Natural substrates of dipeptidyl peptidase IV

Contribution of amino acids in the active site of dipeptidyl peptidase 4 to the catalytic action of the enzyme

Dipeptidyl peptidase 4 (DP4)/CD26 regulates the biological function of various peptide hormones by releasing dipeptides from their N-terminus. The enzyme is a prominent target for the treatment of type-2 diabetes and various DP4 inhibitors have been developed in recent years, but their efficacy and side effects are still an issue. Many available crystal structures of the enzyme give a static picture about enzyme-ligand interactions, but the influence of amino acids in the active centre on binding and single catalysis steps can only be judged by mutagenesis studies. In order to elucidate their contribution to inhibitor binding and substrate catalysis, especially in discriminating the P1 amino acid of substrates, the amino acids R125, N710, E205 and E206 were investigated by mutagenesis studies. Our studies demonstrated, that N710 is essential for the catalysis of dipeptide substrates. We found that R125 is not important for dipeptide binding but interacts in the P1`position of the peptide backbone. In contrast to dipeptide substrates both amino acids play an essential role in the binding and arrangement of long natural substrates, particularly if lacking proline in the P1 position. Thus, it can be assumed that the amino acids R125 and N710 are important in the DP4 catalysed substrate hydrolysis by interacting with the peptide backbone of substrates up- and downstream of the cleavage site. Furthermore, we confirmed the important role of the amino acids E205 and E206. However, NP Y, displaying proline in P1 position, is still processed without the participation of E205 or E206.

An Update on Dipeptidyl Peptidase-IV Inhibiting Peptides

Diabetes is a chronic metabolic disorder. According to the International Diabetes Federation, about 537 million people are living with diabetes. The two types of diabetes are type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM), among which the population affected by T2DM is relatively higher. A major reason for T2DM is that insulin stimulation is hampered due to the inactivation of incretin hormones. Dipeptidyl peptidase-IV (DPP-IV) is a serine protease that is directly involved in the inactivation of incretin hormones, e.g., glucagon-like peptide-1 (GLP-1). Therefore, the inhibition of DPP-IV can be a promising method for managing T2DM, in addition to other enzyme inhibition strategies, such as inhibition of α-amylase and α -glucosidase. Currently, about 12 different gliptin drugs are available in the market that inhibit DPP-IV in a dose-dependent manner. Instead of gliptins, 'peptides' can also be employed as an alternative and promising way to inhibit DPP-IV. Peptide inhibitors of DPP-IV have been identified from various plants and animals. Chemically synthesized peptides have also been experimented for inhibiting DPP-IV. Most peptides have been analysed by biochemical assays, whereas some in vitro assays have also been reported. Molecular docking analysis has been applied to comprehend the mechanism of inhibition. In this review, certain aspects of natural as well as synthetic peptides are described that have been proven to inhibit DPP-IV.

Intestinal Immune Imbalance is an Alarm in the Development of IBD

Immune regulation plays a crucial role in human health and disease. Inflammatory bowel disease (IBD) is a chronic relapse bowel disease with an increasing incidence worldwide. Clinical treatments for IBD are limited and inefficient. However, the pathogenesis of immune-mediated IBD remains unclear. This review describes the activation of innate and adaptive immune functions by intestinal immune cells to regulate intestinal immune balance and maintain intestinal mucosal integrity. Changes in susceptible genes, autophagy, energy metabolism, and other factors interact in a complex manner with the immune system, eventually leading to intestinal immune imbalance and the onset of IBD. These events indicate that intestinal immune imbalance is an alarm for IBD development, further opening new possibilities for the unprecedented development of immunotherapy for IBD.

A Peptide in a Pill - Oral Semaglutide in the Management of Type 2 Diabetes

T2DM (type 2 diabetes mellitus) is a chronic and progressive illness with high morbidity and death rates. Oral semaglutide (Rybelsus®) is a combination of semaglutide, a glucagon-like peptide-1 receptor agonist (GLP-1 RA), and sodium N- (8- [2-hydroxybenzoyl] amino) caprylate (SNAC), an absorption enhancer that facilitates semaglutide absorption across the gastric epithelium in a concentration-dependent manner. This family of drugs apart from glucose lowering effects causes significant weight loss with lower risk of hypoglycemia, and some of them have been linked to a significant reduced major adverse cardiovascular events. GLP-1 RAs may assist persons with T2DM and chronic kidney disease (CKD), a major microvascular consequence of T2DM, in ways other than lowering blood sugar. Several large clinical studies, the bulk of which are cardiovascular outcome trials, show that GLP-1 RA treatment is safe and tolerated for persons with T2DM and impaired renal function and that it may potentially have renoprotective characteristics. This article focuses on the advances of oral GLP1-RA and describes the key milestones and predicted advantages.

Profiling of intact blood proteins by matrix-assisted laser desorption/ionization mass spectrometry without the need for freezing - Dried serum spots as future clinical tools for patient screening

RATIONALE

To open up new ways for matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS)-based patient screening, blood serum is the most preferred specimen because of its richness in patho-physiological information and due to ease of collection. To overcome deleterious freeze/thaw cycles and to reduce high costs for shipping and storage, we sought to develop a procedure which enables MALDI-MS protein profiling of blood serum proteins without the need for serum freezing.

METHODS

Blood sera from patients/donors were divided into portions which after pre-incubation were fast frozen. Thawed aliquots were deposited on filter paper discs and air-dried at room temperature. Intact serum proteins were eluted with acid-labile detergent-containing solutions and were desalted by employing a reversed-phase bead system. Purified protein solutions were screened by MALDI-MS using standardized instrument settings.

RESULTS

MALDI mass spectra from protein solutions which were eluted from filter paper discs and desalted showed on average 25 strong ion signals (mass range m/z 6000 to 10,000) from intact serum proteins (apolipoproteins, complement proteins, transthyretin and hemoglobin) and from proteolytic processing products. Semi-quantitative analysis of three ion pairs: m/z 6433 and 6631, m/z 8205 and 8916, as well as m/z 9275 and 9422, indicated that the mass spectra from either pre-incubated fast-frozen serum or pre-incubated dried serum spot eluted serum contained the same information on protein composition.

CONCLUSIONS

A workflow that avoids the conventional cold-chain and yet enables the investigation of intact serum proteins and/or serum proteolysis products by MALDI-MS profiling was developed. The presented protocol tremendously broadens the clinical application of MALDI-MS and simultaneously allows a reduction in the costs for storage and shipping of serum samples. This will pave the way for clinical screening of patients also in areas with limited access to health care systems, and/or specialized laboratories.

Investigation of CD26, a potential SARS-CoV-2 receptor, as a biomarker of age and pathology

Objective: In some individuals, coronavirus severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection leads to a variety of serious inflammatory symptoms, including blood clotting and acute respiratory distress. Death due to COVID-19 shows a steep rise in relation to age. Comorbidities such as type 2 diabetes mellitus (T2DM), hypertension, and cardiovascular disease also increase susceptibility. It has been reported that T-cell regulatory dipeptidyl peptidase 4 (DPP4; cluster of differentiation 26 (CD26)) binds to the external spike (S) glycoprotein of SARS-CoV-2 as a receptor, for the viral entry into the host cell. CD26 is expressed on many cells, including T and natural killer (NK) cells of the immune system, as a membrane-anchored form. A soluble form (sCD26) is also found in the blood plasma and cerebrospinal fluid (CSF).

Approach and results: To investigate a possible relationship between sCD26 levels, age and pathology, serum samples were collected from control, T2DM and age-related dementia (ARD) subjects. A significant reduction in serum sCD26 levels was seen in relation to age. ARD and T2DM were also associated with lower levels of sCD26. The analysis of blood smears revealed different cellular morphologies: in controls, CD26 was expressed around the neutrophil membrane, whereas in T2DM, excessive sCD26 was found around the mononucleated cells (MNCs). ARD subjects had abnormal fragmented platelets and haemolysis due to low levels of sCD26.

Conclusions: These findings may help to explain the heterogeneity of SARS-CoV-2 infection. High serum sCD26 levels could protect from viral infection by competively inhibiting the virus binding to cellular CD26, whereas low sCD26 levels could increase the risk of infection. If so measuring serum sCD26 level may help to identify individuals at high risk for the COVID-19 infection.

Single-dose escalation study of yogliptin in healthy Chinese volunteers

BACKGROUND

Yogliptin is a novel xanthine dipeptidyl peptidase-4 (DPP-4) inhibitor targeting type 2 diabetes. After promising preclinical pharmacological studies, the first human trial of yogliptin was designed.

METHODS

A randomized, double-blind, parallel, placebo-controlled phase I single-dose escalation study was designed to evaluate the pharmacokinetics, pharmacodynamics, and tolerability after single oral doses of yogliptin in healthy Chinese subjects. Healthy subjects were assigned to nine cohorts, which received a single dose of yogliptin at 2.5, 5, 10, 25, 50, 100, 200, 400, or 600 mg. Two subjects in each cohort received placebo. Blood samples were collected before dosing and up to 192 h afterwards. Urine samples were collected until 120 h after dosing. Plasma and urine drug concentrations were determined using liquid chromatography coupled with tandem mass spectrometry, and DPP-4 activity was measured using a semi-quantitative, fluorescence-based kinetic assay.

RESULTS

A total of 104 subjects were enrolled, 103 of whom completed the study (mean age, 25.3 years; mean weight, 58.8 kg; mean BMI, 21.8 kg/m²). A total of 27 adverse events (AEs) occurred in 25 of 86 yogliptin subjects (29.1%), and 3 AEs occurred in 3 of 18 placebo subjects (16.7%). Yogliptin was absorbed with a median time of maximum observed concentration (T_max) of 3.0 h and was eliminated slowly with a t_1/2 of 25.45-43.84 h. The maximum observed concentration (C_max) and area under the curve (AUC) varied slightly more than dose-proportionally over the dose range from 2.5 to 400 mg. The fraction of drug excreted in urine ranged from 8.39% to 24.77%. Mean DPP-4 inhibition at 24 h after dosing ranged from 97.7% to 99.5%, and DPP-4 inhibition was >80% for 72 h at doses from 25 to 400 mg. DPP-4 inhibition was >80% for 1 week in the group receiving 400 mg.

CONCLUSION

Yogliptin was well tolerated in healthy subjects, with no dose-limiting toxicity observed in the range from 2.5 to 600 mg. Yogliptin inhibited plasma DPP-4 activity for 72 h at single doses of 25-200 mg and for 1 week at 400 mg, suggesting that once-weekly dosing of yogliptin is possible in type 2 diabetes patients.

TRIAL REGISTRATION

ChiCTR-IIR-17010311 (Chictr.org).

Effects of saxagliptin on glucose homeostasis and body composition of obese patients with newly diagnosed pre-diabetes

AIMS

To assess the effect of saxagliptin monotherapy on blood glucose and islet β-cell function in obese patients with newly diagnosed pre-diabetes and abnormal fat metabolism.

METHODS

A 24-week, randomized controlled trial was conducted involving 25 obese subjects with impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT) (mean age 45years) to receive lifestyle intervention only (control group) or combined with saxagliptin 2.5mg or 5mg daily (S2.5 or S5 group), metformin 1500mg daily (Met group). Anthropometrics, body fat and biochemical parameters were measured before and after 4, 12 and 24weeks intervention.

RESULTS

S5 group and Met group showed a significant decrease in fasting plasma glucose (FPG) and HbA1c compared with the control group (all P<0.05) after 24-week intervention. However, the decrease in 2h postprandial plasma glucose levels (2hPPG) in S5 group were greater compared with control group (P<0.01). Insulin resistance (HOMA-IR) was reduced in S5 group, Met group and control group (P<0.05), and the β-cell function (HOMA-β) was improved in all groups (P<0.05). However, the changes in obesity-related indicators including waist circumference, hip circumference, weight, BMI, body fat, percentage of body fat and waist-to-hip fat ratio were greate in Met group (all P<0.05) compared with other groups (P>0.05).

CONCLUSIONS

Saxagliptin monotherapy may prevent or delay the progression of IGT or IFG to type 2 diabetes mellitus in obese patients with newly diagnosed pre-diabetes. ClinicalTrials.gov: NCT01960205.

Rapid and sensitive detection of early esophageal squamous cell carcinoma with fluorescence probe targeting dipeptidylpeptidase IV

Early detection of esophageal squamous cell carcinoma (ESCC) is an important prognosticator, but is difficult to achieve by conventional endoscopy. Conventional lugol chromoendoscopy and equipment-based image-enhanced endoscopy, such as narrow-band imaging (NBI), have various practical limitations. Since fluorescence-based visualization is considered a promising approach, we aimed to develop an activatable fluorescence probe to visualize ESCCs. First, based on the fact that various aminopeptidase activities are elevated in cancer, we screened freshly resected specimens from patients with a series of aminopeptidase-activatable fluorescence probes. The results indicated that dipeptidylpeptidase IV (DPP-IV) is specifically activated in ESCCs, and would be a suitable molecular target for detection of esophageal cancer. Therefore, we designed, synthesized and characterized a series of DPP-IV-activatable fluorescence probes. When the selected probe was topically sprayed onto endoscopic submucosal dissection (ESD) or surgical specimens, tumors were visualized within 5 min, and when the probe was sprayed on biopsy samples, the sensitivity, specificity and accuracy reached 96.9%, 85.7% and 90.5%. We believe that DPP-IV-targeted activatable fluorescence probes are practically translatable as convenient tools for clinical application to enable rapid and accurate diagnosis of early esophageal cancer during endoscopic or surgical procedures.

Quantitative prediction of human pharmacokinetics and pharmacodynamics of imigliptin, a novel DPP-4 inhibitor, using allometric scaling, IVIVE and PK/PD modeling methods

PURPOSE

To predict the pharmacokinetic/pharmacodynamic (PK/PD) profiles of imigliptin, a novel DPP-4 inhibitor, in first-in-human (FIH) study based on the data from preclinical species.

METHODS

Imigliptin was intravenously and orally administered to rats, dogs, and monkeys to assess their PK/PD properties. DPP-4 activity was the PD biomarker. PK/PD profiles of sitagliptin and alogliptin in rats and humans were obtained and digitized from literatures. PK/PD profiles of all dose levels for each drug in each species were analyzed using modeling approach. Human CL, Vss and PK profiles of imigliptin were then predicted using Allometric Scaling (AS), in vitro in vivo extrapolation (IVIVE), and the steady-state plasma drug concentration - mean residence time (Css-MRT) methods. In vitro EC50 corrected by fu and in vivo EC50 in rats corrected by interspecies difference of sitagliptin and alogliptin were utilized separately to predict imigliptin human EC50. The prediction by integrating all above methods was evaluated by comparing observed and simulated PK/PD profiles in healthy subjects.

RESULTS

Full PK/PD profiles in animal were summarized for imigliptin, sitagliptin and alogliptin. Imigliptin CL, Vss, and Fa were predicted to be 19.1L/h, 247L, and 0.81 in humans, respectively. Predicted imigliptin AUCs, AUECs, and Emax in humans were within 0.8-1.2 times of observed values whereas other predicted PK/PD parameters were within 0.5-1.5 times of observed values.

CONCLUSIONS

By integrating available preclinical and clinical data, FIH PK/PD profiles of imigliptin could be accurately predicted.

Modulation of Hematopoietic Chemokine Effects In Vitro and In Vivo by DPP-4/CD26

Dipeptidyl peptidase 4 (DPP4)/CD26 truncates certain proteins, and this posttranslational modification can influence their activity. Truncated (T) colony-stimulating factors (CSFs) are decreased in potency for stimulating proliferation of hematopoietic progenitor cells (HPCs). T-CXCL12, a modified chemokine, is inactive as an HPC chemotactic, survival, and enhancing factor for replating or ex-vivo expansion of HPCs. Moreover, T-CSFs and T-CXCL12 specifically downmodulates the positively acting effects of their own full-length molecule. Other chemokines have DPP4 truncation sites. In the present study, we evaluated effects of DPP4 inhibition (by Diprotin A) or gene deletion of HPC on chemokine inhibition of multicytokine-stimulated HPC, and on chemokine-enhancing effects on single CSF-stimulated HPC proliferation, as well as effects of DPP4 treatment of a number of chemokines. Myelosuppressive effects of chemokines with, but not without, a DPP4 truncation site were greatly enhanced in inhibitory potency by pretreating target bone marrow (BM) cells with Diprotin A, or by assaying their activity on dpp4/cd26(-/-) BM cells. DPP4 treatment of myelosuppressive chemokines containing a DPP4 truncation site produced a nonmyelosuppressive molecule, but one which had the capacity to block suppression by that unmodified chemokine both in vitro and in vivo. Additionally, DPP4 treatment ablated the single cytokine-stimulated HPC-enhancing activity of CCL3/MIP-1α and CCL4/MIP-1β, and blocked the enhancing activity of each unmodified molecule, in vitro and in vivo. These results highlight the functional posttranslational modulating effects of DPP4 on chemokine activities, and information offering additional biological insight into chemokine regulation of hematopoiesis.

Deciphering the main venom components of the ectoparasitic ant-like bethylid wasp, Scleroderma guani

Similar to venom found in most venomous animals, parasitoid venoms contain a complex cocktail of proteins with potential agrichemical and pharmaceutical use. Even though parasitoids are one of the largest group of venomous animals, little is known about their venom composition. Recent few studies revealed high variated venom composition existing not only in different species but also between closely related strains, impling that increasing information on the venom proteins from more greater diversity of species of different taxa is key to comprehensively uncover the complete picture of parasitoid venom. Here, we explored the major protein components of the venom of ectoparasitic ant-like bethylid wasp, Scleroderma guani by an integrative transcriptomic-proteomic approach. Illumina deep sequencing of venom apparatus cDNA produced 49,873 transcripts. By mapping the peptide spectral data derived from venom reservoir against these transcripts, mass spectrometry analysis revealed ten main venom proteins, including serine proteinase, metalloprotease, dipeptidyl peptidase IV, esterase, antithrombin-III, acid phosphatase, neural/ectodermal development factor IMP-L2 like protein, venom allergen 3, and unknown protein. Interestingly, one serine proteinase was firstly identified with rarely high molecular weight about 200 kDa in parasitoid venom. The occurrence of abundant acid phosphatase, antithrombin-III and venom allergen 3 demonstrated that S. guani venom composition is similar to that of social wasp venoms. All identified venom genes showed abundantly biased expression in venom apparatus, indicating their virulent functions involved in parasitization. This study shed light on the more better understanding of parasitoid venom evolution across species and will facilitate the further elucidation of function and toxicity of these venom proteins.

Empagliflozin/linagliptin single-tablet combination: first-in-class treatment option

BACKGROUND

The availability of a dual sodium glucose co-transporter 2/dipeptidyl peptidase-4 inhibitor combination in a single-tablet combination (STC) represents a new therapeutic option for patients with type 2 diabetes. Empagliflozin/linagliptin STC has been recently approved by the US Food and Drug Administration for the treatment of type 2 diabetes mellitus (T2DM).

AIM

The aim of this study was to describe the latest clinical evidence on the efficacy and safety profiles of empagliflozin/linagliptin STCs in comparison with the individual components. Juxtaposition of the STC with dapagliflozin/saxagliptin combination was also presented.

RESULTS

Empagliflozin/linagliptin STC given as initial therapy or on metformin background lowered mean glycated haemoglobin (HbA1c) by approximately 1.1% (mean baseline HbA1c, 8.0%). Furthermore, the STC reduced mean body weight by 2.0-3.0 kg from baseline. With the STC treatment, no confirmed incidents of hypoglycaemia were reported in drug-naïve patients; in patients taking metformin hypoglycaemia occurred at low rates which were comparable with monotherapy. Use of STCs in the treatment of T2DM can simplify drug dosing regimen, reduce pill burden and increase treatment adherence. Empagliflozin/linagliptin STC is a combination that offers potential additional benefits such as body weight loss and moderate reductions in blood pressure, without increasing risk of hypoglycaemia.

CONCLUSION

Empagliflozin/linagliptin STC appears to be a rational choice for a wide range of patients in need of multiple agents for controlling hyperglycaemia. The STC should be particularly useful in patients in whom hypoglycaemia, weight gain and treatment adherence are of concern.

The opioid effects of gluten exorphins: asymptomatic celiac disease

Gluten-containing cereals are a main food staple present in the daily human diet, including wheat, barley, and rye. Gluten intake is associated with the development of celiac disease (CD) and related disorders such as diabetes mellitus type I, depression, and schizophrenia. However, until now, there is no consent about the possible deleterious effects of gluten intake because of often failing symptoms even in persons with proven CD. Asymptomatic CD (ACD) is present in the majority of affected patients and is characterized by the absence of classical gluten-intolerance signs, such as diarrhea, bloating, and abdominal pain. Nevertheless, these individuals very often develop diseases that can be related with gluten intake. Gluten can be degraded into several morphine-like substances, named gluten exorphins. These compounds have proven opioid effects and could mask the deleterious effects of gluten protein on gastrointestinal lining and function. Here we describe a putative mechanism, explaining how gluten could "mask" its own toxicity by exorphins that are produced through gluten protein digestion.

Monitoring of dipeptidyl peptidase-IV (DPP-IV) activity in patients with mucopolysaccharidoses types I and II on enzyme replacement therapy - Results of a pilot study

OBJECTIVES

Mucopolysaccharidoses (MPSs) are a group of rare, inherited metabolic disorders which result from the lack of one of the lysosomal enzymes responsible for the degradation of glycosaminoglycans. Early recognition of MPS is important as it enables prompt implementation of enzyme replacement therapy (ERT). Dipeptidyl peptidase-IV (DPP-IV) is a ubiquitous ectopeptidase which activity has been associated with the cell surface protein CD26. Our aims were to investigate plasma DPP-IV activity in untreated patients with MPS type II in comparison to control individuals and to evaluate changes of DPP-IV during ERT in MPS I or II patients.

DESIGN AND METHODS

One MPS I and five MPS II patients were treated with ERT for up to 19 months. DPP-IV activity was measured in plasma with a colorimetric method using Gly-Pro-p-nitroanilide as a substrate. The reference intervals were observed in 17 healthy donors and in 9 MPS II individuals before ERT implementation.

RESULTS

DPP-IV activity ranged from 557 to 1959 nmol/ml/h (median and interquartile range: 1453 [955– 1554], n = 17) in plasma of control samples. In 9 untreated MPS II individuals, DPP-IV activity was higher and ranged from 2565 to 5968 nmol/ml/h (median and interquartile range: 4458 [4031–5161]). In 6 MPS patients receiving ERT, DPP-IV activity ranged from 2984 to 8628 nmol/ml/h. No declining tendency was observed during the treatment.

CONCLUSIONS

DPP-IV activity is a good, newa nd valuable biomarker distinguishing between MPS and healthy individuals. However, it is not a useful marker of treatment efficacy and is unsuitable for monitoring.

The role of dipeptidyl peptidase 4 (DPP4) in the preservation of renal function: DPP4 involvement in hemoglobin expression

In a previous study, we demonstrated that dipeptidyl peptidase 4 (DPP4)-deficient rats were susceptible to reduced glomerular filtration rate as a result of streptozotocin (STZ)-induced diabetes. Therefore, we proposed that DPP4 might be responsible for the preservation of renal function. In this study, to verify the role of DPP4 in the preservation of renal function, we performed a microarray analysis of the kidneys of WT and DPP4-deficient rats after STZ treatment, and gene expression analysis using rat kidneys, human embryonic kidney 293 (HEK293) cells, and human renal cancer cells (CakI-1). The microarray analysis indicated that the expression levels of the transporter activity, heme-binding, and pheromone binding-related genes changed significantly. The results of gene expression analysis indicated that there were no significant differences in the expression levels of hemoglobin mRNA between the DPP4-deficient and WT rats; however, the expression levels of hemoglobin mRNA in the kidneys of DPP4-deficient rats tended to decrease when compared with those of both the non-STZ-treated and STZ-treated WT rats. The expression levels of hemoglobin in HEK293 and Caki-1 cells were significantly decreased when DPP4 was knocked down by siRNA, were significantly increased by the addition of soluble human DPP4, and were also significantly increased by the addition of the DPP4 inhibitor, sitagliptin. The expression level of DPP4 was also significantly increased by the addition of sitagliptin in both cell types. Our findings indicate that DPP4 regulates the expression of the hemoglobin genes, and might play a role in the preservation of renal function; however, the underlying mechanism of this preservation remains to be elucidated.

Sensory and motor physiological functions are impaired in gastric inhibitory polypeptide receptor-deficient mice

AIMS/INTRODUCTION

Gastric inhibitory polypeptide (GIP) is an incretin secreted from the gastrointestinal tract after an ingestion of nutrients, and stimulates an insulin secretion from the pancreatic islets. Additionally, GIP has important roles in extrapancreatic tissues: fat accumulation in adipose tissue, neuroprotective effects in the central nervous system and an inhibition of bone resorption. In the current study, we investigated the effects of GIP signaling on the peripheral nervous system (PNS).

MATERIALS AND METHODS

First, the presence of the GIP receptor (GIPR) in mouse dorsal root ganglion (DRG) was evaluated utilizing immunohistochemical analysis, western blotting and reverse transcription polymerase chain reaction. DRG neurons of male wild-type mice (WT) were cultured with or without GIP, and their neurite lengths were quantified. Functions of the PNS were evaluated in GIPR-deficient mice (gipr-/-) and WT by using current perception thresholds (CPTs), Thermal Plantar Test (TPT), and motor (MNCV) and sensory nerve conduction velocity (SNCV, respectively). Sciatic nerve blood flow (SNBF) and plantar skin blood flow (PSBF) were also evaluated.

RESULTS

We confirmed the expression of GIPR in DRG neurons. The neurite outgrowths of DRG neurons were promoted by the GIP administrations. The gipr-/- showed impaired perception functions in the examination of CPTs and TPT. Both MNCV and SNCV were delayed in gipr-/- compared with these in WT. There was no difference in SNBF and PSBF between WT and gipr-/-.

CONCLUSIONS

Our findings show that the GIP signal could exert direct physiological roles in the PNS, which might be directly exerted on the PNS.

Clinical utility of the dipeptidyl peptidase-4 inhibitor linagliptin

INTRODUCTION

Dipeptidyl peptidase-4 (DPP-4) inhibitors have emerged as new options in the management of type 2 diabetes mellitus, demonstrating meaningful antihyperglycemic effects and good tolerability profiles. Glycemic control is improved by preventing the DPP-4-mediated degradation of incretin hormones, with a resulting increase in insulin secretion and inhibition of glucagon secretion.

PURPOSE

This article provides a discussion of the clinical utility of linagliptin.

RESULTS AND CONCLUSION

Linagliptin is a xanthine-based, oral DPP-4 inhibitor that has been approved in the United States and Europe. It has been evaluated extensively in clinical trials, and results in improved glycemic control when used as monotherapy, initial combination therapy with metformin or pioglitazone, add-on therapy to metformin and/or a sulfonylurea, or add-on therapy to basal insulin (with or without oral antidiabetic drugs). Consistent with other members of its class, the benefits of linagliptin also include a low risk of hypoglycemia and weight gain. However, linagliptin is the first DPP-4 inhibitor to be approved as a once-daily, 5-mg dose and, due to its primarily non-renal route of excretion, no dosage adjustment is required for patients with renal or hepatic impairment. The pharmacokinetics and pharmacodynamics of linagliptin are not affected to a clinically meaningful degree by race or ethnicity and linagliptin has very low potential for drug-drug interactions.

The DPP-4 inhibitor linagliptin restores β-cell function and survival in human isolated islets through GLP-1 stabilization

CONTEXT

Inhibition of dipeptidyl peptidase-4 (DPP-4) is a potent strategy to increase glucose-dependent insulinotropic polypeptide and glucagon like peptide 1 (GLP-1) induced insulin secretion in diabetes. It is important to know whether new drugs approved for the treatment of type 2 diabetes have direct effects on the β-cell.

OBJECTIVE

Herein we investigated the effect of linagliptin, a novel DPP-4 inhibitor, on β-cell function and survival.

DESIGN

Human islets were exposed to a diabetic milieu (11.1-33.3 mM glucose, 0.5 mM palmitate, the mixture of 2 ng/mL IL-1β+1000 U/mL interferon-γ, or 50 μM H₂O₂) with or without 500 ng/mL IL-1 receptor antagonist (IL-1Ra) or 30-50 nM linagliptin.

RESULTS

Linagliptin restored β-cell function and turnover, which was impaired when islets were exposed to elevated glucose, palmitate, cytokines, or H₂O₂. Pretreatment with IL-1Ra was similarly effective, except against H₂O₂ treatment. Nitrotyrosine concentrations in islet lysates, an indicator of oxidative stress, were highly elevated under diabetic conditions but not in islets treated with linagliptin or IL-1Ra. Linagliptin also reduced cytokine secretion and stabilized GLP-1 in islet supernatants.

CONCLUSIONS

We show that the novel DPP-4 inhibitor linagliptin protected from gluco-, lipo-, and cytokine-toxicity and stabilized active GLP-1 secreted from human islets. This provides a direct GLP-1 mediated protective effect of linagliptin on β-cell function and survival.

Beneficial effects of exendin-4 on experimental polyneuropathy in diabetic mice

OBJECTIVE

The therapeutic potential of exendin-4, an agonist of the glucagon-like peptide-1 receptor (GLP-1R), on diabetic polyneuropathy (DPN) in streptozotocin (STZ)-induced diabetic mice was investigated.

RESEARCH DESIGN AND METHODS

The presence of the GLP-1R in lumbar dorsal root ganglion (DRG) was evaluated by immunohistochemical analyses. DRG neurons were dissected from C57BL6/J mice and cultured with or without Schwann cell-conditioned media in the presence or absence of GLP-1 (7-37) or exendin-4. Then neurite outgrowth was determined. In animal-model experiments, mice were made diabetic by STZ administration, and after 12 weeks of diabetes, exendin-4 (10 nmol/kg) was intraperitoneally administered once daily for 4 weeks. Peripheral nerve function was determined by the current perception threshold and motor and sensory nerve conduction velocity (MNCV and SNCV, respectively). Sciatic nerve blood flow (SNBF) and intraepidermal nerve fiber densities (IENFDs) also were evaluated.

RESULTS

The expression of the GLP-1R in DRG neurons was confirmed. GLP-1 (7-37) and exendin-4 significantly promoted neurite outgrowth of DRG neurons. Both GLP-1R agonists accelerated the impaired neurite outgrowth of DRG neurons cultured with Schwann cell-conditioned media that mimicked the diabetic condition. At the doses used, exendin-4 had no effect on blood glucose or HbA(1c) levels. Hypoalgesia and delayed MNCV and SNCV in diabetic mice were improved by exendin-4 without affecting the reduced SNBF. The decreased IENFDs in sole skins of diabetic mice were ameliorated by exendin-4.

CONCLUSIONS

Our findings indicate that exendin-4 ameliorates the severity of DPN, which may be achieved by its direct actions on DRG neurons and their axons.

Altered dipeptidyl peptidase-4 activity during the progression of hyperinsulinemic obesity and islet atrophy in spontaneously late-stage type 2 diabetic rats

Altered dipeptidyl peptidase-4 (DPP4) activity during the progression of late-stage type 2 diabetes was measured in Otsuka Long-Evans Tokushima fatty (OLETF) rats. Compared with OLETF rats subjected to 30% food restriction, food-satiated OLETF rats exhibited spontaneous hyperphagic obesity, insulin resistance, hyperglycemia, hyperinsulinemia, and increased plasma DPP4 activity during the early phase of the experiment (up to ∼30 wk). Subsequently, their plasma DPP4 activity as well as their body weight, body fat, and plasma insulin concentration declined to control levels during the late phase, resulting in excessive polyuria, proteinuria, dyslipidemia, pancreatic islet atrophy, hypoinsulinemia, and diabetes, which changed from insulin-resistant diabetes to hypoinsulinemic diabetes secondary to progressive islet insufficiency, and their fasting blood glucose level remained high. Since plasma DPP4 activity demonstrated significant positive correlations with body weight and the fasting plasma insulin level but not with the fasting blood glucose level during the late stage of diabetes, body fat and fasting plasma insulin levels may be useful factors for predicting the control of plasma DPP4 activity. In contrast, pancreatic DPP4 activity was significantly increased, and the expression of pancreatic insulin was significantly reduced in late-stage diabetic OLETF rats, suggesting that a relationship exists between the activation of pancreatic DPP4 and insulin depletion in pancreatic islet atrophy. In conclusion, it is suggested that plasma DPP4 activity changes in accordance with the progression of hyperinsulinemic obesity and pancreatic islet atrophy. DPP4 activity may play an important role in insulin homeostasis.

Mechanism of action of inhibitors of dipeptidyl-peptidase-4 (DPP-4)

Dipeptidyl-peptidase IV (DPP-4) inhibitors inhibit the degradation of the incretins, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP). The first available DPP-4 inhibitors are sitagliptin and vildagliptin. These compounds are orally active and have been shown to be efficacious and well tolerated. Two additional DPP-4 inhibitors are under review, and there are several others in clinical development. This article gives an overview on the mechanism of action of DPP-4 inhibitors and focuses on their development and their important physiological actions with regard to the treatment of type 2 diabetes.

DPP4 inhibitors: from sitagliptin monotherapy to the new alogliptin-pioglitazone combination therapy

Diabetes mellitus (DM) is currently considered to be an epidemic disease. A safe and effective treatment has long been sought by scientists. Incretin mimetics and dipeptidyl peptidase-4 (DPP4) inhibitors represent a new class of agents that have recently been included as antidiabetic drugs. Although only a limited number of studies exist regarding the treatment of DM based on the incretin effect, DPP4 inhibitors have so far proved to be safe and effective, both when administered alone or in combination with other antidiabetic medication. This review focuses on incretin-effect physiology, as well as the DPP4 inhibitors, from sitagliptin to the new alogliptin-pioglitazone combination agent, given as monotherapy and in combination with other antidiabetic agents.

Emerging role of dipeptidyl peptidase-4 inhibitors in the management of type 2 diabetes

BACKGROUND

In type 2 diabetes mellitus (T2DM) there is a progressive loss of beta-cell function. One new approach yielding promising results is the use of the orally active dipeptidyl peptidase-4 (DPP-4) inhibitors. However, every new compound for T2DM has to prove long-term safety especially on cardiovascular outcomes.

OBJECTIVES

Systematic review and meta-analysis of the effects of sitagliptin and vildagliptin therapy on main efficacy parameters and safety. SELECTION CRITERIA, DATA COLLECTION, AND ANALYSIS: Randomized controlled clinical studies of at least 12 weeks' duration in T2DM.

RESULTS

DPP-4 inhibitors versus placebo showed glycosylated hemoglobin A1c (A1c) improvements of 0.7% versus placebo but not compared to monotherapy with other hypoglycemic agents (0.3% in favor of controls). The overall risk profile of DPP-4 inhibitors was low, however a 34% relative risk increase (95% confidence interval 10% to 64%, P = 0.004) was noted for all-cause infection associated with sitagliptin use. No data on immune function, health-related quality of life and diabetic complications could be extracted.

CONCLUSIONS

DPP-4 inhibitors have some theoretical advantages over existing therapies with oral antidiabetic compounds but should currently be restricted to individual patients. Long-term data on cardiovascular outcomes and safety are needed before widespread use of these new agents.

Interrelationship of dipeptidyl peptidase IV (DPP4) with the development of diabetes, dyslipidaemia and nephropathy: a streptozotocin-induced model using wild-type and DPP4-deficient rats

We examined the role of dipeptidyl peptidase IV (DPP4) in the development of diabetes, dyslipidaemia and renal dysfunction induced by streptozotocin (STZ). F344/DuCrlCrlj rats, which lack DPP4 activity, and wild-type rats were treated with STZ. Plasma DPP4 activity and biochemical parameters were measured until 42 days after STZ treatment. At the end of the experiment, renal function and DPP4 expressions of the kidney, liver, pancreas and adipose tissues were determined. Increases in blood glucose, cholesterol and triglycerides were evoked by STZ in both rat strains; however, the onset of hyperglycaemia was delayed in DPP4-deficient rats as compared with wild-type rats. By contrast, more severe dyslipidaemia was observed in DPP4-deficient rats than in wild-type rats after STZ treatment. Plasma DPP4 activity increased progressively with time after STZ treatment in wild-type rats. The kidney of wild-type rats showed decreased DPP4 activity with increased Dpp4 mRNA after STZ treatment. In addition, kidney weight, serum creatinine and excreted amounts of urinary protein, glucose and DPP4 enzyme were enhanced by STZ. DPP4-deficient rats showed increased serum creatinine in accordance with decreased creatinine clearance as compared with wild-type rats after STZ treatment. In conclusion, plasma DPP4 activity increased after STZ treatment, positively correlating to blood glucose. DPP4-deficient rats were resistant to developing diabetes, while susceptible to dyslipidaemia and reduction of glomerular filtration rate by STZ. DPP4 activation may be responsible for hyperglycaemia, lipid metabolism and preservation of renal function.

The effect of dipeptidyl peptidase-4 inhibition on gastric volume, satiation and enteroendocrine secretion in type 2 diabetes: a double-blind, placebo-controlled crossover study

OBJECTIVES

The incretin hormone glucagon-like peptide-1 (GLP-1) retards gastric emptying and decreases caloric intake. It is unclear whether increased GLP-1 concentrations achieved by inhibition of the inactivating enzyme dipeptidyl peptidase-4 (DPP-4) alter gastric volumes and satiation in people with type 2 diabetes.

METHODS

In a double-blind, placebo-controlled crossover design, 14 subjects with type 2 diabetes received vildagliptin (50 mg bid) or placebo for 10 days in random order separated by a 2-week washout. On day 7, fasting and postmeal gastric volumes were measured by a (99m)Tc single-photon emission computed tomography (SPECT) method. On day 8, a liquid Ensure meal was consumed at 30 ml/min, and maximum tolerated volume (MTV) and symptoms 30 min later were measured using a visual analogue scale (VAS) to assess effects on satiation. On day 10, subjects ingested water until maximum satiation was achieved. The volume ingested was recorded and symptoms similarly measured using a VAS.

RESULTS

Vildagliptin raised plasma GLP-1 concentrations. However, fasting (248 +/- 21 vs. 247 +/- 19 ml, P = 0.98) and fed (746 +/- 28 vs. 772 +/- 26 ml, P = 0.54) gastric volumes did not differ when subjects received vildagliptin or placebo. Treatment with vildagliptin did not alter the MTV of Ensure (1657 +/- 308 vs. 1389 +/- 197 ml, P = 0.15) or water compared to placebo (1371 +/- 141 vs. 1172 +/- 156 ml, P = 0.23). Vildagliptin was associated with decreased peptide YY (PYY) concentrations 60 min after initiation of the meal (166 +/- 27 vs. 229 +/- 34 pmol/l, P = 0.01).

CONCLUSIONS

Vildagliptin does not alter satiation or gastric volume in people with type 2 diabetes despite elevated GLP-1 concentrations. Compensatory changes in enteroendocrine secretion could account for the lack of gastrointestinal symptoms.

Incretin-based therapies in type 2 diabetes mellitus

CONTEXT

Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide are incretins secreted from enteroendocrine cells postprandially in part to regulate glucose homeostasis. Dysregulation of these hormones is evident in type 2 diabetes mellitus (T2DM). Two new drugs, exenatide (GLP-1 mimetic) and sitagliptin [dipeptidyl peptidase (DPP) 4 inhibitor], have been approved by regulatory agencies for treating T2DM. Liraglutide (GLP-1 mimetic) and vildagliptin (DPP 4 inhibitor) are expected to arrive on the market soon.

EVIDENCE ACQUISITION

The background of incretin-based therapy and selected clinical trials of these four drugs are reviewed. A MEDLINE search was conducted for published articles using the key words incretin, glucose-dependent insulinotropic polypeptide, GLP-1, exendin-4, exenatide, DPP 4, liraglutide, sitagliptin, and vildagliptin.

EVIDENCE SYNTHESIS

Exenatide and liraglutide are injection based. Three-year follow-up data on exenatide showed a sustained weight loss and glycosylated hemoglobin (HbA(1c)) reduction of 1%. Nausea and vomiting are common. Results from phase 3 studies are pending on liraglutide. Sitagliptin and vildagliptin are orally active. In 24-wk studies, sitagliptin reduces HbA(1c) by 0.6-0.8% as monotherapy, 1.8% as initial combination therapy with metformin, and 0.7% as add-on therapy to metformin. Vildagliptin monotherapy lowered HbA(1c) by 1.0-1.4% after 24 wk. Their major side effects are urinary tract and nasopharyngeal infections and headaches. Exenatide and liraglutide cause weight loss, whereas sitagliptin and vildagliptin do not.

CONCLUSIONS

The availability of GLP-1 mimetics and DPP 4 inhibitors has increased our armamentarium for treating T2DM. Unresolved issues such as the effects of GLP-1 mimetics and DPP 4 inhibitors on beta-cell mass, the mechanism by which GLP-1 mimetics lowers glucagon levels, and exactly how DPP 4 inhibitors lead to a decline in plasma glucose levels without an increase in insulin secretion, need further research.

Membrane-bound peptidases regulate human extravillous trophoblast invasion

During human placentation, the extravillous trophoblast (EVT) invades maternal decidua and spiral arteries. However, the precise regulatory mechanisms by which EVT invasion is induced toward maternal arteries or limited within the uterus have not been well characterized. Recently, we found that dipeptidyl peptidase IV, a membrane-bound cell surface peptidase that can degrade chemokines, including RANTES, was expressed on EVT that had already ceased invasion. Another cell surface peptidase, carboxypeptidase-M, was also detected on EVT including the endovascular trophoblast in the maternal arteries. The inhibition of these peptidases increased cell invasion of choriocarcinoma-derived JEG-3 cells. On the other hand, CCR-1, a chemokine receptor for RANTES, was specifically expressed on EVT that migrated toward maternal arteries, while RANTES enhanced invasion of EVT that were isolated from primary villous explant culture. Platelets, which secrete RANTES and other chemokines, were detected among the endovascular trophoblast, and platelets were shown to enhance invasion of cultured EVT. Furthermore, a novel membrane-bound cell surface peptidase, laeverin, was found to be specifically expressed on EVT at deep sites in the maternal decidua. These findings suggest that membrane-bound peptidases regulate EVT invasion in cooperation with a chemokine system during early human placentation.

The incretin system: glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors in type 2 diabetes

Glucagon-like peptide 1 (GLP-1) is a gut-derived incretin hormone that stimulates insulin and suppresses glucagon secretion, inhibits gastric emptying, and reduces appetite and food intake. Therapeutic approaches for enhancing incretin action include degradation-resistant GLP-1 receptor agonists (incretin mimetics), and inhibitors of dipeptidyl peptidase-4 (DPP-4) activity (incretin enhancers). Clinical trials with the incretin mimetic exenatide (two injections per day or long-acting release form once weekly) and liraglutide (one injection per day) show reductions in fasting and postprandial glucose concentrations, and haemoglobin A1c (HbA1c) (1-2%), associated with weight loss (2-5 kg). The most common adverse event associated with GLP-1 receptor agonists is mild nausea, which lessens over time. Orally administered DPP-4 inhibitors, such as sitagliptin and vildagliptin, reduce HbA1c by 0.5-1.0%, with few adverse events and no weight gain. These new classes of antidiabetic agents, and incretin mimetics and enhancers, also expand beta-cell mass in preclinical studies. However, long-term clinical studies are needed to determine the benefits of targeting the incretin axis for the treatment of type 2 diabetes.

Fibroblast activation protein: a serine protease expressed at the remodeling interface in idiopathic pulmonary fibrosis

Fibroblast activation protein (FAPalpha) is a member of the cell surface dipeptidyl peptidase (DPP) family of serine proteases. In its dimer form, FAPalpha exhibits gelatinase, collagenase, and DPP activity in vitro. Reactive fibroblasts in healing wounds and stromal fibroblasts associated with epithelial tumors express FAPalpha. Idiopathic pulmonary fibrosis (IPF) is a disease of the lung characterized by progressive fibrosis with no clear etiology or molecular marker for disease activity. Recently, it has been shown that fibroblast FAPalpha expression is induced in liver cirrhosis, with an expression pattern distinct from alpha-smooth muscle actin (alpha-SMA). In this study, we determine whether FAPalpha expression is selectively induced in areas of ongoing tissue remodeling characterized by fibroblast foci in IPF. Human lung tissue was obtained from patients with IPF, centrilobular emphysema, and normal lung. Immunohistochemical studies were performed using anti-FAPalpha antibody and antibodies against alpha-SMA and CD26 (DPPIV), another member of the DPP family. We found that FAPalpha was not expressed in normal human lung tissue or tissue with evidence of centriacinar emphysema, but was induced in all patients with IPF and With a pattern distinct from that of CD26 found primarily on hyperplastic alveolar epithelium. Specifically, FAPalpha was detected in fibroblast foci and in fibrotic interstitium and not in the interstitium of adjacent architecturally normal lung. Alveolar/airway epithelium and vascular smooth muscle did not express FAPalpha. This is the first report of FAPalpha expression in IPF and our results suggest that FAPalpha is selectively induced in fibrotic foci, but not in normal or emphysematous lung. Future studies will address whether FAPalpha may be used as a marker for disease activity in IPF.

New regulatory mechanisms for human extravillous trophoblast invasion

Human extravillous trophoblasts (EVT) invade maternal deciduas and reconstructed maternal spiral arteries during early placentation. However, the precise regulatory mechanisms to induce EVT invasion toward arteries and/or to protect EVT from further invasion have not been well understood. Recently, it was found that EVT that had already ceased their invasion, specifically expressed cluster of differentiation (CD9) and dipeptidyl peptidase IV (DPPIV) on their cell surface. In addition, EVT migrating to maternal spiral arteries expressed CC chemokine receptor type-1 (CCR-1), which is a chemokine receptor for regulated on activation normal T cell expressed and secreted (RANTES) and so on. CD9 is associated with integrin molecules on the cell surface and is considered to modulate integrin function. In contrast, DPPIV is a cell surface peptidase that can metabolize RANTES at extracellular sites before its accessing to the chemokine receptors. In vitro functional assay showed that CD9, DPPIV and RANTES are involved in the regulation for EVT invasion. From these findings, it can be proposed that CD9 and DPPIV, including chemokines, are new regulatory factors for human extravillous trophoblasts. (Reprod Med Biol 2005; 4: 189-195).

Reduced serum dipeptidyl peptidase-IV after metformin and pioglitazone treatments

Dipeptidyl peptidase-IV (DPP-IV) regulates metabolism by degrading incretins involved in nutritional regulation. Metformin and pioglitazone improve insulin sensitivity whereas glyburide promotes insulin secretion. Zucker diabetic rats were treated with these antidiabetic agents for 2 weeks and DPP-IV activity and expression were determined. Serum DPP-IV activity increased whereas tissue activity decreased as the rats aged. Treatment of rats with metformin, pioglitazone, and glyburide did not alter DPP-IV mRNA expression in liver or kidney. Metformin and pioglitazone significantly (P<0.05) reduced serum DPP-IV activity and glycosylated hemoglobin. Glyburide did not lower DPP-IV activity or glycosylated hemoglobin. Regression analysis showed serum DPP-IV activity correlated with glycosylated hemoglobin (r=0.92) and glucagon-like peptide-1 levels (r=-0.49). Metformin, pioglitazone, and glyburide had no effect on serum DPP-IV activity in vitro, indicating these are not competitive DPP-IV inhibitors. We propose the in vivo inhibitory effects observed with metformin and pioglitazone on serum DPP-IV activity results from reduced DPP-IV secretion.

Synthesis and structure–activity relationships of potent 3- or 4-substituted-2-cyanopyrrolidine dipeptidyl peptidase IV inhibitors

Dipeptidyl peptidase IV (DPP-IV) inhibitors have attracted attention as potential drugs for use in the treatment of type 2 diabetes because they prevent degradation of glucagon-like peptide-1 (GLP-1) and extend its duration of action. A series of 2-cyanopyrrolidines are among the most potent of DPP-IV inhibitors. We focused our attention on substitutions at the 3- or 4-position of 2-cyanopyrrolidines and synthesized and evaluated various derivatives. Among them, the 4-fluoro derivative was found to exhibit better DPP-IV inhibitory activity and higher plasma drug concentrations after oral administration to rats than the 4-unsubstituted derivative. We report here on the synthesis and biological data of the aforementioned derivatives.

One site mutation disrupts dimer formation in human DPP-IV proteins

DPP-IV is a prolyl dipeptidase, cleaving the peptide bond after the penultimate proline residue. It is an important drug target for the treatment of type II diabetes. DPP-IV is active as a dimer, and monomeric DPP-IV has been speculated to be inactive. In this study, we have identified the C-terminal loop of DPP-IV, highly conserved among prolyl dipeptidases, as essential for dimer formation and optimal catalysis. The conserved residue His750 on the loop contributes significantly for dimer stability. We have determined the quaternary structures of the wild type, H750A, and H750E mutant enzymes by several independent methods including chemical cross-linking, gel electrophoresis, size exclusion chromatography, and analytical ultracentrifugation. Wild-type DPP-IV exists as dimers both in the intact cell and in vitro after purification from human semen or insect cells. The H750A mutation results in a mixture of DPP-IV dimer and monomer. H750A dimer has the same kinetic constants as those of the wild type, whereas the H750A monomer has a 60-fold decrease in kcat. Replacement of His750 with a negatively charged Glu (H750E) results in nearly exclusive monomers with a 300-fold decrease in catalytic activity. Interestingly, there is no dynamic equilibrium between the dimer and the monomer for all forms of DPP-IVs studied here. This is the first study of the function of the C-terminal loop as well as monomeric mutant DPP-IVs with respect to their enzymatic activities. The study has important implications for the discovery of drugs targeted to the dimer interface.

Dipeptidyl peptidase IV activity and/or structure homologues (DASH) and their substrates in cancer

Post-translational modification of proteins is an important regulatory event. Numerous biologically active peptides that play an essential role in cancerogenesis contain an evolutionary conserved proline residue as a proteolytic-processing regulatory element. Proline-specific proteases could therefore be viewed as important "check-points". Limited proteolysis of such peptides may lead to quantitative but, importantly, due to the change of receptor preference, also qualitative changes of their signaling potential. Dipeptidyl peptidase-IV (DPP-IV, EC 3.4.14.5, identical with CD26) was for many years believed to be a unique cell membrane protease cleaving X-Pro dipeptides from the N-terminal end of peptides and proteins. Subsequently, a number of other molecules were discovered, exhibiting various degree of structural homology and DPP-IV-like enzyme activity, capable of cleaving similar set of substrates. These comprise for example, seprase, fibroblast activation protein alpha, DPP6, DPP8, DPP9, attractin, N-acetylated-alpha-linked-acidic dipeptidases I, II and L, quiescent cell proline dipeptidase, thymus-specific serine protease and DPP IV-beta. It is tempting to speculate their potential participation on DPP-IV biological function(s). Disrupted expression and enzymatic activity of "DPP-IV activity and/or structure homologues" (DASH) might corrupt the message carried by their substrates, promoting abnormal cell behavior. Consequently, modulation of particular enzyme activity using e.g. DASH inhibitors, specific antibodies or DASH expression modification may be an attractive therapeutic concept in cancer treatment. This review summarizes recent information on the interactions between DASH members and their substrates with respect to their possible role in cancer biology.

3D structure of the CD26-ADA complex obtained by cryo-EM and single particle analysis

The specific binding of adenosine deaminase to the multifunctional membrane glycoprotein dipeptidyl peptidase IV is thought to be immunologically relevant for certain regulatory and co-stimulatory processes. In this study we present the 3D structure of the complete CD26-ADA complex obtained by single particle cryo-EM at 22A resolution. ADA binding occurs at the outer edges of the beta-propeller of CD26. Docking calculations of available CD26 and ADA crystal data into the obtained EM density map revealed that the ADA-binding site is stretched across CD26 beta-propeller blades 4 and 5 involving the outermost distal hydrophobic amino acids L294 and V341 but not T440 and K441 as suggested by antibody binding. Though the docking of the ADA orientation appears less significant due to the lack of distinct surface features, non-ambiguous conclusions can be drawn in the combination with earlier indirect non-imaging methods affirming the crucial role of the ADA alpha2-helix for binding.

Extreme reduction of dipeptidyl peptidase IV activity in F344 rat substrains is associated with various behavioral differences

The enzyme and binding protein dipeptidyl peptidase IV (DPPIV/CD26) has a unique enzymatic specificity in cleaving dipeptides from neuropeptides, chemokines, and hormones. Thus, DPPIV is potentially involved in the regulation of functions of the immune, endocrine, and nervous systems. In the present study, we compared DPPIV-deficient, mutant Japanese [F344/DuCrj(DPPIV-)] and German [F344/Crl(Ger/DPPIV-)] F344 rat substrains with a wild-type-like F344 substrain [F344/Crl(Por)] from the United States in a multitiered strategy using a number of different behavioral tests. General health, neurological and motor functions, and sensory abilities of the different F344 substrains were not different. A reduced body weight and a reduced water consumption were observed in mutant animals. DPPIV-deficient rats exhibited increased pain sensitivity in a non-habituated hot plate test, indicative of a reduced stress-induced analgesia. In line with this finding, reduced stress-like responses in tasks like the open field (OF), social interaction (SI), and passive avoidance test were found. Differences in DPPIV-like activity appear to be involved in neurophysiological processes because DPPIV-deficient animals were less susceptible to the sedative effects of ethanol. The varying phenotypes of the F344 substrains are likely to be mediated by differential degradation of DPPIV substrates such as substance P, glucagon-like peptide (GLP)-1, enterostatin, and especially neuropeptide Y (NPY). Potentially, DPPIV-deficient substrains represent an important tool for biomedical research, focusing on the involvement of DPPIV and its substrates in behavioral and physiological processes.

Localization, transmission, spontaneous mutations, and variation of function of the Dpp4 (Dipeptidyl-peptidase IV; CD26) gene in rats

Dipeptidyl-peptidase IV (DPPIV) is involved in endocrine and immune functions via cleavage of regulatory peptides with a N-terminal proline or alanine such as incretins, neuropeptide Y, or several chemokines. So far no systematic investigations on the localization and transmission of the Dpp4 gene or the natural variations of DPPIV-like enzymatic function in different rat strains have been conducted. Here we mapped the Dpp4 gene to rat chromosome 3 and describe a semi-dominant mode of inheritance for Dpp4 in a mutant F344/DuCrj(DPPIV-) rat substrain lacking endogenous DPPIV-like activity. This mutant F344/DuCrj(DPPIV-) rat substrain constantly exhibits a nearly complete lack of DPPIV-like enzymatic activity, while segregation of DPPIV-like enzymatic activity was observed in another DPPIV-negative F344/Crl(Ger/DPPIV-) rat substrain. Screening of 12 different inbred laboratory rat strains revealed dramatic differences in DPPIV-like activity ranging from 11 mU/microl (LEW/Ztm rats) to 40 mU/microl (BN/Ztm and DA/Ztm rats). A lack of DPPIV-like activity in F344 rats was associated with an improved glucose tolerance and blunted natural killer cell function, which indicates the pleiotropic functional role of DPPIV in vivo. Overall, the variations in DPPIV-like enzymatic activity probably represent important confounding factors in studies using rat models for research on regulatory peptides.