O-acetylated gangliosides in bovine buttermilk. Characterization of 7-O-acetyl, 9-O-acetyl, and 7,9-di-O-acetyl GD3

Gangliosides in neural stem cell fate determination and nerve cell specification--preparation and administration

Gangliosides are sialylated glycosphingolipids with essential but enigmatic functions in healthy and disease brains. GD3 is the predominant species in neural stem cells (NSCs) and GD3-synthase (sialyltransferase II; St8Sia1) knockout (GD3S-KO) revealed reduction of postnatal NSC pools with severe behavioral deficits including cognitive impairment, depression-like phenotypes, and olfactory dysfunction. Exogenous administration of GD3 significantly restored the NSC pools and enhanced the stemness of NSCs with multipotency and self-renewal, followed by restored neuronal functions. Our group discovered that GD3 is involved in the maintenance of NSC fate determination by interacting with epidermal growth factor receptors (EGFRs), by modulating expression of cyclin-dependent kinase (CDK) inhibitors p27 and p21, and by regulating mitochondrial dynamics via associating a mitochondrial fission protein, the dynamin-related protein-1 (Drp1). Furthermore, we discovered that nuclear GM1 promotes neuronal differentiation by an epigenetic regulatory mechanism. GM1 binds with acetylated histones on the promoter of N-acetylgalactosaminyltransferase (GalNAcT; GM2 synthase (GM2S); B4galnt1) as well as on the NeuroD1 in differentiated neurons. In addition, epigenetic activation of the GM2S gene was detected as accompanied by an apparent induction of neuronal differentiation in NSCs responding to an exogenous supplement of GM1. Interestingly, GM1 induced epigenetic activation of the tyrosine hydroxylase (TH) gene, with recruitment of Nurr1 and PITX3, dopaminergic neuron-associated transcription factors, to the TH promoter region. In this way, GM1 epigenetically regulates dopaminergic neuron specific gene expression, and it would modify Parkinson's disease. Multifunctional gangliosides significantly modulate lipid microdomains to regulate functions of important molecules on multiple sites: the plasma membrane, mitochondrial membrane, and nuclear membrane. Versatile gangliosides regulate functional neurons as well as sustain NSC functions via modulating protein and gene activities on ganglioside microdomains. Maintaining proper ganglioside microdomains benefits healthy neuronal development and millions of senior citizens with neurodegenerative diseases. Here, we introduce how to isolate GD3 and GM1 and how to administer them into the mouse brain to investigate their functions on NSC fate determination and nerve cell specification.

9-O Acetylated Gangliosides in Health and Disease

Glycosphingolipids comprise a lipid class characterized by the presence of sugar moieties attached to a ceramide backbone. The role of glycosphingolipids in pathophysiology has gained relevance in recent years in parallel with the development of analytical technologies. Within this vast family of molecules, gangliosides modified by acetylation represent a minority. Described for the first time in the 1980s, their relation to pathologies has resulted in increased interest in their function in normal and diseased cells. This review presents the state of the art on 9-O acetylated gangliosides and their link to cellular disorders.

Restoration of Adult Neurogenesis by Intranasal Administration of Gangliosides GD3 and GM1 in The Olfactory Bulb of A53T Alpha-Synuclein-Expressing Parkinson's-Disease Model Mice

Parkinson's disease (PD) is the second most common neurodegenerative disorder affecting the body and mind of millions of people in the world. As PD progresses, bradykinesia, rigidity, and tremor worsen. These motor symptoms are associated with the neurodegeneration of dopaminergic neurons in the substantia nigra. PD is also associated with non-motor symptoms, including loss of smell (hyposmia), sleep disturbances, depression, anxiety, and cognitive impairment. This broad spectrum of non-motor symptoms is in part due to olfactory and hippocampal dysfunctions. These non-motor functions are suggested to be linked with adult neurogenesis. We have reported that ganglioside GD3 is required to maintain the neural stem cell (NSC) pool in the subventricular zone (SVZ) of the lateral ventricles and the subgranular layer of the dentate gyrus (DG) in the hippocampus. In this study, we used nasal infusion of GD3 to restore impaired neurogenesis in A53T alpha-synuclein-expressing mice (A53T mice). Intriguingly, intranasal GD3 administration rescued the number of bromodeoxyuridine + (BrdU +)/Sox2 + NSCs in the SVZ. Furthermore, the administration of gangliosides GD3 and GM1 increases doublecortin (DCX)-expressing immature neurons in the olfactory bulb, and nasal ganglioside administration recovered the neuronal populations in the periglomerular layer of A53T mice. Given the relevance of decreased ganglioside on olfactory impairment, we discovered that GD3 has an essential role in olfactory functions. Our results demonstrated that intranasal GD3 infusion restored the self-renewal ability of the NSCs, and intranasal GM1 infusion promoted neurogenesis in the adult brain. Using a combination of GD3 and GM1 has the potential to slow down disease progression and rescue dysfunctional neurons in neurodegenerative brains.

Milk polar lipids composition and functionality: a systematic review

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

The Structural Diversity of Natural Glycosphingolipids (GSLs)

Glycosphingolipids (GSLs) are a subclass of glycolipids made of a glycan and a ceramide that, in turn, is composed of a sphingoid base moiety and a fatty acyl group. GSLs represent the vast majority of glycolipids in eukaryotes, and as an essential component of the cell membrane, they play an important role in many biological and pathological processes. Therefore, they are useful targets for the development of novel diagnostic and therapeutic methods for human diseases. Since sphingosine was first described by J. L. Thudichum in 1884, several hundred GSL species, not including their diverse lipid forms that can further amplify the number of individual GSLs by many folds, have been isolated from natural sources and structurally characterized. This review tries to provide a comprehensive survey of the major GSL species, especially those with distinct glycan structures and modification patterns, and the ceramides with unique modifications of the lipid chains, that have been discovered to date. In particular, this review is focused on GSLs from eukaryotic species. This review has listed 251 GSL glycans with different linkages, 127 glycans with unique modifications, 46 sphingoids, and 43 fatty acyl groups. It should be helpful for scientists who are interested in GSLs, from isolation and structural analyses to chemical and enzymatic syntheses, as well as their biological studies and applications.

Intranasal infusion of GD3 and GM1 gangliosides downregulates alpha-synuclein and controls tyrosine hydroxylase gene in a PD model mouse

Parkinson's disease (PD) is characterized by Lewy bodies (composed predominantly of alpha-synuclein [aSyn]) and loss of pigmented midbrain dopaminergic neurons comprising the nigrostriatal pathway. Most PD patients show significant deficiency of gangliosides, including GM1, in the brain, and GM1 ganglioside appears to keep dopaminergic neurons functioning properly. Thus, supplementation of GM1 could potentially provide some rescuing effects. In this study, we demonstrate that intranasal infusion of GD3 and GM1 gangliosides reduces intracellular aSyn levels. GM1 also significantly enhances expression of tyrosine hydroxylase (TH) in the substantia nigra pars compacta of the A53T aSyn overexpressing mouse, following restored nuclear expression of nuclear receptor related 1 (Nurr1, also known as NR4A2), an essential transcription factor for differentiation, maturation, and maintenance of midbrain dopaminergic neurons. GM1 induces epigenetic activation of the TH gene, including augmentation of acetylated histones and recruitment of Nurr1 to the TH promoter region. Our data indicate that intranasal administration of gangliosides could reduce neurotoxic proteins and restore functional neurons via modulating chromatin status by nuclear gangliosides.

Ganglioside isomer analysis using ion polarity switching liquid chromatography-tandem mass spectrometry

Gangliosides are ubiquitously present on cell surface. They are more abundantly expressed in nerve cells and tissues and involved in pathology of various diseases. Diversity of molecular structures in the carbohydrate head group, fatty acyl, and long chain base increases the complexity of analyzing gangliosides. In this study, an ultrahigh-performance liquid chromatography-tandem mass spectrometry method is developed for analysis of the co-eluting ganglioside isomers, which uses ion polarity switching to integrate glycan head isomer identification, ceramide isomer differentiation, and quantification of ganglioside into one analysis. The method is facilitated with an extensive ganglioside target list by combining the various glycan head groups, long chain bases, and the experimentally determined fatty acyls. Correlation between the retention time of ganglioside and its ceramide total carbon number is experimentally validated and used to predict retention time of ganglioside target list for scheduling the final multiple reaction monitoring method. This method was validated according to the FDA guidelines: 96.5% of gangliosides with good accuracy (80-120%), precision (< 15%), and linearity R² > 0.99. The authenticated gangliosides were quantified from mouse brain by isotope dilution. Overall, 165 gangliosides were quantified using 10 mg mouse brain tissue, including 100 isomers of GM1, GM2, GM3, GD1a, GD1b, GD2, GD3, and GT1b.

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

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

Intracerebroventricular Infusion of Gangliosides Augments the Adult Neural Stem Cell Pool in Mouse Brain

We previously reported that ganglioside GD3 is the predominant species in neural stem cells (NSCs) and reduced postnatal NSC pools are observed in both the subventricular zone and dentate gyrus (DG) of GD3-synthase knockout (GD3S-KO) mouse brains. Specifically, deficiency of GD3 in GD3S-KO animals revealed a dramatic reduction in cellularity in the DG of the hippocampus of the developing mouse brain, resulting in severe behavioral deficits in these animals. To further evaluate the functional role of GD3 in postnatal brain, we performed rescue experiments by intracerebroventricular infusion of ganglioside GD3 in adult GD3S-KO animals and found that it could restore the NSC pools and enhance the NSCs for self-renewal. Furthermore, 5xFAD mouse model was utilized, and GD3 restored NSC numbers and GM1 promoted neuronal differentiation. Our results thus demonstrate that exogenously administered gangliosides are capable to restore the function of postnatal NSCs. Since ganglioside expression profiles are associated not only with normal brain development but also with pathogenic mechanisms of diseases, such as Alzheimer’s disease, we anticipate that the administration of exogenous gangliosides, such as GD3 and GM1, may represent a novel and effective strategy for promoting adult neurogenesis in damaged brain for disease treatment.

Exploration of the Sialic Acid World

Sialic acids are cytoprotectors, mainly localized on the surface of cell membranes with multiple and outstanding cell biological functions. The history of their structural analysis, occurrence, and functions is fascinating and described in this review. Reports from different researchers on apparently similar substances from a variety of biological materials led to the identification of a 9-carbon monosaccharide, which in 1957 was designated "sialic acid." The most frequently occurring member of the sialic acid family is N-acetylneuraminic acid, followed by N-glycolylneuraminic acid and O-acetylated derivatives, and up to now over about 80 neuraminic acid derivatives have been described. They appeared first in the animal kingdom, ranging from echinoderms up to higher animals, in many microorganisms, and are also expressed in insects, but are absent in higher plants. Sialic acids are masks and ligands and play as such dual roles in biology. Their involvement in immunology and tumor biology, as well as in hereditary diseases, cannot be underestimated. N-Glycolylneuraminic acid is very special, as this sugar cannot be expressed by humans, but is a xenoantigen with pathogenetic potential. Sialidases (neuraminidases), which liberate sialic acids from cellular compounds, had been known from very early on from studies with influenza viruses. Sialyltransferases, which are responsible for the sialylation of glycans and elongation of polysialic acids, are studied because of their significance in development and, for instance, in cancer. As more information about the functions in health and disease is acquired, the use of sialic acids in the treatment of diseases is also envisaged.

Effects of amyloid β-peptides and gangliosides on mouse neural stem cells

The interaction of amyloid β-proteins (Aβs) with membrane lipids has been postulated as an early event in Aβ fibril formation in Alzheimer's disease. We evaluated the effects of several putative bioactive Aβs and gangliosides on neural stem cells (NSCs) isolated from embryonic mouse brains or the subventricular zone of adult mouse brains. Incubation of the isolated NSCs with soluble Aβ1-40 alone did not cause any change in the number of NSCs, but soluble Aβ1-42 increased their number. Aggregated Aβ1-40 and Aβ1-42 increased the number of NSCs but soluble and aggregated Aβ25-35 decreased the number. Soluble Aβ1-40 and Aβ1-42 did not affect the number of apoptotic cells but aggregated Aβ1-40 and Aβ1-42 did. When NSCs were treated with a combination of GM1 or GD3 and soluble Aβ1-42, cell proliferation was enhanced, indicating that both GM1 and GD3 as well as Aβs are involved in promoting cell proliferation and survival of NSCs. These observations suggest the potential of beneficial effects of using gangliosides and Aβs for promoting NSC proliferation.

Brain gangliosides of a transgenic mouse model of Alzheimer's disease with deficiency in GD3-synthase: expression of elevated levels of a cholinergic-specific ganglioside, GT1aα

In order to examine the potential involvement of gangliosides in AD (Alzheimer's disease), we compared the ganglioside compositions of the brains of a double-transgenic (Tg) mouse model [APP (amyloid precursor protein)/PSEN1 (presenilin)] of AD and a triple mutant mouse model with an additional deletion of the GD3S (GD3-synthase) gene (APP/PSEN1/GD3S(-/-)). These animals were chosen since it was previously reported that APP/PSEN1/GD3S(-/-) triple-mutant mice performed as well as WT (wild-type) control and GD3S(-/-) mice on a number of reference memory tasks. Cholinergic neuron-specific gangliosides, such as GT1aα and GQ1bα, were elevated in the brains of double-Tg mice (APP/PSEN1), as compared with those of WT mice. Remarkably, in the triple mutant mouse brains (APP/PSEN1/GD3S(-/-)), the concentration of GT1aα was elevated and as expected there was no expression of GQ1bα. On the other hand, the level of c-series gangliosides, including GT3, was significantly reduced in the double-Tg mouse brain as compared with the WT. Thus, the disruption of the gene of a specific ganglioside-synthase, GD3S, altered the expression of cholinergic neuron-specific gangliosides. Our data thus suggest the intriguing possibility that the elevated cholinergic-specific ganglioside, GT1aα, in the triple mutant mouse brains (APP/PSEN1/GD3S(-/-)) may contribute to the memory retention in these mice.

Anti-Chol-1 antigen, GQ1bα, antibodies are associated with Alzheimer's disease

The interaction of amyloid β-proteins (Aβ) with membrane gangliosides has been reported to be an early event in Aβ fibril formation in Alzheimer’s disease (AD). Neuronal degeneration in AD has been postulated to be associated with the presence of anti-ganglioside antibodies in patient sera. Using an enzyme-linked immunosorbent assay (ELISA) and high-performance thin-layer chromatography (HPTLC) immunostaining, sera from 27 individuals (10 with AD, 6 with vascular dementia (VD), and 11 non-demented age-matched pathological controls) were examined in order to detect anti-glycosphingolipid (GSL) antibodies, including anti-cholinergic-specific antigen (Chol-1α; GQ1bα) antibodies. All sera had natural antibodies against ganglio-N-tetraosyl gangliosides (brain-type gangliosides). However, sera of demented patients with AD and VD had significantly higher titers of anti-GSL antibodies than those in age-matched pathological controls. Although most serum antibodies, including anti- GM1, -GT1b, -GQ1b, -GQ1bα, were of the IgM type, the presence of the IgG type antibodies was also significantly elevated in the sera of demented patients with AD. Anti-GT1b antibodies of the IgG type were elevated in AD (90%, 9 of 10 cases) and VD (100%), respectively. Most surprisingly, anti-GQ1bα antibodies (IgM) were found in 90% (9/10) and 100% (6/6) in the sera of patients with AD and VD, respectively. Since GQ1bα is present in the cerebral cortex and hippocampus, the presence of anti-GQ1bα antibodies may play an important role in disrupting cholinergic synaptic transmission and may participate in the pathogenesis of dementia. We conclude that elevated anti-GSL antibody titers may be useful as an aid for clinical diagnosis of those dementias.

O-acetylated N-acetylneuraminic acid as a novel target for therapy in human pre-B acute lymphoblastic leukemia

Removal of 9-O-acetyl residues from the cell surface N-acetylneuraminic acid makes ALL cells drug sensitive.

The development of resistance to chemotherapy is a major cause of relapse in acute lymphoblastic leukemia (ALL). Though several mechanisms associated with drug resistance have been studied in detail, the role of carbohydrate modification remains unexplored. Here, we investigated the contribution of 9-O-acetylated N-acetylneuraminic acid (Neu5Ac) to survival and drug resistance development in ALL cells. A strong induction of 9-O-acetylated Neu5Ac including 9-O-acetyl GD3 was detected in ALL cells that developed resistance against vincristine or nilotinib, drugs with distinct cytotoxic mechanisms. Removal of 9-O-acetyl residues from Neu5Ac on the cell surface by an O-acetylesterase made ALL cells more vulnerable to such drugs. Moreover, removal of intracellular and cell surface–resident 9-O-acetyl Neu5Ac by lentiviral transduction of the esterase was lethal to ALL cells in vitro even in the presence of stromal protection. Interestingly, expression of the esterase in normal fibroblasts or endothelial cells had no effect on their survival. Transplanted mice induced for expression of the O-acetylesterase in the ALL cells exhibited a reduction of leukemia to minimal cell numbers and significantly increased survival. This demonstrates that Neu5Ac 9-O-acetylation is essential for survival of these cells and suggests that Neu5Ac de-O-acetylation could be used as therapy to eradicate drug-resistant ALL cells.

Development of a novel therapy for Lipo-oligosaccharide-induced experimental neuritis: use of peptide glycomimics

Recent etiological studies have revealed that molecular mimicry between the lipo-oligosaccharide (LOS) component of Campylobacter jejuni and gangliosides of peripheral nervous system plays an important role in the pathogenesis of Guillain-Barré syndrome (GBS). Previously, we demonstrated GD3 ganglioside molecular mimicry in a model of GBS in Lewis rats by sensitization with GD3-like LOS (LOS(GD3)) from C. jejuni. Since the neuropathophysiological consequences were due largely to the anti-GD3-like antibodies, we subsequently focused our effort upon eliminating the pathogenic antibodies using several strategies to mimic GD3 in this model. Here, we have validated this strategy by the use of peptide glycomimics based on epitopic mimicry between carbohydrates and peptides. We treated rats by i.p. administration of phage-displayed GD3-like peptides. One GD3-like peptide (P(GD3)-4; RHAYRSMAEWGFLYS) induced in treated rats a remarkable restoration of motor nerve functions, as evidenced by improved histopathology, rotarod performance, and motor nerve conduction velocity. P(GD3)-4 effectively decreased the titer of anti-GD3/anti-LOS(GD3) antibodies and ameliorated peripheral nerve dysfunction in the sera of treated rats. The data suggest that peptide glycomimics of ganglioside may be potential powerful reagents for therapeutic intervention in GBS by neutralizing specific pathogenic anti-ganglioside antibodies.

Glycosphingolipids from bovine milk and milk fat globule membranes: a comparative study. Adhesion to enterotoxigenic Escherichia coli strains

Several components of milk fat globule membranes (MFGMs) have been reported to display beneficial health properties and some of them have been implicated in the defense of newborns against pathogens. These observations prompted us to determine the glycosphingolipid content of MFGMs and their interaction with pathogens. A comparative study with whole milk components was also carried out. Milk fat globules and MFGMs were isolated from milk. Gangliosides and neutral glycosphingolipids were obtained from MFGMs and whole milk and their fatty acid contents were determined by gas chromatography-mass spectrometry (GC-MS). MFGMs and whole milk showed similar ganglioside and neutral glycosphingolipid contents, with whole milk having more GM3 and glucosylceramide and less GD3, O-acetyl GD3, O-acetyl GT3, and lactosylceramide. The fatty acid content of gangliosides from both sources showed a similar composition. However, the neutral glycosphingolipid fatty acid content seemed to be quite different. Whole milk had fewer very-long-chain fatty acids (18.1% vs. 46.4% in MFGMs) and more medium-chain and unsaturated C18:1 and C18:2 fatty acids. Milk fat globules, MFGMs, lactosylceramide, and gangliosides GM3 and GD3 were observed to bind enterotoxigenic Escherichia coli strains. Furthermore, bacterial hemagglutination was inhibited by MFGMs and glycosphingolipids.

Glycosphingolipid antigens in neural tumor cell lines and anti-glycosphingolipid antibodies in sera of patients with neural tumors

To characterize biomarkers in neural tumors, we analyzed the acidic lipid fractions of 13 neural tumor cell lines using enzyme-linked immunoabsorbent assay (ELISA) and high-performance thin-layer chromatography (HPTLC) immunostaining. Sulfated glucuronosyl glycosphingolipids (SGGLs) are cell surface molecules that are endowed with the Human Natural Killer-1 (HNK-1) carbohydrate epitope. These glycosphingolipids (GSLs) were expressed in all cell lines with concentrations ranging from 210 to 330 ng per 2 x 10(6) cells. Sulfoglucuronosyl paragloboside (SGPG) was the prominent species with lesser amounts of sulfoglucuronosyl lactosaminyl paragloboside (SGLPG) in these tumor cell lines as assessed by quantitative HPTLC immunostaining. Among the gangliosides surveyed, GD3 and 9-O-acetylated GD3 (OAc-GD3) were expressed in all tumor cell lines. In contrast, fucosyl-GM1 was not found to restrict to small cell lung carcinoma cells. In addition, we have analyzed serum antibody titers against SGPG, GD3, and OAc-GD3 in patients with neural tumors by ELISA and HPTLC immunostaining. All sera had high titers of antibodies of the IgM isotype against SGPG (titers over 1:3,200), especially in tumors such as meningiomas, germinomas, orbital tumors, glioblastomas, medulloblastomas, and subependymomas. Serum in a patient with subependymomas also had a high anti-SGGL antibody titer of the IgG and IgA types (titers over 12,800). The titer of anti-GD3 antibody was also elevated in patients with subependymomas and medulloblastomas; the latter cases also had a high titer of antibody against OAc-GD3. Our data indicate that certain GSL antigens, especially SGGLs, GD3, and OAc-GD3, are expressed in neural tumor cells and may be considered as tumor-associated antigens that represent important biomarkers for neural tumors. Furthermore, antibody titers in sera of patients with these tumors may be of diagnostic value for monitoring the presence of tumor cells and tumor progression.

Sulfated oxysterol, 25HC3S, is a potent regulator of lipid metabolism in human hepatocytes

Recently, a novel oxysterol, 5-cholesten-3beta, 25-diol 3-sulfate (25HC3S) was identified in primary rat hepatocytes following overexpression of the cholesterol transport protein, StarD1. This oxysterol was also detected in human liver nuclei. In the present study, 25HC3S was chemically synthesized. Addition of 25HC3S (6 microM) to human hepatocytes markedly inhibited cholesterol biosynthesis. Quantitative RT-PCR and Western blot analysis showed that 25HC3S markedly decreased HMG-CoA reductase mRNA and protein levels. Coincidently, 25HC3S inhibited the activation of sterol regulatory element binding proteins (SREBPs), suggesting that inhibition of cholesterol biosynthesis occurred via blocking SREBP-1 activation, and subsequently by inhibiting the expression of HMG CoA reductase. 25HC3S also decreased SREBP-1 mRNA levels and inhibited the expression of target genes encoding acetyl CoA carboxylase-1 (ACC-1) and fatty acid synthase (FAS). In contrast, 25-hydroxycholesterol increased SREBP1 and FAS mRNA levels in primary human hepatocytes. The results imply that 25HC3S is a potent regulator of SREBP mediated lipid metabolism.

Inhibition of neuronal migration by JONES antibody is independent of 9-O-acetyl GD3 in GD3-synthase knockout mice

It has been shown previously that the migration of granule neurons in neonatal cerebellum can be inhibited by a monoclonal antibody (Mab) JONES. Because the inhibition is presumed to be mediated through binding of the JONES antibody to 9-O-acetyl GD3, we used GD3-synthase knockout (GD3S-/-) mice that do not express 9-O-acetyl GD3 and also have no detectable defect in brain development, to examine the mechanism of the inhibitory effect. We found no difference between the migration of granule neurons in the neonatal cerebellar explant culture in GD3S-/- mice and in wild-type mice. Addition of the Mab JONES, but not Mab R24 or A2B5, in the culture medium blocked the neuronal migration in the explant culture of the wild-type mice. The inhibitory effect of Mab JONES was also observed, however, in the explant culture of GD3S-/- mice. Immuno-HPTLC analysis showed at least two JONES-positive glycolipids bands in the lipid extract of GD3S+/+ mice, and none was detected in that of GD3S-/- mice. Western blot analysis of the cerebellum homogenate of wild-type and GD3S-/- mice identified at least 3 JONES-positive protein bands, one of which is beta1-integrin. Because the JONES antibody also blocked neuronal migration in the cerebellar explant culture of GD3S-/- mice that do not express 9-O-acetyl-GD3, it suggested an alternative mechanism for the inhibitory effect of the antibody, at least in the GD3S knockout mice, and the inhibitory effect of the JONES antibody on neuronal migration could be mediated through its binding to beta1-integrin.

Bioengineering of Surface GD3 Ganglioside for Immunotargeting Human Melanoma Cells

N-Propionyl, N-butyryl (N-Bu), and N-benzoyl mannosamine, as precursors of sialic acid biosynthesis, were incubated with human melanoma SK-MEL-28 cells and resulted in the replacement of N-acetyl groups on the cell surface sialic acid residues, including those associated with GD3. Meanwhile, vaccines containing GD3 and modified GD3 tetrasaccharide-keyhole limpet hemocyanin conjugates were synthesized, and BALB/c mice were immunized with them together with monophosphoryl lipid A adjuvant. The GD3Bu-keyhole limpet hemocyanin conjugate raised the highest IgG titers without any cross-reactivity to unmodified GD3. Expression of GD3Bu epitopes on the surface of SK-MEL-28 cells was confirmed in vitro and in vivo by the binding of a polyclonal antiserum and monoclonal antibody (mAb) 2A, both of which specifically recognize GD3Bu, and by mass spectroscopic analysis of glycolipids extracted from cells. Following expression of GD3Bu on the surface of SK-MEL-28 cells, the cells could be lysed by mAb 2A and GD3Bu antiserum in the presence of complement. Although less effective in the control of existing large size tumors ( approximately 10 mm inner diameter) on BALB/c nu/nu mice, mAb 2A in combination with ManNBu effectively protected mice from SK-MEL-28 tumor grafting. This approach may provide a method to augment the immunogenicity of sialylated human antigens and to avoid generating an autoimmune response to them at same time.

Characterization and biological activity of gangliosides in buffalo milk

Gangliosides (GS) were evaluated in Swiss cow's milk (SCM), Italian buffalo milk (IBM) and its serum, Pakistan buffalo colostrum (PBC), Pakistan buffalo mature milk (PBM), and Pakistan buffalo milk from rice-growing areas (PBR). Dairy GS were obtained from the Folch's upper (hydrophilic) and lower (lipophilic) extraction phases, respectively, and determined as lipid-bound sialic acid (LBSA) by colorimetry. Molar ratios of LBSA in the hydro- and lipophilic GS fractions were 52:48 to 79:21. Mature buffalo milk types had 40-100% more LBSA in the lipophilic GS fraction compared to SCM. Liquid PBC was higher in LBSA (24 nmol/g) compared to mature milk types (8-11 nmol/g). Thin-layer chromatography (TLC) and scanning densitometry showed distinct profiles of hydrophilic and lipophilic GS fractions. Lipophilic GS (but importantly not hydrophilic GS) from IBM and its serum decreased prostaglandin series 2 production by 75-80% in cultured human colonic epithelial cells exposed to tumor necrosis factor alpha (TNFalpha). Hydrophilic GD(3) and lipophilic GM(3) selectively bound rotavirus particles prepared from a rhesus strain and its mutant. A GS fraction in IBM showed a GM(1)-specific binding to cholera toxin subunit B (CTB). IBM serum (IBMS) was a rich source of LBSA (420 nmol/g proteins). In summary, improved methodology led to increased LBSA recovery and isolation of additional and bioactive milk GS. Human and Italian buffalo milk had similar CTB binding, and both had increased polysialo-GS compared to cows milk. The toxin binding properties of buffalo milk GS, and the anti-inflammatory activity of the lipophilized GS fraction could be important for developing innovative food applications, as well as the subject of future research.

The composition of bovine milk lipids: January 1995 to December 2000

Data from recent publications on bovine milk lipids are presented and discussed. This includes extraction of lipids, triacylglycerols, phospholipids, other complex lipids, sterols, isoflavones, and fatty acids. Improved gas-liquid and high performance liquid chromatography were used. Data on the trans and cis isomers of fatty acid and of conjugated linoleic acids are given, and the analyses are described. Papers about the lipids in milks and dairy products from the United States are few; where with the exception of trans-fatty acid isomers and conjugated linoleic acids, almost no research has been reported.

Bovine milk gangliosides: changes in ceramide moiety with stage of lactation

The stage of lactation is one of the most important factors that influence milk composition. Changes in fatty acids from triacylglycerols and phospholipids have already been reported. In this study, we looked for a lactational change in the ganglioside lipid moiety since ganglioside contents and patterns vary strongly with stage of lactation. Individual gangliosides from four stages were isolated, methanolized to cleave the bonds between individual constituents, and derivatized for gas-liquid chromatography and gas chromatography/mass spectrometry analyses. Ceramide components, both fatty acids (as methyl esters derivatives) and long-chain bases, were identified and quantified. The results pointed to a marked change in ceramide from colostrum to milk that was characterized by a dramatic decrease in saturated and the longest-chain fatty acids as well as an increase in 18:1 and 18:2. The major long-chain base along lactation was a recently described structure, 3-ethoxy-15:0 sphinganine. Other new long-chain base structures appeared in these gangliosides. All these changes suggest differences in the fluidity of the fat globule membrane, reflecting physiological variations in cows with respect to milk production.

Characterization of blood group ABO(H)-active gangliosides in type AB erythrocytes and structural analysis of type A-active ganglioside variants in type A human erythrocytes

Several monosialogangliosides containing the type A-active epitope have been detected in type A erythrocytes on immunological analysis with a monoclonal antibody, and three of them were purified by repeated silica bead column chromatography and by scraping from the TLC plate. Two of these A-active gangliosides were characterized by methylation analysis by GC/MS, negative SIMS, MALDI-TOF/MS, proton nuclear magnetic resonance spectroscopy, and immunological assays, and their structures were concluded to be as follows. A-active ganglioside I:A-active ganglioside II:The reactivity of the purified gangliosides to the anti-A monoclonal antibodies (mAbs) exhibited enhancement after removal of the sialic acid. Therefore, the sialic residue has been shown to inhibit the binding to the terminal A-active epitope through the formation of an immune complex. To confirm the presence of A- (including S-A-I, -II and -III) and B-active gangliosides, the reactivity of anti-A and -B mAbs were investigated using total gangliosides from type A, -B and -AB erythrocytes on TLC plate. The results were that the gangliosides from types A and AB showed positive reaction to anti-A mAbs, whereas in the anti-B mAbs binding the gangliosides from types B and AB were positive. Thus, it revealed that A-active gangliosides were present in type A and -AB, and B-active gangliosides in types B and AB. As there was no difference in respective gangliosides on type AB erythrocytes of 22 individuals, both A- and B-active gangliosides are equally present in type AB erythrocytes. The biological significance of these A- and B-active ganglioside variants remains vague at present. As these molecules exhibit different reactivities to the anti-A mAbs, it is very likely that they can regulate the antigenicity of the A-epitope on the cell surface.

Antibodies to GD3, GT3, and O-acetylated species in Guillain-Barré and Fisher's syndromes: their association with cranial nerve dysfunction

We examined serum antibodies to the four fetal antigens GD3, O-acetyl GD3, GT3, and O-acetyl GT3 ganglioside in patients with Guillain-Barré syndrome (GBS) or its variant Fisher's syndrome (FS). The patients with FS more often had significant IgG antibodies against GD3, GT3, and O-acetyl GT3 than did the healthy controls. Furthermore, anti-GD3 and anti-GT3 IgG antibodies were more often significantly present in the patients with FS than in those with GBS. IgG antibody to GD3, GT3, and O-acetyl GT3 had a significant association with the presence of ophthalmoparesis. These antibodies, however, cross-reacted with GQ1b and we detected no antibodies which specifically reacted with fetal gangliosides. In addition, oculomotor involvement was more closely related to IgG antibodies to GQ1b than to those to fetal gangliosides. No evidence was obtained that the serum antibodies to these fetal gangliosides are associated with specific neurologic signs of cranial nerves.

Neonatal dietary gangliosides

Gangliosides are glycosphingolipids that are widely distributed in vertebrate tissues and body fluids and which are specially abundant in neural tissues. Milk from different species has a particular ganglioside content and profile. Human milk has a higher content of gangliosides than bovine milk. GD3 and GM3 are the predominant individual gangliosides in bovine milk. In human colostrum GD3 is also the main ganglioside whereas in human mature milk GM3 predominates over the other gangliosides. Human milk also contains GM1 and a number of highly polar gangliosides, which may play an important role in infant physiology. GM1 has been shown to inhibit Escherichia coli and Vibrio cholerae enterotoxins. We have found that a ganglioside-supplemented infant formula modifies the intestinal ecology of preterm newborns, increasing the Bifidobacteria content and lowering that of Escherichia coli. Although the exact mechanism by which dietary gangliosides reduce the fecal content of Escherichia coli is unknown, in vitro experiments suggest that they may act as false intestinal receptors for some strains of this bacteria. Since GD3 and other gangliosides have been involved in mechanisms of lymphocyte activation and differentiation, dietary gangliosides might have a function in intestinal immunity development.

New blocking method for the hydroxyl group on carbohydrate. Determination of the O-acylated position of the modified glycolipid

To determine O-esterified positions, a rapid and complete acetalization to prepare an intermediate was established using ethyl vinyl ether as a new reagent. The new method was applied to O-esterified glycolipids followed by GC-MS analysis of the monosaccharide derivatives after methylation and methanolysis, revealing the derivatives with correctly substituted positions. This method was superior in terms of its shorter reaction time and complete acetalization, particularly of the N-glycolyl hydroxyl residue, to previously reported methods using methyl vinyl ether.

Very low density lipoproteins and interleukin 2 enhance the immunogenicity of 9-O-acetyl-GD3 ganglioside in BALB/c mice

Gangliosides expressed by tumor cells constitute potential targets for immunotherapy. A major limitation of protocols aiming to immunize patients against tumor gangliosides is the weak immunogenicity of these molecules. We have previously shown that exogenous gangliosides are essentially bound to serum lipoproteins. In this study we have analyzed the influence of human serum lipoproteins on the immunogenicity of purified human ganglioside 9-O-acetyl-GD3 in BALB/c mice. Although expressed at very low levels in mice, this ganglioside was not immunogenic when administered in the form of micelles. However 9-O-acetyl-GD3 adsorbed onto Very Low Density Lipoproteins (VLDL) was strongly and reproducibly immunogenic, inducing both an IgM and an IgG response, with higher titers than those obtained with total serum. The IgM antibody response appeared after a single injection whereas the IgG response was observed after 3 weeks but was stronger and more durable. The antibody response to 9-O-acetyl-GD3 bound to other serum fractions was weak or absent. The addition of recombinant interleukin 2 (IL-2) enhanced weak antibody responses to 9-O-acetyl-GD3 thereby facilitating responses to ganglioside in micelles and in protein-free Very Low Density Particles. Using in vitro assays, we demonstrated that VLDL-bound ganglioside 14C-GM3 was more sensitive to the effect of neuraminidase than gangliosides bound to other lipoprotein fractions, suggesting greater accessibility of VLDL-bound gangliosides. These results indicate that VLDL-bound gangliosides are the most immunologically active fraction of serum gangliosides. VLDL or similar particles and recombinant IL-2 may be useful adjuvants for immunization with gangliosides.

Novel di-O-acetylated GM3s from equine erythrocytes, one containing 4,9-di-O-acetyl-N-glycolylneuraminic acid and another containing 4-O-acetyl-N-glycolylneuraminic acid and 6-O-acetyl-D-galactose

A novel GM3 O-acetylated at C-4 and at C-9 of N-glycolylneuraminic acid (4,9-di-O-Ac GM3), together with a second GM3 O-acetylated at O-4 of the neuraminic acid and O-6 of D-galactose (4,6'-di-O-Ac GM3) were isolated from equine erythrocytes as a mixture in approximate 1:1 ratio. These two major species were chromatographically inseparable. Their structures, especially the positions of the acetoxy group(s), were determined by means of 1D- and 2D-1H NMR and fast atom bombardment-MS as well as by gas chromatography-MS of partially O-methylated O-trimethylsilylated monosaccharides derived from the di-O-Ac GM3s. In addition, 4-O-Ac GM3 was chemically mono-O-acetylated with trimethyl orthoacetate under acidic conditions, giving exclusively 4,9-di-O-Ac GM3, the NMR and mass spectra of which were used as references to confirm the 4,9-di-O-acetylated structure of the naturally-occurring GM3.

Sulfatide is expressed in both erythrocytes and platelets of bovine origin

A novel sulfated glycosphingolipid containing a sulfated galactosyl residue was isolated from bovine erythrocyte ghosts, and purified to homogeneity by column chromatography on DEAE-Sephadex and silica beads. Structural characterization included compositional analyses, permethylation studies, proton nuclear magnetic resonance (NMR) spectroscopy, negative secondary ion mass spectrometry (SIMS), solvolysis and immunostaining on thin-layer chromatogram. As a result, the structure of this glycolipid is proposed as HSO3-Gal beta 1-1 Cer. The ceramide portion contained d18:1, d18:0 and t18:0, and the predominant fatty acid consisted of palmitate and palmitate with a hydroxy group, as deduced by both compositional analysis and negative SIMS mass spectrometry. The component of this glycosphingolipid probably originates from erythrocytes and platelets as indicated by the results of flow cytometry analysis using Sulph I monoclonal antibody. The yield of galactosyl sulfatide was about 0.37 mg/kg wet bovine erythrocyte membranes, about three times that of human kidney. Our results strongly suggest that galactosylceramide sulfate on erythroid cells may play an important biological role in cell to cell interaction and recognition.

Binding specificity of influenza C-virus to variably O-acetylated glycoconjugates and its use for histochemical detection of N-acetyl-9-O-acetylneuraminic acid in mammalian tissues

The specificity of influenza C-virus binding to sialoglycoconjugates was tested with various naturally O-acetylated gangliosides or synthetically O-acetylated sialic acid thioketosides, which revealed binding to 9-O-acetylated N-acetylneuraminic acid. Binding was also observed with a sample of Neu5,7Ac2-GD3, however at a lower degree. Sialic acids with two or three O-acetyl groups in the side chain of synthetic sialic acid derivatives are not recognized by the virus. In these experiments, bound viruses were detected with esterase substrates. Influenza C-virus was also used for the histological identification of mono-O-acetylated sialic acids in combination with an immunological visualization of the virus bound to thin-sections. The occurrence of these sialic acids was demonstrated in bovine submandibular gland, rat liver, human normal adult and fetal colon and diseased colon, as well as in human sweat gland. Submandibular gland and colon also contain significant amounts of glycoconjugates with two or three acetyl esters in the sialic acid side chain, demonstrating the value of the virus in discriminating between mono- and higher O-acetylation at the same site. The patterns of staining showed differences between healthy persons and patients with colon carcinoma, ulcerative colitis or Crohn's disease. Remarkably, some human colon samples did not show O-acetyl sialic acid-specific staining. The histochemical observations were controlled by chemical analysis of tissue sialic acids.

Characterization of novel mono-O-acetylated GM3s containing 9-O-acetyl sialic acid and 6-O-acetyl galactose in equine erythrocytes

Novel mono-O-acetylated GM3s, one containing 9-O-acetyl N-glycolyl neuraminic acid and another containing 6'-O-acetyl galactose, were isolated as a mixture from equine erythrocytes, and the structures were characterized by one- and two-dimensional proton nuclear magnetic resonance (NMR) and fast atom bombardment-mass spectrometry (FAB-MS). The position of the O-acetyl residue was identified by the downfield shift of the methylene protons at C-9 of N-glycolyl neuraminic acid (9-O-Ac GM3) and C-6 of galactose (6'-O-Ac GM3) in the NMR spectrum, in comparison to the respective non-acetylated counterparts. To confirm the presence of 6'-O-Ac GM3, the O-acetylated GM3 mixture was desialylated with Arthrobacter neuraminidase, giving 6-O-acetyl galactosyl glucosylceramide, the structure of which was estimated by NMR and FAB-MS, together with non-acetylated lactosylceramide with a ratio of 1:1.

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.

7-O-acetyl-GD3 in human T-lymphocytes is detected by a specific T-cell-activating monoclonal antibody

The monoclonal antibody U5, which is a potent inducer of proliferation in human T-cells, was found to bind to an alkali-sensitive derivative of ganglioside GD3. Using immunochemical and spectroscopic methods, the structure of the U5 antigen was determined as 7-O-acetyl-GD3. The antibody U5 did not react with 9-O-acetyl-GD3 and bound severalfold more stronger to 7-O-acetyl-GD3 than to GD3. U5 is the first antibody known to detect preferentially 7-O-acetyl-GD3. Flow cytometric analysis showed that each major class of human leukocytes contained a significant fraction of cells binding the U5 antibody.

Analysis of the antibody response to immunization with purified O-acetyl GD3 gangliosides in patients with malignant melanoma

Gangliosides expressed in malignant melanoma are potential targets for immunotherapy. Immunization of melanoma patients with vaccines containing purified GM2 ganglioside has resulted in induction of GM2 antibodies, and high titers of GM2 antibodies have correlated with increased survival. Melanoma ganglioside 9-O-acetyl GD3 is another candidate for ganglioside vaccine construction because of its limited expression in normal human tissues. As purification of 9-O-acetyl GD3 from human melanoma (9-O-acetylated on the terminal sialic acid) is not practical for broad application, we investigated the antibody response of melanoma patients to O-acetyl GD3 from several additional sources: hamster melanoma (7-O-acetyl GD3), bovine buttermilk (mixture of 7-O-acetyl GD3, 9-O-acetyl GD3 and 7,9-di-O-acetyl GD3) and chemically modified GD3 from bovine brain (9-O-acetylated on the subterminal sialic acid). Only immunization with the buttermilk-derived O-acetyl GD3 preparation resulted in consistent production of IgM antibodies. However, the induced antibodies reacted with the immunogen and with 7-O-acetyl GD3 derived from hamster melanoma but not with 9-O-acetyl GD3 or human melanoma cells expressing 9-O-acetyl GD3 on their cell surface. In contrast, all O-acetyl GD3 derivatives used for immunization were recognized by murine MAbs that reacted with 9-O-acetyl GD3, and immunization of mice with buttermilk-derived O-acetyl GD3 resulted in the production of antibodies that reacted with human melanoma cells expressing 9-O-acetyl GD3. Apparently, the human and murine immune systems preferentially recognize different epitopes on these molecules.

Characterization of blood-group-ABO(H)-active glycosphingolipids in type-AB human erythrocytes

Neutral glycolipids in Folch's upper phase were isolated from human erythrocyte membranes of 22 individuals with blood type AB. On immunostaining by TLC with anti-A IgG, all reactive glycolipids in type A corresponded to reactive glycolipids in type-AB erythrocytes. With anti-B IgM, all reactive glycolipids in type-B erythrocytes also corresponded to reactive glycolipids in type-AB erythrocytes. By comparison of the reactivity to that of the anti-A and anti-B antibodies, it was found that, in type-AB erythrocytes, all glycolipids reactive with either one of the anti-A or anti-B antibodies were detected in both type-A and type-B erythrocytes, and that A-active glycolipids had higher Rf values than B-active glycolipids on TLC plates. A series of glycolipids reactive with both antibodies were purified from the Folch's upper neutral glycolipid fraction of erythrocyte membranes by column chromatography, and was characterized by TLC-immunostaining and negative secondary-ion mass spectrometry. The results strongly suggested that A-active and B-active carbohydrate chain epitopes existed separately as glycolipid molecules in blood-type-AB erythrocytes. It was also confirmed that these phenotypes observed in erythrocyte membranes were exhibited by blood-group-active glycosphingolipids in the small intestine of blood-type-AB individuals. Furthermore, upon treatment of fractions obtained from silicic acid column chromatography with alpha-N-acetylhexosaminidase or alpha-galactosidase, a branched hybrid-type molecule with both A and B determinants was not detected.

Approaches to augmenting the immunogenicity of melanoma gangliosides: from whole melanoma cells to ganglioside-KLH conjugate vaccines

Gangliosides are neuraminic acid containing glycosphingolipids that are anchored into the lipid bilayer of the plasma membrane by their lipophilic ceramide moiety. They are overexpressed on tissues of neuroectodermal origin, particularly in tumors such as melanomas, sarcomas, neuroblastomas and astrocytomas. With the ganglioside-KLH plus immunological adjuvant QS-21 conjugate vaccine, GM2 and GD2 have been shown to be consistently immunogenic, inducing cytotoxic IgM antibodies in most patients. The immunogenicity of other gangliosides also expressed on melanoma cells such as 9-0-acetyl GD3 and GD3 lactone is currently being tested with this conjugate vaccine approach. From the initiation of our adjuvant vaccine trials in 1975 to the present, the immunogenicity of ganglioside vaccines has increased significantly as vaccine development has progressed. For instance, GM2 antibody responses increased from low titer IgM antibodies induced in occasional patients after whole cell vaccines, to moderate titer IgM antibodies in 86% of patients after GM2/BCG vaccines, to higher titer IgM antibodies in 100% of patients treated with the GM2-KLH plus QS-21 vaccine. These antibodies are capable of mediating complement mediated cytotoxicity of GM2 expressing melanoma cells in the majority of patients and such antibodies, whether naturally produced or vaccine induced, have been associated with a significantly improved disease-free and overall survival. An initial double-blind randomized trial in AJCC Stage III melanoma patients comparing GM2/BCG with BCG alone, demonstrated a 14% improvement in disease-free interval at 4 years and an 11% improvement in overall survival, though neither result achieved statistical significance. Based on these encouraging clinical results and the clearly improved immunogenicity of the GM2-KLH plus QS-21 vaccine compared to the previous GM2/BCG vaccine, the following two large clinical trials are anticipated to begin in 1995-1996. The GM2-KLH plus QS-21 vaccine will be tested in the intergroup setting by ECOG in 450 patients with AJCC Stage II or III melanoma who are free of disease after surgery. Also to be tested in a multicenter trial is a GM2-KLH plus GD2-KLH plus QS-21 vaccine in patients with high risk AJCC Stage II-IV sarcoma after surgical excision of all known disease.

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

An improved method for the measurement of total lipid-bound sialic acids after cleavage of alpha 2,8 sialic acid linkage with Vibrio cholerae sialidase in the presence of cholic acid, SDS and Ca2+

In the measurement of total lipid-bound sialic acids involving periodic acid oxidation, as in the periodate-resorcinol assay, the inner sialic acids of disialoglycolipids (such as GD3 and GD2) are not involved because their alpha 2,8 ketosidic linkages are resistant to periodic acid oxidation, even after acid/enzyme hydrolysis or alkali pretreatment. However, the sialic acids from these glycolipids can be recovered completely after cleavage of alpha 2,8 linkages by V. cholerae sialidase in the presence of cholic acid, sodium dodecyl sulphate and calcium. Interestingly, removal of calcium or detergent(s) or both significantly minimizes the sialidase action on the disialyl residues of these gangliosides. Therefore, we recommend sialidase (Vibrio cholerae) pretreatment of the glycolipids in the presence of cholic acid, SDS and Ca2+ for complete recovery of sialic acids from di- and polysialogangliosides and for accurate measurement of total lipid-bound sialic acids by periodate-resorcinol assay.