Retention of gangliosides in serum delipidated by diisopropyl ether-1-butanol extraction

Identification of plasma biomarkers of TBI outcome using proteomic approaches in an APOE mouse model

The current lack of diagnostic and prognostic biomarkers for traumatic brain injury (TBI) confounds treatment and management of patients and is of increasing concern as the TBI population grows. We have generated plasma proteomic profiles from mice receiving TBI by controlled cortical impact at either 1.3 mm or 1.8 mm depth, comparing these against those of sham injured-animals to identify plasma biomarkers specific to mild or severe TBI at 24 hours, 1 month, or 3 months post-injury. To identify possible prognostic biomarkers, we used apolipoprotein E (APOE)3 and APOE4 transgenic mice, which demonstrate relatively favorable and unfavorable outcomes respectively, following TBI. Using a quantitative proteomics approach (isobaric tagging for relative and absolute quantitation--iTRAQ) we have identified proteins that are significantly modulated as a function of TBI and also in response to the TBI*APOE genotype interaction, the latter representing potential prognostic biomarkers. These preliminary data clearly demonstrate plasma protein changes that are not only injury dependent but also interaction dependent. Importantly, these results demonstrate the presence of TBI-dependent and interaction-dependent plasma proteins at a 3-month time point, which is a considerable time post-injury in the mouse model, and will potentially be of significance for combat veterans receiving assessment at extended periods post-injury. Furthermore, our identification of clusters of functionally related proteins indicates disturbance of particular biological modules, which potentially increases their value beyond that of solitary biomarkers.

Severe modifications of ether- ester- or diester-linked glycerolipid and non glycerolipid synthesis in human neuroblastoma LAN-1 cells cultured with octadecylmethylglycerophosphocholine

The growth rate of the human neuroblastoma LAN-1 cells was decreased half after 48 h of incubation with dialkylglycerophosphocholine 1-O-octadecyl 2-O-methyl-sn-glycero-3-phosphocholine (ET-18-O-CH3), at 4 microM. Four radiolabelled precursors, [3H]hexadecanol, [3H]hexadecanoic, [3H]arachidonic acids, or N-acetyl[14C] neuraminic acid were added in the culture medium to follow their cell incorporation among various glycerolipids, gangliosides and eicosanoids. Several modifications of the glycerophospholipid synthesis induced by ET-18-O-CH3 were observed. The inhibition of 1-O-[3H]hexadecanoyl 2-O-acyl glycerophosphocholine synthesis provoked the accumulation of diacylglycerophosphoethanolamine. The inhibition of 1-O-[3H]hexadecyl 2-O-acyl glycerophosphocholine and ethanolamine synthesis enhanced the synthesis of non phosphorous glycerolipids with 1-O-[3H]hexadecyl-sn-glycerol backbone. The eicosanoid synthesis was not disturbed. Alterations of ether- ester- and diester-linked glycerophospholipid and non phosphorous glycerolipid synthesis could modify the lipid membrane distribution and affect the enzymatic pathway of the ceramide synthesis. An excess of [3H]hexadecanoyl-amide molecular species of ceramides in mono- and disialo-gangliosides was observed. By contrast the N-acetyl [14C]neuraminosyl-linkage in these two groups of gangliosides never reached the hypersialylation process described during sialoglyco-peptide synthesis in murine carcinoma kidney cell lines. Both metabolic disturbances of the glycerolipid and ganglioside synthesis reported for the neuroblastoma LAN-1 cell line sensitive to ET-18-O-CH3 extend and confirm the previous studies with other more resistant cell lines from the murine Meth A sarcoma and the rat colon carcinoma.

Immunosuppression by human gangliosides: I. Relationship of carbohydrate structure to the inhibition of T cell responses

Causes of cellular immunodeficiency frequently associated with cancer remain poorly understood. One possible mechanism is tumor cell membrane shedding of immunosuppressive molecules, such as the sialic acid-containing glycosphingolipids, gangliosides. To explore this interesting hypothesis and establish structure-activity relationships, we examined the effects of a series of highly purified human gangliosides on T cell function. In all, ten individual molecular species of two major biosynthetic pathways were compared for their ability to inhibit human T cell proliferative responses. They include GM1, GD1a, GD1b, and GT1b (the predominant normal brain species), and GM4, GM3, GM2, GD3, GD2 and GQ1b. Strikingly, each HPLC-purified molecule, from the simplest monosialoganglioside to the most complex polysialoganglioside, had potent inhibitory activity; even the ganglioside with the most elemental carbohydrate structure (GM4, one sialic acid linked to a monosaccharide) strongly inhibits T cell proliferative responses to tetanus toxoid (ID90 = 1.5 microM). The data also reveal a complex interplay between elements of oligosaccharide structure in determining immunosuppressive activity. Sialic acid is critical to maximal activity, and (i) immunosuppression is most potent in gangliosides containing a terminal sialic acid. (ii) Total desialylation almost abolishes activity and (iii) partial alteration (lactone formation) reduces activity. (iv) Activity is generally but not always higher with higher numbers of sialic acid residues/molecule, and (v) some larger neutral glycosphingolipids retain measurable immunosuppressive activity. Overall, the potent inhibition by gangliosides supports the hypothesis that shedding of these molecules by tumors creates a highly immunosuppressive microenvironment around the tumor, thereby inhibiting the function of infiltrating host leukocytes and contributing to diminished T cell responses in cancer.

Hexadecanoic and neuraminic acid incorporations in two rat colon carcinoma cell lipids: selective influence of 1-O-octadecyl 2-O-methyl-3-phosphocholine on glycerolipid and ganglioside biosynthesis

[3H] hexadecanoic and N-acetyl [14C] neuraminic acids were incorporated in glycerolipids or gangliosides of 2 rat colon carcinoma cell lines, having (PRO cells), or not (REG cells) invasive capacities when inoculated in syngeneic BD IX rats. The cells were cultured (48 h) in presence of 1-0-octadecyl-2-0-methyl-3-phosphocholine (ET 18-0-CH3) 20 or 40 microM, which, on transformed cells, inhibits the cell growth, modifies the glycerolipid biosynthesis, and activates the sialyltransferases. ET 18-0-CH3 20 microM activated, in PRO and in REG cells the incorporation of [3H] hexadecanoate in monosialogangliosides (1.45 fold compared to controls), but not in disialogangliosides and the distribution of this fatty acid between monosialo- (82%) and disialogangliosides (18%) was unchanged with controls. After [14C] neuraminic acid labelings, and for control experiments, the total radioactivities in gangliosides, in PRO cells, were twice higher than in REG cells, a difference which, probably, reflects the ganglioside content. ET 18-0-CH3 20 microM did not increase the incorporation of the [14C] neuraminic acid in PRO and in REG cells, and did not change its distribution between monosialo (70-80% for controls and experiments with ET 18-0-CH3) and disialogangliosides (20-30%). Similar results were obtained with ET 18-0-CH3 40 microM for the distribution of [14C] neuraminic acid in monosialo- and disialogangliosides. Whatever the precursor, the trisialogangliosides were never radiolabeled. Analysis of the [3H] glycerolipids (the main radiolabeled lipid classes in controls were: phosphatidylcholines, triglycerides, sphingomyelins and phosphatidyl-inositols) revealed that ET 18-0-CH3, compared to controls, did not activate the incorporation of [3H] hexadecanoate in total glycerolipids (PRO or REG cells). It activated (3 fold) its incorporation in triglyerides, inhibited it (0.5-0.6 fold) in phosphatidylcholines, sphingomyelins and phosphatidyl-inoditols and all these most noticeable differences were observed in PRO and in REG cells. These findings reflect the impossibility of ET 18-0-CH3 to activate the sialyltransferases during the ganglioside biosynthesis in colon carcinoma cells, while it modified ceramide, glycerophospholipid and neutral glycerolipid biosynthesis.

Ganglioside inhibition of (125I)-plasmin binding to colorectal carcinoma cells

The pre-incubation of human colorectal carcinoma cells SW 1116 with 25 to 100 uM purified gangliosides resulted in 35-60% inhibition of specific (125I)-plasmin binding to the cell surface. After 5 to 6 days in culture, tumor cells were pre-incubated at 4 degrees for 1 to 4 h followed by post-incubation with (125I)-plasmin by techniques previously described. At 25 uM the capacity for inhibition of plasmin binding was GT1b greater than GQ1b greater than or equal to GD1a greater than GM1 less than or equal to GgOse 4Cer. Thus a terminal sialyl moiety appears to be necessary (p less than 0.05) although exogenous N-acetyl neuraminic acid was ineffective (p greater than 0.05), indicating a role for the lipid portion of the ganglioside. Other (glyco)lipids such as sphingosine, fucolipid H-1 and sulfatide were without significant effect. The inhibition could not be reversed by the presence of 10 mM Ca+2, EDTA, pre-treatment of the cell with carboxypeptidase or pretreatment of plasmin with neuraminidases. The inhibition was however reversed by post-incubation in control medium without exogenous ganglioside. Cell counts determined prior to, and after ganglioside incubation showed that the effect was not due to cell death or detachment from the culture surface. The dissociation constant for (125I)-plasmin binding was 5.6 x 10(-8) M (700,000 sites/cell), but in the presence of trisialoganglioside (GT1b), Scatchard plots suggested diversification of binding sites with 280,000 sites/cell at Kd 2.6 x 10(-8) M and 820,000 sites/cell at Kd 2.1 x 10(-7) M. Another interpretation of the Scatchard plot in the presence of ganglioside was that the glycolipid imposed negative cooperativity on plasmin binding to the cell surface. These results suggest that certain gangliosides can affect tumor cell invasiveness by altering protease binding to the cell surface.

A solvent partition method for microscale ganglioside purification

A simple and rapid method for the purification of gangliosides from the total lipid extract of plasma, cells, or tissue is described. The novel component of the method is the partition of the dried total lipid extract in the three-component solvent system consisting of diisopropyl ether, 1-butanol, and 50 mM aqueous NaCl (6/4/5, v/v/v). Gangliosides partition nearly quantitatively into the lower aqueous phase, and other lipids into the upper organic phase, resulting from the mixture of these three solvents. The ganglioside-containing aqueous phase is then freed of salts and other low-molecular-weight impurities by gel filtration. The thin-layer chromatographic patterns of total gangliosides thus obtained are clear and distinct, even when small samples with very low ganglioside concentrations (e.g., 1-ml samples of plasma) are processed by this method. Thus, this new ganglioside purification method is especially applicable to comparative qualitative studies of gangliosides requiring the analysis of multiple small samples.