Dipeptidyl Peptidase IV Inhibitory Activity Research Articles

Characterization of Fish Skin Hydrolysates Exhibiting Dipeptidyl Peptidase IV Inhibitory Activity

Dipeptidyl peptidase IV (DPP-IV) inhibitors are antidiabetic drugs that can lower blood sugar levels. There are still few reports on the DPP-IV inhibitory activity of peptides obtained from discarded fish skin. Therefore, we prepared various enzymatic hydrolysates using the skins of six fish species and investigated their DPP-IV inhibitory effects. As a result, it was found that the DPP-IV inhibitory activity of yellowtail hydrolysate by Alcalase was higher than that of other enzymes. In addition, the IC50 after ethanol fractionation was found to be lower in yellowtail and eel skin hydrolysate. Amino acid composition analysis showed that the hydrolysate obtained from the skin of the yellowtail contained the highest amount of Gly, followed by Pro, Hyp, and Ala, indicating that it was a peptide derived from type I collagen. Fractionation with ethanol showed that the DPP-IV inhibitory components were contained in the low molecular weight fraction. The artificial digestion test observed no DPP-IV inhibitory activity or average molecular weight change. The DPP-IV inhibitory peptide obtained from fish skin has the potential to be applied as a food material to various food products.

Enzymatic characterization and synergistic effects of protease combinations on DPP-IV inhibitory peptide release from bovine casein

This study focused on the enzymatic characteristics, with regard to primary specificity, secondary specificity, and hydrolysis ability of five proteases (Alcalase, Protamex, papain, Flavourzyme, and ProtexA), towards the release of dipeptidyl peptidase-IV (DPP-IV) inhibitory peptides from bovine casein. The secondary specificity of the five proteases, especially the release capability for Xaa-Pro-type peptide played a determining role in the release of DPP-IV inhibitory peptides from bovine casein. Moreover, protease combinations, chosen based on their Xaa-Pro-type peptide release abilities, resulted in superior DPP-IV inhibitory activity compared to other combinations. Particularly, the hydrolysate with the highest DPP-IV inhibitory activity (IC50 value of 0.45 ± 0.07 mg/mL) was obtained by the combination hydrolysis of ProtexA and papain, achieving a 74.63% ± 1.62% (peak area) release of Xaa-Pro-type peptide, and a significant improving glucose tolerance in mice (33.42% ± 1.68% reduction of blood glucose AUC compared with control mice). The mechanistic insights revealed that papain efficiently released long Xaa-Pro-type peptides in the early hydrolysis stage, and subsequently, the synergistic effect of papain and ProtexA led to an accelerated and extensive release of short Xaa-Pro-type peptides. These findings provide valuable insight into enzymatic processes for generating DPP-IV inhibiting peptides from casein.

Bioactive, textural and sensory attributes of soft confections enriched with plant protein hydrolysates

AbstractSoft confections can serve as a reservoir for bioactive peptide delivery in both functional food and food supplement applications. In this study, pectin-based soft confections were fortified with proteolytic plant protein hydrolysates and the residual bioactivity of hydrolysates was studied after processing or simulated digestion. Cold press sunflower or hazelnut cakes were used in the manufacture of protein isolates based on an alkali extraction-isoelectric precipitation (AE-IP) method. Trypsin or bromelain were utilized in the proteolysis of the isolates and thus prepared liquid hydrolysates were used in confectionery manufacture. DPP-IV (dipeptidyl peptidase-IV) inhibitory activity (i.e., in vitro antidiabetic activity) and antioxidative activities were measured. In addition, sensory and textural attributes were investigated. In all cases, a significant concentration of hydrolysates were added to the confections (27%), which lead to significant changes in color, texture and sensory acceptance. The peptide profile and size distribution mostly altered such characteristics, while observed bioactivity was significant after processing. Simulated digestion enhanced DPP-IV inhibitory activity up to approx. 40%, whereas antioxidative performance decreased. While the applicability of the current findings is limited by hydrolysate solubility, ingredient interactions, and processing costs, the relevance of degree of hydrolysis (DH%), peptide characteristics and phenolic-peptide interactions on product quality and eventual bioactivity are being discussed.

Characterization and evaluation of the in vitro and in vivo anti-diabetic activities of camel milk protein hydrolysates derived with different protease digestions

The study aimed to determine the potential anti-diabetic activities of the hydrolysates of camel milk proteins (CMPH). Camel milk proteins were hydrolyzed independently by using 11 proteases, and their anti-diabetic activities were analyzed by in vitro, and in vivo. The results showed that CMPH-Flavourzyme exhibited the best α-glucosidase and dipeptidyl peptidase-IV inhibitory activity, while CMPH-Papain exhibited the highest α-amylase inhibitory activity, and best proliferative effect on streptozotocin-induced NIT-1 cells in vitro. Furthermore, CMPH-Papain exhibited the most effect in decreasing the serum levels of fasting blood glucose, oral glucose tolerance test, pro-inflammatory factors (IL-1β, IL-6) and triglyceride, as well as increasing insulin levels on in vivo streptozotocin-induced diabetic mice. Peptides identification followed with molecular docking and network pharmacology analysis also found the potential anti-diabetic peptides from CMPH-Flavourzyme and CMPH-Papain. Our results indicated the type of protease used for the treatment significantly influences the anti-diabetic activities of the resulting CMPH.

Exploration of novel DPP-IV inhibitory peptides from discarded eggshell membrane: An integrated in silico and in vitro study

Dipeptidyl peptidase-IV (DPP-IV) inhibitory peptides exhibit great potential to alleviate type II diabetes. This study aimed to prepare, identify and explore the molecular mechanism of DPP-IV inhibitory peptides from eggshell membrane (ESM), an abundant byproduct of the food industry, based on combining in silico and in vitro assessments. In silico evaluation of ten major ESM proteins revealed the great potential of ESM as a novel source of DPP-IV inhibitors. Moreover, the optimal combined-enzymatic strategy (alkaline protease + papain) for the efficient production of DPP-IV inhibitory peptides from ESM was designed by simulated proteolysis. Corresponding with in silico predictions, in vitro assessments confirmed that sodium sulfite assisted the screened dual enzymes led to better production of DPP-IV inhibitory peptides from ESM, with preferable total nitrogen recovery (86.61% ± 4.83%), DPP-IV inhibitory activity (64.61% ± 2.75%) and total antioxidant activity (215.27 ± 1.75 μg/mL). Due to the correlation between diabetes and oxidative stress, the antioxidant and DPP-IV inhibitory activities of the hydrolysate facilitate its amelioration of diabetes. Three novel DPP-IV inhibitory peptides with high abundance in ESM hydrolysates (YPEPPPQ, HDGADVS and VTDGQPH) were identified by LC-MS/MS, in silico characterization and molecular docking. These peptides were synthesized and confirmed to possess DPP-IV inhibitory activity, potentially relating to their stable binding with key residues within the S1, S2 pockets and catalytic triad of DPP-IV via hydrogen bonding and hydrophobic interaction. Overall, this research suggests an effective and time-saving strategy to investigate novel DPP-IV inhibitory peptides from ESM, as well as opens new opportunities for ESM application in antidiabetic foods.

Mechanistic Study of Novel Dipeptidyl Peptidase IV Inhibitory Peptides from Goat's Milk Based on Peptidomics and In Silico Analysis.

Two novel dipeptidyl peptidase IV (DPP-IV) inhibitory peptides (YPF and LLLP) were discovered from goat milk protein by peptidomics, in silico analysis, and in vitro assessment. A total of 698 peptides (<23 AA) were successfully identified by LC-MS/MS from goat milk hydrolysates (hydrolyzed by papaian plus proteinase K). Then, 105 potential DPP-IV inhibitory peptides were screened using PeptideRanker, the ToxinPred tool, Libdock, iDPPIV-SCM, and sequence characteristics. After ADME, physicochemical property evaluation, and a literature search, 12 candidates were efficiently selected and synthesized in vitro for functional validation. Two peptides (YPF and LLLP) were found to exert relatively high in vitro chemical system (IC50 = 368.54 ± 12.97 μM and 213.99 ± 0.64 μM) and in situ (IC50 = 159.46 ± 17.40 μM and 154.96 ± 8.41 μM) DPP-IV inhibitory capacities, and their inhibitory mechanisms were further explored by molecular docking. Our study showed that the formation of strong non-bonding interactions with the core residues from the pocket of DPP-IV (such as ARG358, PHE357, GLU205, TYR662, TYR547, and TYR666) might primarily account for the DPP-IV inhibitory activity of two identified peptides. Overall, the two novel DPP-IV inhibitory peptides rapidly identified in this study can be used as functional food ingredients for the control of diabetes.

Preparation and identification of novel DPP-IV inhibitory peptides from Musculus senhousei: Peptidomic analysis, molecular simulation, and validation

Bioactive peptides have been considered effective alternatives for the treatment of type 2 diabetes targeting the dipeptidyl peptidase-IV (DPP-IV). In this study, novel DPP-IV inhibitory peptides were prepared and identified from Musculus senhousei through two-stage chromatographic purification, peptidomic analysis, in silico screening, and validation. Furthermore, molecular simulation was employed to analyze the interaction from a molecular perspective. Results showed that Musculus senhousei hydrolysate produced by 8 h Neutrase hydrolysis exhibited the significant DPP-IV inhibitory activity. Purification and identification led to the discovery of 387 peptide sequences. A total of 11 novel peptides with potential DPP-IV inhibitory activity were screened in silico. Further synthesis and validation of peptide activity showed that LTWR and DPF significantly inhibit DPP-IV in a competitive inhibitory manner, with IC50 values of 1788.67 ± 28.13 and 1399.73 ± 27.15 μM, respectively. Results from molecular docking and dynamic simulations indicated that peptides LTWR and DPF could tightly bind to the catalytic site of DPP-IV through hydrogen-bond and hydrophobic interaction. These findings suggested that Musculus senhousei could serve as a natural source of bioactive peptides for potential treatment of type 2 diabetes.

In Vitro Hypoglycemic Activities of Lactobacilli and Bifidobacterium Strains from Healthy Children's Sources and Their Effect on Stimulating GLP-1 Secretion in STC-1 Cells.

A long-term use of chemical drugs cannot cure type II diabetes mellitus (T2DM) and their numerous toxic side effects can be harmful to human health. In recent years, probiotics have emerged as a natural resource to replace chemical drugs in alleviating many human ailments. Healthy children's intestines have a lot of colonized Lactobacilli and Bifidobacterium, and these beneficial bacteria can help promote overall health. The objective of this study was to isolate potential antidiabetic probiotic strains from healthy children and evaluate their application prospects. Firstly, Lactobacillus and Bifidobacterium strains were isolated from healthy children's feces and identified by the pheS or clpC genes with their respective 16S rRNA genes. Then, hydrophobicity, artificial gastrointestinal fluid tolerance, α-Glucosidase and Dipeptidyl peptidase IV (DPP-IV) inhibitory activities of isolated strains were determined, and antioxidant activities and promoting secretion of GLP-1 in STC-1 cells of candidate strains were tested. Results showed that 6 strains of Lactobacillus and Bifidobacterium were obtained from the feces of healthy children aged 3 years, respectively, including Lacticaseibacillus paracasei L-21 and L-25, Levilactobacillus brevis L-16, Lentilactobacillus buchneri L-9, Lactiplantibacillus plantarum L-8 and L-3, Bifidobacterium bifidum 11-1 and B-84, Bifidobacterium longum subsp. longum 6-1, 6-2, B42 and B53. The hydrophobicity and auto-aggregation levels of all these strains were higher than 30% and 50%, respectively, and the decrease in the number of colonies of all strains in the artificial gastrointestinal fluid was less than 2 log CFU/mL. Strains L-3, L-8, L-9, L-21, 6-1, 11-1, B53 and B84 were selected based on their high α-glucosidase inhibitory activity and DPP-IV inhibitory activity, and results of the antioxidant capacity assay showed that the remaining strains all had intense comprehensive antioxidant activity. Additionally, Lacticaseibacillus paracasei L-21 and Bifidobacterium longum subsp. longum B-53 had the most substantial prompting effect on GLP-1 secretion in the STC-1 cell line. These results indicated that Lacticaseibacillus paracasei L-21 and Bifidobacterium longum subsp. longum B-53 could be used as a potential antidiabetic strain; thus, its application as a food supplement and drug ingredient could be recommended after in vivo mitigation of type II diabetes test.

Enzymatic Preparation and Processing Properties of DPP-IV Inhibitory Peptides Derived from Wheat Gluten: Effects of Pretreatment Methods and Protease Types.

The choice of appropriate proteases and pretreatment methods significantly influences the preparation of bioactive peptides. This study aimed to investigate the effects of different pretreatment methods on the hydrolytic performance of diverse proteases during the production of dipeptidyl peptidase-IV (DPP-IV) inhibitory peptides derived from wheat and their foaming and emulsion properties. Dry heating, aqueous heating, and ultrasound treatment were employed as pretreatments for the protein prior to the enzymatic hydrolysis of wheat gluten. FTIR analysis results indicated that all pretreatment methods altered the secondary structure of the protein; however, the effects of dry heating treatment on the secondary structure content were opposite to those of aqueous heating and ultrasound treatment. Nevertheless, all three methods enhanced the protein solubility and surface hydrophobicity. By using pretreated proteins as substrates, five different types of proteases were employed for DPP-IV inhibitory peptide production. The analysis of the DPP-IV inhibitory activity, degree of hydrolysis, and TCA-soluble peptide content revealed that the specific pretreatments had a promoting or inhibiting effect on DPP-IV inhibitory peptide production depending on the protease used. Furthermore, the pretreatment method and the selected type of protease collectively influenced the foaming and emulsifying properties of the prepared peptides.

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.

Microencapsulation and Peptide identification of purified bioactive fraction from spirulina protein hydrolysates with dipeptidyl peptidase IV (DPP-IV) inhibitory activity

The growing worldwide occurrence of type 2 diabetes mellitus (T2DM) necessitates the development of effective treatments. This study presents a comprehensive investigation into the inhibitory effect of trypsin-digested Spirulina protein hydrolysate (SPH) on the dipeptidyl peptidase IV (DPP-IV) enzyme, responsible for deactivating incretin hormones that stimulate insulin secretion. Following purification through hydrophobic interaction chromatography, the DPP-IV inhibition potential was enhanced, achieving a level of 74.20% ± 5.78%, with a half-maximal inhibitory concentration (IC50) value of 0.46 ± 0.16 mg/ml. By subsequently encapsulating the purified SPH within alginate and chitosan microcapsules, a controlled and sustained release profile of bioactive peptides was achieved while retaining their DPP-IV inhibitory activity. The encapsulation process exhibited an efficiency of 86.30% ± 0.16% and an efficacy of 80.65% ± 0.16% for SPH loading. Further analysis via LC-MS/MS revealed a potent peptide, GPNYASSER, derived from phycocyanin, exhibiting an IC50 value of 0.358 ± 0.188 mM. Beyond the search for specific peptides displaying strong DPP-IV inhibitory properties, the integration of SPH as function components for Type 2 Diabetes Mellitus (T2DM) management holds significant promise as a pathway for long-term preventive strategies.

Chemical and biological characterization of the DPP-IV inhibitory activity exerted by lupin (Lupinus angustifolius) peptides: From the bench to the bedside investigation.

Dipeptidyl peptidase IV (DPP-IV) is considered a key target for the diabetes treatment, since it is involved in glucose metabolism. Although lupin protein consumption shown hypoglycemic activity, there is no evidence of its effect on DPP-IV activity. This study demonstrates that a lupin protein hydrolysate (LPH), obtained by hydrolysis with Alcalase, exerts anti-diabetic activity by modulating DPP-IV activity. In fact, LPH decreased DPP-IV activity in a cell-free and cell-based system. Contextually, Caco-2 cells were employed to identify LPH peptides that can be intestinally trans-epithelial transported. Notably, 141 different intestinally transported LPH sequences were identified using nano- and ultra-chromatography coupled to mass spectrometry. Hence, it was demonstrated that LPH modulated the glycemic response and the glucose concentration in mice, by inhibiting the DPP-IV. Finally, a beverage containing 1g of LPH decreased DPP-IV activity and glucose levels in humans.

Integration of Deep Learning and Sequential Metabolism to Rapidly Screen Dipeptidyl Peptidase (DPP)-IV Inhibitors from Gardenia jasminoides Ellis.

Traditional Chinese medicine (TCM) possesses unique advantages in the management of blood glucose and lipids. However, there is still a significant gap in the exploration of its pharmacologically active components. Integrated strategies encompassing deep-learning prediction models and active validation based on absorbable ingredients can greatly improve the identification rate and screening efficiency in TCM. In this study, the affinity prediction of 11,549 compounds from the traditional Chinese medicine system's pharmacology database (TCMSP) with dipeptidyl peptidase-IV (DPP-IV) based on a deep-learning model was firstly conducted. With the results, Gardenia jasminoides Ellis (GJE), a food medicine with homologous properties, was selected as a model drug. The absorbed components of GJE were subsequently identified through in vivo intestinal perfusion and oral administration. As a result, a total of 38 prototypical absorbed components of GJE were identified. These components were analyzed to determine their absorption patterns after intestinal, hepatic, and systemic metabolism. Virtual docking and DPP-IV enzyme activity experiments were further conducted to validate the inhibitory effects and potential binding sites of the common constituents of deep learning and sequential metabolism. The results showed a significant DPP-IV inhibitory activity (IC50 53 ± 0.63 μg/mL) of the iridoid glycosides' potent fractions, which is a novel finding. Genipin 1-gentiobioside was screened as a promising new DPP-IV inhibitor in GJE. These findings highlight the potential of this innovative approach for the rapid screening of active ingredients in TCM and provide insights into the molecular mechanisms underlying the anti-diabetic activity of GJE.

DPP-IV Inhibitory Peptides from Coix Seed Prolamins: Release, Identification, and Analysis of the Interaction between Key Residues and Enzyme Domains.

Dipeptidyl peptidase IV (DPP-IV) inhibitory peptides can regulate type 2 diabetes by inhibiting the cleavage of glucagon-like peptide-1 and prolonging its half-life. The development of DPP-IV inhibitory peptides is still a hot topic. The primary structure of coix seed prolamins contains peptide sequence fragments that potentially inhibit DPP-IV; however, limited information is available regarding the extraction of peptides from coix seeds and the analysis of their conformational relationships. In this study, novel coix seed prolamin-derived peptides were obtained through single hydrolysis and double-enzyme stepwise hydrolysis. The inhibitory activity of these peptides against DPP-IV was evaluated to explore new functional properties of coix seeds. The results evidenced that the step-by-step enzymolysis (papain and alcalase) compared to single enzymolysis promoted the secondary structure disruption of the hydrolysates, enhanced the β-turn structure, significantly increased the content of peptides below 1 kDa, and exhibited a substantial increase in DPP-IV inhibitory activity (97% inhibition). Three nontoxic DPP-IV inhibitory peptides, namely, LPFYPN, TFFPQ, and ATFFPQ (IC50 = 70.24, 176.87, 268.31 μM), were isolated and identified. All three peptides exhibited strong interactions with DPP-IV (all KA values >103). LPFYPN exhibited competitive inhibition, while TFFPQ and ATFFPQ demonstrated mixed competitive-noncompetitive inhibition. Hydrogen bonding and hydrophobic interactions were the main contributors to the coix seed prolamin peptides binding to DPP-IV. The central residue was a key amino acid in the parent peptide sequence, forming a more stable π-π stacking with residues in the active pocket, which may facilitate peptide activity. This study provides theoretical support for the development of coix seed-derived hypoglycemic peptides.

High pressure-assisted enzymatic hydrolysis promotes the release of a bi-functional peptide from cowhide gelatin with dipeptidyl peptidase IV (DPP-IV) inhibitory and antioxidant activities

The process of generating functional peptides from cowhide gelatin is challenged by inefficient enzymatic hydrolysis. In this study, the researchers attempted to enhance the hydrolysis and potential functional properties of the peptides by subjecting the cowhide gelatin to high-pressure treatment (200, 300, and 400 MPa) for 20 min, followed by enzymatic hydrolysis. The highest 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, 2,2′ azinobis(3 ethylbenzothiazoline 6 sulfonic acid) (ABTS) radical scavenging activity, and DPP-IV inhibitory activity of the hydrolysate were obtained at 200 MPa, accompanied with an increase in the content of hydrophobic, acidic, and basic amino acids (P < 0.05). Correspondingly, the high-pressure pretreatment (200 MPa) reduced the thermal stability, particle size, and morphological integrity of cowhide gelatin, with a corresponding increase in the exposure of hydrophobic regions. Altogether, these results indicated that appropriate high-pressure-assisted enzymatic hydrolysis reinforced the release of bi-functional peptides by modifying the structure of cowhide gelatin.

Bioactivity of collagen peptides derived from commercial animals: In silico investigation

Collagen peptides (CP) obtained from collagen hydrolysis have drawn much attention for their broad bioactivities, such as antioxidant, anti-inflammatory, angiotensin-converting enzyme (ACE) and dipeptidyl peptidase-IV (DPP-IV) inhibitory activities. This study employed an in silico approach to investigate the bioactivities of CP from fish, chicken, cattle, pig, yak, sheep, and donkey. BLAST analysis of amino acid sequences showed CP from mammals had comparable bioactivities but those from fish and chicken possessed different bioactivity potential due to low protein homology. In silico hydrolysis of collagen with gastrointestinal enzymes, including trypsin, pepsin, and proteinase K showed that the number of bioactive CP from chicken (922) and mammals (737–905) was higher than that from fish (544–675) because of the lower content of proline in fish collagen, but the amount of bioactive peptides percentage to the total peptides generated for tilapia was the highest (86.4%). The most common bioactivities were ACE and DPP-IV inhibitory activities. A molecular docking study showed that Thr-Phe and Gly-Phe had the strongest binding energy to enzymes involved in ACE and DPP-IV, respectively, indicating that collagen was a good source of anti-hypotensive and anti-hypoglycaemic peptides.

Processing Enhances Coix Seed Prolamins Structure and Releases Functional Peptides after Digestion: In Silico and In Vitro Studies.

Dipeptidyl peptidase-IV (DPP-IV) is a key target for the treatment of type 2 diabetes mellitus. It is possible that peptides that precisely regulate DPP-IV could be released from coix seed prolamins (CSP), but whether this happens has not yet been investigated. We performed the in silico digestion of CSP and predicted the bioactivity, absorption, transport, toxicity, and allergenicity of the resulting peptides. The simulation predicted that 47 non-toxic bioactive peptides would be released. After screening these, we found that 64.58% of them could possess DPP-IV inhibitory activity. The effect of thermal processing on the amino acid composition and structural properties of CSP was determined, and the DPP-IV inhibitory activity of its digestion-derived peptides was also assessed. The results showed that processing could change the flavour of coix seed and the supply of amino acids. After processing, the spatial conformation of CSP changed from ordered to disordered, and the peptide content and the DPP-IV inhibitory activity of its digestion products significantly increased by 19.89-30.91% and 36.84-42.02%, respectively. These results support the hypothesis that processing can change the protein structure and increase the probability that bioactive peptides will be released. They also have important implications for the development of bioactive peptides and the intensive processing of coix seeds.

Discovery of anthraquinones as DPP-IV inhibitors: Structure-activity relationships and inhibitory mechanism

Dipeptidyl peptidase IV (DPP-IV) is an integrated type II transmembrane protein that reduces endogenous insulin contents and increases plasma glucose levels by hydrolyzing glucagon-like peptide-1 (GLP-1). Inhibition of DPP-IV regulates and maintains glucose homeostasis, making it an attractive drug target for the treatment of diabetes II. Natural compounds have tremendous potential to regulate glucose metabolism. In this study, we examined the DPP-IV inhibitory activity of a series of natural anthraquinones and synthetic structural analogues on DPP-IV using fluorescence-based biochemical assays. The inhibitory efficiency differed among anthraquinone compounds with different structures. Alizarin (7), aloe emodin (11), emodin (13) emerged the outstanding inhibitory potential for DPP-IV with IC50 values lower than 5 μM. To clarifying the inhibitory mechanism, inhibitory kinetics were performed, which showed that alizarin red S (8) and 13 were effective non-competitive inhibitors of DPP-IV, while alizarin complexone (9), rhein (12), and anthraquinone-2-carboxylic acid (23) were mixed inhibitors. Emodin was determined as inhibitor with the strongest DPP-IV-binding affinity determined via molecular docking. Structure-activity relationship (SAR) demonstrated that hydroxyl group at C-1 and C-8 sites and hydroxyl, hydroxymethyl or carboxyl group at the C-2 or C-3 site were very essential for DPP-IV inhibition, replacement of hydroxyl group with amino group at C-1 could led to an increase of the inhibitory potential. Further fluorescence imaging showed that both compounds 7 and 13 significantly inhibited DPP-IV activity in RTPEC cells. Overall, the results indicated that anthraquinones would be a natural functional ingredient for inhibiting DPP-IV and provided new ideas for searching and developing potential antidiabetic compounds.

Identification of Novel Dipeptidyl Peptidase-IV Inhibitory Peptides in Chickpea Protein Hydrolysates.

Dipeptidyl peptidase-IV (DPP-IV) is one of the main targets for blood sugar control. Some food protein-derived peptides are thought to have DPP-IV inhibitory (DPP-IVi) activity. In this study, chickpea protein hydrolysates (CPHs) obtained through Neutrase hydrolysis for 60 min (CPHs-Pro-60) exhibited the highest DPP-IVi activity. DPP-IVi activity after simulated in vitro gastrointestinal digestion was maintained at >60%. Peptide libraries are established after the identification of peptide sequences. Molecular docking verified that the four screened peptides (AAWPGHPEF, LAFP, IAIPPGIPYW, and PPGIPYW) could bind to the active center of DPP-IV. Notably, IAIPPGIPYW exhibited the most potent DPP-IVi activity (half maximal inhibitory concentration (IC50): 12.43 μM). Both IAIPPGIPYW and PPGIPYW exhibited excellent DPP-IVi activity in Caco-2 cells. These results indicated that chickpea could be used as a source of natural hypoglycemic peptides for food and nutritional applications.

In vitro Investigation on Antidiabetic and Antioxidant Assessments of Partially Purified Fractions of Cassia siamea and Butea monosperma: Indigenous Myanmar Medicinal Plant

This study aimed to evaluate the antidiabetic and antioxidant potentials of fractions from Cassia siamea and Butea monosperma. The water, hexane, dichloromethane, and ethyl acetate fractions of tested plants was determined their bioactivities by hemolysis, antiglycation, alpha-glucosidase and dipeptidyl peptidase-IV (DPP-IV) inhibition, glucose uptake by yeast cells, DPPH radical scavenging, and total phenolic content determination assays. Non-hemolytic effects of all fractions were shown by < 20% on RBCs. The best inhibition activities for AGE formation of water and hexane fractions from C. siamea were shown in IC50 values (mg/mL) of 0.17 and 0.14, respectively. For B. monosperma, the EtOAc fraction exhibited the best inhibitory effect with an IC50 value of 0.10 mg/mL. The water and ethyl acetate fractions of C. siamea strongly inhibited α-glucosidase, and their IC50 values were 0.16 mg/mL and 0.17 mg/mL, respectively. Ethyl acetate fractions of B. monosperma significantly inhibited α-glucosidase, with a respective IC50 value of 0.14 mg/mL. DPP-IV inhibitory activities for water, hexane, and ethyl acetate fractions of C. siamea revealed with IC50 values of 0.11, 0.09, and 0.18 mg/mL, respectively and those of B. monosperma were 0.23, 0.13, and 0.24 mg/mL, respectively. The glucose uptake effect observed in the water and ethyl acetate fractions of B. monosperma was better than that observed in the fractions of C. siamea at tested glucose concentrations (5-25 mM). In addition, all tested fractions were very active in antioxidant capacity. This study indicated that the water fraction of C. siamea and ethyl acetate fraction of B. monosperma exhibited the best antidiabetic potential with high antioxidant power.