Dipeptidyl peptidase IV inhibitory and antioxidative properties of milk protein-derived dipeptides and hydrolysates

peer-reviewedSelected synthetic dipeptides and milk protein hydrolysates were evaluated for their dipeptidyl peptidase IV (DPP-IV) inhibitory properties, and their superoxide (SO) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activities. DPP-IV inhibition was seen with eight out of the twelve dipeptides and 5 of the twelve hydrolysates studied. Trp-Val inhibited DPP-IV, however, inhibition was not observed with the reverse peptide Val-Trp. The most potent hydrolysate inhibitors were generated from casein (CasH2) and lactoferrin (LFH1). Two Trp containing dipeptides, Trp-Val and Val-Trp, and three lactoferrin hydrolysates scavenged DPPH. The dipeptides had higher SO EC50 values compared to the milk protein hydrolysates (arising from three lactoferrin and one whey protein hydrolysates). Higher molecular mass fractions of the milk protein hydrolysates were associated with the SO scavenging activity. Trp-Val and one lactoferrin hydrolysate (LFH1) were multifunctional displaying both DPP-IV inhibitory and antioxidant (SO and DPPH scavenging) activities. These compounds may have potential as dietary ingredients in the management of type 2 diabetes by virtue of their ability to scavenge reactive oxygen species and to extend the half-life of incretin molecules. (C) 2012 Elsevier Inc. All rights reserved.ACCEPTEDpeer-reviewe

Tryptophan-containing milk protein-derived dipeptides inhibit xanthine oxidase

peer-reviewedOf twelve dipeptides tested, only the Trp containing peptides Val-Trp and its reverse peptide Trp-Val showed a xanthine oxidase (XO) inhibitory activity. Studies with Val and Trp revealed that XO inhibition was mainly attributed to the Trp residue. No significant difference (P >= 0.05) was found for the XO inhibitory potency (IC50) values for Trp, Val-Trp and Trp-Val, which were about 200 times higher than that for Allopurinol. Lineweaver and Burke analysis demonstrated that Trp, Val-Trp and Trp-Val were non-competitive inhibitors while Allopurinol was a competitive inhibitor. Of the different milk-protein substrates hydrolyzed with gastro-intestinal enzyme activities, only lactoferrin (LF) hydrolyzates displayed XO inhibition. Peptides present in a LF hydrolyzate (GLF-240 min) were adsorbed onto activated carbon followed by subsequent desorption with stepwise elution using acetonitrile (ACN). Separation and detection of Trp containing peptides within the different fractions were achieved using RP-HPLC coupled with fluorescence detection. The desorbed fractions displayed different XO inhibitory properties, with no inhibition in the unbound fraction and highest inhibition in fractions eluted with 30, 40 and 70% ACN. The fraction eluting at 40% ACN was significantly more potent (19.1 +/- 2.3% inhibition at 1.25 mg mL(-1)) than the GLF-240 min hydrolyzate (13.4 +/- 0.4% inhibition at 1.25 mg mL(-1)), showing the potential for enrichment of the bioactive peptides on fractionation with activated carbon. (C) 2012 Elsevier Inc. All rights reserved.ACCEPTEDpeer-reviewe

Partitioning of starter bacteria and added exogenous enzyme activities between curd and whey during Cheddar cheese manufacture

peer-reviewedPartitioning of starter bacteria and enzyme activities was investigated at different stages of Cheddar cheese manufacture using three exogenous commercial enzyme preparations added to milk or at salting. The enzyme preparations used were: Accelase AM317, Accelase AHC50, Accelerzyme CPG. Flow cytometric analysis indicated that AHC50 or AM317 consisted of permeabilised or dead cells and contained a range of enzyme activities. The CPG preparation contained only carboxypeptidase activity. Approximately 90% of starter bacteria cells partitioned with the curd at whey drainage. However, key enzyme activities partitioned with the bulk whey in the range of 22%–90%. An increased level of enzyme partitioning with the curd was observed for AHC50 which was added at salting, indicating that the mode of addition influenced partitioning. These findings suggest that further scope exists to optimise both bacterial and exogenous enzyme incorporation into cheese curd to accelerate ripening.Department of Agriculture, Food and the Marin

Dipeptidyl peptidase IV inhibitory properties of a whey protein hydrolysate: Influence of fractionation, stability to simulated gastrointestinal digestion and food-drug interaction

peer-reviewedThe in vitro dipeptidyl peptidase IV (DPP-IV) inhibitory activity of a whey protein hydrolysate (WPH) generated with a food-grade pancreatic enzyme preparation was studied. The 50 % inhibitory concentration (IC50) value in the presence of WPH was 1.34 ± 0.11 mg.mL-1. Ultrafiltration (UF) fractionation of WPH allowed enrichment in DPP-IV inhibitory peptides. The permeates generated by UF through 5 and 2 kDa membranes along with the hydrophilic fraction isolated by solid-phase extraction were significantly more potent DPP-IV inhibitors than WPH. These samples respectively had IC50 values of 0.95 ± 0.16, 0.48 ± 0.01 and 1.11 ± 0.09 mg.mL-1. Simulated gastrointestinal digestion (SGID) of WPH resulted in an increased DPP- IV inhibitory potency (IC50 value of 1.02 ± 0.05 mg.mL-1). Competitive inhibition of DPP-IV was observed with WPH and all its fractions, indicating a direct interaction of the bioactive peptides therein with the active site of DPP-IV. Combinations of sitagliptin, a conventional drug-inhibitor of DPP-IV, and whey-derived peptides resulted in an additive effect on DPP-IV inhibition.ACCEPTEDpeer-reviewe

Generation of wheat gluten hydrolysates with dipeptidyl peptidase IV (DPP-IV) inhibitory properties

peer-reviewedWheat gluten, a Pro-rich dietary protein, was investigated for its potential to produce dipeptidyl peptidase IV (DPP-IV) inhibitory peptides during enzymatic hydrolysis with Debitrase HYW20. Nine gluten hydrolysates (H1–H9) were generated using a 2 factor × 3 level design of experiments (DOE) including the incubation temperature (40, 50 and 60 °C) and the enzyme: substrate ratio (E:S, 0.5, 1.0 and 1.5% (w/w)). Their DPP-IV half maximal inhibitory concentration (IC50) ranged from 0.24 ± 0.02 (H9) to 0.66 ± 0.06 mg mL−1 (H2A and H7) and their degree of hydrolysis (DH) from 31.7 ± 0.9 (H7) to 62.2 ± 3.0% (H6). Gluten and H9, the most potent DPP-IV inhibitory hydrolysate, were subjected to simulated gastrointestinal digestion (SGID), yielding Gluten_CorPP and H9_CorPP, respectively. H9_CorPP had a higher DPP-IV inhibitory potency than Gluten_CorPP (i.e., DPP-IV IC50 values of 0.33 ± 0.03 vs. 1.45 ± 0.26 mg mL−1, respectively). H9 and H9_CorPP both contained relatively potent DPP-IV inhibitory peptides such as Val-Pro-Leu, Trp-Leu and Trp-Pro which were identified by liquid chromatography tandem mass spectrometry (LC-MS/MS). In addition, several sequences possessing features of DPP-IV inhibitory peptides, mostly consisting of a penultimate or C-terminal Pro, were identified within H9. The presence of Pro-containing peptides within H9 may contribute to its stability to digestive enzymes. Gluten hydrolysates may have antidiabetic potential for human

In Silico approaches applied to the study of peptide analogs of ile-pro-ile in relation to their dipeptidyl peptidase IV inhibitory properties

peer-reviewedInhibition of dipeptidyl peptidase IV (DPP-IV) may be exploited to maintain the incretin effect during the postprandial phase. As a result, glycemic regulation and energy homeostasis may be improved. Food protein-derived peptides have been identified as natural agents capable of inhibiting DPP-IV. Ile-Pro-Ile is the most potent DPP-IV inhibitory peptide identified to date. A minimum analog peptide set approach was used to study peptide analogs of Ile-Pro-Ile. The DPP-IV half maximal inhibitory concentration (IC50) values of the 25 peptides evaluated ranged from 3.9 ± 1.0 μM (Ile-Pro-Ile) to 247.0 ± 32.7 μM (Phe-Pro-Phe). The presence of Pro at position 2 of tripeptides was required to achieve high DPP-IV inhibition. Most peptides behaved as competitive inhibitors of DPP-IV with the exception of peptides with a N-terminal Trp, which were mixed-type inhibitors. While possessing the structure of preferred DPP-IV substrates, most peptides studied were particularly stable during 30 min incubation with DPP-IV. Molecular docking revealed that Ile-Pro-Ile and its peptide analogs interacted in a very similar manner with the active site of DPP-IV. In addition, no correlation was found between the Hydropathic INTeraction score and the DPP-IV IC50 values of the peptides studied. This outcome suggests that free energy may not be directly responsible for enzyme inhibition by the peptides. Finally, novel DPP-IV inhibitory peptides were identified using the strategy employed herein. These results may be relevant for the development of food protein-derived peptides with serum glucose lowering and food intake regulatory properties in humans

Inhibition of dipeptidyl peptidase IV and xanthine oxidase by amino acids and dipeptides

peer-reviewedXanthine oxidase (XO) and dipeptidyl peptidase IV (DPP-IV) inhibition by amino acids and dipeptides was studied. Trp and Trp-containing dipeptides (Arg-Trp, Trp-Val, Val-Trp, Lys-Trp and Ile-Trp) inhibited XO. Three amino acids (Met, Leu and Trp) and eight dipeptides (Phe-Leu, Trp-Val, His-Leu, Glu-Lys, Ala-Leu, Val-Ala, Ser-Leu and Gly-Leu) inhibited DPP-IV. Trp and Trp-Val were multifunctional inhibitors of XO and DPP-IV. Lineweaver and Burk analysis showed that Trp was a non-competitive inhibitor of XO and a competitive inhibitor of DPP-IV. Molecular docking with Autodock Vina was used to better understand the interaction of the peptides with the active site of the enzyme. Because of the non-competitive inhibition observed, docking of Trp-Val to the secondary binding sites of XO and DPP-IV is required. Trp-Val was predicted to be intestinally neutral (between 25% and 75% peptide remaining after 60 min simulated intestinal digestion). These results are of significance for the reduction of reactive oxygen species (ROS) and the increase of the half-life of incretins by food-derived peptides. (C) 2013 Elsevier Ltd. All rights reserved.ACCEPTEDpeer-reviewe

Variable Glycemic Responses to Intact and Hydrolyzed Milk Proteins in Overweight and Obese Adults Reveal the Need for Precision Nutrition

peer-reviewedBackground Dietary modifications can contribute to improved pancreatic β cell function and enhance glycemic control. Objectives The objectives of this study were as follows: 1) to investigate the potential of milk protein hydrolysates to modulate postprandial glucose response; 2) to assess individual responses; and 3) to explore the inter- and intraindividual reproducibility of the response. Methods A 14-d randomized crossover study investigated interstitial glucose levels of participants in response to 12% w/v milk protein drinks (intact caseinate and casein hydrolysate A and B) consumed in random order with a 2-d washout between treatments. Milk protein drinks were consumed immediately prior to study breakfast and evening meals. Twenty participants (11 men, 9 women) aged 50 ± 8 y with a body mass index (in kg/m2) of 30.2 ± 3.1 were recruited. Primary outcome was glucose levels assessed at 15-min intervals with the use of glucose monitors. Results Repeated-measures ANOVA revealed that for breakfast there was a significant difference across the 3 treatment groups (P = 0.037). The ability to reduce postprandial glucose was specific to casein hydrolysate B in comparison with intact caseinate (P = 0.039). However, despite this significant difference, further examination revealed that only 3 out of 18 individuals were classified as responders (P < 0.05). High intraclass correlation coefficients were obtained for glucose response to study meals (intraclass correlation coefficient: 0.892 for breakfast with intact caseinate). The interindividual CVs were higher than the intraindividual CVs. Mean inter- and intraindividual CVs were 19.4% and 5.7%, respectively, for breakfast with intact caseinate. Conclusion Ingestion of a specific casein hydrolysate successfully reduced the postprandial glucose response; however, at an individual level only 3 participants were classified as responders, highlighting the need for precision nutrition. Exploration of high interindividual responses to nutrition interventions is needed, in combination with the development of precision nutrition, potentially through an n-of-1 approach. This clinical trial was registered as ISRCTN61079365 (https://www.isrctn.com/).Food for Health Irelan