A kinetic fluorometric assay of dipeptidyl peptidase IV in viable human blood mononuclear cells

Pediatric phase I trial design using maximum target inhibition as the primary endpoint

The extent to which a drug inhibits a target responsible for a therapeutic effect is a more rational primary endpoint for dose-finding studies of more selective anticancer drugs than the conventional endpoint of dose-limiting toxicity (DLT) used for cytotoxic agents. An adaptive phase I trial design incorporating maximum target inhibition as the primary endpoint was developed to define the optimal dose of talabostat, a dipeptidyl peptidase (DPP) inhibitor, in children with relapsed or refractory solid tumors. The relationship between dose and effect (percent inhibition of serum DPP-4) was assessed using a maximum effect model. Maximum target inhibition was defined as greater than 90% DPP-4 inhibition in five or more of six patients 24 hours post-dose. If DLT was to occur, the trial would adapt to a traditional phase I design with a more conservative dose escalation. At the 600 microg/m(2) dose level, serum DPP-4 inhibition at 24 hours was 85%. No talabostat-related DLT occurred. The maximum effect model predicted that 1200 microg/m(2) of talabostat would maximally inhibit DPP-4. This adaptive trial design appears to be feasible, safe, and efficient and warrants further evaluation for development of molecularly targeted agents.

Up-regulation of gamma-glutamyl transpeptidase (GGT) activity in growth perturbed C6 astrocytes

Activity of gamma-glutamyl transpeptidase (GGT) was studied in astrocyte-like C6 glial cells modulated in growth and maturation by different concentration of serum and dibutyryl cyclic AMP (Db-cAMP) supplement in culture medium. After reduction of serum concentration from 10% to 0.1%, the number of GGT positive cells determined histochemically increased 3.1 times and the GGT activity/mg protein in whole cell lysates was 5.1 times higher. In cultures with 0.1% serum + Db-cAMP, the histochemically and biochemically assayed GGT activity exceeded 5.1 and 7.9 times the values measured in control 10% serum cultures, respectively. The up-regulation of GGT was accompanied by an inhibition of proliferation, enhanced differentiation and hypertrophy of cells. In addition, the process of metabolic perturbation and/or cellular stress was revealed in these cultures by the (i) growth-support release followed by shrinkage and death of a small number of cells and (ii) higher oxidation of 2'7'dichlorofluorescein diacetate to its fluorescent form in the adherent/viable cells. The observed up-regulation of GGT is considered to primarily reflect increased metabolism of glutathione and/or the maintenance of the redox potential in cells stressed by sub-optimal concentration of serum and Db-cAMP supplement. The concomitant cellular hypertrophy and differentiation and their relationship to increased activity of GGT await further investigation. The study suggests that up-regulation of GGT can contribute to adaptation of astrocytic cells to metabolic and/or oxidative perturbances occurring under various pathological conditions, including radiation- and drug-induced toxicity.

CD26/DPPIV and response to hepatitis B vaccination

The prevention of hepatitis B is important, since it is responsible for significant morbidity and mortality around the world. Unfortunately, hepatitis B vaccine does not always induce protective immunity. The lack of immune response to vaccine (non-responders) can depend on individual characteristics. The objective of this study was to correlate the CD26/DPPIV cellular expression and DPPIV serum activity with HBV vaccine response and its possible role as an indicator of immune competence acquisition. We also determined the cellular expression of CD3, CD19, CD56 and CD25 in peripheral blood T lymphocytes. Blood samples were obtained from 28 healthy human volunteers who were enrolled with a vaccination program. There were "responders" (RM = 13) and "non-responders" (NRM = 15), after vaccination. The lymphocyte populations were identified by flow cytometry. DPPIV serum activity was measured fluorimetrically. CD26 expression in responders (55.9 +/- 7.7%) versus in non-responders (51.9 +/- 7.0%) did not show a significant difference. The DPPIV serum activity in responders compared to in non-responder subgroup (59.9 +/- 8.4/50.3 +/- 10.6U/L) showed, however, a significant difference (P < 0.05). The expression of CD3, CD19 and CD56 on peripheral lymphocytes was similar between responders and non-responders. The expression of CD3CD26 (52.2 +/- 8.6%) and CD3CD25 (10.9 +/- 3.8%) in responders versus the expression of CD3CD26 (48.0 +/- 5.7%) and CD3CD25 (8 +/- 4.6%) in non-responders did not show statistically significant difference. CD25 referred as a marker of T lymphocyte activation was increased in responders (15.8 +/- 4.5%) versus in non-responders (10.1 +/- 4.8%), showing a significant difference (P = 0.003). It was, however, impossible to demonstrate an increase in CD3CD25 and CD3CD26 in the responder subgroup. This suggests that different lymphocyte subsets other than T cells are implicated in the response to hepatitis B vaccination.

Isolation of bovine retinal pigment epithelial cells using adhesion to agarose: demonstration of cellular and regional heterogeneity

The retinal pigment epithelium (RPE) shows cell heterogeneity in morphology and enzymatic activity. Routine isolation procedures for RPE cells may reduce enzymatic activity and prevent the quantification of regional enzymatic differences in vivo. We developed a new technique for the isolation of RPE cells based on adhesion of the cells to agarose. The morphology of the isolated cells resembled that of RPE cells in vivo. The cells were viable in the dye exclusion test and showed a histochemical staining pattern as RPE cells in vivo. With this technique, quantitative regional differences in the enzymatic activities were detected.

Expression of attractin and its differential enzyme activity in glioma cells

Attractin/mahogany protein was previously shown to be involved in a number of physiological and pathological events, including immune system regulation, body weight control, pigmentation, myelinization, and tumor susceptibility. Human attractin has an enzymatic activity resembling dipeptidyl peptidase IV (DPP-IV). In the central nervous system, attractin has been detected in neurons but not in glial cells up to now. We show the expression of attractin mRNA and protein in glioma cell lines at different degree of transformation. In human U373 and U87 glioma cells (Grades III and IV), membrane-bound attractin displays hydrolytic activity amounting to 5 and 25% of total cellular DPP-IV-like enzyme activity, respectively. Such activity has not been observed in the rat C6 glioma cells (Grade I). Attractin presence in glioma, but not in normal glial cells, together with its differential enzymatic activity, suggests its role in growth properties of tumors of glial cell origin.

Dipeptidyl peptidase IV in C6 rat glioma cell line differentiation

The C6 rat glioma cell line is broadly used as a model in studies of glial cell differentiation. In the present study we demonstrated a significantly higher total cellular, but especially membrane-associated, activity of dipeptidyl peptidase IV in differentiated C6 cells in comparison with their proliferating counterparts. The majority, but not all, of enzyme isoelectric focusing isoforms from differentiated C6 cells displayed a substantially higher activity compared to the proliferating cells, with G-P-NHMec as the substrate. Non-denaturing polyacrylamide gradient gel electrophoresis showed the presence of one major peak of activity, dipeptidyl peptidase IV (Mr of about 220000), in both proliferating and differentiated C6 cells. The results indicate that dipeptidyl peptidase IV regulation is associated with C6 rat glioma cell differentiation.

Proline specific peptidases

Proline is unique among the 20 amino acids due to its cyclic structure. This specific conformation imposes many restrictions on the structural aspects of peptides and proteins and confers particular biological properties upon a wide range of physiologically important biomolecules. In order to adequately deal with such peptides, nature has developed a group of enzymes that recognise this residue specifically. These peptidases cover practically all situations where a proline residue might occur in a potential substrate. In this paper we endeavour to discuss these enzymes, particularly those responsible for peptide or protein hydrolysis at proline sites. We have detailed their discovery, biochemical attributes and substrate specificities and have provided information as to the methodology used to detect and manipulate their activities. We have also described the roles, or potential roles that these enzymes may play physiologically and the consequences of their dysfunction in varied disease states.

Detection of dipeptidyl peptidase IV in glioma C6 and neuroblastoma SK-N-SH cell lines

The dipeptidyl peptidase IV (DPP-IV) activity of the rat glioma cell line C6 and the human neuroblastoma cell line SK-N-SH was investigated. DPP-IV fluorescent substrate was cleaved by both cell lines. The pH reaction optimum determined was typical for DPP-IV described in other cell models. The reaction was inhibited by specific inhibitors diprotins A and B. Enzyme activity was localized, both on the cell surface and intracellularly. Most of the DPP-IV activity was membrane bound. However, soluble intra-cellular activity was found in both cell lines. Secreted activity was not detected in either cell line. In the C6 line, but not in the SK-N-SH line, we demonstrated depression of the ratio of cell surface to total cell DPP-IV activity at higher cell densities, indicating possible enzyme redistribution during cell growth in culture. Identification of DPP-IV activity is the first step in our study of the role of DPP-IV in the neural system.

Influence of pregnancy on dipeptidyl peptidase IV activity (CD 26 leukocyte differentiation antigen) of circulating lymphocytes

Dipeptidyl peptidase IV (CD 26 leukocyte differentiation antigen) is an enzymic surface marker of a human T lymphocyte subpopulation which has been shown to be associated with their capacity to produce large amounts of interleukin 2 and proliferate strongly in response to mitogenic stimulation. The peptidase activity on the surface of purified human peripheral mononuclear cells was determined spectrophotometrically with the substrate glycyl-L-proline-4-nitroanilide. The peripheral mononuclear cells of pregnant women exhibited depressed mean dipeptidyl peptidase IV activity when compared with the activity of peripheral mononuclear cells from non-pregnant or male individuals. The gestational age (7 to 20 weeks) of the pregnant collective had no effects on peptidase levels. Women taking oral contraceptives had a slightly lower mean activity than the non-pregnant group not using contraceptives. Thus, reduced dipeptidyl peptidase IV activity of peripheral mononuclear cells might reflect impairement of cellular immunity during pregnancy.

Dipeptidyl peptidase IV, prolyl endopeptidase and cathepsin B activities in primary human lung tumors and lung parenchyma

The activities of dipeptidyl peptidase IV (DPP-IV), prolyl endopeptidase (PE) and cathepsin B (CB) were investigated in primary human lung tumours and matched lung parenchyma, using continuous-rate fluorometric assays of the enzymes. Squamous-cell lung carcinomas showed significantly higher specific activities of all three enzymes studied. In lung adenocarcinomas only activities of PE and CB were increased significantly. In a limited number of primary human lung tumours of other histological types the activities of DPP-IV, PE and CB were also elevated. Mixing the matched homogenates of lung tumours and lung parenchyma gave additive activities for each enzyme studied. A significant correlation between tumour/lung ratios of specific activities of DPP-IV and CB was observed.