Modulation of cholinergic responsiveness through the [beta]-adrenoceptor signal transmission pathway in bovine trachealis

Advances in adrenergic receptors for the treatment of chronic obstructive pulmonary disease: 2023 update

INTRODUCTION

Strong scientific evidence and large experience support the use of β2-agonists for the symptomatic alleviation of COPD. Therefore, there is considerable effort in discovering highly potent and selective β2-agonists.

AREAS COVERED

Recent research on novel β2-agonists for the treatment of COPD. A detailed literature search was performed in two major databases (PubMed/MEDLINE and Scopus) up to September 2023."

EXPERT OPINION

Compounds that preferentially activate a Gs- or β-arrestin-mediated signaling pathway via β- adrenoceptors (ARs) are more innovative. Pepducins, which target the intracellular region of β2-AR to modulate receptor signaling output, have the most interesting profile from a pharmacological point of view. They stabilize the conformation of the β2-AR and influence its signaling by interacting with the intracellular receptor-G protein interface. New bifunctional drugs called muscarinic antagonist-β2 agonist (MABA), which have both muscarinic receptor (mAChR) antagonism and β2-agonist activity in the same molecule, are a new opportunity. However, all tested compounds have been shown to act predominantly as mAChR antagonists or β2-agonists. An intriguing idea is to utilize allosteric modulators that bind to β2-ARs at sites different than those bound by orthosteric ligands to augment or reduce the signaling transduced by the orthosteric ligand.

Interactions between glycopyrronium and indacaterol on cholinergic neurotransmission and contractile response in bovine trachealis

BACKGROUND

Muscarinic-receptor antagonists and β-adrenoceptor agonists are used, alone or in combination, as first-line treatment for chronic obstructive pulmonary disease. Both drugs decrease airway smooth muscle tone by post-junctional mechanisms but they may have opposing effects on pre-junctional acetylcholine (ACh)-release.

METHODS

We studied the effects of the muscarinic-receptor antagonist glycopyrronium (GLY), the β-adrenoceptor agonist indacaterol (IND) and their combination on electrically-induced ACh-release and contractile response in isolated bovine trachealis. Data were analyzed by paired t-test and analysis of variance for repeated or independent measures with Newmann-Keuls post-hoc test when appropriate.

RESULTS

GLY 10-8 M decreased contractile response by 19 ± 6% (p = 0.010) without altering ACh-release. GLY 10-7 M and 10-6 M almost abolished contractile responses even if the ACh-release was increased by 27 ± 19% (p < 0.001) and 20 ± 8% (p = 0.004), respectively. IND 10-7 M had no significant effects on contractile response and ACh-release, whereas IND 10-6 M reduced contractile response by 24 ± 12% (p = 0.002) without altering ACh-release. IND 10-5 M decreased contractile response by 51 ± 17% (p < 0.001) and ACh-release by 22 ± 11% (p = 0.004). Co-incubation with GLY 10-8 M and IND 10-7 M did not alter ACh-release but inhibited contractile response by 41 ± 8% (p < 0.001). The latter effect was greater than with GLY 10-8 M, or IND 10-7 M, or IND 10-6 M given separately (p < 0.001 for all). The increment of ACh-release caused by GLY was attenuated by IND 10-5 M, though this did not affect contractile response.

CONCLUSIONS

At equimolar concentration, GLY alone attenuates airway smooth muscle contraction more than IND, despite an increased ACh-release. Combination of GLY with IND at submaximal concentrations has more than additive effect suggesting a synergistic post-junctional effect. Adding GLY to IND provides a greater inhibitory effect on airway smooth muscle contraction than increasing IND concentration.

Pharmacological characterization of the interaction between tiotropium and olodaterol administered at 5:5 concentration-ratio in equine bronchi

Equine airways represent a suitable ex vivo model to study the functional impact of pharmacological treatments on human chronic obstructive pulmonary disorders, such as asthma and chronic obstructive pulmonary disease (COPD). We aimed to characterize the pharmacological interaction between the long-acting muscarinic antagonist (LAMA) tiotropium and the long-acting β₂-agonist (LABA) olodaterol in equine airways. The effect of tiotropium and olodaterol, administered alone and in combination at the ratio of concentrations reproducing ex vivo the concentration-ratio delivered by the currently available fixed-dose combination (FDC) (5:5), was investigated on the cholinergic contractile tone induced by the parasympathetic activation of equine isolated airways. The drug interaction was analysed by using the Bliss Independence and Unified Theory models. Both tiotropium and olodaterol induced a sub-maximal concentration-dependent inhibition of bronchial contractility (E_max: tiotropium 83.6 ± 14.8%, olodaterol 76.9 ± 17.9%; pEC₅₀: tiotropium 8.2 ± 0.5; olodaterol 8.3 ± 0.6). When administered at 5:5 concentration-ratio, tiotropium plus olodaterol completely inhibited the bronchial contractility (E_max 102.7 ± 8.4%; pEC₅₀ 9.0 ± 0.7). Strong synergistic interaction was detected for tiotropium/olodaterol combination (combination index 0.011). When administered at low concentrations, the drug mixture elicited up to 94.6 ± 9.5% effect that was 36.0 ± 8.1% greater than the expected additive effect. The results of this study demonstrate that the co-administration of tiotropium plus olodaterol at 5:5 concentration-ratio leads to synergistic inhibition of equine bronchial contractility when compared with either drug administered alone. These findings suggest that the currently available LABA/LABA FDC may be effective in delivering tiotropium/olodaterol combination at equipotency concentrations of each monocomponent into the lung and, thus, inducing synergistic effect in the airways.

Combination inhaled steroid and long-acting beta₂-agonist in addition to tiotropium versus tiotropium or combination alone for chronic obstructive pulmonary disease

BACKGROUND

The long-acting bronchodilator tiotropium and single-inhaler combination therapy of inhaled corticosteroids and long-acting beta2-agonists (ICS/LABA) are commonly used for maintenance treatment of patients with chronic obstructive pulmonary disease (COPD). Combining these treatments, which have different mechanisms of action, may be more effective than administering the individual components.

OBJECTIVES

To assess relative effects of the following treatments on markers of exacerbations, symptoms, quality of life and lung function in patients with COPD.• Tiotropium plus LABA/ICS versus tiotropium.• Tiotropium plus LABA/ICS versus LABA/ICS.

SEARCH METHODS

We searched the Cochrane Airways Group Specialised Register of Trials (April 2015), ClinicalTrials.gov (www.ClinicalTrials.gov), the World Health Organization (WHO) trials portal and reference lists of relevant articles.

SELECTION CRITERIA

We included parallel, randomised controlled trials (RCTs) lasting three months or longer conducted to compare ICS and LABA combination therapy in addition to inhaled tiotropium versus tiotropium alone or combination therapy alone.

DATA COLLECTION AND ANALYSIS

We independently assessed trials for inclusion, then extracted data on trial quality and outcome results. We contacted study authors to ask for additional information. We collected trial information on adverse effects.

MAIN RESULTS

Tiotropium plus LABA/ICS versus tiotropiumWe included six studies (1902 participants) with low risk of bias that compared tiotropium in addition to inhaled corticosteroid and long-acting beta2-agonist combination therapy versus tiotropium alone. Investigators found no statistically significant differences in mortality between treatments (odds ratio (OR) 1.80, 95% confidence interval (CI) 0.55 to 5.91; two studies; 961 participants), a reduction in all-cause hospitalisations with the use of combined therapy (tiotropium + LABA/ICS) (OR 0.61, 95% CI 0.40 to 0.92; two studies; 961 participants; number needed to treat for an additional beneficial outcome (NNTB) 19.7, 95% CI 10.75 to 123.41). The effect on exacerbations was heterogeneous among trials and was not meta-analysed. Health-related quality of life measured by St. George's Respiratory Questionnaire (SGRQ) showed a statistically significant improvement in total scores with use of tiotropium + LABA/ICS compared with tiotropium alone (mean difference (MD) -3.46, 95% CI -5.05 to -1.87; four studies; 1446 participants). Lung function was significantly different in the combined therapy (tiotropium + LABA/ICS) group, although average benefit with this therapy was small. None of the included studies included exercise tolerance as an outcome.A pooled estimate of these studies did not show a statistically significant difference in adverse events (OR 1.16, 95% CI 0.92 to 1.47; four studies; 1363 participants), serious adverse events (OR 0.86, 95% CI 0.57 to 1.30; four studies; 1758 participants) and pneumonia (Peto OR 1.62, 95% CI 0.54 to 4.82; four studies; 1758 participants). Tiotropium plus LABA/ICS versus LABA/ICSOne of the six studies (60 participants) also compared combined therapy (tiotropium + LABA/ICS) versus LABA/ICS therapy alone. This study was affected by lack of power; therefore results did not allow us to draw conclusions for this comparison.

AUTHORS' CONCLUSIONS

In this update, we found new moderate-quality evidence that combined tiotropium + LABA/ICS therapy compared with tiotropium plus placebo decreases hospital admission. Low-quality evidence suggests an improvement in disease-specific quality of life with combined therapy. However, evidence is insufficient to support the benefit of tiotropium + LABA/ICS for mortality and exacerbations (moderate- and low-quality evidence, respectively). Of note, not all participants enrolled in the included studies would be candidates for triple therapy according to current international guidance.Compared with the use of tiotropium plus placebo, tiotropium + LABA/ICS-based therapy does not increase undesirable effects such as adverse events or serious non-fatal adverse events.

The pharmacological rationale for combining muscarinic receptor antagonists and β-adrenoceptor agonists in the treatment of airway and bladder disease

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Muscarinic receptors increase smooth muscle tone in airways and urinary bladder.

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β-Adrenoceptors relax smooth muscle tone and oppose muscarinic contraction.

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Opposition involves transmitter release, signal transduction and receptor expression.

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This supports the combined use of muscarinic antagonists and β-adrenoceptor agonists.

Muscarinic receptor antagonists and β-adrenoceptor agonists are used in the treatment of obstructive airway disease and overactive bladder syndrome. Here we review the pharmacological rationale for their combination. Muscarinic receptors and β-adrenoceptors are physiological antagonists for smooth muscle tone in airways and bladder. Muscarinic agonism may attenuate β-adrenoceptor-mediated relaxation more than other contractile stimuli. Chronic treatment with one drug class may regulate expression of the target receptor but also that of the opposing receptor. Prejunctional β₂-adrenoceptors can enhance neuronal acetylcholine release. Moreover, at least in the airways, muscarinic receptors and β-adrenoceptors are expressed in different locations, indicating that only a combined modulation of both systems may cause dilatation along the entire bronchial tree. While all of these factors contribute to a rationale for a combination of muscarinic receptor antagonists and β-adrenoceptor agonists, the full value of such combination as compared to monotherapy can only be determined in clinical studies.

Long-acting beta-agonists in the management of chronic obstructive pulmonary disease: current and future agents

Chronic obstructive pulmonary disease (COPD) is characterized by progressive airflow limitation and debilitating symptoms. For patients with moderate-to-severe COPD, long-acting bronchodilators are the mainstay of therapy; as symptoms progress, guidelines recommend combining bronchodilators from different classes to improve efficacy. Inhaled long-acting β2-agonists (LABAs) have been licensed for the treatment of COPD since the late 1990s and include formoterol and salmeterol. They improve lung function, symptoms of breathlessness and exercise limitation, health-related quality of life, and may reduce the rate of exacerbations, although not all patients achieve clinically meaningful improvements in symptoms or health related quality of life. In addition, LABAs have an acceptable safety profile, and are not associated with an increased risk of respiratory mortality, although adverse effects such as palpitations and tremor may limit the dose that can be tolerated. Formoterol and salmeterol have 12-hour durations of action; however, sustained bronchodilation is desirable in COPD. A LABA with a 24-hour duration of action could provide improvements in efficacy, compared with twice-daily LABAs, and the once-daily dosing regimen could help improve compliance. It is also desirable that a new LABA should demonstrate fast onset of action, and a safety profile at least comparable to existing LABAs.A number of novel LABAs with once-daily profiles are in development which may be judged against these criteria. Indacaterol, a LABA with a 24-hour duration of bronchodilation and fast onset of action, is the most advanced of these. Preliminary results from large clinical trials suggest indacaterol improves lung function compared with placebo and other long-acting bronchodilators. Other LABAs with a 24-hour duration of bronchodilation include carmoterol, vilanterol trifenatate and oldaterol, with early results indicating potential for once-daily dosing in humans.The introduction of once-daily LABAs also provides the opportunity to develop combination inhalers of two or more classes of once-daily long-acting bronchodilators, which may be advantageous for COPD patients through simplification of treatment regimens as well as improvements in efficacy. Once-daily LABAs used both alone and in combination with long-acting muscarinic antagonists represent a promising advance in the treatment of COPD, and are likely to further improve outcomes for patients.

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.

Airway smooth muscle as a model for new investigative drugs in asthma

Bronchial asthma as such exists because airway smooth muscle (ASM) contracts excessively in response to various stimuli. After several decades during which research was mainly focused on airway inflammation, increasing attention is now being paid to a possible abnormal behaviour of ASM. Thus, ASM is regarded as a major target for anti-asthma treatments. This review first describes the mechanisms of ASM contraction and airway hyperresponsiveness, through cellular, animal and human models. The developments of new drugs targeting extra and/or intracellular pathway of ASM contraction are discussed.

Positive interaction of the novel beta2-agonist carmoterol and tiotropium bromide in the control of airway changes induced by different challenges in guinea-pigs

This study evaluated the bronchodilating activity of the beta(2)-agonist carmoterol and the muscarinic M(3)-antagonist tiotropium, given intratracheally alone or in combination in anaesthetized artificially ventilated normal and actively sensitized guinea-pigs. Carmoterol (0.3-100pmol) and tiotropium (10-1000pmol) were superfused (0.01ml/min) for 5min before challenges with acetylcholine (20mug/kg i.v.), histamine (10mug/kg i.v.) or ovalbumin (5mg/kg i.v.). Both compounds given alone were markedly active against all the challenges. Tiotropium resulted more effective towards cholinergic challenge and carmoterol was very potent against histamine and ovalbumin-induced reaction, being effective already at 1pmol. In the presence of tiotropium, the bronchodilating activity of carmoterol was significantly augmented. The ED(50) value of carmoterol on the acetylcholine challenge was reduced by about 10 and 28 times (0.1 and 0.3pmol of tiotropium), that on the histamine one by 4.5 and 13 times (1 and 3pmol of tiotropium) and that on the ovalbumin-induced one by 8 and 25 times (10 and 30pmol of tiotropium). A positive interaction was also evident when other parameters were evaluated. The histamine-induced release of thromboxane B(2) was markedly reduced (56%, P<0.001) by combining completely ineffective doses of the two drugs (0.3 and 3pmol for carmoterol and tiotropium, respectively). In ovalbumin-challenged animals the time to death, amounting in control animals to 7.2+/-0.9min, was dose-dependently prolonged up to achieve complete protection from death with combination of 1 and 30pmol of carmoterol and tiotropium, respectively. The favorable interaction between carmoterol and tiotropium can represent a good option in the control of bronchopulmonary diseases marked by an increase of airway resistances.

The functional impact of adding salmeterol and tiotropium in patients with stable COPD

The aim of this double-blind, double-dummy, crossover, randomised, pilot study was to explore the acute effects of adding salmeterol and tiotropium in patients with stable COPD. A total of 20 outpatients with stable COPD were enrolled. Single doses of 18-microg tiotropium, 50-microg salmeterol, and 18-microg tiotropium+ 50-microg salmeterol were given. Serial measurements of forced expiratory volume in 1 s (FEV1) were performed over 24h. The mean maximum increases in FEV1 from pre-dosing value on each of the dosing days were 0.165l (95% CI: 0.098-0.232) for tiotropium, 0.241 l (95% CI: 0.151-0.332) for salmeterol, and 0.290 l (95% CI: 0.228-0.353) for the combination and occurred 4 h after inhalation of tiotropium or salmeterol and 3 h after the combination. At 12h, the mean increases in FEV1 from pre-dosing value were 0.071 l (95% CI: 0.001-0.141; P = 0.047) for tiotropium, 0.069 l (95% CI: 0.018-0.120; P = 0.010) for salmeterol, and 0.108 l (95% CI: 0.047-0.170; P = 0.001) for the tiotropium + salmeterol combination. Only the difference between salmeterol and tiotropium + salmeterol was statistically significant (P = 0.009). At 24h, the mean FEV1 value was still higher than the mean pre-dosing value for tiotropium (0.042 l; 95% CI: -0.012-0.097; P=0.119) and the tiotropium+salmeterol combination (0.051 l; 95% CI: 0.01 5-0.087; P = 0.007), but not for salmeterol alone (-0.013 l; 95% CI: -0.041-0.014; P = 0.324). The FEV1 area under the curve (AUCs0-12h) were 1.657 l (95% CI: 1.152-2.162) for tiotropium, 2.068 (95l CI: 1.385-2.752) for salmeterol, and 2.541 l (95% CI: 1.954-3.129) for tiotropium + salmeterol. Only the difference between tiotropium and the tiotropium +salmeterol combination was statistically significant (P = 0.01). The FEV1 AUCs0-24h were 2.854 l (95% CI: 1.928-3.780) for tiotropium, 2.786 l (95% CI: 1.913-3.660) for salmeterol, and 3.640 l (95% CI: 2.674-4.605) for tiotropium + salmeterol. ALL differences between treatments were not statistically significant (P> 0.05). These results seem to indicate that the use of the tiotropium + salmeterol combination is more efficacious than the single agents alone, but the once-daily administration of the two drugs is inadvisable due to the broncholytic profile of salmeterol.