Effect of curcumin on intestinal mucosal mechanical barrier in rats with non-alcoholic fatty liver disease

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Objective: To investigate the effect of curcumin on intestinal mucosal mechanical barrier in rats with non-alcoholic fatty liver disease. Methods: A total of 30 male Sprague-Dawley rats were equally divided into normal control group, model group, and curcumin intervention group. The rats in the model group and the curcumin intervention group were given high-fat feed for 16 weeks, and those in the curcumin intervention group were given curcumin 200 mg/kg/day by gavage once a day after 8 weeks of high-fat feeding. The rats were sacrificed at the end of week 16. A light microscope was used to observe pathological changes in the liver, an electron microscope was used to observe the tight junction of the intestinal mucosa, an automatic biochemical analyzer was used to measure the serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), chromogenic substrate Limulus amebocyte lysate assay was used to measure plasma lipopolysaccharide (LPS) level, spectrophotometric method was used to measure the activity of serum diamine oxidase, ELISA was used to measure the serum level of tumor necrosis factor-α (TNFα), and immunohistochemistry was used to measure the expression of the tight junction protein occludin. One-way ANOVA test and SNK-q test were used for statistical analysis. Results: Under the light microscope, the control group had no hepatocyte steatosis, the model group had significant hepatocyte steatosis and inflammatory cell infiltration, and the curcumin intervention group had reduced hepatocyte steatosis and inflammatory cell infiltration. Under the electron microscope, the control group had a clear and complete structure of the tight junction of the intestinal mucosa and normal structures of mitochondria and endoplasmic reticulum; in the model group, the structure of the tight junction of the intestinal mucosa was destroyed, the intercellular space was widened, the desmosomes had a loose structure, there was edema in some mitochondria, and the endoplasmic reticulum was dilated; the curcumin intervention group had improvements in the structure of tight junction of the intestinal mucosa, intercellular space, edema in the mitochondria, and dilation of the endoplasmic reticulum. Compared with the control group, the model group had significant increases in the serum levels of AST, ALT, DAO, TNFα, and LPS (q = -15.918, -14.402, -33.700, -8.944, and -10.832, P < 0.05); compared with the model group, the curcumin intervention group had significant reductions in the serum levels of AST, ALT, DAO, TNFα, and LPS (q = 10.457, 7.752, 18.802, 5.202, and 4.279, P < 0.05). In the control group, occludin showed a linear distribution along the top of small intestinal mucosal epithelial cells. The model group had a significant reduction in positive staining compared with the control group, and the curcumin intervention group had a significant increase in positive staining compared with the model group. The relative expression of occludin was 0.29±0.03 in the control group, 0.12±0.02 in the model group, and 0.21±0.02 in the curcumin intervention group (P < 0.05). Conclusion: Intestinal mucosal mechanical barrier is impaired in rats with NAFLD. Curcumin can reduce such damage, and its mechanism of action may be related to up-regulating the expression of occludin in the intestinal mucosa and reducing the levels of TNFα and LPS.