Cardiovascular effects of DPP-4 inhibition: beyond GLP-1

Direct effects of DPP-4 inhibition on the vasculature. Reconciling basic evidence with lack of clinical evidence

Diabetes is burdened by macrovascular and microvascular complications that collectively reduce life expectancy. As the ultimate goal of diabetes treatment is to prevent excess morbidity and mortality associated with its complications, the interest on cardiovascular effects of glucose lowering medications is high. Dipeptidyl peptidase-4 inhibitors (DPP-4i) lower blood glucose by protecting the incretin hormone glucagon-like peptide-1 (GLP-1) from enzymatic degradation, thereby restoring meal-stimulated insulin release. DPP-4 has several non-incretin substrates, including cytokines, chemokines, and neurohormones, which can exert favourable, but also unpredictable, vascular effects, once they are stabilized by DPP-4i. Choi et al. now provide additional evidence that DPP-4i counteracts vascular smooth muscle cell proliferation and migration, resulting in an attenuation of neointimal hyperplasia. Though several other in vitro, preclinical, and preliminary clinical studies on surrogate end-points suggest that DPP-4i can exert similar direct vasculoprotective actions, results of placebo-controlled phase IV trials have so far shown no reduction cardiovascular endpoints by DPP-4i. In this commentary, we put DPP-4 pleiotropy and complexity into context, trying to reconcile why results from basic science have not yet translated into clinical evidence of cardiovascular protection.

DPP4 in Diabetes

Dipeptidyl-peptidase 4 (DPP4) is a glycoprotein of 110 kDa, which is ubiquitously expressed on the surface of a variety of cells. This exopeptidase selectively cleaves N-terminal dipeptides from a variety of substrates, including cytokines, growth factors, neuropeptides, and the incretin hormones. Expression of DPP4 is substantially dysregulated in a variety of disease states including inflammation, cancer, obesity, and diabetes. Since the incretin hormones, glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide (GIP), are major regulators of post-prandial insulin secretion, inhibition of DPP4 by the gliptin family of drugs has gained considerable interest for the therapy of type 2 diabetic patients. In this review, we summarize the current knowledge on the DPP4–incretin axis and evaluate most recent findings on DPP4 inhibitors. Furthermore, DPP4 as a type II transmembrane protein is also known to be cleaved from the cell membrane involving different metalloproteases in a cell-type-specific manner. Circulating, soluble DPP4 has been identified as a new adipokine, which exerts both para- and endocrine effects. Recently, a novel receptor for soluble DPP4 has been identified, and data are accumulating that the adipokine-related effects of DPP4 may play an important role in the pathogenesis of cardiovascular disease. Importantly, circulating DPP4 is augmented in obese and type 2 diabetic subjects, and it may represent a molecular link between obesity and vascular dysfunction. A critical evaluation of the impact of circulating DPP4 is presented, and the potential role of DPP4 inhibition at this level is also discussed.

Dipeptidyl peptidase-4 inhibition by gemigliptin prevents abnormal vascular remodeling via NF-E2-related factor 2 activation

Dipeptidyl peptidase-4 (DPP-4) inhibitors exert a potent anti-hyperglycemic effect and reduce cardiovascular risk in type 2 diabetic patients. Several studies have shown that DPP-4 inhibitors including sitagliptin have beneficial effects in atherosclerosis and cardiac infarction involving reactive oxygen species. Here, we show that gemigliptin can directly attenuate the abnormal proliferation and migration of vascular smooth muscle cells (VSMCs) via enhanced NF-E2-related factor 2 (Nrf2) activity. Gemigliptin dramatically prevented ligation injury-induced neointimal hyperplasia in mouse carotid arteries. Likewise, the proliferation of primary VSMCs was significantly attenuated by gemigliptin in a dose-dependent manner consistent with a decrease in phospho-Rb, resulting in G1 cell cycle arrest. We found that gemigliptin enhanced Nrf2 activity not only by mRNA expression, but also by increasing Keap1 proteosomal degradation by p62, leading to the induction of Nrf2 target genes such as HO-1 and NQO1. The anti-proliferative role of gemigliptin disappeared with DPP-4 siRNA knockdown, indicating that the endogenous DPP-4 in VSMCs contributed to the effect of gemigliptin. In addition, gemigliptin diminished TNF-α-mediated cell adhesion molecules such as MCP-1 and VCAM-1 and reduced MMP2 activity in VSMCs. Taken together, our data indicate that gemigliptin exerts a preventative effect on the proliferation and migration of VSMCs via Nrf2.

Pleiotropic effects of the dipeptidylpeptidase-4 inhibitors on the cardiovascular system

Dipeptidylpeptidase-4 (DPP-4) is a ubiquitously expressed transmembrane protein that removes NH2-terminal dipeptides from various substrate hormones, chemokines, neuropeptides, and growth factors. Two known substrates of DPP-4 include the incretin hormones glucagon-like peptide-1 (GLP-1) and gastric inhibitory peptide, which are secreted by enteroendocrine cells in response to postprandial hyperglycemia and account for 60–70% of postprandial insulin secretion. DPP-4 inhibitors (DPP-4i) block degradation of GLP-1 and gastric inhibitory peptide, extend their insulinotropic effect, and improve glycemia. Since 2006, several DPP-4i have become available for treatment of type 2 diabetes mellitus. Clinical trials confirm that DPP-4i raises GLP-1 levels in plasma and improves glycemia with very low risk for hypoglycemia and other side effects. Recent studies also suggest that DPP-4i confers cardiovascular and kidney protection, beyond glycemic control, which may reduce the risk for further development of the multiple comorbidities associated with obesity/type 2 diabetes mellitus, including hypertension and cardiovascular disease (CVD) and kidney disease. The notion that DPP-4i may improve CVD outcomes by mechanisms beyond glycemic control is due to both GLP-1-dependent and GLP-1-independent effects. The CVD protective effects by DPP-4i result from multiple factors including insulin resistance, oxidative stress, dyslipidemia, adipose tissue dysfunction, dysfunctional immunity, and antiapoptotic properties of these agents in the heart and vasculature. This review focuses on cellular and molecular mechanisms mediating the CVD protective effects of DPP-4i beyond favorable effects on glycemic control.

Risk of hospitalization for heart failure in patients with type 2 diabetes newly treated with DPP-4 inhibitors or other oral glucose-lowering medications: a retrospective registry study on 127,555 patients from the Nationwide OsMed Health-DB Database

AIMS

Oral glucose-lowering medications are associated with excess risk of heart failure (HF). Given the absence of comparative data among drug classes, we performed a retrospective study in 32 Health Services of 16 Italian regions accounting for a population of 18 million individuals, to assess the association between HF risk and use of sulphonylureas, DPP-4i, and glitazones.

METHODS AND RESULTS

We extracted data on patients with type 2 diabetes who initiated treatment with DPP-4i, thiazolidinediones, or sulphonylureas alone or in combination with metformin during an accrual time of 2 years. The endpoint was hospitalization for HF (HHF) occurring after the first 6 months of therapy, and the observation was extended for up to 4 years. A total of 127 555 patients were included, of whom 14.3% were on DPP-4i, 72.5% on sulphonylurea, 13.2% on thiazolidinediones, with average 70.7% being on metformin as combination therapy. Patients in the three groups differed significantly for baseline characteristics: age, sex, Charlson index, concurrent medications, and previous cardiovascular events. During an average 2.6-year follow-up, after adjusting for measured confounders, use of DPP-4i was associated with a reduced risk of HHF compared with sulphonylureas [hazard ratio (HR) 0.78; 95% confidence interval (CI) 0.62-0.97; P = 0.026]. After propensity matching, the analysis was restricted to 39 465 patients, and the use of DPP-4i was still associated with a lower risk of HHF (HR 0.70; 95% CI 0.52-0.94; P = 0.018).

CONCLUSION

In a very large observational study, the use of DPP-4i was associated with a reduced risk of HHF when compared with sulphonylureas.

Dipeptidyl Peptidase 4: A New Link between Diabetes Mellitus and Atherosclerosis?

Type 2 diabetes mellitus (T2DM) has become one of the most prevalent noncommunicable diseases in the past years. It is undoubtedly associated with atherosclerosis and increased risk for cardiovascular diseases. Incretins, which are intestinal peptides secreted during digestion, are able to increase insulin secretion and its impaired function and/or secretion is involved in the pathophysiology of T2DM. Dipeptidyl peptidase 4 (DPP4) is an ubiquitous enzyme that regulates incretins and consequently is related to the pathophysiology of T2DM. DPP4 is mainly secreted by endothelial cells and acts as a regulatory protease for cytokines, chemokines, and neuropeptides involved in inflammation, immunity, and vascular function. In T2DM, the activity of DPP4 seems to be increased and there are a growing number of in vitro and in vivo studies suggesting that this enzyme could be a new link between T2DM and atherosclerosis. Gliptins are a new class of pharmaceutical agents that acts by inhibiting DPP4. Thus, it is expected that gliptin represents a new pharmacological approach not only for reducing glycemic levels in T2DM, but also for the prevention and treatment of atherosclerotic cardiovascular disease in diabetic subjects. We aimed to review the evidences that reinforce the associations between DPP4, atherosclerosis, and T2DM.

Differential cardiovascular outcomes after dipeptidyl peptidase-4 inhibitor, sulfonylurea, and pioglitazone therapy, all in combination with metformin, for type 2 diabetes: a population-based cohort study

Background/Objectives

Data on the comparative effectiveness of oral antidiabetics on cardiovascular outcomes in a clinical practice setting are limited. This study sought to determine whether a differential risk of cardiovascular disease (CVD) exists for the combination of a dipeptidyl peptidase-4 (DPP-4) inhibitor plus metformin versus a sulfonylurea derivative plus metformin or pioglitazone plus metformin.

Methods

We conducted a cohort study of 349,476 patients who received treatment with a DPP-4 inhibitor, sulfonylurea, or pioglitazone plus metformin for type 2 diabetes using the Korean national health insurance claims database. The incidence of total CVD and individual outcomes of myocardial infarction (MI), heart failure (HF), and ischemic stroke (IS) were assessed using the hazard ratios (HRs) estimated from a Cox proportional-hazards model weighted for a propensity score.

Results

During follow-up, 3,881 patients developed a CVD, including 428 MIs, 212 HFs, and 1,487 ISs. The adjusted HR with 95% confidence interval (CI) for a sulfonylurea derivative plus metformin compared with a DPP-4 inhibitor plus metformin was 1.20 (1.09-1.32) for total CVD; 1.14 (1.04-1.91) for MI; 1.07 (0.71-1.62) for HF; and 1.51 (1.28-1.79) for IS. The HRs with 95% CI for total CVD, MI, HF, and IS for pioglitazone plus metformin were 0.89 (0.81-0.99), 1.05 (0.76-1.46), 4.81 (3.53-6.56), and 0.81 (0.67-0.99), respectively.

Conclusions

Compared with a DPP-4 inhibitor plus metformin, treatment with a sulfonylurea drug plus metformin was associated with increased risks of total CVD, MI, and IS, whereas the use of pioglitazone plus metformin was associated with decreased total CVD and IS risks.

Design and baseline characteristics of the CARdiovascular Outcome Trial of LINAgliptin Versus Glimepiride in Type 2 Diabetes (CAROLINA®)

CARdiovascular Outcome Trial of LINAgliptin Versus Glimepiride in Type 2 Diabetes (NCT01243424) is an ongoing, randomized trial in subjects with early type 2 diabetes and increased cardiovascular risk or established complications that will determine the long-term cardiovascular impact of linagliptin versus the sulphonylurea glimepiride. Eligible patients were sulphonylurea-naïve with HbA1c 6.5%-8.5% or previously exposed to sulphonylurea (in monotherapy or in a combination regimen <5 years) with HbA1c 6.5%-7.5%. Primary outcome is time to first occurrence of cardiovascular death, non-fatal myocardial infarction, non-fatal stroke or hospitalization for unstable angina. A total of 631 patients with primary outcome events will be required to provide 91% power to demonstrate non-inferiority in cardiovascular safety by comparing the upper limit of the two-sided 95% confidence interval as being below 1.3 for a given hazard ratio. Hierarchical testing for superiority will follow, and the trial has 80% power to demonstrate a 20% relative cardiovascular risk reduction. A total of 6041 patients were treated with median type 2 diabetes duration 6.2 years, 40.0% female, mean HbA1c 7.2%, 66% on 1 and 24% on 2 glucose-lowering agents and 34.5% had previous cardiovascular complications. The results of CARdiovascular Outcome Trial of LINAgliptin Versus Glimepiride in Type 2 Diabetes may influence the decision-making process for selecting a second glucose-lowering agent after metformin in type 2 diabetes.

Sodium glucose co-transporter 2 (SGLT2) inhibitors: new among antidiabetic drugs

Type 2 diabetes is characterized by decreased insulin secretion and sensitivity. The available oral anti-diabetic drugs act on many different molecular sites. The most used of oral anti-diabetic agents is metformin that activates glucose transport vesicles to the cell surface. Others are: the sulphonylureas; agents acting on the incretin system; GLP-1 agonists; dipetidylpeptidase-4 inhibitors; meglinitide analogues; and the thiazolidinediones. Despite these many drugs acting by different mechanisms, glycaemic control often remains elusive. None of these drugs have a primary renal mechanism of action on the kidneys, where almost all glucose excreted is normally reabsorbed. That is where the inhibitors of glucose reuptake (sodium-glucose cotransporter 2, SGLT2) have a unique site of action. Promotion of urinary loss of glucose by SGLT2 inhibitors embodies a new principle of control in type 2 diabetes that has several advantages with some urogenital side-effects, both of which are evaluated in this review. Specific approvals include use as monotherapy, when diet and exercise alone do not provide adequate glycaemic control in patients for whom the use of metformin is considered inappropriate due to intolerance or contraindications, or as add-on therapy with other anti-hyperglycaemic medicinal products including insulin, when these together with diet and exercise, do not provide adequate glycemic control. The basic mechanisms are improved β-cell function and insulin sensitivity. When compared with sulphonylureas or other oral antidiabetic agents, SGLT2 inhibitors provide greater HbA1c reduction. Urogenital side-effects related to the enhanced glycosuria can be troublesome, yet seldom lead to discontinuation. On this background, studies are analysed that compare SGLT2 inhibitors with other oral antidiabetic agents. Their unique mode of action, unloading the excess glycaemic load, contrasts with other oral agents that all act to counter the effects of diabetic hyperglycaemia.

SGLT-2 inhibitors and cardiovascular risk: proposed pathways and review of ongoing outcome trials

Given the multi-faceted pathogenesis of atherosclerosis in type 2 diabetes mellitus (T2DM), it is likely that interventions to mitigate this risk must address cardiovascular (CV) risk factors beyond glucose itself. Sodium glucose cotransporter-2 (SGLT-2) inhibitors are newer antihyperglycaemic agents with apparent multiple effects. Inherent in their mode of action to decrease glucose reabsorption by the kidneys by increasing urinary glucose excretion, these agents improve glycaemic control independent of insulin secretion with a low risk of hypoglycaemia. In this review, we outline those CV risk factors that this class appears to influence and provide the design features and trial characteristics of six ongoing outcome trials involving more than 41,000 individuals with T2DM. Those risk factors beyond glucose that can potentially be modulated positively with SGLT-2 inhibitors include blood pressure, weight, visceral adiposity, hyperinsulinaemia, arterial stiffness, albuminuria, circulating uric acid levels and oxidative stress. On the other hand, small increases in low-density lipoprotein (LDL)-cholesterol levels have also been observed for the class, which theoretically might offset some of these benefits. The potential translational impact of these effects is being tested with outcome trials, also reviewed in this article, powered to assess both macrovascular as well as certain microvascular outcomes in T2DM. These are expected to begin to report in late 2015.

Milk proteins, peptides, and oligosaccharides: effects against the 21st century disorders

Milk is the most complete food for mammals, as it supplies all the energy and nutrients needed for the proper growth and development of the neonate. Milk is a source of many bioactive components, which not only help meeting the nutritional requirements of the consumers, but also play a relevant role in preventing various disorders. Milk-derived proteins and peptides have the potential to act as coadjuvants in conventional therapies, addressing cardiovascular diseases, metabolic disorders, intestinal health, and chemopreventive properties. In addition to being a source of proteins and peptides, milk contains complex oligosaccharides that possess important functions related to the newborn's development and health. Some of the health benefits attributed to milk oligosaccharides include prebiotic probifidogenic effects, antiadherence of pathogenic bacteria, and immunomodulation. This review focuses on recent findings demonstrating the biological activities of milk peptides, proteins, and oligosaccharides towards the prevention of diseases of the 21st century. Processing challenges hindering large-scale production and commercialization of those bioactive compounds have been also addressed.

Cardiovascular effects of incretins in diabetes

Recent years have seen an enormous increase in the number of therapeutic agents available for lowering blood glucose levels in people with type 2 diabetes. Among these agents, the incretin mimetics glucagon-like peptide-1 (GLP-1) receptor (GLP-1R) agonists and dipeptidyl peptidase 4 (DPP4) inhibitors have received particular attention for the potential of these interventions to positively impact on cardiovascular outcomes. Although the results of large-scale cardiovascular outcome trials eagerly are anticipated, an increasing body of literature from preclinical and early phase clinical studies has indicated that both GLP-1R agonists and DPP4 inhibitors may exert glucose-independent cardiovascular effects. Despite its role in glucose homeostasis, the GLP-1R is surprisingly widely distributed throughout the body, including in the heart. GLP-1 may exert its effects through both receptor-dependent and receptor-independent mechanisms and through the actions of both the intact peptide and its metabolites. In addition, DPP4 inhibition not only augments the circulating levels of incretin hormones, but it also holds the capacity to augment the activity of other biologically important substrates, most notably the small protein stromal cell-derived factor 1 alpha. Whether these collective functions will act to reduce cardiovascular events in patients remains to be determined.

Antidiabetic therapy in post kidney transplantation diabetes mellitus

Post-transplantation diabetes mellitus (PTDM) is a common complication after kidney transplantation that affects up to 40% of kidney transplant recipients. By pathogenesis, PTDM is a diabetes form of its own, and may be characterised by a sudden, drug-induced deficiency in insulin secretion rather than worsening of insulin resistance over time. In the context of deteriorating allograft function leading to a re-occurrence of chronic kidney disease after transplantation, pharmacological interventions in PTDM patients deserve special attention. In the present review, we aim at presenting the current evidence regarding efficacy and safety of the modern antidiabetic armamentarium. Specifically, we focus on incretin-based therapies and insulin treatment, besides metformin and glitazones, and discuss their respective advantages and pitfalls. Although recent pilot trials are available in both prediabetes and PTDM, further studies are warranted to elucidate the ideal timing of various antidiabetics as well as its long-term impact on safety, glucose metabolism and cardiovascular outcomes in kidney transplant recipients.

Incretin-based therapies

Incretin-based therapies are steadily gaining clinical popularity, with many more products in the developmental pipeline. Current treatment recommendations incorporate GLP-1 RAs and DPP-4 inhibitors as important agents for consideration in the treatment of T2DM owing to their low hypoglycemia risk, ability to address postprandial hyperglycemia (DPP-4 inhibitors and short-acting GLP-1 RAs), and potential for weight reduction (GLP-1 RAs). These properties may likewise prove advantageous in older adults in whom hypoglycemia is particularly undesirable, although older adults may be more prone to the nausea and vomiting associated with GLP-1 RA therapy. Other safety issues for incretin-based therapies, such as pancreatitis, C-cell hyperplasia, and renal failure, should be considered when choosing an appropriate patient to receive such therapies. Ongoing CV outcome studies will further inform the health care community regarding the CV safety of incretin-based therapies. The availability of both short-acting and long-acting GLP-1 RAs currently allows practitioners to consider individualized blood glucose trends and therapeutic needs when choosing an optimal agent.

Cardiovascular impact of drugs used in the treatment of diabetes

The International Diabetes Federation predicts that by 2035 10% of the population of the world will have been diagnosed with diabetes, raising serious concerns over the resulting elevated morbidity and mortality as well as the impact on health care budgets. It is also well recognized that cardiovascular disease is the primary cause of the high morbidity and mortality associated with diabetes, raising the concern that appropriate drug therapy should not only correct metabolic dysfunction, but also protect the cardiovascular system from the effects of, in particular, the epigenetic changes that result from hyperglycaemia. A number of new classes of drugs for the treatment of diabetes have been introduced in the past decade, providing the opportunity to optimize treatment; however, comparative information of the cardiovascular benefits, or risks, of the newer drugs versus older therapies such as metformin is variable. This review, in addition to summarizing the cellular basis for the therapeutic action of these drugs, addresses the evidence for their cardiovascular benefits and risks. A particular focus is provided on metformin as it is the first choice drug for most patients with type 2 diabetes.

Dipeptidyl-peptidase-4 Inhibitors and Heart Failure: Class Effect, Substance-Specific Effect, or Chance Effect?

OPINION STATEMENT

The increased risk of heart failure hospitalizations related to treatment with the DPP-4 inhibitor saxagliptin observed in the SAVOR TIMI 53 trial, is likely not to be a chance effect, but rather a previously unrecognized side effect of this drug, as this risk was very consistently apparent across all subgroups of this large multicenter, prospective, randomized trial. Whether this side effect might represent a class effect of all DPP-4 inhibitors remains to be seen. Results of randomized prospective multicenter trials with the DPP-4 inhibitors alogliptin and vildagliptin have in fact generated new uncertainties and clearly not totally excluded the possibility of a class side effect. A meta-analysis of 59 randomized controlled trials with various DPP-4 inhibitors evaluating data from 36,620 patients with diabetes and a minimal observation period of 24 weeks, confirmed a 21 % increase of heart failure events compared to placebo treatment, however, not in comparison to treatment with other blood glucose lowering drugs. German registry data also did not show an increased risk for heart failure for the latter comparison. Potential interactions of DPP-4 inhibitors with other drugs, e.g. ACE inhibitors, have been discussed in relation to the increased heart failure risk, as well as interactions with peptides regulating cardiovascular functions that are also split by DPP-4 enzymes such as BNP, substance P, and NPY. Results from ongoing large multicenter trials with the DPP-4 inhibitors sitagliptin and linagliptin are expected to clarify the potential heart failure issue related to treatment with DPP-4 inhibitors.

The effects of dipeptidyl peptidase-4 inhibition on microvascular diabetes complications

We performed a review of the literature to determine whether the dipeptidyl peptidase-4 inhibitors (DPP4-I) may have the capability to directly and positively influence diabetic microvascular complications. The literature was scanned to identify experimental and clinical evidence that DPP4-I can ameliorate diabetic microangiopathy. We retrieved articles published between 1 January 1980 and 1 March 2014 in English-language peer-reviewed journals using the following terms: ("diabetes" OR "diabetic") AND ("retinopathy" OR "retinal" OR "nephropathy" OR "renal" OR "albuminuria" OR "microalbuminuria" OR "neuropathy" OR "ulcer" OR "wound" OR "bone marrow"); ("dipeptidyl peptidase-4" OR "dipeptidyl peptidase-IV" OR "DPP-4" OR "DPP-IV"); and ("inhibition" OR "inhibitor"). Experimentally, DPP4-I appears to improve inflammation, endothelial function, blood pressure, lipid metabolism, and bone marrow function. Several experimental studies report direct potential beneficial effects of DPP4-I on all microvascular diabetes-related complications. These drugs have the ability to act either directly or indirectly via improved glucose control, GLP-1 bioavailability, and modifying nonincretin substrates. Although preliminary clinical data support that DPP4-I therapy can protect from microangiopathy, insufficient evidence is available to conclude that this class of drugs directly prevents or decreases microangiopathy in humans independently from improved glucose control. Experimental findings and preliminary clinical data suggest that DPP4-I, in addition to improving metabolic control, have the potential to interfere with the onset and progression of diabetic microangiopathy. Further evidence is needed to confirm these effects in patients with diabetes.

Shedding of dipeptidyl peptidase 4 is mediated by metalloproteases and up-regulated by hypoxia in human adipocytes and smooth muscle cells

Dipeptidyl peptidase 4 is an important drug target for diabetes and a novel adipokine. However, it is unknown how soluble DPP4 (sDPP4) is cleaved from the cell membrane and released into the circulation. We show here that MMP1, MMP2 and MMP14 are involved in DPP4 shedding from human vascular smooth muscle cells (SMC) and MMP9 from adipocytes. Hypoxia increased DPP4 shedding from SMC which is associated with increased mRNA expression of MMP1. Our data suggest that constitutive as well as hypoxia-induced DPP4 shedding occurs due to a complex interplay between different MMPs in cell type-specific manner.

Understanding the type 2 diabetes mellitus and cardiovascular disease risk paradox

Patients with diabetes have approximately a 2-fold increase in the risk for coronary heart disease, stroke, and death from vascular causes compared with patients who do not have diabetes. Interventions targeted at modifiable risk factors, such as smoking cessation and management of hypertension and dyslipidemia, reduce the risk of cardiovascular disease (CVD) in patients with type 2 diabetes mellitus (T2DM). Paradoxically, large randomized studies have failed to conclusively show that intensively lowering glucose reduces CVD event rates in patients with T2DM, despite pathophysiologic and epidemiologic evidence suggesting that hyperglycemia contributes to CVD. Although initiation of intensive glycemic control early in the disease course may be associated with a reduction in the long-term risk of cardiovascular (CV) events, this approach in those with long-standing or complicated T2DM is not of clear benefit and may even be harmful in some. Failure to mitigate risk with antihyperglycemic therapy and the potential for some treatments to increase CVD risk underlies a treatment paradox. New glucose-lowering therapies are now subject to close scrutiny for CV safety before and after drug approval. Results from the first trials designed to meet the recent CV regulatory requirements have shown no increased risk of major adverse CV events but also no CV benefit from dipeptidyl peptidase-4 inhibitor therapy, as well as a potentially increased risk of hospitalization for heart failure. Conclusive evidence of CV risk reduction with glucose-lowering therapy is still lacking and scrutiny of additional agents is necessary. Type 2 diabetes mellitus is a heterogeneous disease, for which patient-centered, individualized care, and goal-setting is appropriate. Interventions that focus on the management of CV risk factors and glucose lowering with medications that are not cardiotoxic represent an optimal and attainable treatment approach.

Evidence-based practice use of incretin-based therapy in the natural history of diabetes

The incretin class of anti-hyperglycemic agents, including glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-inhibitors, is an important addition to the therapeutic armamentarium for the management of appropriate patients with type 2 diabetes mellitus as an adjunct to diet and exercise and/or with the agents metformin, sulfonylureas, thiazolidinediones, or any combination thereof. More recently, US Food and Drug Administration (FDA)-approved indications for incretins were expanded to include use with basal insulin. This review article takes an evidence-based practice approach in discussing the importance of aggressive treatment for diabetes, the principles of incretin physiology and pathophysiology, use of glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors, and patient types and contexts where incretin therapy has been found beneficial, from metabolic syndrome to overt diabetes.

GLP-1R activation for the treatment of stroke: updating and future perspectives

Stroke is the leading cause of adult disability in Westernized societies with increased incidence along ageing and it represents a major health and economical threat. Inactive lifestyle, smoking, hypertension, atherosclerosis, obesity and diabetes all dramatically increase the risk of stroke. While preventive strategies based on lifestyle changes and risk factor management can delay or decrease the likelihood of having a stroke, post stroke pharmacological strategies aimed at minimizing stroke-induced brain damage are highly needed. Unfortunately, several candidate drugs that have shown significant preclinical neuroprotective efficacy, have failed in clinical trials and no treatment for stroke based on neuroprotection is available today. Glucagon-like peptide 1 (GLP-1) is a peptide originating in the enteroendocrine L-cells of the intestine and secreted upon nutrient ingestion. The activation of the GLP-1R by GLP-1 enhances glucose-dependent insulin secretion, suppresses glucagon secretion and exerts multifarious extrapancreatic effects. Stable GLP-1 analogues and inhibitors of the proteolytic enzyme dipeptidyl peptidase 4 (DPP-4) (which counteract endogenous GLP-1 degradation) have been developed clinically for the treatment of type 2 diabetes. Besides their antidiabetic properties, experimental evidence has shown neurotrophic and neuroprotective effects of GLP-1R agonists and DPP-4 inhibitors in animal models of neurological disorders. Herein, we review recent experimental data on the neuroprotective effects mediated by GLP-1R activation in stroke. Due to the good safety profile of the drugs targeting the GLP-1R, we also discuss the high potential of GLP-1R stimulation in view of developing a safe clinical treatment against stroke based on neuroprotection in both diabetic and non-diabetic patients.

Dipeptidyl-peptidase 4 inhibition and the vascular effects of glucagon-like peptide-1 and brain natriuretic peptide in the human forearm

BACKGROUND

Dipeptidyl-peptidase 4 (DPP4) inhibitors improve glycemic control in patients with diabetes mellitus by preventing the degradation of glucagon-like peptide-1 (GLP-1). GLP-1 causes vasodilation in animal models but also increases sympathetic activity; the effect of GLP-1 in the human vasculature and how it is altered by DPP4 inhibition is not known. DPP4 also degrades the vasodilator brain natriuretic peptide (BNP) to a less potent metabolite. This study tested the hypothesis that DPP4 inhibition potentiates the vasodilator responses to GLP-1 and BNP in the human forearm.

METHOD AND RESULTS

Seventeen healthy subjects participated in this randomized, double-blinded, placebo-controlled crossover study. On each study day, subjects received DPP4 inhibitor (sitagliptin 200 mg by mouth) or placebo. Sitagliptin increased forearm blood flow and decreased forearm vascular resistance without affecting mean arterial pressure and pulse. GLP-1 and BNP were infused in incremental doses via brachial artery. Venous GLP-1 concentrations were significantly higher during sitagliptin use, yet there was no effect of GLP-1 on forearm blood flow in the presence or absence of sitagliptin. BNP caused dose-dependent vasodilation; however, sitagliptin did not affect this response. GLP-1 and BNP had no effect on net norepinephrine release.

CONCLUSIONS

These data suggest that GLP-1 does not act as a direct vasodilator in humans and does not contribute to sympathetic activation. Sitagliptin does not regulate vascular function in healthy humans by affecting the degradation of GLP-1 and BNP.

CLINICAL TRIAL REGISTRATION URL

www.clinicaltrials.gov/ Unique identifier: NCT01413542.

The nonglycemic actions of dipeptidyl peptidase-4 inhibitors

A cell surface serine protease, dipeptidyl peptidase 4 (DPP-4), cleaves dipeptide from peptides containing proline or alanine in the N-terminal penultimate position. Two important incretin hormones, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP), enhance meal-stimulated insulin secretion from pancreatic β-cells, but are inactivated by DPP-4. Diabetes and hyperglycemia increase the DPP-4 protein level and enzymatic activity in blood and tissues. In addition, multiple other functions of DPP-4 suggest that DPP-4 inhibitor, a new class of antidiabetic agents, may have pleiotropic effects. Studies have shown that DPP-4 itself is involved in the inflammatory signaling pathway, the stimulation of vascular smooth cell proliferation, and the stimulation of oxidative stress in various cells. DPP-4 inhibitor ameliorates these pathophysiologic processes and has been shown to have cardiovascular protective effects in both in vitro and in vivo experiments. However, in recent randomized clinical trials, DPP-4 inhibitor therapy in high risk patients with type 2 diabetes did not show cardiovascular protective effects. Some concerns on the actions of DPP-4 inhibitor include sympathetic activation and neuropeptide Y-mediated vascular responses. Further studies are required to fully characterize the cardiovascular effects of DPP-4 inhibitor.

Sitagliptin attenuates methionine/choline-deficient diet-induced steatohepatitis

AIMS

Accumulating evidence suggests that inhibitors of dipeptidyl peptidase-4 (DPP-4), such as sitagliptin, may play an important role in the prevention of non-alcoholic steatohepatitis (NASH). This study was conducted to elucidate whether sitagliptin could prevent steatohepatitis by inhibiting pathways involved in hepatic steatosis, inflammation, and fibrosis.

METHODS

C57BL/6 mice were fed a methionine/choline-deficient (MCD) diet with or without supplement with sitagliptin for 5 weeks. Liver and adipose tissue from mice were examined histologically and immunohistochemically to estimate the effect of sitagliptin on the development of NASH.

RESULTS

Supplementation with sitagliptin resulted in significant improvement of MCD diet-induced fat accumulation in the liver. In addition, sitagliptin treatment lowered fatty acid uptake, expression of VLDL receptor and hepatic triglyceride content. Sitagliptin also effectively attenuated MCD diet-induced hepatic inflammation, endoplasmic reticulum (ER) stress, and liver injury, as evidenced by reduced proinflammatory cytokine levels, ER stress markers, and TUNEL staining. Expression of CYP2E1 and 4NHE were strongly increased by the MCD diet, but this effect was successfully prevented by sitagliptin treatment. Furthermore, sitagliptin significantly decreased levels of MCD diet-induced fibrosis-associated proteins such as fibronectin and α-SMA in the liver. Inflammatory and atrophic changes of adipose tissue by MCD diet were restored by sitagliptin treatment.

CONCLUSIONS

Sitagliptin attenuated MCD diet-induced hepatic steatosis, inflammation, and fibrosis in mice through amelioration of mechanisms responsible for the development of NASH, including CD36 expression, NF-κB activation, ER stress, CYP2E1 expression, and lipid peroxidation. Treatment with sitagliptin may represent an effective approach for the prevention and treatment of NASH.

Soluble DPP4 induces inflammation and proliferation of human smooth muscle cells via protease-activated receptor 2

DPP4 is an ubiquitously expressed cell-surface protease that is shedded to the circulation as soluble DPP4 (sDPP4). We recently identified sDPP4 as a novel adipokine potentially linking obesity to the metabolic syndrome. The aim of this study was to investigate direct effects of sDPP4 on human vascular smooth muscle cells (hVSMCs) and to identify responsible signaling pathways. Using physiological concentrations of sDPP4, we could observe a concentration-dependent activation of ERK1/2 (3-fold) after 6h, which remained stable for up to 24h. Additionally, sDPP4 treatment induced a 1.5-fold phosphorylation of the NF-κB subunit p65. In accordance with sDPP4-induced stress and inflammatory signaling, sDPP4 also stimulates hVSMC proliferation. Furthermore we could observe an increased expression and secretion of pro-inflammatory cytokines like interleukin (IL)-6, IL-8 and MCP-1 (2.5-, 2.4- and 1.5-fold, respectively) by the sDPP4 treatment. All direct effects of sDPP4 on signaling, proliferation and inflammation could completely be prevented by DPP4 inhibition. Bioinformatic analysis and signaling signature induced by sDPP4 suggest that sDPP4 might be an agonist for PAR2. After the silencing of PAR2, the sDPP4-induced ERK activation as well as the proliferation was totally abolished. Additionally, the sDPP4-induced upregulation of IL-6 and IL-8 could completely be prevented by the PAR2 silencing. In conclusion, we show for the first time that sDPP4 directly activates the MAPK and NF-κB signaling cascade involving PAR2 and resulting in the induction of inflammation and proliferation of hVSMC. Thus, our in vitro data might extend the current view of sDPP4 action and shed light on cardiovascular effects of DPP4-inhibitors.

Cardiovascular effects of incretin therapy in diabetes care

Diabetes patients are at high risk for development of cardiovascular disease. The cardiovascular safety of antidiabetic medications is a concern. Incretin therapies, including glucagon-like peptide 1 receptor (GLP-1) receptor agonists and dipeptidyl peptidase 4 (DPP-4) inhibitors, have recently been introduced to clinical practice and are widely used. Data from phase 2 and 3 trials and retrospective analyses of clinical databases have shown favorable changes in cardiovascular risk factors and outcomes. However, only a few prospective trials have been designed with cardiovascular outcomes as a primary end point. From current data, alogliptin and saxagliptin do not change cardiovascular risk in type 2 diabetes mellitus (T2DM) patients. Vildagliptin does not alter myocardial function in T2DM patients with systolic dysfunction. However, the possibility of an increase in clinical heart failure and worsened outcomes in patients with existing heart failure is suggested by current data. Clinicians need to follow patients on DPP-4 inhibitors carefully for this possibility until more prospective randomized controlled data are available.

The dipeptidyl peptidase-4 inhibitor saxagliptin improves function of circulating pro-angiogenic cells from type 2 diabetic patients

BACKGROUND

Type 2 diabetes (T2D) is associated with reduction and dysfunction of circulating pro-angiogenic cells (PACs). DPP-4 inhibitors, a class of oral agents for T2D, might possess pleiotropic vasculoprotective activities. Herein, we tested whether DPP-4 inhibition with Saxagliptin affects the function of circulating PACs from T2D and healthy subjects.

METHODS

PACs were isolated from T2D (n = 20) and healthy (n = 20) subjects. Gene expression, clonogenesis, proliferation, adhesion, migration and tubulisation were assessed in vitro by incubating PACs with or without Saxagliptin and SDF-1α. Stimulation of angiogenesis by circulating cells from T2D patients treated with Saxagliptin or other non-incretinergic drugs was assessed in vivo using animal models.

RESULTS

Soluble DPP-4 activity was predominant over cellular activity and was successfully inhibited by Saxagliptin. At baseline, T2D compared to healthy PACs contained less acLDL(+)Lectin(+) cells, and showed altered expression of genes related to adhesion and cell cycle regulation. This was reflected by impaired adhesion and clonogenesis/proliferative response of T2D PACs. Saxagliptin + SDF-1α improved adhesion and tube sustaining capacity of PACs from T2D patients. CD14+ PACs were more responsive to Saxagliptin than CD14- PACs. While Saxagliptin modestly reduced angiogenesis by mature endothelial cells, circulating PACs-progeny cells from T2D patients on Saxagliptin treatment displayed higher growth factor-inducible in vivo angiogenetic activity, compared to cells from T2D patients on non-incretinergic regimen.

CONCLUSIONS

Saxagliptin reverses PACs dysfunction associated with T2D in vitro and improves inducible angiogenesis by circulating cells in vivo. These data add knowledge to the potential pleiotropic cardiovascular effects of DPP-4 inhibition.

Dipeptidyl peptidase IV inhibitors and ischemic myocardial injury

Diabetes mellitus is a major risk factor for cardiovascular events and patient death. Many animal and clinical studies are now being conducted exploring the potential of antidiabetic drugs such as glucagon-like peptide 1 (GLP-1) agonists and dipeptidyl peptidase IV (DPP-IV) inhibitors to improve cardiovascular outcomes. This review summarizes the effect of DPP-IV inhibitors on myocardial ischemia-reperfusion injury in animal models. The DPP-IV inhibitors prevent the rapid degradation and inactivation of incretins and lead to the accumulation of GLP-1 and other chemokines and cytokines, which appear to have both GLP-1 receptor-dependent and -independent cardioprotective, antiapoptotic, and anti-inflammatory effects. Conflicting results, however, have been reported regarding the effect of DPP-IV inhibitors on infarct size in nondiabetic and diabetic animal models. Some studies suggest that DPP-IV inhibitors given as part of preconditioning can decrease infarct size while others found no difference in infarct size compared to placebo. As postconditioning, one study suggested it does provide cardioprotection. No clinical trials have yet been conducted addressing the effect of DPP-IV inhibitors on infarct size. Thus far, clinical trials have not demonstrated improvement in cardiovascular events or mortality from any cause in high cardiovascular risk, type 2 diabetic patients with the use of DPP-IV inhibitors. Although further experiments and clinical trials will be warranted to confirm the results of these studies, the myocardial protection afforded by DPP-IV inhibitors in preclinical animal studies poses a potential breakthrough role for antidiabetic medications in attenuation of ischemia-reperfusion injury that occurs with cardiovascular disease.

The use of non-insulin anti-diabetic agents to improve glycemia without hypoglycemia in the hospital setting: focus on incretins

Patients with hyperglycemia in hospital have increased adverse outcomes compared with patients with normoglycemia, and the pathophysiological causes seem relatively well understood. Thus, a rationale for excellent glycemic control exists. Benefits of control with intensive insulin regimes are highly likely based on multiple published studies. However, hypoglycemia frequency increases and adverse outcomes of hypoglycemia accrue. This has resulted in a 'push' for therapeutic nihilism, accepting higher glycemic levels to avoid hypoglycemia. One would ideally prefer to optimize glycemia, treating hyperglycemia while minimizing or avoiding hypoglycemia. Thus, one would welcome therapies and processes of care to optimize this benefit/ risk ratio. We review the logic and early studies that suggest that incretin therapy use in-hospital can achieve this ideal. We strongly urge randomized prospective controlled studies to test our proposal and we offer a process of care to facilitate this research and their use in our hospitalized patients.

Substance P increases sympathetic activity during combined angiotensin-converting enzyme and dipeptidyl peptidase-4 inhibition

Dipeptidyl peptidase-4 inhibitors prevent the degradation of incretin hormones and reduce postprandial hyperglycemia in patients with type 2 diabetes mellitus. Dipeptidyl peptidase-4 degrades other peptides with a penultimate proline or alanine, including bradykinin and substance P, which are also substrates of angiotensin-converting enzyme (ACE). During ACE inhibition, substance P is inactivated primarily by dipeptidyl peptidase-4, whereas bradykinin is first inactivated by aminopeptidase P. This study tested the hypothesis that dipeptidyl peptidase-4 inhibition potentiates vasodilator and fibrinolytic responses to substance P when ACE is inhibited. Twelve healthy subjects participated in this randomized, double-blinded, placebo-controlled crossover study. On each study day, subjects received sitagliptin 200 mg by mouth or placebo. Substance P and bradykinin were infused via brachial artery before and during intra-arterial enalaprilat. Sitagliptin and enalaprilat each reduced forearm vascular resistance and increased forearm blood flow without affecting mean arterial pressure, but there was no interactive effect of the inhibitors. Enalaprilat increased bradykinin-stimulated vasodilation and tissue plasminogen activator release; sitagliptin did not affect these responses to bradykinin. The vasodilator response to substance P was unaffected by sitagliptin and enalaprilat; however, substance P increased heart rate and vascular release of norepinephrine during combined ACE and dipeptidyl peptidase-4 inhibition. In women, sitagliptin diminished tissue plasminogen activator release in response to substance P both alone and during enalaprilat. Substance P increases sympathetic activity during combined ACE and dipeptidyl peptidase-4 inhibition.

CLINICAL TRIAL REGISTRATION

- URL: http://www.clinicaltrials.gov. Unique identifier: NCT01413542.

The emerging role of dipeptidyl peptidase-4 inhibitors in cardiovascular protection: current position and perspectives

Dipeptidyl peptidase-4 (DPP-4 or CD26) inhibitors, a new class of oral anti-hyperglycemic agents that prolong the bioavailability of the endogenously secreted incretin hormone glucagon-like peptide-1 (GLP-1) and the glucose-dependent insulinotropic polypeptide (GIP), are effective in the treatment of diabetes. Accumulating data have indicated that DPP-4 inhibitors play important protective roles in the cardiovascular system. DPP-4 inhibitors act to decrease myocardial infarct size, stabilize the cardiac electrophysiological state during myocardial ischemia, reduce ischemia/reperfusion injury, and prevent left ventricular remodeling after myocardial infarction. Moreover, DPP-4 inhibitors can mobilize stem/progenitor cells to move to sites of cardiovascular injury, thus further promoting tissue repair. In addition, DPP-4 inhibitors not only improve myocardial metabolism but also regulate cardioactive peptides. DPP-4 inhibitors can also protect the vasculature through their anti-inflammatory and anti-atherosclerotic effects and through the ability of the inhibitors to promote vascular relaxation. Finally, the potential effects of DPP-4 inhibitors on blood pressure and lipid metabolism have also been investigated. However, some reports on the cardioprotective activities of DPP-4 inhibitors are controversial. Herein, we summarize the available data on cardiovascular protection by DPP-4 inhibitors that have emerged in recent years and discuss current position and future perspectives concerning the use of DPP-4 inhibitors in cardiovascular medicine.

Sarcoid-like lung granulomas in a hemodialysis patient treated with a dipeptidyl peptidase-4 inhibitor

It has been reported that the inhibition of dipeptidyl peptidase-4 (DPP-4)/CD26 on T-cells by DPP-4 enzymatic inhibitors suppresses lymphocyte proliferation and reduces the production of various cytokines, including tumor necrosis factor (TNF)-α. A 72-year-old female with diabetic nephropathy on hemodialysis developed multiple lung nodules following the administration of vildagliptin. A biopsy demonstrated the histology of granulomas without caseous necrosis. The discontinuation of vildagliptin resulted in the disappearance of the granulomas within 4 months. As granulomatosis often develops in patients under anti-TNF-α therapy, the accumulation of DPP-4 inhibitors or its metabolites is possibly linked to unrecognized complications, such as sarcoid-like lung granulomas.

Recent approaches to medicinal chemistry and therapeutic potential of dipeptidyl peptidase-4 (DPP-4) inhibitors

Dipeptidyl peptidase-4 (DPP-4) is one of the widely explored novel targets for Type 2 diabetes mellitus (T2DM) currently. Research has been focused on the strategy to preserve the endogenous glucagon like peptide (GLP)-1 activity by inhibiting the DPP-4 action. The DPP-4 inhibitors are weight neutral, well tolerated and give better glycaemic control over a longer duration of time compared to existing conventional therapies. The journey of DPP-4 inhibitors in the market started from the launch of sitagliptin in 2006 to latest drug teneligliptin in 2012. This review is mainly focusing on the recent medicinal aspects and advancements in the designing of DPP-4 inhibitors with the therapeutic potential of DPP-4 as a target to convey more clarity in the diffused data.

DPP-4 inhibitors repress foam cell formation by inhibiting scavenger receptors through protein kinase C pathway

Studies show that dipeptidyl peptidase-4 (DPP-4) inhibitors may have an anti-atherosclerotic effect. Since foam cells are key components of atherosclerotic plaque, we studied the effect of DPP-4 inhibitors on foam cell formation. Foam cell formation was studied by treatment of THP-1 macrophages with oxidized low-density lipoprotein in the absence or presence of DPP-4 inhibitors (sitagliptin and NVPDPP728). The expression of scavenger receptors SRA, CD36 and LOX-1 was measured, and their role in foam cell formation in the presence of DPP-4 inhibitors was examined. In additional studies, role of protein kinase C and A in the effect of DPP-4 inhibitors was examined. Foam cell formation was markedly reduced by both DPP-4 inhibitors, as was the expression of CD36 and LOX-1 (CD36 ≫ LOX-1), but not SRA. Simultaneously, there was a reduction in phosphorylated PKC, but not PKA, content. Recovery of phosphorylated PKC following treatment of cells negated the effect of DPP-4 inhibitors on foam cell formation. Further, overexpression of CD36 or LOX-1 blocked the effect of DPP-4 inhibitors on foam cell formation. DPP-4 inhibitors repress foam cell formation through the inhibition of SRs CD36 and LOX-1, most likely via the inhibition of PKC activity. This study provides novel insights into the mechanism of inhibition of atherosclerosis by DPP-4 inhibitors.

Dipeptidyl peptidase-4 inhibitors in cardioprotection: a promising therapeutic approach

Cardiovascular diseases are major killers in all developed societies and rapidly becoming the leading cause of morbidity and mortality in the developing world. Patients with diabetes mellitus are at particular risk of developing cardiovascular diseases. The present treatment options for management of diabetes have expanded since the development of glucagon-like peptide-1 agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors. There is a growing body of evidence that these agents may have cardioprotective effects even in patients who do not have diabetes. Here, we discuss this evidence as well as pathways that DPP-4 inhibitors target in the cardiovascular system. These agents over time will find an appropriate place in the management of cardiovascular diseases.

Protection of glucagon-like peptide-1 in cisplatin-induced renal injury elucidates gut-kidney connection

Accumulating evidence of the beyond-glucose lowering effects of a gut-released hormone, glucagon-like peptide-1 (GLP-1), has been reported in the context of remote organ connections of the cardiovascular system. Specifically, GLP-1 appears to prevent apoptosis, and inhibition of dipeptidyl peptidase-4 (DPP-4), which cleaves GLP-1, is renoprotective in rodent ischemia-reperfusion injury models. Whether this renoprotection involves enhanced GLP-1 signaling is unclear, however, because DPP-4 cleaves other molecules as well. Thus, we investigated whether modulation of GLP-1 signaling attenuates cisplatin (CP)-induced AKI. Mice injected with 15 mg/kg CP had increased BUN and serum creatinine and CP caused remarkable pathologic renal injury, including tubular necrosis. Apoptosis was also detected in the tubular epithelial cells of CP-treated mice using immunoassays for single-stranded DNA and activated caspase-3. Treatment with a DPP-4 inhibitor, alogliptin (AG), significantly reduced CP-induced renal injury and reduced the renal mRNA expression ratios of Bax/Bcl-2 and Bim/Bcl-2. AG treatment increased the blood levels of GLP-1, but reversed the CP-induced increase in the levels of other DPP-4 substrates such as stromal cell-derived factor-1 and neuropeptide Y. Furthermore, the GLP-1 receptor agonist exendin-4 reduced CP-induced renal injury and apoptosis, and suppression of renal GLP-1 receptor expression in vivo by small interfering RNA reversed the renoprotective effects of AG. These data suggest that enhancing GLP-1 signaling ameliorates CP-induced AKI via antiapoptotic effects and that this gut-kidney axis could be a new therapeutic target in AKI.

Glucagon-like peptide-1 (GLP-1) and its split products GLP-1(9-37) and GLP-1(28-37) stabilize atherosclerotic lesions in apoe⁻/⁻ mice

BACKGROUND

[corrected] Glucagon-like peptide-1 (GLP-1) based therapies are new treatment options for patients with type 2 diabetes. Recent reports suggest vasoprotective actions of GLP-1. Similar beneficial effects might be reached by GLP-1(9-37) and the c-terminal GLP-1 split product (28-37) although both peptides do not activate the GLP-1 receptor. We therefore investigated the actions of GLP-1(7-37), GLP-1(9-37) as well as GLP-1(28-37) on vascular lesion formation in a mouse model of atherosclerosis.

METHODS AND RESULTS

GLP-1(7-37), GLP-1(9-37) and GLP-1(28-37) and LacZ (control) were overexpressed for a period of 12 weeks in apoe(-/-) mice on high-fat diet (n = 10/group) using an adeno-associated viral vector system. Neither of the constructs changed overall lesion size. However, GLP-1(7-37), GLP-1(9-37) and GLP-1(28-37) significantly reduced plaque macrophage infiltration (GLP-1(7-37): 40.6%, GLP-1(9-37): 47.0%, GLP-1(28-37): 40.1% decrease, p < 0.05) and plaque MMP-9 expression (GLP-1(7-37): 41.6%, GLP-1(9-37): 50.2%, GLP-1(28-37): 44.0% decrease, p < 0.05) compared to LacZ in the aortic arch. Moreover, all GLP-1 constructs increased plaque collagen content (GLP-1(7-37): 49.3%, GLP-1(9-37): 86.0%, GLP-1(28-37): 81.9% increase, p < 0.05) and increased fibrous cap thickness (GLP-1(7-37): 188.0%, GLP-1(9-37): 179.9% GLP-1(28-37): 111.0% increase, p < 0.05). These effects of GLP-1(7-37), GLP-1(9-37) and GLP-1(28-37) on plaque macrophage infiltration, MMP-9 expression and plaque collagen content were confirmed in the aortic root.

CONCLUSION

GLP-1(7-37), GLP-1(9-37) and GLP-1(28-37) reduce plaque inflammation and increase phenotypic characteristics of plaque stability in a murine model of atherosclerosis. Future studies are needed to determine whether these effects translate into improved plaque stability and less cardiovascular events in high-risk patients with type 2 diabetes.

Lower dipeptidyl peptidase-4 following exercise training plus weight loss is related to increased insulin sensitivity in adults with metabolic syndrome

Dipeptidyl peptidase-4 (DPP-4) is a circulating glycoprotein that impairs insulin-stimulated glucose uptake and is linked to obesity and metabolic syndrome. However, the effect of exercise on plasma DPP-4 in adults with metabolic syndrome is unknown. Therefore, we determined the effect of exercise on DPP-4 and its role in explaining exercise-induced improvements in insulin sensitivity. Fourteen obese adults (67.9±1.2 years, BMI: 34.2±1.1kg/m(2)) with metabolic syndrome (ATP III criteria) underwent a 12-week supervised exercise intervention (60min/day for 5 days/week at ∼85% HRmax). Plasma DPP-4 was analyzed using an enzyme-linked immunosorbent assay. Insulin sensitivity was measured using the euglycemic-hyperinsulinemic clamp (40mU/m(2)/min) and estimated by HOMA-IR. Visceral fat (computerized tomography), 2-h glucose levels (75g oral glucose tolerance), and basal fat oxidation as well as aerobic fitness (indirect calorimetry) were also determined before and after exercise. The intervention reduced visceral fat, lowered blood pressure, glucose and lipids, and increased aerobic fitness (P<0.05). Exercise improved clamp-derived insulin sensitivity by 75% (P<0.001) and decreased HOMA-IR by 15% (P<0.05). Training decreased plasma DPP-4 by 10% (421.8±30.1 vs. 378.3±32.5ng/ml; P<0.04), and the decrease in DPP-4 was associated with clamp-derived insulin sensitivity (r=-0.59; P<0.04), HOMA-IR (r=0.59; P<0.04) and fat oxidation (r=-0.54; P<0.05). Increased fat oxidation also correlated with lower 2-h glucose levels (r=-0.64; P<0.02). Exercise training reduces plasma DPP-4, which may be linked to elevated insulin sensitivity and fat oxidation. Maintaining low plasma DPP-4 concentrations is a potential mechanism whereby exercise plus weight loss prevents/delays the onset of type 2 diabetes in adults with metabolic syndrome.

Direct cardiovascular effects of glucagon like peptide-1

Current gold standard therapeutic strategies for T2DM target insulin resistance or β cell dysfunction as their core mechanisms of action. However, the use of traditional anti-diabetic drugs, in most cases, does not significantly reduce macrovascular morbidity and mortality. Among emerging anti-diabetic candidates, glucagon like peptide-1 (GLP-1) based therapies carry special cardiovascular implications, exerting both direct as well as indirect effects. The direct cardiovascular effects of GLP-1 and its analogs remain the focus of this review.

Saxagliptin efficacy and safety in patients with type 2 diabetes mellitus and cardiovascular disease history or cardiovascular risk factors: results of a pooled analysis of phase 3 clinical trials

OBJECTIVE

This post hoc analysis sought to assess the efficacy, safety, and tolerability of saxagliptin in patients with type 2 diabetes mellitus and cardiovascular (CV) risk factors or disease (CVD).

METHODS

Data from 5 randomized controlled trials were pooled to compare saxagliptin 5 mg with placebo: 2 studies of saxagliptin as monotherapy in drug-naïve patients and 1 each of saxagliptin as add-on therapy to metformin, glyburide, or a thiazolidinedione. Analysis was performed according to the following baseline/trial entry criteria: 1) history/no history of CVD; 2) ≥ 2 versus 0 to 1 CV risk factors; 3) statin use versus no statin use; and 4) hypertension versus no hypertension. Change from baseline glycated hemoglobin (HbA1c), fasting plasma glucose, and postprandial glucose levels; and the proportion of patients achieving an HbA1c level < 7% were analyzed (week 24). Safety was assessed by adverse events, hypoglycemia, and body weight.

RESULTS

In total, 882 patients received saxagliptin 5 mg and 799 received placebo. Differences in adjusted mean change from baseline HbA1c (95% CI) were greater with saxagliptin compared with placebo in patients with a history of CVD (-0.64% [-0.90 to -0.38]) and no history of CVD (-0.68% [-0.78 to -0.58]); with ≥ 2 CV risk factors (-0.73% [-0.85 to -0.60]) and 0 to 1 CV risk factor (-0.62% [-0.75 to -0.48]); with statin use (-0.70% [-0.89 to -0.52]) and no statin use (-0.66% [-0.77 to -0.56]); and with hypertension (-0.69% [-0.82 to -0.57]) and no hypertension (-0.66% [-0.80 to -0.52]). Saxagliptin was well tolerated, with similar adverse event rates and types compared with placebo. There was a < 1% rate of confirmed hypoglycemia in all groups except in patients with CV history who received placebo (2.1%).

CONCLUSION

Saxagliptin improved glycemic measures, resulted in low rates of confirmed hypoglycemia, and was well tolerated in patients with or without CVD and CV risk factors.

Rationale, design, and baseline characteristics of a trial for the prevention of diabetic atherosclerosis using a DPP-4 inhibitor: the Study of Preventive Effects of Alogliptin on Diabetic Atherosclerosis (SPEAD-A)

AIM

Alogliptin, an efficacious inhibitor of DPP-4 that improves glycemic control, as well as the pancreatic beta-cell function, is now increasingly used to accomplish glycemic targets in type 2 diabetic patients. Interestingly, recent experimental studies have shown that alogliptin exerts anti-atherosclerotic effects in GLP-1-dependent and -independent manners. The aim of the present ongoing study is to investigate the preventive effects of alogliptin on the progression of atherosclerosis in type 2 diabetic subjects using the carotid intima-media thickness (IMT), an established marker of cardiovascular disease.

METHODS AND RESULTS

The Study of Preventive Effects of Alogliptin on Diabetic Atherosclerosis (SPEAD-A) is a prospective, randomized, open-label, blinded-endpoint, multicenter, parallel-group, comparative study. Between March 2011 and March 2012, 341 participants were recruited at 11 clinical sites, and were randomly allocated either to an alogliptin treatment group (172 patients) or a conventional treatment group (169 patients). The primary outcomes are the changes in the maximum and mean IMT of the common carotid artery during a 24-month treatment period, as measured by carotid arterial echography. The secondary outcomes include the changes in glycemic control, parameters related to beta-cell function and diabetic nephropathy, the occurrence of cardiovascular events and adverse events and biochemical measurements reflecting vascular function.

CONCLUSIONS

This is the first study to address the effects of DPP-4 inhibitors on the progression of changes in the carotid IMT, with the patients without DPP-4 inhibitor treatment serving as a control group. The results will be available soon, and these findings are expected to provide clinical data that will be helpful in the prevention of diabetic atherosclerosis and subsequent cardiovascular disease.

Cardiovascular effects of dipeptidyl peptidase-4 inhibitors: from risk factors to clinical outcomes

Dipeptidyl peptidase-4 (DPP-4) inhibitors (gliptins) are oral incretin-based glucose-lowering agents with proven efficacy and safety in the management of type 2 diabetes mellitus (T2DM). In addition, preclinical data and mechanistic studies suggest a possible additional non-glycemic beneficial action on blood vessels and the heart, via both glucagon-like peptide-1-dependent and glucagon-like peptide-1-independent effects. As a matter of fact, DPP-4 inhibitors improve several cardiovascular risk factors: they improve glucose control (mainly by reducing the risk of postprandial hyperglycemia) and are weight neutral; may lower blood pressure somewhat; improve postprandial (and even fasting) lipemia; reduce inflammatory markers; diminish oxidative stress; improve endothelial function; and reduce platelet aggregation in patients with T2DM. In addition, positive effects on the myocardium have been described in patients with ischemic heart disease. Results of post hoc analyses of phase 2/3 controlled trials suggest a possible cardioprotective effect with a trend (sometimes significant) toward lower incidence of major cardiovascular events with sitagliptin, vildagliptin, saxagliptin, linagliptin, or alogliptin compared with placebo or other active glucose-lowering agents. However, the definite relationship between DPP-4 inhibition and better cardiovascular outcomes remains to be proven. Major prospective clinical trials involving various DPP-4 inhibitors with predefined cardiovascular outcomes are under way in patients with T2DM and a high-risk cardiovascular profile: the Sitagliptin Cardiovascular Outcome Study (TECOS) on sitagliptin, the Saxagliptin Assessment of Vascular Outcomes Recorded in Patients With Diabetes Mellitus-Thrombolysis in Myocardial Infarction (SAVOR-TIMI) 53 trial on saxagliptin, the Cardiovascular Outcomes Study of Alogliptin in Subjects With Type 2 Diabetes and Acute Coronary Syndrome (EXAMINE) trial on alogliptin, and the Cardiovascular Outcome Study of Linagliptin Versus Glimepiride in Patients With Type 2 Diabetes (CAROLINA) on linagliptin. If these trials confirm that a DPP-4 inhibitor can reduce the cardiovascular burden of T2DM, it would be major progress that would dramatically influence the management of the disease.

Preventive effect of dipeptidyl peptidase-4 inhibitor on atherosclerosis is mainly attributable to incretin's actions in nondiabetic and diabetic apolipoprotein E-null mice

Aim

Several recent reports have revealed that dipeptidyl peptidase (DPP)-4 inhibitors have suppressive effects on atherosclerosis in apolipoprotein E-null (Apoe^−/−) mice. It remains to be seen, however, whether this effect stems from increased levels of the two active incretins, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP).

Methods

Nontreated Apoe^−/− mice, streptozotocin-induced diabetic Apoe^−/− mice, and db/db diabetic mice were administered the DPP-4 inhibitor vildagliptin in drinking water and co-infused with either saline, the GLP-1 receptor blocker, exendin(9–39), the GIP receptor blocker, (Pro³)GIP, or both via osmotic minipumps for 4 weeks. Aortic atherosclerosis and oxidized low-density lipoprotein-induced foam cell formation in exudate peritoneal macrophages were determined.

Results

Vildagliptin increased plasma GLP-1 and GIP levels without affecting food intake, body weight, blood pressure, or plasma lipid profile in any of the animals tested, though it reduced HbA1c in the diabetic mice. Diabetic Apoe^−/− mice exhibited further-progressed atherosclerotic lesions and foam cell formation compared with nondiabetic counterparts. Nondiabetic and diabetic Apoe^−/− mice showed a comparable response to vildagliptin, namely, remarkable suppression of atherosclerotic lesions with macrophage accumulation and foam cell formation in peritoneal macrophages. Exendin(9–39) or (Pro³)GIP partially attenuated the vildagliptin-induced suppression of atherosclerosis. The two blockers in combination abolished the anti-atherosclerotic effect of vildagliptin in nondiabetic mice but only partly attenuated it in diabetic mice. Vildagliptin suppressed macrophage foam cell formation in nondiabetic and diabetic mice, and this suppressive effect was abolished by infusions with exendin(9–39)+(Pro³)GIP. Incubation of DPP-4 or vildagliptin in vitro had no effect on macrophage foam cell formation.

Conclusions

Vildagliptin confers a substantial anti-atherosclerotic effect in both nondiabetic and diabetic mice, mainly via the action of the two incretins. However, the partial attenuation of atherosclerotic lesions by the dual incretin receptor antagonists in diabetic mice implies that vildagliptin confers a partial anti-atherogenic effect beyond that from the incretins.

Cardiovascular safety of the dipetidyl peptidase-4 inhibitor alogliptin in type 2 diabetes mellitus

AIM

As there have been concerns that some classes or agents for the treatment of type 2 diabetes may increase CV risk, we evaluated the cardiovascular profile of the dipeptidyl peptidase-4 inhibitor alogliptin.

METHODS

We evaluated the incidence of CV events in patients treated with alogliptin, placebo or comparator antihyperglycaemic drugs in the clinical trial database for alogliptin using the composite major adverse cardiovascular event (MACE) endpoints of CV death, non-fatal myocardial infarction and non-fatal stroke.

RESULTS

The pooled analysis included 4168 patients exposed to alogliptin 12.5 and 25 mg daily for 2023 patient-years compared to 691 patients treated with placebo for 263 patient-years and 1169 patients treated with other antidiabetic agents (metformin, sulfonylureas and thiazolidinediones) for 703 patient-years. CV events were adjudicated by an expert endpoint committee blinded to treatment allocation. The incidence rates of the combined MACE were not significantly different between patients treated with alogliptin and comparator therapies (hazard ratio=0.635, 95% confidence interval, 0.0, 1.41). Additionally, other types of serious CV events were not significantly different between patients treated with alogliptin and comparator therapies.

CONCLUSION

These analyses have not shown a signal of increased CV risk with alogliptin in patients with type 2 diabetes. Future results from the adequately powered EXAMINE trial will definitively assess the CV safety profile of aloglipin in patients with type 2 diabetes mellitus.