Dipeptidyl Peptidase 4 Substrates Research Articles

Phloridzin's Diabetic Wound Healing Potential through DPP-4 Enzyme Inhibition: A Review Article.

Diabetic wound healing is a dynamic medical process that takes place in an environment within the body that is complex and contains elevated sugar levels, oxygen deprivation, and cellular oxidative stress. Phloridzin (Phlorizin) is one of the most well-known polyphenols found in apples because of its anti-inflammatory, antioxidant, antibacterial, antidiabetic, and antiseptic properties; it can also play a significant part in the healing of diabetic wounds. The study aimed to investigate the role of phloridzin as an efficient DPP-4 inhibitor with additional therapeutic effects in diabetic wound healing, as Dipeptidyl Peptidase-4 (DPP-4) expression increases in response to increases in glucose, Reactive Oxygen Species (ROS), and inflammation. Phloridzin inhibiting DPP-4 preserves Stromal cell-derived Factor-1α (SDF-1α), Insulin-like Growth Factor (IGF), and Glucagon-like Peptide-1 (GLP-1), which are possible DPP-4 substrates involved in wound healing. The accessible material from systemic searches in PubMed, Scopus, and published articles was reviewed with no period of limitation. The in silico study showed strong binding of phloridzin with DPP-4 protein (2P8S); also, in vitro DPP-4 inhibition assay has shown better inhibition by phloridzin. This study offers new research directions for examining phloridzin's capacity to withstand oxidative stress, as well as for redefining its tactical function as a powerful DPP-4 inhibitor to regulate the process involved in the healing of diabetic wounds.

Dipeptidyl-peptidase 4 (DPP4) mediates fatty acid uptake inhibition by glucose via TAS1R3 and GLUT-2 in Caco-2 enterocytes

Both high glucose intake with a high-fat meal and inhibition of dipeptidyl peptidase-4 (DPP4) have been associated with plasma lipid-lowering effects, but mechanistic understanding linking glucose and fat absorption is lacking. We here hypothesized that glucose ameliorates intestinal fatty acid uptake via a pathway involving DPP4. A concentration of 50 mM glucose reduced mean DPP4 activity in differentiated Caco-2 enterocytes by 42.5 % and fatty acid uptake by 66.0 % via nutrient sensing by the sweet taste receptor subunit TAS1R3 and glucose transporter GLUT-2. No effect of the DPP4 substrates GLP-1 and GIP or of the cellular energy status on the reduced uptake of fatty acids was seen, but a direct interaction between DPP4 and fatty acid transporters is suggested. Conclusively we identified DPP4 as a regulator of fatty acid absorption in Caco-2 enterocytes that mediates the inhibition of intestinal fatty acid uptake by glucose via an interplay of GLUT-2 and TAS1R3.

DPP-4 inhibition by linagliptin ameliorates age-related mild cognitive impairment by regulating microglia polarization in mice

Extensive preclinical evidence demonstrates a causative link between insulin signaling dysfunction and the pathogenesis of Alzheimer's disease (AD), and diabetic drugs may represent a promising approach to fighting AD. However, it remains to be determined which antidiabetic drugs are more effective in preventing cognitive impairment. Thus, the present study investigated the effect of dipeptidyl peptidase-4 (DPP-4) inhibitor linagliptin on cognitive impairment in middle-aged mice by comparing it with the effect of metformin. We found that DPP-4 activity increased in the hippocampus of middle-aged mice, and DPP-4 was mainly expressed by microglia rather than astrocytes and oligodendrocytes. DPP-4 directly regulated M1/M2 microglia polarization following LPS or IL-4 stimulation, while DPP-4 inhibitor, linagliptin, suppressed M1-polarized activation and induced M2-polarized activation. Both linagliptin and metformin enhanced cognitive ability, increased hippocampal synaptic plasticity and neurogenesis, and decreased age-related oxidative stress and inflammation by regulating microglia polarization in the hippocampus of middle-aged mice. The combination of linagliptin and metformin showed a maximum protective effect compared to the individual drugs alone. Loss of macrophage inflammatory protein-1α (MIP-1α), a DPP-4 substrate, abrogated the cognitive protection and anti-inflammation effects of linagliptin. Therefore, the current investigation exhibits a potential utility for DPP-4 inhibition in attenuating microglia-mediated inflammation and preventing mild cognitive impairment (MCI) in middle-aged mice, and the effect was partly mediated by MIP-1α.

Use of gliptins reduces levels of SDF-1/CXCL12 in bullous pemphigoid and type 2 diabetes, but does not increase autoantibodies against BP180 in diabetic patients.

The use of dipeptidyl peptidase 4 (DPP4) inhibitors, (also known as gliptins), is associated with an increased risk of bullous pemphigoid (BP), an autoimmune blistering skin disease. To explore the mechanism behind gliptin-associated BP we investigated circulating autoantibodies against the major BP autoantigen BP180 in serum samples from patients with type 2 diabetes (T2D) with preceding gliptin medication (n = 136) or without (n = 136). Sitagliptin was the most frequently prescribed gliptin (125/136 patients). Using an ELISA assay, we showed that IgG autoantibodies against the immunodominant NC16A domain of BP180 were found in 5.9% of gliptin treated and in 6.6% of non-gliptin treated T2D patients. We found that 28% of gliptin treated patients had IgG autoantibodies recognizing the native full-length BP180 in ELISA, but among non-gliptin treated the seropositivity was even higher, at 32%. Further ELISA analysis of additional serum samples (n = 57) found no major changes in the seropositivity against BP180 during a follow-up period of about nine years. In immunoblotting, full-length BP180 was recognized by 71% of gliptin treated and 89% of non-gliptin treated T2D patients, but only by 46% of the age-and sex-matched controls. The chemokine stromal derived factor-1(SDF-1/CXCL12) is one of the major substrates of DPP4. Immunostainings showed that the expression of SDF-1 was markedly increased in the skin of BP patients, but not affected by prior gliptin treatment. We found that the use of gliptins decreased the serum level of SDF-1α in both BP and T2D patients. Our results indicate that the autoantibodies against the linear full-length BP180 are common in patients with T2D, but seropositivity is unaffected by the use of sitagliptin.

Proteomic characterization of primary and metastatic prostate cancer reveals reduced proteinase activity in aggressive tumors

Prostate cancer (PCa) is a heterogeneous group of tumors with variable clinical courses. In order to improve patient outcomes, it is critical to clinically separate aggressive PCa (AG) from non-aggressive PCa (NAG). Although recent genomic studies have identified a spectrum of molecular abnormalities associated with aggressive PCa, it is still challenging to separate AG from NAG. To better understand the functional consequences of PCa progression and the unique features of the AG subtype, we studied the proteomic signatures of primary AG, NAG and metastatic PCa. 39 PCa and 10 benign prostate controls in a discovery cohort and 57 PCa in a validation cohort were analyzed using a data-independent acquisition (DIA) SWATH–MS platform. Proteins with the highest variances (top 500 proteins) were annotated for the pathway enrichment analysis. Functional analysis of differentially expressed proteins in NAG and AG was performed. Data was further validated using a validation cohort; and was also compared with a TCGA mRNA expression dataset and confirmed by immunohistochemistry (IHC) using PCa tissue microarray (TMA). 4,415 proteins were identified in the tumor and benign control tissues, including 158 up-regulated and 116 down-regulated proteins in AG tumors. A functional analysis of tumor-associated proteins revealed reduced expressions of several proteinases, including dipeptidyl peptidase 4 (DPP4), carboxypeptidase E (CPE) and prostate specific antigen (KLK3) in AG and metastatic PCa. A targeted analysis further identified that the reduced expression of DPP4 was associated with the accumulation of DPP4 substrates and the reduced ratio of DPP4 cleaved peptide to intact substrate peptide. Findings were further validated using an independently-collected tumor cohort, correlated with a TCGA mRNA dataset, and confirmed by immunohistochemical stains of PCa tumor microarray (TMA). Our study is the first large-scale proteomics analysis of PCa tissue using a DIA SWATH-MS platform. It provides not only an interrogative proteomic signature of PCa subtypes, but also indicates the critical roles played by certain proteinases during tumor progression. The spectrum map and protein profile generated in the study can be used to investigate potential biological mechanisms involved in PCa and for the development of a clinical assay to distinguish aggressive from indolent PCa.

Teneligliptin, a DPP-4 Inhibitor, Decreases Plasma Levels of Inflammatory Chemokines During a Standard Meal Test in Patients With Type 2 Diabetes

Dipeptidyl peptidase-4 (DPP-4) rapidly inactivates incretin hormones and several chemokines, thus influencing chemokine function. There have recently been several reports that DPP-4 inhibitor therapy is associated with an increased risk of bullous pemphigoid (BP), an autoimmune skin disease. Previous studies have demonstrated an increase of CCL11/Eotaxin, a DPP-4 substrate, in serum and blister fluid from patients with BP. Serum levels of CCL22/macrophage-derived chemokine (MDC) and CXCL10/IP-10, other DPP-4 substrates, are also elevated in BP patients. In patients with type 2 diabetes, we investigated the effect of treatment with teneligliptin (a DPP-4 inhibitor) for 24 weeks on plasma levels of CCL11/Eotaxin, CCL22/MDC and CXCL10/IP-10 during a meal test. Ten consecutive patients with type 2 diabetes who showed inadequate glycemic control by metformin and/or sulfonylureas were recruited. A standard meal test was performed at baseline and after 24 weeks of treatment with teneligliptin at 20 mg/day. Blood samples were collected at 0, 30, 60 and 120 minutes after ingestion of the meal. In addition to plasma levels of the 3 chemokine, plasma DPP-4 enzyme activity and soluble DPP-4 antigen were measured. Treatment with teneligliptin decreased hemoglobin A1c and reduced fasting plasma DPP-4 activity by 90.1% compared with baseline. Unexpectedly, plasma levels of all 3 chemokines (including CCL11/Eotaxin) were not increased after teneligliptin treatment, and instead were significantly lower at every point during the meal test. Teneligliptin reduced the plasma concentrations of 3 chemokines (DPP-4 substrates) that may be related to the occurrence of DPP4 inhibitor-associated BP (UMIN000012508).

MON-474 Dipeptidyl Peptidase-4 (DPP4) Inhibition Decreases Visceral Fat and Improves Glucose Metabolism in Overweight Women with Polycystic Ovarian Syndrome

Background: Women with PCOS have decreased GH secretion.1 Diminished GH is associated with increased visceral adiposity and impaired vascular function. GH releasing hormone is the primary stimulus for GH secretion and a substrate of dipeptidyl peptidase-4 (DPP4).2 We tested the hypothesis that one month of DPP4 inhibition with sitagliptin increases GH secretion and improves glucose metabolism and vascular function in women with PCOS. Methods: Eighteen women with PCOS (BMI ≥ 25 kg/m2) participated in a randomized, double-blinded, cross-over study during which they received sitagliptin 100 mg p.o. vs. placebo daily for one month separated by a minimum eight-week wash-out. At two weeks, women underwent a 75 g oral glucose tolerance test (OGTT). At one month, women were admitted for fasting laboratories, assessment of conduit artery vascular function, and measurement of body composition via DEXA. Overnight GH secretion was assessed using an automated deconvolution algorithm (AutoDecon) previously validated for the analysis of endogenous pulsatile GH secretion from time-series data obtained via frequent venous sampling from an indwelling catheter every ten minutes for twelve hours. Results: Sitagliptin 100 mg daily decreased DPP4 activity (p<0.001 vs. placebo) and increased GLP-1 levels (p<0.001 vs. placebo) during OGTT. Glucose metabolism improved during sitagliptin, as demonstrated by mean decrease in blood glucose of 15.4 mg/dL (95% CI 8.7, 22.1; p<0.001) at 100 minutes as compared to placebo. Sitagliptin enhanced early insulin secretion (from mean insulinogenic index 1.9 ± SD 1.2 to 3.2 ± 3.1; p=0.01). At one month, sitagliptin decreased visceral adipose tissue (VAT) (from 1141.9 g ± 700.7 to 1055.1 ± 710.1; p=0.02) and total cholesterol (from 168.8 mg/dL ± 26.3 to 162.5 ± 22.2; p=0.02) but did not affect vascular function. Sitagliptin did not increase overnight GH secretion, as summarized by area over the curve (AUC) or mean GH, but did increase GH half-life (from 13.9 min ± 3.6 to 16.8 ± 6.2, N=16; p=0.04) and the interpulse interval (from 53.2 min ± 20.0 to 77.3 ± 38.4, N=16; p<0.05). DPP4 activity levels during sitagliptin were associated with overnight GH secretion (GH AUC: rs= -0.60, p=0.01; mean GH: rs= -0.57, p=0.02), VAT mass (rs= 0.66; p<0.01), and insulin resistance (HOMA-IR rs=0.54; p=0.04). Conclusions: Sitagliptin improved blood glucoses following 75 g OGTT in overweight women with PCOS and decreased VAT but did not enhance vascular function. While sitagliptin did not increase overnight GH secretion, it did enhance GH half-life and the interpulse interval. Moreover, the response to sitagliptin was directly related to overnight GH secretion and inversely to VAT and insulin resistance. In this pilot study, sitagliptin improved glucose metabolism and body composition in accordance with GH secretion. 1 deBoer et al., Hum. Reprod. 2004 19: 504. 2 Frohman et al., J Clin Invest. 1986 78:906.

What doesn't kill you makes you stranger: Dipeptidyl peptidase-4 (CD26) proteolysis differentially modulates the activity of many peptide hormones and cytokines generating novel cryptic bioactive ligands.

Dipeptidyl peptidase 4 (DPP4) is an exopeptidase found either on cell surfaces where it is highly regulated in terms of its expression and surface availability (CD26) or in a free/circulating soluble constitutively available and intrinsically active form. It is responsible for proteolytic cleavage of many peptide substrates. In this review we discuss the idea that DPP4-cleaved peptides are not necessarily inactivated, but rather can possess either a modified receptor selectivity, modified bioactivity, new antagonistic activity, or even a novel activity relative to the intact parent ligand. We examine in detail five different major DPP4 substrates: glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), peptide tyrosine-tyrosine (PYY), and neuropeptide Y (NPY), and stromal derived factor 1 (SDF-1 aka CXCL12). We note that discussion of the cleaved forms of these five peptides are underrepresented in the research literature, and are both poorly investigated and poorly understood, representing a serious research literature gap. We believe they are understudied and misinterpreted as inactive due to several factors. This includes lack of accurate and specific quantification methods, sample collection techniques that are inherently inaccurate and inappropriate, and a general perception that DPP4 cleavage inactivates its ligand substrates. Increasing evidence points towards many DPP4-cleaved ligands having their own bioactivity. For example, GLP-1 can work through a different receptor than GLP-1R, DPP4-cleaved GIP can function as a GIP receptor antagonist at high doses, and DPP4-cleaved PYY, NPY, and CXCL12 can have different receptor selectivity, or can bind novel, previously unrecognized receptors to their intact ligands, resulting in altered signaling and functionality. We believe that more rigorous research in this area could lead to a better understanding of DPP4's role and the biological importance of the generation of novel cryptic ligands. This will also significantly impact our understanding of the clinical effects and side effects of DPP4-inhibitors as a class of anti-diabetic drugs that potentially have an expanding clinical relevance. This will be specifically relevant in targeting DPP4 substrate ligands involved in a variety of other major clinical acute and chronic injury/disease areas including inflammation, immunology, cardiology, stroke, musculoskeletal disease and injury, as well as cancer biology and tissue maintenance in aging.

Dipeptidyl peptidase-4 inhibitor teneligliptin accelerates recovery from cisplatin-induced acute kidney injury by attenuating inflammation and promoting tubular regeneration.

Cisplatin is an effective chemotherapeutic agent. However, acute kidney injury (AKI) and subsequent kidney function decline limits its use. Dipeptidyl peptidase-4 (DPP-4) inhibitor has been reported to attenuate kidney injury in some in vivo models, but the mechanisms-of-action in tubule recovery upon AKI remain speculative. We hypothesized that DPP-4 inhibitor teneligliptin (TG) can facilitate kidney recovery after cisplatin-induced AKI. In in vivo experiment, AKI was induced in rats by injecting 5 mg/kg of cisplatin intravenously. Oral administration of 10 mg/kg of TG, once a day, was started just before injecting cisplatin or from Day 5 after cisplatin injection. In an in vitro experiment, proliferation of isolated murine tubular cells was evaluated with 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay, cell cycle analysis and cell counting. Cell viability was analysed by MTT assay or lactate dehydrogenase (LDH) assay. In in vivo experiments, we found that TG attenuates cisplatin-induced AKI and accelerates kidney recovery after the injury by promoting the proliferation of surviving epithelial cells of the proximal tubule. TG also suppressed intrarenal tumour necrosis factor-α expression, and induced macrophage polarization towards the anti-inflammatory M2 phenotype, both indirectly endorsing tubule recovery upon cisplatin injury. In in vitro experiments, TG directly accelerated the proliferation of primary tubular epithelial cells. Systematic screening of the DPP-4 substrate chemokines in vitro identified CXC chemokine ligand (CXCL)-12 as a promoted mitogenic factor. CXCL12 not only accelerated proliferation but also inhibited cell death of primary tubular epithelial cells after cisplatin exposure. CXC chemokine receptor (CXCR)-4 antagonism abolished the proliferative effect of TG. The DPP-4 inhibitor TG can accelerate tubule regeneration and functional recovery from toxic AKI via an anti-inflammatory effect and probably via inhibition of CXCL12 breakdown. Hence, DPP-4 inhibitors may limit cisplatin-induced nephrotoxicity and improve kidney function in cancer patients.

Extracellular Ubiquitin(1-76) and Ubiquitin(1-74) Regulate Cardiac Fibroblast Proliferation.

SDF-1α (stromal cell-derived factor-1α) is a CXCR4-receptor agonist and DPP4 (dipeptidyl peptidase 4) substrate. SDF-1α, particularly when combined with sitagliptin to block the metabolism of SDF-1α by DPP4, stimulates proliferation of cardiac fibroblasts via the CXCR4 receptor; this effect is greater in cells from spontaneously hypertensive rats versus Wistar-Kyoto normotensive rats. Emerging evidence indicates that ubiquitin(1-76) exists in plasma and is a potent CXCR4-receptor agonist. Therefore, we hypothesized that ubiquitin(1-76), similar to SDF-1α, should increase proliferation of cardiac fibroblasts. Contrary to our working hypothesis, ubiquitin(1-76) did not stimulate cardiac fibroblast proliferation, yet unexpectedly antagonized the proproliferative effects of SDF-1α combined with sitagliptin. In this regard, ubiquitin(1-76) was more potent in spontaneously hypertensive versus Wistar-Kyoto cells. In the presence of 6bk (selective inhibitor of insulin-degrading enzyme [IDE]; an enzyme known to convert ubiquitin(1-76) to ubiquitin(1-74)), ubiquitin(1-76) no longer antagonized the proproliferative effects of SDF-1α/sitagliptin. Ubiquitin(1-74) also antagonized the proproliferative effects of SDF-1α/sitagliptin, and this effect of ubiquitin(1-74) was not blocked by 6bk and was >10-fold more potent compared with ubiquitin(1-76). Neither ubiquitin(1-76) nor ubiquitin(1-74) inhibited the proproliferative effects of the non-CXCR4 receptor agonist neuropeptide Y (activates Y1 receptors). Cardiac fibroblasts expressed IDE mRNA, protein, and activity and converted ubiquitin(1-76) to ubiquitin(1-74). Spontaneously hypertensive fibroblasts expressed greater IDE activity. Extracellular ubiquitin(1-76) blocks the proproliferative effects of SDF-1α/sitagliptin via its conversion by IDE to ubiquitin(1-74), a potent CXCR4 antagonist. Thus, IDE inhibitors, particularly when combined with DPP4 inhibitors or hypertension, could increase the risk of cardiac fibrosis.

The Dipeptidyl Peptidase 4 Substrate CXCL12 Has Opposing Cardiac Effects in Young Mice and Aged Diabetic Mice Mediated by Ca2+ Flux and Phosphoinositide 3-Kinase γ.

Blood glucose-lowering therapies can positively or negatively affect heart function in type 2 diabetes, or they can have neutral effects. Dipeptidyl peptidase 4 (DPP-4) inhibitors lower blood glucose by preventing the proteolytic inactivation of glucagon-like peptide 1 (GLP-1). However, GLP-1 is not the only peptide substrate of DPP-4. Here, we investigated the GLP-1-independent cardiac effects of DPP-4 substrates. Pointing to GLP-1 receptor (GLP-1R)-independent actions, DPP-4 inhibition prevented systolic dysfunction equally in pressure-overloaded wild-type and GLP-1R knockout mice. Likewise, DPP-4 inhibition or the DPP-4 substrates substance P or C-X-C motif chemokine ligand 12 (CXCL12) improved contractile recovery after no-flow ischemia in the hearts of otherwise healthy young adult mice. Either DPP-4 inhibition or CXCL12 increased phosphorylation of the Ca2+ regulatory protein phospholamban (PLN), and CXCL12 directly enhanced cardiomyocyte Ca2+ flux. In contrast, hearts of aged obese diabetic mice (which may better mimic the comorbid patient population) had diminished levels of PLN phosphorylation. In this setting, CXCL12 paradoxically impaired cardiac contractility in a phosphoinositide 3-kinase γ-dependent manner. These findings indicate that the cardiac effects of DPP-4 inhibition primarily occur through GLP-1R-independent processes and that ostensibly beneficial DPP-4 substrates can paradoxically worsen heart function in the presence of comorbid diabetes.

The Effect of Gliptins to Improve Functional Outcome after Stroke in Mice Is Mediated by the CXCR4/SDF-1α Pathway

Dipeptidyl peptidase-4 (DPP-4) inhibitors (gliptins) decrease hyperglycemia by inhibiting glucagon-like peptide-1 (GLP-1) cleavage. Gliptins can also improve stroke outcome in rodents independently of GLP-1R. However, the underlying mechanisms are unknown. Stromal cell-derived factor-1α (SDF-1α) is a DPP-4 substrate and CXCR4 agonist that promotes beneficial effects in injured brains. However, SDF-1α involvement in gliptin-mediated neuroprotection is unproven. We aimed to determine whether gliptins improve stroke outcome via SDF-1α/CXCR4 and identify additional targets behind the efficacy. Adult, male C57bl6/j mice (n=101) underwent transient focal cerebral ischemia. Linagliptin was administered for 3 days or 3 weeks. The CXCR4-antagonist AMD3100 was administered starting a day before ischemia. Stroke outcome was assessed by measuring upper-limb function and brain tissue damage. Levels of active GLP-1, gastric inhibitory polypeptide (GIP) and SDF-1α were quantified by ELISA in serum and brain. Mass spectrometry was used to identify additional gliptin-mediated effectors in brain tissue samples. Sustained, post-ischemic treatment with linagliptin reduced motor impairment (p003C0.01) and tissue damage (p003C0.05). Linagliptin increased serum levels of GLP-1 (p003C0.0001), GIP (p003C0.05) and SDF-1α (p003C0.05). However, only SDF-1α levels were increased in the brain (p003C0.001). Linagliptin also decreased the presence of neurogranin-derived peptides and peptides from an isoform of myelin basic protein (MBG, p003C0.05). The inhibition of SDF-1α/CXCR4 pathway diminished the positive effects of linagliptin on stroke outcome (not different from vehicle). We propose a gliptin-mediated neuroprotective mechanism via SDF-1α, which could affect Ca2+ homeostasis, altering neurogranin and MBG processing and potentially decreasing calpain activity. These results provide new insights into restorative gliptin-mediated effects against stroke. Disclosure F. Chiazza: Other Relationship; Self; Boehringer Ingelheim GmbH. H. Tammen: Consultant; Self; Boehringer Ingelheim GmbH. H. Pintana: Other Relationship; Self; Boehringer Ingelheim GmbH. G. Lietzau: Other Relationship; Self; Boehringer Ingelheim GmbH. M. Collino: None. T. Nystrom: Research Support; Self; AstraZeneca. Advisory Panel; Self; Eli Lilly and Company, Novo Nordisk A/S. Speaker's Bureau; Self; Boehringer Ingelheim GmbH. T. Klein: Employee; Self; Boehringer Ingelheim GmbH. V. Darsalia: Other Relationship; Self; Boehringer Ingelheim GmbH. C. Patrone: Other Relationship; Self; Boehringer Ingelheim GmbH.

Involvement of brain natriuretic peptide signaling pathway in the cardioprotective action of sitagliptin.

The current study is focusing on the role of brain natriuretic peptide (BNP), a substrate of dipeptidyl peptidase-4 (DPP-4) enzyme, and its signaling survival pathway in the cardioprotective mechanism of sitagliptin, a DPP-4 inhibitor. Male Wistar rats were randomized into 7 groups, sham, I/R, KT-5823 (selective protein kinase (PK) G inhibitor), 5-HD (selective mito-KATP channel blocker), sitagliptin (300mg/kg, po), sitagliptin+KT-5823, and sitagliptin+5-HD. Sitagliptin was administered for 3 days prior to induction of coronary I/R, while either KT-5823 or 5-HD was administered intravenously 5min before coronary ligation. Pretreatment with sitagliptin provided significant protection against I/R injury as manifested by decreasing, percentage of infarct size, suppressing the elevated ST segment, reducing the increased cardiac enzymes, as well as DPP-4 activity and elevating both heart rate (HR) and left ventricular developed pressure (LVDP). However, the addition of either blocker to sitagliptin regimen reversed partly its cardioprotective effects. Although I/R increased BNP content, it unexpectedly decreased that of cGMP; nevertheless, sitagliptin elevated both parameters, an effect that was not affected by the use of the two blockers. On the molecular level, sitagliptin decreased caspase-3 activity and downregulated the mRNA levels of BNP, Bax, and Cyp D, while upregulated that of Bcl2. The use of either KT-5823 or 5-HD with sitagliptin hindered its effect on the molecular markers tested. The results of the present study suggest that the cardioprotective effect of sitagliptin is mediated partly, but not solely, through the BNP/cGMP/PKG survival signaling pathway.

Saxagliptin Attenuates Albuminuria by Inhibiting Podocyte Epithelial- to-Mesenchymal Transition via SDF-1α in Diabetic Nephropathy.

The dipeptidyl peptidase-4 (DPP-4) inhibitor saxagliptin has been found to reduce progressive albuminuria, but the exact mechanism of inhibition is unclear. Podocyte epithelial-to-mesenchymal transition (EMT) has emerged as a potential pathway leading to proteinuria in diabetic nephropathy (DN). Stromal cell–derived factor-1α (SDF-1α), one of the substrates of DPP-4, can activate the protein kinase A pathway and subsequently inhibit its downstream effector, transforming growth factor-β1 (TGF-β1), which induces podocyte EMT. Thus, this study was designed to test the hypothesis that saxagliptin reduces progressive albuminuria by preventing podocyte EMT through inhibition of SDF-1α cleavage in DN. The results of a series of assays, including ELISA, western blotting, and immunochemistry/immunofluorescence, showed that saxagliptin treatment obviously ameliorated urinary microalbumin excretion and renal histological changes in high-fat diet/streptozotocin-induced diabetic rats. Furthermore, saxagliptin-treated diabetic rats presented with suppression of DPP-4 activity/protein expression accompanied by restoration of SDF-1α levels, which subsequently hindered NOX2 expression and podocyte EMT. In vitro, we consistently observed that saxagliptin significantly inhibited increased DPP-4 activity/expression, oxidative stress and podocyte EMT. Application of an SDF-1α receptor inhibitor (AMD3100) to cultured podocytes further confirmed the essential role of SDF-1α in podocyte EMT inhibition. In sum, we demonstrated for the first time that saxagliptin treatment plays an essential role in ameliorating progressive DN by preventing podocyte EMT through a SDF-1α-related pathway, suggesting that saxagliptin could offer renoprotection and that SDF-1α might be a potential therapeutic target for DN.

Comment on Lovshin et al. Dipeptidyl Peptidase 4 Inhibition Stimulates Distal Tubular Natriuresis and Increases in Circulating SDF-1α1-67 in Patients With Type 2 Diabetes. Diabetes Care 2017;40:1073–1081

We read with interest the study by Lovshin et al. (1) investigating the natriuretic effect of the dipeptidyl peptidase 4 (DPP-4) inhibitor sitagliptin in patients with type 2 diabetes (T2D). The authors report that 1 month of sitagliptin therapy increases creatinine-based fractional sodium excretion (FENa) compared with placebo, which is in line with our previous observation (2). As lithium clearance and (intra)renal hemodynamics were not affected, the authors suggest that sitagliptin inhibits tubular sodium reabsorption at a level that is likely downstream of the macula densa. In parallel with enhanced FENa, DPP-4 inhibition increased intact stromal cell–derived factor (SDF)-1α1–67 levels, suggesting a relevant natriuretic role for this DPP-4 substrate. We agree with the authors that their mechanistic findings are of potential clinical relevance, particularly when hypothesizing about the added natriuretic effect of combined pharmacological DPP-4/sodium–glucose cotransporter …

Dipeptidyl peptidase 4 serum activity and concentration are increased in women with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a complex disease, the aetiology of which is not well understood. Alterations in potential candidate genes involved in the biosynthesis and metabolism of androgens, folliculogenesis and insulin and glucose metabolism have been suggested as possible aetiologies. Dipeptidyl peptidase-4 (DPP4) plays a key role in glucose homoeostasis and, thus, in the regulation of insulin secretion. The aim of our study was to analyse the DPP4 activity and concentrations in the serum of PCOS and non-PCOS patients and, additionally, study the activation of the DPP4 promoter by androgens in vitro. Serum samples were obtained from 288 female patients treated at the Center for Reproductive Medicine and Andrology (154 non-PCOS and 134 patients with PCOS). DPP4 activity was measured by the conversion of the DPP4 substrate Gly-Pro p-nitroanilide hydrochloride and DPP4 concentration with a commercial ELISA. Luciferase reporter assays, qPCR and Western Blot analyses were performed for the in vitro evaluation of the activation of the DPP4 promoter by androgens. DPP4 serum activity was increased in women with PCOS, regardless of which Rotterdam criteria led to the PCOS diagnosis. Furthermore, DPP4 serum levels were strongly correlated with the anti-Müllerian hormone (AMH) serum level. In vitro, the DPP4 promoter was stimulated by androgens in luciferase reporter assays, and DPP4 mRNA expression was increased in KGN granulosa carcinoma cells after androgen treatment. The results suggested that a deregulation of DPP4 serum levels could be an additional characteristic of the metabolic imbalances associated with PCOS.

Sitagliptin, a dipeptidyl peptidase-4 inhibitor, suppresses CXCL5 and SDF-1 and does not accelerate intestinal neoplasia formation in ApcMin/+ mice fed a high-fat diet.

The relationship between type 2 diabetes mellitus and intestinal neoplasia has been shown epidemiologically. A high-fat diet (HFD) is also known to promote insulin resistance, which is a risk factor for intestinal neoplasia. Dipeptidyl peptidase-4 (DPP-4) inhibitors are used in the clinic for the treatment of type 2 diabetes and also to prolong the effects of glucagon-like peptide-1 (GLP-1). However, since the intestinotrophic hormone GLP-2 and chemokines, such as CXCL5 and stromal cell-derived factor-1 (SDF-1), are also substrates of DPP-4, DPP-4 inhibitors may increase the risk of intestinal carcinogenesis. In this study, we evaluated the impact of a DPP-4 inhibitor on intestinal tumorigenesis in ApcMin/+ mice fed a HFD. Six-week-old male ApcMin/+ mice were randomized to either a normal diet (10 kcal% fat) group, a HFD (60 kcal% fat) group, or a HFD group treated with sitagliptin (STG). The mice were euthanized nine weeks after the start of treatment. Daily treatment with STG did not increase number of intestinal tumors in the HFD group; however, this increase was not statistically significant. The mucosal concentration of total GLP-2 was significantly increased in the HFD group. The chemokine protein array showed elevated plasma concentrations of CXCL5 and SDF-1 in the HFD group. The administration of STG significantly suppressed the levels of plasma CXCL5 and SDF-1 in mice fed a HFD. Since CXCL5 expression is increased in patients with type 2 diabetes, and GLP-2, CXCL5 and SDF-1 are associated with tumor progression, DPP-4 inhibition may have potential as an agent for decreasing the risk of cancer in obese or diabetic patients.

Effect of Dipeptidyl Peptidase-4 Inhibitors on Bone Metabolism and the Possible Underlying Mechanisms.

Diabetes mellitus has been demonstrated to be closely associated with osteoporosis. Accordingly, hypoglycemic therapy is considered effective in treating metabolic bone disease. Recently, the effects of dipeptidyl peptidase-4 (DPP-4) inhibitors, a new type of antidiabetic drug, on bone metabolism have been widely studied. This review mainly describes the effects of DPP-4 inhibitors on bone metabolism, including their effects on bone mineral density, bone quality, and fracture risk. In addition, the potential underlying mechanisms are discussed. Based on the current progress in this research field, DPP-4 inhibitors have been proved to reduce fracture risk. In addition, sitagliptin, a strong and highly selective DPP-4 inhibitor, showed its beneficial effects on bone metabolism by improving bone mineral density, bone quality, and bone markers. With regard to the potential underlying mechanisms, DPP-4 inhibitors may promote bone formation and reduce bone resorption through DPP-4 substrates and DPP-4-related energy metabolism. Vitamin D and other related signaling pathways also play a role in affecting bone metabolism. Although these assumptions are controversial, they provide a translational pharmacology approach for the clinical use of DPP-4 inhibitors in the treatment of metabolic diseases. Prior to the use of these drugs in clinic, further studies should be conducted to determine the appropriate type of DPP-4 inhibitor, the people who would benefit the most from this therapy, appropriate dose and duration, and the effects of the treatment.

Lung ischemia reperfusion injury: the therapeutic role of dipeptidyl peptidase 4 inhibition.

Dipeptidyl peptidase 4 (DPP4) is a cell surface protease that has been reported to play a role in glucose homeostasis, cancer, HIV, autoimmunity, immunology and inflammation. A role for DPP4 in ischemia-reperfusion injury (IRI) in the heart has been established. Dipeptidyl peptidase 4 inhibition (DPP4i) appeared to decrease infarct size, improves cardiac function and promotes myocardial regeneration. Lung ischemia reperfusion injury is caused by a complex mechanism in which macrophages and neutrophils play an important role. Generation of reactive oxygen species (ROS), uncoupling of nitric oxide synthase (NOS), activation of nuclear factor-κB (NF-κB), activation of nicotinamide adenine dinucleotide phosphate metabolism, and generation of pro-inflammatory cytokines lead to acute lung injury (ALI). In this review we present the current knowledge on DPP4 as a target to treat IRI in the lung. We also provide evidence of the roles of the DPP4 substrates glucagon-like peptide 1 (GLP-1), vasoactive intestinal peptide (VIP) and stromal cell-derived factor-1α (SDF-1α) in protection against oxidative stress through activation of the mitogen-activated protein kinase (MAPK) 1/2 and phosphatidylinositol 3'-kinase (PI3K)/Akt signal transduction pathways.

DPP4 Inhibition Ameliorates Cardiac Function by Blocking the Cleavage of HMGB1 in Diabetic Mice After Myocardial Infarction.

High mobility group box 1 (HMGB1), a ubiquitous DNA-binding protein, promotes angiogenesis and tissue repair, resulting in restored cardiac function after myocardial infarction (MI). Although dipeptidyl peptidase 4 (DPP4) degrades certain peptides, it remains unclear as to whether HMGB1 is a substrate of DPP4 and whether DPP4 inhibition prevents the cleavage of HMGB1.In transgenic mice with cardiac-specific overexpression of HMGB1 (TG) and wild-type mice (WT), a diabetic state was induced by streptozotocin, and MI was created by ligation of the left anterior descending coronary artery. To inhibit DPP4 activity, a DPP4 inhibitor anagliptin was used. The plasma levels of HMGB1, infarct size, echocardiographic data, angiogenesis, and vascular endothelial growth factor (VEGF) expression in the peri-infarct area were compared among non-diabetic MI WT/TG, diabetic MI WT/TG, and anagliptin-treated diabetic MI WT/TG mice.DPP4 activity was increased in the diabetic state and blocked by anagliptin administration. The HMGB1 plasma levels were reduced in the diabetic TG compared with the non-diabetic TG mice, but DPP4 inhibition with anagliptin increased HMGB1 plasma levels in the diabetic TG mice. The infarct area was significantly larger in the diabetic TG than in the non-diabetic TG mice, and it was reduced by DPP4 inhibition. Cardiac function, angiogenesis, and VEGF expression were impaired in the diabetic TG mice, but they were ameliorated by the DPP4 inhibition to levels similar to those found in the non-diabetic TG mice.The DPP4 inhibitor ameliorated cardiac function by inhibiting the inactivation of HMGB1 in diabetic mice after MI.