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

Potential benefits of melatonin in organ transplantation: a review

Organ transplantation is a useful therapeutic tool for patients with end-stage organ failure; however, graft rejection is a major obstacle in terms of a successful treatment. Rejection is usually a consequence of a complex immunological and nonimmunological antigen-independent cascade of events, including free radical-mediated ischemia-reperfusion injury (IRI). To reduce the frequency of this outcome, continuing improvements in the efficacy of antirejection drugs are a top priority to enhance the long-term survival of transplant recipients. Melatonin (N-acetyl-5-methoxytryptamine) is a powerful antioxidant and ant-inflammatory agent synthesized from the essential amino acid l-tryptophan; it is produced by the pineal gland as well as by many other organs including ovary, testes, bone marrow, gut, placenta, and liver. Melatonin has proven to be a potentially useful therapeutic tool in the reduction of graft rejection. Its benefits are based on its direct actions as a free radical scavenger as well as its indirect antioxidative actions in the stimulation of the cellular antioxidant defense system. Moreover, it has significant anti-inflammatory activity. Melatonin has been found to improve the beneficial effects of preservation fluids when they are enriched with the indoleamine. This article reviews the experimental evidence that melatonin is useful in reducing graft failure, especially in cardiac, bone, otolaryngology, ovarian, testicular, lung, pancreas, kidney, and liver transplantation.

Mass spectrometry-assisted confirmation of the inability of dipeptidyl peptidase-4 to cleave goldfish peptide YY(1-36) and the lack of anorexigenic effects of peptide YY(3-36) in goldfish (Carassius auratus)

Dipeptidyl peptidase-4 (DPP4) is a serine protease of great interest because it has been shown to modulate the activity of several peptidergic factors including peptide YY (PYY) and glucagon-like peptide-1/2. While PYY(1-36) is orexigenic in mammals, PYY(3-36) recently garnered interest as a potent anorexigen. In silico phylogenetic analysis found that the DPP4 cleavage sites are absent in fish PYY sequences. However, no studies were conducted to show that indeed PYY(3-36) is not produced by DPP4 in fish. If DPP4 does not cleave PYY(1-36), is PYY(3-36) an anorexigen in fish? The objectives of this research were to (1) test whether DPP4 cleaves goldfish PYY(1-36) and (2) determine whether PYY(3-36) is an anorexigen in goldfish. First, we identified the highly conserved catalytic region of DPP4 in goldfish. Abundant expression of DPP4 mRNA was found within the gastrointestinal tract. We also report the first MALDI-MS cleavage analysis of DPP4 effects on PYY(1-36) in a non-mammalian vertebrate. Our novel results indicate that DPP4 is unable to cleave goldfish PYY(1-36) to PYY(3-36) in vitro. It also confirms a previously held hypothesis that DPP4 is unable to cleave fish PYY(1-36) that contains N-terminal proline-proline residues. PYY(3-36) had no effects on food intake of goldfish. The appetite inhibitory effects of intraperitoneal and intracerebroventricular injections of 10 ng/g body weight gfPYY(1-36) were abolished by coinjections of BIBP3226, a Y1 receptor antagonist. These results are significant because it shows the lack of generation of endogenous PYY(3-36) and its anorectic effects in goldfish.

Identifying neuropeptide Y (NPY) as the main stress-related substrate of dipeptidyl peptidase 4 (DPP4) in blood circulation

BACKGROUND

Dipeptidyl peptidase 4 (DPP4; EC 3.4.14.5; CD26) is a membrane-bound or shedded serine protease that hydrolyzes dipeptides from the N-terminus of peptides with either proline or alanine at the penultimate position. Substrates of DPP4 include several stress-related neuropeptides implicated in anxiety, depression and schizophrenia. A decline of DPP4-like activity has been reported in sera from depressed patient, but not fully characterized regarding DPP4-like enzymes, therapeutic interventions and protein.

METHODS

Sera from 16 melancholic- and 16 non-melancholic-depressed patients were evaluated for DPP4-like activities and the concentration of soluble DPP4 protein before and after treatment by anti-depressive therapies. Post-translational modification of DPP4-isoforms and degradation of NPY, Peptide YY (PYY), Galanin-like peptide (GALP), Orexin B (OrxB), OrxA, pituitary adenylate cyclase-activating polypeptide (PACAP) and substance P (SP) were studied in serum and in ex vivo human blood. N-terminal truncation of biotinylated NPY by endothelial membrane-bound DPP4 versus soluble DPP4 was determined in rat brain perfusates and spiked sera.

RESULTS

Lower DPP4 activities in depressed patients were reversed by anti-depressive treatment. In sera, DPP4 contributed to more than 90% of the overall DPP4-like activity and correlated with its protein concentration. NPY displayed equal degradation in serum and blood, and was equally truncated by serum and endothelial DPP4. In addition, GALP and rat OrxB were identified as novel substrates of DPP4.

CONCLUSION

NPY is the best DPP4-substrate in blood, being truncated by soluble and membrane DPP4, respectively. The decline of soluble DPP4 in acute depression could be reversed upon anti-depressive treatment. Peptidases from three functional compartments regulate the bioactivity of NPY in blood.

Cut to the chase: a review of CD26/dipeptidyl peptidase-4's (DPP4) entanglement in the immune system

CD26/DPP4 (dipeptidyl peptidase 4/DP4/DPPIV) is a surface T cell activation antigen and has been shown to have DPP4 enzymatic activity, cleaving-off amino-terminal dipeptides with either L-proline or L-alanine at the penultimate position. It plays a major role in glucose metabolism by N-terminal truncation and inactivation of the incretins glucagon-like peptide-1 (GLP) and gastric inhibitory protein (GIP). In 2006, DPP4 inhibitors have been introduced to clinics and have been demonstrated to efficiently enhance the endogenous insulin secretion via prolongation of the half-life of GLP-1 and GIP in patients. However, a large number of studies demonstrate clearly that CD26/DPP4 also plays an integral role in the immune system, particularly in T cell activation. Therefore, inhibition of DPP4 might represent a double-edged sword. Apart from the metabolic benefit, the associated immunological effects of long term DPP4 inhibition on regulatory processes such as T cell homeostasis, maturation and activation are not understood fully at this stage. The current data point to an important role for CD26/DPP4 in maintaining lymphocyte composition and function, T cell activation and co-stimulation, memory T cell generation and thymic emigration patterns during immune-senescence. In rodents, critical immune changes occur at baseline levels as well as after in-vitro and in-vivo challenge. In patients receiving DPP4 inhibitors, evidence of immunological side effects also became apparent. The scope of this review is to recapitulate the role of CD26/DPP4 in the immune system regarding its pharmacological inhibition and T cell-dependent immune regulation.

The contributions of dipeptidyl peptidase IV to inflammation in heart failure

Circulating dipeptidyl peptidase IV (DPPIV) activity correlates with cardiac dysfunction in humans and experimental heart failure (HF) models. Similarly, inflammatory markers are associated with poorer outcomes in HF patients. However, the contributions of DPPIV to inflammation in HF remain elusive. Therefore, this study aimed to investigate whether the cardioprotective effects of DPPIV inhibition after myocardial injury are accompanied by reduced cardiac inflammation, whether circulating DPPIV activity correlates with the levels of systemic inflammatory markers in HF patients, and whether leukocytes and/or splenocytes may be one of the sources of circulating DPPIV in HF. Experimental HF was induced in male Wistar rats by left ventricular myocardial injury after radiofrequency catheter ablation. The rats were divided into three groups: sham, HF, and HF + DPPIV inhibitor (sitagliptin). Six weeks after surgery, cardiac function, perfusion and inflammatory status were evaluated. Sitagliptin treatment improved cardiac function and perfusion, reduced macrophage infiltration, and diminished the levels of inflammatory biomarkers including TNF-α, IL-1β, and CCL2. In HF patients, serum DPPIV activity correlated with CCL2, suggesting that leukocytes may be the source of circulating DPPIV in HF. Unexpectedly, DPPIV release was higher in splenocytes from HF rats and similar in HF circulating mononuclear cells compared with those from sham, suggesting an organ-specific modulation of DPPIV in HF. Collectively, our data provide new evidence that the cardioprotective effects of DPPIV inhibition in HF may be due to suppression of inflammatory cytokines. Moreover, they suggest that a vicious circle between DPPIV and inflammation may contribute to HF development and progression.

Association of DPP4 Gene Polymorphisms with Type 2 Diabetes Mellitus in Malaysian Subjects

Background

Genetic polymorphisms of the Dipeptidyl Peptidase 4 (DPP4) gene may play a role in the etiology of type 2 diabetes mellitus (T2DM). This study aimed to investigate the possible association of single nucleotide polymorphisms (SNPs) of the DPP4 gene in Malaysian subjects with T2DM and evaluated whether they had an effect on the serum levels of soluble dipeptidyl peptidase 4 (sDPP-IV).

Method

Ten DPP4 SNPs were genotyped by TaqMan genotyping assays in 314 subjects with T2DM and 235 controls. Of these, 71 metabolic syndrome (MetS) subjects were excluded from subsequent analysis. The odds ratios (ORs) and their 95% confidence interval (CIs) were calculated using multiple logistic regression for the association between the SNPs of DPP4 and T2DM. In addition, the serum levels of sDPP-IV were investigated to evaluate the association of the SNPs of DPP4 with the sDPP-IV levels.

Results

Dominant, recessive, and additive genetic models were employed to test the association of DPP4 polymorphisms with T2DM, after adjusting for age, race, gender and BMI. The rs12617656 was associated with T2DM in Malaysian subjects in the recessive genetic model (OR = 1.98, p = 0.006), dominant model (OR = 1.95, p = 0.008), and additive model (OR = 1.63, p = 0.001). This association was more pronounced among Malaysian Indians, recessive (OR = 3.21, p = 0.019), dominant OR = 3.72, p = 0.003) and additive model (OR = 2.29, p = 0.0009). The additive genetic model showed that DPP4 rs4664443 and rs7633162 polymorphisms were associated with T2DM (OR = 1.53, p = 0.039), and (OR = 1.42, p = 0.020), respectively. In addition, the rs4664443 G>A polymorphism was associated with increased sDPP-IV levels (p = 0.042) in T2DM subjects.

Conclusions

DPP4 polymorphisms were associated with T2DM in Malaysian subjects, and linked to variations in sDPP-IV levels. In addition, these associations were more pronounced among Malaysian Indian subjects.

Peptide profiling and the bioactivity character of yogurt in the simulated gastrointestinal digestion

This study investigated the relationship between peptide profiles and the bioactivity character of yogurt in simulated gastrointestinal trials. A total of 250, 434 and 466 peptides were identified by LC-MS/MS analyses of yogurt, gastric digest and pancreatic digest. Forty peptides of yogurt survived in gastrointestinal digestion. κ-CN and β-CN contributed the diversity of peptides during the fermentation process and gastrointestinal digestion, respectively. The favorite of κ-CN by lactic acid bacteria complemented gut digestion by hydrolyzing κ-CN, the low abundance milk proteins. The potential bioactivities were evaluated by in vitro ACE and DPP-IV inhibition assays. The ACE inhibition rate of the pancreatic digests was ~4 - and ~2 - fold greater than that of yogurt and the gastric digests. The ACE inhibitory peptides generated during gastrointestinal digestion improved the ACE inhibitory activity of the gastric and pancreatic digests. The DPP-IV inhibition rate of the pancreatic digest was ~6 - and ~3 - fold greater than that of yogurt and the gastric digest. The numbers of potential DPP-IV inhibitory peptides were positively correlated to the DPP-IV inhibitory activity of the gastric and pancreatic digests.

BIOLOGICAL SIGNIFICANCE

The present study describes the characters and bioactivities of peptides from yogurt in a simulated gastrointestinal digestion. The number of peptides identified from yogurt and gastrointestinal digests by LC-MS/MS increased in the simulated gastrointestinal trials. The in vitro ACE and DPP-IV inhibition bioactivities revealed that the bioactivity of yogurt was enhanced during gastrointestinal digestion. The correlation between peptides and bioactivity in vitro indicated that not only the peptides amount but also the proportion of peptides with high bioactivities contributed to increased bioactivity during gastrointestinal digestion. The study of peptides identified from yogurt and digests revealed that the number of released peptides was not determined by the abundance of the parent proteins but by whether the enzymes favored the protein. In summary, peptide profiling and bioactivities of yogurt in simulated gastrointestinal digestion helped to elucidate the health benefits of yogurt peptides. The results further revealed that pre-digestion of milk by lactic acid bacteria are complementary to generate bioactive peptides and to provide particular yogurt functions.

Plasma dipeptidyl peptidase IV activity and measures of body composition in apparently healthy people

AIM

Based on its regulatory action on glucagon-like peptide 1, dipeptidyl peptidase IV (DPP-IV) has increasingly been linked to Type 2 diabetes. However, there is no evidence as to how this normal modulatory enzyme leads to pathology. It is thought that DPP-IV is affected by the development of obesity, which is a common precursor to Type 2 diabetes. Little is known about the relationship between DPP-IV activity in plasma and specific body composition measures.

MAIN METHODS

In the current study, plasma DPP-IV activity and body composition measures were collected from 111 healthy subjects between the ages of 19 and 70 years old for analysis.

KEY FINDINGS

The mean plasma DPP-IV activity was 35.9U/L ± 12.3, falling within normal reference value range presented by Durinx et al. DPP-IV activity was negatively correlated with absolute body fat mass, but absolute lean mass was positively correlated. Consistent with the findings, DPP-IV activity was also negatively correlated with absolute gynoid fat (p = 0.0047). DPP-IV activity did not have a significant correlation with absolute android fat mass, visceral adipose tissue, BMI, and age.

SIGNIFICANCE

From these results, it can be concluded that high activity of DPP-IV is not indicative of pathology, and specific body composition components may influence soluble DPP-IV activity in the blood.

A Case Report of a Middle East Respiratory Syndrome Survivor with Kidney Biopsy Results

A 68-year old man diagnosed with Middle East Respiratory Syndrome-Coronavirus (MERS-CoV) presented with multiple pneumonic infiltrations on his chest X-ray, and the patient was placed on a mechanical ventilator because of progressive respiratory failure. Urinary protein excretion steadily increased for a microalbumin to creatinine ratio of 538.4 mg/g Cr and a protein to creatinine ratio of 3,025.8 mg/g Cr. The isotope dilution mass spectrometry traceable serum creatinine level increased to 3.0 mg/dL. We performed a kidney biopsy 8 weeks after the onset of symptoms. Acute tubular necrosis was the main finding, and proteinaceous cast formation and acute tubulointerstitial nephritis were found. There were no electron dense deposits observed with electron microscopy. We could not verify the virus itself by in situ hybridization and confocal microscopy (MERS-CoV co-stained with dipeptidyl peptidase 4). The viremic status, urinary virus excretion, and timely kidney biopsy results should be investigated with thorough precautions to reveal the direct effects of MERS-CoV with respect to renal complications.

Glucose dependent insulinotropic polypeptide and dipeptidyl peptidase inhibitors: Their roles in management of type 2 diabetes mellitus

This review paper highlights the major advances investigating the roles of glucose dependent insulinotropic polypeptide and its receptors in glucose metabolism and their potential use in management of type 2 diabetes mellitus. It also focusses on the role of dipeptidyl peptidase-4 inhibitors in the treatment of this disease. This study discussed the recent therapeutic development which have occurred in this field, and also covering the evolvement of the potential treatments for diabetes which can be discovered and implemented in the near future to design an effective therapy for diabetes and prediabetes.

GLP-1 and weight loss: unraveling the diverse neural circuitry

Glucagon-like peptide-1 (GLP-1) is currently one of the most promising biological systems for the development of effective obesity pharmacotherapies. Long-acting GLP-1 analogs potently reduce food intake and body weight, and recent discoveries reveal that peripheral administration of these drugs reduces food intake largely through humoral pathways involving direct action on brain GLP-1 receptors (GLP-1R). Thus, it is of critical importance to understand the neural systems through which GLP-1 and long-acting GLP-1 analogs reduce food intake and body weight. In this review, we discuss several neural, physiological, cellular and molecular, as well as behavioral mechanisms through which peripheral and central GLP-1R signaling reduces feeding. Particular attention is devoted to discussion regarding the numerous neural substrates through which GLP-1 and GLP-1 analogs act to reduce food intake and body weight, including various hypothalamic nuclei (arcuate nucleus of the hypothalamus, periventricular hypothalamus, lateral hypothalamic area), hindbrain nuclei (parabrachial nucleus, medial nucleus tractus solitarius), hippocampus (ventral subregion; vHP), and nuclei embedded within the mesolimbic reward circuitry [ventral tegmental area (VTA) and nucleus accumbens (NAc)]. In some of these nuclei [VTA, NAc, and vHP], GLP-1R activation reduces food intake and body weight without concomitant nausea responses, suggesting that targeting these specific pathways may be of particular interest for future obesity pharmacotherapy. The widely distributed neural systems through which GLP-1 and GLP-1 analogs act to reduce body weight highlight the complexity of the neural systems regulating energy balance, as well as the challenges for developing effective obesity pharmacotherapies that reduce feeding without producing parallel negative side effects.

Metabolic role of dipeptidyl peptidase 4 (DPP4) in primary human (pre)adipocytes

Dipeptidyl peptidase 4 (DPP4) is the target of the gliptins, a recent class of oral antidiabetics. DPP4 (also called CD26) was previously characterized in immune cells but also has important metabolic functions which are not yet fully understood. Thus, we investigated the function of DPP4 in human white preadipocytes and adipocytes. We found that both cell types express DPP4 in high amounts; DPP4 release markedly increased during differentiation. In preadipocytes, lentiviral DPP4 knockdown caused significant changes in gene expression as determined by whole-genome DNA-array analysis. Metabolic genes were increased, e.g. PDK4 18-fold and PPARγC1α (=PGC1α) 6-fold, and proliferation-related genes were decreased (e.g. FGF7 5-fold). These effects, contributing to differentiation, were not inhibited by the PPARγ antagonist T0070907. Vice versa, the PPARγ agonist pioglitazone induced a different set of genes (mainly FABP4). DPP4 knockdown also affected growth factor signaling and, accordingly, retarded preadipocyte proliferation. In particular, basal and insulin-induced ERK activation (but not Akt activation) was markedly diminished (by around 60%). This indicates that DPP4 knockdown contributes to adipocyte maturation by mimicking growth factor withdrawal, an early step in fat cell differentiation. In mature adipocytes, DPP4 becomes liberated so that adipose tissue may constitute a relevant source of circulating DPP4.

Unravelling the immunological roles of dipeptidyl peptidase 4 (DPP4) activity and/or structure homologue (DASH) proteins

Dipeptidyl peptidase (DPP) 4 (CD26, DPP4) is a multi-functional protein involved in T cell activation by co-stimulation via its association with adenosine deaminase (ADA), caveolin-1, CARMA-1, CD45, mannose-6-phosphate/insulin growth factor-II receptor (M6P/IGFII-R) and C-X-C motif receptor 4 (CXC-R4). The proline-specific dipeptidyl peptidase also modulates the bioactivity of several chemokines. However, a number of enzymes displaying either DPP4-like activities or representing structural homologues have been discovered in the past two decades and are referred to as DPP4 activity and/or structure homologue (DASH) proteins. Apart from DPP4, DASH proteins include fibroblast activation protein alpha (FAP), DPP8, DPP9, DPP4-like protein 1 (DPL1, DPP6, DPPX L, DPPX S), DPP4-like protein 2 (DPL2, DPP10) from the DPP4-gene family S9b and structurally unrelated enzyme DPP2, displaying DPP4-like activity. In contrast, DPP6 and DPP10 lack enzymatic DPP4-like activity. These DASH proteins play important roles in the immune system involving quiescence (DPP2), proliferation (DPP8/DPP9), antigen-presenting (DPP9), co-stimulation (DPP4), T cell activation (DPP4), signal transduction (DPP4, DPP8 and DPP9), differentiation (DPP4, DPP8) and tissue remodelling (DPP4, FAP). Thus, they are involved in many pathophysiological processes and have therefore been proposed for potential biomarkers or even drug targets in various cancers (DPP4 and FAP) and inflammatory diseases (DPP4, DPP8/DPP9). However, they also pose the challenge of drug selectivity concerning other DASH members for better efficacy and/or avoidance of unwanted side effects. Therefore, this review unravels the complex roles of DASH proteins in immunology.

High Levels of Serum DPP-4 Activity Are Associated with Low Bone Mineral Density in Obese Postmenopausal Women

BACKGROUND

Dipeptidyl peptidase 4/CD26 (DPP-4) is a widely expressed cell surface serine protease. DPP-4 inhibitors, one of common anti-diabetic agents play a protective role in bone metabolism in recent studies. A soluble form of DPP-4 is found in serum, and exhibits DPP-4 enzymatic activity. However, the physiological role of serum or soluble DPP-4 and its relationship with DPP-4 enzymatic function remain poorly understood. The aims of current study were to determine the association between serum DPP-4 activity and bone mineral density (BMD) in postmenopausal women.

METHODS

We recruited data and serum samples from 124 consecutive healthy postmenopausal women aged >50 years. We divided study subjects into obese (body mass index [BMI] ≥25 kg/m²) and non-obese (BMI <25 kg/m²) postmenopausal women and examined the correlation between serum DPP-4 activity and clinical variables in each groups.

RESULTS

A total of 124 postmenopausal women was enrolled, with a mean age of 59.9±7.1 years. The mean BMI of the study patients was 24.4±2.8 kg/m². Regarding bone turnover markers, serum DPP-4 activity was positively correlated with serum calcium concentrations, intact parathyroid hormone, and serum C-telopeptide levels in all of the study subjects. However, there was no association between serum DPP-4 activity and BMD in the spine or femoral neck in all of the study subjects. Serum DPP-4 activity was negatively correlated (R=-0.288, P=0.038) with BMD of the spine in obese postmenopausal women.

CONCLUSION

This study demonstrated for the first time that serum soluble DPP-4 activity was negatively correlated with BMD in obese postmenopausal women.

Short-chain fatty acid sensing in rat duodenum

KEY POINTS

Luminal lipid in the duodenum modulates gastroduodenal functions via the release of gut hormones and mediators such as cholecystokinin and 5-HT. The effects of luminal short-chain fatty acids (SCFAs) in the foregut are unknown. Free fatty acid receptors (FFARs) for long-chain fatty acids (LCFAs) and SCFAs are expressed in enteroendocrine cells. SCFA receptors, termed FFA2 and FFA3, are expressed in duodenal enterochromaffin cells and L cells, respectively. Activation of LCFA receptor (FFA1) and presumed FFA3 stimulates duodenal HCO3(-) secretion via a glucagon-like peptide (GLP)-2 pathway, whereas FFA2 activation induces HCO3(-) secretion via muscarinic and 5-HT4 receptor activation. The presence of SCFA sensing in the duodenum with GLP-2 and 5-HT signals further supports the hypothesis that luminal SCFA in the foregut may contribute towards the generation of functional symptoms.

ABSTRACT

Intraduodenal fatty acids (FA) and bacterial overgrowth, which generate short-chain FAs (SCFAs), have been implicated in the generation of functional dyspepsia symptoms. We studied the mechanisms by which luminal SCFA perfusion affects duodenal HCO3(-) secretion (DBS), a measure of mucosal neurohumoral activation. Free fatty acid receptor (FFAR) 1 (FFA1), which binds long-chain FA (LCFA), and SCFA receptors FFA2 and FFA3 were immunolocalised to duodenal enteroendocrine cells. FFA3 colocalised with glucagon-like peptide (GLP)-1, whereas FFA2 colocalised with 5-HT. Luminal perfusion of the SCFA acetate or propionate increased DBS, enhanced by dipeptidyl peptidase-IV (DPPIV) inhibition, at the same time as increasing GLP-2 portal blood concentrations. Acetate-induced DBS was partially inhibited by monocarboxylate/HCO3(-) exchanger inhibition without affecting GLP-2 release, implicating acetate absorption in the partial mediation of DBS. A selective FFA2 agonist dose-dependently increased DBS, unaffected by DPPIV inhibition or by cholecystokinin or 5-HT3 receptor antagonists, but was inhibited by atropine and a 5-HT4 antagonist. By contrast, a selective FFA1 agonist increased DBS accompanied by GLP-2 release, enhanced by DPPIV inhibition and inhibited by a GLP-2 receptor antagonist. Activation of FFA1 by LCFA and presumably FFA3 by SCFA increased DBS via GLP-2 release, whereas FFA2 activation stimulated DBS via muscarinic and 5-HT4 receptor activation. SCFA/HCO3(-) exchange also appears to be present in the duodenum. The presence of duodenal fatty acid sensing receptors that signal hormone release and possibly signal neural activation may be implicated in the pathogenesis of functional dyspepsia.

Expression of recombinant human α-lactalbumin in milk of transgenic cloned pigs is sufficient to enhance intestinal growth and weight gain of suckling piglets

Human α-lactalbumin (HLA) has very high nutritional value and important physiological functions during the neonatal period. The peptides derived from HLA provide diverse health benefits including antimicrobial, antiviral, immune-modulating, and antihypertensive effects. Thus, it is worth investigating the effects on offspring development of increasing HLA in milk. In this study, we found that recombinant human α-lactalbumin (rHLA) exhibits efficient inhibition of dipeptidyl peptidase-IV (DPP-IV) activity in an in vitro simulated gastrointestinal digestion system. Using a BAC clone containing the complete HLA gene as a candidate vector, we generated two lines of transgenic cloned sows via somatic cell nuclear transfer that over-expressed rHLA. The average concentrations of rHLA in milk from the two lines of transgenic cloned sows were 2.24 ± 0.71 mg/ml and 2.67 ± 1.29 mg/ml. The feeding experiments revealed that rHLA represses dipeptidyl peptidase-IV (DPP-IV) activity in vivo. Furthermore, the piglets reared by rHLA transgenic cloned sows exhibit better performance in gain of body weight and intestine growth than the control piglets reared by non-transgenic sows. Therefore, these findings indicate that rHLA could serve as a natural precursor for a DPP-IV inhibitor, and the transgenic technology that produced the over-expression of rHLA could be a useful method for pig breeders to improve lactation performance.

Dipeptidyl peptidase-4 and kidney fibrosis in diabetes

Diabetic nephropathy (DN) is the most common cause of end-stage kidney disease worldwide and is associated with increased morbidity and mortality in patients with both type 1 and type 2 diabetes. Recent evidence revealed that dipeptidyl peptidase-4 (DPP-4) inhibitors may exhibit a protective effect against DN. In fact, the kidney is the organ where the DPP-4 activity is the highest level per organ weight. A preclinical analysis revealed that DPP-4 inhibitors also ameliorated kidney fibrosis. In this review, we analyzed recent reports in this field and explore the renoprotective effects and possible mechanism of the DPP-4 inhibitors.

A Comparative Review of Animal Models of Middle East Respiratory Syndrome Coronavirus Infection

Middle East respiratory syndrome coronavirus (MERS-CoV) was initially isolated from a Saudi Arabian man with fatal pneumonia. Since the original case in 2012, MERS-CoV infections have been reported in >1500 humans, and the case fatality rate is currently 35%. This lineage C betacoronavirus has been reported to cause a wide range of disease severity in humans, ranging from asymptomatic to progressive fatal pneumonia that may be accompanied by renal or multiorgan failure. Although the clinical presentation of human MERS-CoV infection has been documented, many facets of this emerging disease are still unknown and could be studied with animal models. Several animal models of MERS-CoV have been developed, including New Zealand white rabbits, transduced or transgenic mice that express human dipeptidyl peptidase 4, rhesus macaques, and common marmosets. This review provides an overview of the current state of knowledge on human MERS-CoV infections, the probable origin of MERS-CoV, and the available animal models of MERS-CoV infection. Evaluation of the benefits and limitations of these models will aid in appropriate model selection for studying viral pathogenesis and transmission, as well as for testing vaccines and antivirals against MERS-CoV.

Reduced DPP4 activity improves insulin signaling in primary human adipocytes

DPP4 is a ubiquitously expressed cell surface protease which is also released to the circulation as soluble DPP4 (sDPP4). Recently, we identified DPP4 as a novel adipokine oversecreted in obesity and thus potentially linking obesity to the metabolic syndrome. Furthermore, sDPP4 impairs insulin signaling in an autocrine and paracrine fashion in different cell types. However, it is still unknown which functional role DPP4 might play in adipocytes. Therefore, primary human adipocytes were treated with a specific DPP4 siRNA. Adipocyte differentiation was not affected by DPP4 silencing. Interestingly, DPP4 reduction improved insulin responsiveness of adipocytes at the level of insulin receptor, proteinkinase B (Akt) and Akt substrate of 160 kDa. To investigate whether the observed effects could be attributed to the enzymatic activity of DPP4, human adipocytes were treated with the DPP4 inhibitors sitagliptin and saxagliptin. Our data show that insulin-stimulated activation of Akt is augmented by DPP4 inhibitor treatment. Based on our previous observation that sDPP4 induces insulin resistance in adipocytes, and that adipose DPP4 levels are higher in obese insulin-resistant patients, we now suggest that the abundance of DPP4 might be a regulator of adipocyte insulin signaling.

Coronaviruses and the human airway: a universal system for virus-host interaction studies

Human coronaviruses (HCoVs) are large RNA viruses that infect the human respiratory tract. The emergence of both Severe Acute Respiratory Syndrome and Middle East Respiratory syndrome CoVs as well as the yearly circulation of four common CoVs highlights the importance of elucidating the different mechanisms employed by these viruses to evade the host immune response, determine their tropism and identify antiviral compounds. Various animal models have been established to investigate HCoV infection, including mice and non-human primates. To establish a link between the research conducted in animal models and humans, an organotypic human airway culture system, that recapitulates the human airway epithelium, has been developed. Currently, different cell culture systems are available to recapitulate the human airways, including the Air-Liquid Interface (ALI) human airway epithelium (HAE) model. Tracheobronchial HAE cultures recapitulate the primary entry point of human respiratory viruses while the alveolar model allows for elucidation of mechanisms involved in viral infection and pathogenesis in the alveoli. These organotypic human airway cultures represent a universal platform to study respiratory virus-host interaction by offering more detailed insights compared to cell lines. Additionally, the epidemic potential of this virus family highlights the need for both vaccines and antivirals. No commercial vaccine is available but various effective antivirals have been identified, some with potential for human treatment. These morphological airway cultures are also well suited for the identification of antivirals, evaluation of compound toxicity and viral inhibition.

Glucagon-like peptides 1 and 2: intestinal hormones implicated in the pathophysiology of mucositis

PURPOSE OF REVIEW

Chemotherapy often causes adverse effects, including pain, bloating, diarrhea, and inflammation and ulceration of the mucous membranes lining the digestive tract, which are collectively referred to as mucositis. Unfortunately, no remedy has been found yet to manage these side-effects.

RECENT FINDINGS

The intestinal glucagon-like peptide-2 (GLP-2) is secreted from the intestinal endocrine L cells after nutrient intake, but recent findings show that the peptide concentration in the plasma also rises after intestinal injury and that GLP-2 receptor activation is crucial for intestinal healing. The antidiabetic hormone GLP-1, cosecreted with GLP-2, diminished mucositis in an animal model of the condition. Therefore, both peptides could be involved in the pathophysiology of mucositis.

SUMMARY

The intestinal GLPs have shown beneficial effects in experimental trials and have potential for therapeutic use. In type 2 diabetic and obese patients, GLP secretion is impaired. Elucidating the role of these endogenous hormones could lead to the identification of mucositis risk factors and an alternative preventive therapy for these patients.

Middle East respiratory syndrome coronavirus: a comprehensive review

The Middle East respiratory syndrome coronavirus was first identified in 2012 and has since then remained uncontrolled. Cases have been mostly reported in the Middle East, however travel-associated cases and outbreaks have also occurred. Nosocomial and zoonotic transmission of the virus appear to be the most important routes. The infection is severe and highly fatal thus necessitating rapid and efficacious interventions. Here, we performed a comprehensive review of published literature and summarized the epidemiology of the virus. In addition, we summarized the virological aspects of the infection and reviewed the animal models used as well as vaccination and antiviral tested against it.

CD26/dipeptidylpeptidase IV-chemokine interactions: double-edged regulation of inflammation and tumor biology

Review of how chemokine processing by CD26/DPP IV regulates leukocyte trafficking.

Post‐translational modification of chemokines is an essential regulatory mechanism to enhance or dampen the inflammatory response. CD26/dipeptidylpeptidase IV, ubiquitously expressed in tissues and blood, removes NH₂‐terminal dipeptides from proteins with a penultimate Pro or Ala. A large number of human chemokines, including CXCL2, CXCL6, CXCL9, CXCL10, CXCL11, CXCL12, CCL3L1, CCL4, CCL5, CCL11, CCL14, and CCL22, are cleaved by CD26; however, the efficiency is clearly influenced by the amino acids surrounding the cleavage site and although not yet proven, potentially affected by the chemokine concentration and interactions with third molecules. NH₂‐terminal cleavage of chemokines by CD26 has prominent effects on their receptor binding, signaling, and hence, in vitro and in vivo biologic activities. However, rather than having a similar result, the outcome of NH₂‐terminal truncation is highly diverse. Either no difference in activity or drastic alterations in receptor recognition/specificity and hence, chemotactic activity are observed. Analogously, chemokine‐dependent inhibition of HIV infection is enhanced (for CCL3L1 and CCL5) or decreased (for CXCL12) by CD26 cleavage. The occurrence of CD26‐processed chemokine isoforms in plasma underscores the importance of the in vitro‐observed CD26 cleavages. Through modulation of chemokine activity, CD26 regulates leukocyte/tumor cell migration and progenitor cell release from the bone marrow, as shown by use of mice treated with CD26 inhibitors or CD26 knockout mice. As chemokine processing by CD26 has a significant impact on physiologic and pathologic processes, application of CD26 inhibitors to affect chemokine function is currently explored, e.g., as add‐on therapy in viral infection and cancer.

Dipeptidyl Peptidase 4 Distribution in the Human Respiratory Tract: Implications for the Middle East Respiratory Syndrome

Dipeptidyl peptidase 4 (DPP4, CD26), a type II transmembrane ectopeptidase, is the receptor for the Middle Eastern respiratory syndrome coronavirus (MERS-CoV). MERS emerged in 2012 and has a high mortality associated with severe lung disease. A lack of autopsy studies from MERS fatalities has hindered understanding of MERS-CoV pathogenesis. We investigated the spatial and cellular localization of DPP4 to evaluate an association MERS clinical disease. DPP4 was rarely detected in the surface epithelium from nasal cavity to conducting airways with a slightly increased incidence in distal airways. DPP4 was also found in a subset of mononuclear leukocytes and in serous cells of submucosal glands. In the parenchyma, DPP4 was found principally in type I and II cells and alveolar macrophages and was also detected in vascular endothelium (eg, lymphatics) and pleural mesothelia. Patients with chronic lung disease, such as chronic obstructive pulmonary disease and cystic fibrosis, exhibited increased DPP4 immunostaining in alveolar epithelia (type I and II cells) and alveolar macrophages with similar trends in reactive mesothelia. This finding suggests that preexisting pulmonary disease could increase MERS-CoV receptor abundance and predispose individuals to MERS morbidity and mortality, which is consistent with current clinical observations. We speculate that the preferential spatial localization of DPP4 in alveolar regions may explain why MERS is characterized by lower respiratory tract disease.

Synthesis and biological evaluation of triazole based uracil derivatives as novel DPP-4 inhibitors

Novel 1,2,3-triazole based uracil derivatives were identified as potent, selective, in vivo effective DPP-4 inhibitors.

Sitagliptin, a dipeptidyl peptidase-4 inhibitor, increases the number of circulating CD34⁺CXCR4⁺ cells in patients with type 2 diabetes

We investigated the effects of sitagliptin, a dipeptidyl peptidase (DPP)-4 inhibitor, on the number of circulating CD34(+)CXCR4(+)cells, a candidate for endothelial progenitor cells (EPCs), plasma levels of stromal cell-derived factor (SDF)-1α, a ligand for CXCR4 receptor and a substrate for DPP-4, and plasma levels of interferon-inducible protein (IP)-10, for a substrate for DPP-4, in patients with type 2 diabetes. We studied 30 consecutive patients with type 2 diabetes who had poor glycemic control despite treatment with metformin and/or sulfonylurea. Thirty diabetic patients were randomized in a 2:1 ratio into a sitagliptin (50 mg/day) treatment group or an active placebo group (glimepiride 1 mg/day) for 12 weeks. Both groups showed similar improvements in glycemic control. The number of circulating CD34(+)CXCR4(+) cells was increased from 30.5 (20.0, 47.0)/10(6) cells at baseline to 55.5 (31.5, 80.5)/10(6) cells at 12 weeks of treatment with 50 mg/day sitagliptin (P = 0.0014), while showing no significant changes in patients treated with glimepiride. Plasma levels of SDF-1α and IP-10, both physiological substrates of endogenous DPP-4 and chemokines, were significantly decreased at 12 weeks of sitagliptin treatment. In conclusion, treatment with sitagliptin increased the number of circulating CD34(+)CXCR4(+) cells by approximately 2-fold in patients with type 2 diabetes.

Renal Complications and Their Prognosis in Korean Patients with Middle East Respiratory Syndrome-Coronavirus from the Central MERS-CoV Designated Hospital

Some cases of Middle East Respiratory Syndrome-Coronavirus (MERS-CoV) infection presented renal function impairment after the first MERS-CoV patient died of progressive respiratory and renal failure. Thus, MERS-CoV may include kidney tropism. However, reports about the natural courses of MERS-CoV infection in terms of renal complications are scarce. We examined 30 MERS-CoV patients admitted to National Medical Center, Korea. We conducted a retrospective analysis of the serum creatinine (SCr), estimated glomerular filtration rate (eGFR), urine dipstick tests, urinary protein quantitation (ACR or PCR), and other clinical parameters in all patients. Two consecutive results of more than trace (or 1+) of albumin and blood on dipstick test occurred in 18 (60%) (12 [40%]) and 22 (73.3%) (19 [63.3%]) patients, respectively. Fifteen (50.0%) patients showed a random urine ACR or PCR more than 100 mg/g Cr. Eight (26.7%) patients showed acute kidney injury (AKI), and the mean and median durations to the occurrence of AKI from symptom onset were 18 and 16 days, respectively. Old age was associated with a higher occurrence of AKI in the univariate analysis (HR [95% CI]: 1.069 [1.013-1.128], P = 0.016) and remained a significant predictor of the occurrence of AKI after adjustment for comorbidities and the application of a mechanical ventilator. Diabetes, AKI, and the application of a continuous renal replacement therapy (CRRT) were risk factors for mortality in the univariate analysis (HR [95% CI]: diabetes; 10.133 [1.692-60.697], AKI; 12.744 [1.418-114.565], CRRT; 10.254 [1.626-64.666], respectively). Here, we report renal complications and their prognosis in 30 Korean patients with MERS-CoV.

Sitagliptin, a DPP-4 inhibitor, alters the subsets of circulating CD4+ T cells in patients with type 2 diabetes

OBJECTIVE

CD26/DPP-4 is highly expressed by T cells, especially CD4+ T cells (T helper cells; Th) and may regulate the differentiation, maturation, or proliferation of these cells. We investigated the effects of sitagliptin, a DPP-4 inhibitor, on the absolute number and percentage of various subsets of circulating CD4+ T cells in patients with type 2 diabetes.

METHODS

We enrolled 30 consecutive patients (16 women and 14 men) with type 2 diabetes in a prospective, randomized, open-label, blinded endpoint study. Eligible participants were randomly assigned at a 2:1 ratio to either a sitagliptin group (sitagliptin at 50mg/day) or an active control group (glimepiride at 1mg/day). Patients were followed for 12 weeks with monthly review. Peripheral blood mononuclear cells were examined by flow cytometry for intracellular expression of cytokines (IFN-γ as a marker of Th1cells, IL-4 for Th2 cells, and IL-17 for Th17 cells) and for expression of CD4, CD25, and Foxp3 (regulatory T cells [Treg]).

RESULTS

Both groups showed similar improvement of glycemic control. The total number of CD4+ T cells was decreased by treatment with sitagliptin, while it did not change in the control group. The number and percentage of Th17 cells and Treg cells both decreased significantly in the sitagliptin group, but not in the control group. There was a significant positive correlation between changes in the percentage of Th17 cells and Treg cells after treatment with sitagliptin.

CONCLUSIONS

Treatment with sitagliptin for 12 weeks reduced the number of circulating CD4+ T cells, especially Th17 and Treg cells, in patients with type 2 diabetes.

CD26 costimulatory blockade improves lung allograft rejection and is associated with enhanced interleukin-10 expression

BACKGROUND

The ectoenzyme CD26/dipeptidyl peptidase 4 (DPP4) has costimulatory activity that contributes to T cell activation and proliferation. Here, we aimed to target this costimulatory activity for the attenuation of the alloreactive Th17-cell response during acute rejection after mouse lung transplantation.

METHODS

To test the CD26-costimulatory blockade in vitro, mixed lymphocyte reaction was performed between major histocompatibility complex class I and II fully mismatched cells (CD4(+) splenocytes, C57BL/6, responders, and antigen-presenting cells, BALB/c, stimulators) by adding the CD26 inhibitor vildagliptin (0-15 μg). Lung transplantation between BALB/c (donor) and C57BL/6 (recipient) mice was performed, including controls, CD26-inhibited (CD26-I, daily administration of vildagliptin [GLSynthesis, Worcester, MA], 10 mg/kg subcutaneous), and CD26 knockout (CD26KO) mice was performed. Analysis on Day 1 and 5 after transplant included immunohistochemistry, fluorescence-activated cell sorting, and enzyme-linked immunosorbent assay (ELISA) for immune cell detection and their key cytokines.

RESULTS

In vitro, there was a significant reduction of the Th17 cytokines interleukin (IL)-17 and IL-21. In vivo, CD26-I-treated and CD26KO mice showed significantly preserved macroscopic and histologic characteristics on Day 5 (p < 0.01), a higher partial pressure of arterial oxygen/fraction of inspired oxygen ratio (p ≤ 0.05), fewer infiltrating CD3(+) T cells (p < 0.01), but more interstitial macrophages on Day 1 (p < 0.01) compared with control. Fewer IL-17(+) cells were found in CD26-I allografts on Day 1 (p = 0.05). Higher levels of IL-10 in CD26-I and CD26KO allografts on day 5 were seen (p < 0.05). IL-10/CD206 double-staining (alternative macrophages) revealed more positive cells in CD26-I and CD26KO on Day 1 and 5 (p < 0.01).

CONCLUSIONS

CD26 costimulatory blockade promotes lung allograft acceptance via reduced T cell infiltration, less expression of IL-17, and increased expression of IL-10, likely to be derived from alternatively activated macrophages.

Middle East respiratory syndrome coronavirus shows poor replication but significant induction of antiviral responses in human monocyte-derived macrophages and dendritic cells

In this study we assessed the ability of Middle East respiratory syndrome coronavirus (MERS-CoV) to replicate and induce innate immunity in human monocyte-derived macrophages and dendritic cells (MDDCs), and compared it with severe acute respiratory syndrome coronavirus (SARS-CoV). Assessments of viral protein and RNA levels in infected cells showed that both viruses were impaired in their ability to replicate in these cells. Some induction of IFN-λ1, CXCL10 and MxA mRNAs in both macrophages and MDDCs was seen in response to MERS-CoV infection, but almost no such induction was observed in response to SARS-CoV infection. ELISA and Western blot assays showed clear production of CXCL10 and MxA in MERS-CoV-infected macrophages and MDDCs. Our data suggest that SARS-CoV and MERS-CoV replicate poorly in human macrophages and MDDCs, but MERS-CoV is nonetheless capable of inducing a readily detectable host innate immune response. Our results highlight a clear difference between the viruses in activating host innate immune responses in macrophages and MDDCs, which may contribute to the pathogenesis of infection.

Favorable effects of vildagliptin on metabolic and cognitive dysfunctions in streptozotocin-induced diabetic rats

Progression of diabetes mellitus is accompanied by metabolic disorders together with psychological deficits including cognitive dysfunctions. Herein, we used a murine streptozotocin (STZ)-induced diabetes to investigate the beneficial effects of vildagliptin not only on metabolic abnormalities, but also on diabetes-induced cognitive decline. Sixty rats were divided randomly and equally into 2 groups; one remains normal and the other serves as STZ- induced diabetic. Both groups were further divided equally into 2 groups; one received vehicle and the other received oral vildagliptin for 8 weeks. Cognitive behavior was assessed using novel object recognition test. Blood samples were collected to measure metabolic parameters and dipeptidyl peptidase (DPP)-IV activity. Brains were removed and investigated for the levels of inflammatory and oxidative stress markers malondialdehyde (MDA), superoxide dismutase (SOD) and tumor necrosis factor-α (TNF-α), in addition to brain-derived neurotrophic factor (BDNF) and relative expression of nuclear factor kappa B (NF-κB)/p65. Treatment of STZ-induced diabetic rats with vildagliptin increased their body weight and corrected diabetes-induced memory and learning impairment. Moreover, vildagliptin significantly decreased serum levels of glucose and lipids (except high density lipoprotein) together with brain MDA, TNF-α, serum DPP-IV activities and NF-κB/p65 gene expression. On the other hand, vildagliptin significantly increased brain BDNF, SOD as well as serum insulin. Results suggested that vildagliptin has a protective role in counteracting both metabolic abnormalities and memory deficits in diabetic rats, possibly via its anti-hyperglycemic, anti-inflammatory, antioxidant effects, together with reduction of brain NF-κB/p65 over expression.

Role of dipeptidyl peptidase-4 inhibitors in new-onset diabetes after transplantation

Despite strict pre- and post-transplantation screening, the incidence of new-onset diabetes after transplantation (NODAT) remains as high as 60%. This complication affects the risk of cardiovascular events and patient and graft survival rates. Thus, reducing the impact of NODAT could improve overall transplant success. The pathogenesis of NODAT is multifactorial, and both modifiable and nonmodifiable risk factors have been implicated. Monitoring and controlling the blood glucose profile, implementing multidisciplinary care, performing lifestyle modifications, using a modified immunosuppressive regimen, administering anti-metabolite agents, and taking a conventional antidiabetic approach may diminish the incidence of NODAT. In addition to these preventive strategies, inhibition of dipeptidyl peptidase-4 (DPP4) by the gliptin family of drugs has recently gained considerable interest as therapy for type 2 diabetes mellitus and NODAT. This review focuses on the role of DPP4 inhibitors and discusses recent literature regarding management of NODAT.

Middle East Respiratory Syndrome Coronavirus Causes Multiple Organ Damage and Lethal Disease in Mice Transgenic for Human Dipeptidyl Peptidase 4

Middle East respiratory syndrome coronavirus (MERS-CoV) causes life-threatening disease. Dipeptidyl peptidase 4 (DPP4) is the receptor for cell binding and entry. There is a need for small-animal models of MERS, but mice are not susceptible to MERS because murine dpp4 does not serve as a receptor. We developed transgenic mice expressing human DPP4 (hDPP4) under the control of the surfactant protein C promoter or cytokeratin 18 promoter that are susceptible to infection with MERS-CoV. Notably, mice expressing hDPP4 with the cytokeratin 18 promoter developed progressive, uniformly fatal disease following intranasal inoculation. High virus titers were present in lung and brain tissues 2 and 6 days after infection, respectively. MERS-CoV–infected lungs revealed mononuclear cell infiltration, alveolar edema, and microvascular thrombosis, with airways generally unaffected. Brain disease was observed, with the greatest involvement noted in the thalamus and brain stem. Animals immunized with a vaccine candidate were uniformly protected from lethal infection. These new mouse models of MERS-CoV should be useful for investigation of early disease mechanisms and therapeutic interventions.

Combination of DPP-4 inhibitor and PPARγ agonist exerts protective effects on pancreatic β-cells in diabetic db/db mice through the augmentation of IRS-2 expression

We investigated the effects of long- and short-term treatment with pioglitazone (Pio) and/or alogliptin (Alo) on β-cells in diabetic db/db mice. Six-week-old male db/db mice received Pio (25 mg/kg, oral) and/or Alo (30 mg/kg, oral) for 4 weeks and for 2 days. Blood glucose levels were decreased after 4-week intervention, but not after 2-day intervention. Pio increased adiponectin levels, and Alo decreased glucagon levels and increased active GlP-1 levels. Insulin sensitivity was restored by Pio. After 4-week treatment, β-cell mass was increased (over 2-fold increase) and expression levels of various β-cell-related factors were restored. Expression levels of IRS-2 and various downstream factors were up-regulated by Pio and Alo after 2-day and 4-week intervention. In addition, mRNA and protein levels of IRS-2 and various downstream factors were up-regulated in MIN6 cells after 24-h exposure to Pio and exendin-4. These results suggest that Pio and Alo additively up-regulate IRS-2 expression independently of the alteration of glycemic control. Taken together, combination of Pio and Alo exerts protective effects on β-cells in diabetic db/db mice, at least in part, through the augmentation of IRS-2 expression.

Intraindividual changes of dipeptidyl peptidase-IV in peripheral blood of patients with rheumatoid arthritis are associated with the disease activity

Background

Dipeptidyl peptidase-IV (DPP-IV) is suggested to contribute to the pathogenesis of several autoimmune diseases. The aim of this study was to evaluate the association of DPP-IV presence in blood plasma and mononuclear cells with the disease activity in rheumatoid arthritis (RA).

Methods

Patients with active RA (n = 27) were examined at the study enrolment and a follow-up examination was performed after the regression of the joint effusions and at least 6 months after the first investigation. The control group comprised patients with a noninflammatory joint disease, i.e. osteoarthritis (OA; n = 15). The DPP-IV-like enzymatic activity was measured by a kinetic fluorimetric method, the concentration of DPP-IV in the blood plasma was determined using ELISA and the expression of DPP-IV in leukocytes was assayed by flow cytometry.

Results

Blood plasma DPP-IV-like enzymatic activity (median ± SD 220.15 ± 83.6 pkat/mL in RA vs. 376.9 ± 144.9 pkat/mL in OA, p < 0.001) and concentrations (median ± SD 465.1 ± 215.6 ng/mL in RA vs. 953.3 ± 368.4 ng/mL in OA, p < 0.001) were lower in patients with active RA compared to OA. In RA patients, the blood plasma DPP-IV-like enzymatic activity negatively correlated with the CRP concentration (r = −0.39, p = 0.044). No significant differences were observed in the DPP-IV-like enzymatic activity and DPP-IV expression in blood mononuclear cells between the RA and OA groups. At follow-up, 18 RA patients had a less active disease as demonstrated by an improved DAS28 score. In this group, comparison of the entry and the follow-up values in individual patients revealed an increase of the blood plasma DPP-IV-like enzymatic activity (median ± SD 141 ± 46 % of the patient’s entry values, p = 0.011) and DPP-IV concentration (median ± SD 168 ± 25 %, of the patient’s entry values, p = 0.033). In contrast to the blood plasma, the DPP-IV expression in blood mononuclear cells was reduced in these patients as evidenced by a decrease in the cell surface DPP-IV-like enzymatic activity as well as the median fluorescence intensity of DPP-IV staining in lymphocytes (median ± SD 66 ± 56 %, p = 0.018 and 63 ± 31 % of the patient’s entry values, p = 0.005, respectively).

Conclusions

The association between RA activity and the changes in blood plasma and blood mononuclear cell DPP-IV in individual patients supports the possible relationship of DPP-IV to RA pathophysiology.

Middle East respiratory syndrome

Middle East respiratory syndrome (MERS) is a highly lethal respiratory disease caused by a novel single-stranded, positive-sense RNA betacoronavirus (MERS-CoV). Dromedary camels, hosts for MERS-CoV, are implicated in direct or indirect transmission to human beings, although the exact mode of transmission is unknown. The virus was first isolated from a patient who died from a severe respiratory illness in June, 2012, in Jeddah, Saudi Arabia. As of May 31, 2015, 1180 laboratory-confirmed cases (483 deaths; 40% mortality) have been reported to WHO. Both community-acquired and hospital-acquired cases have been reported with little human-to-human transmission reported in the community. Although most cases of MERS have occurred in Saudi Arabia and the United Arab Emirates, cases have been reported in Europe, the USA, and Asia in people who travelled from the Middle East or their contacts. Clinical features of MERS range from asymptomatic or mild disease to acute respiratory distress syndrome and multiorgan failure resulting in death, especially in individuals with underlying comorbidities. No specific drug treatment exists for MERS and infection prevention and control measures are crucial to prevent spread in health-care facilities. MERS-CoV continues to be an endemic, low-level public health threat. However, the virus could mutate to have increased interhuman transmissibility, increasing its pandemic potential.

Plasma peptidases as prognostic biomarkers in patients with first-episode psychosis

The plasma activity of nine aminopeptidases was monitored over a year in first-episode psychotic patients. We observed significant differences in aminopeptidase B (APB), aminopeptidase N (APN) and dipeptidyl peptidase IV (DPPIV), but not in puromycin-sensitive aminopeptidase (PSA), prolyl endopeptidase (PEP), cysteine aminopeptidase (Cys-AP), aspartate aminopeptidase (Asp-AP), glutamate aminopeptidase (Glu) or piroglutamate aminopeptidase (PGI) in these patients compared to controls, and also a progressive increase in plasma activity, correlated to changes in scores on clinical scales, Global Assessment of Functioning scale (GAF) and Hamilton Depression Rating Scale (HDRS), at 1 month of follow-up. At 1 month after diagnosis, the median score obtained by patients on the GAF was negatively associated with the plasma activity of APB and PEP measured at the beginning of the psychotic episode, indicating a role as a negative prognostic factor that can predict psychiatric symptomatology. In the case of HDRS, scores at 1 month after diagnosis were found to be positively associated with the initial plasma activity of DPPIV, APN and PSA, indicating that their initial elevation is a negative prognostic factor that can predict subsequent depressive symptomatology. Taken together, these results suggest a pathophysiological involvement of plasma peptidases and indicate that aminopeptidase activity can predict the course of first-episode psychosis patients, acting as a prognostic indicator.

Suppression of lung metastases by the CD26/DPP4 inhibitor Vildagliptin in mice

Metastases rather than primary cancers determine nowadays the survival of patients. One of the most common primary malignancies is colorectal cancer and this type of tumor is characterized by a high tendency to spread metastases to the lung and liver. CD26/DPP4 is a transmembrane molecule with enzymatic functions which cleaves biologically active peptides. Recently, CD26/DPP4 has become the focus of cancer research and it was shown that CD26/DPP4-positive cancer cells display increased metastatic activity. Here, we tested if the CD26/DPP4-inhibitor Vildagliptin suppresses the development and growth of mouse colorectal lung metastases. This inhibitor of CD26/DPP4 was employed on mouse (C57BL/6) colorectal lung metastases, established by intravenous injection of the syngeneic cell line MC38. For mechanistic analysis, a subcutaneous tumor model was used. The treatment with Vildagliptin significantly suppressed both, the incidence and growth of lung metastases. Autophagy markers (LC3, p62, and ATF4) decreased, apoptosis increased (TUNEL, pH3/Ki-76), and the cell cycle regulator pCDC2 was inhibited. In conclusion, we here showed an anti-tumor effect of Vildagliptin via downregulation of autophagy resulting in increased apoptosis and modulation of the cell cycle. We therefore propose Vildagliptin for the evaluation as a new therapeutic approach for the treatment of colorectal cancer lung metastases.

Dipeptidylpeptidase 4 (DPP4, CD26) activity in the blood serum of term and preterm neonates with cerebral ischemia

BACKGROUND

To investigate the mechanisms of inflammation in neonates after cerebral ischemia (CI), we evaluated the DPP4 activity in their blood sera and compared these values with clinical indicators.

METHODS

The activity of DPP4 was determined in blood serum by a fluorescent method. We studied the correlation between the blood serum DPP4 activity and clinical, neurological and biochemical parameters in neonates with CI.

RESULTS

No correlation between the DPP4 activity in umbilical blood and the venous blood of mothers was discovered. Increased blood serum DPP4 activity in full-term and pre-term newborns with CI is demonstrated. The interrelation between serum DPP4 activity and the functional disturbances of CNS (such as depression or excitement) was found in mature but not in premature newborns. Enzyme activity was still elevated at 2-3weeks after birth.

CONCLUSION

It is possible that in neonates this enzymatic system operates independently from mothers. It is assumed that increased DPP4 activity in newborns with CI is apparently connected with immune system activation in response to hypoxic stress. The obtained data support the participation of DPP4 in adaptive reactions of newborns and its regulating influence during hypoxemic damage of the CNS due to inflammation and neurodegeneration.

DPP4 in Diabetes

Dipeptidyl-peptidase 4 (DPP4) is a glycoprotein of 110 kDa, which is ubiquitously expressed on the surface of a variety of cells. This exopeptidase selectively cleaves N-terminal dipeptides from a variety of substrates, including cytokines, growth factors, neuropeptides, and the incretin hormones. Expression of DPP4 is substantially dysregulated in a variety of disease states including inflammation, cancer, obesity, and diabetes. Since the incretin hormones, glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide (GIP), are major regulators of post-prandial insulin secretion, inhibition of DPP4 by the gliptin family of drugs has gained considerable interest for the therapy of type 2 diabetic patients. In this review, we summarize the current knowledge on the DPP4–incretin axis and evaluate most recent findings on DPP4 inhibitors. Furthermore, DPP4 as a type II transmembrane protein is also known to be cleaved from the cell membrane involving different metalloproteases in a cell-type-specific manner. Circulating, soluble DPP4 has been identified as a new adipokine, which exerts both para- and endocrine effects. Recently, a novel receptor for soluble DPP4 has been identified, and data are accumulating that the adipokine-related effects of DPP4 may play an important role in the pathogenesis of cardiovascular disease. Importantly, circulating DPP4 is augmented in obese and type 2 diabetic subjects, and it may represent a molecular link between obesity and vascular dysfunction. A critical evaluation of the impact of circulating DPP4 is presented, and the potential role of DPP4 inhibition at this level is also discussed.

Animal models of Middle East respiratory syndrome coronavirus infection

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MERS-CoV has infected >1100 patients to date, with an associated case fatality rate of approximately 40%.

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Animals ranging from mice to rabbits to nonhuman primates have been inoculated with MERS-CoV, with varying outcomes.

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Mice expressing human DPP4 are susceptible to infection and develop severe disease.

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Rhesus macaques and marmosets are also susceptible, but marmosets develop more severe disease.

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Further development of appropriate animal models to conduct medical countermeasure research is a public health priority.

The emergence of the Middle East respiratory syndrome coronavirus (MERS-CoV) in 2012 marked the second time that a new, highly pathogenic coronavirus has emerged in the human population in the 21st century. In this review, we discuss the current state of knowledge of animal models of MERS-CoV infection. Commonly used laboratory animal species such as Syrian hamsters, mice and ferrets are not susceptible to MERS-CoV, due to differences in the MERS-CoV receptor dipeptidyl peptidase 4 (DPP4). The initially developed animal models comprise two nonhuman primate species, the rhesus macaque and the common marmoset. Rhesus macaques develop a mild to moderate respiratory disease upon inoculation, reminiscent of milder MERS cases, whereas marmosets develop a moderate to severe respiratory disease, recapitulating the severe disease observed in some patients. Dromedary camels, considered to be the reservoir for MERS-CoV, develop a mild upper respiratory tract infection with abundant viral shedding. Although normal mice are not susceptible to MERS-CoV, expression of the human DPP4 (hDPP4) overcomes the lack of susceptibility. Transgenic hDPP4 mice develop severe and lethal respiratory disease upon inoculation with MERS-CoV. These hDPP4 transgenic mice are potentially the ideal first line animal model for efficacy testing of therapeutic and prophylactic countermeasures. Further characterization of identified countermeasures would ideally be performed in the common marmoset model, due to the more severe disease outcome. This article forms part of a symposium in Antiviral Research on “From SARS to MERS: research on highly pathogenic human coronaviruses.”

CD26 Expression on T Helper Populations and sCD26 Serum Levels in Patients with Rheumatoid Arthritis

We studied dipeptidyl peptidase IV (DPP-IV, CD26) expression in different T helper cells and serum soluble DPP-IV/sCD26 levels in rheumatoid arthritis (RA) patients, correlated these with disease activity score (DAS), and examined how they were affected by different therapies, conventional or biological (anti-TNF, anti-CD20 and anti-IL6R or Ig-CTLA4). The percentage of CD4⁺CD45R0⁺CD26^- cells was greatly reduced in patients (up to 50%) when compared with healthy subjects. Three other subsets of CD4 cells, including a CD26high Th1-associated population, changed variably with therapies. Data from these subsets (frequency and staining density) significantly correlated with DAS28 or DAS28 components but different in each group of patients undergoing the different therapies. Th17 and Th22 subsets were implicated in RA as independent CCR4⁺ and CCR4^- populations each, with distinct CD26 expression, and were targeted with varying efficiency by each therapy. Serum DPP-IV activity rather than sCD26 levels was lower in RA patients compared to healthy donors. DPP-IV and sCD26 serum levels were found related to specific T cell subsets but not to disease activity. We conclude that, according to their CD26 expression, different cell subsets could serve to monitor RA course, and an uncharacterized T helper CD26^- subset, not targeted by therapies, should be monitored for early diagnosis.

B-type Natriuretic Peptide circulating forms: Analytical and bioactivity issues

B-type Natriuretic Peptide (BNP), A-type and C-type Natriuretic Peptides (ANP and CNP) comprise a family of peptides that retain a common ring structure and conserved amino acid sequences. All are present in the heart, but only BNP and ANP are regarded as primarily cardiac secretory products. BNP and ANP, acting through a guanylyl cyclase receptor, increase sodium and water excretion by the kidney, induce vasodilation, reduce blood pressure, counteract the bioactivity of the renin-angiotensin-aldosterone and sympathetic nervous systems and possess anti-hypertrophic and anti-fibrotic properties. BNP is synthesised in cardiomyocytes first as the precursor peptide preproBNP. Removal of the signal peptide from preproBNP produces proBNP which is cleaved to produce the biologically active carboxy-terminal BNP peptide and the inactive N-terminal fragment, NT-proBNP. BNP, NT-proBNP, proBNP and the C-terminal portion of the BNP signal peptide have been detected in human plasma as well as multiple sub-forms including truncated forms of BNP and NT-proBNP, as well as variable glycosylation of NT-proBNP and proBNP. The origin of these circulating forms, their potential bioactivity and their detection by current analytical methods are presented in this review.

Comparison of the susceptibility of porcine and human dipeptidyl-peptidase IV to inhibition by protein-derived peptides

The enzyme dipeptidyl-peptidase IV (DPP-IV) is recognized to be a promising target for the management of type 2 diabetes. Over the last decade, numerous synthetic molecules and more recently, peptides from dietary proteins, have been reported to be able to inhibit DPP-IV activity. Most studies that have investigated the in vitro effect of these inhibitors have used porcine or human DPP-IV. Although structurally alike, it is unclear whether these two species display similar inhibition patterns. Therefore, the objective of this study was to compare the effects of protein-derived peptides on the activity of porcine and recombinant human DPP-IV. The two species showed different inhibition susceptibility to 43 of the 62 peptide sequences investigated. While 37 protein-derived peptides were more effective at inhibiting the porcine DPP-IV, only six caused a stronger inhibition of the activity of the human enzyme. Although the peptides WR, IPIQY and WCKDDQNPHS were found to be among the most potent inhibitors of both species, the inhibitory effect was greater on the porcine enzyme than on human DPP-IV (αKi or Ki=11.5, 13.4, 13.3 μM and 31.4, 28.2, 75.0 μM for porcine and human DPP-IV, respectively). Investigation into the mode of action of the most effective inhibitory peptides revealed that both species were inhibited in a similar manner by short fragments (≤5 amino acid residues), but that some of the longer peptides acted differently on the enzymes. This study shows that porcine DPP-IV is generally inhibited with greater potency by protein-derived peptides than is the human enzyme.