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.

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.

Modification of low density lipoprotein by desialylation causes lipid accumulation in cultured cells: discovery of desialylated lipoprotein with altered cellular metabolism in the blood of atherosclerotic patients.

Low density lipoprotein (LDL) isolated from the blood of healthy donors was partially desialylated by incubating the lipoprotein with sialidase (neuraminidase). The addition of LDL treated with neuraminidase to cultured human aortic intimal cells of smooth muscle origin caused a substantial increase in intracellular cholesteryl esters, free cholesterol and triglycerides. Cultured cells took up and degraded desialylated LDL much more effectively than untreated (native) LDL. LDL were also isolated from an atherogenic blood plasma of patients with coronary artery disease, i.e. the plasma capable of inducing the accumulation of lipids in cultured cells. Patients' LDL, similarly to the mother plasma, were atherogenic, i.e. stimulated the accumulation of intracellular lipids. LDL isolated from nonatherogenic plasma of healthy donors proved to be nonatherogenic. Atherogenic patients' LDL had a 2- to 5-fold lower level of sialic acid as compared with nonatherogenic LDL of healthy donors. The uptake and degradation of atherogenic patients' LDL were much more effective than in the case of nonatherogenic LDL of healthy donors. We assume that atherogenic properties of LDL obtained from patients' blood plasma are explained exactly by a low sialic acid content.

Neutral glycolipids of atherosclerotic plaques and unaffected human aorta tissue.

The composition, structure and localization of neutral glycosphingolipids of human aorta taken from subjects who had died after myocardial infarction were studied. Individual glycosphingolipids were purified by high-performance liquid chromatography and were characterized on the basis of their chromatographic mobility, carbohydrate composition, methylation analysis and by 1H-NMR spectroscopy. The main aortic glycosphingolipids were identified as glucosylceramide, lactosylceramide, globotriaosylceramide and globotetraosylceramide. Significant differences in the neutral glycosphingolipid composition of intima and media were detected. The neutral glycosphingolipid profile of medial plaques resembled that of unaffected media; however, significant differences were detected between intimal plaques and unaffected intima. Whereas the latter contained trihexosylceramide and globoside as the only neutral glycolipids, the intimal plaque glycolipids consisted mainly of glucosylceramide and also contained appreciable amounts of lactosylceramide which were completely absent in the unaffected intima. In comparison to intimal plaques, unaffected intima is characterized by a much higher content of cerebrosides terminating by beta-galactosyl residues which are known to interact with growth factors and other external stimuli. It thus seems possible that the proliferative activity of smooth muscle cells in atherosclerotic diseases is to some extent associated with their neutral glycolipid profile.

Stimulation of platelet adhesion and activation by ganglioside GD3 adsorbed to plastic.

Platelet interaction with gangliosides GD3, GM3, GM1, GD1a and GT1b has been investigated. These gangliosides were previously identified in the vessel wall and ganglioside GD3 was found to accumulate selectively in the intima of atherosclerotic vessels. Gangliosides were adsorbed to plastic and incubated with 51Cr-labeled platelets. The adhesion of gel-filtered platelets to ganglioside GD3 was 3-4 times higher than to other immobilized gangliosides and to albumin-treated plastic. As was shown by scanning electron microscopy, GD3 stimulated intensive spreading of adherent platelets and formation of surface-bound aggregates, while only single unspread platelets were present on the surfaces coated with other gangliosides. GD3 isolated from milk and from human aorta possess the same stimulating activity. Platelet adhesion to GD3 decreased significantly in the presence of the stable prostacyclin analogue, carbacyclin.

The gangliosides of adult human aorta: intima, media and plaque.

The composition, structure and localization of gangliosides of aorta taken from subjects who had died after myocardial infarction were studied. Individual gangliosides were purified by high-performance liquid chromatography and high-performance thin-layer chromatography and were characterized on the basis of their chromatographic mobility, carbohydrate composition, neuraminidase hydrolysis and methylation analysis. The main aortic gangliosides were identified as GM3, GM1, GD3, GD1a and GT1b. Significant differences in the ganglioside composition of intima and media were detected and the ganglioside profile of atherosclerotic plaques was found to differ markedly from that of unaffected intima. The latter was characterized by high content of GD3, a ganglioside thought to be associated with membrane permeability, cell interaction, adhesiveness and growth and to suppress unspecific immune responses. Possible implications of the results in low-density lipoprotein binding to the arterial wall and in immunological changes induced by atherosclerotic lesions are discussed.

[Glycosphingolipids of human aorta]. / Glikosfingolipidy aorty cheloveka.

The structures of the main gangliosides of human aorta (intima and media) were elucidated. The main component (67%) was identified as N-acetylneuraminosyl-lactosylceramide (ganglioside GM3). The aorta tissue contained also gangliosides GM1, GD3, GD1a, and GT1. All sialic acid residues in gangliosides were present as N-acetyl-neuraminosyl derivatives. Among neutral glycosphingolipids of human aorta, the main components were identified as glucosylceramide, lactosylceramide, globotriaosylceramide and globotetraosylceramide. The preliminary data suggest that the composition of the investigated glycosphingolipids in tissue might vary upon atherosclerosis lesions of aorta.

A study of DNA melting in concentrated water-alcohol solutions.

The DNA melting profiles with high resolution have been studied for conditions corresponding to the B and A conformations of DNA in water-alcohol solutions. The melting profiles of the A-form and B-form DNA, their mean melting temperatures and melting range width were found to differ. DNA was shown to be heterogeneous in respect of the B-A transition, the GC-rich regions more readily converting into the A form than AT-rich ones. The presence of boundaries between the A and B sections within the transition zone did not smooth off the fine structure of melting profiles.