A comprehensive review on preparation, structure-activities relationship, and calcium bioavailability of casein phosphopeptides

Calcium is one of the important elements for human health. Calcium deficiencies can lead to numerous diseases. Calcium chelating peptides have shown potential application in the management of calcium deficiencies. Casein phosphopeptides (CPP) are phosphoseryl-containing fragments of casein by enzymatic hydrolysis or fermentation during manufacture of milk products as well as during intestinal digestion. An increasing number of CPP with the ability to facilitate and enhance the bioavailability of calcium are being discovered and identified. In this review, 249 reported CPP derived from four types of bovine casein (αs1, αs2, β and κ) were collected, and the amino acid sequence and phosphoserine group information were sorted out. This review outlines the current enzyme hydrolysis, detection methods, purification, structure-activity relationship and mechanism of intestinal calcium absorption in vitro and in vivo as well as application of CPP.

Preparation of casein phosphopeptides calcium complex and the promotion in calcium cellular uptake through transcellular transport pathway

This study evaluated the stability of casein phosphopeptides (CPP) and obtained peptide-calcium complex by heating and chelating the peptide with CaCl₂ in a neutral solution. To assess the bioavailability of various calcium formulations, the calcium transport models were established in Caco-2 cells, and the transcellular transport pathways of various calcium formulations were studied by RT-PCR and Western blotting. Results of circular dichroism showed that CPP was a stable polypeptide. The ultraviolet absorption spectrum and Fourier transform-infrared spectrum (FT-IR) indicated that calcium could be chelated by carboxyl oxygen and amino nitrogen atoms of CPP to form peptide calcium chelate, and the calcium bioavailability of peptide calcium chelate was significantly higher than that of CaCl₂ , calcium l-aspartate, and casein phosphopeptides mixed with CaCl₂ . Four calcium sources increased the expression of TRPV5 and TRPV6 genes and proteins. The study intended to provide a basis for developing a novel calcium supplement. PRACTICAL APPLICATIONS: This paper examined the bioavailability of casein phosphopeptides calcium complex, CaCl₂ , calcium l-aspartate, and casein phosphopeptides mixed with CaCl₂ in Caco-2 cells, and the mechanisms were detected by western blotting. The results provide theoretical knowledge for the selection of calcium supplement raw materials and lay a foundation for the development of compound calcium preparations and drugs in the future.

Promoting the Calcium-Uptake Bioactivity of Casein Phosphopeptides in vitro and in vivo

Casein phosphopeptides have been studied widely for their ability to chelate calcium. However, systematic studies on the effects of casein phosphopeptides (CPP) on calcium absorption in vitro and in vivo are scarce. The purities of two commercially available products, CPP1 and CPP2, are 18.37 and 25.12%, respectively. Here, the in vitro calcium binding capacity of CPP2 was 142.56 ± 7.39 mg/g, which was higher than that of CPP1 (107.15 ± 6.27 mg/g). The calcium transport results in a Caco-2 monolayer model indicated that, relative to controls, CPP1 and CPP2 increased calcium transport by 21.78 and 53.68%, respectively. Subsequent animal experiments showed that the CPP2-Ca-H group (1% Ca, 0.4% CPP2) had significant increases in the femur index, serum Ca²⁺ and serum osteocalcin levels, and femoral Ca content. The CPP2-Ca-H animal also had decreased serum alkaline phosphatase levels, parathyroid hormone content, and urinary pyridinoline content. Overall, our results demonstrated that CPP2 had stronger effects on promoting calcium uptake than CPP1.

Partial-, Double-Enzymatic Dephosphorylation and EndoGluC Hydrolysis as an Original Approach to Enhancing Identification of Casein Phosphopeptides (CPPs) by Mass Spectrometry

The identification of phosphopeptides is currently a challenge when they are part of a complex matrix of peptides, such as a milk protein enzymatic hydrolysate. This challenge increases with both the number of phosphorylation sites on the phosphopeptides and their amino acid length. Here, this paper reports a four-phase strategy from an enzymatic casein hydrolysate before a mass spectrometry analysis in order to enhance the identification of phosphopeptides and phosphosites: (i) the control protein hydrolysate, (ii) a two-step enzymatic dephosphorylation of the latter, allowing for the almost total dephosphorylation of peptides, (iii) a one-step enzymatic dephosphorylation, allowing for the partial dephosphorylation of the peptides and (iv) an additional endoGluC enzymatic hydrolysis, allowing for the cleavage of long-size peptides into shorter ones. The reverse-phase high-pressure liquid chromatography–tandem mass spectrometry (RP-HPLC-MS/MS) analyses of hydrolysates that underwent this four-phase strategy allowed for the identification of 28 phosphorylation sites (90%) out of the 31 referenced in UniprotKB/Swiss-Prot (1 June 2021), compared to 17 sites (54%) without the latter. The alpha-S2 casein phosphosites, referenced by their similarity in the UniProt database, were experimentally identified, whereas pSer148, pThr166 and pSer187 from a multiphosphorylated long-size kappa-casein were not. Data are available via ProteomeXchange with identifier PXD027132.

Antioxidant Properties of Casein Phosphopeptides (CPP) and Maillard-Type Conjugated Products

A casein phosphopeptide (CPP) fraction derived from tryptic hydrolysis of bovine casein was evaluated for antioxidant activity. Conjugations or mixtures of CPP with polysaccharide, galactomannan (Gal), or xyloglucan (Xyl) were prepared to evaluate potential enhancement of CPP antioxidant activity. The effect of calcium was also investigated. The CPP preparation alone was effective at scavenging hydroxyl radicals and sequestering Fe2+ to protect against Fenton reaction-induced deoxyribose oxidation in non-site-specific (up 63.3% inhibition) and site-specific (up 32.1% inhibition) binding assays, respectively. CPP also effectively quenched 2,2'-azinobis-3-ethylbenzothiazoline-6-sulfonic acid radicals (ABTS•+) to an extent of 67.6% scavenging in an aqueous system. In a soybean lecithin liposome system, CPP exhibited effective protection against peroxyl radical-induced liposomal peroxidation (38.3% of control in terms of rate of propagation). Conjugating CPP with Gal or Xyl polysaccharides using Maillard reaction conditions significantly reduced activity in the Fenton reaction-deoxyribose assays, while exhibiting no effect on the antioxidant activity of native CPP in both the ABTS and liposome assays, respectively. These results represent comparative antioxidant capacity of the native CPP and associated conjugates in phases that varied in relative hydrophilic and hydrophobic character. We conclude that CPP has the potential to act as both a primary and secondary antioxidant by displaying transition metal ion sequestering activity and free radical quenching activity. Improvements in antioxidant activity of CPP by Maillard-type conjugation with Xyl or Gal were relatively small and model-specific.

Prevention of Zinc Precipitation with Calcium Phosphate by Casein Hydrolysate Improves Zinc Absorption in Mouse Small Intestine ex Vivo via a Nanoparticle-Mediated Mechanism

Casein phosphopeptides are known to enhance zinc absorption, but the underlying mechanism remains unclear. Here, a gastrointestinal casein hydrolysate (CH) was found to keep zinc in solution despite heavy precipitation of calcium and phosphate, the omnipresent mineral nutrients that could co-precipitate zinc out of solution instantly and almost completely under physiologically relevant conditions. Dynamic light scattering, transmission electron microscopy, and energy-dispersive X-ray analysis displayed the CH-mediated formation of zinc/calcium phosphate (Zn/CaP) nanocomplexes aggregated from rather small nanoclusters. The ex vivo mouse ileal loop experiments revealed enhanced intestinal zinc absorption by CH's prevention of zinc co-precipitation with CaP, and the treatments with specific inhibitors unveiled the involvement of macropinocytic internalization, lysosomal degradation, and transcytosis in the intestinal uptake of zinc from Zn/CaP nanocomplexes. A low calcium-to-phosphorus ratio adversely affected CH's efficiency to enhance zinc solubility and absorption. Overall, our study provides a new paradigm for casein phosphopeptides to improve zinc bioavailability.

Overexpression of amyA and glaA substantially increases glucoamylase activity in Aspergillus niger

The purpose of this study was to obtain an engineered Aspergillus niger strain with high glucoamylase activity by overexpressing the glucoamylase gene glaA and α-amylase gene amyA in A. niger CICC2462. Three recombinant strains containing a single copy of amyA (1A), containing two copies of amyA (2A), and coexpressing amyA and glaA (AG), respectively, were constructed. The transcript levels of amyA in 1A and 2A were increased by 2.95 folds and 3.09 folds, respectively. The levels of amyA and glaA in AG were increased by 1.21 folds and 2.86 folds, but the maximum extracellular glucoamylase activities did not differ significantly. In addition, after 1% casein phosphopeptides (CPPs) was added to the fermentation medium, the maximum extracellular glucoamylase activities for strains 1A, 2A, and AG were 35,200, 37,300, and 40,710 U/ml, respectively, which were significantly higher than that of the parental strain CICC2462 (28,250 U/ml), while CPPs alone had no effect on the parental strain CICC2462. We demonstrate that overexpression of amyA and glaA substantially increases the expression and secretion of glucoamylase in A. niger, and CPPs effectively improves the yield of glucoamylase in recombinant A. niger strains overexpressing amyA and glaA. The newly developed strains and culture methods may have extensive industrial applications.

Bioactive Peptides Isolated from Casein Phosphopeptides Enhance Calcium and Magnesium Uptake in Caco-2 Cell Monolayers

The ability of casein phosphopeptides (CPPs) to bind and transport minerals has been previously studied. However, the single bioactive peptides responsible for the effects of CPPs have not been identified. This study was to purify calcium-binding peptides from CPPs and to determine their effects on calcium and magnesium uptake by Caco-2 cell monolayers. Five monomer peptides designated P1 to P5 were isolated and the amino acid sequences were determined using LC-MS/MS. Compared with the CPP-free control, all five monomeric peptides exhibited significant enhancing effects on the uptake of calcium and magnesium (P < 0.05). Interestingly, when calcium and magnesium were presented simultaneously with P5, magnesium was taken up with priority over calcium in the Caco-2 cell monolayers. For example, at 180 min, the amount of transferred magnesium and calcium was 78.4 ± 0.95 μg/well and 2.56 ± 0.64 μg/well, respectively, showing a more than 30-fold difference in the amount of transport caused by P5. These results provide novel insight into the mineral transport activity of phosphopeptides obtained from casein.

Calcium-containing phosphopeptides pave the secretory pathway for efficient protein traffic and secretion in fungi

Casein phosphopeptides (CPPs) containing chelated calcium drastically increase the secretion of extracellular homologous and heterologous proteins in filamentous fungi. Casein phosphopeptides released by digestion of alpha - and beta-casein are rich in phosphoserine residues (SerP). They stimulate enzyme secretion in the gastrointestinal tract and enhance the immune response in mammals, and are used as food supplements. It is well known that casein phosphopeptides transport Ca2+ across the membranes and play an important role in Ca2+ homeostasis in the cells. Addition of CPPs drastically increases the production of heterologous proteins in Aspergillus as host for industrial enzyme production. Recent proteomics studies showed that CPPs alter drastically the vesicle-mediated secretory pathway in filamentous fungi, apparently because they change the calcium concentration in organelles that act as calcium reservoirs. In the organelles calcium homeostasis a major role is played by the pmr1 gene, that encodes a Ca2+/Mn2+ transport ATPase, localized in the Golgi complex; this transporter controls the balance between intra-Golgi and cytoplasmic Ca2+ concentrations. A Golgi-located casein kinase (CkiA) governs the ER to Golgi directionality of the movement of secretory proteins by interacting with the COPII coat of secretory vesicles when they reach the Golgi. Mutants defective in the casein-2 kinase CkiA show abnormal targeting of some secretory proteins, including cytoplasmic membrane amino acid transporters that in ckiA mutants are miss-targeted to vacuolar membranes. Interestingly, addition of CPPs increases a glyceraldehyde-3-phpshate dehydrogenase protein that is known to associate with microtubules and act as a vesicle/membrane fusogenic agent. In summary, CPPs alter the protein secretory pathway in fungi adapting it to a deregulated protein traffic through the organelles and vesicles what results in a drastic increase in secretion of heterologous and also of some homologous proteins.

The effect of McInnes solution on enamel and the effect of Tooth mousse on bleached enamel: An in vitro study

AIMS

To evaluate the effect of McInnes bleaching agent on the micro hardness of enamel before and after bleaching and to evaluate the effect of G C Tooth Mousse on the bleached enamel surface for its microhardness.

MATERIALS AND METHODS

McInnes bleaching solution, Casein phosphopeptide-amorphous calcium phosphate CCP-ACP (G C Tooth mousse) artificial saliva (Dept of Oral Pathology, College of Dental Sciences, Davengere), deionized water, Vickers Micro Hardness tester (Zwick/ZHV, Germany), freshly extracted teeth, cold cure acrylic, Diamond disc (Horico - PFINGST New jersey USA, KAVO- Germany), straight handpiece (kavo peca reta) and plastic moulds (6.5 x 2 mm). The purpose of this study was to evaluate and compare microhardness of the sound enamel surface by Vickers Hardness Number before and after bleaching with McInnes solution, and to evaluate the effect of casein phosphopeptide amorphous calcium phosphate (G C Tooth Mousse) on the bleached enamel surface for its microhardness.

STATISTICAL ANALYSIS

The data obtained from the test were subjected for statistical analysis and are presented as range, mean and standard deviation. P value of 0.05 or less was considered for statistical significance. The changes in microhardness at different times of assessment were analyzed using the paired 't' test

RESULTS

All the samples showed decrease in the microhardness after two cycles of bleaching, though immediately after bleaching the decrease in the microhardness was not significant (P = 0.34). However, after the second cycles, it showed a significant decrease (P<0.01) in the microhardness. After application of remineralization solution (GC Tooth mousse), the samples showed a marginal increase in the microhardness (P<0.05) after seven days and a marked increase after fourteen days (P<0.001).

CONCLUSION

McInnes bleaching agent does decrease the microhardness of enamel by causing enamel demineralization and GC Tooth mousse used in the study causes an increase in the microhardness of bleached enamel by maintaining a high gradient of calcium and phosphate ions at the enamel subsurface.