Glutamine enema regulates colonic ubiquitinated proteins but not proteasome activities during TNBS-induced colitis leading to increased mitochondrial activity.

Ubiquitin proteasome system contributes to the regulation of intestinal inflammatory response as its inhibition is associated with tissue damage improvement. We aimed to evaluate whether glutamine is able to limit inflammation by targeting ubiquitin proteasome system in experimental colitis. Colitis was induced in male rats by intrarectal instillation of 2-4-6-trinitrobenzen sulfonic acid (TNBS) at day 1. From day 2 to day 6, rats daily received either an intrarectal instillation of PBS (TNBS/PBS group) or glutamine (TNBS/Gln). Rats were euthanized at day 7 and colonic samples were taken to evaluate ubiqutinated proteins by proteomic approach combining 2D electrophoresis and immunoblots directed against ubiquitin. Results were then confirmed by evaluating total expression of proteins and mRNA levels. Survival rate, TNFα, and IL-1ß mRNA were improved in TNBS/Gln compared with TNBS/PBS (p < 0.05). Proteasome activities were affected by TNBS but not by glutamine. We identified eight proteins that were less ubiquitinated in TNBS/PBS compared with controls with no effect of glutamine. Four proteins were more ubiquitinated in TNBS/PBS group and restored in TNBS/Gln group. Finally, 12 ubiquitinated proteins were only affected by glutamine. Among proteins affected by glutamine, eight proteins (GFPT1, Gapdh, Pkm2, LDH, Bcat2, ATP5a1, Vdac1, and Vdac2) were involved in metabolic pathways. In conclusion, glutamine may regulate ubiquitination process during intestinal inflammation.

Glutamine supplementation, but not combined glutamine and arginine supplementation, improves gut barrier function during chemotherapy-induced intestinal mucositis in rats.

BACKGROUND & AIMS: Increased intestinal permeability occurs during chemotherapy-induced intestinal mucositis. Previous data suggest that glutamine and arginine may have additive or synergic effects to limit intestinal damage. The present study aimed to evaluate the effects of glutamine and arginine, each alone or in combination, on gut barrier function during methotrexate (MTX)-induced mucositis in rats. METHODS: Eighty Sprague Dawley rats received during 7 days (d) standard chow supplemented with protein powder (PP), glutamine (G, 2%), arginine (A, 1.2%) or glutamine plus arginine (GA). All diets were isonitrogenous. Rats received subcutaneous injections of MTX (2.5 mg/kg) from d0 to d2. The intestinal permeability and tight junction proteins were assessed at d4 and d9 in the jejunum by FITC-dextran and by western blot and immunohistochemistry, respectively. RESULTS: At d4, intestinal permeability was increased in MTX-PP, MTX-A and MTX-GA rats compared with controls but not in MTX-G rats. The expression of claudin-1, occludin and ZO-1 was decreased in MTX-PP group compared with controls but was restored in MTX-G and MTX-A rats. In MTX-GA rats, occludin expression remained decreased. These effects could be explained by an increase of erk phosphorylation and a decrease of IκBα expression in MTX-PP and MTX-GA rats. At d9, Intestinal permeability remained higher only in MTX-GA rats. This was associated with a persistent decrease of occludin expression. CONCLUSIONS: Glutamine prevents MTX-induced gut barrier disruption by regulating occludin and claudin-1 probably through erk and NF-κB pathways. In contrast, combined glutamine and arginine has no protective effect in this model.

Adjunct therapy of n-3 fatty acids to 5-ASA ameliorates inflammatory score and decreases NF-κB in rats with TNBS-induced colitis.

5-aminosalicylic acid (5-ASA) is widely used for the treatment of inflammatory bowel disease (IBD). Recent studies have evaluated the potential of nutritional intervention as adjunct therapy to 5-ASA in IBD. N-3 polyunsaturated fatty acids (PUFA) have shown potent anti-inflammatory properties in gut inflammation. Therefore, we aimed to evaluate the efficacy of the dual therapy (n-3 PUFA plus 5-ASA) in rats with 2, 4, 6-trinitrobenzen sulfonic acid (TNBS)-induced colitis. Colitis was induced by intrarectal injection of TNBS while control rats received the vehicle. Rats received by gavage a fish oil-rich formula (n-3 groups) or an isocaloric and isolipidic oil formula supplemented with 5-ASA for 14 days. A dose response of 5-ASA (5-75 mg. suppression mg kg(-1) d(-1)) was tested. Colitis was evaluated and several inflammatory markers were quantified in the colon. COX-2 expression (P<.05) and pro-inflammatory eicosanoids production of prostaglandin E2 (P<.001) and leukotriene B4 (P<.001) were significantly inhibited by n-3 PUFA or 5-ASA therapy. 5-ASA also reduces mRNA levels of tumor necrosis factor α (P<.05). n-3 PUFA or 5-ASA significantly inhibits nuclear factor κB (NF-κB) activation (P<.01 and P<.05, respectively). The dual therapy n-3 PUFA plus 5-ASA also inhibited inflammatory response by lowering NF-κB activation (P<.01) or inducing peroxisome proliferator-activated receptor-γ (PPARγ) expression (P<.05). These results indicate that 5-ASA plus n-3 PUFAs are more effective than a higher dose of 5-ASA alone to reduce NF-κB activation and to induce PPARγ. By contrast, the dual therapy did not improve the effects of individual treatments on eicosanoids or cytokine production. Use of n-3 PUFA in addition to 5-ASA may reduce dose of standard therapy.

Dietary α-linolenic acid-rich formula reduces adhesion molecules in rats with experimental colitis.

OBJECTIVE: The ω-3 polyunsaturated fatty acid therapy in inflammatory bowel disease is focused on the effects on fish oil-derived polyunsaturated fatty acids. We speculated that a vegetal oil rich in α-linolenic acid (ALA) might also inhibit colitis. Therefore, we evaluated whether dietary ALA would decrease the expression of adhesion molecules by inducing the protective enzyme heme oxygenase-1 (HO-1) in a rat colitis model. METHODS: Colitis was induced at day 0 by an intrarectal injection of 2-4-6-trinitrobenzen sulfonic acid (TNBS), whereas control rats received the vehicle. Rats were fed an ALA-rich formula 450 mg · kg⁻¹ · d⁻¹, whereas the other colitic group (TNBS) and the control group were fed an isocaloric corn oil formula for 14 d (from day -7 to day 7). The colonic expressions of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), vascular endothelial growth factor A receptor-2 (VEGFR2), and HO-1 were studied by immunohistochemistry. RESULTS: The ALA-rich diet significantly decreased the expression of ICAM-1, VCAM-1, and VEGFR-2 compared the TNBS group, but it did not affect the expression of HO-1. CONCLUSION: A vegetal ALA-rich formula decreases the expression of ICAM-1, VCAM-1, and VEGFR-2 and independently of HO-1 in rats with TNBS-induced colitis. Further studies are required to evaluate its therapeutic potential in inflammatory bowel disease as an alternative to fish oil.

Anti-inflammatory and anti-angiogenic effect of long chain n-3 polyunsaturated fatty acids in intestinal microvascular endothelium.

BACKGROUND & AIMS: The role of endothelial cells in inflammatory bowel disease has been recently emphasized. Endothelial activation and expression of adhesion molecules are critical for leukocytes recruitment into the inflammatory wall. Compelling evidence demonstrated anti-inflammatory effects of long chain n-3 PUFA in inflammatory models. We previously showed that long chain n-3 PUFA (EPA and DHA) inhibited inflammatory response in epithelial and dendritic cells. As long chain n-3 PUFA treatment led to a decreased expression of adhesion molecules in endothelial cells from other organs, we have now investigated their effect on intestinal endothelial cells in vitro and in colitic rats. METHODS: In vitro study: Primary culture of human intestinal microvascular endothelial cells (HIMEC) were pre-treated with DHA and then incubated with IL-1ß. In vivo study: Colitis was induced in 2 groups at day0 by intrarectal injection of 2-4-6-trinitrobenzen sulfonic acid (TNBS). Rats received by gavage either fish oil, rich in EPA and DHA (TNBS+n-3) or an isocaloric isolipidic oil formula for 14 days. RESULTS: DHA led to a decreased VCAM-1, TLR4, cyclooxygenase-2 and VEGFR2 expression and a decreased production of IL-6, IL-8 and GM-CSF and a reduced production of PGE(2) and LTB(4) (p < 0.001) in IL-1ß-induced HIMEC. Similarly, dietary intervention with fish oil rich in EPA and DHA significantly decreased colon production of PGE(2) and LTB(4,) endothelial VCAM-1 and VEGFR2 in rats with colitis. CONCLUSIONS: Data obtained from in vitro and in vivo studies reveal a potential anti-angiogenic role of long chain n-3 PUFA in intestinal endothelial cells. This protective effect of long chain n-3 PUFA may partly explain the observed benefit of dietary intake of long chain n-3 PUFA in IBD development.