Trans fatty acids exacerbate dextran sodium sulphate-induced colitis by promoting the up-regulation of macrophage-derived proinflammatory cytokines involved in T helper 17 cell polarization.

Numerous reports have shown that a diet containing large amounts of trans fatty acids (TFAs) is a major risk factor for metabolic disorders. Although recent studies have shown that TFAs promote intestinal inflammation, the underlying mechanisms are unknown. In this study, we examined the effects of dietary fat containing TFAs on dextran sodium sulphate (DSS)-induced colitis. C57 BL/6 mice were fed a diet containing 1·3% TFAs (mainly C16:1, C18:1, C18:2, C20:1, C20:2 and C22:1), and then colitis was induced with 1·5% DSS. Colonic damage was assessed, and the mRNA levels of proinflammatory cytokines and major regulators of T cell differentiation were measured. The TFA diet reduced survival and exacerbated histological damage in mice administered DSS compared with those fed a TFA-free diet. The TFA diet significantly elevated interleukin (IL)-6, IL-12p40, IL-23p19 and retinoic acid-related orphan receptor (ROR)γt mRNA levels in the colons of DSS-treated animals. Moreover, IL-17A mRNA levels were elevated significantly by the TFA diet, with or without DSS treatment. We also examined the expression of proinflammatory cytokines in lipopolysaccharide (LPS)-stimulated RAW264.7 cells and peritoneal macrophages. These cells were exposed to TFAs (linoelaidic acid or elaidic acid) with or without LPS and the mRNA levels of various cytokines were measured. IL-23p19 mRNA levels were increased significantly by TFAs in the absence of LPS. Cytokine expression was also higher in LPS-stimulated cells exposed to TFAs than in unexposed LPS-stimulated cells. Collectively, our results suggest that TFAs exacerbate colonic inflammation by promoting Th17 polarization and by up-regulating the expression of proinflammatory cytokines in the inflamed colonic mucosa.

Interferon-α increases monocyte migration via platelet-monocyte interaction in murine intestinal microvessels.

The aim of this study was to investigate the effect of interferon (IFN)-α on recruitment of platelets and monocytes within the murine small intestinal venular endothelium. Monocytes were isolated from bone marrow of C57B6 mice. Platelets were collected from murine blood. Rolling and adhesion to submucosal microvessels in the small intestine were examined under an intravital fluorescence microscope after injection of fluorescein-labelled monocytes or platelets. In some mice, IFN-α (5×10(5) U/kg) was administered intraperitoneally. After treatment with an antibody against P-selectin, changes in monocyte and platelet migration were also investigated. Changes in monocyte migration under the condition of thrombocytopenia were also investigated. Platelets and monocytes interacted with murine intestinal microvessels, although only few platelets and monocytes showed migration behaviour. Intraperitoneal injection of IFN-α enhanced the migration of both platelets and monocytes in the intestinal microvessels. Pretreatment with anti-P-selectin attenuated the increase in migration of platelets and monocytes induced by administration of IFN-α. Thrombocytopenia decreased the rolling ratio of monocytes, suggesting that the effect of IFN-α on migration was P-selectin-dependent, derived from both the endothelium of microvessels and platelets. The results of this study suggest that IFN-α acts as a potent proinflammatory agent via its stimulatory effect on the endothelium-platelet-monocyte interaction in intestinal microvessels by a P-selectin-dependent mechanism.

Omega-3 polyunsaturated fatty acids ameliorate the severity of ileitis in the senescence accelerated mice (SAM)P1/Yit mice model.

Clinical studies using omega-3 polyunsaturated fatty acids (omega3-PUFA) to Crohn's disease (CD) are conflicting. Beneficial effects of dietary omega3-PUFA intake in various experimental inflammatory bowel disease (IBD) models have been reported. However, animal models of large intestinal inflammation have been used in all previous studies, and the effect of omega3 fat in an animal model of small intestinal inflammation has not been reported. We hypothesized that the effects of omega3 fat are different between large and small intestine. The aim of this study was to determine whether the direct effect of omega3 fat is beneficial for small intestinal inflammation. Senescence accelerated mice (SAM)P1/Yit mice showed remarkable inflammation of the terminal ileum spontaneously. The numbers of F4/80-positive monocyte-macrophage cells as well as beta7-integrin-positive lymphocytes in the intestinal mucosa were increased significantly compared with those in the control mice (AKR-J mice). The area of mucosal addressin cell adhesion molecule-1 (MAdCAM-1)-positive vessels was also increased. The degree of expression levels of monocyte chemoattractant protein-1 (MCP-1), interleukin (IL)-6 and interferon (IFN)-gamma mRNA were increased significantly compared with those in the control mice. The feeding of two different kinds of omega3 fat (fish-oil-rich and perilla-oil-rich diets) for 16 weeks to SAMP1/Yit mice ameliorated inflammation of the terminal ileum significantly. In both the omega3-fat-rich diet groups, enhanced infiltration of F4/80-positive monocytes/macrophages in intestinal mucosa of SAMP1/Yit mice cells and the increased levels of MCP-1, IL-6 and IFN-gamma mRNA expression were ameliorated significantly compared with those in the control diet group. The results suggest that omega3 fat is beneficial for small intestinal inflammation by inhibition of monocyte recruitment to inflamed intestinal mucosa.

Propionibacterium freudenreichii component 1.4-dihydroxy-2-naphthoic acid (DHNA) attenuates dextran sodium sulphate induced colitis by modulation of bacterial flora and lymphocyte homing.

BACKGROUND AND AIMS: 1.4-Dihydroxy-2-naphthoic acid (DHNA), a bifidogenic growth stimulator from Propionibacterium freudenreichii, is thought to have a beneficial effect as a prebiotic; however, its in vivo effect on intestinal inflammation remains unknown. The aim of this study was to determine whether oral administration of DHNA can ameliorate dextran sodium sulphate (DSS) induced colitis and to determine the possible underlying mechanisms. METHOD: Colitis was induced in mice by treatment with 2.0% DSS for seven days. DHNA (0.6 or 2.0 mg/kg) was given in drinking water prior to (preventive study) or after (therapeutic study) DSS administration. Colonic damage was histologically scored, and mucosal addressin cell adhesion molecule 1 (MAdCAM-1) expression and beta7 positive cell infiltration were determined by immunohistochemistry. mRNA levels of proinflammatory cytokines (interleukin (IL)-1beta, IL-6 and tumour necrosis factor alpha (TNF-alpha)) were determined by quantitative real time polymerase chain reaction. In addition, bacterial flora in the caecum, concentrations of short chain acids, and luminal pH were examined. RESULTS: DHNA improved survival rate and histological damage score in mice administered DSS in both the preventive and therapeutic studies. DHNA significantly attenuated the enhanced expression of MAdCAM-1, the increased beta7 positive cell number, and the increased mRNA levels of IL-1beta, IL-6, and TNF-alpha in DSS treated colon. In addition, the decreased number of Lactobacillus and Enterobacteriaceae induced by DSS was recovered by DHNA. Preventive effects on decrease in butyrate concentration and decrease in pH level in mice administered DSS were also observed in the DHNA preventive study. CONCLUSION: DHNA, a novel type of prebiotic, attenuates colonic inflammation not only by balancing intestinal bacterial flora but also by suppressing lymphocyte infiltration through reduction of MAdCAM-1.

Effect of specific antigen stimulation on intraepithelial lymphocyte migration to small intestinal mucosa.

Migration of intraepithelial lymphocytes (IELs) into intestinal epithelium is not yet well understood. We established an IEL-cell line from ovalbumin (OVA) 23-3 transgenic (Tg) mice and investigated the effect of antigen stimulation on the dynamic process of IEL migration into small intestinal mucosa. The cell line was a T cell receptor (TCR) alphabeta(+) CD4(+) CD8(-) phenotype, expressing alphaEbeta7 integrin in 90% of cells. Under intravital microscopy, the lined IELs adhered selectively to the microvessels of the intestinal villus tip of the Tg mice. The accumulation of IELs was significantly inhibited by an antibody against beta7-integrin and MAdCAM-1. When IELs were stimulated with OVA, the accumulation was attenuated compared to that of resting cells, with decreased expression of alphaEbeta7 integrin. In Tg mice fed with OVA, the number of IELs which migrated in the villus mucosa was significantly smaller than in the non-fed controls. The preferential migratory capacity of IELs to villus mucosa may be altered by specific antigen stimulations.

In vivo demonstration of T lymphocyte migration and amelioration of ileitis in intestinal mucosa of SAMP1/Yit mice by the inhibition of MAdCAM-1.

The aetiology of Crohn's disease (CD) remains unknown. Since SAMP1/Yit mice have been reported to develop CD-like spontaneous enteric inflammation, such mice have been studied as an animal model of CD. In this study, using this model we examined T lymphocyte migration in microvessels of intestinal mucosa in vivo and the expression of adhesion molecules by immunohistochemistry. Fluorescence-labelled T lymphocytes isolated from AKR/J (control) mice were injected into the tail veins of recipient mice, and T lymphocyte migration in the postcapillary venules of Peyer's patches, submucosal microvessels, and villus capillaries of the terminal ileum was monitored using an intravital microscope. Adhesion of T lymphocytes was significantly increased in 35 week old SAMP1/Yit mice compared with that in AKR/J or 15 week old SAMP1/Yit mice. Immunohistochemical study showed increased infiltration of CD4, CD8 and beta7-integrin-positive cells and increased expression of MAdCAM-1 and VCAM-1 in the terminal ileum of SAMP1/Yit mice. Antibodies against MAdCAM-1 and VCAM-1 significantly inhibited adhesion of T lymphocytes to microvessels of the terminal ileum, and anti-MAdCAM-1 antibody showed stronger suppressive effect than the anti-VCAM-1 antibody. Periodical administration of anti-MAdCAM-1 antibody twice a week for 7 weeks significantly ameliorated ileitis of SAMP1/Yit mice, but submucosal hypertrophy was not significantly suppressed. Anti-VCAM-1 antibody treatment failed to show significant resolution of ileitis. In addition, anti-MAdCAM-1 antibody treatment also attenuated established ileitis. The results demonstrate that, although MAdCAM-1 and VCAM-1 play an important role in T lymphocyte-endothelial cell interactions in SAMP1/Yit mice, MAdCAM-1 may be a more appropriate target for therapeutic modulation of chronic ileitis.

Increased lymphocyte trafficking to colonic microvessels is dependent on MAdCAM-1 and C-C chemokine mLARC/CCL20 in DSS-induced mice colitis.

Although enhanced lymphocyte trafficking is associated with colitis formation, little information about its regulation is available. The aim of this study was to examine how the murine liver and activation-regulated chemokine (mLARC/CCL20) contributes to lymphocyte recruitment in concert with vascular adhesion molecules in murine chronic experimental colitis. T and B lymphocytes isolated from the spleen were fluorescence-labelled and administered to recipient mice. Lymphocyte adhesion to microvessels of the colonic mucosa and submucosa was observed with an intravital microscope. To induce colitis, the mice received two cycles of treatment with 2% dextran sodium sulphate (DSS). In some of the experiments antibodies against the adhesion molecules or anti-mLARC/CCL20 were administered, or CC chemokine receptor 6 (CCR6) of the lymphocytes was desensitized with excess amounts of mLARC/CCL20. Significant increases in T and B cell adhesion to the microvessels of the DSS-treated mucosa and submucosa were observed. In chronic colitis, the accumulation of lymphocytes was significantly inhibited by anti-mucosal addressin cell adhesion molecule (MAdCAM)-1 mAb, but not by anti-vascular cell adhesion molecule-1. In DSS-treated colonic tissue, the expression of mLARC/CCL20 was significantly increased, the blocking of mLARC/CCL20 by monoclonal antibody or the desensitization of CCR6 with mLARC/CCL20 significantly attenuated the DSS-induced T and B cell accumulation. However, the combination of blocking CCR6 with MAdCAM-1 did not further inhibit these accumulations. These results suggest that in chronic DSS-induced colitis, both MAdCAM-1 and mLARC/CCL20 may play important roles in T and B lymphocyte adhesion in the inflamed colon under flow conditions.

Endotoxin stimulates monocyte-endothelial cell interactions in mouse intestinal Peyer's patches and villus mucosa.

Although monocyte-endothelial cell interactions represent an initial step in controlling the recruitment of monocytes in inflamed tissues, their dynamic processes in microvessels of lymphoid (Peyer's patches) and non-lymphoid (villus) regions in gut-associated lymphoid tissue remain poorly understood. We monitored the migration of fluorescence-labelled monocytes derived from the spleen in intestinal microvessels with or without lipopolysaccharide (LPS) treatment and investigated the role of adhesion molecules, P-selectin, vascular cell adhesion molecule (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1). In control mice, there were few interactions between infused monocytes and the endothelium of intestinal microvessels. The monocyte-endothelial interactions (both rolling and adhesion) were significantly increased in intestinal microvessels of LPS-treated mice compared with those in controls. Anti-P-selectin monoclonal antibody (MoAb) significantly suppressed the LPS-induced increase in monocyte rolling in postcapillary venules of Peyer's patches and submucosal venules. Anti-VCAM-1 MoAbs significantly suppressed the LPS-induced increase in monocyte adhesion to postcapillary venules (PCVs) of Peyer's patches, submucosal venules, and villus capillaries. In contrast, anti-ICAM-1 MoAb significantly suppressed the number of adherent monocytes in PCV of Peyer's patches but not in submucosal venules or villus capillaries. These observations demonstrated that LPS treatment resulted in a significant increase in recruitment of monocytes both in microvessels of lymphoid and non-lymphoid regions and that P-selectin, VCAM-1 and ICAM-1 appeared to play important roles in LPS-induced interactions.

Increased expression of mucosal addressin cell adhesion molecule-1 (MAdCAM-1) and lymphocyte recruitment in murine gastritis induced by Helicobacter pylori.

Although T cell involvement in Helicobactor pylori-induced gastritis is known, mechanism about T cell recruitment is not understood. In this study we examined how mucosal addressin cell adhesion -molecule-1 (MAdCAM-1) is involved in lymphocyte recruitment in murine chronic gastritis induced by H. pylori. C57 BL/6 mice were infected with Sydney strain (SS1). Six months after infection, the stomach was removed. The expression of adhesion molecules, MAdCAM-1, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), and the cell surface antigens CD4, CD8, CD45R/B220 or beta7-integrin were determined by immunohistochemistry. A significant increase in CD4 lymphocytes was observed in the body portion of stomach in SS1-infected mice and most of these CD4 cells express beta7-integrin, a known counter ligand for MAdCAM-1 molecule. Strong MAdCAM-1 expression was observed adjacent to these cells in the lamina propria as well as in the submucosa of SS1-infected stomach. Quantitative analysis showed that the area of MAdCAM-1 expression well correlated with the infiltration of beta7-integrin positive lymphocytes. On the other hand, expression of ICAM-1 or VCAM-1 in the lamina propria was few even in the SS1-infected stomach. Increased expression of MAdCAM-1 was well correlated to the location of lymphocytes, which express CD4 and beta7-integrin. These results suggest the possibility that MAdCAM-1 may be largely involved in the lymphocyte recruitment in the gastritis mucosa with H. pylori.

Intercellular cell adhesion molecule-1 regulates lymphocyte movement into intestinal microlymphatics of rat Peyer's patches.

The objective of this study was to determine whether specific adhesion molecules modulate lymphocyte movement from Peyer's patches into intestinal microlymphatics. The fluorochrome acridine orange was injected via a micropipette into Peyer's patches to fill lymphatics. The flux of labeled lymphocytes into intestinal microlymphatics was monitored with intravital fluorescence microscopy. The lymphatic microvessels in the perifollicular area of Peyer's patches were filled with lymphocytes, most of which remained within the lymphatics. Some lymphocytes became detached and were drained into intestinal lymph. Administration of antibodies directed against ICAM-1 significantly increased lymphocyte flux into interfollicular lymphatics. The immunohistochemical study showed intense ICAM-1 expression on the lymphocytes densely packed in the lymphatics surrounding follicles in Peyer's patches. A large number of lymphocytes are normally sequestered in the lymphatic network of Peyer's patches. This sequestration of lymphocytes is largely mediated by ICAM-1-dependent cell-cell interactions.

Involvement of mucosal addressin cell adhesion molecule-1 (MAdCAM-1) in the pathogenesis of granulomatous colitis in rats.

Although increased expression of mucosal addressin cell adhesion molecule-1 (MAdCAM-1) has been demonstrated in inflammatory sites of various diseases, its role in colitis remains unknown. In this study, we examined whether MAdCAM-1 is involved in the pathogenesis of granulomatous colitis induced by peptidoglycan-polysaccharide (PG-PS). Experimental colitis was induced by intramural injection of PG-PS to rat colon. After 3 weeks the colon was removed and the mucosal inflammation was assessed. The area of MAdCAM-1-positive venules and the subsets of infiltrating cells were determined in colonic mucosa by immunohistochemistry. In another experiment, monoclonal antibody against MAdCAM-1 was administered intraperitoneally to examine its attenuating effect on colitis. The intramural injection of PG-PS induced significant colonic inflammation with granuloma formation. The submucosa was drastically thickened with the infiltration of CD4 positive lymphocytes and ED-1 positive macrophages. Intense MAdCAM-1 expression was observed on endothelium of the submucosal venules in inflamed mucosa. Administration of anti-MAdCAM-1 antibody significantly attenuated the PG-PS-induced colonic damage and cell infiltration. Enhanced expression of MAdCAM-1 was demonstrated in venular endothelium of the inflamed colon in PG-PS-induced colitis. The attenuating effect of anti-MAdCAM-1 suggests the importance of the MAdCAM-1-dependent process in the formation of chronic granulomatous colitis.

Expression of bone morphogenetic proteins in colon carcinoma with heterotopic ossification.

Here we report the case of a 50-year-old woman with adenocarcinoma of the colon, showing heterotopic ossification. The patient was referred to our hospital for investigation of anemia secondary to occult gastrointestinal blood loss. By colonoscopy, an irregular polypoid mass was found in the ascending colon. A biopsy of the lesion revealed moderately to poorly differentiated adenocarcinoma with heterotopic ossification. A right hemicolectomy was done and revealed areas of heterotopic bone within the tumor, but no ossification was evident in the metastatic lesions within the mesenteric lymph nodes. The formation of heterotopic bone in gastrointestinal tumors is rare and its exact mechanism is unknown. Immunohistochemical localization of bone morphogenetic proteins (BMP), known to be primary inducers of new bone formation, was determined. BMP-5 and -6 were prominent in the cytoplasm of tumor cells, and they stained weakly in osteoblast-like cells adjacent to newly formed bone. Cytoplasmic staining for BMP-2 and -4 was weak in tumor cells, osteoblast-like cells, and stromal fibroblast cells. BMP may play an important role in heterotopic ossification in colon adenocarcinoma.

In situ demonstration of intraepithelial lymphocyte adhesion to villus microvessels of the small intestine.

The recirculation of lymphocytes through the intestinal mucosa is important for specific immune defense, but the origin and differentiation of intraepithelial lymphocytes (IEL) are not fully understood. The present study therefore used intravital microscopy to investigate the migration of IEL to the villus mucosa and Peyer's patches of the small intestine. IEL were separated from inverted murine small intestine and mesenteric lymph node (MLN) T cells were also isolated. The adhesion of fluorescence-labeled lymphocytes to postcapillary venules (PCV) of Peyer's patches and arcade microvessels of small intestinal villi was observed after injection. In some experiments, the effect of antibodies against adhesion molecules on cell kinetics were investigated. IEL time-dependently accumulated in villus microvessels of the small intestine, whereas few MLN cells did. Few IEL adhered to the PCV of Peyer's patches. IEL were shown to express alpha(E)beta(7)-integrin but not L-selectin. The accumulation of IEL in villus archade was significantly inhibited by antibody against beta(7)-integrin or mucosal addressin cell adhesion molecules (MAdCAM)-1, but not by alpha(E)-integrin. The combined blocking of beta(7)-integrin and MAdCAM-1 further attenuated the sticking of IEL in this area, although it did not entirely block the IEL adherence. The adherence of CD4(+) or TCRalphabeta IEL to villus microvessels was significantly greater than that of CD4(-) or TCRgammadelta IEL. It was demonstrated in situ for the first time that IEL adhered selectively to the villus microvessels of the small intestine partly via beta(7) and MAdCAM-1.

Reduced sensitivity of inducible nitric oxide synthase-deficient mice to chronic colitis.

BACKGROUND: Overproduction of nitric oxide by the inducible form of nitric oxide synthase (iNOS) has been implicated in colitis. Different authors have postulated both toxic and protective effects of nitric oxide (NO) in the pathophysiology of active inflammation. The objective of this study was to examine the role of iNOS in experimental chronic colitis using iNOS-deficient mice. METHODS: For induction of colitis, mice received three cycles of 2% of dextran sodium sulfate (DSS) (M.W. 40,000) treatment in drinking water. The degree of colonic inflammation, leukocyte infiltration, and the expression of cell adhesion molecules were determined. INOS expression and nitrotyrosine were also determined by immunohistochemistry. RESULTS: After DSS treatment, a moderate colitis with marked cell infiltration was observed. Intense expression of iNOS was observed on infiltrating cells as well as on the colonic mucosal epithelium in these animals. In the iNOS-deficient mice, tissue damage was significantly diminished. No iNOS or nitrotyrosine staining was found in iNOS-deficient mice. The number of infiltrating cells and the expression of mucosal adressin cell adhesion molecule-1 were significantly attenuated in the DSS-treated colon of iNOS-deficient mice. CONCLUSION: Induction of iNOS seems to act as a critical toxic effector molecule in the pathogenesis of chronic colonic inflammation.

Intravital demonstration of modulation of T lymphocyte migration by CINC/gro in rat Peyer's patches.

BACKGROUND/AIMS: Cytokine-induced neutrophil chemoattractant (CINC/gro), a member of interleukin-8 family, was found as a potent chemotactic factor for rat neutrophils. Although several chemokines have been shown to be potent regulators of T cell chemotaxis in vitro, the potential role of chemokines in T-cell migration in gut-associated lymphoid tissues has not been investigated in vivo. In the present study, the effects of CINC/gro on T-lymphocyte migration were examined in rat Peyer's patches. METHODS: T lymphocytes collected from intestinal lymph of rats were fluorescence-labeled and injected into the jugular vein. Peyer's patches of the recipient rats were observed with intravital fluorescence microscopy and the effects of CINC/gro infusion was investigated. Lymphocyte flux in mesenteric collecting lymphatics was also observed. RESULTS: In vivo infusion of CINC/gro significantly attenuated the initial lymphocyte interaction with postcapillary venules of Peyer's patches. However, once these lymphocytes adhered to venules, CINC/gro treatment significantly accelerated the transendothelial migration of T lymphocytes and they also significantly increased their subsequent flux in collecting lymphatics. CONCLUSION: There is a possibility that CINC/gro could modulate the characteristics of T lymphocyte homing in the inflammatory sites of gut.

Amelioration of murine experimental colitis by inhibition of mucosal addressin cell adhesion molecule-1.

Mucosal addressin cell adhesion molecule-1 (MAdCAM-1) is an adhesion molecule that mediates recruitment of lymphocytes into the gut mucosa. Attenuation of excessive expression of MAdCAM-1 in the inflamed mucosa could be useful for treatment of inflammatory bowel diseases. The aim of this study was to investigate whether anti-MAdCAM-1 antibody has a prophylactic effect on experimental colitis induced by dextran sulfate sodium (DSS). Colitis was induced by orally feeding BALB/c mice 5% DSS (mol. wt. 5000). Mice were sacrificed at intervals up to 21 days after administration to evaluate the changes over time in intestinal damage. The infiltrating lymphocytes and their subpopulations, and the expression of cell adhesion molecules were determined by immunohistochemistry. In another set of experiments, the attenuating effect of i.p.-injected anti-MAdCAM-1 antibody on colonic lesions was evaluated on day 14. Significant histological damage with shortening of crypts was observed on day 14 in colonic mucosa of DSS-treated mice. Before mucosal inflammation had become significant, expression of MAdCAM-1 was already increased in the microvessels of lamina propria on day 7. Significant infiltration of beta7-integrin-positive T and B cells in the mucosa was then noted on day 14. Administration of anti-MAdCAM-1 antibody significantly reduced colonic injury as well as the infiltration of beta7-integrin-positive lymphocytes in the colonic mucosa. This antibody also was effective when given 7 days after the start of DSS treatment. In the present study, we demonstrated that anti-MAdCAM-1 antibody significantly ameliorates DSS-induced colitis, suggesting that MAdCAM-1 may be useful for control of inflammatory bowel diseases.

Role of inducible nitric oxide synthase in dextran sulphate sodium-induced colitis.

BACKGROUND: Different authors have postulated both toxic and protective effects for nitric oxide (NO) in the pathophysiology of active inflammation. AIM: To examine the role of NO, especially that produced by the inducible form of nitric oxide synthase (iNOS), by investigating the effects of NOS inhibitors and NO donors on inflammation in experimental acute colitis. METHODS: Acute colitis was induced in rats by dextran sulphate sodium (DSS). White blood cell counts and levels of thiobarbituric acid reactants in the portal blood were determined, as were histological changes in the colonic mucosa. We then evaluated the effects of N(G)-nitro-L-arginine methyl ester (L-NAME), aminoguanidine (AG) and an NO donor on DSS-induced changes in these inflammatory parameters. RESULTS AND CONCLUSIONS: Inhibition of NO production by either L-NAME or AG worsened DSS-induced inflammation, suggesting a protective role for NO in acute colitis. On the other hand, a NO donor also exaggerated DSS-induced inflammatory parameters, suggesting that acute colitis may be aggravated by either too much or too little NO. These results suggest that medical treatment of ulcerative colitis must aim for maintenance of appropriate NO levels in the intestinal mucosa.