Mucosal mast cell proteases are involved in colonic permeability alterations and subsequent bacterial translocation in endotoxemic rats

c-Kit mutation reduce intestinal epithelial cell proliferation and migration, but not influence intestinal permeability stimulated by lipopolysaccharide

The proto-oncogene c-kit, as a marker of interstitial cells of Cajal (ICCs) in the gastrointestinal tract, plays an important role in the ICCs. Although limited evidences showed c-kit is present in the colonic epithelium but its roles remain unclear. In the present study, we aimed to investigate the expression, location and function of c-kit in the intestinal epithelium. Immunofluorescence, western blotting, and RT-PCR were performed to detect the expression and location of c-kit in the intestinal mucosa of WT mice. We investigated intestinal epithelial proliferation and migration in vivo by performing 5-Bromodeoxyuridine (BrdU) incorporation and Ki-67 staining in WT and Wads ^m/m mice. An Ussing chamber with fluorescein-isothiocyanate dextran 4000 was used to detect the transepithelial electric resistance (TER), short circuit current (ISC) and permeability across ex vivo colon segments under control and endotoxaemia conditions. We demonstrated that c-kit was located and expressed in the gut crypt compartment in WT mice, which was demonstrated in the c-kit mutant mice (Wads ^m/m). In addition, both the number of proliferating cells and the percentage of the distance migrated were lower in the Wads ^m/m mice than those in the WT mice. Moreover, the intestinal permeability, TER and tight junction were unaltered in the Wads ^m/m mice under endotoxic conditions compared with those in both the control condition and the WT mice. Altogether, these observations imply that the expression of c-kit in the colonic epithelium is involved in the proliferation and permeability of the colonic epithelium.

Lipopolysaccharides facilitate colonic motor alterations associated to the sensitization to a luminal antigen in rats

Background/Aims

Enteric dysbiosis is a risk factor for dietary proteins-associated intestinal alterations, contributing to the development of food allergies and the symptomatology of functional gastrointestinal disorders, mainly irritable bowel syndrome (IBS). We explored if a dysbiotic-like state, simulated by intraperitoneal administration of bacterial lipopolysaccharides (LPS), facilitates the sensitization to a luminal antigen, ovalbumin (OVA), in rats.

Methods

Rats were exposed to oral OVA for 1 week, alone or with LPS. Thereafter, colonic histology, goblet cell density, mucosal eosinophils and mucosal mast cell (MMC) and connective tissue mast cell (CTMC) were evaluated. Colonic expression (real-time quantitative polymerase chain reaction) of interleukins, IFN-α1 and integrins was assessed to determine local immune responses. Luminal and wall adhered microbiota were characterized by fluorescence in situ hybridization. Colonic contractility (in vitro) served to assess functional changes associated to OVA and/or LPS.

Results

Neither OVA nor LPS, alone or combined, lead to structural alterations, except for a reduced goblet cell density in OVA-LPS-treated rats. MMC density was unaffected, while CTMC counts increased within the submucosa of OVA-LPS-treated animals. Marginal immune activation (IFN-α1 up-regulation) was observed in OVA-LPS-treated rats. LPS induced a dysbiotic-like state characterized by decreased luminal bacterial counts, with a specific loss of clostridia. LPS facilitated Clostridium spp. wall adherence, an effect prevented by OVA. Colonic contractility was altered in OVA-LPS-treated animals, showing increased basal activity and enhanced motor responses to OVA.

Conclusions

Changes in gut microbiota and/or direct effects of LPS might enhance/facilitate local neuroimmune responses to food antigens leading to motor alterations similar to those observed in IBS.

Intraluminal nonbacterial intestinal components control gut and lung injury after trauma hemorrhagic shock

OBJECTIVE

To test whether the mucus layer, luminal digestive enzymes, and intestinal mast cells are critical components in the pathogenesis of trauma shock-induced gut and lung injury.

BACKGROUND

Gut origin sepsis studies have highlighted the importance of the systemic component (ischemia-reperfusion) of gut injury, whereas the intraluminal component is less well studied.

METHODS

In rats subjected to trauma hemorrhagic shock (T/HS) or sham shock, the role of pancreatic enzymes in gut injury was tested by diversion of pancreatic enzymes via pancreatic duct exteriorization whereas the role of the mucus layer was tested via the enteral administration of a mucus surrogate. In addition, the role of mast cells was assessed by measuring mast cell activation and the ability of pharmacologic inhibition of mast cells to abrogate gut and lung injury. Gut and mucus injury was characterized functionally, morphologically, and chemically.

RESULTS

Pancreatic duct exteriorization abrogated T/HS-induced gut barrier loss and limited chemical mucus changes. The mucus surrogate prevented T/HS-induced gut and lung injury. Finally, pancreatic enzyme-induced gut and lung injury seems to involve mast cell activation because T/HS activates mast cells and pharmacologic inhibition of intestinal mast cells prevented T/HS-induced gut and lung injury.

CONCLUSIONS

These results indicate that gut and gut-induced lung injury after T/HS involves a complex process consisting of intraluminal digestive enzymes, the unstirred mucus layer, and a systemic ischemic-reperfusion injury. This suggests the possibility of intraluminal therapeutic strategies.

Changes in intestinal glucocorticoid sensitivity in early life shape the risk of epithelial barrier defect in maternal-deprived rats

Glucocorticoids (GC) contribute to human intestine ontogeny and accelerate gut barrier development in preparation to birth. Rat gut is immature at birth, and high intestinal GC sensitivity during the first two weeks of life resembles that of premature infants. This makes suckling rats a model to investigate postpartum impact of maternal separation (MS)-associated GC release in preterm babies, and whether GC sensitivity may shape MS effects in immature gut. A 4 hours-MS applied once at postnatal day (PND)10 enhanced plasma corticosterone in male and female pups, increased by two times the total in vivo intestinal permeability (IP) to oral FITC-Dextran 4 kDa (FD4) immediately after the end of MS, and induced bacterial translocation (BT) to liver and spleen. Ussing chamber experiments demonstrated a 2-fold increase of permeability to FD4 in the colon immediately after the end of MS, but not in the ileum. Colonic permeability was not only increased for FD4 but also to intact horseradish peroxidase 44 kDa in MS pups. In vivo, the glucocorticoid receptor (GR) antagonist RU486 or ML7 blockade of myosin light chain kinase controlling epithelial cytoskeleton contraction prevented MS-induced IP increase to oral FD4 and BT. In addition, the GR agonist dexamethasone dose-dependently mimicked MS-increase of IP to oral FD4. In contrast, MS effects on IP to oral FD4 and BT were absent at PND20, a model for full-term infant, characterized by a marked drop of IP to FD4 in response to dexamethasone, and decreased GR expression in the colon only compared to PND10 pups. These results show that high intestinal GC responsiveness in a rat model of prematurity defines a vulnerable window for a post-delivery MS, evoking immediate disruption of epithelial integrity in the large intestine, and increasing susceptibility to macromolecule passage and bacteremia.

Chymase inhibition as a pharmacological target: a role in inflammatory and functional gastrointestinal disorders?

Chymase has been extensively studied with respect to its role in the pathophysiology of cardiovascular disease, and is notable for its role in the generation of angiotensin II, a mediator crucial in vascular remodelling. However, in more recent years, an association between chymase and several inflammatory diseases, including gastrointestinal (GI) disorders such as inflammatory bowel diseases (IBD) have been described. Such studies, to date, with respect to IBD at least, are descriptive in the clinical context; nonetheless, preclinical studies implicate chymase in the pathogenesis of gut inflammation. However, studies to elucidate the role of chymase in functional bowel disease are in their infancy, but suggest a plausible role for chymase in contributing to some of the phenotypic changes observed in such disorders, namely increased epithelial permeability. In this short review, we have summarized the current knowledge on the pathophysiological role of chymase and its inhibition with reference to inflammation and tissue injury outside of the GI tract and discussed its potential role in GI disorders. We speculate that chymase may be a novel therapeutic target in the GI tract, and as such, inhibitors of chymase warrant preclinical investigation in GI diseases.

Oral administration of fermented red ginseng suppressed ovalbumin-induced allergic responses in female BALB/c mice

Anti-allergic efficacy of red ginseng (RG) and fermented red ginseng (FRG) was evaluated. RG or FRG were administered to ovalbumin (OVA)-sensitized mice for 8 weeks. Immunoglobulins (Igs), Th1/Th2 type cytokines, and β-lactoglobulin (BLG) in serum, and intestinal barrier-related molecules in jejunum were measured using enzyme-linked immunosorbent assay or reverse transcription-polymerase chain reaction. Mice sensitized with OVA increased serum IgG₁, IgE, OVA-IgG₁, and OVA-IgE. Both RG and FRG decreased serum IgE, OVA-IgE, and pro-inflammatory cytokines. Serum BLG, a marker of gut permeability, was significantly higher in sensitized animals and was decreased in mice fed RG or FRG. In addition, intestinal barrier-related markers such as MMCP-1, IL-4, TNF-α, COX-2, and iNOS mRNA expressions were decreased by RG or FRG. Our results suggest in vivo anti-allergic activities of RG or FRG, which are associated with the regulation of Th1/Th2 balance, intestinal inflammation and subsequent the suppression of IgE.

Sphingosine kinase-1-dependent and -independent inhibitory effects of zanthoxyli fructus to attenuate the activation of mucosal mast cells and ameliorate food allergies in mice

Food allergy (FA) is relatively a common disease in infants, but effective drug therapies are not yet available. Notably, mucosal mast cells, but not connective-tissue mast cells, play important roles in food allergic reactions via the release of inflammatory mediators. Therefore, we screened medicinal herb extracts for in vitro and in vivo antiallergic activity through inhibiting mucosal mast cell activation. As a result, both antigen-induced and calcium ionophore-induced degranulation was significantly inhibited by Zanthoxyli Fructus water extract (ZF) in mucosal-type murine bone marrow-derived mast cells (mBMMCs). ZF suppressed the antigen-induced [Ca²⁺]_i elevation and the antigen-enhanced mRNA expression of TNF-α, IL-4, and IL-13. The transcriptome and real-time PCR analyses revealed that ZF greatly decreased the antigen-enhanced expression level of sphingosine kinase 1 (Sphk1), which plays a key role in the FcεRI-mediated immune responses in mast cells. Furthermore, ZF inhibited allergic symptoms in an ovalbumin-caused murine FA model and decreased the number of infiltrating mucosal mast cells and the enhanced mRNA expression levels of IL-4 and Sphk1 in the FA mice colons. These results indicate that ZF suppresses mucosal mast cell activities mainly through Sphk1-dependent mechanism, and ZF is utilized for the development of a novel, potent anti-FA agent.

Mast cells trigger epithelial barrier dysfunction, bacterial translocation and postoperative ileus in a mouse model

BACKGROUND

Abdominal surgery involving bowel manipulation commonly results in inflammation of the bowel wall, which leads to impaired intestinal motility and postoperative ileus (POI). Mast cells have shown to play a key role in the pathogenesis of POI in mouse models and human studies. We studied whether mast cells contribute to the pathogenesis of POI by eliciting intestinal barrier dysfunction.

METHODS

C57BL/6 mice, and two mast cell-deficient mutant mice Kit(W/W-v) , and Kit(W-sh/W-sh) underwent laparotomy (L) or manipulation of the small bowel (IM). Postoperative inflammatory infiltrates and cytokine production were assessed. Epithelial barrier function was determined in Ussing chambers, by measuring transport of luminal particles to the vena mesenterica, and by assessing bacterial translocation.

KEY RESULTS

In WT mice, IM resulted in pro-inflammatory cytokine and chemokine production, and neutrophil extravasation to the manipulated bowel wall. This response to IM was reduced in mast cell-deficient mice. IM caused epithelial barrier dysfunction in WT mice, but not in the two mast cell-deficient strains. IM resulted in a decrease in mean arterial pressure in both WT and mast cell-deficient mice, indicating that impaired barrier function was not explained by tissue hypoperfusion, but involved mast cell mediators.

CONCLUSIONS & INFERENCES

Mast cell activation during abdominal surgery causes epithelial barrier dysfunction and inflammation of the muscularis externa of the bowel. The impairment of the epithelial barrier likely contributes to the pathogenesis of POI. Our data further underscore that mast cells are bona fide cellular targets to ameliorate POI.

Protease-activated receptor 2 signaling in inflammation

Protease-activated receptors (PARs) are G protein-coupled receptors that are activated by proteolytical cleavage of the amino-terminus and thereby act as sensors for extracellular proteases. While coagulation proteases activate PARs to regulate hemostasis, thrombosis, and cardiovascular function, PAR2 is also activated in extravascular locations by a broad array of serine proteases, including trypsin, tissue kallikreins, coagulation factors VIIa and Xa, mast cell tryptase, and transmembrane serine proteases. Administration of PAR2-specific agonistic and antagonistic peptides, as well as studies in PAR2 knockout mice, identified critical functions of PAR2 in development, inflammation, immunity, and angiogenesis. Here, we review these roles of PAR2 with an emphasis on the role of coagulation and other extracellular protease pathways that cleave PAR2 in epithelial, immune, and neuronal cells to regulate physiological and pathophysiological processes.

Mast cells are an essential component of human radiation proctitis and contribute to experimental colorectal damage in mice

Radiation proctitis is characterized by mucosal inflammation followed by adverse chronic tissue remodeling and is associated with substantial morbidity and mortality. Mast cell hyperplasia has been associated with diseases characterized by pathological tissue remodeling and fibrosis. Rectal tissue from patients treated with radiotherapy shows mast cell hyperplasia and activation, suggesting that these cells play a role in the development of radiation-induced sequelae. To investigate the role of mast cells in radiation damage, experimental radiation proctitis was induced in a mast cell-deficient (W(sh)/W(sh)) mouse model. The colon and rectum of W(sh)/W(sh) and wild-type mice were exposed to 27-Gy single-dose irradiation and studied after 2 and 14 weeks. Irradiated rodent rectum showed mast cell hyperplasia. W(sh)/W(sh) mice developed less acute and chronic rectal radiation damage than their control littermates. Tissue protection was associated with increased tissue neutrophil influx and expression of several inflammatory mediators immediately after radiation exposure. It was further demonstrated that mast cell chymase, tryptase, and histamine could change human muscularis propria smooth muscle cells into a migrating/proliferating and proinflammatory phenotype. These data show that mast cells have deleterious effects on both acute and chronic radiation proctitis, possibly by limiting acute tissue neutrophil influx and by favoring phenotypic orientation of smooth muscle cells, thus making them active participants in the radiation-induced inflammatory process and dystrophy of the rectal wall.

Intestinal mast cells in gut inflammation and motility disturbances

Mast cells may be regarded as prototypes of innate immune cells that can be controlled by neuronal mediators. Their activation has been implicated in many types of neuro-inflammatory responses, and related disturbances of gut motility, via direct or indirect mechanisms that involve several mechanisms relevant to disease pathogenesis such as changes in epithelial barrier function or activation of adaptive or innate immune responses. Here we review the evidence for the involvement of mast cells in the inflammation of the bowel wall caused by bowel manipulation that leads to motility disturbances such as postoperative gastroparesis and ileus. Also in IBD there is substantial evidence for the involvement of mast cells and a mast cell-mediated neuroimmune interaction showing an increased number and an increased degranulation of mast cells. We discuss the potential of mast cell inhibition as a bona fide drug target to relief postoperative ileus. Further research on mast cell-related therapy either by stabilizing the mast cells or by blocking specific mast cell mediators as adjunctive therapy in IBD is encouraged, bearing in mind that several drugs currently used in the treatment of IBD possess properties affecting mast cell activities. This article is part of a Special Issue entitled: Mast cells in inflammation.

Procession to pediatric bacteremia and sepsis: covert operations and failures in diplomacy

Despite advances in diagnosis and treatment, bacterial sepsis remains a major cause of pediatric morbidity and mortality, particularly among neonates, the critically ill, and the growing immunocompromised patient population. Sepsis is the end point of a complex and dynamic series of events in which both host and microbial factors drive high morbidity and potentially lethal physiologic alterations. In this article we provide a succinct overview of the events that lead to pediatric bloodstream infections (BSIs) and sepsis, with a focus on the molecular mechanisms used by bacteria to subvert host barriers and local immunity to gain access to and persist within the systemic circulation. In the events preceding and during BSI and sepsis, Gram-positive and Gram-negative pathogens use a battery of factors for translocation, inhibition of immunity, molecular mimicry, intracellular survival, and nutrient scavenging. Gaps in understanding the molecular pathogenesis of bacterial BSIs and sepsis are highlighted as opportunities to identify and develop new therapeutics.

Mast cells regulate homeostatic intestinal epithelial migration and barrier function by a chymase/Mcpt4-dependent mechanism

Altered intestinal barrier function is postulated to be a central predisposing factor to intestinal diseases, including inflammatory bowel diseases and food allergies. However, the mechanisms involved in maintaining homeostatic intestinal barrier integrity remain undefined. In this study, we demonstrate that mice deficient in mast cells (Kit(W-sh/W-sh) [Wsh]) or mast cell chymase (Mcpt4(-/-)) have significantly decreased basal small intestinal permeability compared with wild-type (WT) mice. Altered intestinal barrier function was linked to decreased intestinal epithelial cell migration along the villus/crypt axis, altered intestinal morphology, and dysregulated claudin-3 crypt expression. Remarkably, engraftment of Wsh mice with WT but not Mcpt4(-/-) mast cells restored intestinal epithelial cell migration, morphology, and intestinal epithelial barrier function. Collectively, these findings identify a mechanism by which mast cells regulate homeostatic intestinal epithelial migration and barrier function.

Oestradiol decreases colonic permeability through oestrogen receptor beta-mediated up-regulation of occludin and junctional adhesion molecule-A in epithelial cells

Oestradiol modulates paracellular permeability and tight junction (TJ) function in endothelia and reproductive tissues, but whether the ovarian hormones and cycle affect the paracellular pathway in the intestinal epithelium remains unclear. Oestrogen receptors (ERs) are expressed in intestinal epithelial cells, and oestradiol regulates epithelium formation. We examined the effects of oestrous cycle stage, oestradiol benzoate (EB), and progesterone (P) on colonic paracellular permeability (CPP) in the female rat, and whether EB affects expression of the TJ proteins in the rat colon and the human colon cell line Caco-2. In cyclic rats, CPP was determined through lumen-to-blood (51)Cr-labelled EDTA clearance, and in Ussing chambers for dextran permeability. CPP was also examined in ovariectomized (OVX) rats treated with P or EB, with and without the ER antagonist ICI 182,780, or with the selective agonists for ER beta (propyl pyrazole triol; PPT) or ER beta (diarylpropionitrile; DPN). In oestrus rats, CPP was reduced (P < 0.01) relative to dioestrus. In OVX rats, EB dose-dependently decreased CPP, an effect mimicked by DPN and blocked by ICI 182,780, whereas P had no effect. Oestradiol increased occludin mRNA and protein in the colon (P < 0.05), but not zona occludens (ZO)-1. Further, EB and DPN enhanced occludin and junctional adhesion molecule (JAM)-A expression in Caco-2 cells without change in ZO-1, an effect blocked by ICI 182,780. These data show that oestrogen reinforces intestinal epithelial barrier through ER beta-mediated up-regulation of the transmembrane proteins occludin and JAM-A determining paracellular spaces. These findings highlight the importance of the ER beta pathway in the control of colonic paracellular transport and mucosal homeostasis.