Restored Insulin Sensitivity Research Articles

OR09-2 Pathway Preferential Estrogens Prevent Hepatosteatosis Due to Ovariectomy and High-Fat Diets

Non-alcoholic fatty liver disease (NAFLD) is the most common form of chronic liver diseases in the United States. Simple and benign steatosis can gradually develop into the more serious conditions of nonalcoholic steatohepatitis (NASH) and cirrhosis. Population studies have demonstrated that men and postmenopausal women have higher incidences of NAFLD compared to premenopausal women, suggesting a protective role for estrogens. The decrease in estrogens due to the onset of menopause make postmenopausal women more susceptible to weight gain, fat redistribution to abdominal areas, dyslipidemia, hypertension and insulin resistance, all of which are major hallmarks of metabolic syndrome and are associated with NAFLD. Pathway preferential estrogen 1 (PaPE-1) is a novel estrogen receptor ligand that has been shown to favorably affect metabolic tissues without stimulating reproductive tissues. Though its effects on weight gain and fat accumulation have been previously investigated, its effects on liver transcriptome and plasma metabolites have yet to be determined. We use transcriptomics and metabolomics analysis to characterize the effects of PaPEs in two different mouse models: diet-induced obesity (DIO) and leptin-deficient (ob/ob) mice. PaPE-1 significantly decreased liver weight and lipid accumulation in both DIO and ob/ob models. Integrated pathway analysis using transcriptomics and metabolomics data showed that PaPE-1 treatment lowered genes associated with inflammation, collagen deposition, and fatty acid metabolism. On the other hand, PaPE-1 significantly increased expression of mitochondrial genes, particularly ones associated with electron transport chain and ribosome synthesis suggesting an increase in energy expenditure and mTOR signaling activity. In addition, PaPE-1 treatment restored insulin sensitivity in hepatocytes. Overall, our data show that PaPE-1 provides a metabolic benefit without stimulation of reproductive tissues.

Systemic inactivation of hypoxia-inducible factor prolyl 4-hydroxylase 2 in mice protects from alcohol-induced fatty liver disease

Alcoholic fatty liver disease (AFLD) is a growing health problem for which no targeted therapy is available. We set out to study whether systemic inactivation of the main hypoxia-inducible factor prolyl 4-hydroxylase, HIF-P4H-2 (PHD2/EglN1), whose inactivation has been associated with protection against metabolic dysfunction, could ameliorate it. HIF-P4H-2-deficient and wild-type (WT) mice or HIF-P4H inhibitor-treated WT mice were subjected to an ethanol diet for 3–4 weeks and their metabolic health, liver and white adipose tissue (WAT) were analyzed. Primary hepatocytes from the mice were used to study cellular ethanol metabolism. The HIF-P4H-2-deficient mice retained a healthier metabolic profile, including less adiposity, better lipoprotein profile and restored insulin sensitivity, while on the ethanol diet than the WT. They also demonstrated protection from alcohol-induced steatosis and liver damage and had less WAT inflammation. In liver and WAT the expression of the key lipogenic and adipocytokine mRNAs, such as Fas and Ccl2, were downregulated, respectively. The upregulation of metabolic and antioxidant hypoxia-inducible factor (HIF) target genes, such as Slcs 16a1 and 16a3 and Gclc, respectively, and a higher catalytic activity of ALDH2 in the HIF-P4H-2-deficient hepatocytes improved handling of the toxic ethanol metabolites and oxidative stress. Pharmacological HIF-P4H inhibition in the WT mice phenocopied the protection against AFLD. Our data show that global genetic inactivation of HIF-P4H-2 and pharmacological HIF-P4H inhibition can protect mice from alcohol-induced steatosis and liver injury, suggesting that HIF-P4H inhibitors, now in clinical trials for renal anemia, could also be studied in randomized clinical trials for treatment of AFLD.

The response of insulin signaling proteins IRS1 and PTP-1B to endurance, HIIT and resistance training in rats with experimental diabetes

Summary Objectives Exercise is widely perceived to be an important component for diabetes. This study designed to evaluate the responses of different exercises (aerobic, HIIT, resistance) to PTP1B and IRS-1 expression of gastrocnemius muscle in experimental diabetes rats. Material and methods 40 diabetic male Wistar rats were divided into: four groups: control group, aerobic, resistance, and HIIT group. The exercises protocols were carried out for 12 weeks. Blood sample was collected for serum glucose and insulin analysis. The animals were then sacrificed and Blood sample was collected for serum glucose and insulin analysis. Gastrocnemius muscle was also exposed for evaluation of PTP-1B and IRS1 genes expression. Results Fasting blood glucose decreased and fasting serum insulin level increased significantly in all trained groups compared to diabetic control group, whereas HOMA_IR index not significantly changed. The expression of IRS1 gene upregulated significantly in aerobic and HIIT trained groups, but no significant difference observed the resistance group compared to the diabetic control group. Moreover, PTP-1B gene expression downregulated significantly in all aerobic, HIIT, and resistance groups compared to control group by different mechanisms. Conclusion The results provide new insights into the mechanism of insulin resistance linked to physical exercise and which exercise protocol restores insulin sensitivity.

Increased Dynamin-Related Protein 1-Dependent Mitochondrial Fission Contributes to High-Fat-Diet-Induced Cardiac Dysfunction and Insulin Resistance by Elevating Tafazzin in Mouse Hearts.

High fat (HF)-diet-induced insulin resistance is a major contributor to the pathogenesis of cardiovascular diseases. However, the molecular mechanisms that regulate cardiac insulin signaling are not fully understood. The regulatory role of tafazzin in the hearts of HF-diet-fed mice is investigated. Mice are fed a HF diet or low fat (LF) diet for up to 24weeks. After 24weeks, it is found that HF-diet-induced cardiac dysfunction is linked to overexpression of the mitochondrial protein tafazzin. Increased tafazzin promotes mitochondrial fission and impairs insulin signaling, which is mediated by dynamin-related protein 1 (Drp-1) translocation from the cytosol to the mitochondria. Furthermore, knockdown of tafazzin with siRNA inhibits palmitic-acid-induced mitochondrial fission and restores insulin sensitivity. Moreover, miR-125b-5p as an upstream regulator targeting tafazzin is identified and palmitate-induced insulin resistance further rescued. In HF-diet-fed mouse hearts, increased tafazzin contributes to insulin resistance via mediating Drp-1 translocation to the mitochondria, and a small non-coding RNA, miR-125b-5p, at least partially regulates this signaling pathway and alleviates insulin resistance.

Duodenal-jejunal lining increases postprandial unconjugated bile acid responses and disrupts the bile acid-FXR-FGF19 axis in humans

Background and AimsPlacement of the duodenal-jejunal bypass liner (DJBL) leads to rapid weight loss and restoration of insulin sensitivity in a similar fashion to bariatric surgery. Increased systemic bile acid levels are candidate effectors for these effects through postprandial activation of their receptors TGR5 and FXR. We aimed to quantify postprandial bile acid, GLP-1 and FGF19 responses and assess their temporal relation to the weight loss and metabolic and hormonal changes seen after DJBL placement. MethodsWe performed mixed meal testing in 17 obese patients with type 2 diabetes mellitus (DM2) directly before, one week after and 6 months after DJBL placement. ResultsBoth fasting and postprandial bile acid levels were unchanged at 1 week after implantation, and greatly increased 6 months after implantation. The increase consisted of unconjugated bile acid species. 3 hour-postprandial GLP-1 levels increased after 1 week and were sustained, whereas FGF19 levels and postprandial plasma courses were unaffected. ConclusionsDJBL placement leads to profound increases in unconjugated bile acid levels after 6 months, similar to the effects of bariatric surgery. The temporal dissociation between the changes in bile acids, GLP-1 and FGF19 and other gut hormone responses warrant caution about the beneficial role of bile acids after DJBL placement. This observational uncontrolled study emphasizes the need for future controlled studies.

Targeted Interleukin-22 Gene Delivery in the Liver by Polymetformin and Penetratin-Based Hybrid Nanoparticles to Treat Nonalcoholic Fatty Liver Disease.

Nonalcoholic fatty liver disease (NAFLD) is now a leading cause of chronic liver disease, and there is currently no available treatment strategy. Interleukin-22 (IL-22) has been recognized as a promising agent for alleviating NAFLD, but the efficacy of IL-22 is far from satisfactory because safe dose of IL-22 elicited limited improvement, whereas higher concentration might induce serious side effects and off-target toxicities. Thus, targeted and sustained expression of IL-22 in the liver is necessary. To meet the challenge, we elaborately developed a novel polymetformin carrier by conjugating biguanide to chitosan, termed chitosan-metformin (CM), which could exert advanced gene delivery efficiency and possess intrinsic therapeutic efficacy from metformin for NAFLD. CM accompanied with penetratin and DSPE-PEG2000 could self-assemble to form stable nanocomplexes with IL-22 gene via electrostatic interaction. This nanoparticle (CDPIA) exerted desirable particle size at ∼100 nm, fine morphology, and efficient cellular internalization. Furthermore, CDPIA also demonstrated a unique superiority in endosomal escape capacity and satisfactory biocompatibility as well as predominant liver accumulation. Most importantly, CDPIA distinctly alleviated hepatic steatosis, restored insulin sensitivity, and improved metabolic syndrome in high-fat-diet-fed mice model. This liver-targeted delivery of IL-22 activated STAT3/Erk1/2 and Nrf2/SOD1 signaling transductions as well as modulated lipid-metabolism-related gene expression. These findings altogether demonstrated that the polymetformin and penetratin-based hybrid nanoparticles could be exploited as a novel safe and efficient strategy for the improvement of NAFLD.

Efficacy of evogliptin and cenicriviroc against nonalcoholic steatohepatitis in mice: a comparative study.

Dipeptidyl peptidase (DPP)-4 inhibitors, or gliptins, are a class of oral hypoglycemic drugs that have been widely used as a second-line treatment for type 2 diabetes. Gliptins, which were introduced for clinical use a decade ago, have been shown to be beneficial against nonalcoholic fatty liver disease/nonalcoholic steatohepatitis (NASH) in animals and humans. Cenicriviroc (CVC), a dual antagonist of C-C chemokine receptor type 2 and 5, is currently under investigation against NASH and fibrosis. It was previously discovered that evogliptin (EVO) reduces hepatic steatosis in diet-induced obese animals but the effectiveness of EVO on NASH remains unexplored. Here, we compared the effectiveness of EVO and CVC against NASH and fibrosis in mice fed a high-fat and high-fructose diet (HFHF). Biochemical and histological analyses showed that mice fed a HFHF for 20 weeks developed severe hepatic steatosis and inflammation with mild fibrosis. Administration of EVO (0.2% wt/wt) for the last 8 weeks of HFHF feeding significantly reduced hepatic triglyceride accumulation, inflammation, and fibrosis as well as restored insulin sensitivity, as evidenced by lowered plasma insulin levels and the improvement in insulin tolerance test curves. Treatment of mice with CVC (0.1% wt/wt) inhibited hepatic inflammation and fibrogenesis with similar efficacy to that of EVO, without affecting hepatic steatosis. CVC treatment also reduced plasma insulin concentrations, despite no improvement in insulin tolerance. In conclusion, EVO administration efficiently ameliorated the development of NASH and fibrosis in HFHF-fed mice, corroborating its therapeutic potential.

Metabolic Effects of Bile Acids: Potential Role in Bariatric Surgery.

Bariatric surgery is the most effective and durable treatment for morbid obesity, with an unexplained yet beneficial side effect of restoring insulin sensitivity and improving glycemia, often before weight loss is observed. Among the many contributing mechanisms often cited, the altered handling of intestinal bile acids is of considerable therapeutic interest. Here, we review a growing body of literature examining the metabolic effects of bile acids ranging from their physical roles in dietary fat handling within the intestine to their functions as endocrine and paracrine hormones in potentiating responses to bariatric surgery. The roles of 2 important bile acid receptors, Takeda G-protein coupled receptor (also known as G-protein coupled bile acid receptor) and farnesoid X receptor, are highlighted as is downstream signaling through glucagon-like polypeptide 1 and its cognate receptor. Additional improvements in other phenotypes and potential contributions of commensal gut bacteria, such as Akkermansia muciniphila, which are manifest after Roux-en-Y gastric bypass and other emulations, such as gallbladder bile diversion to the ileum, are also discussed.

Exendin-4 from Heloderma suspectum venom: From discovery to its latest application as type II diabetes combatant.

Type II diabetes mellitus (T2DM) is a chronic non-communicable disease due to abnormal insulin actions causing uncontrolled hyperglycaemia. The treatment for T2DM, for instance, metformin and incretin mimetic, mainly focuses on the restoration of insulin sensitivity and secretion. Exendin-4 is a short incretin-mimetic peptide consisting of 39 amino acids. It is discovered in the venom of Heloderma suspectum as a full agonist for the glucagon-like peptide 1 (GLP-1) receptor and produces insulinotropic effects. It is more resistant to enzymatic degradation by dipeptidyl-peptidase-4 and has a longer half-life than the endogenous GLP-1; thus, it is further developed as an incretin hormone analogue used to treat T2DM. The helical region of the peptide first interacts with the extracellular N-terminal domain (NTD) of GLP-1 receptor while the C-terminal extension containing the tryptophan cage further enhances its binding affinity. After binding to the NTD of the receptor, it may cause the receptor to switch from its auto-inhibited state of the receptor to its auto-activated state. Exendin-4 enhances the physiological functions of β-cells and the up-regulation of GLP-1 receptors, thus reducing the plasma glucose levels. Moreover, exendin-4 has also been found to ameliorate neuropathy, nephropathy and ventricular remodelling. The therapeutic effects of exendin-4 have also been extrapolated into several clinical trials. Although exendin-4 has a reasonable subcutaneous bioavailability, its half-life is rather short. Therefore, several modifications have been undertaken to improve its pharmacokinetics and insulinotropic potency. This review focuses on the pharmacology of exendin-4 and the structure-function relationships of exendin-4 with GLP-1 receptor. The review also highlights some challenges and future directions in the improvement of exendin-4 as an anti-diabetic drug.

Subversion of Systemic Glucose Metabolism As a Mechanism to Support the Growth of Leukemia Cells

Epidemiological studies indicate that obese populations have an increased risk for leukemia. However, the mechanism underlying this phenomenon remains unclear. In the current study, utilizing both murine AML models and human AML samples, we observe that AML pathogenesis leads to aberrancies in adipose tissue, pancreatic function, and gut/microbiome, all of which contribute to an insulin resistant phenotype. We demonstrate that through induction of insulin resistance, leukemic disease alters systemic metabolism and thereby redirects systemic glucose to be preferentially available to malignant cells.We found that insulin effect on leukemic mice was significantly impaired as shown by insulin tolerance tests (ITT) (Fig.1) as well as by reduced glucose utilization in both adipose and muscle tissues. Interestingly, glucose utilization in leukemia cells was not affected by insulin. Several mechanisms were found to underlie this insulin resistant phenotype. First, leukemia induced a high-level production of IGFBP1 from adipose tissue and led to a 100-fold increase in circulating IGFBP1, which impaired insulin sensitivity (Fig.1). Blocking IGFBP1 partially restored insulin sensitivity and reduced leukemic burden, whereas pretreating with IGFBP1 facilitated leukemic progression. Second, a 95% reduction in the gut-derived circulating serotonin led to a significant decrease in insulin secretion from pancreas in leukemic mice (Fig.2). Serotonin supplementation partially restored serum insulin levels and decreased leukemic burden by 50% (Fig.2). Finally, the profile of gut microbiota in leukemic mice was distinct from normal mice. Leukemia-associated microbiota functionally contributed to the insulin resistant phenotype and therefore promoted disease progression. Mechanistically, decreased productions of microbiota-derived short chain fatty acids (SCFAs) i.e. butyrate and propionate, were found in leukemic fecal materials and butyrate supplementation reduced leukemic burden by 50% (Fig.2). Of note, there was interplay between these mechanisms. For example, agents increasing insulin levels resulted in a decreased IGFBP1 production in leukemic mice. Further, leukemia-associated microbiota also contributed to the elevated IGFBP1 level and the reduced insulin level in leukemic mice.To test the therapeutic relevance of our findings, we combined serotonin supplementation with butyrate, and found this combination (hereafter termed ‘Ser-Bu‘) reduced leukemic burden by 80% (Fig.3) and provided survival benefits. More importantly, multiple assays including PET-CT scanning (Fig.3), 3H-2-DG labeling, and 13C-NMR labeling were employed to demonstrate that Ser-Bu treatment increased glucose uptake/utilization in adipose and muscle tissues by 200% and 50% respectively and reduced glucose uptake/utilization in leukemia cells by 70% (Fig.3). Therefore, leukemia progression can be significantly attenuated solely by modulation of systemic glucose metabolism.To examine the human relevance of our findings, we analyzed serum samples from normal controls, MDS and AML patients and found that a 6-fold and a 14-fold increase of IGFBP1 in MDS and AML serum respectively compared to normal controls (Fig.4). Additionally, other insulin resistance indicators such as serum free fatty acids, inflammatory cytokines and serum Leptin and Resistin levels were all elevated in AML serum. An insulin resistant phenotype and elevated serum IGFBP1 were also observed in a primary human leukemia specimen xenograft model. Further, a 65% reduction in serotonin was found in AML serum compared to normal controls (Fig.4). Impressively, analyses of paired diagnostic, remission and relapsed BM specimens showed that IGFBP1 was decreased in remission samples and rebounded in the relapsed state, whereas serotonin level showed the opposite pattern (Fig.5). Together, these data support that an insulin resistant phenotype is also evident in AML patients.Collectively, our studies suggest that leukemic tumors gain a competitive advantage by co-opting multiple mechanisms to induce a diabetes-like physiological condition and thereby subvert systemic glucose metabolism to facilitate disease progression. Our studies demonstrate that restoration of normal glucose regulation may be a feasible strategy to suppress systemic growth of malignant cell types. DisclosuresPollyea:Gilead: Consultancy; Curis: Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Celyad: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Agios: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Consultancy, Research Funding; Argenx: Consultancy, Membership on an entity's Board of Directors or advisory committees.

SGLT Inhibitors for Type 1 Diabetes: An Obvious Choice or Too Good to Be True?

In the recent past we have been fortunate to find new treatments based on entirely new mechanisms . . . or is that really so? The sodium–glucose cotransporter inhibitors (SGLTi) offer an instructive case in point. These apparently “ new” agents were preceded by phlorizin, a naturally occurring compound that has been used for physiologic studies for over 100 years (1). Given orally it interferes with intestinal absorption of carbohydrates and causes glucosuria. Studies in animal models of diabetes have provided useful insights, such as evidence that reduction of hyperglycemia can restore insulin sensitivity toward normal (2). However, phlorizin was considered unsuited for use by humans due to undesirable side effects. Recently its mechanism of action has been traced to effects on sodium–glucose cotransporters (SGLT) in the intestinal mucosa and the renal proximal tubule (3), and drugs with more nuanced effects on these transporters have been developed (4,5). These newer agents have greater affinity for SGLT2, which is expressed mainly in the kidney, and less for SGLT1, which facilitates intestinal absorption of glucose. Clinical effects of the newer SGLTi drugs in type 2 diabetes (T2D) include modest reductions of plasma glucose and A1C, weight, and blood pressure and are mediated in large part by glucosuria and sodium diuresis. These agents are taken once daily by mouth and do not require dose titration. Symptomatic side effects—mostly urinary or genital irritation or infections—are common but tolerated by most patients. Importantly, the new SGLTi drugs have highly desirable—and somewhat unexpected—cardiac and renal protective effects, as least in selected cohorts. Large trials of empagliflozin and canagliflozin, aiming to demonstrate safety in patients with T2D and high cardiovascular risk, have shown favorable effects on heart failure, cardiovascular death, and progression of albuminuria (6–9). Unwanted effects have been reported as well, including …

A novel recombinant peptide INSR-IgG4Fc (Yiminsu) restores insulin sensitivity in experimental insulin resistance models

Type 2 diabetes mellitus (T2DM) is a chronic degenerative endocrine and metabolic disease with high mortality and morbidity, yet lacks effective therapeutics. We recently generated a novel fusion peptide INSR-IgG4Fc, Yiminsu (YMS), to facilitate the high-affinity binding and transportation of insulin. Thus, the aim of the present study was to determine whether the novel recombinant peptide, YMS, could contribute to restoring insulin sensitivity and glycaemic control in insulin resistance models and revealing its underlying mechanism. Palmitic acid (PA)-treated LO2 cells and high fat diet (HFD)-fed mice were treated with YMS. Therapeutic effects of YMS were measured using Western blotting, ELISA, qPCR, Histology and transmission electron microscopy. We observed that YMS treatment effectively improved insulin signaling in PA-treated LO2 cells and HFD-fed mice. Notably, YMS could significantly reduce serum levels of glucose, triglycerides, fatty acids and cholesterol without affecting the serum insulin levels. Moreover, our data demonstrated that YMS could restore glucose and lipid homeostasis via facilitating insulin transportation and reactivating PI3K/Akt signaling in both PA-treated cells and liver, gastrocnemius and brown fat of HFD-fed mice. Additionally, we noticed that the therapeutic effects of YMS was similar as rosiglitazone, a well-recognized insulin sensitizer. Our findings suggested that YMS is a potentially candidate for pharmacotherapy for metabolic disorders associated with insulin resistance, particularly in T2DM.

P9 - Plant Bioactives and the Intestinal Barrier: Redox Signaling and Implications for Insulin Resistance

Dietary plant bioactives, and in particular flavonoids, can exert actions at the gastrointestinal (GI) tract that can have an impact systemically, e.g. on glucose homeostasis, lipid and energy metabolism. GI barrier permeabilization and the associated increased passage to the circulation of luminal endotoxins underlie in part the pathophysiology of obesity-associated pathologies, including insulin resistance and type 2 diabetes. Endotoxins trigger systemic pro-inflammatory responses that contribute to tissue insulin resistance involving the activation of redox-regulated signals. Among flavonoids, we found that the flavan-3-ol (-)-epicatechin (EC) inhibits high fat (HFD)- and/or high fructose (HFr) diet-induced insulin resistance and steatosis in rodents. These beneficial effects are associated with EC capacity to inhibit HFD-mediated intestinal barrier permeabilization and endotoxemia. In vivo and in vitro studies support intestinal cell NADPH oxidase as a major target involved in EC effects. NADPH oxidase triggers a downstream series of events that cause tight junction disruption: NF-kB and ERK1/2 activation, upregulation of myosin light chain (MLC) kinase, leading to MLC phosphorylation and consequent monolayer permeabilization. Modulation of NADPH oxidase is also involved in the capacity of EC to restore insulin sensitivity in liver and adipose tissues, given that the redox-regulated activation of IKK/NF-kB, JNK1/2 and PKC causes inhibitory serine phosphorylation of the insulin receptor (IR) substrate 1 (IRS1), and upregulation of the IR and IRS1 inhibitory tyrosine phosphatase PTP1B. EC and other structurally related flavonoids (i.e. anthocyanidins (AC)) that directly inhibit NADPH oxidase, share similar chemical structures and capacity to improve insulin sensitivity. Furthermore, inhibition of NF-kB can explain EC-mediated decreased expression of select NADPH isoforms. In summary, the capacity of select bioactives (EC, AC) to improve HFD/HFR-associated insulin resistance is in part mediated through their capacity to modulate NADPH oxidase and redox-regulated pathways, leading to loss of GI tract barrier integrity and downregulation of the insulin pathway.

Hypolipidemic and Antioxidant Effects ofCitrullus colocynthisSeeds Oil in High-Fat Diets Induced Obese Rats

The purpose of the current study is to explore the prominent role of the fixed oil of Citrullus colocynthis seeds as a natural remedy to obesity. Wistar rats were subjected to different diets; one being an 8 week high-fat diet that was established to induce obesity in rats. The results from our experiment show a significant correction in body weight, blood parameters, and in particular, the total cholesterol, triglycerides, HDL-C (high-density lipoprotein cholesterol), and glycemia. There was also an improvement of the redox status shown by the significant increase in antioxidant vitamins levels and decrease in malondialdehyde contents as well as an increase in the hepatic enzymes activities in Citrullus colocynthis seeds oil treated rats compared to obese rats and olive oil treated rats. The results of this study demonstrated that Citrullus colocynthis seeds oil prompted a corrective effect in the antioxidant defense systems, restored insulin sensitivity, and improved lipid profile. To conclude, our study suggests thatCitrullus colocynthisseeds oil is a promising natural tool to combat obesity and its associated complications.

GLP-1 Analogue Liraglutide Attenuates Mutant Huntingtin-Induced Neurotoxicity by Restoration of Neuronal Insulin Signaling.

Huntington’s disease (HD) is a progressive and fatal neurodegenerative disease caused by CAG repeat expansion in the coding region of huntingtin (HTT) protein. The accumulation of mutant HTT (mHTT) contributes to neurotoxicity by causing autophagy defects and oxidative stress that ultimately lead to neuronal death. Interestingly, epidemiologic studies have demonstrated that the prevalence of type-2 diabetes, a metabolic disease mainly caused by defective insulin signaling, is higher in patients with HD than in healthy controls. Although the precise mechanisms of mHTT-mediated toxicity remain unclear, the blockade of brain insulin signaling may initiate or exacerbate mHTT-induced neurodegeneration. In this study, we used an in vitro HD model to investigate whether neuronal insulin signaling is involved in mHTT-mediated neurotoxicity. Our results demonstrated that mHTT overexpression significantly impairs insulin signaling and causes apoptosis in neuronal cells. However, treatment with liraglutide, a GLP-1 analogue, markedly restores insulin sensitivity and enhances cell viability. This neuroprotective effect may be attributed to the contribution of the upregulated expression of genes associated with endogenous antioxidant pathways to oxidative stress reduction. In addition, liraglutide stimulates autophagy through AMPK activation, which attenuates the accumulation of HTT aggregates within neuronal cells. Our findings collectively suggest that liraglutide can rescue impaired insulin signaling caused by mHTT and that GLP-1 may potentially reduce mHTT-induced neurotoxicity in the pathogenesis of HD.

Glucocorticoid-induced insulin resistance is related to macrophage visceral adipose tissue infiltration

Insulin resistance is frequently present in patients with glucocorticoid (GC) excess (Cushing’s syndrome) or treated with high doses of GCs. Furthermore, others similarities between metabolic syndrome (visceral obesity, elevated blood glucose levels, dyslipidemia) and Cushing’s syndrome suggest that GCs could play a role in obesity-linked complications. Here we reported that long-term corticosterone (CORT) exposure in mice induced weight gain, dyslipidemia as well as hyperglycaemia and systemic insulin resistance. CORT-treated mice exhibited an increased 11β-Hsd1 expression and corticosterone levels in fat depots but a specific upregulation of glucocorticoid receptor (Gr) and hexose-6-phosphate dehydrogenase only in gonadal adipose tissue, suggesting that GC could act differentially on various fat depots. Despite fat accumulation in all depots, an increased expression of adipogenic (Pparγ, C/ebpα) and lipogenic (Acc, Fas) key genes was restricted to gonadal adipose tissue. Hypertrophied adipocytes observed in both visceral and subcutaneous depots also resulted from reduced lipolytic activity due to CORT treatment. Surprisingly, GC treatment promoted macrophage infiltration (F4/80, Cd68) within all adipose tissues along with predominant M2-like macrophage phenotype, and can directly act on macrophages to induce this phenotype. Moreover, macrophage infiltration preceded mass gain and adipocyte hypertrophy. Of note, specific macrophage depletion in gonadal fat preferentially reduced the M2-like macrophage content, and partially restored insulin sensitivity in mice with GC-induced obesity and insulin resistance. These data provide evidence that GCs act on adipose tissue in a depot-dependent manner and that gonadal adipose macrophages are key effectors of GC-associated insulin resistance.

INT-767 prevents NASH and promotes visceral fat brown adipogenesis and mitochondrial function.

The bile acid receptors, farnesoid X receptor (FXR) and Takeda G-protein-coupled receptor 5 (TGR5), regulate multiple pathways, including glucose and lipid metabolism. In a rabbit model of high-fat diet (HFD)-induced metabolic syndrome, long-term treatment with the dual FXR/TGR5 agonist INT-767 reduces visceral adipose tissue accumulation, hypercholesterolemia and nonalcoholic steatohepatitis. INT-767 significantly improves the hallmarks of insulin resistance in visceral adipose tissue (VAT) and induces mitochondrial and brown fat-specific markers. VAT preadipocytes isolated from INT-767-treated rabbits, compared to preadipocytes from HFD, show increased mRNA expression of brown adipogenesis markers. In addition, INT-767 induces improved mitochondrial ultrastructure and dynamic, reduced superoxide production and improved insulin signaling and lipid handling in preadipocytes. Both in vivo and in vitro treatments with INT-767 counteract, in preadipocytes, the HFD-induced alterations by upregulating genes related to mitochondrial biogenesis and function. In preadipocytes, INT-767 behaves mainly as a TGR5 agonist, directly activating dose dependently the cAMP/PKA pathway. However, in vitro experiments also suggest that FXR activation by INT-767 contributes to the insulin signaling improvement. INT-767 treatment counteracts HFD-induced liver histological alterations and normalizes the increased pro-inflammatory genes. INT-767 also induces a significant reduction of fatty acid synthesis and fibrosis markers, while increasing lipid handling, insulin signaling and mitochondrial markers. In conclusion, INT-767 significantly counteracts HFD-induced liver and fat alterations, restoring insulin sensitivity and prompting preadipocytes differentiation toward a metabolically healthy phenotype.

Dietary supplementation of vitamin D prevents the development of western diet-induced metabolic, hepatic and cardiovascular abnormalities in rats.

The western diet high in fat and fructose may cause metabolic disorders and cardiovascular diseases. To evaluate whether long-term daily vitamin D3 supplementation prevents hepatic steatosis and cardiovascular abnormalities and restores insulin sensitivity caused by fat diet in rats without vitamin D deficiency. Three groups of rats were fed for 6 months with standard diet (SD), western diet (WD) or WD containing 23 IU/day/rat vitamin D3, respectively. Tail-cuff systolic blood pressure (SBP)measurements in conscious rats and transthoracic echocardiography were performed in basal condition, and after 3 and 6 months of diet. Hepatic steatosis and myocardial fibrosis were assessed in liver and cardiac tissues using standard methods. Serum insulin and 25(OH)D3 concentrations were determined using rat-specific ELISA kits. Insulin resistance was determined according to the homeostasis model assessment of insulin resistance (HOMA-IR) method. Sixty-one per cent of hepatocytes in WD rats had steatotic vacuoles compared with just 27% in rats on a WD plus vitamin D3 (p < 0.05).HOMA-IR was reduced in rats with vitamin D supplementation compared with WD alone (19.4 ± 5.2 vs 41.9 ± 8.9, p < 0.05). Rat blood pressure and left ventricular mass were both reduced by vitamin D3 supplementation. In animal models of liver and cardiovascular metabolic damage, the supplementation of vitamin D3 shows liver and cardio-protective effects.

Interleukin-4 Restores Insulin Sensitivity in Lipid-Induced Insulin-Resistant Adipocytes.

Obesity and latent inflammation in adipose tissue significantly contribute to the development of insulin resistance (IR) and type 2 diabetes. Here we studied whether the antiinflammatory interleukin-4 (IL-4) can restore insulin sensitivity in cultured 3T3-L1 adipocytes. The activity of key components of the insulin signaling cascade was assessed by immunoblotting using phospho-specific antibodies to insulin receptor substrate IRS1 (Tyr612), Akt (Thr308 and Ser473), and AS160 (Ser318) protein that regulates translocation of the GLUT4 glucose transporter to the plasma membrane. IR was induced in mature adipocytes with albumin-conjugated palmitate. IR significantly reduced phosphorylation levels of all the above-mentioned proteins. Addition of IL-4 to the culturing medium during IR induction led to a dose-dependent stimulation of the insulin-promoted phosphorylation of IRS1, Akt, and AS160. At the optimal concentration of 50ng/ml, IL-4 fully restored activation of the insulin cascade in IR cells, but it did not affect insulin signaling activation in the control cells. IL-4 neither upregulated expression of key adipogenesis markers GLUT4 and PPARγ nor caused lipid accumulation in the adipocytes. These results demonstrate that IL-4 can restore insulin sensitivity in adipocytes via mechanisms not associated with induced adipogenesis or de novo formation of lipid depots.

Neuraminidase 1 activates insulin receptor and reverses insulin resistance in obese mice

ObjectivesNeuraminidase 1 (NEU1) cleaves terminal sialic acids of glycoconjugates during lysosomal catabolism. It also modulates the structure and activity of cellular surface receptors affecting diverse pathways. Previously we demonstrated that NEU1 activates the insulin receptor (IR) and that NEU1-deficient CathAS190A-Neo mice (hypomorph of the NEU1 activator protein, cathepsin A/CathA) on a high-fat diet (HFD) develop hyperglycaemia and insulin resistance faster than wild-type animals. The major objective of the current work was to reveal the molecular mechanism by which NEU1 desialylation activates the IR and to test if increase of NEU1 activity in insulin target tissues reverses insulin resistance and glucose intolerance. MethodsTo test if desialylation causes a conformational change in the IR dimer we measured interaction between the receptor subunits by Bioluminescence Resonance Energy Transfer in the HEK293T cells either overexpressing NEU1 or treated with the NEU1 inhibitor. The influence of NEU1 overexpression on insulin resistance was studied in vitro in palmitate-treated HepG2 cells transduced with NEU1-expressing lentivirus and in vivo in C57Bl6 mice treated with HFD and either pharmacological inducer of NEU1, Ambroxol or NEU1-expressing adenovirus. NEU1-deficient CathAS190A-Neo mice were used as a control. ResultsBy desialylation of IR, NEU1 induced formation of its active dimer leading to insulin signaling. Overexpression of NEU1 in palmitate-treated HepG2 cells restored insulin signaling, suggesting that increased NEU1 levels may reverse insulin resistance. Five-day treatment of glycemic C57Bl6 mice receiving HFD with the activator of the lysosomal gene network, Ambroxol, increased NEU1 expression and activity in muscle tissue, normalized fasting glucose levels, and improved physiological and molecular responses to glucose and insulin. Ambroxol did not improve insulin sensitivity in obese insulin-resistant CathAS190A-Neo mice indicating that the Ambroxol effect is mediated through NEU1 induction. Sustained increase of liver NEU1 activity through adenovirus-based gene transfer failed to attenuate insulin resistance most probably due to negative feedback regulation of IR expression. ConclusionTogether our results demonstrate that increase of NEU1 activity in insulin target tissues reverses insulin resistance and glucose intolerance suggesting that a pharmacological modulation of NEU1 activity may be potentially explored for restoring insulin sensitivity and resolving hyperglycemia associated with T2DM.