The role of gut microbiota and amino metabolism in the effects of improvement of islet β-cell function after modified jejunoileal bypass

Abstract

The change in gut microbiota is an important mechanism of the amelioration of type 2 diabetes mellitus (T2DM) after bariatric surgery. Here, we observe that the modified jejunoileal bypass effectively decreases body weight gain, fasting blood glucose, and lipids level in serum; additionally, islet β-cell function, glucose tolerance, and insulin resistance were markedly ameliorated. The hypoglycemic effect and the improvement in islet β-cell function depend on the changes in gut microbiota structure. modified jejunoileal bypass increases the abundance of gut Escherichia coli and Ruminococcus gnavus and the levels of serum glycine, histidine, and glutamine in T2DM rats; and decreases the abundance of Prevotella copri and the levels of serum branched chain amino acids, which are significantly related to the improvement of islet β-cell function in T2DM rats. Our results suggest that amino acid metabolism may contribute to the islet β-cell function in T2DM rats after modified jejunoileal bypass and that improving gut microbiota composition is a potential therapeutic strategy for T2DM.

Figure 1

SSJIBL reduced weight gain, food intake, and fasting blood glucose level, and improved glucose tolerance and insulin sensitivity in GK rats in a time-dependent manner. Rats were randomly divided into 2 groups (n = 8 for SSJIBL, n = 7 for Sham). (A) For the SSJIBL surgery, a point 40 cm proximal to the ileocecal valve was used as the reference point. Starting proximally from this point to 6 cm distal to the Treitz ligament, approximately 60% of the length of the entire small bowel was bypassed, and bowel continuity was restored by a side-to-side anastomosis between the proximal jejunum and the ileum. The luminal occlusion was performed at the first portion of the bypassed segment by using a ligation of 0 silk suture. (B) Body weight of SSJIBL and Sham treated rats. (C) Average daily food intake for the above 2 groups of rats 2 W and 6 W postoperation. (D) Fasting blood glucose level (FBG). (E,F) Effect of SSJIBL on percentage of initial blood glucose level during insulin tolerance test (ITT). (G) Area under the curve (AUC). (H,I) Effect of SSJIBL on glucose tolerance measured by oral glucose tolerance test (OGTT). (J) AUC. Error bars are expressed as means ± SEM. Statistical significance was determined by two-tailed Student’s t test or two-way ANOVA. *P < 0.05, **P < 0.01.

Figure 2

SSJIBL improves lipid homeostasis and liver function, promotes the release of hormones such as insulin and glucagon-like peptid-1, and stimulates the proliferation of pancreatic islet cells. (A) Total TC, TG, FFA, ALT, AST, and ALB/GLB levels in blood. (B) Insulin, GLP-1, PYY, LPS, IL-6, and TNF-α levels in blood. (C) Representative pictures of immunofluorescence of pancreatic tissue (scale bar, 100 μm). Right, integrated optical density (D). Representative pictures of immunohistochemistry of pancreatic tissue (scale bar, 100 μm). Right, average optical density (AO). Error bars are expressed as means ± SEM. Statistical significance was determined by two-tailed Student’s t test. *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 3

SSJIBL altered the gut microbiota composition of GK rats in a time-dependent manner. (A) Venn map. (B) α diversity of gut microbiota. (C) Bray curtis PCoA analysis of gut microbiota based on the OTU data of Sham and SSJIBL groups. (D) Volcano map of different OTUs. (E) Heatmap of the different OTUs altered by SSJIBL treatment. The color of the spots in the left panel represents the relative abundance of the OTU in each group. The phylum, and genus names of the OTUs are shown on the right panel. The analyses were conducted using R software version 3.6.2.

Figure 4

SSJIBL up-regulated gut Escherichia and Ruminococcus and down-regulated Prevotella in GK rats. (A) Bacterial taxonomic profiling at the phylum level of intestinal bacteria from two groups 2 weeks and 6 weeks postoperation. (B) Firmicutes-to-Bacteroidetes ratio in the indicated groups. (C–E) Bacterial taxonomic profiling at the genus level of intestinal bacteria from two groups 2 weeks and 6 weeks postoperation. (F) Heatmap analysis of the Pearson correlation of Escherichia coli, Ruminococcus gnavus and Prevotella copri and glucose homeostasis-related indexes. Red represents positive correlation, and blue indicates negative correlation. (G) A linear discriminant effect size (LEfSe) analysis was performed (alpha value ≥ 0.05, logarithmic LDA score threshold ≥ 3.0) on two groups together. (H) The cladogram represents the phylogenetic relationship of significant OTUs associated with each group. Error bars are expressed as means ± SEM. Statistical significance was determined by two-tailed Student’s t test. *P < 0.05, **P < 0.01, and ***P < 0.001.

Figure 5

Predicted KEGG functional pathway differences between SSJIBL and Sham groups 2 weeks and 6 weeks postoperation. PICRUSt was used to predict functional potential of microbiomes using 16S rDNA gene sequence data. (A) KEGG functional pathway differences at level 1. (B) KEGG functional pathway differences at level 2. (C) KEGG functional pathway differences at level 3. Error bars are expressed as means ± SEM. Statistical significance was determined by two-tailed Student’s t test. *P < 0.05, **P < 0.01.

Figure 6

SSJIBL alters amino acids metabolism in GK rats 6 weeks postoperation. (A) PCoA analysis score plots for discriminating the fecal metabolome from SSJIBL and Sham groups. (B) Volcano map of different metabolites. (C) Disturbed metabolic pathways in the SSJIBL versus Sham groups. (D) Comparison of circulating levels of glycine, histidine, glutamic acid, glutamine, valine, leucine, isoleucine, and phenylalanine in serum by GC–MS in the indicated groups. (E) Heatmap analysis of the Pearson correlation of serum amino acids and glucose homeostasis-related indexes. Red represents positive correlation, and blue indicates negative correlation. Error bars are expressed as means ± SEM. Statistical significance was determined by two-tailed Student’s t test. *P < 0.05, **P < 0.01, ***P < 0.001.