• Preventive Nutrition and Food Science
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• v.7 no.2
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• pp.113-118
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• 2002

Alpha-lipoic acid is a known hypoglycemic agent that may be useful in the treatment of diabetes. The objective of this study was to investigate the fate of glucose in isolated muscles incubated with lipoic acid by determining its direct effects on specific metabolic and signaling pathways. Soleus muscles from healthy rats were incubated with lipoic acid in the absence or presence of insulin. Glucose transport, glycogen synthesis, glucose oxidation and lipid synthesis were determined and affects on major pathways associated with insulin signaling were evaluated. Glucose transport was not significantly altered by the addition of lipoic acid to the incubation medium. However, lipoic acid decreased glycogen synthesis in comparison to controls. Glucose oxidation was moderately increased while de-novo lipid synthesis from glucose was inhibited. Wortmannin repressed insulin stimulation of glucose incorporation into glycogen, an effect that was augmented by the combined treatment of wortmannin and lipoic acid. Basal and insulin-stimulated serine phosphorylation of Akt was not changed by the addition of lipoic acid to the incubation medium. These data show that in this in vitro model, lipoic acid did not significantly affect glucose uptake but dramatically modified pathways of glucose metabolism within muscle tissue.

• Proceedings of the PSK Conference
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• 2003.04a
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• pp.158.2-159
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• 2003

Cadmium is well known as a toxic metal and has insulin mimicking effects in rat adipose tissue. To investigate the effect of CdCl2 on glucose transport and its mechanism, this study was performed in 3T3-L1 adipocytes. 10 and 25mM of CdCl2 exposed to cells for 12 hours increased 2-deoxyglucose uptake to 2.2 and 2.8 fold, respectively. Nifedipine, a calcium channel blocker, inhibited the 2-deoxyglucose uptake stimulated by CdCl2. (omitted)

• Journal of Ginseng Research
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• v.18 no.1
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• pp.17-24
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• 1994

Effect of ginsenoside mixture, ginsenoside $Rb_1$,$Rb_2$,$Rg_1$ and the fat soluble fraction of the roots of Panax ginseng C.A. Meyer on the activity of glucokinase (GK) in vitro has been observed and found that GK activity was increased about 15c1c at the concentration of ginsenoside mixture and/or the fat soluble fraction being $10^{-7}$,$10^{-5}$%. It was also observed that glucose uptake by rat liver was increased in the presence of either ginsenoside mixture or the fat soluble fraction by perfusion technique. Ginsenoside mixture stimulated various enzymes related to glucose metabolism, however, both ginsenoside mixture and the fat soluble fraction did not stimulate GK activity as expected. Primary culture of liver cells showed that the ginsenoside mixture and the fat soluble fraction increased GK activity significantly and they stimulated the GK activity synergistically in the co-presence of insulin.

• Nutrition Research and Practice
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• v.7 no.1
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• pp.15-21
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• 2013

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 $PPAR{\alpha}$, ACO, and CPT-1 in C2C12 cells and $PPAR{\alpha}$ 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.

• Journal of Nutrition and Health
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• v.39 no.4
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• pp.323-330
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• 2006

Peripheral insulin resistance in obese/type II diabetes animals results from an impairment of insulin-stimulated glucose uptake into skeletal muscle. Insulin stimulate the translocation of GLUT4 from intracellular location to the plasma membrane. Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) is implicated in mediation of fusion of GLUT4-containing vesicle with the plasma membrane. Present study investigated regulatory effects of Rhodiola sachalinensis administration and exercise training on the expression of GLUT4 protein and SNAREs protein in skeletal muscles of obese Zucker rats. Experimental animals were randomly assigned into one of five groups ; lean control(LN), obese control(OB), exercise-treated(EXE), Rhodiola sachalinensis-treated(Rho), combine of Rho & EXE (Rho-EXE). All animals of exercise training (EXE, Rho-EXE) performed treadmill running for 8 weeks, and animals of Rho groups (Rho, Rho-EXE) were dosed daily by gastric gavage during the same period. After experiment, blood were taken for analyses of glucose, insulin, and lipids levels. Mitochondrial oxidative enzyme (citrate synthase, CS ; $\beta$-hydroxyacyl-CoA dehydrogenase, $\beta$-HAD) activity were analysed. Skeletal muscles were dissected out for analyses of proteins (GLUT4, VAMP2, syntaxin4, SNAP23). Results are as follows. Exercise and/or Rhodiola sachalinensis administration significantly reduced body weight and improved blood lipids (TG, FFA), and increased insulin sensitivity. Endurance exercise significantly increased the activity of mitochondrial enzymes and the expression of GLUT4 protein, however, administration of Rhodiola sachalinensis did not affect them. The effect of exercise and/or Rhodiola sachalinensis administration on the expression of SNARE proteins was unclear. Our study suggested that improvement insulin sensitivity by exercise and/or Rhodiola sachalinensis administration in obese Zucker rats is independent of expression of SNARE proteins.

• Herbal Formula Science
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• v.27 no.3
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• pp.223-236
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• 2019

Dengropanax morfiferus (D), Broussonitia kazinoki (B), and Cudriania tricuspidata (E), a widely cultivated species in South Korea, has been used as traditional medicine to treat numerous diseases. In this study, we evaluated the antidiabetic effects in a various signaling mechanisms using mixed extract and major component contents were analyzed by HPLC in the combined extracts from Dengropanax morfiferus, Broussonitia kazinoki, and Cudriania tricuspidata (DBCE). DBCE inhibited ${\alpha}$-glucosidase and ${\alpha}$-amylase activation and showed potent antioxidant effects, which are evaluated using DPPH, ABTS, and SOD assay. Cytokines, which are released by inflammatory cells in pancreatic islets, are involved in the pathogenesis of type 1 diabetes mellitus. DBCE showed the protective effects in RINm5F cells against cytokines-induced damage by suppressing inducible nitric oxide (NO) synthase and COX-2 expression and NO production. Insulin resistance is the primary characteristic of type 2 diabetes. Therefore, the regulatory effect of DBCE on glucose uptake and production are investigated in insulin-responsive human HepG2 cells. DBCE stimulated glucose uptake, prevented Glut2 and phosphor-IRS1 downregulation induced by high glucose (HG, 30 mM). Moreover, DBCE pretreatment diminished glucose levels, PEPCK and G6Pase overexpression provoked by HG. These findings suggest that DBCE might be used for diabetes treatment through alpha-glucosidase or alpha-amylase activity regulation, pancreatic beta cell protection, hepatic glucose sensitivity improvement. Cytokines, which are released by inflammatory cells' infiltrations around the pancreatic islets, are involved in the pathogenesis of type 1 diabetes mellitus.

• Journal of Nutrition and Health
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• v.47 no.3
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• pp.167-175
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• 2014

Purpose: Previous studies have shown that treatment with Smilax china L. leaf extract (SCLE) produces antidiabetic effects due to ${\alpha}$-glucosidase inhibition. In this study, we examined the mechanism underlying these antidiabetic effects by examining glucose uptake in HepG2 cells cultured with SCLE. Methods: Glucose uptake and glucokinase activity were examined using an assay kit. Expression of glucose transporter (GLUT)-2, GLUT-4, and HNF-$1{\alpha}$ was measured by RT-PCR or western blot. Results: Treatment with SCLE resulted in enhanced glucose uptake in HepG2 cells, and this effect was especially pronounced when cells were cultured in an insulin-free medium. SCLE induced an increase in expression of GLUT-2 but not GLUT-4. The increase in the levels of HNF-$1{\alpha}$, a GLUT-2 transcription factor, in total protein extract and nuclear fraction suggest that the effects of SCLE may occur at the level of GLUT-2 transcription. In addition, by measuring the change in glucokinase activity following SCLE treatment, we confirmed that SCLE stimulates glucose utilization by direct activation of this enzyme. Conclusion: These results demonstrate that the potential antidiabetic activity of SCLE is due at least in part to stimulation of glucose uptake and an increase in glucokinase activity, and that SCLE-stimulated glucose uptake is mediated through enhancement of GLUT-2 expression by inducing expression of its transcription factor, HNF-$1{\alpha}$.

• Journal of Life Science
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• v.33 no.11
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• pp.859-867
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• 2023

Lupeol is a type of pentacyclic triterpene that has been reported to have therapeutic effects for treating many diseases; however, its effect on insulin resistance is unclear clear. This study examined the inhibitory effect of lupeol on the serine phosphorylation of insulin receptor substrate-1 in insulin resistance-induced 3T3-L1 adipocytes. 3T3-L1 cells were cultured and treated with tumor necrosis factor-α (TNF-α) for 24 hours to induce insulin resistance. Cells treated with different concentrations of lupeol (15 μM or 30 μM) or 100 nM of rosiglitazone were incubated. Then, lysed cells underwent western blotting. Lupeol exhibited a positive effect on the negative regulator of insulin signaling and inflammation-activated protein kinase caused by TNF-α in adipocytes. Lupeol inhibited the activation of protein tyrosine phosphatase-1B (PTP-1B)-a negative regulator of insulin signaling-and c-Jun N-terminal kinase (JNK); it was also an inhibitor of nuclear factor kappa-B kinase (IKK) and inflammation-activated protein kinases. In addition, Lupeol downregulated serine phosphorylation and upregulated tyrosine phosphorylation in insulin receptor substrate-1. Then, the downregulated phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) pathway was activated, the translocation of glucose transporter type 4 was stimulated to the cell membrane, and intracellular glucose uptake increased in the insulin resistance-induced 3T3-L1 adipocytes. Lupeol may improve TNF-α-induced insulin resistance by downregulating the serine phosphorylation of insulin receptor substrate 1 by inhibiting negative regulators of insulin signaling and inflammation-activated protein kinases in 3T3-L1 adipocytes.

• Reproductive and Developmental Biology
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• v.35 no.3
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• pp.239-245
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• 2011

The overexpression of Phosphoprotein Enriched in Astrocytes (PEA15) gene is commonly found in human diabetic patients. The overexpression of this gene in skeletal muscle and fat tissues have been reported to cause insulin resistance, thereby impairing insulin stimulated glucose uptake. We introduced a gene of mouse PEA15 (mPEA15) and enhanced green fluorescent protein (EGFP) into fertilized one cell pig zygotes using microinjection, and produced a piglet that showed overexpression of mPEA15 in the muscle tissues and expression of EGFP in the ear tissues and hooves. RT-PCR RFLP, southern blot and FISH analysis showed that the tissues carried the transgene. Real-time RT-PCR and western blots demonstrated that PEA15 gene was overexpressed in the various tissues and muscle tissues, respectively. These fads suggest that expression vector system is normally expressed in the transgenic (TG) pigs. To use as animal diseases model for type 2 diabetes, further study is necessary to confirm whether diabetes occur in these TG pigs, especially insulin resistance.

• Journal of Life Science
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• v.29 no.5
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• pp.570-579
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• 2019

Diabetes is one of the serious chronic metabolic diseases caused by Westernized eating habits, and the goal of diabetes treatment is to keep blood glucose at a normal level and prevent diabetic complications. This study was designed to investigate the anti-diabetic effects of a mealworm (Tenebrio molitor larva) extract (MWE) on hyperglycemia in an animal model with type 2 diabetes. Diabetic C57BL/Ksj-db/db mice were divided into three groups: diabetic control, rosiglitazone, and MWE. The mice supplemented with MWE showed significantly lower blood levels of glucose and glycosylated hemoglobin when compared with the diabetic control mice. The homeostatic index of insulin resistance was significantly lower in mice supplemented with MWE than in diabetic control mice. MWE supplementation significantly stimulated the phosphorylation of insulin receptor substrate-1 and Akt, and activation of phosphatidylinositol 3-kinase in insulin signaling pathway of skeletal muscles. Eventually, MWE increased the expression of the plasma membrane glucose transporter 4 (GLUT4) via PI3K/Akt activation. These findings demonstrate that the increase in plasma membrane GLUT4 expression by MWE promoted the uptake of blood glucose into cells and relieved hyperglycemia in skeletal muscles of diabetic C57BL/Ksj-db/db mice. Therefore, mealworms are expected to prove useful for the prevention and treatment of diabetes, and further studies are needed to improve type 2 diabetes in the future.