Metformin attenuates the onset of non-alcoholic fatty liver disease and affects intestinal microbiota and barrier in small intestine

Abstract

The antidiabetic drug metformin has been proposed to affect non-alcoholic fatty liver disease (NAFLD) through its effects on intestinal microbiota and barrier function. However, so far most studies focused on long-term effects and more progressed disease stages. The aim of this study was to assess in two experimental settings, if the onset of NAFLD is associated with changes of intestinal microbiota and barrier function and to determine effects of metformin herein. C57Bl/6J mice were fed a liquid control diet (C) or fat-, fructose- and cholesterol-rich diet (FFC) for four days or six weeks ±300 mg/kg BW/day metformin (Met). Markers of liver health, intestinal barrier function and microbiota composition were assessed. Metformin treatment markedly attenuated FFC-induced NAFLD in both experiments with markers of inflammation and lipidperoxidation in livers of FFC + Met-fed mice being almost at the level of controls. Metformin treatment attenuated the loss of tight junction proteins in small intestine and the increase of bacterial endotoxin levels in portal plasma. Changes of intestinal microbiota found in FFC-fed mice were also significantly blunted in FFC + Met-fed mice. Taken together, protective effects of metformin on the onset of NAFLD are associated with changes of intestinal microbiota composition and lower translocation of bacterial endotoxins.

Figure 1

Effect of a chronic (6 weeks) or short-term (4 days) feeding of a FFC or control diet ± metformin on liver in mice. (a,d) Representative pictures of H&E staining in liver tissue (200x, 630x) and (b,e) evaluation of H&E staining via NAFLD Activity Score. (c,f) Number of neutrophilic granulocytes in liver tissue; n = 5–8. Data presented as means ± standard error of means. C: control diet; C + Met: control diet and oral treatment with metformin (300 mg/kg BW/day); DE: diet effect; DExME: interaction between diet and metformin; FFC: fat-, fructose- and cholesterol-rich diet; FFC + Met: fat-, fructose- and cholesterol-rich diet and oral treatment with metformin (300 mg/kg BW/day); H&E: hematoxylin and eosin; ME: metformin effect; Met: metformin; NS: not significant. ^aP < 0.05 compared with mice fed a control diet; ^cP < 0.05 compared with mice fed a control diet treated with metformin; ^dP < 0.05 compared with mice fed a FFC diet treated with metformin.

Figure 2

Effect of a chronic (6 weeks) or short-term (4 days) feeding of a FFC or control diet ± metformin on inflammation and markers of lipidperoxidation in mice. (a,d) Representative pictures (200x) and densitometric analysis of (b,e) 4-HNE protein adducts and (c,f) iNOS protein staining in hepatic tissue; n = 6–8. Data presented as means ± standard error of means. 4-HNE: 4-hydroxynonenal; C: control diet; C + Met: control diet and oral treatment with metformin (300 mg/kg BW/day); DE: diet effect; DExME: interaction between diet and metformin; FFC: fat-, fructose- and cholesterol-rich diet; FFC + Met: fat-, fructose- and cholesterol-rich diet and oral treatment with metformin (300 mg/kg BW/day); iNOS: inducible nitric oxide synthase; ME: metformin effect; Met: metformin; NS: not significant. ^aP < 0.05 compared with mice fed a control diet; ^cP < 0.05 compared with mice fed a control diet treated with metformin; ^dP < 0.05 compared with mice fed a FFC diet treated with metformin.

Figure 3

Effect of a chronic (6 weeks) or short-term feeding (4 days) of a FFC or control diet ± metformin on markers of intestinal permeability and MMP13 in mice. Densitometric analysis of (a) occludin protein and (b) MMP13 protein staining in proximal small intestine in long-term trial. (c) Endotoxin concentration in plasma of portal vein and densitometric analysis of (d) occludin and (e) ZO-1 protein staining in tissue of proximal small intestine, as well as (f) Mmp13 mRNA expression in proximal small intestine; n = 4–8. Data presented as means ± standard error of means. C: control diet; C + Met: control diet and oral treatment with metformin (300 mg/kg BW/day); DE: diet effect; DExME: interaction between diet and metformin; FFC: fat-, fructose- and cholesterol-rich diet; FFC + Met: fat-, fructose- and cholesterol-rich diet and oral treatment with metformin (300 mg/kg BW/day); ME: metformin effect; MMP13: matrix-metalloproteinase 13; NS: not significant; ZO-1: zonula occludens-1. ^aP < 0.05 compared with mice fed a control diet; ^cP < 0.05 compared with mice fed a control diet treated with metformin; ^dP < 0.05 compared with mice fed a FFC diet treated with metformin.

Figure 4

Effect of a short-term feeding (4 days) of a FFC or control diet ± metformin on microbial community in small intestine at species level. (a) PCO plot showing the microbial communities of each sample and relative abundance of OTU with significant difference between (b) control and FFC-fed mice or (c) FFC and FFC + Met-fed mice; n = 4–6. Data presented as means ± standard error of means. C: control diet; C + Met: control diet and oral treatment with metformin (300 mg/kg BW/day); FFC: fat-, fructose- and cholesterol-rich diet; FFC + Met: fat-, fructose- and cholesterol-rich diet and oral treatment with metformin (300 mg/kg BW/day); PCO: principal coordinate analysis; unc: unclassified.