Interaction of low-density lipoproteins with gangliosides

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

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

The study of structural accessibility of free thiol groups in human low-density lipoproteins

The experimental evidence for the apolipoprotein B100 (apoB) domain structuring in low-density lipoprotein (LDL) was investigated focusing on the accessibility of free thiol groups. Three different spectroscopic methods were combined with the biochemical perturbations of LDL particle. The spectrophotometric method was adapted for LDL and the exposure of free thiols was analyzed in the native LDL and LDL exposed to sequential denaturation. The results indicate that 24-h denaturation does not expose all free thiols in LDL. Using thiol-specific spin labeling and electron paramagnetic resonance spectroscopy (EPR), different populations of labeled thiols were resolved. The comparison of the EPR spectra of native LDL and LDL with selectively blocked thiol groups revealed significant difference in the respective hyperfine splittings. The phenomenon can arise due to different polarity and/or mobility of the nitroxides in the microenvironments of spin label binding sites of these two LDL samples. The results indicate that nine thiol groups in apoB are distributed in different domains of LDL: two are more exposed, two are buried deeply in the lipid matrix of the particle and the rest are located in hydrophobic parts of this extremely complex protein-lipid assembly. These observations provide experimental support for the emerging theoretical models of apoB.

Age-dependent changes in liver ganglioside levels

Gangliosides, sialic acid-containing glycosphingolipids, are found in the outer layer of the plasma membrane of all vertebrate tissue cells; the highest concentration is in the central nervous system. In recent years, there has been research on the distribution and quantity of gangliosides in extra-neuronal tissues, such as liver, kidney and intestine. Since liver is the main source of gangliosides that are carried by lipoproteins in the blood, we examined the effect of development and aging on gangliosides in liver tissue. The relationship was investigated between GM1, GD3, GD1a, GD1b, GT1b ganglioside fractions and the aging process in liver tissue of Wistar-Albino rats aged 3, 6, 12 and 24 months. HPLC analysis of liver gangliosides showed the following results: Compared to 3 month-old rats, the GM1 fraction was decreased by 50% in 6 month-old rats, increased in 12 month-old rats and decreased in 24 month-old rats. The GD3 and GD1b fractions increased until 12 months of age and were decreased significantly (p < 0.01) in 24 month-old rats. The GD1a ganglioside fraction was significantly increased in 6 and 24 month-old rats (p < 0.01). We concluded that the increment of the polar fractions, such as GD3 and GD1b, and the variations of the other fractions in the plasma membrane of the hydrophilic liver tissue during the first 12 months were important parameters.

Immune defects observed in patients with primary malignant brain tumors

Malignant glioblastomas (gliomas) account for approximately one third of all diagnosed brain tumors. Yet, a decade of research has made little progress in advancing the treatment of these tumors. In part this lack of progress is linked to the challenge of discovering how glial tumors are capable of both modulating host immune function and neutralizing immune-based therapies. Patients with gliomas exhibit a broad suppression of cell-mediated immunity. The impaired cell-mediated immunity observed in patients with gliomas appears to result from immunosuppressive factor(s) secreted by the tumor. This article reviews what has been elucidated about the immune defects of patients harboring glioma and the glioma-derived factors which mediate this immunosuppression. A model involving systemic cytokine dysregulation is presented to suggest how the immune defects arise in these individuals.

Sialic acid-containing components of lipoproteins influence lipoprotein-proteoglycan interactions

Sialic acid is a negatively charged sugar associated with the protein and lipid portions of lipoproteins. Sialic acid has been hypothesised to play an anti-atherogenic role in lipoprotein metabolism through the electrostatic inhibition of lipoprotein interactions with chondroitin-6-sulphate-rich arterial proteoglycans (APG). We conducted a series of studies using native and modified lipoproteins (VLDL1 Sf 60-400, VLDL2 Sf 20-60, IDL1 Sf 16-20, IDL2 Sf 12-16, LDL(A) Sf 8-12, and LDL(B) Sf0-8) that vary in their sialic acid content to examine the relationship between lipoprotein sialic acid content and its interaction with APG. Lipoprotein sialic acid was greatest in VLDL1 and decreased progressively with particle density until the IDL2 fraction (VLDL1 > VLDL2 > IDL1 > IDL2 = LDL(A) = LDL(B)). The pattern of reactivity of each fraction with APG was different from the pattern observed for lipoprotein sialic acid content (IDL2 > LDL(A) > LDL(B) > IDL1 > VLDL2 > VLDL1). Levels of sialic acid were lower in subjects with CHD as compared to control subjects but the presence of CHD had no effect on lipoprotein-APG complex formation when sex and plasma triglyceride levels were taken into account. There was also no significant relationship between the lipoprotein sialic acid content and the reactivity with APG within each lipoprotein fraction. Treatment of hypertriglyceridaemic subjects with ciprofibrate decreased lipoprotein-APG complex formation in all lipoprotein fractions. This was associated with a decrease in the total sialic acid content of apo B100-containing lipoproteins suggesting that the total sialic acid content of apo B100-containing lipoproteins has no influence on lipoprotein-APG complex formation. We next conducted in vitro experiments to manipulate LDL sialic acid content. Enzymatic removal of sialic acid from LDL with neuraminidase resulted in an increase in LDL-APG complex formation. This was accompanied by an increase in the exposure of free amino groups on LDL possibly due to disruption of interactions between free amino groups and sialic acid-containing components on LDL. Increasing LDL sialic acid content through incubation with ganglioside resulted in a decrease in lipoprotein-APG complex formation without any changes in the exposure of free amino groups on LDL. We conclude that total sialic acid content of lipoproteins is not a major determinant of their binding to APG. However, specific sialic acid-containing components on lipoproteins can affect their interaction with APG.

Autoantibodies to gangliosides in sera of atherosclerotic patients

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

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

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

High-resolution thin-layer chromatography of gangliosides

In this review an updated overview of current improvements on thin-layer chromatography (TLC) of gangliosides over the past decade is provided. Basic general techniques and special advice is given for successful separation of glycosphingolipids. New approaches concerning continuous and multiple development, and several preparative TLC methods are also included. Emphasis is placed on TLC immunostaining and related techniques, i.e. practical applications of carbohydrate-specific antibodies, toxins and bacteria, viruses, lectins and eukaryotic cells. Thus, this review on ganglioside TLC summarizes its power as an analytical tool for a wide range of purposes.

Serum gangliosides as endogenous immunomodulators

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

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)

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.

Ganglioside GM3 stimulates the uptake and processing of low density lipoproteins by macrophages

Preincubation of low density lipoproteins (LDL) with low concentrations of the ganglioside GM3 (1-2x 10(-5) M/2.5 x 10(-6) M LDL-protein) results in an increase of LDL-uptake, enhances cholesterol accumulation and cholesteryl ester formation by macrophages. At the same time the lysosomal degradation of LDL in macrophages was inhibited under these conditions. These effects depended on the ganglioside structure and concentration. It is suggested that the effects observed could be caused by GM3-induced modification of LDL to a form that becomes recognized by macrophages.