The pharmacologic basis for clinical differences among GLP-1 receptor agonists and DPP-4 inhibitors

The incretin system plays an important role in glucose homeostasis, largely through the actions of glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). Unlike GIP, the actions of GLP-1 are preserved in patients with type 2 diabetes mellitus, which has led to the development of injectable GLP-1 receptor (GLP-1R) agonists and oral dipeptidyl peptidase-4 (DPP-4) inhibitors. GLP-1R agonists-which can be dosed to pharmacologic levels-act directly upon the GLP-1R. In contrast, DPP-4 inhibitors work indirectly by inhibiting the enzymatic inactivation of native GLP-1, resulting in a modest increase in endogenous GLP-1 levels. GLP-1R agonists generally lower the fasting and postprandial glucose levels more than DPP-4 inhibitors, resulting in a greater mean reduction in glycated hemoglobin level with GLP-1R agonists (0.4%-1.7%) compared with DPP-4 inhibitors (0.4%-1.0%). GLP-1R agonists also promote satiety and reduce total caloric intake, generally resulting in a mean weight loss of 1 to 4 kg over several months in most patients, whereas DPP-4 inhbitors are weight-neutral overall. GLP-1R agonists and DPP-4 inhibitors are generally safe and well tolerated. The glucose-dependent manner of stimulation of insulin release and inhibition of glucagon secretion by both GLP-1R agonists and DPP-4 inhibitors contribute to the low incidence of hypoglycemia. Although transient nausea occurs in 26% to 28% of patients treated with GLP-1R agonists but not DPP-4 inhibitors, this can be reduced by using a dose-escalation strategy. Other adverse events (AEs) associated with GLP-1R agonists include diarrhea, headache, and dizziness. The main AEs associated with DPP-4 inhibitors include upper respiratory tract infection, nasopharyngitis, and headache. Overall, compared with other therapies for type 2 diabetes mellitus with similar efficacy, incretin-based agents have low risk of hypoglycemia and weight gain. However, GLP-1R agonists demonstrate greater comparative efficacy and weight benefit than DPP-4 inhibitors.     

Incretin-based therapies: Therapeutic rationale and pharmacological promise for type 2 diabetes

Purpose: To highlight the therapeutic promise of the incretin hormone glucagon-like peptide-1 (GLP-1), the consequent rationale for therapies acting through GLP-1-mediated pathways in type 2 diabetes mellitus (T2DM), and the emerging clinical role of the dipeptidyl peptidase-4 (DPP-4) inhibitors and GLP-1 receptor agonists.
Data sources: The PubMed database was searched (using terms including incretins, GLP-1, GIP, DPP-4), along with recent ADA and EASD abstracts.
Conclusions: Many traditional drugs used for T2DM fail to achieve and maintain glycemic control, and possess limitations such as risk for hypoglycemia and weight gain. GLP-1 is a gut-derived hormone that glucose-dependently stimulates insulin secretion while simultaneously reducing gastric emptying and appetite. Other physiological actions of GLP-1 may benefit the cardiovascular system and beta-cell function. Recently developed drug therapies that mimic or prolong the action of this hormone, therefore, have great promise in the treatment of T2DM.
Implications for practice: The GLP-1 receptor agonists and DPP-4 inhibitors are incretin-based therapies that are now becoming established as effective therapies for T2DM to be used either as monotherapy or added to other antidiabetes drugs. They enable improvements to be made in glycemic control without weight gain, with a low risk for hypoglycemia, and with potential additional clinical benefits.     

Complementing Insulin Therapy to Achieve Glycemic Control

Introduction

Most patients with type 2 diabetes mellitus (T2DM) will need incrementally more complex therapeutic regimens to control hyperglycemia as the disease progresses. Insulin is very effective in reducing hyperglycemia and may improve β-cell function in patients with T2DM. However, insulin therapy is associated with weight gain and increased risk of hypoglycemia. Adding other antidiabetes medications to insulin can improve glycemic control and potentially lower the required insulin dose, resulting in less weight gain and lower risk for hypoglycemia. This article summarizes the advantages and disadvantages of different classes of commonly used antidiabetes agents, with emphasis on newer classes, for use as add-on therapy to insulin in patients with T2DM inadequately controlled on insulin therapy.

Methods

A PubMed search from July 1, 2003 to April 15, 2013 for peer-reviewed clinical and review articles relevant to insulin combination or add-on therapy in T2DM was conducted. Search terms included “insulin combination therapy,” “add-on therapy diabetes,” “dipeptidyl peptidase-4 (DPP-4) inhibitors,” “glucagon-like peptide-1 (GLP-1) receptor agonist,” “sodium-glucose cotransporter 2 (SGLT2) inhibitors”, “insulin metformin,” “insulin sulfonylurea,” and “insulin thiazolidinedione.” Bibliographies from retrieved articles were also searched for relevant articles. Study design, clinical relevance, and effect on insulin combination therapy were analyzed.

Results

Therapies used as add-on to insulin include agents associated with weight gain (thiazolidinediones and sulfonylureas) and/or hypoglycemia (sulfonylureas), which, therefore, may exacerbate risks already present with insulin. GLP-1 receptor agonists, DPP-4 inhibitors, and SGLT2 inhibitors improve glycemic control when added to insulin and have a low propensity for hypoglycemia and cause no change (DPP-4 inhibitors) or a reduction (GLP-1 receptor agonists, SGLT2 inhibitors) in body weight.

Conclusion

GLP-1 receptor agonists, DPP-4 inhibitors, and SGLT2 inhibitors improve glycemic control when combined with insulin. They also have low propensity for weight gain and hypoglycemia and so may be preferred treatment options for insulin combination when compared with traditional therapies.     

Raising the bar in research ethics

Abstract

Type 2 diabetes mellitus and obesity share a pathogenic relationship, and both have rapidly increased in prevalence over the past decade. This review evaluates the effects of antidiabetes therapies on weight and glycemic control in the type 2 diabetes mellitus population. A PubMed search was conducted to identify randomized controlled trials that reported the weight effects of antidiabetes treatments. The search focused on the newer in cretin-based therapies, including dipeptidy1 peptidase-4 (DPP-4) inhibitors and glucagon-like peptide-1 (GLP-1) agonists. Antiobesity drugs and treatment options potentially available to patients with type 2 diabetes mellitus, including bariatric surgery, were also examined. Most of the established antidiabetes therapies (eg, sulfonylureas, thiazolidinediones) promote weight gain, thereby exacerbating insulin resistance and glucose intolerance. Dipeptidy1 peptidase-4 inhibitors exhibit a weight-neutral profile, however, and GLP-1 receptor agonists (eg, exenatide, liraglutide) have achieved significant body weight reductions in spite of improved glycemic control, which is often accompanied by weight gain. Antiobesity drugs, such as or listat and sibutramine, are effective weight-lowering agents in patients with type 2 diabetes mellitus, but safety and tolerability concerns may limit their use. Bariatric surgery in obese patients is associated with improved glycemic values and decreased mortality. Clinical evidence substantiating the weight-neutral effects of DPP-4 inhibitors and the weight-loss effects of GLP-1 agonists is promising, offering an expansion of therapeutic options for overweight and obese patients with type 2 diabetes mellitus. Evidence on the clinical utility of antiobesity drugs is more equivocal, and more data are needed to evaluate the safety and tolerability of these agents.     

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

BackgroundGlucose 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.ObjectivesThe 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.MethodsRelevant 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.ResultsPharmacologic 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).ConclusionThe 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.     

The effects of pharmacologic agents for type 2 diabetes mellitus on body weight

Type 2 diabetes mellitus and obesity share a pathogenic relationship, and both have rapidly increased in prevalence over the past decade. This review evaluates the effects of antidiabetes therapies on weight and glycemic control in the type 2 diabetes mellitus population. A PubMed search was conducted to identify randomized controlled trials that reported the weight effects of antidiabetes treatments. The search focused on the newer incretin-based therapies, including dipeptidyl peptidase-4 (DPP-4) inhibitors and glucagon-like peptide-1 (GLP-1) agonists. Antiobesity drugs and treatment options potentially available to patients with type 2 diabetes mellitus, including bariatric surgery, were also examined. Most of the established antidiabetes therapies (eg, sulfonylureas, thiazolidinediones) promote weight gain, thereby exacerbating insulin resistance and glucose intolerance. Dipeptidyl peptidase-4 inhibitors exhibit a weight-neutral profi le, however, and GLP-1 receptor agonists (eg, exenatide, liraglutide) have achieved signifi cant body weight reductions in spite of improved glycemic control, which is often accompanied by weight gain. Antiobesity drugs, such as orlistat and sibutramine, are effective weight-lowering agents in patients with type 2 diabetes mellitus, but safety and tolerability concerns may limit their use. Bariatric surgery in obese patients is associated with improved glycemic values and decreased mortality. Clinical evidence substantiating the weight-neutral effects of DPP-4 inhibitors and the weight-loss effects of GLP-1 agonists is promising, offering an expansion of therapeutic options for overweight and obese patients with type 2 diabetes mellitus. Evidence on the clinical utility of antiobesity drugs is more equivocal, and more data are needed to evaluate the safety and tolerability of these agents.     

Novel therapeutics for type 2 diabetes: Incretin hormone mimetics (glucagon-like peptide-1 receptor agonists) and dipeptidyl peptidase-4 inhibitors

Known treatments of type 2 diabetes mellitus have limitations such as weight gain, and hypoglycaemias. A new perspective is the use of incretin hormones and incretin enhancers. Incretins are defined as being responsible for the higher insulin release after an oral glucose load compared to an intravenous glucose load. The delicate balance of glucose homeostasis, in which incretin hormones are involved, is disturbed in type 2 diabetes mellitus. The incretin GLP-1 helps to maintain glucose homeostasis through stimulation of insulin secretion and inhibition of glucagon release in a glucose-dependent manner. This is associated with reductions in body weight, and no risk of hypoglycaemias. When classical oral agents have failed to maintain adequate glycaemic control, incretin mimetics may be of particular value for obese patients and those who have little control over meal sizes. Exenatide was marketed as a GLP-1 analogue and longer acting incretin mimetics such as liraglutide, albiglutide and others have the same pharmacological profile.In addition to incretin mimetics incretin enhancers which inhibit/delay degradation of incretins were developed: so-called DPP-4 inhibitors such as sitagliptin and vildagliptin are approved in Europe. Their differences from incretin mimetics include: oral bioavailability, less side effects with overdose, no direct CNS effects (nausea and vomiting) and no effect on weight. In rodent models of diabetes, but not yet in humans, GLP-1 receptor agonists and DPP-4 inhibitors increase islet mass and preserve β-cell function.Incretin mimetics and enhancers expand type 2 diabetes treatment, are still not first line therapy and it is discussed if they are to be prophylactically used.     

Focus on incretin-based therapies: targeting the core defects of type 2 diabetes

Glucose homeostasis is regulated by a complex interaction of hormones, principally including insulin, glucagon, amylin, and the incretins. Glucagon, cortisol, catecholamines, and growth hormone serve as the classic glucose counterregulatory hormones. The incretins are hormones released by enteroendocrine cells in the intestine in response to a meal. Classically, type 2 diabetes mellitus (T2DM) has been considered to be a triad of insulin resistance, increased hepatic gluconeogenesis, and progressive β-cell exhaustion/failure. However, disordered enteroendocrine physiology, specifically the reduced activity of glucagon-like peptide-1 (GLP-1), is also a principal pathophysiologic abnormality of the disease. Glucagon-like peptide-1 receptor agonists that have been studied include exenatide and liraglutide, which have been approved by the US Food and Drug Administration for use in patients with T2DM. Sitagliptin and saxagliptin, both approved for use in the United States, modulate incretin physiology by inhibiting degradation of GLP-1 by the enzyme dipeptidyl peptidase-4 (DPP-4). Modulators of incretin physiology have been shown to improve glycemic control with a low risk for hypoglycemia and beneficially affect β-cell function. Unlike the DPP-4 inhibitors, GLP-1 receptor agonist therapy also produces weight loss, an important consideration given the close association among T2DM, overweight/obesity, and cardiovascular disease. The GLP-1 receptor agonists have also demonstrated beneficial effects on cardiovascular risk factors other than hyperglycemia and excess body weight, such as lipid concentrations and blood pressure. This article describes incretin physiology and studies of pharmacologic therapy designed to address the blunted incretin response in patients with T2DM. Information was obtained by a search of the PubMed and MEDLINE databases for articles published from January 1, 1995 to June 1, 2009.     

GLP-1受体激动剂与DPP-4抑制剂比较治疗2型糖尿病效果的系统评价

目的系统评价GLP-1受体激动剂与DPP-4抑制剂治疗2型糖尿病（T2DM）的有效性和安全性。方法计算机检索Pub Med、EMbase、h e Cochrane Library（2013年第4期）、Wan Fang Data、CBM和CNKI数据库,纳入GLP-1受体激动剂与DPP-4抑制剂比较治疗T2DM的随机对照试验（RCT）,检索时限截至2013年4月。由2位研究者按照纳入与排除标准筛选文献、提取资料和评价纳入研究的方法学质量后,采用Rev Man 5.2.5软件进行Meta分析。结果共纳入4个RCT。Meta分析结果显示：与DPP-4抑制剂相比,GLP-1受体激动剂能更有效地降低糖化血红蛋白[MD=–0.46,95%CI（–0.57,–0.35）,P〈0.000 01]、空腹血糖[MD=–1.13,95%CI（–1.39,–0.88）,P〈0.000 01]和体重[MD=–1.59,95%CI（–1.99,–1.19）,P〈0.000 01],其糖化血红蛋白〈7%和≤6.5%的达标率更高,但恶心[OR=4.31,95%CI（2.87,6.47）,P〈0.000 01]和腹泻[OR=2.11,95%CI（1.40,3.18）,P=0.000 4]的发生率明显高于DPP-4抑制剂。结论 GLP-1受体激动剂在控制T2DM患者的血糖和降低体重方面优于DPP-4抑制剂,但胃肠道不良反应更多。     

New developments in incretin-based therapies: The current state of the field

Purpose: To update readers on developments in incretin therapies since the previous JAANP supplement in 2007; specifically, to describe clinical data for currently available incretin-based therapies as well as those under consideration by regulatory agencies.
Data source: Medline search for peer-reviewed publications.
Conclusions: Incretin-based therapies have pharmacologic properties that avoid some key limitations of previous treatments, such as hypoglycemia and weight gain. Certain agents also lower blood pressure and have the potential to reduce cardiovascular risk. The insulin-secreting action of incretin-based therapies only occurs under hyperglycemic conditions, thus minimizing the risk of hypoglycemia, unless combined with a sulfonylurea. The DPP-4 inhibitors are orally administered and demonstrate modest A1c reductions (0.6%–0.8%); the best results occur when combined with metformin. Glucagon-like peptide-1 (GLP-1) receptor agonists liraglutide and exenatide have shown greater A1c reductions (typically ≥ 1.1% and as high as 1.7%), and these agents have beneficial ancillary effects, including weight and systolic blood pressure reduction. Both DPP-4 inhibitors and GLP-1 receptor agonists have shown the ability to improve pancreatic beta-cell function in early studies.
Implications for practice: Data are provided on the efficacy and tolerability of approved incretin therapies, and on treatments currently in regulatory review, in order to inform readers and guide their practice.     

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.     

Dipeptidyl Peptidase-4 Inhibitors in the Elderly: More Benefits or Risks?

Several studies have shown a high prevalence of type 2 diabetes mellitus (T2DM) in the elderly, characterized by a paucity of symptoms, which represents an obstacle for an early diagnosis. Frequently, T2DM in the elderly is diagnosed when a complication occurs, among which are cognitive disorders and/or affective disturbances. Moreover, hypoglycemia is a frequent side effect of therapeutic treatment with insulin, sulfonylureas or glinides, while other treatments (metformin, acarbose, thiazolidinediones, glucagon-like peptide-1 [GLP-1] receptor agonists, and dipeptidyl peptidase-4 [DPP4] inhibitors) are capable of reducing hyperglycemia without inducing hypoglycemia. Thus, considering that older persons are a very heterogeneous group of individuals, management of T2DM in the elderly is challenging but there are no available specific treatment goals or treatment algorithms for older diabetic patients. Metformin is the recommended first-line therapy in all T2DM patients. When metformin is not sufficient to achieve the desired therapeutic targets, a second drug can be added. Available options include sulfonylureas, meglitinides, alfa-glucosidase inhibitors, pioglitazone, insulin, GLP-1 receptor agonists, and DPP-4 inhibitors. The most intriguing therapy for older patients is the one based on the so-called incretins, i.e., gastrointestinal hormones that, mainly secreted in the postprandial phase, stimulate insulin secretion and inhibit glucagon secretion. The two most important human incretins are GLP-1 and glucose-dependent insulinotropic peptide (GIP). These hormones potentiate the acute effects of glucose on pancreatic alfa and beta cells, thus stimulating insulin secretion, and only GLP-1 inhibits glucagon secretion in a glucose-dependent manner (that is, only when glucose levels are increased); as a result, they reduce hyperglycemia with virtually no hypoglycemic risk. Due to their characteristics, DPP-4 inhibitors seem to be particularly interesting as potential agents for the treatment of older patients with T2DM.     

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.     

Differentiating among incretin therapies: a multiple-target approach to type 2 diabetes

What is known and Objective: Incretin-based glucagon-like peptide-1 receptor agonists (GLP-1 RAs) and dipeptidyl peptidase-4 (DPP-4) inhibitor therapies provide glycaemic control with reduced risks associated with weight gain or hypoglycaemia. Incretin therapies are compared with their mechanisms of action, effects on haemoglobin A(1C) (HbA(1C) ), fasting plasma glucose (FPG), post-prandial glucose (PPG), body weight, β-cell function, cardiovascular biomarkers and in their safety profiles to aid clinicians in the selection of individualized pharmacotherapy for patients with type 2 diabetes. Methods: Relevant articles for a systematic review were identified through PubMed. Randomized, head-to-head comparison studies among incretin therapies were identified and included in the review. Additionally, randomized, controlled monotherapy and combination therapy studies examining glycaemic and extraglycaemic effects of individual incretin therapies from 2007 to 2011 were reviewed. Results and Discussion: Glucagon-like peptide-1 receptor agonists are generally preferred over DPP-4 inhibitors because of their greater effectiveness in reducing HbA(1C) , FPG and PPG excursions, and greater weight loss potentiation. As a monotherapy option, longer-acting GLP-1 RAs, including liraglutide and exenatide once-weekly, may be preferred at higher HbA(1C) because of their more pronounced effects on FPG. At lower/near normal HbA(1C) , a short-acting GLP-1 RA, such as exenatide twice-daily, may be a better choice as its effects are more pronounced with PPG. Ideal patients or patient situations for DPP-4 inhibitors include patients who need minimal reduction in HbA(1C,) elderly patients, patients who are unwilling or unable to take an injectable agent, when GLP-1 RAs are contraindicated or when the patient will not benefit from weight loss. Treatment benefits common to all incretin-based therapies include minimal hypoglycaemia risk, potential preservation of β-cell function and effective targeting of multiple organs underlying type 2 diabetes and of comorbidities commonly associated with type 2 diabetes, such as obesity and hypertension. What is new and Conclusion: Key differences in mechanisms of action and in glycaemic and extra-glycaemic treatment outcomes exist among incretin therapies, both within the GLP-1 RA class, and between GLP-1 RAs and DPP-4 inhibitors. Clinical judgment acknowledging important differences among incretin therapies and treatment-related patient characteristics will aid in the selection of the appropriate incretin agent for individualized pharmacotherapy.     

Incretin-based therapy in patients with type 1 diabetes mellitus

GLP-1 has multiple physiological functions including glucose-dependent insulin secretion and glucagon suppression, delay of gastic emptying, suppression of hepatic glucose production, stimulation of beta cell replication and neogenesis, inhibition of beta cell apoptosis. All of these actions are beneficial for the treatment of diabetes. Therefore, incretin-based therapy may be still worthwhile as evidenced by studies demonstrating that beta cell mass may be preserved or expand in animals and that residual insulin secretion may be elevated to reduce the risk of hypoglycemia in patients treated with intensive insulin therapy, although the effect of GLP-1R agonists and DPP-4 inhibitors(DPP-4is) on beta cells may be small because destruction of beta cells leads to absolute insulin deficiency by cell-mediated autoimmune attack. Recent report also showed that DPP-4i might ameliorate an autoimmune attack against beta cells by restoring or increasing the number of regulatory T lymphocytes. Furthermore, GLP-1R-mediated signals might suppress the expression of chemokine ligand CXCL10 which binds to newly identified receptor TLR4 (Toll-like receptor 4), and impairs beta cell function and viability in diabetes. Taken together, incretin-based therapy may be worth testing in patients with type 1 diabetes.     

Saxagliptin: a new DPP-4 inhibitor for the treatment of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a global epidemic with increasing impact on individuals and healthcare providers. Available treatments (such as metformin, sulfonylureas, glitazones, and insulin) have proven unsatisfactory in producing a long-lasting impact on glycemic control. In addition, most of these treatments have undesirable side effects such as weight gain and hypoglycemia. As a result, exploring new treatment targets and new therapies is mandatory in order to treat this condition. The incretin pathway, in particular glucagon-like peptide (GLP-1), plays an important pathological role in the development of T2DM, and treatments targeting the incretin system have recently become available. These can mainly be divided into two broad categories; GLP-1 agonists/analogs (exenatide, liraglutide), and dipeptidyl peptidase-4 (DPP-4; the enzyme responsible for rapid inactivation of incretins) inhibitors (sitagliptin, vildagliptin). Saxagliptin is a novel DPP-4 inhibitor that has recently completed phase 3 studies. Saxagliptin is a potent and specific inhibitor of DPP-4 (in comparison with other dipeptidyl peptidase enzymes) that is given once daily. Current data suggest that saxagliptin as monotherapy or in combination with metformin, glyburide, or a glitazone results in significant reductions in fasting and postprandial plasma glucose and hemoglobin A_1c (HbA_1c). Saxagliptin is well tolerated and does not increase hypoglycemia compared with the placebo, and is probably weight neutral. Saxagliptin will be a new effective drug in the currently available variety of antidiabetic medications for patients with T2DM.     

Incretin related drugs

Incretin, GIP and GLP-1, are blood glucose lowering hormones secreted from K cells and L cells, and are rapidly degenerated by DPP-4 within a few minutes. Recently incretin related drugs, GLP-1 analogs and DPP-4 inhibitors are developed. GLP-1 analogs have amino acid substitutions, which make the GLP-1 peptide resistant to degeneration by DPP-4, while DPP-4 inhibitors prevent endogenous GLP-1 to be degenerated by DPP-4. Since they exert blood glucose lowering effect only when blood glucose levels are high, hypoglycemia rarely occurs when administrated without other anti-diabetic drugs. Incretin related drugs are expected to be a new strategy for treating type 2 diabetes.     

Incorporating Incretin-Based Therapies into Clinical Practice for Patients with Type 2 Diabetes

Background

Effective, evidence-based management of type 2 diabetes (T2D) requires the integration of the best available evidence with clinical experience and patient preferences.

Methods

Studies published from 2000 to 2012 evaluating glucagon-like peptide-1 receptor agonists (GLP-1RAs) or dipeptidyl peptidase-4 inhibitors (DPP-4 inhibitors) were identified using PubMed. The author contextualized the study findings with his clinical experience.

Results

Incretin-based therapy targets multiple dysfunctional organs in T2D. Injectable GLP-1RAs provide substantial glycemic control and weight reduction; while oral DPP-4 inhibitors provide moderate glycemic control and weight neutrality. Both classes are effective, well tolerated, and associated with a low incidence of hypoglycemia when used alone or in combination with other antidiabetes agents. GLP-1RAs are associated with transient nausea and, like DPP-4 inhibitors, rare pancreatitis.

Conclusion

Data indicate and clinical experience confirms that incretins are well tolerated in appropriate patients and provide sustained glycemic control and weight loss or weight neutrality throughout T2D progression.     

Efficacy and Safety of Dipeptidyl Peptidase-4 Inhibitors in Combination with Metformin

Introduction

Use of dipeptidyl peptidase-4 (DPP-4) inhibitors is prevalent for the treatment of type 2 diabetes since they have fewer adverse effects compared with other non-insulin medications currently available; however, as monotherapy, the glycosylated hemoglobin (HbA1c)-lowering power of these agents is moderate. The aim of this article is to evaluate the current literature regarding the safety and efficacy of DPP-4 inhibitors in combination with metformin.

Methods

A literature search was conducted through MEDLINE (from 1950 to October 2012), PubMed (from 1966 to October 2012), EMBASE (from 1966 to October 2012), and International Pharmaceutical Abstracts (from 1970 to October 2012) using the search terms “sitagliptin,” “linagliptin,” “alogliptin,” “vildagliptin,” “saxagliptin,” and “metformin.” Studies that did not evaluate the DPP-4 inhibitors in combination with metformin and those that were not phase 3, were excluded.

Results

Many of the studies evaluated DPP-4 inhibitors in combination with metformin versus glucagon-like peptide-1 (GLP-1) agonists, placebo, DPP-4 inhibitors as monotherapy, thiazolidinediones, and sulfonylureas. The results of these noninferiority trials were that DPP-4 inhibitors as a whole are noninferior to either each other or other agents except for GLP-1 agonists. Also, in superiority studies, GLP-1 agonists proved to have greater HbA1c lowering.

Conclusion

In summary, DPP-4 inhibitors play a vital role in the treatment of diabetes. They have relatively limited adverse effects, especially regarding hypoglycemia. DPP-4 inhibitors in combination with metformin are generally well tolerated and are available as combination products to reduce pill burden and enhance compliance. The limitations to DPP-4 inhibitors are the lack of outcomes data and more limited HbA1c lowering than other medications currently approved for the treatment of type 2 diabetes. However, as previously stated, thiazolidinediones, glinides, sulfonylureas, pramlinitide, and GLP-1 agonists are all quite beneficial in HbA1c lowering but are not without major adverse effects. Therefore, DPP-4 inhibitors have a vital role as an oral add-on agent for the treatment of type 2 diabetes.