Background

Roux-en-Y gastric bypass (RYGB)-induced glycemic improvement is associated with increases in glucagon-like-peptide-1 (GLP-1) secreted from L-cells in the ileum. Proposed mechanisms for GLP-1 changes include shifts in gut microbiota and bile acids, however these are poorly understood. The objective of this study was to analyze changes in ileal bile acids and ileal microbial composition in diet-induced-obesity rats after RYGB to elucidate the early and late effects on L-cells and glucose homeostasis.

Methods

Rats underwent RYGB or sham surgery and were separated into early (2-week) or late (14-week) postoperative cohorts. Metabolic outcomes and ileal samples were analyzed.

Results

In early cohorts, there were no significant changes in L-cell density, GLP-1 or glucose tolerance. In late cohorts, RYGB demonstrated less weight regain, improved glucose tolerance, increased L-cell density, and increased villi height. No difference in the expression of GLP-1 genes was observed. There were lower concentrations of ileal bile acids in the late RYGB cohort. Microbial analysis demonstrated decreased alpha diversity in early RYGB cohorts which normalized in the late group. The early RYGB cohorts had higher abundances of Escherichia-Shigella but lower abundances of Lactobacillus, Adlercreutzia, and Proteus while the late cohorts demonstrated higher abundances of Escherichia-Shigella and lower abundances of Lactobacillus. Shifts in Lactobacillus and Escherichia-Shigella correlated with decreases in multiple conjugated bile acids.

Conclusions

In conclusion, RYGB caused a late and substantial increase in L-cell quantity with associated changes in bile acids which correlated to shifts in Escherichia-Shigella and Lactobacillus. This proliferation of L-cells contributed to improved glucose homeostasis.