Pyrano[2,3-c]pyrazole fused spirooxindole-linked 1,2,3-triazoles as antioxidant agents: Exploring their utility in the development of antidiabetic drugs via inhibition of α-amylase and DPP4 activity

Environment-benign, multicomponent synthetic methodologies are vital in modern pharmaceutical research and facilitates multi-targeted drug development via synergistic approach. Herein, we reported green and efficient synthesis of pyrano[2,3-c]pyrazole fused spirooxindole linked 1,2,3-triazoles using a tea waste supported copper catalyst (TWCu). The synthetic approach involves a one-pot, five-component reaction using N-propargylated isatin, hydrazine hydrate, ethyl acetoacetate, malononitrile/ethyl cyanoacetate and aryl azides as model substrates. Mechanistically, the reaction was found to proceed via in situ pyrazolone formation followed by Knoevenagel condensation, azide alkyne cycloaddition and Michael's addition reactions. The molecules were developed using structure-based drug design. The primary goal is to identifying anti-oxidant molecules with potential ability to modulate α-amylase and DPP4 (dipeptidyl-peptidase 4) activity. The anti-oxidant analysis, as determined via DPPH, suggested that the synthesized compounds, A6 and A10 possessed excellent anti-oxidant potential compared to butylated hydroxytoluene (BHT). In contrast, compounds A3, A5, A8, A9, A13, A15, and A18 were found to possess comparable anti-oxidant potential. Among these, A3 and A13 possessed potential α-amylase inhibitory activity compared to the acarbose, and A3 further emerged as dual inhibitors of both DPP4 and α-amylase with anti-oxidant potential. The relationship of functionalities on their anti-oxidant and enzymatic inhibition was explored in context to their SAR that was further corroborated using in silico techniques and enzyme kinetics.

DPP-4 exacerbates LPS-induced endothelial cells inflammation via integrin-α5β1/FAK/AKT signaling

Endothelial dysfunction plays a pivotal role in the pathogenesis of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Dipeptidyl peptidase IV (DPP-4), a cell surface glycoprotein, has been implicated in endothelial inflammation and barrier dysfunction. In this study, the role of DPP-4 on lipopolysaccharide (LPS)-induced pulmonary microvascular endothelial cells (HPMECs) dysfunction and the underlying mechanism were investigated by siRNA-mediated knockdown of DPP-4. Our results indicated that LPS (1 μg/ml) challenge resulted in either the production and releasing of DPP-4, as well as the secretion of IL-6 and IL-8 in HPMECs. DPP-4 knockdown inhibited chemokine releasing and monolayer hyper-permeability in LPS challenged HPMECs. When cocultured with human polymorphonuclear neutrophils (PMNs), DPP4 knockdown suppressed LPS-induced neutrophil-endothelial adhesion, PMN chemotaxis and trans-endothelial migration. Western blotting showed that DPP-4 knockdown attenuated LPS-induced activation of TLR4/NF-κB pathway. Immunoprecipitation and liquid chromatography-tandem mass spectrometry revealed that DPP-4 mediated LPS-induced endothelial inflammation by interacting with integrin-α5β1. Moreover, exogenous soluble DPP-4 treatment sufficiently activated integrin-α5β1 downstream FAK/AKT/NF-κB signaling, thereafter inducing ICAM-1 upregulation in HPMECs. Collectively, our results suggest that endothelia synthesis and release DPP-4 under the stress of endotoxin, which interact with integrin-α5β1 complex in an autocrine or paracrine manner to exacerbate endothelial inflammation and enhance endothelial cell permeability. Therefore, blocking DDP-4 could be a potential therapeutic strategy to prevent endothelial dysfunction in ALI/ARDS.

(Pro)renin receptor mediates tubular epithelial cell pyroptosis in diabetic kidney disease via DPP4-JNK pathway

BACKGROUND

(Pro)renin receptor (PRR) is highly expressed in renal tubules, which is involved in physiological and pathological processes. However, the role of PRR, expressed in renal tubular epithelial cells, in diabetic kidney disease (DKD) remain largely unknown.

METHODS

In this study, kidney biopsies, urine samples, and public RNA-seq data from DKD patients were used to assess PRR expression and cell pyroptosis in tubular epithelial cells. The regulation of tubular epithelial cell pyroptosis by PRR was investigated by in situ renal injection of adeno-associated virus9 (AAV9)-shRNA into db/db mice, and knockdown or overexpression of PRR in HK-2 cells. To reveal the underlined mechanism, the interaction of PRR with potential binding proteins was explored by using BioGrid database. Furthermore, the direct binding of PRR to dipeptidyl peptidase 4 (DPP4), a pleiotropic serine peptidase which increases blood glucose by degrading incretins under diabetic conditions, was confirmed by co-immunoprecipitation assay and immunostaining.

RESULTS

Higher expression of PRR was found in renal tubules and positively correlated with kidney injuries of DKD patients, in parallel with tubular epithelial cells pyroptosis. Knockdown of PRR in kidneys significantly blunted db/db mice to kidney injury by alleviating renal tubular epithelial cells pyroptosis and the resultant interstitial inflammation. Moreover, silencing of PRR blocked high glucose-induced HK-2 pyroptosis, whereas overexpression of PRR enhanced pyroptotic cell death of HK-2 cells. Mechanistically, PRR selectively bound to cysteine-enrich region of C-terminal of DPP4 and augmented the protein abundance of DPP4, leading to the downstream activation of JNK signaling and suppression of SIRT3 signaling and FGFR1 signaling, and then subsequently mediated pyroptotic cell death.

CONCLUSIONS

This study identified the significant role of PRR in the pathogenesis of DKD; specifically, PRR promoted tubular epithelial cell pyroptosis via DPP4 mediated signaling, highlighting that PRR could be a promising therapeutic target in DKD.

Celiac Disease: A Review from Genetic to Treatment

Celiac disease (CD) is a complex disorder influenced by genetic and environmental factors. When people with a genetic predisposition to CD consume gluten, an inflammatory response is triggered in the small intestine, and this reaction can be alleviated by the elimination of gluten from the diet. The clinical manifestations of CD vary greatly from person to person and begin at a young age or in adulthood. Influence of genetic factors on CD development is evident in carriers of the DQ2 and/or DQ8 allele. HLA genotypes are associated with gut colonization by bacteria, particularly in individuals suffering from CD. In addition, beneficial gut microbes are crucial for the production of DPP-4, which plays a key role in immune function, as well as metabolic and intestinal health. Therefore, probiotics have been recommended as a complementary food supplement in CD.

DrugRep-HeSiaGraph: when heterogenous siamese neural network meets knowledge graphs for drug repurposing

BACKGROUND

Drug repurposing is an approach that holds promise for identifying new therapeutic uses for existing drugs. Recently, knowledge graphs have emerged as significant tools for addressing the challenges of drug repurposing. However, there are still major issues with constructing and embedding knowledge graphs.

RESULTS

This study proposes a two-step method called DrugRep-HeSiaGraph to address these challenges. The method integrates the drug-disease knowledge graph with the application of a heterogeneous siamese neural network. In the first step, a drug-disease knowledge graph named DDKG-V1 is constructed by defining new relationship types, and then numerical vector representations for the nodes are created using the distributional learning method. In the second step, a heterogeneous siamese neural network called HeSiaNet is applied to enrich the embedding of drugs and diseases by bringing them closer in a new unified latent space. Then, it predicts potential drug candidates for diseases. DrugRep-HeSiaGraph achieves impressive performance metrics, including an AUC-ROC of 91.16%, an AUC-PR of 90.32%, an accuracy of 84.63%, a BS of 0.119, and an MCC of 69.31%.

CONCLUSION

We demonstrate the effectiveness of the proposed method in identifying potential drugs for COVID-19 as a case study. In addition, this study shows the role of dipeptidyl peptidase 4 (DPP-4) as a potential receptor for SARS-CoV-2 and the effectiveness of DPP-4 inhibitors in facing COVID-19. This highlights the practical application of the model in addressing real-world challenges in the field of drug repurposing. The code and data for DrugRep-HeSiaGraph are publicly available at https://github.com/CBRC-lab/DrugRep-HeSiaGraph .

Screening compounds for treating the diabetes and COVID-19 from Miao medicine by molecular docking and bioinformatics

Both diabetes and Corona Virus Disease 2019 (COVID-19) are seriously harmful to human health, and they are closely related. It is of great significance to find drugs that can simultaneously treat diabetes and COVID-19. Based on the theory of traditional Chinese medicine for treating COVID-19, this study first sorted out the compounds of Guizhou Miao medicine with "return to the lung channel" and "clear heat and detoxify" effects in China. The active components against COVID-19 were screened by molecular docking with SARS-CoV-2 PLpro and angiotensin-converting enzyme II as targets. Furthermore, the common target dipeptidyl peptidase 4 (DPP4) of diabetes and COVID-19 was used as a screening protein, and molecular docking was used to obtain potential components for the treatment of diabetes and COVID-19. Finally, the mechanism of potential ingredients in the treatment of diabetes and COVID-19 was explored with bioinformatics. More than 80 kinds of Miao medicine were obtained, and 584 compounds were obtained. Further, 110 compounds against COVID-19 were screened, and top 6 potential ingredients for the treatment of diabetes and COVID-19 were screened, including 3-O-β-D-Xylopyranosyl-(1-6)-β-D-glucopyranosyl-(1-6)-β-D-glucopyranosyl oleanolic acid 28-O-β-D-glucopyranosyl ester, Glycyrrhizic acid, Sequoiaflavone, 2-O-Caffeoyl maslinic acid, Pholidotin, and Ambewelamide A. Bioinformatics analysis found that their mechanism of action in treating diabetes and COVID-19 may be related to regulating the expression of DPP4, angiotensin II type 1 receptor, vitamin D receptor, plasminogen, chemokine C-C-motif receptor 6, and interleukin 2. We believe that Guizhou Miao medicine is rich in potential ingredients for the treatment of diabetes and COVID-19.

Mechanism of molecular interaction of sitagliptin with human DPP4 enzyme - New Insights

PURPOSE

Dipeptidyl peptidase 4 (DPP4) inactivates a range of bioactive peptides. The cleavage of insulinotropic peptides and glucagon-like peptide 1 (GLP1) by DPP4 directly influences glucose homeostasis. This study aimed to describe the mode of interaction between sitagliptin (an antidiabetic drug) and human DPP4 using in silico approaches.

MATERIALS AND METHODS

Docking studies were conducted using AutoDock Vina, 2D and 3D schematic drawings were obtained using PoseView and PLIP servers, and the DPP4-sitagliptin complex was visualized with Pymol software.

RESULTS

The best affinity energy to form the DPP4-sitagliptin complex was E-value ​= ​- 8.1 ​kcal ​mol-1, as indicated by docking simulations. This result suggests a strong interaction. According to our observations, hydrophobic interactions involving the amino acids residues Tyr663 and Val712, hydrogen bonds (Glu203, Glu204, Tyr663, and Tyr667), π-Stacking interactions (Phe355 and Tyr667), and halogenic bonds (Arg123, Glu204, and Arg356) were prevalent in the DPP4-sitagliptin complex. Root Mean Square Deviation prediction also demonstrated that the global structure of the human DPP4 did not have a significant change in its topology, even after the formation of the DPP4-sitagliptin complex.

CONCLUSION

The stable interaction between the sitagliptin ligand and the DPP4 enzyme was demonstrated through molecular docking simulations. The findings presented in this work enhance the understanding of the physicochemical properties of the sitagliptin interaction site, supporting the design of more efficient gliptin-like iDPP4 inhibitors.

Whey protein hydrolysates improve high-fat-diet-induced obesity by modulating the brain-peripheral axis of GLP-1 through inhibition of DPP-4 function in mice

PURPOSE

Obesity is a growing global health concern. Recent literature indicates a prominent role of glucagon-like peptide-1 (GLP-1) in glucose metabolism and food intake. The synergistic action of GLP-1 in the gut and brain is responsible for its satiety-inducing effect, suggesting that upregulation of active GLP-1 levels could be an alternative strategy to combat obesity. Dipeptidyl peptidase-4 (DPP-4) is an exopeptidase known to inactivate GLP-1, suggesting that its inhibition could be a crucial strategy for effectively extending the half-life of endogenous GLP-1. Peptides derived from partial hydrolysis of dietary proteins are gaining traction due to their inhibitory activity on DPP-4.

METHODS

Whey protein hydrolysate from bovine milk (bmWPH) was produced using simulated in situ digestion, purified using RP-HPLC, and characterized for DPP-4 inhibition. The antiadipogenic and antiobesity activity of bmWPH was then studied in 3T3-L1 preadipocytes and high-fat diet-induced obesity (HFD) mice model, respectively.

RESULTS

The dose-dependent inhibitory effect of bmWPH on the catalytic activity of DPP-4 was observed. Additionally, bmWPH suppressed adipogenic transcription factors and DPP-4 protein levels, leading to a negative effect on preadipocyte differentiation. In an HFD mice model, co-administration of WPH for 20 weeks downregulated adipogenic transcription factors, resulting in a concomitant reduction in whole body weight and adipose tissues. Mice fed with bmWPH also showed a marked reduction in DPP-4 levels in WAT, liver, and serum. Furthermore, HFD mice fed with bmWPH exhibited increased serum and brain GLP levels, which led to a significant decrease in food intake.

CONCLUSION

In conclusion, bmWPH reduces body weight in HFD mice by suppressing appetite through GLP-1, a satiety-inducing hormone, in both the brain and peripheral circulation. This effect is achieved through modulation of both the catalytic and non-catalytic activity of DPP-4.

An in silico approach to unveil peptides from Acheta domesticus with potential bioactivity against hypertension, diabetes, cardiac and pulmonary fibrosis

Entomophagy is a sustainable alternative source of proteins for human nutrition. Acheta domesticus is one of the three insect species that complies with the European Union Regulation on novel foods, but to date, there are no reports on their potential bioactive peptides. In this study, an in silico approach was applied to simulate the gastrointestinal (GI) digestion of six A. domesticus proteins and identify new peptides with potential anti-hypertensive and/or anti-diabetic properties, resulting from their capability to inhibit the somatic Angiotensin-I converting enzyme (sACE) and/or dipeptidyl peptidase 4 (DPP-4), respectively. A molecular docking protocol was applied to evaluate the binding interactions between the 43 peptides ranked with high probability of being bioactive and three drug targets: DPP-4 and two catalytic domains (N- and C-) of sACE. Five peptides (AVQPCF, CAIAW, IIIGW, DATW and QIVW) showed high docking scores for both enzymes, suggesting their potential to inhibit the DPP-4 and both catalytic domains of sACE, thus possessing multifunctional bioactive properties. Two peptides (PIVCF and DVW) showed higher docking scores for the N-domain of sACE, indicating a potential action as selective inhibitors and consequently with anti-cardiac and pulmonary fibrosis bioactivities. This is the first study identifying peptides originated from the simulated GI digestion of A. domesticus with potential activities against hypertension, diabetes, cardiac and pulmonary fibrosis.

Dipeptidyl peptidase 4 as a potential serum biomarker for disease activity and treatment response in rheumatoid arthritis

BACKGROUND

The treatment of rheumatoid arthritis (RA) related to the disease activity. However, the lack of highly sensitive and simplified markers limits the evaluation of disease activity. We sought to explore potential biomarkers associated with disease activity and treatment response in RA.

METHODS

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) proteomic analysis was performed to determine the differentially expressed proteins (DEPs) in serum collected from RA patients with moderate or high disease activity (determined by DAS28) before and after 24 weeks of treatment. Bioinformatic analysis were performed for DEPs and hub proteins. In the validation cohort, 15 RA patients were enrolled. Key proteins were validated by enzyme-linked immunosorbent assay (Elisa), correlation analysis and ROC curve.

RESULTS

We identified 77 DEPs. The DEPs enriched in humoral immune response, blood microparticle, and serine-type peptidase activity. KEGG enrichment analysis displayed that the DEPs were significantly enriched in cholesterol metabolism and complement and coagulation cascades. Activated CD4 + T cell, T follicular helper cell, natural killer cell, and plasmacytoid dendritic cell significantly increased after treatment. Fifteen hub proteins were screened out. Among them, dipeptidyl peptidase 4 (DPP4) was the most significant protein associated with clinical indicators and immune cells. Serum concentration of DPP4 was testified to significantly increase after treatment and inversely correlate with disease activity indicators (ESR, CRP, DAS28-ESR, DAS28-CRP, CDAI, SDAI). Significant reduction was found in the serum CXC chemokine ligand10 (CXC10) and CXC chemokine receptor 3 (CXCR3) after treatment.

CONCLUSIONS

Overall, our results suggest that serum DPP4 might be a potential biomarker for disease activity assessment and treatment response of RA.

Use of real-world evidence data to evaluate the comparative effectiveness of second-line type 2 diabetes medications on chronic kidney disease

Chronic kidney disease (CKD) is a common complication of type 2 diabetes mellitus (T2DM). Approximately-one-third of patients with T2DM also have CKD. In clinical trial studies, several anti-diabetic medications (ADM) show evidence of preventing the progression of CKD. Biguanides (e.g., metformin) are widely accepted as the first line medication. However, the comparative effectiveness of second line ADMs on CKD outcomes in T2DM is unclear. In addition, results from clinical trials may not generalize into routine clinical practice. In this study, we aimed to investigate the association of second line ADMs with diagnosed incident CKD, CKD hospitalization, and eGFR < 45 mL/min in T2DM patients using real-world data from electronic health records. Our study found that treatment with sodium-glucose cotransporter 2 (SGLT-2) inhibitors was significantly associated with lower risk of diagnosed CKD incidence in both primary analysis (hazard ratio, 0.43; 95 % CI, [0.22;0.87]; p-value,0.02) and secondary analysis (hazard ratio, 0.42; 95 % CI, [0.19;0.92]; p-value, 0.03) compared to use of Sulfonylureas (SU) as a second-line ADM. However, significant associations were not observed when using eGFR < 45 mL/min as the endpoint. Treatment with a dipeptidyl peptidase 4 (DPP-4) inhibitor was significantly associated with lower risk of diagnosed incident CKD (hazard ratio, 0.7; 95 % CI, [0.53;0.96]; p-value, 0.03) and lower risk of CKD hospitalization (hazard ratio, 0.6; 95 % CI, [0.37; 0.96]; p-value, 0.04) in the primary analysis. However, both associations were not significant in the sensitivity analysis. We did not observe significant association between use of glucagon-like peptide 1 receptor agonists (GLP-1RA), Thiazolidinediones (TZD), insulin and diagnosed CKD incidence, hospitalization or eGFR < 45 mL/min compared to use of SU as a second-line ADM.

Proline-specific peptidase activities (DPP4, PRCP, FAP and PREP) in plasma of hospitalized COVID-19 patients

BACKGROUND

COVID-19 patients experience several features of dysregulated immune system observed in sepsis. We previously showed a dysregulation of several proline-selective peptidases such as dipeptidyl peptidase 4 (DPP4), fibroblast activation protein alpha (FAP), prolyl oligopeptidase (PREP) and prolylcarboxypeptidase (PRCP) in sepsis. In this study, we investigated whether these peptidases are similarly dysregulated in hospitalized COVID-19 patients.

METHODS

Fifty-six hospitalized COVID-19 patients and 32 healthy controls were included. Enzymatic activities of DPP4, FAP, PREP and PRCP were measured in samples collected shortly after hospital admission and in longitudinal follow-up samples.

RESULTS

Compared to healthy controls, both DPP4 and FAP activities were significantly lower in COVID-19 patients at hospital admission and FAP activity further decreased significantly in the first week of hospitalization. While PRCP activity remained unchanged, PREP activity was significantly increased in COVID-19 patients at hospitalization and further increased during hospital stay and stayed elevated until the day of discharge.

CONCLUSION

The changes in activities of proline-selective peptidases in plasma are very similar in COVID-19 and septic shock patients. The pronounced decrease in FAP activity deserves further investigation, both from a pathophysiological viewpoint and as its utility as a part of a biomarker panel.

Repurposing of existing antibiotics for the treatment of diabetes mellitus

Proline specific serine protease enzyme, dipeptidyl peptidase IV (DPP-4) has become a promising target for diabetes, as it stops glucagon-like peptide 1 (GLP-1) from becoming inactive, resulting in higher levels of active GLP-1. This lowers glucose levels by increasing insulin secretion and decreasing glucagon secretion. DPP-4 is also linked to a higher BMI and a 0.7 to 1% reduction in HbA1c. Currently available DPP-4 inhibitor drugs showed less promising anti-diabetic activity as this class associated with many side effects due to non-selectivity and therefore searching on more potent DPP-4 inhibitors are still ongoing. In our present study, we investigate the inhibition of DPP-4 through a series of antibiotic compounds which were previously reported to be used in diabetic foot infections and compared with existing DPP-4 inhibitors. To obtain this objective, three-dimensional crystal structure of DPP-4 was retrieved from the protein data bank (PDB id: 1 × 70). A systematic computational method combining molecular docking, MM-GBSA binding energy calculation, MD simulations, MM-PBSA binding free energy calculations and ADME were used to find best DPP-4 inhibitor. Molecular docking results revealed that clindamycin has a higher affinity towards the catalytic sides of DPP-4 and built solid hydrophobic and polar interactions with the amino acids involved in the binding region of DPP-4, such as S1 subsite, S2 subsite and S2 extensive subsite. MD simulations results showed clindamycin as potent virtual hit and suggested that it binds with DPP-4 in competitive manner, which virtually indicate that besides antibiotic activity clindamycin has anti-diabetic activity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40203-021-00118-6.

Anti-diabetic potential of β-boswellic acid and 11-keto-β-boswellic acid: Mechanistic insights from computational and biochemical approaches

β-Boswellic acid (β-BA) and 11-keto-β-boswellic acid (β-KBA) are crucial bioactive compounds, mostly isolated from frankincense. These compounds are known for their potent anticancer and anti-inflammatory activities. Herein, we have explored the complete anti-diabetic potential of β-BA and β-KBA with detailed parameters. This research revealed that treatment with β-BA and β-KBA at a dose of 1, 2, and 10 mg/kg body weight for 21 days significantly improved body weight loss, water consumption, and specifically the concentration of blood glucose level (BGL) in diabetic animals, which indicated that the β-BA and β-KBA possess strong anti-diabetic activities. Serum total superoxide dismutase (SOD) and malondialdehyde (MDA) assays were also performed to evaluate the antioxidant effects. The biochemical analysis revealed that these compounds improve an abnormal level of several biochemical parameters like serum lipid values including total cholesterol (TC), triacylglycerol (TG), low-density lipoprotein cholesterol (LDL-C) to a normal level and the high-density lipoprotein cholesterol level (HDL-C). To understand the mechanism of action of β-BA and β-KBA, their most probable biological targets were searched through the inverse docking approach. Our computational analysis reflects that among other probable targets, the Dipeptidyl peptidase 4 (DPP-4) enzyme could be one of the possible binders of β-BA and β-KBA to produce their anti-diabetic activities. These in-silico results were validated by an in-vitro experiment. It indicates that the anti-diabetic effects of β-BA and β-KBA are produced by the inhibition of DDP-4. Thus, these anti-diabetic, antioxidant, and anti-hyperlipidemic effects of β-BA and β-KBA suggest these compounds as potential therapeutics for diabetic conditions.

Effects of Teneligliptin on HbA1c levels, Continuous Glucose Monitoring-Derived Time in Range and Glycemic Variability in Elderly Patients with T2DM (TEDDY Study)

BACKGROUND

To evaluate the effects of teneligliptin on glycosylated hemoglobin (HbA1c) levels, continuous glucose monitoring (CGM)-derived time in range, and glycemic variability in elderly type 2 diabetes mellitus patients.

METHODS

This randomized, double-blinded, placebo-controlled study was conducted in eight centers in Korea (clinical trial registration number: NCT03508323). Sixty-five participants aged ≥65 years, who were treatment-naïve or had been treated with stable doses of metformin, were randomized at a 1:1 ratio to receive 20 mg of teneligliptin (n=35) or placebo (n=30) for 12 weeks. The main endpoints were the changes in HbA1c levels from baseline to week 12, CGM metrics-derived time in range, and glycemic variability.

RESULTS

After 12 weeks, a significant reduction (by 0.84%) in HbA1c levels was observed in the teneligliptin group compared to that in the placebo group (by 0.08%), with a between-group least squares mean difference of -0.76% (95% confidence interval [CI], -1.08 to -0.44). The coefficient of variation, standard deviation, and mean amplitude of glycemic excursion significantly decreased in participants treated with teneligliptin as compared to those in the placebo group. Teneligliptin treatment significantly decreased the time spent above 180 or 250 mg/dL, respectively, without increasing the time spent below 70 mg/dL. The mean percentage of time for which glucose levels remained in the 70 to 180 mg/dL time in range (TIR70-180) at week 12 was 82.0%±16.0% in the teneligliptin group, and placebo-adjusted change in TIR70-180 from baseline was 13.3% (95% CI, 6.0 to 20.6).

CONCLUSION

Teneligliptin effectively reduced HbA1c levels, time spent above the target range, and glycemic variability, without increasing hypoglycemia in our study population.

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.

SARS-CoV-2 and diabetes: A potential therapeutic effect of dipeptidyl peptidase 4 inhibitors in diabetic patients diagnosed with COVID-19

COVID-19 is caused by severe acute respiratory syndrome coronavirus 2 and has become an urgent economic and health challenge. Dipeptidyl peptidase 4 (DPP4), also mentioned as a cluster of differentiation 26 (CD26) is a serine exopeptidase found in two arrangements: a soluble form (sDPP-4) and a plasma membrane-bound form. Because other coronaviruses enter the cells by binding to DPP-4, it has been speculated that DPP-4 inhibitors may exert activity against COVID-19. Therefore, this review aimed to summarize the potential therapeutic effect of dipeptidyl peptidase 4 inhibitors in diabetic patients diagnosed with COVID-19. To include different studies, publications related to Dipeptidyl peptidase-4 inhibitor use and clinical outcomes from COVID-19 were searched from the databases such as Web of Science, PubMed, Medline, Elsevier, Google Scholar, and SCOPUS, via English key terms. A direct engrossment of DPP4 in COVID-19 needs to be elucidated, there is also evidence confirming that DPP4 inhibitors exert anti-fibrotic and modulate inflammation activity. Thus, the use of DPP-4 inhibitors could reduce mortality due to COVID-19 or improve the progression of COVID-19; this evidence may support the management of diabetic patients diagnosed with COVID-19; however more well-designed investigation is urgently required.

Beneficial effect of omarigliptin on diabetic patients with non-alcoholic fatty liver disease/non-alcoholic steatohepatitis

BACKGROUND

Dipeptidyl peptidase 4 (DPP4) is a serine exopeptidase able to inactivate various oligopeptides, and also a hepatokine. Hepatocyte-specific overexpression of DPP4 is associated with hepatic insulin resistance and liver steatosis.

METHOD

We examined whether weekly DPP4 inhibitor omarigliptin (OMG) can improve liver function as well as levels of inflammation and insulin resistance in type 2 diabetic patients with non-alcoholic fatty liver disease (NAFLD). Further, we investigated the effects of OMG in a diabetic patient with biopsy-confirmed nonalcoholic steatohepatitis (NASH).

RESULTS

In NAFLD patients, OMG significantly decreased levels of aminotransferase, aspartate aminotransferase, gamma-glutamyl transpeptidase, homeostatic model assessment of insulin resistance (HOMA-IR), and high-sensitivity C-reactive protein (hsCRP), while no significant change was seen in hemoglobin A1c or body mass index. In the NASH patient, liver function improved markedly, and levels of the hepatic fibrosis marker FIB-4 decreased in parallel with HOMA-IR and hsCRP. Slight but clear improvements in intrahepatic fat deposition and fibrosis appeared to be seen on diagnostic ultrasonography.

CONCLUSION

Weekly administration of the DPP4 inhibitor OMG in ameliorating hepatic insulin resistance may cause beneficial effects in liver with NAFLD/NASH.

Effects of a DPP-4 Inhibitor and RAS Blockade on Clinical Outcomes of Patients with Diabetes and COVID-19

BACKGROUND

Dipeptidyl peptidase-4 inhibitor (DPP-4i) and renin-angiotensin system (RAS) blockade are reported to affect the clinical course of coronavirus disease 2019 (COVID-19) in patients with diabetes mellitus (DM).

METHODS

As of May 2020, analysis was conducted on all subjects who could confirm their history of claims related to COVID-19 in the National Health Insurance Review and Assessment Service (HIRA) database in Korea. Using this dataset, we compared the short-term prognosis of COVID-19 infection according to the use of DPP-4i and RAS blockade. Additionally, we validated the results using the National Health Insurance Service (NHIS) of Korea dataset.

RESULTS

Totally, data of 67,850 subjects were accessible in the HIRA dataset. Of these, 5,080 were confirmed COVID-19. Among these, 832 subjects with DM were selected for analysis in this study. Among the subjects, 263 (31.6%) and 327 (39.3%) were DPP4i and RAS blockade users, respectively. Thirty-four subjects (4.09%) received intensive care or died. The adjusted odds ratio for severe treatment among DPP-4i users was 0.362 (95% confidence interval [CI], 0.135 to 0.971), and that for RAS blockade users was 0.599 (95% CI, 0.251 to 1.431). These findings were consistent with the analysis based on the NHIS data using 704 final subjects. The adjusted odds ratio for severe treatment among DPP-4i users was 0.303 (95% CI, 0.135 to 0.682), and that for RAS blockade users was 0.811 (95% CI, 0.391 to 1.682).

CONCLUSION

This study suggests that DPP-4i is significantly associated with a better clinical outcome of patients with COVID-19.

Use of DPP4 inhibitors in Italy does not correlate with diabetes prevalence among COVID-19 deaths

In a nationwide study of 3818 charts from patients with fatal COVID-19, we found that geographical differences in Dipeptidyl peptidase 4 (DPP4) inhibitors use did not correlate with diabetes prevalence among COVID-19 deaths, thus not supporting the hypothesis of a clinically relevant involvement of DPP4 inhibition in COVID-19 development and progression.

Human coronavirus spike protein-host receptor recognition

A variety of coronaviruses (CoVs) have infected humans and caused mild to severe respiratory diseases that could result in mortality. The human CoVs (HCoVs) belong to the genera of α- and β-CoVs that originate in rodents and bats and are transmitted to humans via zoonotic contacts. The binding of viral spike proteins to the host cell receptors is essential for mediating fusion of viral and host cell membranes to cause infection. The SARS-CoV-2 originated in bats (RaTG13 SARS-CoV) and is transmitted to humans via pangolins. The presence of 'PRRA' sequence motif in SARS-CoV-2 spike proteins from human, dog, cat, mink, tiger and lion suggests a common viral entry mechanism into host cells. In this review, we discuss structural features of HCoV spike proteins and recognition of host protein and carbohydrate receptors.

In Silico ADMET Evaluation of Natural DPP-IV Inhibitors for Rational Drug Design against Diabetes

BACKGROUND

As a metabolic and lifestyle disorder, diabetes mellitus poses a prodigious health risk. Out of the many key targets, DPP-IV is one of the very imperative therapeutic targets for the treatment of diabetic patients.

METHODS

In our current study, we have done the in silico simulations of ADME-T properties for naturally originated potent DPP-IV inhibitors like quinovic acid, stigmasterol, quinovic acid-3-beta-D-glycopyranoside, zygophyloside E, and lupeol. Structural topographies associated with different pharmacokinetic properties have been systematically assessed.

RESULTS

Glycosylation on quinovic acid is found to be noteworthy for the improvement of pharmacokinetic and toxicological properties, which leads to the prediction that zygophyloside E can be further tailored down to get the lead DPP-IV inhibitor.

CONCLUSION

This assessment provides useful insight into the future development of novel drugs for the treatment of diabetes mellitus.

Vildagliptin, a CD26/DPP4 inhibitor, ameliorates bleomycin-induced pulmonary fibrosis via regulating the extracellular matrix

BACKGROUND

Idiopathic pulmonary fibrosis is a debilitating lung disease. CD26/DPP4 plays promotive roles in pulmonary damage and fibrosis. This study aimed to explore the roles of vildagliptin in bleomycin-induced pulmonary fibrosis, and to address its ameliorative effect on the extracellular matrix (ECM).

METHODS

Idiopathic pulmonary fibrosis mice models were induced by intratracheal injection of bleomycin. DPP4 activity was evaluated, and the fibrosis was investigated by Hematoxylin-eosin, Masson's trichrome staining and hydroxyproline assay. Expression of extracellular matrix proteins including α-SMA, collagen IV, collagen I, FN and TGF-β were analyzed by immunochemistry and western blot. Percentages of the numbers of monocytes, leukocytes, basophils and lymphocytes were classified, and inflammatory factors in plasma as well as lung tissues were examined by enzyme-linked immunosorbent assay and western blot. The influences of vildagliptin on TGF-β1-induced cell proliferation, differentiation and inflammatory factors in MRC-5 cells were detected.

RESULTS

Vildagliptin effectively attenuated inflammation and fibrosis in bleomycin-induced pulmonary tissue via inhibiting the activity of CD26/DPP4. extracellular matrix proteins were suppressed by vildagliptin. Thus, lung tissue fibrosis was efficiently alleviated by vildagliptin.

CONCLUSION

As an inhibitor of CD26/DPP4, Vildagliptin could be a promising therapeutic candidate for idiopathic pulmonary fibrosis.

Decreased shedding dipeptidyl peptidase 4 from membrane in Hashimoto's thyroiditis

AIMS

This study aimed to determine the concentration and enzymatic activity of dipeptidyl peptidase 4 (DPP4) in serum and peripheral blood mononuclear cells (PBMCs) from patients with Hashimoto's thyroiditis (HT) and to explore the potential mechanism of the abnormal DPP4 in HT development.

METHODS

A total of 33 newly diagnosed HT patients and 31 age- and sex-matched healthy controls were enrolled. Clinical characteristics and thyroid function data were collected for all participants. Serum DPP4 and kallikrein-related peptidase 5 (KLK5) concentrations were measured by sandwich enzyme-linked immunosorbent assay. DPP4 enzymatic activities in serum and PBMCs were determined by enzymatic assay. DPP4, KLK5 and interferon (IFN)-γ mRNA expression levels in PBMCs were evaluated by quantitative real-time polymerase chain reaction.

RESULTS

Serum DPP4 level and activity were significantly lower in the HT group compared with the control group. However, DPP4 mRNA expression was significantly increased and both serum KLK5 concentration and KLK5 mRNA expression in PBMCs were significantly decreased in HT patients. Correlation analyses revealed that DPP4 concentration was positively correlated with DPP4 enzymatic activity in serum. No significant difference in DPP4 activity was found in PBMCs. DPP4 enzymatic activity in PBMCs was negatively correlated with DPP4 enzymatic activity in serum. IFN-γ mRNA expression in PBMCs was significantly increased in HT patients.

CONCLUSIONS

DPP4 is involved in the development and pathological process of HT. Decreased cleavage of membrane-anchored DPP4 by KLK5 may be responsible for the decreased serum DPP4 levels in HT patients.

Dipeptidyl peptidase 4 inhibitors and their potential immune modulatory functions

Dipeptidyl peptidase 4 (DPP4) inhibitors (DPP4is) are oral anti-diabetic drugs (OADs) for the treatment of type 2 diabetes mellitus (T2DM) through inhibiting the degradation of incretin peptides. Numerous investigations have been focused on the effects of DPP4is on glucose homeostasis. However, there are limited evidences demonstrating their Potential modulatory functions in the immune system. DPP4, originally known as the lymphocyte cell surface protein CD26, is widely expressed in many types of immune cells including CD4(+) and CD8(+) T cells, B cells, NK cells, dendritic cells, and macrophages; and regulate the functions of these cells. In addition, DPP4 is capable of modulating plenty of cytokines, chemokines and peptide hormones. Accordingly, DPP4/CD26 is speculated to be involved in various immune/inflammatory diseases and DPP4is may become a new drug class applied in these diseases. This review focuses on the regulatory effects of DPP4is on immune functions and their possible underlying mechanisms. Further clinical studies will be necessitated to fully evaluate the administration of DPP4is in diabetic patients with or without immune diseases.

The effects of DPP4 inhibitors on the levels of plasma catecholamines and their metabolites in patients with type 2 diabetes

AIMS

Dipeptidyl peptidase 4 inhibitors (DPP4Is) can increase sympathetic activity. We aimed to evaluate the direct association between serum DPP4 activity and sympathetic activity in humans.

METHODS

Fasting serum DPP4 activity and plasma levels of catecholamines and their metabolites were measured in 211 patients with type 2 diabetes mellitus (T2DM) treated with DPP4I (n = 146) or non-DPP4I therapy (n = 65) and in healthy control subjects (n = 30).

RESULTS

Although there were no differences in plasma levels of catecholamines and their metabolites between the DPP4I and non-DPP4I groups, the levels in both of these groups were lower than those in the healthy control group. In DPP4I-treated patients, serum DPP4 activity showed an inverse correlation with plasma levels of norepinephrine (NE) (r = -0.339, p < 0.01), metanephrine (MET) (r = -0.251, p < 0.01) and normetanephrine (r = -0.312, p < 0.001). In addition, plasma MET level showed a weak inverse correlation with serum DPP4 activity in the combined T2DM group. In DPP4I-treated patients, the inverse correlation between DPP4 activity and plasma NE remained significant even after multiple adjustments.

CONCLUSIONS

Our results suggest that although sympathetic activity is lower in patients with T2DM, the greater the suppression of DPP4 activity by DPP4I therapy, the greater the increase in sympathetic activity is, which may have clinical implications in high risk T2DM patients.

CD26 in autoimmune diseases: The other side of "moonlight protein"

Dipeptidyl peptidase 4 (DPP-4) is a serine protease, which has enzymatic activity to selectively clean the N-terminal dipeptide of peptides and proteins with proline or alanine in the second position. DPP-4 inhibitor has been widely used for the treatment of type 2 diabetes by increasing the level of the glucagon-like peptide-1 and decreasing the glucose level. DPP-4, also known as lymphocyte cell surface protein CD26, plays a core role of T cell immunity. Many roles of CD26 in other immune cells have been found. As a "moonlight protein", the effect of CD26 in autoimmune diseases has attracted more and more attention. The paper reviewed the function and potential effect of CD26 in autoimmune diseases, which shows CD26 may be a new target of autoimmune diseases deserved further study.

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.

Soluble Dipeptidyl Peptidase-4 Levels Are Associated with Decreased Renal Function in Patients with Type 2 Diabetes Mellitus

BACKGROUND

Dipeptidyl peptidase-4 (DPP-4) is strongly expressed in the kidney, and soluble levels of this protein are used as a marker in various chronic inflammatory diseases, including diabetes, coronary artery disease, and cancer. This study examined the association between the serum soluble DPP-4 levels and renal function or cardiovascular risk in patients with type 2 diabetes mellitus.

METHODS

In this retrospective analysis, soluble DPP-4 levels were measured in preserved sera from 140 patients with type 2 diabetes mellitus who had participated in our previous coronary artery calcium (CAC) score study.

RESULTS

The mean±standard deviation soluble DPP-4 levels in our study sample were 645±152 ng/mL. Univariate analyses revealed significant correlations of soluble DPP-4 levels with the total cholesterol (r=0.214, P=0.019) and serum creatinine levels (r=-0.315, P<0.001) and the estimated glomerular filtration rate (eGFR; estimated using the modification of diet in renal disease equation) (r=0.303, P=0.001). The associations of soluble DPP-4 levels with serum creatinine and GFR remained significant after adjusting for age, body mass index, and duration of diabetes. However, no associations were observed between soluble DPP-4 levels and the body mass index, waist circumference, or CAC score.

CONCLUSION

These data suggest the potential use of serum soluble DPP-4 levels as a future biomarker of deteriorated renal function in patients with type 2 diabetes mellitus.

Macrocarpal C isolated from Eucalyptus globulus inhibits dipeptidyl peptidase 4 in an aggregated form

Dipeptidyl peptidase 4 (DPP-4) inhibitors are used for the treatment of type-2 diabetes mellitus. Various synthetic inhibitors have been developed to date, and plants containing natural DPP-4 inhibitors have also been identified. Here, 13 plant samples were tested for their DPP-4 inhibitory activity. Macrocarpals A-C were isolated from Eucalyptus globulus through activity-guided fractionation and shown to be DPP-4 inhibitors. Of these, macrocarpal C showed the highest inhibitory activity, demonstrating an inhibition curve characterised by a pronounced increase in activity within a narrow concentration range. Evaluation of macrocarpal C solution by turbidity, nuclear magnetic resonance spectroscopy and mass spectrometry indicated its aggregation, which may explain the characteristics of the inhibition curve. These findings will be valuable for further study of potential small molecule DPP-4 inhibitors.

Dipeptidyl peptidase inhibitor therapy in type 2 diabetes: Control of the incretin axis and regulation of postprandial glucose and lipid metabolism

Dipeptidyl peptidase 4 (DPP4) is a widely expressed, serine protease which regulates the bioactivity of many peptides through cleavage and inactivation including the incretin hormones, glucagon like peptide -1 (GLP-1) and glucose dependent insulinotropic polypeptide (GIP). Inhibitors of DPP4 are used therapeutically to treat patients with Type 2 Diabetes Mellitus (T2DM) as they potentiate incretin action to regulate islet hormone secretion and improve glycemia and post-prandial lipid excursions. The widespread clinical use of DPP4 inhibitors has increased interest in the molecular mechanisms by which these drugs mediate their beneficial effects. Traditionally, focus has remained on inhibiting the catalytic activity of DPP4 within the plasma compartment, however evidence is emerging on the importance of inactivation of membrane-bound DPP4 in selective tissue beds to potentiate local hormone gradients. Here we review the recent advances in identifying the cellular sources of both circulating and membrane-bound DPP4 important for cleavage of the incretin hormones and regulation of glucose and lipoprotein metabolism.

Inhibition of dipeptidyl peptidase IV prevents high fat diet-induced liver cancer angiogenesis by downregulating chemokine ligand 2

Obesity is a major risk factor for hepatocellular carcinoma (HCC) and is typically accompanied by higher levels of serum dipeptidyl peptidase 4 (DPP4). However, the role of DPP4 in obesity-promoted HCC is unclear. Here, we found that consumption of a high-fat diet (HFD) promoted HCC cell proliferation and metastasis and led to poor survival in a carcinogen-induced model of HCC in rats. Notably, genetic ablation of DPP4 or treatment with a DPP4 inhibitor (vildagliptin) prevented HFD-induced HCC. Moreover, HFD-induced DPP4 activity facilitated angiogenesis and cancer cell metastasis in vitro and in vivo, and vildagliptin prevented tumor progression by mediating the pro-angiogenic role of chemokine ligand 2 (CCL2). Loss of DPP4 effectively reversed HFD-induced CCL2 production and angiogenesis, indicating that the DPP4/CCL2/angiogenesis cascade had key roles in HFD-associated HCC progression. Furthermore, concomitant changes in serum DPP4 and CCL2 were observed in 210 patients with HCC, and high serum DPP4 activity was associated with poor clinical prognosis. These results revealed a link between obesity-related high serum DPP4 activity and HCC progression. Inhibition of DPP4 may represent a novel therapeutic intervention for patients with HCC.

[Advances in the research of relationship between CD26 and hypertrophic scar and keloid]

In recent years, researchers have found that CD26 (dipeptidyl peptidase 4) is closely related to the formation and development of many fibrotic diseases. Hypertrophic scar, keloid, and other skin fibrosis diseases are major problems nowadays, which may affect the patient's appearance and cause joints deformity and dysfunction due to scar contracture. This article briefly reviews the relationship between CD26 and hypertrophic scar and keloid to provide new insights into the treatment of skin fibrotic diseases.

Inhibition of hepatocyte nuclear factor 1b induces hepatic steatosis through DPP4/NOX1-mediated regulation of superoxide

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disorder that is closely associated with insulin resistance and type 2 diabetes. Previous studies have suggested that hepatocyte nuclear factor 1b (HNF1b) ameliorates insulin resistance. However, the role of HNF1b in the regulation of lipid metabolism and hepatic steatosis remains poorly understood. We found that HNF1b expression was decreased in steatotic livers. We injected mice with lentivirus (LV) expressing HNF1b shRNA to generate mice with hepatic knockdown of HNF1b. We also injected high fat (HF) diet-induced obese and db/db diabetic mice with LV expressing HNF1b to overexpress HNF1b. Knockdown of HNF1b increased hepatic lipid contents and induced insulin resistance in mice and in hepatocytes. Knockdown of HNF1b worsened HF diet-induced increases in hepatic lipid contents, liver injury and insulin resistance in mice and PA-induced lipid accumulation and impaired insulin signaling in hepatocytes. Moreover, overexpression of HNF1b alleviated HF diet-induced increases in hepatic lipid content and insulin resistance in mice. Knockdown of HNF1b increased expression of genes associated with lipogenensis and endoplasmic reticulum (ER) stress. DPP4 and NOX1 expression was increased by knockdown of HNF1b and HNF1b directly bound with the promoters of DPP4 and NOX1. Overexpression of DPP4 or NOX1 was associated with an increase in lipid droplets in hepatocytes and decreased expression of DPP4 or NOX1 suppressed the effects of knockdown of HNF1b knockdown on triglyceride (TG) formation and insulin signaling. Knockdown of HNF1b increased superoxide level and decreased glutathione content, which was inhibited by downregulation of DPP4 and NOX1. N-acetylcysteine (NAC) suppressed HNF1b knockdown-induced ER stress, TG formation and insulin resistance. Palmitic acid (PA) decreased HNF1b expression which was inhibited by NAC. Taken together, these studies demonstrate that HNF1b plays an essential role in controlling hepatic TG homeostasis and insulin sensitivity by regulating DPP4/NOX1mediated generation of superoxide.

Vildagliptin ameliorates pulmonary fibrosis in lipopolysaccharide-induced lung injury by inhibiting endothelial-to-mesenchymal transition

BACKGROUND

Pulmonary fibrosis is a late manifestation of acute respiratory distress syndrome (ARDS). Sepsis is a major cause of ARDS, and its pathogenesis includes endotoxin-induced vascular injury. Recently, endothelial-to-mesenchymal transition (EndMT) was shown to play an important role in pulmonary fibrosis. On the other hand, dipeptidyl peptidase (DPP)-4 was reported to improve vascular dysfunction in an experimental sepsis model, although whether DPP-4 affects EndMT and fibrosis initiation during lipopolysaccharide (LPS)-induced lung injury is unclear. The aim of this study was to investigate the anti-EndMT effects of the DPP-4 inhibitor vildagliptin in pulmonary fibrosis after systemic endotoxemic injury.

METHODS

A septic lung injury model was established by intraperitoneal injection of lipopolysaccharide (LPS) in eight-week-old male mice (5 mg/kg for five consecutive days). The mice were then treated with vehicle or vildagliptin (intraperitoneally, 10 mg/kg, once daily for 14 consecutive days from 1 day before the first administration of LPS.). Flow cytometry, immunohistochemical staining, and quantitative polymerase chain reaction (qPCR) analysis was used to assess cell dynamics and EndMT function in lung samples from the mice.

RESULTS

Lung tissue samples from treated mice revealed obvious inflammatory reactions and typical interstitial fibrosis 2 days and 28 days after LPS challenge. Quantitative flow cytometric analysis showed that the number of pulmonary vascular endothelial cells (PVECs) expressing alpha-smooth muscle actin (α-SMA) or S100 calcium-binding protein A4 (S100A4) increased 28 days after LPS challenge. Similar increases in expression were also confirmed by qPCR of mRNA from isolated PVECs. EndMT cells had higher proliferative activity and migration activity than mesenchymal cells. All of these changes were alleviated by intraperitoneal injection of vildagliptin. Interestingly, vildagliptin and linagliptin significantly attenuated EndMT in the absence of immune cells or GLP-1.

CONCLUSIONS

Inhibiting DPP-4 signaling by vildagliptin could ameliorate pulmonary fibrosis by downregulating EndMT in systemic LPS-induced lung injury.

Sodium butyrate has context-dependent actions on dipeptidyl peptidase-4 and other metabolic parameters

Sodium butyrate (SB) has various metabolic actions. However, its effect on dipeptidyl peptidase 4 (DPP-4) needs to be studied further. We aimed to evaluate the metabolic actions of SB, considering its physiologically relevant concentration. We evaluated the effect of SB on regulation of DPP-4 and its other metabolic actions, both in vitro (HepG2 cells and mouse mesangial cells) and in vivo (high fat diet [HFD]-induced obese mice). Ten-week HFD-induced obese C57BL/6J mice were subjected to SB treatment by adding SB to HFD which was maintained for an additional 16 weeks. In HepG2 cells, SB suppressed DPP-4 activity and expression at sub-molar concentrations, whereas it increased DPP-4 activity at a concentration of 1,000 µM. In HFD-induced obese mice, SB decreased blood glucose, serum levels of insulin and IL-1β, and DPP-4 activity, and suppressed the increase in body weight. On the contrary, various tissues including liver, kidney, and peripheral blood cells showed variable responses of DPP-4 to SB. Especially in the kidney, although DPP-4 activity was decreased by SB in HFD-induced obese mice, it caused an increase in mRNA expression of TNF-α, IL-6, and IL-1β. The pro-inflammatory actions of SB in the kidney of HFD-induced obese mice were recapitulated by cultured mesangial cell experiments, in which SB stimulated the secretion of several cytokines from cells. Our results showed that SB has differential actions according to its treatment dose and the type of cells and tissues. Thus, further studies are required to evaluate its therapeutic relevance in metabolic diseases including diabetes and obesity.

Crystal structure of Porphyromonas gingivalis dipeptidyl peptidase 4 and structure-activity relationships based on inhibitor profiling

The Gram-negative anaerobe Porphyromonas gingivalis is associated with chronic periodontitis. Clinical isolates of P. gingivalis strains with high dipeptidyl peptidase 4 (DPP4) expression also had a high capacity for biofilm formation and were more infective. The X-ray crystal structure of P. gingivalis DPP4 was solved at 2.2 Å resolution. Despite a sequence identity of 32%, the overall structure of the dimer was conserved between P. gingivalis DPP4 and mammalian orthologues. The structures of the substrate binding sites were also conserved, except for the region called S2-extensive, which is exploited by specific human DPP4 inhibitors currently used as antidiabetic drugs. Screening of a collection of 450 compounds as inhibitors revealed a structure-activity relationship that mimics in part that of mammalian DPP9. The functional similarity between human and bacterial DPP4 was confirmed using 124 potential peptide substrates.

Prognostic value of plasma DPP4 activity in ST-elevation myocardial infarction

Background

Dipeptidyl peptidase-4 (DPP4) regulates blood glucose levels and inflammation, and it is also implicated in the pathophysiological process of myocardial infarction (MI). Plasma DPP4 activity (DPP4a) may provide prognostic information regarding outcomes for ST-segment elevation MI (STEMI) patients.

Methods

Blood samples were obtained from 625 consecutively admitted, percutaneous coronary intervention-treated STEMI patients with a mean age of 57 years old. DPP4a was quantified using enzymatic assays.

Results

The median follow-up period was 30 months. Multivariate Cox-regression analyses (adjusted for confounding variables) showed that a 1 U/L increase of DPP4a did not associate with risks of major adverse cardiac or cerebrovascular events (MACCE), cardiovascular mortality, MI, heart failure readmission, stroke, non-cardiovascular mortality and repeated revascularization. However, in a subset of 149 diabetic STEMI patients, DPP4a associated with an increased risk of MACCE (HR 1.16; 95% CI 1.04–1.30; p = 0.01).

Conclusions

DPP4a did not associate with cardiovascular events and non-cardiovascular mortality in non-diabetic STEMI patients. However, DPP4a may be associated with future MACCE in diabetic STEMI patients.

Trial registration NCT03046576, registered on 5 February, 2017, retrospectively registered

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-017-0553-3) contains supplementary material, which is available to authorized users.

Truncation of CXCL12 by CD26 reduces its CXC chemokine receptor 4- and atypical chemokine receptor 3-dependent activity on endothelial cells and lymphocytes

The chemokine CXCL12 or stromal cell-derived factor 1/SDF-1 attracts hematopoietic progenitor cells and mature leukocytes through the G protein-coupled CXC chemokine receptor 4 (CXCR4). In addition, it interacts with atypical chemokine receptor 3 (ACKR3 or CXCR7) and glycosaminoglycans. CXCL12 activity is regulated through posttranslational cleavage by CD26/dipeptidyl peptidase 4 that removes two NH₂-terminal amino acids. CD26-truncated CXCL12 does not induce calcium signaling or chemotaxis of mononuclear cells. CXCL12(3-68) was chemically synthesized de novo for detailed biological characterization. Compared to unmodified CXCL12, CXCL12(3-68) was no longer able to signal through CXCR4 via inositol trisphosphate (IP₃), Akt or extracellular signal-regulated kinases 1 and 2 (ERK1/2). Interestingly, the recruitment of β-arrestin 2 to the cell membrane via CXCR4 by CXCL12(3-68) was abolished, whereas a weakened but significant β-arrestin recruitment remained via ACKR3. CXCL12-induced endothelial cell migration and signal transduction was completely abrogated by CD26. Intact CXCL12 hardly induced lymphocyte migration upon intra-articular injection in mice. In contrast, oral treatment of mice with the CD26 inhibitor sitagliptin reduced CD26 activity and CXCL12 cleavage in blood plasma. The potential of CXCL12 to induce intra-articular lymphocyte infiltration was significantly increased in sitagliptin-treated mice and CXCL12(3-68) failed to induce migration under both CD26-inhibiting and non-inhibiting conditions. In conclusion, CD26-cleavage skews CXCL12 towards β-arrestin dependent recruitment through ACKR3 and destroys the CXCR4-mediated lymphocyte chemoattractant properties of CXCL12 in vivo. Hence, pharmacological CD26-blockade in tissues may enhance CXCL12-induced inflammation.

Altered circulating concentrations of active glucagon-like peptide (GLP-1) and dipeptidyl peptidase 4 (DPP4) in obese subjects and their association with insulin resistance

OBJECTIVES

Soluble DPP4 (sDPP4) is a novel adipokine that degrades glucagon-like peptide (GLP-1). We evaluated the fasting serum levels of active GLP-1 and sDPP4 in obese, overweight and normal weight subjects to assess the association between sDPP4 levels, active GLP-1 levels and insulin resistance in obese subjects.

METHODS

The study involved 235 Malaysian subjects who were randomly selected (66 normal weight subjects, 97 overweight, 59 obese subjects, and 13 subjects who were underweight). Serum sDPP4 and active GLP-1 levels were examined by enzyme-linked immunosorbent assay (ELISA). Also, body mass index kg/m² (BMI), lipid profiles, insulin and glucose levels were evaluated. Insulin resistance (IR) was estimated via the homeostasis model assessment for insulin resistance (HOMA-IR).

RESULTS

Serum sDPP4 levels were significantly higher in obese subjects compared to normal weight subjects (p=0.034), whereas serum levels of active GLP-1 were lower (p=0.021). In obese subjects, sDPP4 levels correlated negatively with active GLP-1 levels (r²=-0.326, p=0.015). Furthermore, linear regression showed that sDPP4 levels were positively associated with insulin resistance (B=82.28, p=0.023) in obese subjects.

CONCLUSION

Elevated serum sDPP4 levels and reduced GLP-1 levels were observed in obese subjects. In addition, sDPP4 levels correlated negatively with active GLP-1 levels but was positively associated with insulin resistance. This finding provides evidence that sDPP4 and GLP-1 may play an important role in the pathogenesis of obesity, suggesting that sDPP4 may be valuable as an early marker for the augmented risk of obesity and insulin resistance.

Linagliptin alleviates fatty liver disease in diabetic db/db mice

AIM

To study the effects of linagliptin on the structural signs of non-alcoholic fatty liver disease (NAFLD) in db/db mice.

METHODS

Male diabetic db/db mice (BKS.Cg-Dock7^m+/⁺Lepr^db/J) aged 10 wk received the dipeptidyl peptidase 4 (DPP4) inhibitor linagliptin (10 mg/kg) or saline as a placebo once per day by gavage for 8 wk. Intact db/db mice served as controls. Structural changes in the liver were analyzed from light and electron microscopic images of sections from intact, placebo-treated and linagliptin-treated animals. We estimated the changes in hepatocytes, sinusoidal cells, liver microvasculature and lymphatic roots. Hepatic staining for lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1) was assessed by immunohistochemistry.

RESULTS

In 18-wk-old diabetic mice, liver steatosis (predominantly microvesicular and mediovesicular steatosis) was accompanied by dilation of the roots of the lymphatic system, interlobular blood vessels and bile canaliculi. Compared to saline-treated mice, linagliptin-treated mice exhibited a reduction in the mean numeral densities of hepatocytes with lipid droplets (92.4% ± 1.7% vs 64.9% ± 5.8% per field of view, P = 0.0002) and a lower proportion of hepatocytes with a high density of lipid droplets (20.7% ± 3.6% vs 50.4% ± 3.1%, P = 0.0007). We observed heterogeneous hepatocytes and relatively preserved cell structures in the linagliptin group. Dilation of blood and lymphatic vessels, as well as ultrastructural changes in the hepatocyte endoplasmic reticulum and mitochondria, were alleviated by linagliptin treatment. In intact and placebo-treated mice, immunohistochemical staining for LYVE-1 was observed in the endothelial cells of interlobular lymphatic vessels and on the membranes of some endothelial sinusoidal cells. We observed an enlarged LYVE-1 reaction area in linagliptin-treated mice compared to intact and placebo-treated mice. The improvement in the structural parameters of the liver in linagliptin-treated mice was independent to changes in the plasma glucose levels.

CONCLUSION

The DPP4 inhibitor linagliptin alleviates liver steatosis and structural changes in the hepatic microvasculature and lymphatic roots in a model of NAFLD in diabetic db/db mice.

Boning up on DPP4, DPP4 substrates, and DPP4-adipokine interactions: Logical reasoning and known facts about bone related effects of DPP4 inhibitors

Dipeptidyl peptidase 4 (DPP4) is a conserved exopeptidase with an important function in protein regulation. The activity of DPP4, an enzyme which can either be anchored to the plasma membrane or circulate free in the extracellular compartment, affects the glucose metabolism, cellular signaling, migration and differentiation, oxidative stress and the immune system. DPP4 is also expressed on the surface of osteoblasts, osteoclasts and osteocytes, and was found to play a role in collagen metabolism. Many substrates of DPP4 have an established role in bone metabolism, among which are incretins, gastrointestinal peptides and neuropeptides. In general, their effects favor bone formation, but some effects are complex and have not been completely elucidated. DPP4 and some of its substrates are known to interact with adipokines, playing an essential role in the energy metabolism. The prolongation of the half-life of incretins through DPP4 inhibition led to the development of these inhibitors to improve glucose tolerance in diabetes. Current literature indicates that the inhibition of DPP4 activity might also result in a beneficial effect on the bone metabolism, but the long-term effect of DPP4 inhibition on fracture outcome has not been entirely established. Diabetic as well as postmenopausal osteoporosis is associated with an increased activity of DPP4, as well as a shift in the expression levels of DPP4 substrates, their receptors, and adipokines. The interactions between these factors and their relationship in bone metabolism are therefore an interesting field of study.

Dipeptidyl peptidase 4 - An important digestive peptidase in Tenebrio molitor larvae

Dipeptidyl peptidase 4 (DPP 4) is a proline specific serine peptidase that plays an important role in different regulatory processes in mammals. In this report, we isolated and characterized a unique secreted digestive DPP 4 from the anterior midgut of a stored product pest, Tenebrio molitor larvae (TmDPP 4), with a biological function different than that of the well-studied mammalian DPP 4. The sequence of the purified enzyme was confirmed by mass-spectrometry, and was identical to the translated RNA sequence found in a gut EST database. The purified peptidase was characterized according to its localization in the midgut, and substrate specificity and inhibitor sensitivity were compared with those of human recombinant DPP 4 (rhDPP 4). The T. molitor enzyme was localized mainly in the anterior midgut of the larvae, and 81% of the activity was found in the fraction of soluble gut contents, while human DPP 4 is a membrane enzyme. TmDPP 4 was stable in the pH range 5.0-9.0, with an optimum activity at pH 7.9, similar to human DPP 4. Only specific inhibitors of serine peptidases, diisopropyl fluorophosphate and phenylmethylsulfonyl fluoride, suppressed TmDPP 4 activity, and the specific dipeptidyl peptidase inhibitor vildagliptin was most potent. The highest rate of TmDPP 4 hydrolysis was found for the synthetic substrate Arg-Pro-pNA, while Ala-Pro-pNA was a better substrate for rhDPP 4. Related to its function in the insect midgut, TmDPP 4 efficiently hydrolyzed the wheat storage proteins gliadins, which are major dietary proteins of T. molitor.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Screening of Phenolic Compounds Reveals Inhibitory Activity of Nordihydroguaiaretic Acid Against Three Enzymes Involved in the Regulation of Blood Glucose Level

In this work we have focused on the inhibition of three different enzymes with a role in postprandial glucose management: α-amylase, α-glucosidase and dipeptidyl peptidase 4. The assortment of 29 monomeric phenolic compounds was first screened at a single concentration. Next, the IC50 values of tested compounds were evaluated for compounds that considerably inhibited any of the enzymes. Nordihydroguaiaretic acid, a phenolic compound abundant in Creosote bush Larrea tridentata, possessed inhibitory activity for all tested enzymes. This in vitro mechanism of action supports traditional use of Creosote bush in diabetes treatment.

Dipeptidyl Peptidase 4 Inhibitors and the Risk of Cardiovascular Disease in Patients with Type 2 Diabetes: A Tale of Three Studies

Dipeptidyl peptidase 4 (DPP4) inhibitors have been touted as promising antihyperglycemic agents due to their beneficial effects on glycemia without inducing hypoglycemia or body weight gain and their good tolerability. Beyond their glucose-lowering effects, numerous clinical trials and experimental studies have suggested that DPP4 inhibitors may exert cardioprotective effects through their pleiotropic actions via glucagon-like peptide 1-dependent mechanisms or involving other substrates. Since 2008, regulatory agencies have required an assessment of cardiovascular disease (CVD) safety for the approval of all new anti-hyperglycemic agents, including incretin-based therapies. Three large prospective DPP4 inhibitor trials with cardiovascular (CV) outcomes have recently been published. According to the Saxagliptin Assessment of Vascular Outcomes Recorded in Patients with Diabetes Mellitus (SAVOR-TIMI 53) and EXamination of cArdiovascular outcoMes with alogliptIN versus standard of carE in patients with type 2 diabetes mellitus and acute coronary syndrome (EXAMINE) trials, DPP4 inhibitors, including saxagliptin and alogliptin, did not appear to increase the risk of CV events in patients with type 2 diabetes and established CVD or high risk factors. Unexpectedly, saxagliptin significantly increased the risk of hospitalization for heart failure by 27%, a finding that has not been explained and that requires further exploration. More recently, the Trial Evaluating Cardiovascular Outcomes with Sitagliptin (TECOS) trial demonstrated the CV safety of sitagliptin, including assessments of the primary composite CV endpoint and hospitalization for heart failure in patients with type 2 diabetes and established CVD. The CV outcomes of an ongoing linagliptin trial are expected to provide new evidence about the CV effects of a DPP4-inhibitor in patients with type 2 diabetes.

Incretin-based therapies

Incretin-based therapies are steadily gaining clinical popularity, with many more products in the developmental pipeline. Current treatment recommendations incorporate GLP-1 RAs and DPP-4 inhibitors as important agents for consideration in the treatment of T2DM owing to their low hypoglycemia risk, ability to address postprandial hyperglycemia (DPP-4 inhibitors and short-acting GLP-1 RAs), and potential for weight reduction (GLP-1 RAs). These properties may likewise prove advantageous in older adults in whom hypoglycemia is particularly undesirable, although older adults may be more prone to the nausea and vomiting associated with GLP-1 RA therapy. Other safety issues for incretin-based therapies, such as pancreatitis, C-cell hyperplasia, and renal failure, should be considered when choosing an appropriate patient to receive such therapies. Ongoing CV outcome studies will further inform the health care community regarding the CV safety of incretin-based therapies. The availability of both short-acting and long-acting GLP-1 RAs currently allows practitioners to consider individualized blood glucose trends and therapeutic needs when choosing an optimal agent.

Dipeptidyl peptidase-4 (DPP-4): Localization and activity in human and rodent islets

Dipeptidyl peptidase 4 (DPP-4) was recently found to be expressed in human and mouse islets with different expression patterns. However, whether species-dependent expression pattern is a generalized phenomenon and whether islet DPP-4 activity is regulated are not known. This study was conducted to investigate DPP-4 localization in several different species, and to examine the impact of glucose, incretin hormones, and insulin on islet DPP-4 activity. It was shown by immuofluorescent staining that there were two distinct species-specific expression patterns of islet DPP-4. The enzyme was expressed exclusively in α-cells in human and pig islets, but primarily in β-cells in mouse and rat islets. INS-1 832/13 cells also expressed DPP-4, and inhibition of DPP-4 enhanced insulin secretion in the presence of glucagon-like peptide-1 (GLP-1) in the cells. DPP-4 activity was remarkably robust when cultured with high glucose, incretin hormones, and insulin in mouse and human islets as well as INS-1 832/13 cells and islet DPP-4 activity and expression pattern was not altered in double incretin receptor knockout mice, compared to wild type mice. We conclude that islet DPP-4 is species-specifically expressed in α-cell and β-cell dominant patterns in several species and both patterns remained robust in enzyme activity during short-term metabolic challenge.