Rapid Identification of Dipeptidyl Peptidase-IV (DPP-IV) Inhibitory Peptides from Ruditapes philippinarum Hydrolysate

DPP-IV and FAS inhibitory peptides: therapeutic alternative against diabesity

Diabesity is a modern epidemic that indicates a strong association between obesity and diabetes. Key enzymes have been identified in the development and progression of both diseases, DPP-IV in glucose uptake and FAS in fatty acid synthesis. In both cases, the molecular mechanisms of how each one acts separately have been described, and which are the key inhibitory drugs and molecules for each one. However, although it is known that there is an association between both clinically and molecularly, the mechanism has not been elucidated; therefore, this review focuses on proposing a mechanism of convergence of DPP-IV and FAS in diabesity, and the possible mode of action in which bioactive peptides obtained from plant and animal sources can inhibit these two enzymes in a similar way as drugs do.

Rapid screening and identification of novel dipeptidyl peptidase IV inhibitory peptides from buffalo milk

BACKGROUND

Peptidomics combined with molecular docking is an effective alternative method for rapid screening of novel bioactive peptides in food. Buffalo milk as a potential source of dipeptidyl peptidase-IV (DPP-IV) inhibitory peptides has been less studied. Peptidomics and molecular docking methods were employed to rapidly screen new DPP-IV inhibitory peptides from buffalo milk. The screened DPP-IV inhibitory peptides were further verified using an in vitro inhibition assay and a Caco-2 cell assay.

RESULTS

The DPP-IV inhibition rate of buffalo milk was increased from 73.40 ± 6.01% to 97.23 ± 3.18% in an in vitro digestion assay, suggesting that buffalo milk could be a promising source of DPP-IV inhibitory peptides. Subsequently, two novel peptides (GPFPIIV and FPQYL) with potential DPP-IV inhibitory activity were screened using peptidomics, molecular docking and an in vitro inhibitory assay. The IC50 values for GPFPIIV and FPQYL were 0.2998 ± 0.03 and 0.1407 ± 0.01 mg mL-1, respectively. During simulated gastrointestinal digestion in vitro, FPQYL had an excellent digestive stability of 92.13 ± 1.03%, whereas that of GPFPIIV was 59.52 ± 2.56%. In addition, GPFPIIV and FPQYL (1.00 mg mL-1) showed significant DPP-IV inhibitory effects in a Caco-2 cell assay, with the inhibition rate increasing to 32% and 36%, respectively.

CONCLUSION

In summary, two new DPP-IV inhibitory peptides were screened from buffalo milk through a combination of peptidomics and molecular docking, both of which exhibited significant DPP-IV inhibitory activities. The identified peptides, GPFPIIV and FPQYL, have promising applications in diabetes management. © 2025 Society of Chemical Industry.

Identification of novel α-glucosidase inhibitory peptides in Meretrix meretrix Linnaeus and their inhibitory kinetics using in silico and in vitro analyses

This study aimed to identify novel peptides with α-glucosidase inhibitory activity from Meretrix meretrix Linnaeus hydrolysates (MMLHs) following simulated gastrointestinal digestion (SGD) and to elucidate their inhibitory mechanisms. The molecular weight distribution of MMLHs progressively decreased during SGD, with hydrolysates from the intestinal digestion phase (MMLHs-I) exhibiting the strongest α-glucosidase inhibition (IC50: 0.14 ± 0.02 mg/mL). A total of 127 peptides were identified in MMLHs-I, among which 58 were unique compared to those from the gastric digestion phase. In silico screening and molecular docking identified six novel peptides-FAGDDAPR, VPLF, YRRL, WDH, PPLA, and WSG-with significant α-glucosidase inhibitory activity, displaying IC50 values of 0.90, 1.30, 1.90, 1.20, 1.00, and 1.80 mg/mL, respectively. Among them, FAGDDAPR and PPLA exhibited the highest bioactivity. Kinetic analysis and fluorescence quenching assays demonstrated that both peptides acted as mixed-type inhibitors, forming stable complexes with α-glucosidase. Their inhibitory effects were primarily driven by hydrogen bonding and hydrophobic interactions, which hindered substrate binding and induced conformational changes in the enzyme. These findings suggest that peptides derived from MMLHs through gastrointestinal digestion possess potential antidiabetic properties, highlighting their promise as functional food ingredients for mitigating hyperglycemic damage.

Exploring the Antidiabetic and Antihypertensive Potential of Peptides Derived from Bitter Melon Seed Hydrolysate

BACKGROUND/OBJECTIVES

Type 2 diabetes (T2D) has become a critical global health issue, with an increasing prevalence that contributes to significant morbidity and mortality. Inhibiting dipeptidyl peptidase-IV (DPP4) is a promising strategy for managing T2D. This study aimed to explore the DPP4 inhibitory peptide derived from bitter melon seed protein (BMSP) hydrolysate.

METHODS

Reversed-phase high-performance liquid chromatography (RP-HPLC) was utilized to fractionate the hydrolysate. Peptide in the highest activity fraction was analyzed using liquid chromatography-mass spectrometry (LC-MS/MS). Peptide synthetic was used for further characterizations, such as bioactivity exploration, inhibition mechanism, molecular docking, and peptide stability against in vitro simulated gastrointestinal (SGI) digestion.

RESULTS

The BMSP hydrolysate was digested with gastrointestinal proteases (GP) and assessed for DPP4 inhibitory activity, yielding an IC50 of 1448 ± 105 μg/mL. Following RP-HPLC fractionation, MPHW (MW4) and VPSGAPF (VF7) were identified from fraction F8 with DPP4 IC50 values of 128.0 ± 1.3 µM and 150.6 ± 3.4 µM, respectively. Additionally, MW4 exhibited potential antihypertensive effects through ACE inhibition with an IC50 of 172.2 ± 10.6 µM. The inhibitory kinetics and molecular docking simulations indicated that both MW4 and VF7 were competitive inhibitors of DPP4, while MW4 was also a competitive inhibitor of ACE. Importantly, both peptides remained stable during simulated gastrointestinal digestion, suggesting their resistance to human digestive processes and their capacity to maintain biological activity.

CONCLUSIONS

The findings suggest that BMSP-GP hydrolysate may have potential in terms of the development of health foods or therapeutic agents. However, in vivo studies are also essential for further confirmation of efficacy.

Peptide array screening with anti-GLP-1 monoclonal antibody: Discovery of cysteine-containing DPP-IV inhibitory peptides

Inhibition of dipeptidyl peptidase IV (DPP-IV) is an effective pharmacotherapy for the management of type 2 diabetes. Recent findings have suggested that various dietary proteins can serve as precursors to peptides that inhibit DPP-IV. Although several DPP-IV inhibitory peptides derived from food materials have been reported, more effective inhibitory peptides remain to be discovered. This study aimed to identify potent DPP-IV inhibitory peptides that earlier approaches had overlooked by employing a screening method that combined peptide arrays and neutralizing antibodies. Octa-peptides covering the complete amino acid sequences of four casein proteins and two whey proteins were synthesized on arrays via a solid-phase method. These peptides were then reacted with a monoclonal antibody specifically engineered to recognize glucagon-like peptide 1 (GLP-1), a substrate of DPP-IV. The variable region of the anti-GLP-1 monoclonal antibody is utilized to mimic the substrate-binding region of DPP-IV, enabling the antibody to bind to peptides that interact with DPP-IV. Based on this feature, 26 peptides were selected as DPP-IV inhibitory peptide candidates, 11 of which showed strong DPP-IV inhibitory activity. Five of these peptides consistently contained cysteines positioned two to four residues from the N-terminus. Treatment with disulfide formation decreased the DPP-IV inhibitory activity of these cysteine-containing peptides, while the inhibitory activity of α-lactalbumin hydrolysates increased with reducing treatment. These results revealed that the thiol group is important for DPP-IV inhibitory activity. This study provides a useful screen for DPP-IV inhibitory peptides and indicates the importance of reductive cysteine residues within DPP-IV inhibitory peptides.

DPP-IV Inhibitory Peptide against In Vitro Gastrointestinal Digestion Derived from Goat's Milk Protein and Its Activity Enhancement via Amino Acid Substitution

Goat milk protein can release a variety of bioactive peptides after digestion, while most of them are digested into free amino acids or dipeptides via the GI tract. We investigated the peptide profiles of goat milk protein following in vitro gastrointestinal digestion using LC-MS/MS and identified 683 bioactive peptides, including 105 DPP-IV inhibitory peptides. Among these peptides, ILDKVGINY (IL), derived from β-lactoglobulin, was found to be high in content and resistance to digestion. Herein, we explore the effect of amino acid residue substitution at the second N-terminus on its DPP-IV inhibitory activity. Three 9 polypeptide fragments (peptide IL, IP, and II) were synthesized and subjected to molecular docking and activity analysis. The peptide IL demonstrated the highest affinity for DPP-IV with a binding energy of -8.4 kcal/mol and a moderate IC50 value of 1.431 mg/mL determined based on the Caco-2 cell model. The replacement of specific amino acid residues by Pro and Leu led to an increase in the hydrophobic force interaction between the inhibitor peptide and DPP-IV. The inhibition rates of the three peptides were significantly different (p < 0.05). Peptide II containing an Ile residue instead of Leu resulted in a significant enhancement of DPP-IV inhibitory activity, with an IC50 value of 0.577 mg/mL. The GRAVY changes in the three peptides were consistent with the trend of the inhibitory rates. Therefore, the GRAVY of peptides and branch-chain amino acids should be considered in its activity improvement. The present study revealed the presence and activity of DPP-IV inhibitory peptides in goat milk, providing important insights for further investigation of their potential food functionality and health benefits.

Anti-obesity and anti-diabetic bioactive peptides: A comprehensive review of their sources, properties, and techno-functional challenges

The scourge of obesity arising from obesogens and poor dieting still ravages our planet as half of the global population may be overweight and obese by 2035. This metabolic disorder is intertwined with type 2 diabetes (T2D), both of which warrant alternative therapeutic options other than clinically approved drugs like orlistat with their tendency of abuse and side effects. In this review, we comprehensively describe the global obesity problem and its connection to T2D. Obesity, overconsumption of fats, the mechanism of fat digestion, obesogenic gut microbiota, inhibition of fat digestion, and natural anti-obesity compounds are discussed. Similar discussions are made for diabetes with regard to glucose regulation, the diabetic gut microbiota, and insulinotropic compounds. The sources and production of anti-obesity bioactive peptides (AOBPs) and anti-diabetic bioactive peptides (ADBPs) are also described while explaining their structure-function relationships, gastrointestinal behaviors, and action mechanisms. Finally, the techno-functional applications of AOBPs and ADBPs are highlighted.

Bioactive Peptides from Meretrix lusoria Enzymatic Hydrolysate as a Potential Treatment for Obesity in db/db Mice

Obesity is acknowledged as a significant risk factor for cardiovascular disease, often accompanied by increased inflammation and diabetes. Bioactive peptides derived from marine animal proteins show promise as safe and effective anti-obesity agents by regulating adipocyte differentiation through the AMPK signaling pathway. Therefore, this study aims to investigate the anti-obesity and anti-diabetic effects of bioactive compounds derived from a Meretrix lusoria Protamex enzymatic hydrolysate (MLP) fraction (≤1 kDa) through a 6-week treatment (150 mg/kg or 300 mg/kg, administered once daily) in leptin receptor-deficient db/db mice. The MLP treatment significantly decreased the body weight, serum total cholesterol, triglycerides, and LDL-cholesterol levels while also exhibiting a beneficial effect on hepatic and serum marker parameters in db/db mice. A histological analysis revealed a reduction in hepatic steatosis and epididymal fat following MLP treatment. Furthermore, poor glucose tolerance was improved, and hepatic antioxidant enzyme activities were elevated in MLP-treated mice compared to db/db control mice. Western blot analysis showed an increased expression of the AMPK protein after MLP treatment. In addition, the expression of lipogenic genes decreased in db/db mice. These findings indicate that bioactive peptides, which are known to regulate blood glucose levels, lipid metabolism, and adipogenesis, could be beneficial functional food additives and pharmaceuticals.

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.

iDPPIV-SI: identifying dipeptidyl peptidase IV inhibitory peptides by using multiple sequence information

Currently, diabetes has become a great threaten for people's health in the world. Recent study shows that dipeptidyl peptidase IV (DPP-IV) inhibitory peptides may be a potential pharmaceutical agent to treat diabetes. Thus, there is a need to discriminate DPP-IV inhibitory peptides from non-DPP-IV inhibitory peptides. To address this issue, a novel computational model called iDPPIV-SI was developed in this study. In the first, 50 different types of physicochemical (PC) properties were employed to denote the peptide sequences. Three different feature descriptors including the 1-order, 2-order correlation methods and discrete wavelet transform were applied to collect useful information from the PC matrix. Furthermore, the least absolute shrinkage and selection operator (LASSO) algorithm was employed to select these most discriminative features. All of these chosen features were fed into support vector machine (SVM) for identifying DPP-IV inhibitory peptides. The iDPPIV-SI achieved 91.26% and 98.12% classification accuracies on the training and independent dataset, respectively. There is a significantly improvement in the classification performance by the proposed method, as compared with the state-of-the-art predictors. The datasets and MATLAB codes (based on MATLAB2015b) used in current study are available at https://figshare.com/articles/online_resource/iDPPIV-SI/20085878.Communicated by Ramaswamy H. Sarma.

Screening of novel DPP-IV inhibitory peptides derived from bovine milk proteins using a peptide array platform

Dipeptidyl peptidase IV (DPP-IV) has become an important target in the prevention and treatment of diabetes. Although many DPP-IV inhibitory peptides have been identified by a general approach involving the repeated fractionation of food protein hydrolysates, the obtained results have been dependent on the content of each peptide and fractionation conditions. In the present study, a peptide array that provides comprehensive assays of peptide sequences was used to identify novel DPP-IV inhibitory peptides derived from bovine milk proteins; these peptides were then compared with those identified using the general approach. While the general approach identified only known peptides that were abundant in the hydrolysate, the peptide array-based approach identified 10 novel DPP-IV inhibitory peptides, all of which had proline at the second residue from the N-terminus. The proper or combined use of these two approaches, which have different advantages, will enable the efficient development of novel bioactive foods and drugs.

Hyperglycemia effect of Pinctada martensii hydrolysate in diabetic db/db mice

ETHNOPHARMACOLOGICAL RELEVANCE

Pinctada martensii (Dunker) and other marine shellfish flesh have been traditionally used in China as folk remedies regulate blood sugar.

AIM OF THE STUDY

To investigate the main active constituents and the pharmacological mechanism of Pinctada martensii flesh enzymatic hydrolysate (PMH) against T2DM.

MATERIALS AND METHODS

The hypoglycemic activity of enzymolysis peptides from Pinctada martensii was evaluated by using db/db mice, through the influence of glycemic index, blood lipid and key protein expression of PI3K-Akt pathway. In addition, label-free quantitative proteomics was used to screen the key proteins for Pinctada martensii hydrolysate (PMH) to improve T2DM, and Western blot and qRT-PCR were used to verify the expression difference of differential proteins at protein and mRNA levels between different groups.

RESULTS

PMH were prepared and characterized. In vivo investigations revealed that the PMH could regulate blood glucose and improve glucose tolerance and insulin tolerance, reduced serum total cholesterol, triglyceride, low-density lipoprotein cholesterol levels and increase high-density lipoprotein cholesterol levels in db/db mice. Western blot results showed that PMH could up-regulate IRS-1, P-PI3K/PI3K and P-Akt/Akt levels in db/db mice. Label-free quantitative proteomic approach was used to analyze the proteome in db/db mouse liver, 231 proteins were reversed significantly (p < 0.05), and these proteins were involved in oxidative phosphorylation, glycolysis/gluconeogenesis and other pathways. Further screened 15 proteins with FC > 1.2 could be enriched in the retinol metabolic pathway, and the proteins in this pathway were also verified.

CONCLUSIONS

PMH has hypoglycemic effect and can be used as a potential natural T2DM intervener. The hypoglycemic activity of PMH is related to its regulation of the PI3K/AKT pathway. The PI3K/AKT pathway and the retinol pathway are considered as another potential pathway for PMH to exert hypoglycemic effects.

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

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

Preparation, structural properties, and in vitro and in vivo activities of peptides against dipeptidyl peptidase IV (DPP-IV) and α-glucosidase: a general review

Diabetes is one of the fastest-growing and most widespread diseases worldwide. Approximately 90% of diabetic patients have type 2 diabetes. In 2019, there were about 463 million diabetic patients worldwide. Inhibiting the dipeptidyl peptidase IV (DPP-IV) and α-glucosidase activity is an effective strategy for the treatment of type 2 diabetes. Currently, various anti-diabetic bioactive peptides have been isolated and identified. This review summarizes the preparation methods, structure-effect relationships, molecular binding sites, and effectiveness validation of DPP-IV and α-glucosidase inhibitory peptides in cellular and animal models. The analysis of peptides shows that the DPP-IV inhibitory peptides, containing 2-8 amino acids and having proline, leucine, and valine at their N-terminal and C-terminal, are the highly active peptides. The more active α-glucosidase inhibitory peptides contain 2-9 amino acids and have valine, isoleucine, and proline at the N-terminal and proline, alanine, and serine at the C-terminal.

In silico structure-based design of peptides or proteins as therapeutic tools for obesity or diabetes mellitus: A protocol for systematic review and meta analysis

BACKGROUND

In silico studies using dynamic simulation or molecular docking have boosted the screening and identification of molecules and/or targets in studies aimed at treating diseases such as obesity and diabetes mellitus, optimizing the development of new drugs. This study aims to describe a systematic review protocol on peptides and proteins evaluated in silico as potential therapeutic agents for obesity or diabetes mellitus.

METHODS

This protocol followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses Protocols and was registered in the International Prospective Register of Systematic Reviews database (number: CRD42022355540). The databases to be searched will be PubMed, ScienceDirect, Scopus, Web of Science, virtual health library, and EMBASE. It will be included in silico studies that evaluate the simulation by dynamics or molecular docking of proteins or peptides involved in treating obesity or diabetes mellitus. Two independent reviewers will select studies, extract data, and assess methodological quality using the adapted Strengthening the reporting of empirical simulation studies. A narrative synthesis of the included studies will be performed for the systematic reviews.

RESULTS

This protocol contemplates the production of 2 systematic reviews to be developed focusing on obesity or diabetes mellitus.

CONCLUSION

The reviews will enable knowledge of peptides and proteins involved in research treating these diseases and will emphasize the importance of in silico studies in this context and for the development of future studies.

Identification, Screening, and Comprehensive Evaluation of Novel DPP-IV Inhibitory Peptides from the Tilapia Skin Gelatin Hydrolysate Produced Using Ginger Protease

PURPOSE

Inhibition of dipeptidyl peptidase-IV (DPP-IV) is an effective therapy for treating type II diabetes (T2D) that has been widely applied in clinical practice. We aimed to evaluate the DPP-IV inhibitory properties of ginger protease hydrolysate (GPH) and propose a comprehensive approach to screen and evaluate DPP-IV inhibitors.

METHODS

We evaluated the in vitro inhibitory properties of fish skin gelatin hydrolysates produced by five proteases, namely, neutral protease, alkaline protease, bromelain, papain, and ginger protease, toward DPP-IV. We screened the most potent DPP-IV inhibitory peptide (DIP) using liquid chromatography-tandem mass spectrometry (LC-MS/MS) coupled with in silico analysis. Next, surface plasmon resonance (SPR) technology was innovatively introduced to explore the interactions between DPP-IV and DIP, as well as the IC₅₀. Furthermore, we performed oral administration of DIP in rats to study its in vivo absorption.

RESULTS

GPH displayed the highest degree of hydrolysis (20.37%) and DPP-IV inhibitory activity (65.18%). A total of 292 peptides from the GPH were identified using LC-MS/MS combined with de novo sequencing. Gly-Pro-Hyp-Gly-Pro-Pro-Gly-Pro-Gly-Pro (GPXGPPGPGP) was identified as the most potent DPP-IV inhibitory peptide after in silico screening (Peptide Ranker and molecular docking). Then, the in vitro study revealed that GPXGPPGPGP had a high inhibitory effect on DPP-IV (IC₅₀: 1012.3 ± 23.3 μM) and exhibited fast kinetics with rapid binding and dissociation with DPP-IV. In vivo analysis indicated that GPXGPPGPGP was not absorbed intact but partially, in the form of dipeptides and tripeptides.

CONCLUSION

Overall, the results suggested that GPH would be a natural functional food for treating T2D and provided new ideas for searching and evaluating potential antidiabetic compounds. The obtained GPXGPPGPGP can be structurally optimized for in-depth evaluation in animal and cellular experiments.

Critical Review for the Production of Antidiabetic Peptides by a Bibliometric Approach

The current bibliometric review evaluated recent papers that researched dietary protein sources to generate antidiabetic bioactive peptides/hydrolysates for the management of diabetes. Scopus and PubMed databases were searched to extract bibliometric data and, after a systematic four-step process was performed to select the articles, 75 papers were included in this review. The countries of origin of the authors who published the most were China (67%); Ireland (59%); and Spain (37%). The journals that published most articles on the subject were Food Chemistry (n = 12); Food & Function (n = 8); and Food Research International (n = 6). The most used keywords were ‘bioactive peptides’ (occurrence 28) and ‘antidiabetic’ (occurrence 10). The most used enzymes were Alcalase^® (17%), Trypsin (17%), Pepsin, and Flavourzyme^® (15% each). It was found that different sources of protein have been used to generate dipeptidyl peptidase IV (DPP-IV), α-amylase, and α-glucosidase inhibitory peptides. In addition to antidiabetic properties, some articles (n = 30) carried out studies on multifunctional bioactive peptides, and the most cited were reported to have antioxidant and antihypertensive activities (n = 19 and 17, respectively). The present review intended to offer bibliometric data on the most recent research on the production of antidiabetic peptides from dietary proteins to those interested in their obtention to act as hypoglycemic functional ingredients. The studies available in this period, compiled, are not yet enough to point out the best strategies for the production of antidiabetic peptides from food proteins and a more systematic effort in this direction is necessary to allow a future scale-up for the production of these possible functional ingredients.

Food-derived dipeptidyl peptidase IV inhibitory peptides: Production, identification, structure-activity relationship, and their potential role in glycemic regulation

Dipeptidyl Peptidase IV (DPP-IV) inhibitory peptides are attracting increasing attention, owing to their potential role in glycemic regulation by preventing the inactivation of incretins. However, few reviews have summarized the current understanding of DPP-IV inhibitory peptides and their knowledge gaps. This paper reviews the production, identification and structure-activity relationships (SAR) of DPP-IV inhibitory peptides. Importantly, their bioavailability and hypoglycemic effects are critically discussed. Unlike the traditional method to identifying peptides after separation step by step, the bioinformatics approach identifies peptides via virtual screening that is more convenient and efficient. In addition, the bioinformatics approach was also used to investigate the SAR of peptides. Peptides with proline (Pro) or alanine (Ala) residue at the second position of N-terminal are exhibit strong DPP-IV inhibitory activity. Besides, the bioavailability of DPP-IV inhibitory peptides is related to their gastrointestinal stability and cellular permeability, and in vivo studies showed that the glucose homeostasis has been improved by these peptides. Especially, the intestinal transport of DPP-IV inhibitory peptides and cell biological assays used to evaluate their potential role in glycemic regulation are innovatively summarized. For further successful development of DPP-IV inhibitory peptides in glycemic regulation, future study should elucidate their SAR and in vivo hypoglycemic effects .

Identification and Characterization of Dipeptidyl Peptidase-IV Inhibitory Peptides from Oat Proteins

In this study, flavourzyme, papain, neutrase, and alcalase, as well as gastrointestinal digestion simulated with pepsin and pancreatin, were used to hydrolyze oat protein, and the dipeptidyl peptidase-IV (DPP-IV) inhibitory activities of the oat protein hydrolysates were investigated. The results indicated that the oat protein hydrolysate by neutrase showed the most potent DPP-IV inhibitory property with an IC50 value of 2.55 ± 0.38 mg/mL. Using UPLC-MS/MS, ten new DPP-IV inhibitory peptides were identified from the oat protein hydrolysate by neutrase. Among these peptides, IPQHY, VPQHY, VAVVPF, and VPLGGF exhibited the strongest DPP-IV inhibitory activity with IC50 values below 50 μM, and all of them acted as mixed-type inhibitors. Molecular docking indicated that the above four oat-derived peptides were predicted to form hydrogen bonds, attractive charge, and hydrophobic interactions with the residues of the active site of DPP-IV. Therefore, our results suggest that oat is an excellent protein source for food-derived DPP-IV inhibitory peptides and it has the prospect of becoming a dietary supplement for T2DM.

Exploration of Dipeptidyl Peptidase-IV (DPP-IV) Inhibitory Peptides from Silkworm Pupae (Bombyx mori) Proteins Based on In Silico and In Vitro Assessments

This study aimed at exploring dipeptidyl peptidase-IV (DPP-IV) inhibitory peptides from silkworm pupae proteins by in silico analysis and in vitro assessments. In silico analysis of 274 silkworm pupae proteomes indicated that DPP-IV inhibitory peptides can be released from silkworm pupae proteins. In vitro assessments revealed that pepsin and bromelain led to better production of DPP-IV inhibitory peptides from silkworm pupae protein. Notably, peptide fractions (<1 kDa) from pepsin- and bromelain-treated hydrolysates exhibited more potent DPP-IV inhibitory activities. Two novel DPP-IV inhibitory peptides (Leu-Pro-Pro-Glu-His-Asp-Trp-Arg and Leu-Pro-Ala-Val-Thr-Ile-Arg) were identified by LC-MS/MS with IC₅₀ values of 261.17 and 192.47 μM, respectively. Enzyme kinetics data demonstrated that these two peptides displayed a mixed-type DPP-IV inhibition mode, which was further validated by molecular docking data. Overall, in silico analysis combined with in vitro assessments can serve as an effective and rapid approach for discovery of DPP-IV peptides from silkworm pupae proteins.

Sequential changes in antioxidant activity and structure of curcumin-myofibrillar protein nanocomplex during in vitro digestion

This study aimed to investigate the in vitro digestion of curcumin-myofibrillar protein (MP) complexes characterized by antioxidant activity and structure changes. Curcumin-MP nanocomplexes were prepared by pH-shifting (from 12 to 7) method and then digested in vitro. Results showed that the protein released by dissolved nitrogen and the scavenging rates of DPPH and ABTS free radicals were enhanced significantly by the formation of nanocomplex with curcumin. During simulated digestion, curcumin can reduce the α-helix of protein, along with red shifted and significantly decreased maximum fluorescence intensity. This structural difference may change the restriction sites of MP, resulting in substantial changes in the digested products composition and 11 unique peptides with potential bioactivity appearance in the digested products of curcumin-MP complex. Our finding revealed the Curcumin-MP nanocomplexes has unique protein digestion fate which has potential application on functional enhanced food.

Generation, characterization and molecular binding mechanism of novel dipeptidyl peptidase-4 inhibitory peptides from sorghum bicolor seed protein

Food proteins and their constituent peptides impart huge health benefits besides their nutritional attributes. Sorghum bicolor protein hydrolysates (SPH) and derived bioactive peptides generated by simulated gastrointestinal digestion were studied for DPP-4 inhibitory properties using in vitro and in situ assays. Identified peptides, LSICGEESFGTGSDHIR (PEP1), SLGESLLQEDVEAHK (PEP2) and QLRDIVDK (PEP4) displayed potent DPP-4 inhibition with IC50 values of 73.5, 82.5 and 8.55 µM respectively. DPP-4 inhibition mechanism by the peptides was investigated by DPP4-peptide inhibition kinetics, molecular docking and microscale thermophoresis binding studies. The peptides bound to DPP-4 with micromolar affinities and PEP4 showed significantly increased affinity. The mixed type enzyme inhibition by peptides suggested that the peptides either block the active site of DPP-4 or changes the enzyme conformation via a secondary binding site. Overall, the results demonstrate that sorghum seeds are an adequate source of peptides with DPP-4 inhibitory properties that could be used in functional food formulations.

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

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

Evaluating Peptides of Picrorhiza kurroa and Their Inhibitory Potential against ACE, DPP-IV, and Oxidative Stress

Picrorhiza kurroa Royle ex Benth. is a high-altitude plant having great medicinal value. However, its medicinal value at the peptide level is still unknown, which limits its utility in the development of peptide-based therapeutics. Here, we identify 65 peptides fromP. kurroa hydrolysate. Sequence analysis suggests that one novel bioactive peptide, ASGLCPEEAVPRR (BP1), has antioxidant potential and shows angiotensin-converting enzyme (ACE) and dipeptidyl peptidase-IV (DPP-IV) inhibitory activities. The molecular docking study showed that BP1 has a lower binding energy and strong affinity toward active pockets of ACE and DPP-IV, which explains its higher ACE [IC₅₀ = 59.90 ± 9.52 μg/mL (43.40 μM)] and DPP-IV [IC₅₀ = 3.04 ± 0.26 μg/mL (2.2 μM)] inhibitory activities. BP1 protects HEK293 cells from H₂O₂-induced oxidative damage by inhibiting intracellular reactive oxygen species (ROS) and malondialdehyde accumulation and activating the intrinsic antioxidant defense system. Additionally, phase-contrast microscopy studies revealed that pre-treatment of BP1 to HEK293 cells before exposure to H₂O₂ retains the normal morphology and blocks apoptosis. Furthermore, it also suppresses ROS-induced mitochondrial apoptosis via restoring the mitochondrial membrane potential (ΔΨm) and inhibiting caspase 3/7 activity. Therefore, BP1 has antioxidant potential and ACE and DPP-IV inhibitory activities that could be used for peptide-based formulation(s) in pharmaceuticals to treat diabetes, cardiovascular diseases, and other diseases associated with ROS.

Magnetic ligand fishing using immobilized DPP-IV for identification of antidiabetic ligands in lingonberry extract

In this work, a new magnetic ligand fishing probe for discovery of DPP-IV inhibitory ligands was developed and it was tested as a proof of concept on the fruit extract of Vaccinium vitis-idaea (lingonberry). The ligands were shown to have appreciable dipeptidyl peptidase IV (DPP-IV) inhibitory activity (IC₅₀: 31.8 μg mL-1).) Inhibition of DPP-IV is a well-known therapeutic approach for management of type 2 diabetes (T2D). DPP-IV was successfully immobilized onto magnetic beads and was shown to retain its catalytic activity and selectivity over a model mixture. A total of four ligands were successfully fished out and identified as cyanidin-3-galactoside (2), cyanidin-3-arabinoside (3), proanthocynidin A (4), and 10-carboxyl-pyranopeonidin 3-O-(6″-O-p-coumaroyl)-glucoside (5) using HPLC/HRMS.

Assessment of the DPP-IV inhibitory activity of a novel octapeptide derived from rapeseed using Caco-2 cell monolayers and molecular docking analysis

The Octapeptide ELHQEEPL, which was identified from the rapeseed protein napin showed prominent Dipeptidyl peptidase-IV (DPP-IV) inhibitory activity. The objective of this study was to investigate the DPP-IV inhibitory activity and transepithelial transport of ELHQEEPL in an approaching intestinal condition using Caco-2 cell monolayers. ELHQEEPL and its degraded fragments EL, HQEEP, and methylated ELHQEEPL were transported across Caco-2 cell monolayers through different pathways. Compared with the nonbiological enzyme inhibition test, the in vitro experiment on Caco-2 cell monolayers showed that the IC50 value of DPP-IV inhibition increased by 43.11% for ELHQEEPL. There was no significant change in DPP-IV gene expression in the Caco-2 cell monolayers upon treatment with ELHQEEPL. Furthermore, molecular docking predicted that the weaker binding between inhibitory peptide and enzyme for the degradation products from ELHQEEPL during transepithelial transport greatly limited its role in inhibiting DPP-IV. PRACTICAL APPLICATIONS: The DPP-IV inhibitory activity of ELHQEEPL was confirmed using Caco-2 cell monolayers as a novel assessment tool, although its potency was reduced by metabolic degradation. In general, this study reported the use of Caco-2 cell monolayers as a tool for comprehensively studying peptides as sources of DPP-IV inhibitors. A Caco-2 cell-based approach with molecular docking can be adapted for the investigation of intestinal absorption and activity attenuation of food peptides being considered for enzymatic action. Moreover, since the Caco-2 cells express a wide range of enzymes, this method can be used for screening for other active food peptides such as for the inhibitors of ACE and a-glucosidase.

Dipeptidyl Peptidase-IV Inhibitory Activity and Related Molecular Mechanism of Bovine α-Lactalbumin-Derived Peptides

Identifying DPP-IV inhibitory peptides from dietary protein has attracted increased attention. In the present study, bovine α-lactalbumin hydrolysates were generated by alcalase for various hydrolysis times, and DPP-IV inhibitory activity of these hydrolysates was determined. The 4 h hydrolysates displayed the most potent DPP-IV inhibitory activity, with DPP-IV inhibition rate of 82.30 ± 1.39% at concentration of 1.0 mg/mL. DPP-IV inhibitory peptides were isolated from the 4 h-hydrolysates with gel filtration chromatography and reversed-phase high-performance liquid chromatography (RP-HPLC). Using liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI MS/MS), two DPP-IV inhibitory peptides were identified, and their amino acid sequences were Glu-Leu-Lys-Asp-Leu-Lys-Gly-Tyr (ELKDLKGY) and Ile-Leu-Asp-Lys-Val-Gly-Ile-Asn-Tyr (ILDKVGINY), respectively. Furthermore, molecular docking analysis showed that peptides ELKDLKGY and ILDKVGINY could form hydrogen bonds, pi-cation interactions, and salt bridges with DPP-IV. These findings indicated that bovine α-lactalbumin may be a potential source of natural DPP-IV inhibitor.

Generation and characterization of dipeptidyl peptidase-IV inhibitory peptides from trypsin-hydrolyzed α-lactalbumin-rich whey proteins

Dipeptidyl peptidase-IV (DPP-IV) is an enzyme that break down the antidiabetic hormone glucagon-like peptide-1. Therefore, inhibition of DPP-IV could be an effective strategy to treat Type 2 diabetes (T2D). The α-lactalbumin-rich whey protein concentrate was hydrolyzed by trypsin, and the hydrolysates were then fractionated at a semi-preparative scale using a Superdex Gel filtration Chromatography. The peptides were analyzed by using HPLC coupled with tandem mass spectrometry (RP-HPLC-MS/MS), and their Dipeptidyl peptidase-IV inhibitory activity was determined by the enzymatic assay. Among tested fragments, a potent fragment (LDQWLCEKL), with the half-maximal inhibitory concentration (IC₅₀) of 131 μM was obtained. Further analysis shows that the LDQWLCEKL peptide corresponds to the amino acid sequence of f(115-123) in α-lactalbumin. Furthermore, LDQWLCEKL exhibited a typical non-competitive mode of inhibition. The results indicate that α-lactalbumin contains active peptides with DPP-IV inhibitory activity that may be used to prevent and treat T2D.

Peptidomic Investigation of the Interplay between Enzymatic Tenderization and the Digestibility of Beef Semimembranosus Proteins

This work investigated the influence of enzymatic tenderization on digestibility changes of beef semimembranosus proteins using peptidomics methods. Hydrolysis by proteinase K and bromelain elevated the average bitterness index of identified peptides by generating high-Q values peptides (1714-1790 Cal/mol), including KDLFDPIIQ, LIDDHFLFDKPVSPL, and QLIDDHFLFDKPVSPLLL. Proteolysis during enzymatic tenderization acted as a "pre-digestion" step and significantly elevated the degree of hydrolysis of beef protein (by 4.5-17.3%) in subsequent simulated gastrointestinal digestion. Peptidomics analysis of digests revealed large variations in the peptide composition, which was positively correlated with the degree of proteolysis during enzymatic tenderization. Enzymatic tenderization with proteinase K- (for 0.5 h) or bromelain-treated samples largely increased the survival rate (by 65.5 or 82.8%) of peptides during simulated digestion, possibly because of the "secondary enzyme-substrate interaction" effect. This work could provide a new sight into the possible influence of enzymatic tenderization on meat nutrition.

In Vitro Metabolic Stability of a Casein-Derived Dipeptidyl Peptidase-IV (DPP-IV) Inhibitory Peptide VPYPQ and Its Controlled Release from Casein by Enzymatic Hydrolysis

The aim of this study was to investigate the dipeptidyl peptidase-IV (DPP-IV) inhibition and metabolic stability of a casein-derived peptide Val-Pro-Tyr-Pro-Gln (VPYPQ) and its fragments as well as their release from casein following hydrolysis. Results showed that VPYPQ was the most potent DPP-IV inhibitory peptide among them with an IC₅₀ value of 41.45 μM. This might be due to its two internal Pro residues at positions 2 and 4. Moreover, VPYPQ was resistant to hydrolysis by gastrointestinal enzymes and was relatively more stable to hydrolysis by DPP-IV and peptidases in plasma compared with its fragments. Additionally, oral administration of VPYPQ at a dose of 90 μmol/kg body weight could reduce the postprandial blood glucose levels in mice. More importantly, VPYPQ could be released efficiently from casein following hydrolysis by a combination of papain and in vitro digestion, reaching up to 3211.15 μg/g. Therefore, VPYPQ was a promising casein-derived DPP-IV inhibitor.

Prediction of Bioactive Peptides from Chlorella sorokiniana Proteins Using Proteomic Techniques in Combination with Bioinformatics Analyses

Chlorella is one of the most nutritionally important microalgae with high protein content and can be a good source of potential bioactive peptides. In the current study, isolated proteins from Chlorella sorokiniana were subjected to in silico analysis to predict potential peptides with biological activities. Molecular characteristics of proteins were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and proteomics techniques. A total of eight proteins were identified by proteomics techniques from 10 protein bands of the SDS-PAGE. The predictive result by BIOPEP's profile of bioactive peptides tools suggested that proteins of C. sorokiniana have the highest number of dipeptidyl peptidase-IV (DPP IV) inhibitors, with high occurrence of other bioactive peptides such as angiotensin-I converting enzyme (ACE) inhibitor, glucose uptake stimulant, antioxidant, regulating, anti-amnestic and antithrombotic peptides. In silico analysis of enzymatic hydrolysis revealed that pepsin (pH > 2), bromelain and papain were proteases that can release relatively larger quantity of bioactive peptides. In addition, combinations of different enzymes in hydrolysis were observed to dispense higher numbers of bioactive peptides from proteins compared to using individual proteases. Results suggest the potential of protein isolated from C. sorokiniana could be a source of high value products with pharmaceutical and nutraceutical application potential.

Discovery of Food-Derived Dipeptidyl Peptidase IV Inhibitory Peptides: A Review

Diabetes is a chronic metabolic disorder which leads to high blood sugar levels over a prolonged period. Type 2 diabetes mellitus (T2DM) is the most common form of diabetes and results from the body's ineffective use of insulin. Over ten dipeptidyl peptidase IV (DPP-IV) inhibitory drugs have been developed and marketed around the world in the past decade. However, owing to the reported adverse effects of the synthetic DPP-IV inhibitors, attempts have been made to find DPP-IV inhibitors from natural sources. Food-derived components, such as protein hydrolysates (peptides), have been suggested as potential DPP-IV inhibitors which can help manage blood glucose levels. This review focuses on the methods of discovery of food-derived DPP-IV inhibitory peptides, including fractionation and purification approaches, in silico analysis methods, in vivo studies, and the bioavailability of these food-derived peptides. Moreover, food-derived DPP-IV inhibitory peptides discovered during this decade are listed and distributed in a 3D scatter plot graph based on their IC50, molecular weight, and grand average of hydropathicity values, which can help us to understand the relationship between the features of the peptides and their activities.