Preventive and therapeutic effects of nitrite supplementation in experimental inflammatory bowel disease.

BACKGROUND: Inorganic nitrate and nitrite have emerged as alternative substrates for nitric oxide (NO) generation in the gastrointestinal tract, and have shown to be protective against drug-induced gastric injury. The aim of this study was to investigate the preventive and therapeutic effects of nitrate and nitrite in a model of experimental colitis. METHODS: Colitis was induced in mice by administrating dextran sulfate sodium (DSS) with concurrent administration of nitrite (1 mM) or nitrate (10 mM) in the drinking water for 7 days. A therapeutic approach was also investigated by initiating nitrite treatment 3 days after DSS-induced colitis. Clinical and inflammatory markers were assessed and the colonic mucus thickness was measured in vivo. The effect of nitrite on wound healing was evaluated using colon epithelial cells. RESULTS: Concurrent administration of DSS and nitrite (1 mM) alleviated inflammation as determined by reduced disease activity index score (DAI) and increased colon length, while nitrate (10 mM) only reduced the DAI-score. Nitrite also displayed therapeutic effects by ameliorating established colonic inflammation with reduced colonic expression of iNOS and improving histopathology. DSS-induced decrease in colonic mucus thickness was completely prevented by nitrite administration. In addition, goblet cell abundance was lower by DSS treatment, but was increased by addition of nitrite. Further studies using colon epithelial cells revealed an NO-dependent improvement in wound healing with nitrite administration. CONCLUSION: Nitrite exerts both preventive and therapeutic effects in colonic inflammation. The protective effects involve preservation of an intact adherent mucus layer and regulation of epithelial cell restitution.

Propionic and butyric acids, formed in the caecum of rats fed highly fermentable dietary fibre, are reflected in portal and aortic serum.

SCFA are important end products formed during colonic fermentation of dietary fibre (DF). It has been suggested that propionic and butyric acids affect metabolic parameters, low-grade systemic inflammation, insulin resistance and obesity. The aim of the present study was to investigate whether the various SCFA profiles observed after fermentation in the caecum of rats fed pectin, guar gum and fructo-oligosaccharides (FOS) were also represented in hepatic portal and aortic serum. The SCFA in serum were extracted using hollow fibre-supported liquid membrane extraction before GLC analysis. The concentrations of acetic, propionic and butyric acids in caecal content correlated well with those in portal serum (P< 0·001) for all the three diets. A weaker correlation was found for propionic and butyric acids between the caecal content and aortic serum (P< 0·05). Butyric acid concentration in caecal content was also reflected in the aortic serum (P= 0·019) of rats fed FOS. FOS gave rather low amounts of the SCFA, especially butyric acid, but caecal tissue weight was higher with FOS than with the other two diets. This may be explained by rapid fermentation and quick utilisation/absorption of the SCFA. The present study also showed that propionic acid was metabolised/utilised to a higher extent than butyric acid by colonocytes before reaching the liver. We conclude that the formation of propionic and butyric acids in the caecum is reflected by increased concentrations in the aortic blood. This approach may therefore simplify the evaluation and study of SCFA from DF in human subjects.

Dietary conjugated linoleic acid activates PPARγ and the intestinal trefoil factor in SW480 cells and mice with dextran sulfate sodium-induced colitis.

A central event in inflammatory bowel disease is the disruption of the mucosal homeostasis. Trefoil peptides [(TFF)] are emerging as key mediators in the defense and repair of the gastrointestinal mucosa. Here, we demonstrate induction of TFF by CLA with therapeutic antiinflammatory effects in a mouse model of inflammatory bowel disease. SW480 cells were treated with linoleic acid or CLA (0-2.5 µmol/L) in the absence or presence of the PPARγ inhibitor GW9662. Cells treated with CLA showed an upregulation of the intestinal trefoil factor, which was prevented by pretreatment with GW9662. Dextran sulfate sodium (2%) was used to induce colitis in mice and they were simultaneously fed with a standard or a CLA-supplemented (100 mg · kg(-1) · d(-1)) diet for 7 d. The CLA-enriched diet prevented the colon shortening induced by DSS and markedly reduced the disease activity index and the colonic expression of inducible NO synthase and NF-κB. Immunohistochemistry revealed an increase in PPARγ and TFF3 expression after CLA administration. Altogether, these results indicate that dietary CLA protects against DSS-induced colitis in a process involving induction of PPARγ and TFF3.

Decreased leukocyte recruitment by inorganic nitrate and nitrite in microvascular inflammation and NSAID-induced intestinal injury.

Nitric oxide (NO) generated by vascular NO synthases can exert anti-inflammatory effects, partly through its ability to decrease leukocyte recruitment. Inorganic nitrate and nitrite, from endogenous or dietary sources, have emerged as alternative substrates for NO formation in mammals. Bioactivation of nitrate is believed to require initial reduction to nitrite by oral commensal bacteria. Here we investigated the effects of inorganic nitrate and nitrite on leukocyte recruitment in microvascular inflammation and in NSAID-induced small-intestinal injury. We show that leukocyte emigration in response to the proinflammatory chemokine MIP-2 is reduced by 70% after 7 days of dietary nitrate supplementation as well as by acute intravenous nitrite administration. Nitrite also reduced leukocyte adhesion to a similar extent and this effect was inhibited by the soluble guanylyl cyclase inhibitor ODQ, whereas the effect on emigrated leukocytes was not altered by this treatment. Further studies in TNF-α-stimulated endothelial cells revealed that nitrite dose-dependently reduced the expression of ICAM-1. In rats and mice subjected to a challenge with diclofenac, dietary nitrate prevented the increase in myeloperoxidase and P-selectin levels in small-intestinal tissue. Antiseptic mouthwash, which eliminates oral nitrate reduction, markedly blunted the protective effect of dietary nitrate on P-selectin levels. Despite attenuation of the acute immune response, the overall ability to clear an infection with Staphylococcus aureus was not suppressed by dietary nitrate as revealed by noninvasive IVIS imaging. We conclude that dietary nitrate markedly reduces leukocyte recruitment to inflammation in a process involving attenuation of P-selectin and ICAM-1 upregulation. Bioactivation of dietary nitrate requires intermediate formation of nitrite by oral nitrate-reducing bacteria and then probably further reduction to NO and other bioactive nitrogen oxides in the tissues.