Pre-treatment with a DPP-4 inhibitor is infarct sparing in hearts from obese, pre-diabetic rats

The benefits of oral glucose-lowering agents: GLP-1 receptor agonists, DPP-4 and SGLT-2 inhibitors on myocardial ischaemia/reperfusion injury

Myocardial infarction (MI) is a life-threatening cardiovascular disease that, on average, results in 8.5 million deaths worldwide each year. Timely revascularization of occluded vessels is a critical method of myocardial salvage. However, reperfusion paradoxically leads to the worsening of myocardial damage known as myocardial ischaemia/reperfusion injury (MI/RI). Therefore, reducing the size of myocardial infarction after reperfusion is critical and remains an important therapeutic goal. The susceptibility of the myocardium to MI/RI may be increased by diabetes. Currently, some traditional antidiabetic agents such as metformin reduce MI/RI by decreasing inflammation, inhibiting oxidative stress, and improving vascular endothelial function. This appears to be a new direction for the treatment of MI/RI. Recent cardiovascular outcome trials have shown that several oral antidiabetic agents, including glucagon-like peptide-1 receptor agonists (GLP-1RAs), dipeptidyl peptidase-4 inhibitors (DPP-4is), and sodium-glucose-linked transporter-2 inhibitors (SGLT-2is), not only have good antidiabetic effects but also have a protective effect on myocardial protection. This article aims to discuss the mechanisms and effects of oral antidiabetic agents, including GLP-1RAs, DPP-4is, and SGLT-2is, on MI/RI to facilitate their clinical application.

The Functional Interplay between Gut Microbiota, Protein Hydrolysates/Bioactive Peptides, and Obesity: A Critical Review on the Study Advances

Diet is an essential factor determining the ratio of pathogenic and beneficial gut microbiota. Hydrolysates and bioactive peptides have been described as crucial ingredients from food protein that potentially impact human health beyond their roles as nutrients. These compounds can exert benefits in the body, including modulation of the gut microbiota, and thus, they can reduce metabolic disorders. This review summarized studies on the interaction between hydrolysates/peptides, gut microbes, and obesity, focusing on how hydrolysates/peptides influence gut microbiota composition and function that improve body weight. Findings revealed that gut microbes could exert anti-obesity effects by controlling the host’s energy balance and food intake. They also exhibit activity against obesity-induced inflammation by changing the expression of inflammatory-related transcription factors. Protein hydrolysates/peptides can suppress the growth of pro-obesity gut bacteria but facilitate the proliferation of those with anti-obesity effects. The compounds provide growth factors to the beneficial gut bacteria and also improve their resistance against extreme pH. Hydrolysates/peptides are good candidates to target obesity and obesity-related complications. Thus, they can allow the development of novel strategies to fight incidences of obesity. Future studies are needed to understand absorption fate, utilization by gut microbes, and stability of hydrolysates/peptides in the gut under obesity.

A Roadmap to Cardiac Tissue-Engineered Construct Preservation: Insights from Cells, Tissues, and Organs

Worldwide, over 26 million patients suffer from heart failure (HF). One strategy aspiring to prevent or even to reverse HF is based on the transplantation of cardiac tissue-engineered (cTE) constructs. These patient-specific constructs aim to closely resemble the native myocardium and, upon implantation on the diseased tissue, support and restore cardiac function, thereby preventing the development of HF. However, cTE constructs off-the-shelf availability in the clinical arena critically depends on the development of efficient preservation methodologies. Short- and long-term preservation of cTE constructs would enable transportation and direct availability. Herein, currently available methods, from normothermic- to hypothermic- to cryopreservation, for the preservation of cardiomyocytes, whole-heart, and regenerative materials are reviewed. A theoretical foundation and recommendations for future research on developing cTE construct specific preservation methods are provided. Current research suggests that vitrification can be a promising procedure to ensure long-term cryopreservation of cTE constructs, despite the need of high doses of cytotoxic cryoprotective agents. Instead, short-term cTE construct preservation can be achieved at normothermic or hypothermic temperatures by administration of protective additives. With further tuning of these promising methods, it is anticipated that cTE construct therapy can be brought one step closer to the patient.

Comparison of cardiovascular outcomes and cardiometabolic risk factors between patients with type 2 diabetes treated with sodium-glucose cotransporter-2 inhibitors and dipeptidyl peptidase-4 inhibitors: a meta-analysis

AIMS 

Prevention of cardiovascular outcomes is a goal of the management of patients with type 2 diabetes mellitus patients as important as lowering blood glucose levels. Among the various glucose-lowering agents, the effects of sodium-glucose cotransporter-2 inhibitors (SGLT-2Is) and dipeptidyl peptidase-4 inhibitors (DPP-4Is) on cardiovascular outcomes have become the focus of recent researches.

METHODS AND RESULTS 

A systematic search was performed through several online database. All studies that compared the effects of SGLT-2Is and DPP-4Is on cardiovascular outcomes and cardiometabolic risk factors were reviewed. A total of 30 studies were included. Compared with DPP-4Is, SGLT-2Is treatment reduced the risk of stroke [risk ratio (RR) = 0.80; 95% confidence interval (CI), 0.76-0.84], myocardial infarction (RR = 0.85; 95% CI, 0.81-0.89), heart failure (RR = 0.58; 95% CI, 0.54-0.62), cardiovascular mortality (RR = 0.55; 95% CI, 0.51-0.60), and all-cause mortality (RR = 0.60; 95% CI, 0.57-0.63). In addition, SGLT-2Is presented favourable effects on hemoglobinA1c, fasting plasma glucose, systolic blood pressure, and diastolic blood pressure. The differences in blood lipids were also compared.

CONCLUSION

Sodium-glucose cotransporter-2 inhibitors are superior to DPP-4Is in terms of cardiovascular outcomes. Sodium-glucose cotransporter-2 inhibitors bring more benefits with respect to the cardiometabolic risk factors.

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.

DPP-4 inhibition enhanced renal tubular and myocardial GLP-1 receptor expression decreased in CKD with myocardial infarction

Background

Chronic kidney disease (CKD) is strongly associated with cardiovascular disease and is a significant risk factor for increased morbidity and mortality. In contrast, GLP-1 receptor (GLP-1R) activation has been shown to confer both renal and cardiovascular protection, though its relationship with CKD and CKD with myocardial ischemia/reperfusion (MI/R) remains poorly understood. Here, we investigated changes in renal and myocardial GLP-1R expression in the CKD rat model with MI/R.

Methods

Male Sprague Dawley rats with 5/6 nephrectomy were used as a rat model of CKD and CKD with MI/R. For myocardial ischemia, the left coronary artery was ligated and released for 30 min 1 week after 5/6 nephrectomy. Dipeptidyl-peptidase 4 (DPP-4) inhibitors were administered orally with linagliptin once daily for 8 weeks. Renal cortical and myocardial GLP-1R expression were measured via immunohistochemistry and western blot analysis.

Results

DPP-4 activity was increased in CKD. Western blot density of GLP-1R in renal cortex extracts revealed increased abundance 2 weeks after 5/6 nephrectomy, followed by a decrease at 8 weeks. In contrast, CKD and CKD with MI/R rats showed decreases in renal and cardiac expression of GLP-1R; these effects were attenuated in rats treated with linagliptin.

Conclusions

In CKD with MI/R, linagliptin attenuated renal injury and increased renal and myocardial GLP-1R expression. These data suggest that activation of renal and myocardial GLP-1R expression may provide both cardio- and renoprotective effects.

Electronic supplementary material

The online version of this article (10.1186/s12882-019-1243-z) contains supplementary material, which is available to authorized users.

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.

Treatment with a fixed dose combination antiretroviral therapy drug containing tenofovir, emtricitabine and efavirenz is associated with cardioprotection in high calorie diet-induced obese rats

HIV-infection, certain antiretroviral drug classes, especially protease inhibitors (PI), and obesity are associated with increased ischaemic heart disease (IHD) risk. However, the effect of PI-free fixed dose combination (FDC) antiretroviral therapy (ART) on hearts exposed to ischaemia-reperfusion injury (I/R) is unknown, particularly in obesity. This is becoming relevant as World Health Organisation guidelines recommend a FDC ART containing (non-) nucleoside reverse transcriptase inhibitors (tenofovir (TDF), emtricitabine (FTC) and efavirenz (EFV)) as first-line HIV treatment. Additionally, obesity rates are rising in HIV-infected populations, not only in ART-experienced individuals, but also at the time of ART initiation, which may further increase the risk of IHD. Therefore, we investigated the effects of PI-free FDC ART in myocardial I/R-exposed hearts from obese rats. Obesity was induced in male wistar rats via a 16-week high calorie diet. At week 10, treatment with a FDC ART drug containing TDF/FTC/EFV was initiated. Biometric and metabolic parameters, as well as myocardial functional recovery and infract size (IS), and myocardial signalling proteins following I/R were assessed after 16 weeks. Obese rats presented with increased body and intraperitoneal fat mass, elevated triglyceride and TBARS levels, whilst the hearts responded to I/R with impaired functional performance and increased IS. The FDC ART treatment did not alter biometric and metabolic parameters in obese rats. In a novel finding, ART protected obese hearts against I/R as shown by improved functional performance and smaller IS vs. untreated obese hearts. Cardioprotection was underscored by increased myocardial phosphorylated endothelial nitric oxide synthase (eNOS) and reduced AMP-kinase levels. In conclusion, these results demonstrate for the first time, that 6-weeks treatment of obese rats with a FDC ART drug specifically containing TDF/FTC/EFV conferred cardioprotection against I/R. The FDC ART-induced cardioprotection was seemingly unrelated to metabolic changes, but rather due to direct cardiac mechanisms including the up-regulation of myocardial eNOS.

Linagliptin improved myocardial function recovery in rat hearts after a prolonged hypothermic preservation

AIMS

To determine whether linagliptin, a dipeptidyl peptidase 4 inhibitor, can promote the recovery of cardiac function after hypothermic preservation.

MAIN METHODS

Rat hearts were preserved in cold Celsior solution with or without linagliptin for 9 h. Cardiac function was evaluated at 60 min of reperfusion after hypothermic preservation. Cardiac mitochondrial morphology was observed using transmission electron microscope. The expression of dynamin-related protein 1 (Drp1), NADPH oxidase 2 (NOX2), calmodulin-dependent protein kinase II (CaMKII) were detected using Western blot.

KEY FINDINGS

Compared with Celsior group, supplement of Celsior solution with linagliptin (0.25-0.75 nM) could significantly prevent hypothermic preservation-induced cardiac dysfunction. The expression of NOX2 protein, ROS level and MDA content in cardium were increased after hypothermic preservation, which was inhibited by linagliptin. Although the mitofusin1, 2, optic atrophy type 1, and total Drp1 expression in myocardium did not change, the level of p-Drp1 S616 and mitochondrial Drp1 were enhanced after hypothermic preservation. Linagliptin supplement could inhibit the hypothermic preservation-induced increase in p-Drp1 S616 and mitochondrial Drp1 protein, and mitigate the mitochondrial fragmentation. Level of p-CaMKII protein enhanced after hypothermic preservation, which could be prevented by linagliptin or a NOX2 inhibitor Phox-I2. Both Phox-I2 and a CaMKII inhibitor KN-93 could reduce the hypothermic preservation-induced increase in p-Drp1 S616 and mitochondrial Drp1 protein.

SIGNIFICANCE

Supplement Celsior solution with linagliptin could improve cardiac function recovery in 9-h hypothermic preserved rat hearts. The cardioprotective effect of linagliptin might be due to the inhibition of Drp1 phosphorylation and mitochondrial translocation by preventing NOX2-mediated CaMKII activation.

Neuroprotective effect of vildagliptin against cerebral ischemia in rats

Stroke is the leading cause of death worldwide. Dipeptidyl peptidase-4 (DPP-4) inhibitors are a class of anti-diabetic drugs for treatment of type-2 diabetes mellitus. The aim of this study is to evaluate the possible neuroprotective effect of a dipeptidyl peptidase-4 inhibitor, vildagliptin, independent of its anti-diabetic properties in non-diabetic rats subjected to cerebral ischemia. Anesthetized Wistar rats were subjected to either left middle cerebral artery occlusion (MCAO) or sham operation followed by reperfusion after 30 min of MCAO. The other three groups were orally administered vildagliptin at 3 dose levels (2.5, 5, 10 mg/kg) for 3 successive weeks before subjected to left focal cerebral ischemia/reperfusion and till the end of the study. Neurological deficit scores and motor activity were assessed 24 h following reperfusion. Forty-eight hours following reperfusion, rats were euthanized and their left brain hemispheres were harvested and used in biochemical, histopathological, and immunohistochemical investigations. Vildagliptin pretreatment improved neurological deficit score, locomotor activity, and motor coordination in MCAO rats. Moreover, vildagliptin reduced malondialdehyde (MDA), elevated reduced glutathione (GSH), phosphotylinosital 3 kinase (PI3K), phosphoryated of protein kinase B (p-AKT), and mechanistic target of rapamycin (mTOR) brain contents in addition to reducing protein expression of caspase-3. Also, vildagliptin showed a dose-dependent attenuation in neuronal cell loss and histopathological alterations in MCAO rats. This study proves that vildagliptin exerted a neuroprotective effect in a dose-dependent manner as shown in the attenuation of the infarct area, neuronal cell loss, and histopathological damage in MCAO rats, which may be mediated by attenuating neuronal and motor deficits, its antioxidant property, activation of the PI3K/AKT/mTOR pathway, and its anti-apoptotic effect.

Vildagliptin Can Alleviate Endoplasmic Reticulum Stress in the Liver Induced by a High Fat Diet

Purpose. We investigated whether a DDP-4 inhibitor, vildagliptin, alleviated ER stress induced by a high fat diet and improved hepatic lipid deposition. Methods. C57BL/6 mice received standard chow diet (CD), high fat diet (HFD), and HFD administered with vildagliptin (50 mg/Kg) (V-HFD). After administration for 12 weeks, serum alanine aminotransferase, glucose, cholesterol, triglyceride, and insulin levels were analyzed. Samples of liver underwent histological examination and transmission electron microscopy, real-time PCR for gene expression levels, and western blots for protein expression levels. ER stress was induced in HepG2 cells with palmitic acid and the effects of vildagliptin were investigated. Results. HFD mice showed increased liver weight/body weight (20.27%) and liver triglycerides (314.75%) compared to CD mice, but these decreased by 9.27% and 21.83%, respectively, in V-HFD mice. In the liver, HFD induced the expression of ER stress indicators significantly, which were obviously decreased by vildagliptin. In vitro, the expressions of molecular indicators of ER stress were reduced in HepG2 when vildagliptin was administered. Conclusions. Vildagliptin alleviates hepatic ER stress in a mouse high fat diet model. In HepG2 cells, vildagliptin directly reduced ER stress. Therefore, vildagliptin may be a potential agent for nonalcoholic fatty liver disease.

Pravastatin improves risk factors but not ischaemic tolerance in obese rats

Statins are effective in management of dyslipidaemia, and a cornerstone of CVD prevention strategies. However, the impacts of their pleiotropic effects on other cardiovascular risk factors and myocardial responses to infarction are not well characterised. We hypothesised that pravastatin treatment in obesity improves lipid profiles, insulin-resistance and myocardial resistance to ischaemia/reperfusion (I/R) injury. Wistar rats were fed a control (C) chow or high carbohydrate and fat diet (HCFD) for 16 weeks with vehicle or pravastatin (prava 7.5 mg/kg/day) treatment for 8 weeks. At 16 weeks HOMAs were performed, blood samples collected and hearts excised for Langendorff perfusions/biochemical analyses. Anti-oxidant activity and proteins regulating mitochondrial fission/fusion and apoptosis were assessed. The HCFD increased body weight (736±15 vs. 655±12 g for C; P<0.001), serum triglycerides (2.91±0.52 vs. 1.64±0.26 mmol/L for C; P<0.001) and insulin-resistance (HOMA- 6.9±0.8 vs. 4.2±0.5 for C; P<0.05) while prava prevented diet induced changes and paradoxically increased lipid peroxidation. The HCFD increased infarct size (34.1±3.1% vs. 18.8±3.0% of AAR for C; P<0.05), which was unchanged by prava in C and HCFD animals. The HCFD decreased cardiac TxR activity and mitochondrial MFN-1 and increased mitochondrial DRP-1 (reducing MFN-1:DRP-1 ratio) and Bax expression, with the latter changes prevented by prava. While unaltered by diet, cytosolic levels of Bax and caspase-3 were reduced by prava in C and HCFD hearts (without changes in cleaved caspase-3). We conclude that obesity, hyper-triglyceridemia and impaired glycemic control in HCFD rats are countered by prava. Despite improved risk factors, prava did not reduce myocardial infarct size, potentially reflecting its complex pleiotropic impacts on cardiac GPX activity and MFN-1, DRP-1, caspase-3 and Bcl-2 proteins.

The Impact of Chronic Glycogen Synthase Kinase-3 Inhibition on Remodeling of Normal and Pre-Diabetic Rat Hearts

PURPOSE

There is an ongoing search for new drugs and drug targets to treat diseases like Alzheimer's disease, cancer and type 2 diabetes (T2D). Both obesity and T2D are characterized by the development of a cardiomyopathy associated with increased hypertension and compensatory left ventricular hypertrophy. Small, specific glycogen synthase kinase-3 (GSK-3) inhibitors were developed to replace lithium chloride for use in psychiatric disorders. In addition, they were advocated as treatment for T2D since GSK-3 inhibition improves blood glucose handling. However, GSK-3 is a regulator of hypertrophic signalling in the heart via phosphorylation of NFATc3 and β-catenin respectively. In view of this, we hypothesized that chronic inhibition of GSK-3 will induce myocardial hypertrophy or exacerbate existing hypertrophy.

METHODS

Rats with obesity-induced prediabetes were treated orally with GSK-3 inhibitor (CHIR118637 (CT20026)), 30 mg/kg/day for the last 8 weeks of a 20-week diet high in sugar content vs a control diet. Biometric and biochemical parameters were measured, echocardiography performed and localization and co-localization of NFATc3 and GATA4 determined in cardiomyocytes.

RESULTS

Obesity initiated myocardial hypertrophy, evidenced by increased ventricular mass (1.158 ± 0.029 vs 0.983 ± 0.03 g) and enlarged cardiomyocytes (18.86 ± 2.25 vs 14.92 ± 0.50um(2)) in association with increased end-diastolic diameter (EDD = 8.48 ± 0.11 vs 8.15 ± 0.10 mm). GSK-3 inhibition (i) increased ventricular mass only in controls (1.075 ± 0.022 g) and (ii) EDD in both groups (controls: 8.63 ± 0.07; obese: 8.72 ± 0.15 mm) (iii) localized NFATc3 and GATA4 peri-nuclearly.

CONCLUSION

Indications of onset of myocardial hypertrophy in both control and obese rats treated with a GSK-3 inhibitor were found. It remains speculation whether these changes were adaptive or maladaptive.

Myocardial susceptibility to ischaemia/reperfusion in obesity: a re-evaluation of the effects of age

Background

Reports on the effect of age and obesity on myocardial ischaemia/reperfusion (I/R) injury and ischaemic preconditioning are contradictory. The aim of this study was to re-evaluate the effects of age and diet-induced obesity (DIO) on myocardial I/R injury and preconditioning potential.

Methods

Four groups of Wistar male rats were used: age-matched controls (AMC) receiving standard rat chow for (i) 16 weeks and (ii) 16 months respectively; DIO rats receiving a sucrose-supplemented diet for (iii) 16 weeks and (iv) 16 months respectively. The ages of groups (i) and (iii) were 22 weeks (“young”) and groups (ii) and (iv) 17 months (“middle-aged”) at time of experimentation. Isolated perfused working hearts were subjected to 35 min regional ischaemia/1 h reperfusion. Endpoints were infarct size (tetrazolium staining) and functional recovery. Hearts were preconditioned by 3 × 5 min ischaemia/5 min reperfusion. Results were processed using GraphPad Prism statistical software.

Results

Age did not affect baseline heart function before induction of ischaemia and I/R damage as indicated by infarct size and similar values were obtained in hearts from both age groups. Age also had no effect on functional recovery of hearts during reperfusion after regional ischaemia in AMC rats, but cardiac output during reperfusion was better in hearts from middle-aged than young DIO rats.

The diet reduced infarct size in hearts from young rats (% of area at risk: AMC: 32.4 ± 3.6; DIO: 20.7 ± 2.9, p < 0.05), with no differences in hearts from middle-aged rats (AMC: 24.6 ± 4.6; DIO: 28.3 ± 13.5, p = NS). Compared to their respective AMC, diet-induced obesity had no significant effect on functional recovery of hearts from both age groups after exposure to regional ischaemia.

When exposed to the more severe stress of global ischaemia, the functional recovery potential of middle-aged DIO rats appeared to be impeded compared to hearts of young DIO rats, while age had no effect on the functional recovery of AMC hearts.

Preconditioning reduced infarct size in hearts from young control rats and both middle-aged groups, but not from young DIO rats. Age had a significant effect on functional recovery in preconditioning: it was improved in hearts from young control and DIO rats, but depressed in both middle-aged groups.

Conclusions

The data showed that middle-age and obesity had no effect on baseline myocardial function and did not increase susceptibility to I/R damage upon exposure to regional ischaemia. On the contrary, obesity reduced I/R damage in young rats. Preconditioned aging hearts showed a decreased infarct size, but a reduction in functional recovery.

Perspectives on cardiovascular effects of incretin-based drugs: From bedside to bench, return trip

Recently, cardiovascular outcome trials with glucose-lowering drugs used in type 2 diabetes mellitus, namely glucagon-like peptide-1 receptor agonists (GLP-1RA), liraglutide and semaglutide, showed a reduction in cardiovascular events, which had not been observed in trials with other incretin-based drugs, such as lixisenatide or with dipeptidyl peptidase-4 inhibitors (DPP4i). Mechanisms underlying the observed cardiovascular differences between DPP4i and GLP1-RA, and across individual GLP1-RA are poorly understood. This review is aimed at collecting and summarizing available evidence from experimental and mechanistic studies on the action of GLP1-RA and DPP4i on the cardiovascular system, both deriving from clinical and pre-clinical sources. The results of cardiovascular outcome trials are interpreted on the basis of the experimental preclinical data available, paying particular attention to the heart failure results, and suggesting some novel intriguing hypotheses to explain some of the unexpected findings of cardioprotection of incretin-based drugs. In particular, we discuss the possible contribution to the incretin cardiovascular effects of a direct cardiac action of GLP-1 metabolites through GLP-1 receptor-independent pathways, and of DPP4 substrates other than GLP-1.

Cardiovascular safety of therapies for type 2 diabetes

INTRODUCTION

Dipeptidyl peptidase-4 (DPP4) inhibitors, glucagon-like peptide-1 (GLP-1) analogs and sodium-glucose cotransporter 2 (SGLT2) inhibitors are relatively new therapies for the treatment of type 2 diabetes mellitus. Given the high prevalence of cardiovascular complications in patients with type 2 diabetes and recent concerns questioning CV safety of newer antidiabetic medications, cardiovascular safety of these medications requires evaluation. Areas covered: Cardiovascular effects of these drug classes from preclinical and clinical data as well as non-cardiovascular safety issues are delineated from literature searches covering the last decade and up to June 2016. Major clinical trials assessing the cardiovascular safety of GLP-1 agonists (ELIXA and LEADER), DPP-4 inhibitors (SAVOR-TIMI 53, EXAMINE, and TECOS) and SGLT2 inhibitors (EMPA-REG OUTCOME) are reviewed and interpreted. Expert opinion: Based on review of the present evidence, these 3 classes of antihyperglycemic therapies have acceptably safe CV safety profiles for patients with type 2 diabetes. The latest evidence from LEADER and EMPA-REG OUTCOME trials indicate that liraglutide and empagliflozin have cardiovascular benefits that may prove to be of clinical importance in the management of type 2 DM.

Vildagliptin reduces cardiac ischemic-reperfusion injury in obese orchiectomized rats

Obesity and testosterone deprivation are associated with coronary artery disease. Testosterone and vildagliptin (dipeptidyl peptidase-4 inhibitors) exert cardioprotection during ischemic-reperfusion (I/R) injury. However, the effect of these drugs on I/R heart in a testosterone-deprived, obese, insulin-resistant model is unclear. This study investigated the effects of testosterone and vildagliptin on cardiac function, arrhythmias and the infarct size in I/R heart of testosterone-deprived rats with obese insulin resistance. Orchiectomized (O) or sham operated (S) male Wistar rats were divided into 2 groups to receive normal diet (ND) or high-fat diet (HFD) for 12 weeks. Orchiectomized rats in each diet were divided to receive testosterone (2 mg/kg), vildagliptin (3 mg/kg) or the vehicle daily for 4 weeks. Then, I/R was performed by a 30-min left anterior descending coronary artery ligation, followed by a 120-min reperfusion. LV function, arrhythmia scores, infarct size and cardiac mitochondrial function were determined. HFD groups developed insulin resistance at week 12. At week 16, cardiac function was impaired in NDO, HFO and HFS rats, but was restored in all testosterone- and vildagliptin-treated rats. During I/R injury, arrhythmia scores, infarct size and cardiac mitochondrial dysfunction were prominently increased in NDO, HFO and HFS rats, compared with those in NDS rats. Treatment with either testosterone or vildagliptin similarly attenuated these impairments during I/R injury. These finding suggest that both testosterone replacement and vildagliptin share similar efficacy for cardioprotection during I/R injury by decreasing the infarct size and attenuating cardiac mitochondrial dysfunction caused by I/R injury in testosterone-deprived rats with obese insulin resistance.

The impaired myocardial ischemic tolerance in adult offspring of diabetic pregnancy is restored by maternal melatonin treatment

Diabetic pregnancy, with ever increasing prevalence, adversely affects embryogenesis and increases vasculometabolic disorder risks in adult offspring. However, it remains poorly understood whether maternal diabetes increases the offspring's susceptibility to heart injuries in adulthood. In this study, we observed that cardiac function and structure were comparable between adult offspring born to diabetic mice and their counterparts born to nondiabetic mice at baseline. However, in response to myocardial ischemia/reperfusion (MIR), diabetic mother offspring exhibited augmented infarct size, cardiac dysfunction, and myocardial apoptosis compared with control, in association with exaggerated activation of mitochondria- and endoplasmic reticulum (ER) stress-mediated apoptosis pathways and oxidative stress. Molecular analysis showed that the impaired myocardial ischemic tolerance in diabetic mother offspring was mainly attributable to blunted cardiac insulin receptor substrate (IRS)-1/Akt signaling. Furthermore, the effect of maternal melatonin administration on offspring's response to MIR was determined, and the results indicated that melatonin treatment in diabetic dams during pregnancy significantly improved the tolerance to MIR injury in their offspring, via restoring cardiac IRS-1/Akt signaling. Taken together, these data suggest that maternal diabetes predisposes offspring to augmented MIR injury in adulthood, and maternal melatonin supplementation during diabetic pregnancy may hold promise for improving myocardial ischemic tolerance in the offspring.

The incretin system ABCs in obesity and diabetes - novel therapeutic strategies for weight loss and beyond

Incretins are gastrointestinal-derived hormones released in response to a meal playing a key role in the regulation of postprandial secretion of insulin (incretin effect) and glucagon by the pancreas. Both incretins, glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 (GLP-1), have several other actions by peripheral and central mechanisms. GLP-1 regulates body weight by inhibiting appetite and delaying gastric, emptying actions that are dependent on central nervous system GLP-1 receptor activation. Several other hormones and gut peptides, including leptin and ghrelin, interact with GLP-1 to modulate appetite. GLP-1 is rapidly degraded by the multifunctional enzyme dipeptidyl peptidase-4 (DPP-4). DPP-4 is involved in adipose tissue inflammation, which is associated with insulin resistance and diabetes progression, being a common pathophysiological mechanism in obesity-related complications. Furthermore, the incretin system appears to provide the basis for understanding the high weight loss efficacy of bariatric surgery, a widely used treatment for obesity, often in association with diabetes. The present review brings together new insights into obesity pathogenesis, integrating GLP-1 and DPP-4 in the complex interplay between obesity and inflammation, namely, in diabetic patients. This in turn will provide the basis for novel incretin-based therapeutic strategies for obesity and diabetes with promising benefits in addition to weight loss. © 2016 World Obesity.

Dipeptidyl peptidase-4 inhibition and narrow-band ultraviolet-B light in psoriasis (DINUP): study protocol for a randomised controlled trial

BACKGROUND

Moderate to severe psoriasis is a systemic inflammatory disease associated with insulin resistance, obesity and type 2 diabetes (T2DM). Sitagliptin is a dipeptidyl peptidase-4 (DPP-4) inhibitor that improves glycaemia and has a marketing authorisation for the treatment of T2DM. Non-immunosuppressive therapies that are effective for psoriasis and its associated comorbidities would be a significant advance in the treatment of this chronic disease.

METHODS/DESIGN

This is a single centre, 39-week, prospective, randomised, open label, clinical trial of oral sitagliptin (Januvia(®)) in psoriasis patients who are due to undergo a course of narrow-band ultraviolet-B (NB-UVB) phototherapy. We plan to enrol 120 participants and allocate participants on a random and 1:1 basis to receive sitagliptin 100 mg daily for 24 weeks combined with NB-UVB or NB-UVB monotherapy. Participants will be followed up for 12 weeks after sitagliptin therapy is discontinued. The primary endpoint is the change in Psoriasis Area and Severity Index (PASI) 24 weeks after treatment initiation. Secondary endpoints include cumulative NB-UVB dose, number of NB-UVB treatments required to clear psoriasis, proportions of participants who achieve PASI-50 (50 % reduction in PASI from baseline), PASI-75, PASI-90 and the proportion of participants who relapse in each group. We will also analyse changes in cardiovascular disease risk factors, serum cytokine and hormone levels and peripheral blood mononuclear expression of immune proteins at 24 and 36 weeks. A subgroup of participants will have skin biopsies taken and analysed for skin levels and expression of immune cells, receptors, hormones and immune proteins. The genetic or epigenetic profile that predicts best response to DPP-4 inhibitor therapy will be analysed. The safety endpoints include the rate and severity of adverse events.

DISCUSSION

This is the first randomised clinical trial assessing dipeptidyl peptidase-4 inhibition therapy in psoriasis. We hypothesise that sitagliptin therapy in combination with NB-UVB improves psoriasis severity compared to NB-UVB monotherapy.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier NCT02347501 (Date of registration: 27 January 2015).

Cardiovascular Effects of Incretin-Based Therapies

The incretin-based therapies, dipeptidyl peptidase-4 (DPP4) inhibitors and glucagon-like peptide-1 (GLP-1) analogs, are important new classes of therapy for type 2 diabetes mellitus (T2DM). These agents prolong the action of the incretin hormones, GLP-1 and glucose-dependent insulinotropic polypeptide (GIP), by inhibiting their breakdown. The incretin hormones improve glycemic control in T2DM by increasing insulin secretion and suppressing glucagon levels. The cardiovascular (CV) effects of the incretin-based therapies have been of substantial interest since 2008, when the US Food and Drug Administration began to require that all new therapies for diabetes undergo rigorous assessment of CV safety through large-scale CV outcome trials. This article reviews the most recent CV outcome trials of the DPP-4 inhibitors (SAVOR-TIMI 53, EXAMINE, and TECOS) as evidence that the incretin-based therapies have acceptable CV safety profiles for patients with T2DM. The studies differ with regard to patient population, trial duration, and heart failure outcomes but show similar findings for CV death, nonfatal myocardial infarction, and stroke, as well as hospitalization for unstable angina.

Glucagon-like peptide-1 protects cardiomyocytes from advanced oxidation protein product-induced apoptosis via the PI3K/Akt/Bad signaling pathway

Cardiomyocyte apoptosis is a major event in the pathogenesis of diabetic cardiomyopathy. Currently, no single effective treatment for diabetic cardiomyopathy exists. The present study investigated whether advanced oxidative protein products (AOPPs) have a detrimental role in the survival of cardiomyocytes and if glucagon-like peptide-1 (GLP-1) exerts a cardioprotective effect under these circumstances. The present study also aimed to determine the underlying mechanisms. H9c2 cells were exposed to increasing concentrations of AOPPs in the presence or absence of GLP-1, and the viability and apoptotic rate were detected using a cell counting kit-8 assay and flow cytometry, respectively. In addition, a phosphatidylino-sitol-4,5-bisphosphate 3-kinase (PI3K) inhibitor, LY294002, was employed to illustrate the mechanism of the antiapoptotic effect of GLP-1. The expression levels of the apoptotic-associated proteins, Akt, B-cell lymphoma (Bcl)-2, Bcl-2-associated death promoter (Bad), Bcl-2-associated X protein (Bax) and caspase-3 were measured by western blotting. It was revealed that GLP-1 significantly attenuated AOPP-induced cell toxicity and apoptosis. AOPPs inactivated the phosphorylation of Akt, reduced the phosphorylation of Bad, decreased the expression of Bcl-2, increased the expression of Bax and the activation of caspase-3 in H9c2 cells. GLP-1 reversed the above changes induced by AOPPs and the protective effects of GLP-1 were abolished by the PI3K inhibitor, LY294002. In conclusion, the present data suggested that GLP-1 protected cardiomyocytes against AOPP-induced apoptosis, predominantly via the PI3K/Akt/Bad pathway. These results provided a conceivable mechanism for the development of diabetic cardiomyopathy and rendered a novel application of GLP-1 exerting favorable cardiac effects for the treatment of diabetic cardiomyopathy.

Roles of obese-insulin resistance and anti-diabetic drugs on the heart with ischemia-reperfusion injury

The incidence of obesity with insulin resistance is increasing worldwide. This condition is also known as a risk factor of coronary artery disease and associated with increased arrhythmias, impaired left ventricular function, and increased infarct size during cardiac ischemia-reperfusion (I/R) injury. The proposed mechanisms are due to impaired glucose utilization and pro-survival signaling molecules, and increased inflammatory cytokines, which have been demonstrated in the I/R hearts in various models of obese-insulin resistance. However, the cardiac effects of diets in the I/R heart are still unsettled since several studies reported that high-caloric diet consumption might protect the heart from I/R injury. Although several therapeutic strategies such as anti-diabetic drugs, natural compounds as well as treadmill exercise have been proposed to exert cardioprotection in the I/R heart in obese-insulin resistant animals, some interventions including ischemic post-conditioning failed to protect the heart from I/R injury. In this comprehensive review, reports from both genetic deletion and dietary-induced obese-insulin resistant animal models regarding the effects of obese-insulin resistance on metabolic parameters, cardiac function, infarct size, and molecular mechanisms under I/R injury are summarized. Moreover, the effects of anti-diabetic drugs and other pharmacological interventions on these parameters in an obese-insulin resistant model under I/R injury are also comprehensively summarized and discussed.

Diet-induced pre-diabetes slows cardiac conductance and promotes arrhythmogenesis

Background

Type 2 diabetes is associated with abnormal electrical conduction and sudden cardiac death, but the pathogenic mechanism remains unknown. This study describes electrophysiological alterations in a diet-induced pre-diabetic rat model and examines the underlying mechanism.

Methods

Sprague–Dawley rats were fed either high-fat diet and fructose water or normal chow and water for 6 weeks. The electrophysiological properties of the whole heart was analyzed by in vivo surface ECG recordings, as wells as ex vivo in Langendorff perfused hearts during baseline, ischemia and re-perfussion. Conduction velocity was examined in isolated tissue strips. Ion channel and gap junction conductances were analyzed by patch-clamp studies in isolated cardiomyocytes. Fibrosis was examined by Masson’s Trichrome staining and thin-layer chromatography was used to analyze cardiac lipid content. Connexin43 (Cx43) expression and distribution was examined by western blotting and immunofluorescence respectively.

Results

Following 6 weeks of feeding, fructose-fat fed rats (FFFRs) showed QRS prolongation compared to controls (16.1 ± 0.51 (n = 6) vs. 14.7 ± 0.32 ms (n = 4), p < 0.05). Conduction velocity was slowed in FFFRs vs. controls (0.62 ± 0.02 (n = 13) vs. 0.79 ± 0.06 m/s (n = 11), p < 0.05) and Langendorff perfused FFFR hearts were more prone to ventricular fibrillation during reperfusion following ischemia (p < 0.05). The patch-clamp studies revealed no changes in Na⁺ or K⁺ currents, cell capacitance or gap junctional coupling. Cx43 expression was also unaltered in FFFRs, but immunofluorescence demonstrated an increased fraction of Cx43 localized at the intercalated discs in FFFRs compared to controls (78 ± 3.3 (n = 5) vs. 60 ± 4.2 % (n = 6), p < 0.01). No fibrosis was detected but FFFRs showed a significant increase in cardiac triglyceride content (1.93 ± 0.19 (n = 12) vs. 0.77 ± 0.13 nmol/mg (n = 12), p < 0.0001).

Conclusion

Six weeks on a high fructose-fat diet cause electrophysiological changes, which leads to QRS prolongation, decreased conduction velocity and increased arrhythmogenesis during reperfusion. These alterations are not explained by altered gap junctional coupling, Na⁺, or K⁺ currents, differences in cell size or fibrosis.

Prolonged survival by combined treatment with granulocyte colony-stimulating factor and dipeptidyl peptidase IV inhibitor in a rat small-for-size liver transplantation model

AIM

Despite the great advances and excellent outcomes of liver transplantation (LT), small-for-size (SFS) graft syndrome is a life-threatening complication that remains to be overcome. In the present study, we investigated the therapeutic effect of combined treatment with granulocyte colony-stimulating factor (G-CSF) and a dipeptidyl peptidase IV (DPP-IV) inhibitor on SFS liver graft syndrome.

METHODS

The transplantation of small-sized Lewis donor livers into green fluorescent protein (GFP) transgenic Wistar rats was performed and the recipients were randomly assigned to one of four groups (without treatment, DPP-IV inhibitor treatment, G-CSF treatment and G-CSF/DPP-IV inhibitor combination). Recombinant human G-CSF was injected s.c. at a dose of 2 μg/kg per day starting 5 days prior to transplantation. G-CSF was combined with the p.o. administration of a DPP-IV inhibitor (2 mg/kg per day) after transplantation until the end of the observation period.

RESULTS

The post-transplant survival and liver function of rats treated with G-CSF/DPP-IV inhibitor combination therapy were significantly improved with an increased number of recipient-derived GFP positive cells into the liver grafts. A confocal microscopy study showed cytokeratin (CK)-18 and GFP positive hepatic progenitor cells in the parenchyma of the liver allografts. Untreated rats and rats treated with either G-CSF or DPP-IV inhibitor did not exhibit the prolonged survival and had less GFP and CK-18 positive cells in the liver grafts after SFS LT.

CONCLUSION

Our results suggest that combined treatment with G-CSF and DPP-IV inhibitor may synergistically induce migration and differentiation of recipient-derived stem cells into the hepatic progenitor cells, resulting in the amelioration of SFS liver graft syndrome.

Recent Advances in Dipeptidyl-Peptidase-4 Inhibition Therapy: Lessons from the Bench and Clinical Trials

DPP4 inhibitors (DPP4i) are a class of newly developed antidiabetic drugs which preserve incretin hormones and promote postprandial insulin secretion. Although the cardiovascular effect of DPP4 inhibition has been substantially studied, the exact role of DPP4 in cardiovascular disease especially in humans remains elusive. Previous small studies and meta-analyses have suggested a benefit in both surrogate outcomes and cardiovascular events for these agents. However, there was growing evidence in recent years questioning the cardioprotective effect of DPP4i. Further, a signal of heart failure hospitalization in a recent large scale clinical trial SAVOR-TIMI 53 has called into question the safety of these agents and their utility in the treatment of cardiovascular disease. In this review, we will revisit the physiologic function of DPP4 and discuss its role in cardiometabolic disease based on recent experimental and clinical studies.

An interaction between glucagon-like peptide-1 and adenosine contributes to cardioprotection of a dipeptidyl peptidase 4 inhibitor from myocardial ischemia-reperfusion injury

Dipeptidyl peptidase 4 (DPP4) inhibitors suppress the metabolism of the potent antihyperglycemic hormone glucagon-like peptide-1 (GLP-1). DPP4 was recently shown to provide cardioprotection through a reduction of infarct size, but the mechanism for this remains elusive. Known interactions between DPP4 and adenosine deaminase (ADA) suggest an involvement of adenosine signaling in DPP4 inhibitor-mediated cardioprotection. We tested whether the protective mechanism of the DPP4 inhibitor alogliptin against myocardial ischemia-reperfusion injury involves GLP-1- and/or adenosine-dependent signaling in canine hearts. In anesthetized dogs, the coronary artery was occluded for 90 min followed by reperfusion for 6 h. A 4-day pretreatment with alogliptin reduced the infarct size from 43.1 ± 2.5% to 17.1 ± 5.0% without affecting collateral flow and hemodynamic parameters, indicating a potent antinecrotic effect. Alogliptin also suppressed apoptosis as demonstrated by the following analysis: 1) reduction in the Bax-to-Bcl2 ratio; 2) cytochrome c release, 3) an increase in Bad phosphorylation in the cytosolic fraction; and 4) terminal deoxynucleotidyl transferase dUTP nick end labeling assay. This DPP4 inhibitor did not affect blood ADA activity or adenosine concentrations. In contrast, the nonselective adenosine receptor blocker 8-(p-sulfophenyl)theophylline (8SPT) completely blunted the effect of alogliptin. Alogliptin did not affect Erk1/2 phosphorylation, but it did stimulate phosphorylation of Akt, glycogen synthase kinase-3β, and cAMP response element-binding protein (CREB). Only 8SPT prevented alogliptin-induced CREB phosphorylation. In conclusion, the DPP4 inhibitor alogliptin suppresses ischemia-reperfusion injury via adenosine receptor- and CREB-dependent signaling pathways.

Remote conditioning the heart overview: translatability and mechanism

Conditioning the heart to resist predictable and unpredictable ischaemia-reperfusion (IR) injury is one of the fastest growing areas of bench to bedside research within cardiology. Basic science has provided important insights into signalling pathways and protective mechanisms in the heart, and a growing number of clinical studies have, with important exceptions, shown the potential applicability and beneficial effect of various mechanical conditioning strategies achieved by intermittent short-lasting-induced ischaemia of the heart itself or a remote tissue. Remote ischaemic conditioning (RIC) in particular has been utilized in a number of clinical settings with promising results. However, while many novel 'downstream' mechanisms of RIC have been discovered, translation to pharmacological conditioning has not yet been convincingly demonstrated in clinical studies. One explanation for this apparent failure may be that most pharmacological approaches mimic a single instrument in a complex orchestra activated by mechanical conditioning. Recent studies, however, provide important insights into upstream events occurring in RIC, which may allow for development of drugs activating more complex systems of biological organ protection. With this review, we will systematically examine the first generation of pharmacological cardioprotection studies and then provide a summary of the recent discoveries in basic science that could illuminate the path towards more advanced approaches in the next generation of pharmacological agents that may work by reproducing the diverse effects of RIC, thereby providing protection against IR injury.

Incretin-based therapies in prediabetes: Current evidence and future perspectives

The prevalence of type 2 diabetes (T2D) is evolving globally at an alarming rate. Prediabetes is an intermediate state of glucose metabolism that exists between normal glucose tolerance (NGT) and the clinical entity of T2D. Relentless β-cell decline and failure is responsible for the progression from NGT to prediabetes and eventually T2D. The huge burden resulting from the complications of T2D created the need of therapeutic strategies in an effort to prevent or delay its development. The beneficial effects of incretin-based therapies, dipeptidyl peptidase-4 inhibitors and glucagon-like peptide-1 (GLP-1) receptor agonists, on β-cell function in patients with T2D, together with their strictly glucose-depended mechanism of action, suggested their possible use in individuals with prediabetes when greater β-cell mass and function are preserved and the possibility of β-cell salvage is higher. The present paper summarizes the main molecular intracellular mechanisms through which GLP-1 exerts its activity on β-cells. It also explores the current evidence of incretin based therapies when administered in a prediabetic state, both in animal models and in humans. Finally it discusses the safety of incretin-based therapies as well as their possible role in order to delay or prevent T2D.

DPP-4 inhibitors: focus on safety

INTRODUCTION

Dipeptidyl peptidase inhibitors (DPP-4-i) are highly selective inhibitors of the enzyme DPP-4. They act by increasing levels of incretin hormones, which have potent effects on insulin and glucagon release, gastric emptying, and satiety. Our goal is to review the safety issues related to DPP-4-i.

AREAS COVERED

This review is based upon a PubMed search of the literature using keywords alogliptin, linagliptin, saxagliptin, sitagliptin and vildagliptin, DPP-4-i, glucagon-like polypeptide-1 agonists, as well as extensive personal clinical trial experience with each of these agents. The current DPP-4-i have very different chemical structures. Saxagliptin has significant cytochrome P450 metabolism and carries a risk of drug interactions. Linagliptin has primarily entero-hepatic excretion, a benefit in renally impaired patients. A concern arose related to congestive heart failure in the SAVOR TIMI trial of saxagliptin. Several major cardiac studies are underway, with two concluded. Despite lingering uncertainty related to pancreatitis and pancreatic cancer, large randomized trials have not shown an increased risk with DPP-4-i treatment. Cutaneous adverse effects occur with a low frequency with some of these agents.

EXPERT OPINION

DPP-4-i are an additional choice in the group of anti-hyperglycemics. Their principal advantage is a low incidence of hypoglycemia, making these agents desirable in patients such as the elderly and those with cardiac disease. Several large trials have hinted at less cardiac risk with DPP-4-i than with sulfonylureas. The CAROLINA Trial comparing linagliptin and glimepiride may provide a conclusive answer to this question.

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.

Variable effects of anti-diabetic drugs in animal models of myocardial ischemia and remodeling: a translational perspective for the cardiologist

Diabetes and heart failure are very prevalent, and affect each other's incidence and severity. Novel therapies to reduce post-myocardial infarction (MI) remodeling that progresses into heart failure are urgently needed, especially in diabetic patients. Clinical studies have suggested that some oral anti-diabetic agents like metformin exert cardiovascular protective effects in heart failure patients with diabetes, whereas other agents may be deleterious. In the current review, we provide an overview of the cardio-specific effects of oral anti-diabetic drugs in animal models of acute MI, post-MI remodeling, and heart failure. Metformin has consistently been shown to ameliorate cardiac remodeling after ischemia/reperfusion (I/R) injury, as well as in several models of heart failure. Sulfonylurea derivatives are controversial with respect to their direct effects on the cardiovascular system. Thiazolidinediones protect against myocardial I/R injury, but their effects on post-MI remodeling are less clear and clinical studies raised concerns about their cardiovascular safety. Glucagon-like peptide-1 analogs have potential beneficial effects on the cardiovascular system that require further confirmation, whereas the results with dipeptidyl peptidase-4 inhibitors are equivocal. Current clinical guidelines, in the absence of prospective clinical trials that evaluated if certain oral anti-diabetic agents are superior over others, only provide generic recommendations, and do not take into account interesting experimental and mechanistic data. The available experimental evidence indicates that some anti-diabetic agents should be preferred over others if cardioprotective effects are warranted. These experimental clues need to be confirmed by clinical trials.

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.

The potential for renoprotection with incretin-based drugs

Incretin-based drugs, i.e., glucagon-like peptide-1 (GLP-1) receptor agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors, are widely used for the treatment of type 2 diabetes. In addition to the primary role of incretins in stimulating insulin secretion from pancreatic β-cells, they have extra pancreatic functions beyond glycemic control. Indeed, recent studies highlight the potential beneficial effects of incretin-based therapy in diabetic kidney disease (DKD). Experimental studies using various diabetic models suggest that incretins protect the vascular endothelium from injury by binding to GLP-1 receptors, thereby ameliorating oxidative stress and the local inflammatory response, which reduces albuminuria and inhibits glomerular sclerosis. In addition, there is some evidence that GLP-1 receptor agonists and DPP-4 inhibitors mediate sodium excretion and diuresis to lower blood pressure. The pleiotropic actions of DPP-4 inhibitors are ascribed primarily to their effects on GLP-1 signaling, but other substrates of DPP-4, such as brain natriuretic peptide and stromal-derived factor-1α, may have roles. In this review, we summarize recent studies of the roles of incretin-based therapy in ameliorating DKD and its complications.

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.

Incretin-based therapies: can we achieve glycemic control and cardioprotection?

Glucagon-like (GLP-1) is a peptide hormone secreted from the small intestine in response to nutrient ingestion. GLP-1 stimulates insulin secretion in a glucose-dependent manner, inhibits glucagon secretion and gastric emptying, and reduces appetite. Because of the short circulating half-life of the native GLP-1, novel GLP-1 receptor (GLP-1R) agonists and analogs and dipeptidyl peptidase 4 (DPP-4) inhibitors have been developed to facilitate clinical use. Emerging evidence indicates that GLP-1-based therapies are safe and may provide cardiovascular (CV) benefits beyond glycemic control. Preclinical and clinical studies are providing increasing evidence that GLP-1 therapies may positively affect CV function and metabolism by salutary effects on CV risk factors as well as via direct cardioprotective actions. However, the mechanisms whereby the various classes of incretin-based therapies exert CV effects may be mechanistically distinct and may not necessarily lead to similar CV outcomes. In this review, we will discuss the potential mechanisms and current understanding of CV benefits of native GLP-1, GLP-1R agonists and analogs, and of DPP-4 inhibitor therapies as a means to compare their putative CV benefits.

Dipeptidyl peptidase IV inhibitors and ischemic myocardial injury

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

Dipeptidyl peptidase-4 inhibitor reduces infarct size and preserves cardiac function via mitochondrial protection in ischaemia-reperfusion rat heart

AIM

We hypothesized that dipeptidyl peptidase (DPP)-4 inhibitor (vildagliptin) reduces fatal arrhythmias, cardiac dysfunction and infarct size caused by ischaemia-reperfusion (I/R) injury via its attenuation of cardiac mitochondrial dysfunction.

METHODS

In total, 26 rats were randomized to receive either 1 mL normal saline solution or 2.0 mg/kg vildagliptin intravenously (n = 13/group) 30 min prior to a 30-min left anterior descending coronary artery occlusion, followed by a 120-min reperfusion. Arrhythmia scores, cardiac functions, infarct size and mitochondrial function were evaluated.

RESULTS

Vildagliptin reduced the infarct size by 44% and mitigated cardiac dysfunction by preserving cardiac function without altering the incidence of cardiac arrhythmias. Vildagliptin increased expression of Bcl-2 and pro-caspase3 in the ischaemic area, whereas Bax and phosphorylated-connexin43/total-connexin43 were not altered. Vildagliptin attenuated cardiac mitochondrial dysfunction by reducing the reactive oxygen species level and mitochondrial swelling.

CONCLUSIONS

DPP-4 inhibitor provides cardioprotection by reducing the infarct size and ameliorating cardiac dysfunction in I/R hearts by attenuating cardiac mitochondrial dysfunction and cardiomyocyte apoptosis.

GLP-1-Based Strategies: A Physiological Analysis of Differential Mode of Action

DPP4 inhibitors and GLP-1 receptor agonists used in incretin-based strategies treat Type 2 diabetes with different modes of action. The pharmacological blood GLP-1R agonist concentration targets pancreatic and some extrapancreatic GLP-1R, whereas DPP4i favors the physiological activation of the gut-brain-periphery axis that could allow clinicians to adapt the management of Type 2 diabetes, according to the patient's pathophysiological characteristics.

Effect of vildagliptin add-on treatment to metformin on plasma asymmetric dimethylarginine in type 2 diabetes mellitus patients

Aims

A close association has been demonstrated between increased cardiovascular risk and high asymmetric dimethylarginine (ADMA) levels in type 2 diabetes mellitus (DM) patients. We planned to measure serum ADMA levels in type 2 DM patients using vildagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor.

Materials and methods

A total of 68 type 2 DM patients who were on metformin were enrolled in the study. Based on the glycemic levels of patients, vildagliptin was added on to treatment in 33 patients. Patients were followed for 6 months. Serum ADMA, C-reactive protein, and fibrinogen levels were compared in groups of patients using metformin or metformin + vildagliptin, after 6 months.

Results

Serum ADMA levels were found to be significantly lower in the group using vildagliptin compared to the group using metformin + vildagliptin (P<0.001). However, serum C-reactive protein and fibrinogen levels were statistically similar in the two study groups (P=0.34 and P=0.23, respectively).

Conclusion

Metformin + vildagliptin treatment was observed to lower serum ADMA levels in type 2 DM patients. Our findings notwithstanding, large-scale prospective randomized controlled studies are warranted to conclude that vildagliptin provides cardiovascular protection along with diabetes regulation.

Chronic dipeptidyl peptidase-4 inhibition with sitagliptin is associated with sustained protection against ischemic left ventricular dysfunction in a pilot study of patients with type 2 diabetes mellitus and coronary artery disease

BACKGROUND

The incretin hormone, glucagon-like peptide-1, promotes myocardial glucose uptake and may improve myocardial tolerance to ischemia. Endogenous glucagon-like peptide-1 (7-36) is augmented by pharmacological inhibition of dipeptidyl peptidase-4. We investigated whether chronic dipeptidyl peptidase-4 inhibition by sitagliptin protected against ischemic left ventricular dysfunction during dobutamine stress in patients with type 2 diabetes mellitus and coronary artery disease.

METHODS AND RESULTS

A total of 19 patients with type 2 diabetes mellitus underwent dobutamine stress echocardiography with tissue Doppler imaging on 2 separate occasions: the first (control) while receiving oral hypoglycemic agents, and the second after the addition of sitagliptin (100 mg once daily) for ≈4 weeks. Sitagliptin increased plasma glucagon-like peptide-1 (7-36) levels and, at peak stress, enhanced both global (ejection fraction, 70.5±7.0 versus 65.7±8.0%; P<0.0001; mitral annular systolic velocity, 11.7±2.6 versus 10.9±2.3 cm/s; P=0.01) and regional left ventricular function, assessed by peak systolic velocity and strain rate in 12 paired, nonapical segments. This was predominantly because of a cardioprotective effect on ischemic segments (strain rate in ischemic segments, -2.27±0.65 versus -1.98±0.58 s(-1); P=0.001), whereas no effect was seen in nonischemic segments (-2.19±0.48 versus -2.18±0.54 s(-1); P=0.87). At 30 minutes recovery, dipeptidyl peptidase-4 inhibition mitigated the postischemic stunning seen in the control scan.

CONCLUSIONS

The addition of dipeptidyl peptidase-4 inhibitor therapy with sitagliptin to the treatment regime of patients with type 2 diabetes mellitus and coronary artery disease is associated with a sustained improvement in myocardial performance during dobutamine stress and a reduction in postischemic stunning.

CLINICAL TRIAL REGISTRATION

URL: http://www.isrctn.org. Unique identifier ISRCTN61646154.

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.

Dipeptidyl-peptidase 4 inhibition: linking metabolic control to cardiovascular protection

Dipeptidyl peptidases 4 (DPP4) inhibitors are a new class of oral anti-hyperglycemic drugs for the treatment of type 2 diabetes (T2DM). They are also called "incretins" because they act by inhibiting the degradation of endogenous incretin hormones, in particular GLP-1, that mediates their main metabolic effects. DPP4 is an ubiquitous protease that regulates not only glucose and lipid metabolism, but also exhibits several systemic effects at different site levels. DPP4 inhibition improves endothelial function, reduces the pro-oxidative and the pro-inflammatory state, and exerts renal effects. These actions are mediated by different DPP4 ligands, such as cytokines, growth factors, neuotransmitters etc. Clinical and experimental studies have demonstrated that DPP4 inhibitors are efficient in protecting cardiac, renal and vascular systems, through antiatherosclerotic and vasculoprotective mechanisms. For these reasons DDP4 inhibitors are thought to be "cardiovascular protective" as well as anti-diabetic drugs. Clinical trials aimed to demonstrate the efficacy of DPP4 inhibitors in reducing cardiovascular events, independent of their anti-hyperglycemic action, are ongoing. These trials will also give necessary information on their safety.

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

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

Cardioprotective and anti-hypertensive effects of Prosopis glandulosa in rat models of pre-diabetes

Aim

Obesity and type 2 diabetes present with two debilitating complications, namely, hypertension and heart disease. The dried and ground pods of Prosopis glandulosa (commonly known as the Honey mesquite tree) which is part of the Fabaceae (or legume) family are currently marketed in South Africa as a food supplement with blood glucose-stabilising and anti-hypertensive properties. We previously determined its hypoglycaemic effects, and in the current study we determined the efficacy of P glandulosa as anti-hypertensive agent and its myocardial protective ability.

Methods

Male Wistar rats were rendered either pre-diabetic (diet-induced obesity: DIO) or hypertensive (high-fat diet: HFD). DIO animals were treated with P glandulosa (100 mg/kg/day for the last eight weeks of a 16-week period) and compared to age-matched controls. Hearts were perfused ex vivo to determine infarct size. Biometric parameters were determined at the time of sacrifice. Cardiac-specific insulin receptor knock-out (CIRKO) mice were similarly treated with P glandulosa and infarct size was determined. HFD animals were treated with P glandulosa from the onset of the diet or from weeks 12–16, using captopril (50 mg/kg/day) as the positive control. Blood pressure was monitored weekly.

Results

DIO rats and CIRKO mice: P glandulosa ingestion significantly reduced infarct size after ischaemia–reperfusion. Proteins of the PI-3-kinase/PKB/Akt survival pathway were affected in a manner supporting cardioprotection. HFD model: P glandulosa treatment both prevented and corrected the development of hypertension, which was also reflected in alleviation of water retention.

Conclusion

P glandulosa was cardioprotective and infarct sparing as well as anti-hypertensive without affecting the body weight or the intra-peritoneal fat depots of the animals. Changes in the PI-3-kinase/PKB/Akt pathway may be causal to protection. Results indicated water retention, possibly coupled to vasoconstriction in the HFD animals, while ingestion of P glandulosa alleviated both. We concluded that treatment of pre-diabetes, type 2 diabetes or hypertension with P glandulosa poses possible beneficial health effects.