Abstract:

Type 2 diabetes mellitus can lead to a variety of severe complications and affects more than 400 million people worldwide. Studies have found that probiotics can stimulate intestinal L cells to secrete glucagon-like peptide-1 （GLP-1）， thereby achieving a significant blood glucose-lowering effect. This study aimed to screen bacterial strains that significantly promote GLP-1 secretion， with the goal of providing a new therapeutic strategy for type 2 diabetes mellitus. The enzyme-linked immunosorbent assay （ELISA） was used to compare the GLP-1 secretion levels of 5 candidate bacterial strains in stimulating the mouse small intestine endocrine cell line （STC-1）， so as to screen out the strain with the highest GLP-1 secretion. The inhibitory activity of this strain against glucose-related metabolic enzymes （α-amylase） was evaluated. Physiological and biochemical experiments were conducted to assess the safety of the strain， providing data support for its application. Quantitative real-time PCR （qPCR） was used to detect the relative expression levels of G protein-coupled receptors （Gpr41 and Gpr43）， so as to conduct a preliminary exploration of its blood glucose-lowering mechanism. The fermentation supernatant of Limosilactobacillus fermentum TH02105 could promote GLP-1 secretion in STC-1 cells， with a secretion level of 140.340 ng·mL^-1， which was significantly higher than that of other strains （P0.001）. Its inhibition rate against α-amylase reached 66.30%. The logarithmic growth phase of L. fermentum TH02105 was 2~8 h， with an optimal temperature of 37 ℃ and an optimal pH of 6. After being treated with artificial simulated intestinal fluid and gastric fluid for 2.5 h， the survival rate of this strain was more than 50%， and the number of its adhesion to human colonic adenocarcinoma cells Caco-2 was 334.02 CFU·cell^-1. Meanwhile， the antibiotics nitrofurantoin， minocycline， polymyxin B， ciprofloxacin， chloramphenicol， norfloxacin， and levofloxacin could all inhibit the activity of this strain. In addition， this strain significantly upregulated the relative expression levels of Gpr41/43 genes （P0.01）. A strain of L.fermentum TH02105 was screened out， which can significantly promote GLP-1 secretion and exert a blood glucose-lowering effect. At the same time， this strain has good tolerance to gastrointestinal fluids and good adhesion to Caco-2 cells， which is conducive to its colonization. The study provides a potential bacterial strain for the development of drugs and health products for the prevention and treatment of diabetes.

Key words: type 2 diabetes mellitus, GLP-1, Limosilactobacillus fermentum, α-amylase, Caco-2