The DPP-4 inhibitor linagliptin and the GLP-1 receptor agonist exendin-4 improve endothelium-dependent relaxation of rat mesenteric arteries in the presence of high glucose

Linagliptin's impact on lymphatic barrier and lymphangiogenesis in oral cancer with high glucose

OBJECTIVES

Uncertainties remain regarding the effect of elevated glucose levels on lymphatic metastasis of cancer cells. Our study elucidated the mechanisms linking high glucose to lymphangiogenesis and lymphatic barrier-related factors and investigated the protective role of linagliptin against lymphatic barrier dysfunction.

MATERIALS AND METHODS

A CAL-27-LEC co-culture system was established. Sodium fluorescein permeability assay observed lymphatic endothelial cell permeability. Western blotting and RT-qPCR detected protein and mRNA expression under different conditions, respectively. CCK-8, scratch wound healing, and transwell assays revealed cell migration and proliferation. Tube formation experiment tested capacity for endothelial tube formation. Immunohistochemical staining analyzed tissue sections from 43 oral cancer individuals with/without diabetes.

RESULTS

In high-glucose co-culture system, we observed increased lymphatic barrier permeability and decreased expression of ZO-1 and occludin, two tight-junction proteins; conversely, the expression of PAR2, a high permeability-related protein, was increased. Following linagliptin treatment, the expression levels of VEGF-C, VEGFR-3, and PAR2 decreased, while those of ZO-1 and occludin increased. Considerably higher levels of LYVE-1 expression in individuals with diabetes than in those without diabetes.

CONCLUSIONS

By ameliorating the high glucose-induced disruption of the lymphatic endothelial barrier, linagliptin may reduce lymphangiogenesis and exhibit an inhibitory effect on lymphatic metastasis in oral cancer patients with diabetes.

Pylorus ligation-induced hyperacidity: synergistic prophylactic effects of linagliptin and L-arginine via up-regulation of EP4 receptor subtype and improvement of vascular endothelial damage

Gastric hyperacidity and ulceration are chronic diseases characterized by repeated healing followed by re-exacerbation. The study aims to protect against gastric hyperacidity without interfering with gastric acid secretion. Pylorus ligation-induced hyperacidity is commonly utilized in the induction of gastric ulcers.Forty-two rats were distributed into seven groups (n = 6). Group I comprised sham-operated group. Group II served as pylorus-ligation group. Groups III-VII were given oral Linagliptin (LN; 3 and 6 mg/kg), L-arginine (LA; 150 and 300 mg/kg) and their combination (LN 3 + LA 150 mg/kg), respectively for 7 days. On the 8th day, groups II-VII were subjected to pylorus-ligation.Treatment of pylorus-ligated rats with LN, LA and their combination improved the gastric hyperacidity as exhibited by a marked reduction in the gastric juice volume, total and free acidities and pepsin contents with a noticeable increase in pH. Pre-treatment with LN, LA and their combination showed a marked alleviation in the gastric inflammatory indicators evidenced by reduction in the gastric levels of MCP-1and Il-1β as well as elevation of eNOS levels versus the sham-operated group. A marked up-regulation in the gastric gene expression of PGE, EP4 and VEGF accompanied by an improvement of the histopathologic pictures/scores, and TNF-α and caspase-3 immuno-staining were also recorded.By estimating the combination-index, it can be concluded that combining LN with LA exhibited prophylactic synergistic effects in ameliorating pylorus ligated-induced hyperacidity, mainly via up-regulation of EP4 receptor and improvement of vascular endothelial damage through VEGF expression in gastric mucosa.

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

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

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

AIMS

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

MATERIALS AND METHODS

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

KEY FINDINGS

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

SIGNIFICANCE

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

A single dose of exenatide had no effect on blood flow velocity in the middle cerebral artery in elderly healthy volunteers: Randomized, placebo-controlled, double-blind clinical trial

Background and aims

Glucagon-like peptide 1 (GLP-1) receptor agonists (GLP-1RA) are widely used for the treatment of type 2 diabetes, and recent studies indicate that they may be cardio- and neuroprotective. The safety and effect of a single dose of exenatide, a short-acting GLP-1RA, on cerebral and peripheral arterial function remain unknown.

Methods

In this randomized, double-blind pilot trial, we assigned elderly healthy volunteers without diabetes and no previous history of stroke to receive a single dose of subcutaneous exenatide (5 μg) or placebo. Primary outcome was immediate changes over time in blood flow velocity of the middle cerebral arteries (V_MCA) assessed by repeated transcranial Doppler measurements. Secondary outcomes were changes in peripheral arterial function with finger plethysmography, ankle-brachial index (ABI), and inflammatory- and endothelial-specific biomarkers.

Results

Healthy volunteers (13 women and 17 men) were included: (mean ± standard deviation) age: 62 ± 8 years; body weight: 79.6 ± 12.7 kg; V_MCA: 65.3 ± 10.7 cm/s; fasting plasma glucose: 5.5 ± 0.5 mmol/L; HbA1c: 33.9 ± 4.1 mmol/mol (5.3 ± 0.38%). No differences between exenatide and placebo group were seen regarding V_MCA (p = 0.058), systolic ABI (p = 0.71), plethysmography (p = 0.45), tumor necrosis factor (p = 0.33), interleukin-6 (p = 0.11), interleukin-1β (p = 0.34), vascular cell adhesion molecule 1 (p = 0.73), intercellular adhesion molecule 1 (p = 0.74), or E-selectin (p = 0.31). No severe adverse events were observed.

Conclusion

A single dose of exenatide did not change cerebral blood flow velocity or peripheral vessel function in elderly healthy volunteers. The medication was safe to use in persons without diabetes allowing us to investigate this drug further in search of the neuroprotective mechanisms.

Clinical Trial Registration

https://clinicaltrials.gov, Identifier NCT02838589.

The Effect of an Atherogenic Diet and Acute Hyperglycaemia on Endothelial Function in Rabbits Is Artery Specific

Hyperglycaemia has a toxic effect on blood vessels and promotes coronary artery disease. It is unclear whether the dysfunction caused by hyperglycaemia is blood vessel specific and whether the dysfunction is exacerbated following an atherogenic diet. Abdominal aorta, iliac, and mesenteric arteries were dissected from New Zealand White rabbits following either a 4-week normal or atherogenic diet (n = 6–12 per group). The arteries were incubated ex vivo in control or high glucose solution (20 mM or 40 mM) for 2 h. Isometric tension myography was used to determine endothelial-dependent vasodilation. The atherogenic diet reduced relaxation as measured by area under the curve (AUC) by 25% (p < 0.05), 17% (p = 0.06) and 40% (p = 0.07) in the aorta, iliac, and mesenteric arteries, respectively. In the aorta from the atherogenic diet fed rabbits, the 20 mM glucose altered EC₅₀ (p < 0.05). Incubation of the iliac artery from atherogenic diet fed rabbits in 40 mM glucose altered EC₅₀ (p < 0.05). No dysfunction occurred in the mesentery with high glucose incubation following either the normal or atherogenic diet. High glucose induced endothelial dysfunction appears to be blood vessel specific and the aorta may be the optimal artery to study potential therapeutic treatments of hyperglycaemia induced endothelial dysfunction.

Exendin-4, a GLP-1 receptor agonist regulates retinal capillary tone and restores microvascular patency after ischaemia-reperfusion injury

Background and Purpose

The aim of this study is to investigate the vasorelaxant effect of exendin‐4, a GLP‐1 receptor agonist on retinal capillaries under normal and ischaemia–reperfusion (I/R) conditions.

Experimental Approach

Capillary diameters in the whole‐mounted retina were directly observed using infrared differential interference contrast microscopy. A model of retinal I/R was established inraats,using high perfusion pressure in an anterior chamber. To assess the effects of exendin‐4, it was administered through subcutaneous injection, intravitreal injection, or eye drops. The underlying mechanism was explored by immunofluorescence, qPCR, and capillary western blots.

Key Results

Immunofluorescence staining showed that GLP‐1 receptors were expressed in endothelial cells of retinal capillaries. Exendin‐4 relaxed the capillaries precontracted by noradrenaline, an effect abolished by denuding endothelium with CHAPS and inhibited by GLP‐1 receptor antagonist exendin‐9‐39, endothelial NOS (eNOS) inhibitor l‐NAME, and the guanylate cyclase blocker ODQ but not by a COX inhibitor, indomethacin. Retinal capillaries were constricted in I/R injury, an effect reversed by perfusion of exendin‐4. Expression of PI3K and Akt, phosphorylation level of eNOS and NO production after I/R were lower than that in the normal control group. Administration of exendin‐4 improved the changes.

Conclusion and Implications

Exendin‐4 can restore injured microvascular patency in I/R. Exendin‐4 may regulate retinal capillaries through the GLP‐1 receptor‐PI3K/Akt‐eNOS/NO‐cGMP pathway. Therefore, exendin‐4 may be an effective treatment for improving tissue perfusion in I/R‐related conditions.

DPP-4 inhibition by linagliptin prevents cardiac dysfunction and inflammation by targeting the Nlrp3/ASC inflammasome

We compared the effects of linagliptin (Lina, a DPP4 inhibitor) and GLP-1 receptor activation by exenatide followed by exendin-4 in an infusion pump (EX) on infarct size (IS), post-infarction activation of the inflammasome and remodeling in wild-type (WT) and db/db diabetic mice. Mice underwent 30 min ischemia followed by 24 h reperfusion. IS was assessed by TTC. Additional mice underwent permanent coronary artery occlusion. Echocardiography was performed 2w after infarction. Activation of the inflammasome in the border zone of the infarction was assessed by rt-PCR and ELISA 2w after reperfusion. Further in vitro experiments were done using primary human cardiofibroblasts and cardiomyocytes exposed to simulated ischemia-reoxygenation. Lina and EX limited IS in both the WT and the db/db mice. Lina and EX equally improved ejection fraction in both the WT and the db/db mice. mRNA levels of ASC, NALP3, IL-1β, IL-6, Collagen-1, and Collagen-3 were higher in the db/db mice than in the WT mice. Infarction increased these levels in the WT and db/db mice. Lina more than EX attenuated the increase in ASC, NALP3, IL-1β, IL-6, Collagen-1 and Collagen-3, TNFα and IL-1β, and decreased apoptosis, especially in the db/db mice. In vitro experiments showed that Lina, but not EX, attenuated the increase in TLR4 expression, an effect that was dependent on p38 activation with downstream upregulation of Let-7i and miR-146b levels. Lina and EX had similar effects on IS and post-infarction function, but Lina attenuated the activation of the inflammasome and the upregulation of collagen-1 and collagen-3 more than direct GLP-1 receptor activation. This effect depends on p38 activation with downstream upregulation of miR-146b levels that suppresses TLR4 expression.

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

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

Combined treatment with DPP-4 inhibitor linagliptin and SGLT2 inhibitor empagliflozin attenuates neointima formation after vascular injury in diabetic mice

Incretin therapy has emerged as one of the most popular medications for type 2 diabetes. We have previously reported that the dipeptidyl peptidase-4 (DPP-4) inhibitor linagliptin attenuates neointima formation after vascular injury in non-diabetic mice. In the present study, we examined whether combined treatment with linagliptin and the sodium glucose cotransporter 2 (SGLT2) inhibitor empagliflozin attenuates neointima formation in diabetic mice after vascular injury. Diabetic db/db mice were treated with 3 mg/kg/day linagliptin and/or 30 mg/kg/day empagliflozin from 5 to 10 weeks of age. Body weight was significantly decreased by empagliflozin and the combined treatment. Blood glucose levels and glucose tolerance test results were significantly improved by empagliflozin and the combined treatment, but not by linagliptin. An insulin tolerance test suggested that linagliptin and empagliflozin did not improve insulin sensitivity. In a model of guidewire-induced femoral artery injury in diabetic mice, neointima formation was significantly decreased in mice subjected to combined treatment. In an in vitro assay using rat aortic smooth muscle cells (RASMC), 100, 500, or 1000 nM empagliflozin significantly decreased the RASMC number in a dose-dependent manner. A further significant reduction in RASMC proliferation was observed after combined treatment with 10 nM linagliptin and 100 nM empagliflozin. These data suggest that combined treatment with the DPP-4 inhibitor linagliptin and SGLT2 inhibitor empagliflozin attenuates neointima formation after vascular injury in diabetic mice in vivo and smooth muscle cell proliferation in vitro.

Glucagon-like peptide-1 (GLP-1) mediates the protective effects of dipeptidyl peptidase IV inhibition on pulmonary hypertension

Background

Pulmonary hypertension (PH) is a progressive disease leading to death ultimately. Our recently published data demonstrated that inhibiting dipeptidyl peptidase IV (DPP-4) alleviated pulmonary vascular remodeling in experimental PH. However, whether glucagon-like peptide-1 (GLP-1) mediated the protective effect of DPP-4 inhibition (DPP-4i) on PH is unclear.

Results

In the present study, GLP-1 receptor antagonist (exendin-3) abolished the protective effects of DPP-4 inhibitor (sitagliptin) on right ventricular systolic pressure (RVSP) and pulmonary vascular remodeling (PVR) in monocrotaline (MCT, 60 mg/kg)-induced PH in rat. Notably, activation of GLP-1 receptor by GLP-1 analogue liraglutide directly attenuated RVSP and PVR in MCT-induced PH, as well as bleomycin- and chronic hypoxia-induced PH. Moreover, liraglutide potently inhibited MCT-induced inflammation and suppressed MCT-induced down-regulation of vascular endothelial marker (VE-cadherin and vWF) in lung. In vitro studies showed liraglutide reversed TGF-β1 (5 ng/ml) combining IL-1β (5 ng/ml) induced endothelial-mesenchymal transition (EndMT) in human umbilical vein endothelial cells (HUVECs), which could be abolished by GLP-1 receptor antagonist (exendin-3). Furtermore, liraglutide suppressed TGF-β1-IL-1β-induced phosphorylation of both Smad3 and ERK1/2.

Conclusions

Our data suggest that GLP-1 mediated the protective effects of DPP-4i on pulmonary vascular and RV remodeling in experimental PH, which may be attributed to the inhibitory effect on EndMT.

THE IN VITRO CYTOTOXICITY, GENOTOXICITY AND OXIDATIVE DAMAGE POTENTIAL OF THE ORAL DIPEPTIDYL PEPTIDASE-4 INHIBITOR, LINAGLIPTIN, ON CULTURED HUMAN MONONUCLEAR BLOOD CELLS

BACKGROUND

Linagliptin (LNG) is a selective dipeptidyl peptidase-4 (DPP-4) inhibitor that ameliorates blood glucose control of patients with type 2 diabetes, without developing hypoglycemic risk and weight gain with a good clinical and biological tolerance profile. To the best of our knowledge, its cytotoxic, genotoxic and oxidative effects have never been studied on any cell line.

AIM

To evaluate the in vitro cytotoxic, genotoxic damage potential and antioxidant/oxidant activity of LNG in cultured peripheral blood mononuclear cells (PBMC).

MATERIAL AND METHODS

After exposure to different doses (from 0.5 to 500 mg/L) of LNG, cell viability was measured by the MTT (3,(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and lactate dehydrogenase (LDH) leakage tests. The antioxidant activity was assessed by the total antioxidant capacity (TAC) and total oxidative stress (TOS) assays. To evaluate the genotoxic damage potential, chromosomal aberration (CA) frequencies and 8-oxo-2'-deoxyguanosine (8-oxo-dG) levels were determined.

RESULTS

Treatment with LNG did not cause statistically significant decreases of cell viability at lower concentrations than 100 mg/L as compared to untreated cultures. However, LNG exhibited cytotoxic action at 250 and 500 mg/L. Also, IC20 and IC50 values of LNG were determined as 8.827 and 70.307 mg/L, respectively. In addition, the oxidative analysis revealed that LNG supported antioxidant capacity at concentrations of 2.5, 5, 10, 25, 50 and 100 mg/L without generating oxidative stress. Besides, the results of CA and 8-oxo-dG assays showed in vitro non-genotoxic feature of LNG. As a conclusion, our findings clearly revealed that LNG had no cytotoxic and genotoxic actions, but exhibited antioxidative activity. In conclusion, therefore it is suggested that LNG use in diabetic patients is safe and provides protection against diabetic vascular and oxidative complications.

Influence of type-4 dipeptidyl peptidase inhibition on endothelium-dependent relaxation of aortae from a db/db mouse model of type 2 diabetes: a comparison with the effect of glimepiride

PURPOSE

The aim of this study was to investigate the effects of the type-4 dipeptidyl peptidase (DPP-4) inhibitors linagliptin and vildagliptin as well as the sulfonylurea glimepiride on endothelium-dependent relaxation of aortae from female db/db mice with established hyperglycemia to determine whether these treatments were able to attenuate diabetes-induced endothelial dysfunction.

MATERIALS AND METHODS

The mice were treated with glimepiride (2 mg/kg po per day, weeks 1-6, n=12), glimepiride plus vildagliptin (glimepiride 2 mg/kg po per day, weeks 1-6; vildagliptin 3 mg/kg po per day, weeks 4-6, n=11), glimepiride plus linagliptin (glimepiride 2 mg/kg po per day, weeks 1-6; linagliptin 3 mg/kg po per day, weeks 4-6, n=11) or linagliptin (3 mg/kg po per day, weeks 1-6, n=12). Endothelium-dependent relaxation using acetylcholine was assessed in the absence and presence of pharmacological tools (TRAM-34 1 μM; apamin 1 μM; N-nitro-L-arginine [L-NNA] 100 μM; 1H-[1,2,4]oxadiazolo [4,3-a]quinoxalin-1-one [ODQ] 10 μM) to distinguish relaxation mediated by nitric oxide (NO).

RESULTS

Linagliptin was associated with a significant improvement in endothelium-dependent relaxation (ACh Rmax; db/db 41±1%, linagliptin 73±6%, p<0.05). The enhanced response was maintained in the presence of TRAM-34+ apamin (ACh Rmax; db/db 23±6%, linagliptin 60±6%, p<0.01), ie, when the endothelium-dependent relaxation was mediated by NO. There was no evidence for a contribution from K_Ca channel opening to responses under any conditions. Glimepiride had no effect on endothelium-dependent relaxation when given alone (ACh Rmax 38±3%). The addition of linagliptin or vildagliptin to glimepiride did not significantly improve endothelium-dependent relaxation. All treatments caused some decrease in aortic superoxide production but the effect of linagliptin was significantly greater than glimepiride (linagliptin 534±60 relative luminescence unit [RLU], glimepiride 1471±265 RLU, p<0.05).

CONCLUSION

Linagliptin is superior to glimepiride in regard to the preservation of endothelium-dependent relaxation in the presence of hyperglycemia and the improvement in endothelial function in response to linagliptin treatment is associated with greater antioxidant activity compared to glimepiride.

Different mechanisms involved in liraglutide and glucagon-like peptide-1 vasodilatation in rat mesenteric small arteries

BACKGROUND AND PURPOSE

Glucagon-like peptide-1 (GLP-1) is an incretin hormone that regulates insulin biosynthesis and secretion in a glucose-dependent manner and has been reported to induce vasodilatation. Here, we examined the possible vasorelaxant effect of GLP-1 and its underlying mechanisms.

EXPERIMENTAL APPROACH

Rat mesenteric arteries (diameter ≈ 200-400 μm) and human s.c. arteries were mounted in microvascular myographs for isometric tension recordings. The effect of GLP-1 on vascular responses was examined under normoglycaemic conditions and at high glucose concentrations.

KEY RESULTS

In rat mesenteric arteries and human s.c. arteries without branches, physiological concentrations (1-100 nM) of GLP-1(7-36) and liraglutide failed to cause relaxation or affect contractions evoked by electrical field stimulation. In contrast to GLP-1(7-36), liraglutide induced relaxations antagonized by the GLP-1 receptor antagonist, exendin-(9-39), in branched mesenteric arteries. In contrast to liraglutide, GLP-1 leftward shifted the concentration relaxation curves for bradykinin in s.c. arteries from patients with peripheral arterial disease, an effect resistant to exendin-(9-39). Under normoglycaemic conditions, neither GLP-1 nor liraglutide affected ACh relaxation in rat mesenteric arteries. In arteries exposed to 40 mM glucose, GLP-1, in contrast to liraglutide, potentiated ACh-induced relaxation by a mechanism that was not antagonized by exendin-(9-39). GLP-1 decreased superoxide levels measured with dihydroethidium in rat mesenteric arteries exposed to 40 mM glucose.

CONCLUSIONS AND IMPLICATIONS

GLP-1 receptors are involved in the liraglutide-induced relaxation of branched arteries, under normoglycaemic conditions, while GLP-1 inhibition of vascular superoxide levels contributes to GLP-1 receptor-independent potentiation of endothelium-dependent vasodilatation in hyperglycaemia.

Potentiation of endothelium-dependent vasorelaxation of mesenteric arteries from spontaneously hypertensive rats by gemigliptin, a dipeptidyl peptidase-4 inhibitor class of anti-diabetic drug

Dipeptidyl peptidase4 (DPP4) inhibitors such as gemigliptin are anti-diabetic drugs elevating plasma concentration of incretins such as GLP-1. In addition to the DPP4 inhibition, gemigliptin might directly improve the functions of vessels under pathological conditions. To test this hypothesis, we investigated whether the acetylcholine-induced endothelium dependent relaxation (ACh-EDR) of mesenteric arteries (MA) are altered by gemigliptin pretreatment in Spontaneous Hypertensive Rats (SHR) and in Wistar-Kyoto rats (WKY) under hyperglycemia-like conditions (HG; 2 hr incubation with 50 mM glucose). ACh-EDR of WKY was reduced by the HG condition, which was significantly recovered by 1 µM gemigliptin while not by saxagliptin and sitagliptin up to 10 µM. The ACh-EDR of SHR MA was also improved by 1 µM gemigliptin while similar recovery was observed with higher concentration (10 µM) of saxagliptin and sitagliptin. The facilitation of ACh-EDR by gemigliptin in SHR was not observed under pretreatment with NOS inhibitor, L-NAME. In the endotheliumdenuded MA of SHR, sodium nitroprusside induced dose-dependent relaxation was not affected by gemigliptin. The ACh-EDR in WKY was decreased by treatment with 30 µM pyrogallol, a superoxide generator, which was not prevented by gemigliptin. Exendin-4, a GLP-1 analogue, could not enhance the ACh-EDR in SHR MA. The present results of ex vivo study suggest that gemigliptin enhances the NOS-mediated EDR of the HG-treated MA as well as the MA from SHR via GLP-1 receptor independent mechanism.

Dipeptidyl peptidase IV (DPP-4) inhibition alleviates pulmonary arterial remodeling in experimental pulmonary hypertension

Dipeptidyl peptidase IV (DPP-4) is well known for its role in glucose homeostasis, and DPP-4 inhibitor (DPP-4i) exhibits multiple actions in cardiovascular diseases. However, the effect of DPP-4i on pulmonary hypertension (PH) remains unclear. Therefore, this study aims to investigate the effect of DPP-4i on pulmonary arterial remodeling in rats with PH and the potential underlying mechanisms. Our results show that DPP-4 was expressed in epithelial cells, endothelial cells, smooth muscle cells, and inflammatory cells in lung. DPP-4i (Sitagliptin) attenuated right ventricular systolic pressure (RVSP), right ventricle remodeling, hypertrophy of pulmonary arterial medial layer, inflammatory cell infiltration, and endothelial-mesenchymal transition (EndMT) in monocrotaline (MCT)-induced PH rats. Similarly, DPP-4i also alleviated bleomycin- and chronic hypoxia-induced PH in rats. In cultured human pulmonary arterial smooth muscle cells (PASMCs), DPP-4i inhibited platelet derived growth factor (PDGF)-BB-induced proliferation and migration, which was abolished by phosphatase and tensin homolog deleted on chromosome ten (PTEN) knockout. These results demonstrate that DPP-4 inhibition alleviates pulmonary arterial remodeling in experimental PH by inhibiting proliferation and migration of PASMCs.

After the LEADER trial and SUSTAIN-6, how do we explain the cardiovascular benefits of some GLP-1 receptor agonists?

Recent cardiovascular outcome trials - the LEADER with liragutide and SUSTAIN-6 with semaglutide - have shown significant reductions of major cardiovascular (CV) events with these glucagon-like peptide (GLP)-1 receptor agonists. Progressive separation of the treatment and placebo curves, starting clearly between 12 and 18 months of the trial period, and significant reductions in the risk of myocardial infarction and stroke, indicate that the beneficial CV effects observed with GLP-1 receptor agonists could be due to an antiatherogenic effect. So far, the reasons for such an effect of GLP-1 receptor agonists have not been entirely clear, although several hypotheses may be proposed. As the reductions in glycated haemoglobin and systolic blood pressure (SBP) in these trials were modest, and both trials lasted only a short period of time, reductions in hyperglycaemia and SBP are unlikely to be involved in the beneficial CV effects of GLP-1 receptor agonists. On the other hand, their effect on lipids and, in particular, the dramatic decrease in postprandial hypertriglyceridaemia may explain their beneficial CV actions. Reduction of body weight, including a significant decrease in visceral fat in patients using GLP-1 receptor agonists, may also have beneficial CV effects by reducing chronic proatherogenic inflammation. In addition, there are in-vitro data showing a direct anti-inflammatory effect with these agents that could also be involved in their beneficial CV effects. Moreover, studies in humans have shown significant beneficial effects on ischaemic myocardium after a very short treatment period, suggesting a direct effect of GLP-1 receptor agonists on myocardium, although the precise mechanism remains unclear. Finally, as a reduction in insulin resistance has been associated with a decrease in CV risk, it cannot be ruled out that the lowering of insulin resistance induced by GLP-1 receptor agonists might also be involved in their beneficial CV actions.

The role of renal dipeptidyl peptidase-4 in kidney disease: renal effects of dipeptidyl peptidase-4 inhibitors with a focus on linagliptin

Emerging evidence suggests that dipeptidyl peptidase-4 (DPP-4) inhibitors used to treat type 2 diabetes may have nephroprotective effects beyond the reduced renal risk conferred by glycemic control. DPP-4 is a ubiquitous protein with exopeptidase activity that exists in cell membrane-bound and soluble forms. The kidneys contain the highest levels of DPP-4, which is increased in diabetic nephropathy. DPP-4 inhibitors are a chemically heterogeneous class of drugs with important pharmacological differences. Of the globally marketed DPP-4 inhibitors, linagliptin is of particular interest for diabetic nephropathy as it is the only compound that is not predominantly excreted in the urine. Linagliptin is also the most potent DPP-4 inhibitor, has the highest affinity for this protein, and has the largest volume of distribution; these properties allow linagliptin to penetrate kidney tissue and tightly bind resident DPP-4. In animal models of kidney disease, linagliptin elicited multiple renoprotective effects, including reducing albuminuria, glomerulosclerosis, and tubulointerstitial fibrosis, independent of changes in glucagon-like peptide-1 (GLP-1) and glucose levels. At the molecular level, linagliptin prevented the pro-fibrotic endothelial-to-mesenchymal transition by disrupting the interaction between membrane-bound DPP-4 and integrin β1 that enhances signaling by transforming growth factor-β1 and vascular endothelial growth factor receptor-1. Linagliptin also increased stromal cell derived factor-1 levels, ameliorated endothelial dysfunction, and displayed unique antioxidant effects. Although the nephroprotective effects of linagliptin are yet to be translated to the clinical setting, the ongoing Cardiovascular and Renal Microvascular Outcome Study with Linagliptin in Patients with Type 2 Diabetes Mellitus (CARMELINA®) study will definitively assess the renal effects of this DPP-4 inhibitor. CARMELINA® is the only clinical trial of a DPP-4 inhibitor powered to evaluate kidney outcomes.

Endothelial dysfunction in renal arcuate arteries of obese Zucker rats: The roles of nitric oxide, endothelium-derived hyperpolarizing factors, and calcium-activated K+ channels

The roles of nitric oxide (NO), endothelium-derived hyperpolarizing factors (EDHF), and calcium-activated K⁺ (K_Ca) channels in diabetes-associated endothelial dysfunction of small renal arteries are not clear. The present study investigated acetylcholine (ACh)-induced vasorelaxation of renal arcuate arteries from obese Zucker (OZ) rats at different diabetes durations, and the relative contribution of NO, EDHF, and K_Ca channels to the endothelial dysfunction. OZ rats of 7 weeks (prediabetic stage), 12 weeks (early diabetic stage), and 20 weeks (late diabetic stage), and time-matched lean control rats, were studied. Segments of arcuate arteries (130 to 180 μm) were isolated, cannulated and pressurized. Vascular endothelial functions were tested using ACh-induced vasodilation. Our experiments demonstrated: (1) ACh-elicited vasodilation was impaired in OZ rats of 20 weeks, but not in rats of 7 and 12 weeks; (2) inhibition of NO or EDHF (contributed by epoxyeicosatrienoic acids [EETs]) production significantly decreased ACh-induced vasodilation in both lean and OZ rats of 20 weeks. The reduction of ACh-induced vasodilation by inhibition of NO or EDHF formation was less in OZ rats, as compared to lean rats; and (3) inhibition of K_Ca channels markedly reduced ACh-induced vasodilation in lean control rats, but not in OZ rats of 20 weeks. Our observations indicated that endothelium-dependent vasodilation in renal arcuate arteries is impaired in diabetes mellitus; NO and EDHF, mainly EETs, dominate the ACh-induced vasodilation in renal arcuate arteries; the contribution of NO and EETs is impaired in diabetic rats; K_Ca channels are involved in ACh-induced vasodilation; and the activity of K_Ca channels is downregulated in diabetes mellitus.

Exendin-4 protects HUVECs from tunicamycin-induced apoptosis via inhibiting the IRE1a/JNK/caspase-3 pathway

PURPOSE

The abnormal increase of apoptosis of endothelial cells induced by endoplasmic reticulum stress is a significant factor for vascular disease, especially for atherosclerosis. Protecting endothelial cells from endoplasmic reticulum stress is a crucial strategies to combate these diseases. The goal of this study was to explore the effect of Exendin-4, a glucagon-like peptide-1 receptor agonist, on tunicamycin-induced apoptosis in human umbilical vein endothelial cells.

METHODS

All studies were performed in primary human umbilical vein endothelial cells treated with tunicamycin with or without Exendin-4 pretreatment. Markers of cell viability and apoptosis were assessed in all cells, as well as the protein expression levels of IRE1α (inositol requiring enzyme-1а), p-IRE1α, JNK (c-Jun N-terminal kinase), p-JNK, and caspase-3.

RESULTS

Following tunicamycin administration, human umbilical vein endothelial cells viability was gradually reduced in a dose-dependent manner, and fluorescence microscopy confirmed that tunicamycin was inducing human umbilical vein endothelial cells apoptosis. This apoptotic effect was attenuated by Exendin-4 pretreatment. Similarly, the ratio of p-IRE1α/IRE1α, p-JNK/JNK and active caspase-3/procaspase-3 were increased by tunicamycin (10 μg/ml); an effect that was counteracted by Exendin-4. The effect of exendin-4 was similar to that of the anti-endoplasmic reticulum stress agent, tauroursodeoxycholic acid (TUDCA).

CONCLUSIONS

This study demonstrates that Exendin-4 can protect human umbilical vein endothelial cells from tunicamycin-induced apoptosis. Furthermore, our data suggests that the mechanism for this effect is mediated by inhibiting the IRE1α/JNK/caspase-3 pathway.

Impact of DPP-4 inhibition on acute and chronic endothelial function in humans with type 2 diabetes on background metformin therapy

Cell culture and animal work indicate that dipeptidyl peptidase-4 (DPP-4) inhibition may exert cardiovascular benefits through favorable effects on the vascular endothelium. Prior human studies evaluating DPP-4 inhibition have shown conflicting results that may in part be related to heterogeneity of background anti-diabetes therapies. No study has evaluated the acute response of the vasculature to DPP-4 inhibition in humans. We recruited 38 patients with type 2 diabetes on stable background metformin therapy for a randomized, double-blind, placebo-controlled crossover trial of DPP-4 inhibition with sitagliptin (100 mg/day). Each treatment period was 8 weeks long separated by 4 weeks of washout. Endothelial function and plasma markers of endothelial activation (intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1)) were measured prior to and 2 hours following acute dosing of sitagliptin or placebo, as well as following 8 weeks of intervention with each pill. Thirty subjects completed the study and were included in analyses. Neither acute nor chronic sitagliptin therapy resulted in significant changes in vascular endothelial function. While post-acute sitagliptin ICAM-1 levels were lower than that post-chronic sitagliptin, the ICAM-1 concentration was not significantly different than pre-acute sitagliptin levels or levels measured in relationship to placebo. There were no significant changes in plasma VCAM-1 levels at any time point. Acute and chronic sitagliptin therapies have neutral effects on the vascular endothelium in the setting of metformin background therapy. In conclusion, our findings suggest DPP-4 inhibition has a neutral effect on cardiovascular risk in patients without a history of heart failure or renal insufficiency.

TRIAL REGISTRATION

NCT01859793.

Endothelial dysfunction and vascular disease - a 30th anniversary update

The endothelium can evoke relaxations of the underlying vascular smooth muscle, by releasing vasodilator substances. The best-characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO) which activates soluble guanylyl cyclase in the vascular smooth muscle cells, with the production of cyclic guanosine monophosphate (cGMP) initiating relaxation. The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDH-mediated responses). As regards the latter, hydrogen peroxide (H₂ O₂ ) now appears to play a dominant role. Endothelium-dependent relaxations involve both pertussis toxin-sensitive G_i (e.g. responses to α₂ -adrenergic agonists, serotonin, and thrombin) and pertussis toxin-insensitive G_q (e.g. adenosine diphosphate and bradykinin) coupling proteins. New stimulators (e.g. insulin, adiponectin) of the release of EDRFs have emerged. In recent years, evidence has also accumulated, confirming that the release of NO by the endothelial cell can chronically be upregulated (e.g. by oestrogens, exercise and dietary factors) and downregulated (e.g. oxidative stress, smoking, pollution and oxidized low-density lipoproteins) and that it is reduced with ageing and in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively lose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and EDH, in particular those due to H₂ O₂ ), endothelial cells also can evoke contraction of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factors. Recent evidence confirms that most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells and that prostacyclin plays a key role in such responses. Endothelium-dependent contractions are exacerbated when the production of nitric oxide is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive and diabetic patients. In addition, recent data confirm that the release of endothelin-1 can contribute to endothelial dysfunction and that the peptide appears to be an important contributor to vascular dysfunction. Finally, it has become clear that nitric oxide itself, under certain conditions (e.g. hypoxia), can cause biased activation of soluble guanylyl cyclase leading to the production of cyclic inosine monophosphate (cIMP) rather than cGMP and hence causes contraction rather than relaxation of the underlying vascular smooth muscle.

Possible vasculoprotective role of linagliptin against sodium arsenite-induced vascular endothelial dysfunction

Vascular endothelial dysfunction (VED) interrupts the integrity and function of endothelial lining through enhanced markers of oxidative stress and decrease endothelial nitric oxide synthase (eNOS) expression. The main aim of the present study has been designed to investigate the possible vasculoprotective role of linagliptin against sodium arsenite-induced VED. Sodium arsenite (1.5 mg/kg, i.p., 2 weeks) abrogated the acetylcholine-induced, endothelium-dependent vasorelaxation by depicting the decrease in serum nitrite/nitrate concentration, reduced glutathione level, and simultaneously enhance the thiobarbituric acid reactive substances (TBARS) level, superoxide level, and tumor necrosis factor-alpha. These elevated markers interrupt the integrity of endothelial lining of thoracic aorta which was assessed histologically. The study elicits dose dependent effect of linagliptin (1.5 mg/kg, i.p. and 3 mg/kg, i.p.) or atorvastatin (30 mg/kg, p.o.) treatment, improved the endothelium-dependent independent relaxation, improve the integrity of endothelium lining which was assessed histologically by enhancing the serum nitrite/nitrate level, reduced glutathione level and simultaneously decreasing the TBARS level, superoxide anion level and tumor necrosis factor-alpha (TNF-α) level. L-NAME (25 mg/kg, i.p.), eNOS inhibitor, abrogated the ameliorative potential of linagliptin. However, the ameliorative potential of linagliptin has been enhanced by l-arginine (200 mg/kg, i.p.) which elicits that ameliorative potential of linagliptin was through eNOS signaling cascade and it may be concluded that linagliptin 3 mg/kg, i.p. has more significantly activated the eNOS and decreased the oxidative markers than linagliptin 1.5 mg/kg, i.p. and prevented sodium arsenite-induced VED.

Serelaxin (recombinant human relaxin-2) prevents high glucose-induced endothelial dysfunction by ameliorating prostacyclin production in the mouse aorta

Diabetes-induced endothelial dysfunction is a critical initiating factor in the development of cardiovascular complications. Treatment with relaxin improves tumour necrosis factor α-induced endothelial dysfunction by enhancing endothelial nitric oxide synthase (eNOS) activity and restoring superoxide dismutase 1 protein in rat aortic rings ex vivo. It is, therefore, possible that relaxin treatment could alleviate endothelial dysfunction in diabetes. This study aimed to test the hypothesis that serelaxin (recombinant human relaxin-2) prevents high glucose-induced vascular dysfunction in the mouse aorta. Abdominal aortae were isolated from C57BL/6 male mice and incubated in M199 media for 3days with either normal glucose (5.5mM) or high glucose (30mM), and co-incubated with placebo (20mM sodium acetate) or 10nM serelaxin at 37°C in 5% CO2. Vascular function was analysed using wire-myography. High glucose significantly reduced the sensitivity to the endothelium-dependent agonist, acetylcholine (ACh) (pEC50; normal glucose=7.66±0.10 vs high glucose=7.29±0.10, n=11-12, P<0.05) and the contraction induced by NOS inhibitor, L-NAME (200μM) (normal glucose=59.9±8.3% vs high glucose=38.7±4.3%, n=6, P<0.05), but had no effect on the endothelium-independent agonist, sodium nitroprusside (SNP)-mediated relaxation. Treatment with serelaxin restored endothelial function (pEC50; 7.83±0.11, n=11) but not NO availability. The presence of the cyclooxygenase (COX) inhibitor, indomethacin (1μM) (pEC50; control=7.29±0.10 vs indo=7.74±0.18, n=6-12, P<0.05) and a superoxide dismutase mimetic, tempol (10μM) (pEC50; control=7.29±0.10 vs tempol=7.82±0.05, n=6-12, P<0.01) significantly improved sensitivity to ACh in high glucose treated aortae, but had no effect in serelaxin treated aortae. This suggests that high glucose incubation alters the superoxide and COX-sensitive pathway, which was normalized by co-incubation with serelaxin. Neither high glucose incubation nor serelaxin treatment had an effect on cyclooxygenase 1 and 2 (Ptgs1, Ptgs2), prostacyclin synthase (PTGIS) and receptor (Ptgir) as well as thromboxane A2 receptor (Tbxa2r) mRNA expression. Importantly, production of prostacyclin was significantly (P<0.05) attenuated in high glucose treated aortae, which was prevented by serelaxin treatment. Our data show that serelaxin treatment for 3 days restores high glucose-induced endothelial dysfunction by ameliorating vasodilator prostacyclin production and possibly through the reduction of superoxide in the mouse aorta.

Diabetes-mediated middle cerebral artery remodeling is restored by linagliptin: Interaction with the vascular smooth muscle cell endothelin system

INTRODUCTION

Endothelin-1 (ET-1) mediates cerebrovascular remodeling in vascular smooth muscle layer of the middle cerebral arteries (MCA) in type-2 diabetic Goto-Kakizaki (GK) rats. While metformin, oral glucose lowering agent, prevent/restores vascular remodeling and reduce systemic and local ET-1 levels whether this effect was specific to metformin remained unknown. Our working hypotheses were 1) linagliptin, a DPP-IV inhibitor, can reverse diabetes-mediated cerebrovascular remodeling and this is associated with decreased ET-1, and 2) linagliptin prevents the high glucose induced increase in ET-1 and ET receptors in brain vascular smooth muscle cells (bVSMCs).

METHODS

Diabetic and non-diabetic GK rats were treated with linagliptin (4weeks). MCAs were fixed in buffered 4% paraformaldehyde and used for morphometry. Human bVSMCs incubated in normal glucose (5.5mM)/high glucose (25mM) conditions were treated with the linagliptin (100nM; 24h). ET-1 secretion and ET receptors were measured in media and cell lysate respectively. Immunostaining was performed for ET-A and ET-B receptor. ET receptors were also measured in cells treated with ET-1 (100nM) and linagliptin.

RESULTS

Linagliptin treatment regressed vascular remodeling of MCAs in diabetic animals but had no effect on blood glucose. bVSMCs in normal/high glucose condition did not show any significant difference in ET-1 secretion or ET-A and ET-B receptor expression. ET-1 treatment in high glucose condition significantly increased the ET-A receptors and this effect was inhibited by linagliptin.

CONCLUSIONS

Linagliptin is effective in reversing established pathological cerebrovascular remodeling associated with diabetes. Attenuation of the ET system could be a pleiotropic effect of linagliptin that provides vascular protection.

Insights into the molecular mechanisms of diabetes-induced endothelial dysfunction: focus on oxidative stress and endothelial progenitor cells

Diabetes mellitus is a heterogeneous, multifactorial, chronic disease characterized by hyperglycemia owing to insulin insufficiency and insulin resistance (IR). Recent epidemiological studies showed that the diabetes epidemic affects 382 million people worldwide in 2013, and this figure is expected to be 600 million people by 2035. Diabetes is associated with microvascular and macrovascular complications resulting in accelerated endothelial dysfunction (ED), atherosclerosis, and cardiovascular disease (CVD). Unfortunately, the complex pathophysiology of diabetic cardiovascular damage is not fully understood. Therefore, there is a clear need to better understand the molecular pathophysiology of ED in diabetes, and consequently, better treatment options and novel efficacious therapies could be identified. In the light of recent extensive research, we re-investigate the association between diabetes-associated metabolic disturbances (IR, subclinical inflammation, dyslipidemia, hyperglycemia, dysregulated production of adipokines, defective incretin and gut hormones production/action, and oxidative stress) and ED, focusing on oxidative stress and endothelial progenitor cells (EPCs). In addition, we re-emphasize that oxidative stress is the final common pathway that transduces signals from other conditions-either directly or indirectly-leading to ED and CVD.

The Dipeptidyl Peptidase-4 Inhibitor Linagliptin Preserves Endothelial Function in Mesenteric Arteries from Type 1 Diabetic Rats without Decreasing Plasma Glucose

The aim of the study was to investigate the effect of the DPP-4 inhibitor linagliptin on the mechanism(s) of endothelium-dependent relaxation in mesenteric arteries from STZ-induced diabetic rats. Both normal and diabetic animals received linagliptin (2 mg/kg) daily by oral gavage for a period of 4 weeks. To measure superoxide generation in mesenteric arteries, lucigenin-enhanced chemiluminescence was used. ACh-induced relaxation of mesenteric arteries was assessed using organ bath techniques and Western blotting was used to investigate protein expression. Pharmacological tools (1μM TRAM-34, 1μM apamin, 100 nM Ibtx, 100 μM L-NNA, 10 μM ODQ) were used to distinguish between NO and EDH-mediated relaxation. Linagliptin did not affect plasma glucose, but did decrease vascular superoxide levels. Diabetes reduced responses to ACh but did not affect endothelium-independent responses to SNP. Linagliptin improved endothelial function indicated by a significant increase in responses to ACh. Diabetes impaired the contribution of both nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH) to endothelium-dependent relaxation and linagliptin treatment significantly enhanced the contribution of both relaxing factors. Western blotting demonstrated that diabetes also increased expression of Nox2 and decreased expression and dimerization of endothelial NO synthase, effects that were reversed by linagliptin. These findings demonstrate treatment of type 1 diabetic rats with linagliptin significantly reduced vascular superoxide levels and preserved both NO and EDH-mediated relaxation indicating that linagliptin can improve endothelial function in diabetes independently of any glucose lowering activity.

The Role of Dipeptidyl Peptidase - 4 Inhibitors in Diabetic Kidney Disease

Despite major advances in the understanding of the molecular mechanisms that underpin the development of diabetic kidney disease, current best practice still leaves a significant proportion of patients with end-stage kidney disease requiring renal replacement therapy. This is on a background of an increasing diabetes epidemic worldwide. Although kidney failure is a major cause of morbidity the main cause of death remains cardiovascular in nature. Hence, diabetic therapies which are both “cardio-renal” protective seem the logical way forward. In this review, we discuss the dipeptidyl peptidase 4 (DPP4) inhibitors (DPP4inh), which are glucose-lowering agents used clinically and their role in diabetic kidney disease with specific focus on renoprotection and surrogate markers of cardiovascular disease. We highlight the novel pleiotropic effects of DPP4 that make it an attractive additional target to combat the fibrotic and inflammatory pathways in diabetic kidney disease and also discuss the current literature on the cardiovascular safety profile of DPP4inh. Clearly, these observed renoprotective effects will need to be confirmed by clinical trials to determine whether they translate into beneficial effects to patients with diabetes.

Dipeptidyl peptidase-4 inhibitor, linagliptin, ameliorates endothelial dysfunction and atherogenesis in normoglycemic apolipoprotein-E deficient mice

BACKGROUND

Dipeptidyl peptidase-4 (DPP-4) inhibitors have vasoprotective effects. This study investigated whether a recently approved DPP-4 inhibitor, linagliptin (Lina), suppresses atherogenesis in non-diabetic apolipoprotein-E deficient (ApoE(-/-)) mice, and examined its effects on endothelial function.

METHODS AND RESULTS

Lina (10mg/kg/day) was administered orally to ApoE(-/-) mice for 20 weeks. Lina reduced atherogenesis without alteration of metabolic parameters including blood glucose level compared with control (P<0.05). Results of immunohistochemical analyses and quantitative RT-PCR demonstrated that Lina significantly decreased inflammatory molecule expression and macrophage infiltration in the atherosclerotic aorta. Lina administration to ApoE(-/-) mice for 9 weeks ameliorated endothelium-dependent vasodilation compared with that in untreated mice. Plasma active glucagon-like peptide-1 (GLP-1) level was significantly higher in the treated group (P<0.05). Exendin-4 (Ex-4), a GLP-1 analog, ameliorated endothelium-dependent vasodilation impaired by palmitic acid (PA) in wild-type mouse aortic segments. Ex-4 promoted phosphorylation of eNOS(Ser1177) and Akt, both of which were abrogated by PA, in human umbilical vein endothelial cells. In addition, Lina administration to ApoE(-/-) mice decreased oxidative stress, as determined by urinary 8-OHdG secretion and NADPH oxidase subunit expression in the abdominal aorta.

CONCLUSION

Lina inhibited atherogenesis in non-diabetic ApoE(-/-) mice. Amelioration of endothelial dysfunction associated with a reduction of oxidative stress by GLP-1 contributes to the atheroprotective effects of Lina.