Differential inflammatory modulation of canine ileal longitudinal and circular muscle cells.
The aim of this study was to identify the subtypes of muscarinic receptors that mediate in vivo and in vitro canine ileal longitudinal muscle contractions and whether their role is modulated by inflammation. Previous studies have reported that circular muscle contractions are suppressed in ileal inflammation induced by mucosal exposure to ethanol and acetic acid. We found that inflammation had no significant effect on in vivo and in vitro spontaneous or muscarinic receptor-mediated contractions of the longitudinal muscle. The longitudinal muscle contractions were mediated primarily by the M(3) receptor subtype. However, the IC(50) of the M(2) receptor antagonist methoctramine was only 10 times greater than that of the M(3) receptor antagonist 4-DAMP in the longitudinal muscle, whereas it was 224 times greater in the circular muscle. M(2) receptor-coupled decrease of intracellular cAMP occurred in the longitudinal but not in the circular muscle from the normal ileum. Inflammation did not alter this coupling in the longitudinal muscle but established it in the circular muscle. In conclusion, M(2) receptors may play a greater role in the mediation of longitudinal muscle contractions than circular muscle contractions. Inflammation does not alter the contractility or the relative role of muscarinic receptor subtypes in longitudinal muscle cells. However, it modulates the M(2) receptor coupling to adenylate cyclase in the circular muscle. (+info
Characterization of M cell development during indomethacin-induced ileitis in rats.
BACKGROUND: M cells play an important role in the intestinal immune system as they have a high capacity for transcytosis of a wide range of microorganisms and macromolecules. However, little is known about the role of M cells during intestinal inflammation. AIM: We studied M cell development during indomethacin-induced intestinal inflammation in rats. METHODS: Ileitis in rats was induced by two subcutaneous injections with indomethacin (7.5 mg/kg) given 24 h apart. Rats were sacrificed after 14 days and tissue was analysed by fluorescence microscopy and electron microscopy. M cells could be visualized by using the FITC-labelled mAb anti-cytokeratin (CK)-8 (clone 4.1.18), which was recently identified as specific M cell marker in rats. The number of cytokeratin-8 positive M cells was related to the surface of the follicle associated epithelium. For morphological studies, we used both transmission electron microscopy (T.E.M.) and scanning electron microscopy (S.E.M.). RESULTS: In non-inflamed ileum M cells were scarce. Only 4% of the follicle associated epithelium were M cells, whereas an increase of M cells up to 11% was found in inflamed follicle associated epithelium (P < 0.001). The rate of M cell induction depended on the macroscopic degree of inflammation. T.E.M./S.E.M. studies showed that in inflamed tissue most M cells underwent apoptosis with typical morphological signs. In contrast to apoptotic M cells, the neighbouring enterocytes usually appeared intact. The number of mononuclear cells below the follicle associated epithelium was significantly increased. S.E.M. studies revealed that during induced ileitis mononuclear cells migrated from the lamina propria into the gut lumen by passing through apoptotic M cells. CONCLUSIONS: During indomethacin-induced ileitis in rats the increase in M cell number in association with apoptosis of M cells may alter the intestinal barrier function. These observations may play a pivotal role in the pathogenesis of chronic intestinal inflammation, e.g. in inflammatory bowel disease. (+info
Mechanism of glucocorticoid-mediated reversal of inhibition of Cl(-)/HCO(-)(3) exchange during chronic ileitis.
In the normal ileum, coupled NaCl absorption occurs via the dual operation of Na(+)/H(+) and Cl(-)/HCO(-)(3) exchange on the brush-border membrane (BBM) of villus cells. In a rabbit model of chronic small intestinal inflammation we determined the cellular mechanism of inhibition of NaCl absorption and the effect of steroids on this inhibition. Cl(-)/HCO(-)(3) but not Na(+)/H(+) exchange was reduced in the BBM of villus cells during chronic ileitis. Cl(-)/HCO(-)(3) exchange was inhibited secondary to a decrease in the affinity for Cl(-) rather than an alteration in the maximal rate of uptake of Cl(-) (V(max)). Methylprednisolone (MP) stimulated Cl(-)/HCO(-)(3) exchange in the normal ileum by increasing the V(max) of Cl(-) uptake rather than altering affinity for Cl(-). MP reversed the inhibition of Cl(-)/HCO(-)(3) exchange in rabbits with chronic ileitis. However, MP alleviated the Cl(-)/HCO(-)(3) exchange inhibition by restoring the affinity for Cl(-) rather than altering the V(max) of Cl(-) uptake. These data suggest that glucocorticoids mediate the alleviation of Cl(-)/HCO(-)(3) exchange inhibition in chronically inflamed ileum by reversing the same mechanism that was responsible for inhibition of this transporter rather than exerting a direct effect on the transporter itself, as was the case in normal ileum. (+info
Effect of chronic inflammation on ileal short-chain fatty acid/bicarbonate exchange.
Short-chain fatty acids (SCFA) have been demonstrated to at least partially ameliorate chronic intestinal inflammation. However, whether and how intestinal SCFA absorption may be altered during chronic intestinal inflammation is unknown. A rabbit model of chronic ileitis produced by coccidia was used to determine the effect of chronic inflammation on ileal SCFA/HCO(-)(3) exchange. SCFA/HCO(-)(3) exchange was present in the brush-border membrane (BBM) of villus but not crypt cells from normal rabbit ileum. An anion-exchange inhibitor, DIDS, significantly inhibited SCFA/HCO(-)(3) exchange. Extravesicular Cl(-) did not alter the uptake of SCFA, suggesting that SCFA/HCO(-)(3) exchange is a transport process distinct from Cl(-)/HCO(-)(3) exchange. In chronically inflamed ileum, SCFA/HCO(-)(3) exchange was also present only in BBM of villus cells. The exchanger was sensitive to DIDS and was unaffected by extravesicular Cl(-). However, SCFA/HCO(-)(3) exchange was significantly reduced in villus cell BBM vesicles (BBMV) from chronically inflamed ileum. Kinetic studies demonstrated that the maximal rate of uptake of SCFA, but not the affinity for SCFA, was reduced in chronically inflamed rabbit ileum. These data demonstrate that a distinct SCFA/HCO(-)(3) exchange is present on BBMV of villus but not crypt cells in normal rabbit ileum. SCFA/HCO(-)(3) exchange is inhibited in chronically inflamed rabbit ileum. The mechanism of inhibition is most likely secondary to a reduction in transporter numbers rather than altered affinity for SCFA. (+info
Lessons from genetically engineered animal models XI. Novel mouse models to study pathogenic mechanisms of Crohn's disease.
Crohn's Disease (CD) affects more than 500,000 individuals in the United States and represents the second most common chronic inflammatory disorder after rheumatoid arthritis. Although major advances have been made in defining the basic mechanisms underlying chronic intestinal inflammation, the precise etiopathogenesis of CD remains unknown. We have recently characterized two novel mouse models of enteritis that express a CD-like phenotype, namely the TNF DeltaARE model of tumor necrosis factor (TNF) overexpression and the SAMP1/Yit model of spontaneous ileitis. The unique feature of these models is that they closely resemble CD for location and histopathology. These genetically manipulated new models of intestinal inflammation offer a powerful tool to investigate potential causes of human disease and may allow the development of novel disease-modifying therapeutic modalities for the treatment of CD. (+info
Advances in gastroenterology and hepatology.
This is a review of some of the most important growing points in the specialties of gastroenterology and hepatology. It does not aim to be completely comprehensive but to pick out major areas of importance to examination candidates and doctors without special experience in the field. Topics covered include: upper gastrointestinal haemorrhage; Barrett's oesophagus; carcinoma of the oesophagus; achalasia; Helicobacter pylori; duodenal ulcer prevention; coeliac disease; dermatitis herpetiformis; Crohn's disease; small bowel overgrowth; ulcerative colitis; carcinoma of the large bowel; obesity; endoscope sterilisation; gall stones; liver transplantation; autoimmune liver disease; viral hepatitis; metabolic liver diseases; and pancreatic insufficiency. (+info
Focal up-regulation of E-cadherin-catenin complex in inflamed bowel mucosa but reduced expression in ulcer-associated cell lineage.
The E-cadherin-catenin complex is important for the maintenance of epithelial architecture. We studied its expression in Crohn disease, ulcerative colitis, acute ileitis, and controls. Immunohistochemical stainings for E-cadherin, alpha-catenin, beta-catenin and gamma-catenin were performed. E-cadherin messenger RNA (mRNA) was detected using riboprobes. In active inflammation, there was up-regulation of the complex. In particular, epithelium adjacent to ulcers showed increased expression of protein and mRNA, but in ulcer-associated cell lineage, the intensity of staining was weak to negative. In focal inflammation, up-regulation was found in affected areas. Reparative epithelium growing over denuded areas showed weaker expression. Since structural or functional perturbation in any of the molecules of the E-cadherin-catenin complex results in loss of intercellular adhesion, the preexistent epithelium may benefit from up-regulation to try to maintain its normal architecture under inflammatory conditions. Reduced expression in reparative epithelium and ulcer-associated cell lineage could facilitate the motility of these cells. (+info
Consequences of intestinal inflammation on the enteric nervous system: neuronal activation induced by inflammatory mediators.
The ENS is responsible for the regulation and control of all gastrointestinal functions. Because of this critical role, and probably as a consequence of its remarkable plasticity, the ENS is often relatively well preserved in conditions where the architecture of the intestine is seriously disrupted, such as in IBD. There are structural and functional changes in the enteric innervation in animal models of experimental intestinal inflammation and in IBD. These include both up and down regulation of transmitter expression and the induction of new genes in enteric neurons. Using Fos expression as a surrogate marker of neuronal activation it is now well established that enteric neurons (and also enteric glia) respond to inflammation. Whether this "activation" is limited to a short-term functional response, such as increased neuronal excitability, or reflects a long-term change in some aspect of the neuronal phenotype (or both) has yet to be firmly established, but it appears that enteric neurons are highly plastic in their response to inflammation. (+info