Impact of incretin therapy on islet dysfunction: an underlying defect in the pathophysiology of type 2 diabetes

Differential Effects of Linagliptin on the Function of Human Islets Isolated from Non-diabetic and Diabetic Donors

Linagliptin is a dipeptidyl Peptidase-4 (DPP-4) inhibitor that inhibits the degradation of glucagon-like peptide 1 (GLP-1), and has been approved for the treatment of type 2 diabetes (T2D) in clinic. Previous studies have shown linagliptin improves β cell function using animal models and isolated islets from normal subjects. Since β cell dysfunction occurs during diabetes development, it was not clear how human islets of T2D patients would respond to linagliptin treatment. Therefore, in this study we employed human islets isolated from donors with and without T2D and evaluated how they responded to linagliptin treatment. Our data showed that linagliptin significantly improved glucose-stimulated insulin secretion for both non-diabetic and diabetic human islets, but its effectiveness on T2D islets was lower than on normal islets. The differential effects were attributed to reduced GLP-1 receptor expression in diabetic islets. In addition, linagliptin treatment increased the relative GLP-1 vs glucagon production in both non-diabetic and diabetic islets, suggesting a positive role of linagliptin in modulating α cell function to restore normoglycemia. Our study indicated that, from the standpoint of islet cell function, linagliptin would be more effective in treating early-stage diabetic patients before they develop severe β cell dysfunction.

Multifactorial effects of vildagliptin added to ongoing metformin therapy in patients with type 2 diabetes mellitus

BACKGROUND

To assess the efficacy of a vildagliptin and metformin combination therapy to a metformin monotherapy in type 2 diabetes mellitus patients.

METHODS

Sixty-one patients with diabetes inadequately controlled by a metformin monotherapy were randomized to treatment with a combination therapy of vildagliptin 100mg and a metformin versus metformin monotherapy. This was a 12-week randomized parallel group study. During the study we assessed parameters of glycemic and lipid metabolism as well as the treatment effects on the release of proinflammatory and antiinflammatory cytokines.

RESULTS

Compared with baseline values we observed a significant improvement of glycaemic parameters such as HbA1c, FPG, PPG, FPI, HOMA-IR and HOMA-β index as well as decrease of TCh, TG and LDL and an increase of HDL with the greatest extent of vildagliptin plus a low-dose metformin therapy group. A metformin combination therapy significantly decreased such inflamation parameters as hs-CRP, ox-LDL, TNF-α and IL-1β levels relative to monotherapies. All treatments were well tolerated and there was no incidence of hypoglycaemia.

CONCLUSIONS

Vildagliptin added to an ongoing metformin therapy allows to achieve better metabolic control parameters in comparison with a metformin monotherapy and the combination treatment is well tolerated and has a low risk of serious adverse effects.

Incretin hormones and the satiation signal

Recent research has indicated that appetite-regulating hormones from the gut may have therapeutic potential. The incretin hormone, glucagon-like peptide-1 (GLP-1), appears to be involved in both peripheral and central pathways mediating satiation. Several studies have also indicated that GLP-1 levels and responses to meals may be altered in obese subjects. Clinical trial results have shown further that two GLP-1 receptor agonists (GLP-1 RAs), exenatide and liraglutide, which are approved for the treatment of hyperglycemia in patients with type 2 diabetes, also produce weight loss in overweight subjects without diabetes. Thus, GLP-1 RAs may provide a new option for pharmacological treatment of obesity.

Current treatments and strategies for type 2 diabetes: can we do better with GLP-1 receptor agonists?

Abstract Diet, lifestyle modification, and pharmacotherapy with metformin are appropriate initial treatments for many patients with type 2 diabetes (T2DM). However, most individuals do not maintain glycemic control with metformin alone. Addition of other oral antidiabetes drugs (OADs), including sulfonylurea, meglitinide, or thiazolidinedione, is often the next step. Newer options, including incretin-based glucagon-like peptide-1 (GLP-1) receptor agonists (RAs) and dipeptidyl peptidase-4 (DPP-4) inhibitors, offer important benefits as monotherapies or in combination with OADs, with low risk for hypoglycemia. Reductions in glycated hemoglobin (A1C) have been reported among patients treated with GLP-1 RAs (exenatide, -0.8 to -1.1%; liraglutide, -0.8 to -1.6%), as has weight loss (exenatide, -1.6 to -3.1 kg; liraglutide, -1.6 to -3.2 kg). GLP-1 RAs also stimulate β-cell responses and have positive effects on cardiovascular risk factors often present in patients with T2DM. The most common adverse events associated with GLP-1 RAs are nausea, which diminishes over time, and hypoglycemia (when used in combination with a sulfonylurea). A large number of trials demonstrated benefits of GLP-1 RAs, suggesting they could provide suitable treatment options for patients with T2DM.

Clarifying the role of incretin-based therapies in the treatment of type 2 diabetes mellitus

BACKGROUND

Glucose homeostasis is the result of a complex interaction of a spectrum of hormones, including insulin, glucagon, amylin, and the incretins. Incretins are released by enteroendocrine cells in the intestine in response to a meal. Incretin dysfunction, along with a number of other defects, has been implicated in contributing to the pathogenesis of type 2 diabetes mellitus (T2DM). Therapies that restore incretin activity may reduce the pathophysiologic consequences of diabetes.

OBJECTIVES

The aim of this article was to review incretin physiology and studies of incretin therapy with glucagon-like peptide-1 (GLP-1) receptor agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors that were developed to specifically address the blunted incretin response in patients with T2DM.

METHODS

Relevant English-language publications between 1995 and 2010 were identified through a search of the MEDLINE and EMBASE databases using the search terms incretin, type 2 diabetes mellitus, GLP-1, glucose-dependent insulinotropic polypeptide, and DPP-4. Review articles and preclinical and clinical trials that described relevant details of the epidemiology of diabetes and incretin physiology in health and in T2DM were selected for review and inclusion. Clinical trials were used to describe the clinical efficacy and safety of the GLP-1 receptor agonists and DPP-4 inhibitors in patients with T2DM. An occasional systematic review article and/or meta-analysis summarizing numerous clinical trials of a particular agent was selected for summarizing key data.

RESULTS

Pharmacologic modulation of incretin pathophysiology by GLP-1 receptor agonists and DPP-4 inhibitors significantly improved glycemic control, benefited β-cell function, improved dyslipidemia, and lowered the risk of hypoglycemia compared with insulin and sulfonylureas. Unlike the DPP-4 inhibitors, GLP-1 receptor agonist therapy also produced weight loss, an important consideration given the close association among T2DM, overweight/obesity, and cardiovascular disease. The most common adverse events with GLP-1 receptor agonist therapy included nausea (28%-44%), vomiting (13%-17%), and diarrhea (11%-17%), which generally reduced in incidence and severity with continued therapy. The tolerability profile of the DPP-4 inhibitors was very good, with the incidence of adverse events similar to that of placebo. There was a suggestion of an increased incidence of nasopharyngitis versus placebo (5%-6% vs 3%-4%) with sitagliptin and urinary tract infection (6.8% vs 6.1% with placebo) and headache with saxagliptin (6.5% vs 5.9% with placebo).

CONCLUSION

The 2 incretin drug classes provided effective and consistent glycemic control with a good tolerability profile. These agents might also improve long-term β-cell function and either reduce body weight or be weight neutral. Their role in the therapeutic armamentarium of T2DM is evolving as their potential strengths and weaknesses become better defined.

Effectiveness of adding vildagliptin to the treatment of diabetic patients nonresponsive to the combination of metformin and a sulphonylurea

OBJECTIVE: To evaluate the effectiveness of adding vildagliptin to the treatment of patients with inadequately controlled type 2 diabetes mellitus (T2DM) treated with a combination of metformin and a sulphonylurea. SUBJECTS AND METHODS: 37 T2DM patients with HbA1c ranging from 7.7% to 12.4% (mean of 9.30 ± 1.38), despite the use of metformin in combination with a sulphonylurea, were additionally treated with vildagliptin (100 mg/day) for at least 6 months. RESULTS: During triple oral therapy (TOT) HbA1c levels < 7% were achieved in 11 patients (29.7%), whereas levels of fasting plasma glucose (FPG) < 120 mg/dL were observed in 12 patients (32.4%). Both findings were observed in 10 patients (27.0%). Compared to nonresponsive subjects, lower mean baseline HbA1c and FPG levels were seen in responsive patients, but the difference was only statistically significant for fasting plasma glucose (FPG). Moreover, there was considerable overlap between the two groups. CONLUSION: Our preliminary results suggest that TOT with metformin, a sulphonylurea and vildagliptin may be useful for some T2DM patients nonresponsive to combination therapy with metformin and sulphonylurea.

A physiologic and pharmacological basis for implementation of incretin hormones in the treatment of type 2 diabetes mellitus

Progressive deterioration of β-cell function is a hallmark of type 2 diabetes mellitus (DM). Together with increasing insulin resistance in peripheral tissues (in both the liver and the skeletal muscle), the inability of pancreatic insulin secretion to manage fasting and postprandial glucose levels results in hyperglycemia. Currently available oral antidiabetes agents improve glycemic parameters, but no single drug addresses the numerous pathophysiologic defects known to contribute to hyperglycemia in patients with type 2 DM. Dysregulation in the incretin system is another component of the pathophysiologic processes that lead to DM. Agents used to correct defects in the incretin system, such as glucagon-like peptide 1 receptor agonists and dipeptidyl peptidase 4 inhibitors, offer the potential to restore glucose-dependent insulin secretion and improve β-cell function. Glucagon-like peptide 1 receptor agonists also promote weight loss and provide beneficial effects on cardiovascular risk factors. A new approach that promotes the selection of pharmacotherapy for the treatment of patients with DM, with the goal of slowing or reversing the natural history of the disease, may be in order. Clinicians can select agents to address specific pathophysiologic defects to improve glycemia, with the hope of preventing the development of complications.

Type 2 diabetes: an expanded view of pathophysiology and therapy

Type 2 diabetes mellitus is a complicated metabolic disease affecting millions of individuals worldwide. The medications used to manage the disease are based on different pharmacologic approaches, including decreasing hepatic gluconeogenesis, stimulating pancreatic insulin production, slowing polysaccharide digestion, and increasing insulin sensitivity in muscle, liver, and fat to lower blood glucose. Incretin-based therapies, including glucagon-like peptide-1 (GLP-1) receptor agonists, mimic the effects of native GLP-1, while dipeptidyl peptidase-4 inhibitors increase circulating concentrations of endogenous GLP-1. This review focuses on means by which primary care physicians might evaluate the utility of pharmacologic agents based on their relation to the pathogenesis of type 2 diabetes. In general, patients with type 2 diabetes should be treated to their lowest targeted glycemic goals as soon as they are diagnosed, for as long as possible, as safely as possible, and as rationally as possible.

DPP-4 inhibitors in clinical practice

Type 2 diabetes is a very common worldwide disorder, with major consequences for patients, society, and health care services. Good glycemic control is an important aspect of diabetes management because it has a significant impact on diabetes-related microvascular and possibly macrovascular complications. Based on our understanding of the pathogenesis of diabetes, multiple pharmacological interventions have been developed in the past 60 years. Although effective, none have had a lasting effect on glycemic control because of the progressive nature of type 2 diabetes requiring combination therapies and insulin treatment. In addition, several pharmacologic interventions have undesirable side effects, including hypoglycemia and weight gain. Drugs targeting the incretin pathway are the latest addition to the available antidiabetes agents. Incretin-based therapy is either delivered orally (dipeptidyl peptidase-4 [DPP-4]) inhibitors or injected subcutaneously (glucagon-like peptide-1 [GLP-1] mimetics and analogues). Dipeptidyl peptidase-4 inhibitors are effective either as a single or combination therapy in lowering glycated hemoglobin, fasting and postprandial glucose levels, with a low incidence of hypoglycemia and no weight gain. There are 3 DPP-4 inhibitors currently available (sitagliptin, saxagliptin, and vildagliptin), with more expected to be available in the future. In this article, we review the scientific background for incretin-based therapy and the available evidence regarding the role and efficacy of DPP-4 inhibitors in the treatment of patients with type 2 diabetes.

The role of basal insulin and glucagon-like peptide-1 agonists in the therapeutic management of type 2 diabetes--a comprehensive review

The treatment of type 2 diabetes mellitus (T2DM) has been revolutionized by the introduction of novel therapeutic regimens following the clinical approval of the long-acting basal insulin glargine 10 years ago, followed by insulin detemir and, more recently, agents that target the glucagon-like peptide (GLP)-1 system with dipeptidyl peptidase 4 (DPP-4)-resistant products, such as liraglutide and exenatide, and DPP-4 inhibitors, such as sitagliptin, saxagliptin, alogliptin, and vildagliptin. The position and clinical efficacy of the GLP-1 mimetics are less well understood, however, and how they should be best used in the context of the established clinical efficacy of long-acting insulin analogs is yet to be defined. The aim of this review is to provide a summary of the efficacy, safety, and weight changes associated with long-acting insulin analogs (insulin glargine and insulin detemir) and two GLP-1 mimetics (exenatide and liraglutide). MEDLINE, EMBASE, and BIOSIS databases were searched with a timeframe of January 1, 2003-January 12, 2009 using the following terms: "Insulin glargine," with the co-indexing terms "LANTUS" and "HOE901"; "Insulin detemir," with the co-indexing term "Levemir"; "Exenatide"; and "Liraglutide." This literature review demonstrates that GLP-1 and basal insulin therapies are effective treatment options for insulin-naïve patients with suboptimal glycemic control with oral hypoglycemic agents. There are potential advantages of basal insulin and GLP-1 therapies in particular populations of patients. Further comparative data are needed to fully investigate the relative positioning of these therapies within the T2DM treatment paradigm.

Saxagliptin added to a thiazolidinedione improves glycemic control in patients with type 2 diabetes and inadequate control on thiazolidinedione alone

CONTEXT

Due to the natural progression of type 2 diabetes (T2D), most patients require combination therapy to maintain glycemic control.

OBJECTIVE

Our objective was to evaluate efficacy and safety of saxagliptin plus thiazolidinedione (TZD) in patients with T2D and inadequate glycemic control on TZD monotherapy.

DESIGN

The study was a multicenter, randomized, double-blind, placebo (PBO)-controlled phase 3 trial conducted from March 13, 2006, to October 15, 2007.

SETTING

Patients were recruited from 172 outpatient centers.

PATIENTS

Patients with inadequately controlled T2D [glycosylated hemoglobin (HbA(1c)) 7.0-10.5%], 18-77 yr, receiving stable TZD monotherapy (pioglitazone 30 or 45 mg or rosiglitazone 4 or 8 mg) for at least 12 wk before screening were eligible.

INTERVENTIONS

A total of 565 patients were randomized and treated with saxagliptin (2.5 or 5 mg) or PBO, once daily, plus stable TZD dose for 24 wk.

MAIN OUTCOME MEASURES

Primary outcome was change in HbA(1c) from baseline to wk 24. Secondary outcomes were change from baseline to wk 24 in fasting plasma glucose, proportion of patients achieving HbA(1c) less than 7.0%, and postprandial glucose area under the curve.

RESULTS

At 24 wk, saxagliptin (2.5 and 5 mg) plus TZD demonstrated statistically significant adjusted mean decreases vs. PBO in HbA(1c) [-0.66% (P = 0.0007) and -0.94% (P < 0.0001) vs. -0.30%] and fasting plasma glucose [-0.8 mmol/liter (P = 0.0053) and -1 mmol/liter (P = 0.0005) vs. -0.2 mmol/liter]. Proportion of patients achieving HbA(1c) less than 7.0% was greater for saxagliptin (2.5 and 5 mg) plus TZD vs. PBO [42.2% (P = 0.001) and 41.8% (P = 0.0013) vs. 25.6%]. Postprandial glucose area under the curve was significantly reduced [-436 mmol x min/liter (saxagliptin 2.5 mg plus TZD) and -514 mmol x min/liter (saxagliptin 5 mg plus TZD) vs. -149 mmol x min/liter (PBO)]. Saxagliptin was generally well tolerated; adverse event occurrence and reported hypoglycemic events were similar across all groups.

CONCLUSIONS

Saxagliptin added to TZD provided statistically significant improvements in key parameters of glycemic control vs. TZD monotherapy and was generally well tolerated.

Efficacy and safety of incretin based therapies: clinical trial data

OBJECTIVE

Provide a comprehensive overview of efficacy and safety data on incretin-based agents in the treatment of type 2 diabetes.

DATA SOURCES

A PubMed search was conducted for the years 2000-2009, using as keywords the names of glucagon-like peptide-1 (GLP-1) receptor agonists (exenatide and liraglutide) and dipeptidyl peptidase-4 (DPP-4) inhibitors (sitagliptin, alogliptin, and saxagliptin). World Diabetes Congress abstracts from 2008 to 2009 were also searched for clinical studies of these agents.

STUDY SELECTION

The author included randomized controlled trials of incretin therapies that were published in English and enrolled > or =100 participants.

DATA EXTRACTION

Data on the effects of incretins on glycemic control, weight, beta-cell function, blood pressure, lipid levels, safety, and tolerability were extracted and summarized.

DATA SYNTHESIS

A total of 27 randomized controlled studies of incretin therapy were identified and included in the review. GLP-1 receptor agonists and DPP-4 inhibitors were evaluated at different points in the diabetes treatment spectrum, i.e., added to diet and exercise alone (monotherapy) or added to oral antihyperglycemic regimens (combination therapy).

CONCLUSION

In addition to decreasing glycemia in type 2 diabetes, incretin therapies may improve other important parameters, including beta-cell function, blood pressure, and lipid levels, with a low risk for hypoglycemia. A comparison of the study data differentiates the clinical profiles of the GLP-1 receptor agonists, which are associated with weight loss, and DPP-4 inhibitors, which are weight neutral, as well as the individual agents within each class.

Insights from the Liraglutide Clinical Development Program--the Liraglutide Effect and Action in Diabetes (LEAD) studies

Standard therapies for type 2 diabetes often fail to maintain glycemic control over the long term, in part because they do not target the underlying cause. Current treatments may also be associated with weight gain, hypoglycemia, and other adverse effects, and can be difficult to use. Disease progression is accompanied by a progressive decline in beta-cell function, which begins early in the disease course, and an impaired incretin response. The recently developed glucagon-like peptide-1 (GLP-1) receptor agonists overcome some of the limitations of conventional treatments. This article summarizes the key results of the new GLP-1 receptor agonist (liraglutide) phase 3 Liraglutide Effect and Action in Diabetes (LEAD) studies. This series of 6 randomized controlled studies involved > 4400 patients with type 2 diabetes who were unable to maintain glycemic control with diet and exercise alone or with oral treatment, approximately 2700 of whom received liraglutide. The studies demonstrated the efficacy and safety of liraglutide both as monotherapy and as combination therapy with 1 or 2 oral agents. In addition to providing robust glycemic control in these studies, liraglutide reduced weight in most patients, improved beta-cell function, lowered blood pressure and triglycerides, and was well tolerated with minimal risk of hypoglycemia.