Incretin mimetics and dipeptidyl peptidase-IV inhibitors: a review of emerging therapies for type 2 diabetes

Metabolic Syndrome and Neuroprotection

Introduction: Over the years the prevalence of metabolic syndrome (MetS) has drastically increased in developing countries as a major byproduct of industrialization. Many factors, such as the consumption of high-calorie diets and a sedentary lifestyle, bolster the spread of this disorder. Undoubtedly, the massive and still increasing incidence of MetS places this epidemic as an important public health issue. Hereon we revisit another outlook of MetS beyond its classical association with cardiovascular disease (CVD) and Diabetes Mellitus Type 2 (DM2), for MetS also poses a risk factor for the nervous tissue and threatens neuronal function. First, we revise a few essential concepts of MetS pathophysiology. Second, we explore some neuroprotective approaches in MetS pertaining brain hypoxia. The articles chosen for this review range from the years 1989 until 2017; the selection criteria was based on those providing data and exploratory information on MetS as well as those that studied innovative therapeutic approaches.

Pathophysiology: The characteristically impaired metabolic pathways of MetS lead to hyperglycemia, insulin resistance (IR), inflammation, and hypoxia, all closely associated with an overall pro-oxidative status. Oxidative stress is well-known to cause the wreckage of cellular structures and tissue architecture. Alteration of the redox homeostasis and oxidative stress alter the macromolecular array of DNA, lipids, and proteins, in turn disrupting the biochemical pathways necessary for normal cell function.

Neuroprotection: Different neuroprotective strategies are discussed involving lifestyle changes, medication aimed to mitigate MetS cardinal symptoms, and treatments targeted toward reducing oxidative stress. It is well-known that the routine practice of physical exercise, aerobic activity in particular, and a complete and well-balanced nutrition are key factors to prevent MetS. Nevertheless, pharmacological control of MetS as a whole and pertaining hypertension, dyslipidemia, and endothelial injury contribute to neuronal health improvement.

Conclusion: The development of MetS has risen as a risk factor for neurological disorders. The therapeutic strategies include multidisciplinary approaches directed to address different pathological pathways all in concert.

Replacement of the C-terminal Trp-cage of exendin-4 with a fatty acid improves therapeutic utility

Exendin-4, a 39 amino acid peptide isolated from the saliva of the Gila monster, plays an important role in regulating glucose homeostasis, and is used clinically for the treatment of type 2 diabetes. Exendin-4 shares 53% sequence identity with the incretin hormone glucagon-like peptide 1 (GLP-1) but, unlike GLP-1, is highly resistant to proteolytic enzymes such as dipeptidyl peptidase IV (DPP-IV) and neutral endopeptidase 24.11 (NEP 24.11). Herein, we focused on the structure and function of the C-terminal Trp-cage of exendin-4, and suggest that it may be structurally required for resistance to proteolysis by NEP 24.11. Using a series of substitutions and truncations of the C-terminal Trp-cage, we found that residues 1-33, including the N-terminal and helical regions of wild-type (WT) exendin-4, is the minimum motif required for both high peptidase resistance and potent activity toward the GLP-1 receptor comparable to WT exendin-4. To improve the therapeutic utility of C-terminally truncated exendin-4, we incorporated various fatty acids into exendin-4(1-33) in which Ser³³ was substituted with Lys for acylation. Exendin-4(1-32)K-capric acid exhibited the most well balanced activity, with much improved therapeutic utility for regulating blood glucose and body weight relative to WT exendin-4.

A Computational Method to Determine Glucose Infusion Rates for Isoglycemic Intravenous Glucose Infusion Study

The results of the isoglycemic intravenous glucose infusion (IIGI) study need to mimic the dynamic glucose profiles during the oral glucose tolerance test (OGTT) to accurately calculate the incretin effect. The glucose infusion rates during IIGI studies have historically been determined by experienced research personnel using the manual ad-hoc method. In this study, a computational method was developed to automatically determine the infusion rates for IIGI study based on a glucose-dynamics model. To evaluate the computational method, 18 subjects with normal glucose tolerance underwent a 75 g OGTT. One-week later, Group 1 (n = 9) and Group 2 (n = 9) underwent IIGI studies using the ad-hoc method and the computational method, respectively. Both methods were evaluated using correlation coefficient, mean absolute relative difference (MARD), and root mean square error (RMSE) between the glucose profiles from the OGTT and the IIGI study. The computational method exhibited significantly higher correlation (0.95 ± 0.03 versus 0.86 ± 0.10, P = 0.019), lower MARD (8.72 ± 1.83% versus 13.11 ± 3.66%, P = 0.002), and lower RMSE (10.33 ± 1.99 mg/dL versus 16.84 ± 4.43 mg/dL, P = 0.002) than the ad-hoc method. The computational method can facilitate IIGI study, and enhance its accuracy and stability. Using this computational method, a high-quality IIGI study can be accomplished without the need for experienced personnel.

Therapeutic stimulation of GLP-1 and GIP protein with DPP-4 inhibitors for type-2 diabetes treatment

Dipeptidyl peptidase-4 (DPP-4) inhibition is a new treatment for type-2 diabetes. DPP-4 inhibition increases levels of active GLP-1. GLP-1 enhances insulin secretion and diminishes glucagon secretion, in this manner reducing glucose concentrations in blood. A number of DPP-4 inhibitors are under clinical development. However, the durability and long-term safety of DPP-4 inhibition remain to be established. These synthetic DPP-4 inhibitors are showing some side effects. Herbal medicines are alternative medicine over synthetic drugs that can relieve the patients. Various research studies have been carried all over the world to evaluate the efficacy of herbs in the treatment of Type II diabetes mellitus. For a long time type II diabetes mellitus has been treated orally with herbal medicines, because plant products are frequently prescribed due to their less toxicity than conventional medicines.

Exenatide at therapeutic and supratherapeutic concentrations does not prolong the QTc interval in healthy subjects

Aims

Exenatide has been demonstrated to improve glycaemic control in patients with type 2 diabetes, with no effect on heart rate corrected QT (QT_c) at therapeutic concentrations. This randomized, placebo- and positive-controlled, crossover, thorough QT study evaluated the effects of therapeutic and supratherapeutic exenatide concentrations on QT_c.

Methods

Intravenous infusion was employed to achieve steady-state supratherapeutic concentrations in healthy subjects within a reasonable duration (i.e. days). Subjects received exenatide, placebo and moxifloxacin, with ECGs recorded pre-therapy and during treatment. Intravenous exenatide was expected to increase heart rate to a greater extent than subcutaneous twice daily or once weekly formulations. To assure proper heart rate correction, a wide range of baseline heart rates was assessed and prospectively defined methodology was applied to determine the optimal QT correction.

Results

Targeted steady-state plasma exenatide concentrations were exceeded (geometric mean ± SEM 253 ± 8.5 pg ml⁻¹, 399 ± 11.9 pg ml⁻¹ and 627 ± 21.2 pg ml⁻¹). QT_cP, a population-based method, was identified as the most appropriate heart rate correction and was prespecified for primary analysis. The upper bound of the two-sided 90% confidence interval for placebo-corrected, baseline-adjusted QT_cP (ΔΔQT_cP) was <10 ms at all time points and exenatide concentrations. The mean of three measures assessed at the highest steady-state plasma exenatide concentration of ∼500 pg ml⁻¹ (ΔΔQT_cP^avg) was −1.13 [−2.11, −0.15). No correlation was observed between ΔΔQT_cP and exenatide concentration. Assay sensitivity was confirmed with moxifloxacin.

Conclusions

These results demonstrated that exenatide, at supratherapeutic concentrations, does not prolong QT_c and provide an example of methodology for QT assessment of drugs with an inherent heart rate effect.

Caffeic acid phenethyl amide improves glucose homeostasis and attenuates the progression of vascular dysfunction in Streptozotocin-induced diabetic rats

BACKGROUND

Glucose intolerance and cardiovascular complications are major symptoms in patients with diabetes. Many therapies have proven beneficial in treating diabetes in animals by protecting the cardiovascular system and increasing glucose utilization. In this study, we evaluated the effects of caffeic acid phenethyl amide (CAPA) on glucose homeostasis and vascular function in streptozotocin (STZ)-induced type 1 diabetic rats.

METHODS

Diabetes (blood glucose levels > 350 mg/dL), was induced in Wistar rats by a single intravenous injection of 60 mg/kg STZ. Hypoglycemic effects were then assessed in normal and type 1 diabetic rats. In addition, coronary blood flow in Langendorff-perfused hearts was evaluated in the presence or absence of nitric oxide synthase (NOS) inhibitor. The thoracic aorta was used to measure vascular response to phenylephrine. Finally, the effect of chronic treatment of CAPA and insulin on coronary artery flow and vascular response to phenylephrine were analyzed in diabetic rats.

RESULTS

Oral administration of 0.1 mg/kg CAPA decreased plasma glucose in normal (32.9 ± 2.3% decrease, P < 0.05) and diabetic rats (11.8 ± 5.5% decrease, P < 0.05). In normal and diabetic rat hearts, 1-10 μM CAPA increased coronary flow rate, and this increase was abolished by 10 μM NOS inhibitor. In the thoracic aorta, the concentration/response curve of phenylephrine was right-shifted by administration of 100 μM CAPA. Coronary flow rate was reduced to 7.2 ± 0.2 mL/min at 8 weeks after STZ-induction. However, 4 weeks of treatment with CAPA (3 mg/kg, intraperitoneal, twice daily) started at 4 weeks after STZ induction increased flow rate to 11.2 ± 0.5 mL/min (P < 0.05). In addition, the contractile response induced by 1 μM phenylephrine increased from 6.8 ± 0.6 mN to 11.4 ± 0.4 mN (P < 0.05) and 14.9 ± 1.4 mN (P < 0.05) by insulin (1 IU/kg, intraperitoneal) or CAPA treatment, respectively.

CONCLUSIONS

CAPA induced hypoglycemic activity, increased coronary blood flow and vascular response to phenylephrine in type 1 diabetic rats. The increase in coronary blood flow may result from endothelial NOS activation. However, the detailed cellular mechanisms need to be further evaluated.

Impact of postprandial glycaemia on health and prevention of disease

Postprandial glucose, together with related hyperinsulinemia and lipidaemia, has been implicated in the development of chronic metabolic diseases like obesity, type 2 diabetes mellitus (T2DM) and cardiovascular disease (CVD). In this review, available evidence is discussed on postprandial glucose in relation to body weight control, the development of oxidative stress, T2DM, and CVD and in maintaining optimal exercise and cognitive performance. There is mechanistic evidence linking postprandial glycaemia or glycaemic variability to the development of these conditions or in the impairment in cognitive and exercise performance. Nevertheless, postprandial glycaemia is interrelated with many other (risk) factors as well as to fasting glucose. In many studies, meal-related glycaemic response is not sufficiently characterized, or the methodology with respect to the description of food or meal composition, or the duration of the measurement of postprandial glycaemia is limited. It is evident that more randomized controlled dietary intervention trials using effective low vs. high glucose response diets are necessary in order to draw more definite conclusions on the role of postprandial glycaemia in relation to health and disease. Also of importance is the evaluation of the potential role of the time course of postprandial glycaemia.

Altered dipeptidyl peptidase-4 activity during the progression of hyperinsulinemic obesity and islet atrophy in spontaneously late-stage type 2 diabetic rats

Altered dipeptidyl peptidase-4 (DPP4) activity during the progression of late-stage type 2 diabetes was measured in Otsuka Long-Evans Tokushima fatty (OLETF) rats. Compared with OLETF rats subjected to 30% food restriction, food-satiated OLETF rats exhibited spontaneous hyperphagic obesity, insulin resistance, hyperglycemia, hyperinsulinemia, and increased plasma DPP4 activity during the early phase of the experiment (up to ∼30 wk). Subsequently, their plasma DPP4 activity as well as their body weight, body fat, and plasma insulin concentration declined to control levels during the late phase, resulting in excessive polyuria, proteinuria, dyslipidemia, pancreatic islet atrophy, hypoinsulinemia, and diabetes, which changed from insulin-resistant diabetes to hypoinsulinemic diabetes secondary to progressive islet insufficiency, and their fasting blood glucose level remained high. Since plasma DPP4 activity demonstrated significant positive correlations with body weight and the fasting plasma insulin level but not with the fasting blood glucose level during the late stage of diabetes, body fat and fasting plasma insulin levels may be useful factors for predicting the control of plasma DPP4 activity. In contrast, pancreatic DPP4 activity was significantly increased, and the expression of pancreatic insulin was significantly reduced in late-stage diabetic OLETF rats, suggesting that a relationship exists between the activation of pancreatic DPP4 and insulin depletion in pancreatic islet atrophy. In conclusion, it is suggested that plasma DPP4 activity changes in accordance with the progression of hyperinsulinemic obesity and pancreatic islet atrophy. DPP4 activity may play an important role in insulin homeostasis.

A population model evaluating the costs and benefits associated with different oral treatment strategies in people with type 2 diabetes

AIM

The attainment of near-normal glycaemia is an important feature in reducing complications in people with type 2 diabetes. Current treatment pathways advocate a failure-driven therapy algorithm for blood-glucose lowering that leads to the sequential addition of therapies. The addition and combination of multiple blood-glucose lowering agents may be associated with significant side effects, such as weight gain and hypoglycaemia, resulting in a detrimental quality of life. The objective of this study is to quantify the overall costs and quality-adjusted life years (QALY) associated with therapy escalation via oral only treatment strategies with different adverse event profiles as a function of target HbA1c achievement.

METHODS

A previously published model was adapted to run as a non-terminating simulation model. The model is designed to evaluate the cost utility of treatment strategies in a population of type 2 diabetes mellitus patients. Model outputs include incidence of micro- and macrovascular complications, hypoglycaemia and diabetes-specific and all-cause mortality.

RESULTS

The total number of vascular events predicted by the model varied little across the four treatment strategies because of the glycaemic profile associated with each therapy strategy being similar. The strategy with sequential addition of thiazolidinediones (TZDs) and sulphonylureas (SUs) to metformin (MF) was associated with greatest predicted hypoglycaemia burden. The addition of SU and dipeptidyl peptidase (DPP-4) inhibitors to MF was associated with the highest estimated QALYs.

CONCLUSIONS

A treatment strategy involving the sequential addition of SU and TZD to first-line MF therapy is associated with the lowest cost and lowest gain across a population, whereas addition of TZD and SU sequentially to first-line MF therapy resulted in the highest cost and incrementally less QALY gain when compared with treatment strategies involving the addition of a DPP-4 inhibitor and SU to first-line MF (irrespective of the treatment sequence) that were associated with both less cost and greatest QALY gain.

Cardiovascular prevention in type 2 diabetes mellitus patients: the role of oral glucose-lowering agents

Diabetes mellitus (DM) is a metabolic disorder that requires medical diagnosis and treatment. Type 2 DM is due to a combination of defective secretion of and responsiveness to insulin. In early stages, the predominant abnormality is reduced insulin sensitivity, and hyperglycemia can be reversed by a variety of measures and medications. In this stage, the cornerstone of glucose-lowering therapy is lifestyle modification, but when counseling does not adequately achieve the recommended glycemic targets, at least five classes of oral drugs are available. In general, alpha-glucosidase inhibitors delay carbohydrate absorption, metiglinides and sulfonylureas increase insulin supply, and biguanides and thiazolidinediones enhance insulin action. Given the high cardiovascular morbidity and mortality in type 2 DM patients, the attempt to reduce cardiovascular complications, beyond the glucose lowering itself, is an extremely relevant task. Indeed, the role of oral glucose-lowering agents concerning hyperglycemia reduction is defined; however, they have not clearly demonstrated to reduce micro- and macrovascular disease, and hitherto, no firm evidence favors one pharmacological treatment over another. The aim of this update is to describe the existing experiences with oral glucose-lowering agents for type 2 DM treatment with respect to cardiovascular prevention.

Discovery of DPP IV inhibitors by pharmacophore modeling and QSAR analysis followed by in silico screening

Dipeptidyl peptidase IV (DPP IV) deactivates the natural hypoglycemic incretin hormones. Inhibition of this enzyme should restore glucose homeostasis in diabetic patients making it an attractive target for the development of new antidiabetic drugs. With this in mind, the pharmacophoric space of DPP IV was explored using a set of 358 known inhibitors. Thereafter, genetic algorithm and multiple linear regression analysis were employed to select an optimal combination of pharmacophoric models and physicochemical descriptors that yield selfconsistent and predictive quantitative structure-activity relationships (QSAR) (r(2) (287)=0.74, F-statistic=44.5, r(2) (BS)=0.74, r(2) (LOO)=0.69, r(2) (PRESS) against 71 external testing inhibitors=0.51). Two orthogonal pharmacophores (of cross-correlation r(2)=0.23) emerged in the QSAR equation suggesting the existence of at least two distinct binding modes accessible to ligands within the DPP IV binding pocket. Docking experiments supported the binding modes suggested by QSAR/pharmacophore analyses. The validity of the QSAR equation and the associated pharmacophore models were established by the identification of new low-micromolar anti-DPP IV leads retrieved by in silico screening. One of our interesting potent anti-DPP IV hits is the fluoroquinolone gemifloxacin (IC(50)=1.12 muM). The fact that gemifloxacin was recently reported to potently inhibit the prodiabetic target glycogen synthase kinase 3beta (GSK-3beta) suggests that gemifloxacin is an excellent lead for the development of novel dual antidiabetic inhibitors against DPP IV and GSK-3beta.

Transplant-associated hyperglycemia

As patient survival after solid organ transplantation continues to improve, comorbidites associated with chronic hyperglycemia will assume increasing importance in limiting outcomes and quality of life. New-onset diabetes mellitus commonly occurs in the posttransplant setting and is associated with multiple complications including graft loss, cardiovascular disease, infection, and death. Furthermore, recent studies have begun to highlight the very high posttransplant prevalence and the significant cardiovascular implications of the prediabetic states of impaired fasting glucose and impaired glucose tolerance, indicating that the overall burden of transplantation-associated hyperglycemia is far greater than previously appreciated. Shared and distinct pathogenic factors and clinical repercussions exist among the organ-specific transplant scenarios. Diabetogenic immunosuppressive agents are common to all organ transplant settings, whereas glucose regulation is also strained by the restoration of failed hepatic and renal function. The atherogenic properties of hyperglycemia are particularly significant in the kidney transplant population, which has a marked predisposition to cardiovascular disease, whereas accelerated cardiac allograft vasculopathy and liver fibrosis have been associated with hyperglycemia in the heart and liver transplant settings, respectively. Aggressive screening will effectively detect transplant-associated hyperglycemia, whereas risk factor modification, lifestyle intervention and, where appropriate, drug therapy, may decrease its impact. Topics of future investigation should include the use of emerging diabetes therapies and avenues for the prevention and reversal of transplant-associated hyperglycemia.

The potential role of vildagliptin in the management and prevention of type 2 diabetes mellitus

Proper control of blood sugar in type 2 diabetes mellitus (T2DM) is not adequate till now in spite of use of well-planned dosage regimens containing oral hypoglycemic agents/insulin or both. Recently, the role of ‘incretins,’ particularly that of glucagon-like peptide-1 (GLP-1) in glucose homeostasis has been firmly established. The peptide (GLP-1) increases insulin secretion while decreasing that of glucagon in response to rise in plasma glucose in addition to delay of gastric emptying time, reduction of appetite, preservation of beta-cell function, and increase in beta-cell mass all of which will contribute toward lowering of blood sugar in T2DM. But the peptide hormone cannot be used orally as such because of its very short plasma half-life (2 min) and chemical nature, which needs continuous i.v. infusion or repeated s.c. or i.v. injections at short intervals. Hence, to prolong the duration of action of endogenous GLP-1, compounds have been synthesized which inhibit the enzyme dipeptidyl peptidase-4 (DPP-4), the enzyme responsible for metabolic degradation of GLP-1. One such compound is vildagliptin. In this article, an attempt has been made to compile some of the established recent advances in the therapeutic utility of vildagliptin along with a discussion about the physiological role of endogenous GLP-1 and its metabolism by DPP-4.

Pathophysiology and treatment of patients with type 2 diabetes exhibiting failure to oral drugs

It is generally accepted that a poor glycaemic control increases the risk for development of vascular complications in diabetic patients. This advocates for early introduction of insulin treatment in patients with type 2 diabetes exhibiting a secondary failure to oral treatment. This strategy is facilitated by introduction of long-acting insulin glargine and biphasic insulin aspart 70/30. The introduction of Glucagon-like peptide-1 (GLP-1) mimetics and dipeptidyl peptidase 4 (DPP-4) inhibitors in treatment of type 2 diabetes will however, to a large extent, influence therapeutic policy. Thus we suggest that DPP-4 inhibitors or long-acting GLP-1 mimetics will be used as either first-line therapy or as an early addition to metformin. The already generated results in animal and clinical studies suggest that these two classes of antidiabetic drugs may in addition to improving glycaemic control protect islet beta-cell mass and thereby postpone development of a secondary failure. When patients treated with metformin, sulfonylurea (SU), tiazolidinediones or a combination of these drugs fail, the GLP-1 mimectics may be preferred to insulin treatment. First, the risk of hypoglycaemia is less if not combined with SU. Secondly, the body weight is usually decreased while insulin treatment increases weight. Patients not responding to GLP-1 mimetics or experiencing significant side effects will be treated with insulin. Irrespective of the policy used for the drug treatment of type 2 diabetes, exercise and proper diet will remain important for optimization of metabolic control.

The physiology of glucagon-like peptide 1

Glucagon-like peptide 1 (GLP-1) is a 30-amino acid peptide hormone produced in the intestinal epithelial endocrine L-cells by differential processing of proglucagon, the gene which is expressed in these cells. The current knowledge regarding regulation of proglucagon gene expression in the gut and in the brain and mechanisms responsible for the posttranslational processing are reviewed. GLP-1 is released in response to meal intake, and the stimuli and molecular mechanisms involved are discussed. GLP-1 is extremely rapidly metabolized and inactivated by the enzyme dipeptidyl peptidase IV even before the hormone has left the gut, raising the possibility that the actions of GLP-1 are transmitted via sensory neurons in the intestine and the liver expressing the GLP-1 receptor. Because of this, it is important to distinguish between measurements of the intact hormone (responsible for endocrine actions) or the sum of the intact hormone and its metabolites, reflecting the total L-cell secretion and therefore also the possible neural actions. The main actions of GLP-1 are to stimulate insulin secretion (i.e., to act as an incretin hormone) and to inhibit glucagon secretion, thereby contributing to limit postprandial glucose excursions. It also inhibits gastrointestinal motility and secretion and thus acts as an enterogastrone and part of the "ileal brake" mechanism. GLP-1 also appears to be a physiological regulator of appetite and food intake. Because of these actions, GLP-1 or GLP-1 receptor agonists are currently being evaluated for the therapy of type 2 diabetes. Decreased secretion of GLP-1 may contribute to the development of obesity, and exaggerated secretion may be responsible for postprandial reactive hypoglycemia.

Metabolic syndrome and type 2 diabetes: can we stop the weight gain with diabetes?

Many patients with type 2 diabetes also have the metabolic syndrome with its cardinal features of central adiposity, insulin resistance, dyslipidemia, and hypertension. Although there is strong evidence for the importance of tight glycemic control in minimizing the microvascular complications of diabetes, many of the current therapies used for optimizing glycemic control also cause weight gain. With this treatment-induced weight gain, there is a risk of worsening the patient's insulin resistance. Physicians need to be aware of this vicious cycle in their overweight type 2 diabetic patients. This article reviews the strategies currently available to achieve glycemic control while at the same time minimizing weight gain and the associated complications.

Exenatide and rimonabant: new treatments that may be useful in the management of diabetes and obesity

Diabetes mellitus and obesity have become increasingly prevalent problems worldwide. Unfortunately, with traditionally prescribed glucose-lowering medications most individuals with diagnosed diabetes do not achieve and maintain adequate glycemic control over time; it may be even more challenging to lower blood glucose to an appropriate level without inducing a significant associated weight gain. Exenatide and rimonabant are recently developed agents that have demonstrated benefit in both glucose lowering and reduction of body weight. These medications may well prove to be attractive alternatives or additions to our more established diabetes therapies; however, these drugs have a side-effect profile that may limit their applicability to certain populations.

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.

3D-QSAR studies of Dipeptidyl peptidase IV inhibitors using a docking based alignment

Dipeptidyl peptidase IV (DPP-IV) deactivates the incretin hormones GLP-1 and GIP by cleaving the penultimate proline or alanine from the N-terminal (P1-position) of the peptide. Inhibition of this enzyme will prevent the degradation of the incretin hormones and maintain glucose homeostasis; this makes it an attractive target for the development of drugs for diabetes. This paper reports 3D-QSAR analysis of several DPP-IV inhibitors, which were aligned by the receptor-based technique. The conformation of the molecules in the active site was obtained through docking methods. The QSAR models were generated on two training sets composed of 74 and 25 molecules which included phenylalanine, thiazolidine, and fluorinated pyrrolidine analogs. The 3D-QSAR models are robust with statistically significant r(2), q(2), and r(pred)(2) values. The CoMFA and CoMSIA models were used to design some new inhibitors with several fold higher binding affinity.

The GLP-1 agonist exendin-4 reduces food intake in nonhuman primates through changes in meal size

Exendin-4 (Ex4), a long-acting glucagon-like peptide-1 (GLP-1) receptor agonist, has been shown to reduce food intake and suppress gastric emptying in rodents and humans. In this study we investigated the effects of peripheral administration of Ex4 on food intake and meal patterns in adult male rhesus macaques. Rhesus macaques (n = 4) that had been trained to lever press for food pellets were injected intramuscularly 15 min before the start of their 6-h daily feeding period. Ex4 was given at doses of 0.10, 0.32, 0.56, 1.0, and 3.0 microg/kg. Ex4 suppressed food intake in a dose-dependent manner, with the 3.0 microg/kg dose completely preventing feeding during the 6-h period and the 0.10 microg/kg dose suppressing intake by 17%. Doses of 0.32, 0.56, 1.0, and 3.0 microg/kg caused significant reductions in cumulative intake at all six hourly time points. Ex4 inhibited food intake through a specific effect on meal size. Meal size was significantly reduced in a dose-dependent manner with significant reductions at the 0.32 and 1.0 microg/kg doses (P < 0.05). Day 2 and 3 intakes returned to baseline levels with no compensation for Ex4-induced feeding suppression. Administration of doses of 0.32 and 0.56 microg/kg Ex4 over 5 consecutive days led to sustained reductions in intake with no evidence of compensation. Again, these reductions were due to specific effects on meal size. These results demonstrate that activation of GLP-1 pathways has potent effects on the controls of meal size and overall food intake in a nonhuman primate model.

Glucagon-like peptide-1 gene therapy in obese diabetic mice results in long-term cure of diabetes by improving insulin sensitivity and reducing hepatic gluconeogenesis

Long-term treatment with glucagon-like peptide (GLP)-1 or its analog can improve insulin sensitivity. However, continuous administration is required due to its short half-life. We hypothesized that continuous production of therapeutic levels of GLP-1 in vivo by a gene therapy strategy may remit hyperglycemia and maintain prolonged normoglycemia. We produced a recombinant adenovirus expressing GLP-1 (rAd-GLP-1) under the cytomegalovirus promoter, intravenously injected it into diabetic ob/ob mice, and investigated the effect of this treatment on remission of diabetes, as well as the mechanisms involved. rAd-GLP-1-treated diabetic ob/ob mice became normoglycemic 4 days after treatment, remained normoglycemic over 60 days, and had reduced body weight gain. Glucose tolerance tests found that exogenous glucose was cleared normally. rAd-GLP-1-treated diabetic ob/ob mice showed improved beta-cell function, evidenced by glucose-responsive insulin release, and increased insulin sensitivity, evidenced by improved insulin tolerance and increased insulin-stimulated glucose uptake in adipocytes. rAd-GLP-1 treatment increased basal levels of insulin receptor substrate (IRS)-1 in the liver and activation of IRS-1 and protein kinase C by insulin in liver and muscle; increased Akt activation was only observed in muscle. rAd-GLP-1 treatment reduced hepatic glucose production and hepatic expression of phosphoenolpyruvate carboxykinase, glucose-6-phosphatase, and fatty acid synthase in ob/ob mice. Taken together, these results show that a single administration of rAd-GLP-1 results in the long-term remission of diabetes in ob/ob mice by improving insulin sensitivity through restoration of insulin signaling and reducing hepatic gluconeogenesis.

Dipeptidyl peptidase-4 inhibitors and the management of type 2 diabetes mellitus

PURPOSE OF REVIEW

To review recent clinical trials of oral dipeptidyl peptidase-4 inhibitors and examine their role in managing type 2 diabetes mellitus.

RECENT FINDINGS

Oral dipeptidyl peptidase-4 inhibitors improve islet function by increasing alpha-cell and beta-cell responsiveness to glucose, resulting in improved glucose-dependent insulin secretion and reduced inappropriate glucagon secretion. These agents appear to have physiologically based antihyperglycemic effects and may modify the progressive nature of type 2 diabetes mellitus. In clinical trials sitagliptin and vildagliptin have modest demonstrated effectiveness, with clinically meaningful reductions of glycated hemoglobin when used as monotherapy. They appear promising in combination or added to ongoing therapy with other antidiabetic drugs (e.g. metformin, thiazolidinediones, or insulin). Dipetidyl peptidase-4 inhibitors themselves are not associated with hypoglycemia or weight gain and appear to have a benign safety profile.

SUMMARY

Oral dipeptidyl peptidase-4 inhibitors may prove valuable in the treatment of diabetes, given their effectiveness in reducing glycated hemoglobin with neutral weight effects and without the adverse events associated with other agents. Dipeptidyl peptidase-4 inhibitors appear to improve islet function and may modify the course of diabetes; this, however, must be confirmed with long-term controlled studies to demonstrate sustained glycemic control that translates into beta-cell preservation.

Activation of μ-opioid receptors improves insulin sensitivity in obese Zucker rats

In the current study we investigated the effect of mu-opioid receptor activation on insulin sensitivity. In obese Zucker rats, an intravenous injection of loperamide (18 microg/kg, three times daily for 3 days) decreased plasma glucose levels and the glucose-insulin index. Both effects of loperamide were subsequently inhibited by the administration of 10 microg/kg of naloxone or 10 microg/kg of naloxonazine, doses sufficient to block mu-opioid receptors. Other metabolic defects characteristic of obese Zucker rats, such as defects in insulin signaling, the decreased expression of insulin receptor substrate (IRS)-1, the p85 regulatory subunit of phosphatidylinositol 3-kinase (PI3 kinase), and the glucose transporter subtype 4 (GLUT 4), and the reduction of phosphorylation in IRS-1 or Akt serine, were also studied. These defects were all reversed by loperamide treatment in a dose which overcame mu-opioid receptor blockade. Moreover, loss of tolbutamide-induced plasma glucose lowering action (10 mg/kg) in wild-type mice given a fructose-rich diet was markedly delayed by repeated treatment with loperamide; however, this delay induced by loperamide did not occur in mu-opioid receptor knockout mice. These results indicate an important role of peripheral mu-opioid receptors in the loperamide-induced improvement of insulin sensitivity. Our results suggest that activation of peripheral mu-opioid receptors can ameliorate insulin resistance in animals, and provide a new target for therapy of insulin resistance.

Discovery of non-covalent dipeptidyl peptidase IV inhibitors which induce a conformational change in the active site

A series of non-covalent inhibitors of the serine protease dipeptidyl peptidase IV (DPP-IV) were found to adopt a U-shaped binding conformation in X-ray co-crystallization studies. Remarkably, Tyr547 undergoes a 70 degrees side-chain rotation to accommodate the inhibitor and allows access to a previously unexposed area of the protein backbone for hydrogen bonding.

Diabetes mellitus and heart failure: epidemiology, mechanisms, and pharmacotherapy

Diabetes mellitus and heart failure (HF), both of which are associated with high rates of adverse cardiovascular outcomes, commonly coexist. Given the marked increases in diabetes prevalence in developed countries, the proportion of the population with both conditions is likely to increase substantially. This article reviews the epidemiology of HF and diabetes, the mechanisms whereby diabetes causes HF, and the pharmacotherapy of both HF and diabetes. Specific challenges in treating patients with both HF and diabetes are also addressed.

Transplant-associated hyperglycemia: a new look at an old problem

New-onset diabetes has long been recognized as a common complication of kidney transplantation, promoting cardiovascular disease, death, and graft failure. Studies in recent years have begun to highlight the very high posttransplantation prevalence of the prediabetic states of impaired fasting glucose and impaired glucose tolerance and the significant repercussions of these states on cardiovascular health. Therefore, the overall burden of transplant-associated hyperglycemia (TAH), which encompasses new-onset diabetes and the prediabetic states, is far greater than previously appreciated. The kidney transplant population is predisposed to insulin resistance and to additional insults of hypertension and hyperlipidemia that, together with hyperglycemia, compose the metabolic syndrome and promote atherosclerosis. When recipients with an underlying, frequently nonmodifiable predisposition to glucose dysregulation encounter transplant-specific, often modifiable, diabetogenic exposures, TAH manifests. Aggressive screening will effectively detect TAH, whereas risk factor modification, lifestyle intervention, and, when appropriate, drug therapy may decrease its impact. Topics of future investigation should include the use of emerging diabetes therapies and avenues for the prevention and reversal of TAH.

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.

Inhaled human insulin ((insulin human [rDNA origin]) Inhalation Powder) in diabetes mellitus

Inhaled human insulin ((insulin human [rDNA origin]) Inhalation Powder) is a prandial insulin approved in the EU and the US for the treatment of adults with diabetes. Its glycaemic control is comparable to subcutaneous insulin in Type 1 and 2 diabetes, and has superior efficacy versus oral antidiabetic agents in Type 2 diabetes. Hypoglycaemia and mild-to-moderate cough are the main side effects. The treatment group differences in pulmonary function occur early, and are small, nonprogressive for up to 2 years and reversible following discontinuation. Patient-reported outcomes data displays higher diabetes treatment satisfaction, improvements in some quality-of-life scores, and treatment preference with inhaled human insulin versus traditional means. Availability of inhaled insulin may increase insulin acceptance and thus improve glycaemic control in patients with diabetes.