Effect of Glucagon-Like Peptide-1(7–36) and Exendin-4 on the Vascular Reactivity in Streptozotocin/Nicotinamide-Induced Diabetic Rats

Association of the rs17574 DPP4 Polymorphism with Premature Coronary Artery Disease in Diabetic Patients: Results from the Cohort of the GEA Mexican Study

Previously, it has been reported that hypoalphalipoproteinemia (HA) is associated with rs17574 DDP4 polymorphism. Considering that in diabetic patients, HA is often present and is a risk factor for premature coronary artery disease (pCAD), the study aimed to evaluate the association of this polymorphism with pCAD in diabetic individuals. We genotyped the rs17574 polymorphism in 405 pCAD patients with T2DM, 736 without T2DM, and 852 normoglycemic individuals without pCAD and T2DM as controls. Serum DPP4 concentration was available in 818 controls, 669 pCAD without T2DM, and 339 pCAD with T2DM. The rs17574 polymorphism was associated with lower risk of pCAD (padditive = 0.007; pdominant = 0.003, pheterozygote = 0.003, pcodominant1 = 0.003). In pCAD with T2DM patients, DPP4 levels were lower when compared with controls (p < 0.001). In the whole sample, individuals with the rs17574 GG genotype have the lowest protein levels compared with AG and AA (p = 0.039) carriers. However, when the same analysis was repeated separately in all groups, a significant difference was observed in the pCAD with T2DM patients; carriers of the GG genotype had the lowest protein levels compared with AG and AA (p = 0.037) genotypes. Our results suggest that in diabetic patients, the rs17574G DPP4 allele could be considered as a protective genetic marker for pCAD. DPP4 concentrations were lower in the diabetic pCAD patients, and the rs17574GG carriers had the lowest protein levels.

GLP-1 Relaxes Rat Coronary Arteries by Enhancing ATP-Sensitive Potassium Channel Currents

GLP-1 is a new type of antidiabetic agent that possesses many beneficial effects. Although its cardiovascular actions have been widely examined, little is known about GLP-1's effects on the rat coronary artery (RCA) or about the mechanisms underpinning these effects. Here, we report that GLP-1 inhibits depolarization- or thromboxane receptor agonist (U46619)-induced RCA contraction in a dosage-dependent manner. Vasorelaxation was attenuated by denuding the endothelium, L-NAME (nitric oxide synthase inhibitor), and glyburide (K_ATP channel blocker) but was not affected by indomethacin (cyclooxygenase inhibitor), iberiotoxin [Ca²⁺-activated K⁺ channel (K_Ca) blocker], or 4-aminopyridine (K_V channel blocker). Furthermore, GLP-1 increased outward K⁺ currents by enhancing the K_ATP channel in rat coronary arterial smooth muscle cells (RCASMCs). These results show that GLP-1 is an endothelial-dependent vasospasmolytic agent in the RCA and imply that the relaxant effect is regulated by enhancing K_ATP rather than K_V or K_Ca currents in RCASMCs.

Effects of Acute GLP-1 Infusion on Pulmonary and Systemic Hemodynamics in Patients With Heart Failure: A Pilot Study

PURPOSE

Cardiovascular-safety studies assessing glucagon-like peptide (GLP)-1 receptor agonists and dipeptidyl peptidase 4 inhibitors have provided inconsistent data on the risk for developing heart failure. Animal studies have shown that GLP-1 is a vasodilator; if confirmed in humans, this may ameliorate heart failure symptoms.

METHODS

In a single-center, observational pilot study, we recruited 10 patients with advanced heart failure undergoing right heart catheterization, and we recorded pulmonary hemodynamic measures, including cardiac output calculated by thermodilution and the indirect Fick method before and after a 15-minute continuous infusion of native GLP-1 (7-36) NH₂.

FINDINGS

There was a neutral effect of GLP-1 on all pressure and hemodynamics indices as derived by cardiac output calculated by thermodilution. However, there was a small but consistent reduction in cardiac output as calculated by the indirect Fick method after GLP-1 infusion (baseline, 4.0 [1.1] L/min vs GLP-1, 3.6 [0.9] L/min; P = 0.003), driven by a consistent reduction in mixed venous oxygen saturation after GLP-1 infusion (baseline, 62.2% [7.0%] vs GLP-1, 59.3% [6.8%]; P < 0.001), whereas arterial saturation remained constant (baseline, 96.8% [3.3%] vs GLP-1, 97.0% [3.2%]; P = 0.34). This resulted in an increase in systemic vascular resistance by Fick (baseline, 1285 [228] dyn · s/cm⁵ vs GLP-1, 1562 [247] dyn · s/cm⁵; P = 0.001).

IMPLICATIONS

Acute infusion of GLP-1 has a neutral hemodynamic effect, when assessed by thermodilution, in patients with heart failure. However, GLP-1 reduces mixed venous oxygen saturation. ClinicalTrials.gov identifier: NCT02129179.

Increased endothelin-1-mediated vasoconstrictor tone in human obesity: effects of gut hormones

The heavy impact of obesity on the development and progression of cardiovascular disease has sparked sustained efforts to uncover the mechanisms linking excess adiposity to vascular dysfunction. Impaired vasodilator reactivity has been recognized as an early hemodynamic abnormality in obese patients, but also increased vasoconstrictor tone importantly contributes to their vascular damage. In particular, upregulation of the endothelin (ET)-1 system, consistently reported in these patients, might accelerate atherosclerosis and its complication, given the pro-inflammatory and mitogenic properties of ET-1. In recent years, a number of gut hormones, in addition to their role as modulators of food intake, energy balance, glucose and lipid metabolism, and insulin secretion and action, have demonstrated favorable vascular actions. They increase the bioavailability of vasodilator mediators like nitric oxide, but they have also been shown to inhibit the ET-1 system. These features make gut hormones promising tools for targeting both the metabolic and cardiovascular complications of obesity, a view supported by recent large-scale clinical trials indicating that novel drugs for type 2 diabetes with cardiovascular potential may translate into clinically significant advantages. Therefore, there is real hope that better understanding of the properties of gut-derived substances might provide more effective therapies for the obesity-related cardiometabolic syndrome.

Exendin‑4 reverses endothelial dysfunction in mice fed a high‑cholesterol diet by a GTP cyclohydrolase‑1/tetrahydrobiopterin pathway

The present study examined whether exendin‑4 (Ex4) can improve the endothelial dysfunction of apolipoprotein E knockout (APOE‑KO) mice fed a high‑cholesterol diet and the potential mechanism by which it acts. Genetically wild‑type (WT) C57BL/6 mice and APOE‑KO mice of C57BL/6 background, were each randomly assigned to receive either Ex4 treatment (Ex4‑treated, for 8 weeks) or not (control). The 4 groups were fed the same high‑cholesterol diet for 8 weeks. The following were measured at the end of the eighth week: Endothelium‑dependent vasodilation of the arteries; plasma nitric oxide (NO) and metabolic index; levels of endothelial NO synthase (eNOS); phosphorylated eNOS (p‑eNOS; Ser‑1,177); guanosine triphosphate cyclohydrolase‑1 (GCH1); and tetrahydrobiopterin (THB). Ex4 treatment was associated with higher p‑eNOS levels in the WT group and in the APOE‑KO group, and higher vascular expression of GCH1 and higher arterial THB content, compared with baseline values. The results of the present study suggested that Ex4 may exert cardioprotective effects by reversing high‑cholesterol diet‑induced endothelial dysfunction in APOE‑KO mice. The protective mechanism is probably associated with the promotion of the expression levels of GCH1 protein and THB that maintain the normal function of eNOS.

Identification of therapeutic effect of glucagon-like peptide 1 in the treatment of STZ-induced diabetes mellitus in rats by restoring the balance of intestinal flora

OBJECTIVE

The objective of this study was to identify the therapeutic effect and the underlying mechanism of glucagon-like peptide 1 (GLP-1) in the treatment of STZ-induced diabetes mellitus (DM).

METHODS

Mice were treated with STZ to establish an animal model of DM, which was further treated with a GLP-1 receptor agonist. Subsequently, the status of glucose, insulin, nitric oxide, inflammatory and oxidative factors was evaluated and compared among Sham, STZ, and STZ + GLP-1 groups. In addition, the intestinal flora spectrum in each group was also evaluated.

RESULTS

In this study, it was found that the administration of STZ increased the level of glucose and glycosylated hemoglobin but reduced the level of insulin. It was also found that the levels of inflammation and oxidative stress in STZ-induced DM were both enhanced, as evidenced by a decreased level of catalase, superoxide dismutase, glutathione peroxidase, as well as increased levels of malonyldialdehyde, interleukin-1β (IL-1β), and IL-6. Meanwhile, the expression of nitric oxide, a factor associated with both oxidative stress and inflammation, was also suppressed in STZ-induced DM. More importantly, the imbalance of intestinal flora was observed in STZ-induced DM, as shown by a decreased level of both total bacteria and that of some strains including Clostridium, Bacteroides, Lactobacilli, and Bifidobacteria.

CONCLUSION

In summary, the findings of this study confirmed the antihyperglycemic effect of GLP-1 and demonstrated that the therapeutic effect of GLP-1 in the treatment of STZ-induced DM was mediated, at least partially, by its ability to restore the balance of intestinal flora.

Effects of linagliptin on renal endothelial function in patients with type 2 diabetes: a randomised clinical trial

AIMS/HYPOTHESIS

Endothelial dysfunction predicts cardiovascular damage and renal involvement. Animal experiments and human studies indicate an increased nitric oxide (NO) activity and endothelial NO synthase (NOS) expression in the early stage of type 2 diabetes. The aim of the study was to assess the effect of linagliptin on the endothelial function of the renal vasculature.

METHODS

In this randomised, double-blind, parallel-group, investigator-initiated trial, 62 patients with type 2 diabetes were randomly assigned (by computer-generated random code) to receive linagliptin 5 mg (n = 30) or placebo (n = 32) for 4 weeks. The primary objective was to assess endothelial function of the renal vasculature, by constant-infusion input-clearance and urinary albumin/creatinine ratio (UACR), both before and after blockade of NOS with N ^G-monomethyl-L-arginine (L-NMMA).

RESULTS

Treatment with linagliptin for 4 weeks reduced fasting, postprandial blood glucose and HbA_1c, although not significantly; no change occurred with placebo. Renal plasma flow (RPF) did not change after linagliptin or placebo. After 4 weeks the absolute change in RPF due to L-NMMA was smaller in the linagliptin group than in the placebo group (-46.8 ± 34 vs -65.1 ± 36 ml/min, p = 0.045), indicating a lower basal NO activity after treatment with linagliptin. Consistently, the response of UACR to L-NMMA increased in the placebo group (p = 0.059) but not in the linagliptin group (p = 0.276), pointing to an upregulation of NO activity in the placebo group. No clinically meaningful safety concerns were evident.

CONCLUSIONS/INTERPRETATION

Our data suggest that treatment with the dipeptidyl peptidase-4 inhibitor linagliptin for 4 weeks prevented the impairment of renal endothelial function due to hyperglycaemia in type 2 diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01835678 FUNDING: : This study was funded by Boehringer Ingelheim.

Pleiotropic effects of insulin and GLP-1 receptor agonists: Potential benefits of the association

The combination of basal insulin and glucagon-like peptide-1 receptor agonists (GLP-1RAs) is an emerging option for patients with type 2 diabetes (T2D). GLP-1RAs have been shown to improve glycaemic control with a low risk of hypoglycaemia and to promote body weight loss. However, GLP-1 receptors (GLP-1Rs) are widely expressed in extrapancreatic tissues and could sustain pleiotropic actions of GLP-1RAs beyond glycaemic control. The underlying molecular mechanisms maintaining these extrapancreatic actions of GLP-1 are complex, and involve GLP-1R signalling in both the brain and several peripheral tissues. The present review focuses specifically on the role of GLP-1RAs in the cardiovascular system and liver. Preclinical data in rodents and pilot studies in humans suggest that GLP-1RAs may have potential beneficial effects on heart function, blood pressure, postprandial lipaemia, liver steatosis and non-alcoholic steatohepatitis (NASH). Long-term studies are now warranted to determine the safety and clinical relevance of the association between insulin and GLP-1RAs in T2D.

Rationale and design of the EXenatide Study of Cardiovascular Event Lowering (EXSCEL) trial

Exenatide once-weekly is an extended release formulation of exenatide, a glucagon-like peptide-1 receptor agonist, which can improve glycemic control, body weight, blood pressure, and lipid levels in patients with type 2 diabetes mellitus (T2DM). The EXenatide Study of Cardiovascular Event Lowering (EXSCEL) will compare the impact of adding exenatide once-weekly to usual care with usual care alone on major cardiovascular outcomes. EXSCEL is an academically led, phase III/IV, double-blind, pragmatic placebo-controlled, global trial conducted in 35 countries aiming to enrol 14,000 patients with T2DM and a broad range of cardiovascular risk over approximately 5 years. Participants will be randomized (1:1) to receive exenatide once-weekly 2 mg or matching placebo by subcutaneous injections. The trial will continue until 1,360 confirmed primary composite cardiovascular end points, defined as cardiovascular death, nonfatal myocardial infarction, or nonfatal stroke, have occurred. The primary efficacy hypothesis is that exenatide once-weekly is superior to usual care with respect to the primary composite cardiovascular end point. EXSCEL is powered to detect a 15% relative risk reduction in the exenatide once-weekly group, with 85% power and a 2-sided 5% alpha. The primary safety hypothesis is that exenatide once-weekly is noninferior to usual care with respect to the primary cardiovascular composite end point. Noninferiority will be concluded if the upper limit of the CI is <1.30. EXSCEL will assess whether exenatide once-weekly can reduce cardiovascular events in patients with T2DM with a broad range of cardiovascular risk. It will also provide long-term safety information on exenatide once-weekly in people with T2DM. ClinicalTrials.gov Identifier: NCT01144338.

Does Glucagon-like Peptide-1 Ameliorate Oxidative Stress in Diabetes? Evidence Based on Experimental and Clinical Studies

Glucagon-like peptide-1 (GLP-1) has shown to influence the oxidative stress status in a number of in vitro, in vivo and clinical studies. Well-known effects of GLP-1 including better glycemic control, decreased food intake, increased insulin release and increased insulin sensitivity may indirectly contribute to this phenomenon, but glucose-independent effects on ROS level, production and antioxidant capacity have been suggested to also play a role. The potential 'antioxidant' activity of GLP-1 along with other proposed glucose-independent modes of action related to ameliorating redox imbalance remains a controversial topic but could hold a therapeutic potential against micro- and macrovascular diabetic complications. This review discusses the presently available knowledge from experimental and clinical studies on the effects of GLP-1 on oxidative stress in diabetes and diabetes-related complications.

Exenatide reduces TNF-α expression and improves hippocampal neuron numbers and memory in streptozotocin treated rats

Recent studies suggest a possible link between type 2 diabetes and Alzheimer's disease (AD). Glucogan-like peptide 1 (GLP-1) facilitates insulin release from pancreas under hyperglycemic conditions. In addition to its metabolic effects, GLP-1 and its long-lasting analogs, including exenatide can stimulate neurogenesis and improve cognition in rodent AD model. The aim of the present study was to investigate the effects of exenatide on hippocampal cellularity, cognitive performance and inflammation response in a rat model of AD. Fourteen rats were used to create AD model using intracerebroventricular (ICV) streptozotocin (STZ) infusion while 7 rats were administered 0.9% NaCl only (sham-operated group). Following stereotaxic surgery, STZ received rats were randomly distributed into two groups, and treated with either saline or exenatide 20 µgr/kg/day through intraperitoneally for two weeks. Then, cognitive performance (passive avoidance learning), brain tumor necrosis factor alpha (TNF-α) levels, choline acetyltransferase (ChAT) activity and hippocampal neuronal count were determined. While the brain TNF-α levels were significantly high in the saline-treated STZ group, exenatide treatment suppressed the increase in TNF-α levels. Saline-treated STZ group showed reduced ChAT activity compared to sham group. However, exenatide significantly preserved brain ChAT activity. The cognitive performance was also impaired in saline group while exenatide improved memory in rats. Moreover, exenatide treatment significantly prevented the decrease in hippocampal neurons. Overall, the results of the present study clearly indicated exenatide might have beneficial effects on impaired cognitive performance and hippocampal neuronal viability in AD by suppressing the inflammation response and increasing cholinergic activity.

Δ9-tetrahydrocannabinol treatment improved endothelium-dependent relaxation on streptozotocin/nicotinamide-induced diabetic rat aorta

OBJECTIVE

In this study, we investigated the possible effect of Δ(9)-tetrahydrocannabinol (THC), a peroxisome proliferator-activated receptor gamma (PPARγ) agonist, on metabolic control and vascular complications of diabetes in streptozotocin/nicotinamide (STZ/NIC) induced type 2 diabetes mellitus.

MATERIAL AND METHODS

Type 2 diabetes was induced with 65 mg/kg STZ, 15 minute later 85 mg/kg NIC was given intraperitoneally (i.p.) to rats. Three days after diabetes induction, THC (3 mg/kg/day, i.p.) was given for 7 days to diabetic rats. Body weight and plasma glucose levels of rats were measured in all groups before and at the end of 3 weeks after diabetes induction. Acetylcholine (Ach) and sodium nitroprusside (SNP) potency and maximum relaxant effects were calculated on aortic rings pre-contracted with noradrenaline (NA).

RESULTS

At the end of 3 weeks, blood glucose levels of diabetic group significantly increased in comparison with the control group. Increased plasma glucose levels were significantly decreased by the treatment of THC. Ach induced relaxation was impaired whereas endothelium-independent relaxation to SNP was unaffected on isolated diabetic rat aorta. THC treatment enhanced Ach induced relaxation on diabetic rat aortas.

DISCUSSION

These results suggested that THC improved endothelium-dependent relaxation in STZ/NIC induced diabetic rat aorta and that these effects were mediated at least in part, by control of hyperglycemia and enhanced endothelial nitric oxide bioavailability.

The DPP-4 inhibitor linagliptin and the GLP-1 receptor agonist exendin-4 improve endothelium-dependent relaxation of rat mesenteric arteries in the presence of high glucose

The aim of the study was to investigate the effects of the DPP-4 inhibitors and GLP-1R agonist, exendin-4 on the mechanism(s) of endothelium-dependent relaxation in rat mesenteric arteries exposed to high glucose concentration (40 mM). Organ bath techniques were employed to investigate vascular endothelial function in rat mesenteric arteries in the presence of normal (11 mM) or high (40 mM) glucose concentrations. Pharmacological tools (1μM TRAM-34, 1μM apamin, 100 nM Ibtx, 100 μM l-NNA, 10 μM ODQ) were used to distinguish between NO and EDHF-mediated relaxation. Superoxide anion levels were assessed by L-012 and lucigenin enhanced-chemiluminescence techniques. Incubation of mesenteric rings with high glucose for 2 h caused a significant increase in superoxide anion generation and a significant impairment of endothelium-dependent relaxation. Exendin-4 and DPP-4 inhibitor linagliptin, but not sitagliptin or vildagliptin, significantly reduced vascular superoxide and improved endothelium-dependent relaxation in the presence of high glucose. The beneficial actions of exendin-4, but not linagliptin, were attenuated by the GLP-1R antagonist exendin fragment (9-39). Further experiments demonstrated that the presence of high glucose impaired the contribution of both nitric oxide and endothelium-dependent hyperpolarisation to relaxation and that linagliptin improved both mechanisms involved in endothelium-dependent relaxation. These findings demonstrate that high glucose impaired endothelium-dependent relaxation can be improved by exendin-4 and linagliptin, likely due to their antioxidant activity and independently of any glucose lowering effect.

Selective targeting of glucagon-like peptide-1 signalling as a novel therapeutic approach for cardiovascular disease in diabetes

Glucagon-like peptide-1 (GLP-1) is an incretin hormone whose glucose-dependent insulinotropic actions have been harnessed as a novel therapy for glycaemic control in type 2 diabetes. Although it has been known for some time that the GLP-1 receptor is expressed in the CVS where it mediates important physiological actions, it is only recently that specific cardiovascular effects of GLP-1 in the setting of diabetes have been described. GLP-1 confers indirect benefits in cardiovascular disease (CVD) under both normal and hyperglycaemic conditions via reducing established risk factors, such as hypertension, dyslipidaemia and obesity, which are markedly increased in diabetes. Emerging evidence indicates that GLP-1 also exerts direct effects on specific aspects of diabetic CVD, such as endothelial dysfunction, inflammation, angiogenesis and adverse cardiac remodelling. However, the majority of studies have employed experimental models of diabetic CVD and information on the effects of GLP-1 in the clinical setting is limited, although several large-scale trials are ongoing. It is clearly important to gain a detailed knowledge of the cardiovascular actions of GLP-1 in diabetes given the large number of patients currently receiving GLP-1-based therapies. This review will therefore discuss current understanding of the effects of GLP-1 on both cardiovascular risk factors in diabetes and direct actions on the heart and vasculature in this setting and the evidence implicating specific targeting of GLP-1 as a novel therapy for CVD in diabetes.

Incretin attenuates diabetes-induced damage in rat cardiac tissue

Glucagon-like peptide-1 (GLP-1), as a member of the incretin family, has a role in glucose homeostasis, its receptors distributed throughout the body, including the heart. The aim was to investigate cardiac lesions following diabetes induction, and the potential effect of GLP-1 on this type of lesions and the molecular mechanism driving this activity. Adult male rats were classified into: normal, diabetic, 4-week high-dose exenatide-treated diabetic rats, 4-week low-dose exenatide-treated diabetic rats, and 1-week exenatide-treated diabetic rats. The following parameters were measured: in blood: glucose, insulin, lactate dehydrogenase (LDH), total creatine kinase (CK), creatine kinase MB isoenzyme (CK-MB), and CK-MB relative index; in cardiac tissue: lipid peroxide (LPO) and some antioxidant enzymes. The untreated diabetic group displayed significant increases in blood level of glucose, LDH, and CK-MB, and cardiac tissue LPO, and a significant decrease in cardiac tissue antioxidant enzymes. GLP-1 supplementation in diabetic rats definitely decreased the hyperglycemia and abolished the detrimental effects of diabetes on the cardiac tissue. The effect of GLP-1 on blood glucose and on the heart also appeared after a short supplementation period (1 week). It can be concluded that GLP-1 has beneficial effects on diabetes-induced oxidative cardiac tissue damage, most probably via its antioxidant effect directly acting on cardiac tissue and independent of its hypoglycemic effect.

Cardiovascular and hemodynamic effects of glucagon-like peptide-1

Glucagon-like peptide-1 (GLP-1) is an incretin hormone that has been shown to have hemodynamic and cardioprotective capacity in addition to its better characterized glucoregulatory actions. Because of this, emerging research has focused on the ability of GLP-1 based therapies to drive myocardial substrate selection, enhance cardiac performance and regulate heart rate, blood pressure and vascular tone. These studies have produced consistent and reproducible results amongst numerous laboratories. However, there are obvious disparities in findings obtained in small animal models versus those of higher mammals. This species dependent discrepancy calls to question, the translational value of individual findings. Moreover, few studies of GLP-1 mediated cardiovascular action have been performed in the presence of a pre-existing comorbidities (e.g. obesity/diabetes) which limits interpretation of the effectiveness of incretin-based therapies in the setting of disease. This review addresses cardiovascular and hemodynamic potential of GLP-1 based therapies with attention to species specific effects as well as the interaction between therapies and disease.

Diabetes and cardiovascular disease: focus on glucagon-like peptide-1 based therapies

Type 2 diabetes is a well known risk factor for cardiovascular disease (CVD). While glycemic control has consistently been shown to prevent microvascular complications, large randomized trials have not demonstrated the same consistent beneficial effects of intensive glycemic control in improving cardiovascular (CV) outcomes. Thus, optimal glucose control alone is not sufficient to reduce CV risk. Aggressive management of CV risk factors such as blood pressure, lipids, and body weight is also necessary. A growing body of evidence suggests that the recently available glucagon-like peptide 1 receptor (GLP-1R) agonists have beneficial CV effects beyond glucose control. Studies have demonstrated beneficial effects in the myocardium, endothelium, vasculature and various markers of cardiovascular risk such as body weight, blood pressure and dyslipidemia. Despite the growing evidence, large, randomized, blinded clinical trials with hard CV endpoints have not been performed. Most human studies have been small, and have focused on surrogate endpoints. The findings need to be confirmed by prospective, randomized cardiovascular outcomes trials. In this review we examine the GLP-1R agonist data on weight reduction, blood pressure lowering, beneficial changes in dyslipidemia, and improvements in myocardial and endothelial function. The safety as well as potential role of these agents in treatment regimens for type 2 diabetes is also addressed.

Adding liraglutide to the backbone therapy of biguanide in patients with coronary artery disease and newly diagnosed type-2 diabetes (the AddHope2 study): a randomised controlled study protocol

INTRODUCTION

Newly diagnosed type 2 diabetes mellitus (T2DM) in patients with coronary artery disease (CAD) more than doubles the risk of death compared with otherwise matched glucose tolerant patients. The biguanide metformin is the drug of choice in treatment of T2DM and has shown to ameliorate cardiovascular morbidity in patients with T2DM and myocardial infarction (MI). The incretin hormone, glucagon-like peptide-1 (GLP-1) improves β-cell function, insulin sensitivity and causes weight loss and has been suggested to have beneficial effects on cardiac function. The GLP-1 receptor agonist (GLP-1RA), liraglutide, is currently used for treatment of T2DM but its potential effect on cardiac function has not been investigated in detail. We hypothesised that liraglutide added to metformin backbone therapy in patients with CAD and newly diagnosed T2DM will improve β-cell function and left ventricular systolic function during dobutamine stress.

METHODS AND ANALYSES

40 patients with CAD and newly diagnosed T2DM will receive the intervention liraglutide+metformin and placebo+metformin in this investigator-initiated, double blind, randomised, placebo-controlled, cross-over 12 plus 12 weeks intervention study with a 2-week washout period. The primary cardiovascular end point is changes in left ventricular ejection fraction during stress echocardiography. The primary endocrine end point is β-cell function evaluated during a frequently sampled intravenous glucose tolerance test. Secondary end points include heart rate variability, diurnal blood pressure, glucagon suppression and inflammatory response (urine, blood and adipose tissue).

ETHICS AND DISSEMINATION

This study is approved by the Danish Medicines Agency, the Danish Dataprotection Agency and the Regional Committee on Biomedical Research Ethics of the Capital Region of Denmark. The trial will be carried out under the guidance from the GCP unit at Copenhagen University Hospital of Bispebjerg and in accordance with the ICH-GCP guidelines and the Helsinki Declaration.

TRIAL REGISTRATIONS NUMBER

Clinicaltrials.gov ID: NCT01595789, EudraCT: 2011-005405-78.

Characterization of [¹²⁵I]GLP-1(9-36), a novel radiolabeled analog of the major metabolite of glucagon-like peptide 1 to a receptor distinct from GLP1-R and function of the peptide in murine aorta

AIMS

Glucagon-like peptide 1 (GLP-1) is an insulin secretagogue, released in response to meal ingestion and efficiently lowers blood glucose in Type 2 diabetic patients. GLP-1(7-36) is rapidly metabolized by dipeptidyl peptidase IV to the major metabolite GLP-1(9-36)-amide, often thought to be inactive. Inhibitors of this enzyme are widely used to treat diabetes. Our aim was to characterize the binding of GLP-1(9-36) to native mouse tissues and to cells expressing GLP1-R as well as to measure functional responses in the mouse aorta compared with GLP-1(7-36).

MAIN METHODS

The affinity of [(125)I]GLP-1(7-36) and [(125)I]GLP-1(9-36) was measured in mouse tissues by saturation binding and autoradiography used to determine receptor distribution. The affinity of both peptides was compared in binding to recombinant GLP-1 receptors using cAMP and scintillation proximity assays. Vasoactivity was determined in mouse aortae in vitro.

KEY FINDINGS

In cells expressing GLP-1 receptors, GLP-1(7-36) bound with the expected high affinities (0.1 nM) and an EC50 of 0.07 nM in cAMP assays but GLP-1(9-36) bound with 70,000 and 100,000 fold lower affinities respectively. In contrast, in mouse brain, both labeled peptides bound with a single high affinity, with Hill slopes close to unity, although receptor density was an order of magnitude lower for [(125)I]GLP-1(9-36). In functional experiments both peptides had similar potencies, GLP-1(7-36), pD2=7.40 ± 0.24 and GLP-1(9-36), pD2=7.57 ± 0.64.

SIGNIFICANCE

These results suggest that GLP-1(9-36) binds and has functional activity in the vasculature but these actions may be via a pathway that is distinct from the classical GLP-1 receptor and insulin secretagogue actions.

Exendin-4 shows no effects on the prostatic index in high-fat-diet-fed rat with benign prostatic hyperplasia by improving insulin resistance

Benign prostatic hyperplasia (BPH) is a prevalent disease globally, and accumulating evidence has indicated an association between BPH, insulin resistance (IR) and diabetes. Exendin-4 is widely used in clinics, which could enhance the proliferation of pancreatic β cells. The ability of exendin-4 to promote tumorigenesis has been of concern, and whether exendin-4 would enhance the propagation of BPH is not fully understood. We aimed to determine whether glucagon-like peptide-1 receptors (GLP-1Rs) were expressed in rat prostate and to determine the effect of exendin-4 on prostate of BPH. Male Wistar rats were used and assigned to six groups: normal diet (ND), high-fat diet (HFD), HFD + exendin-4, HFD + BPH, HFD + BPH + exendin-4 and HFD + BPH + rosiglitazone group. After castration, steroids were injected subcutaneously for 4 weeks to induce BPH. Rats were kept on high-fat diet to induce IR. Treatment groups were treated with exendin-4 and rosiglitazone. Prostatic index and HOMA-IR index were used to evaluate the prostatic hyperplasia status and the degree of IR respectively. The expression of GLP-1R was indicated not only by immunohistochemistry, but also by Western blot analysis. The expression of GLP-1R was significantly higher, and HOMA-IR index and body weight significantly decreased after administration of exendin-4. However, no significant differences in the prostatic index were observed between exendin-4 treatment groups and non-exendin-4 treatment groups. Prostatic index was not influenced by exendin-4 maybe by improving IR and weight loss.

Effects of saxagliptin on early microvascular changes in patients with type 2 diabetes

Background

Patients with diabetes mellitus are at increased risk for microvascular complications. Early changes in microcirculation are characterized by hyperperfusion (e.g. in the retina and kidney) and increased pulse wave reflection leading to increased aortic pressure. We investigated the effects of the DPP-4-inhibitor saxagliptin on early retinal microvascular changes.

Methods

In this double-blind, controlled, cross-over trial 50 patients (without clinical signs of microvascular alterations) with type-2 diabetes (mean duration of 4 years) were randomized to receive placebo or 5 mg saxagliptin for 6 weeks. Retinal arteriolar structure and retinal capillary flow (RCF) at baseline and during flicker-light exposure was assessed by scanning laser Doppler flowmetry. Central hemodynamics were assessed by pulse wave analysis.

Results

Postprandial blood glucose (9.27 ± 0.4 versus 10.1 ± 0.4 mmol/L; p = 0.001) and HbA1c (6.84 ± 0.15 (51 ± 1.6) versus 7.10 ± 0.17% (54 ± 1.9 mmol/mol); p < 0.001) were significantly reduced with saxagliptin treatment compared to placebo. RCF was significantly reduced after treatment with saxagliptin (288 ± 13.2 versus 314 ± 14.1 AU; p = 0.033). This was most pronounced in a subgroup of patients (n = 32) with a fall in postprandial blood glucose (280 ± 12.1 versus 314 ± 16.6 AU; p = 0.011). No significant changes in RCF were seen during flicker-light exposure between placebo and saxagliptin, but the vasodilatory capacity increased two-fold with saxagliptin treatment. Central augmentation pressure tended to be lower after treatment with saxagliptin (p = 0.094), and central systolic blood pressure was significantly reduced (119 ± 2.3 versus 124 ± 2.3 mmHg; p = 0.038).

Conclusions

Our data suggest that treatment with saxagliptin for 6 weeks normalizes retinal capillary flow and improves central hemodynamics in type-2 diabetes.

Trial registration

The study was registered at (ID: NCT01319357).

Optimising cardioprotection during myocardial ischaemia: targeting potential intracellular pathways with glucagon-like peptide-1

Coronary heart disease and type-2 diabetes are both major global health burdens associated with an increased risk of myocardial infarction (MI). Following MI, ischaemia-reperfusion injury (IRI) remains a significant contributor to myocardial injury at the cellular level. Research has focussed on identifying a strategy or intervention to minimise IRI to optimise reperfusion therapy, with the aim of delivering a superior clinical outcome. The incretin hormone glucagon-like peptide-1, already an established basis for the treatment of type-2 diabetes, also has the potential to protect against IRI. We explain the physiology and cellular processes involved in IRI, and the intracellular pathways activated by GLP-1, which could intercept IRI and deliver cardioprotection. The review also examines the current preclinical and clinical evidence for GLP-1 in cardioprotection and future directions for research as we look for an effective adjunctive treatment to minimise IRI.

Direct cardiovascular effects of glucagon like peptide-1

Current gold standard therapeutic strategies for T2DM target insulin resistance or β cell dysfunction as their core mechanisms of action. However, the use of traditional anti-diabetic drugs, in most cases, does not significantly reduce macrovascular morbidity and mortality. Among emerging anti-diabetic candidates, glucagon like peptide-1 (GLP-1) based therapies carry special cardiovascular implications, exerting both direct as well as indirect effects. The direct cardiovascular effects of GLP-1 and its analogs remain the focus of this review.

Glucagon-like peptide-1 and its cardiovascular effects

Recently, the crucial role of GLP-1 in cardiovascular disease has been suggested by both preclinical and clinical studies. In vivo and in vitro studies have demonstrated cardio-protective effects of GLP-1 by activating cell survival signal pathways, which have greatly reduced ischemia/reperfusion injury and also cardiac dysfunction in various congestive heart failure animal models. Clinically, beneficial effects of GLP-1 have been shown in patients with myocardial infarction, hypertension, and heart failure, and 2 classes of incretin enhancers, GLP-1 receptor agonists and DPP-4 inhibitors, are currently available for the treatment of type 2 diabetes mellitus. In this review, we will summarize the role of incretins in various cardiovascular events such as hypertension and heart failure and postprandial lipoprotein secretion, and discuss their molecular mechanisms and potentials as a new therapeutic as well as preventive drug type for reducing cardiovascular events in both diabetic and nondiabetic patients.

Effects of GLP-1 on forearm vasodilator function and glucose disposal during hyperinsulinemia in the metabolic syndrome

OBJECTIVE

Patients with the metabolic syndrome (MetS) have impaired insulin-induced enhancement of vasodilator responses. The incretin hormone glucagon-like peptide 1 (GLP-1), beyond its effects on blood glucose, has beneficial actions on vascular function. This study, therefore, aimed to assess whether GLP-1 affects insulin-stimulated vasodilator reactivity in patients with the MetS.

RESEARCH DESIGN AND METHODS

Forearm blood flow responses to acetylcholine (ACh) and sodium nitroprusside (SNP) were assessed in MetS patients before and after the addition of GLP-1 to an intra-arterial infusion of saline (n = 5) or insulin (n = 5). The possible involvement of oxidative stress in the vascular effects of GLP-1 in this setting was investigated by infusion of vitamin C (n = 5). The receptor specificity of GLP-1 effect during hyperinsulinemia was assessed by infusing its metabolite GLP-1(9-36) (n = 5). The metabolic actions of GLP-1 were also tested by analyzing forearm glucose disposal during hyperinsulinemia (n = 5).

RESULTS

In MetS patients, GLP-1 enhanced endothelium-dependent and -independent responses to ACh and SNP, respectively, during hyperinsulinemia (P < 0.001 for both), but not during saline (P > 0.05 for both). No changes in vasodilator reactivity to ACh and SNP were seen after GLP-1 was added to insulin and vitamin C (P > 0.05 for both) and after GLP-1(9-36) was given during hyperinsulinemia (P > 0.05 for both). Also, GLP-1 did not affect forearm glucose extraction and uptake during hyperinsulinemia (P > 0.05 for both).

CONCLUSIONS

In patients with the MetS, GLP-1 improves insulin-mediated enhancement of endothelium-dependent and -independent vascular reactivity. This effect may be influenced by vascular oxidative stress and is possibly exerted through a receptor-mediated mechanism.

Dipeptidyl peptidase-4 inhibitors attenuate endothelial function as evaluated by flow-mediated vasodilatation in type 2 diabetic patients

BACKGROUND

Endothelial dysfunction is an independent predictor for cardiovascular events in patients with type 2 diabetes (T2DM). Glucagon like peptide-1 (GLP-1) reportedly exerts vasodilatory actions, and inhibitors of dipeptidyl peptidase-4 (DPP-4), an enzyme-degrading GLP-1, are widely used to treat T2DM. We therefore hypothesized that DPP-4 inhibitors (DPP-4Is) improve endothelial function in T2DM patients and performed 2 prospective, randomized crossover trials to compare the DPP-4I sitagliptin and an α-glucosidase inhibitor, voglibose (in study 1) and the DPP-4Is sitagliptin and alogliptin (in study 2).

METHODS AND RESULTS

In study 1, 24 men with T2DM (46±5 years) were randomized to sitagliptin or voglibose for 6 weeks without washout periods. Surprisingly, sitagliptin significantly reduced flow-mediated vasodilatation (FMD; -51% compared with baseline, P<0.05) of the brachial artery despite improved diabetic status. In contrast, voglibose did not affect FMD. To confirm this result and determine whether it is a class effect, we conducted another trial (study 2) to compare sitagliptin and alogliptin in 42 T2DM patients (66±8 years) for 6 weeks with 4-week washout periods. Both DPP-4Is improved glycemic control but significantly attenuated FMD (7.2/4.3%, P<0.001, before/after sitagliptin; 7.0/4.8%, P<0.001, before/after alogliptin, respectively). Interestingly, FMD reduction was less evident in subjects who were on statins or whose LDL cholesterol levels were reduced by them, but this was not correlated with parameters including DPP-4 activity and GLP-1 levels or diabetic parameters.

CONCLUSIONS

Our 2 independent trials demonstrated that DPP-4 inhibition attenuated endothelial function as evaluated by FMD in T2DM patients. This unexpected unfavorable effect may be a class effect of DPP-4Is.

CLINICAL TRIAL REGISTRATION

URL: http://center.umin.ac.jp, Unique Identifiers: UMIN000005682 (sitagliptin versus voglibose) and UMIN000005681 (sitagliptin versus alogliptin).

Beyond glycemic control in diabetes mellitus: effects of incretin-based therapies on bone metabolism

Diabetes mellitus (DM) and osteoporosis (OP) are common disorders with a significant health burden, and an increase in fracture risk has been described both in type 1 (T1DM) and in type 2 (T2DM) diabetes. The pathogenic mechanisms of impaired skeletal strength in diabetes remain to be clarified in details and they are only in part reflected by a variation in bone mineral density. In T2DM, the occurrence of low bone turnover together with a decreased osteoblast activity and compromised bone quality has been shown. Of note, some antidiabetic drugs (e.g., thiazolidinediones, insulin) may deeply affect bone metabolism. In addition, the recently introduced class of incretin-based drugs (i.e., GLP-1 receptor agonists and DPP-4 inhibitors) is expected to exert potentially beneficial effects on bone health, possibly due to a bone anabolic activity of GLP-1, that can be either direct or indirect through the involvement of thyroid C cells. Here we will review the established as well as the putative effects of incretin hormones and of incretin-based drugs on bone metabolism, both in preclinical models and in man, taking into account that such therapeutic strategy may be effective not only to achieve a good glycemic control, but also to improve bone health in diabetic patients.

Polymorphisms in dipeptidyl peptidase IV gene are associated with the risk of myocardial infarction in patients with atherosclerosis

BACKGROUND

Dipeptidyl peptidase IV (DPP-IV) is not only important in pancreatic β-cell regulation but also has proinflammatory actions that can contribute to atherosclerosis progression. Previously, we showed that DPP-IV is co-localized with CD31 (an endothelial cell marker) in the neovessels within the human atherosclerotic plaques. These characteristics of DPP-IV may predispose patients with coronary artery disease (CAD) to plaque rupture and thus to myocardial infarction. The goal of this investigation was to determine whether genetic alterations in DPP-IV predispose to plaque vulnerability and myocardial infarction (MI).

METHODS

Between Aug 2004, and March 2007, blood samples of patients (age <60) with angiographically documented CAD were collected. Demographic, clinical, risk factor, and angiographic data were recorded. Eight hundred and seventy five patients of European ancestry with angiographic CAD were divided into those with MI (n=421) and those without (n=454). A genome-wide association study was performed using the Affymetrix 6.0 chip to identify loci that predispose to MI. In the current study we only focused on DPP4 gene to assess the association of single nucleotide polymorphisms (SNPs) in the DPP-IV gene and risk of MI in patients with CAD. For genotyped SNPs, association was tested by logistic regression with significance level of 0.05. Plasma DPP-IV level was measured using a commercial ELISA kit.

RESULTS

Average patients' age at diagnosis of CAD was 46.8years for MI group and 50.8 in the non MI group. There was no difference in distribution of traditional risk factors between the two groups. We identified one SNP (rs3788979) that was significantly related to angiographic CAD with MI, vs. without MI (OR: 1.36, p=0.03). The association of the identified SNP to MI risk was not attenuated after adjustment for traditional risk factors. The SNP was associated with lower levels of plasma DPP-IV (p=0.005). Moreover, CAD patients with the major alleles (GG) and no MI had highest plasma DPP-IV levels. (481.6, p=0.002).

CONCLUSIONS

A polymorphism in the DPP-IV gene in patients with known CAD may increase the risk of MI. This SNP is associated with decreased plasma DPP4 level in patients with MI.

Harnessing the incretin system beyond glucose control: potential cardiovascular benefits of GLP-1 receptor agonists in type 2 diabetes

The management of type 2 diabetes continues to evolve as new data emerge. Although glycaemic control is still important, other risk factors--such as hypertension, dyslipidaemia and obesity--must also be addressed in order to reduce the long-term risks of cardiovascular complications and mortality. In this context, targeting the incretin system, and glucagon-like peptide-1 (GLP-1) in particular, has generated much interest. GLP-1 is released from the gut in response to food ingestion and plays a crucial role in glucose homeostasis. GLP-1 receptors are expressed in the heart and vasculature, prompting evaluation of their physiological role and pharmacological stimulation, both in healthy and disease states. These studies indicate that GLP-1 and GLP-1-based therapies appear to have direct, beneficial effects on the cardiovascular system, in addition to their glucose-lowering properties, such as modulation of blood pressure, endothelial function, and myocardial contractility. Intriguingly, some of these effects appear to be independent of GLP-1 receptor signalling. Data from clinical studies of the GLP-1 receptor agonists, exenatide and liraglutide on cardiovascular risk factors, in patients with type 2 diabetes are also promising and the results from prospective studies to assess cardiovascular outcomes are eagerly awaited.

The cardiovascular effects of GLP-1 receptor agonists

Glucagon-like peptide-1 receptor (GLP-1R) agonists have been shown to regulate blood glucose concentrations by mechanisms including enhanced insulin synthesis/secretion, suppressed glucagon secretion, slowed gastric emptying, and enhanced satiety. GLP-1 receptors have also been identified in the heart, kidneys, and blood vessels, leading to the hypothesis that GLP-1R agonists may affect cardiovascular function or cardiovascular disease (CVD). The aim of this literature review was to assemble and assess preclinical and clinical data of potential medical importance regarding the cardiovascular effects of GLP-1R agonists. Preclinical studies with the GLP-1R agonists GLP-1, exenatide, or liraglutide provided evidence that GLP-1R stimulation favorably affects endothelial function, sodium excretion, recovery from ischemic injury, and myocardial function in animals. Similar observations have been made in exploratory studies on GLP-1 infusion in normal subjects and patients with type 2 diabetes. Post hoc analyses of phase III studies of patients with type 2 diabetes treated with exenatide(bid or qw) or liraglutide(qd) showed that these GLP-1R agonists reduced blood pressure, an effect largely independent of weight loss, and that liraglutide slightly increased heart rate. Preliminary data also indicated that GLP-1R agonists reduced markers of CVD risk such as C-reactive protein and plasminogen activator inhibitor-1. Ongoing studies are examining the effects of administering GLP-1R agonists to patients at risk of CVD, postangioplasty patients, post-CABG patients, and patients with heart failure. Additional studies should provide meaningful data to determine whether GLP-1R agonists provide unique treatment benefits to patients at risk for or with established CVD.

Streptozotocin-nicotinamide-induced diabetes in the rat. Characteristics of the experimental model

Administration of both streptozotocin (STZ) and nicotinamide (NA) has been proposed to induce experimental diabetes in the rat. STZ is well known to cause pancreatic B-cell damage, whereas NA is administered to rats to partially protect insulin-secreting cells against STZ. STZ is transported into B-cells via the glucose transporter GLUT2 and causes DNA damage leading to increased activity of poly(ADP-ribose) polymerase (PARP-1) to repair DNA. However, exaggerated activity of this enzyme results in depletion of intracellular NAD(+) and ATP, and the insulin-secreting cells undergo necrosis. The protective action of NA is due to the inhibition of PARP-1 activity. NA inhibits this enzyme, preventing depletion of NAD(+) and ATP in cells exposed to STZ. Moreover, NA serves as a precursor of NAD(+) and thereby additionally increases intracellular NAD(+) levels. The severity of diabetes in experimental rats strongly depends on the doses of STZ and NA given to these animals. Therefore, in diabetic rats, blood glucose may be changed in a broad range--from slight hyperglycemia to substantial hyperglycemia compared with control animals. Similarly, blood insulin may be only slightly decreased or substantial hypoinsulinemia may be induced. In vitro studies demonstrated that the insulin-secretory response to glucose is attenuated in STZ-NA-induced diabetic rats compared with control animals. This is due to reduced B-cell mass as well as metabolic defects in the insulin-secreting cells. Results of numerous experiments have demonstrated that this model of diabetes is useful in studies of different aspects of diabetes.

Incretin-based therapies and cardiovascular risk

BACKGROUND

Glucagon-like peptide-1 (GLP-1) receptor agonists and dipeptidyl peptidase 4 (DPP4) inhibitors are currently used as glucose-lowering agents in type 2 diabetes, due to their effects on insulin and glucagon secretion. These agents, which are effective in improving glucose control, could also have a beneficial effect on the incidence of cardiovascular events. The analysis of major cardiovascular events reported during trials with metabolic endpoints shows a significant reduction of risk with both classes of drugs. Longer-term trials specifically designed to assess the effects of GLP-1 receptor agonists and DPP4 inhibitors on major cardiovascular events are currently ongoing.

SCOPE

In order to elucidate potential mechanisms of cardiovascular protection with incretin-based therapies, a Medline search (any date up to December 15th, 2011) was performed using the terms 'cardiovascular' and ('DPP-4' or 'GLP-1' or any single name of incretin-based drugs); papers which were considered relevant for the aim of this review were selected by the authors, on the basis of their judgment.

FINDINGS

Incretin-based drugs have beneficial effects on cardiovascular risk factors, such as blood pressure and, to a lesser extent, cholesterol and triglyceride. GLP-1 receptor agonists also reduce body weight. A number of experimental studies has suggested that GLP-1 has direct, beneficial effects on myocardial and endothelial cells, but some of these actions could be mediated via GLP-1 receptor-independent pathways. Available experimental evidence, together with a few pilot studies in humans, shows that GLP-1 receptor agonists and DPP4 inhibitors are capable of ameliorating myocardial function and protect myocardiocytes from ischemic damage, independent of their glucose-lowering effects. Furthermore, both classes of drugs enhance endothelial function. In addition, DPP4 inhibitors increase the availability of endothelial progenitor cells, via a GLP-1 receptor-independent pathway.

CONCLUSION

Taken together, available data suggest that incretin-based therapies could prevent cardiovascular disease via multiple mechanisms.

Intracoronary glucagon-like peptide 1 preferentially augments glucose uptake in ischemic myocardium independent of changes in coronary flow

We examined the acute dose-dependent effects of intracoronary glucagon-like peptide (GLP)-1 (7-36) on coronary vascular tone, cardiac contractile function and metabolism in normal and ischemic myocardium. Experiments were conducted in open chest, anesthetized dogs at coronary perfusion pressures (CPP) of 100 and 40 mmHg before and during intracoronary GLP-1 (7-36) infusion (10 pmol/L to 1 nmol/L). Isometric tension studies were also conducted in isolated coronary arteries. Cardiac and coronary expression of GLP-1 receptors (GLP-1R) was assessed by Western blot and immunohistochemical analysis. GLP-1R was present in the myocardium and the coronary vasculature. The tension of intact and endothelium-denuded coronary artery rings was unaffected by GLP-1. At normal perfusion pressure (100 mmHg), intracoronary GLP-1 (7-36) (targeting plasma concentration 10 pmol/L to 1 nmol/L) did not affect blood pressure, coronary blood flow or myocardial oxygen consumption (MVO(2)); however, there were modest reductions in cardiac output and stroke volume. In untreated control hearts, reducing CPP to 40 mmHg produced marked reductions in coronary blood flow (0.50 ± 0.10 to 0.17 ± 0.03 mL/min/g; P < 0.001) and MVO(2) (27 ± 2.3 to 15 ± 2.7 μL O(2)/min/g; P < 0.001). At CPP = 40 mmHg, GLP-1 had no effect on coronary blood flow, MVO(2) or regional shortening, but dose-dependently increased myocardial glucose uptake from 0.11 ± 0.02 μmol/min/g at baseline to 0.17 ± 0.04 μmol/min/g at 1 nmol/L GLP-1 (P < 0.001). These data indicate that acute, intracoronary administration of GLP-1 (7-36) preferentially augments glucose metabolism in ischemic myocardium, independent of effects on cardiac contractile function or coronary blood flow.

GLP-1, exendin-4 and C-peptide regulate pancreatic islet microcirculation, insulin secretion and glucose tolerance in rats

GLP-1 (glucagon-like peptide 1) and its mimetic exendin-4 are used against Type 2 diabetes. C-peptide has also proven promising to enhance insulin action. Since insulin secretion in vivo can be rapidly tuned by changes in islet microcirculation, we evaluated the influence of GLP-1, exendin-4 and C-peptide on pancreatic IBF (islet blood flow), and dynamic changes in insulin secretion and glycaemia in the rat. Adult male Wistar rats were divided into four groups given intravenous saline, GLP-1, exendin-4 or C-peptide respectively and administered either saline or 30% glucose. Furthermore, we investigated the effect of intravenous infusion of different doses of exendin-4 into either the femoral vein or the portal vein on islet microcirculation. A non-radioactive microsphere technique was adopted to measure the regional blood flow. Both GLP-1 and exendin-4 prevented the glucose-induced PBF (pancreatic blood flow) redistribution into the islets. Infusion of exendin-4 into the portal vein did not alter pancreatic islet microcirculation, while infusion of exendin-4 into femoral vein significantly decreased basal IBF. C-peptide increased basal IBF and the proportion of IBF out of total PBF, but did not affect the islet microcirculation after glucose administration. GLP-1, exendin-4 and C-peptide stimulated insulin secretion and significantly decreased glycaemia. Blocking NO formation did not prevent the decreased IBF and post-load glycaemia evoked by exendin-4, but further decreased IBF and KBF (kidney blood flow) and increased basal glycaemia. Blocking the vagus nerve enhanced pancreatic IBF and further decreased post-load glycaemia and KBF and increased basal glycaemia. The vascular modulatory effect on pancreatic islet microcirculation described herein, with subsequent effects on in vivo insulin secretion and glycaemia, might be one of the mechanisms underlying the anti-diabetic actions of GLP-1 and its long acting mimetic exendin-4, as well as that of C-peptide.

The effect of glucagon-like peptide 1 on cardiovascular risk

Glucagon-like peptide 1 (GLP-1) is an incretin hormone responsible for amplification of insulin secretion when nutrients are given orally, as opposed to intravenously, and it retains its insulinotropic activity in patients with type 2 diabetes mellitus. GLP-1-based therapies, such as GLP-1 receptor agonists and inhibitors of dipeptidyl peptidase 4, an enzyme that degrades endogenous GLP-1, have established effectiveness in lowering glucose levels and are routinely used to treat patients with type 2 diabetes. These agents regulate glucose metabolism through multiple mechanisms and have several effects on cardiovascular parameters. These effects, possibly independent of the glucose-lowering activity, include changes in blood pressure, endothelial function, body weight, cardiac metabolism, lipid metabolism, left ventricular function, atherosclerosis, and the response to ischemia-reperfusion injury. Thus, GLP-1-based therapies could potentially target both diabetes and cardiovascular disease. This Review highlights the mechanisms targeted by GLP-1-based therapies, and emphasizes current developments in incretin research that are relevant to cardiovascular risk and disease, as well as treatment with GLP-1 receptor agonists.

Cardiovascular comorbidities of type 2 diabetes mellitus: defining the potential of glucagonlike peptide-1-based therapies

The global epidemic of diabetes mellitus (~95% type 2 diabetes) has been fueled by a parallel increase in obesity and overweight. Together, these metabolic disease epidemics have contributed to the increasing incidence and prevalence of cardiovascular disease. The accumulation of metabolic and cardiovascular risk factors in patients with type 2 diabetes--risk factors that may exacerbate one another--complicates treatment. Inadequate treatment, treatment that fails to achieve goals, increases the risk for cardiovascular morbidity and mortality. From a clinical perspective, type 2 diabetes is a cardiovascular disease, an observation that is supported by a range of epidemiologic, postmortem, and cardiovascular imaging studies. Vascular wall dysfunction, and particularly endothelial dysfunction, has been posited as a "common soil" linking dysglycemic and cardiovascular diseases. Vascular wall dysfunction promoted by environmental triggers (e.g., sedentary lifestyle) and metabolic triggers (chronic hyperglycemia, obesity) has been associated with the upregulation of reactive oxygen species and chronic inflammatory and hypercoagulable states, and as such with the pathogenesis of type 2 diabetes, atherosclerosis, and cardiovascular disease. Glucagon-like peptide-1 (GLP)-1, an incretin hormone, and synthetic GLP-1 receptor agonists represent promising new areas of research and therapeutics in the struggle not only against type 2 diabetes but also against the cardiovascular morbidity and mortality associated with type 2 diabetes. In a number of small trials in humans, as well as in preclinical and in vitro studies, both native GLP-1 and GLP-1 receptor agonists have demonstrated positive effects on a range of cardiovascular disease pathologies and clinical targets, including such markers of vascular inflammation as high-sensitivity C-reactive protein, plasminogen activator inhibitor-1, and brain natriuretic peptide. Reductions in markers of dyslipidemia such as elevated levels of triglycerides and free fatty acids have also been observed, as have cardioprotective functions. Larger trials of longer duration will be required to confirm preliminary findings. In large human trials, GLP-1 receptor agonists have been associated with significant reductions in both blood pressure and weight.

Emerging cardiovascular actions of the incretin hormone glucagon-like peptide-1: potential therapeutic benefits beyond glycaemic control?

Glucagon-like peptide-1 (GLP-1) is an incretin hormone secreted by the small intestine in response to nutrient ingestion. It has wide-ranging effects on glucose metabolism, including stimulation of insulin release, inhibition of glucagon secretion, reduction of gastric emptying and augmentation of satiety. Importantly, the insulinotropic actions of GLP-1 are uniquely dependent on ambient glucose concentrations, and it is this particular characteristic which has led to its recent emergence as a treatment for type 2 diabetes. Although the major physiological function of GLP-1 appears to be in relation to glycaemic control, there is growing evidence to suggest that it may also play an important role in the cardiovascular system. GLP-1 receptors (GLP-1Rs) are expressed in the heart and vasculature of both rodents and humans, and recent studies have demonstrated that GLP-1R agonists have wide-ranging cardiovascular actions, such as modulation of heart rate, blood pressure, vascular tone and myocardial contractility. Importantly, it appears that these agents may also have beneficial effects in the setting of cardiovascular disease (CVD). For example, GLP-1 has been found to exert cardioprotective actions in experimental models of dilated cardiomyopathy, hypertensive heart failure and myocardial infarction (MI). Preliminary clinical studies also indicate that GLP-1 infusion may improve cardiac contractile function in chronic heart failure patients with and without diabetes, and in MI patients after successful angioplasty. This review will discuss the current understanding of GLP-1 biology, examine its emerging cardiovascular actions in both health and disease and explore the potential use of GLP-1 as a novel treatment for CVD.

Endothelial dysfunction induced by triglycerides is not restored by exenatide in rat conduit arteries ex vivo

Exenatide (synthetic exendin-4) is a stable analogue of glucagon-like peptide 1 (GLP-1) and has recently been approved for clinical use against type 2 diabetes. Exenatide is believed to exert its effects via the GLP-1 receptor with almost the same potency as GLP-1 in terms of lowering blood glucose. Short term exenatide treatment normalizes the altered vascular tone in type 2 diabetic rats, probably due to the reduction in glycemia. The aim of this study was to investigate whether exenatide directly protects against triglyceride-induced endothelial dysfunction in rat femoral arterial rings ex vivo. Short term pre-incubation with Intralipid (0.5 and 2%) was found to dose-dependently induce endothelial dysfunction, in that it elicited a significant reduction in ACh-induced vasorelaxation by 29% and 35%, respectively. Paradoxically, this occurred with a concomitant increase in endothelial nitric oxide synthase (eNOS) activity. No such reduction in vasorelaxation by Intralipid was seen in response to the NO donor sodium nitroprusside (SNP), revealing an endothelium-dependent vascular dysfunction by Intralipid. However, exenatide did not protect against Intralipid-induced endothelial dysfunction. More surprisingly, the maximum vasorelaxation induced by exenatide (without Intralipid was only 3+/-2%, compared to the 23+/-4%, 38+/-4%, 79+/-3% and 97+/-4% relaxations induced by GLP-1, GLP-1 (9-36), ACh and SNP, respectively. This unexpected finding prompted us to ascertain that the exenatide preparation was biologically active, and both exenatide (10(-11) mol/l) and GLP-1 (10(-9) mol/l) significantly increased insulin secretion in pancreatic beta-cells from ob/ob mice in vitro. In conclusion, exenatide could neither confer any acute protective effects against triglyceride-induced endothelial dysfunction nor exert any significant vasorelaxant actions in this model of rat conduit arteries ex vivo.

Glucagon-like peptide-1 and its receptor agonist exendin-4 modulate cholangiocyte adaptive response to cholestasis

BACKGROUND & AIMS

Cholangiopathies are characterized by progressive dysregulation of the balance between proliferation and death of cholangiocytes. In the course of cholestasis, cholangiocytes undergo a neuroendocrine transdifferentiation and their biology is regulated by neuroendocrine hormones. Glucagon-like peptide-1 (GLP-1), secreted by neuroendocrine cells, sustains beta-cell survival in experimental diabetes and induces the neuroendocrine transdifferentiation of pancreatic ductal cells. GLP-1 receptor (GLP-1R) selective agonist exendin-4 is used in humans as a novel therapeutic tool for diabetes. The aim of this study was to define if GLP-1 modulates cholangiocyte biologic response to cholestasis.

METHODS

Expression of GLP-1R in cholangiocytes was determined. Effects on cholangiocyte proliferation of the in vitro and in vivo exposure to GLP-1 or exendin-4, together with the intracellular signals, were then studied. Synthesis of GLP-1 by cholangiocytes and the effects of GLP-1R blockage on their growth were also determined.

RESULTS

Cholangiocytes express the GLP-1 receptor, which is up-regulated in the course of cholestasis. GLP-1 and exendin-4 increase cholangiocyte growth both in vitro and in vivo. The GLP-1R signal is mediated by the phosphatidyl-inositol-3-kinase, cAMP/Protein Kinase A, and Ca(2+)-CamKIIalpha but not by the ERK1/2 and PKCalpha pathways. Proliferating cholangiocytes synthesize GLP-1: neutralization of its action by GLP-1R antagonist blunts cholangiocyte response to cholestasis.

CONCLUSIONS

GLP-1 is required for the cholangiocyte adaptive response to cholestasis. Cholangiocytes are susceptible to the activation of GLP-1R and respond with increased proliferation and functional activity. Exendin-4 availability for employment in humans and these data may open novel perspectives for the medical treatment of cholangiopathies.

Animal models of type 2 diabetes with reduced pancreatic beta-cell mass

Type 2 diabetes is increasingly viewed as a disease of insulin deficiency due not only to intrinsic pancreatic beta-cell dysfunction but also to reduction of beta-cell mass. It is likely that, in diabetes-prone subjects, the regulated beta-cell turnover that adapts cell mass to body's insulin requirements is impaired, presumably on a genetic basis. We still have a limited knowledge of how and when this derangement occurs and what might be the most effective therapeutic strategy to preserve beta-cell mass. The animal models of type 2 diabetes with reduced beta-cell mass described in this review can be extremely helpful (a) to have insight into the mechanisms underlying the defective growth or accelerated loss of beta-cells leading to the beta-cell mass reduction; (b) to investigate in prospective studies the mechanisms of compensatory adaptation and subsequent failure of a reduced beta-cell mass. Furthermore, these models are of invaluable importance to test the effectiveness of potential therapeutic agents that either stimulate beta-cell growth or inhibit beta-cell death.