Loss of dipeptidylpeptidase IV activity in chronic rhinosinusitis contributes to the neurogenic inflammation induced by substance P in the nasal mucosa

DPP-IV Inhibitor-Associated Angioedema in Patient With Known History of ACE Inhibitor Angioedema

The patient is a 69-year-old male with a past medical history of intellectual disability, hypertension, type 2 diabetes mellitus, and angiotensin-converting enzyme (ACE) inhibitor–associated angioedema who presented to the emergency department with difficulty breathing. On physical examination, the patient had significant facial edema. Nasal fiber-optic visualization revealed extensive airway edema involving the supraglottic region and the arytenoids. The patient was successfully intubated through the collective teamwork of ENT, anesthesia, and critical care teams. He was managed in the intensive care unit until recovery. Workup for markers for allergic causes of angioedema were within normal limits. Further investigation revealed that symptoms developed following the initiation of a dipeptidyl peptidase 4 (DPP-IV) inhibitor. The angiotensin-converting enzyme and DPP-IV play a significant role in the metabolism of bradykinin and substance P to their inactive metabolites. The complex interplay between the enzymes in the high-molecular-weight kininogen (HWMK) system may increase the risk of angioedema in patients with a known history of ACE inhibitor–associated angioedema when placed on a DPP-IV inhibitor. This case report highlights the pathophysiology involved.

Revised Korean Cough Guidelines, 2020: Recommendations and Summary statements

Cough is the most common respiratory symptom that can have various causes. It is a major clinical problem that can reduce a patient’s quality of life. Thus, clinical guidelines for the treatment of cough were established in 2014 by the cough guideline committee under the Korean Academy of Tuberculosis and Respiratory Diseases. From October 2018 to July 2020, cough guidelines were revised by members of the committee based on the first guidelines. The purpose of these guidelines is to help clinicians efficiently diagnose and treat patients with cough. This article highlights the recommendations and summary of the revised Korean cough guidelines. It includes a revised algorithm for the evaluation of acute, subacute, and chronic cough. For a chronic cough, upper airway cough syndrome (UACS), cough variant asthma (CVA), and gastroesophageal reflux disease (GERD) should be considered in differential diagnoses. If UACS is suspected, first-generation antihistamines and nasal decongestants can be used empirically. In cases with CVA, inhaled corticosteroids are recommended to improve cough. In patients with suspected chronic cough due to symptomatic GERD, proton pump inhibitors are recommended. Chronic bronchitis, bronchiectasis, bronchiolitis, lung cancer, aspiration, intake of angiotensin-converting enzyme inhibitor, intake of dipeptidyl peptidase-4 inhibitor, habitual cough, psychogenic cough, interstitial lung disease, environmental and occupational factors, tuberculosis, obstructive sleep apnea, peritoneal dialysis, and unexplained cough can also be considered as causes of a chronic cough. Chronic cough due to laryngeal dysfunction syndrome has been newly added to the guidelines.

Systems pharmacology-based study of Tanreqing injection in airway mucus hypersecretion

ETHNOPHARMACOLOGICAL RELEVANCE

Mucus hypersecretion (MH) is recognized as a key pathophysiological and clinical feature of many airway inflammatory diseases. MUC5AC is a major component of airway mucus. Tanreqing injection (TRQ) is a widely used herbal formula for the treatment of respiratory inflammations for years in China. However, a holistic network pharmacology approach to understanding its therapeutic mechanisms against MH has not been pursued.

AIM OF THE STUDY

This study aimed to explore the systems-level potential active compounds and therapeutic mechanisms of TRQ in the treatment of MH.

MATERIALS AND METHODS

We established systems pharmacology-based strategies comprising compound screenings, target predictions, and pathway identifications to speculate the potential active compounds and therapeutic targets of TRQ. We also applied compound-target and target-disease network analyses to evaluate the possible action mechanisms of TRQ. Then, lipopolysaccharide (LPS)-induced Sprague-Dawley (SD) rat model was constructed to assess the effect of TRQ in the treatment of MH and to validate the possible molecular mechanisms as predicted in systems pharmacology approach.

RESULTS

The comprehensive compound collection successfully generated 55 compound candidates from TRQ. Among them, 11 compounds with high relevance to the potential targets were defined as representative and potential active ingredients in TRQ formula. Target identification revealed 172 potential targets, including pro-inflammatory cytokines of tumor necrosis factor α (TNF-α), interleukin (IL)-6, and IL-8. Pathway analyses uncovered the possible action of TRQ in the regulation of IL-17 signaling pathway and its downstream protein MUC5AC. Then in vivo experiment indicated that TRQ could significantly inhibit LPS stimulated MUC5AC over-production as well as the expression of TNF-α, IL-6, IL-8, and IL-17A, in both protein and mRNA levels.

CONCLUSIONS

Based on the systems pharmacology method and in vivo experiment, our work provided a general knowledge on the potential active compounds and possible therapeutic targets of TRQ formula in its anti-MH process. This work might suggest directions for further research on TRQ and provide more insight into better understanding the chemical and pharmacological mechanisms of complex herbal prescriptions in a network perspective.

Axonal Guidance Signaling Pathway Is Suppressed in Human Nasal Polyps

Background Dysfunctional innervation might contribute to the pathogenesis of chronic rhinosinusitis with nasal polyps (CRSwNP), but the state of the axonal outgrowth signaling in CRSwNP is unknown. The purpose of this study was to explore the axonal outgrowth pathway-related protein expression in CRSwNP. Methods Institutional review board approved study in which tissue proteomes were compared between control and CRSwNP patients (n = 10/group) using an aptamer-based proteomic array and confirmed by whole transcriptomic analysis. Results Compared with controls, proteins associated with axonal guidance signaling pathway such as beta-nerve growth factor, semaphorin 3A, Ras-related C3 botulinum toxin substrate 1, Bcl-2, protein kinase C delta type, and Fyn were significantly decreased in patients with CRSwNP (fold change [FC] = -1.17, P = .002; FC = -1.09, P < .001; FC = -1.33, P < .001; FC = -1.31, P < .001; FC = -1.31, P = .004; and FC = -1.20, P = 0.012, respectively). In contrast, reticulon-4 receptor, an inhibitory factor, was significantly increased in patients with CRSwNP (FC = 1.25, P < .001). Furthermore, neuronal growth-associated proteins such as ciliary neurotrophic factor receptor subunit alpha, neuronal growth regulator 1, neuronal cell adhesion molecule, neural cell adhesion molecule L1, platelet-derived growth factor subunit A, and netrin-4 were all significantly decreased in patients with CRSwNP (FC = -1.25, P < .001; FC = -1.27, P = .002; FC = -1.65, P = .013; FC = -4.20, P < .001; FC = -1.28, P < .001; and FC = -2.31, P < .001, respectively). In contrast, tissue eosinophil count ( P < .001) and allergic inflammation factors such as IgE, periostin, and galectin-10 were all significantly increased in patients with CRSwNP (FC = 12.28, P < .001; FC = 3.95, P < .001; and FC = 2.44, P < .001, respectively). Furthermore, the log FC of the studied proteins expression significantly and positively correlated with log FC of their mRNA expression ( P < .001, r = .88). Conclusions Axonal guidance signaling and neural growth factors pathways proteins are significantly suppressed in eosinophilic CRSwNP.

An Opportunistic Pathogen Afforded Ample Opportunities: Middle East Respiratory Syndrome Coronavirus

The human coronaviruses (CoV) include HCoV-229E, HCoV-OC43, HCoV-NL63, and HCoV-HKU1, some of which have been known for decades. The severe acute respiratory syndrome (SARS) CoV briefly emerged into the human population but was controlled. In 2012, another novel severely human pathogenic CoV—the Middle East Respiratory Syndrome (MERS)-CoV—was identified in the Kingdom of Saudi Arabia; 80% of over 2000 human cases have been recorded over five years. Targeted research remains key to developing control strategies for MERS-CoV, a cause of mild illness in its camel reservoir. A new therapeutic toolbox being developed in response to MERS is also teaching us more about how CoVs cause disease. Travel-related cases continue to challenge the world’s surveillance and response capabilities, and more data are needed to understand unexplained primary transmission. Signs of genetic change have been recorded, but it remains unclear whether there is any impact on clinical disease. How camels came to carry the virus remains academic to the control of MERS. To date, human-to-human transmission has been inefficient, but virus surveillance, characterisation, and reporting are key to responding to any future change. MERS-CoV is not currently a pandemic threat; it is spread mainly with the aid of human habit and error.

The expression of proline-specific enzymes in the human lung

The pathophysiology of lung diseases is very complex and proteolytic enzymes may play a role or could be used as biomarkers. In this review, the literature was searched to make an overview of what is known on the expression of the proline-specific peptidases dipeptidyl peptidase (DPP) 4, 8, 9, prolyl oligopeptidase (PREP) and fibroblast activation protein α (FAP) in the healthy and diseased lung. Search terms included asthma, chronic obstructive pulmonary disease (COPD), lung cancer, fibrosis, ischemia reperfusion injury and pneumonia. Knowledge on the loss or gain of protein expression and activity during disease might tie these enzymes to certain cell types, substrates or interaction partners that are involved in the pathophysiology of the disease, ultimately leading to the elucidation of their functional roles and a potential therapeutic target. Most data could be found on DPP4, while the other enzymes are less explored. Published data however often appear to be conflicting, the applied methods divers and the specificity of the assays used questionable. In conclusion, information on the expression of the proline-specific peptidases in the healthy and diseased lung is lacking, begging for further well-designed research.

Identifying neuropeptide Y (NPY) as the main stress-related substrate of dipeptidyl peptidase 4 (DPP4) in blood circulation

BACKGROUND

Dipeptidyl peptidase 4 (DPP4; EC 3.4.14.5; CD26) is a membrane-bound or shedded serine protease that hydrolyzes dipeptides from the N-terminus of peptides with either proline or alanine at the penultimate position. Substrates of DPP4 include several stress-related neuropeptides implicated in anxiety, depression and schizophrenia. A decline of DPP4-like activity has been reported in sera from depressed patient, but not fully characterized regarding DPP4-like enzymes, therapeutic interventions and protein.

METHODS

Sera from 16 melancholic- and 16 non-melancholic-depressed patients were evaluated for DPP4-like activities and the concentration of soluble DPP4 protein before and after treatment by anti-depressive therapies. Post-translational modification of DPP4-isoforms and degradation of NPY, Peptide YY (PYY), Galanin-like peptide (GALP), Orexin B (OrxB), OrxA, pituitary adenylate cyclase-activating polypeptide (PACAP) and substance P (SP) were studied in serum and in ex vivo human blood. N-terminal truncation of biotinylated NPY by endothelial membrane-bound DPP4 versus soluble DPP4 was determined in rat brain perfusates and spiked sera.

RESULTS

Lower DPP4 activities in depressed patients were reversed by anti-depressive treatment. In sera, DPP4 contributed to more than 90% of the overall DPP4-like activity and correlated with its protein concentration. NPY displayed equal degradation in serum and blood, and was equally truncated by serum and endothelial DPP4. In addition, GALP and rat OrxB were identified as novel substrates of DPP4.

CONCLUSION

NPY is the best DPP4-substrate in blood, being truncated by soluble and membrane DPP4, respectively. The decline of soluble DPP4 in acute depression could be reversed upon anti-depressive treatment. Peptidases from three functional compartments regulate the bioactivity of NPY in blood.

Cut to the chase: a review of CD26/dipeptidyl peptidase-4's (DPP4) entanglement in the immune system

CD26/DPP4 (dipeptidyl peptidase 4/DP4/DPPIV) is a surface T cell activation antigen and has been shown to have DPP4 enzymatic activity, cleaving-off amino-terminal dipeptides with either L-proline or L-alanine at the penultimate position. It plays a major role in glucose metabolism by N-terminal truncation and inactivation of the incretins glucagon-like peptide-1 (GLP) and gastric inhibitory protein (GIP). In 2006, DPP4 inhibitors have been introduced to clinics and have been demonstrated to efficiently enhance the endogenous insulin secretion via prolongation of the half-life of GLP-1 and GIP in patients. However, a large number of studies demonstrate clearly that CD26/DPP4 also plays an integral role in the immune system, particularly in T cell activation. Therefore, inhibition of DPP4 might represent a double-edged sword. Apart from the metabolic benefit, the associated immunological effects of long term DPP4 inhibition on regulatory processes such as T cell homeostasis, maturation and activation are not understood fully at this stage. The current data point to an important role for CD26/DPP4 in maintaining lymphocyte composition and function, T cell activation and co-stimulation, memory T cell generation and thymic emigration patterns during immune-senescence. In rodents, critical immune changes occur at baseline levels as well as after in-vitro and in-vivo challenge. In patients receiving DPP4 inhibitors, evidence of immunological side effects also became apparent. The scope of this review is to recapitulate the role of CD26/DPP4 in the immune system regarding its pharmacological inhibition and T cell-dependent immune regulation.

Neuropeptide Y is a physiological substrate of fibroblast activation protein: Enzyme kinetics in blood plasma and expression of Y2R and Y5R in human liver cirrhosis and hepatocellular carcinoma

Fibroblast activation protein (FAP) is a dipeptidyl peptidase (DPP) and endopeptidase that is weakly expressed in normal adult human tissues but is greatly up-regulated in activated mesenchymal cells of tumors and chronically injured tissue. The identities and locations of target substrates of FAP are poorly defined, in contrast to the related protease DPP4. This study is the first to characterize the physiological substrate repertoire of the DPP activity of endogenous FAP present in plasma. Four substrates, neuropeptide Y (NPY), peptide YY, B-type natriuretic peptide and substance P, were analyzed by mass spectrometry following proteolysis in human or mouse plasma, and by in vivo localization in human liver tissues with cirrhosis and hepatocellular carcinoma (HCC). NPY was the most efficiently cleaved substrate of both human and mouse FAP, whereas all four peptides were efficiently cleaved by endogenous DPP4, indicating that the in vivo degradomes of FAP and DPP4 differ. All detectable DPP-specific proteolysis and C-terminal processing of these neuropeptides was attributable to FAP and DPP4, and plasma kallikrein, respectively, highlighting their combined physiological significance in the regulation of these neuropeptides. In cirrhotic liver and HCC, NPY and its receptor Y2R, but not Y5R, were increased in hepatocytes near the parenchymal-stromal interface where there is an opportunity to interact with FAP expressed on nearby activated mesenchymal cells in the stroma. These novel findings provide insights into the substrate specificity of FAP, which differs greatly from DPP4, and reveal a potential function for FAP in neuropeptide regulation within liver and cancer biology.

DNA Methylation Modulates Nociceptive Sensitization after Incision

DNA methylation is a key epigenetic mechanism controlling DNA accessibility and gene expression. Blockade of DNA methylation can significantly affect pain behaviors implicated in neuropathic and inflammatory pain. However, the role of DNA methylation with regard to postoperative pain has not yet been explored. In this study we sought to investigate the role of DNA methylation in modulating incisional pain and identify possible targets under DNA methylation and contributing to incisional pain. DNA methyltranferase (DNMT) inhibitor 5-Aza-2′-deoxycytidine significantly reduced incision-induced mechanical allodynia and thermal sensitivity. Aza-2′-deoxycytidine also reduced hindpaw swelling after incision, suggesting an anti-inflammatory effect. Global DNA methylation and DNMT3b expression were increased in skin after incision, but none of DNMT1, DNMT3a or DNMT3b was altered in spinal cord or DRG. The expression of proopiomelanocortin Pomc encoding β-endorphin and Oprm1 encoding the mu-opioid receptor were upregulated peripherally after incision; moreover, Oprm1 expression was further increased under DNMT inhibitor treatment. Finally, local peripheral injection of the opioid receptor antagonist naloxone significantly exacerbated incision-induced mechanical hypersensitivity. These results suggest that DNA methylation is functionally relevant to incisional nociceptive sensitization, and that mu-opioid receptor signaling might be one methylation regulated pathway controlling sensitization after incision.

Middle East respiratory syndrome: An emerging coronavirus infection tracked by the crowd

In 2012 in Jordan, infection by a novel coronavirus (CoV) caused the first known cases of Middle East respiratory syndrome (MERS). MERS-CoV sequences have since been found in a bat and the virus appears to be enzootic among dromedary camels across the Arabian Peninsula and in parts of Africa. The majority of human cases have occurred in the Kingdom of Saudi Arabia (KSA). In humans, the etiologic agent, MERS-CoV, has been detected in severe, mild and influenza-like illness and in those without any obvious signs or symptoms of disease. MERS is often a lower respiratory tract disease associated with fever, cough, breathing difficulties, pneumonia that can progress to acute respiratory distress syndrome, multiorgan failure and death among more than a third of those infected. Severe disease is usually found in older males and comorbidities are frequently present in cases of MERS. Compared to SARS, MERS progresses more rapidly to respiratory failure and acute kidney injury, is more often observed as severe disease in patients with underlying illnesses and is more often fatal. MERS-CoV has a broader tropism than SARS-CoV, rapidly triggers cellular damage, employs a different receptor and induces a delayed proinflammatory response in cells. Most human cases have been linked to lapses in infection prevention and control in healthcare settings, with a fifth of virus detections reported among healthcare workers. This review sets out what is currently known about MERS and the MERS-CoV, summarises the new phenomenon of crowd-sourced epidemiology and lists some of the many questions that remain unanswered, nearly three years after the first reported case.

The pharmacokinetic considerations and adverse effects of DPP-4 inhibitors [corrected]

INTRODUCTION

Dipeptidyl-peptidase-4 (DPP-4) inhibitors are a class of anti-hyperglycemic agents with proven efficacy in patients with type 2 diabetes mellitus (T2DM).

AREAS COVERED

This review considers the pharmacokinetic profile, adverse effects and drug interactions of DPP-4 inhibitors. DPP-4 inhibitors have certain differences in their structure, metabolism, route of elimination and selectivity for DPP-4 over structurally related enzymes, such as DPP-8/DPP-9. They have a low potential for drug interactions, with the exception of saxagliptin that is largely metabolized by cytochrome CYP3A4/A5. Reports of pancreatitis and pancreatic cancer have raised concerns regarding the safety of DPP-4 inhibitors and are under investigation. Post-marketing surveillance has revealed less common adverse effects, especially a number of skin- and immune-related adverse effects. These issues are covered in the present review.

EXPERT OPINION

DPP-4 inhibitors are useful and efficient drugs. DPP-4 inhibitors have similar mechanism of action and similar efficacy. However, DPP-4 inhibitors have certain differences in their pharmacokinetic properties that may be associated with different clinical effects and adverse event profiles. Although clinical trials indicated a favorable safety profile, post-marketing reports revealed certain safety aspects that need further investigation. Certainly, more research is needed to clarify if the differences among DPP-4 inhibitors could lead to a different clinical and safety profile.

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

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

Longer term safety of dipeptidyl peptidase-4 inhibitors in patients with type 2 diabetes mellitus: systematic review and meta-analysis

Dipeptidyl peptidase-4 (DPP-4) inhibitors are oral antidiabetic agents that hold the potential of slowing the progress of type 2 diabetes mellitus. Their long-term safety is still a subject of debate. A systematic review of randomized, controlled trials was undertaken to comprehensively profile the safety of chronic treatment of type 2 diabetes mellitus with DPP-4 inhibitors. We searched data sources including MEDLINE, CENTRAL, publishers' and manufacturers' databases. Eligible trials were double-blind, randomized, placebo or active-controlled trials with ≥18 weeks duration in patients with type 2 diabetes reporting safety outcomes. Meta-analysis was performed separately for trials in which the control group received placebo (44 studies), another gliptin (3 studies) and any other antidiabetic drug (20 studies). Risk ratios with 95% confidence intervals were computed using a Mantel-Haenszel fixed-effect model for general safety outcomes, hypoglycaemia and adverse events by system organ class. Of 307 publications retrieved, 67 randomized, controlled trials met the eligibility criteria and were included in this review (4 alogliptin, 8 linagliptin, 8 saxagliptin, 20 sitagliptin, and 27 vildagliptin trials). Adverse events with gliptin treatment were at placebo level (relative risk (RR) 1.02 [0.99, 1.04]). No increased risk of infections was detectable (RR 0.98 [0.93, 1.05] compared to placebo and 1.02 [0.97, 1.07] compared to other antidiabetic drugs). Asthenia (RR 1.57 [1.09, 2.27]) as well as cardiac (RR 1.37 [1.00, 1.89]) and vascular disorders (RR 1.74 [1.05, 2.86] for linagliptin) emerged as adverse events associated with DPP-4 inhibitor treatment. The risk of hypoglycaemia was low with DPP-4 inhibitor treatment (RR 0.92 [0.74, 1.15] compared to placebo, RR 0.20 [0.17, 0.24] compared to sulphonylureas) in the absence of sulphonylurea or insulin co-therapy, but significantly elevated for combination therapy of sulphonylurea or insulin with sitagliptin or linagliptin (RR 1.86 [1.46, 2.37] compared to placebo). A large body of data supports the long-term safety of gliptin treatment and refutes an increased risk of infections. Further research is needed to clarify a possible link to asthenia, cardiac and vascular events. For combination therapy with insulin or insulin secretagogues, a careful choice of the agent used may limit the risk of hypoglycaemia.

Role of GLP-1 and DPP-4 in diabetic nephropathy and cardiovascular disease

Although there have been major advances in the understanding of the molecular mechanisms that contribute to the development of diabetic nephropathy, current best practice still leaves a significant treatment gap. The incidence of diabetes and associated nephropathy is increasing, with the main cause of mortality being related to cardiovascular causes. Novel therapies which are both 'cardio-renal'-protective seem the logical way forward. In the present review, we discuss the GLP-1 (glucagon-like peptide-1) receptor agonists and DPP-4 (dipeptidyl peptidase-4) inhibitors (incretin-based therapies), which are novel antidiabetic agents used in clinical practice and their role in diabetic nephropathy with specific focus on renoprotection and surrogate markers of cardiovascular disease. We discuss the pleiotropic effects of the incretin-based therapies apart from glucose-lowering and highlight the non-GLP-1 effects of DPP (dipeptidyl peptidase) inhibition. Large-scale clinical studies with cardiovascular end points are underway; however, studies with renal end points are lacking but much needed.

Effects of chemosignals from sad tears and postprandial plasma on appetite and food intake in humans

Chemosignals from human body fluids may modulate biological functions in humans. The objective of this study was to examine whether chemosignals from human sad tears and postprandial plasma modulate appetite. We obtained fasting and postprandial plasma from male participants and sad tears and saline, which was trickled below the eyelids, from female volunteers. These samples were then randomly distributed to male participants to sniff with a band-aid containing 100 µl of each fluid on four consecutive days in a double-blind fashion. We checked appetite by a visual analogue scale (VAS) and food intake by measuring the consumption of a test meal. In addition, the serum levels of total testosterone and LH were measured. Twenty men (mean age 26.3±4.6 years) were enrolled in this study. They could not discriminate between the smell of fasting and postprandial plasma and the smell of sad tears and trickled saline. Appetite and the amount of food intake were not different between the groups. Although the VAS ratings of appetite correlated with the food intake upon sniffing fasting plasma, postprandial plasma, and trickled saline, there was no such correlation upon sniffing sad tears. In addition, the decrease in serum testosterone levels from the baseline was greater with sad tears than with the trickled saline (−28.6±3.3% vs. −14.0±5.2%; P = 0.019). These data suggest that chemosignals from human sad tears and postprandial plasma do not appear to reduce appetite and food intake. However, further studies are necessary to examine whether sad tears may alter the appetite-eating behavior relation.

Decreased soluble dipeptidyl peptidase IV activity as a potential serum biomarker for COPD

OBJECTIVES

The objective of this study was to measure soluble dipeptidyl peptidase IV (sDPPIV) activity in sera of patients with stable chronic obstructive pulmonary disease (COPD) in comparison to healthy controls. The main goal was to assess changes in the enzyme activity in relation to severity of the disease, age and smoking history and to evaluate diagnostic accuracy for prediction of COPD by level of serum sDPPIV activity.

DESIGN AND METHODS

The study included 106 patients with stable COPD (GOLD II-GOLD IV stages) and 38 healthy controls. Serum sDPPIV activity as well as some inflammatory markers (CRP, total and differential leukocyte counts) was measured. Multivariate logistic regression models were applied to analyze association of sDPPIV activity and inflammatory markers in risk estimation for COPD development.

RESULTS

sDPPIV activity in COPD patients was significantly reduced when compared to healthy controls. Decrease was observed already in GOLD II stage. Age and smoking history did not influence sDPPIV activity. Very good diagnostic accuracy (AUC=0.833; sensitivity and specificity of 85.7% and 78.9%, respectively) for GOLD II and good diagnostic accuracy (AUC=0.801; sensitivity and specificity of 65.1% and 86.8%, respectively) for total cohort of COPD patients were found. The multivariate logistic regression model showed that the use of sDPPIV in combination with CRP and lymphocyte proportion improved diagnostic strength and gave an AUC of 0.933.

CONCLUSIONS

sDPPIV activity is decreased in COPD patients as early as in GOLD II stage. Very good diagnostic accuracy of sDPPIV activity suggests it as a candidate biomarker for early diagnosis of COPD.

Expression and spatial heterogeneity of dipeptidyl peptidases in endothelial cells of conduct vessels and capillaries

Dipeptidyl peptidase IV (DPPIV)/CD26 is by far the most extensively studied member of the prolyl oligopeptidase family of serine proteases. The discovery of the related enzymes DPP8 and DPP9 necessitates a (re-)evaluation of the DPPIV-like enzymatic activity in cells and organs. In this study, we aimed (1) to investigate the expression of the individual dipeptidyl peptidases in different types of endothelial cells (ECs) and (2) to reconsider published data in relation to our findings. Examination of DPP expression in rat primary ECs of aortic, endocardial and cardiac microvascular origin revealed the presence of DPPIV-like activity in all cell lysates. More than half of this activity could be attributed to DPP8/9. Western blot analysis revealed an abundance of the DPP8 protein as compared to DPP9. The expression of DPPIV and DPP8 was significantly higher in the cardiac microvascular endothelium than in the other ECs, suggesting a more pronounced role of these DPPs in the microvasculature. In situ, DPP activity in ventricular microvasculature was completely inhibited by sitagliptin, indicating that DPPIV is the predominant DPPIV-like enzyme in this organ. By contrast, immunohistochemical studies indicated DPP9 as the predominant DPP in human carotid artery ECs. In conclusion, our results support a highly regulated expression of individual DPPs in ECs, with a spatial heterogeneity in the cardiovascular tree.

Substance P-induced skin inflammation is not modulated by a single dose of sitagliptin in human volunteers

Substance P (SP), an undecapeptide belonging to the tachykinin family, is released during the activation of sensory nerves, and causes vasodilation, edema and pain through activation of tissular Neurokinin 1 receptors. SP proinflammatory effects are terminated by angiotensin converting enzyme (ACE) and neutral endopeptidase (NEP), while the aminopeptidase dipeptidylpeptidase IV (DPPIV) can also play a role. The aim of this randomized, crossover, double-blind study was to assess the cutaneous vasoreactivity (flare and wheal reaction, burning pain sensation) to intradermal injection of ascending doses of SP in six volunteers receiving a single therapeutic dose of the DPPIV inhibitor sitagliptin or a matching placebo. Cutaneous SP challenges produced the expected, dose-dependent flare and wheal response, while eliciting mild to moderate local pain sensation with little dose dependency. However, no differences were shown in the responses observed under sitagliptin compared with placebo, while the study would have been sufficiently powered to detect a clinically relevant increase in sensitivity to SP. The results of this pilot study are in line with proteolytic cleavage of SP by ACE and NEP compensating the blockade of DPPIV to prevent an augmentation of its proinflammatory action.

Incretin-based therapies in complex patients: practical implications and opportunities for maximizing clinical outcomes: a discussion with Dr. Vivian A. Fonseca

Elderly patients and patients with renal impairment present unique challenges in the management of diabetes mellitus. Impaired renal function is a common comorbidity (or complication) associated with type 2 diabetes, as well as a complicating factor in the treatment of the disease. Renal insufficiency, which can result in elevated plasma concentrations of pharmaceutical agents, may preclude the use of some antihyperglycemic medications and require that the dosages of others be reduced. Failure to select and dose medications carefully in these patients may increase the risk of hypoglycemia and other adverse effects. For example, elevated plasma concentrations of some sulfonylureas may increase the risk of hypoglycemia. Because patients with chronic renal insufficiency tend to retain fluids, treatment with a thiazolidinedione--a class of agents associated with fluid retention--may exacerbate the risk of edema. Older patients with type 2 diabetes--like patients with renal insufficiency an important and populous subgroup--also have issues with therapy selection and dosing regimens. As a result of the effects of aging on kidney function, older patients may also be subject to elevated plasma levels with consequent additional risk of hypoglycemia and other adverse events. Because older patients tend to be treated with multiple medications for multiple comorbidities, it becomes challenging to design regimens that avoid or reduce the risk of drug-drug interactions. For both older patients and patients with chronic renal insufficiency, the most important drug-related adverse effect to avoid is hypoglycemia. Accordingly, incretin-based agents have an advantage because they are unlikely to cause hypoglycemia.

Incretin-based therapies for type 2 diabetes mellitus: properties, functions, and clinical implications

The incretin hormones, glucose-dependent insulinotropic polypeptide (GIP) and glucagonlike peptide-1 (GLP-1), which are secreted by cells of the gastrointestinal tract in response to meal ingestion, exercise important glucoregulatory effects, including the glucose-dependent potentiation of insulin secretion by pancreatic β-cells. Research on the defective incretin action in type 2 diabetes mellitus suggests that the observed loss of insulinotropic activity may be due primarily to a decreased responsiveness of β-cells to GIP. GLP-1 does retain efficacy, albeit not at physiologic levels. Accordingly, augmentation of GLP-1 is a logical therapeutic strategy to ameliorate this deficiency, although the short metabolic half-life of the native hormone renders direct infusion impractical. GLP-1 receptor agonists that resist degradation by the enzyme dipeptidyl peptidase-4 (DPP-4) and have protracted-action kinetics have been developed, and DPP-4 inhibitors that slow the enzymatic cleavage of native GLP-1 provide alternative approaches to enhancing incretin-mediated glucose control. However, GLP-1 receptor agonists and DPP-4 inhibitors are premised on highly divergent mechanisms of action. DPP-4 is ubiquitously expressed in many tissues and is involved in a wide range of physiologic processes in addition to its physiologic influence on incretin hormone biological activity. GLP-1 receptor agonists provide a pharmacologic level of GLP-1 receptor stimulation, whereas DPP-4 inhibitors appear to increase levels of circulating GLP-1 to within the physiologic range. This article examines the physiology of the incretin system, mechanistic differences between GLP-1 receptor agonists and DPP-4 inhibitors used as glucose-lowering agents in the treatment of type 2 diabetes, and the implications of these differences for treatment. The results of recent head-to-head trials are reviewed, comparing the effects of incretin-based therapies on a range of clinical parameters, including glycemia, β-cell function, weight, and cardiovascular function.

Rhinorrhea, cough and fatigue in patients taking sitagliptin

Sitagliptin is a dipeptidyl peptidase-4 (DPP IV, CD26) inhibitor indicated for treatment of Type II diabetes as a second line therapy after metformin. We report fifteen sitagliptin intolerant patients who developed anterior and posterior rhinorrhea, cough, dyspnea, and fatigue. Symptoms typically developed within 1 to 8 weeks of starting, and resolved within 1 week of stopping the drug. Peak expiratory flow rates increased 34% in 8 patients who stopped sitagliptin. Similar changes were found in 4 out of 5 persons who had confirmatory readministration. Chart review identified 17 patients who tolerated sitagliptin and had no symptomatic changes. The sitagliptin intolerant group had higher rates of clinically diagnosed allergic rhinitis (15/15 vs. 6/18; p = 0.00005), Fisher's Exact test) and angiotensin converting enzyme inhibitor - induced cough (6/13 vs. 1/18; p = 0.012). Nasal and inhaled glucocorticoids may control the underlying allergic inflammation and abrogate this new sitagliptin - induced pharmacological syndrome. Potential mucosal and central nervous system mechanisms include disruption of neuropeptides and/or cytokines that rely on DPP IV for activation or inactivation, and T cell dysfunction.

Dutogliptin, a selective DPP4 inhibitor, improves glycaemic control in patients with type 2 diabetes: a 12-week, double-blind, randomized, placebo-controlled, multicentre trial

AIM

To determine efficacy and tolerability of dutogliptin, a dipeptidyl peptidase 4 (DPP4) inhibitor, in patients with type 2 diabetes mellitus.

METHODS

This was a 12-week, multicentre, randomized, double-blind, placebo-controlled trial in 423 patients with type 2 diabetes with suboptimal metabolic control. Following a 2-week single-blind placebo run-in, patients aged 18-75 years with a body mass index of 25-48 kg/m(2) and baseline HbA1c of 7.3-11.0% were randomized 2:2:1 to receive once-daily oral therapy with either dutogliptin (400 or 200 mg) or placebo on a background medication of either metformin alone, a thiazolidinedione (TZD) alone or a combination of metformin plus a TZD.

RESULTS

Average HbA1c at baseline was 8.4%. Administration of dutogliptin 400 and 200 mg for 12 weeks decreased HbA1c by -0.52% (p < 0.001) and -0.35% (p = 0.006), respectively (placebo-corrected values), with absolute changes in HbA1c for the 400 mg, 200 mg and placebo groups of -0.82, -0.64 and -0.3%, respectively. The proportion of patients achieving an HbA1c < 7% was 27, 21 and 12% at dutogliptin doses of 400 and 200 mg or placebo, respectively (p = 0.008 for comparison of 400 mg vs. placebo). Fasting plasma glucose (FPG) levels were significantly reduced in both active treatment groups compared to placebo: the placebo-corrected difference was -1.00 mmol/l (p < 0.001) for the 400 mg group and -0.88 mmol/l (p = 0.003) for the 200 mg group. Dutogliptin caused significantly greater reductions in postprandial glucose AUC (0-2h) in both the 400 and 200 mg groups (placebo corrected values -2.58 mmol/l/h, p < 0.001 and -1.63 mmol/l/h, p = 0.032, respectively). In general, patients tolerated the study drug well. There were minor, not clinically meaningful differences in adverse events (AEs) between dutogliptin-treated patients and placebo controls, and 60% of all reported AEs were mild. Vital signs and body weight were stable, and routine safety laboratory parameters did not change compared with placebo. Trough ex vivo DPP4 inhibition at the end of the 12-week treatment period was 80 and 70%, at the 400 and 200 mg doses of dutogliptin, respectively.

CONCLUSIONS

Dutogliptin treatment for 12 weeks improved glycaemic control in patients with type 2 diabetes who were on a background medication of metformin, a TZD or metformin plus a TZD. Tolerability was favourable for both doses tested. The 400 mg dose of dutogliptin resulted in larger changes of HbA1c and FPG and more subjects reached an HbA1c target of < 7% than the 200 mg dose.

On the origin of serum CD26 and its altered concentration in cancer patients

Dipeptidyl peptidase IV (DPP-IV), assigned to the CD26 cluster, is expressed on epithelial cells and lymphocytes and is a multifunctional or pleiotropic protein. Its peptidase activity causes degradation of many biologically active peptides, e.g. some incretins secreted by the enteroendocrine system. DPP-IV has, therefore, become a novel therapeutic target for inhibitors that extend endogenously produced insulin half-life in diabetics, and several reviews have appeared in recent months concerning the clinical significance of CD26/DPP-IV. Biological fluids contain relatively high levels of soluble CD26 (sCD26). The physiological role of sCD26 and its relation, if any, to CD26 functions, remain poorly understood because whether the process for CD26 secretion and/or shedding from cell membranes is regulated or not is not known. Liver epithelium and lymphocytes are often cited as the most likely source of sCD26. It is important to establish which tissue or organ is the protein source as well as the circumstances that can provoke an abnormal presence/absence or altered levels in many diseases including cancer, so that sCD26 can be validated as a clinical marker or a therapeutic target. For example, we have previously reported low levels of sCD26 in the blood of colorectal cancer patients, which indicated the potential usefulness of the protein as a biomarker for this cancer in early diagnosis, monitoring and prognosis. Through this review, we envisage a role for sCD26 and the alteration of normal peptidase capacity (in clipping enteroendocrine or other peptides) in the complex crosstalk between the lymphoid lineage and, at least, some malignant tumours.

Kinetic study of neuropeptide Y (NPY) proteolysis in blood and identification of NPY3-35: a new peptide generated by plasma kallikrein

There is little information on how neuropeptide Y (NPY) proteolysis by peptidases occurs in serum, in part because reliable techniques are lacking to distinguish different NPY immunoreactive forms and also because the factors affecting the expression of these enzymes have been poorly studied. In the present study, LC-MS/MS was used to identify and quantify NPY fragments resulting from peptidolytic cleavage of NPY(1-36) upon incubation with human serum. Kinetic studies indicated that NPY(1-36) is rapidly cleaved in serum into 3 main fragments with the following order of efficacy: NPY(3-36) >> NPY(3-35) > NPY(2-36). Trace amounts of additional NPY forms were identified by accurate mass spectrometry. Specific inhibitors of dipeptidyl peptidase IV, kallikrein, and aminopeptidase P prevented the production of NPY(3-36), NPY(3-35), and NPY(2-36), respectively. Plasma kallikrein at physiological concentrations converted NPY(3-36) into NPY(3-35). Receptor binding assays revealed that NPY(3-35) is unable to bind to NPY Y1, Y2, and Y5 receptors; thus NPY(3-35) may represent the major metabolic clearance product of the Y2/Y5 agonist, NPY(3-36).

Substance P scavenger enhances antioxidant defenses and prevents prothrombotic effects on the rat lung after acute exposure to oil smoke

Background

Airborne particulate matter, from cooking oil, smoking, engine exhaust and other sources, is associated with the development of atherosclerosis and myocardial infarction. In order to explore the cellular and molecular events following exposure of rats to lard oil smoke, we measured the generation of reactive oxygen species (ROS), substance P, cellular adhesion molecules, and thrombosis in relation to inhibitors of substance P, the NK-1 receptor, and antioxidants.

Methods

Rats were exposed to oil smoke for 120 min with or without 20 min pretreatment with lovastatin (substance P scavenger), L733060 (NK-1 receptor antagonist), vitamin E (antioxidant) or catechins (antioxidant). The levels of substance P and ROS were measured. Histological studies observed ROS damage in the form of HEL adducts. The prothrombotic effects of oil smoke exposure were measured by experimental induction of thrombosis in vivo.

Results

Oil smoke exposure significantly increased substance P levels, ROS levels, ROS damage (HEL adduct levels), and the size of experimentally induced thrombi. The pretreatments reduced all of these effects of oil smoke exposure; at many time points the reductions were statistically significant.

Conclusion

We established a connection between oil smoke exposure and thrombosis which involves substance P and its receptor, the NK-1 receptor, and ROS. This study helps establish a mechanistic explanation of how airborne particulate matter can increase the risk of cardiovascular illness.

Histoplasma capsulatum encodes a dipeptidyl peptidase active against the mammalian immunoregulatory peptide, substance P

The pathogenic fungus Histoplasma capsulatum secretes dipeptidyl peptidase (Dpp) IV enzyme activity and has two putative DPPIV homologs (HcDPPIVA and HcDPPIVB). We previously showed that HcDPPIVB is the gene responsible for the majority of secreted DppIV activity in H. capsulatum culture supernatant, while we could not detect any functional contribution from HcDPPIVA. In order to determine whether HcDPPIVA encodes a functional DppIV enzyme, we expressed HcDPPIVA in Pichia pastoris and purified the recombinant protein. The recombinant enzyme cleaved synthetic DppIV substrates and had similar biochemical properties to other described DppIV enzymes, with temperature and pH optima of 42°C and 8, respectively. Recombinant HcDppIVA cleaved the host immunoregulatory peptide substance P, indicating the enzyme has the potential to affect the immune response during infection. Expression of HcDPPIVA under heterologous regulatory sequences in H. capsulatum resulted in increased secreted DppIV activity, indicating that the encoded protein can be expressed and secreted by its native organism. However, HcDPPIVA was not required for virulence in a murine model of histoplasmosis. This work reports a fungal enzyme that can function to cleave the immunomodulatory host peptide substance P.

Pathogenesis of dermatophytosis

Despite the superficial localization of most dermatophytosis, host-fungus relationship in these infections is complex and still poorly elucidated. Though many efforts have been accomplished to characterize secreted dermatophytic proteases at the molecular level, only punctual insights have been afforded into other aspects of the pathogenesis of dermatophytosis, such as fungal adhesion, regulation of gene expression during the infection process, and immunomodulation by fungal factors. However, new genetic tools were recently developed, allowing a more rapid and high-throughput functional investigation of dermatophyte genes and the identification of new putative virulence factors. In addition, sophisticated in vitro infection models are now used and will open the way to a more comprehensive view of the interactions between these fungi and host epidermal cells, especially keratinocytes.

The dipeptidyl peptidase-4 inhibitor PHX1149 improves blood glucose control in patients with type 2 diabetes mellitus

AIM

To determine the efficacy and tolerability of PHX1149, a novel dipeptidyl peptidase-4 (DPP4) inhibitor, in patients with type 2 diabetes.

METHODS

This is a multicentre, randomized, double-blind, placebo-controlled, 4-week study in patients with type 2 diabetes with suboptimal metabolic control. Patients with a baseline haemoglobin A(1c) (HbA(1c)) of 7.3 to 11.0% were randomized 1 : 1 : 1 : 1 to receive once-daily oral therapy with either PHX1149 (100, 200 or 400 mg) or placebo; patients were on a constant background therapy of either metformin alone or metformin plus a glitazone.

RESULTS

Treatment with 100, 200 or 400 mg of PHX1149 significantly decreased postprandial glucose area under the curve AUC(0-2 h) by approximately 20% (+0.11 +/- 0.50, -2.08 +/- 0.51, -1.73 +/- 0.49 and -1.88 +/- 0.48 mmol/l x h, respectively, for placebo and 100, 200 and 400 mg (p = 0.002, 0.008 and 0.004 vs. placebo). Postprandial AUC(0-2 h) of intact glucagon-like peptide-1, the principal mediator of the biological effects of DPP4 inhibitors, was increased by 3.90 +/- 2.83, 11.63 +/- 2.86, 16.42 +/- 2.72 and 15.75 +/- 2.71 pmol/l x h, respectively, for placebo and 100, 200 and 400 mg (p = 0.053, 0.001 and 0.002 vs. placebo). Mean HbA(1c) was lower in all dose groups; the placebo-corrected change in the groups receiving 400 mg PHX1149 was -0.28% (p = 0.02). DPP4 inhibition on day 28 was 53, 73 and 78% at 24 h postdose in the groups receiving 100, 200 and 400 mg PHX1149, respectively. There were no differences in adverse events between PHX1149-treated and placebo subjects.

CONCLUSIONS

Addition of the DPP4 inhibitor PHX1149 to a stable regimen of metformin or metformin plus a glitazone in patients with type 2 diabetes was well tolerated and improved blood glucose control.

Implication of dipeptidylpeptidase IV activity in human bronchial inflammation and in bronchoconstriction evaluated in anesthetized rabbits

BACKGROUND

Decreased dipeptidylpeptidase IV (DPPIV) activity within the human nasal mucosa has previously been shown to contribute to the severity of chronic inflammatory rhinosinusitis.

OBJECTIVE

To investigate and correlate the role of DPPIV activity with regard to bronchial inflammation.

METHODS

DPPIV/CD26 activity/concentration was investigated in the bronchial tissue of human subjects suffering from chronic bronchial inflammation. In addition, the effect of a recombinant Aspergillus fumigatus DPPIV (fuDPPIV) was investigated on histamine-induced bronchoconstriction in anesthetized rabbits.

RESULTS AND CONCLUSIONS

DPPIV/CD26 was present in submucosal seromucous glands, in leukocytes and to a very low degree in endothelial cells of human bronchi. DPPIV activity was correlated with tissue CD26 content measured by immunoassay. As previously reported for the nasal mucosa, DPPIV/CD26 activity was inversely correlated with the degree of airway inflammation. Systemic pretreatment with recombinant fuDPPIV markedly reduced the increase in histamine-induced airway resistance in rabbits. In conclusion, DPPIV activity modulates lower airway tone by degrading unknown peptidic substrates released by histamine in response to an allergen. Contrasting with our observations in the nose, this modulation is apparently not mediated via a neurokinin (NK1) receptor.

Dipeptidyl peptidase IV deficiency increases susceptibility to angiotensin-converting enzyme inhibitor-induced peritracheal edema

BACKGROUND

Serum dipeptidyl peptidase IV (DPPIV) activity is decreased in some individuals with ACE inhibitor-associated angioedema. ACE and DPPIV degrade substance P, an edema-forming peptide. The contribution of impaired degradation of substance P by DPPIV to the pathogenesis of ACE inhibitor-associated angioedema is unknown.

OBJECTIVES

We sought to determine whether DPPIV deficiency results in increased edema formation during ACE inhibition. We also sought to develop an animal model using magnetic resonance imaging to quantify ACE inhibitor-induced edema.

METHODS

The effect of genetic DPPIV deficiency on peritracheal edema was assessed in F344 rats after treatment with saline, captopril (2.5 mg/kg), or captopril plus the neurokinin receptor antagonist spantide (100 mug/kg) by using serial T2-weighted magnetic resonance imaging.

RESULTS

Serum dipeptidyl peptidase activity was dramatically decreased in DPPIV-deficient rats (P < .001). The volume of peritracheal edema was significantly greater in captopril-treated DPPIV-deficient rats than in saline-treated DPPIV-deficient rats (P = .001), saline-treated rats of the normal substrain (P < .001), or captopril-treated rats of the normal substrain (P = .001). Cotreatment with spantide attenuated peritracheal edema in captopril-treated DPPIV-deficient rats (P = .005 vs captopril-treated DPPIV-deficient rats and P = .57 vs saline-treated DPPIV-deficient rats).

CONCLUSIONS

DPPIV deficiency predisposes to peritracheal edema formation when ACE is inhibited through a neurokinin receptor-dependent mechanism. Magnetic resonance imaging is useful for modeling ACE inhibitor-associated angioedema in rats.

CLINICAL IMPLICATIONS

Genetic or environmental factors that decrease DPPIV activity might increase the risk of ACE inhibitor-associated angioedema.

Chromatographic characterization of substance P endopeptidase in the rat brain reveals affected enzyme activity following heat stress

This paper describes a study of substance P endopeptidase (SPE)-like activity in various regions of the brain from male rats subjected to heat stress (HS). The enzyme activity was found to be affected in several brain areas including cerebellum, cerebral cortex, hippocampus, hypothalamus[sol ]thalamus and the spinal cord following HS. Significant increases in SPE activity were observed in, for example, hippocampus and the spinal cord. SPE-containing extracts from hippocampus were pooled and subsequently purified by size exclusion chromatography (using a Superdex 75 HR column) and by anion-exchange chromatography (using Resource Q column). The gel permeation chromatography separated the SPE-like activity into two fractions, one of which was suggested to be identical to neutral endopeptidase owing to its molecular size and inhibitory profile. The other active enzyme fraction behaved in conformity with SPE, previously identified in human cerebrospinal fluid. The activity of the purified fraction of these two enzymes was found to be increased (27%) in HS-treated animals.

Stress and substance P but not the substance P-metabolite SP5-11 trigger murine abortion by augmenting TNF-alpha levels at the feto-maternal interface

In a well-established murine abortion model, stress is thought to trigger fetal rejection by inducing a proinflammatory immune response via substance P (SP), being tumour necrosis factor (TNF)-alpha-producing CD8+ T cells involved. Interestingly, the SP metabolite SP5-11 also binds to SP receptors and mediates SP-like effects on immune cells at sites of inflammation. No data were available regarding the effects of SP5-11 on pregnancy outcome in the CBA/J x DBA/2J abortion-prone combination. We investigated the influence of SP5-11 in contrast to stress or SP on the abortion rate and the cytokine production by lymphocytes as well as on the levels of CD8+ T cells. Stress and SP boosted the abortion rate and increased the percentage of type 1 [TNF-alpha, interferon-gamma, interleukin (IL)-12] and type 2 (IL-4 and IL-10) cytokine-producing lymphocytes in blood and decidua, predominantly CD8+ T cells. Interestingly, SP5-11 did not significantly affect the abortion rate or cytokine production in the decidua, while increasing the Th1 and Th2 cytokine production systemically. Our data suggest that stress and SP induce abortion by augmenting the local levels of TNF-alpha, which seems therefore to be a potent trigger of miscarriage. On the contrary, the SP metabolite SP5-11 only affects the systemic cytokine production without boosting the abortion rate in this experimental model.

Therapeutic assessment of glucagon-like peptide-1 agonists compared with dipeptidyl peptidase IV inhibitors as potential antidiabetic drugs

The most prevalent form of diabetes is non-insulin-dependent or Type 2 diabetes. Innovative strategies to enhance insulin secretion and thereby improve glucose tolerance in patients with this type of diabetes are currently under preclinical and clinical investigation. These therapies include the applications of incretin hormones; gut hormones released postprandially that stimulate insulin secretion in pancreatic beta-cells. Because incretin actions are rapidly terminated by N-terminal cleavage of these peptide hormones by the amino-peptidase dipeptidyl peptidase IV (DPP IV, CD26), the utility of DPP IV inhibitors for the treatment of Type 2 diabetes is also under investigation. This review compares the therapeutic potential and possible side effects of metabolically stable analogues/peptide agonists of the incretin glucagon-like peptide-1 (GLP-1) with the application of DPP IV inhibitors that reduce the rate of endogenous degradation of GLP-1 and other incretins. GLP-1 analogues have been shown to be highly efficacious in the treatment of Type 2 diabetes, with minimal side effects. Of particular importance is the fact that they do not induce hypoglycaemia. However, they are currently available only in an injectable form. In contrast, DPP IV inhibitors have the clear advantage of oral application resulting in better patient compliance. Furthermore, they also potentiate the actions of other incretins normally degraded by the action of DPP IV. However, they possess more potential side effects. Taken together, both approaches offer promising new drugs for the treatment of Type 2 diabetes.

Cell-surface peptidases

The cell surface has various functions: communicating with other cells, integrating into the tissue, and interacting with the extracellular matrix. Proteases play a key role in these processes. This review focuses on cell-surface peptidases (ectopeptidases, oligopeptidases) that are involved in the inactivation or activation of extracellular regulatory peptides, hormones, paracrine peptides, cytokines, and neuropeptides. The nomenclature of cell-surface peptidases is explained in relation to other proteases, and information is provided on membrane anchoring, catalytic sites, regulation, and, in particular, on their physiological and pharmacological importance. Furthermore, nonenzymatic (binding) functions and participation in intracellular signal transduction of cell surfaces peptidases are described. An overview on the different cell-surface peptidases is given, and their divergent functions are explained in detail. An example of actual pharmacological importance, dipeptidyl-peptidase IV (CD26), is discussed.

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

Dipeptidyl-peptidase IV/CD26 (DPP IV) is a cell-surface protease belonging to the prolyloligopeptidase family. It selectively removes the N-terminal dipeptide from peptides with proline or alanine in the second position. Apart from its catalytic activity, it interacts with several proteins, for instance, adenosine deaminase, the HIV gp120 protein, fibronectin, collagen, the chemokine receptor CXCR4, and the tyrosine phosphatase CD45. DPP IV is expressed on a specific set of T lymphocytes, where it is up-regulated after activation. It is also expressed in a variety of tissues, primarily on endothelial and epithelial cells. A soluble form is present in plasma and other body fluids. DPP IV has been proposed as a diagnostic or prognostic marker for various tumors, hematological malignancies, immunological, inflammatory, psychoneuroendocrine disorders, and viral infections. DPP IV truncates many bioactive peptides of medical importance. It plays a role in glucose homeostasis through proteolytic inactivation of the incretins. DPP IV inhibitors improve glucose tolerance and pancreatic islet cell function in animal models of type 2 diabetes and in diabetic patients. The role of DPP IV/ CD26 within the immune system is a combination of its exopeptidase activity and its interactions with different molecules. This enables DPP IV/CD26 to serve as a co-stimulatory molecule to influence T cell activity and to modulate chemotaxis. DPP IV is also implicated in HIV-1 entry, malignant transformation, and tumor invasion.

Therapeutic potential of dipeptidyl peptidase IV inhibitors for the treatment of type 2 diabetes

Incretins are peptide hormones, exemplified by glucose-dependent insulinotropic peptide and glucagon-like peptide 1 that are released from the gut in response to nutrient ingestion and enhance glucose-stimulated insulin secretion. Incretin action is terminated due to N-terminal cleavage of the peptides by the aminopeptidase dipeptidyl peptidase IV (DPP-IV). Hence, inhibition of glucose-dependent insulinotropic peptide and glucagon-like peptide 1 degradation via reduction of DPP-IV activity represents an innovative strategy for enhancing incretin action in vivo. This review summarises the biology of incretin action, the structure, expression and pleiotropic biological activities of DPP-IV and provides an overview of the rationale, potential merits and theoretical pitfalls in the development of DPP-IV inhibitors for the treatment of type 2 diabetes.