CD26: a multifunctional integral membrane and secreted protein of activated lymphocytes

Is Transgenic Porcine Skin as Good as Allogeneic Skin for Regenerative Medicine? Comparison of Chosen Properties of Xeno- and Allogeneic Material

BACKGROUND

Burn treatment is associated with the need of dressing large cutaneous defects. There is a need of alternative search for the allogeneic skin as a source of grafting for a clinical use. Such sources include animals. For many years, porcine skin was used as a biological dressing for wounds or donor's fields, or residual fields after skin grafting. Current studies aim to minimize immunogenicity, inter alia, through the decellularization process.

MATERIALS AND METHODS

The decellularization methods and porcine skin resettlement of human keratinocytes and fibroblasts were evaluated. The mechanical properties of the dressings and their influence on the viability, apoptosis, population doubling, and cell cycle of keratinocytes and fibroblasts were examined. The inheritance of cell antigens responsible for histocompatibility on the human keratinocyte and fibroblast surface in the cultures incubated with examined variants of dressings from porcine skin were analyzed.

RESULTS

The most effective acellularization method is trypsinization. Morphology of the cell remained proper and stable during the whole experiment. In both fibroblast and keratinocyte cultures, the highest number of apoptotic cells was observed when samples were incubated with allogeneic skin. In the keratinocyte cultures, the highest number of live cells was observed when incubated with porcine transgenic acellular dermal matrix. The acellular matrices influence the increase of population doubling of keratinocytes in the cultures.

CONCLUSION

For routine acellurization, trypsinization was chosen as the most effective method with preservation of tissue properties.

Decreased shedding dipeptidyl peptidase 4 from membrane in Hashimoto's thyroiditis

AIMS

This study aimed to determine the concentration and enzymatic activity of dipeptidyl peptidase 4 (DPP4) in serum and peripheral blood mononuclear cells (PBMCs) from patients with Hashimoto's thyroiditis (HT) and to explore the potential mechanism of the abnormal DPP4 in HT development.

METHODS

A total of 33 newly diagnosed HT patients and 31 age- and sex-matched healthy controls were enrolled. Clinical characteristics and thyroid function data were collected for all participants. Serum DPP4 and kallikrein-related peptidase 5 (KLK5) concentrations were measured by sandwich enzyme-linked immunosorbent assay. DPP4 enzymatic activities in serum and PBMCs were determined by enzymatic assay. DPP4, KLK5 and interferon (IFN)-γ mRNA expression levels in PBMCs were evaluated by quantitative real-time polymerase chain reaction.

RESULTS

Serum DPP4 level and activity were significantly lower in the HT group compared with the control group. However, DPP4 mRNA expression was significantly increased and both serum KLK5 concentration and KLK5 mRNA expression in PBMCs were significantly decreased in HT patients. Correlation analyses revealed that DPP4 concentration was positively correlated with DPP4 enzymatic activity in serum. No significant difference in DPP4 activity was found in PBMCs. DPP4 enzymatic activity in PBMCs was negatively correlated with DPP4 enzymatic activity in serum. IFN-γ mRNA expression in PBMCs was significantly increased in HT patients.

CONCLUSIONS

DPP4 is involved in the development and pathological process of HT. Decreased cleavage of membrane-anchored DPP4 by KLK5 may be responsible for the decreased serum DPP4 levels in HT patients.

Dipeptidyl Peptidase-4 at the Interface Between Inflammation and Metabolism

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

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

CD26 and Asthma: a Comprehensive Review

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

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

CD markers variations in chronic lymphocytic leukemia: New insights into prognosis

Chronic lymphocytic leukemia (CLL) is one of the most commonly occurring adult leukemias that is associated with clonal accumulation of mature apoptosis-resistant B-cells in bone marrow, peripheral blood, and specific tissues. Different pathogenesis factors can contribute to the aggression of the clinical course in this disease. Cytogenetic abnormalities and surface biomarkers of neoplastic CLL cells can be effective in the outcome of CLL, and the examination of changing CD markers expressions in the progression of CLL can be related to the prognosis of this disease. Changing expression levels of CD markers on lymphocytes and other cells in CLL patients can play a role in the aggressive clinical outcomes such as organomegaly, immunodeficiency, and advanced disease stages through their interaction with CLL microenvironment. Given the involvement of CD markers in the pathogenesis of CLL, it can be stated that recognizing the expression changes of CD markers in the cells involved in CLL can be a proper approach to evaluate prognosis among these patients.

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

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

Dipeptidyl peptidase-4 and adenosine deaminase enzyme levels in polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is one of the most common endocrinopathies in reproductive age women and insulin resistance (IR) and hyperinsulinism play a critical role in the pathogenesis. Glucagon-like peptide-1 (GLP-1), promotes insulin secretion, inhibits glucagon secretion. GLP-1 is degraded by dipeptidyl peptidase-4 (DPP-4). DPP-4, also interacts with adenosine deaminase (ADA). Therefore, IR may have a significant connection with ADA activity. The aim of this study is to compare levels of DPP-4 and ADA enzymes in PCOS and infertile patients. Forty-four patients with PCOS and 44 infertile patients with normal ovarian reserve were enrolled in the study. Serum ADA, DPP-4, AMH, glucose and insulin levels were measured. HOMA-IR method was used to assess insulin sensitivity. ADA, DPP-4, AMH, HOMA-IR (p < .05) and insulin levels (p < .01) were found to be increased in PCOS patients. Considering all study participants AMH levels were found to be positively correlated with ADA (r: 0.734) and DPP-4 (r: 0.449) levels. Also ADA levels were found to be positively correlated with DPP-4 (r: 0.472), insulin (r: 0.216) and HOMA-IR (r: 0.223). Our findings about the elevation of DPP-4 levels in patients with PCOS suggest that the use of DPP-4 inhibitors may be beneficial in treatment of these patients.

Drug fever and acute inflammation from hypercytokinemia triggered by dipeptidyl peptidase-4 inhibitor vildagliptin

A 69-year-old man started taking the dipeptidyl peptidase-4 inhibitor, vildagliptin. One week later, C-reactive protein and plasma immunoglobulin E levels were markedly elevated, and the vildagliptin was stopped. After the patient's laboratory findings were normalized, we decided to restart vildagliptin with the patient's agreement. The next day, he had a high fever, and C-reactive protein and procalcitonin levels were elevated. Although we failed to find a focus of infection, we started antibiotics therapy. Two days later, the high fever had improved, and the C-reactive protein level had decreased. A drug lymphocyte stimulation test showed a positive result for vildagliptin. We examined various kinds of cytokine and infection markers just before and after the treatment with vildagliptin. Finally, we diagnosed the patient with vildagliptin-induced drug fever, probably based on the increase of various inflammatory cytokine levels and the response to this. Taken together, we should be aware of the possibility of vildagliptin inducing drug fever and/or acute inflammation.

Lymphocytes are a major source of circulating soluble dipeptidyl peptidase 4

Dipeptidyl peptidase 4 (DPP4, CD26) is a serine protease that is expressed constitutively by many haematopoietic and non-haematopoietic tissues. It exists as a membrane-associated protein, as well as in an active, soluble form (herein called sDPP4), present at high concentrations in bodily fluids. Despite the proposed use of sDPP4 as a biomarker for multiple diseases, its cellular sources are not well defined. Here, we report that individuals with congenital lymphocyte immunodeficiency had markedly lower serum concentrations of sDPP4, which were restored upon successful treatment and restoration of lymphocyte haematopoiesis. Using irradiated lymphopenic mice and wild-type to Dpp4-/- reciprocal bone marrow chimeric animals, we found that haematopoietic cells were a major source of circulating sDPP4. Furthermore, activation of human and mouse T lymphocytes resulted in increased sDPP4, providing a mechanistic link between immune system activation and sDPP4 concentration. Finally, we observed that acute viral infection induced a transient increase in sDPP4, which correlated with the expansion of antigen-specific CD8+ T cell responses. Our study demonstrates that sDPP4 concentrations are determined by the frequency and activation state of lymphocyte populations. Insights from these studies will support the use of sDPP4 concentration as a biomarker for inflammatory and infectious diseases.

Dipeptidyl Peptidase 4 Inhibitors Reduce Hepatocellular Carcinoma by Activating Lymphocyte Chemotaxis in Mice

BACKGROUND & AIMS

CD26, a multifunctional transmembrane glycoprotein, is expressed in various cancers and functions as dipeptidyl peptidase 4 (DPP4). We investigated whether CD26 expression is associated with hepatocellular carcinoma (HCC) progression and whether DPP4 inhibitors exert antitumor effects against HCC.

METHODS

CD26 expression was examined in 41 surgically resected HCC specimens. The effects of DPP4 inhibitors on HCC were examined by using HCC cell lines (Huh-7 and Li-7), xenograft tumors in nude mice, and a nonalcoholic steatohepatitis-related HCC mouse model.

RESULTS

CD26 expression in HCC specimens was associated with increased serum DPP4 activity, as well as a more advanced stage, less tumor immunity, and poorer prognosis in HCC patients. The HCC cell lines and xenograft tumors exhibited CD26 expression and DPP4 activity. The DPP4 inhibitors did not exhibit antitumor effects in vitro, but natural killer (NK) and/or T-cell tumor accumulation suppressed growth of xenograft tumor and HCC in vivo. The antitumor effects of DPP4 inhibitors were abolished by the depletion of NK cells or the neutralization of CXCR3, a chemokine receptor on NK cells. EZ-TAXIScan, an optical horizontal chemotaxis apparatus, identified enhanced NK and T-cell chemotaxis by DPP4 inhibitors ex vivo in the presence of Huh-7 cells and the chemokine CXCL10, which binds to CXCR3. The DPP4 inhibitors prevented the biologically active form of CXCL10 from being truncated by Huh-7 cell DPP4 activity. DPP4 inhibitors also suppressed tumor angiogenesis.

CONCLUSIONS

These results provide a rationale for verifying whether DPP4 inhibitors clinically inhibit the progression of HCC or augment the antitumor effects of molecular-targeting drugs or immunotherapies against HCC.

Differences in kidney-specific DPP-4 inhibition by linagliptin and sitagliptin

The two dipeptidyl peptidase (DPP)-4 inhibitors, linagliptin and sitagliptin, were shown to exert different binding kinetics in vitro. Twenty-four hours after oral dosing particularly in vivo inhibition of renal-specific DPP-4 activity was more sustained in Sprague Dawley rats after exposure to linagliptin than it was after sitagliptin.

The Potential Role of the Dipeptidyl Peptidase-4-Like Activity From the Gut Microbiota on the Host Health

The Dipeptidyl peptidase-4 (DPP-4) activity influences metabolic, behavioral and intestinal disorders through the cleavage of key hormones and peptides. Some studies describe the existence of human DPP-4 homologs in commensal bacteria, for instance in Prevotella or Lactobacillus. However, the role of the gut microbiota as a source of DPP-4-like activity has never been investigated. Through the comparison of the DPP-4 activity in the cecal content of germ-free mice (GFM) and gnotobiotic mice colonized with the gut microbiota of a healthy subject, we bring the proof of concept that a significant DPP-4-like activity occurs in the microbiota. By analyzing the existing literature, we propose that DPP-4-like activity encoded by the intestinal microbiome could constitute a novel mechanism to modulate protein digestion as well as host metabolism and behavior.

Pyrrole: An insight into recent pharmacological advances with structure activity relationship

Pyrrole is a heterocyclic ring template with multiple pharmacophores that provides a way for the generation of library of enormous lead molecules. Owing to its vast pharmacological profile, pyrrole and its analogues have drawn much attention of the researchers/chemists round the globe to be explored exhaustively for the benefit of mankind. This review focusses on recent advancements; pertaining to pyrrole scaffold, discussing various aspects of structure activity relationship and its bioactivities.

Citrus bioflavonoids dipeptidyl peptidase-4 inhibition compared with gliptin antidiabetic medications

This study compared dipeptidyl peptidase-4 (DPP-4) inhibitory activity of citrus bioflavonoid nutraceuticals compared with three gliptins. Citrus bioflavonoid standards and three commercially available citrus bioflavonoid supplements (Thompson's Super Bioflavonoid Complex^®(SB), Ethical Nutrients Bioflavonoids Plus Vitamin C^®(EN), and Country Life Citrus Bioflavonoids and Rutin^®(CB)) were considered in this study. Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) analysis was undertaken to identify and quantitate the citrus bioflavonoids present in each supplement. The DPP-4 inhibitory activity was determined by fluorometric assay. All of the tested individual citrus flavonoids demonstrated DPP-4 inhibitory activity, with IC₅₀ values ranging from 485 μM (rutin) to 5700 μM (hesperitin and eriodictyol). Similarly, the flavonoid supplements had IC₅₀ values of 16.9 mg/mL (EN), 3.44 mg/mL (SB) and 2.72 mg/mL (CB). These values compare with gliptin IC₅₀ values of 0.684 μM (sitagliptin), 0.707 μM (saxagliptin) and 2.286 μM (vildagliptin). The supplement flavonoid content varied from 11.98% (CB) to 5.26% (EN) and 14.51% (SB) of tablet mass, corresponding to daily flavonoid doses of around 300, 150 and 400 mg, respectively, with CB and SB containing rutin at levels of 7.0% and 7.5% of tablet mass, respectively. While our data demonstrated that citrus bioflavonoid based supplements do possess DPP-4 inhibitory activity, they are several orders of magnitude less potent than gliptins. Further studies using higher concentrations of citrus bioflavonoids, as well as investigations into antioxidant properties which may add additional benefit are warranted.

Dipeptidyl peptidase-4 inhibition and renoprotection: the role of antifibrotic effects

PURPOSE OF REVIEW

This article analyzes the potential beneficial effects of dipeptidyl peptidase (DPP)-4 inhibitors on renal diseases.

RECENT FINDINGS

The pathological significance of DPP-4, either dependent or independent on catalytic activities, on renal diseases has been reported in preclinical studies. With regard to this, we have shown that damaged endothelial cells are converted to a mesenchymal cell phenotype, which is associated with the induction of DPP-4 in endothelial cells. The endothelial mesenchymal transition may contribute to kidney fibrosis; indeed, the antifibrotic effects of DPP-4 inhibitors have been reported elsewhere. However, even though such potential benefits of DPP-4 inhibitors on renal diseases were shown in preclinical studies, clinical trials have not yet revealed significant benefits in renal hard outcomes of DPP-4 inhibitors.

SUMMARY

To completely understand the beneficial effects of DPP-4 inhibitors, both the following studies are required: first, preclinical studies that analyze deeper molecular mechanisms of DPP-4 inhibition, and, second, clinical studies that investigate whether such potential beneficial effects of DPP-4 inhibitors are relevant to the patients in the clinic.

DPP4/CD26 overexpression in urothelial carcinoma confers an independent prognostic impact and correlates with intrinsic biological aggressiveness

Urothelial carcinoma (UC) is common cancer worldwide. The molecular aberrations regarding tumor progression remain unclear. Pericellular proteolysis is crucial in tumorigenesis, but its significance is unexplored in UC. By data mining the datasets in Gene Expression Omnibus, specifically focus on the proteolysis pathway, and followed by a preliminary validation in a pilot batch of tumor samples, we identified that the upregulation of dipeptidyl peptidase 4 (DPP4) was most significantly associated with clinical aggressiveness of UCs. Quantitative RT-PCR confirmed upregulation of DPP4 mRNA in advanced stage UCs. The clinical significance of DPP4 expression was validated in our large cohort consists of 635 UCs from upper urinary tract and urinary bladder. Univariate and multivariate analyses show that DPP4 is an independent prognosticatory biomarker for disease-specific survival and metastasis-free survival. Comparing the DPP4 expression level of three urothelial cell lines with normal urothelial cells, J82 and RTCC-1 showed a significantly increased in transcript and protein expression. DPP4 knockdown as conducted by using short-hairpin RNA resulted in a significantly decreased cell viability, proliferation, migration, and invasion in J82 and RTCC-1 cells. These findings implicate that DPP4 plays a role in the aggressiveness of UCs, and can serve as a novel prognostic marker and therapeutic target.

Impaired secretion of active GLP-1 in patients with hypertriglyceridaemia: A novel lipotoxicity paradigm?

BACKGROUND

Lipotoxicity plays an important role in the pathogenesis of β-cell dysfunction. Glucagon-like peptide-1 (GLP-1) is an incretin hormone that exerts beneficial effects on the number and function of islet β cells. However, the effect of lipotoxicity on GLP-1 secretion is still unknown.

METHODS

Twenty-five patients who were newly diagnosed with diabetes were recruited from 400 subjects based on 75-g Oral Glucose Tolerance Test. Patients were divided into diabetes (DM) and DM combined with hypertriglyceridaemia (DM + HTG) groups according to their serum triglyceride (TG) levels. Seventy-one normal controls and 17 patients with isolated hypertriglyceridaemia were matched by age and gender.

RESULTS

Total and active fasting GLP-1 and 2-hour GLP-1 levels were not significantly altered among the 4 groups. However, total and active ΔGLP-1 levels (the difference between 2-hour GLP-1 and fasting GLP-1 levels) were significantly reduced in the isolated HTG, DM, and DM + HTG groups, particularly the DM + HTG group. The ratio of serum active GLP-1 (AGLP-1) to total GLP-1 (TGLP-1) levels was also decreased in patients with isolated HTG, suggesting that active GLP-1 secretion may be more seriously impaired. Both ΔTGLP-1 and ΔAGLP-1 levels were negatively correlated with serum TG levels, body mass index and fasting plasma glucose (FPG) levels and positively correlated with HDL-C levels. According to the multivariate linear regression analysis, only TG and FPG levels were independently associated with ΔTGLP-1 and ΔAGLP-1 levels.

CONCLUSION

Impaired GLP-1 secretion was associated with hypertriglyceridaemia and diabetes, and a more obvious association was noted in hypertriglyceridaemic patients with diabetes.

Potential disease biomarkers: dipeptidyl peptidase 4 and fibroblast activation protein

The importance of the dipeptidyl peptidase 4 (DPP4) gene family in regulating critical biochemical pathways continues to emerge. The two most well-studied members of the family, DPP4 and fibroblast activation protein (FAP), have been investigated both as therapeutic targets for disease and as diagnostic biomarkers. The interest in DPP4 and FAP as potential disease biomarkers has been driven primarily by observations of altered expression profiles in inflammatory diseases and cancer. Furthermore, the stability and persistence of soluble DPP4 and FAP in the serum make them attractive candidate serology markers. This review summarises investigations into DPP4 and FAP as biomarkers of autoimmune disease, gut inflammation, psychosomatic disorders and malignancy and discusses their potential likelihood as clinically useful tools.

Exploration of DPP-IV inhibitors with a novel scaffold by multistep in silico screening

Dipeptidyl peptidase-IV (DPP-IV), an enzyme that degrades incretins-hormones that promote insulin secretion-is a therapeutic target for type 2 diabetes, with a number of its inhibitors having been launched as therapies for diabetes. Since adverse effects of these inhibitors have recently been reported, the development of novel DPP-IV inhibitors with higher efficacy and safety is required. We, therefore, screened for novel DPP-IV inhibitors using the combination of an in silico drug discovery technique and a DPP-IV assay system. We initially selected seven candidate compounds as DPP-IV inhibitors from a database consisting of four million compounds by a multistep in silico screening procedure combining pharmacophore-based screening, docking calculation and the analysis of three-dimensional quantitative structure-activity relationship. We then measured the inhibitory activity of the selected compounds and identified a hit compound. In addition, we discuss the structure-activity relationship between the binding mode model and inhibitory activity of the hit compound.

Human monoclonal antibodies as candidate therapeutics against emerging viruses

The emergence of new pathogens, such as severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), and Ebola virus, poses serious challenges to global public health and highlights the urgent need for novel antiviral approaches. Monoclonal antibodies (mAbs) have been successfully used to treat various diseases, particularly cancer and immunological disorders. Antigen-specific mAbs have been isolated using several different approaches, including hybridoma, transgenic mice, phage display, yeast display, and single B-cell isolation. Consequently, an increasing number of mAbs, which exhibit high potency against emerging viruses in vitro and in animal models of infection, have been developed. In this paper, we summarize historical trends and recent developments in mAb discovery, compare the advantages and disadvantages of various approaches to mAb production, and discuss the potential use of such strategies for the development of antivirals against emerging diseases. We also review the application of recently developed human mAbs against SARS-CoV, MERS-CoV, and Ebola virus and discuss prospects for the development of mAbs as therapeutic agents against emerging viral diseases.

Combined treatment with dipeptidyl peptidase-4 inhibitor (sitagliptin) and angiotensin-II type 1 receptor blocker (losartan) suppresses progression in a non-diabetic rat model of steatohepatitis

AIM

Dipeptidyl peptidase-4 (DPP4) inhibitors (DPP4-I) are oral glucose-lowering drugs for type 2 diabetes mellitus. Previously, we reported that DPP4-I (sitagliptin) exerted suppressive effects on experimental liver fibrosis in rats. Blockade of the renin-angiotensin system by angiotensin-II type 1 receptor blocker (losartan), commonly used in the management of hypertension, has been shown to significantly alleviate hepatic fibrogenesis and carcinogenesis. We aimed to elucidate the effects and possible mechanisms of a sitagliptin + losartan combination on the progression of non-diabetic non-alcoholic steatohepatitis (NASH) in a rat model.

METHODS

To induce NASH, Fischer 344 rats were fed a choline-deficient L-amino acid-defined diet for 12 weeks. We elucidated the chemopreventive effects of sitagliptin + losartan, especially in conjunction with hepatic stellate cell (HSC) activation, angiogenesis, and oxidative stress, all known to play important roles in the progression of NASH.

RESULTS

Sitagliptin + losartan suppressed choline-deficient L-amino acid-defined diet-induced hepatic fibrogenesis and carcinogenesis. The combination treatment exerted a greater inhibitory effect than monotherapy. These inhibitory effects occurred almost concurrently with the suppression of HSC activation, neovascularization, and oxidative stress. In vitro studies showed that sitagliptin + losartan inhibited angiotensin II-induced proliferation and expression of transforming growth factor-β1 and α1 (I)-procollagen mRNA of activated HSC and in vitro angiogenesis, in parallel with the suppression observed in in vivo studies.

CONCLUSIONS

The widely and safely used sitagliptin + losartan combination treatment in clinical practice could be an effective strategy against NASH.

KLK5 induces shedding of DPP4 from circulatory Th17 cells in type 2 diabetes

OBJECTIVE

Increasing plasma levels and activity of dipeptidyl peptidase-4 (DPP4 or CD26) are associated with rapid progression of metabolic syndrome to overt type 2 diabetes mellitus (T2DM). While DPP4 inhibitors are increasingly used as anti-hyperglycemic agents, the reason for the increase in plasma DPP4 activity in T2DM patients remains elusive.

METHODS

We looked into the source of plasma DPP4 activity in a cohort of 135 treatment naive nonobese (BMI < 30) T2DM patients. A wide array of ex vivo, in vitro, and in silico methods were employed to study enzyme activity, gene expression, subcellular localization, protease identification, surface expression, and protein-protein interactions.

RESULTS

We show that circulating immune cells, particularly CD4+ T cells, served as an important source for the increase in plasma DPP4 activity in T2DM. Moreover, we found kallikrein-related peptidase 5 (KLK5) as the enzyme responsible for cleaving DPP4 from the cell surface by directly interacting with the extracellular loop. Expression and secretion of KLK5 is induced in CD4+ T cells of T2DM patients. In addition, KLK5 shed DPP4 from circulating CD4+ T helper (Th)17 cells and shed it into the plasma of T2DM patients. Similar cleavage and shedding activities were not seen in controls.

CONCLUSIONS

Our study provides mechanistic insights into the molecular interaction between KLK5 and DPP4 as well as CD4+ T cell derived KLK5 mediated enzymatic cleavage of DPP4 from cell surface. Thus, our study uncovers a hitherto unknown cellular source and mechanism behind enhanced plasma DPP4 activity in T2DM.

Inhibitor-Decorated Polymer Conjugates Targeting Fibroblast Activation Protein

Proteases are directly involved in cancer pathogenesis. Expression of fibroblast activation protein (FAP) is upregulated in stromal fibroblasts in more than 90% of epithelial cancers and is associated with tumor progression. FAP expression is minimal or absent in most normal adult tissues, suggesting its promise as a target for the diagnosis or treatment of various cancers. Here, we report preparation of a polymer conjugate (an iBody) containing a FAP-specific inhibitor as the targeting ligand. The iBody inhibits both human and mouse FAP with low nanomolar inhibition constants but does not inhibit close FAP homologues dipeptidyl peptidase IV, dipeptidyl peptidase 9, and prolyl oligopeptidase. We demonstrate the applicability of this iBody for the isolation of FAP from cell lysates and blood serum as well as for its detection by ELISA, Western blot, flow cytometry, and confocal microscopy. Our results show the iBody is a useful tool for FAP targeting in vitro and potentially also for specific anticancer drug delivery.

The effect of anagliptin on intimal hyperplasia of rat carotid artery after balloon injury

The present study evaluated the effect of anagliptin on intimal hyperplasia following carotid artery injury in Sprague-Dawley rats. Sprague-Dawley rats weighing 280–300 g were injured using a 2F Fogarty balloon embolectomy catheter. The rats were divided into injury-(saline) and anagliptin-(10 mg/kg/day) treated groups. vascular injuries were induced in the left carotid artery, followed by evaluation of neointima formation at 28 days. The right and left carotid arteries were harvested and evaluated with histological evaluation, and the plasma activity of glucagon-like peptide 1 receptor (GLP-1), stromal cell-derived factor (SDF)-1α, interleukin (IL)-6, IL-1β and tumor necrosis factor (TNF)-α were detected by ELISA analysis. Treatment with anagliptin decreased balloon injury-induced neointima formation, compared with the injury group (P<0.01). Body weight and food consumption did not alter following treatment with anagliptin. Anagliptin caused an increase in the serum active GLP-1 concentration, compared with the injury group. In addition, serum SDF-1α was significantly decreased by treatment with anagliptin (P<0.001). Anagliptin altered the serum activity of IL-6, IL-1β and TNF-α (P<0.01). The results of the present study demonstrated that anagliptin appeared to attenuate neointimal formation by inhibiting inflammatory cytokines and chemokines following balloon injury, and that treatment with a dipeptidyl peptidase 4 inhibitor may be useful for future preclinical studies and potentially for the inhibition of thrombosis formation following percutaneous coronary intervention.

Adenosine Deaminase (ADA)-Deficient Severe Combined Immune Deficiency (SCID): Molecular Pathogenesis and Clinical Manifestations

Deficiency of adenosine deaminase (ADA, EC3.5.4.4), a housekeeping enzyme of purine metabolism encoded by the Ada gene, is a cause of human severe combined immune deficiency (SCID). Numerous deleterious mutations occurring in the ADA gene have been found in patients with profound lymphopenia (T^- B^- NK^-), thus underscoring the importance of functional purine metabolism for the development of the immune defense. While untreated ADA SCID is a fatal disorder, there are multiple life-saving therapeutic modalities to restore ADA activity and reconstitute protective immunity, including enzyme replacement therapy (ERT), allogeneic hematopoietic stem cell transplantation (HSCT) and gene therapy (GT) with autologous gene-corrected hematopoietic stem cells (HSC). We review the pathogenic mechanisms and clinical manifestations of ADA SCID.

Glycosaminoglycans Regulate CXCR3 Ligands at Distinct Levels: Protection against Processing by Dipeptidyl Peptidase IV/CD26 and Interference with Receptor Signaling

CXC chemokine ligand (CXCL)9, CXCL10 and CXCL11 direct chemotaxis of mainly T cells and NK cells through activation of their common CXC chemokine receptor (CXCR)3. They are inactivated upon NH₂-terminal cleavage by dipeptidyl peptidase IV/CD26. In the present study, we found that different glycosaminoglycans (GAGs) protect the CXCR3 ligands against proteolytic processing by CD26 without directly affecting the enzymatic activity of CD26. In addition, GAGs were shown to interfere with chemokine-induced CXCR3 signaling. The observation that heparan sulfate did not, and heparin only moderately, altered CXCL10-induced T cell chemotaxis in vitro may be explained by a combination of protection against proteolytic inactivation and altered receptor interaction as observed in calcium assays. No effect of CD26 inhibition was found on CXCL10-induced chemotaxis in vitro. However, treatment of mice with the CD26 inhibitor sitagliptin resulted in an enhanced CXCL10-induced lymphocyte influx into the joint. This study reveals a dual role for GAGs in modulating the biological activity of CXCR3 ligands. GAGs protect the chemokines from proteolytic cleavage but also directly interfere with chemokine–CXCR3 signaling. These data support the hypothesis that both GAGs and CD26 affect the in vivo chemokine function.

Changes in serum levels of lipopolysaccharides and CD26 in patients with Crohn's disease

BACKGROUND/AIMS

Lipopolysaccharide (LPS) is a molecule formed by lipids and polysaccharides and is the major cell wall component of gram-negative bacteria. High LPS levels are known to block CD26 expression by activating Toll-like receptor 4. The aim of this study was to correlate the serum levels of LPS and CD26 in Crohn's disease (CD) patients with serum levels of C-reactive protein (CRP), interleukins, CD activity index, and tumor necrosis factor-α (TNF-α).

METHODS

Serum samples were collected from 27 individuals (10 with active CD, 10 with inactive CD, and 7 controls) and the levels of LPS, CD26, TNF-α, interleukin-1β (IL-1β), IL-6, IL-17, and CRP were determined by enzyme-linked immunosorbent assay. The levels of LPS and CD26 were then tested for correlation with TNF-α, IL-1β, IL-6, IL-17, and CRP.

RESULTS

Serum levels of LPS were significantly elevated in the active CD group (P=0.003). Levels of IL-1β (P=0.002), IL-6 (P=0.003), and IL-17 (P<0.001) were lower in the CD groups. Serum TNF-α levels were increased in the active CD group. The CRP levels were elevated in the CD groups when compared to controls (P<0.001). The CD26 levels were lower in the CD groups than in the control group (P<0.001). Among the variables analyzed, there was a correlation between LPS and CRP (r=-0.53, P=0.016) in the CD groups.

CONCLUSIONS

Individuals with CD exhibited higher serum levels of LPS varying from a 2- to 6-fold increase depending on disease activity, when compared with healthy controls. CD26 levels were lower in the CD groups. Both LPS and CD26 correlated with disease severity and serve as potential CD biomarkers.

Regulation and roles of CD26/DPPIV in hematopoiesis and diseases

Dipeptidyl peptidase IV (DPPIV),¹ on the surface of certain cells, where it is also referred to as CD26, is involved in a vast majority of biological and pathological processes. CD26/DPPIV function contributes to cancer and tumor metastasis as well as inhibition of its expression which alters the expression of immune response-related genes. CD26/DPPIV is a widely distributed multifunctional integral membrane and secreted protein that is defined as early predictive biomarker in HIV, cancer and autoimmunity diseases like diabetes and multiple sclerosis. CD26/DPPIV-chemokine interaction may have a functional role in T-cells and overall immune function. It is expressed at low density on resting T cells, but is upregulated with T cell activation. In this review, we summarize valuable information about detailed biological aspects and pharmacokinetic characteristics of CD26/DPPIV and its clinical efficacy, focusing particularly on the role of CD26/DPPIV in immunological and non-immunological diseases. We also describe our recent work about umbilical cord blood (UCB)² hematopoietic stem cell transplantation strategies in which identified CD26+ cells can be differentiated to immune cells under certain culture condition.

The Dipeptidyl Peptidase-4 Inhibitor Teneligliptin Reduces Aortic Damage from Hypercholesterolaemia in Apolipoprotein E-Deficient Mice

Objective

Hypercholesterolaemia is a well-established risk factor for blood vessel damage, which can lead to cardiovascular diseases. An abundance of clinical data show that dipeptidyl peptidase-4 inhibitors protect against aortic damage in patients with diabetes. The goal of this study was to investigate the possible protective effects of teneligliptin against aortic damage in apolipoprotein E knockout (ApoE^-/-) mice.

Methods

Eight-week-old male ApoE^-/- mice were randomly divided into 3 groups: a control group fed a normal diet, a high-cholesterol diet (HD group), and an HD diet mixed with teneligliptin (HD + Tene group), and all the groups were fed with the different treatments for 6 weeks.

Results and Conclusion

The metabolic characteristics of total cholesterol, low-density lipoprotein-cholesterol, and high-sensitivity C-reactive protein were lower in ApoE^-/- HD + Tene mice than in ApoE^-/- HD mice. Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) gene and protein expression were lower in the aortic tissue of ApoE^-/- HD + Tene mice than in ApoE^-/- HD mice. IL-6 and TNF-α gene expression were lower in ApoE^-/- HD + Tene mice than in ApoE^-/- HD mice. These results indicate that teneligliptin may provide a potential therapeutic target for the aortic damage from hypercholesterolaemia.

Effects of linagliptin on human immortalized podocytes: a cellular system to study dipeptidyl-peptidase 4 inhibition

BACKGROUND AND PURPOSE

Dipeptidyl-peptidase 4 (DPP4) is expressed by resident renal cells, including glomerular cells. DPP4 inhibitors (gliptins) exert albuminuria lowering effects, but the role of renal DPP4 as a pharmacological target has not been elucidated. To better understand the actions of gliptins, the effects of linagliptin on the behaviour of immortalized human podocytes and mesangial cells were evaluated.

EXPERIMENTAL APPROACH

The expression of DPP4 was measured at both the mRNA and protein levels. The effects of linagliptin on DPP4 activity, cell growth and cell cycle progression were determined. The contribution of the stromal cell-derived factor-1- CXCR4/CXCR7 signalling pathways was evaluated by studying the effects of AMD3100 (a CXCR4 antagonist and CXCR7 agonist) alone and in combination with linagliptin. The contribution of ERK1/2 activation was analysed by studying the effects of the MAPK kinase 1/2 inhibitor AZD6244.

KEY RESULTS

DPP4 was highly expressed in podocytes. The activity of DPP4 and podocyte growth were reduced by linagliptin. The effects of sitagliptin on podocyte growth were similar to those of linagliptin, were associated with inhibition of cell proliferation and mimicked by AMD3100. Moreover, linagliptin and AMD3100 were found to have a synergistic interaction, whereas no interaction was seen between linagliptin and AZD6244.

CONCLUSIONS AND IMPLICATIONS

Our cultures of human glomerular cells represent a reliable system for investigating the actions of gliptins. Moreover, DPP4 contributes to the regulation of podocyte behaviour. Inhibition of DPP4 in podocytes could underlie the effects of linagliptin on glomerular cells.

The expression of proline-specific enzymes in the human lung

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

Enzyme-Histochemistry Technique for Visualizing the Dipeptidyl-Peptidase IV (DPP-IV) Activity in the Liver Biliary Tree

Dipeptidyl-peptidase IV is an enzyme involved in a lot of biochemical processes, where it modifies a number of regulatory proteins by removing the terminal peptides by hydrolysis. Here we describe a histochemical method to demonstrate with accuracy and precision its in situ activity on cryostatic section of Wistar rat liver by means of a simultaneous azo-coupling method.

The dipeptidyl peptidase-4 inhibitor teneligliptin reduces kidney damage from hypercholesterolemia in apolipoprotein E-deficient mice

Hypercholesterolemia is a well-established risk factor for kidney injury that can lead to chronic kidney disease (CKD).

Circulating fibroblast activation protein and dipeptidyl peptidase 4 in rheumatoid arthritis and systemic sclerosis

AIM

To quantify circulating fibroblast activation protein (cFAP) and dipeptidyl peptidase 4 (cDPP4) protease activities in patients with rheumatoid arthritis (RA), systemic sclerosis (SSc), and a control group with mechanical back pain and to correlate plasma levels with disease characteristics.

METHODS

Plasma was collected from patients with RA (n = 73), SSc (n = 37) and control subjects (n = 26). DPP4 and FAP were quantified using specific enzyme activity assays.

RESULTS

Median cDPP4 was significantly lower in the RA group (P = 0.02), and SSc group (P = 0.002) compared with controls. There were no significant differences in median cFAP between the three groups. DPP4 and FAP demonstrated a negative correlation with inflammatory markers and duration of disease. There were no associations with disease subtypes in RA, including seropositive and erosive disease. Decreased cDPP4 was found in SSc patients with myositis. Plasma FAP was lower in RA patients receiving prednisone (P = 0.001) or leflunomide (P = 0.04), but higher with biologic agents (P = 0.01). RA patients receiving leflunomide also had decreased cDPP4 (P = 0.014). SSc patients receiving prednisone (P = 0.02) had lower cDPP4 but there was no association with cFAP.

CONCLUSIONS

No association was found between cFAP and RA or SSc. Plasma DPP4 was decreased in RA and SSc when compared with controls. cDPP4 and cFAP correlated negatively with inflammatory markers and there were no significant correlations with disease characteristics in this RA cohort.

CD8+ T Cells and Macrophages Regulate Pathogenesis in a Mouse Model of Middle East Respiratory Syndrome

Middle East respiratory syndrome coronavirus (MERS-CoV) is an important emerging pathogen that was first described in 2012. While the cell surface receptor for MERS-CoV has been identified as dipeptidyl peptidase 4 (DPP4), the mouse DPP4 homologue does not allow virus entry into cells. Therefore, development of mouse models of MERS-CoV has been hampered by the fact that MERS-CoV does not replicate in commonly available mouse strains. We have previously described a mouse model in which mDPP4 was replaced with hDPP4 such that hDPP4 is expressed under the endogenous mDPP4 promoter. In this study, we used this mouse model to analyze the host response to MERS-CoV infection using immunological assays and transcriptome analysis. Depletion of CD4⁺ T cells, CD8⁺ T cells, or macrophages has no effect on MERS-CoV replication in the lungs of infected mice. However, we found that depletion of CD8⁺ T cells protects and depletion of macrophages exacerbates MERS-CoV-induced pathology and clinical symptoms of disease. Overall, we demonstrate an important role for the inflammatory response in regulating MERS-CoV pathogenesis in vivo IMPORTANCE: The Middle East respiratory syndrome coronavirus (MERS-CoV) is a highly pathogenic respiratory virus that emerged from zoonotic sources in 2012. Human infections are still occurring throughout Saudi Arabia at a 38% case fatality rate, with the potential for worldwide spread via air travel. In this work, we identify the host response to the virus and identify inflammatory pathways and cell populations that are critical for protection from severe lung disease. By understanding the immune response to MERS-CoV we can develop targeted therapies to inhibit pathogenesis in the future.

Hepatic Dipeptidyl Peptidase-4 Controls Pharmacokinetics of Vildagliptin In Vivo

The main route of elimination of vildagliptin, which is an inhibitor of dipeptidyl peptidase-4 (DPP-4), in humans is cyano group hydrolysis to produce a carboxylic acid metabolite M20.7. Our in vitro study previously demonstrated that DPP-4 itself greatly contributed to the hydrolysis of vildagliptin in mouse, rat, and human livers. To investigate whether hepatic DPP-4 contributes to the hydrolysis of vildagliptin in vivo, in the present study, we conducted in vivo pharmacokinetics studies of vildagliptin in mice coadministered with vildagliptin and sitagliptin, which is another DPP-4 inhibitor, and also in streptozotocin (STZ)-induced diabetic mice. The area under the plasma concentration-time curve (AUC) value of M20.7 in mice coadministered with vildagliptin and sitagliptin was significantly lower than that in mice administered vildagliptin alone (P < 0.01). Although plasma DPP-4 expression level was increased 1.9-fold, hepatic DPP-4 activity was decreased in STZ-induced diabetic mice. The AUC values of M20.7 in STZ-induced diabetic mice were lower than those in control mice (P < 0.01). Additionally, the AUC values of M20.7 significantly positively correlated with hepatic DPP-4 activities in the individual mice (Rs = 0.943, P < 0.05). These findings indicated that DPP-4 greatly contributed to the hydrolysis of vildagliptin in vivo and that not plasma, but hepatic DPP-4 controlled pharmacokinetics of vildagliptin. Furthermore, enzyme assays of 23 individual human liver samples showed that there was a 3.6-fold interindividual variability in vildagliptin-hydrolyzing activities. Predetermination of the interindividual variability of hepatic vildagliptin-hydrolyzing activity might be useful for the prediction of blood vildagliptin concentrations in vivo.

Regulation of Chemokine Activity - A Focus on the Role of Dipeptidyl Peptidase IV/CD26

Chemokines are small, chemotactic proteins that play a crucial role in leukocyte migration and are, therefore, essential for proper functioning of the immune system. Chemokines exert their chemotactic effect by activation of chemokine receptors, which are G protein-coupled receptors (GPCRs), and interaction with glycosaminoglycans (GAGs). Furthermore, the exact chemokine function is modulated at the level of posttranslational modifications. Among the different types of posttranslational modifications that were found to occur in vitro and in vivo, i.e., proteolysis, citrullination, glycosylation, and nitration, NH₂-terminal proteolysis of chemokines has been described most intensively. Since the NH₂-terminal chemokine domain mediates receptor interaction, NH₂-terminal modification by limited proteolysis or amino acid side chain modification can drastically affect their biological activity. An enzyme that has been shown to provoke NH₂-terminal proteolysis of various chemokines is dipeptidyl peptidase IV or CD26. This multifunctional protein is a serine protease that preferably cleaves dipeptides from the NH₂-terminal region of peptides and proteins with a proline or alanine residue in the penultimate position. Various chemokines possess such a proline or alanine residue, and CD26-truncated forms of these chemokines have been identified in cell culture supernatant as well as in body fluids. The effects of CD26-mediated proteolysis in the context of chemokines turned out to be highly complex. Depending on the chemokine ligand, loss of these two NH₂-terminal amino acids can result in either an increased or a decreased biological activity, enhanced receptor specificity, inactivation of the chemokine ligand, or generation of receptor antagonists. Since chemokines direct leukocyte migration in homeostatic as well as pathophysiologic conditions, CD26-mediated proteolytic processing of these chemotactic proteins may have significant consequences for appropriate functioning of the immune system. After introducing the chemokine family together with the GPCRs and GAGs, as main interaction partners of chemokines, and discussing the different forms of posttranslational modifications, this review will focus on the intriguing relationship of chemokines with the serine protease CD26.

A step towards clinical application of acellular matrix: A clue from macrophage polarization

The outcome of tissue engineered organ transplants depends on the capacity of the biomaterial to promote a pro-healing response once implanted in vivo. Multiple studies, including ours, have demonstrated the possibility of using the extracellular matrix (ECM) of animal organs as platform for tissue engineering and more recently, discarded human organs have also been proposed as scaffold source. In contrast to artificial biomaterials, natural ECM has the advantage of undergoing continuous remodeling which allows adaptation to diverse conditions. It is known that natural matrices present diverse immune properties when compared to artificial biomaterials. However, how these properties compare between diseased and healthy ECM and artificial scaffolds has not yet been defined. To answer this question, we used decellularized renal ECM derived from WT mice and from mice affected by Alport Syndrome at different time-points of disease progression as a model of renal failure with extensive fibrosis. We characterized the morphology and composition of these ECMs and compared their in vitro effects on macrophage activation with that of synthetic scaffolds commonly used in the clinic (collagen type I and poly-L-(lactic) acid, PLLA). We showed that ECM derived from Alport kidneys differed in fibrous protein deposition and cytokine content when compared to ECM derived from WT kidneys. Yet, both WT and Alport renal ECM induced macrophage differentiation mainly towards a reparative (M2) phenotype, while artificial biomaterials towards an inflammatory (M1) phenotype. Anti-inflammatory properties of natural ECMs were lost when homogenized, hence three-dimensional structure of ECM seems crucial for generating an anti-inflammatory response. Together, these data support the notion that natural ECM, even if derived from diseased kidneys promote a M2 protolerogenic macrophage polarization, thus providing novel insights on the applicability of ECM obtained from discarded organs as ideal scaffold for tissue engineering.

DPP-4 inhibitors in diabetic complications: role of DPP-4 beyond glucose control

Dipeptidyl peptidase-4 (DPP-4) inhibitors (gliptins) are an emerging class of antidiabetic drugs that constitutes approximately fifty percent of the market share of the oral hypoglycemic drugs. Its mechanism of action for lowering blood glucose is essentially via inhibition of the rapid degradation of incretin hormones, such as glucagon-like peptide (GLP)-1 and gastric inhibitory polypeptide (GIP), thus the plasma concentration of GLP-1 increases, which promotes insulin secretion from the pancreatic β cells and suppresses glucagon secretion from the α cells. In addition to the direct actions on the pancreas, GLP-1 exhibits diverse actions on different tissues through its action on GLP-1 receptor, which is expressed ubiquitously. Moreover, DPP-4 has multiple substrates besides GLP-1 and GIP, including cytokines, chemokines, neuropeptides, and growth factors, which are involved in many pathophysiological conditions. Recently, it was suggested that DPP-4 is a new adipokine secreted from the adipose tissue, which plays an important role in the regulation of the endocrine function in obesity-associated type 2 diabetes. Consequently, DPP-4 inhibitors have been reported to exhibit cytoprotective functions against various diabetic complications affecting the liver, heart, kidneys, retina, and neurons. This review outlines the current understanding of the effect of DPP-4 inhibitors on the complications associated with type 2 diabetes, such as liver steatosis and inflammation, dysfunction of the adipose tissue and pancreas, cardiovascular diseases, nephropathy, and neuropathy in preclinical and clinical studies.

The pathological significance of dipeptidyl peptidase-4 in endothelial cell homeostasis and kidney fibrosis

Endothelial dysfunction and tubulointerstitial fibrosis are characteristics of diabetic kidneys. Recent evidence has suggested that the diabetic kidney is associated with dipeptidyl peptidase (DPP)-4 overexpression in endothelial cells. Several insults can induce endothelial cells to alter their phenotype into a mesenchymal-like phenotype via endothelial-mesenchymal transition (EndMT), which plays pivotal roles in tissue fibrosis. We have recently revealed the fibrogenic role of DPP-4 through the induction of EndMT in diabetic kidneys. This review mainly focuses on the biological and pathological significance of DPP-4 overexpression in endothelial cells through the mechanisms of endothelial homeostasis defects, EndMT, and kidney fibrosis.