Determination of lipid-bound sulfate by ion chromatography and its application to quantification of sulfolipids from kidneys of various mammalian species

A variety of procedures have been developed for determining the sulfate ester content of various biomolecules. Ion chromatography (IC), that is, quantitation of ionic substances by ion conductimetry after separation by anion-exchange chromatography, has been increasingly utilized for the determination of inorganic sulfate in clinical and environmental samples. We adopted suppressed-mode IC to the determination of lipid- or glycolipid-bound sulfate released by acid hydrolysis and found that it has the advantage of increased precision for wide concentration ranges (30 pmol to approximately micromol) and lack of interference from other lipids. To minimize deterioration of the separation column, the lipophilic constituents in the acid hydrolysate were removed by a two-phase partition system of chloroform-methanol-water. The inorganic sulfate was quantitatively extracted into the aqueous phase by replacing water with an alkaline buffer. By this method, the concentration of sulfolipids was determined in the kidney of mammals with various body mass. Sulfolipids were more concentrated in the kidney of smaller animals, which have higher maximum urine concentrating activity per gram of body mass, supporting the hypothesis of the function of sulfolipids as an ion barrier on the luminal surface of renal tubules.

A novel plasmal conjugate to glycerol and psychosine ("glyceroplasmalopsychosine"): isolation and characterization from bovine brain white matter

A novel plasmal conjugate of glycosphingolipid having cationic lipid properties was isolated from the white matter of bovine brain. Linkage analysis of galactosyl residue by methylation, liquid secondary ion, and electrospray ionization mass spectrometry of intact and methylated derivatives, and by (1)H- and (13)C-NMR spectroscopy, identified the structure unambiguously as an O-acetal conjugate of plasmal to the primary hydroxyl group of glycerol and to the 6-hydroxyl group of galactosyl residue of beta-galactosyl 1-->1 sphingosine (psychosine). This novel compound is hereby termed "glyceroplasmalopsychosine"; its structure is shown below (see text).

Kidney lipids in galactosylceramide synthase-deficient mice. Absence of galactosylsulfatide and compensatory increase in more polar sulfoglycolipids

UDP-galactose:ceramide galactosyltransferase (CGT) catalyzes the final step in the synthesis of galactosylceramide (GalCer). It has previously been shown that CGT-deficient mice do not synthesize GalCer and its sulfated derivative GalCer I(3)-sulfate (galactosylsulfatide, SM4s) but form myelin containing glucosylceramide (GlcCer) and sphingomyelin with 2-hydroxy fatty acids. Because relatively high concentrations of GalCer and SM4s are present also in mammalian kidney, we analyzed the composition of lipids in the kidney of Cgt(-/-) and, as a control, Cgt(+/-) and wild-type mice. The homozygous mutant mice lacked GalCer, galabiaosylceramide (Ga(2)Cer), and SM4s. Yet, they did not show any major morphological or functional defects in the kidney. A slight increase in GlcCer containing 4-hydroxysphinganine was evident among neutral glycolipids. Intriguingly, more polar sulfoglycolipids, that is, lactosylceramide II(3)-sulfate (SM3) and gangliotetraosylceramide II(3),IV(3)-bis-sulfate (SB1a), were expressed at 2 to 3 times the normal levels in Cgt(-/-) mice, indicating upregulation of biosynthesis of SB1a from GlcCer via SM3. Given that SM4s is a major polar glycolipid constituting renal tubular membrane, the increase in SM3 and SB1a in the mice deficient in CGT and thus SM4s appears to be a compensatory process, which could partly restore kidney function in the knockout mice.

Requirement of seminolipid in spermatogenesis revealed by UDP-galactose: Ceramide galactosyltransferase-deficient mice

Although seminolipid has long been suspected to play an essential role in spermatogenesis because of its uniquely abundant and temporally regulated expression in the spermatocytes, direct experimental evidence has been lacking. We have tested the hypothesis by examining the testis of the UDP-galactose:ceramide galactosyltransferase-deficient mouse, which is incapable of synthesizing seminolipid. Spermatogenesis in homozygous affected males is arrested at the late pachytene stage and the spermatogenic cells degenerate through the apoptotic process. This stage closely follows the phase of rapid seminolipid synthesis in the wild-type mouse. These observations not only provide the first experimental evidence that seminolipid is indeed essential for normal spermatogenesis but also support the broader concept that cell surface glycolipids are important in cellular differentiation and cell-to-cell interaction.

Determination of N-acetyl- and N-glycolylneuraminic acids in gangliosides by combination of neuraminidase hydrolysis and fluorometric high-performance liquid chromatography using a GM3 derivative as an internal standard

A highly sensitive method for quantification of sialic acids in gangliosides was developed. The sialic acids, released by hydrolysis of gangliosides, were converted to fluorescent derivatives with 1,2-diamino-4,5-(methylenedioxy)benzene (DMB) and separated on a reversed-phase C18 column with an isocratic elution. As little as 0.1-1.0 nmol of sialic acid in ganglioside was quantified. The use of acetate buffer instead of water in the mobile phase could prevent damage on the column and reduce background peaks derived from the reagents. When gangliosides were subjected to acid hydrolysis, the velocity of hydrolysis varied depending on their structures and a part of the sialic acid liberated decomposed with prolonged heating time. Therefore gangliosides were hydrolyzed by Arthrobacter ureafaciens neuraminidase in the presence of sodium cholate after addition of an internal standard. For the internal standard, GM3 with N-propionylneuraminic acid (GM3(NeuPr)) was synthesized from GM3(NeuAc) by N-deacylation followed by N-propionylation. Folch partition was used to decrease lipophilic materials included in the sample, and the sialic acids released were recovered from the upper phase. The present method has a satisfactory sensitivity in the simultaneous quantification of NeuAc and NeuGc in purified gangliosides as well as in crude lipid fractions containing a variety of gangliosides.

The major acidic glycolipids from the kidney of the Pacific salmon (Oncorhynchus keta): characterization of a novel ganglioside, fucosyl-N-acetylgalactosaminyl-GM1

Two fractions of a major ganglioside from the kidney of the pacific salmon, Oncorhynchus keta, were eluted from a DEAE-Sephadex column in the monosialosyl fraction. The faster moving ganglioside (X1) on TLC was separated from the slower moving one (X2) by HPLC using a silica beads column. By methylation analysis, chemical and enzymatic degradation, reaction with monoclonal antibodies, LSIMS, and (1)H-NMR spectroscopy, X1 was determined to be a monosialosyl ganglioside belonging to the ganglio-series with a unique Fucalpha1-3GalNAc linkage at the nonreducing terminal: Fucalpha1-3GalNAcbeta1-3Galbeta1-3GalNAcbeta1-4[ NeuAcalpha2-3]Galbeta 1-4Glcbeta1-1Cer. Analysis of the lipophilic moiety indicated predominance of 24:1 fatty acid in combination with sphingenine. X2 was found to have a glycon structure identical to X1. The ceramide of X2 consisted predominantly of saturated fatty acids (18:0 and 16:0). The tissue concentrations of X1 and X2 in kidney were 3.7 and 2.8 nmol/g, respectively.

Isolation and characterization of a unique sulfated ganglioside, sulfated GM1a, from rat kidney

A novel class of sulfoglycosphingolipid, a sulfate analog of ganglioside, was isolated from mammals for the first time. This sulfated ganglioside was purified from rat kidney by column chromatographies on anion exchangers and silica beads. One-dimensional 1H NMR, compositional and permethylation analyses showed that this glycolipid has a Gg4Cer core with 1 mol each of sulfate ester and N- glycolylneuraminic acid (NeuGc) at C-3 of galactose. The major ceramide consisted of nonhydroxy fatty acids (24:0 and 22:0) and 4-hydroxysphinganine (t18:0), deduced from the compositional analysis and negative liquid secondary ion mass spectrometry (LSIMS). Mild acid hydrolysis and solvolysis produced compounds which correspond to Gg4Cer IV3-sulfate (SM1b) and II3NeuGcalpha-Gg4Cer (GM1a (NeuGc)), respectively. The abundant ions characteristic for sulfated mono- and disaccharides in high-energy collision-induced dissociation (CID) spectra were consistent with the structure at the non-reducing terminus, HSO3 -O- Hex -O- HexNAc- rather than the alternative structure, NeuGc -O- Hex -O- HexNAc-. The two-dimensional 1H NMR further evidenced the presence of a 3 -O- sulfated galactose in the molecule. From these results the complete structure was proposed to be HSO3-3Galbeta-3GalNAcbeta-4(NeuGcalpha-3)Galb eta-4Glcbeta-1Cer (II3NeuGcalpha-Gg4Cer IV3-sulfate).

Structural characterization of a novel mono-sulfated gangliotriaosylceramide containing a 3-O-sulfated N-acetylgalactosamine from rat kidney

A novel mono-sulfated glycosphingolipid based on the gangliotriaose core structure was isolated from rat kidney. The isolation procedure involved extraction of lipids with chloroform/methanol, mild alkaline methanolysis, column chromatographies with anion exchangers and silica beads. The structure was characterized by compositional analysis, FTIR spectroscopy, methylation analysis, 1H-NMR spectroscopy and negative-ion liquid secondary ion mass spectrometry (LSMIS) using the intact glycolipid and its desulfation product. The two dimensional chemical shift correlated spectroscopy provided information on the sugar sequence as well as anomeric configurations, and indicated the presence of a 3-O-sulfated N-acetylgalactosamine within the molecule. Negative-ion LSIMS with high- and low-energy collision-induced dissociation defined the sugar sequence and ceramide composition, confirming the presence of a sulfated N-acetylgalactosamine at the non-reducing terminus. From these results, the complete structure was proposed to be HSO3-3GalNAc beta 1-4Gal beta 1-4Glc beta 1-1Cer (Gg3Cer III3-sulfate, SM2b).

Structural analysis of mono- and bis-sulfated glycosphingolipids by negative liquid secondary ion mass spectrometry with high- and low-energy collision-induced dissociation

Several underivatized mono- and bis-sulfated glycosphingolipids having gangliotriaose or gangliotetraose core structure were analyzed by negative liquid secondary ion mass spectrometry (LSIMS) with high- and low-energy collision-induced dissociation (CID). In the normal negative LSIMS spectra, each mono-sulfated glycolipid gave abundant [M - H]- ions and each bis-sulfated glycolipid gave abundant [M + Na - 2H]- ions as well as the hydrogen sulfate anion [OSO3H]-. In high-energy CID spectra of the deprotonated molecule, only ions containing a sulfate ester were clearly observed. When a sulfate was present on the non-reducing terminal saccharide residue, a series of ions corresponding to sulfated mono- to tetra-saccharides, resulting from sequential cleavage of glycosidic bonds, were observed. If the sulfate was attached to an internal hexose of the sugar chain, the product ions corresponding to the non-sulfated, non-reducing terminal residue were absent. In contrast, the low-energy CID resulted in extremely simple spectra that contained only one or two major product ions characteristic of each sulfated glycolipid. These results provided clear information on the overall sugar and ceramide compositions, and allowed saccharide structures differing in location and number of sulfate esters to be distinguished.

Enzymatic sulfation of gangliotriaosylceramide in human renal cancer cells

Biosynthesis of sulfoglycolipid is markedly increased in a human renal cancer cell line, SMKT-R3. We investigated the sulfotransferase catalyzing the transfer of sulfate from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to gangliotriaosylceramide (Gg3Cer) in SMKT-R3 cells. On thin-layer chromatography, the reaction product comigrated with Gg3Cer III3-sulfate (SM2b), not with Gg3Cer II3-sulfate (SM2a). To examine which monosaccharide of Gg3Cer was sulfated, the product was treated with beta-hexosaminidase A. Unlike authentic SM2a, of which the non-reducing terminal N-acetylgalactosamine was cleaved off, the product was not hydrolyzed. These results suggest that sulfate was transferred to the non-reducing terminal N-acetylgalactosamine. Gg3Cer sulfotransferase activity was independent of divalent cations but stimulated by Fe2+, and the optimal pH was approximately 6.5. The apparent Km values were 102 microM for PAPS and 348 microM for Gg3Cer. Gg3Cer II3,III3-bis-sulfate (SB2) and a sulfotransferase activity synthesizing SB2 from SM2a were also detected in SMKT-R3 cells.

A novel mono-sulfated pentaglycosylceramide with the isoglobo-series core structure in rat kidney

A five-sugar sulfated glycosphingolipid containing an isoglobo-series carbohydrate core was isolated from rat kidney and its structure characterized by compositional analysis, FTIR spectroscopy, methylation analysis and 1H NMR spectroscopy of the intact glycolipid and its limited degradation products, and negative liquid secondary ion mass spectrometry (LSIMS). The two dimensional chemical shift correlated spectroscopy and NOE spectroscopy provided information on the sugar sequence and linkage as well as anomeric configurations, so as to establish the presence of a 3-O-sulfated galactose and a Gal alpha 1-3Gal structure within the molecule. Negative LSIMS with collision-induced dissociation defined the sugar sequence and ceramide composition, allowing to confirm the presence, and indicating the position, of the sulfate group. The glycosphingolipid was found to be a mono-sulfated derivative of the isoglobo-series core, with the following structure: HSO3(-)-3Gal beta 1-3GalNAc beta 1-3Gal alpha 1-3Gal beta 1-4Glc beta 1-1Cer (iGb5Cer V3-sulfate).

Sulfated glycolipids are ligands for a lymphocyte homing receptor, L-selectin (LECAM-1), Binding epitope in sulfated sugar chain

Specific sugar ligands which bind to rat L-selectin (LECAM-1, lymphocyte homing receptor)-IgG chimera were investigated by thin-layer chromatography-binding assay and ELISA. Rat L-selectin-IgG bound to native sulfated glycolipids such as sulfatide (I3SO3-GalCer), seminolipid, SM3(II3SO3-LacCer), SB2(III3SO3,II3SO3-Gg3Cer), SB1a (IV3SO3,II3SO3-Gg4Cer). The binding activity of the SM2 (II3SO3-Gg3Cer) carrying the internal sulfated Gal was very low, indicating that non-reducing terminal SO3H-3Gal beta 1- structure is essential for the binding. The reactivity of sulfatide was higher than that of sialyl Le(x) [Neu5Ac alpha 2-3Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3Gal beta 1-4Glc beta 1-Ceramide] either in the presence of 1 mM Ca2+ or 1 mM Ca2+ and 5 mM EGTA. All the non-fucosylated gangliosides including ganglio-series and lacto-series type I and II chains tested gave a negative reaction. Neutral glycosphingolipids tested were all negative. Binding assay using synthetic sulfatide analogs indicated that the L-selectin-binding to its sulfated sugar ligands is position specific and depends on the number of the sulfate group, i.e., (SO3)3-3,4,6Gal- > (SO3)2-3,6Gal- > SO3-3Gal- > SO3-3Glc- > SO3-6Gal- > SO3-2Gal-. Lower reactivity of the chimera to SO3-3Glc-rather than SO3-3Gal- indicates that the chimera recognizes the configuration of hydroxyl group linked to the 4 carbon atom of the pyranose ring in galactose.

Isolation and structural characterization of a mono-sulfated isoglobotetraosylceramide, the first sulfoglycosphingolipid of the isoglobo-series, from rat kidney

A novel sulfoglycosphingolipid based on the isoglobo-series core structure was isolated from rat kidney and purified by column chromatographies with DEAE-Sephadex and silica beads. The structure was characterized by solvolysis, compositional analysis, proton NMR spectroscopy, Fourier-transform infrared spectroscopy, methylation analysis and liquid secondary ion mass spectrometry (LSIMS). The characteristic fragment ions for a sulfate and a sulfated N-acetylhexosamine were observed in LSIMS spectra. The two-dimensional chemical-shift-correlated spectroscopy (COSY) and nuclear Overhauser enhancement spectroscopy experiments evidenced the presence of a 3-O-sulfated N-acetylgalactosamine and a Gal alpha 1-3Gal structure in the molecule. The major ceramide consisted of 4-hydroxysphinganine linked to a C24 nonhydroxy fatty acid, deduced from both compositional analysis and LSIMS. From the above results, the following structure was established for this glycolipid: HSO3-3GalNAc beta 1-3Gal alpha 1-3Gal beta 1-4Glc beta 1-1Cer, isoglobotetraosylceramide (iGb4Cer) IV3-sulfate. Rat kidney also contained globotetraosylceramide (Gb4Cer) IV3-sulfate which has a carbohydrate core identical to that from human kidney. The yields of iGb4Cer IV3-sulfate and Gb4Cer IV3-sulfate were 0.27 and 0.07 nmol/g wet tissue, respectively.

Accumulation of highly acidic sulfated glycosphingolipids in human hepatocellular carcinoma defined by a series of monoclonal antibodies

An accumulation of sulfated and very complex, highly acidic glycolipids was observed in cultured human hepatocellular carcinoma cells. Among the cells tested, PLC/PRF/5 cells contained a significant amount of very complex sulfated acidic glycolipids, and HepG2 cells were characterized as having a large amount of relatively simple sulfated glycolipids. Several monoclonal antibodies (all IgM) directed to these sulfated and highly acidic glycolipids were established. Among them, 49-D6 and 7-E10 were both directed to SM3 (LacCer-II3-sulfate), a relatively simple sulfated glycolipid, and 34-A4 was directed to SD1a (GgOse4Cer II3,IV3-disulfate) and more complex sulfated glycolipids. The other four antibodies, 26-A10, 34-B9, 79-C8, and 16-E10, reacted with unknown highly acidic glycolipids, which were eluted in 0.9-2.7 M ammonium acetate in DEAE chromatography, indicating that these antigenic glycolipids were far more acidic than the usual glycolipids described until now. Analysis of the glycolipids extracted from the hepatocellular carcinoma tissues and cirrhotic livers of patients and from a normal liver with these monoclonal antibodies revealed that sulfated glycolipids having simple carbohydrate structures such as SM3 accumulated significantly in the cirrhotic liver (2 of 4 cases) as well as hepatocellular carcinoma tissue (15 of 17 cases, 88%), and more complex sulfated glycolipids and highly acidic glycolipids were much more specific to hepatocellular carcinoma tissues (10 of 17 cases, 59%) compared to the cirrhotic liver (0 of 4 cases).

Preparation and enzymatic degradation of monosulfogangliotriaosylceramide

Gangliotriaosylceramide 3'-sulfate (GgOse3Cer-II3-sulfate) contains the sugar sequence similar to that of GM2 ganglioside except that the NeuAc in GM2 is replaced by a sulfate group. Due to this structural similarity, we have studied the in vitro synthesis of GgOse3Cer-II3-sulfate using the system for GM2. Our results showed that GgOse3Cer-II3-sulfate could be synthesized from lactosylceramide 3'-sulfate and UDP-GalNAc catalyzed by N-acetylgalactosaminyltransferase prepared from rat brain (Dicesare, J. L., and Dain, J. A. (1971) Biochim. Biophys. Acta 231, 385-393). As in the case of GM2, the GgOse3Cer-II3-sulfate biosynthesized in vitro or isolated from rat kidney could also be cleaved by human beta-hexosaminidase A in the presence of GM2-activator (Li, S.-C., Hirabayashi, Y., and Li, Y.-T. (1981) J. Biol. Chem. 256, 6234-6240). The fact that the GM2-activator could stimulate beta-hexosaminidase A to hydrolyze both GM2 and Gg-Ose3Cer-II3-sulfate indicates that these two glycolipids may be catabolyzed by the same mechanism.

Acidic glycolipids from dolphin kidney

The composition and contents of acidic glycolipids in the kidney of a striped dolphin (Stenella coeruleoalba, the order Cetacea, whales) were determined. The following eight acidic glycolipids were isolated and characterized: SM4s (124.2 nmol/g tissue), SM3 (8.7), GM3 (NeuAc) (12.3), GM3 (NeuGc) (31.6), GD3 (NeuAc-NeuAc) (14.7), GD3 (NeuAc-NeuGc) (II3 alpha(NeuAc alpha 2-8NeuGc)-LacCer) (9.8), GD3 (NeuGc-NeuAc) (II3 alpha(NeuGc alpha 2-8NeuAc)-LacCer) (5.3), and GD3 (NeuGc-NeuGc) (15.8). The assignment of the four types of GD3 was further confirmed as described below. Evidence indicating 2-8 linkages of the disialosyl residues of GD3 was obtained on methylation analysis of sialic acid. GD3 (NeuAc-NeuAc) and GD3 (NeuGc-NeuAc) were degraded to GM3 (NeuAc), and GD3 (NeuAc-NeuGc) and GD3 (NeuGc-NeuGc) yielded GM3 (NeuGc) on mild acid hydrolysis. Fragment ions characteristic of the carbohydrate and lipophilic moieties of the permethylated GD3 were observed in direct inlet-electron impact-mass spectra. The presence of these four types of GD3 in a tissue has not been reported previously. GD3 contained non-hydroxy (69-84%) and hydroxy fatty acids (16-31%) with 16-24 carbons. The long chain base of all GD3, except GD3 (NeuGc-NeuAc) (not analyzed), consisted of 4-sphingenine (d18:1) and 4-hydroxysphinganine (t18:0) in almost equal amounts. The total amount of renal lipid-bound acidic groups (sulfate and sialic acid) of the dolphin (190 mumol/animal) is considerably higher than that of a terrestrial mammal (88 mumol/animal) with a body weight comparable to that of the dolphin. This deviation suggests that the amount of renal acidic amphiphiles required to maintain the osmotic balance of body fluids in marine mammals might be higher than that in terrestrial ones.

Characterization of sulfoglycosphingolipids by direct probe electron impact mass spectrometry

Novel mono- and bis-sulfoglycolipids, monosulfogangliotriaosylceramide, bis-sulfogangliotriaosylceramide, and bis-sulfogangliotetraosylceramide, were recently isolated from rat kidney. These sulfoglycolipids and their partially- or fully-desulfated products were characterized by direct probe electron impact mass spectrometry as permethylated derivatives. The fragment ions obtained from permethylated-fully-desulfated-remethylated glycolipids included ions containing up to four monosaccharides plus C-1 and C-2 of acylated sphingoids as well as those plus C-1 to C-3 of acylated sphingoids. By the use of trideuteriomethyl iodide instead of methyl iodide in the remethylation step after desulfation, the sequences of the monosaccharides containing the sulfate ester were established. When the sulfate ester was present, the intensity of the ions derived from the carbohydrate moiety was much weaker in comparison to that of those from the permethylated-fully desulfated derivative. Instead, the intensity of the fragments from the ceramide moiety was very strong in the presence of the sulfate ester.

Determination of peracetylated sulfoglycolipids using the azure A method

Several sulfoglycolipids, including sulfogalactosylceramide, sulfolactosylceramide, monosulfogangliotriaosylceramide, monosulfogangliotetraosylceramide, bis-sulfogangliotriaosylceramide, bis-sulfogangliotetraosylceramide, seminolipid, and lysoseminolipid, were assayed by the azure A procedure (Kean, E.L. 1968. J. Lipid Res. 9: 319-327). The color yields were different significantly among each sulfoglycolipid. The accurate determination of monosulfoglycolipids having longer carbohydrate chains than sulfolactosylceramide as well as bis-sulfoglycolipids could not be achieved because of the low color yields, turbidity, and/or formation of an additional chromogen. However, the quantitative determination of these complex sulfoglycolipids could be achieved using the azure A procedure when these compounds were assayed after peracetylation. Using the modified Kean procedure, the behavior of these sulfoglycolipids in the chloroform-methanol-water partition system was compared.