Does glucagon-like peptide-1 receptor agonist therapy add value in the treatment of type 2 diabetes? Focus on exenatide

GLP-1 Receptor Agonists in Type 2 Diabetes Mellitus

The rising epidemic of type 2 diabetes mellitus & associated complications is a serious cause of concern for humanity. Glucagon-like peptide-1 receptor agonists commonly abbreviated as GLP-1 RAs, emerged as a promising therapeutic class based on incretin therapy that regulates glucose metabolism through multiple mechanisms. In the present study, various investigational & clinically used GLP-1 RAs have been reviewed with emphasis on their efficacy, structural modifications, adverse effects and toxicities. Various clinical trials justifying their efficacy have also been included, which highlighted the potential of GLP-1 RAs over conventional anti hyperglycaemic agents through a study of pooled effect on glycemic efficacy and weight-loss. The significant potency and appreciable safety of GLP-1 RAs manifested their potential as a logical approach for the management of type 2 diabetes.

Glucagon like peptide-1 receptor agonists may ameliorate the metabolic adverse effect associated with antiretroviral therapy

The number of people living with HIV and AIDS (PLWHA) reached to almost 40 million, half of which are under antiretroviral treatment (ART). Although the introduction of this therapy significantly improved the life span and quality of PLWHA, metabolic complications of these people remains to be an important issue. These metabolic complications include hyperlipidemia, abnormal fat redistribution and diabetes mellitus, which are defined as lipodystrophy syndrome. Glucagon-like peptide-1 (GLP-1) is a neuropeptide secreted from intestinal L cells and recently developed GLP-1 receptor agonists (GLP-1RAs) stimulate insulin secretion, improve weight control and reduce cardiovascular outcomes. This class of drugs may be a valuable medication in the treatment of HIV-associated metabolic adverse effects and extend the life expectancy of patients infected with HIV.

In vitro and in vivo sustained release of exenatide from vesicular phospholipid gels for type II diabetes

Diabetes is a chronic disease that requires daily treatment to maintain a stable blood glucose level. Sustained-release formulations can thus benefit the treatment of diabetes by reducing the repeated administration of therapeutics. Our study aimed to develop a sustained-release platform for exenatide that is biocompatible and capable of mass production. Vesicular phospholipid gels (VPGs) are semisolid phospholipid dispersions with controlled release profiles. Exenatide-VPGs prepared via simple magnetic stirring showed excellent biocompatibility with an average particle size of about 15 μm after redispersion. VPGs were shown to achieve sustained release for up to 21 days in vitro with no obvious burst effect. The in vivo release study showed that VPGs sustained the release of the exenatide for up to 11 days. Moreover, after subcutaneous injection of the exenatide-VPGs in the diabetic rats, the hypoglycemic effect lasted for 10 days compared with exenatide solution. In sum, the exenatide-VPGs system represents a promising sustained-release formulation for exenatide with a long-acting therapeutic efficacy in vivo.

Effects of glucagon-like peptide 1 on appetite and body weight: focus on the CNS

The delivery of nutrients to the gastrointestinal tract after food ingestion activates the secretion of several gut-derived mediators, including the incretin hormone glucagon-like peptide 1 (GLP-1). GLP-1 receptor agonists (GLP-1RA), such as exenatide and liraglutide, are currently employed successfully in the treatment of patients with type 2 diabetes mellitus. GLP-1RA improve glycaemic control and stimulate satiety, leading to reductions in food intake and body weight. Besides gastric distension and peripheral vagal nerve activation, GLP-1RA induce satiety by influencing brain regions involved in the regulation of feeding, and several routes of action have been proposed. This review summarises the evidence for a physiological role of GLP-1 in the central regulation of feeding behaviour and the different routes of action involved. Also, we provide an overview of presently available data on pharmacological stimulation of GLP-1 pathways leading to alterations in CNS activity, reductions in food intake and weight loss.

The effect of alogliptin and pioglitazone combination therapy on various aspects of β-cell function in patients with recent-onset type 2 diabetes

OBJECTIVE

Type 2 diabetes mellitus (T2DM) management requires continuous treatment intensification due to progressive decline in β-cell function in insulin resistant individuals. Initial combination therapy of a dipeptidyl peptidase (DPP)-4 inhibitor with a thiazolidinedione (TZD) may be rational. We assessed the effects of the DPP4 inhibitor alogliptin (ALO) combined with the TZD pioglitazone (PIO), vs ALO monotherapy or placebo (PBO), on β-cell function and glycemic control in T2DM.

MATERIAL AND METHODS

A 16-week, two-center, randomized, double-blind, PBO-controlled, parallel-arm intervention study in 71 patients with well-controlled T2DM (age 59.1±6.3 years; A1C 6.7±0.1%) treated with metformin, sulfonylurea, or glinide monotherapy was conducted. Patients were treated with combined ALO 25 mg and PIO 30 mg daily or ALO 25 mg daily monotherapy or PBO. Main outcome measures included change in A1C and fasting plasma glucose (FPG) from baseline to week 16. In addition, change in β-cell function parameters obtained from standardized meal tests at baseline and at week 16 was measured.

RESULTS

ALO/PIO and ALO decreased A1C from baseline by 0.9±0.1 and 0.4±0.2% respectively (both P<0.001 vs PBO). FPG was decreased to a greater extent by ALO/PIO compared with ALO monotherapy (P<0.01). ALO/PIO treatment improved β-cell glucose sensitivity (vs PBO; P<0.001) and fasting secretory tone (vs PBO; P=0.001), while ALO monotherapy did not change β-cell function parameters. All treatments were well tolerated.

CONCLUSION

Short-term treatment with ALO/PIO or ALO improved glycemic control in well-controlled T2DM patients, but only combined ALO/PIO improved β-cell function. These data support that initial combination therapy with a DPP4 inhibitor and TZD to address multiple core defects in T2DM may be a sensible approach.

Extra-pancreatic effects of incretin-based therapies: potential benefit for cardiovascular-risk management in type 2 diabetes

Development of cardiovascular disease is one of the major complications of type 2 diabetes mellitus (T2DM). The chronic hyperglycaemic state is often accompanied by dyslipidaemia, hypertension, low-grade systemic inflammation and oxidative stress which collectively result in a high risk of micro- and macrovascular complications. Current glucose-lowering agents do not sufficiently address fore-mentioned macrovascular-risk factors. Recently, new therapeutic agents were introduced, based on the incretin hormone glucagon-like peptide-1 (GLP-1), that is, the GLP-1 receptor agonists (GLP-1RA) and dipeptidyl-peptidase 4 (DPP-4) inhibitors. Beside its effect on pancreatic insulin secretion, GLP-1 exerts several extra-pancreatic effects such as slowing down gastric emptying, promoting satiety and reducing food intake and weight loss. Also, GLP-1 and GLP-1RA were shown to improve cardiovascular-risk profiles, by reducing body fat content, blood pressure, circulating lipids and inflammatory markers in patients with T2DM. This review summarizes the presently known evidence with regard to extra-pancreatic effects of the incretin-based agents, focusing on the actions that improve the cardiovascular-risk profile. We present available data from clinical trials of at least 24 week duration, but also findings from small-sized clinical 'proof of principle' studies. We conclude that GLP-1 RA and to a lesser extent DPP-4 inhibitors are promising agents with regard to their effects on body weight, blood pressure and lipids, which collectively ameliorate the cardiovascular-risk profile and as such may have added value in the treatment of T2DM. However, large-sized long-term outcome studies are warranted to show the true added value of these agents in the treatment of patients with T2DM.

Does interference with the renin-angiotensin system protect against diabetes? Evidence and mechanisms

Agents interfering with the renin-angiotensin system (RAS) were consistently shown to lower the incidence of type 2 diabetes mellitus (T2DM), as compared to other antihypertensive drugs, in hypertensive high-risk populations. The mechanisms underlying this protective effect of RAS blockade using angiotensin-converting enzyme inhibitors or angiotensin-receptor blockers on glucose metabolism are not fully understood. In this article, we will review the evidence from randomized controlled trials and discuss the proposed mechanisms as to how RAS interference may delay the onset of T2DM. In particular, as T2DM is characterized by β-cell dysfunction and obesity-related insulin resistance, we address the mechanisms that underlie RAS blockade-induced improvement in β-cell function and insulin sensitivity.

Gastric stimulation for weight loss

The prevalence of obesity is growing to epidemic proportions, and there is clearly a need for minimally invasive therapies with few adverse effects that allow for sustained weight loss. Behavior and lifestyle therapy are safe treatments for obesity in the short term, but the durability of the weight loss is limited. Although promising obesity drugs are in development, the currently available drugs lack efficacy or have unacceptable side effects. Surgery leads to long-term weight loss, but it is associated with morbidity and mortality. Gastric electrical stimulation (GES) has received increasing attention as a potential tool for treating obesity and gastrointestinal dysmotility disorders. GES is a promising, minimally invasive, safe, and effective method for treating obesity. External gastric pacing is aimed at alteration of the motility of the gastrointestinal tract in a way that will alter absorption due to alteration of transit time. In addition, data from animal models and preliminary data from human trials suggest a role for the gut-brain axis in the mechanism of GES. This may involve alteration of secretion of hormones associated with hunger or satiety. Patient selection for gastric stimulation therapy seems to be an important determinant of the treatment’s outcome. Here, we review the current status, potential mechanisms of action, and possible future applications of gastric stimulation for obesity.

Different incretin responses after pancreatoduodenectomy and distal pancreatectomy

OBJECTIVES

Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are known as incretins to stimulate insulin secretion. The aims of this study were to investigate the postoperative β-cell function and hormonal responses of GLP-1 and GIP after pancreatoduodenectomy (PD) and distal pancreatectomy (DP).

METHODS

Oral glucose tolerance tests were performed in 34 patients (20 PD and 14 DP) before and 1 month after operation. The changes in the serum glucose and insulin concentrations, homeostasis model assessment of insulin resistance, and pancreatic β-cell function (BCF) were analyzed. GLP-1 and GIP were also measured.

RESULTS

There was no patient with postoperative deterioration of glucose tolerance after PD, whereas impairment of glucose metabolism was observed after DP. Homeostasis model assessment of insulin resistance decreased after PD, whereas those after DP showed no change. The postoperative BCF were lower than preoperative values in both groups. GLP-1 increased after DP but not after PD, whereas GIP decreased after PD but not after DP.

CONCLUSIONS

The changes in glucose metabolism and incretin responses were different between PD and DP. The increased level of GLP-1 after DP might reflect the relatively insufficient BCF; and thus, perioperative administration of GLP-1 might improve the diabetic condition after DP.

Glucagon-like peptide-1 receptor agonists versus insulin in inadequately controlled patients with type 2 diabetes mellitus: a meta-analysis of clinical trials

To compare the effect and safety of glucagon-like peptide-1 receptor agonists (GLP-1 RA) with insulin therapy on type 2 diabetes mellitus (T2DM) patients inadequately controlled with metformin and/or sulfonylurea. A systematic literature search on MEDLINE, Embase and Cochrane for randomized controlled trials (RCTs) was conducted using specific search terms 'GLP-1 insulin type 2 diabetes clinical trials' and eight eligible studies were retrieved. Data on mean change in haemoglobin A1c (HbA1C), weight loss, fasting plasma glucose (FPG), incidence of hypoglycaemia and gastrointestinal adverse events were extracted from each study and pooled in meta-analysis. Data on postprandial plasma glucose (PPG) and adverse events were also described or tabulated. Data from eight RCTs enrolling 2782 patients were pooled using a random-effects model. The mean net change [95% confidence interval (CIs)] for HbA1c, weight loss and FPG for patients treated with GLP-1 RA as compared with insulin was -0.14% (-2 mmol/mol) [95% CI; (-0.27, -0.02)%; p = 0.03]; -4.40 kg [95% CI; (-5.23, -3.56) kg; p < 0.01] and 1.18 mmol/l [95% CI; (0.43, 1.93) mmol/l; p < 0.01], respectively, with negative values favouring GLP-1 and positive values favouring insulin. The GLP-1 group was associated with a greater reduction in PPG than the insulin group. Overall, hypoglycaemia was reported less in the GLP-1 group [Mantel-Haenszel odds ratio (M-H OR) 0.45 (0.27, 0.76); p < 0.01], while there was no significant difference in occurrence of severe hypoglycaemia [M-H OR 0.65 (0.29,1.45); p = 0.29]. A significantly higher number of gastrointestinal adverse events were reported with GLP-1 group [M-H OR 15.00 (5.44,41.35) p < 0.01]. GLP-1 RA are promising new agents compared with insulin. Further prospective clinical trials are expected to fully evaluate the long-term effectiveness and safety of these therapies within the T2DM treatment paradigm.

Structure-activity relationship studies on isoindoline inhibitors of dipeptidyl peptidases 8 and 9 (DPP8, DPP9): is DPP8-selectivity an attainable goal?

This work represents the first directed study to identify modification points in the topology of a representative DPP8/9-inhibitor, capable of rendering selectivity for DPP8 over DPP9. The availability of a DPP8-selective compound would be highly instrumental for studying and untwining the biological roles of DPP8 and DPP9 and for the disambiguation of biological effects of nonselective DPP-inhibitors that have mainly been ascribed to blocking of DPPIV's action. The cell-permeable DPP8/9-inhibitor 7 was selected as a lead and dissected into several substructures that were modified separately for evaluating their potential to contribute to selectivity. The obtained results, together with earlier work from our group, clearly narrow down the most probable DPP8-selectivity imparting modification points in DPP8/9 inhibitors to parts of space that are topologically equivalent to the piperazine ring system in 7. This information can be considered of high value for future design of compounds with maximal DPP8 selectivity.

The role of IGF-1 resistance in obesity and type 2 diabetes-mellitus-related insulin resistance and vascular disease

IMPORTANCE OF THE FIELD

The insulin-resistant conditions of type 2 diabetes mellitus (T2DM) and obesity are a major cause of cardiovascular disease on a global scale. These disorders are not only a cause of ill health but are a huge financial drain on healthcare systems. T2DM leads to an increased risk of cardiovascular mortality equivalent to over 10 years of ageing while obesity independent of T2DM also leads to a substantially increased risk of acute myocardial infarction. Recent trials of therapeutic agents and approaches to preventing the cardiovascular complications of type 2 diabetes have been disappointing.

AREAS COVERED IN THIS REVIEW

The role of insulin resistance in the endothelium in the regulation of the anti-atherosclerotic signalling molecule NO and a potential important role for IGF-1 in vascular NO production.

WHAT THE READER WILL GAIN

A comprehensive understanding of how insulin and IGF-1 regulate vascular function and the effect of type 2 diabetes on these pathways.

TAKE HOME MESSAGE

The roles of insulin and IGF-1 in vascular function are complex and intimately related. Nevertheless IGF-1 signalling in the arterial wall has the potential to be manipulated to protect the vasculature against the development of atherosclerosis and its devastating complications.

Non-peptidic glucose-like peptide-1 receptor agonists: aftermath of a serendipitous discovery

Glucagon-like peptide-1 (GLP-1) receptor is an ideal target in the development of incretin-based therapies for diabetes and obesity. Two approaches have been adopted: GLP-1 receptor agonists that mimic the effects of native GLP-1 and dipeptidyl peptidase-4 inhibitors that increase endogenous GLP-1 levels. During the past two decades, search for orally active, non-peptidic GLP-1 receptor agonists has been the focal point of research and development activities in many multinational pharmaceutical companies. Such efforts have not resulted in any success thus far. Serendipitous discovery of substituted cyclobutanes represented by Boc5 as a new class of GLP-1 receptor agonists led us to believe that a small molecule approach to class B G-protein coupled receptor agonism is no longer a fantasy but a reality. However, major obstacles still pose great challenges, and the reasons of which are discussed in this perspectives.