[The impact of dietary methionine-restriction on tight junction expression and function in a rat colonitis model].

OBJECTIVE: To study the impact of methionine restriction (MetR) on mucosal histopathology, permeability and tight junction composition in a dextran sulfate sodium (DSS)-induced colitis model, and to explore its underlying mechanism. METHODS: SD rats were randomly divided into 4 groups: normal rats fed by a complete amino acid (AA group) diet, normal rats fed by MetR diet (MetR group), DSS treated rats fed by a complete amino acid (DSS+AA group) and DSS treated rats fed by MetR diet (DSS+MetR group), each group had 15 rats.Abdominal aorta blood sampling was taken at day 21 after DSS model been established to analyze blood routine examination, liver and kidney function and level of electrolyte. Morphological changes in colonic mucosa were evaluated and scored by light microscopy. Myeloperoxidase (MPO) activity was measured. The effect of MetR on mucosal permeability of colon strips was detected by Ussing chamber. Claudin2, occludin, claudin3, ZO-1 expression were quantified by Western blot. RESULTS: The early clinical manifestation in the DSS treated rats were loose stool or diarrhea, hematochezia positive and bleeding, and weight losing. HE observation showed prominent colitis in distal colon with manifestations of crypt abscess and infiltration of inflammatory cells. Although MPO activity and WBC account between the DSS+MetR and DSS+AA group did not significantly changed, treatment with MetR diet significantly decreased the extent and severity of epithelial injury of DSS+MetR group (10.55 ± 3.62 vs 15.00 ± 4.89, P = 0.003). There were no significant difference in PCNA immunohistochemical result between the DSS+MetR group and DSS+AA group. Compared to the rats on AA diet, transepithelial electrical resistance (TEER) in DSS+AA group was obvious lower [(28.40 ± 6.78) Ω·cm² vs (46.53 ± 4.03) Ω·cm², P < 0.05], and TEER in MetR group were obviously higher [(60.64 ± 8.40) Ω·cm² vs (46.53 ± 4.03) Ω·cm², P < 0.05]. However, short-circuit current (Isc) in DSS+MetR group was obviously higher that of DSS+AA group [(35.01 ± 2.19) µA/cm² vs (29.61 ± 1.19) µA/cm², P < 0.05]. Western blot suggested that colon claudin2 expression was not found in colon epithelium of normal rats, and an obviously increase expression of claudin3 protein was found in the MetR group, compared to AA group; and an significantly increase in the abundance of claudin3 was found in the DSS+MetR group, but amount of claudin2 was decreased, compared with the DSS+MetR group. CONCLUSION: The MetR diet has obvious therapeutic effect on ulcerative colitis model rats induced by DSS, and its mechanism may not by regulating inflammatory cell infiltration and the way of promoting intestinal cell growth to alleviate inflammatory injury, but probably by changing the structure and function of tight junction protein and improve the intestinal mucosal barrier function, and promote the repair of damaged intestinal mucosa.

[Changes in tight junction protein expression and permeability of colon mucosa in rats with dextran sulfate sodium-induced inflammatory bowel disease].

OBJECTIVE: To develop an experimental rat model of inflammatory bowel disease (IBD) by administration of dextran sulfate sodium (DSS), and to observe changes in the tight junction protein expression and permeability of colon mucosa. METHODS: Male Sprague-Dawley (SD) rats were randomly divided into control (n=27) and IBD model groups (n=27). In the IBD model group, IBD was induced by 6-day administration of 3% DSS in water followed by 14-day administration of water only. The control group was fed with water only. Pathological changes in colon mucosae were observed on days 7, 14 and 21 after DSS administration. Colon tissue specimens were collected on day 21 for measuring myeloperoxidase (MPO) activity. The transepithelial electric resistance (TEER), transepithelial potential difference (TEPD) and short circuit current (Isc) of the specimens were measured by Ussing chamber. Real-time PCR and Western blot were used to measure the mRNA and protein expression of tight junction proteins in colon epithelia. RESULTS: In the IBD model group, diarrhea, hemafecia and weight loss were seen. Inflammation occurred mainly in the distal colon and was characterized by crypt abscess and inflammatory cell infiltration. The IBD model group showed significantly increased MPO activity (P<0.01), significantly decreased TEER (P<0.01) and TEPD (P<0.01), and significantly increased Isc (P<0.01) compared with the control group. No claudin 2 expression of mRNA and protein was detected in the control group, and they were expressed in the IBD model group. The expression levels of claudin 3, occludin and ZO-1 in the IBD model group were significantly decreased compared with in the control group (P<0.01). CONCLUSIONS: IBD rats show colonic barrier dysfunction and changes in the expression of tight junction proteins. The changes in the expression of tight junction proteins may contribute to colonic barrier dysfunction in cases of IBD in the chronic recovery stage.