Curcumin improves insulin sensitivity in high-fat diet-fed mice through gut microbiota

Insulin resistance precedes metabolic syndrome which increases the risk of type 2 diabetes and cardiovascular disease. However, there is a lack of safe and long-lasting

The effects of curcumin on promoting insulin sensitivity were dependent on gut microbiota in HFD-fed mice. Moreover, curcumin at least partly exerted its effects on increasing insulin sensitivity via FGF15 upregulation. This study provided new ideas on nutritional manipulations of gut microbiota for the treatment of metabolic diseases.

Glucose, insulin, and pyruvate tolerance were tested and hepatic triglycerides (TGs) content was measured in HFD-fed mice treated with curcumin (100 mg kg-1 d-1, p.o.) or vehicle for 4 weeks and aforementioned mice after gut microbiota depletion via antibiotic treatment for 4 weeks. Fecal microbiota transplantation (FMT) was conducted in endogenous gut microbiota-depleted HFD-fed mice. Glucose and lipid metabolic phenotypes were also measured in recipient mice colonized microbiota from vehicle- or curcumin-treated HFD-fed mice. The mechanisms underlying the effects of curcumin on increasing insulin sensitivity were testified by Western blotting, real-time quantitative polymerase chain reaction and enzyme-linked immunosorbent assay (ELISA).

Curcumin ameliorated HFD-induced glucose intolerance, insulin resistance, pyruvate intolerance, and hepatic TGs accumulation, while these effects were mediated by gut microbiota. Curcumin induced insulin-stimulated Akt phosphorylation levels in insulin-regulated peripheral tissues. The inhibitory effects of curcumin on the expressions of genes involved in hepatic gluconeogenesis and de novo lipogenesis were dependent on gut microbiota. Meanwhile, curcumin upregulated the expression of fibroblast growth factor 15 (FGF15) through gut microbiota. Conclusions: The effects of curcumin on promoting insulin sensitivity were dependent on gut microbiota in HFD-fed mice. Moreover, curcumin at least partly exerted its effects on increasing insulin sensitivity via FGF15 upregulation. This study provided new ideas on nutritional manipulations of gut microbiota for the treatment of metabolic diseases.