Dipeptidyl-peptidase IV from bench to bedside: an update on structural properties, functions, and clinical aspects of the enzyme DPP IV

Neuropathogenesis and Neurologic Manifestations of the Coronaviruses in the Age of Coronavirus Disease 2019: A Review

Importance

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in December 2019, causing human coronavirus disease 2019 (COVID-19), which has now spread into a worldwide pandemic. The pulmonary manifestations of COVID-19 have been well described in the literature. Two similar human coronaviruses that cause Middle East respiratory syndrome (MERS-CoV) and severe acute respiratory syndrome (SARS-CoV-1) are known to cause disease in the central and peripheral nervous systems. Emerging evidence suggests COVID-19 has neurologic consequences as well.

Observations

This review serves to summarize available information regarding coronaviruses in the nervous system, identify the potential tissue targets and routes of entry of SARS-CoV-2 into the central nervous system, and describe the range of clinical neurological complications that have been reported thus far in COVID-19 and their potential pathogenesis. Viral neuroinvasion may be achieved by several routes, including transsynaptic transfer across infected neurons, entry via the olfactory nerve, infection of vascular endothelium, or leukocyte migration across the blood-brain barrier. The most common neurologic complaints in COVID-19 are anosmia, ageusia, and headache, but other diseases, such as stroke, impairment of consciousness, seizure, and encephalopathy, have also been reported.

Conclusions and Relevance

Recognition and understanding of the range of neurological disorders associated with COVID-19 may lead to improved clinical outcomes and better treatment algorithms. Further neuropathological studies will be crucial to understanding the pathogenesis of the disease in the central nervous system, and longitudinal neurologic and cognitive assessment of individuals after recovery from COVID-19 will be crucial to understand the natural history of COVID-19 in the central nervous system and monitor for any long-term neurologic sequelae.

A comparative overview of COVID-19, MERS and SARS: Review article

Following the severe acute respiratory syndrome coronavirus (SARS-CoV) and the Middle East respiratory syndrome coronavirus (MERS-CoV), a third, highly pathogenic coronavirus, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) appearing at end of 2019 led to a pandemic, increased panic and attracted global attention. This review analyzes the epidemiology, etiology, clinical characteristics, treatment and sequelae of the severe acute respiratory syndrome (SARS), the Middle East respiratory syndrome (MERS) and the 2019 novel coronavirus disease (COVID-19) to help provide direction for further studies that can help understand COVID-19.

DPP-4 Cleaves α/β-Peptide Bonds: Substrate Specificity and Half-Lives

The incorporation of β-amino acids into a peptide sequence has gained particular attention as β- and α/β-peptides have shown remarkable proteolytic stability, even after a single homologation at the scissile bond. Several peptidases have been shown to cleave such bonds with high specificity but at a much slower rate compared to α-peptide bonds. In this study, a series of analogs of dipeptidyl peptidase-4 (DPP-4) substrate inhibitors were synthesized in order to investigate whether β-amino acid homologation at the scissile bond could be a valid approach to improving peptide stability towards DPP-4 degradation. DPP-4 cleaved the α/β-peptide bond after the N-terminal penultimate Pro with a broad specificity and retained full activity regardless of the β³ -amino acid side chain and peptide length. Significantly improved half-lives were observed for β³ Ile-containing peptides. Replacing the penultimate Pro with a conformationally constrained Pro mimetic led to proteolytic resistance. DPP-4 cleavage of α/β-peptide bonds with a broad promiscuity represents a new insight into the stability of peptide analogs containing β-amino acids as such analogs were thought to be stable towards enzymatic degradation.

Role of angiotensin-converting enzyme 2 (ACE2) in COVID-19

An outbreak of pneumonia caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that started in Wuhan, China, at the end of 2019 has become a global pandemic. Both SARS-CoV-2 and SARS-CoV enter host cells via the angiotensin-converting enzyme 2 (ACE2) receptor, which is expressed in various human organs. We have reviewed previously published studies on SARS and recent studies on SARS-CoV-2 infection, named coronavirus disease 2019 (COVID-19) by the World Health Organization (WHO), confirming that many other organs besides the lungs are vulnerable to the virus. ACE2 catalyzes angiotensin II conversion to angiotensin-(1-7), and the ACE2/angiotensin-(1-7)/MAS axis counteracts the negative effects of the renin-angiotensin system (RAS), which plays important roles in maintaining the physiological and pathophysiological balance of the body. In addition to the direct viral effects and inflammatory and immune factors associated with COVID-19 pathogenesis, ACE2 downregulation and the imbalance between the RAS and ACE2/angiotensin-(1-7)/MAS after infection may also contribute to multiple organ injury in COVID-19. The SARS-CoV-2 spike glycoprotein, which binds to ACE2, is a potential target for developing specific drugs, antibodies, and vaccines. Restoring the balance between the RAS and ACE2/angiotensin-(1-7)/MAS may help attenuate organ injuries. SARS-CoV-2 enters lung cells via the ACE2 receptor. The cell-free and macrophage-phagocytosed virus can spread to other organs and infect ACE2-expressing cells at local sites, causing multi-organ injury.

Dipeptidyl peptidase-4 (DPP4) inhibition in COVID-19

AIMS

SARS-CoV-2 causes severe respiratory syndrome (COVID-19) with high mortality due to a direct cytotoxic viral effect and a severe systemic inflammation. We are herein discussing a possible novel therapeutic tool for COVID-19.

METHODS

Virus binds to the cell surface receptor ACE2; indeed, recent evidences suggested that SARS-CoV-2 may be using as co-receptor, when entering the cells, the same one used by MERS-Co-V, namely the DPP4/CD26 receptor. The aforementioned observation underlined that mechanism of cell entry is supposedly similar among different coronavirus, that the co-expression of ACE2 and DPP4/CD26 could identify those cells targeted by different human coronaviruses and that clinical complications may be similar.

RESULTS

The DPP4 family/system was implicated in various physiological processes and diseases of the immune system, and DPP4/CD26 is variously expressed on epithelia and endothelia of the systemic vasculature, lung, kidney, small intestine and heart. In particular, DPP4 distribution in the human respiratory tract may facilitate the entrance of the virus into the airway tract itself and could contribute to the development of cytokine storm and immunopathology in causing fatal COVID-19 pneumonia.

CONCLUSIONS

The use of DPP4 inhibitors, such as gliptins, in patients with COVID-19 with, or even without, type 2 diabetes, may offer a simple way to reduce the virus entry and replication into the airways and to hamper the sustained cytokine storm and inflammation within the lung in patients diagnosed with COVID-19 infection.

A proopiomelanocortin-derived peptide sequence enhances plasma stability of peptide drugs

Bioactive peptide drugs hold promise for therapeutic application due to their high potency and selectivity but display short plasma half-life. Examination of selected naturally occurring peptide hormones derived from proteolytic cleavage of the proopiomelanocortin (POMC) precursor lead to the identification of significant plasma-stabilizing properties of a 12-amino acid serine-rich orphan sequence NSSSSGSSGAGQ in human γ3-melanocyte-stimulating hormone (MSH) that is homologous to previously discovered NS_n GGH (n = 4-24) sequences in owls. Notably, transfer of this sequence to des-acetyl-α-MSH and the therapeutically relevant peptide hormones neurotensin and glucagon-like peptide-1 likewise enhance their plasma stability without affecting receptor signaling. The stabilizing effect of the sequence module is independent of plasma components, suggesting a direct effect in cis. This natural sequence module may provide a possible strategy to enhance plasma stability, complementing existing methods of chemical modification.

Immunohistochemical Pharmacokinetics of the Anti-diabetes Drug Alogliptin in Rat Kidney and Liver

Alogliptin is one of a new class of therapeutic agents for type 2 diabetes called dipeptidyl peptidase-4 inhibitors. Here, we used immunohistochemistry to investigate the pharmacokinetics of alogliptin at the cell and tissue levels in the rat kidney and liver. One hour after alogliptin administration, the most noticeable immunoreactivity in the kidney was a moderate-to-strong staining in proximal tubule S3 segment epithelial cells. On the other hand, immunostaining was found only in the microvilli of S1 and S2 segment cells. Immunoreactivity was also observed in the glomerulus and distal tubules. Positive cells and almost negative cells coexisted in the collecting ducts. Twenty-four hours after administration, moderate immunostaining remained in the S3 segment but staining in other regions had almost disappeared. In the liver 1 hr after administration, hepatocyte staining differed in the hepatic lobule, with zone III being stronger than zone I. Immunostaining had almost disappeared 24 hr after administration. These findings suggest that alogliptin reabsorption at the kidney and uptake at the hepatocyte vary from region to region and that one or more types of transporter are involved in these processes. In addition, long-term alogliptin use may cause the drug to accumulate in S3 segment, leading to adverse events.

Antiproteinuric effect of DPP-IV inhibitors in diabetic and non-diabetic kidney diseases

Diabetes Mellitus (DM) is a chronic and severe metabolic disease, characterized by chronic hyperglycemia due to insulin resistance and/or reduced insulin secretion. Concerning the non-insulin glucose-lowering therapy for diabetes, Dipeptidyl-peptidase-4 (DPP-4) inhibitors, members of the incretin family, represent new agents, capable of a glycemic control improvement with an advantageous safety profile, given the absence of weight gain, the low incidence of hypoglycemia and the good renal tolerance in patients suffering from chronic renal failure. In addition to demonstrating efficacy in glycemic control through inhibition of GLP-1 degradation, DPP-4 inhibitors (DPP-4is) seem to demonstrate pleiotropic effects, which also make them interesting in both diabetic and non-diabetic nephropathies, especially for their capacity of reducing proteinuria. Several studies about diabetic nephropathy on patients' cohorts and murine models have demonstrated a solid direct relationship between DPP-4 activity and urinary albumin excretion (UAE), thus confirming the capacity of DPP-4is to reduce proteinuria; the mechanism responsible for that effect was studied to assess if it was the result of a direct action on renal impairment or a secondary consequence of the better glycemic control related to these agents. As a result of these more in-depth studies, DPP-4is have demonstrated an improvement of renal inflammation markers and consequent proteinuria reduction, regardless of glucose concentrations. Considering the nephroprotective effects of DPP-4is might be glycemic independent, several studies were conducted to prove the validity of the same effects in non-diabetic nephropathies. Among these studies, DPP-4is demonstrated an improvement of various renal inflammatory markers on several models of non-diabetes dependent renal impairment, confirming their capacity to reduce proteinuria, independently from the action on glucose metabolism. The objective of this review is to present and discuss the so far demonstrated antiproteinuric effect of DPP-4is and their effects on diabetic and non-diabetic nephropathies.

Infectivity of human coronavirus in the brain

A new strain of human coronaviruses (hCoVs), Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), has been identified to be responsible for the current outbreak of the coronavirus disease 2019 (COVID-19). Though major symptoms are primarily generated from the respiratory system, neurological symptoms are being reported in some of the confirmed cases, raising concerns of its potential for intracranial invasion and neurological manifestations, both in the acute phase and in the long-term. At present, it remains unclear the extent to which SARS-CoV-2 is present in the brain, and if so, its pathogenic role in the central nervous system (CNS). Evidence for neuroinvasion and neurovirulence of hCoVs has been recognised in animal and human studies. Given that SARS-CoV-2 belongs to the same family and shares characteristics in terms of receptor binding properties, it is worthwhile exploring its potential CNS manifestations. This review summarises previous findings from hCoVs in relation to the CNS, and compares these with the new strain, aiming to provide a better understanding of the effects of SARS-CoV-2 on the CNS.

Teneligliptin, a DPP-4 Inhibitor, Decreases Plasma Levels of Inflammatory Chemokines During a Standard Meal Test in Patients With Type 2 Diabetes

BACKGROUND

Dipeptidyl peptidase-4 (DPP-4) rapidly inactivates incretin hormones and several chemokines, thus influencing chemokine function. There have recently been several reports that DPP-4 inhibitor therapy is associated with an increased risk of bullous pemphigoid (BP), an autoimmune skin disease. Previous studies have demonstrated an increase of CCL11/Eotaxin, a DPP-4 substrate, in serum and blister fluid from patients with BP. Serum levels of CCL22/macrophage-derived chemokine (MDC) and CXCL10/IP-10, other DPP-4 substrates, are also elevated in BP patients.

MATERIALS AND METHODS

In patients with type 2 diabetes, we investigated the effect of treatment with teneligliptin (a DPP-4 inhibitor) for 24 weeks on plasma levels of CCL11/Eotaxin, CCL22/MDC and CXCL10/IP-10 during a meal test. Ten consecutive patients with type 2 diabetes who showed inadequate glycemic control by metformin and/or sulfonylureas were recruited. A standard meal test was performed at baseline and after 24 weeks of treatment with teneligliptin at 20 mg/day. Blood samples were collected at 0, 30, 60 and 120 minutes after ingestion of the meal. In addition to plasma levels of the 3 chemokine, plasma DPP-4 enzyme activity and soluble DPP-4 antigen were measured.

RESULTS

Treatment with teneligliptin decreased hemoglobin A1c and reduced fasting plasma DPP-4 activity by 90.1% compared with baseline. Unexpectedly, plasma levels of all 3 chemokines (including CCL11/Eotaxin) were not increased after teneligliptin treatment, and instead were significantly lower at every point during the meal test.

CONCLUSIONS

Teneligliptin reduced the plasma concentrations of 3 chemokines (DPP-4 substrates) that may be related to the occurrence of DPP4 inhibitor-associated BP (UMIN000012508).

Dipeptidyl peptidase 4 inhibitors and their potential immune modulatory functions

Dipeptidyl peptidase 4 (DPP4) inhibitors (DPP4is) are oral anti-diabetic drugs (OADs) for the treatment of type 2 diabetes mellitus (T2DM) through inhibiting the degradation of incretin peptides. Numerous investigations have been focused on the effects of DPP4is on glucose homeostasis. However, there are limited evidences demonstrating their Potential modulatory functions in the immune system. DPP4, originally known as the lymphocyte cell surface protein CD26, is widely expressed in many types of immune cells including CD4(+) and CD8(+) T cells, B cells, NK cells, dendritic cells, and macrophages; and regulate the functions of these cells. In addition, DPP4 is capable of modulating plenty of cytokines, chemokines and peptide hormones. Accordingly, DPP4/CD26 is speculated to be involved in various immune/inflammatory diseases and DPP4is may become a new drug class applied in these diseases. This review focuses on the regulatory effects of DPP4is on immune functions and their possible underlying mechanisms. Further clinical studies will be necessitated to fully evaluate the administration of DPP4is in diabetic patients with or without immune diseases.

A poor prognosis in human hepatocellular carcinoma is associated with low expression of DPP4

This study aimed to explore the prognostic role of dipeptidyl peptidase 4 (DPP4) expression in hepatocellular carcinoma (HCC). DPP4 expression was measured in formalin-fixed paraffin-embedded specimens that were gathered from 327 HCC patients. Immunohistochemistry analyses were utilized to examine DPP4 expression characteristics and prognostic values (overall survival (OS) and time to recurrence) of DDP4 in HCC tissues. In addition, a patient-derived xenograft (PDX) model was used to assess the correlation between DPP4 expression and tumor growth in vivo. DPP4 was expressed in low levels in HCC tissues in contrast to paired peritumoral tissues (38 cases were down-regulated in a total of 59 cases, 64.4%. P=0.0202). DPP4 expression was significantly correlated with TNM stage (P=0.038), tumor number (P=0.035), and vascular invasion (P=0.024), and significantly reduced in patients who were in TNM stages II and III-V, with multiple tumors, and with microvascular invasion compared to patients with TNM stage I, single tumor, and no microvascular invasion. Notably, HCC tissues with low expression of DPP4 had poor OS (P=0.016) compared with HCC tissues with high expression of DPP4, and results from PDX model showed that tumor growth was significantly faster in HCC patients that lowly expressed DPP4 compared to those with highly expressed DPP4. Our findings suggested that low levels of DPP4 could impact the aggressiveness of HCC and contribute to a poor prognosis.

Dipeptidyl Peptidase-4 at the Interface Between Inflammation and Metabolism

Dipeptidyl peptidase-4 (DPP4) is a serine protease that rapidly inactivates the incretin peptides, glucagon-like peptide-1, and glucose-dependent insulinotropic polypeptide to modulate postprandial islet hormone secretion and glycemia. Dipeptidyl peptidase-4 also has nonglycemic effects by controlling the progression of inflammation, which may be mediated more through direct protein-protein interactions than catalytic activity in the context of nonalcoholic fatty liver disease (NAFLD), obesity, and type 2 diabetes (T2D). Failure to resolve inflammation resulting in chronic subclinical activation of the immune system may influence the development of metabolic dysregulation. Thus, through both its cleavage and regulation of the bioactivity of peptide hormones and its influence on inflammation, DPP4 exhibits a diverse array of effects that can influence the progression of metabolic disease. Here, we highlight our current understanding of the complex biology of DPP4 at the intersection of inflammation, obesity, T2D, and NAFLD. We compare and review new mechanisms identified in basic laboratory and clinical studies, which may have therapeutic application and relevance to the pathogenesis of obesity and T2D.

Dipeptidyl Peptidase IV as a Muscle Myokine

Dipeptidyl peptidase IV (DPP-IV) is a unique serine protease that exists in a membrane bound state and in a soluble state in most tissues in the body. DPP-IV has multiple targets including cytokines, neuropeptides, and incretin hormones, and plays an important role in health and disease. Recent work suggests that skeletal muscle releases DPP-IV as a myokine and participates in control of muscle blood flow. However, few of the functions of DPP-IV as a myokine have been investigated to date and there is a poor understanding about what causes DPP-IV to be released from muscle.

Dipeptidyl Peptidase-4 Is a Target Protein of Epigallocatechin-3-Gallate

Epigallocatechin-3-gallate (EGCG), a major active ingredient in green tea, has various health benefits. It affects glucose metabolism, but the mechanism is not well understood. This study aimed to identify targets of EGCG related to glucose metabolism. The core fragment of EGCG is a flavonoid. The flavonoid scaffold was used as a substructure to find proteins cocrystallized with flavonoids in the Protein Data Bank. The proteins identified were screened in PubMed for known relationships with diabetes. Dipeptidyl peptidase-4 (DPP4; PDB 5J3J) was identified following this approach. By molecular docking, the interactions of EGCG and DPP4 were assessed. To test the stability of the interactions between EGCG and DPP4, molecular dynamics simulation for 100 ns was performed using Desmond software. In vitro, the concentration of EGCG required to inhibit DPP4 activity by 50% (the IC50 value) was 28.42 μM. These data provide a theoretical basis for intervention in glucose metabolism with EGCG.

The emerging role of dipeptidyl-peptidase-4 as a therapeutic target in lung disease

Introduction: Dipeptidyl-peptidase-4 (DPP-4) is a surface bound ectopeptidase that is commonly known as CD26 or adenosine deaminase binding protein. DPP-4 is membrane anchored but it can be cleaved by numerous proteases including matrix-metalloproteinases (MMPs). DPP-4 is expressed by endothelial and epithelial cells, the kidney, intestine and cells of the immune system; it has a broad spectrum of biological functions in immune regulation, cancer biology and glucose metabolism.Areas covered: This article sheds light on the functions of DPP-4, the molecular mechanisms that govern its expression, it's role in the pathogenesis of common respiratory illnesses and potential as a therapeutic target.Expert opinion: DPP-4 has a deleterious role in respiratory disease. Its biological functions, key molecular pathways, interactions and associations are slowly being elucidated. Progressing our knowledge of the role of this multi-faceted molecule may yield vital and novel therapies for respiratory diseases such as lung cancer, asthma, and chronic obstructive pulmonary disease (COPD).

Inhibition of inflammation-mediated DPP-4 expression by linagliptin increases M2 macrophages in atherosclerotic lesions

BACKGROUND AND AIMS

Dipeptidyl peptidase-4 (DPP-4) inhibitors have been reported to suppress atherosclerosis progression in atherosclerotic mouse models through unclear mechanisms. In this study, we investigated the effect of the DPP-4 inhibitor, linagliptin, on macrophage polarization in vitro and in vivo.

METHODS

Mouse bone marrow macrophages (BMMs) were used in in vitro assays. High fat diet (HFD)-fed Apoe^-/- mice were treated orally with linagliptin (10 mg/kg^-1•day^-1) or a vehicle (water) control.

RESULTS

In in vitro assays using BMMs, treatment with LPS and IFNγ decreased the mRNA-expression levels of alternatively activated macrophage (M2) markers, and linagliptin treatment prevented these reductions. The mRNA levels of M2 markers and the number of M2 macrophages in the aorta were higher in linagliptin groups than in control groups. Linagliptin decreased the size of atherosclerotic lesions in HFD-fed Apoe^-/- mice. Interestingly, inflammatory stimulation increased DPP-4 expression, and linagliptin suppressed these effects in BMMs. Treatment with DPP-4 small-interfering RNA (siRNA) reproduced linagliptin-mediated alteration of M2 polarization.

CONCLUSIONS

Linagliptin increased M2 macrophage polarization by inhibiting DPP-4 expression and activity. These findings may indicate the beneficial effects of DPP-4 inhibitors on the progression of diabetic macrovascular complications.

Screening for Potential Novel Probiotics With Dipeptidyl Peptidase IV-Inhibiting Activity for Type 2 Diabetes Attenuation in vitro and in vivo

Diabetes has become the second most severe disease to human health. Probiotics are important for maintaining gastrointestinal homeostasis and energy balance and have been demonstrated to play a positive role in the prevention and treatment of metabolic syndromes, such as obesity, inflammation, dyslipidemia, and hyperglycemia. The objective of this study was to screen potential antidiabetic strains in vitro and evaluate its effects in vivo. For the in vitro section, dipeptidyl peptidase IV (DPP-IV) inhibitory and antioxidant activities of 14 candidate Lactobacillus spp. strains were tested. Then hydrophobicity and acid and bile salt tolerance assays were determined. The most promising in vitro strain was further evaluated for its antidiabetic properties in vivo using type 2 diabetes mice induced by high-fat diet and intraperitoneal injection of streptozotocin (STZ). The reference strain for this study was Lactobacillus rhamnosus GG. Results showed that cell-free excretory supernatants and cell-free extracts of Lactobacillus acidophilus KLDS1.0901 had better DPP-IV inhibitory activity, antioxidative activities, and biological characteristics than other strains. At the end of the treatment, we found that L. acidophilus KLDS1.0901 administration decreased the levels of fasting blood glucose (FBG), glycosylated hemoglobin, insulin in serum and AUC_glucose, and increased the level of glucagon-like peptide 1 in serum compared with diabetic mice (p < 0.05). Moreover, L. acidophilus KLDS1.0901 supplementation increased the activities of superoxide dismutase, glutathione peroxidase, the level of glutathione, and reduced the level of malondialdehyde in serum. These results indicated that L. acidophilus KLDS1.0901 could be used as a potential antidiabetic strain; its application as food supplement and drug ingredient is thus recommended.

Sixty Years of Drug Discovery for Type 2 Diabetes: Where Are We Now?

Today, excluding insulin, there are eight classes of anti-diabetic medicines that have been added to the pharmacy since the introduction of metformin in the mid-1950s; the sulfonylureas, biguanides, thiazolidinediones, α-glucosidase inhibitors, meglitinides, incretins, and sodium glucose transport 2 inhibitors. Does the fact that metformin is still first-line treatment suggest that our drug discovery efforts over the past 60 years have not been good enough? Or does it suggest that diabetes is such a complex disorder that no single treatment, other than gastric bypass surgery, can affect true normalization of not only blood sugar but also the underlying pathologies? Our understanding of the disease has most definitely improved which may bring hope for the future in terms of science, but for it to be beneficial, this science has to be translated into better drug treatments for the disease. In this review, I have examined the eight classes of anti-diabetes drugs from a drug discovery perspective.

The Effects of DPP4 Inhibitors on Lipid Status and Blood Pressure in Rats with Diabetes Mellitus Type 2

The aim of the present study was to examine, evaluate and compare the effects of administered dipeptidyl peptidase-4 (DPP4) inhibitors saxagliptin and sitagliptin on lipid status parameters and blood pressure in rats with streptozotocine induced diabetes mellitus type 2. Forty-eight Wistar albino rats were divided randomly into 4 groups: 1. group I: control healthy group; 2. group II: rats with diabetes mellitus type 2; 3. group III: rats with diabetes mellitus type 2+ treated with 0.6 mg/kg of sitagliptin; 4. group IV: rats with diabetes mellitus type 2 treated with 0.45 mg/kg of saxagliptin. The rats from experimental groups were fed with a high-fat diet for 4 weeks and after 6–8 h of starvation received one dose of streptozotocin (STZ) intraperitoneally (25 mg/kg body weight) to induce type 2 diabetes mellitus (T2DM). Animals with fasting glucose above 7 mmol/L and insulin over 6 mmol/L were included in the study as rats with T2DM. Upon completion of the experiments, the blood was collected from the anesthetized animals and serum triglyceride (TG), total cholesterol (TCH), high density lipoprotein (HDL), and low density lipoprotein (LDL) were measured using spectrophotometry and commercial kits. At the beginning of the study and the day before sacrificing animals, the blood pressure and heart rate were measured by a tail-cuff noninvasive method. DPP4 inhibitors, as glucagon-like peptide-1 (GLP-1) agonists, were associated with modest reductions in DBP, LDL-C, TCH, and TGL and significant improvement in HDL, SBP and HR.

The Role of GLP1 in Rat Steatotic and Non-Steatotic Liver Transplantation from Cardiocirculatory Death Donors

In liver transplantation (LT), organ shortage has led to the use of steatotic and non-steatotic grafts from donors after cardiocirculatory death (DCD). However, these grafts, especially those with steatosis, exhibit poor post-operative outcomes. To address this problem, we investigated the roles of gut-derived glucagon-like peptide 1 (GLP1) and dipeptidyl peptidase 4 (DPP4), the serine protease that cleaves it, in steatotic and non-steatotic LT from DCDs. Using Zucker rats, liver grafts from DCDs were cold stored and transplanted to recipients. GLP1 was administered to donors. The levels of GLP1 in intestine and of both GLP1 and DDP4 in circulation were unaltered following cardiocirculatory death (CD). In steatotic livers from DCD, increased GLP1 and decreased DPP4 were recorded, and administration of GLP1 caused a rise in hepatic GLP1 and a reduction in DDP4. This protected against inflammation, damage, and proliferation failure. Conversely, low GLP1 and high DDP4 were observed in non-steatotic livers from DCD. The exogenous GLP1 did not modify hepatic DDP4, and the accumulated GLP1 exerted harmful effects, increasing damage, inflammation, and regeneration failure. Herein, we show that there are differences in GLP1/DDP4 regulation depending on the type of liver implanted, suggesting that GLP1 can be used as a novel and effective therapy in steatotic grafts from DCDs but that it is not appropriate for non-steatotic DCDs.

The CD26/DPP4-inhibitor vildagliptin suppresses lung cancer growth via macrophage-mediated NK cell activity

CD26/dipeptidyl peptidase 4 (DPP4) is a transmembrane protein which is expressed by various malignant cells. We found that the expression of CD26/DPP4 was significantly higher in lung adenocarcinoma samples in our own patient cohort compared to normal lung tissue. We therefore hypothesize that the inhibition of CD26/DPP4 can potentially suppress lung cancer growth. The CD26/DPP4 inhibitor vildagliptin was employed on Lewis Lung Carcinoma (LLC) cell line and a human lung adenocarcinoma (H460) cell line. Two weeks after subcutaneous injection of tumor cells into C57BL/6 and CD1/nude mice, the size of LLC and H460 tumors was significantly reduced by vildagliptin. Immunohistochemically, the number of macrophages (F4/80+) and NK cells (NKp46+) was significantly increased in vildagliptin-treated tumor samples. Mechanistically, we found in vitro that lung cancer cell lines expressed increased levels of surfactant protein upon vildagliptin treatment thereby promoting the pro-inflammatory activity of macrophages. By the depletion of macrophages with clodronate and by using NK cell deficient (IL-15-/-) mice, tumors reversed to the size of controls, suggesting that indeed macrophages and NK cells were responsible for the observed tumor-suppressing effect upon vildagliptin treatment. FACS analysis showed tumor-infiltrating NK cells to express tumor necrosis-related apoptosis-inducing ligand (TRAIL) which induced the intra-cellular stress marker γH2AX. Accordingly, we found upregulated γH2AX in vildagliptin-treated tumors and TRAIL-treated cell lines. Moreover, the effect of vildagliptin-mediated enhanced NK cell cytotoxicity could be reversed by antagonizing the TRAIL receptor. Our data provide evidence that the CD26/DPP4-inhibitor vildagliptin reduces lung cancer growth. We could demonstrate that this effect is exerted by surfactant-activated macrophages and NK cells that act against the tumor via TRAIL-mediated cytotoxicity.

Discovery of Highly Polar β-Homophenylalanine Derivatives as Nonsystemic Intestine-Targeted Dipeptidyl Peptidase IV Inhibitors

Although intensively expressed within intestine, the precise roles of intestinal dipeptidyl peptidase IV (DPPIV) in numerous pathologies remain incompletely understood. Here, we first reported a nonsystemic intestine-targeted (NSIT) DPPIV inhibitor with β-homophenylalanine scaffold, compound 7, which selectively inhibited the intestinal rather than plasmatic DPPIV at an oral dosage as high as 30 mg/kg. We expect that compound 7 could serve as a qualified tissue-selective tool to determine undetected physiological or pathological roles of intestinal DPPIV.

DPP4 Inhibitor Attenuates Severe Acute Pancreatitis-Associated Intestinal Inflammation via Nrf2 Signaling

Severe acute pancreatitis (SAP) is a challenging disease with high morbidity and mortality, often complicated by multiple organ dysfunction syndrome (MODS). The intestine, a major organ involved in MODS, correlates strongly with the evolution of the disease. In this study, we demonstrated that the DPP4 inhibitor, sitagliptin, protects SAP-associated intestinal injury both in vitro and in vivo. These beneficial effects were achieved by suppressing oxidative stress and inflammatory responses. Moreover, in sitagliptin-treated SAP mice, expression of Nrf2 was induced and that of NF-κB was reduced, compared to the control SAP mice. In addition, we used Nrf2^−/− mice to test the protective effect of Nrf2 during sitagliptin treatment of SAP; our results indicated that Nrf2^−/− mice had greater pancreatic and intestinal injury than wild-type mice. Taken together, high levels of ROS induced by SAP may be inhibited by sitagliptin, possibly by inactivating the Nrf2-NF-κB pathway.

Detailed quantum mechanical, molecular docking, QSAR prediction, photovoltaic light harvesting efficiency analysis of benzil and its halogenated analogues

The structural, spectroscopic various physico-chemical and biological characteristics of the organic molecule benzil (BZL) and derivatives, 1,2-bis(4-methylphneyl)-1,2-ethanedione (DMB), 4,4′-difluorobenzil (DFB), 4,4′-dichlorobenzil (DCB) and 4,4′-dibromobenzil (DBB) have been studied by various computational methods. The experimental and scaled simulated Raman and IR spectra were compared and found close agreement. Assignments of important peaks are also presented. Detailed information pertaining to the local and global reactivity and other properties like electrophilic and nucleophilic characteristics were analysed. The hyperactive pressure was measured in terms of polarizability and corresponding biological properties were validated to identity reactive sites. Prediction of Activity Spectral Studies (PASS) predicts the biological activity of the compounds and it is found that the candidate molecules can be used as feruloyl esterase inhibitor, bisphosphoglycerate phosphatase inhibitor and Prolylaminopeptidase inhibitor. The crystals structures of those receptors are taken from the protein data bank and docking studies indicates stable complex with the receptors and candidate molecules. Light harvesting efficiency, followed by photovoltaic modelling shows that DMB is the best compound to be used in the DSSC to get the best output.

Elevated Human Dipeptidyl Peptidase 4 Expression Reduces the Susceptibility of hDPP4 Transgenic Mice to Middle East Respiratory Syndrome Coronavirus Infection and Disease

Background

The ongoing Middle East respiratory syndrome coronavirus (MERS-CoV) infections pose threats to public health worldwide, making an understanding of MERS pathogenesis and development of effective medical countermeasures (MCMs) urgent.

Methods

We used homozygous (+/+) and heterozygous (+/−) human dipeptidyl peptidase 4 (hDPP4) transgenic mice to study the effect of hDPP4 on MERS-CoV infection. Specifically, we determined values of 50% lethal dose (LD₅₀) of MERS-CoV for the 2 strains of mice, compared and correlated their levels of soluble (s)hDPP4 expression to susceptibility, and explored recombinant (r)shDPP4 as an effective MCM for MERS infection.

Results

hDPP4^+/+ mice were unexpectedly more resistant than hDPP4^+/− mice to MERS-CoV infection, as judged by increased LD₅₀, reduced lung viral infection, attenuated morbidity and mortality, and reduced histopathology. Additionally, the resistance to MERS-CoV infection directly correlated with increased serum shDPP4 and serum virus neutralizing activity. Finally, administration of rshDPP4 led to reduced lung virus titer and histopathology.

Conclusions

Our studies suggest that the serum shDPP4 levels play a role in MERS pathogenesis and demonstrate a potential of rshDPP4 as a treatment option for MERS. Additionally, it offers a validated pair of Tg mice strains for characterizing the effect of shDPP4 on MERS pathogenesis.

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.

Effect of six Korean plants on glucagon like peptide-1 release

Glucagon like peptide-1 (GLP-1) plays a major role in the regulation of energy homeostasis as it causes satiety and suppresses appetite. Angelica dahurica, Coreanomecon hylomeconoides, Chrysanthemum morifolium, Portulaca oleracea, Stellaria alsine, and Stellaria media have traditionally been used as famine relief foods in Korea. The aim of the present study was to determine whether the aqueous ethanolic extracts of the six plants stimulate GLP-1 secretion. The results demonstrated that each extract of the plants stimulated GLP-1 secretion from enteroendocrine NCI-H716 cells, respectively. Among the extracts examined, the extract of Portulaca oleracea showed the highest activity on GLP-1 release. The results may suggest that the GLP-1 secretion induced by the six plants is a possible mechanism for the six plants exerting effects on satiety increase and appetite suppression.

Sick fat: the good and the bad of old and new circulating markers of adipose tissue inflammation

Adipose tissue (AT) is one of the largest endocrine organs contributing to metabolic homeostasis. The functional pleiotropism of AT depends on its ability to secrete a large number of hormones, cytokines, extracellular matrix proteins and growth factors, all influencing many local and systemic physiological and pathophysiological processes. In condition of chronic positive energy balance, adipocyte expansion, hypoxia, apoptosis and stress all lead to AT inflammation and dysfunction, and it has been demonstrated that this sick fat is a main risk factor for many metabolic disorders, such as type 2 diabetes mellitus, fatty liver, cardiovascular disease and cancer. AT dysfunction is tightly associated with aberrant secretion of bioactive peptides, the adipocytokines, and their blood concentrations often reflect the expression in the AT. Despite the existence of an association between AT dysfunction and systemic pro-inflammatory state, most of the circulating molecules detectable in obese and dysmetabolic individuals do not identify specifically the condition of sick fat. Based on this premise, this review provides a concise overview of "classic" and novel promising adipocytokines associated with AT inflammation and discusses possible critical approaches to their interpretation in clinical practice.

Postnatal morphological lung development of wild type and CD26/DPP4 deficient rat pups in dependency of LPS exposure

BACKGROUND

Rodents are born with morphological immature lungs and an intact surfactant system. CD26/DPP4 is a multifactorial transmembrane integral type II protein, which is involved in physiological and pathophysiological processes and is already expressed during development. CD26/DPP4, called CD26 in the following, is able to enhance or dampen differently triggered inflammation. LPS exposure often used to simulate perinatal infection delays lung development.

OBJECTIVE

A perinatal LPS rat model was used to test the hypothesis that CD26 deficiency modulates LPS-induced retardation in morphological lung development.

METHODS

New born Fischer CD26 positive (CD26⁺) and deficient (CD26^-) rats were exposed to LPS on postnatal day (day post partum, dpp) 3 and 5. Morphological parameters of lung development were determined stereologically. Lung development was analysed in 7, 10 14 and 21day old rats.

RESULTS

Compared to controls LPS application resulted (1) in a mild inflammation independent of the strain, (2) in significantly lower total surface and volume of alveolar septa combined with significantly higher total volume of airspaces and alveolar size on dpp 7 in both substrains. However, compared to controls in LPS treated CD26^- rats significant lower values of total septal surface and volume combined with higher values of total parenchymal airspaces and alveolar size were found until the end of classical alveolarization (dpp14). In LPS treated CD26⁺ rat pups the retardation was abolished already on dpp 10.

CONCLUSION

In absence of CD26, LPS enhances the delay of morphological lung development. Morphological recovery was slower after the end of LPS exposure in CD26 deficient lungs.

Recombinant adenoviral vaccine encoding the spike 1 subunit of the Middle East Respiratory Syndrome Coronavirus elicits strong humoral and cellular immune responses in mice

Background and Aim

Middle East respiratory syndrome coronavirus (MERS-CoV) has rapidly spread throughout the Middle East since its discovery in 2012. The virus poses a significant global public health threat with potentially devastating effects. In this study, a recombinant adenoviral-based vaccine encoding the spike 1 (S1) subunit of the MERS-CoV genome was constructed, and its humoral, and cellular immune responses were evaluated in mice.

Materials and Methods

Mice were immunized initially by intramuscular injection and boosted 3 weeks later by intranasal application. Expression of the S1 protein in the lungs and kidneys was detected using conventional polymerase chain reaction (PCR) and immunohistochemistry (IHC) targeting specific regions within the S1 subunit at weeks 3, 4, 5, and 6 after the first vaccination. Antigen-specific humoral and cellular immune responses were evaluated in serum and in cell culture following in vitro stimulation with a specific 9-mer epitope within the S1 protein (CYSSLILDY).

Results

S1 protein expression was only detected by IHC in the kidneys of the Ad-MERS-S1 group at week 6 from first immunization, and in both lungs and kidneys of Ad-MERS-S1 group by conventional PCR at weeks 3 and 5 post-prime. The vaccine elicited a specific S1-immunoglobulin G antibody response, which was detected in the sera of the vaccinated mice at weeks 4 and 6 from the onset of the first immunization. There was a significant increase in the amount of Th1-related cytokines (interferon-γ and interleukin [IL] 12), and a significant decrease in the Th2-related cytokine IL-4 in splenocyte cell culture of the vaccinated group compared with the control groups.

Conclusion

The results of this study suggest that this recombinant adenovirus vaccine encoding the S1 subunit of MERS-CoV elicits potentially protective antigen-specific humoral and cellular immune responses in mice. This study demonstrates a promising vaccine for the control and/or prevention of MERS-CoV infection in humans.

Greater circulating DPP4 activity is associated with impaired flow-mediated dilatation in adults with type 2 diabetes mellitus

BACKGROUND AND AIM

Dipeptidyl peptidase 4 (DPP4) is a key enzyme involved in the regulation of the incretin system exerted by cleaving the glucagon-like peptide 1 (GLP-1); the blockage of DPP4, exerted by the antidiabetic agents DPP4-inhibitors (DPP4-I), results in greater GLP-1 concentration and improved glycaemic control. DPP4 acts also as a pro-inflammatory molecule and mediates vascular damage in experimental models. The relationship between DPP4 activity and endothelial function in diabetes has not been explored yet. Aim of this study was to investigate systemic plasma DPP4 activity in relation to endothelial function in patients with type 2 diabetes mellitus (T2DM).

METHODS AND RESULTS

Sixty-two T2DM individuals were recruited in our Diabetes outpatient clinics, Sapienza University, Rome, Italy. All participants underwent complete clinical work-up; endothelial function was evaluated by flow-mediated dilatation (FMD) test; plasma DPP4 activity was assessed by measuring the 7-amino-4-methylcoumarin (AMC) cleavage rate from the synthetic substrate H-glycyl-prolyl-AMC and compared with DPP4 activity measured in sixty-two age-, sex-, BMI-matched non-diabetic subjects. Patients with T2DM had significantly higher DPP4 activity than non-diabetic individuals (211,466 ± 87657 vs 158,087 ± 60267 nmol/min/ml, p < 0.001); in T2DM patients, greater DPP4 activity significantly correlated with lower FMD whereas was not associated with BMI and metabolic control. Greater systemic DPP4 activity was an independent predictor of reduced FMD after adjusting for age, gender and other confounders.

CONCLUSIONS

Circulating DPP4 activity is increased in individuals with T2DM and associated with signs of endothelial dysfunction such as impaired FMD. DPP4 may negatively affect endothelial function through mechanisms beyond glucose homeostasis and metabolic control.

The perceptions of natural compounds against dipeptidyl peptidase 4 in diabetes: from in silico to in vivo

Dipeptidyl peptidase IV (DPP-4), an incretin glucagon-like peptide-1 (GLP-1) degrading enzyme, contains two forms and it can exert various physiological functions particular in controlling blood glucose through the action of GLP-1. In diabetic use, the DPP-4 inhibitor can block the DDP-4 to attenuate GLP-1 degradation and prolong GLP-1 its action and sensitize insulin activity for the purpose of lowering blood glucose. Nonetheless the adverse effects of DPP-4 inhibitors severely hinder their clinical applications, and notably there is a clinical demand for novel DPP-4 inhibitors from various sources including chemical synthesis, herbs, and plants with fewer side effects. In this review, we highlight various strategies, namely computational biology (in silico), in vitro enzymatic and cell assays, and in vivo animal tests, for seeking natural DPP-4 inhibitors from botanic sources including herbs and plants. The pros and cons of all approaches for new inhibitor candidates or hits will be under discussion.

Recent advances in vasoactive intestinal peptide physiology and pathophysiology: focus on the gastrointestinal system

Vasoactive intestinal peptide (VIP), a gut peptide hormone originally reported as a vasodilator in 1970, has multiple physiological and pathological effects on development, growth, and the control of neuronal, epithelial, and endocrine cell functions that in turn regulate ion secretion, nutrient absorption, gut motility, glycemic control, carcinogenesis, immune responses, and circadian rhythms. Genetic ablation of this peptide and its receptors in mice also provides new insights into the contribution of VIP towards physiological signaling and the pathogenesis of related diseases. Here, we discuss the impact of VIP on gastrointestinal function and diseases based on recent findings, also providing insight into its possible therapeutic application to diabetes, autoimmune diseases and cancer.

Effect of gemigliptin on cardiac ischemia/reperfusion and spontaneous hypertensive rat models

Diabetes is associated with an increased risk of cardiovascular complications. Dipeptidyl peptidase-4 (DPP-IV) inhibitors are used clinically to reduce high blood glucose levels as an antidiabetic agent. However, the effect of the DPP-IV inhibitor gemigliptin on ischemia/reperfusion (I/R)-induced myocardial injury and hypertension is unknown. In this study, we assessed the effects and mechanisms of gemigliptin in rat models of myocardial I/R injury and spontaneous hypertension. Gemigliptin (20 and 100 mg/kg/d) or vehicle was administered intragastrically to Sprague-Dawley rats for 4 weeks before induction of I/R injury. Gemigliptin exerted a preventive effect on I/R injury by improving hemodynamic function and reducing infarct size compared to the vehicle control group. Moreover, administration of gemigliptin (0.03% and 0.15%) powder in food for 4 weeks reversed hypertrophy and improved diastolic function in spontaneously hypertensive rats. We report here a novel effect of the gemigliptin on I/R injury and hypertension.

The dipeptidyl peptidase-4 inhibitory effect of flavonoids is hindered in protein rich environments

Dipeptidyl peptidase-4 (DPP-4) inhibitors present a unique approach for the management of type 2 diabetes (T2D). In the present study, the inhibition of DPP-4 was evaluated for a large panel of flavonoids, important components of the human diet, using in vitro and ex vivo models. The activity of the isolated enzyme was assayed in vitro. Subsequently, the most active flavonoids were tested ex vivo in human whole blood and plasma. In this study, contrary to the in vitro fluorometric tests, flavonoids did not show inhibitory activity against DPP-4. Due to the discrepancy in the results between the in vitro and ex vivo approaches, plasma protein binding values were determined, presenting values from 43.9 to 100.0%. This work provides a new insight into the inhibitory activity for DPP-4, based on the flavonoid scaffold. Additionally, the obtained results showed that the inhibitory effect of flavonoids against DPP-4 was hindered in protein rich environments, like that occurring in blood, and indicated the need for experimental refinement in drug discovery for blood targets.

More than just an enzyme: Dipeptidyl peptidase-4 (DPP-4) and its association with diabetic kidney remodelling

PURPOSE OF THE REVIEW

This review article discusses recent advances in the mechanism of dipeptidyl peptidase-4 (DPP-4) actions in renal diseases, especially diabetic kidney fibrosis, and summarizes anti-fibrotic functions of various DPP-4 inhibitors in diabetic nephropathy (DN).

RECENT FINDINGS

DN is a common complication of diabetes and is a leading cause of the end-stage renal disease (ESRD). DPP-4 is a member of serine proteases, and more than 30 substrates have been identified that act via several biochemical messengers in a variety of tissues including kidney. Intriguingly, DPP-4 actions on the diabetic kidney is a complex mechanism, and a variety of pathways are involved including increasing GLP-1/SDF-1, disrupting AGE-RAGE pathways, and integrin-β- and TGF-β-Smad-mediated signalling pathways that finally lead to endothelial to mesenchymal transition. Interestingly, an array of DPP-4 inhibitors is well recognized as oral drugs to treat type 2 diabetic (T2D) patients, which promote better glycemic control. Furthermore, recent experimental and preclinical data reveal that DPP-4 inhibitors may also exhibit protective effects in renal disease progression including anti-fibrotic effects in the diabetic kidney by attenuating above signalling cascade(s), either singly or as a combinatorial effect. In this review, we discussed the anti-fibrotic effects of DPP-4 inhibitors based on recent reports along with the possible mechanism of actions and future perspectives to underscore the beneficial effects of DPP-4 inhibitors in DN.

SUMMARY

With recent experimental, preclinical, and clinical evidence, we summarized DPP-4 activities and its mechanism of actions in diabetic kidney diseases. A knowledge gap of DPP-4 inhibition in controlling renal fibrosis in DN has also been postulated in this review for future research perspectives.

The Role of DPP-4 Inhibitors in the Treatment Algorithm of Type 2 Diabetes Mellitus: When to Select, What to Expect

Type 2 diabetes mellitus is a growing global public health problem, the prevalence of which is projected to increase in the succeeding decades. It is potentially associated with many complications, affecting multiple organs and causing a huge burden to the society. Due to its multi-factorial pathophysiology, its treatment is varied and based upon a multitude of pharmacologic agents aiming to tackle the many aspects of the disease pathophysiology (increasing insulin availability [either through direct insulin administration or through agents that promote insulin secretion], improving sensitivity to insulin, delaying the delivery and absorption of carbohydrates from the gastrointestinal tract, or increasing urinary glucose excretion). DPP-4 (dipeptidyl peptidase-4) inhibitors (or “gliptins”) represent a class of oral anti-hyperglycemic agents that inhibit the enzyme DPP-4, thus augmenting the biological activity of the “incretin” hormones (glucagon-like peptide-1 [GLP-1] and glucose-dependent insulinotropic polypeptide [GIP]) and restoring many of the pathophysiological problems of diabetes. They have already been used over more than a decade in the treatment of the disease. The current manuscript will review the mechanism of action, therapeutic utility, and the role of DPP-4 inhibitors for the treatment of type 2 diabetes mellitus.

[Drug-induced angioedema : Focus on bradykinin]

On a pathophysiological level, angioedema can be differentiated into histamine- and bradykinin-mediated types. The prototype drug-associated, bradykinin-mediated form of angioedema is angiotensin-converting enzyme (ACE) inhibitor-induced angioedema. The hypothesized cause is a decrease in bradykinin degradation via ACE inhibition. In this scenario, other bradykinin-degrading enzymes assume major importance. When the effect of these enzymes is also diminished, e. g., due to genetic variants or external factors, compensation for the inhibition of ACE may be insufficient. An increased risk of angioedema has also been reported for other drugs, particularly when prescribed in combination with ACE inhibitors. Here, the suspected cause also relates to the degradation of bradykinin. When angioedema arises within the context of concomitant ACE inhibitor use, additive bradykinin degradation effects may be implicated.

CD26 in autoimmune diseases: The other side of "moonlight protein"

Dipeptidyl peptidase 4 (DPP-4) is a serine protease, which has enzymatic activity to selectively clean the N-terminal dipeptide of peptides and proteins with proline or alanine in the second position. DPP-4 inhibitor has been widely used for the treatment of type 2 diabetes by increasing the level of the glucagon-like peptide-1 and decreasing the glucose level. DPP-4, also known as lymphocyte cell surface protein CD26, plays a core role of T cell immunity. Many roles of CD26 in other immune cells have been found. As a "moonlight protein", the effect of CD26 in autoimmune diseases has attracted more and more attention. The paper reviewed the function and potential effect of CD26 in autoimmune diseases, which shows CD26 may be a new target of autoimmune diseases deserved further study.

CD26 and Asthma: a Comprehensive Review

Asthma is a heterogeneous and chronic inflammatory family of disorders of the airways with increasing prevalence that results in recurrent and reversible bronchial obstruction and expiratory airflow limitation. These diseases arise from the interaction between environmental and genetic factors, which collaborate to cause increased susceptibility and severity. Many asthma susceptibility genes are linked to the immune system or encode enzymes like metalloproteases (e.g., ADAM-33) or serine proteases. The S9 family of serine proteases (prolyl oligopeptidases) is capable to process peptide bonds adjacent to proline, a kind of cleavage-resistant peptide bonds present in many growth factors, chemokines or cytokines that are important for asthma. Curiously, two serine proteases within the S9 family encoded by genes located on chromosome 2 appear to have a role in asthma: CD26/dipeptidyl peptidase 4 (DPP4) and DPP10. The aim of this review is to summarize the current knowledge about CD26 and to provide a structured overview of the numerous functions and implications that this versatile enzyme could have in this disease, especially after the detection of some secondary effects (e.g., viral nasopharyngitis) in type II diabetes mellitus patients (a subset with a certain risk of developing obesity-related asthma) upon CD26 inhibitory therapy.

Dipeptidyl peptidase IV inhibitors as a potential target for diabetes: patent review (2015-2018)

INTRODUCTION

Dipeptidyl peptidase 4 (DPP-4) belongs to the family of serine proteases and is involved in the degradation of GLP-1 and GIP hormones, which enhance the production and release of insulin. Targeting DPP-4 inhibitors is increasingly being considered as promising paradigms to treat type 2 diabetes mellitus and therefore DPP-4 inhibitors are being considered as promising antidiabetic drugs.

AREAS COVERE

This review provides an overview of published patents describing natural and synthetic DPP-4 inhibitors from January 2015 to December 2018.

EXPERT OPINION

A fair number of new synthetic and natural DPP-4 inhibitors have been reported in the last four years which describe the progress in the development of various heterocyclic scaffolds or heterocyclic hybrid compounds. As a result of this, many marketed DPP-4 inhibitors that have been approved by the appropriate governing bodies during the past decade, have been introduced as inhibitors. Molecular hybridization is an emerging idea in medicinal chemistry and therefore hybrid compounds of DPP-4 inhibitors with other DPP-4 inhibitors or with antidiabetic drugs should be formulated for a comprehensive evaluation. More detailed pharmacovigilance of DPP-4 inhibitors is required because this will address the pancreas-related adverse events as well as their impact on cardiovascular outcomes via long-term studies.

Dipeptidyl peptidase-4 inhibitors lower the risk of autoimmune disease in patients with type 2 diabetes mellitus: A nationwide population-based cohort study

AIMS

To evaluate the real-world effect of dipeptidyl peptidase-4 inhibitor (DPP4i) on the incidence of autoimmune diseases (AD), including rheumatoid arthritis (RA), inflammatory bowel diseases, multiple sclerosis and systemic lupus erythematosus.

METHODS

We identified new users of DPP4i (n = 497 619) or non-DPP4i (n = 643 165) oral combination therapy between 1 January 2011 and 30 June 2015 among patients with type 2 diabetes mellitus in the Korean national health insurance claims database. Patients were followed from the date of initiation of combination therapy until AD outcome, censoring for treatment discontinuation or switching, death or end of study (31 August 2016). Adjusted hazard ratios (aHR) and 95% confidence intervals (CI) for RA, inflammatory bowel diseases, other AD (multiple sclerosis and systemic lupus erythematosus), and the composite of all outcomes were estimated using propensity score (PS)-adjusted Cox model.

RESULTS

In the PS-weighted and PS-matched analysis, the risk of incident RA was decreased for DPP4i initiators compared with non-DPP4i initiators (aHR 0.67 [95% CI 0.49-0.92] and aHR 0.72 [95% CI 0.51-1.01], respectively). In both analyses, the risk of incident composite AD was also decreased for DPP4i initiators compared with non-DPP4i initiators (aHR 0.82 [95% CI 0.68-0.99] and aHR 0.76 [95% CI 0.62-0.93], respectively).

CONCLUSIONS

In this large population-based cohort study, upfront DPP4i combination therapy was associated with a lower risk of composite AD compared with initial non-DPP4i combination therapy.

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.

Relevance of Autophagy Induction by Gastrointestinal Hormones: Focus on the Incretin-Based Drug Target and Glucagon

The biology of autophagy in health and disease conditions has been intensively analyzed for decades. Several potential interventions can induce autophagy in preclinical research; however, none of these interventions are ready for translation to clinical practice yet. The topic of the current review is the molecular regulation of autophagy by glucagon, glucagon-like peptide (GLP)-1 and the GLP-1-degrading enzyme dipeptidyl peptidase-4 (DPP-4). Glucagon is a well-known polypeptide that induces autophagy. In contrast, GLP-1 has been shown to inhibit glucagon secretion; GLP-1 also has been related to the induction of autophagy. DPP-4 inhibitors can induce autophagy in a GLP-1-dependent manner, but other diverse effects could be relevant. Here, we analyze the distinct molecular regulation of autophagy by glucagon, GLP-1, and DPP-4 inhibitors. Additionally, the potential contribution to autophagy by glucagon and GLP-1 after bariatric surgery is discussed.

Impact of dapagliflozin, an SGLT2 inhibitor, on serum levels of soluble dipeptidyl peptidase-4 in patients with type 2 diabetes and non-alcoholic fatty liver disease

AIMS

Soluble dipeptidyl peptidase-4 (sDPP-4) is secreted by hepatocytes and induces adipose tissue inflammation and insulin resistance. Sodium-glucose co-transporter-2 (SGLT2) inhibitors can improve hepatic steatosis by inhibiting hepatic de novo lipogenesis. We investigated the effects of dapagliflozin (an SGLT2 inhibitor) on serum levels of sDPP-4 in patients with type 2 diabetes and non-alcoholic fatty liver disease (NAFLD).

METHODS

Fifty-seven patients with type 2 diabetes and NAFLD were randomized to a dapagliflozin group (5 mg/d for 24 weeks) (n = 33) or the control group (n = 24). Serum levels of sDPP-4 were measured with a commercial ELISA kit. Visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) areas were measured by dual bioelectrical impedance analysis.

RESULTS

In a total of 57 patients, baseline serum sDPP-4 was positively correlated with aspartate aminotransferase (AST), alanine aminotransferase (ALT), γ-glutamyl transferase (GGT) and HOMA-IR Both VAT and SAT areas decreased significantly in the dapagliflozin group alone. Liver enzymes were decreased at 24 weeks in the dapagliflozin group, but were unchanged in the control group. Although both groups showed significant reduction of serum sDPP-4 after 24 weeks of treatment, the magnitude of decrease was significantly larger in the dapagliflozin group. Changes in liver enzymes during treatment with dapagliflozin were positively correlated with the change in serum sDPP-4, but not with changes in VAT volume or HbA1c.

CONCLUSIONS

Improvement of liver dysfunction after treatment with dapagliflozin was associated with a decrease in serum sDPP-4, suggesting that reduction of serum sDPP-4 by SGLT2 inhibitors may be a therapeutic strategy for NAFLD/NASH in patients with type 2 diabetes that is independent of glucose lowering or weight loss.