Incretin Mimetics as Emerging Treatments for Type 2 Diabetes

Exendin-4, a glucagon-like peptide-1 receptor agonist, alleviates muscular dysfunction and wasting in a streptozotocin-induced diabetic mouse model compared to metformin

Diabetic muscular atrophy is becoming a fast-growing problem worldwide, including sarcopenia, which is associated with substantial mortality and morbidity risk. Glucagon-like peptide-1 receptor agonists (GLP-1RAs) have been marketed and suggested to exert protective effects on not only glycemic control but also diabetic complications in diabetic patients. In this study, we investigated the therapeutic use of GLP-1RAs exendin-4, compared to antidiabetic drug metformin, for the intervention of muscular dysfunction during diabetic conditions using a streptozotocin (STZ)-induced diabetic mouse model. The results showed that both exendin-4 and metformin could effectively alleviate hyperglycemia in diabetic mice, and also counteract diabetes-induced muscle weight loss, weaker grip, and changes in muscle fiber cross-sectional area distribution. Unexpectedly, exendin-4, but not metformin, enhanced the increased kidney weight and histological change in diabetic mice. Taken together, these findings suggest that both exendin-4 and metformin could effectively improve the diabetic hyperglycemia and muscular dysfunction; but exendin-4 may aggravate the nephropathy in STZ-induced diabetic mice.

The Effects of pH and Excipients on Exenatide Stability in Solution

Exenatide, a glucagon-like peptide-1 receptor agonist, is the active pharmaceutical ingredient in Byetta^® and Bydureon^®, two type 2 diabetes drug products that have generics and multiple follow-up formulations currently in development. Even though exenatide is known to be chemically and physically unstable at pH 7.5, there lacks a systematic evaluation of the impact of pH and excipients on the peptide solution stability. In this study, we established analytical methods to measure the chemical and physical degradation of the peptide in solution. Exenatide remained relatively stable at pH 4.5 when incubated at 37 °C. At pH 5.5-6.5, degradation was driven by oxidation, while driven by deamidation at pH 7.5-8.5. Significant aggregation of exenatide at pH 7.5 and 8.5 was detected by size exclusion chromatography and dynamic light scattering. Each pH value greater than 4.5 exhibited unique profiles corresponding to a loss of α-helical content and an increase in unordered structures. The addition of sugars, including mannitol, sorbitol and sucrose, conferred small protective effects against peptide aggregation when incubating at pH 7.5 and 37 °C, as measured by size-exclusion chromatography and dynamic light scattering. The results of this study will be useful for investigators developing generic exenatide products, peptide analogs and novel exenatide drug delivery systems.

From thiol-subtilisin to omniligase: Design and structure of a broadly applicable peptide ligase

Omniligase-1 is a broadly applicable enzyme for peptide bond formation between an activated acyl donor peptide and a non-protected acyl acceptor peptide. The enzyme is derived from an earlier subtilisin variant called peptiligase by several rounds of protein engineering aimed at increasing synthetic yields and substrate range. To examine the contribution of individual mutations on S/H ratio and substrate scope in peptide synthesis, we selected peptiligase variant M222P/L217H as a starting enzyme and introduced successive mutations. Mutation A225N in the S1′ pocket and F189W of the S2′ pocket increased the synthesis to hydrolysis (S/H) ratio and overall coupling efficiency, whereas the I107V mutation was added to S4 pocket to increase the reaction rate. The final omniligase variants appeared to have a very broad substrate range, coupling more than 250 peptides in a 400-member library of acyl acceptors, as indicated by a high-throughput FRET assay. Crystal structures and computational modelling could rationalize the exceptional properties of omniligase-1 in peptide synthesis

Bariatric Surgery in the Treatment of Type 2 Diabetes

PURPOSE OF REVIEW

We seek to characterize the impact of bariatric surgery on diabetes mellitus by recalling its history, examining the clinical data, exploring the putative mechanisms of action, and anticipating its future.

RECENT FINDINGS

Results of clinical trials reveal that bariatric surgery induces remission of diabetes in 33-90% of individuals at 1-year post-treatment versus 0-39% of medically managed. Remission rates decrease over time but remain higher in surgically treated individuals. Investigations have revealed numerous actions of surgery including effects on intestinal physiology, neuronal signaling, incretin hormone secretion, bile acid metabolism, and microbiome changes. Bariatric surgery improves control of diabetes through both weight-dependent and weight-independent actions. These various mechanisms help explain the difference between individuals treated surgically vs. medically. They also explain differing effects of various bariatric surgery procedure types. Understanding how surgery affects diabetes will help optimize utilization of the therapy for both disease prevention and treatment.

Rebirth of the Incretin Concept: Its conception and early development

This paper describes the resurrection of the Incretin Concept in the early 1960s. It began with the more or less simultaneous discovery by three groups working independently in London. Dupre demonstrated that secretin given intravenously with glucose increased its rate of disappearance from the blood, McIntyre and co-workers established that hyperglycaemia evoked by oral glucose stimulated more insulin secretion than comparable hyperglycaemia produced by intravenous glucose and Marks and Samols established the insulinotropic properties of glucagon. The concept evolved with the discovery by Samols and co-workers that oral glucose stimulated the release of immunoreactive glucagon-like substances from the gut mucosa and the subsequent isolation of glucagon immunoreactive compounds, most notably oxyntomodulin and glicentin, and of gastic inhibitory polypetide (GIP). It concluded with the isolation and characterisation of glucagon-like peptide 1 (7-36) amide.

Formulary Forum: Exenatide: A New Option for the Treatment of Type 2 Diabetes

Objective:

To evaluate available literature characterizing the pharmacology, pharmacokinetics, drug interactions, efficacy, and safety of exenatide in patients with type 2 diabetes.

Data Sources:

A PubMed database search (1966–May 2006) was conducted, using exenatide as the search term. The manufacturer's prescribing information was also used.

Study Selection and Data Extraction:

English-language articles were selected and data were extracted with a focus on clinical outcomes associated with the treatment of patients with type 2 diabetes.

Data Synthesis:

Exenatide exerts a glucoregulatory effect by various mechanisms including secretion of glucose-dependent insulin, suppression of inappropriately high glucagon levels in patients with type 2 diabetes, delayed gastric emptying, and reduction of food intake. In placebo-controlled clinical studies, plasma exenatide concentrations appeared to exhibit dose-proportional kinetics, reaching peak plasma levels between 2 and 3 hours after a single subcutaneous injection. Exenatide's elimination half-life ranged from 3.3 to 4.0 hours, and the time to reach maximum concentration was about 2 hours. Interactions between exenatide and agents such as digoxin and lisinopril were not considered significant. In Phase III trials, exenatide demonstrated significant reduction of hemoglobin A1c levels from baseline and compared with placebo after 30 weeks of treatment in patients unable to achieve optimal glycemic control with metformin, a sulfonylurea, or oral combination therapy (0.4–0.9%). Patients' weight decreased with exenatide (0.9–2.8 kg), but adverse gastrointestinal (GI) events were common. Exenatide combined with thiazolidonediones, D-phenylalanine derivatives, meglitinides, or alpha glucosidase inhibitors has not been studied.

Conclusions:

Clinical trials have demonstrated that exenatide improves glycemic control when added to sulfonylureas and metformin, and it may be an alternative to insulin glargine in patients requiring additional therapy. Hypoglycemia has been encountered in clinical trials of exenatide, especially upon initiation of therapy with sulfonylureas (not with metformin); close patient monitoring is therefore recommended. Further studies should assess the impact of exenatide on clinical outcomes such as micro- and macrovascular disease.

Prospective QSAR-Based Prediction Models with Pharmacophore Studies of Oxadiazole-Substituted α-Isopropoxy Phenylpropanoic Acids with Dual Activators of PPARα and PPARγ

A series of oxadiazole-substituted [Formula: see text]-isopropoxy phenylpropanoic acids with dual activators of PPARα and PPARγ derivatives were subjected to two-dimensional and k-Nearest Neighbors molecular field analysis. The statistically significant best 2D-QSAR (PPARα ) model having good predictive ability with statistical values of r(2) = 0:8725; q(2) = 0:7957and pred_r(2) = 0:8136 was developed by GA-PLS with the descriptors like SsClcount, SddsN (nitro) count and SsOHcount that contribute significantly to the biological activity. The best 3D-QSAR studies (PPARα ) were performed using the genetic algorithm selection k-nearest neighbor molecular field analysis approach; a leave-one-out cross-validated correlation coefficient q(2) = 0:7188 and predicate activity pred_r(2) = 0.7508 were obtained. The influences of steric and electrostatic field effects generated by the contribution plots are discussed. The best pharmacophore model includes three features, viz. hydrogen bond donor, hydrogen bond acceptor and aromatic features. The information rendered by 2D-QSAR and 3D-QSAR models may lead to a better understanding of structural requirements of substituted α-isopropoxy phenylpropanoic derivatives and also aid in designing novel potent PPARα and PPARγ for antihyperglycemic molecules.

Epidemiology and management of antiretroviral-associated cardiovascular disease

Risk and manifestations of cardiovascular disease (CVD) in patients infected with human immunodeficiency virus (HIV) will continue to evolve as improved treatments and life expectancy of these patients increases. Although initiation of antiretroviral (ARV) therapy has been shown to reduce this risk, some ARV medications may induce metabolic abnormalities, further compounding the risk of CVD. In this patient population, both pharmacologic and nonpharmacologic strategies should be employed to treat and reduce further risk of CVD. This review summarizes epidemiology data of the risk factors and development of CVD in HIV and provides recommendations to manage CVD in HIV-infected patients.

Prospective QSAR-based prediction models with pharmacophore studies of oxadiazole-substituted α-isopropoxy phenylpropanoic acids on with dual activators of PPARα and PPARγ

A series of oxadiazole-substituted α-isopropoxy phenylpropanoic acids with dual activators of PPARα and PPARγ derivatives were subjected to two dimensional and k-nearest neighbour Molecular field analysis. The statistically significant best 2D-QSAR (PPARα) model having good predictive ability with statistical values of r2 = 0.8725, q2 = 0.7957 and pred_r2 = 0.8136, was developed by GA-PLS with the descriptors like SsClcount, SddsN (nitro) count and SsOHcount contribute significantly to the biological activity. The best 3D-QSAR studies (PPARα) were performed using the genetic algorithm selection k-nearest neighbor molecular field analysis approach; a leave-one-out cross-validated correlation coefficient q2=0.7188 and predicate activity pred_r2 =0.7508 were obtained. The influences of steric and electrostatic field effects generated by the contribution plots are discussed. The best pharmacophore model includes three features viz. hydrogen bond donor, hydrogen bond acceptor, and aromatic features were developed. The information rendered by 2D, 3D QSAR models may lead to a better understanding of structural requirements of substituted α-isopropoxy phenylpropanoic derivatives and also aid in designing novel potent PPARα and PPARγ for antihyperglycemic molecules.

Behavioural profile of exendin-4/naltrexone dose combinations in male rats during tests of palatable food consumption

RATIONALE

The glucagon-like peptide 1 receptor (GLP-1R) agonist exendin-4 potently suppresses food intake in animals and humans. However, little is known about the behavioural specificity of this effect either when administered alone or when co-administered with another anorectic agent.

OBJECTIVES

The present study characterises the effects of exendin-4, both alone and in combination with naltrexone, on behaviours displayed by male rats during tests with palatable mash.

METHODS

Experiment 1 examined the dose-response effects of exendin-4 (0.025-2.5 μg/kg, IP), while experiment 2 profiled the effects of low-dose combinations of the peptide (0.025 and 0.25 μg/kg) and naltrexone (0.1 mg/kg).

RESULTS

In experiment 1, exendin-4 dose dependently suppressed food intake as well as the frequency and rate of eating. However, these effects were accompanied by dose-dependent reductions in all active behaviours and, at 2.5 μg/kg, a large increase in resting and disruption of the behavioural satiety sequence (BSS). In experiment 2, while exendin-4 (0.25 μg/kg) and naltrexone each produced a significant reduction in intake and feeding behaviour (plus an acceleration in the BSS), co-treatment failed to produce stronger effects than those seen in response to either compound alone.

CONCLUSION

Similarities between the behavioural signature of exendin-4 and that previously reported for the emetic agent lithium chloride would suggest that exendin-4 anorexia is related to the aversive effects of the peptide. Furthermore, as low-dose combinations of the peptide with naltrexone failed to produce an additive/synergistic anorectic effect, this particular co-treatment strategy would not appear to have therapeutic significance.

Exenatide extended-release: a review of its use in type 2 diabetes mellitus

Subcutaneous exenatide extended-release (ER; Bydureon™; also known as exenatide once weekly), a glucagon-like peptide-1 receptor agonist, provides a convenient, simple, once-weekly regimen that is approved in adult patients with type 2 diabetes as adjunctive monotherapy to diet plus exercise (in the US; not as first-line therapy) and/or as combination therapy with specific oral antihyperglycaemic drugs (OADs) in patients with inadequately controlled type 2 diabetes despite treatment with these OADs (US and Europe). This article reviews the clinical efficacy and tolerability of exenatide ER in the treatment of adult patients with type 2 diabetes and gives a brief overview of its pharmacological properties. In several short-term (24-30 weeks) well designed trials, adjunctive subcutaneously injectable exenatide ER once weekly, as monotherapy or in combination with OADs, significantly improved glycaemic control, bodyweight and some surrogate markers of cardiovascular risk in adult patients with inadequately controlled type 2 diabetes despite diet and exercise and/or treatment with OADs. Furthermore, the beneficial effects of adjunctive exenatide ER therapy were sustained in extension studies of up to 3 years of treatment. Overall, the intensity of glycaemic control with exenatide ER was generally better than that observed with the exenatide immediate-release formulation (twice daily), sitagliptin or insulin glargine. Exenatide ER was shown to be noninferior to metformin in terms of glycaemic efficacy, but did not meet the criteria for noninferiority versus liraglutide. In treatment-naive patients, exenatide ER treatment did not meet noninferiority criteria versus pioglitazone, whereas in treatment-experienced patients, exenatide ER provided better glycaemic control than pioglitazone. Improvements in glycaemic control with exenatide ER and, in general, with other antihyperglycaemic agents were reflected in significant improvements from baseline in treatment satisfaction and health-related quality-of-life measures. Exenatide ER was generally well tolerated in patients participating in these trials, with most treatment-emergent adverse events being of a gastrointestinal nature, of mild to moderate severity, transient and of a similar nature and incidence to those occurring with the exenatide immediate-release formulation. Thus, exenatide ER is a useful option for the treatment of type 2 diabetes, particularly in patients where bodyweight loss is an essential aspect of the individual patient's management.

Bowels control brain: gut hormones and obesity

Peptide hormones are released from the gastrointestinal tract in response to nutrients and communicate information regarding the current state of energy balance to the brain. These hormones regulate appetite, energy expenditure and glucose homeostasis. They can act either via the circulation at target peripheral tissues, by activation of the vagus nerve or by acting on key brain regions implicated in energy homeostasis such as the hypothalamus and brainstem. This review gives an overview of the main gut hormones implicated in the regulation of food intake and how some of these are being targeted to develop anti obesity treatments.

Exenatide BID Observational Study (ExOS): results for primary and secondary endpoints of a prospective research study to evaluate the clinical effectiveness of exenatide BID use in patients with type 2 diabetes in a real-world setting

OBJECTIVE

The Exenatide BID Observational Study (ExOS) was designed to evaluate the clinical effectiveness of exenatide BID use in patients with type 2 diabetes (T2D) in a real-world clinical practice setting in the United States.

METHODS

Patients were enrolled from 74 practice sites from 9/2007 through 1/2009 and followed for 12 months. The primary effectiveness endpoint was achieving or maintaining hemoglobin A1C of ≤7.0%, or an absolute drop of 0.5% from baseline. Secondary measures included absolute and percentage change from baseline for a variety of clinical measures (lipid markers, weight, BMI, etc.), and quality of life (QOL) was assessed using the Impact of Weight on Quality of Life (IWQOL)-Lite.

RESULTS

A total of 452 patients were included in the primary study population. At baseline, patients (60% female) had mean (SD) age of 55 (11), T2D duration of 9 (8) years, HbA1c of 8.0 (1.7) %, and body mass index (BMI) of 38.2 (7.4) kg/m(2). Family history of T2D was reported in 73.9% of patients. Hypertension was reported in 61.5% of patients, and 47.1% had hyperlipidemia. The HbA1c goal was achieved in 76.3% of the 118 patients with A1C measurements available at 12 months (P < 0.0001). Patients with available clinical measurements achieved significant improvements in HbA1c, weight, BMI, and QOL measurements at 12 months. A mean improvement of 4.56 was seen in the total IWQOL-Lite score at 12 months (P = 0.001). The single-arm design of this study is a limitation; however, the overall objective of the study was to observe patients on exenatide BID therapy over time, comparing their status at endpoint to baseline, rather than to make comparisons among different drug therapies.

CONCLUSIONS

The Exenatide BID Observational Study supports the clinical effectiveness of exenatide BID observed in previous clinical trials and retrospective database studies.

The role of the gut/brain axis in modulating food intake

Peptide hormones released from the gastrointestinal tract communicate information about the current state of energy balance to the brain. These hormones regulate appetite and energy expenditure via the vagus nerve or by acting on key brain regions implicated in energy homeostasis such as the hypothalamus and brainstem. This review gives an overview of the main gut hormones implicated in the regulation of food intake. Research in this area has provided novel targets for the pharmacological treatment of obesity. This article is part of a Special Issue entitled 'Central Control Food Intake'

Exenatide: a new promising antidiabetic agent

Exenatide is a unique agent which can effectively control blood glucose levels in type 2 diabetes mellitus without producing dangerous adverse effects. In addition, it can lower body weight which is very essential for the treatment of obese type 2 diabetes mellitus patients. Since it can delay the destruction of islet beta-cells, type 2 diabetes mellitus patients are not rapidly converted to type 1 diabetes mellitus and ultimately appearance of complications of the disease is halted or delayed. Its long-acting-release formula, which would be used once per week, simultaneously retaining all the properties of twice-daily subcutaneous administration, is undergoing clinical trial. This drug is considered as an adjunct to metformin/sulfonylureas/insulin.

Peripheral glucagon-like peptide-1 (GLP-1) and satiation

Peripheral GLP-1 is produced by post-translational processing of pro-glucagon in enteroendocrine L-cells and is released in response to luminal nutrient (primarily carbohydrate and fat) stimulation. GLP-1 is well known for its potent insulinotropic and gluco-regulatory effects. GLP-1 receptors (GLP-1R) are expressed in the periphery and in several brain areas that are implicated in the control of eating. Both central and peripheral administration of GLP-1 have been shown to reduce food intake. Unresolved, however, is whether these effects reflect functions of endogenous GLP-1. Data collected in our laboratory indicate that in chow-fed rats: 1) Remotely controlled, intra-meal intravenous (IV) or intraperitoneal (IP) GLP-1 infusions selectively reduce meal size; 2) hindbrain GLP-1R activation is involved in the eating-inhibitory effect of IV infused GLP-1, whereas intact abdominal vagal afferents are necessary for the eating-inhibitory effect of IP, but not IV, infused GLP-1; 3) GLP-1 degradation in the liver prevents a systemic increase in endogenous GLP-1 during normal chow meals in rats; and 4) peripheral or hindbrain GLP-1R antagonism by exendin-9 does not affect spontaneous eating. Also, although our data indicate that peripheral GLP-1 can act in two different sites to inhibit eating, they argue against a role of systemic increases in endogenous GLP-1 in satiation in chow-fed rats. Therefore, further studies should examine whether a local paracrine action of GLP-1 in the intestine or and endocrine action in the hepatic-portal area is physiologically relevant for satiation.

Development of a new class of benzoylpyrrole-based PPARα/γ activators

Starting with a subtle blood glucose-lowering effect of a TGF-β inhibitor, we designed and synthesized a series of benzoylpyrrole-based carboxylic acids as PPARs activators. Among these compounds, 10sNa exhibited favorable blood glucose-lowering effect without body weight gain. We assume that the beneficial effect of 10sNa is attributed to not only its compound PPARα agonistic activity but also its PPARγ partial agonistic activity.

Liraglutide in the treatment of type 2 diabetes mellitus: clinical utility and patient perspectives

Type 2 diabetes mellitus (T2DM) is a progressive disease associated with significant morbidity and mortality. There is good evidence that intensive glycemic control reduces the development and progression of complications in patients with diabetes. In order to achieve glycemic targets, patients often require a combination of oral therapy and/or insulin in addition to lifestyle modification. Unfortunately many currently available therapies for T2DM are associated with weight gain and hypoglycemia resulting in poor compliance and subsequent worsening glycemic control. Glucagon like peptide-1 (GLP-1) is an incretin hormone secreted from the small intestine that lowers fasting and postprandial glucose through multiple mechanisms including glucose-dependent insulin secretion, reduction of glucagon secretion, delaying gastric emptying and increased satiety. Liraglutide is a long acting GLP-1 mimetic that is administered once a day by subcutaneous injection and is now licensed for the treatment of T2DM. Phase 3 clinical trials have demonstrated beneficial effects on glycemic control and weight with liraglutide therapy. Within this article, we provide an overview of pharmacology, efficacy, safety and patient experience on liraglutide in the management of T2DM.

A review of exenatide as adjunctive therapy in patients with type 2 diabetes

Background

Incretin glucagon-like peptide-1 (GLP-1) is a hormone released from cells in the gastrointestinal tract (GI), leading to glucose-dependent insulin release from the pancreas. It also suppresses postprandial hyperglycemia, glucagon secretion and slows gastric emptying. Exenatide (EXE), a functional analog of human GLP-1, was approved by the US FDA in April 2005.

Objective

This article reviews current primary literature on the clinical efficacy and safety of EXE in the treatment of type 2 diabetes mellitus (DM) and describes the pharmacokinetics, pharmacodynamics, dosing and administration of EXE.

Methods

English-language articles were identified through a search of MEDLINE (1966 to March 2009), International Pharmaceutical Abstracts (1970 to present), and Cochrane Database of Systemic Reviews (1995 to March 2009). Search terms included EXE, diabetes mellitus, postprandial hyperglycemia, gastric emptying, glucagon, pharmacokinetics and pharmacodynamics. Articles were selected for review if their designs were randomized, blinded and of controlled design that focused on clinical outcomes of patients with type 2 DM.

Results

EXE is administered subcutaneously in the thigh, abdomen or upper arm within the 60-minute period before the morning and evening meals. Its C_max is reached within 2.1 hours, and its T_1/2 in 2.4 hours. EXE’s metabolism is primarily through the kidneys. For the patients who received EXE 10 μg SC BID in three, 30-week, placebo-controlled studies with background sulfonylureas (SUs), metformin (MET), or SU + MET, there were significant reductions in HbA_1c (0.77 to 0.86%), fasting plasma glucose (0.6 mmol/L) and body weight (1.6 to 2.8 kg) (P ≤ 0.05 vs PCB) that were sustained in patients who completed two open-label phase trials with an additional 52 weeks of therapy. The use of thiazolidinediones was associated with a slight advantage over EXE in improving HbA_1c along with increased weight gain; those who received EXE lost weight, but experienced more GI adverse effects. Patients who received EXE lost significant body weight while patients who received insulin gained weight. Patients receiving insulin had lower fasting, prelunch and predinner glucose excursions while patients in the EXE groups had lower postprandial glucose levels. Nausea was most frequently (>20%) reported in patients receiving the highest dose of EXE (10 μg SC BID vs 5 μg SC BID).

Conclusions

EXE at the dose of 10 μg SC BID has been proven to decrease HbA_lc by 1.3% ± 0.1% and decrease body weight by up to 5.3 ± 0.8 kg at week 82. Nausea was the most frequently reported adverse event (>20%) especially in patients being treated with EXE 10 μg SC BID. EXE can be safely added to MET therapy, SU therapy or MET + SU combination to effectively target glycemic goals in patients with type 2 DM. Long-term, head-to-head studies assessing the effect of the EXE ± oral agents/insulins in patients with HbA_lc ≥ 10% are still needed to fully clarify the role of EXE in poorly controlled patients with type 2 DM.

Present and Prospective Pharmacotherapy for the Management of Patients with Type 2 Diabetes

Diabetes Mellitus is a chronic condition prevalent worldwide. Type 2 diabetes is the most common form of diabetes, comprising 90% to 95% of all cases. Over the last few decades, the importance of glycemic control and its impact on prevention of diabetes-related complications has been documented in multiple clinical trials. As most patients with type 2 diabetes will require pharmacologic intervention to achieve and maintain appropriate glycemic control, new medications targeting different aspects of the pathophysiology of type 2 diabetes have been a significant focus of research and development. During the last decade, multiple new medications for diabetes management have become available: these medications have novel mechanisms of action, differences in effectiveness, and varying side effect profiles which will be reviewed in this article. Some of these newer medications, such as the GLP-1 analogues and DPP-4 inhibitors, have become widely accepted as therapeutic options for the management of type 2 diabetes.Additional classes of glucose-lowering medications are expected to become available in the near future. This manuscript will summarize available data regarding these newer and prospective medications for the management of type 2 diabetes.

Exenatide and liraglutide: different approaches to develop GLP-1 receptor agonists (incretin mimetics)--preclinical and clinical results

The GLP-1 analogues exenatide and liraglutide stimulate insulin secretion and inhibit glucagon output in a glucose-dependent manner, slow gastric emptying and decrease appetite. The injectable glucagon-like peptide-1 (GLP-1) receptor agonist exenatide significantly improves glycaemic control, with average reductions in HbA1c of about 1.0% point, fasting plasma glucose of about 1.4 mmol l(-1), and causes a weight loss of approximately 2-3 kg after 30 weeks of treatment. The adverse effects are transient nausea and vomiting. The long-acting once-daily human GLP-1 receptor agonist liraglutide reduces HbA1c by about 1.0-2.0% point, weight by 1-3 kg and seems to have fewer gastrointestinal side effects than exenatide. The final place of the GLP-1 receptor agonists in the diabetes treatment algorithm will be clarified when we have long-term trials with cardiovascular end-points and data illustrating the effects on the progression of type 2 diabetes.

Combination of the insulin sensitizer, pioglitazone, and the long-acting GLP-1 human analog, liraglutide, exerts potent synergistic glucose-lowering efficacy in severely diabetic ZDF rats

OBJECTIVE

Severe insulin resistance and impaired pancreatic beta-cell function are pathophysiological contributors to type 2 diabetes, and ideally, antihyperglycaemic strategies should address both.

RESEARCH DESIGN AND METHODS

Therapeutic benefits of combining the long-acting human glucagon-like peptide-1 (GLP-1) analog, liraglutide (0.4 mg/kg/day), with insulin sensitizer, pioglitazone (10 mg/kg/day), were assessed in severely diabetic Zucker diabetic fatty rats for 42 days. Impact on glycaemic control was assessed by glycated haemoglobin (HbA(1C)) at day 28 and by oral glucose tolerance test at day 42.

RESULTS

Liraglutide and pioglitazone synergistically improved glycaemic control as reflected by a marked decrease in HbA(1C) (liraglutide + pioglitazone: 4.8 +/- 0.3%; liraglutide: 8.8 +/- 0.6%; pioglitazone: 7.9 +/- 0.4%; vehicle: 9.7 +/- 0.3%) and improved oral glucose tolerance at day 42 (area under the curve; liraglutide + pioglitazone: 4244 +/- 445 mmol/l x min; liraglutide: 7164 +/- 187 mmol/l x min; pioglitazone: 7430 +/- 446 mmol/l x min; vehicle: 8093 +/- 139 mmol/l x min). A 24-h plasma glucose profile at day 38 was significantly decreased only in the liraglutide + pioglitazone group. In addition, 24-h insulin profile was significantly elevated only in the liraglutide + pioglitazone group. Liraglutide significantly decreased food intake alone and in combination with pioglitazone, while pioglitazone alone increased cumulated food intake. As a result, rats on liraglutide alone gained significantly less weight than vehicle-treated rats, whereas rats on pioglitazone alone gained significantly more body weight than vehicle-treated rats. However, combination therapy with liraglutide and pioglitazone caused the largest weight gain, probably reflecting marked improvement of energy balance because of reduction of glucosuria.

CONCLUSIONS

Combination therapy with insulinotropic GLP-1 agonist liraglutide and insulin sensitizer, pioglitazone, improves glycaemic control above and beyond what would be expected from additive effects of the two antidiabetic agents.

Investigational treatments for Type 2 diabetes mellitus: exenatide and liraglutide

Although a number of compounds are currently used to treat Type 2 diabetes mellitus, achieving a sustained glycaemic control over time is often not possible using oral antidiabetics. Endogenous incretins exhibit beneficial effects that could be useful for Type 2 diabetes mellitus treatment, such as stimulating insulin secretion during hyperglycaemia, improving beta-cell mass and function, reducing glucagon secretion, delaying gastric emptying, reducing postprandial hyperglycaemia and diminishing body weight; however, their short half-life makes them unsuitable for treatment. Incretin mimetics such as liraglutide and exenatide were developed to overcome this limitation. This review discusses the effects of these compounds and their potential as a new class of antidiabetic agents.

Regulation of cAMP dynamics by Ca2+ and G protein-coupled receptors in the pancreatic beta-cell: a computational approach

In this report we describe a mathematical model for the regulation of cAMP dynamics in pancreatic beta-cells. Incretin hormones such as glucagon-like peptide 1 (GLP-1) increase cAMP and augment insulin secretion in pancreatic beta-cells. Imaging experiments performed in MIN6 insulinoma cells expressing a genetically encoded cAMP biosensor and loaded with fura-2, a calcium indicator, showed that cAMP oscillations are differentially regulated by periodic changes in membrane potential and GLP-1. We modeled the interplay of intracellular calcium (Ca(2+)) and its interaction with calmodulin, G protein-coupled receptor activation, adenylyl cyclases (AC), and phosphodiesterases (PDE). Simulations with the model demonstrate that cAMP oscillations are coupled to cytoplasmic Ca(2+) oscillations in the beta-cell. Slow Ca(2+) oscillations (<1 min(-1)) produce low-frequency cAMP oscillations, and faster Ca(2+) oscillations (>3-4 min(-1)) entrain high-frequency, low-amplitude cAMP oscillations. The model predicts that GLP-1 receptor agonists induce cAMP oscillations in phase with cytoplasmic Ca(2+) oscillations. In contrast, observed antiphasic Ca(2+) and cAMP oscillations can be simulated following combined glucose and tetraethylammonium-induced changes in membrane potential. The model provides additional evidence for a pivotal role for Ca(2+)-dependent AC and PDE activation in coupling of Ca(2+) and cAMP signals. Our results reveal important differences in the effects of glucose/TEA and GLP-1 on cAMP dynamics in MIN6 beta-cells.

Safety and adverse effects associated with GLP-1 analogues

The incretin mimetics are an emerging class of agents for the treatment of diabetes. So far, exenatide is licensed for use in the US and also became available in the UK in May 2007. Within development and Phase III trials, liraglutide may also be made available within the next 2 years. These agents enhance glucose-dependent insulin secretion and exhibit other antihyperglycaemic actions, which are of particular benefit to overweight patients with Type 2 diabetes. This article reviews the profile of adverse effects for these agents in relation to their current (exenatide) and anticipated (liraglutide) role in the management of Type 2 diabetes.

A comparison of twice-daily exenatide and biphasic insulin aspart in patients with type 2 diabetes who were suboptimally controlled with sulfonylurea and metformin: a non-inferiority study

AIMS/HYPOTHESIS

The aim of this 52-week, open-label, non-inferiority trial was to compare the safety and efficacy of exenatide (an incretin mimetic) with that of biphasic insulin aspart.

MATERIALS AND METHODS

Patients on metformin and a sulfonylurea were randomised to exenatide (n = 253; 5 microg twice daily for 4 weeks, 10 microg thereafter) or biphasic insulin aspart (n = 248; twice-daily doses titrated for optimal glucose control), while continuing with metformin and sulfonylurea treatment.

RESULTS

Glycaemic control achieved with exenatide was non-inferior to that achieved with biphasic insulin aspart (mean+/-SEM, HbA(1c) change: exenatide -1.04 +/- 0.07%, biphasic insulin aspart -0.89 +/- 0.06%; difference -0.15 [95% CI -0.32 to 0.01]%). Exenatide-treated patients lost weight, while patients treated with biphasic insulin aspart gained weight [between-group difference -5.4 (95% CI -5.9 to -5.0) kg]. Both treatments reduced fasting serum glucose (exenatide -1.8 +/- 0.2 mmol/l, p < 0.001; biphasic insulin aspart -1.7 +/- 0.2 mmol/l, p < 0.001). Greater reductions in postprandial glucose excursions following morning (p < 0.001), midday (p = 0.002) and evening meals (p < 0.001) were observed with exenatide. The withdrawal rate was 21.3% (54/253) for exenatide and 10.1% (25/248) for biphasic insulin aspart. Nausea (33% incidence, 3.5% discontinuation) was the most common adverse event observed with exenatide.

CONCLUSIONS/INTERPRETATION

Exenatide treatment resulted in HbA(1c) reduction similar to biphasic insulin aspart and provided better postprandial glycaemic control, making it a potential alternative for the treatment of type 2 diabetes. Treatment with biphasic insulin aspart was associated with weight gain and lower risk of adverse gastrointestinal events. Although the availability of glucose-lowering agents associated with weight reduction may be considered a therapeutic advance, the long-term implications of progressive weight reduction observed with exenatide have yet to be defined.

Design and synthesis of oxime ethers of α-acyl-β-phenylpropanoic acids as PPAR dual agonists

Oxime ethers of alpha-acyl-beta-phenylpropanoic acids were prepared to apply as PPARalpha and gamma dual agonists. Among them, compound 11l proved to exhibit potent in vitro activities with EC(50) of 19 and 13nM in PPARalpha and gamma, respectively. It showed better glucose lowering effects than rosiglitazone 1 and ameliorated the lipid profile like plasma triglyceride in db/db mice model.

Exenatide

Exenatide (Byetta) is a novel, synthetic, incretin mimetic, glucoregulatory peptide approved in the US and Europe for the treatment of patients with type 2 diabetes mellitus who have inadequate glycaemic control despite receiving treatment with maximum tolerated doses of metformin and/or a sulfonylurea. In randomised, controlled, phase III trials and post hoc completer analyses in this patient population, the addition of subcutaneous exenatide twice daily significantly improved glycaemic control and was associated with progressive and significant bodyweight reduction from baseline for up to 2 years. The overall intensity of glycaemic control with exenatide was similar to that achieved with once-daily insulin glargine or twice-daily biphasic insulin aspart. Exenatide was generally well tolerated. Most adverse events were mild to moderate in severity and gastrointestinal in nature. The overall rate of hypoglycaemia was similar to rates observed with placebo (when administered with metformin) and insulin comparators (when administered with metformin and a sulfonylurea). The addition of exenatide to therapy with metformin and a sulfonylurea provided significant improvements in treatment satisfaction and patients' health-related quality of life (HR-QOL). The drug was also cost effective compared with pioglitazone, glibenclamide (glyburide), insulin glargine (all in combination with metformin and/or a sulfonylurea) and metformin alone. Overall, adjunctive therapy with exenatide is a valuable therapeutic option in patients with type 2 diabetes requiring moderate improvements in glycaemic control despite treatment with metformin and/or a sulfonylurea.

Management of Diabetes in Older Adults

Enhanced life expectancy and the aging of society have conspired with rising rates of obesity and physical inactivity to cause an unprecedented increase in diabetes prevalence worldwide. The disease and its chronic complications have unique presentations and challenges in the elderly. Postprandial hyperglycemia may be the predominant manifestation, comorbid health conditions are often present, and the risk of cardiovascular disease is vastly increased. Periodic screening is essential for early diagnosis and proper treatment. The principles of multidisciplinary management emphasizing nutrition, exercise, education, psychosocial care, attention to concomitant metabolic risk factors, and prudent use of pharmacologic agents are the mainstay of therapy for older adults. Treatment should be tailored to the individual patient, and the assistance of family and caregivers should be combined with rational utilization of community resources. An evidence-based, comprehensive, and proactive approach is needed to reduce the burden of morbidity and mortality from diabetes in the elderly.

Exenatide and biotin in conjunction with a protein-sparing fast for normalization of beta cell function in type 2 diabetics

The dysdifferentiation of beta cells in type 2 diabetes appears to be caused and maintained by a vicious cycle of glucolipotoxicity: chronic elevations of glucose and free fatty acids induce beta cell dysdifferentiation as well as apoptosis; the resulting failure of glucose-stimulated insulin secretion tends to maintain the elevations of glucose and free fatty acids. Since extended fasts restore normoglycemia in diabetics, the resulting relief from glucotoxicity has been associated with a marked improvement in beta cell function that can be conserved after the fast if the factors precipitating diabetes--obesity, fatty and high-glycemic-index diets, sedentary lifestyle--have been adequately addressed. The new drug exenatide, an analog of the incretin hormone glucagon-like peptide-1, may be a worthwhile adjuvant to such fasting therapy, since it tends to counteract the glucolipotoxicity-induced down-regulation of the crucially important beta cell transcription factor IDX-1. Exenatide also exerts trophic effects on beta cell mass that in the longer term might help to restore diminished beta cell mass. Supraphysiological concentrations of biotin, possibly because they activate the soluble guanylate cyclase, also promote induction of IDX-1 and counteract the adverse impact of glucolipotoxicity in this regard; thus, high-dose biotin, which is well tolerated, may represent an additional adjuvant for therapeutic fasting intended to normalize beta cell function in type 2 diabetics.

The obesity pipeline: current strategies in the development of anti-obesity drugs

This review provides a summary of currently available pharmaceutical therapies for the treatment of obesity, along with an overview of the pipeline of products currently in development, and the key mechanisms on which the major development candidates are based. In particular, the recent increase in understanding of the role of gut peptides in energy homeostasis is highlighted as a promising source of potential future obesity therapies.

Obesity and the role of gut and adipose hormones in female reproduction

Reproductive function declines at both extremes of human energy balance. The relationship between obesity and reproductive function is complex and incompletely understood. The literature has established the negative impact of excess energy stores on ovulatory function and investigated the mechanisms whereby this occurs. Furthermore, weight loss in obese anovulatory women increases ovulation and conception. Obesity and anti-obesity therapy effects on the endometrium, implantation and early fetal development have received less attention. The discovery of adipokines and enterokines greatly expands the ability to investigate the relationship between obesity, therapies to produce weight loss and reproductive function. In this review, we discuss select adipose and enteric signals. We focus on in vitro, animal and human data that lend biological plausibility to adipokines and enterokines as mediators of obesity and reproduction. Very little published work exists that directly addresses adipocyte and enteric signals in this specific role; therefore, much of this review is on the basis of a synthesis of the literature in three areas: (i) in vitro and in vivo evidence regarding the reproductive effects of these signals; (ii) adipokine and enterokine changes that occur with weight-loss therapies, focusing on hypocaloric diets, bariatric surgery and drugs that target adipocyte or enteric signals and (iii) reproductive changes produced by these weight-loss therapies.

Exenatide

Exenatide is an incretin mimetic. It improves glycaemic control via various glucoregulatory mechanisms, including glucose-dependent insulinotropism, suppression of inappropriately high glucagon levels, delayed gastric emptying and reduction of food intake. In three large, well designed, phase III trials in adults with type 2 diabetes mellitus and suboptimal glycaemic control despite treatment with metformin and/or a sulfonylurea, mean changes from baseline in glycosylated haemoglobin (HbA(1c)) significantly favoured subcutaneous exenatide 5 or 10microg twice daily over placebo after 30 weeks' treatment (primary endpoint). Relative to placebo, reductions from baseline in bodyweight were significantly greater with twice-daily exenatide 5microg (in two studies) or 10microg (in all three studies). Post hoc completer analyses revealed that the beneficial effects of exenatide on HbA(1c) and bodyweight were maintained for up to 82 weeks. Adjunctive therapy with subcutaneous exenatide 10microg twice daily improved glycaemic control to a similar extent as insulin glargine in patients with type 2 diabetes suboptimally controlled with metformin plus a sulfonylurea in a large, well designed, 26-week, phase III trial. Subcutaneous exenatide was generally well tolerated in patients with type 2 diabetes. The incidence of hypoglycaemia in patients receiving exenatide plus metformin was similar to that seen in placebo plus metformin recipients; however, in patients receiving a sulfonylurea (with or without metformin), the incidence of hypoglycaemia was numerically higher with exenatide than with placebo.

Exenatide

PURPOSE

The pharmacology, pharmacokinetics, clinical efficacy, adverse effects, drug interactions, and dosage and administration of exenatide are discussed.

SUMMARY

Exenatide, derived from a compound found in the saliva of the Gila monster, is an incretin mimetic agent that enhances glucose-dependent insulin secretion and has several other antihyperglycemic actions. The drug is indicated as adjunctive therapy to improve glycemic control in patients with type 2 diabetes mellitus who are taking metformin, a sulfonylurea, or both but who have not achieved adequate glycemic control. Peak plasma concentration following subcutaneous administration of exenatide is attained in 2.1 hours. The mean apparent volume of distribution after administration of a single subcutaneous dose is 28.3 L. The terminal half-life of the drug is 2.4 hours. Based on animal studies, the bioavailability of exenatide after subcutaneous injection has been estimated to be between 65% and 75%. The drug is predominantly eliminated by glomerular filtration followed by proteolytic degradation. Clinical trials have shown that exenatide given subcutaneously twice daily significantly reduced glycosylated hemoglobin values when maximum doses of a sulfonylurea, metformin, or both were ineffective. The most common adverse effects are nausea, vomiting, diarrhea, jitteriness, dizziness, headache, and dyspepsia. Drug-drug interactions with digoxin, lovastatin, lisinopril, and acetaminophen have been documented. The recommended starting dosage is 5 microg subcutaneously twice daily within one hour before the morning and evening meals.

CONCLUSION

Exenatide offers a novel treatment option for patients with type 2 diabetes mellitus who are refractory to metformin or sulfonylurea therapy or both.

Major contributions of comparative endocrinology to the development and exploitation of the incretin concept

An incretin is a factor released by the gut in response to nutrients that facilitates uptake of glucose by peripheral tissues. The incretin concept predates the discovery of insulin but it is now clear that incretins act by stimulating secretion of this hormone. As glucagon has insulin-releasing activity, it was speculated that intestinal glucagon-like immunoreactivity (enteroglucagon) was involved in the incretin effect but it was an achievement in the field of comparative endocrinology that led to the demonstration that the preproglucagon gene encodes the most potent incretin in the human. Characterization of cloned cDNAs encoding two preproglucagons from the Brockmann body of the anglerfish Lophius americanus demonstrated that the glucagon sequence is flanked by a 34 amino-acid-residue sequence with appreciable structural similarity to glucagon that was termed glucagon-like peptide (GLP). A 36 amino-acid-residue ortholog of anglerfish GLP was subsequently identified in human preproglucagon but this peptide had only weak insulin-releasing activity. However, alignment of GLP sequences from human and teleost fish showed that the human ortholog is extended from its N-terminus by a hexapeptide. Removal of this extension by an endogenous protease generates GLP-1-(7-36)amide, the potent and effective form of the incretin. More recently, comparative endocrinology has contributed to the exploitation of incretins as antidiabetic drugs. Exendin-4, a GLP-1 receptor agonist first isolated from the venom of the Gila monster Heloderma suspectum, is a clinically valuable, long-acting incretin and the skins of several species of frogs synthesize potent insulin-releasing peptides with therapeutic potential.

Role of glucagon-like peptide-1 in the pathogenesis and treatment of diabetes mellitus

Glucagon-like peptide-1 (GLP-1) is an incretin hormone secreted from enteroendocrine L cells in response to ingested nutrients. The first recognized and most important action of GLP-1 is the potentiation of glucose-stimulated insulin secretion in beta-cells, mediated by activation of its seven transmembrane domain G-protein-coupled receptor. In addition to its insulinotropic actions, GLP-1 exerts islet-trophic effects by stimulating replication and differentiation and by decreasing apoptosis of beta-cells. The GLP-1 receptor is expressed in a variety of other tissues important for carbohydrate metabolism, including pancreatic alpha-cells, hypothalamus and brainstem, and proximal intestinal tract. GLP-1 also appears to exert important actions in liver, muscle and fat. Thus, GLP-1 suppresses glucagon secretion, promotes satiety, delays gastric emptying and stimulates peripheral glucose uptake. The impaired GLP-1 secretion observed in type 2 diabetes suggests that GLP-1 plays a role in the pathogenesis of this disorder. Thus, because of its multiple actions, GLP-1 is an attractive therapeutic target for the treatment of type 2 diabetes, and major interest has resulted in the development of a variety of GLP-1 receptor agonists for this purpose. Ongoing clinical trials have shown promising results and the first analogs of GLP-1 are expected to be available in the near future.

New therapeutic strategies for the treatment of type 2 diabetes mellitus based on incretins

Orally ingested glucose leads to a greater insulin response compared to intravenously administered glucose leading to identical postprandial plasma glucose excursions, a phenomenon referred to as the "incretin effect". The incretin effect comprises up to 60% of the postprandial insulin secretion and is diminished in type 2 diabetes. One of the very important gastrointestinal hormones promoting this effect is glucagon-like peptide 1 (GLP-1). It only stimulates insulin secretion and normalizes blood glucose in humans under hyperglycemic conditions, therefore it does not cause hypoglycemia. Other important physiological actions of GLP-1 are the inhibition of glucagon secretion and gastric emptying. It further acts as a neurotransmitter in the hypothalamus stimulating satiety. In vitro and animal data demonstrated that GLP-1 increases beta-cell mass by stimulating islet cell neogenesis and by inhibiting apoptosis of islets. In humans, the improvement of beta-cell function can be indirectly observed from the increased insulin secretory capacity after GLP-1 infusions. GLP-1 represents an attractive therapeutic principle for type 2 diabetes. However, native GLP-1 is degraded rapidly upon exogenous administration and is therefore not feasible for routine therapy. The first long-acting GLP-1 analog ("incretin mimetic") Exenatide (Byetta) has just been approved for type 2 diabetes therapy. Other compounds are being investigated in clinical trials (e.g. liraglutide, CJC1131). Dipeptidyl-peptidase IV inhibitors (DPP-IV inhibitors; e.g. Vildagliptin, Sitagliptin) that inhibit the enzyme responsible for incretin degradation are also under study.

Glucagon-like peptide-1 as a treatment option for type 2 diabetes and its role in restoring beta-cell mass

The "incretin effect" describes the enhanced insulin response from orally ingested glucose compared with intravenous glucose leading to identical postprandial plasma glucose excursions. It makes up to 60% of the postprandial insulin secretion but is diminished in type 2 diabetes. Gastrointestinal hormones promoting the incretin effect are called incretins. Glucagon-like peptide- 1 (GLP-1) is an important incretin. In vitro and animal data have demonstrated that GLP-1 increases beta-cell mass by stimulating islet cell neogenesis and by inhibiting apoptosis of islets. The improvement of beta-cell function can be indirectly observed from the increased insulin secretory capacity of humans receiving GLP-1 or incretin mimetics that act like GLP-1. Furthermore, GLP-1 inhibits glucagon secretion and rarely causes hypoglycemia. It may represent an attractive therapeutic method for type 2 diabetes because of its multiple effects, including a slowing of gastric emptying and the simulation of satiety by acting as a transmitter in the CNS. Native GLP-1 is degraded rapidly upon intravenous or subcutaneous administration and is therefore not feasable for routine therapy. Long-acting GLP-1 analogs (e.g., Liraglutide [Novo Nordisk, Copenhagen, Denmark]) and exenadin-4 (Exenatide [Eli Lilly, Indianapolis, IN]) that are resistant to degradation, called "incretin mimetics," are being investigated in clinical trials. Dipeptidyl peptidase IV inhibitors (e.g., Vildagliptin [Novartis, Basel, Switzerland]) that inhibit the enzyme responsible for incretin degradation are also under study.