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

Sitagliptin attenuates arterial calcification by downregulating oxidative stress-induced receptor for advanced glycation end products in LDLR knockout mice

Diabetes is a complex disease characterized by hyperglycemia, dyslipidemia, and insulin resistance. Plasma advanced glycation end products (AGEs) activated the receptor for advanced glycation end products (RAGE) and the activation of RAGE is implicated to be the pathogenesis of type 2 diabetic mellitus (T2DM) patient vascular complications. Sitagliptin, a dipeptidyl peptidase-4 (DPP4) inhibitor, is a new oral hypoglycemic agent for the treatment of T2DM. However, the beneficial effects on vascular calcification remain unclear. In this study, we used a high-fat diet (HFD)-fed low-density lipoprotein receptor deficiency (LDLR^−/−) mice model to investigate the potential effects of sitagliptin on HFD-induced arterial calcification. Mice were randomly divided into 3 groups: (1) normal diet group, (2) HFD group and (3) HFD + sitagliptin group. After 24 weeks treatment, we collected the blood for chemistry parameters and DPP4 activity measurement, and harvested the aorta to evaluate calcification using immunohistochemistry and calcium content. To determine the effects of sitagliptin, tumor necrosis factor (TNF)-α combined with S100A12 was used to induce oxidative stress, activation of nicotinamide adenine dinucleotide phosphate (NADPH), up-regulation of bone markers and RAGE expression, and cell calcium deposition on human aortic smooth muscle cells (HASMCs). We found that sitagliptin effectively blunted the HFD-induced artery calcification and significantly lowered the levels of fasting serum glucose, triglyceride (TG), nitrotyrosine and TNF-α, decreased the calcium deposits, and reduced arterial calcification. In an in-vitro study, both S100A12 and TNF-α stimulated RAGE expression and cellular calcium deposits in HASMCs. The potency of S100A12 on HASMCs was amplified by the presence of TNF-α. Sitagliptin and Apocynin (APO), an NADPH oxidase inhibitor, inhibited the TNF-α + S100A12-induced NADPH oxidase and nuclear factor (NF)-κB activation, cellular oxidative stress, RAGE expression, osteo transcription factors expression and calcium deposition. In addition, treatment with sitagliptin, knockdown of RAGE or TNF-α receptor blunted the TNF-α + S100A12-induced RAGE expression. Our findings suggest that sitagliptin may suppress the initiation and progression of arterial calcification by inhibiting the activation of NADPH oxidase and NF-κB, followed by decreasing the expression of RAGE.

DPP-4 Inhibitors Have Different Effects on Endothelial Low-Grade Inflammation and on the M1-M2 Macrophage Polarization Under Hyperglycemic Conditions

PURPOSE

We explored the anti-inflammatory role of the DPP-4 inhibitor teneligliptin, using sitagliptin as comparator, in different in vitro models of low-grade inflammation (LGI), evaluating the hyperglycemia-induced endothelial inflammation, the macrophage polarization, and the endothelium-macrophage interaction.

METHODS

The effects of DPP-4 and its inhibitors on macrophage polarization were evaluated in THP-1 cells by measuring mRNA expression of M1-M2 markers. HUVEC cells were used to analyze the effects of DPP-4 inhibitors on endothelial inflammation under normal and high glucose conditions. To evaluate the link between eNO and M1-M2 polarization, HUVECs were transfected with eNOS siRNA and co-cultured with THP-1 cells. The effects of DPP-4 inhibitors on macrophage polarization and eNO content were evaluated in a co-culture model of differentiated THP-1 cells + HUVECs under normal glucose (NG), high glucose (HG) and high metabolic memory (HM) conditions.

RESULTS

DPP-4 regulated M1/M2 macrophage polarization. Teneligliptin reduced M1 and enhanced M2 macrophage phenotype under DPP-4 stimulation, and attenuated hyperglycemia-induced endothelial inflammation. In THP-1 cells co-cultured with eNOS depleted HUVECs, M1 markers were enhanced, while M2 reduced, indicating an important role of eNO in polarization to M2 phenotype. In the co-culture model with HUVECs exposed to HG and HM, teneligliptin reduced M1 and enhanced M2 population, by increasing eNO levels. The anti-inflammatory effects of sitagliptin were not observed in these LGI models.

CONCLUSION

Teneligliptin, but not sitagliptin, has anti-inflammatory effects in the various LGI models, by promoting a switch from M1 toward M2 phenotype and by decreasing hyperglycaemia-induced endothelial inflammation, suggesting that effects for LGI are different among DPP-4 inhibitors.

Linagliptin Regulates the Mitochondrial Respiratory Reserve to Alter Platelet Activation and Arterial Thrombosis

Background: The pharmacological inhibition of dipeptidyl peptidase-4 (DPP-4) potentiates incretin action, and DPP-4 is a drug target for type 2 diabetes and reducing cardiovascular risk. However, little is known about the non-enteroendocrine pathways by which DPP-4 might contribute to ischaemic cardiovascular events.

Methods: We tested the hypothesis that inhibition of DPP-4 can inhibit platelet activation and arterial thrombosis by preventing platelet mitochondrial dysfunction and release. The effects of pharmacological DPP-4 inhibition on carotid artery thrombosis, platelet aggregation, and platelet mitochondrial respiration signaling pathways were studied in mice.

Results: Platelet-dependent arterial thrombosis was significantly delayed in mice treated with high dose of linagliptin, a potent DPP-4 inhibitor, and fed normal chow diet compared to vehicle-treated mice. Thrombin induced DPP-4 expression and activity, and platelets pretreated with linagliptin exhibited reduced thrombin-induced aggregation. Linagliptin blocked phosphodiesterase activity and contrained cyclic AMP reduction when thrombin stimulates platelets. Linagliptin increases the inhibition of platelet aggregation by nitric oxide. The bioenergetics profile revealed that platelets pretreated with linagliptin exhibited decreased oxygen consumption rates in response to thrombin. In transmission electron microscopy, platelets pretreated with linagliptin showed markedly reversed morphological changes in thrombin-activated platelets, including the secretion of α-granules and fewer mitochondria.

Conclusion: Collectively, these findings identify distinct roles for DPP-4 in platelet function and arterial thrombosis.

A Comprehensive Review on Preclinical Diabetic Models

BACKGROUND

Preclinical experimental models historically play a critical role in the exploration and characterization of disease pathophysiology. Further, these in-vivo and in-vitro preclinical experiments help in target identification, evaluation of novel therapeutic agents and validation of treatments.

INTRODUCTION

Diabetes mellitus (DM) is a multifaceted metabolic disorder of multidimensional aetiologies with the cardinal feature of chronic hyperglycemia. To avoid or minimize late complications of diabetes and related costs, primary prevention and early treatment are therefore necessary. Due to its chronic manifestations, new treatment strategies need to be developed, because of the limited effectiveness of the current therapies.

METHODS

The study included electronic databases such as Pubmed, Web of Science and Scopus. The datasets were searched for entries of studies up to June, 2018.

RESULTS

A large number of in-vivo and in-vitro models have been presented for evaluating the mechanism of anti-hyperglycaemic effect of drugs in hormone-, chemically-, pathogen-induced animal models of diabetes mellitus. The advantages and limitations of each model have also been addressed in this review.

CONCLUSION

This review encompasses the wide pathophysiological and molecular mechanisms associated with diabetes, particularly focusing on the challenges associated with the evaluation and predictive validation of these models as ideal animal models for preclinical assessments and discovering new drugs and therapeutic agents for translational application in humans. This review may further contribute to discover a novel drug to treat diabetes more efficaciously with minimum or no side effects. Furthermore, it also highlights ongoing research and considers the future perspectives in the field of diabetes.

Inhibition of neointima hyperplasia by the combined therapy of linagliptin and metformin via AMPK/Nox4 signaling in diabetic rats

BACKGROUND

Neointima hyperplasia is the pathological basis of atherosclerosis and restenosis which have been associated with diabetes mellitus (DM). It is controversial for linagliptin and metformin to protect against vascular neointimal hyperplasia caused by DM. Given the combined therapy of linagliptin and metformin in clinical practice, we investigated whether the combination therapy inhibited neointimal hyperplasia in the carotid artery in diabetic rats.

METHODS AND RESULTS

Neointima hyperplasia in the carotid artery was induced by balloon-injury in the rats fed with high fat diet (HFD) combined with low dose streptozotocin (STZ) administration. In vitro, vascular smooth muscle cells (VSMCs) were incubated with high glucose (HG, 30 mM) and the proliferation, migration, apoptosis and collagen deposition were analyzed in VSMCs. We found that the combined therapy, not the monotherapy of linagliptin and metformin significantly inhibited the neointima hyperplasia and improved the endothelium-independent contraction in the balloon-injured cardia artery of diabetic rats, which was associated with the inhibition of superoxide (O₂^-.) production in the cardia artery. In vitro, HG-induced VSMC remodeling was shown as the remarkable upregulation of PCNA, collagan1, MMP-9, Bcl-2 and migration rate as well as the decreased apoptosis rate. Such abnormal changes were dramatically reversed by the combined use of linagliptin and metformin. Moreover, the AMP-activated protein kinase (AMPK)/Nox4 signal pathway was found to mediate VSMC remodeling responding to HG. Linagliptin and metformin were synergistical to target AMPK/Nox4 signal pathway in VSMCs incubated with HG and in the cardia artery of diabetic rats, which was superior to the monotherapy.

CONCLUSIONS

We demonstrated that the potential protection of the combined use of linagliptin and metformin on VSMC remodeling through AMPK/Nox4 signal pathway, resulting in the improvement of neointima hyperplasia in diabetic rats. This study provided new therapeutic strategies for vascular stenosis associated with diabetes.

The effect of exenatide (a GLP-1 analog) and sitagliptin (a DPP-4 inhibitor) on plasma platelet-activating factor acetylhydrolase (PAF-AH) activity and concentration in normal and fructose-fed rats

Inflammation and oxidative stress are the two processes crucial in atherogenesis. Platelet-activating factor acetylhydrolase (PAF-AH), a plasma lipoprotein-associated enzyme, degrades pro-inflammatory lipids generated within oxidatively modified lipoproteins. Extensive evidence shows that incretin-based drugs, a new class of anti-diabetic agents, can provide cardiovascular protection that cannot be attributed to their glucose-lowering effects. The present study was undertaken to determine whether the antiatherogenic effects of the GLP-1(glucagon-like peptide-1) receptor agonist (exenatide) and DPP-4(dipeptidyl peptidase-4) inhibitors (sitagliptin) may occur via the regulation of platelet-activating factor acetylhydrolase (PAF-AH) activity/mass and inhibition of low-density lipoprotein (LDL) oxidation in the fructose-fed rats. Normal and fructose-fed rats (8 wk) were treated (4 wk) with sitagliptin (5 and 10 mg/kg p.o.) or with exenatide (5 and 10 µg/kg, s.c.). Plasma PAF-AH activity and phosphatidylcholine (PC) concentration were measured colorimetrically. Plasma PAF-AH concentration, oxidized LDL (oxLDL), hexanoyl-Lys adduct (HEL), lyso-PC, apolipoprotein A-I (apoA-I), apoB, platelet-activating factor (PAF), monocyte chemoattractant protein-1 (MCP-1) and endothelin-1 (ET-1) were measured by ELISA. The four-week exenatide (5 µg/kg, sc.) treatment of fructose fed-rats significantly increased plasma PAF-AH activity (+33%, P < 0.001) and decreased the level of circulating oxLDL (-42%, P < 0.05) and MCP-1 (-23%, P < 0.01). These changes were accompanied by the decrease in plasma PC/lyso-PC (-47%, P < 0.001) and apoB/apoA-I ratio (-75%, P < 0.001). The effect of exenatide on enzyme activity was associated with only a minor effect on metabolic parameters and was independent of weight reduction. Exenatide but not sitagliptin inhibits oxidative modification of LDL probably due to favorable effect on plasma PAF-AH activity.

Linagliptin protects rat carotid artery from balloon injury and activates the NRF2 antioxidant pathway

Percutaneous coronary intervention (PCI) is main treatment for acute coronary syndrome (ACS). However, restenosis caused by PCI-induced injury influences the outcome of patients. Linagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, has been reported to ameliorate intimal hyperplasia post vascular injury. The underlying mechanisms by which linagliptin protects against balloon injury are unclear and require to be explored. Herein, Wistar rats with carotid artery balloon injury were given 1, 2 or 3 mg/kg/day linagliprin for 6 weeks. We found that linagliptin attenuated vascular injury-mediated neointima formation in rats without affecting body weight and blood glucose levels. ELISA results indicated that linagliptin significantly reduced overproduction of cytokines including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and IL-6 post balloon injury. By detecting the level of malondialdehyde (MDA) and the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), we found that linagliptin prevented balloon injury-induced oxidative stress. Additionally, linagliptin decreased the level of Kelch ECH-associating protein 1 (KEAP1) compared with injury group. Results of Western blots and electrophoretic mobility shift assay (EMSA) demonstrated that linagliptin augmented nuclear accumulation of nuclear factor-E2-related factor 2 (NRF2) and its binding ability to target genes in rats with balloon injury. Moreover, heme oxygenase-1 (HO-1) and NAD (P) H quinine oxidoreductase 1 (NQO1), two downstream targets of NRF2, were further up-regulated after linagliptin treatment compared with injury group. In conclusion, our data suggest that linagliptin protects carotid artery from balloon injury-induced neointima formation and activates the NRF2 antioxidant pathway.

Differences in kidney-specific DPP-4 inhibition by linagliptin and sitagliptin

The two dipeptidyl peptidase (DPP)-4 inhibitors, linagliptin and sitagliptin, were shown to exert different binding kinetics in vitro. Twenty-four hours after oral dosing particularly in vivo inhibition of renal-specific DPP-4 activity was more sustained in Sprague Dawley rats after exposure to linagliptin than it was after sitagliptin.

Anagliptin prevents apoptosis of human umbilical vein endothelial cells by modulating NOX-4 signaling pathways

Dipeptidyl peptidase IV (DPP-IV) inhibitors are novel oral anti-hyperglycemic agents. Here, the anti-apoptotic effect of Anagliptin in human umbilical vein endothelial cells (HUVECs) was evaluated. Cultured HUVECs were pre-incubated with Anagliptin, and then treated hydrongen peroxide (H₂O₂) to induce apoptosis. The apoptosis of HUVECs were detected by viability, LIVE/DEAD staining assay and flow cytometry assays. HUVECs were transfected with plasmid harboring human NADPH oxidases (NOX) 4 or an empty vector. The formation of reactive oxygen species (ROS) was measured by immunofluorescence. Apoptotic and anti-apoptotic factor were detected by Western Blot. Pre-incubation with Anagliptin protected HUVECs from H₂O₂ induced apoptosis. The transfection assay also indicated that pre-incubation with Anagliptin inhibited the apoptosis of HUVECs induced by NADPH oxidase 4 (NOX-4) overexpression. Immunofluorescence demonstrated that pre-incubation with Anagliptin suppressed the formation of ROS in apoptotic HUVECs. Pre-incubation with Anagliptin inhibited NOX-4 mediated the Bax, caspase-3, cleave caspase-3 and Cyto C overexpression, but up-regulated the protein level of Bcl-2 in HUVECs. The data help us to better understand the effect of Anagliptin on apoptosis, and will be valuable in identifying new targets to prevent the endothelial cell apoptosis after injury.

The role of dipeptidylpeptidase-4 inhibitors in management of cardiovascular disease in diabetes; focus on linagliptin

Multiple population based analyses have demonstrated a high incidence of cardiovascular disease (CVD) and cardiovascular (CV) mortality in subjects with T2DM that reduces life expectancy by as much as 15 years. Importantly, the CV system is particularly sensitive to the metabolic and immune derangements present in obese pre-diabetic and diabetic individuals; consequently, CV dysfunction is often the initial CV derangement to occur and promotes the progression to end organ/tissue damage in T2DM. Specifically, diabetic CVD can manifest as microvascular complications, such as nephropathy, retinopathy, and neuropathy, as well as, macrovascular impairments, including ischemic heart disease, peripheral vascular disease, and cerebrovascular disease. Despite some progress in prevention and treatment of CVD, mainly via blood pressure and dyslipidemia control strategies, the impact of metabolic disease on CV outcomes is still a major challenge and persists in proportion to the epidemics of obesity and diabetes. There is abundant pre-clinical and clinical evidence implicating the DPP-4-incretin axis in CVD. In this regard, linagliptin is a unique DPP-4 inhibitor with both CV and renal safety profiles. Moreover, it exerts beneficial CV effects beyond glycemic control and beyond class effects. Linagliptin is protective for both macrovascular and microvascular complications of diabetes in preclinical models, as well as clinical models. Given the role of endothelial-immune cell interactions as one of the key events in the initiation and progression of CVD, linagliptin modulates these cell–cell interactions by affecting two important pathways involving stimulation of NO signaling and potent inhibition of a key immunoregulatory molecule.

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.

Teneligliptin enhances the beneficial effects of GLP-1 in endothelial cells exposed to hyperglycemic conditions

High-glucose-induced oxidative stress contributes to cardiovascular endothelial damage in diabetes. Glucagon-like peptide 1 (GLP-1) is beneficial to endothelial cells, but its effects are diminished when cells are continuously exposed to high glucose. Teneligliptin is a dipeptidyl peptidase-4 (DPP-4) inhibitor that prevents oxidative stress, apoptosis and the metabolic memory effect. We explored the potential additive effects of Teneligliptin and GLP-1 in hyperglycemia-damaged endothelial cells. Human umbilical vein endothelial cells (HUVECs) were exposed to normal-glucose (5 mmol/L) or high-glucose (HG, 25 mmol/L) for 21 days, or to HG for 14 days followed by normal-glucose for 7 days (HM). These cells were continually treated with Teneligliptin 3.0 μmol/L, alone or in combination with an acute dose of GLP-1 50 nmol/L. DPP-4 was upregulated under hyperglycemic conditions, but Teneligliptin reduced DPP-4 expression and activity. Simultaneous Teneligliptin and GLP-1 synergistically increased the antioxidant response and reduced ROS levels in HG- and HM-exposed HUVECs. Concurrent treatment also enhanced cell proliferation, reduced apoptotic gene expression and ameliorated endoplasmic reticulum stress in HG- and HM-exposed HUVECs. Thus, long-term Teneligliptin treatment reduced DPP-4 levels and activity in HUVECs exposed to chronic hyperglycemia. Moreover, Teneligliptin enhanced the beneficial effects of GLP-1 on oxidative stress, proliferation, apoptosis and endoplasmic reticulum homeostasis.

Dipeptidyl peptidase IV inhibitors as novel regulators of vascular disease

Dipeptidyl peptidase IV (DPP-IV) has been revealed as an adipokine with potential relevance in cardiovascular disease (CVD), while clinically used DPP-IV inhibitors have demonstrated beneficial cardiovascular effects in several experimental studies. Perivascular adipose tissue (PVAT) is a unique adipose tissue depot in close anatomical proximity and bidirectional functional interaction with the vascular wall, which is a source of DPP-IV and its biology may be influenced by DPP-IV inhibition. Recently, DPP-IV inhibition has been associated with decreased local inflammation and oxidative stress both in the vascular wall and the PVAT, potentially regulating atherogenesis progression in vivo. DPP-IV inhibition may thus be a promising target in cardiovascular disease. However, the exact pleiotropic mechanisms that underlie the cardiovascular effects of DPP-IV inhibition need to be clarified, while the in vivo benefit of DPP-IV inhibition in humans remains unclear.

Periostin antisense oligonucleotide prevents adhesion formation after surgery in mice

To study the role of periostin in adhesion formation, the effect of periostin antisense oligonucleotide (PAO) on adhesion formation was evaluated in mice. Under anesthesia, the serous membrane of the cecum was abraded, and the adhesion score and mRNA levels of periostin and its related factors were determined after surgery. Saline, 40 mg/kg of negative sense oligonucleotide (NSO), or 40 mg/kg of PAO were injected into the abdomen after surgery, and the adhesion score and mRNA levels were evaluated 14 days later. Filmy adhesion formation was observed 1 day after surgery, and the adhesion score increased gradually to 14 days. The mRNA levels of periostin, transforming growth factor (TGF)-β, and collagen I increased gradually from 3 days to 14 days. The adhesion score of PAO was significantly lower than of saline or NSO 14 days after surgery. The mRNA levels of periostin, TGF-β, and collagen I were also significantly attenuated by treatment with PAO compared with saline or NSO. Thus, these results demonstrated that the periostin mRNA level increased in the abraded cecum, and PAO prevented adhesion formation along with attenuation of the periostin mRNA level.

The DPP4 Inhibitor Linagliptin Protects from Experimental Diabetic Retinopathy

Background/aims

Dipeptidyl peptidase 4 (DPP4) inhibitors improve glycemic control in type 2 diabetes, however, their influence on the retinal neurovascular unit remains unclear.

Methods

Vasculo- and neuroprotective effects were assessed in experimental diabetic retinopathy and high glucose-cultivated C. elegans, respectively. In STZ-diabetic Wistar rats (diabetes duration of 24 weeks), DPP4 activity (fluorometric assay), GLP-1 (ELISA), methylglyoxal (LC-MS/MS), acellular capillaries and pericytes (quantitative retinal morphometry), SDF-1a and heme oxygenase-1 (ELISA), HMGB-1, Iba1 and Thy1.1 (immunohistochemistry), nuclei in the ganglion cell layer, GFAP (western blot), and IL-1beta, Icam1, Cxcr4, catalase and beta-actin (quantitative RT-PCR) were determined. In C. elegans, neuronal function was determined using worm tracking software.

Results

Linagliptin decreased DPP4 activity by 77% and resulted in an 11.5-fold increase in active GLP-1. Blood glucose and HbA_1c were reduced by 13% and 14% and retinal methylglyoxal by 66%. The increase in acellular capillaries was diminished by 70% and linagliptin prevented the loss of pericytes and retinal ganglion cells. The rise in Iba-1 positive microglia was reduced by 73% with linagliptin. In addition, the increase in retinal Il1b expression was decreased by 65%. As a functional correlate, impairment of motility (body bending frequency) was significantly prevented in C. elegans.

Conclusion

Our data suggest that linagliptin has a protective effect on the microvasculature of the diabetic retina, most likely due to a combination of neuroprotective and antioxidative effects of linagliptin on the neurovascular unit.

Effects of linagliptin on renal endothelial function in patients with type 2 diabetes: a randomised clinical trial

AIMS/HYPOTHESIS

Endothelial dysfunction predicts cardiovascular damage and renal involvement. Animal experiments and human studies indicate an increased nitric oxide (NO) activity and endothelial NO synthase (NOS) expression in the early stage of type 2 diabetes. The aim of the study was to assess the effect of linagliptin on the endothelial function of the renal vasculature.

METHODS

In this randomised, double-blind, parallel-group, investigator-initiated trial, 62 patients with type 2 diabetes were randomly assigned (by computer-generated random code) to receive linagliptin 5 mg (n = 30) or placebo (n = 32) for 4 weeks. The primary objective was to assess endothelial function of the renal vasculature, by constant-infusion input-clearance and urinary albumin/creatinine ratio (UACR), both before and after blockade of NOS with N ^G-monomethyl-L-arginine (L-NMMA).

RESULTS

Treatment with linagliptin for 4 weeks reduced fasting, postprandial blood glucose and HbA_1c, although not significantly; no change occurred with placebo. Renal plasma flow (RPF) did not change after linagliptin or placebo. After 4 weeks the absolute change in RPF due to L-NMMA was smaller in the linagliptin group than in the placebo group (-46.8 ± 34 vs -65.1 ± 36 ml/min, p = 0.045), indicating a lower basal NO activity after treatment with linagliptin. Consistently, the response of UACR to L-NMMA increased in the placebo group (p = 0.059) but not in the linagliptin group (p = 0.276), pointing to an upregulation of NO activity in the placebo group. No clinically meaningful safety concerns were evident.

CONCLUSIONS/INTERPRETATION

Our data suggest that treatment with the dipeptidyl peptidase-4 inhibitor linagliptin for 4 weeks prevented the impairment of renal endothelial function due to hyperglycaemia in type 2 diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01835678 FUNDING: : This study was funded by Boehringer Ingelheim.

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.

DPP-4 Inhibition by Linagliptin Attenuates Obesity-Related Inflammation and Insulin Resistance by Regulating M1/M2 Macrophage Polarization

Dipeptidyl peptidase 4 (DPP-4) cleaves a large number of chemokine and peptide hormones involved in the regulation of the immune system. Additionally, DPP-4 may also be involved in macrophage-mediated inflammation and insulin resistance. Thus, the current study investigated the effect of linagliptin, an inhibitor of DPP-4, on macrophage migration and polarization in white adipose tissue (WAT) and liver of high-fat diet-induced obese (DIO) mice. DPP-4(+) macrophages in lean and obese mice were quantified by fluorescence-activated cell sorting (FACS) analysis. DPP-4 was predominantly expressed in F4/80(+) macrophages in crown-like structures compared with adipocytes in WAT of DIO mice. FACS analysis also revealed that, compared with chow-fed mice, DIO mice exhibited a significant increase in DPP-4(+) expression in cells within adipose tissue macrophages (ATMs), particularly M1 ATMs. Linagliptin showed a greater DPP-4 inhibition and antioxidative capacity than sitagliptin and reduced M1-polarized macrophage migration while inducing an M2-dominant shift of macrophages within WAT and liver, thereby attenuating obesity-induced inflammation and insulin resistance. Loss of macrophage inflammatory protein-1α, a chemokine and DPP-4 substrate, in DIO mice abrogated M2 macrophage-polarizing and insulin-sensitizing effects of linagliptin. Therefore, the inhibition of DPP-4 by linagliptin reduced obesity-related insulin resistance and inflammation by regulating M1/M2 macrophage status.

Incretin-Based Therapies for Diabetic Complications: Basic Mechanisms and Clinical Evidence

An increase in the rates of morbidity and mortality associated with diabetic complications is a global concern. Glycemic control is important to prevent the development and progression of diabetic complications. Various classes of anti-diabetic agents are currently available, and their pleiotropic effects on diabetic complications have been investigated. Incretin-based therapies such as dipeptidyl peptidase (DPP)-4 inhibitors and glucagon-like peptide-1 receptor agonists (GLP-1RA) are now widely used in the treatment of patients with type 2 diabetes. A series of experimental studies showed that incretin-based therapies have beneficial effects on diabetic complications, independent of their glucose-lowering abilities, which are mediated by anti-inflammatory and anti-oxidative stress properties. Based on these findings, clinical studies to assess the effects of DPP-4 inhibitors and GLP-1RA on diabetic microvascular and macrovascular complications have been performed. Several but not all studies have provided evidence to support the beneficial effects of incretin-based therapies on diabetic complications in patients with type 2 diabetes. We herein discuss the experimental and clinical evidence of incretin-based therapy for diabetic complications.

DPP-4 inhibitors and cardiovascular disease in type 2 diabetes mellitus. Expectations, observations and perspectives

AIMS

Cardiovascular disease (CVD) is the greatest burden of type 2 diabetes mellitus (T2DM) in terms of morbility, mortality and costs for individuals and societies. Therefore, its prevention is a major goal in diabetes care. Optimal treatment of hyperglycemia is certainly instrumental to CVD prevention. Optimal treatment means both establishing the most appropriate glycemic target for the given individual and selecting the medication(s) with the most favourable benefit/safety ratio. CVD safety, if not a clear CVD benefit, is certainly required for all antidiabetic agents. Dipeptidyl-peptidase-4 (DPP-4) inhibitors are among the classes of antidiabetic agents most recently made available for diabetes care. A major question to be addressed is the effect of these compounds on CVD. Expectations were high for their mechanism of action, which targets also post-prandial glucose and minimize hypoglycemia risk, thereby providing a sort of global glucose control, and for some potentially beneficial extra-glycemic effects. This article reviews the existing literature on this issue.

DATA SYNTHESIS

Data published so far document that DPP-4 inhibitors have a wide spectrum of glycemic and extra-glycemic effects potentially reducing the risk of CVD as well as favourable effects on intermediate or surrogate CVD endpoints. These data heralded a better CVD outcome. Accordingly, pooling CVD safety data from phase 3 and 4 studies conducted with DPP-4 inhibitors suggested that their use might translate into a better CVD outcome. Data from three CVD outcome RCTs with alogliptin, saxagliptin and sitagliptin documented no harm but did not show any benefit on major CVD events. A modest but significant increased risk of hospitalization for heart failure was observed with saxagliptin and with alogliptin (only in subjects with no history of heart failure before randomization) but not with sitagliptin. A study currently in progress with linagliptin will provide further insights in the issue of CVD safety and benefit.

CONCLUSIONS

It should be considered that most alternative oral antidiabetic agents generally do not possess a better CVD risk profile than DPP-4 inhibitors and that some of them, indeed, should be used with caution because of potentially adverse effects on heart and vasculature. Overall, the selection of antidiabetic agent(s) with the most favourable CVD profile is mandatory but still challenging in diabetes care.

Dipeptidyl peptidase-4 and kidney fibrosis in diabetes

Diabetic nephropathy (DN) is the most common cause of end-stage kidney disease worldwide and is associated with increased morbidity and mortality in patients with both type 1 and type 2 diabetes. Recent evidence revealed that dipeptidyl peptidase-4 (DPP-4) inhibitors may exhibit a protective effect against DN. In fact, the kidney is the organ where the DPP-4 activity is the highest level per organ weight. A preclinical analysis revealed that DPP-4 inhibitors also ameliorated kidney fibrosis. In this review, we analyzed recent reports in this field and explore the renoprotective effects and possible mechanism of the DPP-4 inhibitors.

Tissue distribution of teneligliptin in rats and comparisons with data reported for other dipeptidyl peptidase-4 inhibitors

We investigated the tissue distribution of teneligliptin, a dipeptidyl peptidase (DPP)-4 inhibitor, in rats, and compared it with tissue distributions previously reported for other DPP-4 inhibitors. Following the oral administration of [¹⁴ C]teneligliptin to Sprague-Dawley rats, it was predominantly distributed to the kidney and liver, followed by the lung, spleen, and pituitary gland. The elimination half-life (t_1/2 ) of [¹⁴ C]teneligliptin was 68.3 and 69.0 h in the kidney and liver, respectively; these values were about 10 times greater than the plasma t_1/2 . Of note, the elimination of [¹⁴ C]teneligliptin from tissues with high DPP-4 activity (kidney, liver, and lung) was slower in wild-type rats than in DPP-4-deficient rats, especially in the kidney. By contrast, in the heart and pancreas, which weakly express DPP-4, we observed no difference in [¹⁴ C]teneligliptin concentrations between the two animal strains. In the kidney, most radioactivity was attributable to unchanged teneligliptin from 0.5 to 72 h after administration. The marked difference in the distribution of [¹⁴ C]teneligliptin between the two strains suggests that the high binding affinity of teneligliptin for DPP-4 is involved in its tissue distribution. The currently marketed DPP-4 inhibitors are highly distributed to the liver, kidney, and lung, but the extent of tissue distribution varies greatly among the drugs. The differences in the tissue distributions of DPP-4 inhibitors might be related to differences in their pleiotropic effects. This article is protected by copyright. All rights reserved.

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

The aim of the study was to investigate the effects of the DPP-4 inhibitors and GLP-1R agonist, exendin-4 on the mechanism(s) of endothelium-dependent relaxation in rat mesenteric arteries exposed to high glucose concentration (40 mM). Organ bath techniques were employed to investigate vascular endothelial function in rat mesenteric arteries in the presence of normal (11 mM) or high (40 mM) glucose concentrations. Pharmacological tools (1μM TRAM-34, 1μM apamin, 100 nM Ibtx, 100 μM l-NNA, 10 μM ODQ) were used to distinguish between NO and EDHF-mediated relaxation. Superoxide anion levels were assessed by L-012 and lucigenin enhanced-chemiluminescence techniques. Incubation of mesenteric rings with high glucose for 2 h caused a significant increase in superoxide anion generation and a significant impairment of endothelium-dependent relaxation. Exendin-4 and DPP-4 inhibitor linagliptin, but not sitagliptin or vildagliptin, significantly reduced vascular superoxide and improved endothelium-dependent relaxation in the presence of high glucose. The beneficial actions of exendin-4, but not linagliptin, were attenuated by the GLP-1R antagonist exendin fragment (9-39). Further experiments demonstrated that the presence of high glucose impaired the contribution of both nitric oxide and endothelium-dependent hyperpolarisation to relaxation and that linagliptin improved both mechanisms involved in endothelium-dependent relaxation. These findings demonstrate that high glucose impaired endothelium-dependent relaxation can be improved by exendin-4 and linagliptin, likely due to their antioxidant activity and independently of any glucose lowering effect.

Efficacy of dipeptidyl peptidase-4 inhibitor linagliptin in patients with type 2 diabetes undergoing hemodialysis

BACKGROUND

Incretin therapy is feasible in patients with type 2 diabetes mellitus undergoing hemodialysis (HD). However, few studies have examined the safety and efficacy of this therapeutic approach in patients with diabetes and renal impairment. Here, we examined glycemic control and the anti-oxidative-stress effects of the dipeptidyl peptidase (DPP)-4 inhibitor linagliptin in patients with type 2 diabetes undergoing HD.

METHODS

Thirty-five patients with type 2 diabetes undergoing HD (including 13 insulin-treated patients) were switched from ongoing therapy to linagliptin (5 mg, once daily). Levels of fasting blood glucose, C-peptide immunoreactivity (CPR), glycated albumin, B-type natriuretic peptide, oxidized low-density lipoprotein (oxLDL), high-sensitivity C-reactive protein, 8-hydroxy-2'-deoxyguanosine (8OHdG), body mass index, blood pressure, and other biologic characteristics (liver function, renal function, lipid profile) were determined before and 3 months after linagliptin treatment. Patients were classified into insulin-treated and non-insulin groups.

RESULTS

With the exception of levels of total bilirubin, aspartate aminotransferase, and CPR, none of the patients exhibited changes in glucose metabolism after switching to linagliptin treatment. However, oxLDL levels were decreased significantly by linagliptin therapy in the non-insulin-treated group despite the absence of changes in glycemic control.

CONCLUSION

Linagliptin can decrease serum levels of oxLDL in patients with type 2 diabetes undergoing HD independent of its glucose-lowering effect.

Dipeptidyl peptidase-4 inhibitor linagliptin attenuates neointima formation after vascular injury

BACKGROUND

Recently, glucagon-like peptide-1 (GLP-1)-based therapy, including dipeptidyl peptidase-4 (DPP-4) inhibitors and GLP-1 receptor agonists, has emerged as one of the most popular anti-diabetic therapies. Furthermore, GLP-1-based therapy has attracted increased attention not only for its glucose-lowering ability, but also for its potential as a tissue-protective therapy. In this study, we investigated the vascular-protective effect of the DPP-4 inhibitor, linagliptin, using vascular smooth muscle cells (VSMCs).

METHODS

Six-week-old male C57BL/6 mice were divided into control (n =19) and linagliptin (3 mg/kg/day, n =20) treated groups. Endothelial denudation injuries were induced in the femoral artery at 8 weeks of age, followed by evaluation of neointima formation at 12 weeks. To evaluate cell proliferation of rat aortic smooth muscle cells, a bromodeoxyuridine (BrdU) incorporation assay was performed.

RESULTS

Linagliptin treatment reduced vascular injury-induced neointima formation, compared with controls (p <0.05). In these non-diabetic mice, the body weight and blood glucose levels did not change after treatment with linagliptin. Linagliptin caused an approximately 1.5-fold increase in serum active GLP-1 concentration, compared with controls. In addition, the vascular injury-induced increase in the oxidative stress marker, urinary 8-OHdG, was attenuated by linagliptin treatment, though this attenuation was not statistically significant (p =0.064). Moreover, linagliptin did not change the serum stromal cell-derived factor-1α (SDF-1α) or the serum platelet-derived growth factor (PDGF) concentration. However, linagliptin significantly reduced in vitro VSMC proliferation.

CONCLUSION

Linagliptin attenuates neointima formation after vascular injury and VSMC proliferation beyond the glucose-lowering effect.