The role of quantitative changes in the epxression of insulin receptor substrate-1 and nuclear ubiquitin in abnormal glycometabolism in the livers of KKay mice and the relative therapeutic mechanisms of Astragalus polysaccharide.

Ubiquitin and the ubiquitination pathway are important regulators of insulin signaling. The insulin receptor substrate­1 (IRS-1), an ubiquitin-interacting adaptor protein, serves as the key docking protein in insulin signaling. The effects of this dynamic interaction and the changes in ubiquitin expression on hepatic insulin signaling, as well as the relative therapeutic effects of Astragalus polysaccharide (APS) have not yet been elucidated. In this study, we aimed to investigate the abnormal changes which occur in the levels of IRS-1 and ubiquitin in the livers of mice (mice with insulin resistance and diabetes), and to elucidate the possible mechanisms responsible for these changes. A control group (CG), an insulin resistance group (IG) and a diabetes group (DG) were respectively composed of 12-week-old C57BL/6J mice fed a normal diet, C57BL/6J mice fed a high­fat diet and KKay mice fed a high­fat diet, and treatment groups were composed of corresponding groups treated with APS (CG + A, IG + A, DG + A). All the mice were age-matched and grouped at random. After eight weeks, the mouse models were successfully established and the related physiological or biochemical indexes were detected using corresponding methods. Ubiquitin expression in the liver was detected by immunohistochemisty, and western blot analysis was used to detect the expression of IRS-1 and ubiquitin. The results revealed that the expression of IRS-1 in the DG was significantly lower compared to that in the CG and IG; however, the nuclear expression of ubiquitin and the ubiquitination levels of IRS-1, including body weight and blood glucose and triglyceride levels in the DG were significantly higher compared to those in the CG or IG (P<0.05). There was a significant improvement in the ubiquitination levels in DG + A, including the blood glucose and triglyceride levels compared with the DG (P<0.05). From the stage of insulin resistance to the stage of diabetes, the reduced expression of IRS-1 and its enhanced ubiquitination levels combined with the overexpression of nuclear ubiquitin contributed to the abnormal glycometabolism and the disruption of insulin signaling. APS showed beneficial effects, such as lowering body weight, as well as blood glucose and triglyceride levels, and these effects correlated with the downregulation of the ubiquitination levels of IRS-1 and the nuclear expression of ubiquitin.

Astragalus polysaccharide induces anti-inflammatory effects dependent on AMPK activity in palmitate-treated RAW264.7 cells.

Astragalus polysaccharide (APS) has been reported to increase insulin sensitization and to ameliorate diabetes in animal models, and studies have demonstrated that this effect may be correlated with its anti-inflammatory roles in vivo and in vitro. However, the potential pharmacological mechanisms of APS in anti-inflammatory regulation are still poorly understood. Herein, RAW264.7 cells treated with APS showed anti-inflammatory effects. Interleukin (IL)-10 protein levels and expression of most of the anti-inflammatory genes, including IL-10, macrophage mannose receptor (MMR), arginase, Dectin-1, YM-1 and YM-2, were significantly increased after treatment with APS for 24 h. Furthermore, to determine whether APS plays a potential role in RAW264.7 cell inflammation, we pretreated RAW264.7 cells with APS in the presence of palmitate. The results showed that APS markedly recovered the impairment of AMPK activity induced by palmitate. Furthermore, APS induced IL-10 protein production and anti-inflammatory gene expression of IL-10, MMR, Dectin-1, arginase, YM-1 and YM-2. Additionally, APS inhibited IL-1ß protein production and expression of most of the pro-inflammatory genes, such as IL-1ß, iNOS, MCP-1, IL-6 and CD11c but not tumor necrosis factor (TNF)-α. Notably, the effect of APS on inflammatory genes, except for TNF-α, was abrogated when AMPK activity was inhibited using a DN-AMPK plasmid. These results suggest that APS effectively ameliorates palmitate-induced pro-inflammatory responses through AMPK activity.

The effect of astragalin on the VEGF production of cultured Müller cells under high glucose conditions.

Diabetic retinopathy (DR) is a severe complication of diabetes mellitus (DM) and often causes vision loss or even blindness. Vascular endothelial growth factor (VEGF) in the retina, which is mainly derived from Müller cells, is a crucial biological factor in the development of DR. Astragalin is extracted from Astragalus membranaceus and has many pharmacological properties. Studies showed that astragalin has beneficial effects on hyperglycemia. To evaluate the effect of astragalin in preventing and treating DR and determine astragalin's mechanism of action, Müller cells were collected from rat retina, cultured in vitro and identified using immunocytochemistry. They were divided into four groups: the high glucose group (20 mmol/l), the normal control group, the astragalin group (400 mg/l) and the high glucose (20 mmol/l) + astragalin (400 mg/l) group. After 3 days of treatment, immunocytochemical and reverse transcription-polymerase chain reaction (RT-PCR) analysis of VEGF was carried out. Our results demonstrated that astragalin decreased the overexpression of VEGF in Müller cells and alleviated the effects caused by high glucose. Thus, astragalin has promising application in preventing and treating DR caused by DM.

Astragalus polysaccharide improves insulin sensitivity in KKAy mice: regulation of PKB/GLUT4 signaling in skeletal muscle.

ETHNOPHARMACOLOGICAL RELEVANCE: Astragalus polysaccharide (APS) is an important bioactive component of Astragalus membranaceus Bunge (Leguminosae) that has been used in traditional Chinese medicine for treating diabetes. AIM OF THE STUDY: To study the mechanisms by which APS ameliorates diabetes, we examined whether treatment with APS improves insulin sensitivity in insulin-resistant mice and whether this is associated with an improvement of dysregulated protein kinase B and glucose transporter 4 expressions in skeletal muscle. METHODS: APS (700 mg kg(-1)day(-1)) or vehicle was administered to 12-week-old diabetic KKAy and nondiabetic C57BL/6J mice for 8 weeks. Changes in body weight, blood glucose level, insulin resistance index, and oral glucose tolerance were routinely evaluated. The expressions of protein kinase B and glucose transporter 4 in skeletal muscle tissues were determined with Western blot. RESULTS: KKAy mice developed persistent hyperglycemia, impaired glucose tolerance and insulin resistance. Insulin-stimulated protein kinase B phosphorylation and glucose transporter 4 translocation were significantly decreased in KKAy compared to age-matched C57BL/6J mice. APS treatment ameliorated hyperglycemia and insulin resistance. Although the content of protein kinase B and glucose transporter 4 in KKAy skeletal muscle were not affected by APS, insulin-induced protein kinase B Ser-473 phosphorylation and glucose transporter 4 translocation in skeletal muscle were partially restored by APS treatment. In contrast, APS did not have any effect on C57BL/6J mice. CONCLUSIONS: These results indicate that APS can regulate part of the insulin signaling in insulin-resistant skeletal muscle, and that APS could be a potential insulin sensitizer for the treatment of type 2 diabetes.

Hypoglycemic effect of polysaccharide enriched extract of Astragalus membranaceus in diet induced insulin resistant C57BL/6J mice and its potential mechanism.

Our previous studies found that Astragalus polysaccharide (APS) exerts insulin-sensitizing and hypoglycemic activities in type 2 diabetic (T2DM) rats. The present study was designed to further confirm the hypoglycemic effect of APS and to investigate its possible mechanism underlying the improvement of insulin resistance in vivo and in vitro. Diet-induced insulin resistant C57BL/6J mice treated with or without APS (orally, 700 mg/kg/d) for 8 weeks were analyzed and compared. Simultaneously, an insulin resistant C(2)C(12) cell model and an ER stressed HepG2 cell model were established and incubated with or without APS (200 microg/ml) for 24h respectively. Systematic insulin sensitivity was measured with an insulin-tolerance test (ITT) and an homeostasis model assessment (HOMA IR) index. Metabolic stress variation was analyzed for biochemical parameters and pathological variations. The expression and activity of protein tyrosine phosphatase 1B (PTP1B), which plays a very important role in insulin signaling and in the ER stress response, was measured by immunoprecipitation and Western blot. The ER stress response was analyzed through XBP1 transcription and splicing by real-time PCR. APS could alleviate insulin resistance and ER stress induced by high glucose in vivo and in vitro, respectively. The hyperglycemia, hypolipemia, and hyperinsulinemia status were controlled with APS therapy. Insulin action in the liver of insulin resistant mice was restored significantly with APS administration. APS enhanced adaptive capacity of the ER and promoted insulin signaling by the inhibition of the expression and activity of PTP1B. Furthermore, the anti-obesity effect and hypolipidemia effects of APS were probably due partly to decreasing the leptin resistance of mice, which would positively couple with the normalization of plasma insulin levels. We have shown that APS has beneficial effects on insulin resistance and hyperglycemia. The mechanism is related to the alleviation of ER stress and insulin resistance under hyperglycemia conditions.

Propofol dose-dependently reduces tumor necrosis factor-alpha-Induced human umbilical vein endothelial cell apoptosis: effects on Bcl-2 and Bax expression and nitric oxide generation.

We investigated whether propofol can inhibit tumor necrosis factor (TNF)-alpha-induced apoptosis in cultured human umbilical vein endothelial cells (HUVECs). Isolated HUVECs were cultured in Dulbecco's modified Eagle medium supplemented with 20% bovine calf serum. HUVECs in untreated and propofol control groups were cultured at 37 degrees C for 24.5 h. HUVECs in the TNF treatment groups were initially cultured for 30 min in the presence of TNF or various concentrations of propofol, respectively, which were then cultured for 24 h with the addition of TNF at 40 ng/mL in the medium. Apoptosis was detected using terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) and confirmed by electron microscopy. The antiapoptotic Bcl-2 and proapoptotic Bax protein expressions were measured by immunocytochemical analysis. TNF stimulation resulted in a reduced Bcl-2/Bax ratio and increased apoptotic index (AI: percentage of apoptotic cells) in HUVECs. Propofol, at concentrations >/=12 muM, significantly (P < 0.001) and dose-dependently attenuated TNF-induced increase in AI and decrease in Bcl-2/Bax ratio. This was accompanied by increases in nitric oxide production. There is an inverse correlation between the ratio of Bcl-2/Bax expression and AI (P = 0.0009). These results suggest that propofol, at clinical relevant concentrations, can reduce TNF-induced HUVEC apoptosis.