Abstract: Objective To investigate the effects of interleukin 22 (IL-22) on tight junction proteins Occludin and ZO-1 in the ileum of mice with alcohol liver fibrosis, as well as its impact on nuclear factor-E2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) antioxidant pathway.Methods Sixty clean-grade healthy male C57/6j mice were used to construct a composite model of ALF by feeding with chronic ethanol plus intraperitoneal injection of CCL4. The mice were divided into a normal group (Group N), a control group (Group C), a model group (Group M), an IL-22 group, and an IL-22+ML385 (Nrf2 inhibitor) group, with 12 mice in each group. Immunohistochemistry was used to detect the expression levels of ileal tight junction proteins Occludin, ZO-1 and Nrf2, as well as their downstream genes heme oxygenase-1 (HO-1) and NAD(P)H quinone oxidoreductase 1 [NQO1]. Immunofluorescence was used to detect the expression level of Occludin and ZO-1 in the ileal mucosal epithelium. Researchers observed the pathological changes of liver and ileum, as well as the degree of hepatic fibrosis. Results Compared with group C, the mean optical density values of ileal tissue for Occludin and ZO-1 were lower in group M (0.292±0.015, 0.237±0.036 vs. 0.236±0.025, 0.158±0.025, P<0.05), and the fluorescence intensity was significantly weakened. The mean optical density values of Nrf2, NQO1, and HO-1 were higher (0.141±0.011、0.196±0.019、0.166±0.033 vs. 0.172±0.042、0.223±0.011、0.215±0.044, P<0.05). The collagen fiber deposition in liver tissue significantly increased (1.723±0.415 vs. 19.759±1.319, P<0.05). Compared with the M group, the mean optical density values of Occludin, ZO-1, Nrf2, NQO1 and HO-1 in ileal tissues were higher in the IL-22 group (0.322±0.020, 0.289±0.024, 0.217±0.012, 0.321±0.018, 0.273±0.030, P<0.05). The fluorescence intensity of Occludin and ZO-1 was significantly increased. There was a reduction in collagen fiber deposition in liver tissue (10.851±0.951, P>0.05). Compared with the IL-22 group, the mean optical density values of Occludin, ZO-1, Nrf2, NQO1 and HO-1 were lower in the IL-22+ML385 group (0.248±0.011, 0.175±0.030, 0.179±0.013, 0.229±0.053, 0.218±0.030, P<0.05). The fluorescence intensity of Occludin and ZO-1 was reduced, and there was a decrease in collagen fiber deposition in liver tissue (19.264±0.932, P<0.05). ML385 inhibited the Nrf2/HO-1 pathway, resulting in a notable reduction in the protective effect of IL-22 on ileal tissue injury in ALF mice. There was no significant difference between group N and group C in any of the above results (P>0.05). Conclusion The dysfunction of ileal barrier,caused by a decrease in the expression of ileal tight junction proteins in ALF mice, may be influenced by oxidative stress. On the other hand, IL-22 enhanced the Nrf2/HO-1 antioxidant pathway in the ileun, leading to increased expression of tight junction proteins in the ileal epithelial cells and improvement in the barrier function of the ileum. As a result, the progression of ALF was inhibited.

Key words: Alcoholic liver fibrosis, Oxidative stress, Tight junction protein, IL-22, Nrf2