Salmeterol is a competitive antagonist at beta-adrenoceptors mediating inhibition of respiratory burst in guinea-pig eosinophils

Analysis of the Indacaterol-Regulated Transcriptome in Human Airway Epithelial Cells Implicates Gene Expression Changes in the Adverse and Therapeutic Effects of β2-Adrenoceptor Agonists

The contribution of gene expression changes to the adverse and therapeutic effects of β₂-adrenoceptor agonists in asthma was investigated using human airway epithelial cells as a therapeutically relevant target. Operational model-fitting established that the long-acting β₂-adrenoceptor agonists (LABA) indacaterol, salmeterol, formoterol, and picumeterol were full agonists on BEAS-2B cells transfected with a cAMP-response element reporter but differed in efficacy (indacaterol ≥ formoterol > salmeterol ≥ picumeterol). The transcriptomic signature of indacaterol in BEAS-2B cells identified 180, 368, 252, and 10 genes that were differentially expressed (>1.5- to <0.67-fold) after 1-, 2-, 6-, and 18-hour of exposure, respectively. Many upregulated genes (e.g., AREG, BDNF, CCL20, CXCL2, EDN1, IL6, IL15, IL20) encode proteins with proinflammatory activity and are annotated by several, enriched gene ontology (GO) terms, including cellular response to interleukin-1, cytokine activity, and positive regulation of neutrophil chemotaxis The general enriched GO term extracellular space was also associated with indacaterol-induced genes, and many of those, including CRISPLD2, DMBT1, GAS1, and SOCS3, have putative anti-inflammatory, antibacterial, and/or antiviral activity. Numerous indacaterol-regulated genes were also induced or repressed in BEAS-2B cells and human primary bronchial epithelial cells by the low efficacy LABA salmeterol, indicating that this genomic effect was neither unique to indacaterol nor restricted to the BEAS-2B airway epithelial cell line. Collectively, these data suggest that the consequences of inhaling a β₂-adrenoceptor agonist may be complex and involve widespread changes in gene expression. We propose that this genomic effect represents a generally unappreciated mechanism that may contribute to the adverse and therapeutic actions of β₂-adrenoceptor agonists in asthma.

Understanding how long-acting β2 -adrenoceptor agonists enhance the clinical efficacy of inhaled corticosteroids in asthma - an update

In moderate-to-severe asthma, adding an inhaled long-acting β₂ -adenoceptor agonist (LABA) to an inhaled corticosteroid (ICS) provides better disease control than simply increasing the dose of ICS. Acting on the glucocorticoid receptor (GR, gene NR3C1), ICSs promote anti-inflammatory/anti-asthma gene expression. In vitro, LABAs synergistically enhance the maximal expression of many glucocorticoid-induced genes. Other genes, including dual-specificity phosphatase 1(DUSP1) in human airways smooth muscle (ASM) and epithelial cells, are up-regulated additively by both drug classes. Synergy may also occur for LABA-induced genes, as illustrated by the bronchoprotective gene, regulator of G-protein signalling 2 (RGS2) in ASM. Such effects cannot be produced by either drug alone and may explain the therapeutic efficacy of ICS/LABA combination therapies. While the molecular basis of synergy remains unclear, mechanistic interpretations must accommodate gene-specific regulation. We explore the concept that each glucocorticoid-induced gene is an independent signal transducer optimally activated by a specific, ligand-directed, GR conformation. In addition to explaining partial agonism, this realization provides opportunities to identify novel GR ligands that exhibit gene expression bias. Translating this into improved therapeutic ratios requires consideration of GR density in target tissues and further understanding of gene function. Similarly, the ability of a LABA to interact with a glucocorticoid may be suboptimal due to low β₂ -adrenoceptor density or biased β₂ -adrenoceptor signalling. Strategies to overcome these limitations include adding-on a phosphodiesterase inhibitor and using agonists of other Gs-coupled receptors. In all cases, the rational design of ICS/LABA, and derivative, combination therapies requires functional knowledge of induced (and repressed) genes for therapeutic benefit to be maximized.

Why use long acting bronchodilators in chronic obstructive lung diseases? An extensive review on formoterol and salmeterol

Long-acting β2-adrenoceptor agonists, formoterol and salmeterol, represent a milestone in the treatments of chronic obstructive lung diseases. Although no specific indications concerning the choice of one molecule rather than another are provided by asthma and COPD guidelines, they present different pharmacological properties resulting in distinct clinical employment possibilities. In particular, salmeterol has a low intrinsic efficacy working as a partial receptor agonist, while formoterol is a full agonist with high intrinsic efficacy. From a clinical perspective, in the presence of low β2-adrenoceptors availability, like in inflamed airways, a full agonist can maintain its bronchodilatory and non-smooth muscle activities while a partial agonist may be less effective. Furthermore, formoterol presents a faster onset of action than salmeterol. This phenomenon, combined with the molecule safety profile, leads to a prompt amelioration of the symptoms, and allows using this drug in asthma as an "as needed" treatment in patients already on regular treatment. The fast onset of action and the full agonism of formoterol need to be considered in order to select the best pharmacological treatment of asthma and COPD.

Potential mechanisms to explain how LABAs and PDE4 inhibitors enhance the clinical efficacy of glucocorticoids in inflammatory lung diseases

Inhaled glucocorticoids acting via the glucocorticoid receptor are a mainstay treatment option for individuals with asthma. There is a consensus that the remedial actions of inhaled glucocorticoids are due to their ability to suppress inflammation by modulating gene expression. While inhaled glucocorticoids are generally effective in asthma, there are subjects with moderate-to-severe disease in whom inhaled glucocorticoids fail to provide adequate control. For these individuals, asthma guidelines recommend that a long-acting β₂-adrenoceptor agonist (LABA) be administered concurrently with an inhaled glucocorticoid. This so-called “combination therapy” is often effective and clinically superior to the inhaled glucocorticoid alone, irrespective of dose. LABAs, and another class of drug known as phosphodiesterase 4 (PDE4) inhibitors, may also enhance the efficacy of inhaled glucocorticoids in chronic obstructive pulmonary disease (COPD). In both conditions, these drugs are believed to work by elevating the concentration of cyclic adenosine-3',5'-monophosphate (cAMP) in target cells and tissues. Despite the success of inhaled glucocorticoid/LABA combination therapy, it remains unclear how an increase in cAMP enhances the clinical efficacy of an inhaled glucocorticoid. In this report, we provide a state-of-the-art appraisal, including unresolved and controversial issues, of how cAMP-elevating drugs and inhaled glucocorticoids interact at a molecular level to deliver enhanced anti-inflammatory benefit over inhaled glucocorticoid monotherapy. We also speculate on ways to further exploit this desirable interaction. Critical discussion of how these two drug classes regulate gene transcription, often in a synergistic manner, is a particular focus. Indeed, because interplay between glucocorticoid receptor and cAMP signaling pathways may contribute to the superiority of inhaled glucocorticoid/LABA combination therapy, understanding this interaction may provide a logical framework to rationally design these multicomponent therapeutics that was not previously possible.

Corticosteroid insensitivity is reversed by formoterol via phosphoinositide-3-kinase inhibition

BACKGROUND AND PURPOSE

Patients with chronic obstructive pulmonary disease (COPD) show a poor response to corticosteroids, which has been linked to oxidative stress. Here we show that the long-acting β(2) -agonist formoterol (FM) reversed corticosteroid insensitivity under oxidative stress via inhibition of phosphoinositide-3-kinase (PI3K) signalling.

EXPERIMENTAL APPROACH

Responsiveness to corticosteroids dexamethasone (Dex), budesonide (Bud) and fluticasone propionate (FP) was determined, as IC(50) values on TNF-α-induced interleukin 8 release, in U937 monocytic cell line treated with hydrogen peroxide (H(2) O(2) ) or peripheral blood mononuclear cells (PBMCs) from patients with COPD or severe asthma.

KEY RESULTS

PBMCs from severe asthma and COPD were less sensitive to Dex compared with those from healthy subjects. Both FM (10(-9)  M) and salmeterol (SM, 10(-8)  M) reversed Dex insensitivity in severe asthma, but only FM restored Dex sensitivity in COPD. Although H(2) O(2) exposure decreased steroid sensitivity in U937 cells, FM restored responsiveness to Bud and FP while the effects of SM were weaker. Additionally, FM, but not SM, partially inhibited H(2) O(2) -induced PI3Kδ-dependent (PKB) phosphorylation. H(2) O(2) decreased SM-induced cAMP production in U937 cells, but did not significantly affect the response to FM. The reduction of SM effects by H(2) O(2) was reversed by pretreatment with LY294002, a PI3K inhibitor, or IC87114, a PI3Kδ inhibitor.

CONCLUSION AND IMPLICATIONS

FM reversed oxidative stress-induced corticosteroid insensitivity and decreased β(2) adrenoceptor-dependent cAMP production via inhibition of PI3Kδ signalling. FM will be more effective than SM, when combined with corticosteroids, for the treatment of respiratory diseases under conditions of high oxidative stress, such as in COPD.

Formoterol

Inhaled formoterol is a long-acting selective beta2-adrenoceptor agonist, with an onset of action of 5 minutes postdose and a bronchodilator effect that lasts for at least 12 hours. Statistically significant and clinically relevant (>120 ml) improvements in lung function [assessed using standardized/normalized area under the forced expiratory volume in 1 second (FEV1) versus time curve (AUC FEV1)] were observed with inhaled formoterol 12 microg twice daily (the approved dosage in the US) compared with placebo in 12-week and 12-month, randomized, double-blind trials in patients with chronic obstructive pulmonary disease (COPD). The bronchodilator efficacy of formoterol 12 microg twice daily was greater than that of oral slow-release theophylline (individualized dosages) in a 12-month trial or inhaled ipratropium bromide 40 microg four times daily in a 12-week trial. Improvement in AUC FEV1 with formoterol, but not theophylline, compared with placebo was observed in patients with irreversible or poorly-reversible airflow obstruction. Formoterol also significantly improved health-related quality of life compared with ipratropium bromide or placebo and significantly reduced symptoms compared with placebo. Combination therapy with formoterol 12 microg twice daily plus ipratropium bromide 40 microg four times daily was significantly more effective than albuterol (salbutamol) 200 microg four times daily plus the same dosage of ipratropium bromide in a 3-week, randomized, double-blind, double-dummy, crossover trial. Inhaled formoterol was well tolerated in clinical trials. The incidence of investigator-determined drug-related adverse events with inhaled formoterol 12 microg twice daily was similar to that with placebo and inhaled ipratropium bromide 40 microg four times daily but lower than that with oral slow-release theophylline (individualized dosages). Importantly, there were no significant differences between formoterol and placebo or comparator drugs in cardiovascular adverse events in patients with COPD and corrected QT interval values within the normal range. In conclusion, inhaled formoterol improved lung function and health-related quality of life and reduced symptoms relative to placebo in clinical trials in patients with COPD. The drug had greater bronchodilator efficacy than oral slow-release theophylline or inhaled ipratropium bromide and showed efficacy in combination with ipratropium bromide. The adverse events profile (including cardiovascular adverse events) with formoterol was similar to that with placebo. Thus, inhaled formoterol may be considered as a first-line option for the management of bronchoconstriction in patients with COPD who require regular bronchodilator therapy for the management of symptoms.

Formoterol in the management of chronic obstructive pulmonary disease

Bronchodilators represent the hallmark of symptomatic treatment of Chronic Obstructive Pulmonary Disease (COPD). There are four categories of bronchodilators: anticholinergics, methylxanthines, short-acting β₂-agonists, and long-acting β₂-agonists such as formoterol. Significant research has been performed to investigate the efficacy, safety and tolerability of formoterol in the therapeutic field of COPD. Formoterol exhibits a rapid onset of bronchodilation similar to that observed with salbutamol, yet its long bronchodilatory duration is comparable to salmeterol. In addition, formoterol presents with a clear superiority in lung function improvement compared with either ipratropium bromide or oral theophylline, while its efficacy improves when administered in combination with ipratropium. Formoterol has been shown to better reduce dynamic hyperinflation, which is responsible for exercise intolerance and dyspnea in COPD patients, compared with other bronchodilators, whereas it exerts synergistic effect with tiotropium. Moreover, formoterol reduces exacerbations, increases days free of use of rescue medication and improves patients’ quality of life and disease symptoms. Formoterol has a favorable safety profile and is better tolerated than theophylline. Collectively, data extracted from multicenter clinical trials support formoterol as a valid therapeutic option in the treatment of COPD.

Cooperative inhibitory effects of budesonide and formoterol on eosinophil superoxide production stimulated by bronchial epithelial cell conditioned medium

BACKGROUND

Improved asthma control by combinations of inhaled glucocorticosteroids (GCs) and long-acting beta(2)-agonists (LABAs) includes a reduced frequency and severity of exacerbations. In view of the association of exacerbations with increased airway inflammation, the question has arisen as to whether LABAs are able to complement the known anti-inflammatory activity of GCs. To address this, we studied the effects of a LABA, formoterol (FORM), and a GC, budesonide (BUD), alone and in combination, on bronchial epithelial cell-mediated eosinophil superoxide production in vitro.

METHODS

We employed 2 experimental approaches. First, superoxide production by human eosinophils incubated with conditioned medium (CM) from human bronchial epithelial cells cultured for 24 h with vehicle, BUD, FORM or BUD + FORM was measured (Epi/Eos assay). Second, eosinophils were stimulated with vehicle-CM to which the drugs were added (Eos assay). Superoxide production was determined as the superoxide dismutase-inhibitable reduction of ferricytochrome C.

RESULTS

CM increased eosinophil superoxide generation (p < 0.01) and epithelial-derived granulocyte macrophage colony-stimulating factor was the mediator responsible. In both assays, FORM dose-dependently inhibited eosinophil superoxide similarly and in the same concentration range as BUD. The BUD + FORM combination was more effective than BUD alone, and it completely inhibited CM-induced superoxide production in the Epi/Eos assay, suggesting complementary effects of both drugs on bronchial epithelial cells and eosinophils.

CONCLUSIONS

The cooperative, inhibitory effects of BUD and FORM on eosinophils and bronchial epithelial cells, in terms of their effects on eosinophil superoxide production, may represent a possible mechanism for the enhanced anti-inflammatory efficacy of BUD and FORM combination therapy of asthma.

Past, present and future--beta2-adrenoceptor agonists in asthma management

The beta-adrenoceptor agonists (beta-agonists) have been used to relieve bronchoconstriction for at least 5000 years. beta-agonists are based on adrenaline and early forms, such as isoprenaline, Lacked bronchial selectivity and had unpleasant side effects. Modern beta-agonists are more selective for the beta2-adrenoceptors (beta2-receptors) located in bronchial smooth muscle and have less cardiotoxicity. Traditional beta2-adrenoceptor agonists (beta2-agonists), such as salbutamol, terbutaline and fenoterol, were characterised by a rapid onset but relatively short duration of action. While valuable as reliever medication, their short duration gave inadequate night-time relief and limited protection from exercise-induced bronchoconstriction. beta2-agonists with longer durations of action, formoterol and salmeterol, were subsequently discovered or developed. When combined with inhaled corticosteroids they improved lung function, and reduced symptoms and exacerbations more than an increased dose of corticosteroids. However, tolerance to the bronchprotective effects of long-acting beta2-agonists and cross-tolerance to the bronchodilator effects of short-acting beta2-agonists is apparent despite use of inhaled corticosteroids. The role of beta2-receptor polymorphisms in the development of tolerance has yet to be fully determined. Formoterol is unique in having both a long-lasting bronchodilator effect (> 12 h) and a fast onset of action (1-3min from inhalation), making it effective both as maintenance and reliever medication. The recent change in classification from short- and long-acting beta2-agonists to rapid-acting and/or long-acting agents reflects the ongoing evolution of beta2-agonist therapy.

Long-acting beta2-agonists: comparative pharmacology and clinical outcomes

Salmeterol and formoterol are both long-acting beta(2)-adrenoceptor agonists (beta(2)-agonists). They both provide excellent bronchodilating and bronchoprotective effects in patients with asthma but their are some differences between these two long-acting beta(2)-agonists in vitro and in vivo. Formoterol has a greater potency and intrinsic activity than salmeterol, which can become especially apparent at higher doses than that clinically recommended, and in contracted bronchi. Long-term use of long-acting beta(2)-agonists can induce tolerance, which can be partially reversed with corticosteroids. Long-acting beta(2)-agonists have some anti-inflammatory effects in vitro, but data in vivo are less convincing. Compared with doubling the dose of inhaled corticosteroids, the addition of inhaled long-acting beta(2)-agonists to inhaled corticosteroids improves symptom control in patients with asthma and reduces both the exacerbation rate of asthma and hospital admission rate. No enhanced airway responsiveness or loss of perception of dyspnea has been observed with the use of inhaled long-acting beta(2)-agonists. Monotherapy with long-acting beta(2)-agonists is not recommended.

One week treatment with salmeterol does not prevent early and late asthmatic responses and sputum eosinophilia induced by allergen challenge in asthmatics

Salmeterol is an effective long-acting beta(2)-agonist bronchodilator, able to inhibit, as a single dose, asthmatic responses induced by several stimuli including allergen, and the subsequent increase in sputum eosinophilia. Aim of the present study was to investigate whether these effects of salmeterol persisted after 1 week of continuous treatment, or whether a loss of the bronchoprotective effects of salmeterol can occur over time. We investigated in a cross-over double blind placebo-controlled study, the protective effect of 1 week treatment with salmeterol on allergen-induced early and late responses and the associated airway inflammation in 15 atopic asthmatic subjects. Eosinophil percentage and Eosinophil Cationic Protein (ECP) concentration in peripheral blood and in hypertonic saline induced sputum were measured at baseline and 24 h after allergen inhalation. Salmeterol partially inhibited early asthmatic response, but it did not inhibit late asthmatic response in comparison with placebo. Salmeterol did not inhibit also the increase in sputum eosinophils percentage 24 h after allergen inhalation (E%, median: 22.7 and 15%, after placebo and after salmeterol respectively, p=n.s. between two post-allergen sputum samples). Also, the increase in blood eosinophils and both sputum and serum ECP at 24 h after allergen challenge was not affected by salmeterol pre-treatment. In conclusion, 1 week treatment with salmeterol causes a loss of its protective effect on allergen-induced airway bronchoconstriction, and does not prevent the subsequent increase in sputum and serum eosinophilic markers.

Inhibition by fenoterol of human eosinophil functions including beta2-adrenoceptor-independent actions

Agonists at beta2 adrenoceptors are used widely as bronchodilators in treating bronchial asthma. These agents also may have important anti-inflammatory effects on eosinophils in asthma. We examined whether widely prescribed beta2-adrenoceptor agonists differ in ability to suppress stimulus-induced eosinophil effector functions such as superoxide anion (O2-) generation and degranulation. To examine involvement of cellular adhesion in such responses, we also investigated effects of beta2 agonists on cellular adhesion and on CD11b expression by human eosinophils. O2- was measured using chemiluminescence. Eosinophil degranulation and adhesion were assessed by a radioimmunoassay for eosinophil protein X (EPX). CD11b expression was measured by flow cytometry. Fenoterol inhibited platelet-activating factor (PAF)-induced O2- generation by eosinophils significantly more than salbutamol or procaterol. Fenoterol partially inhibited PAF-induced degranulation by eosinophils similarly to salbutamol or procaterol. Fenoterol inhibited phorbol myristate acetate (PMA)-induced O2- generation and degranulation by eosinophils, while salbutamol or procaterol did not. Fenoterol inhibition of PMA-induced O2- generation was not reversed by ICI-118551, a selective beta2-adrenoceptor antagonist. Fenoterol, but not salbutamol or procaterol, significantly inhibited PAF-induced eosinophil adhesion. Fenoterol inhibited O2- generation and degranulation more effectively than salbutamol or procaterol; these effects may include a component involving cellular adhesion. Inhibition also might include a component not mediated via beta2 adrenoceptors.

Alternative mechanisms for long-acting beta(2)-adrenergic agonists in COPD

beta(2)-Adrenergic agonists are commonly used as bronchodilators to treat patients with COPD. In addition to prolonged bronchodilation, long-acting beta(2)-agonists (LABAs) exert other effects that may be of clinical relevance. These include inhibition of airway smooth-muscle cell proliferation and inflammatory mediator release, as well as nonsmooth-muscle effects, such as stimulation of mucociliary transport, cytoprotection of the respiratory mucosa, and attenuation of neutrophil recruitment and activation. This review details the possible alternative mechanisms of action of the LABAs, salmeterol and formoterol, in COPD.

Effect of a single dose of salmeterol on the increase in airway eosinophils induced by allergen challenge in asthmatic subjects

BACKGROUND

The long acting beta2 agonist salmeterol is very effective in preventing asthmatic responses to specific stimuli, and this effect could theoretically be due to some anti-inflammatory property in addition to bronchodilator property.

METHODS

The protective effect of a single dose of salmeterol (50 microg) on allergen induced early and late responses and on the associated airway inflammation was investigated in a double blind, placebo controlled, crossover study in 11 atopic asthmatic subjects. Eosinophil percentages and concentrations of eosinophil cationic protein (ECP) in peripheral blood and in hypertonic saline induced sputum were measured 24 hours after allergen inhalation.

RESULTS

Salmeterol effectively inhibited both early and late asthmatic responses in comparison with placebo. Salmeterol also inhibited the increase in the percentage of eosinophils in the sputum 24 hours after allergen inhalation (median (range) baseline 6% (1-36), after placebo 31% (5-75), after salmeterol 12% (1-63)). However, the increase in both sputum and serum ECP concentrations 24 hours after allergen challenge was not affected by pretreatment with salmeterol.

CONCLUSIONS

A single dose of salmeterol inhibits the allergen induced airway responses and the increase in sputum eosinophils after allergen challenge.

Differential effect of formoterol on adenosine monophosphate and histamine reactivity in asthma

Short-acting beta2-agonists provide greater protection against bronchoconstriction induced by adenosine 5'-monophosphate (AMP) than by direct-acting bronchoconstrictors such as histamine and methacholine. AMP is thought to cause bronchoconstriction via release of mediators from mast cells, which suggests that these drugs stabilize mast cells in vivo. This in vivo property has not yet been demonstrated for long-acting beta2-agonists. We undertook a double-blind, randomized, placebo-controlled, cross-over study to investigate the effects of a single dose of formoterol inhaled via Turbuhaler (12 micrograms) and of albuterol inhaled via Turbuhaler (200 micrograms) on airway responsiveness to AMP and histamine in 16 subjects with mild atopic asthma. Albuterol reduced airway responsiveness to AMP and histamine by 4.1 +/- 0.5 and 3.5 +/- 0.4 doubling doses, respectively. In contrast, formoterol caused a greater protective effect against AMP than against histamine challenge, decreasing airway responsiveness by 6.0 +/- 0.8 and 4.2 +/- 0.4 doubling doses, respectively (p < 0.05). Thus, the long-acting beta2-agonist formoterol appears to have a mast cell-stabilizing effect in vivo in mild asthma.

Signal transduction and activation of the NADPH oxidase in eosinophils

Activation of eosinophil NADPH oxidase and the subsequent release of toxic oxygen radicals has been implicated in the mechanism of parasite killing and inflammation. At present, little is known of the signal transduction pathway that govern agonist-induced activation of the respiratory burst and is the subject of this review. In particular, we focus on the ability of leukotrine B4 to activate the NADPH oxidase in guinea-pig peritoneal eosinophils which can be obtained in sufficient number and purity for detailed biochemical experiments to be performed.

Effects of some anti-asthma drugs on human eosinophil superoxide anions release and degranulation

BACKGROUND

Eosinophil infiltration of bronchial tissues and subsequent release of inflammatory mediators by them are the hallmarks of bronchial asthma but it has not yet been clarified whether anti-asthma drugs affect these cells directly. In this study, we investigated the direct effects of 8 clinically used anti-asthma drugs [salbutamol, salmeterol, theophylline, denbufylline, disodium cromoglycate (DSCG), azelastine, ketotifen and dexamethasone] on superoxide anions (O2-) and eosinophil peroxidase (EPO) release from human blood eosinophils in vitro.

METHODS

Highly purified eosinophils were stimulated for O2- release with platelet-activating factor (PAF) or interleukin-5 (IL-5), while for EPO release complement fragment (C5a) or N-formyl-methionyl-leucyl-phenylalanine (FMLP) was employed. Generated products were assayed by standard techniques.

RESULTS

All the drugs, except ketotifen and dexamethasone, inhibited PAF-induced O2- release in a dose-dependent manner. The IC50 values were 0.7, 5.8, 330, 3,500, 4,200 and 6,250 nM for DSCG, denbufylline, salmeterol, azelastine, salbutamol and theophylline, respectively. On IL-5-induced release, the effects were similar except that salbutamol completely failed to inhibit the release induced by this stimulus. In contrast, EPO release was generally poorly inhibited, especially when the release was induced by C5a. Only theophylline and azelastine (both at 10(-4) M or more) were able to inhibit EPO release by both C5a and FMLP. Salbutamol and, to a lesser extent, salmeterol inhibited FMLP-, but not C5a-induced EPO release, while all the other drugs tested were inactive.

CONCLUSIONS

The results show that some of the anti-asthma drugs, but not all, do exert direct effects on human blood eosinophils but these effects may be stimulus-dependent and by far more pronounced against O2- release than against degranulation.

Comparison of salmeterol and albuterol-induced bronchoprotection against adenosine monophosphate and histamine in mild asthma

Short-acting beta(2)-agonists provide greater protection to bronchoconstriction induced by adenosine-5'-monophosphate (AMP) than does methacholine. Because AMP produces bronchoconstriction through release of mediators from mast cells, and methacholine directly constricts airway smooth muscle, this suggests that beta(2)-agonists stabilize mast cells in vivo. This in vivo property has not been demonstrated with long-acting beta(2)-agonists. We undertook two double-blind, randomized, crossover, placebo-controlled studies to investigate the effects of salmeterol and albuterol on airway responsiveness (AR) to AMP and histamine in patients with mild asthma. In the first study, 19 patients attended on four occasions to inhale salmeterol 50 micrograms or placebo 2 h before challenge with AMP or histamine. In the second study 16 patients (13 of whom had participated in the first study) were studied in a similar fashion but inhaled albuterol 400 micrograms or placebo 30 min prior to challenge. Salmeterol reduced AR to AMP and histamine by 3.4 +/- 0.3 and 3.9 +/- 0.3 doubling doses, respectively (NS). In contrast, albuterol demonstrated a greater protective effect on AMP than on histamine, reducing AR by 5.1 +/- 0.3 and 3.8 +/- 0.2 doubling doses, respectively (p < 0.005). Thus, in contrast to albuterol, salmeterol did not demonstrate mast-cell stabilizing properties in vivo at a time corresponding to maximal bronchodilatation. These findings might be explained by the unique pharmacologic profile of salmeterol in combination with the differential beta(2)-adrenoceptor pharmacology of bronchial mast cells and bronchial smooth muscle.

Salmeterol. A review of its pharmacological properties and clinical efficacy in the management of children with asthma

Salmeterol xinafoate is a selective beta 2-adrenoceptor agonist indicated for the maintenance treatment of adults and children with asthma. When administered as a dry powder or aerosol, salmeterol produces bronchodilation for at least 12 hours and protects against methacholine and exercise-induced bronchoconstriction. Salmeterol is not recommended for the treatment of acute exacerbations of asthma. Recent clinical studies have demonstrated the efficacy and tolerability of inhaled salmeterol in the management of asthma in children. Salmeterol improved symptom control and lung function more effectively than placebo or regularly administered salbutamol. In children who were symptomatic despite regular inhaled corticosteroid therapy, the addition of salmeterol to treatment produced a significant improvement in morning and evening peak expiratory flow and forced expiratory volume in 1 second, and a significant reduction in the incidence of asthma exacerbations compared with placebo. Notably, the long duration of action of salmeterol makes it particularly suitable for the prevention of nocturnal asthma symptoms and exercise-induced asthma (EIA) in children. Current data suggest that salmeterol should not be used as a substitute for corticosteroid therapy in children, but rather as an adjunct to therapy. Thus, salmeterol may be a suitable adjunct to therapy in children with asthma receiving inhaled corticosteroids. In addition, salmeterol also has a potentially important role in the prevention of EIA and nocturnal asthma symptoms.

The effect of salmeterol on human eosinophils is both stimulus- and response-dependent

Salmeterol, a long-acting beta 2-adrenoceptor agonist, also possesses some anti-inflammatory properties, but whether eosinophils are the target of such action has been equivocal. To clarify the direct effect of salmeterol on eosinophil functions, we have studied the effect of the drug on the various responses of purified human eosinophils. Superoxide anions (O2-) release and adherence to fibronectin-coated plastic plates induced by platelet-activating factor (PAF), interleukin-5 (IL-5), leukotriene B4 (LTB4) and phorbol myristate acetate (PMA), as well as degranulation induced by C5a and formyl methionyl leucyl phenylalanine (FMLP), in the presence of cytochalasin B (CB) were studied. In the concentration range 10(-8)-10(-5) M, the drug inhibited PAF- and IL-5-induced O2- release, with an IC50 values of 3.2 +/- 1.2 x 10(-7) M and 2.2 +/- 0.4 x 10(-6) M, respectively, Superoxide anion release by LTB4 was only modestly inhibited while that due to PMA was completely unaffected. On the other hand, eosinophil adherence induced by all the 4 stimuli were significantly inhibited within the same concentration range. On eosinophil degranulation, the drug failed to significantly inhibit the release of eosinophil peroxidase (EPO) induced by either C5a or FMLP. In contrast, beta-hexoseaminidase (beta-HA) release by the same agents was significantly inhibited, the inhibition being more pronounced for FMLP-induced, than C5a-induced release. None of the effects of the drug was reversed by the selective beta 2-adrenoceptor antagonist ICI 118551 at a concentration of 10(-7) M. These results show that salmeterol may have some direct inhibitory effects on human eosinophil functions but that these effects are both stimulus- and response-dependent, and are unlikely to be mediated via beta 2 adrenoceptors.

Effects of salmeterol and terbutaline on IgE-mediated dermal reactions and inflammatory events in skin chambers in atopic patients

The objective of the present study was to investigate the potential of the long-acting beta 2-agonist salmeterol as an inhibitor of various components of IgE-mediated inflammatory in man. For this purpose, we measured gross skin reactivity (diameters of wheal and flare reaction [WFR] and late cutaneous reaction [LCR] as well as inflammatory cells, mediators, and protein in cutaneous suction blister chambers in eight subjects with allergic rhinitis. Blisters were induced, two on each forearm, by gentle suction and heating, and were unroofed 12 h later, after which plastic chambers were placed over the denuded area. The chambers were challenged for 2 h with antihuman IgE (titer 1:10) in the presence and absence of salmeterol or terbutaline. Normal goat IgG served as negative control. Chamber fluids were removed hourly for the first 4 h, and this followed by a 4-h incubation before final collection. Salmeterol (10(-6)M) and terbutaline (10(-5)M) injected intradermally 30 min before, aw well as together with anti-IgE (titer 1:100), inhibited the WFRs by up to 30%. The effect of salmeterol on the ensuing LCR (75% inhibition at 24 h) tended to be more pronounced than the corresponding inhibition by terbutaline. Both salmeterol and terbutaline very effectively inhibited the anti-IgE-induced extravasation of alpha 2-macroglobulin into skin chambers, with a significantly more sustained effect by salmeterol. Interestingly, only terbutaline reduced the histamine release evoked by anti-IgE. With the present experimental design, where both drugs were washed out from the chambers after 2 h, neither drug inhibited recruitment of leukocytes (including eosinophils). Taken together, salmeterol had a more sustained inhibitory effect than terbutaline on indices of IgE-mediated edema formation (late induration and plasma protein extravasation). On the other hand, under the present experimental conditions, salmeterol failed to reduce the histamine release (in contrast to terbutaline), and neither salmeterol nor terbutaline affected the recruitment of leukocytes.

Effects of agents which elevate cyclic AMP on guinea-pig eosinophil homotypic aggregation

1. Eosinophil recruitment and activation in inflamed tissue is thought to play an important role in the pathophysiology of allergic diseases. Experimental evidence suggests that elevating cyclic AMP is an effective means of reducing eosinophil recruitment in vivo and may therefore have therapeutic benefit. In the present study, we have assessed the capacity of cyclic AMP-elevating agents to modulate guinea-pig eosinophil homotypic aggregation, a CD18-dependent process, which may be an important component of eosinophil function in vivo. 2. Prostaglandin E1 (PGE1, 10(-16) to 10(-6) M) inhibited platelet activating-factor (PAF)- and C5a-induced eosinophil aggregation in a concentration-dependent manner. However, PAF-induced responses were more potently and more effectively inhibited by PGE1. The inhibitory effects of PGE1 on PAF-induced aggregation were reversed by pretreatment of eosinophils with the protein kinase A inhibitors H89 and KT5720. 3. The beta 2-adrenoceptor agonists, salbutamol and salmeterol, concentration-dependently inhibited eosinophil aggregation induced by C5a and PAF and, again. PAF-induced responses were more effectively reduced. The inhibitory effect of salmeterol was mediated by beta-adrenoceptors, as assessed by the reversal after pretreatment with propranolol. 4. Rolipram, a selective phosphodiesterase 4 (PDE4) inhibitor, also attenuated PAF- and C5a-induced aggregation and at a low concentration which did not affect aggregation per se, had a synergistic effect with PGE1 and salbutamol to suppress this response. 5. Activation of eosinophils with PAF or C5a induced a small but significant increase in the level of CD18 expression on the eosinophil surface. PGE1 (10(-7) M) decreased PAF- and C5a-induced upregulation of CD18 by 93% and 62%, respectively. 6. These results demonstrate that cyclic AMP-elevating agents effectively inhibit eosinophil aggregation, a CD18-dependent functional response. Because CD18 has been shown to be important for eosinophil recruitment to inflamed tissue in vivo, our findings may be of relevance to the efficacy of cyclic AMP-elevating agents at inhibiting eosinophil trafficking.

Some pharmacodynamic aspects on long-acting beta-adrenoceptor agonists

1. Formoterol and salmeterol are the first members of a new generation of long-acting beta(2)-adrenoceptor agonists for inhalation. The discovery of the long effect duration of formoterol was made by chance, while the development of salmeterol appeared to follow a purposeful research strategy. 2. Preclinical evaluation predictive of the clinical duration of effect of long-acting bronchodilators is not straightforward. Experiments in vitro may give false positive results, while experiments in vivo may show false negative results. 3. Once the principle of a long duration of effect was established, a number of novel long-acting beta(2)-adrenoceptor agonists of various chemical structure have emerged. 4. There are two alternative models for the explanation of the long duration of effect: the exosite binding explaining the mode of action of salmeterol, and the more general diffusion microkinetic model applicable for both formoterol and salmeterol. 5. Long-acting beta-adrenoceptor agonists with a relatively low efficacy like salmeterol may, under certain circumstances, inhibit competitively the relaxing effect of agonists with higher efficacy like formoterol and salbutamol. 6. Like all other beta(2)-adrenoceptor agonists in current clinical use, formoterol and salmeterol comprise racemic mixtures. Only the RR- and R-enantiomers are pharmacologically active. The experimental compounds TA-2005 and picumeterol have been developed as pure RR- and R-enantiomers, respectively.

Involvement of cyclic AMP in the effects of phosphodiesterase IV inhibitors on arachidonate release from mononuclear cells

The effects of selective phosphodiesterase inhibitors, cyclic AMP (cAMP) elevating agents and stable analogues of cyclic nucleotides, on the release of arachidonate induced by N-formyl-Met-Leu-Phe (fMLP) were investigated on human peripheral blood mononuclear cells. The selective phosphodiesterase IV inhibitors, rolipram and Ro 20-1724, and the non-selective phosphodiesterase inhibitor, theophylline, elicited a concentration-dependent inhibition of arachidonate release (EC50 = 1.3 x 10(-6) M, 3.2 x 10(-6) M and 3.7 x 10(-4) M respectively). The selective phosphodiesterase III inhibitor, milrinone (10(-5) M), only caused a slight effect while the phosphodiesterase V inhibitor, zaprinast (10(-5) M), the beta 2-adrenoceptor agonists, salbutamol and fenoterol (10(-5) M), failed to inhibit arachidonate release. Forskolin (10(-5) M) and N6,2'-O- dibutyryladenosine 3':5'-cyclic monophosphate (db-cAMP), 10(-3) M) elicited a moderate inhibition. Forskolin increased the effects of rolipram and Ro 20-1724 (EC50 = 4.5 10(-7) M and 4 x 10(-7) M respectively). Incubation of the cells with rolipram (10(-8) to 10(-5) M), Ro 20-1724 (10(-8) to 10(-5) M, forskolin (10(-5) M) or salbutamol (10(-5) M) alone, induced a moderate increase or no increase at all in intracellular cAMP. However, in the presence of forskolin, rolipram (10(-8) to 10(-6) M) and Ro 20-1724 (10(-8) to 10(-6) M) induced significant and concentration-dependent increase in intracellular levels of cAMP. These results suggest that the potent inhibition of arachidonate release from mononuclear cells by selective phosphodiesterase IV inhibitors may be due to increases in discrete pools of intracellular cAMP.

The interaction between salmeterol and beta 2-adrenoceptor agonists with higher efficacy on guinea-pig trachea and human bronchus in vitro

1. In guinea-pig tracheal preparations precontracted with 1 mumol l-1 carbachol, formoterol, procaterol, fenoterol, salmefamol, salbutamol and terbutaline (in that order of potency) caused a concentration-dependent and almost complete, relaxation. However, under these conditions, the maximum relaxation by salmeterol was approximately 30% of the maximum attainable relaxation. 2. We have therefore explored the ability of salmeterol to inhibit the relaxant response to beta 2-adrenoceptor agonists of different chemical structure and relatively higher efficacy in smooth muscle preparations from guinea-pig trachea and human bronchus. 3. With 1 mumol l-1 salmeterol in the organ bath, the concentration-effect curves for the other agonists were shifted to the right in a variable way by 1.8-2.8 log units, fenoterol and salbutamol being the extremes. 4. When 20 mumol l-1 sulfonterol, another low efficacy beta 2-adrenoceptor agonist, was substituted for salmeterol, the difference in the magnitude of the rightward shift between fenoterol and salbutamol was eliminated. 5. In the human bronchus, formoterol and terbutaline had a higher apparent efficacy than salmeterol. With 1 mumol l-1 salmeterol in the organ bath, the concentration-effect curve for formoterol was shifted 2.7 log units to the right. 6. Salmeterol inhibits, competitively, relaxant responses to beta 2-adrenoceptor agonists with higher efficacy. The degree of inhibition seems to be dependent on the agonist used. This contrasts with results obtained with sulfonterol and suggests that salmeterol interacts with the beta 2-adrenoceptor in a complex way.

Long acting inhaled beta-adrenoceptor agonists the comparative pharmacology of formoterol and salmeterol

Formoterol and salmeterol are chemically distinct, highly selective beta-2-adrenoceptor agonists developed to provide sustained (12h+) relief of airway obstruction in diseases such as asthma. Despite their similar long duration of action, these drugs differ. Formoterol has a faster onset of action in both experimental and clinical tests than that of salmeterol. Salmeterol, but not formoterol, behaves as a beta-adrenoceptor antagonist in some experimental models due to its considerably weaker efficacy at the beta 2-adrenoceptor in vitro although their are no established clinical consequences of this antagonism. Both formoterol and salmeterol display a peculiar "reassertion" behaviour in isolated airway smooth muscle subjected to beta-adrenoceptor antagonism and then washed with antagonist-free buffer. Both formoterol and salmeterol are highly efficient inhibitors of a number of indices of acute inflammatory processes in cells and tissues of human or animal origin. However, neither of these drugs has a proven clinical anti-inflammatory effect in chronic asthma in humans. Surprisingly, recent biophysical studies of formoterol and salmeterol have provided strong evidence that their individual patterns of onset speed, duration of action and "reassertion" are due to a common drug-lipid membrane interaction rather than drug-adrenoceptor interactions. A membrane-drug diffusion microkinetic model is presented to describe these phenomena.

Beta-adrenoceptors on smooth muscle, nerves and inflammatory cells

Although the bronchodilator action of beta 2-adrenoceptor agonists in asthma is largely due to relaxation of airway smooth muscle, these agents have other effects which may contribute to their anti-asthma action. Human airway smooth muscle contains only beta 2-receptors which, when stimulated, stimulate a rise in intracellular cAMP and activation of PKA (protein kinase A), which in turn phosphorylates several cellular proteins, resulting in relaxation. However, beta-agonists also influence membrane K+ channels and induce smooth muscle relaxation without a rise in cAMP, and this mechanism appears to be the major feature of bronchodilatation in asthma. There is also evidence that beta-agonists may modulate neurotransmission in airways via prejunctional receptors on airway nerves, both sensory and motor. Blockade of prejunctional beta 2-receptors in asthma patients may lead to marked rise in acetylcholine release, with severe bronchoconstriction. Although beta-agonists have little or no effect on the chronic inflammatory response which underlies chronic airway hyper-responsiveness, they do inhibit the release of histamine from mast cells in vitro. The presence of beta-receptors has also been detected not only on mast cells but also on eosinophils, macrophages, lymphocytes and neutrophils, but beta-agonists have little or no inhibitory action on the activities of all these cells due to rapid tachyphylaxis.