Glycosphingolipids of human plasma

Selective Enrichment via TiO2 Magnetic Nanoparticles Enables Deep Profiling of Circulating Neutral Glycosphingolipids

Circulating neutral glycosphingolipids (neutral GSLs (nGSLs)) are a unique subset of nGSLs that detach from organs or cell membranes and enter the bloodstream. Altered molecular distribution of circulating nGSL is increasingly associated with diseases. However, profiling of circulating nGSLs presents a lasting challenge due to their low abundances and structural complexity. Although TiO2 magnetic nanoparticles (TiO2 MNPs) were effective for the enrichment of nGSLs in brain tissue, the protocol showed limited selectivity for circulating nGSLs because their abundances were 100-times lower in human plasma than in brain tissue. In this work, we optimized the key parameters of selective enrichment by TiO2 MNPs and achieved 1:10,000 selectivity for nGSLs over interfering phospholipids, while maintaining ∼70% recovery for different subclasses of nGSLs. By integrating TiO2 MNP-based selective enrichment with reversed-phase liquid chromatography mass spectrometry and charge-tagging Paternò-Büchi derivatization, we achieved deep profiling of over 300 structures of nGSLs and sulfatides across 5 orders of magnitude in relative abundances, a significant leap regarding lipid coverage. We also depicted the structural atlas of nGSLs with defined headgroup, long-chain base, N-acyl chain, the location of desaturation, and 2-hydroxylation. Such information provides a valuable resource for lipidomic studies concerning the roles of circulating nGSLs in health and diseases.

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.

Comprehensive Profiling of Glycosphingolipid Glycans Using a Novel Broad Specificity Endoglycoceramidase in a High-Throughput Workflow

The biological function of glycosphingolipids (GSLs) is largely determined by their glycan headgroup moiety. This has placed a renewed emphasis on detailed GSL headgroup structural analysis. Comprehensive profiling of GSL headgroups in biological samples requires the use of endoglycoceramidases with broad substrate specificity and a robust workflow that enables their high-throughput analysis. We present here the first high-throughput glyco-analytical platform for GSL headgroup profiling. The workflow features enzymatic release of GSL glycans with a novel broad-specificity endoglycoceramidase I (EGCase I) from Rhodococcus triatomea, selective glycan capture on hydrazide beads on a robotics platform, 2AB-fluorescent glycan labeling, and analysis by UPLC-HILIC-FLD. R. triatomea EGCase I displayed a wider specificity than known EGCases and was able to efficiently hydrolyze gangliosides, globosides, (n)Lc-type GSLs, and cerebrosides. Our workflow was validated on purified GSL standard lipids and was applied to the characterization of GSLs extracted from several mammalian cell lines and human serum. This study should facilitate the analytical workflow in functional glycomics studies and biomarker discovery.

Plasmatic Ganglioside Profile and Age-Related Macular Degeneration: A Case-Control Study

PURPOSE

Gangliosides are glycosphingolipids that are particularly abundant in the nervous system, including the retina. However, their precise role in this tissue and its pathologies remain poorly understood. The objective of the present study was to characterize the ganglioside profile of human plasma and to determine whether it is affected in age-related macular degeneration (AMD).

METHODS

Eighty-three subjects were included: control subjects (n = 25), atrophic AMD patients (n = 27) and exudative AMD patients (n = 31). For each subject, gangliosides were extracted from plasma and analyzed by liquid chromatography coupled to mass spectrometry.

RESULTS

GM3 appeared to be by far the major ganglioside of human plasma, associated with GD3. No specific ganglioside class was detected in the plasma of AMD patients. Fourteen molecular species of GM3 and 9 species of GD3, accounting for the variability of the ceramide moiety of the ganglioside molecule, were identified and characterized. Analyses revealed no significant differences in the proportion of these species between control, atrophic and exudative AMD patient groups. Total GM3 levels did not differ either.

CONCLUSION

Although gangliosides are considered important for the retina's structure and function, it seems that circulating gangliosides are not associated with the retinal damage occurring during the course of AMD.

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.

Neutral glycosphingolipids in human blood: a precise mass spectrometry analysis with special reference to lipoprotein-associated Shiga toxin receptors

Shiga toxin (Stx)-producing Escherichia coli are the leading cause of hemorrhagic colitis and life-threatening extraintestinal complications in humans. Stx1 and Stx2 are transferred by yet to be delineated mechanisms from the intestine to the circulation where they injure microvascular endothelial cells. The resulting vascular lesions cause renal failure and brain damage. Because lipoproteins are potential carriers of Stx through the circulation, we investigated human lipoprotein-associated neutral glycosphingolipids (GSLs) with emphasis on high (globotriaosylceramide) and low (globotetraosylceramide) affinity Stx-receptors. TLC overlay employing Stx1, Stx2, and anti-GSL antibodies demonstrated preferential distribution of globo-series GSLs to very low- and low-density lipoproteins compared with minor association with high-density lipoproteins. Electrospray ionization quadrupole time-of-flight mass spectrometry portrayed C24:0/C24:1 and C16:0 as the major fatty acid of the ceramide moieties of Stx-receptors carrying nonvarying d18:1 sphingosine. This structural heterogeneity was also found in precursor lactosylceramide, glucosylceramide, and galactosylceramide, the last showing an exceptionally high degree of hydroxylated C24 fatty acids. Our findings provide the basis for exploring the functional role of lipoprotein-associated Stx-receptors in human blood.

Software utilities for the interpretation of mass spectrometric data of glycoconjugates: application to glycosphingolipids of human serum

Glycosphingolipids (GSLs) are major components of the outer leaflet of the cell membrane. These lipids are involved in many cell surface events and show disease-related expression changes. GSLs could thus serve as useful targets for biomarker discovery. The GSL structure is characterized by two entities: a hydrophilic glycan and a hydrophobic ceramide moiety. Both components exhibit numerous structural variations, the combination of which results in a large diversity of GSL structures that can potentially exist. Mass spectrometry (MS) is a powerful tool for high-throughput analysis of GSL expression analysis and structural elucidation. Yet, the assignment of GSL structures using MS data is tedious and demands highly specialized expertise. SysBioWare, a software platform developed for MS data evaluation in glycomics, was here applied for the MS analysis of human serum GSLs. The program was tuned to provide automated compositional assignment, supporting a variety of glycan and ceramide structures. Upon in silico fragmentation, the masses of predicted ions arising from cleavages in the glycan as well as the ceramide moiety were calculated, thus enabling structural characterization of both entities. Validation of proposed structures was achieved by matching in silico calculated fragment ions with those of experimental MS/MS data. These results indicate that SysBioWare can facilitate data interpretation and, furthermore, help the user to deal with large sets of data by supporting management of MS and non-MS data. SysBioWare has the potential to be a powerful tool for high-throughput glycosphingolipidomics in clinical applications.

Relationships between biochemical bone turnover markers, season, and inflammatory status indices in prepubertal Gambian boys

Seasonal and interindividual differences in food availability and illnesses cause variations in growth, including bone growth, in children in developing countries. We investigated seasonal differences in biochemical (serum) markers of bone metabolism and relationships between these markers (procollagen type I N propeptide [P1NP], serum C-terminal telopeptide of type 1 collagen [S-CTX]) and serum markers of inflammation (alpha(1)- antichymotrypsin [ACT], C-reactive protein [CRP], sialic acid) in prepubertal Gambian boys. Three seasonal time points were chosen: August, mid-rainy season; October, late rainy season (both are associated with decreased food supply, increased prevalence of infection, reduced weight gain, and stunting); and April, late dry season, when environmental conditions are better and rates of weight gain are higher. The prevalence of raised inflammatory markers was high: 29% of ACT values >0.40 g/L in August, 42% >0.40 g/L in October, and 18% >0.40 g/L in April. Of CRP values, 92-96% were >0.47 mg/L and 30%, 46%, and 18% were >3.95 mg/L in August, October, and April, respectively. Also, 42-52% of sialic acid values were >648 mg/L. Of the bone markers, S-CTX exhibited the highest values in August; P1NP did not vary with season. Inverse relationships between each bone marker and the acute phase markers occurred, with the strongest relationships between P1NP and ACT or sialic acid. We conclude that bone collagen synthesis and turnover are reduced during inflammation in rural Gambian boys. Biochemical indices can provide powerful, single-time point evidence of infection and growth-faltering episodes.

Gangliosides are not essential for influenza virus infection

Sialic acid is known to be an essential part of influenza virus receptors, but the specific identity of the receptor molecules on target cells is still not defined. In particular, the relative roles played by cellular sialylglycoproteins and gangliosides in virus entry into target cells remain unclear. To test whether gangliosides are essential for virus infection, we used the GM-95 mutant cell line of mouse B16 melanoma which lacks synthesis of major glycosphingolipids including gangliosides. We found that GM-95 cells grown in serum-containing medium harboured substantial amounts of ganglioside receptors for influenza virus due to incorporation of serum gangliosides. To obtain ganglioside-free cells, we adapted GM-95 cells to growth in defined serum-free (sf) medium. Ganglioside-free GM-95-sf cells could be infected by avian and human influenza A viruses and produced infectious virus progeny demonstrating that gangliosides were neither absolutely necessary for the early nor for the late stages of the infection. However, sensitivity of the GM-95-sf cells to the viruses was 2-4 times lower than that of the ganglioside-containing parent cell line. Further studies are needed to specify whether this effect was due to the lack of gangliosides, neutral glycosphingolipids, or other effects.

Specificity of human trans-sialidase as probed with gangliosides

It has been shown that human blood contains a soluble 67 kDa enzyme, belonging by its donor-acceptor properties to trans-sialidases. The enzyme is capable of both cleaving and synthesizing alpha2-3 and alpha2-6 sialosides [Atherosclerosis2001, 159, 103]. In this work the study of donor-acceptor specificity of the new enzyme was extended. It has been demonstrated in vitro that trans-sialidase possesses the ability of transferring Neu5Ac residue to acceptor (asialofetuin) both from alpha2-3- (GM1, GM3, GD1a), and alpha2-8-sialylated gangliosides (GD3 and GD1b, but not GT1b and GQ1b). Transfer of radiolabeled Neu5Ac from fetuin to glycosphingolipids demonstrated that Lac-Cer>mono- and disialogangliosides>GT1b>GQ1b were acceptors for this enzyme. Two methods were used to reveal whether alpha2-8 bond can be formed between Neu5Ac residues during trans-sialylation, that is immunochemical detection using monoclonal antibodies specific to alpha2-8 di- and oligosialic acids, and fluorometric C7/C9 analysis. Both methods demonstrated the formation of Neu5Acalpha2-8Neu5Ac termination by trans-sialidase, for example, in case of the use 3'SL as sialic acid donor and Neu5Ac-PAA or LDL as acceptor. Thus, human trans-sialidase in vitro displays wide substrate specificity: the enzyme is capable of digesting as well as synthesizing alpha2-3, alpha2-6, and alpha2-8 sialosides.

Infantile-onset symptomatic epilepsy syndrome caused by a homozygous loss-of-function mutation of GM3 synthase

We identified an autosomal recessive infantile-onset symptomatic epilepsy syndrome associated with developmental stagnation and blindness. Assuming a founder effect in a large Old Order Amish pedigree, we carried out a genome-wide screen for linkage and identified a single region of homozygosity on chromosome 2p12-p11.2 spanning 5.1 cM (maximum lod score of 6.84). We sequenced genes in the region and identified a nonsense mutation in SIAT9, which is predicted to result in the premature termination of the GM3 synthase enzyme (also called lactosylceramide alpha-2,3 sialyltransferase). GM3 synthase is a member of the sialyltransferase family and catalyzes the initial step in the biosynthesis of most complex gangliosides from lactosylceramide. Biochemical analysis of plasma glycosphingolipids confirmed that affected individuals lack GM3 synthase activity, as marked by a complete lack of GM3 ganglioside and its biosynthetic derivatives and an increase in lactosylceramide and its alternative derivatives. Although the relationship between defects in ganglioside catabolism and a range of lysosomal storage diseases is well documented, this is the first report, to our knowledge, of a disruption of ganglioside biosynthesis associated with human disease.

Serum total ganglioside level correlates with clinical course in melanoma patients after immunotherapy with therapeutic cancer vaccine

The authors tested the hypothesis that the therapeutic destruction of residual tumors may be reflected in the level of serum total gangliosides (sTG). The sTG level was evaluated in 17 patients with in-transit melanoma and 70 patients with resected regional node metastasis, who have received a polyvalent therapeutic melanoma cell vaccine. The treatment response was determined by regression of in-transit metastases or by overall survival after resection. sTG levels were measured, blinded, before and after immunotherapy. The mean sTG level of the in-transit melanoma patients increased from 18.57 +/- 3.18 mg/dL pretreatment to 23.7 +/- 5.5 mg/dL between weeks 2 and 16 after initiation of treatment (p(2) < 0.0001). By week 24, the level had returned to its prevaccine level in the seven clinical responders (18.1 +/- 2.3 mg/dL vs. 20.4 +/- 3.2 mg/dL; p(2) < 0.050) but remained higher than its prevaccine level in the 10 nonresponders (23.3 +/- 5.1 mg/dl vs. 17.2 +/- 2.7 mg/dL). Similarly, the sTG level of the patients with nodal metastases increased between weeks 2 and 16 after the first vaccine treatment; by week 24, it had returned to pretreatment level in patients who survived more than 56 weeks but remained significantly elevated (p(2) < 0.01) in patients who survived less than 56 weeks. The sTG level increased between weeks 2 and 16 in all vaccine recipients and returned to prevaccine level by week 24 in all who showed measurable regression of in-transit melanoma (7 of 17 patients) or improved overall survival (53 of 70 patients). The data suggest that sTG level could be a potential tool for assessing the response to immunotherapy in melanoma patients by week 24.

Cryosurgical ablation of liver tumors in colon cancer patients increases the serum total ganglioside level and then selectively augments antiganglioside IgM

Cryosurgical ablation (CSA) of tumors induces disruptive necrosis. Necrosis may release tumor gangliosides into circulation and they may augment serum antiganglioside antibodies depending on the nature of gangliosides released. The hypothesis is tested by determining the level of serum total gangliosides (STG) and their antibody titers in the sera of colon cancer patients with cryoablated liver tumors. As controls, we examined the sera of patients who underwent radiofrequency ablation (RFA) and regular surgery (RS), none of which cause disruptive necrosis. The STG level (expressed as lipid-bound sialic acids, LBSA) is higher (p(2)<0.001) in 35 patients (stage IV) than in 38 healthy case-controls (median 23.48 mg/dL, Q-range 7.1 vs 16.04 mg/dL, Q-range 4.5). The mean STG level increased significantly to 31.2+/-6.0mg/dL (p(2)<0.03) after CSA. Concomitantly, the IgM titer against colon cancer-associated gangliosides (GM(2), GD(1a), GT(1b)), increased significantly, but no increase was observed against normal tissue gangliosides (GM(3) or GM(1)). Also after RFA and RS, no such increase was observed either in the level of STG or in IgM titer against tumor gangliosides. The results suggest that CSA-induced necrosis might have acted as an adjuvant, because purified gangliosides without exogenous adjuvants even after repeated immunization failed to elicit antibody response. The post-CSA decline in the STG level correlated with the increase in the antibodies, suggesting a homeostatic role of the antibodies.

Neutral glycosphingolipid-dependent inactivation of coagulation factor Va by activated protein C and protein S

To test whether neutral glycosphingolipids can serve as anticoagulant cofactors, the effects of incorporation of neutral glycosphingolipids into phospholipid vesicles on anticoagulant and procoagulant reactions were studied. Glucosylceramide (GlcCer), lactosylceramide (LacCer), and globotriaosylceramide (Gb(3)Cer) in vesicles containing phosphatidylserine (PS) and phosphatidylcholine (PC) dose dependently enhanced factor Va inactivation by the anticoagulant factors, activated protein C (APC) and protein S. Addition of GlcCer to PC/PS vesicles enhanced protein S-dependent APC cleavage in factor Va at Arg-506 by 13-fold, whereas PC/PS vesicles alone minimally affected protein S enhancement of this reaction. Incorporation into PC/PS vesicles of GlcCer, LacCer, or Gb(3)Cer, but not galactosylceramide or globotetraosylceramide, dose dependently prolonged factor Xa-1-stage clotting times of normal plasma in the presence of added APC without affecting baseline clotting times in the absence of APC, showing that certain neutral glycosphingolipids enhance anticoagulant but not procoagulant reactions in plasma. Thus, certain neutral glycosphingolipids (e.g. GlcCer, LacCer, and Gb(3)Cer) can enhance anticoagulant activity of APC/protein S by mechanisms that are distinctly different from those of phospholipids alone. We speculate that under some circumstances certain neutral glycosphingolipids either in lipoprotein particles or in cell membranes may help form antithrombotic microdomains that might enhance down-regulation of thrombin by APC in vivo.

High-performance liquid chromatography analysis of ganglioside carbohydrates at the picomole level after ceramide glycanase digestion and fluorescent labeling with 2-aminobenzamide

The functional importance of glycolipids has emphasized the need for more sensitive methods of detection, characterization, and quantification than has often been possible using traditional thin-layer chromatographic techniques. We describe the use of ceramide glycanase and HPLC to identify and quantify gangliosides in which the carbohydrate is in Glcbeta1--> linkage with ceramide. Detection of released carbohydrate was by fluorescent labeling with 2-aminobenzamide at the reducing terminal prior to HPLC analysis. Under the conditions described, ceramide glycanase hydrolyzed all of the common gangliosides studied, offering a broad spectrum of specificity. Release and detection of carbohydrate were linear over a wide range (over two orders of magnitude) of micromolar glycolipid substrate concentrations. Use of an N-linked glycan as an internal standard allowed accurate quantification and a recovery of 93% was achieved. The method additionally maintained the sensitivity (chromatographic peaks containing 1 pmol were readily detected from tissue samples) and comparable resolution to related assays. This was shown by the separation, not only of isomeric carbohydrates from the "a" and "b" series, but also of ganglioside carbohydrate differing only by the presence of either N-acetyl- or N-glycolylneuraminic acid. Application of the method to neutral glycosphingolipids and to tissue samples, including 10-microl quantities of plasma, is illustrated. Glycan structures were confirmed by exoglycosidase digestion and/or matrix-assisted laser desorption/ionization mass spectrometry.

Human plasma trans-sialidase causes atherogenic modification of low density lipoprotein

In earlier studies we have found that incubation of low density lipoprotein (LDL) with autologous blood plasma-derived serum leads to a loss of sialic acid from lipoprotein particles. In this study we demonstrated that sialic acid removed from LDL was transferred to glycoconjugates of lipoproteins, glycoproteins and sphingolipids of human serum. This showed that human serum contained the trans-sialidase activity. Gel-filtration chromatography of human blood serum demonstrated the presence of trans-sialidase activity in lipoprotein subfractions as well as in lipoprotein-deficient serum. Trans-sialidase (about 65 kDa) was isolated from lipoprotein-deficient serum using affinity chromatography carried out with Neu5Acalpha2-8Neu5Ac-sepharose FF-6. Optimal pH values for the trans-sialidase were 3.0, 5.0 and 7.0. Calcium and magnesium ions stimulated the enzyme activity at millimolar concentrations. Isolated enzyme can remove sialic acid from LDL, IDL, VLDL, and HDL particles (in decreasing rate order). Serum trans-sialidase transferred sialic acid from glycoconjugates of plasma proteins (fetuin, transferrin) and gangliosides (GM3, GD3, GM1, GD1a, GD1b). Sialylated glycoconjugates of human blood erythrocytes also served as substrate for serum trans-sialidase. We have found that sialic acid can also be removed from N- and O-linked glycans, sialylated Le(x) and Le(a), oligosialic acids, and sphingolipid carbohydrate chains. The rate of sialic acid release decreased in the following order: alpha2,6>alpha2,3>>alpha2,8. Transferred molecule of sialic acid can form alpha2,6, alpha2,3 and to a lesser degree alpha2,8 linkage with galactose, N-acetyl-galactosamine or sialic acid of acceptors. The glycoconjugates of erythrocytes, lipoprotein particles, plasma proteins, neutral sphingolipids and gangliosides may serve as acceptors of transferred sialic acid. Trans-sialidase-treated native LDL becomes desialylated and then can induce cholesteryl ester accumulation in human aortic intimal smooth muscle cells. Thus, trans-sialidase may be involved in the early stages of atherogenesis characterized by foam cell formation.

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 total sialic acid in cholangiocarcinoma patients: an ROC curve analysis

OBJECTIVES

This study was undertaken to establish the diagnostic utility of serum total sialic acid (TSA) for patients with cholangiocarcinoma (CCA).

DESIGN AND METHODS

Serum TSA was determined in 89 histologically confirmed CCA patients, 38 with benign hepatobiliary diseases (BHD) and 43 healthy persons. To check whether the test could adequately discriminate between these groups, complete statistical Receiver Operating Characteristic (ROC) curves were analyzed.

RESULTS

The mean value of serum TSA in CCA patients (2.75 +/- 0.67 mmol/L) was significantly higher than that in the BHD (2.33 +/- 0.69 mmol/L p < 0.002) and healthy persons (1.89 +/- 0.46 mmol/L p < 0.001) groups. The areas under the ROC curves were 0.6699 and 0.8558, respectively. A cut-off value of 2.33 mmol/L discriminated between the CCA, BHD and healthy groups with a sensitivity of 71.9% and a positive predictive value range of 80 to 89%.

CONCLUSION

Determination of TSA yielded high diagnostic values for differentiating between CCA, BHD and healthy persons. The determination of serum TSA would be most useful as an adjunct diagnosis rather than an early detection and screening tool because of the apparent nonspecificity of SA to a given disease.

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.

Occurrence of sialic acids in healthy humans and different disorders

Sialic acid (SA), N-acetylated derivatives of neuraminic acid, play a central role in the biomedical functioning of humans. The normal range of total sialic acid (TSA) level in serum/plasma is 1.58-2.22 mmol L-1, the free form of SA only constituting 0.5-3 mumol L-1 and the lipid-associated (LSA) forms 10-50 mumol L-1. Notably, considerably higher amounts of free SA are found in urine than in serum/plasma (approximately 50% of the total SA). In inherited SA storage diseases such as Salla's disease, SA levels are elevated many times over, and their determination during clinical investigation is well established. Furthermore, a number of reports describe elevated SA levels in various other diseases, tentatively suggesting broader clinical utility for SA markers. Increased SA concentrations have been reported during inflammatory processes, probably resulting from increased levels of richly sialylated acute-phase glycoproteins. A connection between increased SA levels and elevated stroke and cardiovascular mortality risk has also been reported. In addition, SA levels are slightly increased in cancer, positively correlating with the degree of metastasis, as well as in alcohol abuse, diabetes, chronic renal failure and chronic glomerulonephritis. Several different mechanisms are assumed to underlie the elevated SA concentrations in these disorders. The apparent non-specificity of SA to a given disease limits the potential clinical usefulness of SA determination. In addition, some non-pathological factors, such as aging, pregnancy and smoking, may cause changes in SA concentrations. The absolute increases in SA levels are also rather small (save those in inherited SA storage disorders); this further limits the clinical potential of SA as a marker. Tentatively, SA markers might serve as adjuncts, when combined with other markers, in disease screening, disease progression follow-up, and in the monitoring of treatment response. To become clinically useful, however, the existing SA determination assays need to be considerably refined to reduce interferences, to be specific for certain SA forms, and to be more easy to use.

A new procedure for determining ganglioside GD3 a potential glial cell activation marker in cerebrospinal fluid

Increased amounts of ganglioside GD3 [II3 (NeuAc)2-LacCer], associated with reactive gliosis, have been documented in a variety of neurodegenerative disorders. GD3 expression has also been reported in microglial cells, not only during development but also in reactive states, where the glial activation is considered to be part of the repair process. It is important to find markers in cerebrospinal fluid that will enable us to identify damage and register changes in pathological processes within the brain. A sensitive and practically applicable method for determination of GD3 ganglioside in cerebrospinal fluid has been developed. The procedure, which includes extraction, purification on silica gel and thin-layer enzyme-linked immunostaining, also allows determination of sulphatide, a marker of demyelinating processes, in the same portion of CSF. The method has been applied to CSF samples from 101 normal individuals aged 2-83 years. The GD3 concentration was found to be significantly correlated to age and reflecting the concentrations within the brain. GD3 ganglioside analysis by means of this method might be useful for studying glial changes during brain maturation as well as in brain disorders.

Thermotropic behavior of galactosylceramides with cis-monoenoic fatty acyl chains

To define the thermotropic behavior of galactosylceramides (GalCer) containing cis monounsaturated acyl chains, N-X:1Delta(X-9) cis galactosylsphingosines (GalSph) were synthesized (where X=24, 22, 20, or 18) and investigated by differential scanning calorimetry (DSC). After hydration of dried glycolipid, aqueous dispersions were prepared by repetitive heating and freeze-thaw cycles. The DSC data clearly showed that introducing a single cis double bond into the acyl chain of GalCer lowers the transition temperature of the main endothermic peak and affects the kinetics of formation of various metastable and stable gel phases. More importantly, the data emphasize the role that double bond location in concert with acyl chain length play in modulating the thermotropic behavior of GalCers. In contrast to the 18:1 GalCer and 20:1 GalCer endotherms which remain unchanged after identical repetitive heating scans and low temperature incubations, the thermotropic responses of 22:1 GalCer and 24:1 GalCer depended directly upon incubation time at lower temperatures following a heating scan. Only after extended incubation (4-5 days) did the endotherms revert to behavior observed during the initial heating scan that followed sample preparation by cyclic heating and freeze-thaw methods. The extended incubation times required for 22:1 GalCer and 24:1 GalCer to assume their more stable packing motifs appear to be consistent with nucleation events that promote transbilayer interdigitation. Yet, due to the slow kinetics of the process, the presence of cis monounsaturation in very long acyl chains that are common to GalCer may effectively inhibit transbilayer lipid interdigitation under physiological conditions.

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.

Evaluation of the efficiency of an assay procedure for gangliosides in human serum

An efficiency assessment of a ganglioside assay procedure was carried out on human serum gangliosides from healthy subjects of different sex and age. The analysis of the gangliosides, extracted with chloroform/methanol and purified by lipid partitioning, ion exchange column chromatographic separation and desalting procedures as described by Senn et al. (1989) Eur J Biochem 181: 657-62, was performed by HPTLC followed by densitometric quantification. The yield of the procedure, expressed as radioactivity recovery, was determined by adding GM3 ganglioside, tritium labelled at the sialic acid acetyl group and at the C3 position of sphingosine, to the lyophilized serum or by associating it with the serum lipoproteins. In spite of the fact that the extraction and purification procedures were performed exactly as described we found the radioactivity recovery to be variable (25-50%) and much lower than that proposed. Much of the radioactivity was found in the organic phase after lipid partitioning, whilst all the ganglioside purification steps led to some further loss. After the introduction of some modifications to the procedure the recovery improved, reaching 67-79%. The analyses on 33 samples of 5 ml showed a human serum ganglioside content of about 10 nmol ml-1 (as corrected for the recovery), and confirmed that GM3 ganglioside is the main component of the total serum ganglioside mixture.

Glycosphingolipid accumulation in the aortic wall is another feature of human atherosclerosis

High accumulation of lipids is a typical feature of an atherosclerotic lesion. We have previously identified the chemical structure of the major glycosphingolipids (GSLs) of human aorta; however, quantification of the absolute concentration of GSLs was not carried out. In the present study, for the first time we have performed a quantitative comparative analysis of GSL composition in the media and two sublayers of the intima taken from normal regions, fatty streaks, and atherosclerotic plaques of the human aorta. The intimal tissue containing fatty streaks and atherosclerotic plaques accumulated GSLs, predominantly glucosylceramide (GlcCer), lactosylceramide (LacCer), and ganglioside GM3. GSL levels in plaques were highest: GlcCer was 18- and 8-fold, LacCer was 8- and 7-fold, and GM3 was 2.5- and 12-fold higher than in musculoelastic and elastic-hyperplastic intimal layers of normal regions, respectively. We did not observe a significant increase in other GSLs. An increase in the content of gangliosides GD3 and GD1a was detected in the media underlying atherosclerotic lesions. On the basis of an analysis of the ratio of GlcCer, LacCer, and GM3 accumulated in the tissue and cells of the elastic-hyperplastic layer of intima, we have concluded that the accumulation of the above-mentioned GSLs occurs mainly in the extracellular space of the intima. In this study, we have also demonstrated that extracellular lipid liposomes, which appear in the early stages of atherogenesis, are one locus of GSL accumulation in the extracellular space of the intima.(ABSTRACT TRUNCATED AT 250 WORDS)

Circulating gangliosides of breast-cancer patients

Gangliosides were isolated from the sera of recently diagnosed breast-cancer patients and from individuals who were apparently free of disease. Quantificative and qualitative analyses were carried out by 2-dimensional high-performance thin-layer chromatography and gas chromatography. The locations of isolated gangliosides on thin-layer chromatograms were determined by visualization with resorcinol, and each spot was quantified by digital image densitometry. The ganglioside profiles of cancer patients were compared to those of the control group, revealing a significant increase in total lipid-bound sialic acid and a specific increase in polysialogangliosides in the patients with breast cancer. Furthermore, an increase was noted in the ratio of gangliosides of the b-series biosynthetic pathway over those of the a-series in the cancer sera, as compared to the controls. Gas chromatographic analysis of the peracetylated methanolysis mixtures derived from the total ganglioside fraction of cancer patients supported the HPTLC data, with an increase in total sialic acid, galactose, and sphingosine residues. No unusual gangliosides were found in the mixture from breast-cancer patients.

Gangliosides and atherosclerosis

The ganglioside levels in atherosclerotic lesions of human aorta are considerably higher than those in unaffected areas of aorta, and atherosclerotic patients frequently have increased concentrations of serum gangliosides. The present review summarizes recent findings that suggest the possible involvement of aortic gangliosides in platelet activation and adhesion of platelets to the vessel wall. The effect of gangliosides on the structure of low density lipoproteins (LDL), on the interaction of LDL with macrophages and hepatic cells and on the LDL-regulated biosynthesis of cholesterol is also discussed. In vitro experiments have demonstrated that a major ganglioside of the intima of atherosclerotic aorta induces rapid adhesion, aggregation and spreading of platelets. Moreover, gangliosides present in elevated amounts in the intercellular space of atherosclerotic aortic tissue modify the surface structure and stimulate aggregation of LDL. Ganglioside-modified LDL are readily recognized and taken up by macrophages, while preincubation of LDL with low concentrations of gangliosides inhibits LDL binding to hepatic cells. Thus, ganglioside enrichment of LDL is likely to interfere with LDL clearance via the hepatic cells. Thus, ganglioside enrichment of LDL is likely to interfere with LDL clearance via the hepatic LDL receptor, and to stimulate binding of LDL to the scavenger receptor of macrophages. It is postulated that high ganglioside levels in the aorta and serum may be an additional risk factor in atherosclerosis.

Shedding of GD2 ganglioside in patients with retinoblastoma

Retinoblastoma is a rare tumor of the young child with an intraocular localization that leads to certain problems of diagnosis. With the aim of defining a biochemical marker--which is still lacking for this disease--the gangliosides of a pool of fresh retinoblastoma tumors were analyzed. The ganglioside pattern was shown to have GM3, GM2, GM1, GD3, GD2, GD1b and GT1b as the major components. The occurrence of a high concentration of GD2 in the tumors led us to investigate the possibility of changes in the level of GD2 in the sera of retinoblastoma patients, using quantitative immunostaining with GD2-specific mouse monoclonal antibodies (MAbs). In 9 out of 10 tumor-bearing patients, the serum level of GD2 ganglioside was significantly higher than the average value found in normal individuals. A 2-year follow-up of patients showed that successful treatment resulted in a rapid decrease in the serum level of GD2 down to the normal range, from which a subsequent elevation was seen only in relapsing patients. Although the clinical study needs further development, the results obtained to date suggest that GD2 is shed in the serum of tumor-bearing patients and that the level of GD2 could be a potential serum marker of human retinoblastoma.

Measurement of sialic acid in serum and urine: clinical applications and limitations

Many recent studies have examined the sialic acid content of serum or urine in various pathological states. We have briefly reviewed the substances which contribute to the observed total sialic acid concentration, and given an overview of assay methods used. Three major areas of clinical interest in sialic acid metabolism are discussed. Serum total sialic acid, 'lipid-bound' and 'protein bound' sialic acid have all been proposed as tumour markers; but the usefulness of any of these tests is severely limited by changes due to accompanying inflammatory processes. Serum total sialic acid is not a valuable simple marker of an acute phase response. Urinary free and bound sialic acid measurements should be included in screening protocols for inherited disorders of lysosomal metabolism. Current developments in research and potential applications within the clinical biochemistry laboratory are briefly discussed.

Human serum gangliosides in hypercholesterolemia, before and after extracorporeal elimination of LDL

Total content, pattern and transport by lipoproteins of gangliosides have been studied in the sera of 10 patients with hypercholesterolemia and manifest cardiovascular disease. Half of the patients with hypercholesterolemia and 3 healthy controls were treated with heparin-induced extracorporeal LDL precipitation (HELP). In the sera of the untreated group total gangliosides and cholesterol were elevated about 2-fold. Ratios of normal ganglioside components were not altered and abnormal ganglioside species not detected. Treatment with HELP resulted in an almost selective removal of lipid-bound sialic acid carried on LDL. The re-increase of total serum gangliosides was strictly correlated to that of LDL-cholesterol and apolipoprotein B. Total gangliosides and ratios of individual components carried on single LDL- and HDL-particles were not altered by the HELP treatment. Our results indicate that gangliosides are excreted into the serum along with nascent apolipoprotein B-containing lipoproteins, which are of hepatic origin. In hypercholesterolemia excretion of gangliosides into the circulation is elevated and surplus of circulating gangliosides is bound to increased numbers of 'atherogenic' LDL. Biosynthesis of different ganglioside components, most probably by the liver, and total amount of gangliosides bound to lipoprotein particles seem not to be altered.

Biosynthesis and excretion of gangliosides by the isolated perfused rat liver

De novo synthesis and excretion into perfusate and bile fluid of hepatic gangliosides were studied in isolated perfused rat livers. Addition of N-acetyl-[6-3H(n)]D-mannosamine to the perfusate resulted in radioactive synthesis of at least eight gangliosides labeled in their sialic acid residues. About 10% of total de novo synthesized gangliosides were excreted into the perfusate, less than 1% into the bile fluid. Labeled gangliosides were tentatively identified by cochromatography with known standards. All of them are known to occur in rat liver and sera. The results indicate that most, if not all, normal serum gangliosides are synthesized in the liver; excretion with bile fluid is negligible. They explain previous observations, and indicate clinical implications, which are discussed.

Interaction of low-density lipoproteins with gangliosides

The ganglioside uptake capacity of human serum low-density lipoproteins (LDL), the mode of ganglioside-LDL binding, and the influence of gangliosides on the floatation properties, size distribution, stability and fluorescence of LDL were investigated. The data obtained suggest that both hydrophobic and electrostatic forces are involved in formation of ganglioside-LDL complexes, but the former appear to be more important. Although association of gangliosides with LDL is predominantly unspecific, nonsaturable, and weak, a small saturable component due to specific ganglioside-apolipoprotein binding, also appears to be involved. In the presence of gangliosides the lipoprotein particles aggregate, the intrinsic fluorescence of LDL and their interaction with antibodies against apo-B change indicating that the state of apo-B [corrected] is modified by gangliosides.

Gangliosides of human cerebrospinal fluid in various neurologic diseases

Simultaneous profile determination and quantification of human cerebrospinal fluid (CSF) gangliosides in various neurologic diseases (n = 71) was examined. Gangliosides were extracted with methanol/chloroform from clinically available amounts of CSF (4-5 ml), then separated and quantified by high-performance thin-layer chromatography (HPTLC) and direct densitometry. Based on chromatographic comparison with standards, the percentage of lipid-bound NeuAc positive fractions in 'normal' CSF samples were: GM1 (II3 NeuAc-GgOse4Cer) (3%); GD3 (II3 NeuAc2-Lac-Cer) (4%); GD1a (IV3 NeuAc, II3 NeuAc-GgOse4 Cer) (15%); X1 (3%); GD1b (II3(NeuAc)2-GgOse4 Cer) (16%); X2 (4%); GT1b (IV3 NeuAc, II3(NeuAc)2-GgOse4-Cer) (40%); and GQ1b (IV3(NeuAc)2, II3(NeuAc)2-GgOse4-Cer (15%). Similarity between CSF and CSF and human cerebellar cortex, particularly in proportion of "b" series gangliosides (GQ1b, GT1b, GD1b), could be observed. A higher proportion of GD1a ganglioside, with decreased GQ1b was found in infancy. The total ganglioside content (mean +/- 2 SD) varied between 645-894 micrograms/l. Significant alterations of the CSF ganglioside profile, with an increase in less polar gangliosides, GM3 and GD3, correlated with the blood-brain barrier dysfunction (CSF hemorrhages, compressive syndrome), or some malignant processes (metastatic brain melanoma). A statistically significant increase in the content of total CSF gangliosides was found in the following groups of patients as compared to controls: (1) ischemic cerebrovascular accident (CVI) with good outcome (P less than 0.02); (2) peripheral neuropathy and polyneuropathy (P less than 0.001) and (3) intravertebral discopathy (P less than 0.05). A significant decrease in the content of total CSF gangliosides was found in CVI group with lethal outcome (P less than 0.05).

Altered biosynthesis of gangliosides in developing biliary cirrhosis in the rat

The biosynthesis of gangliosides was studied in developing biliary cirrhosis in rats 14, 28, and 42 days after bile duct obstruction. The total content and patterns of gangliosides in livers and sera, and the activity of six hepatic ganglioside synthases in a cell-free system were determined. Up to 7-fold increased synthase activities were strictly correlated in time and extent with increased total contents of gangliosides in liver and serum. In addition, altered patterns of serum gangliosides were observed. The results clearly demonstrate that the liver is the main source of elevated serum gangliosides in biliary cirrhosis in the rat. Increased hepatic biosynthesis and the secretion of gangliosides into the serum appear to be an important pathogenetic event. Alterations of hepatic enzyme activities indicate that GL2 and GM3 synthase regulate total hepatic ganglioside content. However, certain abnormalities in ganglioside patterns which were observed in the liver and sera of cirrhotic animals can not be explained by changes in hepatic enzyme activity. They indicate additional pathobiochemical mechanisms to be involved, e.g., altered hepatocellular processing and/or impaired secretion into bile.

Characteristic binding of human plasma apolipoprotein B to gangliotetraosylceramide and gangliotriaosylceramide

The binding of human plasma low-density lipoproteins (LDL), freshly prepared by discontinuous ultracentrifugation, to several neutral and acidic glycosphingolipids was examined by TLC immunostaining with the anti [apolipoprotein B (apoB)] antibody. ApoB was found to bind characteristically to the asialogangliosides, gangliotetraosylceramide (Gg4Cer) and gangliotriaosylceramide (Gg3Cer), the former being a more potent receptor than the latter, indicating that the sequences Gal beta 1-3GalNAc beta 1-4Gal and GalNAc beta 1-4Gal are involved in the binding of apoB. A weak positive reaction with fucosylgangliotetraosylceramide (IV2Fuc-Gg4Cer), which has the same internal recognition sequences, was also observed (the binding ability was only 1/7 of that in the case of Gg4Cer). No binding to other neutral glycosphingolipids, or glycosphingolipid sulfates (I3-SO3-GalCer) and gangliosides, was detected, and therefore substitution of the receptor glycolipid with sialic acid was thought to inhibit the binding. The results indicate that, along with the binding of apoB to the LDL-binding domain of the receptor glycoprotein, interaction with some carbohydrate chains in the receptor, or with glycolipids coexisting on the plasma membrane, may be important for the binding of apoB to cells.

Altered concentrations, patterns and distribution in lipoproteins of serum gangliosides in liver diseases of different etiologies

Concentrations, patterns and distribution in different lipoprotein classes of human serum gangliosides were investigated in acute and chronic liver diseases of different etiologies. The total concentrations of gangliosides were moderately elevated in sera of patients with cirrhosis and acute B or NANB virus hepatitis, but almost 3-fold in those with severe cholestasis. Up to three unknown gangliosides appeared in the sera of six out of nine patients with alcoholic cirrhosis. They accounted for 11-27% of total serum gangliosides. In acute viral hepatitis very small amounts of these gangliosides were inconsistently detected. In severe cholestasis (bilirubin greater than 10 mg/dl) the distribution of serum gangliosides was altered in different lipoprotein classes including lipoprotein X (LP(x)). The results indicate that the liver produces serum gangliosides. The diseased liver is supposed to affect the total concentration, pattern and distribution of serum gangliosides in different lipoprotein classes as a result of at least two different pathogenetic events: the qualitative and quantitative alterations of their biosynthesis and secretion into the circulation (cirrhosis); and the alteration of lipoprotein metabolism following cholestasis.

Evaluation and limitations of the lipid-associated sialic acid test for the detection of human cancer

Previous studies and those of the authors have reported about raised levels of lipid-bound sialic acid (LSA) in sera of patients with various neoplasms. Most authors have used the method of Katopodis and Stock for isolating serum LSA. Because of the discrepancy of the amount of extracted LSA with the content of pure gangliosides in sera reported by other groups the authors analyzed the composition of the extracted LSA by immunochemical approaches. They were able to isolate considerable amounts of glycoproteins containing sialic acid as acid alpha-1-glycoprotein, antitrypsin, haptoglobin, antichymotrypsin, and immunoglobulins from the so-called "LSA" fraction. There is a very strong correlation between the raised LSA levels and the content of acid-alpha-1-glycoprotein in the sera of patients with malignancy. Therefore the term lipid-bound sialic acid applied to this test is misleading, since glycoproteins containing sialic acid are mostly responsible for the high "LSA" levels.

Gangliosides in normal human serum. Concentration, pattern and transport by lipoproteins

The total content and pattern of gangliosides were determined in the unfractionated sera of 11 healthy human adults and in isolated lipoproteins. The total content of lipid-bound sialic acid was 10.5 +/- 3.2 nmol/ml serum. The ganglioside profile consisted of more than ten different components. The major ganglioside was GM3, followed by GD3, GD1a, GM2, GT1b, MG-3 (sialosyllactoneotetraosylceramide), GD1b and GQ1b. Traces of four additional gangliosides could not be quantified reliably. Ganglioside patterns did not vary in sera taken from healthy adults of different age and sex. Approximately 98% of human serum gangliosides were transported by serum lipoproteins, predominantly by LDL (66%), followed by HDL (25%) and VLDL (7%). The quantitative distribution of individual gangliosides in VLDL and LDL was almost the same as that in the unfractionated serum; some differences existed with the ganglioside profile in HDL.

Diagnostic value of ganglioside patterns in plasma of human diseases

A method that could be facilitated for the quantitation and qualitation of gangliosides in human plasma was developed and applied in the present study for characterization of ganglioside patterns in plasmas of patients with neoplastic diseases including gastric cancer, adult T-cell leukemia (ATL), and acute lymphocytic leukemia (ALL). As a retrovirus-infected disease with different clinical entity, human T-cell lymphotropic virus type I-associated myelopathy (HAM) was also subjected to this study. The results were compared with the patterns obtained from normal control plasmas. The analytical data revealed that GM3 increased in gastric cancer, GT1b decreased in HAM and ATL, and GD3, GM1 and GM3 decreased in ALL. There were close correlations between various human diseases and the presence of gangliosides with their specific patterns. Furthermore, gangliosides purified from plasma of patients with HAM significantly inhibited the expression of CD4 antigen on human T lymphocyte membrane. Therefore, analytical studies of plasma gangliosides could provide diagnostic and therapeutic values in retroviral infections.

Structure of a ganglioside with Cad blood group antigen activity

The Cad antigen is a rare erythrocyte blood group antigen expressed on both sialoglycoprotein and ganglioside structures. It is related both serologically and biochemically to the Sda blood group antigen expressed on over 90% of Caucasian erythrocytes. We reported previously that Cad erythrocytes contain a novel ganglioside that binds Helix pomatia lectin and inhibits human anti-Sda antibody. We have now purified the Cad ganglioside and determined its structure. The ganglioside contained Glc-Gal-GlcNAc-GalNAc-NeuAc in a molar ratio of 1.00:1.94:0.95:0.93:1.05. Its chromatographic mobility was between that of GM1 and GD3. After treatment with beta-hexosaminidase (human placenta Hex A), the product migrated with 2-3-sialosylparagloboside (IV3NeuAcnLc4OseCer), it no longer bound H. pomatia lectin, and it acquired the ability to bind an antibody to sialosylparagloboside. Treatment of this material with neuraminidase (Vibrio cholerae) yielded a product with the mobility of paragloboside (nLc4OseCer) that bound monoclonal antibody 1B2, which is specific for terminal N-acetyllactosaminyl structures. Treatment of the Cad ganglioside with Arthrobacter ureafaciens neuraminidase yielded a product reactive with monoclonal antibody 2D4, which is specific for terminal GalNAc beta (1-4)Gal structures. These data provide strong evidence that the Cad ganglioside structure is GalNAc beta (1-4)[NeuAc alpha (2-3)]Gal beta (1-3)Gal beta (1-4)GlcCer. 1H NMR analysis also supports the conclusion that the terminal GalNAc is linked beta (1-4) to Gal. High-performance thin-layer chromatographic ganglioside patterns from three blood group Cad individuals showed a direct correlation between the quantity of Cad ganglioside and the strength of Cad antigen expression on the erythrocytes, as measured by hemagglutination.(ABSTRACT TRUNCATED AT 250 WORDS)

Monoclonal antibodies that bind to galactosylgloboside (SSEA-3 antigen)

The 3-fucosyllactosamine (3-FL) antigenic determinant, Gal(beta 1-4)[Fuc(alpha 1-3)]-GlcNAc-R, is very immunogenic in BALB/c mice. A panel of monoclonal antibodies was raised against a novel glycosphingolipid that contains a terminal 3-FL structure (structure 1): (formula: see text) Surprisingly, most of these antibodies reacted with the internal galactosylgloboside structure rather than with the terminal 3-FL epitope. The specificities of two of these antibodies, 5A3 and 8A7, were analyzed by enzyme-linked immunosorbent assay and immunostaining procedures, and compared with MC631 (anti-SSEA-3), the only other monoclonal antibody known to bind to galactosylgloboside. 5A3 and 8A7 bound equally well to structure 1 and to galactosylgloboside. These antibodies also bound to structure 1 from which the terminal galactose, or the galactose and fucose, had been removed, but not to globoside or sialylated galactosylgloboside. In contrast, MC631 did not bind to structure 1 but, as described previously, did bind to globoside and sialylated galactosylgloboside. Galactosylgloboside is a developmentally regulated antigen of mouse embryos, human teratocarcinomas, and mouse embryonic brain. Antibodies 5A3 and 8A7 will complement MC631 in the analysis of the distribution and regulation of galactosylgloboside.