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Luminal Nitric Oxide and Epithelial Expression of Inducible and Endothelial Nitric Oxide Synthase in Collagenous and Lymphocytic Colitis

Background: Colonic nitric oxide (NO) production in collagenous colitis (CC) has been studied in a small number of patients and found increased. The cellular source of NO is believed to be the colonic epithelial cells. The aim of this study was to investigate colonic NO levels in patients with CC lymphocytic colitis (LC), to compare with the histopathological status and with the clinical activity, and to assess the epithelial expression of inducible and endothelial nitric oxide (iNOS and eNOS). Methods: We included 19 patients with CC, 8 patients with LC and 15 controls. During colonoscopy, luminal gas was sampled and NO levels were measured using the chemiluminescence technique. Mucosal biopsies were obtained for routine histopathologic examination and immunohistochemical studies of iNOS and eNOS. Clincal activity, as measured by the mean frequency of daily bowel movements during the week prior to colonoscopy, was assessed. Results: Luminal NO levels, median (25-75 percentiles), in the patients with CC and LC were greatly increased compared to the controls, 1673 (145-8143) parts per billion (ppb) and 1838 (1065-2694) ppb versus 28 (20-46) ppb (P ≺ 0.005, both). A positive association was seen between NO levels and histopathological status as well as clinical activity. Strong expression of iNOS was seen in the surface epithelium in 5 of 6 patients with CC and in 2 of 5 patients with LC. Conclusions: The fact that luminal NO levels are related to histopathological status and correlate with clinical activity indicates that NO is involved in the pathophsiology of CC and LC. The epithelial cells are the most likely source of luminal NO.