Proteins and bioactive peptides: Mechanisms of action on diabetes management

Legume-Derived Bioactive Peptides in Type 2 Diabetes: Opportunities and Challenges

Diabetes mellitus is a complex disorder characterized by insufficient insulin production or insulin resistance, which results in a lifelong dependence on glucose-lowering drugs for almost all patients. During the fight with diabetes, researchers are always thinking about what characteristics the ideal hypoglycemic drugs should have. From the point of view of the drugs, they should maintain effective control of blood sugar, have a very low risk of hypoglycemia, not increase or decrease body weight, improve β-cell function, and delay disease progression. Recently, the advent of oral peptide drugs, such as semaglutide, brings exciting hope to patients with chronic diabetes. Legumes, as an excellent source of protein, peptides, and phytochemicals, have played significant roles in human health throughout human history. Some legume-derived peptides with encouraging anti-diabetic potential have been gradually reported over the last two decades. Their hypoglycemic mechanisms have also been clarified at some classic diabetes treatment targets, such as the insulin receptor signaling pathway or other related pathways involved in the progress of diabetes, and key enzymes including α-amylase, α-glucosidase, and dipeptidyl peptidase-IV (DPP-4). This review summarizes the anti-diabetic activities and mechanisms of peptides from legumes and discusses the prospects of these peptide-based drugs in type 2 diabetes (T2D) management.

In Vitro Assessment Methods for Antidiabetic Peptides from Legumes: A Review

Almost 65% of the human protein supply in the world originates from plants, with legumes being one of the highest contributors, comprising between 20 and 40% of the protein supply. Bioactive peptides from various food sources including legumes have been reported to show efficacy in modulating starch digestion and glucose absorption. This paper will provide a comprehensive review on recent in vitro studies that have been performed on leguminous antidiabetic peptides, focusing on the α-amylase inhibitor, α-glucosidase inhibitor, and dipeptidyl peptidase-IV (DPP-IV) inhibitor. Variations in legume cultivars and methods affect the release of peptides. Different methods have been used, such as in sample preparation, including fermentation (t, T), germination (t), and pre-cooking; in protein extraction, alkaline extraction, isoelectric precipitation, phosphate buffer extraction, and water extraction; in protein hydrolysis enzyme types and combination, enzyme substrate ratio, pH, and time; and in enzyme inhibitory assays, positive control type and concentration, inhibitor or peptide concentration, and the unit of inhibitory activity. The categorization of the relative scale of inhibitory activities among legume samples becomes difficult because of these method differences. Peptide sequences in samples were identified by means of HPLC/MS. Software and online tools were used in bioactivity prediction and computational modelling. The identification of the types and locations of chemical interactions between the inhibitor peptides and enzymes and the type of enzyme inhibition were achieved through computational modelling and enzyme kinetic studies.

Preparation Process Optimization of Peptides from Agaricus blazei Murrill, and Comparison of Their Antioxidant and Immune-Enhancing Activities Separated by Ultrafiltration Membrane Technology

Agaricus blazei murrill (ABM), a large fungus, is reported to have extensive biological activities but the antioxidant and immune-regulatory capacities have been less studied and the components responsible for the functions are unclear. This study prepared ABM peptides (ABMP) using ultrasound-assisted enzymatic extraction (UAEE) strategy and cascade ultrafiltration (UF) membrane technology. The UAEE extraction conditions were optimized using response surface methodology (RSM) with four factors and three levels to achieve the maximum ABMP yield (34.03%); the optimal conditions were an enzyme amount of 4%, ratio of ABM to water of 1:30, ultrasonic power of 360 W, and ultrasonic time of 30 min. Four ABMP fractions were obtained after UF with different pore size and their antioxidant and immune-regulatory abilities were evaluated and compared. The results showed that they could effectively scavenge DPPH, hydroxyl, and ABTS radicals, especially for ABMP-2; the scavenging rate of the above radicals were 79.31%, 63.60%, and 96.08%, respectively. In addition, four ABMP fractions also activated macrophage activity through strengthening phagocytosis and the production of NO, IL-6, IL-1β, and TNF-α in a dose-dependent manner. Notably, the ABMP-2 fraction with a MW of 3-5 kDa and peptide purity of 82.88% was found to have the best effect, showing the maximum phagocytosis (189.37%) as well as NO (7.98 μM), IL-6 (195.05 pg/mL), IL-1β (876.15 pg/mL), and TNF-α (1620 pg/mL) secretion at a treatment concentration of 150 μg/mL. The findings indicated that the ABMP, especially for the separate ABMP-2, could be used as dietary supplements and have the potential to be exploited as immune-enhancing agents.

The Potential Role of Cyclopeptides from Pseudostellaria heterophylla, Linum usitatissimum and Drymaria diandra, and Peptides Derived from Heterophyllin B as Dipeptidyl Peptidase IV Inhibitors for the Treatment of Type 2 Diabetes: An In Silico Study

Dipeptidyl peptidase 4 (DPP4) inhibitors can treat type 2 diabetes by slowing GLP-1 degradation to increase insulin secretion. Studies have reported that Pseudostellaria heterophylla, Linum usita-tissimum (flaxseed), and Drymaria diandra, plants rich in Caryophyllaceae-type cyclopeptides and commonly used as herbal or dietary supplements, are effective in controlling blood sugar. The active site of DPP4 is in a cavity large enough to accommodate their cyclopeptides. Molecular modeling by AutoDock Vina reveals that certain cyclopeptides in these plants have the potential for DPP4 inhibition. In particular, “Heterophyllin B” from P. heterophylla, “Cyclolinopeptide C” from flaxseed, and “Diandrine C” from D. diandra, with binding affinities of −10.4, −10.0, and −10.7 kcal/mol, are promising. Docking suggests that DPP4 inhibition may be one of the reasons why these three plants are beneficial for lowering blood sugar. Because many protein hydrolysates have shown the effect of DPP4 inhibition, a series of peptides derived from Heterophyllin B precursor “IFGGLPPP” were included in the study. It was observed that IFWPPP (−10.5 kcal/mol), IFGGWPPP (−11.4 kcal/mol), and IFGWPPP (−12.0 kcal/mol) showed good binding affinity and interaction for DPP4. Various IFGGLPPP derivatives have the potential to serve as scaffolds for the design of novel DPP4 inhibitors.

In vitro dipeptidyl peptidase IV inhibitory activity and in situ insulinotropic activity of milk and egg white protein digests

Dietary proteins are involved in the regulation of glucose homeostasis by different mechanisms. Food protein digestion products are reported to inhibit dipeptidyl peptidase IV (DPP-IV), induce incretin secretion or directly exert an insulinotropic effect in pancreatic β-cells. This study illustrates the DPP-IV inhibitory activity of gastric and intestinal digests of casein, whey and egg white proteins determined in vitro, using Gly-Pro-AMC, and in situ using non-differentiated Caco-2 cells. Comparable trends in the DPP-IV inhibitory profiles were obtained by these two methods although the extent of inhibition in situ was consistently lower than the inhibition observed in vitro. Casein intestinal digests and whey protein gastric and intestinal digests showed potent DPP-IV inhibitory activities in Caco-2 cells with IC₅₀ values ranging from 0.8 to 1.2 mg mL^-1. The absorbed fraction of the intestinal digests from whey and egg white protein induced insulin secretion in BRIN-BD11 cells when determined using a two-tiered cellular model (Caco-2 and BRIN-BD11). However, the gastric digests from the same substrates showed no insulin secretion. This may be related to limited trans-epithelial transport through the Caco-2 monolayer of the gastric digestion products. However, both, gastric and intestinal digests were able to induce insulin secretion in BRIN-BD11 cells when the monolayer was composed of a co-culture of STC-1 and Caco-2 cells. This result may be attributed to the activation of STC-1 cells and subsequent incretin secretion, induced by the gastric digest, as shown by an enhanced intracellular calcium uptake.

Macroalgal protein hydrolysates from Palmaria palmata influence the 'incretin effect' in vitro via DPP-4 inhibition and upregulation of insulin, GLP-1 and GIP secretion

PURPOSE

This study investigated metabolic benefits of protein hydrolysates from the macroalgae Palmaria palmata, previously shown to inhibit dipeptidylpeptidase-4 (DPP-4) activity in vitro.

METHODS

Previously, Alcalase/Flavourzyme-produced P. palmata protein hydrolysate (PPPH) improved glycaemia and insulin production in streptozotocin-induced diabetic mice. Here the PPPH, was compared to alternative Alcalase, bromelain and Promod-derived hydrolysates and an unhydrolysed control. All PPPH's underwent simulated gastrointestinal digestion (SGID) to establish oral bioavailability. PPPH's and their SGID counterparts were tested in pancreatic, clonal BRIN-BD11 cells to assess their insulinotropic effect and associated intracellular mechanisms. PPPH actions on the incretin effect were assessed via measurement of DPP-4 activity, coupled with GLP-1 and GIP release from GLUTag and STC-1 cells, respectively. Acute in vivo effects of Alcalase/Flavourzyme PPPH administration on glucose tolerance and satiety were assessed in overnight-fasted mice.

RESULTS

PPPH's (0.02-2.5 mg/ml) elicited varying insulinotropic effects (p < 0.05-0.001). SGID of the unhydrolysed protein control, bromelain and Promod PPPH's retained, or improved, bioactivity regarding insulin secretion, DPP-4 inhibition and GIP release. Insulinotropic effects were retained for all SGID-hydrolysates at higher PPPH concentrations. DPP-4 inhibitory effects were confirmed for all PPPH's and SGID counterparts (p < 0.05-0.001). PPPH's were shown to directly influence the incretin effect via upregulated GLP-1 and GIP (p < 0.01-0.001) secretion in vitro, largely retained after SGID. Alcalase/Flavourzyme PPPH produced the greatest elevation in cAMP (p < 0.001, 1.7-fold), which was fully retained post-SGID. This hydrolysate elicited elevations in intracellular calcium (p < 0.01) and membrane potential (p < 0.001). In acute in vivo settings, Alcalase/Flavourzyme PPPH improved glucose tolerance (p < 0.01-0.001) and satiety (p < 0.05-0.001).

CONCLUSION

Bioavailable PPPH peptides may be useful for the management of T2DM and obesity.

In Vitro and In Vivo Effects of Palmaria palmata Derived Peptides on Glucose Metabolism

Three synthetic peptides, ILAP, LLAP and MAGVDHI, derived from a Palmaria palmata protein hydrolysate were assessed for their antidiabetic potential in vitro and in vivo. In addition to inhibiting dipeptidyl peptidase-IV in a cell-based in situ assay all three peptides significantly increased the half-life of the incretin hormone glucagon-like peptide-1 (GLP-1). ILAP and LLAP mediated a significant increase (p < 0.001) in insulin secretion from BRIN-BD11 cells compared to the glucose control, while MAGVDHI had no insulinotropic activity at an eqimolar concentration (10–6 M). A significant increase in the concentration of cyclic adenosine monophosphate production in BRIN-BD11 cells mediated by ILAP (p < 0.001) and LLAP (p < 0.01) compared to the basal control, would indicate that insulin secretion may be mediated by membrane based activation. Furthermore, ILAP and LLAP acted as glucose-dependent insulinotropic polypeptide (GIP) secretagogues, stimulating a significant increase (p < 0.01) in the concentration of GIP released from enteroendocrine STC-1 cells compared to the glucose control. When tested in vivo in healthy male NIH Swiss mice, ILAP and LLAP, mediated a significant increase (p < 0.01) in plasma insulin and decrease (p < 0.05) in blood glucose, respectively, compared to the control. MAGVDHI mediated a significant (p < 0.001) sustained reduction in food intake in food deprived trained mice. These results demonstrate that the Palmaria palmata peptides studied herein have prospective antidiabetic activity and have the potential to act as agents that can be used alone or in combination with drugs, to aid in the prevention and management of Type 2 diabetes mellitus.

Physicochemical, Nutritional and In Vitro Antidiabetic Characterisation of Blue Whiting (Micromesistiuspoutassou) Protein Hydrolysates

Protein hydrolysates from low-value underutilised fish species are potential sources of high-quality dietary protein and health enhancing peptides. Six blue whiting soluble protein hydrolysates (BW-SPH-A_F), generated at industrial scale using different hydrolysis conditions, were assessed in terms of their protein equivalent content, amino acid profile and score and physicochemical properties in addition to their ability to inhibit dipeptidyl peptidase IV (DPP-IV) and stimulate the secretion of insulin from BRIN-BD11 cells. Furthermore, the effect of simulated gastrointestinal digestion (SGID) on the stability of the BW-SPHs and their associated in vitro antidiabetic activity was investigated. The BW-SPHs contained between 70–74% (w/w) protein and all essential and non-essential amino acids. All BW-SPHs mediated DPP-IV inhibitory (IC₅₀: 2.12–2.90 mg protein/mL) and insulin secretory activity (2.5 mg/mL; 4.7 to 6.4-fold increase compared to the basal control (5.6 mM glucose alone)). All BW-SPHs were further hydrolysed during SGID. While the in vitro DPP-IV inhibitory and insulin secretory activity mediated by some BW-SPHs was reduced following SGID, the activity remained high. In general, the insulin secretory activity of the BW-SPHs were 4.5–5.4-fold higher than the basal control following SGID. The BW-SPHs generated herein provide potential for anti-diabetic related functional ingredients, whilst also enhancing environmental and commercial sustainability.

Effect of bioactive proteins on gait kinematics and systemic inflammatory markers in mature horses

Twenty-seven mature Quarter horses were used in a randomized design to determine the effects of bioactive protein supplementation on gait kinematics and systemic inflammatory markers in a 34-d trial. Treatments consisted of oral doses of 230 g/d of pelleted supplements containing 0 g (CON; n = 9), 40 g of bioactive protein (40BP; n = 9; LIFELINE, APC, LLC, Ankeny, IA), and 80 g of bioactive protein (80BP; n = 9) daily. Horses were fed a commercial concentrate at 0.5% BW (as-fed) and received ad libitum coastal bermudagrass (Cynodon dactylon) hay daily. On day 33, horses consistent in exercise (CON, n = 6; 40BP, n = 8; 80BP, n = 7) participated in a trailering and riding challenge. Kinematic gait analysis was performed on day 0 for use as a covariate, and on day 14, 28, and 34 to allow for the determination of potential time and dosage effects. Video footage was collected and analyzed using gait analysis software (EquineTec, Monroe, GA) for the determination of stride length (SL) and range of motion (ROM). Blood was collected via jugular venipuncture on days 0, 14, 28, and 34 for determination of systemic expression of tumor necrosis factor (TNF)-α and IL-1β. Data were analyzed using PROC MIXED of SAS. A trend towards treatment × time interaction was observed in ROM of the knee at the walk (P = 0.10), due to the increasing ROM for 40BP and 80BP as time increased and decreasing ROM for CON. A treatment × time interaction was observed (P < 0.01) for hock ROM at a walk resulting from CON and 80BP decreasing from day 14 to 28 with 40BP increasing, while from day 28 to 34 ROM at a walk decreased for 40BP and increased for 80BP. The main effect of treatment on hock ROM at the walk was quadratic (P < 0.01) and characterized by higher ROM values for 40BP compared to CON or 80BP. Dietary treatment lengthened (P = 0.04) SL of the hind limb at the walk for 40BP and 80BP compared to CON on both days 14 and 28. A significant treatment × time interaction was observed in the expression of IL-1β (P < 0.01) and can be explained by lower concentrations of IL-1β for 80BP on day 34 compared to the other treatments, with 40BP being intermediate and CON being the highest. Increased articular ROM with decreased expression of IL-1β may indicate potential anti-inflammatory effects of 80 g/d of bioactive proteins.

Recent Progress in Enzymatic Release of Peptides in Foods of Animal Origin and Assessment of Bioactivity

There is a wide variety of peptides released from food proteins that are able to exert a relevant benefit for human health, such as angiotensin-converting enzyme inhibition, antioxidant, anti-inflammatory, hypoglucemic, or antithrombotic activity, among others. This manuscript is reviewing the recent advances on enzymatic mechanisms for the hydrolysis of proteins from foods of animal origin, including the types of enzymes and mechanisms of action involved, the strategies followed for the isolation and identification of bioactive peptides through advanced proteomic tools, and the assessment of bioactivity and its beneficial effects. Specific applications in fermented and/or ripened foods where a significant number of bioactive peptides have been reported with relevant in vivo physiological effects on laboratory rats and humans as well as the hydrolysis of animal food proteins for the production of bioactive peptides are also reviewed.

Bioactive peptides from beans with the potential to decrease the risk of developing noncommunicable chronic diseases

Several studies have demonstrated that peptides obtained from the proteins of different bean species have the potential to act on therapeutic targets of noncommunicable chronic diseases or NCDs. However, peptides with great structural diversity can be obtained from the hydrolysis of proteins present in foods. Therefore, the present review had the objective of identifying, in silico, the possibility of obtaining peptides with potential biological activity from the storage globulin proteins of the bean species Phaseolus vulgaris (L.), Vigna angularis (Willd.), Vigna radiata (L.) and Vigna unguiculata (L.) Walp., using the UniProtKB, BIOPEP and PeptideRanker databases, as well as reviewing available research reports that showed evidence bioactive properties of peptides obtained from beans via in vitro assays. For all the species studied, the highest frequency of the occurrence of bioactive fragments was found for the inhibition of dipeptidyl peptidase-IV, followed by the inhibition of the angiotensin-converting enzyme and by antioxidant activity. The inhibition of the two enzymes is the therapeutic target of drugs used for type 2 diabetes mellitus (T2DM) and for hypertension, respectively, while the antioxidant activity can prevent the development of several chronic diseases related to oxidative stress.

Identification and characterisation of peptides from a boarfish (Capros aper) protein hydrolysate displaying in vitro dipeptidyl peptidase-IV (DPP-IV) inhibitory and insulinotropic activity

Twenty-two novel dipeptidyl peptidase-IV (DPP-IV) inhibitory peptides (with IC₅₀ values <200 µM) and fifteen novel insulinotropic peptides were identified in a boarfish protein hydrolysate generated at semi-pilot scale using Alcalase 2.4L and Flavourzyme 500L. This was achieved by bioassay-driven semi-preparative reverse phase-high performance liquid chromatography fractionation, liquid chromatography-mass spectrometry and confirmatory studies with synthetic peptides. The most potent DPP-IV inhibitory peptide (IPVDM) had a DPP-IV half maximal inhibitory concentration (IC₅₀) value of 21.72 ± 1.08 µM in a conventional in vitro and 44.26 ± 0.65 µM in an in situ cell-based (Caco-2) DPP-IV inhibition assay. Furthermore, this peptide stimulated potent insulin secretory activity (1.6-fold increase compared to control) from pancreatic BRIN-BD11 cells grown in culture. The tripeptide IPV exhibited potent DPP-IV inhibitory activity (IC₅₀: 5.61 ± 0.20 µM) comparable to that reported for the known DPP-IV inhibitor IPI (IC₅₀: 3.20 µM). Boarfish proteins contain peptide sequences with potential to play a role in glycaemic management in vivo.

A Systematic Review on Synthetic Drugs and Phytopharmaceuticals Used to Manage Diabetes

BACKGROUND

Diabetes is a multifactorial disease and a major cause for many microvascular and macrovascular complications. The disease will ultimately lead to high rate mortality if it is not managed properly. Treatment of diabetes without any side effects has always remained a major challenge for health care practitioners.

INTRODUCTION

The current review discusses the various conventional drugs, herbal drugs, combination therapy and the use of nutraceuticals for the effective management of diabetes mellitus. The biotechnological aspects of various antidiabetic drugs are also discussed.

METHODS

Structured search of bibliographic databases for previously published peer-reviewed research papers was explored and data was sorted in terms of various approaches that are used for the treatment of diabetes.

RESULTS

More than 170 papers including both research and review articles, were included in this review in order to produce a comprehensive and easily understandable article. A series of herbal and synthetic drugs have been discussed along with their current status of treatment in terms of dose, mechanism of action and possible side effects. The article also focuses on combination therapies containing synthetic as well as herbal drugs to treat the disease. The role of pre and probiotics in the management of diabetes is also highlighted.

CONCLUSION

Oral antihyperglycemics which are used to treat diabetes can cause many adverse effects and if given in combination, can lead to drug-drug interactions. The combination of various phytochemicals with synthetic drugs can overcome the challenge faced by the synthetic drug treatment. Herbal and nutraceuticals therapy and the use of probiotics and prebiotics are a more holistic therapy due to their natural origin and traditional use.

Incorporating salal berry (Gaultheria shallon) and blackcurrant (Ribes nigrum) pomace in yogurt for the development of a beverage with antidiabetic properties

In this study aqueous extracts from salal berry (SB) and blackcurrant pomace (BCP) were used to reformulate yogurt and the anti-diabetic properties of the beverage were investigated during 4 weeks of cold storage at 4 °C. Results indicated that α-amylase, α-glucosidase and DPP-IV inhibitory activities increased with storage time for all samples. At the end of storage period α-amylase, α-glucosidase and DPP-IV inhibition were >61%, 62% and 56% respectively for all yogurt types. This increase in bioactivity during cold storage is attributed to the viability of lactic acid bacteria (∼108 cfu/g), which is maintained for 4 weeks. Enzyme inhibition increased similarly for all yogurt types at 4 °C except for α-glucosidase. Yogurt with BCP showed the highest potency to inhibit α-glucosidase (>90%) with an IC50 value of 0.20 mg/ml (week 4). A peptidomic approach based on liquid chromatography coupled with mass spectrometry (LC-MS) was used for the separation and identification of peptides generated in three types of yogurt. A total of 486 peptides mainly from caseins were identified, of which 15 have documented bioactivity, predominantly as antimicrobial agents or ACE-inhibitors.

Black bean peptides inhibit glucose uptake in Caco-2 adenocarcinoma cells by blocking the expression and translocation pathway of glucose transporters

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Common bean protein fractions decreased glucose uptake in colorectal cancer cells.

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Protein fractions decreased SGLT1 and GLUT2 gene and protein expression and translocation.

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Black bean protein fractions could be used as anticancer drug adjuvants.

The objective was to evaluate the effect of black bean protein fraction (PFRA), and its derived peptides on glucose uptake, SGLT1 and GLUT2 expression and translocation on Caco-2 cells. The effect of treatments was evaluated on glucose uptake, protein expression and localization and gene expression on Caco-2 cells. PFRA (10 mg/mL) lowered glucose uptake from 27.4% after 30 min to 33.9% after 180 min of treatment compared to untreated control (p < 0.05). All treatments lowered GLUT2 expression after 30 min of treatment compared to untreated control (31.4 to 48.6%, p < 0.05). Similarly, after 24 h of treatment, GLUT2 was decreased in all treatments (23.5% to 48.9%) (p < 0.05). SGLT1 protein expression decreased 18.3% for LSVSVL (100 μM) to 45.1% for PFRA (10 mg/mL) after 24 h. Immunofluorescence microscopy showed a decrease in expression and membrane translocation of GLUT2 and SGLT1 for all treatments compared to untreated control (p < 0.05). Relative gene expression of SLC2A2 (GLUT2) and SLC5A1 (SGLT1) was downregulated significantly up to two-fold change compared to the untreated control after 24 h treatment. Black bean protein fractions are an inexpensive, functional ingredient with significant biological potential to reduce glucose uptake and could be used as an adjuvant in the treatment of colorectal cancer.

Atlantic salmon (Salmo salar) co-product-derived protein hydrolysates: A source of antidiabetic peptides

Large quantities of low-value protein rich co-products, such as salmon skin and trimmings, are generated annually. These co-products can be upgraded to high-value functional ingredients. The aim of this study was to assess the antidiabetic potential of salmon skin gelatin and trimmings-derived protein hydrolysates in vitro. The gelatin hydrolysate generated with Alcalase 2.4L and Flavourzyme 500L exhibited significantly higher (p < 0.001) insulin and GLP-1 secretory activity from pancreatic BRIN-BD11 and enteroendocrine GLUTag cells, respectively, when tested at 2.5 mg/mL compared to hydrolysates generated with Alcalase 2.4L or Promod 144MG. The gelatin hydrolysate generated with Alcalase 2.4L and Flavourzyme 500L showed significantly more potent (p < 0.01) DPP-IV inhibitory activity than those generated with Alcalase 2.4L or Promod 144MG. No significant difference was observed in the insulinotropic activity mediated by any of the trimmings-derived hydrolysates when tested at 2.5 mg/mL. However, the trimmings hydrolysate generated with Alcalase 2.4L and Flavourzyme 500L exhibited significantly higher DPP-IV inhibitory (p < 0.05:Alcalase 2.4L and p < 0.01:Promod 144MG) and GLP-1 (p < 0.001, 2.5 mg/mL) secretory activity than those generated with Alcalase 2.4L or Promod 144MG. The salmon trimmings hydrolysate generated with Alcalase 2.4L and Flavourzyme 500L when subjected to simulated gastrointestinal digestion (SGID) was shown to retain its GLP-1 secretory and DPP-IV inhibitory activities, in addition to improving its insulin secretory activity. However, the gelatin hydrolysate generated with Alcalase 2.4L and Flavourzyme 500L was shown to lose GLP-1 secretory activity following SGID. A significant increase in membrane potential (p < 0.001) and intracellular calcium (p < 0.001) by both co-product hydrolysates generated with Alcalase 2.4L and Flavourzyme 500L suggest that both hydrolysates mediate their insulinotropic activity through the K_ATP channel-dependent pathway. Additionally, by stimulating a significant increase in intracellular cAMP release (p < 0.05) it is likely that the trimmings-derived hydrolysate may also mediate insulin secretion through the protein kinase A pathway. The results presented herein demonstrate that salmon co-product hydrolysates exhibit promising in vitro antidiabetic activity.

Cucurbitaceae Seed Protein Hydrolysates as a Potential Source of Bioactive Peptides with Functional Properties

Seeds from Cucurbitaceae plants (squashes, pumpkins, melons, etc.) have been used both as protein-rich food ingredients and nutraceutical agents by many indigenous cultures for millennia. However, relatively little is known about the bioactive components (e.g., peptides) of the Cucurbitaceae seed proteins (CSP) and their specific effects on human health. Therefore, this paper aims to provide a comprehensive review of latest research on bioactive and functional properties of CSP isolates and hydrolysates. Enzymatic hydrolysis can introduce a series of changes to the CSP structure and improve its bioactive and functional properties, including the enhanced protein solubility over a wide range of pH values. Small-sized peptides in CSP hydrolysates seem to enhance their bioactive properties but adversely affect their functional properties. Therefore, medium degrees of hydrolysis seem to benefit the overall improvement of bioactive and functional properties of CSP hydrolysates. Among the reported bioactive properties of CSP isolates and hydrolysates, their antioxidant, antihypertensive, and antihyperglycaemic activities stand out. Therefore, they could potentially substitute synthetic antioxidants and drugs which might have adverse secondary effects on human health. CSP isolates and hydrolysates could also be implemented as functional food ingredients, thanks to their favorable amino acid composition and good emulsifying and foaming properties.

Generation of bioactive peptides during food processing

Large amounts of peptides are naturally generated in foods through the proteolysis phenomena taking place during processing. Such proteolysis is carried out either by endogenous enzymes in ripened foods or by the combined action of endogenous and microbial enzymes when fermented. Food proteins can also be isolated and hydrolysed by peptidases to produce hydrolysates. endo-peptidases act first followed by the successive action of exo-peptidases (mainly, tri- and di-peptidylpeptidases, aminopeptidases and carboxypeptidases). The generated peptides may be further hydrolysed through the gastrointestinal digestion resulting in a pool of peptides with different sequences and lengths, some of them with relevant bioactivity. However, these peptides should be absorbed intact through the intestinal barrier and reach the blood stream to exert their physiological action. This manuscript is reporting the enzymatic routes and strategies followed for the generation of bioactive peptides.

Optimization of enzymatic production of anti-diabetic peptides from black bean (Phaseolus vulgaris L.) proteins, their characterization and biological potential

The aim was to optimize the production of bioactive peptides from black bean (Phaseolus vulgaris L.) protein isolate and to determine their biological potential using biochemical and in silico approaches. Protein fractions were generated using eight commercially available proteases after 2, 3 and 4 h and 1:20, 1:30 and 1:50 enzyme/substrate (E/S) ratios. The best combination of conditions to generate anti-diabetic peptides was with alcalase for 2 h and E/S of 1:20; with inhibition values for dipeptidyl peptidase IV (DPP-IV, 96.7%), α-amylase (53.4%) and α-glucosidase (66.1%). Generated peptides were characterized using LC-ESI-MS/MS. Molecular docking analysis was performed to predict individual peptide biological potential using DockingServer®. Peptides EGLELLLLLLAG, AKSPLF and FEELN inhibited DPP-IV more efficiently in silico through free energy interactions of -9.8, -9.6 and -9.5 kcal mol(-1), respectively, than the control sitagliptin (-8.67 kcal mol(-1)). The peptide TTGGKGGK (-8.97 kcal mol(-1)) had higher inhibitory potential on α-glucosidase compared to the control acarbose (-8.79 kcal mol(-1)). Peptides AKSPLF (-10.2 kcal mol(-1)) and WEVM (-10.1 kcal mol(-1)) generated a lower free energy interaction with the catalytic site of α-amylase in comparison with acarbose (-9.71 kcal mol(-1)). Bean peptides inhibited the tested enzymes through hydrogen bonds, polar and hydrophobic interactions. The main bindings on the catalytic site were with ASP192, GLU192 and ARG 253 on DPP-IV; TYR151, HIS201 and ILE235 on α-amylase; and ASP34, THR83 and ASN32 on α-glucosidase. For the first time, a systematic evaluation and characterization of the anti-diabetic peptides from black bean protein isolate is presented with the potential for inhibiting important molecular markers related to diabetes.

Milk proteins as a source of tryptophan-containing bioactive peptides

Tryptophan (W) is an essential amino acid which is primarily required for protein synthesis. It also acts as a precursor of key biomolecules for human health (serotonin, melatonin, tryptamine, niacin, nicotinamide adenine dinucleotide (NAD), phosphorylated NAD (NADP), quinolinic acid, kynureric acid, etc.). Among dietary proteins, milk proteins are particularly rich in W. W residues within milk proteins may be released by proteolytic/peptidolytic enzymes either as a free amino acid or as part of peptide sequences. Different W-containing peptides originating from milk proteins have been shown in vitro to display a wide range of bioactivities such as angiotensin converting enzyme (ACE) inhibition along with antioxidant, antidiabetic and satiating related properties. Free W has been shown in certain instances to have an effect on cognition and the aforementioned bioactive properties. However, a higher bioactive potency has generally been observed with specific W-containing peptides compared to free W. Since W is thermolabile, the impact of processing on the stability of W-containing peptides needs to be considered. Milk protein-derived W-containing peptides may have significant potential as natural health promoting agents in humans.