The role of GLP-1 in the life and death of pancreatic beta cells

The health benefits of dietary short-chain fatty acids in metabolic diseases

Short-chain fatty acids (SCFAs) are a subset of fatty acids that play crucial roles in maintaining normal physiology and developing metabolic diseases, such as obesity, diabetes, cardiovascular disease, and liver disease. Even though dairy products and vegetable oils are the direct dietary sources of SCFAs, their quantities are highly restricted. SCFAs are produced indirectly through microbial fermentation of fibers. The biological roles of SCFAs in human health and metabolic diseases are mainly due to their receptors, GPR41 and GPR43, FFAR2 and FFAR3. Additionally, it has been demonstrated that SCFAs modulate DNMTs and HDAC activities, inhibit NF-κB-STAT signaling, and regulate G(i/o)βγ-PLC-PKC-PTEN signaling and PPARγ-UCP2-AMPK autophagic signaling, thus mitigating metabolic diseases. Recent studies have uncovered that SCFAs play crucial roles in epigenetic modifications of DNAs, RNAs, and post-translational modifications of proteins, which are critical regulators of metabolic health and diseases. At the same time, dietary recommendations for the purpose of SCFAs have been proposed. The objective of the review is to summarize the most recent research on the role of dietary SCFAs in metabolic diseases, especially the signal transduction of SCFAs in metabolic diseases and their functional efficacy in different backgrounds and models of metabolic diseases, at the same time, to provide dietary and nutritional recommendations for using SCFAs as food ingredients to prevent metabolic diseases.

Regulation of dietary fiber on intestinal microorganisms and its effects on animal health

The animal gut harbors diverse microbes that play an essential role in the well-being of their host. Specific diets, such as those rich in dietary fiber, are vital in disease prevention and treatment because they affect intestinal flora and have a positive impact on the metabolism, immunity, and intestinal function of the host. Dietary fiber can provide energy to colonic epithelial cells, regulate the structure and metabolism of intestinal flora, promote the production of intestinal mucosa, stimulate intestinal motility, improve glycemic and lipid responses, and regulate the digestion and absorption of nutrients, which is mainly attributed to short-chain fatty acids (SCFA), which is the metabolite of dietary fiber. By binding with G protein-coupled receptors (including GPR41, GPR43 and GPR109A) and inhibiting the activity of histone deacetylases, SCFA regulate appetite and glucolipid metabolism, promote the function of the intestinal barrier, alleviate oxidative stress, suppress inflammation, and maintain immune system homeostasis. This paper reviews the physicochemical properties of dietary fiber, the interaction between dietary fiber and intestinal microorganisms, the role of dietary fiber in maintaining intestinal health, and the function of SCFA, the metabolite of dietary fiber, in inhibiting inflammation. Furthermore, we consider the effects of dietary fiber on the intestinal health of pigs, the reproduction and lactation performance of sows, and the growth performance and meat quality of pigs.

Norlignans as potent GLP-1 secretagogues from the fruits of Amomum villosum

The dried fruit of Amomum villosum (Amomi Fructus) is an important spices and traditional Chinese medicine. In this study, the EtOH extract of Amomi Fructus was revealed with hypoglycemic effects on db/db mice by increasing plasma insulin levels. After extracted with EtOAc, the EtOAc fraction showed increased activity in stimulating glucagon-like peptide-1 (GLP-1) secretion compared with the EtOH extract. In order to clarify the antidiabetic constituents, four undescribed norlignans, amovillosumins A‒D, were isolated from the EtOAc fraction, and the subsequent chiral resolution yielded three pairs of enantiomers. Their structures were determined by extensive spectroscopic data (1D and 2D NMR, HRESIMS, IR, UV and [α]_D) and ECD calculations. Amovillosumins A and B significantly stimulated GLP-1 secretion by 375.1% and 222.7% at 25.0 μM, and 166.9% and 62.7% at 12.5 μM, representing a new type of GLP-1 secretagogues.

Long-Term Diabetes Improvement After Duodenal Exclusion in Zucker Diabetic Fatty Rats Is Associated with Prevention of Strain-Specific Pancreatic Remodeling and Increased Beta Cell Proliferation

Background

Response to metabolic surgery is heterogeneous and the metabolic states that underpin weight loss and metabolic improvement are still unclear. In this study, we investigate parameters of post-bariatric fasting glucoregulation and leverage artificial intelligence-assisted whole-slide image analyses to characterize associated immunohistologic features of the pancreas.

Materials and Methods

We performed either loop duodeno-jejunostomy (DJOS) with exclusion of 1/3 of total intestinal length, loop duodeno-ileostomy with exclusion of 2/3 of total intestinal length (DiOS), or a sham operation on 8-week-old male obese ZDF rats. Six months post-operative, we measured blood metabolites and hormones. Subsequently, pancreatic and intestinal tissue was removed, formalin fixed, and paraffin embedded. Immunohistologic (IHC) analyses included proliferating cell nuclear antigen (PCNA) to visualize the proliferation fraction and pancreatic and duodenal homeobox 1 (PDX 1) as a measure of pancreatic cell differentiation. For IHC quantification, all slides were digitalized and analyzed using QuPath. All analyzed slides were reviewed by two independent pathologists for correctness.

Results

DJOS and DiOS were associated with preserved fasting insulin production compared to sham. Histopathologic evaluation showed significantly higher numbers of beta cells and specifically of clustered cell organization in DJOS and DiOS compared to sham. Cell proliferation (PCNA) was significantly elevated in DJOS and DiOS compared to sham.

Conclusion

In this interventional model of bariatric surgery in severe genetic diabetes, we demonstrate post-operative histologic and immunohistologic features of the pancreas associated with improved fasting glucose homeostasis.

Graphical abstract

Short Chain Fatty Acids, pancreatic dysfunction and type 2 diabetes

The microbiota living in gut influence the immune response, metabolism, mood and behavior. The diet plays a pivotal role in maintaining healthy gut microbiota composition and its fermentation leads to production of Short Chain Fatty Acids (SCFAs) mainly acetate, propionate and butyrate. During pancreatic dysfunction, insulin mediated suppression of glucagon is impaired leading to uncontrolled glucose production by liver and state of hyperglycemia. Insulin and glucagon balance is as important as insulin sensitivity which is reduced during Type 2 Diabetes (T2D). Glucagon like peptide-1 (GLP1) produced by Intestinal epithelial cells regulates insulin and glucagon secretion directly via GLP1 receptor on pancreatic cells or via nervous system. But half-life period of GLP1 is very short i.e. about 2 min, after which it is cleaved and inactivated. SCFAs are well documented to induce GLP1 but its direct effect on pancreatic dysfunction has not been reported. This review opens a new avenue to study the role of SCFAs as treatment to pancreatic dysfunction and T2D.

Common Channel Length in Bypass Surgery Does Not Impact T2DM in Diabetic Zucker Rats

INTRODUCTION

Metabolic surgery is known to impact glucose tolerance but the exact mechanism is still unclear. Based on recently-published data, especially the role of the hindgut may require redefinition.

METHODS

Either a loop duodeno-jejunostomy (DJOS) with exclusion of one third of total intestinal length, a loop duodeno-ileostomy (DiOS, exclusion of two thirds), or SHAM operation was performed in 9-week-old Zucker diabetic fatty rats. One, 3, and 6 months after surgery, an oral glucose tolerance test (OGTT) and glucose-stimulated hormone analyses were conducted. Body weight was documented weekly.

RESULTS

DJOS and DiOS animals showed significantly better glucose control in all OGTTs than the SHAM group (two-way ANOVA p < 0.0001). Body weight developed largely parallel in both intervention groups; SHAM animals had gained significantly less weight after 6 months (Mann-Whitney DJOS/DiOS vs. SHAM p < 0.05, DJOS vs. DiOS p > 0.05). Operative interventions had no impact on GLP-1 and GIP levels at any time point (Mann-Whitney p > 0.05 for all). DJOS/DiOS operations could preserve insulin production up to 6 months, while there was already a sharp decline of insulin levels in the SHAM group (Mann-Whitney: DJOS/DiOS vs. SHAM p < 0.05 for all time points). Additionally, insulin sensitivity was improved significantly 1 month postoperative in both intervention groups compared to SHAM (Mann-Whitney DJOS/DiOS vs. SHAM p < 0.05).

CONCLUSION

The data of the current study demonstrate a sharp amelioration of glucose control after duodenal exclusion with unchanged levels of GLP-1 and GIP. Direct or delayed hindgut stimulation had no impact on glucose control in our model.

Efficacy and Safety of the Dipeptidyl Peptidase-4 Inhibitor Sitagliptin on Atherosclerosis, β-Cell Function, and Glycemic Control in Japanese Patients with Type 2 Diabetes Mellitus Who are Treatment Naïve or Poorly Responsive to Antidiabetes Agents: A Multicenter, Prospective Observational, Uncontrolled Study

BACKGROUND

Sitagliptin, a dipeptidyl peptidase-4 inhibitor, is widely used in patients with type 2 diabetes. However, the pleiotropic effects of sitagliptin is not well understood.

OBJECTIVE

To assess the clinical efficacy and safety of sitagliptin on atherosclerosis, β-cell function, and glycemic control in Japanese patients with type 2 diabetes.

METHODS

A prospective observational study of 270 patients with type 2 diabetes mellitus was carried out. Patients (aged 64.3 [12.4] years, body mas index 25.2 [4.3]) with glycated hemoglobin >6.9% (52 mmol/mol) or fasting plasma glucose >130 mg/dL were treated with sitagliptin for 12 months. The primary end point was glycated hemoglobin level changes from baseline to 3 months. The secondary end points included changes in several biomarkers related to inflammation and β-cell function from baseline to 3 months, as well as changes in glycated hemoglobin level from baseline to 12 months.

RESULTS

Glycated hemoglobin levels were significantly lower in patients treated with sitagliptin for 3 months than at baseline (8.1% [1.4%]-7.3% [1.2%]) (65 [16.9]-56 [13.1] mmol/mol]) (P < 0.0001), which continued after 12 months (7.4% [1.3%]) (56 [15.2] mmol/mol) (P < 0.0001). In addition, a marker of vascular-specific inflammation, pentraxin-3, and a marker of β-cell function (proinsulin/insulin ratio), respectively, were lower after treatment with sitagliptin for 3 months than at baseline (1.88 [0.78]-1.65 [0.63] ng/mL [P = 0.0038] and 0.20 [0.14]-0.17 [0.11] [P = 0.01], respectively). On the other hand, a biomarker reflecting whole body inflammation; that is, high-sensitivity C-reactive protein level, was unchanged. Adverse events occurred in 14 patients (5.18%).

CONCLUSIONS

Sitagliptin may have beneficial effects on vascular inflammation and β-cell function in Japanese patients with type 2 diabetes. Pentraxin-3 may be an early predictive marker for detecting the antiatherosclerotic effects of dipeptidyl peptidase-4.

Diabetes: Rationale for Dipeptidyl Peptidase 4 Inhibitors: A New Class of Oral Agents for the Treatment of Type 2 Diabetes Mellitus

Objective:

To review advances in understanding the pathophysiologic basis of type 2 diabetes mellitus and the pharmacology and mechanism of action of dipeptidyl peptidase 4 (DPP-4) inhibition in correcting the underlying defects in glycemic control.

Data Sources:

Articles were identified through MEDLINE for the period 1966 through November 2006. Abstracts and presentations from the American Diabetes Association Scientific Sessions and the European Association for the Study of Diabetes (2002–2006) were also searched for scientific reports on DPP-4 inhibitors.

Study Selection And Data Extraction:

Abstracts, original clinical and preclinical research reports, and review articles published in the English language were identified for review. Literature discussing glucose regulation, incretin hormones, type 2 diabetes pathophysiology, and DPP-4 inhibition were evaluated and selected based on consideration of their support for the proof of concept, mechanistic and in vivo findings, and timeliness.

Data Synthesis:

The search for new and effective therapies for type 2 diabetes has led to the identification of a novel therapeutic target, the incretin hormones, which play a role in mediating glucose homeostasis via effects on glucagon and insulin secretion from pancreatic islet α- and β-cells, respectively. The incretins' glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide are rapidly inactivated by the enzyme DPP-4. DPP-4 inhibitor agents act by blocking the active site of DPP-4, thereby preventing inactivation of and prolonging the duration of action of incretins, which in turn helps to correct the defective insulin and glucagon secretion that marks type 2 diabetes. Clinical studies to date indicate that DPP-4 inhibitors effectively stimulate insulin secretion, suppress glucagon release, and improve glucose control in patients with type 2 diabetes. These agents are well tolerated and have a low incidence of adverse effects.

Conclusions:

The DPP-4 inhibitors are novel agents for the treatment of type 2 diabetes. Compounds under development in this new class of oral antidiabetic drugs may be free of the limitations of current therapies.

Review: Inhibition of dipeptidyl peptidase-4 with vildagliptin: a potential new treatment for type 2 diabetes

Type 2 diabetes mellitus is a growing problem in most parts of the world. There is now good evidence that controlling hyperglycaemia can help prevent many of the serious complications associated with the disease. Despite this evidence and the availability of several classes of oral antidiabetic agents and insulin, many people with diabetes do not achieve adequate glycaemic control (i.e. HbA1C< 6.5 or 7.0%). Thus, there is an urgent unmet medical need to develop new and better treatments for type 2 diabetes. Among the most promising new classes of drugs for type 2 diabetes are those that leverage the incretin hormone glucagon-like peptide-1 (GLP-1). Vildagliptin, an orally available, potent and specific inhibitor of dipeptidyl peptidase-4 (DPP-4), the enzyme that rapidly inactivates GLP-1, augments endogenous active GLP-1 and gastric inhibitory polypeptide/glucose-dependent insulinotropic polypeptide (GIP) and reduces hyperglycaemia in patients with type 2 diabetes. Studies to date in patients exposed for up to one year indicate that vildagliptin produces clinically significant reductions in HbA1C when used as monotherapy and in combination with metformin, glimepiride, or insulin. In general, the drug has proved to be well tolerated with low rates of hypoglycaemia and gastrointestinal side effects (including nausea) and no weight gain or oedema.

Sitagliptin/metformin fixed-dose combination in type 2 diabetes mellitus: an evidence-based review of its place in therapy

Type 2 diabetes mellitus is a progressive disease associated with significant morbidity and mortality. There is good evidence showing that intensive glycemic control reduces the development and progression of complications. In order to achieve glycemic targets, patients often require a combination of oral therapy and/or insulin in addition to lifestyle modification. Unfortunately, many of the traditional therapies for type 2 diabetes are associated with weight gain and hypoglycemia, resulting in poor compliance and subsequent worsening of glycemic control. The dipeptidyl peptidase-4 inhibitor sitagliptin is a therapy for type 2 diabetes and is available as a fixed-dose combination with metformin. Phase III clinical trials have demonstrated beneficial effects on glycemic control and minimal untoward effects with this combination. In this article, we provide an overview of the pharmacology, efficacy, and safety and examine the role of this combination within current practice.

Food protein-derived bioactive peptides in management of type 2 diabetes

BACKGROUND

Type 2 diabetes (T2D), one of the major common human health problems, is growing at an alarming rate around the globe. Alpha-glucosidase and dipeptidyl peptidase IV (DPP-IV) enzymes play a significant role in development of T2D. Hence, reduction or inhibition of their activity can be one of the important strategies in management of T2D. Studies in the field of bioactive peptides have shown that dietary proteins could be natural source of alpha-glucosidase and DPP-IV inhibitory peptides.

PURPOSE

The purpose of this review is to provide an overview of food protein-derived peptides as potential inhibitors of alpha-glucosidase and DPP-IV with major focus on milk proteins.

METHODS

Efforts have been made to review the available information in literature on the relationship between food protein-derived peptides and T2D. This review summarizes the current data on alpha-glucosidase and dipeptidyl peptidase IV inhibitory bioactive peptides derived from proteins and examines the potential value of these peptides in the treatment and prevention of T2D. In addition, the proposed modes of inhibition of peptide inhibitors are also discussed.

RESULTS

Studies revealed that milk and other food proteins-derived bioactive peptides play a vital role in controlling T2D through several mechanisms, such as the satiety response, regulation of incretin hormones, insulinemia levels, and reducing the activity of carbohydrate degrading digestive enzymes.

CONCLUSIONS

The bioactive peptides could be used in prevention and management of T2D through functional foods or nutraceutical supplements. Further clinical trials are necessary to validate the findings of in vitro studies and to confirm the efficiency of these peptides for applications.

Effects of Dulaglutide on Thyroid C Cells and Serum Calcitonin in Male Monkeys

Glucagon-like peptide-1 (GLP-1) receptor agonists, used for the treatment of type 2 diabetes, have caused hyperplasia/neoplasia of thyroid C cells in rodent carcinogenicity studies. Studies in monkeys have not identified an effect of GLP-1 receptor agonists on thyroid C cells; however, group sizes were small. Dulaglutide is a once-weekly, long-acting human GLP-1 receptor agonist recently approved in the United States and the European Union. The objective of this study was to determine whether dulaglutide altered C-cell mass in monkeys. Male cynomolgus monkeys (20 per group) were sc injected with dulaglutide 8.15 mg/kg (∼500-fold maximum human plasma exposure) or a vehicle control twice weekly for 52 weeks. Basal and calcium gluconate-stimulated serum calcitonin concentrations were obtained at 3, 6, 9, and 12 months. Thyroid glands were weighed, fixed, and sectioned at 500-μm intervals. C-cell volumes were measured using an automated image analysis. C-cell proliferation was estimated using Ki67/calcitonin colabeling and cell counting. Administration of dulaglutide 8.15 mg/kg twice weekly for 52 weeks did not increase serum calcitonin in monkeys or affect thyroid weight, histology, C-cell proliferation, or absolute/relative C-cell volume. This study represents a comprehensive evaluation of the monkey thyroid C cells after dosing with a GLP-1 receptor agonist, with a large group size, and measurement of multiple relevant parameters. The lack of effect of dulaglutide on C cells is consistent with other studies in monkeys using GLP-1 receptor agonists and suggests that nonhuman primates are less sensitive than rodents to the induction of proliferative changes in thyroid C cells by GLP-1 receptor agonists.

Screening of randomly mutagenized glucagon-like peptide-1 library by using an integrated yeast-mammalian assay system

Glucagon-like peptide-1 (GLP1) is a 30-amino acid peptide hormone activating the GLP1 receptor (GLP1R), a class B G-protein coupled receptor (GPCR), and is considered to be effective for treating diabetes and other metabolic diseases. Phage display is the first innovative technology in order to prepare and screen a large polypeptide library including GLP1R agonists, but this methodology is not as effective in discovering functional peptides such as activators for GPCRs. Here, we report a novel functional screening system for GPCR-acting peptides, which integrates a yeast peptide secretion system into a biological detection system with GPCR-producing mammalian cells. Using this screening system, we found attractive GLP1R agonists with several substitutions from a random mutant GLP1 library which was secreted by yeast, Saccharomyces cerevisiae. This system established here not only enables peptides to be analyzed in the soluble form but also needs no chemical synthesis, purification, and condensation of peptides of interests, and therefore, can be widely applied to the discovery of novel bioactive peptides acting on GPCRs.

Absence of glucagon and insulin action reveals a role for the GLP-1 receptor in endogenous glucose production

The absence of insulin results in oscillating hyperglycemia and ketoacidosis in type 1 diabetes. Remarkably, mice genetically deficient in the glucagon receptor (Gcgr) are refractory to the pathophysiological symptoms of insulin deficiency, and therefore, studies interrogating this unique model may uncover metabolic regulatory mechanisms that are independent of insulin. A significant feature of Gcgr-null mice is the high circulating concentrations of GLP-1. Hence, the objective of this report was to investigate potential noninsulinotropic roles of GLP-1 in mice where GCGR signaling is inactivated. For these studies, pancreatic β-cells were chemically destroyed by streptozotocin (STZ) in Gcgr(-/-):Glp-1r(-/-) mice and in Glp-1r(-/-) animals that were subsequently treated with a high-affinity GCGR antagonist antibody that recapitulates the physiological state of Gcgr ablation. Loss of GLP-1 action substantially worsened nonfasting glucose concentrations and glucose tolerance in mice deficient in, and undergoing pharmacological inhibition of, the GCGR. Further, lack of the Glp-1r in STZ-treated Gcgr(-/-) mice elevated rates of endogenous glucose production, likely accounting for the differences in glucose homeostasis. These results support the emerging hypothesis that non-β-cell actions of GLP-1 analogs may improve metabolic control in patients with insulinopenic diabetes.

TAK-875, a GPR40/FFAR1 agonist, in combination with metformin prevents progression of diabetes and β-cell dysfunction in Zucker diabetic fatty rats

BACKGROUND AND PURPOSE

TAK-875, a selective GPCR40/free fatty acid receptor 1 agonist, improves glycaemic control by increasing glucose-dependent insulin secretion. Metformin is a first-line drug for treatment of type 2 diabetes that improves peripheral insulin resistance. Based on complementary mechanism of action, combining these agents is expected to enhance glycaemic control. Here, we evaluated the chronic effects of TAK-875 monotherapy and combination therapy with metformin in diabetic rats.

EXPERIMENTAL APPROACH

Long-term effects on glycaemic control and β-cell function were evaluated using Zucker diabetic fatty (ZDF) rats, which develop diabetes with hyperlipidaemia and progressive β-cell dysfunction.

KEY RESULTS

Single doses of TAK-875 (3-10 mg·kg(-1) ) and metformin (50-150 mg·kg(-1) ) significantly improved both postprandial and fasting hyperglycaemia, and additive improvements were observed in their combination. Six-week treatment with TAK-875 (10 mg·kg(-1) , b.i.d.) significantly decreased glycosylated Hb (GHb) by 1.7%, and the effect was additively enhanced by combination with metformin (50 mg·kg(-1) , q.d.; GHb: -2.4%). This improvement in glycaemic control in the combination group was accompanied by significant 3.2-fold increase in fasting plasma insulin levels. Pancreatic insulin content was maintained at a level comparable to that in normal rats by combination treatment (vehicle: 26, combination: 67.1; normal lean: 69.1 ng·mg(-1) pancreas) without affecting pancreatic glucagon content. Immunohistochemical analyses revealed normal morphology, enhanced pancreas duodenum homeobox-1 expression and increased PCNA-positive cells in islets of the combination group.

CONCLUSION AND IMPLICATIONS

Our results indicate that combination therapy with TAK-875 and metformin could be a valuable strategy for glycaemic control and β-cell preservation in type 2 diabetes.

DPP-4 inhibition and islet function

During recent years, dipeptidyl peptidase‐4 (DPP‐4) inhibition has been included in the clinical management of type 2 diabetes, both as monotherapy and as add‐on to several other therapies. DPP‐4 inhibition prevents the inactivation of the incretin hormones, glucose‐dependent insulinotropic polypeptide (GIP) and glucagon‐like peptide‐1 (GLP‐1). This results in stimulation of insulin secretion and inhibition of glucagon secretion, and there is also a potential β‐cell preservation effect, as judged from rodent studies; that is, it might target the key islet dysfunction in the disease. In type 2 diabetes. This reduces 24‐h glucose levels and reduces HbA_1c by ≈ 0.8–1.1% from baseline levels of 7.7–8.5%. DPP‐4 inhibition is safe, with a very low risk for adverse events including hypoglycemia, and it prevents weight gain. The present review summarizes the studies on the influence of DPP‐4 inhibition on islet function. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2011.00184.x, 2012)

Diabetes drugs and neurological disorders: new views and therapeutic possibilities

Type 2 diabetes is a metabolic disease characterised by insulin resistance with hyperglycaemia and dyslipidaemia. It is associated with increased risk of stroke and vascular dementia, and might contribute to the development of Alzheimer's disease. Recent studies have shown that several antidiabetic drugs can promote neuronal survival and lead to a significant clinical improvement of memory and cognition in different clinical settings. We discuss these emerging data, with a focus on metformin, thiazolidinediones, and the more recently developed compounds targeting the glucagon-like peptide-1 receptor. Data show that these antidiabetic drugs affect brain metabolism, neuroinflammation, and regeneration. Evidence thus far strongly indicates that these antidiabetic drugs could be developed as disease-modifying therapies for human brain diseases in patients with and without diabetes.

Insulin plus incretin: A glucose-lowering strategy for type 2-diabetes

There are many advantages of combining incretin therapy [glucagon-like peptide-1 (GLP-1) receptor agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors] with insulin therapy as a glucose-lowering strategy in type 2 diabetes. One important advantage is the complementary mode of the mechanistic action of incretin and insulin therapy. Another advantage is the reduction in risk of hypoglycemia and weight gain when adding incretin therapy to insulin. Several clinical trials have studied the addition of GLP-1 receptor agonists [exenatide BID (twice daily), lixisenatide, albiglutide] or DPP-4 inhibitors (vildagliptin, sitagliptin, saxagliptin, alogliptin, linagliptin) to ongoing insulin therapy or adding insulin to ongoing therapy with a GLP-1 receptor agonist (liraglutide). These studies show improved glycemia in the presence of limited risk for hypoglycemia and weight gain with the combination of incretin therapy with insulin. This article reviews the background and clinical studies on this combination.

Pathogenesis and management of postprandial hyperglycemia: role of incretin-based therapies

Postprandial plasma glucose concentrations are an important contributor to glycemic control. There is evidence suggesting that postprandial hyperglycemia may be an independent risk factor for cardiovascular disease. Glucagon-like peptide-1 (GLP-1) receptor agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors are antidiabetic agents that predominantly reduce postprandial plasma glucose levels. DPP-4 inhibitors are associated with fewer gastrointestinal side effects than GLP-1 receptor agonists and are administered orally, unlike GLP-1 analogs, which are administered as subcutaneous injections. GLP-1 receptor agonists are somewhat more effective than DPP-4 inhibitors in reducing postprandial plasma glucose and are usually associated with significant weight loss. For these reasons, GLP-1 receptor agonists are generally preferred over DPP-4 inhibitors as part of combination treatment regimens in patients with glycated hemoglobin levels above 8.0%. This article reviews the pathogenesis of postprandial hyperglycemia, the mechanisms by which GLP-1 receptor agonists and DPP-4 inhibitors reduce postprandial plasma glucose concentrations, and the results of recent clinical trials (ie, published 2008 to October 2012) that evaluated the effects of these agents on postprandial plasma glucose levels when evaluated as monotherapy compared with placebo or as add-on therapy to metformin, a sulfonylurea, or insulin. Findings from recent clinical studies suggest that both GLP-1 receptor agonists and DPP-4 inhibitors could become valuable treatment options for optimizing glycemic control in patients unable to achieve glycated hemoglobin goals on basal insulin, with the added benefits of weight loss and a low risk of hypoglycemia.

Combination therapy with DPP-4 inhibitors and insulin in patients with type 2 diabetes mellitus: what is the evidence?

As type 2 diabetes mellitus (T2DM) progresses, most patients will require insulin replacement therapy. Whether oral antidiabetic drug (OAD) therapy should be retained when initiating insulin is still debated. While the rationale to keep metformin with insulin is strong (mostly as an insulin-sparing agent to limit weight gain), the evidence is less clear for other OADs. In particular, the question now comes up what the expected benefit could be of combining the newer agents, such as the dipeptidyl peptidase-4 (DPP-4) inhibitors with insulin. Additionally, when metformin is no longer a treatment option, as in the case of patients with severe renal impairment, insulin is often used as monotherapy, with little evidence of benefit in maintaining other OADs. In this specific situation, it is also of interest to evaluate the potential benefit of combined treatment with a DPP-4 inhibitor and insulin. Among the classic limitations of insulin therapy in patients with T2DM, hypoglycemia remains a major barrier to glycemic control, along with weight gain exacerbation. The oral DPP-4 inhibitors improve glycemic control by increasing the sensitivity of the islet cells to glucose, and thus are not associated with an increased risk for hypoglycemia and are weight neutral. In addition to the expected benefits associated with limiting insulin dose and regimen complexity, the specific advantages the DPP-4 inhibitor drug class on hypoglycemia and weight gain could justify combining DPP-4 inhibitors with insulin; additionally, a DPP-4 inhibitor may be of special value to decrease glycemic excursions that are not properly addressed by basal insulin therapy and metformin use, even after optimizing titration of the basal insulin. However, given the common original perception that treatment with DPP-4 inhibitors may be less beneficial with increasing disease progression because of the loss of β-cell function, the potential relevance of these agents in the setting of advanced T2DM treated with insulin was not necessarily anticipated. Promising data from studies on the use of these new agents in insulin-treated patients with T2DM have started to emerge. Our article provides a comprehensive overview of the currently available evidence from controlled randomized clinical trials and we discuss the potential role of DPP-4 inhibitors in the this setting. Further clinical experience will allow to fully assess the positioning of these agents in insulin-treated T2DM populations.

Predictive clinical parameters and glycemic efficacy of vildagliptin treatment in korean subjects with type 2 diabetes

BACKGROUND

The aims of this study are to investigate the glycemic efficacy and predictive parameters of vildagliptin therapy in Korean subjects with type 2 diabetes.

METHODS

In this retrospective study, we retrieved data for subjects who were on twice-daily 50 mg vildagliptin for at least 6 months, and classified the subjects into five treatment groups. In three of the groups, we added vildagliptin to their existing medication regimen; in the other two groups, we replaced one of their existing medications with vildagliptin. We then analyzed the changes in glucose parameters and clinical characteristics.

RESULTS

Ultimately, 327 subjects were analyzed in this study. Vildagliptin significantly improved hemoglobin A1c (HbA1c) levels over 6 months. The changes in HbA1c levels (ΔHbA1c) at month 6 were -2.24% (P=0.000), -0.77% (P=0.000), -0.80% (P=0.001), -0.61% (P=0.000), and -0.34% (P=0.025) for groups 1, 2, 3, 4, and 5, respectively, with significance. We also found significant decrements in fasting plasma glucose levels in groups 1, 2, 3, and 4 (P<0.05). Of the variables, initial HbA1c levels (P=0.032) and history of sulfonylurea use (P=0.026) were independently associated with responsiveness to vildagliptin treatment.

CONCLUSION

Vildagliptin was effective when it was used in subjects with poor glycemic control. It controlled fasting plasma glucose levels as well as sulfonylurea treatment in Korean type 2 diabetic subjects.

Impact of insulin resistance, body mass index, disease duration, and duration of metformin use on the efficacy of vildagliptin

INTRODUCTION

The optimal stage for dipeptidyl peptidase-4 (DPP-4) inhibitor therapy in the course of type 2 diabetes mellitus (T2DM) is still under discussion, with often a perception that treatment with these agents may be less beneficial with increasing disease progression, due to loss of beta-cell function, and with increasing insulin resistance (IR), where beta-cell function is less prominent. This work, therefore, aimed to assess the impact of such factors on the efficacy of the DPP-4 inhibitor, vildagliptin, in add-on therapy to metformin.

METHODS

A pooled analysis of 24-week efficacy data of vildagliptin 50 mg twice daily (b.i.d.) (n = 2,478) from four add-on to metformin studies was performed. Analyses for changes in hemoglobin A(1c) (HbA(1c)) were stratified according to baseline IR stage (homeostasis model assessment [Homa IR] <5, ≥5), body mass index (BMI) (<27, ≥27 to <30, ≥30 kg/m(2)), T2DM duration (0 to <1, ≥1 to <5, ≥5 years), and duration of metformin use (0 to <1, ≥1 to <5, ≥5 years). Data from patients treated with sulfonylureas (SUs) (n = 2,010) in the pooled studies are provided as reference.

RESULTS

Patients in the vildagliptin and SU groups had mean age, HbA(1c), BMI, Homa IR, duration of T2DM and metformin use of 58 years, 7.7%, 32 kg/m(2), 4.3, 5.9 years and 3.0 years, respectively. Reductions from baseline in HbA(1c) with vildagliptin were very similar across Homa IR (mean 2.8 and 8.6), BMI (mean 24.9, 28.5, and 35.3 kg/m(2)), T2DM duration (mean 0.6, 2.9, and 9.7 years), and duration of metformin use (mean 0.6, 2.6, and 7.9 years) categories, showing significant drops in HbA(1c) of approximately -0.7% (baseline 7.7%). The results in patients receiving SUs were comparable to those seen in the vildagliptin group.

CONCLUSION

Vildagliptin add-on therapy to metformin was efficacious independent of IR stage and BMI, as well as disease duration and duration of prior metformin use, indicating that, contrary to a not uncommon perception, more obese patients and patients with long-standing T2DM can benefit from treatment with the DPP-4 inhibitor, vildagliptin.

The structure and function of the glucagon-like peptide-1 receptor and its ligands

Glucagon-like peptide-1(7-36)amide (GLP-1) is a 30-residue peptide hormone released from intestinal L cells following nutrient consumption. It potentiates the glucose-induced secretion of insulin from pancreatic beta cells, increases insulin expression, inhibits beta-cell apoptosis, promotes beta-cell neogenesis, reduces glucagon secretion, delays gastric emptying, promotes satiety and increases peripheral glucose disposal. These multiple effects have generated a great deal of interest in the discovery of long-lasting agonists of the GLP-1 receptor (GLP-1R) in order to treat type 2 diabetes. This review article summarizes the literature regarding the discovery of GLP-1 and its physiological functions. The structure, function and sequence-activity relationships of the hormone and its natural analogue exendin-4 (Ex4) are reviewed in detail. The current knowledge of the structure of GLP-1R, a Family B GPCR, is summarized and discussed, before its known interactions with the principle peptide ligands are described and summarized. Finally, progress in discovering non-peptide ligands of GLP-1R is reviewed. GLP-1 is clearly an important hormone linking nutrient consumption with blood sugar control, and therefore knowledge of its structure, function and mechanism of action is of great importance.

Using albumin to improve the therapeutic properties of diabetes treatments

Achieving tight glycaemic control remains an unmet need for many patients with type 2 diabetes, despite improved treatments. To meet glycaemic targets, attempts have been made to improve existing drugs and to develop new classes of drugs. Recent advances include insulin analogues that more closely mimic physiologic insulin levels, and incretin-based therapies, which capitalize on the glucoregulatory properties of native glucagon-like peptide-1 (GLP-1). Although promising, these agents are associated with limitations, including hypoglycaemia with insulin, gastrointestinal adverse events with GLP-1 receptor agonists and frequent dosing with both classes. Albumin is an abundant natural drug carrier that has been used to improve the half-life, tolerability and efficacy of a number of bioactive agents. Here, we review the physiologic roles of albumin and how albumin technologies are being used to prolong duration of action of therapies for diabetes, including insulin and incretin-based therapies.

The future of incretin-based therapy: novel avenues--novel targets

Incretin-based therapy for type 2 diabetes is based on the antidiabetic effects of glucagon-like peptide-1 (GLP-1) and instituted by GLP-1 receptor agonists and dipeptidyl peptidase-4 inhibitors targeting the key islet defects of the disease. The treatment is clinically efficient and safe, and associated with a low risk of adverse events. It can be used both in early and late stages of the disease and both as monotherapy and add-on to other therapies. Current research on the future of incretin-based therapy focuses on optimizing its place in diabetes treatment and examines its potential in type 1 diabetes, in subjects with obesity without type 2 diabetes and in cardiovascular and neurodegenerative disorders. Other studies aim at prolonging the duration of action of the GLP-1 receptor agonists to allow weekly administration, and to develop orally GLP-1 receptor agonists. Furthermore, other investigators focus on stimulation of GLP-1 secretion by activating GLP-1-producing L-cells or using gene therapy. Finally, also other gastro-entero-pancreatic bioactive peptides are potential targets for drug development as are synthetic peptides engineered as co-agonists stimulating more than one receptor. We can therefore expect a dynamic development within this field in the coming years.

Preservation of beta-cell function in type 2 diabetes

OBJECTIVE

To review available data on preservation and potential improvement of beta-cell function in patients with type 2 diabetes mellitus (T2DM) with use of currently available strategies and agents.

METHODS

Using key words, we performed a MEDLINE search of the relevant literature published through 2009 regarding the effects of available agents on beta-cell function in humans with T2DM.

RESULTS

On the basis of current clinical data, no uniformly effective treatment for beta-cell preservation has been found. Lifestyle intervention and early intensive insulin therapy appear to have some preservative properties on beta-cell function. Glucagonlike peptide-1 agonists, dipeptidyl- peptidase-4 inhibitors, and thiazolidinediones result in maintenance and often improvement of beta-cell function during their active use; however, data on their ability to preserve beta-cell function when patients are not receiving active treatment are limited.

CONCLUSION

The continuous loss of beta-cell mass and beta-cell function is a critical mechanism underlying the progressive deterioration of glycemic control in T2DM. In light of the projected increase in individuals at risk for developing T2DM, strategies and agents aimed at delaying or preventing the progression and inducing a remission of the disease are needed. Future research on this topic should include comparative efficacy trials with washout periods incorporating currently available and novel medications and strategies for preservation of beta cells.

Are sulfonylureas less desirable than DPP-4 inhibitors as add-on to metformin in the treatment of type 2 diabetes?

Sulfonylureas (SUs) are commonly used as add-on to metformin in treatment of type 2 diabetes in patients who are insufficiently controlled by metformin alone. They have good efficacy and have been shown to prevent microvascular complications. However, treatment with SUs is also associated with a high frequency of hypoglycemia, increased body weight, and a high risk of secondary failure. During recent years, dipeptidyl peptidase-4 (DPP-4) inhibitors have emerged as alternatives to SUs. They show similar efficacy as SUs but with lower risk of hypoglycemia, and reduction or no change in body weight, and if confirmed in humans, they may preserve islet function and thereby minimize the risk for secondary failure. Their limitation at present is the lack of long-term (>5 years) experience on durability and safety. Overall, therefore, the conclusion emerges that SUs are less desirable than DPP-4 inhibitors in management of hyperglycemia in type 2 diabetes.

GLP-1 for type 2 diabetes

Glucagon-like peptide-1 (GLP-1)-based therapy of type 2 diabetes is executed either by GLP-1 receptor agonists, which stimulate the GLP-1 receptors, or by dipeptidyl peptidase-4 (DPP-4) inhibitors, which prevent the inactivation of endogenous GLP-1 thereby increasing the concentration of endogenous active GLP-1. GLP-1 activates pancreatic receptors resulting in improved glycemia through glucose-dependent stimulation of insulin secretion and inhibition of glucagon secretion. There is also a potential beta cell preservation effect, as judged from rodent studies. GLP-1 receptors are additionally expressed in extrapancreatic tissue, having potential for the treatment to reduce body weight and to potentially have beneficial cardio- and endothelioprotective effects. Clinical trials in subjects with type 2 diabetes have shown that in periods of 12 weeks or more, these treatments reduce HbA(1c) by ≈ 0.8-1.1% from baseline levels of 7.7-8.5%, and they are efficient both as monotherapy and in combination therapy with metformin, sulfonylureas, thiazolidinediones or insulin. Furthermore, GLP-1 receptor agonists reduce body weight, whereas DPP-4 inhibitors are body weight neutral. The treatment is safe with very low risk for adverse events, including hypoglycaemia. GLP-1 based therapy is thus a novel and now well established therapy of type 2 diabetes, with a particular value in combination with metformin in patients who are inadequately controlled by metformin alone.

Glucagon-like Peptide-1 receptor agonists activate rodent thyroid C-cells causing calcitonin release and C-cell proliferation

Liraglutide is a glucagon-like peptide-1 (GLP-1) analog developed for type 2 diabetes. Long-term liraglutide exposure in rodents was associated with thyroid C-cell hyperplasia and tumors. Here, we report data supporting a GLP-1 receptor-mediated mechanism for these changes in rodents. The GLP-1 receptor was localized to rodent C-cells. GLP-1 receptor agonists stimulated calcitonin release, up-regulation of calcitonin gene expression, and subsequently C-cell hyperplasia in rats and, to a lesser extent, in mice. In contrast, humans and/or cynomolgus monkeys had low GLP-1 receptor expression in thyroid C-cells, and GLP-1 receptor agonists did not activate adenylate cyclase or generate calcitonin release in primates. Moreover, 20 months of liraglutide treatment (at >60 times human exposure levels) did not lead to C-cell hyperplasia in monkeys. Mean calcitonin levels in patients exposed to liraglutide for 2 yr remained at the lower end of the normal range, and there was no difference in the proportion of patients with calcitonin levels increasing above the clinically relevant cutoff level of 20 pg/ml. Our findings delineate important species-specific differences in GLP-1 receptor expression and action in the thyroid. Nevertheless, the long-term consequences of sustained GLP-1 receptor activation in the human thyroid remain unknown and merit further investigation.

Combination treatment with alogliptin and voglibose increases active GLP-1 circulation, prevents the development of diabetes and preserves pancreatic beta-cells in prediabetic db/db mice

AIM

Alogliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, and voglibose, an alpha-glucosidase inhibitor, have different but complementary mechanisms of action on glucagon-like peptide-1 (GLP-1) regulation and glucose-lowering effects. The present study evaluated the chronic effects of combination treatment with alogliptin and voglibose in prediabetic db/db mice.

METHODS

Alogliptin (0.03%) and voglibose (0.001%) alone or in combination were administered in the diet to prediabetic db/db mice.

RESULTS

After 3 weeks, voglibose treatment increased GLP-1 secretion (voglibose alone, 1.6-fold; alogliptin plus voglibose, 1.5-fold), while it decreased plasma glucose-dependent insulinotropic polypeptide (GIP) (voglibose alone, -30%; alogliptin plus voglibose, -29%). Alogliptin, voglibose and combination treatment decreased plasma DPP-4 activity by 72, 15 and additively by 80%, respectively, and increased plasma active GLP-1 levels by 4.5-, 1.8- and synergistically by 9.1-fold respectively. Combination treatment increased plasma insulin by 3.6-fold (alogliptin alone, 1.3-fold; voglibose alone, 1.8-fold), decreased plasma glucagon by 30% (alogliptin alone, 11%; voglibose alone, 8%), and prevented the development of diabetes, much more effectively than either agent alone. After 4 weeks, alogliptin, voglibose and combination treatment increased pancreatic insulin content by 1.6-, 3.4- and synergistically by 8.5-fold respectively. Furthermore, combination treatment resulted in an increased expression of insulin, pancreatic and duodenal homeobox 1 (PDX1) and glucose transporter 2 (GLUT2), and maintenance of normal beta/alpha-cell distribution in the pancreatic islet.

CONCLUSIONS

Chronic treatment with alogliptin in combination with voglibose concurrently increased active GLP-1 circulation, increased insulin secretion, decreased glucagon secretion, prevented the onset of the disease, and preserved pancreatic beta-cells and islet structure in prediabetic db/db mice.

Role of glucotoxicity and lipotoxicity in the pathophysiology of Type 2 diabetes mellitus and emerging treatment strategies

Type 2 diabetes mellitus is a disease characterized by persistent and progressive deterioration of glucose tolerance. Both insulin resistance and impaired insulin secretion contribute to development of Type 2 diabetes. However, whilst insulin resistance is fully apparent in the pre-diabetic condition, impairment of insulin secretion worsens over the time, being paralleled by a progressive decline in both pancreatic B-cell function and B-cell mass. Intense research has identified a number of genetic variants that may predispose to impaired B-cell function, but such predisposition can be precipitated and worsened by toxic effects of hyperglycaemia (glucotoxicity) and elevated levels of free fatty acids (lipotoxicity). All these aspects of the pathogenesis of Type 2 diabetes are discussed in this review. Moreover, treatments that target reduction in glucotoxicity or lipotoxicity are outlined, including emerging strategies that target the role of glucagon-like peptide 1 and sodium glucose co-transporter 2.

Poly-GLP-1, a novel long-lasting glucagon-like peptide-1 polymer, ameliorates hyperglycaemia by improving insulin sensitivity and increasing pancreatic beta-cell proliferation

AIM

The clinical value of glucagon-like peptide-1 (GLP-1) is restricted because of its short half-life. To overcome this limitation, a new polymer of GLP-1 was developed by prodrug strategy, termed Poly-GLP-1, and its pharmacological properties were investigated.

METHODS

The in vitro release kinetics of GLP-1 from Poly-GLP-1 was analysed by Western blot. Plasma GLP-1 levels following a single administration of Poly-GLP-1 were determined by enzyme-linked immunosorbent assay. The in vitro effects of Poly-GLP-1 were evaluated using isolated pancreatic islets. The acute effects on glycaemic control and food intake were investigated in C57BL/6J mice s.c. administered with Poly-GLP-1. The chronic effects of Poly-GLP-1 on glycaemic control were further assessed in C57BL/6J and db/db mice treated twice daily for 6 weeks.

RESULTS

Pro-GLP-1 dose dependently increased insulin secretion and decreased glucose, but did not exhibit the insulinotropic action in isolated pancreatic islets without plasma. The glucose-lowering actions of Poly-GLP-1 (3 nmol/kg) remained no less than 12 h after a single injection. Poly-GLP-1 caused a durable restoration of glycaemic control, food intake and body weight gain in db/db mice following 6-week administration. The chronic treatment with Poly-GLP-1 improved glucose tolerance and insulin sensitivity and increased beta-cell mass and proliferation in db/db mice. There was little effect on normal mice treated in the same manner.

CONCLUSIONS

Our results indicated that Poly-GLP-1, a novel GLP-1 polymer, has long-lasting and potent effects on glycaemic control in vivo, and these beneficial effects may be because of improvement of insulin sensitivity and promotion of islet growth and function.

Clinical results of treating type 2 diabetic patients with sitagliptin, vildagliptin or saxagliptin--diabetes control and potential adverse events

Inhibition of dipeptidyl peptidase-4 (DPP-4) is a novel oral treatment for type 2 diabetes. DPP-4 inhibition increases insulin secretion and reduces glucagon secretion by preventing the inactivation of glucagon-like peptide-1 (GLP-1), thereby lowering glucose levels. Several DPP-4 inhibitors are in clinical development; more studies exist for sitagliptin and vildagliptin. They improve metabolic control in type 2 diabetes in monotherapy and also in combination with metformin, sulphonylurea and thiazolidinediones. HbA(1c) is reduced by approximately 0.6-1.1% in studies up to 52 weeks. Similar, although more limited, results were obtained for saxagliptin. DPP-4 inhibitors are safe and tolerable with no increased risk of adverse events compared to placebo and have a low risk of hypoglycaemia. DPP-4 inhibitors are body weight-neutral. The DPP-4 inhibitors are recommended for use in the early stage of type 2 diabetes, in combination with metformin in subjects with inadequate glycaemic control. DPP-4 inhibition may also be used in combination with sulphonylurea and thiazolidinediones and potentially also in combination with insulin. The durability and long-term safety of DPP-4 inhibitors remain to be established.

Combining a dipeptidyl peptidase-4 inhibitor, alogliptin, with pioglitazone improves glycaemic control, lipid profiles and beta-cell function in db/db mice

BACKGROUND AND PURPOSE

Alogliptin, a highly selective dipeptidyl peptidase-4 (DPP-4) inhibitor, enhances incretin action and pioglitazone enhances hepatic and peripheral insulin actions. Here, we have evaluated the effects of combining these agents in diabetic mice.

EXPERIMENTAL APPROACH

Effects of short-term treatment with alogliptin alone (0.01%-0.1% in diet), and chronic combination treatment with alogliptin (0.03% in diet) and pioglitazone (0.0075% in diet) were evaluated in db/db mice exhibiting early stages of diabetes.

KEY RESULTS

Alogliptin inhibited plasma DPP-4 activity up to 84% and increased plasma active glucagon-like peptide-1 by 4.4- to 4.9-fold. Unexpectedly, alogliptin alone lacked clear efficacy for improving glucose levels. However, alogliptin in combination with pioglitazone clearly enhanced the effects of pioglitazone alone. After 3-4 weeks of treatment, combination treatment increased plasma insulin by 3.8-fold, decreased plasma glucagon by 41%, both of which were greater than each drug alone, and increased plasma adiponectin by 2.4-fold. In addition, combination treatment decreased glycosylated haemoglobin by 2.2%, plasma glucose by 52%, plasma triglycerides by 77% and non-esterified fatty acids by 48%, all of which were greater than each drug alone. Combination treatment also increased expression of insulin and pancreatic and duodenal homeobox 1 (PDX1), maintained normal beta-cell/alpha-cell distribution in islets and restored pancreatic insulin content to levels comparable to non-diabetic mice.

CONCLUSIONS AND IMPLICATIONS

These results indicate that combination treatment with alogliptin and pioglitazone at an early stage of diabetes improved metabolic profiles and indices that measure beta-cell function, and maintained islet structure in db/db mice, compared with either alogliptin or pioglitazone monotherapy.

Emerging dipeptidyl peptidase-4 inhibitors for the treatment of diabetes

Inhibition of dipeptidyl peptidase-4 (DPP-4) prevents the inactivation of glucagon-like peptide-1 (GLP-1). This increases circulating levels of active GLP-1, stimulates insulin secretion and inhibits glucagon secretion, resulting in lowering of glucose levels and improvement of glycemic control in patients with type 2 diabetes. Several DPP-4 inhibitors are emerging for therapeutic use. Most experience exists for sitagliptin, vildagliptin, saxagliptin and alogliptin. They all improve metabolic control in type 2 diabetes in monotherapy and in combination therapy with metformin, sulfonylurea and thiazolidinediones. Vildagliptin and alogliptin have also been shown to improve glycemic control when added to insulin therapy, and sitagliptin improves glycemic control in triple therapy with metformin plus thiazolidinedione. DPP-4 inhibition also shows a favorable safety profile, high tolerability, only a minimal risk of hypoglycemia, and body-weight neutrality. The main clinical indication for DPP-4 inhibitors will be in the early stage of type 2 diabetes, in combination with metformin or other treatments in subjects with inadequate glycemic control on these treatments alone. The durability and long-term safety of DPP-4 inhibition, as well as clinical positioning in relation to GLP-1 mimetics, remain now to be established.

The dipeptidyl peptidase-4 inhibitor alogliptin in combination with pioglitazone improves glycemic control, lipid profiles, and increases pancreatic insulin content in ob/ob mice

The combination of two agents with different but complementary mechanisms of action is a logical approach for treating patients with type 2 diabetes. Thus, we evaluated chronic combination therapy with alogliptin, a highly selective dipeptidyl peptidase-4 inhibitor that enhances the action of incretins, and pioglitazone, a thiazolidinedione that improves peripheral and hepatic insulin sensitivity. Studies were designed to investigate the chronic metabolic and pancreatic effects of alogliptin (0.03%) plus pioglitazone (0.003%) combination treatment in obese ob/ob mice. After 4-5 weeks of treatment, alogliptin significantly increased plasma active glucagon-like peptide-1 levels up to 4.1-fold and decreased plasma glucagon up to 25%, whereas pioglitazone significantly increased plasma adiponectin up to 1.3-fold. Combination treatment exhibited a complementary effect, increasing plasma insulin levels by 3.2-fold (alogliptin alone, 1.6-fold; pioglitazone alone, 1.5-fold) and decreasing glycosylated hemoglobin by 2.3% (alogliptin alone, 1.0%; pioglitazone alone, 1.5%), and non-fasting and fasting plasma glucose by 37% and 62% (alogliptin alone, 17% and 24%; pioglitazone alone, 30% and 45%), respectively. Combination treatment also decreased plasma triglycerides by 67% and non-esterified fatty acids by 25% (alogliptin alone, 24% and 11%; pioglitazone alone, 54% and 8%). Moreover, combination treatment increased pancreatic insulin content by 2.2-fold (alogliptin alone, 1.3-fold; pioglitazone alone, 1.6-fold), with no significant changes in body weight. These results indicate that combination treatment with alogliptin and pioglitazone improved glycemic control, lipid profiles and increased pancreatic insulin content in ob/ob mice by preventing incretin inactivation and improving insulin resistance. These results provide a strong argument for using alogliptin in combination with pioglitazone.

Beta-cell apoptosis in type 2 diabetes: quantitative and functional consequences

Type 2 diabetes, the most common form of diabetes in humans, is characterized by impaired insulin secretion paralleled by a progressive decline in beta-cell function and chronic insulin resistance. Several authors have showed that in type 2 diabetes there is a reduction of islet and/or insulin-containing cell mass or volume. Regulation of the beta-cell mass appears to involve a balance of beta-cell replication and apoptosis but, at the molecular level, pancreatic beta-cell loss by apoptosis appears to play an important role in the development of insulin deficiency and the onset and/or progression of the disease. The mechanisms favoring apoptosis in type 2 diabetic pancreatic islets and new potential therapeutic approaches to prevent beta-cell death and maintain beta-cell mass are discussed.

DPP4 inhibitors: a new approach in diabetes treatment

The role of dipeptidyl peptidase-IV (DPP4) as both a regulatory enzyme and a signalling factor has been evaluated and described in many studies. DPP4 inhibition results in increased blood concentration of the incretin hormones glucagon-like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP). This causes an increase in glucose-dependent stimulation of insulin secretion, resulting in a lowering of blood glucose levels. Recent studies have shown that DPP4 inhibitors can induce a significant reduction in glycosylated haemoglobin (HbA(1c)) levels, either as monotherapy or as a combination with other antidiabetic agents. Research has also demonstrated that DPP4 inhibitors portray a very low risk of hypoglycaemia development. This review article focuses on the two leading agents of this category (sitagliptin and vildagliptin), providing an overview of their function along with the latest data regarding their clinical efficacy as antidiabetic agents.

Beta-cell failure in type 2 diabetes mellitus

Diabetes mellitus has been defined as a "group of metabolic diseases characterized by hyperglycemia resulting from defects in insulin secretion, insulin action, or both" and encompasses a wide range of heterogeneous conditions. Common type 2 diabetes mellitus (T2DM) results from a combination of genetic and acquired factors. However, lifestyle factors, particularly overeating and physical inactivity, are the major clinical determinants of T2DM. Insulin resistance is a common feature of T2DM, but it is unlikely to cause T2DM unless progressive loss of beta-cell function develops. Significant reduction in beta-cell function is already present at the time of T2DM diagnosis, and it continuously declines irrespective of treatment. As such, the progressive loss of beta-cell function dictates the rate of worsened glycemic control. Development of progressive deterioration accelerates via gluco- and lipotoxicity, loss of beta-cell function, and shrinkage of beta-cell mass. Understanding the causes for beta-cell failure is therefore of capital importance to develop new and more effective therapeutic strategies.

Effects of exendin-4 on islets from type 2 diabetes patients

Exendin-4 is a dipeptidyl peptidase IV (DPP-IV)-resistant glucagon-like peptide 1 (GLP-1) mimetic and its synthetic counterpart, exenatide, is being used in the therapy of type 2 diabetes (T2DM). No information, however, is currently available as for the direct action of exendin-4 on human T2DM islets. In the present study, we exposed pancreatic islets prepared from non-diabetic and T2DM subjects to exendin-4 for 48 h and found that the compound had several, direct beneficial actions on insulin secretion and the expression of genes involved in beta-cell function and differentiation.

Novel combination treatment of type 2 diabetes DPP-4 inhibition + metformin

Inhibition of dipeptidyl peptidase-4 (DPP-4) as a novel therapy for type 2 diabetes is based on prevention of the inactivation process of bioactive peptides, the most important in the context of treatment of diabetes of which is glucagon-like peptide-1 (GLP-1). Most clinical experience with DPP-4 inhibition is based on vildagliptin (GalvusR, Novartis) and sitagliptin (JanuviaR, Merck). These compounds improve glycemic control both in monotherapy and in combination with other oral hyperglycemic agents. Both have also been shown to efficiently improve glycemic control when added to ongoing metformin therapy in patients with inadequate glycemic control. Under that condition, they reduce HbA1C levels by 0.65%-1.1% (baseline HbA1C 7.2-8.7%) in studies up to 52 weeks of duration in combination versus continuous therapy with metformin alone. Sitagliptin has also been examined in initial combination therapy with metformin have; HbA1 was reduced by this combination by 2.1% (baseline HbA1C 8.8%) after 24 weeks of treatment. Both fasting and prandial glucose are reduced by DPP-4 inhibition in combination with metformin in association with improvement of insulin secretion and insulin resistance and increase in concentrations of active GLP-1. The combination of DPP-4 inhibition and metformin has been shown to be highly tolerable with very low risk of hypoglycemia. Hence, DPP-4 inhibition in combination with metformin is an efficient, safe and tolerable combination therapy for type 2 diabetes.

DPP-4 inhibitors

Inhibition of dipeptidyl peptidase 4 (DPP-4) is a novel treatment for type-2 diabetes. DPP-4 inhibition prevents the inactivation of glucagon-like peptide 1 (GLP-1), which increases levels of active GLP-1. This increases insulin secretion and reduces glucagon secretion, thereby lowering glucose levels. Several DPP-4 inhibitors are in clinical development. Most experience so far has been with sitagliptin (Merck; approved by the FDA) and vildagliptin (Novartis; filed). These are orally active compounds with a long duration, allowing once-daily administration. Both sitagliptin and vildagliptin improve metabolic control in type-2 diabetes, both in monotherapy and in combination with metformin and thiazolidinediones. A reduction in HbA(1c) of approximately 1% is seen in studies of DPP-4 inhibition of up to 52 weeks' duration. DPP-4 inhibition is safe and well tolerated, the risk of hypoglycaemia is minimal, and DPP-4 inhibition is body-weight neutral. DPP-4 inhibition is suggested to be a first-line treatment of type-2 diabetes, particularly in its early stages in combination with metformin. However, the durability and long-term safety of DPP-4 inhibition remain to be established.