Bronchial Reactivity to Histamine Is Correlated With Airway Remodeling in Adults With Moderate to Severe Asthma

Endogenous Adenosine 5'-Monophosphate, But Not Acetylcholine or Histamine, is Associated with Asthma Control, Quality of Life, and Exacerbations

OBJECTIVE

Endogenous adenosine 5'-monophosphate (AMP), acetylcholine (ACh), and histamine (HA) are known to be important in bronchial contraction, but their clinical relevance to asthma is poorly understood. We aimed to quantify endogenous AMP, ACh, and HA in induced sputum samples and explore their relationships with asthma control and exacerbations.

METHODS

20 healthy subjects and 112 asthmatics underwent clinical assessment, sputum induction, and blood sampling. The level of asthma control was determined by the asthma control test (ACT) questionnaire. Asthma exacerbation was evaluated according to the criteria of the American Thoracic Society/European Respiratory Society. Levels of AMP, ACh, and HA in sputum were measured by liquid chromatography coupled to tandem mass spectrometry. IL-β, IL-4, IL-5, IL-6, IL-8, IL-13, IL-17A, TNF-α, IFN-γ, and macrophage-derived chemokine (MDC) were also measured.

RESULTS

Compared to healthy controls, asthmatics had higher levels of HA, lower levels of ACh, and similar levels of AMP in induced sputum samples. Compared to controlled asthma (n = 54), uncontrolled asthma (n = 58) showed higher AMP levels (P = 0.002), but similar HA and ACh levels. AMP was negatively correlated with ACT scores (r = - 0.348) and asthma quality of life questionnaire scores (r = - 0.188) and positively correlated with blood monocytes percentage (r = 0.195), sputum MDC (r = 0.214), and IL-6 levels (r = 0.196). Furthermore, AMP was associated with an increased risk of exacerbations in the preceding year.

CONCLUSION

Endogenous AMP, but not ACh or HA, was associated with asthma control, quality of life, and exacerbations in the previous year, which indicates that AMP could be a clinically useful biomarker of asthma.

Cellular and molecular mechanisms of allergic asthma

Asthma is a chronic disease of the airways, which affects more than 350 million people worldwide. It is the most common chronic disease in children, affecting at least 30 million children and young adults in Europe. Asthma is a complex, partially heritable disease with a marked heterogeneity. Its development is influenced both by genetic and environmental factors. The most common, as well as the most well characterized subtype of asthma is allergic eosinophilic asthma, which is characterized by a type 2 airway inflammation. The prevalence of asthma has substantially increased in industrialized countries during the last 60 years. The mechanisms underpinning this phenomenon are incompletely understood, however increased exposure to various environmental pollutants probably plays a role. Disease inception is thought to be enabled by a disadvantageous shift in the balance between protective and harmful lifestyle and environmental factors, including exposure to protective commensal microbes versus infection with pathogens, collectively leading to airway epithelial cell damage and disrupted barrier integrity. Epithelial cell-derived cytokines are one of the main drivers of the type 2 immune response against innocuous allergens, ultimately leading to infiltration of lung tissue with type 2 T helper (T_H2) cells, type 2 innate lymphoid cells (ILC2s), M2 macrophages and eosinophils. This review outlines the mechanisms responsible for the orchestration of type 2 inflammation and summarizes the novel findings, including but not limited to dysregulated epithelial barrier integrity, alarmin release and innate lymphoid cell stimulation.

Role of Histamine in Modulating the Immune Response and Inflammation

Inflammatory mediators, including cytokines, histamine, bradykinin, prostaglandins, and leukotrienes, impact the immune system, usually as proinflammatory factors. Other mediators act as regulatory components to establish homeostasis after injury or prevent the inflammatory process. Histamine, a biogenic vasoactive amine, causes symptoms such as allergies and has a pleiotropic effect that is dependent on its interaction with its four histamine receptors. In this review, we discuss the dualistic effects of histamine: how histamine affects inflammation of the immune system through the activation of intracellular pathways that induce the production of inflammatory mediators and cytokines in different immune cells and how histamine exerts regulatory functions in innate and adaptive immune responses. We also evaluate the interactions between these effects.

Effects of inhaled corticosteroids on the expression of TNF family molecules in murine model of allergic asthma

BACKGROUND

The tumor necrosis factor superfamily member LIGHT (the official gene symbol approved by NCBI Gene Database), an inflammatory factor secreted by T cells after allergen exposure, recently discovered to play crucial roles in asthmatic airway remodeling. However, it is unclear whether LIGHT could be controlled by inhaled corticosteroids, a key component of asthma management. This study was to investigate the effects and potential mechanisms of inhaled budesonide on the expressions of LIGHT and its receptors (LTβR and HVEM) of lung tissues in ovalbumin-sensitized mice.

MATERIALS AND METHODS

Thirty-three BALB/c mice were randomly divided into the control, asthma model, and budesonide treatment groups (11 in each group). Mice were sensitized and challenged by OVA to develop mouse model of chronic asthma, and treated with aerosolized budesonide before OVA challenge. Bronchoalveolar lavage fluid (BALF) and lungs were obtained after the final OVA challenge. Protein and mRNA Levels of LIGHT, LTβR, and HVEM in the lungs were investigated by immunohistochemistry, image analysis, and real-time PCR. Expressions of IL-6 and IFN-γ in BALF were measured by ELISA.

RESULTS

Inhaled budesonide significantly reduced protein and mRNA levels of lung LIGHT, LTβR, and HVEM in asthmatic mice. Correspondingly, the number of eosinophils and neutrophils and IL-6 levels in BALF after budesonide treatment were found to be decreased, whereas the IFN-γ levels in BALF were increased. Moreover, the expressions of LIGHT and HVEM mRNA showed positive correlation with IL-6 levels in the treatment group.

CONCLUSIONS

Inhaled budesonide can down-regulate the expressions of LIGHT, LTβR, and HVEM in the lungs of asthmatic mice, and LIGHT/LTβR/HVEM interactions may be a potentially key target for asthma treatment.

Histamine receptor 2 modifies iNKT cell activity within the inflamed lung

BACKGROUND

Histamine is a key immunoregulatory mediator and can dampen proinflammatory responses via activation of histamine receptor 2 (H₂ R). The aim of this study was to determine the role of H₂ R in modulating lung inflammatory responses.

METHODS

H₂ R was blocked using famotidine or activated using dimaprit in both the ovalbumin (OVA) and house dust mite extract (HDM) murine models of respiratory inflammation. H₂ R-deficient animals and CD1d/H₂ R-deficient animals were utilized to examine the CD1d presentation of lipid antigens (αGalCer or OCH) to invariant natural killer T (iNKT) cells.

RESULTS

Famotidine treatment resulted in more severe airway disease in the OVA model, while dimaprit treatment significantly reduced disease severity. Both OVA and HDM-induced airway diseases were more severe in H₂ R-deficient animals. Flow cytometric analysis of lung tissue from H₂ R-deficient animals revealed increased numbers of CD1d⁺ dendritic cells and increased numbers of iNKT cells. In vitro, αGalCer-stimulated iNKT cells from H₂ R-deficient mice secreted higher levels of IL-4, IL-5, and GM-CSF. In vivo, αGalCer or OCH administration to the lung resulted in enhanced mucus secretion, inflammatory cell recruitment, and cytokine production in H₂ R-deficient or famotidine-treated animals, while dimaprit dampened the lung iNKT cell response to αGalCer. Removal of iNKT cells in H₂ R-deficient (CD1d^-/- H₂ R^-/- ) animals normalized the lung response to HDM.

CONCLUSION

The deliberate activation of H₂ R, or its downstream signaling molecules, may represent a novel therapeutic target for chronic lung inflammatory diseases, especially when CD1d-mediated presentation of lipid antigens to iNKT cells is contributing to the pathology.

Etiology of epithelial barrier dysfunction in patients with type 2 inflammatory diseases

Epithelial barriers of the skin, gastrointestinal tract, and airway serve common critical functions, such as maintaining a physical barrier against environmental insults and allergens and providing a tissue interface balancing the communication between the internal and external environments. We now understand that in patients with allergic disease, regardless of tissue location, the homeostatic balance of the epithelial barrier is skewed toward loss of differentiation, reduced junctional integrity, and impaired innate defense. Importantly, epithelial dysfunction characterized by these traits appears to pre-date atopy and development of allergic disease. Despite our growing appreciation of the centrality of barrier dysfunction in initiation of allergic disease, many important questions remain to be answered regarding mechanisms disrupting normal barrier function. Although our external environment (proteases, allergens, and injury) is classically thought of as a principal contributor to barrier disruption associated with allergic sensitization, there is a need to better understand contributions of the internal environment (hormones, diet, and circadian clock). Systemic drivers of disease, such as alterations of the endocrine system, metabolism, and aberrant control of developmental signaling, are emerging as new players in driving epithelial dysfunction and allergic predisposition at various barrier sites. Identifying such central mediators of epithelial dysfunction using both systems biology tools and causality-driven laboratory experimentation will be essential in building new strategic interventions to prevent or reverse the process of barrier loss in allergic patients.

Update on noninfectious inflammatory diseases of the lower airway

Inflammatory airway disease and recurrent airway obstruction are 2 nonseptic diseases of the equine respiratory system with a shared cause of exposure to particulate matter. They appear to occupy 2 ends of a spectrum of disease, but are differentiated by history, clinical signs, and response to treatment. Diagnosis can be made by sampling of respiratory fluids and lung function testing. Treatment consists of environmental modification and pharmacologic treatment with systemic or inhaled corticosteroids and bronchodilators.

Effect of TRPV1 channel on proliferation and apoptosis of airway smooth muscle cells of rats

Airway remodeling is an important pathological feature of asthma and the basis of severe asthma. Proliferation of airway smooth muscle cells (ASMCs) is a major contributor to airway remodeling. As an important Ca(2+) channel, transient receptor potential vanilloid 1 (TRPV1) plays the key role in the cell pathological and physiological processes. This study investigated the expression and activity of TRPV1 channel, and further clarified the effect of TRPV1 channel on the ASMCs proliferation and apoptosis in order to provide the scientific basis to treat asthmatic airway remodeling in clinical practice. Immunofluorescence staining and reverse transcription polymerase chain reaction (RT-PCR) were used to detect the expression of TRPV1 in rat ASMCs. Intracellular Ca(2+) was detected using the single cell confocal fluorescence microscopy measurement loaded with Fluo-4/AM. The cell cycles were observed by flow cytometry. MTT assay and Hoechst 33258 staining were used to detect the proliferation and apoptosis of ASMCs in rats respectively. The data showed that: (1) TRPV1 channel was present in rat ASMCs. (2) TRPV1 channel agonist, capsaicin, increased the Ca(2+) influx in a concentration-dependent manner (EC50=284.3±58 nmol/L). TRPV1 channel antagonist, capsazepine, inhibited Ca(2+) influx in rat ASMCs. (3) Capsaicin significantly increased the percentage of S+G2M ASMCs and the absorbance of MTT assay. Capsazepine had the opposite effect. (4) Capsaicin significantly inhibited the apoptosis, whereas capsazepine had the opposite effect. These results suggest that TRPV1 is present and mediates Ca(2+) influx in rat ASMCs. TRPV1 activity stimulates proliferation of ASMCs in rats.

Link between vitamin D and airway remodeling

In the last decade, many epidemiologic studies have investigated the link between vitamin D deficiency and asthma. Most studies have shown that vitamin D deficiency increases the risk of asthma and allergies. Low levels of vitamin D have been associated with asthma severity and loss of control, together with recurrent exacerbations. Remodeling is an early event in asthma described as a consequence of production of mediators and growth factors by inflammatory and resident bronchial cells. Consequently, lung function is altered, with a decrease in forced expiratory volume in one second and exacerbated airway hyperresponsiveness. Subepithelial fibrosis and airway smooth muscle cell hypertrophy are typical features of structural changes in the airways. In animal models, vitamin D deficiency enhances inflammation and bronchial anomalies. In severe asthma of childhood, major remodeling is observed in patients with low vitamin D levels. Conversely, the antifibrotic and antiproliferative effects of vitamin D in smooth muscle cells have been described in several experiments. In this review, we briefly summarize the current knowledge regarding the relationship between vitamin D and asthma, and focus on its effect on airway remodeling and its potential therapeutic impact for asthma.

The effect of Shenmai injection on the proliferation of Rat airway smooth muscle cells in asthma and underlying mechanism

BACKGROUND

Over-proliferation of airway smooth muscle cell (ASMC) is one of the important contributors to airway remodeling in asthma. The aim of this study was to investigate the effect of Shenmai injection (SMI) on the proliferation of the rat ASMC in asthma.

METHODS

Rats were randomly divided into three groups: the control group, the asthma group, and the SMI treatment group. Reverse transcription-polymerase chain reaction (RT-PCR) and immunocytochemistry staining were used to detect the mRNA and protein expression of transient receptor potential vanilloid 1 (TRPV1) and proliferating cell nuclear antigen (PCNA) in rat ASMC respectively. Intracellular Ca²⁺ concentration ( [Ca²⁺](i)) in rat ASMC were measured with Fluo-3/AM by confocal microscopy. The proliferation was detected by MTT assay.

RESULTS

Compared with the control group, the asthma group showed an increased expression of TRPV1 and [Ca²⁺](i) in rat ASMC. The expression of PCNA and absorbance of MTT assay in asthma rat ASMC was also significantly increased. SMI could significantly decrease the expression of TRPV1 channel and [Ca²⁺](i) in the asthmatic rat ASMC. Furthermore, the expression of PCNA and absorbance of MTT assay in asthmatic rat ASMC was significantly reduced after SMI treatment.

CONCLUSIONS

SMI may prevent asthma-induced ASMC over-proliferation probably by inhibiting the expression of TRPV1 channel, which regulates the intracellular calcium concentration.

Effect of TRPV1 channel on the proliferation and apoptosis in asthmatic rat airway smooth muscle cells

BACKGROUND

Hyperplasia of airway smooth muscle cells (ASMC) is a major contributor to airway remodeling in asthma. Transient receptor potential vanilloid 1 (TRPV1) is an important channel to mediate Ca(2+) influx. This study explores the expression of TRPV1 channel and its effect on the proliferation and apoptosis in rat ASMC, in order to find a new target to treat airway remodeling in asthma.

METHODS

Rats were sensitized and challenged with ovalbumin to replicate asthmatic models. Proliferating cell nuclear antigen (PCNA) was detected by immunohistochemistry. Reverse transcriptase-polymerase chain reaction, immunocytochemistry, and Western blot were used to detect the mRNA and protein expression of TRPV1 channel. Intracellular calcium ([Ca(2+)]i) was detected using confocal fluorescence Ca(2+) imaging. [(3)H] thymidine incorporation and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay were used to observe the DNA synthesis and proliferation. TUNEL assay was used to detect the apoptosis of ASMC.

RESULTS

(1) The expression of PCNA was significantly increased in intact asthmatic rat ASMC. (2) The expression of TRPV1 channel was significantly increased in asthmatic rat ASMC. (3) [Ca(2+)]i in ASMC of the asthmatic group was significantly increased. After treatment with TRPV1 agonist capsaicin (CAP), [Ca(2+)]i was further increased, whereas [Ca(2+)]i was decreased after administration of TRPV1 antagonist capsazepine (CPZ) in ASMC of the asthmatic group. (4) The DNA synthesis and absorbance of MTT were significantly increased, while apoptosis was significantly decreased in asthmatic ASMC. CAP further enhanced proliferation and decreased apoptosis. CPZ significantly inhibited the effect of CAP in asthmatic ASMC.

CONCLUSION

TRPV1 channel was involved in the regulation of proliferation and apoptosis in asthmatic ASMC.

Markers for step-down of inhaled corticosteroid therapy in adult asthmatics

BACKGROUND

Treatment guidelines recommend the use of inhaled corticosteroids (ICS) as first-line therapy for all stages of persistent asthma. However, it is unknown whether ICS dose reduction in adult asthmatics is compatible with maintaining asthma control. Moreover, there are no predictors of efficacy in maintaining asthma control upon ICS reduction.

METHODS

We recruited 90 adult patients with moderate or severe asthma but no clinical symptoms of asthma for at least 6 months. All patients reduced their ICS doses by half but continued taking other asthma-related medications. As a primary outcome, we measured asthma exacerbations during the 12 months following ICS reduction. We also further monitored patients from the above study who had maintained total asthma control for 12 months after ICS reduction and who had continued on their reduced doses of ICS or had further reduced, or stopped, their ICS.

RESULTS

Forty of ninety patients (44.4%) experienced exacerbations after ICS reduction (time to first exacerbation: 6.4 ± 3.6 months). Multivariate logistic regression modeling revealed a rank order of predictors of success in ICS reduction while retaining asthma control: acetylcholine (ACh) PC(20) (p < 0.01); length of time with no clinical symptoms before ICS reduction (p < 0.01); FeNO (p = 0.028); and forced expiratory volume in 1 s (FEV(1); % predicted) (p = 0.03). Finally thirty-nine of 50 patients maintained total asthma control for at least 2 years after the initial ICS reduction.

CONCLUSIONS

In asthma patients with normalized AChPC(20) of 20mg/mL or 10mg/mL and no clinical symptoms for at least 12 or 24 months it may be possible to successfully reduce ICS without increasing exacerbations for long time.

Diagnostic tools assessing airway remodelling in asthma

Asthma is an inflammatory disease of the lower airways characterised by the presence of airway inflammation, reversible airflow obstruction and airway hyperresponsiveness and alterations on the normal structure of the airways, known as remodelling. Remodelling is characterised by the presence of metaplasia of mucous glands, thickening of the lamina reticularis, increased angiogenesis, subepithelial fibrosis and smooth muscle hypertrophy/hyperplasia. Several techniques are being optimised at present to achieve a suitable diagnosis for remodelling. Diagnostic tools could be divided into two groups, namely invasive and non-invasive methods. Invasive techniques bring us information about bronchial structural alterations, obtaining this information directly from pathological tissue, and permit measure histological modification placed in bronchi layers as well as inflammatory and fibrotic cell infiltration. Non-invasive techniques were developed to reduce invasive methods disadvantages and measure airway remodelling-related markers such as cytokines, inflammatory mediators and others. An exhaustive review of diagnostic tools used to analyse airway remodelling in asthma, including the most useful and usually employed methods, as well as the principal advantages and disadvantages of each of them, bring us concrete and summarised information about all techniques used to evaluate alterations on the structure of the airways. A deep knowledge of these diagnostic tools will make an early diagnosis of airway remodelling possible and, probably, early diagnosis will play an important role in the near future of asthma.