Interaction of gangliosides with low-density proteins from human blood

Gangliosides have been shown to modulate the receptor-mediated endocytosis of low density lipoproteins (LDL). The direct interaction of LDL with various gangliosides has been studied. Binding of gangliosides to LDL immobilized on CNBr-Sepharose (LDL-Sepharose) and the influence of gangliosides on the fluorescence of LDL containing anthrylvinyl-labeled sphingomyelin were investigated. The binding of 3H-gangliosides to LDL-Sepharose, as well as fluorescence polarization of LDL were found to depend on the structure and concentration of the gangliosides in a specific saturable manner. The data obtained indicate that gangliosides interact with apolipoprotein B via specific binding sites.     

Modified lipid-protein interactions in Tangier beta lipoprotein (LDL2) demonstrated by fluorescence quenching

Fluorescence quenching by iodide ions has been found to be higher in isolated Tangier low density lipoprotein (LDL2) than in isolated normal LDL2. Apolipoprotein (apo) B-100 is the main protein component of these lipoproteins and its tryptophanyl residues (Trp) are known to be the most hydrophobic and to be responsible for protein fluorescence. Trp exposure can thus be calculated; it was 0.50 in Tangier and 0.42 and 0.41 in insulin-dependent diabetics (IDD) and normal controls, respectively. The greater fluorescence quenching of Tangier LDL2 reveals a shallower embedding of Trp which is principally due to a lowered free cholesterol (FC) level in the shell and a smaller lipid core, itself dependent on a drop in cholesterol esters (CE). This is in accordance with the electrophoretic properties of Tangier LDL2 and suggests that Tangier LDL2 may be considered to be modified.     

肌动蛋白结合脂筏促进巨噬细胞摄入土拉弗朗西斯菌

观察土拉弗朗西斯菌LVS借助脂筏以肌动蛋白为动力被鼠巨噬细胞摄入的过程。细胞胆固醇用菲律平Ⅲ染色,结合神经节苷酯GM1的霍乱毒素B亚基用键合了Alexa 594的兔抗霍乱毒素B亚基二抗显色;肌动蛋白用键合了Alexa 594的鬼笔环肽显色。免疫荧光显微镜观察到脂筏成分中的胆固醇、神经节苷酯GM1均可与细菌共定位;胆固醇可与肌动蛋白共定位。随着感染时间的延长,细菌可离开脂筏。离开脂筏的细菌囊泡可与肌动蛋白共定位。这些发现提示肌动蛋白与脂筏结合,在弗朗西斯菌早期进入巨噬细胞期间发挥重要作用。     

Interaction of gangliosides with plasma low density lipoproteins

The role of gangliosides in the reception of low density lipoproteins (LDL) was studied using as targets mouse ascites hepatoma 22a (MAH) cells which bind LDL through a specific high affinity receptor. Low density lipoprotein binding and uptake by MAH cells decreased after brief treatment of the cells with neuraminidase to partially remove surface sialic acid residues. The LDL uptake capability of the neuraminidasetreated MAH cells was fully restored after incorporation of exogeneous G_M1- and G_D1a-gangliosides into the cell surface. In contrast, free (extracellular) gangliosides inhibited LDL uptake by native MAH cells. This inhibitory effect was seen at ganglioside concentrations corresponding to the ganglioside content of serum and was most pronounced with gangliosides whose sialic acids were linked to a terminal galactose residue (G_M3, G_D1a, G_T1b) but was smaller or absent with gangliosides whose sialic acids were attached to an internal galactose (G_M1, G_M2). The binding of gangliosides to LDL was structure and concentration dependent, saturable and trypsin sensitive. The LDL-ganglioside interaction was further investigated by steady state fluorescence spectroscopy. Changes in the LDL fluorescence polarization were observed with as little as 0.01 M concentrations of the gangliosides. The magnitude and nature of the effect depended on the type of ganglioside. We conclude that the LDL surface possesses sites recognizing specific carbohydrate sequences of glycoconjugates and that changes in the cell surface concentrations of sialic acids significantly modulate the LDL uptake. It is postulated that shedding of gangliosides into the blood stream may be a factor involved in regulation of cholesterol homeostasis.Abbreviations MAH mouse ascites hepatoma 22a - LDL low density lipoprotein - ASM anthrylvinyl-labeled sphingomyelin [N-12-(9-anthryl-trans-dodecanoyl-sphingosine-1-phosphocholine] - RITC rhodamine isothiocyanate. The designation of gangliosides follows the IUPAC-IUB recommendation [1]: G_M3, II³NeuAc-LacCer, II³-N-acetylneuraminosyllactosylceramide - G_M2 II³-NeuAc-GgOse₃Cer, II³-N-acetylneuraminosylgangliotriaosylceramide - G_M1 II³-NeuAc-GgOse₄Cer, II³-N-acetylneuraminosylgangliotetraosylceramide - G_D1a, II³ IV³(NeuAc)₂-GgOse₄Cer, II³, IV³-di(N-acetylneuraminosyl)gangliotetraosylceramide - G_T1b II³(NeuAc)₂, IV³ NeuAc-GgOse₄Cer, II³-di-N-acetylneuraminosyl, IV³-N-acetylneuraminosylgangliotetraosylceramide     

Effects of oxidative modification of cholesterol in isolated low density lipoproteins on cultured smooth muscle cells

Summary It has been proposed that low density lipoprotein (LDL) must undergo oxidative modification before it can participate in atherosclerosis. The present paper studied the effect of cholesterol oxidation in LDL on cultured vascular smooth muscle cells. LDL was oxidized by cholesterol oxidase (3--hydroxy-steroid oxidase) which catalyzes the oxidation of cholesterol to 4-cholesten-3 one and other oxidized cholesterol derivatives. Cholesterol oxidase treatment of LDL did not result in lipid peroxidation. Cultured rabbit aortic smooth muscle cells were morphologically changed following exposure to cholesterol oxidized LDL. Nile red, a hydrophobic probe which can selectively stain intracellular lipid droplets, was applied to detect the cellular lipid content after treatment with oxidized or non-oxidized LDL cholesterol. LDL which did not undergo oxidation of its cholesterol had no effect on the cells. However, cellular nile red fluorescence intensity was increased as the pre-incubation time of cholesterol oxidase with LDL increased. This was supported by HPLC analysis which revealed that the oxidized cholesterol content of treated cells increased. These findings suggest that cholesterol oxidation of LDL can alter lipid deposition in the cells and change cell morphology. The oxidation of cholesterol in vivo may play an important role in the modification of LDL which could contribute to the generation of the lipid-laden foam cells.     

Structural basis for thermal stability of human low-density lipoprotein

The stability of human low-density lipoprotein (LDL), the major cholesterol carrier in plasma, was analyzed by heating samples of different concentrations at a rate from 11 to 90 K/h. Correlation of the calorimetric, circular dichroism, fluorescence, turbidity, and electron microscopic data shows that thermal disruption of LDL involves irreversible changes in the particle morphology and protein conformation but no global protein unfolding. Heating to 85 degrees C induces LDL conversion into smaller and larger particles and apparent partial dissociation, but not unfolding, of its sole protein, apoB. Further heating leads to partial unfolding of the beta-sheets in apoB and to fusion of the protein-depleted LDL into large aggregated lipid droplets, resulting in a previously unidentified high-temperature calorimetric peak. These lipid droplets resemble in size and morphology the extracellular lipid deposits formed in the arterial wall in early atherosclerosis. The strong concentration dependence of LDL fusion revealed by near-UV/visible CD, turbidity, and calorimetry indicates high reaction order, and the heating rate dependence suggests high activation energy that arises from transient disruption of lipid and/or protein packing interactions in the course of particle fusion and apparent apoB dissociation. Consequently, thermal stability of LDL is modulated by kinetic barriers. Similar barriers may confer structural integrity to LDL subclasses in vivo.     

Fluidity changes and chemical composition of lipoproteins in type IIa hyperlipoproteinemia

The chemical composition and the physical properties of lipoproteins (VLDL, LDL and HDL) were studied in two groups of patients: 14 healthy normolipidemic subjects and 15 type IIa familial hypercholesterolemic patients. The steady-state fluorescence anisotropy rs was estimated in lipoproteins by the fluorescence depolarization of two fluorescent probes: the DPH (1,6-diphenyl-1,3,5-hexatriene) and the TMA-DPH (1,4-trimethylammonium phenyl-6-1,3,5-hexatriene). A structured order parameter S was calculated from the DPH fluorescence anisotropy. The flow activation energies were calculated for LDL and HDL from both groups from the Arrhenius plots (log r DPH versus 1/T). By using TNBS (trinitrobenzene sulfonic acid) as a distance control quencher, the two probes were located in the outer shell of LDL. In HDL, TMA-DPH remained at the surface of the particles, while DPH was more deeply embedded in the lipid core. There was no difference in the physico-chemical properties of VLDL between the two groups studied. DPH fluorescence anisotropies were significantly increased in LDL and HDL from the hypercholesterolemic group compared to the control particles (P less than 0.05 and P less than 0.01, respectively). In LDL this modification of the fluorescence anisotropy can be related to a change in the lipid composition of particles. LDL from hypercholesterolemic patients contained significantly less triacylglycerol (P less than 0.01) and more cholesteryl ester (N.S.). Their cholesteryl ester to triacylglycerol ratio was significantly higher. In HDL, there was no difference in chemical composition between the two groups. The increase in DPH fluorescence anisotropy can be related to the presence of smaller particles in HDL from HC group. No difference was noted in the TMA-DPH fluorescence anisotropy at 37 degrees C in the LDL from the two groups. In contrast, TMA-DPH fluorescence anisotropy in HDL from hypercholesterolemic group was significantly higher than in control HDL. The flow activation energy of DPH was also significantly higher in both LDL and HDL from the hypercholesterolemic group than in control group particles. In both LDL and HDL from the control group, DPH fluorescence anisotropy was negatively correlated with TG/protein and TG/PL ratios and positively correlated with the CE/TG ratio. No correlation was observed between lipid composition and DPH fluorescence anisotropy values in hypercholesterolemic particles. The modification in fluidity parameters, especially the increase in the flow activation energies in LDL and HDL from hypercholesterolemic patients, could lead to a restriction of cholesterol movements in these particles. From a physiological point of view, this could represent a loss of functional capacity.     

Oxidative modification of low-density lipoprotein: lipid peroxidation by myeloperoxidase in the presence of nitrite

Oxidative modification of low-density lipoprotein (LDL) is a pivotal process in early atherogenesis and can be brought about by myeloperoxidase (MPO), which is capable of reacting with nitrite, a NO metabolite. We studied MPO-mediated formation of conjugated dienes in isolated human LDL in dependence on the concentrations of nitrite and chloride. This reaction was strongly stimulated by low concentrations (5-50 microM) of nitrite which corresponds to the reported concentration in the arterial vessel wall. Under these conditions no protein tyrosine nitration occurred; this reaction required much higher nitrite concentrations (100 microM-1 mM). Chloride neither supported lipid peroxidation alone nor was its presence mandatory for the effect of nitrite. We propose a prominent role of lipid peroxidation for the proatherogenic action of the MPO/nitrite system, whereas peroxynitrite may be competent for protein tyrosine nitration of LDL. Monomeric and oligomeric flavan-3-ols present in cocoa products effectively counteracted, at micromolar concentrations, the MPO/nitrite-mediated lipid peroxidation of LDL. Flavan-3-ols also suppressed protein tyrosine nitration induced by MPO/nitrite or peroxynitrite as well as Cu2+-mediated lipid peroxidation of LDL. This multi-site protection by (-)-epicatechin or other flavan-3-ols against proatherogenic modification of LDL may contribute to the purported beneficial effects of dietary flavan-3-ols for the cardiovascular system.     

A novel method of following oxidation of low-density lipoprotein using a sensitive fluorescent probe,diphenyl-1-pyrenylphosphine

Diphenyl-1-pyrenylphosphine (DPPP), which reacts with lipid hydroperoxide stoichiometrically to yield a fluorescent product DPPP oxide (DPPP=O) and the corresponding hydroxide, was used as a fluorescent probe for lipid peroxidation in low-density lipoprotein (LDL). DPPP was successfully incorporated into LDL using the dispersion reagent Pluronic F-127. Incorporation of DPPP into LDL was confirmed by gel filtration chromatography. Reaction of DPPP with hydroperoxide within an LDL particle was examined by monitoring the increase in fluorescence intensity of the LDL. It was found that lipid-soluble hydroperoxides such as methyl linoleate hydroperoxide preferably reacted with DPPP, whereas hydrogen peroxide did not. Fluorescence was increased at the early stages in the oxidation of DPPP-labeled LDL by an azo radical initiator or human neutrophils. LDL, which was labeled with DPPP or DPPP=O, was taken up by cells such as THP-1-derived macrophages and human umbilical vein endothelial cells. The fluorescence of DPPP=O could be observed in cells using fluorescence microscopy equipped with a cooled charge coupled device camera in a nondestructive manner. The present study shows that DPPP is a sensitive, selective, and quantitative probe for monitoring LDL oxidation and visualizing intracellular oxidation.     

Modification of the lipid-protein interaction in human low-density lipoprotein destabilizes ApoB-100 and decreases oxidizability

The interactions of the lipid and protein moiety of human low-density lipoprotein (LDL) and their influence on the oxidation behavior of LDL were modified using an amphipathic peptide, melittin, as a probe. The interaction of melittin with the LDL phospholipid surface resulted in a destabilization of apolipoprotein B-100 (apoB-100) as monitored by differential scanning calorimetry, while the characteristics of lipid core melting remained nearly unchanged. Binding of melittin caused a restriction of lipid chain mobility near the glycerol backbone, but not in the middle or near the methyl terminus of the fatty acyl chains as observed by electron paramagnetic resonance. Also, upon melittin addition, the level of copper binding to apoB-100 and the oxidizability of LDL by Cu2+ ions were greatly reduced, as indicated by abolished tryptophan fluorescence quenching upon Cu2+ binding and, during oxidation, prolongation of the lag phase of oxidation, attenuated consumption of alpha-tocopherol, and a lowered maximal rate of conjugated diene formation. This reduction of oxidizability could not be reversed by increasing the Cu2+ concentration. It is deduced that interaction of Cu2+ and alpha-tocopherol is required for reductive activation of the metal. It can be abolished by interfering with the interactions between apoB-100 and the lipid moiety of LDL which modifies the conformation of LDL and, as a consequence, hinders copper binding to apoB-100.     

Physico-chemical properties of low density lipoproteins isolated in an equilibrium density gradient

The tryptophanyls of total low density lipoproteins (LDL) (1.006-1.063 g/ml) from coronary heart disease (CHD) patients and subjects without CHD signs had different accessibility to fluorescence quenchers (I-and acrylamide). LDL were separated into subfractions in equilibrium density gradient. The coefficient of extinction , quantum yield and other spectral characteristics of LDL intrinsic fluorescence, rotational mobility of maleimide spin labels and fatty acid spin probe were different in LDL subfractions from healthy subjects. LDL subfractions with hydrated density 1.045-1.05 g/ml bound to B,E-receptors of cultured fibroblasts more effectively than did subfractions with density 1.01-1.03 g/ml. Structural differences of apo-B in the particles with different lipid to protein ratio are supposed.     

The location of protein in serum lipoproteins: a fluorescence quenching study.

Quenching of the tryptophan fluorescence of pig serum HDL3 and LDL2 lipoproteins by iodide and succinimide has been used to estimate the accessibility of the fluorophores to the solvent and, by inference, the location of the protein in the macromolecular complexes. At least 80% of the protein is thought to be located at or near the surface in both lipoproteins but its accessibility is hindered especially in LDL2. A difference in surface topography in the two lipoproteins is suggested with the protein in LDL2 more buried in lipid and further away from the charged phospholipid polar groups than in HDL3. A refined treatment of the quenching data has been developed to take account of the heterogeneity of quenching sites found in the lipoproteins.     

Why is glycated LDL more sensitive to oxidation than native LDL? A comparative study

It is well established that oxidative modification of low-density lipoprotein (LDL) plays a causal role in human atherogenesis and the risk of atherosclerosis is increased in patients with diabetes mellitus. To examine the influence of different agents which may influence LDL-glycation and oxidation, experiments including glycation with glucose, glucose 6-phosphate, metal chelators (EDTA) and antioxidants (BHT) were performed. The influence of time dependence on the glycation process and the alteration of the electrophoretic mobility of LDL under diverse glycation and/or oxidation conditions was also investigated. The formation of conjugated dienes and levels of lipid peroxides in these different LDL-modifications were estimated. The copper-induced oxidation of LDL in vitro was determined by measurement of thiobarbituric acid reactive substances (TBARS) and expressed as nmol MDA/mg of LDL protein. We found that glycated LDL is more prone to oxidation than native LDL. Using native LDL, the maximal oxidation effect was found to reach a value of 49.72 nmol MDA/mg protein after 8 h. The maximum oxidation of the 31 days, glycated LDL with glucose was 71.76 nmol MDA/mg protein amounting to 144.33% of the value found for native LDL. In the case of glucose 6-phosphate glycation, the maximum oxidation under the same conditions amounted to 173.77% of the value found for native LDL. To measure the extent of glycation, fluorescence of advanced glycation end products (AGEs) was determined (370 nm excitation and 440 nm emission). The most potent glycation agent was glucose 6-phosphate leading to the formation of very high amounts of AGEs. This process was promoted in the absence of EDTA, which prevents the oxidative cleavage of modified Amadori products (ketoamines) to AGEs. We therefore conclude that both processes, glycation and oxidation, result in the modification of LDL. The lower the glycation-rate (+/- EDTA) as measured by relative fluorescence units RFU (generation of AGEs), the lower the additional oxidation rate after glycation as measured by TBARS (generation of MDA equivalents). Glycation and/or oxidation change the electrophoretic mobility of LDL.     

Lateral diffusion of phospholipids in the lipid surface of human low-density lipoprotein measured with a pyrenyl phospholipid probe

Human low-density lipoprotein (LDL) was labelled with the excimeric fluorescent phospholipid analogue 1-palmitoyl-2-(1'-pyreneoctanoyl)-sn-glycero-3-phosphocholine by using phosphatidylcholine-specific transfer protein for the probe insertion. The lateral diffusivity of the probe in the phospholipid/cholesterol surface monolayer of LDL was determined from the measured dependence of the pyrene monomer fluorescence yield on probe concentration. The data were analyzed by the milling-crowd model (J. Eisinger et al. (1986) Biophys. J. 49, 987-1001] to obtain the short-range lateral diffusivity of the probe. The lateral mobility of the probe in LDL was compared to that in model lipid systems, i.e. in protein-free LDL-like lipid particles and in small unilamellar vesicles, with a phospholipid/cholesterol composition characteristic of LDL. This analysis with the probability PE = 1 for excimer production between nearest-neighbour probes gives the lower limits for f, the frequency of translational lipid--lipid exchanges of the probe of 0.62 x 10(8), 0.19 x 10(8) and 0.19 x 10(8)s-1 in LDL, LDL-like lipid particles, and small unilamellar vesicles, respectively. The lower limits for the corresponding lateral diffusion constants are 16, 5 and 5 microns 2 s-1. The results suggest that the translational mobility of phospholipid molecules in the lipid--protein surface of LDL is not constrained by the apolipoprotein B-100 moiety or the neutral lipid core of the lipoprotein. Instead, the protein moiety may perturb the lipid order with the lipid--associating peptide domains and thus fluidize the amphiphilic surface monolayer of LDL relative to the protein-free model systems. In general, lateral diffusivity of the pyrenyl phospholipid probe in LDL and the model lipid systems is comparable to the lateral mobility of lipid analogue probes in a variety of model and biological membranes.     

Diffusion of nitric oxide into low density lipoprotein.

A key early event in the development of atherosclerosis is the oxidation of low density lipoprotein (LDL) via different mechanisms including free radical reactions with both protein and lipid components. Nitric oxide (( small middle dot)NO) is capable of inhibiting LDL oxidation by scavenging radical species involved in oxidative chain propagation reactions. Herein, the diffusion of ( small middle dot)NO into LDL is studied by fluorescence quenching of pyrene derivatives. Selected probes 1-(pyrenyl)methyltrimethylammonium (PMTMA) and 1-(pyrenyl)-methyl-3-(9-octadecenoyloxy)-22,23-bisnor-5-cholenate (PMChO) were chosen so that they could be incorporated at different depths of the LDL particle. Indeed, PMTMA and PMChO were located in the surface and core of LDL, respectively, as indicated by changes in fluorescence spectra, fluorescence quenching studies with water-soluble quenchers and the lifetime values (tau(o)) of the excited probes. The apparent second order rate quenching constants of ( small middle dot)NO (k(NO)) for both probes were 2.6-3.8 x 10(10) m(-1) s(-1) and 1.2 x 10(10) m(-1) s(-1) in solution and native LDL, respectively, indicating that there is no significant barrier to the diffusion of ( small middle dot)NO to the surface and core of LDL. Nitric oxide was also capable of diffusing through oxidized LDL. Considering the preferential partitioning of ( small middle dot)NO in apolar milieu (6-8 for n-octanol:water) and therefore a larger ( small middle dot)NO concentration in LDL with respect to the aqueous phase, a corrected k(NO) value of approximately 0.2 x 10(10) m(-1) s(-1) can be determined, which still is sufficiently large and consistent with a facile diffusion of ( small middle dot)NO through LDL. Applying the Einstein-Smoluchowsky treatment, the apparent diffusion coefficient (D(')NO) of ( small middle dot)NO in native LDL is on average 2 x 10(-5) cm(2) s(-1), six times larger than that previously reported for erythrocyte plasma membrane. Thus, our observations support that ( small middle dot)NO readily traverses the LDL surface accessing the hydrophobic lipid core of the particle and affirm a role for ( small middle dot)NO as a major lipophilic antioxidant in LDL.     

Congregation of gangliosides at the junction between two model membranes.

The diversity and distribution of gangliosides in vertebrate tissue suggests an important role in cellular recognition. Two types of experiments are reported to test the hypothesis that gangliosides can congregate to form an adhesive junction between two membranes. First, to monitor ganglioside distribution and mobility in different regions of two large spherical bilayer membranes, fluorescent derivatives of natural gangliosides were synthesized. Second, the cation carrier nonactin was used as a conductance probe to measure the membrane surface potential, which would be altered if there were a redistribution of the charged gangliosides. These studies were conducted in large spherical artificial membranes made from egg phosphatidylcholine or oleoylpalmitoylphosphatidylcholine with 0-12 mol % bovine brain gangliosides dissolved in n-decane. The fluorescent gangliosides utilized were lucifer yellow adducts to the sialic acids (LY-gangliosides) or a cis-paranaric acid substitution of the N-acyl moiety in the ceramide portion of gangliosides GM1 and GD1a (paranaryl-GM1 and paranaryl-GD1a). The polarized fluorescence from the adhesive junction between two membranes containing LY-gangliosides or either paranarylganglioside was compared to that in nonadhesive regions. For LY-gangliosides, total fluorescence in the junction decreased with time, possibly due to electrostatic repulsion of this highly charged derivative. For paranarylgangliosides, fluorescence in the junction increased 7-fold with time, suggesting congregation of this ganglioside. In both cases, a measure of rotational mobility, fluorescence anisotropy, increased dramatically, about 2-fold, as expected for restricted mobility of adhesive compounds. Independent evidence for congregation of charge-bearing gangliosides was found with the conductance probe nonactin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Genistein prevents the glucose autoxidation mediated atherogenic modification of low density lipoprotein

Hyperglycemia has been assumed to be responsible for oxidative stress in diabetes. In this respect, glucose autoxidation and advanced glycation end products (AGE) may play a causal role in the etiology of diabetic complications as e.g. atherosclerosis. There is now growing evidence that the oxidative modification of LDL plays a potential role in atherogenesis. Glucose derived oxidants have been shown to peroxidise LDL. In the present study, genistein, a compound derived from soy with a flavonoid chemical structure (4′, 5, 7-trihydroxyisoflavone) has been evaluated for its ability to act as an antioxidant against the atherogenic modification of LDL by glucose autoxidation radical products. Daidzein, (4′, 7-dihydroxyisoflavone) an other phytoestrogen of soy, was tested in parallel. Genistein — in contrast to daidzein — effectively prevented the glucose mediated LDL oxidation as measured by thiobarbituric acid-reactive substance formation (TBARS), alteration in electrophoretic mobility, lipid hydroperoxides and fluorescence quenching of tryptophan residues of the lipoprotein. In addition the potential of glucose-oxidized LDL to increase tissue factor (TF) synthesis in human endothelial cells (HUVEC) was completely inhibited when genistein was present during LDL oxidative modification by glucose. Both phytoestrogens did not influence the nonenzymatic protein glycation reaction as measured by the in vitro formation of glycated LDL. As the protective effect of genistein on LDL atherogenic modification was found at glucose/genistein molar ratios which may occur in vivo, our findings support the suggested beneficial action of a soy diet in preventing chronic vascular diseases and early atherogenic events.     

Genistein prevents the glucose autoxidation mediated atherogenic modification of low density lipoprotein

Hyperglycemia has been assumed to be responsible for oxidative stress in diabetes. In this respect, glucose autoxidation and advanced glycation end products (AGE) may play a causal role in the etiology of diabetic complications as e.g. atherosclerosis. There is now growing evidence that the oxidative modification of LDL plays a potential role in atherogenesis. Glucose derived oxidants have been shown to peroxidise LDL. In the present study, genistein, a compound derived from soy with a flavonoid chemical structure (4', 5, 7-trihydroxyisoflavone) has been evaluated for its ability to act as an antioxidant against the atherogenic modification of LDL by glucose autoxidation radical products. Daidzein, (4', 7-dihydroxyisoflavone) an other phytoestrogen of soy, was tested in parallel. Genistein — in contrast to daidzein — effectively prevented the glucose mediated LDL oxidation as measured by thiobarbituric acid-reactive substance formation (TBARS), alteration in electrophoretic mobility, lipid hydroperoxides and fluorescence quenching of tryptophan residues of the lipoprotein. In addition the potential of glucose-oxidized LDL to increase tissue factor (TF) synthesis in human endothelial cells (HUVEC) was completely inhibited when genistein was present during LDL oxidative modification by glucose. Both phytoestrogens did not influence the nonenzymatic protein glycation reaction as measured by the in vitro formation of glycated LDL. As the protective effect of genistein on LDL atherogenic modification was found at glucose/genistein molar ratios which may occur in vivo, our findings support the suggested beneficial action of a soy diet in preventing chronic vascular diseases and early atherogenic events.     

Fluidity of natural membranes and phosphatidylserine and ganglioside dispersions. Effect of local anesthetics, cholesterol and protein.

The microviscosity of artificial lipid membranes and natural membranes was measured by the fluorescence polarization technique employing perylene as the probe. Lipid dispersions composed of brain gangliosides exhibited greater microviscosity than phosphatidylserine (268 cP vs 173 cP, at 25 degrees C). Incorporation of cholesterol (30-50%) increased the microviscosity of lipid phases by 200-500 cP. Cholesterol's effect on membrane fluidity was completely reversed by digitonin but not by amphotericin B. Incorporation of membrane proteins into lipid vesicles gave varying results. Cytochrome b5 did not alter membrane fluidity. However, myelin proteolipid produced an apparent increase in microviscosity, but this effect might be due to partitioning of perylene between lipid and protein binding sites since tha latter have a higher fluorescence anisotropy than the lipid. The local anesthetics tetracain and butacaine increased the fluidity of lipid dispersions, natural membranes and intact ascites tumor cell membranes. The effect of anesthetics appears to be due to an increased disordering of lipid structure. The fluidity of natural membranes at 25 degrees C varied as follows: polymorphonuclear leukocytes, 335 cP; bovine brain myelin, 270 cP; human erythrocyte, 180 cP; rat liver microsomes, 95 cP; rat liver mitochondria, 90 cP. In most cases the microviscosity of natural membranes reflects their cholesterol: phospholipid ratio. The natural variations in fluidity of cellular membranes probably reflect important functional requirements. Similarly, the effects of some drugs which alter membrane permeability may be the result of their effects on membrane fluidity.     

The surface lipid layer of human low density lipoprotein probed by dipyrenyl phospholipids

Properties of the surface lipid-protein layer of human low density lipoprotein (LDL) have been studied with fluorescent phosphatidylcholine analogues containing a pyrenyl fatty acid of variable length at both sn-1 and sn-2 position of the glycerol moiety. Only intramolecular excimer formation takes place at low concentrations, as indicated by the independence of the ratio of excimer to monomer fluorescence intensities (E/M) on the amount of the incorporated dipyrenyl phospholipid. The E/M parameter which depends on the fluidity of the probe's environment were measured for a series of dipyrenyl phospholipids in three systems, i.e. in LDL, LDL-like lipid particles (LDp) and small unilamellar phosphatidylcholine/sphingomyelin/cholesterol vesicles (SUV). The data indicate that the fluidity of the phospholipid acyl chain region decreases in the order: SUV greater than LDp greater than LDL. This suggests that interactions with both the core lipids and the protein moiety (apoB-100) contribute to the rigidity of the surface lipid layer of LDL. Dipyrenyl phospholipids also detect the thermotropic transition of the core lipids of both LDL and LDp, suggesting that this transition influences the fluidity of the surface lipid layer.