteers received four inhalations of extra-fine BDP/formoterol (100/6 µg) using (i) pMDI alone, (ii) pMDI and AeroChamber Plus™ and (iii) pMDI and charcoal ingestion.

RESULTS

Compared with pMDI alone, use of AeroChamber Plus™ increased the peak plasma concentrations (C(max)) of BDP (2822.3 ± 1449.9 vs. 5454.9 ± 3197.1 pg ml(-1)), its active metabolite beclometasone 17-monopropionate (17-BMP) (771.6 ± 288.7 vs. 1138.9 ± 495.6 pg ml(-1)) and formoterol (38.4 ± 17.8 vs. 54.7 ± 20.0 pg ml(-1)). For 17-BMP and formoterol, the AUC(0,30 min), indicative of lung deposition, was increased in the AeroChamber Plus™ group by 41% and 45%, respectively. This increase was mainly observed in subjects with inadequate inhalation technique. However, use of AeroChamber Plus™ did not increase the total systemic exposure to 17-BMP and formoterol. Results after ingestion of charcoal confirmed that AUC(0,30 min) can be taken as an index of lung bioavailability and that more than 30% of the inhaled dose of extra-fine BDP/formoterol 100/6 µg was delivered to the lung using the pMDI alone.

CONCLUSIONS

The use of AeroChamber Plus™ optimizes the delivery of BDP and formoterol to the lung in subjects with inadequate inhalation technique. The total systemic exposure was not increased, supporting the safety of extra-fine BDP/formoterol pMDI with AeroChamber Plus™.

Effects of intranasal salmeterol and fluticasone given alone and in combination in persistent allergic rhinitis

BACKGROUND

β(2)-Agonists have previously been shown to be effective inhibitors of mediator release from airway mucosal mast cells.

OBJECTIVE

To evaluate the effects of intranasal salmeterol and fluticasone propionate alone and in combination on the response to nasal adenosine monophosphate (AMP) challenge to assess mast cell activation.

METHODS

Twenty-three patients with persistent allergic rhinitis completed a randomized, double-blind, placebo-controlled, 4-way crossover trial. They received once daily treatment with placebo, salmeterol, 50 μg, fluticasone propionate, 500 μg, or fluticasone propionate and salmeterol combination, 500/50 μg, delivered via an antistatic spacer with nasal adapter for 1 week each, with trough measurements being made 12 hours after the first and last dose. The primary outcome was the maximum percentage decrease in peak nasal inspiratory flow after nasal AMP challenge.

RESULTS

For the primary outcome there was significant protection after single and long-term dosing with fluticasone alone and fluticasone-salmeterol combination, whereas salmeterol alone only afforded protection after the first dose. Fluticasone-salmeterol combination and fluticasone but not salmeterol conferred significant chronic dosing effects on secondary outcomes of nasal symptoms and disease-specific quality of life. There was no potentiation of the response to fluticasone by salmeterol on any outcomes when given in combination.

CONCLUSION

Chronic dosing with fluticasone but not salmeterol confers anti-inflammatory activity against nasal AMP challenge, but there was no potentiation of fluticasone when given in combination with salmeterol. Thus, salmeterol may not be an effective treatment for use in allergic rhinitis.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT01388595.

New perspectives regarding β(2) -adrenoceptor ligands in the treatment of asthma

In the last two decades several significant changes have been proposed in the receptor theory that describes how ligands can interact with G protein-coupled receptors (GPCRs). Here we briefly summarize the evolution of receptor theory and detail recent prominent advances. These include: (i) the existence of spontaneously active GPCRs that are capable of signalling even though they are unoccupied by any ligand; (ii) the discovery of ligands that can inactivate these spontaneously active receptors; (iii) the notion that a ligand may simultaneously activate more than one GPCR signalling pathway; and (iv) the notion that certain ligands may be able to preferentially direct receptor signalling to a specific pathway. Because the data supporting these receptor theory ideas are derived primarily from studies using artificial expression systems, the physiological relevance of these new paradigms remains in question. As a potential example of how these new perspectives in receptor theory relate to drug actions and clinical outcomes, we discuss their relevance to the recent controversy regarding the chronic use of β(2) -adrenoceptor agonists in the treatment of asthma.

Comparative lung bioavailability of fluticasone/salmeterol via a breath-actuated spacer and conventional plastic spacers

PURPOSE

This study compares the in vivo relative lung bioavailability of Hydrofluoroalkane (HFA) Seretide delivered via unprimed and unwashed Aerochamber Plus (AP) or Volumatic (VM) spacers, a integrated breath-actuated vortex Synchro-Breathe (SB) device and an Evohaler pMDI (EH) device using adrenal suppression and early fall in serum potassium (K) as surrogates for respirable dose.

METHODS

Seventeen healthy volunteers completed this randomised double-blind, double-dummy crossover study. Single doses of placebo/Seretide 250 (total dose ex valve fluticasone 2000 mcg/salmeterol 200 mcg) were administered via the devices. Overnight urinary cortisol/creatinine (OUCC) and serum K were measured at baseline and after each dose.

RESULTS

Significant suppression of OUCC and K occurred from baseline with the SB, AP and VM but not with the EH devices. The geometric mean fold suppression (95% confidence interval, p) was: EH, 1.59 (0.80-3.14, p=0.40); AP, 4.26 (3.01-6.02, p<0.001); VM, 3.11 (1.99-4.78, p<0. 001); SB, 3.29 (2.04-5.24, p<0.001). For K, the arithmetic mean fall (mmol/l) (95% confidence interval; p) was: EH, -0.10 (-0.25-0.05, p=0.18); AP, -0.23 (-0.41 to -0.04, p=0.02); VM, -0.22 (-0.44 to -0.01, p=0.04); SB, -0.28 (-0.42 to -0.13, p=0.001).

CONCLUSIONS

The breath-actuated SB device was comparable to 'out of the box' small and large volume spacers and produced similar improvements in relative systemic lung bioavailability for fluticasone and salmeterol.

Systemic bioavailability of hydrofluoroalkane (HFA) formulations of fluticasone/salmeterol in healthy volunteers via pMDI alone and spacer

AIM

To compare a test version of HFA fluticasone/salmeterol (FP/SM) combination inhaler (Neolab, UK) with the reference product Seretide (GlaxoSmithKline, UK).

METHODS

An in vitro Anderson cascade impactor was used to compare the fine particle dose (<4.7 microm). Two separate randomized cross-over studies were performed to compare the systemic bioavailability of test vs. reference (T vs. R) formulations of FP/SM 250/25 microg pMDI in healthy volunteers. In study 1 blood pharmacokinetic analysis using oral charcoal block was performed over 24 h following a single dose of four puffs via pMDI alone. In study 2 systemic bioactivity was measured following single doses of four and eight puffs via a spacer device: serum potassium (K(+)) to reflect SM, and overnight urinary cortisol : creatinine (OUCC) for FP. An early pharmacokinetic profile was also assessed over 120 min.

RESULTS

The in vitro fine particle dose was similar for test vs. reference pMDI alone and via spacer. The results of both studies were consistent: No significant differences between formulations were seen in terms of FP kinetics. Analysis of SM kinetics revealed superiority of the test product. No significant dose-response or difference in T : R ratio was noted for OUCC. Fall in K(+) revealed a significant dose-response with a non-significant T : R ratio.

CONCLUSIONS

The in vitro fine particle dose may not predict pharmacokinetic and systemic pharmacodynamic outcomes. Single dosing studies with fluticasone/salmeterol 250/25 microg via pMDI or with spacer showed pharmacokinetic equivalence with FP, but not SM. No significant difference between formulations was seen with either adrenal suppression or hypokalaemia.

The effect of stepping down combination therapy on airway hyperresponsiveness to mannitol

RATIONALE

Controversy exists about the safety of long acting beta2-agonist (LABA) treatment, in particular in children. Combination therapy with a LABA and an inhaled corticosteroid (ICS) is prescribed to children with moderate asthma and can be stepped down by withdrawal of the LABA when asthma is well controlled.

OBJECTIVE

To analyze the effect of stepping down from LABA/ICS combination therapy to monotherapy with the same dose of ICS on the airway response to mannitol in asthmatic children.

METHODS

17 children, aged 12-17 years, with clinically stable asthma, receiving combination therapy, were analyzed in this observational prospective open-label study. Children performed a mannitol challenge at baseline and 30±4 days after their medication was stepped down to ICS monotherapy. The changes in the provoking dose of mannitol to cause a 15% fall in FEV(1) (PD(15)), response-dose ratio and recovery time following a short acting beta2-agonist to ≥95% of baseline FEV(1) were assessed.

RESULTS

Mannitol PD(15) and response-dose ratio did not significantly change after stepping down. The recovery time following a short acting beta2-agonist to ≥95% of baseline FEV(1) was significantly shorter (p=0.01) after the withdrawal of the LABA.

CONCLUSIONS

In short-term follow-up, stepping down clinically stable asthmatic children from combination therapy to monotherapy with an ICS does not change airway hyperresponsiveness (AHR) to mannitol but does shorten recovery time to baseline lung function following a rescue short acting beta2-agonist.

Pilot study: The effect of reducing treatment on exercise induced bronchoconstriction

SUMMARY RATIONALE: Asthma therapy should be stepped up or stepped down in response to changes in asthma control. However, there is little evidence available on the optimal timing, sequence, and degree of medication reductions. In this study we analyzed clinically stable asthmatic children who underwent a medication reduction from a combination preparation consisting of an inhaled corticosteroid (ICS) and long acting beta2-agonist (LABA) to monotherapy with the same dose of the ICS. We hypothesized that the extent of exercise-induced bronchoconstriction (EIB) would not increase after the cessation of the LABA.

METHODS

Nineteen children, aged 8-16 years, with clinically stable asthma, receiving LABA/ICS combination therapy, were analyzed in this open-label pilot study. Children performed an exercise challenge at baseline and 3 weeks after the medication reduction. Best values of spirometric measurements of the forced expiratory volume in 1 sec (FEV(1)) were used for statistical calculations.

RESULTS

Maximum percent fall in FEV(1) was significantly lower after 3 weeks of ICS monotherapy (P = 0.03). Eight of 19 children had a >or=15% fall in FEV(1) after exercise at the initial exercise challenge. In this subgroup, maximum percent fall in FEV(1) after the medication reduction was significantly lower (P < 0.01), and in six children it decreased to <15%, indicating they no longer had EIB.

CONCLUSION

In clinically stable asthmatic children on LABA/ICS combination therapy, the cessation of the LABA can reduce and in most cases abolish EIB.

Effect of montelukast or salmeterol added to inhaled fluticasone on exercise-induced bronchoconstriction in children

OBJECTIVES

To evaluate the effect of montelukast, 5 mg, or inhaled salmeterol, 50 microg, added to inhaled fluticasone in reducing the maximum percentage decrease in forced expiratory volume in 1 second (FEV1) after a standardized exercise challenge and response to rescue bronchodilation with albuterol in children aged 6 to 14 years with persistent asthma and exercise-induced bronchoconstriction (EIB).

METHODS

Randomized, double-blind, double-dummy, multicenter, 2-period, 4-week, crossover study conducted between December 22, 2005 and November 14, 2008 at 30 centers in Europe, Asia, Mexico, and South America. Patients with asthma receiving inhaled corticosteroids demonstrated an FEV1 of 70% or higher of the predicted value and EIB (defined as a decrease in FEV1 > or = 15% compared with preexercise baseline FEV1 on 2 occasions before randomization). Standardized exercise challenges were performed at baseline (prerandomization) and at the end of each active treatment period.

RESULTS

Of 154 patients randomized, 145 completed the study. Montelukast, compared with salmeterol, significantly reduced the mean maximum percentage decrease in FEV1 (10.6% vs 13.8%; P = .009), mean area under the curve for the first 20 minutes after exercise (116.0% x min vs 168.8% x min; P = .006), and median time to recovery (6.0 vs 11.1 minutes; P = .04). Response to albuterol rescue after exercise challenge was significantly greater (P < .001) with montelukast. Montelukast and salmeterol were generally well tolerated.

CONCLUSIONS

Attenuation and response of EIB to albuterol rescue after exercise challenge were significantly better with montelukast than with salmeterol after 4 weeks of treatment.

Salmeterol use and risk of hospitalization among emergency department patients with acute asthma

BACKGROUND

The safety of inhaled long-acting beta2-agonists (LABAs) in the treatment of chronic asthma remains controversial and has not been evaluated in emergency department (ED) patients with acute asthma.

OBJECTIVE

To determine whether ED patients undergoing long-term LABA therapy would have increased risk of asthma-related hospitalization compared with those not undergoing LABA therapy and whether concurrent long-term inhaled corticosteroid (ICS) therapy would mitigate this risk.

METHODS

Prospective cohort study of patients aged 12 to 54 years with acute asthma in 115 EDs. Four patient groups were created based on their asthma regimen: no ICS or salmeterol (group A), salmeterol monotherapy (group B), ICS monotherapy (group C), and combination ICS and salmeterol (group D).

RESULTS

Of the 2,236 included patients, group A had 1,221 patients (55%), group B had 48 patients (2%), group C had 787 patients (35%), and group D had 180 patients (8%); 489 patients (22%) required hospitalization. In a multivariable model controlling for 20 factors and using group A as the reference, group B had an increased risk of hospitalization (odds ratio [OR], 2.2; 95% confidence interval [CI], 1.0-4.9), whereas groups C (OR, 1.1; 95% CI, 0.8-1.5) and D (OR, 1.2; 95% CI, 0.8-1.9) did not.

CONCLUSION

Among ED patients with acute asthma, those undergoing salmeterol monotherapy had an increased risk of hospitalization; however, this risk was not seen among patients undergoing combination ICS-salmeterol therapy. Our findings provide data from a unique ED population on clinical response to acute asthma treatment among patients undergoing long-term LABA therapy.

Beta-Adrenergic Agonists

Inhaled β₂-adrenoceptor (β₂-AR) agonists are considered essential bronchodilator drugs in the treatment of bronchial asthma, both as symptoms-relievers and, in combination with inhaled corticosteroids, as disease-controllers. In this article, we first review the basic mechanisms by which the β₂-adrenergic system contributes to the control of airway smooth muscle tone. Then, we go on describing the structural characteristics of β₂-AR and the molecular basis of G-protein-coupled receptor signaling and mechanisms of its desensitization/ dysfunction. In particular, phosphorylation mediated by protein kinase A and β-adrenergic receptor kinase are examined in detail. Finally, we discuss the pivotal role of inhaled β₂-AR agonists in the treatment of asthma and the concerns about their safety that have been recently raised.

[Long-acting beta(2)-adrenoceptor agonists for asthma and COPD]

The introduction of long-acting beta(2)-adrenoceptor agonists such as salmeterol and formoterol has opened new perspectives for the treatment of asthma and, possibly, also COPD. These drugs are particularly useful in bronchial asthma and meet the requirements of several treatment guidelines to combine long-acting bronchodilator therapy with inhaled corticosteroids in patients with persistent asthma. The role of long-acting beta(2)-adrenoceptor agonists for management of COPD is less clear. While effects on lung function will be small, parameters of improved quality of life and exercise tolerance may verify the clinical role of long-acting beta(2)-adrenoceptor agonists for COPD treatment in the future.

Pharmacotherapy of asthma: regular treatment or on demand?

Some studies have raised the question of the need for chronic controller therapy in mild persistent asthma as suggested by international guidelines. Although the Improving Asthma Control (IMPACT) and Beclomethasone plus Salbutamol (BEST) studies suggest that on-demand therapy in some patients with mild persistent asthma achieves a similar degree of asthma control based on symptoms and functional outcomes, the IMPACT study indicates that regular and on-demand therapy is not equivalent for controlling airway inflammation. Persistent airway inflammation might lead to airway remodelling with onset or worsening of symptoms, deterioration in lung function, and reduced response to pharmacological therapy. However, the relationships between chronic airway inflammation and airway remodelling need to be clarified. Choosing the 'right' pharmacological strategy (regular versus on-demand treatment) for asthma control is currently difficult due to the fact that (1) inflammatory outcome measures were not generally incorporated into asthma clinical trials; (2) the relationships between chronic airway inflammation and airway remodelling are largely unknown; (3) current clinical asthma trials that are generally based on symptomatic and functional outcome measures are too short to assess the impact of regular anti-inflammatory therapy on natural history of asthma; (4) asthma is an heterogeneous disease and different phenotypes of asthma patients likely requiring a different therapeutic approach can be identified, even in the same class of asthma severity. Guidelines for asthma management are valuable tools, although they are necessarily based on a strategy directed to the best outcome in a group of patients. Asthma phenotyping is becoming central for asthma management. The issue of regular versus on-demand treatment of intermittent and mild persistent asthma would be better addressed if considered within an individualized approach to asthma management and assessment. Identification of clinical, functional, morphological and biochemical phenotypes of patients with asthma and its clinical implications is likely to lead to a tailored, individualized, pharmacological therapy and asthma management.

A novel breath-actuated integrated vortex spacer device increases relative lung bioavailability of fluticasone/salmeterol in combination

BACKGROUND

Spacer devices facilitate respirable drug delivery. A novel breath-actuated antistatic spacer with integrated vortex chamber (Synchro-Breathe) device has been developed, which is compact,portable and user friendly as compared to conventional spacers which are bulky and cumbersome. The relative bioavailability to the lung of inhaled fluticasone and salmeterol combination is primarily dependent on respirable dose delivery and can be reliably quantified using adrenal suppression and early fall in serum potassium (marker of systemic beta-2 adrenoreceptor response) as surrogate markers for delivered lung dose.

AIMS AND OBJECTIVES

To compare the in vivo relative bioavailability to the lung of Hydrofluoroalkane(HFA) Seretide delivered via Synchro-Breathe (SB); an optimally prepared 750 ml large volume plastic spacer, Volumatic (VM); and conventional Evohaler pMDI (EH).

METHODS

Nineteen healthy volunteers completed the study using a randomised double blind, double dummy crossover design. Single doses of placebo or Seretide HFA 250 (total dose ex-valve: fluticasone 2000 mcg/salmeterol 200 mcg) were administered via SB, VM and EH. Overnight urinary cortisol creatinine (OUCC) and serum potassium (K) were measured at baseline and after each dose as systemic surrogates of relative respirable dose delivery for the fluticasone and salmeterol moieties, respectively.

RESULTS

Significant suppression of OUCC and K occurred from baseline with SB and VM but not EH devices(geometric mean fold suppression, 95% CI, p and arithmetic mean fall mmol/L, 95% CI, respectively); EH:1.51(0.43-1.01), p 1/4 0.06; VM: 2.52(1.57-4.04), p < 0.001; SB: 2.66(1.57-4.49), p < 0.001(equating to 33.8%,60.2% and 62.3% falls, respectively). For K, the falls for EH were 0.09(0.25 to 0.07), p 1/4 0.69; VM: 0.27(0.46 to 0.08), p 1/4 0.003; SB: 0.32(0.53 to 0.11), p 1/4 0.002 (equating to 2.2%, 6.8%, and 8.06% fall,respectively). There were no significant differences between SB and VM.

CONCLUSION

The breath-actuated Synchro-Breathe device was comparable to an optimally prepared Volumatic spacer, and resulted in commensurate improvement in relative lung bioavailability for both fluticasone and salmeterol moieties compared to pMDI.

ultra-long-acting beta2-adrenoceptor agonists: an emerging therapeutic option for asthma and COPD?

There has been a real interest recently in developing once-daily beta(2)-adrenoceptor agonists (ultra-long-acting beta(2)-adrenoceptor agonists [ultra-LABAs]) for treating asthma and chronic obstructive pulmonary disease (COPD) in an attempt to simplify their management, although an increasing amount of convincing data show an association of LABAs with a rise in asthma-related deaths and life-threatening experiences. This paper reviews the effects of different ultra-LABAs that are at varying stages of development. Arformoterol, carmoterol, indacaterol and GSK-159797 are ultra-LABAs that are likely to be introduced into the market before 2010. It is plausible that once-daily dose administration of an LABA will lead to increased convenience for patients, which may also lead to enhancement of adherence, and may have advantages leading to improved overall clinical outcomes in patients with asthma and COPD.

Regulation of mast cells by beta-agonists

The human lung mast cell is known to be a critical effector cell in the mediation of asthma. Activation of the mast cell by allergens and other stimuli leads to the release and generation of a wide variety of autacoids that cause bronchoconstriction, promote inflammation, and may influence airway remodeling. Therefore, the stabilization of mast cells has obvious value in the prevention of asthma. Among the drugs used to treat asthma, only beta-agonists are effective stabilizers of mast cells. Both short- and long-acting beta-agonists are effective against mast cells, but there are differences between agonists regarding the extent of inhibitory activity attained. Consequently, the type of beta-agonist prescribed influences the degree of mast cell stabilization possible. Despite the potential value of attenuating mast cell activity with beta-agonists, this benefit may diminish with time because of the development of tolerance. Both short- and long-acting beta-agonists can induce tolerance to mast cell stabilization, and generally, higher efficacy agonists tend to induce greater levels of tolerance; however, weaker agonists induce greater levels of tolerance than might be expected. Tolerance to the mast-cell-stabilizing effects of beta- agonists may be an issue clinically, because this occurs more readily than tolerance to smooth muscle relaxation. This could lead to a situation in which beta-agonists fail to prevent the release of mediators from mast cells but can still effectively relax airway smooth muscle. The continued ability to bronchodilate could mask the unfavorable consequences of unchecked mediator release from mast cells.

Clinical concerns with inhaled beta2-agonists: adult asthma

Inhaled beta2-agonists, when used regularly, cause subtle but significant worsening of asthma control. Overuse of inhaled beta2-agonists is associated with increased risk of death from asthma in a dose-response fashion. beta2-Agonists enhance airway responses to allergens, including induced airway hyperresponsiveness and induced airway inflammation. This is a plausible explanation for beta2-agonist-worsened asthma control. These direct effects of inhaled beta2-agonists, including increased airway response to allergen, tolerance, etc., may partially explain the association of overuse with asthma death. However, it is probable that the major reason for the association of beta2-agonists overuse and asthma mortality is an indirect effect. Inhaled beta2-agonists are effective relievers and preventers of bronchoconstriction and asthma symptoms but fail to treat the underlying pathogenesis, namely the airway inflammation. Thus, overuse may mask the true asthma severity and result in both an underappreciation and undertreatment of the disease. This would provide a rational explanation for the relationship of inhaled beta2-agonist use and mortality and also would fit the dose-response pattern. Inhaled beta2-agonists should be used exclusively as needed for relief of symptoms and their requirement should be infrequent: the need for excessive doses of beta2-agonists provides a useful marker of asthma (lack of) control.

Long-acting beta2-agonists for chronic asthma in adults and children where background therapy contains varied or no inhaled corticosteroid

BACKGROUND

Asthma is a common respiratory disease among both adults and children and short acting inhaled beta-2 agonists are used widely for 'reliever' bronchodilator therapy. Long acting beta-2 agonists (LABA) were introduced as prospective 'symptom controllers' in addition to inhaled corticosteroid 'preventer' therapy (ICS). In this updated review we have included studies in which patients were either not on ICS as a group, or in which some patients, but not all, were on ICS to complement previous systematic reviews of studies where LABA was given in patients uniformly receiving ICS. We have focussed particularly on serious adverse events, given previous concerns about potential risks, especially of death, from regular beta-2 agonist use.

OBJECTIVES

This review aimed to determine the benefit or detriment on the primary outcome of asthma control with the regular use of LABA compared with placebo, in mixed populations in which only some were taking ICS and in populations not using ICS therapy.

SEARCH STRATEGY

We carried out searches using the Cochrane Airways Group trial register, most recently in October 2005. We searched bibliographies of identified RCTs for additional relevant RCTs and contacted authors of identified RCTs for other published and unpublished studies.

SELECTION CRITERIA

All randomised studies of at least four weeks duration, comparing a LABA given twice daily with a placebo, in chronic asthma. Selection criteria to this updated review have been altered to accommodate recently published Cochrane reviews on combination and addition of LABA to ICS therapy. Studies in which all individuals were uniformly taking ICS were excluded from this review.

DATA COLLECTION AND ANALYSIS

Two reviewers performed data extraction and study quality assessment independently. We contacted authors of studies for missing data.

MAIN RESULTS

Sixty-seven studies (representing 68 experimental comparisons) randomising 42,333 participants met the inclusion criteria. Salmeterol was used as long-acting agent in 50 studies and formoterol fumarate in 17. The treatment period was four to nine weeks in 29 studies, and 12 to 52 weeks in 38 studies. Twenty-four studies did not permit the use of ICS, and forty permitted either inhaled corticosteroid or cromones (in three studies this was unclear). In these studies between 22% and 92% were taking ICS, with a median of 62%. There were significant advantages to LABA treatment compared to placebo for a variety of measurements of airway calibre including morning peak expiratory flow (PEF), evening PEF and FEV1. They were associated with significantly fewer symptoms, less use of rescue medication and higher quality of life scores. This was true whether patients were taking LABA in combination with ICS or not. Findings from SMART (a recently published surveillance study) indicated significant increases in asthma related deaths, respiratory related deaths and combined asthma related deaths and life threatening experiences. The absolute increase in asthma-related mortality was consistent with an increase of around one per 1250 patients treated with LABA for six months, but the confidence intervals are wide (from 700 to 10,000). Post-hoc exploratory subgroups suggested that African-Americans and those not on inhaled corticosteroids were at particular risk for the primary end-point of death or life-threatening asthma event. There was also a suggestion of an increase in exacerbation rate in children. Pharmacologically predicted side effects such as headache, throat irritation, tremor and nervousness were more frequent with LABA treatment.

AUTHORS' CONCLUSIONS

LABA are effective in the control of chronic asthma in the "real-life" subject groups included. However there are potential safety issues which call into question the safety of LABA, particularly in those asthmatics who are not taking ICS, and it is not clear why African-Americans were found to have significant differences in comparison to Caucasians for combined respiratory-related death and life threatening experiences, but not for asthma-related death.