Anti-arthritic effects of the novel dipeptidyl peptidase IV inhibitors TMC-2A and TSL-225

New insights into the role of dipeptidyl peptidase 8 and dipeptidyl peptidase 9 and their inhibitors

Dipeptidyl peptidase 8 (DPP8) and 9 (DPP9) are widely expressed in mammals including humans, mainly locate in the cytoplasm. The DPP8 and DPP9 (DPP8/9) belong to serine proteolytic enzymes, they can recognize and cleave N-terminal dipeptides of specific substrates if proline is at the penultimate position. Because the localization of DPP8/9 is different from that of DPP4 and the substrates for DPP8/9 are not yet completely clear, their physiological and pathological roles are still being further explored. In this article, we will review the recent research advances focusing on the expression, regulation, and functions of DPP8/9 in physiology and pathology status. Emerging research results have shown that DPP8/9 is involved in various biological processes such as cell behavior, energy metabolism, and immune regulation, which plays an essential role in maintaining normal development and physiological functions of the body. DPP8/9 is also involved in pathological processes such as tumorigenesis, inflammation, and organ fibrosis. In recent years, related research on immune cell pyroptosis has made DPP8/9 a new potential target for the treatment of hematological diseases. In addition, DPP8/9 inhibitors also have great potential in the treatment of tumors and chronic kidney disease.

Anti-arthritic effect of chicken embryo tissue hydrolyzate against adjuvant arthritis in rats (X-ray microtomographic and histopathological analysis)

Finding new, safe strategies to prevent and control rheumatoid arthritis is an urgent task. Bioactive peptides and peptide-rich protein hydrolyzate represent a new trend in the development of functional foods and nutraceuticals. The resulting tissue hydrolyzate of the chicken embryo (CETH) has been evaluated for acute toxicity and tested against chronic arthritis induced by Freund's full adjuvant (modified Mycobacterium butyricum) in rats. The antiarthritic effect of CETH was studied on the 28th day of the experiment after 2 weeks of oral administration of CETH at doses of 60 and 120 mg/kg body weight. Arthritis was evaluated on the last day of the experiment on the injected animal paw using X-ray computerized microtomography and histopathology analysis methods. The CETH effect was compared with the non-steroidal anti-inflammatory drug diclofenac sodium (5 mg/kg). Oral administration of CETH was accompanied by effective dose-dependent correction of morphological changes caused by the adjuvant injection. CETH had relatively high recovery effects in terms of parameters for reducing inflammation, inhibition of osteolysis, reduction in the inflammatory reaction of periarticular tissues, and cartilage degeneration. This study presents for the first time that CETH may be a powerful potential nutraceutical agent or bioactive component in the treatment of rheumatoid arthritis.

Insulin Signaling in Arthritis

Inflammatory arthritis is burdened by an increased risk of metabolic disorders. Cytokines and other mediators in inflammatory diseases lead to insulin resistance, diabetes and hyperlipidemia. Accumulating evidence in the field of immunometabolism suggests that the cause-effect relationship between arthritis and metabolic abnormalities might be bidirectional. Indeed, the immune response can be modulated by various factors such as environmental agents, bacterial products and hormones. Insulin is produced by pancreatic cells and regulates glucose, fat metabolism and cell growth. The action of insulin is mediated through the insulin receptor (IR), localized on the cellular membrane of hepatocytes, myocytes and adipocytes but also on the surface of T cells, macrophages, and dendritic cells. In murine models, the absence of IR in T-cells coincided with reduced cytokine production, proliferation, and migration. In macrophages, defective insulin signaling resulted in enhanced glycolysis affecting the responses to pathogens. In this review, we focalize on the bidirectional cause-effect relationship between impaired insulin signaling and arthritis analyzing how insulin signaling may be involved in the aberrant immune response implicated in arthritis and how inflammatory mediators affect insulin signaling. Finally, the effect of glucose-lowering agents on arthritis was summarized.

Is there an association between dipeptidyl peptidase-4 inhibitors and autoimmune disease? A population-based study

The association of dipeptidyl peptidase-4 inhibitors (DPP4is) with autoimmune diseases is controversial. While these agents were proposed as a novel therapeutic approach for several inflammatory diseases by blocking T cell proliferation and cytokine production, they were found to trigger inflammatroy bowel disease, inflammatory arthritis and bullous pemphigoid. Our objective is to examine the association between DPP4i and autoimmune diseases. This study was conducted as a cross-sectional study utilizing the database of Clalit Health Services. The prevalence of 15 autoimmune-/immune-mediated diseases was compared between patients on DPP4i treatment and age-, sex-, and ethnicity-matched controls. Univariate analysis was performed using chi-square and the Student t test and multivariate analysis was performed using a logistic regression model. The study included 283 patients treated with DPP4i agents and 5660 age-, sex-, and ethnicity-matched diabetic control subjects. The prevalence of Crohn's disease (1.1 vs. 0.3%; odds ratios (OR), 3.56; 95% CI, 1.04-12.21, P = 0.031), psoriasis (2.5 vs. 1.2%; OR, 2.12; 95% CI, 0.99-4.66; P = 0.050), and Hashimoto's thyroiditis (16.6 vs. 12.6%; OR, 1.38; 95% CI, 1.00-1.91; P = 0.049) was significantly higher in patients on DPP4i treatment than in controls. The prevalence of the remaining autoimmune diseases did not differ significantly between DPP4i-treated patients and their matched control subjects. In conclusion, this population-based study demonstrates an association of DPP4i intake with three autoimmune and inflammatory diseases noted to be part of a distinct autoimmune cluster that includes multiple sclerosis, psoriasis, thyroiditis, bullous pemphigoid, and inflammatory bowel disease. Experimental studies are required to define the role of DPP4i in this autoimmune cluster.

Dipeptidyl peptidase-4 inhibitors in type 2 diabetes may reduce the risk of autoimmune diseases: a population-based cohort study

OBJECTIVE

Dipeptidyl peptidase-4 (DPP4), also known as CD26, is a transmembrane glycoprotein that has a costimulatory function in the immune response. DPP4 inhibitors (DPP4i) are oral glucose-lowering drugs for type 2 diabetes mellitus (T2DM). This study evaluated the risk of incident rheumatoid arthritis (RA) and other autoimmune diseases (AD) such as systemic lupus erythematosus, psoriasis, multiple sclerosis and inflammatory bowel disease, associated with DPP4i in patients with T2DM.

METHODS

Using US insurance claims data (2005-2012), we conducted a population-based cohort study that included initiators of combination therapy with DPP4i (DPP4i plus metformin) and non-DPP4i (non-DPP4i plus metformin). RA and other AD were identified with ≥2 diagnoses and ≥1 dispensing for AD-specific immunomodulating drugs or steroids. Composite AD includes RA or other AD. Propensity score (PS)-stratified Cox proportional hazards models compared the risk of AD in DPP4i initiators versus non-DPP4i, controlling for potential confounders.

RESULTS

After asymmetric trimming on the PS, 73 928 patients with T2DM starting DPP4i combination therapy and 163 062 starting non-DPP4i combination therapy were selected. Risks of incident RA and composite AD were lower in the DPP4i group versus non-DPP4i with the PS-stratified HR of 0.66 (95% CI 0.44 to 0.99) for RA, 0.73 (0.51 to 1.03) for other AD and 0.68 (95% CI 0.52 to 0.89) for composite AD.

CONCLUSIONS

In this large cohort of diabetic patients, those initiating DPP4i combination therapy appear to have a decreased risk of incident AD including RA compared with those initiating non-DPP4i combination therapy. These results may suggest possible pharmacological pathways for prevention or treatment of AD.

The Dipeptidyl Peptidase Family, Prolyl Oligopeptidase, and Prolyl Carboxypeptidase in the Immune System and Inflammatory Disease, Including Atherosclerosis

Research from over the past 20 years has implicated dipeptidyl peptidase (DPP) IV and its family members in many processes and different pathologies of the immune system. Most research has been focused on either DPPIV or just a few of its family members. It is, however, essential to consider the entire DPP family when discussing any one of its members. There is a substantial overlap between family members in their substrate specificity, inhibitors, and functions. In this review, we provide a comprehensive discussion on the role of prolyl-specific peptidases DPPIV, FAP, DPP8, DPP9, dipeptidyl peptidase II, prolyl carboxypeptidase, and prolyl oligopeptidase in the immune system and its diseases. We highlight possible therapeutic targets for the prevention and treatment of atherosclerosis, a condition that lies at the frontier between inflammation and cardiovascular disease.

Low DPP4 expression and activity in multiple sclerosis

Multiple sclerosis (MS) is a prototypic Th1/Th17 chronic autoimmune disease of the central nervous system. Dipeptidyl peptidase 4 (DPP4 or CD26) is a multifunctional molecule involved in autoimmune diseases' pathophysiology. We sought to integrate disparate pieces of data and analyze the plasma levels of sDPP4, DPP activity and DPP4 surface expression on T-cells in 129 MS patients with different clinical forms and 53 healthy controls, across two independent cohorts. Herein, we provide new evidence that sDPP4 concentration and DPP activity are significantly lower in MS patients than controls (p < 0.0001 and p < 0.01, respectively). In contrast, the frequency of circulating CD8(+)DPP4(hi) T-cells (p = 0.02) was increased in MS patients. This is the first study that simultaneously analyzes DPP4 expression and function in a large cohort of MS patients. Our data indicate a putative role for DPP4 in MS pathophysiology and suggest that a deeper understanding of surface versus shed DPP4 biology is warranted.

A new diketopiperazine alkaloid from Aspergillus oryzae

Investigation of bioactive secondary metabolites from terrestrial Aspergillus oryzae sp. MMAO1 using M2 medium afforded a new diketopiperazine alkaloid, 7,9-dihydroxy-3-(1H-indol-3-ylmethyl)-8-methoxy-2,3,11,11a-tetrahydro-6H-pyrazino[1,2-b]isoquinoline-1,4-dione (1a), containing the unusual amino acid L-6,8-dihydroxy-7-methoxyphenylalanine. This was co-isolated with ditryptophenaline (2), cyclo-(Tryp,Tyr) (4), cyclo-(Pro,Val), α-cyclopiazonic acid (3), kojic acid and uridine. Re-cultivation of the fungal strain on Dox medium led to the production of bisdethio(bismethylthio)gliotoxin (5), pseurotin A (6) along with linoleic acid, α-cyclopiazonic acid (3) and kojic acid. The chemical structure of the new diketopiperazine alkaloid including the relative configuration was determined by 1D and 2D NMR spectroscopy and HR-ESI-MS spectrometry, and by comparison with the related literature. The new alkaloid (1a) showed no antimicrobial activity or cytotoxicity against brine shrimps.

Identification of a gene involved in the synthesis of a dipeptidyl peptidase IV inhibitor in Aspergillus oryzae

WYK-1 is a dipeptidyl peptidase IV inhibitor produced by Aspergillus oryzae strain AO-1. Because WYK-1 is an isoquinoline derivative consisting of three l-amino acids, we hypothesized that a nonribosomal peptide synthetase was involved in its biosynthesis. We identified 28 nonribosomal peptide synthetase genes in the sequenced genome of A. oryzae RIB40. These genes were also identified in AO-1. Among them, AO090001000009 (wykN) was specifically expressed under WYK-1-producing conditions in AO-1. Therefore, we constructed wykN gene disruptants of AO-1 after nonhomologous recombination was suppressed by RNA interference to promote homologous recombination. Our results demonstrated that the disruptants did not produce WYK-1. Furthermore, the expression patterns of 10 genes downstream of wykN were similar to the expression pattern of wykN under several conditions. Additionally, homology searches revealed that some of these genes were predicted to be involved in WYK-1 biosynthesis. Therefore, we propose that wykN and the 10 genes identified in this study constitute the WYK-1 biosynthetic gene cluster.

NPY suppressed development of experimental autoimmune encephalomyelitis in Dark Agouti rats by disrupting costimulatory molecule interactions

Neuropeptide Y (NPY) suppressed clinical experimental autoimmune encephalomyelitis (EAE) and reduced numbers of CD28+, CD11b+ and CD80+ cells among spinal cord infiltrating cells at the peak of disease in Dark Agouti rat strain. Suppression of EAE was accompanied by the reduced expression of costimulatory CD80 and CD86 molecules on ED1+ macrophages and OX62+ dendritic cells in draining lymph nodes during the inductive phase of EAE. An inhibitor of dipeptidyl peptidase 4, an enzyme which terminates the action of NPY on Y1 receptor subtype, did not sustain the suppressive effect of NPY on the EAE development, suggesting involvement of Y2 and Y5 receptors.

Dipeptidyl peptidase in autoimmune pathophysiology

CD26 is a 110-kDa surface glycoprotein with intrinsic dipeptidyl peptidase IV (DPPIV) activity that is expressed on various cell types and has many biological functions. An important aspect of CD26 biology is its peptidase activity and its functional and physical association with molecules with key roles in human immunological programs. CD26 role in immune regulation has been extensively characterized, with recent findings elucidating its link age with signaling pathways and structures involved in T cell activation a well as antigen-presenting cell-T cell interaction, being a marker of diseas behavior clinically as well as playing an important role in autoimmune pathogenesis and development. Through the use of various experimental approaches and agents to influence CD26/DPPIV expression and activity, such as anti-CD26 antibodies, CD26/DPPIV chemical inhibitors, siRNAs to inhibit CD26 expression, overexpressing CD26 transfectants, soluble CD26 molecules and proteomic approach, we have shown that CD26 interacts with structures with essential cellular functions in T cell responses. We will review emerging data that suggest CD26 may be an appropriate therapeutic target for the treatment of selected immune disorders.

PETIR-001, a dual inhibitor of dipeptidyl peptidase IV (DP IV) and aminopeptidase N (APN), ameliorates experimental autoimmune encephalomyelitis in SJL/J mice

Cellular dipeptidyl peptidase IV (DP IV, CD26) and amino-peptidase N (APN, CD13) play regulatory roles in T cell activation and represent potential targets for treatment of inflammatory disorders. We have developed a novel therapeutic strategy, 'peptidase-targeted Immunoregulation' (PETIR™), which simultaneously targets both cellular DP IV and APN via selective binding sites different from the active sites with a single inhibitor. To prove the therapeutic concept of PETIR™ in autoimmunity of the central nervous system (CNS), we evaluated the effect of a single substance, PETIR-001, in an animal model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE) in SJL/J mice. Administration of PETIR-001 significantly delayed and decreased clinical signs of active EAE, when given in a therapeutic manner intraperitoneally from day 15 to day 24 after induction of EAE. Both the acute phase and the first relapse of EAE were markedly inhibited. Importantly, a similar therapeutic benefit was obtained after oral administration of PETIR-001 from day 12 to day 21 after disease induction. Our results demonstrate that PETIR-001 exhibits a therapeutic effect on EAE in SJL/J mice. Thus, PETIR™ represents a novel and efficient therapeutic approach for immunotherapy of CNS inflammation.

Role of dipeptidyl peptidase IV (DP IV)-like enzymes in T lymphocyte activation: investigations in DP IV/CD26-knockout mice

BACKGROUND

Dipeptidyl peptidase IV (DP IV, CD26) and DP IV-like enzymes, such as dipeptidyl peptidase II (DP II), dipeptidyl peptidase 8 (DP8), and dipeptidyl peptidase 9 (DP9), have been recognized to regulate T lymphocyte activation. Lys[Z(NO2)]-thiazolidide (LZNT) and Lys[Z(NO2)]-pyrrolidide (LZNP), non-selective inhibitors of DP IV-like activity known to target DP IV as well as DP II, DP8, and DP9, suppress T lymphocyte proliferation in vitro. Moreover, these inhibitors are capable of attenuating the severity of autoimmune diseases, such as experimental autoimmune encephalomyelitis, the animal model of multiple sclerosis, and experimental arthritis, a model of human rheumatoid arthritis, in vivo, particularly in combination with inhibitors of aminopeptidase N (APN, CD13) enzymatic activity.

METHODS

Here, we studied the influence of non-selective and selective inhibitors of DP IV-like enzymes on DNA synthesis in mitogen-stimulated splenocytes from wild-type C57BL/6 mice and DP IV/CD26-knockout (DP IV/CD26-KO) mice.

RESULTS

LZNT and LZNP, the non-selective inhibitors of DP IV-like activity, suppressed the DNA synthesis in stimulated splenocytes from wild-type and DP IV/ CD26-KO mice to a comparable extent. Further, a selective inhibitor of DP8/DP9 activity was capable of suppressing DNA synthesis in mitogen-stimulated splenocytes of both wild-type and knockout mice to the same extent. In contrast, selective inhibitors of DP IV and DP II lacked this suppressive activity.

CONCLUSIONS

Our data support the hypothesis that DP8 and/or DP9 represent additional pharmacological targets for the suppression of T cell proliferation and for anti-inflammatory therapy.

TGF-beta1-mediated control of central nervous system inflammation and autoimmunity through the inhibitory receptor CD26

The T cell marker CD26/dipeptidyl peptidase (DP) IV is associated with an effector phenotype and markedly elevated in the human CNS disorder multiple sclerosis. However, little is known about the in vivo role of CD26/DP IV in health and disease, and the underlying mechanism of its function in CNS inflammation. To directly address the role of CD26/DP IV in vivo, we examined Th1 immune responses and susceptibility to experimental autoimmune encephalomyelitis in CD26(-/-) mice. We show that gene deletion of CD26 in mice leads to deregulation of Th1 immune responses. Although production of IFN-gamma and TNF-alpha by pathogenic T cells in response to myelin Ag was enhanced in CD26(-/-) mice, production of the immunosuppressive cytokine TGF-beta1 was diminished in vivo and in vitro. In contrast to the reduction in TGF-beta1 production, responsiveness to external TGF-beta1 was normal in T cells from CD26(-/-) mice, excluding alterations in TGF-beta1 sensitivity as a mechanism causing the loss of immune regulation. Natural ligands of CD26/DP IV induced TGF-beta1 production in T cells from wild-type mice. However, natural ligands of CD26/DP IV failed to elicit TGF-beta1 production in T cells from CD26(-/-) mice. The striking functional deregulation of Th1 immunity was also seen in vivo. Thus, clinical experimental autoimmune encephalomyelitis scores were significantly increased in CD26(-/-) mice immunized with peptide from myelin oligodendrocyte glycoprotein. These results identify CD26/DP IV as a nonredundant inhibitory receptor controlling T cell activation and Th1-mediated autoimmunity, and may have important therapeutic implications for the treatment of autoimmune CNS disease.

Dipeptidyl peptidase IV activity and/or structure homologs: contributing factors in the pathogenesis of rheumatoid arthritis?

Several of the proinflammatory peptides involved in rheumatoid arthritis pathogenesis, including peptides induced downstream of tumor necrosis factor-α as well as the monocyte/T cell-attracting chemokines RANTES and stromal cell-derived factor (SDF)-1α and the neuropeptides vasoactive intestinal peptide (VIP) and substance P, have their biological half-lives controlled by dipeptidyl peptidase IV (DPPIV). Proteolysis by DPPIV regulates not only the half-life but also receptor preference and downstream signaling. In this article, we examine the role of DPPIV homologs, including CD26, the canonical DPPIV, and their substrates in the pathogenesis of rheumatoid arthritis. The differing specific activities of the DPPIV family members and their differential inhibitor response provide new insights into therapeutic design.

Structure and function studies of glucagon-like peptide-1 (GLP-1): the designing of a novel pharmacological agent for the treatment of diabetes

Glucagon-like peptide-1 (GLP-1) is a proglucagon-derived peptide secreted from gut endocrine cells in response to nutrient ingestion. The multifaceted actions of GLP-1 include the following: (1) the stimulation of insulin secretion and of its gene expression, (2) the inhibition of glucagon secretion, (3) the inhibition of food intake, (4) the proliferation and differentiation of beta cells, and (5) the protection of beta-cells from apoptosis. The therapeutic utility of the native GLP-1 molecule is limited by its rapid enzymatic degradation by a serine protease termed dipeptidyl peptidase-IV (DPP-IV). The present article reviews the research studies aimed at elucidating the biosynthesis, metabolism, and molecular characteristics of GLP-1 since it is from these studies that the development of a GLP-1-like pharmacological agent may be derived.

Circulating CD26 is negatively associated with inflammation in human and experimental arthritis

Dipeptidyl peptidase IV (DPPIV, CD26), a protease-cleaving N-terminal X-Pro dipeptide from selected proteins including some chemokines, is expressed both as a soluble form in plasma and on the cell surface of various immune and nonimmune cell types. To gain insights into the pathophysiological role of CD26 in arthritis, we explored DPPIV/CD26 expression during murine antigen-induced arthritis (AIA), an experimental model of arthritis. AIA induction led to reduced plasma DPPIV activity. In CD26-deficient mice, the severity of AIA was increased as assessed by enhanced technetium uptake and by increased histological parameters of inflammation (synovial thickness and exudate). We demonstrated that CD26 controls the in vivo half-life of the intact active form of the proinflammatory chemokine stromal cell-derived factor-1 (SDF-1). CD26-deficient mice exhibited increased levels of circulating active SDF-1, associated with increased numbers of SDF-1 receptor (CXCR4)-positive cells infiltrating arthritic joints. In a clinical study, plasma levels of DPPIV/CD26 from rheumatoid arthritis patients were significantly decreased when compared to those from osteoarthritis patients and inversely correlate with C-reactive protein levels. In conclusion, decreased circulating CD26 levels in arthritis may influence CD26-mediated regulation of the chemotactic SDF-1/CXCR4 axis.

Inhibitors of dipeptidyl peptidase IV: a novel approach for the prevention and treatment of Type 2 diabetes?

Inhibitors of the enzyme dipeptidyl peptidase IV (DPP IV) are of increasing interest to both diabetologists and the pharmaceutical industry alike, as they may become established as the next member of the oral antidiabetic class of therapeutic agents, designed to lower blood glucose and, possibly, prevent the progressive impairment of glucose metabolism in patients with impaired glucose tolerance and Type 2 diabetes. DPP IV has become a focus of attention for drug design, as it has a pivotal role in the rapid degradation of at least two of the hormones released during food ingestion, a property that has warranted the design of inhibitor-based drugs. At the molecular level, DPP IV cleaves two amino acids from the N-terminus of the intact, biologically active forms of both so-called incretin hormones, glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide (formerly known as gastric inhibitory polypeptide), resulting in truncated metabolites, which are largely inactive. Inhibition of the enzyme, therefore, is thought to increase levels of the active forms of both incretin hormones, culminating in an increase in insulin release after a meal, in a fully glucose-dependent manner. DPP IV inhibitors combine several features of interest to the drug design process. They can be readily optimised for their target and be designed as low molecular weight, orally active entities compatible with once-daily administration.

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.

Different modes of dipeptidyl peptidase IV (CD26) inhibition by oligopeptides derived from the N-terminus of HIV-1 Tat indicate at least two inhibitor binding sites

Dipeptidyl peptidase IV (DP IV, CD26) plays an essential role in the activation and proliferation of lymphocytes, which is shown by the immunosuppressive effects of synthetic DP IV inhibitors. Similarly, both human immunodeficiency virus-1 (HIV-1) Tat protein and the N-terminal peptide Tat(1-9) inhibit DP IV activity and T cell proliferation. Therefore, the N-terminal amino acid sequence of HIV-1 Tat is important for the inhibition of DP IV. Recently, we characterized the thromboxane A2 receptor peptide TXA2-R(1-9), bearing the N-terminal MWP sequence motif, as a potent DP IV inhibitor possibly playing a functional role during antigen presentation by inhibiting T cell-expressed DP IV [Wrenger, S., Faust, J., Mrestani-Klaus, C., Fengler, A., Stöckel-Maschek, A., Lorey, S., Kähne, T., Brandt, W., Neubert, K., Ansorge, S. & Reinhold, D. (2000) J. Biol. Chem.275, 22180-22186]. Here, we demonstrate that amino acid substitutions at different positions of Tat(1-9) can result in a change of the inhibition type. Certain Tat(1-9)-related peptides are found to be competitive, and others linear mixed-type or parabolic mixed-type inhibitors indicating different inhibitor binding sites on DP IV, at the active site and out of the active site. The parabolic mixed-type mechanism, attributed to both non-mutually exclusive inhibitor binding sites of the enzyme, is described in detail. From the kinetic investigations and molecular modeling experiments, possible interactions of the oligopeptides with specified amino acids of DP IV are suggested. These findings give new insights for the development of more potent and specific peptide-based DP IV inhibitors. Such inhibitors could be useful for the treatment of autoimmune and inflammatory diseases.

Dipeptidyl peptidase IV on activated T cells as a target molecule for therapy of rheumatoid arthritis

The extracellular domain of the T cell co-stimulatory molecule CD26 possesses dipeptidyl peptidase IV (DP IV) enzyme activity. Activated T cells are known to increase expression of cell surface DP IV and some specific inhibitors of this enzyme have been reported to suppress T cell function. Previously we have identified a DP IV inhibitor, designated TMC-2, found in culture supernatant of Aspergillus oryzae. Administration of TMC-2 to rats with adjuvant arthritis caused marked suppression of paw swelling. To elucidate the mechanism of TMC-2 antiarthritic activity, we have studied its effects on T cell function. Here we show that TMC-2 inhibited DP IV activity of CD26 immunoprecipitated from T cell lysates, and also inhibited proliferative responses of T cells to specific antigen or anti-CD3 antibody. Suppression of IL-2 production was demonstrated at both the mRNA and protein levels. TMC-2 did not alter the PTPase activity of pure CD45, but when this molecule was co-precipitated from T cell lysates together with associated CD26, its PTPase was virtually completely abolished by TMC-2. These results suggest that modulation of CD45 PTPase activity might be responsible for functional suppression of T cells by TMC-2. Because the effects of TMC-2 on T cells were reversible and it was not toxic at the concentrations used, TMC-2 may be a candidate novel therapeutic agent for rheumatoid arthritis.

The role of dipeptidyl peptidase IV (DP IV) enzymatic activity in T cell activation and autoimmunity

Activated T lymphocytes express high levels of dipeptidyl peptidase IV (DP IV)/CD26. Recent studies support the notion that DP IV may play an important role in the regulation of differentiation and growth of T lymphocytes. This article gives a short overview on DP IV/CD26 expression and effects on immune cells in vitro and in vivo. A major focus of this review are clinical aspects of the function of CD26 on hematopoietic cells and the potential usage of synthetic DP IV inhibitors as therapeutics in inflammatory disorders.

Decrease of serum dipeptidylpeptidase activity in severe sepsis patients: relationship to procalcitonin

A significant decrease of DPP IV activity has been found in patients with severe sepsis in relationship to the increase of procalcitonin. These findings might be explained by the high concentration of other substrates for DPP IV present in these patients. It can be hypothesized that this enzymatic decrease is bound to some changes in immunomodulation. Further studies will be necessary to elucidate the clinical importance of these findings.

Down-regulation of T cell activation following inhibition of dipeptidyl peptidase IV/CD26 by the N-terminal part of the thromboxane A2 receptor

Using synthetic inhibitors, it has been shown that the ectopeptidase dipeptidyl peptidase IV (DP IV) (CD26) plays an important role in the activation and proliferation of T lymphocytes. The human immunodeficiency virus-1 Tat protein, as well as the N-terminal nonapeptide Tat(1-9) and other peptides containing the N-terminal sequence XXP, also inhibit DP IV and therefore T cell activation. Studying the effect of amino acid exchanges in the N-terminal three positions of the Tat(1-9) sequence, we found that tryptophan in position 2 strongly improves DP IV inhibition. NMR spectroscopy and molecular modeling show that the effect of Trp(2)-Tat(1-9) could not be explained by significant alterations in the backbone structure and suggest that tryptophan enters favorable interactions with DP IV. Data base searches revealed the thromboxane A2 receptor (TXA2-R) as a membrane protein extracellularly exposing N-terminal MWP. TXA2-R is expressed within the immune system on antigen-presenting cells, namely monocytes. The N-terminal nonapeptide of TXA2-R, TXA2-R(1-9), inhibits DP IV and DNA synthesis and IL-2 production of tetanus toxoid-stimulated peripheral blood mononuclear cells. Moreover, TXA2-R(1-9) induces the production of the immunosuppressive cytokine transforming growth factor-beta1. These data suggest that the N-terminal part of TXA2-R is an endogenous inhibitory ligand of DP IV and may modulate T cell activation via DP IV/CD26 inhibition.