Distribution of adenosine deaminase complexing protein (ADCP) in human tissues

Saxagliptin Cardiotoxicity in Chronic Heart Failure: The Role of DPP4 in the Regulation of Neuropeptide Tone

Dipeptidyl-peptidase-4 (DPP4) inhibitors are novel medicines for diabetes. The SAVOR-TIMI-53 clinical trial revealed increased heart-failure-associated hospitalization in saxagliptin-treated patients. Although this side effect could limit therapeutic use, the mechanism of this potential cardiotoxicity is unclear. We aimed to establish a cellular platform to investigate DPP4 inhibition and the role of its neuropeptide substrates substance P (SP) and neuropeptide Y (NPY), and to determine the expression of DDP4 and its neuropeptide substrates in the human heart. Western blot, radio-, enzyme-linked immuno-, and RNA scope assays were performed to investigate the expression of DPP4 and its substrates in human hearts. Calcein-based viability measurements and scratch assays were used to test the potential toxicity of DPP4 inhibitors. Cardiac expression of DPP4 and NPY decreased in heart failure patients. In human hearts, DPP4 mRNA is detectable mainly in cardiomyocytes and endothelium. Treatment with DPP4 inhibitors alone/in combination with neuropeptides did not affect viability but in scratch assays neuropeptides decreased, while saxagliptin co-administration increased fibroblast migration in isolated neonatal rat cardiomyocyte-fibroblast co-culture. Decreased DPP4 activity takes part in the pathophysiology of end-stage heart failure. DPP4 compensates against the elevated sympathetic activity and altered neuropeptide tone. Its inhibition decreases this adaptive mechanism, thereby exacerbating myocardial damage.

Cellular expression of CD26/dipeptidyl peptidase IV

Dipeptidyl peptidase 4 (DPP4), a serine protease expressed on luminal and apical cell membrane, is identical to the lymphocyte cell surface protein CD26. DPP4 rapidly deactivates hormones and cytokines by cleaving their NH₂-terminal dipeptides. Its functions are based on membrane digestion and/or binding of bioactive peptides, signal molecules, and extracellular matrix components. The soluble form is also present in body fluids such as serum, urine, semen, and synovial fluid. The extremely broad distribution of CD26/DPP4 indicates its divergent roles depending on cell type and activated conditions. The cellular localization was earlier examined by enzyme histochemistry and subsequently by immunohistochemistry. Although immunohistochemical analyses are higher in specificity and easier to use at electron microscopic levels than enzyme histochemistry, the immunoreaction is considerably affected by the animal species, types of tissue sections, and specificity of antibodies. Understanding of the functional significance and advancement of its clinical use (diagnosis and treatment of diseases) require precise information on the cellular distribution including subcellular localization and pathological changes. This short review summarizes in particular immunohistochemical findings on CD26/DPP4.

Anti-inflammatory Effects of Empagliflozin and Gemigliptin on LPS-Stimulated Macrophage via the IKK/NF-κB, MKK7/JNK, and JAK2/STAT1 Signalling Pathways

Background

Sodium-glucose cotransporter 2 (SGLT2) and dipeptidyl peptidase-4 (DPP-4) inhibitors are glucose-lowering drugs whose anti-inflammatory properties have recently become useful in tackling metabolic syndromes in chronic inflammatory diseases, including diabetes and obesity. We investigated whether empagliflozin (SGLT2 inhibitor) and gemigliptin (DPP-4 inhibitor) improve inflammatory responses in macrophages, identified signalling pathways responsible for these effects, and studied whether the effects can be augmented with dual empagliflozin and gemigliptin therapy.

Methods

RAW 264.7 macrophages were first stimulated with lipopolysaccharide (LPS), then cotreated with empagliflozin, gemigliptin, or empagliflozin plus gemigliptin. We conducted quantitative RT-PCR (qRT-PCR) to determine the most effective anti-inflammatory doses without cytotoxicity. We performed ELISA and qRT-PCR for inflammatory cytokines and chemokines and flow cytometry for CD80, the M1 macrophage surface marker, to evaluate the anti-inflammatory effects of empagliflozin and gemigliptin. NF-κB, MAPK, and JAK2/STAT signalling pathways were examined via Western blotting to elucidate the molecular mechanisms of anti-inflammation.

Results

LPS-stimulated CD80⁺ M1 macrophages were suppressed by coincubation with empagliflozin, gemigliptin, and empagliflozin plus gemigliptin, respectively. Empagliflozin and gemigliptin (individually and combined) inhibited prostaglandin E₂ (PGE₂) release and COX-2, iNOS gene expression in LPS-stimulated RAW 264.7 macrophages. These three treatments also attenuated the secretion and mRNA expression of proinflammatory cytokines, such as TNF-α, IL-1β, IL-6, and IFN-γ, and proinflammatory chemokines, such as CCL3, CCL4, CCL5, and CXCL10. All of them blocked NF-κB, JNK, and STAT1/3 phosphorylation through IKKα/β, MKK4/7, and JAK2 signalling.

Conclusions

Our study demonstrated the anti-inflammatory effects of empagliflozin and gemigliptin via IKK/NF-κB, MKK7/JNK, and JAK2/STAT1 pathway downregulation in macrophages. In all cases, combined empagliflozin and gemigliptin treatment showed greater anti-inflammatory properties.

Changes in Saliva Analytes in Dairy Cows during Peripartum: A Pilot Study

Simple Summary

The use of saliva as a biological fluid to assess welfare and health status is gaining interest nowadays since it can be collected by non-invasive methods without specialized staff. The possibility of measuring analytes in saliva by techniques adapted to automated analyzers is cost-effective, reliable, and replicable. These analytes can provide information useful for the evaluation of welfare and health in dairy cows. In this pilot study, a total of 26 salivary analytes were measured in healthy dairy cows along their peripartum period to assess possible changes and associations with their inflammatory, energy, and milk yield status. Salivary analytes related to stress (cortisol, salivary alpha-amylase, butyrylcholinesterase, and total esterase), immunity (adenosine deaminase), oxidative status (Trolox equivalent antioxidant capacity and the advanced oxidation protein products), and general metabolism (creatine kinase, γ-glutamyl transferase, urea, triglycerides, glucose, and lactate) had significant changes throughout this period. This study indicated that the saliva of dairy cows shows changes in its composition during the transition period and potentially can be a source of biomarkers for monitoring health and welfare.

Abstract

This pilot study aimed to study the possible changes in a profile of 26 salivary analytes in thirteen healthy dairy cows along their peripartum period. Analytes associated with the stress (salivary cortisol, salivary alpha-amylase, butyrylcholinesterase, and total esterase), inflammation (adenosine deaminase), oxidative status (total antioxidant capacity and the advanced oxidation protein products), and general metabolism (creatine kinase, γ-glutamyl transferase, urea, triglycerides, glucose, and lactate) varied along the sampling times. A positive correlation between the white blood cells counts, and the lipase, Trolox equivalent antioxidant capacity, advanced oxidation protein products, and lactate levels in saliva were observed at the delivery. A linear association between selected salivary analytes at different sampling times and the milk yield after calving was observed. In conclusion, in our experimental conditions, it was observed that the peripartum period in dairy cows can induce changes in salivary analytes. Some of them were associated with inflammatory status and the capacity of milk production after calving.

Apigenin upregulation of CD26/DPPIV on colon epithelial cells requires inhibition of casein kinase 2

CD26/DPPIV is a cell surface glycoprotein found on cells of the intestinal epithelium including those of the colon. We have previously shown that the dietary flavone apigenin (4',5,7-trihydroxyflavone) upregulates CD26/DPPIV on colon cells. Flavonoids such as apigenin interfere with the action of multiple cellular protein kinases and have the capacity to modulate the cell exterior and its ability to interface with the local environment through different signaling pathways. We show here that the ability of apigenin to upregulate CD26/DPPIV is exerted through and requires the activity of casein kinase 2 (CK2). Inhibitors of CK2 that are distinct from apigenin (emodin, 6-methyl-1,3,8-trihydroxyanthraquinone; TBB, 4,5,6,7-tetrabromobenzotriazole; and DRB, 5,6-dichlorobenzimidazole 1-β-D-ribofuranoside) showed a dose-dependent ability to increase CD26/DPPIV and had the same maximal effect when combined with apigenin at submaximal concentrations. Knockdown of CK2 with siRNA abrogated the ability of apigenin to upregulate CD26/DPPIV. Apigenin treatment of cells had no effect on the levels of CK2 protein, consistent with an inhibition of activity of the enzyme. Apigenin's upregulation of CD26/DPPIV in differentiated human colon epithelial cells depends upon inhibition of CK2 activity. This is a key step in enabling apigenin's ability to regulate the functions of intestinal epithelial cells.

Degranulation of human cytotoxic lymphocytes is a major source of proteolytically active soluble CD26/DPP4

Dipeptidyl peptidase 4 (DPP4, CD26) is a serine protease detected on several immune cells and on epithelial cells of various organs. Besides the membrane-bound enzyme, a catalytically active soluble form (sCD26/DPP4) is detected in several body fluids. Both variants cleave off dipeptides from the N-termini of various chemokines, neuropeptides, and hormones. CD26/DPP4 plays a fundamental role in the regulation of blood glucose levels by inactivating insulinotropic incretins and CD26/DPP4 inhibitors are thus routinely used in diabetes mellitus type 2 therapy to improve glucose tolerance. Such inhibitors might also prevent the CD26/DPP4-mediated inactivation of the T-cell chemoattractant CXCL10 released by certain tumors and thus improve anti-tumor immunity and immunotherapy. Despite its implication in the regulation of many (patho-)physiological processes and its consideration as a biomarker and therapeutic target, the cellular source of sCD26/DPP4 remains highly debated and mechanisms of its release are so far unknown. In line with recent reports that activated T lymphocytes could be a major source of sCD26/DPP4, we now demonstrate that CD26/DPP4 is stored in secretory granules of several major human cytotoxic lymphocyte populations and co-localizes with effector proteins such as granzymes, perforin, and granulysin. Upon stimulation, vesicular CD26/DPP4 is rapidly translocated to the cell surface in a Ca2+-dependent manner. Importantly, activation-induced degranulation leads to a massive release of proteolytically active sCD26/DPP4. Since activated effector lymphocytes serve as a major source of sCD26/DPP4, these results might explain the observed disease-associated alterations of sCD26/DPP4 serum levels and also indicate a so far unknown role of CD26/DPP4 in lymphocyte-mediated cytotoxicity.

Bullous Pemphigoid Associated with the Dipeptidyl Peptidase-4 Inhibitor Sitagliptin in a Patient with Liver Cirrhosis Complicated with Rapidly Progressive Hepatocellular Carcinoma

A 78-year-old man presented with cutaneous blisters of the limbs and abdominal distension. He had been treated for various diseases, including liver cirrhosis. He had begun receiving sitagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, for diabetes mellitus three years before the hospitalization. A skin biopsy demonstrated bullous pemphigoid. Ultrasonography (US) revealed multiple liver tumors, although he had been receiving regular US studies. We stopped sitagliptin and started insulin and corticosteroids. However, his renal dysfunction progressed, and he died 14 days after the hospitalization. We should therefore be careful of various complications, including bullous pemphigoid and progression of tumors, when using DPP-4 inhibitors.

Liraglutide alters DPP4 in the circumvallate papillae of type 2 diabetic rats

Liraglutide, a human glucagon-like peptide (GLP1) analog that partially inhibits dipeptidyl-peptidase 4 (DPP4), can decrease glucose levels and suppress appetite in patients with type 2 diabetes (T2DM). GLP1 and its receptor (GLP1R) also exist in the taste buds of rodents and regulate taste sensitivity. DPP4, a protease, functions in homeostasis of blood glucose, lipids, and body weight. Interactions among GLP1, GLP1R, and DPP4 likely affect taste and food-intake behavior. The aim of the present study was to investigate DPP4 expression in the taste buds of the circumvallate papillae (CV) in T2DM rats, and determine the effects of liraglutide treatment. Rats were divided into diabetic control (T2DM-C), normal control (NC), and liraglutide-treated diabetic (T2DM+LIR) groups. DPP4 localization and gene expression levels were evaluated by immunohistochemistry and quantitative reverse transcription-polymerase chain reaction (RT-qPCR), respectively. DPP4 immunoreactive cells were localized in the taste buds of the rat CV. RT-qPCR showed significantly higher expression of Dpp4 mRNA in both the taste buds and hypothalamus of T2DM-C rats compared with NC rats. However, in the T2DM+LIR group, Dpp4 expression differed between the taste buds and hypothalamus, with significantly higher and lower levels compared with the T2DM-C group, respectively. Dpp4 mRNA expression is increased in the taste buds of the CV of T2DM rats. Liraglutide simultaneously upregulated (taste buds) and downregulated (hypothalamus) Dpp4 expression in T2DM rats. Therefore, DPP4 may be closely associated with the anorexigenic signaling and weight loss induced by the treatment of liraglutide in type 2 diabetic patients.

Localization of dipeptidyl peptidase-4 (CD26) to human pancreatic ducts and islet alpha cells

AIM

DPP-4/CD26 degrades the incretins GLP-1 and GIP. The localization of DPP-4 within the human pancreas is not well documented but is likely to be relevant for understanding incretin function. We aimed to define the cellular localization of DPP-4 in the human pancreas from cadaveric organ donors with and without diabetes.

METHODS

Pancreas was snap-frozen and immunoreactive DPP-4 detected in cryosections using the APAAP technique. For co-localization studies, pancreas sections were double-stained for DPP-4 and proinsulin or glucagon and scanned by confocal microscopy. Pancreata were digested and cells in islets and in islet-depleted, duct-enriched digests analyzed for expression of DPP-4 and other markers by flow cytometry.

RESULTS

DPP-4 was expressed by pancreatic duct and islet cells. In pancreata from donors without diabetes or with type 2 diabetes, DPP-4-positive cells in islets had the same location and morphology as glucagon-positive cells, and the expression of DPP-4 and glucagon overlapped. In donors with type 1 diabetes, the majority of residual cells in islets were DPP-4-positive.

CONCLUSION

In the human pancreas, DPP-4 expression is localized to duct and alpha cells. This finding is consistent with the view that DPP-4 regulates exposure to incretins of duct cells directly and of beta cells indirectly in a paracrine manner.

Dipeptidyl peptidase IV as a potential target for selective prodrug activation and chemotherapeutic action in cancers

The efficacy of chemotherapeutic drugs is often offset by severe side effects attributable to poor selectivity and toxicity to normal cells. Recently, the enzyme dipeptidyl peptidase IV (DPPIV) was considered as a potential target for the delivery of chemotherapeutic drugs. The purpose of this study was to investigate the feasibility of targeting chemotherapeutic drugs to DPPIV as a strategy to enhance their specificity. The expression profile of DPPIV was obtained for seven cancer cell lines using DNA microarray data from the DTP database, and was validated by RT-PCR. A prodrug was then synthesized by linking the cytotoxic drug melphalan to a proline-glycine dipeptide moiety, followed by hydrolysis studies in the seven cell lines with a standard substrate, as well as the glycyl-prolyl-melphalan (GP-Mel). Lastly, cell proliferation studies were carried out to demonstrate enzyme-dependent activation of the candidate prodrug. The relative RT-PCR expression levels of DPPIV in the cancer cell lines exhibited linear correlation with U95Av2 Affymetrix data (r(2) = 0.94), and with specific activity of a standard substrate, glycine-proline-p-nitroanilide (r(2) = 0.96). The significantly higher antiproliferative activity of GP-Mel in Caco-2 cells (GI₅₀ = 261 μM) compared to that in SK-MEL-5 cells (GI₅₀ = 807 μM) was consistent with the 9-fold higher specific activity of the prodrug in Caco-2 cells (5.14 pmol/min/μg protein) compared to SK-MEL-5 cells (0.68 pmol/min/μg protein) and with DPPIV expression levels in these cells. Our results demonstrate the great potential to exploit DPPIV as a prodrug activating enzyme for efficient chemotherapeutic drug targeting.

Co-expression of the homologous proteases fibroblast activation protein and dipeptidyl peptidase-IV in the adult human Langerhans islets

Fibroblast activation protein (FAP, seprase, EC 3.4.21.B28) and dipeptidyl peptidase-IV (DPP-IV, CD26, EC 3.4.14.5) are homologous serine proteases implicated in the modulation of the bioavailability and thus the function of a number of biologically active peptides. In spite of their generally nonoverlapping expression patterns, DPP-IV and FAP are co-expressed and probably co-regulated in certain cell types suggesting that for some biological processes their functional synergy is essential. By an in situ enzymatic activity assay, we show an abundant DPP-IV-like enzymatic activity sensitive to a highly specific DPP-IV inhibitor sitagliptin and corresponding DPP-IV immunoreactivity in the adult human islets of Langerhans. Moreover, the homologous protease FAP was present in the human endocrine pancreas and was co-expressed with DPP-IV. DPP-IV and FAP were found in the pancreatic alpha cells as determined by the co-localization with glucagon immunoreactivity. In summary, we show abundant enzymatic activity of the canonical DPP-IV (CD26) in Langerhans islets in the natural tissue context and demonstrate for the first time the co-expression of FAP and DPP-IV in pancreatic alpha cells in adult humans. Given their ability to proteolytically modify several biologically active peptides, both proteases have the potential to modulate the paracrine signaling in the human Langerhans islets.

Mechanisms regulating airway nucleotides

In the respiratory system, extracellular nucleotides and nucleosides serve as signaling molecules for a wide spectrum of biological functions regulating airway defenses against infection and toxic material. Their concentrations are controlled by a complex network of cell surface enzymes named ectonucleotidases. This highly integrated metabolic network combines the activities of three dephosphorylating ectonucleotidases, namely nucleoside triphosphate diphosphohydrolases (NTPDases), nucleotide pyrophosphatase/phosphodiesterases (NPPs) and alkaline phosphatases (APs). Extracellular nucleotides are also inter-converted by the transphosphorylating activities of ecto adenylate kinase (ectoAK) and nucleoside diphosphokinase (NDPK). Different cell types use specific combinations of ectonucleotidases to regulate local concentrations of P2 receptor agonists (ATP, UTP, ADP and UDP). In addition, they provide AMP for the activity of ecto 5'-nucleotidase (ecto 5'-NT; CD73), which produces the P1 receptor agonist: adenosine (ADO). Finally, mechanisms are in place to prevent the accumulation of airway ADO, namely adenosine deaminases and nucleoside transporters. This chapter reviews the properties of each enzyme and transporter, and the current knowledge on their distribution and regulation in the airways.

Reduced levels of active GLP-1 in patients with cystic fibrosis with and without diabetes mellitus

Glucagon like peptide 1 (GLP-1) is an incretin hormone released as a bioactive peptide from intestinal L-cells in response to eating. It acts on target cells and exerts several functions as stimulating insulin and inhibiting glucagon. It is quickly deactivated by the serine protease dipeptidyl peptidase IV (DPP-IV) as an important regulatory mechanism. GLP-1 analogues are used as antidiabetic drugs in patients with type 2 diabetes. We served patients with cystic fibrosis (CF, n=29), cystic fibrosis related diabetes (CFRD, n=19) and healthy controls (n=18) a standardized breakfast (23 g protein, 25 g fat and 76 g carbohydrates) after an overnight fasting. Blood samples were collected before meal as well as 15, 30, 45 and 60 min after the meal in tubes prefilled with a DPP-IV inhibitor. The aim of the study was to compare levels of GLP-1 in patients with CF, CFRD and in healthy controls. We found that active GLP-1 was significantly decreased in patients with CF and CFRD compared to in healthy controls (p<0.01). However, levels in patients with CFRD tended to be lower but were not significantly lower than in patients with CF without diabetes (p=0.06). Total GLP-1 did not differ between the groups, which points to that the inactive form of GLP-1 is more pronounced in CF patients. The endogenous insulin production (measured by C-peptide) was significantly lower in patients with CFRD as expected. However, levels in non-diabetic CF patients did not differ from the controls. We suggest that the decreased levels of GLP-1 could affect the progression toward CFRD and that more studies need to be performed in order to evaluate a possible treatment with GLP-1 analogues in CF-patients.

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

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

New bioinformatics approach to analyze gene expressions and signaling pathways reveals unique purine gene dysregulation profiles that distinguish between CD and UC

BACKGROUND

Expression of purine genes is modulated by inflammation or experimental colitis and altered expression leads to disrupted gut function. We studied purine gene dysregulation profiles in inflammatory bowel disease (IBD) and determined whether they can distinguish between Crohn's disease (CD) and ulcerative colitis (UC) using Pathway Analysis and a new Comparative Analysis of Gene Expression and Selection (CAGES) method.

METHODS

Raw datasets for 22 purine genes and 36 probe-sets from National Center for Biotechnology Information (NCBI) GEO (Gene Expression Omnibus) (http://www.ncbi.nlm.nih.gov/projects/geo/) were analyzed by National Cancer Institute (NCI) Biological Resources Branch (BRB) array tools for random-variance of multiple/36 t-tests in colonic mucosal biopsies or peripheral blood mononuclear cells (PBMCs) of CD, UC or control subjects. Dysregulation occurs in 59% of purine genes in IBD including ADORA3, CD73, ADORA2A, ADORA2B, ADAR, AMPD2, AMPD3, DPP4, P2RY5, P2RY6, P2RY13, P2RY14, and P2RX5.

RESULTS

In CD biopsies, expression of ADORA3, AMPD3, P2RY13, and P2RY5 were negatively correlated with acute inflammatory score, Crohn's Disease Activity Index (CDAI) or disease chronicity; P2RY14 was positively correlated in UC. In mucosal biopsies or PBMCs, CD and UC were distinguished by unique patterns of dysregulation (up- or downregulation) in purine genes. Purine gene dysregulation differs between PBMCs and biopsies and possibly between sexes for each disease. Ingenuity Pathway Analysis (IPA) revealed significant associations between alterations in the expression of CD73 (upregulation) or ADORA3 (downregulation) and inflammatory or purine genes (<or=10% of 57 genes) as well as G-protein coupled receptors, cAMP-dependent, and inflammatory pathways; IPA distinguishes CD from UC.

CONCLUSION

CAGES and Pathway Analysis provided novel evidence that UC and CD have distinct purine gene dysregulation signatures in association with inflammation, cAMP, or other signaling pathways. Disease-specific purine gene signature profiles and pathway associations may be of therapeutic, diagnostic, and functional relevance.

Serum adenosine deaminase levels in pancreatic diseases

BACKGROUND

Adenosine deaminase (ADA) is found in most tissues including the pancreas. Its role in inflammation and malignancy has been studied experimentally. To date, serum ADA levels in pancreatic diseases have not been studied before.

AIM

To assess the levels of ADA in patients with pancreatitis and cancer of the pancreas.

METHODOLOGY

Serum levels of ADA were investigated in 14 cases with acute pancreatitis (mean age 46 years; male/female 5/9), 38 with chronic pancreatitis (mean age 46 years; male/female 25/13), 21 with cancer of the pancreas (mean age 67 years; male/female 11/10), and 21 healthy controls (mean age 40 years; male/female 11/10). The ADA levels were also compared among patients with pancreatic cancer with regard to tumor size and localization and the presence of metastases. Correlation analysis between ADA and CA 19.9 was also performed.

RESULTS

Serum ADA levels were 12.66 (9.54-20.72), 12.51 (8.88-26.64), 15.36 (10.20-21.05) and 9.39 (6.58-11.84) U/l in patients with acute pancreatitis, chronic pancreatitis, pancreatic cancer, and healthy controls, respectively. Serum ADA levels were significantly higher in acute and chronic pancreatitis, and pancreatic cancer patients compared to the control group (p < 0.05). Pancreatic cancer patients had significantly higher serum ADA levels when compared with acute and chronic pancreatitis cases (p < 0.05). The serum ADA levels were comparable according to tumor size and location and the presence of metastases. There was a linear correlation between serum ADA and CA 19-9 levels (p = 0.027, r = 0.552).

CONCLUSIONS

Our data suggest that the ADA enzyme may play a role in inflammatory diseases of the pancreas. Serum ADA levels increase in pancreatic disorders especially in pancreatic cancer. It may be a serum marker for the diagnosis of pancreatic cancer.

Adenosine downregulates DPPIV on HT-29 colon cancer cells by stimulating protein tyrosine phosphatase(s) and reducing ERK1/2 activity via a novel pathway

The multifunctional cell-surface protein dipeptidyl peptidase IV (DPPIV/CD26) is aberrantly expressed in many cancers and plays a key role in tumorigenesis and metastasis. Its diverse cellular roles include modulation of chemokine activity by cleaving dipeptides from the chemokine NH(2)-terminus, perturbation of extracellular nucleoside metabolism by binding the ecto-enzyme adenosine deaminase, and interaction with the extracellular matrix by binding proteins such as collagen and fibronectin. We have recently shown that DPPIV can be downregulated from the cell surface of HT-29 colorectal carcinoma cells by adenosine, which is a metabolite that becomes concentrated in the extracellular fluid of hypoxic solid tumors. Most of the known responses to adenosine are mediated through four different subtypes of G protein-coupled adenosine receptors: A(1), A(2A), A(2B), and A(3). We report here that adenosine downregulation of DPPIV from the surface of HT-29 cells occurs independently of these classic receptor subtypes, and is mediated by a novel cell-surface mechanism that induces an increase in protein tyrosine phosphatase activity. The increase in protein tyrosine phosphatase activity leads to a decrease in the tyrosine phosphorylation of ERK1/2 MAP kinase that in turn links to the decline in DPPIV mRNA and protein. The downregulation of DPPIV occurs independently of changes in the activities of protein kinases A or C, phosphatidylinositol 3-kinase, other serine/threonine phosphatases, or the p38 or JNK MAP kinases. This novel action of adenosine has implications for our ability to manipulate adenosine-dependent events within the solid tumor microenvironment.

Reduced serum dipeptidyl peptidase-IV after metformin and pioglitazone treatments

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

Lineage relationship between LNCaP and LNCaP-derived prostate cancer cell lines

BACKGROUND

LNCaP and its derivative cell lines, which include C4-2 (and the related C4-2B) and CL1, are used as models of prostate cancer. Unlike LNCaP, the other cell lines show features of progressed disease such as metastatic capability and hormone independence. Analyses were done to determine if C4-2 or CL1 cells were selected from pre-existent subpopulations in LNCaP.

METHODS

Prostate cancer cells were characterized by cluster designation (CD) phenotyping. Specific cell populations were sorted by flow cytometry. DNA array analysis was used to probe differential gene expression.

RESULTS

CD phenotyping showed that CL1 and C4-2 (and C4-2B) were very dissimilar, and C4-2 was more similar to LNCaP. One common difference between LNCaP and its derivatives was CD26, in which virtually all C4-2 or CL1 cells were CD26(+) but only approximately 10% of LNCaP cells were CD26(+). The CD26(+) subpopulation of LNCaP was isolated and cultured in vitro. After culture, a high percentage of the cells (descended from the sorted cells) were CD26(+), in contrast to those sorted by CD13 or CD44. The cultured CD13 and CD44 populations did not show a high percentage of CD13(+) and CD44(+) cells, respectively. CD13 and CD44 are markers, in addition to CD26, for CL1 but not for C4-2.

CONCLUSIONS

C4-2 arose probably from CD26(+) LNCaP cells, while CL1 arose de novo.

Adenosine down-regulates the surface expression of dipeptidyl peptidase IV on HT-29 human colorectal carcinoma cells: implications for cancer cell behavior

Dipeptidyl peptidase IV (DPPIV) is a multifunctional cell-surface protein that, as well as having dipeptidase activity, is the major binding protein for adenosine deaminase (ADA) and also binds extracellular matrix proteins such as fibronectin and collagen. It typically reduces the activity of chemokines and other peptide mediators as a result of its enzymatic activity. DPPIV is aberrantly expressed in many cancers, and decreased expression has been linked to increases in invasion and metastasis. We asked whether adenosine, a purine nucleoside that is present at increased levels in the hypoxic tumor microenvironment, might affect the expression of DPPIV at the cell surface. Treatment with a single dose of adenosine produced an initial transient (1 to 4 hours) modest (approximately 10%) increase in DPPIV, followed by a more profound (approximately 40%) depression of DPPIV protein expression at the surface of HT-29 human colon carcinoma cells, with a maximal decline being reached after 48 hours, and persisting for at least a week with daily exposure to adenosine. This down-regulation ofDPPIV occurred at adenosine concentrations comparable to those present within the extracellular fluid of colorectal tumors growing in vivo, and was not elicited by inosine or guanosine. Neither cellular uptake of adenosine nor its phosphorylation was necessary for the down-regulation of DPPIV. The decrease in DPPIV protein at the cell surface was paralleled by decreases in DPPIV enzyme activity, binding of ADA, and the ability of the cells to bind to and migrate on cellular fibronectin. Adenosine, at concentrations that exist within solid tumors, therefore acts at the surface of colorectal carcinoma cells to decrease levels and activities of DPPIV. This down-regulation of DPPIV may increase the sensitivity of cancer cells to the tumor-promoting effects of adenosine and their response to chemokines and the extracellular matrix, facilitating their expansion and metastasis.

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.

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

CD26 has proved interesting in the fields of immunology, endocrinology, cancer biology and nutrition owing to its ubiquitous and unusual enzyme activity. This dipeptidyl aminopeptidase (DPP IV) activity generally inactivates but sometimes alters or enhances the biological activities of its peptide substrates, which include several chemokines. CD26 costimulates both the CD3 and the CD2 dependent T-cell activation and tyrosine phosphorylation of TCR/CD3 signal transduction pathway proteins. CD26 in vivo has integral membrane protein and soluble forms. Soluble CD26 is at significant levels in serum, these levels alter in many diseases and soluble CD26 can modulate in vitro T-cell proliferation. CD26, being an adenosine deaminase binding protein (ADAbp), functions as a receptor for ADA on lymphocytes. The focus of this review is the structure and function of CD26 and the influence of its ligand binding activity on T-cell proliferation and the T cell costimulatory activity of CD26.

The binding site of human adenosine deaminase for CD26/Dipeptidyl peptidase IV: the Arg142Gln mutation impairs binding to cd26 but does not cause immune deficiency

Human, but not murine, adenosine deaminase (ADA) forms a complex with the cell membrane protein CD26/dipeptidyl peptidase IV. CD26-bound ADA has been postulated to regulate extracellular adenosine levels and to modulate the costimulatory function of CD26 on T lymphocytes. Absence of ADA-CD26 binding has been implicated in causing severe combined immunodeficiency due to ADA deficiency. Using human-mouse ADA hybrids and ADA point mutants, we have localized the amino acids critical for CD26 binding to the helical segment 126-143. Arg142 in human ADA and Gln142 in mouse ADA largely determine the capacity to bind CD26. Recombinant human ADA bearing the R142Q mutation had normal catalytic activity per molecule, but markedly impaired binding to a CD26(+) ADA-deficient human T cell line. Reduced CD26 binding was also found with ADA from red cells and T cells of a healthy individual whose only expressed ADA has the R142Q mutation. Conversely, ADA with the E217K active site mutation, the only ADA expressed by a severely immunodeficient patient, showed normal CD26 binding. These findings argue that ADA binding to CD26 is not essential for immune function in humans.

Expression of CD26/dipeptidyl-peptidase IV in benign and malignant pigment-cell lesions of the skin

The T-cell activation antigen CD26 or dipeptidyl-peptidase IV (DPP-IV) belongs to a group of membrane-bound proteases that are variably expressed by melanoma cell lines. In vitro studies have suggested that loss of CD26 is associated with tumour progression. To correlate its expression with the histological stage of tumour progression of malignant melanoma (MM), we studied the distribution of CD26/DPP-IV in paraffin sections of a series of 110 benign and malignant pigment-cell lesions of the skin using a cocktail of anti-CD26 monoclonal antibodies and the three-step ABC method. Only two of 44 benign lesions focally expressed CD26 in their junctional compartment. In MM, expression of CD26 was not related to any of the known histological prognostic factors, but was associated with the stage of tumour progression; thus, CD26 was expressed in the situ or invasive radial growth phase in 34% of MM, whereas only 12% of MM expressed CD26 in the vertical growth phase. No CD26 expression occurred in metastatic melanomas. These data suggest that this proteinase plays a part in the early invasion of MM. Thus, CD26 may serve in the binding to, and enzymatic degradation, components of the extracellular matrix of the papillary dermis. Loss of CD26 in the vertical growth phase may contribute to the insufficient inactivation of regulatory peptides and unlimited action of growth factors.

CD26/dipeptidyl peptidase IV does not work as an adenosine deaminase-binding protein in rat cells

In this paper, we describe further characterization of the membrane-associated molecule CD26/dipeptidyl peptidase IV (DPP IV), which is said to be adenosine deaminase-binding protein (ADA-bp) in humans, to clarify its association with ADA in rat immune cells. For this purpose, we used three types of rats: DPP IV+ rats; DPP IV- rats, which lack enzyme activity and immunological reactivity of DPP IV; and ADA- rats, which have reduced ADA activity due to continuous peritoneal injection of 2'-DCF, a potent inhibitor of ADA. ADA existed in the cells of DPP IV+ and DPP IV- rats, but it did not exist on the cell surface in either rat. ADA- rats showed a decrease in ADA activity and in the number of immune cells, but no effect on DPP IV was observed. These data suggest that in rats, in contrast to humans, DPP IV does not exist as ADA-bp.

Binding of adenosine deaminase to the lymphocyte surface via CD26

The relationship between CD26/dipeptidyl peptidase IV, an ectopeptidase involved in T cell activation, and the binding protein for adenosine deaminase (ADAbp) was studied. Monoclonal antibodies (mAb) against CD26 and ADAbp, respectively, showed a similar binding profile on various lymphocyte subsets from the peripheral blood. The adenosine deaminase (ADA) itself blocked the binding of a specific set of anti-CD26 mAb (among these the anti-TA5.9 mAb) on lymphocytic CD26; ADA also hindered the binding of soluble CD26 to the same immobilized anti-CD26 mAb. In addition, the interaction between immobilized ADA and purified CD26/DPP IV was inhibited by the anti-TA5.9 mAb. ADA did not inhibit the specific peptidase activity of CD26. Neither soluble nor immobilized ADA was able to down-modulate CD26 on the lymphocyte surface. Our data thus confirm the identity between ADAbp and CD26 and identify some epitopes, crucial in the binding of ADA to CD26.

A marker for neoplastic progression of human melanocytes is a cell surface ectopeptidase

Adenosine deaminase binding protein (ADAbp) is a cell surface glycoprotein that is expressed by normal melanocytes but not by melanoma, the malignant counterpart. ADAbp is specifically downregulated during malignant transformation of melanocytes. Recently, we have developed a system that progressively transforms melanocytes in vitro in defined steps. Transduction with v-Ha-ras oncogene followed by long-term culture leads to a cell phenotype and genotype that specifically mimics human melanoma. Loss of ADAbp expression occurred concomitantly with the emergence of growth factor independence and appearance of specific chromosomal abnormalities. The cellular function of ADAbp has not been defined. To characterize ADAbp, the mature 110-kD form was purified from human kidney. Five tryptic peptides from purified human ADAbp revealed 100% homology to a serine protease, human dipeptidyl peptidase IV (DPP IV), also known as CD26. DPP IV activity was detected in lysates from human melanocytes and renal carcinoma cells but not melanoma cells, and DPP IV activity could be specifically isolated from melanocytes by binding to ADA or to S27 monoclonal antibody against ADAbp. These findings show that ADAbp is a cell surface ectopeptidase that is tightly regulated during neoplastic transformation of melanocytes.

Adenosine deaminase complexing protein (ADCP) expression and metastatic potential in prostatic adenocarcinomas

The expression of the adenosine deaminase complexing protein (ADCP) was investigated by immunohistochemistry in the normal and hyperplastic human prostate, in 30 prostatic adenocarcinomas, and in seven human prostatic adenocarcinoma cell lines grown as xenografts in athymic nude mice. In the normal and hyperplastic prostate, ADCP was localized exclusively in the apical membrane and the apical cytoplasm of the glandular epithelial cells. In prostatic adenocarcinomas, four distinct ADCP expression patterns were observed: diffuse cytoplasmic, membranous, both cytoplasmic and membranous, and no ADCP expression. The expression patterns were compared with the presence of metastases. We found an inverse correlation between membranous ADCP immunoreactivity and metastatic propensity. Exclusively membranous ADCP immunoreactivity occurred only in non-metastatic tumours. In contrast, the metastatic tumours showed no or diffuse cytoplasmic ADCP immunoreactivity. This suggests that immunohistochemical detection of ADCP might predict the biological behaviour of prostatic cancer. However, the occurrence of membranous ADCP immunoreactivity in the xenograft of a cell line (PC-EW), derived from a prostatic carcinoma metastasis, indicates that not only the tendency to metastasize modulates ADCP expression.