Acute DPP IV inhibition modulates vascular tone through GLP-1 independent pathways. Vascul Pharmacol. 2011;55:2-9. [PMID: 21397040 DOI: 10.1016/j.vph.2011.03.001]

Effects of dipeptidyl peptidase 4 inhibition on the endothelial control of the vascular tone

Dipeptidyl peptidase 4 (DPP4) is a serine protease known to cleave incretin hormones, which stimulate insulin secretion after food intake, a fact that supported the development of its inhibitors (DPP4i or gliptins) for the treatment of type 2 diabetes mellitus. In addition to their glucose-lowering effects, DPP4i show benefits for the cardiovascular system that could be related, at least in part, to their protective action on vascular endothelium. DPP4i have been associated with the reversal of endothelial dysfunction, an important predictor of cardiovascular events and a hallmark of diseases such as atherosclerosis, diabetes mellitus, hypertension, and heart failure. In animal models of these diseases, DPP4i increase nitric oxide bioavailability and limits oxidative stress, thereby improving the endothelium-dependent relaxation. Similar effects on flow-mediated dilation and attenuation of endothelial dysfunction have also been noted in human studies, suggesting a value for gliptins in the clinical scenario, despite the variability of the results regarding the DPP4i used, treatment duration, and presence of comorbidities. In this mini-review, we discuss the advances in our comprehension of the DPP4i effects on endothelial regulation of vascular tone. Understanding the role of DPP4 and its involvement in the signaling mechanisms leading to endothelial dysfunction will pave the way for a broader use of DPP4i in conditions that endothelial dysfunction is a pivotal pathophysiological player.

Incretins-Based Therapies and Their Cardiovascular Effects: New Game-Changers for the Management of Patients with Diabetes and Cardiovascular Disease

Atherosclerosis is the leading cause of death worldwide, especially in patients with type 2 diabetes mellitus (T2D). GLP-1 receptor agonists and DPP-4 inhibitors were demonstrated to play a markedly protective role for the cardiovascular system beyond their glycemic control. Several cardiovascular outcome trials (CVOT) reported the association between using these agents and a significant reduction in cardiovascular events in patients with T2D and a high cardiovascular risk profile. Moreover, recent evidence highlights a favorable benefit/risk profile in myocardial infarction and percutaneous coronary revascularization settings. These clinical effects result from their actions on multiple molecular mechanisms involving the immune system, platelets, and endothelial and vascular smooth muscle cells. This comprehensive review specifically concentrates on these cellular and molecular processes mediating the cardiovascular effects of incretins-like molecules, aiming to improve clinicians' knowledge and stimulate a more extensive use of these drugs in clinical practice as helpful cardiovascular preventive strategies.

DPP-4 inhibitors for treating T2DM - hype or hope? an analysis based on the current literature

DPP-4 inhibition is an interesting line of therapy for treating Type 2 Diabetes Mellitus (T2DM) and is based on promoting the incretin effect. Here, the authors have presented a brief appraisal of DPP-4 inhibitors, their modes of action, and the clinical efficiency of currently available drugs based on DPP-4 inhibitors. The safety profiles as well as future directions including their potential application in improving COVID-19 patient outcomes have also been discussed in detail. This review also highlights the existing queries and evidence gaps in DPP-4 inhibitor research. Authors have concluded that the excitement surrounding DPP-4 inhibitors is justified because in addition to controlling blood glucose level, they are good at managing risk factors associated with diabetes.

Dipeptidyl peptidase 4 inhibition rescues PKA-eNOS signaling and suppresses aortic hypercontractility in male rats with heart failure

AIMS

Vascular dysfunction and elevated circulating dipeptidyl peptidase 4 (DPP4) activity are both reported to be involved in the progression of heart failure (HF). While the cardiac benefits of DPP4 inhibitors (DPP4i) have been extensively studied, little is known about the effects of DPP4i on vascular dysfunction in nondiabetic HF. This study tested the hypothesis that vildagliptin (DPP4i) mitigates aortic hyperreactivity in male HF rats.

MATERIALS AND METHODS

Male Wistar rats were subjected to left ventricle (LV) radiofrequency ablation to HF induction or sham operation (SO). Six weeks after surgery, radiofrequency-ablated rats who developed HF were treated with vildagliptin (120 mg⸱kg^-1⸱day^-1) or vehicle for 4 weeks. Thoracic aorta reactivity, dihydroethidium fluorescence, immunoblotting experiments, and enzyme-linked immunosorbent assays were performed.

KEY FINDINGS

DPP4i ameliorated the hypercontractility of HF aortas to the α-adrenoceptor agonist phenylephrine towards SO levels. In HF, the reduced endothelium and nitric oxide (NO) anticontractile effect on phenylephrine response was restored by DPP4i. At the molecular level, this vasoprotective effect of DPP4i was accompanied by (i) reduced oxidative stress and NADPH oxidase 2 (Nox2) expression, (ii) enhanced total endothelial nitric oxide synthase (eNOS) expression and phosphorylation at Ser1177, and (iii) increased PKA activation, which acts upstream of eNOS. Additionally, DPP4i restored the higher serum angiotensin II concentration towards SO.

SIGNIFICANCE

Our data demonstrate that DPP4i ameliorates aortic hypercontractility, most likely by enhancing NO bioavailability, showing that the DPP4i-induced cardioprotection in male HF may arise from effects not only in the heart but also in conductance arteries.

Acute effects of linagliptin on intact and total glucagon-like peptide-1 and gastric inhibitory polypeptide levels in insulin-dependent type 2 diabetes patients with and without moderate renal impairment

AIMS

To investigate the effect of renal impairment on incretin metabolism in patients with type 2 diabetes mellitus (T2DM) before and after treatment with the dipeptidyl peptidase-4 (DPP-4) inhibitor linagliptin.

MATERIALS AND METHODS

Long-standing T2DM patients with normal (estimated glomerular filtration rate [eGFR] >90 mL/min/1.73m² ) and impaired (eGFR <60 mL/min/1.73m² ) renal function on stable treatment with insulin were included. Before and after 8 days of treatment with 5 mg linagliptin once daily, patients underwent a 75-g oral glucose tolerance test (OGTT) and total and intact glucagon-like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP), glucose, insulin, C-peptide and glucagon concentrations were measured. The primary outcome was the difference between the study groups in change of intact GLP-1 concentrations.

RESULTS

Of 115 patients screened, 29 were analysed (15 [51.7%] with and 14 [48.3%] without renal impairment). Renal function differed significantly between the groups (101 ± 11 vs. 47 ± 13 mL/min/1.73m² ; P < 0.0001), while glycaemic control was similar (glycated haemoglobin 68 ±  5 vs. 66 ± 5 mmol/mol; P = 0.45). Baseline GLP-1 and GIP levels were comparable. Glucose concentrations during the OGTT were significantly lowered by linagliptin treatment in patients with renal impairment (P = 0.017), but not in those with normal renal function (P = 0.17). Treatment with linagliptin resulted in a significant increase in intact GLP-1 and GIP levels in patients with normal (P = 0.048 and P = 0.0001, respectively) and impaired (P = 0.040 and P = 0.0011, respectively) renal function during the OGTT. However, the primary outcome (difference between the groups in change of intact GLP-1 concentrations) was not significant (P = 0.22). Overall, linagliptin was well tolerated.

CONCLUSIONS

Treatment with linagliptin increases intact incretin levels in patients with T2DM. Impaired renal function does not compromise the effects of linagliptin on active or total incretin levels as well as on glucagon secretion. Thus, treatment with linagliptin is suitable for patients with T2DM, independently of renal function.

Metabolic Syndrome: Updates on Pathophysiology and Management in 2021

Metabolic syndrome (MetS) forms a cluster of metabolic dysregulations including insulin resistance, atherogenic dyslipidemia, central obesity, and hypertension. The pathogenesis of MetS encompasses multiple genetic and acquired entities that fall under the umbrella of insulin resistance and chronic low-grade inflammation. If left untreated, MetS is significantly associated with an increased risk of developing diabetes and cardiovascular diseases (CVDs). Given that CVDs constitute by far the leading cause of morbidity and mortality worldwide, it has become essential to investigate the role played by MetS in this context to reduce the heavy burden of the disease. As such, and while MetS relatively constitutes a novel clinical entity, the extent of research about the disease has been exponentially growing in the past few decades. However, many aspects of this clinical entity are still not completely understood, and many questions remain unanswered to date. In this review, we provide a historical background and highlight the epidemiology of MetS. We also discuss the current and latest knowledge about the histopathology and pathophysiology of the disease. Finally, we summarize the most recent updates about the management and the prevention of this clinical syndrome.

Effects of dipeptidyl peptidase-4 inhibition on portal hypertensive and cirrhotic rats

BACKGROUND

Portal hypertension is a pathophysiological abnormality with distinct vascular derangements associated with liver cirrhosis. Dipeptidyl peptidase-4 (DPP-4) inhibitors are antidiabetic agents which exert pleiotropic vascular effects, but their relevant impact on portal hypertension and liver cirrhosis remains unclear. This study aims to clarify this issue.

METHODS

Rats receiving partial portal vein ligation (PVL) and common bile duct ligation (BDL) served as experimental models for portal hypertension and cirrhosis, respectively. After linagliptin (a DPP-4 inhibitor) treatment, the survival rate, hemodynamics, biochemistry parameters and liver histopathology were evaluated. In addition, the collateral vascular responsiveness and severity of portal-systemic shunting were examined. mRNA and protein expression in the vasculature and liver were also examined.

RESULTS

Linagliptin significantly reduced portal pressure (control vs linagliptin: 12.9 ± 1.2 vs 9.1 ± 2.0 mmHg, p = 0.001) and upregulated nitric oxide synthase expression in the collateral vessel, superior mesentery artery, and liver of PVL rats. However, the portal hypotensive effect was insignificant in BDL rats. Glucose plasma levels, liver and renal biochemistry parameters were not significantly altered by linagliptin. The degree of portal-systemic shunting and collateral vascular responsiveness were also not significantly altered by linagliptin treatment. Linagliptin did not improve liver fibrosis and hepatic inflammation in BDL rats.

CONCLUSION

DPP-4 inhibition by linagliptin reduced portal pressure in portal hypertensive rats but not in cirrhotic rats. It may act by decreasing intrahepatic resistance via upregulation of hepatic nitric oxide synthase in portal hypertensive rats.

Acute and long-term effects of saxagliptin on a set of cardiovascular targets measured at fasting and post-prandially in obese patients with impaired glucose tolerance: A placebo-controlled study

BACKGROUND AND AIMS

Studies of dipeptidyl peptidase inhibitors (DPP4is) report heterogeneous effects on cardiovascular targets in type 2 diabetes. This study aimed to investigate, in patients with impaired glucose tolerance (IGT), whether saxagliptin, a DPP4i, had beneficial cardiovascular effects at fasting and during the post-prandial state.

METHODS AND RESULTS

In this randomized, placebo-controlled, double-blind, single-center pilot exploratory study, we included obese individuals with IGT. Twenty-four individuals (BMI 36.8 ± 4.8 kg/m²) were randomized to receive for 12 weeks either saxagliptin 5 mg a day or placebo. They were explored before and after a standardized breakfast for biological markers; microcirculatory blood flow at baseline and after transcutaneous administration of acetylcholine (Periflux System 5000® PERIMED); post-occlusive digital reactive hyperhemia (Endopat2000®); pulse wave velocity, augmentation index, central pulse pressure and subendocardial viability ratio (Sphygmocor®); cardiac hemodynamic parameters and cardiovascular autonomic nervous system activity (Task force monitor®). The results of all the investigations were similar after breakfast in the two groups at Visit 1 (acute post-prandial effects, after the first tablet) and Visit 2 (long-term post-prandial effects), and at fasting at Visit 1 and 2 (long-term effects, after 12 weeks of treatment). Only at Visit 2 the decrease in cardiac vagal activity occurring after breakfast was more sustained in the saxagliptin group than in the placebo group (interaction between treatment and time effect: p = 0.016).

CONCLUSION

In obese patients with IGT, the effects of saxagliptin on the large set of cardiovascular parameters measured are neutral, except for a more marked post-prandial depression of vagal activity.

CLINICAL TRIAL REGISTRATION NUMBER

NCT01521312.

The Diabetic Cardiomyopathy: The Contributing Pathophysiological Mechanisms

Individuals with diabetes mellitus (DM) disclose a higher incidence and a poorer prognosis of heart failure (HF) than non-diabetic people, even in the absence of other HF risk factors. The adverse impact of diabetes on HF likely reflects an underlying “diabetic cardiomyopathy” (DM–CMP), which may by exacerbated by left ventricular hypertrophy and coronary artery disease (CAD). The pathogenesis of DM-CMP has been a hot topic of research since its first description and is still under active investigation, as a complex interplay among multiple mechanisms may play a role at systemic, myocardial, and cellular/molecular levels. Among these, metabolic abnormalities such as lipotoxicity and glucotoxicity, mitochondrial damage and dysfunction, oxidative stress, abnormal calcium signaling, inflammation, epigenetic factors, and others. These disturbances predispose the diabetic heart to extracellular remodeling and hypertrophy, thus leading to left ventricular diastolic and systolic dysfunction. This Review aims to outline the major pathophysiological changes and the underlying mechanisms leading to myocardial remodeling and cardiac functional derangement in DM-CMP.

Evaluation of Dual Inhibitory Effect of Anagliptin, Ramipril, and Lisinopril on Angiotensin-Converting Enzyme and DPP-4 Activities

BACKGROUND

We previously tested two angiotensin-converting enzyme (ACE) inhibitors and two dipeptidyl peptidase-4 (DPP-4) inhibitors for dual enzyme inhibitory effect. Only two DPP-4 inhibitors, linagliptin and sitagliptin, were able to inhibit ACE.

OBJECTIVE

In the present study, we investigated if other inhibitors of ACE or DPP-4 could simultaneously inhibit the activities of both DPP-4 and ACE.

METHODS

Forty Sprague Dawley rats were used. The control group received saline only. The other three groups were treated with anagliptin, ramipril, or lisinopril. Two different doses were tested, separated with a 6-day drug-free interval. Angiotensin II (ang II) levels, the activities of ACE, and DPP-4 were measured from blood samples at baseline and days 1, 10, and 14. After the oral glucose challenge, levels of the active form of glucagon-like peptide-1 (GLP-1) were measured.

RESULTS

Regardless of the dose, anagliptin did not show any inhibitory effect on the activity of ACE or ang II levels. For ramipril and lisinopril, only a high dose of lisinopril was able to produce a modest reduction of the DPP-4 activity, but it was not enough to inhibit the inactivation of GLP-1.

CONCLUSION

It seems that while most ACE inhibitors cannot affect DPP-4 activity, inhibitors of DPP-4 vary in their effect on ACE activity. The selection of DPP-4 inhibitors under different clinical situations should take into account the action of these drugs on ACE.

DPP4 Activity, Hyperinsulinemia, and Atherosclerosis

CONTEXT

Obesity and type 2 diabetes are associated with chronic hyperinsulinemia, elevated plasma levels of dipeptidyl peptidase-4 (DPP4), and a pro-atherosclerotic milieu.

EVIDENCE ACQUISITION

PubMed search of the term "insulin and atherosclerosis," "hyperinsulinemia," "atherosclerosis," or "cardiovascular outcomes" cross-referenced with "DPP4." Relevant research and review articles were reviewed.

EVIDENCE SYNTHESIS

Hyperinsulinemia in the setting of insulin resistance promotes vascular inflammation, vascular smooth muscle cell growth, pathological cholesterol profile, hypertension, and recruitment of immune cells to the endothelium, all contributing to atherosclerosis. DPP4 has pleiotropic functions and its activity is elevated in obese humans. DPP4 mirrors hyperinsulinemia's atherogenic actions in the insulin resistant state, and genetic deletion of DPP4 protects rodents from developing insulin resistance and improves cardiovascular outcomes. DPP4 inhibition in pro-atherosclerotic preclinical models results in reduced inflammation and oxidative stress, improved endothelial function, and decreased atherosclerosis. Increased incretin levels may have contributed to but do not completely account for these benefits. Small clinical studies with DPP4 inhibitors demonstrate reduced carotid intimal thickening, improved endothelial function, and reduced arterial stiffness. To date, this has not been translated to cardiovascular risk reduction for individuals with type 2 diabetes with prior or exaggerated risk of cardiovascular disease.

CONCLUSION

DPP4 may represent a key link between central obesity, insulin resistance, and atherosclerosis. The gaps in knowledge in DPP4 function and discrepancy in cardiovascular outcomes observed in preclinical and large-scale randomized controlled studies with DPP4 inhibitors warrant additional research.

Effects of sitagliptin on ß-adrenoceptor mediated relaxation in streptozotocin-diabetic rat aorta

Background/aim

Dipeptidyl peptidase-4 (DPP4) inhibitors, a class of oral antidiabetic drugs, have been shown to be protective on the vascular system because of their antiinflammatory, antiatherosclerotic, and vasodilatory effects. ß2-adrenoceptors (ß2-ARs) mediate the vasorelaxation in the aorta. However, ß3-adrenoceptor-mediated relaxation has not been studied in diabetic aorta yet. Thus, we aimed to study the effect of sitagliptin treatment on ß2- and ß3-adrenoceptor-mediated relaxations in the diabetic rat aorta.

Materials and methods

Eight-week old Sprague Dawley rats were divided into three groups: control, diabetic, sitagliptin treated diabetic. Diabetes was induced by injection of streptozotocin (35 or 40 mg/kg, intraperitoneally). After 10 weeks of diabetes, some of the diabetic rats were treated with sitagliptin (orally, 10mg/kg/day). ß2- and ß3-AR-mediated relaxation responses were evaluated by using isoprenaline and CL 316,243, respectively. ß3-AR-mediated relaxation experiments were repeated in presence of L-NAME. Western blotting and immunohistochemistry were performed to determine the abundance of ß3-adrenoceptor and endothelial nitric oxide synthase (eNOS).

Results

The isoprenaline-mediated relaxation response was impaired in the diabetic group and sitagliptin treatment did not improve it. There was no significant change in CL316,243 mediated-relaxation or protein expression of ß3-ARs among the groups. However, the ratio of phosphorylated eNOS/NOS protein was increased markedly in the sitagliptin treated group, which points the stimulating effect of this drug towards the eNOS pathway.

Conclusion

Our results indicate that sitagliptin treatment does not alter ß-AR-mediated relaxation in streptozotocin-diabetic rat aorta; however, it significantly stimulates the eNOS pathway. Future studies are needed to clarify the relationship between the eNOS pathway and DPP-4 inhibition.

The anti-diabetic drug alogliptin induces vasorelaxation via activation of Kv channels and SERCA pumps

In the present study, we investigated the vasorelaxant effects of alogliptin, an oral antidiabetic drug in the dipeptidyl peptidase-4 (DPP-4) inhibitor class, using phenylephrine (Phe)-induced pre-contracted aortic rings. Alogliptin induced vasorelaxation in a dose-dependent manner. Pre-treatment with the voltage-dependent K⁺ (Kv) channel inhibitor 4-aminopyridine (4-AP) significantly decreased the vasorelaxant effect of alogliptin, whereas pre-treatment with the inwardly rectifying K⁺ (Kir) channel inhibitor Ba²⁺, ATP-sensitive K⁺ (K_ATP) channel inhibitor glibenclamide, and large-conductance Ca²⁺-activated K⁺ (BK_Ca) channel inhibitor paxilline did not alter the effects of alogliptin. Although pre-treatment with the Ca²⁺ channel inhibitor nifedipine did not affect the vasorelaxant effect of alogliptin, pre-treatment with the sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) pump inhibitors thapsigargin and cyclopiazonic acid effectively attenuated the vasorelaxant response of alogliptin. Neither cGMP/protein kinase G (PKG)-related signaling pathway inhibitors (guanylyl cyclase inhibitor ODQ and PKG inhibitor KT 5823) nor cAMP/protein kinase A (PKA)-related signaling pathway inhibitors (adenylyl cyclase inhibitor SQ 22536 and PKA inhibitor KT 5720) reduced the vasorelaxant effect of alogliptin. Similarly, the vasorelaxant effect of alogliptin was not changed by endothelium removal or pre-treatment with the nitric oxide (NO) synthase inhibitor L-NAME or the small- and intermediate-conductance Ca²⁺-activated K⁺ (SK_Ca and IK_Ca) channel inhibitors apamin and TRAM-34. Based on these results, we suggest that alogliptin induced vasorelaxation in rabbit aortic smooth muscle by activating Kv channels and the SERCA pump independent of other K⁺ channels, cGMP/PKG-related or cAMP/PKA-related signaling pathways, and the endothelium.

Blood Pressure-Lowering Effect of Newer Antihyperglycemic Agents (SGLT-2 Inhibitors, GLP-1 Receptor Agonists, and DPP-4 Inhibitors)

The prevalence of arterial hypertension is high in patients with diabetes mellitus (DM). When DM and hypertension coexist, they constitute a dual cardiovascular threat and should be adequately controlled. Novel antihyperglycemic agents, including sodium-glucose co-transporter 2 (SGLT-2) inhibitors, glucagon-like peptide-1 receptor agonists (GLP-1 RAs), and dipeptidyl peptidase-4 (DPP-4) inhibitors, have recently been used in the treatment of DM. Beyond their glucose-lowering effects, these drugs have shown beneficial pleiotropic cardiovascular effects, including lowering of arterial blood pressure (BP), as acknowledged in the 2019 European Society of Cardiology/European Association for the Study of Diabetes guidelines on diabetes, prediabetes, and cardiovascular diseases. The purpose of this review was to summarize the available information on the BP-reducing effects of these new glucose-lowering drug classes and provide a brief report on underlying pathophysiological mechanisms. We also compare the three drug classes (SGLT-2 inhibitors, GLP-1 RAs, and DPP-4 inhibitors) in terms of their BP-lowering effect and show that the greater BP reduction seems to be achieved with SGLT-2 inhibitors, whereas DPP-4 inhibitors have probably the mildest antihypertensive effect.

Vildagliptin, a dipeptidyl peptidase-4 inhibitor, attenuated endothelial dysfunction through miRNAs in diabetic rats

INTRODUCTION

Dipeptidyl peptidase-4 (DPP-4) inhibitors have various cellular effects that are associated with vascular protection. Here, we examined whether vildagliptin protected endothelial function in diabetic rats and explored the involved mechanism.

MATERIAL AND METHODS

Experimental diabetic rats were obtained by feeding a high-fat diet and administering an intraperitoneal injection of streptozotocin. Rats were randomly divided into four groups: controls (CON), diabetes (DM), diabetes + low dose of vildagliptin (Lvil, 10 mg/kg/day), and diabetes + high dose of vildagliptin (Hvil, 20 mg/kg/day). The metabolic parameters, endothelial function, and whole miRNA expression were measured.

RESULTS

After a 12-week treatment, vildagliptin-treated rats showed a significant reduction in blood glucose and blood lipid levels. Moreover, vildagliptin recovered aortic endothelial function in diabetic rats. We identified 31 miRNAs that were differentially expressed in the Hvil group compared with the diabetic group. Importantly, through miRNA target biological function and pathway analysis, we found that vildagliptin activated miR-190-5p to inhibit Ccl2 expression and inhibited miR-134-5p and miR-375-3p to increase Bdnf and Pdk1 expression in the aorta.

CONCLUSIONS

Our present study indicates that vildagliptin can recover endothelial function in diabetic rats. Anti-inflammatory and anti-apoptosis mechanisms and endothelial moderation may be the intervention targets of vildagliptin to protect the cardiovascular system through miRNA regulation.

Diabetic rats are more susceptible to cognitive decline in a model of microemboli-mediated vascular contributions to cognitive impairment and dementia

Vascular disease plays an important role in all kinds of cognitive impairment and dementia. Diabetes increases the risk of vascular disease and dementia. However, it is not clear how existing vascular disease in the brain accelerates the development of small vessel disease and promotes cognitive dysfunction in diabetes. We used microemboli (ME) injection model in the current study to test the hypothesis that cerebrovascular dysfunction in diabetes facilitates entrapment of ME leading to inflammation and cognitive decline. We investigated cognitive function, axonal/white matter (WM) changes, neurovascular coupling, and microglial activation in control and diabetic male and female Wistar rats subjected to sham or low/high dose ME injection. Diabetic male animals had cognitive deficits, WM demyelination and greater microglial activation than the control animals even at baseline. Functional hyperemia gradually declined in diabetic male animals after ME injection. Both low and high ME injection worsened WM damage and increased microglial activation in diabetic male and female animals. Low ME did not cause cognitive decline in controls, while promoting learning/memory deficits in diabetic female rats and no further decline in diabetic male animals. High ME led to cognitive decline in control male rats and exacerbated the deficits in diabetic cohort. These results suggest that the existing cerebrovascular dysfunction in diabetes may facilitate ME-mediated demyelination leading to cognitive decline. It is important to integrate comorbidities/sex as a biological variable into experimental models for the development of preventive or therapeutic targets.

The Dipeptidyl Peptidase-4 Inhibitor Linagliptin Directly Enhances the Contractile Recovery of Mouse Hearts at a Concentration Equivalent to that Achieved with Standard Dosing in Humans

Despite a similar mechanism of action underlying their glucose-lowering effects in type 2 diabetes, dipeptidyl peptidase-4 (DPP-4) inhibitors have diverse molecular structures, raising the prospect of agent-specific, glucose-independent actions. To explore the issue of possible DPP-4 inhibitor cardiac heterogeneity, we perfused different DPP-4 inhibitors to beating mouse hearts ex vivo, at concentrations equivalent to peak plasma levels achieved in humans with standard dosing. We studied male and female mice, young non-diabetic mice, and aged diabetic high fat diet-fed mice and observed that linagliptin enhanced recovery after ischemia-reperfusion, whereas sitagliptin, alogliptin, and saxagliptin did not. DPP-4 transcripts were not detected in adult mouse cardiomyocytes by RNA sequencing and the addition of linagliptin caused ≤0.2% of cardiomyocyte genes to be differentially expressed. In contrast, incubation of C166 endothelial cells with linagliptin induced cell signaling characterized by phosphorylation of Akt and endothelial nitric oxide synthase, whereas the nitric oxide (NO) donor, S-nitroso-N-acetylpenicillamine increased serine 16 phosphorylation of the calcium regulatory protein, phospholamban in cardiomyocytes. Furthermore, linagliptin increased cardiomyocyte cGMP when cells were co-cultured with C166 endothelial cells, but not when cardiomyocytes were cultured alone. Thus, at a concentration comparable to that achieved in patients, linagliptin has direct effects on mouse hearts. The effects of linagliptin on cardiomyocytes are likely to be either off-target or indirect, mediated through NO generation by the adjacent cardiac endothelium.

Dipeptidyl peptidase-4 inhibitors as new tools for cardioprotection

Previous studies have demonstrated that individuals with type 2 diabetes mellitus (T2DM) have a two- to fourfold propensity to develop cardiovascular disease (CVD) than nondiabetic population, making CVD a major cause of death and disability among people with T2DM. The present treatment options for management of diabetes propose the earlier and more frequent use of new antidiabetic drugs that could control hyperglycaemia and reduce the risk of cardiovascular events. Findings from basic and clinical studies pointed out DPP-4 inhibitors as potentially novel pharmacological tools for cardioprotection. There is a growing body of evidence suggesting that these drugs have ability to protect the heart against acute ischaemia-reperfusion injury as well as reduce the size of infarction. Consequently, the prevention of degradation of the incretin hormones by the use of DPP-4 inhibitors represents a new strategy in the treatment of patients with T2DM and reduction of CV events in these patients. Here, we discuss the cardioprotective effects of DPP-4 inhibitors as well as proposed pathways that these hypoglycaemic agents target in the cardiovascular system.

Diabetes and calcification: The potential role of anti-diabetic drugs on vascular calcification regression

Vascular calcification (VC) has been well-established as an independent and strong predictor of cardiovascular diseases (CVD) as well as major cardiac adverse events (MACE). VC is associated with increased mortality in patients with CVD. Pathologically, VC is now believed to be a multi-directional active process ultimately resulting in ectopic calcium deposition in vascular beds. On the other hand, prevalence of diabetes mellitus (DM) is gradually increasing thus making the current population more prone to future CVD. Although the mechanisms involved in development and progression of VC in DM patients are not fully understood, a series of evidences demonstrated positive association between DM and VC. It has been highlighted that different cellular pathways are involved in this process. These intermediates such as tumor necrosis factor alpha (TNF-α), various interleukins (ILs) and different cell-signaling pathways are over-expressed in DM patients leading to development of VC. Thus, considering the burden and significance of VC it is of great importance to find a therapeutic approach to prevent or minimize the development of VC in DM patients. Over the past few years various anti diabetic drugs (ADDs) have been introduced and many of them showed desired glucose control. But no study demonstrated the effects of these medications on regression of VC. In this review, we will briefly discuss the current understanding on DM and VC and how commonly used ADDs modulate the development or progression of VC.

Can dipeptidyl peptidase-4 inhibitors treat cognitive disorders?

The linkage of neurodegenerative diseases with insulin resistance (IR) and type 2 diabetes mellitus (T2DM), including oxidative stress, mitochondrial dysfunction, excessive inflammatory responses and abnormal protein processing, and the correlation between cerebrovascular diseases and hyperglycemia has opened a new window for novel therapeutics for these cognitive disorders. Various antidiabetic agents have been studied for their potential treatment of cognitive disorders, among which the dipeptidyl peptidase-4 (DPP-4) inhibitors have been investigated more recently. So far, DPP-4 inhibitors have demonstrated neuroprotection and cognitive improvements in animal models, and cognitive benefits in diabetic patients with or without cognitive impairments. This review aims to summarize the potential mechanisms, advantages and limitations, and currently available evidence for developing DPP-4 inhibitors as a treatment of cognitive disorders.

Endothelium as a Therapeutic Target in Diabetes Mellitus: From Basic Mechanisms to Clinical Practice

Endothelium plays an essential role in human homeostasis by regulating arterial blood pressure, distributing nutrients and hormones as well as providing a smooth surface that modulates coagulation, fibrinolysis and inflammation. Endothelial dysfunction is present in Diabetes Mellitus (DM) and contributes to the development and progression of macrovascular disease, while it is also associated with most of the microvascular complications such as diabetic retinopathy, nephropathy and neuropathy. Hyperglycemia, insulin resistance, hyperinsulinemia and dyslipidemia are the main factors involved in the pathogenesis of endothelial dysfunction. Regarding antidiabetic medication, metformin, gliclazide, pioglitazone, exenatide and dapagliflozin exert a beneficial effect on Endothelial Function (EF); glimepiride and glibenclamide, dipeptidyl peptidase-4 inhibitors and liraglutide have a neutral effect, while studies examining the effect of insulin analogues, empagliflozin and canagliflozin on EF are limited. In terms of lipid-lowering medication, statins improve EF in subjects with DM, while data from short-term trials suggest that fenofibrate improves EF; ezetimibe also improves EF but further studies are required in people with DM. The effect of acetylsalicylic acid on EF is dose-dependent and lower doses improve EF while higher ones do not. Clopidogrel improves EF, but more studies in subjects with DM are required. Furthermore, angiotensin- converting-enzyme inhibitors /angiotensin II receptor blockers improve EF. Phosphodiesterase type 5 inhibitors improve EF locally in the corpus cavernosum. Finally, cilostazol exerts favorable effect on EF, nevertheless, more data in people with DM are required.

Alogliptin inhibits IL-1β-induced inflammatory response in fibroblast-like synoviocytes

Excessive production of pro-inflammatory cytokines such as interleukin (IL)-1β plays an important role in the chronic inflammation in fibroblast-like synoviocytes (FLS) in rheumatoid arthritis (RA). Alogliptin, an important selective dipeptidyl peptidase-4 (DPP-4) inhibitor licensed for the treatment of type 2 diabetes, has displayed a wide range of pharmacological capacities. In the present study, we aimed to investigate whether alogliptin possessed a protective effect against IL-1β-induced insult in FLS. Our results indicate that alogliptin treatment ameliorated IL-1β-induced production of reactive oxygen species, the expression of matrix metalloproteinase-3 (MMP-3) and MMP-13, secretions of tumor necrosis factor-α (TNF-α), IL-6, and IL-8. Additionally, we found that alogliptin inhibited c-Jun N-terminal kinase (JNK)/activator protein 1 (AP-1) signaling by reducing IL-1β-induced phosphorylation of JNK, the expression of c-Jun and c-Fos, and the luciferase activity of AP-1. Importantly, alogliptin suppressed IL-1β-induced activation of IκBα/NF-κB signaling by preventing the phosphorylation and degradation of IκBα, nuclear translocation of NF-κB p65, as well as the luciferase activity of AP-1. These findings suggest that alogliptin might have therapeutic potential for the treatment of chronic inflammation in RA.

The protective role of DPP4 inhibitors in atherosclerosis

Diabetes is a chronic non-communicable disease whose incidence continues to grow rapidly, and it is one of the most serious and critical public health problems. Diabetes complications, especially atherosclerosis-related chronic vascular complications, are a serious threat to human life and health. Growing evidence suggests that dipeptidyl peptidase 4 (DPP4) inhibitors, beyond their role in improving glycemic control, are helpful in ameliorating endothelial dysfunction in humans and animal models of T2DM. In fact, DPP4 inhibitors have been shown by successive studies to play a protective effect against vascular complications. On one hand, in addition to their hypoglycemic effects, DPP4 inhibitors participate in the control of atherosclerotic risk factors by regulating blood lipids and lowering blood pressure. On the other hand, DPP4 inhibitors exert anti-atherosclerotic effects directly through multiple mechanisms, including improving endothelial cell dysfunction, increasing circulating endothelial progenitor cell (EPCs) levels, regulating mononuclear macrophages and smooth muscle cells, inhibiting inflammation and oxidative stress and improving plaque instability. Herein, we review the beneficial roles of DPP4 inhibitors in atherosclerosis as detailed.

LC-MS analysis of Myrica rubra extract and its hypotensive effects via the inhibition of GLUT 1 and activation of the NO/Akt/eNOS signaling pathway

In the area of medicine food homology, Myrica rubra ((Lour.) Siebold & Zucc.) has been used in medicine as an astringent and anti-diarrheal. However, there are few in-depth studies evaluating the antihypertensive chemical components and antihypertensive mechanisms of Myrica rubra. Thus, the aim in this study was to assess the protective effects of an ethanol extract of bayberry (BE) on spontaneous hypertension in rats. In this study, liquid chromatography-mass spectroscopy (LC-MS) coupled with biochemical assays and western blot have been employed to study the protective effects of BE against hypertension. A total of 28 compounds were identified in BE. According to this study, treatment with BE (2 g kg^-1) resulted in the potent and persistent reduction of high blood pressure, even after drug withdrawal. The results indicate that the mechanisms of action might involve protection against damage to the vascular structure. Bayberry extract could enhance the endothelium-independent vascular function, inhibiting the abnormal proliferation of smooth muscle by inhibition of glucose transporter-1 (GLUT 1) and regulation of nitric oxide (NO)/serine/threonine kinases (Akt)/endothelial nitric oxide synthase (eNOS). The results of molecular docking and in vitro research indicated six compounds in BE that might be responsible for the antihypertensive effect attributed to GLUT 1, eNOS and Akt, and further in vivo studies are needed to verify this.

The Effects of DPP-4 Inhibitors, GLP-1RAs, and SGLT-2/1 Inhibitors on Heart Failure Outcomes in Diabetic Patients With and Without Heart Failure History: Insights From CVOTs and Drug Mechanism

Patients with type 2 diabetes (T2D) have a higher risk of heart failure (HF) than healthy people, and the prognosis of patients with diabetes and current or previous HF is worse than that of patients with only diabetes. We reviewed the HF outcomes in recently published cardiovascular outcome trials (CVOTs) of three new classes of anti-diabetic agents, namely, dipeptidyl peptidase-4 inhibitors (DPP-4is), glucagon-like-peptide 1 receptor agonists (GLP-1RAs), and sodium glucose cotransporter-2 inhibitors (SGLT-2is) or SGLT-2 and SGLT-1 dual inhibitors and divided the patients into two groups based on the history of HF (with or without) and analyzed their risks of HHF based on the receipt of the aforementioned anti-diabetes drug types. Since the follow-up period differed among the trials, we expressed the rate of HHF as events/1,000 person-years to describe the HF outcome. At last we pooled the data and analyzed their different effects and mechanisms on heart failure outcomes. Although DPP-4is did not increase the risk of HHF in T2D patients with a history of HF, they were associated with a significantly higher risk of HHF among patients without history of HF. Some GLP-1RAs reduced the risk of macrovascular events, but none of these drugs reduced the risk of HHF in patients with T2D irrespective of their HF history. It was not clarified whether SGLT-1/2is can improve the prognosis of macrovascular events in patients with T2D, but these drugs reduced the risk of HHF regardless of patients' histories of HF. This information may be useful or referential for the "precise" selection of hyperglycemic medications. Further researches still needed to clarify the mechanisms of these anti-diabetic medications.

The Effects of DPP4 Inhibitors on Lipid Status and Blood Pressure in Rats with Diabetes Mellitus Type 2

The aim of the present study was to examine, evaluate and compare the effects of administered dipeptidyl peptidase-4 (DPP4) inhibitors saxagliptin and sitagliptin on lipid status parameters and blood pressure in rats with streptozotocine induced diabetes mellitus type 2. Forty-eight Wistar albino rats were divided randomly into 4 groups: 1. group I: control healthy group; 2. group II: rats with diabetes mellitus type 2; 3. group III: rats with diabetes mellitus type 2+ treated with 0.6 mg/kg of sitagliptin; 4. group IV: rats with diabetes mellitus type 2 treated with 0.45 mg/kg of saxagliptin. The rats from experimental groups were fed with a high-fat diet for 4 weeks and after 6–8 h of starvation received one dose of streptozotocin (STZ) intraperitoneally (25 mg/kg body weight) to induce type 2 diabetes mellitus (T2DM). Animals with fasting glucose above 7 mmol/L and insulin over 6 mmol/L were included in the study as rats with T2DM. Upon completion of the experiments, the blood was collected from the anesthetized animals and serum triglyceride (TG), total cholesterol (TCH), high density lipoprotein (HDL), and low density lipoprotein (LDL) were measured using spectrophotometry and commercial kits. At the beginning of the study and the day before sacrificing animals, the blood pressure and heart rate were measured by a tail-cuff noninvasive method. DPP4 inhibitors, as glucagon-like peptide-1 (GLP-1) agonists, were associated with modest reductions in DBP, LDL-C, TCH, and TGL and significant improvement in HDL, SBP and HR.

Vildagliptin, a DPP-4 Inhibitor, Attenuates Endothelial Dysfunction and Atherogenesis in Nondiabetic Apolipoprotein E-Deficient Mice

Dipeptidyl peptidase-4 (DPP-4) inhibitors are novel antidiabetic agents with possible vascular protection effects. Endothelial dysfunction is an initiation step in atherogenesis. The purpose of this study was to investigate whether vildagliptin (Vilda) attenuates the development of endothelial dysfunction and atherosclerotic lesions in nondiabetic apolipoprotein E-deficient (ApoE^-/-) mice. Eight-week-old nondiabetic ApoE^-/- mice fed a Western-type diet received Vilda (50 mg/kg/day) for 20 weeks or 8 weeks. After 20 weeks of treatment, Vilda administration reduced atherogenesis in the aortic arch as determined by en face Sudan IV staining compared with the vehicle group (P < 0.05). Vilda also reduced lipid accumulation (P < 0.05) and vascular cell adhesion molecule-1 (VCAM-1) expression (P < 0.05) and tended to decrease macrophage infiltration (P = 0.05) into atherosclerotic plaques compared with vehicle. After 8 weeks of treatment, endothelium-dependent vascular reactivity was examined. Vilda administration significantly attenuated the impairment of endothelial function in nondiabetic ApoE^-/- mice compared with the vehicle group (P < 0.05). Vilda treatment did not alter metabolic parameters, including blood glucose level, in both study protocols. To investigate the mechanism, aortic segments obtained from wild-type mice were incubated with exendin-4 (Ex-4), a glucagon-like peptide-1 (GLP-1) analog, in the presence or absence of lipopolysaccharide (LPS). Ex-4 attenuated the impairment of endothelium-dependent vasodilation induced by LPS (P < 0.01). Furthermore, Ex-4 promoted phosphorylation of eNOS at Ser1177 which was decreased by LPS in human umbilical endothelial cells (P < 0.05). Vilda inhibited the development of endothelial dysfunction and prevented atherogenesis in nondiabetic ApoE^-/- mice. Our results suggested that GLP-1-dependent amelioration of endothelial dysfunction is associated with the atheroprotective effects of Vilda.

Dipeptidyl Peptidase 4 Inhibition Increases Postprandial Norepinephrine via Substance P (NK1 Receptor) During RAAS Inhibition

CONTEXT

Dipeptidyl peptidase 4 (DPP4) inhibitors may increase the risk of heart failure. Decreased degradation of vasoactive peptides like substance P [also degraded by angiotensin-converting enzyme (ACE)] and Y1 agonists peptide YY (PYY 1-36) and neuropeptide Y (NPY 1-36) could contribute.

OBJECTIVE

This study tested the hypothesis that there is an interactive effect of DPP4 inhibition and ACE inhibition (vs antihypertensive control subjects) on vasoactive peptides after a mixed meal.

PARTICIPANTS AND DESIGN

Fifty-three patients with type 2 diabetes and hypertension were randomized to double-blind treatment with ramipril, valsartan, or amlodipine for 15 weeks in parallel groups. During the 5th, 10th, and 15th weeks, participants also received placebo + placebo, sitagliptin 100 mg/d + placebo, and sitagliptin + aprepitant 80 mg/d in random order. On the last day of each crossover treatment, participants underwent a mixed-meal study.

RESULTS

Sitagliptin increased postprandial glucagon-like peptide-1 and decreased glucose in all antihypertensive groups. Sitagliptin increased NPY 1-36 and decreased Y2 agonists NPY 3-36 and PYY 3-36 in all groups. During ramipril or valsartan, but not amlodipine, sitagliptin increased postprandial norepinephrine; substance P receptor blockade with aprepitant prevented this effect. Despite increased norepinephrine, sitagliptin decreased postprandial blood pressure during ACE inhibition.

CONCLUSION

DPP4 inhibition increases postprandial concentrations of the Y1 agonist NPY 1-36. During treatment with an ACE inhibitor or angiotensin receptor blocker, DPP4 inhibition increased postprandial norepinephrine through a substance P receptor-dependent mechanism. Increased NPY 1-36 and norepinephrine could increase risk of heart failure but did not result in higher postprandial blood pressure.

Dipeptidyl peptidase-4 inhibitors can inhibit angiotensin converting enzyme

Angiotensin-1 converting enzyme inhibitors (ACEIs) improve insulin sensitivity. Inhibitors of dipeptidyl peptidase-4 (DPP-4) are anti-diabetic drugs with several cardio-renal effects. Both ACE and DPP-4 share common features. Thus, we tested if they could be inhibited by one inhibitor. First, in silico screening was used to investigate the ability of different DPP-4 inhibitors or ACEIs to interact with DPP-4 and ACE. The results of screening were then extrapolated into animal study. Fifty Sprague Dawley rats were randomly assigned into 5 groups treated with vehicle, captopril, enalapril, linagliptin or sitagliptin. Both low and high doses of each drug were tested. Baseline blood samples and samples at days 1, 8, 10, 14 were used to measure plasma DPP-4 and ACE activities and angiotensin II levels. Active glucagon-like peptide-1 (GLP-1) levels were measured after oral glucose challenge. All tested DPP-4 inhibitors could interact with ACE at a relatively reasonable binding energy while most of the ACEIs only interacted with DPP-4 at a predicted high inhibition constant. In rats, high dose of sitagliptin was able to inhibit ACE activity and reduce angiotensin II levels while linagliptin had only a mild effect. ACEIs did not significantly affect DPP-4 activity or prevent GLP-1 degradation. It seems that some DPP-4 inhibitors could inhibit ACE and this could partially explain the cardio-renal effects of these drugs. Further studies are required to determine if such inhibition could take place in clinical settings.

Endothelium-Dependent Hyperpolarization (EDH) in Diabetes: Mechanistic Insights and Therapeutic Implications

Diabetes mellitus is one of the major risk factors for cardiovascular disease and is an important health issue worldwide. Long-term diabetes causes endothelial dysfunction, which in turn leads to diabetic vascular complications. Endothelium-derived nitric oxide is a major vasodilator in large-size vessels, and the hyperpolarization of vascular smooth muscle cells mediated by the endothelium plays a central role in agonist-mediated and flow-mediated vasodilation in resistance-size vessels. Although the mechanisms underlying diabetic vascular complications are multifactorial and complex, impairment of endothelium-dependent hyperpolarization (EDH) of vascular smooth muscle cells would contribute at least partly to the initiation and progression of microvascular complications of diabetes. In this review, we present the current knowledge about the pathophysiology and underlying mechanisms of impaired EDH in diabetes in animals and humans. We also discuss potential therapeutic approaches aimed at the prevention and restoration of EDH in diabetes.

Possible mechanisms of direct cardiovascular impact of GLP-1 agonists and DPP4 inhibitors

Diabetes mellitus is a leading cause of cardiovascular morbidity and mortality worldwide. Traditional antidiabetic therapies targeting hyperglycemia reduce diabetic microvascular complications but have minor effects on macrovascular complications, including cardiovascular disease. Instead, cardiovascular complications are improved by antidiabetic medications (metformin) and other therapies (statins, antihypertensive medications) ameliorating insulin resistance and other associated metabolic abnormalities. Novel classes of antidiabetic drugs have proven efficacious in improving glycemia, while at the same time exert beneficial effects on pathophysiologic mechanisms of diabetes-related cardiovascular disease. In the present review, we will present current evidence of the cardiovascular effects of two new classes of antidiabetic medications, glucagon-like peptide 1 (GLP-1) agonists and dipeptidyl peptidase-4 (DPP4) inhibitors, focusing from mechanistic preclinical and clinical investigation to late-phase clinical testing.

Pharmacology of dipeptidyl peptidase-4 inhibitors and its use in the management of metabolic syndrome: a comprehensive review on drug repositioning

OBJECTIVES

Despite advances in our understanding of metabolic syndrome (MetS) and the treatment of each of its components separately, currently there is no single therapy approved to manage it as a single condition. Since multi-drug treatment increases drug interactions, decreases patient compliance and increases health costs, it is important to introduce single therapies that improve all of the MetS components.

EVIDENCE ACQUISITION

We conducted a PubMed, Scopus, Google Scholar, Web of Science, US FDA, utdo.ir and clinicaltrial.gov search, gathered the most relevant preclinical and clinical studies that have been published since 2010, and discussed the beneficial effects of dipeptidyl peptidase (DPP)-4 inhibitors to prevent and treat different constituent of the MetS as a single therapy. Furthermore, the pharmacology of DPP-4 inhibitors, focusing on pharmacodynamics, pharmacokinetics, drug interactions and their side effects are also reviewed.

RESULTS

DPP-4 inhibitors or gliptins are a new class of oral anti-diabetic drugs that seem safe drugs with no severe side effects, commonly GI disturbance, infection and inflammatory bowel disease. They increase mass and function of pancreatic β-cells, and insulin sensitivity in liver, muscle and adipose tissue. It has been noted that gliptin therapy decreases dyslipidemia. DPP-4 inhibitors increase fatty oxidation, and cholesterol efflux, and decrease hepatic triglyceride synthase and de novo lipogenesis. They delay gastric emptying time and lead to satiety. Besides, gliptin therapy has anti-inflammatory and anti-atherogenic impacts, and improves endothelial function and reduces vascular stiffness.

CONCLUSION

The gathered data prove the efficacy of DPP-4 inhibitors in managing MetS in some levels beyond anti-diabetic effects. This review could be a lead for designing new DPP-4 inhibitors with greatest effects on MetS in future. Introducing drugs with polypharmacologic effects could increase the patient's compliance and decrease the health cost that there is not in multi-drug therapy. Graphical abstract ᅟ.

Endogenous dipeptidyl peptidase IV modulates skeletal muscle arteriolar diameter in rats

The purpose of this study is to investigate that dipeptidyl peptidase IV (DPP‐IV) released from skeletal and vascular smooth muscle can increase arteriolar diameter in a skeletal muscle vascular bed by reducing neuropeptide Y (NPY)‐mediated vasoconstriction. We hypothesized that the effect of myokine DPP‐IV would be greatest in the smallest and least in the largest arterioles. Eight male Sprague Dawley rats (age 7–9 weeks; mass, mean ± SD: 258 ± 41 g) were anesthetized and the gluteus maximus dissected in situ for intravital microscopy analysis of arteriolar diameter of the vascular network. Computational modeling was performed on the diameter measurements to evaluate the overall impact of diameter changes on network resistance and flow distribution. In the first set of experiments, whey protein isolate powder was added to physiological saline solution, put in a heated reservoir, and applied to the preparation to induce release of DPP‐IV from the muscle. This resulted in an order‐dependent increase in arteriolar diameter, with the largest change in the 6A arterioles (63% more reactive than 1A arterioles; P < 0.05). This effect was abolished by adding the DPP‐IV inhibitor, Diprotin A. To test if the DPP‐IV released was affecting NPY‐mediated vasoconstriction, we applied NPY and whey protein, which resulted in attenuated vasoconstriction. These findings suggest that DPP‐IV is released from muscle and has a unique effect on blood flow, which appears to act on NPY to attenuate vasoconstriction. The findings suggest that DPP‐IV released from the skeletal or smooth muscle can alter muscle blood flow.

The neurovascular protective effect of alogliptin in murine MCAO model and brain endothelial cells

Endothelial damage and blood brain barrier disruption contribute to ischemic stroke and brain injury. Gliptins are a novel class of treatment agents for diabetes, and recent studies have linked the use of gliptins to neuroprotection. Alogliptin is a type of orally available gliptin that was approved for clinical use by the FDA in 2013. In this study, we investigated the neurovascular protective effects of alogliptin both in vivo and in vitro. In a murine middle cerebral artery occlusion (MCAO) stroke model, administration of alogliptin ameliorated cerebral infarction and disruption of brain vascular permeability, and restored expression of the endothelial tight junction proteins occludin and zona occludens 1 (ZO-1). In brain vascular endothelial cells exposed to oxygen and glucose deprivation/reperfusion (OGD/R), alogliptin prevented OGD/R-induced high permeability of the endothelial monolayer. Alogliptin treatment recovered the reduction in occludin and ZO-1 induced by OGD/R. Moreover, alogliptin treatment prevented OGD/R-induced induction of metalloproteinase (MMP)-2 and MMP-9, and restored expression of tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2. Collectively, our data indicate that alogliptin can improve neurovascular integrity and exerts neuroprotective effects.

Is there a Chance to Promote Arteriogenesis by DPP4 Inhibitors Even in Type 2 Diabetes? A Critical Review

Cardiovascular diseases (CVD) are still the prevailing cause of death not only in industrialized countries, but even worldwide. Type 2 diabetes mellitus (type 2 DM) and hyperlipidemia, a metabolic disorder that is often associated with diabetes, are major risk factors for developing CVD. Recently, clinical trials proved the safety of gliptins in treating patients with type 2 DM. Gliptins are dipeptidyl-peptidase 4 (DPP4/CD26) inhibitors, which stabilize glucagon-like peptide-1 (GLP-1), thereby increasing the bioavailability of insulin. Moreover, blocking DPP4 results in increased levels of stromal cell derived factor 1 (SDF-1). SDF-1 has been shown in pre-clinical animal studies to improve heart function and survival after myocardial infarction, and to promote arteriogenesis, the growth of natural bypasses, compensating for the function of an occluded artery. Clinical trials, however, failed to demonstrate a superiority of gliptins compared to placebo treated type 2 DM patients in terms of cardiovascular (CV) outcomes. This review highlights the function of DPP4 inhibitors in type 2 DM, and in treating cardiovascular diseases, with special emphasis on arteriogenesis. It critically addresses the potency of currently available gliptins and gives rise to hope by pointing out the most relevant questions that need to be resolved.

Protective effects of gemigliptin against type II collagen degradation in human chondrocytes

Degradation of components of the extracellular matrix such as type II collagen in articular cartilage induced by matrix metalloproteinases (MMPs) has been considered as a major pathological characteristic of osteoarthritis (OA). Gemigliptin is a potent and a highly selective dipeptidyl peptidase-IV (DPP-IV) inhibitor, which has been clinically used as an oral agent for the treatment of type 2 diabetes. However, the effects of gemigliptin on articular cartilage destruction and the pathogenesis of OA remain unknown. In the current study, we addressed for the first time the inhibitory property of gemigliptin against interleukin-1β (IL-1β)-induced degradation of type II collagen in human chondrocytes. Our results demonstrate that gemigliptin treatment inhibited the expression of matrix metalloproteinase 1 (MMP-1), matrix metalloproteinase 3 (MMP-3), and matrix metalloproteinase 13 (MMP-13) at both the gene and protein levels. Mechanistically, our results indicate that gemigliptin inhibited activation of the nuclear factor-κB (NF-κB) signaling pathway by suppressing phosphorylation of IκB kinase (IKK)/nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor α (IκBα) and p38. Our results implicate that gemigliptin treatment might be a potential therapeutic strategy for chondroprotective therapy.

The role of dipeptidylpeptidase-4 inhibitors in management of cardiovascular disease in diabetes; focus on linagliptin

Multiple population based analyses have demonstrated a high incidence of cardiovascular disease (CVD) and cardiovascular (CV) mortality in subjects with T2DM that reduces life expectancy by as much as 15 years. Importantly, the CV system is particularly sensitive to the metabolic and immune derangements present in obese pre-diabetic and diabetic individuals; consequently, CV dysfunction is often the initial CV derangement to occur and promotes the progression to end organ/tissue damage in T2DM. Specifically, diabetic CVD can manifest as microvascular complications, such as nephropathy, retinopathy, and neuropathy, as well as, macrovascular impairments, including ischemic heart disease, peripheral vascular disease, and cerebrovascular disease. Despite some progress in prevention and treatment of CVD, mainly via blood pressure and dyslipidemia control strategies, the impact of metabolic disease on CV outcomes is still a major challenge and persists in proportion to the epidemics of obesity and diabetes. There is abundant pre-clinical and clinical evidence implicating the DPP-4-incretin axis in CVD. In this regard, linagliptin is a unique DPP-4 inhibitor with both CV and renal safety profiles. Moreover, it exerts beneficial CV effects beyond glycemic control and beyond class effects. Linagliptin is protective for both macrovascular and microvascular complications of diabetes in preclinical models, as well as clinical models. Given the role of endothelial-immune cell interactions as one of the key events in the initiation and progression of CVD, linagliptin modulates these cell–cell interactions by affecting two important pathways involving stimulation of NO signaling and potent inhibition of a key immunoregulatory molecule.

Renal Effects of Incretin-Based Diabetes Therapies: Pre-clinical Predictions and Clinical Trial Outcomes

PURPOSE OF REVIEW

The purpose of this review is to correlate predictions based on pre-clinical data with outcomes from clinical trials that examine the effects of incretin-based diabetes treatments on the kidney. The incretin-based treatments include agonists of the glucagon-like peptide 1 receptor (GLP-1R) and inhibitors of the enzyme, dipeptidyl peptidase-4 (DPP-4). In addition, what is known about the incretin-based therapies will be compared to what is known about the renal effects of SGLT2 inhibitors.

RECENT FINDINGS

Large-scale clinical trials have shown that SGLT2 inhibitors reduce albuminuria and preserve estimated glomerular filtration rate (eGFR) in patients with diabetic nephropathy. A concise and plausible hemodynamic mechanism is supported by pre-clinical research on the physiology and pharmacology of SGLT2. Large-scale clinical trials have shown that incretin-based therapies mitigate albuminuria but have not shown beneficial effects on eGFR. Research on the incretin-based therapies has yielded a diverse array of direct effects throughout the body, which fuels speculation as to how these drugs might benefit the diabetic kidney and affect its function(s). But in vivo experiments have yet to confirm that the proposed mechanisms underlying emergent phenomena, such as proximal tubular fluid reabsorption, are the ones predicted by cell and molecular experiments. There may be salutary effects of incretin-based treatments on the diabetic kidney, but the system is complex and not amenable to simple explanation or prior prediction. This contrasts with the renal effects of SGLT2 inhibitors, which can be explained concisely.

Worsening Heart Failure During the Use of DPP-4 Inhibitors: Pathophysiological Mechanisms, Clinical Risks, and Potential Influence of Concomitant Antidiabetic Medications

Although dipeptidyl peptidase (DPP)-4 inhibitors have been reported to have a neutral effect on thromboembolic vaso-occlusive events in large-scale trials, they act to potentiate several endogenous peptides that can exert deleterious cardiovascular effects. Experimentally, DPP-4 inhibitors may augment the ability of glucagon-like peptide-1 to stimulate cyclic adenosine monophosphate in cardiomyocytes, and potentiation of the effects of stromal cell-derived factor-1 by DPP-4 inhibitors may aggravate cardiac fibrosis. These potentially deleterious actions of DPP-4 inhibitors might not become clinically apparent if these drugs were to promote sodium excretion. However, the natriuretic effect of DPP-4 inhibitors is modest, because they act on the distal (rather than proximal) renal tubules. Accordingly, both clinical trials and observational studies have reported an increase in the risk of heart failure in patients with type 2 diabetes who were receiving DPP-4 inhibitors. This risk may be muted in trials with a high prevalence of metformin use or with low and declining background use of insulin and thiazolidinediones. Still, the most vulnerable patients (i.e., those with established heart failure) were not well represented in these studies. The only trial that specifically evaluated patients with pre-existing left ventricular dysfunction observed important drug-related adverse structural and clinical effects. In conclusion, an increased risk of worsening heart failure appears to be a class effect of DPP-4 inhibitors, even in patients without a history of heart failure. Additional clinical trials are urgently needed to elucidate the benefits and risks of DPP-4 inhibitors in patients with established left ventricular dysfunction.

Dipeptidyl peptidase-4 inhibitor decreases the risk of atrial fibrillation in patients with type 2 diabetes: a nationwide cohort study in Taiwan

BACKGROUND

Whether dipeptidyl peptidase-4 inhibitor (DPP4i) is associated with a lower risk of new-onset atrial fibrillation (AF) in patients with diabetes remains unclear. This study aimed to evaluate the risk of AF associated with use of DPP4i among a longitudinal cohort of patients with diabetes.

METHODS

Over a 3-year period, 480,000 patients with diabetes were analyzed utilizing Taiwan's National Health Insurance Research Database and 90,880 patients taking metformin as first-line therapy were enrolled. Patients were further divided into two groups: (1) DPP4i users: those taking DPP4i and (2) non-DPP4i users: those prescribed other hypoglycemic agents (HAs) as second-line drug. Study end point was defined by diagnosis of AF, addition of any third-line HA, or the end of the study period (December 31, 2013), whichever came first.

RESULTS

A total of 16,017 DPP4i users and 74,863 non-DPP4i users were eligible for the study. For the DPP4i group, most patients were prescribed sitagliptin (n = 12,180; 76%). Among the non-DPP4i group, most patients took sulfonylurea (n = 60,606; 81%) as their second-line medication. DPP4i users were associated with a lower risk of new-onset AF compared with non-DPP4i users after propensity-score weighting (hazard ratio 0.65; P < 0.0001). Subgroup analysis showed that DPP4i user were associated with a lower risk of new-onset AF compared with non-DPP4i users in most subgroups. Multivariate analysis indicated that use of DPP4i was associated with lower risk of new-onset AF and age > 65 years, presence of hypertension, and ischemic heart disease were independent risk factors for new-onset AF.

CONCLUSIONS

Among patients with diabetes prescribed with metformin, the patients with DPP4i as second HA were associated with a lower risk of AF compared with the patients with other drugs as second HAs in real-world practice.

Sitagliptin reduces inflammation, fibrosis and preserves diastolic function in a rat model of heart failure with preserved ejection fraction

BACKGROUND AND PURPOSE

Heart failure with preserved ejection fraction (HFpEF) is a systemic syndrome driven by co-morbidities, and its pathophysiology is poorly understood. Several studies suggesting that dipeptidyl peptidase 4 (DPP4) might be involved in the pathophysiology of heart failure have prompted experimental and clinical investigations of DPP4 inhibitors in the cardiovascular system. Here we have investigated whether the DPP4 inhibitor sitagliptin affected the progression of HFpEF independently of its effects on glycaemia.

EXPERIMENTAL APPROACH

Seven-week-old Dahl salt-sensitive rats were fed a high-salt diet for 5 weeks to induce hypertension. Then the rats continued with the high-salt diet and were treated with either sitagliptin (10 mg·kg-1 ) or vehicle for the following 8 weeks. Blood pressure and cardiac function were measured in vivo. Histochemical and molecular biology analyses of myocardium were used to assay cytokines, fibrotic markers, DPP4 and glucagon-like peptide-1 (GLP-1)/GLP-1 receptor.

KEY RESULTS

Treatment with sitagliptin attenuated diastolic dysfunction, reduced mortality and reduced cardiac DPP4 activity, along with increased circulating GLP-1 and myocardial expression of GLP-1 receptors. Myocardial levels of pro-inflammatory cytokines (TNF-α, IL-6 and CCL2) were reduced. Sitagliptin treatment decreased the levels of endothelial NOS monomer, responsible for generation of ROS, while the amount of NO-producing dimeric form increased. Markers of oxidative and nitrosative stress were decreased. Moreover, increased collagen deposition and activation of pro-fibrotic signalling, inducing elevated myocardial stiffness, were attenuated by sitagliptin treatment.

CONCLUSIONS AND IMPLICATIONS

Sitagliptin positively modulated active relaxation and passive diastolic compliance by decreasing inflammation-related endothelial dysfunction and fibrosis, associated with HFpEF.

LINKED ARTICLES

This article is part of a themed section on Targeting Inflammation to Reduce Cardiovascular Disease Risk. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.22/issuetoc and http://onlinelibrary.wiley.com/doi/10.1111/bcp.v82.4/issuetoc.

Metformin Improves Endothelial Function and Reduces Blood Pressure in Diabetic Spontaneously Hypertensive Rats Independent from Glycemia Control: Comparison to Vildagliptin

Metformin confers vascular benefits beyond glycemia control, possibly via pleiotropic effects on endothelial function. In type-1-diabetes-mellitus (T1DM-)patients metformin improved flow-mediated dilation but also increased prostaglandin(PG)-F_2α, a known endothelial-contracting factor. To explain this paradoxical finding we hypothesized that metformin increased endothelial-vasodilator mediators (e.g. NO and EDHF) to an even larger extent. Spontaneously-hypertensive-rats (SHR) display impaired endothelium-dependent relaxation (EDR) involving contractile PGs. EDR was studied in isolated SHR aortas and the involvement of PGs, NO and EDHF assessed. 12-week metformin 300 mg/kg/day improved EDR by up-regulation of NO and particularly EDHF; it also reduced blood pressure and increased plasma sulphide levels (a proxy for H₂S, a possible mediator of EDHF). These effects persisted in SHR with streptozotocin (STZ)-induced T1DM. Vildagliptin (10 mg/kg/day), targeting the incretin axis by increasing GLP-1, also reduced blood pressure and improved EDR in SHR aortas, mainly via the inhibition of contractile PGs, but not in STZ-SHR. Neither metformin nor vildagliptin altered blood glucose or HbA_1c. In conclusion, metformin reduced blood pressure and improved EDR in SHR aorta via up-regulation of NO and particularly EDHF, an effect that was independent from glycemia control and maintained during T1DM. A comparison to vildagliptin did not support effects of metformin mediated by GLP-1.

Dipeptidyl peptidase-4 inhibitor gemigliptin protects against vascular calcification in an experimental chronic kidney disease and vascular smooth muscle cells

Although dipeptidyl peptidase-4 inhibitors, a class of antidiabetic drugs, have various pleiotropic effects, it remains undetermined whether gemigliptin has a beneficial effect on vascular calcification. Therefore, this study was performed to evaluate the effect of gemigliptin on vascular calcification in a rat model of adenine-induced chronic kidney disease and in cultured vascular smooth muscle cells. Gemigliptin attenuated calcification of abdominal aorta and expression of RUNX2 in adenine-induced chronic kidney disease rats. In cultured vascular smooth muscle cells, phosphate-induced increase in calcium content was reduced by gemigliptin. Gemigliptin reduced phosphate-induced PiT-1 mRNA expression, reactive oxygen species generation, and NADPH oxidase mRNA expression (p22phox and NOX4). The reduction of oxidative stress by gemigliptin was associated with the downregulation of phospho-PI3K/AKT expression. High phosphate increased the expression of frizzled-3 (FDZ3) and decreased the expression of dickkopf-related protein-1 (DKK-1) in the Wnt pathway. These changes were attenuated by gemigliptin treatment. Gemigliptin restored the decreased expression of vascular smooth muscle cells markers (α-SMA and SM22α) and increased expression of osteogenic makers (CBFA1, OSX, E11, and SOST) induced by phosphate. In conclusion, gemigliptin attenuated vascular calcification and osteogenic trans-differentiation in vascular smooth muscle cells via multiple steps including downregulation of PiT-1 expression and suppression of reactive oxygen species generation, phospho-PI3K/AKT, and the Wnt signaling pathway.

The regulatory role of DPP4 in atherosclerotic disease

The increasing prevalence of atherosclerosis has become a worldwide health concern. Although significant progress has been made in the understanding of atherosclerosis pathogenesis, the underlying mechanisms are not fully understood. Recent studies suggest dipeptidyl peptidase-4 (DPP4), a regulator of inflammation and metabolism, may be involved in the development of atherosclerotic diseases. There has been increasing clinical and pre-clinical evidence showing DPP4-incretin axis is involved in cardiovascular disease. Although the cardiovascular outcome of DPP4 inhibition or incretin analogues has been or being evaluated by several large scale clinical trials, the exact role of DPP4 in atherosclerotic diseases is not completely understood. In the current review, we will summarize the recent advances in direct and indirect regulatory role of DPP4 in atherosclerosis.

Dipeptidyl peptidase‑4 inhibitor sitagliptin prevents high glucose‑induced apoptosis via activation of AMP‑activated protein kinase in endothelial cells

Diabetes mellitus (DM), which is a chronic metabolic disorder, is the primary risk factor of life‑threatening vascular complications. Endothelial apoptosis is important in the development of the initial vascular lesion preceding the diabetic disease. Sitagliptin is a dipeptidyl peptidase‑4 (DPP‑4) inhibitor and extensively used in the clinical treatment of DM. DPP‑4 inhibitors have been demonstrated to be beneficial in the improvement of endothelial homeostasis, however the molecular mechanism by which they exhibit these effects remains to be elucidated. The effect of sitagliptin on endothelial apoptosis was examined in cultured human umbilical vein endothelial cells (HUVECs) incubated with high glucose (HG). The present study demonstrated that treatment of HUVECs with HG increased reactive oxygen species (ROS) production, stimulated mitochondrial depolarization and resulted in cell apoptosis. Pretreatment of HUVECs with sitagliptin significantly prevented HG‑induced endothelial apoptosis. It was further demonstrated that sitagliptin effectively inhibited ROS generation and mitochondrial membrane potential collapse. Similarly, adenosine monophosphate‑activated protein kinase (AMPK) activation by sitagliptin protected against HG‑induced ROS production, mitochondrial membrane potential collapse and endothelial cell apoptosis, as detected via western blotting and flow cytometry analysis. The present study therefore revealed a novel mechanism of sitagliptin‑mediated AMPK activation in preventing endothelial apoptosis and indicated the therapeutic potential of sitagliptin in vascular complications associated with endothelial apoptosis.