New strategies for profiling and characterization of human milk oligosaccharides

Comprehensive profiling and development of a collision cross section database for milk oligosaccharides via orthogonal UPLC-cyclic ion mobility-mass spectrometry system

Human milk oligosaccharides (HMOs) have attracted immense interest in the infant formula industry for their health benefits. Herein, we utilized liquid chromatography-cyclic ion mobility-mass spectrometry (LC-cIM-MS) to develop a robust and multidimensional HMO profiling workflow. This workflow relies on a self-built glycan library, allowing high-throughput searching of oligosaccharides. cIM-MS demonstrated high resolving power in discriminating glycan isomers and increasing peak capacity. This also facilitated the accurate elucidation of most oligosaccharides at sequence levels. A remarkably diverse milk oligosaccharide profile (n = 98) was observed and enabled the discovery of distinctive chromatographic retention patterns. To provide supplementary selectivity for future routine assignment in the absence of standards, we further developed a comprehensive database of experiment-derived traveling wave collision cross section in nitrogen (TWCCSN2) for 98 HMOs, including isomer-resolved TWCCSN2 values. Finally, the profile revealed 64 oligosaccharides unique to human milk compared with infant formula, indicating the potential ingredients for formula improvement.

Glycosyltransferases: glycoengineers in human milk oligosaccharide synthesis and manufacturing

Human milk oligosaccharides (HMOs) are a diverse group of complex carbohydrates that play crucial roles in infant health, promoting a beneficial gut microbiota, modulating immune responses, and protecting against pathogens. Central to the synthesis of HMOs are glycosyltransferases, a specialized class of enzymes that catalyse the transfer of sugar moieties to form the complex glycan structures characteristic of HMOs. This review provides an in-depth analysis of glycosyltransferases, beginning with their classification based on structural and functional characteristics. The catalytic activity of these enzymes is explored, highlighting the mechanisms by which they facilitate the precise addition of monosaccharides in HMO biosynthesis. Structural insights into glycosyltransferases are also discussed, shedding light on how their conformational features enable specific glycosidic bond formations. This review maps out the key biosynthetic pathways involved in HMO production, including the synthesis of lactose, and subsequent fucosylation and sialylation processes, all of which are intricately regulated by glycosyltransferases. Industrial methods for HMO synthesis, including chemical, enzymatic, and microbial approaches, are examined, emphasizing the role of glycosyltransferases in these processes. Finally, the review discusses future directions in glycosyltransferase research, particularly in enhancing the efficiency of HMO synthesis and developing advanced analytical techniques to better understand the structural complexity and biological functions of HMOs.

Robust and High-Resolution All-Ion Fragmentation LC-ESI-IM-MS Analysis for In-Depth Characterization or Profiling of Up to 200 Human Milk Oligosaccharides

Human milk oligosaccharides (HMOs) represent the third most abundant fraction of biomolecules in human milk (HM) and play a crucial role in infant health and development. The unique contributions of HMOs to healthy development of breast-fed infants are assumed to rely on the extraordinary complexity and diversity of HMO isomeric structures, which in turn still cause a huge analytical challenge. Many contemporary analytical methods aiming for more detailed HMO characterization combine ion mobility (IM) with LC-MS for enhanced structural resolution but are typically lacking the robustness necessary for application to HM cohorts with hundreds of samples. To overcome these challenges, we introduce a novel, robust all-ion fragmentation (AIF) LC-ESI-IM-MS method integrating four analytical dimensions: high-resolution LC separation, IM drift time, accurate mass precursor, and fragment ion measurements. This four-dimensional (4D) analytical characterization is sufficient for resolving various HMO structural isomers in an efficient way. Thereby, up to 200 HMO compounds with a maximum degree of polymerization of 13 could be simultaneously identified and relatively quantified. We devised two methods using this 4D analytical approach. One intended for in-depth characterization of multiple known but also novel HMO structures and the second is designed for robust, increased-throughput analyses. With the first approach, five trifucosyl-lacto-N-tetraose isomers (TF-LNTs), four of which were never detected before in HM, as well as additional difucosyl-lacto-N-heaose isomers (DF-LNHs), were revealed and structures fully elucidated by AIF and IM. This exemplifies the potential of our method for in-depth characterization of novel complex HMO structures. Furthermore, the increased-throughput method featuring a shorter LC gradient was applied to real-world HM samples. Here, we could differentiate the HM types I-IV based on a broader range of partly new marker HMOs. We could also derive valuable new insights into variations of multiple and rare HMOs up to DP 11 across lactational stages. Overall, our AIF LC-ESI-IM-MS approach facilitates in-depth monitoring and confident identification of a broad array of distinct and simple to very complex HMOs. We envision this robust AIF LC-ESI-IM-MS approach to advance HMO research by facilitating the characterization of a broad range of HMOs in high numbers of HM samples. This may help to further extend our understanding about HMOs structure-function relationships relevant for infants' healthy development.

Recent advances in the science of human milk oligosaccharides

Human colostrum and mature milk contain oligosaccharides (Os), designated as human milk oligosaccharides (HMOs). Approximately 200 varieties of HMOs have been characterized. Although HMOs are not utilized as an energy source by infants, they have important protective functions, including pathogenic bacteria and viral infection inhibitors and immune modulators, among other functions, and HMOs stimulate brain-nerve development. The Os concentration is average 11 g/L in human milk but >100 mg/L in mature bovine milk, which is used to manufacture infant formula, suggesting that human-identical milk oligosaccharides (HiMOs) should be incorporated into milk substitutes. Some infant formulas incorporating 2'-fucosyllactose and lacto-N-neotetraose are now commercially available, and intervention trials have been concluded. We review basic HMO information, including their chemical structures and concentrations, attempts to synthesize HMOs at small and plant scale, studies that clarified HMO biological functions, and interventions with milk substitutes incorporating HiMOs in formula-fed infants.

Comparative study of the oligosaccharide profile in goat, bovine, sheep, and human milk whey

Milk oligosaccharides are high added value compounds that could be obtained by exploiting cheese whey, a byproduct of dairy industry. The objective was to compare the abundance and diversity of oligosaccharides in whey samples from domestic animals and humans. During fresh cheese making, whey samples were collected and analyzed by untargeted and targeted small molecule analysis using high-resolution mass-spectrometry. A great similarity in the metabolite profile between goat and sheep was observed. Up to 11 oligosaccharides were observed in the sheep whey from those typically found in humans. The concentration of 2'-Fucosyllactose (0.136 ± 0.055 g/L) and 3-Fucosyllactose (0.079 ± 0.009 g/L) were significantly higher (p-value <0.01) in sheep whey, while the concentration of 3'-Sialyllactose (0.826 ± 0.638 g/L) was higher in goat whey. No significant differences were observed between goat and sheep whey for the other oligosaccharides (p-value >0.05). Therefore, sheep and goat whey could become an important source of oligosaccharides through their revalorization.

Human milk oligosaccharides: bridging the gap in intestinal microbiota between mothers and infants

Breast milk is an essential source of infant nutrition. It is also a vital determinant of the structure and function of the infant intestinal microbial community, and it connects the mother and infant intestinal microbiota. Human milk oligosaccharides (HMOs) are a critical component in breast milk. HMOs can reach the baby's colon entirely from milk and become a fermentable substrate for some intestinal microorganisms. HMOs can enhance intestinal mucosal barrier function and affect the intestinal function of the host through immune function, which has a therapeutic effect on specific infant intestinal diseases, such as necrotizing enterocolitis. In addition, changes in infant intestinal microbiota can reflect the maternal intestinal microbiota. HMOs are a link between the maternal intestinal microbiota and infant intestinal microbiota. HMOs affect the intestinal microbiota of infants and are related to the maternal milk microbiota. Through breastfeeding, maternal microbiota and HMOs jointly affect infant intestinal bacteria. Therefore, HMOs positively influence the establishment and balance of the infant microbial community, which is vital to ensure infant intestinal function. Therefore, HMOs can be used as a supplement and alternative therapy for infant intestinal diseases.

Analysis of human milk oligosaccharides from women with gestational diabetes mellitus

Human milk oligosaccharides (HMOs) are bioactive components which play an important role in infant health. HMO composition is vulnerable to changes of maternal conditions including lactation stages and maternal phenotypes. Pregnant diseases such as gestational diabetes mellitus (GDM) are commonly found in women during pragnancy, and may cause disorder in maternal physiological metabolism which is harmful to infants. Unfortunately, anlysis of oligosaccharides from women with GDM is limited. To address this issue, we analyzed HMO compositions and profiles in breast milk from women with GDM using an established 96-well plate permethylation platform and MALDI-TOF-MS. We enrolled 127 women with GDM, and investigated HMO abundances in colostrum, transition milk, and mature milk respectively. We found that GDM affected HMO compositions in breast milk, and the level of fucosylation became higher over the course of lactation for all the women with GDM. Interestingly, the relative abundances of fucosylated HMOs in different lactation stages were affected differentially by GDM, with the most pronounced effect in colostrum. In particular, the relative abundances of H3N1F1 and H3N1F2 sharply decreased over time, showing very low levels in late lactation. These differences in our findings need further investigation to develop optimal feeding for mothers with GDM.

Human Milk Oligosaccharides: Decoding Their Structural Variability, Health Benefits, and the Evolution of Infant Nutrition

Human milk oligosaccharides (HMOs), the third most abundant solid component in human milk, vary significantly among women due to factors such as secretor status, race, geography, season, maternal nutrition and weight, gestational age, and delivery method. In recent studies, HMOs have been shown to have a variety of functional roles in the development of infants. Because HMOs are not digested by infants, they act as metabolic substrates for certain bacteria, helping to establish the infant's gut microbiota. By encouraging the growth of advantageous intestinal bacteria, these sugars function as prebiotics and produce short-chain fatty acids (SCFAs), which are essential for gut health. HMOs can also specifically reduce harmful microbes and viruses binding to the gut epithelium, preventing illness. HMO addition to infant formula is safe and promotes healthy development, infection prevention, and microbiota. Current infant formulas frequently contain oligosaccharides (OSs) that differ structurally from those found in human milk, making it unlikely that they would reproduce the unique effects of HMOs. However, there is a growing trend in producing OSs resembling HMOs, but limited data make it unclear whether HMOs offer additional therapeutic benefits compared to non-human OSs. Better knowledge of how the human mammary gland synthesizes HMOs could direct the development of technologies that yield a broad variety of complex HMOs with OS compositions that closely mimic human milk. This review explores HMOs' complex nature and vital role in infant health, examining maternal variation in HMO composition and its contributing factors. It highlights recent technological advances enabling large-scale studies on HMO composition and its effects on infant health. Furthermore, HMOs' multifunctional roles in biological processes such as infection prevention, brain development, and gut microbiota and immune response regulation are investigated. The structural distinctions between HMOs and other mammalian OSs in infant formulas are discussed, with a focus on the trend toward producing more precise replicas of HMOs found in human milk.

Development of a cyclic ion mobility spectrometry-mass spectrometry-based collision cross-section database of permethylated human milk oligosaccharides

Human milk oligosaccharides (HMOs) are an important class of biomolecules responsible for the healthy development of the brain-gut axis of infants. Unfortunately, their accurate characterization is largely precluded due to a variety of reasons - there are over 200 possible HMO structures whereas only 10s of these are available as authentic analytical standards. Furthermore, their isomeric heterogeneity stemming from their many possible glycosidic linkage positions and corresponding α/β anomericities further complicates their analyses. While liquid chromatography coupled to tandem mass spectrometry remains the gold standard for HMO analyses, it often times cannot resolve all possible isomeric species and thus warrants the development of other orthogonal approaches. High-resolution ion mobility spectrometry coupled to mass spectrometry has emerged as a rapid alternative to condensed-phase separations but largely has remained limited to qualitative information related to the resolution of isomers. In this work, we have assessed the use of permethylation to improve both the resolution and sensitivity of HMO analyses with cyclic ion mobility separations coupled with mass spectrometry. In addition to this, we have developed the first-ever high-resolution collision cross-section database for permethylated HMOs using our previously established calibration protocol. We envision that this internal reference database generated from high-resolution cyclic ion mobility spectrometry-mass spectrometry will greatly aid in the accurate characterization of HMOs and provide a valuable, orthogonal, approach to existing liquid chromatography-tandem mass spectrometry-based methods.

Unlocking the mysteries of milk oligosaccharides: Structure, metabolism, and function

Milk oligosaccharides (MOs), complex carbohydrates prevalent in human breast milk, play a vital role in infant nutrition. Serving as prebiotics, they inhibit pathogen adherence, modulate the immune system, and support newborn brain development. Notably, MOs demonstrate significant variations in concentration and composition, both across different species and within the same species. These characteristics of MOs lead to several compelling questions: (i) What distinct beneficial functions do MOs offer and how do the functions vary along with their structural differences? (ii) In what ways do MOs in human milk differ from those in other mammals, and what factors drive these unique profiles? (iii) What are the emerging applications of MOs, particularly in the context of their incorporation into infant formula? This review delves into the structural characteristics, quantification methods, and species-specific concentration differences of MOs. It highlights the critical role of human MOs in infant growth and their potential applications, providing substantial evidence to enhance infant health and development.

Isolation of Human Milk Difucosyl Nona- and Decasaccharides by Ultrahigh-Temperature Preparative PGC-HPLC and Identification of Novel Difucosylated Heptaose and Octaose Backbones by Negative-Ion ESI-MSn

Despite their many important physiological functions, past work on the diverse sequences of human milk oligosaccharides (HMOs) has been focused mainly on the highly abundant HMOs with a relatively low degree of polymerization (DP) due to the lack of efficient methods for separation/purification and high-sensitivity sequencing of large-sized HMOs with DP ≥ 10. Here we established an ultrahigh-temperature preparative HPLC based on a porous graphitized carbon column at up to 145 °C to overcome the anomeric α/β splitting problem and developed further the negative-ion ESI-CID-MS/MS into multistage MSn using a combined product-ion scanning of singly charged molecular ion and doubly charged fragment ion of the branching Gal and adjacent GlcNAc residues. The separation and sequencing method allows efficient separation of a neutral fraction with DP ≥ 10 into 70 components, among which 17 isomeric difucosylated nona- and decasaccharides were further purified and sequenced. As a result, novel branched difucosyl heptaose and octaose backbones were unambiguously identified in addition to the conventional linear and branched octaose backbones. The novel structures of difucosylated DF-novo-heptaose, DF-novo-LNO I, and DF-novo-LNnO I were corroborated by NMR. The various fucose-containing Lewis epitopes identified on different backbones were confirmed by oligosaccharide microarray analysis.

The evolving world of milk oligosaccharides: Biochemical diversity understood by computational advances

Milk oligosaccharides, complex carbohydrates unique to mammalian milk, play crucial roles in infant nutrition and immune development. This review explores their biochemical diversity, tracing the evolutionary paths that have led to their variation across different species. We highlight the intersection of nutrition, biology, and chemistry in understanding these compounds. Additionally, we discuss the latest computational methods and analytical techniques that have revolutionized the study of milk oligosaccharides, offering insights into their structural complexity and functional roles. This brief but essential review not only aims to provide a deeper understanding of milk oligosaccharides but also discuss the road toward their potential applications.

Simple Routes to Stable Isotope-Coded Native Glycans

Understanding the biological role of protein-linked glycans requires the reliable identification of glycans. Isomer separation and characterization often entail mass spectrometric detection preceded by high-performance chromatography on porous graphitic carbon. To this end, stable isotope-labeled glycans have emerged as powerful tools for retention time normalization. Hitherto, such standards were obtained by chemoenzymatic or purely enzymatic methods, which introduce, e.g., 13C-containing N-acetyl groups or galactose into native glycans. Glycan release with anhydrous hydrazine opens another route for heavy isotope introduction via concomitant de-N-acetylation. Here, we describe that de-N-acetylation can also be achieved with hydrazine hydrate, which is a more affordable and less hazardous reagent. Despite the slower reaction rate, complete conversion is achievable in 72 h at 100 °C for glycans with biantennary glycans with or without sialic acids. Shorter incubation times allow for the isolation of intermediate products with a defined degree of free amino groups, facilitating introduction of different numbers of heavy isotopes. Mass encoded glycans obtained by this versatile approach can serve a broad range of applications, e.g., as internal standards for isomer-specific studies of N-glycans, O-glycans, and human milk oligosaccharide by LC-MS on either porous graphitic carbon or─following permethylation─on reversed phase.

Human milk oligosaccharides and the association with microbiota in colostrum: a pilot study

HMOs (Human milk oligosaccharide) has an impact on maternal and infant health. Colostrum samples of 70 breastfeeding women in China were collected and recorded clinical characteristics. The major oligosaccharides and microbiota were quantitated in colostrum. The concentration of fucosylated HMOs in primipara was higher than that of multipara (p = 0.030). The concentration of N-acetylated HMOs in vaginal delivery milk was less than that of cesarean (p = 0.038). Non-fucosylated HMOs of breastfeeding women were less than that of breast pump (p = 0.038). Meanwhile, the concentration of LNT was positively correlated with Lactobacillus (r = 0.250, p = 0.037). DS-LNT was negatively correlated with Staphylococcus (r = - 0.240, p = 0.045). There was a positive correlation of Streptococcus with LNFP II (r = 0.314, p = 0.011) and 3-SL (r = 0.322, p = 0.009). In addition, there was a negative correlation between 2'-FL and 3-FL (r = - 0.465, p = 0.001). There was a positive correlation between LNT and LNnT (r = 0.778, p = 0.001). Therefore, the concentration of HMOs is related to number of deliveries, delivery mode, lactation mode and perinatal antibiotic. The concentration of HMOs is related to Lactobacillus, Streptococcus and Streptococcus in colostrum. In addition, there are connections between different oligosaccharides in content. The study protocol was also registered in the ClinicalTrails.gov (ChiCTR2200064454) (Oct. 2022).

Qualitative and Quantitative Changes of Oligosaccharides in Human and Animal Milk over Lactation

The aim of this study was to investigate the changes in human and animal milk oligosaccharides over lactation. In total, 89, 97, 115, and 71 oligosaccharides were identified in human, bovine, goat, and camel milk. The number of common oligosaccharides between camel and human milk was the highest (16 and 17 in transitional and mature milk). With respect to the absolute concentration of eight oligosaccharides (2'-FL, 3-FL, α3'-GL, LNT, LNnT, 3'-SL, 6'-SL, and DSL), 2'-FL, 3'-FL, LNT, and LNnT were much higher in human than three animal species. 3'-SL had a similar concentration in bovine colostrum (322.2 μg/mL) and human colostrum (321.0 μg/mL), followed by goat colostrum (105.1 μg/mL); however, it had the highest concentration in camel mature milk (304.5 μg/mL). The ratio of 6'-SL and 3'-SL (1.77) in goat colostrum was similar to that in human colostrum (1.68), followed by bovine colostrum (0.13). In terms of changes of eight oligosaccharides over lactation, they all decreased with the increase of lactation in bovine and goat milk; however, α3'-GL, 2'-FL, and 3-FL increased in camel species, and LNT increased first and then decreased over lactation in human milk. This study provides a better understanding of the variation of milk oligosaccharides related to lactation and species.

Comprehensive investigation of milk oligosaccharides in different mammalian species and the effect of breed and lactation period on sheep milk oligosaccharides

Milk oligosaccharides (MOs) have unique health benefits for newborns, and MOs are important components in mammalian milk. The present study was conducted to provide a comprehensive analysis of MOs in important domestic animals, including goats, cows, camels and sheep. The comparison with human MOs was conducted simultaneously. Furthermore, analysis of the relative abundance of sheep MOs among different breeds (Hu sheep, East Friesen sheep, East Friesen-Hu crossbred sheep) and lactation periods (colostrum, mature milk) was performed. In general, 35, 24 19, 26, and 16 MOs were identified in human, goat, bovine, camel and sheep milk, respectively. The type of sheep MOs was not greatly influenced by the breeds and lactation period. Hu sheep colostrum had the highest abundance of MOs among six sheep milks, followed by East Friesen sheep colostrum, while East Friesen-Hu crossbred sheep mature milk had the lowest abundance of MOs. These findings provide evidence for the potential value of MOs from domestic animal milk for the commercial applications.

Breast Milk Oligosaccharides Contain Immunomodulatory Glucuronic Acid and LacdiNAc

Breast milk is abundant with functionalized milk oligosaccharides (MOs) to nourish and protect the neonate. Yet we lack a comprehensive understanding of the repertoire and evolution of MOs across Mammalia. We report ∼400 MO-species associations (>100 novel structures) from milk glycomics of nine mostly understudied species: alpaca, beluga whale, black rhinoceros, bottlenose dolphin, impala, L'Hoest's monkey, pygmy hippopotamus, domestic sheep, and striped dolphin. This revealed the hitherto unknown existence of the LacdiNAc motif (GalNAcβ1-4GlcNAc) in MOs of all species except alpaca, sheep, and striped dolphin, indicating the widespread occurrence of this potentially antimicrobial motif in MOs. We also characterize glucuronic acid-containing MOs in the milk of impala, dolphins, sheep, and rhinoceros, previously only reported in cows. We demonstrate that these GlcA-MOs exhibit potent immunomodulatory effects. Our study extends the number of known MOs by >15%. Combined with >1900 curated MO-species associations, we characterize MO motif distributions, presenting an exhaustive overview of MO biodiversity.

Comparative analysis of oligosaccharides in the milk of human and animals by using LC-QE-HF-MS

The complex oligosaccharides (OS) in different milk are more difficult to detect and complicated to analyze as their enormous structural complexity. UPLC-QE-HF-MS was supposed to be a highly effective method for OS identification. In present study, 70 human milk oligosaccharides (HMOs), 14 bovine milk oligosaccharides (BMOs), 23 goat milk oligosaccharides (GMOs) and 24 rat milk oligosaccharides (RMOs) were detected by using UPLC-QE-HF-MS, respectively. There were highly differences in number and composition between the four milk OS. 14 neutral and 3 acidic OS were firstly found in rat milk. The composition and abundances of RMOs were might more similar to that of HMOs, comparing with BMOs and GMOs. The similarity between HMOs and RMOs might provide theoretical basis for better application of rats in biological/biomedical studies of HMOs as models. The BMOs and GMOs were expected to be suitable for applications in medical and functional foods as a promising bioactive molecular.

Mammalian milk glycomes: Connecting the dots between evolutionary conservation and biosynthetic pathways

Milk oligosaccharides (MOs) are among the most abundant constituents of breast milk and are essential for health and development. Biosynthesized from monosaccharides into complex sequences, MOs differ considerably between taxonomic groups. Even human MO biosynthesis is insufficiently understood, hampering evolutionary and functional analyses. Using a comprehensive resource of all published MOs from >100 mammals, we develop a pipeline for generating and analyzing MO biosynthetic networks. We then use evolutionary relationships and inferred intermediates of these networks to discover (1) systematic glycome biases, (2) biosynthetic restrictions, such as reaction path preference, and (3) conserved biosynthetic modules. This allows us to prune and pinpoint biosynthetic pathways despite missing information. Machine learning and network analysis cluster species by their milk glycome, identifying characteristic sequence relationships and evolutionary gains/losses of motifs, MOs, and biosynthetic modules. These resources and analyses will advance our understanding of glycan biosynthesis and the evolution of breast milk.

Comparative Analysis of Oligosaccharides in Breast Milk and Feces of Breast-Fed Infants by Using LC-QE-HF-MS: A Communication

Currently, it must be acknowledged that little is known about the quantity and make-up of oligosaccharides (OS) found in breast-fed babies' feces as well as their metabolic fate. In the present work, UPLC-QE-HF-MS was successfully adopted to identify the profiles of human milk oligosaccharides (HMOs) in the breast milk of four mothers and fecal OS in the feces of their breast-fed infant. There were significant variations and differences in both number and composition between HMOs and fecal OS. The early-life gastrointestinal microbiota metabolism may be triggered into the advanced breakdown, synthesis, bioconversion, or redesign of HMOs. The fate of HMOs during passage through the gastrointestinal tract may be profoundly informed by the comparison of OS between breast milk and fecal OS profiles. The characterization of fecal OS could be applied as a valuable tool for monitoring the gastrointestinal fate of HMOs and reflecting infant development at different stages of lactation. Further research on the gastrointestinal bioconversion of HMOs profiles is required, including secretor type and the lactation time of milk, as well as baby feeding.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2019-2020

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2020. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. The review is basically divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of arrays. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other areas such as medicine, industrial processes and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. The reported work shows increasing use of incorporation of new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented nearly 40 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show little sign of diminishing.

High-Throughput Glycomic Methods

Glycomics aims to identify the structure and function of the glycome, the complete set of oligosaccharides (glycans), produced in a given cell or organism, as well as to identify genes and other factors that govern glycosylation. This challenging endeavor requires highly robust, sensitive, and potentially automatable analytical technologies for the analysis of hundreds or thousands of glycomes in a timely manner (termed high-throughput glycomics). This review provides a historic overview as well as highlights recent developments and challenges of glycomic profiling by the most prominent high-throughput glycomic approaches, with N-glycosylation analysis as the focal point. It describes the current state-of-the-art regarding levels of characterization and most widely used technologies, selected applications of high-throughput glycomics in deciphering glycosylation process in healthy and disease states, as well as future perspectives.

In silico analysis of the human milk oligosaccharide glycome reveals key enzymes of their biosynthesis

Human milk oligosaccharides (HMOs) form the third most abundant component of human milk and are known to convey several benefits to the neonate, including protection from viral and bacterial pathogens, training of the immune system, and influencing the gut microbiome. As HMO production during lactation is driven by enzymes that are common to other glycosylation processes, we adapted a model of mucin-type GalNAc-linked glycosylation enzymes to act on free lactose. We identified a subset of 11 enzyme activities that can account for 206 of 226 distinct HMOs isolated from human milk and constructed a biosynthetic reaction network that identifies 5 new core HMO structures. A comparison of monosaccharide compositions demonstrated that the model was able to discriminate between two possible groups of intermediates between major subnetworks, and to assign possible structures to several previously uncharacterised HMOs. The effect of enzyme knockouts is presented, identifying β-1,4-galactosyltransferase and β-1,3-N-acetylglucosaminyltransferase as key enzyme activities involved in the generation of the observed HMO glycosylation patterns. The model also provides a synthesis chassis for the most common HMOs found in lactating mothers.

Liquid chromatography and capillary electrophoresis in glycomic and glycoproteomic analysis

Glycosylation is one of the most significant and abundant post-translational modifications in cells. Glycomic and glycoproteomic analyses involve the characterization of oligosaccharides (glycans) conjugated to proteins. Glycomic and glycoproteomic analysis is highly challenging because of the large diversity of structures, low abundance, site-specific heterogeneity, and poor ionization efficiency of glycans and glycopeptides in mass spectrometry (MS). MS is a key tool for characterization of glycans and glycopeptides. However, MS alone does not always provide full structural and quantitative information for many reasons, and thus MS is combined with some separation technique. This review focuses on the role of separation techniques used in glycomic and glycoproteomic analyses, liquid chromatography and capillary electrophoresis. The most important separation conditions and results are presented and discussed.

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Association of human milk oligosaccharides and nutritional status of young infants among Bangladeshi mother-infant dyads

Human milk oligosaccharides (HMOs) support the development of a healthy gut microbiome and the growth of infants. We aimed to determine the association of different HMOs with severe acute malnutrition (SAM) among Bangladeshi young infants. This study was nested within a single-blind, randomized, pilot clinical trial (NCT0366657). A total of 45 breastmilk samples from mothers of < 6 months old infants who had SAM (n = 26) or were non-malnourished (n = 19) and were analyzed for constituent HMOs. Of the infants with SAM, 14 (53.85%) had secretor mothers, and 11 (57.89%) of the non-malnourished infants had secretor mothers. A one-unit increase in the relative abundance of sialylated HMOs was associated with higher odds of SAM in age and sex adjusted model (aOR = 2.00, 90% CI 1.30, 3.06), in age, sex, and secretor status adjusted model (aOR = 1.96, 90% CI 1.29, 2.98), and also in age and sex adjusted model among non-secretor mothers (aOR = 2.86, 90% CI 1.07, 7.62). In adjusted models, there was no evidence of a statistically significant association between SAM and fucosylated or undecorated HMOs. Our study demonstrates that a higher relative abundance of sialylated HMOs in mothers’ breastmilk may have a negative impact on young infants’ nutritional status.

Current Advances in Structure-Function Relationships and Dose-Dependent Effects of Human Milk Oligosaccharides

HMOs (human milk oligosaccharides) are the third most important nutrient in breast milk. As complex glycans, HMOs play an important role in regulating neonatal intestinal immunity, resisting viral and bacterial infections, displaying anti-inflammatory characteristics, and promoting brain development. Although there have been some previous reports of HMOs, a detailed literature review summarizing the structure-activity relationships and dose-dependent effects of HMOs is lacking. Hence, after introducing the structures and synthetic pathways of HMOs, this review summarizes and categorizes identified structure-function relationships of HMOs. Differential mechanisms of different structural HMOs utilization by microorganisms are summarized. This review also emphasizes the recent advances in the interactions between different health benefits and the variance of dosage effect based on in vitro cell tests, animal experiments, and human intervention studies. The potential relationships between the chemical structure, the dosage selection, and the physiological properties of HMOs as functional foods are vital for further understanding of HMOs and their future applications.

Structural characterization of human milk oligosaccharides using ultrahigh performance liquid chromatography-helium charge transfer dissociation mass spectrometry

The combination of helium charge transfer dissociation mass spectrometry (He-CTD-MS) with ultrahigh performance liquid chromatography (UHPLC) is presented for the analysis of a complex mixture of acidic and neutral human milk oligosaccharides (HMOs). The research focuses on the identification of the monosaccharide sequence, the branching patterns, the sialylation/fucosylation arrangements, and the differentiation of isomeric oligosaccharides in the mixture. Initial studies first optimized the conditions for the UHPLC separation and the He-CTD-MS conditions. Results demonstrate that He-CTD is compatible with UHPLC timescales and provides unambiguous glycosidic and cross-ring cleavages from both the reducing and the nonreducing ends, which is not typically possible using collision-induced dissociation. He-CTD produces informative fragments, including 0,3An and 0,4An ions, which have been observed with electron transfer dissociation, electron detachment dissociation, and ultraviolet photodissociation (UVPD) and are crucial for differentiating the α-2,3- versus α-2,6-linked sialic acid (Neu5Ac) residues present among sialyllacto-N-tetraose HMOs. In addition to the linkage positions, He-CTD is able to differentiate structural isomers for both sialyllacto-N-tetraoses and lacto-N-fucopentaoses structures by providing unique, unambiguous cross-ring cleavages of types 0,2An, 0,2Xn, and 1,5An while preserving most of the labile Neu5Ac and fucose groups.

Recent understanding of human milk oligosaccharides in establishing infant gut microbiome and roles in immune system

Human milk oligosaccharides (HMOs) are complex sugars with distinctive structural diversity present in breast milk. HMOs have various functional roles to play in infant development starting from establishing the gut microbiome and immune system to take it up to the mature phase. It has been a major energy source for human gut microbes that confer positive benefits on infant health by directly interacting through intestinal cells and generating short-chain fatty acids. It has recently become evident that each species of Bifidobacterium and other genera which are resident of the infant gut employ distinct molecular mechanisms to capture and digest diverse structural HMOs to avoid competition among themselves and successfully maintain gut homeostasis. HMOs also directly modulate gut immune responses and can decoy receptors of pathogenic bacteria and viruses, inhibiting their binding on intestinal cells, thus preventing the emergence of a disease. This review provides a critical understanding of how different gut bacteria capture and utilize selective sugars from the HMO pool and how different structural HMOs protect infants from infectious diseases.

Trapped ion mobility spectrometry time-of-flight mass spectrometry for high throughput and high resolution characterization of human milk oligosaccharide isomers

The microbiome and immune system of infants are shaped by various bioactive components of human breastmilk, notably human milk oligosaccharides (HMOs). HMOs represent the third component of breastmilk and exhibit extremely high structural diversity with many isomers. Here, we propose a high throughput and high resolution approach to characterize main oligosaccharides present in breastmilk with high identification level thanks to ion mobility spectrometry. Four pairs of standard HMO isomers, that are (LNT/LNnT), (LNFP I/LNFP V), (3'-SL/6'-SL) and (2'-FL/3-FL), were first investigated under both positive and negative ionization mode using direct introduction-trapped ion mobility spectrometry-time-of-flight mass spectrometry (TIMS-TOF). By examining all the ionic species formed (i.e. protonated and deprotonated ions as well as adduct species), every isomer pair could be distinguished through the separation of at least one species, even with a small difference in collision cross section values (as small as 1.5%) thanks to the flexible resolution capacity of the TIMS instrument. Although multiple mobility peaks resulting from different glycan anomeric conformers, open-ring and/or different ionic isomer structures (i.e. various charge site locations), could be observed for some HMO species. The reduction at the reducing-end of HMOs did not significantly facilitate the isomer distinction. Finally, the unambiguous identification of the studied HMOs in a breastmilk sample showed the potential of the approach combining ion mobility separation and MS/MS experiments for high throughput distinction of HMO isomers in complex breastmilk samples without laborious sample preparation.

Advances in mass spectrometry-based glycomics-An update covering the period 2017-2021

The wide variety of chemical properties and biological functions found in proteins is attained via post-translational modifications like glycosylation. Covalently bonded to proteins, glycans play a critical role in cell activity. Complex structures with microheterogeneity, the glycan structures that are associated with proteins are difficult to analyze comprehensively. Recent advances in sample preparation methods, separation techniques, and MS have facilitated the quantitation and structural elucidation of glycans. This review focuses on highlighting advances in MS-based techniques for glycomic analysis that occurred over the last 5 years (2017-2021) as an update to the previous review on the subject. The topics of discussion will include progress in glycomic workflow such as glycan release, purification, derivatization, and separation as well as the topics of ionization, tandem MS, and separation techniques that can be coupled with MS. Additionally, bioinformatics tools used for the analysis of glycans will be described.

Toward Sequencing the Human Milk Glycome: High-Resolution Cyclic Ion Mobility Separations of Core Human Milk Oligosaccharide Building Blocks

Human milk oligosaccharides (HMOs) are an unconjugated class of glycans that have been implicated for their role in promoting the healthy development of the brain-gut axes of infants. Production of HMOs is ever-changing and specifically tailored for each infant in response to various biological factors (e.g., cognitive development, diseases, or allergies). While every HMO consists of up to only five monosaccharides, their structures can be composed of many possible glycosidic linkage positions and corresponding α/β anomericities, linear or branched chains, and potential fucosylation/sialylation modifications, thus leading to a tremendous degree of isomeric heterogeneity. With limited availability of authentic standards for every putative HMO structure (estimated to be >200 total), new analytical methods are needed for their accurate characterization. Complete sequencing of the human milk glycome would enable a better understanding of their infant-specific biological roles and potentially lead to their widespread incorporation into infant formula. Herein, we explore the use of our high-resolution cyclic ion mobility spectrometry-mass spectrometry (cIMS-MS)-based platform for the separation of core disaccharide and trisaccharide isomer building blocks as a first step toward the sequencing of larger HMOs. By utilizing the flexible capabilities of the cIMS array, separation pathlengths were extended up to 40 m, thus enabling the resolution of all seven sets of sialylated, fucosylated galactosyllactose and lactosamine HMO building block isomers. Additionally, we assessed the utility of pre-/post-cIMS tandem mass spectrometry (MS/MS) and tandem cIMS (cIMS/cIMS) for the characterization of HMOs based on their diagnostic fragmentation patterns and mobility fingerprints. We anticipate that our presented cIMS-MS-based methodology will enable the better characterization of larger, unknown HMOs when incorporated into an overall workflow that also includes online liquid chromatography and enzymatic hydrolyses.

Engineered Microbial Routes for Human Milk Oligosaccharides Synthesis

Human milk oligosaccharides (HMOs) are one of the important ingredients in human milk, which have attracted great interest due to their beneficial effect on the health of newborns. The large-scale production of HMOs has been researched using engineered microbial routes due to the availability, safety, and low cost of host strains. In addition, the development of molecular biology technology and metabolic engineering has promoted the effectiveness of HMOs production. According to current reports, 2'-fucosyllactose (2'-FL), 3-fucosyllactose (3-FL), lacto-N-tetraose (LNT), lacto-N-neotetraose (LNnT), 3'-sialyllactose (3'-SL), 6'-sialyllactose (6'-SL), and some fucosylated HMOs with complex structures have been produced via the engineered microbial route, with 2'-FL having been produced the most. However, due to the uncertainty of metabolic patterns, the selection of host strains has certain limitations. Aside from that, the expression of appropriate glycosyltransferase in microbes is key to the synthesis of different HMOs. Therefore, finding a safe and efficient glycosyltransferase has to be addressed when using engineered microbial pathways. In this review, the latest research on the production of HMOs using engineered microbial routes is reported. The selection of host strains and adapting different metabolic pathways helped researchers designing engineered microbial routes that are more conducive to HMOs production.

Prospecting Human Milk Oligosaccharides as a Defense Against Viral Infections

In addition to providing maximal nutritional value for neonatal growth and development, human milk functions as an early defense mechanism against invading pathogens. Human milk oligosaccharides (HMOs), which are abundant in human milk, are a diverse group of heterogeneous carbohydrates with wide ranging protective effects. In addition to promoting the colonization of beneficial intestinal flora, HMOs serve as decoy receptors, effectively blocking the attachment of pathogenic bacteria. HMOs also function as bacteriostatic agents, inhibiting the growth of gram-positive bacteria. Based on this precedence, an emerging area in the field has focused on characterizing the antiviral properties of HMOs. Indeed, HMOs have been evaluated as antiviral agents, with many possessing activity against life-threatening infections. This targeted review provides insight into the known glycan-binding interactions between select HMOs and influenza, rotavirus, respiratory syncytial virus, human immunodeficiency virus, and norovirus. Additionally, we review the role of HMOs in preventing necrotizing enterocolitis, an intestinal disease linked to viral infections. We close with a discussion of what is known broadly regarding human milk oligosaccharides and their interactions with coronaviruses.

Separation of Permethylated O-Glycans, Free Oligosaccharides, and Glycosphingolipid-Glycans Using Porous Graphitized Carbon (PGC) Column

Glycosylation is one of the most common and complex post-translational modifications of proteins. However, there are other carbohydrates such as free oligosaccharides and glycosphingolipids-glycans that are associated with important biological and clinical roles. To analyze these molecules using liquid chromatography coupled with mass spectrometry (LC-MS), the permethylation approach was utilized. Although permethylation is a commonly utilized glycan derivatization technique, separation of permethylated glycans released from glycosphingolipid (GSL) by LC-MS has never been previously demonstrated. Here, a nanoflow porous graphitized carbon (PGC) column coupled with a high-resolution mass spectrometer was used to achieve isomeric separation of these permethylated glycans. We demonstrate the separation of free reducing end and reduced end O-glycans, free oligosaccharides derived from human milk, and GSL glycans derived from the MDA-MB-231BR cancer cell line using PGC-LC-MS.