Eicosanoids in asthma, allergic inflammation, and host defense

Eicosanoids are diverse mediators of inflammation that derive from a single cell membrane phospholipid-associated precursor, arachidonic acid. This precursor is metabolized to several groups of lipid mediators, including (but not limited to) prostaglandins, leukotrienes, and lipoxins, in a tightly regulated, coordinated, cell- and context-specific manner. Each mediator serves regulatory and homeostatic functions in the onset and resolution of inflammation, immune responses, and tissue repair. The cloning of biosynthetic enzymes and G protein-coupled receptors for each of these mediators, the development of transgenic mice deficient in these molecules, and the availability of selective antagonists have permitted studies that have rapidly expanded our understanding of the scope of biologic functions for these mediators, with potential ramifications for the pathogenesis and treatment of human asthma. This review summarizes these findings and reviews the data from both mouse and human studies pertinent to the pathobiologic role of each mediator.     

Emerging roles of DP and CRTH2 in allergic inflammation

The lipid mediator prostaglandin D(2) (PGD(2)) has long been implicated in various inflammatory diseases including asthma. PGD(2) elicits biological responses by activating two seven-transmembrane (7TM) G-protein-coupled receptors, the D-prostanoid receptor DP and the chemoattractant receptor homologous-molecule expressed on T-helper-type-2 cells (CRTH2), which are linked to different signaling pathways. Understanding how immune cells integrate and coordinate signals that are triggered by the same ligand is crucial for the development of novel anti-inflammatory therapies. Here, we examine the roles of DP and CRTH2 in the orchestration of complex inflammatory processes, and discuss their importance as emerging targets for the treatment of asthma and inflammatory diseases.     

Cyclooxygenase enzymes in allergic inflammation and asthma

The cyclooxygenase enzyme system produces eicosanoids which mediate many important physiological and pathological functions. Experimental and clinical data suggest a role for this enzyme system in the pathogenesis of allergic inflammation and asthma. This article focuses on the function of this pathway in the lung, reviews evidence implicating the involvement of this pathway in asthma and allergic airway inflammation, and discusses implications for the treatment of asthmatics with cyclooxygenase inhibitors.     

Activation of the prostaglandin D2 receptor DP2/CRTH2 increases allergic inflammation in mouse

Allergic pathologies are often associated with IgE production, mast cell activation, and eosinophilia. PGD2 is the major eicosanoid, among several inflammatory mediators, released by mast cells. PGD2 binds to two membrane receptors, D prostanoid receptor (DP)1 and DP2, endowed with antagonistic properties. In humans, DP2 is preferentially expressed on type 2 lymphocytes, eosinophils, and basophils and mediates chemotaxis in vitro. Although not yet supported by in vivo studies, DP2 is thought to be important in the promotion of Th2-related inflammation. Herein, we demonstrate that mouse eosinophils express both DP1 and DP2 and that PGD2 exerts in vitro chemotactic effects on eosinophils through DP2 activation. Furthermore, 13,14-dihydro-15-keto-PGD2, a specific DP2 agonist not only increases eosinophil recruitment at inflammatory sites but also the pathology in two in vivo models of allergic inflammation: atopic dermatitis and allergic asthma. By contrast, DP1 activation tends to ameliorate the pathology in asthma. Taken together, these results support the hypothesis that DP2 might play a critical role in allergic diseases and underline the interest of DP2 antagonists in human therapy.     

The neutrophil-activating protein of Helicobacter pylori down-modulates Th2 inflammation in ovalbumin-induced allergic asthma

The Helicobacter pylori neutrophil-activating protein (HP-NAP) is able in vitro to elicit IL-12 and IL-23 production via agonistic interaction with toll-like receptor 2, and to promote Th1 polarization of allergen-specific T-cell responses. This study was aimed to assess whether systemic/intraperitoneal and/or mucosal HP-NAP administration inhibited the Th2-mediated bronchial inflammation using a mouse model of allergic asthma induced by inhaled ovalbumin (OVA). Systemic HP-NAP delivery markedly reduced the lung eosinophilia in response to repeated challenge with aerosolized OVA. Likewise, the production of IL-4, IL-5 and GM-CSF was significantly lower in the bronchoalveolar lavage of animals treated with systemic HP-NAP plus OVA than that of animals treated with OVA alone. Systemic HP-NAP also significantly resulted in both reduction of total serum IgE and increase of IL-12 plasma levels. Mucosal administration of HP-NAP was equally successful as the systemic delivery in reducing eosinophilia, IgE and Th2 cytokine levels in bronchoalveolar lavage. However, no suppression of lung eosinophilia and bronchial Th2 cytokines was observed in toll-like receptor 2-knock-out mice following HP-NAP treatment. These results identify HP-NAP as a candidate for novel strategies of prevention and treatment of allergic diseases.     

DA-9601, Artemisia asiatica herbal extract, ameliorates airway inflammation of allergic asthma in mice

We previously reported that DA-9601, ethanol herbal extract of Artemisia asiatica, inhibited histamine and leukotriene releases in guinea pig lung mast cells activated with specific antigen/antibody reaction. This study aimed to evaluate the inhibitory effect of DA-9601 on the OVA-induced airway inflammation in allergic asthma mouse model. BALB/c mice were sensitized and challenged with OVA. DA-9601 was administered orally 1 h before every local OVA-challenge. OVA-specific serum IgE was measured by ELISA, recruitment of inflammatory cells in BAL fluids and lung tissues by Diff-Quik and H&E staining, respectively, the expressions of CD40, CD40L and VCAM-1 by immunohistochemistry, goblet cell hyperplasia by PAS staining, activities of MMPs by gelatin zymography, expressions of mRNA and proteins of cytokines by RT-PCR and ELISA, activities of MAP kinases by western blot, and activity of NF-KappaB by EMSA. DA-9601 reduced IgE level, recruitment of inflammatory cells into the BAL fluid and lung tissues, expressions of CD40, CD40L and VCAM-1 molecules, goblet cell hyperplasia, MMPs activity, expressions of mRNA and productions of various cytokines, activities of MAP kinases and NK-KappaB increased from OVA-challenged mice. These data suggest that DA-9601 may be developed as a clinical therapeutic agent in allergic diseases due to suppressing the airway allergic inflammation via regulation of various cellular molecules expressed by MAP kinases/NF-KappaB pathway.     

A broad-spectrum caspase inhibitor attenuates allergic airway inflammation in murine asthma model

Asthma is characterized by acute and chronic airway inflammation, and the severity of the airway hyperreactivity correlates with the degree of inflammation. Many of the features of lung inflammation observed in human asthma are reproduced in OVA-sensitized/challenged mice. T lymphocytes, particularly Th2 cells, are critically involved in the genesis of the allergic response to inhaled Ag. In addition to antiapoptotic effects, broad-spectrum caspase inhibitors inhibit T cell activation in vitro. We investigated the effect of the broad-spectrum caspase inhibitor, N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (z-VAD-fmk), on airway inflammation in OVA-sensitized/challenged mice. OVA-sensitized mice treated with z-VAD-fmk immediately before allergen challenge showed marked reduction in inflammatory cell infiltration in the airways and pulmonary blood vessels, mucus production, and Th2 cytokine production. We hypothesized that the caspase inhibitor prevented T cell activation, resulting in the reduction of cytokine production and eosinophil infiltration. Treatment with z-VAD-fmk in vivo prevented subsequent T cell activation ex vivo. We propose that caspase inhibitors may offer a novel therapeutic approach to T cell-dependent inflammatory airway diseases.     

IL-17-producing alveolar macrophages mediate allergic lung inflammation related to asthma

IL-17 is a pivotal proinflammatory molecule in asthmatics. However, the cellular source of IL-17 in asthma has not been identified to date. In this study, we report that macrophages rather than Th17 cells are the main producer of IL-17 in allergic inflammation related to asthma. After OVA challenge in a mouse model mimicking allergic asthma, the increased IL-17(+) cells in the lung were mainly CD11b(+)F4/80(+) macrophages, instead of T cells or others. Importantly, IL-17(+) alveolar macrophages (AMs), but not IL-17(+) interstitial macrophages, were significantly increased after allergen challenge. The increase of IL-17(+) AMs was not due to the influx of IL-17(+) macrophages from circulation or other tissues, but ascribed to the activation of AMs by mediator(s) secreted by IgE/OVA-activated mast cells. Depleting alveolar macrophages or neutralizing IL-17 prevented the initiation of OVA-induced asthma-related inflammation by inhibiting the increase of inflammatory cells and inflammatory factors in bronchoalveolar lavage fluid. Th2 cytokine IL-10 could down-regulate IL-17 expression in alveolar macrophages. The increased IL-17 and the decreased IL-10 in bronchoalveolar lavage fluid were further confirmed in asthmatic patients. These findings suggest that IL-17 is mainly produced by macrophages but not Th17 cells in allergic inflammation related to asthma. Mast cell-released mediators up-regulate the expression of IL-17 by macrophages, whereas IL-10 down-regulates IL-17 expression.     

Polyopes affinis alleviates airway inflammation in a murine model of allergic asthma

Marine algae have been utilized in food as well as medicine products for a variety of purposes. The purpose of this study was to determine whether an ethanol extract of Polyopes affinis (P.affinis) can inhibit the pathogenesis of T helper 2 (Th2)-mediated allergen-induced airway inflammation in a murine model of asthma. Mice that were sensitized and challenged with ovalbumin (OVA) evidenced typical asthmatic reactions such as the following: an increase in the number of eosinophils in the bronchoalveolar lavage (BAL) fluid; a marked influx of inflammatory cells into the lung around blood vessels and airways as well as the narrowing of the airway luminal; the development of airway hyperresponsiveness (AHR); the presence of pulmonary Th2 cytokines; and the presence of allergenspecific immunoglobulin E (IgE) in the serum. The successive intraperitoneal administration of P. affinis ethanolic extracts before the last airway OVA-challenge resulted in a significant inhibition of all asthmatic reactions. These data suggest that P. affinis ethanolic extracts possess therapeutic potential for the treatment of pulmonary allergic disorders such as allergic asthma.     

Role of lysophosphatidic acid receptor LPA2 in the development of allergic airway inflammation in a murine model of asthma

Background

Lysophosphatidic acid (LPA) plays a critical role in airway inflammation through G protein-coupled LPA receptors (LPA_1-3). We have demonstrated that LPA induced cytokine and lipid mediator release in human bronchial epithelial cells. Here we provide evidence for the role of LPA and LPA receptors in Th2-dominant airway inflammation.

Methods

Wild type, LPA₁ heterozygous knockout mice (LPA₁^+/-), and LPA₂ heterozygous knockout mice (LPA₂^+/-) were sensitized with inactivated Schistosoma mansoni eggs and local antigenic challenge with Schistosoma mansoni soluble egg Ag (SEA) in the lungs. Bronchoalveolar larvage (BAL) fluids and lung tissues were collected for analysis of inflammatory responses. Further, tracheal epithelial cells were isolated and challenged with LPA.

Results

BAL fluids from Schistosoma mansoni egg-sensitized and challenged wild type mice (4 days of challenge) showed increase of LPA level (~2.8 fold), compared to control mice. LPA₂^+/- mice, but not LPA₁^+/- mice, exposed to Schistosoma mansoni egg revealed significantly reduced cell numbers and eosinophils in BAL fluids, compared to challenged wild type mice. Both LPA₂^+/- and LPA₁^+/- mice showed decreases in bronchial goblet cells. LPA₂^+/- mice, but not LPA₁^+/- mice showed the decreases in prostaglandin E2 (PGE2) and LPA levels in BAL fluids after SEA challenge. The PGE2 production by LPA was reduced in isolated tracheal epithelial cells from LPA₂^+/- mice. These results suggest that LPA and LPA receptors are involved in Schistosoma mansoni egg-mediated inflammation and further studies are proposed to understand the role of LPA and LPA receptors in the inflammatory process.     

Cyclic nitroxide radicals attenuate inflammation and Hyper-responsiveness in a mouse model of allergic asthma

The effects of stable cyclic nitroxide radicals have been extensively investigated both in vivo and in vitro demonstrating anti-inflammatory, radioprotective, anti-mutagenic, age-retardant, hypotensive, anti-cancer and anti-teratogenic activities. Yet, these stable radicals have not been evaluated in asthma and other airway inflammatory disorders. The present study investigated the effect of 4-hydroxy-2,2,6,6-tetramethyl-piperidine-N-oxyl (TPL) and 3-carbamoyl-proxyl (3-CP) in a mouse model of ovalbumin (OVA)-induced allergic asthma. Both 3-CP and TPL were non-toxic when administered either orally (1% w/w nitroxide-containing chow) or via intraperitoneal (IP) injection (∼300 mg/kg). Feeding the mice orally demonstrated that 3-CP was more effective than TPL in reducing inflammatory cell recruitment into the airway and in suppressing airway hyper-responsiveness (AHR) in OVA-challenged mice. To characterize the optimal time-window of intervention and mode of drug administration, 3-CP was given orally during allergen sensitization, during allergen challenge or during both sensitization and challenge stages, and via IP injection or intranasal instillation for 3 days during the challenge period. 3-CP given via all modes of delivery markedly inhibited OVA-induced airway inflammation, expression of cytokines, AHR and protein nitration of the lung tissue. Oral administration during the entire experiment was the most efficient delivery of 3-CP and was more effective than dexamethasone a potent corticosteroid used for asthma treatment. Under a similar administration regimen (IP injection before the OVA challenge), the effect of 3-CP was similar to that of dexamethasone and even greater on AHR and protein nitration. The protective effect of the nitroxides, which preferentially react with free radicals, in suppressing the increase of main asthmatic inflammatory markers substantiate the key role played by reactive oxygen and nitrogen species in the molecular mechanism of asthma. The present results demonstrate the therapeutic potential of nitroxides for the treatment of asthma.     

CXC chemokines modulate IgE secretion and pulmonary inflammation in a model of allergic asthma

The pathophysiology of asthma is influenced by exposure to allergens and endotoxin. Although the role of allergen-induced eosinophilia has been widely studied, neutrophil-mediated responses remain elusive. A role for neutrophils in the asthmatic responses is likely since human neutrophils have been shown to express IgE receptors, as well as receptors for many cytokines and chemokines implicated in the pathogenesis of asthma. In this study we investigated neutrophil involvement in a novel, house dust extract (HDE) induced model of asthma-like pulmonary inflammation. Mice were immunized and challenged with HDE containing high levels of cockroach allergens, 377 U/ml Bla g1 and 6249 ng/ml Bla g2. The biological activity of the murine chemokines KC and MIP-2 was inhibited with specific rabbit antisera. Differential counting of cells recovered from the bronchoalveolar lavage (BAL) fluid showed that neutralization of KC and MIP-2 significantly decreased pulmonary recruitment of neutrophils (reduced 86%) and lymphocytes (reduced 76%). Neutralization of these chemokines also exerted a systemic effect with a significant decrease in plasma IgE levels, 547 ng/ml+/-65 compared to 1314 ng/ml+/-247 for control sera treated animals. This study shows that CXC chemokines play an important role in allergy and asthma both at the level of pulmonary cell recruitment and systemic immune responses.     

Schistosoma japonicum peptide SJMHE1 suppresses airway inflammation of allergic asthma in mice

Helminths and their products can shape immune responses by modulating immune cells, which are dysfunctional in inflammatory diseases such as asthma. We previously identified SJMHE1, a small molecule peptide from the HSP60 protein of Schistosoma japonicum. SJMHE1 can inhibit delayed‐type hypersensitivity and collagen‐induced arthritis in mice. In the present study, we evaluated this peptide's potential intervention effect and mechanism on ovalbumin‐induced asthma in mice. SJMHE1 treatment suppressed airway inflammation in allergic mice, decreased the infiltrating inflammatory cells in the lungs and bronchoalveolar lavage fluid, modulated the production of pro‐inflammatory and anti‐inflammatory cytokines in the splenocytes and lungs of allergic mice, reduced the percentage of Th2 cells and increased the proportion of Th1 and regulatory T cells (Tregs). At the same time, Foxp3 and T‐bet expression increased, and GATA3 and RORγt decreased in the lungs of allergic mice. We proved that SJMHE1 can interrupt the development of asthma by diminishing airway inflammation in mice. The down‐regulation of Th2 response and the up‐regulation of Th1 and Tregs response may contribute to the protection induced by SJMHE1 in allergic mice. SJMHE1 can serve as a novel therapy for asthma and other allergic or inflammatory diseases.     

Autophagy induces eosinophil extracellular traps formation and allergic airway inflammation in a murine asthma model

Studies have shown autophagy participation in the immunopathology of inflammatory diseases. However, autophagy role in asthma and in eosinophil extracellular traps (EETs) release is poorly understood. Here, we attempted to investigate the autophagy involvement in EETs release and in lung inflammation in an experimental asthma model. Mice were sensitized with ovalbumin (OVA), followed by OVA challenge. Before the challenge with OVA, mice were treated with an autophagy inhibitor, 3-methyladenine (3-MA). We showed that 3-MA treatment decreases the number of eosinophils, eosinophil peroxidase (EPO) activity, goblet cells hyperplasia, proinflammatory cytokines, and nuclear factor kappa B (NFκB) p65 immunocontent in the lung. Moreover, 3-MA was able to improve oxidative stress, mitochondrial energy metabolism, and Na⁺, K⁺-ATPase activity. We demonstrated that treatment with autophagy inhibitor 3-MA reduced EETs formation in the airway. On the basis of our results, 3-MA treatment can be an interesting alternative for reducing lung inflammation, oxidative stress, mitochondrial damage, and EETs formation in asthma.     

The purinergic G protein-coupled receptor 6 inhibits effector T cell activation in allergic pulmonary inflammation

We show that the P2Y(6) receptor, a purinergic G protein-coupled receptor with a high affinity for the nucleotide uridine diphosphate, is an important endogenous inhibitor of T cell function in allergic pulmonary inflammation. Mice conditionally deficient in P2Y(6) receptors [p2ry6 (flox/flox);cre/+ mice] exhibited severe airway and tissue pathology relative to P2Y(6)-sufficient [p2ry6 (flox/flox)] littermates (+/+ mice) when treated intranasally with an extract of the dust mite Dermatophagoides farinae (Df). P2Y(6) receptors were inducibly expressed by lung, lymph node, and splenic CD4(+) and CD8(+) T cells of Df-treated +/+ mice. Df-restimulated P2Y(6)-deficient lymph node cells produced higher levels of Th1 and Th2 cytokines, and polyclonally stimulated P2Y(6)-deficient CD4(+) T cells proliferated faster than comparably stimulated P2Y(6)-sufficient cells. The absence of P2Y(6) receptors on CD4(+) cells, but not APCs, was sufficient to amplify cytokine generation. Thus, P2Y(6) receptors protect the lung against exuberant allergen-induced pulmonary inflammation by inhibiting the activation of effector T cells.     

Modulation of lung inflammation by vessel dilator in a mouse model of allergic asthma

Background

Atrial natriuretic peptide (ANP) and its receptor, NPRA, have been extensively studied in terms of cardiovascular effects. We have found that the ANP-NPRA signaling pathway is also involved in airway allergic inflammation and asthma. ANP, a C-terminal peptide (amino acid 99–126) of pro-atrial natriuretic factor (proANF) and a recombinant peptide, NP73-102 (amino acid 73–102 of proANF) have been reported to induce bronchoprotective effects in a mouse model of allergic asthma. In this report, we evaluated the effects of vessel dilator (VD), another N-terminal natriuretic peptide covering amino acids 31–67 of proANF, on acute lung inflammation in a mouse model of allergic asthma.

Methods

A549 cells were transfected with pVD or the pVAX1 control plasmid and cells were collected 24 hrs after transfection to analyze the effect of VD on inactivation of the extracellular-signal regulated receptor kinase (ERK1/2) through western blot. Luciferase assay, western blot and RT-PCR were also performed to analyze the effect of VD on NPRA expression. For determination of VD''s attenuation of lung inflammation, BALB/c mice were sensitized and challenged with ovalbumin and then treated intranasally with chitosan nanoparticles containing pVD. Parameters of airway inflammation, such as airway hyperreactivity, proinflammatory cytokine levels, eosinophil recruitment and lung histopathology were compared with control mice receiving nanoparticles containing pVAX1 control plasmid.

Results

pVD nanoparticles inactivated ERK1/2 and downregulated NPRA expression in vitro, and intranasal treatment with pVD nanoparticles protected mice from airway inflammation.

Conclusion

VD''s modulation of airway inflammation may result from its inactivation of ERK1/2 and downregulation of NPRA expression. Chitosan nanoparticles containing pVD may be therapeutically effective in preventing allergic airway inflammation.     

Anti-IL-33 antibody treatment inhibits airway inflammation in a murine model of allergic asthma

Interleukin (IL)-33 is a recently described member of the IL-1 family and has been shown to induce production of T helper type 2 cytokines. In this study, an anti-IL-33 antibody was evaluated against pulmonary inflammation in mice sensitized and challenged with ovalbumin. The anti-IL-33 or a control antibody (150 μg/mouse) was given intraperitoneally as five doses before the sensitization and antigen challenge. Treatment with anti-IL-33 significantly reduced serum IgE secretion, the numbers of eosinophils and lymphocytes, and concentrations of IL-4, IL-5, and IL-13 in bronchoalveolar lavage fluid compared with administration of a control antibody. Histological examination of lung tissue demonstrated that anti-IL-33 significantly inhibited allergen-induced lung eosinophilic inflammation and mucus hypersecretion. Our data demonstrate for the first time that anti-IL-33 antibody can prevent the development of asthma in a mouse model and indicate that blockade of IL-33 may be a new therapeutic strategy for allergic asthma.     

肠道菌群与过敏性哮喘

近年来随着过敏性哮喘发病率的持续升高,人们开始注意到环境、生活方式的改变可能会影响过敏性哮喘的发生。流行病学调查显示,过敏性哮喘的发生和发展与生命早期肠道菌群的紊乱密切相关。本研究主要综述近年来肠道菌群对过敏性哮喘发生的影响及机制,探讨影响肠道菌群定植的主要因素,以及微生态调节剂在过敏性哮喘等变应性疾病中的预防和治疗作用。