Korean J Physiol Pharmacol.  2017 May;21(3):279-286. 10.4196/kjpp.2017.21.3.279.

Identification of AMPK activator from twelve pure compounds isolated from Aralia Taibaiensis: implication in antihyperglycemic and hypolipidemic activities

• Li Y
• Park J
• Wu Y
• Cui J
• Jia N
• Xi M
• Wen A

• KMID: 2376955
• DOI: http://doi.org/10.4196/kjpp.2017.21.3.279

Abstract

The root bark extract of Aralia taibaiensis is used traditionally for the treatment of diabetes mellitus in China. The total saponin extracted from Aralia Taibaiensis (sAT) has effective combined antihyperglycemic and hypolipidemic activities in experimental type 2 diabetic rats. However, the active compounds have not yet been fully investigated. In the present study, we examined effects of twelve triterpenoid saponins on AMP-activated protein kinase (AMPK) activation, and found that compound 28-O-β-D-glucopyranosyl ester (AT12) significantly increased phosphorylation of AMPK and Acetyl-CoA carboxylase (ACC). AT12 effectively decreased blood glucose, triglyceride (TG), free fatty acid (FFA) and low density lipoprotein-cholesterol (LDL-C) levels in the rat model of type 2 diabetes mellitus (T2DM). The mechanism by which AT12 activated AMPK was subsequently investigated. Intracellular ATP level and oxygen consumption were significantly reduced by AT12 treatment. The findings suggested AT12 was a novel AMPK activator, and could be useful for the treatment of metabolic diseases.

Keyword

AMPK; Antihyperglycemic activity; Hypolipidemic activity; T2DM; 28-O-β-D-glucopyranosyl ester (AT12)

MeSH Terms

Acetyl-CoA Carboxylase
Adenosine Triphosphate
AMP-Activated Protein Kinases*
Animals
Aralia*
Blood Glucose
China
Diabetes Mellitus
Diabetes Mellitus, Type 2
Metabolic Diseases
Models, Animal
Oxygen Consumption
Phosphorylation
Rats
Saponins
Triglycerides
AMP-Activated Protein Kinases
Acetyl-CoA Carboxylase
Adenosine Triphosphate
Blood Glucose
Saponins

Figure

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  Fig. 1 Structures of 12 pure compounds isolated from Aralia Taibaiensis.The Figure shows structures of 12 pure compounds isolated from Aralia Taibaiensis Ara. Ara, α-L-arabinopyranosyl; Glc, β-D-glucopyranosyl.

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  Fig. 2 Effects of sAT and the compounds on glucose or lipid metabolism, and AMPK phosphorylation.STZ induced T2DM rats (n=6) were intragastricly administrated daily with different doses of sAT (L: 75 mg/kg/d; M: 150 mg/kg/d; H: 300 mg/kg/d) and glibenclamide (0.25 mg/kg/d) for 4 weeks. After treatment, all of the rats were fasted overnight. (A) The body weight and (B) fasting blood glucose levels were measured. The data were presented as the mean±SD from three independent experiments. *p<0.05, **p<0.01 vs. T2DM rats treated with vehicle alone.

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  Fig. 3 Effects of 12 triterpenoid saponins on AMPK and ACC phosphorylation.C2C12 myocytes were treated with 12 species of triterpenoid saponins (1 µg/ml) for 30 min respectively. Whole cell lysates were separated by SDS-PAGE and then immunoblot was performed using indicated antibodies (top); The phosphorylation of AMPK and ACC were determined and normalized to total (bottom). The data were presented as the mean±SD from three independent experiments. *p<0.05, **p<0.01 vs. vehicle.

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  Fig. 4 Effects of four triterpenoid saponins on blood glucose and lipid levels.(A) T2DM rats (n=6) were intragastricly administrated daily with AT4, AT10, AT11 or AT12 (300 mg/kg/d) respectively for 4 weeks. After treatment, all of the rats were fasted overnight. The fasting blood glucose level was measured; (B) TG and FFA levels in the serum were measured. The data were presented as the mean±SD from three independent experiments. #p<0.05, ##p<0.01 vs. normal rats; *p<0.05, **p<0.01 vs. T2DM rats treated with vehicle alone.

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  Fig. 5 AT12 increased phosphorylation of AMPK and ACC in skeletal muscle.Immunoblot of phosphorylated AMPK and ACC levels in the skeletal muscles of T2DM rats and T2DM rats treated with AT12. Relative band intensity was shown. *p<0.05, **p<0.01 vs. T2DM rats treated with vehicle alone.

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  Fig. 6 AT12 decreased the intracellular ATP level and oxygen consumption.(A) C2C12 cells were treated with 0.5, 1, 2 µg/ml AT12 for 2 h. Total intracellular ATP levels were measured; (B) Equal volumes of packed C2C12 cells were separated into aliquots in wells of a 96-well BD Oxygen Biosensor plate in the presence of vehicle or 1 µg/ml AT12. The fluorescence in each well was recorded with a SAFIRE multimode microplate spectrophotometer. The data were presented as the mean±SD from three independent experiments. *p<0.05, **p<0.01 vs. vehicle.

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