Eosinophils in the gastrointestinal tract and their role in the pathogenesis of major colorectal disorders

Eosinophils are currently regarded as versatile mobile cells controlling and regulating multiple biological pathways and responses in health and disease. These cells store in their specific granules numerous biologically active substances (cytotoxic cationic proteins, cytokines, growth factors, chemokines, enzymes) ready for rapid release. The human gut is the main destination of eosinophils that are produced and matured in the bone marrow and then transferred to target tissues through the circulation. In health the most important functions of gut-residing eosinophils comprise their participation in the maintenance of the protective mucosal barrier and interactions with other immune cells in providing immunity to microbiota of the gut lumen. Eosinophils are closely involved in the development of inflammatory bowel disease (IBD), when their cytotoxic granule proteins cause damage to host tissues. However, their roles in Crohn’s disease and ulcerative colitis appear to follow different immune response patterns. Eosinophils in IBD are especially important in altering the structure and protective functions of the mucosal barrier and modulating massive neutrophil influx to the lamina propria followed by transepithelial migration to colorectal mucus. IBD-associated inflammatory process involving eosinophils then appears to expand to the mucus overlaying the internal gut surface. The author hypothesises that immune responses within colorectal mucus as well as ETosis exerted by both neutrophils and eosinophils on the both sides of the colonic epithelial barrier act as additional pathogenetic factors in IBD. Literature analysis also shows an association between elevated eosinophil levels and better colorectal cancer (CRC) prognosis, but mechanisms behind this effect remain to be elucidated. In conclusion, the author emphasises the importance of investigating colorectal mucus in IBD and CRC patients as a previously unexplored milieu of disease-related inflammatory responses.

Bradykinin in asthma: Modulation of airway inflammation and remodelling

Bradykinin, a pro-inflammatory molecule, and its related peptides have been studied for their effects on acute reactions in upper and lower airways, where they can be synthesised and metabolized after exposure to different stimuli including allergens and viral infection. Bradykinin B₁ and B₂ receptors are constitutively expressed in the airways on several residential and/or immune cells. Their expression can also be induced by inflammatory mediators, usually associated with eosinophil and neutrophil recruitment, such as IL-4, IL-13, TNF-α, IL-6 and IL-8, via intracellular MAPK and NF-κB signalling. In turn, the latters up-regulate both bradykinin receptors. Bradykinin activates epithelial/endothelial and immune cells, neurons and mesenchymal cells (such as fibroblasts, myofibroblasts and smooth muscle cells), which are implicated in the development of airway chronic inflammation, responsiveness and remodelling (a major feature of severe asthma). This review highlights the role of bradykinin and its receptors in respect to chronic inflammatory response involving eosinophils/neutrophils and to vascular/matrix-related airway remodelling in asthmatic airways. This scenario is especially important for understanding the mechanisms involved in the pathogenesis of eosinophilic and/or neutrophilic asthma and hence their therapeutic approach.

G Protein-Coupled Kinin Receptors and Immunity Against Pathogens

For decades, immunologists have considered the complement system as a paradigm of a proteolytic cascade that, acting cooperatively with the immune system, enhances host defense against infectious organisms. In recent years, advances made in thrombosis research disclosed a functional link between activated neutrophils, monocytes, and platelet-driven thrombogenesis. Forging a physical barrier, the fibrin scaffolds generated by synergism between the extrinsic and intrinsic (contact) pathways of coagulation entrap microbes within microvessels, limiting the systemic spread of infection while enhancing the clearance of pathogens by activated leukocytes. Insight from mice models of thrombosis linked fibrin formation via the intrinsic pathway to the autoactivation of factor XII (FXII) by negatively charged "contact" substances, such as platelet-derived polyphosphates and DNA from neutrophil extracellular traps. Following cleavage by FXIIa, activated plasma kallikrein (PK) initiates inflammation by liberating the nonapeptide bradykinin (BK) from an internal domain of high molecular weight kininogen (HK). Acting as a paracrine mediator, BK induces vasodilation and increases microvascular permeability via activation of endothelial B2R, a constitutively expressed subtype of kinin receptor. During infection, neutrophil-driven extravasation of plasma fuels inflammation via extravascular activation of the kallikrein-kinin system (KKS). Whether liberated by plasma-borne PK, tissue kallikrein, and/or microbial-derived proteases, the short-lived kinins activate immature dendritic cells via B2R, thus linking the infection-associated innate immunity/inflammation to the adaptive arm of immunity. As inflammation persists, a GPI-linked carboxypeptidase M removes the C-terminal arginine from the primary kinin, converting the B2R agonist into a high-affinity ligand for B1R, a GPCR subtype that is transcriptionally upregulated in injured/inflamed tissues. As reviewed here, lessons taken from studies of kinin receptor function in experimental infections have shed light on the complex proteolytic circuits that, acting at the endothelial interface, reciprocally couple immunity to the proinflammatory KKS.

Integrative information theoretic network analysis for genome-wide association study of aspirin exacerbated respiratory disease in Korean population

BACKGROUND

Aspirin Exacerbated Respiratory Disease (AERD) is a chronic medical condition that encompasses asthma, nasal polyposis, and hypersensitivity to aspirin and other non-steroidal anti-inflammatory drugs. Several previous studies have shown that part of the genetic effects of the disease may be induced by the interaction of multiple genetic variants. However, heavy computational cost as well as the complexity of the underlying biological mechanism has prevented a thorough investigation of epistatic interactions and thus most previous studies have typically considered only a small number of genetic variants at a time.

METHODS

In this study, we propose a gene network based analysis framework to identify genetic risk factors from a genome-wide association study dataset. We first derive multiple single nucleotide polymorphisms (SNP)-based epistasis networks that consider marginal and epistatic effects by using different information theoretic measures. Each SNP epistasis network is converted into a gene-gene interaction network, and the resulting gene networks are combined as one for downstream analysis. The integrated network is validated on existing knowledgebase of DisGeNET for known gene-disease associations and GeneMANIA for biological function prediction.

RESULTS

We demonstrated our proposed method on a Korean GWAS dataset, which has genotype information of 440,094 SNPs for 188 cases and 247 controls. The topological properties of the generated networks are examined for scale-freeness, and we further performed various statistical analyses in the Allergy and Asthma Portal (AAP) using the selected genes from our integrated network.

CONCLUSIONS

Our result reveals that there are several gene modules in the network that are of biological significance and have evidence for controlling susceptibility and being related to the treatment of AERD.

Bradykinin B2 receptor expression in the bronchial mucosa of allergic asthmatics: the role of NF-kB

BACKGROUND

Bradykinin (BK) mediates acute allergic asthma and airway remodelling. Nuclear factor-kappa B (NF-kB) is potentially involved in BK B2 receptor (B2R) regulation.

OBJECTIVE

In this observational cross-sectional study, B2R and NF-kB expression was evaluated in bronchial biopsies from mild asthmatics (after diluent/allergen challenge) and healthy controls, examining the role of NF-kB in B2R expression in primary human fibroblasts from normal and asthmatic subjects (HNBFb and HABFb).

METHODS

B2R and NF-kB (total and nuclear) expression was analysed by immunohistochemistry in biopsies from 10 mild intermittent asthmatics (48 h after diluent/allergen challenge) and 10 controls undergoing bronchoscopy. B2R co-localization in 5B5(+) and αSMA(+) mesenchymal cells was studied by immunofluorescence/confocal microscopy, and B2R expression in HABFb/HNBFb incubated with interleukin (IL)-4/IL-13 with/without BK, and after NF-kB inhibitor, by Western blotting.

RESULTS

Bronchial mucosa B2R and nuclear NF-kB expression was higher in asthmatics after diluent (B2R only) and allergen challenge than in controls (P < 0.05), while B2R and NF-kB (total and nuclear) increased after allergen compared with after diluent (P < 0.05). Allergen exposure increased B2R expression in 5B5(+) and αSMA(+) cells. Constitutive B2R protein expression was higher in HABFb than in HNBFb (P < 0.05) and increased in both cell types after IL-13 or IL-4/IL-13 and BK treatment. This increase was suppressed by a NF-kB inhibitor (P < 0.05).

CONCLUSIONS & CLINICAL RELEVANCE

Bronchial B2R expression is constitutively elevated in allergic asthma and is further increased after allergen exposure together with NF-kB expression. NF-kB inhibitor blocked IL-4/IL-13-induced increase in B2R expression in cultured fibroblasts, suggesting a role as potential anti-asthma drug.

Pharmacological evaluation of a selective bradykinin B1 antagonist in a canine model of arthritis

The effects of a selective bradykinin 1 receptor antagonist, compound A, were evaluated in a canine model of acute inflammatory model of arthritis. Despite detection of the B₁ receptor in canine type B synoviocytes using a fluorescent ligand, oral administration of compound A (9 and 27 mg/kg) did not improve weight bearing of dogs injected intra-articularly with IL-1β in a force plate analysis. Analysis of the synovial fluid of IL-1β-treated dogs indicated high levels of bradykinin postchallenge. Excellent exposure, coupled with evidence of the presence of the B₁ receptor during an acute inflammatory model of pain, indicates an inability of the receptor to mediate inflammatory pain in canines.

Kinin B1 receptor antagonist BI113823 reduces allergen-induced airway inflammation and mucus secretion in mice

Kinin B1 receptors are implicated in asthmatic airway inflammation. Here we tested this hypothesis by examining the anti-inflammatory effects of BI113823, a novel non-peptide orally active kinin B1 receptor antagonist in mice sensitized to ovalbumin (OVA). Male Balb-c mice were randomly assigned to four study groups: (1) control, (2) OVA+vehicle, (3) OVA+BI113823, (4) OVA+dexamethasone. Mice were sensitized intraperitoneally with 75μg ovalbumin on days 1 and 8. On days 15-17, mice were challenged intranasally with 50μg of ovalbumin. Mice received vehicle, BI113823, or dexamethasone (positive control) on days 16-18. On day 19, bronchoalveolar lavage (BAL) and lung tissue were collected for biochemical and immuno-histological analysis. Compared to controls treatment with BI113823 significantly reduced the numbers of BAL eosinophils, macrophages, neutrophils and lymphocytes by 58.3%, 61.1%, 66.4% and 56.0%, respectively. Mice treated with dexamethasone showed similar reductions in BAL cells. Treatment with BI113823 and dexamethasone also significantly reduced total protein content, IgE, TNF-α and IL-1β in lavage fluid, reduced myeloperoxidase activity, mucus secretion in lung tissues, and reduced the expression of B1 receptors, matrix metalloproteinase (MMP)-2 and cyclooxygenase (COX)-2 compared to vehicle-treated mice. Only BI113823 reduced MMP-9 and inducible nitric oxide synthase (iNOS). BI113823 effectively reduced OVA-induced inflammatory cell, mediator and signaling pathways equal to or greater than that seen with steroids in a mouse asthma model. BI113823 might be useful in modulating inflammation in asthma.

Downregulation of kinin B1 receptor function by B2 receptor heterodimerization and signaling

Signaling through the G protein-coupled kinin receptors B1 (kB1R) and B2 (kB2R) plays a critical role in inflammatory responses mediated by activation of the kallikrein-kinin system. The kB2R is constitutively expressed and rapidly desensitized in response to agonist whereas kB1R expression is upregulated by inflammatory stimuli and it is resistant to internalization and desensitization. Here we show that the kB1R heterodimerizes with kB2Rs in co-transfected HEK293 cells and natively expressing endothelial cells, resulting in significant internalization and desensitization of the kB1R response in cells pre-treated with kB2R agonist. However, pre-treatment of cells with kB1R agonist did not affect subsequent kB2R responses. Agonists of other G protein-coupled receptors (thrombin, lysophosphatidic acid) had no effect on a subsequent kB1R response. The loss of kB1R response after pretreatment with kB2R agonist was partially reversed with kB2R mutant Y129S, which blocks kB2R signaling without affecting endocytosis, or T342A, which signals like wild type but is not endocytosed. Co-endocytosis of the kB1R with kB2R was dependent on β-arrestin and clathrin-coated pits but not caveolae. The sorting pathway of kB1R and kB2R after endocytosis differed as recycling of kB1R to the cell surface was much slower than that of kB2R. In cytokine-treated human lung microvascular endothelial cells, pre-treatment with kB2R agonist inhibited kB1R-mediated increase in transendothelial electrical resistance (TER) caused by kB1R stimulation (to generate nitric oxide) and blocked the profound drop in TER caused by kB1R activation in the presence of pyrogallol (a superoxide generator). Thus, kB1R function can be downregulated by kB2R co-endocytosis and signaling, suggesting new approaches to control kB1R signaling in pathological conditions.

Transforming growth factor-beta 1 pathways in inflammatory airway diseases

Transforming growth factor-beta 1 (TGF-β1) has been reported being involved in the remodeling and immunosuppression processes of inflammatory airway diseases; understanding the regulation of TGF-β1 is therefore a key to unravel the pathomechanisms of these diseases. This review briefly summarizes the current knowledge on the influencing factors for driving TGF-β1 and its regulatory pathways in inflammatory airway diseases and discusses possible therapeutic approaches to TGF-β1 control. The factors include smoking and oxidative stress, prostaglandins (PGs), leukotrienes (LTs), bradykinin (BK), and microRNAs (miRs). Based on the summary, new innovative treatment strategies may be developed for inflammatory airway diseases with an impaired expression of TGF-β1.

Novel kinin B₁ receptor splice variant and 5'UTR regulatory elements are responsible for cell specific B₁ receptor expression

The kinin B₁ receptor (B₁R) is rapidly upregulated after tissue trauma or inflammation and is involved in cancer and inflammatory diseases such as asthma. However, the role of the: promoter; a postulated alternative promoter; and spliced variants in airway epithelial and other lung cells are poorly understood.

We identified, in various lung cell lines and leucocytes, a novel, naturally occurring splice variant (SV) of human B₁R gene with a shorter 5′untranslated region. This novel SV is ≈35% less stable than the wild-type (WT) transcript in lung adenocarcinoma cells (H2126), but does not influence translation efficiency. Cell-specific differences in splice variant expression were observed post des[Arg10]-kallidin stimulation with delayed upregulation of SV compared to WT suggesting potentially different regulatory responses to inflammation. Although an alternative promoter was not identified in our cell-lines, several cell-specific regulatory elements within the postulated alternative promoter region (negative response element (NRE) −1020 to −766 bp in H2126; positive response element (PRE) −766 to −410 bp in 16HBE; −410 to +1 region acts as a PRE in H2126 and NRE in 16HBE cells) were found.

These findings reveal complex regulation of B₁R receptor expression in pulmonary cells which may allow future therapeutic manipulation in chronic pulmonary inflammation and cancer.

Human eosinophil adhesion and receptor expression

Eosinophils migrate from the bone marrow in response to cytokines and chemokines which induce the expression and activation of adhesion receptors. In understanding the recruitment of eosinophils, protocols to identify eosinophil adhesion and receptor expression have been identified. In this summary, the eosinophil peroxidase and fluorescent labeling assays are described as measurements of indirect and direct eosinophil adhesion, respectively. Additional protocols that identify eosinophil receptor expression via immunofluorescent microscopy and flow cytometry are also described.

MAPK/NF-κB-dependent upregulation of kinin receptors mediates airway hyperreactivity: a new perspective for the treatment

Airway hyperreactivity (AHR) is a major feature of asthmatic and inflammatory airways. Cigarette smoke exposure, and bacterial and viral infections are well-known environmental risk factors for AHR, but knowledge about the underlying molecular mechanisms on how these risk factors lead to the development of AHR is limited. Activation of intracellular mitogen-activated protein kinase (MAPK)/nuclear factor-kappa B (NF-κB) and their related signal pathways including protein kinase C (PKC), phosphoinositide 3-kinase (PI3K) and protein kinase A (PKA) signaling pathways may result in airway kinin receptor upregulation, which is suggested to play an important role in the development of AHR. Environmental risk factors trigger the production of pro-inflammatory mediators such as tumor necrosis factor-α (TNF-α) and interleukins (ILs) that activate intracellular MAPK- and NF-κB-dependent inflammatory pathways, which subsequently lead to AHR via kinin receptor upregulation. Blockage of intracellular MAPK/NF-κB signaling prevents kinin B₁ and B₂ receptor expression in the airways, resulting in a decrease in the response to bradykinin (kinin B₂ receptor agonist) and des-Arg⁹-bradykinin (kinin B₁ receptor agonist). This suggests that MAPK- and NF-κB-dependent kinin receptor upregulation can provide a novel option for treatment of AHR in asthmatic as well as in other inflammatory airway diseases.

Short Communication: Some Observations on the Role of Bradykinin in Immunity to Teladorsagia circumcincta in Sheep

Bradykinin is a physiologically active peptide involved in vasodilation and smooth muscle contraction and is previously shown to be increased in gastrointestinal mucus during nematode challenge in sheep. Here, it is shown that bradykinin in the abomasum is positively correlated with both mast cells and globule leukocytes in the abomasum, and that all three of these parameters are negatively associated with numbers of adult Teladorsagia circumcincta during the challenge of immune sheep. It is suggested that bradykinin either stimulates the degranulation of mast cells, or is released during this degranulation process, or both. Multiple regression showed that almost 60% of the variation of in adult T. circumcincta could be explained by two variables, bradykinin and T. circumcincta—specific IgG₁ in plasma. This provides further evidence that bradykinin may be a mechanism of protective immunity in sheep, although its involvement in asthma and other allergic disorders raises questions about its role in unwanted immunopathology.

Lys-des[Arg9]-bradykinin alters migration and production of interleukin-12 in monocyte-derived dendritic cells

This study tested the hypothesis that proinflammatory kinin peptides are involved in modulating human dendritic cell (DC) function. Inflammation is accompanied by an increased maturation of DCs and the generation of kinins, particularly Lys-des[Arg(9)]-bradykinin (Lda-BK). We assessed the role of Lda-BK in the activation and migration of human monocyte-derived DCs (hMo-DCs) matured through the use of LPS, TNF-α + IL-1β, or CD40 ligand. Kinin B(1) and B(2) receptor mRNA and protein expression were assessed by confocal microscopy, flow cytometry, and RT-PCR. The effects of Lda-BK on the migration of mature hMo-DCs were assessed in Transwell chambers, whereas the expression of costimulatory molecules and the secretion of IL-12 were assessed by flow cytometry and ELISA, respectively. The expression of the kinin B(1) receptor (B(1)R) was down-regulated during the maturation of hMo-DCs, whereas the expression of B(2)R was unchanged. The B(1)R agonist Lda-BK was not chemotactic for hMo-DCs matured using LPS, TNF-α + IL-1β, or CD40 ligand, but Lda-BK enhanced the secretion of IL-12p70 and inhibited the secretion of IL-12p40 by mature hMo-DCs. However, the exposure of hMo-DCs matured with TNF-α + IL-1β to Lda-BK for 6 hours decreased subsequent migration in response to Lda-BK, the chemokine CCL19, or Lda-BK combined with CCL19. The expression of B(1)R was increased in hMo-DCs from subjects with asthma compared with subjects without asthma, in keeping with a tendency toward increased in vitro migration of asthmatic hMo-DCs in response to Lda-BK. The increased formation of Lda-BK and the enhanced expression of B(1)R as a consequence of inflammation may alter the migration of mature, antigen-laden DCs to regional lymph nodes in response to CCL19, may modulate the secretion of cytokines by these DCs, and may contribute to the accumulation of mature DCs in the lungs of patients with asthma.

Distribution and expression of B2-kinin receptor on human leukocyte subsets in young adults and elderly using flow cytometry

The kallikrein-kinin system has been investigated in many experimental models. Dysregulations of the KKS are likely to be involved in pathologies such as inflammation, cancer and cardiovascular diseases. Previous works on the human KKS mostly rely on gene polymorphism and mRNA expression. In order to assess the KKS in human at the protein level, we have developed an approach based on flow cytometric analysis of leukocytes. Whole blood samples were collected and erythrocytes were lysed. Permeabilised leukocytes were incubated with anti-B2R (IgG2b), anti-IgG2b-PE, anti-CD3-PerCP (lymphocytes) and anti-CD14-APC (monocytes) antibodies. FACScalibur analyzed fluorescence intensities. Results were expressed as per cent of B2R-positive cells in each leukocyte subset and as B2R fluorescence intensity per positive cell. Detection of the B2R protein by this methodology was validated by (i) correlation with Western blotting using two different B2R antibodies, (ii) BK-induced Erk activation, (iii) B2R mRNA expression. The methodology was then applied to evaluate variations of B2R expression in a population including young healthy, elderly healthy, and elderly treated hypertensive men and women. In the young healthy subjects, B2R distribution was: monocytes>polymorphonuclear neutrophils (PMN)>lymphocytes and no difference with gender was observed. Moreover, no difference was observed on PMN B2R expression. B2R expression remained unchanged in the elderly healthy or hypertensive men. By contrast, monocytes and lymphocytes B2R expressions were decreased in the elderly healthy women. Finally, FACS analysis of B2R expression on leukocytes subsets provides single cell quantification of B2R expression allowing comparison of cellular sub-populations. This approach provides a new efficient tool to investigate B2R profiling of immune system in pathological states.

Bradykinin B(1) receptor antagonist R954 inhibits eosinophil activation/proliferation/migration and increases TGF-beta and VEGF in a murine model of asthma

In the present study the effects of bradykinin receptor antagonists were investigated in a murine model of asthma using BALB/c mice immunized with ovalbumin/alum and challenged twice with aerosolized ovalbumin. Twenty four hours later eosinophil proliferation in the bone marrow, activation (lipid bodies formation), migration to lung parenchyma and airways and the contents of the pro-angiogenic and pro-fibrotic cytokines TGF-beta and VEGF were determined. The antagonists of the constitutive B(2) (HOE 140) and inducible B(1) (R954) receptors were administered intraperitoneally 30min before each challenge. In sensitized mice, the antigen challenge induced eosinophil proliferation in the bone marrow, their migration into the lungs and increased the number of lipid bodies in these cells. These events were reduced by treatment of the mice with the B(1) receptor antagonist. The B(2) antagonist increased the number of eosinophils and lipid bodies in the airways without affecting eosinophil counts in the other compartments. After challenge the airway levels of VEGF and TGF-beta significantly increased and the B(1) receptor antagonist caused a further increase. By immunohistochemistry techniques TGF-beta was found to be expressed in the muscular layer of small blood vessels and VEGF in bronchial epithelial cells. The B(1) receptors were expressed in the endothelial cells. These results showed that in a murine model of asthma the B(1) receptor antagonist has an inhibitory effect on eosinophils in selected compartments and increases the production of cytokines involved in tissue repair. It remains to be determined whether this effects of the B(1) antagonist would modify the progression of the allergic inflammation towards resolution or rather towards fibrosis.