iNOS-Dependent Increase in Colonic Mucus Thickness in DSS-Colitic Rats

Abstract

AimTo investigate colonic mucus thickness in vivo in health and during experimental inflammatory bowel disease.MethodsColitis was induced with 5% DSS in drinking water for 8 days prior to experiment, when the descending colonic mucosa of anesthetized rats was studied using intravital microscopy. Mucus thickness was measured with micropipettes attached to a micromanipulator. To assess the contributions of NOS and prostaglandins in the regulation of colonic mucus thickness, the non-selective NOS-inhibitor L-NNA (10 mg/kg bolus followed by 3 mg/kg/h), the selective iNOS-inhibitor L-NIL (10 mg/kg bolus followed by 3 mg/kg/h) and the non-selective COX-inhibitor diclofenac (5 mg/kg) were administered intravenously prior to experiment. To further investigate the role of iNOS in the regulation of colonic mucus thickness, iNOS −/− mice were used.ResultsColitic rats had a thicker firmly adherent mucus layer following 8 days of DSS treatment than untreated rats (88±2 µm vs 76±1 µm). During induction of colitis, the thickness of the colonic mucus layer initially decreased but was from day 3 significantly thicker than in untreated rats. Diclofenac reduced the mucus thickness similarly in colitic and untreated rats (−16±5 µm vs −14±2 µm). While L-NNA had no effect on colonic mucus thickness in DSS or untreated controls (+3±2 µm vs +3±1 µm), L-NIL reduced the mucus thickness significantly more in colitic rats than in controls (−33±4 µm vs −10±3 µm). The importance of iNOS in regulating the colonic mucus thickness was confirmed in iNOS−/− mice, which had thinner colonic mucus than wild-type mice (35±3 µm vs 50±2 µm, respectively). Furthermore, immunohistochemistry revealed increased levels of iNOS in the colonic surface epithelium following DSS treatment.ConclusionBoth prostaglandins and nitric oxide regulate basal colonic mucus thickness. During onset of colitis, the thickness of the mucus layer is initially reduced followed by an iNOS mediated increase.

The Effect of N. Acetylcysteine and Ginger on Acetic Acid Induced Colitis in Adult Male Albino Rat: Histological, Immunohistochemical and Morphometric Study

“…Recently, impaired differentiation of goblet cells from intestinal stem cells was found in inflammatory bowel diseases and this resulted in defective mucus layer [46,47]. Contrary to the present results, other investigators found increased number of goblet cells in dextran sulfate sodium-colitis rats [48]. The authors explained their findings by the heterogeneity of colonic inflammation with depleted goblet cell areas and increased in another areas with mucus overproduction previously suggested by Nakano et al [49].…”

“…Also, it was localized in the inflammatory and normal mucosa of patients with ulcerative colitis [58]. Schreiber et al [48] reported that increased i.NOS mediates an increase in mucus layer thickness. The current results found marked up-regulation of i.NOS immunoexpression in induced colitis model accompanied by dense inflammatory cellular infiltration, mucosal and submucosal.…”

Oat β-glucan ameliorates dextran sulfate sodium (DSS)-induced ulcerative colitis in mice

“…The latter one was now determined as an important cytokine in the pathogenesis of IBD. 46 These pro-inflammatory cytokines amplify the inflammatory cascade of inflammatory mediators, destructive enzymes, and free radicals that cause tissue damage. 42 DSS-induced colitis increased the expression level of the iNOS protein in the surface epithelial cells.…”

Inflammatory bowel disease: clinical aspects and treatments

“…External microorganisms that are able to breach the epithelial wall have unrestricted access to the circulation, which is one of the main causes of gastrointestinal disease. Indeed, murine and human studies have demonstrated that IBDs, such as Crohn’s disease, are characterized by a defect in the epithelial barrier and altered mucus production, leading to an increase in intestinal permeability and toxins adherence in the intestinal cells 15,19…”