Determination of sialic acids in milks and milk-based products

Avian and Human Influenza A Virus Receptors in Bovine Mammary Gland

An outbreak of influenza A (H5N1) virus was detected in dairy cows in the United States. We detected influenza A virus sialic acid -α2,3/α2,6-galactose host receptors in bovine mammary glands by lectin histochemistry. Our results provide a rationale for the high levels of H5N1 virus in milk from infected cows.

HPLC-QQQ-MS/MS-based authentication and determination of free and bound sialic acids content in human, bovine, sheep, goat milk, and infant formula

An accurate method for qualitative and quantitative analysis of lipid-bound (LB), protein-bound (PB), oligosaccharides-bound, and free sialic acids in milk was developed by using high-performance liquid chromatography -triple quadrupole-tandem mass spectrometer. The profile of free and bound sialic acids in milk (human, bovine, goat, and sheep) and infant formula (IF) was examined in the present study. Human milk contains only N-acetylneuraminic acid (Neu5Ac) and was mainly present in the form of oligosaccharide-bound. The content of total Neu5Ac (T-Neu5Ac), free and bound Neu5Ac in human milk decreased with the prolongation of lactation. The most intriguing finding was the increase in the proportion of PB and LB sialic acids. The sialic acids in bovine and sheep milk were mainly PB and oligosaccharides-bound Neu5Ac. T-Neu5Ac in goat milk (GM) was 67.44-89.72 µg/mL and was mainly PB Neu5Ac, but total N-glycolylneuraminic acid (T-Neu5Gc) content of GM can be as high as 100.01 µg/mL. The concentration of T-Neu5Gc in sheep and GM was significantly higher than that of bovine milk (BM). T-Neu5Gc content of GM -based IF was 264.86 µg/g, whereas T-Neu5Gc content of BM -based IF was less (2.26-17.01 µg/g). Additionally, our results found that there were also sialic acids in IF ingredients, which were mainly bound with protein and oligosaccharides, primarily derived from desalted whey powder and whey protein concentrate.

Sialylation of dietary mucin modulate its digestibility and the gut microbiota of elderly individuals

Food-derived mucins are glycoproteins rich in sialic acid, but their digestive properties and potential health benefits for humans have been scarcely investigated. In this work, ovomucin (OVM, rich in N-acetylneuraminic acid, about 3 %), porcine small intestinal mucin (PSIM, rich in N-glycolylneuraminic acid, about 1 %), the desialylated OVM (AOVM) and the desialylated PSIM (APSIM) were selected to examine their digestion and their impact on the gut microbiota of elderly individuals. The results shown that, the proportion of low-molecular-weight proteins increased after simulated digestion of these four mucins, with concomitant comparable antioxidant activity observed. Desialylation markedly increased the degradation and digestion rate of mucins. In vitro fecal fermentation was conducted with these mucins using fecal samples from individuals of different age groups: young, low-age and high-age elderly. Fecal fermentation with mucin digestive solution stimulated the production of organic acids in the group with fecal sample of the elderly individuals. Among them, the OVM group demonstrated the most favorable outcomes. The OVM and APSIM groups elevated the relative abundance of beneficial bacteria such as Lactobacillus and Bifidobacterium, while diminishing the presence of pathogenic bacteria such as Klebsiella. Conversely, the probiotic effects of AOVM and PSIM were attenuated or even exhibited adverse effects. Hence, mucins originating from different sources and possessing distinct glycosylation patterns exhibit diverse biological functions. Our findings can offer valuable insights for developing a well-balanced and nutritious diet tailored to the elderly population.

N-glycolylneuraminic acid in red meat and processed meat is a health concern: A review on the formation, health risk, and reduction

One of the most consistent epidemiological associations between diet and human disease risk is the impact of consuming red meat and processed meat products. In recent years, the health concerns surrounding red meat and processed meat have gained worldwide attention. The fact that humans have lost the ability to synthesize N-glycolylneuraminic acid (Neu5Gc) makes red meat and processed meat products the most important source of exogenous Neu5Gc for humans. As our research of Neu5Gc has increased, it has been discovered that Neu5Gc in red meat and processed meat is a key factor in many major diseases. Given the objective evidence of the harmful risk caused by Neu5Gc in red meat and processed meat to human health, there is a need for heightened attention in the field of food. This updated review has several Neu5Gc aspects given including biosynthetic pathway of Neu5Gc and its accumulation in the human body, the distribution of Neu5Gc in food, the methods for detecting Neu5Gc, and most importantly, a systematic review of the existing methods for reducing the content of Neu5Gc in red meat and processed meat. It also provides some insights into the current status and future directions in this area.

Insights into the Structure, Metabolism, Biological Functions and Molecular Mechanisms of Sialic Acid: A Review

Sialic acid (SA) is a kind of functional monosaccharide which exists widely in edible bird's nest (EBN), milk, meat, mucous membrane surface, etc. SA is an important functional component in promoting brain development, anti-oxidation, anti-inflammation, anti-virus, anti-tumor and immune regulation. The intestinal mucosa covers the microbial community that has a significant impact on health. In the gut, SA can also regulate gut microbiota and metabolites, participating in different biological functions. The structure, source and physiological functions of SA were reviewed in this paper. The biological functions of SA through regulating key signaling pathways and target genes were discussed. In summary, SA can modulate gut microbiota and metabolites, which affect gene expressions and exert its biological activities. It is helpful to provide scientific reference for the further investigation of SA in the functional foods.

Quantitation of bioactive components in infant formulas: Milk oligosaccharides, sialic acids and corticosteroids

Human milk is considered the optimal food for infants with abundant nutrients and bioactive components, which play key roles in infant health and development. Infant formulas represent appropriate substitutes for human milk. There are many brands of infant formula with different ingredient sources and functions on the market. The present study aims to quantify important bioactive components, i.e., milk oligosaccharides (MOS), sialic acids (Sia) and corticosteroids, in different infant formulas and compare these to human milk. In total, 12 different infant formulas available on the Dutch market were analyzed in this study. The concentrations of MOS and Sia were characterized by UHPLC-FLD and LC-MS, while corticosteroids were determined using established UHPLC-MS/MS methods. Among infant formulas, 15 structures of oligosaccharides were identified, of which 2'-Fucosyllactose (2'FL), 3'-Galactosyllactose (3'GL) and 6'-Galactosyllactose (6́'GL) were found in all infant formulas. The oligosaccharide concentrations differed between milk source and brands and were 3-5 times lower than in human milk. All infant formulas contained Sia, N-acetylneuraminic acid (Neu5Ac) was dominant in bovine milk-based formulas, while N-glycolylneuraminic acid (Neu5Gc) was major in goat milk-based formula. All infant formulas contained corticosteroids, yet, at lower concentrations than human milk. Insight in concentrations of bioactive components in infant formula compared to human milk may give direction to dietary advices and/or novel formula design.

Elevated concentrations of Neu5Ac and Neu5,9Ac2 in human plasma: potential biomarkers of cardiovascular disease

Cardiovascular disease (CVD) is a group of health conditions affecting the heart and vascular system with very high prevalence and mortality rates. The presence of CVD is characterised by high levels of inflammation which have previously been associated with increased plasma concentrations of N-acetyl neuraminic acid (Neu5Ac). While Neu5Ac has been studied in the context of CVD, Neu5,9Ac2 has not, despite being the second most abundant sialic acid in human plasma. A small-scale pilot study of thirty plasma samples from patients with diagnosed CVD, and thirty age and sex-matched healthy controls, was designed to gain insight into sialic acids as biomarkers for CVD and potential future areas of study. Each sample was assayed for Neu5Ac and Neu5,9Ac2 concentrations. Mean Neu5Ac and Neu5,9Ac2 concentrations were significantly elevated in patients with CVD compared to healthy controls (Neu5Ac: P < 0.001; Neu5,9Ac2: P < 0.04). Receiver operator curve (ROC) analysis indicated that both Neu5Ac and Neu5,9Ac2 have reasonable predictive power for the presence of CVD (Neu5Ac AUC: 0.86; Neu5,9Ac2 AUC: 0.71). However, while Neu5Ac had both good sensitivity (0.82) and specificity (0.81), Neu5,9Ac2 had equivalent specificity (0.81) but very poor sensitivity (0.44). A combination marker of Neu5Ac + Neu5,9Ac2 showed improvement over Neu5Ac alone in terms of predictive power (AUC: 0.93), sensitivity (0.87), and specificity (0.90). Comparison to a known inflammatory marker, high sensitivity c-reactive protein (hs-CRP: P-value: NS, ROC:0.50) was carried out, showing that both Neu5Ac and Neu5,9Ac2 outperformed this marker. Further to this, hs-CRP values were combined with the three different sialic acid markers to determine any effect on the AUC values. A slight improvement in AUC was noted for each of the combinations, with Neu5Ac + Neu5,9Ac2 + hs-CRP giving the best AUC of 0.97 overall. Thus, Neu5Ac would appear to offer good potential as a predictive marker for the presence of CVD, which the addition of Neu5,9Ac2 predictive power improves, with further improvement seen by the addition of hs-CRP.

Determining the safety and efficacy of dietary supplementation with 3'-sialyllactose or 6'-sialyllactose on growth, tolerance, and brain sialic acid concentrations

Sialylated oligosaccharides, including 3'-sialyllactose (3'-SL) and 6'-sialyllactose (6'-SL), comprise a large portion of human milk and have been known to support development over the first year of life. While research has investigated the impact of early-life supplementation, longer-term supplementation remains relatively unexplored. Consequently, the following study assesses the impact of supplementation of either 3'-SL or 6'-SL on growth performance, tolerance, and brain sialic acid concentrations. Two-day-old piglets (n = 75) were randomly assigned to a commercial milk replacer ad libitum without or with 3'-SL or 6'-SL (added at 0.2673% on an as-is basis). Daily body weight and feed disappearance were recorded to assess growth performance and tolerance. Pigs were euthanized for sample collection on postnatal day 33 (n = 30) or 61 (n = 33), respectively. Across growth performance, clinical chemistry and hematology, histomorphology, and sialic acid quantification, dietary differences were largely unremarkable at either time-point. Overall, SA was well-tolerated both short-term and long-term.

Dietary sialic acids: distribution, structure, and functions

Sialic acids (Sias), a group of over 50 structurally distinct acidic saccharides on the surface of all vertebrate cells, are neuraminic acid derivatives. They serve as glycan chain terminators in extracellular glycolipids and glycoproteins. In particular, Sias have significant implications in cell-to-cell as well as host-to-pathogen interactions and participate in various biological processes, including neurodevelopment, neurodegeneration, fertilization, and tumor migration. However, Sia is also present in some of our daily diets, particularly in conjugated form (sialoglycans), such as those in edible bird's nest, red meats, breast milk, bovine milk, and eggs. Among them, breast milk, especially colostrum, contains a high concentration of sialylated oligosaccharides. Numerous reviews have concentrated on the physiological function of Sia as a cellular component of the body and its relationship with the occurrence of diseases. However, the consumption of Sias through dietary sources exerts significant influence on human health, possibly by modulating the gut microbiota's composition and metabolism. In this review, we summarize the distribution, structure, and biological function of particular Sia-rich diets, including human milk, bovine milk, red meat, and egg.

Genetic-Phenotype Analysis of Bifidobacterium bifidum and Its Glycoside Hydrolase Gene Distribution at Different Age Groups

Human gut microbiota interfere with host development and aging. Bifidobacterium is a microbial genus found in the human digestive tract that has probiotic activities such as improving constipation and enhancing immunity. The species and numbers present change with age, but there has been limited research on probiotic gut microbiota at specific ages. This study analyzed the distribution of 610 bifidobacteria in subjects in several age groups (0-17, 18-65, and 66-108 y) using 486 fecal samples and determined the distribution of glycoside hydrolases based on genetic analysis of strains representing 85% of the Bifidobacterium species abundance in each age group. 6'-Sialyllactose is a major component of acidic breast milk oligosaccharides, which can promote human neurogenesis and bifidobacteria growth. Using genotypic and phenotypic association analysis, we investigated the utilization of 6'-sialyllactose by six B. bifidum strains isolated from subjects 0-17 and 18-65 y. A comparative genomic analysis of the six B. bifidum strains revealed differences in genomic features across age groups. Finally, the safety of these strains was evaluated by antibiotic gene and drug resistance phenotype analysis. Our results reveal that the distribution of glycoside hydrolase genes in B. bifidum varies with age, thus affecting the phenotypic results. This provides important insights for the design and application of probiotic products for different ages.

A Schematic Colorimetric Assay for Sialic Acid Assay Based on PEG-Mediated Interparticle Crosslinking Aggregation of Gold Nanoparticles

Sialic acid (SA) is a well-known component of glycoproteins, which have applications in various functional processes on the cell's surface. The colorimetric is a simpler and more convenient method for measuring SA due to its low-cost apparatus and visual signal changes. This work focused on the unpredictable interparticle crosslinking aggregation of the functionalized gold nanoparticles (AuNPs) in complex media. We proposed a balance of the Derjaguin-Landau-Verwey-Overbeek (DLVO)-type aggregation and molecule-based interaction method to solve this problem. Here, we report a novel colorimetric assay for the determination of SA using 4-mercaptophenyl boronic acid (4-MPBA) as an analyte's recognition molecule, and negative charge PEG₄₀₀ was used to repulsive the interparticle crosslinking. The proposed sensing platform shows a linear relationship between the ratio of the absorbance intensity (A₅₂₅/A₆₆₀) and concentration of SA from 0.05 to 8 mM (R² = 0.997) and a detection limit of 48 μM was observed. The novel gold-based colorimetric sensor is easy to fabricate, reproducible in its test performance and has been successfully applied for the detection of SA in biological and healthcare product samples.

Milk Polysialic Acid Levels Rapidly Decrease in Line with the N-Acetylneuraminic Acid Concentrations during Early Lactation in Dairy Cows

Sialylated milk oligosaccharides and glycoconjugates have several positive effects on the mucosal barrier, the gut microbiome, and an effective immune system. For this reason, they are important biomolecules for mammary gland health and optimal development of offspring. In milk, the major sialic acid, N-acetylneuraminic acid (Neu5Ac), can be attached as monosialyl-residues or as polymers. To investigate the sialylation processes during lactation of German Holstein cows, we analyzed udder tissue in addition to milk at different time points of lactation. The analysis of the milk samples revealed that both the levels of Neu5Ac and its polymer, polysialic acid (polySia), rapidly decreased during the first three days of lactation, and a high interindividual variance was observed. In mature milk, however, the sialylation status remains relatively constant. The results indicate that mammary gland epithelial cells are one source for milk polySia, since immunohistochemistry of udder tissue exhibited strong polySia staining in these cells. Furthermore, both polysialyltransferases, ST8SiaII and ST8SiaIV, are expressed. Based on known functions of monosialyl residues and polySia, we discuss the potential impact of these biomolecules and the consequences of the heterogeneous sialylation status of milk in relation to udder health and offspring health.

Determination of N-acetylneuraminic and N-glycolylneuraminic acids in unprocessed milk of four cattle breeds

This research communication reports concentrations of two sialic acids (SA), N-acetylneuraminic (Neu5Ac) and N-glycolylneuraminic (Neu5Gc), in fresh milk from different cow breeds throughout lactation. According to published studies, the two SA types found in animal-derived products have diverse and conflicting effects on human health, but SA content is not routinely analysed in individual milk cows samples. We measured the content of Neu5Ac and Neu5Gc in milk from Holstein Friesian (HO), Simmental (SM), Simmental × Holstein crossbred (SM×HO), and Podolica (POD) cows at 60 and 120 d following calving. HO, SM and SM×HO were reared in an intensive production while POD were raised in an extensive system. Results showed that total Neu5Ac was overall thirty times more abundant than Neu5Gc, and their concentrations were higher at 120 d than at 60 d (P < 0.001). Neu5Gc values were greater in HO, SM, and SM × HO than in POD (P < 0.001), while HO had a higher Neu5Ac value than the other three breeds (P < 0.001). These findings shed light on the differences in SA content among cow breeds and lay the groundwork for future research to select animals that produce milk with desirable characteristics for human health.

Milk polar lipids composition and functionality: a systematic review

Polar lipids including glycerophospholipids and sphingophospholipids are important nutrients and milk is a major source, particularly for infants. This systematic review describes the human and bovine milk polar lipid composition, structural organization, sources for formulation, and physiological functionality. A total of 2840 records were retrieved through Scopus, 378 were included. Bovine milk is a good source of polar lipids, where yield and composition are highly dependent on the choice of dairy streams and processing. In milk, polar lipids are organized in the milk fat globule membrane as a tri-layer encapsulating triglyceride. The overall polar lipid concentration in human milk is dependent on many factors including lactational stage and maternal diet. Here, reasonable ranges were determined where possible. Similar for bovine milk, where differences in milk lipid concentration proved the largest factor determining variation. The role of milk polar lipids in human health has been demonstrated in several areas and critical review indicated that brain, immune and effects on lipid metabolism are best substantiated areas. Moreover, insights related to the milk fat globule membrane structure-function relation as well as superior activity of milk derived polar lipid compared to plant-derived sources are emerging areas of interest regarding future research and food innovations.

Sialic acid, the secret gift for the brain

The human brain grows rapidly in early life which requires adequate nutrition. Human milk provides optimal nutrition for the developing brain, and breastfeeding significantly improves the cognition development of infants. These benefits have been largely attributed to human milk oligosaccharides (HMOS), associated with sialic acid (Sia). Subsequently, sialylated HMOS present a vital source of exogenous Sia to infants. Sialic acid is a key molecule essential for proper development of gangliosides, and therefore critical in brain development and function. Recent pre-clinical studies suggest dietary supplementation with Sia or sialylated oligosaccharides enhances intelligence and cognition performance in early and later life. Furthermore, emerging evidence suggests the involvement of Sia in brain homeostasis and disbalance correlates with common pathologies such as Alzheimer's disease (AD). Therefore, this review will discuss early brain health and development and the role of Sia in this process. Additionally, studies associating breastfeeding and specific HMOS to benefits in cognitive development are critically assessed. Furthermore, the review will assess studies implying the potential role of HMOS and microbiota in brain development via the gut-brain axis. Finally, the review will summarize recent advances regarding the role of Sia in neurodegenerative disease in later life and potential roles of dietary Sia sources.

Qualitative and Quantitative Analysis of Edible Bird's Nest Based on Peptide Markers by LC-QTOF-MS/MS

Edible bird's nest (EBN) is an expensive health food. There are many adulterants in the market. It remains challenging to discriminate EBN from its adulterants due to a lack of high-specificity markers. Besides, the current markers are confined to soluble fraction of EBN. Here, both soluble and insoluble fractions were analyzed by LC-QTOF-MS/MS. A total of 26 high-specificity peptides that were specific to EBN were selected as qualitative authentication markers. Among them, 10 markers can discriminate EBN from common adulterants, 13 markers discriminate white EBN from grass EBN/common adulterants, and 3 markers discriminate grass EBN from white EBN/common adulterants. Three of them, which showed high signal abundance (Peak area ≥ 10⁶) and satisfactory linearity (R² ≥ 0.995) with EBN references, were selected as the assay marker; and their peptide sequences were confidently identified by searching database/de novo sequencing. Based on these markers, a qualitative and quantitative analytical method was successfully developed and well-validated in terms of linearity, precision, repeatability, and accuracy. The method was subsequently applied to detect EBN products on the market. The results indicated that more than half of EBN products were not consistent with what the merchants claimed.

Biology of human milk oligosaccharides: from Basic Science to Clinical Evidence

Human milk oligosaccharides (HMOs) have been researched by scientists for over 100 years, driven by the substantial evidence for the nutritional and health benefits of mother's milk. Yet research has truly bloomed during the last decade, thanks to the progress in biotechnology, which allowed the production of large amounts of bona fide HMOs. The availability of HMOs has been particularly crucial for the renewed interest in HMO research because of the low abundance or even absence of HMOs in farmed animal milk. This interest is reflected in the increasing number of original research publications and reviews on HMOs. Here, we provide an overview and critical discussion on structure function relations of HMOs that highlight why they are such interesting and important components of human milk. Clinical observations in breastfed infants backed by basic research from animal models provide guidance as to what physiological roles for HMOs are to be expected. From an evidence-based nutrition viewpoint, we discuss the current data supporting clinical relevance of specific HMOs based on randomized placebo controlled clinical intervention trials in formula-fed infants. This article is protected by copyright. All rights reserved.

O-Acetylation of Capsular Polysialic Acid Enables Escherichia coli K1 Escaping from Siglec-Mediated Innate Immunity and Lysosomal Degradation of E. coli-Containing Vacuoles in Macrophage-Like Cells

Escherichia coli K1 causes bacteremia and meningitis in human neonates. The K1 capsule, an α2,8-linked polysialic acid (PSA) homopolymer, is its essential virulence factor. PSA is usually partially modified by O-acetyl groups. It is known that O-acetylation alters the antigenicity of PSA, but its impact on the interactions between E. coli K1 and host cells is unclear. In this study, a phase variant was obtained by passage of E. coli K1 parent strain, which expressed a capsule with 44% O-acetylation whereas the capsule of the parent strain has only 3%. The variant strain showed significantly reduced adherence and invasion to macrophage-like cells in comparison to the parent strain. Furthermore, we found that O-acetylation of PSA enhanced the modulation of trafficking of E. coli-containing vacuoles (ECV), enabling them to avoid fusing with lysosomes in these cells. Intriguingly, by using quartz crystal microbalance, we demonstrated that the PSA purified from the parent strain interacted with human sialic acid-binding immunoglobulin-like lectins (Siglecs), including Siglec-5, Siglec-7, Siglec-11, and Siglec-14. However, O-acetylated PSA from the variant interacted much less and also suppressed the production of Siglec-mediated proinflammatory cytokines. The adherence of the parent strain to human macrophage-like cells was significantly blocked by monoclonal antibodies against Siglec-11 and Siglec-14. Furthermore, the variant strain caused increased bacteremia and higher lethality in neonatal mice compared to the parent strain. These data elucidate that O-acetylation of K1 capsule enables E. coli to escape from Siglec-mediated innate immunity and lysosomal degradation; therefore, it is a strategy used by E. coli K1 to regulate its virulence.

IMPORTANCEEscherichia coli K1 is a leading cause of neonatal meningitis. The mortality and morbidity of this disease remain significantly high despite antibiotic therapy. One major limitation on advances in prevention and therapy for meningitis is an incomplete understanding of its pathogenesis. E. coli K1 is surrounded by PSA, which is observed to have high-frequency variation of O-acetyl modification. Here, we present an in-depth study of the function of O-acetylation in PSA at each stage of host-pathogen interaction. We found that a high level of O-acetylation significantly interfered with Siglec-mediated bacterial adherence to macrophage-like cells, and blunted the proinflammatory response. Furthermore, the O-acetylation of PSA modulated the trafficking of ECVs to prevent them from fusing with lysosomes, enabling them to escape degradation by lysozymes within these cells. Elucidating how subtle modification of the capsule enhances bacterial defenses against host innate immunity will enable the future development of effective drugs or vaccines against infection by E. coli K1.

Review of sialic acid's biochemistry, sources, extraction and functions with special reference to edible bird's nest

Sialic acids are a group of nine-carbon α-keto acids. Sialic acid exists in more than 50 forms, with the natural types discovered as N-acetylneuraminic acid (Neu5Ac), deaminoneuraminic acid (2-keto-3-deoxy-nonulononic acid or Kdn), and N-glycolylneuraminic acid (Neu5Gc). Sialic acid level varies depending on the source, where edible bird's nest (EBN), predominantly Neu5Ac, is among the major sources of sialic acid. Due to its high nutritive value and complexity, sialic acid has been studied extensively through acid, aqueous, and enzymatic extraction. Although detection by chromatographic methods or mass spectrometry is common, the isolation and recovery work remained limited. Sialic acid is well-recognised for its bioactivities, including brain and cognition development, immune-enhancing, anti-hypertensive, anticancer, and skin whitening properties. Therefore, sialic acid can be used as a functional ingredient in the various industries. This paper reviews the current trend in the biochemistry, sources, extraction, and functions of sialic acids with special reference to EBN.

An overview and future prospects of sialic acids

Sialic acids (Sias) are negatively charged functional monosaccharides present in a wide variety of natural sources (plants, animals and microorganisms). Sias play an important role in many life processes, which are widely applied in the medical and food industries as intestinal antibacterials, antivirals, anti-oxidative agents, food ingredients, and detoxification agents. Most Sias are composed of N-acetylneuraminic acid (Neu5Ac, >99%), and Sia is its most commonly used name. In this article, we review Sias in terms of their structures, applications, determination methods, metabolism, and production strategies. In particular, we summarise and compare different production strategies, including extraction from natural sources, chemical synthesis, polymer decomposition, enzymatic synthesis, whole-cell catalysis, and de novo biosynthesis via microorganism fermentation. We also discuss research on their physiological functions and applications, barriers to efficient production, and strategies for overcoming these challenges. We focus on efficient de novo biosynthesis strategies for Neu5Ac via microbial fermentation using novel synthetic biology tools and methods that may be applied in future. This work provides a comprehensive overview of recent advances on Sias, and addresses future challenges regarding their functions, applications, and production.

Large-scale preparation and glycan characterization of sialylglycopeptide from bovine milk glycomacropeptide and its bifidogenic properties

Bovine glycomacropeptide (GMP) is a 7,000-Da glycopolypeptide released from κ-casein during cheese making. The O-glycan chains linked to GMP have many biological activities, but their utilization for nutraceutical products is limited due to their low content. To concentrate the functional glycan chains of GMP, we prepared sialylglycopeptide concentrate (SGC) from GMP-containing whey protein concentrate via proteolytic digestion of peptide chains and concentration of sialylglycopeptide by ultrafiltration using membranes with a molecular weight cut-off of 1,000 Da. The abundant saccharides detected in the prepared SGC were N-acetylneuraminic acid (Neu5Ac: 32.3% wt/wt), N-acetylgalactosamine (11.3%), and galactose (10.2%), which constitute O-glycans attached to GMP. The Neu5Ac content in SGC was found concentrated at approximately 4.8-fold of its content in GMP-containing whey protein concentrate (6.8%). Structural analysis of O-glycopeptides by liquid chromatography tandem mass spectrometry identified 88 O-glycopeptides. Moreover, O-acetylated or O-diacetylated Neu5Ac was detected in addition to the previously characterized O-glycans of GMP. Quantitative analysis of O-glycan in SGC by fluorescence labeling of chemically released O-glycan revealed that a disialylated tetrasaccharide was the most abundant glycan (76.6% of the total O-glycan). We further examined bifidogenic properties of SGC in vitro, which revealed that SGC served as a more potent carbon source than GMP and contributes to the growth-promoting effects on certain species of bifidobacteria. Overall, our study findings indicate that SGC contains abundant O-glycans and has a bifidogenic activity. Moreover, the protocol for the preparation of SGC described herein is relatively simple, providing a high yield of glycan, and can be used for large-scale preparation.

Optimization and Pretreatment for Hot Water Extraction of Korean Deer (Cervus canadensis Erxleben) Velvet Antlers

Velvet antler (VA) is a historically traditional medicinal supplement and is well known in Asian countries for its pharmaceutical and health benefits. The objectives for this study were to optimize the hot water extraction (HWE) of VA for the Korean VA industry, and to determine the most effective pretreatment method among microwave (MW), ultrasonication (US), and enzymatic (EZ) techniques. Using response surface methodology, optimum extraction temperatures and times were determined by central composite design configuration based on extraction yield and sialic acid content. Various quality parameters of VA extract including yield, soluble solid, protein, and sialic acid contents were also compared with the conjunction of HWE and pretreatment. The yield and sialic acid content of VA extract were determined to be 40% and 0.73 mg/g, respectively, under an optimum temperature of 100°C at 24 h of extraction time. The yields from VA extracts pretreated with MW, US, and EZ were 17.42%, 19.73%, and 29.15%, respectively. Among the tested commercial enzymes, pepsin was the most effective proteolytic enzyme and led to the highest yield (47.65%), soluble solids (4.03 °brix), protein (1.12 mg/ml), and sialic acid (3.04 mg/ml) contents from VA extract.

Potential role of ovomucin and its peptides in modulation of intestinal health: A review

Intestinal dysfunction, which may cause a series of metabolic diseases, has become a worldwide health problem. In the past few years, studies have shown that consumption of poultry eggs has the potential to prevent a variety of metabolic diseases, and increasing attention has been directed to the bioactive proteins and their peptides in poultry eggs. This review mainly focused on the biological activities of an important egg-derived protein named ovomucin. Ovomucin and its derivatives have good anti-inflammatory, antioxidant, immunity-regulating and other biological functions. These activities may affect the physical, biological and immune barriers associated with intestinal health. This paper reviewed the structure and the structure-activity relationship of ovomucin，the potential role of ovomucin and its derivatives in modulation of intestinal health are also summarized. Finally, the potential applications of ovomucin and its peptides as functional food components to prevent and assist in the pretreatment of intestinal health problems are prospected.

Enzymatic Synthesis of Trideuterated Sialosides

Sialic acids are a family of acidic monosaccharides often found on the termini of cell surface proteins or lipid glycoconjugates of higher animals. Herein we describe the enzymatic synthesis of the two isotopically labeled sialic acid derivatives d₃-X-Gal-α-2,3-Neu5Ac and d₃-X-Gal-α-2,3-Neu5Gc. Using deuterium oxide as the reaction solvent, deuterium atoms could be successfully introduced during the enzymatic epimerization and aldol addition reactions when the sialosides were generated. NMR and mass spectrometric analyses confirmed that the resulting sialosides were indeed tri-deuterated. These compounds may be of interest as internal standards in liquid chromatography/mass spectrometric assays for biochemical or clinical studies of sialic acids. This was further exemplified by the use of this tri-deuterated sialosides as internal standards for the quantification of sialic acids in meat and egg samples.

Sialic Acids Content Analysis of the Innovator and Biosimilar Darbepoetin Alfa by Fluorometric HPLC Assay

Background:

Erythropoietin is a highly glycosylated protein hormone, used medically for the treatment of anemia associated with chronic renal disease. Due to patent expirations, we expect biosimilar erythropoietins to play an increasing role in healthcare in coming years. </P><P> Objective: Here, we have developed a chromatograpy method for determination of Neu5AC and Neu5Gc in darbepoetin alfa.

Methods:

Sialic acids (Sias) analysis provides the contents of the two most abundant sialic acids Neu5Ac and Neu5Gc. It has often been utilized for the evaluation of sialylated glycoprotein to ensure the biopharmtherapeutic safety and efficacy. In this work, the application of the DMB derivatization of Sias from darbepoetin alfa followed by the separation of the resulting adducts based on HPLC-FLD was presented.

Results:

Our work demonstrated that the method is characteristics of simple operation, and high reproducibility and sensitivity, and easy to set up for compliance analysis in a routine laboratory.

Conclusion:

By using a water:acetonitrile gradient, high resolution of Sias was obtained within a 1 min analysis time. The detection limits of NeuAc and NeuGc were 2.9 µg/L and 1.5 µg/L, respectively. The RSDs of the intraday and interday precisions in terms of retention time and peak areas of the analytes are below 1%, and from 3.8% to 4.2% respectively. Therefore, this developed method can be widely applied for simple determination of Neu5Ac, Neu5Gc, and O-acetylated Sias in the derivatized samples. Especially, high levels of O-acetylation were detected on darbepoetin alfa N-glycans, which are critical to establishing the bioequivalence of darbepoetin alfa biosimilars.

Potentiometric analysis of sialic acid with a flexible carbon cloth based on boronate affinity and molecularly imprinted polymers

A potentiometric sensor for sialic acid detection was designed based on a boronic acid-containing MIP modified carbon cloth electrode.

Preparation of a molecularly imprinted sensor based on quartz crystal microbalance for specific recognition of sialic acid in human urine

A novel molecularly imprinted quartz crystal microbalance (QCM) sensor was successfully prepared for selective determination of sialic acid (SA) in human urine samples. To obtain the QCM sensor, we first modified the gold surface of the QCM chip by self-assembling of allylmercaptane to introduce polymerizable double bonds on the chip surface. Then, SA molecularly imprinted polymer (MIP) nanofilm was attached to the modified QCM chip surface. For comparison, we have also characterized the nonmodified and improved surfaces of the QCM sensor by using atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy. We then tested the selectivity and detection limit of the imprinted QCM sensor via a series of adsorption experiments. The results show a linear response in the range of 0.025-0.50 μmol L^-1 for sialic acid. Moreover, the limit of detection (LOD) of the prepared imprinted QCM sensor was found to be 1.0 nmol L^-1 for sialic acid, and high recovery values range from 87.6 to 108.5% with RSD < 8.7 (n = 5) for the spiked urine sample obtained. Overall, this work presents how a novel QCM sensor was developed and used to detect sialic acid in human urine samples. Graphical abstract Specific recognition of sialic acid by the MIP-QCM sensor system.

Dietary Sialyllactose Does Not Influence Measures of Recognition Memory or Diurnal Activity in the Young Pig

Sialic acid (SA) is an integral component of gangliosides and signaling molecules in the brain and its dietary intake may support cognitive development. We previously reported that feeding sialyllactose, a milk oligosaccharide that contains SA, alters SA content and diffusivity in the pig brain. The present research sought to expand upon such results and describe the effects of feeding sialyllactose on recognition memory and sleep/wake activity using a translational pig model. Pigs were provided ad libitum access to a customized milk replacer containing 0 g/L or 380 g/L of sialyllactose from postnatal day (PND) 2-22. Beginning on PND 15, pigs were fitted with accelerometers to track home-cage activity and testing on the novel object recognition task began at PND 17. There were no significant effects of diet on average daily body weight gain, average daily milk intake, or the gain-to-feed ratio during the study (all p ≥ 0.11). Pigs on both diets were able to display recognition memory on the novel object recognition task (p < 0.01), but performance and exploratory behavior did not differ between groups (all p ≥ 0.11). Total activity and percent time spent sleeping were equivalent between groups during both day and night cycles (all p ≥ 0.56). Dietary sialyllactose did not alter growth performance of young pigs, and there was no evidence that providing SA via sialyllactose benefits the development of recognition memory or gross sleep-related behaviors.

Intestinal anti-inflammatory effects of goat whey on DNBS-induced colitis in mice

This study evaluated the intestinal anti-inflammatory effects of goat whey in a mouse model of colitis induced by 2,4-dinitrobenzenesulfonic acid that resembles human IBD. At a concentration of 4 g/kg/day, the goat whey improved the symptoms of intestinal inflammation, namely by decreasing the disease activity index, colonic weight/length, and leukocyte infiltration. Moreover, goat whey inhibited NF-κB p65 and p38 MAPK signaling pathways and consequently down-regulated the gene expression of various proinflammatory markers such as IL-1β, IL-6, IL-17, TNF-α, iNOS, MMP-9, ICAM-1. Also, goat whey increased the expression of proteins such as mucins, occludin proteins and cytokine signalling suppressors. The immunomodulatory properties of goat whey were also evaluated in vitro using the murine macrophage cell line Raw 264 and CMT-93 cells derived from mouse rectum carcinomas. The results revealed the ability of goat whey to inhibit the production of NO and reduce IL-6 production in LPS-stimulated cells. In conclusion, goat whey exhibited anti-inflammatory effects in the DNBS model of intestinal inflammation, and these observations were confirmed by its immunomodulatory properties in vitro. Together, our results indicate that goat whey could have applications for the treatment of IBD.

Safety of synthetic N-acetyl-d-neuraminic acid as a novel food pursuant to Regulation (EC) No 258/97

Following a request from the European Commission, the EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) was asked to deliver a scientific opinion on synthetic N‐acetyl‐d‐neuraminic acid (NANA) as a novel food (NF) submitted pursuant to Regulation (EC) No 258/97. The information on the composition, the specifications, the batch‐to‐batch variability, stability and production process of the NF is sufficient and does not raise concerns about the safety of the NF. The NF is intended to be marketed as an ingredient in formulae and foods for infants and young children as well as an ingredient in a variety of foods and in food supplements for the general population. NANA is naturally present in human milk, in a bound and free form. The Margin of Exposure, which was based on the no‐observed‐adverse effect level (NOAEL) of 493 mg/kg body weight (bw) per day from a subchronic study and the anticipated daily intake of the NF, was considered to be sufficient for fortified foods for the general population and for food supplements for individuals above 10 years of age, as the anticipated daily intake was in the range of the exposure to free NANA from the consumption of early human milk, which is considered to be safe. The Panel concludes that the NF is safe when added to foods other than food supplements at the proposed uses and use levels for the general population; is safe in food supplements alone at the proposed uses and use levels for individuals above 10 years of age; is safe at the combined intake from fortified foods plus food supplements in individuals above 10 years of age; the safety of the NF is not established in food supplements alone at the proposed uses and use levels for individuals below 10 years of age.

Rapid and high-efficiency discrimination of different sialic acid species using dipeptide-based fluorescent sensors

A novel fluorescence sensing matrix is developed by combining six dipeptide-based fluorescent sensors, which allows rapid discrimination of different sialic acid species.

Evaluation of Sialic Acid in Infant Feeding: Contents and Bioavailability

Sialic acid (Sia) contents and bioaccessibility (BA) in human milk (HM) and infant formulas (IFs) were determined, and Sia intakes by infants between 0 and 6 months of age were evaluated. Total Sia contents in HM decreased during lactation from 136.14 to 24.47 mg/100 mL. The total Sia contents in IFs (13.15-25.78 mg/100 mL) were lower than in HM and were not related to the addition of ingredients acting as sources of Sia in their formulation. The Sia intakes derived from IF consumption were lower than in HM, and only one IF reached the intakes provided by HM from the age of 2 months. Despite the lower total Sia content in IFs, the BA of Sia in IFs (88.08-92.96%) was significantly greater than in mature HM (72.51%) and similar to that found in colostrum (96.43%). However, the Sia contents in the available soluble fraction of IFs did not reach those provided by HM.

Developmental changes in the level of free and conjugated sialic acids, Neu5Ac, Neu5Gc and KDN in different organs of pig: a LC-MS/MS quantitative analyses

Recent studies have shown a relationship between the level of the sialic acid (Sia), N-glycolylneuraminic acid (Neu5Gc) in red meat and its risk in cancer, cardiovascular and inflammatory diseases. Unresolved is the Sia concentration in different organs of piglets during development. Our aim was to determine the level of free and conjugated forms of Neu5Gc, N-acetylneuraminic acid (Neu5Ac) and ketodeoxynonulsonic acid (Kdn) in fresh and cooked spleen, kidney, lung, heart, liver, and skeletal muscle from 3-days-old (n = 4-8), 38-days-old (n = 10) and adult piglets (n = 4) by LC-MS/MS. Our findings show: (1) Lung tissue from 3 days-old piglets contained the highest level of total Sia (14.6 μmol/g protein) compared with other organs or age groups; (2) Unexpectedly, Neu5Gc was the major Sia in spleen (67-79 %) and adult lung (36-49 %) while free Kdn was the major Sia in skeletal muscle. Conjugated Neu5Ac was the highest Sia in other organs (61-84 %); (3) Skeletal muscle contained the lowest concentration of Neu5Gc in fresh and cooked meat; (4) Kdn accounted for <5 % of the total Sia in most organs; (5) During development, the total Sia concentration showed a 44-79 % decrease in all organs; (6) In adult piglets, the high to low rank order of total Sia was lung, heart, spleen, kidney, liver and skeletal muscle. In conclusion, the high level of Neu5Gc in all organs compared to skeletal muscle is a potential risk factor suggesting that dietary consumption of organ meats should be discouraged in favor of muscle to protect against cancer, cardiovascular and other inflammatory diseases.

Sensitive and accurate determination of sialic acids in serum with the aid of dispersive solid-phase extraction using the zirconium-based MOF of UiO-66-NH2 as sorbent

An zirconium-based MOFs of UiO-66-NH₂ has been synthetized and characterized in a dispersive solid-phase extraction procedure combined with HPLC with fluorescence detection for the pre-concentration and detection of sialic acids in serum samples.

Affinity Capillary Electrophoresis for Selective Control of Electrophoretic Mobility of Sialic Acid Using Lanthanide-Hexadentate Macrocyclic Polyazacarboxylate Complexes

It is difficult to control the electrophoretic mobility in order to obtain high resolution among saccharides in complex samples. We report herein on a new affinity capillary electrophoresis (ACE) method for an anionic monosaccharide, N-acetylneuraminic acid (Neu5Ac), which is important in terms of pathological diagnosis, using lanthanide-hexadentate macrocyclic polyazacarboxylate complexes (Ln-NOTA) as affinity reagents. It was shown that Ln-NOTA complexes increased the anionic mobility of Neu5Ac by approximately 40% through selective complexation with Neu5Ac. The extent of change in the mobility strongly depended on the type of central metal ion of Ln-NOTA. The stability constant (K) of Lu-NOTA with Neu5Ac was determined by ACE to be log Kb = 3.62 ± 0.04, which is the highest value among artificial receptors for Neu5Ac reported so far. Using this ACE, the Neu5Ac content in a glycoprotein sample, α1-acid glycoprotein (AGP), was determined after acid hydrolysis. Complete separation between Neu5Ac and hydrolysis products was successful by controlling the mobility to determine the concentration of Neu5Ac.