Astragalus polysaccharide stimulates glucose uptake in L6 myotubes through AMPK activation and AS160/TBC1D4 phosphorylation.

AIM: To establish the mechanism responsible for the stimulation of glucose uptake by Astragalus polysaccharide (APS), extracted from Astragalus membranaceus Bunge, in L6 myotubes in vitro. METHODS: APS-stimulated glucose uptake in L6 myotubes was measured using the 2-deoxy-[(3)H]-D-glucose method. The adenine nucleotide contents in the cells were measured by HPLC. The phosphorylation of AMP-activated protein kinase (AMPK) and Akt substrate of 160 kDa (AS160) was examined using Western blot analysis. The cells transfected with 4P mutant AS160 (AS160-4P) were constructed using gene transfer approach. RESULTS: Treatment of L6 myotubes with APS (100-1600 µg/mL) significantly increased glucose uptake in time- and concentration-dependent manners. The maximal glucose uptake was reached in the cells treated with APS (400 µg/mL) for 36 h. The APS-stimulated glucose uptake was significantly attenuated by pretreatment with Compound C, a selective AMPK inhibitor or in the cells overexpressing AS160-4P. Treatment of L6 myotubes with APS strongly promoted the activation of AMPK. We further demonstrated that either Ca(2+)/calmodulin-dependent protein kinase kinase ß (CaMKKß) or liver kinase B1 (LKB1) mediated APS-induced activation of AMPK in L6 myotubes, and the increased cellular AMP: ATP ratio was also involved. Treatment of L6 myotubes with APS robustly enhanced the phosphorylation of AS160, which was significantly attenuated by pretreatment with Compound C. CONCLUSION: Our results demonstrate that APS stimulates glucose uptake in L6 myotubes through the AMP-AMPK-AS160 pathway, which may contribute to its hypoglycemic effect.

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

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.

Efficient generation of CD34+ progenitor-derived dendritic cells from G-CSF-mobilized peripheral mononuclear cells does not require hematopoietic stem cell enrichment.

As a result of their potent antigen-presentation function, dendritic cells (DC) are important tools for cell therapy programs. In vitro-generated DC from enriched CD34+ hematopoietic stem cells (HSC; enriched CD34 DC) have already proven their efficiency in Phase I/II clinical trials. Here, we investigated whether enrichment of CD34+ HSC before the onset of culture was absolutely required for their differentiation into DC. With this aim, we developed a new two-step culture method. PBMC harvested from G-CSF-mobilized, healthy patients were expanded for 7 days during the first step, with early acting cytokines, such as stem cell factor, fetal liver tyrosine kinase 3 ligand (Flt-3L), and thrombopoietin. During the second step, expanded cells were then induced to differentiate into mature DC in the presence of GM-CSF, Flt-3L, and TNF-alpha for 8 days, followed by LPS exposure for 2 additional days. Our results showed that the rate of CD34+/CD38+/lineageneg cells increased 19.5+/-10-fold (mean+/-sd) during the first step, and the expression of CD14, CD1a, CD86, CD80, and CD83 molecules was up-regulated markedly following the second step. When compared with DC generated from enriched CD34+ cells, which were expanded for 7 days before differentiation, DC derived from nonenriched peripheral blood stem cells showed a similar phenotye but higher yields of production. Accordingly, the allogeneic stimulatory capacity of the two-step-cultured DC was as at least as efficient as that of enriched CD34 DC. In conclusion, we report herein a new two-step culture method that leads to high yields of mature DC without any need of CD34+ HSC enrichment.

The regulatory role of dendritic cells in the immune tolerance.

Immune homeostasis is important for the protection of a host from pathogen aggression, as well as for preventing autoimmunity. Dendritic cells (DCs), the most potent antigen presenting cells, are critical in innate, adaptive immunity and in central tolerance. Recently, their involvement in peripheral tolerance has been shown. Whether DCs induce immunity or tolerance depends on their state of maturation. Different subsets of tolerogenic DCs have been identified in vivo, either in physiological, or pathological conditions, such as tumors, or GVHD. Moreover, tolerogenic DCs can be generated in vitro, by using different culture conditions, such as IL-10 or TGF-beta. In our study, we obtained tolerogenic DCs, by culturing them in the presence of human mesenchymal stem cells (MSCs).

Human mesenchymal stem cells license adult CD34+ hemopoietic progenitor cells to differentiate into regulatory dendritic cells through activation of the Notch pathway.

The mechanisms underlying the immunomodulatory functions of mesenchymal stem cells (MSC) on dendritic cells (DC) have been shown to involve soluble factors, such as IL-6 or TGF-beta, or cell-cell contact, or both depending on the report referenced. In this study, we intend to clarify these mechanisms by examining the immunosuppressive effect of human adult MSC on adult DC differentiated from CD34(+) hemopoietic progenitor cells (HPC). MSC have been shown to inhibit interstitial DC differentiation from monocytes and umbilical CD34(+) HPC. In this study, we confirm that MSC not only halt interstitial DC but also Langerhans cell differentiation from adult CD34(+) HPC, as assessed by the decreased expression of CD1a, CD14, CD86, CD80, and CD83 Ags on their cell surface. Accordingly, the functional capacity of CD34(+) HPC-derived DC (CD34-DC) to stimulate alloreactive T cells was impaired. Furthermore, we showed that 1) MSC inhibited commitment of CD34(+) HPC into immature DC, but not maturation of CD34-DC, 2) this inhibitory effect was reversible, and 3) DC generated in coculture with MSC (MSC-DC) induced the generation of alloantigen-specific regulatory T cells following secondary allostimulation. Conditioned medium from MSC cultures showed some inhibitory effect independent of IL-6, M-CSF, and TGF-beta. In comparison, direct coculture of MSC with CD34(+) HPC resulted in much stronger immunosuppressive effect and led to an activation of the Notch pathway as assessed by the overexpression of Hes1 in MSC-DC. Finally, DAPT, a gamma-secretase inhibitor that inhibits Notch signaling, was able to overcome MSC-DC defects. In conclusion, our data suggest that MSC license adult CD34(+) HPC to differentiate into regulatory DC through activation of the Notch pathway.

Astragalus polysaccharide reduces hepatic endoplasmic reticulum stress and restores glucose homeostasis in a diabetic KKAy mouse model.

AIM: To examine the potential effects of Astragalus polysaccharide (APS) on hepatic endoplasmic reticulum (ER) stress in vivo and in vitro and its link with hypoglycemia activity, thus establishing the mechanism underlying the hypoglycemic action of APS. METHODS: The obese and type 2 diabetic KKAy mouse model, which is the yellow offspring of the KK mice expressed Ay gene (700 mg/kg-1/d-1, 8 weeks) and a high glucose-induced HepG2 cell model (200 microg/mL, 24 h) were treated with APS. The oral glucose tolerance test was measured to reflex insulin sensitivity with the calculated homeostasis model assessment (HOMA-IR) index. XBP1 (XhoI site-binding protein 1) transcription and splicing, an indicator of ER stress, was analyzed by RT-PCR and real-time PCR. The expression and activation of glycogen synthase kinase 3 beta (GSK3beta), an insulin signaling protein, was measured by Western blotting. RESULTS: APS can alleviate ER stress in cultured cells in vivo. The hyperglycemia status, systemic insulin sensitivity, fatty liver disease, and insulin action in the liver of diabetic mice were partly normalized or improved in response to APS administration. CONCLUSION: Our results indicate that APS enables insulin-sensitizing and hypoglycemic activity at least in part by enhancing the adaptive capacity of the ER, which can further promote insulin signal transduction. Thus, APS has promising application in the treatment of type 2 diabetes.

Pharmacological actions of sodium ferulate in cardiovascular system.

Sodium ferulate (SF) or 3-methoxy-4-hydroxy-cinamate sodium is an active principle from Angelica sinensis, Cimicifuga heracleifolia, Lignsticum chuangxiong, and other plants. It has been used in traditional Chinese medicine and is approved by State Drugs Administration of China as a drug for treatment of cardiovascular and cerebrovascular diseases. SF has antithrombotic, platelet aggregation inhibitory and antioxidant activities in animals and humans. For several decades SF has been widely used in China to treat cardiovascular and cerebrovascular diseases and to prevent thrombosis. Exciting clinical results have been obtained with SF in coronary heart disease, atherosclerosis, pulmonary heart disease and thrombosis. Its safety and efficacy have been demonstrated in clinical practice. This article briefly reviews basic pharmacology, pharmacokinetics, toxicology and clinical pharmacology of SF. The in vitro and in vivo data support the view that SF is a useful drug for the treatment of cardiovascular diseases.

Effect of protein kinase C alpha, caspase-3, and survivin on apoptosis of oral cancer cells induced by staurosporine.

AIM: To elucidate inhibition of protein kinase C alpha (PKC alpha) activity by staurosporine on apoptosis of oral cancer cell line tongue squamous cell carcinoma (TSCCa) cells and to clarify the role of survivin and caspase-3 in mediating apoptosis. METHODS: TSCCa cell viability was measured by MTT assay after 100 nmol/L staurosporine treatment. Apoptotic cells were identified by using phase contrast microscopy, acridine orange/ethidium bromide staining, and flow cytometry. Level of PKC alpha and its subcellular location were investigated using Western blot analysis. Expression of survivin and caspase-3 were evaluated using immunocytochemistry. RESULTS: Staurosporine significantly inhibited the cell viability of TSCCa cells in a dose- and time-dependent manner. Marked cell accumulation in G2/M phase was observed after 100 nmol/L staurosporine exposure for 6 h and 12 h. In addition, the percentage of apoptosis increased in a time-dependent manner, from 2.9% in control cultures to approximately 27.4% at 100 nmol/L staurosporine treatment for 24 h. Staurosporine displayed difference in inhibitory efficacy between cytosolic and membrance-derived PKC alpha. The content of PKCalpha in membrane versus cytosol decreased quickly, from 0.45 in ethanol-treated control cultures to 0.18 after staurosporine exposure for 24 h (P<0.01). After treatment with staurosporine, a time-dependent reduction of survivin and an activation of caspase-3 were observed in TSCCa cells. CONCLUSION: Staurosporine inhibited cell viability and promoted apoptosis in TSCCa cells. Inhibition of PKCalpha activity might be a potential mechanism for staurosporine to induce apoptosis in this cell line. The cleavage of survivin and activation of caspase-3 signaling pathway might contribute to PKC alpha inhibition-induced apoptosis.

Hypoglycemic effect of Astragalus polysaccharide and its effect on PTP1B.

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 p.o.) 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 beta-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.