A dipeptidyl peptidase-4 inhibitor, des-fluoro-sitagliptin, improves endothelial function and reduces atherosclerotic lesion formation in apolipoprotein E-deficient mice

Sirtuin 6 expression and inflammatory activity in diabetic atherosclerotic plaques: effects of incretin treatment

The role of sirtuin 6 (SIRT6) in atherosclerotic progression of diabetic patients is unknown. We evaluated SIRT6 expression and the effect of incretin-based therapies in carotid plaques of asymptomatic diabetic and nondiabetic patients. Plaques were obtained from 52 type 2 diabetic and 30 nondiabetic patients undergoing carotid endarterectomy. Twenty-two diabetic patients were treated with drugs that work on the incretin system, GLP-1 receptor agonists, and dipeptidyl peptidase-4 inhibitors for 26 ± 8 months before undergoing the endarterectomy. Compared with nondiabetic plaques, diabetic plaques had more inflammation and oxidative stress, along with a lesser SIRT6 expression and collagen content. Compared with non-GLP-1 therapy-treated plaques, GLP-1 therapy-treated plaques presented greater SIRT6 expression and collagen content, and less inflammation and oxidative stress, indicating a more stable plaque phenotype. These results were supported by in vitro observations on endothelial progenitor cells (EPCs) and endothelial cells (ECs). Indeed, both EPCs and ECs treated with high glucose (25 mmol/L) in the presence of GLP-1 (100 nmol/L liraglutide) presented a greater SIRT6 and lower nuclear factor-κB expression compared with cells treated only with high glucose. These findings establish the involvement of SIRT6 in the inflammatory pathways of diabetic atherosclerotic lesions and suggest its possible positive modulation by incretin, the effect of which is associated with morphological and compositional characteristics of a potential stable plaque phenotype.

Effects of sitagliptin on coronary atherosclerosis evaluated using integrated backscatter intravascular ultrasound in patients with type 2 diabetes: rationale and design of the TRUST study

Patients with diabetes mellitus are at high risk for developing coronary artery disease (CAD), even if they are treated with statins. Several studies have shown the beneficial effects of dipeptidyl peptidase-4 (DPP-4) inhibitors on the cardiovascular system in an animal model. However, recent clinical trials using DPP-4 inhibitors have shown that these inhibitors fail to reduce the occurrence of cardiovascular events. Therefore, this study will be performed to evaluate the effects of sitagliptin, a DPP-4 inhibitor, on coronary atherosclerosis in patients with type 2 diabetes. This study will be a prospective, open-label, randomized multicenter trial performed in 6 centers in Japan. Stable CAD patients with type 2 diabetes who have undergone successful percutaneous coronary intervention under integrated backscatter (IB)-intravascular ultrasound (IVUS) guidance will be studied. They will be randomly assigned to either the sitagliptin group or a control group. After 48 weeks' treatment, the IVUS examination will be repeated in the same coronary artery as at baseline. The primary end point will be the percentage change in plaque volume measured using grayscale IVUS from baseline to the 48-week follow-up. This study will be the first multicenter trial to evaluate the effects of a DPP-4 inhibitor on coronary atherosclerosis evaluated using IB-IVUS, and the findings will clarify the anti-atherogenic effects of sitagliptin.

Dipeptidyl-peptidase-4 inhibitor, alogliptin, attenuates arterial inflammation and neointimal formation after injury in low-density lipoprotein (LDL) receptor-deficient mice

Background

The results of recent studies suggest that dipeptidyl‐peptidase‐4 inhibitors have antiatherogenic effects. However, whether or not dipeptidyl‐peptidase‐4 inhibitors could suppress arterial inflammation and intimal hyperplasia after injury remains undetermined. The present study aims to clarify the anti‐inflammatory effects of the dipeptidyl‐peptidase‐4 inhibitor, alogliptin (AGP), on the arteries of atherogenic low‐density lipoprotein receptor‐deficient (LKO) mice.

Methods and Results

We compared intimal hyperplasia in LKO mice 2 weeks after femoral artery injury using an external vascular cuff model. All mice received oral injection of AGP (20 mg/kg per day) or normal saline (control) once daily for 14 days. Fasting blood sugar levels, serum cholesterol levels, or blood pressure did not significantly differ between the 2 groups. Plasma levels of active glucagon‐like peptide‐1 were higher in the AGP than in the control LKO mice (22.2±1.9 versus 15.6±0.9 pg/mL; P<0.05). Compared with saline, AGP significantly reduced intimal hyperplasia (1087±127 versus 1896±140 μm²; P<0.001) as well as the intima/media ratio (0.08±0.01 versus 0.16±0.02; P<0.001). Immunostaining showed that AGP reduced proliferating cells (proliferating cell nuclear antigen–positive nuclei; P<0.001), percent smooth‐muscle cell area (α‐SMA‐positive cells; P<0.001), inflammatory cells infiltration (lymphocyte antigen 6 complex–positive cells; P<0.05), tumor necrosis factor‐α expression (P<0.05), and percent phospho‐NF‐κB‐positive cell compared with saline. Levels of tumor necrosis factor ‐α (0.5‐fold P<0.05), monocyte chemoattractant protein 1 (0.3‐fold P<0.01), and interleukin‐1β (0.2‐fold P<0.05) mRNA were lower in the injured arteries of the AGP than in the control group.

Conclusions

AGP appeared to suppress neointimal formation by inhibiting inflammation, independently of its effects on glucose or cholesterol metabolism in atherogenic LKO mice.

Glucagon-Like Peptide 1 Protects against Hyperglycemic-Induced Endothelial-to-Mesenchymal Transition and Improves Myocardial Dysfunction by Suppressing Poly(ADP-Ribose) Polymerase 1 Activity

Under high glucose conditions, endothelial cells respond by acquiring fibroblast characteristics, that is, endothelial-to-mesenchymal transition (EndMT), contributing to diabetic cardiac fibrosis. Glucagon-like peptide-1 (GLP-1) has cardioprotective properties independent of its glucose-lowering effect. However, the potential mechanism has not been fully clarified. Here we investigated whether GLP-1 inhibits myocardial EndMT in diabetic mice and whether this is mediated by suppressing poly(ADP-ribose) polymerase 1 (PARP-1). Streptozotocin diabetic C57BL/6 mice were treated with or without GLP-1 analog (24 nmol/kg daily) for 24 wks. Transthoracic echocardiography was performed to assess cardiac function. Human aortic endothelial cells (HAECs) were cultured in normal glucose (NG) (5.5 mmol/L) or high glucose (HG) (30 mmol/L) medium with or without GLP-1analog. Immunofluorescent staining and Western blot were performed to evaluate EndMT and PARP-1 activity. Diabetes mellitus attenuated cardiac function and increased cardiac fibrosis. Treatment with the GLP-1 analog improved diabetes mellitus-related cardiac dysfunction and cardiac fibrosis. Immunofluorescence staining revealed that hyperglycemia markedly increased the percentage of von Willebrand factor (vWF)(+)/alpha smooth muscle actin (α-SMA)(+) cells in total α-SMA(+) cells in diabetic hearts compared with controls, which was attenuated by GLP-1 analog treatment. In cultured HAECs, immunofluorescent staining and Western blot also showed that both GLP-1 analog and PARP-1 gene silencing could inhibit the HG-induced EndMT. In addition, GLP-1 analog could attenuate PARP-1 activation by decreasing the level of reactive oxygen species (ROS). Therefore, GLP-1 treatment could protect against the hyperglycemia-induced EndMT and myocardial dysfunction. This effect is mediated, at least partially, by suppressing PARP-1 activation.

Dipeptidyl peptidase 4 inhibitor reduces intimal hyperplasia in rabbit autologous jugular vein graft under poor distal runoff

BACKGROUND

Dipeptidyl peptidase 4 inhibitors are widely used in patients with type 2 diabetes mellitus to accomplish glycemic control through an increase in the blood glucagon-like peptide 1 (GLP-1) concentration. These agents also inhibit vascular inflammation (eg, in atherosclerosis). This study was undertaken to determine whether and how vildagliptin (a potent dipeptidyl peptidase 4 inhibitor) might reduce intimal hyperplasia in vein grafts.

METHODS

Twelve rabbits were randomly divided into two groups; one group received vildagliptin orally (10 mg/kg/d; n = 6), whereas the control group (n = 6) did not. Vildagliptin administration was started 7 days before rabbits underwent interposition reversed autologous jugular vein grafting and ended at graft harvesting (28 days after the operation). Histochemical changes in the vascular wall were examined, as were changes in the acetylcholine-induced effects on the endothelial Ca(2+) concentration ([Ca(2+)]i) and endothelium-dependent relaxation.

RESULTS

Under fasting conditions, vildagliptin increased the plasma GLP-1 concentration, without affecting plasma glucose or insulin. Acetylcholine induced endothelium-dependent relaxation only in the vildagliptin group, and this was blocked by the nitric oxide synthase inhibitor N(ω)-nitro-l-arginine. Acetylcholine did not modify the endothelial [Ca(2+)]i in either the control or vildagliptin group. Intimal hyperplasia was significantly less in the vildagliptin group (0.11 ± 0.02 mm, n = 5) than in the controls (0.31 ± 0.06 mm, n = 4; P < .01).

CONCLUSIONS

Vildagliptin increased the plasma GLP-1 concentration. It also enhanced acetylcholine-induced [Ca(2+)]i-independent endothelial nitric oxide release and reduced vein graft intimal hyperplasia, independently of any glycemic control action.

Gliptin and GLP-1 analog treatment improves survival and vascular inflammation/dysfunction in animals with lipopolysaccharide-induced endotoxemia

Dipeptidyl peptidase (DPP)-4 inhibitors are used to treat hyperglycemia by increasing the incretin glucagon-like peptide-1 (GLP-1). Previous studies showed anti-inflammatory and antiatherosclerotic effects of DPP-4 inhibitors. Here, we compared the effects of linagliptin versus sitagliptin and liraglutide on survival and vascular function in animal models of endotoxic shock by prophylactic therapy and treatment after lipopolysaccharide (LPS) injection. Gliptins were administered either orally or subcutaneously: linagliptin (5 mg/kg/day), sitagliptin (50 mg/kg/day) or liraglutide (200 µg/kg/day). Endotoxic shock was induced by LPS injection (mice 17.5-20 mg/kg i.p., rats 10 mg/kg/day). Linagliptin and liraglutide treatment or DPP-4 knockout improved the survival of endotoxemic mice, while sitagliptin was ineffective. Linagliptin, liraglutide and sitagliptin ameliorated LPS-induced hypotension and vascular dysfunction in endotoxemic rats, suppressed inflammatory parameters such as whole blood nitrosyl-iron hemoglobin (leukocyte-inducible nitric oxide synthase activity) or aortic mRNA expression of markers of inflammation as well as whole blood and aortic reactive oxygen species formation. Hemostasis (tail bleeding time, activated partial thromboplastin time) was impaired in endotoxemic rats and recovered under cotreatment with linagliptin and liraglutide. Finally, the beneficial effects of linagliptin on vascular function and inflammatory parameters in endotoxemic mice were impaired in AMP-activated kinase (alpha1) knockout mice. The improved survival of endotoxemic animals and other data shown here may warrant further clinical evaluation of these drugs in patients with septic shock beyond the potential improvement of inflammatory complications in diabetic individuals with special emphasis on the role of AMP-activated kinase (alpha1) in the DPP-4/GLP-1 cascade.

Sitagliptin protects rat kidneys from acute ischemia-reperfusion injury via upregulation of GLP-1 and GLP-1 receptors

AIM

Sitagliptin, an oral glucose-lowering agent, has been found to produce cardiovascular protection possibly via anti-inflammatory and anti-atherosclerotic activities of glucagon-like peptide-1 receptor (GLP-1). The aim of this study was to investigate whether sitagliptin protected the kidney function from acute ischemia-reperfusion (IR) injury in rats.

METHODS

Adult male SD rats were categorized into 4 groups: sham control, IR injury, IR+sitagliptin (300 mg/kg) and IR+sitagliptin (600 mg/kg). Acute renal IR injury of both kidneys was induced by clamping the renal pedicles for 1 h. The drug was orally administered at 1, 24 and 48 h after acute IR. Blood samples and 24-h urine were collected before and at 72 h after acute IR. Then the rats were sacrificed, and the kidneys were harvested for biochemical and immunohistochemical studies.

RESULTS

Acute IR procedure markedly increased serum levels of creatinine and BUN and the ratio of urine protein to creatinine. The kidney injury score, inflammatory biomarkers (MMP-9, TNF-α and NF-κB) levels and CD68+ cells in IR kidneys were considerably increased. The expression of oxidized protein, reactive oxygen species (NOX-1, NOX-2) and apoptosis proteins (Bax, caspase-3, PARP) in IR kidneys was also significantly upregulated. All these pathological changes were suppressed by sitagliptin in a dose-dependent manner. Furthermore, the serum GLP-1 level, and the expression of GLP-1 receptor, anti-oxidant biomarkers (HO-1 and NQO-1 cells, as well as SOD-1, NQO-1 and HO-1 proteins), and angiogenesis markers (SDF-1α+ and CXCR4+ cells) in IR kidneys were significantly increased, and further upregulated by sitagliptin.

CONCLUSION

Sitagliptin dose-dependently protects rat kidneys from acute IR injury via upregulation of serum GLP-1 and GLP-1 receptor expression in kidneys.

Animal models of diabetic macrovascular complications: key players in the development of new therapeutic approaches

Diabetes mellitus is a lifelong, incapacitating metabolic disease associated with chronic macrovascular complications (coronary heart disease, stroke, and peripheral vascular disease) and microvascular disorders leading to damage of the kidneys (nephropathy) and eyes (retinopathy). Based on the current trends, the rising prevalence of diabetes worldwide will lead to increased cardiovascular morbidity and mortality. Therefore, novel means to prevent and treat these complications are needed. Under the auspices of the IMI (Innovative Medicines Initiative), the SUMMIT (SUrrogate markers for Micro- and Macrovascular hard end points for Innovative diabetes Tools) consortium is working on the development of novel animal models that better replicate vascular complications of diabetes and on the characterization of the available models. In the past years, with the high level of genomic information available and more advanced molecular tools, a very large number of models has been created. Selecting the right model for a specific study is not a trivial task and will have an impact on the study results and their interpretation. This review gathers information on the available experimental animal models of diabetic macrovascular complications and evaluates their pros and cons for research purposes as well as for drug development.

Inhibition of dipeptidyl peptidase-IV enzyme activity protects against myocardial ischemia-reperfusion injury in rats

Background

We investigated whether attenuating dipeptidyl peptidase-IV (DPP4) enzyme activity protected rat heart from ischemia-reperfusion (IR) injury (40-min left anterior descending coronary artery ligation followed by 72 h reperfusion).

Methods and results

Adult male Fischer 344 rats (n = 24) were equally divided into sham-control (WT-SC), WT-IR, and WT-IR-Sita (oral sitagliptin 400 mg/kg/day for 3 days) groups, whereas adult male DPP4-deficiency (DPP4^D) rats (n = 16) were equally divided into DPP4^D-SC and DPP4^D-IR groups. Animals were sacrificed at 72 h after reperfusion with collection of heart specimens. Infarct area (H&E), collagen deposition (Sirius-red stain), fibrotic area (Masson's trichrome), and fluorescent-ROS intensity (H₂DCFDA-labeling myocardium) of left ventricle were significantly higher in WT-IR than those in other groups, significantly higher in WT-IR-Sita and DPP4^D-IR groups than in WT-SC and DPP4^D-SC groups (all p < 0.001), but there was no difference between the latter two groups. Protein expressions of oxidative stress (oxidized protein), reactive oxygen species (NOX-1, NOX-2), inflammation (TNF-α, NF-κB, MMP-9, VCAM-1), apoptosis (mitochondrial Bax, cleaved caspase-3 and PARP), myocardial damage markers (cytosolic cytochrome-C, γ-H2AX), and number of inflammatory cells (CD14+, CD68+, CD40+ cells) showed a pattern identical to that of histological changes among all groups (all p < 0.005), whereas markers of anti-apoptosis (Bcl-2) and mitochondrial integrity (mitochondrial cytochrome-C) as well as left ventricular ejection fraction showed an opposite pattern (all p < 0.001). Protein expressions of anti-oxidants (HO-1, NQO-1), angiogenesis factors (SDF-1α, CXCR4), and glycogen-like-peptide-1-receptor were significantly higher inWT-IR-Sita and DPP4^D-IR than those in other groups (all p < 0.001).

Conclusion

Abrogation of DPP4 activity protects against myocardial IR injury and preserved heart function.

C-reactive protein promotes atherosclerosis by increasing LDL transcytosis across endothelial cells

BACKGROUND AND PURPOSE

The retention of plasma low-density lipoprotein (LDL) particles in subendothelial space following transcytosis across the endothelium is the initial step of atherosclerosis. Whether or not C-reactive protein (CRP) can directly affect the transcytosis of LDL is not clear. Here we have examined the effect of CRP on transcytosis of LDL across endothelial cells and have explored the underlying mechanisms.

EXPERIMENTAL APPROACH

Effects of CRP on transcytosis of FITC-labelled LDL were examined with human umbilical vein endothelial cells and venous rings in vitro and, in vivo, ApoE(-/-) mice. Laser scanning confocal microscopy, immunohistochemistry and Oil Red O staining were used to assay LDL.

KEY RESULTS

CRP increased transcytosis of LDL. An NADPH oxidase inhibitor, diphenylene iodonium, and the reducing agent, dithiothreitol partly or completely blocked CRP-stimulated increase of LDL transcytosis. The PKC inhibitor, bisindolylmaleimide I and the Src kinase inhibitor, PP2, blocked the trafficking of the molecules responsible for transcytosis. Confocal imaging analysis revealed that CRP stimulated LDL uptake by endothelial cells and vessel walls. In ApoE(-/-) mice, CRP significantly promoted early changes of atherosclerosis, which were blocked by inhibitors of transcytosis.

CONCLUSIONS AND IMPLICATIONS

CRP promoted atherosclerosis by directly increasing the transcytosis of LDL across endothelial cells and increasing LDL retention in vascular walls. These actions of CRP were associated with generation of reactive oxygen species, activation of PKC and Src, and translocation of caveolar or soluble forms of the N-ethylmaleimide-sensitive factor attachment protein.

Selective targeting of glucagon-like peptide-1 signalling as a novel therapeutic approach for cardiovascular disease in diabetes

Glucagon-like peptide-1 (GLP-1) is an incretin hormone whose glucose-dependent insulinotropic actions have been harnessed as a novel therapy for glycaemic control in type 2 diabetes. Although it has been known for some time that the GLP-1 receptor is expressed in the CVS where it mediates important physiological actions, it is only recently that specific cardiovascular effects of GLP-1 in the setting of diabetes have been described. GLP-1 confers indirect benefits in cardiovascular disease (CVD) under both normal and hyperglycaemic conditions via reducing established risk factors, such as hypertension, dyslipidaemia and obesity, which are markedly increased in diabetes. Emerging evidence indicates that GLP-1 also exerts direct effects on specific aspects of diabetic CVD, such as endothelial dysfunction, inflammation, angiogenesis and adverse cardiac remodelling. However, the majority of studies have employed experimental models of diabetic CVD and information on the effects of GLP-1 in the clinical setting is limited, although several large-scale trials are ongoing. It is clearly important to gain a detailed knowledge of the cardiovascular actions of GLP-1 in diabetes given the large number of patients currently receiving GLP-1-based therapies. This review will therefore discuss current understanding of the effects of GLP-1 on both cardiovascular risk factors in diabetes and direct actions on the heart and vasculature in this setting and the evidence implicating specific targeting of GLP-1 as a novel therapy for CVD in diabetes.

Cardiovascular impact of drugs used in the treatment of diabetes

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

Treating coronary disease and the impact of endothelial dysfunction

Ischemic heart disease is the leading cause of morbidity and mortality throughout the world. Many clinical trials have suggested that lifestyle and pharmacologic interventions are effective in attenuating atherosclerotic disease progression and events development. However, an individualized approach with careful consideration to comprehensive vascular health is necessary to perform successful intervention strategies. Endothelial dysfunction plays a pivotal role in the early stage of atherosclerosis and is also associated with plaque progression and occurrence of atherosclerotic complications. The assessment of endothelial function provides us with important information about individual patient risk, progress and vulnerability of disease, and guidance of therapy. Thus, the application of endothelial function assessment might enable clinicians to innovate ideal individualized medicine. In this review, we summarize the current knowledge on the impact of pharmacological therapies for atherosclerotic cardiovascular disease on endothelial dysfunction, and argue for the utility of non-invasive assessment of endothelial function aiming at individualized medicine.

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

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

Vildagliptin stimulates endothelial cell network formation and ischemia-induced revascularization via an endothelial nitric-oxide synthase-dependent mechanism

Dipeptidyl peptidase-4 inhibitors are known to lower glucose levels and are also beneficial in the management of cardiovascular disease. Here, we investigated whether a dipeptidyl peptidase-4 inhibitor, vildagliptin, modulates endothelial cell network formation and revascularization processes in vitro and in vivo. Treatment with vildagliptin enhanced blood flow recovery and capillary density in the ischemic limbs of wild-type mice, with accompanying increases in phosphorylation of Akt and endothelial nitric-oxide synthase (eNOS). In contrast to wild-type mice, treatment with vildagliptin did not improve blood flow in ischemic muscles of eNOS-deficient mice. Treatment with vildagliptin increased the levels of glucagon-like peptide-1 (GLP-1) and adiponectin, which have protective effects on the vasculature. Both vildagliptin and GLP-1 increased the differentiation of cultured human umbilical vein endothelial cells (HUVECs) into vascular-like structures, although vildagliptin was less effective than GLP-1. GLP-1 and vildagliptin also stimulated the phosphorylation of Akt and eNOS in HUVECs. Pretreatment with a PI3 kinase or NOS inhibitor blocked the stimulatory effects of both vildagliptin and GLP-1 on HUVEC differentiation. Furthermore, treatment with vildagliptin only partially increased the limb flow of ischemic muscle in adiponectin-deficient mice in vivo. GLP-1, but not vildagliptin, significantly increased adiponectin expression in differentiated 3T3-L1 adipocytes in vitro. These data indicate that vildagliptin promotes endothelial cell function via eNOS signaling, an effect that may be mediated by both GLP-1-dependent and GLP-1-independent mechanisms. The beneficial activity of GLP-1 for revascularization may also be partially mediated by its ability to increase adiponectin production.

Impact of sitagliptin on carotid intima-media thickness in patients with coronary artery disease and impaired glucose tolerance or mild diabetes mellitus

Sitagliptin has been widely used for the treatment of diabetes and shown recently to have beneficial pleiotropic outcomes on cardiovascular systems in experimental studies. However, little is known about the influence of sitagliptin on atherosclerosis-related cardiovascular diseases in a clinical setting. This study examined the effect of sitagliptin on carotid intima-media thickness (IMT). A total of 76 patients with clinically stable and documented coronary artery disease, who were newly diagnosed with impaired glucose tolerance or mild type 2 diabetes mellitus, were allocated, randomly, to receive either sitagliptin 100 mg/day or the placebo control. Common carotid IMT, glucose profiles, glycosylated hemoglobin (HbA1c), and lipid profiles were measured at baseline and repeated at 12 months. Sitagliptin-treated patients showed less IMT progression than the control group (p = 0.02). In addition, the sitagliptin group showed greater reductions in body weight (2.2%), 2-hour glucose levels on the 75-g oral glucose tolerance test (17.3%), HbA1c (4.7%), and low-density lipoprotein cholesterol levels (7.9%) from that at baseline. In conclusion, treatment with sitagliptin for 12 months was associated with a beneficial effect in the prevention of carotid IMT progression, compared with the diet control.

Significance of vascular dipeptidyl peptidase-4 inhibition on vascular protection in Zucker diabetic fatty rats

To clarify the role of dipeptidyl peptidase-4 (DPP-4) inhibition in vascular tissues, we compared the effects of the poorly tissue-penetrative DPP-4 inhibitor sitagliptin to the highly tissue-penetrative DPP-4 inhibitor linagliptin in Zucker diabetic fatty (ZDF) rats. Six-week-old ZDF rats were orally treated with placebo, sitagliptin (10 mg/kg), or linagliptin (3 mg/kg) for 4 weeks. Sitagliptin and linagliptin produced equivalent decreases in blood glucose concentrations and increased plasma insulin concentrations during oral glucose tolerance tests after the first and the last treatments. In isolated arteries, acetylcholine-induced vascular relaxation was significantly augmented by sitagliptin and linagliptin, with significantly stronger relaxation observed with linagliptin compared to sitagliptin. Vascular DPP-4 activity was attenuated by these drugs, with linagliptin producing significant greater attenuation than sitagliptin. Vascular malondialdehide levels were significantly lower with linagliptin compared to sitagliptin. Significantly greater attenuation of vascular gene expressions of p22(phox) and monocyte chemoattractant protein-1 by linagliptin, compared with sitagliptin, was also observed. In conclusion, the superior vascular protection by linagliptin compared with sitagliptin was unrelated to the regulation of circulating glucose and insulin levels, and the stronger vascular DPP-4 inhibition by linagliptin may contribute to the mechanism of vascular protection.

Emerging roles of dipeptidyl peptidase 4 inhibitors: anti-inflammatory and immunomodulatory effect and its application in diabetes mellitus

Dipeptidyl peptidase 4 (DPP4) inhibitors have been widely used in the treatment of type 2 diabetes mellitus. It is well known that DPP4 inhibitors exert their antidiabetes effects mainly by inhibiting the enzymatic degradation of glucagon-like peptide-1 and glucose-dependent insulinotropic peptide. The anti-inflammatory effect of DPP4 inhibitors was proved by preclinical and clinical studies of type 2 diabetes and coronary artery disease. Preclinical data using DPP4 inhibitors-based therapies in studies of nonobese diabetic mice demonstrated additional effects, including immunomodulation, preserving beta-cell mass, promoting beta-cell regeneration and reversing newly diagnosed diabetes. Thus, these data show that DPP4 inhibitors may be effective for type 1 diabetes mellitus. However, their potential clinical benefits for type 1 diabetes remain to be evaluated. This paper will provide an overview of the progress of the anti-inflammatory and immunomodulatory effects of DPP4 inhibitors in treating both type 1 and type 2 diabetes.

Dipeptidyl petidase-IV inhibitor (gemigliptin) inhibits tunicamycin-induced endoplasmic reticulum stress, apoptosis and inflammation in H9c2 cardiomyocytes

The direct effects of dipeptidyl peptidase-IV (DPP-IV) inhibitors on endoplasmic reticulum (ER) stress-induced apoptosis and inflammation in cardiomyocytes have not been elucidated. H9c2 cell viability, which was reduced by tunicamycin, was increased after DPP-IV inhibitor gemigliptin treatment. Gemigliptin significantly decreased the tunicamycin-mediated increase in glucose regulated protein 78 (GRP78) expression and ER stress-mediated signaling molecules such as protein kinase RNA-like endoplasmic reticulum kinase (PERK)/C-EBP homologous protein (CHOP) and inositol-requiring enzyme 1α (IRE1α)/c-Jun N-terminal kinase (JNK)-p38. Furthermore, gemigliptin effectively induced Akt phosphorylation in a dose-dependent manner. Using flow cytometry and Hoechst staining, we showed that treatment with Akt inhibitor significantly blocked the anti-apoptotic effects mediated by gemigliptin. The reduction in tunicamycin-induced GRP78 level and PERK/CHOP pathway activity by gemigliptin was reversed after treatment with Akt inhibitor. In conclusion, gemigliptin effectively inhibited ER stress-induced apoptosis and inflammation in cardiomyocytes via Akt/PERK/CHOP and IRE1α/JNK-p38 pathways, suggesting its direct protective role in cardiovascular diseases.

The DPP-4 inhibitor sitagliptin and endothelial function in patients with acute coronary syndromes and newly detected glucose perturbations: A report from the BEGAMI study

OBJECTIVE

Compromised endothelial function contributes to poor prognosis in patients with coronary artery disease and type 2 diabetes. Incretin-based therapy may exert beneficial cardiovascular effects beyond glucose lowering. We tested whether sitagliptin improves endothelial function.

RESEARCH DESIGN AND METHODS

In the double-blind BEta-cell function in patients with Glucose Abnormalities and Acute Myocardial Infarction (BEGAMI) trial, acute coronary syndrome (ACS)-patients with newly detected impaired glucose tolerance (IGT) or type 2 diabetes mellitus (T2DM) were randomised to sitagliptin 100 mg (n = 31) or placebo (n = 33) during 12 weeks. Endothelial function was studied as reactive hyperaemia index (RHI).

RESULTS

At baseline, the RHI was slightly compromised in both groups (sitagliptin 1.67; Q1;Q3: 1.46;2.17 vs placebo 1.61; 1.44;1.96; ns). The RHI did not change during the study period and was 1.57 (1.40;2.36) in the sitagliptin and 1.60 (1.46;1.81; ns) in the placebo group after treatment.

CONCLUSION

Sitagliptin did not improve endothelial function in patients with ACS and newly detected glucose perturbations.

The dipeptidyl peptidase-4 inhibitor sitagliptin protects against dyslipidemia-related kidney injury in Apolipoprotein E knockout mice

The goal of this study was to investigate the possible protective effects of sitagliptin against dyslipidemia-related kidney injury in apolipoprotein E knockout (apoE^−/−) mice. Eight-week-old male apoE^−/− mice were randomized to receive either a high fat diet (HFD, apoE^−/− group) or HFD mixed with sitagliptin (sita + apoE^−/− group) for 16 weeks. A control group of age- and gender-matched C57BL/6J mice were fed a HFD. The apoE^−/− group exhibited increases in body weight and serum lipid levels in addition to high-density lipoprotein, and increases in 24-h urinary 8-hydroxy-2-deoxyguanosine and albuminuria excretion. Decreased insulin sensitivity was also observed in the apoE^−/− group. These mice additionally contained enlargements of the glomerular mesangial matrix area, lipid deposition area, and renal interstitium collagen area. The apoE^−/− group also demonstrated down-regulation of phosphorylated AMP-activated protein kinase (AMPK), increases in renal mRNA expression of transforming growth factor-beta 1 (TGF-β1) and fibronectin (FN), and increased protein expression of Akt, TGF-β1, FN and p38/ERK mitogen-activated protein kinase (MAPK). Sitagliptin treatment successfully ameliorated all the deleterious effects of dyslipidemia tested. To our knowledge, this is the first time that sitagliptin has been shown to reverse the renal dysfunction and structural damage induced by dyslipidemia in apoE^−/− mice. Our results suggest that the renoprotective mechanism of sitagliptin may be due to a reduction in Akt levels, a restoration of AMPK activity, and inhibition of TGF-β1, FN, and p38/ERK MAPK signaling pathways.

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.

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

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

Increased plasma DPP4 activities predict new-onset atherosclerosis in association with its proinflammatory effects in Chinese over a four year period: A prospective study

OBJECTIVE

DPP4, a novel proinflammatory cytokine, is involved in the inflammatory process through its interaction with IGF-II/M6P receptor. We aimed to investigate whether it could predict new-onset atherosclerosis in Chinese.

METHODS

A prospective study was conducted of 590 adults (213 men and 377 women) aged 18-70 years without atherosclerosis examined in 2007(baseline) and 2011(follow-up). Circulating DPP4 activity, inflammatory markers, IGF-II/M6P receptor and common carotid artery Intima-Media Thickness (C-IMT) were measured at baseline and four years later.

RESULTS

At baseline, individuals in the highest quartile of DPP4 activity had higher age, WHR, BMI, SBP, fasting insulin, 2h-PG, TG, LDL-C, IL-6, hs-CRP, IGF-II/M6P-R, C-IMT and lower HDL-C compared with individuals in the lowest quartile. After a 4-year follow-up, 71 individuals developed atherosclerosis. In multiple linear regression analysis, baseline DPP4 activity was an independent predictor of an increase in inflammatory markers, IGF-II/M6P receptor, and C-IMT over a 4-year period (all P < 0.01). In multivariable-adjusted models, the odds ratio (OR) for incident atherosclerosis comparing the highest with the lowest quartiles of DPP4 activity was 3.17 (95%CI 1.33-7.58) after adjustment for confounding risk factors (P = 0.009). The incidence of atherosclerosis owing to DPP4 activity increased by 12.41%.

CONCLUSIONS

DPP4 activity is an important predictor of the onset of inflammation and atherosclerosis in apparently healthy Chinese. This finding may have important implications for understanding the proinflammatory role of DPP-4 in the pathogenesis of atherosclerosis.

Exendin-4 inhibits endothelial protein C receptor shedding in vitro and in vivo

Exendin-4 (EX4), a glucagon-like peptide-1 receptor agonist, has been reported to attenuate myocardial ischemia and reperfusion (I/R) injury, inflammatory and oxidative responses. Increasing evidence has demonstrated that beyond its role in activation of protein C, endothelial cell protein C receptor (EPCR) is involved in vascular inflammation. EPCR activity is markedly decreased by ectodomain cleavage and release as the soluble EPCR. EPCR can be shed from the cell surface, which is mediated by tumor necrosis factor-α converting enzyme (TACE). However, little is known about the effects of EX4 on EPCR shedding. Data from this study showed that EX4 induced potent inhibition of phorbol-12-myristate 13-acetate (PMA), tumor necrosis factor (TNF)-α, and interleukin (IL)-1β-induced EPCR shedding in human umbilical vein endothelial cells (HUVECs), and cecal ligation and puncture (CLP)-induced EPCR shedding in mice. EX4 also inhibited expression and activity of TACE induced by PMA in HUVECs. In addition, treatment with EX4 resulted in reduced PMA-stimulated phosphorylation of p38, extracellular regulated kinases (ERK) 1/2, and c-Jun N-terminal kinase (JNK). These results demonstrate the potential of EX4 as an anti-sEPCR shedding reagent against PMA and CLP-mediated EPCR shedding.

Role of Endothelial Cell–Derived Angptl2 in Vascular Inflammation Leading to Endothelial Dysfunction and Atherosclerosis Progression

Objective—

Cardiovascular disease (CVD), the most common morbidity resulting from atherosclerosis, remains a frequent cause of death. Efforts to develop effective therapeutic strategies have focused on vascular inflammation as a critical pathology driving atherosclerosis progression. Nonetheless, molecular mechanisms underlying this activity remain unclear. Here, we ask whether angiopoietin-like protein 2 (Angptl2), a proinflammatory protein, contributes to vascular inflammation that promotes atherosclerosis progression.

Approach and Results—

Histological analysis revealed abundant Angptl2 expression in endothelial cells and macrophages infiltrating atheromatous plaques in patients with cardiovascular disease. Angptl2 knockout in apolipoprotein E–deficient mice ( ApoE −/− / Angptl2 −/− ) attenuated atherosclerosis progression by decreasing the number of macrophages infiltrating atheromatous plaques, reducing vascular inflammation. Bone marrow transplantation experiments showed that Angptl2 deficiency in endothelial cells attenuated atherosclerosis development. Conversely, ApoE −/− mice crossed with transgenic mice expressing Angptl2 driven by the Tie2 promoter ( ApoE −/− /Tie2- Angptl2 Tg), which drives Angptl2 expression in endothelial cells but not monocytes/macrophages, showed accelerated plaque formation and vascular inflammation because of increased numbers of infiltrated macrophages in atheromatous plaques. Tie2- Angptl2 Tg mice alone did not develop plaques but exhibited endothelium-dependent vasodilatory dysfunction, likely because of decreased production of endothelial cell–derived nitric oxide. Conversely, Angptl2 −/− mice exhibited less severe endothelial dysfunction than did wild-type mice when fed a high-fat diet. In vitro, Angptl2 activated proinflammatory nuclear factor-κB signaling in endothelial cells and increased monocyte/macrophage chemotaxis.

Conclusions—

Endothelial cell–derived Angptl2 accelerates vascular inflammation by activating proinflammatory signaling in endothelial cells and increasing macrophage infiltration, leading to endothelial dysfunction and atherosclerosis progression.

A glucagon-like peptide-1 analog liraglutide suppresses macrophage foam cell formation and atherosclerosis

Macrophage foam cell formation, characterized by cholesterol ester accumulation catalyzed by acyl-CoA:cholesterol acyltransferase 1 (ACAT1), is the hallmark of early atherogenesis. We previously demonstrated the suppressive effects of incretins, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), on the development of atherosclerotic lesions in apolipoprotein E-deficient (apoE(-/-)) mice. The present study was performed to evaluate the suppressive effects of these incretins and GLP-1 analogs, such as exendin-4 and liraglutide, on human macrophage foam cell formation in vitro and those of liraglutide on atherosclerotic lesion development in apoE(-/-) mice. We investigated the suppressive effects of GLP-1, GIP, exendin-4, and liraglutide against oxidized low-density lipoprotein (oxLDL)-induced foam cell formation in primary cultured human monocyte-derived macrophages. Seventeen-week-old apoE(-/-) mice were administered a long-acting GLP-1 analog liraglutide by osmotic mini-pumps for 4 weeks. Aortic atherosclerosis, oxLDL-induced foam cell formation, and related gene expression in exudate peritoneal macrophages were determined in vivo and ex vivo. Receptors for GLP-1 and GIP were expressed at high levels in human aortic smooth muscle cells and monocytes, but at relatively low levels in human macrophages and foam cells. GLP-1, GIP, exendin-4, and liraglutide significantly suppressed oxLDL-induced foam cell formation mainly associated with ACAT1 down-regulation in human monocyte-derived macrophages. The infusion of liraglutide into apoE(-/-) mice significantly retarded atherosclerotic lesions with monocyte/macrophage infiltration in the aortic wall and suppressed foam cell formation and ACAT1 expression in macrophages. These findings indicate that liraglutide could prevent the development of atherosclerotic lesions by suppressing macrophage foam cell formation mainly associated with ACAT1 down-regulation.

Dietary A1 β-casein affects gastrointestinal transit time, dipeptidyl peptidase-4 activity, and inflammatory status relative to A2 β-casein in Wistar rats

We compared the gastrointestinal effects of milk-based diets in which the β-casein component was either the A1 or A2 type in male Wistar rats fed the experimental diets for 36 or 84 h. Gastrointestinal transit time was significantly greater in the A1 group, as measured by titanium dioxide recovery in the last 24 h of feeding. Co-administration of naloxone decreased gastrointestinal transit time in the A1 diet group but not in the A2 diet group. Colonic myeloperoxidase and jejunal dipeptidyl peptidase (DPP)-4 activities were greater in the A1 group than in the A2 group. Naloxone attenuated the increase in myeloperoxidase activity but not that in DPP-4 activity in the A1 group. Naloxone did not affect myeloperoxidase activity or DPP-4 activity in the A2 group. These results confirm that A1 β-casein consumption has direct effects on gastrointestinal function via opioid-dependent (gastrointestinal transit and myeloperoxidase activity) and opioid-independent (DPP-4 activity) pathways.

The dipeptidyl peptidase-4 inhibitor teneligliptin improved endothelial dysfunction and insulin resistance in the SHR/NDmcr-cp rat model of metabolic syndrome

Diabetes mellitus, hypertension and metabolic syndrome are major risk factors for the occurrence of cardiovascular events. In this study, we used spontaneous hypertensive rat (SHR)/NDmcr-cp (cp/cp) (SHRcp) rats as a model for metabolic syndrome to examine the effects of dipeptidyl peptidase (DPP)-4 inhibition on hypertension, glucose metabolism and endothelial dysfunction. First, we confirmed that SHRcp rats showed very severe obesity, hypertension and endothelial dysfunction phenotypes from 14 to 54 weeks of age. Next, we examined whether the DPP-4 inhibitor teneligliptin (10 mg kg(-1) per day per os for 12 weeks) could modify any of these phenotypes. Treatment with teneligliptin significantly improved hyperglycemia and insulin resistance, as evidenced by an oral glucose tolerance test and homeostasis model assessment for insulin resistance, respectively. Teneligliptin showed no effects on systolic blood pressure or heart rate. In regard to endothelial function, the vasodilator response to acetylcholine was significantly impaired in SHRcp rats when compared with WKY rats. Long-term treatment with teneligliptin significantly attenuated endothelial dysfunction through the upregulation of endothelium-derived nitric oxide synthase mRNA. These results demonstrate that long-term treatment with teneligliptin significantly improved endothelial dysfunction and glucose metabolism in a rat model of metabolic syndrome, suggesting that teneligliptin treatment might be beneficial for patients with hypertension and/or diabetes.

Rationale, design, and baseline characteristics of a clinical trial for prevention of atherosclerosis in patients with insulin-treated type 2 diabetes mellitus using DPP-4 inhibitor: the Sitagliptin Preventive study of Intima-media thickness Evaluation (SPIKE)

BACKGROUND

Sitagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, is currently used to achieve glycemic targets in patients with type 2 diabetes mellitus (T2DM). The addition of DPP-4 inhibitors to ongoing insulin therapy is expected to reduce insulin dosage, leading to a reduction in the frequency of hypoglycaemia and/or weight gain. Recent studies have demonstrated potential anti-atherosclerotic effects for DPP-4 inhibitors. The aim of the present ongoing study is to assess the effects of sitagliptin on the progression of atherosclerosis in patients with insulin-treated T2DM using carotid intima-media thickness (IMT), an established marker of cardiovascular disease.

METHODS AND DESIGN

The Sitagliptin Preventive study of Intima media thickness Evaluation (SPIKE) is a prospective, randomized, open-label, blinded-endpoint, multicenter, parallel-group, comparative study. Between February 2012 and September 2012, 282 participants who failed to achieve glycemic control despite insulin therapy were recruited at 12 clinics and randomly allocated to the sitagliptin group (n = 142) or the control group (n = 140). Primary outcomes are changes in maximum and mean IMT of the common carotid artery after 24-month treatment period measured by carotid arterial echography. Secondary outcomes include changes in glycemic control, parameters related to beta-cell function and diabetic nephropathy, occurrence of cardiovascular events and adverse events such as hypoglycaemia, and biochemical markers of vascular function.

DISCUSSION

The present study is designed to assess the effects of sitagliptin on the progression of carotid IMT. Results will be available in the near future, and the findings are expected to provide new strategy to prevent atherosclerosis in patients with insulin-treated T2DM.

CLINICAL TRIAL REGISTRATION

UMIN000007396.

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

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

Impact of glucose fluctuation and monocyte subsets on coronary plaque rupture

BACKGROUND AND AIMS

It remains unclear whether glycemic fluctuation can affect plaque rupture in acute myocardial infarction (AMI). Here we investigate the impact of glucose fluctuation on plaque rupture, as observed by optical coherence tomography (OCT), and monocyte subsets in patients with AMI.

METHODS AND RESULTS

We studied 37 consecutive patients with AMI. All patients underwent OCT examination, which revealed 24 patients with plaque rupture and 13 patients without plaque rupture at the culprit site. Peripheral blood sampling was performed on admission. Three monocyte subsets (CD14(+)CD16(-), CD14(bright)CD16(+), and CD14(dim)CD16(+)) were assessed by flow cytometry. Glycemic variability, expressed as the mean amplitude of glycemic excursion (MAGE), was determined by a continuous glucose monitoring system 7 days after the onset of AMI. MAGE was significantly higher in the rupture patients than in the non-rupture patients (P=0.036). Levels of CD14(bright)CD16(+) monocytes from the rupture patients were significantly higher than those from the non-rupture patients (P=0.042). Of interest, levels of CD14(bright)CD16(+) monocytes correlated positively and significantly with MAGE (r=0.39, P=0.02).

CONCLUSION

Dynamic glucose fluctuation may be associated with coronary plaque rupture, possibly through the preferential increase in CD14(bright)CD16(+) monocyte levels.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

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

Anti-inflammatory effects of linagliptin in hemodialysis patients with diabetes

Inflammation and glycemic control are important prognosis-related factors for hemodialysis (HD) patients; moreover, inflammation affects insulin secretion. Here, we evaluated the anti-inflammatory effects of monotherapy with linagliptin-a dipeptidase-4 inhibitor-in HD patients with type 2 diabetes. We examined 21 diabetic HD patients who were not receiving oral diabetes drugs or insulin therapy and with poor glycemic control (glycated albumin [GA] level, >20%). Linagliptin (5 mg) was administered to the patients daily. The levels of prostaglandin E2 (PGE2), interleukin-6 (IL-6), high-sensitivity C-reactive protein, GA, blood glucose, and active glucagon-like peptide-1 were determined before and 6 months after treatment. Body weight and serum levels of albumin, hemoglobin, total cholesterol, and low-density lipoprotein cholesterol were also recorded before and after treatment. The levels of PGE2 and GA were significantly decreased 1 month after starting linagliptin therapy, whereas the IL-6 levels were significantly decreased 6 months after starting linagliptin therapy. After 6 months of treatment, the PGE2 levels decreased from 188 ± 50 ng/mL to 26 ± 5 ng/mL; IL-6 levels, from 1.5 ± 0.4 pg/mL to 0.6 ± 0.1 pg/mL; and GA levels, from 21.3% ± 0.6% to 18.0% ± 0.6%. Glucagon-like peptide-1 levels increased 2.5-fold during the treatment. Over the 6-month treatment period, body weight and levels of high-sensitivity C-reactive protein, blood glucose, albumin, hemoglobin, and cholesterol did not change; none of the patients exhibited hypoglycemia. The anti-inflammatory effects of linagliptin monotherapy indicate that it may serve as a useful glucose control strategy for HD patients with diabetes.

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.

Cardiovascular actions of GLP-1 and incretin-based pharmacotherapy

Incretin-based therapy became recently available as antihyperglycemic treatment for patients with type 2 diabetes (T2DM). Incretin therapy comprises glucagon-like peptide receptor agonists (GLP-1RA) and dipeptidyl-peptidase 4 inhibitors (DPP4-I): these classes of drugs not only have the ability to reduce blood glucose, but also can exert several cardioprotective effects. They have been shown to positively influence some risk factors for cardiovascular disease (CVD), to improve endothelial function, and to directly affect cardiac function. For these reasons incretins are considered not only antidiabetic drugs, but also cardiovascular effective. The first clinical trials aimed to demonstrate the safety of DPP4 inhibitors have been recently published: their clinical significance will be discussed in light of the prior experimental findings.

Dipeptidyl peptidase-4 inhibitors: multitarget drugs, not only antidiabetes drugs

Dipeptidyl peptidase (DPP)-4 inhibitors are a new class of antidiabetic agents that reduce blood glucose by preventing the degradation of the endogenous incretin hormones glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide. Protection by DPP-4 inhibitors of β-cell function has been demonstrated in patients with type 2 diabetes. Because DPP-4 is an enzyme widely expressed in humans, DPP-4 inhibitors are speculated to be multitarget agents. However, other potential therapeutic benefits of DPP-4 inhibitors remain unknown. Recently, some therapeutic effects of DPP-4 inhibitors, such as immune regulation, cardiovascular protection, and anti-inflammatory effects, have been observed. This article provides a systematic and comprehensive review of current research into the newly found effects and mechanism of action of DPP-4 inhibitors in a therapeutic context.

Exendin-4 and sitagliptin protect kidney from ischemia-reperfusion injury through suppressing oxidative stress and inflammatory reaction

BACKGROUND

This study tested the hypothesis that exendin-4 and sitagliptin can effectively protect kidney from acute ischemia-reperfusion (IR) injury.

METHODS

Adult SD-rats (n = 48) equally divided into group 1 (sham control), group 2 (IR injury), group 3 [IR + sitagliptin 600 mg/kg at post-IR 1, 24, 48 hr)], and group 4 [IR + exendin-4 10 μm/kg at 1 hr after procedure] were sacrificed after 24 and 72 hrs (n = 6 at each time from each group) following clamping of bilateral renal pedicles for 60 minutes (groups 2-4).

RESULTS

Serum creatinine level and urine protein to creatinine ratio were highest in group 2 and lowest in group 1 (all p < 0.001) without notable differences between groups 3 and 4. Kidney injury score, expressions of inflammatory biomarkers at mRNA (MMP-9, TNF-α, IL-1β, PAI-1), protein (TNF-α, NF-κB and VCAM-1), and cellular (CD68+) levels in injured kidneys at 24 and 72 hr showed an identical pattern compared to that of creatinine level in all groups (all p < 0.0001). Expressions of oxidized protein, reactive oxygen species (NOX-1, NOX-2), apoptosis (Bax, caspase-3 and PARP), and DNA damage marker (γH2AX+) of IR kidney at 24 and 72 hrs exhibited a pattern similar to that of inflammatory mediators among all groups (all p < 0.01). Renal expression of glucagon-like peptide-1 receptor, and anti-oxidant biomarkers at cellular (GPx, GR) and protein (NQO-1, HO-1, GPx) levels at 24 and 72 hr were lowest in group 1, significantly lower in group 2 than in groups 3 and 4 (all p < 0.01).

CONCLUSION

Exendin-4 and sitagliptin provided significant protection for the kidneys against acute IR injury.

Dipeptidyl peptidase IV and its inhibitors: therapeutics for type 2 diabetes and what else?

The proline-specific dipeptidyl aminopeptidase IV (DPP IV, DPP-4, CD26), widely expressed in mammalians, releases X-Pro/Ala dipeptides from the N-terminus of peptides. DPP IV is responsible of the degradation of the incretin peptide hormones regulating blood glucose levels. Several families of DPP IV inhibitors have been synthesized and evaluated. Their positive effects on the degradation of the incretins and the control of blood glucose levels have been demonstrated in biological models and in clinical trials. Presently, several DPP IV inhibitors, the "gliptins", are approved for type 2 diabetes or are under clinical evaluation. However, the gliptins may also be of therapeutic interest for other diseases beyond the inhibition of incretin degradation. In this Perspective, the biological functions and potential substrates of DPP IV enzymes are reviewed and the characteristics of the DPP IV inhibitors are discussed in view of type 2 diabetes and further therapeutic interest.

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

BACKGROUND

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

METHODS AND RESULTS

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

CONCLUSION

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

Elevated plasma GLP-1 levels and enhanced expression of cardiac GLP-1 receptors as markers of left ventricular systolic dysfunction: a cross-sectional study

OBJECTIVE

We aimed to elucidate usefulness of plasma glucagon-like peptide-1 (GLP-1) levels for the assessment of left ventricular (LV) dysfunction by examining the relationship among plasma GLP-1 levels, expression of cardiac GLP-1 receptors and LV function in patients with impaired and preserved LV function.

DESIGN

Prospective study.

SETTING

Number of participating center: 1, Gifu, Japan.

PARTICIPANTS

Number of patients enrolled: 102 patients who underwent elective cardiac catheterisation for coronary artery disease, cardiomyopathy and valvular heart disease, and 6 patients who underwent cardiac biopsy.

RESULTS

The plasma GLP-1 level was significantly increased in patients with impaired LV function (5.7±1.9 pmol/L) as compared with those with preserved LV function (2.7±1.6 pmol/L). Plasma GLP-1 and plasma brain natriuretic peptide (BNP) levels were inversely correlated with the LV ejection fraction(EF), respectively. Plasma GLP-1 level positively correlated with plasma BNP level. Multivariate logistic regression analysis revealed that plasma GLP-1 level was an independent determinant of the impaired LV function, whereas plasma BNP level was not. Intensity of immunostaining for GLP-1 receptor protein was significantly enhanced in patients with impaired LV function compared with those with preserved LV function.

CONCLUSIONS

The plasma GLP-1 level was increased in patients with impaired systolic LV function and inversely correlated with the LVEF. The expressions of GLP-1 receptors were enhanced in hearts with impaired LV function. These may suggest that endogenous GLP-1-GLP-1 receptor system serves as a compensatory mechanism for systolic LV dysfunction.

TRIAL REGISTRATION

UMIN-CTR, ID=UMIN000009361, registration number: R000011000.

The dipeptidyl peptidase-4 inhibitor-sitagliptin modulates calcium dysregulation, inflammation, and PPARs in hypertensive cardiomyocytes

BACKGROUND

Hypertension induces cardiac dysfunction, calcium (Ca(2+)) dysregulation, and arrhythmogenesis. Dipeptidyl peptidase (DPP)-4 inhibitors, an antidiabetic agent with anti-inflammation and anti-hypertension potential, may regulate peroxisome proliferator-activated receptors (PPARs)-α, -γ, and -δ and Ca(2+) homeostasis.

OBJECTIVE

The purpose of this study was to investigate whether DPP-4 inhibitor, sitagliptin, can modulate PPARs and Ca(2+) handling proteins in hypertensive hearts.

METHODS

A Western blot analysis was used to evaluate protein expressions of myocardial PPAR isoforms, tumor necrosis factor (TNF)-α, interleukin (IL)-6, sarcoplasmic reticulum ATPase (SERCA2a), Na(+)-Ca(2+) exchanger (NCX), ryanodine receptor (RyR), voltage-dependent Ca(2+) (CaV1.2), slow-voltage potassium currents (Kvs), angiotensin II type 1 receptor (AT1R), and receptor of advanced glycated end-products (RAGE) from Wistar-Kyoto (WKY) rats, spontaneously hypertensive rats (SHR), and SHR treated with sitagliptin (10mg/kg for 4weeks). Conventional microelectrodes were used to record action potentials (APs) in the ventricular myocytes from each group.

RESULTS

Compared to the control group, SHR had lower cardiac PPAR-α and PPAR-δ protein expressions, but had greater cardiac PPAR-γ levels, and TNF-α, IL-6, RAGE, and AT1R protein expressions, which were ameliorated in the sitagliptin-treated SHR. SHR had prolonged QT interval and AP duration with less SERCA2a and RyR, and greater CaV1.2 expressions, which were also attenuated in sitagliptin-treated SHR.

CONCLUSIONS

Sitagliptin significantly changed the cardiac electrophysiological characteristics and Ca(2+) regulation, which may have been caused by its effects on cardiac PPARs, proinflammatory cytokines, and AT1R.

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

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

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

Aim

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

Methods

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

Results

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

Conclusions

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