Role of mast cells in early and delayed radiation injury in rat intestine

Intestinal fibrosis in human and experimental inflammatory bowel disease

Fibrosis is a serious complication of Crohn disease for which there is no effective therapy. It is unclear why fibrosis, particularly fibrosis of the mucosal layer, develops in Crohn disease and not in ulcerative colitis. Smooth muscle cells, subepithelial myofibroblasts, and fibroblasts have traditionally been considered mediators of fibrosis, but new information points to a role of interstitial cells of Cajal and mast cells. Recent evidence about the role of each of these cell types in fibrosis in Crohn disease or other inflammatory bowel diseases is described. Hypothetical models to describe how altered function of these cells could underlie fibrosis of the mucosa or submucosal layers are presented. Fibrosis is not well characterized in any animal model of inflammatory bowel disease. The merits of several animal models for defining the mechanisms of inflammation-induced intestinal fibrosis are reviewed.

Substance P (NK1) receptor in relation to substance P innervation in rat duodenum after irradiation

It has previously been shown that high dose of irradiation to the rat abdomen leads to an increased level of substance P (SP) in the duodenum. In the present study the pattern of distribution of NK1 receptors (NK1-R) in rat duodenum after irradiation (5-30 Gy), was examined at the same time-point (7 days) after irradiation, comparisons being made with the distribution of SP-innervation. Immunohistochemical methods were used. In controls, NK1-R-like immunoreactivity (-LI) was detected in epithelial cells, in cells in the region of the intestinal cells of Cajal within the deep muscular plexus (ICC-DMP), in neuronal cells in the myenteric plexus, and variably in granulocytes in the mucosa. Irradiation with 5-10 Gy did not lead to obvious changes in the pattern of NK1-R-LI. After irradiation with the highest doses (25-30 Gy), the mucosa was often gravely damaged, displaying granulation tissue. No epithelial NK1-R-LI was detected in this tissue, but was present in less affected mucosa after these doses. In the region of the ICC-DMP, in the myenteric plexus, and in granulocytes, NK1-R-LI was detected also after high dose irradiation. However, the degree of NK1-R-LI in the region of the ICC-DMP was somewhat lower than seen in controls and after low doses. SP-immunoreactive nerve fibers were present in the regions where NK1-R-LI was detected. These findings support a suggestion that an increased level of SP after irradiation may contribute to the dose-dependent gastrointestinal adverse effects that occur after radiotherapy.

Radiation-induced granulocyte transmigration predicts development of delayed structural changes in rat intestine

We examined whether early radiation-induced granulocyte transmigration (assessed by the fecal transferrin excretion ELISA assay) predicts subsequent development of (consequential) chronic radiation enteropathy. After accounting for the effect of radiation dose, transferrin excretion remained an independent predictor of overall tissue injury, intestinal fibrosis, and mucosal ulcers, but not TGF-beta immunoreactivity.

Fibrogenesis. IV. Fibrosis and inflammatory bowel disease: cellular mediators and animal models

The cellular mediators of intestinal fibrosis and the relationship between fibrosis and normal repair are not understood. Identification of the types of intestinal mesenchymal cells that produce collagen during normal healing and fibrosis is vital for elucidating the answers to these questions. Acute injury may cause normal mesenchymal cells to convert to a fibrogenic phenotype that is not maintained during normal healing but may lead to fibrosis when inappropriately sustained. Proliferation of normal or fibrogenic mesenchymal cells may lead to muscularis overgrowth associated with fibrosis. The presence of increased numbers of vimentin-positive cells within fibrotic, hypertrophied muscularis in Crohn's disease suggests that changes in mesenchymal cell phenotype and number may indeed be associated with fibrosis. Fibrosis is induced in rats by peptidoglycan polysaccharides or trinitrobenzene sulfonic acid-ethanol administration, but inducing fibrosis in mice has been technically challenging. The development of current mouse models of colitis, such as dextran sodium sulfate or trinitrobenzene sulfonic acid-ethanol administration, into models of fibrosis will allow us to use genetic manipulation to study molecular mediators of fibrosis.