El tratamiento con sofosbuvir mejora la resistencia a la insulina Inducida por el virus de la hepatitis C / Sofosbuvir treatment improves hepatitis C virus-induced insulin resistance

La infección crónica por el virus de la hepatitis C (VHC) está asociada con la resistencia a la insulina y la diabetes tipo 2. El objetivo general de este estudio fue evaluar los efectos del sofosbuvir sobre la resistencia a la insulina inducida por el VHC. Para ello, se realizó un estudio clínico que incluyó 42 pacientes con VHC resistentes a la insulina, que fueron tratados con diferentes regímenes antivirales basados en sofosbuvir. Asimismo, se utilizó una línea de hepatocitos humanos que expresan un replicón del VHC de manera estable para determinar los mecanismos moleculares implicados en la acción de la insulina regulada por sofosbuvir. Todos los pacientes alcanzaron una respuesta virológica sostenida después del tratamiento con sofosbuvir y se observó una reducción significativa en los marcadores de daño hepático, así como en el estadio de fibrosis. El índice de resistencia a la insulina (HOMA) mejoró significativamente a lo largo del estudio. A nivel molecular, el tratamiento con sofosbuvir mejoró la activación de la cascada de señalización de la insulina tras la estimulación con dicha hormona en los hepatocitos con VHC, y, en consecuencia, revirtió la expresión elevada de genes gluconeogénicos, el aumento de la producción de glucosa y la deficiencia de la síntesis de glucógeno en estas células. En conclusión, estos resultados sugieren que el sofosbuvir mejora la respuesta deficiente a la insulina originada por la infección del VHC, proporcionando novedosas evidencias en cuanto a los mecanismos moleculares implicados en la sensibilización a la insulina inducida por este tratamiento

Chronic hepatitis C virus (HCV) infection is associated with insulin resistance and type 2 diabetes. The overall aim of this study was to evaluate the effects of sofosbuvir (SOF) on HCV-induced insulin resistance. Clinical parameters were recorded and insulin resistance index (HOMA) calculated from 42 insulin-resistant HCV-patients who underwent SOF-based regimens, at baseline, at the end of treatment (EoT), and at one year after the EoT. Likewise, Huh7 cells expressing full-length HCV replicons were used to elucidate the molecular mechanisms involved in insulin action regulated by SOF. All patients reached a sustained virological response after SOF treatment and, as expected, a significant reduction in liver damage markers and fibrosis stage was observed at the EoT that remained one year later. HOMA significantly improved throughout the study time period. Besides, an increase of total cholesterol, low-density lipoprotein cholesterol and apolipoprotein B levels were maintained over time after the EoT. At the molecular level, SOF treatment improved the activation of the insulin signalling cascade after stimulation with the hormone in HCV-hepatocytes and, accordingly, reversed the elevated expression of gluconeogenic genes, the increased glucose production and the impairment of glycogen synthesis induced by HCV. Furthermore, SOF challenge induced an increase of insulin receptor substrate 1 (IRS1) content parallel to a reduction in its serine phosphorylation in HCV-hepatocytes. These results provide novel evidence about the molecular mechanisms involved in the hepatic insulin sensitization induced by SOF treatment involving the recovery of IRS1 protein levels as a hallmark of SOF effects

Beta-sitosterol attenuates insulin resistance in adipose tissue via IRS-1/Akt mediated insulin signaling in high fat diet and sucrose induced type-2 diabetic rats.

In our previous study, we have shown that ß-sitosterol (SIT) enhances glycemic control by increasing the activation of insulin receptor (IR) and glucose transporter 4 (GLUT4) proteins in adipose tissue. However, the possible role of SIT on the regulation of post-receptor insulin signal transduction is not known. Hence, the study was aimed to assess the effects of SIT on IRS-1/Akt mediated insulin signaling molecules in high-fat diet and sucrose induced type-2 diabetic rats. An oral effective dose of SIT (20 mg/kg b.wt) was given for 30 days to high fat-fed type-2 diabetic rats to find out whether SIT regulates IRS-1/Akt pathway of insulin signaling. The results showed that SIT attenuated the insulin receptor substrate-1 serine phosphorylation (p-IRS-1Ser636) (P = 0.0003). However, it up-regulated the mRNA expression of IR (P = 0.0036) and post-receptor insulin signaling molecules such as IRS-1 (P < 0.0001), ß-arrestin-2 (P < 0.0058), Akt (P = 0.0008), AS160 (P = 0.0030) and GLUT4 (P < 0.0001) with a concomitant increase in the levels of IRS-1(P < 0.0001), p-IRS1-1Tyr632 (P = 0.0014), Akt (P < 0.0001), p-AktSer473/Thr308 (P = 0.0006; P < 0.0001), AS160 and p-AS160Thr642 (P < 0.0001) compared with type-2 diabetic rats. In Silico analysis was also performed and it showed that SIT possesses the greater binding affinity with ß-arrestin-2, c-Src, and IRS-1 as well as Akt proteins and proved to attenuate insulin resistance as this study coincides with in vivo findings. Our present study clearly shows that SIT attenuates high fat diet-induced detrimental changes in adipose tissue. Therefore, it is concluded from the present findings that, SIT could be used as potential therapeutic phytomedicine for the management of type-2 diabetes.

The diabetes drug semaglutide reduces infarct size, inflammation, and apoptosis, and normalizes neurogenesis in a rat model of stroke.

Stroke is a condition with few medical treatments available. Semaglutide, a novel Glucagon-like peptide-1 (GLP-1) analogue, has been brought to the market as a treatment for diabetes. We tested the protective effects of semaglutide against middle cerebral artery occlusion injury in rats. Animals were treated with 10 nmol/kg bw ip. starting 2 h after surgery and every second day for either 1, 7, 14 or 21 days. Semaglutide-treated animals showed significantly reduced scores of neurological impairments in several motor and grip strength tasks. The cerebral infarction size was also reduced, and the loss of neurons in the hippocampal areas CA1, CA3 and the dentate gyrus was much reduced. Chronic inflammation as seen in levels of activated microglia and in the activity of the p38 MAPK - MKK - c-Jun- NF-κB p65 inflammation signaling pathway was reduced. In addition, improved growth factor signaling as shown in levels of activated ERK1 and IRS-1, and a reduction in the apoptosis signaling pathway C-raf, ERK2, Bcl-2/BAX and Caspase-3 was observed. Neurogenesis had also been normalized by the drug treatment as seen in increased neurogenesis (DCX-positive cells) in the dentate gyrus and a normalization of biomarkers for neurogenesis. In conclusion, semaglutide is a promising candidate for re-purposing as a stroke treatment.

[Effects of AdipoRon orally on the functions of spleen and pancreas in type 2 diabetic mice].

OBJECTIVE: To observe the effects of AdipoRon orally on the functions of spleen and pancreas in type 2 diabetic mice, in order to present data for clinical application. METHODS: Forty C57/BL6 male mice were randomly divided into 2 groups: normal control group (n=10) and model group (n=30), the former group was fed normally, while the later group was fed with high fat and sugar for 4 weeks.After that, type 2 diabetes model was established in DM group induced by intraperitoneal injection of streptozotocin (STZ, 40 mg/kg).As type 2 diabetes model established successfully, the model mice were randomly divided into three groups (n=10): diabetes mellitus (DM) group, high dose of AdipoRon group (DM + H) and low dose of adiponRon group (DM + L).All the four groups were treated with saline, saline, AdipoRon at the doses of 20 mg/kg and 50 mg/kg by gavages respectively, once a day for 10 days.And then put them to death for collecting blood, pancreas and spleen.Pathological changes of pancreas were observed with a light microscope after HE staining.Protein contents of insulin receptor (INSR), insulin receptor substrate 1( IRS-1) and tumor necrosis factor-α(TNF-α) in pancreatic and spleen tissues were detected by ELISA.The protein level of phosphorylation insulin receptor substrate 1(p-IRS-1) in pancreas was determined by Western blot, and the expression of insulin mRNA in pancreas was tested by RT-PCR. RESULTS: Under the light microscope, it was visible that the pancreatic tissue in NC group was full and closely packed, and the islet was big.Pancreatic tissue of DM mice was incompact and the islet of DM mice was smaller than that of normal mice.As for the mice treated with AdipoRon orally, the pancreatic tissue was full and closely arranged, and the islet was slightly smaller.Compared with NC group, the levels of TNF-α in pancreas and spleen of DM group were increased markedly, the levels of INSR and IRS-1 were decreased, the spleen coefficient, p-IR-1 protein level and insulin mRNA expression in pancreas were decreased, all were significant statistically (P＜0.05).Compared with DM group, the levels of TNF-α in pancreas and spleen of AdipoRon groups were decreased, the levels of INSR and IRS-1 in pancreas and spleen of AdipoRon groups were increased, while the spleen coefficient was increased (P＜0.05).The p-IRS-1 protein level and insulin mRNA expression in pancreas in DM+H group were increased (P＜0.05).Compared with DM + L group, the level of TNF-α was decreased, and the levels of INSR and IRS-1 were significantly increased (P＜0.05) in DM + H group (P＜0.05). CONCLUSION: Oral administration of AdipoRon can protect the spleen and pancreas of diabetic mice by decreasing the inflammatory response, up-regulating the expression of INSR, and increasing p-IRS-1 level in diabetic mice.

Effects of Lactobacillus Plantarum and Lactobacillus Helveticus on Renal Insulin Signaling, Inflammatory Markers, and Glucose Transporters in High-Fructose-Fed Rats.

Background and Objectives: The excess consumption of fructose in the diet may cause metabolic syndrome, which is associated with an increased risk of kidney disease. There is limited data on probiotic treatment in high-fructose-induced metabolic syndrome. The present study aims to investigate whether the supplementation of Lactobacillus plantarum (L. plantarum) and Lactobacillus helveticus (L. helveticus) could provide an improving effect on the renal insulin signaling effectors, inflammatory parameters, and glucose transporters in fructose-fed rats. Materials and Methods: The model of metabolic syndrome in male Wistar rats was produced by fructose, which was given as 20% solution in drinking water for 15 weeks. L. plantarum and L. helveticus supplementations were given by gastric gavage from 10 to 15 weeks of age. Results: High-fructose consumption in rats reduced renal protein expressions of insulin receptor substrate (IRS)-1, protein kinase B (AKT), and endothelial nitric oxide synthase (eNOS), which were improved by L. plantarum and partially by L. helveticus supplementations. Dietary fructose-induced elevations in renal tissue levels of tumor necrosis factor α (TNF-α), interleukin (IL)-1ß, IL-6, and IL-10, as well as expression of IL-6 mRNA, were attenuated, especially in L. plantarum treated rats. The increased renal expression of sodium-glucose cotransporter-2 (SGLT2), but not that of glucose transporter type-5 (GLUT5), was suppressed by the treatment with L. plantarum. Conclusion: Suppression in insulin signaling pathway together with the induction of inflammatory markers and upregulation of SGLT2 in fructose-fed rats were improved by L. plantarum supplementation. These findings may offer a new approach to the management of renal dysregulation induced by dietary high-fructose.

Effects of pomegranate aril juice and its punicalagin on some key regulators of insulin resistance and oxidative liver injury in streptozotocin-nicotinamide type 2 diabetic rats.

Nowadays, medicinal plants have been widely used everywhere to provide essential care for many disorders including diabetes. Recent reports assumed that the antidiabetic activities of pomegranate aril juice (PAJ) may be ascribed to its punicalagin (PCG). Therefore, the present study evaluated and compared the antidiabetic activities of PAJ and its PCG, and monitored some mechanisms of their actions in streptozotocin-nicotinamide (STZ-NA) type 2 diabetic rats. STZ-NA diabetic rats were given, orally/daily, PAJ (100 or 300 mg/kg body weight, containing 2.6 and 7.8 mg of PCG/kg body weight, respectively), pure PCG (2.6 or 7.8 mg/kg body weight), or distilled water (vehicle) for 6 weeks. PAJ (especially at the high dose) alleviated significantly (P < 0.05-0.001) most signs of type 2 diabetes including body-weight loss, insulin resistance (IR) and hyperglycemia through decreasing serum tumor necrosis factor-α concentration and the expression of hepatic c-Jun N-terminal kinase, and increasing the skeletal muscle weight and the expression of hepatic insulin receptor substrate-1 in STZ-NA diabetic rats. Also, it decreased significantly (P < 0.001) the oxidative liver injury in STZ-NA diabetic rats through decreasing the hepatic lipid peroxidation and nitric oxide production, and improving the hepatic antioxidant defense system. Although the low dose of PCG induced some modulation in STZ-NA diabetic rats, the high dose of PCG did not show any valuable antidiabetic activity, but induced many side effects. In conclusion, PAJ was safer and more effective than pure PCG in alleviating IR and oxidative liver injury in STZ-NA diabetic rats.

Caffeine-mediated BDNF release regulates long-term synaptic plasticity through activation of IRS2 signaling.

Caffeine has cognitive-enhancing properties with effects on learning and memory, concentration, arousal and mood. These effects imply changes at circuital and synaptic level, but the mechanism by which caffeine modifies synaptic plasticity remains elusive. Here we report that caffeine, at concentrations representing moderate to high levels of consumption in humans, induces an NMDA receptor-independent form of LTP (CAF LTP) in the CA1 region of the hippocampus by promoting calcium-dependent secretion of BDNF, which subsequently activates TrkB-mediated signaling required for the expression of CAF LTP. Our data include the novel observation that insulin receptor substrate 2 (IRS2) is phosphorylated during induction of CAF LTP, a process that requires cytosolic free Ca2+ . Consistent with the involvement of IRS2 signals in caffeine-mediated synaptic plasticity, phosphorylation of Akt (Ser473) in response to LTP induction is defective in Irs2-/- mice, demonstrating that these plasticity changes are associated with downstream targets of the phosphoinositide 3-kinase (PI3K) pathway. These findings indicate that TrkB-IRS2 signals are essential for activation of PI3K during the induction of LTP by caffeine.

Effect of Alkaloids from Nelumbinis Plumula against Insulin Resistance of High-Fat Diet-Induced Nonalcoholic Fatty Liver Disease in Mice.

This study aimed to investigate the effects of total alkaloids from Nelumbinis Plumula (NPA) on insulin resistance (IR) of high-fat diet- (HFD-) induced nonalcoholic fatty liver disease (NAFLD). Rats were fed with HFD for 8 weeks to induce NAFLD. Then, the effect of NPA on ameliorating IR in HFD-induced NAFLD was evaluated. Fasting serum insulin was determined using an enzyme-linked immunosorbent assay (ELISA) kit for insulin following the manufacturer's protocol. Some inflammatory cytokines such as tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL-6) were determined using ELISA kits to assess the inflammatory burden in rats. The results showed that HFD could induce a significant increase in blood glucose and IR in rats. However, rats treated with NPA (400 or 600 mg/kg) showed improved IR and reduction in serum inflammatory cytokines TNF-α and IL-6. Further investigation indicated that NPA could inhibit IR by restoring the insulin receptor substrate-1 (IRS-1) and suppressing the expression of c-Jun N-terminal kinase (JNK) phosphorylation. The present results supported the view that the pathogenesis of NAFLD was complex with inflammation, together with increasing serum glucose and IR. Also, JNK and IRS phosphorylation were suggested for their involvement in the modulating of IR during NAFLD progression. Therefore, NPA may serve as a potential natural remedy against IR in NAFLD.

Urotensin II-induced insulin resistance is mediated by NADPH oxidase-derived reactive oxygen species in HepG2 cells.

AIM: To investigated the effects of urotensin II (UII) on hepatic insulin resistance in HepG2 cells and the potential mechanisms involved. METHODS: Human hepatoma HepG2 cells were cultured with or without exogenous UII for 24 h, in the presence or absence of 100 nmol/L insulin for the last 30 min. Glucose levels were detected by the glucose-oxidase method and glycogen synthesis was analyzed by glycogen colorimetric/fluorometric assay. Reactive oxygen species (ROS) levels were detected with a multimode reader using a 2',7'-dichlorofluorescein diacetate probe. The protein expression and phosphorylation levels of c-Jun N-terminal kinase (JNK), insulin signal essential molecules such as insulin receptor substrate -1 (IRS-1), protein kinase B (Akt), glycogen synthase kinase-3ß (GSK-3ß), and glucose transporter-2 (Glut 2), and NADPH oxidase subunits such as gp91(phox), p67(phox), p47(phox), p40(phox), and p22(phox) were evaluated by Western blot. RESULTS: Exposure to 100 nmol/L UII reduced the insulin-induced glucose consumption (P < 0.05) and glycogen content (P < 0.01) in HepG2 cells compared with cells without UII. UII also abolished insulin-stimulated protein expression (P < 0.01) and phosphorylation of IRS-1 (P < 0.05), associated with down-regulation of Akt (P < 0.05) and GSK-3ß (P < 0.05) phosphorylation levels, and the expression of Glut 2 (P < 0.001), indicating an insulin-resistance state in HepG2 cells. Furthermore, UII enhanced the phosphorylation of JNK (P < 0.05), while the activity of JNK, insulin signaling, such as total protein of IRS-1 (P < 0.001), phosphorylation of IRS-1 (P < 0.001) and GSK-3ß (P < 0.05), and glycogen synthesis (P < 0.001) could be reversed by pretreatment with the JNK inhibitor SP600125. Besides, UII markedly improved ROS generation (P < 0.05) and NADPH oxidase subunit expression (P < 0.05). However, the antioxidant/NADPH oxidase inhibitor apocynin could decrease UII-induced ROS production (P < 0.05), JNK phosphorylation (P < 0.05), and insulin resistance (P < 0.05) in HepG2 cells. CONCLUSION: UII induces insulin resistance, and this can be reversed by JNK inhibitor SP600125 and antioxidant/NADPH oxidase inhibitor apocynin targeting the insulin signaling pathway in HepG2 cells.

Neuregulin improves response to glucose tolerance test in control and diabetic rats.

Neuregulin (NRG) is an EGF-related growth factor that binds to the tyrosine kinase receptors ErbB3 and ErbB4, thus inducing tissue development and muscle glucose utilization during contraction. Here, we analyzed whether NRG has systemic effects regulating glycemia in control and type 2 diabetic rats. To this end, recombinant NRG (rNRG) was injected into Zucker diabetic fatty (ZDF) rats and their respective lean littermates 15 min before a glucose tolerance test (GTT) was performed. rNRG enhanced glucose tolerance without promoting the activation of the insulin receptor (IR) or insulin receptor substrates (IRS) in muscle and liver. However, in control rats, rNRG induced the phosphorylation of protein kinase B (PKB) and glycogen synthase kinase-3 (GSK-3) in liver but not in muscle. In liver, rNRG increased ErbB3 tyrosine phosphorylation and its binding to phosphatidylinositol 3-kinase (PI3K), thus indicating that rNRG activates the ErbB3/PI3K/PKB signaling pathway. rNRG increased glycogen content in liver but not in muscle. rNRG also increased the content of fructose-2,6-bisphosphate (Fru-2,6-P2), an activator of hepatic glycolysis, and lactate in liver but not in muscle. Increases in lactate were abrogated by wortmannin, a PI3K inhibitor, in incubated hepatocytes. The liver of ZDF rats showed a reduced content of ErbB3 receptors, entailing a minor stimulation of the rNRG-induced PKB/GSK-3 cascade and resulting in unaltered hepatic glycogen content. Nonetheless, rNRG increased hepatic Fru-2,6-P2 and augmented lactate both in liver and in plasma of diabetic rats. As a whole, rNRG improved response to the GTT in both control and diabetic rats by enhancing hepatic glucose utilization.

Hypoglycemic Activity through a Novel Combination of Fruiting Body and Mycelia of Cordyceps militaris in High-Fat Diet-Induced Type 2 Diabetes Mellitus Mice.

Diabetes mellitus (DM) is currently ranked among leading causes of death worldwide in which type 2 DM is reaching an epidemic proportion. Hypoglycemic medications for type 2 DM have either proven inadequate or posed adverse effects; therefore, the Chinese herbal products are under investigation as an alternative treatment. In this study, a novel combination of fruiting body and mycelia powder of herbal Cordyceps militaris number 1 (CmNo1) was administered to evaluate their potential hypoglycemic effects in high-fat diet- (HFD-) induced type 2 DM in C57BL/6J mice. Body weight, fasting blood glucose (FBG), oral glucose tolerance test (OGTT), and blood biochemistry indexes were measured. Results indicated that CmNo1 lowered the blood glucose level by increasing insulin sensitivity, while no change in body weight was observed. Increased protein expression of IRS-1, pIRS-1, AKT, pAKT, and GLUT-4 in skeletal muscle and adipose tissue was found indicating restoration of insulin signaling. Additionally, PPAR-γ expression in adipose tissue restored the triglyceride and cholesterol levels. Finally, our results suggest that CmNo1 possesses strong hypoglycemic, anticholesterolemic, and antihypertriglyceridemic actions and is more economical alternate for DM treatment.

L-Citrulline increases hepatic sensitivity to insulin by reducing the phosphorylation of serine 1101 in insulin receptor substrate-1.

BACKGROUND: Insulin resistance is characterized by deficient responses to insulin in its target tissues. In the present study, we examined the effects of L-Citrulline (L-Cit) on insulin sensitivity and signaling cascades in rat hepatoma H4IIE cells and SHRSP.Z-Leprfa/IzmDmcr rats. METHODS: H4IIE cells were pretreated in the presence or absence of 250 µM L-Cit in serum-free medium and then incubated in the presence or absence of 0.1 nM insulin. Rats were allocated into 2 groups; a control group (not treated) and L-Cit group (2 g/kg/day, L-Cit) and treated for 8 weeks. RESULTS: L-Cit enhanced the insulin-induced phosphorylation of Akt in H4IIE cells. Moreover, the inhibited expression of Dex/cAMP-induced PEPCK mRNA by insulin was enhanced by the L-Cit treatment. The phosphorylation of tyrosine, which is upstream of Akt, in insulin receptor substrate-1 (IRS-1) was increased by the L-Cit treatment. The L-Cit-induced enhancement in insulin signaling was not related to the binding affinity of insulin to the insulin receptor or to the expression of the insulin receptor, but to a decrease in the phosphorylation of serine 1101 in IRS-1. These results were also confirmed in animal experiments. In the livers of L-Cit-treated rats, PI3K/Akt signaling was improved by decreases in the phosphorylation of serine 1101. CONCLUSIONS: We herein demonstrated for the first time the beneficial effects of L-Cit on improved insulin resistance associated with enhanced insulin sensitivity. These results may have clinical applications for insulin resistance and the treatment of type-2 diabetes.

Selective decontamination of the digestive tract ameliorates severe burn-induced insulin resistance in rats.

BACKGROUND: Severe burns often initiate the prevalence of hyperglycemia and insulin resistance, significantly contributing to adverse clinical outcomes. However, there are limited treatment options. This study was designed to investigate the role and the underlying mechanisms of oral antibiotics to selectively decontaminate the digestive tract (SDD) on burn-induced insulin resistance. MATERIALS AND METHODS: Rats were subjected to 40% of total body surface area full-thickness burn or sham operation with or without SDD treatment. Translocation of FITC-labeled LPS was measured at 4h after burn. Furthermore, the effect of SDD on post-burn quantity of gram-negative bacteria in gut was investigated. Serum or muscle LPS and proinflammatory cytokines were measured. Intraperitoneal glucose tolerance test and insulin tolerance test were used to determine the status of systemic insulin resistance. Furthermore, intracellular insulin signaling (IRS-1 and Akt) and proinflammatory related kinases (JNK and IKKß) were assessed by western blot. RESULTS: Burn increased the translocation of LPS from gut 4h after injury. SDD treatment effectively inhibited post-burn overgrowth of gram-negative enteric bacilli in gut. In addition, severe burns caused significant increases in the LPS and proinflammatory cytokines levels, activation of proinflammatory related kinases, and systemic insulin resistance as well. But SDD treatment could significantly attenuate burn-induced insulin resistance and improve the whole-body responsiveness to insulin, which was associated with the inhibition of gut-derived LPS, cytokines, proinflammatory related kinases JNK and IKKß, as well as activation of IRS-1 and Akt. CONCLUSIONS: SDD appeared to have an effect on proinflammatory signaling cascades and further reduced severe burn-induced insulin resistance.

Minireview: Novel aspects of M3 muscarinic receptor signaling in pancreatic ß-cells.

The release of insulin from pancreatic ß-cells is regulated by a considerable number of G protein-coupled receptors. During the past several years, we have focused on the physiological importance of ß-cell M3 muscarinic acetylcholine receptors (M3Rs). At the molecular level, the M3R selectively activates G proteins of the G(q) family. Phenotypic analysis of several M3R mutant mouse models, including a mouse strain that lacks M3Rs only in pancreatic ß-cells, indicated that ß-cell M3Rs play a key role in maintaining blood glucose levels within a normal range. Additional studies with transgenic M3R mouse models strongly suggest that strategies aimed to enhance signaling through ß-cell M3Rs may prove useful in the treatment of type 2 diabetes. More recently, we analyzed transgenic mice that expressed an M3R-based designer receptor in a ß-cell-specific fashion, which enabled us to chronically activate a ß-cell G(q)-coupled receptor by a drug that is otherwise pharmacologically inert. Drug-dependent activation of this designer receptor stimulated the sequential activation of G(q), phospholipase C, ERK1/2, and insulin receptor substrate 2 signaling, thus triggering a series of events that greatly improved ß-cell function. Most importantly, chronic stimulation of this pathway protected mice against experimentally induced diabetes and glucose intolerance, induced either by streptozotocin or by the consumption of an energy-rich, high-fat diet. Because ß-cells are endowed with numerous receptors that mediate their cellular effects via activation of G(q)-type G proteins, these findings provide a rational basis for the development of novel antidiabetic drugs targeting this class of receptors.

Decrease of microRNA-122 causes hepatic insulin resistance by inducing protein tyrosine phosphatase 1B, which is reversed by licorice flavonoid.

UNLABELLED: Protein tyrosine phosphatase 1B (PTP1B) inhibits hepatic insulin signaling by dephosphorylating tyrosine residues in insulin receptor (IR) and insulin receptor substrate (IRS). MicroRNAs may modulate metabolic functions. In view of the lack of understanding of the regulatory mechanism of PTP1B and its chemical inhibitors, this study investigated whether dysregulation of specific microRNA causes PTP1B-mediated hepatic insulin resistance, and if so, what the underlying basis is. In high-fat-diet-fed mice or hepatocyte models with insulin resistance, the expression of microRNA-122 (miR-122), the most abundant microRNA in the liver, was substantially down-regulated among those predicted to interact with the 3'-untranslated region of PTP1B messenger RNA (mRNA). Experiments using miR-122 mimic and its inhibitor indicated that miR-122 repression caused PTP1B induction. Overexpression of c-Jun N-terminal kinase 1 (JNK1) resulted in miR-122 down-regulation with the induction of PTP1B. A dominant-negative mutant of JNK1 had the opposite effect. JNK1 facilitated inactivating phosphorylation of hepatocyte nuclear factor 4α (HNF4α) responsible for miR-122 expression, as verified by the lack of HNF4α binding to the gene promoter. The regulatory role of JNK1 in PTP1B induction by a decrease in miR-122 level was strengthened by cell-based assays using isoliquiritigenin and liquiritigenin (components in Glycyrrhizae radix) as functional JNK inhibitors; JNK inhibition enabled cells to restore IR and IRS1/2 tyrosine phosphorylation and insulin signaling against tumor necrosis factor alpha, and prevented PTP1B induction. Moreover, treatment with each of the agents increased miR-122 levels and abrogated hepatic insulin resistance in mice fed a high-fat diet, causing a glucose-lowering effect. CONCLUSION: Decreased levels of miR-122 as a consequence of HNF4α phosphorylation by JNK1 lead to hepatic insulin resistance through PTP1B induction, which may be overcome by chemical inhibition of JNK.

Effect of ginsenosides Rg3 and Re on glucose transport in mature 3T3-L1 adipocytes.

Ginsenosides, the active component of Panax ginseng, have been shown to evidence a variety of biological activities associated with hyperglycemia, obesity and type 2 diabetes mellitus. This study evaluated the effects of the ginsenosides, Rg3 and Re, on glucose uptake and the glucose transport system in mature 3T3-L1 cells. The results demonstrated that the glucose uptake of ginsenosides Rg3 and Re at concentrations of 1-10 µM significantly increased by approximately ∼10% and ∼12%, respectively. Furthermore, the glucose transporter 4 (GLUT4) mRNA expression of ginsenosides Rg3 and Re at 10 µM was increased by approximately ∼1.73 and 1.43 fold, respectively. It was further confirmed in a series of experiments that ginsenosides Rg3 and Re stimulated the mRNA expression of insulin receptor substrate (IRS-1) and the expression of phosphatidylinositol 3-kinase (PI3K)-110α protein, which is involved in downstream events in the insulin signaling pathway. These findings demonstrate that ginsenosides Rg3 and Re may stimulate glucose uptake via the PI3K pathways involving IRS-1. Further, our results suggest that both of these ginsenosides might prove useful as effective antidiabetic and antihyperglycemic agents.

Effect of insulin in combination with selenium on Irs/PI3K-mediated GLUT4 expression in cardiac muscle of diabetic rats.

BACKGROUND: Oral administration of selenium is an effective treatment for diabetes in animal models. However, selenium exerts these effects at high doses and several toxic effects are produced. Low doses of selenium are relatively safe but are unable to elicit any antidiabetic effect. OBJECTIVES: The present study explored the prospect of using low doses of insulin in combination with selenium to evaluate their antidiabetic effect, and to evaluate their effect on IRS-1, PI3K and GLUT4 levels in cardiac muscle of diabetic rats. MATERIALS AND METHODS: Diabetic rats were treated with insulin, selenium, and insulin and selenium in combination for four weeks. The effect of these antidiabetic compounds was examined on general physiological parameters and distribution of IRS-1, PI3K and GLUT4 in cardiac muscle by immunoblotting and immunohistochemistry. RESULTS: Insulin in combination with selenium could significantly revive normoglycemia, and restore the disturbances in IRS-1, PI3K and GLUT4 levels in cardiac muscle. Treatment with insulin was only partially effective in the restoration of diabetic alterations. CONCLUSION: The treatment of diabetic rats with combined doses of insulin and selenium was most effective in controlling glycaemia, and remarkably restored GLUT4 distribution by IRS-1/PI3K-dependent pathway in cardiac muscle of diabetic rat.

Genetic variants of the insulin receptor substrate-1 are influencing the therapeutic efficacy of oral antidiabetics.

AIM: The therapeutic efficacy of oral hypoglycaemic drugs varies between individuals, and pharmacogenetic factors contribute to this variability. The Gly972Arg polymorphism in the insulin receptor substrate-1 (IRS-1) has been shown to play a role in insulin signal transduction and therapeutic failure to sulphonylurea drugs. METHODS: We studied the association between the IRS-1 polymorphism and the haemoglobin A1c (HbA1c) level in diabetic patients treated with insulinotropic versus non-insulinotropic hypoglycaemic drugs as a marker for the efficacy of an antidiabetic treatment. Genotyping of the IRS-1 Arg(972) variant was performed in type 2 diabetes patients treated with either sulphonylurea drugs, glinides or insulin or with metformin, acarbose or glitazones using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. RESULTS: Significantly higher HbA1c levels were observed in carriers of the Arg(972) variant after treatment with insulinotropic drugs compared to wild-type carriers (8.3 vs. 7.6%, p = 0.005, independent t-test). Furthermore, patients with secondary failure to insulinotropic hypoglycaemic drugs switching finally to insulin showed even higher HbA1c levels in carriers of Arg(972) compared to wild-type (8.7 vs. 7.6%, p = 0.005, independent t-test). CONCLUSIONS: Thus, we were able to replicate the earlier findings of an association between the IRS-1 Arg(972) variant and secondary failure to sulphonylurea drugs, and further observed a general association between HbA1c and this polymorphism in type 2 diabetes patients treated with insulinotropic hypoglycaemic drugs but not with metformin.

SOCS3 inhibits insulin signaling in porcine primary adipocytes.

Insulin resistance is a major player in the pathogenesis of type II diabetes, the metabolic syndrome, and obesity. SOCS3 plays an important role in the development of insulin resistance. To investigate the role of SOCS3 in porcine adipocyte insulin signaling, we first detected the effect of insulin on SOCS3 mRNA and protein expression in porcine primary adipocytes by real-time RT-PCR and Western blotting. Then, we constructed a recombinant adenovirus encoding SOCS3 gene (Ad-SOCS3) which was used to infect differentiated porcine primary adipocytes for 3 days. The expression and phosphorylation of main insulin signaling components were detected by Western blotting. The results showed that 100 nM insulin could induce SOCS3 mRNA expression but not protein expression, and overexpression of SOCS3 decreased IRS1 protein level, insulin-stimulated IRS1 tyrosine phosphorylation, PI3K activation, and Akt phosphorylation, but increased IRS1 serine phosphorylation in porcine primary adipocytes. These results indicate that SOCS3 is an important negative regulator of insulin signaling in porcine adipocytes. Thus, SOCS3 may be a novel therapeutic target for the prevention or treatment of insulin resistance and type II diabetes.