Therapeutic efficacy of liraglutide versus metformin in modulating the gut microbiota for treating type 2 diabetes mellitus complicated with nonalcoholic fatty liver disease

Abstract

Metformin and liraglutide are used in the treatment of type 2 diabetes mellitus (T2DM) complicated with nonalcoholic fatty liver disease (NAFLD). Although these drugs can alter the intestinal microbiome, clinical data are required to explore their mechanisms of action. Using 16S sequencing technology, we analyzed and compared the intestinal bacterial community structure and function between patients before and after treatment (12 weeks) with the two drugs (metformin or liraglutide, n = 15) and healthy controls (n = 15). Moreover, combined with 19 clinical indices, the potential therapeutic mechanisms of the two drugs were compared. The studied clinical indices included those associated with islet β-cell function (FPG, FINS, HbA1c, and HOMA-IR), inflammation (TNF-α, IL-6, and APN), lipid metabolism (TC, TG, and LDL-C), and liver function (ALT, AST, and GGT); the values of all indices changed significantly after treatment (p < 0.01). In addition, the effect of the two drugs on the intestinal bacterial community varied. Liraglutide treatment significantly increased the diversity and richness of the intestinal bacterial community (p < 0.05); it significantly increased the relative abundances of Bacteroidetes, Proteobacteria, and Bacilli, whereas metformin treatment significantly increased the relative abundance of Fusobacteria and Actinobacteria (p < 0.05). Metformin treatment increased the complexity and stability of the intestinal bacterial network. However, liraglutide treatment had a weaker effect on the intestinal bacterial network, and the network after treatment was similar to that in healthy controls. Correlation matrix analysis between dominant genera and clinical indicators showed that the correlation between the bacterial community and islet β-cell function was stronger after liraglutide treatment, whereas the correlation between the bacterial community and inflammation-related factors was stronger after metformin treatment. Functional prediction showed that liraglutide could significantly affect the abundance of functional genes related to T2DM and NAFLD (p < 0.05), but the effect of metformin was not significant. This study is the first to report the changes in the intestinal bacterial community in patients treated with metformin or liraglutide and the differences between the mechanisms of action of metformin and liraglutide. Metformin or liraglutide has a therapeutic value in T2DM complicated with NAFLD, with liraglutide having a weaker effect on the intestinal bacterial community but a better therapeutic efficacy.

Keywords: NAFLD; T2DM; intestinal microorganism; liraglutide; metformin.

Figure 1

(A) Difference in the Shannon diversity index of the intestinal bacterial community between healthy controls and patients before and after metformin or liraglutide treatment. (B) Difference in the Chao richness index of the intestinal bacterial community between healthy controls and patients before and after metformin or liraglutide treatment. (C) β-diversity of the intestinal bacterial community in healthy controls and patients before and after metformin or liraglutide treatment. Different letters indicate significant differences between groups. p value < 0.05 indicates that the differences are significant. “**” and “***” indicate significant differences at the levels of 0.01 and 0.001.

Figure 2

(A) Differences in the intestinal bacterial community structure (phylum level) between healthy controls and patients before and after metformin or liraglutide treatment. (B) Differences in the intestinal bacterial community structure at the genus level between healthy controls and patients before and after metformin or liraglutide treatment.

Figure 3

(A) Linear discriminant analysis effect size (LEfSe) of the intestinal bacterial community structure in healthy controls and patients before treatment (MetA & LiraA groups). (B) LEfSe of the intestinal bacterial community structure of patients before and after metformin treatment and healthy controls. (C) LEfSe of the intestinal bacterial community structure of patients before and after liraglutide treatment and healthy controls.

Figure 4

(A) Network analysis of the intestinal bacterial community in patients before metformin treatment. (B) Network analysis of the intestinal bacterial community in patients before liraglutide treatment. (C) Network analysis of the intestinal bacterial community in patients after metformin treatment. (D) Network analysis of the intestinal bacterial community in patients after liraglutide treatment. (E) Network Analysis of the intestinal bacterial community in healthy controls.

Figure 5

(A) Network robustness after exclusion of a proportion of species before and after metformin or liraglutide treatment. (B) Network community stability before and after metformin or liraglutide treatment. (C) Network vulnerability before and after metformin or liraglutide treatment.

Figure 6

(A) Correlation analysis of islet β cell indices and intestinal bacterial community after metformin treatment. (B) Correlation analysis of islet β cell indices and intestinal bacterial community after liraglutide treatment. (C) Correlation analysis of inflammation-related factors and intestinal bacterial community after metformin treatment. (D) Correlation analysis of inflammation-related factors and intestinal bacterial community after liraglutide treatment. (E) Correlation analysis of lipid metabolism indices and intestinal bacterial community after metformin treatment. (F) Correlation analysis of lipid metabolism indices and intestinal bacterial community after liraglutide treatment. (G) Correlation analysis of liver function indices and intestinal bacterial community after metformin treatment. (H) Correlation analysis of liver function indices and intestinal bacterial community after liraglutide treatment.

Figure 7

Differences in intestinal bacterial community function between healthy controls and patients before and after metformin or liraglutide treatment. “*” indicates significant differences at 0.05 level between the groups.