Bioactive Peptides from Germinated Soybean with Anti-Diabetic Potential by Inhibition of Dipeptidyl Peptidase-IV, α-Amylase, and α-Glucosidase Enzymes

Identification of dipeptidyl peptidase IV (DPP-IV) inhibitory peptides from vegetable protein sources

Vegetable proteins are appearing as a sustainable source for human consumption. Food-derived peptides are an important field of research in terms of bioactive molecules. In this study, seven vegetable proteins were enzymatically hydrolysed following an optimised treatment (sequential hydrolysis with subtilisin-trypsin-flavourzyme) to obtain dipeptidyl peptidase IV (DPP-IV) inhibitory peptides. Hydrolysates were fractionated by size exclusion chromatography and, from the most bioactive fractions (corresponding to Glycine max, Chenopodium quinoa and Lupinus albus proteins); peptides responsible for this bioactivity were identified by mass spectrometry. Peptides with adequate molecular features and based on in silico analysis were proposed as DPP-IV inhibitors from soy (EPAAV) lupine (NPLL), and quinoa (APFTVV). These vegetable protein sources are adequate to obtain protein hydrolysates for functional food.

Bioactive Peptides as Potential Nutraceuticals for Diabetes Therapy: A Comprehensive Review

Diabetes mellitus is a major public health concern associated with high mortality and reduced life expectancy. The alarming rise in the prevalence of diabetes is linked to several factors including sedentary lifestyle and unhealthy diet. Nutritional intervention and increased physical activity could significantly contribute to bringing this under control. Food-derived bioactive peptides and protein hydrolysates have been associated with a number health benefits. Several peptides with antidiabetic potential have been identified that could decrease blood glucose level, improve insulin uptake and inhibit key enzymes involved in the development and progression of diabetes. Dietary proteins, from a wide range of food, are rich sources of antidiabetic peptides. Thus, there are a number of benefits in studying peptides obtained from food sources to develop nutraceuticals. A deeper understanding of the underlying molecular mechanisms of these peptides will assist in the development of new peptide-based therapeutics. Despite this, a comprehensive analysis of the antidiabetic properties of bioactive peptides derived from various food sources is still lacking. Here, we review the recent literature on food-derived bioactive peptides possessing antidiabetic activity. The focus is on the effectiveness of these peptides as evidenced by in vitro and in vivo studies. Finally, we discuss future prospects of peptide-based drugs for the treatment of diabetes.

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.

In vitro protein digestibility and biochemical characteristics of soaked, boiled and fermented soybeans

Protein digestibility of soybean obtained from the main manufacturing steps for natto, such as soaking (soaked soybeans 'S'), boiling (boiled soybeans 'B'), and fermentation (fermented soybeans 'F'), was examined in this study. Biochemical indices for the processed soybeans from each manufacturing step and those digested fractions by simulated in vitro gastrointestinal digestion were also evaluated. The result showed a significant (P < 0.05) increase in the protein digestibility of B (48.71 ± 0.04%) and F (50.21 ± 0.45%) compared to that of S (20.58 ± 0.25%), accompanying the accumulation of small protein sub-fractions and essential amino acids. Besides, antioxidant activity indices of all digested fractions increased around two to fourfold at the end of the simulated digestion. F showed a consistently increasing trend when the digestion stage progressed and maximum values overall at the final digestion stage.  Soybeans from fermentation step showed higher protein digestibility and indispensable amino acids as well as potential bioactivities than those from boiling and soaking step. The results demonstrated that manufacturing steps improved nutritional values of soybean protein, such as bioavailability of amino acids and certain bioactivities.

Chemical Group Profiling, In Vitro and In Silico Evaluation of Aristolochia ringens on α-Amylase and α-Glucosidase Activity

Diabetes mellitus (DM) has become a global scourge, and there is a continuous search for novel compounds as viable alternatives to synthetic drugs which are often accompanied by severe adverse effects. Aristolochia ringens is among the scientifically implicated botanicals effective in the management of several degenerative diseases including DM. The current study evaluated the inhibitory mechanism(s) of root extract of A. ringens on α-amylase and α-glucosidase in vitro and in silico, while its constituents were characterized using liquid chromatography-mass spectrometric technique. The extract had concentration-dependent inhibitory effect on the study enzymes, and the inhibition compared well with that of standard drug (acarbose) with respective IC₅₀ values of 0.67 mg/mL (α-amylase) and 0.57 mg/mL (α-glucosidase) compared with that of the extract (0.63 and 0.54 mg/mL). The extract competitively and uncompetitively inhibited α-amylase and α-glucosidase, respectively. Of the identified compounds, dianoside G (−12.4, −12.5 kcal/mol) and trilobine (−10.0, −10.0 kcal/mol) had significant interactions with α-amylase and α-glucosidase, respectively, while magnoflorine and asiatic acid also interacted keenly with both enzymes, with quercetin 3-O-glucuronide and strictosidine showing better affinity towards α-glucosidase. These observations are suggestive of involvement of these compounds as probable ligands contributing to antidiabetic potential of the extract. While studies are underway to demystify the yet to be identified compounds in the extract, the data presented have lent scientific credence to the acclaimed in vivo antidiabetic potential of the extract and suggested it as a viable source of oral hypoglycaemic agent.

Role of zonulin and GLP-1/DPP-IV in alleviation of diabetes mellitus by peptide/polypeptide fraction of Aloe vera in streptozotocin- induced diabetic wistar rats

ETHNO-PHARMACOLOGICAL RELEVANCE

The genus Aloe has a long history of usage in medicine. Aloe barbadensis Miller, commonly known as Aloe vera, is said to possess anti-diabetic, anti-inflammatory, anti-cancer, anti-microbial, immunomodulation, wound healing properties.

AIM OF THE STUDY

In diabetes mellitus, loss in intestinal permeability is observed with high levels of zonulin and low levels of glucagon-like peptide-1 (GLP-1) leading to hyperglycemia. The aim of the study was to understand the role of peptide/polypeptide fraction (PPF) of Aloe vera in the alleviation of diabetes through maintaining the intestinal permeability by regulating the zonulin and GLP-1 levels.

MATERIALS AND METHODS

The PPF of Aloe vera was obtained through trichloroacetic acid precipitation. The anti-diabetic potential of the PPF was tested through DPP-IV inhibition, glucose diffusion assay, and by using Rin-m5F cells. The anti-diabetic potential of the PPF was tested at a dose of 0.450 mg/kg bw in vivo using streptozotocin-induced diabetic Wistar rats. The effect of PPF on fasting plasma glucose, insulin, glucagon, Zonulin, GLP-1, DPP-IV, levels were studied in diabetic rats. The histopathological studies of the pancreas, small intestine, and liver were carried out for organ-specific effects.

RESULTS

PPF has the ability to reduce fasting plasma glucose levels with concomitant increase in insulin levels in streptozotocin-induced diabetic rats. It was also observed that increase in GLP-1 levels with a decrease in DPP-IV and zonulin levels thereby mitigating the loss of intestinal permeability. These findings correlate with the small intestine's histopathological observation where the excessive proliferation of epithelium in the small intestine of diabetic rats was reduced after PPF treatment.

CONCLUSION

These results suggest that the PPF of Aloe vera alleviates diabetes through islet cell rejuvenation via GLP-1/DPP-IV pathway and thereby suggesting the usage of PPF as an alternate medicine for diabetes mellitus with the possibility to reduce the intestinal permeability and zonulin levels.

Insetos comestíveis como potenciais fontes de proteínas para obtenção de peptídeos bioativos

Resumo O consumo de insetos como uma fonte alternativa de proteínas é considerado uma tendência futura e uma estratégia viável, com potencial notório para garantia do fornecimento de alimentos em nível global. Os insetos são uma fonte não convencional de proteínas, seja para consumo humano direto ou indiretamente, como ingredientes em alimentos formulados. Além disso, estudos científicos têm demonstrado que a hidrólise enzimática destas proteínas resulta na produção de peptídeos com atividades biológicas de grande interesse, como atividade antioxidante, antidiabética, anti-hipertensiva e antimicrobiana. O uso desses peptídeos com fim nutracêutico pode substituir ou reduzir o uso de drogas sintéticas, as quais estão associadas a efeitos colaterais indesejáveis. O presente trabalho teve como objetivo abordar o uso de insetos na alimentação humana, destacando sua aplicação como substrato proteico na hidrólise enzimática para produção de peptídeos bioativos. As principais propriedades bioativas dos peptídeos foram relatadas.

Anti-diabetic effects of bioactive peptides: recent advances and clinical implications

Diabetes mellitus, particularly type 2 diabetes, is a major global health issue, the prevalence of which seems to be on the rise worldwide. Interventions such as healthy diet, physical activity, maintaining a healthy weight, and medication (for those with a diagnosis of diabetes) are among the most effective strategies to prevent and control diabetes. Three-quarters of patients diagnosed with diabetes are in countries with poor financial infrastructure, nutritional awareness and health care systems. Concomitantly, the cost involved in managing diabetes through the intake of antidiabetic drugs makes it prohibitive for majority of patients. Food protein-derived bioactive peptides have the potential of being formulated as nutraceuticals and drugs in combating the pathogenesis and pathophysiology of metabolic disorders with little or "no known" complications in humans. Coupled with lifestyle modifications, the potential of bioactive peptides to maintain normoglycemic range is actualized by influencing the activities of incretins, DPP-IV, α-amylase, and α-glucosidase enzymes. This article discusses the biofunctionality and clinical implications of anti-diabetic bioactive peptides in controlling the global burden of diabetes.

Identification and characterization of novel α-amylase and α-glucosidase inhibitory peptides from camel whey proteins

This study explores the inhibitory properties of camel whey protein hydrolysates (CWPH) toward α-amylase (AAM) and α-glucosidase (AG). A general full factorial design (3 × 3) was applied to study the effect of temperature (30, 37, and 45°C), time (120, 240, and 360 min), and enzyme (pepsin) concentration (E%; 0.5, 1, and 2%). The results showed that maximum degree of hydrolysis was obtained when hydrolysis was carried out at higher temperature (45°C; P < 0.05), compared with lower temperatures of 30 and 37°C. Electrophoretic pattern displays degradation of all protein bands upon hydrolysis by pepsin at various hydrolysis conditions applied. All the 27 CWPH generated showed significant AAM and AG inhibitory potential as indicated by their lower IC₅₀ values (mg/mL) compared with intact whey proteins. In total 196 peptides were identified from selected hydrolysates and 15 potential peptides (PepSite score > 0.8; http://pepsite2.russelllab.org/) were explored via in silico approach. Novel peptides PAGNFLMNGLMHR, PAVACCLPPLPCHM, MLPLMLPFTMGY, and PAGNFLPPVAAAPVM were identified as potential inhibitors for both AAM and AG due to their high number of binding sites and highest binding probability toward the target enzymes. CCGM and MFE, as well as FCCLGPVPP were identified as AG and AAM inhibitory peptides, respectively. This is the first study that reports novel AG and AAM inhibitory peptides from camel whey proteins. The future direction for this research involves synthesis of these potential AG and AAM inhibitory peptides in a pure form and investigate their antidiabetic properties in the in vitro, as well as in vivo models. Thus, CWPH can be considered for potential applications in glycaemic regulation.

Proteins and peptides from vegetable food sources as therapeutic adjuvants for the type 2 diabetes mellitus

Proteins and peptides are fundamental components of the cereals, pseudocereals, and legumes, giving them numerous health-beneficial properties. Previous studies have demonstrated that these molecules exerted effects on current therapeutic targets related to type 2 diabetes mellitus, such as incretin hormones (responsible for appetite suppression), dipeptidyl peptidase IV (an enzyme involved in the inactivation and degradation of the incretin hormones), and glucose transporters (molecules that transport glucose in or out of cells). Therefore, this review presents the current biological activity of protein derivatives and peptides isolated from cereals, pseudocereals, and legumes on these therapeutic markers, highlighting their potential as a possible pharmacological treatment for type 2 diabetes mellitus.

In-vitro anti-diabetic activity and in-silico studies of binding energies of palmatine with alpha-amylase, alpha-glucosidase and DPP-IV enzymes

Palmatine a protoberberine alkaloid has been previously reported to possess in vivo antidiabetic and antioxidant property. The aim of the experiment is to evaluate the in vitro antidiabetic activity and in-silico studies of the binding energies of Palmatine, acarbose, and Sitagliptin with the three enzymes of alpha-amylase, alpha-glucosidase, and dipeptidyl peptidase-IV (DPP-IV). The in vitro antidiabetic study was done by evaluating the inhibitory effect of palmatine on the activities of alpha-amylase, alpha-glucosidase, and DPP-IV. Acarbose, and sitagliptin was used as standard drug. The molecular docking study was performed to study the binding interactions of palmatine with alpha-glucosidase, a-amylase, and DPP-IV. The binding interactions were compared with the standard compounds Sitagliptin and acarbose. Palmatine with IC50 (1.31 ± 0.27 µM) showed significant difference of (&lt; 0.0001) higher inhibiting effect on alpha-amylase and weak inhibiting effect on alpha-glucosidase enzyme with IC50 (9.39 ± 0.27 µM) and DPP-IV with IC50 (8.7 ± 1.82 µM). Palmatine possess inhibition effect on the three enzymes.

Membrane-based preparative methods and bioactivities mapping of tempe-based peptides

This study was aimed to produce bioactive peptides from optimally fermented tempe, and map their overall bioactivities. There were three preparative methods utilized for producing tempe-based peptides, such as water-facilitated extraction, alcalase, and papain hydrolysis, and in combination with membrane filtration. Fermenting soybean at 144 h was selected as the optimum time based on protein content and degree of hydrolysis. Through SDS-PAGE analysis, an increased degree of hydrolysis with longer fermentation time was confirmed. The best preparative method for producing bioactive peptides was through papain hydrolysis and followed by 5 kDa membrane filtration. By this, the enhancement was distinct for antioxidant activity, ACE-, α-glucosidase-, and Kunitz trypsin-inhibitory activity. The annotated peptide sequences resulting from Nano LC Ultimate 3000 Series System tandem Q Exactive™ Hybrid Quadrupole-Orbitrap™ Mass Spectrometer were matched with the BIOPEP database. The major bioactivities of tempe peptides obtained were as an ACE inhibitor, antioxidant, and antithrombotic.

Gastrointestinal Digestion of Food Proteins under the Effects of Released Bioactive Peptides on Digestive Health

The gastrointestinal tract represents a specialized interface between the organism and the external environment. Because of its direct contact with lumen substances, the modulation of digestive functions by dietary substances is supported by a growing body of evidence. Food-derived bioactive peptides have demonstrated a plethora of activities in the organism with increasing interest toward their impact over the digestive system and related physiological effects. This review updates the biological effects of food proteins, specifically milk and soybean proteins, associated to gastrointestinal health and highlights the study of digestion products and released peptides, the identification of the active form/s, and the evaluation of the mechanisms of action underlying their relationship with the digestive cells and receptors. The approach toward the modifications that food proteins and peptides undergo during gastrointestinal digestion and their bioavailability is a crucial step for current investigations on the field. The recent literature on the regulation of digestive functions by peptides has been mostly considered in terms of their influence on gastrointestinal motility and signaling, oxidative damage and inflammation, and malignant cellular proliferation. A final section regarding the actual challenges and future perspectives in this scientific topic is critically discussed.

Antidiabetic Food-Derived Peptides for Functional Feeding: Production, Functionality and In Vivo Evidences

Bioactive peptides released from the enzymatic hydrolysis of food proteins are currently a trending topic in the scientific community. Their potential as antidiabetic agents, by regulating the glycemic index, and thus to be employed in food formulation, is one of the most important functions of these peptides. In this review, we aimed to summarize the whole process that must be considered when talking about including these molecules as a bioactive ingredient. In this regard, at first, the production, purification and identification of bioactive peptides is summed up. The detailed metabolic pathways described included carbohydrate hydrolases (glucosidase and amylase) and dipeptidyl-peptidase IV inhibition, due to their importance in the food-derived peptides research field. Then, their characterization, concerning bioavailability in vitro and in situ, stability and functionality in food matrices, and ultimately, the in vivo evidence (from invertebrate animals to humans), was described. The future applicability that these molecules have due to their biological potential as functional ingredients makes them an important field of research, which could help the world population avoid suffering from several diseases, such as diabetes.

Regulatory T Cells in Bioactive Peptides-Induced Oral Tolerance; a Two-Edged Sword Related to the Risk of Chronic Diseases: A Systematic Review

This systematic review assesses the literature regarding beneficial and potential detrimental effects of bioactive peptides (BPs), focusing on evidence of regulatory T cells (T-regs) mediated oral tolerance (OT), collagen hydrolysate (CH) supplementation in osteoarthritis (OA) and the association of T-regs with chronic disease. The systematic search was done for articles published from inception to April 2019 using the PubMed and Scopus databases. About 3081 papers were identified by three different search strategies and screened against inclusion criteria which resulted in the inclusion of 22 articles. From the included articles, 12 papers were related to treatment of different disease in vivo by oral administration of BPs, six articles evaluated the effects of CH supplementation, as a rich source of BPs, on OA pain-relief and four observational studies assessed the association of circulating T-regs and risk of cancer and cardiovascular disease (CVD). The evidence obtained from first search strategy, indicated that oral administration of BPs improve clinical manifestations of animal models of allergy, arthritis, atherosclerosis, ulcerative colitis and allograft rejection by T-regs expansion; while, observational studies showed that although higher levels of circulating T-regs reduced risk of CVD and allergy, but, increased risk of solid cancers.

A comprehensive review of bioactive peptides obtained from animal byproducts and their applications

Livestock generates high quantities of residues, which has become a major socioeconomic issue for the meat industry. This review focuses on the identification of bioactive peptides (BPs) in animal byproducts and meat wastes. Firstly, the main bioactivities that peptides can have will be described and the methods for their evaluation will be discussed. Secondly, the various origins of these BPs will be studied. Then, the techniques and tools for the generation of BPs will be detailed in order to discuss, in the final part, how peptides could be used and assimilated. BPs possess diverse biological activities and can be strategic candidates for substituting synthetic molecules. In silico potentiality studies are a helpful tool to understand and predict BPs released from proteins and their potential activities. However, in vitro validation is often required. Although BP use is compelled by strict regulations in relation to the field of application, they are also limited by their low bioavailability and bioaccessibility. Therefore, it is important to test peptide stability during gastrointestinal digestion. Protective strategies have been discussed since their use could improve the stability and effectiveness of BPs.

Exploration of dipeptidyl-peptidase IV (DPP IV) inhibitors in a low-molecular mass extract of the earthworm Eisenia fetida and identification of the inhibitors as amino acids like methionine, leucine, histidine, and isoleucine

We have reported previously that the water extract of the earthworm Eisenia fetida has inhibitory effect on human dipeptidyl-peptidase IV (DPP IV) in vitro. Here we studied to identify DPP IV inhibitors in a low-molecular mass extract (designated U3EE) under 3 kDa prepared from the water extract. U3EE showed 50 % inhibition (IC₅₀) at the concentration of 5.3 ± 0.3 mg/mL. An inhibitory active fraction obtained by solid-phase extraction of U3EE was separated into three parts by reversed-phase HPLC. These parts were shown by GC/MS to be composed of ten (Ala, Gly, Thr, Ser, Asn, Asp, Lys, His, Orn, and cystine), two (Leu and Ile), and one (Met) amino acids, respectively. Among them, Met, Leu, and His showed strong inhibition with IC₅₀ values of 3.4 ± 0.3, 6.1 ± 0.3 and 14.7 ± 1.2 mM, respectively; Ala, Lys, Orn, and Ile showed rather weaker inhibition than those, while the others showed no inhibition. Met, Leu, and Ile were competitive inhibitors and His was a mixed-type one. DPP IV inhibition by U3EE might be due to additive and/or synergistic effects of the inhibitory amino acids, suggesting that it could be useful as pharmaceutical and supplement for diabetes prevention.

Bioprocessing of common pulses changed seed microstructures, and improved dipeptidyl peptidase-IV and α-glucosidase inhibitory activities

Type 2 diabetes mellitus (T2DM) is a leading cause of death globally. T2DM patients experience glucose intolerance, and inhibitors of dipeptidyl peptidase IV (DPP-IV) and α-glucosidase are used as drugs for T2DM management. DPP-IV and α-glucosidase inhibitors are also naturally contained in foods, but their potency can be affected by the food matrix and processing methods. In this study, germination and solid-state fermentation (SSF) were used to alter pulse seed microstructures, to convert compounds into more bioactive forms, and to improve their bioaccessibility. Germination substantially modified the seed microstructure, protein digestibility, contents and profiles of phenolic compounds in all the pulses. It also increased DPP-IV and α-glucosidase inhibitory activities in chickpeas, faba beans and yellow peas. Compared to germination, SSF with Lactobacillus plantarum changed the content and the profile of phenolic compounds mainly in yellow peas and green lentils because of greater disruption of the seed cell wall. In the same pulses, heat treatment and SSF of flour increased DPP-IV and α-glucosidase inhibitory activities. The results of this study suggest that germination and SSF with L. plantarum are effective and simple methods for modulating phenolic and protein profiles of common pulses and improve the action on DPP-IV and α-glucosidase.

Bioactive Constituents of F. esculentum Bee Pollen and Quantitative Analysis of Samples Collected from Seven Areas by HPLC

Bee pollen contains all the essential amino acids needed by humans. China is the largest producer of bee pollen in the world. In the present study, we identified 11 fatty acids in F. esculentum bee pollen oil by GC-MS analysis, and 16 compounds were isolated from F. esculentum bee pollen by column chromatography and identified. A high-performance liquid chromatography-diode array detector (HPLC-DAD) method was established for the quality control of F. esculentum bee pollen. A validated HPLC-DAD method was successfully applied to the simultaneous characterization and quantification of nine main constituents in seven samples collected from seven different areas in China. The results showed that all standard calibration curves exhibited good linearity (R2 > 0.999) in HPLC-DAD analysis with excellent precision, repeatability and stability. The total amount in the samples from the seven regions ranged from 23.50 to 46.05 mg/g. In addition, seven compounds were studied for their bioactivity using enzymic methods, whereby kaempferol (3) showed high α-glucosidase inhibitory activity (IC50: 80.35 μg/mL), ergosterol peroxide (8) showed high tyrosinase inhibitory activity (IC50: 202.37 μg/mL), and luteolin (1) had strong acetylcholinesterase inhibitory activity (IC50: 476.25 μg/mL). All results indicated that F. esculentum bee pollen could be a nutritious health food.

Soybean Peptides Exert Multifunctional Bioactivity Modulating 3-Hydroxy-3-Methylglutaryl-CoA Reductase and Dipeptidyl Peptidase-IV Targets in Vitro

This study was aimed at evaluating the cellular mechanism through which peptic (P) and tryptic (T) soybean hydrolysates modulate the targets involved in hypocholesterolemic pathways in HepG2 and antidiabetic pathways in Caco-2 cells. Both hydrolysates (tested in the concentration range of 0.5-2.5 mg/mL) inhibited the 3-hydroxy-3-methylglutaryl-CoA reductase activity in HepG2 cells. In addition, Soybean P increased LDLR protein levels on HepG2 membranes by 51.5 ± 11.6% and 63.0 ± 6.9% (0.5-1.0 mg/mL) whereas Soybean T increased them by 55.2 ± 9.7% and 85.8 ± 21.5% (0.5-1.0 mg/mL) vs the control, with a final improved HepG2 capacity in the uptake of extracellular LDL. Soybean P reduced in vitro the dipeptidyl peptidase-IV activity by 16.3 ± 3.0% and 31.4 ± 0.12% (1.0 and 2.5 mg/mL), whereas Soybean T reduced it by 15.3 ± 11.0% and 11.0 ± 0.30% (1.0 and 2.5 mg/mL) vs the control. Finally, both hydrolysates inhibited dipeptidyl peptidase-IV activity in situ in human intestinal Caco-2 cells. This investigation may help to explain the activities observed in experimental and clinical studies.

Anti-α-Glucosidase Activity by a Protease from Bacillus licheniformis

Anti-α-glucosidase (AAG) compounds have received great attention due to their potential use in treating diabetes. In this study, Bacillus licheniformis TKU004, an isolated bacterial strain from Taiwanese soil, produced AAG activity in the culture supernatant when squid pens were used as the sole carbon/nitrogen (C/N) source. The protein TKU004P, which was isolated from B. licheniformis TKU004, showed stronger AAG activity than acarbose, a commercial anti-diabetic drug (IC₅₀ = 0.1 mg/mL and 2.02 mg/mL, respectively). The molecular weight of TKU004P, determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), was 29 kDa. High-performance liquid chromatography (HPLC) analysis showed that TKU004P may be a protease that demonstrates AAG activity by degrading yeast α-glucosidase. Among the four chitinous sources of C/N, TKU004P produced the highest AAG activity in the culture supernatant when shrimp head powder was used as the sole source (470.66 U/mL). For comparison, 16 proteases, were investigated for AAG activity but TKU004P produced the highest levels. Overall, the findings suggest that TKU004P could have applications in the biochemical and medicinal fields thanks to its ability to control the activity of α-glucosidase.

A Novel Dipeptidyl Peptidase IV Inhibitory Tea Peptide Improves Pancreatic β-Cell Function and Reduces α-Cell Proliferation in Streptozotocin-Induced Diabetic Mice

Dipeptidyl peptidase IV (DPP-IV) inhibitors occupy a growing place in the drugs used for the management of type 2 diabetes. Recently, food components, including food-derived bioactive peptides, have been suggested as sources of DPP-IV inhibitors without side effects. Chinese black tea is a traditional health beverage, and it was used for finding DPP-IV inhibitory peptides in this study. The ultra-filtrated fractions isolated from the aqueous extracts of black tea revealed DPP-IV inhibitory activity in vitro. Four peptides under 1 kDa were identified by SDS-PAGE and LC-MS/MS (Liquid Chromatography-Mass Spectrometry-Mass Spectrometry) from the ultra-filtrate. The peptide II (sequence: AGFAGDDAPR), with a molecular mass of 976 Da, showed the greatest DPP-IV inhibitory activity (in vitro) among the four peptides. After administration of peptide II (400 mg/day) for 57 days to streptozotocin (STZ)-induced hyperglycemic mice, the concentration of glucagon-like peptide-1 (GLP-1) in the blood increased from 9.85 ± 1.96 pmol/L to 19.22 ± 6.79 pmol/L, and the insulin level was increased 4.3-fold compared to that in STZ control mice. Immunohistochemistry revealed the improved function of pancreatic beta-cells and suppressed proliferation of pancreatic alpha-cells. This study provides new insight into the use of black tea as a potential resource of food-derived DPP-IV inhibitory peptides for the management of type 2 diabetes.