The effects of leptin on airway smooth muscle responses

Impact of obesity on airway remodeling in asthma: pathophysiological insights and clinical implications

The prevalence of obesity among asthma patients has surged in recent years, posing a significant risk factor for uncontrolled asthma. Beyond its impact on asthma severity and patients' quality of life, obesity is associated with reduced lung function, increased asthma exacerbations, hospitalizations, heightened airway hyperresponsiveness, and elevated asthma-related mortality. Obesity may lead to metabolic dysfunction and immune dysregulation, fostering chronic inflammation characterized by increased pro-inflammatory mediators and adipocytokines, elevated reactive oxygen species, and reduced antioxidant activity. This chronic inflammation holds the potential to induce airway remodeling in individuals with asthma and obesity. Airway remodeling encompasses structural and pathological changes, involving alterations in the airway's epithelial and subepithelial layers, hyperplasia and hypertrophy of airway smooth muscle, and changes in airway vascularity. In individuals with asthma and obesity, airway remodeling may underlie heightened airway hyperresponsiveness and increased asthma severity, ultimately contributing to the development of persistent airflow limitation, declining lung function, and a potential increase in asthma-related mortality. Despite efforts to address the impact of obesity on asthma outcomes, the intricate mechanisms linking obesity to asthma pathophysiology, particularly concerning airway remodeling, remain incompletely understood. This comprehensive review discusses current research investigating the influence of obesity on airway remodeling, to enhance our understanding of obesity's role in the context of asthma airway remodeling.

Mechanistic Links Between Obesity and Airway Pathobiology Inform Therapies for Obesity-Related Asthma

Obesity-related asthma is associated with a high disease burden and a poor response to existent asthma therapies, suggesting that it is a distinct asthma phenotype. The proposed mechanisms that contribute to obesity-related asthma include the effects of the mechanical load of obesity, adipokine perturbations, and immune dysregulation. Each of these influences airway smooth muscle function. Mechanical fat load alters airway smooth muscle stretch affecting airway wall geometry, airway smooth muscle contractility, and agonist delivery; weight loss strategies, including medically induced weight loss, counter these effects. Among the metabolic disturbances, insulin resistance and free fatty acid receptor activation influence distinct signaling pathways in the airway smooth muscle downstream of both the M2 muscarinic receptor and the β2 adrenergic receptor, such as phospholipase C and the extracellular signal-regulated kinase signaling cascade. Medications that decrease insulin resistance and dyslipidemia are associated with a lower asthma disease burden. Leptin resistance is best understood to modulate muscarinic receptors via the neural pathways but there are no specific therapies for leptin resistance. From the immune perspective, monocytes and T helper cells are involved in systemic pro-inflammatory profiles driven by obesity, notably associated with elevated levels of interleukin-6. Clinical trials on tocilizumab, an anti-interleukin antibody, are ongoing for obesity-related asthma. This armamentarium of therapies is distinct from standard asthma medications, and once investigated for its efficacy and safety among children, will serve as a novel therapeutic intervention for pediatric obesity-related asthma. Irrespective of the directionality of the association between asthma and obesity, airway-specific mechanistic studies are needed to identify additional novel therapeutic targets for obesity-related asthma.

Crosstalk between CD4+ T Cells and Airway Smooth Muscle in Pediatric Obesity-related Asthma

Rationale: Pediatric obesity-related asthma is a nonatopic asthma phenotype with high disease burden and few effective therapies. RhoGTPase upregulation in peripheral blood T helper (Th) cells is associated with the phenotype, but the mechanisms that underlie this association are not known. Objectives: To investigate the mechanisms by which upregulation of CDC42 (Cell Division Cycle 42), a RhoGTPase, in Th cells is associated with airway smooth muscle (ASM) biology. Methods: Chemotaxis of obese asthma and healthy-weight asthma Th cells, and their adhesion to obese and healthy-weight nonasthmatic ASM, was investigated. Transcriptomics and proteomics were used to determine the differential effect of obese and healthy-weight asthma Th cell adhesion to obese or healthy-weight ASM biology. Measurements and Main Results: Chemotaxis of obese asthma Th cells with CDC42 upregulation was resistant to CDC42 inhibition. Obese asthma Th cells were more adherent to obese ASM compared with healthy-weight asthma Th cells to healthy-weight ASM. Compared with coculture with healthy-weight ASM, obese asthma Th cell coculture with obese ASM was positively enriched for genes and proteins involved in actin cytoskeleton organization, transmembrane receptor protein kinase signaling, and cell mitosis, and negatively enriched for extracellular matrix organization. Targeted gene evaluation revealed upregulation of IFNG, TNF (tumor necrosis factor), and Cluster of Differentiation 247 (CD247) among Th cell genes, and of Ak strain transforming (AKT), Ras homolog family member A (RHOA), and CD38, with downregulation of PRKCA (Protein kinase C-alpha), among smooth muscle genes. Conclusions: Obese asthma Th cells have uninhibited chemotaxis and are more adherent to obese ASM, which is associated with upregulation of genes and proteins associated with smooth muscle proliferation and reciprocal nonatopic Th cell activation.

From Beneath the Skin to the Airway Wall: Understanding the Pathological Role of Adipose Tissue in Comorbid Asthma-Obesity

This article provides a contemporary report on the role of adipose tissue in respiratory dysfunction. Adipose tissue is distributed throughout the body, accumulating beneath the skin (subcutaneous), around organs (visceral), and importantly in the context of respiratory disease, has recently been shown to accumulate within the airway wall: "airway-associated adipose tissue." Excessive adipose tissue deposition compromises respiratory function and increases the severity of diseases such as asthma. The mechanisms of respiratory impairment are inflammatory, structural, and mechanical in nature, vary depending on the anatomical site of deposition and adipose tissue subtype, and likely contribute to different phenotypes of comorbid asthma-obesity. An understanding of adipose tissue-driven pathophysiology provides an opportunity for diagnostic advancement and patient-specific treatment. As an exemplar, the potential impact of airway-associated adipose tissue is highlighted, and how this may change the management of a patient with asthma who is also obese. © 2023 American Physiological Society. Compr Physiol 13:4321-4353, 2023.

Leptin and Asthma: What Are the Interactive Correlations?

Leptin is an adipokine directly correlated with the proinflammatory obese-associated phenotype. Leptin has been demonstrated to inhibit adipogenesis, promote fat demarcation, promote a chronic inflammatory state, increase insulin sensitivity, and promote angiogenesis. Leptin, a regulator of the immune response, is implicated in the pathology of asthma. Studies involved in the key cell reaction and animal models of asthma have provided vital insights into the proinflammatory role of leptin in asthma. Many studies described the immune cell and related cellular pathways activated by leptin, which are beneficial in asthma development and increasing exacerbations. Subsequent studies relating to animal models support the role of leptin in increasing inflammatory cell infiltration, airway hyperresponsiveness, and inflammatory responses. However, the conclusive effects of leptin in asthma are not well elaborated. In the present study, we explored the general functions and the clinical cohort study supporting the association between leptin and asthma. The main objective of our review is to address the knowns and unknowns of leptin on asthma. In this perspective, the arguments about the different faces of leptin in asthma are provided to picture the potential directions, thus yielding a better understanding of asthma development.

Paucigranulocytic Asthma: Potential Pathogenetic Mechanisms, Clinical Features and Therapeutic Management

Asthma is a heterogeneous disease usually characterized by chronic airway inflammation, in which several phenotypes have been described, related to the age of onset, symptoms, inflammatory characteristics and treatment response. The identification of the inflammatory phenotype in asthma is very useful, since it allows for both the recognition of the asthmatic triggering factor as well as the optimization of treatment The paucigranulocytic phenotype of asthma (PGA) is characterized by sputum eosinophil levels <1−3% and sputum neutrophil levels < 60%. The precise characteristics and the pathobiology of PGA are not fully understood, and, in some cases, it seems to represent a previous eosinophilic phenotype with a good response to anti-inflammatory treatment. However, many patients with PGA remain uncontrolled and experience asthmatic symptoms and exacerbations, irrespective of the low grade of airway inflammation. This observation leads to the hypothesis that PGA might also be either a special phenotype driven by different kinds of cells, such as macrophages or mast cells, or a non-inflammatory phenotype with a low grade of eosinophilic inflammation. In this review, we aim to describe the special characteristics of PGA and the potential therapeutic interventions that could be offered to these patients.

Maternal diabetes promotes offspring lung dysfunction and inflammation in a sex-dependent manner

Exposure to maternal diabetes is increasingly recognized as a risk factor for chronic respiratory disease in children. It is currently unclear, however, whether maternal diabetes affects the lung health of male and female offspring equally. This study characterizes the sex-specific impact of a murine model of diet-induced gestational diabetes (GDM) on offspring lung function and airway inflammation. Female adult mice are fed a high-fat (45% kcal) diet for 6-weeks prior to mating. Control offspring are from mothers fed a low fat (10% kcal) diet. Offspring were weaned and fed a chow diet until 10-weeks of age, at which point lung function was measured and lung lavage was collected. Male, but not female offspring exposed to GDM had increased lung compliance and reduced lung resistance at baseline. Female offspring exposed to GDM displayed increased methacholine reactivity and elevated levels of pro-inflammatory cytokines (e.g. interleukin (IL)-1β, IL-5, and CXCL1) in lung lavage. Female GDM offspring also displayed elevated abundance of matrix metalloproteinases (MMP) within their airways, namely MMP-3 and MMP-8. These results indicate disparate effects of maternal diabetes on lung health and airway inflammation of male and female offspring exposed to GDM. Female mice may be at greater risk of inflammatory lung conditions, such as asthma, while male offspring display changes that more closely align with models of chronic obstructive pulmonary disease. In conclusion, there are important sex-based differences in the impact of maternal diabetes on offspring lung health that could signal differences in future disease risk.

Mediator production and severity of aspirin-induced respiratory reactions: Impact of sampling site and body mass index

BACKGROUND

Patients with aspirin-exacerbated respiratory disease can experience severe reactions during aspirin challenge that are associated with high levels of mast cell mediators. The tissue source and clinical factors contributing to systemic mediator levels are unknown.

OBJECTIVE

To determine the concordance between respiratory tract and systemic inflammatory mediator levels and identify clinical factors associated with these mediators.

METHODS

We performed an oral aspirin challenge in 30 subjects with aspirin-exacerbated respiratory disease. Respiratory symptoms and function, nasal mucosal fluid, blood, and urine were collected at baseline, at the onset of a respiratory reaction and over a 3-hour observation period. Changes in nasal and systemic mediator levels were compared.

RESULTS

Neither tryptase nor leukotriene E₄ levels in nasal fluid correlated with serum tryptase or urinary leukotriene E₄ at baseline or during reactions. We observed no association between the baseline or aspirin-induced change in nasal versus urinary leukotriene E₄ and serum tryptase levels. Body mass index inversely correlated with baseline and aspirin-induced urinary leukotriene E₄, prostaglandin D₂ metabolite, and serum tryptase levels, as well as with aspirin-induced symptoms and respiratory function, but not with nasal mediators.

CONCLUSION

The levels of nasal and systemic aspirin-induced mast cell products are discordant in aspirin-exacerbated respiratory disease. Systemically detected levels are likely derived from mast cells outside of the sinonasal cavity and do not accurately reflect upper respiratory tract production. Increased body mass index decreases systemic mast cell mediator production and reaction severity, supporting a contribution of metabolic regulation in aspirin-induced systemic reactions.

Regulatory Peptides in Asthma

Numerous regulatory peptides play a critical role in the pathogenesis of airway inflammation, airflow obstruction and hyperresponsiveness, which are hallmarks of asthma. Some of them exacerbate asthma symptoms, such as neuropeptide Y and tachykinins, while others have ameliorating properties, such as nociception, neurotensin or β-defensin 2. Interacting with peptide receptors located in the lungs or on immune cells opens up new therapeutic possibilities for the treatment of asthma, especially when it is resistant to available therapies. This article provides a concise review of the most important and current findings regarding the involvement of regulatory peptides in asthma pathology.

PPAR Gamma: From Definition to Molecular Targets and Therapy of Lung Diseases

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor superfamily that regulate the expression of genes related to lipid and glucose metabolism and inflammation. There are three members: PPARα, PPARβ or PPARγ. PPARγ have several ligands. The natural agonists are omega 9, curcumin, eicosanoids and others. Among the synthetic ligands, we highlight the thiazolidinediones, clinically used as an antidiabetic. Many of these studies involve natural or synthetic products in different pathologies. The mechanisms that regulate PPARγ involve post-translational modifications, such as phosphorylation, sumoylation and ubiquitination, among others. It is known that anti-inflammatory mechanisms involve the inhibition of other transcription factors, such as nuclear factor kB(NFκB), signal transducer and activator of transcription (STAT) or activator protein 1 (AP-1), or intracellular signaling proteins such as mitogen-activated protein (MAP) kinases. PPARγ transrepresses other transcription factors and consequently inhibits gene expression of inflammatory mediators, known as biomarkers for morbidity and mortality, leading to control of the exacerbated inflammation that occurs, for instance, in lung injury/acute respiratory distress. Many studies have shown the therapeutic potentials of PPARγ on pulmonary diseases. Herein, we describe activities of the PPARγ as a modulator of inflammation, focusing on lung injury and including definition and mechanisms of regulation, biological effects and molecular targets, and its role in lung diseases caused by inflammatory stimuli, bacteria and virus, and molecular-based therapy.

Leptin receptor stimulation in late pregnant mouse uterine tissue inhibits spontaneous contractions by increasing NO and cGMP

The adipokine, leptin exerts inhibitory effect on both spontaneous and oxytocin-induced contractions in myometrium. However, the mechanisms involved in leptin-induced effect are not clear. In the present study, we studied the altered characteristics of uterine contractions in the presence of leptin and the possible mechanisms of its effect in late pregnant (18.5 day) mouse uterus. We conducted functional, biochemical and molecular biology studies to demonstrate the mechanism of leptin-induced response. Leptin exerted an inhibitory response (E_max 40.5 ± 3.99%) on basal uterine contractions. The extent of inhibition was less than that obtained with known uterine relaxants, salbutamol (E_max103 ± 8.66%) and BRL-37344 (E_max 84.79 ± 8.12%). Leptin-induced uterine response was inhibited by leptin receptor antagonist SHLA and JAK-STAT pathway inhibitor, AG-490. The relaxant response was also subdued by NO-cGMP-PK-G pathway blockers L-NAME, 1400W, ODQ and KT-5823. Further, leptin enhanced the levels of NO and cGMP in uterine tissues. Also, SHLA, AG-490 and a combination of 1400 W and L-NAME prevented leptin-induced increase in NO. Similar effect was observed on cGMP levels in presence of leptin and SHLA. However, leptin did not influence CaCl₂-induced response in potassium-depolarized tissues. We also detected leptin receptor protein in late pregnant mouse uterus located in endometrial luminal epithelium and myometrial layers. Real-time PCR studies revealed significantly higher expression of short forms of the receptor (ObRa and ObRc) in comparison to the long form (ObRb). In conclusion, the results of the present study suggest that leptin inhibits mouse uterine contraction by stimulating short forms of the leptin receptors and activating NO pathway in a JAK-STAT-dependent manner.

The Thousand Faces of Leptin in the Lung

Leptin is a pleotropic hormone known to regulate a wide range of systemic functions, from satiety to inflammation. Increasing evidence has shown that leptin and its receptor (ObR) are not only expressed in adipose tissue but also in several organs, including the lungs. Leptin levels were first believed to be elevated only in the lungs of obese patients, and leptin was suspected to be responsible for obesity-related lung complications. Aside from obesity, leptin displays many faces in the respiratory system, independently of body weight, as this cytokine-like hormone plays important physiological roles, from the embryogenic state to maturation of the lungs and the control of ventilation. The leptin-signaling pathway is also involved in immune modulation and cell proliferation, and its dysregulation can lead to the onset of lung diseases. This review article addresses the thousand faces of leptin and its signaling in the lungs under physiological conditions and in disease.

Leptin induces a contracting effect on guinea pig tracheal smooth muscle via the Ob-R receptor mechanism: novel evidence

The purpose of this study was to explore the potential contracting effect of leptin on isolated guinea pig tracheal smooth muscle (TSM), the possible mechanism, and the impact of epithelium denudation or allergen sensitization, respectively. An in vitro experiment investigated the effect of leptin at a concentration of 250-1000 nmol/L on isolated guinea pig TSM with an intact or denuded epithelium. Ovalbumin and IgE were used to test the impact of active and passive sensitization. The isolated TSM strips were incubated in Krebs solution and aerated with carbogen (95% O₂ and 5% CO₂) via an automated tissue organ bath system (n = 4 for each group). Isometric contractions were recorded digitally using iox2 data acquisition software. The possible mechanism of leptin-induced TSM contraction was examined by preincubation with leptin receptor (Ob-R) antagonist. Leptin had significant concentration-dependent contraction effects on guinea pig TSM (p < 0.05). Epithelium denuding and active or passive sensitization significantly increased the potency of the leptin. Preincubation with a leptin receptor (Ob-R) antagonist significantly reduced the contraction effects, suggesting an Ob-R-mediated mechanism. Leptin had a contracting effect on airway smooth muscles potentiated by either epithelium denuding or sensitization, and the Ob-R mechanism was a possible effect mediator.

Mechanisms and therapeutic strategies for non-T2 asthma

Non-T2 asthma is traditionally defined as asthma without features of T2 asthma. The definition is arbitrary and is generally based on the presence of neutrophils in sputum, or the absence (or normal levels) of eosinophils or other T2 markers in sputum (paucigranulocytic), airway biopsies or in blood. This definition may be imprecise as we gain more knowledge from applying transcriptomics and proteomics to blood and airway samples. The prevalence of non-T2 asthma is also difficult to estimate as most studies are cross-sectional and influenced by concomitant treatment with glucocorticosteroids, and by the presence of recognized or unrecognized airway infections. No specific therapies have shown any clinical benefits in patients with asthma that is associated with a non-T2 inflammatory process. It remains to be seen if such an endotype truly exists and to identify treatments to target that endotype. Meanwhile, identifying intense airway neutrophilia as an indicator of airway infection and airway hyperresponsiveness as an indicator of smooth muscle dysfunction, and treating them appropriately, and not increasing glucocorticosteroids in patients who do not have obvious T2 inflammation, seem reasonable.

Fatty airways: implications for obstructive disease

Epidemiological studies report that overweight or obese asthmatic subjects have more severe disease than those of a healthy weight. We postulated that accumulation of adipose tissue within the airway wall may occur in overweight patients and contribute to airway pathology. Our aim was to determine the relationship between adipose tissue within the airway wall and body mass index (BMI) in individuals with and without asthma.Transverse airway sections were sampled in a stratified manner from post mortem lungs of control subjects (n=15) and cases of nonfatal (n=21) and fatal (n=16) asthma. The relationship between airway adipose tissue, remodelling and inflammation was assessed. The areas of the airway wall and adipose tissue were estimated by point count and expressed as area per mm of basement membrane perimeter (Pbm). The number of eosinophils and neutrophils were expressed as area densities.BMI ranged from 15 to 45 kg·m^-2 and was greater in nonfatal asthma cases (p<0.05). Adipose tissue was identified in the outer wall of large airways (Pbm >6 mm), but was rarely seen in small airways (Pbm <6 mm). Adipose tissue area correlated positively with eosinophils and neutrophils in fatal asthma (Pbm >12 mm, p<0.01), and with neutrophils in control subjects (Pbm >6 mm, p=0.04).These data show that adipose tissue is present within the airway wall and is related to BMI, wall thickness and the number of inflammatory cells. Therefore, the accumulation of airway adipose tissue in overweight individuals may contribute to airway pathophysiology.

Pathobiological mechanisms underlying metabolic syndrome (MetS) in chronic obstructive pulmonary disease (COPD): clinical significance and therapeutic strategies

Chronic obstructive pulmonary disease (COPD) is a major incurable global health burden and is currently the 4th largest cause of death in the world. Importantly, much of the disease burden and health care utilisation in COPD is associated with the management of its comorbidities (e.g. skeletal muscle wasting, ischemic heart disease, cognitive dysfunction) and infective viral and bacterial acute exacerbations (AECOPD). Current pharmacological treatments for COPD are relatively ineffective and the development of effective therapies has been severely hampered by the lack of understanding of the mechanisms and mediators underlying COPD. Since comorbidities have a tremendous impact on the prognosis and severity of COPD, the 2015 American Thoracic Society/European Respiratory Society (ATS/ERS) Research Statement on COPD urgently called for studies to elucidate the pathobiological mechanisms linking COPD to its comorbidities. It is now emerging that up to 50% of COPD patients have metabolic syndrome (MetS) as a comorbidity. It is currently not clear whether metabolic syndrome is an independent co-existing condition or a direct consequence of the progressive lung pathology in COPD patients. As MetS has important clinical implications on COPD outcomes, identification of disease mechanisms linking COPD to MetS is the key to effective therapy. In this comprehensive review, we discuss the potential mechanisms linking MetS to COPD and hence plausible therapeutic strategies to treat this debilitating comorbidity of COPD.

Roles of airway smooth muscle dysfunction in chronic obstructive pulmonary disease

The airway smooth muscle (ASM) plays an indispensable role in airway structure and function. Dysfunction in ASM plays a central role in the pathogenesis of chronic obstructive pulmonary disease (COPD) and contributes to alterations of contractility, inflammatory response, immunoreaction, phenotype, quantity, and size of airways. ASM makes a key contribution in COPD by various mechanisms including altered contractility and relaxation induce by [Ca²⁺]_i, cell proliferation and hypertrophy, production and modulation of extracellular cytokines, and release of pro-and-anti-inflammatory mediators. Multiple dysfunctions of ASM contribute to modulating airway responses to stimuli, remodeling, and fibrosis, as well as influence the compliance of lungs. The present review highlights regulatory roles of multiple factors in the development of ASM dysfunction in COPD, aims to understand the regulatory mechanism by which ASM dysfunctions are initiated, and explores the clinical significance of ASM on alterations of airway structure and function in COPD and development of novel therapeutic strategies for COPD.

Intrauterine Malnutrition Reduced Long Leptin Receptor Isoform Expression and Proinflammatory Cytokine Production in Male Rat Pulmonary Endothelial Cells Stimulated by Lipopolysaccharide

Background/Aims

We have previously shown that low birth weight (LBW) rats exposed to intrauterine malnutrition have an impaired lung inflammatory response and reduced levels of inflammatory mediators; however, circulating leptin levels were not increased. We evaluated long leptin receptor isoform (ObRb) expression in lung endothelial cells from low birth weight rats and examined its role in the production of lipid mediators and cytokines.

Methods

Lung endothelial cells were obtained from normal birth weight (NBW) rats or LBW rats subjected to intrauterine malnutrition. These cells were stimulated with leptin (10 ng/mL), LPS (lipopolysaccharide, 1 μg/mL), or leptin plus LPS. Six hours after stimulation, the production of inflammatory mediators (PGE₂, LTB₄, IL-1β, and IL-6) was evaluated using commercial ELISA kits, and Western blotting was performed to investigate p38MAPK, NF-κB, and ObRb expression.

Results

Leptin increased IL-1β levels in only cells from the NBW group, whereas LPS increased PGE₂ and LTB₄ levels in cells from both groups; leptin addition potentiated lipid mediator production induced by LPS in the NBW group. LPS enhanced the production of IL-1β and IL-6 in only endothelial cells from NBW rats. Leptin receptor expression was decreased (63%) in endothelial cells from LBW rats. None of the stimuli increased NF-κB or p38 signaling pathway expression in cells from LBW rats.

Conclusion

These results suggest that intrauterine malnutrition compromises leptin receptor expression and cytokine production in pulmonary endothelial cells stimulated by LPS; these effects seem to involve the NF-κB and p38MAPK signaling pathways.

Modulation of human airway smooth muscle biology by human adipocytes

Background

Asthma and obesity, two growing epidemics worldwide, may share an underlying causal relationship. Airway hyperresponsiveness (AHR), a defining component of asthma, has been documented in both ‘obese’ animal models and non-asthmatic obese individuals. However, there is a paucity of evidence that obesity-derived factors directly affect human airway smooth muscles (ASM).

Methods

Experiments were designed with primary ASM and adipocytes isolated from the same human tissue explants (n = 6). The modulatory effects of human adipocytes extracted from subcutaneous (extrathoracic) and visceral (intrathoracic) depots, on ASM biology was examined with respect to proliferation, migration, contractility and pro-inflammatory cytokine synthesis.

Results

Adipocyte-conditioned media as well as myocyte-adipocyte co-cultures failed to show any significant changes in the proliferative or migrational properties of the ASM. Adipocyte-conditioned media also had no effect on the contractility or relaxation of bovine tracheal muscle strips. In contrast, there was a moderate yet significant increase of IL-6 and eotaxin release by ASM incubated with adipocyte-conditioned media (P = 0.0035 and P = 0.0067, vs. control, respectively), thereby further consolidating the altered inflammatory state reported for both diseases.

Conclusion

We report, for the first time, that adipocytes from either subcutaneous or visceral depots can trigger an inflammatory state in the ASM, with negligible modulatory effects on hyperplasia, hypertrophy or contractile properties.

Electronic supplementary material

The online version of this article (10.1186/s12931-018-0741-z) contains supplementary material, which is available to authorized users.

Neuropeptides and breathing in health and disease

Regulatory neuropeptides control and regulate breathing in physiological and pathophysiological conditions. While they have been identified in the neurons of major respiratory areas, they can be active not only at the central level, but also at the periphery via chemoreceptors, vagal afferents, or locally within lungs and airways. Some neuropeptides, such as leptin or substance P, are respiratory stimulants; others, such as neurotensin, produce variable effects on respiration depending on the site of application. Some neuropeptides have been implicated in pathological states, such as obstructive sleep apnea or asthma. This article provides a concise review of the possible role and functions of several selected neuropeptides in the process of breathing in health and disease and in lung pathologies.

Pulmonary Function and Sleep Breathing: Two New Targets for Type 2 Diabetes Care

Population-based studies showing the negative impact of type 2 diabetes (T2D) on lung function are overviewed. Among the well-recognized pathophysiological mechanisms, the metabolic pathways related to insulin resistance (IR), low-grade chronic inflammation, leptin resistance, microvascular damage, and autonomic neuropathy are emphasized. Histopathological changes are exposed, and findings reported from experimental models are clearly differentiated from those described in humans. The accelerated decline in pulmonary function that appears in patients with cystic fibrosis (CF) with related abnormalities of glucose tolerance and diabetes is considered as an example to further investigate the relationship between T2D and the lung. Furthermore, a possible causal link between antihyperglycemic therapies and pulmonary function is examined. T2D similarly affects breathing during sleep, becoming an independent risk factor for higher rates of sleep apnea, leading to nocturnal hypoxemia and daytime sleepiness. Therefore, the impact of T2D on sleep breathing and its influence on sleep architecture is analyzed. Finally, the effect of improving some pathophysiological mechanisms, primarily IR and inflammation, as well as the optimization of blood glucose control on sleep breathing is evaluated. In summary, the lung should be considered by those providing care for people with diabetes and raise the central issue of whether the normalization of glucose levels can improve pulmonary function and ameliorate sleep-disordered breathing. Therefore, patients with T2D should be considered a vulnerable group for pulmonary dysfunction. However, further research aimed at elucidating how to screen for the lung impairment in the population with diabetes in a cost-effective manner is needed.

Regulation of human airway smooth muscle cell migration and relevance to asthma

Airway remodelling is an important feature of asthma pathogenesis. A key structural change inherent in airway remodelling is increased airway smooth muscle mass. There is emerging evidence to suggest that the migration of airway smooth muscle cells may contribute to cellular hyperplasia, and thus increased airway smooth muscle mass. The precise source of these cells remains unknown. Increased airway smooth muscle mass may be collectively due to airway infiltration of myofibroblasts, neighbouring airway smooth muscle cells in the bundle, or circulating hemopoietic progenitor cells. However, the relative contribution of each cell type is not well understood. In addition, although many studies have identified pro and anti-migratory agents of airway smooth muscle cells, whether these agents can impact airway remodelling in the context of human asthma, remains to be elucidated. As such, further research is required to determine the exact mechanism behind airway smooth muscle cell migration within the airways, how much this contributes to airway smooth muscle mass in asthma, and whether attenuating this migration may provide a therapeutic avenue for asthma. In this review article, we will discuss the current evidence with respect to the regulation of airway smooth muscle cell migration in asthma.

Cyclooxygenase 2: its regulation, role and impact in airway inflammation

Cyclooxygenase 2 (COX-2: official gene symbol - PTGS2) has long been regarded as playing a pivotal role in the pathogenesis of airway inflammation in respiratory diseases including asthma. COX-2 can be rapidly and robustly expressed in response to a diverse range of pro-inflammatory cytokines and mediators. Thus, increased levels of COX-2 protein and prostanoid metabolites serve as key contributors to pathobiology in respiratory diseases typified by dysregulated inflammation. But COX-2 products may not be all bad: prostanoids can exert anti-inflammatory/bronchoprotective functions in airways in addition to their pro-inflammatory actions. Herein, we outline COX-2 regulation and review the diverse stimuli known to induce COX-2 in the context of airway inflammation. We discuss some of the positive and negative effects that COX-2/prostanoids can exert in in vitro and in vivo models of airway inflammation, and suggest that inhibiting COX-2 expression to repress airway inflammation may be too blunt an approach; because although it might reduce the unwanted effects of COX-2 activation, it may also negate the positive effects. Evidence suggests that prostanoids produced via COX-2 upregulation show diverse actions (and herein we focus on prostaglandin E2 as a key example); these can be either beneficial or deleterious and their impact on respiratory disease can be dictated by local concentration and specific interaction with individual receptors. We propose that understanding the regulation of COX-2 expression and associated receptor-mediated functional outcomes may reveal number of critical steps amenable to pharmacological intervention. These may prove invaluable in our quest towards future development of novel anti-inflammatory pharmacotherapeutic strategies for the treatment of airway diseases.

The ADP antagonist MRS2179 regulates the phenotype of smooth muscle cells to limit intimal hyperplasia

PURPOSE

ADP plays an important part in platelet aggregation by activating P2Y1 and P2Y12 receptors. The ADP antagonist MRS2179 has been used in thrombosis-related treatments but its effects on vein graft (VG) remodeling is undefined. We examined the effect of MRS2179 on VG intimal hyperplasia and explored the mechanism of action.

METHODS

A mouse model of VG transplantation was established. Mice underwent surgery and received MRS2179 by intraperitoneal injection every other day for 3 weeks. VG remodeling was assessed 4-weeks later. Vascular smooth muscle cells (VSMCs) were isolated and treated with MRS2179. The effect of MRS2179 on the proliferation, migration and inflammatory-cytokine expression of VSMCs was also evaluated.

RESULTS

MRS2179 significantly inhibited VSMC proliferation compared with the control group. Significant inhibitory effects of MRS2179 on VSMC migration was observed in two-dimensional and three-dimensional models. The extent of intimal hyperplasia was significantly less in MRS2179 treated mice than in controls. Reduced migration of macrophage was found in MRS2179 treated mice. Expression of the inflammatory cytokines IL-1β and TNF-α was decreased significantly in the MRS2179 treated group. In addition, decreased phosphorylation was found on Akt, Erk1/2 and p38.

CONCLUSIONS

These data demonstrate that MRS2179 inhibits neointima formation in VGs by regulating the proliferation, and migration of VSMCs, macrophage migration, inflammatory-cytokine secretion and related signaling pathway. Our study provides novel insights regarding purinergic signaling in SMCs in vivo. The P2Y1 receptor may serve as a therapeutic target in neointima formation.

Control of respiratory and cardiovascular functions by leptin

Leptin, a peptide hormone produced by adipose tissue, acts in brain centers that control critical physiological functions such as metabolism, breathing and cardiovascular regulation. The importance of leptin for respiratory control is evident by the fact that leptin deficient mice exhibit impaired ventilatory responses to carbon dioxide (CO2), which can be corrected by intracerebroventricular leptin replacement therapy. Leptin is also recognized as an important link between obesity and hypertension. Humans and animal models lacking either leptin or functional leptin receptors exhibit many characteristics of the metabolic syndrome, including hyperinsulinemia, insulin resistance, hyperglycemia, dyslipidemia and visceral adiposity, but do not exhibit increased sympathetic nerve activity (SNA) and have normal to lower blood pressure (BP) compared to lean controls. Even though previous studies have extensively focused on the brain sites and intracellular signaling pathways involved in leptin effects on food intake and energy balance, the mechanisms that mediate the actions of leptin on breathing and cardiovascular function are only beginning to be elucidated. This mini-review summarizes recent advances on the effects of leptin on cardiovascular and respiratory control with emphasis on the neural control of respiratory function and autonomic activity.

A short review of adipokines, smooth muscle and uterine contractility

Obesity is a major health problem worldwide. The prevalence of obesity is increasing in both developed and developing countries. In the UK, for example, 60% of adults are overweight and 25% are obese. Obesity is associated with many pathological complications including respiratory, cardiovascular and endocrine, but it also affects fertility and is associated with many reproductive complications. This has led us and others to investigate links between women with high BMI, pregnancy outcome and uterine function. These studies in turn have led investigators to ask how obesity can have such an impact on reproduction and, as part of this, to consider the role of the adipokines released from adipose tissues. Our focus in this short review is on adipokines and myometrial activity, and for completeness we overview their effects on other smooth muscles. To date four adipokines (leptin, visfatin, apelin and ghrelin) have been investigated and all affect myometrial contractility, but some more potently than others. We consider the possible mechanisms involved in how adipokines may modify uterine contractility, and discuss the potential impact on labor and delivery.

Endocrine regulation of airway contractility is overlooked

Asthma is a prevalent respiratory disorder triggered by a variety of inhaled environmental factors, such as allergens, viruses, and pollutants. Asthma is characterized by an elevated activation of the smooth muscle surrounding the airways, as well as a propensity of the airways to narrow excessively in response to a spasmogen (i.e. contractile agonist), a feature called airway hyperresponsiveness. The level of airway smooth muscle (ASM) activation is putatively controlled by mediators released in its vicinity. In asthma, many mediators that affect ASM contractility originate from inflammatory cells that are mobilized into the airways, such as eosinophils. However, mounting evidence indicates that mediators released by remote organs can also influence the level of activation of ASM, as well as its level of responsiveness to spasmogens and relaxant agonists. These remote mediators are transported through circulating blood to act either directly on ASM or indirectly via the nervous system by tuning the level of cholinergic activation of ASM. Indeed, mediators generated from diverse organs, including the adrenals, pancreas, adipose tissue, gonads, heart, intestines, and stomach, affect the contractility of ASM. Together, these results suggest that, apart from a paracrine mode of regulation, ASM is subjected to an endocrine mode of regulation. The results also imply that defects in organs other than the lungs can contribute to asthma symptoms and severity. In this review, I suggest that the endocrine mode of regulation of ASM contractility is overlooked.

Lungs, bone marrow, and adipose tissue. A network approach to the pathobiology of chronic obstructive pulmonary disease

Patients with chronic obstructive pulmonary disease (COPD) often suffer other concomitant disorders, such as cardiovascular diseases and metabolic disorders, that influence significantly (and independently of lung function) their health status and prognosis. Thus, COPD is not a single organ condition, and disturbances of a complex network of interorgan connected responses occur and modulate the natural history of the disease. Here, we propose a novel hypothesis that considers a vascularly connected network with (1) the lungs as the main external sensor of the system and a major source of "danger signals"; (2) the endothelium as an internal sensor of the system (also a potential target tissue); and (3) two key responding elements, bone marrow and adipose tissue, which produce both inflammatory and repair signals. According to the model, the development of COPD, and associated multimorbidities (here we focus on cardiovascular disease as an important example), depend on the manner in which the vascular connected network responds, adapts, or fails to adapt (dictated by the genetic and epigenetic background of the individual) to the inhalation of particles and gases, mainly in cigarette smoke. The caveats and limitations of the hypothesis, as well as the experimental and clinical research needed to test and explore the proposed model, are also briefly discussed.

Adiponectin, Leptin, and Resistin in Asthma: Basic Mechanisms through Population Studies

Adipokines, factors produced by adipose tissue, may be proinflammatory (such as leptin and resistin) or anti-inflammatory (such as adiponectin). Effects of these adipokines on the lungs have the potential to evoke or exacerbate asthma. This review summarizes basic mechanistic data through population-based and clinical studies addressing the potential role of adipokines in asthma. Augmenting circulating concentrations of adiponectin attenuates allergic airway inflammation and airway hyperresponsiveness in mice. Murine data is supported by human data that suggest that low serum adiponectin is associated with greater risk for asthma among women and peripubertal girls. Further, higher serum total adiponectin may be associated with lower clinical asthma severity among children and women with asthma. In contrast, exogenous administration of leptin results in augmented allergic airway hyperresponsiveness in mice. Alveolar macrophages obtained from obese asthmatics are uniquely sensitive to leptin in terms of their potential to augment inflammation. Consistent with this basic mechanistic data, epidemiologic studies demonstrate that higher serum leptin is associated with greater asthma prevalence and/or severity and that these associations may be stronger among women, postpubertal girls, and prepubertal boys. The role of adipokines in asthma is still evolving, and it is not currently known whether modulation of adipokines may be helpful in asthma prevention or treatment.

Leptin, ghrelin and calprotectin: inflammatory markers in childhood asthma?

Background

Appetite-modulating hormones ghrelin and leptin might be relevant to asthma with their pro-inflammatory effects, and calprotectin has been recognized as a promising marker of inflammation. The purpose of this study was to explore whether asthma, atopy and lung functions has a relation with serum levels of leptin, ghrelin and calprotectin as inflammatory markers in children.

Methods

A cross-sectional study was performed by searching the doctor diagnosed asthma through questionnaires filled in by parents who were phoned, and children were invited to supply fasting blood samples in order to measure serum levels of leptin, ghrelin and calprotectin, and to perform skin prick test and spirometry. Participants were divided into Group 1, children with previous diagnosis of asthma, and Group 2, children without previous diagnosis of asthma.

Results

One thousand and two hundred questionnaires were distributed and 589 of them were returned filled in. Out of 74 children whose parents accepted to participate in the study, 23 were in Group 1 and 51 were in Group 2. There was no statistical difference in serum levels of leptin, ghrelin, calprotectin, forced expiratory volume in one second (FEV₁₎, forced vital capacity (FVC), peak expiratory flow (PEF) , forced expiratory flow between 25 and 75% of vital capacity (FEF_25-75) values , and skin prick test results between the two groups (p values are 0.39, 0.72, 0.5, 0.17, 0.5, 0.27, 0.18, and 0.81 respectively).

Conclusion

In this study the inflammation in asthmatic children could not be shown by using serum leptin, ghrelin and calprotectin levels and this is possibly due to the low number of children with ever asthma and equal skin prick test positivity in both groups. This study is the first study aimed to show the relation between serum calprotectin levels and inflammation in asthma. As this study was a cross-sectional study, further prospectively designed randomized controlled studies are necessary to show the association of these markers and inflammation in asthma.

Adiponectin is associated with dynamic hyperinflation and a favourable response to inhaled glucocorticoids in patients with COPD

OBJECTIVES

Adipokines are protein mediators first described as products of adipose tissue regulating energy metabolism and appetite. Recently, adipokines have also been found to modulate inflammation and smooth muscle cell responses. Therefore we investigated the association of two adipokines, adiponectin and leptin, with the degree of emphysema, pulmonary function, symptoms and glucocorticoid responsiveness in patients with COPD.

METHODS

Plasma adiponectin and leptin levels, spirometry, body plethysmography and symptoms were measured in 43 male COPD patients with smoking history ≥ 20 pack-years, post bronchodilator FEV1/FVC < 0.7 and pulmonary emphysema on HRCT. The measurements were repeated in a subgroup of patients after 4 weeks' treatment with inhaled fluticasone.

RESULTS

In patients with COPD, plasma adiponectin levels correlated positively with airway resistance (Raw) (r = 0.362, p = 0.019) and functional residual capacity (FRC) (r = 0.355, p = 0.046). Furthermore, the baseline adiponectin concentration correlated negatively with the fluticasone induced changes in St George's Respiratory questionnaire (SGRQ) symptom score (r = -0.413, p = 0.040) and in FRC % pred (r = -0.428, p = 0.003), i.e. a higher baseline plasma adiponectin level was associated with more pronounced alleviation of symptoms and dynamic hyperinflation. Plasma leptin levels were not related to the measures of lung function, symptoms or glucocorticoid responsiveness.

CONCLUSIONS

Plasma adiponectin levels were associated with peripheral airway obstruction and dynamic hyperinflation in patients with COPD. A higher adiponectin level predicted more favourable relief of symptoms and hyperinflation during glucocorticoid treatment. Adiponectin may have a role in the COPD pathogenesis; it may also be a biomarker of disease severity and treatment responses in this disease.

Leptin and urinary leukotriene E4 and 9α,11β-prostaglandin F2 release after exercise challenge

BACKGROUND

Leptin-related effects on inflammation and bronchial hyperresponsiveness (BHR) in the human airway have not been demonstrated.

OBJECTIVES

To investigate the relationship between the levels of serum leptin and BHR and urinary leukotriene E4 (LTE4) and 9α,11β-prostaglandin F2 (9α,11β-PGF(2)) release after exercise challenge in asthmatic children.

METHODS

Eighty-six prepubertal children between 6 and 10 years old were enrolled and divided into 4 groups: 19 obese asthmatic children, 25 normal-weight asthmatic children, 21 obese nonasthmatic children, and 21 healthy controls. We measured serum leptin levels and urinary LTE4 and 9α,11β-PGF2 levels in children before and 30 minutes after the exercise challenge.

RESULTS

Serum leptin levels were significantly higher in obese asthmatic children compared with normal-weight asthmatic children. Significant increases in urinary levels of LTE4 and 9α,11β-PGF2 were observed in obese asthmatic children after the exercise challenge. Although smaller than in obese asthmatic children, significant increases in the urinary levels of LTE4 and 9α,11β-PGF2 were also observed in the normal-weight. Asthmatic children Logarithmic serum leptin values were significantly associated with the logarithmic maximum percentage change in forced expiratory volume in 1 second, the logarithmic urinary LTE4 change, and the logarithmic urinary 9α,11β-PGF2 change from baseline to after exercise in both obese and normal-weight asthmatic children.

CONCLUSION

The serum levels of leptin were significantly associated with BHR and urinary LTE4 and 9α,11β-PGF2 release induced by exercise challenge in asthmatic children.

Expression of peroxisome proliferator-activated receptor (PPAR)-α and PPAR-γ in the lung tissue of obese mice and the effect of rosiglitazone on proinflammatory cytokine expressions in the lung tissue

Purpose

We investigated the mRNA levels of peroxisome proliferator-activated receptor (PPAR)-α, PPAR-γ, adipokines, and cytokines in the lung tissue of lean and obese mice with and without ovalbumin (OVA) challenge, and the effect of rosiglitazone, a PPAR-γ agonist.

Methods

We developed 6 mice models: OVA-challenged lean mice with and without rosiglitazone; obese mice with and without rosiglitazone; and OVA-challenged obese mice with and without rosiglitazone. We performed real-time polymerase chain reaction for leptin, leptin receptor, adiponectin, vascular endothelial growth factor (VEGF), tumor necrosis factor (TNF)-α, transforming growth factor (TGF)-β, PPAR-α and PPAR-γ from the lung tissue and determined the cell counts and cytokine levels in the bronchoalveolar lavage fluid.

Results

Mice with OVA challenge showed airway hyperresponsiveness. The lung mRNA levels of PPARα and PPAR-γ increased significantly in obese mice with OVA challenge compared to that in other types of mice and decreased after rosiglitazone administeration. Leptin and leptin receptor expression increased in obese mice with and without OVA challenge and decreased following rosiglitazone treatment. Adiponectin mRNA level increased in lean mice with OVA challenge. Lung VEGF, TNF-α, and TGF-β mRNA levels increased in obese mice with and without OVA challenge compared to that in the control mice. However, rosiglitazone reduced only TGF-β expression in obese mice, and even augmented VEGF expression in all types of mice. Rosiglitazone treatment did not reduce airway responsiveness, but increased neutrophils and macrophages in the bronchoalveolar lavage fluid.

Conclusion

PPAR-α and PPAR-γ expressions were upregulated in the lung tissue of OVA-challenged obese mice however, rosiglitazone treatment did not downregulate airway inflammation in these mice.

Adipokine adiponectin is a potential protector to human bronchial epithelial cell for regulating proliferation, wound repair and apoptosis: comparison with leptin and resistin

Epidemiological data indicate an increasing incidence of asthma in the obese individuals recent decades, while very little is known about the possible association between them. Here, we compared the roles of adipocyte-derived factors, including leptin, adiponectin and resistin on proliferation, wound repair and apoptosis in human bronchial epithelial cells (HBECs) which play an important role in the pathogenesis of asthma. The results showed that exogenous globular adiponectin (gAd) promoted proliferation, cell-cycle and wound repair of HBECs. This effect may be relevant to Ca(2+)/calmodulin signal pathway. Besides, gAd inhibited apoptosis induced by ozone and release of lactate dehydrogenase (LDH) of HBECs via regulated adipoR1 and reactive oxygen species. No effects of leptin or resistin on proliferation, wound repair and apoptosis of HBECs were detectable. These data indicate that airway epithelium is the direct target of gAd which plays an important role in protecting HBECs from mechanical or oxidant injuries and may have therapeutic implications in the treatment of asthma.

Inhibition of leptin regulation of parasympathetic signaling as a cause of extreme body weight-associated asthma

Impaired lung function caused by decreased airway diameter (bronchoconstriction) is frequently observed whether body weight is abnormally high or low. That these opposite conditions affect the airways similarly suggests that the regulation of airway diameter and body weight are intertwined. We show here that, independently of its regulation of appetite, melanocortin pathway, or sympathetic tone, leptin is necessary and sufficient to increase airway diameter by signaling through its cognate receptor in cholinergic neurons. The latter decreases parasympathetic signaling through the M(3) muscarinic receptor in airway smooth muscle cells, thereby increasing airway diameter without affecting local inflammation. Accordingly, decreasing parasympathetic tone genetically or pharmacologically corrects bronchoconstriction and normalizes lung function in obese mice regardless of bronchial inflammation. This study reveals an adipocyte-dependent regulation of bronchial diameter whose disruption contributes to the impaired lung function caused by abnormal body weight. These findings may be of use in the management of obesity-associated asthma.

Leptin, adiponectin, and ghrelin levels in female patients with asthma during stable and exacerbation periods

OBJECTIVE

The mechanisms underlying the relationship between obesity and asthma have not been fully established. Data in the literature suggest that adipose tissue-derived hormones may be implicated. However, no definite conclusions regarding the role of leptin and adiponectin with asthma are available. No studies have examined the role of ghrelin in asthma.

METHODS

We assessed the circulating concentrations of leptin, adiponectin, and ghrelin in 32 postmenopausal stable asthma patients, 37 female asthmatics during exacerbations and 8 weeks later, and 22 controls. We examined the relationship between the three peptides and indexes of pulmonary function, airway inflammation, and atopy.

RESULTS

Stable asthma patients exhibited higher leptin and lower ghrelin concentrations compared with controls. Patients with severe asthma had higher leptin and lower adiponectin levels versus patients with mild to moderate asthma. Both leptin concentrations and leptin/adiponectin ratio served as markers for discriminating asthma patients from controls on the one hand, and severe from mild to moderate asthmatics on the other. Leptin levels were inversely correlated with both FEV(1)/FVC and FEF(25-75) in patients with mild to moderate asthma. Atopic asthma patients had higher leptin concentrations than nonatopic asthma patients. There was a positive correlation between serum leptin and total IgE levels in atopic asthmatics. Finally, serum leptin levels and leptin/adiponectin ratio were significantly increased during asthma exacerbations, while adiponectin and ghrelin levels were significantly decreased.

CONCLUSION

Our findings suggest that leptin, adiponectin, and ghrelin may play a significant role in the pathogenesis of asthma during both stable state and asthma exacerbation, independent of obesity.

Leptin, adiponectin and pulmonary diseases

Adipose tissue produces leptin and adiponectin - energy-regulating adipokines that may also play a role in inflammatory pulmonary conditions, as suggested by some murine studies. Leptin and adiponectin and their respective receptors are expressed in the human lung. The association between systemic or airway leptin and asthma in humans is currently controversial, particularly among adults. The majority of the evidence among children however suggests that systemic leptin may be associated with greater asthma prevalence and severity, particularly among prepubertal boys and peripubertal/postpubertal girls. Systemic and airway leptin concentrations may also be disproportionately higher in chronic obstructive pulmonary disease (COPD) patients, particularly among women, and reflect greater airway inflammation and disease severity. Quite like leptin, the association between systemic and airway adiponectin and asthma in humans is also controversial. Some but not all studies, demonstrate that serum adiponectin concentrations are protective against asthma among premenopausal women and peripubertal girls. On the other hand, serum adiponectin concentrations are inversely associated with asthma severity among boys but positively associated among men. Further, systemic and airway adiponectin concentrations are higher in COPD patients than controls, as demonstrated by case-control studies of men. Systemic adiponectin is also positively associated with lung function in healthy adults but inversely associated with lung function in subjects with COPD. It is therefore possible that pro-inflammatory effects of adiponectin dominate under certain physiologic conditions and anti-inflammatory effects under others. The adipokine-lung disease literature has critical gaps that include a lack of adequately powered longitudinal or weight-intervention studies; inadequate adjustment for confounding effect of obesity; and unclear understanding of potential sex interactions. It is also uncertain whether adipokine derangements precede pulmonary disease or are a consequence of it. Future research will determine whether modulation of adipokines, independent of BMI, may allow novel ways to prevent or treat inflammatory pulmonary conditions.

Reduction in the leptin concentration as a predictor of improvement in lung function in obese adolescents

OBJECTIVE

To assess the effects of weight loss on adipokines, asthma-related symptoms, exercise-induced bronchospasm (EIB) and lung function, and to evaluate the role of leptin and adiponectin levels on lung function after treatment in obese adolescents.

METHODS

84 postpubertal obese adolescents were enrolled and distributed in quartiles according to weight loss (low (<2.5 kg), low to moderate (>2.5 and <8 kg), moderate (<8 and <14 kg) and massive (<14 kg)). Body composition was measured by plethysmography, and visceral and subcutaneous fat were detected by ultrasound. Serum levels of adiponectin and leptin were analyzed. Lung function, asthma and EIB were evaluated according to the American Thoracic Society criteria. Patients were submitted to 1 year of interdisciplinary intervention consisting of physiotherapy, medical, nutritional, exercise, and psychological therapy.

RESULTS

After treatment the moderate and massive weight loss promoted an increase in adiponectin and adiponectin/leptin (A/L) ratio as well as a decrease in leptin levels and a reduction in EIB frequency and asthma-related symptoms. Furthermore, the reduction in leptin levels was a predictor factor to improvement in lung function.

CONCLUSION

Interdisciplinary therapy was able to decrease EIB and asthma-related symptoms and to improve pro/anti-inflammatory adipokines. Additionally, the leptin concentration was a predictor factor to explain changes in lung function.

Toward understanding the role of leptin and leptin receptor antagonism in preclinical models of rheumatoid arthritis

A potential link between obesity, circulating leptin levels and autoimmune disease symptoms suggests that targeting the leptin receptor (ObR) might be a viable novel strategy to combat rheumatoid arthritis (RA). However, studies in animal models and evaluation of clinical cases did not provide clear view on leptin's involvement in RA. To validate ObR as RA target, we used our peptide-based ObR agonists and antagonist in different in vitro and in vivo models of the disease. In human peripheral blood mononuclear cells, leptin and its agonist fragment, desI(2)-E1/Aca, moderately induced constitutive activation of a major proinflammatory transcription factor, NF-κB, while the ObR antagonist peptide Allo-aca inhibited the process. Leptin administration itself did not induce arthritis in rats, but worsened the clinical condition of mice given K/BxN serum transfer arthritis. Simultaneous administration of Allo-aca reduced leptin-dependent increase in disease severity by more than 50%, but the antagonist was ineffective when injected with a 3-day delay. In rats inflicted with mild adjuvant-induced arthritis, both leptin and Allo-aca reduced the extent of joint swelling and the number of arthritic joints. In a more aggressive disease stage, Allo-aca decreased the number of arthritic joints in a dose-dependent manner but did not affect other arthritis markers. In summary, leptin exerts diverse effects on RA depending on the experimental model. This might reflect the heterogeneous character of RA, which is differently impacted by leptin and is unmasked by ObR antagonism. Nevertheless, the results suggest that ObR antagonists might become useful therapeutics in leptin-sensitive early stages of RA.

Does airway smooth muscle express an inflammatory phenotype in asthma?

In addition to hyperresponsiveness in asthma, airway smooth muscle (ASM) also manifests an inflammatory phenotype characterized by augmented expression of mediators that enhance inflammation, contribute to tissue remodelling and augment leucocyte trafficking and activity. Our present review summarizes contemporary understanding of ASM-derived mediators and their paracrine and autocrine actions in airway diseases.

Identification of the nasal mucosa as a new target for leptin action

The aim of this study was to examine systemic and local nasal leptin and leptin receptor expression in patients with nasal polyposis and healthy controls.

METHODS AND RESULTS

Serum leptin and soluble leptin receptor levels were examined by enzyme-linked immunosorbent assay (ELISA). The presence of leptin and leptin receptor mRNA was investigated using reverse transcriptase-polymerase chain reaction (RT-PCR), and tissue leptin and leptin receptor protein expression was analysed by immunohistochemistry and ELISA. Serum levels of biologically active leptin were significantly elevated in patients with nasal polyps compared with control subjects. These serum leptin levels were strongly correlated with the levels found in tissue in both study groups, although leptin was not significantly elevated in nasal polyp tissue. Using RT-PCR, we showed that both leptin and its receptors were produced in nasal mucosa. Finally, immunohistochemistry showed that leptin and leptin receptor protein were expressed in several cells of the normal and inflamed nasal mucosa.

CONCLUSIONS

Leptin receptors and their biological ligand leptin are expressed in the nasal mucosa, suggesting a possible role in upper airway immunology.

The role of leptin in the respiratory system: an overview

Since its cloning in 1994, leptin has emerged in the literature as a pleiotropic hormone whose actions extend from immune system homeostasis to reproduction and angiogenesis. Recent investigations have identified the lung as a leptin responsive and producing organ, while extensive research has been published concerning the role of leptin in the respiratory system. Animal studies have provided evidence indicating that leptin is a stimulant of ventilation, whereas researchers have proposed an important role for leptin in lung maturation and development. Studies further suggest a significant impact of leptin on specific respiratory diseases, including obstructive sleep apnoea-hypopnoea syndrome, asthma, COPD and lung cancer. However, as new investigations are under way, the picture is becoming more complex. The scope of this review is to decode the existing data concerning the actions of leptin in the lung and provide a detailed description of leptin's involvement in the most common disorders of the respiratory system.

Onset of obesity in carboxypeptidase E-deficient mice and effect on airway responsiveness and pulmonary responses to ozone

When compared with lean, wild-type mice, obese Cpefat mice, 14 wk of age and older, manifest innate airway hyperresponsiveness (AHR) to intravenous methacholine and enhanced pulmonary inflammation following acute exposure to ozone (O3). The purpose of this study was to examine the onset of these augmented pulmonary responses during the onset of obesity. Thus airway responsiveness and O3-induced pulmonary inflammation and injury were examined in 7- and 10-wk-old Cpefat and age-matched, wild-type, C57BL/6 mice. Compared with age-matched controls, 7- and 10-wk-old Cpefat mice were approximately 25 and 61% heavier, respectively. Airway responsiveness to intravenous methacholine was assessed via forced oscillation in unexposed Cpefat and wild-type mice. The 10- but not 7-wk-old Cpefat mice exhibited innate AHR. O3 exposure (2 ppm for 3 h) increased markers of pulmonary inflammation and injury in the bronchoalveolar lavage fluid of all mice. However, most markers were greater in Cpefat vs. wild-type mice, regardless of age. Serum levels of leptin, a satiety hormone and proinflammatory cytokine, were increased in Cpefat vs. wild-type mice of both age groups, but the serum levels of other systemic inflammatory markers were greater only in 10-wk-old Cpefat vs. wild-type mice. These results demonstrate that a 25% increase in body weight is sufficient to augment pulmonary responses to O3, but innate AHR is not manifest until the mice become much heavier. These results suggest that the mechanistic bases for these responses are different and may develop according to the nature and degree of the chronic systemic inflammation that is present.

Obesity, adipokines, and lung disease

This review summarizes the state of the current literature relating to the associations of lung disease on obesity and adipokines (proteins produced by adipose tissue) in humans. Obesity is an independent risk factor for asthma. Recent studies suggest that obesity is also an independent risk factor for chronic airflow obstruction, as is seen with chronic obstructive pulmonary disease (COPD). The mechanistic basis for these associations in humans is not established, although a possible role for adipokines has been invoked. Leptin, a proinflammatory adipokine, and adiponectin, an anti-inflammatory adipokine, are causally associated with asthma in mice. Although human studies are currently inconclusive, high-serum leptin and low-serum adiponectin concentrations predict asthma, independent of obesity, in select population groups, such as premenopausal women in the United States. In contradistinction, low-serum leptin and high-serum adiponectin concentrations are associated with stable COPD, although these associations are likely confounded by fat mass. Interestingly, leptin may promote systemic and airway inflammation in stable COPD patients. On the other hand, COPD may upregulate systemic and lung adiponectin expression. The precise mechanism and significance of the associations between these adipokines and lung disease at the current stage is confusing and frankly paradoxical in places. This area of research needs additional study that may open up novel therapeutic strategies for these lung diseases.

Obesity is not associated with mild asthma diagnosis in a population of Spanish adults

BACKGROUND

Several studies have suggested a relationship between asthma and obesity. Moreover, atopy is an important risk factor for asthma, but the relationship between obesity and atopy is uncertain.

METHODS

A cross-sectional multicenter study was conducted in a population of Spanish adults between November 2007 and July 2008. The subjects included had experienced asthma symptoms in the last year but had a forced expiratory volume in 1 second (FEV(1))/forced vital capacity (FVC) > 70%. Mild asthma diagnosis was confirmed by measuring airway hyperresponsiveness to methacholine. Body mass index in kg/m(2) was used as measure of obesity. Subjects were considered atopic when they had at least one positive skin prick test to common aeroallergens. Adjusted odd ratios (OR) were obtained by logistic regression.

RESULTS

A total of 662 subjects were included and 234 subjects (35.3%) were diagnosed with asthma (consistent symptoms and positive methacholine test). After adjusting the model for age, gender, atopy, baseline FEV(1), and FEV(1)/FVC ratio, there was no association between overweight or obesity with asthma diagnosis, with OR of 0.889 (95% CI, 0.60-1.38) and 0.925 (95% CI, 0.577-1.48), respectively. A multivariable logistic regression analysis confirmed that atopy increases the risk of asthma (p = 0.008). The non-atopic obese group had an increased risk of asthma compared to the non-atopic group with normal weight or overweight (p = 0.0032).

CONCLUSIONS

In this study obesity was not associated with a diagnosis of asthma. The presence of atopy was a risk factor for asthma, independent of obesity. Obesity, however, may be a risk factor for the development of asthma among non-atopic subjects.

Obesity, adipokines and asthma

BACKGROUND

The prevalence of asthma and obesity is increasing concomitantly, but many aspects of this link are unclear. Our objective was to examine whether obesity is associated with asthma in three time points of life, and whether immunomodulatory adipokines, leptin and adiponectin are linked to overweight-associated asthma.

METHODS

We studied the association between obesity and asthma at ages 3-18 years [mean (SD), 10 years (5), n = 3582, year 1980], 9-24 years [16 years (5), n = 2764, 1986] and 24-39 years [32 years (5), n = 2620, 2001] in a prospective cohort study and further tested for associations with serum leptin and adiponectin concentrations. Data on allergy status, smoking and other laboratory values (serum insulin, plasma C-reactive protein and serum lipid values) were also analyzed.

RESULTS

Allergy and parental asthma were significantly associated with asthma at all ages. At ages 24-39 years, but not earlier, body mass index (BMI) (odds ratio, OR 1.05; P = 0.019) and female gender (OR 1.56; P = 0.031) were independently associated with asthma. Increase in BMI was also associated with incident asthma during adulthood (OR 1.08; P = 0.030). Levels of leptin, adiponectin or any other obesity-related biomarker were not independently associated with asthma.

CONCLUSIONS

Asthma is linked with obesity in adults, but our results do not support a significant role for leptin, adiponectin or any other obesity-related biomarker studied in this association. Other factors should be sought for better understanding the connection between obesity and asthma.