The effects and mechanisms of chronic stress on intestinal and liver injuries in rats / 中华行为医学与脑科学杂志

ABSTRACT

Objective:To investigate the effects and its mechanism of chronic unpredictable stress on intestine and liver injuries in rats, and explore the possibility of the existence of brain-gut-liver axis.Methods:Twenty male SD rats were randomly divided into control group and stress group (with 10 in each group). The rats in the stress group were stimulated by chronic unpredictable stress for 4 weeks to prepare the chronic stress model. The rats in the control group were fed normally without stress stimulation. After modeling, ten rats in the control group and seven rats in the stress group were included. The depressive behavior of the two groups was evaluated by sugar water preference experiment. Then the rats were sacrificed. The diversity of gut flora in intestinal feces was analyzed by 16S rRNA sequencing analysis. The pathological injuries of ileum and liver were detected by HE staining. The expressions of occludin in ileum and Toll-like receptor 4 (TLR4) in liver were detected by immunohistochemistry. The expression of TLR4 protein in liver tissue was detected by Western blot. The level of lipopolysaccharide (LPS) in rat portal vein serum was detected by AZO chromogenic limulus test and blood biochemical method was used to detect liver function.Statistical analysis was performed using SPSS 25.0 software, and t-test or Mann-Whitney U test was used for comparison between the two groups. Using STAMP software, Wilcoxon rank sum test was used to analyze the difference in bacterial abundance between the two groups. Results:The consumption of sugar water ((7.86±0.90)ml) and the preference rate of sugar water ((43.06±5.65)%) in the stress group were lower than those in the control group ((15.10±1.51)ml, (76.81±6.44)%), and the difference were statistically significant ( t=11.33, 11.16, both P<0.01). Chronic stress caused pathological damage to rat ileum tissue. Compared with the control group, the ileum villi of rats in the chronic stress group were longer ((448.93±12.71)μm, (497.12±16.72)μm, t=-5.88, P<0.01) and thicker ((81.99±16.54)μm, (133.93±6.78)μm, t=-7.12, P<0.01), and the expression of occludin was significantly down-regulated ((0.236±0.011), (0.130±0.026), t=9.12 , P<0.01), the LPS level increased significantly ((18.83±2.62)EU/L, (38.64±2.51)EU/L, t=-5.79, P<0.01). The Beta diversity of rat intestinal flora changed under chronic stress, and the abundance of WPS-2 phylum in intestinal tract of rats in stress group was higher than that in control group ( t=2.76, P<0.05). Chronic stress caused pathological damage to the liver tissue of rats. Compared with the control group, the expression of TLR4 protein in the liver tissue of the chronic stress group increased ((0.169±0.014), (0.475±0.034), Z=-2.37, P<0.05). Compared with the control group, the ALT ((39.7±6.2)U/L, (82.9±43.1)U/L, Z=-2.35, P<0.05) and AST((130.9±28.9)U/L, (472.7±263.3)U/L, Z=-2.64, P<0.05) levels of the chronic stress group increased, especially in AST. Conclusion:Chronic stress cause synchronous damage to the intestine and liver in rats. The mechanism may be related to the results caused by chronic stress such as the changes of the diversity of intestinal flora, the increasing of intestinal permeability, the action of LPS translocated through portal vein blood on TLR4 in liver.