Caseinphosphopeptides (CPP) in feces and contents in digestive tract of rats fed casein and CPP preparations

Bioactive milk peptides: an updated comprehensive overview and database

Partial digestion of milk proteins leads to the formation of numerous bioactive peptides. Previously, our research team thoroughly examined the decades of existing literature on milk bioactive peptides across species to construct the milk bioactive peptide database (MBPDB). Herein, we provide a comprehensive update to the data within the MBPDB and a review of the current state of research for each functional category from in vitro to animal and clinical studies, including angiotensin-converting enzyme (ACE)-inhibitory, antimicrobial, antioxidant, dipeptidyl peptidase (DPP)-IV inhibitory, opioid, anti-inflammatory, immunomodulatory, calcium absorption and bone health and anticancer activity. This information will help drive future research on the bioactivities of milk peptides.

Enhanced Anti-Allergic Activity of Milk Casein Phosphopeptide by Additional Phosphorylation in Ovalbumin-Sensitized Mice

The proteolytic digest of milk casein, known as casein phosphopeptide (CPP-III), exhibits diverse biological activities, including calcium absorption and antioxidant activities. We hypothesized that the additional phosphorylation of this peptide can enhance its immunomodulatory activity such as suppression of allergy-associated cytokine and antigen-specific immune response. This study was conducted to assess whether oral intake of additionally phosphorylated CPP-III (P-CPP) attenuates ovalbumin (OVA)-induced IgE-mediated allergic reactions because of the additional phosphate groups. Female BALB/c mice were intraperitoneally sensitized with OVA twice at intervals of 14 days and then orally fed native CPP-III (N-CPP), P-CPP, and dephosphorylated CPP-III (D-CPP) for 6 weeks. Next, the mice were orally challenged with 50 mg of OVA. Oral administration of P-CPP suppressed total and specific IgE levels in the serum. Mice fed P-CPP exhibited low levels of OVA-specific IgG1 and increased OVA-specific IgG2a. P-CPP also suppressed IL-4 production, while D-CPP showed similar a level compared to that of the control. Further, P-CPP increased the population of the T follicular helper (Tfh) cell in the spleen. These results suggest that additional phosphorylation of CPP can enhance the attenuation of allergen-specific IgE-modulated allergic reactions in a murine food allergy model.

Identification of Novel Phosphopeptides After Simulated Digestion of αs2-casein by Tandem Mass Spectrometry

Casein phosphopeptides (CPPs) are encrypted in αs1-, αs2-and β-casein (CN) and can be released by in vitro, in vivohydrolysis or food processing of dairy foods. Bovine αs2-CN contains two cluster sequences of anionic phosphoseryl and glutamyl residues SpSpSpEE in its structure (residues 8–12 and 56–63), which can modulate mineral bioavailability. In this study αs2-casein (αs2-CN) was subjected to simulated gastrointestinal digestion. CPPs released were sequenced by on-line reversed-phase high performance liquid chromatography coupled to electrospray ionisation tandem mass spectrometry (RP-HPLC-ESIMS/MS). Six novel αs2-CN derived CPPs, Three of them (αs2-CN(54–87)4P,αs2-CN(24–70)4P and αs2-CN(14–73)5P) with the mineral binding cluster sequence SpSpSpEE were identified and characterised. CPPs from αs2-CN identified in this study resist simulated gastrointestinal digestion. As the molecular weights of these CPPs are approx. 2,165–7,112Da, they could be absorbed by intestinal cells. Consequently, these αs2-CN derived CPPs could be promising candidates for incorporation to mineral fortified foods as functional ingredients.

Phosphorylation and coordination bond of mineral inhibit the hydrolysis of the beta-casein (1-25) peptide by intestinal brush-border membrane enzymes

Caseinophosphopeptides (CPP) are food mineral-rich components that may resist intestinal enzyme hydrolysis. We wondered whether phosphorylation and/or mineral binding induces resistance of CPP to intestinal hydrolysis. We used intestinal brush-border membrane vesicles to digest different forms of the beta-casein (1-25) peptide: unphosphorylated and phosphorylated carrier of varied cations. The results showed that the activity of alkaline phosphatase seems not to be specific to either the phosphorylation degree or the phosphorylation sites whereas phosphorylations limited the action of peptidases. Studying the mechanism and the kinetics of hydrolysis of the different peptides allows understanding how some cations prevent more CPP from hydrolysis than others. The action of both exo- and endopeptidases was limited for the beta-CN (1-25) peptide bound to zinc or copper. Actually the peptide bound to copper was almost not hydrolyzed during the digestion, suggesting that coordination bond of copper to CPP inhibits the action of both phosphatase and peptidases.

Milk versus caseinophosphopeptides added to fruit beverage: resistance and release from simulated gastrointestinal digestion

The influence of simulated gastrointestinal digestion on caseinophosphopeptides (CPPs) formation in milk-based fruit beverage was evaluated, together with resistance of a pool of CPPs added to fruit beverage. In milk-based fruit beverage, four CPPs were identified that can be justified by their presence in raw milk or due to processing. When it was subjected to simulated gastrointestinal digestion, 10 CPPs were identified, and only 1 presented the cluster (SpSpSpEE) (3 phosphoseryl group followed by 2 glutamic acid residues), which corresponded to alpha(s2)-CN(1-19)4P. CPPs added to fruit beverage are resistant to simulated gastrointestinal digestion, and 16 CPPs were identified originating from the fragmentation of added CPPs, and with a greater presence of the cluster compared with CPPs originating from milk-based fruit beverage. This could justify the use of CPPs as functional ingredients, and offer a good alternative to milk-based fruit beverage for improving mineral bioavailability.

Improved absorption of caseinophosphopeptide-bound iron: role of alkaline phosphatase

Hydrolysis of proteins could lessen their inhibiting effect on the poor absorption of cow's milk iron (Fe), which is responsible for the high incidence of Fe deficiency worldwide. When bound to Fe, caseinophosphopeptides (CPP) derived from milk proteins resist luminal digestion, enhance Fe solubility and could improve its bioavailability; brush border enzyme alkaline phosphatase activity could influence iron absorption by releasing free Fe; this study assessed its role in the absorption of CPP-bound Fe. Rat duodenal loops were perfused with Fe gluconate or Fe bound to the CPP of beta casein [beta-CN (1-25)], with or without the addition of an inhibitor of alkaline phosphatase, Na2WO4. The uptake of Fe-beta-CN (1-25) was greater than Fe gluconate. Na2WO4 enhanced the uptake of Fe-beta-CN (1-25) and not of Fe gluconate. So the release of free, insoluble Fe, by alkaline phosphatase seems to be prevented by providing Fe in the Fe-beta-CN (1-25) complex form. Its good disappearance rate makes beta-CN (1-25)-bound Fe a candidate for food fortification.

NMR studies of a novel calcium, phosphate and fluoride delivery vehicle-αS1-casein(59–79) by stabilized amorphous calcium fluoride phosphate nanocomplexes

The repair of early tooth enamel lesions has been recently demonstrated by tryptic phosphopeptides derived from milk caseins that associate with amorphous calcium phosphate (ACP) forming stable complexes. These casein phosphopeptides (CPP), containing the cluster sequence-Ser(P)-Ser(P)-Ser(P)-Glu-Glu-, form calcium phosphate delivery vehicles that retard enamel demineralization and promote remineralization. Recently, we have shown that these peptides also stabilize calcium fluoride phosphate as soluble complexes. These complexes designated CPP-ACFP, have the potential to provide superior clinical efficacy in preventing dental caries and treating and repairing early stages of disease. In an approach to determine the ultrastructure of the casein phosphopeptide-amorphous calcium fluoride phosphate complexes, we have studied the structure of the predominant peptide alpha(S1)-CN(59-79) bound to ACFP using nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction. The alpha(S1)-CN(59-79) peptide stabilized calcium fluoride phosphate as amorphous nanocomplexes with a hydrodynamic radius of 2.12+/-0.26 nm. The nanocomplexes exhibited stoichiometry of one peptide to 15 calcium, nine phosphate and three fluoride ions. Sequence-specific resonance assignments were determined for the peptide alpha(S1)-CN(59-79) complexed to the ACFP. The secondary structure of the peptide alpha(S1)-CN(59-79) was characterized by sequential (i, i+1), medium-range (i, i+2) nOes and H alpha chemical shifts. The spectral data were compared with that of the peptide alpha(S1)-CN(59-79) bound to calcium ions, revealing that the structurally significant secondary NH and alpha-chemical shifts were similar.

Nascent helix in the multiphosphorylated peptide alphaS2-casein(2-20)

Sequence-specific nuclear magnetic resonance (NMR) assignments have been determined for the peptide alphaS2-CN(2-20) containing the multiphosphorylated motif-8Ser(P)-Ser(P)-Ser(P)-Glu-Glu12- in the presence of molar excess Ca2+. The secondary structure of the peptide was characterized by sequential (i,i + 1), medium-range (i,i + 2/3/4) nOes and H alpha chemical shifts. Molecular modelling of the peptide based on these constraints suggests a nascent helix for residues Ser(P)9 to Glu12. The spectral data for alphaS2-CN(2-20) were compared with those of other casein phosphopeptides beta-CN(1-25) and alphaS1-CN(59-79) that also contain the multiphosphorylated motif. This comparison revealed a similar pattern of secondary amide chemical shifts in the multiphosphorylated motif. However, the patterns of medium-range nOe connectivities in the three peptides suggests they have distinctly different conformations in the presence of Ca2+ despite having a high degree of sequential similarity.

Cation-dependent structural features of beta-casein-(1-25)

Complete sequence-specific, proton-resonance assignments have been determined for the calcium phosphate-stabilizing tryptic peptide beta-casein-(1-25) containing the phosphorylated sequence motif Ser(P)(17)-Ser(P)-Ser(P)-Glu-Glu(21). Spectra of the peptide have been recorded, in separate experiments, in the presence of excess ammonium ions, sodium ions and calcium ions, and of the dephosphorylated peptide in the presence of excess sodium ions. We observed significant changes to chemical shifts for backbone and side-chain resonances that were dependent upon the nature of the cation present. Medium-range nuclear Overhauser effect (nOe) enhancements, characteristic of small structured regions in the peptide, were observed and also found to be cation dependent. The secondary structure of the peptide was characterized by sequential and medium-range (i, i+2/3/4, which denotes an interaction between residue i and residue i+2, i+3 or i+4 in the peptide) nOe connectivities, and Halpha chemical shifts. Four structured regions were identified in the calcium-bound peptide: residues Arg(1) to Glu(4) were involved in a loop-type structure, and residues Val(8) to Glu(11), Ser(P)(17) to Glu(20) and Glu(21) to Thr(24) were implicated in beta-turn conformations. Comparison of the patterns of medium-range nOe connectivities in beta-casein-(1-25) with those in alpha(S1)-casein-(59-79) suggest that the two peptides have distinctly different conformations in the presence of calcium ions, despite having a high degree of sequential and functional similarity.

Effects of bioactive substances in milk on mineral and trace element metabolism with special reference to casein phosphopeptides

Bioactivity of phosphopeptides yielded after tryptic hydrolysis of casein (CPP) was reported more than 50 years ago when CPP were found to improve calcium balance in rachitic newborns. Several investigations have been carried out to study the effects of CPP mainly on calcium metabolism but also on other minerals like iron and zinc. Most of the experiments were in vitro studies or short-term experiments like the effects of CPP after single meals or their effect on mineral disappearance from intestinal everted sac or ligated loop. Investigations on calcium balance were also mainly short term, i.e. 3-4 weeks, and mainly done in rats. A few experiments have been carried out in minipigs, an animal model that is closer to the human than the rat. Studies in human were rare and short term. To date a variety of other peptides have been isolated after enzymatic hydrolysis, and some have been investigated for bioactivity, with equivocal findings. Bioactivity of phosphopeptides seemed to be more obvious when investigations were done in vitro or short term. Results were less clear in metabolic balance studies, especially under physiological conditions. The composition of the basal diet, i.e. content of calcium and phytate, or the protein source had a significant impact on the effect of phosphopeptides. It was concluded that phosphopeptides revealed positive effects on mineral solubility and absorbability, and bone mineralisation under certain experimental conditions. Accordingly they could have a beneficial effect on bone health for some groups of the population.

Sensitivity of β-casein phosphopeptide-iron complex to digestive enzymes in ligated segment of rat duodenum

Binding iron to the phosphorylated beta(1-25) peptide derived from beta-casein improves iron bioavailability in the rat. The aim of the present work was to learn how injected beta(1-25) and iron-beta(1-25) complex behave in the duodenum of rats using the technique of intestinal ligation in situ and reversed-phase (RP)-high performance liquid chromatography-electrospray mass spectrometry analysis of the lumen contents. The results demonstrate that beta(1-25) is sensitive to digestive enzymes including proteases/peptidases and phosphatases during duodenal transit. The lumen contents of rats perfused with iron free beta(1-25) contained all peptidic sequences derived from beta(1-25). In contrast, the phosphorylated part of beta(1-25) [i.e., beta(15-24)] was not detected in lumen of rats perfused with iron-beta(1-25) complex.

Iron tissue storage and hemoglobin levels of deficient rats repleted with iron bound to the caseinophosphopeptide 1-25 of beta-casein

Caseinophosphopeptides (CPP) issued from enzyme digestion of caseins bind cations and keep them soluble in the digestive tract. They could be used as ligands to improve iron (Fe) bioavailability. Fe-deficient young rats were repleted with Fe (40 or 200 mg/kg of diet) bound either to the beta-CN (1-25) of beta-casein or to whole beta-casein or as FeSO(4). A control pair-fed group was given 200 mg of Fe (FeSO(4))/kg of diet for 6 weeks. After repletion, hemoglobin concentration of the control group was reached only by the ) animals fed 200 mg of Fe/kg; beta-CN (1-25) bound Fe (40 and 200 mg) produced higher Fe liver and spleen stores than FeSO(4). Binding Fe to the whole, nonhydrolyzed beta-casein gave results intermediate between the other experimental groups. Binding Fe to phosphoserine residues of low molecular weight CPP improved its ability to cure anemia and to restore iron tissue stores, as compared to Fe bound to the whole casein and to inorganic salts.