O-glycosylation of α-1-acid glycoprotein of human milk is lactation stage related

O-linked glycosylations in human milk casein and major whey proteins during lactation

As glycosylations are difficult to analyze, their roles and effects are poorly understood. Glycosylations in human milk (HM) differ across lactation. Glycosylations can be involved in antimicrobial activities and may serve as food for beneficial microorganisms. This study aimed to identify and analyze O-linked glycans in HM by high-throughput mass spectrometry. 184 longitudinal HM samples from 66 donors from day 3 and months 1, 2, and 3 postpartum were subjected to a post-translational modification specific enrichment-based strategy using TiO2 and ZrO2 beads for O-linked glycopeptide enrichment. β-CN was found to be a major O-linked glycoprotein, additionally, αS1-CN, κ-CN, lactotransferrin, and albumin also contained O-linked glycans. As glycosyltransferases and glycosidases are involved in assembling the glycans including O-linked glycosylations, these were further investigated. Some glycosyltransferases and glycosidases were found to be significantly decreasing through lactation, including two O-linked glycan initiator enzymes (GLNT1 and GLNT2). Despite their decrease, the overall level of O-linked glycans remained stable in HM over lactation. Three different motifs for O-linked glycosylation were enriched in HM proteins: Gly-Xxx-Xxx-Gly-Ser/Thr, Arg-Ser/Thr and Lys-Ser/Thr. Further O-linked glycan motifs on β-CN were observed to differ between intact proteins and endogenous peptides in HM.

Analysis of Minor Proteins Present in Breast Milk by Using WGA Lectin

Breast milk is a complex and dynamic biological fluid and considered an essential source of nutrition in early life. In its composition, the proteins have a relevant biological activity and are related to the multiple benefits demonstrated when compared with artificial milks derived from cow’s milk. Understanding human milk composition provides an important tool for health care providers toward the management of infant feeding and the establishment of breastfeeding. In this work, a new technique was developed to increase the knowledge of human milk, because many of the components remain unknown. To isolate minor proteins present in breast milk by using WGA lectin, breast milk was centrifuged to remove cells and separate the fat phase from the serum phase. The serum obtained was separated into two groups: control (n = 3; whole serum sample from mature milk) and WGA lectin (n = 3; sample processed with WGA lectin to isolate glycosylated proteins). The samples were analyzed by high-performance liquid chromatography coupled to mass spectrometry (HPLC/MS). A total of 84 different proteins were identified from all of the samples. In the WGA lectin group, 55 different proteins were isolated, 77% of which had biological functions related to the immune response. Of these proteins, there were eight WGA lectin group exclusives, and two had not previously been described in breast milk (polyubiquitin-B and POTE ankyrin domain family member F). Isolation by WGA lectin is a useful technique to detect minor proteins in breast milk and to identify proteins that could not be observed in whole serum.

Gestational Diabetes Mellitus-Induced Changes in Proteomes and Glycated/Glycosylated Proteomes of Human Colostrum

Gestational diabetes mellitus (GDM) not only has a bad effect on the development of infants but also causes variations in breastmilk composition. This study aims to investigate the changes in the protein profile of colostrum between mothers with GDM and healthy mothers (H) by sequential windowed acquisition of all theoretical fragment ion proteomics techniques. A total of 1295 proteins were detected, with 192 proteins being significantly different between GDM and H. These significantly different proteins were enriched with the carbohydrate and lipid metabolism pathway as well as immunity. Some proteins had an AOC value of 1, such as apolipoprotein E and lipoprotein lipase. In addition, we identified 42 glycated and 93 glycosylated peptides in colostrum without any enrichment, with glycated peptides being upregulated and glycosylated peptides being downregulated in colostrum with GDM. These results help us to better understand the GDM-induced changes in proteomes and glycated and glycosylated level and provide guidance on infant formula adjustment for infants from mothers with GDM.

Lectin-Based Method for Deciphering Human Milk IgG Sialylation

In light of the immunoprotective function of human milk and the incontestable impact of IgG glycosylation on its immune functions, characterization of the sialylation profile of human milk IgG is needed. Lectins as a molecular probe were applied in lectin-IgG-ELISA to analyze the sialylation and galactosylation pattern of skim milk IgG of mothers who delivered at term and prematurely. Well-defined biotinylated lectins were used: Maackia amurensis II (MAA II), Sambucus nigra (SNA), Ricinus communis I (RCA I), and Griffonia simplicifolia II (GSL II) specific to α2,3-Neu5Ac, α2,6-Neu5Ac, Gal(β1,4)GlcNAc, and agalactosylated glycans, respectively. The sialylation pattern of milk IgG differs qualitatively and quantitatively from maternal plasma IgG and is related to lactation stage and perinatal risk factors. Expression of MAA-, SNA-, and GSL-reactive glycotopes on term milk IgG showed a positive correlation with milk maturation from days 1 to 55. Preterm birth was associated with an increase of MAA-reactive and a decrease of RCA-reactive IgG glycotopes. Moreover, higher SNA- and GSL-reactive and lower RCA-reactive glycoform levels of milk IgG were associated with infection of lactating mothers. Application of a specific and simple method, lectin-IgG-ELISA, reveals the sialylation pattern of milk IgG over milk maturation. However, further investigations are needed in this area.

Sialic acid levels in breast milk from HIV-positive Tanzanian women and impact of maternal diet

OBJECTIVE

To quantify total sialic acid in milk from HIV-positive Tanzanian mothers and to determine the impact of maternal diet on milk sialic acid levels.

DESIGN

Milk samples were analyzed from 74 HIV-positive, Tanzanian women enrolled in a randomized, controlled clinical study of a dietary macronutrient supplement. Women were provided with a daily protein-calorie supplement and a micronutrient supplement or micronutrient supplement only during the last trimester of pregnancy and up to the first 6 months of breastfeeding.

METHODS

Milk samples were collected at approximately 2 weeks and at least 3 months postpartum and assayed for total sialic acid. Milk sialic acid was assessed relative to maternal macronutrient intake, age, BMI, CD4+ cell count and infant birth weight.

RESULTS

The mean concentration of milk sialic acid was highest in the first 2 weeks postpartum (6.89 ± 2.79 mmol/l) and declined rapidly by 3 months (2.49 ± 0.60 mmol/l). Sialic acid content in milk was similar between both treatment arms of the study, and did not correlate with maternal macronutrient intake. No correlation was found between maternal age, BMI, CD4+ cell count or infant birth weight and total milk sialic acid concentration.

CONCLUSION

Milk sialic acid levels in HIV-positive, Tanzanian women without malnutrition are comparable with reported values for women of European descent and show a similar temporal decline during early lactation. These findings suggest that total milk sialic acid is maintained despite macronutrient deficiencies in maternal diet and support a conserved role for milk sialic acid in neonatal development.

Quantitative N-glycoproteomics of milk fat globule membrane in human colostrum and mature milk reveals changes in protein glycosylation during lactation

The present study profiled the N-glycoproteome and quantified the changes of N-glycosylation site occupancy of MFGM proteins during lactation.