Gangliosides and atherosclerosis

Brain-derived gangliosides prime human platelet aggregation and induce platelet-leukocyte aggregate formation

BACKGROUND

Platelet activation and interaction with leukocytes are crucial in inflammation. Gangliosides, sialic acid-containing glycosphingolipids, have been linked to different inflammatory conditions related to cardio- and neurodegenerative disorders. The role of gangliosides in platelet and leukocyte function, although reported, still needs further investigation.

OBJECTIVES

We aimed to study the role of gangliosides in platelet activation and platelet-leukocyte interaction in vitro.

METHODS

Platelet activation was studied through aggregometry in platelet-rich plasma from apparently healthy human volunteers. Signaling protein phosphorylation was analyzed by immunoblotting. Platelet P-selectin expression and platelet-leukocyte aggregate formation were measured by flow cytometry.

RESULTS

The gangliosides monosialoganglioside GM1, disialoganglioside GD1a, and trisialoganglioside GT1b did not induce by themselves any platelet aggregation. Conversely, when preincubated with platelets, they potentiate platelet aggregation induced by submaximal adenosine diphosphate and collagen concentrations and increased P-selectin expression. Incubation of platelets with free sialic acid and the soluble part of monosialoganglioside GM1 induced a similar potentiating effect on platelet aggregation but not on platelet P-selectin expression. Consistently, analyzing the signaling protein phosphorylation, only the entire gangliosides activated extracellular stimuli-responsive kinase 1/2 suggesting that a complete ganglioside is crucial for its action on platelets. Both the priming effect on platelet aggregation and ERK1/2 activation were prevented by aspirin. Moreover, incubation of citrated whole blood with gangliosides induced platelet-leukocyte aggregate formation accompanied by increased expression of granulocyte and monocyte CD11b compared with untreated blood, suggesting a primary leukocyte activation.

CONCLUSION

Gangliosides may act in vitro both on platelet and leukocyte activation and on their interaction. The observed effects might contribute to inflammatory processes in clinical conditions.

Glycosphingolipids in Cardiovascular Disease: Insights from Molecular Mechanisms and Heart Failure Models

This review explores the crucial role of glycosphingolipids (GSLs) in the context of cardiovascular diseases (CVDs), focusing on their biosynthesis, metabolic pathways, and implications for clinical outcomes. GSLs are pivotal in regulating a myriad of cellular functions that are essential for heart health and disease progression. Highlighting findings from both human cohorts and animal models, this review emphasizes the potential of GSLs as biomarkers and therapeutic targets. We advocate for more detailed mechanistic studies to deepen our understanding of GSL functions in cardiovascular health, which could lead to innovative strategies for diagnosis, treatment, and personalized medicine in cardiovascular care.

Comprehensive Glycomic Approach Reveals Novel Low-Molecular-Weight Blood Group-Specific Glycans in Serum and Cerebrospinal Fluid

ABO blood antigens on the human red blood cell membrane as well as different cells in various human tissues have been thoroughly studied. Anti-A and -B antibodies of IgM are present in serum/plasma, but blood group-specific glyco-antigens have not been extensively described. In this study, we performed comprehensive and quantitative serum glycomic analyses of various glycoconjugates and free oligosaccharides in all blood groups. Our comprehensive glycomic approach revealed that blood group-specific antigens in serum/plasma are predominantly present on glycosphingolipids on lipoproteins rather than glycoproteins. Expression of the ABO antigens on glycosphingolipids depends not only on blood type but also on secretor status. Blood group-specific glycans in serum/plasma were classified as type I, whereas those on RBCs had different structures including hexose and hexosamine residues. Analysis of free oligosaccharides revealed that low-molecular-weight blood group-specific glycans, commonly containing lacto-N-difucotetraose, were expressed in serum/plasma according to blood group. Furthermore, comprehensive glycomic analysis in human cerebrospinal fluid showed that many kinds of free oligosaccharides were highly expressed, and low-molecular-weight blood group-specific glycans, which existed in plasma from the same individuals, were present. Our findings provide the first evidence for low-molecular-weight blood group-specific glycans in both serum/plasma and cerebrospinal fluid.

TNF differentially regulates ganglioside biosynthesis and expression in breast cancer cell lines

Gangliosides are glycosphingolipids concentrated in glycolipid-enriched membrane microdomains. Mainly restricted to the nervous system in healthy adult, complex gangliosides such as GD3 and GD2 have been shown to be involved in aggressiveness and metastasis of neuro-ectoderm derived tumors such as melanoma and neuroblastoma. GD3 synthase (GD3S), the key enzyme that controls the biosynthesis of complex gangliosides, was shown to be over-expressed in Estrogen Receptor (ER)-negative breast cancer tumors, and associated with a decreased overall survival of patients. We previously demonstrated that GD3S expression in ER-negative breast cancer cells induced a proliferative phenotype and an increased tumor growth. In addition, our results clearly indicate that Tumor Necrosis Factor (TNF) induced GD3S over-expression in breast cancer cells via NFκB pathway. In this study, we analyzed the effect of TNF on ganglioside biosynthesis and expression in breast cancer cells from different molecular subtypes. We showed that TNF up-regulated the expression of GD3S in MCF-7 and Hs578T cells, whereas no change was observed for MDA-MB-231. We also showed that TNF induced an increased expression of complex gangliosides at the cell surface of a small proportion of MCF-7 cells. These results demonstrate that TNF differentially regulates gangliosides expression in breast cancer cell lines and establish a possible link between inflammation at the tumor site environment, expression of complex gangliosides and tumor development.

Siglec-7 restores β-cell function and survival and reduces inflammation in pancreatic islets from patients with diabetes

Chronic inflammation plays a key role in both type 1 and type 2 diabetes. Cytokine and chemokine production within the islets in a diabetic milieu results in β-cell failure and diabetes progression. Identification of targets, which both prevent macrophage activation and infiltration into islets and restore β-cell functionality is essential for effective diabetes therapy. We report that certain Sialic-acid-binding immunoglobulin-like-lectins (siglecs) are expressed in human pancreatic islets in a cell-type specific manner. Siglec-7 was expressed on β-cells and down-regulated in type 1 and type 2 diabetes and in infiltrating activated immune cells. Over-expression of Siglec-7 in diabetic islets reduced cytokines, prevented β-cell dysfunction and apoptosis and reduced recruiting of migrating monocytes. Our data suggest that restoration of human Siglec-7 expression may be a novel therapeutic strategy targeted to both inhibition of immune activation and preservation of β-cell function and survival.

Role of Cytokine-Induced Glycosylation Changes in Regulating Cell Interactions and Cell Signaling in Inflammatory Diseases and Cancer

Glycosylation is one of the most important modifications of proteins and lipids, and cell surface glycoconjugates are thought to play important roles in a variety of biological functions including cell-cell and cell-substrate interactions, bacterial adhesion, cell immunogenicity and cell signaling. Alterations of glycosylation are observed in number of diseases such as cancer and chronic inflammation. In that context, pro-inflammatory cytokines have been shown to modulate cell surface glycosylation by regulating the expression of glycosyltransferases involved in the biosynthesis of carbohydrate chains. These changes in cell surface glycosylation are also known to regulate cell signaling and could contribute to disease pathogenesis. This review summarizes our current knowledge of the glycosylation changes induced by pro-inflammatory cytokines, with a particular focus on cancer and cystic fibrosis, and their consequences on cell interactions and signaling.

[Serum IgG antibodies to GD1a and GM1 gangliosides in elderly people]

Nowadays, the percentage of elderly people in society grows. Good nutrition and medical care help older people to have a normal life over 80 to 90 years. In the last ten years it is of critical importance to establish the clinical significance of serum IgG anti-GD1a and anti-GM1 ganglioside antibodies as potential biomarkers for neuronal damage in neurodegenerative diseases and immune-mediated neuropathies and demyelination. In the current study, the diagnostic values of IgG anti-GD1a and anti-GM1 antibodies were determined by the ELISA method in serum samples of 18 elderly patients (71-91 years). Significantly elevated serum IgG anti-GD1a and anti-GM1 antibodies titers were detected only in patients over 80 years. These data suggest that the immune-mediated neuropathies, neurodegeneration and demyelination in healthy elderly occur after 80 years old. Therefore, IgG anti-GD1a and anti-GM1 antibodies can serve as biomarkers, showing the nervous system dysfunction.

Quantitative GSL-glycome analysis of human whole serum based on an EGCase digestion and glycoblotting method

Glycosphingolipids (GSLs) are lipid molecules linked to carbohydrate units that form the plasma membrane lipid raft, which is clustered with sphingolipids, sterols, and specific proteins, and thereby contributes to membrane physical properties and specific recognition sites for various biological events. These bioactive GSL molecules consequently affect the pathophysiology and pathogenesis of various diseases. Thus, altered expression of GSLs in various diseases may be of importance for disease-related biomarker discovery. However, analysis of GSLs in blood is particularly challenging because GSLs are present at extremely low concentrations in serum/plasma. In this study, we established absolute GSL-glycan analysis of human serum based on endoglycoceramidase digestion and glycoblotting purification. We established two sample preparation protocols, one with and the other without GSL extraction using chloroform/methanol. Similar amounts of GSL-glycans were recovered with the two protocols. Both protocols permitted absolute quantitation of GSL-glycans using as little as 20 μl of serum. Using 10 healthy human serum samples, up to 42 signals corresponding to GSL-glycan compositions could be quantitatively detected, and the total serum GSL-glycan concentration was calculated to be 12.1-21.4 μM. We further applied this method to TLC-prefractionated serum samples. These findings will assist the discovery of disease-related biomarkers by serum GSL-glycomics.

Circulating levels of ganglioside GM3 in metabolic syndrome: A pilot study

SUMMARY

BACKGROUND

Insulin resistance is a characteristic feature of metabolic syndrome. Ganglioside GM3 [α-Neu5Ac-(2-3)-β-Gal-(1-4)-β-Glc-(1-1)-ceramide] may impair insulin sensitivity in adipose tissue. We investigated the relationship between serum GM3 levels and adiposity indices, as well as between serum GM3 levels and metabolic risk variables.

METHODS

Study 1: we assessed serum GM3 levels in normal subjects and in patients with hyperglycemia and/or hyperlipidemia (HL). Study 2: we investigated the relationship between serum GM3 levels and metabolic risk variables in patients with type 2 diabetes.

RESULTS

Study 1: serum GM3 levels were higher in hyperglycemic patients (1.4-fold), hyperlipidemic patients (1.4-fold) and hyperglycemic patients with hyperlipidemia (1.6-fold), than in normal subjects. Study 2: serum GM3 levels were significantly increased in type 2 diabetic patients with severe obesity (visceral fat area (VFA) >200 cm(2), BMI > 30). The GM3 level was positively correlated with LDL-c (0.403, p = 0.012) in type 2 diabetes mellitus, but not affected by blood pressure. In addition, the high levels of small dense LDL (>10 mg/dL) were associated with the elevation of GM3.

CONCLUSIONS

Serum GM3 levels was affected by glucose and lipid metabolism abnormalities and by visceral obesity. GM3 may be a useful marker for severity of metabolic syndrome.

The ganglioside G(D2) induces the constitutive activation of c-Met in MDA-MB-231 breast cancer cells expressing the G(D3) synthase

We have recently established and characterized cellular clones deriving from MDA-MB-231 breast cancer cells that express the human G(D3) synthase (GD3S), the enzyme that controls the biosynthesis of b- and c-series gangliosides. The GD3S positive clones show a proliferative phenotype in the absence of serum or growth factors and an increased tumor growth in severe immunodeficient mice. This phenotype results from the constitutive activation of the receptor tyrosine kinase c-Met in spite of the absence of ligand and subsequent activation of mitogen-activated protein kinase/extracellular signal-regulated kinase and phosphoinositide 3-kinase/Akt pathways. Here, we show by mass spectrometry analysis of total glycosphingolipids that G(D3) and G(D2) are the main gangliosides expressed by the GD3S positive clones. Moreover, G(D2) colocalized with c-Met at the plasma membrane and small interfering RNA silencing of the G(M2)/G(D2) synthase efficiently reduced the expression of G(D2) as well as c-Met phosphorylation and reversed the proliferative phenotype. Competition assays using anti-G(D2) monoclonal antibodies also inhibit proliferation and c-Met phosphorylation of GD3S positive clones in serum-free conditions. Altogether, these results demonstrate the involvement of the disialoganglioside G(D2) in MDA-MB-231 cell proliferation via the constitutive activation of c-Met. The accumulation of G(D2) in c-Met expressing cells could therefore reinforce the tumorigenicity and aggressiveness of breast cancer tumors.

ID2 (inhibitor of DNA binding 2) is a rhythmically expressed transcriptional repressor required for circadian clock output in mouse liver

Id2 is a helix-loop-helix transcription factor gene expressed in a circadian manner in multiple tissues with a phase-locked relationship with canonical clock genes. Our previous studies have identified circadian phenotypes in Id2 null mice, including enhanced photo-entrainment and disruption of activity rhythms, and have demonstrated a potent inhibitory effect of ID proteins upon CLOCK-BMAL1 transactivation of clock gene and clock-controlled gene activity. We have now begun to explore the potential role that ID2 may play in specifically regulating clock output. Here we show that ID2 protein is rhythmically expressed in mouse liver. Time-of-day-specific liver gene expression in Id2(+/+) and Id2(-/-) mice under circadian conditions was studied using DNA microarray analysis, identifying 651 differentially expressed genes, including a subset of 318 genes deemed rhythmically expressed in other studies. Examination of individual time courses reveals that these genes are dysregulated in a highly time-specific manner. A cohort of different functional groups were identified, including genes associated with glucose and lipid metabolism, e.g. serum protein Igfbp1 and lipoprotein lipase. We also reveal that the Id2(-/-) mice show a reduction in lipid storage in the liver and white adipose tissue, suggesting that disruption of normal circadian activity of components of lipid metabolism can result in overt physiological alterations. These data reveal a role for the transcriptional repressor ID2 as a circadian output regulator in the periphery.

GD3 synthase overexpression enhances proliferation and migration of MDA-MB-231 breast cancer cells

The disialoganglioside G(D3) is an oncofetal marker of a variety of human tumors including melanoma and neuroblastoma, playing a key role in tumor progression. G(D3) and 9-O-acetyl-G(D3) are overexpressed in approximately 50% of invasive ductal breast carcinoma, but no relationship has been established between disialoganglioside expression and breast cancer progression. In order to determine the effect of G(D3) expression on breast cancer development, we analyzed the biosynthesis of gangliosides in several breast epithelial cell lines including MDA-MB-231, MCF-7, BT-20, T47-D, and MCF10A, by immunocytochemistry, flow cytometry, and real-time PCR. Our results show that, in comparison to tumors, cultured breast cancer cells express a limited pattern of gangliosides. Disialogangliosides were not detected in any cell line and G(M3) was only observed at the cell surface of MDA-MB-231 cells. To evaluate the influence of G(D3) in breast cancer cell behavior, we established and characterized MDA-MB-231 cells overexpressing G(D3) synthase. We show that G(D3) synthase expressing cells accumulate G(D3), G(D2), and G(T3) at the cell surface. Moreover, G(D3) synthase overexpression bypasses the need of serum for cell growth and increases cell migration. This suggests that G(D3) synthase overexpression may contribute to increasing the malignant properties of breast cancer cells.

Renal gangliosides are involved in lead intoxication

The biological effects of lead are well defined; however, neither the risk exposure level nor the subcellular mechanism of its action is completely clear. The present work was undertaken to investigate the effects of low level and long term lead exposure on the composition and expression of rat renal gangliosides. In order to identify ganglioside expression, frozen sections of kidneys were stained with monoclonal antibodies GMB16 (GM1 specific), GM28 (GM2 specific), AMR-10 (GM4 specific) and CDW 60 (9-O-Ac-GD3 specific). Strong reactivity was observed for GMB28, AMR-10 and CDW 60, while GMB16 developed only weak labelling in treated kidney compared with the control. The alterations in the expression of renal gangliosides observed by immunohistochemistry were accompanied by quantitative and qualitative changes in the thin layer chromatography of total gangliosides isolated from kidney tissues. Lead treatment produced a significant increase in 9-O-Ac GD3, a ganglioside involved in apoptotic processes. In agreement with this result, a significant decrease in the number of apoptotic glomerular cells was observed with the TUNEL assay. These findings lead us to suggest that alterations in renal gangliosides produced by low level lead exposure are associated with the apoptotic processes that take place in the kidney. These findings provide evidence that low level and long term lead exposure produces renal ganglioside alterations with urinary microalbumin excretion. The results suggest that lead levels within the limits of biological tolerance already cause molecular renal damage without clinical signs of toxicity.

The possible contribution of a general glycosphingolipid transporter, GM2 activator protein, to atherosclerosis

We previously found that oxidized low-density lipoprotein (LDL) elevated the expression of mRNA of GalNAcbeta1-4[NeuNAcalpha2-3]Galbeta1-4Glc-Cer (GM2) ganglioside activator protein, in human monocyte-derived macrophages. Recently, GM2 activator protein has become known as a general glycosphingolipid transporter as well as a specific cofactor for the hydrolysis of GM2 ganglioside by lysosomal beta-hexosaminidase A. Accumulation of glycosphingolipids has been observed in the serum or aorta of atherosclerotic model animals and humans. The proliferation of aortic smooth muscle cells, elevation of LDL uptake by macrophages, interfering LDL clearance by the liver, and enhancement of platelet adhesion to collagen have been proposed as the underlying mechanisms of glycosphingolipid-mediated atherogenesis. The GM2 activator protein can bind, solubilize and transport a broad spectrum of lipid molecules, indicating that GM2 activator protein may function as a general intra- and inter-cellular lipid transport protein. Collectively, elevated levels of GM2 activator protein in the aorta may be another feature of human atherosclerosis.

Disialoganglioside GD3 increases in the secretion of apoB-containing lipoproteins

The function of gangliosides, sialic acid-containing glycolipids, on the secretion and assembly of apoB-containing lipoproteins is poorly understood. Here, we report that the GD3 synthase is involved in apoB secretion in retinoic acid (RA)-treated Chang liver cells via transcriptional induction of microsomal triglyceride transfer protein (MTP). The overexpression of GD3 synthase in Chang liver cells increases the expression of the MTP gene, but GM3 synthase-transfected cells did not. The levels of GM3 and GD3 gangliosides in each of the transfected cells were increased in the cell extract as well as the medium. In addition, GD3 synthase-transfected cells showed an increased secretion of triglyceride-enriched apoB. In contrast, the triglyceride content in GM3 synthase-transfected cells was relatively lower. Treatment with small interfering RNAs (siRNAs) and GD3 antibody decreased apoB secretion. These results indicate that plasma membrane associated GD3 play important roles in apoB secretion, and that an enhancement in GD3 levels might be a risk factor for the development of atherosclerosis by increasing the secretion of triglyceride-enriched apoB containing lipoproteins.

Evaluation of SAT-1, SAT-2 and GalNAcT-1 mRNA in colon cancer by real-time PCR

By qualitative and quantitative PCR, we evaluated the expression of three messengers coding for SAT-1, SAT-2 and GalNAcT-1 in human samples of intestinal cancer and some cell lines (breast cancer and melanomas). Qualitative PCR demonstrated, in human tissues but not in the cell lines examined, the presence of an mRNA that lacks hexon 3; experiments performed on transfected SKMEL-28 excluded a regulative role of this noncanonical mRNA. Data from real-time PCR, statistically analysed by ANOVA indicated that the mRNA expression of all the considered glycosyltransferases (SAT-1, SAT-2 and GalNAcT-1) was significantly different in tumours versus their own control. The ganglioside patterns in the examined samples did not correlate with mRNA expression; this finding demonstrates that ganglioside expression is the result of a very complex balance between anabolic and catabolic enzyme activities. Although this study is still preliminary, it opens a new possibility for neoplastic prognosis finding potential molecular markers among the mRNAs that codify for glycosyltransferases.

Glycoimmunomics of human cancer: current concepts and future perspectives

Future strategies for the treatment of human cancer require a full appreciation of the intracellular and extracellular changes that accompany neoplastic transformation. The changes may involve a variety of micro- and macro-molecules, including, but not restricted to, peptides, proteins (with sugar and/or lipid moieties), oligosaccharides, glycolipids (neutral or acidic, e.g., gangliosides), ceramides, fatty acids and other lipids. Although several therapeutic approaches have been well developed in recent years, most of the reported studies focus on proteins and peptides. Glycoantigens and lipoantigens have been neglected. Elucidation of the profiles and properties of all molecules associated with tumor progression is required to develop a successful strategy to treat human cancer. This review describes the unique immunomics of tumor-associated glycoantigens and explains why the field of glycoimmunomics may yield clinically important biomarkers and treatments for the management of human cancer.

Inhibition of atherosclerosis by the serine palmitoyl transferase inhibitor myriocin is associated with reduced plasma glycosphingolipid concentration

Glycosphingolipids (GSL) have been implicated as potential atherogenic lipids. Inhibition of hepatic serine palmitoyl transferase (SPT) reduces plasma sphingomyelin (SM) levels in the absence of changes in cholesterol or triglyceride (TG) concentration and this leads to a reduction of atherosclerosis in apolipoprotein-E gene knockout (apoE(-/-)) mice. The possibility that the reduced atherosclerosis resulting from SPT inhibition is associated with decreases in plasma GSL concentration has not been examined and was the primary aim of this investigation. We show that intraperitoneal delivery of the SPT inhibitor myriocin for 9 weeks inhibits atherosclerosis in apoE(-/-) mice fed a high fat diet. Lesion inhibition was most pronounced at the aortic arch and distal sites of the thoracic and abdominal aorta. There was also a trend towards a reduction in lesion area at the aortic root. Myriocin treatment resulted in significant reductions in both plasma SM and GSL concentration of 42% and 25%, as assessed by enzymatic and HPLC methods, respectively. Moreover, SM and GSL concentrations were significantly correlated, indicating that SPT inhibition suppresses the synthesis of both these sphingolipids concomitantly. The inhibition of atherosclerosis induced by myriocin was not associated with changes in plasma cholesterol or TG concentrations or lipoprotein profiles as determined by FPLC. These data indicate that therapeutic reduction of plasma SM and/or GSL concentrations may offer a novel treatment for atherosclerosis.

The Ganglioside GD3 as the Greek Goddess Hecate: Several Faces Turned Towards as Many Directions

The disialoganglioside GD3 can mediate biological functions as diverse as proliferation, differentiation, and apoptosis. Since intracellular level of GD3 is crucial for the cell, understanding the mechanisms by which GD3 metabolism is tightly regulated seems of particular importance. GD3 can be enlisted among the most potent natural inducers of mitochondrial damage and apoptosis. However, some cell types resist GD3-mediated mitochondrial damage through complex mechanisms which are beginning to be unveiled.

Alcohol Reduces GM1 Ganglioside Content in the Serum of Inbred Mouse Strains

BACKGROUND

Endogenous and exogenous gangliosides in the plasma affect physiologic and pathologic processes such as angiogenesis and atherogenesis. However, the genetic and environmental factors that regulate the expression of plasma gangliosides are not well known. As shown in the liver and the brain, profiles of gangliosides in the plasma may be strain-specific and can be altered by intake of alcohol. Therefore, we analyzed serum gangliosides derived from inbred mouse strains with and without alcohol treatment.

METHODS

C57BL/6ByJ (B6By) and BALB/cJ mice (60-70 days old) were injected with 20% alcohol (1-6 g/kg) or saline intraperitoneally, and the ganglioside content of the serum, liver, and cerebellum was measured 4 hr after the injection. Also, the effect of oral alcohol self-administration for 18 days with escalating (3-12%) concentrations of alcohol on the serum GM1 content was studied in B6By mice. The quantification of GM1 was performed with a thin-layer chromatography-staining procedure using a cholera toxin B subunit, and the content of other gangliosides was measured after staining with resorcinol reagent.

RESULTS

We found that basal GM1 (containing N-glycolylneuraminic acid) content in the serum of BALB/cJ mice (4.8 +/- 0.26 ng/microl) was 25 times higher than that of B6By mice (0.19 +/- 0.01 ng/microl); the major ganglioside in both strains was GM2. The ganglioside profile in the liver was similar to that of the serum, and the GM1 content in BALB/cJ was nine times higher than that of B6By. Both injection and oral self-administration of alcohol lowered GM1 levels in the serum.

CONCLUSIONS

Endogenous ganglioside profiles in the serum are under genetic control among inbred mouse strains, and they can be altered by acute and chronic alcohol administration. These genetic and alcohol-induced differences in the plasma gangliosides, which appear to reflect ganglioside metabolism in the liver, may affect alcohol-related behaviors and pathologic processes.

Effect of gangliosides on the copper-induced oxidation of human low-density lipoproteins

The role of gangliosides in the copper-induced oxidative modification of human low-density lipoprotein (LDL) was studied focusing on the early stage of LDL oxidation in which the concentration of conjugated dienes increases only weakly. The changes in the protein and lipid component were followed using fluorescence spectroscopy. The results indicate that binding of gangliosides to LDL causes slower destruction of tryptophan fluorescence and suppresses cross-linking between the reactive groups of the protein and the products of lipid peroxidation. The protective role of gangliosides could be assigned to their interference with the lipid-protein interaction in the LDL particle, which might be important for the maintenance of the native plasma antioxidant status in vivo.

GD3 ganglioside and apoptosis

Lipid and glycolipid mediators are important messengers of the adaptive responses to stress, including apoptosis. In mammalian cells, the intracellular accumulation of ganglioside GD3, an acidic glycosphingolipid, contributes to mitochondrial damage, a crucial event during the apoptopic program. GD3 is a minor ganglioside in most normal tissues. Its expression increases during development and in pathological conditions such as cancer and neurodegenerative disorders. Intriguingly, GD3 can mediate additional biological events such as cell proliferation and differentiation. These diverse and opposing effects indicate that tightly regulated mechanisms, including 9-O-acetylation, control GD3 function, by affecting intracellular levels, localization and structure of GD3, and eventually dictate biological outcomes and cell fate decisions.

GD3 in cellular ageing and apoptosis

Lipid and glycolipid mediators are important components of the adaptive responses to stress, including apoptosis. In mammalian cells, the intracellular accumulation of ganglioside GD3, an acidic glycosphingolipid, contributes to mitochondrial damage, a crucial event during the apoptotic program. GD3 is a minor ganglioside in most normal tissues. Its expression increases during development and in pathological conditions such as cancer and neurodegenerative disorders. Interestingly, GD3 expression also increases with the normal ageing process. Moreover, GD3 can also mediate biological events like proliferation and differentiation. Since organism integrity requires a tight balance between cell proliferation, apoptosis and senescence, controlling the intracellular level of GD3 appears of particular importance for cell fate determination.

Characterization of human apolipoprotein B100 oligosaccharides in LDL subfractions derived from normal and hyperlipidemic plasma: deficiency of alpha-N-acetylneuraminyllactosyl-ceramide in light and small dense LDL particles

The carbohydrate composition of apolipoprotein (apo) B100, particularly its degree of sialylation, may contribute to the atherogenic properties of low-density lipoprotein (LDL). We analyzed LDL apoB100 glycans derived from normolipidemic, hypercholesterolemic, and hypertriglyceridemic diabetic subjects. Using exoglycosidase carbohydrate sequencing and matrix-assisted laser desorption/ionization mass spectrometry to analyze fluorescently labeled oligosaccharides, we report evidence for several carbohydrates not previously identified on apoB100, including truncated complex biantennary N-glycans and hybrid N-glycans. The distribution and diversity of the apoB100 glycans isolated from all individuals was highly conserved. The N-glycan composition of apoB100 derived from five LDL subpopulations (LDL1, d = 1.018-1.023; LDL2, d = 1.023-1.030; LDL3, d = 1.030-1.040; LDL4, d = 1.040-1.051; LDL5, d = 1.051-1.065 g/ml) did not vary in normolipidemic or hypercholesterolemic subjects. Furthermore, we found no evidence for "desialylated" apoB100 glycans in any of the samples analyzed. Analysis of the most abundant LDL ganglioside, alpha-N-acetylneuraminyllactosyl-ceramide, revealed a deficiency in small dense LDL and in the most buoyant subpopulation. These data provide a novel explanation for the apparent deficiency of sialic acid in small dense LDL and indicate that the global apoB100 N-glycan composition is invariable in the patient groups studied.

Serum ganglioside patterns in multiple sclerosis

The relative distribution of gangliosides was determined in the serum of 37 patients with multiple sclerosis (MS) and of 30 healthy subjects. There was a significant increase of GM1 and GD1a, and a decrease of GM3 proportion in the serum of relapsing-remitting MS patients (RRMS) during their first MS attack. The RRMS patients in relapse with a long duration of the disease had a significant decrease of GM1 and an increase of GD1a portion in the serum. An increase of GD1a, one of the major brain neuron ganglioside fraction, suggested the neuron injury in the early and with a long duration RRMS. The finding of an increase of GM1, the main human myelin ganglioside, during the first MS attack in RRMS patients confirms previous evidence for the possible involvement of gangliosides in the early pathological course of demyelination in MS.

Sphingolipids in food and the emerging importance of sphingolipids to nutrition

Eukaryotic organisms as well as some prokaryotes and viruses contain sphingolipids, which are defined by a common structural feature, i.e. , a "sphingoid base" backbone such as D-erythro-1,3-dihydroxy, 2-aminooctadec-4-ene (sphingosine). The sphingolipids of mammalian tissues, lipoproteins, and milk include ceramides, sphingomyelins, cerebrosides, gangliosides and sulfatides; plants, fungi and yeast have mainly cerebrosides and phosphoinositides. The total amounts of sphingolipids in food vary considerably, from a few micromoles per kilogram (fruits) to several millimoles per kilogram in rich sources such as dairy products, eggs and soybeans. With the use of the limited data available, per capita sphingolipid consumption in the United States can be estimated to be on the order of 150-180 mmol (approximately 115-140 g) per year, or 0.3-0.4 g/d. There is no known nutritional requirement for sphingolipids; nonetheless, they are hydrolyzed throughout the gastrointestinal tract to the same categories of metabolites (ceramides and sphingoid bases) that are used by cells to regulate growth, differentiation, apoptosis and other cellular functions. Studies with experimental animals have shown that feeding sphingolipids inhibits colon carcinogenesis, reduces serum LDL cholesterol and elevates HDL, suggesting that sphingolipids represent a "functional" constituent of food. Sphingolipid metabolism can also be modified by constituents of the diet, such as cholesterol, fatty acids and mycotoxins (fumonisins), with consequences for cell regulation and disease. Additional associations among diet, sphingolipids and health are certain to emerge as more is learned about these compounds.

Autoantibodies to gangliosides in sera of atherosclerotic patients

Using ELISA we studied the levels and clinical correlation of serum antibodies against gangliosides and 5-hydroxytryptamine (5-HT) in patients with atherosclerosis and clinical manifestations of cardiovascular disease. A range of 70-80% of the patients showed higher titers of anti-GM3(L) and anti-5HT as compared to normal serum. The anti-GM3(L) antibodies appeared to be directed mainly against GM3 present in platelets and were much less reactive against GM3 isolated from the aorta. We concluded that the antigens responsible for the elevated anti-GM3(L) and anti 5-HT levels in atherosclerotic sera are released by vessel-wall activated platelets. These results provide further evidence of on-going autoimmune processes in atherosclerosis. The content of total sialic (TS) and lipid-bound sialic acid (LBS) was measured in sera of patients with IHD and of similar numbers of healthy donors. In the patient groups the average TS and LBS concentration was about 25% higher than in the control group. These changes appeared to be associated with higher degrees of protein sialylation and larger amounts of LDL in the patient sera than in those of healthy controls.

Inhibition of glycosphingolipid synthesis by threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) and the modulation of IL-1beta-stimulated expression of inducible nitric oxide synthase in rat aortic smooth muscle cells

1. The composition of glycosphingolipids is altered in atherosclerotic tissue. In order to study the possible modulation of interleukin-1beta (IL-1beta)-induced expression of inducible nitric oxide synthase (iNOS) by endogenously synthesized glycosphingolipids, we investigated rat aortic vascular smooth muscle cells (VSMC) grown in the presence of the inhibitor of glycosphingolipid synthesis, threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP). 2. Depletion of glycosphingolipids by PDMP (20-30 microM) was demonstrated by thin-layer chromatography of D-[1-(14)C]-galactose- or L-[-U14C]-serine-labelled glycosphingolipids. Nitrite generation was measured by the diaminonaphthalene assay, nitric oxide was determined by the oxyhaemoglobin technique and iNOS protein was detected by immunocytochemistry. 3. In VSMC grown in the presence of PDMP, the glycosphingolipid content was reduced by 30-50%. In PDMP-treated VSMC, IL-1beta (3 micro ml[-1])-stimulated release of nitrite (135 +/- 4 nmol mg(-1) protein 48 h[-1]) was significantly increased as compared to IL-1beta-stimulated control cells (40 +/- 3 nmol mg(-1) protein 48 h(-1); n = 6, P < 0.001). Similarly, IL-1beta (3 micro ml(-1), 36 h)-stimulated release of nitric oxide was higher in PDMP-treated VSMC (6.1 +/- 0.5 nmol mg(-1) protein h[-1]) as compared to untreated cells (2.0 +/- 0.6 nmol mg(-1) protein h(-1); n = 3, P < 0.01). These findings were confirmed by the demonstration of increased expression of iNOS protein (14.9 +/- 1.2% vs 6.4 +/- 0.2%; n = 4, P < 0.001), as shown by immunocytochemistry. 4. Evidence is presented that endogenous glycosphingolipids are important modulators of cytokine-induced iNOS expression. In view of an altered glycosphingolipid profile in atherosclerotic arteries, these mechanisms might be of relevance for the pathogenesis of atherosclerosis and restenosis subsequent to vessel injury.

Incorporation and localisation of ganglioside GM3 in human intimal atherosclerotic lesions

Immunohistochemical examination showed that sections of intimal atherosclerotic plaques contained cells and cell clusters as well as areas of extracellular matrix specifically stained with antibodies against ganglioside GM3. No immunohistochemical staining was observed in areas bordering the plaques where there was no histological evidence of atherosclerosis. To determine whether the ganglioside GM3 deposits in the intimal plaques derived directly from plasma or were synthesised by intimal cells. intimal plaque and plasma LDL were assayed for ganglioside GM3 fatty acid composition. This assay showed that more than 50% of the fatty acids of GM3 isolated from both atherosclerotic and normal intima are either minor fatty acids or those absent from LDL GM3. We conclude that the GM3 deposits present in intimal plaque arise in intimal cells and do not derive from plasma LDL.

Serum gangliosides as endogenous immunomodulators

Gangliosides suppress various immune activities in vitro and in vivo. Their level is significantly elevated in tumors and atherosclerotic aorta tissue, as well as in the sera of patients with tumors or atherosclerosis. Here, Lev Bergelson suggests that ganglioside-induced immunomodulation might be involved in atherogenesis and carcinogenesis, and describes a hypothesis that cites gangliosides as a factor interfering with the clearance of low-density lipoproteins (LDLs) and promoting the formation of atherosclerotic plaques.