Tetrahydrocurcumin ameliorates diabetes profiles of db/db mice by altering the composition of gut microbiota and up-regulating the expression of GLP-1 in the pancreas.

Diabetes is a worldwide healthy concern, which affects approximately 9% of the population. Tetrahydrocurcumin (THC) is the main metabolite of curcumin, which exerts the anti-diabetic activity. However, the underlying mechanism has not been clarified. In the research, we investigated whether THC could improve diabetes by regulating the gut microbiota and the expression of pancreatic glucagon-like peptide-1 (GLP-1) in the db/db mice. After 8-week THC administration (ig., once a day, THCH group: 200 mg/kg, THCL group: 100 mg/kg), the fasting blood glucose (FBG) was measured every two weeks. Serum insulin levels, the expression of GLP-1 in the pancreas, the histopathology of pancreas and the composition of gut microbiota were evaluated at the end of the experiment. Compared to the diabetic group, THC treatment decreased significantly blood glucose, increased the secretion of insulin and the expression of GLP-1 in the pancreas. Histomorphological analysis revealed that THC could protect pancreatic islet cells against hyperglycemic insult. Furthermore, the data from the sequencing of the 16S rDNA genes in gut microbiome displayed that THC could restore the intestinal dysbiosis, including the lowered relative abundance of Proteobacteria, Actinobacteria and the ratio of Firmicutes to Bacteroidetes. The linear regression analysis showed a close correlation between the GLP-1 expression and the proportion of the intestinal microflora. Altogether, these results demonstrated that THC might have a direct regulatory effect on gut microflora, which indirectly decrease the FBG levels by modulating GLP-1 expression in the pancreas.