Role of Inducible Nitric Oxide Synthase in Murine Colitis

Abstract

To examine the role of inducible nitric oxide synthase (iNOS) in the development of colitis, we characterized the expression of iNOS in a murine colitis model and the effects of a selective inhibitor of iNOS production, aminoguanidine (AMG). Furthermore, we examined the correlation between the production of inflammatory cytokines and nitric oxide (NO) in human colonic epithelial cells. Colitis was induced in C.B-17-SCID mice transferred with CD45RB^high CD4⁺ T cells from BALB/c mice. Expression of iNOS in the intestine was determined by reverse transcriptase poly-merase chain reaction and immunohitochemistry. Anti-interleukin-6 receptor (anti-IL-6R) monoclonal antibody (mAb) or AMG was administered after T cell transfer. Furthermore, NO activity and iNOS production in HT-29 cells were examined after stimulation with interferon-γ (IFNγ), tumor necrosis factor-α (TNFα), IL-Iβ, IL-6, and soluble (s) IL-6R. There was increased expression of iNOS in colonic epithelial cells in the murine colitis model, but expression of iNOS and development of colitis were suppressed by administration of anti-IL-6R mAb. Severe colitis was induced when iNOS was inhibited by administration of AMG. In HT-29 cells, production of iNOS was induced in the presence of IFNγ. Although no induction of iNOS production was observed in the presence of IL-6 alone, NO production mediated by INFγ was increased in the presence of INFγ plus IL-6 and soluble IL-6R. The production of NO induced by IFNγ was thus stimulated by the addition of IL-6 in human colonic epithelial cells. In the colitis model, NO induced by inflammatory cytokines at the onset of colitis may suppress the development of inflammation.