Effects of DPP-4 inhibition on cardiac metabolism and function in mice

Dipeptidyl-peptidase 4 (DPP4) mediates fatty acid uptake inhibition by glucose via TAS1R3 and GLUT-2 in Caco-2 enterocytes

Both high glucose intake with a high-fat meal and inhibition of dipeptidyl peptidase-4 (DPP4) have been associated with plasma lipid-lowering effects, but mechanistic understanding linking glucose and fat absorption is lacking. We here hypothesized that glucose ameliorates intestinal fatty acid uptake via a pathway involving DPP4. A concentration of 50 mM glucose reduced mean DPP4 activity in differentiated Caco-2 enterocytes by 42.5 % and fatty acid uptake by 66.0 % via nutrient sensing by the sweet taste receptor subunit TAS1R3 and glucose transporter GLUT-2. No effect of the DPP4 substrates GLP-1 and GIP or of the cellular energy status on the reduced uptake of fatty acids was seen, but a direct interaction between DPP4 and fatty acid transporters is suggested. Conclusively we identified DPP4 as a regulator of fatty acid absorption in Caco-2 enterocytes that mediates the inhibition of intestinal fatty acid uptake by glucose via an interplay of GLUT-2 and TAS1R3.

Lipid metabolism reprogramming in cardiac fibrosis

Cardiac fibrosis is a critical pathophysiological process that occurs with diverse types of cardiac injury. Lipids are the most important bioenergy substrates for maintaining optimal heart performance and act as second messengers to transduce signals within cardiac cells. However, lipid metabolism reprogramming is a double-edged sword in the regulation of cardiomyocyte homeostasis and heart function. Moreover, lipids can exert diverse effects on cardiac fibrosis through different signaling pathways. In this review, we provide a brief overview of aberrant cardiac lipid metabolism and recent progress in pharmacological research targeting lipid metabolism alterations in cardiac fibrosis.

Reciprocal Regulation of Hepatic TGF-β1 and Foxo1 Controls Gluconeogenesis and Energy Expenditure

Obesity and insulin resistance are risk factors for the pathogenesis of type 2 diabetes (T2D). Here, we report that hepatic TGF-β1 expression positively correlates with obesity and insulin resistance in mice and humans. Hepatic TGF-β1 deficiency decreased blood glucose levels in lean mice and improved glucose and energy dysregulations in diet-induced obese (DIO) mice and diabetic mice. Conversely, overexpression of TGF-β1 in the liver exacerbated metabolic dysfunctions in DIO mice. Mechanistically, hepatic TGF-β1 and Foxo1 are reciprocally regulated: fasting or insulin resistance caused Foxo1 activation, increasing TGF-β1 expression, which, in turn, activated protein kinase A, stimulating Foxo1-S273 phosphorylation to promote Foxo1-mediated gluconeogenesis. Disruption of TGF-β1→Foxo1→TGF-β1 looping by deleting TGF-β1 receptor II in the liver or by blocking Foxo1-S273 phosphorylation ameliorated hyperglycemia and improved energy metabolism in adipose tissues. Taken together, our studies reveal that hepatic TGF-β1→Foxo1→TGF-β1 looping could be a potential therapeutic target for prevention and treatment of obesity and T2D.

ARTICLE HIGHLIGHTS

Hepatic TGF-β1 levels are increased in obese humans and mice. Hepatic TGF-β1 maintains glucose homeostasis in lean mice and causes glucose and energy dysregulations in obese and diabetic mice. Hepatic TGF-β1 exerts an autocrine effect to promote hepatic gluconeogenesis via cAMP-dependent protein kinase-mediated Foxo1 phosphorylation at serine 273, endocrine effects on brown adipose tissue action, and inguinal white adipose tissue browning (beige fat), causing energy imbalance in obese and insulin-resistant mice. TGF-β1→Foxo1→TGF-β1 looping in hepatocytes plays a critical role in controlling glucose and energy metabolism in health and disease.

An Overview of the Cardioprotective Effects of Novel Antidiabetic Classes: Focus on Inflammation, Oxidative Stress, and Fibrosis

Metabolic diseases, particularly diabetes mellitus (DM), are significant global public health concerns. Despite the widespread use of standard-of-care therapies, cardiovascular disease (CVD) remains the leading cause of death among diabetic patients. Early and evidence-based interventions to reduce CVD are urgently needed. Large clinical trials have recently shown that sodium-glucose cotransporter-2 inhibitors (SGLT2i) and glucagon-like peptide-1 receptor agonists (GLP-1RA) ameliorate adverse cardiorenal outcomes in patients with type 2 DM. These quite unexpected positive results represent a paradigm shift in type 2 DM management, from the sole importance of glycemic control to the simultaneous improvement of cardiovascular outcomes. Moreover, SGLT2i is also found to be cardio- and nephroprotective in non-diabetic patients. Several mechanisms, which may be potentially independent or at least separate from the reduction in blood glucose levels, have already been identified behind the beneficial effect of these drugs. However, there is still much to be understood regarding the exact pathomechanisms. This review provides an overview of the current literature and sheds light on the modes of action of novel antidiabetic drugs, focusing on inflammation, oxidative stress, and fibrosis.

Evogliptin, a DPP-4 inhibitor, prevents diabetic cardiomyopathy by alleviating cardiac lipotoxicity in db/db mice

Dipeptidyl peptidase-4 (DPP-4) inhibitors are glucose-lowering drugs for type 2 diabetes mellitus (T2DM). We investigated whether evogliptin® (EVO), a DPP-4 inhibitor, could protect against diabetic cardiomyopathy (DCM) and the underlying mechanisms. Eight-week-old diabetic and obese db/db mice were administered EVO (100 mg/kg/day) daily by oral gavage for 12 weeks. db/db control mice and C57BLKS/J as wild-type (WT) mice received equal amounts of the vehicle. In addition to the hypoglycemic effect, we examined the improvement in cardiac contraction/relaxation ability, cardiac fibrosis, and myocardial hypertrophy by EVO treatment. To identify the mechanisms underlying the improvement in diabetic cardiomyopathy by EVO treatment, its effect on lipotoxicity and the mitochondrial damage caused by lipid droplet accumulation in the myocardium were analyzed. EVO lowered the blood glucose and HbA1c levels and improved insulin sensitivity but did not affect the body weight or blood lipid profile. Cardiac systolic/diastolic function, hypertrophy, and fibrosis were improved in the EVO-treated group. EVO prevented cardiac lipotoxicity by reducing the accumulation of lipid droplets in the myocardium through suppression of CD36, ACSL1, FABP3, PPARgamma, and DGAT1 and enhancement of the phosphorylation of FOXO1, indicating its inhibition. The EVO-mediated improvement in mitochondrial function and reduction in damage were achieved through activation of PGC1a/NRF1/TFAM, which activates mitochondrial biogenesis. RNA-seq results for the whole heart confirmed that EVO treatment mainly affected the differentially expressed genes (DEGs) related to lipid metabolism. Collectively, these findings demonstrate that EVO improves cardiac function by reducing lipotoxicity and mitochondrial injury and provides a potential therapeutic option for DCM.

Guidelines on Models of Diabetic Heart Disease

Diabetes is a major risk factor for cardiovascular diseases, including diabetic cardiomyopathy, atherosclerosis, myocardial infarction, and heart failure. As cardiovascular disease represents the number one cause of death in people with diabetes, there has been a major emphasis on understanding the mechanisms by which diabetes promotes cardiovascular disease, and how antidiabetic therapies impact diabetic heart disease. With a wide array of models to study diabetes (both type 1 and type 2), the field has made major progress in answering these questions. However, each model has its own inherent limitations. Therefore, the purpose of this guidelines document is to provide the field with information on which aspects of cardiovascular disease in the human diabetic population are most accurately reproduced by the available models. This review aims to emphasize the advantages and disadvantages of each model, and to highlight the practical challenges and technical considerations involved. We will review the preclinical animal models of diabetes (based on their method of induction), appraise models of diabetes-related atherosclerosis and heart failure, and discuss in vitro models of diabetic heart disease. These guidelines will allow researchers to select the appropriate model of diabetic heart disease, depending on the specific research question being addressed.

Fibrosis of the diabetic heart: Clinical significance, molecular mechanisms, and therapeutic opportunities

In patients with diabetes, myocardial fibrosis may contribute to the pathogenesis of heart failure and arrhythmogenesis, increasing ventricular stiffness and delaying conduction. Diabetic myocardial fibrosis involves effects of hyperglycemia, lipotoxicity and insulin resistance on cardiac fibroblasts, directly resulting in increased matrix secretion, and activation of paracrine signaling in cardiomyocytes, immune and vascular cells, that release fibroblast-activating mediators. Neurohumoral pathways, cytokines, growth factors, oxidative stress, advanced glycation end-products (AGEs), and matricellular proteins have been implicated in diabetic fibrosis; however, the molecular links between the metabolic perturbations and activation of a fibrogenic program remain poorly understood. Although existing therapies using glucose- and lipid-lowering agents and neurohumoral inhibition may act in part by attenuating myocardial collagen deposition, specific therapies targeting the fibrotic response are lacking. This review manuscript discusses the clinical significance, molecular mechanisms and cell biology of diabetic cardiac fibrosis and proposes therapeutic targets that may attenuate the fibrotic response, preventing heart failure progression.

Role of Artesunate on cardiovascular complications in rats with type 1 diabetes mellitus

BACKGROUND

The present study aimed to evaluate the effect of artesunate (ART) on the reduction of cardiovascular complications in a type 1 diabetes model and to investigate the associated mechanism based on the receptor for advanced glycation end-product (RAGE)/NF-κB signaling pathway.

METHODS

A total of 40 male Sprague-Dawley rats were randomly divided into five groups: The healthy, diabetic, 50 mg/kg ART (ig) treatment diabetic, 100 mg/kg ART (ig) treatment diabetic, and 6 U/kg insulin (iH) treatment diabetic groups. The treatment lasted 4 weeks after the diabetic model was established via intraperitoneal injection of streptozotocin. Blood samples were collected, and cardiovascular tissues were harvested and processed to measure various parameters after the animals were sacrificed. The myocardium and aortic arch tissues were evaluated using hematoxylin-eosin and Masson staining. Expression levels of RAGE, NF-κB, matrix metalloproteinase MMP9, MMP1 and CD68 in the myocardium and aortic arch tissues were detected using immunohistochemistry, and mRNA expression was determined using reverse transcription-quantitative PCR.

RESULTS

The results of the present study demonstrated that ART treatment may restrain diabetes-induced cardiovascular complications by maintaining heart and body weight while reducing blood glucose, as well as regulating blood lipid indicators to normal level (P < 0.05). The expression levels of NF-κB, CD68, MMP1, MMP9 and RAGE were decreased in the ART-treated diabetic rats (P < 0.05).

CONCLUSIONS

ART treatment may have a protective role against diabetes-associated cardiovascular complications in diabetic rats by inhibiting the expression of proteins in the RAGE/NF-κB signaling pathway and downstream inflammatory factors. High concentrations of ART had a hypoglycemic effect, while a low concentration of ART prevented cardiovascular complications.

Evogliptin Suppresses Calcific Aortic Valve Disease by Attenuating Inflammation, Fibrosis, and Calcification

Calcific aortic valve disease (CAVD) accompanies inflammatory cell infiltration, fibrosis, and ultimately calcification of the valve leaflets. We previously demonstrated that dipeptidyl peptidase-4 (DPP-4) is responsible for the progression of aortic valvular calcification in CAVD animal models. As evogliptin, one of the DPP-4 inhibitors displays high specific accumulation in cardiac tissue, we here evaluated its therapeutic potency for attenuating valvular calcification in CAVD animal models. Evogliptin administration markedly reduced calcific deposition accompanied by a reduction in proinflammatory cytokine expression in endothelial nitric oxide synthase-deficient mice in vivo, and significantly ameliorated the mineralization of the primary human valvular interstitial cells (VICs), with a reduction in the mRNA expression of bone-associated and fibrosis-related genes in vitro. In addition, evogliptin ameliorated the rate of change in the transaortic peak velocity and mean pressure gradients in our rabbit model as assessed by echocardiography. Importantly, evogliptin administration in a rabbit model was found to suppress the effects of a high-cholesterol diet and of vitamin D2-driven fibrosis in association with a reduction in macrophage infiltration and calcific deposition in aortic valves. These results have indicated that evogliptin prohibits inflammatory cytokine expression, fibrosis, and calcification in a CAVD animal model, suggesting its potential as a selective therapeutic agent for the inhibition of valvular calcification during CAVD progression.

The Impact of Antidiabetic Therapies on Diastolic Dysfunction and Diabetic Cardiomyopathy

Diabetic cardiomyopathy is more prevalent in people with type 2 diabetes mellitus (T2DM) than previously recognized, while often being characterized by diastolic dysfunction in the absence of systolic dysfunction. This likely contributes to why heart failure with preserved ejection fraction is enriched in people with T2DM vs. heart failure with reduced ejection fraction. Due to revised mandates from major health regulatory agencies, all therapies being developed for the treatment of T2DM must now undergo rigorous assessment of their cardiovascular risk profiles prior to approval. As such, we now have data from tens of thousands of subjects with T2DM demonstrating the impact of major therapies including the sodium-glucose co-transporter 2 (SGLT2) inhibitors, glucagon-like peptide-1 receptor (GLP-1R) agonists, and dipeptidyl peptidase 4 (DPP-4) inhibitors on cardiovascular outcomes. Evidence to date suggests that both SGLT2 inhibitors and GLP-1R agonists improve cardiovascular outcomes, whereas DPP-4 inhibitors appear to be cardiovascular neutral, though evidence is lacking to determine the overall utility of these therapies on diastolic dysfunction or diabetic cardiomyopathy in subjects with T2DM. We herein will review the overall impact SLGT2 inhibitors, GLP-1R agonists, and DPP-4 inhibitors have on major parameters of diastolic function, while also highlighting the potential mechanisms of action responsible. A more complete understanding of how these therapies influence diastolic dysfunction will undoubtedly play a major role in how we manage cardiovascular disease in subjects with T2DM.

Role of AMP-activated protein kinase on cardio-metabolic abnormalities in the development of diabetic cardiomyopathy: A molecular landscape

Cardiovascular complications associated with diabetes mellitus remains a leading cause of morbidity and mortality across the world. Diabetic cardiomyopathy is a descriptive pathology that in absence of co-morbidities such as hypertension, dyslipidemia initially characterized by cardiac stiffness, myocardial fibrosis, ventricular hypertrophy, and remodeling. These abnormalities further contribute to diastolic dysfunctions followed by systolic dysfunctions and eventually results in clinical heart failure (HF). The clinical outcomes associated with HF are considerably worse in patients with diabetes. The complexity of the pathogenesis and clinical features of diabetic cardiomyopathy raises serious questions in developing a therapeutic strategy to manage cardio-metabolic abnormalities. Despite extensive research in the past decade the compelling approaches to manage and treat diabetic cardiomyopathy are limited. AMP-Activated Protein Kinase (AMPK), a serine-threonine kinase, often referred to as cellular "metabolic master switch". During the development and progression of diabetic cardiomyopathy, a plethora of evidence demonstrate the beneficial role of AMPK on cardio-metabolic abnormalities including altered substrate utilization, impaired cardiac insulin metabolic signaling, mitochondrial dysfunction and oxidative stress, myocardial inflammation, increased accumulation of advanced glycation end-products, impaired cardiac calcium handling, maladaptive activation of the renin-angiotensin-aldosterone system, endoplasmic reticulum stress, myocardial fibrosis, ventricular hypertrophy, cardiac apoptosis, and impaired autophagy. Therefore, in this review, we have summarized the findings from pre-clinical and clinical studies and provided a collective overview of the pathophysiological mechanism and the regulatory role of AMPK on cardio-metabolic abnormalities during the development of diabetic cardiomyopathy.

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.

AMPK is associated with the beneficial effects of antidiabetic agents on cardiovascular diseases

Diabetics have higher morbidity and mortality in cardiovascular disease (CVD). A variety of antidiabetic agents are available for clinical choice. Cardiovascular (CV) safety assessment of these agents is crucial in addition to hypoglycemic effect before clinical prescription. Adenosine 5'-monophosphate-activated protein kinase (AMPK) is an important cell energy sensor, which plays an important role in regulating myocardial energy metabolism, reducing ischemia and ischemia/reperfusion (I/R) injury, improving heart failure (HF) and ventricular remodeling, ameliorating vascular endothelial dysfunction, antichronic inflammation, anti-apoptosis, and regulating autophagy. In this review, we summarized the effects of antidiabetic agents to CVD according to basic and clinical research evidence and put emphasis on whether these agents can play roles in CV system through AMPK-dependent signaling pathways. Metformin has displayed definite CV benefits related to AMPK. Sodium-glucose cotransporter 2 inhibitors also demonstrate sufficient clinical evidence for CV protection, but the mechanisms need further exploration. Glucagon-likepeptide1 analogs, dipeptidyl peptidase-4 inhibitors, α-glucosidase inhibitors and thiazolidinediones also show some AMPK-dependent CV benefits. Sulfonylureas and meglitinides may be unfavorable to CV system. AMPK is becoming a promising target for the treatment of diabetes, metabolic syndrome and CVD. But there are still some questions to be answered.

Abundance, localization, and functional correlates of the advanced glycation end-product carboxymethyl lysine in human myocardium

Advanced glycation end‐products (AGEs) play a role in the pathophysiology of diabetes mellitus (DM) and possibly hypertension (HTN). In experimental DM, AGEs accumulate in myocardium. Little is known about AGEs in human myocardium. We quantified abundance, localization, and functional correlates of the AGE carboxymethyl lysine (CML) in left ventricular (LV) myocardium from patients undergoing coronary bypass grafting (CBG). Immunoelectron microscopy was used to quantify CML in epicardial biopsies from 98 patients (71 M, 27 F) with HTN, HTN + DM or neither (controls), all with normal LV ejection fraction. Myofilament contraction‐relaxation function was measured in demembranated myocardial strips. Echocardiography was used to quantify LV structure and function. We found that CML was abundant within cardiomyocytes, but minimally associated with extracellular collagen. CML counts/μm² were 14.7% higher in mitochondria than the rest of the cytoplasm (P < 0.001). There were no significant sex or diagnostic group differences in CML counts [controls 45.6 ± 3.6/μm² (±SEM), HTN 45.8 ± 3.6/μm², HTN + DM 49.3 ± 6.2/μm²; P = 0.85] and no significant correlations between CML counts and age, HgbA1c or myofilament function indexes. However, left atrial volume was significantly correlated with CML counts (r = 0.41, P = 0.004). We conclude that in CBG patients CML is abundant within cardiomyocytes but minimally associated with collagen, suggesting that AGEs do not directly modify the stiffness of myocardial collagen. Coexistent HTN or HTN + DM do not significantly influence CML abundance. The correlation of CML counts with LAV suggests an influence on diastolic function independent of HTN, DM or sex whose mechanism remains to be determined.

Molecular and clinical roles of incretin-based drugs in patients with heart failure

Glucagon-like peptide-1 (GLP-1) agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors produce some beneficial and deleterious effects in diabetic patients not mediated by their glycemic lowering effects, and there is a need for better understanding of the molecular basis of these effects. They possess antioxidant and anti-inflammatory effects with some direct vasodilatory action (animal and human trial data) that may indirectly influence heart failure (HF). Unlike GLP-1R agonists, signaling for HF adverse effects was observed with two DPP-4 inhibitors, saxagliptin and alogliptin. Accordingly, these drugs should be used with caution in heart failure patients.

SGLT-2 Inhibition with Dapagliflozin Reduces the Activation of the Nlrp3/ASC Inflammasome and Attenuates the Development of Diabetic Cardiomyopathy in Mice with Type 2 Diabetes. Further Augmentation of the Effects with Saxagliptin, a DPP4 Inhibitor

PURPOSE

We assessed whether (1) dapagliflozin (Dapa, an SGLT2-inhibitor) attenuates the deterioration of heart function Nlrp3 and inflammasome activation in diabetic mice. (2) The effects can be augmented with saxagliptin (Saxa), a DDP4-inhibitor. (3) Dapa effect is possibly SGLT2-independent on cardiofibroblasts in vitro.

METHODS

Type 2 diabetic (BTBR ob/ob) and wild-type (WT) mice received vehicle, Dapa, or Dapa+Saxa for 8 weeks. Glucose tolerance test and echocardiogram were performed. Cardiofibroblasts from WT and BTBR hearts were incubated with Dapa and exposed to LPS.

RESULTS

Left ventricular ejection fraction (LVEF) was 81 ± 1% in the WT and 53 ± 1% in the T2D-cont mice. Dapa and Dapa+Saxa improved LVEF to 68 ± 1 and 74.6 ± 1% in the BTBR mice (p < 0.001). The mRNA levels of NALP3, ASC, IL-1β, IL-6, caspase-1, and TNFα were significantly higher in the BTBR compared to the WT hearts; and Dapa and Dapa+Saxa significantly attenuated these levels. Likewise, protein levels of NLRP3, TNFα, and caspase-1 were higher in the BTBR compared to the WT hearts and Dapa, and to a greater extent Dapa+Saxa, attenuated the increase in the BTBR mice. Collagen-1 and collagen-3 mRNA levels significantly increased in the BTBR mice and these increases were attenuated by Dapa and Dapa+Saxa. P-AMPK/total-AMPK ratio was significantly lower in the BTBR mice than in the WT mice. Dapa and Dapa+Saxa equally increased the ratio in the BTBR mice. This in vitro study showed that NALP3, ASC, IL-1β, and caspase-1 mRNA levels were higher in the BTBR cardiofibroblasts and attenuated with Dapa. The effect was AMPK-dependent and SGLT1-independent.

CONCLUSIONS

Dapa attenuated the activation of the inflammasome, fibrosis, and deterioration of LVEF in BTBR mice. The anti-inflammatory, anti-fibrotic effects are likely SGLT2- and glucose-lowering-independent, as they were replicated in the in vitro model. The effects on remodeling were augmented when Saxa was added to Dapa. Yet, adding Saxa to Dapa did not result in a greater effect on myocardial fibrosis and collagen levels.

Dipeptidyl peptidase 4 inhibitor attenuates obesity-induced myocardial fibrosis by inhibiting transforming growth factor-βl and Smad2/3 pathways in high-fat diet-induced obesity rat model

Obesity-induced myocardial fibrosis may lead to diastolic dysfunction and ultimately heart failure. Activation of the transforming growth factor (TGF)-βl and its downstream Smad2/3 pathways may play a pivotal role in the pathogenesis of obesity-induced myocardial fibrosis, and the antidiabetic dipeptidyl peptidase 4 inhibitors (DPP4i) might affect these pathways. We investigated whether DPP4i reduces myocardial fibrosis by inhibiting the TGF-β1 and Smad2/3 pathways in the myocardium of a diet-induced obesity (DIO) rat model. Eight-week-old male spontaneously hypertensive rats (SHRs) were fed either a normal fat diet (chow) or a high-fat diet (HFD) and then the HFD-fed SHRs were randomized to either the DPP4i (MK-0626) or control (distilled water) groups for 12weeks. At 20weeks old, all the rats underwent hemodynamic and metabolic studies and Doppler echocardiography. Compared with the normal fat diet (chow)-fed SHRs, the HFD-fed SHRs developed a more intense degree of hyperglycemia and dyslipidemia and showed a constellation of left ventricular (LV) diastolic dysfunction, and exacerbated myocardial fibrosis, as well as activation of the TGF-β1 and Smad2/3 pathways. DPP4i significantly improved the metabolic and hemodynamic parameters. The echocardiogram showed that DPP4i improved the LV diastolic dysfunction (early to late ventricular filling velocity [E/A] ratio, 1.49±0.21 vs. 1.77±0.09, p<0.05). Furthermore, DPP4i significantly reduced myocardial fibrosis and collagen production by the myocardium and suppressed TGF-β1 and phosphorylation of Smad2/3 in the heart. In addition, DPP4i decreased TGF-β1-induced collagen production and TGF-β1-mediated phosphorylation and nuclear translocation of Smad2/3 in rat cardiac fibroblasts. In conclusion, DPP4 inhibition attenuated myocardial fibrosis and improved LV diastolic dysfunction in a DIO rat model by modulating the TGF-β1 and Smad2/3 pathways.

Dipeptidyl Peptidase-4 Inhibitors and Risk of Heart Failure in Patients With Type 2 Diabetes Mellitus: A Population-Based Cohort Study

BACKGROUND

The association between dipeptidyl-peptidase IV inhibitors (DPP-4i) and heart failure (HF) remains unclear. In 1 randomized controlled trial and some observational studies, DPP-4i reportedly increased the risk of HF, but 2 other randomized controlled trials and observational studies have shown no such risk. Here, we evaluated the risk of HF and cardiovascular outcomes of DPP-4i compared with sulfonylureas.

METHODS AND RESULTS

A population-based retrospective cohort study was conducted using the Korean Health Insurance Review and Assessment Service database from January 1, 2009, to December 31, 2015. Incident users of sulfonylurea and DPP-4i who were not prescribed the comparator drug in the year before treatment initiation were included. DPP-4i-treated and sulfonylurea-treated patients were matched on propensity score, calculated with >40 variables. The risk of hospitalization for HF was evaluated with a Cox proportional hazards model in 255 691 matched pairs. Analyses were conducted in the total patient population and in both strata divided by the presence of cardiovascular disease during the baseline period. The hazard ratios (HRs) of hospitalization for HF for DPP-4i-treated patients were 0.78 (95% confidence interval [CI], 0.67-0.86) in all of the patients, 0.77 (95% CI, 0.68-0.79) in patients with baseline cardiovascular disease, and 0.71 (95% CI, 0.56-0.90) in patients without baseline cardiovascular disease compared with HRs for sulfonylurea-treated patients. Sitagliptin and linagliptin showed statistically lower risk for hospitalization for HF (HR, 0.76; 95% CI, 0.67-0.86 for sitagliptin-prescribed patients; HR, 0.74; 95% CI, 0.59-0.92 for linagliptin-prescribed patients) than for sulfonylurea. The HRs for hospitalization for myocardial infarction and stroke with the use of a DPP-4i versus sulfonylurea were HR, 0.76 (95% CI, 0.67-0.87) and HR, 0.63 (95% CI, 0.60-0.67), respectively.

CONCLUSIONS

Our findings suggest that DPP-4i use did not increase the risk of HF compared with sulfonylurea. In addition, the risks for cardiovascular outcomes were not elevated in DPP-4i-treated patients compared with sulfonylurea-treated patients.

Dipeptidyl Peptidase IV as a Prognostic Marker and Therapeutic Target in Papillary Thyroid Carcinoma

CONTEXT

Dipeptidyl peptidase IV (DPP4) is overexpressed in thyroid cancer and certain malignancies. Furthermore, DPP4 has been identified as a discriminatory marker for thyroid cancer. However, it remains unclear whether DPP4 expression plays a prognostic role.

OBJECTIVE

The aim of this study was to investigate the expression and function of DPP4 in thyroid cancer and the mechanisms involved.

DESIGN

We determined the expression of DPP4 by immunohistochemistry in tissue microarrays of thyroid tumors. In vitro functional studies were performed after genetic and pharmacological inhibition of DPP4. Gene expression and pathway analyses were used to identify downstream targets. The therapeutic potential of DPP4 inhibition was evaluated in a mouse xenograft model.

RESULTS

High DPP4 expression was associated with extrathyroidal extension (P < 0.001), BRAF mutation (P < 0.001), and advanced tumor stage (P = 0.007) in papillary thyroid cancer. Patients in the high-DPP4 expression group were less likely to be classified as having no evidence of disease at final follow-up (P = 0.042). DPP4 silencing or treatment with DPP4 inhibitors significantly suppressed colony formation, cell migration, and invasion. Analysis of differentially expressed genes after DPP4 knockdown suggested that the transforming growth factor-β signaling pathway is involved. In vivo experiments revealed that sitagliptin treatment reduced tumor growth and xenograft transforming growth factor-β receptor I expression.

CONCLUSIONS

Increased DPP4 expression is associated with cellular invasion and more aggressive disease in papillary thyroid cancer. Targeting DPP4 may be a therapeutic strategy for DPP4-expressing thyroid cancer.

Dipeptidyl Peptidase-4, Wound Healing, Scarring, and Fibrosis

Scarring and fibrosis are an enormous public health concern, resulting in excessive morbidity and mortality in addition to countless lost health care dollars. Recent advances in cell and developmental biology promise a better understanding of scarring and fibrosis and may translate to new clinical therapies.

Effects of linagliptin and liraglutide on glucose- and angiotensin II-induced collagen formation and cytoskeleton degradation in cardiac fibroblasts in vitro

AIM

Glucagon-like peptide-1 (GLP-1) agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors can not only lower blood glucose levels, but also alleviate cardiac remodeling after myocardial ischemia and hypertension. In the present study, we investigated the effects of a DPP-4 inhibitor (linagliptin) and a GLP-1 activator (liraglutide) on glucose- and angiotensin II (Ang II)-induced collagen formation and cytoskeleton reorganization in cardiac fibroblasts in vitro, and elucidated the related mechanisms.

METHODS

Cardiac fibroblasts were isolated from the hearts of 6-week-old C57BL/6 mice, and then exposed to different concentrations of glucose or Ang II for 24 h. The expression of fibrotic signals (fibronectin, collagen-1, -3 and -4), as well as ERK1/2 and NF-κB-p65 in the fibroblasts was examined using Western blotting assays. F-actin degradation was detected under inverted laser confocal microscope in fibroblasts stained with Rhodamine phalloidin.

RESULTS

Glucose (1-40 mmol/L) and Ang II (10^-8-10^-5 mol/L) dose-dependently increased the expression of fibronectin, collagens, phospho-ERK1/2 and phospho-NF-κB-p65 in cardiac fibroblasts. High concentrations of glucose (≥40 mmol/L) and Ang II (≥10^-6 mol/L) caused a significant degradation of F-actin (less assembly F-actin fibers and more disassembly fibers). ERK1/2 inhibitor U0126 (10 μmol/L) and NF-κB inhibitor JSH-23 (10 μmol/L) both markedly suppressed glucose- and angiotensin II-induced fibronectin and collagen expressions in cardiac fibroblasts. Furthermore, pretreatment with liraglutide (10-100 nmol/L) or linagliptin (3 and 30 nmol/L) significantly decreased glucose- and Ang II-induced expression of fibrotic signals, phospho-ERK1/2 and phospho-NF-κB-p65 in cardiac fibroblasts. Moreover, pretreatment with liraglutide (30 nmol/L) or liraglutide (100 nmol/L) markedly inhibited glucose-induced F-actin degradation, however, only liraglutide inhibited Ang II-induced F-actin degradation.

CONCLUSION

Linagliptin and liraglutide inhibit glucose- and Ang II-induced collagen formation in cardiac fibroblasts via activation of the ERK/NF-κB/pathway. Linagliptin and liraglutide also markedly inhibit glucose-induced F-actin degradation in cardiac fibroblasts, but only liraglutide inhibits Ang II-induced F-actin degradation.

Linagliptin Ameliorates Methylglyoxal-Induced Peritoneal Fibrosis in Mice

Recent studies have reported increases of methylglyoxal (MGO) in peritoneal dialysis patients, and that MGO-mediated inflammation plays an important role in the development of peritoneal fibrosis through production of transforming growth factor-β1 (TGF-β1). Linagliptin, a dipeptidyl peptidase-4 inhibitor, exerts anti-inflammatory effects independent of blood glucose levels. In this study, we examined whether linagliptin suppresses MGO-induced peritoneal fibrosis in mice. Male C57/BL6 mice were divided into three groups: control, MGO injection plus saline, and MGO injection plus linagliptin (n = 6 per group). Peritoneal fibrosis was induced by daily intraperitoneal injection of saline containing 40 mmol/L MGO for 21 days. Saline was administered intraperitoneally to the control group. Linagliptin (10 mg/kg) or saline were administrated by once-daily oral gavage from 3 weeks before starting MGO injections. Immunohistochemical staining revealed that linagliptin suppressed expression of α-smooth muscle actin and fibroblast-specific protein-1, deposition of type I and III collagen, and macrophage (F4/80) infiltration. Peritoneal equilibration testing showed improved peritoneal functions in mice treated with linagliptin. Peritoneal injection of MGO increased plasma levels of glucagon-like peptide-1 (GLP-1) in mice, and a further increase was observed in linagliptin-treated mice. Although MGO increased plasma glucose levels, linagliptin did not decrease plasma glucose levels. Moreover, linagliptin reduced the TGF-β1 concentration in the peritoneal fluid of MGO-treated mice. GLP-1 receptor (GLP-1R) was expressed in monocytes/macrophages and linagliptin suppressed GLP-1R expression in MGO-injected mice. These results suggest that oral administration of linagliptin ameliorates MGO-induced peritoneal fibrosis.

Effect of metformin and sitagliptin on doxorubicin-induced cardiotoxicity in adult male albino rats

The use of doxorubicin (DOX) as an antitumor therapeutic agent is limited due to its cardiotoxic effects. Metformin (Met) and sitagliptin (Sitg) are suggested to improve cardiac function. The present study aimed to determine the potential protective effects of Met and Sitg on DOX-induced cardiotoxicity. Rats were divided into six groups: groups I, II, and III received normal saline, Met, and Sitg, respectively. Groups IV, V, and VI received DOX only, Met + DOX, and Sitg + DOX, respectively. Heart tissue was used for biochemical assays which measured cardiac reduced glutathione (GSH), thiobarbituric acid reactive substances (TBARS), and tumor necrosis factor α (TNF-α). Serum creatinine kinase (CK) and lactate dehydrogenase (LDH) were also measured. The heart apex was prepared for histological (hematoxylin and eosin) and immunohistochemical examination. Intoxication of DOX was associated with a significant elevation in serum CK-MB and LDH, reduction in cardiac GSH, and increased TBARS and TNF-α compared to the controls. Administration of Met or Sitg to DOX-intoxicated rats suppressed serum CK-MB and LDH. Moreover, cardiac GSH was elevated with decreased TBARS and TNF-α. These results were confirmed by histological study. Met and Sitg caused inhibition of caspase 3 and upregulation of B-cell lymphoma 2 (Bcl-2) expression in DOX-intoxicated animals. Sitg was found to exert a significantly better protective effect compared to that of Met. It was concluded that Sitg might be more effective than Met in reducing myocardial injury in DOX-induced cardiotoxicity in rats.

Modulation of myocardial injury and collagen deposition following ischaemia-reperfusion by linagliptin and liraglutide, and both together

Studies have indicated that dipeptidyl peptidase-4 (DPP-4) inhibitors and glucagon-like peptide-1 (GLP-1) agonists reduce infarct size after myocardial ischaemia. Whether these agents modify cardiac remodelling after ischaemia is unclear. Furthermore, it is not known if combination of the two types of drugs is superior to either agent alone. We investigated the modulatory effect of the DPP-4 inhibitor linagliptin alone, the GLP-1 activator liraglutide alone, or the two agents together on myocardial infarct size, left ventricular contractile function and cardiac remodelling signals after a brief period of left coronary artery (LCA) occlusion. C57BL/6 mice were treated with vehicle, the DPP-4 inhibitor linagliptin, the GLP-1 activator liraglutide, or both agents together for 5 days, and then subjected to LCA occlusion (1 h) and reperfusion (3 h). Ischaemia-reperfusion increased reactive oxygen species (ROS) generation and expression of NADPH oxidase (p47(phox), p22(phox) and gp91(phox) subtypes), collagens, fibronectin and proinflammatory cytokines (interleukin 6, tumour necrosis factor α and monocyte chemoattractant protein-1) in the LCA-supplied regions. Pre-treatment with linagliptin or liraglutide reduced infarct size, protected cardiomyocytes from injury and preserved cardiac contractile function in a similar fashion. It is interesting that profibrotic (collagen deposition) signals were expressed soon after ischaemia-reperfusion. Both linagliptin and liraglutide suppressed ROS generation, NADPH oxidase and proinflammatory signals, and reduced collagen deposition. Addition of linagliptin or liraglutide had no significant additive effect above and beyond that of liraglutide and linagliptin given alone. In conclusion, linagliptin and liraglutide can improve cardiac contractile function and indices of cardiac remodelling, which may be related to their role in inhibition of ROS production and proinflammatory cytokines after ischaemia.

Sitagliptin attenuated brain damage and cognitive impairment in mice with chronic cerebral hypo-perfusion through suppressing oxidative stress and inflammatory reaction

BACKGROUND

Sitagliptin, a new antidiabetic drug that inhibits dipeptidyl peptidase (DPP)-4 enzyme activity, has been reported to possess neuroprotective property. We tested the protective effects of sitagliptin against chronic cerebral hypoperfusion (CHP) in mice after bilateral carotid artery stenosis (BCAS).

METHOD

Thirty C57BL/6 mice were divided into three groups: sham control (n = 10), CHP (n = 10) and CHP-sitagliptin (orally 600 mg/kg/day) (n = 10). Working memory was assessed with novel-object recognition test. MRI was performed at day 0 and day 90 after BCAS procedure prior to sacrifice.

RESULTS

Immunohistochemical (IHC) staining showed significantly enhanced white matter lesions, microglia activation and astrocytosis of white matter in CHP group than in sham control, but the changes were significantly suppressed after sitagliptin treatment (all P < 0.01). The mRNA expressions of inflammatory [tumour necrosis factor-alpha (TNF-α), monocyte chemoattractant protein (MCP-1) and matrix metalloproteinase (MMP)-2] and apoptotic (Bax) biomarkers showed an identical pattern, whereas the anti-inflammatory (interleukin, IL-10) and antiapoptotic (Bcl-2) biomarkers showed an opposite pattern compared with that of IHC among all groups (all P < 0.01). The protein expressions of oxidative stress (NOX-I, NOX-II, nitrotyrosin, oxidized protein), inflammatory [nuclear factor-kappa B (NF-κB), TNF-α and MMP-2], apoptotic [mitochondrial Bax, cleaved poly(ADP-ribose) polymerase (PARP)] and DNA-damage (γ-H2AX) markers showed an identical pattern, while expression pattern of antiapoptotic marker (Bcl-2) was opposite to that of IHC (all P < 0.01). Glycogen-like peptide-1 receptor protein expression progressively increased from sham control to CHP-sitagliptin (P < 0.01). The short-term working-memory loss and MRI/diffusion tensor imaging (DTI) showed a pattern identical to that of IHC in all groups (all P < 0.01).

CONCLUSION

Sitagliptin protected against cognitive impairment and brain damage in a murine CHP model.

Cardioprotective effects of sitagliptin against doxorubicin-induced cardiotoxicity in rats

There is a large body of evidence suggesting that inhibitors of dipeptidyl peptidase-4, such as sitagliptin, may exhibit beneficial effects against different inflammatory disorders. This investigation was conducted to elucidate the potential ability of sitagliptin to counteract the injurious effects of doxorubicin in cardiac tissue. Male Wistar rats were pretreated with sitagliptin for 10 days then treated with a single dose of doxorubicin (20 mg/kg, i.p). Electrocardiography, biochemical estimation of serum and tissue markers, and histo- and immunopathological examinations were done. Results have shown that supplementation with sitagliptin resulted in significant improvement of cardiac function with contaminant decrease in serum markers of doxorubicin-induced cardiotoxicity. These results were supported by the histopathological results. Furthermore, a marked protection against oxidative stress was evident through reduction of lipid peroxidation and prevention of reduced glutathione content depletion and superoxide dismutase activity reduction in cardiac tissue of rats pretreated with sitagliptin in combination with doxorubicin. Moreover, sitagliptin ameliorated the activation of nuclear factor kappa-B and the release of inflammatory cytokines, tumour necrosis factor-alpha and nitric oxide. Finally, sitagliptin attenuated doxorubicin-induced increase in the expression of pro-apoptotic protein Bax and in the apoptotic marker, caspase-3. Collectively, these data indicate that sitagliptin pretreatment could alleviate doxorubicin-induced cardiotoxicity via reducing oxidative damage and its subsequent inflammation and apoptosis.

AMPK in cardiac fibrosis and repair: Actions beyond metabolic regulation

Fibrosis is a general term encompassing a plethora of pathologies that span all systems and is marked by increased deposition of collagen. Injury of variable etiology gives rise to complex cascades involving several cell-types and molecular signals, leading to the excessive accumulation of extracellular matrix that promotes fibrosis and eventually leads to organ failure. Cardiac fibrosis is a dynamic process associated notably with ischemia, hypertrophy, volume- and pressure-overload, aging and diabetes mellitus. It has profoundly deleterious consequences on the normal architecture and functioning of the myocardium and is associated with considerable mortality and morbidity. The AMP-activated protein kinase (AMPK) is a ubiquitously expressed cellular energy sensor and an essential component of the adaptive response to cardiomyocyte stress that occurs during ischemia. Nevertheless, its actions extend well beyond its energy-regulating role and it appears to possess an essential role in regulating fibrosis of the myocardium. In this review paper, we will summarize the main elements and crucial players of cardiac fibrosis. In addition, we will provide an overview of the diverse roles of AMPK in the heart and discuss in detail its implication in cardiac fibrosis. Lastly, we will highlight the recently published literature concerning AMPK-targeting current therapy and novel strategies aiming to attenuate fibrosis.

Adenosine A1 receptor activation attenuates cardiac hypertrophy and fibrosis in response to α1 -adrenoceptor stimulation in vivo

BACKGROUND AND PURPOSE

Adenosine has been proposed to exert anti-hypertrophic effects. However, the precise regulation and the role of the different adenosine receptor subtypes in the heart and their effects on hypertrophic signalling are largely unknown. We aimed to characterize expression and function of adenosine A1 receptors following hypertrophic stimulation in vitro and in vivo.

EXPERIMENTAL APPROACH

Pro-hypertrophic stimuli and adenosine A1 receptor stimulation of neonatal rat cardiomyocytes and male C57/Bl6 mice, sc. drug administration, real-time PCR, (3) [H]-leucine-incorporation assay, immunostaining, tissue staining, Western blots, gravimetric analyses and echocardiography were applied in this study.

KEY RESULTS

In neonatal rat cardiomyocyte cultures, phenylephrine, but not angiotensin II or insulin-like growth factor 1 (IGF1), up-regulated adenosine A1 receptors concentration-dependently. The hypertrophic phenotype (cardiomyocyte size, sarcomeric organization, total protein synthesis, c-fos expression) mediated by phenylephrine (10 μM), but not that by angiotensinII (1 μM) or IGF1 (20 ng·mL(-1) ), was counteracted by the selective A1 receptor agonist, N6-cyclopentyladenosine. In C57/BL6 mice, continuous N6-cyclopentyladenosine infusion (2 mg·kg(-1) ·day(-1) ; 21 days) blunted phenylephrine (120 mg·kg(-1) ·day(-1) ; 21 days) induced hypertrophy (heart weight, cardiomyocyte size and fetal genes), fibrosis, MMP 2 up-regulation and generation of oxidative stress - all hallmarks of maladaptive remodelling. Concurrently, phenylephrine administration increased expression of adenosine A1 receptors.

CONCLUSIONS AND IMPLICATIONS

We have presented evidence for a negative feedback mechanism attenuating pathological myocardial hypertrophy following α1 -adrenoceptor stimulation. Our results suggest adenosine A1 receptors as potential targets for therapeutic strategies to prevent transition from compensated myocardial hypertrophy to decompensated heart failure due to chronic cardiac pressure overload.

Effects of telmisartan and linagliptin when used in combination on blood pressure and oxidative stress in rats with 2-kidney-1-clip hypertension

OBJECTIVE

To investigate the effects of linagliptin alone and in combination with the angiotensin II receptor blocker (ARB), telmisartan on blood pressure (BP), kidney function, heart morphology and oxidative stress in rats with renovascular hypertension.

METHODS

Fifty-seven male Wistar rats underwent unilateral surgical stenosis of the renal artery [2-kidney-1-clip (2k1c) method]. Animals were randomly divided into four treatment groups (n = 14-18 per group) receiving: telmisartan (10 mg/kg per day in drinking water), linagliptin (89 ppm in chow), combination (linagliptin 89 ppm + telmisartan 10 mg/kg per day) or placebo. An additional group of 12 rats underwent sham surgery. BP was measured one week after surgery. Hypertensive animals entered a 16-week dosing period. BP was measured 2, 4, 8, 12 and 16 weeks after the initiation of treatment. Blood and urine were tested for assessment of kidney function and oxidative stress 6, 10, 14 and 18 weeks after surgery. Blood and urine sampling and organ harvesting were finally performed.

RESULTS

Renal stenosis caused an increase in mean ± SD systolic BP as compared with the sham group (157.7 ± 29.3 vs. 106.2 ± 20.5 mmHg, respectively; P < 0.001). Telmisartan alone and in combination with linagliptin, normalized SBP (111.1 ± 24.3 mmHg and 100.4 ± 13.9 mmHg, respectively; P < 0.001 vs. placebo). Telmisartan alone and in combination with linagliptin significantly prevented cardiac hypertrophy, measured by heart weight and myocyte diameter. Renal function measured by cystatin C was not affected by 2k1c surgery. Telmisartan significantly increased plasma concentration of cystatin C. 2k1c surgery initiated fibrosis in both kidneys. Telmisartan promoted further fibrotic changes in the clipped kidney, as measured by protein expression of Col1a1 and histology for interstitial fibrosis and glomerulosclerosis. In non-clipped kidneys, telmisartan demonstrated antifibrotic properties, reducing Col1a1 protein expression. Plasma levels of oxidized low-density lipoprotein were higher in the placebo-treated 2k1c rats as compared to sham-operated animals. The increase was abolished by linagliptin alone (P = 0.03 vs. placebo) and in combination with telmisartan (P = 0.02 vs. placebo). Combination therapy also significantly reduced plasma concentration of carbonyl proteins (P = 0.04 vs. placebo).

CONCLUSION

Inhibition of type 4 dipeptidyl peptidase with linagliptin did not counter BP-lowering effects of ARB in 2k1c rats. Linagliptin reduced lipid and protein oxidation in 2k1c rats, and this effect was BP-independent.

Smad3 Signaling Promotes Fibrosis While Preserving Cardiac and Aortic Geometry in Obese Diabetic Mice

BACKGROUND

Heart failure in diabetics is associated with cardiac hypertrophy, fibrosis and diastolic dysfunction. Activation of transforming growth factor-β/Smad3 signaling in the diabetic myocardium may mediate fibrosis and diastolic heart failure, while preserving matrix homeostasis. We hypothesized that Smad3 may play a key role in the pathogenesis of cardiovascular remodeling associated with diabetes mellitus and obesity.

METHODS AND RESULTS

We generated leptin-resistant db/db Smad3 null mice and db/db Smad3+/- animals. Smad3 haploinsufficiency did not affect metabolic function in db/db mice, but protected from myocardial diastolic dysfunction, while causing left ventricular chamber dilation. Improved cardiac compliance and chamber dilation in db/db Smad3+/- animals were associated with decreased cardiomyocyte hypertrophy, reduced collagen deposition, and accentuated matrix metalloproteinase activity. Attenuation of hypertrophy and fibrosis in db/db Smad3+/- hearts was associated with reduced myocardial oxidative and nitrosative stress. db/db Smad3 null mice had reduced weight gain and decreased adiposity associated with attenuated insulin resistance, but also exhibited high early mortality, in part, because of spontaneous rupture of the ascending aorta. Ultrasound studies showed that both lean and obese Smad3 null animals had significant aortic dilation. Aortic dilation in db/db Smad3 null mice occurred despite reduced hypertension and was associated with perturbed matrix balance in the vascular wall.

CONCLUSIONS

Smad3 mediates diabetic cardiac hypertrophy, fibrosis, and diastolic dysfunction, while preserving normal cardiac geometry and maintaining the integrity of the vascular wall.

Effects of vildagliptin versus sitagliptin, on cardiac function, heart rate variability and mitochondrial function in obese insulin-resistant rats

BACKGROUND AND PURPOSE

Long-term high-fat diet (HFD) consumption has been shown to cause insulin resistance, which is characterized by hyperinsulinaemia with metabolic inflexibility. Insulin resistance is associated with cardiac sympathovagal imbalance, cardiac dysfunction and cardiac mitochondrial dysfunction. Dipeptidyl peptidase-4 (DPP-4) inhibitors, vildagliptin and sitagliptin, are oral anti-diabetic drugs often prescribed in patients with cardiovascular disease. Therefore, in this study, we sought to determine the effects of vildagliptin and sitagliptin in a murine model of insulin resistance.

EXPERIMENTAL APPROACH

Male Wistar rats weighing 180-200 g, were fed either a normal diet (20% energy from fat) or a HFD (59% energy from fat) for 12 weeks. These rats were then divided into three subgroups to receive vildagliptin (3 mg·kg(-1)·day(-1)), sitagliptin (30 mg·kg(-1)·day(-1)) or vehicle for another 21 days. Metabolic parameters, oxidative stress, heart rate variability (HRV), cardiac function and cardiac mitochondrial function were determined.

KEY RESULTS

Rats that received HFD developed insulin resistance characterized by increased body weight, plasma insulin, total cholesterol and oxidative stress levels along with a decreased high-density lipoprotein (HDL) level. Moreover, cardiac dysfunction, depressed HRV, cardiac mitochondrial dysfunction and cardiac mitochondrial morphology changes were observed in HFD rats. Both vildagliptin and sitagliptin decreased plasma insulin, total cholesterol and oxidative stress as well as increased HDL level. Furthermore, vildagliptin and sitagliptin attenuated cardiac dysfunction, prevented cardiac mitochondrial dysfunction and completely restored HRV.

CONCLUSIONS AND IMPLICATIONS

Both vildagliptin and sitagliptin share similar efficacy in cardioprotection in obese insulin-resistant rats.

Targeting metabolic disturbance in the diabetic heart

Diabetic cardiomyopathy is defined as ventricular dysfunction initiated by alterations in cardiac energy substrates in the absence of coronary artery disease and hypertension. In addition to the demonstrated burden of cardiovascular events associated with diabetes, diabetic cardiomyopathy partly explains why diabetic patients are subject to a greater risk of heart failure and a worse outcome after myocardial ischemia. The raising prevalence and accumulating costs of cardiovascular disease in diabetic patients underscore the deficiencies of tertiary prevention and call for a shift in medical treatment. It is becoming increasingly clearer that the effective prevention and treatment of diabetic cardiomyopathy require measures to regulate the metabolic derangement occurring in the heart rather than merely restoring suitable systemic parameters. Recent research has provided deeper insight into the metabolic etiology of diabetic cardiomyopathy and numerous heart-specific targets that may substitute or reinforce current strategies. From both experimental and translational perspectives, in this review we first discuss the progress made with conventional therapies, and then focus on the need for prospective metabolic targets that may avert myocardial vulnerability and functional decline in next-generation diabetic care.

Crosstalk between advanced glycation end products (AGEs)-receptor RAGE axis and dipeptidyl peptidase-4-incretin system in diabetic vascular complications

Advanced glycation end products (AGEs) consist of heterogenous group of macroprotein derivatives, which are formed by non-enzymatic reaction between reducing sugars and amino groups of proteins, lipids and nucleic acids, and whose process has progressed at an accelerated rate under diabetes. Non-enzymatic glycation and cross-linking of protein alter its structural integrity and function, contributing to the aging of macromolecules. Furthermore, engagement of receptor for AGEs (RAGE) with AGEs elicits oxidative stress generation and subsequently evokes proliferative, inflammatory, and fibrotic reactions in a variety of cells. Indeed, accumulating evidence has suggested the active involvement of accumulation of AGEs in diabetes-associated disorders such as diabetic microangiopathy, atherosclerotic cardiovascular diseases, Alzheimer's disease and osteoporosis. Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are incretins, gut hormones secreted from the intestine in response to food intake, both of which augment glucose-induced insulin release, suppress glucagon secretion, and slow gastric emptying. Since GLP-1 and GIP are rapidly degraded and inactivated by dipeptidyl peptidase-4 (DPP-4), inhibition of DPP-4 and/or DPP-4-resistant GLP-1 analogues have been proposed as a potential target for the treatment of diabetes. Recently, DPP-4 has been shown to cleave multiple peptides, and blockade of DPP-4 could exert diverse biological actions in GLP-1- or GIP-independent manner. This article summarizes the crosstalk between AGEs-RAGE axis and DPP-4-incretin system in the development and progression of diabetes-associated disorders and its therapeutic intervention, especially focusing on diabetic vascular complications.

The dual PPARα/γ agonist aleglitazar increases the number and function of endothelial progenitor cells: implications for vascular function and atherogenesis

BACKGROUND AND PURPOSE

Aleglitazar is a dual PPARα/γ agonist but little is known about its effects on vascular function and atherogenesis. Hence, we characterized its effects on circulating angiogenic cells (CAC), neoangiogenesis, endothelial function, arteriogenesis and atherosclerosis in mice.

EXPERIMENTAL APPROACH

C57Bl/6 wild-type (WT, normal chow), endothelial NOS (eNOS)(-/-) (normal chow) and ApoE(-/-) (Western-type diet) mice were treated with aleglitazar (10 mg·kg(-1) ·day(-1) , i.p.) or vehicle.

KEY RESULTS

Aleglitazar enhanced expression of PPARα and PPARγ target genes, normalized glucose tolerance and potently reduced hepatic fat in ApoE(-/-) mice. In WT mice, but not in eNOS(-/-) , aleglitazar up-regulated Sca-1/VEGFR2-positive CAC in the blood and bone marrow and up-regulated diLDL/lectin-positive CAC. Aleglitazar augmented CAC migration and enhanced neoangiogenesis. In ApoE(-/-) mice, aleglitazar up-regulated CAC number and function, reduced markers of vascular inflammation and potently improved perfusion restoration after hindlimb ischaemia and aortic endothelium-dependent vasodilatation. This was associated with markedly reduced formation of atherosclerotic plaques. In human cultured CAC from healthy donors and patients with coronary artery disease with or without diabetes mellitus, aleglitazar increased migration and colony-forming units in a concentration-dependent manner. Furthermore, oxidative stress-induced CAC apoptosis and expression of p53 were reduced, while telomerase activity and expression of phospho-eNOS and phospho-Akt were elevated. Comparative agonist and inhibitor experiments revealed that aleglitazar's effects on CAC migration and colony-forming units were mediated by both PPARα and PPARγ signalling and required Akt.

CONCLUSIONS AND IMPLICATIONS

Aleglitazar augments the number, function and survival of CAC, which correlates with improved vascular function, enhanced arteriogenesis and prevention of atherosclerosis in mice.

Left ventricular diastolic dysfunction and myocardial stiffness in diabetic mice is attenuated by inhibition of dipeptidyl peptidase 4

AIMS

Obesity and Type 2 diabetes mellitus (DM) induce left ventricular (LV) diastolic dysfunction, which contributes to an increasing prevalence of heart failure with a preserved LV ejection fraction. We investigated the effects of sitagliptin (SITA), an inhibitor of dipeptidylpeptidase-4 (DPP-4) and anti-diabetic drug, on LV structure and function of obese mice with Type 2 DM.

METHODS AND RESULTS

Obese Type 2 diabetic mice (Lepr(db/db), BKS.Cg-Dock7(m)+/+ Lepr(db)/J), displaying increased cardiomyocyte and LV stiffness at the age of 16 weeks, were treated with SITA (300 mg/kg/day) or vehicle for 8 weeks. SITA severely impaired serum DPP-4 activity, but had no effect on glycaemia. Invasive haemodynamic recordings showed that SITA reduced LV passive stiffness and increased LV stroke volume; LV end-systolic elastance remained unchanged. In addition, SITA reduced resting tension of isolated single cardiomyocytes and intensified phosphorylation of the sarcomeric protein titin. SITA also increased LV concentrations of cGMP and increased activity of protein kinase G (PKG). In vitro activation of PKG decreased resting tension of cardiomyocytes from vehicle-treated mice, but had no effect on resting tension of cardiomyocytes from SITA-treated mice.

CONCLUSIONS

In obese Type 2 diabetic mice, in the absence of hypoglycaemic effects, inhibition of DPP-4 decreases LV passive stiffness and improves global LV performance. These effects seem at least partially mediated by stimulatory effects on the myocardial cGMP-PKG pathway and, hence, on the phosphorylation status of titin and the hereto coupled cardiomyocyte stiffness modulus.

Impact of glucagon-like peptide-1 on myocardial glucose metabolism revisited

The gut hormone glucagon-like peptide-1 (GLP-1) is an insulinotropic incretin with significant cardiovascular impact. Two classes of medication, GLP-1 analogues and DPP-4 inhibitors, have been developed that circumvent the rapid degradation of GLP-1 by the enzyme dipeptidyl peptidase-4 (DPP-4), both enhance the incretin effect and were developed for the treatment of type 2 diabetes. Several mechanisms suggesting that DPP-4 inhibitors, GLP-1, and analogues could have a protective effect on the cardiovascular risk profile have been forwarded; e.g., reductions of blood glucose, body weight, blood pressure, improvement in left ventricular ejection fraction, myocardial perfusion, atherosclerosis development, and endothelial function. Despite this, the reasons for a decreased risk of developing cardiovascular disease and reduced post-ischaemia damage are still poorly understood. The potentially beneficial effect of GLP-1 stimulation may rely on, among others, improved myocardial glucose metabolism. This review focuses on the dogma that GLP-1 receptor stimulation may provide beneficial cardiovascular effects, possibly due to enhanced myocardial energetic efficiency, by increasing myocardial glucose uptake. The published literature was systematically reviewed and the applied models evaluated since the outcomes of varying studies differ substantially. Reports on the effect of GLP-1R stimulation on myocardial metabolism are conflicting and should be evaluated carefully. There is limited and conflicting information on the impact of these agents in real life patients and while clinical outcome studies investigating the cardiovascular effects of GLP-1 based therapies have been initiated, the first two studies, both on DPP-4 inhibitors, designed specifically to evaluate cardiac safety reported largely neutral outcomes.

Dipeptidyl peptidase inhibition prevents diastolic dysfunction and reduces myocardial fibrosis in a mouse model of Western diet induced obesity

OBJECTIVE

Consumption of a high-fat/high-fructose Western diet (WD) is linked to rising obesity and heart disease, particularly diastolic dysfunction which characterizes early obesity/metabolic cardiomyopathy. Mounting evidence supports a role for inflammation, oxidative stress and fibrosis in the pathophysiology of metabolic cardiomyopathy. Dipeptidyl peptidase-4 (DPP-4) is a circulating exopeptidase recently reported to be elevated in the plasma of patients with insulin resistance (IR), obesity and heart failure. We hypothesized that a model of WD induced obesity/metabolic cardiomyopathy would exhibit increased DPP-4 activity and cardiac fibrosis with DPP-4 inhibition preventing cardiac fibrosis and the associated diastolic dysfunction.

MATERIALS/METHODS

Four-week-old C57BL6/J mice were fed a high-fat/high-fructose WD with the DPP-4 inhibitor MK0626 for 16 weeks. Cardiac function was examined by high-resolution cine-cardiac magnetic resonance imaging (MRI). Phenotypic analysis included measurements of body and heart weight, systemic IR and DPP-4 activity. Immunohistochemistry and transmission electron microscopy (TEM) were utilized to identify underlying pathologic mechanisms.

RESULTS

We found that chronic WD consumption caused obesity, IR, elevated plasma DPP-4 activity, heart enlargement and diastolic dysfunction. DPP-4 inhibition with MK0626 in WD fed mice resulted in >75% reduction in plasma DPP-4 activity, improved IR and normalized diastolic relaxation. WD consumption induced myocardial oxidant stress and fibrosis with amelioration by MK0626. TEM of hearts from WD fed mice revealed abnormal mitochondrial and perivascular ultrastructure partially corrected by MK0626.

CONCLUSIONS

This study provides evidence of a role for increased DPP-4 activity in metabolic cardiomyopathy and a potential role for DPP-4 inhibition in prevention and/or correction of oxidant stress/fibrosis and associated diastolic dysfunction.

Cardiovascular actions of incretin-based therapies

Glucagon-like peptide-1 receptor (GLP-1R) agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors represent 2 distinct classes of incretin-based therapies used for the treatment of type 2 diabetes mellitus. Activation of GLP-1R signaling or inhibition of DPP-4 activity produces a broad range of overlapping and unique cardiovascular actions. Native GLP-1 regulates cardiovascular biology via activation of the classical GLP-1R, or through GLP-1(9-36), a cardioactive metabolite generated by DPP-4-mediated cleavage. In contrast, clinically approved GLP-1R agonists are not cleaved to GLP-1(9-36) and produce the majority of their actions through the classical GLP-1R. The cardiovascular mechanisms engaged by DPP-4 inhibition are more complex, encompassing increased levels of intact GLP-1, reduced levels of GLP-1(9-36), and changes in levels of numerous cardioactive peptides. Herein we review recent experimental and clinical advances that reveal how GLP-1R agonists and DPP-4 inhibitors affect the normal and diabetic heart and coronary vasculature, often independent of changes in blood glucose. Improved understanding of the complex science of incretin-based therapies is required to optimize the selection of these therapeutic agents for the treatment of diabetic patients with cardiovascular disease.

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.

Glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1: Incretin actions beyond the pancreas

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are the two primary incretin hormones secreted from the intestine on ingestion of various nutrients to stimulate insulin secretion from pancreatic β-cells glucose-dependently. GIP and GLP-1 undergo degradation by dipeptidyl peptidase-4 (DPP-4), and rapidly lose their biological activities. The actions of GIP and GLP-1 are mediated by their specific receptors, the GIP receptor (GIPR) and the GLP-1 receptor (GLP-1R), which are expressed in pancreatic β-cells, as well as in various tissues and organs. A series of investigations using mice lacking GIPR and/or GLP-1R, as well as mice lacking DPP-4, showed involvement of GIP and GLP-1 in divergent biological activities, some of which could have implications for preventing diabetes-related microvascular complications (e.g., retinopathy, nephropathy and neuropathy) and macrovascular complications (e.g., coronary artery disease, peripheral artery disease and cerebrovascular disease), as well as diabetes-related comorbidity (e.g., obesity, non-alcoholic fatty liver disease, bone fracture and cognitive dysfunction). Furthermore, recent studies using incretin-based drugs, such as GLP-1 receptor agonists, which stably activate GLP-1R signaling, and DPP-4 inhibitors, which enhance both GLP-1R and GIPR signaling, showed that GLP-1 and GIP exert effects possibly linked to prevention or treatment of diabetes-related complications and comorbidities independently of hyperglycemia. We review recent findings on the extrapancreatic effects of GIP and GLP-1 on the heart, brain, kidney, eye and nerves, as well as in the liver, fat and several organs from the perspective of diabetes-related complications and comorbidities.

Linagliptin-mediated DPP-4 inhibition ameliorates kidney fibrosis in streptozotocin-induced diabetic mice by inhibiting endothelial-to-mesenchymal transition in a therapeutic regimen

Kidney fibrosis is the final common pathway of all progressive chronic kidney diseases, of which diabetic nephropathy is the leading cause. Endothelial-to-mesenchymal transition (EndMT) has emerged as one of the most important origins of matrix-producing fibroblasts. Dipeptidyl peptidase-4 (DPP-4) inhibitors have been introduced into the market as antidiabetes drugs. Here, we found that the DPP-4 inhibitor linagliptin ameliorated kidney fibrosis in diabetic mice without altering the blood glucose levels associated with the inhibition of EndMT and the restoration of microRNA 29s. Streptozotocin-induced diabetic CD-1 mice exhibited kidney fibrosis and strong immunoreactivity for DPP-4 by 24 weeks after the onset of diabetes. At 20 weeks after the onset of diabetes, mice were treated with linagliptin for 4 weeks. Linagliptin-treated diabetic mice exhibited a suppression of DPP-4 activity/protein expression and an amelioration of kidney fibrosis associated with the inhibition of EndMT. The therapeutic effects of linagliptin on diabetic kidneys were associated with the suppression of profibrotic programs, as assessed by mRNA microarray analysis. We found that the induction of DPP-4 observed in diabetic kidneys may be associated with suppressed levels of microRNA 29s in diabetic mice; linagliptin restored microRNA 29s and suppressed DPP-4 protein levels. Using cultured endothelial cells, we found that linagliptin inhibited TGF-β2-induced EndMT, and such anti-EndMT effects of linagliptin were mediated through microRNA 29 induction. These results indicate the possible novel pleiotropic action of linagliptin to restore normal kidney function in diabetic patients with renal impairment.

Treatment with brain natriuretic peptide prevents the development of cardiac dysfunction in obese diabetic db/db mice

AIMS/HYPOTHESIS

Obesity and diabetes increase the risk of developing cardiovascular diseases and heart failure. These metabolic disorders are generally reflected by natriuretic peptide system deficiency. Since brain natriuretic peptide (BNP) is known to influence metabolism and cardioprotection, we investigated the effect of chronic exogenous BNP treatment on adverse myocardial consequences related to obesity and diabetes.

METHODS

Ten-week-old C57BL/KsJ-db/db obese diabetic mice (db/db) and their lean control littermates (db/+) were treated with BNP (0.6 μg kg(-1) h(-1)) or saline for 12 weeks (n = 10/group). Serial blood and tomography analysis were performed. Cardiac function was determined by echocardiography, and biochemical and histological heart and fat analyses were also performed.

RESULTS

BNP treatment resulted in an average increase in plasma BNP levels of 70 pg/ml. An improvement in the metabolic profile of db/db mice was observed, including a reduction in fat content, increased insulin sensitivity, improved glucose tolerance and lower blood glucose, despite increased food intake. db/db mice receiving saline displayed both early systolic and diastolic dysfunction, whereas these functional changes were prevented by BNP treatment. The cardioprotective effects of BNP were attributed to the inhibition of cardiomyocyte apoptosis, myocardial fibrosis, cardiac hypertrophy and the AGE-receptor for AGE (RAGE) system as well as normalisation of cardiac AMP-activated protein kinase and endothelial nitric oxide synthase activities.

CONCLUSIONS/INTERPRETATION

Our results indicate that chronic BNP treatment at low dose improves the metabolic profile and prevents the development of myocardial dysfunction in db/db mice.

Dipeptidyl peptidase-4 inhibitors and their effects on the cardiovascular system

It is well known that patients with type 2 diabetes mellitus (T2DM) are at increased risk of cardiovascular (CV) disease. Elevated plasma glucose levels that independently lead to increased cardiovascular risk, combined with associated co-morbidities such as obesity, hypertension, and dyslipidemia, further contribute to the development of CV complications. Dipeptidyl peptidase 4 inhibitors (DPP-4 inhibitors) are a relatively new class of drugs used for the treatment of diabetes and recently have been widely used in clinical practice. They exert their actions through degradation inhibition of endogenous glucagon-like peptides (GLP-1) and glucose-dependent insulinotropic peptides (GIP), with a resulting increase in glucose mediated insulin secretion and a suppression of glucagon secretion. Since GLP-1 is known to have an impact not only on plasma glucose levels but also to have cardiovascular protective effects there is increased speculation of whether DPP-4 inhibitors will have similar effects. Though many short-term studies have been encouraging, ongoing long-term clinical trials on humans are needed to provide further clarity to the complete safety profiles of these agents in terms of cardiovascular risk, and whether they may exert potential cardiovascular benefit. This review includes available data on the cardiovascular effects of DPP-4 inhibitors as well as their overall safety profile.

The DPP-4 inhibitor sitagliptin attenuates the progress of atherosclerosis in apolipoprotein-E-knockout mice via AMPK- and MAPK-dependent mechanisms

BACKGROUND

The dipeptidyl peptidase-4 inhibitor sitagliptin, a new anti-diabetic medicine, is effective in treating type 2 diabetes mellitus by increasing the activation and duration of action of glucagon-like peptide-1. Since atherosclerosis is the main pathological feature of diabetic cardiovascular complications, it is important to investigate the anti-atherosclerotic effect of sitagliptin and explore the relevant mechanisms.

METHODS

Male apolipoprotein-E-knockout mice were randomly divided into two groups and fed either high-fat diet (HFD) or HFD plus sitagliptin at a concentration of 0.3% for 16 weeks. Body weight, food intake, blood glucose, serum lipids and adhesion molecules were measured. The atherosclerotic plaque area and its histological composition were analyzed using Sudan staining and immunohistochemistry. The expression of inflammatory cytokines (monocyte chemoattractant protein (MCP)-1 and interleukin (IL)-6) and the activation of AMP-activated protein kinase (AMPK) and mitogen-activated protein kinase (MAPK) in the aortas were determined using quantitative polymerase chain reaction and western blot, respectively.

RESULTS

Mice treated with sitagliptin developed fewer atherosclerotic plaques than the control group (7.64 ± 1.98% vs 12.91 ± 1.15%, p < 0.001), particularly in the aortic arch and abdominal aorta, where plaques were decreased 1.92- and 2.74-fold, respectively (p < 0.05 and p < 0.01). Sitagliptin significantly reduced the content of collagen fiber in plaques 1.2-fold (p < 0.05). Moreover, sitagliptin significantly reduced the expression of monocyte chemoattractant protein-1 and interleukin-6 in the aorta (p < 0.01 and p < 0.05), as well as the serum levels of soluble vascular cell adhesion molecule-1 and P-selectin (both p < 0.05). In addition, Sitagliptin induced phosphorylation of AMPK and Akt (p < 0.05 and p < 0.01), while suppressed phosphorylation of p38 and extracellular signal-regulated kinase (Erk) 1/2 (p < 0.05 and p < 0.01) in aortas.

CONCLUSIONS

Our present study indicates that sitagliptin can reduce the area of the atherosclerotic lesion, possibly by regulating the AMPK and MAPK pathways and then reducing leukocyte -endothelial cell interaction and inflammation reactions. These actions are independent of weight loss and glucose-reducing effects.

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.