Incretin-based therapies for type 2 diabetes mellitus: current status and future prospects

Effect of sitagliptin on glucose control in type 2 diabetes mellitus after Roux-en-Y gastric bypass surgery

The present study was a 4-week randomized trial to assess the efficacy and safety of sitagliptin, a dipeptidyl-peptidase-4 inhibitor, in persistent or recurring type 2 diabetes after Roux-en-Y gastric bypass surgery (RYGB). Participants (n = 32) completed a mixed meal test (MMT) and self-monitoring of plasma glucose (SMPG) before and 4 weeks after randomization to either sitagliptin 100 mg daily or placebo daily. Questionnaires were administered to assess gastrointestinal discomfort. Outcome variables were glucose, active glucagon-like peptide-1 and β-cell function during the MMT, and glucose levels during SMPG. Age (56.3 ± 8.2 years), body mass index (34.4 ± 6.7 kg/m2 ), glycated haemoglobin (7.21 ± 0.77%), diabetes duration (12.9 ± 10.0 years), years since RYGB (5.6 ± 3.3 years) and β-cell function did not differ between the placebo and sitagliptin groups at pre-intervention. Sitagliptin was well tolerated, decreased postprandial glucose levels during the MMT (from 8.31 ± 1.92 mmol/L to 7.67 ± 1.59 mmol/L, P = 0.03) and mean SMPG levels, but had no effect on β-cell function. In patients with diabetes and mild hyperglycemia after RYGB, a short course of sitagliptin provided a small but significant glucose-lowering effect, with no identified improvement in β-cell function.

Consumption of Amaranth Induces the Accumulation of the Antioxidant Protein Paraoxonase/Arylesterase 1 and Modulates Dipeptidyl Peptidase IV Activity in Plasma of Streptozotocin-Induced Hyperglycemic Rats

BACKGROUND/AIM

Amaranth is a source of several bioactive compounds, among which peptides with inhibitory activity upon dipeptidyl peptidase IV (DPP-IV) have been reported. However, there is no information about the action of amaranth DPP-IV-inhibitory peptides using in vivo models. The aim of this work was to evaluate the effect of amaranth consumption on plasma and kidney DPP-IV activity as well the changes in plasma proteome profile of streptozotocin (STZ)-induced hyperglycemic rats.

METHODS

Rats were fed for 12 weeks with a diet containing 20% popped amaranth grain. Kidneys and blood samples were collected for lipid profile, DPP-IV activity and expression, and proteomic analysis.

RESULTS

Total cholesterol and DPP-IV activity in plasma was increased in hyperglycemic rats, but this effect was reverted by amaranth consumption. Triacylglycerols were increased in the hyperglycemic group fed amaranth, and the highest levels of high-density lipoproteins were also observed in this group. These data correlated with the accumulation of apolipoprotein A-II in plasma. Accumulation of the antioxidant protein paraoxonase/arylesterase 1 in STZ-induced hyperglycemic rats was observed when amaranth was supplied in the diet.

CONCLUSION

This study provides new insights into the molecular mechanisms by which amaranth exerts its beneficial health action in a hyperglycemic state.

Efficacy and safety of liraglutide, a once-daily human glucagon-like peptide-1 receptor agonist, in African-American people with Type 2 diabetes: a meta-analysis of sub-population data from seven phase III trials

AIM

To evaluate the efficacy and safety of the glucagon-like peptide-1 (GLP-1) receptor agonist liraglutide in African-American people with Type 2 diabetes.

METHODS

Analyses were performed on patient-level data from individuals self-defined as African-American or non-African-American in seven phase III studies. Endpoints included change in HbA_1c level, fasting plasma glucose level and body weight from baseline, proportion of patients reaching HbA_1c target [< 53 mmol/mol (< 7.0%)], and incidence of hypoglycaemia and nausea. Analyses used data obtained after 26 weeks. Within-population comparisons of liraglutide were performed vs placebo for African-American and non-African-American patient groups. In addition, between-population comparisons with non-African-American patients were performed for each treatment.

RESULTS

In African-American patients (n = 225), HbA_1c was significantly reduced at 26 weeks with liraglutide 1.2 and 1.8 mg (-11 and -14 mmol/mol, respectively compared with placebo; P < 0.0001). There were also significant reductions in fasting plasma glucose (-2.4 and -3.1 mmol/l, respectively, compared with placebo; P < 0.0001). Statistically significant reductions in body weight were observed with 1.8 mg liraglutide (-2.1 kg compared with placebo; P = 0.0056), but not with 1.2 mg liraglutide (-0.26 kg; P = 0.7307). The P value for interaction between treatment and race was significant for body weight (P = 0.0355). The incidence of non-severe hypoglycaemia with liraglutide was low (11-15% of patients), and < 25% of patients receiving liraglutide experienced nausea.

CONCLUSIONS

This meta-analysis suggests that liraglutide is well tolerated and efficacious for treatment of Type 2 diabetes in African-American patients, with an efficacy that was shown not to differ from that observed in non-African-American patients over 26 weeks.

Exenatide Alters Gene Expression of Neural Cell Adhesion Molecule (NCAM), Intercellular Cell Adhesion Molecule (ICAM), and Vascular Cell Adhesion Molecule (VCAM) in the Hippocampus of Type 2 Diabetic Model Mice

Background

Glucagon-like peptide-1 (GLP-1), a potent and selective agonist for the GLP-1 receptor, ameliorates the symptoms of diabetes through stimulation of insulin secretion. Exenatide is a potent and selective agonist for the GLP-1 receptor. Cell adhesion molecules are members of the immunoglobulin superfamily and are involved in synaptic rearrangements in the mature brain.

Material/Methods

The present study demonstrated the effects of exenatide treatment (0.1 μg/kg, subcutaneously, twice daily for 2 weeks) on the gene expression levels of cell adhesion molecules, neural cell adhesion molecule (NCAM), intercellular cell adhesion molecule (ICAM), and vascular cell adhesion molecule (VCAM) in the brain tissue of diabetic BALB/c male mice by real-time quantitative polymerase chain reaction (PCR). Diabetes was induced by streptozotocin/nicotinamide (STZ-NA) injection to male mice.

Results

The results of this study revealed that hippocampal gene expression of NCAM, ICAM, and VCAM were found to be up-regulated in STZ-NA-induced diabetic mice compared to those of controls. A significant decrease in the gene expression levels of NCAM, ICAM, and VCAM were determined after 2 weeks of exenatide administration.

Conclusions

Cell adhesion molecules may be involved in the molecular mechanism of diabetes. Exenatide has a strong beneficial action in managing diabetes induced by STZ/NA by altering gene expression of NCAM, ICAM, and VCAM.

Efficacy and safety of liraglutide, a once-daily human glucagon-like peptide-1 analogue, in Latino/Hispanic patients with type 2 diabetes: post hoc analysis of data from four phase III trials

The aim of the present analysis was to evaluate the efficacy of the glucagon-like peptide-1 receptor agonist liraglutide in Latino/Hispanic individuals with type 2 diabetes, in addition to comparing its treatment effects with those observed in non-Latino/Hispanic individuals. Analyses were performed on patient-level data from a subset of individuals self-defined as Latino/Hispanic from four phase III studies, the LEAD-3, LEAD-4, LEAD-6 and 1860-LIRA-DPP-4 trials. Endpoints included change in glycated haemoglobin (HbA1c) and body weight from baseline. In Latino/Hispanic patients (n = 505; 323 treated with liraglutide) after 26 weeks, mean HbA1c reductions were significantly greater with both liraglutide 1.2 and 1.8 mg versus comparator or placebo in the LEAD-3 and LEAD-4 studies, and with 1.8 mg liraglutide in the 1860-LIRA-DPP-4 trial. In LEAD-3 both doses led to significant differences in body weight change among Latino/Hispanic patients versus the comparator. With 1.8 mg liraglutide, difference in weight change was significant only in the 1860-LIRA-DPP-4 trial versus sitagliptin. For both endpoints Latino/Hispanic and non-Latino/Hispanic patients responded to liraglutide similarly. In summary, liraglutide is efficacious for treatment of type 2 diabetes in Latino/Hispanic patients, with a similar efficacy to that seen in non-Latino/Hispanic patients.

Exenatide enhances cognitive performance and upregulates neurotrophic factor gene expression levels in diabetic mice

Exenatide is a potent and selective agonist for the GLP-1 (glucagon-like peptide-1) receptor. Recent studies are focused on the effects of GLP-1 analogues on hippocampal neurogenesis, cognition, learning and memory functions. The aim of this study was to assess the effects of chronic exenatide treatment (0.1 μg/kg, s.c, twice daily for 2 weeks) on spatial memory functions by using the modified elevated plus maze (mEPM) test and emotional memory functions by using the passive avoidance (PA) test in streptozotocin/nicotinamide (STZ-NA)-induced diabetic mice. As the genes involved in neurite remodelling are among the primary targets of regulation, the effects of diabetes and chronic administration of exenatide on brain-derived neurotrophic factor (BDNF) and cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) messenger ribonucleic acid (mRNA) levels in the hippocampus of mice were also determined using quantitative real-time polymerase chain reaction (RT-PCR). This study revealed that in the mEPM and PA tests, type-2 diabetes-induced mice exhibited significant impairment of learning and memory which were ameliorated by GLP-1 receptor agonist exenatide. Quantitative RT-PCR revealed that CREB and BDNF gene expression levels were downregulated in diabetic mice, and these alterations were increased by exenatide treatment. Since, exenatide improves cognitive ability in STZ/NA-induced diabetic mice and activates molecular mechanisms of memory storage in response to a learning experience, it may be a candidate for alleviation of mood and cognitive disorder.

Glucagon-Like Peptide-1 Receptor Agonists for Type 2 Diabetes: A Clinical Update of Safety and Efficacy

INTRODUCTION

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are increasingly being used for the treatment of type 2 diabetes mellitus, but consideration of benefits and potential adverse events is required. This review examines the state of glycemic control, weight loss, blood pressure, and tolerability, as well as the current debate about the safety of GLP-1 RAs, including risk of pancreatitis, pancreatic cancer, and thyroid cancer.

METHODS

A MEDLINE search (2010-2015) identified publications that discussed longer-acting GLP-1 RAs. Search terms included GLP-1 receptor agonists, liraglutide, exenatide, lixisenatide, semaglutide, dulaglutide, albiglutide, efficacy, safety, pancreatitis, pancreatic cancer, and thyroid cancer. Abstracts from the American Diabetes Association, European Association for the Study of Diabetes, and American Association of Clinical Endocrinologists from 2010 to 2015 were also searched. Efficacy and safety studies, pooled analyses, and meta-analyses were prioritized.

RESULTS

Research has confirmed that GLP-1 RAs provide robust glycemic control, weight loss, and blood pressure re-duction. Current studies do not prove increased risk of pancreatitis, pancreatic cancer, or thyroid cancer but more trials are needed since publications that indicate safety or suggest increased risk have methodological flaws that prevent firm conclusions to be drawn about these rare, long-term events.

CONCLUSION

GLP-1 RA therapy in the context of individualized, patient-centered care continues to be supported by current literature. GLP-1 RA therapy provides robust glycemic control, blood pressure reduction, and weight loss, but studies are still needed to address concerns about tolerability and safety, including pancreatitis and cancer.

Dulaglutide: an evidence-based review of its potential in the treatment of type 2 diabetes

Introduction

As the prevalence of type 2 diabetes mellitus (T2DM) is anticipated to continue to rise worldwide, so too are the treatment options also continuing to expand. Current guidelines recommend individualized treatment plans which allow for provider choice and diversity of pharmacotherapeutic regimens. The glucagon-like peptide-1 receptor agonist (GLP-1 RA) class is rapidly expanding, with dulaglutide (Trulicity™) as a once-weekly agent recently approved.

Aims

This article examines the evidence currently available on the efficacy and safety of dulaglutide for use in T2DM.

Evidence review

Dulaglutide has been shown to have similar efficacy and safety to other newer GLP-1 RAs, and better glycemic control than placebo. It lowers glycated hemoglobin (A_1c), fasting and postprandial glucose levels, and promotes weight loss when used as first-, second-, or third-line therapy. It has also been shown to improve β-cell function and provide cardiovascular benefits, such as lower blood pressure and improved lipid levels. Dulaglutide also has a low risk for hypoglycemia and a similar adverse effect profile to other GLP-1 RAs in the class, with transient gastrointestinal problems and potential risk for pancreatitis.

Place in therapy

While long-term data on safety and efficacy are forthcoming, dulaglutide is positioned to be placed at the same level as other GLP-1 RAs in the class: as second-line therapy in addition to diet and exercise in those patients who cannot achieve glycemic control on monotherapy metformin. It may also be useful as first-line therapy instead of metformin.

Conclusion

Dulaglutide is a once-weekly GLP-1 RA approved for the treatment of T2DM that has shown similar efficacy to other agents in this class.

An updated review on cancer risk associated with incretin mimetics and enhancers

Incretin-based therapies, including the use of incretin mimetics of glucagon-like peptide-1 receptor (GLP-1R) agonists and incretin enhancers of dipeptidyl-peptidase 4 (DPP-4) inhibitors, are widely used by clinicians for glucose lowering in patients with type 2 diabetes mellitus. These agents have benefits of a lower risk of hypoglycemia, being neutral for body weight for DPP-4 inhibitors and having a potential for weight reduction with GLP-1R agonists. They may also have a neutral or beneficial cardiovascular effect. Despite these benefits, an increased risk of cancer (especially pancreatic cancer and thyroid cancer) associated with incretin-based therapies has been reported. In this article, we reviewed related literature of experimental animal and observational human studies, clinical trials, and meta-analyses published until December 15, 2014. Current studies suggested a probable role of GLP-1R activation on the development of pancreatic cancer and thyroid cancer in rodents, but such an effect in humans is not remarkable due to the lower or lack of expression of GLP-1R on human pancreatic ductal cells and thyroid tissues. Findings in human studies are controversial and inconclusive. In the analyses of the US Food and Drug Administration adverse events reporting system, a significantly higher risk of pancreatic cancer was observed for GLP-1R agonists and DPP-4 inhibitors, but a significantly higher risk of thyroid cancer was only observed for GLP-1R agonists. Such a higher risk of pancreatic cancer or thyroid cancer could not be similarly demonstrated in other human observational studies or analyses of data from clinical trials. With regards to cancers other than pancreatic cancer and thyroid cancer, available studies supported a neutral association in humans. Some preliminary studies even suggested a potentially beneficial effect on the development of other cancers with the use of incretins. Based on current evidence, continuous monitoring of the cancer issues related to incretin-based therapies is required, even though the benefits may outweigh the potential cancer risk in the general patients with type 2 diabetes mellitus.

Exendin-4 promotes endothelial barrier enhancement via PKA- and Epac1-dependent Rac1 activation

Among emerging antidiabetic agents, glucagon-like peptide-1 (GLP-1)-based therapies carry special cardiovascular implications, exerting both direct and indirect effects. The control of vascular permeability is of pivotal importance in vascular pathologies. The objective of the present study was to determine the effect of GLP-1 on endothelial barrier function and assess the underlying mechanism(s). Here we show for the first time that the stable GLP-1 analog exendin-4 attenuated the leakage of subcutaneous blood vessels in mice indexed by dye extravasation caused by injections of thrombin. Moreover, in cultured endothelial cells, exendin-4 significantly prevented the thrombin-induced FITC-dextran permeability of endothelial monolayers via GLP-1 receptor. Immunofluorescence microscopy reveals that exendin-4 abrogates detrimental effects of thrombin on VE-cadherin and the F-actin cytoskeleton, with decreased stress fiber and gap formation. Importantly, exendin-4 reduced thrombin-induced tyrosine phosphorylation of VE-cadherin at Y731 and Y658. Moreover, small GTPase Rac1 was significantly activated as a result of exendin-4 treatment. The efficacy of exendin-4 to counteract the barrier-compromising effect of thrombin was blunted when Rac1 was inactivated by Rac1 inhibitor NSC-23766. Inhibition of PKA activity or small-interfering RNA for exchange protein directly activated by cAMP 1 (Epac1) decreased exendin-4-induced Rac1 activation and barrier enhancement, indicating the participation of both PKA and Epac1 in the barrier-stabilizing effect of exendin-4 elicited on thrombin-impaired barrier function. Thus, our findings have uncovered an unpredicted role for exendin-4 in the coordination of vascular permeability and clarified the molecular underpinnings that contribute to barrier restoration initiated by exendin-4.

Acute effects of pistachio consumption on glucose and insulin, satiety hormones and endothelial function in the metabolic syndrome

BACKGROUND/OBJECTIVE

Nut consumption has been found to decrease risk of coronary heart disease and diabetes and to promote healthy body weights possibly related to their favorable macronutrient profile. We therefore assessed the effect of pistachios on postprandial glucose and insulin levels, gut hormones related to satiety and endothelial function.

SUBJECTS/METHODS

In this randomized crossover study, 20 subjects with metabolic syndrome consumed five study meals over 5-10 weeks. The meals differed in fat type and quantity, but were matched according to available carbohydrates (CHOs). Three meals had 50 g available CHO: white bread (WB50g), white bread, butter and cheese (WB+B+Ch) and white bread and pistachios (WB+P). Two meals had 12 g available CHO: white bread (WB12g) and pistachios (P).

RESULTS

Within each group of available CHO meals, postprandial glucose levels were the highest following the white bread-only meals, and glucose response was significantly attenuated when butter and cheese or pistachios were consumed (P<0.05). Postprandial insulin levels were highest after the WB+B+Ch meal (P<0.05), but did not differ between the white bread-only and pistachio meals. Both endothelial function (reactive hyperemia index) and arterial stiffness (augmentation index) significantly increased after the white bread-only meals compared with the WB+B+Ch meal (all P<0.05). Insulin secretagogue levels were higher when butter and cheese or pistachios were consumed than when white bread only was consumed (P<0.05).

CONCLUSIONS

Compared with white bread, pistachio consumption reduced postprandial glycemia, increased glucagon-like-peptide levels and may have insulin-sparing properties. These effects could be beneficial for individuals with diabetes and metabolic syndrome.

A comparative study of the effects of a dipeptidyl peptidase-IV inhibitor and sulfonylurea on glucose variability in patients with type 2 diabetes with inadequate glycemic control on metformin

BACKGROUND

This study aimed to compare the effects of sitagliptin on glycemic change and 24-h blood glucose variability with those of the sulfonylurea glimepiride.

SUBJECTS AND METHODS

A 4-week randomized double blind-labeled prospective design was used. We recruited 33 patients who had been treated with metformin for at least 2 months. Each participant prescribed with metformin was randomly assigned to either the sitagliptin (100 mg) or the glimepiride (2 mg) group. Continuous glucose monitoring (CGM) was used to monitor glycemic changes for 3 successive days in both groups at baseline and at the 4-week follow-up. Glycemic changes and glucose variability were obtained using CGM, and these data were averaged over all subjects.

RESULTS

The comparison of glycated hemoglobin (HbA1c) between baseline and the 4-week follow-up showed that HbA1c was significantly reduced in the sitagliptin group (7.0 ± 0.5% to 6.6 ± 0.4%, P<0.001) and the glimepiride group (7.3 ± 0.4% to 6.9 ± 0.4%, P<0.001). The sitagliptin and glimepiride groups had similar HbA1c levels after 4 weeks, and there were no significant differences between the two groups. The mean amplitude of glycemic excursions (MAGE) decreased significantly in the sitagliptin group (4.9 ± 1.0 to 3.7 ± 0.9 mmol/L, P<0.001), but no significant difference was observed in the glimepiride group (5.7 ± 1.5 to 5.0 ± 1.4 mmol/L, P=0.175). The SD and oxidative stress markers did not differ significantly between the two groups.

CONCLUSIONS

When sitagliptin was combined with metformin, the patients showed much more efficient blood glucose controlling effects, not only the three indexes of fasting blood glucose, postprandial blood glucose, and glycated hemoglobin, but also MAGE.

Population pharmacodynamic modeling of exenatide after 2-week treatment in STZ/NA diabetic rats

The purpose of this study is to investigate the effect of exenatide on glycemic control following two administration routes in a streptozotocin/nicotinamide (STZ/NA)-induced diabetic rat model, and to develop a pharmacodynamic model to better understand the disease progression and the action of exenatide in this experimental system. Two groups of STZ/NA-induced diabetic rats were treated for 2 weeks with 20 (μg/kg/day) of exenatide, either by continuous subcutaneous (SC) infusion or two SC injections daily. Disease progression was associated with slower glucose utilization. Fasting blood glucose was significantly reduced by 30 mg/dL in both treatment groups at the end of 2 weeks. A subsequent intravenous glucose tolerance test (IVGTT) confirmed an improved glucose tolerance in both treatment groups; however, overall glycemic control was similar between groups, likely due to the relatively low and short-term drug exposure. A population indirect response model was successfully developed to simultaneously describe the STZ/NA-induced disease progression, responses to an IVGTT, and exenatide effects on these systemic challenges. The unified model includes a single set of parameters, and the cumulative area under the drug-receptor concentration curve was used as a unique driving force to account for systemic effects long after drug elimination.

The GLP-1 receptor agonist liraglutide inhibits progression of vascular disease via effects on atherogenesis, plaque stability and endothelial function in an ApoE(-/-) mouse model

Liraglutide, a once-daily glucagon-like peptide-1 receptor (GLP-1R) agonist, has been approved as a new treatment for type 2 diabetes and is the subject of a clinical trial programme to evaluate the effects on cardiovascular disease and safety. The current study aimed to determine the in vivo effect of liraglutide on progression of atherosclerotic vascular disease in the apolipoprotein E-deficient (ApoE(-/-)) mouse model and identify underlying mechanisms responsible. Liraglutide treatment inhibited progression of early onset, low-burden atherosclerotic disease in a partially GLP-1R-dependent manner in the ApoE(-/-) mouse model. In addition, liraglutide treatment inhibited progression of atherosclerotic plaque formation and enhanced plaque stability, again in a partially GLP-1R-dependent manner. No significant effect of liraglutide on progression of late onset, high-burden atherosclerotic disease was observed. In addition, no significant endothelial cell dysfunction was identified in ApoE(-/-) mice with early onset, low-burden atherosclerotic disease, although significant prevention of weight gain was observed in liraglutide-treated mice using this dietary protocol. Taken together, these results suggest a potential role for liraglutide in the prevention and stabilisation of atherosclerotic vascular disease together with possible protection against major cardiovascular events.

Postprandial dysmetabolism and the heart

Epidemiologic evidence indicates that abnormal elevations in glycemia and lipidemia after a meal, termed postprandial dysmetabolism, are linked with increased risk of morbidity and mortality due to cardiovascular disease in individuals with or without type 2 diabetes. Both postprandial hyperglycemia and postprandial hyperlipidemia are independently associated with deteriorating endothelial function and vascular damage, which are likely mediated by increased oxidative stress and are more pronounced when both derangements coexist. Pharmacotherapies that target postprandial hyperglycemia and/or postprandial dyslipidemia are likely to improve endothelial function, which may have positive implications for cardiovascular outcomes.

A continued saga of Boc5, the first non-peptidic glucagon-like peptide-1 receptor agonist with in vivo activities

Glucagon-like peptide-1 (GLP-1)-based therapy presents a promising option for treating type 2 diabetes. However, there are several limitations relative to the peptidic GLP-1 mimetics currently on the market or under development. This concern has led to a continued interest in the search for non-peptidic agonists for GLP-1 receptor (GLP-1R). Here, we briefly review the discovery, characterization and current status of a novel class of cyclobutane-derivative-based non-peptidic agonists for GLP-1R, including Boc5 and its newly discovered analogue WB4-24. Although the oral bioavailability of such compounds still poses great challenges, the progress made so far encourages us to identify a truly 'druggable' small molecule agonist for GLP-1R.

Special considerations with insulin therapy in older adults with diabetes mellitus

Aging is associated with alterations in insulin secretion and action. However, aging per se does not alter the pharmacokinetics of commercially available insulin and its analogues. Insulin therapy in older adults is complicated by psychosocial and physiological changes of aging. Several new insulin and insulin analogue preparations are now available for clinical use. Used as prandial (e.g. insulin lispro, insulin aspart or insulin glulisine) and basal insulin (e.g. insulin glargine, insulin detemir), these analogues simulate physiological insulin profiles more closely than the older conventional insulins. The availability of multiple insulin products provides new opportunities to achieve control of diabetes mellitus. The choice of initial insulin therapy can be made based on blood glucose profiles. Overall, these profiles can be divided into three general patterns that include: (i) round-the-clock hyperglycaemia; (ii) fasting hyperglycaemia with daytime euglycaemia; and (iii) daytime hyperglycaemia with normal fasting blood glucose levels. The prescription of insulin is a dynamic process, and the insulin regimen should be adjusted based on individual response. The goal of diabetes care in older adults is to enhance quality of life without subjecting individuals to complicated treatment regimens that may interfere with their independence in carrying out daily activities.

Pharmacokinetic/pharmacodynamic modeling of GLP-1 in healthy rats

PURPOSE

To provide a mechanism-based model to quantitatively describe GLP-1 pharmacokinetics (PK) and pharmacodynamics (PD) in rats.

METHODS

Intravenous (IV), infusion (IF), subcutaneous (SC), and intraperitoneal (IP) doses of GLP-1 were administered after glucose challenge in healthy Sprague-Dawley rats. Blood was analyzed for GLP-1, glucose, and insulin. The PK-PD modeling was performed with ADAPT 5. The concentration-response curve was generated and analyzed in comparison with other incretin-related therapeutics.

RESULTS

The PK of GLP-1 was described using a two-compartment model with a zero-order input accounting for endogenous GLP-1 synthesis. For SC and IP dosing, sequential zero-order and first-order absorption models reasonably described the rapid absorption process and flip-flop kinetics. In dynamics, GLP-1 showed insulinotropic effects (3-fold increase) after IV glucose challenge in a dose-dependent manner. The concentration-response curve was bell-shaped, which was captured using a biphasic two-binding site Adair model. Receptor binding of GLP-1 exhibited high capacity and low affinity kinetics for both binding sites (K(D) = 9.94 × 10(3) pM, K(2) = 1.56 × 10(-4) pM(-1)).

CONCLUSIONS

The PK of GLP-1 was linear and bi-exponential and its PD showed glucose-dependent insulinotropic effects. All profiles were captured by the present mechanistic model and the dynamic analysis yields several implications for incretin-related therapies.

Administration of an acylated GLP-1 and GIP preparation provides added beneficial glucose-lowering and insulinotropic actions over single incretins in mice with Type 2 diabetes and obesity

The present study examined the glucose-lowering and insulinotropic properties of acylated GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide) peptides in Type 2 diabetes and obesity. GLP-1, GIP, Liraglutide, N-AcGIP(Lys(37)Myr) (N-acetylGIP with myristic acid conjugated at Lys(37)), a simple combination of both peptides and a Lira-AcGIP preparation [overnight preparation of Liraglutide and N-AcGIP(Lys(37)Myr)] were incubated with DPP-IV (dipeptidyl peptidase-IV) to assess peptide stability, and BRIN-BD11 cells were used to evaluate cAMP production and insulin secretion. Acute glucose-lowering and insulinotropic actions were evaluated in Swiss TO mice. Subchronic studies on glucose homoeostasis, insulin secretion, food intake and bodyweight were evaluated in ob/ob mice. Liraglutide, N-AcGIP(Lys(37)Myr), a simple combination of both peptides and the Lira-AcGIP preparation demonstrated improved DPP-IV resistance (P<0.001), while stimulating cAMP production and insulin secretion (1.4-2-fold; P<0.001). The Lira-AcGIP preparation was more potent at lowering plasma glucose (20-51% reduction; P<0.05-P<0.001) and stimulating insulin secretion (1.5-1.8-fold; P<0.05-P<0.001) compared with Liraglutide and N-AcGIP(Lys(37)Myr) or a simple peptide combination. Daily administration of the Lira-AcGIP preparation to ob/ob mice lowered bodyweight (7-9%; P<0.05), food intake (23%; P<0.05) and plasma glucose (46% reduction; P<0.001), while increasing plasma insulin (1.5-1.6-fold; P<0.001). The Lira-AcGIP preparation enhanced glucose tolerance, insulin response to glucose and insulin content (P<0.05-P<0.001). These findings demonstrate that a combined preparation of the acylated GLP-1 and GIP peptides Liraglutide and N-AcGIP(Lys(37)Myr) markedly improved glucose-lowering and insulinotropic properties in diabetic obesity compared with either incretin mimetic given individually.

Tolerability of dipeptidyl peptidase-4 inhibitors: a review

BACKGROUND

Oral glucose-lowering agents are used to treat patients with type 2 diabetes mellitus (T2DM). Most patients require multiple agents to maintain glycemic targets. Dipeptidyl peptidase-4 (DPP-4) inhibitors are administered as monotherapy and in combination therapy for the treatment of T2DM.

OBJECTIVE

The aim of this article was to provide a thorough review of published tolerability data on 5 DPP-4 inhibitors.

METHODS

PubMed and Web of Science were searched for English-language clinical trials published from January 2000 to June 2001, using the following key words: dipeptidyl peptidase-4 inhibitor, vildagliptin, alogliptin, sitagliptin, saxagliptin, linagliptin, safety, tolerability, efficacy, effect, AE, and adverse effect. Studies were considered for inclusion if they were randomized, double-blind trials performed in patients ≥18 years of age with T2DM and with a hemoglobin A(1c) of ≥6.5%; included ≥1 arm that received monotherapy with DPP-4; and reported adverse events (AEs). Studies in patients with a history of type 1 or secondary forms of diabetes, significant diabetic complications or cardiovascular disease within the 6 months before the start of the study, hepatic disease or abnormalities, and/or renal abnormalities were excluded.

RESULTS

A total of 45 clinical trials, 5 pharmacokinetic studies, and 28 meta-analyses or reviews were included. The duration of studies ranged from 7 days to 104 weeks. The most commonly reported AEs were nasopharyngitis, upper respiratory infections, all-cause infections, headache, gastrointestinal symptoms, and musculoskeletal pain. Based on the findings from the studies, the DPP-4 inhibitors had minimal impact on weight and were not associated with an increased risk for hypoglycemia relative to placebo. Rates of nasopharyngitis were higher with the DDP-4 inhibitors than with placebo. Pancreatitis was reported at lower rates with the DPP-4 inhibitors compared with other oral antihyperglycemic agents. Cardiovascular events were limited, and postmarketing studies are ongoing.

CONCLUSIONS

The tolerability of DPP-4 inhibitors is supported by published clinical trials. The rates of weight gain, gastrointestinal AEs, and hypoglycemia were minimal with the DPP-4 inhibitors studied.

Emerging therapeutic approaches for the management of diabetes mellitus and macrovascular complications

Type 2 diabetes mellitus (DM) affects an estimated 25.8 million people in the United States and is the 7th leading cause of death. While effective therapy can prevent or delay the complications that are associated with diabetes, according to the Center for Disease Control, 35% of Americans with DM are undiagnosed, and another 79 million Americans have blood glucose levels that greatly increase their risk of developing DM in the next several years. One of the Healthy People 2020 goals is to reduce the disease and economic burden of DM and improve the quality of life for all persons who have, or are at risk for, DM. Achieving this goal requires a concentrated focus on improving the management of diabetes and in targeting prevention of macrovascular complications. This article reviews established and emerging therapeutic approaches for managing DM and prevention of macrovascular complications.

Administration of a dipeptidyl peptidase IV inhibitor enhances the intestinal adaptation in a mouse model of short bowel syndrome

BACKGROUND

Glucagon-like peptide-2 induces small intestine mucosal epithelial cell proliferation and may have benefit for patients who suffer from short bowel syndrome. However, glucagon-like peptide-2 is inactivated rapidly in vivo by dipeptidyl peptidase IV. Therefore, we hypothesized that selectively inhibiting dipeptidyl peptidase IV would prolong the circulating life of glucagon-like peptide-2 and lead to increased intestinal adaptation after development of short bowel syndrome.

METHODS

Eight-week old C57BL/6J mice underwent a 50% proximal small bowel resection and were treated with either sitagliptin, a dipeptidyl peptidase IV-inhibitor, starting 1 day before surgery versus placebo. The efficacy of dipeptidyl peptidase IV-inhibitor was assessed 3 days after resection, including intestinal morphology, epithelial cell apoptosis, and epithelial cell proliferation. Adaptive mechanisms were assessed with quantitative real-time polymerase chain reaction, and plasma bioactive glucagon-like peptide-2 was measured by radioimmunoassay.

RESULTS

Body weight loss and peripheral blood glucose levels did not change compared with short bowel syndrome controls. Dipeptidyl peptidase IV-inhibitor treatment led to significant increases in villus height and crypt depth. Dipeptidyl peptidase IV-inhibitor treatment did not change EC apoptosis rates significantly, but it did increase crypt epithelial cell proliferation significantly versus placebo-short bowel syndrome controls. Dipeptidyl peptidase IV-inhibitor treatment markedly increased messenger RNA expression of β-catenin and c-myc in ileal mucosa. Plasma glucagon-like peptide-2 levels increased significantly (∼ 40.9%) in dipeptidyl peptidase IV-inhibitor short bowel syndrome mice.

CONCLUSION

Dipeptidyl peptidase IV-inhibitor treatment increased short bowel syndrome adaptation and might potentially be useful for short bowel syndrome patients.

From theory to clinical practice in the use of GLP-1 receptor agonists and DPP-4 inhibitors therapy

Promoting long-term adherence to lifestyle modification and choice of antidiabetic agent with low hypoglycemia risk profile and positive weight profile could be the most effective strategy in achieving sustained glycemic control and in reducing comorbidities. From this perspective, vast interest has been generated by glucagon-like peptide-1 (GLP-1) receptor agonists and dipeptidyl peptidase-4 inhibitors (DPP-4i). In this review our ten-year clinical and laboratory experience by in vitro and in vivo studies is reported. Herein, we reviewed available data on the efficacy and safety profile of GLP-1 receptor agonists and DPP-4i. The introduction of incretin hormone-based therapies represents a novel therapeutic strategy, because these drugs not only improve glycemia with minimal risk of hypoglycemia but also have other extraglycemic beneficial effects. In clinical studies, both GLP-1 receptor agonists and DPP-4i, improve β cell function indexes. All these agents showed trophic effects on beta-cell mass in animal studies. The use of these drugs is associated with positive or neucral effect on body weight and improvements in blood pressure, diabetic dyslipidemia, hepatic steazosis markets, and myocardial function. These effects have the potential to reduce the burden of cardiovascular disease, which is a major cause of mortality in patients with diabetes.

Sitagliptin or exenatide once weekly for type 2 diabetes: comparison of the clinical trials

INTRODUCTION

There is a need for new and improved treatments for type 2 diabetes. Glucagon-like peptide 1 (GLP-1) is a gut hormone that stimulates insulin secretion and the levels of GLP-1 can be increased by inhibiting DPP-4. Sitagliptin is one of the DDP-4 inhibitors used to increase the levels of GLP-1. Exenatide is an agonist at the GLP-1 receptors, which is resistant to breakdown and has a longer action than GLP-1.

AREAS COVERED

This review compares the clinical trials of sitagliptin and exenatide once weekly in the treatment of type 2 diabetes. Only peer-reviewed trials listed on PubMed were included.

EXPERT OPINION

Both sitagliptin and exenatide once weekly are capable of reducing HbA1c and plasma glucose levels, but exenatide once weekly is more potent than sitagliptin and this may lead to different roles for these agents in the treatment of type 2 diabetes.

Therapy in the early stage: incretins

The complex pathological mechanisms responsible for development of type 2 diabetes are not fully addressed by conventional drugs, which are also associated with inconvenient side effects such as weight gain or hypoglycemia. Two types of incretin-based therapies are now in use: incretin mimetics (glucagon-like peptide-1 [GLP-1] receptor agonists that bind specific receptors and mimic the action of natural GLP-1) and incretin enhancers (inhibitors of the enzyme that degrade the incretin hormones and thus prolong their activity). Both offer important advantages over previous agents. In addition to the proven glucose-lowering efficacy, they promote weight loss (or are weight neutral) by slowing gastric emptying and inducing satiety, inhibit glucagon secretion with maintenance of counterregulatory mechanisms, and exhibit cardiovascular benefits, while having a low risk profile. Importantly, short-term studies have shown that incretins/incretin-based therapies protect β-cells (by enhancing cell proliferation and differentiation and inhibiting apoptosis) and stimulate their function (by recruiting β-cells to the secretory process and increasing insulin biosynthesis/secretion). These therapies have the opportunity to interfere with the disease progression if used as an early intervention, when enough β-cell mass/function can still be preserved or restored.

Effects of increasing doses of glucagon-like peptide-1 on insulin-releasing phases during intravenous glucose administration in mice

The increase in insulin secretion caused by glucagon-like peptide-1 (GLP-1) and GLP-1 mimetics observed during an intravenous glucose test (IVGTT) has been reported in both normal and disease animal models, as well as in humans. In this study, a hierarchical population modeling approach is used, together with a previously reported model relating glucose to insulin appearance, to determine quantitative in vivo dose-response relationships between GLP-1 dose level and both first- and second-phase insulin release. Parameters of the insulin kinetic model were estimated from the complete set of glucose and insulin data collected in 219 anesthetized nonfasted NMR-imaged mice after intravenous injection of glucose (1 g/kg) alone or with GLP-1 (0.03-100 nmol/kg). The resulting dose-response curves indicate a difference in GLP-1 effect on the two release phases, as is also evident from the different ED(50) parameter values (0.107 vs. 6.65 nmol/kg for phase 1 vs. phase 2 insulin release parameters). The first phase of insulin release is gradually augmented with increasing GLP-1 dose, reaching saturation at a dose of ~1 nmol/kg, while the second-phase release changes more abruptly at GLP-1 doses between 3 and 10 nmol/kg and shows a more pronounced 100-fold increase between control and the high GLP-1 dose of 100 nmol/kg Moreover, separate disposition indices calculated for phase 1 and 2 insulin release, show a different pattern of increase with increasing GLP-1 dose.

Whey proteins as source of dipeptidyl dipeptidase IV (dipeptidyl peptidase-4) inhibitors

Preclinical and clinical studies suggest that whey proteins can reduce postprandial glucose levels and stimulate insulin release in healthy subjects and in subjects with type 2 diabetes by reducing dipeptidyl peptidase-4 (DPP-4) activity in the proximal bowel and hence increasing intact incretin levels. Our aim was to identify DPP-4 inhibitors among short peptides occurring in hydrolysates of β-lactoglobulin, the major whey protein found in the milk of ruminants. We proved that the bioactive peptide Ile-Pro-Ala can be regarded as a moderate DPP-4 inhibitor.

A GLP-1 receptor agonist liraglutide inhibits endothelial cell dysfunction and vascular adhesion molecule expression in an ApoE-/- mouse model

The glucagon like peptide-1 receptor (GLP-1R) agonist liraglutide attenuates induction of plasminogen activator inhibitor type-1 (PAI-1) and vascular adhesion molecule (VAM) expression in human vascular endothelial cells (hVECs) in vitro and may afford protection against endothelial cell dysfunction (ECD), an early abnormality in diabetic vascular disease. Our study aimed to establish the dependence of the in vitro effects of liraglutide on the GLP-1R and characterise its in vivo effects in a mouse model of ECD. In vitro studies utilised the human vascular endothelial cell line C11-STH and enzyme-linked immunosorbent assays (ELISA) for determination of PAI-1 and VAM expression. In vivo studies of vascular reactivity and immunohistochemical analysis were performed in the ApoE(-/-) mouse model. In vitro studies demonstrated GLP-1R-dependent liraglutide-mediated inhibition of stimulated PAI-1 and VAM expression. In vivo studies demonstrated significant improvement in endothelial function in liraglutide treated mice, a GLP-1R dependent effect. Liraglutide treatment also increased endothelial nitric oxide synthase (eNOS) and reduced intercellular adhesion molecule-1 (ICAM-1) expression in aortic endothelium, an effect again dependent on the GLP-1R. Together these studies identify in vivo protection, by the GLP-1R agonist liraglutide, against ECD and provide a potential molecular mechanism responsible for these effects.

Dipeptidyl peptidase IV inhibitor sitagliptin reduces local inflammation in adipose tissue and in pancreatic islets of obese mice

Adipose tissue inflammation and reduced pancreatic β-cell function are key issues in the development of cardiovascular disease and progressive metabolic dysfunction in type 2 diabetes mellitus. The aim of this study was to determine the effect of the DPP IV inhibitor sitagliptin on adipose tissue and pancreatic islet inflammation in a diet-induced obesity model. C57Bl/6J mice were placed on a high-fat (60% kcal fat) diet for 12 wk, with or without sitagliptin (4 g/kg) as a food admix. Sitagliptin significantly reduced fasting blood glucose by 21% as well as insulin by ∼25%. Sitagliptin treatment reduced body weight without changes in overall body mass index or in the epididymal and retroperitoneal fat mass. However, sitagliptin treatment led to triple the number of small adipocytes despite reducing the number of the very large adipocytes. Sitagliptin significantly reduced inflammation in the adipose tissue and pancreatic islet. Macrophage infiltration in adipose tissue evaluated by immunostaining for Mac2 was reduced by sitagliptin (P < 0.01), as was the percentage of CD11b+/F4/80+ cells in the stromal vascular fraction (P < 0.02). Sitagliptin also reduced adipocyte mRNA expression of inflammatory genes, including IL-6, TNFα, IL-12(p35), and IL-12(p40), 2.5- to fivefold as well as 12-lipoxygenase protein expression. Pancreatic islets were isolated from animals after treatments. Sitagliptin significantly reduced mRNA expression of the following inflammatory cytokines: MCP-1 (3.3-fold), IL-6 (2-fold), IL-12(p40) (2.2-fold), IL-12(p35) (5-fold, P < 0.01), and IP-10 (2-fold). Collectively, the results indicate that sitagliptin has anti-inflammatory effects in adipose tissue and in pancreatic islets that accompany the insulinotropic effect.