Asiaticoside ameliorates type 2 diabetes mellitus in rats by modulating carbohydrate metabolism and regulating insulin signaling

Objective:To evaluate the effect of asiaticoside on streptozotocin(STZ)and nicotinamide(NAD)-induced carbohydrate metabolism abnormalities and deregulated insulin signaling pathways in rats.Methods:Asiaticoside(50 and 100 mg/kg body weight)was administered to STZ-NAD-induced diabetic rats for 45 days,and its effects on hyperglycaemic,carbohydrate metabolic,and insulin signaling pathway markers were examined.Results:Asiaticoside increased insulin production,lowered blood glucose levels,and enhanced glycolysis by improving hexokinase activity and suppressing glucose-6-phosphatase and fructose-1,6-bisphosphatase activities.Abnormalities in glycogen metabolism were mitigated by increasing glycogen synthase activity and gluconeogenesis was decreased by decreasing glycogen phosphorylase activity.Furthermore,asiaticoside upregulated the mRNA expressions of IRS-1,IRS-2,and GLUT4 in STZ-NAD-induced diabetic rats and restored the beta cell morphology to normal.Conclusions:Asiaticoside has the potential to ameliorate type 2 diabetes by improving glycolysis,gluconeogenesis,and insulin signaling pathways.

Naringin ameliorates H_(2)O_(2)-induced oxidative damage in cells and prolongs the lifespan of female Drosophila melanogaster via the insulin signaling pathway

Naringin exists in a wide range of Chinese herbal medicine and has proven to possess several pharmacological properties.In this study,PC12,HepG2 cells,and female Drosophila melanogaster were used to investigate the antioxidative and anti-aging effects of naringin and explore the underlying mechanisms.The results showed that naringin inhibited H_(2)O_(2)-induced decline in cell viability and decreased,the content of reactive oxygen species in cells.Meanwhile,naringin prolonged the lifespan of flies,enhanced the abilities of climbing and the resistance to stress,improved the activities of antioxidant enzymes,and decreased malondialdehyde content.Naringin also improved intestinal barrier dysfunction and reduced abnormal proliferation of intestinal stem cells.Moreover,naringin down-regulated the mRNA expressions of inr,chico,pi 3k,and akt-1,and up-regulated the mRNA expressions of dilp2,dilp3,dilp5,and foxo,thereby activating autophagy-related genes and increasing the number of lysosomes.Furthermore,the mutant stocks assays and computer molecular simulation results further indicated that naringin delayed aging by inhibiting the insulin signaling(IIS)pathway and activating the autophagy pathway,which was consistent with the result of network pharmacological predictions.

Icariin ameliorates memory deficits through regulating brain insulin signaling and glucose transporters in 3×Tg-AD mice

Icariin,a major prenylated flavonoid found in Epimedium spp.,is a bioactive constituent of Herba Epimedii and has been shown to exert neuroprotective effects in experimental models of Alzheimer’s disease.In this study,we investigated the neuroprotective mechanism of icariin in an APP/PS1/Tau triple-transgenic mouse model of Alzheimer’s disease.We performed behavioral tests,pathological examination,and western blot assay,and found that memory deficits of the model mice were obviously improved,neuronal and synaptic damage in the cerebral cortex was substantially mitigated,and amyloid-βaccumulation and tau hyperphosphorylation were considerably reduced after 5 months of intragastric administration of icariin at a dose of 60 mg/kg body weight per day.Furthermore,deficits of proteins in the insulin signaling pathway and their phosphorylation levels were significantly reversed,including the insulin receptor,insulin receptor substrate 1,phosphatidylinositol-3-kinase,protein kinase B,and glycogen synthase kinase 3β,and the levels of glucose transporter 1 and 3 were markedly increased.These findings suggest that icariin can improve learning and memory impairments in the mouse model of Alzheimer’s disease by regulating brain insulin signaling and glucose transporters,which lays the foundation for potential clinical application of icariin in the prevention and treatment of Alzheimer’s disease.

Distinguishing normal brain aging from the development of Alzheimer＇s disease：inflammation,insulin signaling and cognition

As populations age, prevalence of Alzheimer＇s disease（AD） is rising. Over 100 years of research has provided valuable insights into the pathophysiology of the disease, for which age is the principal risk factor. However, in recent years, a multitude of clinical trial failures has led to pharmaceutical corporations becoming more and more unwilling to support drug development in AD. It is possible that dependence on the amyloid cascade hypothesis as a guide for preclinical research and drug discovery is part of the problem. Accumulating evidence suggests that amyloid plaques and tau tangles are evident in non-demented individuals and that reducing or clearing these lesions does not always result in clinical improvement. Normal aging is associated with pathologies and cognitive decline that are similar to those observed in AD, making differentiation of AD-related cognitive decline and neuropathology challenging. In this mini-review, we discuss the difficulties with discerning normal, age-related cognitive decline with that related to AD. We also discuss some neuropathological features of AD and aging, including amyloid and tau pathology, synapse loss, inflammation and insulin signaling in the brain, with a view to highlighting cognitive or neuropathological markers that distinguish AD from normal aging. It is hoped that this review will help to bolster future preclinical research and support the development of clinical tools and therapeutics for AD.

Novel soybean peptide iglycin ameliorates insulin resistance of high-fat diet fed C57BL/6J mice and differentiated 3T3L1 adipocytes with improvement of insulin signaling and mitochondrial function

Soy consumption has been associated with potential health benefits in reducing chronic diseases.These physiological functions have been attributed to soy proteins or more commonly to bioactive peptides.Thus,more studies are required to identify these bioactive peptides,and elucidate their biological mechanisms of action.In the present study,a novel peptide iglycin was purifi ed from soybean seeds with a molecular mass of 3.88 k Da.Thereafter,iglycin reduced fasting blood glucose and restored insulin sensitivity of C57 BL/6 J mice on a high-fat diet with increased phosphorylation of insulin receptor substrate 1(IRS1)and AKT in adipose tissue.Furthermore,it improved glucose uptake,induced translocation of intracellular GLUT4 to plasma membrane and activation of insulin signaling in adipocytes under insulin-resistant condition.In addition,it decreased reactive oxygen species production,lipid peroxidation and inhibited adipocyte apoptosis with improved mitochondrial function as evidenced by up-regulation of succinate dehydrogenase activity,mitochondrial membrane potential and intracellular ATP store.These data suggested that iglycin ameliorated insulin resistance via activation of insulin signaling,which was associated with inhibition of oxidative stress,adipocyte apoptosis,and improvement of mitochondrial function.

Pomegranate peel polyphenols alleviate insulin resistance through the promotion of insulin signaling pathway in skeletal muscle of metabolic syndrome rats

Insulin resistance(IR) has been considered to be an important causative factor of metabolic syndrome(Met S). The present study investigated whether pomegranate peel polyphenols(PPPs) could prevent the development of Met S by improving IR in rats. Male Sprague-Dawley(SD) rats were fed high fat diet(HFD) to induce Met S and supplemented with different dosages of PPPs for 12 weeks. The results showed that HFD-induced insulin resistant rats had disordered metabolism of blood glucose, blood lipid, and terrible muscle fiber morphology when compared with normal diet-fed rats, but PPPs treatment at a dosage of 300 mg/kg·day significantly reversed these negative effects. Moreover, in skeletal muscle tissue of insulin resistant rats, PPPs treatments significantly increased the protein expressions of insulin receptor(Ins R) and phosphorylated insulin receptor substrate 1(IRS-1), stimulated peroxisome proliferator activated receptor gamma(PPARγ) and phosphoinositide 3-kinase(PI3K)/protein kinase B(AKT/PKB) signaling pathway, and aggrandized the protein levels of phosphorylated glycogen synthase kinase-3β(GSK-3β) and glucose transporter 4(GLUT4). Our results suggest that PPPs possess of the beneficial effects on alleviating IR by enhancing insulin sensitivity and regulating glucose metabolism.

Bitter gourd extract improves glucose homeostasis and lipid profile via enhancing insulin signaling in the liver and skeletal muscles of diabetic rats

Objective:To investigate the modulatory effects of bitter gourd extract on the insulin signaling pathway in the liver and skeletal muscle tissues of diabetic rats.Methods:The ethanolic extract of bitter gourd was prepared and its contents of total polyphenols and flavonoids were assayed.A neonatal streptozotocin-induced diabetic rat model was established and the diabetic rats were assigned into different groups and were treated with different doses of bitter gourd extract(100,200,400,or 600 mg/kg)or with glibenclamide(0.1 mg/kg)for 30 d.Fasting blood glucose,insulin,and lipid profile were evaluated and the insulin signaling pathway in the liver and skeletal muscle of rats was investigated.The correlations between homeostasis model assessment(HOMA)and the components of insulin signaling pathway were also evaluated.Results:Different doses of bitter gourd extract significantly ameliorated fasting blood glucose level and HOMA index for insulin resistance.Moreover,bitter gourd extract increased serum insulin and improved disrupted serum lipid profile.The levels of insulin receptor substrate-1(IRS-1),p-insulin receptorβ(p-IR-β),protein kinase C(PKC),GLUT2,and GLUT4 were improved by treatment with bitter gourd extract.The best results were obtained with 400 mg/kg dose of the extract,the effect of which was equivalent to that of glibenclamide.HOMA in the bitter gourd treated rats was negatively correlated with p-IR-β,IRS-1 and PKC in hepatic and skeletal muscle.HOMA was also negatively correlated with skeletal muscle GLUT4.Conclusions:Bitter gourd extract improves glucose homeostasis and lipid profile in diabetic rats via enhancement of insulin secretion and sensitivity.Therefore,bitter gourd can be used as a potential pharmacological agent for the treatment of type 2 diabetes mellitus.

Effects of Omethoate on Liver Insulin Signaling in Mice

According to the report of the International Diabetes Federation, there were 382 million people affected with diabetes in 2013 and it is expected that this number will increase to 592 million by the year 2035;. Diabetes is caused due to the interaction between environmental and genetic factors;.

Diet restriction and exercise alleviate cognitive reduction of high fat diet (HFD)-induced obese mice by rescuing inflammation-mediated compromised insulin signaling pathway through activating AMPK/SIRT1 signal pathway and suppressing TLR4 signal pathway

Obesity,caused by excessive energy,leads to body weight gain and various diseases,including cognitive impairment.Current studies suggest that diet restriction such as optimal fasting and regular exercise are crucial for improving cognitive capacity.However,further exploration is needed to understand the specific mechanisms of high fat diet(HFD)-induced cognitive decline in obesity.In the present study,4-month-old mice were subjected to HFD feeding for 18 weeks,followed by aerobic exercise and high-intensity intermittent exercise,regular diet feeding,and intermittent fasting for 8 weeks,and then used to evaluate cognitive capacity,inflammation,compromised insulin signaling pathway,and apoptosis in hippocampal tissue,as well as AMPK/SIRT1 and TLR4 signal pathways.Obese mice revealed impaired cognitive capacity as compared with mice fed with regular diets.In contrast,aerobic exercise,high-intensity intermittent exercise,regular diet,and intermittent fasting could inhibit apoptosis caused by inflammation-mediated compromised insulin signaling pathway in hippocampal tissues through activating the AMPK/SIRT1 signal pathway and suppressing the TLR4 signal pathway,thereby rescuing the cognitive impairment of obese mice.Therefore,diet restriction and exercise interventions may play a positive role in reverting obesity-induced cognitive impairment.

LRP6 Bidirectionally Regulates Insulin Sensitivity through Insulin Receptor and S6K Signaling in Rats with CG-IUGR

Objective Intrauterine growth restriction followed by postnatal catch-up growth(CG-IUGR)increases the risk of insulin resistance-related diseases.Low-density lipoprotein receptor-related protein 6(LRP6)plays a substantial role in glucose metabolism.However,whether LRP6 is involved in the insulin resistance of CG-IUGR is unclear.This study aimed to explore the role of LRP6 in insulin signaling in response to CG-IUGR.Methods The CG-IUGR rat model was established via a maternal gestational nutritional restriction followed by postnatal litter size reduction.The mRNA and protein expression of the components in the insulin pathway,LRP6/β-catenin and mammalian target of rapamycin(mTOR)/S6 kinase(S6K)signaling,was determined.Liver tissues were immunostained for the expression of LRP6 andβ-catenin.LRP6 was overexpressed or silenced in primary hepatocytes to explore its role in insulin signaling.Results Compared with the control rats,CG-IUGR rats showed higher homeostasis model assessment for insulin resistance(HOMA-IR)index and fasting insulin level,decreased insulin signaling,reduced mTOR/S6K/insulin receptor substrate-1(IRS-1)serine307 activity,and decreased LRP6/β-catenin in the liver tissue.The knockdown of LRP6 in hepatocytes from appropriate-for-gestational-age(AGA)rats led to reductions in insulin receptor(IR)signaling and mTOR/S6K/IRS-1 serine307 activity.In contrast,LRP6 overexpression in hepatocytes of CG-IUGR rats resulted in elevated IR signaling and mTOR/S6K/IRS-1 serine307 activity.Conclusion LRP6 regulated the insulin signaling in the CG-IUGR rats via two distinct pathways,IR and mTOR-S6K signaling.LRP6 may be a potential therapeutic target for insulin resistance in CG-IUGR individuals.

Protective effects of Huanglian Wendan Decoction aganist cognitive deficits and neuronal damages in rats with diabetic encephalopathy by inhibiting the release of inflammatory cytokines and repairing insulin signaling pathway in hippocampus

Huanglian Wendan decoction(HLWDD) has been used for the treatment of symptom of "Re", one of major causes in diabetes and metabolic disorders, according to the theory of traditional Chinese medicine. The present study aimed at investigating the cerebral protective effects of HLWDD on diabetic encephalopathy(DE), one of the major diabetic complications. The effects of HLWDD and metformin were analyzed in the streptozocin(STZ) + high-glucose-fat(HGF) diet-induced DE rats by gastric intubation. In the present study, the effects of HLWDD on cognition deficits were investigated after 30-day intervention at two daily dose levels(3 and 6 g·kg^(-1)). To explore the potential mechanisms underlying the effects of HLWDD, we detected the alterations of neuronal damages, inflammatory cytokines, and impaired insulin signaling pathway in hippocampus of the DE rats. Based on our results from the present study, we concluded that the protective effects of HLWDD against the cognitive deficits and neuronal damages through inhibiting the release of inflammatory cytokines and repairing insulin signaling pathway in hippocampus of the DE rats.

Deregulation of brain insulin signaling in Alzheimer's disease

Contrary to the previous belief that insulin does not act in the brain, studies in the last three decades have demonstrated important roles of insulin and insulin signal transduction in various functions of the central nervous system. Deregulated brain insulin signaling and its role in molecular pathogenesis have recently been reported in Alzheimer＇s disease （AD）. In this article, we review the roles of brain insulin signaling in memory and cognition, the metabolism of amyloid 13 precursor protein, and tau phosphorylation. We further discuss deficiencies of brain insulin signaling and glucose metabolism, their roles in the development of AD, and recent studies that target the brain insulin signaling pathway for the treatment of AD. It is clear now that deregulation of brain insulin signaling plays an important role in the development of sporadic AD. The brain insulin signaling pathway also offers a promising therapeutic target for treating AD and probably other neurodegenerative disorders.

Jiaotai Pill(交泰丸) Enhances Insulin Signaling through Phosphatidylinositol 3-Kinase Pathway in Skeletal Muscle of Diabetic Rats

objective： To investigate the effect of Jiaotai Pill （交泰丸, JTP） at different constitutional proportions on insulin signaling through phosphatidylinositol 3-kinase （PI3K） pathway in the skeletal muscle of diabetic rats. Methods： The rat model of type 2 diabetes mellitus （T2DM） was established by intravenous injection of a small dose of streptozotoein plus high fat diet feeding. JTP at the same dosage of cinnamon and the increasing dosage of Coptis chinensis was administered to diabetic rats for nine weeks respectively. Plasma glucose and insulin levels were assayed. The expressions of proteins were determined by Western blot method. Results： All the three formulations of JTP decreased plasma glucose and fasting insulin levels as well as increased the protein expressions of insulin receptor β （InsR β） subunit, insulin receptor substrate-1 （IRS-1）, PI3K p85 subunit and glucose transporter 4 （GLUT4） in skeletal muscle. Meanwhile, JTP increased the tyrosine phosphorylation of InsRβ subunit and IRS-1, and reduced the serine phosphorylation of IRS-1 in skeletal muscle. Interestingly, the effect of JTP on improving insulin sensitivity was not dose-dependent. In contrast, JTP containing the least amount of Coptis chinensis exhibited the best effect. Conclusion： JTP at different constitutional proportions attenuates the development of diabetes in a rat model of T2DM. The mechanism might be associated with enhancing insulin signaling through PI3K pathway in the skeletal muscle.

Chronic Hyperinsulinism Induced Down-regulation of Insulin Post-Receptor Signaling Transduction in Hep G2 Cells

To study the regulatory effect of acute and chronic insulin treatmenton insulin post- re- ceptor signaling transduction pathway in a human hepatom a cell line (Hep G2 ) ,Hep G2 cells were incubated in the presence or absence of insulin with different concentrations in serum free m edia for16 h and then stim ulated with10 0 nmol/ L insulin for1m in.Protein levels of insulin receptor β- subunit(IRβ) ,insulin receptor substrate- 1(IRS- 1) and p85 subunit of phosphatidylinositol3- kinase(PI3- kinase) were determined in total cell lysates by Western- im munoblot.Phosphorylat- ed proteins IRβ,IRS- 1and interaction of PI3- kinase with IRS- 1were determ ined by im munopre- cipitation.Results showed that 1- min insulin stimulation rapidly induced tyrosine phosphorylation of IRβ and IRS- 1,which in turn,resulting in association of PI 3- kinase with IRS- 1.1- 10 0 nm ol/ L chronic insulin treatment induced a dose- dependent decrease in the protein level of IRβ and a slight decrease in the protein level of IRS- 1.There was a m ore marked reduction in the phospho- rylation of IRβ,IRS- 1,reaching a nadir of2 2 % (P<0 .0 1) and15 % (P<0 .0 1) of control lev- els,respectively,after16 h treatment with 10 0 nm ol/ L insulin.The association between IRS- 1 and PI3- kinase was decreased by6 6 % (P<0 .0 1) .There was no significant change in PI3- ki- nase protein levels. These data suggest that chronic insulin treatm ent can induce alterations of IRβ,IRS- 1and PI 3- kinase three early steps in insulin action,which contributes significantly to insulin resistance,and may account for desensitization of insulin action.

The regulatory subunits of PI3K, p85α and p85β, differentially affect BRD7-mediated regulation of insulin signaling

Bromodomain-containing protein 7 (BRD7) has been shown to interact with the regulatory subunit of phosphatidylinositol 3-kinase(PI3K), p85, in the insulin signaling pathway. Here, we show that upregulation of hepatic BRD7 improves glucose homeostasiseven in the absence of either p85 isoform, p85a or p85b. However, BRD7 leads to differential activation of downstream effectorproteins in the insulin signaling pathway depending on which isoform of p85 is present. In the presence of only p85a, BRD7 overexpression increases phosphorylation of insulin receptor (IR) upon insulin stimulation, without increasing the recruitment of p85to IR substrate. Overexpression of BRD7 also increases activation of Akt in response to insulin, but does not affect basal phosphorylation levels of Akt. Meanwhile, the phosphorylation of glycogen synthase kinase 3b (GSK3b) is increased by overexpression ofBRD7. On the other hand, in the presence of only p85b, BRD7 overexpression does not affect phosphorylation levels of IR, and Aktphosphorylation is not affected by insulin stimulation following BRD7 upregulation. However, BRD7 overexpression leads to increased basal phosphorylation levels of Akt and GSK3b. These data demonstrate that BRD7’s action on glucose homeostasis doesnot require the presence of both p85 isoforms, and p85a and p85b have unique roles in insulin signaling in the liver.

Mechanism by which statins influence insulin signaling pathway

Recent studies have shown that statins can influence insulin resistance （IR） in animal models and inhumans.1.2 However, the mechanism by which statins influence the insulin signaling pathway （ISP） remains obscure. It has been proposed that the pleiotropic effects of statins might be involved in regulation of IR.The phosphatidylinositol 3-kinase （PI3K）-Akt/protein kinase B （PKB） pathway is the main ISE Insulin binding to insulin receptor initiates PI3K-Akt pathway by phosphorylates tyrosine residue of IR substrate proteins （IRSs） including IRS-1 and IRS-2. Activation of the PI3K leads to the accumulation of phosphatidylinositol 3,4,5-triphosphate （PIP3）. PIP3 activates serine/ threonine kinase （Akt）. Glucose transporter-4 （GLUT-4） translocates to plasma membrane from cytosol by serine phosphorylation of Akt and directly regulates glucose metabolism in liver, muscle and adipose tissue （Figure 1）. However, an overall mechanism by which statins influence ISP remained obscure.

A New Link Between Insulin Signaling and Fragile X Syndrome

Fragile X syndrome （FXS） is the most common cause of inherited intellectual disability and the most common known genetic cause of autism or autism spectrum disorders. FXS is caused by silencing or mutation of the fragile X mental retardation gene （FMR1）, a known RNA-binding protein that acts as a negative regulator of translation [1, 2]. FXS patients demonstrate a myriad of symptoms that can vary widely between individuals, including impaired cognition, physical abnormalities, sleep problems, hyperarousal to sensory stimuli, increased anxiety, obsessive compulsive disorder-like behavior, attention-deficit hyperactive disorder symptoms, self-injurious behavior, aggression, and increased risk of seizures [3]. The molecular mechanisms underlying FXS are not clear, and currently there is no ideal treatment.

Effect of glucagon-like peptide-1 agonist on insulin signaling pathway in skeletal muscle of mice with insulin resistance

Objective To study the effect of glucagon-like peptide-1 agonist(exendin-4)on insulin signaling pathway in skeletal muscle of mice with insulin resistance(IR).Methods Thirty male KM mice were divided into normal control group(NC group,n=10)and IR group(n=20).The mice in NC group and IR group were fed

Maslinic acid modulates glycogen metabolism by enhancing the insulin signaling pathway and inhibiting glycogen phosphorylase

AIM: To investigate the molecular signaling mechanism by which the plant-derived, pentacyclic triterpene maslinic acid(MA) exerts anti-diabetic effects. METHOD: HepG2 cells were stimulated with various concentrations of MA. The effects of MA on glycogen phosphorylase a(GPa) activity and the cellular glycogen content were measured. Western blot analyses were performed with anti-insulin receptor β(IRβ), protein kinase B(also known as Akt), and glycogen synthase kinase-3β(GSK3β) antibodies. Activation status of the insulin pathway was investigated using phospho-IRβ, as well as phospho-Akt, and phospho-GSK3β antibodies. The specific PI3-kinase inhibitor wortmannin was added to the cells to analyze the Akt expression. Enzyme-linked immunosorbent assay(ELISA) was used to measure the effect of MA on IRβ auto-phosphorylation. Furthermore, the effect of MA on glycogen metabolism was investigated in C57BL/6J mice fed with a high-fat diet(HFD). RESULTS: The results showed that MA exerts anti-diabetic effects by increasing glycogen content and inhibiting glycogen phosphorylase activity in HepG2 cells. Furthermore, MA was shown to induce the phosphorylation level of IRβ-subunit, Akt, and GSK3β. The MA-induced activation of Akt appeared to be specific, since it could be blocked by wortmannin. Finally, MA treatment of mice fed with a high-fat diet reduced the model-associated adiposity and insulin resistance, and increased the accumulated hepatic glycogen content. CONCLUSION: The results suggested that maslinic acid modulates glycogen metabolism by enhancing the insulin signaling pathway and inhibiting glycogen phosphorylase.

Defect of insulin signal in peripheral tissues: important role of ceramide

In healthy people,balance between glucose production and its utilization is precisely controlled.When circulating glucose reaches a critical threshold level,pancreaticβcells secrete insulin that has two major actions:to lower circulating glucose levels by facilitating its uptake mainly into skeletal muscle while inhibiting its production by the liver.Interestingly,dietary triglycerides are the main source of fatty acids to fulfill energy needs of oxidative tissues.Normally,the unconsumed fraction of excess of fatty acids is stored in lipid droplets that are localized in adipocytes to provide energy during fasting periods.Thus,adipose tissue acts as a trap for fatty acid excess liberated from plasma triglycerides.When the buffering action of adipose tissue to store fatty acids is impaired,fatty acids that build up in othertissues are metabolized as sphingolipid derivatives such as ceramides.Several studies suggest that ceramides are among the most active lipid second messengers to inhibit the insulin signaling pathway and this review describes the major role played by ceramide accumulation in the development of insulin resistance of peripherals tissues through the targeting of specific proteins of the insulin signaling pathway.