Hyperglycaemia increases dipeptidyl peptidase IV activity in diabetes mellitus

Aims/hypotheses Chronic hyperglycaemia increases dipeptidyl peptidase IV (DPP-IV) activity in endothelial cells in vitro. The present study was designed to assess the effect of high glucose on circulating DPP-IV activity in patients with type 1 and type 2 diabetes.Methods Plasma DPP-IV activity was measured in 29 patients with type 1 diabetes and 29 age-, sex- and BMI-matched control subjects. We also assessed DPP-IV activity in 31 type 2 diabetic patients with HbA₁c >8.5% and in plasma from matched groups of 31 newly diagnosed diabetic subjects with HbA₁c <7.5%, 31 subjects with IGT and 62 subjects with NGT. In a further sample of 66 type 2 diabetic patients, a longitudinal study was also performed to evaluate variations in DPP-IV activity and HbA₁c over 3 months.Results DPP-IV activity in type 1 diabetic patients was not significantly different from that in control subjects; however, a significant correlation between DPP-IV and HbA₁c was observed in diabetic subjects (r=0.47; p<0.01). Type 2 diabetic patients with HbA₁c >8.5% showed significantly (p<0.05) higher DPP-IV activity (mean±SD 27.7±7.1 U/l) than newly diagnosed diabetic patients and subjects with IGT (22.1±6.0 and 18.8±8.8 U/l, respectively). Variations in DPP-IV activity over 3 months in type 2 diabetic patients showed a significant positive correlation with variations in HbA₁c (r=0.26; p<0.05).Conclusions/interpretation Chronic hyperglycaemia induces a significant increase in DPP-IV activity in type 1 and type 2 diabetes. This phenomenon could contribute to the reduction in circulating active glucagon-like peptide-1 and to the consequent postprandial hyperglycaemia in type 2 diabetic patients with poor metabolic control.     

Promotion of vascular integrity in sepsis through modulation of bioactive adrenomedullin and dipeptidyl peptidase 3

Sepsis represents one of the major medical challenges of the 21st century. Despite substantial improvements in the knowledge on pathophysiological mechanisms, this has so far not translated into novel adjuvant treatment strategies for sepsis. In sepsis, both vascular tone and vascular integrity are compromised, and contribute to the development of shock, which is strongly related to the development of organ dysfunction and mortality. In this review, we focus on dipeptidyl peptidase 3 (DPP3) and adrenomedullin (ADM), two molecules that act on the vasculature and are involved in the pathophysiology of sepsis and septic shock. DPP3 is an ubiquitous cytosolic enzyme involved in the degradation of several important signalling molecules essential for regulation of vascular tone, including angiotensin II. ADM is a key hormone involved in the regulation of vascular tone and endothelial barrier function. Previous studies have shown that circulating concentrations of both DPP3 and ADM are independently associated with the development of organ failure and adverse outcome in sepsis. We now discuss new evidence illustrating that these molecules indeed represent two distinct pathways involved in the development of septic shock. Recently, both ADM-enhancing therapies aimed at improving endothelial barrier function and vascular tone and DPP3-blocking therapies aimed at restoring systemic angiotensin responses have been shown to improve outcome in various preclinical sepsis models. Given the current lack of effective adjuvant therapies in sepsis, additional research on the therapeutic application of these peptides in humans is highly warranted.     

二肽基肽酶4抑制剂对骨代谢影响的研究进展

DM患者患骨质疏松症的患病风险较高。二肽基肽酶4(DPP-4)广泛表达于全身组织器官。DPP-4抑制剂通过诱导间充质干细胞分化、减少AGEs聚集、增加IGF-1自分泌、抑制炎症因子表达、延长GLP-1及葡萄糖依赖性促胰岛素分泌多肽半衰期、促进APN分泌、改善维生素D水平、降低硬骨素水平等途径,对骨代谢产生一定影响。本文对DPP-4抑制剂对骨代谢的研究进展进行综述,旨在为临床治疗DM合并骨质疏松症提供依据。     

Involvement of dipeptidyl peptidase IV in extravillous trophoblast invasion and differentiation

Previously, we reported that dipeptidyl peptidase IV (DPPIV), a membrane-bound peptidase, was expressed on human placental cytotrophoblasts. In the present study, we focused on DPPIV expression on extravillous trophoblasts (EVTs). In the first trimester, DPPIV was expressed in the proximal part of the cell column and some EVTs located in the deep portion of the decidua and myometrium. EVTs migrating in the decidua from the cell column were negative for DPPIV. In the second and third trimesters, almost all EVTs were positive for DPPIV. Because negative DPPIV expression was associated with migration or the invasive phenotype of EVTs, using JEG-3 cells (choriocarcinoma cell line) that endogenously produce DPPIV, the influence of DPPIV on the invasive activity was examined. When a competitive inhibitor of DPPIV, diprotin A, was added in Matrigel invasion assay system, JEG-3 cells exhibited a significant enhancement of invasion. Because hypoxia is reported to reduce trophoblastic invasion, the effect of hypoxia was examined on JEG-3 cells. JEG-3 cells became less invasive with increased expression of DPPIV when cultured under hypoxic conditions (1% O(2)). These results suggest that DPPIV is important for the noninvasive EVT phenotype and the down-regulation of this enzyme was strongly associated with migration or invasive EVT phenotype.     

Heterogeneity of dipeptidyl peptidase IV from C6 rat glioma cells

Dipeptidyl peptidase IV is known to be involved, due to both hydrolytic and non-hydrolytic mechanisms, in various cell functions of normal and cancer cells as well. In this report dipeptidyl peptidase IV substrate and pH preferences, some inhibition parameters, freezing/thawing sensitivity and stability against hydrolysis by trypsin were studied in C6 rat glioma cells. Our results confirmed substantial heterogeneity of dipeptidyl peptidase IV population. Such observation is important to avoid methodological artifacts and to decrease risk of misinterpretations in biological studies.     

Effects of dipeptidyl peptidase IV on the satiety actions of peptide YY

Aims/hypothesis Dipeptidyl peptidase IV (DP IV) inhibitors are currently being developed to prolong the biological activity of insulinotropic peptides as a novel approach in the treatment of diabetes. We hypothesised that DP IV inhibition could attenuate the satiety actions of peptide YY (PYY) by altering the conversion of PYY(1–36) to PYY(3–36).Materials and methods The effects of PYY delivered by osmotic mini-pumps were assessed in rats treated with a DP IV inhibitor and in a rat model deficient in DP IV.Results Pharmacological levels of total PYY were found in the circulation after the exogenous administration of PYY(3–36). While both PYY(1–36) and PYY(3–36) reduced food intake in normal rats, PYY(1–36) was ineffective in rats deficient in DP IV. When re-fed after a 24-h fast, DP IV-deficient rats exhibited higher food intake and weight gain than normal rats. Moreover, unlike controls, there was no postprandial increase in PYY levels in DP IV-deficient rats. Despite these findings, administration of a DP IV inhibitor, Pro-boroPro, did not alter the acute anorectic effects of exogenous PYY(1–36) in normal rats. This could be the result of the protection of other appetite regulatory peptides or the generation of PYY(3–36) by remaining DP IV activity or other dipeptidyl peptidases.Conclusions/interpretation Although DP IV inhibition with Pro-boroPro attenuated the generation of PYY(3–36), our results indicate that short-term DP IV inhibition does not eliminate the satiety actions of exogenously administered PYY(1–36) at the doses tested.     

Human luteal cells express dipeptidyl peptidase IV on the cell surface.

We previously reported that human theca interna cells and small luteal cells express membrane-bound aminopeptidase N, and suggested that membrane-bound peptidases are involved in folliculogenesis and luteal function by regulating extracellular peptide concentrations. In this study, we examined the expression of dipeptidyl peptidase IV (DPP IV), which is a membrane-bound peptidase and has its catalytic domain at extracellular sites, in human granulosa cells, thecal cells of growing, preovulatory, and atretic follicles, as well as corpora lutea. Indirect immunofluorescence staining of ovarian tissues with specific monoclonal antibodies revealed that DPP IV was present in large and small luteal cells in corpora lutea. DPP IV peptidase activity was also detected histochemically in corpora lutea. In growing, preovulatory, and atretic follicles, there was weak immunoreactivity and DPP IV peptidase activity on luteinized theca interna cells, but not on granulosa cells. The expression of DPP IV on the cell surface of large and small luteal cells was confirmed by indirect immunofluorescence staining of freshly isolated luteal cells. These results indicate that DPP IV is a useful surface differentiation marker of human luteal cells and suggest that peptidases are involved in luteal function.     

Mice lacking dipeptidyl peptidase IV are protected against obesity and insulin resistance

Dipeptidyl peptidase IV (DP-IV), a member of the prolyl oligopeptidase family of peptidases, is involved in the metabolic inactivation of a glucose-dependent insulinotropic hormone, glucagon-like peptide 1 (GLP-1), and other incretin hormones. Here, we investigated the impact of DP-IV deficiency on body weight control and insulin sensitivity in mice. Whereas WT mice displayed accelerated weight gain and hyperinsulinemia when fed a high-fat diet (HFD), mice lacking the gene encoding DP-IV (DP-IV-/-) are refractory to the development of obesity and hyperinsulinemia. Pair-feeding and indirect calorimetry studies indicate that reduced food intake and increased energy expenditure accounted for the resistance to HFD-induced obesity in the DP-IV-/- mice. Ablation of DP-IV also is associated with elevated GLP-1 levels and improved metabolic control in these animals, resulting in improved insulin sensitivity, reduced pancreatic islet hypertrophy, and protection against streptozotocin-induced loss of beta cell mass and hyperglycemia. Together, these observations suggest that chronic deletion of DP-IV gene has significant impact on body weight control and energy homeostasis, providing validation of DP-IV inhibition as a viable therapeutic option for the treatment of metabolic disorders related to diabetes and obesity.     

Synergistic effect of α‐glucosidase inhibitors and dipeptidyl peptidase 4 inhibitor treatment

Monotherapy of α‐glucosidase inhibitor (α‐GI) or dipeptidyl peptidase 4 (DPP4) inhibitor does not sufficiently minimize glucose fluctuations in the diabetic state. In the present study, we evaluated the combined effects of various of α‐GI inhibitors (acarbose, voglibose or miglitol) and sitagliptin, a DPP4 inhibitor, on blood glucose fluctuation, insulin and active glucagon‐like peptide‐1 (GLP‐1) levels after nutriment loading in mice. Miglitol and sitagliptin elicited a 47% reduction (P < 0.05) of the area under the curve of blood glucose levels for up to 2 h after maltose‐loading, a 60% reduction (P < 0.05) in the range of blood glucose fluctuation, and a 32% decrease in plasma insulin compared with the control group. All three of the combinations elicited a 2.5–4.9‐fold synergistic increase in active GLP‐1 (P < 0.05 vs control). Thus, combined treatment with the α‐GI miglitol, which more strongly inhibits the early phase of postprandial hyperglycemia, and DPP4 inhibitor yields both complementary and synergistic effects, and might represent a superior anti‐hyperglycemic therapy. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00081.x, 2011)     

肥胖非酒精性脂肪肝儿童血清二肽基肽酶Ⅳ的水平

随着人们生活水平的提高、饮食结构和生活方式的改变,肥胖、高脂血症、糖尿病及由此引起的非酒精性脂肪肝(NAFLD)的发病率不断上升.单纯性脂肪肝和非酒精性脂肪性肝炎的发病率在中、重度肥胖儿童中已达到46.27％,这在西方国家被认为是儿童肝脏疾病中最普遍的原因.有研究发现血清二肽基肽酶Ⅳ(DPP Ⅳ)与慢性肝病有一定的关联性,本研究对肥胖NAFLD儿童血清DPP Ⅳ进行检测,旨在了解血清DPP Ⅳ与NAFLD之间的关系.     

Long-lasting antidiabetic effect of a dipeptidyl peptidase IV-resistant analog of glucagon-like peptide-1

Glucagon-like peptide-1(7-37) (GLP-1) is the most potent insulinotropic hormone characterized thus far. Because its activity is preserved in non-insulin-dependent diabetes mellitus (NIDDM) patients, it is considered a potential new drug for the treatment of this disease. One limitation in its therapeutic use is a short half-life in vivo (5 minutes), due in part to a fast degradation by the endoprotease dipeptidylpeptidase IV (DPPIV). Recently, it was reported that GLP-1 became resistant to DPPIV when the alanine residue at position 8 was replaced by a glycine (GLP-1-Gly8). We report here that this change slightly decreased the affinity of the peptide for its receptor (IC50, 0.41 +/- 0.14 and 1.39 +/- 0.61 nmol/L for GLP-1 and GLP-1-Gly8, respectively) but did not change the efficiency to stimulate accumulation of intracellular cyclic adenosine monophosphate (cAMP) (EC50, 0.25 +/- 0.05 and 0.36 +/- 0.06 nmol/L for GLP-1 and GLP-1-Gly8, respectively). Second, we demonstrate for the first time that this mutant has an improved insulinotropic activity compared with the wild-type peptide when tested in vivo in an animal model of diabetes. A single injection of 0.1 nmol GLP-1-Gly8 in diabetic mice fed a high-fat diet can correct fasting hyperglycemia and glucose intolerance for several hours, whereas the activity of 1 nmol GLP-1 vanishes a few minutes after injection. These actions were correlated with increased insulin and decreased glucagon levels. Interestingly, normoglycemia was maintained over a period that was longer than the predicted peptide half-life, suggesting a yet undescribed long-term effect of GLP-1-Gly8. GLP-1-Gly8 thus has a markedly improved therapeutic potential compared with GLP-1, since it can be used at much lower doses and with a more flexible schedule of administration.     

Regulation of dipeptidyl peptidase 8 and 9 expression in activated lymphocytes and injured liver

AIM:To investigate the expression of dipeptidyl peptidase(DPP) 8 and DPP9 in lymphocytes and various models of liver fibrosis.METHODS:DPP8 and DPP9 expression were measured in mouse splenic CD4 + T-cells,CD8 + T-cells and B-cells(B220 +),human lymphoma cell lines and mouse splenocytes stimulated with pokeweed mitogen(PWM) or lipopolysaccharide(LPS),and in dithiothreitol(DTT) and mitomycin-C treated Raji cells.DPP8 and DPP9 expression were measured in epidermal growth factor(EGF) treated Huh7 hepatoma cells,in fibrotic liver samples from mice treated with carbon tetrachloride(CCl 4) and from multidrug resistance gene 2(Mdr2 /Abcb4) gene knockout(gko) mice with biliary fibrosis,and in human end stage primary biliary cirrhosis(PBC).RESULTS:All three lymphocyte subsets expressed DPP8 and DPP9 mRNA.DPP8 and DPP9 expression were upregulated in both PWM and LPS stimulated mouse splenocytes and in both Jurkat T-and Raji B-cell lines.DPP8 and DPP9 were downregulated in DTT treated and upregulated in mitomycin-C treated Raji cells.DPP9transfected Raji cells exhibited more annexin V + cells and associated apoptosis.DPP8 and DPP9 mRNA were upregulated in CCl 4 induced fibrotic livers but not in the lymphocytes isolated from such livers,while DPP9 was upregulated in EGF stimulated Huh7 cells.In contrast,intrahepatic DPP8 and DPP9 mRNA expression levels were low in the Mdr2 gko mouse and in human PBC compared to non-diseased livers.CONCLUSION:These expression patterns point to biological roles for DPP8 and DPP9 in lymphocyte activation and apoptosis and in hepatocytes during liver disease pathogenesis.     

Inhibition of dipeptidyl peptidase IV activity by oral metformin in Type 2 diabetes.

AIMS: Glucagon-like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP) are important insulinotropic hormones that enhance the insulin secretory response to feeding. Their potential for treating Type 2 diabetes is limited by short biological half-life owing to degradation by dipeptidyl peptidase IV (DPP IV). We investigated the acute effects of metformin on DPP IV activity in Type 2 diabetes to elucidate inhibition of DPP IV as a possible mechanism of action. METHODS: Eight fasting subjects with Type 2 diabetes (5M/3F, age 53.1+/-4.2 years, BMI 36.8+/-1.8 kg/m2, glucose 8.9+/-1.2 mmol/l, HbA1c 7.8+/-0.6%) received placebo or metformin 1 g orally 1 week apart in a random, crossover design. RESULTS: Following metformin, DPP IV activity was suppressed compared with placebo (AUC0-6 h 3230+/-373 vs. 5764+/-504 nmol ml/l, respectively, P=0.001). Circulating glucose, insulin and total GLP-1 were unchanged. Metformin also concentration-dependently inhibited endogenous DPP IV activity in vitro in plasma from Type 2 diabetic subjects. CONCLUSION: Oral metformin effectively inhibits DPP IV activity in Type 2 diabetic patients, suggesting that the drug may have potential for future combination therapy with incretin hormones.     

Enteroinsular axis of db/db mice and efficacy of dipeptidyl peptidase IV inhibition

In type 2 diabetic patients, the administration of glucagon-like peptide-1 (GLP-1), known as an incretin, exerts antidiabetic effects. However, GLP-1 is rapidly degraded by dipeptidyl peptidase IV (DPPIV) after its release. DPPIV inhibition is thought to be a rational strategy to treat type 2 diabetes. In this study, using C57BLKS/J-db/db (db/db) mice as a model of type 2 diabetes, we examined the effect of acute DPPIV inhibition on glucose tolerance at the early and later stages of diabetes, determining plasma active GLP-1 and insulin levels. In addition, we investigated changes of plasma DPPIV activity. Compared with normal C57BL6/J (B6) and db/+ mice, significantly increased plasma DPPIV activities were observed in db/db mice. Expression of the proglucagon gene encoding GLP-1 was significantly upregulated in the colon of db/db mice. The administration of valine-pyrrolidide, a DPPIV inhibitor, resulted in potentiated insulin secretion mediated by increased endogenous GLP-1 action, leading to improved glucose tolerance in db/db mice at 6 weeks of age. However, although acute DPPIV inhibition with valine-pyrrolidide resulted in higher plasma active GLP-1 and insulin levels in db/db mice at 23 weeks of age, it did not improve glucose tolerance. The function of the enteroinsular axis is preserved in both stage of diabetes and the DPPIV inhibitor potentiated it, but the progression of insulin resistance appeared to block the improvement of glucose tolerance through DPPIV inhibition. Our results suggest that DPPIV inhibition is a suitable approach for treatment of impaired glucose tolerance (IGT), and type 2 diabetes in the early stage.     

Enhancement of antigen-induced T-cell proliferation by soluble CD26/dipeptidyl peptidase IV.

The addition of a soluble recombinant CD26 (sCD26) enhanced proliferation of peripheral blood lymphocytes induced by the recall antigen tetanus toxoid. sCD26 itself did not provide a mitogenic signal and did not augment the proliferative response of T cells to other mitogenic stimuli such as phytohemagglutinin and anti-CD3. Dipeptidyl peptidase IV-negative sCD26 did not have this enhancement effect, implying a requirement for enzyme activity. It was found that there exists a large variation in the levels of human plasma sCD26/dipeptidyl peptidase IV in vivo which may regulate T-cell activity. Peripheral blood lymphocytes from individuals whose plasma sCD26 was high and responded strongly to tetanus toxoid stimulation were insensitive to the enhancing effects of exogenously added sCD26. This suggests that plasma sCD26 had modulated the responsiveness of T cells of these individuals in vivo and that the endogenous plasma sCD26 regulates immune responses by allowing antigen-specific T cells to exert a maximal response to their specific antigen.     

Entropy-driven binding of opioid peptides induces a large domain motion in human dipeptidyl peptidase III

Opioid peptides are involved in various essential physiological processes, most notably nociception. Dipeptidyl peptidase III (DPP III) is one of the most important enkephalin-degrading enzymes associated with the mammalian pain modulatory system. Here we describe the X-ray structures of human DPP III and its complex with the opioid peptide tynorphin, which rationalize the enzyme's substrate specificity and reveal an exceptionally large domain motion upon ligand binding. Microcalorimetric analyses point at an entropy-dominated process, with the release of water molecules from the binding cleft ("entropy reservoir") as the major thermodynamic driving force. Our results provide the basis for the design of specific inhibitors that enable the elucidation of the exact role of DPP III and the exploration of its potential as a target of pain intervention strategies.