Original Articles

Hypoglycemic effect of Astragalus polysaccharide and its effect on PTP1B

Authors: Yong WU, Jing-ping OU-YANG, Ke WU, Ya WANG, Yun-feng ZHOU, Chong-yuan WEN

Abstract

Aim: To examine the effects of Astragalus polysaccharide (APS), a component of
an aqueous extract of Astragalus membranaceus roots, on protein tyrosine phosphatase
1B (PTP1B), a negative regulator of insulin-receptor (IR) signal
transduction, and its potential role in the amelioration of insulin resistance.
Methods:Ten-week-old fat-fed streptozotocin (STZ)-treated rats, an animal model
of type II diabetes mellitus (TIIDM), were treated with APS (400 mg/kg po) for 5
weeks. Insulin sensitivity was identified by the insulin-tolerance test. Further analyses
on the possible changes in insulin signaling occurring in skeletal muscle and
liver were performed by immunoprecipitation or Western blotting. PTP1B activity
was measured by an assay kit. Results: The diabetic rats responded to APS
with a significant decrease in body weight, plasma glucose, and improved insulin
sensitivity. The activity and expression of PTP1B were elevated in the skeletal
muscle and liver of TIIDM rats. Thus the insulin signaling in target tissues was
diminished. APS reduced both PTP1B protein level and activity in the muscle,
but not in the liver of TIIDM rats. Insulin-induced tyrosine phosphorylation of the
IR β-subunit and insulin receptor substrate-1 (IRS-1) were increased in the muscle,
but not in the liver of APS-treated TIIDM rats. There was no change in the activity
or expression of PTP1B in APS-treated normal rats, and blood insulin levels did
not change in TIIDM rats after treatment with APS. Conclusion: APS enables
insulin-sensitizing and hypoglycemic activity at least in part by decreasing the
elevated expression and activity of PTP1B in the skeletal muscles of TIIDM rats.
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