Antidiabetic effects of flavonoids from Sophora flavescens EtOAc extract in type 2 diabetic KK-ay mice

Ethnopharmacological relevance: Bitter and cold Chinese medicines have been long used for the treatment for diabetes mellitus (DM) for thousands of years in China. The roots of Sophora flavescens Ait., one of bitter and cold Chinese medicines commonly used to remove lung heat have been used to counteract DM and exerted good clinical effects for diabetic patients in some folk hospitals in Fujian province, PR China. However, the corresponding active principles and antidiabetic mechanism of this Traditional Chinese Medicine remain unclear. Therefore, in this study, we aim at chemical profiling of the active principles, validating the potential antidiabetic effects of the active EtOAc extract (SF-EtOAc) in vitro and in vivo, and elucidating its probable antidiabetic mechanism as well as evaluating its acute oral toxicity.

Materials and methods: An off-line semi-preparative LC-NMR and LC-UV-ESI MS protocol was developed to determine the chemical principles of the active EtOAc extract rapidly and unambiguously. The effect of SF-EtOAc on the glucose transporter type 4 (GLUT4) translocation in L6 myotubes was examined. T2DM KK-Ay mice were induced by high-fat diet. SF-EtOAc was orally administration at the dose of 30, 60 and 120 mg/kg/d, for 21 days. Metformin was used as positive control. Body weight, plasma glucose, oral glucose tolerance test, serum Insulin and blood-lipid indexes were measured. Phosphorylation of the AMP-activated protein kinase (AMPK) expression in liver was measured.

Results: We found that SF-EtOAc significantly improved oral glucose tolerance, increased serum high density lipoprotein Cholesterol (HDL-C) and reduced body weight, blood glucose levels and other related blood-lipid indexes. Mechanistically, SF-EtOAc elevated phosphorylation of AMP-activated protein kinase (AMPK) and stimulated membrane translocation of GLUT4. Moreover, it was unveiled that oral median lethal dose (LD50) of SF-EtOAc was more than 7500 mg/kg, suggesting that SF-EtOAc was practically non-toxic for mice.

Conclusions: SF-EtOAc improves glucose tolerance, reduces hyperglycemia and resumes Insulin levels, at least in part, by activating GLUT4 translocation which may be modulated by AMPK pathway. According to the results of the present study, SF-EtOAc possesses a potent antidiabetic activity and could be used as a safe remedy for the treatment of diabetes.