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

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

Acarbose Mitigates Age-Dependent Alterations in Erythrocyte Membrane Transporters During Aging in Rats

Acarbose (ACA), a well-studied and effective inhibitor of α-amylase and α-glucosidase, is a postprandial-acting antidiabetic medicine. The membrane of the erythrocyte is an excellent tool for analyzing different physiological and biochemical activities since it experiences a range of metabolic alterations throughout aging. It is uncertain if ACA modulates erythrocyte membrane activities in an age-dependent manner. As a result, the current study was conducted to explore the influence of ACA on age-dependent deteriorated functions of transporters/exchangers, disrupted levels of various biomarkers such as lipid hydroperoxides (LHs), protein carbonyl (PCO), sialic acid (SA), total thiol (-SH), and erythrocyte membrane osmotic fragility. In addition to a concurrent increase in Na+/H+ exchanger activity and concentration of LH, PCO, and osmotic fragility, we also detected a considerable decrease in membrane-linked activities of Ca2+-ATPase (PMCA) and Na+/K+-ATPase (NKA), as well as concentrations of SA and -SH in old-aged rats. The aging-induced impairment of the activities of membrane-bound ATPases and the changed levels of redox biomarkers were shown to be effectively restored by ACA treatment.

Improved methods to characterize the length and quantity of highly unstable PolySialic acids subject category: (Carbohydrates, chromatographic techniques)

Polysialic acid (polySia) is a linear homopolymer of α2-8-linked sialic acids that is highly expressed during early stages of mammalian brain development and modulates a multitude of cellular functions. While degree of polymerization (DP) can affect such functions, currently available methods do not accurately characterize this parameter, because of the instability of the polymer. We developed two improved methods to characterize the DP and total polySia content in biological samples. PolySia chains with exposed reducing termini can be derivatized with DMB for subsequent HPLC analysis. However, application to biological samples of polySia-glycoproteins requires release of polySia chains from the underlying glycan, which is difficult to achieve without concurrent partial hydrolysis of the α2-8-linkages of the polySia chain, affecting its accurate characterization. We report an approach to protect internal α2-8sia linkages of long polySia chains, using previously known esterification conditions that generate stable polylactone structures. Such polylactonized molecules are more stable during acid hydrolysis release and acidic DMB derivatization. Additionally, we used the highly specific Endoneuraminidase-NF enzyme to discriminate polysialic acid and other sialic acid and developed an approach to precisely measure the total content of polySia in a biological sample. These two methods provide improved quantification and characterization of polySia.

Sialic Acid and Sialylated Oligosaccharide Supplementation during Lactation Improves Learning and Memory in Rats

Sialic acids (Sia) are postulated to improve cognitive abilities. This study evaluated Sia effects on rat behavior when administered in a free form as N-acetylneuraminic acid (Neu5Ac) or conjugated as 6'-sialyllactose (6'-SL). Rat milk contains Sia, which peaks at Postnatal Day 9 and drops to a minimum by Day 15. To bypass this Sia peak, a cohort of foster mothers was used to raise the experimental pups. A group of pups received a daily oral supplementation of Neu5Ac to mimic the amount naturally present in rat milk, and another group received the same molar amount of Sia as 6'-SL. The control group received water. After weaning, rats were submitted to behavioral evaluation. One year later, behavior was re-evaluated, and in vivo long-term potentiation (LTP) was performed. Brain samples were collected and analyzed at both ages. Adult rats who received Sia performed significantly better in the behavioral assessment and showed an enhanced LTP compared to controls. Within Sia groups, 6'-SL rats showed better scores in some cognitive outcomes compared to Neu5Ac rats. At weaning, an effect on polysialylated-neural cell adhesion molecule (PSA-NCAM) levels in the frontal cortex was only observed in 6'-SL fed rats. Providing Sia during lactation, especially as 6'-SL, improves memory and LTP in adult rats.

Mass spectrometry for protein sialoglycosylation

Sialic acids are a family of structurally unique and negatively charged nine-carbon sugars, normally found at the terminal positions of glycan chains on glycoproteins and glycolipids. The glycosylation of proteins is a universal post-translational modification in eukaryotic species and regulates essential biological functions, in which the most common sialic acid is N-acetyl-neuraminic acid (2-keto-5-acetamido-3,5-dideoxy-D-glycero-D-galactononulopyranos-1-onic acid) (Neu5NAc). Because of the properties of sialic acids under general mass spectrometry (MS) conditions, such as instability, ionization discrimination, and mixed adducts, the use of MS in the analysis of protein sialoglycosylation is still challenging. The present review is focused on the application of MS related methodologies to the study of both N- and O-linked sialoglycans. We reviewed MS-based strategies for characterizing sialylation by analyzing intact glycoproteins, proteolytic digested glycopeptides, and released glycans. The review concludes with future perspectives in the field.

Identification of Sialic Acid Linkages on Intact Glycopeptides via Differential Chemical Modification Using IntactGIG-HILIC

Mass spectrometric analysis of intact glycopeptides can reveal detailed information about glycosite, glycan structural features, and their heterogeneity. Sialyl glycopeptides can be positively, negatively, or neutrally charged depending on pH of their buffer solution and ionization conditions. To detect sialoglycopeptides, a negative-ion mode mass spectrometry may be applied with a minimal loss of sialic acids, although the positively charged or neutral glycopeptides may be excluded. Alternatively, the sialyl glycopeptides can be identified using positive-ion mode analysis by doping a high concentration of sodium salts to the analytes. Although manipulation of unmodified sialoglycopeptides can be useful for analysis of samples, less than optimal ionization, facile loss of sialyl and unfavorable ionization of accompanying non-sialyl peptides make such strategies suboptimal. Currently available chemical derivatization methods, while stabilizing for sialic acid, mask sialic acid linkage configuration. Here, we report the development of a novel approach to neutralize sialic acids via sequentially chemical modification that also reveals their linkage configuration, often an important determinant in biological function. This method utilizes several components to facilitate glycopeptide identification. These include the following: solid phase derivatization, enhanced ionization of sialoglycopeptides, differentiation of sialic acid linkage, and enrichment of the modified glycopeptides by hydrophilic interaction liquid chromatography. This technology can be used as a tool for quantitative analysis of protein sialylation in diseases with determination of sialic acid linkage configuration. Graphical Abstract ᅟ.

Discrimination of Isomers of Released N- and O-Glycans Using Diagnostic Product Ions in Negative Ion PGC-LC-ESI-MS/MS

Profiling cellular protein glycosylation is challenging due to the presence of highly similar glycan structures that play diverse roles in cellular physiology. As the anomericity and the exact linkage type of a single glycosidic bond can influence glycan function, there is a demand for improved and automated methods to confirm detailed structural features and to discriminate between structurally similar isomers, overcoming a significant bottleneck in the analysis of data generated by glycomics experiments. We used porous graphitized carbon-LC-ESI-MS/MS to separate and detect released N- and O-glycan isomers from mammalian model glycoproteins using negative mode resonance activation CID-MS/MS. By interrogating similar fragment spectra from closely related glycan isomers that differ only in arm position and sialyl linkage, product fragment ions for discrimination between these features were discovered. Using the Skyline software, at least two diagnostic fragment ions of high specificity were validated for automated discrimination of sialylation and arm position in N-glycan structures, and sialylation in O-glycan structures, complementing existing structural diagnostic ions. These diagnostic ions were shown to be useful for isomer discrimination using both linear and 3D ion trap mass spectrometers when analyzing complex glycan mixtures from cell lysates. Skyline was found to serve as a useful tool for automated assessment of glycan isomer discrimination. This platform-independent workflow can potentially be extended to automate the characterization and quantitation of other challenging glycan isomers. Graphical Abstract ᅟ.

Sialic Acid Derivatization for the Rapid Subclass- and Sialic Acid Linkage-Specific MALDI-TOF-MS Analysis of IgG Fc-Glycopeptides

Matrix-assisted laser desorption/ionization (MALDI)-time-of-flight (TOF)-mass spectrometry (MS) is a highly suitable method for the rapid analysis of IgG glycopeptides, providing a wealth of structural information. A limitation of this approach is that it generates a bias when analyzing sialylated species due to the labile nature of sialic acid glycosidic linkages. One way to overcome this problem is by chemical derivatization of the sialic acids. The method presented here results in both the stabilization of the sialic acids, as well as the differentiation of α2,3- and α2,6-linked sialic acids by mass. Described in this chapter are the isolation of IgG from plasma or serum, tryptic digestion of the samples, derivatization, and finally MALDI-TOF-MS measurement and data analysis.

Effect of Lead on the Blood Serum, Liver and Brain Sialoglycoconjugate Levels in Rats

Rats were exposed to an acute dose of lead (Pb) to study the effect of Pb intoxication on different sialoglycoconjugates in serum, brain and liver. Serum levels of total sialic acid (TSA), perchloric acid (PCA)-soluble sialic acid (PSA), lipid-bound sialic acid (LBSA), free sialic acid (FSA) and α1-acid glycoprotein (α1-AG) were determined. They were also estimated in brain and liver tissues, except for LBSA and FSA. All these constituents were found to be significantly raised in the serum but not in the brain. In the case of the liver, only α1-AG levels were found to be increased significantly, the rest were not altered. The levels of these sialoglycoconjugates in serum might be useful as biomarkers of heavy metal toxicity.

Advanced Technologies in Sialic Acid and Sialoglycoconjugate Analysis

Although the structural diversity of sialic acid (Sia) is rapidly expanding, understanding of its biological significance has lagged behind. Advanced technologies to detect and probe diverse structures of Sia are absolutely necessary not only to understand further biological significance but also to pursue medicinal and industrial applications. Here we describe analytical methods for detection of Sia that have recently been developed or improved, with a special focus on 9-O-acetylated N-acetylneuraminic acid (Neu5,9Ac), N-glycolylneuraminic acid (Neu5Gc), deaminoneuraminic acid (Kdn), O-sulfated Sia (SiaS), and di-, oligo-, and polysialic acid (diSia/oligoSia/polySia) in glycoproteins and glycolipids. Much more attention has been paid to these Sia and sialoglycoconjugates during the last decade, in terms of regulation of the immune system, neural development and function, tumorigenesis, and aging.

Liquid chromatography/tandem mass spectrometry with fluorous derivatization method for selective analysis of sialyl oligosaccharides

RATIONALE

A separation-oriented derivatization method using a specific fluorous affinity between perfluoroalkyl-containing compounds was applied to selective liquid chromatography/tandem mass spectrometric (LC/MS/MS) analysis of sialyl oligosaccharides. The perfluoroalkyl-labeled sialyl oligosaccharides could be selectively retained on an LC column with the perfluoroalkyl-modified stationary phase and effectively distinguished from non-derivatized species.

METHODS

Sialyl oligosaccharides (3'-sialyllactose, 6'-sialyllactose, sialyllacto-N-tetraose a, sialyllacto-N-tetraose b, sialyllacto-N-tetraose c, and disialyllacto-N-tetraose) were derivatized with 4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-heptadecafluoroundecylamine via amidation in the presence of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (condensation reagent). The obtained derivatives were directly injected onto the fluorous LC column without any pretreatments and then detected by positive electrospray ionization MS/MS.

RESULTS

The method enabled accurate determination of the sialyl oligosaccharides in biological samples such as human urine and human milk, because there was no interference with matrix-induced effects during LC/MS/MS analysis. The limits of detection of the examined sialyl oligosaccharides, defined as signal-to-noise (S/N) = 3, were in the range 0.033-0.13 nM. Accuracy in the range 95.6-108% was achieved, and the precision (relative standard deviation) was within 9.4%.

CONCLUSIONS

This method enabled highly selective and sensitive analysis of sialyl oligosaccharides, enabling accurate measurement of even their trace amounts in biological matrices. The proposed method may prove to be a powerful tool for the analysis of various sialyl oligosaccharides.

Enzymatic sialylation of IgA1 O-glycans: implications for studies of IgA nephropathy

Patients with IgA nephropathy (IgAN) have elevated circulating levels of IgA1 with some O-glycans consisting of galactose (Gal)-deficient N-acetylgalactosamine (GalNAc) with or without N-acetylneuraminic acid (NeuAc). We have analyzed O-glycosylation heterogeneity of naturally asialo-IgA1 (Ale) myeloma protein that mimics Gal-deficient IgA1 (Gd-IgA1) of patients with IgAN, except that IgA1 O-glycans of IgAN patients are frequently sialylated. Specifically, serum IgA1 of healthy controls has more α2,3-sialylated O-glycans (NeuAc attached to Gal) than α2,6-sialylated O-glycans (NeuAc attached to GalNAc). As IgA1-producing cells from IgAN patients have an increased activity of α2,6-sialyltransferase (ST6GalNAc), we hypothesize that such activity may promote premature sialylation of GalNAc and, thus, production of Gd-IgA1, as sialylation of GalNAc prevents subsequent Gal attachment. Distribution of NeuAc in IgA1 O-glycans may play an important role in the pathogenesis of IgAN. To better understand biological functions of NeuAc in IgA1, we established protocols for enzymatic sialylation leading to α2,3- or α2,6-sialylation of IgA1 O-glycans. Sialylation of Gal-deficient asialo-IgA1 (Ale) myeloma protein by an ST6GalNAc enzyme generated sialylated IgA1 that mimics the Gal-deficient IgA1 glycoforms in patients with IgAN, characterized by α2,6-sialylated Gal-deficient GalNAc. In contrast, sialylation of the same myeloma protein by an α2,3-sialyltransferase yielded IgA1 typical for healthy controls, characterized by α2,3-sialylated Gal. The GalNAc-specific lectin from Helix aspersa (HAA) is used to measure levels of Gd-IgA1. We assessed HAA binding to IgA1 sialylated at Gal or GalNAc. As expected, α2,6-sialylation of IgA1 markedly decreased reactivity with HAA. Notably, α2,3-sialylation also decreased reactivity with HAA. Neuraminidase treatment recovered the original HAA reactivity in both instances. These results suggest that binding of a GalNAc-specific lectin is modulated by sialylation of GalNAc as well as Gal in the clustered IgA1 O-glycans. Thus, enzymatic sialylation offers a useful model to test the role of NeuAc in reactivities of the clustered O-glycans with lectins.

Estimation of Luminal Mucin Content in Rats by Measurement ofO-Linked Oligosaccharide Chains and Direct ELISA

Changes in the small intestinal mucin contents in rats were evaluated by two methods, viz., a newly established ELISA and a method based on the measurement of O-linked oligosaccharide chains (OSC) as a mucin marker. Significant correlation was observed between the values of ELISA-derived mucins and OSC. The results confirm the usefulness of measurement of OSC as an alternative method for mucin determination.

Determination of sialic acids in immune system cells (coelomocytes) of sea urchin, Paracentrotus lividus, using capillary LC-ESI-MS/MS

Coelomocytes are considered to be immune effectors of sea urchins. Coelomocytes are the freely circulating cells in the body fluid contained in echinoderm coelom and mediate the cellular defence responses to immune challenges by phagocytosis, encapsulation, cytotoxicity and the production of antimicrobial agents. Coelomocytes have the ability to recognize self from non-self. Considering that sialic acids play important roles in immunity, we determined the presence of sialic acid types in coelomocytes of Paracentrotus lividus. Homogenized coelomocytes were kept in 2 M aqueous acetic acid at 80 °C for 3 h to liberate sialic acids. Sialic acids were determined by derivatization with 1,2-diamino-4,5-methylenediaoxy-benzene dihydrochloride (DMB) followed by capillary liquid-chromatography-electrospray ionization/tandem mass spectrometry (CapLC-ESI-MS/MS). Standard sialic acids; Neu5Ac, Neu5Gc, KDN and bovine submaxillary mucin showing a variety of sialic acids were used to confirm sialic acids types. We found ten different types of sialic acids (Neu5Gc, Neu5Ac, Neu5Gc9Ac, Neu5Gc8Ac, Neu5,9Ac2, Neu5,7Ac2, Neu5,8Ac2, Neu5,7,9Ac3, Neu5Gc7,9Ac2, Neu5Gc7Ac) isolated in limited amounts from total coelomocyte population. Neu5Gc type of sialic acids in coelomocytes was the most abundant type sialic acid when compared with other types. This is the first report on the presence of sialic acid types in coelomocytes of P. lividus using CapLC-ESI-MS/MS-Ion Trap system (Capillary Liquid Chromatography-Electrospray Ionization/Tandem Mass Spectrometry).

Quantum dot nanometal surface energy transfer based biosensing of sialic acid compositions and linkages in biological samples

Current methods for analyzing sialic acid diversity in modifications and linkages require multistep processing, derivatization, and chromatographic analyses. We here report a single-step optical method for identification and quantification of different compositions of sialoglycans on glycoproteins and in serum. This was achieved by measuring and quantifying nanometal surface energy transfer (NSET) signals between quantum dots and gold nanoparticles bound to specific sialic acid binding proteins (SBPs) and sialic acid moieties, respectively. The biosensing process is based on the NSET turn-on by external sialic acid species that compete for binding to the SBPs. Selectivity of the biosensor toward sialoglycans can be designed to detect the total amount, glycosylation linkages (α2-6 vs α2-3), and modifications (9-O-acetyl and N-glycolyl groups) in the samples. This nanobiosensor is a prototype expected to achieve limits of the detection down to the micromolar range for high-throughput quantification and analysis of different compositions of sialoglycans present in biological or biomedical samples.

Mass spectrometric analysis of sialylated glycans with use of solid-phase labeling of sialic acids

The analysis of sialylated glycans is critical for understanding the role of sialic acid in normal biological processes as well as in disease. However, the labile nature of sialic acid typically renders routine analysis of this monosaccharide by mass spectrometric methods difficult. To overcome this difficulty we pursued derivatization methodologies, extending established acetohydrazide approaches to aniline-based methods, and finally to optimized p-toluidine derivatization. This new quantitative glycoform profiling method with use of MALDI-TOF in positive ion mode was validated by first comparing N-glycans isolated from fetuin and serum and was then exploited to analyze the effects of increased metabolic flux through the sialic acid pathway in SW1990 pancreatic cancer cells by using a colabeling strategy with light and heavy toluidine. The latter results established that metabolic flux, in a complementary manner to the more well-known impact of sialyltransferase expression, can critically modulate the sialylation of specific glycans while leaving others virtually unchanged.

Melatonin controls photoperiodic changes in tanycyte vimentin and neural cell adhesion molecule expression in the Djungarian hamster (Phodopus sungorus)

The Djungarian hamster displays photoperiodic variations in gonadal size synchronized to the seasons by the nightly secretion of the pineal hormone melatonin. In short photoperiod (SP), the gonads regress in size, and circulating sex steroids levels decline. Thus, the brain is subject to seasonal variations of both melatonin and sex steroids. Tanycytes are specialized glial cells located in the ependymal lining of the third ventricle. They send processes either to the meninges or to blood vessels of the medio-basal hypothalamus. Furthermore, they are known to locally modulate GnRH release in the median eminence and to display seasonal structural changes. Seasonal changes in tanycyte morphology might be mediated either through melatonin or sex steroids. Therefore, we analyzed the effects of photoperiod, melatonin, and sex steroids 1) on tanycyte vimentin expression by immunohistochemistry and 2) on the expression of the neural cell adhesion molecule (NCAM) and polysialic acid as markers of brain plasticity. Vimentin immunostaining was reduced in tanycyte cell bodies and processes in SP. Similarly, tanycytes and their processes contained lower amounts of NCAM in SP. These changes induced by SP exposure could not be restored to long photoperiod (LP) levels by testosterone supplementation. Likewise, castration in LP did not affect tanycyte vimentin or NCAM expression. By contrast, late afternoon melatonin injections mimicking a SP-like melatonin peak in LP hamsters reduced vimentin and NCAM expression. Thus, the seasonal changes in vimentin and NCAM expression in tanycytes are regulated by melatonin independently of seasonal sex steroid changes.

A gel-capture assay for characterizing the sialyl-glycan selectivity of influenza viruses

Sialic acids (SA) usually linked to galactose (Gal) in an α2,6- or α2,3-configuration are considered the main cell receptors for influenza viruses, in particular for their hemagglutinins (HA). The typing of influenza virus HA receptor selectivity is relevant for understanding the transmissibility of avian and swine viruses to the human population. In this study we developed a simple and inexpensive gel-capture assay (GCA) of the influenza virus HA receptor-binding selectivity. Its principle is the binding of soluble influenza virus to pentasaccharide analogs, representatives of receptors of human and avian influenza viruses, immobilized on a gel resin. The human and avian analogs consisted of a sialyllactose-N-tetraose c (LSTc) [Neu5Ac(α2,6)Gal(β1-3)GlcNAc(β1-3)Gal(β1-4)Glc] and a sialyllactose-N-tetraose a (LSTa) [Neu5Ac(α2,3)Gal(β1-3)GlcNAc(β1-3)Gal(β1-4)Glc], respectively. Following equilibration, the unbound virus is washed away and the bound one is assayed via HA by densitometry as a function of the analog concentration. Using GCA, the receptor selectivity of three influenza viruses of different HA subtype was investigated. The results showed that the egg-adapted A/California/07/2009 (H1N1) virus exhibited an avian α2,3-linked LSTa selectivity, however, it retained the ability to bind to the α2,6-linked LSTc human receptor analog. Influenza B virus B/Florida/4/2006 showed α2,6-linked LSTc selectivity and a poor α2,3-linked LSTa avidity. The H3N2 virus A/Wisconsin/15/2009 displayed almost comparable avidity for both receptor analogs with a marginally greater α2,3-linked LSTa avidity. The described assay protocol provides a simple and rapid method for the characterization of influenza virus HA receptor binding selectivity.

An alternative to animal testing in the quality control of erythropoietin

A physico-chemical method has been developed as an alternative to the current bioassay in normocythaemic mice for estimating the biological activity of erythropoietin batches. Capillary zone electrophoresis was used for quantification of the isoforms and their substructures were further elucidated by N-glycan mapping techniques. The analytical study was carried out on a total of 40 batches of epoetin beta which were selected to cover an adequate range of precisely established potency values. The relationship between the biological and chemical parameters was evaluated statistically in order to identify suitable covariates for the prediction of the biological activity. Out of several alternatives, a prediction model which is based on the percentages of isoforms per batch and the degree of sialidation was selected and tested. This model is comparable in terms of accuracy to the established in vivo bioassay, but is far superior in terms of precision. Further advantages of the method are improved animal welfare and savings in time and effort. The question whether the prediction model already meets the requirements for replacing the bioassay according to the ICH guideline Q6B is discussed.

[Sialic acids and O-acetyl groups as markers of biological activity of microbial polysaccharides in plague and cholera agents]

AIM

To determine sialic acids and O-acetyl groups content in Yersinia pestis and Vibrio cholerae antigens in order to establish their association with biological activity.

MATERIALS AND METHODS

The following antigens of Y. pestis EV NIIEG strain--capsular antigen (F1), major somatic antigen (MSA), lipopolysaccharide (LPS), Pla-protease, allergen pestin PP--as well as O-antigens (O-AG) of V. cholerae serogroups O1 and O139 were used in the study. Sialic acids were identified by the thiobarbituric method, and O-acetyl groups--according to Alicino. Specific polysaccharides in the MSA and O-antigens were detected by the immunodiffusion assay.

RESULTS

Sialic acids were found in LPS, Pla-protease, allergen pestin PP, and all cholera O-AG; their absence was demonstrated in MSA and F1. O-acetyl groups were identified in cholera O-AG of both studied serogroups as well as in LPS, Pla-protease, MSA and pestin PP of Y. pestis. Tendency to correlation between O-acetyl groups content in MSA and serological activity titer was observed.

CONCLUSION

Sialic acids and O-acetyl groups identified in carbohydrate-containing antigens of Y. pestis and V. cholerae could be characterized as reaction-active markers of pathogenetic mechanisms of cholera and plague infections as well as immunochemical activity of microbial polysaccharides.

Lactose does not interfere with the analysis of sialic acids as their 1,2-diamino-4,5-methylenedioxybenzene derivatives

In 2007, Martin et al. developed a method for the analysis of sialic acids by HPLC following 1,2-diamino-4,5-methylenedioxybenzene (DMB) derivatisation (Martín et al., Anal Bioanal Chem 387:2943-2949, 2007). Within the article, the authors noted that lactose interfered with the analysis, giving erroneously high results when lactose-containing products were analysed. Such an observation is important when analysing milk-based products, yet was contradictory to the observations of Nakamura et al. (Chem Pharm Bull 35(2):687-692, 1987) who demonstrated that DMB was specific for α-keto acids and did not react with simple sugars such as glucose or lactose. In order to clarify the situation, this phenomenon was investigated and it was confirmed that lactose does not interfere with the analysis. However, it was found that most commercial preparations of lactose do contain small amounts of sialic acids, either as the free monosaccharide or bound to lactose in the form of 3'- and 6'-sialyllactose.

In vivo functional heterogeneity among β-cells

The concept of functional heterogeneity among β-cells proposes that each cell differs in its sensitivity to glucose and is recruited in a glucose-dependent manner into both biosynthetic and secretory active states in order to adapt insulin secretion to the metabolic environment. Therefore, characterization of β-cell populations with different metabolic sensitivities would lead to the development of new therapeutic strategies. Based on heterogeneous surface PSA-NCAM expression on β-cells, we have recently characterized two groups of cells, namely β(high) and β(low)-cells, in rat. Differences in insulin secretory capacity and in gene expression profiles suggest that β(low)-cells are immature and/or non-functional cells in contrast to highly glucose responsive fully functional β(high)-cells. Moreover, the relative distribution of β(high) and β(low)-cells correlated with physiological and pathological states regarding the functional β-cell mass. Here we summarize our main results on β(high) and β(low)-cell populations and discuss some of the open remaining questions.

[Criteries of the regeneration intensity in bone jaw's tissue during treatment of inflammatory destructive processes]

Study of some biochemical parameters of oral fluid in patients with periapical jaws' inflammatory destructive processes in the process of operative treatment was conducted. It was established that dynamics of these indicators could be indirect criterion of permissive value of activity and completeness of bone tissue reparative regeneration processes. Advantage of the method is in its small invasiveness.

Methods for mucin analysis: a comparative study

The aim was to compare five techniques commonly used to quantify mucin concentrations in ileal digesta collected from three growing pigs that had been fed a diet in which the sole protein was casein. Ileal mucin output was estimated by the periodic acid-Schiff, ethanol precipitation, and phenol-sulfuric acid methods as 25.1, 19.3, and 20.7 g kg-1 of dry matter intake (DMI), respectively. The mucin concentration estimated from sialic acid was only 5.9 g kg-1 of DMI. On the basis of the concentrations of the hexosamines N-acetylglucosamine and N-acetylgalactosamine, mucin output was estimated as 44.9 g kg-1 pf DMI. Of the five assays studied, the ethanol precipitation, periodic acid-Schiff, phenol-sulfuric acid, and sialic acid methods may considerably underestimate mucin in the digesta, which calls into question the accuracy of all of these approaches. In contrast, the gas chromatography method for the determination of hexosamines gave more information on the type and state of the mucin present.

Altered terminal glycosylation of thyroglobulin in papillary thyroid carcinoma

Samples of thyroglobulin (Tg) were isolated from specimens of differentiated thyroid carcinoma of the papillary type and from normal adjacent glandular tissue, and the content of sialic acid was estimated. Also the in vitro incorporation of 14C-sialic acid, in the form of both CMP (cytidine 5'-monophospho-)--activated and non-activated N-acetyl-neuraminic acid, into Tg of malignant and morphologically normal thyroid. The sialic acid content of Tg preparations from papillary thyroid carcinomas varied considerably (0.27-0.92 mg/100 mg Tg). In six cancerous Tg samples the content of sialic acid was markedly lower than that in Tg from the corresponding apparently normal thyroid tissue (0.71:1.11 mg per 100 mg Tg). In addition, in comparison with the control, the incorporation of non-activated 14C-sialic acid into Tg of malignant thyroid tissue was considerably lower (-41%). However, the incorporation of CMP-activated 14C-sialic acid into cancerous Tg was greater than into Tg of morphologically unchanged tissue of the same gland (+29%). The reduced content and incorporation rate of sialic acid into Tg of differentiated thyroid carcinoma is probably the consequence of disturbances in terminal glycosylation of the Tg molecule in malignantly transformed thyroid tissue. The enhanced incorporation of CMP-sialic acid into cancerous Tg suggests that Tg sialylation in carcinoma is probably altered in the sialic acid activation phase.

Crude urinary human chorionic gonadotropin contains variant forms of HCG with low sialic acid content that exhibit an increased thyrotropic activity in CHO cells expressing the human TSH receptor

Hyperthyroidism occurs in association with pregnancy or trophoblastic tumours. This is due to the secretion of thyroid stimulators by trophoblastic cells, most likely hCG or a variant form of hCG. In the present studies we sought to identify hCG variants with enhanced thyrotropic activity contained in crude hCG extract from pregnancy urine (hCGc). Such studies seem now feasible, because highly sensitive assays employing CHO cells transfected with the recombinant human TSH receptor recently became available. Initially, we found the activity of hCGc to both inhibit the binding of 125I-bTSH to CHO-TSHr cells and to stimulate the cAMP release by the cells to be increased, compared to highly purified hCG (hCGp), which was tested in comparable immunological concentrations. We then processed hCGc on a DEAE-52 anionexchange column to separate materials of interest, termed hCGv, from hCGp. HCGv was further purified by gel chromatography, and found to be enriched in terms of both, its holo-hCG immunoactivity and its TSH binding inhibiting activity, compared to hCGc where it was derived from. It also proved more potent than hCGp to bind to recombinant hTSH receptor and to stimulate adenylate cyclase activity in CHO-TSHr cells. Enzymatic desialylation was able to increase the potency of both hCGv and hCGp, and rendered the two desialylated hCG forms nearly equipotent. Isoelectric focusing and direct measurement of sialic acid contents revealed hCGv to be less sialylated than hCGp.(ABSTRACT TRUNCATED AT 250 WORDS)

Adhesion and junction molecules in embryonic and adult lens cell differentiation

The expression of the neural cell adhesion molecule NCAM and its polysialic acid (PSA) moiety was documented during embryonic development and adult differentiation of chicken lens cells. In both the embryo and adult, NCAM is predominantly found in the epithelium and the zone of young elongating cells of the annular pad. NCAM abundance drops markedly in the cortical fibers and is further reduced in the lens nucleus. Epithelial cell NCAM is more highly poly-sialylated in the adult than in the embryonic lens. Three isoforms of NCAM at 180, 140, and 120 kDa were detected in the lens and predominantly associated with the unit membrane-enriched plasma membranes of fiber cells. The distribution of NCAM relative to MP26 and the adherence junction-associated glycoprotein N-cadherin suggests that NCAM could influence the formation of fiber cell gap junctions and adherence junctions.

Nature of the heterogeneity within genetic variants of bovine serum transferrin

A comparison is made of the four main components of an homozygous variant (A or D2D2) of bovine serum transferrin. These are designated I-IV in order of increasing mobility in electrophoresis at pH 7.5. Components I, II, III and IV have 2,2,3 and 3 residues of sialic acid per transferrin molecule and appear to correspond to components 2a, 2b, 3a and 3b respectively of Stratil & Spooner (1971). The difference between components I and II and between III and IV does not reside in sialic acid differences. On the basis of peptide maps of reduced carboxamidomethylated components, urea-starch gel electrophoresis and quantitative sequence studies, it is concluded that components II and IV have a scission in the peptide chain. By homology with the sequency of MacGillivray et al. (1977) for human serum transferrin it is suggested that the scission occurs between residues 55 and 54 from the C-terminus and this portion of the chain has a 'molecular' weight of ca. 6000. The implications are briefly discussed.

Effect of androgen on different biochemical constituents of human semen

Changes in the levels of fructose, sialic acid, ascorbic acid, cholesterol and acid and alkaline phosphatases in the semen were studied in eight azoospermic volunteers during administration of testosterone propionate over a four week period. In order of responsiveness, elevations were observed in the levels of acid phosphatase, fructose, sialic acid and alkaline phosphatase during androgen therapy. No changes were seen in the levels of cholesterol and ascorbic acid.

A simple two-step protocol for the purification of human pancreatic beta cells

AIMS/HYPOTHESIS

Isolated pure human beta cells would be helpful for a number of research purposes. However, lack of beta cell-specific surface antigens has been a major problem. We aimed to develop a simple method for human beta cell isolation based on the initial elimination of ductal cells by their expression of carbohydrate antigen 19-9 (CA19-9), followed by positive selection of beta cells by their expression of polysialic acid-neural cell adhesion molecule (PSA-NCAM).

METHODS

Cell type-specific expression of CA19-9, NCAM and PSA-NCAM was studied in sections of adult human pancreas and in cultured primary endocrine and exocrine cells. Dispersed human islet cells were purified in two steps, after 4 days of suspension culture, by binding to magnetic microbeads coupled to antibodies against CA19-9 and PSA-NCAM.

RESULTS

NCAM expression was detected in ducts and islets in the human pancreas. In contrast, PSA-NCAM immunoreactivity was detected only in islets. PSA-NCAM staining in dispersed cells revealed that the marker is expressed in all endocrine cell types, but not in duct cells. Purification of dispersed islet cells using PSA-NCAM microbeads alone did not completely eliminate contaminating duct cells. However, elimination of the duct cells by CA19-9 microbeads followed by positive sorting of the PSA-NCAM-positive cells in five consecutive islet preparations resulted in 90 to 98% pure endocrine cells, of which 89 to 97% were beta cells.

CONCLUSIONS/INTERPRETATION

We describe a simple and reproducible method for purification of viable human pancreatic beta cells devoid of exocrine acini and ducts.

Glycoproteins secreted by sublingual glands of the echidna (Tachyglossus aculeatus)

The portion of echnida sublingual glycoproteins which could be solubilized was fractionated by electrophoresis in polyacrylamide gel and by filtration on a column of Sephadex G-100. Analyses for carbohydrate and amino acid are given and are compared with those of the submaxillary mucins of cattle, dog, pig and sheep. The molar ratio of galactosamine to sialic acid was roughly 1:1 in the echidna fractions, the sialic acid was N-acetyl-neuraminic acid, and there was very little neutral sugar. Proline was relatively high in amount, and isoleucine, half-cystine, methionine, leucine, tyrosine, and phenylalanine were absent or present to a very small extent. The material was weakly antigenic in the rabbit.

The molecular components of human transferrin type C

Immunologically pure human transferrin type C (TfC) was isolated from the plasmas of 11 individual healthy donors. After conversion into the 2Fe-form, the preparations were analysed by polyacrylamide gel electrophoresis and chromatography on DEAE-cellulose. In all samples studied by either method the presence of three components, designated A, B and C, was observed. Calculations from eight chromatograms yielded the following relative proportions for the components: A:6%, B:62% and C:32%. The quantity of iron bound played no role in this chromatographic resolution. The components were immunologically identical but their sialic acid content increased inthe order of A less than B less than C. The presence of galactose as an ultimate residue of the oligosaccharide chains in TfC component A was confirmed by a biological test. This observation together with the results of earlier analyses for hexose, hexosamine and galactose in the subfractions from Behringwerke human transferrin, suggests that sialic acid is probably the only variable among TfC components A, B and C. Loss of sialic acid from component C during the isolation of TfC was excluded as an explanation for the presence of the other two components. The electrophoretic appearance of TfC samples from five patients with liver disease (chronic active hepatitis, cirrhosis or alcoholic liver) did not noticeably differ from that of TfC FROM HEALTHY PERSONS. Baboon transferrin resembles TfC with respect to sialic acid heterogeneity. This species was therefore studied to decide whether sialic acid is gradually lost from transferrin in the circulation or whether transferrin is not fully sialylated before discharge from the hepatocyte. Using DEAE-cellulose chromatography no difference was found between baboon transferrin molecules which were less than 6h old and those which had a mean age of 8.9 days. By inference it is suggested that the reason for the multiplicity of TfC is also likely to be biosynthetic.

Chemical studies on a hamster sublingual glycoprotein

A secretory glycoprotein was isolated from the hamster sublingual gland. It contains 65% carbohydrates, the remainder being protein. The principal type of sialic acid was identified as N-acetylneuraminic acid with about 1/4 of the molecules O-acetylated. The hexosamine occurs mainly as N-acetylgalactosamine; other sugars present are galactose and fucose. The carbohydrate side chains are linked to the protein core by an O-glycosyl linkage between seryl and threonyl residues and N-acetylgalactosamine. The glycoprotein has an apparent molecular weight of 330,000. The sialogly coprotein may act as a biological antifreeze. Relevant differences in the chemical composition of the secretory glycoproteins of the sublingual and submaxillary salivary glands of this species are briefly discussed.

Some observations on the carbohydrate composition of purified transferrin

Five subfractions were isolated on DEAE-cellulose from samples of a commercially available human transferrin preparation and their carbohydrate composition was analysed. Hexosamine, galactose and total hexose were determined in four subfractions and sialic acid in all five. The data obtained indicate that the excess number of electrophoretic bands observed in transferrin from this source is due to the loss of carbohydrates which only affects sialic acid and none of the other sugar types. The availability of the penultimate galactose residues as the terminal residues in the subfractions deficient in sialic acid was also confirmed by a biological test utilizing the rat liver. The reason for the gradual loss of sialic acid from transferrin is unknown. Freezing-thawing and lyophilization did not detectably affect the sialic acid content of purified transferrin. However, free sialic acid did appear in some preparations on storage. It is concluded that similar changes in the carbohydrate composition of other plasma glycoproteins before, during, or after purification can be expected to exert an adverse effect on their usefulness as metabolic tracers.

Preliminary X-ray crystallographic and physico-chemical investigations of human ceruloplasmin

Single crystals of the plasma protein ceruloplasmin (CP) and its two modified forms: neuraminidase-treated CP (asialoCP) and NaN3-inhibited CP (NaN3-CP) suitable for X-ray studies have been grown. The native CP crystallizes as described previously by Magdoff-Fairchield et al. (1969) in the tetragonal space group 14 (a = b = 268.2 A, c = 129.1 A) with two protein molecules in the asymmetric part of a unit cell. AsialoCP crystals belong to the trigonal space group P 3(1)21 or P321 (a = b = 215.0 A, c = 84.5 A) and have one protein molecule in the asymmetric part of a unit cell. NaN3-CP crystals are isomorphous to crystals of native CP. Despite some differences in electrophoretic mobility and optical properties, the conformations of the native CP molecule and its modified forms are similar, as can be concluded from a study of ORD and CD spectra.

Derivatization of sialic acids for stabilization in matrix-assisted laser desorption/ionization mass spectrometry and concomitant differentiation of alpha(2 --> 3)- and alpha(2 --> 6)-isomers

Sialylated carbohydrates usually decompose by loss of sialic acid when ionized by matrix-assisted laser desorption/ionization (MALDI) as the result of the labile carboxylic proton. Stabilization has previously been achieved by forming methyl esters with methyl iodide, a procedure that eliminates the labile proton. In this paper, we describe an alternative procedure for methyl ester formation that provides information on the sialic acid linkage directly from the MALDI spectrum. The sugars were desalted, dissolved in methanol, and treated with 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM). After removal of the solvent, the products were transferred directly to the MALDI target and examined from 2,5-dihydroxybenzoic acid. Small amounts of N-glycans derived from biological sources benefited from an additional clean-up stage involving Nafion 117. alpha(2 --> 6)-Linked sialic acid produced only methyl esters whereas alpha(2 --> 3)-linked sialic acids were converted into their lactones providing a 32 Da difference in mass. Negative ion collision-induced decomposition (CID) mass spectra of these neutralized glycans provided information, in many cases, on the antenna of N-linked glycans to which the variously linked sialic acids were attached. The method was applied to N-linked glycans released from bovine fetuin and porcine thyroglobulin.

Asthma induction in mice leads to appearance of alpha2-3- and alpha2-6-linked sialic acid residues in respiratory goblet-like cells

Allergic asthmatic inflammation in mice was induced by sensitization with ovalbumin and lipopolysaccharide from Escherichia coli and visualized in the airways of asthmatic mice by spatial and temporal changes of carbohydrates containing sialic acid residues. Immunohistochemistry was used to demonstrate binding of lectins and antibodies that detect alpha2-3- and alpha2-6-linked sialic acid residues. After sensitization and challenge, the histology of the lung changed markedly, and goblet-like cells appeared, most likely caused by Clara cell metaplasia. Normal Clara cells showed no reaction after incubation with the sialic acid detecting agents, while the goblet-like cells expressed both alpha2-3- and alpha2-6-linked sialic acid residues in the asthmatic animals. The lectins but not the antibodies reacted with intestinal goblet cells. Instead, an antibody recognizing a disialoganglioside, stained large mononuclear cells in the submucosa, indicating a difference in sialylation between goblet cells in the intestine and goblet-like cells developed from Clara cells.

Chemical aspects of tracheal glycoproteins

The chemical characteristics of tracheal mucus obtained directly from the epithelial surface of the trachea indicate that the mucus from each animal source consists of a group of sulphated sialic acid-containing glycoproteins. Fractionation of the native glycoprotein from the cat by gel chromatography in the presence of urea and dithiothreitol suggests a value of about 3 X 10(6) for the molecular weights. The chief monosaccharide constituents are N-acetylneuraminic acid, N-acetylglucosamine, N-acetylgalactosamine, fucose and galactose. In the goose tracheal mucin, mannose is present (serum proteins being absent). Doubly labelled cat mucus, obtained by giving Na235SO4 and [3H]glucose simultaneously into the lumen of the trachea, is massively released by parasympathetic agents, e.g. pilocarpine. The resulting mucus has a high content of 35S and is derived largely from submucosal gland cells. Subsequent exposure to an irritant, ammonia, releases a low sulphation fraction, highly labelled with 3H, arising from goblet cells. Evidence supports the view that the overall mucus is composed of mixed secretions, chemically distinct, from different cellular synthesizing sites. Differential nervous stimulation of the various sites may cause far-reaching changes in the chemical and physical properties of the mucus by selective action on the secretion of one or more of the contributing glycoproteins.

Development of sensitive chemical and immunochemical methods for detecting sulfated sialic acids and their application to glycoconjugates from sea urchin sperm and eggs

Sulfated sialic acid (SiaS) is a unique sialic acid (Sia) derivative in which an additional anionic group is attached to a carboxylated monosaccharide. Very little is known about the occurrence and biologic function of SiaS, due to the limitations of analytical methods to detect it in minute amounts. In this study, to develop methods and probes for detecting and pursuing the functions of SiaS, we developed sensitive chemical and immunochemical detection methods. First, we synthesized as model compounds 4-methylumbelliferyl glycosides of 8-O- and 9-O-sulfated Sia consisting of N-acetylneuraminic acid (Neu5Ac), N-glycolylneuraminic acid (Neu5Gc), and deaminoneuraminic acid (Kdn). Second, we applied fluorometric high performance liquid chromatography (HPLC) analysis to these synthetic glycosides. After acid hydrolysis of the samples, the liberated SiaS were labeled with a fluorescent reagent, 1,2-diamino-4,5-methylenedioxybenzene, and analyzed on fluorometric HPLC. We established an optimal elution condition for successful separation of 8-O- and 9-O-sulfated Neu5Ac, Neu5Gc, and Kdn on HPLC. Third, we generated a monoclonal antibody (mAb) 2C4 against SiaS using sea urchin egg components as the immunogen. mAb.2C4 recognizes both 8-O-sulfated Neu5Ac (Neu5Ac8S) and Neu5Gc8S, whereas the previously prepared mAb.3G9 only recognizes Neu5Ac8S. Finally, using the fluorometric HPLC and monoclonal antibodies, we demonstrated that glycoconjugates from sea urchin sperm exclusively contained Neu5Ac8S, whereas those from eggs contained Neu5Gc8S. Furthermore, we clarified the quantitative differences in the SiaS content in eggs and sperm from two different species of sea urchins. Immunostaining using mAb.2C4 showed that Neu5Gc8S is localized in the cortical granules in unfertilized eggs, whereas it is localized in the outer surface of the fertilization layer as well as in the inner surface of fertilized eggs. Thus, 8-O-sulfation is dependent on the species, gametic cell-type, site-localization of the eggs, and glycoconjugates.

Thyroid gangliosides with high affinity for thyrotropin: potential role in thyroid regulation

Thyroid cell membranes contain a multiplicity of gangliosides, some of which inhibit thyrotropin binding to thyroid membranes. The most potent inhibitor is a ganglioside which is present in only trace amounts and appears to have a novel structure. Thyroid gangliosides may play a role in relaying the hormonal message to the thyroid cell.

Erythrocyte surface sialic acid levels of clinically healthy mongrel and exotic (alsatian and terrier) breeds of dogs

The erythrocyte surface sialic acid concentration of clinically healthy mongrel and exotic (Alsatian i.e. German shepherd and Terrier) breeds of dogs was analyzed in order to determine their role in the genetic resistance of these breeds of dogs to diseases that cause anaemia. The mean erythrocyte surface sialic acid (ESA) concentration was 57.08 +/- 1.67, 34.50 +/- 2.30 and 20.20 +/- 3.54 mg/dl for Mongrel, Alsatian (German shepherd) and Terrier breeds of dogs, respectively, on acid hydrolysis. The mean values of ESA obtained following enzymic hydrolysis of haemoglobin-free erythrocyte membranes using Clostridium chauvoei (Jakari strain) sialidase were 49.08 +/- 0.41, 30.97 +/- 1.82 and 18.64 +/- 0.75 mg/dl for Mongrel, Alsatian (German shepherd) and Terrier dogs respectively. When Trypanosoma vivax sialidase was used the ESA values obtained were 50.81 +/- 0.37, 41.70 +/- 0.94 and 19.65 + 0.65 mg/dl for Mongrel, Alsatian (German shepherd) and Terrier breeds of dogs respectively. This represents a statistically significant difference (P < 0.001) between the mean ESA concentration of all the breeds of dogs investigated in this study. The higher mean ESA concentration in Mongrel dogs, compared to the exotic breeds may be responsible for their resistance to disease conditions, whose aetiologic agents produce neuraminidase and also cause anaemia.

Derivatization for stabilizing sialic acids in MALDI-MS

While matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is useful in oligosaccharide analysis, the sialic acid, or N-acetylneuraminic acid (NANA), moiety of an oligosaccharide is liable to dissociation in- or postsource during mass measurement. In this study, we tried to stabilize the moiety by amidation, as in the case of peptides (Sekiya, S.; Wada, Y. Tanaka, K. Anal. Chem. 2004, 76, 5894-5902), and found 4-(4,6-dimethoxy-1,3,5-triazin-2yl)-4-methylmorpholinium chloride to be a desirable condensing agent. Amidation stabilized the glycosidic bond with NANA and suppressed its preferential cleavage by in-source decay, postsource decay, or collision-induced dissociation. In addition, the suppressed dissociation considerably improved the yield of the B/Y type ions for structural analysis by MS/MS. These results demonstrate that amidation is an effective derivatization to reinforce the structural analysis of sialylated oligosaccharides by MALDI-MS. In addition, amidation with (15)N-labeled ammonium chloride decreases the mass shift from the acid to amide form to just 0.013, reducing the complexity of mass spectral interpretation and database searching.

Reduced diversity of the human erythrocyte membrane sialic acids in polycythemia vera. Absence of N-glycolylneuraminic acid and characterisation of N-acetylneuraminic acid 1,7 lactone

Sialic acids from the erythrocyte (RBC) membrane of a patient suffering from polycythemia vera, a malignant orphan disorder of hematopoietic cells, was studied using GC/MS. We found that the sialic acid diversity of these membranes was drastically reduced since only four entities were identified: Neu5Ac (91.5%) and its 1,7 lactone Neu5Ac1,7L (7.5%) which is absent in normal RBC, Neu4,5Ac(2) (0.50%) and Neu4,5Ac(2) 9Lt (0.50%); in normal RBC, Neu5,7Ac(2), Neu5,9Ac(2), Neu5Ac9Lt, Neu5Ac8S and Neu, as well as traces of Kdn, were also present. Neu5Gc and its O-alkylated or O-acetylated derivatives, which are considered by various authors as cancer markers, were not detected.

Alpha2,6-linked sialic acid acts as a receptor for Feline calicivirus

Feline calicivirus (FCV) is a major causative agent of respiratory disease in cats. It is also one of the few cultivatable members of the family Caliciviridae. It has recently been reported that FCV binding is in part due to interaction with junction adhesion molecule-A. This report describes the characterization of additional receptor components for FCV. Chemical treatment of cells with sodium periodate showed that FCV recognized carbohydrate moieties on the surface of permissive cells. Enzymic treatment with Vibrio cholerae neuraminidase demonstrated that sialic acid was a major determinant of virus binding. Further characterization using linkage-specific lectins from Maackia amurensis and Sambucus nigra revealed that FCV recognized sialic acid with an alpha2,6 linkage. Using various proteases and metabolic inhibitors, it was shown that alpha2,6-linked sialic acid recognized by FCV is present on an N-linked glycoprotein.

Human neuroblasts migrate to the olfactory bulb via a lateral ventricular extension

The rostral migratory stream (RMS) is the main pathway by which newly born subventricular zone cells reach the olfactory bulb (OB) in rodents. However, the RMS in the adult human brain has been elusive. We demonstrate the presence of a human RMS, which is unexpectedly organized around a lateral ventricular extension reaching the OB, and illustrate the neuroblasts in it. The RMS ensheathing the lateral olfactory ventricular extension, as seen by magnetic resonance imaging, cell-specific markers, and electron microscopy, contains progenitor cells with migratory characteristics and cells that incorporate 5-bromo-2'-deoxyuridine and become mature neurons in the OB.

Structural analysis of naturally occurring sialic acids

Over the years several methodologies have been developed for the structural analysis of naturally occurring sialic acids (Sias), a family with more than 62 members. Currently there are two primary instrumental approaches: analysis of volatile Sia derivatives by gas-liquid chromatography (GLC) combined with electron-impact mass spectrometry (EI/MS), and analysis of fluorescently labeled Sias by high-performance liquid chromatography (HPLC) eventually coupled with electrospray mass spectrometry (ESI/MS). This chapter presents both approaches in detail. The volatile Sia derivatives are comprised of trimethylsilylated methyl ester derivatives, heptafluorobutylated methyl ester derivatives, or pertrimethylsilylated derivatives. The fluorescent Sia derivatives are prepared by reaction with 1,2-diamino-4,5-methylenedioxybenzene. For the identification of the different Sia derivatives, detailed GLC, HPLC, EI/MS, and ESI/MS data are included.

Diversity in cell surface sialic acid presentations: implications for biology and disease

Sialic acids (Sias) are typically found as terminal monosaccharides attached to cell surface glycoconjugates. They play many important roles in many physiological and pathological processes, including microbe binding that leads to infections, regulation of the immune response, the progression and spread of human malignancies and in certain aspects of human evolution. This review will provide some examples of these diverse roles of Sias and briefly address immunohistochemical approaches to their detection.

Structure of the O-antigen of Providencia stuartii O20, a new polysaccharide containing 5,7-diacetamido-3,5,7,9-tetradeoxy-l-glycero-d-galacto-non-2-ulosonic acid

The O-polysaccharide chain of the lipopolysaccharide (LPS) of Providencia stuartii O20 was found to contain d-glucuronic acid, N-acetyl-d-glucosamine, and a rarely occurring higher sugar 5,7-diacetamido-3,5,7,9-tetradeoxy-l-glycero-d-galacto-non-2-ulosonic acid (di-N-acetyl-8-epilegionaminic acid, 8eLeg5Ac7Ac). Degradation of the LPS with dilute acetic acid caused depolymerization of the polysaccharide chain by the ketosidic linkage to give a tetrasaccharide corresponding to the repeating unit of the polysaccharide. Based on sugar and methylation analyses of the tetrasaccharide and O-deacylated LPS as well as ESIMS, (1)H and (13)C NMR spectroscopy data, the structure of the O-polysaccharide of P. stuartii O20 was established.