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The Distributive Study of Plasmalogen in Guinea Pig Tissues.

The content of plasmalogen and plasmenylethanolamine (PE-plasmalogen) in the guinea pig brain, heart, liver, lung, kidney and muscle were examined and compare to the total phospholipids and total phosphatidylethanolamine (PE) of these organs, by the methods of Gottfried iodine and thin layer chromatography. The highest content of plasmalogen and PE-plasmalogen was found in the brain, which was 9.28 and 6.54 &mgr;mol/g of tissue respectively, followed was in the heart which was 5.29 and 2.01 &mgr;mol/g of tissue respectively. The lowest content of plasmalogen and PE-plasmalogen was in the liver, which was 1.47 and 0.67 &mgr;mol/g of tissue respectively. It was also found that the content of PE-plasmalogen in the muscle of the guinea pig was higher than that in the kidney, lung and liver, it accounts for 40.1% of the total PE. The distributing regularity and biological significance of plasmalogen in guinea pig tissues were discussed.

Journal Article↗

HPLC of plasmalogen-containing phosphatidylcholine under reverse-phase or argentation conditions.

Two approaches to the high pressure liquid chromatography (HPLC) isolation of intact plasmalogens were investigated. The first used reversed-phase HPLC and sought to take advantage of subtle differences in the hydrophobicity of the alk-1-enyl chain from the acyl counterpart. On a C-18 column, bovine heart phosphatidylcholine (PC), which was 47% plasmalogen, was separated into a number of fractions that differed in their molecular species composition. One combination of fractions amounted to a 26% yield of PC enriched to 82% plasmalogen. The second approach sought to take advantage of the uniquely electron-rich functionality of the plasmalogens, the alk-1-enyl ether double bond, and its potential to coordinate with heavy metal ions. Specifically, bovine heart PC was applied to a cation-exchange type HPLC column in the silver ion mode. Although complete exchange of all the active sites of the column with silver ion led to complete retention of PC, partial activation with silver ion resulted in the separation of the PC into fractions, according to the degree of unsaturation. Plasmalogen-rich fractions eluted last and remained intact during the process. One combination of these fractions amounted to a 49% yield of PC enriched to 72% plasmalogen. Use of a cation-exchange system in the mercuric ion mode led to on-column hydrolysis of the plasmalogen; with palladium ion, the metallic species was stripped from the column by the eluting lipid.

Animals↗

Effects of aging and dietary n-3 fatty acids on rat brain phospholipids: focus on plasmalogens.

The aging brain undergoes modifications in the lipid composition of cell membranes and especially in plasmalogens. These phospholipids represent between one-half and two-thirds of the ethanolamine phospholipids in the brain. They are known to facilitate membrane fusion and act as endogenous antioxidants. During normal aging and in some pathological conditions, plasmalogen and DHA levels fall. In this context, we aimed to evaluate the influence of n-3 FA intake on plasmalogens in the brain during aging. Littermates from two generations of n-3-deficient rats were fed an n-3-deficient diet or an equilibrated diet containing either alpha-linolenic acid alone (alpha-LNA) or with two doses of DHA (0.3 or 0.6% w/w). After weaning, 9 mon of diet, or 21 mon of diet, plasmalogen levels were assessed, and the sn-2 substitutions of plasmenylethanolamines were analyzed in the cortex, striatum, and hippocampus. Our results showed that plasmalogen contents were not influenced by the diet. Plasmalogen levels were significantly decreased in aged rats compared with adults, whereas DHA levels increased in the hippocampus and remained stable in the cortex and striatum. DHA levels were significantly and similarly increased in total phospholipids and especially in plasmenylethanolamines after 9 mon of diet containing alpha-LNA alone or combined with DHA. This study showed that each structure sustained specific age-induced modifications. Dietary n-3 FA may not oppose the physiological decrease in brain plasmalogen levels during aging. Moreover, alpha-LNA appears to be equally as potent as preformed DHA at replacing DHA in the brain of our rat model.

Aging↗

Delay of copper-catalyzed oxidation of low density lipoprotein by in vitro enrichment with choline or ethanolamine plasmalogens.

Low density lipoprotein (LDL) isolated from human serum of different donors was enriched with plasmalogens and their diacyl analogs in order to investigate a possible effect of these phospholipids on the rate of lipid peroxidation in this lipoprotein. LDL was incubated with either vesicles of choline plasmalogen or phosphatidylcholine in presence of lipoprotein- deficient serum, or with liposomes of ethanolamine plasmalogen or phosphatidylethanolamine together with the non-specific phospholipid transfer protein isolated from beef liver. After re-isolation of LDL by ultracentrifugation, a dose-dependent incorporation of the exogenous phospholipids was obtained. Enrichment of LDL with choline plasmalogen resulted in a delay of the copper-catalyzed oxidation of LDL from five different donors. LDL from two donors was also enriched with diacylglycerophosphocholine which led to a delay of oxidation, but the protective effect was smaller than with choline plasmalogen. Enrichment of LDL from two additional donors with ethanolamine plasmalogen resulted in the strongest protection against oxidation, whereas, diacylglycerophospho-ethanolamine had little effect. The delay of the copper-catalyzed LDL oxidation may be due to a direct antioxidative action of the plasmalogens, which are partially degraded during the lag phase of oxidation, or to an indirect effect caused by alteration of the LDL surface in the presence of an excess of glycerophospholipids.

Antioxidants↗

On the plasmalogenation of myocardial choline glycerophospholipid during maturation of various vertebrates.

1. The plasmalogen profiles of a series of hearts from fish to mammals were obtained by various TLC analyses. 2. All specimens (ventricular) contained ethanolamine plasmalogen and some choline plasmalogen, as well. 3. The distribution of these two plasmalogen species was relatable, in part, to (a) phylogeny and (b) ontogeny. 4. There were exceptions. 5. The appearance of choline plasmalogen was preceded by its alkylacyl precursor, suggesting plasmalogenation by a base-specific delta 1-alkyl desaturase. 6. From the data, we have raised some questions as to the metabolic role played by the plasmalogens and precursors as occupants of myocardial mitchondrial membranes.

Animals↗

Eosinophil peroxidase-derived reactive brominating species target the vinyl ether bond of plasmalogens generating a novel chemoattractant, alpha-bromo fatty aldehyde.

Plasmalogens are a subclass of glycerophospholipids that are enriched in the plasma membrane of many mammalian cells. The vinyl ether bond of plasmalogens renders them susceptible to oxidation. Accordingly, it was hypothesized that reactive brominating species, a unique oxidant formed at the sites of eosinophil activation, such as in asthma, might selectively target plasmalogens for oxidation. Here we show that reactive brominating species produced by the eosinophil peroxidase system of activated eosinophils attack the vinyl ether bond of plasmalogens. Reactive brominating species produced by eosinophil peroxidase target the vinyl ether bond of plasmalogens resulting in the production of a neutral lipid and lysophosphatidylcholine. Chromatographic and mass spectrometric analyses of this neutral lipid demonstrated that it was 2-bromohexadecanal (2-BrHDA). Reactive brominating species produced by eosinophil peroxidase attacked the plasmalogen vinyl ether bond at acidic pH. Bromide was the preferred substrate for eosinophil peroxidase, and chloride was not appreciably used even at a 1000-fold molar excess. Furthermore, 2-BrHDA production elicited by eosinophil peroxidase-derived reactive brominating species in the presence of 100 microM NaBr doubled with the addition of 100 mM NaCl. The potential physiological significance of this pathway was suggested by the demonstration that 2-BrHDA was produced by phorbol myristate acetate-stimulated eosinophils and by the demonstration that 2-BrHDA is a phagocyte chemoattractant. Taken together, the present studies demonstrate the targeting of the vinyl ether bond of plasmalogens by the reactive brominating species produced by eosinophil peroxidase and by activated eosinophils, resulting in the production of brominated fatty aldehydes.

Acetaldehyde↗

Essential fatty acids and serine as plasmalogen precursors in relation to competing metabolic pathways.

Interest in altered ether-lipid metabolism, associated with peroxisomal disorders including adrenoleukodystrophy and Zellweger's syndrome, has highlighted present limitations in our understanding of the biosynthesis and turnover of plasmalogens. These 1-alkenyl ethanolamine phosphoglycerides are major phospholipids in brain, vascular tissue, neutrophils, and most tumors, and they constitute 15-20% of total phospholipids in cultured glioma cell. In glioma, turnover of polyunsaturated acyl chains in the sn-2 position of plasmalogens was examined in relation to selectivity for the (n - 3) and (n - 6) families. Remodeling of acyl chains was more dependent on chain length than on selectivity between families, consistent with plasmalogens enriched in polyunsaturated, but not specifically (n - 3), fatty acids. Extracellular serine was a precursor of serine and ethanolamine phosphoglycerides and was associated with plasmalogens due to decarboxylation and headgroup exchange. Incorporation of extracellular serine ceased within 8 h, even though more than 50% of the label remain in the medium. Analyses of medium and cellular water-soluble components indicated rapid conversion of serine to glycine and other metabolites not used in phospholipid biosynthesis. Thus, nutrient molecules as precursors of plasmalogens are involved in complex competitive interactions. As functions of plasmalogens are clarified, regulation of plasmalogen turnover becomes an increasingly important issue and elucidation of these processes is essential.

Adrenoleukodystrophy↗

Quantification of long-chain aldehydes by gas chromatography coupled to mass spectrometry as a tool for simultaneous measurement of plasmalogens and their aldehydic breakdown products.

The cleavage of the specific vinyl ether linkage at the sn-1 position of plasmalogens leads to the formation of two products: the 1-lyso-2-acyl glycerophospholipid and a long-chain fatty aldehyde. Plasmalogens are measured by quantifying one of these two products. In this paper, we describe a rapid and sensitive procedure for measuring plasmalogens via quantification of long-chain fatty aldehydes. After lipid extraction, the sn-1 vinyl ether bond of plasmalogens is cleaved by acidic hydrolysis. The produced aldehydes are then derivatized with (pentafluorobenzyl)hydroxylamine hydrochloride and analyzed by gas chromatography/mass spectrometry in selected-ion mode. Plasmalogens are then indirectly quantified by subtracting the free aldehydes obtained without prior HCl treatment from the total aldehydes obtained after acidic hydrolysis. This method is applied to three rat brain areas selected for this study. Two of these are affected in neurodegenerative diseases (cerebral cortex and hippocampus) and one is rich in white matter (cerebellum). In comparison to other procedures, the advantages of this method are not only its usefulness in plasmalogen quantification but also the identification of aldehydic breakdown products.

Aldehydes↗

Evidence against a major role of plasmalogens in the resistance of astrocytes in lactic acid-induced oxidative stress in vitro.

Astrocytes are known to play a key role in buffering extracellular pH variations and, in addition, they are particularly resistant to oxidative stress and subsequent lipid peroxidation. This great resistance may be ascribed to the presence of high concentrations of certain antioxidants, but another explanation may be the presence of a high quantity of plasmalogens, which are a special group of glycerophospholipids characterized by a vinyl ether bond instead of an ester bond in the sn-1 position of the glycerol backbone. Plasmalogens are sensitive to free radical attack and acidity, and numerous works have supported the hypothesis that they may be antioxidant molecules that protect cells from oxidative stress. The aim of this work was to investigate, on astrocytes in lactic acid-induced oxidative stress (pH 5.5), the behavior of phospholipids and, in particular, plasmalogens. Two main techniques, based on the susceptibility of the vinyl ether bond to hydrolysis, were employed in this study to measure plasmalogen levels. In both cases, the sn-1 vinyl ether linkage was cleaved using mercuric chloride, producing a lysophospholipid that was assessed by phosphorus measurement or using HCl treatment, producing a long-chain fatty aldehyde assayed by gas chromatography/mass spectrometry. On astrocytes in culture, only plasmenylethanolamine (PlmEtn) was evidenced, representing 40% of glycerophosphoethanolamine lipids. When astrocytes were incubated with lactic acid, no modification in the amount of PlmEtn was seen. Furthermore, free aldehydes and aldehydes corresponding to the quantity of intact plasmalogens were similar to those observed on controls. In addition, the constancy of two lipid peroxidation markers, thiobarbituric acid reactive substances and polyunsaturated fatty acids, was clear evidence of the resistance of these cells in lactic acid conditions. In conclusion, our results fail to demonstrate a major role of plasmalogens in the resistance of astrocytes in lactic acid-induced oxidative stress.

Acidosis, Lactic↗

Fatty acids of serine, ethanolamine, and choline plasmalogens in some marine bivalves.

The FA composition of glycerophospholipid (GPL) classes and subclasses was investigated in whole animals of three marine bivalve mollusks: the Japanese oyster Crassostrea gigas, the blue mussel Mytilus edulis, and the Manila clam Ruditapes philippinarum. Individual organs (gills, mantle, foot, siphon, and muscle) of the Manila clam also were examined. The PS plasmalogen (PSplsm), PE plasmalogen (PEplsm), and PC plasmalogen (PCplsm) subclasses were isolated by HPLC, and their individual FA compositions were examined using GC. Plasmalogen forms of PS and PE, when compared to their respective diacyl forms, were found to be specifically enriched with non-methylene-interrupted (NMI) FA (7,15-22:2, 7,13-22:2, and their precursors) and 20:1 n-11 FA. Such a clear specific association was not found for PCplsm. Interestingly, this trend was most apparent in PSplsm, and the above FA were found to be, respectively, the predominant PUFA and monounsaturated FA in the PSplsm isolated from the three species. This specificity was maintained in all the analyzed organs of the Manila clam but varied in proportions: The highest level of plasmalogens, NMI FA, and 20:1 n-11 was measured in gills and the lowest was in muscle. These results represent the first comprehensive report on a FA composition of the PSplsm subclass isolated from mollusks. The fact that NMI FA and 20:1 n-11, which are thought to be biosynthesized FA, were mainly associated with aminophospholipid plasmalogens (PE and PS) is likely to have a functional significance in bivalve membranes.

Animals↗

Structure and dynamics of plasmalogen model membranes containing cholesterol: a deuterium NMR study.

Deuterium nuclear magnetic resonance (2H-NMR) was used to investigate the structure and dynamics of the sn-2 hydrocarbon chain of semi-synthetical choline and ethanolamine plasmalogen in bilayers containing 0, 30, and 50 mol% cholesterol. The deuterium NMR spectra of the choline plasmalogen yielded well-resolved quadrupolar splittings which could be assigned to the corresponding hydrocarbon chain deuterons. The sn-2 acyl chain was found to adopt a similar conformation as observed in the corresponding diacyl phospholipid, however, the flexibility at the level of the C-2 methylene segment of the plasmalogen was increased. Deuterium NMR spectra of bilayers composed of the ethanolamine plasmalogen yielded quadrupolar splittings of the C-2 segment much larger than those of the corresponding diacyl lipids, suggesting that the sn-2 chain is oriented perpendicular to the membrane surface at all segments. Cholesterol increased the ordering of the choline plasmalogen acyl chain to the same extent as in diacyl lipid bilayers. T1 relaxation time measurements demonstrated only minor dynamical differences between choline plasmalogen and diacyl lipids in model membranes.

Cholesterol↗

Influence of plasmalogen deficiency on membrane fluidity of human skin fibroblasts: a fluorescence anisotropy study.

The influence of plasmalogen deficiency on membrane lipid mobility was determined by measuring fluorescence anisotropy of trimethylammoniumdiphenylhexatriene (TMA-DPH) and diphenylhexatrienylpropanoylhydrazylstachyose (glyco-DPH) inserted in the plasma membranes of human skin fibroblasts deficient in plasmalogens. The cells used were from patients affected with cerebrohepatorenal (Zellweger) syndrome (CHRS) or rhizomelic chondrodysplasia punctata. Their plasmalogen content (0-5% of total phospholipid) is significantly reduced compared with that of control cells from healthy donors (13-15% of total phospholipid) or of CHRS fibroblasts supplemented with the plasmalogen precursor, hexadecylglycerol. Plasmalogen-deficient cells consistently showed lower fluorescence anisotropies of membrane-bound DPH fluorophores corresponding to higher membrane lipid mobilities as compared to controls. However, very similar lipid mobilities were found for sonicated aqueous dispersions of phospholipids extracted either from CHRS or control cells. Therefore, the differences observed with living cells are not due to differences in the overall physical properties of the membrane lipid constituents. Other phenomena such as lipid asymmetry and/or plasmalogen-protein interactions may be responsible for the effects observed in the biomembranes.

Cell Membrane↗

Triggered release of hydrophilic agents from plasmalogen liposomes using visible light or acid.

Triggered release from liposomes composed of semi-synthetic 1-alk-1'-enyl-2-acyl-sn-glycero-3-phosphocholine (plasmalogen) lipids has been demonstrated using either aerobic visible illumination or low pH to induce leakage. The photodynamic release system consists of three functional components: (1) small (less than 1000 A) unilamellar plasmalogen vesicles (SUVs) containing encapsulated glucose, (2) oxygen and (3) zinc phthalocyanine (ZnPc) incorporated within the hydrophobic region of the SUV membrane. Irradiation (lambda greater than 640 nm) at 37 degrees C of air-saturated 1-alk-1'-enyl-2-palmitoyl-sn-glycero-3-phosphocholine (PlasPPC)/1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) (8:1, mol/mol) liposomes at physiologically relevant temperatures results in glucose release rates that are twice those of the corresponding dark control. Photolysis of argon-saturated PlasPPC/DPPC liposomes or of identical vesicles lacking either ZnPc or the plasmalogen vinyl ether bond exhibit glucose release curves which are indistinguishable from the dark control. Irradiation under identical conditions, but in the presence of 100 mM sodium azide, also results in no increased rate of glucose release above that of the dark control. TLC analysis indicates that oxidized lipid species are produced only in air-saturated, irradiated plasmalogen liposomes. The acid lability of the plasmalogen vinyl ether linkage has also been used to trigger release of entrapped calcein. At pH 4.2, the release rate at 37 degrees C is increased 4-fold over rates observed at pH 8. TLC analysis indicates formation of a lysoplasmalogen product. Taken together, these results indicate that both photodynamic and acid triggering can be used to increase plasmalogen liposome permeability and suggest that these liposomes are potentially useful for drug delivery applications.

1,2-Dipalmitoylphosphatidylcholine↗

The cerebro-hepato-renal (Zellweger) syndrome. Impaired de novo biosynthesis of plasmalogens in cultured skin fibroblasts.

In tissues of patients with the cerebro-hepato-renal (Zellweger) syndrome the plasmalogen content is very low. In order to study the biosynthesis of plasmalogens, skin fibroblasts of Zellweger patients, controls and heterozygotes, and amniotic fluid cells of controls were cultured in a medium supplemented with [1-14 C]hexadecanol or 1-O-[9,10-3H2]octadecylglycerol. The incorporation of 14C-label into the alkenyl moiety of plasmalogens was strongly reduced in Zellweger patients as compared to controls. The low concentration of 14C-labeled plasmalogens was not compensated for by an elevated levels of 14C-labeled alkyl phospholipids. Hexadecanol was partly oxidized to fatty acid in all cell lines and the incorporation of 14C-labeled fatty acid into phospholipids was comparable for patients and controls. [3H]Alkylglycerol was incorporated into plasmalogens with the same efficiency in Zellweger patients as in controls. These results indicate that only the reaction(s) involved in the introduction of the ether bond in the process of plasmalogen synthesis are deficient in Zellweger patients. The results also suggest that the hexadecanol incorporation patterns can be used for the (prenatal) diagnosis of the Zellweger syndrome.

Amniotic Fluid↗

Physical studies on the membranes and lipids of plasmalogen-deficient Megasphaera elsdenii.

Membrane fluidity and thermotropic phase behavior in the wild-type and plasmalogen-deficient strains of Megasphaera elsdenii have been studied by means of diphenylhexatiene steady state fluorescence anisotropy in isolated membranes, and by 31P-NMR and X-ray diffraction of the isolated phospholipids. Compared to the wild-type plasmalogen content of greater than 75%, plasmalogen-deficient strains had less than 5% plasmalogen, consisting largely of phosphatidylethanolamine and phosphatidylserine. Steady state fluorescence anisotropy measurements yielded an order parameter which was 6% lower in the plasmalogen-deficient membranes from 10 degrees to 40 degrees C, indicating higher membrane lipid mobilities. Both 31P-NMR and X-ray diffraction revealed the formation of a hexagonal phase in the lipids from the wild-type strain starting above 30 degrees C. In general the transition was not complete by 80 degrees C. In contrast, phospholipids from plasmalogen-deficient strains appeared to form a relatively stable lamellar phase.

Cell Membrane↗

Plasmalogen oxidation in human serum lipoproteins.

The content of plasmalogens in lipoproteins--very low density lipoprotein (VLDL), low density lipoprotein (LDL) and high density lipoprotein (HDL)--in human serum was determined and compared with that after oxidation of the lipoproteins. Similarly, the content of alpha-hydroxyaldehydes produced from plasmalogens via their epoxids during lipidperoxidation (LPO) was studied. Incubation with Fe+ +/ascorbate results in a dramatic decrease in plasmalogens that correlates with an appropriate increase in alpha-hydroxyaldehydes. VLDL and LDL plasmalogens were oxidized to a greater extend (99% decrease) compared to HDL plasmalogens (35%). This finding is discussed with respect to atherogenesis and the recently postulated protective qualities of plasmalogens.

Aldehydes↗

Is the high propensity of ethanolamine plasmalogens to form non-lamellar lipid structures manifested in the properties of biomembranes?

Plasmalogens are glycerophospholipids characterized by an alk-1'-enylether bond in position sn-1 and an acyl bond in position sn-2. These ubiquitous etherlipids exhibit a different molecular structure as compared to diacyl phospholipids. The most peculiar change is a perpendicular orientation of the sn-2 acyl chain at all segments to the membrane surface. This extended conformation results in an effectively longer aliphatic chain in plasmalogen than in the diacyl analog. Moreover, the lack of the carbonyl oxygen in position sn-1 affects the hydrophilicity of the headgroup and allows stronger intermolecular hydrogen-bonding between the headgroups of the lipid. These properties favour the formation of non-lamellar structures which are expressed in the high affinity of ethanolamine plasmalogen to adopt the inverse hexagonal phase. Such structures may be involved in membrane processes, either temporarily, like in membrane fusion or locally, e.g. to affect the activity of membrane-bound proteins. The predominant distribution of ethanolamine plasmalogens in some cellular membranes like nerve tissues or plasma membranes and their distinctly different properties in model membranes as compared to diacyl phospholipids impose the question, whether these differences are also manifested in the heterogeneous environment of biological membranes. The integration of biophysical studies and biochemical findings clearly indicated that the high propensity of ethanolamine plasmalogen to form non-lamellar structures is reflected in several physiological functions. So far it seems to be evident that ethanolamine plasmalogens play an important role in maintaining the balance between bilayer and non-lamellar phases which is crucial for proper cell function. Furthermore, they are the major phospholipid component of inverse hexagonal phase inclusions in native retina and are able to mediate membrane fusion as demonstrated between neurotransmitter vesicles and presynaptic membranes.

Cell Membrane↗

The ether lipid-deficient mouse: tracking down plasmalogen functions.

Chemical and physico-chemical properties as well as physiological functions of major mammalian ether-linked glycerolipids, including plasmalogens were reviewed. Their chemical structures were described and their effect on membrane fluidity and membrane fusion discussed. The recent generation of mouse models with ether lipid deficiency offered the possibility to study ether lipid and particularly plasmalogen functions in vivo. Ether lipid-deficient mice revealed severe phenotypic alterations, including arrest of spermatogenesis, development of cataract and defects in central nervous system myelination. In several cell culture systems lack of plasmalogens impaired intracellular cholesterol distribution affecting plasma membrane functions and structural changes of ER and Golgi cisternae. Based on these phenotypic anomalies that were accurately described conclusions were drawn on putative functions of plasmalogens. These functions were related to cell-cell or cell-extracellular matrix interactions, formation of lipid raft microdomains and intracellular cholesterol homeostasis. There are several human disorders, such as Zellweger syndrome, rhizomelic chondrodysplasia punctata, Alzheimer's disease, Down syndrome, and Niemann-Pick type C disease that are distinguished by altered tissue plasmalogen concentrations. The role plasmalogens might play in the pathology of these disorders is discussed.

Acyltransferases↗