Cross-talk between the dipeptidyl peptidase-4 and stromal cell-derived factor-1 in stem cell homing and myocardial repair: Potential impact of dipeptidyl peptidase-4 inhibitors.Pharmacol Ther. 2016;167:100-107. [PMID: 27484974 DOI: 10.1016/j.pharmthera.2016.07.009]

Impact of immunosuppressive drugs on efficacy of mesenchymal stem cell therapy for suppressing renal fibrosis

Preemptive regenerative medicine using mesenchymal stem cells (MSCs) may provide a novel therapeutic approach to prevent the progression from organ damage to organ failure. Although immunosuppressive drugs are often used in patients with organ disorder, their impact on MSC therapy remains unclear. We investigated the effects of immunosuppressive drugs on the therapeutic efficacy of MSCs. We created unilateral ureteral obstruction models, as a well-established model of renal fibrosis, a preliminary stage of organ failure. Three immunosuppressive drugs (methylprednisolone, cyclosporine, and cyclophosphamide) were intraperitoneally administered 3 days after surgery, and MSCs were injected via tail vein the following day. Preadministration of methylprednisolone or cyclophosphamide interfered with MSC activation by reducing expression of interferon-gamma (IFN-γ) and high-mobility group box-1 protein, thus significantly attenuating the therapeutic efficacy of MSCs. Preadministration of cyclophosphamide downregulated the expression of stromal cell-derived factor-1/C-X-C motif ligand 12, which is a potent migration factor for MSCs, resulting in reduced MSC engraftment in the renal cortex. IFN-γ-preconditioned activated MSCs were unaffected by these drugs and maintained their beneficial therapeutic effects. Cyclosporine preadministration had no effect on the therapeutic efficacy of MSCs. Our study demonstrated that the administration of certain immunosuppressive drugs interfered with MSC activation and engraftment at the site of injury, resulting in a significant attenuation of their therapeutic efficacy. These findings provide crucial information for selecting patients suitable for MSC therapy. Use of MSCs preactivated with IFN-γ or other means is preferred for patients on methylprednisolone or cyclophosphamide.

Bis(benzimidazol-2-yl)amine-Based DPP-4 Inhibitors Potentially Suitable for Combating Diabetes and Associated Nervous System Alterations

Bis(benzimidazol-2-yl)amine scaffold is not present in dipeptidyl peptidase-4 (DPP-4) inhibitors published so far. Herein, the inhibitory potential of bis(benzimidazol-2-yl)amine derivatives against DPP-4 was evaluated. In non-competitive inhibition mode, three representatives 5, 6, and 7 inhibited DPP-4 in vitro with IC50 values below 50 μM. The assessed binding pocket of DPP-4 for these benzimidazoles includes the S2 extensive subsite's residues Phe357 and Arg358. None of the lead compounds showed cytotoxicity to human neuroblastoma SH-SY5Y cells at concentrations lower than 10 μM. None showed significant binding affinity at dopamine D2, D3, and histamine H1, H3 receptors, at concentrations lower than 10 μM, leading to preferable outcomes due to mutually opposite effects of these neurotransmitters on each other. The potential beneficial effects on dopamine synthesis and the survival of dopaminergic neurons could be mediated by DPP-4 inhibition. These effective noncompetitive DPP-4 inhibitors, with inhibitory potential better than reference diprotin A (relative inhibitory potency compared to diprotin A is 3.39 and 1.54 for compounds 7 and 5, respectively), with the absence of cytotoxicity to SH-SY5Y cells, are valuable candidates for further evaluation for the treatment of diabetes and associated disruption of neuronal homeostasis.

One Endothelium-Targeted Combined Nucleic Acid Delivery System for Myocardial Infarction Therapy

Acute myocardial infarction (MI) and ischemic heart disease are the leading causes of heart failure and mortality. Currently, research on MI treatment is focused on angiogenic and anti-inflammatory therapies. Although endothelial cells (ECs) are critical for triggering inflammation and angiogenesis, no approach has targeted them for the treatment of MI. In this study, we proposed a nonviral combined nucleic acid delivery system consisting of an EC-specific polycation (CRPPR-grafted ethanolamine-modified poly(glycidyl methacrylate), CPC) that can efficiently codeliver siR-ICAM1 and pCXCL12 for the treatment of MI. Animals treated with the combination therapy exhibited better cardiac function than those treated with each nucleic acid alone. In particular, the combination therapy of CPC/siR-ICAM1 and CPC/pCXCL12 significantly improved cardiac systolic function, anti-inflammatory responses, and angiogenesis compared to the control group. In conclusion, CPC-based combined gene delivery systems show impressive performance in the treatment of MI and provide a programmed strategy for the development of codelivery systems for various EC-related diseases.

Saxagliptin promotes random skin flap survival

BACKGROUND

Flap necrosis is a common issue encountered in clinical flap transplantation surgery. Here, we assessed the effects of saxagliptin, a dipeptidyl peptidase-4 inhibitor, on flap survival and explored the underlying mechanisms.

METHODS

A dorsal McFarlane flap model was established in 36 rats, which were randomly divided into a high-dose saxagliptin (HS) group (saxagliptin, 30 mg/kg/day, n = 12), low-dose saxagliptin (LS) group (saxagliptin, 10 mg/kg/day, n = 12), and control group (n = 12). On day 7, flap survival was examined by eye in six rats from each group, along with determination of blood perfusion by laser Doppler flowmetry and angiogenesis by angiography. The remaining rats were sacrificed for harvesting of flap tissue. The status of the flap tissue was examined histopathologically by staining with hematoxylin and eosin (H&E). Oxidative stress was evaluated by determination of superoxide dismutase (SOD) activity and malonaldehyde (MDA) content. Gasdermin D (GSDMD), vascular endothelial growth factor (VEGF), tumor necrosis factor-α (TNF-α), NOD-like receptor pyrin domain containing 3 (NLRP3), interleukin (IL)-6, IL-18, Toll-like receptor 4 (TLR4), IL-1β, caspase-1, and nuclear factor-κB (NF-κB) expression were detected by immunohistochemical analysis.

RESULTS

The experimental group exhibited a larger area of flap survival, with more blood perfusion and neovascularization and better histopathological status than the control group. The degree of oxidative stress and the levels of NF-κB, TLR4, proinflammatory cytokines, and pyroptosis-associated protein were decreased in the experimental group, while the VEGF level was increased in a saxagliptin dose-dependent manner.

CONCLUSION

Saxagliptin promotes random skin flap survival.

Multi-omics analysis reveals a molecular landscape of the early recurrence and early metastasis in pan-cancer

Cancer remains a formidable challenge in medicine due to its propensity for recurrence and metastasis, which can result in unfavorable treatment outcomes. This challenge is particularly acute for early-stage patients, who may experience recurrence and metastasis without timely detection. Here, we first analyzed the differences in clinical characteristics among the primary tumor, recurrent tumor, and metastatic tumor in different stages of cancer, which may be caused by the molecular level. Moreover, the importance of predicting early cancer recurrence and metastasis is emphasized by survival analyses. Next, we used a multi-omics approach to identify key molecular changes associated with early cancer recurrence and metastasis and discovered that early metastasis in cancer demonstrated a high degree of genomic and cellular heterogeneity. We performed statistical comparisons for each level of omics data including gene expression, mutation, copy number variation, immune cell infiltration, and cell status. Then, various analytical techniques, such as proportional hazard model and Fisher's exact test, were used to identify specific genes or immune characteristics associated with early cancer recurrence and metastasis. For example, we observed that the overexpression of BPIFB1 and high initial B-cell infiltration levels are linked to early cancer recurrence, while the overexpression or amplification of ANKRD22 and LIPM, mutation of IGHA1 and MUC16, high fibroblast infiltration level, M1 polarization of macrophages, cellular status of DNA repair are all linked to early cancer metastasis. These findings have led us to construct classifiers, and the average area under the curve (AUC) of these classifiers was greater than 0.75 in The Cancer Genome Atlas (TCGA) cancer patients, confirming that the features we identified could be biomarkers for predicting recurrence and metastasis of early cancer. Finally, we identified specific early sensitive targets for targeted therapy and immune checkpoint inhibitor therapy. Once the biomarkers we identified changed, treatment-sensitive targets can be treated accordingly. Our study has comprehensively characterized the multi-omics characteristics and identified a panel of biomarkers of early cancer recurrence and metastasis. Overall, it provides a valuable resource for cancer recurrence and metastasis research and improves our understanding of the underlying mechanisms driving early cancer recurrence and metastasis.

Therapeutic Perspectives of CD26 Inhibitors in Imune-Mediated Diseases

The enzymatic activity of CD26/DPP4 (dipeptidyl peptidase 4/DPP4) is highlighted in multiple studies to play a vital role in glucose metabolism by cleaving and inactivating the incretins glucagon-like peptide-1 (GLP) and gastric inhibitory protein (GIP). A large number of studies demonstrate that CD26 also plays an integral role in the immune system, particularly in T cell activation. CD26 is extensively expressed in immune cells, such as T cells, B cells, NK cells, dendritic cells, and macrophages. The enzymatic activity of CD26 cleaves and regulates numerous chomokines and cytokines. CD26 inhibitors have been widely used for the treatment of diabetes mellitus, while it is still under investigation as a therapy for immune-mediated diseases. In addition, CD26’s involvement in cancer immunology was also described. The review aims to summarize the therapeutic effects of CD26 inhibitors on immune-mediated diseases, as well as the mechanisms that underpin them.

Repositioning Linagliptin for the Mitigation of Cadmium-Induced Testicular Dysfunction in Rats: Targeting HMGB1/TLR4/NLRP3 Axis and Autophagy

Cadmium, a ubiquitous environmental toxicant, disrupts testicular function and fertility. The dipeptidyl peptidase-4 inhibitor linagliptin has shown pronounced anti-inflammatory and anti-apoptotic features; however, its effects against cadmium-evoked testicular impairment have not been examined. Herein, the present study investigated targeting inflammation, apoptosis, and autophagy by linagliptin for potential modulation of cadmium-induced testicular dysfunction in rats. After 60 days of cadmium chloride administration (5 mg/kg/day, by gavage), testes, epididymis, and blood were collected for analysis. The present findings revealed that linagliptin improved the histopathological lesions, including spermatogenesis impairment and germ cell loss. Moreover, it improved sperm count/motility and serum testosterone. The favorable effects of linagliptin were mediated by curbing testicular inflammation seen by dampening of HMGB1/TLR4 pathway and associated lowering of nuclear NF-κBp65. In tandem, linagliptin suppressed the activation of NLRP3 inflammasome/caspase 1 axis with consequent lowering of the pro-inflammatory IL-1β and IL-18. Jointly, linagliptin attenuated testicular apoptotic responses seen by Bax downregulation, Bcl-2 upregulation, and suppressed caspase 3 activity. With respect to autophagy, linagliptin enhanced the testicular autophagy flux seen by lowered accumulation of p62 SQSTM1 alongside upregulation of Beclin 1. The observed autophagy stimulation was associated with elevated AMPK (Ser487) phosphorylation and lowered mTOR (Ser2448) phosphorylation, indicating AMPK/mTOR pathway activation. In conclusion, inhibition of testicular HMGB1/TLR4/NLRP3 pro-inflammatory axis and apoptosis alongside stimulation of autophagy were implicated in the favorable actions of linagliptin against cadmium-triggered testicular impairment.

The Roles of Dipeptidyl Peptidase 4 (DPP4) and DPP4 Inhibitors in Different Lung Diseases: New Evidence

CD26/Dipeptidyl peptidase 4 (DPP4) is a type II transmembrane glycoprotein that is widely expressed in various organs and cells. It can also exist in body fluids in a soluble form. DPP4 participates in various physiological and pathological processes by regulating energy metabolism, inflammation, and immune function. DPP4 inhibitors have been approved by the Food and Drug Administration (FDA) for the treatment of type 2 diabetes mellitus. More evidence has shown the role of DPP4 in the pathogenesis of lung diseases, since it is highly expressed in the lung parenchyma and the surface of the epithelium, vascular endothelium, and fibroblasts of human bronchi. It is a potential biomarker and therapeutic target for various lung diseases. During the coronavirus disease-19 (COVID-19) global pandemic, DPP4 was found to be an important marker that may play a significant role in disease progression. Some clinical trials on DPP4 inhibitors in COVID-19 are ongoing. DPP4 also affects other infectious respiratory diseases such as Middle East respiratory syndrome and non-infectious lung diseases such as pulmonary fibrosis, lung cancer, chronic obstructive pulmonary disease (COPD), and asthma. This review aims to summarize the roles of DPP4 and its inhibitors in infectious lung diseases and non-infectious diseases to provide new insights for clinical physicians.

Influence of Dipeptidyl Peptidase-4 (DPP4) on Mesenchymal Stem-Cell (MSC) Biology: Implications for Regenerative Medicine - Review

Dipeptidyl peptidase IV (DPP4) is a ubiquitous protease that can be found in membrane-anchored or soluble form. Incretins are one of the main DPP4 substrates. These hormones regulate glucose levels, by stimulating insulin secretion and decreasing glucagon production. Because DPP4 levels are high in diabetes, DPP4 inhibitor (DPP4i) drugs derived from gliptin are widespread used as hypoglycemic agents for its treatment. However, as DPP4 recognizes other substrates such as chemokines, growth factors and neuropeptides, pleiotropic effects have been observed in patients treated with DPP4i. Several of these substrates are part of the stem-cell niche. Thus, they may affect different physiological aspects of mesenchymal stem-cells (MSC). They include viability, differentiation, mobilization and immune response. MSC are involved in tissue homeostasis and regeneration under both physiological and pathological conditions. Therefore, such cells and their secretomes have a high clinical potential in regenerative medicine. In this context, DPP4 activity may modulate different aspects of MSC regenerative capacity. Therefore, the aim of this review is to analyze the effect of different DPP4 substrates on MSC. Likewise, how the regulation of DPP4 activity by DPP4i can be applied in regenerative medicine. That includes treatment of cardiovascular and bone pathologies, cutaneous ulcers, organ transplantation and pancreatic beta-cell regeneration, among others. Thus, DPP4i has an important clinical potential as a complement to therapeutic strategies in regenerative medicine. They involve enhancing the differentiation, immunomodulation and mobilization capacity of MSC for regenerative purposes.

Acute and long-term effects of saxagliptin on a set of cardiovascular targets measured at fasting and post-prandially in obese patients with impaired glucose tolerance: A placebo-controlled study

BACKGROUND AND AIMS

Studies of dipeptidyl peptidase inhibitors (DPP4is) report heterogeneous effects on cardiovascular targets in type 2 diabetes. This study aimed to investigate, in patients with impaired glucose tolerance (IGT), whether saxagliptin, a DPP4i, had beneficial cardiovascular effects at fasting and during the post-prandial state.

METHODS AND RESULTS

In this randomized, placebo-controlled, double-blind, single-center pilot exploratory study, we included obese individuals with IGT. Twenty-four individuals (BMI 36.8 ± 4.8 kg/m²) were randomized to receive for 12 weeks either saxagliptin 5 mg a day or placebo. They were explored before and after a standardized breakfast for biological markers; microcirculatory blood flow at baseline and after transcutaneous administration of acetylcholine (Periflux System 5000® PERIMED); post-occlusive digital reactive hyperhemia (Endopat2000®); pulse wave velocity, augmentation index, central pulse pressure and subendocardial viability ratio (Sphygmocor®); cardiac hemodynamic parameters and cardiovascular autonomic nervous system activity (Task force monitor®). The results of all the investigations were similar after breakfast in the two groups at Visit 1 (acute post-prandial effects, after the first tablet) and Visit 2 (long-term post-prandial effects), and at fasting at Visit 1 and 2 (long-term effects, after 12 weeks of treatment). Only at Visit 2 the decrease in cardiac vagal activity occurring after breakfast was more sustained in the saxagliptin group than in the placebo group (interaction between treatment and time effect: p = 0.016).

CONCLUSION

In obese patients with IGT, the effects of saxagliptin on the large set of cardiovascular parameters measured are neutral, except for a more marked post-prandial depression of vagal activity.

CLINICAL TRIAL REGISTRATION NUMBER

NCT01521312.

Dipeptidyl peptidase-4 inhibitor-induced autoimmune diseases: Current evidence

Dipeptidyl peptidase-4 inhibitors (DPP-4i) have an important place in the management of type 2 diabetes. The DPP-4 enzyme is ubiquitously distributed throughout the human body and has multiple substrates through which it regulates several important physiological functions. DPP-4 regulates several immune functions, including T-cell activation, macrophage function, and secretion of cytokines. Studies have reported an increase in autoimmune diseases like bullous pemphigoid, inflammatory bowel disease, and arthritis with DPP-4i use. The relationship of DPP-4i and autoimmune diseases is a complex one and warrants further research into the effect of DPP-4 inhibition on the immune system to understand the pathogenesis more clearly. Whether a particular cluster of autoimmune diseases is associated with DPP-4i use remains an important contentious issue. Nevertheless, a heightened awareness from the clinicians is required to identify and treat any such diseases. Through this review, we explore the clinical and pathophysiological characteristics of this association in light of recent evidence.

Modifying strategies for SDF-1/CXCR4 interaction during mesenchymal stem cell transplantation

Mesenchymal stem cell (MSC) transplantation is regarded as a promising candidate for the treatment of ischaemic heart disease. The major hurdles for successful clinical translation of MSC therapy are poor survival, retention, and engraftment in the infarcted heart. Stromal cell-derived factor-1/chemokine receptor 4 (SDF-1/CXCR4) constitutes one of the most efficient chemokine/chemokine receptor pairs regarding cell homing. In this review, we mainly focused on previous studies on how to regulate the SDF-1/CXCR4 interaction through various priming strategies to maximize the efficacy of mesenchymal stem cell transplantation on ischaemic hearts or to facilitate the required effects. The strengthened measures for enhancing the therapeutic efficacy of the SDF-1/CXCR4 interaction for mesenchymal stem cell transplantation included the combination of chemokines and cytokines, hormones and drugs, biomaterials, gene engineering, and hypoxia. The priming strategies on recipients for stem cell transplantation included ischaemic conditioning and device techniques.

Purine adducts as a presumable missing link for aristolochic acid nephropathy-related cellular energy crisis, potential anti-fibrotic prevention and treatment

Aristolochic acid nephropathy is a progressive exposome-induced disease characterized by tubular atrophy and fibrosis culminating in end-stage renal disease and malignancies. The molecular mechanisms of the energy crisis as a putative cause of fibrosis have not yet been elucidated. In light of the fact that aristolochic acid forms DNA and RNA adducts by covalent binding of aristolochic acid metabolites to exocyclic amino groups of (deoxy)adenosine and (deoxy)guanosine, we hypothesize here that similar aristolochic acid adducts may exist with other purine-containing molecules. We also provide new insights into the aristolochic acid-induced energy crisis and presumably a link between already known mechanisms. In addition, an overview of potential targets in fibrosis treatment is provided, which is followed by recommendations on possible preventive measures that could be taken to at least postpone or partially alleviate aristolochic acid nephropathy.

Structure-Activity Relationship Analysis of Cocrystallized Gliptin-like Pyrrolidine, Trifluorophenyl, and Pyrimidine-2,4-Dione Dipeptidyl Peptidase-4 Inhibitors

Approved and potent reported dipeptidyl peptidase-4 (DPP-4) inhibitors with gliptin-like structures are classified here according to their structures and mechanisms of the inhibition in three groups: (i) those with pyrrolidine or analogs as P1 fragment with α-aminoacyl linker, (ii) structures with trifluorophenyl moiety or analogs as P1 fragment with β-aminobutanoyl linker, and (iii) DPP-4 inhibitors with pyrimidine-2,4-dione or analogs as P1' fragment. The structure-activity relationship analysis was performed for those whose cocrystallized structures with the enzyme were published. While inhibitors with pyrrolidine and trifluorophenyl moiety or analogs as P1 fragment bind in a similar way in S1, S2 and S2 extensive domains of the enzyme, the binding mode of pyrimidine-2,4-dione derivatives/analogs differs with additional interactions in S1' and S2' pockets. Three general schemes of fragmented gliptins and gliptin-like structures with the enzyme and protein-ligand interaction fingerprints were made, which might be useful in the creation of DPP-4 inhibitor's design strategies.

The Diabetic Cardiomyopathy: The Contributing Pathophysiological Mechanisms

Individuals with diabetes mellitus (DM) disclose a higher incidence and a poorer prognosis of heart failure (HF) than non-diabetic people, even in the absence of other HF risk factors. The adverse impact of diabetes on HF likely reflects an underlying “diabetic cardiomyopathy” (DM–CMP), which may by exacerbated by left ventricular hypertrophy and coronary artery disease (CAD). The pathogenesis of DM-CMP has been a hot topic of research since its first description and is still under active investigation, as a complex interplay among multiple mechanisms may play a role at systemic, myocardial, and cellular/molecular levels. Among these, metabolic abnormalities such as lipotoxicity and glucotoxicity, mitochondrial damage and dysfunction, oxidative stress, abnormal calcium signaling, inflammation, epigenetic factors, and others. These disturbances predispose the diabetic heart to extracellular remodeling and hypertrophy, thus leading to left ventricular diastolic and systolic dysfunction. This Review aims to outline the major pathophysiological changes and the underlying mechanisms leading to myocardial remodeling and cardiac functional derangement in DM-CMP.

Role of Dipeptidyl Peptidase-4 in Atherosclerotic Cardiovascular Disease in Humans and Animals with Chronic Stress

Exposure to psychosocial stress is a risk factor for cardiovascular disease, including vascular atherosclerosis-based cardiovascular disease (ACVD). Dipeptidyl peptidase-4 (DPP-4) is a complex enzyme that acts as a membrane-anchored cell surface exopeptidase. DPP-4 is upregulated in metabolic and inflammatory cardiovascular disorders. DPP-4 exhibits many physiological and pharmacological functions by regulating its extremely abundant substrates, such as glucagon-like peptide-1 (GLP-1). Over the last 10 years, emerging data have demonstrated unexpected roles of DPP-4 in extracellular and intracellular signaling, immune activation, inflammation, oxidative stress production, cell apoptosis, insulin resistance, and lipid metabolism. This mini-review focuses on recent novel findings in this field, highlighting a DPP-4-mediated regulation of GLP-1-dependent and -independent signaling pathways as a potential therapeutic molecular target in treatments of chronic psychological stress-related ACVD in humans and animals.

Cell augmentation strategies for cardiac stem cell therapies

Myocardial infarction (MI) has been the primary cause of death in developed countries, resulting in a major psychological and financial burden for society. Current treatments for acute MI are directed toward rapid restoration of perfusion to limit damage to the myocardium, rather than promoting tissue regeneration and subsequent contractile function recovery. Regenerative cell therapies (CTs), in particular those using multipotent stem cells (SCs), are in the spotlight for treatment post‐MI. Unfortunately, the efficacy of CTs is somewhat limited by their poor long‐term viability, homing, and engraftment to the myocardium. In response, a range of novel SC‐based technologies are in development to provide additional cellular modalities, bringing CTs a step closer to the clinic. In this review, the current landscape of emerging CTs and their augmentation strategies for the treatment post‐MI are discussed. In doing so, we highlight recent advances in cell membrane reengineering via genetic modifications, recombinant protein immobilization, and the utilization of soft biomimetic scaffold interfaces.

Glucose-Lowering Medications and Cardiovascular Outcomes

PURPOSE OF THE REVIEW

The purpose of this review is to examine recent evidence supporting CV safety profile and improvement of CV outcomes of some of the newer classes of diabetic medications.

RECENT FINDINGS

Diabetes mellitus (DM) is associated with increased risk of cardiovascular disease (CVD). Thus, CVD management is critical in diabetic patients. Since 2008, the US Food and Drug Administration (FDA) has mandated that all newer diabetic medications should establish cardiovascular safety before it is approved for use. Diabetic medications that also lower CV risk would be a significant advancement as shown in recent studies. There are 3 new class of diabetic medications: Dipeptidyl peptidase-4 inhibitors (DPP-4), glucagon-like peptide receptor agonists (GLP-1 RA), and sodium-glucose cotransporter type 2 (SGLT 2) inhibitors which have established both CV safety and improvement in CV outcomes with some drugs. In patients with type 2 diabetes and established atherosclerotic cardiovascular disease, multiple atherosclerotic cardiovascular disease risk factors, or diabetic kidney disease, a sodium-glucose cotransporter 2 inhibitor, or a glucagon-like peptide 1 receptor agonist with demonstrated cardiovascular benefit is recommended to reduce the risk of major adverse cardiovascular events.

Novel Antidiabetic Agents: Cardiovascular and Safety Outcomes

BACKGROUND

Concerns of elevated cardiovascular risk with some anti-diabetic medications warranted trials on the cardiovascular outcome to demonstrate cardiovascular safety of newly marketed anti-diabetic drugs. Although these trials were initially designed to evaluate safety, some of these demonstrated significant cardiovascular benefits.

PURPOSE OF REVIEW

We reviewed the cardiovascular and safety outcomes of novel antidiabetic agents in patients with type 2 diabetes and established cardiovascular disease or at high risk of it. We included the outcomes of safety trials, randomized controlled trials, meta-analysis, large cohort studies, and real-world data, which highlighted the cardiovascular profile of DPP-4is, GLP-1RAs and SGLT-2is.

CONCLUSION

Although DPP-4is demonstrated non-inferiority to placebo, gaining cardiovascular safety, as well market authorization, SGLT-2is and most of the GLP-1RAs have shown impressive cardiovascular benefits in patients with T2D and established CVD or at high risk of it. These favorable effects of novel antidiabetic agents on cardiovascular parameters provide novel therapeutic approaches in medical management, risk stratification and prevention.

Adverse event profiles of dipeptidyl peptidase-4 inhibitors: data mining of the public version of the FDA adverse event reporting system

BACKGROUND

To describe and analyze the patterns of adverse events associated with dipeptidyl peptidase-4 inhibitors (DPP-4is) (sitagliptin, saxagliptin, linagliptin, vildagliptin, and alogliptin) from the FDA Adverse Event Reporting System (FAERS) and to highlight areas of safety concerns.

METHODS

Adverse events spontaneously submitted to the FAERS between 2004 Q1 to 2019 Q2 were included. The online tool OpenVigil 2.1 was used to query the database. The research relied on definitions of preferred terms (PTs) specified by the Medical Dictionary for Regulatory Activities (MedDRA) and the standardized MedDRA Queries (SMQ). The reporting odds ratio (ROR), with 95% confidence intervals (CIs) was calculated for disproportionality analysis.

RESULTS

Over 16 years, a total of 9706 adverse event reports were identified. Alogliptin was excluded from further analysis due to insufficient sample size. Compared with the non-insulin antidiabetic drugs, the four DPP-4is were all disproportionately associated with four SMQs: "gastrointestinal nonspecific inflammation and dysfunctional conditions," "hypersensitivity," "severe cutaneous adverse reactions," and "noninfectious diarrhoea". As for PT level analyses, DPP-4is are associated with higher reporting of the gastrointestinal tract, pancreas, malignancies, infection, musculoskeletal disorders, general disorders, hypersensitivity, and skin AEs.

CONCLUSIONS

Data mining of the FAERS is useful for examining DPP-4 inhibitors-associated adverse events. The findings of the present study are compatible with clinical experience, and it provides valuable information to decision-makers and healthcare providers in clinical practice.

The Vicious Circle of Left Ventricular Dysfunction and Diabetes: From Pathophysiology to Emerging Treatments

CONTEXT

Diabetes and heart failure (HF) are 2 deadly and strictly related epidemic disorders. The aim of this review is to present an updated discussion of the epidemiology, pathophysiology, clinical presentation and treatment options for HF in diabetes.

EVIDENCE ACQUISITION

Relevant references published up to February 2020 were identified through searches in PubMed. Quality was graded using the Newcastle-Ottawa score in observational studies and the Cochrane Collaboration tool in randomized studies.

EVIDENCE SYNTHESIS

Metabolic and neurohumoral derangements, oxidative stress, inflammation, micro- and macroangiopathy all contribute through complex molecular and cellular mechanisms to cardiac dysfunction in diabetes, which in turn, results as one the most frequent underlying conditions affecting up to 42% of patients with HF and causing a 34% increased risk of cardiovascular death. On top of traditional guideline-based HF medical and device therapies, equally effective in patients with and without diabetes, a new class of glucose-lowering agents acting through the sodium-glucose cotransporter 2 (SGLT2) inhibition showed impressive results in reducing HF outcomes in individuals with diabetes and represents an active area of investigation.

CONCLUSIONS

Diabetes and HF are strictly linked in a bidirectional and deadly vicious circle difficult to break. Therefore, preventive strategies and a timely diagnosis are crucial to improve outcomes in such patients. SGLT2 inhibitors represent a major breakthrough with remarkably consistent findings. However, it is still not clear whether their benefits may be definitely extended to patients with HF with preserved ejection fraction, to those without diabetes and in the acute setting.

DPP-4 Inhibitors in the Prevention/Treatment of Pulmonary Fibrosis, Heart and Kidney Injury Caused by COVID-19-A Therapeutic Approach of Choice in Type 2 Diabetic Patients?

Since the outbreak of SARS-CoV-2 virus more than 12,500,000 cases have been reported worldwide. Patients suffering from diabetes and other comorbidities are particularly susceptible to severe forms of the COVID-19, which might result in chronic complications following recovery. Dipeptidyl peptidase-4 inhibitors exert beneficial effects in prevention/treatment of pulmonary fibrosis, heart, and kidney injury, and since they may be a long-term consequence caused by COVID-19, it is reasonable to expect that DPP-4 inhibitors might be beneficial in alleviating long-term consequences of COVID-19. With that in mind, we would like to voice our concerns over chronic implications following recovery from COVID-19, especially not only in diabetic but also in non-diabetic patients, and to indicate that some preventive measures could be undertaken by application of DPP-4 inhibitors.

Effect of Stem Cells, Ascorbic Acid and SERCA1a Gene Transfected Stem Cells in Experimentally Induced Type I Diabetic Myopathy

Background and Objectives

Sarco/endoplasmic reticulum Ca^2＋-ATPase (SERCA) inhibition was proved in streptozotocin (STZ)-diabetic rats. The present study aimed at investigating and comparing the therapeutic effect of bone marrow mesenchymal stem cells (BMMSCs), BMMSCs combined with ascorbic acid (AA) and SERCA1a gene transfected BMMSCs in induced type I diabetic myopathy of male albino rat.

Methods and Results

54 rats were divided into donor group of 6 rats for isolation, propagation and characterization of BMMSCs and SERCA1a transfected BMMSCs, groups I∼V 48 rats. Group I of 8 control rats, group II (Diabetic) of 10 rats given STZ 50 mg/kg intraperitoneal, group III (BMMSCs) of 10 rats given STZ and BMMSCs intravenous (IV), group IV (BMMSCs and AA) of 10 rats given STZ, BMMSCs IV and AA 500 mg/kg and group V (SERCA 1a transfected BMMSCs) of 10 rats given STZ and SERCA1a transfected BMMSCs IV. The rats were sacrificed after 8 weeks. Gastrocnemius specimens were subjected to biochemical, histological, morphometric and statistical studies. Diabetic rats revealed inflammatory and degenerative muscle changes, a significant increase in blood glucose level, mean DNA fragmentation and mean MDA values and a significant decrease in mean GSH and catalase values, area of pale nuclei, area% of CD105 and CD34 ＋ve cells, SERCA1a protein and gene values. The morphological changes regressed by therapy. In group III significant decrease in DNA fragmentation and MDA, significant increase in GSH and catalase, significant increase in the mean area of pale nuclei, area % of CD105 and CD34 ＋ve cells versus diabetic group. In group IV, same findings as group III versus diabetic and BMMSCs groups. In group V, same findings as group IV versus diabetic and treated groups. Western blot and PCR proved a mean value of SERCA1a protein and gene comparable to the control group. Mean calcium concentration values revealed a significant increase in the diabetic group, in BMMSCs and AA group versus control and SERCA1a group.

Conclusions

SERCA1a transfected BMMSCs proved a definite therapeutic effect, more remarkable than BMMSCs combined with AA. This effect was evidenced histologically and confirmed by significant changes in the biochemical tests indicating oxidative stress, muscle calcium concentration, morphometric parameters and PCR values of SERCA1a.

The Effects of DPP-4 Inhibitors, GLP-1RAs, and SGLT-2/1 Inhibitors on Heart Failure Outcomes in Diabetic Patients With and Without Heart Failure History: Insights From CVOTs and Drug Mechanism

Patients with type 2 diabetes (T2D) have a higher risk of heart failure (HF) than healthy people, and the prognosis of patients with diabetes and current or previous HF is worse than that of patients with only diabetes. We reviewed the HF outcomes in recently published cardiovascular outcome trials (CVOTs) of three new classes of anti-diabetic agents, namely, dipeptidyl peptidase-4 inhibitors (DPP-4is), glucagon-like-peptide 1 receptor agonists (GLP-1RAs), and sodium glucose cotransporter-2 inhibitors (SGLT-2is) or SGLT-2 and SGLT-1 dual inhibitors and divided the patients into two groups based on the history of HF (with or without) and analyzed their risks of HHF based on the receipt of the aforementioned anti-diabetes drug types. Since the follow-up period differed among the trials, we expressed the rate of HHF as events/1,000 person-years to describe the HF outcome. At last we pooled the data and analyzed their different effects and mechanisms on heart failure outcomes. Although DPP-4is did not increase the risk of HHF in T2D patients with a history of HF, they were associated with a significantly higher risk of HHF among patients without history of HF. Some GLP-1RAs reduced the risk of macrovascular events, but none of these drugs reduced the risk of HHF in patients with T2D irrespective of their HF history. It was not clarified whether SGLT-1/2is can improve the prognosis of macrovascular events in patients with T2D, but these drugs reduced the risk of HHF regardless of patients' histories of HF. This information may be useful or referential for the "precise" selection of hyperglycemic medications. Further researches still needed to clarify the mechanisms of these anti-diabetic medications.

Benzo[4,5]thieno[2,3-d]pyrimidine phthalimide derivative, one of the rare noncompetitive inhibitors of dipeptidyl peptidase-4

A small library of benzo[4,5]thieno[2,3-d]pyrimidine phthalimide and amine derivatives was evaluated for inhibitory activity against dipeptidyl peptidase-4 (DPP-4). The phthalimide derivatives exhibited better activity than the amine precursors, with 2-(2-(3-chlorobenzyl)-5,6,7,8-tetrahydrobenzo[4,5]thieno[2,3-d]pyrimidin-4-yl)isoindoline-1,3-dione (compound 14) as the most effective inhibitor (IC₅₀  = 34.17 ± 5.11 μM). The five most potent selected inhibitors did not show cytotoxicity to a greater extent on Caco-2 cells, even at a concentration of 250 μM. Compound 14 is considered as a novel representative of the rare noncompetitive DPP-4 inhibitors. Molecular docking and dynamics simulation indicated the importance of the Tyr547, Lys554, and Trp629 residues of DPP-4 in the formation of the enzyme-inhibitor complex. These observations could be potentially utilized for the rational design and optimization of novel (structurally similar, with phthalimide moiety, or different) noncompetitive DPP-4 inhibitors, which are anyway rare, but favorable in terms of the saturation of substrate competition.

Heart failure in the patient with diabetes: Epidemiology, aetiology, prognosis, therapy and the effect of glucose-lowering medications

In people with type 2 diabetes the frequency of heart failure (HF) is increased and mortality from HF is higher than with non-diabetic HF. The increased frequency of HF is attributable to the cardiotoxic tetrad of ischaemic heart disease, left ventricular hypertrophy, diabetic cardiomyopathy and an extracellular volume expansion resistant to atrial natriuretic peptides. Activation of the renin-angiotensin-aldosterone system and sympathetic nervous systems results in cardiac remodelling, which worsens cardiac function. Reversal of remodelling can be achieved, and cardiac function improved in people with HF with reduced ejection fraction (HFrEF) by treatment with angiotensin-converting enzyme inhibitors and β-blockers. However, with HF with preserved ejection fraction (HFpEF), only therapy for the underlying risk factors helps. Blockers of mineralocorticoid receptors may be beneficial in both HFrEF and HFpEF. Glucose-lowering drugs can have a negative effect (insulin, sulphonylureas, dipeptidyl peptidase-4 inhibitors and thiazolidinediones), a neutral effect (α-glucosidase inhibitors and glucagon-like peptide-1 receptor agonists) or a positive effect (sodium-glucose co-transporter-2 inhibitors and metformin).

What doesn't kill you makes you stranger: Dipeptidyl peptidase-4 (CD26) proteolysis differentially modulates the activity of many peptide hormones and cytokines generating novel cryptic bioactive ligands

Dipeptidyl peptidase 4 (DPP4) is an exopeptidase found either on cell surfaces where it is highly regulated in terms of its expression and surface availability (CD26) or in a free/circulating soluble constitutively available and intrinsically active form. It is responsible for proteolytic cleavage of many peptide substrates. In this review we discuss the idea that DPP4-cleaved peptides are not necessarily inactivated, but rather can possess either a modified receptor selectivity, modified bioactivity, new antagonistic activity, or even a novel activity relative to the intact parent ligand. We examine in detail five different major DPP4 substrates: glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), peptide tyrosine-tyrosine (PYY), and neuropeptide Y (NPY), and stromal derived factor 1 (SDF-1 aka CXCL12). We note that discussion of the cleaved forms of these five peptides are underrepresented in the research literature, and are both poorly investigated and poorly understood, representing a serious research literature gap. We believe they are understudied and misinterpreted as inactive due to several factors. This includes lack of accurate and specific quantification methods, sample collection techniques that are inherently inaccurate and inappropriate, and a general perception that DPP4 cleavage inactivates its ligand substrates. Increasing evidence points towards many DPP4-cleaved ligands having their own bioactivity. For example, GLP-1 can work through a different receptor than GLP-1R, DPP4-cleaved GIP can function as a GIP receptor antagonist at high doses, and DPP4-cleaved PYY, NPY, and CXCL12 can have different receptor selectivity, or can bind novel, previously unrecognized receptors to their intact ligands, resulting in altered signaling and functionality. We believe that more rigorous research in this area could lead to a better understanding of DPP4's role and the biological importance of the generation of novel cryptic ligands. This will also significantly impact our understanding of the clinical effects and side effects of DPP4-inhibitors as a class of anti-diabetic drugs that potentially have an expanding clinical relevance. This will be specifically relevant in targeting DPP4 substrate ligands involved in a variety of other major clinical acute and chronic injury/disease areas including inflammation, immunology, cardiology, stroke, musculoskeletal disease and injury, as well as cancer biology and tissue maintenance in aging.

DPP-4 inhibition: А novel therapeutic approach to the treatment of pulmonary hypertension?

Pulmonary hypertension (PH) is a progressive disorder characterized by alterations of the vascular structure and function in the lungs. Despite the success in its stabilisation by targeting pulmonary vascular tone and endothelial dysfunction, the prognosis remains poor and new therapeutic approaches via neglected macromolecular targets are needed. In the pathophysiology of PH the early stages of vascular remodelling are considered to be reversible, while endothelial to mesenchymal transition and proliferation/migration of fibroblasts play a critical role in staging the irreversible phase. Dipeptidyl peptidase-4 (DPP-4)/CD26 is present and active in the lungs and is expressed constitutively on lung fibroblasts, on which it exerts proliferative effects. Further, it is a marker of migrating fibroblasts and of their functional activation, including collagen synthesis and inflammatory cytokine secretion. Inhibiting DPP-4 improves the reversible phases of vascular dysfunction in PH, but is also highly likely to attenuate endothelial to mesenchymal transition and decrease the proliferation and migration of fibroblasts, preventing fibrosis and, consequently, should prolong or even inhibit entrance to the potentially irreversible phase of PH. Proposed mechanisms that support the multifaceted aspects of DPP-4 inhibition in terms of improving PH, involve pathways and mediators in pulmonary vascular and connective tissue remodelling. The latter are affected by the inhibition of this protease resulting in the synergistic beneficial antioxidative, anti-inflammatory and antifibrotic effects. We offer here an evidence-supported hypothesis that DPP-4 inhibitors are likely to be effective in the irreversible phase of remodelling in PH. Accordingly, we propose PH as a possible novel therapeutic indication for existing and new DPP-4 inhibitors.

CD26/DPP4 - a potential biomarker and target for cancer therapy

CD26/dipeptidyl peptidase (DPP)4 is a membrane-bound protein found in many cell types of the body, and a soluble form is present in body fluids. There is longstanding evidence that various primary tumors and also metastases express CD26/DPP4 to a variable extent. By cleaving dipeptides from peptides with a proline or alanine in the penultimate position at the N-terminus, it regulates the activity of incretin hormones, chemokines and many other peptides. Due to these effects and interactions with other molecules, a tumor promoting or suppressing role can be attributed to CD26/DPP4. In this review, we discuss the existing evidence on the expression of soluble or membrane-bound CD26/DPP4 in malignant diseases, along with the most recent findings on CD26/DPP4 as a therapeutic target in specific malignancies. The expression and possible involvement of the related DPP8 and DPP9 in cancer are also reviewed. A higher expression of CD26/DPP4 is found in a wide variety of tumor entities, however more research on CD26/DPP4 in the tumor microenvironment is needed to fully explore its use as a tumor biomarker. Circulating soluble CD26/DPP4 has also been studied as a cancer biomarker, however, the observed decrease in most cancer patients does not seem to be cancer specific. Encouraging results from experimental work and a recently reported first phase clinical trial targeting CD26/DPP4 in mesothelioma, renal and urological tumors pave the way for follow-up clinical studies, also in other tumor entities, possibly leading to the development of more effective complementary therapies against cancer.

An Overview, Advantages and Therapeutic Potential of Nonpeptide Positive Allosteric Modulators of Glucagon-Like Peptide-1 Receptor

Due to uncomfortable injection regimens of peptidic agonists of glucagon-like peptide-1 receptor (GLP-1R), orally available nonpeptide positive allosteric modulators (PAMs) of GLP-1Rs are foreseen as the possible future mainstream therapy for type 2 diabetes. Herein, current GLP-1R PAMs are reviewed. Based on the effectiveness and in silico predicted physicochemical properties, pharmacokinetics, and toxicity, possible candidates for further development as oral drugs were selected. The suggestion is that GLP-1R PAMs might be used orally alone or in combination with dipeptidyl peptidase-4 (DPP-4) inhibitors, which could offer an optimal treatment option next to metformin monotherapy in type 2 diabetes mellitus, or in a wider spectrum of indications. Quercetin acts as a GLP-1R PAM and DPP-4 inhibitor, and therefore, might be considered as a pioneering agent with a dual mechanism of action, in terms of GLP-1R positive allosteric modulation and DPP-4 inhibition for potentiating GLP-1 dependent effects.

The DPP-4 inhibitor saxagliptin ameliorates ox-LDL-induced endothelial dysfunction by regulating AP-1 and NF-κB

Diabetes-associated cardiovascular complications are the leading cause of death for diabetic patients. Dipeptidyl peptidase 4 (DPP-4) inhibitor agents, known as gliptins, are a class of potent anti-glycemic agents developed to treat diabetes. Recently, gliptins have been shown to have independent cardiovascular benefits. In this study, we revealed the protective role of saxagliptin in vascular endothelial cells. Our data show that saxagliptin suppresses oxidized low-density lipoprotein cholesterol (ox-LDL)-induced expression of its receptor lectin-like ox-LDL receptor-1 (LOX-1). Saxagliptin treatment reduces ox-LDL-induced production of cytokines and vascular adhesion molecules including tumor necrosis factor (TNF-α), interleukin-1β (IL-1β), vascular cell adhesion molecule 1 (VCAM-1), and intercellular cell adhesion molecule-1 (ICAM-1). The presence of saxagliptin suppressed ox-LDL-induced adhesion of monocytes to endothelial cells in co-culture adhesion experiments. Moreover, saxagliptin mitigated ox-LDL-induced production of reactive oxygen species and suppressed elevated expression of endothelial nicotinamide adenine dinucleotide phosphate oxidase subunit (NOX-4) induced by ox-LDL. Mechanistically, saxagliptin exerted inhibitory effects against ox-LDL-induced phosphorylation of JNK kinase, expression of the activator protein 1 (AP-1) subunits c-Jun/c-fos, and AP-1 promoter activity. Saxagliptin also suppressed nuclear factor κB (NF-κB) p65 accumulation and inhibited its promoter activity. Our data elaborate the molecular mechanism of saxagliptin-mediated endothelial protection and indicate that saxagliptin could have vascular benefits independent on its anti-glycemic function.

Cardiovascular Effects of New Oral Glucose-Lowering Agents: DPP-4 and SGLT-2 Inhibitors

Cardiovascular disease (CVD) is a major challenge in the management of type 2 diabetes mellitus. Glucose-lowering agents that reduce the risk of major cardiovascular events would be considered a major advance, as recently reported with liraglutide and semaglutide, 2 glucagon-like peptide-1 receptor agonists, and with empagliflozin and canagliflozin, 2 SGLT-2 (sodium-glucose cotransporter type 2) inhibitors, but not with DPP-4 (dipeptidyl peptidase-4) inhibitors. The present review is devoted to CV effects of new oral glucose-lowering agents. DPP-4 inhibitors (gliptins) showed some positive cardiac and vascular effects in preliminary studies, and initial data from phase 2 to 3 clinical trials suggested a reduction in major cardiovascular events. However, subsequent CV outcome trials with alogliptin, saxagliptin, and sitagliptin showed noninferiority but failed to demonstrate any superiority compared with placebo in patients with type 2 diabetes mellitus and high CV risk. An unexpected higher risk of hospitalization for heart failure was reported with saxagliptin. SGLT-2 inhibitors (gliflozins) promote glucosuria, thus reducing glucose toxicity and body weight, and enhance natriuresis, thus lowering blood pressure. Two CV outcome trials in type 2 diabetes mellitus patients mainly in secondary prevention showed remarkable positive results. Empagliflozin in EMPA-REG-OUTCOME (EMPAgliflozin Cardiovascular OUTCOME Events in Type 2 Diabetes Mellitus Patients) reduced major cardiovascular events, CV mortality, all-cause mortality, and hospitalization for heart failure. In CANVAS (Canagliflozin Cardiovascular Assessment Study), the reduction in CV mortality with canagliflozin failed to reach statistical significance despite a similar reduction in major cardiovascular events. The underlying protective mechanisms of SGLT-2 inhibitors remain unknown and both hemodynamic and metabolic explanations have been proposed. CVD-REAL studies (Comparative Effectiveness of Cardiovascular Outcomes in New Users of Sodium-Glucose Cotransporter-2 Inhibitors; with the limitation of an observational approach) suggested that these favorable results may be considered as a class effect shared by all SGLT-2 inhibitors (including dapagliflozin) and be extrapolated to a larger population of patients with type 2 diabetes mellitus in primary prevention. Ongoing CV outcome trials with other DPP-4 (linagliptin) and SGLT-2 (dapagliflozin, ertugliflozin) inhibitors should provide additional information about CV effects of both pharmacological classes.

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.

Worsening Heart Failure During the Use of DPP-4 Inhibitors: Pathophysiological Mechanisms, Clinical Risks, and Potential Influence of Concomitant Antidiabetic Medications

Although dipeptidyl peptidase (DPP)-4 inhibitors have been reported to have a neutral effect on thromboembolic vaso-occlusive events in large-scale trials, they act to potentiate several endogenous peptides that can exert deleterious cardiovascular effects. Experimentally, DPP-4 inhibitors may augment the ability of glucagon-like peptide-1 to stimulate cyclic adenosine monophosphate in cardiomyocytes, and potentiation of the effects of stromal cell-derived factor-1 by DPP-4 inhibitors may aggravate cardiac fibrosis. These potentially deleterious actions of DPP-4 inhibitors might not become clinically apparent if these drugs were to promote sodium excretion. However, the natriuretic effect of DPP-4 inhibitors is modest, because they act on the distal (rather than proximal) renal tubules. Accordingly, both clinical trials and observational studies have reported an increase in the risk of heart failure in patients with type 2 diabetes who were receiving DPP-4 inhibitors. This risk may be muted in trials with a high prevalence of metformin use or with low and declining background use of insulin and thiazolidinediones. Still, the most vulnerable patients (i.e., those with established heart failure) were not well represented in these studies. The only trial that specifically evaluated patients with pre-existing left ventricular dysfunction observed important drug-related adverse structural and clinical effects. In conclusion, an increased risk of worsening heart failure appears to be a class effect of DPP-4 inhibitors, even in patients without a history of heart failure. Additional clinical trials are urgently needed to elucidate the benefits and risks of DPP-4 inhibitors in patients with established left ventricular dysfunction.

Have dipeptidyl peptidase-4 inhibitors ameliorated the vascular complications of type 2 diabetes in large-scale trials? The potential confounding effect of stem-cell chemokines

Drugs that inhibit dipeptidyl peptidase-4 (DPP-4) are conventionally regarded as incretin-based agents that signal through the glucagon-like peptide-1 (GLP-1) receptor. However, inhibition of DPP-4 also potentiates the stem cell chemokine, stromal cell-derived factor-1 (SDF-1), which can promote inflammation, proliferative responses and neovascularization. In large-scale cardiovascular outcome trials, enhanced GLP-1 signaling has reduced the risk of atherosclerotic ischemic events, potentially because GLP-1 retards the growth and increases the stability of atherosclerotic plaques. However, DPP-4 inhibitors have not reduced the risk of major adverse cardiovascular events, possibly because potentiation of SDF-1 enhances plaque growth and instability, activates deleterious neurohormonal mechanisms, and promotes cardiac inflammation and fibrosis. Similarly, trials with GLP-1 agonists and sodium-glucose cotransporter 2 inhibitors have reported favorable effects on renal function, even after only 3-4 years of treatment. In contrast, no benefits on the rate of decline in glomerular filtration rate have been seen in trials of DPP-4 inhibitors, perhaps because the renal actions of DPP-4 inhibitors are primarily mediated by potentiation of SDF-1, not GLP-1. Experimentally, SDF-1 can promote podocyte injury and glomerulosclerosis. Furthermore, the natriuretic action of SDF-1 occurs primarily in the distal tubules, where it cannot utilize tubuloglomerular feedback to modulate the deleterious effects of glomerular hyperfiltration. Potentiation of SDF-1 in experimental models may also exacerbate both retinopathy and neuropathy. Therefore, although DPP-4 inhibitors have attractive clinical features, the benefits that might be expected from GLP-1 signaling may be undermined by their actions to enhance SDF-1.

High glucose-induced endothelial progenitor cell dysfunction

Vascular complications contribute significantly to morbidity and mortality of diabetes mellitus. The primary cause of vascular complications in diabetes mellitus is hyperglycaemia, associated with endothelial dysfunction and impaired neovascularization. Circulating endothelial progenitor cells was shown to play important roles in vascular repair and promoting neovascularization. In this review, we will demonstrate the individual effect of high glucose on endothelial progenitor cells. Endothelial progenitor cells isolated from healthy subjects exposed to high glucose conditions or endothelial progenitor cells isolated from diabetic patients exhibit reduced number of endothelial cell colony forming units, impaired abilities of differentiation, proliferation, adhesion and migration, tubulization, secretion, mobilization and homing, whereas enhanced senescence. Increased production of reactive oxygen species by the mitochondria seems to play a crucial role in high glucose-induced endothelial progenitor cells deficit. Later, we will review the agents that might be used to alleviate dysfunction of endothelial progenitor cells induced by high glucose. The conclusions are that the relationship between hyperglycaemia and endothelial progenitor cells dysfunction is only beginning to be recognized, and future studies should pay more attention to the haemodynamic environment of endothelial progenitor cells and ageing factors to discover novel treatment agents.

Diabetic microangiopathy: Pathogenetic insights and novel therapeutic approaches

Diabetic microangiopathy, including retinopathy, is characterized by abnormal growth and leakage of small blood vessels, resulting in local edema and functional impairment of the depending tissues. Mechanisms leading to the impairment of microcirculation in diabetes are multiple and still largely unclear. However, a dysregulated vascular regeneration appears to play a key role. In addition, oxidative and hyperosmolar stress, as well as the activation of inflammatory pathways triggered by advanced glycation end-products and toll-like receptors, have been recognized as key underlying events_. Here, we review recent knowledge on cellular and molecular pathways of microvascular disease in diabetes. We also highlight how new insights into pathogenic mechanisms of vascular damage in diabetes may indicate new targets for prevention and treatment.