Rosiglitazone reverses salbutamol-induced β(2) -adrenoceptor tolerance in airway smooth muscle

Therapeutic Approaches for Chronic Obstructive Pulmonary Disease (COPD) Exacerbations

Chronic Obstructive Pulmonary Disease (COPD) is a progressive pulmonary disorder underpinned by poorly reversible airflow resulting from chronic bronchitis or emphysema. The prevalence and mortality of COPD continue to increase. Pharmacotherapy for patients with COPD has included antibiotics, bronchodilators, and anti-inflammatory corticosteroids (but with little success). Oral diseases have long been established as clinical risk factors for developing respiratory diseases. The establishment of a very similar microbiome in the mouth and the lung confirms the oral-lung connection. The aspiration of pathogenic microbes from the oral cavity has been implicated in several respiratory diseases, including pneumonia and chronic obstructive pulmonary disease (COPD). This review focuses on current and future pharmacotherapeutic approaches for COPD exacerbation including antimicrobials, mucoregulators, the use of bronchodilators and anti-inflammatory drugs, modifying epigenetic marks, and modulating dysbiosis of the microbiome.

Drug interaction and chronic obstructive respiratory disorders

Chronic obstructive respiratory disorders uncontrolled by monotherapy should be given combinations of drugs that act by distinct mechanisms of action. The rationale for combining different classes of drugs should be to elicit a synergistic interaction, lower the dose of the single components in the combinations and, thus, reduce the risk of adverse events.

The aim of this systematic review was to investigate the combined effect of drugs acting on human airways, by including studies that used a validated method for assessing the nature of drug interaction.

Current evidence indicates that drug combinations modulating the bronchial contractility induce a synergistic relaxant effect when the individual components are combined at isoeffective concentrations. There are several mechanisms of action underlying drug interactions. Pharmacological research has been directed to elucidate what causes the synergism between long-acting β₂-adrenoceptor (β₂-AR) agonists (LABAs), long-acting muscarinic antagonist (LAMAs), and inhaled corticosteroids (ICS) administered as dual or triple combination. Conversely, the mechanisms behind the additive interaction between phosphodiesterase 3 and 4 inhibitors and LAMAs, and the synergistic interaction between proliferator-activated receptor gamma ligands and β₂ agonists have been only hypothesized. Overall, the synergism elicited by combined drugs for the treatment of chronic respiratory disorders is an effect of class, rather than specific for drug combinations. Optimal synergy can be achieved only when the single agents are combined at isoeffective concentrations, and when monocomponents are given concurrently to reach together the same levels of the bronchial tree.

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Drug interaction should be identified with validated pharmacological models.

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Synergistic efficacy is the rationale for combining drugs for respiratory diseases.

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Synergy is favored when combined agents act by distinct mechanisms of action.

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Optimal synergy is achieved when drugs are combined at isoeffective concentrations.

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Synergy is a class effect and is not specific for single drug combinations.

The future of bronchodilation: looking for new classes of bronchodilators

Available bronchodilators can satisfy many of the needs of patients suffering from airway disorders, but they often do not relieve symptoms and their long-term use raises safety concerns. Therefore, there is interest in developing new classes that could help to overcome the limits that characterise the existing classes.At least nine potential new classes of bronchodilators have been identified: 1) selective phosphodiesterase inhibitors; 2) bitter-taste receptor agonists; 3) E-prostanoid receptor 4 agonists; 4) Rho kinase inhibitors; 5) calcilytics; 6) agonists of peroxisome proliferator-activated receptor-γ; 7) agonists of relaxin receptor 1; 8) soluble guanylyl cyclase activators; and 9) pepducins. They are under consideration, but they are mostly in a preclinical phase and, consequently, we still do not know which classes will actually be developed for clinical use and whether it will be proven that a possible clinical benefit outweighs the impact of any adverse effect.It is likely that if developed, these new classes may be a useful addition to, rather than a substitution of, the bronchodilator therapy currently used, in order to achieve further optimisation of bronchodilation.

Emerging concepts in smooth muscle contributions to airway structure and function: implications for health and disease

Airway structure and function are key aspects of normal lung development, growth, and aging, as well as of lung responses to the environment and the pathophysiology of important diseases such as asthma, chronic obstructive pulmonary disease, and fibrosis. In this regard, the contributions of airway smooth muscle (ASM) are both functional, in the context of airway contractility and relaxation, as well as synthetic, involving production and modulation of extracellular components, modulation of the local immune environment, cellular contribution to airway structure, and, finally, interactions with other airway cell types such as epithelium, fibroblasts, and nerves. These ASM contributions are now found to be critical in airway hyperresponsiveness and remodeling that occur in lung diseases. This review emphasizes established and recent discoveries that underline the central role of ASM and sets the stage for future research toward understanding how ASM plays a central role by being both upstream and downstream in the many interactive processes that determine airway structure and function in health and disease.

Isoproterenol Increases Uncoupling, Glycolysis, and Markers of Beiging in Mature 3T3-L1 Adipocytes

Beta-adrenergic activation stimulates uncoupling protein 1 (UCP1), enhancing metabolic rate. In vitro, most work has studied brown adipocytes, however, few have investigated more established adipocyte lines such as the murine 3T3-L1 line. To assess the effect of beta-adrenergic activation, mature 3T3-L1s were treated for 6 or 48 hours with or without isoproterenol (10 and 100 μM) following standard differentiation supplemented with thyroid hormone (T3; 1 nM). The highest dose of isoproterenol increased lipid content following 48 hours of treatment. This concentration enhanced UCP1 mRNA and protein expression. The increase in UCP1 following 48 hours of isoproterenol increased oxygen consumption rate. Further, coupling efficiency of the electron transport chain was disturbed and an enhancement of glycolytic rate was measured alongside this, indicating an attempt to meet the energy demands of the cell. Lastly, markers of beige adipocytes (protein content of CD137 and gene transcript of CITED1) were also found to be upregulated at 48 hours of isoproterenol treatment. This data indicates that mature 3T3-L1 adipocytes are responsive to isoproterenol and induce UCP1 expression and activity. Further, this finding provides a model for further pharmaceutical and nutraceutical investigation of UCP1 in 3T3-L1s.

Salbutamol inhibits RhoA activation in normal but not in desensitized bronchial smooth muscle cells

OBJECTIVE

This study was aimed at investigating whether the β2 -adrenoceptor agonist, salbutamol, could modulate RhoA activation in normal and homologously desensitized bronchial smooth muscle cells (BSMC).

METHODS

Serum-starved BSMCs were stimulated with the Rho-activating compound calpeptin in the presence or absence of salbutamol, the Epac activator, 8-pCPT-2'-O-Me-cAMP, or the site-selective activator of cAMP-dependent protein kinase A (PKA), 6-Bnz-cAMP. Activated RhoA was assessed by immunocytochemical detection and by RhoA G-LISA assay.

KEY FINDINGS

Stimulation with calpeptin caused translocation of RhoA from cytosol to plasma membrane, a condition required for the functional coupling of RhoA with its cellular targets. Pretreatment with salbutamol 10 μm for 15 min was found to block calpeptin-induced activation of RhoA in normal, but not in homologously desensitized cells. Pretreatment of calpeptin-stimulated BSMC with 8-pCPT-2'-O-Me-cAMP or 6-Bnz-cAMP could reproduce the effect of salbutamol.

CONCLUSIONS

These findings demonstrated that salbutamol inhibits RhoA activation in human BSMC through β2 -adrenoceptor/Epac/PKA pathway. An important pharmacological implication of these finding is the possible contribution of RhoA pathway to the molecular mechanism involved in airway smooth muscle relaxation caused by acute/chronic exposure to β2-adrenoceptor agonists.

Use of a novel one-nostril mask-spacer device to evaluate airway hyperresponsiveness (AHR) in horses after chronic administration of albuterol

Inflammatory airway disease (IAD) is very common in stabled horses. Short-acting beta agonist (SABA) drugs are often used to relieve clinical signs, although long-term exposure to these drugs may result in rebound bronchoconstriction. The purpose of this study was twofold: i) to describe the deposition of radiolabeled drugs using a novel one-nostril design mask-spacer combination with a breath-activated inhaler (BAI), and ii) to determine whether treatment for 10 d with inhaled albuterol using this device would impair the ability of albuterol to prevent bronchospasm during a histamine challenge test. The percentage of radio-aerosol deposited in the total lung was 12.39% ± 5.05%. All study horses demonstrated airway hyperresponsiveness (AHR) before enrollment in the study [mean provocative concentration eliciting 35% increase in delta flow (PC35) < 6 mg/mL histamine]. There was no significant difference in airway hyperresponsiveness to post-albuterol histamine challenge before or after treatment with albuterol. A 10-d treatment with placebo, however, caused a significant increase in airway hyperresponsiveness in all horses (P < 0.001). The results of this study show that the novel mask-spacer device was effective in delivering radiolabeled aerosolized drug to the lung and that delivery of a SABA for 10 d using this device did not result in increased airway hyperresponsiveness.

Synergistic interaction between PPAR ligands and salbutamol on human bronchial smooth muscle cell proliferation

BACKGROUND AND PURPOSE

An important objective in asthma therapy is to prevent the accelerated growth of airway smooth muscle cells which leads to hyperplasia and bronchial hyperreactivity. We investigated the effect of combination of salbutamol and PPARγ agonists on growth factor-stimulated human bronchial smooth muscle cell (BSMC) proliferation.

EXPERIMENTAL APPROACH

Synergism was quantified by the combination index-isobologram method. Assays used here included analyses of growth inhibition, cell viability, DNA fragmentation, gene transcription, cell cycle and protein expression.

KEY RESULTS

The PPARγ gene was highly expressed in BSMC and the protein was identified in cell nuclei. Single-agent salbutamol or PPARγ agonists prevented growth factor-induced human BSMC proliferation within a micromolar range of concentrations through their specific receptor subtypes. Sub-micromolar levels of combined salbutamol-PPARγ agonist inhibited growth by 50% at concentrations from ∼2 to 12-fold lower than those required for each drug alone, without induction of apoptosis or necrosis. Combination treatments also promoted cell cycle arrest at the G1/S transition phase and inhibition of ERK phosphorylation.

CONCLUSIONS AND IMPLICATIONS

The synergistic interaction between PPARγ agonists and β(2) -adrenoceptor agonists on airway smooth muscle cell proliferation highlights the anti-remodelling potential of this combination in chronic lung diseases.

Airway smooth muscle in airway reactivity and remodeling: what have we learned?

It is now established that airway smooth muscle (ASM) has roles in determining airway structure and function, well beyond that as the major contractile element. Indeed, changes in ASM function are central to the manifestation of allergic, inflammatory, and fibrotic airway diseases in both children and adults, as well as to airway responses to local and environmental exposures. Emerging evidence points to novel signaling mechanisms within ASM cells of different species that serve to control diverse features, including 1) [Ca(2+)]i contractility and relaxation, 2) cell proliferation and apoptosis, 3) production and modulation of extracellular components, and 4) release of pro- vs. anti-inflammatory mediators and factors that regulate immunity as well as the function of other airway cell types, such as epithelium, fibroblasts, and nerves. These diverse effects of ASM "activity" result in modulation of bronchoconstriction vs. bronchodilation relevant to airway hyperresponsiveness, airway thickening, and fibrosis that influence compliance. This perspective highlights recent discoveries that reveal the central role of ASM in this regard and helps set the stage for future research toward understanding the pathways regulating ASM and, in turn, the influence of ASM on airway structure and function. Such exploration is key to development of novel therapeutic strategies that influence the pathophysiology of diseases such as asthma, chronic obstructive pulmonary disease, and pulmonary fibrosis.

Protective effect of high-dose montelukast on salbutamol-induced homologous desensitisation in airway smooth muscle

Montelukast (MK) is a potent cysteinyl-leukotriene receptor antagonist that causes dose-related improvements in chronic asthma. We sought to determine whether MK was able to prevent salbutamol-induced tolerance in airway smooth muscle. Homologous β2-adrenoceptor desensitisation models were established in guinea-pigs and in human bronchial smooth muscle cells (BSMC) by chronic salbutamol administration. Characterisation tools included measurement of the response of tracheal smooth muscle tissues to salbutamol, analysis of gene expression and receptor trafficking, evaluation of intracellular cAMP levels and phosphodiesterase (PDE) activity in human bronchial smooth muscle cells. Salbutamol-induced β2-adrenoceptor desensitisation was characterised by β2-agonist hyporesponsiveness (-30%, p < 0.001) in desensitised tracheal smooth muscle, as compared to controls. MK, given intraperitoneally at 5 mg/kg/day for 6 consecutive days, completely restored tissue responsiveness to salbutamol. Prolonged salbutamol treatment significantly decreased cAMP synthesis, induced a complete removal of the β2-adrenoceptor from plasma membrane with a parallel increase in the cytosol and increased PDE4D5 gene transcription and PDE activity in human bronchial smooth muscle cells. In homologously desensitised BSMC, MK 30 μM for 24 h was able to prevent salbutamol subsensitivity and such an effect was associated with inhibition of salbutamol-induced PDE4 activity and restoration of membrane β2-adrenoceptor expression and function. These findings suggest the presence of a favourable interaction between MK and β2-adrenoceptor agonists that might improve the therapeutic index of bronchodilators in patients with chronic respiratory diseases.

Activation of Peroxisome Proliferator-Activated Receptor γ Prolongs Islet Allograft Survival

Exposing donor mice to carbon monoxide (CO) protects transplanted islet allografts from immune rejection after transplantation (referred as the “donor” effect). In an attempt to understand the mechanisms of the donor effect of CO, we found that donor treatment with CO upregulates expression of peroxisome proliferatoractivated receptor γ (PPARγ), a transcriptional regulator, in isolated islets. In this study, we evaluated whether PPARγ contributes to the survival and function of transplanted islets and whether PPARγ mediates the protective effect of CO in a major mismatch islet allogeneic transplantation model. BALB/c (H-2d) islets in which PPARγ activity was induced by its agonists, 15-deoxy-Δ12–14-prostaglandin J2 (15d-PGJ2) or troglitazone were transplanted into C57BL/6 (H-2b) recipients that had been rendered diabetic by streptozotocin (STZ). Blood glucose levels of recipients were monitored to determine the function of transplanted islets. Our data indicated that PPARγ activation in islets led to a high percentage of BALB/c islets survived long-term in C57BL/6 recipients. Activation of PPARγ in the donor suppresses expressions of proinflammatory cytokines including tumor necrosis factor-α (TNF-α) and inducible nitric oxide synthase (iNOS) in transplanted islets. Blocking PPARγ activity by its antagonist, GW9662, abrogated the donor effect of CO in vivo and in vitro. Our data demonstrate that PPARγ plays a critical role in the survival and function of transplanted islets after transplantation in the recipient. The protective effects of CO are at least in part mediated by PPARγ.

PPARγ Ligands Regulate Noncontractile and Contractile Functions of Airway Smooth Muscle: Implications for Asthma Therapy

In asthma, the increase in airway smooth muscle (ASM) can contribute to inflammation, airway wall remodeling and airway hyperresponsiveness (AHR). Targetting peroxisome proliferator-activated receptor γ (PPARγ), a receptor upregulated in ASM in asthmatic airways, may provide a novel approach to regulate these contributions. This review summarises experimental evidence that PPARγ ligands, such as rosiglitazone (RGZ) and pioglitazone (PGZ), inhibit proliferation and inflammatory cytokine production from ASM in vitro. In addition, inhaled administration of these ligands reduces inflammatory cell infiltration and airway remodelling in mouse models of allergen-induced airways disease. PPARγ ligands can also regulate ASM contractility, with acute treatment eliciting relaxation of mouse trachea in vitro through a PPARγ-independent mechanism. Chronic treatment can protect against the loss of bronchodilator sensitivity to β₂-adrenoceptor agonists and inhibit the development of AHR associated with exposure to nicotine in utero or following allergen challenge. Of particular interest, a small clinical trial has shown that oral RGZ treatment improves lung function in smokers with asthma, a group that is generally unresponsive to conventional steroid treatment. These combined findings support further investigation of the potential for PPARγ agonists to target the noncontractile and contractile functions of ASM to improve outcomes for patients with poorly controlled asthma.

Age-related impairment in insulin release: the essential role of β(2)-adrenergic receptor

In this study, we investigated the significance of β(2)-adrenergic receptor (β(2)AR) in age-related impaired insulin secretion and glucose homeostasis. We characterized the metabolic phenotype of β(2)AR-null C57Bl/6N mice (β(2)AR(-/-)) by performing in vivo and ex vivo experiments. In vitro assays in cultured INS-1E β-cells were carried out in order to clarify the mechanism by which β(2)AR deficiency affects glucose metabolism. Adult β(2)AR(-/-) mice featured glucose intolerance, and pancreatic islets isolated from these animals displayed impaired glucose-induced insulin release, accompanied by reduced expression of peroxisome proliferator-activated receptor (PPAR)γ, pancreatic duodenal homeobox-1 (PDX-1), and GLUT2. Adenovirus-mediated gene transfer of human β(2)AR rescued these defects. Consistent effects were evoked in vitro both upon β(2)AR knockdown and pharmacologic treatment. Interestingly, with aging, wild-type (β(2)AR(+/+)) littermates developed impaired insulin secretion and glucose tolerance. Moreover, islets from 20-month-old β(2)AR(+/+) mice exhibited reduced density of β(2)AR compared with those from younger animals, paralleled by decreased levels of PPARγ, PDX-1, and GLUT2. Overexpression of β(2)AR in aged mice rescued glucose intolerance and insulin release both in vivo and ex vivo, restoring PPARγ/PDX-1/GLUT2 levels. Our data indicate that reduced β(2)AR expression contributes to the age-related decline of glucose tolerance in mice.