Focus on Incretin-Based Therapies: Targeting the Core Defects of Type 2 Diabetes

Liraglutide Suppresses Tau Hyperphosphorylation, Amyloid Beta Accumulation through Regulating Neuronal Insulin Signaling and BACE-1 Activity

Neuronal insulin resistance is a significant feature of Alzheimer's disease (AD). Accumulated evidence has revealed the possible neuroprotective mechanisms of antidiabetic drugs in AD. Liraglutide, a glucagon-like peptide-1 (GLP-1) analog and an antidiabetic agent, has a benefit in improving a peripheral insulin resistance. However, the neuronal effect of liraglutide on the model of neuronal insulin resistance with Alzheimer's formation has not been thoroughly investigated. The present study discovered that liraglutide alleviated neuronal insulin resistance and reduced beta-amyloid formation and tau hyperphosphorylation in a human neuroblostoma cell line, SH-SY5Y. Liraglutide could effectively reverse deleterious effects of insulin overstimulation. In particular, the drug reversed the phosphorylation status of insulin receptors and its major downstream signaling molecules including insulin receptor substrate 1 (IRS-1), protein kinase B (AKT), and glycogen synthase kinase 3 beta (GSK-3β). Moreover, liraglutide reduced the activity of beta secretase 1 (BACE-1) enzyme, which then decreased the formation of beta-amyloid in insulin-resistant cells. This indicated that liraglutide can reverse the defect of phosphorylation status of insulin signal transduction but also inhibit the formation of pathogenic Alzheimer's proteins like Aβ in neuronal cells. We herein provided the possibility that the liraglutide-based therapy may be able to reduce such deleterious effects caused by insulin resistance. In view of the beneficial effects of liraglutide administration, these findings suggest that the use of liraglutide may be a promising therapy for AD with insulin-resistant condition.

The Role of Glucagon-like Peptide-1 Receptor Agonists in the Treatment of Type 2 Diabetes

The role of GLP-1 agonists in the treatment of type 2 diabetes have been shown to be viable options for add-on therapy in diabetic patients, as well as potential monotherapy options. With six available GLP-1 agents, and new combination products in the pipeline, they are a promising drug class for type 2 diabetic patients, especially due to their extended dosing interval and potential weight loss benefits.

Benefits of exenatide on obesity and non-alcoholic fatty liver disease with elevated liver enzymes in patients with type 2 diabetes

BACKGROUND

The purpose of this study was to evaluate the advantages of exenatide treatment on obesity and non-alcoholic fatty liver disease (NAFLD) with elevated liver enzymes in patients with type 2 diabetes (T2D).

METHODS

A total of 60 newly diagnosed patients with obesity, NAFLD with elevated liver enzymes and T2D were included in the study. The patients were randomly divided into two groups. The exenatide treatment group (n = 30) were treated with exenatide and insulin glargine, and the intensive insulin therapy group (n = 30) were treated with insulin aspart and insulin glargine for 12 weeks. Selected clinical characteristics were determined, and ultrasonography was performed at both baseline and 12 weeks following treatment.

RESULTS

At baseline, the clinical characteristics were matched between the two groups. After 12 weeks, fasting blood glucose (FBG), postprandial blood glucose (PBG), glycosylated haemoglobin (HbA1c), total cholesterol (TC), triglyceride (TG) and total bilirubin levels were significantly decreased in the two groups (p < 0.001). Body weight and waist circumference were significantly decreased in the exenatide group but increased in the intensive insulin group (p < 0.001). The levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and γ-glutamyl transpeptidase (γGGT) in the exenatide group were significantly lower than in the intensive insulin group (p < 0.001). The mean body weight change correlated with the levels of ALT, AST and γGGT change (ALT, r = 0.761; AST, r = 0.733; γGGT, r = 0.752; p < 0.001). Moreover, the reversal rate of fatty liver was significantly higher in the exenatide group (93.3%) than the intensive insulin group (66.7%) (p < 0.01).

CONCLUSIONS

Exenatide has a better hepatic-protective effect than intensive insulin therapy and perhaps represents a unique option for adjunctive therapy for patients with obesity, non-alcoholic fatty liver disease with elevated liver enzymes and T2D.

The cardiovascular safety of incretin-based therapies: a review of the evidence

Cardiovascular disease (CVD) is a leading cause of morbidity and mortality in people with diabetes and therefore managing cardiovascular (CV) risk is a critical component of diabetes care. As incretin-based therapies are effective recent additions to the glucose-lowering treatment armamentarium for type 2 diabetes mellitus (T2D), understanding their CV safety profiles is of great importance. Glucagon-like peptide-1 (GLP-1) receptor agonists have been associated with beneficial effects on CV risk factors, including weight, blood pressure and lipid profiles. Encouragingly, mechanistic studies in preclinical models and in patients with acute coronary syndrome suggest a potential cardioprotective effect of native GLP-1 or GLP-1 receptor agonists following ischaemia. Moreover, meta-analyses of phase 3 development programme data indicate no increased risk of major adverse cardiovascular events (MACE) with incretin-based therapies. Large randomized controlled trials designed to evaluate long-term CV outcomes with incretin-based therapies in individuals with T2D are now in progress, with the first two reporting as this article went to press.

A retrospective audit of type 2 diabetes patients prescribed liraglutide in real-life clinical practice

BACKGROUND

In phase 3 trials, the once-daily human glucagon-like peptide-1 analog liraglutide provided effective glycemic control with low rates of hypoglycemia, weight loss, and reduced systolic blood pressure (SBP) in patients with type 2 diabetes. Through a retrospective clinical audit, the authors aimed to assess the clinical effectiveness of liraglutide, from initiation to first hospital visit, when prescribed at a center in Northern Ireland.

METHODS

Patients attending Ulster Hospital who were prescribed liraglutide (June 2009-September 2010) and assessed both at baseline and first post-initiation visit were included in the analysis. The primary endpoint was change in glycated hemoglobin (HbA1c) from baseline. Weight, blood pressure, and frequency of hypoglycemic events were also assessed.

RESULTS

Data from 193 patients are reported (baseline HbA1c 9.0%, mean age 55.8 years, diabetes duration 8.8 years, 66.8% male). Average time to first visit after initiation was 13.5 weeks, at which point 174 patients (90.2%) were prescribed 1.2 mg liraglutide. Mean change in HbA1c from initiation to first visit was -0.9%, while mean body weight change was -2.4 kg and change in SBP was -2.0 mmHg. Transient gastrointestinal side effects were experienced by 11.9% of patients. The number of patients experiencing minor hypoglycemic events was low (5.7%) and no major events were reported.

CONCLUSION

Data from clinical studies translate into clinical practice: liraglutide provided improved glycemic control after 13.5 weeks of treatment, accompanied by weight loss and low incidence of hypoglycemia.

Clinical use of liraglutide in type 2 diabetes and its effects on cardiovascular risk factors

OBJECTIVE

To assess whether liraglutide, a glucagon-like peptide-1 receptor agonist, has cardioprotective properties in addition to its glycemic effects.

METHODS

We performed a retrospective analysis of medical records of 110 obese patients with type 2 diabetes mellitus treated with liraglutide for at least 6 months between March 2010 and April 2011 at our tertiary care referral center. The variables analyzed were body mass index, hemoglobin A(1c) (A1C), systolic blood pressure (SBP), plasma C-reactive protein (CRP) concentrations, and serum lipids.

RESULTS

In our overall study cohort, we noted a reduction in mean weight from 120 ± 5 kg to 115 ± 3 kg and a decrease in mean A1C from 7.8% ± 0.6% to 7.2% ± 0.2%. The mean triglyceride concentration decreased from 173 ± 19 mg/dL to 151 ± 15 mg/dL, the mean SBP was reduced from 132 ± 6 mm Hg to 125 ± 4 mm Hg, and the mean CRP concentration declined from 4.7 ± 0.8 mg/L to 3.2 ± 0.4 mg/L after treatment with liraglutide for a minimal duration of 6 months and a mean duration of 7.5 months (for all the foregoing changes, P<.05). These variables decreased whether these patients were previously treated with orally administered hypoglycemic agents alone or in combination with insulin or exenatide.

CONCLUSION

Our findings in a clinical practice show that liraglutide is a potent antidiabetes drug, whether given in combination with orally administered agents or insulin or as a substitution for exenatide. It lowers body weight, A1C levels, SBP, and CRP and triglyceride concentrations.

Deletion of GαZ protein protects against diet-induced glucose intolerance via expansion of β-cell mass

Insufficient plasma insulin levels caused by deficits in both pancreatic β-cell function and mass contribute to the pathogenesis of type 2 diabetes. This loss of insulin-producing capacity is termed β-cell decompensation. Our work is focused on defining the role(s) of guanine nucleotide-binding protein (G protein) signaling pathways in regulating β-cell decompensation. We have previously demonstrated that the α-subunit of the heterotrimeric G(z) protein, Gα(z), impairs insulin secretion by suppressing production of cAMP. Pancreatic islets from Gα(z)-null mice also exhibit constitutively increased cAMP production and augmented glucose-stimulated insulin secretion, suggesting that Gα(z) is a tonic inhibitor of adenylate cyclase, the enzyme responsible for the conversion of ATP to cAMP. In the present study, we show that mice genetically deficient for Gα(z) are protected from developing glucose intolerance when fed a high fat (45 kcal%) diet. In these mice, a robust increase in β-cell proliferation is correlated with significantly increased β-cell mass. Further, an endogenous Gα(z) signaling pathway, through circulating prostaglandin E activating the EP3 isoform of the E prostanoid receptor, appears to be up-regulated in insulin-resistant, glucose-intolerant mice. These results, along with those of our previous work, link signaling through Gα(z) to both major aspects of β-cell decompensation: insufficient β-cell function and mass.

Exenatide, a GLP-1 agonist in the treatment of Type 2 diabetes

Incretin-based therapies represent a new and innovative treatment modality in the management of Type 2 diabetes. Their therapeutic actions address many of the key metabolic defects in the pathophysiology of diabetes. Incretin hormones augment insulin secretion in a glucose-dependent manner. They have a low risk of inducing hypoglycemia, unlike many other antidiabetic medications. They also have the beneficial effect of being associated with early satiety, decreased caloric intake and weight loss. Exenatide was the first incretin-based therapy to be licensed for use and has now been developed in a once-weekly preparation. We review the evidence base for the use of exenatide and discuss the implications for the management of diabetes.

Incretin therapy--present and future

Although newer treatments for type 2 diabetes (T2D) patients have produced continual improvements in outcome, a large and growing population with prediabetes remains under-treated. In the last few years, incretin-based therapies have become an important treatment option for patients with T2D. There are two classes of incretin agents: the dipeptidyl peptidase-4 (DPP-4) inhibitors and the glucagon like peptide 1 (GLP-1) receptor agonists. The ultimate goal of agents within both of these classes is to increase GLP-1 signaling, which results in augmented glucose-induced insulin secretion, inhibition of glucagon secretion, and decreased appetite. This should result in improved regulation of glucose homeostasis. GLP-1 receptor agonists enable patients to achieve significant weight loss. In contrast, DPP-4 inhibitors result in a less dramatic increase in GLP-1 levels; therefore, they are weight neutral. Incretin therapies are currently recommended for use early in the treatment algorithm for T2D patients whose disease is not manageable by diet and exercise alone, but the potential for these agents may be farther reaching. Current studies are evaluating the potential benefits of combining incretin therapies with basal insulin to provide continuous glucose control before and after meals. In addition, these agents may be promising for patients with prediabetes since they effectively reduce glycosylated hemoglobin levels and fasting plasma glucose levels, enable weight control, and have the potential to preserve β-cell function. Clearly, all of these properties are desirable for patients with prediabetes.