The oxidation hypothesis of atherogenesis: the role of oxidized phospholipids and HDL

For more than two decades, there has been continuing evidence of lipid oxidation playing a central role in atherogenesis. The oxidation hypothesis of atherogenesis has evolved to focus on specific proinflammatory oxidized phospholipids that result from the oxidation of LDL phospholipids containing arachidonic acid and that are recognized by the innate immune system in animals and humans. These oxidized phospholipids are largely generated by potent oxidants produced by the lipoxygenase and myeloperoxidase pathways. The failure of antioxidant vitamins to influence clinical outcomes may have many explanations, including the inability of vitamin E to prevent the formation of these oxidized phospholipids and other lipid oxidation products of the myeloperoxidase pathway. Preliminary data suggest that the oxidation hypothesis of atherogenesis and the reverse cholesterol transport hypothesis of atherogenesis may have a common biological basis. The levels of specific oxidized lipids in plasma and lipoproteins, the levels of antibodies to these lipids, and the inflammatory/anti-inflammatory properties of HDL may be useful markers of susceptibility to atherogenesis. Apolipoprotein A-I (apoA-I) and apoA-I mimetic peptides may both promote a reduction in oxidized lipids and enhance reverse cholesterol transport and therefore may have therapeutic potential.     

The effect of the phase transition on the hydration and electrical conductivity of phospholipids.

Adsorption isotherms for various saturated phosphatidylcholines have been obtained. Lipids above and below their phase transition temperature differ only in the amount of water adsorbed and not in the nature of their adsorption isotherms. Cholesterol has an effect similar to that of increasing unsaturation in the hydrocarbon chains. Decreasing the length of the hydrocarbon chains for lipids below their phase transition temperature has no effect on the isotherms. If the chain length is short enough so that the lipids are above their transition temperature, however, a large increase in water adsorption occurs. All of the phospholipids exhibit a rapid increase of electrical conductivity for a few water molecules adsorbed per lipid molecule. All of the phospholipids show a saturation in conductivity at greater amounts of adsorbed water; the shape of the saturation region depends on whether the lipids are above or below their phase transition temperature. The activation energy for the electrical conductivity process depends on whether the hydrated lipids are in the "liquid-like" of the crystalline state, being lower for phospholipids in the liquid-like state. If the lipids are hydrated above their phase transition temperatures, their activation energies are lower than if they are hydrated below the transition temperature. Cholesterol lowers the activation energy. The phosphatidylcholines can be characterized by different activation energies, depending both upon their physical state and the presence of unsaturation in their hydrocarbon chains.     

Studies on the diversity of inositol-containing yeast phospholipids: incorporation of 2-deoxyglucose into lipid

Seven inositol-containing phospholipids in Saccharomyces cerevisiae can be resolved by two-dimensional chromatography on silicic acid-impregnated paper. Four of these lipids are stable to mild alkaline methanolysis; one of these has already been characterized as a mannosyl di(inositolphosphoryl) ceramide. Addition of labeled 2-deoxy-d-glucose to a growing culture results in label appearing in five lipids, some of which are alkali-stable and have the same R(F) values as the alkali-stable inositol-containing phospholipids. These lipids are labeled rapidly. The deoxyglucose is incorporated intact, probably in a glycosidic link, since the deoxyglucose is released by mild acid treatment.     

A molecular dynamics study of the interaction between domain I-BAR of the IRSp53 protein and negatively charged membranes

The methods of computer simulation in all-atom and coarse-grained approximations have been used to study specific interactions of the isolated domain I-BAR of the actin-binding protein IRSp53 with model membranes containing neutral phospholipids and those including negatively charged PI(4,5)P₂ phospholipids. It has been shown that the I-BAR domain does not interact with neutral lipids but induces bending of the synthetic membrane rich in negatively charged phospholipids. Clustering of charged lipids on the surface of the membrane at the sites of its interaction with the protein has been observed. This indicates that the interaction of I-BAR with negatively charged lipids is of electrostatic and hydrophobic nature.     

Use of spin-labeled and fluorescent lipids to study the activity of the phospholipid transfer protein from maize seedlings.

The transfer of spin-labeled and fluorescent lipids between sonicated vesicles and different host membranes has been measured in the presence or absence of a phospholipid transfer protein purified from maize seedlings. It was found that the protein has little specificity towards the phospholipid head group and allows the transfer of hydrophobic long chain phospholipids. By contrast, no transfer of a cholesterol analogue could be detected. By EPR spectroscopy, evidence is presented that shows that the protein catalyzes the incorporation of labeled phospholipids in the outer monolayer of the acceptor membranes. The efficiency of the transfer depends largely on the nature of the acceptor: erythrocytes are more difficult to label than chromaffin granules or liposomes made with unsaturated lipids. Thus, consistent with the high activation energy observed, the transfer is facilitated when it involves fluid membranes. These results are in favor of a process involving the exchange of phospholipids, facilitated by a shuttle protein rather than a fusion mechanism.     

Polar-group behaviour in mixed monolayers of phospholipids and fusogenic lipids.

1. The surface potentials of mixed monolayers of synthetic phospholipids with lipids that are fusogenic for hen erythrocytes were investigated. 2. At pH 5.6 and 10, but not at pH2, mixed monolayers of the fusogenic lipid, glycerol mono-oleate, with phosphatidylcholine exhibited negative deviations from the ideality rule in surface potential per molecule which were accompanied by negative deviations in mean molecular area. 3. Interactions of this type were not seen with chemically related but non-fusogenic lipids, nor were they found in mixed monolayers of any of the lipids with phosphatidylethanolamine. 4. Experiments with dihexadecyl phosphate and hexadecyltrimethyl-ammonium indicated that the complete head group of phosphatidylcholine is required for its observed behaviour with fusogenic lipids. 5. Bivalent cations (Ca2+, UO2(2+) or Zn2+) in the subphase at pH 5.6 significantly modified the behaviour of mixed monolayers of fusogenic lipids with phospholipids; there was a parallel perturbing effect of fusogenic lipids on interactions between monolayers of phospholipids and bivalent cations. 6. Possible molecular interactions of fusogenic lipids with membrane phospholipids, and the role of Ca2+, are discussed which may be relevant to cell fusion in erythrocytes induced by low-melting lipids in the presence of Ca2+.     

Lipid peroxidation in rat uterus

Lipid peroxidation in rat uterus has been studied using NADPH- and ascorbate-induced systems. Lipid peroxidation in rat uterus is low as compared to rat liver. Uterus is more sensitive to ascorbate-induced lipid peroxidation than that induced by NADPH. Uterus contains lower amounts of phospholipids and has a lesser degree of unsaturation in lipids. Co-factor studies show that Fe2+ is more important for ascorbate-induced lipid peroxidation. Endometrium is more sensitive to ascorbate-induced lipid peroxidation than myometrium. It also contains more total lipids and phospholipids besides having a higher degree of unsaturation in the lipids as compared to myometrium. Among the subcellular fractions, mitochondria are more prone to ascorbate-induced lipid peroxidation, whereas microsomes are more sensitive to NADPH-induced lipid peroxidation. Uteri from old rats (24 months) and pregnant rats are more resistant to lipid peroxidation than those from 3-month-old control rats. Uterus of pregnant rats contains more factors which inhibit lipid peroxidation and also has a lesser degree of unsaturation in lipids compared with uterus of control rats. The possible consequences of the resistance of uterus to lipid peroxidation, especially during pregnancy and senescence, are discussed.     

Effect of mercury chloride on the level of lipids and products of their peroxidation in rat vital organs

The influence of mercury chloride on peroxidation processes of lipids and level of common lipids, phospholipids and spectrum of neutral lipids in liver, heart, lung and kidney of rats has been investigated. Administration of mercury chloride in a dose 0.7 mg/100 g of body weight to animals has invoked accumulation of lipids peroxide products in fractions of neutral lipids and phospholipids so it testifies the development of oxidative stress. Decrease of the most sensitive to oxidation fractions in the early stages of oxidative stress development and increase of free cholesterol and its ethers content in kidney and free cholesterol in the heart in more later terms as a result of mercury chloride administration have been revealed.     

Structural characterization of the polar lipids of Clostridium novyi NT. Further evidence for a novel anaerobic biosynthetic pathway to plasmalogens

A study of the polar lipids of Clostridium novyi NT has revealed the presence of phosphatidylethanolamine (PE) and cardiolipin as major phospholipids with smaller amounts of phosphatidylglycerol (PG), lysyl-PG and alanyl-PG. Other minor phospholipids included phosphatidic acid, CDP-diacylglycerol, phosphatidylserine (PS) and phosphatidylthreonine (PT). PE, PG and amino acyl PG were present in both the diacyl and alk-1'-enyl acyl (plasmalogen) forms and cardiolipin plasmalogens were found to contain one or two alk-1'-enyl chains. In contrast, the precursor lipids phosphatidic acid, CDP-diacylglycerol and PS were present almost exclusively as diacyl phospholipids. These findings are consistent with the hypothesis that plasmalogens are formed from diacylated phospholipids at a late stage of phospholipid formation in Clostridium species. This novel pathway contrasts with the route in animals in which a saturated ether bond is formed at an early stage of plasmalogen biosynthesis and the alk-1-enyl bond is formed by an aerobic mechanism.     

DNA-bound lipids from eukaryotic (loach spermatozoa, pigeon erythrocytes) and prokaryotic (E. coli B, phage T2) cells

Using thin-layer chromatography, some specific DNA-bound neutral lipids and phospholipids of loach spermatozoa, pigeon erythrocytes, E. coli B and phage T2 cells were studied. These lipids are represented by loosely and firmly bound components. The content of neutral lipids in the above DNAs (per mg of DNA) is 10.6, 4.8, 7.81 and 1.43 micrograms, respectively; that of phospholipids is 4.31, 1.28, 1.14 and 0.54 micrograms, respectively. The eucaryotic DNA-bound lipids are highly deficient of free cholesterol, phosphatidylcholine, phosphatidylinositol and phosphatidylserine but are rich in cardiolipin, phosphatidylethanolamine, cholesterol esters, diglycerides and free fatty acids. The quantitative and qualitative composition of DNA-bound lipids of loach spermatozoa changes during the transition from the superhelical to the relaxed conformation of DNA. Procaryotic DNA-bound neutral lipids are also represented by the free cholesterol, diglyceride and free fatty acid fractions, whereas the DNA-bound phospholipids of procaryotes consist of only two fractions, i.e., cardiolipin and phosphatidylethanolamine. The role of DNA-bound lipids in the structural and functional organization of eucaryotic and procaryotic genomes is discussed.     

Biological activity of polar lipids from bifidobacteria

Fractions of polar lipids have been isolated from bifidobacteria, and the immunoreactivity and serological specificity of glycolipids and phospholipids have been studied. Enzyme immunoassay (dot-EIA) of polar lipids demonstrates that the fractions of glycolipids and phospholipids of bifidobacteria are highly immunoreactive. Pronounced reactions of major glycolipids and phospholipids with a homologous polyvalent antiserum against B. adolescentis 94-BIM have been observed at antigen concentrations of approximately 100 ng. The antiserum contained high titers of specific antibodies against glycolipids and phospholipids of bifidobacteria, as demonstrated by heterogeneous solid-phase enzyme immunoassay (ELISA). Experimental data confirming the presence of subpopulations of specific antibodies (antiglycolipid and antiphospholipid) in the blood sera of immunized animals lead to the conclusion that the major glycolipids and phospholipids of bifidobacteria are specific markers appropriate for serological diagnostics.     

Phospholipid uptake by Plasmodium knowlesi infected erythrocytes

The uptake of phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylserine (PS) in Plasmodium knowlesi infected erythrocytes has been studied. Whereas uptake of phospholipids, in the absence of phospholipid transfer proteins, is negligible in control cells, the infected cells can incorporate considerable amounts of added phospholipids. The uptake is enhanced by the presence of lipid transfer proteins. Doubly labeled [3H]oleate, [14C]choline) PC does not undergo any appreciable remodelling following uptake, which strongly suggests that plasma PC is used as such for the biogenesis of the parasite membranes. Transport of extracellularly offered PS and PE towards the intraerythrocytic parasite and utilization of these lipids by the parasite are confirmed by the observation that these lipids are converted into respectively PE and PC. The extent and rate of these conversions depend on the way the phospholipids are introduced into the infected cells.     

Lipids at the stages of early osteogenesis in human long tubular bones

In 240 long tubular bone anlagen (LTBA) of extremities in 40 human embryos and prefetuses at the age of 6-12 weeks of the prenatal development the investigation has been performed concerning localization, dynamics of contents and spectrum of neutral lipids and phospholipids. Lipids are stained with Sudan III and IV, phospholipids-with Sudan black with corresponding control extractive methods and quantitative estimation of these substances values. The material for electron microscopical investigation of the lipids is treated according to the method, that preserves their safety. The spectrum of lipids and phospholipids in the LTBA is studied by means of the thin layered chromatography method. The data of the histochemical investigation and chromatography demonstrate decreasing contents of neutral lipids with the gradient from the zone of the preserved cartilage up to the ossification zone of the epiphyseal cartilage of the LTBA in the human embryos and prefetuses. Increased concentration of phospholipids and complication of their spectrum is noted in the areas of intensive deposits of calcium salts. An essential role of the substance of lipid origin is supposed in ossification and mineralization of the human LTBA.     

Effect of ionizing radiation on the lipid composition of aminoacyl-tRNA-synthetase complexes

The effect of X-radiation (0.21 C/kg) on a lipid component of aminoacyl-tRNA-synthetase complexes from rat liver (for instance, phospholipids, neutral lipids, and prostaglandins) has been studied. The content of prostaglandins and lysophosphatidyl choline increases and that of phospholipids and neutral lipids decreases 60 min after irradiation. In 24 h, the content of prostaglandins, fatty acids, cholesterol, and phosphatidyl ethanolamine approaches the control level.     

Fatty Acids from Degenerating Myelin Lipids Are Conserved and Reutilized for Myelin Synthesis During Regeneration in Peripheral Nerve

Abstract: Following nerve crush, cholesterol from degenerating myelin is conserved and reutilized for new myelin synthesis during nerve regeneration. The possibility that other myelin lipids are salvaged and reutilized has not been investigated previously. We examined the fate of myelin phospholipids and their fatty acyl moieties following nerve crush by electron microscopic autoradiography of myelin lipids prelabeled with [³H]oleate or [2-³H]-glycerol. Both precursors were incorporated predominantly (>90%) into phospholipids; >85% of the [³H]oleate was incorporated as oleate, with the remainder in longer-chain fatty acids. Before nerve crush, both labels were restricted to myelin sheaths. Following nerve crush and subsequent regeneration, over half the label from [³H]oleate, but little from [2-³H]glycerol, remained in nerve. The oleate label was present as fatty acyl moieties in phospholipids and was localized to newly formed myelin sheaths. Among the extracellular soluble lipids within the degenerating nerve, the bulk of the labeled phospholipids floated at the same density as lipoprotein particles. These data indicate that myelin phospholipids are completely hydrolyzed during nerve degeneration, that at least half the resultant free fatty acids are salvaged and reutilized for new myelin synthesis, and that these salvaged fatty acids are transported by a lipoprotein-mediated mechanism similar to that functioning in cholesterol reutilization.     

Rat liver nuclear lipids. Composition and biosynthesis

A characteristic of rat liver nuclear lipids is their high content in neutral lipids especially of tryglycerides and free fatty acids. These compounds do not arise due to hydrolysis of more complex lipids during the isolation of the nuclei. The neutral lipids fatty acid pattern is more saturated than the phospholipid one. The presence of phosphatidylinositol mono- and diphosphate in nuclei has been confirmed. Nuclei are unable to synthesize de novo phospholipids but are capable of incorporating inorganic phosphate into lipids synthesized via a kinase pathway.     

Studies on mixed monolayers of phospholipids and fusogenic lipids.

1. The behaviour of mixed monolayers of 14 different lipids with preparations of erythrocyte lipids, purified natural and synthetic phospholipids, cholesterol and galactosylceramide was investigated. 2. The mean areas occupied per molecule in mixed films containing lipids that are fusogenic for hen erythrocytes were compared with those for corresponding films containing lipids that are inactive as fusogens. 3. Fusogenic lipids were found to exhibit interactions, which were not shown by non-fusogenic lipids, in mixed monolayers with several species of phospholipid, particularly those containing a choline head group. 4. Heterogeneity in the hydrophobic chains of phosphatidylcholine, their degree of unsaturation and the presence of cholesterol had little effect on the interaction of phosphatidylcholine with fusogenic lipids. 5. Fusogenic lipids showed little specific interaction with natural or synthetic preparations of phosphatidylethanolamine. 6. The possible significance of these observations in relation to the action of fusogenic lipids on biological membranes is discussed in the light of the asymmetrical distribution of phospholipids in erythrocyte membranes.     

Biological Activity of Polar Lipids from Bifidobacteria

Fractions of polar lipids have been isolated from bifidobacteria, and the immunoreactivity and serological specificity of glycolipids and phospholipids have been studied. Enzyme immunoassay (dot-EIA) of polar lipids demonstrates that the fractions of glycolipids and phospholipids of bifidobacteria are highly immunoreactive. Pronounced reactions of major glycolipids and phospholipids with a homologous polyvalent antiserum against B. adolescentis 94-BIM have been observed at antigen concentrations of approximately 100 ng. The antiserum contained high titers of specific antibodies against glycolipids and phospholipids of bifidobacteria, as demonstrated by heterogeneous solid-phase enzyme immunoassay (ELISA). Experimental data confirming the presence of subpopulations of specific antibodies (antiglycolipid and antiphospholipid) in the blood sera of immunized animals lead to the conclusion that the major glycolipids and phospholipids of bifidobacteria are specific markers appropriate for serological diagnostics.     

Plasma and muscle phospholipids are involved in the metabolic response to long-distance migration in a shorebird

We studied: (1) concentrations and fatty acid compositions of plasma non-esterified fatty acids, neutral lipids, and phospholipids, and (2) fatty acid composition of flight muscle phospholipids in wintering, premigratory, and spring and fall migrating western sandpipers ( Calidris mauri). Plasma neutral lipid and phospholipid levels were elevated in migrants, reflecting high rates of fat deposition. An important role of phospholipids in fattening is suggested by the fact that the amount of fatty acids in plasma phospholipids was similar to, or in spring as much as twice, that of neutral lipids. Changes in the ratio of plasma neutral lipids to phospholipids may indicate seasonal changes in triacylglycerol stores of invertebrate prey. Monounsaturation and total unsaturation of plasma neutral lipids and phospholipids increased during migration. Muscle phospholipids were more monounsaturated in spring and fall, but total unsaturation was reduced in fall. Arachidonic acid [20:4(n-6)] was especially abundant in muscle phospholipids in winter (29%) and declined during migration (19-22%), contributing to a decline in the ratio of n-6 to n-3 fatty acids. The abundance of plasma phospholipids and variability of neutral lipid to phospholipid ratio indicates that measurement of plasma phospholipids will improve methods for assessment of fattening rates of birds. The functional significance of changes in muscle phospholipids is unclear, but may relate to depletion of essential n-6 fatty acids during exercise.     

Docosahexaenoic acid-enriched egg phospholipids supplementation induces accretion of arachidonic acid in rat blood lipids.

Animal and humans studies have shown that supplementation with triacylglycerides containing omega3 fatty acids, mainly docosahexaenoic acid (DHA) and eicosapentaenoic acid, can induce a decrease in arachidonic acid (AA) in blood lipids. Interestingly, we observed in a previous work that a supplementation with DHA enriched eggs in a healthy elderly population induced an accretion of AA in their blood lipids. The present study investigates whether purified DHA enriched egg phospholipids could be responsible for this effect. Four groups of rats were supplemented daily, for eight weeks, with DHA phospholipids (10, 30 or 60 mg/kg) or with soybean phospholipids. Red blood cell membranes and plasma fatty acid levels were compared with that of rats without supplementation. Soybean phospholipids supplementation increased the level of AA in blood lipids but decreased that of DHA. The doses of DHA phospholipids, 30 and 60 mg/kg, induced greater amounts of AA without affecting significantly DHA levels. In contrast, DHA phospholipids supplementation, 10 mg/kg, in which there was the greatest amount of AA, induced only a slight increase in AA levels. Moreover, DHA levels were decreased by this supplementation. These results demonstrate that specific increases in AA levels are preferentially associated with DHA phospholipids levels in supplementation.