Role of MUC5AC in the pathogenesis of exercise-induced bronchoconstriction

Development and qualification of an LC-MS/MS method for quantification of MUC5AC and MUC5B mucins in spontaneous sputum

AIM

Airway mucins in sputum are promising respiratory disease biomarkers, despite posing substantial analytical challenges due to their physicochemical properties and rare and heterogenous nature of the matrix. We aimed to identify a suitable sputum collection and processing method, and qualify a bioanalytical method for MUC5AC and MUC5B quantification in clinical samples.

METHOD

Mucins were quantified in induced and spontaneous sputum collected from the same COPD patients, following various sample processing procedures. LC-MS/MS method used truncated recombinant mucins as surrogate analytes in surrogate matrix.

RESULTS

Frozen spontaneous sputum was found to be a suitable and convenient matrix for mucin quantification and fit-for-purpose method qualification was performed.

CONCLUSION

Our methodology provides accurate and reliable MUC5AC and MUC5B quantification and facilitates multi-site clinical sputum collection.

Association of temperature and absolute humidity with incidence of exercise-induced bronchoconstriction in children

AIM

Exercise test outdoors is widely used to diagnose asthma in children, but it is unclear how much outdoor air factors affect the results.

METHODS

We analysed 321 outdoor exercise challenge tests with spirometry in children 6-16 years conducted due to suspicion of asthma or for assessing the effect of medication on asthma. We studied the association of FEV1 decrease and incidence of exercise-induced bronchoconstriction (EIB) with temperature, relative humidity (RH) and absolute humidity (AH).

RESULTS

Asthma was diagnosed in 57% of the subjects. AH ≥5 g/m3, but not RH or temperature, was associated with the EIB incidence (p = 0.035). In multivariable logistic regression, AH ≥5 g/m3 was negatively associated (OR = 0.51, 95% CI [0.28─0.92], p = 0.026) while obstruction before exercise (OR = 2.11, 95% CI [1.16─3.86], p = 0.015) and IgE-mediated sensitisation were positively associated with EIB (OR = 2.24, 95% CI [1.11─4.51], p = 0.025). AH (r = -0.12, p = 0.028) and temperature (r = -0.13, p = 0.023) correlated with decrease in FEV1. In multivariable linear regression, only AH was associated with FEV1 decrease (coefficient = -0.044, 95% CI [-0.085 to -0.004], p = 0.033).

CONCLUSION

AH of outdoor air associates with occurrence and severity of EIB in outdoor exercise tests in children. Care should be taken when interpreting negative outdoor exercise test results if AH of air is high.

Overuse of Short-Acting Beta-2 Agonists (SABAs) in Elite Athletes: Hypotheses to Explain It

The use of short-acting beta-2 agonists (SABAs) is more common in elite athletes than in the general population, especially in endurance sports. The World Anti-Doping Code places some restrictions on prescribing inhaled β2-agonists. These drugs are used in respiratory diseases (such as asthma) that might reduce athletes’ performances. Recently, studies based on the results of the Olympic Games revealed that athletes with confirmed asthma/airway hyperresponsiveness (AHR) or exercise-induced bronchoconstriction (EIB) outperformed their non-asthmatic rivals. This overuse of SABA by high-level athletes, therefore, raises some questions, and many explanatory hypotheses are proposed. Asthma and EIB have a high prevalence in elite athletes, especially within endurance sports. It appears that many years of intensive endurance training can provoke airway injury, EIB, and asthma in athletes without any past history of respiratory diseases. Some sports lead to a higher risk of asthma than others due to the hyperventilation required over long periods of time and/or the high environmental exposure while performing the sport (for example swimming and the associated chlorine exposure). Inhaled corticosteroids (ICS) have a low efficacy in the treatment of asthma and EIB in elite athletes, leading to a much greater use of SABAs. A significant proportion of these high-level athletes suffer from non-allergic asthma, involving the th1-th17 pathway.

Exercise-Induced Bronchoconstriction in Children

Exercise-induced bronchoconstriction (EIB) is a transient airflow obstruction, typically 5-15 min after physical activity. The pathophysiology of EIB is related to the thermal and osmotic changes of the bronchial mucosa, which cause the release of mediators and the development of bronchoconstriction in the airways. EIB in children often causes an important limitation to physical activities and sports. However, by taking appropriate precautions and through adequate pharmacological control of the condition, routine exercise is extremely safe in children. This review aims to raise awareness of EIB by proposing an update, based on the latest studies, on pathological mechanisms, diagnosis, and therapeutic approaches in children.

Location of eosinophils in the airway wall is critical for specific features of airway hyperresponsiveness and T2 inflammation in asthma

Eosinophils are implicated as effector cells in asthma but the functional implications of the precise location of eosinophils in the airway wall is poorly understood. We aimed to quantify eosinophils in the different compartments of the airway wall and associate these findings with clinical features of asthma and markers of airway inflammation.In this cross-sectional study, we utilised design-based stereology to accurately partition the numerical density of eosinophils in both the epithelial compartment and the subepithelial space (airway wall area below the basal lamina including the submucosa) in individuals with and without asthma and related these findings to airway hyperresponsiveness (AHR) and features of airway inflammation.Intraepithelial eosinophils were linked to the presence of asthma and endogenous AHR, the type of AHR that is most specific for asthma. In contrast, both intraepithelial and subepithelial eosinophils were associated with type-2 (T2) inflammation, with the strongest association between IL5 expression and intraepithelial eosinophils. Eosinophil infiltration of the airway wall was linked to a specific mast cell phenotype that has been described in asthma. We found that IL-33 and IL-5 additively increased cysteinyl leukotriene (CysLT) production by eosinophils and that the CysLT LTC₄ along with IL-33 increased IL13 expression in mast cells and altered their protease profile.We conclude that intraepithelial eosinophils are associated with endogenous AHR and T2 inflammation and may interact with intraepithelial mast cells via CysLTs to regulate airway inflammation.

Role for Mucin-5AC in Upper and Lower Airway Pathogenesis in Mice

Mucin-5AC (MUC5AC) is a major secreted mucin in pathogenic airways. To determine its role in mucus-related airway disorders, Muc5ac-deficient (Muc5ac^-/-) and wild-type (Muc5ac^+/+) mice were compared in bleomycin-induced pulmonary fibrosis, respiratory syncytial virus (RSV) disease, and ozone toxicity. Significantly greater inflammation and fibrosis by bleomycin were developed in Muc5ac^-/- lungs compared to Muc5ac^+/+ lungs. More severe mucous cell metaplasia in fibrotic Muc5ac^-/- lungs coincided with bronchial Muc2, Muc4, and Muc5b overexpression. Airway RSV replication was higher in Muc5ac^-/- than in Muc5ac^+/+ during early infection. RSV-caused pulmonary epithelial death, bronchial smooth muscle thickening, and syncytia formation were more severe in Muc5ac^-/- compared to Muc5ac^+/+. Nasal septal damage and subepithelial mucoserous gland enrichment by RSV were greater in Muc5ac^-/- than in Muc5ac^+/+. Ozone exposure developed more severe nasal airway injury accompanying submucosal gland hyperplasia and pulmonary proliferation in Muc5ac^-/- than in Muc5ac^+/+. Ozone caused periodic acid-Schiff-positive secretion only in Muc5ac^-/- nasal airways. Lung E-cadherin level was relatively lower in Muc5ac^-/- than in Muc5ac^+/+ basally and after bleomycin, RSV, and ozone exposure. Results indicate that MUC5AC is an essential mucosal component in acute phase airway injury protection. Subepithelial gland hyperplasia and adaptive increase of other epithelial mucins may compensate airway defense in Muc5ac^-/- mice.

Asthma, atopy, and exercise: Sex differences in exercise-induced bronchoconstriction

Asthma is a chronic inflammatory lung disease affecting approximately 7.7% of the US population. Sex differences in the prevalence, incidence, and severity of asthma have been widely described throughout the lifespan, showing higher rates in boys than girls before puberty, but a reversed pattern in adults. Asthma is often associated with atopy, i.e. the tendency to develop allergic diseases, and can be worsened by environmental stimuli and/or exercise. While not exclusive to patients with asthma, exercise-induced bronchoconstriction (EIB) is a common complication of athletes and individuals who exercise regularly. Currently, there is limited research on sex differences in EIB and its relationship with atopy and asthma in men and women. In this minireview, we summarize the available literature on this topic. Overall, the collective knowledge supports the notion that physiological changes triggered during exercise affect males and females differently, suggesting an interaction among sex, exercise, sex hormones, and atopic status in the course of EIB pathophysiology. Understanding these differences is important to provide personalized management plans to men and women who exercise regularly and suffer from underlying asthma and/or atopy.

Overexpression of Substance P in pig airways increases MUC5AC through an NF-kβ pathway

Substance P (SP) is a tachykinin that regulates airway mucous secretion in both health and disease. Our study aimed to determine whether overexpression of SP without pre‐existing inflammation was sufficient to induce changes in mucin secretion and transport in small airways. Utilizing porcine precision‐cut lung slices, we measured the impact of AAV‐mediated overexpression of SP on airway physiology ex vivo. Immunofluorescence signal intensity for MUC5AC was significantly increased in SP‐overexpressed precision‐cut lung slices compared to GFP controls. No difference in MUC5B signal intensity between treatments was detected. SP‐overexpressed precision‐cut lung slices also exhibited decreased IL10 mRNA, an important inhibitor of mucous cell metaplasia. Overt deficits in mucociliary transport were not noted, though a trend for decreased mean transport speed was detected in methacholine‐challenged airways overexpressing SP compared to GFP controls. Pharmacologic inhibition of the NF‐kβ pathway abrogated the effects of overexpression of SP on both MUC5AC and IL10. Collectively, these data suggest that overexpression of SP in the absence of existing inflammation increases MUC5AC via activation of the NF‐kβ pathway. Thus, these data further highlight SP as a key driver of abnormal mucous secretion and underscore NF‐kβ signaling as a pathway of potential therapeutic intervention.

Exercise-induced bronchoconstriction in elite or endurance athletes:: Pathogenesis and diagnostic considerations

OBJECTIVE

To review the pathogenesis and evaluation of exercise-induced bronchoconstriction pertaining to the elite or endurance athlete, as well as propose a diagnostic algorithm based on the current literature.

DATA SOURCES

Studies were identified using Ovid MEDLINE and reference lists of key articles.

STUDY SELECTIONS

Randomized controlled trials were selected when available. Systematic reviews and meta-analyses of peer-reviewed literature were included, as were retrospective studies and observational studies of clinical interest.

RESULTS

Exercise-induced bronchoconstriction (EIB) is the physiologic entity in which exercise induces acute narrowing of the airways and occurs in patients both with and without asthma. It may present with or without respiratory symptoms, and the underlying cause is likely attributable to environment stressors to the airway encountered during exercise. These include the osmotic effects of inhaled dry air, temperature variations, autonomic nervous system dysregulation, sensory nerve reactivity, and airway epithelial injury. Deposition of allergens, particulate matter, and gaseous pollutants into the airway also contribute. Elite and endurance athletes are exposed to these stressors more frequently and in greater duration than the general population.

CONCLUSION

A greater awareness of EIB among elite and endurance athletes is needed, and a thorough evaluation should be performed if EIB is suspected in this population. We propose an algorithm to aid in this evaluation. Symptoms should not be solely relied on for diagnosis but should be taken into the context of bronchoprovocative challenges, which should replicate the competitive environment as closely as possible. Further research is needed to validate these tests' predictive values.

Asthma among elite athletes, mechanism of occurrence and impact on respiratory parameters: A review of literature

Introduction: It is generally accepted that physical activity benefits every person but athletes diagnosed with asthma face various challenges during their training to keep the symptoms of the disease under control. Prolonged exposure to agents in the environment in which athletes train favors the development of permanent changes in the airways. Their action leads to permanent hyper-reactivity with development of an inflammatory response and the release of mediators (IL-8, leukotrienes, eicosanoids) that lead to damage epithelial cells with breaking connection between them and consequent dysfunction of the respiratory system. This condition is called exercise-induced asthma (EIA). This fact is especially important for athletes who have long endurance training. The best way to check the condition of breathing system is with a diagnostic method which is the " gold" standard spirometry. Aim: The point of this systematic review is to get closer the mechanism occurrence of EIA/(exercise-induced bronchoconstriction)-EIB, prevalence and incidence of EIA/EIB, changes of pulmonary function and quality of life in elite athletes. We searched papers from PubMed and Cochrane database using keywords: 'exercise-induced asthma', 'athletes', 'spirometry', 'bronchoconstriction', 'bronchospasm', 'physical activity', 'physical training', 'prevalence', 'incidence'. We have studied 48 scientific papers in total. Conclusion: The prevalence of asthma among elite athletes, especially endurance athletes is higher than in general population. The explanation of this phenomenon is related to the whole mechanism of occurrence, it is still insufficiently clarified, but one thing is for sure that with good disease control athletes can play and compete undisturbed for many years.

Mechanisms and Biomarkers of Exercise-Induced Bronchoconstriction

Exercise is a common trigger of bronchoconstriction. In recent years, there has been increased understanding of the pathophysiology of exercise-induced bronchoconstriction. Although evaporative water loss and thermal changes have been recognized stimuli for exercise-induced bronchoconstriction, accumulating evidence points toward a pivotal role for the airway epithelium in orchestrating the inflammatory response linked to exercise-induced bronchoconstriction. Overproduction of inflammatory mediators, underproduction of protective lipid mediators, and infiltration of the airways with eosinophils and mast cells are all established contributors to exercise-induced bronchoconstriction. Sensory nerve activation and release of neuropeptides maybe important in exercise-induced bronchoconstriction, but further research is warranted.

ERS technical standard on bronchial challenge testing: pathophysiology and methodology of indirect airway challenge testing

Recently, this international task force reported the general considerations for bronchial challenge testing and the performance of the methacholine challenge test, a "direct" airway challenge test. Here, the task force provides an updated description of the pathophysiology and the methods to conduct indirect challenge tests. Because indirect challenge tests trigger airway narrowing through the activation of endogenous pathways that are involved in asthma, indirect challenge tests tend to be specific for asthma and reveal much about the biology of asthma, but may be less sensitive than direct tests for the detection of airway hyperresponsiveness. We provide recommendations for the conduct and interpretation of hyperpnoea challenge tests such as dry air exercise challenge and eucapnic voluntary hyperpnoea that provide a single strong stimulus for airway narrowing. This technical standard expands the recommendations to additional indirect tests such as hypertonic saline, mannitol and adenosine challenge that are incremental tests, but still retain characteristics of other indirect challenges. Assessment of airway hyperresponsiveness, with direct and indirect tests, are valuable tools to understand and to monitor airway function and to characterise the underlying asthma phenotype to guide therapy. The tests should be interpreted within the context of the clinical features of asthma.

Neuropeptides in asthma, chronic obstructive pulmonary disease and cystic fibrosis

The nervous system mediates key airway protective behaviors, including cough, mucus secretion, and airway smooth muscle contraction. Thus, its involvement and potential involvement in several airway diseases has become increasingly recognized. In the current review, we focus on the contribution of select neuropeptides in three distinct airway diseases: asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis. We present data on some well-studied neuropeptides, as well as call attention to a few that have not received much consideration. Because mucus hypersecretion and mucus obstruction are common features of many airway diseases, we place special emphasis on the contribution of neuropeptides to mucus secretion. Finally, we highlight evidence implicating involvement of neuropeptides in mucus phenotypes in asthma, COPD and cystic fibrosis, as well as bring to light knowledge that is still lacking in the field.

Exercise-induced bronchoconstriction update-2016

The first practice parameter on exercise-induced bronchoconstriction (EIB) was published in 2010. This updated practice parameter was prepared 5 years later. In the ensuing years, there has been increased understanding of the pathogenesis of EIB and improved diagnosis of this disorder by using objective testing. At the time of this publication, observations included the following: dry powder mannitol for inhalation as a bronchial provocation test is FDA approved however not currently available in the United States; if baseline pulmonary function test results are normal to near normal (before and after bronchodilator) in a person with suspected EIB, then further testing should be performed by using standardized exercise challenge or eucapnic voluntary hyperpnea (EVH); and the efficacy of nonpharmaceutical interventions (omega-3 fatty acids) has been challenged. The workgroup preparing this practice parameter updated contemporary practice guidelines based on a current systematic literature review. The group obtained supplementary literature and consensus expert opinions when the published literature was insufficient. A search of the medical literature on PubMed was conducted, and search terms included pathogenesis, diagnosis, differential diagnosis, and therapy (both pharmaceutical and nonpharmaceutical) of exercise-induced bronchoconstriction or exercise-induced asthma (which is no longer a preferred term); asthma; and exercise and asthma. References assessed as relevant to the topic were evaluated to search for additional relevant references. Published clinical studies were appraised by category of evidence and used to document the strength of the recommendation. The parameter was then evaluated by Joint Task Force reviewers and then by reviewers assigned by the parent organizations, as well as the general membership. Based on this process, the parameter can be characterized as an evidence- and consensus-based document.

Air quality and temperature effects on exercise-induced bronchoconstriction

Exercise-induced bronchoconstriction (EIB) is exaggerated constriction of the airways usually soon after cessation of exercise. This is most often a response to airway dehydration in the presence of airway inflammation in a person with a responsive bronchial smooth muscle. Severity is related to water content of inspired air and level of ventilation achieved and sustained. Repetitive hyperpnea of dry air during training is associated with airway inflammatory changes and remodeling. A response during exercise that is related to pollution or allergen is considered EIB. Ozone and particulate matter are the most widespread pollutants of concern for the exercising population; chronic exposure can lead to new-onset asthma and EIB. Freshly generated emissions particulate matter less than 100 nm is most harmful. Evidence for acute and long-term effects from exercise while inhaling high levels of ozone and/or particulate matter exists. Much evidence supports a relationship between development of airway disorders and exercise in the chlorinated pool. Swimmers typically do not respond in the pool; however, a large percentage responds to a dry air exercise challenge. Studies support oxidative stress mediated pathology for pollutants and a more severe acute response occurs in the asthmatic. Winter sport athletes and swimmers have a higher prevalence of EIB, asthma and airway remodeling than other athletes and the general population. Because of fossil fuel powered ice resurfacers in ice rinks, ice rink athletes have shown high rates of EIB and asthma. For the athlete training in the urban environment, training during low traffic hours and in low traffic areas is suggested.

Exercise-induced bronchoconstriction: new evidence in pathogenesis, diagnosis and treatment

The acute airway narrowing that occurs as a result of exercise is defined exercise-induced bronchoconstriction (EIB). Most recent guidelines recommend distinguishing EIB with underlying clinical asthma (EIB_A) from the occurrence of bronchial obstruction in subjects without other symptoms and signs of asthma (EIBw_A). EIB has been in fact reported in up to 90 % of asthmatic patients, reflecting the level of disease control, but it may develop even in subjects without clinical asthma, particularly in children, athletes, patients with atopy or rhinitis and following respiratory infections. Both EIB_A and EIBw_A have peculiar pathogenic mechanisms, diagnostic criteria and responses to treatment and prevention. The use of biomarkers, proteomic approaches and innovative technological procedures will hopefully contribute to better define peculiar phenotypes and to clarify the role of EIB as risk factor for the development of asthma, as well as an occupational disease.

The role of sports and exercise in allergic disease: drawbacks and benefits

Although training and exercise have several benefits, overdoing it might not necessarily be a good thing. For instance, elite athletes have an increased risk for asthma and allergy. Several mechanisms can be implicated for this risk, which include the interplay between environmental training factors and athlete's personal risk factors, such as genetic susceptibility, neurogenic-mediated inflammation, and epithelial sensitivity. However, an overwhelming amount of scientific evidence shows the positive effects of sports as part of a healthy lifestyle. Training reduces breathlessness and asthma symptoms and attenuates Th2-mediated inflammatory responses. Taken together, the benefits far outweigh the potential hazards of training. An easily administered therapeutic healthy lifestyle intervention, which could be used alongside current treatment, must be developed.

Advances in the diagnosis of exercise-induced bronchoconstriction

Exercise-induced bronchoconstriction (EIB) describes the post exercise phenomenon of acute airway narrowing in association with physical activity. A high prevalence of EIB is reported in both athletic and recreationally active populations. Without treatment, EIB has the potential to impact upon both health and performance. It is now acknowledged that clinical assessment alone is insufficient as a sole means of diagnosing airway dysfunction due to the poor predictive value of symptoms. Furthermore, a broad differential diagnosis has been established for EIB, prompting the requirement of objective evidence of airway narrowing to secure an accurate diagnosis. This article provides an appraisal of recent advances in available methodologies, with the principle aim of optimising diagnostic assessment, treatment and overall clinical care.

Regulation and function of epithelial secreted phospholipase A2 group X in asthma

RATIONALE

Indirect airway hyperresponsiveness (AHR) is a fundamental feature of asthma that is manifest as exercise-induced bronchoconstriction (EIB). Secreted phospholipase A2 group X (sPLA2-X) plays a key role in regulating eicosanoid formation and the development of inflammation and AHR in murine models.

OBJECTIVES

We sought to examine sPLA2-X in the airway epithelium and airway wall of patients with asthma, the relationship to AHR in humans, and the regulation and function of sPLA2-X within the epithelium.

METHODS

We precisely phenotyped 34 patients with asthma (19 with and 15 without EIB) and 10 normal control subjects to examine in vivo differences in epithelial gene expression, quantitative morphometry of endobronchial biopsies, and levels of secreted protein. The regulation of sPLA2-X gene (PLA2G10) expression was examined in primary airway epithelial cell cultures. The function of epithelial sPLA2-X in eicosanoid formation was examined using PLA2 inhibitors and murine tracheal epithelial cells with Pla2g10 deletion.

MEASUREMENTS AND MAIN RESULTS

We found that sPLA2-X protein is increased in the airways of patients with asthma and that epithelial-derived sPLA2-X may be increased in association with indirect AHR. The expression of sPLA2-X increases during in vitro epithelial differentiation; is regulated by inflammatory signals including tumor necrosis factor, IL-13, and IL-17; and is both secreted from the epithelium and directly participates in the release of arachidonic acid by epithelial cells.

CONCLUSIONS

These data reveal a relationship between epithelial-derived sPLA2-X and indirect AHR in asthma and that sPLA2-X serves as an epithelial regulator of inflammatory eicosanoid formation. Therapies targeting epithelial sPLA2-X may be useful in asthma.

Epithelial regulation of eicosanoid production in asthma

Alterations in the airway epithelium have been associated with the development of asthma in elite athletes and in subjects that are susceptible to exercise-induced bronchoconstriction (EIB). The syndrome of EIB refers to acute airflow obstruction that is triggered by a period of physical exertion. Asthmatics who are susceptible to EIB have increased levels of cysteinyl leukotrienes (CysLTs, i.e., LTs C₄, D₄, and E₄) in induced sputum and exhaled breath condensate, and greater shedding of epithelial cells into the airway lumen. Exercise challenge in individuals susceptible to this disorder initiates a sustained increase in CysLTs in the airways, and secreted mucin release and smooth muscle constriction, which may be mediated in part through activation of sensory nerves. We have identified a secreted phospholipase A₂ (sPLA₂) with increased levels in the airways of patients with EIB called sPLA₂ group X(sPLA₂-X).We have found that sPLA₂-X is strongly expressed in the airway epithelium in asthma. Further,we discovered that transglutaminase 2 (TGM2) is expressed at increased levels in asthma and serves asa regulator of sPLA₂-X. Finally, we demonstrated that sPLA₂-X acts on target cells such as eosinophils to initiate cellular eicosanoid synthesis. Collectively, these studies identify a novel mechanism linking the airway epithelium to the production of inflammatory eicosanoids by leukocytes.

Pathogenesis of exercise-induced bronchoconstriction

This article presents the various potential mechanisms responsible for the development of exercise-induced bronchoconstriction (EIB). Although the etiology of EIB is multifactorial, and the physiologic processes involved may vary between individuals (especially between those with and without asthma), drying of the small airways with an associated inflammatory response seems prerequisite for EIB. Dysregulated repair processes following exercise-induced airway epithelial injury may also serve as basis for EIB development/progression.

Where to from here for exercise-induced bronchoconstriction: the unanswered questions

The role of epithelial injury is an unanswered question in those with established asthma and in elite athletes who develop features of asthma and exercise-induced bronchorestriction (EIB) after years of training. The movement of water in response to changes in osmolarity is likely to be an important signal to the epithelium that may be central to the onset of EIB. It is generally accepted that the mast cell and its mediators play a major role in EIB and the presence of eosinophils is likely to enhance EIB severity.

Role of cells and mediators in exercise-induced bronchoconstriction

A susceptible group of subjects with asthma develops airflow obstruction in response to the transfer of water out of the airways during exercise. The transfer of water or the challenge with a hypertonic solution serves as a strong stimulus to the airway epithelium. Susceptible subjects have epithelial shedding into the airway lumen, and airway inflammation that leads to the overproduction of leukotrienes and other eicosanoids following exercise challenge. The sensory nerves of the airways may serve as a critical link that mediates the effect of eicosanoids, leading to bronchoconstriction and mucus production in response to exercise challenge.

Refractoriness to exercise challenge: a review of the mechanisms old and new

This article discusses the available literature on refractoriness in exercise-induced bronchoconstriction, namely, a decrease in airway responsiveness with repeated exercise challenges. The mechanisms of this naturally occurring protective feature is unknown. Reviewing previous studies together with findings in more recent studies, the authors propose desensitization of the G protein-coupled cysteinyl leukotriene receptor1 as the mechanism of refractoriness and that this desensitization occurs as a result of interplay between leukotrienes and prostaglandins.

Exercise-induced bronchoconstriction

OBJECTIVE

To review the literature regarding the pathophysiology of exercise-induced bronchoconstriction (EIB).

DATA SOURCES

The databases of PubMed, Ovid MEDLINE, and Scopus were searched for articles using the subject headings and/or keywords asthma, exercise-induced/etiology, exercise, mechanism, pathogenesis, and bronchoconstriction.

STUDY SELECTIONS

Articles were selected based on their relevance to the focus of this review, with emphasis on the specific pathophysiologic mechanisms of EIB.

RESULTS

EIB occurs in response to the loss of water from the lower airways that results from heating and humidifying large volumes of air in a short period. The resulting hyperosmolar environment activates various cellular mechanisms to release mediators from mast cells, eosinophils, epithelial cells, and sensory nerves. These mediators, in turn, lead to airway smooth muscle contraction and bronchoconstriction. Airway hyperresponsiveness in elite athletes may develop from a process of airway injury and changes in the contractile properties of airway smooth muscle.

CONCLUSION

EIB commonly affects individuals with and without clinically recognized asthma, especially those who participate in competitive athletics. Through years of research, the pathophysiology of EIB is now better understood and involves a complex interaction between several different cell types and mediators. Continued research to improve the knowledge regarding the mechanisms of EIB should aid the identification, diagnosis, and treatment of this common condition.

Immunopathology of exercise-induced bronchoconstriction in athletes--a new modified inflammatory hypothesis

Elite athletes have a higher prevalence of exercise-induced bronchoconstriction than the general population. The pathogenesis of exercise-induced bronchoconstriction is not fully elucidated. Increasing evidence suggests that airway inflammation plays a major role in the immunopathogenesis of exercise-induced bronchoconstriction. The aim of our review is to discuss existing evidence and to present a new, modified inflammatory hypothesis of exercise-induced bronchoconstriction. Exercise alters the number and function of circulating immune cells. Episodes of upper respiratory symptoms in elite athletes do not follow the usual seasonal patterns. Moreover, they have an unusual short-term duration, which suggests a non-infectious etiology. If the pro-inflammatory response to exercise has the potential to induce symptoms that mimic respiratory tract infection, it definitely up-regulates pro-inflammatory cytokine expression in the airways. We can conclude that exercise up-regulates airway cytokine expression in a way that favors inflammation and allergic reactions in bronchi and lowers the threshold for bronchoconstriction to different stimuli like cool, dry air, allergens, and pollutants.

Cellular and molecular biology of airway mucins

Airway mucus constitutes a thin layer of airway surface liquid with component macromolecules that covers the luminal surface of the respiratory tract. The major function of mucus is to protect the lungs through mucociliary clearance of inhaled foreign particles and noxious chemicals. Mucus is comprised of water, ions, mucin glycoproteins, and a variety of other macromolecules, some of which possess anti-microbial, anti-protease, and anti-oxidant activities. Mucins comprise the major protein component of mucus and exist as secreted and cell-associated glycoproteins. Secreted, gel-forming mucins are mainly responsible for the viscoelastic property of mucus, which is crucial for effective mucociliary clearance. Cell-associated mucins shield the epithelial surface from pathogens through their extracellular domains and regulate intracellular signaling through their cytoplasmic regions. However, neither the exact structures of mucin glycoproteins, nor the manner through which their expression is regulated, are completely understood. This chapter reviews what is currently known about the cellular and molecular properties of airway mucins.

Exercise-related respiratory symptoms and exercise-induced bronchoconstriction in industrial bakers

In order to assess prevalence and characteristics of exercise-related respiratory symptoms (ERRS) and exercise-induced bronchoconstriction (EIB) in industrial bakery, the authors performed a cross-sectional study including 57 bakers and an equal number of office workers studied as a control. Evaluation of examined subjects included completion of a questionnaire, skin prick tests to common inhalant and occupational allergens, spirometry, and exercise and histamine challenge. The authors found a similar prevalence of ERRS and EIB in both bakers and controls. EIB was significantly associated with atopy, asthma, family history of asthma, and positive histamine challenge in either group, whereas in bakers it was closely related to sensitization to occupational allergens (p = .032). Bronchial reaction to exercise was significantly higher in bakers with EIB (25.7% vs 19.2%; p = .021). These findings suggest that occupational exposure in industrial bakery may accentuate bronchoconstrictive response to exercise.

Glucocorticoid receptor and histone deacetylase-2 mediate dexamethasone-induced repression of MUC5AC gene expression

Airway occlusion in obstructive airway diseases is caused in part by the overproduction of secretory mucin glycoproteins through the up-regulation of mucin (MUC) genes by inflammatory mediators. Some pharmacological agents, including the glucocorticoid dexamethasone (Dex), repress mucin concentrations in lung epithelial cancer cells. Here, we show that Dex reduces the expression of MUC5AC, a major airway mucin gene, in primary differentiated normal human bronchial epithelial (NHBE) cells in a dose-dependent and time-dependent manner, and that the Dex-induced repression is mediated by the glucocorticoid receptor (GR) and two glucocorticoid response elements (GREs) in the MUC5AC promoter. The pre-exposure of cells to RU486, a GR antagonist, and mutations in either the GRE3 or GRE5 cis-sites abolished the Dex-induced repression. Chromatin immunoprecipitation (ChIP) assays showed a rapid temporal recruitment of GR to the GRE3 and GRE5 cis-elements in the MUC5AC promoter in NHBE and in A549 cells. Immunofluorescence showed nuclear colocalization of GR and histone deacetylase-2 (HDAC2) in MUC5AC-expressing NHBE cells. ChIP also showed a rapid temporal recruitment of HDAC2 to the GRE3 and GRE5 cis-elements in the MUC5AC promoter in both cell types. The knockdown of HDAC2 by HDAC2-specific short interfering RNA prevented the Dex-induced repression of MUC5AC in NHBE and A549 cells. These data demonstrate that GR and HDAC2 are recruited to the GRE3 and GRE5 cis-sites in the MUC5AC promoter and mediate the Dex-induced cis repression of MUC5AC gene expression. A better understanding of the mechanisms whereby glucocorticoids repress MUC5AC gene expression may be useful in formulating therapeutic interventions in chronic lung diseases.

Distinctive bronchial inflammation status in athletes: basophils, a new player

The aim of the study was to establish bronchial inflammation status and to measure eicosanoids in sputum obtained from active elite athletes. A total of 68 subjects were enrolled. Twelve were non-athletes and non-asthmatic (NAtNAs), 21 non-athlete asthmatics (NAtAs), 11 athlete non-asthmatics (AtNAs), and 24 athletes with asthma (AtAs) with positive indirect or direct bronchial challenges. Induced sputum was used to measure cells and eicosanoids. Sputum differential cell counts in all the subject groups revealed eosinophilia with the exception of NAtNAs control subjects. Athletes with and without diagnosed asthma showed a significant increase in bronchial epithelial cells and lymphocytes present in their sputum. Also, flow cytometry revealed that a significantly higher number of basophils were present in sputum from athletes (without and with asthma) when compared with non-athletes (without and with asthma). Asthmatic athletes and non-athletes showed a higher increase in LTC(4) levels and PGE(2) metabolites in sputum when compared with healthy controls. The present study identifies basophils as a new player present in athletes bronchial inflammation defining athlete status and not necessarily associated with exercise-induced bronchoconstriction.

New insights into pathogenesis of exercise-induced bronchoconstriction

PURPOSE OF REVIEW

Exercise-induced bronchoconstriction (EIB) refers to acute airflow obstruction that is triggered by a period of physical exertion. Here we review recent findings about the epidemiology of EIB, immunopathology leading to EIB, and the latest understanding of the pathogenesis of EIB.

RECENT FINDINGS

Longitudinal studies demonstrated that airway hyper-responsiveness to exercise or cold air at an early age are among the strongest predictors of persistent asthma. Patients that are susceptible to EIB have epithelial disruption and increased levels of inflammatory eicosanoids such as cysteinyl leukotrienes (CysLT)s. The leukocytes implicated in production of eicosanoids in the airways include both a unique mast cell population as well as eosinophils. A secreted phospholipase A(2) (sPLA(2)) enzyme that serves as a regulator of CysLT formation is present in increased quantities in asthma. Transglutaminase 2 (TGM2) is expressed at increased levels in asthma and serves as a regulator of secreted phospholipase A(2) group X (sPLA(2)-X). Further, sPLA(2)-X acts on target cells such as eosinophils to initiate cellular eicosanoid synthesis.

SUMMARY

Recent studies have advanced our understanding of EIB as a syndrome that is caused by the increased production of inflammatory eicosanoids. The airway epithelium may be an important regulator of the production of inflammatory eicosanoids by leukocytes.

Airway remodeling and inflammation in competitive swimmers training in indoor chlorinated swimming pools

BACKGROUND

Airway disorders are common in regular chlorinated swimming pool attendees, particularly competitive athletes, but the impact of intense swimming training on airway function and structure remains unclear.

OBJECTIVE

This study aimed to evaluate airway inflammation and remodeling in elite swimmers.

METHODS

Twenty-three elite swimmers were tested during off-training season. All had exhaled nitric oxide measurement, methacholine test, eucapnic voluntary hyperpnea challenge, allergy skin prick tests, and bronchoscopy with bronchial biopsies. Clinical data and tissues from 10 age-matched mild-asthmatic and 10 healthy nonallergic subjects were used for comparison.

RESULTS

Swimmers had increased airway mucosa eosinophil and mast cell counts than did controls (P < .05). They had more goblet cell hyperplasia and higher mucin expression than did healthy or asthmatic subjects (P < .05). A greater submucosal type I and III collagen expression and tenascin deposition was also observed in swimmers than in controls (P < .05). Neither exhaled nitric oxide nor airway responsiveness to methacholine or eucapnic voluntary hyperpnea challenge correlated with these inflammatory and remodeling changes.

CONCLUSION

Intense, long-term swimming training in indoor chlorinated swimming pools is associated with airway changes similar to those seen in mild asthma, but with higher mucin expression. These changes were independent from airway hyperresponsiveness. The long-term physiological and clinical consequences of these changes remain to be clarified.

Role of epithelial mucins during airway infection

Airway surface fluid contains two layers of mucins consisting mainly of 5 different mucin gene products. While the outer layer contains two gel-forming mucins (MUC5AC and MUC5B) that are tightly associated with various biologically active, defensive molecules, the inner layer contains three membrane-tethered mucins (MUC1, MUC4 and MUC16) shed from the apical cell surface. During airway infection, all of these mucins serve as a major protective barrier against pathogens. MUC1 mucin produced by virtually all the surface columnar epithelial cells in the respiratory tract as well as Type II pneumocytes in the alveoli plays an additional, perhaps more critical role during respiratory infection by controlling the resolution of inflammation that is essential to prevent the development of inflammatory lung disease.

An update on the role of leukotrienes in asthma

PURPOSE OF REVIEW

Leukotrienes are lipid mediators involved in the pathogenesis of asthma. There is significant new information about the actions of leukotrienes in asthma and the evolving role of antileukotriene therapies. We review recent findings on regulation of leukotriene synthesis, biological function of leukotrienes in disease models, and use of leukotriene modifiers in clinical practice.

RECENT FINDINGS

Our understanding of the regulation of leukotriene synthesis at a molecular level has greatly advanced. Recent evidence indicates that genetic variation in the leukotriene synthetic pathway affects the clinical response to leukotriene modifiers. The participation of leukotriene B4 in the allergic sensitization process in animal models suggests a larger role for leukotriene B4 in asthma. Preclinical and in-vitro models suggest that the cysteinyl leukotrienes are important in airway remodeling. Leukotrienes are key mediators of exercise-induced bronchoconstriction with recent studies demonstrating that leukotriene modifiers reduce the severity of exercise-induced bronchoconstriction during short-term and long-term use.

SUMMARY

Leukotrienes are clearly involved in airway inflammation and certain clinical features of asthma. Evolving evidence indicates that leukotriene B4 has an important role in the development of asthma and that cysteinyl leukotrienes are key mediators of the airway remodeling process.

Transglutaminase 2, a novel regulator of eicosanoid production in asthma revealed by genome-wide expression profiling of distinct asthma phenotypes

Background

A frequent manifestation of asthma, exercise-induced bronchoconstriction (EIB), occurs in 30–50% of asthmatics and is characterized by increased release of inflammatory eicosanoids. The objective of this study was to identify genes differentially expressed in EIB and to understand the function of these genes in the biology of asthma.

Methodology/Principal Findings

Genome-wide expression profiling of airway leukocytes and epithelial cells obtained by induced sputum was conducted in two groups of subjects with asthma with and without EIB (n = 7 per group), at baseline and following exercise challenge. Based on the results of the gene expression study, additional comparisons were made with a normal control group (n = 10). Localization studies were conducted on epithelial brushings and biopsies from an additional group of asthmatics with EIB (n = 3). Genes related to epithelial repair and mast cell infiltration including β-tryptase and carboxypeptidase A3 were upregulated by exercise challenge in the asthma group with EIB. A gene novel to asthma pathogenesis, transglutaminase 2 (TGM2), was the most differentially expressed at baseline between the groups. In vivo studies confirmed the increased expression of TGM2 in airway cells and airway lining fluid, and demonstrate that TGM2 is avidly expressed in the asthmatic airway epithelium. In vitro studies using recombinant human enzymes reveal that TGM2 augments the enzymatic activity of secreted phospholipase A₂ (PLA₂) group X (sPLA₂-X), an enzyme recently implicated in asthma pathogenesis.

Conclusions/Significance

This study found that TGM2, a mediator that is novel to asthma pathogenesis, is overexpressed in asthmatic airways and functions to increase sPLA₂-X enzymatic activity. Since PLA₂ serves as the first rate-limiting step leading to eicosanoid formation, these results suggest that TGM2 may be a key initiator of the airway inflammatory cascade in asthma.

Role of leukotrienes in exercise-induced bronchoconstriction

Exercise-induced bronchoconstriction (EIB) refers to acute airflow obstruction that is triggered by a period of physical exertion. EIB occurs mainly in individuals with other features of asthma but is especially prominent in a subset of asthmatics with pronounced indirect airway hyperresponsiveness. Leukotrienes (LTs) play a critical role in the pathophysiology of EIB. Asthmatics who are susceptible to EIB have increased levels of cysteinyl LTs (cysLTs [ie, LTs C4, D4, and E4]) in induced sputum and exhaled breath condensate. Exercise challenge in individuals susceptible to this disorder initiates the sustained increase in cysLTs in the airways and an increase in the ratio of cysLTs to prostaglandin E(2). The effects of cysLTs leading to secreted mucin release and smooth muscle constriction may be mediated in part through activation of sensory nerves. Therapies that block cysLT production or the cysLT(1) receptor effectively reduce the severity of EIB.

Increased leukotriene concentration in submandibular glands from rats with experimental periodontitis

OBJECTIVE AND DESIGN

In the present study, we investigated the relation between the inflammatory mediators such as nitric oxide, prostaglandins, and cysteinyl-leukotrienes with mucin release and the sympathetic system in submandibular glands from rats with experimental periodontitis.

MATERIALS OR SUBJECTS

Submandibular glands from rats with experimental periodontitis.

TREATMENT

For the first experiment, rats were treated with hydrocortisone sc, 1 mg/kg for 3 days. All other experiments were carried out in isolated submandibular glands from untreated rats. Submandibular glands were treated with cysteinyl-leukotrienes, isoproterenol, NDGA, FPL 55712, L-NMMA, Nio, Nz, AMG, indomethacin, DuP 697 and atenolol.

METHODS

Nitric oxide synthase activity, prostaglandin and cysteinyl-leukotriene productions and mucin secretion were determined. The Newman-Keuls statistical test was applied after analysis of variance.

RESULTS

In rats with periodontitis hydrocortisone-induced a 36.6% (P < 0.05) decrease in mucin release. Only cysteinyl-leukotriene production was increased in rats with ligature (79.2%, P < 0.001). Either the inhibition of cysteinyl-leukotriene production or the block of leukotriene receptor abolished the increase in mucin secretion by 25.6% (P < 0.05) and 37% (P < 0.01), respectively, in glands from rats with ligature. On the other hand, the presence of cysteinyl-leukotrienes in the incubation medium induced mucin release from submandibular glands. Atenolol diminished by 24% (P < 0.05), the increase in cysteinyl-leukotrienes observed in rats with periodontitis. Besides, isoproterenol induced cysteinyl-leukotriene production in both groups.

CONCLUSION

In submandibular glands from rats with periodontitis, the increment in mucin release and cysteinyl-leukotrienes production are related events and both are associated with the sympathetic system.

New insights into mechanisms of immunoregulation in 2007

Substantial progress in understanding the mechanisms of immune regulation in allergic diseases and asthma has been made during the last year. In asthma, rhinitis, and atopic dermatitis the immune system is activated by allergens, autoantigens, and components of superimposed infectious agents. Immune regulation in the lymphatic organs and in the tissue has an important role in the control and suppression of allergic disease in all stages of the inflammatory process, such as cell migration to tissues, cells gaining an inflammatory and tissue-destructive phenotype in the tissues, and their interaction with resident tissue cells to augment the inflammation. After the discovery of regulatory T cells, the importance of their unique suppressive capacity was strongly emphasized for the suppression of effector T-cell responses. However, it seems that all 3 subsets of effector T(H)1, T(H)2, and T(H)17 cells, as well as regulatory T cells, regulate each other at the level of transcription, major cytokines, and surface molecules. This review highlights key advances in immune regulation that were published in the Journal of Allergy and Clinical Immunology.

Analysis of mucins: role in laboratory diagnosis

Mucins are high molecular weight glycoproteins with complex oligosaccharide side chains attached to the apomucin protein backbone byO-glycosidic linkage; they are found in crude mucus gels that protect epithelial surfaces in the major tracts of the body and as transmembrane proteins expressed on the apical cell surface of glandular and ductal epithelia of various organs. Changes in the sequence of glycosylation of mucins in different settings generate a variety of epitopes in the oligosaccharide side chains of mucins, including newly expressed blood-group antigens, distinguishing between normal and diseased states. Tumour-associated epitopes on mucins and their antigenicity make them suitable as immunotargets on malignant epithelial cells and their secretions, creating a surge of interest in mucins as diagnostic and prognostic markers for various diseases, and even influencing the design of mucin-based vaccines. This review discusses the emerging roles of mucins such as MUC1 and MUC4 in cancer and some other diseases, and stresses how underglycosylated and truncated mucins are exploited as markers of disease and to monitor widespread metastasis, making them useful in patient management. Furthermore the type, pattern and amount of mucin secreted in some tissues have been considered in the classification and terminology of neoplasia and in specific organs such as the pancreas. These factors have been instrumental in pathological classification, diagnosis and prognostication of neoplasia.

Airway injury as a mechanism for exercise-induced bronchoconstriction in elite athletes

Exercise-induced bronchoconstriction (EIB) is a consequence of evaporative water loss in conditioning the inspired air. The water loss causes cooling and dehydration of the airway surface. One acute effect of dehydration is the release of mediators, such as prostaglandins, leukotrienes, and histamine, that can stimulate smooth muscle, causing contraction and a change in vascular permeability. Inspiring cold air increases dehydration of the surface area and causes changes in bronchial blood flow. This article proposes that the pathogenesis of EIB in elite athletes relates to the epithelial injury arising from breathing poorly conditioned air at high flows for long periods of time or high volumes of irritant particles or gases. The evidence to support this proposal comes from many markers of injury. The restorative process after injury involves plasma exudation and movement of cells into the airways, a process repeated many times during a season of training. This process has the potential to expose smooth muscle to a wide variety of plasma- and cell-derived substances. The exposure to these substances over time can lead to an alteration in the contractile properties of the smooth muscle, making it more sensitive to mediators of bronchoconstriction. It is proposed that cold-weather athletes have airway hyperresponsiveness (AHR) to pharmacologic agents as a result of epithelial injury. In those who are allergic, AHR can also be expressed as EIB. The role of beta(2)-receptor agonists in inhibiting and enhancing the development of AHR and EIB is discussed.

Provocative challenges to help diagnose and monitor asthma: exercise, methacholine, adenosine, and mannitol

PURPOSE OF REVIEW

To review bronchial provocations tests used in the measurement of bronchial hyperresponsiveness to help in the diagnosis of asthma.

RECENT FINDINGS

The bronchial provocations tests reviewed include exercise, methacholine, AMP and mannitol, with reference to methodology and monitoring of treatment.

SUMMARY

Methacholine is used for identifying bronchial hyperresponsiveness and to guide treatment. Exercise is used as a bronchial provocation test because demonstrating prevention of exercise-induced asthma is an indication for use of a drug. Both of these tests are being used to study tolerance to beta2 agonists. There is increasing use of eucapnic voluntary hyperpnea as a surrogate bronchial provocation test for exercise to identify exercise-induced asthma, particularly in athletes. For methacholine and AMP there is concern about the different breathing patterns used to inhale these aerosols and the impact they have on the cutoff point for identifying bronchial hyperresponsiveness. A new test that uses a kit containing prepacked capsules of different doses of mannitol and a delivery device is discussed. There is increasing interest in using tests that act indirectly by release of mediators because the bronchial hyperresponsiveness itself is an indicator of the presence of inflammation. Since treatment of inflammation leads to loss of bronchial hyperresponsiveness to indirect stimuli, these tests are well suited to identify success of treatment.

Secreted phospholipase A2 group X overexpression in asthma and bronchial hyperresponsiveness

RATIONALE

Secreted phospholipase A(2) enzymes (sPLA(2)s) play key regulatory roles in the biosynthesis of eicosanoids, such as the cysteinyl leukotrienes, but the role of these enzymes in the pathogenesis of asthma is not known.

OBJECTIVES

To establish if sPLA(2)s are overexpressed in the airways of patients with asthma, and to determine if these enzymes may play a role in the generation of eicosanoids in exercise-induced bronchoconstriction.

METHODS

Induced sputum samples were obtained from subjects with asthma with exercise-induced bronchoconstriction and nonasthmatic control subjects at baseline, and on a separate day 30 minutes after exercise challenge. The expression of the PLA(2)s in induced sputum cells and supernatant was determined by quantitative polymerase chain reaction, immunocytochemistry, and Western blot.

MEASUREMENTS AND MAIN RESULTS

The sPLA(2)s expressed at the highest levels in airway cells of subjects with asthma were groups X and XIIA. Group X sPLA(2) (sPLA(2)-X) was differentially overexpressed in asthma and localized to airway epithelial cells and bronchial macrophages. The gene expression, immunostaining in airway epithelial cells and bronchial macrophages, and the level of the extracellular sPLA(2)-X protein in the airways increased in response to exercise challenge in the asthma group, whereas the levels were lower and unchanged after challenge in nonasthmatic control subjects.

CONCLUSIONS

Increased expression of sPLA(2)-X may play a key role in the dysregulated eicosanoid synthesis in asthma.