In this study, celecoxib, at dosages greater than those indicated clinically, was associated with a lower incidence of symptomatic ulcers and ulcer complications combined, as well as other clinically important toxic effects, compared with NSAIDs at standard dosages. The decrease in upper GI toxicity was strongest among patients not taking aspirin concomitantly. JAMA. 2000;284:1247-1255

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We identified cellular and molecular mechanisms within the stem cell niche that control the activity of colonic epithelial progenitors (ColEPs) during injury. Here, we show that while WT mice maintained ColEP proliferation in the rectum following injury with dextran sodium sulfate, similarly treated Myd88 -/-(TLR signaling-deficient) and prostaglandin-endoperoxide synthase 2 -/-(Ptgs2 -/-) mice exhibited a profound inhibition of epithelial proliferation and cellular organization within rectal crypts. Exogenous addition of 16,16-dimethyl PGE 2 (dmPGE 2 ) rescued the effects of this injury in both knockout mouse strains, indicating that Myd88 signaling is upstream of Ptgs2 and PGE 2 . In WT and Myd88 -/-mice, Ptgs2 was expressed in scattered mesenchymal cells. Surprisingly, Ptgs2 expression was not regulated by injury. Rather, in WT mice, the combination of injury and Myd88 signaling led to the repositioning of a subset of the Ptgs2-expressing stromal cells from the mesenchyme surrounding the middle and upper crypts to an area surrounding the crypt base adjacent to ColEPs. These findings demonstrate that Myd88 and prostaglandin signaling pathways interact to preserve epithelial proliferation during injury using what we believe to be a previously undescribed mechanism requiring proper cellular mobilization within the crypt niche.

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Intestinal inflammatory diseases are mediated by dysregulated immune responses to undefined luminal antigens. Feeding hen egg-white lysozyme to mice expressing a transgenic T-cell receptor that recognizes hen egg-white lysozyme peptide 46-61 resulted in no intestinal pathology; however, simultaneous administration of cyclooxygenase-2 inhibitors and dietary hen egg-white lysozyme resulted in increased proliferation of lamina propria mononuclear cells and crypt epithelial cells, crypt expansion and villus blunting. Lamina propria mononuclear cells produce high levels of cyclooxygenase-2-dependent arachidonic acid metabolites, which act as immunomodulators in the immune response to dietary antigen. These findings establish that cyclooxygenase-2-dependent arachidonic acid metabolites are essential in the development and maintenance of intestinal immune homeostasis.

BackgroundThe small intestinal epithelium is highly sensitive to radiation and is a major site of injury during radiation therapy and environmental overexposure.ObjectiveTo examine probiotic bacteria as potential radioprotective agents in the intestine.Methods8-week-old C57BL/6 wild-type or knockout mice were administered probiotic by gavage for 3 days before 12 Gy whole body radiation. The intestine was evaluated for cell-positional apoptosis (6 h) and crypt survival (84 h).ResultsGavage of 5×107 Lactobacillus rhamnosus GG (LGG) improved crypt survival about twofold (p<0.01); the effect was observed when administered before, but not after, radiation. Conditioned medium (CM) from LGG improved crypt survival (1.95-fold, p<0.01), and both LGG and LGG-CM reduced epithelial apoptosis particularly at the crypt base (33% to 18%, p<0.01). LGG was detected in the distal ileal contents after the gavage cycle, but did not lead to a detectable shift in bacterial family composition. The reduction in epithelial apoptosis and improved crypt survival offered by LGG was lost in MyD88−/−, TLR-2−/− and cyclo-oxygenase-2−/− (COX-2) mice but not TLR-4−/− mice. LGG administration did not lead to increased jejunal COX-2 mRNA or prostaglandin E2 levels or a change in number of COX-2-expressing cells. However, a location shift was observed in constitutively COX-2-expressing cells of the lamina propria from the villi to a position near the crypt base (villi to crypt ratio 80:20 for control and 62:38 for LGG; p<0.001). Co-staining revealed these COX-2-expressing small intestinal lamina propria cells to be mesenchymal stem cells.ConclusionsLGG or its CM reduce radiation-induced epithelial injury and improve crypt survival. A TLR-2/MyD88 signalling mechanism leading to repositioning of constitutive COX-2-expressing mesenchymal stem cells to the crypt base is invoked.