Obesity increases airway smooth muscle responses to contractile agonists

A Systematic Review of Proteomics in Obesity: Unpacking the Molecular Puzzle

PURPOSE OF REVIEW

The present study aims to review the existing literature to identify pathophysiological proteins in obesity by conducting a systematic review of proteomics studies. Proteomics may reveal the mechanisms of obesity development and clarify the links between obesity and related diseases, improving our comprehension of obesity and its clinical implications.

RECENT FINDINGS

Most of the molecular events implicated in obesity development remain incomplete. Proteomics stands as a powerful tool for elucidating the intricate interactions among proteins in the context of obesity. This methodology has the potential to identify proteins involved in pathological processes and to evaluate changes in protein abundance during obesity development, contributing to the identification of early disease predisposition, monitoring the effectiveness of interventions and improving disease management overall. Despite many non-targeted proteomic studies exploring obesity, a comprehensive and up-to-date systematic review of the molecular events implicated in obesity development is lacking. The lack of such a review presents a significant challenge for researchers trying to interpret the existing literature. This systematic review was conducted following the PRISMA guidelines and included sixteen human proteomic studies, each of which delineated proteins exhibiting significant alterations in obesity. A total of 41 proteins were reported to be altered in obesity by at least two or more studies. These proteins were involved in metabolic pathways, oxidative stress responses, inflammatory processes, protein folding, coagulation, as well as structure/cytoskeleton. Many of the identified proteomic biomarkers of obesity have also been reported to be dysregulated in obesity-related disease. Among them, seven proteins, which belong to metabolic pathways (aldehyde dehydrogenase and apolipoprotein A1), the chaperone family (albumin, heat shock protein beta 1, protein disulfide-isomerase A3) and oxidative stress and inflammation proteins (catalase and complement C3), could potentially serve as biomarkers for the progression of obesity and the development of comorbidities, contributing to personalized medicine in the field of obesity. Our systematic review in proteomics represents a substantial step forward in unravelling the complexities of protein alterations associated with obesity. It provides valuable insights into the pathophysiological mechanisms underlying obesity, thereby opening avenues for the discovery of potential biomarkers and the development of personalized medicine in obesity.

FLECS technology for high-throughput screening of hypercontractile cellular phenotypes in fibrosis: A function-first approach to anti-fibrotic drug discovery

The pivotal role of myofibroblast contractility in the pathophysiology of fibrosis is widely recognized, yet HTS approaches are not available to quantify this critically important function in drug discovery. We developed, validated, and scaled-up a HTS platform that quantifies contractile function of primary human lung myofibroblasts upon treatment with pro-fibrotic TGF-β1. With the fully automated assay we screened a library of 40,000 novel small molecules in under 80 h of total assay run-time. We identified 42 hit compounds that inhibited the TGF-β1-induced contractile phenotype of myofibroblasts, and enriched for 19 that specifically target myofibroblasts but not phenotypically related smooth muscle cells. Selected hits were validated in an ex vivo lung tissue models for their inhibitory effects on fibrotic gene upregulation by TGF-β1. Our results demonstrate that integrating a functional contraction test into the drug screening process is key to identify compounds with targeted and diverse activity as potential anti-fibrotic agents.

High-fat Western diet alters crystalline silica-induced airway epithelium ion transport but not airway smooth muscle reactivity

OBJECTIVES

Silicosis is an irreversible occupational lung disease resulting from crystalline silica inhalation. Previously, we discovered that Western diet (HFWD)-consumption increases susceptibility to silica-induced pulmonary inflammation and fibrosis. This study investigated the potential of HFWD to alter silica-induced effects on airway epithelial ion transport and smooth muscle reactivity.

METHODS

Six-week-old male F344 rats were fed a HFWD or standard rat chow (STD) and exposed to silica (Min-U-Sil 5®, 15 mg/m3, 6 h/day, 5 days/week, for 39 d) or filtered air. Experimental endpoints were measured at 0, 4, and 8 weeks post-exposure. Transepithelial potential difference (Vt), short-circuit current (ISC) and transepithelial resistance (Rt) were measured in tracheal segments and ion transport inhibitors [amiloride, Na+ channel blocker; NPPB; Cl- channel blocker; ouabain, Na+, K+-pump blocker] identified changes in ion transport pathways. Changes in airway smooth muscle reactivity to methacholine (MCh) were investigated in the isolated perfused trachea preparation.

RESULTS

Silica reduced basal ISC at 4 weeks and HFWD reduced the ISC response to amiloride at 0 week compared to air control. HFWD + silica exposure induced changes in ion transport 0 and 4 weeks after treatment compared to silica or HFWD treatments alone. No effects on airway smooth muscle reactivity to MCh were observed.

Metabolomics in Animal Models of Bronchial Asthma and Its Translational Importance for Clinics

Bronchial asthma is an extremely heterogenous chronic respiratory disorder with several distinct endotypes and phenotypes. These subtypes differ not only in the pathophysiological changes and/or clinical features but also in their response to the treatment. Therefore, precise diagnostics represent a fundamental condition for effective therapy. In the diagnostic process, metabolomic approaches have been increasingly used, providing detailed information on the metabolic alterations associated with human asthma. Further information is brought by metabolomic analysis of samples obtained from animal models. This article summarizes the current knowledge on metabolomic changes in human and animal studies of asthma and reveals that alterations in lipid metabolism, amino acid metabolism, purine metabolism, glycolysis and the tricarboxylic acid cycle found in the animal studies resemble, to a large extent, the changes found in human patients with asthma. The findings indicate that, despite the limitations of animal modeling in asthma, pre-clinical testing and metabolomic analysis of animal samples may, together with metabolomic analysis of human samples, contribute to a novel way of personalized treatment of asthma patients.

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.

A Total Diet Replacement Weight Management Program for Difficult-to-Treat Asthma Associated With Obesity: A Randomized Controlled Feasibility Trial

BACKGROUND

Obesity is often associated with uncontrolled, difficult-to-treat asthma and increased morbidity and mortality. Previous studies suggest that weight loss may improve asthma outcomes, but with heterogenous asthma populations studied and unclear consensus on the optimal method of weight management. The Counterweight-Plus Programme (CWP) for weight management is an evidence-based, dietitian-led total diet replacement (TDR) program.

RESEARCH QUESTION

Can use of the CWP compared with usual care (UC) improve asthma control and quality of life in patients with difficult-to-treat asthma and obesity?

STUDY DESIGN AND METHODS

We conducted a 1:1 (CWP to UC) randomized, controlled single-center trial in adults with difficult-to-treat asthma and BMI of ≥ 30 kg/m2. The CWP was a 12-week TDR phase (800 kcal/d low-energy formula) followed by stepwise food reintroduction and weight loss maintenance for up to 1 year. The primary outcome was the change in Asthma Control Questionnaire 6 (ACQ6) score over 16 weeks. The secondary outcome was change in Asthma Quality of Life Questionnaire (AQLQ) score.

RESULTS

Thirty-five participants were randomized (36 screened) and 33 attended the 16-week follow-up (n = 17 in the CWP group, n = 16 in the UC group). Overall, mean ACQ6 score at baseline was 2.8 (95% CI, 2.4-3.1). Weight loss was greater in the CWP than UC group (mean difference, -12.1 kg; 95% CI, -16.9 to -7.4; P < .001). ACQ6 score improved more in the CWP than UC group (mean difference, -0.69; 95% CI, -1.37 to -0.01; P = .048). A larger proportion of participants achieved the minimal clinically important difference in ACQ6 score with CWP than with UC (53% vs 19%; P = .041; Number needed to treat, 3 [95% CI, 1.5-26.9]). AQLQ score improvement was greater in the CWP than UC group (mean difference, 0.76; 95% CI, 0.18-1.34; P = .013).

INTERPRETATION

Using a structured weight management program results in clinically important improvements in asthma control and quality of life over 16 weeks compared with UC in adults with difficult-to-treat asthma and obesity. This generalizable program is easy to deliver for this challenging phenotype. Longer-term outcomes continue to be studied.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT03858608; URL: www.

CLINICALTRIALS

gov.

Aging-Related Mechanisms Contribute to Corticosteroid Insensitivity in Elderly Asthma

Asthma in elderly populations is an increasing health problem that is accompanied by diminished lung function and frequent exacerbations. As potent anti-inflammatory drugs, corticosteroids are commonly used to reduce lung inflammation, improve lung function, and manage disease symptoms in asthma. Although effective for most individuals, older patients are more insensitive to corticosteroids, making it difficult to manage asthma in this population. With the number of individuals older than 65 continuing to increase, it is important to understand the distinct mechanisms that promote corticosteroid insensitivity in the aging lung. In this review, we discuss corticosteroid insensitivity in asthma with an emphasis on mechanisms that contribute to persistent inflammation and diminished lung function in older individuals.

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.

Pediatric obesity and severe asthma: Targeting pathways driving inflammation

Asthma affects more than 300 million people of all ages worldwide, including about 10-15% of school-aged children, and its prevalence is increasing. Severe asthma (SA) is a particular and rare phenotype requiring treatment with high-dose inhaled corticosteroids plus a second controller and/or systemic glucocorticoid courses to achieve symptom control or remaining "uncontrolled" despite this therapy. In SA, other diagnoses have been excluded, and potential exacerbating factors have been addressed. Notably, obese asthmatics are at higher risk of developing SA. Obesity is both a major risk factor and a disease modifier of asthma in children and adults: two main "obese asthma" phenotypes have been described in childhood with high or low levels of Type 2 inflammation biomarkers, respectively, the former characterized by early onset and eosinophilic inflammation and the latter by neutrophilic inflammation and late-onset. Nevertheless, the interplay between obesity and asthma is far more complex and includes obese tissue-driven inflammatory pathways, mechanical factors, comorbidities, and poor response to corticosteroids. This review outlines the most recent findings on SA in obese children, particularly focusing on inflammatory pathways, which are becoming of pivotal importance in order to identify selective targets for specific treatments, such as biological agents.

Metabolic Contributions to Pathobiology of Asthma

Asthma is a heterogenous disorder driven by inflammatory mechanisms that result in multiple phenotypes. Given the complex nature of this condition, metabolomics is being used to delineate the pathobiology of asthma. Metabolomics is the study of metabolites in biology, which includes biofluids, cells, and tissues. These metabolites have a vital role in a disease as they contribute to the pathogenesis of said condition. This review describes how macrometabolic and micrometabolic studies pertaining to these metabolites have contributed to our current understanding of asthma, as well as its many phenotypes. One of the main phenotypes this review will discuss in further detail is obesity as well as diabetes. Distinct roles of metabolites in endotyping asthma and their translation to potential therapy development for asthma is also discussed in this review.

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.

Starving a Cell Promotes Airway Smooth Muscle Relaxation: Inhibition of Glycolysis Attenuates Excitation-Contraction Coupling

Bronchomotor tone modulated by airway smooth muscle shortening represents a key mechanism that increases airway resistance in asthma. Altered glucose metabolism in inflammatory and airway structural cells is associated with asthma. Although these observations suggest a causal link between glucose metabolism and airway hyperresponsiveness, the mechanisms are unclear. We hypothesized that glycolysis modulates excitation-contraction coupling in human airway smooth muscle (HASM) cells. Cultured HASM cells from human lung donors were subject to metabolic screenings using Seahorse XF cell assay. HASM cell monolayers were treated with vehicle or PFK15 (1-(Pyridin-4-yl)-3-(quinolin-2-yl)prop-2-en-1-one), an inhibitor of PFKFB3 (PFK-1,6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3) that generates an allosteric activator for glycolysis rate-limiting enzyme PFK1 (phosphofructokinase 1), for 5-240 minutes, and baseline and agonist-induced phosphorylation of MLC (myosin light chain), MYPT1 (myosin phosphatase regulatory subunit 1), Akt, RhoA, and cytosolic Ca2+ were determined. PFK15 effects on metabolic activity and contractile agonist-induced bronchoconstriction were determined in human precision-cut lung slices. Inhibition of glycolysis attenuated carbachol-induced excitation-contraction coupling in HASM cells. ATP production and bronchodilator-induced cAMP concentrations were also attenuated by glycolysis inhibition in HASM cells. In human small airways, glycolysis inhibition decreased mitochondrial respiration and ATP production and attenuated carbachol-induced bronchoconstriction. The findings suggest that energy depletion resulting from glycolysis inhibition is a novel strategy for ameliorating HASM cell shortening and bronchoprotection of human small airways.

Obesity-related asthma in children and adolescents

There is substantial epidemiological and experimental evidence of an obesity-related asthma phenotype. Compared to children of healthy weight, children with obesity are at higher risk of asthma. Children with obesity who have asthma have greater severity and poorer control of their asthma symptoms, more frequent asthma exacerbations, and overall lower asthma-related quality of life than children with asthma who have a healthy weight. In this Review, we examine some of the latest evidence on the characteristics of this phenotype and its main underlying mechanisms, including genetics and genomics, changes in airway mechanics and lung function, sex hormone differences, alterations in immune responses, systemic and airway inflammation, metabolic dysregulation, and modifications in the microbiome. We also review current recommendations for the treatment of these children, including in the management of their asthma, and current evidence for weight loss interventions. We then discuss initial evidence for potential novel therapeutic approaches, such as dietary modifications and supplements, antidiabetic medications, and statins. Finally, we identify knowledge gaps and future directions to improve our understanding of asthma in children with obesity, and to improve outcomes in these susceptible children. We highlight important needs, such as designing paediatric-specific studies, implementing large multicentric trials with standardised interventions and outcomes, and including racial and ethnic groups along with other under-represented populations that are particularly affected by obesity and asthma.

Obesity elicits a unique metabolomic signature in human airway smooth muscle cells

Obesity can aggravate asthma by enhancing airway hyperresponsiveness (AHR) and attenuating response to treatment. However, the precise mechanisms linking obesity and asthma remain unknown. Human airway smooth muscle (HASM) cells exhibit amplified excitation-contraction (EC) coupling and force generation in obesity. Therefore, we posit that airway smooth muscle (ASM) cells obtained from obese donors manifest a metabolomic phenotype distinct from that of nonobese donor cells and that a differential metabolic phenotype, at least in part, drives enhanced ASM cell EC coupling. HASM cells derived from age-, sex-, and race-matched nonobese [body mass index (BMI) ≤ 24.9 kg·m-2] and obese (BMI ≥ 29.9 kg·m-2) lung donors were subjected to unbiased metabolomic screening. The unbiased metabolomic screening identified differentially altered metabolites linked to glycolysis and citric acid cycle in obese donor-derived cells compared with nonobese donor cells. The Seahorse assay measured the bioenergetic profile based on glycolysis, mitochondrial respiration, palmitate oxidation, and glutamine oxidation rates in HASM cells. Glycolytic rate and capacity were elevated in obese donor-derived HASM cells, whereas mitochondrial respiration, palmitate oxidation, and glutamine oxidation rates were comparable between obese and nonobese groups. PFKFB3 mRNA and protein expression levels were also elevated in obese donor-derived HASM cells. Furthermore, pharmacological inhibition of PFKFB3 attenuated agonist-induced myosin light chain (MLC) phosphorylation in HASM cells derived from obese and nonobese donors. Our findings identify elevated glycolysis as a signature metabolic phenotype of obesity and inhibition of glycolysis attenuates MLC phosphorylation in HASM cells. These findings identify novel therapeutic targets to mitigate AHR in obesity-associated asthma.

Epinephrine evokes shortening of human airway smooth muscle cells following β2 adrenergic receptor desensitization

Epinephrine (EPI), an endogenous catecholamine involved in the body's fight-or-flight responses to stress, activates α1-adrenergic receptors (α1ARs) expressed on various organs to evoke a wide range of physiological functions, including vasoconstriction. In the smooth muscle of human bronchi, however, the functional role of EPI on α1ARs remains controversial. Classically, evidence suggests that EPI promotes bronchodilation by stimulating β2-adrenergic receptors (β2ARs). Conventionally, the selective β2AR agonism of EPI was thought to be, in part, due to a predominance of β2ARs and/or a sparse, or lack of α1AR activity in human airway smooth muscle (HASM) cells. Surprisingly, we find that HASM cells express a high abundance of ADRA1B (the α1AR subtype B) and identify a spontaneous "switch-like" activation of α1ARs that evokes intracellular calcium, myosin light chain phosphorylation, and HASM cell shortening. The switch-like responses, and related EPI-induced biochemical and mechanical signals, emerged upon pharmacological inhibition of β2ARs and/or under experimental conditions that induce β2AR tachyphylaxis. EPI-induced procontractile effects were abrogated by an α1AR antagonist, doxazosin mesylate (DM). These data collectively uncover a previously unrecognized feed-forward mechanism driving bronchospasm via two distinct classes of G protein-coupled receptors (GPCRs) and provide a basis for reexamining α1AR inhibition for the management of stress/exercise-induced asthma and/or β2-agonist insensitivity in patients with difficult-to-control, disease subtypes.

Role of Obesity in Inflammation and Remodeling of Asthmatic Airway

Obesity is considered as an important risk factor for the onset of asthma and plays a key role in enhancing the disease's severity. Obese asthmatic individuals represent a distinct phenotype of asthma that is associated with additional symptoms, more severe exacerbation, decreased response to standard medication, and poor quality of life. Obesity impairs the function of the lung airway in asthmatic individuals, leading to increased inflammation and severe remodeling of the bronchus; however, the molecular events that trigger such changes are not completely understood. In this manuscript, we review the current findings from studies that focused on understanding the role of obesity in modulating the functions of airway cells, including lung immune cells, epithelial cells, smooth muscle cells, and fibroblasts, leading to airway inflammation and remodeling. Finally, the review sheds light on the current knowledge of different therapeutic approaches for treating obese asthmatic individuals. Given the fact that the prevalence of asthma and obesity has been increasing rapidly in recent years, it is necessary to understand the molecular mechanisms that play a role in the disease pathophysiology of obese asthmatic individuals for developing novel therapies.

Obesity, Inflammation, and Severe Asthma: an Update

Purpose of Review

Obesity-associated difficult asthma continues to be a substantial problem and, despite a move to address treatable traits affecting asthma morbidity and mortality, it remains poorly understood with limited phenotype-specific treatments. The complex association between asthma, obesity, and inflammation is highlighted and recent advances in treatment options explored.

Recent Findings

Obesity negatively impacts asthma outcomes and has a causal link in the pathogenesis of adult-onset asthma. Imbalance in the adipose organ found in obesity favours a pro-inflammatory state both systemically and in airways. Obesity may impact currently available asthma biomarkers, and obesity-associated asthma specific biomarkers are needed. Whilst surgical weight loss interventions are associated with improvements in asthma control and quality of life, evidence for pragmatic conservative options are sparse. Innovative approaches tackling obesity-mediated airway inflammation may provide novel therapies.

Summary

The immunopathological mechanisms underlying obesity-associated asthma require further research that may lead to novel therapeutic options for this disease. However, weight loss appears to be effective in improving asthma in this cohort and focus is also needed on non-surgical treatments applicable in the real-world setting.

Impact of obesity and ovariectomy on respiratory function in female mice

Obesity and the corresponding variations in female sex hormones are associated with severe lung disease. We determined the potential effects of obesity and sex hormones in female mice by investigating changes in lung structure and respiratory function in an obesity model induced by postnatal overnutrition. Obese female mice exhibited pronounced weight gain, abdominal fat accumulation and collagen type I deposition in the airways. However, neither elastic tissue nor estrogen receptors-α/-β were affected in obese female mice after ovariectomy or sham-operated mice. Bronchoconstriction in response to methacholine challenge in obese sham-operated mice was higher than in the obese group after ovariectomy. Our results suggest that the coexistence of obesity and ovariectomy impacted on respiratory system and airway resistance (attenuates bronchoconstriction after methacholine), on collagen I deposition and on airway estrogen β-receptors of mice.

Metabolomics in asthma: A platform for discovery

Asthma, characterized by airway hyperresponsiveness, inflammation and remodeling, is a chronic airway disease with complex etiology. Severe asthma is characterized by frequent exacerbations and poor therapeutic response to conventional asthma therapy. A clear understanding of cellular and molecular mechanisms of asthma is critical for the discovery of novel targets for optimal therapeutic control of asthma. Metabolomics is emerging as a powerful tool to elucidate novel disease mechanisms in a variety of diseases. In this review, we summarize the current status of knowledge in asthma metabolomics at systemic and cellular levels. The findings demonstrate that various metabolic pathways, related to energy metabolism, macromolecular biosynthesis and redox signaling, are differentially modulated in asthma. Airway smooth muscle cell plays pivotal roles in asthma by contributing to airway hyperreactivity, inflammatory mediator release and remodeling. We posit that metabolomic profiling of airway structural cells, including airway smooth muscle cells, will shed light on molecular mechanisms of asthma and airway hyperresponsiveness and help identify novel therapeutic targets.

T2-"Low" Asthma: Overview and Management Strategies

Although the term "asthma" has been applied to all patients with airway lability and variable chest symptoms for centuries, phenotypes of asthma with distinct clinical and molecular features that may warrant different treatment approaches are well recognized. Patients with type 2 (T2)-"high" asthma are characterized by upregulation of T2 immune pathways (ie, IL-4 and IL-13 gene sets) and eosinophilic airway inflammation, whereas these features are absent in patients with T2-"low" asthma and may contribute to poor responsiveness to corticosteroid treatment. This review details definitions and clinical features of T2-"low" asthma, potential mechanisms and metabolic aspects, pediatric considerations, and potential treatment approaches. Priority research questions for T2-"low" asthma are also discussed.

TGF-β: The missing link in obesity-associated airway diseases?

Obesity is emerging as a global public health epidemic. The co-morbidities associated with obesity significantly contribute to reduced quality of life, mortality, and global healthcare burden. Compared to other asthma comorbidities, obesity prominently engenders susceptibility to inflammatory airway diseases such as asthma and chronic obstructive pulmonary disease (COPD), contributes to greater disease severity and evokes insensitivity to current therapies. Unlike in other metabolic diseases associated with obesity, the mechanistic link between obesity and airway diseases is only poorly defined. Transforming growth factor-β (TGF-β) is a pleiotropic inflammatory cytokine belonging to a family of growth factors with pivotal roles in asthma. In this review, we summarize the role of TGF-β in major obesity-associated co-morbidities to shed light on mechanisms of the diseases. Literature evidence shows that TGF-β mechanistically links many co-morbidities with obesity through its profibrotic, remodeling, and proinflammatory functions. We posit that TGF-β plays a similar mechanistic role in obesity-associated inflammatory airway diseases such as asthma and COPD. Concerning the role of TGF-β on metabolic effects of obesity, we posit that TGF-β has a similar mechanistic role in obesity-associated inflammatory airway diseases in interplay with different comorbidities such as hypertension, metabolic diseases like type 2 diabetes, and cardiomyopathies. Future studies in TGF-β-dependent mechanisms in obesity-associated inflammatory airway diseases will advance our understanding of obesity-induced asthma and help find novel therapeutic targets for prevention and treatment.

Insulin acutely increases agonist-induced airway smooth muscle contraction in humans and rats

Obesity increases incidence and severity of asthma but the molecular mechanisms are not completely understood. Hyperinsulinemia potentiates vagally induced bronchoconstriction in obese rats. Since bronchoconstriction results from airway smooth muscle contraction, we tested whether insulin changed agonist-induced airway smooth muscle contraction. Obesity-prone and resistant rats were fed a low-fat diet for 5 wk and treated with insulin (Lantus, 3 units/rat sc) 16 h before vagally induced bronchoconstriction was measured. Ex vivo, contractile responses to methacholine were measured in isolated rat tracheal rings and human airway smooth muscle strips before and after incubation (0.5-2 h) with 100 nM insulin or 13.1 nM insulin like growth factor-1 (IGF-1). M₂ and M₃ muscarinic receptor mRNA expression was quantified by qRT-PCR and changes in intracellular calcium were measured in response to methacholine or serotonin in isolated rat tracheal smooth muscle cells treated with 1 µM insulin. Insulin, administered to animals 16 h prior, potentiated vagally induced bronchoconstriction in both obese-prone and resistant rats. Insulin, not IGF-1, significantly increased methacholine-induced contraction of rat and human isolated airway smooth muscle. In cultured rat tracheal smooth muscle cells, insulin significantly increased M₂, not M_3, mRNA expression and enhanced methacholine- and serotonin-induced increase in intracellular calcium. Insulin alone did not cause an immediate increase in intracellular calcium. Thus, insulin acutely potentiated agonist-induced increase in intracellular calcium and airway smooth muscle contraction. These findings may explain why obese individuals with hyperinsulinemia are prone to airway hyperreactivity and give insights into future targets for asthma treatment.

The Association between Excess Body Mass and Disturbances in Somatic Mineral Levels

Background: Obesity and excess body weight are significant epidemiological issues, not only because they are costly to treat, but also because they are among the leading causes of death worldwide. In 2016, an estimated 40% of the global population was overweight, reflecting the importance of the issue. Obesity is linked to metabolism malfunction and concomitantly with altered mineral levels in the body. In this paper, we review alterations in somatic levels of iron, calcium, magnesium, copper, iodine, chromium, selenium, and zinc in relation to excess body mass. Methodology: An electronic literature search was performed using PubMed. Our search covered original English research articles published over the past five years, culminating in 63 papers included for study. Results: The reviewed papers presented correlation between obesity and hypomagnesemia and hypozincemia. They also indicated that patients with excess body mass present increased body copper levels. Studies have similarly indicated that obesity appears to be associated with lower selenium levels in both blood and urine, which may be correlated with the decline and weakening of defenses against oxidative stress. It has been found that decreased level of chromium is connected with metabolic syndrome. Chromium supplementation influences body mass, but the effect of the supplementation depends on the chemical form of the chromium. It is hypothesized that obesity poses a risk of iodine deficiency and iodine absorption may be disrupted by increased fat intake in obese women. A range of studies have suggested that obesity is correlated with iron deficiency. On the other hand, some reports have indicated that excess body mass may coexist with iron excess. The relation between obesity and body iron level requires further investigation. Calcium signaling seems to be disturbed in obesity, due to the increased production of reactive oxygen species and low level of fast troponin isoform responsible for mediating calcium sensitivity of muscle relaxation. Correlation between excess body mass and calcium levels needs further research. Conclusions: Excess body mass is associated with alterations in mineral levels in the body, in particular hypomagnesemia and decreased selenium (Se) and zinc (Zn) levels. Chromium (Cr) deficiency is associated with metabolic syndrome. Obese patients are at risk of iodine deficiency. Excess body mass is associated with elevated levels of copper (Cu). Data on the association between obesity and iron (Fe) levels are contradictory. Obesity coexists with disturbed calcium (Ca) signaling pathways. The association between obesity and body Ca levels has not been investigated in detail.

Association of obesity with severity outcomes in hospitalized pediatric asthma exacerbations

INTRODUCTION

While there seems to be an association between obesity and asthma, the exact nature of the relationship remains unknown. It is unclear if there is increased severity of exacerbation for those that require hospitalization. We examine the association between obesity and severity outcomes such as hospital length of stay, intensive care admissions, and need for continuous albuterol or magnesium administration.

METHODS

Patients 4 to 17 years old admitted between 1/1/2012-1/1/2016 with asthma identified by discharge codes were reviewed. Obesity was defined as BMI ≥95%. Clinical data such as age, gender, family history of asthma, use of controller medication along with outcome data such as length of stay, ICU admission, use of continuous albuterol, and use of magnesium were collected. Binary outcomes were analyzed with multivariate logistic regression while length of stay was analyzed with negative binomial regression.

RESULTS

Overall, 995 patients met inclusion criteria. The median age was 7 years old with 170 (17%) patients categorized as obese. We find no difference in length of stay (IRR 0.99 [0.91, 1.09], p = 0.9), PICU admission (OR 0.72 [0.43, 1.21], p = 0.22), or magnesium administration (OR 1.34 [0.95, 1.88], p = 0.09) between obese and non-obese patients. There were increased odds of continuous albuterol use (OR 1.47 [1.02, 2.11]) for obese patients.

CONCLUSION

We find no association between obesity and outcomes of length of stay, ICU admission, or magnesium administration. While growing evidence links obesity with asthma, our study suggests it may not be associated with the severity of exacerbation.

Physiological signature of late-onset nonallergic asthma of obesity

INTRODUCTION

Obesity can lead to a late-onset nonallergic (LONA) form of asthma for reasons that are not understood. We sought to determine whether this form of asthma is characterised by any unique physiological features.

METHODS

Spirometry, body plethysmography, multiple breath nitrogen washout (MBNW) and methacholine challenge were performed in four subject groups: Lean Control (n=11), Lean Asthma (n=11), Obese Control (n=11) and LONA Obese Asthma (n=10). The MBNW data were fitted with a novel computational model that estimates functional residual capacity (FRC), dead space volume (VD), the coefficient of variation of regional specific ventilation (CV,V'E) and a measure of structural asymmetry at the level of the acinus (sacin).

RESULTS

Body mass index and waist circumference values were similar in both obese groups, and significantly greater than in lean asthmatic individuals and controls. Forced vital capacity was significantly lower in the LONA Asthma group compared with the other groups (p<0.001). Both asthma groups exhibited similar hyperresponsiveness to methacholine. FRC was reduced in the Obese LONA Asthma group as measured by MBNW, but not in obese controls, whereas FRC was reduced in both obese groups as measured by plethysmography. VD, CV,V'E and sacin were not different between groups.

CONCLUSIONS

Chronic lung compression characterises all obese subjects, as reflected by reduced plethysmographic FRC. Obese LONA asthma is characterised by a reduced ability to recruit closed lung units, as seen by reduced MBNW FRC, and an increased tendency for airway closure as seen by a reduced forced vital capacity.

Clinical profile of severe asthmatics receiving biological treatment: see behind the scenes

The clinical phenotyping of severe asthma could improve treatment outcomes, quality of life, morbidity, and mortality of asthma patients. The growing availability of rich clinical data could provide opportunities to address a broad range of real-world questions regarding clinical phenotyping and effective therapeutic approaches of severe asthma. Accordingly, in this Letter to the Editor, we provide data relevant to constructing the clinical profile of a Greek severe asthma patient cohort who receive biological treatment.

Pediatric obesity-related asthma: A prototype of pediatric severe non-T2 asthma

Childhood obesity contributes to many diseases, including asthma. There is literature to suggest that asthma developing as a consequence of obesity has a nonallergic or non-T2 phenotype. In this review, obesity-related asthma is utilized as a prototype of non-T2 asthma in children to discuss several nonallergic mechanisms that underlie childhood asthma. Obesity-related asthma is associated with systemic T helper (Th)1 polarization occurring with monocyte activation. These immune responses are mediated by insulin resistance and dyslipidemia, metabolic abnormalities associated with obesity, that are themselves associated with pulmonary function deficits in obese asthmatics. As in other multifactorial diseases, there is both a genetic and an environmental contribution to pediatric obesity-related asthma. In addition to genetic susceptibility, differential DNA methylation is associated with non-T2 immune responses in pediatric obesity-related asthma. Initial investigations into the biology of non-T2 immune responses have identified the upregulation of genes in the CDC42 pathway. CDC42 is a RhoGTPase that plays a key role in Th cell physiology, including preferential naïve Th cell differentiation to Th1 cells, and cytokine production and exocytosis. Although these novel pathways are promising findings to direct targeted therapy development for obesity-related asthma to address the disease burden, there is evidence to suggest that dietary interventions, including diet modification, rather than caloric restriction alone, decrease disease burden. Adoption of a diet rich in micronutrients, including carotenoids and 25-OH cholecalciferol, a vitamin D metabolite, may be beneficial since these are positively correlated with pulmonary function indices, while being protective against metabolic abnormalities associated with the obese asthma phenotype.

Shared genetic and experimental links between obesity-related traits and asthma subtypes in UK Biobank

BACKGROUND

Clinical and epidemiologic studies have shown that obesity is associated with asthma and that these associations differ by asthma subtype. Little is known about the shared genetic components between obesity and asthma.

OBJECTIVE

We sought to identify shared genetic associations between obesity-related traits and asthma subtypes in adults.

METHODS

A cross-trait genome-wide association study (GWAS) was performed using 457,822 subjects of European ancestry from the UK Biobank. Experimental evidence to support the role of genes significantly associated with both obesity-related traits and asthma through a GWAS was sought by using results from obese versus lean mouse RNA sequencing and RT-PCR experiments.

RESULTS

We found a substantial positive genetic correlation between body mass index and later-onset asthma defined by asthma age of onset at 16 years or greater (Rg = 0.25, P = 9.56 × 10-22). Mendelian randomization analysis provided strong evidence in support of body mass index causally increasing asthma risk. Cross-trait meta-analysis identified 34 shared loci among 3 obesity-related traits and 2 asthma subtypes. GWAS functional analyses identified potential causal relationships between the shared loci and Genotype-Tissue Expression (GTEx) quantitative trait loci and shared immune- and cell differentiation-related pathways between obesity and asthma. Finally, RNA sequencing data from lungs of obese versus control mice found that 2 genes (acyl-coenzyme A oxidase-like [ACOXL] and myosin light chain 6 [MYL6]) from the cross-trait meta-analysis were differentially expressed, and these findings were validated by using RT-PCR in an independent set of mice.

CONCLUSIONS

Our work identified shared genetic components between obesity-related traits and specific asthma subtypes, reinforcing the hypothesis that obesity causally increases the risk of asthma and identifying molecular pathways that might underlie both obesity and asthma.

Obesity Does Not Increase the Risk of Asthma Readmissions

The relationship between obesity and asthma exacerbations is still under debate. The aim of our work is to analyse the relationship between obesity and hospital re-admissions in asthmatics. A review was retrospectively performed on all hospital admissions of adult patients due to asthma exacerbation occurring in our hospital for 11 years. All those cases with asthma as the first diagnosis in the discharge report were included, or those with asthma as the second diagnosis provided when the first diagnosis was respiratory infection or respiratory failure. Only the first hospital admission of each patient was included in this study. The Odds Ratios of a higher incidence of early/late readmissions due to asthma exacerbation were calculated using a binary logistic regression, using the body mass index (BMI) as independent variable, adjusted for all the variables included in the study. The study included 809 patients with a mean age of 55.6 years, and 65.2% were female. The majority (71.4%) were obese or overweight. No significant relationship was observed in the univariate or multivariate analyses between overweight or obesity and the early or late hospital readmissions due to asthma. Therefore, obesity does not seem to be a determining factor in the risk of asthma exacerbations.

FFAR1 activation attenuates histamine-induced myosin light chain phosphorylation and cortical tension development in human airway smooth muscle cells

BACKGROUND

Activation of free fatty acid receptors (FFAR1 and FFAR4) which are G protein-coupled receptors (GPCRs) with established (patho)physiological roles in a variety of obesity-related disorders, induce human airway smooth muscle (HASM) cell proliferation and shortening. We reported amplified agonist-induced cell shortening in HASM cells obtained from obese lung donors. We hypothesized that FFAR1 modulate excitation-contraction (EC) coupling in HASM cells and play a role in obesity-associated airway hyperresponsiveness.

METHODS

In HASM cells pre-treated (30 min) with FFAR1 agonists TAK875 and GW9508, we measured histamine-induced Ca²⁺ mobilization, myosin light chain (MLC) phosphorylation, and cortical tension development with magnetic twisting cytometry (MTC). Phosphorylation of MLC phosphatase and Akt also were determined in the presence of the FFAR1 agonists or vehicle. In addition, the effects of TAK875 on MLC phosphorylation were measured in HASM cells desensitized to β₂AR agonists by overnight salmeterol treatment. The inhibitory effect of TAK875 on MLC phosphorylation was compared between HASM cells from age and sex-matched non-obese and obese human lung donors. The mean measurements were compared using One-Way ANOVA with Dunnett's test for multiple group comparisons or Student's t-test two-group comparison. For cortical tension measurements by magnetic twisted cytometry, mixed effect model using SAS V.9.2 was applied. Means were considered significant when p ≤ 0.05.

RESULTS

Unexpectedly, we found that TAK875, a synthetic FFAR1 agonist, attenuated histamine-induced MLC phosphorylation and cortical tension development in HASM cells. These physiological outcomes were unassociated with changes in histamine-evoked Ca²⁺ flux, protein kinase B (AKT) activation, or MLC phosphatase inhibition. Of note, TAK875-mediated inhibition of MLC phosphorylation was maintained in β₂AR-desensitized HASM cells and across obese and non-obese donor-derived HASM cells.

CONCLUSIONS

Taken together, our findings identified the FFAR1 agonist TAK875 as a novel bronchoprotective agent that warrants further investigation to treat difficult-to-control asthma and/or airway hyperreactivity in obesity.

Estrogen receptors differentially regulate intracellular calcium handling in human nonasthmatic and asthmatic airway smooth muscle cells

Asthma is defined as chronic inflammation of the airways and is characterized by airway remodeling, hyperresponsiveness, and acute bronchoconstriction of airway smooth muscle (ASM) cells. Clinical findings suggest a higher incidence and severity of asthma in adult women, indicating a concrete role of sex steroids in modulating the airway tone. Estrogen, a major female sex steroid mediates its role through estrogen receptors (ER) ERα and ERβ, which are shown to be expressed in human ASM, and their expression is upregulated in lung inflammation and asthma. Previous studies suggested rapid, nongenomic signaling of estrogen via ERs reduces intracellular calcium ([Ca²⁺]_i), thereby promoting relaxation of ASM. However, long-term ER activation on [Ca²⁺]_i regulation in human ASM during inflammation or in asthma is still not known. In Fura-2-loaded nonasthmatic and asthmatic human ASM cells, we found that prolonged (24 h) exposure to ERα agonist (PPT) increased [Ca²⁺]_i response to histamine, whereas ERβ activation (WAY) led to decreased [Ca²⁺] compared with vehicle. This was further confirmed by ER overexpression and knockdown studies using various bronchoconstrictor agents. Interestingly, ERβ activation was more effective than 17β-estradiol in reducing [Ca²⁺]_i responses in the presence of TNF-α or IL-13, while no observable changes were noticed with PPT in the presence of either cytokine. The [Ca²⁺]_i-reducing effects of ERβ were mediated partially via L-type calcium channel inhibition and increased Ca²⁺ sequestration by sarcoplasmic reticulum_. Overall, these data highlight the differential signaling of ERα and ERβ in ASM during inflammation. Specific ERβ activation reduces [Ca²⁺]_i in the inflamed ASM cells and is likely to play a crucial role in regulating ASM contractility, thereby relaxing airways.

Novel Insights on Sex-Related Differences in Asthma

PURPOSE OF REVIEW

Asthma, a common respiratory disease that affects about 10% of the US population, represents a significant public health issue. In the last decade, cumulative evidence has demonstrated sex disparities in asthma, including significant differences in epidemiology, clinical presentation, response to therapies, and health outcomes. Understanding sex-related differences in asthma enables clinicians to provide personalized asthma care and improve asthma outcome.

RECENT FINDINGS

Recent studies on sex-related differences in asthma inform us on mechanism underlying asthma pathogenesis across all age groups. Sex hormones directly modulate immune pathways crucial in asthma pathogenesis and affect individual's response to environmental triggers and medications, such as leukokotriene inhibitors. Not surprisingly, the use of external sex hormone supplementations appears to modulate asthma risk. Identification of sex-specific asthma risk loci through genome-wide association studies also provides supporting evidence on sex-related differences in asthma. There is an interaction between sex and obesity, an interaction that could place females at higher risk for systemic inflammation and, consequently, asthma. In this article, we review epidemiological and clinical studies on sex-related differences in asthma, with a special focus on the role of sex hormones, including hormonal therapies and the asthma-obesity interaction.

Association of pediatric obesity and asthma, pulmonary physiology, metabolic dysregulation, and atopy; and the role of weight management

Introduction: Obesity affects about 40% of US adults and 18% of children. Its impact on the pulmonary system is best described for asthma. Areas covered: We reviewed the literature on PubMed and Google Scholar databases and summarize the effect of obesity, its associated metabolic dysregulation and altered systemic immune responses, and that of weight gain and loss on pulmonary mechanics, asthma inception, and disease burden. We include a distinct approach for diagnosing and managing the disease, including pulmonary function deficits inherent to obesity-related asthma, in light of its poor response to current asthma medications. Expert opinion: Given the projected increase in obesity, obesity-related asthma needs to be addressed now. Research on the contribution of metabolic abnormalities and systemic immune responses, intricately linked with truncal adiposity, and that of lack of atopy, to asthma disease burden, and pulmonary function deficits among obese children is fairly consistent. Since current asthma medications are more effective for atopic asthma, investigation for atopy will guide management by distinguishing asthma responsive to current medications from the non-responsive disease. Future research is needed to elucidate mechanisms by which obesity-mediated metabolic abnormalities and immune responses cause medication non-responsive asthma, which will inform repurposing of medications and drug discovery.

Evidence for lifestyle interventions in asthma

Asthma is a chronic inflammatory airways disease, estimated to affect 300 million people worldwide. Asthma management plans focus on optimisation of asthma pharmacotherapy. Lifestyle interventions also hold great promise for asthma sufferers as they are accessible, low cost and have minimal side-effects, thus making adherence more likely. This review explores lifestyle interventions that have been tested in asthma, including improving nutrition, increasing physical activity and introduction of relaxation therapies such as yoga and massage therapy. Available evidence suggests a protective effect of increasing fruit, vegetable and wholegrain intake and increasing physical activity levels in asthma. Weight loss is recommended for obese asthmatic patients, as just 5–10% weight loss has been found to improve quality of life and asthma control in most obese asthmatic patients. Other lifestyle interventions such as meditation, yoga and massage therapy show promise, with positive effects on asthma seen in some studies. However, the study protocols are highly variable and the results are inconsistent. Additional research is needed to further develop and refine recommendations regarding lifestyle modifications that can be implemented to improve asthma.

Lifestyleinterventions may be key to living well with asthma, as increasing fruit, vegetable and wholegrain intake and exercise levels are shown to improve asthma. Future recommendations may include yoga, meditation and massage.http://bit.ly/2wbJp2J

Salicylic acid amplifies Carbachol-induced bronchoconstriction in human precision-cut lung slices

BACKGROUND

Asthma exacerbations evoke emergency room visits, progressive loss of lung function and increased mortality. Environmental and industrial toxicants exacerbate asthma, although the underlying mechanisms are unknown. We assessed whether 3 distinct toxicants, salicylic acid (SA), toluene diisocyanate (TDI), and 1-chloro-2,4-dinitrobenzene (DNCB) induced airway hyperresponsiveness (AHR) through modulating excitation-contraction coupling in human airway smooth muscle (HASM) cells. The toxicants include a non-sensitizing irritant (SA), respiratory sensitizer (TDI) and dermal sensitizer (DNCB), respectively. We hypothesized that these toxicants induce AHR by modulating excitation-contraction (EC) coupling in airway smooth muscle (ASM) cells.

METHODS

Carbachol-induced bronchoconstriction was measured in precision-cut human lung slices (hPCLS) following exposure to SA, TDI, DNCB or vehicle. Culture supernatants of hPCLS were screened for mediator release. In HASM cells treated with the toxicants, surrogate readouts of EC coupling were measured by phosphorylated myosin light chain (pMLC) and agonist-induced Ca²⁺ mobilization ([Ca²⁺]_i). In addition, Nrf-2-dependent antioxidant response was determined by NAD(P) H quinone oxidoreductase 1 (NQO1) expression in HASM cells.

RESULTS

In hPCLS, SA, but not TDI or DNCB, potentiated carbachol-induced bronchoconstriction. The toxicants had little effect on release of inflammatory mediators, including IL-6, IL-8 and eotaxin from hPCLS. In HASM cells, TDI amplified carbachol-induced MLC phosphorylation. The toxicants also had little effect on agonist-induced [Ca²⁺]_i. CONCLUSION: SA, a non-sensitizing irritant, amplifies agonist-induced bronchoconstriction in hPCLS via mechanisms independent of inflammation and Ca²⁺ homeostasis in HASM cells. The sensitizers TDI and DNCB, had little effect on bronchoconstriction or inflammatory mediator release in hPCLS.

IMPLICATIONS

Our findings suggest that non-sensitizing irritant salicylic acid may evoke AHR and exacerbate symptoms in susceptible individuals or in those with underlying lung disease.

Obesity and severe asthma

Obesity is an important global health issue for both children and adults. Obesity increases the prevalence and incidence of asthma and also increases the risk for severe asthma. Here we describe the features of severe asthma phenotypes for which obesity is a defining characteristic, including steroid resistance, airway inflammation, and co-morbidities. We also review current concepts regarding the mechanistic basis for the impact of obesity in severe asthma, including possible roles for vitamin D deficiency, systemic inflammation, and the microbiome. Finally, we describe data indicating a role for diet, weight loss, and exercise in the treatment of severe asthma with obesity. Better understanding of the mechanistic basis for the role of obesity in severe asthma could lead to new therapeutic options for this population.

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.