143 research outputs found
Recovery of ischaemic injured porcine ileum: evidence for a contributory role of COX-1 and COX-2
Background: We have previously shown that the non-selective cyclooxygenase (COX) inhibitor indomethacin retards recovery of intestinal barrier function in ischaemic injured porcine ileum. However, the relative role of COX-1 and COX-2 elaborated prostaglandins in this process is unclear
PG-mediated closure of paracellular pathway and not restitution is the primary determinant of barrier recovery in acutely injured porcine ileum
Small bowel epithelium is at the frontline of intestinal barrier function. Restitution is considered to be the major determinant of epithelial repair as function recovers in parallel with restitution after acute injury. As such, studies of intact mucosa have largely been replaced by migration assays of cultured epithelia. These latter studies fail to account for the simultaneous roles played by villous contraction and paracellular permeability in recovery of barrier function. Non-steroidal anti-inflammatory drugs (NSAID) result in increased intestinal permeability and disease exacerbation in patients with IBD. Thus, we examined the reparative attributes of endogenous prostaglandins (PG) after injury of ileal mucosa by deoxycholate (6 mM) in Ussing chambers. Recovery of transepithelial resistance (TER) from 20â40 âŠ.cm2 was abolished by indomethacin (INDO), whereas restitution of 40â100% of the villous surface was unaffected despite concurrent arrest of villous contraction. In the presence of PG, resident crypt and migrating epithelial cells were tightly apposed. In tissues treated with INDO, crypt epithelial cells had dilated intercellular spaces that were accentuated in the migrating epithelium. TER was fully rescued from the effects of INDO by osmotic-driven collapse of the paracellular space and PG-mediated recovery was significantly impaired by blockade of Clâ secretion. These studies are the first to clearly distinguish the relative contribution of paracellular resistance versus restitution to acute recovery of epithelial barrier function. Restitution was ineffective in the absence of PG-mediated paracellular space closure. Failure of PG-mediated repair mechanisms may underlie barrier failure resulting from NSAID use in patients with underlying enteropathy
Prostaglandins I2 and E2 have a synergistic role in rescuing epithelial barrier function in porcine ileum.
Prostaglandins (PG) are cytoprotective for gastrointestinal epithelium, possibly because they enhance mucosal repair. The objective of the present studies was to assess the role of prostaglandins in intestinal repair. Intestinal mucosa from porcine ileum subjected to 1 h of ischemia was mounted in Ussing chambers. Recovery of normal transepithelial electrical resistance occurred within 2 h, and continued to increase for a further 2 h to a value twice that of control. The latter response was blocked by inhibition of prostaglandin synthesis, and restored by addition of both carbacyclin (an analog of PGI2) and PGE2, whereas the addition of each alone had little effect. Histologically, prostaglandins had no effect on epithelial restitution or villous contraction, indicating that elevations in transepithelial resistance were associated with increases in paracellular resistance. Furthermore, prostaglandin-stimulated elevations in resistance were inhibited with cytochalasin D, an agent known to stimulate cytoskeletal contraction. Synergistic elevations in transepithelial resistance, similar to those of carbacyclin and PGE2, were also noted after treatment with cAMP and {"type":"entrez-nucleotide","attrs":{"text":"A23187","term_id":"833253","term_text":"A23187"}}A23187 (a calcium ionophore). We conclude that PGE2 and PGI2 have a synergistic role in restoration of intestinal barrier function by increasing intracellular cAMP and Ca2+, respectively, which in turn signal cytoskeletal-mediated tight junction closure
Glutamine metabolism stimulates intestinal cell MAPKs by a cAMP-inhibitable, RAF-independent mechanism
AbstractBackground & Aims: Infectious diarrhea caused by viruses plus enterotoxigenic bacteria is often more severe than diarrhea induced by either pathogen alone. We postulated that the increased cell adenosine 3',5'-cyclic monophosphate (cAMP) concentration observed during infection by enterotoxigenic organisms retards the intestinal repair process by blocking activation of mitogen-activated protein kinases (MAPKs) in proliferating intestinal cells. Methods: We evaluated the effects of glutamine on MAPK activity, thymidine incorporation, and cell number in glutamine-starved and -sufficient rat intestinal crypt cells (IEC-6). Results: In glutamine-starved cells, 10 mmol/L glutamine in the absence of serum stimulated [3H]thymidine incorporation 8-fold. This effect was inhibited by 60% with 8-(4-chlorophenylthio) (8-CPT)-cAMP (100 ÎŒmol/L) + isobutyl methylxanthine (100 ÎŒmol/L). In cells not starved of glutamine, glutamine stimulated thymidine incorporation by 3-fold, and 8-CPT-cAMP completely blocked the mitogenic effect. Inhibition of proliferation by cAMP persisted for at least 68 hours after cAMP removal. In vitro kinase assays showed that glutamine signaling requires an intact ERK (extracellular signalârelated kinase) pathway in unstarved cells. In starved cells, at least one other pathway (JNK) was activated by glutamine, and the mitogenic inhibition by 8-CPT-cAMP was incomplete. Other intestinal fuels (glucose and acetate) were not mitogenic. Conclusions: Increased levels of intracellular cAMP inhibit ERKs but only partially reduce glutamine-stimulated proliferation in enterocytes adapted to low glutamine.GASTROENTEROLOGY 2000;118:90-10
Cryptosporidium Priming Is More Effective than Vaccine for Protection against Cryptosporidiosis in a Murine Protein Malnutrition Model
Cryptosporidium is a major cause of severe diarrhea, especially in malnourished children. Using a murine model of C. parvum oocyst challenge that recapitulates clinical features of severe cryptosporidiosis during malnutrition, we interrogated the effect of protein malnutrition (PM) on primary and secondary responses to C. parvum challenge, and tested the differential ability of mucosal priming strategies to overcome the PM-induced susceptibility. We determined that while PM fundamentally alters systemic and mucosal primary immune responses to Cryptosporidium, priming with C. parvum (106 oocysts) provides robust protective immunity against re-challenge despite ongoing PM. C. parvum priming restores mucosal Th1-type effectors (CD3+CD8+CD103+ T-cells) and cytokines (IFNÎł, and IL12p40) that otherwise decrease with ongoing PM. Vaccination strategies with Cryptosporidium antigens expressed in the S. Typhi vector 908htr, however, do not enhance Th1-type responses to C. parvum challenge during PM, even though vaccination strongly boosts immunity in challenged fully nourished hosts. Remote non-specific exposures to the attenuated S. Typhi vector alone or the TLR9 agonist CpG ODN-1668 can partially attenuate C. parvum severity during PM, but neither as effectively as viable C. parvum priming. We conclude that although PM interferes with basal and vaccine-boosted immune responses to C. parvum, sustained reductions in disease severity are possible through mucosal activators of host defenses, and specifically C. parvum priming can elicit impressively robust Th1-type protective immunity despite ongoing protein malnutrition. These findings add insight into potential correlates of Cryptosporidium immunity and future vaccine strategies in malnourished children
Electronic monitoring of rumination activity as an indicator of health status and production traits in high-yielding dairy cows
Saccharomyces boulardii Improves Intestinal Cell Restitution through Activation of the α2ÎČ1 Integrin Collagen Receptor
Intestinal epithelial cell damage is frequently seen in the mucosal lesions of inflammatory bowel diseases such as ulcerative colitis or Crohn's disease. Complete remission of these diseases requires both the cessation of inflammation and the migration of enterocytes to repair the damaged epithelium. Lyophilized Saccharomyces boulardii (Sb, Biocodex) is a nonpathogenic yeast widely used as a therapeutic agent for the treatment and prevention of diarrhea and other gastrointestinal disorders. In this study, we determined whether Sb could accelerate enterocyte migration. Cell migration was determined in Sb force-fed C57BL6J mice and in an in vitro wound model. The impact on α2ÎČ1 integrin activity was assessed using adhesion assays and the analysis of α2ÎČ1 mediated signaling pathways both in vitro and in vivo. We demonstrated that Sb secretes compounds that enhance the migration of enterocytes independently of cell proliferation. This enhanced migration was associated with the ability of Sb to favor cell-extracellular matrix interaction. Indeed, the yeast activates α2ÎČ1 integrin collagen receptors. This leads to an increase in tyrosine phosphorylation of cytoplasmic molecules, including focal adhesion kinase and paxillin, involved in the integrin signaling pathway. These changes are associated with the reorganization of focal adhesion structures. In conclusion Sb secretes motogenic factors that enhance cell restitution through the dynamic regulation of α2ÎČ1 integrin activity. This could be of major importance in the development of novel therapies targeting diseases characterized by severe mucosal injury, such as inflammatory and infectious bowel diseases
Endotoxin-induced changes in expression of cyclooxygenase isoforms in the lamellar tissue of extracorporeally haemoperfused equine limbs
Intestinal fatty-acid binding protein and gut permeability responses to exercise
Purpose
Intestinal cell damage due to physiological stressors (e.g. heat, oxidative, hypoperfusion/ischaemic) may contribute to increased intestinal permeability. The aim of this study was to assess changes in plasma intestinal fatty acid-binding protein (I-FABP) in response to exercise (with bovine colostrum supplementation, Col, positive control) and compare this to intestinal barrier integrity/permeability (5 h urinary lactulose/rhamnose ratio, L/R).
Methods
In a double-blind, placebo-controlled, crossover design, 18 males completed two experimental arms (14 days of 20 g/day supplementation with Col or placebo, Plac). For each arm participants performed two baseline (resting) intestinal permeability assessments (L/R) pre-supplementation and one post-exercise following supplementation. Blood samples were collected pre- and post-exercise to determine I-FABP concentration.
Results
Two-way repeated measures ANOVA revealed an arm?Ă?time interaction for L/R and I-FABP (P?<?0.001). Post hoc analyses showed urinary L/R increased post-exercise in Plac (273% of pre, P?<?0.001) and Col (148% of pre, P?<?0.001) with post-exercise values significantly lower with Col (P?<?0.001). Plasma I-FABP increased post-exercise in Plac (191% of pre-exercise, P?=?0.002) but not in the Col arm (107%, P?=?0.862) with post-exercise values significantly lower with Col (P?=?0.013). Correlations between the increase in I-FABP and L/R were evident for visit one (P?=?0.044) but not visit two (P?=?0.200) although overall plots/patterns do appear similar for each.
Conclusion
These findings suggest that exercise-induced intestinal cellular damage/injury is partly implicated in changes in permeability but other factors must also contribute
The role of prostaglandin E2 (PGE 2) in toll-like receptor 4 (TLR4)-mediated colitis-associated neoplasia
<p>Abstract</p> <p>Background</p> <p>We have previously found that TLR4-deficient (TLR4-/-) mice demonstrate decreased expression of mucosal PGE <sub>2 </sub>and are protected against colitis-associated neoplasia. However, it is still unclear whether PGE <sub>2 </sub>is the central factor downstream of TLR4 signaling that promotes intestinal tumorigenesis. To further elucidate critical downstream pathways involving TLR4-mediated intestinal tumorigenesis, we examined the effects of exogenously administered PGE <sub>2 </sub>in TLR4-/- mice to see if PGE <sub>2 </sub>bypasses the protection from colitis-associated tumorigenesis.</p> <p>Method</p> <p>Mouse colitis-associated neoplasia was induced by azoxymethane (AOM) injection followed by two cycles of dextran sodium sulfate (DSS) treatment. Two different doses of PGE <sub>2 </sub>(high dose group, 200 Όg, n = 8; and low dose group, 100 Όg, n = 6) were administered daily during recovery period of colitis by gavage feeding. Another group was given PGE <sub>2 </sub>during DSS treatment (200 Όg, n = 5). Inflammation and dysplasia were assessed histologically. Mucosal Cox-2 and amphiregulin (AR) expression, prostanoid synthesis, and EGFR activation were analyzed.</p> <p>Results</p> <p>In control mice treated with PBS, the average number of tumors was greater in WT mice (n = 13) than in TLR4-/- mice (n = 7). High dose but not low dose PGE <sub>2 </sub>treatment caused an increase in epithelial proliferation. 28.6% of PBS-treated TLR4-/- mice developed dysplasia (tumors/animal: 0.4 ± 0.2). By contrast, 75.0% (tumors/animal: 1.5 ± 1.2, P < 0.05) of the high dose group and 33.3% (tumors/animal: 0.3 ± 0.5) of the low dose group developed dysplasia in TLR4-/- mice. Tumor size was also increased by high dose PGE <sub>2 </sub>treatment. Endogenous prostanoid synthesis was differentially affected by PGE <sub>2 </sub>treatment during acute and recovery phases of colitis. Exogenous administration of PGE <sub>2 </sub>increased colitis-associated tumorigenesis but this only occurred during the recovery phase. Lastly, PGE <sub>2 </sub>treatment increased mucosal expression of AR and Cox-2, thus inducing EGFR activation and forming a positive feedback mechanism to amplify mucosal Cox-2.</p> <p>Conclusions</p> <p>These results highlight the importance of PGE <sub>2 </sub>as a central downstream molecule involving TLR4-mediated intestinal tumorigenesis.</p
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