Propolis modulates the gut microbiota and improves the intestinal mucosal barrier function in diabetic rats

Objective: Diabetes mellitus is associated with gut microbiota disturbance and intestinal mucosal injuries. This study investigated the influence of propolis on the gut microbiota and intestinal mucosa in rats with diabetes. Methods: Sprague-Dawley (SD) rats were randomly assigned to the control group, model group, and three propolis groups (supplemented with 80, 160, and 240 mg/kg·bw propolis, respectively). A high-fat diet combined with a streptozotocin (STZ) abdominal injection were used to induce diabetes in the rats. After 4 weeks, the intestinal histopathological analysis of the ileum was observed by transmission electron microscopy. The fasting blood glucose (FBG), plasma insulin, glucose tolerance (OGTT) and glycosylated hemoglobin (HbA1c) levels were measured. The expression of tight junction (TJ) proteins in the ileum was measured using western blotting. The molecular ecology of the fecal gut microbiota was analyzed by 16S rDNA high-throughput sequencing. The contents of the short-chain fatty acids (SCFAs) in feces were measured using high-performance liquid chromatography (HPLC). Results: After propolis treatment, compared to the model group, FBG and HbA1c levels declined, while the glucose tolerance and insulin sensitivity index (ISI) increased. The levels of TJ proteins in the ileum increased in the propolis groups. The tight junctions and gap junctions of the intestinal epithelium were also improved in the propolis groups. The contents of the feces acetic acid, propionic acid and butyrate were increased in the propolis groups. 16S rDNA high-throughput sequencing revealed that the composition of the gut microbiota of rats in the propolis supplement group was significantly improved. Conclusions: Compared to the model group, propolis exerted hypoglycemic effects in diabetic rats, and it repaired intestinal mucosal damage, benefited the communities of the gut microbiota and increased SCFA levels in diabetic rats