Interferon-gamma (IFN-γ)- and tumour necrosis factor (TNF)-induced nitric oxide as toxic effector molecule in chronic dextran sulphate sodium (DSS)-induced colitis in mice

Abstract

Excess nitric oxide formation caused by the activity of the inducible nitric oxide synthase has been implicated as a toxic effector molecule in the pathogenesis of experimental colitis and inflammatory bowel disease. It was therefore investigated whether inhibition of this synthase or the cytokines TNF and IFN-gamma, inducers of nitric oxide synthase, had effects on chronic colitis in mice. Chronic colitis was induced in mice by repeated feeding of DSS. Cytokines were neutralized by treatment with MoAbs and nitric oxide synthase was inhibited by aminoguanidine. The degree of colonic inflammation was assessed by a histological score and colon length. Aminoguanidine treatment reduced nitric oxide activity by 60% (P = 0. 0004), the histological score by 31% (P = 0.005) and increased colon length by 1.4 cm (P = 0.002). Neutralization of TNF and IFN-gamma resulted in increased colon length (0.7 cm, P = 0.07 and 0.8 cm, P = 0.03), improved histological score (19%, P = 0.045 and 25%, P = 0. 013), and reduced nitric oxide activity (31%, P = 0.07 and 54%, P = 0.004) compared with controls. The combination of anti-cytokine treatments had additive effects. TNF and IFN-gamma are involved in perpetuation of chronic DSS-induced colitis, and induction of excessive nitric oxide activity could be their common effector mechanism.

Overview of cytokines and nitric oxide involvement in immuno-pathogenesis of inflammatory bowel diseases

“…In both patients and animal models of IBD, a positive correlation between the overproduction of pro-inflammatory cytokines (e.g., IL-1b, TNF-α, IFN-γ) and an overexpression of iNOS was found. This expression was primarily detected in the lamina propria mononuclear cells and the colon epithelial cells of the inflamed mucosa [6,16,17,27,30,71,72] . Several studies conducted on a dextran sulfate sodium (DSS)-induced experimental model of colitis in BALB/c mice indicated that the neutralization of endogenous TNF-α and/or IFN-γ ameliorated the chronic colitis and concomitantly decreased the generation of NO.…”

“…This observation suggests a possible use of serum NO levels for monitoring disease activity in both types of IBD [16,28,29] . While several studies conducted using animal models indicate the deleterious effect of NO, recent studies have shown that NO may also exert a protective effect against colitis [29][30][31][32] . One study conducted using a DSSinduced colitis model found that nitrite administration exerts both preventive and therapeutic effects in colonic inflammation [33] .…”

“…These cytokines had an additive effect on the severity of histological damage and NO colonic levels. However, it seems that IFN-f is the most potent inducer of iNOS in macrophages and epithelial cells than TNF-α, since its neutralization was more effective in attenuating the experimental colitis [30] . Moreover, our studies reported an up-regulation of iNOS expression in the inflamed colonic mucosa which correlates with high systemic levels of NO, IFN-γ, and IL-12.…”

Bacterial Flora Play Important Roles in Acute Dextran Sulphate Sodium-Induced Colitis But Are Not Involved in Gal-3 Dependent Modulation of Colon Inflammation

“…Sections were analysed for damage to the epithelium including damage to crypts, submucosal oedema, haemorrhage, and infiltration by immune cells. The histology score for each mouse was calculated as the sum of 'Infiltration' and 'Damage of Epithelium' sub-scores, as previously described (18).…”

IL‐15 protects intestinal epithelial cells

“…The distal third of the colon was removed and used for histological analysis as described before [60,63]. Three sections were evaluated obtained each at a 100-lm distance.…”