As DPP-4 inhibitors are used to treat patients with type 2 diabetes, it is important to consider whether and how modulation of DPP-4 activity might affect the biology of the heart and blood vessels.

Three cardiovascular outcome studies have examined the safety of the DPP-4 inhibitors, saxagliptin, and alogliptin.

In the SAVOR TIMI 53 trial, 16,492 diabetic subjects with a history of MI, or documented atherosclerosis, or at least one of hyertension, smoking, or dyslipidemia and HbA1c 6.5-12% were randmized to receive saxagliptin or placebo. Additional anti-diabetic agents were prescribed at the discretion of the treating physician trhoughout the study. The primary endpoint was a composite of cardiovascular death, non fatal MI or non fatal ischemic stroke. Median F/U time was 2.1 years and maximum follow up time was 2.9 yrs. No differences in cardiovascular endpoints were observed in saxagliptin vs. placebo-treated patients. No differences in multiple safety endpoints, including pancreatitis or cancer, were observed across groups. Angioedema and hospitalization for heart failure was more common in saxagliptin-treated subjects. Saxagliptin and Cardiovascular Outcomes in Patients with Type 2 Diabetes Mellitus September 2, 2013DOI: 10.1056/NEJMoa1307684

In the EXAMINE (Examination of cardiovascular outcomes with alogliptin) study, 5380 patients with a recent (15-90 days) MI or unstable angina requiring hospitalization were randomized to alogliptin or placebo and followed for a median 18 months (up to 40 months). No differences in the primary endpoint (composite of death from cardiovascular causes, non-fatal MI or non fatal stroke) was observed between groups. Rates of pancreatitis, cancer, and hypoglycemia, were also similar between groups. Event rates were ~ 11% during the F/U period. Alogliptin after Acute Coronary Syndrome in Patients with Type 2 Diabetes September 2, 2013DOI: 10.1056/NEJMoa1305889

In the TECOS study, the cardiocascular safety of sitagliptin vs. usual diabetes care was examined in 14,671 patients over ~3 years. Sitagliptin-treated patients experienced a slightly greater reduction in a1c (0.3%); sitagliptin ws non-inferior to placebo in regard to reported MACE events or CV or all cause mortality, with no differences reported in rates of hospitalization for heart failure, or major AEs such as pancreatitis or pancreatic cancer Effect of Sitagliptin on Cardiovascular Outcomes in Type 2 Diabetes N Engl J Med. 2015 Jul 16;373(3):232-42.

Clinical Data

Analyses of whether DPP-4 inhibitors exert direct or indirect effects on blood vessels, and specifically, endothelial function (EF), have yielded conflicting results, depending on the experimental model, or the design of the clinical study. Ayaori and colleagues carried out two different randomized controlled trials examining the effects of either ssitagliptin vs. voglibose for 6 weeks (Study 1) or sitagliptin vs. alogliptin for 6 weeks, with changes in endothelial function representing the primary study endpoint. In study 1, inclusion criteria inclued age 20-75, HbA1c > 6.2% after dietary or medical intervention for 8 weeks; subjects with secondary illnesses or poorly controlled diabetes were excluded. Subjects (mean age ~46,received either sitagliptin 50 mg daily or voglibose, 0.9 mg daily, for 6 weeks, and parameters of ET function were performed prior to and after 6 weeks of drug treatment. EF was assessed by quantification of flow mediated vasodilation (FMD) of the brachial artery in the am, in the absence of acute drug ingestion. Endothelium-independent vasodilation was also assessed in the same subjects (all men in study 1) administered nitroglycerin (NTG). There were no major difference in parameters of glycemic or metabolic control after 6 weeks of sitagliptin vs. voglibose. FMD was markedly attenuated after treatment with sitagliptin, relative to changes with voglibose, however NMD did not change after either treatment. In study 2 a cross over design was utilized to compare the effects of alogliptin vs. sitagliptin. Each patient underwent a 6 week drug treatment period separated by a 4 week drug washout. Inclusion criteria included a HbA1c of 6.5%. 45 patients, mean age 66, were randomized to received either 50 mg sitagliptin, or 25 mg alogliptin, for 6 weeks, with each study subject then crossed over to the alternate medication. Although both alogliptin and sitagliptin reduced HbA1c, both drugs significantly reduced FMD, by 32 and 40%, respectively. Subjects treated with statins had smaller relative reductions in FMD. Dipeptidyl peptidase-4 inhibitors attenuate endothelial function as evaluated by flow-mediated vasodilatation in type 2 diabetic patients J Am Heart Assoc. 2013 Jan 28;2(1):e003277

The effects of sitagliptin on hemodynamics in human subjects with ischemic heart disease have been examined in a study of 14 non-diabetic patients with stable CAD subjected to dobutamine stress echocardiography (DSE). Patients were administered an oral glucose challenge, with or without a single administration of sitagliptin 100 mg. Sitagliptin-treated subjects exhibited a significant increase in ejection fraction, and enhanced LV regional wall motion, with improved contractile velocity in ischemic segments. DPP-4 Inhibition by Sitagliptin Improves the Myocardial Response to Dobutamine Stress and Mitigates Stunning in a Pilot Study of Patients with Coronary Artery Disease Circ Cardiovasc Imaging. 2010 2010 Mar;3(2):195-201   

In  follow-up study from the same group, McCormick and colleagues studied ventricular function by echocardiography in in subjects with type 2 diabetes, 16 males, with at least one 50% or greater proximal coronary arter stenosis, initially treated alone with oral hypoglycemic agents (19 metformin, 7 SU, 4 TZD), then restudied 4 weeks after the addition of sitagliptin. Patients were excluded if they had baseline wall motion dysfunction, or valvular heart disease, and/or previous history of MI or EF < 40%. Patients underwent 2 sequential dobutamine stress tests 4 weeks apart, with no beta blockers for 48 hrs, after an overnight fast, with oral agents withheld the morning of the study. Plasma GLP-1 levels were 5-8x higher after sitagliptin therapy, however insulin levels were not significantly different. 19 patients completed the study, 12 (63%) had single-vessel CAD, four (21%) had two-vessel disease, and three (16%) had triple-vessel disease. At peak stress, there was a greater increase in LV function after DPP-4 inhibition (70.5±7.0 [sitagliptin] versus 65.7±8.0% [control], and this improved performance persisted into recovery. Sitagliptin preferentially improved wall motion performance in paired ischemic segments, with improved parameters of both global and regional LV performance at peak stress and at 30 minutes into recovery.  Chronic DPP-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 Circ Cardiovasc Imaging. 2014 Feb 6.

Witteles and colleagues examined 12 non-diabetic patients (9 men, 3 women) with non-ischemic cardiomyopathy, NYHA class I-III, prior to and after 4 weeks of treatment with sitagliptin 100 mg daily. Mean LVEF was 39% at baseline. Myocardial glucose uptake, assessed by PET scanning, increased 19% after sitagliptin; 6 patients responded and 6 did not. Dipeptidyl peptidase 4 inhibition increases myocardial glucose uptake in nonischemic cardiomyopathy J Card Fail. 2012 Oct;18(10):804-9

Rahmi and colleagues carried out a prospective non-randomized study and compared the effects of repaglinide vs. vildagliptin in human subjects with T2DM with documented CAD and preserved ventricular function undergoing two sequential exercise tests separated by 30 minutes, followed by exposure to anti-diabetic drugs for 6 days. After 6 days of drug therapy, the 2 sequential exercise stress tests were repeated. In phase 1 in the absence of study drug, all patients demonstrated improvement in their stress EKGs during the second stress test. Exposure to repaglinide resulted in more patients experiencing earlier ischemia in their second stress test, whereas patients treated with vildagliptin exhibited greater preservation of ischemic preconditioning. Repaglinide preserved IPC in 17% whereas vildagliptin preserved IPC in 76% of patients. Effect of Hypoglycemic Agents on Ischemic Preconditioning in Patients With Type 2 Diabetes and Symptomatic Coronary Artery Disease Diabetes Care. 2012 Dec 18

The SITAGRAMI-Trial (Safety and efficacy of SITAgliptin plus GRanulocyte-colony-stimulating factor in patients suffering from Acute Myocardial Infarction). Based on the results of preclinical studies, a randomized clinical trial is underway in human subjects with myocardial infarction and successful PCI who then receive a 5 day treatment of G-CSF and 28 days of sitagliptin.The primary study outcome is change in global myocardial function after 6 months, taken to be an indirect reflection of cardiac regeneration. Interim safety analysis of the first 36 patients did not raise any concerns as outlined in Safety and efficacy of SITAgliptin plus GRanulocyte-colony-stimulating factor in patients suffering from Acute Myocardial Infarction (SITAGRAMI-Trial) - Rationale, design and first interim analysis. Int J Cardiol. 2010 Jan 3. [Epub ahead of print]. Long term follow-up of subjects enrolled in the SITAGRAMI study reported results for 173 randomized patients, with 167 patients completing long term FU (mean 4.5 years). The primary outcome was a classical 3 point MACE composite (death, MI, stroke) was not significantly different in subjects asigned to placebo vs. sitagliptin (28 days plus G-CSF for 5 days). No differences in functional NYHA classes or adverse events were observed between groups over the period of long term FU. Combined therapy with sitagliptin plus granulocyte-colony stimulating factor in patients with acute myocardial infarction - Long-term results of the SITAGRAMI trial Int J Cardiol. 2016 Jul 15;215:441-5

The effect of sitagliptin vs. placebo over 12 weeks was studied in human diabetic subjects presenting with and hospitalized for ACS, who were found to have IGT or T2DM in the BEGAMI study (Beta Cell Function and Glucose Abnormalities and Acute Myocardial Infarction). Glucose tolerance and parameters of beta cell function improved after 12 weeks, without any significant difference in HbA1c. Systolic BP and levels were increased, BNP and CRP levels were reduced and lipid profiles improved after sitagliptin administration. Sitagliptin improves beta-cell function in patients with acute coronary syndromes and newly diagnosed glucose abnormalities: the BEGAMI study. J Intern Med. 2013 Jan 19. doi: 10.1111/joim.12032

Barbierie and colleagues reported the analysis of multiple clinical variables with IMT regression in patients treated with either vildagliptin or sitagliptin for 12 weeks. The main study results (PPG, oxidative stress) were previously described in Reduction of oxidative stress and inflammation by blunting daily acute glucose fluctuations in patients with type 2 diabetes: role of dipeptidyl peptidase-IV inhibition Diabetes Care. 2012 Oct;35(10):2076-82. Remarkably 45 patients treated with vildagliptin, but not sitagliptin, exhibited a significant reduction in intimal media thickness after 12 weeks of therapy, despite no changes in HbA1c between groups. The study did not involve a control group. Using multivariate analyses, the authors concluded that changes in MAGE and LDL cholesterol in the vildagliptin group correlated with reductions in IMT. Decreased carotid atherosclerotic process by control of daily acute glucose fluctuations in diabetic patients treated by DPP-IV inhibitors Atherosclerosis. 2013 Jan 17. doi:pii: S0021-9150(12)0087 9.10.1016/ j.atherosclerosis. 2012.12.018. [Epub ahead of print]

Matsubara and colleagues assessed changes in endothelial function in 40 Japanese patients with coronary artery disease and diabetes, treated with or without sitagliptin for 6 months. Starting mean HbA1c was 7.4%. Patients were assigned (not randomized) to sitagliptin (20) or conventional therapy (20). Endothelial function was assessed by reactive hyperemia peripheral arterial tonometry. Systolic blood pressure was significantly lower by 7 mm Hg in the sitagliptin group, whereas systolic BP rose by 3 mm in the non-sitagliptin group, representing a final treatment difference of 13 mm Hg between groups. HbA1c was not different after 6 months. Patients with sitagliptin experienced a greater improvement in RHI (endothelial function) relative to the control group, and reductions in CRP correlated with improved endothelial function Dipeptidyl Peptidase-4 Inhibitor, Sitagliptin, Improves Endothelial Dysfunction in Association With Its Anti-Inflammatory Effects in Patients With Coronary Artery Disease and Uncontrolled Diabetes. Circ J. 2013 Feb 2.

Preclinical Data

The vast majority of the preclinical literature, partially highlighted below, illustrate that reduction of DPP4 activity, achieved using highly selective DPP4 inhibitors, or through genetic reduction of DPP4 activity in mice or rats, results in a cardioprotective phenotype in animal models of experimental cardiovascular injury. This discrepancy between generally favorable cardioprotecive effects of DPP4 inhibitors in preclinical studies, usually carried out in young healthy rodents, vs. results from clinical CV safety studies in human diabetic subjects with pre-existing atherosclerosis, has been much discussed. It seems clear that young healthy, non-diabetic, non-hypertensive, normolipidemic rodents may not represent a useful model for understanding the cardiovascular actions of DPP4 inhibitors in older diabetic human hypertensive subjects with long standing diabetes. Mulvihill, Varin and colleagues studied young healthy Dpp4-/- mice following experimental induction of hypertensive cardiomyopathy via transaortic constriction (TSC) and contrasted the results obtained in experiments using older, high fat fed, dyslipidemic, diabetic mice, also exposed to TAC, and treated with the GLP-1R agonist liraglutide, vs the selective DPP4 inhibitor, MK-0626. Consistent with the results of numerous studies highlighted below, normoglycemic Dpp4-/- mice were resistant to DIO and exhibited a cardioprotective response to TAC, with preservation of ventricular function and increased exercise capacity. Surprisngly however, Dpp4-/- hearts exhibited a gene expression profile consistent with increased inflammation. In contrast, older diabetic dyslipidemic high fat fed mice treated with a highly selective DPP4 inhibitor, MK-0626, exhibited modest cardiac hypertrophy, impairment of cardiac function, reduced exercise capacity, and dysregulated expression of genes and proteins controlling inflammation and cardiac fibrosis. A similar cohort of mice subjected to TAC and treated with liraglutide did not exhibit impairment of ventricular function or cardiac fibrosis. These findings highlight the importance of selecting context-appropriate animal models in preclinical studies with potential translational relevance. Inhibition of Dipeptidyl Peptidase-4 impairs ventricular function and promotes cardiac fibrosis in high fat-fed diabetic mice Diabetes December 15 online doi: 10.2337/db15-1224

Sauve et al examined the cardiovascular consequences of LAD ligation in normoglycemic Dpp4-/- mice, and in diabetic WT mice treated with sitagliptin or metformin. DPP4-/- hearts from normoglycemic mice exhibited increased basal expression of cardioprotective genes and proteins and Dpp4-/- mice exhibited normal cardiac structure and function yet significantly increased survival after LAD ligation. Treatment of diabetic WT mice with metformin or sitagliptin produced significant improvements in survival following LAD ligation. The cardioprotective effects of sitagliptin on ischemic myocardium are likely to be indirect, as sitagliptin did not improve functional recovery in ischemic murine hearts studied ex vivo, however administration of sitagliptin to mice for 24 hrs prior to experimental ischemia significantly improved LV function in isolated murine hearts studied ex vivo. Genetic deletion or pharmacological inhibition of dipeptidyl peptidase-4 improves cardiovascular outcomes following myocardial infarction in mice Diabetes 2010 Apr;59(4):1063-73

Consistent with these findings, Chang and colleagues demonstrated that treatment of non-diabetic male Sprague Dawley rats with sitagliptin for 2 weeks reduced cardiomyocyte apoptosis in the left ventricle, reduced plasma levels of CK-MB and LDH, increased myocardial levels of SOD and GSH-Px , improved function of the ischemic ventricles ( LV dp/dt) ex vivo, findings blocked by acute administration of exendin(9-39) and to some extent, LY294002. Protective effects of sitagliptin on myocardial injury and cardiac function in ischemia/reperfusion rat model Eur J Pharmacol. 2013 Sep 13. doi:pii: S0014-2999(13)00657-2

Shigeta et. al used normoglycemic and diabetic rat models to probe the biology of DPP-4 in the heart. DPP-4 expression was predominantly localized to endothelial cells in the rat and human heart and experimental diabetes was associated with increased DPP-4 activity assessed using a colorimetric assay. Fischer DPP4-/- rats were protected against experimental diabetes and exhibited preserved LV function and resistance to hypoxic injury. Levels of SDF-1a assessed by ELISA were lower in diabetic hearts and preserved in DPP4-/- rats. Similarly, the numbers of CXCR4+KDR+ cells were higher in non-diabetic and DPP4-/- rat hearts, as assessed by immunohistochemistry. Cardiac fibrosis, as assessed by picro-Sirius red staining and changes in fibrosis-related gene expression, was increased in WT diabetic rat hearts and attenuated in DPP4-/- Fischer rat hearts. Treatment with vildagliptin for 4 weeks attenuated ventricular diastolic dysfunction in diabetic rats without changes in capillary density. Vildagliptin also reserved DM-associated reductions in SDF-1 and Akt/eNOS phosphorylation. Fischer DPP4 mutant rats exhibited preservation of LV function after aortic constriction. Human diabetic subjects were shown to have modestly but significantly increased DPP-4 activity in coronary sinus blood samples. Dipeptidyl Peptidase-4 Modulates Left Ventricular Dysfunction in Chronic Heart Failure via Angiogenesis-Dependent and -Independent Actions Circulation. 2012 Oct 9;126(15):1838-51.

Thiess and colleagues assessed the effects of vildagliptin or sitagliptin alone (6 days) or in combination with G-CSF, on stem cell mobilization, cardiac homing of bone marrow derived stem cells, infarct size, cardiovascular function (pressure volume loops on day 6 and day 28 of surviving mice), and survival, in C57 BL/6 mice. Drug administration was commenced immediately after LAD ligation. Both DPP-4 inhibitors increased the mobilization and cardiac homing of bone marrow-derived stem cells after MI, actions potentiated by G-CSF. Therapy with DPP-4i plus G-CSF also increased the proportion of resident cardiac stem cells. Sitagliptin alone reduced infarct size and increased LV wall thickness and capillary density in the infarct zone, and ejection fraction at day 6 and day 28 and addition of G-CSF produced no additional change in infarct size or other parameters beyond stem cell mobilization with the exception of survival, which was greatest at day 28 in mice receiving both G-CSF and a DPP-4 inhibitor. Antidiabetic gliptins in combination with G-CSF enhances myocardial function and survival after acute myocardial infarction Int J Cardiol. 2013 May 10. doi:pii: S0167-5273(13)00768-7

Liu and colleagues used several different experimental models to examine the effects of DPP-4 on renal blood vessels. Sitagliptin administered for 2 weeks reduced systolic blood pressure and improved renal blood flow in SHR rats. Remarkably, sitagliptin treatment also increased the expression of GLP-1 and the GLP-1R (assessed by Western blotting) in rat renal arteries and sitagliptin augmented the acetylcholine-induced relaxation of SHR renal arteries ex vivo, in association with enhanced PKA, LKB1, AMPK, and eNOS phosphorylation. These phosphorylation changes and vasorelaxation were blocked by incubation of arteries ex vivo with SQ22536 and H89, consistent with cAMP-dependent effects of sitagliptin. Remarkably, treatment of human renal arteries with exendin-4 for 12 hrs improved Ach-mediated vasorelaxation, and increased GLP-1R, p-AMPK, p-eNOS and p-PKA protein expression Dipeptidyl peptidase 4 inhibitor sitagliptin protects endothelial function in hypertension through a glucagon-like peptide 1-dependent mechanism Hypertension. 2012 Sep;60(3):833-41

Ku assessed cardiac performance following induction of ischemia ex vivo in DPP4-deficient rats, with and without exendin(9-39). Although baseline cardiovascular function was comparable in DPP4-/- rats and WT controls, cardiac performance was maintained to a greater extent in Fischer344 DPP4-/- rats, and partially sensitive to the GLP-1R antagonist exendin(9-39). Infarct size after 45 minutes of coronary artery occlusion followed by 2 h of perfusion was amazingly reduced by almost 80% in DPP4-/- rats, and partially reversed by exendin(9-39). These cardioprotective effects were associated with increased levels of phosphorylated Akt and GSK3beta in cardiac tissue after ischemia/reperfusion, effects sensitive to exendin(9-39). Administration of GLP-1(9-36) to DPP-4-deficient rats did not produce any additional reduction in infarct size. DPP4 deficiency preserves cardiac function via GLP-1 signaling in rats subjected to myocardial ischemia/reperfusion Naunyn Schmiedebergs Arch Pharmacol. 2011 Aug;384(2):197-207

Ye and colleagues compared the effects of sitagliptin and pioglitazone on infarct size and signal transduction in rodent models of ischemia. Treatment of mice with sitagliptin or pioglitazone for 3  or 14 days reduced infarct size using an in vivo model of ischemia re-perfusion injury. Sitagliptin increased cardiac levels of cAMP, and infusion of the PKA inhibitor attenuate the cardioprotective actions of sitagliptin but not pioglitazone. Pioglitazone and sitagliptin exerted different effects on cPLA2 and Cox2 activity, and both agents increased eNOS and CREB phosphorylation. Sitagliptin alone had no effect in isolated cardiomyocytes, whereas sitagliptin plus exogenous GLP-1 reduced cardiomyocyte injury in a cellular model of simulated ischemia-reperfusion injury The myocardial infarct size limiting effects of sitagliptin is PKA-dependent, whereas the protective effect of pioglitazone is partially dependent on PKA. Am J Physiol Heart Circ Physiol. 2010 298(5):H1454-65

Contrasting results were obtained in studies by Yin and colleagues in male Sprague Dawley non-diabetic rats (n= 8-10 rat per group) with LAD ligation that were either pretreated with vildagliptin (15 mg/kg/day) for 2 days, or vildagliptin was commenced 3 weeks after LAD ligation, and continued for another 9 weeks. Cardiovascular function was assessed in the chronic treatment group by Echo and invasive hemodynamics. Active levels of GLP-1 were significantly increased and DPP-4 activity was reduced by 70% in vildagliptin-treated rats. Infarct size trended lower in vildagliptin-treated rats. Cardiac capillary density was lower after MI and not affected by vildagliptin. Cadiomyocyte size was higher after MI but not significantly different with vildagliptin; similarly vildagliptin did not reverse the extent of LV hypertrophy. After MI, all rats exhibited LV dilation and systolic dysfunction, findings not changed by vildagliptin treatment. No significant differences in cardiomyocyte gene expression were reported. Early and late effects of the DPP-4 inhibitor vildagliptin in a rat model of post-myocardial infarction heart failure Cardiovasc Diabetol. 2011 Sep 28;10(1):85

Ku and colleagues compared the resistance of WT and DPP4-/- (Fischer 344 rats) adult rat cardiomyocytes to H2O2-induced cell injury. DPP4 protein expression and DPP4 activity was reduced in total heart and CM cultures from F344 rats. DPP4-/- CM cultures were significantly more resistant to H2O2, and exhibited lower levels of ROS after cell injury. Levels of Bax and caspase-3 activity were also reduced and pAKT levels were higher and contractile function was greater in H2O2-treated DPP4-/- CMs. DPP4 Deficiency Exerts Protective Effect against H(2)O(2) Induced Oxidative Stress in Isolated Cardiomyocytes PLoS One. 2013;8(1):e54518

Gomez and colleagues examined the effects of sitagliptin therapy in a pacing-induced model of heart failure in normoglycemic pigs. Sitagliptin was administered for 3 weeks, commencing 1 week after initiation of rapid pacing. Sitagliptin-treated pigs exhibited increased heart rate, yet increased stroke volume and preservation of GFR. Sitagliptin did not attenuate LV dilation. Dipeptidyl peptidase IV inhibition improves cardiorenal function in overpacing-induced heart failure Eur J Heart Fail. 2011 Nov 1.

Matsubara and colleagues examined the effects of a sitagliptin analogue, des-fluoro-sitagliptin (DFS) in macrophages and blood vessels from ApoE-/- mice treated with or without DFS in a high fat diet for 16 weeks. DFS treatment reduced the extent of atherosclerosis, decreased macrophage and lymphocyte accumulation in plaque,  and reduced expression of inflammatory cytokine genes in the aorta. DFS-treated mice also exhibited enhanced endothelium-dependent relaxation in response to acetylcholine ex vivo in association with increased protein levels of phospho-eNOS. DFS also potentiated the direct anti-inflammatory actions of GLP-1 on THP-1 cell-derived macrophages, and potentiated the stimulatory effects of exogenous GLP-1 on macrophage cAMP accumulation and anti-inflammatory pathways. Similar salutary effects were seen on the potentiation of GLP-1 prosurvival and anti-apoptotic actions on human coronary endothelial cells. The authors also found that fasting levels of GLP-1 appeared to be lower in a subset of patients with cornorary artery disease. A dipeptidyl peptidase-4 inhibitor, des-fluoro-sitagliptin, improves endothelial function and reduces atherosclerotic lesion formation in apolipoprotein e-deficient mice J Am Coll Cardiol. 2012 Jan 17;59(3):265-76.

Hemmeryckx and colleagues studied the effects of two doses of sitagliptin, 10 or 50 mg/kg/day administered for 3-4 months to diabetic Akita mice. Low dose sitagliptin had no effect on glycemia or echocardiographic parameters of ventricular function. In contrast, after 3 months of a high fat high cholesterol diet, mice treated with 50mg/kg/day sitagliptin exhibited reduced A1c, decreased levels of GLP-1, and evidence for ventricular hypertrophy (increased LV end diastolic diameter, LV volume, SV, and cardiac output with no significant improvement in fractional shortening or ejection fraction. Effect of sitagliptin treatment on metabolism and cardiac function in genetic diabetic mice Eur J Pharmacol. 2014 Jan 6. pii: S0014-2999(13)00964-3. doi: 10.1016/j.ejphar.2013.12.036

Does DPP-4 modulate thrombolytic activity in the heart or coronary microvascular arteries? Krijnen and colleagues examined DPP-4 expression and in situ activity in frozen histological sections of DPP-4 activity in hearts from 82 subjects, focusing on human coronary microvascular arteries from hearts obtained at autopsy from patients with recent myocardial infarction (73/82 hearts). Cardiomyocytes were "immunonegative" for DPP-4 immunoreactivity, whereas endothelial cells were positive. DPP-4 expression and activity were correlated and reduced in the area surrounding the infarct. Tissue factor expression was increased in blood vessels and cardiomyocytes surrounding the infarct. Reduction of DPP-4 activity correlated with reduced tissue factor expression. Culture of HUVEC cells under limiting conditions (2-deoxyglucose, hydrogen peroxide, apocynin, TNF-alpha) reduced DPP-4 expression and induced tissue factor expression ex vivo. The non-selective protease inhibitor diprotin A also enhanced platelet adherence to HUVEC cells in vitro. The totality of the data prompted the authors to speculate that the ability of DPP-4 to acts as an anti-fibrinolytic agent and cleave fibrin and enhance coronary flow was relatively impaired in the experimental models and human materials employed for analysis. Loss of DPP4 activity is related to a prothrombogenic status of endothelial cells: implications for the coronary microvasculature of myocardial infarction patients Basic Res Cardiol. 2012 Jan;107(1):1-13

 

Lee and colleagues treated Wistar rats with sitagliptin 4 weeks following indction of experimental MI and examined ventrocular function, cyclic AMP and arrhythmogenic potential largely in hearts ex vivo. Sitagliptin-treated infarcted rats had significantly lower LV norepinephrine and NGF levels and attenuated the shortening of ventricular effective refractory period (VERP).  Sitagliptin also significantly decreased the inducibility of ventricular tachyarrhythmias compared to thevehicle-treated infarcted group. Dipeptidyl Peptidase-4 Inhibition Attenuates Arrhythmias via a Protein Kinase A-Dependent Pathway in Infarcted Hearts Circ J. 2015 Sep 24

Reverse cholesterol transport

Briand and colleagues studied the effects of sitagliptin on reverse cholesterol transport and macrophage cholesterol efflux in mice. Male CETP/human ApoB transgenic mice were placed on a high fat diet for 3 months, then treated with sitagliptin 500 mg/kg in the drinking water for 4 weeks. Control mice were treated with metformin. Sitagliptin reduced body weight by 29%, without a change in food intake, with a 63% reduction in fat mass. Sitagliptin decreased total hepatic cholesterol, and significantly increased levels of fetal cholesterol, but fecal bile acid levels were unchanged. Sitagliptin reduced the absorption of 14-C labelled olive oil and reduced plasma levels of apoB100 and ApoB48 and also increased the appearance of 3-H-cholesterol in stool after administration of cholesterol loaded macrophages to mice. Sitagliptin Promotes Macrophage-to-feces Reverse Cholesterol Transport Through Reduced Intestinal Cholesterol Absorption in Obese Insulin Resistant CETP-apoB100 Transgenic Mice Diabetes Obes Metab. 2012 Jan 23. doi: 10.1111/j.1463-1326.2012.01568.

GLP-1(9-36): A DPP-4 generated metabolite and cardioactive peptide

Unexpectedly, both GLP-1 and GLP-1(9-36) amide  were found to improve left ventricular functioning in dogs with pacing-induced dilated cardiomyopathy (DCM) Active metabolite of GLP-1 mediates myocardial glucose uptake and improves left ventricular performance in conscious dogs with dilated cardiomyopathy. Am J Physiol Heart Circ Physiol. 2005 Dec;289(6):H2401-8.  DCM was induced by rapid right ventricular pacing for 28 days. Rapid pacing was suspended, and dogs either received a 48-hour iv infusion of GLP-1 (1.5 pmol/kg/min, n=9), GLP-1(9-36) (1.5 pmol/kg/min, n=7), or saline control. Both GLP-1 and GLP-1(9-36) significantly reduced LVEDP, and increased the first derivative of LV pressure. These improvements were nearly identical with each form of peptide. Both GLP-1 and GLP-1(9-36) significantly improved LV stroke volume, LVEF, and cardiac output to a comparable degree. GLP-1(9-36) also reduced ischemic damage following ischemia/reperfusion injury in the isolated mouse heart. Twenty minutes of GLP-1(9-36) (0.3 nM) treatment, administered immediately following ischemia during the reperfusion phase, significantly improved functional recovery of the left ventricle in wild-type and unexpectedly, in hearts from Glp1r-/- mice. GLP-1(9-36) (0.3 nM) also increased cGMP release measured from coronary effluent samples taken at various time points from normoxic perfused hearts of wild-type and Glp1r-/- mice. Both GLP-1 and GLP-1(9-36) induced vasodilation and significantly increased coronary flow to the same magnitude. The addition of sitagliptin (5 μM) to GLP-1-treated mesenteric arteries reduced, but did not abolish, the vasodilatory response to GLP-1. This suggests that both GLP-1 and the metabolite GLP-1(9-36) have vasodilatory actions. Consistent with this observation, both GLP-1 and GLP-1(9-36) elicited vasodilation in arteries from Glp1r-/- mice Cardioprotective and vasodilatory actions of glucagon-like peptide 1 receptor are mediated through both glucagon-like peptide 1 receptor-dependent and -independent pathways Circulation. 2008 May 6;117(18):2340-50

 

Stromal cell-derived factor-1 (SDF-1)

SDF-1 is an endogenous DPP-4 substrate. Plasma from Dpp4-/- mice contains exclusively C-terminally truncated SDF-1, whereas SDF-1 was degraded at both the C- and N-terminus in wild-type mice Circulating CD26 is negatively associated with inflammation in human and experimental arthritis Am J Pathol. 2005 Feb;166(2):433-42 . Preclinical data indicates that SDF-1 expression is upregulated in the ischemic myocardium in mice immediately following infarction Stromal cell-derived factor-1alpha plays a critical role in stem cell recruitment to the heart after myocardial infarction but is not sufficient to induce homing in the absence of injury Circulation. 2004 Nov 23;110(21):3300-5 , and myocardial SDF-1 gene transfer increases the mobilization and homing of stem cells toward ischemic myocardium, leading to neovascularization and enhanced post-infarction recovery in rats and mice Effect of stromal-cell-derived factor 1 on stem-cell homing and tissue regeneration in ischaemic cardiomyopathy Lancet. 2003 Aug 30;362(9385):697-703  and Mobilizing of haematopoietic stem cells to ischemic myocardium by plasmid mediated stromal-cell-derived factor-1alpha (SDF-1alpha) treatment. Regul Pept. 2005 Feb 15;125(1-3):1-8  

SDF-1 has been shown to protect against deterioration of cardiac function in mice after acute myocardial infarction via angiogenesis promotion Stromal cell-derived factor-1alpha is cardioprotective after myocardial infarction Circulation. 2008 Apr 29;117(17):2224-31. The essential role of SDF-1 in the recruitment of stem and progenitor cells toward the ischemic/hypoxic myocardium is through its cognate receptor, CXC chemokine receptor 4 (CXCR4). Zaruba et al. utilized a model of combined genetic or pharmacologic inhibition of DPP-4 with granulocyte- colony stimulating factor (G-CSF)-mediated stem cell mobilization after MI in mice. This approach lead to increased myocardial homing of circulating CXCR4+ stem-cells, reduced cardiac remodeling, and improved heart function and survival. Dpp4-/- mouse myocardium showed no DPP-4 activity 2 days post-MI, with low levels of DPP-4 activity in serum. Use of the DPP-4 inhibitor Diprotin-A in combination with G-CSF (100 μg/kg/day ip), lead to decreased DPP-4 activity following MI in the myocardium but not in serum of wild-type mice. Flow cytometry analyses of heart tissue 48h after MI revealed that both genetic and pharmacological inhibition of DPP-4 in combination with G-CSF resulted in significantly increased recruitment of CD45+/CD34+/c-kit+, CD45+/CD34+/Sca-1+, CD45+/CD34+/CXCR4+, and CD45+/CD34+/Flk-1+ progenitor cells as well as lin-c-kit+Sca-1+ hematopoietic stem cells into ischemic myocardium. This effect was reversed when these mice were treated with the CXCR4 antagonist AMD3100 (ip,1.25 mg/kg). Loss or inhibition of DPP-4 function in combination with G-CSF treatment reduced scar tissue and apoptosis and ameliorated thickness of the LV wall 30 days post-MI, as analyzed by histology. Finally, G-CSF administration in Dpp4-/- mice, or Diprotin-A-treated wild-type mice improved survival, as well as LVEF, cardiac output, and contractility Synergy between CD26/DPP-IV inhibition and G-CSF improves cardiac function after acute myocardial infarction Cell Stem Cell. 2009 Apr 3;4(4):313-23.

As SDF-1 is an essential DPP-4 substrate that mobilizes endothelial progenitor cells to sites of vascular or myocardial injury, the finding that sitagliptin treatment of subjects with T2DM also results in an increase in circulating endothelial progenitor cells is intriguing The oral dipeptidyl peptidase-4 inhibitor sitagliptin increases circulating endothelial progenitor cells in patients with type 2 diabetes mellitus. Possible role of stromal derived factor-1{alpha} Diabetes Care. 2010 Mar 31. [Epub ahead of print]

Other hormones that exert their actions through GPCRs also may reduce infarct size after experimental MI in mice through related mechanisms, namely enhanced SDF-1-directed stem cell mobilization and repair of injured myocardial tissue through the SDF-1:Cxcr4 axis. For example parathyroid hormone (PTH) administration to mice after LAD ligation and experimental MI improves survival in association with enhanced number of bone marrow-derived cells in the injured heart Parathyroid hormone treatment after myocardial infarction promotes cardiac repair by enhanced neovascularization and cell survival Cardiovasc Res. 2008 Mar 1;77(4):722-31. Surprisngly, PTH also inhibits the activity of DPP-4 both in vitro and in mice after exogenous PTH administration. Hence, the beneficial effects of PTH in the context of experimental MI may be linked to enhanced mobilization of CXCR4+ bone marrow cells to the injured myocardium, in part through direct effects of PTH on the bone marrow, and perhaps in part through DPP-4-mediated stabilization of SDF-1 Parathyroid hormone is a DPP-IV inhibitor and increases SDF-1-driven homing of CXCR4+ stem cells into the ischemic heart Cardiovasc Res. 2011 Jan 18.

BNP

BNP is a peptide hormone synthesized in the heart and is a major contributor in the regulation of cardiovascular homeostasis, mediating vasodilation, lusitropism, natriuresis, and supression of renin secretion. The physiological concentration of BNP in plasma noticeably increases in patients with cardiac overload. Therefore, BNP has largely been used in a clinical setting as a prognostic marker for patients with cardiac hypertrophy and heart failure. DPP-4 removes the two NH2-terminal amino acids of BNP to produce BNP(3-32) Dipeptidyl-peptidase IV converts intact B-type natriuretic peptide into its des-SerPro form Clin Chem. 2006 Jan;52(1):82-7. With respect to cardio-renal actions of BNP(3-32), this peptide has reduced renal actions when compared to full-length BNP, and lacks any vasodilating ability Des-serine-proline brain natriuretic peptide 3-32 in cardiorenal regulation Am J Physiol Regul Integr Comp Physiol. 2007 Feb;292(2):R897-901. The endogenous levels of BNP in Dpp4-/- mice and in mice and humans treated with a DPP-4 inhibitor are currently unknown, and the potential influence of BNP on cardiac remodeling and contractile dysfunction following MI requires further study.

Neuropeptide Y

Neuropeptide Y (NPY) is a 36 amino acid peptide, originally isolated from the porcine brain. NPY is primarily synthesized and released by neurons, and belongs to a family of neuroendocrine peptides. NPY is found colocalized with norepinephrine in all sympathetic nerves that innervate the cardiovascular system, and is the most abundant neuropeptide in the heart. Human coronary arteries in particular, are abundantly innervated with fibers containing NPY. The NPY receptor Y1 is the major vascular receptor in that it mediates vasoconstriction in small arteries of coronary and splanchnic vascular beds and arterial smooth muscle cell proliferation. In humans and animals, plasma NPY levels are increased in response to tissue injury and ischemia, and in a variety of conditions with sympathetic hyperactivity, such as hypertension and congestive heart failure.

Intact NPY(1-36) binds the Y1 receptor (Y1R ). Cleavage of NPY from a Y1R agonist to non-Y1 (a Y2/Y5 R ligand) is dependent on DPP-4 Proteolytic processing of neuropeptide Y and peptide YY by dipeptidyl peptidase IV Regul Pept. 1993 Dec 10;49(2):133-44. with NPY and DPP-4 being colocalized in blood vessels. DPP-4-cleaved NPY(3-36) is the second major circulating form of the peptide, and is capable of activation of all non-Y1 receptors, namely Y2, Y3 and Y5. These receptors are found not only in the central and peripheral nervous system , but also in blood vessels. DPP-4 conversion of NPY to NPY(3-36) is necessary for angiogenic activity, as the use of a DPP-4 neutralizing antibody resulted in the loss of NPY-mediated endothelial cell migration in an endothelial wound assay Critical role of dipeptidyl peptidase IV in neuropeptide Y-mediated endothelial cell migration in response to wounding Peptides. 2001 Mar;22(3):453-8

A potential increase in circulating NPY as a result of reduced DPP-4 activity may have effects on blood pressure. Jackson et al. found that DPP-4 inhibition by sitagliptin augmented the ability of exogenous NPY(1-36) to enhance renovascular responses to angiotensin II (AngII) in kidneys from genetically hypertensive rats. Administration of Ang II (0.3 nmol/L) to isolated, perfused kidneys from adult spontaneously hypertensive rats (SHR) resulted in increased perfusion pressure, indicative of vasoconstriction, that was significantly enhanced when exogenous NPY(1-36) (6 nmol/L) was added to the perfusate. This effect was blocked when kidneys were pretreated for 20 minutes with 1 μM BIBP3226 (a highly selective Y1 receptor blocker), or the DPP-4 inhibitor sitagliptin (1 μM) Sitagliptin augments sympathetic enhancement of the renovascular effects of angiotensin II in genetic hypertension Hypertension. 2008 Jun;51(6):1637-42

Blood pressure and endothelial function

Nevertheless, no problems with blood pressure have been detected in clinical trials examining the effects of DPP-4 inhibitors in diabetic subjects. A short-term study in 19 non-diabetic, mild to moderately hypertensive patients revealed no effects of sitagliptin treatment (50 or 100 mg BID for 5 days) on 24-hour ambulatory blood pressure measurements Effect of sitagliptin, a dipeptidyl peptidase-4 inhibitor, on blood pressure in nondiabetic patients with mild to moderate hypertension. J Clin Pharmacol. 2008 May;48(5):592-8. The endogenous levels of NPY in Dpp4-/- mice and in mice treated with a DPP-4 inhibitor have not been reported, and the potential influence of NPY on coronary vasoconstriction is unknown.

Shah and colleagues used the DPP-4 inhibitos, alogliptin, to assess the direct consequences of DPP-4 inhibitoon on vascular tone of preconstricted aortic rings from C57BL/6 mice. Alogliptin produced a profound dose-dependent relaxation response that was not affected by the GLP-1R antagonist exendin(9-39), but was partially attenuated by denudation of the endothelium, or by pre-treatement with the NO synthase inhibitor LNMMA and the guanyl cyclase inhibitor ODQ. Combined inhibition of eNOS and K+ channel conductance with multiple inhibitors completely blocked the vasodilatory effect of alogliptin. Alogliptin also caused rapid release of NO from HUVEC cells, together with increased phsophorylation of NO and Akt. The vasodilatory effects of alogliptin were also reduced by the signal transduction inhibitors SH6, wortmannin, and PP2. The extent of inhibition achieved with alogliptin was not described Acute DPP-4 inhibition modulates vascular tone through GLP-1 independent pathways Vascul Pharmacol. 2011 Mar 9. [Epub ahead of print]

Similar results were obtained byRomacho and colleagues examining the effects of soluble DPP4 (sDPP4) on vascular reactivity in mesenteric blood vessels from 3 month old WT mice. sDPP4 impaired endothelium-dependent vasorelaxation in the isolated arteries, findings reversed by co-treatment with two different DPP4 inhibitors, K579 and alogliptin. The effects of sDPP4 were also blunted in the presence of a PAR2 inhibitor or a COx inhibitor or a thromboxane receptor antagonist Soluble dipeptidyl peptidase-4 induces microvascular endothelial dysfunction through proteinase-activated receptor-2 and thromboxane A2 release J Hypertens. 2016 Feb 18

Ta and colleagues examined the effects of alogliptin on atherosclerosis development in normoglycemic and diabetic ApoE-/- mice. Male mice were placed on a 60% high fat diet, and at age 12 weeks, STZ was administered to induce diabetes in some mice. Four weeks later, several groups of mice were administered alogliptin 15 mg/kg via daily gavage. Diabetic mice lost weight and exhibited reduced insulin levels. Alogliptin therapy for 24 weeks improved glycemia (473 vs 349 mg/dl), and decreased levels of cholesterol and triglycerides. Intimal lesion area in the aorta was greater in diabetic mice; alogliptin therapy had no effect on lesion size in non-diabetic mice but did significantly reduce lesion size in diabetic mice. Immunohistochemical quantification revealed reduced IL-6 and IL-1b in the atherosclerotic placques of alogliptin-treated diabetic mice. Alogliptin also reduced IL-6 secretion and IL-6 expression in LPS-stimulated U937 cells. Gene expression studies demonstrated that alogliptin had broad actions to reduce cytokine expression in LPS-stimualted U937 mononuclear cells DPP-4 (CD26) Inhibitor Alogliptin Inhibits Atherosclerosis in Diabetic Apolipoprotein E-Deficient Mice J Cardiovasc Pharmacol. 2011 May 6. [Epub ahead of print]

The actions of alogliptin, and in some instances, sitagliptin, were also examined by Shah and colleagues, primarily in Ldlr-/- mice, with or without a high fat diet for 12 weeks. A number of salutary changes in inflammatory gene expression, cell migration, reduction of aortic plaque and reduced plaque inflammatory cell infiltration were noted in alogliptin-treated mice. Long-Term Dipeptidyl-Peptidase 4 Inhibition Reduces Atherosclerosis and Inflammation via Effects on Monocyte Recruitment and Chemotaxis Circulation. 2011 Oct 17. [Epub ahead of print

Coagulation

An antiplatelet effect (reduced platelet aggregation) was described in human diabetic subjects treated with sitagliptin (monotherapy) for 1 and 3 months (10-30% reduction in aggregation), and direct incubation of platelets from normal non-diabetic human donors with sitagliptin ex vivo resulted in reduced platelet aggregation, and a reduction in the rise of intracellular calcium after thrombin stimulation. Furthermore, the intensity of phosphotyrosine proteins on Western blotting was reduced after sitagliptin treatment of thrombin-stimulated platelets Sitagliptin: Anti-platelet effect in diabetes and healthy volunteers Platelets. 2012 Sep 5.

Several cardiovascular outcome studies are underway in human subjects treated with DPP-4 inhibitors.

These include: TECOS: A Randomized, Placebo Controlled Clinical Trial to Evaluate Cardiovascular Outcomes After Treatment With Sitagliptin in Patients With Type 2 Diabetes Mellitus and Inadequate Glycemic Control

SAVOR- TIMI 53: A Multicentre, Randomised, Double-Blind, Placebo-Controlled Phase IV Trial to Evaluate the Effect of Saxagliptin on the Incidence of Cardiovascular Death, Myocardial Infarction or Ischaemic Stroke in Patients With Type 2 Diabetes

EXAMINE: A Multicenter, Randomized, Double-Blind, Placebo-Controlled Study to Evaluate Cardiovascular Outcomes Following Treatment With Alogliptin in Addition to Standard of Care in Subjects With Type 2 Diabetes and Acute Coronary Syndrome The study inclusion criteria, endpoints and trial design for EXAMINE are also described in EXamination of CArdiovascular OutcoMes with AlogliptIN versus Standard of CarE in Patients with Type 2 Diabetes Mellitus and Acute Coronary Syndrome (EXAMINE) A cardiovascular safety study of the dipeptidyl peptidase 4 inhibitor alogliptin in patients with type 2 diabetes with acute coronary syndrome Am Heart J. 2011 Oct;162(4):620-626.e1. Epub 2011 Sep 14

CAROLINA: A Multicentre, International, Randomised, Parallel Group, Double Blind Study to Evaluate Cardiovascular Safety of Linagliptin Versus Glimepiride in Patients With Type 2 Diabetes Mellitus at High Cardiovascular Risk