• Proceedings of the Korean Society of Food Science and Nutrition Conference
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• 2004.11a
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• pp.185-197
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• 2004

Type 2 diabetes is characterized by hyperglycemia and hyperinsulinemia, features of insulin resistance. In vivo treatment of ob/ob mice with hydrolyzed fibroin reverses these pathological attributes (6). To explore the mechanism underlying this effect, we have used the 3T3-Ll adipocytes as a cell type which would represent the periphery, in vivo. Exposure of 3T3-Ll adipocytes to chronic insulin leads to the a 50% loss of insulin-stimulated glucose uptake. Chronic exposure to fibroin blocked, in part, the response to chronic insulin but also increased the sensitivity of control cells to the acute action of insulin. The later effect was most robust at physiological concentrations of insulin. Fibroin did not prevent the insulin-induced down-regulation of the insulin receptor or the tyrosine kinase activity associated with the receptor. Further, fibroin had no affect on the loss in activity of the insulin-sensitive down-stream kinase, Akt. Interestingly, fibroin accelerated glucose metabolism and glycogen turnover independent of insulin action. In addition, fibroin up-regulated GLUT1 which increased its expression at the cell surface and caused the redistribution of GLUT4 to the plasma membrane. Together, these later effects would lead to an improvement in hyperglycemia in vivo which would in turn reduce the need for insulin.

• Archives of Pharmacal Research
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• v.21 no.2
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• pp.140-146
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• 1998

Hypoglycemic action of brazilin was found to be based on the improvement of peripheral glucose utility, and this action might be correlated with the insulin action pathway. In the present study we investigated the effect of brazilin on the insulin receptor autophosphorylation, protein kinase C (PKC), protein phosphatase and insulin receptor serine kinase in order to confirm whether the hypoglycemic mechanism is concerned with insulin action pathway. Brazilin was found to inhibit PKC and insulin receptor serine kinase, which are involved in the regulation of insulin signal pathway. But any significant effect was not shown on insulin receptor tyrosine kinase activity, autophosphorylation and phosphatase activity. These findings suggest that brazilin might enhance insulin receptor function by decreasing serine phosphorylation, which might mediate hypoglycemic effect of brazilin.

• Preventive Nutrition and Food Science
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• v.8 no.1
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• pp.61-65
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• 2003

This study was investigated to identify the regulatory mechanism of ACC gene expression by hormones and nutrition. The fragment of ACC promoter I (PI) -220 bp region was recombined to pGL3-Basic vector with luciferase as a reporter gene. The primary hepatocyte from the rat was used to investigate the regulation of ACC PI activity. ACC PI (-220 bp)/luciferase chimeric plasmid was transfected into primary rat hepatocyte by using lipofectin. ACC PI activity was shown by measuring luciferase activity. The addition of insulin, dexamethasone, and triiodothyronine to the culture medium increased the activity of ACC PI by 2.5-, 2.3- and 1.8-fold, respectively. In the presence of 1 $\mu$M dexamethasone, the effects of insulin was amplified about 1.2-fold showing the additional effects of dexamethasone. Moreover the activity of luciferase was increased by insulin, dexamethasone, and triiodothyronine treatment approximately 4-fold. These results indicated that insulin, dexamethasone and thyroid hormone coordinately regulate ACC gene expression via regulation of promoter I activity. On the -220 to ＋21 region of ACC PI, the addition of the glucose to the culture medium increased the activity of ACC PI. With 25 mM glucose, luciferase activity increased by 7-fold. On the other hand, on the -220 bp region, ACC PI activity was not changed by polyunsaturated fatty acids. Therefore, it can be postulated that there are response elements for insulin, triiodothyronine, dexamethasone, and glucose, but not PUFAs on the -220 bp region of ACC PI.

• Journal of Nutrition and Health
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• v.25 no.2
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• pp.109-115
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• 1992

This study was undertaken to determine the effect of dietary fat to carbohydrate ratio on plasma glucose. free fatty acid level and hepatic glucokinase activity in normal or insulin treated diabetic rats. Sprague-Dawley male rats were fed with 3 different but isocaloric diets for 5 weeks. Diet 1 made to have low fat(4% corn oil and 65.8% corn starch wt/wt) : diet 2 medium fat (12% : 47.8%) : diet 3 high fat (20% : 29.8%) In the normal rats an apparent increase of GK activity was observed from the animal fed low fat diet when compared with other groups. GK activities were decreased in all the alloxan-diabetic rats than the normal rats. When insulin was injected the GK activities in all the livers of alloxan-diabetic rats restored to normal level and GK activity was highest in low fat group. In the entire group significant relationships were seen between the plasma glucose and GK activities(r=-0.6, p<0.001) FFA levels and GK activities(r=-0.63 p<0.001) Both in normal and insulin treated diabetic rats significantly depressed level of hepatic GK activity was observed in the livers of animals fed high fat diet for 5 weeks and depressed level of GK activity may be related to insulin resistance.

• Proceedings of the Korean Society of Applied Pharmacology
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• 2001.11a
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• pp.101-101
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• 2001

In the present study, we explored to determine if insulin has any effect on the nuclear translocation of insulin receptor and tyrosine phosphoryaltion of nuclear proteins in the UMR-106 cells. Significant amount of insulin receptors and IRS-1 proteins were detected in the nucleus. IRS-1 and PI$_3$-Kinase appeared to translocate to the nucleus in a time dependent manner. Tyrosine phosphorylation of a number of proteins including 180 KDa, 85 KDa protein in the nucleus was significantly stimulated by insulin, suggesting IRS-1 and PI$_3$-Klnase was activated in the nucleus by insulin treatment. In addition, p70 S6 Kinase, a downstream target of PI3-Kinase was transiently appeared in the nucleus by insulin and its activity was stimulated by insulin. These results suggest that the insulin signaling system containing insulin receptor, IRS-1, PI$_3$-Kinase and p70 S6 Kinase operates in the nucleus of osteoblast cells. The nuclear insulin-mediated tyrosine phosphorylation may play an essential role in the gene expression, differentiation and growth of osteoblast cells.

• The Korean Journal of Pharmacology
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• v.29 no.2
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• pp.253-261
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• 1993

Possible changes in the role of insulin-sensitive cyclic nucleotide phosphodiesterase(PDE) in mediating the antilipolytic action of insulin were investigated in adipocytes from streptozotocin-induced diabetic rats. Isolated adipocytes prepared from epididymal adipose tissue were incubated, with or without insulin, at $37^{\circ}C$ for 15 min following pretreatment with various drugs or toxins, and three (plasma membranes, microsomal membranes, and cytosol) fractions prepared by differential centrifugation were then assayed for cAMP phosphodiesterase activity. The PDE activities only in the crude microsomal (P2) fractions were activated by insulin both in diabetic and control rats. The basal PDE activities in P2 fractions of adipocytes from diabetic rats were higher than those from control rats, although the maximal effects observed at 2 nM of insulin, $100\;{\mu}M$ of isoproterenol or the combination of both were not significantly different from each other. The insulin-stimulated PDE activities in P2 fractions of adipocytes from diabetic rats were not changed by PIA, a $A_{1}$ adenosine receptor agonist, whereas they were decreased to the basal PDE activities in those from control rats. In addition, the adipocytes from diabetic rats showed an increased sensitivity to pertussis toxin compared to those from controls. There were no differences between diabetic and control rats in the sensitivity of adipocytes to cholera toxin. These data indicate that the impaired signalling through inhibitory receptors such as adenosine receptors in adipocytes from streptozotocin-induced diabetes relates to the loss or the decreased function of $G_i$ proteins, and leads to the increased activity of the insulin-dependent PDE at the basal states.

• The Journal of Korean Medicine
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• v.31 no.4
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• pp.79-100
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• 2010

Objective: Production of ROS from glucose toxicity results in injury of pancreatic $\beta$-cells in diabetes models. This study was undertaken to examine the influence of Lespedeza Cuneata extract (LCE) on cytoprotective effects on glucose toxicity, insulin secretion and gene expression in RIN-m5F cells. Methods: First, we measured LCE's antioxidant activity by DPPH free radical-scavenging activity and SOD activity. After the various concentrations of LCE were added to the RIN-m5F cells, we measured cell viability with glucose stimulation by MTT assay and glucose-stimulated insulin secretion. We analyzed gene expression with Agilent whole mouse genome 44K oligo DNA microarray and searched for related pathways in KEGG (Kyoto Encyclopedia of Genes and Genomes). Lastly we measured INS-1, INS-2, INS-R, IRS-1, IRS-2, IRS-3, GLP-1R, and GLP-2R mRNA expression by real time RT-PCR. Results: Free radical-scavenging activity, SOD activity and insulin secretion increased dependent on LCE concentration, but LCE did not show considerable cytoprotective effect on RIN-m5F cells. More than twice expressed gene was 6362 in Oligo DNA chip. In KEGG, the most related pathway was the metabolic pathway. In the insulin signaling pathway, up expressed genes were Irs1, Mapk8, Akt1, and Lipe and down expressed genes were Rhoq, Fbp2, Prkar2b, Gck, and Prkag1. In real time RT-PCR, IRS-2, and IRS-3 expression increased significantly compared to the control group on LCE $12{\mu}g/m{\ell}$ concentration and GCK expression decreased significantly compared to the control group. Conclusions: These results show that LCE encourages insulin secretion and insulin metabolism by complicated gene mechanisms. Further mechanism study and clinical study seem to be necessary about Lespedeza Cuneata.

• International Journal of Molecular Medicine
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• v.44 no.3
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• pp.1161-1171
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• 2019

The present study investigated whether glucagon like peptide-1 (GLP-1) improves glucose uptake through glucose transporter type 4 (GLUT4), mediated by the activation of sirtuin 1 (SIRT1), in skeletal muscle cells with palmitate induced-insulin resistance. The levels of glucose uptake, GLUT4, protein kinase A (PKA), and cyclic adenosine monophosphate (cAMP) were determined in human skeletal muscle myotubes (HSMMs) exposed to palmitate and GLP-1. Then, to determine whether PKA/cAMP were downstream signals of GLP-1, a PKA inhibitor was used. To determine whether SIRT-1 contributes to GLP-1 action in HSMMs with palmitate-induced insulin resistance, the levels of peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α) deacetylation and SIRT-1 activity were assessed using a SIRT1 inhibitor and small interfering RNA (siRNA). The phosphorylation levels of protein kinase B (Akt) and insulin receptor substrate 1 (IRS-1) as insulin signaling pathways, were assessed in GLP-1-treated HSMMs exposed to palmitate. The influence of SIRT1 on the GLP-1-induced activation of insulin signaling pathway was determined using a SIRT1 inhibitor. GLP-1 restored the palmitate-induced reductions in the levels of glucose uptake, GLUT4 mRNA, GLUT4 promoter activity, and GLUT4 protein in HSMMs. PKA and cAMP, as GLP-1 downstream signals, played a role in this process. GLP-1 increased the deacetylation levels of PGC1α, and stimulated SIRT1 in HSMMs. Moreover, the SIRT1 inhibitor and siRNA of SIRT1 suppressed the effect of GLP-1 on GLUT4 expression in HSMMs exposed to palmitate. The SIRT1 inhibitor also prevented the GLP-1-induced phosphorylation of IRS-1 and Akt in palmitate-treated HSMMs. The present findings suggest that in palmitate-induced insulin-resistant HSMM, GLP-1 activates SIRT1 through the PKA/cAMP pathway, which in turn enhances glucose uptake through GLUT4 and the insulin signaling pathway.

• Journal of Nutrition and Health
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• v.30 no.1
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• pp.25-31
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• 1997

The effects of Trichosanthes kirilowii Max. subfractions, which has long been used as a wild vegetable and folk medicine, on insulin activity and acute toxicity were investigated. Diabetes melitus was induced in male Sprague-Dawley rats by the injection of streptozotocin(STZ) into the tail vein at a dose of 45mg/kg. The hexane fraction of the plant was subfractioned by silica gel column chromatography and were administered orally for 14 days and the normal and STZ-control group were orally administered with tween 80. The body weight gain was monitored and plasma levels of glucose, cholesterol, triglyceride, free fatty acid HDL-cholesterol were determined. The plasma activities of aspartate aminotransferase(AST) and alanine aminotransferase (ALT) were analysed. The subjraction A of hexane fraction lowered plasma glucose levels significantly and increased insulin activity compared to that of STZ-control. The activities of AST and ALT were decreased by administration of subfractions A and C of hexane fraction. The intakes of the hexane fraction of Trichosanthes kirilowii Max. did not showed the acute toxicity. It is suggested from the results that the subfraction A of the hexane fraction of Trichosanthes kirilowii Max. showed a hypoglycemic effect on diabetic rats and that the subfraction may be beneficial for insulin secreation.

• Molecular & Cellular Toxicology
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• v.4 no.4
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• pp.348-354
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• 2008

Bisphenol A (BPA), an environmental endocrine disrupter, enters the human body continuously in food and drink. Young children are likely to be more vulnerable than adults to chemical exposure due to the immaturities of their organ systems, rapid physical development, and higher ventilation, metabolic rates, and activity levels. The direct effect of BPA on peripheral tissue might also be of importance to the development of insulin resistance. However, the influence that BPA has on insulin signaling molecules in skeletal muscle has not been previously investigated. In this study, we examined the effect of BPA on fasting blood glucose (FBG) in post-weaned Wistar rats and on insulin signaling proteins in C2C12 skeletal muscle cells. Subsequently, we investigated the effects of BPA on insulin-mediated Akt phosphorylation in C2C12 myotubes. In rats, BPA treatment (0.1-1,000 ng/mL for 24 hours) resulted in the increase of FBG and plasma insulin levels, and reduced insulin-mediated Akt phosphorylation. Furthermore, the mRNA expression of insulin receptor (IR) was decreased after 24 hours of BPA treatment in C2C12 cells in a dose-dependent manner, whereas the mRNA levels of other insulin signaling proteins, including insulin receptor substrate-1 (IRS-1) and 5'-AMP-dependent protein kinase (AMPK), were unaffected. Treatment with BPA increased GLUT4 expression and protein tyrosine phosphatase 1B (PTP1B) activity in C2C12 myotubes, but not in protein levels. We conclude that exposure to BPA can induce insulin resistance by decreasing IR gene expression, which is followed by a decrease in insulin- mediated Akt activation and increased PTP1B activity.