Combined effects of Scutellaria baicalensis with metformin on glucose tolerance of patients with type 2 diabetes via gut microbiota modulation

Metformin is a widely prescribed antidiabetic agent, whereas Scutellaria baicalensis (SB) is a commonly used medicinal herb for treatment of type 2 diabetes (T2D). Gut microbiota is involved in pathophysiology of metabolic diseases including T2D, and intestinal microbiota may be one of the important therapeutic targets for the ailment. This study was conducted to investigate the effects of SB combined with metformin on treatment of T2D while evaluating changes in the gut microbiota composition. Patients with T2D were randomized into control and treatment groups. Subjects who had already been prescribed metformin were allotted to additional SB (3.52 g/day) group or placebo group. The initial treatment session was 8 wk, and after washout period for 4 wk they were crossed over to the opposite treatment for another 8 wk. The influence of SB and placebo on the intestinal microbiota was analyzed by MiSeq system based on 16S rRNA gene. Glucose tolerance was lower in the SB group than the placebo group. Similarly, the relative RNA expression of TNF-α was significantly reduced after SB treatment. SB treatment influenced the gut microbiota, especially Lactobacillus and Akkermansia, which showed remarkable increases after SB treatment. Some subjects showed high liver enzyme levels after SB treatment, and their microbiota composition at baseline differed with subjects whose liver enzymes were not affected. We also predicted that selenocompound metabolism was increased and naphthalene degradation was decreased after SB treatment. These results suggest that SB with metformin treatment may improve the glucose tolerance and inflammation and influence the gut microbiota community in T2D.