Dipeptidyl-peptidase IV from bench to bedside: an update on structural properties, functions, and clinical aspects of the enzyme DPP IV

Comparative clinical pharmacokinetics of dipeptidyl peptidase-4 inhibitors

Dipeptidyl peptidase-4 (DPP-4) inhibitors collectively comprise a presently unique form of disease management for persons with type 2 diabetes mellitus. The aim of this review is to compare the clinical pharmacokinetics of available DPP-4 inhibitors (alogliptin, linagliptin, saxagliptin, sitagliptin and vildagliptin) for the purpose of identifying potential selection preferences according to individual patient variables and co-morbidities. DPP-4 inhibitors are readily absorbed orally. Following oral ingestion, absorption occurs mainly in the small intestine, with median times to maximum (peak) plasma concentration ranging from 1 to 3 hours. The fraction of each dose absorbed ranges from approximately 30% with linagliptin to 75-87% for all others. Numerical differences in maximum (peak) plasma drug concentrations and areas under the plasma concentration-time curve among the DPP-4 inhibitors vary by an order of magnitude. However, functional capacity measured in terms of glucose-lowering ability remains comparable among all available DPP-4 inhibitors. Distribution of DPP-4 inhibitors is strongly influenced by both lipophilicity and protein binding. Apparent volumes of distribution (V(d)) for most agents range from 70 to 300 L. Linagliptin exhibits a V(d) of more than 1000 L, indicating widespread distribution into tissues. Binding to target proteins in plasma and peripheral tissues exerts a major influence upon broadening linagliptin distribution. DPP-4 inhibitor metabolism is widely variable, with reported terminal half-lives ranging from approximately 3 to more than 200 hours. Complex relationships between rates of receptor binding and dissociation appear to strongly influence the durations of action of those DPP-4 inhibitors with comparatively shorter half-lives. Durations of activity often are not reflective of clearance and, with the exception of vildagliptin which may be administered either once daily in the evening or twice daily, these medications are effective when used with a once-daily dosing schedule. Saxagliptin and, to a lesser extent, sitagliptin are largely metabolized by hepatic cytochrome P450 (CYP) 3A4 and 3A5 isoforms. With the exception of the primary hydroxylated metabolite of saxagliptin, which is 2-fold less potent than its parent molecule, metabolic products of hepatic biotransformation are minimally active and none appreciably contribute to either the therapeutic or the toxic effects of DPP-4 inhibitors. No DPP-4 inhibitor has been shown to inhibit or to induce hepatic CYP-mediated drug metabolism. Accordingly, the number of clinically significant drug-drug interactions associated with these agents is minimal, with only saxagliptin necessitating dose adjustment if administered concurrently with medications that strongly inhibit CYP3A4. Linagliptin undergoes enterohepatic cycling with a large majority (85%) of the absorbed dose eliminated in faeces via biliary excretion. Other DPP-4 inhibitors predominantly undergo renal excretion, with 60-85% of each dose eliminated as unchanged parent compound in the urine. Systematic reviews of clinical trials suggest that the overall efficacy of DPP-4 inhibitors in patients with type 2 diabetes generally is similar. Apart from these generalizations, pharmacokinetic distinctions that potentially influence product selection are tentative. When considered in total, data reviewed in this report suggest that the best overall balance between potency and the clinical pharmacokinetic characteristics of distribution, metabolism and elimination may be observed with linagliptin followed closely by vildagliptin, saxagliptin, sitagliptin and alogliptin.

Pharmacokinetics and metabolism of [14C]anagliptin, a novel dipeptidyl peptidase-4 inhibitor, in humans

1. The disposition of anagliptin, an orally active, highly selective dipeptidyl peptidase-4 inhibitor, was investigated after a single oral dose of 100 mg/1.92 MBq [(14)C]anagliptin to six healthy men. Almost all the dose (98.2%) was recovered within 168 h: 73.2% in urine and 25.0% in faeces. 2. Anagliptin was rapidly absorbed, with peak plasma concentrations of unchanged drug attained at a mean time of 1.8-h postdose. Mean fraction of the dose absorbed was >73%. Unchanged drug and a carboxylate metabolite (M1) were the major components in plasma, accounting for 66.0 and 23.4% of total plasma radioactivity area under the curve, respectively. 3. Anagliptin was incompletely metabolized, with about 50% dose eliminated as unchanged drug (46.6% in urine and 4.1% in faeces). Metabolism to M1 accounted for 29.2% of the dose. No other metabolite accounted for >1% dose in excreta or yielded measurable systemic exposure. Terminal half-life of anagliptin and M1 was 4.37 and 9.88 h, respectively. Renal clearance of unbound anagliptin and unbound M1 far exceeded glomerular filtration rate, indicating active renal elimination: that might reflect the fact that anagliptin may be a substrate of OAT1, OAT3, MDR1 and MRP2, and M1 a substrate of OAT3, BCRP, MRP2 and MRP4.

Overview of the mechanisms regulating chemokine activity and availability

Physiological leukocyte homing and extravasation of leukocytes during inflammatory processes is directed by a number of proteins including adhesion molecules, proteases, cytokines and chemokines. Tight regulation of leukocyte migration is essential to ensure appropriate migration. A number of mechanisms exist that regulate leukocyte migration including up- or down-regulation of chemokine or chemokine receptor gene expression. However, chemokine availability in vivo also depends on the interaction of chemokines with specific glycosaminoglycans such as heparan sulfate on the surface of endothelial layers. Modification of the interaction of chemokines with these glycosaminoglycans alters the presentation of chemokines to chemokine receptors on circulating leukocytes. On top, binding of chemokines to atypical chemokine receptors that do not signal through G proteins affects chemokine availability on the endothelial layers. In addition to mechanisms that modulate chemokine availability, this review summarizes mechanisms that fine-tune chemokine function. These include synergy or antagonism between chemokines and alternative splicing of chemokine genes. Moreover, chemokines may be posttranslationally modified leading to molecules with enhanced or reduced potency to bind to G protein-coupled receptors or GAGs or generating chemokines with altered receptor specificity. Cross-talk between these different mechanisms generates a complex regulatory network that allows the organism to modulate leukocyte migration in a highly specific manner.

Dipeptidyl peptidase IV inhibition upregulates GLUT4 translocation and expression in heart and skeletal muscle of spontaneously hypertensive rats

The purpose of the current study was to test the hypothesis that the dipeptidyl peptidase IV (DPPIV) inhibitor sitagliptin, which exerts anti-hyperglycemic and anti-hypertensive effects, upregulates GLUT4 translocation, protein levels, and/or mRNA expression in heart and skeletal muscle of spontaneously hypertensive rats (SHRs). Ten days of treatment with sitagliptin (40 mg/kg twice daily) decreased plasma DPPIV activity in both young (Y, 5-week-old) and adult (A, 20-week-old) SHRs to similar extents (~85%). However, DPPIV inhibition only lowered blood pressure in Y-SHRs (119 ± 3 vs. 136 ± 4 mmHg). GLUT4 translocation, total protein levels and mRNA expression were decreased in the heart, soleus and gastrocnemius muscle of SHRs compared to age-matched Wistar Kyoto (WKY) normotensive rats. These differences were much more pronounced between A-SHRs and A-WKY rats than between Y-SHRs and Y-WKY rats. In Y-SHRs, sitagliptin normalized GLUT4 expression in the heart, soleus and gastrocnemius. In A-SHRs, sitagliptin increased GLUT4 expression to levels that were even higher than those of A-WKY rats. Sitagliptin enhanced the circulating levels of the DPPIV substrate glucagon-like peptide-1 (GLP-1) in SHRs. In addition, stimulation of the GLP-1 receptor in cardiomyocytes isolated from SHRs increased the protein level of GLUT4 by 154 ± 13%. Collectively, these results indicate that DPPIV inhibition upregulates GLUT4 in heart and skeletal muscle of SHRs. The underlying mechanism of sitagliptin-induced upregulation of GLUT4 in SHRs may be, at least partially, attributed to GLP-1.

Dipeptidyl peptidase IV inhibition potentiates amino acid- and bile acid-induced bicarbonate secretion in rat duodenum

Intestinal endocrine cells release gut hormones, including glucagon-like peptides (GLPs), in response to luminal nutrients. Luminal L-glutamate (L-Glu) and 5'-inosine monophosphate (IMP) synergistically increases duodenal HCO3- secretion via GLP-2 release. Since L cells express the bile acid receptor TGR5 and dipeptidyl peptidase (DPP) IV rapidly degrades GLPs, we hypothesized that luminal amino acids or bile acids stimulate duodenal HCO3- secretion via GLP-2 release, which is enhanced by DPPIV inhibition. We measured HCO3- secretion with pH and CO2 electrodes using a perfused rat duodenal loop under isoflurane anesthesia. L-Glu (10 mM) and IMP (0.1 mM) were luminally coperfused with or without luminal perfusion (0.1 mM) or intravenous (iv) injection (3 μmol/kg) of the DPPIV inhibitor NVP728. The loop was also perfused with a selective TGR5 agonist betulinic acid (BTA, 10 μM) or the non-bile acid type TGR5 agonist 3-(2-chlorophenyl)-N-(4-chlorophenyl)-N,5-dimethylisoxazole-4-carboxamide (CCDC; 10 μM). DPPIV activity visualized by use of the fluorogenic substrate was present on the duodenal brush border and submucosal layer, both abolished by the incubation with NVP728 (0.1 mM). An iv injection of NVP728 enhanced L-Glu/IMP-induced HCO3- secretion, whereas luminal perfusion of NVP728 had no effect. BTA or CCDC had little effect on HCO3- secretion, whereas NVP728 iv markedly enhanced BTA- or CCDC-induced HCO3- secretion, the effects inhibited by a GLP-2 receptor antagonist. Coperfusion of the TGR5 agonist enhanced L-Glu/IMP-induced HCO3- secretion with the enhanced GLP-2 release, suggesting that TGR5 activation amplifies nutrient sensing signals. DPPIV inhibition potentiated luminal L-Glu/IMP-induced and TGR5 agonist-induced HCO3- secretion via a GLP-2 pathway, suggesting that the modulation of the local concentration of the endogenous secretagogue GLP-2 by luminal compounds and DPPIV inhibition helps regulate protective duodenal HCO3- secretion.

A novel, potent, and long-lasting dipeptidyl peptidase-4 inhibitor, teneligliptin, improves postprandial hyperglycemia and dyslipidemia after single and repeated administrations

Dipeptidyl peptidase-4 (DPP-4) inhibitors have been demonstrated to improve glycemic control, in particular postprandial hyperglycemic control, in patients with type 2 diabetes. Teneligliptin is a novel chemotype prolylthiazolidine-based DPP-4 inhibitor. The present study aimed to characterize the pharmacological profiles of teneligliptin in vitro and in vivo. Teneligliptin competitively inhibited human plasma, rat plasma, and human recombinant DPP-4 in vitro, with IC(50) values of approximately 1 nmol/l. Oral administration of teneligliptin in Wistar rats resulted in the inhibition of plasma DPP-4 with an ED(50) of 0.41 mg/kg. Plasma DPP-4 inhibition was sustained even at 24h after administration of teneligliptin. An oral carbohydrate-loading test in Zucker fatty rats showed that teneligliptin at ≥ 0.1mg/kg increased the maximum increase in plasma glucagon-like peptide-1 and insulin levels, and reduced glucose excursions. This effect was observed over 12h after a dose of 1mg/kg. An oral fat-loading test in Zucker fatty rats also showed that teneligliptin at 1mg/kg reduced triglyceride and free fatty acid excursions. In Zucker fatty rats, repeated administration of teneligliptin for two weeks reduced glucose excursions in the oral carbohydrate-loading test and decreased the plasma levels of triglycerides and free fatty acids under non-fasting conditions. The present studies indicate that teneligliptin is a potent, competitive, and long-lasting DPP-4 inhibitor that improves postprandial hyperglycemia and dyslipidemia by both single and repeated administrations.

Clinical pharmacokinetics and pharmacodynamics of linagliptin

Linagliptin is an orally active small-molecule inhibitor of dipeptidyl peptidase (DPP)-4, which was first licensed in the US, Europe, Japan and other territories in 2011 to improve glycaemic control in adults with type 2 diabetes mellitus. Linagliptin is the first and thus far the only DPP-4 inhibitor, and oral antihyperglycaemic drug in general, to be approved as a single-strength once-daily dose (5 mg). Compared with other available DPP-4 inhibitors, linagliptin has a unique pharmacokinetic/pharmacodynamic profile that is characterized by target-mediated nonlinear pharmacokinetics, concentration-dependent protein binding, minimal renal clearance and no requirements for dose adjustment for any intrinsic or extrinsic factor. After single or multiple oral doses of 1-10 mg, linagliptin displays less than dose-proportional increases in maximum plasma concentration (C(max)) and area under the plasma concentration-time curve (AUC). Linagliptin is rapidly absorbed after oral administration, with C(max) occurring after approximately 90 minutes, and reaches steady-state concentrations within 4 days. With the therapeutic dose, steady-state C(max) (11-12 nmol/L) and AUC (∼150 nmol · h/L) are approximately 1.3-fold greater than after a single dose, indicating little drug accumulation with repeat dosing. Linagliptin exhibits concentration-dependent protein binding in human plasma in vitro (99% at 1 nmol/L to 75-89% at >30 nmol/L) and has a large apparent volume of distribution, demonstrating extensive distribution into tissues. The nonlinear pharmacokinetics of linagliptin are best described by a two-compartmental model that incorporates target-mediated drug disposition resulting from high-affinity, saturable binding to DPP-4. The oral bioavailability of linagliptin estimated with this model is approximately 30%. Linagliptin has a long terminal half-life (>100 hours); however, its accumulation half-life is much shorter (approximately 10 hours), accounting for the rapid attainment of steady state. The majority of linagliptin is eliminated as parent compound, demonstrating that metabolism plays a minor role in the overall pharmacokinetics in humans. The main, pharmacologically inactive S-3-hydroxypiperidinyl metabolite accounted for approximately 17% of the total drug-related compounds in plasma. Linagliptin is eliminated primarily in faeces, with only around 5% of the oral therapeutic dose excreted in the urine at steady state. Linagliptin potently inhibits DPP-4 (inhibition constant 1 nmol/L), and trough drug concentrations achieved with therapeutic dosing inhibit >80% of plasma DPP-4 activity, the threshold associated with maximal antihyperglycaemic effects in animal models. There are no clinically relevant alterations in linagliptin pharmacokinetics resulting from renal impairment, hepatic impairment, coadministration with food, race, body weight, sex or age. In vitro, linagliptin is a weak substrate and weak inhibitor of cytochrome P450 (CYP) 3A4 and permeability glycoprotein (P-gp) but not of other CYP isozymes or ATP-binding cassette transporters. Clinical studies have revealed no relevant drug interactions when coadministered with other drugs commonly prescribed to patients with type 2 diabetes, including the narrow therapeutic index drugs warfarin and digoxin. Linagliptin plasma exposure is reduced by potent inducers of CYP3A4 or P-gp. Linagliptin has demonstrated a large safety window (>100-fold the recommended daily dose) and clinically relevant antihyperglycaemic effects in patients with type 2 diabetes.

Regulation of hindbrain Pyy expression by acute food deprivation, prolonged caloric restriction, and weight loss surgery in mice

PYY is a gut-derived putative satiety signal released in response to nutrient ingestion and is implicated in the regulation of energy homeostasis. Pyy-expressing neurons have been identified in the hindbrain of river lamprey, rodents, and primates. Despite this high evolutionary conservation, little is known about central PYY neurons. Using in situ hybridization, PYY-Cre;ROSA-EYFP mice, and immunohistochemistry, we identified PYY cell bodies in the gigantocellular reticular nucleus region of the hindbrain. PYY projections were present in the dorsal vagal complex and hypoglossal nucleus. In the hindbrain, Pyy mRNA was present at E9.5, and expression peaked at P2 and then decreased significantly by 70% at adulthood. We found that, in contrast to the circulation, PYY-(1-36) is the predominant isoform in mouse brainstem extracts in the ad libitum-fed state. However, following a 24-h fast, the relative amounts of PYY-(1-36) and PYY-(3-36) isoforms were similar. Interestingly, central Pyy expression showed nutritional regulation and decreased significantly by acute starvation, prolonged caloric restriction, and bariatric surgery (enterogastroanastomosis). Central Pyy expression correlated with body weight loss and circulating leptin and PYY concentrations. Central regulation of energy metabolism is not limited to the hypothalamus but also includes the midbrain and the brainstem. Our findings suggest a role for hindbrain PYY in the regulation of energy homeostasis and provide a starting point for further research on gigantocellular reticular nucleus PYY neurons, which will increase our understanding of the brain stem pathways in the integrated control of appetite and energy metabolism.

Renin-angiotensin system inhibitors and angioedema: anesthetic implications

PURPOSE OF REVIEW

Angioedema is a serious complication of renin-angiotensin system inhibitor therapy. The incidence is 0.1-0.7%. It consists of nonpitting edema and involves the face and lips. In severe cases, it extends to pharyngeal and laryngeal structures.

RECENT FINDINGS

Decreased degradation of bradykinin and its metabolites is thought to be a culprit. When the angiotensin-converting enzyme is inhibited, bradykinin metabolism is dependent on degradation by neutral endopeptidase, dipeptidyl peptidase IV, and aminopeptidase P. When these enzymes are inhibited, as in treatment of diabetes or in transplant recipients, the incidence of angioedema increases significantly. African-Americans, people over 65, women, and those with a history of smoking are especially at risk. A fiberoptic laryngeal examination should be performed in all patients. Patients with rapid progression of symptoms are at risk for airway compromise. Supportive treatment with steroids and antihistamines is not very effective. Recently, icatibant, a bradykinin receptor antagonist, has been used to successfully shorten the resolution of edema.

SUMMARY

Trauma of the airway, especially during difficult intubation, may precipitate severe angioedema. In cases with laryngeal involvement, fiberoptic intubation may be necessary. After the episode of angioedema, lifetime discontinuation of all renin-angiotensin inhibitors may be warranted.

Serum activity of DPPIV and its expression on lymphocytes in patients with melanoma and in people with vitiligo

Background

Dipeptidyl peptidase IV, a multifunctional serine protease, is implicated in regulation of malignant transformation, promotion and further progression of cancer, exerting tumor-suppressing or even completely opposite - tumor-promoting activities.

The aim of present research was to determine the serum DPPIV activity, as well as the percentages of CD26+ lymphocytes, CD26+ overall white blood cells and the mean fluorescence intensity of CD26 expression on lymphocytes in patients with melanoma, people with vitiligo and in healthy controls.

Methods

The activity of DPPIV in serum was determined by colorimetric test. Expression of DPPIV (as CD26) on immunocompetent peripheral white blood cells was done using flow cytometry analysis.

Results

Data from our study show for the first time statistically significant decrease: in the serum DPPIV activity, in the percentage of CD26+ overall white blood cells and in the percentage of lymphocytes in patients with melanoma in comparison to healthy control people. In addition, significantly lower serum DPPIV activity was found in the group of patients with melanoma in relation to people with vitiligo too.

Conclusion

This study indicates the need for exploring the cause and the importance of the disturbances in the serum DPPIV activity and in the CD26 expression on immunocompetent cells in complex molecular mechanisms underlying the development and progression of melanoma.

[Dipeptidyl peptidase IV in inflammatory bowel diseases (DPP IV/CD26)]

Inflammatory bowel diseases (Crohn's disease, ulcerative colitis, undetermined colitis) are a group of chronic autoimmune inflammatory diseases distinguished by recurrent inflammation of various parts of the gastrointestinal (GI) system and presenting a significant public health problem. Despite large basic and clinical research, the aetiology of these diseases and the pathogenesis of inflammation itself remain elusive. Previous studies have confirmed a causal relationship between mediators of inflammatory response and molecules involved in the regulation of their biological activity, especially proteases. The aim of this review is to summarise earlier findings on different aspects of inflammatory bowel diseases, paying particular attention to the involvement of dipeptidyl peptidase IV (CD26 molecule, DPP IV/CD26) in the etiopathogenesis of inflammatory processes in the GI tract. Animal studies of colitis have significantly contributed to the understanding and treatment of these diseases, investigations of ulcerative colitis (DSS-colitis) and Crohn's disease (TNBS-colitis) on the murine model in particular.

Dipeptidyl peptidase IV-activated prodrugs of anti-varicella zoster virus bicyclic nucleoside analogues containing different self-cleavage spacer systems

A new type of double prodrug of the antiviral family of bicyclic nucleoside analogues (BCNA) bearing cyclization self-cleavage spacers between the Val-Pro dipeptide sequence as well as the parent compound were synthesized and evaluated with regard to activation by the DPPIV/CD26 enzyme and for their stability in human and bovine serum. In buffer solution, carbamate and ester prodrugs were found to be chemically stable. Most prodrugs containing a dipeptidyl linker efficiently converted into the BCNA parent drug. In contrast, the Val-Pro alkyldiamino prodrugs converted predominantly into their alkyldiamino prodrug intermediates in the presence of CD26 and human serum. A marked increase in water solubility was observed for all prodrugs. In contrast to the parent compound, a tetrapeptide prodrug containing the Val-Val dipeptide as a self-cleavage spacer released substantial amounts of the BCNA parent drug at the basolateral side of Caco-2 cell cultures and exhibited 15- to 20-fold increased bioavailability in mice relative to the poorly bioavailable parent compound.

GLP-1 based therapies: differential effects on fasting and postprandial glucose

Glucagon-like peptide-1 (GLP-1), a gut-derived hormone secreted in response to nutrients, has several glucose and weight regulating actions including enhancement of glucose-stimulated insulin secretion, suppression of glucagon secretion, slowing of gastric emptying and reduction in food intake. Because of these multiple effects, the GLP-1 receptor system has become an attractive target for type 2 diabetes therapies. However, GLP-1 has significant limitations as a therapeutic due to its rapid degradation (plasma half-life of 1-2 min) by dipeptidyl peptidase-4 (DPP-4). Two main classes of GLP-1-mediated therapies are now in use: DPP-4 inhibitors that reduce the degradation of GLP-1 and DPP-4-resistant GLP-1 receptor (GLP-1R) agonists. The GLP-1R agonists can be further divided into short- and long-acting formulations which have differential effects on their mechanisms of action, ultimately resulting in differential effects on their fasting and postprandial glucose lowering potential. This review summarizes the similarities and differences among DPP-4 inhibitors, short-acting GLP-1R agonists and long-acting GLP-1R agonists. We propose that these different GLP-1-mediated therapies are all necessary tools for the treatment of type 2 diabetes and that the choice of which one to use should depend on the specific needs of the patient. This is analogous to the current use of modern insulins, as short-, intermediate- and long-acting versions are all used to optimize the 24-h plasma glucose profile as needed. Given that GLP-1-mediated therapies have advantages over insulins in terms of hypoglycaemic risk and weight gain, optimized use of these compounds could represent a significant paradigm shift for the treatment of type 2 diabetes.

Chronic DPP-IV inhibition with PKF-275-055 attenuates inflammation and improves gene expressions responsible for insulin secretion in streptozotocin induced diabetic rats

Inhibitors of dipeptidyl peptidase-4 (DPP-IV), a key regulator of the actions of incretin hormones, exert antihyperglycemic effects in type 2 diabetic patients. A major question concerns the potential ability of long term DPP-IV inhibition to have beneficial disease-modifying effects, specifically to attenuate loss of pancreatic β-cell mass due to oxidative stress induced inflammation. Here, we investigated the effects of a potent and selective DPP-4 inhibitor, an analog of vildagliptin (PKF-275-055), on glycemic control, pancreatic β-cell mass, genes and proteins expressions, tumor necrosis factor-alpha, and nitric oxide in an n2-STZ diabetic model of rat with defects in insulin sensitivity and secretion. To induce NIDDM, streptozotocin (STZ) 90 mg/kg was administered i.p. to a group of 2 days old pups. Diabetic rats were administered orally with vildagliptin analog PKF-275-055. Saline treated animals served as diabetic control. Significant and dose-dependent correction of postprandial hyperglycemia was observed in diabetic rats following 8 weeks of chronic therapy. Treatment with PKF-275-055 showed increased the number of insulin-positive β-cells in islets and improved the expressions of genes and proteins are responsible for insulin secretions. In addition, treatment of rats with PKF-275-055 significantly increased insulin content, glycogen content and total proteins content; and decreased the inflammatory markers i.e. nitric oxide and TNF-alpha. The present studies indicate that PKF-275-055 is a novel selective DPP-IV inhibitor having potential to reduce inflammation that might be a potential agent for type 2 diabetes.

DPP4 inhibition improves functional outcome after renal ischemia-reperfusion injury

Dipeptidyl peptidase 4 (DPP4) is an exopeptidase which modulates the function of its substrates, among which are insulin-releasing incretins. DPP4 inhibitors are currently used to improve glucose tolerance in type 2 diabetes patients. Inhibition of DPP4 exhibits protective effects on ischemia-reperfusion injury (IRI) of the heart and lung. As DPP4 and its substrates are also expressed in the kidney, we studied the effect of the DPP4 inhibitor vildagliptin on the outcome of IRI-induced acute kidney injury in rats in a model of 30-min unilateral renal ischemia, followed by contralateral nephrectomy. Saline, 1, or 10 mg/kg vildagliptin (VG1/VG10) was administered intravenously 15 min before the surgery. Animals were euthanized after 2, 12, amd 48 h of reperfusion. DPP4 inhibition resulted in a significant dose-dependent decrease in serum creatinine (1.31 ± 0.32 and 0.70 ± 0.19 mg/dl for VG1 and VG10, respectively, vs. 1.91 ± 0.28 mg/dl for controls at 12 h; P < 0.01). Tubular morphology (PAS-PCNA) revealed significantly reduced tubular necrosis at 12 h (62.1 ± 18.0 and 77.5 ± 22.0% in VG10 and saline, respectively). VG did not affect regeneration but decreased apoptosis, as shown by twofold decreased Bax/Bcl-2 mRNA expression and a threefold decrease in apoptotic bodies on terminal deoxynucleotidyl transferase dUTP nick-end labeling-stained sections. VG treatment significantly reduced serum malondialdehyde twofold in both VG1- and VG10-treated ischemic and sham-operated animals compared with controls and also resulted in a significant decrease in mRNA expression of the proinflammatory marker CXCL10 at 2 h of reperfusion. Through a mechanism yet to be fully understood, VG treatment results in a functional protection of the kidney against IRI. This protection was associated with antiapoptotic, immunological, and antioxidative changes.

Expression profiling of dipeptidyl peptidase 8 and 9 in breast and ovarian carcinoma cell lines

Proteases, particularly serine proteases like dipeptidyl peptidase 4 (DP4) and fibroblast activation protein (FAP), play an important role in cancer invasion and angiogenesis. Aberrant expression of DP4 and FAP is associated with numerous cancers, including breast and epithelial ovarian carcinoma. We investigated the mRNA levels, protein expression and enzyme activity of the structural homologs DP8 and DP9, in addition to DP4 and FAP, in three breast carcinoma (MDA-MB-231, MDA-MB-453, MCF-7), three epithelial ovarian carcinoma (EOC) (OVCA-432, OVCA-429, SKOV3), 293T and HeLa cell lines. In addition, DP2 and prolyl endopeptidase (PEP) mRNA and enzyme levels were measured and compared in each cell line. Ubiquitous but differential expression of DP8 and DP9 mRNA and protein was observed across all cell lines. Relative to EOC, DP8 protein was lower in the breast carcinoma cell lines (p=0.057), suggesting that DP8 may play differing roles in different cancer cell types. A strong, negative, non-reciprocal relationship was identified between DP9 protein and DP4 mRNA (r=-0.903, p=0.002) and protein (r=-0.810, p=0.015). This suggests that DP4 expression plays an important role in the post-transcriptional regulation of DP9 in breast and ovarian cancer cell lines. Overall, this study suggests a potential role for DP8 and DP9 in breast and ovarian cancer and further investigations in this area are required.

Effect of heart failure on dipeptidyl peptidase IV activity in plasma of dogs

BACKGROUND

In congestive heart failure (HF), plasma B-type natriuretic peptide (BNP) seems devoid of biological effectiveness. BNP(1-32) could be truncated into BNP(3-32) by dipeptidyl peptidase IV (DPP4), and BNP(3-32) has reduced biological activities.

HYPOTHESIS

Increased DPP4 activity is associated with pathophysiology of HF.

ANIMALS

One hundred twenty-eight client-owned dogs and 9 experimental Beagles from the Clinical Veterinary Unit of the University of Liège.

METHODS

We prospectively measured plasma DPP4 activity in 5 groups of dogs: normal growing dogs (n = 21), normal adult dogs (n = 60), healthy Beagle (n = 9), dogs with myxomatous mitral valve disease (n = 35), and dogs with dilated cardiomyopathy (n = 12). The final diagnosis and the severity of HF were determined by Doppler echocardiography. Plasma DPP4 activity was measured kinetically by a fluorimetric method.

RESULTS

In growing dogs, DPP4 activity was higher than in adults (P < .001) and inversely correlated with age (r = -0.57, P < .01). In adults, DPP4 activity increased linearly with body weight (r = 0.39, P < .01), but there was no influence of age or sex. No effect of the circadian rhythm was noted. DPP4 activity was significantly higher in HF ISACHC I (16.3 ± 1.14 U/L) compared with healthy adults (12.4 ± 0.65 U/L, P < .05) and HF ISACHC III (11.0 ± 1.50 U/L, P < .05). Mean DPP4 activity in ISACHC II was 15.1 ± 1.4 U/L.

CONCLUSION AND CLINICAL IMPORTANCE

We did not find evidence that plasma DPP4 activity is responsible for the "BNP resistance" in overt congestive HF, but it may be implicated in early stages.

Decreased soluble dipeptidyl peptidase IV activity as a potential serum biomarker for COPD

OBJECTIVES

The objective of this study was to measure soluble dipeptidyl peptidase IV (sDPPIV) activity in sera of patients with stable chronic obstructive pulmonary disease (COPD) in comparison to healthy controls. The main goal was to assess changes in the enzyme activity in relation to severity of the disease, age and smoking history and to evaluate diagnostic accuracy for prediction of COPD by level of serum sDPPIV activity.

DESIGN AND METHODS

The study included 106 patients with stable COPD (GOLD II-GOLD IV stages) and 38 healthy controls. Serum sDPPIV activity as well as some inflammatory markers (CRP, total and differential leukocyte counts) was measured. Multivariate logistic regression models were applied to analyze association of sDPPIV activity and inflammatory markers in risk estimation for COPD development.

RESULTS

sDPPIV activity in COPD patients was significantly reduced when compared to healthy controls. Decrease was observed already in GOLD II stage. Age and smoking history did not influence sDPPIV activity. Very good diagnostic accuracy (AUC=0.833; sensitivity and specificity of 85.7% and 78.9%, respectively) for GOLD II and good diagnostic accuracy (AUC=0.801; sensitivity and specificity of 65.1% and 86.8%, respectively) for total cohort of COPD patients were found. The multivariate logistic regression model showed that the use of sDPPIV in combination with CRP and lymphocyte proportion improved diagnostic strength and gave an AUC of 0.933.

CONCLUSIONS

sDPPIV activity is decreased in COPD patients as early as in GOLD II stage. Very good diagnostic accuracy of sDPPIV activity suggests it as a candidate biomarker for early diagnosis of COPD.

Effect of a dipeptidyl peptidase-IV inhibitor, des-fluoro-sitagliptin, on neointimal formation after balloon injury in rats

BACKGROUND

Recently, it has been suggested that enhancement of incretin effect improves cardiac function. We investigated the effect of a DPP-IV inhibitor, des-fluoro-sitagliptin, in reducing occurrence of restenosis in carotid artery in response to balloon injury and the related mechanisms.

METHODS AND FINDINGS

Otsuka Long-Evans Tokushima Fatty rats were grouped into four: control (normal saline) and sitagliptin 100, 250 and 500 mg/kg per day (n = 10 per group). Sitagliptin or normal saline were given orally from 1 week before to 2 weeks after carotid injury. After 3 weeks of treatment, sitagliptin treatment caused a significant and dose-dependent reduction in intima-media ratio (IMR) in obese diabetic rats. This effect was accompanied by improved glucose homeostasis, decreased circulating levels of high-sensitivity C-reactive protein (hsCRP) and increased adiponectin level. Moreover, decreased IMR was correlated significantly with reduced hsCRP, tumor necrosis factor-α and monocyte chemoattractant protein-1 levels and plasminogen activator inhibitor-1 activity. In vitro evidence with vascular smooth muscle cells (VSMCs) demonstrated that proliferation and migration were decreased significantly after sitagliptin treatment. In addition, sitagliptin increased caspase-3 activity and decreased monocyte adhesion and NFκB activation in VSMCs.

CONCLUSIONS

Sitagliptin has protective properties against restenosis after carotid injury and therapeutic implications for treating macrovascular complications of diabetes.

Dipeptidyl peptidase IV, aminopeptidase N and DPIV/APN-like proteases in cerebral ischemia

Background

Cerebral inflammation is a hallmark of neuronal degeneration. Dipeptidyl peptidase IV, aminopeptidase N as well as the dipeptidyl peptidases II, 8 and 9 and cytosolic alanyl-aminopeptidase are involved in the regulation of autoimmunity and inflammation. We studied the expression, localisation and activity patterns of these proteases after endothelin-induced occlusion of the middle cerebral artery in rats, a model of transient and unilateral cerebral ischemia.

Methods

Male Sprague-Dawley rats were used. RT-PCR, immunohistochemistry and protease activity assays were performed at different time points, lasting from 2 h to 7 days after cerebral ischemia. The effect of protease inhibitors on ischemia-dependent infarct volumes was quantified 7 days post middle cerebral artery occlusion. Statistical analysis was conducted using the t-test.

Results

Qualitative RT-PCR revealed these proteases in ipsilateral and contralateral cortices. Dipeptidyl peptidase II and aminopeptidase N were up-regulated ipsilaterally from 6 h to 7 days post ischemia, whereas dipeptidyl peptidase 9 and cytosolic alanyl-aminopeptidase were transiently down-regulated at day 3. Dipeptidyl peptidase 8 and aminopeptidase N immunoreactivities were detected in cortical neurons of the contralateral hemisphere. At the same time point, dipeptidyl peptidase IV, 8 and aminopeptidase N were identified in activated microglia and macrophages in the ipsilateral cortex. Seven days post artery occlusion, dipeptidyl peptidase IV immunoreactivity was found in the perikarya of surviving cortical neurons of the ipsilateral hemisphere, whereas their nuclei were dipeptidyl peptidase 8- and amino peptidase N-positive. At the same time point, dipeptidyl peptidase IV, 8 and aminopeptidase N were targeted in astroglial cells. Total dipeptidyl peptidase IV, 8 and 9 activities remained constant in both hemispheres until day 3 post experimental ischemia, but were increased (+165%) in the ipsilateral cortex at day 7. In parallel, aminopeptidase N and cytosolic alanyl-aminopeptidase activities remained unchanged.

Conclusions

Distinct expression, localization and activity patterns of proline- and alanine-specific proteases indicate their involvement in ischemia-triggered inflammation and neurodegeneration. Consistently, IPC1755, a non-selective protease inhibitor, revealed a significant reduction of cortical lesions after transient cerebral ischemia and may suggest dipeptidyl peptidase IV, aminopeptidase N and proteases with similar substrate specificity as potentially therapy-relevant targets.

Alogliptin benzoate for the treatment of type 2 diabetes

INTRODUCTION

Alogliptin is a highly selective inhibitor of the enzyme dipeptidyl peptidase-4 (DPP-4). It is one of several agents of this class now available for treatment of type 2 diabetes.

AREAS COVERED

This review is based upon a PubMed search and personal experience with alogliptin. The pharmacokinetics and pharmacodynamics of alogliptin are reviewed. The glucose-lowering effect of this agent is discussed as monotherapy and in combination with metformin, sulfonylurea, piogilitazone and insulin. The potential adverse effects of alogliptin are summarized. Alogliptin is compared with the other available DPP-4 inhibitors.

EXPERT OPINION

Alogliptin is an additional choice in the group of DPP-4 inhibitors. As a group, these agents have a relatively modest glucose-lowering effect, inferior to that of metformin, sulfonylureas, and insulin. They do not have the benefit of weight loss offered by the glucagon-like polypeptide (GLP)-1 agonists. The primary use of DPP-4 inhibitors is in combination with other hypoglycemic agents, mainly metformin. Their principal advantage is a low incidence of hypoglycemia, making these agents desirable in patients such as the elderly and those with cardiac disease. A greater use of alogliptin and other DPP-4 inhibitors will occur if long-term studies show reduced cardiac events or long-term retention of insulin secretory capacity. The Examine Trial, a large study of alogliptin in coronary disease patients, is now underway and could provide important supportive data.

Serum level of soluble CD26/dipeptidyl peptidase-4 (DPP-4) predicts the response to sitagliptin, a DPP-4 inhibitor, in patients with type 2 diabetes controlled inadequately by metformin and/or sulfonylurea

Dipeptidyl peptidase 4 (DPP-4) inhibitors is a new class of antihyperglycemic agents that is now available for the treatment of type 2 diabetes. We investigated the relationship between the baseline serum level of soluble CD 26/DPP-4 and the response to treatment with sitagliptin, a DPP-4 inhibitor, over 24 weeks in patients who had type 2 diabetes inadequately controlled by metformin and/or sulfonylurea therapy. We studied 52 consecutive patients with type 2 diabetes who had poor glycemic control despite treatment with metformin and/or sulfonylurea. All patients were given 50 mg/day of sitagliptin and were followed at monthly intervals for 24 weeks. Treatment with sitagliptin decreased significantly hemoglobin A1c (HbA1c) from 7.91 ± 1.08% at baseline to 6.96 ± 1.18% at 8 weeks, 7.04 ± 0.77% at 16 weeks, and 7.08 ± 0.80% at 24 weeks. The baseline serum level of sCD26 was correlated positively with HbA1c at both 16 weeks and 24 weeks. Furthermore, the serum sCD26 level at baseline was also correlated positively with the changes from baseline of HbA1c at 16 and 24 weeks (r = 0.318, P = 0.0296 and r = 0.516, P = 0.0003, respectively). In a multivariate logistic regression model that explained 56.1% (R(2) = 0.561) of the variation of the changes from baseline of HbA1c at 24 weeks, the baseline HbA1c (β = -0.638, P < 0.001) and serum sCD26 (β = 0.357, P = 0.041) were independent determinants of the change of HbA1c at 24 weeks. In conclusions, a higher serum level of sCD26 is associated with a worse response to sitagliptin in patients with type 2 diabetes controlled inadequately by metformin and/or sulfonylurea therapy.

Proteomics in the characterization of adipose dysfunction in obesity

Adipose tissue plays a central role in body weight homeostasis, inflammation, and insulin resistance via serving as a fat-buffering system, regulating lipid storage and mobilization and releasing a large range of adipokines and cytokines. Adipose tissue is also the major inflammation-initiated site in obesity. Adipose-derived adipokines and cytokines are known to be involved in the modulation of a wide range of important physiological processes, particularly immune response, glucose and lipid homeostasis and insulin resistance. Adipose tissue dysfunction, characterized by an imbalanced secretion of pro- and anti-inflammatory adipokines and cytokines, decreased insulin-stimulated glucose uptake, dysregulation of lipid storage and release and mitochondrial dysfunction, has been linked to obesity and its associated metabolic disorders. Proteomic technology has been a powerful tool for identifying key components of the adipose proteome, which may contribute to the pathogenesis of adipose tissue dysfunction in obesity. In this review, we summarized the recent advances in the proteomic characterization of adipose tissue and discussed the identified proteins that potentially play important roles in insulin resistance and lipid homeostasis.

Comparison of the activity levels and localization of dipeptidyl peptidase IV in normal and tumor human lung cells

Dipeptidyl peptidase IV (DPPIV) was studied in three human lung cells - P (fetal lung-derived cells), A549 (lung adenocarcinoma) and SK-MES-1 (squamous cell carcinoma) using a fluorescent cytochemical procedure developed on the basis of the substrate 4-(glycyl-L-prolyl hydrazido)-N-hexyl-1,8-naphthalimide. The observed differences in the enzyme expression were confirmed by measuring the enzyme hydrolysis of glycyl-L-prolyl-para-nitroanilide. The surface and total dipeptidyl peptidase activities of P cells were correspondingly 7-8 and 3-10 times higher than those of SK-MES-1 and A549 cells. The ratio surface per total activity showed that in P (95%) and A549 (93%) cells the enzyme is associated with the plasmalemma while in SK-MES-1 cells (35%) it is bound to intracellular membranes. In order to compare the results from cell cultures with those in human tumor, the enzyme activity was investigated in cryo-sections of three cases of diagnosed squamous lung carcinoma. DPPIV activity was restricted to the connective tissue stroma surrounding the DPPIV-negative tumor foci.

CD26/dipeptidyl-peptidase IV and adenosine deaminase serum levels in psoriatic patients treated with cyclosporine, etanercept, and psoralen plus ultraviolet A phototherapy

OBJECTIVE

The aim of this study is to determine serum levels of soluble forms of CD26/dipeptidyl-peptidase IV (DPP-IV) and adenosine deaminase (ADA), thought to be markers of T-cell activation, and changes in their levels in response to cyclosporine, etanercept, and psoralen plus ultraviolet A (PUVA) treatments with respect to disease activity.

METHODS

This study is designed as a prospective clinical study with a control group and three months of follow-up. The study included 41 patients with psoriasis and 41 healthy controls that were older than 18years of age. There were three different treatment groups: PUVA (n=15), cyclosporine (n=15), and etanercept (n=11). To determine disease severity of patients with psoriasis, psoriasis area and severity index (PASI) scores were calculated.

RESULTS

Only mean serum ADA levels were different between patients with psoriasis [mean1±standard deviation (SD)=13.9±3.3U/ml] and control group (mean±SD=12±3.5U/ml). Mean serum ADA levels were significantly higher before treatment than after treatment (mean±SD=12.4±3.4U/ml). Contrarily, following three months of therapy, mean serum CD26 levels increased significantly from 777.7±214.6 to 835.3±203ng/ml (P<0.05) and mean serum DPP-IV activity increased significantly from 12.1±4 to 15.9±4.2nmol/min (P<0.05). There was no correlation between ADA and CD 26/DPP-IV with PASI values.

CONCLUSIONS

 The results show that ADA might be a useful marker indicating disease activity and T-cell activation. As significant changes were observed in serum CD26/DPP-IV before and after treatment, we think CD26/DPP-IV might play a role in psoriasis pathogenesis, which should be clarified by further studies.

Dipeptidyl peptidase IV (DPPIV/CD26) inhibition does not improve engraftment of unfractionated syngeneic or allogeneic bone marrow after nonmyeloablative conditioning

In order to develop minimally toxic bone marrow transplantation (BMT) protocols suitable for use in a wider range of indications, it is important to identify ways to enhance BM engraftment at a given level of recipient conditioning. CXCL12/stromal cell-derived factor-1α plays a crucial physiological role in homing of hematopoietic stem cells to BM. It is regulated by the ectopeptidase dipeptidyl peptidase IV (DPPIV; DPP4) known as CD26, which cleaves dipeptides from the N-terminus of polypeptide chains. Blocking DPPIV enzymatic activity had a beneficial effect on hematopoietic stem cell engraftment in various but very specific experimental settings. Here we investigated whether inhibition of DPPIV enzymatic activity through Diprotin A or sitagliptin (Januvia) improves BM engraftment in nonmyeloablative murine models of syngeneic (i.e., CD45-congenic) and allogeneic (i.e., Balb/c to B6) BMT (1 Gy total body irradiation, 10–15 × 10⁶ unseparated BM cells/mouse). Neither Diprotin A administered in vivo at the time of BMT and/or used for in vitro pretreatment of BM nor sitagliptin administered in vivo had a detectable effect on the level of multilineage chimerism (follow-up >20 weeks). Similarly, sitagliptin did not enhance chimerism after allogeneic BMT, even though DPPIV enzymatic activity measured in serum was profoundly inhibited (>98% inhibition at peak exposure). Our results provide evidence that DPPIV inhibition via Diprotin A or sitagliptin does not improve engraftment of unseparated BM in a nonmyeloablative BMT setting.

Dipeptidyl peptidase IV inhibition improves cardiorenal function in overpacing-induced heart failure

AIMS

Recent studies indicate that brain natriuretic peptide (BNP(1-32)) may be truncated into BNP(3-32) by dipeptidyl peptidase IV (DPP4) and that BNP(3-32) has reduced biological activities compared with BNP(1-32). We investigated if DPP4 contributes to the cardiorenal alterations and to the attenuated response to BNP seen in heart failure.

METHODS AND RESULTS

Haemodynamic and renal assessment was performed in 12 pigs at baseline, 4 weeks after pacing-induced heart failure, and during BNP infusion. They were randomized to either placebo or treatment with a DPP4 inhibitor, sitagliptin. After 4 weeks of pacing, heart rate was reduced compared with baseline in the sitagliptin group (60 ± 2 vs. 95 ± 16 b.p.m., P < 0.01), and an increase in stroke volume was observed in the sitagliptin group compared with placebo (+24 ± 6% vs. -17 ± 7%, P < 0.01). Glomerular filtration rate declined at week 4 compared with baseline in the placebo group (1.3 ± 0.4 vs. 2.3 ± 0.3 mL/kg/min, P < 0.01) but remained preserved in the sitagliptin group [1.8 ± 0.2 vs. 2.0 ± 0.3 mL/kg/min, P = NS (non-significant)]. In the sitagliptin group, BNP infusion improved end-systolic elastance (68 ± 5 vs. 31 ± 4 mmHg/kg/mL, P < 0.05), ventricular-arterial coupling, and mechanical efficiency. Compared with controls (n = 6), myocardial gene expression of BNP, interleukin-6, Na(+)-Ca(2+) exchanger, and calmodulin was up-regulated in the placebo group, but not in the sitagliptin group.

CONCLUSION

In pacing-induced heart failure, DPP4 inhibition preserves the glomerular filtration rate, modulates stroke volume and heart rate, and potentiates the positive inotropic effect of exogenous BNP at no energy expense.

DA-1229, a novel and potent DPP4 inhibitor, improves insulin resistance and delays the onset of diabetes

AIM

To characterize the pharmacodynamic profile of DA-1229, a novel dipeptidyl peptidase (DPP) 4 inhibitor.

MAIN METHODS

Enzyme inhibition assays against DPP4, DPP8 and DPP9. Antidiabetic effects of DA-1229 in HF-DIO mice and young db/db mice.

KEY FINDINGS

DA-1229 was shown to potently inhibit the DPP4 enzyme in human and murine soluble forms and the human membrane-bound form with IC(50) values of 0.98, 3.59 and 1.26 nM, respectively. As a reversible and competitive inhibitor, DA-1229 was more selective to human DPP4 (6000-fold) than to human DPP8 and DPP9. DA-1229 (0.1-3mg/kg) dose-dependently inhibited plasma DPP4 activity, leading to increased levels of plasma GLP-1 and insulin, and thereby lowering blood glucose levels in mice. In high fat diet-fed (HF) mice, a single oral dose of 100mg/kg of DA-1229 reduced plasma DPP4 activity by over 80% during a 24h period. Long-term treatment with DA-1229 for 8 weeks revealed significant improvements in glucose intolerance and insulin resistance, accompanied by significant body weight reduction. However, it remains unclear whether there is a direct causal relationship between DPP4 inhibition and body weight reduction. In young db/db mice, the DA-1229 treatment significantly reduced blood glucose excursions for the first 2 weeks, resulting in significantly lower levels of HbA1c at the end of the study. Furthermore, the pancreatic insulin content of the treatment group was significantly higher than that of the db/db control.

SIGNIFICANCE

DA-1229 as a novel and selective DPP4 inhibitor improves the insulin sensitivity in HF mice and delays the onset of diabetes in young db/db mice.

Key considerations in pharmacotherapy for type 2 diabetes mellitus: a multiple target organ approach

WHAT IS KNOWN AND OBJECTIVE

Type 2 diabetes mellitus (T2DM) is a progressive multisystem disease, and less than half the population with T2DM has achieved the recommended glycosylated haemoglobin A1c goal. We aim to present key points to consider when selecting pharmacotherapy for the management of T2DM. The selection of pharmacotherapy is discussed within the context of the underlying pathophysiology of T2DM, currently available treatment options highlighting newer agents and current clinical guidelines.

COMMENT

Combination therapy regimens that target the multiple organ systems involved in the pathophysiology of T2DM can be developed based on the mechanism of action (MOA) of each class of agents. We compare the pathophysiology of T2DM with the MOA of the currently available non-insulin therapeutic options.

WHAT IS NEW AND CONCLUSION

Combination therapy that efficiently and effectively targets multiorgan correction with the least risk for serious adverse events, such as hypoglycaemia and drug interactions, is needed when initial treatment fails to achieve the desired clinical outcomes. Newer agents, now incorporated in treatment guidelines, increase the range of options available to the clinician.

Medicinal Chemistry and Applications of Incretins and DPP-4 Inhibitors in the Treatment of Type 2 Diabetes Mellitus

Diabetes mellitus (DM) is a major metabolic disorder currently affecting over 200 million people worldwide. Approximately 90% of all diabetic patients suffer from Type 2 diabetes mellitus (T2DM). The world's economy coughs out billions of dollars annually to diagnose, treat and manage patients with diabetes. It has been shown that the naturally occurring gut hormones incretins, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) can preserve the morphology and function of pancreatic beta cell. In addition, GIP and GLP-1 act on insulin receptors to facilitate insulin-receptor binding, resulting in optimal glucose metabolism. This review examines the medicinal chemistry and roles of incretins, specifically, GLP-1 and drugs which can mimic its actions and prevent its enzymatic degradation. The review discussed GLP-1 agonists such as exenatide, liraglutide, taspoglutide and albiglutide. The paper also identified and reviewed a number of inhibitors, which can block dipeptidyl peptidase 4 (DPP-4), the enzyme responsible for the rapid degradation of GLP-1. These DPP-4 inhibitors include sitagliptin, saxagliptin, vildagliptin and many others which are still in the experimental phase.

A follow-up case-control association study of tractable (druggable) genes in recurrent major depression

The High-Throughput Disease-specific target Identification Program (HiTDIP) aimed to study case-control association samples for 18 common diseases. Here we present the results of a follow-up case-control association study of HiTDIP in major depressive disorder (MDD). The HiTDIP in MDD was conducted in a sample of 974 cases of recurrent MDD of white German origin collected at the Max-Planck Institute (MP-GSK) and 968 ethnically matched controls screened for lifetime absence of depression. Six genes were identified as of interest for a follow-up, based on the strength of the association and based on the interest as potential candidate target for developing new treatment for depression: Solute Carrier Family 4 Member 10 (SLC4A10), Dipeptidyl Peptidase IV (DPP4), Dopamine Receptor D3 (DRD3), Zinc Finger Protein 80 (ZNF80), Nitric Oxide Synthase 2A (NOS2A) and Peroxisome Proliferator-Activated Receptor-Gamma, Coactivator 1, Alpha (PPARGC1A). Within the current study, we attempted to follow-up these findings in a sample from the UK, the Depression Case Control (DeCC) sample consisting of 1,196 cases and 842 screened controls, phenotyped using exactly the same methods as the MP-GSK sample. Performing Cochran-Mantel-Haenzel statistics to test for genotypic and/or allelic differences between the DeCC and MP-GSK samples, we found no significant differences, thus being able to combine the two samples for association testing. In the combined sample of 2,170 MDD cases and 1,810 controls, there were positive findings in the Nitric Oxide Synthase 2A (NOS2A) gene both using single SNP analysis and haplotype analysis.

Biomarkers of immune dysfunction following combination antiretroviral therapy for HIV infection

Combination antiretroviral therapy (cART) has significantly reduced morbidity and mortality of HIV-infected patients, yet their life expectancy remains reduced compared with the general population. Most HIV-infected patients receiving cART have some persistent immune dysfunction characterized by chronic immune activation and premature aging of the immune system. Here we review biomarkers of T-cell activation (CD69, -25 and -38, HLA-DR, and soluble CD26 and -30); generalized immune activation (C-reactive protein, IL-6 and D-dimer); microbial translocation (lipopolysaccharide, 16S rDNA, lipopolysaccharide-binding protein and soluble CD14); and immune dysfunction of specific cellular subsets (T cells, natural killer cells and monocytes) in HIV-infected patients on cART and their relationship to adverse clinical outcomes including impaired CD4 T-cell recovery, as well as non-AIDS clinical events, such as cardiovascular disease.

DPP-4 inhibitor des-F-sitagliptin treatment increased insulin exocytosis from db/db mice β cells

Incretin promotes insulin secretion acutely. Recently, orally-administered DPP-4 inhibitors represent a new class of anti-hyperglycemic agents. Indeed, inhibitors of dipeptidyl peptidase-IV (DPP-4), sitagliptin, has just begun to be widely used as therapeutics for type 2 diabetes. However, the effects of sitagliptin-treatment on insulin exocytosis from single β-cells are yet unknown. We therefore investigated how sitagliptin-treatment in db/db mice affects insulin exocytosis by treating db/db mice with des-F-sitagliptin for 2 weeks. Perfusion studies showed that 2 weeks-sitagliptin treatment potentiated insulin secretion. We then analyzed insulin granule motion and SNARE protein, syntaxin 1, by TIRF imaging system. TIRF imaging of insulin exocytosis showed the increased number of docked insulin granules and increased fusion events from them during first-phase release. In accord with insulin exocytosis data, des-F-sitagliptin-treatment increased the number of syntaxin 1 clusters on the plasma membrane. Thus, our data demonstrated that 2-weeks des-F-sitagliptin-treatment increased the fusion events of insulin granules, probably via increased number of docked insulin granules and that of syntaxin 1 clusters.

Serum DPPIV activity and CD26 expression on lymphocytes in patients with benign or malignant breast tumors

The aim of this work was to determine serum DPPIV activity as well as the percentage of CD26+ white blood cells and of CD26+ lymphocytes and the mean fluorescence intensity (MFI) of CD26 expression on lymphocytes in groups of patients with benign or malignant breast tumors and in healthy control people. Serum DPPIV activity was determined by colorimetric test, while CD26+ cells were counted using flow cytometer. Results of this study show that there is no statistically significant difference in serum DPPIV activity between examined groups of patients and healthy controls. However, two times higher frequency of patients with breast cancers had the enhanced DPPIV enzymatic activity in comparison to controls. Significant decrease in the percentage of CD26+ total white blood cells was found in the group of breast cancer patients and in patients with benign breast tumors compared to that found for healthy people. Although there was decrease in the percentage of lymphocytes in patients with breast tumors it was not statistically significant. The MFI of CD26 expression on these cells was significantly lower for cancer patients in comparison to healthy controls. In conclusion, this work showed the enhanced frequency of breast cancer patients with higher serum DPPIV activity. Decreased percentage of CD26+ white blood cells and decreased CD26 expression on lymphocytes are also characteristics of this group of patients. Determination of the clinical outcome of analyzed patients, 1 and 2 years after the surgical resection of the tumor, would clarify potential prognostic values of examined parameters for breast cancer.

Nature of action of Sitagliptin, the dipeptidyl peptidase-IV inhibitor in diabetic animals

Objective:

The aim of this study was to evaluate the dipeptidyl peptidase-IV (DPP-IV) inhibitor sitagliptin with respect to mode of inhibition and its in vivo duration of inhibition and efficacy in type 2 diabetes animal model.

Materials and Methods:

DPP-IV enzyme assay was carried out in human plasma (10 μL) or human recombinant enzyme (10 ng) using H-Gly-Pro-AMC as a substrate. The competitive nature was estimated by plotting IC₅₀ values measured at different substrate concentrations on the Y axis and substrate concentration on the X axis. The tight binding nature was estimated by plotting IC₅₀ values measured at different plasma volumes on the Y axis and plasma volumes on the X axis. Fast binding kinetics was assessed by progressive curves at different inhibitor concentrations in the DPP-IV assay. The reversibility of the inhibitor was assessed by a dissociation study of the DPP-IV-sitagliptin complex. Durations of DPP-IV inhibition and efficacy were shown in ob/ob mice dosed at 10 mg/kg, p.o.

Results:

Sitagliptin is a competitive, reversible, fast and tight binding DPP-IV inhibitor. In ob/ob mice, 10 mg/kg, (p.o.) showed a long duration of inhibition of > 70% at 8 h. The duration was translated into long duration of efficacy (~ 35% glucose excursion at 8 h) in the same model and the effect was comparable to vildagliptin.

Conclusion:

The DPP-IV inhibitor sitagliptin behaves as a competitive, tight, and fast binding inhibitor. Sitagliptin differs mechanistically from vildagliptin and exhibits comparable efficacy to that of latter. The finding may give an understanding to develop-second generation DPP-IV inhibitors with desired kinetic profiles.

Isolation of dipeptidyl peptidase IV (DP 4) isoforms from porcine kidney by preparative isoelectric focusing to improve crystallization

In the present studies we resolved the post-translational microheterogeneity of purified porcine dipeptidyl peptidase IV (DP 4) from kidney cortex. Applying SDS-homogeneous DP 4 onto an analytical agarose isoelectric focusing (IEF) gel, pH 4–6, activity staining resulted in at least 17 isoforms between pH 4.8–6.0. These could be separated into fractions with only two to six isoforms by means of preparative liquid-phase IEF, using a Rotofor cell. Starting off with three parallel Rotofor runs under the same conditions at pH 5–6, the fractions were pooled according to the specific activity of DP 4, pH and analytical IEF profile, and further refractionated without any additional ampholytes. Since excessive dilution of ampholytes and proteins was kept to the minimum, a second refractionation step could be introduced, resulting in pH gradients between 0.022 and 0.028 pH increments per fraction. By performing two consecutive refractionation steps, the high resolution necessary for the separation of DP 4 isoforms could be achieved. This represents an alternative method if isolation of isoforms with similar pI's results in precipitation and denaturation in presence of a narrow pH range. Furthermore, it demonstrates that preparative IEF is a powerful tool to resolve post-translational microheterogeneity of a purified protein required for crystallization processing.

Dipeptidyl peptidase 4 is a novel adipokine potentially linking obesity to the metabolic syndrome

OBJECTIVE

Comprehensive proteomic profiling of the human adipocyte secretome identified dipeptidyl peptidase 4 (DPP4) as a novel adipokine. This study assessed the functional implications of the adipokine DPP4 and its association to the metabolic syndrome.

RESEARCH DESIGN AND METHODS

Human adipocytes and skeletal and smooth muscle cells were used to monitor DPP4 release and assess the effects of soluble DPP4 on insulin signaling. In lean and obese subjects, depot-specific expression of DPP4 and its release from adipose tissue explants were determined and correlated to parameters of the metabolic syndrome.

RESULTS

Fully differentiated adipocytes exhibit a substantially higher release of DPP4 compared with preadipocytes or macrophages. Direct addition of DPP4 to fat and skeletal and smooth muscle cells impairs insulin signaling. A fivefold higher level of DPP4 protein expression was seen in visceral compared with subcutaneous fat of obese patients, with no regional difference in lean subjects. DPP4 serum concentrations significantly correlated with adipocyte size. By using adipose tissue explants from lean and obese subjects, we observed a twofold increase in DPP4 release that strongly correlated with adipocyte volume and parameters of the metabolic syndrome and was decreased to the lean level after weight reduction. DPP4 released from adipose tissue correlated positively with an increasing risk score for the metabolic syndrome.

CONCLUSIONS

DPP4 is a novel adipokine that may impair insulin sensitivity in an autocrine and paracrine fashion. Furthermore, DPP4 release strongly correlates with adipocyte size, potentially representing an important source of DPP4 in obesity. Therefore, we suggest that DPP4 may be involved in linking adipose tissue and the metabolic syndrome.