The evolving place of incretin-based therapies in type 2 diabetes

A Review of Current Trends with Type 2 Diabetes Epidemiology, Aetiology, Pathogenesis, Treatments and Future Perspectives

Type 2 diabetes (T2D), which has currently become a global pandemic, is a metabolic disease largely characterised by impaired insulin secretion and action. Significant progress has been made in understanding T2D aetiology and pathogenesis, which is discussed in this review. Extrapancreatic pathology is also summarised, which demonstrates the highly multifactorial nature of T2D. Glucagon-like peptide (GLP)-1 is an incretin hormone responsible for augmenting insulin secretion from pancreatic beta-cells during the postprandial period. Given that native GLP-1 has a very short half-life, GLP-1 mimetics with a much longer half-life have been developed, which are currently an effective treatment option for T2D by enhancing insulin secretion in patients. Interestingly, there is continual emerging evidence that these therapies alleviate some of the post-diagnosis complications of T2D. Additionally, these therapies have been shown to induce weight loss in patients, suggesting they could be an alternative to bariatric surgery, a procedure associated with numerous complications. Current GLP-1-based therapies all act as orthosteric agonists for the GLP-1 receptor (GLP-1R). Interestingly, it has emerged that GLP-1R also has allosteric binding sites and agonists have been developed for these sites to test their therapeutic potential. Recent studies have also demonstrated the potential of bi- and tri-agonists, which target multiple hormonal receptors including GLP-1R, to more effectively treat T2D. Improved understanding of T2D aetiology/pathogenesis, coupled with the further elucidation of both GLP-1 activity/targets and GLP-1R mechanisms of activation via different agonists, will likely provide better insight into the therapeutic potential of GLP-1-based therapies to treat T2D.

Efficacy and Safety of Teneligliptin in Patients With Type 2 Diabetes Mellitus: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background: Teneligliptin is a 3rd-generation dipeptidyl peptidase-4 (DPP-4) inhibitor. There is a limited evidence regarding the effect of teneligliptin. Therefore, this study is to assess the efficacy and safety of teneligliptin in type 2 diabetes mellitus (T2DM) patients with inadequately glycemic controlled.

Methods: A search of PubMed, Medline, Embase, and The Cochrane Library during 2000.01–2018.03 was performed for randomized controlled trials of teneligliptin compared to placebo in patients with T2DM with monotherapy or add-on treatment.

Results: Ten trials with 2119 patients were analyzed. Teneligliptin produced absolute reductions in glycated hemoglobin A1c (HbA1c) levels (weighted mean difference (WMD) 0.82%, 95% confidence interval (CI) [−0.91 to −0.72], p < 0.00001) compared with placebo. However, after 36–42 weeks of follow-up (open-label), HbA1c level rise higher than duration (double-blind) in teneligliptin group. Teneligliptin led to greater decrease of fasting plasma glucose (FPG) level (vs. placebo, WMD −18.32%, 95% CI [−21.05 to −15.60], p < 0.00001). Teneligliptin also significantly decreased the 2 h post-prandial plasma glucose (2 h PPG) (WMD −46.94%, 95% CI [−51.58 to −42.30], p < 0.00001) and area under the glucose plasma concentration-time curve from 0 to 2 h (AUC_0−2h) for PPG (WMD −71.50%, 95% CI [−78.09 to −64.91], p < 0.00001) compared with placebo. Patients treated with teneligliptin achieved increased homeostasis model assessment of β cell function (HOMA-β) with 9.31 (WMD, 95% CI [7.78–10.85], p < 0.00001). However, there was no significant difference between teneligliptin and placebo in overall adverse effects (0.96 risk ratio (RR), 95% CI [0.87, 1.06], p = 0.06). The risks of hypoglycemia were not significantly different between teneligliptin and placebo (1.16 RR, 95% CI [0.59, 2.26], p = 0.66).

Conclusions: Teneligliptin improved blood glucose levels and β-cells function with low risk of hypoglycemia in patients with T2DM. Common adverse effects of teneligliptin including hypoglycemia were identified and reviewed. Risks of cardiovascular events are less certain, and more data for long-term effects are needed.

Dipeptidyl peptidase 4 serum activity and concentration are increased in women with polycystic ovary syndrome

OBJECTIVE

Polycystic ovary syndrome (PCOS) is a complex disease, the aetiology of which is not well understood. Alterations in potential candidate genes involved in the biosynthesis and metabolism of androgens, folliculogenesis and insulin and glucose metabolism have been suggested as possible aetiologies. Dipeptidyl peptidase-4 (DPP4) plays a key role in glucose homoeostasis and, thus, in the regulation of insulin secretion. The aim of our study was to analyse the DPP4 activity and concentrations in the serum of PCOS and non-PCOS patients and, additionally, study the activation of the DPP4 promoter by androgens in vitro.

DESIGN, PATIENTS AND MEASUREMENTS

Serum samples were obtained from 288 female patients treated at the Center for Reproductive Medicine and Andrology (154 non-PCOS and 134 patients with PCOS). DPP4 activity was measured by the conversion of the DPP4 substrate Gly-Pro p-nitroanilide hydrochloride and DPP4 concentration with a commercial ELISA. Luciferase reporter assays, qPCR and Western Blot analyses were performed for the in vitro evaluation of the activation of the DPP4 promoter by androgens.

RESULTS

DPP4 serum activity was increased in women with PCOS, regardless of which Rotterdam criteria led to the PCOS diagnosis. Furthermore, DPP4 serum levels were strongly correlated with the anti-Müllerian hormone (AMH) serum level. In vitro, the DPP4 promoter was stimulated by androgens in luciferase reporter assays, and DPP4 mRNA expression was increased in KGN granulosa carcinoma cells after androgen treatment.

CONCLUSIONS

The results suggested that a deregulation of DPP4 serum levels could be an additional characteristic of the metabolic imbalances associated with PCOS.

Hypoxia Alters the Expression of Dipeptidyl Peptidase 4 and Induces Developmental Remodeling of Human Preadipocytes

Dipeptidyl peptidase 4 (DPP4), a transmembrane protein, has been identified in human adipose tissue and is considered to be associated with obesity-related type 2 diabetes. Since adipose tissue is relatively hypoxic in obese participants, we investigated the expression of DPP4 in human preadipocytes (hPA) and adipocytes in hypoxia, during differentiation and upon insulin stimulation. The results show that DPP4 is abundantly expressed in hPA but very sparsely in adipocytes. During differentiation in vitro, the expression of DPP4 in hPA is reduced on the addition of differentiation medium, indicating that this protein can be hPA marker. Long term hypoxia altered the expression of DPP4 in hPA. In in vitro hypoxic conditions the protease activity of shed DPP4 is reduced; however, in the presence of insulin, the increase in DPP4 expression is potentiated by hypoxia.

Distinct regions in the C-Terminus required for GLP-1R cell surface expression, activity and internalisation

The glucagon-like peptide-1 (GLP-1) receptor (GLP-1R), an important drug target in the treatment of type 2 diabetes, is a G-protein coupled receptor (GPCR) that mediates insulin secretion by GLP-1. The N-terminus controls GLP-1R biosynthetic trafficking to the cell surface but the C-terminus involvement in that trafficking is unknown. The aim of this study was to identify distinct regions within the C-terminal domain required for human GLP-1R (hGLP-1R) cell surface expression, activity and internalisation using a number of C-terminal deletions and site-directed mutations. The results of this study revealed that the residues 411-418 within the C-terminal domain of the hGLP-1R are critical in targeting the newly synthesised receptor to the plasma membrane. The residues 419-430 are important for cAMP producing activity of the receptor, most likely by coupling to Gαs. However, the residues 431-450 within the C-terminus are essential for agonist-induced hGLP-1R internalisation. In conclusion, these findings demonstrate the hGLP-1R has distinct regions within the C-terminal domain required for its cell surface expression, activity and agonist-induced internalisation.

The effects of glucose-lowering therapies on diabetic kidney disease

Chronic hyperglycemia and its associated metabolic products are key factors responsible for the development and progression of diabetic chronic kidney disease (CKD). Endocrinologists are tasked with detection and management of early CKD before patients need referral to a nephrologist for advanced CKD or dialysis evaluation. Primary care physicians are increasingly becoming aware of the importance of managing hyperglycemia to prevent or delay progression of CKD. Glycemic control is an integral part of preventing or slowing the advancement of CKD in patients with diabetes; however, not all glucose-lowering agents are suitable for this patient population. The availability of the latest information on treatment options may enable physicians to thwart advancement of serious renal complication in patients suffering from diabetes. This review presents clinical data that shed light on the risk/benefit profiles of three relatively new antidiabetes drug classes, the dipeptidyl peptidase-4 inhibitors, glucagon-like peptide-1 analogs, and sodium glucose co-transporter 2 inhibitors, particularly for patients with diabetic CKD, and summarizes the effects of these therapies on renal outcomes and glycemic control for endocrinologists and primary care physicians. Current recommendations for screening and diagnosis of CKD in patients with diabetes are also discussed.

The regions within the N-terminus critical for human glucagon like peptide-1 receptor (hGLP-1R) cell surface expression

The hGLP-1R is a target for the treatment of type 2 diabetes and belongs to the class B family of GPCRs. Like other class B GPCRs, the GLP-1R contains an N-terminal signal peptide (SP) and undergoes N-linked glycosylation, which are important for its trafficking and maturation. This study analysed the role of the SP, the hydrophobic region after the SP (HRASP), glycosylation and the conserved residues within the N-terminus in GLP-1R trafficking. HGLP-1R targeted to the cell surface showed no SP, and the SP deleted mutant, but not the mutants defective in SP cleavage, showed cell surface expression, demonstrating the importance of SP cleavage for hGLP-1R cell surface expression. The N-terminal deletions of hGLP-1R revealed that the HRASP, not the SP, is essential for cell surface expression of GLP-1R. Further, inhibition of hGLP-1R glycosylation prevented cell surface expression of the receptor. Mutation of Trp³⁹, Tyr⁶⁹ and Tyr⁸⁸, which are required for agonist binding, in the GLP-1R abolished cell surface expression of the receptor independent of the SP cleavage or N-linked glycosylation. In conclusion, the N-terminus of hGLP-1R regulates receptor trafficking and maturation. Therefore this study provides insight into the role of hGLP-1R N-terminus on the receptor cell surface expression.

The glucose-lowering potential of exenatide delivered orally via goblet cell-targeting nanoparticles

PURPOSE

Exenatide, a potent insulinotropic agent, can be used for the treatment of non-insulin-dependent diabetes mellitus. However, the need for frequent injections seriously limits its therapeutic utility. The aim of present report was to develop an orally available exenatide formulation using goblet cell-targeting nanoparticles (NPs).

METHOD

The exenatide-loaded nanoparticles were prepared with modified chitosan which was conjugated with a goblet cell-target peptide, CSKSSDYQC (CSK) peptide.

RESULTS

The CSK-chitosan nanoparticles shown reduced chitosan toxicity and enhanced the permeation of drugs across the Caco-2/HT-29 co-cultured cell monolayer, which simulated the intestinal epithelium. Following the oral administration of near-infrared fluorescent probe Cy-7-loaded NPs to mice, the distribution of the drugs was investigated with a near-infrared in vivo image system (FX Pro, Bruker, USA). The results showed that Cy-7 fluorescence disseminated from the oesophagus, then to stomach and small intestine and then was absorbed into hepatic, finally into the bladder; over time, Cy-7 was metabolized and excreted. The bioavailability of the modified nanoparticles was found to be 1.7-fold higher compared with the unmodified ones, and the hypoglycemic effect was also better.

CONCLUSION

CSK peptide-modified chitosan nanoparticles could be a potential therapeutics for Type II diabetes patients.

Clinical therapeutic strategies for early stage of diabetic kidney disease

Diabetic kidney disease (DKD) is the most common cause of chronic kidney disease, leading to end-stage renal disease and cardiovascular disease. The overall number of patients with DKD will continue to increase in parallel with the increasing global pandemic of type 2 diabetes. Based on landmark clinical trials, DKD has become preventable by controlling conventional factors, including hyperglycemia and hypertension, with multifactorial therapy; however, the remaining risk of DKD progression is still high. In this review, we show the importance of targeting remission/regression of microalbuminuria in type 2 diabetic patients, which may protect against the progression of DKD and cardiovascular events. To achieve remission/regression of microalbuminuria, several steps are important, including the early detection of microalbuminuria with continuous screening, targeting HbA1c < 7.0% for glucose control, the use of renin angiotensin system inhibitors to control blood pressure, the use of statins or fibrates to control dyslipidemia, and multifactorial treatment. Reducing microalbuminuria is therefore an important therapeutic goal, and the absence of microalbuminuria could be a pivotal biomarker of therapeutic success in diabetic patients. Other therapies, including vitamin D receptor activation, uric acid-lowering drugs, and incretin-related drugs, may also be promising for the prevention of DKD progression.

Cardiovascular outcome trials in type 2 diabetes and the sulphonylurea controversy: rationale for the active-comparator CAROLINA trial

Sulphonylureas (SUs) are widely used glucose-lowering agents in type 2 diabetes mellitus (T2DM) with apparent declining efficacy over time. Concerns have been raised from observational retrospective studies on the cardiovascular (CV) safety of SUs but there are few long-term data on CV outcomes from randomized controlled trials (RCTs) involving the use of this class of agents. Most of the observational studies and registry data are conflicting and vary with study population and methodology used for analyses. To address the SU controversy, we reviewed the recently published literature (until end of the year 2011) to evaluate the impact of SUs on CV outcomes in modern, longer-term (≥72 weeks) RCTs where they were compared in a head-to-head fashion versus an active comparator or were used as part of a treatment strategy. We identified 15 trials and found no report of an increase in the incidence of CV events with the use of SUs. However, the available data are limited, and, most importantly, there was no adequately powered formal head-to-head CV outcome trial designed to address CV safety. Since SUs are still being advocated as second-line therapy added-on to metformin, as one of several classes, and in certain circumstances first-line therapy in T2DM management, definitive data from a dedicated RCT addressing the CV safety question with SUs would be informative. Cardiovascular Outcome Study of Linagliptin versus Glimepiride in Patients with Type 2 Diabetes (CAROLINA) is such a trial, ongoing since November 2010, and is currently the largest head-to-head CV outcome trial that involves a comparison of a SU (glimepiride) with a dipeptidyl peptidase-4 (DPP-4) inhibitor (linagliptin) and will provide a unique perspective with respect to CV outcomes with these two commonly used agents.

Introduction to diabetes mellitus

The chronic metabolic disorder diabetes mellitus is a fast-growing global problem with huge social, health, and economic consequences. It is estimated that in 2010 there were globally 285 million people (approximately 6.4% of the adult population) suffering from this disease. This number is estimated to increase to 430 million in the absence of better control or cure. An ageing population and obesity are two main reasons for the increase. Furthermore it has been shown that almost 50% of the putative diabetics are not diagnosed until 10 years after onset of the disease, hence the real prevalence of global diabetes must be astronomically high. This chapter introduces the types of diabetes and diabetic complications such as impairment of immune system, periodontal disease, retinopathy, nephropathy, somatic and autonomic neuropathy, cardiovascular diseases and diabetic foot. Also included are the current management and treatments, and emerging therapies.

Clinical overview of linagliptin, a dipeptidyl peptidase-4 inhibitor, in patients with Type 2 diabetes mellitus

Linagliptin is a pharmacologically unique, orally active, once-daily dipeptidyl peptidase-4 inhibitor indicated for the treatment of hyperglycemia in patients with Type 2 diabetes mellitus. Compared with other dipeptidyl peptidase-4 inhibitors, linagliptin has a favorable pharmacokinetic profile with a primarily nonrenal route of elimination that avoids the need for dose adjustment in patients with renal impairment. When administered as monotherapy or in combination with other antihyperglycemic drugs, linagliptin treatment leads to clinically meaningful reductions in glycated hemoglobin, fasting plasma glucose and postprandial plasma glucose levels. In addition, pancreatic β-cell function is enhanced. Linagliptin treatment is well tolerated, with weight-neutral effects and no increased risk of hypoglycemia. Of note, linagliptin treatment was associated with a significantly reduced risk of cardiovascular events in clinical trials of ≤2 years, although this finding remains to be confirmed in larger and longer clinical outcomes studies.

Role of GLP-1 and DPP-4 in diabetic nephropathy and cardiovascular disease

Although there have been major advances in the understanding of the molecular mechanisms that contribute to the development of diabetic nephropathy, current best practice still leaves a significant treatment gap. The incidence of diabetes and associated nephropathy is increasing, with the main cause of mortality being related to cardiovascular causes. Novel therapies which are both 'cardio-renal'-protective seem the logical way forward. In the present review, we discuss the GLP-1 (glucagon-like peptide-1) receptor agonists and DPP-4 (dipeptidyl peptidase-4) inhibitors (incretin-based therapies), which are novel antidiabetic agents used in clinical practice and their role in diabetic nephropathy with specific focus on renoprotection and surrogate markers of cardiovascular disease. We discuss the pleiotropic effects of the incretin-based therapies apart from glucose-lowering and highlight the non-GLP-1 effects of DPP (dipeptidyl peptidase) inhibition. Large-scale clinical studies with cardiovascular end points are underway; however, studies with renal end points are lacking but much needed.

Obesity and type 2 diabetes: which patients are at risk?

An estimated 72.5 million American adults are obese, and the growing US obesity epidemic is responsible for substantial increase in morbidity and mortality, as well as increased health care costs. Obesity results from a combination of personal and societal factors, but is often viewed as a character flaw rather than a medical condition. This leads to stigma and discrimination towards obese individuals and decreases the likelihood of effective intervention. Conditions related to obesity are increasingly common, such as metabolic syndrome, impaired fasting glucose (IFG) and impaired glucose tolerance (IGT), all of which indicate high risk for type 2 diabetes (T2DM). This paper reviews the progression from obesity to diabetes, identifying physiological changes that occur along this path as well as opportunities for patient identification and disease prevention. Patients with prediabetes (defined as having IFG, IGT or both) and/or metabolic syndrome require interventions designed to preserve insulin sensitivity and β-cell function, both of which start to deteriorate prior to T2DM diagnosis. Lifestyle modification, including both healthy eating choices and increased physical activity, is essential for weight management and diabetes prevention. Although sustained weight loss is often considered by patients and physicians as being impossible to achieve, effective interventions do exist. Specifically, the Diabetes Prevention Program (DPP) and programs modelled along its parameters have shown repeated successes, even with long-term maintenance. Recent setbacks in the development of medications for weight loss further stress the importance of lifestyle management. By viewing obesity as a metabolic disorder rather than a personal weakness, we can work with patients to address this increasingly prevalent condition and improve long-term health outcomes.

Linagliptin, a dipeptidyl peptidase-4 inhibitor with a unique pharmacological profile, and efficacy in a broad range of patients with type 2 diabetes

INTRODUCTION

Increasing population age, obesity and physical inactivity mean that type 2 diabetes mellitus (T2DM) is increasingly common. Current treatments may be limited by adverse events, drug-drug interactions or contraindication/need for dose adjustment in patients with renal impairment.

AREAS COVERED

This paper reviews studies that evaluate the pharmacokinetics, pharmacodynamics and clinical efficacy and safety of linagliptin , a dipeptidyl peptidase-4 (DPP-4) inhibitor, recently approved in the US, Japan and Europe for the treatment of T2DM.

EXPERT OPINION

Oral linagliptin, 5 mg once daily, is an effective, well-tolerated DPP-4 inhibitor, suitable for use in a wide range of patients with T2DM. It is weight-neutral, without increasing the risk of hypoglycemia, and can be administered either alone or in combination with other diabetes treatments. It has a unique pharmacological profile within its class and, unlike other DPP-4 inhibitors, linagliptin does not require dose adjustment in patients with renal impairment.

Structure and mechanism for recognition of peptide hormones by Class B G-protein-coupled receptors

Class B G-protein-coupled receptors (GPCRs) are receptors for peptide hormones that include glucagon, parathyroid hormone, and calcitonin. These receptors are involved in a wide spectrum of physiological activities, from metabolic regulation and stress control to development and maintenance of the skeletal system. As such, they are important drug targets for the treatment of diabetes, osteoporosis, and stress related disorders. Class B GPCRs are organized into two modular domains: an extracellular domain (ECD) and a helical bundle that contains seven transmembrane helices (TM domain). The ECD is responsible for the high affinity and specificity of hormone binding, and the TM domain is required for receptor activation and signal coupling to downstream G-proteins. Although the structure of the full-length receptor remains unknown, the ECD structures have been well characterized for a number of Class B GPCRs, revealing a common fold for ligand recognition. This review summarizes the general structural principles that guide hormone binding by Class B ECDs and their implications in the design of peptide hormone analogs for therapeutic purposes.

Glucagon-like peptide-1 analogues for Type 2 diabetes mellitus: current and emerging agents

Novel therapeutic options for type 2 diabetes mellitus based on the action of the incretin hormone glucagon-like peptide (GLP)-1 were introduced in 2005. As injectable GLP-1 receptor agonists acting on the GLP-1 receptor, exenatide and liraglutide are available in many countries. In type 2 diabetes treatment, incretin-based therapies are attractive and more commonly used because of their mechanism of action and safety profile. Stimulation of insulin secretion and inhibition of glucagon secretion by these agents occur in a glucose-dependent manner. Therefore, incretin-based therapies have no intrinsic risk for hypoglycaemia. Furthermore, GLP-1 receptor agonists allow weight loss and lower systolic blood pressure. This review gives a brief overview of the mechanism of action and summarizes the clinical data available on exenatide and liraglutide as established substances. It further highlights the clinical study data of exenatide once weekly as the first long-acting GLP-1 receptor agonist and covers other new long acting GLP-1 receptor agonists currently in clinical development. The placement of GLP-1 receptor agonists in the treatment algorithm of type 2 diabetes is discussed.

Targeting thermogenesis and related pathways in anti-obesity drug discovery

The health consequences of the obesity epidemic are a huge burden on patients and society. Yet it remains an unmet therapeutic need. Lifestyle or behaviour modification, although desirable, seems to benefit only a few and bariatric surgery is not an option for all and not without risks. Nevertheless, bariatric surgery is currently the gold standard in terms of weight loss therapy and any weight loss agent will be in combination with management of lifestyle modification. Sadly, there is a poor history for the pharmacological treatment of obesity and repeated safety concerns have attracted intense regulatory scrutiny. Indeed, recent market withdrawals leave us with just one agent approved for the long term treatment of obesity and that is only mildly efficacious in terms of weight loss, although it is beneficial in terms of metabolic health. There are two broad pharmacological approaches that can be applied in obesity drug discovery: reduce intake (or absorption) or increase expenditure (thermogenesis) of calories. In this review we will look at the latter approach. We will cover regulatory requirements and the rationale for this approach. We believe that post-obese subjects display abnormal metabolic responses to weight loss that almost inevitably leads to weight regain. We will then explore a number of approaches that potentially increase thermogenesis in humans. The challenge we have is in accumulating enough human data to validate this approach using drugs.

A quantitative assessment of patient barriers to insulin

AIM

To assess diabetes treatment preferences with a focus on patient barriers to insulin treatment.

MATERIALS AND METHODS

A questionnaire using indirect and direct methods was administered as part of the International Diabetes Management Practices Study (IDMPS). Discrete choice modelling was used to assess how product attributes influence patients' preferences for diabetes treatment. A multinomial logit model was used to find the odds ratio for each parameter, representing the probability of selecting a chosen alternative given a choice set. This allowed for the derivation of relative attribute importance, an indication of how influential product attributes are in the respondents' choices.

RESULTS

The IDMPS questionnaire was administered to 14,033 individuals with diabetes in 18 countries. The majority of respondents were women (53%) and had Type 2 diabetes mellitus (T2DM; 85%). Across subgroups, administration (i.e. oral vs. injection) was a driver of preference. Patient preferences varied according to diabetes type; individuals with T2DM assigned much higher relative importance to administration than those with Type 1 diabetes mellitus (T1DM; 30.86% vs. 4.99%; p<0.0001). Individuals with T2DM treated with insulin placed less importance on administration than insulin-naïve T2DM patients (3.09% vs. 47.48%; p<0.0001). Diabetes education also had a significant effect on the priority given to administration between T2DM patients who received diabetes training and those who did not (28.21% vs. 33.68%, respectively; p<0.0001).

CONCLUSION

The insulin barriers perceived by patients with diabetes evolved with their disease experience. While administration was the primary preference driver for insulin-naïve patients, patients were increasingly concerned with more clinically relevant barriers as they gained experience with insulin. This finding suggests that patients using insulin understand the importance of achieving an optimal balance between safety and efficacy.