Obesity and asthma: an inflammatory disease of adipose tissue not the airway

[Asthma and metabolic syndrome: Clinical and pathogenetic relationships]

Asthma and metabolic syndrome (MS) are common and social diseases. External and internal factors influencing the development and manifestations of asthma are identified; among which there is obesity that is a major risk factor for MS. Accordingly, the concurrence of asthma and MS and to study their clinical and pathogenetic relationships are a topical problem. There is a tendency to identify a particular asthma phenotype that is characterized by later-onset disease in the presence of obesity; the low prevalence of atopy, low serum level of IgE, and a poorly-controlled course with a trend of standard therapy resistance. It is necessary to understand the essence of asthma cause-effect relationships in the presence of obesity for defining management tactics for this group of patients.

Association between Western diet pattern and adult asthma: a focused review

OBJECTIVE

Radical changes in diet have paralleled the increase in asthma with shifts toward a "Western" diet pattern, characterized by the high intake of processed meats and refined grains, high-fat dairy products, and sugary desserts and drinks. Because diet represents a modifiable risk factor in numerous chronic diseases, the authors examined the association between consumption of a Western diet pattern and asthma incidence, prevalence, and morbidity in adults.

DATA SOURCES

PubMed, Cochrane, Web of Science, and Scopus were searched for peer-reviewed publications published from January 1980 to April 2014.

STUDY SELECTION

Studies retrieved for inclusion assessed dietary patterns representative of a Western diet and asthma incidence, prevalence, respiratory symptoms, and lung function.

RESULTS

Ten observational studies conducted in North American, European, and Asian countries, ranging from 153 to more than 70,000 individuals, did not provide evidence to support an association between a Western dietary pattern and asthma incidence and prevalence. Five of these studies also investigated asthma morbidity, with variable findings.

CONCLUSION

Current evidence does not support an association between a Western diet and incident or prevalent adult asthma but does suggest a possible link between a Western diet pattern and adult asthma morbidity.

Obesity and asthma: pathophysiology and implications for diagnosis and management in primary care

The effects of obesity on asthma diagnosis, control, and exacerbation severity are increasingly recognized; however, the underlying pathophysiology of this association is poorly understood. Mainstream clinical practice has yet to adopt aggressive management of obesity as a modifiable risk factor in asthma care, as is the case with a risk factor like tobacco or allergen exposure. This review summarizes existing data that support the pathophysiologic mechanisms underlying the association between obesity and asthma, as well as the current and future state of treatment for the obese patient with asthma. Our review suggests that evidence of chronic inflammatory response linking obesity and asthma indicates a need to address obesity during asthma management, possibly using patient-centered approaches such as shared decision making. There is a need for research to better understand the mechanisms of asthma in the obese patient and to develop new therapies specifically targeted to this unique patient population.

Potential role of the airway wall in the asthma of obesity

The pathogenesis of late-onset TH2-low asthma in obesity is thought to be related to weight-related decreases in lung volume, but why only a subset of individuals with obesity develop this condition is unknown. We tested the hypothesis that natural variations in both airway wall stiffness and airway wall thickness could lead to a subpopulation of hyperresponsive individuals exhibiting the symptoms of asthma in the setting of obesity. Increases in airway resistance (Raw) after airway smooth muscle stimulation were simulated using a computational model of an elastic airway embedded in elastic parenchyma. Using a range of randomly chosen values for both airway wall stiffness and thickness, we determined the resulting probability distributions of Raw responsiveness for a variety of different levels of transpulmonary pressure (Ptp). As Ptp decreased from 5 to 1 cmH2O, the resulting distributions of Raw moved toward progressively higher levels of responsiveness. With appropriate choices for the mean and standard deviation of the parameter that controls either airway wall stiffness or thickness, the model predicts a relationship between airway hyperresponsiveness and body mass index that is similar to that which has been reported in populations with obesity. We conclude that natural variations in airway wall mechanics and geometry between different individuals can potentially explain why an increasing percentage of the population exhibits the symptoms of asthma as the obesity of the population increases.

The many faces of asthma in obesity

Obesity is a major risk factor for the development of asthma, and causes severe, uncontrolled disease that responds poorly to therapy. The obese state alters early onset allergic asthma, and leads to the development of a novel form of late onset asthma secondary to obesity. The presentation of early onset allergic asthma is altered through effects on immune function. Factors such as mechanical loading, effects of adipokines on airways, altered diet, insulin resistance and altered metabolism of nitric oxide likely all contribute to increased airway reactivity in obesity, causing late onset asthma in obesity. Obesity also alters responses to environmental factors such as ozone and particulate matter. Focused studies to understand the importance of these factors in the pathogenesis of airway disease in obesity will be essential to develop therapies to intervene in this new epidemic of airway disease.

Macrophage activation, age and sex effects of immunometabolism in obese asthma

Obese asthma is characterised by infiltration of adipose tissue by activated macrophages and mast cells. The aim of this study was to examine the age and sex effects of immunometabolism in obese asthma. Obese and non-obese asthmatic children and adults underwent spirometry, body composition assessment by dual energy X-ray absorptiometry and measurement of serum soluble CD163 (sCD163), tryptase, C-reactive protein (CRP) and other adipocytokines. Plasma CRP (p<0.01) and leptin (p<0.01) were elevated in obese asthmatic adults, and sCD163 (p=0.003) was elevated in obese asthmatic children. We observed significantly higher sCD163 in obese female children compared to obese female adults and male children, and higher CRP in obese female adults compared to obese male children and adults. Serum tryptase concentrations were not significantly different across age groups. sCD163 positively correlated with the proportion of android fat in obese female children (r=0.70, p=0.003) and obese female adults (r=0.65, p=0.003). In obese female children, sCD163 was inversely associated with forced expiratory volume in 1 s % predicted (r=-0.55, p=0.02) and was positively associated with the Asthma Control Questionnaire (r=0.57, p=0.02). Obese children with asthma have sex-specific macrophage activation, which may contribute to worse asthma control and lung function. The heterogeneous systemic inflammatory profile across age and sex suggests the existence of sub-phenotypes in obese asthma at the molecular level.

Adiposity, fractional exhaled nitric oxide, and asthma in U.S. children

RATIONALE

Whether allergic airway inflammation mediates the association between overweight or obesity and childhood asthma is unknown.

OBJECTIVES

To examine adiposity, asthma, and fractional exhaled nitric oxide (FeNO) in U.S. children.

METHODS

Cross-sectional study of indicators of adiposity or obesity, FeNO (a biomarker of eosinophilic airway inflammation), and asthma in 2,681 children aged 6-17 years in the 2007-2010 National Health and Nutrition Examination Survey. Adiposity measures included body mass index (BMI), percent body fat (PBF), and waist circumference (WC).

MEASUREMENTS AND MAIN RESULTS

BMI, PBF, and WC were associated with asthma among children with low FeNO (odds ratio, 1.54-1.68; P < 0.01), but not among children with increased FeNO. Among children without asthma, BMI, PBF, and WC were associated with higher FEV1 and FVC, and lower FEV1/FVC. Among children with asthma and a high FeNO, all adiposity indicators were associated with decreased FEV1/FVC (β = -1.5% to -1.7% per z score) but not with FEV1 or FVC. Higher BMI or PBF was associated with worse asthma severity or control in children with asthma and increased FeNO, but not in children with asthma and low FeNO. Similar results were obtained in a secondary multivariate analysis of overweight or obesity (defined as BMI ≥85th percentile) and asthma or indicators of asthma severity or control, stratified by FeNO level.

CONCLUSIONS

Adiposity indicators are associated with asthma in children with low FeNO. Among children with asthma, adiposity indicators are associated with worse asthma severity or control in those with high FeNO.

Mechanisms of obesity in asthma

PURPOSE OF REVIEW

Obesity and asthma are chronic conditions affecting millions of people worldwide. The two conditions also appear to be linked with an increased risk of asthma in people who are obese. The purpose of this review is to describe mechanism(s) that may explain the association between asthma and obesity.

RECENT FINDINGS

Current evidence suggests that the association between asthma and obesity is linked by two major phenotypes and three important pathways of obesity-related asthma: one phenotype with primary (often atopic) asthma that is aggravated by obesity and a second phenotype with late-onset nonatopic asthma, which predominantly affects women and primarily seems to be associated with neutrophilic inflammation. Proposed pathways include the mechanical effects of obesity (fewer deep inspirations leading to increased airway hyperresponsiveness), an inflammatory pathway driven by obesity-related cytokines (adipokines), and finally environment and lifestyle changes that have led to an increasing prevalence of obesity over the past 50 years (including exposures in utero, physical activity, and diet) may also result in asthma in predisposed individuals. How these environmental changes influence the occurrence and expression of asthma may depend on the age of exposure and on interactions with genetic susceptibilities.

SUMMARY

Future research should be directed to shed light on the associations between obesity and asthma phenotypes, modern lifestyles and environmental exposures and genetic susceptibilities.

VIDEO ABSTRACT

http://links.lww.com/COAI/A6.

Influence of distinct asthma phenotypes on lung function following weight loss in the obese

BACKGROUND AND OBJECTIVE

There appears to be two distinct clinical phenotypes of obese patients with asthma-those with early-onset asthma and high serum IgE (TH2-high), and those with late-onset asthma and low serum IgE (TH2-low). The aim of the present study was to determine in the two phenotypes of obese asthma the effect of weight loss on small airway function.

METHODS

TH2-low (n = 8) and TH2-high (n = 5) obese asthmatics underwent methacholine challenge before and 12 months following bariatric surgery. Dose-response slopes as measures of sensitivity to airway closure and narrowing were measured as maximum % fall forced vital capacity (FVC) and forced expiratory volume in 1 s/FVC, respectively, divided by dose. Resting airway mechanics were measured by forced oscillation technique.

RESULTS

Weight loss reduced sensitivity to airway closure in TH 2-low but not TH2-high obese asthmatics (pre-post mean change ± 95% confidence interval: 1.8 ± 0.8 doubling doses vs -0.3 ± 1.7 doubling doses, P = 0.04). However, there was no effect of weight loss on the sensitivity to airway narrowing in either group (P = 0.8, TH2-low: 0.8 ± 1.0 doubling doses, TH2-high: -1.1 ± 2.5 doubling doses). In contrast, respiratory resistance (20 Hz) improved in TH2-high but not in TH2-low obese asthmatics (pre-post change median interquartile range: 1.5 (1.3-2.8) cmH₂O/L/s vs 0.6 (-1.8-0.8) cmH₂O/L/s, P = 0.03).

CONCLUSIONS

TH2-low obese asthmatics appear to be characterized by increased small airway responsiveness and abnormalities in resting airway function that may persist following weight loss. However, this was not the case for TH2-high obese asthmatics, highlighting the complex interplay between IgE status and asthma pathophysiology in obesity.

The nonallergic asthma of obesity. A matter of distal lung compliance

RATIONALE

The pathogenesis of asthma in obesity is poorly understood, but may be related to breathing at low lung volumes.

OBJECTIVES

To determine if lung function in obese patients with asthma and control subjects would respond differently to weight loss.

METHODS

Lung function was evaluated by conventional clinical tests and by impulse oscillometry in female late-onset, nonallergic patients with asthma and control subjects before, and 12 months after, bariatric surgery.

MEASUREMENTS AND MAIN RESULTS

Patients with asthma (n = 10) had significantly lower FEV1 (79.8 ± 10.6 vs. 95.5 ± 7.0%) and FVC (82.4 ± 13.2 vs. 93.7 ± 8.9%) compared with control subjects (n = 13). There were no significant differences in FRC or TLC at baseline. Twelve months after surgery, control subjects had significant increases in FEV1 (95.5 ± 7.0 to 100.7 ± 5.9), FVC (93.6 ± 8.9 to 98.6 ± 8.3%), FRC (45.4 ± 18.5 to 62.1 ± 15.3%), and TLC (84.8 ± 15.0 to 103.1 ± 15.3%), whereas patients with asthma had improvement only in FEV1 (79.8 ± 10.6 to 87.2 ± 11.5). Control subjects and patients with asthma had a significantly different change in respiratory system resistance with weight loss: control subjects exhibited a uniform decrease in respiratory system resistance at all frequencies, whereas patients with asthma exhibited a decrease in frequency dependence of resistance. Fits of a mathematical model of lung mechanics to these impedance spectra suggest that the lung periphery was more collapsed by obesity in patients with asthma compared with control subjects.

CONCLUSIONS

Weight loss decompresses the lung in both obese control subjects and patients with asthma, but the more pronounced effects of weight loss on lung elastance suggest that the distal lung is inherently more collapsible in people with asthma.

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.

Effect of antigen sensitization and challenge on oscillatory mechanics of the lung and pulmonary inflammation in obese carboxypeptidase E-deficient mice

Atopic, obese asthmatics exhibit airway obstruction with variable degrees of eosinophilic airway inflammation. We previously reported that mice obese as a result of a genetic deficiency in either leptin (ob/ob mice) or the long isoform of the leptin receptor (db/db mice) exhibit enhanced airway obstruction in the presence of decreased numbers of bronchoalveolar lavage fluid (BALF) eosinophils compared with lean, wild-type mice following antigen (ovalbumin; OVA) sensitization and challenge. To determine whether the genetic modality of obesity induction influences the development of OVA-induced airway obstruction and OVA-induced pulmonary inflammation, we examined indices of these sequelae in mice obese as a result of a genetic deficiency in carboxypeptidase E, an enzyme that processes prohormones and proneuropeptides involved in satiety and energy expenditure (Cpe(fat) mice). Accordingly, Cpe(fat) and lean, wild-type (C57BL/6) mice were sensitized to OVA and then challenged with either aerosolized PBS or OVA. Compared with genotype-matched, OVA-sensitized and PBS-challenged mice, OVA sensitization and challenge elicited airway obstruction and increased BALF eosinophils, macrophages, neutrophils, IL-4, IL-13, IL-18, and chemerin. However, OVA challenge enhanced airway obstruction and pulmonary inflammation in Cpe(fat) compared with wild-type mice. These results demonstrate that OVA sensitization and challenge enhance airway obstruction in obese mice regardless of the genetic basis of obesity, whereas the degree of OVA-induced pulmonary inflammation is dependent on the genetic modality of obesity induction. These results have important implications for animal models of asthma, as modeling the pulmonary phenotypes for subpopulations of atopic, obese asthmatics critically depends on selecting the appropriate mouse model.

Effects of BMI, fat mass, and lean mass on asthma in childhood: a Mendelian randomization study

BACKGROUND

Observational studies have reported associations between body mass index (BMI) and asthma, but confounding and reverse causality remain plausible explanations. We aim to investigate evidence for a causal effect of BMI on asthma using a Mendelian randomization approach.

METHODS AND FINDINGS

We used Mendelian randomization to investigate causal effects of BMI, fat mass, and lean mass on current asthma at age 7½ y in the Avon Longitudinal Study of Parents and Children (ALSPAC). A weighted allele score based on 32 independent BMI-related single nucleotide polymorphisms (SNPs) was derived from external data, and associations with BMI, fat mass, lean mass, and asthma were estimated. We derived instrumental variable (IV) estimates of causal risk ratios (RRs). 4,835 children had available data on BMI-associated SNPs, asthma, and BMI. The weighted allele score was strongly associated with BMI, fat mass, and lean mass (all p-values<0.001) and with childhood asthma (RR 2.56, 95% CI 1.38-4.76 per unit score, p = 0.003). The estimated causal RR for the effect of BMI on asthma was 1.55 (95% CI 1.16-2.07) per kg/m2, p = 0.003. This effect appeared stronger for non-atopic (1.90, 95% CI 1.19-3.03) than for atopic asthma (1.37, 95% CI 0.89-2.11) though there was little evidence of heterogeneity (p = 0.31). The estimated causal RRs for the effects of fat mass and lean mass on asthma were 1.41 (95% CI 1.11-1.79) per 0.5 kg and 2.25 (95% CI 1.23-4.11) per kg, respectively. The possibility of genetic pleiotropy could not be discounted completely; however, additional IV analyses using FTO variant rs1558902 and the other BMI-related SNPs separately provided similar causal effects with wider confidence intervals. Loss of follow-up was unlikely to bias the estimated effects.

CONCLUSIONS

Higher BMI increases the risk of asthma in mid-childhood. Higher BMI may have contributed to the increase in asthma risk toward the end of the 20th century. Please see later in the article for the Editors' Summary.

Is there a link between obesity and asthma?

Increasing epidemiological data identify a link between obesity and asthma incidence and severity. Based on experimental data, it is possible that shared inflammatory mechanisms play a role in determining this linkage. Although controversial, the role of adipokines may be central to this association and the maintenance of the asthma phenotype. While leptin and adiponectin have a causal link to experimental asthma in mice, data in humans are less conclusive. Recent studies demonstrate that adipokines can regulate the survival and function of eosinophils and that these factors can affect eosinophil trafficking from the bone marrow to the airways. In addition, efferocytosis, the clearance of dead cells, by airway macrophages or blood monocytes appears impaired in obese asthmatics and is inversely correlated with glucocorticoid responsiveness. This review examines the potential mechanisms linking obesity to asthma.

Skewing of immune cell cytokine production by mediators from adipocytes and endothelial cells

Since adipose tissue is composed of adipocytes as well as other cell types including endothelial cells, this study sought to determine how mediators from adipocytes and from endothelial cells impact on immune cell production of cytokines. A minimalistic design was used in which media conditioned by adipocytes or by endothelial cells were added individually or as a mixture to normal spleen cells. Media from adipocytes or endothelial cells each stimulated spleen cell production of Th1 cytokines, Th2 cytokines, most of the measured inflammatory cytokines, and some chemokines. However, a mixture of media conditioned by adipocytes and by endothelial cells inhibited production of Th1 cytokines and skewed reactivity toward a Th2 and inflammatory phenotype. Adiponectin, but not leptin, was shown to contribute to the skewing of immune responsiveness to endothelial cell-derived mediators.

High sputum total adiponectin is associated with low odds for asthma

OBJECTIVE

Adipose tissue produces adiponectin, an anti-inflammatory protein. High systemic total adiponectin is associated with a low risk for incident asthma but the association with lung adiponectin is not known. Our objective was to evaluate the association between sputum total adiponectin and asthma.

METHODS

This case-control study included 44 cases with objectively-confirmed asthma and an equal number of body mass index (BMI) and sex-matched controls. Serum and sputum adiponectin were estimated by ELISA and Western Blot technique, respectively. While Fisher's exact test, t-test and Spearman's correlations were used for univariate analyses, Spearman and regression analyses were performed for multivariable analyses.

RESULTS

While high-molecular-weight adiponectin was the dominant isoform in serum, medium-molecular-weight isoform was dominant in sputum. Sputum total adiponectin was not correlated with serum adiponectin or BMI. Sputum total adiponectin was lower among asthmatics than controls (p = 0.03), although individual sputum isoforms were not similarly associated. High sputum total adiponectin was associated with lower odds for asthma (OR 0.33, 95% C.I. 0.12, 0.91), even after adjustment for systemic adiposity measures including serum adiponectin.

CONCLUSIONS

High sputum total adiponectin predicted lower odds for asthma, even after adjustment for serum adiponectin. Although not studied, it is possible that pharmacological modulation of sputum adiponectin may suggest new ways to prevent and/or treat asthma.

Obesity in asthma: approaches to treatment

There is mounting evidence that obesity is associated with asthma, both of which are seeing a dramatic increase in prevalence. Not only is obesity a risk factor for the development of asthma but it is also associated with poor asthma control. Asthma phenotypes associated with obesity include early-onset allergic asthma and late-onset non-allergic asthma. The pathogenesis of the linkage is complex; obesity causes a variety of mechanical, metabolic, and immunological changes that can affect the airways. The treatment of asthma in obesity can be challenging, as obesity is associated with poor response to standard controller medications. A tailored approach that involves combining pharmacologic and non-pharmacologic therapies including weight loss, dietary interventions, and exercise, along with identification and treatment of obstructive sleep apnea, should therefore be considered in this population.

Airway dysfunction in obesity: response to voluntary restoration of end expiratory lung volume

Introduction

Abnormality in distal lung function may occur in obesity due to reduction in resting lung volume; however, airway inflammation, vascular congestion and/or concomitant intrinsic airway disease may also be present. The goal of this study is to 1) describe the phenotype of lung function in obese subjects utilizing spirometry, plethysmography and oscillometry; and 2) evaluate residual abnormality when the effect of mass loading is removed by voluntary elevation of end expiratory lung volume (EELV) to predicted FRC.

Methods

100 non-smoking obese subjects without cardio-pulmonary disease and with normal airflow on spirometry underwent impulse oscillometry (IOS) at baseline and at the elevated EELV.

Results

FRC and ERV were reduced (44±22, 62±14% predicted) with normal RV/TLC (29±9%). IOS demonstrated elevated resistance at 20 Hz (R₂₀, 4.65±1.07 cmH₂O/L/s); however, specific conductance was normal (0.14±0.04). Resistance at 5–20 Hz (R₅₋₂₀, 1.86±1.11 cmH₂O/L/s) and reactance at 5 Hz (X₅, −2.70±1.44 cmH₂O/L/s) were abnormal. During elevation of EELV, IOS abnormalities reversed to or towards normal. Residual abnormality in R₅₋₂₀ was observed in some subjects despite elevation of EELV (1.16±0.8 cmH₂O/L/s). R₅₋₂₀ responded to bronchodilator at baseline but not during elevation of EELV.

Conclusions

This study describes the phenotype of lung dysfunction in obesity as reduction in FRC with airway narrowing, distal respiratory dysfunction and bronchodilator responsiveness. When R₅₋₂₀ normalized during voluntary inflation, mass loading was considered the predominant mechanism. In contrast, when residual abnormality in R₅₋₂₀ was demonstrable despite return of EELV to predicted FRC, mechanisms for airway dysfunction in addition to mass loading could be invoked.

The misuse of asthma drugs

There are three major problems with asthma care in the USA and misuse of asthma drug therapy contributes to each. Asthma patients suffer from symptoms regularly partly because healthcare providers do not understand the Expert Panel Report III (EPR3) recommendations on assessing asthma symptoms to determine drug treatment and, consequently, undertreat the disease. Asthma patients experience exacerbations often in part because the EPR3 provides limited guidance on using exacerbation risk to guide asthma treatment, again leading to undertreatment. The EPR3 recommends inhaled corticosteroids as the preferred therapy for mild persistent asthma but American healthcare providers disregard this recommendation based on different perceptions about the risks and benefits of inhaled corticosteroids and choose drug treatments with higher healthcare costs.

The lung inflammation and skeletal muscle wasting induced by subchronic cigarette smoke exposure are not altered by a high-fat diet in mice

Obesity and cigarette smoking independently constitute major preventable causes of morbidity and mortality and obesity is known to worsen lung inflammation in asthma. Paradoxically, higher body mass index (BMI) is associated with reduced mortality in smoking induced COPD whereas low BMI increases mortality risk. To date, no study has investigated the effect of a dietary-induced obesity and cigarette smoke exposure on the lung inflammation and loss of skeletal muscle mass in mice. Male BALB/c mice were exposed to 4 cigarettes/day, 6 days/week for 7 weeks, or sham handled. Mice consumed either standard laboratory chow (3.5 kcal/g, 12% fat) or a high fat diet (HFD, 4.3 kcal/g, 32% fat). Mice exposed to cigarette smoke for 7 weeks had significantly more inflammatory cells in the BALF (P<0.05) and the mRNA expression of pro-inflammatory cytokines and chemokines was significantly increased (P<0.05); HFD had no effect on these parameters. Sham- and smoke-exposed mice consuming the HFD were significantly heavier than chow fed animals (12 and 13%, respectively; P<0.05). Conversely, chow and HFD fed mice exposed to cigarette smoke weighed 16 and 15% less, respectively, compared to sham animals (P<0.05). The skeletal muscles (soleus, tibialis anterior and gastrocnemius) of cigarette smoke-exposed mice weighed significantly less than sham-exposed mice (P<0.05) and the HFD had no protective effect. For the first time we report that cigarette smoke exposure significantly decreased insulin-like growth factor-1 (IGF-1) mRNA expression in the gastrocnemius and tibialis anterior and IGF-1 protein in the gastrocnemius (P<0.05). We have also shown that cigarette smoke exposure reduced circulating IGF-1 levels. IL-6 mRNA expression was significantly elevated in all three skeletal muscles of chow fed smoke-exposed mice (P<0.05). In conclusion, these findings suggest that a down-regulation in local IGF-1 may be responsible for the loss of skeletal muscle mass following cigarette smoke exposure in mice.

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.

Three phenotypes of adult-onset asthma

RATIONALE

Adult-onset asthma differs from childhood-onset asthma in many respects. It is more heterogeneous, often severe and frequently associated with loss of lung function. To identify underlying mechanisms of adult-onset asthma and to capture predictors of disease progression, detailed characterization and phenotyping is necessary.

OBJECTIVES

To characterize adult-onset asthma and identify subphenotypes of adult-onset asthma.

METHODS

A cohort of 200 patients with adult-onset (>18 year) asthma (age 54 (26-75) year) was recruited from one academic and three nonacademic pulmonary outpatient clinics in Amsterdam, the Netherlands. These patients were fully characterized with respect to clinical, functional and inflammatory markers. After data reduction, K-means nonhierarchical cluster analysis was performed to identify clusters of adult-onset asthma.

MEASUREMENTS AND MAIN RESULTS

Patients with adult-onset asthma were predominately female (61%) and nonatopic (55%). Within this group of patients were identified three clusters of adult-onset asthma. Cluster 1 (n = 69) consisted of patients with severe eosinophilic inflammation-predominant asthma and persistent airflow limitation despite high-intensity anti-inflammatory treatment, with relatively low symptom scores. The second cluster was characterized by obese women with frequent symptoms, high healthcare utilization and low sputum eosinophils. The third cluster consisted of patients with mild-to-moderate, well-controlled asthma with normal lung function and low inflammatory markers. Repeatability accuracy was 98.2%.

CONCLUSIONS

Amongst patients with adult-onset asthma, three subphenotypes can be identified with distinct clinical and inflammatory characteristics. These subphenotypes help to understand the underlying pathobiology and provide clinicians with directions for personalized management.

Obese mice are resistant to eosinophilic airway inflammation induced by diesel exhaust particles

Particulate matter can exacerbate respiratory diseases such as asthma. Diesel exhaust particles are the substantial portion of ambient particulate matter with a <2.5 µm diameter in urban areas. Epidemiological data indicate increased respiratory health effects of particulate matter in obese individuals; however, the association between obesity and diesel exhaust particle-induced airway inflammation remains unclear. We aimed to investigate the differences in susceptibility to airway inflammation induced by exposure to diesel exhaust particles between obese mice (db/db) and lean mice (db/+m). Female db/db and db/+m mice were intratracheally administered diesel exhaust particles or vehicle every 2 weeks for a total of seven times. The cellular profile of bronchoalveolar lavage fluid and histological changes in the lungs were assessed and the lungs and serum were analyzed for the generation of cytokines, chemokines and soluble intercellular adhesion molecule 1. Diesel exhaust particle exposure-induced eosinophilic infiltration in db/+m mice accompanied by T-helper 2 cytokine, chemokine and soluble intercellular adhesion molecule 1 expression in the lungs. In contrast, it induced mild neutrophilic airway inflammation accompanied by elevated cytokines and chemokines in db/db mice. The lungs of db/db mice exhibited decreased expression of eosinophil activators/chemoattractants such as interleukin-5, interleukin-13 and eotaxin compared with those of db/+m mice. In addition, serum eotaxin and monocyte chemotactic protein-1 levels were significantly higher in db/db mice than in db/+m mice. In conclusion, obesity can affect susceptibility to diesel exhaust particle-induced airway inflammation, which is possibly due to differences in local and systemic inflammatory responses between lean and obese individuals.

Immunometabolism in obese asthmatics: are we there yet?

Obesity is now recognised as a worldwide epidemic. The recent International Association for the Study of Obesity/International Obesity Taskforce (IASO/IOTF) analysis estimates that approximately 1.0 billion adults are currently overweight and a further 475 million are obese. Obesity has huge psychosocial impact with obese children and adolescents facing discrimination and stigmatization in many areas of their lives leading to body dissatisfaction, low self-esteem and depression. Indeed, obesity is recognised as an important risk factor for the development of several chronic diseases such as hypertension, cancer, asthma and metabolic syndrome. Chronic low grade systemic inflammation is considered as a hallmark of obesity and may possibly explain the link between obesity and chronic disease, in particular the increased incidence, prevalence and severity of asthma in obese individuals. There is now strong evidence for infiltration of immune and inflammatory cells into adipose tissue that drives systemic inflammation and subsequent end organ damage. In addition to adipocytes, the key adipose tissue resident immune cells are macrophages and mast cells. Immunometabolism, as an emerging field of investigation, explores the pivotal role of these immune cells in translating immunological changes to metabolic effects in obesity. Abundance of free fatty acids, along with other inflammatory cytokines shift the balance of metabolic homeostasis to pro-inflammatory status by influencing the development of inflammatory cell lineage, which, further exhibits distinct functional phenotypes. There is emerging evidence for macrophage activation and functional polarization of an anti-inflammatory M₂ phenotype towards a pro-inflammatory M₁ phenotype of macrophages in obese adipose tissue. Similarly, studies in both obese humans and murine models reveal the pathognomic presence of an increased number of mast cells in visceral adipose tissue. These suggest a possible contribution of mast cells to the unique metabolome of obese asthma. This review examines proposed multilevel interactions between metabolic and immune systems in obese asthmatics that underlie the negative effects of obesity and may offer significant therapeutic promise.

Complex phenotypes in asthma: current definitions

Asthma is increasingly recognized as a heterogeneous disease. However, identification of different subgroups or phenotypes has been complex and controversial. The convergence of both clinical and statistical approaches to grouping patients and their characteristics, in association with increasing recognition of molecular patterns is now beginning to move the field forward. Integration of efficacy data with targeted molecular therapies will eventually lead to more complete understanding of these "molecular phenotypes" and eventually lead to the identification of fully defined endotypes. This process should improve our ability to treat more complex and severe forms of asthma.

Severe adult-onset asthma: A distinct phenotype

BACKGROUND

Some patients with adult-onset asthma have severe disease, whereas others have mild transient disease. It is currently unknown whether patients with severe adult-onset asthma represent a distinct clinical phenotype.

OBJECTIVE

We sought to investigate whether disease severity in patients with adult-onset asthma is associated with specific phenotypic characteristics.

METHODS

One hundred seventy-six patients with adult-onset asthma were recruited from 1 academic and 3 nonacademic outpatient clinics. Severe refractory asthma was defined according to international Innovative Medicines Initiative criteria, and mild-to-moderate persistent asthma was defined according to Global Initiative for Asthma criteria. Patients were characterized with respect to clinical, functional, and inflammatory parameters. Unpaired t tests and χ(2) tests were used for group comparisons; both univariate and multivariate logistic regression were used to determine factors associated with disease severity.

RESULTS

Apart from the expected high symptom scores, poor quality of life, need for high-intensity treatment, low lung function, and high exacerbation rate, patients with severe adult-onset asthma were more often nonatopic (52% vs 34%, P = .02) and had more nasal symptoms and nasal polyposis (54% vs 27%, P ≤ .001), higher exhaled nitric oxide levels (38 vs 27 ppb, P = .02) and blood neutrophil counts (5.3 vs 4.0 10(9)/L, P ≤ .001) and sputum eosinophilia (11.8% vs 0.8%, P ≤ .001). Multiple logistic regression analysis showed that increased blood neutrophil (odds ratio, 10.9; P = .002) and sputum eosinophil (odds ratio, 1.5; P = .005) counts were independently associated with severe adult-onset disease.

CONCLUSION

The majority of patients with severe adult-onset asthma are nonatopic and have persistent eosinophilic airway inflammation. This suggests that severe adult-onset asthma has a distinct underlying mechanism compared with milder disease.

Role of obesity in asthma control, the obesity-asthma phenotype

Asthma is a disease with distinct phenotypes that have implications for both prognosis and therapy. Epidemiologic studies have demonstrated an association between asthma and obesity. Further studies have shown that obese asthmatics have poor asthma control and more severe asthma. This obese-asthma group may represent a unique phenotype. The mechanisms behind poor asthma control in obese subjects remain unclear, but recent research has focused on adipokines and their effects on the airways as well as the role of oxidative stress. Both surgical and nonsurgical weight loss therapy have shown promising results with improvements in asthma control and decreased asthma severity. Comorbid conditions such as gastroesophageal reflux disease and obstructive sleep apnea may also have a role in poor asthma control in obese asthmatics. Further research is needed to define the mechanisms behind this phenotype which will guide the development of targeted therapies.

Adult-onset asthma: is it really different?

Asthma that starts in adulthood differs from childhood-onset asthma in that it is often non-atopic, more severe and associated with a faster decline in lung function. Understanding of the underlying mechanism of adult-onset asthma and identification of specific phenotypes may further our understanding of pathophysiology and treatment response, leading to better targeting of both existing and new approaches for personalised management. Pivotal studies in past years have led to sustained progress in many areas, ranging from risk factors for development, identification of different phenotypes, and introduction of new therapies. This review highlights and discusses literature on adult-onset asthma, with special focus on the differences from childhood-onset asthma, risk factors for development, phenotypes of adult-onset asthma and new approaches for personalised management.

Risk factors for airway hyperresponsiveness in severely obese women

Obesity affects airway diameter and tidal ventilation pattern, which could perturb smooth muscle function. The objective was to assess the pathophysiology of airway hyperresponsiveness in obesity while controlling for gastro-oesophageal reflux disease. Obese women (n=118, mean±SD BMI 46.1±6.8kg/m(-2)) underwent pulmonary function testing (including tidal ventilation monitoring and methacholine challenge) and oesogastro-duodenal fibroscopy. Fifty-seven women (48%, 95% CI: 39-57%) exhibited hyperresponsiveness (dose-response slope ≥2.39% decrease/μmol) that was independently and positively correlated with predicted % FRC, Raw0.5 and negatively correlated with sigh frequency during tidal ventilation. Obese women had an increased breathing frequency but a similar sigh frequency than healthy lean women (n=30). Twenty-two obese women (19%, 95% CI: 12-26%) were classified as asthmatics (hyperresponsiveness and suggestive symptoms) without confounding effect of gastro-oesophageal reflux disease. In conclusion, in women referred for bariatric surgery, unloading of bronchial smooth muscle (reduced airway calibre and sigh frequency) is associated with hyperresponsiveness.

Proinflammatory, anti-inflammatory cytokines and adiponkines in students with central obesity

Several studies have investigated the correlation between central obesity and inflammatory cytokines and the anti-inflammatory cytokine adiponectin. But, the correlation between central obesity and the anti-inflammatory cytokines IL-4, IL-5 has not been studied yet. Thus, we aimed to study the IL-4 and IL-5 correlation to central obesity in adolescent Egyptian girls among proinflammatory and anti-inflammatory cytokines. The study was carried out on 86 obese adolescent girls (BMI>95 percentile) divided into two groups according to central obesity. The group I with waist to hip ratio <0.8 as a control and group II with waist to hip ratio >0.8 (central obesity). There was a significant increase in TNF-alpha (p<0.0001), and IL-1β (p<0.0001), as proinflammatory cytokines in group II, as compared to their corresponding group I. Group II showed a significant increase in the anti-inflammatory cytokines IL-4 and IL-5 than group I at (p<0.0001) and (p<0.0005) respectively. In addition there was a significant decrease in the anti-inflammatory adiponectin and an increase in the inflammatory leptin levels in group II at (p<0.0001) and (p<0.0001) respectively in comparison to group I. A high positive correlation has been observed between waist to hip ratio, leptin, TNF-α, IL-1-β, IL-4 and IL-5 at (r=0.331, p<0.03), (r=0.559, p<0.001), (r=0.435, p<0.004), (r=0.509, p<0.001), (r=0.550, p<0.0015), in group II respectively and a high negative one with adiponectin at (r=-0.410, p<0.0001). We concluded that central obesity lowers adiponectin plasma level through increasing proinflammatory adipokines such as TNF-α, IL-1β, leptin. Further studies are needed to explore the positive correlation we found between central obesity and the anti-inflammatory cytokines IL-4 and IL-5 known to be associated with bronchial asthma.