The water extract of Radix scutellariae, its total flavonoids and baicalin inhibited CYP7A1 expression, improved bile acid, and glycolipid metabolism in T2DM mice

Radix scutellariae (the root of Scutellaria baicalensis Georgi), is a traditional Chinese medicine (TCM) used to treat type 2 diabetes mellitus (T2DM). Abundant flavonoids are the antidiabetic components of Radix scutellariae, of which baicalin (Baicalein 7-O-glucuronide, BG) is the major bioactive component. Our previous studies found that the water extract of Radix scutellariae (WESB) could exert hypoglycemic and hypolipidemic efficacies by adjusting the ileum FXR-medicated interaction between gut microbiota and bile acid (BA) metabolism. However, it remains unclear whether WESB and its biologically active ingredients exert an antidiabetic effect through bile acid signaling mediated by FXR-CYP7A1. To explore the mechanism of WESB and its total flavonoids (TF) further and BG on BA signals and glycolipid metabolism in T2DM mice. The antidiabetic effects of WESB, TF and BG were evaluated by indexing the body weight, fasting blood glucose (FBG) and oral glucose tolerance test (OGTT) in HFD/STZ-induced (high-fat diet and streptozocin) diabetic mice, and comparing them with the positive control (metformin). The lipids in the mouse liver and the total bile acids (TBA) in the mouse liver and bile were detected by commercial kits. The concentration of BAs in the mouse feces was determined by liquid chromatography-tandem mass spectrometry. The protein expression levels of cholesterol 7α-hydroxylase (CYP7A1), farnesol X receptor (FXR), etc., in the liver and/or ileum, play a key role in the BAs metabolism of T2DM mice were evaluated by immunoblot analysis. The hyperglycemia and impaired glucose tolerance of T2DM mice were improved after WESB, TF and BG treatment. Especially after BG administration, the levels of low-density lipoprotein-cholesterol (LDL-c) and total glyceride (TG) in the T2DM mouse liver were significantly decreased (p < 0.05). While the level of high-density lipoprotein cholesterol (HDL-c) was significant increased (p < 0.001). Meanwhile, the levels of TBA in both the liver and bile of T2DM mice were significantly decreased by BG (p < 0.05). Moreover, the high expression of CYP7A1 in the liver of T2DM mice was significantly inhibited by WESB, TF and BG (p < 0.05), and the high expression of FXR in the ileum of T2DM mice was significantly inhibited by TF (p < 0.05). These results indicated that the hypoglycemic effects of WESB, TF and BG might be exerted by inhibiting the expression of CYP7A1 in T2DM mice, and TF inhibited expression of intestinal FXR by inducing changes in fecal BA profile. BG significantly improved hepatic lipid metabolism. Moreover, BG reduced lipid accumulation in the liver and bile by inhibiting the expression of CYP7A1 in T2DM mice. These findings provide useful explanations for the antidiabetic mechanism of Radix scutellariae.