Astragalus polysaccharides alleviates glucose toxicity and restores glucose homeostasis in diabetic states via activation of AMPK

Abstract

Aim: To establish the mechanism underlying the improvement of glucose toxicity by Astragalus polysaccharide (APS), which occurred via an AMP activated protein kinase (AMPK)-dependent pathway.

Methods: In vivo and in vitro effects of APS on glucose homeostasis were examined in a type 2 diabetes mellitus (T2DM) rat model. The T2DM rat model was duplicated by a high-fat diet (58% fat, 25.6% carbohydrate, and 16.4% protein) and a small dose of streptozotocin (STZ, 25 mg/kg, ip). After APS therapy (700 mg.kg(-1).d(-1), ig) for 8 weeks, blood glucose, glycosylated hemoglobin, and serum insulin were measured. Insulin sensitivity was evaluated by the comprehensive analysis of oral glucose tolerance tests (OGTT) and HOMA IR index. Hepatic glycogen was observed by the PAS staining method. The expression and activity of skeletal muscle AMPKalpha and acetyl-CoA carboxylase (ACC), and the phosphorylation of hepatic glycogen synthase (GS), the glycogen synthase (GS),were measured by Western blotting. Glucose uptake was measured with the 2-deoxy-[(3)H]-D-glucose method in C2C12 cells.

Results: The hyperglycemia status, insulin sensitivity, glucose uptake, and activation level of AMPK in diabetic rats were improved in response to APS administration. APS could also alleviate glucose toxicity in cultured mouse cells by the activation of AMPK.

Conclusion: APS can alleviate glucose toxicity by increasing liver glycogen synthesis and skeletal muscle glucose translocation in the T2DM rat model, via activation of AMPK.

Figure 1

Oral glucose tolerance tests (OGTT) test of experimental animals at the end of 9th week (A) and at the end of 17th week (B). All data are expressed by Mean±SEM. ^bP<0.05 vs A group. ^eP<0.05 vs C group, ^hP<0.05 vs DM group (at the same age).

Figure 2

Effect of APS on the content of hepatic glycogen and expression of protein of glycogen synthase (GS) and P-GS in the liver of animal models by Western immunoblotting. (A) Effect of APS on the content of hepatic glycogen in the liver of animal models. (B) Effect of APS on the hepatic glycogen in the liver of animal models (×1000, n=3). (C) Effect of APS on the expression of P-GS and GS in the liver of animal models (n=3). All data are expressed by mean±SEM. ^bP<0.05 vs C group (at the same age). ^eP<0.05 vs DM group (at the same age).

Figure 3

Effect of APS on the expression of protein of P-AMPKα, P-ACC AMPKα and Acetyl-CoA carboxylase (ACC) in the skeleton muscle of animal models by Western immunoblotting. All data are expressed by mean±SEM. n=3. ^bP<0.05 vs C group (at the same age). ^eP<0.05 vs DM group (at the same age).

Figure 4

Effect of APS on the expression of protein of GLUT4 in the plasmalemma lysate of skeleton muscle extract and cells extract of animal models by Western immunoblotting. All data are expressed by mean±SEM.n=3. ^bP<0.05 vs C group(at the same age); ^eP<0.05 vs DM group (at the same age).

Figure 5

Effect of APS on the expression of protein of P-AMPKα and AMPKα in the APS-treated C2C12 cell model by Western immunoblotting. Control cells were treated with the vehicle (DMSO) in an identical manner. Cells from APS group were treated with APS for 48 h, cells from AICAR group were ere treated with AICAR (0.5 mmol/L) for 30 min. All data are expressed by mean±SEM. n=3. ^bP<0.05 vs Control group.

Figure 6

Concentration for insulin (100 nmol/L, 15 min), APS (200 μg/mL, 48 h), AICAR (5 mmol/L, 30 min), and Compound C (20 μmol/L, 30 min) treatment on 2-deoxy-[³H]-D-glucose uptake in differentiated C2C12 cells. All data are expressed by mean±SEM. n=4. ^bP<0.05 vs DMSO group; ^eP<0.05 vs APS group.

Figure 7

Effect of APS on the high glucose (HG)-treated C2C12 cell model. Analysis of the expression of protein of P-AMPKα by Western immunoblotting and glucose uptake by 2-deoxy-[³H]-D-glucose method. (A) Effect of APS on the expression of P-AMPKα of high glucose-treated C2C12 cell model (n=3). (B) Effect of APS on the glucose uptake of high glucose-treated C2C12 cell model (n=4). All data are expressed by mean±SEM. ^bP<0.05 vs DMSO group; ^eP<0.05 vs HG group, ^hP<0.05 vs HG+APS group.