关键词: 非酒精性脂肪肝, 肠道菌群, 肝脏炎症, 鸢尾素, 有氧运动, 抗阻运动

Abstract: BACKGROUND: Nonalcoholic fatty liver disease is a liver disease with abnormal accumulation of lipid in hepatocytes and inflammatory response. Aerobic exercise can regulate the homeostasis of intestinal microenvironment, and then alleviate inflammatory response and improve nonalcoholic fatty liver disease through the "microbiotic-gut-liver" axis. However, it is unclear whether the motility factor irisin mediates the regulation of the gut microbiota, and whether different exercise methods such as resistance exercise can also improve nonalcoholic fatty liver disease through the above mechanism has not been reported.
OBJECTIVE: To study the effects of different exercise methods on inflammatory response in mice with nonalcoholic fatty liver disease, and to explore the correlation between gut microbiota and inflammatory response and exercise factor irisin.
METHODS: After adaptive feeding for 1 week, 48 C57BL/6J mice were randomly divided into a control group (n=12) and a high-fat diet group (n=36). The mice in the control group were fed with normal diet, while in the high-fat diet group, nonalcoholic fatty liver disease models were induced by feeding with 60% fat diet for 12 weeks. The successful model mice were randomly subdivided into high-fat group, aerobic exercise group and resistance exercise group, and the intervention continued in the latter two groups for 8 weeks. During the intervention, the high-fat group, aerobic exercise group and resistance exercise group were fed with high-fat diet until the end of the experiment. 16S rRNA gene sequencing was used to analyze the composition of gut microbiota in each group, hematoxylin-eosin staining was used to observe the steatosis score of hepatocytes in each group, and microplate method was used to detect blood lipids and liver function related indicators in each group. Western blot assay was used to detect the protein expression levels of nucleotide-binding oligomerization domain-like receptor protein 3, nuclear factor-κB, interleukin-1β, tumor necrosis factor-α and irisin in the liver of mice in each group.
RESULTS AND CONCLUSION: (1) Compared with the control group, mice in the high-fat group exhibited significant increases in serum total cholesterol, triglycerides, and low-density lipoprotein (P < 0.05), while high-density lipoprotein levels were significantly decreased (P < 0.05). The indicators of exercise capacity, namely grip strength and anti-fatigue ability, deteriorated (P < 0.05). The mouse liver showed a large number of vacuoles and inflammatory cell infiltration (P < 0.05). The protein expression of nucleotide-binding oligomerization domain-like receptor protein 3, nuclear factor-κB, interleukin-1β, and tumor necrosis factor-α was significantly upregulated (P < 0.05), while irisin protein expression was significantly downregulated (P < 0.01). (2) Compared with the high-fat group, both aerobic exercise and resistance exercise significantly improved the aforementioned physiological indicators, reducing serum total cholesterol, triglycerides, and low-density lipoprotein levels (P < 0.05) while upregulating high-density lipoprotein levels (P < 0.05). These interventions also reduced liver vacuoles and inflammatory cell infiltration, enhanced exercise capacity (P < 0.05), downregulated the protein expression of nucleotide-binding oligomerization domain-like receptor protein 3, nuclear factor-κB, interleukin-1β, and tumor necrosis factor-α (P < 0.05), and promoted irisin protein expression (P < 0.05). The improvement effects of aerobic exercise were more pronounced. (3) Microbiota α-diversity analysis revealed significant differences in the sobs, chao, and coverage indices among the four groups (P < 0.05). Compared with the control group, the sob and chao indices in the high-fat group were significantly decreased (P < 0.05), while the coverage index was significantly increased (P < 0.05). β-diversity analysis showed significant separation between the control group and the other three groups at both the operational taxonomic unit and genus levels (P < 0.01). At the phylum level, the Firmicutes/Bacteroidota ratio was significantly higher in the high-fat and resistance exercise groups than in the control group (P < 0.01), but was significantly reduced in the aerobic exercise group compared with the control group (P < 0.01). Differential microbiota analysis indicated that aerobic exercise could adjust the increased abundance of Escherichia-Shigella and Leuconostoc in the high-fat group (P < 0.05). (4) Correlation analysis showed a highly significant negative correlation between irisin and Escherichia-Shigella. To conclude, compared with resistance exercise, aerobic exercise can more effectively improve peripheral lipid metabolic disorders, enhance exercise capacity, inhibit the activation of the nuclear factor-κB/nucleotide-binding oligomerization domain-like receptor protein 3 inflammatory signaling pathway, and reshape the gut microbiota composition. Moreover, under the pathological background of fatty liver, the anti-inflammatory effects of irisin may be related to changes in the gut microbiota composition.

Key words: nonalcoholic fatty liver disease, gut microbiota, hepatic inflammation, irisin, aerobic exercise, resistance exercise