Su2089 Fibrotic Remodelling and Damage of the Colonic Neuromuscular Compartment in the Presence of Bowel Inflammation

Objective. The aim of this study has been to assess tissue remodelling of the colonic wall in a rat model of colitis, with a particular focus on the neuromuscular compartment. The rationale of the study is based on the notion that there is currently a scarcity of animal models of intestinal fibrosis, and that new methods to induce fibrosis as well as reliable parameters to evaluate the progress of fibrotic remodelling in the gut wall are highly expected. In particular, there is limited information on the pathophysiology of fibrotic processes secondary to chronic bowel inflammation, which might account for dysfunctions of intestinal motility and abdominal pain, at least in part through alterations of the enteric nervous system. Methods. Colitis was induced in rats by intrarectal administration of 2,4-dinitrobenzenesulfonic acid (DNBS, 30 mg/rat in 0.25 ml ethanol 50%). After 6, 12 and 21 days, the following parameters were assessed on paraffin sections from distal colonic samples: gross morphologic damage and tissue inflammatory infiltration by routine histology; collagen and elastic fibers by histochemistry; HuC/D antigen for neurons, glial fibrillar acid protein (GFAP) for glial cells, nestin for myenteric plexus, and c-Kit antigen for interstitial cells of Cajal (ICCs) by immunohistochemistry. Results. The presence and severity of colitis were assessed by macroscopic and microscopic scoring. At day-6, inflammatory and ulcerative alterations were observed in the colon of all DNBS-treated rats, and they progressed towards fibrotic lesions at day-21. Inflammatory infiltrates were abundant within and around the ulcerated lesions (neutrophils and eosinophils), and the presence of eosinophils within the colonic wall persisted up to day-21. Colitis was associated with a significant increase in the deposition of collagen fibers, which occurred in parallel with a dramatic decrease in elastic fibers throughout the whole wall thickness. Besides collagen deposition, the colonic neuromuscular compartment of inflamed animals displayed: significant decrease in myenteric HuC/D+ neuron density in concomitance with an increased immunoreactivity for GFAP and nestin; marked neovessel formation; reduced density of ICCs within the deep muscular and myenteric plexus. Conclusions. The DNBS model of colitis displays a significant degree of bowel remodelling characterized mainly by: a) enhanced collagen deposition in concomitance with elastic fiber reduction; b) altered myenteric neuron/glia proportion; c) increased vasculogenesis; d) impairment of ICC apparatus. Based on the present findings, the patterns of bowel tissue alterations in this model of colitis are suitable for investigating the pathophysiology of colonic inflammation and evaluating the impact of new therapeutic strategies on the activity of inflammatory bowel diseases.