Peptide degradation and the role of DPP-4 inhibitors in the treatment of type 2 diabetes

Optimizing expression, purification, structural and functional assessments of a novel dimeric incretin (GLP-1cpGLP-1)

Glucagon-like peptide-1 (GLP-1) is an incretin hormone that reduces postprandial glycemic excursions by enhancing insulin secretion. In this study, a new dimeric GLP-1 analogue (GLP-1cpGLP-1) was designed by inserting human insulin C-peptide (CP) in the middle of a dimer of [Gly8] GLP-1 (7-36). Then, the dimeric incretin (GLP-1cpGLP-1) was ligated to human αB-crystallin (αB-Cry) to create a hybrid protein, abbreviated as αB-GLP-1cpGLP-1. The constructed gene was well expressed in the bacterial host system. After specific chemical release from the hybrid protein, the dimeric incretin was purified by size exclusion chromatography (SEC). Finally, the RP-HPLC analysis indicated a purity of >99 % for the dimeric incretin. The secondary structure assessments by various spectroscopic methods, and in silico analysis suggested that the dimeric incretin has α-helical rich structure. The dynamic light scattering (DLS) analysis indicates that our dimeric incretin forms large oligomeric structures. This incretin analogue significantly reduced blood glucose levels in both healthy and diabetic mice while effectively triggering insulin release. The size exclusion HPLC also indicates the interaction of the new incretin analogue with human serum albumin, the main carrier protein in the bloodstream. Consistent with the results obtained from the biological activity assessments, this significant interaction indicates its potential as a viable therapeutic agent with a long-lasting effect. The results of our research represent a significant breakthrough in the successful design of an active incretin dimer capable of effectively controlling blood sugar levels and inducing insulin secretion in the realm of diabetes treatment.

Preclinical pharmacokinetics, pharmacodynamics, and toxicity of novel small-molecule GPR119 agonists to treat type-2 diabetes and obesity

The escalating global prevalence of type-2 diabetes (T2D) and obesity necessitates the development of novel oral medications. Agonism at G-protein coupled receptor-119 (GPR119) has been recognized for modulation of metabolic homeostasis in T2D, obesity, and fatty liver disease. However, off-target effects have impeded the advancement of synthetic GPR119 agonist drug candidates. Non-systemic, gut-restricted GPR119 agonism is suggested as an alternative strategy that may locally stimulate intestinal enteroendocrine cells (EEC) for incretin secretion, without the need for systemic drug availability, consequently alleviating conventional class-related side effects. Herein, we report the preclinical acute safety, efficacy, and pharmacokinetics (PK) of novel GPR119 agonist compounds ps297 and ps318 that potentially target gut EEC for incretin secretion. In a proof-of-efficacy study, both compounds demonstrated glucagon-like peptide-1 (GLP-1) secretion capability during glucose and mixed-meal tolerance tests in healthy mice. Furthermore, co-administration of sitagliptin with investigational compounds in diabetic db/db mice resulted in synergism, with GLP-1 concentrations rising by three-fold. Both ps297 and ps318 exhibited low gut permeability assessed in the in-vitro Caco-2 cell model. A single oral dose PK study conducted on healthy mice demonstrated poor systemic bioavailability of both agents. PK measures (mean ± SD) for compound ps297 (Cmax 23 ± 19 ng/mL, Tmax range 0.5 - 1 h, AUC0-24 h 19.6 ± 21 h*ng/mL) and ps318 (Cmax 75 ± 22 ng/mL, Tmax range 0.25 - 0.5 h, AUC0-24 h 35 ± 23 h*ng/mL) suggest poor oral absorption. Additionally, examinations of drug excretion patterns in mice revealed that around 25 % (ps297) and 4 % (ps318) of the drugs were excreted through faeces as an unchanged form, while negligible drug concentrations (<0.005 %) were excreted in the urine. These acute PK/PD assessments suggest the gut is a primary site of action for both agents. Toxicity assessments conducted in the zebrafish and healthy mice models confirmed the safety and tolerability of both compounds. Future chronic in-vivo studies in relevant disease models will be essential to confirm the long-term safety and efficacy of these novel compounds.

Stimulating intestinal GIP release reduces food intake and body weight in mice

OBJECTIVE

Glucose dependent insulinotropic polypeptide (GIP) is well established as an incretin hormone, boosting glucose-dependent insulin secretion. However, whilst anorectic actions of its sister-incretin glucagon-like peptide-1 (GLP-1) are well established, a physiological role for GIP in appetite regulation is controversial, despite the superior weight loss seen in preclinical models and humans with GLP-1/GIP dual receptor agonists compared with GLP-1R agonism alone.

METHODS

We generated a mouse model in which GIP expressing K-cells can be activated through hM3Dq Designer Receptor Activated by Designer Drugs (DREADD, GIP-Dq) to explore physiological actions of intestinally-released GIP.

RESULTS

In lean mice, Dq-stimulation of GIP expressing cells increased plasma GIP to levels similar to those found postprandially. The increase in GIP was associated with improved glucose tolerance, as expected, but also triggered an unexpected robust inhibition of food intake. Validating that this represented a response to intestinally-released GIP, the suppression of food intake was prevented by injecting mice peripherally or centrally with antagonistic GIPR-antibodies, and was reproduced in an intersectional model utilising Gip-Cre/Villin-Flp to limit Dq transgene expression to K-cells in the intestinal epithelium. The effects of GIP cell activation were maintained in diet induced obese mice, in which chronic K-cell activation reduced food intake and attenuated body weight gain.

CONCLUSIONS

These studies establish a physiological gut-brain GIP-axis regulating food intake in mice, adding to the multi-faceted metabolic effects of GIP which need to be taken into account when developing GIPR-targeted therapies for obesity and diabetes.

Barosmin against postprandial hyperglycemia: outputs from computational prediction to functional responses in vitro

Previously, barosmin has been demonstrated to possess anti-diabetic action. However, its effect to inhibit α-amylase and α-glucosidase, including glucose utilization efficacy, has yet to be revealed. Hence, the current study attempted to assess the efficiency of barosmin in inhibiting the α-amylase, α -glucosidase, and dipeptidyl peptidase 4 enzymes, including glucose uptake efficacy. Molecular docking and simulation were performed using AutoDock Vina and Gromacs respectively followed by gene ontology analysis using the database for annotation, visualization, and integrated discovery. Further, in vitro enzyme inhibitory activities and glucose uptake assay were performed in L6 cell lines. Density functional theory analysis detailed mechanistic insights into the crucial interaction sites of barosmin of which the electron-dense region was prone to nucleophilic attack (O-atoms) whereas hydroxyl groups (-OH) showed affinity for electrophilic attacks. Barosmin showed good binding affinity with α-amylase (-9.2 kcal/mol), α-glucosidase (-10.7 kcal/mol), and dipeptidyl peptidase 4 (-10.0 kcal/mol). Barosmin formed stable nonbonded contacts with active site residues of aforementioned enzymes throughout 200 ns molecular dynamics simulation. Further, it regulated pathway concerned with glucose homeostasis i.e. tumor necrosis factor signaling pathway. In addition, barosmin showed α-amylase (IC50= 95.77 ± 23.33 µg/mL), α-glucosidase (IC50= 68.13 ± 2.95 µg/mL), and dipeptidyl peptidase 4 (IC50= 13.27 ± 1.99 µg/mL) inhibitory activities including glucose uptake efficacy in L6 cell lines (EC50= 12.46 ± 0.90 µg/mL) in the presence of insulin. This study presents the efficacy of the barosmin to inhibit α-amylase and α-glucosidase and glucose uptake efficacy in L6 cell lines via the use of multiple system biology tools and in vitro techniques.Communicated by Ramaswamy H. Sarma.

Safety, tolerability, pharmacokinetics and pharmacokinetic-pharmacodynamic modeling of cetagliptin in patients with type 2 diabetes mellitus

Aims

To evaluate the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of cetagliptin (CAS number:2243737-33-7) in Chinese patients with type 2 diabetes mellitus (T2DM). A population PK/PD model was developed to quantify the PK and PD characteristics of cetagliptin in patients.

Materials and methods

32 Chinese adults with T2DM were enrolled in this study. The subjects were randomly assigned to receive either cetagliptin (50 mg or 100 mg), placebo, or sitagliptin (100 mg) once daily for 14 days. Blood samples were collected for PK and PD analysis. Effects on glucose, insulin, C-peptide, and glucagon were evaluated following an oral glucose tolerance test (OGTT) (day15). Effects on HbA1c and glycated albumin (GA), and safety assessments were also conducted. Meanwhile, a population PK/PD model was developed by a sequential two-step analysis approach using Phoenix.

Results

Following multiple oral doses, cetagliptin was rapidly absorbed and the mean half-life were 34.9-41.9 h. Steady-state conditions were achieved after 1 week of daily dosing and the accumulation was modest. The intensity and duration of DPP-4 inhibition induced by 50 mg cetagliptin were comparable with those induced by sitagliptin, and 100 mg cetagliptin showed a much longer sustained DPP-4 inhibition (≥80%) than sitagliptin. Compared with placebo group, plasma active GLP-1 AUEC0-24h increased by 2.20- and 3.36-fold in the 50 mg and 100 mg cetagliptin groups. A decrease of plasma glucose and increase of insulin and C-peptide were observed following OGTT in cetagliptin groups. Meanwhile, a tendency of reduced GA was observed, whereas no decreasing trend was observed in HbA1c. All adverse events related to cetagliptin and sitagliptin were assessed as mild. A population PK/PD model was successfully established. The two-compartment model and Sigmoid-Emax model could fit the observed data well. Total bilirubin (TBIL) was a covariate of volume of peripheral compartment distribution (V2), and V2 increased with the increase of TBIL.

Conclusions

Cetagliptin was well tolerated, inhibited plasma DPP-4 activity, increased plasma active GLP-1 levels, and exhibited a certain trend of glucose-lowering effect in patients with T2DM. The established population PK/PD model adequately described the PK and PD characteristics of cetagliptin.

GLP-1 metabolite GLP-1(9-36) is a systemic inhibitor of mouse and human pancreatic islet glucagon secretion

AIMS/HYPOTHESIS

Diabetes mellitus is associated with impaired insulin secretion, often aggravated by oversecretion of glucagon. Therapeutic interventions should ideally correct both defects. Glucagon-like peptide 1 (GLP-1) has this capability but exactly how it exerts its glucagonostatic effect remains obscure. Following its release GLP-1 is rapidly degraded from GLP-1(7-36) to GLP-1(9-36). We hypothesised that the metabolite GLP-1(9-36) (previously believed to be biologically inactive) exerts a direct inhibitory effect on glucagon secretion and that this mechanism becomes impaired in diabetes.

METHODS

We used a combination of glucagon secretion measurements in mouse and human islets (including islets from donors with type 2 diabetes), total internal reflection fluorescence microscopy imaging of secretory granule dynamics, recordings of cytoplasmic Ca2+ and measurements of protein kinase A activity, immunocytochemistry, in vivo physiology and GTP-binding protein dissociation studies to explore how GLP-1 exerts its inhibitory effect on glucagon secretion and the role of the metabolite GLP-1(9-36).

RESULTS

GLP-1(7-36) inhibited glucagon secretion in isolated islets with an IC50 of 2.5 pmol/l. The effect was particularly strong at low glucose concentrations. The degradation product GLP-1(9-36) shared this capacity. GLP-1(9-36) retained its glucagonostatic effects after genetic/pharmacological inactivation of the GLP-1 receptor. GLP-1(9-36) also potently inhibited glucagon secretion evoked by β-adrenergic stimulation, amino acids and membrane depolarisation. In islet alpha cells, GLP-1(9-36) led to inhibition of Ca2+ entry via voltage-gated Ca2+ channels sensitive to ω-agatoxin, with consequential pertussis-toxin-sensitive depletion of the docked pool of secretory granules, effects that were prevented by the glucagon receptor antagonists REMD2.59 and L-168049. The capacity of GLP-1(9-36) to inhibit glucagon secretion and reduce the number of docked granules was lost in alpha cells from human donors with type 2 diabetes. In vivo, high exogenous concentrations of GLP-1(9-36) (>100 pmol/l) resulted in a small (30%) lowering of circulating glucagon during insulin-induced hypoglycaemia. This effect was abolished by REMD2.59, which promptly increased circulating glucagon by >225% (adjusted for the change in plasma glucose) without affecting pancreatic glucagon content.

CONCLUSIONS/INTERPRETATION

We conclude that the GLP-1 metabolite GLP-1(9-36) is a systemic inhibitor of glucagon secretion. We propose that the increase in circulating glucagon observed following genetic/pharmacological inactivation of glucagon signalling in mice and in people with type 2 diabetes reflects the removal of GLP-1(9-36)'s glucagonostatic action.

G protein-coupled receptors driven intestinal glucagon-like peptide-1 reprogramming for obesity: Hope or hype?

'Globesity' is a foremost challenge to the healthcare system. The limited efficacy and adverse effects of available oral pharmacotherapies pose a significant obstacle in the fight against obesity. The biology of the leading incretin hormone glucagon-like-peptide-1 (GLP-1) has been highly captivated during the last decade owing to its multisystemic pleiotropic clinical outcomes beyond inherent glucoregulatory action. That fostered a pharmaceutical interest in synthetic GLP-1 analogues to tackle type-2 diabetes (T2D), obesity and related complications. Besides, mechanistic insights on metabolic surgeries allude to an incretin-based hormonal combination strategy for weight loss that emerged as a forerunner for the discovery of injectable 'unimolecular poly-incretin-agonist' therapies. Physiologically, intestinal enteroendocrine L-cells (EECs) are the prominent endogenous source of GLP-1 peptide. Despite comprehending the potential of various G protein-coupled receptors (GPCRs) to stimulate endogenous GLP-1 secretion, decades of translational GPCR research have failed to yield regulatory-approved endogenous GLP-1 secretagogue oral therapy. Lately, a dual/poly-GPCR agonism strategy has emerged as an alternative approach to the traditional mono-GPCR concept. This review aims to gain a comprehensive understanding by revisiting the pharmacology of a few potential GPCR-based complementary avenues that have drawn attention to the design of orally active poly-GPCR agonist therapy. The merits, challenges and recent developments that may aid future poly-GPCR drug discovery are critically discussed. Subsequently, we project the mechanism-based therapeutic potential and limitations of oral poly-GPCR agonism strategy to augment intestinal GLP-1 for weight loss. We further extend our discussion to compare the poly-GPCR agonism approach over invasive surgical and injectable GLP-1-based regimens currently in clinical practice for obesity.

Immunomodulatory activity of dipeptidyl peptidase-4 inhibitors in immune-related diseases

Dipeptidyl peptidase-4 (DPP-4), also known as CD26, is a 110-kDa cell surface glycoprotein with enzymatic and signal transducing activity. DPP-4/CD26 is expressed by various cells, including CD4+ and CD8+ T cells, B cells, dendritic cells, macrophages, and NK cells. DPP-4 inhibitors (DPP-4i) were introduced to clinics in 2006 as new oral antihyperglycemic drugs approved for type 2 diabetes mellitus treatment. In addition to glucose-lowering effects, emerging data, from clinical studies and their animal models, suggest that DPP-4i could display anti-inflammatory and immunomodulatory effects as well, but the molecular and immunological mechanisms of these actions are insufficiently investigated. This review focuses on the modulatory activity of DPP-4i in the immune system and the possible application of DPP-4i in other immune-related diseases in patients with or without diabetes.

Sitagliptin Induces Tolerogenic Human Dendritic Cells

Sitagliptin, an anti-diabetic drug, is a dipeptidyl peptidase (DPP)-4/CD26 inhibitor with additional anti-inflammatory and immunomodulatory properties. In this study, we investigated for the first time the effect of sitagliptin on the differentiation and functions of human dendritic cells generated from monocytes (MoDCs) for 4 days using the standard GM-CSF/IL-4 procedure. LPS/IFN-γ treatment for an additional 24 h was used for maturation induction of MoDCs. Sitagliptin was added at the highest non-cytotoxic concentration (500 µg/mL) either at the beginning (sita 0d protocol) or after MoDC differentiation (sita 4d protocol). Sitagliptin impaired differentiation and maturation of MoDCs as judged with the lower expression of CD40, CD83, CD86, NLRP3, and HLA-DR, retention of CD14 expression, and inhibited production of IL-β, IL-12p70, IL-23, and IL-27. In contrast, the expression of CD26, tolerogenic DC markers (ILT4 and IDO1), and production of immunoregulatory cytokines (IL-10 and TGF-β) were increased. Generally, the sita 0d protocol was more efficient. Sitagliptin-treated MoDCs were poorer allostimulators of T-cells in MoDC/T-cell co-culture and inhibited Th1 and Th17 but augmented Th2 and Treg responses. Tolerogenic properties of sitagliptin-treated MoDCs were additionally confirmed by an increased frequency of CD4+CD25+CD127- FoxP3+ Tregs and Tr1 cells (CD4+IL-10+FoxP3-) in MoDC/T-cell co-culture. The differentiation of IL-10+ and TGF-β+ Tregs depended on the sitagliptin protocol used. A Western blot analysis showed that sitagliptin inhibited p65 expression of NF-kB and p38MAPK during the maturation of MoDCs. In conclusion, sitagliptin induces differentiation of tolerogenic DCs, and the effect is important when considering sitagliptin for treating autoimmune diseases and allotransplant rejection.

Discovery and Characterization of a Dual-Function Peptide Derived from Bitter Gourd Seed Protein Using Two Orthogonal Bioassay-Guided Fractionations Coupled with In Silico Analysis

The hydrolysate of bitter gourd seed protein, digested by the combined gastrointestinal proteases (BGSP-GPs), exhibited the most potent inhibition on angiotensin-I-converting enzyme (ACE) with an IC50 value of 48.1 ± 2.0 µg/mL. Using two independent bioassay-guided fractionations, fraction F5 from reversed-phase chromatography and fraction S1 from strong cation exchange chromatography exhibited the highest ACE inhibitory (ACEI) activity. Three identical peptides were simultaneously detected from both fractions and, based on the in silico appraisal, APLVSW (AW6) was predicted as a promising ACEI peptide. Their dipeptidyl peptidase-IV (DPP4) inhibitory (DPP4I) activity was also explored. The IC50 values of AW6 against ACE and DPP4 were calculated to be 9.6 ± 0.3 and 145.4 ± 4.4 µM, respectively. The inhibitory kinetics and intermolecular interaction studies suggested that AW6 is an ACE competitive inhibitor and a DPP4 non-competitive inhibitor. The quantities of AW6 in BGSP-GP hydrolysate, fractions F5 and S1, were also analyzed using liquid chromatography-tandem mass spectrometry. Notably, AW6 could resist hydrolysis in the human gastrointestinal tract according to the result of the simulated gastrointestinal digestion. To the best of our knowledge, this is the first discovery and characterization of a dual-function (ACEI and DPP4I activities) peptide derived from bitter gourd seed protein.

A Cell-Based Assessment of the Muscle Anabolic Potential of Blue Whiting (Micromesistius poutassou) Protein Hydrolysates

Blue whiting (BW) represents an underutilised fish species containing a high-quality protein and amino acid (AA) profile with numerous potentially bioactive peptide sequences, making BW an economic and sustainable alternative source of protein. This study investigated the impact of three different BW protein hydrolysates (BWPH-X, Y and Z) on growth, proliferation and muscle protein synthesis (MPS) in skeletal muscle (C2C12) myotubes. BWPHs were hydrolysed using different enzymatic and heat exposures and underwent simulated gastrointestinal digestion (SGID), each resulting in a high degree of hydrolysis (33.41-37.29%) and high quantities of low molecular mass peptides (86.17-97.12% <1 kDa). C2C12 myotubes were treated with 1 mg protein equivalent/mL of SGID-BWPHs for 4 h. Muscle growth and myotube thickness were analysed using an xCelligence™ platform. Anabolic signalling (phosphorylation of mTOR, rpS6 and 4E-BP1) and MPS measured by puromycin incorporation were assessed using immunoblotting. BWPH-X significantly increased muscle growth (p < 0.01) and myotube thickness (p < 0.0001) compared to the negative control (amino acid and serum free media). Muscle protein synthesis (MPS), as measured by puromycin incorporation, was significantly higher after incubation with BWPH-X compared with the negative control, but did not significantly change in response to BWPH-Y and Z treatments. Taken together, these preliminary findings demonstrate the anabolic potential of some but not all BWPHs on muscle enhancement, thus providing justification for human dietary intervention studies to confirm and translate the results of such investigations to dietary recommendations and practices.

Physiological and pharmacological actions of glucagon like peptide-1 (GLP-1) in domestic animals

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GLP-1 improves peripheral glucose uptake in healthy dogs and cats.

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GLP-1 analogues administration in diabetic cats reduces exogenous insulin requirement.

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Dogs cardiomyocytes apoptosis is reduced by GLP-1-derived molecules action.

Analogues of glucagon like peptide-1 (GLP-1) and other drugs that increase this peptide half-life are used worldwide in human medicine to treat type 2 diabetes mellitus (DM) and obesity. These molecules can increase insulin release and satiety, interesting effects that could also be useful in the treatment of domestic animals pathologies, however their use in veterinary medicine are still limited. Considering the increasing incidence of DM and obesity in cats and dogs, the aim of this review is to summarize the available information about the physiological and pharmacological actions of GLP-1 in domestic animals and discuss about its potential applications in veterinary medicine. In diabetic dogs, the use of drugs based on GLP-1 actions reduced blood glucose and increased glucose uptake, while in diabetic cats they reduced glycemic variability and exogenous insulin administration. Thus, available evidence indicates that GLP-1 based drugs could become alternatives to DM treatment in domestic animals. Nevertheless, current data do not provide enough elements to recommend these drugs widespread clinical use.

Emodin Alleviates High-Glucose-Induced Pancreatic β-Cell Pyroptosis by Inhibiting NLRP3/GSDMD Signaling

Diabetes mellitus (DM) is a chronic noninfectious disease that is mainly featured by pancreatic β-cell (β-cell) dysfunction and impaired glucose homeostasis. Currently, the pathogenesis of dysfunction of the β-cells in DM remains unclear, and therapeutic approaches to it are limited. Emodin (EMD), a natural anthraquinone derivative, has been preliminarily proven to show antidiabetic effects. However, the underlying mechanism of EMD on β-cells still needs to be elucidated. In this study, we investigated the protective effects of EMD on the high glucose (50 mM)-induced INS-1 cell line and the underlying mechanism. INS-1 cells were treated with EMD (5, 10, and 20 μM) when exposed to high glucose. The effects of EMD were examined by using the inverted phase-contrast microscope, qRT-PCR, ELISA, and western blot. The results showed that EMD could alleviate cellular morphological changes, suppress IL-1β and LDH release, and promote insulin secretion in high-glucose-induced INS-1 cells. Furthermore, EMD inhibits NOD-like receptor protein 3 (NLRP3) activation and gasdermin D (GSDMD) cleavage to alleviate pyroptosis induced by high glucose. Overexpression of NLRP3 reversed the above changes caused by EMD. Collectively, our findings suggest that EMD attenuates high-glucose-induced β-cell pyroptosis by inhibiting NLRP3/GSDMD signaling.

Influence of Dipeptidyl Peptidase-4 (DPP4) on Mesenchymal Stem-Cell (MSC) Biology: Implications for Regenerative Medicine - Review

Dipeptidyl peptidase IV (DPP4) is a ubiquitous protease that can be found in membrane-anchored or soluble form. Incretins are one of the main DPP4 substrates. These hormones regulate glucose levels, by stimulating insulin secretion and decreasing glucagon production. Because DPP4 levels are high in diabetes, DPP4 inhibitor (DPP4i) drugs derived from gliptin are widespread used as hypoglycemic agents for its treatment. However, as DPP4 recognizes other substrates such as chemokines, growth factors and neuropeptides, pleiotropic effects have been observed in patients treated with DPP4i. Several of these substrates are part of the stem-cell niche. Thus, they may affect different physiological aspects of mesenchymal stem-cells (MSC). They include viability, differentiation, mobilization and immune response. MSC are involved in tissue homeostasis and regeneration under both physiological and pathological conditions. Therefore, such cells and their secretomes have a high clinical potential in regenerative medicine. In this context, DPP4 activity may modulate different aspects of MSC regenerative capacity. Therefore, the aim of this review is to analyze the effect of different DPP4 substrates on MSC. Likewise, how the regulation of DPP4 activity by DPP4i can be applied in regenerative medicine. That includes treatment of cardiovascular and bone pathologies, cutaneous ulcers, organ transplantation and pancreatic beta-cell regeneration, among others. Thus, DPP4i has an important clinical potential as a complement to therapeutic strategies in regenerative medicine. They involve enhancing the differentiation, immunomodulation and mobilization capacity of MSC for regenerative purposes.

Preproglucagon Products and Their Respective Roles Regulating Insulin Secretion

Historically, intracellular function and metabolic adaptation within the α-cell has been understudied, with most of the attention being placed on the insulin-producing β-cells due to their role in the pathophysiology of type 2 diabetes mellitus. However, there is a growing interest in understanding the function of other endocrine cell types within the islet and their paracrine role in regulating insulin secretion. For example, there is greater appreciation for α-cell products and their contributions to overall glucose homeostasis. Several recent studies have addressed a paracrine role for α-cell-derived glucagon-like peptide-1 (GLP-1) in regulating glucose homeostasis and responses to metabolic stress. Further, other studies have demonstrated the ability of glucagon to impact insulin secretion by acting through the GLP-1 receptor. These studies challenge the central dogma surrounding α-cell biology describing glucagon's primary role in glucose counterregulation to one where glucagon is critical in regulating both hyper- and hypoglycemic responses. Herein, this review will update the current understanding of the role of glucagon and α-cell-derived GLP-1, placing emphasis on their roles in regulating glucose homeostasis, insulin secretion, and β-cell mass.

Characteristics of Food Protein-Derived Antidiabetic Bioactive Peptides: A Literature Update

Diabetes, a glucose metabolic disorder, is considered one of the biggest challenges associated with a complex complication of health crises in the modern lifestyle. Inhibition or reduction of the dipeptidyl peptidase IV (DPP-IV), alpha-glucosidase, and protein-tyrosine phosphatase 1B (PTP-1B) enzyme activities or expressions are notably considered as the promising therapeutic strategies for the management of type 2 diabetes (T2D). Various food protein-derived antidiabetic bioactive peptides have been isolated and verified. This review provides an overview of the DPP-IV, PTP-1B, and α-glucosidase inhibitors, and updates on the methods for the discovery of DPP-IV inhibitory peptides released from food-protein hydrolysate. The finding of novel bioactive peptides involves studies about the strategy of separation fractionation, the identification of peptide sequences, and the evaluation of peptide characteristics in vitro, in silico, in situ, and in vivo. The potential of bioactive peptides suggests useful applications in the prevention and management of diabetes. Furthermore, evidence of clinical studies is necessary for the validation of these peptides’ efficiencies before commercial applications.

Therapeutic of Candesartan and Music Therapy in Diabetic Retinopathy with Depression in Rats

This study aimed to investigate the therapeutic effects of candesartan combined with music therapy on diabetic retinopathy with depression and to assess the molecular mechanisms. Associated animal model of diabetes mellitus and depression was established in rats. Pathological changes in the hippocampus were detected by haematoxylin eosin (H&E) staining. Terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) was used to detect retinal cell apoptosis. Angiotensin II (Ang II) in peripheral blood and neurotransmitters, including serotonin (5-HT), dopamine (DA), and norepinephrine (NE) in the hippocampus, was measured by enzyme linked immunosorbent assay (ELISA). Fluorescence quantitative PCR and western blotting were used to detect the expression of brain-derived neurotrophic factor (BDNF) and c-fos in the hippocampus. Our data showed that chromatin aggregation and cytoplasmic vacuolation were observable in the hippocampal cells of the rats in the model group, while candesartan and music therapy could reduce morphological changes in the hippocampus of diabetic rats with depression. Compared with the control group, the apoptosis of retinal cells was significantly higher, the contents of 5-HT, DA, and NE in the hippocampus were significantly lower, Ang II level in peripheral blood was significantly higher, and the expression of BDNF and c-fos in the hippocampus decreased significantly in the model group. By contrast, candesartan or candesartan + music therapy ameliorated the changes in retina cell apoptosis, reduction of neurotransmitters, increase in AII, and the expression of c-fos and BDNF. Especially, music therapy further improved the effects of candesartan on retina cell apoptosis and neurotransmitter release in diabetic retinopathy rats with depression. In conclusion, candesartan and music therapy have an additive effect in DM with both visual impairment and depression, which might serve a potential alternative treatment for this complex disease.

Investigation of Hypoglycemic Peptides Derived from Conserved Regions of adMc1 to Reveal Their Antidiabetic Activities

Diabetes mellitus is the most common chronic disorder and leading cause of renal, neurological, and gastrointestinal manifestations in developed and developing countries. Despite of many drugs and combinational therapies, the complications of diabetes are still listed due to severe consequences of those drugs. In past few years, plant-derived drugs draw special attention due to their higher efficacy and fewer side-effects. Momordica charantia also known as bitter melon is referred as an antidiabetic and hypoglycemic plant in native populations of Asia and East Africa. In current study, an in silico approach was used to evaluate the interactions and binding patterns of plant-derived peptides devised from a hypoglycemic protein adMc1 of M. charantia as potential inhibitor of DPP-IV, SGLT1, and GLUT2 receptor proteins. The study has described a novel approach to investigate hypoglycemic peptides to cure diabetes. A total of eighty tetra-, penta-, and hexapeptides were devised from conserved regions of adMc1 homologs. The molecular docking approach using MOE software was employed to reveal inhibiting potentials of devised peptides against three selected proteins. Out of 30 shortlisted ligands six peptides (i.e. SMCG, DECC, TTIT, RTTI, ARNL and TVEV) accomplished the criteria of being good drug candidates against selected receptor proteins following the drugability assessment test. The overall results are acceptable on the basis of ADMET profiling for being good drug candidates against selected proteins.

Dysregulation of Leukocyte Trafficking in Type 2 Diabetes: Mechanisms and Potential Therapeutic Avenues

Type 2 Diabetes Mellitus (T2DM) is a chronic inflammatory disorder that is characterized by chronic hyperglycemia and impaired insulin signaling which in addition to be caused by common metabolic dysregulations, have also been associated to changes in various immune cell number, function and activation phenotype. Obesity plays a central role in the development of T2DM. The inflammation originating from obese adipose tissue develops systemically and contributes to insulin resistance, beta cell dysfunction and hyperglycemia. Hyperglycemia can also contribute to chronic, low-grade inflammation resulting in compromised immune function. In this review, we explore how the trafficking of innate and adaptive immune cells under inflammatory condition is dysregulated in T2DM. We particularly highlight the obesity-related accumulation of leukocytes in the adipose tissue leading to insulin resistance and beta-cell dysfunction and resulting in hyperglycemia and consequent changes of adhesion and migratory behavior of leukocytes in different vascular beds. Thus, here we discuss how potential therapeutic targeting of leukocyte trafficking could be an efficient way to control inflammation as well as diabetes and its vascular complications.

A comprehensive review on the antidiabetic activity of flavonoids targeting PTP1B and DPP-4: a structure-activity relationship analysis

Type 2 diabetes (T2D) is an expanding global health problem, resulting from defects in insulin secretion and/or insulin resistance. In the past few years, both protein tyrosine phosphatase 1B (PTP1B) and dipeptidyl peptidase-4 (DPP-4), as well as their role in T2D, have attracted the attention of the scientific community. PTP1B plays an important role in insulin resistance and is currently one of the most promising targets for the treatment of T2D, since no available PTP1B inhibitors were still approved. DPP-4 inhibitors are among the most recent agents used in the treatment of T2D (although its use has been associated with possible cardiovascular adverse events). The antidiabetic properties of flavonoids are well-recognized, and include inhibitory effects on the above enzymes, although hitherto not therapeutically explored. In the present study, a comprehensive review of the literature of both synthetic and natural isolated flavonoids as inhibitors of PTP1B and DPP-4 activities is made, including their type of inhibition and experimental conditions, and structure-activity relationship, covering a total of 351 compounds. We intend to provide the most favorable chemical features of flavonoids for the inhibition of PTP1B and DPP-4, gathering information for the future development of compounds with improved potential as T2D therapeutic agents.

Engineering-inspired approaches to study β-cell function and diabetes

Strategies to mitigate the pathologies from diabetes range from simply administering insulin to prescribing complex drug/biologic regimens combined with lifestyle changes. There is a substantial effort to better understand β-cell physiology during diabetes pathogenesis as a means to develop improved therapies. The convergence of multiple fields ranging from developmental biology to microfluidic engineering has led to the development of new experimental systems to better study complex aspects of diabetes and β-cell biology. Here we discuss the available insulin-secreting cell types used in research, ranging from primary human β-cells, to cell lines, to pluripotent stem cell-derived β-like cells. Each of these sources possess inherent strengths and weaknesses pertinent to specific applications, especially in the context of engineered platforms. We then outline how insulin-expressing cells have been used in engineered platforms and how recent advances allow for better mimicry of in vivo conditions. Chief among these conditions are β-cell interactions with other endocrine organs. This facet is beginning to be thoroughly addressed by the organ-on-a-chip community, but holds enormous potential in the development of novel diabetes therapeutics. Furthermore, high throughput strategies focused on studying β-cell biology, improving β-cell differentiation, or proliferation have led to enormous contributions in the field and will no doubt be instrumental in bringing new diabetes therapeutics to the clinic.

Talabostat Alleviates Obesity and Associated Metabolic Dysfunction via Suppression of Macrophage-Driven Adipose Inflammation

OBJECTIVE

Adipose tissue macrophages (ATMs) play critical roles in obesity-associated inflammation that contributes to metabolic dysfunction. Talabostat (TB) exerts some therapeutic effects on tumors and obesity. However, it remains unknown whether the metabolic benefits of TB on obesity is dependent on ATM-mediated adipose inflammation.

METHODS

Male C57BL/6J mice were fed a normal chow diet (NCD) or a high-fat diet for 12 weeks, and mice were orally administered TB daily at a low dose (0.5 mg/kg).

RESULTS

Administration of TB to mice fed a high-fat diet significantly improved adiposity and obesity-associated metabolic dysfunction, including glucose intolerance and insulin resistance, hyperlipidemia and hepatic steatosis, which were accompanied by increased whole-body energy expenditure. RNA sequencing analysis revealed extensive alterations in the transcriptome profiles associated with lipid metabolism and immune responses in adipose tissue of obese mice. Notably, TB treatment led to a significant reduction in ATM accumulation and a shift of the activation state of ATMs from the proinflammatory M1-like to the anti-inflammatory M2-like phenotype. Moreover, depletion of ATMs significantly abolished the TB-induced metabolic benefits.

CONCLUSIONS

Our study demonstrates that TB at a low dose could increase energy expenditure and control ATM-mediated adipose inflammation in obese mice, thereby alleviating obesity and its associated metabolic dysfunction.

Metabolic Messengers: glucagon-like peptide 1

Glucagon like peptide-1 (GLP-1), a peptide hormone from the intestinal tract, plays a central role in the coordination of postprandial glucose homeostasis through actions on insulin secretion, food intake and gut motility. GLP-1 forms the basis for a variety of current drugs for the treatment of type 2 diabetes and obesity, as well as new agents currently being developed. Here, we provide a concise overview of the core physiology of GLP-1 secretion and action, and the role of the peptide in human health, disease and therapeutics.

Dipeptidyl peptidase 4 inhibitors in the treatment of type 2 diabetes mellitus

Dipeptidyl peptidase 4 inhibitors (DPP4i) have been available for treating type 2 diabetes mellitus since 2006. Although they are a diverse group, DPP4i are all small, orally available molecules that interact with the catalytic site of DPP4 without disturbing any of its other known functions, including its effects on the immune system. DPP4i have no intrinsic glucose-lowering activity, so their efficacy as anti-diabetic agents is related directly to their ability to inhibit DPP4 activity and is mediated through the effects of the substrates they protect. Of these, the incretin hormone, glucagon-like peptide 1, is probably the most important. As the effects of glucagon-like peptide 1 are glucose-dependent, the risk of hypoglycaemia with DPP4i is low. Class effects, which are directly related to the mechanism of action, are common to all DPP4i; these include their overall good safety profile and tolerability, as well as their efficacy in improving glycaemic control, but also, potentially, a small increased risk of acute pancreatitis. Compound-specific effects are those related to their differing chemistries and/or pharmacokinetic profiles. These compound-specific effects could affect the way in which individual DPP4i are used therapeutically and potentially explain off-target adverse effects, such as hospitalization for heart failure, which is seen only with one DPP4i. Overall, DPP4i have a favourable therapeutic profile and are safe and effective in the majority of patients with type 2 diabetes mellitus.

Management of type 2 diabetes for prevention of cardiovascular disease. An expert opinion of the Italian Diabetes Society

AIMS

Type 2 diabetes mellitus is characterized by an increased risk of developing long-term cardiovascular complications. Several underlying mechanisms have been proposed for the diabetes-related increase in cardiovascular risk, i.e. chronic hyperglycemia, duration of the disease, drug-induced hypoglycemia, coexistence of multiple cardiovascular risk factors, etc. In the last few years, new pharmacological approaches capable of treating chronic hyperglycemia without increasing the risk of hypoglycemia have emerged for the treatment of diabetes.

DATA SYNTHESIS

With data mainly obtained from randomized controlled trials recruiting patients with type 2 diabetes in secondary prevention of cardiovascular disease, some of these newer antihyperglycemic drugs have shown to significantly reduce the risk of cardiovascular disease. In addition, the combined control of traditional cardiovascular risk factors, e.g. dyslipidemia, hypertension, etc., has demonstrated to be effective in reducing the burden of cardiovascular diseases in patients with type 2 diabetes.

CONCLUSIONS

In this document written by some experts of the Italian diabetes society (SID), we will focus our attention on oral antihyperglycemic agents for people with type 2 diabetes in primary or secondary prevention of cardiovascular disease, excluding for brevity the injection therapies for diabetes, such as insulin and glucagon-like peptide-1 receptor agonists.

DPP-4 Inhibitors: Renoprotective Potential and Pharmacokinetics in Type 2 Diabetes Mellitus Patients with Renal Impairment

The continuously increasing incidence of diabetes worldwide has attracted the attention of the scientific community and driven the development of a novel class of antidiabetic drugs that can be safely and effectively used in diabetic patients. Of particular interest in this context are complications associated with diabetes, such as renal impairment, which is the main cause of high cardiovascular morbidity and mortality in diabetic patients. Intensive control of glucose levels and other risk factors associated with diabetes and metabolic syndrome provides the foundations for both preventing and treating diabetic nephropathy. Dipeptidyl peptidase-4 (DPP-4) inhibitors represent a highly promising novel class of oral agents used in the treatment of type 2 diabetes mellitus that may be successfully combined with currently available antidiabetic therapeutics in order to achieve blood glucose goals. Beyond glycemic control, emerging evidence suggests that DPP-4 inhibitors may have desirable off-target effects, including renoprotection. All type 2 diabetes mellitus patients with impaired renal function require dose adjustment of any DPP-4 inhibitor administered except for linagliptin, for which renal excretion is a minor elimination pathway. Thus, linagliptin is the drug most frequently chosen to treat type 2 diabetes mellitus patients with renal failure.

Glucagon from the phylogenetically ancient paddlefish provides a template for the design of a long-acting peptide with effective anti-diabetic and anti-obesity activities

This study has examined the in vitro and in vivo anti-diabetic properties of the peptidase-resistant analogues [D-Ser²]palmitoyl-paddlefish glucagon and [D-Ser²]palmitoyl-lamprey glucagon. The peptides stimulated insulin release from BRIN-BD11 clonal β-cells and isolated mouse pancreatic islets and also enhanced cAMP production in cells transfected with the human GLP-1 receptor and with the human glucagon receptor. The insulinotropic actions of the peptides were attenuated in INS-1 cells lacking GLP-1 and glucagon receptors. [D-Ser²]palmitoyl-paddlefish glucagon stimulated proliferation of BRIN-BD11 cells and protected against cytokine-mediated apoptosis as effectively as GLP-1. The analogue was more effective than the native peptide or the lamprey glucagon analogue in acutely lowering blood glucose and elevating plasma insulin in lean mice even when administered up to 4 h before a glucose load. Twice daily administration of [D-Ser²]palmitoyl-paddlefish glucagon to high-fat fed mice over 21 days reduced food intake, body weight, non-fasting blood glucose and plasma insulin concentrations, as well as significantly improving glucose tolerance and insulin resistance and decreasing α-cell area and pancreatic insulin content. Islet expression of the Gcgr, Glp1r, Gipr and Slc2a2 (GLUT-2) genes significantly increased. These data demonstrate that long-acting peptide [D-Ser²]palmitoyl-paddlefish glucagon exerts beneficial metabolic properties in diabetic mice via Ggcr- and Glp1r-activated pathways and so shows potential as a template for further development into an agent for treatment of patients with obesity-related Type 2 diabetes.

Metabolism of GIP and the contribution of GIP to the glucose-lowering properties of DPP-4 inhibitors

Glucose-dependent insulinotropic polypeptide (GIP) is a gastrointestinal hormone with insulinotropic and glucagonotropic actions, and is believed to be the more physiologically important incretin hormone in healthy humans. Together with the other incretin hormone, glucagon-like peptide-1 (GLP-1), it plays an important role in regulating glucose homeostasis. Both GLP-1 and GIP are substrates of the enzyme dipeptidyl peptidase-4 (DPP-4), and DPP-4 inhibitors, which potentiate their effects on glycaemic control, are now used to treat type 2 diabetes (T2D). This review describes how post-translational processing of the GIP precursor molecule and post-release degradation of the secretory products give rise to multiple isoforms of GIP, some, but not all of which are biologically active, and discusses how this impacts upon their measurement by immunological- and bioassay-based methods. DPP-4 inhibitors reduce degradation of GIP, and although the insulinotropic effects of GIP are impaired in patients with T2D, they can be at least partially restored if glycaemic control is improved. Therefore, given that studies with incretin receptor antagonists indicate that not all of the glucose-lowering effects of DPP-4 inhibition can be accounted for by GLP-1 alone, evidence supports the notion that GIP may play a role in mediating the anti-hyperglycaemic effects of DPP-4 inhibition, while its glucagonotropic actions at lower glucose levels may contribute to the low risk of hypoglycaemia associated with DPP-4 inhibitors.

Identification and characterisation of peptides from a boarfish (Capros aper) protein hydrolysate displaying in vitro dipeptidyl peptidase-IV (DPP-IV) inhibitory and insulinotropic activity

Twenty-two novel dipeptidyl peptidase-IV (DPP-IV) inhibitory peptides (with IC₅₀ values <200 µM) and fifteen novel insulinotropic peptides were identified in a boarfish protein hydrolysate generated at semi-pilot scale using Alcalase 2.4L and Flavourzyme 500L. This was achieved by bioassay-driven semi-preparative reverse phase-high performance liquid chromatography fractionation, liquid chromatography-mass spectrometry and confirmatory studies with synthetic peptides. The most potent DPP-IV inhibitory peptide (IPVDM) had a DPP-IV half maximal inhibitory concentration (IC₅₀) value of 21.72 ± 1.08 µM in a conventional in vitro and 44.26 ± 0.65 µM in an in situ cell-based (Caco-2) DPP-IV inhibition assay. Furthermore, this peptide stimulated potent insulin secretory activity (1.6-fold increase compared to control) from pancreatic BRIN-BD11 cells grown in culture. The tripeptide IPV exhibited potent DPP-IV inhibitory activity (IC₅₀: 5.61 ± 0.20 µM) comparable to that reported for the known DPP-IV inhibitor IPI (IC₅₀: 3.20 µM). Boarfish proteins contain peptide sequences with potential to play a role in glycaemic management in vivo.

The Role of α-Cells in Islet Function and Glucose Homeostasis in Health and Type 2 Diabetes

Pancreatic α-cells are the major source of glucagon, a hormone that counteracts the hypoglycemic action of insulin and strongly contributes to the correction of acute hypoglycemia. The mechanisms by which glucose controls glucagon secretion are hotly debated, and it is still unclear to what extent this control results from a direct action of glucose on α-cells or is indirectly mediated by β- and/or δ-cells. Besides its hyperglycemic action, glucagon has many other effects, in particular on lipid and amino acid metabolism. Counterintuitively, glucagon seems also required for an optimal insulin secretion in response to glucose by acting on its cognate receptor and, even more importantly, on GLP-1 receptors. Patients with diabetes mellitus display two main alterations of glucagon secretion: a relative hyperglucagonemia that aggravates hyperglycemia, and an impaired glucagon response to hypoglycemia. Under metabolic stress states, such as diabetes, pancreatic α-cells also secrete GLP-1, a glucose-lowering hormone, whereas the gut can produce glucagon. The contribution of extrapancreatic glucagon to the abnormal glucose homeostasis is unclear. Here, I review the possible mechanisms of control of glucagon secretion and the role of α-cells on islet function in healthy state. I discuss the possible causes of the abnormal glucagonemia in diabetes, with particular emphasis on type 2 diabetes, and I briefly comment the current antidiabetic therapies affecting α-cells.

Structure-activity relationships study on biological activity of peptides as dipeptidyl peptidase IV inhibitors by chemometric modeling

The aim of this study is to identify the potential descriptors affecting the inhibitory activity of the peptides inhibiting dipeptidyl peptidase IV (DPP-IV). This study provides important information for assessing the biological activity of the new peptide sequences of food origin or making structural modifications to the current inhibitors to improve their performance. For this purpose, the chemometric method describing the relationship between the structure of food peptides and their biological activity (structure-activity relationship [SAR]) was used to theoretically predict the potential of bioactivity of peptides. Data on the physicochemical properties of amino acids in the dipeptides acting as inhibitors of DPP-IV were collected and analyzed for using these properties as descriptors in further analysis. A total of 252 dipeptide sequences with confirmed DPP-IV inhibitory activity available in the BIOPEP-UWM database were included in the analysis, and 16 descriptors defining individual amino acids (such as molecular weight, polarity, hydropathicity, bulkiness, buried residue, and acceptable and normalized frequency of alpha-helix and beta-sheet) were identified. Based on this information, a data matrix was constructed and used in the chemometric analysis (principal component analysis and multiple linear regression). From the SAR model created, a multiple regression equation was derived to predict the biological activity of the dipeptide DPP-IV inhibitors.

Acipimox Acutely Increases GLP-1 Concentrations in Overweight Subjects and Hypopituitary Patients

CONTEXT

Glucagon-like peptide-1 (GLP-1) is an incretin hormone used therapeutically in type 2 diabetes and obesity. The interplay between ambient free fatty acids (FFAs) and GLP-1 remains unclear. Acipimox suppresses adipose tissue lipolysis via activation of the PUMA-G (also known as HCA2 and GPR109a) receptor.

OBJECTIVE

To investigate whether lowering of serum FFA level with acipimox affects GLP-1 secretion.

DESIGN

Two randomized crossover studies were performed in human subjects. Rat intestine was perfused intra-arterially and intraluminally, and l-cells were incubated with acipimox.

PARTICIPANTS

The participants were healthy overweight subjects and hypopituitary adult patients.

INTERVENTIONS

The overweight participants received acipimox 250 mg 60 minutes before an oral glucose test. The hypopituitary patients received acipimox 250 mg 12, 9, and 2 hours before and during the metabolic study day, when they were studied in the basal state and during a hyperinsulinemic euglycemic clamp.

RESULTS

Acipimox suppressed FFA but did not affect insulin in the clinical trials. In overweight subjects, the GLP-1 increase after the oral glucose tolerance test (area under the curve) was more than doubled [4119 ± 607 pmol/L × min (Acipimox) vs 1973 ± 375 pmol/L × min (control), P = 0.004]. In hypopituitary patients, acipimox improved insulin sensitivity (4.7 ± 0.8 mg glucose/kg/min (Acipimox) vs 3.1 ± 0.5 mg glucose/kg/min (control), P = 0.005], and GLP-1 concentrations increased ~40%. An inverse correlation between FFA and GLP-1 concentrations existed in both trials. In rat intestine, acipimox did not affect GLP-1 secretion, and l-cells did not consistently express the putative receptor for acipimox.

CONCLUSIONS

Acipimox treatment increases systemic GLP-1 levels in both obese subjects and hypopituitary patients. Our in vitro data indicate that the underlying mechanisms are indirect.

Ten years of experience with DPP-4 inhibitors for the treatment of type 2 diabetes mellitus

Achieving and maintaining recommended glycemic targets without causing adverse e ffects, including hypoglycemia, is challenging, especially in older patients with type 2 diabetes mellitus (T2DM). The introduction of dipeptidyl peptidase-4 (DPP-4) inhibitors, more than 10 years ago, has provided an alternative to conventional medications for the intensification of glucose-lowering treatment after failure of metformin monotherapy, and therefore, marked an important advance in the management of T2DM. By prolonging the activity of incretin hormones, DPP-4 inhibitors induce insulin release and decrease glucagon secretion in a glucose-dependent manner. This results in a more physiologic glycemic control as compared to that ensured by insulin secretagogues (sulfonylureas and glinides). Overall, DPP-4 inhibitors have a favorable safety profile and can be used without dose adjustments in older adults and in patients with mild renal impairment; they have a neutral effect on body weight and do not cause hypoglycemia by themselves. Safety issues, reported mainly in post-marketing surveillance programs and including cardiovascular outcomes and the risk of acute pancreatitis, are being extensively investigated. The aim of this review is to discuss the impact of DPP-4 inhibitors on the treatment of T2DM, after 10 years of experience, with an emphasis on diabetes care in Italy. We will first describe T2DM treatment in Italy and then provide an overview of the main findings from randomized controlled trials, real-world studies and post-marketing surveillance programs with DPP-4 inhibitors.

Dipeptidyl dipeptidase-4 inhibitor recovered ischemia through an increase in vasculogenic endothelial progenitor cells and regeneration-associated cells in diet-induced obese mice

Metabolic syndrome (MS), overlapping type 2 diabetes, hyperlipidemia, and/or hypertension, owing to high-fat diet, poses risk for cardiovascular disease. A critical feature associated with such risk is the functional impairment of endothelial progenitor cells (EPCs). Dipeptidyl dipeptidase-4 inhibitors (DPP-4 i) not only inhibit degradation of incretins to control blood glucose levels, but also improve EPC bioactivity and induce anti-inflammatory effects in tissues. In the present study, we investigated the effects of such an inhibitor, MK-06266, in an ischemia model of MS using diet-induced obese (DIO) mice. EPC bioactivity was examined in MK-0626-administered DIO mice and a non-treated control group, using an EPC colony-forming assay and bone marrow cKit⁺ Sca-1⁺ lineage-cells, and peripheral blood-mononuclear cells. Our results showed that, in vitro, the effect of MK-0626 treatment on EPC bioactivities and differentiation was superior compared to the control. Furthermore, microvascular density and pericyte-recruited arteriole number increased in MK-0626-administered mice, but not in the control group. Lineage profiling of isolated cells from ischemic tissues revealed that MK-0626 administration has an inhibitory effect on unproductive inflammation. This occurred via a decrease in the influx of total blood cells and pro-inflammatory cells such as neutrophils, total macrophages, M1, total T-cells, cytotoxic T-cells, and B-cells, with a concomitant increase in number of regeneration-associated cells, such as M2/M ratio and T_reg/T-helper. Laser Doppler analysis revealed that at day 14 after ischemic injury, blood perfusion in hindlimb was greater in MK-0626-treated DIO mice, but not in control. In conclusion, the DPP-4 i had a positive effect on EPC differentiation in MS model of DIO mice. Following ischemic injury, DPP-4 i sharply reduced recruitment of pro-inflammatory cells into ischemic tissue and triggered regeneration and reparation, making it a promising therapeutic agent for MS treatment.

Impact of Gut Microbiota on Host Glycemic Control

Given that obesity and associated disorder type II diabetes mellitus have reached epidemic proportions worldwide, the development of efficient prevention and therapeutic interventions is a global public health interest. There is now a large body of evidence suggesting that the micro-organisms colonizing the human gut, known as gut microbiota, play a central role in human physiology and metabolism. Understanding how gut microbiota affects and regulates key metabolic functions such as glucose regulation and insulin resistance is an important health issue. The present review summarizes recent advances in our understanding of how gut bacterial species interfere with host metabolic phenotype. We will examine key biological molecular mechanisms underlying the impact of gut microbiota on host glycemic control including: incretin secretion, short-chain fatty acid production, bile acid metabolism, and adipose tissue regulation. We will highlight how prebiotic/probiotic interventions affect these bacterial processes and are now considered as promising approaches to treat obese and diabetic patients.

Physiology and Pharmacology of DPP-4 in Glucose Homeostasis and the Treatment of Type 2 Diabetes

Dipeptidyl peptidase-4 (DPP-4), also known as the T-cell antigen CD26, is a multi-functional protein which, besides its catalytic activity, also functions as a binding protein and a ligand for a variety of extracellular molecules. It is an integral membrane protein expressed on cells throughout the body, but is also shed from the membrane and circulates as a soluble protein in the plasma. A large number of bioactive molecules can be cleaved by DPP-4 in vitro, but only a few of these have been demonstrated to be physiological substrates. One of these is the incretin hormone, glucagon-like peptide-1 (GLP-1), which plays an important role in the maintenance of normal glucose homeostasis, and DPP-4 has been shown to be the key enzyme regulating its biological activity. This pathway has been targeted pharmacologically through the development of DPP-4 inhibitors, and these are now a successful class of anti-hyperglycaemic agents used to treat type 2 diabetes (T2DM). DPP-4 may additionally influence metabolic control via its proteolytic effect on other regulatory peptides, but it has also been reported to affect insulin sensitivity, potentially mediated through its non-enzymatic interactions with other membrane proteins. Given that altered expression and activity of DPP-4 are associated with increasing body mass index and hyperglycaemia, DPP-4 has been proposed to play a role in linking obesity and the pathogenesis of T2DM by functioning as a local mediator of inflammation and insulin resistance in adipose and hepatic tissue. As well as these broader systemic effects, it has also been suggested that DPP-4 may be able to modulate β-cell function as part of a paracrine system involving GLP-1 produced locally within the pancreatic islets. However, while it is evident that DPP-4 has the potential to influence glycaemic control, its overall significance for the normal physiological regulation of glucose homeostasis in humans and its role in the pathogenesis of metabolic disease remain to be established.

Fibroblast activation protein is dispensable for control of glucose homeostasis and body weight in mice

Objective

Fibroblast Activation Protein (FAP), an enzyme structurally related to dipeptidyl peptidase-4 (DPP-4), has garnered interest as a potential metabolic drug target due to its ability to cleave and inactivate FGF-21 as well as other peptide substrates. Here we investigated the metabolic importance of FAP for control of body weight and glucose homeostasis in regular chow-fed and high fat diet-fed mice.

Methods

FAP enzyme activity was transiently attenuated using a highly-specific inhibitor CPD60 and permanently ablated by genetic inactivation of the mouse Fap gene. We also assessed the FAP-dependence of CPD60 and talabostat (Val-boroPro), a chemical inhibitor reportedly targeting both FAP and dipeptidyl peptidase-4

Results

CPD60 robustly inhibited plasma FAP activity with no effect on DPP-4 activity. Fap gene disruption was confirmed by assessment of genomic DNA, and loss of FAP enzyme activity in plasma and tissues. CPD60 did not improve lipid tolerance but modestly improved acute oral and intraperitoneal glucose tolerance in a FAP-dependent manner. Genetic inactivation of Fap did not improve glucose or lipid tolerance nor confer resistance to weight gain in male or female Fap^−/− mice fed regular chow or high-fat diets. Moreover, talabostat markedly improved glucose homeostasis in a FAP- and FGF-21-independent, DPP-4 dependent manner.

Conclusion

Although pharmacological FAP inhibition improves glucose tolerance, the absence of a metabolic phenotype in Fap^−/−mice suggest that endogenous FAP is dispensable for the regulation of murine glucose homeostasis and body weight. These findings highlight the importance of characterizing the specificity and actions of FAP inhibitors in different species and raise important questions about the feasibility of mouse models for targeting FAP as a treatment for diabetes and related metabolic disorders.

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Acute inhibition of FAP enzyme activity improves glucose tolerance in mice.

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Fap knockout mice exhibit normal glucose and lipid tolerance.

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Fap knockout mice do not resist obesity after high fat feeding.

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Talabostat robustly lowers glucose in a FAP and FGF21-independent manner.

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Talabostat, but not CPD60, requires DPP4 to exert its full metabolic activity.

Bioactive Peptides from Germinated Soybean with Anti-Diabetic Potential by Inhibition of Dipeptidyl Peptidase-IV, α-Amylase, and α-Glucosidase Enzymes

Functional foods containing peptides offer the possibility to modulate the absorption of sugars and insulin levels to prevent diabetes. This study investigates the potential of germinated soybean peptides to modulate postprandial glycaemic response through inhibition of dipeptidyl peptidase IV (DPP-IV), salivary α-amylase, and intestinal α-glucosidases. A protein isolate from soybean sprouts was digested by pepsin and pancreatin. Protein digest and peptide fractions obtained by ultrafiltration (<5, 5⁻10 and >10 kDa) and subsequent semipreparative reverse phase liquid chromatography (F1, F2, F3, and F4) were screened for in vitro inhibition of DPP-IV, α-amylase, maltase, and sucrase activities. Protein digest inhibited DPP-IV (IC50 = 1.49 mg/mL), α-amylase (IC50 = 1.70 mg/mL), maltase, and sucrase activities of α-glucosidases (IC50 = 3.73 and 2.90 mg/mL, respectively). Peptides of 5⁻10 and >10 kDa were more effective at inhibiting DPP-IV (IC50 = 0.91 and 1.18 mg/mL, respectively), while peptides of 5⁻10 and <5 kDa showed a higher potency to inhibit α-amylase and α-glucosidases. Peptides in F1, F2, and F3 were mainly fragments from β-conglycinin, glycinin, and P34 thiol protease. The analysis of structural features of peptides in F1⁻F3 allowed the tentative identification of potential antidiabetic peptides. Germinated soybean protein showed a promising potential to be used as a nutraceutical or functional ingredient for diabetes prevention.