No abstract

Stress-induced intestinal barrier dysfunction may be involved in chronic intestinal disorders. Glucagon-like peptide-2 (GLP-2) is an intestinotrophic growth hormone that can rapidly improve intestinal epithelial barrier function. Here, we investigated whether mouse intestine is responsive to chronic psychological stress and whether pretreatment with GLP-2 can ameliorate stress-induced changes. Mice were subjected to water avoidance stress (WAS; 1 h/day for 10 days) with GLP-2 or saline administered 4 h before each WAS session. After the final stress period, the intestine was removed for assessment of physiological/morphological changes. Compared with controls (sham-stressed mice), stressed mice demonstrated enhanced ion secretion and permeability in the jejunum, ileum, and colon. In addition, increased numbers of bacteria were observed adhering to and/or penetrating the epithelium, associated with infiltration of mononuclear cells into the mucosa. GLP-2 treatment improved intestinal barrier function in stressed mice and ameliorated other aspects of impaired host defense. Our study extends previous findings in rats of stress-induced intestinal dysfunction and provides insights into potential novel therapeutics.

The intestinal epithelium acts as a barrier restricting uptake of luminal macromolecules such as dietary antigens and microbes. Here, we examined the role of cholinergic signalling in the regulation of permeability to macromolecules. Mouse jejunum was mounted in Ussing chambers and permeability was determined by measuring the flux of the antigen-sized protein, horseradish peroxidase (HRP), across the tissue. Baseline HRP permeability was significantly reduced by neural blockade with tetrodotoxin or cholinergic muscarinic antagonism with atropine, suggesting that ongoing release of endogenous acetylcholine from enteric nerves regulates barrier function. Exogenous addition of the muscarinic agonist bethanechol caused significant increases in both HRP flux and the area of HRP-containing endosomes in enterocytes. Bethanechol-enhanced HRP flux was abrogated by the M3 receptor antagonist, 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP), the phospholipase A(2) inhibitor quinacrine, and the cyclooxygenase inhibitor indomethacin. Complementary in vitro studies showed direct effects of bethanechol on T84 epithelial cells, where increased HRP uptake was associated with increased F-actin, and increased cytosolic phospholipase A(2) (cPLA(2)) phosphorylation. Taken together, these results provide evidence for cholinergic regulation of transepithelial transport of macromolecules, mainly mediated by activation of M3 receptors with subsequent involvement of phospholipase A(2) and cyclooxygenase products.

A characteristic of many enteropathies is increased epithelial permeability, a potentially pathophysiological event that can be evoked by T helper (Th)-1 (i.e., IFN-gamma) and Th2 (i.e., IL-4) cytokines and bacterial infection [e.g., enteropathogenic Escherichia coli (EPEC)]. The green tea polyphenol (-)-epigallocatechin gallate (EGCG) has immunosuppressive properties, and we hypothesized that it would ameliorate the increased epithelial permeability induced by IFN-gamma, IL-4, and/or EPEC. EGCG, but not the related epigallocatechin, completely prevented the increase in epithelial (i.e., T84 cell monolayer) permeability caused by IFN-gamma exposure as gauged by transepithelial resistance and horseradish peroxidase flux; EGCG did not alleviate the barrier disruption induced by IL-4 or EPEC. IFN-gamma-treated T84 and THP-1 (monocytic cell line) cells displayed STAT1 activation (tyrosine phosphorylation on Western blot analysis, DNA binding on EMSA) and upregulation of interferon response factor-1 mRNA, a STAT1-dependent gene. All three events were inhibited by EGCG pretreatment. Aurintricarboxylic acid also blocked IFN-gamma-induced STAT1 activation, but it did not prevent the increase in epithelial permeability. Additionally, pharmacological blockade of MAPK signaling did not affect IFN-gamma-induced epithelial barrier dysfunction. Thus, as a potential adjunct anti-inflammatory agent, EGCG can block STAT1-dependent events in gut epithelia and monocytes and prevent IFN-gamma-induced increased epithelial permeability. The latter event is both a STAT1- and MAPK-independent event.

. Glucagon-like peptide-2-enhanced barrier function reduces pathophysiology in a model of food allergy. Am J Physiol Gastrointest Liver Physiol 284: G905-G912, 2003. First published January 29, 2003 10.1152/ajpgi.00231. 2002.-Penetration of the gut epithelial barrier by intact luminal antigen is necessary for immunologically mediated pathophysiology in the context of food allergy. We investigated if glucagon-like peptide-2 (GLP-2) could affect immediate hypersensitivity and late-phase allergic inflammation in a murine model. Mice were sensitized to horseradish peroxidase (HRP); studies were conducted 14 days later. Mice were treated with 5 g GLP-2 subcutaneously 4 h before antigen challenge. For immediate hypersensitivity, jejunal segments in Ussing chambers were challenged by luminal HRP antigen. GLP-2 treatment reduced the uptake of HRP and the antigen-induced secretory response after luminal challenge. GLP-2 appears to reduce macromolecular uptake independent of the CD23-mediated enhanced antigen uptake pathway. For the late phase, mice were gavaged with antigen, and 48 h later the function and histology of the jejunum were examined. GLP-2 prevented the usual prolonged permeability defect and reduced the number of inflammatory cells in the mucosa. Our studies demonstrate that a single treatment of sensitized mice with GLP diminishes both immediate and late-phase hypersensitivity reactions characteristic of food allergy by inhibiting transepithelial uptake of antigen. food allergy; transcellular and paracellular permeability; epithelial barrier function GLUCAGON-LIKE PEPTIDE-2 (GLP-2) is a 33-amino acid peptide secreted by the enteroendocrine L cells of the intestinal epithelium (16). The biological activities of GLP-2 include augmented growth of the gut mucosa [by both increased crypt cell proliferation and decreased enterocyte apoptosis (20)], stimulation of nutrient absorption (7), and enhanced barrier function (2). Such changes may account for the beneficial effects of GLP-2 in models of massive small bowel resection (18), total parenteral nutrition (8), and intestinal inflammation (6, 11). Specifically, improved barrier function may prevent the uptake of luminal antigens, bacterial products, and other proinflammatory material into the mucosa where they can provoke immune/inflammatory reactions, although this hypothesis has not yet been tested precisely. However, our previous study (2) in mice demonstrated that GLP-2 was able to reduce penetration of the epithelium by both small and large molecules; this effect was documented within 4 h after a single subcutaneous injection.Food allergy is a condition in which ingested food antigens rapidly provoke gastrointestinal symptoms in sensitized individuals (in humans or rodent models; reviewed in Ref. 9). Food allergic reactions are caused by antigen cross-linking of IgE bound to mucosal mast cells in the subepithelial compartment. Released mast cell mediators then act on cell receptors to induce intestinal anaphylaxis involving ion secretion, the driving force...