Dipeptidyl Peptidase Activity Research Articles

Chickpea proteins are potential sources of bioactive peptides that induce glucose uptake via AMP-activated protein kinase

Food proteins are a critical source of nutraceutical bioactive peptides that promote health and prevent diseases. Legume seed proteins have been extensively studied to produce peptides with diverse biological activities. Several legume protein hydrolysates and bioactive peptides have been identified that inhibit the activity of α-amylase, α-glucosidase, and dipeptidyl peptidase IV for the purpose of preventing diabetes. Herein, we observed that chickpea peptides (CPP), prepared using the enzymatic digestion of chickpea protein, induced glucose uptake in C2C12 myotubes. Further, liquid chromatography-tandem mass spectrometry and 2-deoxyglucose uptake assay were used to identify a bioactive CPP, defined as CPP737, REGDIIAVPTGVVF, a part of the legumin A-like protein. CPP737 induced AMP-activated protein kinase phosphorylation and glucose transporter type 4 membrane translocation, but not protein kinase B in C2C12 myotubes. Thus, chickpea protein is a potential source of bioactive peptides that can prevent insulin resistance and hyperglycemia through glucose uptake in the skeletal muscle.

Distinguishing two distinct types of salivary extracellular vesicles: a potential tool for understanding their pathophysiological roles.

Extracellular vesicles (EVs), which are found in almost all cells and human body fluids, are currently being studied as a source of pathophysiological information. Previously, we demonstrated that at least two types of EVs can be isolated from human whole saliva (WS) using enzymatic activity of dipeptidyl peptidase IV (DPP IV) as a marker for differentiating the EV subsets. In the present study, EV fractions, termed EV-I 20 k-ppt and EV-II 100 k-ppt, were prepared by a combination of size-exclusion chromatography of improved condition and sequential centrifugation. The EV-I 20 k-ppt fraction contained medium/large EVs with a diameter of 100-1,000nm, including aminopeptidase N (APN), mucin 1, ezrin, and Annexin A1. EV-II 100 k-ppt contained small EVs with a diameter of 20-70nm, with DPP IV and CD9, programmed cell death 6-interacting protein, and tumor susceptibility gene 101 as characteristic proteins. Proteomic analyses also revealed distinctive repertoires of constituent proteins. Immunoprecipitation of several membrane proteins of the EVs with respective antibodies suggested their differential local membrane environment between the two types of salivary vesicles. Thus, we identified two distinctive types of EVs, one is APN/MUC1- rich EVs (EV-I, large/medium EVs) and the other is DPP IV/CD9-rich EVs (EV-II, small EVs). Furthermore, analysis of the binding of the EVs to coronavirus spike proteins showed that EV-II 100 k-ppt, but not EV-I 20 k-ppt, significantly bound to the spike protein of Middle East respiratory syndrome coronavirus (MERS-CoV). Finally, we developed a simple method to prepare two distinctive EVs from only 1mL of human WS using sequential immunoprecipitation. Elucidating the features and functions of these two types of salivary EVs may help us understand their pathophysiological roles in the oral cavity and gastrointestinal tract.

Anti-diabetic properties of brewer's spent yeast peptides. In vitro, in silico and ex vivo study after simulated gastrointestinal digestion.

Brewer's spent yeast (BSY) hydrolysates are a source of antidiabetic peptides. Nevertheless, the impact of in vitro gastrointestinal digestion of BSY derived peptides on diabetes has not been assessed. In this study, two BSY hydrolysates were obtained (H1 and H2) using β-glucanase and alkaline protease, with either 1 h or 2 h hydrolysis time for H1 and H2, respectively. These hydrolysates were then subjected to simulated gastrointestinal digestion (SGID), obtaining dialysates D1 and D2, respectively. BSY hydrolysates inhibited the activity of α-glucosidase and dipeptidyl peptidase IV (DPP-IV) enzymes. Moreover, although D2 was inactive against these enzymes, D1 IC50 value was lower than those found for the hydrolysates. Interestingly, after electrophoretic separation, D1 mannose-linked peptides showed the highest α-glucosidase inhibitory activity, while non-glycosylated peptides had the highest DPP-IV inhibitory activity. Kinetic analyses showed a non-competitive mechanism in both cases. After peptide identification, GILFVGSGVSGGEEGAR and IINEPTAAAIAYGLDK showed the highest in silico anti-diabetic activities among mannose-linked and non-glycosylated peptides, respectively (AntiDMPpred score: 0.70 and 0.77). Molecular docking also indicated that these peptides act as non-competitive inhibitors. Finally, an ex vivo model of mouse jejunum organoids was used to study the effect of D1 on the expression of intestinal epithelial genes related to diabetes. The reduction of the expression of genes that codify lactase, sucrase-isomaltase and glucose transporter 2 was observed, as well as an increase in the expression of Gip (glucose-dependent insulinotropic peptide) and Glp1 (glucagon-like peptide 1). This is the first report to evaluate the anti-diabetic effect of BSY peptides in mouse jejunum organoids.

Potential elevation of exopeptidase activity of Glu-specific endopeptidase I/GluV8 mediated by hydrophobic P1′-position amino acid residue

We recently reported that the activities of dipeptidyl-peptidase (DPP)7 and DPP11, S46-family exopeptidases were significantly elevated by the presence of prime-side amino acid residues of substrates caused by an increase in kcat [Ohara-Nemoto Y. et al., J Biol Chem 298(3):101585. doi: 10.1016/j.jbc.2022]. In the present study, the effects of prime-side residues on Glu-specific endopeptidase I/GluV8 from Staphylococcus aureus were investigated using a two-step cleavage method with tetrapeptidyl-methycoumaryl-7-amide (MCA) carrying P2- to P2′-position residues coupled with DPP11 as the second enzyme. GluV8 showed maximal activity toward benzyloxycarbonyl (Z)-LLE-MCA, while the effects of hydrolysis of substrates one residue shorter, such as acetyl (Ac)-Val-Glu- and Leu-Glu-MCA, were negligible. Nevertheless, activity towards Ac-VE-|-ID-MCA, a substrate carrying P1′ and P2′ residues, emerged and reached a level 44 % of that for Z-LLE-MCA. Among 11 Ac-HAXD-MCA (X is a varied amino acid), the highest level of activity enhancement was achieved with P1′-Leu and Ile, followed by Phe, Val, Ser, Tyr, and Ala, while Gly and Lys showed scant effects. This activation order was in parallel with the hydrophobicity indexes of these amino acids. The prime-side residues increased kcat/KM primarily through a maximum 500-fold elevation of kcat as well as S46-family exopeptidases. The MEROPS substrate database also indicates a close relationship between activity and hydrophobicity of the P1′ residues in 93 N-terminal-truncated substrates, though no correlation was observed among all 4328 GluV8 entities examined. Taken together, these results are the first to demonstrate N-terminal exopeptidase activity of GluV8, considered to be prompted by hydrophobic P1′ amino acid residues.

CXCR2 inhibition overcomes ponatinib intolerance by eradicating chronic myeloid leukemic stem cells through PI3K/Akt/mTOR and dipeptidylpeptidase Ⅳ (CD26)

This study explores the therapeutic potential of targeting CXCR2 in patients afflicted with ponatinib-resistant chronic myeloid leukemia (CML). Ponatinib, a third-generation tyrosine kinase inhibitor (TKI), was initially designed for treating patients with CML harboring the T315I mutation. However, resistance or intolerance issues may lead to treatment discontinuation. Additionally, TKIs have exhibited limitations in eradicating quiescent CML stem cells. Our investigation reveals the activation of CXC chemokine receptor 2 (CXCR2) signaling in response to chemotherapeutic stress. Treatment with the CXCR2 antagonist, SB225002, effectively curtails cell proliferation and triggers apoptosis in ponatinib-resistant CML cells. SB225002 intervention also results in the accumulation of reactive oxygen species and disruption of mitochondrial function, phenomena associated with TKI chemoresistance and apoptosis. Furthermore, we demonstrate that activated CXCR2 expression induces the activity of dipeptidylpeptidase Ⅳ (DPP4/CD26), a CML leukemic stem cell marker, and concomitantly inhibits the PI3K/Akt/mTOR pathway cascades. These findings underscore the novel role of CXCR2 in the regulation of not only ponatinib-resistant CML cells, but also CML leukemic stem cells. Consequently, our study proposes that targeting CXCR2 holds promise as a viable therapeutic strategy for addressing patients with CML grappling with ponatinib resistance.

The Activity of Adenosine Deaminase and Dipeptidyl Peptidase IV in Children With Attention Deficit Hyperactivity Disorder

Objective: In this study, to investigate the place of T cell-mediated immunity in the etiology of ADHD, for which we do not have enough information; we aimed to investigate the activity of DPP IV and ADA, which are T cell-related enzymes, and the relationship of these enzymes with ADHD symptoms in children with ADHD. Methods: Twenty-seven children aged 6 to 12 years with a diagnosis of attention deficit hyperactivity disorder and 27 children aged 6 to 12 years without any psychiatric disease were included in the study. Results: While serum ADA and DPP-IV activity were found to be statistically significantly higher in the group with ADHD. There was no statistically significant correlation between serum ADA and DPP-IV activities and CTRS-R-L and CPRS-R-L in both groups. Conclusion: We think that T cell mediated inflammation may play a role in the etiology of ADHD due to changes in ADA and DPP-IV levels in children.

Cathepsin C: structure, function, and pharmacological targeting

Cathepsin C is a papain-like cysteine peptidase known primarily for its involvement in the activation of serine peptidases in neutrophils and other immune cells. Its critical role in this process qualifies cathepsin C as a target for the treatment of inflammatory diseases, and its most advanced inhibitor, brensocatib (Insmed), is currently in phase 3 clinical trials for the treatment of non-cystic fibrosis bronchiectasis. Beyond neutrophils, its importance is highlighted by loss-of-function mutations that cause the recessively inherited Papillon-Lefèvre syndrome. At the molecular level, cathepsin C has several structural and functional features that set it apart from other members of the family and enable its selective targeting. It possesses dipeptidyl-peptidase activity (its other common name is dipeptidyl-peptidase I) due to the presence of an additional exclusion domain that also controls its stepwise tetramerization during maturation. In this review article, we summarize the current state of the art regarding the biochemical properties of cathepsin C, its physiological and pathological roles in neutrophils and beyond, and recent advances in the development and evaluation of cathepsin C inhibitors.

DPP4 inhibition impairs senohemostasis to improve plaque stability in atherosclerotic mice.

Senescent vascular smooth muscle cells (VSMCs) accumulate in the vasculature with age and tissue damage, and secrete factors that promote atherosclerotic plaque vulnerability and disease. Here, we report increased levels and activity of dipeptidyl peptidase 4 (DPP4), a serine protease, in senescent VSMCs. Analysis of the conditioned media from senescent VSMCs revealed a unique senescence-associated secretory phenotype (SASP) signature comprising many complement and coagulation factors; silencing or inhibiting DPP4 reduced these factors and increased cell death. Serum samples from persons with high risk for cardiovascular disease contained high levels of DPP4-regulated complement and coagulation factors. Importantly, DPP4 inhibition reduced senescent cell burden and coagulation and improved plaque stability, while single-cell resolution of senescent VSMCs reflected the senomorphic and senolytic effects of DPP4 inhibition in murine atherosclerosis. We propose that DPP4-regulated factors could be exploited therapeutically to reduce senescent cell function, reverse senohemostasis, and improve vascular disease.

Establishment of FAP-overexpressing Cells for FAP-targeted Theranostics.

Fibroblast activation protein (FAP) has been widely studied and exploited for its clinical applications. One of the difficulties in interpreting reports of FAP-targeted theranostics is due to the lack of accurate controls, making the results less specific and less confirmative. This study aimed to establish a pair of cell lines, in which one highly expresses FAP (HT1080-hFAP) and the other has no detectable FAP (HT1080-vec) as control, to accurately evaluate the specificity of the FAP-targeted theranostics in vitro and in vivo. The cell lines of the experimental group (HT1080-hFAP) and no-load group (HT1080-vec) were obtained by molecular construction of the recombinant plasmid pIRES-hFAP. The expression of hFAP in HT1080 cells was detected by PCR, Western blotting and flow cytometry. CCK-8, Matrigel transwell invasion assay, scratch test, flow cytometry and immunofluorescence were used to verify the physiological function of FAP. The activities of human dipeptidyl peptidase (DPP) and human endopeptidase (EP) were detected by ELISA in HT1080-hFAP cells. PET imaging was performed in bilateral tumor-bearing nude mice models to evaluate the specificity of FAP. RT-PCR and Western blotting demonstrated the mRNA and protein expression of hFAP in HT1080-hFAP cells but not in HT1080-vec cells. Flow cytometry confirmed that nearly 95% of the HT1080-hFAP cells were FAP positive. The engineered hFAP on HT1080 cells had its ability to retain enzymatic activities and a variety of biological functions, including internalization, proliferation-, migration-, and invasion-promoting activities. The HT1080-hFAP xenografted tumors in nude mice bound and took up 68GA-FAPI-04 with superior selectivity. High image contrast and tumor-organ ratio were obtained by PET imaging. The HT1080-hFAP tumor retained the radiotracer for at least 60 min. This pair of HT1080 cell lines was successfully established, making it feasible for accurate evaluation and visualization of therapeutic and diagnostic agents targeting the hFAP.

Postprandial glucose-lowering effects by sago (Metroxylon sagu Rottb.) resistant starch in spontaneously type 2 diabetes, Goto-Kakizaki rat.

Introduction: The beneficial effects of resistant starch (RS) consumption on health in terms of reducing postprandial hyperglycaemia are evident. However, the potential of local Sarawak sago RS in regulating glucose has not been extensively studied. Objectives: This study aims to identify glucose-lowering effects of Sarawak sago RS, namely native (RS2) and chemically modified (RS4). Methodology: An oral glucose tolerance test (OGTT) was performed before and after 1 month treatment with sago RS2 and RS4 in spontaneously type 2 diabetes (T2D), Goto-Kakizaki (GK) rat. The mechanisms involved were further explored by screening the in vitro inhibitory activities of α-glucosidase and dipeptidyl peptidase (DPP)-IV. Histopathology examination for pancreas, kidney and liver tissues was done in response to sago RS intake using haematoxylin and eosin (H&E) staining. Results and discussion: The incremental area under the curve (iAUC) for blood glucose in RS-treated groups was decreased and significant in RS2-treated group (p < 0.05). Improved iAUC for insulin and higher glucagon-like peptide (GLP-1) levels were observed in all RS-treated groups (p < 0.05). Both sago RS may have potential roles in regulating glucose via α- glucosidase and DPP-IV inhibitory activities by reducing intestinal glucose absorption. For histopathology, although insignificant, sago RS2 and RS4 attenuated lesion scores of pancreatic tissue whereas the liver and kidney tissues significantly showed lesser lesion scores compared to the control diabetic group suggesting the potential of RS in reducing cell degeneration. Conclusion: Findings of this study indicates that RS2 showed greater glucose-lowering effect when compared to RS4, thus the therapeutic potential in the T2D management should be further explored.

In vitro characterization of lactic acid bacterial strains isolated from fermented foods with anti-inflammatory and dipeptidyl peptidase-IV inhibition potential.

Probiotics are known to stimulate, modulate, and regulate host immune response by regulating specific sets of genes and improve glucose homeostasis through regulating dipeptidyl peptidase (DPP-IV) activity, but the mechanism behind their protective role is not clearly understood. Therefore, the present study was designed to isolate indigenous lactic acid bacterial (LAB) strains from different fermented food samples, vegetables, and human infant feces exhibiting anti-inflammatory, antioxidant, and DPP-IV inhibitory activity. A total of thirty-six Gram-positive, catalase-negative, and rod-shaped bacteria were isolated and screened for their anti-inflammatory activity using lipopolysaccharide (LPS)-induced inflammation on the murine (RAW264.7) macrophages. Among all, sixteen strains exhibited more than 90% reduction in nitric oxide (NO) production by the LPS-treated RAW264.7 cells. Prioritized strains were characterized for their probiotic attributes as per the DBT-ICMR guidelines and showed desirable probiotic attributes in a species and strain-dependent manner. Accordingly, Lacticaseibacillus rhamnosus LAB3, Levilactobacillus brevis LAB20, Lactiplantibacillus plantarum LAB31, Pediococcus acidilactici LAB8, and Lactiplantibacillus plantarum LAB39 were prioritized. Furthermore, these strains when co-supplemented with LPS and treated on RAW264.7 cells inhibited the mitogen-activated protein kinases (MAPKs), i.e., p38 MAPK, ERK1/2, and SAPK/JNK, cyclooxygenase-2 (COX-2), relative to the LPS-alone-treated macrophages. LAB31 and LAB39 also showed 64 and 95% of DPP-IV inhibitory activity relative to the Lacticaseibacillus rhamnosus GG ATCC 53103, which was used as a reference strain in all the studies. Five prioritized strains ameliorated the LPS-induced inflammation by downregulating the JNK/MAPK pathway and could be employed as an alternative bio-therapeutic strategy in mitigating gut-associated inflammatory conditions. The potential mechanism of action of prioritized LAB strains in preventing the LPS-induced inflammation in RAW 264.7 macrophage cells.

Comprehensive Evaluation of Probiotic Property, Hypoglycemic Ability and Antioxidant Activity of Lactic Acid Bacteria.

Taking lactic acid bacteria is an important strategy to alleviate or prevent diabetes, but the candidate strains with good genetic stability and excellent functions still need to be supplemented. In this study, the hypoglycemic ability (α-amylase, α-glucosidase and dipeptidyl peptidase 4), probiotic property and antioxidant activity of lactic acid bacteria were comprehensively evaluated by a principal component analysis (PCA) and analytic hierarchy process (AHP). The results showed that Lactobacillus paracasei (L. paracasei) had a higher survival rate (82.78%) in gastric juice and good tolerance to bile salt, and can be colonized in HT-29 cells. L. paracasei had a remarkable inhibitive activity of α-amylase (82.21%), α-glucosidase (84.29%) and dipeptidyl peptidase 4 (42.51%). L. paracasei had better scavenging activity of free radicals, total antioxidant activity (FRAP) and superoxide dismutase activity. According to the scores of the PCA, L. paracasei had the best hypoglycemic ability, and Lactococcus lactis (L. lactis) had the highest probiotic property. According to AHP, L. paracasei was the best potential hypoglycemic probiotic; furthermore, L. lactis showed the highest comprehensive performance except Lactobacillus. All lactic acid bacteria in this test had good safety. L. paracasei is expected to become a new potential hypoglycemic strain.

Analysis of the Structure and Activity of Dipeptidyl Peptidase IV (DPP-IV) Inhibitory Oligopeptides from Sorghum Kafirin.

Potential dipeptidyl peptidase IV (DPP-IV) inhibitory oligopeptides from sorghum kafirin were developed using in silico and in vitro methodologies for the management of diabetes. Twenty-eight peptides with 5-10 residues were identified from the papain hydrolysates of sorghum kafirin. Sixteen nontoxic DPP-IV inhibitory peptides were screened with a computer method based on molecular docking. Molecular docking revealed that LPFYPQ (LP6), GPVTPPILG (GP9), and LPFYPQGV (LP8) effectively inactivated DPP-IV by binding to its active sites with a low interaction energy. An in silico analysis of these three inhibitory oligopeptides indicated that they were all bound to the S1 and S2 active pockets of DPP-IV through hydrogen bonds and hydrophobic interactions. The in vitro inhibitory activity was also verified. The DPP-IV inhibitory activities of LP6 and LP8 decreased after gastric digestion and remained stable after intestinal digestion, and the GP9 inhibitory activity remained stable after gastrointestinal digestion. Experimental results from Caco-2 cells showed further inhibitory effects of oligopeptides on DPP-IV. The results are relevant to the exploration of biofunctional DPP-IV inhibitory peptides from sorghum as a treatment for patients with diabetes or in medical research.

7-Aminocoumarin-4-acetic Acid as a Fluorescent Probe for Detecting Bacterial Dipeptidyl Peptidase Activities in Water-in-Oil Droplets and in Bulk.

Droplet-based microfluidic systems are a powerful tool for biological assays with high throughput. Water-in-oil droplets (WODLs) are typically used in droplet-based microfluidic systems to culture microorganisms and perform enzyme assays. However, because of the oil surrounding the nanoliter and picoliter volumes of WODLs, availability of suitable substrates is limited. For instance, although 7-amino-4-methylcoumarin (AMC) is commonly used as a fluorescent probe of the substrate to detect peptidase activity, AMC leaks from WODLs to the oil phase due to its high hydrophobicity. Thus, AMC substrates cannot be used in droplet-based microfluidic systems with WODLs. In this study, we developed a peptidase substrate consisting of a dipeptide and 7-aminocoumarin-4-acetic acid (ACA), an AMC-derived fluorogenic compound. ACA was retained in the WODL for more than 7 days, and the dipeptidyl ACA substrate detected dipeptidyl peptidase (DPP) activity in the WODL. Compared to AMC substrates, the substrate specificity constants of DPPs for ACA substrates increased up to 4.7-fold. Fluorescence-activated droplet sorting made high-throughput screening of microorganisms based on DPP activity using the dipeptidyl ACA substrate possible. Since ACA could be applied to various substrates as a fluorescent probe, detectable microbial enzyme activities for droplet-based microfluidic systems can be largely expanded.

β-lactoglobulin peptides obtained by chymotrypsin hydrolysis

Objective: Whey proteins, as β-lactoglobulin, have biological activity. Controlled hydrolysis of this protein could generate peptides with some biological function. The aim of this work was to analyze the peptides resulting from the in vitro hydrolysis with chymotrypsin in order to evaluate the presence of bioactive peptides.&#x0D; Design/methodology/approach: Chymotrypsin was used in the hydrolysis of β-lactoglobulin, and its peptides were evaluated by ultrafiltration, electrophoresis, and mass spectrometry.&#x0D; Findings/conclusion: Results showed that 2 h of chymotrypsin hydrolysis (T1) released peptides with molecular weight values of 8 and 9 KDa, while 4 h of hydrolysis (T2) produced peptides with molecular mass weight values of 7 and 5 KDa. The mass spectrometry (MALDI-TOF) showed six peaks and five of them were comparable with those obtained by in silico hydrolysis results (done previously by Fonseca Ayala, 2018). The identified peptides (DTDYK, DAQSAPL and LKPTPEGDL) in the fraction &lt;1 kDa showed inhibitory activity of angiotensin converting enzyme and inhibitory activity of enzyme dipeptidyl peptidase IV according BIOPEP database. These results showed that β-lactoglobulin peptides obtained by chymotrypsin hydrolysis could have biological activity that can be used in different types of industries as pharmaceutical and food.&#x0D; Limitations on study/implications: The in vitro evaluation of the biological activity of the characterized peptides is necessary.

FAP and FAPI-PET/CT in Malignant and Non-Malignant Diseases: A Perfect Symbiosis?

Simple SummaryFAPI represents a novel class of radiotracers demonstrating promising results in terms of a high uptake in concordance with low background noise in several malignancies. Thereby, FAPI-PET/CT achieves sharp contrasts facilitating staging as well as tumor delineation and detection. However, FAP is also overexpressed for several non-oncological reasons allowing for benign indications as well. This review summarizes the current state of oncological and non-oncological FAPI-PET/CT in accordance with FAP in order to highlight future perspectives and identify areas where research is urgently warranted.A fibroblast activation protein (FAP) is an atypical type II transmembrane serine protease with both endopeptidase and post-proline dipeptidyl peptidase activity. FAP is overexpressed in cancer-associated fibroblasts (CAFs), which are found in most epithelial tumors. CAFs have been implicated in promoting tumor cell invasion, angiogenesis and growth and their presence correlates with a poor prognosis. However, FAP can generally be found during the remodeling of the extracellular matrix and therefore can be detected in wound healing and benign diseases. For instance, chronic inflammation, arthritis, fibrosis and ischemic heart tissue after a myocardial infarction are FAP-positive diseases. Therefore, quinoline-based FAP inhibitors (FAPIs) bind with a high affinity not only to tumors but also to a variety of benign pathologic processes. When these inhibitors are radiolabeled with positron emitting radioisotopes, they provide new diagnostic and prognostic tools as well as insights into the role of the microenvironment in a disease. In this respect, they deliver additional information beyond what is afforded by conventional FDG PET scans that typically report on glucose uptake. Thus, FAP ligands are considered to be highly promising novel tracers that offer a new diagnostic and theranostic potential in a variety of diseases.

Transient Dexamethasone Loading Induces Prolonged Hyperglycemia in Male Mice With Histone Acetylation in Dpp-4 Promoter.

Glucocorticoid causes hyperglycemia, which is common in patients with or without diabetes. Prolonged hyperglycemia can be experienced even after the discontinuation of glucocorticoid use. In the present study, we examined the time course of blood glucose level in hospital patients who received transient glucocorticoid treatment. In addition, the mechanism of prolonged hyperglycemia was investigated by using dexamethasone (Dexa)-treated mice and cultured cells. The blood glucose level in glucose tolerance tests, level of insulin and glucagon-like peptide 1 (GLP-1), and the activity of dipeptidyl peptidase 4 (DPP-4) were examined during and after Dexa loading in mice, with histone acetylation level of the promoter region. Mice showed prolonged hyperglycemia during and after transient Dexa loading accompanied by persistently lower blood GLP-1 level and higher activity of DPP-4. The expression level of Dpp-4 was increased in the mononuclear cells and the promoter region of Dpp-4 was hyperacetylated during and after the transient Dexa treatment. In vitro experiments also indicated development of histone hyperacetylation in the Dpp-4 promoter region during and after Dexa treatment. The upregulation of Dpp-4 in cultured cells was significantly inhibited by a histone acetyltransferase inhibitor. Moreover, the histone hyperacetylation induced by Dexa was reversible by treatment with a sirtuin histone deacetylase activator, nicotinamide mononucleotide. We identified persistent reduction in blood GLP-1 level with hyperglycemia during and after Dexa treatment in mice, associated with histone hyperacetylation of promoter region of Dpp-4. The results unveil a novel mechanism of glucocorticoid-induced hyperglycemia, and suggest therapeutic intervention through epigenetic modification of Dpp-4.

High-Fat Diets Modify the Proteolytic Activities of Dipeptidyl-Peptidase IV and the Regulatory Enzymes of the Renin-Angiotensin System in Cardiovascular Tissues of Adult Wistar Rats.

(1) Background: The replacement of diets high in saturated fat (SAFA) with monounsaturated fatty acids (MUFA) is associated with better cardiovascular function and is related to the modulation of the activity of the local renin–angiotensin system (RAS) and the collagenase activity of dipeptidyl peptidase IV (DPP-IV). The objective of the work was to verify the capacity of different types of dietary fat on the regulatory activities of RAS and DPP-IV. (2) Methods: Male Wistar rats were fed for 24 weeks with three different diets: the standard diet (S), the standard diet supplemented with virgin olive oil (20%) (VOO), or with butter (20%) plus cholesterol (0.1%) (Bch). The proteolytic activities were determined by fluorometric methods in the soluble (sol) and membrane-bound (mb) fractions of the left ventricle and atrium, aorta, and plasma samples. (3) Results: With the VOO diet, angiotensinase values were significantly lower than with the Bch diet in the aorta (GluAP and ArgAP (mb)), ventricle (ArgAP (mb)) and atrium (CysAP (sol)). Significant decreases in DPP-IV (mb) activity occurred with the Bch diet in the atrium and aorta. The VOO diet significantly reduced the activity of the cardiac damage marker LeuAP (mb) in the ventricle and aorta, except for LeuAP (sol) in the ventricle, which was reduced with the Bch diet. (4) Conclusions: The introduction into the diet of a source rich in MUFA would have a beneficial cardiovascular effect on RAS homeostasis and cardiovascular functional stability.

Fortification of Maize Tortilla with an Optimized Chickpea Hydrolysate and Its Effect on DPPIV Inhibition Capacity and Physicochemical Characteristics.

Chickpea hydrolysates have shown bioactivity towards type 2 diabetes by inhibiting dipeptidyl peptidase (DPPIV) activity. The objective was to compare the effect of adding different levels of an optimized bromelain hydrolysate from chickpea isolated protein on DPPIV inhibition capacity and physicochemical properties of maize tortilla. White and blue maize tortillas, with no added chickpea hydrolysates were compared with fortified tortillas at the levels of 5%, 10%, and 15% w/w. Changes in color (L* a* b*, hue angle, and ), texture (hardness, cohesiveness, and puncture force), and moisture were tested. Soluble protein determination and SDS-PAGE electrophoresis were used to characterize the protein profiles, and LC-MS-MS was used to sequence the peptides. DPPIV inhibition was evaluated before and after simulated gastrointestinal digestion. Peptides in the hydrolysates had high hydrophobicity (7.97–27.05 kcal * mol −1) and pI (5.18–11.13). Molecular docking of peptides showed interaction with DPPIV with an energy of affinity of –5.8 kcal/mol for FDLPAL in comparison with vildagliptin (−6.2 kcal/mol). The lowest fortification level increased soluble protein in 105% (8 g/100 g tortilla). DPPIV inhibition of white maize tortilla increased from 11% (fresh control) to 91% (15% fortification), and for blue tortilla from 26% to 95%. After simulated digestion, there was not a difference between blue or maize tortillas for DPPIV inhibition. Fortification of maize tortilla with chickpea hydrolysate inhibits DPPIV and can potentially be used in the prevention and management of type 2 diabetes. However, due to observed physicochemical changes of the fortified tortilla, sensory properties and consumer acceptance need to be evaluated.

Inhibitory effects of acorn (Quercus variabilis Blume) kernel-derived polyphenols on the activities of α-amylase, α-glucosidase, and dipeptidyl peptidase IV

The chemical constituents of the free and bound polyphenols extracted from acorn kernels were analyzed, and the predominant chemical components in the free polyphenol extract were quercetin, azelaic acid, and gallic acid, while the bound polyphenol extract mainly contained ellagic acid, gallic acid, and ferulic acid. The inhibitory activities of the four main components on α-glucosidase showed the following trend: ellagic acid > quercetin > azelaic acid > gallic acid. The IC50 values of the free and bound polyphenol extracts on α-amylase were 5.25 and 1.37 mg/mL, respectively. The free polyphenol extract exhibited a greater ability to inhibit α-glucosidase and dipeptidyl peptidase IV (DPP-IV) than the bound polyphenol extract. The polyphenols were found to change the secondary structures of α-amylase, α-glucosidase and DPP-IV. The inhibitory effects of the polyphenols on the three enzymes may give rise to low postprandial blood glucose after eating acorn-containing foods and can be beneficial to diabetics.