Determination of sialic acid and gangliosides in biological samples and dairy products: A review

Detection Strategies for Sialic Acid and Sialoglycoconjugates

Glycoconjugates are a vast class of biomolecules implicated in biological processes important for human health and disease. The structural complexity of glycoconjugates remains a challenge to deciphering their precise biological roles and for their development as biomarkers and therapeutics. Human glycoconjugates on the outside of the cell are modified with sialic (neuraminic) acid residues at their termini. The enzymes that install sialic acids are sialyltransferases (SiaTs), a family of 20 different isoenzymes. The removal and degradation of sialic acids is mediated by neuraminidase (NEU; sialidase) enzymes, of which there are four isoenzymes. In this review, we discuss chemical and biochemical approaches for the detection and analysis of sialoglycoconjugate (SGC) structures and their enzymatic products. The most common methods include affinity probes and synthetic substrates. Fluorogenic and radiolabelled substrates are also important tools for many applications, including screening for enzyme inhibitors. Strategies that give insight into the native substrate-specificity of enzymes that regulate SGCs (SiaT & NEU) are necessary to improve our understanding of the role of sialic acid metabolism in health and disease.

Preparation of milk fat globule membrane ingredients enriched in polar lipids: Composition characterization and digestive properties

In this study, milk fat globule membrane (MFGM) ingredients enriched in polar lipids were prepared using membrane filtration, including microfiltration, diafiltration, and ultrafiltration from butter serum powder. Polar lipids (phospholipids, sterols, and gangliosides) in prepared MFGM ingredients were analyzed by 31P nuclear magnetic resonance spectroscopy, GC-MS, and ultra-performance liquid chromatography (UPLC)-MS/MS, respectively. The lipolysis degree and microstructure of MFGM ingredient and soybean lecithin (SL) emulsions during in vitro digestion were also analyzed. Microfiltration showed higher concentration efficiency than ultrafiltration, which increased by 2.16% and 2.73% in phospholipids, respectively. Moreover, diafiltration concentrated more polar lipids (6.39% of phospholipids) than microfiltration. Milk fat globule membrane ingredients had high levels of sphingomyelin (1.27%-1.36%) and ratio of GD3 to GM3 is 9.25- to 9.88-fold. The different lipolysis behaviors between MFGM ingredient emulsions and SL emulsions were correlated with their different polar lipid compositions. Phospholipids from both MFGM ingredients and SL could help maintain the initial structure during the gastric digestion. These results could provide a scientific basis for developing high-polar-lipids food, particularly infant formulas and special functional foods.

Characterization of an Aptamer Targeting Neu5Gc, as an Endogenous Pathogenic Factor Derived from Red Meat

N-glycolylneuraminic acid (Neu5Gc), a sialic acid predominantly found in the non-neurohumoral fluids of hind-mouthed animals, is incapable of synthesizing Neu5Gc due to a deletion in the CMAH exon of the gene encoding human CMP-Neu5Gc hydroxylase. But consumption of animal-derived foods that contain Neu5Gc, such as red meat, can instigate an immune response in humans, as Neu5Gc is recognized as a foreign substance by the human immune system. This recognition leads to the production of anti-Neu5Gc antibodies, subsequently resulting in chronic inflammation. When Neu5Gc is consumed excessively or frequently, it may contribute to the development of heart disease and cancer. This makes Neu5Gc, an endogenous pathogenic factor derived from red meat, a new hot topic in red meat safety research. In this study, aptamers obtained by the magnetic bead SELEX technique were subjected to homology and secondary structure prediction analysis as well as affinity determination. The result indicated that the aptamer 2B.N2A9 exhibited a robust binding affinity, with an affinity constant (Ka) of 1.87 × 108 L/mol. This aptamer demonstrated optimal binding specificity within a pH range of 5.4 to 7.4. Molecular docking analysis further revealed that aptamer 2B.N2A9 formed stable binding interactions with the target Neu5Gc at specific sites, namely G-14, C-15, G-13, G-58, G-60, and C-59. An Enzyme-Linked Oligonucleotide Sorbent Assay (ELOSA) methodology was established to detect the endogenous pathogenic factor Neu5Gc present in red meat. This method demonstrated a limit of detection (LOD) of 0.71 ng/mL, along with an average recovery rate of 92.23%. The aptamer obtained in this study exhibited favorable binding properties to Neu5Gc. The assay was relatively convenient and demonstrated good sensitivity. Further investigation into the distribution of Neu5Gc in various red meats is of public health significance and scientific potential. A practical detection method should be provided to guide red meat diets and ensure the nutrition and safety of meat products.

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.

Advances in Mass Spectrometry of Gangliosides Expressed in Brain Cancers

Gangliosides are highly abundant in the human brain where they are involved in major biological events. In brain cancers, alterations of ganglioside pattern occur, some of which being correlated with neoplastic transformation, while others with tumor proliferation. Of all techniques, mass spectrometry (MS) has proven to be one of the most effective in gangliosidomics, due to its ability to characterize heterogeneous mixtures and discover species with biomarker value. This review highlights the most significant achievements of MS in the analysis of gangliosides in human brain cancers. The first part presents the latest state of MS development in the discovery of ganglioside markers in primary brain tumors, with a particular emphasis on the ion mobility separation (IMS) MS and its contribution to the elucidation of the gangliosidome associated with aggressive tumors. The second part is focused on MS of gangliosides in brain metastases, highlighting the ability of matrix-assisted laser desorption/ionization (MALDI)-MS, microfluidics-MS and tandem MS to decipher and structurally characterize species involved in the metastatic process. In the end, several conclusions and perspectives are presented, among which the need for development of reliable software and a user-friendly structural database as a search platform in brain tumor diagnostics.

Preparation and properties of boron affinity molecularly imprinted mesoporous polymers based on Mn-doped ZnS quantum dots

Sialic acid (SA), known as N-acetyl neuraminic acid, is a natural 9-carbomonosaccharide derivative. SA has been widely applied in the early diagnosis of diseases as therapeutic target. However, the abundance of SA is very low in biological samples, which is usually interfered by the similar molecules coexisting at high abundance. Combining the advantages of high selectivity and specificity of molecularly imprinted technology, high specific surface area of mesoporous materials and excellent optical properties of quantum dots, we chose Mn-doped ZnS quantum dots as signal elements, and sialic acid as the template molecule. KH-4-MAPB with recognition ability to SA was synthesized by one-step hydrothermal method using thiolene click reaction as functional monomer. Based on the principle of boron affinity, molecularly imprinted polymers with highly ordered mesoporous structure were prepared, and the structure and fluorescence properties of fluorescent molecularly imprinted polymers were studied. FT-IR, XRD, TEM and nitrogen adsorption-desorption experiments were used to characterize the structure and morphology of the molecularly imprinted polymers. The results showed that the prepared molecularly imprinted polymers had highly ordered mesoporous structure and a large number of imprinted holes, which ensured the specific selectivity of the molecularly imprinted polymers. The fluorescence properties of MIMPs were characterized and analyzed by fluorescence spectra, equilibrium adsorption kinetics experiments were conducted and imprinting properties were recorded under different pH. The above experimental results showed that the fluorescence quenching was successfully achieved when the template molecule SA was captured by the molecularly imprinted polymer. When the concentration of SA was 1.25-100 × 10^-2 g/L, the fluorescence quenching degree of MIMPs showed a fine linear relationship with SA. The correlation coefficient was 0.9946, and the detection equation was F₀/F - 1 = 0.0215 [CSA] + 0.0241. MIMPs had a high recognition ability for SA, and the imprinting factor was 2.44. As a fluorescent sensor for SA, the response time of MIMPs was 20 min. When the buffer solution pH was 7, the imprinting factor was the largest. Under the best conditions, MIMPs revealed good selectivity and specificity for the fluorescence recognition of SA. MIMPS were also applied to the analysis of SA in real human serum samples with satisfactory results.

An efficient and robust HPLC method to determine the sialylation levels of human epithelial cells

Sialyltransferase, an enzyme responsible for attaching sialic acid to the cell surface, is reported to play a key role in cancer, making sialyltransferase a potential therapeutic target in drug development. Several methods have been developed to quantify sialic acids in biological samples however limitations exists and quantification in complex cell matrices lack investigation. Hence, this paper outlines a simple method to detect and quantify sialic acids in cancer cells for evaluating sialyltransferase activity of potential therapeutic compounds. An efficient method was developed using a reverse-phase ion-pairing HPLC-UV using triisopropanolamine as the ion-pairing agent with a C18 column. Neu5Ac was successfully eluted with the retention time 6.344 min with a flow rate of 0.4 mL/min. The proposed method was validated appropriately according to the AOAC guidelines (2013). This work demonstrates that the proposed method is not only relatively simple but also cost and time effective compared to pre-existing methods to successfully determine both free and protein-bound Neu5Ac in a complex cancer cell matrix. Furthermore, by applying the proposed method, a statistically significant decrease was observed for both HeLa and HuCCT1 cell lines with the application of deoxycholic acid-a known sialyltransferase inhibitor. Hence, the proposed method seems promisingly applicable to evaluate the effectiveness of potential sialyltransferase inhibitors.

Development and validation of capillary electrophoresis method for quantification of gangliosides in brain synaptosomes

Gangliosides are sialic acid containing glycosphingolipids of the plasma membrane with diverse biological functions. They are most abundant in neural tissues where their dysregulation has been suggested to be involved in various pathological conditions. Due to their importance, efficient analytical methods are needed to determine individual gangliosides in biological samples. Here we report a capillary electrophoresis method, optimized and validated for the simultaneous quantification of major neural gangliosides GM1, GD1a, GD1b, GT1b and GQ1b in their underivatized form. The most abundant extraneural monosialogangloside, GM3 can also be separated by this method. Micelles of the highly amphiphilic gangliosides were disrupted with cyclodextrins (CyDs) in the aqueous separation buffer. Among the tested CyDs, the best resolution was observed using 20 mM randomly methylated alpha-CyD in alkaline sodium borate buffer enabling the separation of all studied gangliosides. The method was applied for the quantification of gangliosides in rat cerebral and cerebellar synaptosomes.

The Potential for Sialic Acid and Sialylated Glycoconjugates as Feed Additives to Enhance Pig Health and Production

Simple Summary

This review discusses the current challenges in the pig industry and the potential nutritional significance of sialic acid (Sia) and glycoconjugates (Sia-GC’s) for pig health and nutrition. Sia is a nine-carbon acidic sugar which is present in various organs and body fluids of humans and animals. Sias contribute to many beneficial biological functions including pathogen resistance, immunomodulation, gut microbiota development, gut maturation, anti-inflammation and neurodevelopment. The role of Sias in regulating the metabolism of pigs has seldom been reported. However, we have documented significant beneficial effects of specific Sia-GC’s on health and production performance of sows and piglets. These findings are reviewed in relation to other studies while noting the beneficial effects of the inclusion of Sia, Sia containing oligosaccharide or the sialo-protein lactoferrin in the diets of gilts and sows. The importance of the passive transfer of of Sia and Sia-GC’s through milk to the young and the implications for their growth and development is also reviewed. This information will assist in optimizing the composition of sow/gilt milk replacers designed to increases the survival of IUGR piglets or piglets with dams suffering from agalactia, a common problem in pig production systems worldwide.

Abstract

Swine are one of the most important agricultural species for human food production. Given the significant disease challenges confronting commercial pig farming systems, introduction of a new feed additive that can enhance animal performance by improving growth and immune status represents a major opportunity. One such candidate is sialic acid (Sia), a diverse family of nine-carbon acidic sugar, present in various organs and body fluid, as well as an essential structural and functional constituent of brain ganglioside of humans and animals. Sias are key monosaccharide and biomarker of sialylated milk oligosaccharide (Sia-MOS’s), sialylated glycoproteins and glycolipids in milk and all vertebrate cells. Sias accomplish many critical endogenous functions by virtue of their physiochemical properties and via recognition by intrinsic receptors. Human milk sialylated glycoconjugates (Sia-GC’s) are bioactive compounds known to act as prebiotics that promote gut microbiota development, gut maturation, pathogen resistance, immunomodulation, anti-inflammation and neurodevelopment. However, the importance of Sia in pig health, especially in the growth, development, immunity of developing piglet and in pig production remains unknown. This review aims to critically discuss the current status of knowledge of the biology and nutritional role of Sia and Sia-GC’s on health of both female sow and newborn piglets.

A comprehensive review of edible bird's nest

Edible bird's nest (EBN) is built by seven species of Aerodramus and Collocalia (Apodidae), using salivary gland secretion mixed with feathers or grass during the breeding. Its rich nutritional values such as anti-aging activity, immunomodulatory and antioxidant activity make consumers flock to it. Consumers' pursuit, on the one hand, aroused the arrogance of counterfeiters, which eventually leads to food safety problems. On the other hand, it promotes the in-depth studies of EBN in all aspects, such as compositions, biological activities, authenticity identification, quality control, and so on. This paper presented the origins and classifications of EBN and the current situation of EBN industry in detail; reviewed the nutritional compositions, pharmacological actions, identification, inspection and content determination of EBN comprehensively; and prospected the future research directions to provide suggestions for the further study.

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.

Analysis of sialic acid levels in Chinese intravenous immunoglobulins by high-performance liquid chromatography with fluorescence detection

Intravenous immunoglobulin (IVIg) is increasingly used for the treatment of autoimmune and systemic inflammatory diseases with both licensed and off-label indications. Recent studies indicated that IVIg-mediated immunomodulation and anti-inflammation are closely associated with the IgG sialylation, especially with IgG crystallizable fragment (Fc) sialylation. The sialic acid levels of the IgG molecules and Fc fragments in 12 IVIg preparations from six Chinese manufacturers were evaluated. The Fc fragments were derived from the papain digestion of IVIg, followed by affinity and size exclusion chromatography. The sialic acid levels in Fc fragments and IVIg preparations were determined by high-performance liquid chromatography with fluorescence detection, after the sialic acid residues were released from the proteins. The results showed that the sialic acid levels in Chinese IVIg preparations ranged from 0.875 (mol/mol IgG) to 1.085 (mol/mol IgG), and the sialic acid levels in Fc fragments were from 0.321 (mol/mol Fc) to 0.361 (mol/mol Fc). Furthermore, the sialic acid levels of IVIg preparations and Fc fragments from different Chinese manufactures were significantly different. These findings will contribute to an increased understanding of Chinese IVIg preparations and the relationship between the sialic acid levels in IVIg preparations and their clinical efficacy in future clinical studies.

Variable sialic acid content in milk of Indian cattle and buffalo across different stages of lactation

The aim of this Research Communication was to contribute to the knowledge of milk sialic acid concentration of bovines with specific focus on India. Sialic acids (SA) are important constituents of mammalian milks. Buffaloes are the main milk producing species in India, therefore, our research focused on both cow and buffalo. Two Indian cattle (Bos indicus) breeds (Sahiwal, Tharparkar), one cross bred cattle – Karan Fries (Tharparkar × Holstein Friesian) and a buffalo breed (Murrah) were selected. Systematic comparisons of the total, free and bound form of SA and also its distribution over the course of lactation- colostrums and mature milk (120–140 d) was generated. Animal management, sample collection and methodology of SA estimation were identical for the different groups. Colostrum had the highest concentration of SA, which declined with the progress of lactation in all the groups. Majority of the SA existed in bound form. No significant (P < 0.05) difference was recorded in the total, bound or free SA across all the groups. However, differences were obvious in the total and bound SA level in the mature milk. Indian cattle, Sahiwal and Tharparkar were equivalent, but had higher concentration of total and bound SA than crossbred cattle. Milk of buffalo had SA equivalent to that of crossbred cattle. The mean (se) levels of total SA was 23.4 (0.8), 25.8 (2.4), 20.3 (0.6) and 20.2 (1.2) in Sahiwal, Tharparkar, cross bred and Murrah buffalo, respectively. The findings suggested that milk of indigenous cattle may be a potential source of SA, a bioactive compound with beneficial effect on human health and a potential functional ingredient in foods. Results add value to the currently declining indigenous cattle of India.

Fucosyl monosialoganglioside: Quantitative analysis of specific potential biomarkers of lung cancer in biological matrices using immunocapture extraction/tandem mass spectrometry

RATIONALE

Certain lung cancer patients express elevated Fucosyl Monosialoganglioside (Fuc-GM1) in circulation compared to control groups. Several sensitive methods involving characterization of Fuc-GM1 have been reported. However, a highly specific and sensitive method for quantifying multiple potential Fuc-GM1 biomarkers present in various biological matrices has not been reported to date.

METHODS

Individual Fuc-GM1 analogs in a commercially obtained standard mixture were characterized using HPLC/UV/MS and high-resolution mass spectrometry (HRMS). Proprietary antibodies, mAb1 and mAb2, were used to selectively capture and pre-concentrate the soluble and drug-bound forms of Fuc-GM1 molecules present in human serum and whole blood, eliminating the background matrix components. Immunocapture extraction (ICE) followed by HPLC/MS/MS was used to quantify specific Fuc-GM1 analogs in biological matrices.

RESULTS

The concentration of individual Fuc-GM1 analogs in the standard mixture was estimated to be 7-34%, using HPLC/UV/MS. Using the standard mixture spiked into the biological matrices (100 μL), the lower limit of quantification (LLOQ) of each analog was 0.2-0.4 ng/mL with a dynamic range of up to 200 ng/mL. The applicability of the ICE-HPLC/MS/MS method was demonstrated by detecting endogenous Fuc-GM1 analogs present in rat blood and in several lung cancer cell lines.

CONCLUSIONS

This highly specific and sensitive HPLC/MS/MS method for quantifying individual potential Fuc-GM1 biomarkers in serum and whole blood can play a critical role in patient stratification strategies and during drug treatment. This method can be employed for monitoring both free (soluble) form and antibody drug-bound Fuc-GM1.

Application of industrial treatments to donor human milk: influence of pasteurization treatments, storage temperature, and time on human milk gangliosides

Donor milk is the best option when mother’s own milk is unavailable. Heat treatments are applied to ensure donor milk safety. The effects of heat treatments on milk gangliosides—bioactive compounds with beneficial antibacterial, anti-inflammatory, and prebiotic roles—have not been studied. The most abundant gangliosides in non-homogenized human milk were characterized and quantified by liquid chromatography–mass spectrometry (LC–MS)/MS before and after pasteurization treatments mimicking industrial conditions (63 °C/30 min, 72 °C/15 s, 127 °C/5 s, and 140 °C/6 s). Ganglioside stability over a 3-month period was assessed following the storage at 4 and 23 °C. Independent of the heat treatment applied, gangliosides were stable after 3 months of storage at 4 or 23 °C, with only minor variations in individual ganglioside structures. These findings will help to define the ideal processing and storage conditions for donor milk to maximize the preservation of the structure of bioactive compounds to enhance the health of fragile newborns. Moreover, these results highlight the need for, and provide a basis for, a standardized language enabling biological and food companies, regulatory agencies, and other food stakeholders to both annotate and compute the ways in which production, processing, and storage conditions alter or maintain the nutritive, bioactive, and organoleptic properties of ingredients and foods, as well as the qualitative effects these foods and ingredients may have on conferring phenotype in the consuming organism.

Donor human milk, the best alternative to mother’s own milk, usually needs to be pasteurized before use out of safety concerns. Daniela Barile at University of California Davis, USA, and colleagues studied the effects of heat treatment and storage temperature and time on milk gangliosides, a class of sugar-derived compounds important for neural and brain development of newborns, among other bioactivities. They found that, while there were minor structural changes during mimicked industrial pasteurization processes, gangliosides remain stable for at least three months either in the refrigerator or at room temperature. These results may help standardize the processing protocols and storage conditions for donor milk, and the methods can be extended to other bioactive components.

Hydrophilic Interaction Liquid Chromatography-Mass Spectrometry Characterization of Gangliosides in Biological Samples

The hydrophilic interaction liquid chromatography (HILIC) coupled to a negative-ion electrospray ionization tandem mass spectrometry (ESI-MS/MS) method has been developed for the identification of a wide range of gangliosides in biological samples. Gangliosides consist of a backbone of sphingoid base and a polar oligosaccharide chain containing at least one sialic acid. Gangliosides are extracted by chloroform-methanol-water mixture, where an upper aqueous layer containing gangliosides and other polar lipid subclasses is further purified by C18 solid-phase extraction. The optimization of chromatographic conditions includes the column selection, mobile-phase composition, pH value, buffer type, and concentration with the goal to achieve the best chromatographic resolution and MS sensitivity. The identification of gangliosides and other polar lipids is based on accurate m/z values of [M-H]^- ions and fragment ions as well measured by high-resolution MS. The detailed interpretation of MS/MS spectra enables the generalization of fragmentation pathways, which is then used for the differentiation of a, b, and c series of gangliosides. The structural assignment is further confirmed by agreement with the predicted retention behavior in HILIC mode on the basis of the correlation among the ganglioside retention, the number of saccharide units, and their sequence. The final HILIC/ESI-MS/MS method is applied for the analysis of porcine brain, human kidney, lungs, plasma, and erythrocytes resulting in unambiguous identification of 145 ganglioside species from 19 subclasses, which represents the highest number of reported gangliosides. Moreover, 71 sulfatides and 59 polar phospholipids (phosphatidylserines, phosphatidylinositols, lysophosphatidylinositols, and phosphatidylglycerols) are detected within a 15 min run.

Rational Design of a Stimuli-Responsive Polymer Electrode Interface Coupled with in Vivo Microdialysis for Measurement of Sialic Acid in Live Mouse Brain in Alzheimer's Disease

Sensitive and selective monitoring of sialic acid (SA) in cerebral nervous system is of great importance for studying the role that SA plays in the pathological process of Alzheimer's disease (AD). In this work, we first reported an electrochemical biosensor based on a novel stimuli-responsive copolymer for selective and sensitive detection of SA in mouse brain. Notably, through synergetic hydrogen-bonding interactions, the copolymer could translate the recognition of SA into their conformational transition and wettability switch, which facilitated the access and enrichment of redox labels and targets to the electrode surface, thus significantly improving the detection sensitivity with the detection limit down to 0.4 pM. Besides amplified sensing signals, the proposed method exhibited good selectivity toward SA in comparison to potential interference molecules coexisting in the complex brain system due to the combination of high affinity between phenylboronic acid (PBA) and SA and the directional hydrogen-bonding interactions in the copolymer. The electrochemical biosensor with remarkable analytical performance was successfully applied to evaluate the dynamic change of SA level in live mouse brain with AD combined with in vivo midrodialysis. The accurate concentration of SA in different brain regions of live mouse with AD has been reported for the first time, which is beneficial for progressing our understanding of the role that SA plays in physiological and pathological events in the brain.

Large-Scale Glycomics of Livestock: Discovery of Highly Sensitive Serum Biomarkers Indicating an Environmental Stress Affecting Immune Responses and Productivity of Holstein Dairy Cows

Because various stresses strongly influence the food productivity of livestock, biomarkers to indicate unmeasurable environmental stress in domestic animals are of increasing importance. Thermal comfort is one of the basic principles of dairy cow welfare that enhances productivity. To discover sensitive biomarkers that monitor such environmental stresses in dairy cows, we herein performed, for the first time, large-scale glycomics on 336 lactating Holstein cow serum samples over 9 months between February and October. Glycoblotting combined with MALDI-TOF/MS and DMB/HPLC allowed for comprehensive glycomics of whole serum glycoproteins. The results obtained revealed seasonal alterations in serum N-glycan levels and their structural characteristics, such as an increase in high-mannose type N-glycans in spring, the occurrence of di/triantennary complex type N-glycans terminating with two or three Neu5Gc residues in summer and autumn, and N-glycans in winter dominantly displaying Neu5Ac. A multivariate analysis revealed a correlation between the serum expression levels of these season-specific glycoforms and productivity.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2009-2010

This review is the sixth update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2010. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, arrays and fragmentation are covered in the first part of the review and applications to various structural typed constitutes the remainder. The main groups of compound that are discussed in this section are oligo and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Many of these applications are presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis.

A biomimetic platform to study the interactions of bioelectroactive molecules with lipid nanodomains

In this work, we developed a biomimetic platform where the study of membrane associated redox processes and high-resolution imaging of lipid nanodomains can be both performed, based on a new functional gold modification, l-cysteine self-assembled monolayer. This monolayer proved to be ideal for the preparation of defect-free planar supported lipid bilayers (SLBs) where nanodomains with height difference of ∼1.5 nm are clearly resolved by atomic force microscopy. Single and multicomponent lipid compositions were used, leading to the formation of different phases and domains mimicking the lateral organization of cellular membranes, and in all cases stable and continuous bilayers were obtained. These platforms were tested toward the interaction with bioelectroactive molecules, the antioxidant quercetin, and the hormone epinephrine. Despite the weak interaction detected between epinephrine and lipid bilayers, our biomimetic interface was able to sense the redox process of membrane-bound epinephrine, obtain its surface concentration (9.36 × 10(-11) mol/cm(2) for a fluid bilayer), and estimate a mole fraction membrane/water partition coefficient (Kp) from cyclic voltammetric measurements (1.13 × 10(4) for a fluid phase membrane). This Kp could be used to quantitatively describe the minute changes observed in the photophysical properties of epinephrine intrinsic fluorescence upon its interaction with liposome suspensions. Moreover, we showed that the lipid membrane stabilizes epinephrine structure, preventing its oxidation, which occurs in neutral aqueous solution, and that epinephrine partition and mobility in membranes depends on lipid phase, expanding our knowledge on hormone membrane interactions.

Longitudinal evolution of the concentration of gangliosides GM3 and GD3 in human milk

It has been reported that dietary gangliosides may have an important role in preventing infections and in brain development during early infancy. However, data related to the evolution of their concentration over the different stages of lactation are scarce. Liquid chromatography coupled with electrospray ionization high resolution mass spectrometer (LC/ESI-HR-MS) has been optimized to quantify the two major ganglioside classes, i.e., aNeu5Ac(2-8)aNeu5Ac(2-3)bDGalp(1-4)bDGlcp(1-1)Cer (GD3) and aNeu5Ac(2-3)bDGalp(1-4)bDGlcp(1-1)Cer (GM3) in human milk. Gangliosides were extracted using chloroform and methanol, further purified by solid-phase extraction and separated by reversed-phase liquid chromatography. Repeatability, intermediate reproducibility, and recovery values were assessed to validate the method. In human milk, GD3 and GM3 could be quantified at the level of 0.1 and 0.2 μg/mL, respectively, with relative standard deviation of repeatability [CV(r)] and intermediate reproducibility [CV(iR)] values ranging from 1.9 to 15.0 % and 1.9 to 22.5 %, respectively. The described method was used to quantify GD3 and GM3 in human milk samples collected from 450 volunteers between 0 and 11 days and at 30, 60 and 120 days postpartum, providing for the first time the concentration of these minor lipids in a large cohort. The content of total gangliosides ranged from 8.1 and 10.7 μg/mL and the mean intake of gangliosides in infants 30, 60 and 120 days postpartum could be estimated at about 5.5, 7.0 and 8.6 mg of total gangliosides per day, respectively, when infants were exclusively breastfed.

Quantitative determination and confirmatory analysis of N-acetylneuraminic and N-glycolylneuraminic acids in serum and urine by solid-phase extraction on-line coupled to liquid chromatography-tandem mass spectrometry

N-acetylneuraminic acid (Neu5Ac) and N-acetylglycolylneuraminic acid (Neu5Gc), two acylated derivatives of 9-C carboxylated monosaccharides, are involved in a number of biological processes as modulators of glycoconjugates. A partially automated method is here presented for determination of these sialic acids in the two most important biofluids for clinical analysis: serum and urine. For this purpose, a solid-phase extraction (SPE) workstation was on-line connected to an LC-MS/MS triple quadrupole mass detector. Hydrolysis to release sialic acids bound to glycoconjugates and derivatization were the two steps implemented as sample preparation prior to SPE-LC-MS/MS analysis. Following thorough optimization of the SPE and LC-MS/MS conditions, the analytical method was validated using the standard addition approach to assess the presence of matrix effects. The proposed method affords detection limits of 0.03ng/mL and 0.04ng/mL for Neu5Ac and Neu5Gc, respectively. The precision (expressed as relative standard deviation) was 1.7 and 4.6% for within-day variability, and 4.8 and 7.2% for between-days variability. Accuracy, estimated using spiked (between 1 and 50ng/mL) and non-spiked samples of both biofluids, ranged from 95.2 to 99.6%. The method was applied to human serum and urine of healthy volunteers, thus showing its suitability for application in both clinical and research laboratories.

Involvement of a non-human sialic Acid in human cancer

Sialic acids are common monosaccharides that are widely expressed as outer terminal units on all vertebrate cell surfaces, and play fundamental roles in cell–cell and cell–microenvironment interactions. The predominant sialic acids on most mammalian cells are N-glycolylneuraminic acid (Neu5Gc) and N-acetylneuraminic acid (Neu5Ac). Neu5Gc is notable for its deficiency in humans due to a species-specific and species-universal inactivating deletion in the CMAH gene encoding the hydroxylase that converts CMP-Neu5Ac to CMP-Neu5Gc. However, Neu5Gc is metabolically incorporated into human tissues from dietary sources (particularly red meat), and detected at even higher levels in some human cancers. Early life exposure to Neu5Gc-containing foods in the presence of certain commensal bacteria that incorporate dietary Neu5Gc into lipooligosaccharides can lead to generation of antibodies that are also cross-reactive against Neu5Gc-containing glycans in human tissues (“xeno-autoantigens”). Such anti-Neu5Gc “xeno-autoantibodies” are found in all humans, although ranging widely in levels among individuals, and displaying diverse and variable specificities for the underlying glycan. Experimental evidence in a human-like Neu5Gc-deficient Cmah^−/−mouse model shows that inflammation due to “xenosialitis” caused by this antigen–antibody interaction can promote tumor progression, suggesting a likely mechanism for the well-known epidemiological link between red meat consumption and carcinoma risk. In this review, we discuss the history of this field, mechanisms of Neu5Gc incorporation into tissues, the origin and specificities of human anti-Neu5Gc antibodies, their use as possible cancer biomarkers, implications of xenosialitis in cancer initiation and progression, and current and future approaches toward immunotherapy that could take advantage of this unusual human-specific phenomenon.

Ganglioside biochemistry

Gangliosides are sialic acid-containing glycosphingolipids. They occur especially on the cellular surfaces of neuronal cells, where they form a complex pattern, but are also found in many other cell types. The paper provides a general overview on their structures, occurrence, and metabolism. Key functional, biochemical, and pathobiochemical aspects are summarized.

Direct estimation of sialic acid in milk and milk products by fluorimetry and its application in detection of sweet whey adulteration in milk

Sialic acid, being a biologically active compound, is recognised as an important component of milk and milk products. Almost all the sialic acid estimation protocols in milk require prior hydrolysis step to release the bound sialic acid followed by its estimation. The objective of this work was to estimate sialic acid in milk and milk products by fluorimetric assay which does not require a prior hydrolysis step thus decreasing the estimation time. The recovery of added sialic acid in milk was 91·6 to 95·8%. Sialic acid in milk was found to be dependent on cattle breed and was in the range of 1·68–3·93 g/kg (dry matter basis). The assay was further extended to detect adulteration of milk with sweet whey which is based on the detection of glycomacropeptide (GMP) bound sialic acid in adulterated milk. GMP is the C-terminal part of κ-casein which is released into the whey during cheese making. For detection of adulteration, selective precipitation of GMP was done using trichloroacetic acid (TCA). TCA concentration in milk was first raised to 5% to precipitate milk proteins, especially κ-casein, followed by raising the TCA concentration to 14% to precipitate out GMP. In the precipitates GMP bound sialic acid was estimated using fluorimetric method and the fluorescence intensity was found to be directly proportional to the level of sweet whey in adulterated milk samples. The method was found to detect the presence of 5% sweet whey in milk.

Determination of sialic acids in infant formula by chromatographic methods: a comparison of high-performance anion-exchange chromatography with pulsed amperometric detection and ultra-high-performance liquid chromatography methods

Sialic acid determination in an infant formula presents many challenges, including efficient sialic acid release from glycoconjugates, effective sample preparation, and rugged chromatography. This work compares 2 chromatographic assays developed for determination of sialic acids in infant formula. Prior to chromatography, both assays release sialic acids by acid hydrolysis and treat the hydrolysate with a subsequent anion-exchange sample preparation. Both high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) and fluorescence ultra-high-performance liquid chromatography (UHPLC) sample analysis methods were evaluated to compare assay performance and convenience. Calibration ranges were chosen to encompass the expected amounts of 2 sialic acids in infant formula: N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc). Response was linear by either method with coefficients of determination of 1.00 by HPAEC-PAD between 5.0 and 100pmol of Neu5Ac and between 0.34 and 6.8 pmol of Neu5Gc and >0.99 by UHPLC between 5.0 and 260 pmol of Neu5Ac and between 0.20 and 9.8 pmol of Neu5Gc. Both methods had sufficient sensitivity to determine these sialic acids in infant formula. Three infant formulas were analyzed to evaluate accuracy and precision of the assays. The HPAEC-PAD assay was found to be faster overall and the UHPLC assay was more sensitive. Reaction efficiency, and therefore sensitivity, was dependent on the sample matrix. This work illustrates sample-specific complexity that must be considered in choosing an assay.

Lipidomics of glycosphingolipids

Glycosphingolipids (GSLs) contain one or more sugars that are attached to a sphingolipid moiety, usually to a ceramide, but in rare cases also to a sphingoid base. A large structural heterogeneity results from differences in number, identity, linkage, and anomeric configuration of the carbohydrate residues, and also from structural differences within the hydrophobic part. GSLs form complex cell-type specific patterns, which change with the species, the cellular differentiation state, viral transformation, ontogenesis, and oncogenesis. Although GSL structures can be assigned to only a few series with a common carbohydrate core, their structural variety and the complex pattern are challenges for their elucidation and quantification by mass spectrometric techniques. We present a general overview of the application of lipidomics for GSL determination. This includes analytical procedures and instrumentation together with recent correlations of GSL molecular species with human diseases. Difficulties such as the structural complexity and the lack of standard substances for complex GSLs are discussed.

Fluorous derivatization combined with liquid chromatography/tandem mass spectrometry: a method for the selective and sensitive determination of sialic acids in biological samples

We have developed a novel method for selective and sensitive analysis of sialic acids (N-acetylneuraminic, N-glycolylneuraminic, and 2-keto-3-deoxy-D-glycero-D-galactonononic acid) utilizing liquid chromatography/tandem mass spectrometry (LC/MS/MS) combined with a fluorous derivatization technique. In this method, the carboxylic groups in the sialic acids are derivatized via amidation with heptadecafluoroundecylamine, a commercially available perfluoroalkylamine reagent. This reaction proceeds rapidly and readily at room temperature in the presence of a condensation reagent. Subsequently, the derivatives are retained specifically on an LC column with a perfluoroalkyl stationary phase by means of a fluorophilic or 'fluorous' interaction, and detected by positive electrospray ionization MS/MS. The detection limits of the examined sialic acids are in the range of 60-750 amol on column. We show that the proposed method can be used to analyze trace amounts of sialic acids in biological samples.