Duodenal GLP-1 signaling regulates hepatic glucose production through a PKC-δ-dependent neurocircuitry.

Intestinal glucagon-like peptide-1 (GLP-1) is a hormone that stimulates insulin secretion and acts as a neuropeptide to control glucose homeostasis, but little is known whether intestinal GLP-1 has any effect in the control of hepatic glucose production (HGP). Here we found that intraduodenal infusion of GLP-1 activated duodenal PKC-δ, lowered HGP and was accompanied by a decrease in hepatic expression of gluconeogenic enzymes and an increase in hepatic insulin signaling in rats. However, gut co-infusion of either the GLP-1 receptor antagonist Ex-9, or the PKC-δ inhibitor rottlerin with GLP-1, negated the ability of gut GLP-1 to lower HGP and to increase hepatic insulin signaling during clamps. The metabolic and molecular signal effects of duodenal GLP-1 were also negated by co-infusion with tetracaine, pharmacologic inhibition of N-methyl-d-aspartate receptors within the dorsalvagal complex, or hepatic vagotomy in rats. In summary, we identified a neural glucoregulatory function of gut GLP-1 signaling.

NAMPT knockdown attenuates atherosclerosis and promotes reverse cholesterol transport in ApoE KO mice with high-fat-induced insulin resistance.

NAMPT has been suggested association with atherosclerosis and insulin resistance. However, the impact of NAMPT on atherosclerosis remained unknown. Therefore, the objective of this study was to use a NAMPT loss-of-function approach to investigate the effect of NAMPT on atherosclerosis in hypercholesterolemic mice. We demonstrated that a specific NAMPT knockdown increased plasma HDL-C levels, reduced the plaque area of the total aorta en face and the cross-sectional aortic sinus, decreased macrophage number and apoptosis, and promoted RCT in HFD-fed ApoE KO mice. These changes were accompanied by increased PPARα, LXRα, ABCA1 and ABCG1 expressions in the liver. NAMPT knockdown also facilitated cholesterol efflux in RAW264.7 cells. We further investigated the effect of NAMPT knockdown on the PPARα-LXRα pathway of cholesterol metabolism with MK886 (a selective inhibitor of PPARα) in RAW264.7 macrophages. MK886 abolished the ability of NAMPT knockdown to decrease intracellular cholesterol levels to enhance the rate of (3)H-cholesterol efflux and to increase ABCA1/G1 and LXRα expressions in RAW264.7 macrophages. Our observations demonstrate that NAMPT knockdown exerted antiatherogenic effects by promoting cholesterol efflux and macrophage RCT through the PPARα- LXRα- ABCA1/G1pathway in vitro and in vivo.

Stressful life events are associated with insulin resistance among Chinese immigrant women in the United States.

BACKGROUND: Chinese immigrants experience increased chronic disease risk following migration to the US. Although the impact of lifestyle changes (e.g., diet) on disease risk has been extensively studied, associations of psychosocial stress and disease risk have attracted less attention. Thus, the objective of the present study was to examine associations between stress and insulin resistance in foreign-born Chinese American women. METHODS: From October, 2005 to April, 2008, 423 women recruited from southeastern Pennsylvania completed questionnaires reporting stressful life events. Blood samples were analyzed for fasting insulin and fasting glucose levels, which were used to estimate insulin resistance according to the homeostasis model assessment (HOMAIR). RESULTS: In logistic regression analyses, a greater number of negative life events was associated with insulin resistance (OR=1.17, 95% CI=1.02-1.34), controlling for age, level of acculturation, marital status, body mass index, and waist circumference. Similarly, greater negative life event impact ratings were also associated with insulin resistance (OR=1.08, 95% CI=1.01-1.16) controlling for relevant covariates. CONCLUSIONS: This is one of the first studies to examine associations between psychosocial stress and insulin resistance in Chinese immigrant women. These findings contribute to a growing body of literature on stress and diabetes risk in an immigrant population.

Excessive caloric intake acutely causes oxidative stress, GLUT4 carbonylation, and insulin resistance in healthy men.

Obesity-linked insulin resistance greatly increases the risk for type 2 diabetes, hypertension, dyslipidemia, and non-alcoholic fatty liver disease, together known as the metabolic or insulin resistance syndrome. How obesity promotes insulin resistance remains incompletely understood. Plasma concentrations of free fatty acids and proinflammatory cytokines, endoplasmic reticulum ( ER) stress, and oxidative stress are all elevated in obesity and have been shown to induce insulin resistance. However, they may be late events that only develop after chronic excessive nutrient intake. The nature of the initial event that produces insulin resistance at the beginning of excess caloric intake and weight gain remains unknown. We show that feeding healthy men with ~6000 kcal/day of the common U.S. diet [~50% carbohydrate (CHO), ~ 35% fat, and ~15% protein] for 1 week produced a rapid weight gain of 3.5 kg and the rapid onset (after 2 to 3 days) of systemic and adipose tissue insulin resistance and oxidative stress but no inflammatory or ER stress. In adipose tissue, the oxidative stress resulted in extensive oxidation and carbonylation of numerous proteins, including carbonylation of GLUT4 near the glucose transport channel, which likely resulted in loss of GLUT4 activity. These results suggest that the initial event caused by overnutrition may be oxidative stress, which produces insulin resistance, at least in part, via carbonylation and oxidation-induced inactivation of GLUT4.

Tissue factor and Toll-like receptor (TLR)4 in hyperglycaemia-hyperinsulinaemia. Effects in healthy subjects, and type 1 and type 2 diabetes mellitus.

Diabetes mellitus (DM) patients have an increased incidence of cardiovascular events. Blood tissue factor-procoagulant activity (TF-PCA), the initiating mechanism for blood coagulation, is elevated in DM. We have shown that hyperglycaemia (HG), hyperinsulinaemia (HI) and combined HG+HI (induced using 24-hour infusion clamps) increases TF-PCA in healthy and type 2 DM (T2DM) subjects, but not in type 1 DM (T1DM) subjects. The mechanisms for this are unknown. DM patients have elevated plasma lipopolysaccharide (LPS), a toll-like receptor (TLR) 4 ligand. We postulated that TLR4 plays a role in modulating TF levels. We studied the effect of HG+HI on TLR4 and TF-PCA in vivo during 24-hour HG+HI infusion clamps in healthy subjects, and T1DM and T2DM subjects, and in vitro in blood. In vivo, in healthy subjects, 24-hour HG + HI infusion increased TLR4 six-fold, which correlated with TF-PCA (r= 0.91, p<0.0001). T2DM patients showed smaller increases in both. In T1DM subjects, TLR4 declined (50%, p<0.05) and correlated with TF-PCA (r=0.55; p<0.05). In vitro, HG (200 mg/dl added glucose) and HI (1-100 nM added insulin) increased TF-PCA in healthy subjects (~2-fold, 2-4 hours). Insulin inhibited by ~30% LPS-induced increase in TF-PCA and high glucose reversed it. TLR4 levels paralleled TF-PCA (r=0.71, p<0.0001); HG and HI increased TLR4 and insulin inhibited LPS-induced TLR4 increase. This is first evidence that even in healthy subjects, HG of short duration increases TLR4 and TF-PCA, key players in inflammation and thrombosis. TLR4-TF interplay is strikingly different in non-diabetic, T1DM and T2DM subjects.

Overexpression of JAZF1 protected ApoE-deficient mice from atherosclerosis by inhibiting hepatic cholesterol synthesis via CREB-dependent mechanisms.

Genome wide association studies have suggested an association of Juxtaposed with another zinc finger gene 1(JAZF1) with type 2 diabetes mellitus (T2DM). As an inhibitor of the TAK1/TR4 signaling pathway, JAZF1 has been shown to be involved in gluconeogenesis, lipid metabolism and insulin sensitivity. However, its role in insulin resistance and atherosclerosis in vivo remains unknown. The present study was designed to investigate in vivo the impact of JAZF1 on insulin resistance-associated dyslipidemia and atherosclerosis. Adenovirus-mediated JAZF1 overexpression was used to characterize the role of JAZF1 in the regulation of lipid metabolism and the development of atherosclerosis in normal chow- or HFD-fed ApoE KO mice. Insulin sensitivity was examined by EHC. Cholesterol de novo synthesis was measured by intraperitoneal [1-(14)C] acetate injection and atherosclerotic plaques were quantified by histological analysis. A dual-luciferase reporter assay was used to assess the ability of JAZF1 to regulate HMGCR transcriptional activity. JAZF1 overexpression improved HFD-induced hepatic insulin resistance in C57BL/6J mice. In HFD-fed ApoE KO mice, JAZF1 overexpression decreased serum cholesterol levels and hepatic cholesterol synthesis by inhibiting CREB-dependent HMGCR promoter transcriptional activity. Analysis of atherosclerotic lesion showed that JAZF1 overexpression had significantly reduced aortic and aortic sinus en face and cross-sectional plaque areas in HFD-fed ApoE KO mice. These data provide the first evidence for an important role of JAZF1 in increasing hepatic insulin sensitivity and preventing atherosclerosis.

Alterations in insulin-signaling and coagulation pathways in platelets during hyperglycemia-hyperinsulinemia in healthy non-diabetic subject.

INTRODUCTION: Diabetes mellitus (DM) is a prothrombotic and proinflammatory state. Hyperglycemia (HG) is encountered even in patients without DM. We have shown that combined HG and hyperinsulinemia (HI) in healthy non-diabetic subjects increased circulating tissue factor (TF) and thrombin generation. To understand the changes in platelet and monocyte pathways induced by combined HG and HI in healthy non-diabetic state, we performed whole genome expression profiling of leukocyte-depleted platelets and monocytes before and after 24 hours of combined HG (glucose ~200mg/dL) and HI by glucose infusion clamp in a healthy non-diabetic subject. RESULTS: We defined time-dependent differential mRNA expression (24 versus 0 hour fold change (FC) ≥ 2) common to platelets and monocytes. Ingenuity Pathways Analysis revealed alterations in canonical insulin receptor signaling and coagulation pathways. A preliminary group of 9 differentially expressed genes was selected for qRT-PCR confirmation. Platelet 24 hour sample was compared to the 0 hour sample plus 4 controls. Five transcripts in platelets and 6 in monocytes were confirmed. Platelet GSK3B and PTPN1 were upregulated, and STXBP4 was downregulated in insulin signaling, and F3 and TFPI were upregulated in coagulation pathways. Monocyte, PIK3C3, PTPN11 and TFPI were downregulated. Platelet GSKß3 and PTPN11 protein and TF antigen in platelets and monocytes was increased. CONCLUSIONS: Even in non-diabetic state, HG+HI for 24 hours induces changes in platelets and monocytes. They suggest downregulation of insulin signaling and upregulation of TF. Further studies are needed to elucidate cellular alterations leading to the prothrombotic and proinflammatory state in DM.

Insulin resistance is associated with diminished endoplasmic reticulum stress responses in adipose tissue of healthy and diabetic subjects.

We recently showed that insulin increased ER stress in human adipose tissue. The effect of insulin resistance on ER stress is not known. It could be decreased, unchanged, or increased, depending on whether insulin regulates ER stress via the metabolic/phosphoinositide 3-kinase (PI3K) or alternate signaling pathways. To address this question, we examined effects of lipid-induced insulin resistance on insulin stimulation of ER stress. mRNAs of several ER stress markers were determined in fat biopsies obtained before and after 8-h hyperglycemic-hyperinsulinemic clamping in 13 normal subjects and in 6 chronically insulin-resistant patients with type 2 diabetes mellitus (T2DM). In normal subjects, hyperglycemia-hyperinsulinemia increased after/before mRNA ratios of several ER stress markers (determined by ER stress pathway array and by individual RT-PCR). Lipid infusion was associated with inhibition of the PI3K insulin-signaling pathway and with a decrease of hyperinsulinemia-induced ER stress responses. In chronically insulin-resistant patients with T2DM, hyperglycemic-hyperinsulinemia did not increase ER stress response marker mRNAs. In summary, insulin resistance, either produced by lipid infusions in normal subjects or chronically present in T2DM patients, was associated with decreased hyperinsulinemia-induced ER stress responses. This suggests, but does not prove, that these two phenomena were causally related.

Silencing of FGF-21 expression promotes hepatic gluconeogenesis and glycogenolysis by regulation of the STAT3-SOCS3 signal.

Insulin resistance is a metabolic disorder associated with type 2 diabetes. Recent reports have shown that fibroblast growth factor-21 (FGF-21) plays an important role in the progression of insulin resistance. However, the biochemical and molecular mechanisms by which changes in FGF-21 activation result in changes in the rates of hepatic gluconeogenesis and glycogenolysis remain to be elucidated. In this study, we developed adenovirus-mediated shRNA against FGF-21 to inhibit FGF-21 expression in ApoE knockout mice. Using this mouse model, we determined the effects of FGF-21 knockdown in vivo on hepatic glucose production, gluconeogenesis and glycogenolysis, and their relationship with the signal transducer and activator of transcription 3 (STAT3)/suppressor of cytokine signaling 3 (SOCS3) signal pathways. We show that liver-specific knockdown of FGF-21 in high-fat diet-fed ApoE knockout mice resulted in a 39% increase in glycogenolysis and a 75% increase in gluconeogenesis, accompanied by increased hepatic expression of glucose-6-phosphatase and phosphoenolpyruvate carboxykinase. Furthermore, FGF-21 knockdown decreased phosphorylation of STAT3 and SOCS3 expression in high-fat diet-fed mice. Our data suggest that hepatic FGF-21 knockdown increases gluconeogenesis and glycogenolysis by activation of glucose-6-phosphatase and phosphoenolpyruvate carboxykinase via the STAT3/SOCS3 pathway, ultimately leading to exacerbation of hepatic insulin resistance.

Efficacy and safety of aldose reductase inhibitor for the treatment of diabetic cardiovascular autonomic neuropathy: systematic review and meta-analysis.

BACKGROUND: Aldose reductase inhibitors (ARIs) can block the metabolism of the polyol pathway, and have been used to slow or reverse the progression of diabetic cardiovascular autonomic neuropathy (DCAN). The purpose of this study was to review the effectiveness and safety of ARIs in the treatment of DCAN as determined by five cardiac autonomic neuropathy function tests. METHODS: CENTRAL, MEDLINE, EMBASE, Scopus databases (inception to May 2012) were searched to identify randomized controlled trials (RCTs) and non-randomized controlled trials (non-RCTs) investigating ARIs for the treatment of DCAN with an English-language restriction. The data were analyzed using RevMan 5.0, and the heterogeneity between the trials was evaluated using the Cochrane's Q-test as well as the I² test. The type of model (random or fixed) used for analysis was based on heterogeneity. Weighted mean differences (WMD) with 95% confidence intervals (CI) were computed for the five cardiac automatic neuropathy function tests to evaluate the effects. RESULTS: Ten articles met the prerequisites for this review. Analysis of the results showed that ARIs significantly improved function in at least three of the five automatic neuropathy tests, including the resting heart rate variation coefficients (WMD = 0.25, 95%CI 0.02 to 0.48, P = 0.040); the 30∶15 ratio (WMD = 0.06, 95%CI 0.01 to 0.10, P = 0.010) and the postural systolic blood pressure change (WMD = -5.94, 95%CI -7.31 to -4.57, P = 0.001). The expiration/inspiration ratio showed a marginally significant benefit (WMD = 0.05, 95%CI 0.00 to 0.09, P = 0.040). Glycaemic control was not significantly affected by ARIs. Adverse effects of ARIs except for Tolerestat were minimal. CONCLUSIONS: Based on these results, we conclude that ARIs could ameliorate cardiac automatic neuropathy especially mild or asymptomatic DCAN but need further investigation.

Hypothalamic nesfatin-1/NUCB2 knockdown augments hepatic gluconeogenesis that is correlated with inhibition of mTOR-STAT3 signaling pathway in rats.

Nesfatin-1, an 82-amino acid neuropeptide, has recently been characterized as a potent metabolic regulator. However, the metabolic mechanisms and signaling steps directly associated with the action of nesfatin-1 have not been well delineated. We established a loss-of-function model of hypothalamic nesfatin-1/NUCB2 signaling in rats through an adenoviral-mediated RNA interference. With this model, we found that inhibition of central nesfatin-1/NUCB2 activity markedly increased food intake and hepatic glucose flux and decreased glucose uptake in peripheral tissue in rats fed either a normal chow diet (NCD) or a high-fat diet (HFD). The change of hepatic glucose fluxes in the hypothalamic nesfatin-1/NUCB2 knockdown rats was accompanied by increased hepatic levels of glucose-6-phosphatase and PEPCK and decreased insulin receptor, insulin receptor substrate 1, and AKT kinase phosphorylation. Furthermore, knockdown of hypothalamic nesfatin-1 led to decreased phosphorylation of mammalian target of rapamycin (mTOR) and signal transducer and activator of transcription 3 (STAT3) and the subsequent suppressor of cytokine signaling 3 levels. These results demonstrate that hypothalamic nesfatin-1/NUCB2 plays an important role in glucose homeostasis and hepatic insulin sensitivity, which is, at least in part, associated with the activation of the mTOR-STAT3 signaling pathway.

Changes in insulin sensitivity and insulin secretion with the sodium glucose cotransporter 2 inhibitor dapagliflozin.

AIM: This randomized, double-blind, placebo-controlled parallel-group study assessed the effects of sodium glucose cotransporter 2 inhibition by dapagliflozin on insulin sensitivity and secretion in subjects with type 2 diabetes mellitus (T2DM), who had inadequate glycemic control with metformin (with or without an insulin secretagogue). SUBJECTS AND METHODS: Forty-four subjects were randomized to receive dapagliflozin 5 mg or matching placebo once daily for 12 weeks. Subjects continued stable doses of background antidiabetes medication throughout the study. Insulin sensitivity was assessed by measuring the glucose disappearance rate (GDR) during the last 40 min of a 5-h hyperinsulinemic, euglycemic clamp. Insulin secretion was determined as the acute insulin response to glucose (AIRg) during the first 10 min of a frequently sampled intravenous glucose tolerance test. Where noted, data were adjusted for baseline values and background antidiabetes medication. RESULTS: An adjusted mean increase from baseline in GDR (last observation carried forward), at Week 12, was observed with dapagliflozin (7.98%) versus a decrease with placebo (-9.99%). The 19.97% (95% confidence interval 5.75-36.10) difference in GDR versus placebo was statistically significant (P=0.0059). A change from baseline in adjusted mean AIRg of 15.39 mU/L min was observed with dapagliflozin at Week 12, versus -12.73 mU/L min with placebo (P=0.0598). Over 12 weeks, numerical reductions from baseline in glycosylated hemoglobin (HbA1c), fasting plasma glucose, and body weight were observed with dapagliflozin (-0.38%, -0.39 mmol/L, and -1.58%, respectively) versus slight numerical increases with placebo (0.03%, 0.26 mmol/L, and 0.62%, respectively). CONCLUSIONS: In patients with T2DM and inadequate glycemic control, dapagliflozin treatment improved insulin sensitivity in the setting of reductions in HbA1c and weight.

Insulin regulates the unfolded protein response in human adipose tissue.

Endoplasmic reticulum (ER) stress is increased in obesity and is postulated to be a major contributor to many obesity-related pathologies. Little is known about what causes ER stress in obese people. Here, we show that insulin upregulated the unfolded protein response (UPR), an adaptive reaction to ER stress, in vitro in 3T3-L1 adipocytes and in vivo, in subcutaneous (sc) adipose tissue of nondiabetic subjects, where it increased the UPR dose dependently over the entire physiologic insulin range (from ∼ 35 to ∼ 1,450 pmol/L). The insulin-induced UPR was not due to increased glucose uptake/metabolism and oxidative stress. It was associated, however, with increased protein synthesis, with accumulation of ubiquitination associated proteins, and with multiple posttranslational protein modifications (acetylations, methylations, nitrosylations, succinylation, and ubiquitinations), some of which are potential causes for ER stress. These results reveal a new physiologic role of insulin and provide a putative mechanism for the development of ER stress in obesity. They may also have clinical and therapeutic implications, e.g., in diabetic patients treated with high doses of insulin.

Comparison of in vivo effects of insulin on SREBP-1c activation and INSIG-1/2 in rat liver and human and rat adipose tissue.

OBJECTIVE: The stimulatory effects of insulin on de novo lipogenesis (DNL) in the liver, where it is an important contributor to non-alcoholic fatty liver disease (NAFLD), hepatic and systemic insulin resistance, is strong and well established. In contrast, insulin plays only a minor role in DNL in adipose tissue. The reason why insulin stimulates DNL more in liver than in fat is not known but may be due to differential regulation of the transcription and post-translational activation of sterol regulatory element binding proteins (SREBPs). To test this hypothesis, we have examined effects of insulin on activation of SREBP-1c in liver of rats and in adipose tissue of rats and human subjects. DESIGN AND METHODS: Liver and epidydimal fat were obtained from alert rats and subcutaneous adipose tissue from human subjects in response to 4 h euglycemic-hyperinsulinemic clamps. RESULTS: Here we show that acutely raising plasma insulin levels in rats and humans increased SREBP-1 mRNA comparably 3-4 fold in rat liver and rat and human adipose tissue, but increased post-translational activation of SREBP-1c only in rat liver, while decreasing it in adipose tissue. These differential effects of insulin on SREBP-1c activation in liver and adipose tissue were associated with robust changes in the opposite direction of INSIG-1 and to a lesser extent of INSIG-2 mRNA and proteins. CONCLUSIONS: We conclude that these findings support the hypothesis that insulin stimulated activation of SREBP-1c in the liver, at least in part, by suppressing INSIG-1 and -2, whereas in adipose tissue, an increase in INSIG-1 and -2 prevented SREBP-1c activation.

Why does obesity increase the risk for cardiovascular disease?

Insulin resistance and inflammation are recognized as important links between obesity and cardiovascular disease (CVD). Plasma free fatty acids (FFA), either released from the abnormally enlarged adipose tissue or as part of the excessive nutrient intake, produce insulin resistance and inflammation. Both insulin resistance and inflammation are tightly linked to several independent CVD risk factors such as type 2 diabetes (T2DM), hypertension, dyslipidemia and disorders of blood coagulation. Several hypotheses have been proposed to explain how increased plasma FFA levels can cause insulin resistance including a) the lipid metabolite hypothesis, b) the inflammation hypothesis, c) the hyperinsulinemia hypothesis and d) the endoplasmic reticulum (ER) stress hypothesis. The latter does not require presence of elevated plasma FFA levels and thus provides a mechanism to explain the development of insulin resistance and inflammation in all obese individuals, i.e., those with and without elevated plasma FFA levels. Hyperinsulinemia per se has been suspected to cause CVD based on epidemiologic studies which have associated chronic hyperinsulinemia with CVD without, however, establishing a cause and effect relationship. There are, however, newer results which support the hypothesis that chronic hyperinsulinemia per se can promote the development of CVD. For instance, hyperinsulinemia can activate triglyceride formation, several matrix metalloproteinases (MMP), and the tissue factor pathway of blood coagulation, all of which are known to be associated with CVD, even in the presence of "metabolic insulin resistance".

Systematic review of the effectiveness of hyperbaric oxygenation therapy in the management of chronic diabetic foot ulcers.

OBJECTIVE: To assess the efficacy and safety of hyperbaric oxygenation (HBO) therapy as adjunctive treatment for diabetic foot ulcers with a systematic review and meta-analysis of the literature. METHODS: MEDLINE, EMBASE, and the Cochrane Library were searched to find relevant articles published up to April 20, 2012, without restriction as to language or publication status. All controlled trials that evaluated adjunctive treatment with HBO therapy compared with treatment without HBO for chronic diabetic foot ulcers were selected. A meta-analysis was performed to assess the efficacy and safety of hyperbaric oxygen in managing foot ulcers. RESULTS: Thirteen trials (a total of 624 patients), including 7 prospective randomized trials, performed between January 1, 1966, and April 20, 2012, were identified as eligible for inclusion in the study. Pooling analysis revealed that, compared with treatment without HBO, adjunctive treatment with HBO resulted in a significantly higher proportion of healed diabetic ulcers (relative risk, 2.33; 95% CI, 1.51-3.60). The analysis also revealed that treatment with HBO was associated with a significant reduction in the risk of major amputations (relative risk, 0.29; 95% CI, 0.19-0.44); however, the rate of minor amputations was not affected (P=.30). Adverse events associated with HBO treatment were rare and reversible and not more frequent than those occurring without HBO treatment (P=.37). CONCLUSIONS: This meta-analysis reveals that treatment with HBO improved the rate of healing and reduced the risk of major amputations in patients with diabetic foot ulcers. On the basis of these effects, we believe that quality of life could be improved in selected patients treated with HBO.

GLP-1 analogue prevents NAFLD in ApoE KO mice with diet and Acrp30 knockdown by inhibiting c-JNK.

BACKGROUND & AIMS: Liraglutide, a Glucagon-like peptide-1(GLP-1) analogue with 97% sequence identity to human GLP-1, increases insulin secretion and insulin sensitivity. Its effect on non-alcoholic fatty liver disease (NAFLD) remains poorly understood. In this study, we examined whether liraglutide can protect against inflammatory stress by inhibiting activation of c-Jun N-terminal protein kinase (JNK). METHODS: ApoE KO and adiponectin (Acrp30) knockdown mice fed a high-fat diet (HFD) were treated with liraglutide (1 mg/kg, twice daily) for 8 weeks. Liver tissue was procured for histological examination, real-time RT-PCR and Western blot analysis. RESULTS: The results showed that the combination of HFD, Acrp30 knockdown and ApoE deficiency had additive effects on the development of insulin resistance (IR) and NAFLD. Administration of liraglutide prevented the development of HFD and hypoadiponectinaemia-induced IR and NAFLD in this model. Liraglutide also attenuated the expression of proinflammatory cytokines or transcription factor, including TNF-α and NF-κB(65) , and the expression of two lipogenesis-related genes, Acetyl-CoA Carboxylase (ACC) and fatty acid synthase (FAS). These changes were accompanied by elevated plasma of Acrp30, increased Acrp30 mRNA, AMP Kinase phosphorylation, and decreased mitogen-activated protein kinase 4 (MKK4) mRNA expression and JNK phosphorylation. CONCLUSIONS: Our study also showed potent inhibitory effects of liraglutide on MKK4/JNK signalling which may be a mechanism for the observed improved insulin sensitivity and inflammatory stress induced by HFD and hypoadiponectinaemia.

Zinc-α2-glycoprotein is associated with insulin resistance in humans and is regulated by hyperglycemia, hyperinsulinemia, or liraglutide administration: cross-sectional and interventional studies in normal subjects, insulin-resistant subjects, and subjects with newly diagnosed diabetes.

OBJECTIVE: Zinc-α2-glycoprotein (ZAG) has been proposed to play a role in the pathogenesis of insulin resistance. Previous studies in humans and in rodents have produced conflicting results regarding the link between ZAG and insulin resistance. The objective of this study was to examine the relationships between ZAG and insulin resistance in cross-sectional and interventional studies. RESEARCH DESIGN AND METHODS: Serum ZAG (determined with ELISA) was compared with various parameters related to insulin resistance in subjects with normal glucose tolerance, impaired glucose tolerance (IGT), and newly diagnosed type 2 diabetes mellitus (T2DM), and in women with or without polycystic ovary syndrome (PCOS). Euglycemic-hyperinsulinemic clamps were performed in healthy and PCOS women. Real-time RT-PCR and Western blotting were used to assess mRNA and protein expression of ZAG. The effect of a glucagon-like peptide-1 agonist on ZAG was studied in a 12-week liraglutide treatment trial. RESULTS: Circulating ZAG was lower in patients with IGT and newly diagnosed T2DM than in controls. Circulating ZAG correlated positively with HDL cholesterol and adiponectin, and correlated inversely with BMI, waist-to-hip ratio, body fat percentage, triglycerides, fasting blood glucose, fasting insulin, HbA1c, and homeostasis model assessment of insulin resistance (HOMA-IR). On multivariate analysis, ZAG was independently associated with BMI, HOMA-IR, and adiponectin. ZAG mRNA and protein were decreased in adipose tissue of T2DM patients. Moreover, circulating ZAG levels were lower in women with PCOS than in women with high insulin sensitivity. Liraglutide treatment for 12 weeks significantly increased circulating ZAG levels. CONCLUSIONS: We conclude that ZAG may be an adipokine associated with insulin resistance.

Liraglutide increases FGF-21 activity and insulin sensitivity in high fat diet and adiponectin knockdown induced insulin resistance.

BACKGROUND: Liraglutide is a glucagon-like peptide-1 analogue that stimulates insulin secretion and improves ß-cell function. However, it is not clear whether liraglutide achieves its glucose lowering effect only by its known effects or whether other as yet unknown mechanisms are involved. The aim of this study was to examine the effects of liraglutide on Fibroblast growth factor-21 (FGF-21) activity in High-fat diet (HFD) fed ApoE(-/-) mice with adiponectin (Acrp30) knockdown. METHOD: HFD-fed ApoE(-/-) mice were treated with adenovirus vectors expressing shAcrp30 to produce insulin resistance. Hyperinsulinemic-euglycemic clamp studies were performed to evaluate insulin sensitivity of the mouse model. QRT-PCR and Western blot were used to measure the mRNA and protein expression of the target genes. RESULTS: The combination of HFD, ApoE deficiency, and hypoadiponectinemia resulted in an additive effect on insulin resistance. FGF-21 mRNA expressions in both liver and adipose tissues were significantly increased while FGF-21 receptor 1 (FGFR-1) and ß-Klotho mRNA levels in adipose tissue, as well as FGFR-1-3 and ß-Klotho mRNA levels in liver were significantly decreased in this model. Liraglutide treatment markedly improved insulin resistance and increased FGF-21 expression in liver and FGFR-3 in adipose tissue, restored ß-Klotho mRNA expression in adipose tissue as well as FGFR-1-3, ß-Klotho levels and phosphorylation of FGFR1 up to the levels observed in control mice in liver. Liraglutide treatment also further increased FGF-21 proteins in liver and plasma. In addition, as shown by hyperinsulinemic-euglycemic clamp, liraglutide treatment also markedly improved glucose metabolism and insulin sensitivity in these animals. CONCLUSION: These findings demonstrate an additive effect of HFD, ApoE deficiency, and adiponectin knockdown on insulin resistance and unveil that the regulation of glucose metabolism and insulin sensitivity by liraglutide may be partly mediated via increased FGF-21 and its receptors action.