Metformin Attenuates Hepatic Fibrosis in Mice by Altering the Gut Microbiota

Background: Metformin is a first-line drug widely used in the treatment of type 2 diabetes. It has been shown to improve liver fibrosis; however, the underlying mechanism remains unclear. Objectives: This study investigates the relationship between metformin and gut microbiota in the treatment of liver fibrosis. Methods: Carbon tetrachloride (CCl₄) was injected intraperitoneally to induce liver fibrosis in mice, followed by metformin treatment for 4 weeks. A CCl₄-induced hepatic fibrosis mouse model was established. The mice were divided into two groups: Metformin treatment and control groups. Hematoxylin-eosin (HE) staining was used to evaluate the overall liver condition, Sirius red staining to assess the degree of hepatic fibrosis, α-smooth muscle actin (α-SMA) immunohistochemical staining to determine the activation of hepatic stellate cells (HSCs), oil red O staining to observe intracellular lipid droplets in hepatocytes, and 16sRNA sequencing to analyze fecal microbiota. Results: In the untreated CCl₄-induced hepatic fibrosis model, hepatic tissue exhibited edema, degeneration, intracellular lipid deposition in hepatocytes, and inflammatory cell infiltration between lobules. Metformin treatment attenuated hepatic fibrosis (area reduced from 1.383% to 0.669%, P < 0.001), decreased inflammatory cell infiltration, reduced intracellular lipid accumulation in hepatocytes (area reduced from 0.457% to 0.086%, P < 0.001), and decreased α-SMA protein expression (area reduced from 1.509% to 0.598%, P < 0.05). Additionally, metformin reduced harmful bacteria and increased the abundance of beneficial bacteria in the intestinal tract of the mice. Conclusions: These findings indicate that metformin reduces liver inflammation, alleviates liver fibrosis, and alters the intestinal microbiota. The modification of gut flora may be a significant mechanism by which metformin exerts its therapeutic effects on liver fibrosis.