Nutr Res Pract.  2013 Feb;7(1):15-21.

Sasa borealis extract exerts an antidiabetic effect via activation of the AMP-activated protein kinase

• Nam JS
• Chung HJ
• Jang MK
• Jung IA
• Park SH
• Cho SI
• Jung MH

Abstract

Leaf of Sasa borealis, a species of bamboo, has been reported to exhibit anti-hyperglycemic effect. However, its antidiabetic mechanism is not fully understood. In this study, we examined whether an extract of S. borealis activates AMP-activated protein kinase (AMPK) and exerts anti-hyperglycemic effects. Treatment with the S. borealis extract increased insulin signaling and phosphorylation of AMPK and stimulated the expression of its downstream targets, including PPARalpha, ACO, and CPT-1 in C2C12 cells and PPARalpha in HepG2 cells. However, inhibition of AMPK activation attenuated insulin signaling and prevented the stimulation of AMPK target genes. The S. borealis extract increased glucose uptake in C2C12 cells and suppressed expression of the gluconeogenic gene, PEPCK in HepG2 cells. The extract significantly reduced blood glucose and triglyceride levels in STZ-induced diabetic mice. The extract enhanced AMPK phosphorylation and increased Glut-4 expression in the skeletal muscle of the mice. These findings demonstrated that the S. borealis extract exerts its anti-hyperglycemic effect through activation of AMPK and enhancement of insulin signaling.

Keyword

Antidiabetic effect; AMP-activated protein kinase; Sasa borealis; insulin signaling

MeSH Terms

AMP-Activated Protein Kinases
Animals
Blood Glucose
Glucose
Hep G2 Cells
Insulin
Mice
Muscle, Skeletal
Phosphorylation
PPAR alpha
Sasa
AMP-Activated Protein Kinases
Blood Glucose
Glucose
Insulin
PPAR alpha

Figure

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  Fig. 1 Cytotoxicity of Sasa borealis extracts. C2C12 or HepG2 cells were treated with three different concentractions of the extract (Ext) (10, 20, 40 µg/ml) for 24 h. Cell cytotoxicity was measured by MTT assay.

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  Fig. 2 Sasa borealis extract augments insulin signaling in C2C12 and HepG2 cells. C2C12 or HepG2 cells were treated with the extract (Ext) (40 µg/ml) for 24 h and then incubated with insulin (100 nM) for 1 h. Levels of phosphorylated IRS-1 (pIRS-1) was evaluated by western blotting. All experiments were performed three times, and representative figures are shown. The bars represent the relative densitometric values compared to untreated samples. The values are expressed as the mean ± SE (*P < 0.05).

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  Fig. 3 Sasa borealis extract activates AMPK in C2C12 and HepG2 cells. (A) C2C12 cells were treated with the extract (40 µg/ml) for 24 h in the absence or presence of compound C (10 µM) (Comp.C). Phosphorylated AMPK (pAMPK) was assessed by western blotting. The expression of AMPK target genes was evaluated by RT-PCR using gene specific primers. (B) HepG2 cells were treated with the extract (40 µg/ml) for 24 h in the absence or presence of compound C (10 µM). Levels of pAMPK were assessed by western blotting. The expression of AMPK target genes was assessed by RT-PCR, Actin was used as the internal control. All experiments were performed three times, and representative figures are shown. The bars represent the relative densitometric values compared to untreated samples. The values are expressed as the mean ± SE (*P < 0.05; **P < 0.01).

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  Fig. 4 Sasa borealis extract activates insulin signaling through AMPK activation. C2C12 cells or HepG2 cells were treated with the extract (40 µg/ml) for 24 h in the absence or presence of compound C (10 µM) and incubated with insulin for 1 h. Level of pIRS-1 was assessed by western blotting. All experiments were performed three times, and representative figures are shown. The bars represent the relative densitometric values compared to untreated samples. The values are expressed as the mean ± SE (*P < 0.05, **P < 0.01).

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  Fig. 5 Sasa borealis extract enhances glucose uptake in C2C12 cells and suppresses PEPCK gene expression in HepG2. (A) C2C12 cells were treated with the extract (40 µg/ml) and incubated with insulin for 1 h, and insulin-stimulated 2-NBDG uptake was measured. The relative fluorescence intensities, minus the background levels, were used for statistical analyses. The values are expressed as the mean ± SE and were determined from 3 independent experiments (*P < 0.05). (B) HepG2 cells were treated with the extract (40 µg/ml) for 24 h in the absence or presence of cAMP/dexamethasone (Dex). PEPCK expression was evaluated by RT-PCR. Actin was used as the internal control.

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  Fig. 6 Sasa borealis extract decreases blood glucose and triglyceride levels in mice with STZ-induced diabetes. The extracts (300 and 500 mg/kg body weight) were administrated daily to STZ-mice for 2 weeks. The blood glucose levels from fasting mice were determined on the indicated day. Values are the mean ± SE (n = 7) (*P < 0.05; **P < 0.001).

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  Fig. 7 Sasa borealis extract increased AMPK phosphorylation and Glut4 expression in skeletal muscle of STZ-mice. (A) Lysates of soleus skeletal muscles were prepared from mice treated with STZ alone (STZ) or with STZ and extract (500 mg/kg) (STZ + 500) and were subjected to western blotting using an antibody specific for pAMPK. (B) Total RNA was prepared from soleus skeletal muscles of STZ-treated mice and subjected to RT-PCR using Glut4-specific primers.

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