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Plasmalogens in rat liver chromatin: new molecules involved in cell proliferation.

A minor component of chromatin, the phospholipid fraction, changes during cell cycle as result of the activation of intranuclear lipid metabolism enzymes including phosphatidylcholine-dependent phospholipase C activity. It is known that this enzyme may be activated by phosphatidylcholine plasmalogen (Plg). Until now, there has been little evidences for the presence of Plgs inside the nucleus. The aim of our study is to ascertain if they are present in the nucleus and are responsible of the activation of phosphatidylcholine-dependent phospholipase C during cell proliferation and apoptosis. Therefore, we have analysed the Plg composition of the whole homogenate, cytosol, nuclei and chromatin of hepatocytes. The phosphatidylcholine-dependent phospholipase C activity was assayed using both phosphatidylcholine and plasmalogenyl-phosphatidylcholine as substrates. Our results show, for the first time, that Plgs are present in chromatin and the plasmalogenyl-phosphatidylcholine stimulates the phosphatidylcholine-dependent phospholipase C activity more than phosphatidylcholine. Finally, in order to verify the possible role of these molecules during cell proliferation and apoptosis, we used liver of rats fed with ciprofibrate which stimulates hepatocytes proliferation during the treatment and, after withdrawal, apoptosis. After 3 days of ciprofibrate treatment, the chromatin plasmalogenyl-phosphatidylcholine increases as well as the phosphatidylcholine-dependent phospholipase C activity. After drug withdrawal, when the hepatocytes undergo to apoptosis, the plasmalogenyl-phosphatidylcholine content together with phosphatidylcholine-dependent phospholipase C activity decreases. Therefore, it can be concluded that plamalogens are present in the chromatin, and probably may have a function both in regulating phosphatidylcholine dependent phospholipase C and cell cycle.

Animals↗

Comparison of two molecular species of ethanolamine plasmalogen in multiple sclerosis and normal myelin.

A TLC procedure which resolves two molecular species of ethanolamine plasmalogen, Pl-PE-1 and Pl-PE-2, was used to compare the ratio of these was species in myelin isolated from normal appearing white matter from brains of 17 multiple sclerosis (MS) patients, 17 normal (N) individuals, 1 patient with subacute sclerosing panencephalitis (SSPE) and 1 patient with a non-demyelinating neurological disease (OND). One of these species (Pl-PE-2) has been reported to be unique to myelin and has primarily 18:1 in both the 1 and 2 positions of glycerol. The other species (Pl-PE-1) is also present in other membranes and has primarily a saturated chain in the 1 position and a polyunsaturated chain in the 2 position. The Pl-PE-1 to Pl-PE-2 ratio was quantitated by scanning the plates with a densitometer. The ratio was similar to normal in most of the MS samples, 0.88 +/- 0.09, but was much less th an normal in 4 of the MS samples and the SSPE sample. This is attributed to increased decomposition or hydrolysis of Pl-PE-1 relative to Pl-PE-2 at some stage, either during the disease process or due to post-mortem decomposition. Although the reason for the enhanced decomposition of Pl-PE-1 is not known it suggests that Pl-PE-2 is more stable chemically. This may be related to the unique occurrence of Pl-PE-2 in myelin.

Chromatography, Thin Layer↗

The precursors of fecapentaenes: purification and properties of a novel plasmalogen.

Fecapentaene-12 and fecapentaene-14 are genotoxic poly-unsaturated ether-lipids produced by the colonic microflora in humans and pigs. Although the fecapentaenes have been extensively characterized, little is known about the nature of the precursors from which they are produced. We purified one form of these precursors from feces of an individual who excreted high levels of fecapentaene-12 and its precursors. Purification was carried out by a series of extractions and precipitation in organic solvents followed by silica and amine high performance liquid chromatography. The purified precursor had identical UV spectral characteristics as the fecapentaenes indicating that it contained the same ether-linked pentaenyl functional group. However, it was not mutagenic. The precursor was amphiphilic in nature, behaving like a synthetic "model" ether-phospholipid on silica and C18 thin layer chromatography. When incorporated into phosphatidylcholine micelles it could be hydrolyzed in vitro by a combination of lipase and phospholipase C to fecapentaene-12. Our findings indicate that the general structure of this precursor is that of a phospholipid, specifically a plasmalogen--the exact structures of which remain to be determined.

Adult↗

Evidence that plasmalogen is protective against oxidative stress in the rat brain.

The antioxidant capabilities of phosphatidylethanolamine plasmalogen (PlsEtn), in vivo, against lipid peroxidation were investigated via acute phosphine (PH(3)) administration in rats. Oxidative stress was assessed from measures of malondialdehyde and various enzyme activities, while NMR analyses of lipid and aqueous tissue extracts provided metabolic information in cerebellum, brainstem, and cortex. Brainstem had the highest basal [PlsEtn], and showed only moderate PH(3)-induced oxidative damage with no loss of ATP. The lowest basal [PlsEtn] was observed in cortex, where PH(3) caused a 51% decrease in [ATP]. The largest oxidative effect occurred in cerebellum, but [ATP] was unaffected. Myo-inositol+ethanolamine pretreatment attenuated all PH(3) effects. Specifically, the pretreatment attenuated the ATP decrease in cortex, and elevated brain [PlsEtn] in the cerebellum, nearly abolishing the cerebellar oxidative effects. Our data suggest a high basal [PlsEtn], or the capacity to synthesize new ethanolamine lipids (particularly PlsEtn) may protect against PH(3) toxicity.

Aldehydes↗

Total cholesterol, fatty acids, and plasmalogens can be reliably quantitated by analysis on chromarods after the methylation step required for fatty acid analysis by gas-liquid chromatography.

A new method of simultaneous quantitation of total fatty acids, plasmalogens, and cholesterol using thin-layer chromatography with flame-ionization detection (TLC-FID) is presented. This method only requires methanolysis of the crude lipid extracts, an operation usually performed for fatty acid analysis by gas-liquid chromatography (GLC), and both analyses can thus be carried out in one step. Because of its resolution power and sensitivity, the TLC-FID technique can be used to analyze microsamples routinely assayed in capillary GLC (less than 15 micrograms of total fatty acids). The data obtained by capillary GLC and those provided by TLC-FID after careful individual calibration of the rods are almost identical. Reproducibility of the TLC-FID measurements is lower for fatty acid methyl esters and dimethylacetals, but equivalent for cholesterol quantitation, if the samples are analyzed twice on chromarods.

Cholesterol↗

Continuous spectrophotometric assay of phospholipase A2 activity hydrolyzing plasmalogens using coupling enzymes.

We developed a continuous spectrophotometric assay of the phospholipase A2 activity specific for choline plasmalogen using rat liver lysoplasmalogenase and horse liver alcohol dehydrogenase as coupling enzymes and Naja naja venom phospholipase A2 as a source of the phospholipase A2 activity. In these coupling reactions, choline lysoplasmalogen is hydrolyzed by lysoplasmalogenase to glycerophosphocholine and free aldehyde. The free aldehyde is quantitatively converted to alcohol by alcohol dehydrogenase with the oxidation of NADH. The disappearance of NADH is measured spectrophotometrically at 340 nm. The assay is sensitive to about 0.2 nmol aldehyde produced/ml/min and also is rapid, convenient, and continuous.

Animals↗

Accelerated maximal velocity of the red blood cell Na+/K+ pump in hyperlipidemia is related to increase in 1-palmitoyl,2-arachidonoyl-plasmalogen phosphatidylethanolamine.

Among several phospholipid classes and molecular species of phosphatidylcholine and phosphatidylethanolamine (PE) analyzed, only the percentage of the molecular species 1-palmitoyl,2-arachidonoyl (16: 0/20: 4)-plasmalogen-(alkenylacyl)-PE showed positive relations to the maximal activity and to the dissociation constant of the red blood cell Na+/K+ pump for Na+ in normo- and hyperlipidemic donors. A preferential interaction of this molecular species with the Na+/K+ pump is proposed.

Adult↗

Translocation of fluorescent ether phospholipid, but not its diacyl counterpart, after insertion in plasma membranes of control and plasmalogen-deficient fibroblasts.

Fluorescently labelled ether phospholipid (1-O-alkyl/alkenyl-2-acyl- glycerophosphocholine) readily internalizes at low temperatures (2 degrees C) after insertion into the plasma membrane of cultured fibroblasts. This fate differs markedly from that of its diacyl phospholipid analogue, which remains associated with the plasma membrane under similar conditions. Analysis by thin-layer chromatography reveals that the translocation involves transfer of the intact ether phosphatidylcholine molecules. Relative to control cells, a 2-fold increase of ether phosphatidylcholine uptake was noted when plasmalogen deficient fibroblasts were used. Back-exchange experiments demonstrate that more than 60% of the cell-associated ether lipid is translocated within the cells, irrespective of the cell strain that was used. The potential mechanism by which the translocation process is accomplished is discussed.

Cell Membrane↗

Substrate specificity in plasmalogen biosynthesis. Desaturation of 1-O-hexadecyloxyethyl-2-acylglycero-3-phosphoethanolamine in developing rat brain.

1-O-[1'-14C]Hexadecyloxyethyl rac-glycerol was administered to 18-day-old rats by intracerebral injection, and incorporation of radioactivity into the brain lipids was determined after 6, 24 and 48 h. Some of the substrate was catabolized by oxidative cleavage of either of the two ether bonds. Cleavage in the hexadecyloxyethyl moiety yielded labeled palmitic acid, whereas oxidative cleaveage of the glycol glycerol ether bond produced O-hexadecyl glycolic acid. The substrate was also incorporated as such into both ethanolamine and choline phospholipids. Evidence is presented for the desaturation by rat brain of 1-O-hexadecyloxyethyl-2-acyl-sn-glycero-3-phosphoethanolamine to the plasmalogen analogue, while the corresponding choline phospholipid was not desaturated.

Animals↗

Alk-1-enyl ether phospholipids (plasmalogens) and glycolipids of Treponema hyodysenteriae. Analysis of acyl and alk-1-enyl moieties.

The lipids of Treponema hyodysenteriae B78, the etiologic agent of swine dysentery, comprised 16.4% of the cell dry weight, and consisted of 37.4% glycolipids, 28.6% phospholipids, and 34.0% neutral lipids. Monogalactosyldiacylglycerol, a major lipid in all Treponema except Treponema pallidum, comprised 80% of the glycolipids. An unidentified galactolipid less polar than monogalactosyldiacylglycerol was also detected. Phosphatidylglycerol (19.5% of the total lipids) was the major phospholipid. Phosphatidylcholine, characteristically the major phospholipid of treponemes, comprised 6.1% of the total lipids. Cardiolipin and lysophosphatidylcholine were minor components. The alk-1-enyl ether forms of both the phospholipids (plasmalogens) and glycolipids predominated. The alk-1-enyl ether forms of monogalactosyldiacylglycerol, the unidentified galactolipid, phosphatidylglycerol, cardiolipin, and phosphatidylcholine were 88.3, 96.4, 74.8, 60.6, and 6.3%, respectively. The acyl and alk-1-enyl chains of the organism were qualitatively similar and differed dramatically from those of the medium indicating a capability for fatty acid synthesis that most Treponema do not possess. Saturated C14, C15, and C16 chains comprised more than 95% of the acyl and alk-1-enyl groups. About 25% of the chains were iso-15:0, anteiso-15:0, and other branched moieties.

Fatty Acids↗

Changes in the composition of two molecular species of ethanolamine plasmalogen in normal human myelin during development.

Changes in the ratio of two molecular species of ethanolamine plasmalogen, PI-LE-1 and PI-PE-2, of human central nervous system myelin during development were measured by a TLC procedure. The ratio was found to decrease sharply with age up to 6 months as a result of an increase in the amount of PI-PE-2, believed to be a unique myelin lipid with 18:1 chains in both positions of the glycerol. The ratio continued to decrease gradually with age and did not reach the adult level until an age of 17 years.

Adolescent↗

Disease and anatomic specificity of ethanolamine plasmalogen deficiency in Alzheimer's disease brain.

A significant and selective deficiency of ethanolamine plasmalogen (PPE) relative to phosphatidylethanolamine was identified in post mortem brain samples from patients with Alzheimer's disease (AD). This lipid defect showed anatomic specificity, being more marked at a site of neurodegeneration in AD brain than in a region relatively spared by the disease (mid-temporal cortex vs. cerebellum) and disease specificity for AD: it was not observed at the primary site of neurodegeneration in Huntington's disease (caudate nucleus) nor Parkinson's disease (substantia nigra). PPE deficiency parallels an inherent tendency towards membrane bilayer instability previously detected in AD brain which is necessarily due to a change in membrane lipid composition, and which may contribute to AD pathogenesis.

Aged↗

Biosynthetic preparation of radioactively labelled ethanolamine plasmalogen (1-O-[1'-14C]octadec-1'-enyl-2-acyl-sn-glycero-3-phosphoethanola mine) using a protozoan cell culture.

Ethanolamine plasmalogen radiolabelled mainly in the O-alkenyl moiety was prepared from cell suspension cultures of the flagellate Leishmania donovani previously incubated with [1-14C]octadecanol over one growth period. The optimal concentration of [1-14C]octadecanol for labelling was shown to be 1 microM, when 60% of total lipid radioactivity appeared in the 1,2-diradyl-sn-glycero-3-phosphoethanolamine fraction, with an overall yield of approx. 35%. Analysis of this fraction revealed that 93% of the label was present in O-octa-dec-1-enyl, 3% in O-alkyl and 4% in acyl moieties. A specific radioactivity of approx. 14 mCi/mmol was determined. Raising the culture medium concentration of [1-14C]octadecanol to 2 microM yielded a product with a specific radioactivity of 25 mCi/mmol.

Animals↗

Fluorescence lifetime distributions of parinaroyl phospholipids in choline plasmalogen and phosphatidylcholine bilayers containing different amounts of cholesterol.

The fluorescence decay of alkenylparinaroyl- and palmitoylparinaroyl glycerophosphocholines in vesicles of the unlabeled alkenyloleoyl and palmitoyloleoyl analogs was determined by multifrequency phase and modulation fluorometry. The measured phase angles and demodulations could be equally well fitted to a biexponential decay, as well as unimodal or bimodal continuous lifetime distributions. The latter model was applied to study the influence of cholesterol on parinaroyl phospholipid fluorescence in vesicles. The long-living component of a bimodal lifetime distribution was sensitive toward the presence of the sterol. Upon increasing cholesterol concentrations, its lifetime center increased and its distribution widths decreased. Lifetime distribution widths in vesicles of alkenyloleoyl- or palmitoyloleoyl-glycerophosphocholine (choline plasmalogen and phosphatidylcholine, respectively) were reduced by the sterol to the same extent. We interprete the sterol-induced lifetime distribution narrowing as an effect due to an increase of membrane homogeneity in cholesterol-phospholipid membranes.

Cholesterol↗

Plasmalogens in the gill lipids of aquatic animals.

Lipids constituted 0.6-2.2% wet wt of the gills of 11 species of aquatic animals (4 bivalves, a crustacean and 6 fishes). Phospholipids, largely phosphatidylcholine (PC) and phosphatidylethanolamine (PE), are major components of all species. The plasmalogen contents of these lipids were 47-291 mumol/g, with the highest values found for bivalve gill total lipids and the catfish phospholipid fraction.

Animals↗

Inhibitory effect of ethanolamine plasmalogen on iron- and copper-dependent lipid peroxidation.

The effect of ethanolamine plasmalogen (EtnPm) on lipid peroxidation was investigated in liposomal suspension of egg yolk phosphatidylcholine. EtnPm inhibited iron- and copper-dependent peroxidation in the presence of preformed hydroperoxides, although it was not effective for radical initiator mediated lipid peroxidation. EtnPm resulted in complete binding of iron to liposomal lipids, suggesting that EtnPm exerts its inhibitory effect on lipid peroxidation through inhibiting preformed peroxide decomposition by trapping transition metal ions.

Antioxidants↗

Plasmalogens protect unsaturated lipids against UV-induced oxidation in monolayer.

Oxidative stress results from the attack by free radicals of several cellular targets (proteins, DNA and lipids). The cell equilibrium is a direct consequence of the pro-/antioxidant balance. In order to understand the physiological processes involved in oxidative stress, we followed oxidation of unsaturated lipids using a biomimetic system: Langmuir monolayers. The oxidation mode chosen was UV-irradiation and the lipid model was a polyunsaturated phospholipid: 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DLPC). The monomolecular film technique was used to measure membrane rheology before and after UV-irradiation. We showed that the UV-irradiation of a DLPC monomolecular film led to a molecular area and surface elasticity modulus decrease that attests to the apparition of new molecular species at the air-water interface. The antioxidant effect of a synthetic plasmalogen (1-O-(1'-(Z)-hexadecenyl)-2-O-oleoyl-sn-glycero-3-phosphocholine or P(PLM)OPE) was tested on the oxidation of DLPC. Indeed, for about 25% mol P(PLM)OPE in mixed DLPC/P(PLM)OPE monolayers, a complete inhibition of the molecular area and the surface elasticity modulus decreases was observed in our experimental conditions. Lower P(PLM)OPE quantities delayed but did not prevent the DLPC oxidation in mixed monolayers.

Antioxidants↗