Dipeptidyl Peptidase IV Inhibitory Activity Research Articles

DPP-IV Inhibitory Potentials of Flavonol Glycosides Isolated from the Seeds of Lens culinaris: In Vitro and Molecular Docking Analyses.

Dipeptidyl peptidase IV (DPP-IV), a new target for the treatment of type 2 diabetes mellitus, degrades incretins such as glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide. DPP-IV inhibitors shorten the inactivation of GLP-1, permitting the incretin to stimulate insulin release, thereby combating hyperglycemia. In our ongoing search for new DPP-IV inhibitors from medicinal plants and foods, three flavonol glycosides (1–3) were isolated from the seeds of Lens culinaris Medikus (Fabaceae) and tested for their DPP-IV–inhibitory activity. We demonstrated for the first time, that compounds 1–3 inhibited DPP-IV activity in a concentration-dependent manner in our in vitro bioassay system. In addition, molecular docking experiments of compounds 1–3 within the binding pocket of DPP-IV were conducted. All investigated compounds readily fit within the active sites of DPP-IV, in low-energy conformations characterized by the flavone core structure having optimal electrostatic attractive interactions with the catalytic triad residues of DPP-IV.

In silico methods to identify ACE and DPP-IV inhibitory activities of ribosomal hazelnut proteins

In this study, an in silico attempt was made to evaluate the biological functionality of hazelnut (Corylus avellana L.) peptides, using three gastrointestinal (GI) and three non-GI enzymes. As of March 2017, 469 hazelnut proteins were listed on UniProt database. Here, a small subset (i.e., 23 ribosomal proteins) was investigated. Using in silico proteolysis, the efficacy of gastrointestinal proteases (i.e., trypsin, pepsin, chymotrypsin) were compared to various other non-GI proteases such as thermolysin, papain and bromelain for the generation of bioactive peptides. In most cases, gastrointestinal proteases (i.e., trypsin, pepsin, chymotrypsin) were shown to be less efficient compared to various other non-GI proteases such as thermolysin, papain and bromelain in the generation of bioactive peptides. After in silico proteolysis, the extent of angiotensin-converting enzyme (ACE)-inhibitory peptide content (A′) accounted for approximately 5.1, 7.9 and 9.1% of all amino acids present for bromelain, thermolysin and papain treatments, respectively, while comparable results were obtained for dipeptidyl peptidase-IV (DPP-IV) inhibitory activity (4.8, 8, and 10.9%). In all cases, ACE- and DPP-IV inhibitory activities were dominant to all other activities. Based on the current findings, ribosomal hazelnut proteins could be considered as a valuable source of bioactive peptides.

Isolation and characterization of peptides with dipeptidyl peptidase IV (DPPIV) inhibitory activity from natto using DPPIV from Aspergillus oryzae

Human-derived dipeptidyl peptidase IV (DPPIV) is a costly material used in the discovery of drugs for diabetes. In this study, we demonstrated the efficacy of DPPIV from Aspergillus oryzae as an alternative to human-derived DPPIV for identifying DPPIV inhibitors. Fermented soybean, also called natto, suppresses blood glucose levels in humans; however, the underlying mechanism remains unknown. This study determined the in vitro DPPIV inhibitory activity of isolated peptides from natto. Amino acid sequences of two peptides isolated from natto were identified by LC/MS/MS as Lys-Leu and Leu-Arg. These isolated peptides inhibited DPPIV in a dose-dependent manner, with IC50 values of 41.40 ± 2.68 and 598.02 ± 18.35 μg/ml, respectively. These results indicate the potential mechanism of blood glucose control by natto and novel roles of Lys-Leu and Leu-Arg as DPPIV inhibitors.

Investigation of medicinal plants from Madagascar against DPP-IV linked to type 2 diabetes

The Madagascarian plants which have been investigated in this study have been used as antidiabetic plants in traditional medicine. As the control of dipeptidyl peptidase IV (DPP-IV) activity is an important aspect in management of type 2 diabetes, the purpose of the present study was evaluation of DPP-IV inhibitory activity of medicinal plants from Madagascar. Ethyl acetate extracts were screened for DPP-IV inhibitory activity. High-resolution DPP-IV inhibition profiling was employed for identification of active peaks. Preparative-scale HPLC was performed for isolation, and elucidation of the compound structure was done by high-performance liquid chromatography-high-resolution mass spectrometry-solid-phase extraction-nuclear magnetic resonance spectroscopy, HPLC-HRMS-SPE-NMR. Only the ethyl acetate extract of Antidesma madagascariense Lam. leaves showed DPP-IV inhibitory activity with an IC50 value of 79.2±2.8μg/mL. Amentoflavone, which was identified for the first time in A. madagascariense, was identified as DPP-IV inhibitor, with an IC50 value of 3.9±0.5μM. This is the first report on DPP-IV inhibition by amentoflavone. Thus, this plant is a promising species for use in herbal medicine as a DPP-IV inhibitor.

Investigation on antioxidant, angiotensin converting enzyme and dipeptidyl peptidase IV inhibitory activity of Bambara bean protein hydrolysates

Protein isolate was hydrolysed by Alcalase, thermolysin and trypsin. BBPH produced by Alcalase showed highest angiotensin-converting enzyme (ACE) inhibitory properties (IC50: 52 µg/mL). Hydrolysates produced by Alcalase and thermolysin exhibited similar dipeptidyl peptidase-IV (DPP-IV) inhibitory activity (IC50: 1.73 mg/mL), while low inhibitory activity was observed for hydrolysate produced by trypsin. BBPH also showed protective effect against oxidative stress with significant 2,2-diphenyl-1-picrylhydrazyl radical scavenging and ferrous chelating activity. Bioactive peptides of BBPH produced by thermolysin showed better resistance to simulated gastrointestinal digestion (SGID), while the DPP-IV and ACE inhibitory properties were significantly reduced. Molecular weight distribution showed significant reduction in peptides of the molecular weight range 200–400 Da in BBPH produced by Alcalase, after SGID. LC-ESI-TOF-MS and in silico analysis showed the presence of potential peptides with both ACE and DPP-IV inhibitory properties in BBPH produced by thermolysin.

Angiotensin converting enzyme and dipeptidyl peptidase-IV inhibitory activities of transglutaminase treated sodium caseinate hydrolysates

Angiotensin converting enzyme (ACE) and dipeptidyl peptidase-IV (DPP-IV) inhibitory activities of cross-linked and non-cross-linked sodium caseinate (NaCN) hydrolysates were studied. Three different samples were generated: NaCN hydrolysed with Prolyve 1000™ (Prolyve), NaCN cross-linked with transglutaminase (TGase) pre-Prolyve hydrolysis and NaCN cross-linked post-Prolyve hydrolysis. Gel filtration and reverse phase HPLC analysis of the resulting samples indicated that the hydrolysates had similar peptide profiles. Hydrolysates showed higher (p < 0.05) ACE and DPP-IV inhibitory activity compared with intact protein, but no significant (p > 0.05) differences in activity were found between cross-linked and non-cross-linked hydrolysate samples. Hydrolysate IC50 values for ACE and DPP-IV inhibition ranged from 0.10 to 0.17 mg mL−1 and 0.85–1.18 mg mL−1, respectively. Simulated gastrointestinal digestion had no significant (p > 0.05) effect on the bioactivities of the hydrolysates. The results demonstrated that incubation with TGase before or after NaCN hydrolysis with Prolyve had no effect on ACE or DPP-IV inhibitory activities.

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

Dipeptidyl peptidase-IV (DPP-IV) inhibitory peptides were rapidly identified from Ruditapes philippinarum hydrolysate. The hydrolysate was fractionated by ethanol precipitation and preparative reverse phase high-performance liquid chromatography (RP-HPLC). The fraction which showed the highest DPP-IV inhibitory activity was then analyzed by a high-throughput nano-liquid chromatography electrospray ionization tandem mass spectrometry (nano-LC ESI-MS/MS) method, and the sequences of peptides were identified based on the MS/MS spectra against the Mollusca protein data from the UniProt database. In total, 50 peptides were identified. Furthermore, molecular docking was used to identify potential DPP-IV inhibitors from the identified peptides. Docking results suggested that four peptides: FAGDDAPR, LAPSTM, FAGDDAPRA, and FLMESH, could bind pockets of DPP-IV through hydrogen bonds, π-π bonds, and charge interactions. The four peptides were chemically synthesized and tested for DPP-IV inhibitory activity. The results showed that they possessed DPP-IV inhibitory activity with IC50 values of 168.72 μM, 140.82 μM, 393.30 μM, and >500 μM, respectively. These results indicate that R. philippinarum-derived peptides may have potential as functional food ingredients for the prevention of diabetes.

Purification, identification and molecular mechanism of two dipeptidyl peptidase IV (DPP-IV) inhibitory peptides from Antarctic krill (Euphausia superba) protein hydrolysate.

Dipeptidyl peptidase IV (DPP-IV) played an important role in blood glucose regulation. Inhibition of DPP-IV may improve glycemic control in diabetics by preventing the rapid breakdown of incretin hormones and prolonging their physiological action. In this study, Antarctic krill (Euphausia superba) protein was hydrolyzed using animal proteolytic enzymes. The hydrolysate was purified sequentially by ultrafiltration, gel filtration chromatography and reversed phase high-performance liquid chromatography (RP-HPLC). DPP-IV inhibitory activity of the fractions achieved from Antarctic krill protein was determined by DPP-IV screening reagent kit. Two purified peptides were identified by Xevo G2-XS QTof mass spectrometer (QTOF-MS). One peptide purified was Ala-Pro (AP) with IC50 values of 0.0530mg/mL, the other Ile-Pro-Ala (IPA) with IC50 values of 0.0370mg/mL. They both exhibited strong DPP-IV inhibitory activity. The molecular docking analysis revealed that DPP-IV inhibition by AP and IPA was mainly due to formation of a strong interaction surface force with the 91-96 and 101-105 amino acids of the DPP-IV. Our results suggested that the protein hydrolysate from Antarctic krill can be considered as a promising natural source of DPP-IV inhibitory peptides in the management of diabetes.

Dipeptidyl peptidase IV and quorum sensing signaling in biofilm-related virulence of Prevotella aurantiaca

Biofilm formation and dipeptidyl peptidase IV (DPPIV) enzyme activity contribute to the virulence of oral bacteria, and these virulence factors are partly regulated by quorum sensing signaling system. We recently demonstrated that estradiol regulates growth properties and DPPIV activity of Prevotella intermedia, Prevotella nigrescens, and Prevotella pallens. Here, we examined the DPPIV dependency of biofilm formation of Prevotella aurantiaca. Three strains (two clinical strains AHN 37505 and 37552 and the type strain CCUG 57723) were incubated in three estradiol concentrations (30, 90, and 120 nmol/L). Regulation of DPPIV activity, biofilm and fimbria formation, and coaggregation of bacterial strains were analyzed after incubation with four concentrations (10 nM, 100 nM, 1 μM, 10 μM) of dihydroxy-2,3-pentaedione (DPD), the universal precursor of autoinducer -2 (AI-2), and analogs (ethyl-DPD, butyl-DPD, and isobutyl-DPD) for 24 h. Estradiol enhanced the planktonic growth, coaggregation, and biofilm formation of P. aurantiaca strains. The whole cell extract of AHN 37505 had the highest DPPIV activity, followed by CCUG 57723 and AHN 37552. Inhibition of DPPIV activity with di-isopropylfluorophosphate suppressed the effect of estradiol on biofilm formation. At 100 nM and 10 μM concentrations of DPD, butyl DPD, and isobutyl DPD, biofilm formation of P. aurantiaca was significantly inhibited. Fimbriae formation was enhanced up to concentrations of 100 nM and 1 μM followed by a significant inhibition at higher concentrations of DPD and all analogs. A slight but significant inhibitory effect of DPD and analogs on DPPIV activity was observed. Our results indicate that DPPIV plays a key role in the estradiol-regulated biofilm formation of P. aurantiaca. Quorum sensing autoinducer DPD and C1-alkyl analogs could inhibit biofilm-related virulence of P. aurantiaca.

P 158 - GLP-2 in the capacity of (-)-epicatechin and anthocyanidins to improve insulin sensitivity

Glucagon-like peptide-2 (GLP-2) is an incretin involved in energy balance through the regulation of postprandial glycaemia. GLP-2 is generated from the post-translational cleavage of proglucagon, being rapidly degraded in the bloodstream by dipeptidyl peptidase IV (DPP-IV). We currently investigated the effects of (-)-epicatechin (EC) and anthocyanidins (AC) to modulate GLP-2 using in vivo and in vitro approaches. To assess in vivo effects on proglucagon mRNA and plasma GLP-2 concentrations, male C57BL/6 J mice were fed for 14 w control (C) or high fat (HF) diets without or with 20 mg EC/kg or 40 mg AC/kg BW. Supplementation with EC and AC mitigated HF-induced insulin resistance (improved GTT, ITT, plasma insulin and glucose levels). Plasma GLP-2 levels were 148 and 200% higher in C mice supplemented with EC and AC compared to non-supplemented C mice, and 83 and 46% higher in HF mice supplemented with EC and AC compared to non-supplemented HF mice. Colon proglucagon mRNA levels were higher (84%) in AC-supplemented vs unsupplemented C mice, while EC had no effect. In vitro, cyanidin, but not EC, inhibited DPP-IV activity. The improvement of insulin sensitivity by EC and AC in a model of high fat diet-induced type 2 diabetes could be in part due to GLP-2 upregulation. The underlying mechanisms for AC involve an increase in proglucagon expression and decreased GLP-2 degradation.

Two Novel Bioactive Peptides from Antarctic Krill with Dual Angiotensin Converting Enzyme and Dipeptidyl Peptidase IV Inhibitory Activities.

Inhibition of dipeptidyl peptidase IV (DPP-IV) and angiotensin converting enzyme (ACE) are considered useful in managing 2 often associated conditions: diabetes and hypertension. In this study, corolase PP was used to hydrolyze Antarctic krill protein. The hydrolysate (AKH) was isolated by ultrafiltration and purified by size-exclusion chromatography, ion exchange chromatography and reversed-phase high-performance liquid chromatography (RP-HPLC) sequentially. The in vitro inhibitory activities of all AKHs and several fractions obtained against ACE and DPP-IV were assessed. Two peptides, purified with dual-strength inhibitory activity against ACE and DPP-IV, were identified by TOF-MS/MS. Results indicated that not all fractions exhibited dual inhibitory activities of ACE and DPP-IV. The purified peptide Lys-Val-Glu-Pro-Leu-Pro had half-maximal inhibitory concentrations (IC50 ) of 0.93±0.05 and 0.73±0.04 mg/mL against ACE and DPP-IV, respectively. The other peptide Pro-Ala-Leu had IC50 values of 0.64±0.05 and 0.88±0.03 mg/mL against ACE and DPP-IV, respectively. This study firstly reported the sequences of dual bioactive peptides from Antarctic krill proteins, further provided new insights into the bioactive peptides responsible for the ACE and DPP-IV inhibitory activities from the Antarctic krill protein hydrolysate to manage hypertension and diabetes.

Production and identification of antioxidant and angiotensin-converting enzyme inhibition and dipeptidyl peptidase IV inhibitory peptides from bighead carp (Hypophthalmichthys nobilis) muscle hydrolysate

We investigated bioactive peptides obtained from muscle protein hydrolysate of bighead carp by evaluating in vitro dipeptidyl peptidase IV (DPP-IV) and angiotensin-converting enzyme (ACE) inhibitory capacities and antioxidant activity. Peptide sequences were identified from pepsin hydrolysates. Met-Lys-Ala-Val-Cys-Phe-Ser-Leu was one of the most effective sequences with 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity (EC50=4.58±0.15μM) and relatively high ACE inhibitory capacity (IC50=3.68±0.13μM). Tyr-Asn-Leu-Lys-Glu-Arg-Tyr-Ala-Ala-Trp (IC50=1.35±0.23μM) and Tyr-Asn-Arg-Leu-Pro-Glu-Leu (IC50=3.42±0.39μM) exhibited the most potent ACE inhibitory activity. Ile-Ala-Asp-His-Phe-Leu showed the highest DPP-IV inhibitory activity with an IC50 value of 610.1±82.6μM. All selected peptides were non-toxic, and most were non-allergenic according to in silico predictions. These results indicate the promising potential of bighead carp muscle hydrolysates as functional additives in foods and pharmaceuticals.

A study to evaluate the potential of an in silico approach for predicting dipeptidyl peptidase-IV inhibitory activity in vitro of protein hydrolysates

A total of 294 edible protein sequences and 5 commercial proteases listed in the BIOPEP database were analyzed in silico. The frequency (A), a parameter in silico described previously, was examined further to calculating the ratio of truncated peptides with Xaa-proline and/or Xaa-alanine to all peptide fragments in a protein hydrolyzed with a protease, using the BIOPEP database. Then the in vitro DPP-IV inhibitory activity was determined using the same 15 protein and protease combinations to evaluate their relationship. The result shows that A values considering the number of Xaa-proline+Xaa-alanine exhibited a strong correlation with in vitro DPP-IV inhibition rates by Pearson’s correlation analysis (r=0.6993; P<0.05). Therefore, the in silico approach is effective to predict DPP-IV inhibitory activities in vitro of protein hydrolysates.

IN VITRO ANTIDIABETIC EFFECTS OF FERULA ASSA-FOETIDA EXTRACTS THROUGH DIPEPTIDYL PEPTIDASE IV AND α-GLUCOSIDASE INHIBITORY ACTIVITY

Objective: Diabetes mellitus (DM) causes hyperglycemia, which is one of the most common diseases in the world. One of the strategies for the treatment of diabetes is maintaining postprandial glucose level through inhibition of dipeptidyl peptidase IV (DPP-IV) and α-glucosidase enzymes. The aim of this study was to determine in vitro antidiabetic potential of Ferula assa-foetida via DPP-IV and α-glucosidase inhibitory activities.Methods: F. assa-foetida seeds were extracted in methanol, ethanol, ethanol-methanol, and water. Inhibitory activity on DPP-IV and α-glucosidase wasperformed in vitro and measured spectrophotometrically at λ=405 nm.Results: The result showed that the F. assa-foetida seed extract is effective against both enzymes. All fractions had DPP-IV inhibitory activity, but the ethanolic fraction had the highest inhibitory activity on DPP-IV enzyme and significantly decreased DPP-IV activity (24.5%). With respect to α-glucosidase inhibitory activity, the aqueous extract has the highest inhibitory activity (28%).Conclusion: According to the results of this study, F. assa-foetida contains DPP-IV and α-glucosidase inhibitors and could be a potential source for the discovery of active constituents as α-glucosidase and DPP-IV inhibitors to treat Type 2 DM.Keywords: Diabetes mellitus, Herbal medicine, Dipeptidyl peptidase IV, α-glucosidase.

CMD-05, a novel promising clinical anti-diabetic drug candidate, in vivo and vitro studies

Dipeptidyl peptidase IV (DPP-IV) inhibitor has been expected to be a new class of anti-diabetic agent. The present study was designed to characterize the pharmacological profiles of CMD-05, a novel DPP-IV inhibitor discovered in our laboratory, in vitro and in vivo. The IC50 of CMD-05 on DPP-IV inhibitory activity was approximately 12 nM while vildagliptin was 3.5 nM in vitro. In diabetes rat model established by high fat diet/low dose streptozotocin, CMD-05 inhibited DPP-IV activity, significantly improved glucose tolerance, increased GLP-1 and insulin levels in plasma. Long-term administration of CMD-05 decreased HbA1c and TG levels and improved the islet function without significantly effect on body weight. Furthermore, CMD-05 reduced INS-1 cell apoptosis and increased GLP-1 secretion in NCI-H716. After oral administration, CMD-05 reached peak concentration at 30 min with half-life of 288 minutes and the inhibitory rate of DPP-IV greater than 50% lasted for 15 h. In fasted normal rats, CMD-05 didn’t cause significant hypoglycemia. CMD-05 had a lower cytotoxicity than vildagliptin in vitro and its maximum tolerance dose in mice is beyond 2000 mg/kg. These results indicated that CMD-05 has similar activity with vildagliptin in vivo and has a much longer half-life and lower cytotoxicity than vildagliptin.

Structural Requirements for some 3-amino-N-substituted-4-(substituted phenyl) Butanamides as Dipeptidyl Peptidase-IV Inhibitors Using 3D-QSAR and Molecular Docking Approaches

Dipeptidyl peptidase-IV is well thought out as one of the key targets for treatment of type 2 diabetes mellitus and diverse scaffolds have proven effective in designing novel dipeptidyl peptidase-IV inhibitors. To this end, three dimensional quantitative structure activity relationship analysis and molecular docking studies were performed on a set of 3-amino-N-substituted- 4-(substituted phenyl) butanamides to explore the structural requirements for dipeptidyl peptidase-IV inhibitory activity using k-nearest neighbour molecular field analysis and AutoDock Vina, respectively. The compounds were arbitrarily assigned to active, moderately active and less active classes according to their biological activities. The most significant k-nearest neighbour model exhibited internal cross validation coefficient (q2) and external cross validation coefficient (pred_r2) as 0.67 and 0.82, respectively while the best partial least squares regression model showed 70% internal and 77% external predictability. Subsequent rigorous external validation through q2(F2), q2(F3), concordance correlation coefficient and mean absolute error provided further confidence in the predictability of both the models. Apropos the docking results, the compounds from active, moderately active and less active classes exhibited different binding patterns. Whereas the active compounds such as 12x and 12v occupied a similar space in the active site cavity as the crystallographic ligand (sitagliptin) (PDBID:1X70); the binding modes of compounds from moderately active and inactive classes were distinct from the latter. The findings of this study can provide an impetus for design of prospective potent dipeptidyl peptidase-IV inhibitors.

Effects of heat and pH treatments and in vitro digestion on the biological activity of protein hydrolysates of Amaranthus hypochondriacus L. grain.

The aim of this work was to assess the effects of temperature (T), time (t) and pH treatments and an in vitro digestion on the stability of the angiotensin I-converting-enzyme-inhibitory activity (ACEIA) and antithrombotic activity (ATA; assessed as inhibition of platelet aggregation) of selected protein hydrolysates of amaranth named Alb1H103 and GloH88 and GluH24 with dipeptidyl peptidase IV inhibitory activity (DPPIVIA). Heat treatment (40-100°C) for 1h showed no significant differences among ACEIA, DPPIVIA and ATA of the heated hydrolysates at pH 4 and 7. There was no statistically significant loss of any bioactivity under heat treatment for 3h at pH 4.0. Alb1H103 and GluH24 maintained the inhibitory activity of ACE and ATA at pH 7.0 for 3h, whereas GloH88 maintained ACEIA and ATA for 2.0h at pH 7.0. The pH effect on hydrolysates bioactivity was assessed in the range of 2.0-12.0. This was negligible on ACEIA, ATA and DPPIVIA. The in vitro digestion was performed using pepsin, trypsin (T) and α-chymotrypsin (C). A previous treatment of hydrolysates with pepsin improved the proteolytic activities of T and C. The hydrolysates kept at 100°C for 1h at pH 4.0, showed a significant increase in bioactivity. Conversely, a treatment at pH 7.0 showed no significant difference (p<0.05) in the hydrolysates bioactivities after their digestion. Thus, biological activity of hydrolysates may be preserved or enhanced, depending on their processing conditions.

Enzymatic production of protein hydrolysates from steelhead (Oncorhynchus mykiss) skin gelatin as inhibitors of dipeptidyl-peptidase IV and angiotensin-I converting enzyme

The objective of this study was to generate protein hydrolysates with dual in vitro inhibitory activities against dipeptidyl-peptidase IV (DPP-IV) and angiotensin-I converting enzyme (ACE), by proteolytic enzymes acting either individually or sequentially on steelhead skin gelatin. The results showed strong dual bioactivity in the low molecular weight (<3kDa) fractions obtained by ultrafiltration of hydrolysates produced using the enzymes pepsin, CorolaseN or papain. Alternatively, unfractionated hydrolysates exhibiting high ACE and DPP-IV inhibitory activities as well as yields could be attained by strategic selection of two enzymes for successive hydrolysis of gelatin. In particular, hydrolysates produced using 4% papain for 2h followed either by ultrafiltration or by a second hydrolysis with 1% CorolaseN for 2h, presented potent dual activity as ACE and DPP-IV inhibitors, and should be investigated further as potential functional food ingredients or nutraceuticals for the management of hypertension and diabetes.

Bioactive peptides from Atlantic salmon (Salmo salar) with angiotensin converting enzyme and dipeptidyl peptidase IV inhibitory, and antioxidant activities

The pH shift method was utilised for the recovery of proteins from salmon trimmings (ST), yielding 93% (w/w) protein. ST protein (STP) hydrolysates were generated with different enzyme preparations. STP incubated with Corolase PP for 1h (STP-C1) had the most potent angiotensin converting enzyme (ACE) and dipeptidyl peptidase IV (DPP-IV) inhibitory and oxygen radical absorbance capacity (ORAC) activities. Analysis of fractions of STP-C1 using UPLC-MS/MS identified sixteen peptides/amino acids. Tyr-Pro had the highest ACE inhibitory activity (ACE IC50=5.21±0.94μM). The highest DPP-IV inhibitory activity was found with the amino acid Tyr (DPP-IV IC50=75.15±0.84μM). Val-Pro had the highest ORAC activity (19.45±2.15μmol of TEg−1). To our knowledge, the peptides Gly-Pro-Ala-Val, Val-Cys, and Phe-Phe have not been previously identified to have the activities tested in this study. These results indicate that STP hydrolysates are potential sources of bioactive peptides.

Oral Administration of Collagen Hydrolysates Improves Glucose Tolerance in Normal Mice Through GLP-1-Dependent and GLP-1-Independent Mechanisms.

The aim of this study was to evaluate the antidiabetic properties of collagen hydrolysates (CHs). CHs exhibited dipeptidyl peptidase-IV inhibitory activity and stimulated glucagon-like-peptide-1 (GLP-1) secretion in vitro. We also determined whether CHs improve glucose tolerance in normal mice. Oral administration of CHs suppressed the glycemic response during the oral and intraperitoneal glucose tolerance tests (OGTT and IPGTT), but the effects were weaker in IPGTT than in OGTT. CHs had no effect on the gastric emptying rate. A pretreatment with the GLP-1 receptor antagonist, exendin 9-39 (Ex9), partially reversed the glucose-lowering effects of CHs, but only when coadministered with glucose. CHs administered 45 min before the glucose load potentiated the glucose-stimulated insulin secretion. This potentiating effect on insulin secretion was not reversed by the pretreatment with Ex9, it appeared to be enhanced. These results suggest that CHs improve glucose tolerance by inhibiting intestinal glucose uptake and enhancing insulin secretion, and also demonstrated that GLP-1 was partially involved in the inhibition of glucose uptake, but not essential for the enhancement of insulin secretion.