Characterization of glycosphingolipids by direct inlet chemical ionization mass spectrometry

Structural determination of glucosylceramides in the distillation remnants of shochu, the Japanese traditional liquor, and its production by Aspergillus kawachii

Shochu is traditional Japanese liquor produced from various crops and fungi Aspergillus kawachi or A. awamorii . The amount of unutilized shochu distillation remnants is increasing because of the recent prohibition of ocean dumping of these remnants. In this Article, we first describe the structures of glucosylceramides contained in shochu distillation remnants by fragment ion analysis using ESI-tandem mass spectrometry. Shochu distillation remnant produced from barley contained glucosylceramides d18:2/C16:0h, d18:2/C20:0h, d19:2/C18:1h, and d18:2/C18:0h. Koji (barley fermented with A. kawachii) contained the same glucosylceramides. Shochu distillation remnants produced from rice contained glucosylceramides d18:2/C18:0h and d19:2/C18:1h. The culture broth of A. kawachii contained glucosylceramides d19:2/C18:1h and d19:2/C18:0h. These results indicate that the glucosylceramides contained in crops and those produced by A. kawachii transfer through the processes of fermentation with yeast and distillation to the shochu distillation remnant. This information will enable utilization of shochu distillation remnants and koji as novel sources of sphingolipids.

Structural determination of glucosylceramides isolated from marine sponge by fast atom bombardment collision-induced dissociation linked scan at constant B/E

Five glucosylceramides (GlcCers) were isolated by reversed phase high-performance liquid chromatography from the MeOH extracts of a marine sponge, Haliclona (Reniera) sp., collected from the coast of Ulleung Island, Korea, and analyzed by fast atom bombardment mass spectrometry (FAB-MS) in positive-ion mode. FAB-mass spectra of these compounds included protonated molecules [M + H](+) and abundant sodiated molecules [M + Na](+) from a mixture of m-NBA and NaI. The structures of these GlcCers, which were similar, were elucidated by FAB-linked scan at constant B/E. To find diagnostic ions for their characterization, the GlcCers were analyzed by collision-induced dissociation (CID) linked scan at constant B/E. The CID-linked scan at constant B/E of [M + H](+) and [M + Na](+) precursor ions resulted in the formation of numerous characteristic product ions via a series of dissociative processes. The product ions formed by charge-remote fragmentation provided important information for the characterization of the fatty N-acyl chain moiety and the sphingoid base, commonly referred to as the long-chain base. The product ions at m/z 203 and 502 were diagnostic for the presence of a sodiated sugar ring and beta-D-glucosylsphinganine, respectively. For further confirmation of the structure of the fatty N-acyl chain moiety in each GlcCer, fatty acid methyl esters were obtained from the five GlcCers by methanolysis and analyzed by FAB-MS in positive-ion mode. On the basis of these dissociation patterns, the structures of the five GlcCers from marine sponge were elucidated. In addition, the accurate mass measurement was performed to obtain the elemental composition of the GlcCers isolated from marine sponge.

Sphingolipidomics: methods for the comprehensive analysis of sphingolipids

Sphingolipids comprise a highly diverse and complex class of molecules that serve as both structural components of cellular membranes and signaling molecules capable of eliciting apoptosis, differentiation, chemotaxis, and other responses in mammalian cells. Comprehensive or "sphingolipidomic" analyses (structure specific, quantitative analyses of all sphingolipids, or at least all members of a critical subset) are required in order to elucidate the role(s) of sphingolipids in a given biological context because so many of the sphingolipids in a biological system are inter-converted structurally and metabolically. Despite the experimental challenges posed by the diversity of sphingolipid-regulated cellular responses, the detection and quantitation of multiple sphingolipids in a single sample has been made possible by combining classical analytical separation techniques such as high-performance liquid chromatography (HPLC) with state-of-the-art tandem mass spectrometry (MS/MS) techniques. As part of the Lipid MAPS consortium an internal standard cocktail was developed that comprises the signaling metabolites (i.e. sphingoid bases, sphingoid base-1-phosphates, ceramides, and ceramide-1-phosphates) as well as more complex species such as mono- and di-hexosylceramides and sphingomyelin. Additionally, the number of species that can be analyzed is growing rapidly with the addition of fatty acyl Co-As, sulfatides, and other complex sphingolipids as more internal standards are becoming available. The resulting LC-MS/MS analyses are one of the most analytically rigorous technologies that can provide the necessary sensitivity, structural specificity, and quantitative precision with high-throughput for "sphingolipidomic" analyses in small sample quantities. This review summarizes historical and state-of-the-art analytical techniques used for the identification, structure determination, and quantitation of sphingolipids from free sphingoid bases through more complex sphingolipids such as sphingomyelins, lactosylceramides, and sulfatides including those intermediates currently considered sphingolipid "second messengers". Also discussed are some emerging techniques and other issues remaining to be resolved for the analysis of the full sphingolipidome.

The total syntheses of D-erythro-sphingosine, N-palmitoylsphingosine (ceramide), and glucosylceramide (cerebroside) via an azidosphingosine analog

The total synthesis of D-erythro-sphingosine (9) was performed by a chirospecific method starting from D-galactose via an azidosphingosine intermediate to give highly homogeneous (>99.9% C18:1) sphingosine base (9) which contained no observable olefin isomerization by product and was demonstrated to be optically pure by a novel method utilizing Mosher's acid. Ceramide (10) was prepared from this sphingosine (9) with highly homogeneous (99.8% C16:0) palmitic acid by two methods. The cerebroside glucosylceramide (23) was the next sphingolipid in this series to be synthesized in a highly homogeneous form. These three sphingolipids are currently being used for biophysical studies of the structures of their hydrated bio-molecular assemblies.

Electrospray ionization tandem mass spectrometric analysis of sulfatide. Determination of fragmentation patterns and characterization of molecular species expressed in brain and in pancreatic islets

The sphingolipid sulfatide is a component of myelin and some non-neuronal cells. Antibodies to sulfatide occur in some patients with autoimmune neuropathies and in patients with insulin-dependent diabetes mellitus (IDDM) caused by immunologic destruction of insulin-secreting pancreatic islet beta-cells. Distinct sulfatide molecular species may differ in immunogenicity, and facile means to identify sulfatide species in islets and other tissues obtainable in only small amounts could be useful. Electrospray ionization mass spectrometry (ESI/MS) permits structural determination of small quantities of phospholipids and is applied here to sulfatide analysis. We find that sulfatide standards are readily analyzed by negative ion ESI/MS, and tandem mass spectra of individual species exhibit some ions common to all species and other ions that reflect distinct fatty acid substituents in different sulfatide molecules. A signature ion cluster resulting from cleavage directed by the alpha-hydroxy group of sulfatide species with a hydroxylated fatty acid substituent identifies such species. Sulfatide profiles in tissue lipid extracts can be obtained by ESI/MS/MS scanning for common sulfatide ions and for ions reflecting fatty acid substituents. Islets are demonstrated to contain sulfatide and to exhibit a profile of species different from that of brain.

Expression and localization of Lewis(x) glycolipids and GD1a ganglioside in human glioma cells

We analysed the glycolipid composition of glioma cells (N-370 FG cells), which are derived from a culture of transformed human fetal glial cells. The neutral and acidic glycolipid fractions were isolated by column chromatography on DEAE-Sephadex and analysed by high-performance thin-layer chromatography (HPTLC). The neutral glycolipid fraction contained 1.6 micrograms of lipid-bound glucose/galactose per mg protein and consisted of GlcCer (11.4% of total neutral glycolipids), GalCer (21.5%), LacCer (21.4%), Gb4 (21.1%), and three unknown neutral glycolipids (23%). These unknown glycolipids were characterized as Lewis(x) (fucosylneolactonorpentaosyl ceramide; Le(x)), difucosylneolactonorhexaosyl ceramide (dimeric Le(x)), and neolactonorhexaosyl ceramide (nLc6) by an HPTLC-overlay method for glycolipids using specific mouse anti-glycolipid antibodies against glycolipid and/or liquid-secondary ion (LSI) mass spectrometry. The ganglioside fraction contained 0.6 micrograms of lipid-bound sialic acid per mg protein with GD1a as the predominant ganglioside species (83% of the total gangliosides) and GM3, GM2, and GM1 as minor components. Trace amounts of sialyl-Le(x) and the complex type of sialyl-Le(x) derivatives were also present. Immunocytochemical studies revealed that GD1a and GalCer were primarily localized on the surface of cell bodies. Interestingly, Le(x) glycolipids and sialyl-Le(x) were localized not only on the cell bodies but also on short cell processes. Especially, sialyl-Le(x) glycolipid was located on the tip of fine cellular processes. The unique localization of the Le(x) glycolipids suggests that they may be involved in cellular differentiation and initiation of cellular growth in this cell line.

Accumulation of isogloboside and ganglio-N-tetraosyl ceramide having blood group B determinant in the hepatomas of female LEC rats

We have studied the neutral glycolipid composition of spontaneous hepatomas in LEC female rats. Neutral lipid fractions were isolated and purified by column chromatographies on DEAE-Toyopearl 650(M) and Iatrobeads. The neutral glycolipid fraction contained 3.2 to 4.4 micrograms lipid-bound glucose (Glc) per mg protein, and consisted of isogloboside (iso-Gb4, 50.8% of total neutral glycolipids) and IV3Gal, IV2Fuc, GgOse4Cer (asialo-BGM1, 13.5%) as the major neutral glycolipids and Gb3 and iso-Gb3 (9.2%), GlcCer (7.2%), LacCer (6.1%) as the other species. The structure of iso-Gb4 was elucidated by gas-liquid chromatography (GLC), permethylation study, liquid secondary ion (LSI) mass spectrometry, and nuclear Overhauser enhancement spectroscopy (NOESY) and that for asialo-BGM1 by GLC, LSI mass spectrometry, and high-performance thin-layer chromatography (HPTLC)-overlay method using anti-asialo-BGM1 antibody. Isogloboside and asialo-BGM1 which are found in negligible amounts in normal liver tissues may represent excellent markers for studying tumor metastasis and cellular adhesion.

Differential Effects of Glycosphingolipids n Protein Kinase C Activity in PC12D Pheochromocytoma Cells

Previous studies have shown that certain glycosphingolipids may function as modulators of protein kinase C (PKC) activity. To study the structure-activity relationship, we examined the effects of 17 gangliosides, 10 neutral glycolipids, as well as sulfatide, psychosine and ceramide on PKC activity in PC12D cells. Using an in vitro assay system, we found that all but one (GQ1b) ganglioside inhibited PKC activity at concentrations between 25 and 100 &mgr;M, and the potency was proportional to the number of sialic acid residues. However, at lower concentrations several gangliosides, including GM1 and LM1 behaved as mild activators of PKC activity. GQ1b had no effect within the range 0.1-10 &mgr;M, but acted as a mild activator of PKC activity at 25 &mgr;M. On the other hand, fucosyl-GM1 and GM1 containing blood group B determinant, which are abundant in PC12 cells, were potent inhibitors of PKC activity. Among the neutral glycosphingolipids tested, LacCer, Gb3, GalGb3, and GA1, all of which have a terminal galactose residue, were found to be ineffective or acted as mild activators of PKC activity. In contrast, GA2, Gb4 and Gb5 which have a terminal N-acetylgalactosamine residue, were potent inhibitors of the PKC activity. Thus, the terminal sugar residue may play a pivotal role in determining the effect of glycosphingolipids in modulating PKC activity. In addition, we also found that GalCer containing normal fatty acids acted as potent activators of PKC activity. Ceramide and GlcCer appeared to be ineffective in modulating PKC activity, wheras psychosine and sulfatides appeared to be inhibitory. We conclude that the carbohydrate head groups and the hydrophobic groups of gangliosides and neutral glycolipids may modulate the PKC system in unique manners, which may in turn affect various biological processes in the cell. Copyright 1994 S. Karger AG, Basel

Neutral glycolipid abnormalities in a t-complex mutant mouse embryo

The content of neutral glycolipids was studied in normal and twl/twl mutant mouse embryos at embryonic day 11 (E-11). The twl mutation is part of the T/t complex on chromosome 17 and causes embryonic lethality from defects in the developing neural tube. Previous studies suggested that the mutation could involve a defect in ganglioside biosynthesis. Although the total neutral glycolipid content was similar in the normal and mutant whole embryos (approximately 80 nmol glucose/100 mg dry weight), marked differences were detected for the distribution of specific glycolipids. The content of lactosylceramide, globotriaosylceramide, and globotetraosylceramide was significantly higher in the mutant than in the normal embryos, whereas that of glucosylceramide was significantly reduced. The Forssman glycolipid was slightly elevated. The neutral glycolipid composition was similar in embryonic head and body regions of normal embryos, suggesting that the glycolipid abnormalities observed in the mutants are expressed in most embryonic cells and tissues. These and the previously reported ganglioside abnormalities in the twl/twl mutants could result from an inherited defect in glycolipid biosynthesis.

Autoantibodies against Forssman glycolipids in Graves' disease and Hashimoto's thyroiditis

Sera from patients with Graves' disease and Hashimoto's thyroiditis have been shown to react with the Forssman glycolipid antigen (Gb5) using the techniques of high performance thin-layer chromatography (HPTLC) immunostaining and ELISA. Human monoclonal antibodies (MoAbs) have been prepared by fusion of human myeloma with peripheral lymphocytes from patients with Graves' disease. A MoAb, TRMo-4, reacted strongly and specifically with Gb5. These results suggest that anti-Forssman antibody may be involved in the pathogenesis of these autoimmune diseases. The detection of anti-Forssman glycolipid antibody may provide a useful means for clinical diagnosis and therapy.

Glycolipid changes in murine myelogenous leukemias: neutral glycolipids as markers for specific populations of leukemias

We have studied the glycolipid composition of six different murine myelogenous leukemias as well as that of T-cell leukemias and normal spleen cells. Neutral and acidic lipid fractions were isolated by column chromatography on DEAE-Sephadex and analyzed by high-performance thin-layer chromatography (HPTLC) and an HPTLC overlay method. Murine myelogenous leukemias were found to contain globo- and ganglio-series neutral glycolipids, e.g., glucosylceramide (Glc-cer), lactosylceramide (Lac-cer), globotriaosylceramide (Gb3), globoside (Gb4), Forssman glycolipid (Gb5), and asialo-GM1 (GA1). Monoblastic leukemia cells contained increased proportions of Gb3, Gb4, Gb5, and GA1. Monocytic and myelomonocytic leukemia cells contained increased proportions of Glc-cer and Lac-cer. Especially, Glc-cer accounted for approximately 60% of the total neutral glycolipids in monocytic leukemia cells. Gb3 was the major neutral glycolipid in reticulum cell neoplasm type A, and it accounted for approximately 75% of the neutral glycolipids. GA1 was the major neutral glycolipid in myeloblastic and granulocytic leukemia cells as well as T-cell leukemias. Especially, granulocytic leukemia cells contained predominantly GA1, and it accounted for approximately 80% of the total neutral glycolipids. The pattern of gangliosides in myelogenous leukemias was more complex when compared with that of the neutral glycolipids; murine myelogenous leukemias contained at least 13 gangliosides, including such major gangliosides as GM1, GM1b containing N-acetyl neuraminic acid and N-glycolyl neuraminic acid, and Ga1NAc-GM1b. Alterations of glycolipid composition in murine myeloid leukemias may be associated with cellular differentiation and maturation, and therefore these characteristic glycolipid species may be regarded as markers for specific populations of leukemia cells.

Purification and characterization of CMP-NeuAc:GM1 (Gal beta 1-4GalNAc) alpha 2-3 sialyltransferase from rat brain

A CMP-NeuAc:GM1 alpha 2-3 sialyltransferase (GD1a synthase, 2.4.99.2) has been purified from the Triton extract of rat brain. The enzyme was purified and resolved by affinity chromatography on CDP-Sepharose column by a linear NaCl gradient elution. Final purification was achieved by elution from a 'GM1-acid'-Sepharose column. SDS-PAGE of the enzyme revealed a single protein band with an apparent Mr 44 kDa. It catalyzed specifically the sialylation of GD1b, GM1 and asialo-GM1. Enzyme products were identified by TLC in three different solvent systems. The Km value for GM1 was 7.5 x 10(-2) M, and for CMP-NeuAc it was 6.5 x 10(-5) M.

Analysis of native neutral glycosphingolipids by combined high performance liquid chromatography/mass spectrometry

Conditions for normal phase high performance liquid chromatography-chemical ionization mass spectrometry of underivatized glycosphingolipids with the use of a moving belt transport interface were investigated. Chromatography was performed on a 2 mm ID X 3 cm column packed with 5 micron spherical silica. A gradient of increasing methanol and water in methylene chloride was used to resolve mono-, di-, tri-, and tetraglycosylceramides and sulfatides in less than 15 min. A polyimide belt was used to transport the sample residues to the mass spectrometer where ammonia chemical ionization mass spectrometry was used to obtain spectra. One to 5 micrograms of each component was sufficient to obtain full spectral scans. Mono- and dihexosylceramide spectra showed [M + H]+ ions of good abundance, while the higher glycosphingolipids have molecular weights that exceed the range of the mass spectrometer utilized. All glycosphingolipids gave ions characteristic of their ceramide, fatty acid, long chain base and carbohydrate components. Sequence information which reflected the relative position of hexose and N-acetylhexosamine residues was also obtained.

Enhancement of structural information in FAB ionized carbohydrate samples by neutral gas collision

Fast atom bombardment (FAB) ionization and two coupled analyzers (BE-EB) have been combined with neutral gas collision (C) to enhance structural information in the mass spectra of oligosaccharides. (B and E are abbreviations for magnetic and electric sectors respectively.) FAB ionization and the first analysers (BE) have provided parent ions free from biological and liquid matrix contaminants. Structural detail of these products were observed after collision and daughter ion analysis in a second coupled analyser (EB). Starting from complex mixtures, this instrumental approach, BE-C-EB, has provided specific oligomeric sequence information which was not observed in the normal FAB mass spectra. Collision spectra obtained from isomeric linear and branched oligosaccharides show unique fragments that can be directly related to structure.

Structural characterization of glycosphingolipids by direct chemical ionization mass spectrometry

This report describes the use of direct chemical ionization mass spectrometry with ammonia as the reagent gas (NH3-DCI) for structure analysis of underivatized, permethylated and permethylated and reduced glycosphingolipids. In contrast to ionization by electron impact, the NH3-DCI mass spectra exhibit intense molecular and carbohydrate sequence-related ions using microgram amounts of sample. Underivatized glycosphingolipids with up to two sugar residues yield abundant protonated and ammonia-cationized molecular ions and structurally significant fragments. Permethylation in conjunction with NH3-DCI can be used to obtain molecular weight as well as oligosaccharide sequence and branching information on neutral, acidic and complex-type glycosphingolipids with up to five sugar residues. Reduction of the permethylated derivatives gives rise to several new, structurally significant fragments in the corresponding NH3-DCI mass spectra which enable fatty acid and base compositions to be determined. Isotopically labeled reagent gases have been used to confirm the assignment of fragment structures and to demonstrate that the ions observed are unique to the NH3-DCI mass spectra.

Chemical-ionization mass spectra of the permethylated sialo-oligosaccharides liberated from gangliosides

Permethylated mono- and di-sialo-oligosaccharides liberated from several parent gangliosides have been examined by chemical-ionization mass spectrometry with ammonia as the reagent gas in order to elucidate their structures. Several major fragment-ions, in addition to both the protonated and ammonium adduct molecular-ions, may be readily assigned without interference from the ceramide moiety. Sialic acid-containing di-, tri-, and tetra-saccharide ions can be clearly observed and used to determine the sugar residue to which the sialic acid residue is attached. The neutral-sugar skeletons produced by the loss of sialic acid give rise to both the protonated and the ammonium adduct ions; in the case of tetrasaccharides, these are further degraded to produce di- and tri-saccharide ions. These characteristic ions are useful for the determination of the number of sugar residues and their sequence in an oligosaccharide structure. The chemical-ionization mass spectra of GM3- and GM1-oligosaccharides with isobutane show the ions corresponding to each monosaccharide residue. These results indicate that chemical-ionization mass spectrometry is highly useful in determining the complete sugar-sequence of gangliosides.