Changes in the ?-casein and ?-casein concentrations in human milk during lactation

Longitudinal Changes in the Concentration of Major Human Milk Proteins in the First Six Months of Lactation and Their Effects on Infant Growth

Our knowledge related to human milk proteins is still limited. The present study determined the changes in multiple human milk proteins during the first six months of lactation, investigated the influencing factors of milk proteins, and explored the impact of milk proteins on infant growth. A total of 105 lactating women and their full-term infants from China were prospectively surveyed in this research. Milk samples were collected at 1–5 days, 8–14 days, 1 month, and 6 months postpartum. Concentrations of total protein and α-lactalbumin were measured in all milk samples, and concentrations of lactoferrin, osteopontin, total casein, β-casein, α_s−1 casein, and κ-casein were measured in milk from 51 individuals using ultra performance liquid chromatography coupled with mass spectrometry. The concentration of measured proteins in the milk decreased during the first six months of postpartum (p-trend < 0.001). Maternal age, mode of delivery, maternal education, and income impacted the longitudinal changes in milk proteins (p-interaction < 0.05). Concentrations of α_s−1 casein in milk were inversely associated with the weight-for-age Z-scores of the infants (1 m: r −0.29, p 0.038; 6 m: r −0.33, p 0.020). In conclusion, the concentration of proteins in milk decreased over the first six months postpartum, potentially influenced by maternal demographic and delivery factors. Milk protein composition may influence infant weights.

Norepinephrine transporter expressed on mammary epithelial cells incorporates norepinephrine in milk into the cells

Mammary epithelial cells synthesize and secrete norepinephrine (NE) into breast milk to regulate β-casein expression through the adrenergic β₂ receptor. We investigated the expression, localization, and roles of NE transporter (NET) in the mammary epithelium during lactation. mRNA and protein levels of NET were determined in primary normal human mammary epithelial cells (pHMECs) and non-malignant human mammary epithelial MCF-12A cells. In nursing CD1 mice, NET localized to the apical membranes of the mammary epithelium. The intracellular NE content of pHMECs incubated with NE increased. Although the β-casein concentration in milk was slightly higher at day 10 than at day 2 of lactation, the NE concentration and lactation-related proteins were only slightly changed on days 2-10. Restraint stress increased the NE concentration in milk from nursing mice and NET protein levels were significantly higher than in non-stressed nursing mice. NET is expressed on the apical membrane of mammary epithelial cells and incorporates NE in milk into cells, potentially regulating the NE concentration in milk.

Advances in Infant Formula Science

Human milk contains a plethora of nutrients and bioactive components to help nourish the developing neonate and is considered the “gold standard” for early life nutrition—as befits the only food “designed” by evolution to feed human infants. Over the past decade, there is considerable evidence that highlights the “intelligence” contained in milk components that contribute to infant health beyond basic nutrition—in areas such as programming the developing microbiome and immune system and protecting against infection. Such discoveries have led to new opportunities for infant milk formula (IMF) manufacturers to refine nutritional content in order to simulate the functionality of breast milk. These include the addition of specialized protein fractions as well as fatty acid and complex carbohydrate components—all of which have mechanistic supporting evidence in terms of improving the health and nutrition of the infant. Moreover, IMF is the single most important dietary intervention whereby the human microbiome can be influenced at a crucial early stage of development. In this respect, it is expected that the complexity of IMF will continue to increase as we get a greater understanding of how it can modulate microbiota development (including the development of probiotics, prebiotics, and synbiotics) and influence long-term health. This review provides a scientific evaluation of key features of importance to infant nutrition, including differences in milk composition and emerging “humanized” ingredients.

Construction of a recombinant human FGF1 expression vector for mammary gland-specific expression in human breast cancer cells

Human Fibroblast growth factor 1 (FGF1) has been recognized as a valuable protein drug for the treatment of many diseases because of its multiple functions in regulating a variety of biological processes involved in embryonic development, cell growth and differentiation, morphogenesis, tissue repair, and others. The aim of this study was to develop an FGF1 mammary gland-specific expression vector to produce FGF1 on a large scale from transgenic cows to meet the demand for FGF1 in medical use. In this study, we generated an FGF1 mammary gland-specific expression vector and validated its function in human MCF-7 cells. This vector was shown to successfully express functional FGF1, thus potentially enabling the generation of transgenic cows to be used as mammary gland bioreactors.

Application of capillary zone electrophoresis to the characterisation of the human milk protein profile and its evolution throughout lactation

This work describes the use of capillary zone electrophoresis for the characterisation of human milk proteins. The major proteins were identified following different strategies, such as the treatment with enzymes for selective protein modification. Using this method we studied the proteins in human milk from different donors throughout lactation. Qualitative and quantitative differences in the composition of the individual proteins were observed. The different beta-casein phosphoforms were separated and quantified. The average proportion of the 0P:1P:2P:3P:4P:5P was, approximately, 3:6:9:4:10:2. The evolution of the ratio of the different beta-casein phosphoforms during lactation is reported.

Reconstituted Micelle Formation Using Reduced, Carboxymethylated Bovine κ-Casein and Human β-Casein

In milk, kappa-casein, a mixture of disulfide-bonded polymers, stabilizes and regulates the size of the unique colloidal complex of protein, Ca2+ and inorganic phosphate (Pi) termed the casein (CN) micelle. However, reduced, carboxymethylated bovine kappa-CN (RCM-kappa) forms fibrils at 37 degrees C and its micelle-forming ability is in question. Here, the doubly- and quadruply-phosphorylated human beta-CN forms and 1:1 (wt:wt) mixtures were combined with RCM-kappa at different beta/kappa weight ratios. Turbidity (OD(400 nm)) and a lack of precipitation up to 37 degrees C were used as an index of micelle formation. Studies were with 0, 5 and 10 mM Ca2+ and 4 and 8 mM Pi. The RCM-kappa does form concentration-dependent micelles. Also, beta-CN phosphorylation level influences micelle formation. Complexes were low-temperature reversible and RCM-kappa fibrils were seen. There appears to be equilibrium between fibrillar and soluble forms since the solution still stabilized after fibril removal. The RCM-kappa stabilized better than native bovine kappa-CN.

Kappa-casein interactions in the suspension of the two major calcium-sensitive human beta-caseins

The possible effects of both the beta-casein (beta-CN) phosphorylation level and the kappa-CN glycosylation level on micelle formation were studied using the doubly-phosphorylated form (beta-CN-2P) and the quadruply-phosphorylated form (beta-CN-4P) of human beta-CN, along with bovine kappa-CN to compare with previous studies using the more highly glycosylated human kappa-CN. Addition of bovine kappa-CN to human beta-CN-2P, beta-CN-4P, or a 1/1 (wt/wt) mixture of the two was at kappa/beta molar ratios from 0.0 to approximately 0.6 and micelles were reconstituted by addition of Ca+2 either directly at 37 degrees C for determination of the fraction suspended or at an initial temperature of 4 degrees that was gradually increased to 37 degrees C with the change in particle size monitored by turbidity measurements. Analysis of the data indicates that the 4P form requires more kappa-CN for stabilization than the 2P form but that the mixture of the two is more like the 4P form in that lateral kappa-kappa interactions may enhance beta-kappa interactions and micelle formation. Above a kappa/beta molar ratio of about 0.2, the caseins were fully suspended into reconstituted micelles. However, micelle size decreased at a higher ratio, indicating that the kappa-CN probably occupies a surface position and may regulate micelle size by its relative abundance. A comparison with published results suggests that the higher glycosylation level of human kappa-CN may protect a larger surface area and result in smaller micelles. Changes in reconstituted micelle size with pH indicate that positively charged groups in the kappa-CN may interact with the negatively charged phosphate esters in the beta-CN moieties in addition to kappa-beta hydrophobic interactions.

Measurement of nine human milk proteins by nephelometric immunoassays: application to the determination of mature milk protein profile

OBJECTIVES

Microparticle-enhanced nephelometric immunoassays for six human milk proteins (beta-casein, kappa-casein, alpha-lactalbumin, serum albumin, lactoferrin, and lysozyme) and conventional immunonephelometry assays for immunoglobulin A, C3, and C4 complement proteins were developed and characterized.

DESIGN AND METHODS

Microparticle-enhanced nephelometric immunoassays are competitive assays based on the nephelometric quantification of the inhibition of microparticle-protein conjugates immunoagglutination by the proteins to be assayed.

RESULTS

High precision (CVs ranged from 1% to 14% in within- and between-assays) and recovery (linear recovery in dilution-overloading assay) ensure a reliable determination of the main human milk proteins by single-step homogeneous nephelometric immunoassays, accurate over wide ranges of concentration. These immunoassays were easily applied to a large number of mature human milk samples (between 373 and 503 according to the proteins tested).

CONCLUSIONS

The immunoassays developed could be applied to the fast determination of human milk protein profile usable for nursery milk bank and fortification.