Lymphocytes are a major source of circulating soluble dipeptidyl peptidase 4

Transport functions of intestinal lymphatic vessels

Lymphatic vessels are crucial for fluid absorption and the transport of peripheral immune cells to lymph nodes. However, in the small intestine, the lymphatic fluid is rich in diet-derived lipids incorporated into chylomicrons and gut-specific immune cells. Thus, intestinal lymphatic vessels have evolved to handle these unique cargoes and are critical for systemic dietary lipid delivery and metabolism. This Review covers mechanisms of lipid absorption from epithelial cells to the lymphatics as well as unique features of the gut microenvironment that affect these functions. Moreover, we discuss details of the intestinal lymphatics in gut immune cell trafficking and insights into the role of inter-organ communication. Lastly, we highlight the particularities of fat absorption that can be harnessed for efficient lipid-soluble drug distribution for novel therapies, including the ability of chylomicron-associated drugs to bypass first-pass liver metabolism for systemic delivery. In all, this Review will help to promote an understanding of intestinal lymphatic-systemic interactions to guide future research directions.

Soluble CD26: From Suggested Biomarker for Cancer Diagnosis to Plausible Marker for Dynamic Monitoring of Immunotherapy

Soluble CD26 (sCD26), a glycoprotein with dipeptidyl peptidase (DPP4) enzymatic activity, can contribute to early diagnosis of colorectal cancer and advanced adenomas and has been studied, including for prognostic purposes, across various other types of cancer and disease. The latest research in this field has confirmed that most, though not all, serum/plasma sCD26 is related to inflammation. The shedding and/or secretion of sCD26 from different immune cells are being investigated, and blood DPP4 activity levels do not correlate very strongly with protein titers. Some of the main substrates of this enzyme are key chemokines involved in immune cell migration, and both soluble and cell-surface CD26 can bind adenosine deaminase (ADA), an enzyme involved in the metabolism of immunosuppressor extracellular adenosine. Of note, there are T cells enriched in CD26 expression and, in mice tumor models, tumor infiltrating lymphocytes exhibited heightened percentages of CD26+ correlating with tumor regression. We employed sCD26 as a biomarker in the follow-up after curative resection of colorectal cancer for the early detection of tumor recurrence. Changes after treatment with different biological disease-modifying antirheumatic drugs, including Ig-CTLA4, were also observed in rheumatoid arthritis. Serum soluble CD26/DPP4 titer variation has recently been proposed as a potential prognostic biomarker after a phase I trial in cancer immunotherapy with a humanized anti-CD26 antibody. We propose that dynamic monitoring of sCD26/DPP4 changes, in addition to well-known inflammatory biomarkers such as CRP already in use as informative for immune checkpoint immunotherapy, may indicate resistance or response during the successive steps of the treatment. As tumor cells expressing CD26 can also produce sCD26, the possibility of sorting immune- from non-immune-system-originated sCD26 is discussed.

Exploring the conformational dynamics and key amino acids in the CD26-caveolin-1 interaction and potential therapeutic interventions

This study aimed to decipher the interaction between CD26 and caveolin-1, key proteins involved in cell signaling and linked to various diseases. Using computational methods, we predicted their binding conformations and assessed stability through 100 ns molecular dynamics (MD) simulations. We identified two distinct binding conformations (con1 and con4), with con1 exhibiting superior stability. In con1, specific amino acids in CD26, namely GLU237, TYR241, TYR248, and ARG147, were observed to engage in interactions with the F-J chain of Caveolin-1, establishing hydrogen bonds and cation or π-π interactions. Meanwhile, in con4, CD26 amino acids ARG253, LYS250, and TYR248 interacted with the J chain of Caveolin-1 via hydrogen bonds, cation-π interactions, and π-π interactions. Virtual screening also revealed potential small-molecule modulators, including Crocin, Poliumoside, and Canagliflozin, that could impact this interaction. Additionally, predictive analyses were conducted on the potential bioactivity, drug-likeness, and ADMET properties of these three compounds. These findings offer valuable insights into the binding mechanism, paving the way for new therapeutic strategies. However, further validation is required before clinical application. In summary, we provide a detailed understanding of the CD26 and caveolin-1 interaction, identifying key amino acids and potential modulators, essential for developing targeted therapies.

Increased Thyroid DPP4 Expression Is Associated With Inflammatory Process in Patients With Hashimoto Thyroiditis

CONTEXT

Dipeptidyl peptidase-4 (DPP4) is originally described as a surface protein in lymphocytes. Lymphocyte infiltration and subsequent destruction of thyroid tissue have been considered as the central pathological mechanism in Hashimoto thyroiditis (HT).

OBJECTIVE

The present study aimed to investigate DPP4 expression in peripheral blood and thyroid tissue in HT patients, and explore the role of DPP4 in the pathophysiological process of HT.

METHODS

This case-control study recruited 40 drug-naive HT patients and 81 control individuals. Peripheral blood and thyroid specimens were collected for assessing the expression and activity of DPP4. Moreover, single-cell RNA sequencing (scRNA-seq) analysis of 6 "para-tumor tissues" samples from scRNA-seq data set GSE184362 and in vitro cell experiments were also conducted.

RESULTS

The HT patients had similar DPP4 serum concentration and activity as the controls. However, the expression and activity of DPP4 was significantly increased in the thyroid of the HT group than in the control group. The scRNA-seq analysis showed that DPP4 expression was significantly increased in the HT group, and mainly expressed in T cells. Further in vitro studies showed that inhibition of lymphocyte DPP4 activity with sitagliptin downregulated the production of inflammatory factors in co-cultured thyroid cells.

CONCLUSION

DPP4 expression was significantly increased in the thyroid of the HT group compared with the control group, and was mainly localized in the lymphocytes. Inhibition of lymphocyte DPP4 activity reduced the production of inflammatory factors in co-cultured thyroid cells. Therefore, inhibition of DPP4 may have a beneficial effect by alleviating inflammatory reactions in HT patients.

StructuralDPPIV: a novel deep learning model based on atom structure for predicting dipeptidyl peptidase-IV inhibitory peptides

MOTIVATION

Diabetes is a chronic metabolic disorder that has been a major cause of blindness, kidney failure, heart attacks, stroke, and lower limb amputation across the world. To alleviate the impact of diabetes, researchers have developed the next generation of anti-diabetic drugs, known as dipeptidyl peptidase IV inhibitory peptides (DPP-IV-IPs). However, the discovery of these promising drugs has been restricted due to the lack of effective peptide-mining tools.

RESULTS

Here, we presented StructuralDPPIV, a deep learning model designed for DPP-IV-IP identification, which takes advantage of both molecular graph features in amino acid and sequence information. Experimental results on the independent test dataset and two wet experiment datasets show that our model outperforms the other state-of-art methods. Moreover, to better study what StructuralDPPIV learns, we used CAM technology and perturbation experiment to analyze our model, which yielded interpretable insights into the reasoning behind prediction results.

AVAILABILITY AND IMPLEMENTATION

The project code is available at https://github.com/WeiLab-BioChem/Structural-DPP-IV.

A Systems Biology Approach Unveils a Critical Role of DPP4 in Upper Gastrointestinal Cancer Patient Outcomes

Gastrointestinal (GI) cancers comprise of cancers that affect the digestive system and its accessory organs. The late detection and poor prognosis of GI cancer emphasizes the importance of identifying reliable and precise biomarkers for early diagnosis and prediction of prognosis. The membrane-bound glycoprotein dipeptidyl-peptidase 4 (DPP4), also known as CD26, is ubiquitously expressed and has a wide spectrum of biological roles. The role of DPP4/CD26 in tumor progression in different types of cancers remains elusive. However, the link between DPP4 and tumor-infiltrating cells, as well as its prognostic significance in malignancies, still require further investigation. This study was intended to elucidate the correlation of DPP4 expression and survival along with prognosis, followed by its associated enriched molecular pathways and immune cell marker levels in upper GI cancers. Results demonstrated a strong correlation between increased DPP4 expression and a worse prognosis in esophageal and gastric cancer and the co-expressed common genes with DPP4 were associated with crucial molecular pathways involved in tumorigenesis. Additionally, DPP4 was shown to be significantly linked to several immune infiltrating cell marker genes, including Macrophages (M1, M2 and Tumor Associated Macrophages), neutrophils, Treg, T-cell exhaustion, Th1 and Th2. Overall, our findings suggest that DPP4 may serve as a substantial prognostic biomarker, a possible therapeutic target, as well as it can play a critical role in the regulation of immune cell invasion in patients with gastroesophageal (esophageal, gastroesophageal junction and gastric) cancer. KEY WORDS: DPP4, integrated analysis, GI cancer, gastroesophageal cancer, gastroesophageal junction, prognosis.

Diabetic individuals with COVID-19 exhibit reduced efficacy of gliptins in inhibiting dipeptidyl peptidase 4 (DPP4). A suggested explanation for increased COVID-19 susceptibility in patients with type 2 diabetes mellitus (T2DM)

AIMS

Dipeptidyl peptidase 4 (DPP4) has been proposed as a coreceptor for SARS-CoV-2 cellular entry. Considering that type 2 diabetes mellitus (T2DM) has been identified as the most important risk factor for SARS-CoV-2, and that gliptins (DPP4 inhibitors) are a prescribed diabetic treatment, this study aims to unravel the impact of DPP4 in the intersection of T2DM/COVID-19.

MATERIALS AND METHODS

We analyzed 189 serum human samples, divided into six clinical groups (controls, T2DM, T2DM + gliptins, COVID-19, COVID-19 + T2DM, and COVID-19 + T2DM + gliptins), measuring DPP4 protein concentration and activity by Western blot, ELISA, and commercial activity kits. The obtained results were verified in Huh-7 cellular models.

KEY FINDINGS

Both DPP4 concentration and activity were decreased in COVID-19 patients, and as in T2DM patients, compared to controls. Despite these lower levels, the ratio of DPP4 activity/concentration in COVID-19 sera was the highest (0.782 ± 0.289 μU/ng vs. 0.547 ± 0.050 μU/ng in controls, p < 0.0001), suggesting a compensating mechanism in these patients. Supernatants of Huh-7 cells incubated with COVID-19 serum showed a consistent and significantly lower DPP4 concentration and activity. Furthermore, COVID-19 + T2DM + gliptins patients showed a higher serum DPP4 concentration and activity than T2DM + gliptin subjects (p < 0.05), indicating that sera from COVID-19 convalescents interfere with gliptins.

SIGNIFICANCE

Either SARS-CoV-2 or some metabolites present in the sera of COVID-19-convalescent patients interact with soluble DPP4 or even gliptins themselves since the inhibitory effect of gliptins on DPP4 activity is being prevented. The interactions between DPP4, gliptins, and SARS-CoV-2 should be further elucidated to reveal the mechanism of action for these interesting observations.

The serum concentration and activity of DPP4 is positively related with the severity of hyperthyroidism in patients with Graves' disease

OBJECTIVE

Graves' disease (GD) is an organ-specific autoimmune disease. The production of anti-thyrotropin receptor antibodies (TRAb) is associated with a loss of immune tolerance. Dipeptidyl peptidase-4 (DPP-4) is expressed on multiple immune cells. This study aimed to investigate the relationship between serum concentration/activity of DPP4 and the severity of hyperthyroidism in GD patients.

METHODS

A total of 82 newly diagnosed drug-naive patients with GD hyperthyroidism, 20 patients with non-autoimmune thyrotoxicosis and 122 age- and sex- matched healthy controls were enrolled. The clinical parameters and serum concentration and activity of DPP4 were measured.

RESULTS

The GD group had increased serum concentration and activity of DPP4 than the healthy controls and patients with non-autoimmune thyrotoxicosis, while no significant difference was observed in the latter two groups. Multivariate linear regression indicated that the serum concentration/activity of DPP4 were positively associated with FT3, FT4 and TRAb levels in the GD patients. And the positive association between serum concentration/activity of DPP4 and TRAb was remained even after adjustment for confounding factors (all p < 0.05).

CONCLUSIONS

The GD patients had significantly increased serum concentration/activity of DPP4. And the serum concentration/activity of DPP4 was positively associated with the severity of hyperthyroidism in GD patients.Key messagesThe activity and concentration of DPP4 in patients with Graves' disease were higher than those in healthy controls.There was a significant positive correlation between serum DPP4 concentration and TRAb levels in patients with Graves' disease.In patients with Graves 'disease, serum DPP4 activity was positively correlated with TRAb levels.

Dipeptidyl Peptidase 4/Midline-1 Axis Promotes T Lymphocyte Motility in Atherosclerosis

T cells play a crucial role in atherosclerosis, with its infiltration preceding the formation of atheroma. However, how T-cell infiltration is regulated in atherosclerosis remains largely unknown. Here, this work demonstrates that dipeptidyl peptidase-4 (DPP4) is a novel regulator of T-cell motility in atherosclerosis. Single-cell ribonucleic acid (RNA) sequencing and flow cytometry show that CD4+ T cells in atherosclerotic patients display a marked increase of DPP4. Lack of DPP4 in hematopoietic cells or T cells reduces T-cell infiltration and atherosclerotic plaque volume in atherosclerosis mouse models. Mechanistically, DPP4 deficiency reduces T-cell motility by suppressing the expression of microtubule associated protein midline-1 (Mid1) in T cells. Deletion of either DPP4 or Mid1 inhibits chemokine-induced shape change and motility, while restitution of Mid1 in Dpp4-/- T cell largely restores its migratory ability. Thus, DPP4/Mid1, as a novel regulator of T-cell motility, may be a potential inflammatory target in atherosclerosis.

The number of circulating CD26 expressing cells is decreased in critical COVID-19 illness

We evaluated the number of CD26 expressing cells in peripheral blood of patients with COVID-19 within 72 h of admission and on day 4 and day 7 after enrollment. The majority of CD26 expressing cells were presented by CD3+ CD4+ lymphocytes. A low number of CD26 expressing cells were found to be associated with critical-severity COVID-19 disease. Conversely, increasing numbers of CD26 expressing T cells over the first week of standard treatment was associated with good outcomes. Clinically, the number of circulating CD26 cells might be a marker of recovery or the therapeutic efficacy of anti-COVID-19 treatment. New therapies aimed at preserving and increasing the level of CD26 expressing T cells may prove useful in the treatment of COVID-19 disease.

Urinary dipeptidyl peptidase-4 is a useful marker for tubulitis, and it is released from the tubular cells of kidney transplant recipients

Background

Biomarkers are needed to diagnose kidney rejection in transplant recipients. We evaluated whether dipeptidyl peptidase-4 (DPP-4) could serve as a biomarker of rejection.

Methods

We determined DPP-4 concentrations and enzymatic activities in serum and urine, as well as DPP-4 expression in 49 kidney biopsy samples from 28 kidney transplant recipients. This study was approved by the ethical standards of the institutional research committee and comply with Helsinki declaration. All patients provided their informed consent. Donors were not from prisoners and were not paid or coerced.

Results

Serum and urinary DPP-4 activities closely correlated with DPP-4 concentrations, but were suppressed by DPP-4 inhibitors. Urinary DPP-4 concentrations increased with acute T cell-mediated rejection (ATCMR; p = 0.030) and higher Banff t and i scores (p < 0.001), and correlated with urinary protein/creatinine ratios (r = 0.450), and inversely with estimated glomerular filtration rate (r =  − 0.604). The area under the receiver operator characteristics curves for urinary DPP-4 concentrations with either Banff t3 or i3 scores were 0.811 (95% confidence interval: 0.687–0.934). The expression of DPP-4 in renal tubular cells was decreased in patients with ATCMR and higher in those with Banff t, i, ct, ci, ah, and ti scores, but was not associated with interstitial fibrosis/tubular atrophy.

Conclusions

We speculated that ATCMR leads to DPP-4 release from tubular cells into urine, resulting in a decrease in tubular cell expression. If so, then ATCMR would induce the elevation of urinary DPP-4 and could therefore serve as a biomarker of tubulitis.

DPP4 as a Potential Candidate in Cardiovascular Disease

The rising prevalence of cardiovascular disease has become a global health concern. The occurrence of cardiovascular disease is the result of long-term interaction of many risk factors, one of which is diabetes. As a novel anti-diabetic drug, DPP4 inhibitor has been proven to be cardiovascular safe in five recently completed cardiovascular outcome trials. Accumulating studies suggest that DPP4 inhibitor has potential benefits in a variety of cardiovascular diseases, including hypertension, calcified aortic valve disease, coronary atherosclerosis, and heart failure. On the one hand, in addition to improving blood glucose control, DPP4 inhibitor is involved in controlling cardiovascular risk factors. On the other hand, DPP4 inhibitor directly regulates the occurrence and progression of cardiovascular diseases through a variety of mechanisms. In this review, we summarize the recent advances of DPP4 in cardiovascular disease, aiming to discuss DPP4 inhibitor as a potential option for cardiovascular therapy.

Evaluation of Blood Soluble CD26 as a Complementary Biomarker for Colorectal Cancer Screening Programs

Fecal hemoglobin immunodetection (FIT) in combination with endoscopy has been implemented to reduce mortality from colorectal cancer (CRC), although there are issues that can be improved in relation to participation rates. We studied whether the blood biomarker soluble-CD26 (sCD26), related at least in part to the immune system and inflammation, and/or its dipeptidyl peptidase enzyme activity (DPP4), could help reduce false positives. In a cohort of 1703 individuals who underwent colonoscopy and had a serum sample, sCD26 and DPP4 activity showed statistically significant differences regarding sex and age. According to the colonoscopy findings, sCD26 and DPP4 activity progressively decreased in advanced adenomas and CRC, with statistically significant differences, even between both groups; 918 of them had a FIT result (n = 596 positive cases) with approximately 70% of these (n = 412) false positives. With cut-offs of 440 ng/mL for sCD26, 42 mU/mL for DPP4, and 11 ng/mU for their ratio, the combined information of the three biomarkers (at least positive for one biomarker) identified almost all advanced adenomas and CRC cases in the FIT cohort with approximately half of the false positives compared to FIT. A sequential testing strategy with FIT and our blood biomarker test is proposed.

Diversity of adenosine deaminase in children with EBV-related diseases

Background

Adenosine deaminase (ADA) is an enzyme involved in purine metabolism with an important role in cellular immunity. Thus, this study investigated the association between ADA and Epstein–Barr virus (EBV)-related diseases.

Methods

We retrospectively collected data from all children admitted to the Children’s Hospital of Soochow University, Suzhou, China, between May 1, 2018, and March 31, 2019, who underwent plasma EBV-DNA polymerase chain reaction, alanine aminotransferase (ALT), and ADA testing.

Results

Of 6868 children, 1877 had an elevated level of ADA, and 4991 had a level within the normal range. Multivariate logistic regression analysis indicated that ALT (adjusted odds radio [aOR] = 1.001, 95% confidence interval [CI]: 1.001–1.002), EBV infection (aOR = 8.486, 95% CI: 6.753–10.663), inflammatory disease (aOR = 3.915, 95% CI: 3.198–4.794), autoimmune disease (aOR = 2.307, 95% CI: 1.823–2.920), and malignant disease (aOR = 1.381; 95% CI: 1.101–1.734) were risk factors for an elevated ADA level. Furthermore, the ADA levels among EBV-related diseases significantly differed, including infectious mononucleosis, atypical EBV infection, respiratory infection, malignant disease, and other diseases (P < 0.05). In addition, the ADA level positively correlated with the Epstein–Barr viral load (r = 0.501, P < 0.05).

Conclusions

This large, retrospective study identified a correlation between ADA and EBV-related diseases, which may help clinicians detect these diseases earlier based on the plasma ADA concentration.

Sex-Based Differences in Human Neutrophil Chemorepulsion

A considerable amount is known about how eukaryotic cells move toward an attractant, and the mechanisms are conserved from Dictyostelium discoideum to human neutrophils. Relatively little is known about chemorepulsion, where cells move away from a repellent signal. We previously identified pathways mediating chemorepulsion in Dictyostelium, and here we show that these pathways, including Ras, Rac, protein kinase C, PTEN, and ERK1 and 2, are required for human neutrophil chemorepulsion, and, as with Dictyostelium chemorepulsion, PI3K and phospholipase C are not necessary, suggesting that eukaryotic chemorepulsion mechanisms are conserved. Surprisingly, there were differences between male and female neutrophils. Inhibition of Rho-associated kinases or Cdc42 caused male neutrophils to be more repelled by a chemorepellent and female neutrophils to be attracted to the chemorepellent. In the presence of a chemorepellent, compared with male neutrophils, female neutrophils showed a reduced percentage of repelled neutrophils, greater persistence of movement, more adhesion, less accumulation of PI(3,4,5)P₃, and less polymerization of actin. Five proteins associated with chemorepulsion pathways are differentially abundant, with three of the five showing sex dimorphism in protein localization in unstimulated male and female neutrophils. Together, this indicates a fundamental difference in a motility mechanism in the innate immune system in men and women.

Mechanisms of COVID-19 Pathogenesis in Diabetes

Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus, is a global pandemic impacting 254 million people in 190 countries. Comorbidities, particularly cardiovascular disease, diabetes, and hypertension, increase the risk of infection and poor outcomes. SARS-CoV-2 enters host cells through the angiotensin-converting enzyme-2 receptor, generating inflammation and cytokine storm, often resulting in multiorgan failure. The mechanisms and effects of COVID-19 on patients with high-risk diabetes are not yet completely understood. In this review, we discuss the variety of coronaviruses, structure of SARS-CoV-2, mutations in SARS-CoV-2 spike proteins, receptors associated with viral host entry, and disease progression. Furthermore, we focus on possible mechanisms of SARS-CoV-2 in diabetes, leading to inflammation and heart failure. Finally, we discuss existing therapeutic approaches, unanswered questions, and future directions.

Insight into the role of DPP-4 in fibrotic wound healing

Wound healing is a complex and long-term process consisting of hemostasis, inflammation, proliferation, and maturation/remodeling. These four stages overlap and influence each other; they affect wound healing in different ways, and if they do not function perfectly, they may cause scarring, proliferative scarring and keloid formation. A therapeutic target affecting wound healing in multiple ways will help the healing process proceed more effectively. DPP-4/CD26 is a multifunctional dimorphic glycoprotein widely distributed on the surface of a variety of cells, including fibroblasts and keratin-forming cells. It has been found to affect periwound inflammation, re-epithelialization, extracellular matrix secretion and skin fibrosis and is a potential target for promoting wound healing and inhibiting scar formation. After presenting a brief introduction of the wound healing process and DPP-4/CD26, this paper summarizes the effects of DPP-4/CD26 on cells involved in different stages of wound healing and discusses the feasibility of DPP-4/CD26 as a multifunctional target for the treatment of wound healing and inhibition of scar formation.

Withaniasomnifera phytochemicals possess SARS-CoV-2 RdRp and human TMPRSS2 protein binding potential

ABSTRACT

Coronavirus disease-19 (COVID-19) pandemic caused by severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) has infected approximately 26 million people and caused more than 6 million deaths globally. Spike (S)-protein on the outer surface of the virus uses human trans-membrane serine protease-2 (TMPRSS2) to gain entry into the cell. Recent reports indicate that human dipeptidyl peptidase-4 inhibitors (DPP4 or CD26) could also be utilized to check the S-protein mediated viral entry into COVID-19 patients. RNA dependent RNA polymerase (RdRp) is another key virulence protein of SARS-CoV-2 life cycle. The study aimed to identify the potential anti-SARS-CoV-2 inhibitors present in Withania somnifera (Solanaceae) using computer aided drug discovery approach. Molecular docking results showed that flavone glycoside, sugar alcohol, and flavonoid present in W. somnifera showed - 11.69, - 11.61, - 10.1, - 7.71 kcal/mole binding potential against S-protein, CD26, RdRp, and TMPRSS2 proteins. The major standard inhibitors of the targeted proteins (Sitagliptin, VE607, Camostat mesylate, and Remdesivir) showed the - 7.181, - 6.6, - 5.146, and - 7.56 kcal/mole binding potential. Furthermore, the lead phytochemicals and standard inhibitors bound and non-bound RdRp and TMPRSS2 proteins were subjected to molecular dynamics (MD) simulation to study the complex stability and change in protein conformation. The result showed energetically favorable and stable complex formation in terms of RMSD, RMSF, SASA, Rg, and hydrogen bond formation. Drug likeness and physiochemical properties of the test compounds exhibited satisfactory results. Taken together, the present study suggests the presence of potential anti-SARS-CoV-2 phytochemicals in W. somnifera that requires further validation in in vitro and in vivo studies.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s42535-022-00404-4.

Low levels of soluble DPP4 among Saudis may have constituted a risk factor for MERS endemicity

Most of the cases of Middle East respiratory syndrome coronavirus (MERS-CoV) were reported in Saudi Arabia. Dipeptidyl peptidase-4 (DPP4) was identified as the receptor for the virus. The level of soluble DPP4 (sDPP4) was found to be reduced in MERS-CoV infected patients while high levels of sDPP4 were suggested to be protective against MERS-CoV in animal models. We investigated whether the Saudi population has lower levels of sDPP4 which makes them more susceptible to MERS-CoV infection and, therefore, could explain the larger number of cases from the country. Blood samples were collected from 219 Saudi blood donors and 200 blood donors from other ethnic groups. The plasma level of sDPP4 was measured by ELISA and the following SNPs in the DPP4 gene; rs35128070, rs1861978, rs79700168, and rs17574, were genotyped by TaqMan SNP genotyping assay. The average level of plasma sDDP4 was significantly lower in Saudis than other Arabs and non-Arabs (P value 0.0003 and 0.012, respectively). The genotypes AG of rs35128070 and GT of rs1861978 were significantly associated with lower sDPP4 among Saudis (P value 0.002 for each). While both genotypes AA and AG of rs79700168 and rs17574 were associated with significantly lower average sDPP4 level in Saudis compared to other ethnic groups (P value 0.031 and 0.032, and 0.027 and 0.014, respectively). Herein, we report that the Saudi population has lower levels of plasma sDPP4 than other ethnic groups, which is associated with genetic variants in the DPP4 gene. This may have contributed to increase the susceptibility of the Saudi population to MERS-CoV infection and could be a factor in the long-lasting persistence of the virus in the country.

Induction of IDO1 and Kynurenine by Serine Proteases Subtilisin, Prostate Specific Antigen, CD26 and HtrA: A New Form of Immunosuppression?

Several serine proteases have been linked to autoimmune disorders and tumour initiation although the mechanisms are not fully understood. Activation of the kynurenine pathway enzyme indoleamine-2,3-dioxygenase (IDO1) modulates cellular activity in the brain, tolerogenesis in the immune system and is a major checkpoint in cancer development. We now report that IDO1 mRNA and IDO1 protein expression (generating kynurenine) are induced in human monocyte-derived macrophages by several chymotryptic serine proteases with direct links to tumorigenesis, including Prostate Specific Antigen (PSA), CD26 (Dipeptidyl-peptidase-4, CD26/DPP-4), High Temperature Requirement protein-A (HtrA), and the bacterial virulence factor subtilisin. These proteases also induce expression of the pro-inflammatory cytokine genes IL1B and IL6. Other serine proteases tested: bacterial glu-C endopeptidase and mammalian Pro-protein Convertase Subtilase-Kexin-3 (PCSK3, furin), urokinase plasminogen activator (uPA), cathepsin G or neutrophil elastase, did not induce IDO1, indicating that the reported effects are not a general property of all serine proteases. The results represent a novel mechanism of activating immunosuppressive IDO1 and inducing kynurenine generation which, together with the production of inflammatory cytokines, would contribute to tumour initiation and progression, providing a new target for drug development. In addition, the proteasomal S20 serine protease inhibitor carfilzomib, used in the treatment of myeloma, prevented the induction of IDO1 and cytokine gene expression, potentially contributing to its clinical anti-cancer activity.

Intra- and Extracellular Effector Vesicles From Human T And NK Cells: Same-Same, but Different?

Cytotoxic T lymphocytes (CTL) and Natural Killer (NK) cells utilize an overlapping effector arsenal for the elimination of target cells. It was initially proposed that all cytotoxic effector proteins are stored in lysosome-related effector vesicles (LREV) termed "secretory lysosomes" as a common storage compartment and are only released into the immunological synapse formed between the effector and target cell. The analysis of enriched LREV, however, revealed an uneven distribution of individual effectors in morphologically distinct vesicular entities. Two major populations of LREV were distinguished based on their protein content and signal requirements for degranulation. Light vesicles carrying FasL and 15 kDa granulysin are released in a PKC-dependent and Ca²⁺-independent manner, whereas dense granules containing perforin, granzymes and 9 kDa granulysin require Ca²⁺-signaling as a hallmark of classical degranulation. Notably, both types of LREV do not only contain the mentioned cytolytic effectors, but also store and transport diverse other immunomodulatory proteins including MHC class I and II, costimulatory and adhesion molecules, enzymes (i.e. CD26/DPP4) or cytokines. Interestingly, the recent analyses of CTL- or NK cell-derived extracellular vesicles (EV) revealed the presence of a related mixture of proteins in microvesicles or exosomes that in fact resemble fingerprints of the cells of origin. This overlapping protein profile indicates a direct relation of intra- and extracellular vesicles. Since EV potentially also interact with cells at distant sites (apart from the IS), they might act as additional effector vesicles or intercellular communicators in a more systemic fashion.

Decreased circulating dipeptidyl peptidase-4 enzyme activity is prognostic for severe outcomes in COVID-19 inpatients

Aim:

To investigate the serum circulating DPP4 activity in patients with COVID-19 disease.

Materials & methods:

Serum samples from 102 hospitalized COVID-19 patients and 43 post-COVID-19 plasma donors and 39 SARS-CoV-2 naive controls and their medical data were used. Circulating DPP4 activities according to different COVID-19 disease peak severity (WHO) groups at sampling and at peak were assessed.

Results:

A significant decrease (p < 0.0001) in serum DPP4 activity was found in study groups of higher disease severity. When the circulating DPP4 activity was assessed as a prognostic marker, the logistic regression (p = 0.0023) indicated that the enzyme activity is a predictor of mortality (median 9.5 days before death) with receiver operating characteristic area under the curves of 73.33% (p_{[area = 0.5]} < 0.0001) as single predictor and 83.45% (p_{[area = 0.5]} < 0.0001) in combination with age among hospitalized patients with COVID-19.

Conclusion:

Decreased circulating DPP4 activity is associated with severe COVID-19 disease and is a strong prognostic biomarker of mortality.

Circulating Dipeptidyl Peptidase Activity Is a Potential Biomarker for Inflammatory Bowel Disease

INTRODUCTION

Dipeptidyl peptidase (DPP)-4 is part of a larger family of proteases referred to as DPPs. DPP4 has been suggested as a possible biomarker for inflammatory bowel disease (IBD). Circulating DPP4 (cDPP4) enzyme activity was investigated as a potential biomarker for IBD. In addition, DPP enzyme activity and gene expression were quantified in colonic tissue of patients with IBD and non-IBD.

METHODS

In study 1, DPP enzyme activity was quantified in plasma samples from 220 patients with IBD (Crohn's disease [CD] n = 130 and ulcerative colitis [UC] n = 90) and non-IBD controls (n = 26) using a colorimetric assay. In study 2, tissue and plasma samples were collected from 26 patients with IBD and 20 non-IBD controls. Plasma C-reactive protein (CRP) was quantified in all patients. Colonic DPP4, DPP8, DPP9, and fibroblast activation protein (FAP) gene expression was determined by quantitative polymerase chain reaction. cDPP and cFAP enzyme activity was also measured. Sensitivity and specificity were determined by receiver operating characteristic curve analysis.

RESULTS

In study 1, total cDPP activity was found to differentiate patients with CD with active disease (n = 18) from those in remission (n = 19; sensitivity 78% and specificity 63%). In study 2, total cDPP and cFAP activity was 28% and 48% lower in patients with elevated CRP (>10 mg/L), respectively, compared with patients with normal CRP. Gene expression of DPP4, FAP, and DPP8 was also significantly higher in colonic biopsies from patients with IBD compared with non-IBD patients (P < 0.05).

DISCUSSION

Our findings implicate the DPP enzyme family in intestinal inflammation and suggest future biomarker applications to differentiate the pathophysiological aspects of IBD.

Potential Effect of DPP-4 Inhibitors Towards Hepatic Diseases and Associated Glucose Intolerance

Dipeptidyl-peptidase-4 (DPP-4) is an enzyme having various properties and physiological roles in lipid accumulation, resistance to anticancer agents, and immune stimulation. DPP-4 includes membrane-bound peptidases and is a kind of enzyme that cleaves alanine or proline-containing peptides such as incretins, chemokines, and appetite-suppressing hormones (neuropeptide) at their N-terminal dipeptides. DPP-4 plays a role in the final breakdown of peptides produced by other endo and exo-peptidases from nutritious proteins and their absorption in these tissues. DPP-4 enzyme activity has different modes of action on glucose metabolism, hunger regulation, gastrointestinal motility, immune system function, inflammation, and pain regulation. According to the literature survey, as DPP-4 levels increase in individuals with liver conditions, up-regulation of hepatic DPP-4 expression is likely to be the cause of glucose intolerance or insulin resistance. This review majorly focuses on the cleavage of alanine or proline-containing peptides such as incretins by the DPP-4 and its resulting conditions like glucose intolerance and cause of DPP-4 level elevation due to some liver conditions. Thus, we have discussed the various effects of DPP-4 on the liver diseases like hepatitis C, non-alcoholic fatty liver, hepatic regeneration and stem cell, hepatocellular carcinoma, and the impact of elevated DPP-4 levels in association with liver diseases as a cause of glucose intolerance and their treatment drug of choices. In addition, the effect of DPP-4 inhibitors on obesity and their negative aspects are also discussed in brief.

StackDPPIV: A novel computational approach for accurate prediction of dipeptidyl peptidase IV (DPP-IV) inhibitory peptides

The development of efficient and effective bioinformatics tools and pipelines for identifying peptides with dipeptidyl peptidase IV (DPP-IV) inhibitory activities from large-scale protein datasets is of great importance for the discovery and development of potential and promising antidiabetic drugs. In this study, we present a novel stacking-based ensemble learning predictor (termed StackDPPIV) designed for identification of DPP-IV inhibitory peptides. Unlike the existing method, which is based on single-feature-based methods, we combined five popular machine learning algorithms in conjunction with ten different feature encodings from multiple perspectives to generate a pool of various baseline models. Subsequently, the probabilistic features derived from these baseline models were systematically integrated and deemed as new feature representations. Finally, in order to improve the predictive performance, the genetic algorithm based on the self-assessment-report was utilized to determine a set of informative probabilistic features and then used the optimal one for developing the final meta-predictor (StackDPPIV). Experiment results demonstrated that StackDPPIV could outperform its constituent baseline models on both the training and independent datasets. Furthermore, StackDPPIV achieved an accuracy of 0.891, MCC of 0.784 and AUC of 0.961, which were 9.4%, 19.0% and 11.4%, respectively, higher than that of the existing method on the independent test. Feature analysis demonstrated that our feature representations had more discriminative ability as compared to conventional feature descriptors, which highlights the combination of different features was essential for the performance improvement. In order to implement the proposed predictor, we had built a user-friendly online web server at http://pmlabstack.pythonanywhere.com/StackDPPIV.

The Serine Protease CD26/DPP4 in Non-Transformed and Malignant T Cells

Simple Summary

The transmembrane serine protease CD26/Dipeptidylpeptidase 4 modulates T-cell activation, proliferation, and effector function. Due to their remarkable tumoricidal properties CD26-positive T cells are considered promising candidates for T cell-based immunotherapies while in cutaneous T cell lymphoma CD26/DPP4 expression patterns are established markers for diagnosis and possibly prognosis. With a focus on T cells, we review current knowledge on the regulation of CD26/DPP4 expression and release, its implication in T-cell effector function and the suitability CD26/DPP4 as a diagnostic and/or prognostic factor in T-cell malignancies.

Abstract

CD26/Dipeptidylpeptidase 4 is a transmembrane serine protease that cleaves off N-terminal dipeptides. CD26/DPP4 is expressed on several immune cell types including T and NK cells, dendritic cells, and activated B cells. A catalytically active soluble form of CD26/DPP4 can be released from the plasma membrane. Given its wide array of substrates and interaction partners CD26/DPP4 has been implicated in numerous biological processes and effects can be dependent or independent of its enzymatic activity and are exerted by the transmembrane protein and/or the soluble form. CD26/DPP4 has been implicated in the modulation of T-cell activation and proliferation and CD26/DPP4-positive T cells are characterized by remarkable anti-tumor properties rendering them interesting candidates for T cell-based immunotherapies. Moreover, especially in cutaneous T-cell lymphoma CD26/DPP4 expression patterns emerged as an established marker for diagnosis and treatment monitoring. Surprisingly, besides a profound knowledge on substrates, interaction partners, and associated signal transduction pathways, the precise role of CD26/DPP4 for T cell-based immune responses is only partially understood.

Distinctive CD26 Expression on CD4 T-Cell Subsets

Immune system CD4 T-cells with high cell-surface CD26 expression show anti-tumoral properties. When engineered with a chimeric antigen receptor (CAR), they incite strong responses against solid cancers. This subset was originally associated to human CD4 T helper cells bearing the CD45R0 effector/memory phenotype and later to Th17 cells. CD26 is also found in soluble form (sCD26) in several biological fluids, and its serum levels correlate with specific T cell subsets. However, the relationship between glycoprotein sCD26 and its dipeptidyl peptidase 4 (DPP4) enzymatic activity, and cell-surface CD26 expression is not well understood. We have studied ex vivo cell-surface CD26 and in vitro surface and intracellular CD26 expression and secretome's sCD26 in cultured CD4 T cells under different polarization conditions. We show that most human CD26negative CD4 T cells in circulating lymphocytes are central memory (TCM) cells while CD26high expression is present in effector Th1, Th2, Th17, and TEM (effector memory) cells. However, there are significant percentages of Th1, Th2, Th17, and Th22 CD26 negative cells. This information may help to refine the research on CAR-Ts. The cell surface CD45R0 and CD26 levels in the different T helper subsets after in vitro polarization resemble those found ex vivo. In the secretomes of these cultures there was a significant amount of sCD26. However, in all polarizations, including Th1, the levels of sCD26 were lower (although not significantly) compared to the Th0 condition (activation without polarization). These differences could have an impact on the various physiological functions proposed for sCD26/DPP4.

Dipeptidyl peptidase-4 inhibitor-induced autoimmune diseases: Current evidence

Dipeptidyl peptidase-4 inhibitors (DPP-4i) have an important place in the management of type 2 diabetes. The DPP-4 enzyme is ubiquitously distributed throughout the human body and has multiple substrates through which it regulates several important physiological functions. DPP-4 regulates several immune functions, including T-cell activation, macrophage function, and secretion of cytokines. Studies have reported an increase in autoimmune diseases like bullous pemphigoid, inflammatory bowel disease, and arthritis with DPP-4i use. The relationship of DPP-4i and autoimmune diseases is a complex one and warrants further research into the effect of DPP-4 inhibition on the immune system to understand the pathogenesis more clearly. Whether a particular cluster of autoimmune diseases is associated with DPP-4i use remains an important contentious issue. Nevertheless, a heightened awareness from the clinicians is required to identify and treat any such diseases. Through this review, we explore the clinical and pathophysiological characteristics of this association in light of recent evidence.

Dipeptidyl peptidase 4 inhibitors: Applications in innate immunity?

Dipeptidyl peptidase (DPP)-4 inhibitors are a class of orally available, small molecule inhibitors that prolong the insulinotropic activity of the incretin hormone glucagon-like peptide-1 (GLP-1) and are highly effective for the treatment of Type-2 diabetes. DPP4 can also cleave several immunoregulatory peptides including chemokines. Emerging evidence continues to implicate DPP4 inhibitors as immunomodulators, with recent findings suggesting DPP4 inhibitors modify specific aspects of innate immunity. This review summarises recent insights into how DPP4 inhibitors could be implicated in endothelial, neutrophil and monocyte/macrophage mediated immunity. Additionally, this review highlights additional avenues of research with DPP4 inhibitors in the context of the COVID-19 pandemic.

Inhibiting adipose tissue M1 cytokine expression decreases DPP4 activity and insulin resistance in a type 2 diabetes mellitus mouse model

Adipose tissue inflammation is a major cause of the pathogenesis of obesity and comorbidities. To study the involvement of M1/M2 cytokine expression of adipose tissue in the regulatory mechanisms of dipeptidyl peptidase 4 (DPP4) and insulin resistance in diabetes, stromal vascular fractions (SVFs) were purified from inguinal adipose tissue of diabetic (Lepr^db/db) and non-diabetic (Lepr^+/+) mice followed by analysis of M1/M2 cytokine expression. SVFs of Lepr^db/db mice exhibited increased TNF-α, IL-6, IL-1β, CCL2, and DPP4 mRNA expression but decreased IL-10 mRNA expression. Plasma from Lepr^db/db mice induced TNF-α, IL-6, IL-1β, CCL2, and DPP4 mRNA expression and plasma from Lepr^+/+ mice induced IL-10 mRNA expression in SVFs from Lepr^db/db mice. Injection of Lepr^+/+ plasma into the adipose tissue of Lepr^db/db mice decreased mRNA expression of TNF-α, IL-6, IL-1β, CCL2, and DPP4 and protein expression of pJNK and DPP4 in SVFs, reduced mRNA expression of ICAM, FMO3, IL-1β, iNOS, TNF-α, IL-6, and DPP4 and protein expression of ICAM, FMO3, and DPP4 in liver, and suppressed mRNA expression of TNF-α, IL-6, IL-1β, and DPP4 in Kupffer cells. Plasma from Lepr^db/db mice did not induce M1 cytokine expression in SVFs from Lepr^db/db-Jnk1^-/- mice. Altogether, we demonstrate that diabetes induces M1 but decreases M2 cytokine expression in adipose tissue. Diabetic plasma-induced M1 expression is potentially through pJNK signaling pathways. Non-diabetic plasma reverses M1/M2 cytokine expression, plasma CCL2 levels, DPP4 activity, and Kupffer cell activation in diabetes. Our results suggest M1/M2 cytokine expression in adipose tissue is critical in diabetes-induced DPP4 activity, liver inflammation, and insulin resistance.

Dipeptidyl peptidase IV is required for endometrial carcinoma cell proliferation and tumorigenesis via the IL-6/STAT3 pathway

AIM

To study the functions and signaling pathways controlled by dipeptidyl peptidase IV (DPPIV) in endometrial carcinoma (EC).

METHODS

DPPIV expression in EC cells was detected by flow cytometry, reverse transcription-polymerase chain reaction analysis and Western blot. Interleukin-6 (IL-6) expression in the supernatant was measured by enzyme-linked immunosorbent assay. The protein levels of signal transducers and activators of transcription-3 (STAT3), phosphorylate STAT3, cellular Myc, and vascular endothelial growth factor in EC cells were measured by Western blot. Colony formation assays were used to assess the clonogenicity of EC cells. Ki67 immunostaining and cell counting were used to test the proliferative ability of EC cells. Nude mouse tumorigenicity assay was used to confirm DPPIV promotes the tumorigenicity of EC cells. A cell counting kit-8 assay was used to determine the half-maximal inhibitory concentration of sitagliptin.

RESULTS

Overexpression of DPPIV in EC cells with low DPPIV expression promoted cell proliferation in vitro (p < 0.01) and enhanced tumorigenicity in vivo (p < 0.05). Conversely, knocking down DPPIV expression in EC cells with high DPPIV expression inhibited cell proliferation (p < 0.01) and in vivo tumorigenicity (p < 0.01). DPPIV promoted EC cell proliferation via activation of IL-6/STAT3 signaling pathway, and that IL-6 could trigger a positive feedback loop that increased DPPIV expression (p < 0.01). Furthermore, the DPPIV inhibitor reduced STAT3 expression (p < 0.01) and inhibited growth of EC cells (p < 0.001).

CONCLUSION

DPPIV enhances the properties that allow tumorigenesis in EC via IL-6 and STAT3 signaling.

Serum levels of soluble dipeptidyl peptidase-4 in type 2 diabetes are associated with severity of liver fibrosis evaluated by transient elastography (FibroScan) and the FAST (FibroScan-AST) score, a novel index of non-alcoholic steatohepatitis with significant fibrosis

AIM

To investigate the relationship in people with type 2 diabetes between serum soluble dipeptidyl peptidase-4 (sDDP-4) and degree of liver fibrosis assessed as the liver stiffness measurement (LSM) and FAST (FibroScan-AST) score, both of which were measured by transient elastography (FibroScan).

SUBJECTS AND METHODS

In this cross-sectional study, we examined 115 patients with type 2 diabetes. With transient elastography (FibroScan), we assessed the controlled attenuation parameter (CAP) and liver stiffness measurement (LSM) as measures of hepatic steatosis and liver fibrosis, respectively. We calculated the FAST score, which identifies progressive non-alcoholic steatohepatitis (NASH), from CAP, LSM, and the serum aspartate aminotransferase level. Significant hepatic steatosis was defined as CAP ≥280 dB/m; and significant liver fibrosis, as LSM ≥ 8.0 kPa. LSM was divided into 3 severity levels: significant fibrosis (8.0 to <9.7 kPa); advanced fibrosis, (9.7 to <13.0 kPa); and liver cirrhosis (≥ 13.0 kPa).

RESULTS

Serum sDPP-4 correlated positively with liver enzymes, CAP, LSM, and FAST score. Multivariate analysis showed that LSM remained to be an independent factor for serum sDDP-4. Serum sDPP-4 was significantly higher in patients with LSM ≥ 8.0 kPa than in those with LSM <8.0 kPa and was significantly elevated in patients who are at risk for non-alcoholic steatohepatitis (NASH) with fibrosis (FAST score ≥ 035 or 0.67). Patients with both hepatic steatosis and liver fibrosis had the highest serum sDPP-4.

CONCLUSION

Serum sDPP-4 was strongly associated with severity of liver fibrosis evaluated by LSM and the FAST score and was markedly elevated in diabetic patients with LSM ≥ 13.0 kPa indicating probable cirrhosis.

Delineating the Association Between Soluble CD26 and Autoantibodies Against G-Protein Coupled Receptors, Immunological and Cardiovascular Parameters Identifies Distinct Patterns in Post-Infectious vs. Non-Infection-Triggered Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Soluble cluster of differentiation 26 (sCD26) has a wide range of enzymatic functions affecting immunological, metabolic and vascular regulation. Diminished sCD26 concentrations have been reported in various autoimmune diseases and also in Myalgic Encephalomyelitis/Chronic fatigue syndrome (ME/CFS). Here we re-evaluate sCD26 as a diagnostic marker and perform a comprehensive correlation analysis of sCD26 concentrations with clinical and paraclinical parameters in ME/CFS patients. Though this study did find significantly lower concentrations of sCD26 only in the female cohort and could not confirm diagnostic suitability, results from correlation analyses provide striking pathomechanistic insights. In patients with infection-triggered onset, the associations of low sCD26 with elevated autoantibodies (AAB) against alpha1 adrenergic (AR) and M3 muscarinic acetylcholine receptors (mAChR) point to a pathomechanism of infection-triggered autoimmune-mediated vascular and immunological dysregulation. sCD26 concentrations in infection-triggered ME/CFS were found to be associated with activated T cells, liver enzymes, creatin kinase (CK) and lactate dehydrogenase (LDH) and inversely with Interleukin-1 beta (IL-1b). Most associations are in line with the known effects of sCD26/DPP-4 inhibition. Remarkably, in non-infection-triggered ME/CFS lower sCD26 in patients with higher heart rate after orthostatic challenge and postural orthostatic tachycardia syndrome (POTS) suggest an association with orthostatic regulation. These findings provide evidence that the key enzyme sCD26 is linked to immunological alterations in infection-triggered ME/CFS and delineate a different pathomechanism in the non-infectious ME/CFS subset.

Effects of the Antidiabetic Drugs Evogliptin and Sitagliptin on the Immune Function of CD26/DPP4 in Th1 Cells

This study aimed to investigate whether the antidiabetic drugs dipeptidyl peptidase 4 (DPP4) inhibitors such as evogliptin and sitagliptin affect the membrane DPP4 (mDPP4) enzymatic activity and immune function of T helper1 (Th1) cells in terms of cytokine expression and cell profiles. The mDPP4 enzymatic activity, cytokine expression, and cell profiles, including cell counts, cell viability, DNA synthesis, and apoptosis, were measured in pokeweed mitogen (PWM)-activated CD4⁺CD26⁺ H9 Th1 cells with or without the DPP4 inhibitors, evogliptin and sitagliptin. PWM treatment alone strongly stimulated the expression of mDPP4 and cytokines such as interleukin (IL)-2, IL-10, tumor necrosis factor-alpha, interferon-gamma, IL-13, and granulocyte-macrophage colony stimulating factor in the CD4⁺CD26⁺ H9 Th1 cells. Evogliptin or sitagliptin treatment potently inhibited mDPP4 activity in a dose-dependent manner but did not affect either the cytokine profile or cell viability in PWM-activated CD4⁺CD26⁺ H9 Th1 cells. These results suggest that, following immune stimulation, Th1 cell signaling pathways for cytokine expression function normally after treatment with evogliptin or sitagliptin, which efficiently inhibit mDPP4 enzymatic activity in Th1 cells.

DPP4 Inhibitors and COVID-19-Holy Grail or Another Dead End?

A novel coronavirus disease, COVID-19, has emerged as a global public health issue. Clinical course of disease significantly correlates with the occurrence of some comorbidities, among them type 2 diabetes. According to recent structural studies the dipeptidyl peptidase 4, a key molecule in the pathophysiology of diabetes, may influence the course of COVID-19. Since DPP4 inhibitors, gliptins, are widely used in diabetes patients, the exact role of DPP4 modulation in SARS-CoV-2 infection, at least in that group, urgently needs to be clarified. In this short review, we discuss this issue with more detail.

DPP4 Inhibitor Sitagliptin Enhances Lymphocyte Recruitment and Prolongs Survival in a Syngeneic Ovarian Cancer Mouse Model

Immunity plays a key role in epithelial ovarian cancer (EOC) progression with a well-documented correlation between patient survival and high intratumoral CD8+ to T regulatory cell (Treg) ratios. We previously identified dysregulated DPP4 activity in EOCs as a potentially immune-disruptive influence contributing to a reduction in CXCR3-mediated T-cell infiltration in solid tumours. We therefore hypothesized that inhibition of DPP4 activity by sitagliptin, an FDA-approved inhibitor, would improve T-cell infiltration and function in a syngeneic ID8 mouse model of EOC. Daily oral sitagliptin at 50 mg/kg was provided to mice with established primary EOCs. Sitagliptin treatment decreased metastatic tumour burden and significantly increased overall survival and was associated with significant changes to the immune landscape. Sitagliptin increased overall CXCR3-mediated CD8+ T-cell trafficking to the tumour and enhanced the activation and proliferation of CD8+ T-cells in tumour tissue and the peritoneal cavity. Substantial reductions in suppressive cytokines, including CCL2, CCL17, CCL22 and IL-10, were also noted and were associated with reduced CD4+ CD25+ Foxp3+ Treg recruitment in the tumour. Combination therapy with paclitaxel, however, typical of standard-of-care for patients in palliative care, abolished CXCR3-specific T-cell recruitment stimulated by sitagliptin. Our data suggest that sitagliptin may be suitable as an adjunct therapy for patients between chemotherapy cycles as a novel approach to enhance immunity, optimise T-cell-mediated function and improve overall survival.

An expanded role for dipeptidyl peptidase 4 in cell regulation

PURPOSE OF REVIEW

Dipeptidyl peptidase 4 (DPP4) is a serine protease with diverse regulatory functions in healthy and diseased cells. Much remains unknown about the mechanisms and targets of DPP4. Here we discuss new studies exploring DPP4-mediated cellular regulation, provide an updated list of potential targets of DPP4, and discuss clinical implications of each.

RECENT FINDINGS

Recent studies have sought enhanced efficacy of targeting DPP4's role in regulating hematopoietic stem and progenitor cells for improved clinical application. Further studies have identified DPP4 functions in different cellular compartments and have proposed ways to target this protein in malignancy. These findings, together with an expanded list of putative extracellular, cell surface, and intracellular DPP4 targets, provide insight into new DPP4-mediated cell regulation.

SUMMARY

DPP4 posttranslationally modifies proteins and peptides with essential roles in hematopoietic cell regulation, stem cell transplantation, and malignancy. Targets include secreted signaling factors and may include membrane proteins and transcription factors critical for different hematopoietic functions. Knowing these targets and functions can provide insight into new regulatory roles for DPP4 that may be targeted to enhance transplantation, treat disease, and better understand different regulatory pathways of hematopoiesis.

Investigation of CD26, a potential SARS-CoV-2 receptor, as a biomarker of age and pathology

Objective: In some individuals, coronavirus severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection leads to a variety of serious inflammatory symptoms, including blood clotting and acute respiratory distress. Death due to COVID-19 shows a steep rise in relation to age. Comorbidities such as type 2 diabetes mellitus (T2DM), hypertension, and cardiovascular disease also increase susceptibility. It has been reported that T-cell regulatory dipeptidyl peptidase 4 (DPP4; cluster of differentiation 26 (CD26)) binds to the external spike (S) glycoprotein of SARS-CoV-2 as a receptor, for the viral entry into the host cell. CD26 is expressed on many cells, including T and natural killer (NK) cells of the immune system, as a membrane-anchored form. A soluble form (sCD26) is also found in the blood plasma and cerebrospinal fluid (CSF).

Approach and results: To investigate a possible relationship between sCD26 levels, age and pathology, serum samples were collected from control, T2DM and age-related dementia (ARD) subjects. A significant reduction in serum sCD26 levels was seen in relation to age. ARD and T2DM were also associated with lower levels of sCD26. The analysis of blood smears revealed different cellular morphologies: in controls, CD26 was expressed around the neutrophil membrane, whereas in T2DM, excessive sCD26 was found around the mononucleated cells (MNCs). ARD subjects had abnormal fragmented platelets and haemolysis due to low levels of sCD26.

Conclusions: These findings may help to explain the heterogeneity of SARS-CoV-2 infection. High serum sCD26 levels could protect from viral infection by competively inhibiting the virus binding to cellular CD26, whereas low sCD26 levels could increase the risk of infection. If so measuring serum sCD26 level may help to identify individuals at high risk for the COVID-19 infection.

Hematopoietic cell- versus enterocyte-derived dipeptidyl peptidase-4 differentially regulates triglyceride excursion in mice

Postprandial triglycerides (TGs) are elevated in people with type 2 diabetes (T2D). Glucose-lowering agents, such as glucagon-like peptide-1 (GLP-1) receptor agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors, also reduce postprandial TG excursion. Although the glucose-lowering mechanisms of DPP-4 have been extensively studied, how the reduction of DPP-4 activity improves lipid tolerance remains unclear. Here, we demonstrate that gut-selective and systemic inhibition of DPP-4 activity reduces postprandial TG excursion in young mice. Genetic inactivation of Dpp4 simultaneously within endothelial cells and hematopoietic cells using Tie2-Cre reduced intestinal lipoprotein secretion under regular chow diet conditions. Bone marrow transplantation revealed a key role for hematopoietic cells in modulation of lipid responses arising from genetic reduction of DPP-4 activity. Unexpectedly, deletion of Dpp4 in enterocytes increased TG excursion in high-fat diet–fed (HFD-fed) mice. Moreover, chemical reduction of DPP-4 activity and increased levels of GLP-1 were uncoupled from TG excursion in older or HFD-fed mice, yet lipid tolerance remained improved in older Dpp4^–/– and Dpp4^EC–/– mice. Taken together, this study defines roles for specific DPP-4 compartments, age, and diet as modifiers of DPP-4 activity linked to control of gut lipid metabolism.

Gut-selective and systemic inhibition of dipeptidyl peptidase-4 activity reveals roles in gut lipid metabolism.

Plasma levels of DPP4 activity and sDPP4 are dissociated from inflammation in mice and humans

Dipeptidyl peptidase-4 (DPP4) modulates inflammation by enzymatic cleavage of immunoregulatory peptides and through its soluble form (sDPP4) that directly engages immune cells. Here we examine whether reduction of DPP4 activity alters inflammation. Prolonged DPP4 inhibition increases plasma levels of sDPP4, and induces sDPP4 expression in lymphocyte-enriched organs in mice. Bone marrow transplantation experiments identify hematopoietic cells as the predominant source of plasma sDPP4 following catalytic DPP4 inhibition. Surprisingly, systemic DPP4 inhibition increases plasma levels of inflammatory markers in regular chow-fed but not in high fat-fed mice. Plasma levels of sDPP4 and biomarkers of inflammation are lower in metformin-treated subjects with type 2 diabetes (T2D) and cardiovascular disease, yet exhibit considerable inter-individual variation. Sitagliptin therapy for 12 months reduces DPP4 activity yet does not increase markers of inflammation or levels of sDPP4. Collectively our findings dissociate levels of DPP4 enzyme activity, sDPP4 and biomarkers of inflammation in mice and humans.

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 roles of dipeptidyl peptidase-4 and its inhibitors in the regulation of airway epithelial-mesenchymal transition

Objective: Dipeptidyl peptidase 4 (DPP4), also known as CD26, is a transmembrane glycoprotein with peptidase activity expressed on epithelial cells and some immune cells. It also occurs as a soluble form. Studies have revealed that the expression level of lymphocyte sCD26/sDPP4 was elevated in the asthmatic patients. Airway remodeling increases in asthma severity and these structural changes include, amongst others, the loss of epithelial integrity because of cell shedding, goblet cell hyperplasia, destruction of ciliated cells, and EMT. So we try to find whether sCD26/sDPP4 has a role in pathological/dysregulated transition from bronchial epithelial cells into fibroblasts cells in response to TGFβ1 exposure in vitro. Therefore, our purpose in the present work was to identify the role of sCD26/sDPP4 in airway EMT regulation. Methods: The EMT cell model was established based on human 16HBE cells. The effects of sCD26/sDPP4 and its inhibitors on airway EMT and that of sCD26/sDPP4 on Th17/IL-17 and its role in airway EMT were investigated in vitro. Results: The mRNA and protein level of E-Cadherin decreased after the treatment of TGF-β1 in 16HBE cells, while α-SMA was up-regulated. The level of E-Cadherin was significantly down-regulated after the sCD26/sDPP4 stimulation, and that of α-SMA was dramatically elevated. DPP4 inhibitors promoted the level of E-cadherin and inhibited that of α-SMA. Additionally, in the DPP4-treated IL-17 cells group, E-Cadherin was markedly down-regulated at the mRNA and protein level, while α-SMA was reversely up-regulated. Conclusion: The TGF-β1-induced EMT of human bronchial epithelial cells could be promoted by sCD26/sDPP4. The suppression of EMT in human bronchial epithelial cells was achieved by DPP4 inhibitor, and the TGF-β1-mediated EMT of human airway cells was promoted by the synergy of IL-17 and sCD26/sDPP4 in vitro.

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 at the Interface Between Inflammation and Metabolism

Dipeptidyl peptidase-4 (DPP4) is a serine protease that rapidly inactivates the incretin peptides, glucagon-like peptide-1, and glucose-dependent insulinotropic polypeptide to modulate postprandial islet hormone secretion and glycemia. Dipeptidyl peptidase-4 also has nonglycemic effects by controlling the progression of inflammation, which may be mediated more through direct protein-protein interactions than catalytic activity in the context of nonalcoholic fatty liver disease (NAFLD), obesity, and type 2 diabetes (T2D). Failure to resolve inflammation resulting in chronic subclinical activation of the immune system may influence the development of metabolic dysregulation. Thus, through both its cleavage and regulation of the bioactivity of peptide hormones and its influence on inflammation, DPP4 exhibits a diverse array of effects that can influence the progression of metabolic disease. Here, we highlight our current understanding of the complex biology of DPP4 at the intersection of inflammation, obesity, T2D, and NAFLD. We compare and review new mechanisms identified in basic laboratory and clinical studies, which may have therapeutic application and relevance to the pathogenesis of obesity and T2D.

Degranulation of human cytotoxic lymphocytes is a major source of proteolytically active soluble CD26/DPP4

Dipeptidyl peptidase 4 (DPP4, CD26) is a serine protease detected on several immune cells and on epithelial cells of various organs. Besides the membrane-bound enzyme, a catalytically active soluble form (sCD26/DPP4) is detected in several body fluids. Both variants cleave off dipeptides from the N-termini of various chemokines, neuropeptides, and hormones. CD26/DPP4 plays a fundamental role in the regulation of blood glucose levels by inactivating insulinotropic incretins and CD26/DPP4 inhibitors are thus routinely used in diabetes mellitus type 2 therapy to improve glucose tolerance. Such inhibitors might also prevent the CD26/DPP4-mediated inactivation of the T-cell chemoattractant CXCL10 released by certain tumors and thus improve anti-tumor immunity and immunotherapy. Despite its implication in the regulation of many (patho-)physiological processes and its consideration as a biomarker and therapeutic target, the cellular source of sCD26/DPP4 remains highly debated and mechanisms of its release are so far unknown. In line with recent reports that activated T lymphocytes could be a major source of sCD26/DPP4, we now demonstrate that CD26/DPP4 is stored in secretory granules of several major human cytotoxic lymphocyte populations and co-localizes with effector proteins such as granzymes, perforin, and granulysin. Upon stimulation, vesicular CD26/DPP4 is rapidly translocated to the cell surface in a Ca2+-dependent manner. Importantly, activation-induced degranulation leads to a massive release of proteolytically active sCD26/DPP4. Since activated effector lymphocytes serve as a major source of sCD26/DPP4, these results might explain the observed disease-associated alterations of sCD26/DPP4 serum levels and also indicate a so far unknown role of CD26/DPP4 in lymphocyte-mediated cytotoxicity.

The perceptions of natural compounds against dipeptidyl peptidase 4 in diabetes: from in silico to in vivo

Dipeptidyl peptidase IV (DPP-4), an incretin glucagon-like peptide-1 (GLP-1) degrading enzyme, contains two forms and it can exert various physiological functions particular in controlling blood glucose through the action of GLP-1. In diabetic use, the DPP-4 inhibitor can block the DDP-4 to attenuate GLP-1 degradation and prolong GLP-1 its action and sensitize insulin activity for the purpose of lowering blood glucose. Nonetheless the adverse effects of DPP-4 inhibitors severely hinder their clinical applications, and notably there is a clinical demand for novel DPP-4 inhibitors from various sources including chemical synthesis, herbs, and plants with fewer side effects. In this review, we highlight various strategies, namely computational biology (in silico), in vitro enzymatic and cell assays, and in vivo animal tests, for seeking natural DPP-4 inhibitors from botanic sources including herbs and plants. The pros and cons of all approaches for new inhibitor candidates or hits will be under discussion.

Expansion of different subpopulations of CD26-/low T cells in allergic and non-allergic asthmatics

CD26 displays variable levels between effector (TH₁₇ ≫ TH₁ > TH₂ > Treg) and naïve/memory (memory > naïve) CD4⁺ T lymphocytes. Besides, IL-6/IL⁻6R is associated with TH₁₇-differentiation and asthma severity. Allergic/atopic asthma (AA) is dominated by TH₂ responses, while TH₁₇ immunity might either modulate the TH₂-dependent inflammation in AA or be an important mechanism boosting non-allergic asthma (NAA). Therefore, in this work we have compared the expression of CD26 and CD126 (IL-6Rα) in lymphocytes from different groups of donors: allergic (AA) and non-allergic (NAA) asthma, rhinitis, and healthy subjects. For this purpose, flow cytometry, haematological/biochemical, and in vitro proliferation assays were performed. Our results show a strong CD26-CD126 correlation and an over-representation of CD26⁻ subsets with a highly-differentiated effector phenotype in AA (CD4⁺CD26^−/low T cells) and NAA (CD4⁻CD26⁻ γδ-T cells). In addition, we found that circulating levels of CD26 (sCD26) were reduced in both AA and NAA, while loss of CD126 expression on different leukocytes correlated with higher disease severity. Finally, selective inhibition of CD26-mRNA translation led to enhanced T cell proliferation in vitro. These findings support that CD26 down-modulation could play a role in facilitating the expansion of highly-differentiated effector T cell subsets in asthma.

CD26/DPP4 - a potential biomarker and target for cancer therapy

CD26/dipeptidyl peptidase (DPP)4 is a membrane-bound protein found in many cell types of the body, and a soluble form is present in body fluids. There is longstanding evidence that various primary tumors and also metastases express CD26/DPP4 to a variable extent. By cleaving dipeptides from peptides with a proline or alanine in the penultimate position at the N-terminus, it regulates the activity of incretin hormones, chemokines and many other peptides. Due to these effects and interactions with other molecules, a tumor promoting or suppressing role can be attributed to CD26/DPP4. In this review, we discuss the existing evidence on the expression of soluble or membrane-bound CD26/DPP4 in malignant diseases, along with the most recent findings on CD26/DPP4 as a therapeutic target in specific malignancies. The expression and possible involvement of the related DPP8 and DPP9 in cancer are also reviewed. A higher expression of CD26/DPP4 is found in a wide variety of tumor entities, however more research on CD26/DPP4 in the tumor microenvironment is needed to fully explore its use as a tumor biomarker. Circulating soluble CD26/DPP4 has also been studied as a cancer biomarker, however, the observed decrease in most cancer patients does not seem to be cancer specific. Encouraging results from experimental work and a recently reported first phase clinical trial targeting CD26/DPP4 in mesothelioma, renal and urological tumors pave the way for follow-up clinical studies, also in other tumor entities, possibly leading to the development of more effective complementary therapies against cancer.

Circulating Levels of Soluble Dipeptidyl Peptidase-4 Are Dissociated from Inflammation and Induced by Enzymatic DPP4 Inhibition

Dipeptidyl peptidase-4 (DPP-4) controls glucose homeostasis through enzymatic termination of incretin action. We report that plasma DPP-4 activity correlates with body weight and fat mass, but not glucose control, in mice. Genetic disruption of adipocyte Dpp4 expression reduced plasma DPP-4 activity in older mice but did not perturb incretin levels or glucose homeostasis. Knockdown of hepatocyte Dpp4 completely abrogated the obesity-associated increase in plasma DPP-4 activity, reduced liver cytokine expression, and partially attenuated inflammation in adipose tissue without changes in incretin levels or glucose homeostasis. In contrast, circulating levels of soluble DPP4 (sDPP4) were dissociated from inflammation in mice with endothelial-selective or global genetic inactivation of Dpp4. Remarkably, inhibition of DPP-4 enzymatic activity upregulated circulating levels of sDPP4 originating from endothelial or hematopoietic cells without inducing systemic or localized inflammation. Collectively, these findings reveal unexpected complexity in regulation of soluble versus enzymatic DPP-4 and control of inflammation and glucose homeostasis.

Polyalthia Clerodane Diterpene Potentiates Hypoglycemia via Inhibition of Dipeptidyl Peptidase 4

Serine protease dipeptidyl peptidase 4 (DPP-4) is involved in self/non-self-recognition and insulin sensitivity. DPP-4 inhibitors are conventional choices for diabetic treatment; however, side effects such as headache, bronchus infection, and nasopharyngitis might affect the daily lives of diabetic patients. Notably, natural compounds are believed to have a similar efficacy with lower adverse effects. This study aimed to validate the DPP-4 inhibitory activity of clerodane diterpene 16-hydroxycleroda-3,13-dien-15,16-olide (HCD) from Polyalthia longifolia, rutin, quercetin, and berberine, previously selected through molecular docking. The inhibitory potency of natural DPP-4 candidates was further determined by enzymatic, in vitro Caco-2, and ERK/PKA activation in myocyte and pancreatic cells. The hypoglycemic efficacy of the natural compounds was consecutively analyzed by single-dose and multiple-dose administration in diet-induced obese diabetic mice. All the natural-compounds could directly inhibit DPP-4 activity in enzymatic assay and Caco-2 inhibition assay, and HCD showed the highest inhibition of the compounds. HCD down-regulated LPS-induced ERK phosphorylation in myocyte but blocked GLP-1 induced PKA expression. For in vivo tests, HCD showed hypoglycemic efficacy only in single-dose administration. After 28-days administration, HCD exhibited hypolipidemic and hepatoprotective efficacy. These results revealed that HCD performed potential antidiabetic activity via inhibition of single-dose and long-term administrations, and could be a new prospective anti-diabetic drug candidate.