This experiment was conducted to investigate the effects of succinic acid on intestinal inflammation of mice infected with enterotoxigenic Escherichia coli (ETEC) K88 and its mechanism. Forty 7-week-old C57BL/6J male mice were selected and randomly divided into 4 groups (10 replicates in each group): normal control group (NC group), succinic acid group (SUC group), Escherichia coli group (ETEC group) and succinic acid+Escherichia coli group (SUC+ETEC group). Mice in four groups were all drank deionized water, and mice in SUC group and SUC+ETEC group added 20 mmol/L succinic acid in drinking water. On day 4 of the experiment, mice in ETEC group and SUC+ETEC group were gavage administration 0.2 mL of ETEC K88 bacterial solution with a concentration of 1×1010 CFU/mL every day for 3 d and recovered for 1 d. The adaptation period was 7 days, and the experimental period was 8 days. The results showed as follows: 1) compared with NC group, the body weight after modeling of ETEC group was significantly decreased (P<0.05); compared with ETEC group, the body weight after modeling and jejunal villus height and villus height/crypt depth of SUC+ETEC group were significantly increased (P<0.05). 2) Compared with NC group, the concentrations of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in plasma and jejunum of ETEC group were significantly increased (P<0.05), and the interleukin-10 (IL-10) and interleukin-4 (IL-4) concentrations were significantly decreased (P<0.05); compared with ETEC group, the plasma IL-6 concentration of SUC+ETEC group was significantly decreased (P<0.05), the concentrations of TNF-α and IL-6 in jejunum were significantly decreased (P<0.05), and the jejunal IL-10 concentration was significantly increased (P<0.05). 3) Compared with NC group, the concentrations of endotoxin, diamine oxidase (DAO) and D-lactic acid (D-LA) in plasma of ETEC group were significantly increased (P<0.05); compared with ETEC group, the concentrations of endotoxin and D-LA in plasma of SUC+ETEC group were significantly decreased (P<0.05). 4) Compared with NC group, the expression levels of Claudin-1 and Occludin in jejunum of ETEC group were significantly decreased (P<0.05); compared with ETEC group, the expression levels of Claudin-1 and Occludin in jejunum of SUC+ETEC group were significantly increased (P<0.05). In conclusion, adding succinic acid to drinking water can enhance the expression of tight junction protein in jejunum, improve the intestinal permeability, regulate the secretion of inflammatory factors, and alleviate the intestinal inflammation in mice caused by ETEC K88 infection.
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