Water Extract of Potentilla discolor Bunge Improves Hepatic Glucose Homeostasis by Regulating Gluconeogenesis and Glycogen Synthesis in High-Fat Diet and Streptozotocin-Induced Type 2 Diabetic Mice

Abstract

Potentilla discolor Bunge, as a traditional Chinese medicine, exhibits many phytochemical activities. The aim of the present study was to investigate the effects of Potentilla discolor Bunge water extract (PDBW) and its underlying mechanisms on gluconeogenesis and glycogen synthesis in high-fat diet/streptozotocin (HFD/STZ)-induced type 2 diabetic mice. LC-MS/MS analyses of PDBW identified 6 major compounds including apigenin-7-O-β-D-glucoside, epicatechin, quercetin 3-O-β-D-glucuronide, kaempferol-3-O-β-D-glucopyranoside, scutellarin, and quercitrin. In the study, a mouse model of type 2 diabetes was induced by 4-week HFD combined with STZ (40 mg/kg body weight) for 5 days. After oral administration of PDBW at 400 mg/kg body weight daily for 8 weeks, the mice with type 2 diabetes showed significant decrease in the levels of fasting blood glucose and glycated hemoglobin A1c (HbA1c), and increase in the insulin level. PDBW improved the glucose tolerance, insulin sensitivity and lipid profiles. Furthermore, PDBW inhibited the mRNA levels of key gluconeogenic enzymes [phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase)] in liver. PDBW also promoted glycogen synthesis by raising the liver glycogen content, decreasing the phosphorylation of glycogen synthase (GS) and increasing the phosphorylation of glycogen synthase kinase3β (GSK3β). Besides, PDBW induced the activation of protein kinase B (Akt) and AMP-activated protein kinase (AMPK), which might explain changes in the phosphorylation of above enzymes. In summary, PDBW supplementation ameliorates metabolic disorders in a HFD/STZ diabetic mouse model, suggesting the potential application of PDBW in prevention and amelioration of type 2 diabetes.

Keywords: Potentilla discolor Bunge; gluconeogenesis; glycogen synthesis; insulin sensitivity; type 2 diabetes.

Figure 1

LC-MS/MS spectra of main components in Potentilla discolor Bunge water extract (PDBW): (1) apigenin-7-O-β-D-glucoside, (2) epicatechin, (3) quercetin 3-O-β-D-glucuronide, (4) kaempferol-3-O-β-D-glucopyranoside, (5) scutellarin, and (6) quercitrin.

Figure 2

Effects of Potentilla discolor Bunge water extract (PDBW) on fasting blood glucose and HbA1c levels in HFD-STZ induced diabetic mice. (A) The levels of fasting blood glucose after PDBW treatment. (B) The levels of HbA1c after 8 weeks treatment with PDBW. All values are means ± SEM (n = 8); Values marked with different lower-case letters in superscript format indicate significant differences among groups (p < 0.05).

Figure 3

Effects of Potentilla discolor Bunge water extract (PDBW) on oral glucose tolerance (OGTT), intraperitoneal insulin tolerance (IPITT), and pyruvate tolerance test (PTT) in HFD-STZ induced diabetic mice. Blood glucose levels (A) and area under the curve (AUC) (B) for the blood glucose levels during OGTT. Blood glucose levels (C) and AUC (D) for the blood glucose levels during IPITT. The graph displays blood glucose levels expressed as a percentage of the initial blood glucose level following an overnight fast. Blood glucose levels (E) and AUC (F) for the blood glucose levels during PTT. All values are the mean ± standard error (n = 8); Values marked with different lower-case letters in superscript format indicate significant differences between three groups (p < 0.05).

Figure 4

Effects of Potentilla discolor Bunge water extract (PDBW) on histological changes in liver (H&E, 200×) of HFD-STZ induced diabetic mice. Blue arrows indicate central veins. Yellow arrows indicate lipid droplets.

Figure 5

Effects of Potentilla discolor Bunge water extract (PDBW) on the phosphoenolpyruvate carboxykinase and glucose-6-phosphatase mRNA gene expression in liver of HFD-STZ induced diabetic mice. All values are the mean ± standard error (n = 6); Values marked with different lower-case letters in superscript format indicate significant differences between three groups (p < 0.05).

Figure 6

Effects of Potentilla discolor Bunge water extract (PDBW) on glycogenesis in liver of HFD-STZ induced diabetic mice. (A) Hepatic glycogen content. (B) Hepatic protein expression of p-GSK3β, GSK3β, p-GS, and GSK3β. All values are the mean ± standard error (n = 6); Values marked with different lower-case letters in superscript format indicate significant differences between three groups (p < 0.05).

Figure 7

Effects of Potentilla discolor Bunge water extract (PDBW) on hepatic protein contents of p-Akt, Akt, p-AMPK, and AMPK. All values are the mean ± standard error (n = 6); Values marked with different lower-case letters in superscript format indicate significant differences between three groups (p < 0.05).