Alpha-lipoic acid mitigates insulin resistance in Goto-Kakizaki rats.

Impaired glucose uptake and metabolism by peripheral tissues is a common feature in both type I and type II diabetes mellitus. This phenomenon was examined in the context of oxidative stress and the early events within the insulin signalling pathway using soleus muscles derived from non-obese, insulin-resistant type II diabetic Goto-Kakizaki (GK) rats, a well-known genetic rat model for human type II diabetes. Insulin-stimulated glucose transport was impaired in soleus muscle from GK rats. Oxidative and non-oxidative glucose disposal pathways represented by glucose oxidation and glycogen synthesis in soleus muscles of GK rats appear to be resistant to the action of insulin when compared to their corresponding control values. These diabetes-related abnormalities in glucose disposal were associated with a marked diminution in the insulin-mediated enhancement of protein kinase B (Akt/PKB) and insulin receptor substrate-1 (IRS-1)-associated phosphatidylinostol 3-kinase (PI 3-kinase) activities; these two kinases are key elements in the insulin signalling pathway. Moreover, heightened state of oxidative stress, as indicated by protein bound carbonyl content, was evident in soleus muscle of GK diabetic rats. Chronic administration of the hydrophobic/hydrophilic antioxidant alpha -lipoic-acid (ALA, 100 mg/kg, i.p.) partly ameliorated the diabetes-related deficit in glucose metabolism, protein oxidation as well as the activation by insulin of the various steps of the insulin signalling pathway, including the enzymes Akt/PKB and PI-3 kinase. Overall, the current investigation illuminates the concept that oxidative stress may indeed be involved in the pathogenesis of certain types of insulin resistance. It also harmonizes with the notion of including potent antioxidants such as ALA in the armamentarium of antidiabetic therapy.     

Antidiabetic,Antihyperlipidemic and Antioxidant Activities of a Novel Proteoglycan from Ganoderma Lucidum Fruiting Bodies on db/db Mice and the Possible Mechanism

Previously, we screened a proteoglycan for anti-hyperglycemic, named FYGL, from Ganoderma Lucidum. For further research of the antidiabetic mechanisms of FYGL in vivo, the glucose homeostasis, activities of insulin-sensitive enzymes, glucose transporter expression and pancreatic function were analyzed using db/db mice as diabetic models in the present work. FYGL not only lead to a reduction in glycated hemoglobin level, but also an increase in insulin and C-peptide level, whereas a decrease in glucagons level and showed a potential for the remediation of pancreatic islets. FYGL also increased the glucokinase activities, and simultaneously lowered the phosphoenol pyruvate carboxykinase activities, accompanied by a reduction in the expression of hepatic glucose transporter protein 2, while the expression of adipose and skeletal glucose transporter protein 4 was increased. Moreover, the antioxidant enzyme activities were also increased by FYGL treatment. Thus, FYGL was an effective antidiabetic agent by enhancing insulin secretion and decreasing hepatic glucose output along with increase of adipose and skeletal muscle glucose disposal in the late stage of diabetes. Furthermore, FYGL is beneficial against oxidative stress, thereby being helpful in preventing the diabetic complications.     

Procyanidins modify insulinemia by affecting insulin production and degradation

Previous studies from our research group have suggested that procyanidins modify glycemia and insulinemia. The aim of this work was to evaluate the effects of procyanidins on β-cell functionality in a nonpathological system. Four groups of healthy rats were studied. The animals were given daily acute doses of grape seed procyanidin extract (GSPE) for different time periods and at different daily amounts. A β-cell line (INS-1E) was treated with 25 mg GSPE/L for 24 h to identify possible mechanisms of action for the procyanidins. In vivo experiments showed that different doses of GSPE affected insulinemia in different ways by modifying β-cell functionality and/or insulin degradation. The islets isolated from rats that were treated with 25 mg GSPE/kg of body weight for 45 days exhibited a limited response to glucose stimulation. In addition, insulin gene expression, insulin synthesis and expression of genes related to insulin secretion were all down-regulated. In vitro studies revealed that GSPE decreased the ability of β-cells to secrete insulin in response to glucose. GSPE increased glucose uptake in β-cells under high-glucose conditions but impaired glucose-induced mitochondrial hyperpolarization, decreased adenosine triphosphate (ATP) synthesis and altered cellular membrane potentials. GSPE also modified Glut2, glucokinase and Ucp2 gene expression as well as altered the expression of hepatic insulin-degrading enzyme (Ide), thereby altering insulin degradation. At some doses, procyanidins changed β-cell functionality by modifying insulin synthesis, secretion and degradation under nonpathological conditions. Membrane potentials and Ide provide putative targets for procyanidins to induce these effects.     

The effect of streptozotocin-induced diabetes on glycogen metabolism in rat kidney and its relationship to the liver system.

The effects in kidney of streptozotocin-induced diabetes and of insulin supplementation to diabetic animals on glycogen-metabolizing enzymes were determined. Kidney glycogen levels were approximately 30-fold higher in diabetic animals than in control or insulintreated diabetic animals. The activities of glycogenolytic enzymes i.e., phosphorylase (both a and b), phosphorylase kinase, and protein kinase were not significantly altered in the diabetic animals. Glycogen synthase (I form) activity decreased in the diabetic animals whereas total glycogen synthase (I + D) activity significantly increased in these animals. The activities were restored to control values after insulin therapy. Diabetic animals also showed a 3-fold increase in glucose 6-phosphate levels. These data suggest that higher accumulation of glycogen in kidneys of diabetic animals is due to increased amounts of total glycogen synthase and its activator glucose 6-phosphate.     

Outer membrane vesicles of Porphyromonas gingivalis attenuate insulin sensitivity by delivering gingipains to the liver

Outer membrane vesicles (OMVs) are nanosized particles derived from the outer membrane of gram-negative bacteria. Oral bacterium Porphyromonas gingivalis (Pg) is known to be a major pathogen of periodontitis that contributes to the progression of periodontal disease by releasing OMVs. The effect of Pg OMVs on systemic diseases is still unknown. To verify whether Pg OMVs affect the progress of diabetes mellitus, we analyzed the cargo proteins of vesicles and evaluated their effect on hepatic glucose metabolism. Here, we show that Pg OMVs were equipped with Pg-derived proteases gingipains and translocated to the liver in mice. In these mice, the hepatic glycogen synthesis in response to insulin was decreased, and thus high blood glucose levels were maintained. Pg OMVs also attenuated the insulin-induced Akt/glycogen synthase kinase-3 β (GSK-3β) signaling in a gingipain-dependent fashion in hepatic HepG2 cells. These results suggest that the delivery of gingipains mediated by Pg OMV elicits changes in glucose metabolisms in the liver and contributes to the progression of diabetes mellitus.     

Dietary cocoa reduces metabolic endotoxemia and adipose tissue inflammation in high-fat fed mice

In diet-induced obesity, adipose tissue (AT) is in a chronic state of inflammation predisposing the development of metabolic syndrome. Cocoa (Theobroma cacao) is a polyphenol-rich food with putative anti-inflammatory activities. Here, we examined the impact and underlying mechanisms of action of cocoa on AT inflammation in high fat-fed mice. In the present study, male C57BL/6 J mice were fed a high fat diet (HF), a HF diet with 8% (w/w) unsweetened cocoa powder (HFC), or a low-fat diet (LF) for 18 weeks. Cocoa supplementation decreased AT mRNA levels of tumor necrosis factor-α, interleukin-6, inducible nitric oxide synthase, and EGF-like module-containing mucin-like hormone receptor-like 1 by 40–60% compared to HF group, and this was accompanied by decreased nuclear protein levels of nuclear factor-κB. Cocoa treatment reduced the levels of arachidonic acid in the AT by 33% compared to HF controls. Moreover, cocoa treatment also reduced protein levels of the eicosanoid-generating enzymes, adipose-specific phospholipase A₂ and cycloxygenase-2 by 53% and 55%, respectively, compared to HF-fed mice. Finally, cocoa treatment ameliorated metabolic endotoxemia (40% reduction in plasma endotoxin) and improved gut barrier function (as measured by increased plasma levels of glucagon-like peptide-2). In conclusion, the present study has shown for the first time that long-term cocoa supplementation can reduce AT inflammation in part by modulating eicosanoid metabolism and metabolic endotoxemia.     

Deteriorating insulin resistance due to WL15 peptide from cysteine and glycine-rich protein 2 in high glucose-induced rat skeletal muscle L6 cells

This study investigates the antioxidant and antidiabetic activity of the WL15 peptide derived from Channa striatus on regulating the antioxidant property in the rat skeletal muscle cell line (L6) and enhancing glucose uptake via glucose metabolism. Increased oxidative stress plays a major role in the development of diabetes and its complications. Strategies are needed to mitigate the oxidative stress that can reduce these pathogenic processes. Our results showed that with treatment with WL15 peptide, the reactive oxygen species significantly decreased in L6 myotubes in a dose-dependent manner, and increased antioxidant enzymes help to prevent the formation of lipid peroxidation in L6 myotubes. The cytotoxicity of WL15 is evaluated in the L6 cells and found to be non-cytotoxic at the tested concentration. Also, for the analysis of glucose uptake activity in L6 cells, the 2-(N-[7-nitrobenz-2-oxa-1,3-diazol-4-yl]amino)-2-deoxy- d -glucose assay was performed in the presence of wortmannin and genistein inhibitors. WL15 demonstrated antidiabetic activities through a dose-dependent increase in glucose uptake (64%) and glycogen storage (7.8 mM). The optimal concentration for the maximum activity was found to be 50 µM. In addition, studies of gene expression in L6 myotubes demonstrated upregulation of antioxidant genes and genes involved in the pathway of insulin signaling. In cell-based assays, WL15 peptide decreased intracellular reactive oxygen species levels and demonstrated insulin mimic activity by enhancing the primary genes involved in the insulin signaling pathway by increased glucose uptake indicating that glucose transporter type 4 (GLUT4) is regulated from the intracellular pool to the plasma membrane.     

Blood pressure and cardiovascular risk: What about cocoa and chocolate?

Cocoa flavonoids are able to reduce cardiovascular risk by improving endothelial function and decreasing blood pressure (BP). Interest in the biological activities of cocoa is daily increasing. A recent meta-analysis shows flavanol-rich cocoa administration decreases mean systolic (−4.5 mm Hg; p < 0.001) and diastolic (−2.5 mm Hg; p < 0.001) BP. A 3-mm Hg systolic BP reduction has been estimated to decrease the risk of cardiovascular and all-cause mortality. This paper summarizes new findings concerning cocoa effects on cardiovascular health focusing on putative mechanisms of action and nutritional and “pharmacological” viewpoints. Cocoa consumption could play a pivotal role in human health.     

Time-dependent effects of fatty acids on skeletal muscle metabolism

Increased plasma levels of free fatty acids (FFA) occur in states of insulin resistance such as type 2 diabetes mellitus, obesity, and metabolic syndrome. These high levels of plasma FFA seem to play an important role for the development of insulin resistance but the mechanisms involved are not known. We demonstrated that acute exposure to FFA (1 h) in rat incubated skeletal muscle leads to an increase in the insulin-stimulated glycogen synthesis and glucose oxidation. In conditions of prolonged exposure to FFA, however, the insulin-stimulated glucose uptake and metabolism is impaired in skeletal muscle. In this review, we discuss the differences between the effects of acute and prolonged exposure to FFA on skeletal muscle glucose metabolism and the possible mechanisms involved in the FFA-induced insulin resistance.     

Role of glucose and insulin in regulating glycogen synthase and phosphorylase activities in rainbow trout hepatocytes

This study, using ¹³C nuclear magnetic resonance spectroscopy showed enrichment of glycogen carbon (C1) from ¹³C-labelled (C1) glucose indicating a direct pathway for glycogen synthesis from glucose in rainbow trout (Oncorhynchus mykiss) hepatocytes. There was a direct relationship between hepatocyte glycogen content and total glycogen synthase, total glycogen phosphorylase and glycogen phosphorylase a activities, whereas the relationship was inverse between glycogen content and % glycogen synthase a and glycogen synthase a/glycogen phosphorylase a ratio. Incubation of hepatocytes with glucose (3 or 10 mmol·1^-1) did not modify either glycogen synthase or glycogen phosphorylase activities. Insulin (porcine, 10^-8 mol·1^-1) in the medium significantly decreased total glycogen phosphorylase and glycogen phosphorylase a activities, but had no significant effect on glycogen synthase activities when compared to the controls (absence of insulin). In the presence of 10 mmol·1^-1 glucose, insulin increased % glycogen synthase a and decreased % glycogen phosphorylase a activities in trout hepatocytes. Also, the effect of insulin on the activities of % glycogen synthase a and glycogen synthase a/glycogen phosphorylase a ratio were more pronounced at low than at high hepatocyte glycogen content. The results indicate that in trout hepatocytes both the glycogen synthetic and breakdown pathways are active concurrently in vitro and any subtle alterations in the phosphorylase to synthase ratio may determine the hepatic glycogen content. Insulin plays an important role in the regulation of glycogen metabolism in rainbow trout hepatocytes. The effect of insulin on hepatocyte glycogen content may be under the control of several factors, including plasma glucose concentration and hepatocyte glycogen content.     

Ameliorative property of Sesbania grandiflora on carbohydrate metabolic enzymes in the liver and kidney of streptozotocin-induced diabetic rats

In diabetic condition, endogenous glucose synthesis will be elevated due to defect in the action of vital enzymes involved in carbohydrate metabolism, which is the main cause for hyperglycemia. The current study was designed to explore the anti-hyperglycemic efficacy of Sesbania grandiflora flower (SGF) extract by evaluating the concentration of C-peptide, insulin, glucose, glycosylated hemoglobin (HbA_1C), hemoglobin (Hb), glycogen and carbohydrate metabolic enzymes activities in diabetic rats. The study found to lower the level of glucose, HbA_1C and simultaneously ameliorated concentrations of C-peptide, insulin, hemoglobin (Hb), glycogen and carbohydrate metabolic enzymes activities in SGF treated (250 mg/kg body weight for 45 days) diabetic rats. Moreover, SGF administered diabetic rats showed diminished consumption of food and water at the same time improved body weight. The results obtained from the present study were compared with glibenclamide treated (600 µg/kg body weight) diabetic rats. SGF were supplemented to normal rats to rule out toxic effect of SGF, to explore any significant alteration in the above parameters. Hence, the results depict that SGF modulated the carbohydrate metabolic enzymes activities through ameliorating the secretion of insulin and diminishing the level of glucose concentration in STZ-induced diabetic rats by its bioactive compounds.     

Contribution of free fatty acids to impairment of insulin secretion and action: mechanism of beta-cell lipotoxicity

Type 2 diabetes is characterized by two major defects: a dysregulation of pancreatic hormone secretion (quantitative and qualitative--early phase, pulsatility--decrease of insulin secretion, increase in glucagon secretion), and a decrease in insulin action on target tissues (insulin resistance). The defects in insulin action on target tissues are characterized by a decreased in muscle glucose uptake and by an increased hepatic glucose production. These abnomalities are linked to several defects in insulin signaling mechanisms and in several steps regulating glucose metabolism (transport, key enzymes of glycogen synthesis or of mitochondrial oxidation). These postreceptors defects are amplified by the presence of high circulating concentrations of free fatty acids. The mechanisms involved in the of long-chain fatty acids are reviewed in this paper. Indeed, elevated plasma free fatty acids contribute to decrease muscle glucose uptake (mainly by reducing insulin signaling) and to increase hepatic glucose production (stimulation of gluconeogenesis by providing cofactors such as acetyl-CoA, ATP and NADH). Chronic exposure to high levels of plasma free fatty acids induces accumulation of long-chain acyl-CoA into pancreatic beta-cells and to the death of 50 % of beta-cell by apoptosis (lipotoxicity).     

Chronic consumption of a flavanol- and procyanindin-rich diet is associated with reduced levels of 8-hydroxy-2'-deoxyguanosine in rat testes

Cocoa can contain a high concentration of flavanols and procyanidins which have been reported to have strong antioxidative activity. In the present study, male Sprague-Dawley rats were fed diets containing 0, 0.5, 1, or 2% cocoa rich in flavanols for two weeks. Blood, liver, heart and testes were collected and analyzed for markers of oxidative damage. Plasma epicatechin concentrations, 8-hydroxy-2'-deoxyguanosine (8OH2'dG), and oxidized and reduced glutathione were quantitated by HPLC with electrochemical detection. Plasma F(2)-isoprostanes were measured using an enzyme immunoassay. Plasma epicatechin concentrations increased in a dose-dependant fashion according to the amount of cocoa in the diet (128 nM-790 nM). Cocoa supplementation was associated with lower than normal concentrations of 8OH2'dG in the testes (0.590 + 0.40 vs. 0.328 + 0.29; p < 0.05). Liver and heart 8OH2'dG levels were unaffected by dietary treatment. In erythrocytes, the glutathione pool was significantly less oxidized in the cocoa fed group compared to controls (p < 0.05). In liver and testes, no differences in superoxide dismutase activities were detected. Concentrations of plasma F(2)-isoprostanes and thiobarbituric acid reactive substances were similar in all groups. These results support the concept that a diet rich in flavanols and procyanidins can improve oxidant defense and reduce tissue markers for oxidative stress, although these effects can be tissue specific.     

Oral Porphyromonas gingivalis translocates to the liver and regulates hepatic glycogen synthesis through the Akt/GSK-3β signaling pathway

Periodontal diseases are common chronic inflammatory disorders that result in the destruction of tissues around teeth. Many clinical studies suggest that periodontal diseases are risk factors for insulin resistance and diabetic mellitus development. However, the molecular mechanisms by which periodontal diseases regulate the progress of diabetes mellitus remain unknown. In this study, we investigated whether Porphyromonas gingivalis (P.g.), a major pathogen of periodontal diseases, present in the oral cavity, moves to the liver and affects hepatic glycogen synthesis. SNAP26b-tagged P.g. (SNAP-P.g.) was introduced into the oral cavity to induce periodontal disease in 4-week old female Balb/c mice. SNAP-P.g. was detected in the liver extracted from SNAP-P.g.-treated mice using nested PCR analysis. High blood glucose levels tended to promote SNAP-P.g. translocation from the oral cavity to the liver in mice. Periodic acid-Schiff staining suggested that hepatic glycogen synthesis decreased in SNAP-P.g.-treated mice. SNAP-P.g. was also internalized into the human hepatoma cell line HepG2, and this attenuated the phosphorylation of insulin receptor substrate (IRS)-1, Akt and glycogen synthase kinase-3β induced by insulin. Insulin-induced glycogen synthesis was suppressed by SNAP-P.g. in HepG2 cells. Our results suggest that P.g. translocation from the oral cavity to the liver may contribute to the progress of diabetes mellitus by influencing hepatic glycogenesis.     

成纤维细胞生长因子(FGF)-21改善胰岛素抵抗肝细胞对葡萄糖的吸收和肝糖原的合成

在体外建立胰岛素抵抗肝细胞模型,探讨在胰岛素抵抗状态下成纤维细胞生长因子(FGF)-21对模型细胞糖代谢的影响及机制．将HepG2细胞置于10^-7 mol/L 的胰岛素培养基中培养24 h,建立胰岛素抵抗细胞模型．分别用不同浓度的胰岛素和FGF-21处理模型细胞,采用葡萄糖氧化酶-过氧化物酶(GOD-POD)法检测细胞对葡萄糖的摄取情况,并检查胰岛素与FGF-21的协同作用．利用实时荧光定量PCR检测FGF-21对模型细胞葡萄糖转运蛋白1(GLUT1)mRNA表达的影响,蒽酮法检测模型细胞糖原合成量,探讨FGF-21对胰岛素抵抗细胞模型葡萄糖摄取的影响及机制．结果发现,用高浓度胰岛素处理HepG2细胞24 h后,细胞对胰岛素的敏感性显著降低,说明成功建立了胰岛素抵抗细胞模型,抵抗状态可维持48 h,未发现细胞形态学变化．FGF-21能改善胰岛素抵抗模型细胞的葡萄糖摄取,参与肝糖原的合成,并与胰岛素产生协同作用．实时荧光定量PCR结果发现,FGF-21作用模型细胞后,细胞的GLUT1 mRNA表达量显著增加,说明FGF-21促进模型细胞摄取葡萄糖的作用机制与其增加GLUT1的表达有关．     

Possible molecular mechanisms of glucose-lowering activities of Momordica charantia (karela) in diabetes

Diabetes mellitus is a highly prevalent metabolic disorder which is characterized by impaired glucose tolerance, with a relative or absolute insulin deficiency and profound changes in the metabolism of macronutrients. Traditional and complementary medicine is therapeutic strategies that have both been applied to improving glycemic control. Momordica charantia is one of the plant-based, folk medicines that used for improving glycemic control. We aimed to review, the effects of M. charantia on blood glucose with a clarification of the molecular pathways involved. Of the compounds derived from the plants, the insulin-like peptide, charantin, and the alkaloid vicine, have been reported to have hypoglycemic effects. Different mechanisms contribute to the antidiabetic activities of M. charantia, these include increasing pancreatic insulin secretion, decreasing insulin resistance and increasing peripheral and skeletal muscle cell glucose utilization, inhibition of intestinal glucose absorption and suppressing of key enzymes in the gluconeogenic pathways.     

Irisin ameliorates hepatic glucose/lipid metabolism and enhances cell survival in insulin-resistant human HepG2 cells through adenosine monophosphate-activated protein kinase signaling

Irisin is a newly identified myokine that promotes the browning of white adipose tissue, enhances glucose uptake in skeletal muscle and modulates hepatic metabolism. However, the signaling pathways involved in the effects on hepatic glucose and lipid metabolism have not been resolved. This study aimed to examine the role of irisin in the regulation of hepatic glucose/lipid metabolism and cell survival, and whether adenosine monophosphate-activated protein kinase (AMPK), a master metabolic regulator in the liver, is involved in irisin’s actions. Human liver-derived HepG2 cells were cultured in normal glucose-normal insulin (NGNI) or high glucose-high insulin (HGHI/insulin-resistant) condition. Hepatic glucose and lipid metabolism was evaluated by glucose output and glycogen content or triglyceride accumulation assays, respectively. Our results showed that irisin stimulated phosphorylation of AMPK and acetyl-CoA-carboxylase (ACC) via liver kinase B1 (LKB1) rather than Ca²⁺/calmodulin-dependent protein kinase kinase β (CaMKKβ) in HepG2 cells. Irisin ameliorated hepatic insulin resistance induced by HGHI condition. Irisin reduced hepatic triglyceride content and glucose output, but increased glycogen content, with those effects reversed by dorsomorphin, an AMPK inhibitor. Furthermore, irisin also stimulated extracellular signal-regulated kinase (ERK) 1/2 phosphorylation and promoted cell survival in an AMPK-dependent manner. In conclusion, our data indicate that irisin ameliorates dysregulation of hepatic glucose/lipid metabolism and cell death in insulin-resistant states via AMPK activation. These findings reveal a novel irisin-mediated protective mechanism in hepatic metabolism which provides a scientific basis for irisin as a potential therapeutic target for the treatment of insulin resistance and type 2 diabetes mellitus.     

Antidiabetic and antihyperlipidemic effect of Duvalia corderoyi in rats with streptozotocin-induced diabetes

Diabetes mellitus (DM) is a metabolic syndrome distinguished with glucose increasing in blood, insulin resistance, and hyperlipidemia. It results in decease of millions of people yearly. Duvalia corderoyi is a traditional diabetes and hypertension medicine from the Arabian region. D. corderoyi extract was administered to diabetes rats for estimate its anti-diabetic and antihyperlipidemic activities in Wistar rats were induced using (60 mg/kg) of streptozotocin (STZ) intraperitoneally. The rats were randomly divided into five groups: control, diabetic, diabetic receiving glibenclamide, and two diabetic D. corderoyi-treatment groups. Rats were weighted weekly, and the biochemical analysis were carried out in serum, and liver homogenate samples. Body weight of diabetic rats was lessening significantly D. corderoyi improved body weight, glucose concentration, lipid profiles, hepatic enzymes, urea, creatinine, insulin, and HDL-C. These results are the first to indicate the potential antidiabetic and antihyperlipidemic activities of D. corderoyi.