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Lipid composition of the isolated rat intestinal microvillus membrane.

1. Rat intestinal microvillus plasma membranes were prepared from previously isolated brush borders and the lipid composition was analysed. 2. The molar ratio of cholesterol to phospholipid was greatest in the membranes and closely resembled that reported for myelin. 3. Unesterified cholesterol was the major neutral lipid. However, 30% of the neutral lipid fraction was accounted for by glycerides and fatty acid. 4. Five phospholipid components were identified and measured, including phosphatidylethanolamine, phosphatidylcholine, phosphatidylserine, sphingomyelin and lysophosphatidylcholine. Though phosphatidylethanolamine was the chief phospholipid, no plasmalogen was detected. 5. In contrast with other plasma membranes in the rat, the polar lipids of the microvillus membrane were rich in glycolipid. The cholesterol:polar lipid (phospholipid+glycolipid) ratio was about 1:3 for the microvillus membrane. Published data suggest that this ratio resembles that of the liver plasma membrane more closely than myelin or the erythrocyte membrane. 6. The fatty acid composition of membrane lipids was altered markedly by a single feeding of safflower oil. Membrane polar lipids did not contain significantly more saturated fatty acids than cellular polar lipids. Differences in the proportion of some fatty acids in membrane and cellular glycerides were noted. These differences may reflect the presence of specific membrane glycerides.

Animals↗

Effect of adrenaline on 32 P incorporation into rat fat-cell phospholipids.

1. The phospholipid composition of fat-cells prepared from rat epididymal fat-pad was determined. 2. The incorporation of [(32)P]P(i) into the phospholipids of fat-cells incubated in glucose-free medium and the effect of adrenaline and of alpha- and beta-adrenergic blocking agents, were studied. 3. Incorporation of [(32)P]P(i) into fat-cell phospholipid increased with time; incubation with adrenaline resulted in increased incorporation that was related to the concentration of adrenaline. 4. The pattern of incorporation of [(32)P]P(i) into the individual phospholipids of fat-cells after incubation for 1h was determined; adrenaline (5.4mum) resulted in increased incorporation into phosphatidylcholine. 5. Incubation of fat-cells with propranolol (34mum) and adrenaline (5.4mum) resulted in abolition of adrenaline-stimulated lipolysis; there was a decrease in the specific radioactivity of phosphatidylcholine and an increase in the specific radioactivity of phosphatidylethanolamine, phosphatidic acid, phosphatidylinositol and cardiolipin compared with cells incubated with adrenaline alone. 6. Incubation of fat-cells with phenoxybenzamine (0.1mm) and adrenaline (5.4mum) resulted in stimulation of lipolysis, and in diminished specific radioactivities of phosphatidylcholine, phosphatidic acid, phosphatidylinositol, phosphatidylglycerol and choline plasmalogen compared with cells stimulated with adrenaline alone.

Adipose Tissue↗

Arachidonic acid release from diacyl phosphatidylethanolamine by human platelet membranes.

At pH9.5 in the presence of 10 mM-Ca2+, human platelet membranes released 22% (167 of 785 nmol) of arachidonic acid that was esterified to phospholipids. With the use of synthetic choline (dinonadecanoyl) and ethanolamine (diheptadecanoyl) phosphoglycerides as internal reference compounds, 115 nmol of the released arachidonic acid was shown to be derived from endogenous breakdown of the phosphatidylethanolamine fraction. Further, the lysophosphatidylethanolamine that was released along with the arachidonic acid was shown virtually to lack fatty aldehydes and to contain a preponderance of fatty acids that have a preference for esterification at the 1-position of naturally occurring phosphatidylethanolamine of human platelets. These findings ruled out plasmalogen phosphatidylethanolamine as the source of the released arachidonic acid. We conclude that diacyl phosphatidylethanolamine was the principal source of arachidonic acid released by human platelet membranes under the conditions described.

Aldehydes↗

Complex lipids of a lipolytic and general-fatty-acid-requiring Butyrivibrio sp. isolated from the ovine rumen.

The complex lipids of the naturally-occurring general-fatty-acid-auxotroph Butyrivibrio S2 [Hazlewood & Dawson (1979) J. Gen. Microbiol. 112, 15-27] grown with palmitic acid as sole fatty-acid supplement have been investigated and some have been isolated in a state of purity and analysed. The majority are phospholipids (84%) and many contain galactose. They typically possess few esterified long-chain fatty-acid residues (C16:0), but are rich in esterified butyric acid and C16-alkenyl groups. Most of the phosphorus-containing lipids, including the two major lipids of the organism, contain esterified diabolic acid, a long-chain vicinal dimethyl-substituted dicarboxylic acid [Klein, Hazlewood, Kemp & Dawson (1979) Biochem. J. 183, 691-700] in definite stoichiometric relationship to phosphorus. No phosphatidylglycerol was present, but its monobutyroyl ester was detected as a minor component. Galactofuranosyldiacylglycerol (plasmalogen) and its monobutyroyl ester, cetyl alcohol and diacylglycerol were also identified.

Chemical Phenomena↗

Acylation of 1-alkenyl-glycerophosphocholine and 1-acyl-glycerophosphocholine in guinea pig heart.

The deacylation-reacylation process has been shown to be an important pathway for phospholipids to attain the desired acyl groups at the C-2 position. The acylation of 1-acyl-glycerophosphocholine (-GPC) in mammalian hearts has been well documented, but the acylation of 1-alkenyl-GPC has not been described. In this paper, we demonstrate the presence of acyl-CoA: 1-alkenyl-GPC acyltransferase for the acylation of 1-alkenyl-GPC in mammalian hearts; the highest activity is found in guinea pig heart. The guinea pig heart 1-alkenyl-GPC acyltransferase has only 10-40% of the 1-acyl-GPC acyltransferase activity, and both activities are located in the microsomal fraction. However, these two enzymes respond differently to cations, detergents and heat treatment, and the two enzymes also display different acyl specificity. Kinetic studies indicate that both reactions could not be accommodated by the same catalytic site. The results provide strong evidence that the two activities are from separate and distinct proteins. The specificity of 1-alkenyl-GPC acyltransferase for unsaturated species of acyl-CoA may play an important role in the maintenance of the high degree of unsaturated acyl groups found in guinea pig heart plasmalogens.

1-Acylglycerophosphocholine O-Acyltransferase↗

Effects of glycosaminoglycans and glycosphingolipids on cytosolic phospholipases A2 from bovine brain.

Two forms of Ca(2+)-independent cytosolic phospholipase A2 activity (110 kDa and 39 kDa) were found in bovine brain. They were separated by Sephadex G-75 column chromatography. The 110 kDa phospholipase A2 was much more active with phosphatidylethanolamine and was not affected by glycosaminoglycans, whereas the 39 kDa phospholipase A2 was much more active with ethanolamine plasmalogen and was markedly inhibited by glycosaminoglycans. Heparan sulphate was the most potent inhibitor, followed by chondroitin sulphate, hyaluronic acid and heparin. Gangliosides, especially the GM3 ganglioside, but not other glycosphingolipids, inhibited the activity of the 39 kDa phospholipase A2 in a dose-dependent manner. The heat-inactivation profiles of the 110 kDa and 39 kDa phospholipases A2 provide further evidence for the differences between these cytosolic enzymes. Interactions between glycosaminoglycans, gangliosides and phospholipases A2 may be involved in the maintenance of membrane function.

Animals↗

A novel class of microbial phosphocholine-specific phospholipases C.

In this report we describe the 1,500-fold purification and characterization of the haemolytic phospholipase C (PLC) of Pseudomonas aeruginosa, the paradigm member of a novel PLC/phosphatase superfamily. Members include proteins from Mycobacterium tuberculosis, Bordetella spp., Francisella tularensis and Burkholderia pseudomallei. Purification involved overexpression of the plcHR1,2 operon, ion exchange chromatography and native preparative polyacrylamide gel electrophoresis. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry confirmed the presence of two proteins in the purified sample with sizes of 17,117.2 Da (PlcR2) and 78,417 Da (PlcH). Additionally, liquid chromatography electrospray mass spectrometry (LCMS) revealed that PlcH and PlcR2 are at a stoichiometry of 1 : 1. Western blot analysis demonstrated that the enzyme purifies as a heterodimeric complex, PlcHR2. PlcHR2 is only active on choline-containing phospholipids. It is equally active on phosphatidylcholine (PC) and sphingomyelin (SM) and is able to hydrolyse plasmenylcholine phospholipids (plasmalogens). Neither PlcHR2 nor the M. tuberculosis homologues are inhibited by D609 a widely used, competitive inhibitor of the Bacillus cereus PLC. PlcH, PlcR2, and the PlcHR2 complex bind calcium. While calcium has no detectable effect on enzymatic activity, it inhibits the haemolytic activity of PlcHR2. In addition to being required for the secretion of PlcH, the chaperone PlcR2 affects both the enzymatic and haemolytic properties of PlcH. Inclusive in these data is the conclusion that the members of this PC-PLC and phosphatase family possess a novel mechanism for the recognition and hydrolysis of their respective substrates.

Amino Acid Sequence↗

Ether lipids in the cell membrane of Mycoplasma fermentans.

Two new ether lipids, 1-O-alkyl/alkenyl-2-O-acyl-glycero-3-phosphocholine and its lyso form, 1-O-alkyl/alkenyl-glycero-3-phosphocholine, were identified in the cell membrane of Mycoplasma fermentans using chemical analyses, GLC-MS, MALDI-TOF MS, and 1D and 2D NMR spectroscopy. The lipids are heterogeneous with respect to both acyl and alkyl/alkenyl residues. The acyl residues at position 2 of glycerol are hexadecanoyl and octadecanoyl in a molar ratio of 3.6 : 1 with a trace amount of octadecenoyl. The alkyl/alkenyl residues at position 1 of glycerol are hexadecyl (78%), octadecyl (7%), octadecenyl (14%), and hexadecenyl (traces). In the octadecenyl residue, the double bond has a cis configuration and is located at either position 1' (plasmalogen-type lipid) or 9' in a ratio approximately 1 : 1. This is the first report of the presence of alkyl and vinyl (alk-1'-enyl) ether lipids in the cell membrane of aerobically grown mycoplasmas. Lipids of this type have been found in some Gram-positive bacteria, thus supporting the hypothesized close taxonomical relationship of these bacteria to mycoplasmas. The ether lipids of M. fermentans are structurally similar to platelet activating factor; it was demonstrated that the 2-O-acetylated lyso form lipid can mimic platelet-activating factor activity in isolated perfused and ventilated rat lungs.

Animals↗

Lipid composition in scrapie-infected mouse brain: prion infection increases the levels of dolichyl phosphate and ubiquinone.

The neutral and phospholipid composition of mouse brain infected with scrapie prions was investigated. During the later stages of this disease, the level of dolichol decreased by 30% whereas the level of dolichyl phosphate increased by 30%. In terminally ill mice, there was also a 2.5-fold increase in both total ubiquinone and its reduced form. Furthermore, alpha-tocopherol was elevated at this stage by 50%. In contrast, no changes were observed in phospholipid amount, in phospholipid composition, and in phosphatidylethanolamine plasmalogen content during the entire disease process. The fatty acid and aldehyde composition of individual phospholipids remained unaltered as well. No modifications could be detected in cholesterol content. Thus, the majority of membrane lipids in scrapie-infected mouse brain are modified in neither quantity nor structure, but specific changes occur to a few polyisoprenoid lipids. This specificity indicates that, although prions accumulate in lysosomes, the infection process is not associated with a general membrane destruction caused by lysosomal enzyme leakage.

Animals↗

Substantial sulfatide deficiency and ceramide elevation in very early Alzheimer's disease: potential role in disease pathogenesis.

In addition to pathology in the gray matter, there are also abnormalities in the white matter in Alzheimer's disease (AD). Sulfatide species are a class of myelin-specific sphingolipids and are involved in certain diseases of the central nervous system. To assess whether sulfatide content in gray and white matter in human subjects is associated with both the presence of Alzheimer's disease (AD) pathology as well as the stage of dementia, we analyzed the sulfatide content of brain tissue lipid extracts by electrospray ionization mass spectrometry from 22 subjects whose cognitive status at time of death varied from no dementia to very severe dementia. All subjects with dementia had AD pathology. The results demonstrate that: (i) sulfatides were depleted up to 93% in gray matter and up to 58% in white matter from all examined brain regions from AD subjects with very mild dementia, whereas all other major classes of lipid (except plasmalogen) in these subjects were not altered in comparison to those from age-matched subjects with no dementia; (ii) there was no apparent deficiency in the biosynthesis of sulfatides in very mild AD subjects as characterized by the examination of galactocerebroside sulfotransferase activities in post-mortem brain tissues; (iii) the content of ceramides (a class of potential degradation products of sulfatides) was elevated more than three-fold in white matter and peaked at the stage of very mild dementia. The findings demonstrate that a marked decrease in sulfatides is associated with AD pathology even in subjects with very mild dementia and that these changes may be linked with early events in the pathological process of AD.

Aged↗

Pro- and antioxidant activities of docosahexaenoic acid on human blood platelets.

n - 3 polyunsaturated fatty acids may protect against vascular diseases, however, their high accumulation in membranes may increase lipid peroxidation and subsequently induce deleterious effects in patients suffering from oxidative stress. This led us to investigate in vitro the dose-dependent effect of docosahexaenoic acid (DHA) on the redox status of human platelets. We have compared the effect of different DHA concentrations (0.5, 5 and 50 micro mol L(-1)) corresponding to DHA/albumin ratios of 0.01, 0.1 and 1. At the highest concentration, DHA elicited a marked oxidative stress, as evidenced by high malondialdehyde and low vitamin E levels whereas the lowest DHA concentration significantly decreased the malondialdehyde formation, with no change in vitamin E. The proportion of DHA was only increased in plasmalogen phosphatidylethanolamine at low concentration to rise in all phosphatidyl-choline and -ethanolamine subclasses at high concentration. Thus, the results show a biphasic effect of DHA with antioxidant and prooxidant effects at low and high concentrations, respectively, with a possible relationship with the phospholipid subclass in which it accumulates.

Blood Platelets↗

Aldehydes from n-6 fatty acid peroxidation. Effects on aminophospholipids.

4-Hydroxy-nonenal (4-HNE) is a major by-product of n-6 fatty acid peroxidation. It has been described to covalently bind biomolecules expressing primary amine, especially the Lys residues in proteins. Low-density lipoproteins (LDL) are well-described macromolecules to be modified by 4-HNE, making them available to scavenger receptors on macrophages. Those macrophages then become foam cells and play an active role in atherogenesis. This paper reports on the covalent binding of 4-HNE to phosphatidylethanolamine (PE), a major aminophospholipid in biological membranes. In contrast, phosphatidylserine (PS) is virtually not modified by 4-HNE. One stable adduct, the Michael adduct PE/4-HNE is a poor substrate of secreted phospholipase A(2) and is not cleaved by phospholipase D. Plasmalogen PE, an important subclass of PE, is covalently modified by 4-HNE as well, but appears to be further degraded on its sn-1 position, the alkenyl chain, which might alter the antioxidant potential of the molecule. An aldehyde homologous to 4-HNE has been characterized as a breakdown product of 12-hydroperoxyeicosatetraenoic acid (12-HpETE) and named 4-hydroxy-2E,6Z-dodecadienal (4-HDDE). This compound as well as 4-HNE was detected in human plasma. Finally, 4-HDDE appears almost 3-fold more active than 4-HNE to make covalent adducts with PE. We conclude that 4-HNE and 4-HDDE are two biologically relevant markers of n-6 fatty acid peroxidation that may alter the phospholipid-dependent cell signaling.

Aldehydes↗

Protein- and lipid modification of natural bovine surfactant. Effects in experimental lung failure with special consideration of the response in neonates.

UNLABELLED: Surfactant therapy does not lead to a uniform, optimal and sustained effect on gas exchange in neonatal respiratory distress syndrome (RDS) and acute respiratory distress syndrome (ARDS). The aim of the present study therefore was to compare the effects of a lipid-enriched and protein-modified natural surfactant preparations with a licensed, clinically used bovine surfactant preparation - SF-Ril (Alveofact). METHODS: SF-Ril was enriched with phosphatidylglycerol, sphingomyeline, phosphatidylethanolamine plasmalogen, phosphatidylethanolamine. Furthermore, SF-Ril was modified with increased surfactant protein B (SP-B)/surfactant protein C (SP-C) content and finally a mercaptoethanol (ME) treated preparation for breaking the sulfhydril bondage of SP-B/SP-C by chemical reduction in methylene chloride using ME was developed. Finally ME was removed by vacuum extraction. These modified surfactants were tested at a dosage of 100 mg/ kg each in a model of respiratory failure induced by lung lavage in male adult rats and compared with SF-Ril at an identical dosage. Mechanical ventilation was standardised with fraction of inspiratory oxygen (FiO2) 1.0 and time-cycled pressure limited ventilation 16/0.8 cmH2O before and 26/6 cmH2O (peak inspiratory pressure/positive endexpiratory pressure) after lung lavage (target arterial oxygen pressure [pa02] < 100 mmHg), respiratory rate 36/min, inspiration/expiration time ratio 1:2. RESULTS: During the observation period of 120 min, the sphingomyeline substituted and protein-modified (ME reduced) surfactant preparations exerted improved and sustained oxygenation compared with SF-Ril. Similar effects were observed for tidal volumes. All other preparations were equal or inferior to SF-Ril in our model. CONCLUSION: For the development of surfactant preparations less prone for inactivation the above mentioned data may provide useful information, provided they can be confirmed in further investigations employing other alternative models.

Animals↗

NMR spectroscopy study of heart phospholipids. An exercise and anabolic steroids effect.

Because 31P NMR spectral analysis of phospholipid (PL) is an accurate and rapid technique for resolving the quantity of PL resonances and involving minimum chemical manipulations that may affect the integrity of the tissue (24-26), we studied the effect of anabolic steroid injection, exercise training, or a combination of both treatments on whole heart phospholipids using 31P NMR spectral analysis. Male Sprague-Dawley rats were randomly assigned to 4 groups of 11 each: sedentary control (C), steroid-treated (ST), exercise-trained (E), and exercise plus steroid-treated (ES). The ST and ES rats were administered nandrolone decanoate by i.m. injection every 7-9 d during the 10 wk study, while the C and E rats were injected with glycerol. The exercise rats ran on a treadmill, wearing a collar weight for 50 min/day, 5 days/wk. There was a significant difference in body wt among the four groups at the conclusion of the study; however, no significant differences in heart wt or in the ratio of heart wt:body wt were observed among the four groups. Myocardial phospholipid profiles of the exercise-trained rats were significantly (p less than 0.05) different from those of the untrained rats. The changes were enhanced somewhat by the steroid treatment. The profiles differed in the relative amounts of four of the nine myocardial phospholipids detected: phosphatidylcholine, phosphatidylethanolamine (PE), PE plasmalogen, and phosphatidylserine. We conclude that the observed changes in whole heart phospholipid compositions are due to experimental treatment specifically from exhaustive exercise and not from anabolic steroids or cardiac hypertrophy.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Some thoughts on the neurobiology of the leukodystrophies.

The known leukodystrophies are genetic diseases involving defects in oligodendroglial function and myelinogenesis. The various steps in the process of myelination and myelin maintenance are outlined beginning with gliogenesis and ending with myelin catabolism. A gene defect affecting any one of these steps has the potential to lead either to a leukodystrophy or to a more systemic disease. The shiverer mouse mutant involves deletion of the gene for basic protein, and the quaking mutant may involve defective myelin assembly. Zellweger's syndrome, a systemic human disease, has a severe deficiency of plasmalogens, which are major myelin lipids. This deficiency is presumably a consequence of absent peroxisomes, organelles that contain the essential synthetic enzymes for these lipids. The three human leukodystrophies for which metabolic lesions are known (metachromatic leukodystrophy, globoid cell leukodystrophy and adrenoleukodystrophy), however, all have deficits in the very end stage of myelinogenesis, that of catabolism of myelin lipids. Is this coincidence? Perhaps some of the undiagnosed neurological diseases of children, as well as known diseases with unknown genetic defects, involve deletions or mutations in genes controlling earlier stages of myelinogenesis.

Adrenoleukodystrophy↗

Central nervous system malformations and white matter changes in pseudo-neonatal adrenoleukodystrophy.

Clinical, biochemical and morphological findings in a 16-month-old infant girl with pseudo-neonatal adrenoleukodystrophy are reported. The parents were first cousins and the baby was born at term, small for gestational age. The neonatal period was characterized by convulsions resistant to treatment, generalized, severe muscle hypotonus, feeding difficulties and poor weight gain. Developmentally she remained at a neonatal level. A CT-scan showed low density of cerebral white matter and MR examination white matter changes, a thin corpus callosum, cerebellar malformation and dorsal displacement of the brainstem. There was an accumulation of very long chain fatty acids (VLCFA) in serum lipids and cultured skin fibroblasts but plasmalogen and phytanic acid levels were normal. A liver biopsy revealed enlarged peroxisomes staining for catalase. Three similar cases have been reported previously; in two of these there was a deficiency of acyl-CoA oxidase. MR evidence of leukodystrophy combined with gross cerebral and cerebellar morphologic changes have not been reported earlier.

Acyl-CoA Oxidase↗

Specific labeling of mouse brain membrane phospholipids with [20-3H]phorbol 12-p-azidobenzoate 13-benzoate, a photolabile phorbol ester.

As part of our effort to characterize receptors for the phorbol ester tumor promoters, a phorbol ester photoaffinity probe, [20-3H]phorbol 12-p-azidobenzoate 13-benzoate (PaBzBz), was synthesized. In the dark, PaBzBz bound reversibly to brain particulate fractions with a dissociation constant (Kd) of 0.81 +/- 0.09 x 10(-9) M. Specific binding of PaBzBz, at a concentration equal to its Kd, represented 85% of the total bound. At saturation, 24 +/- 5 pmol of PaBzBz were bound per mg of brain protein, a level similar to that observed with [20-3H]phorbol 12,13-dibutyrate. Under the conditions used (concentrations greater than the Kd for PaBzBz), irradiation caused 45% of the PaBzBz binding to become irreversible. Most of the binding (approximately equal to 60%), including most of the specific irreversible binding, was to phospholipid rather than to protein. Based on susceptibility to enzymatic digestion and on chromatographic mobility, the specifically labeled phospholipids were identified as phosphatidylserine, phosphatidylethanolamine, and phosphatidylethanolamine plasmalogen. Although the PaBzBz specifically labeled lipid, labeling was blocked by pretreatment of membranes at 100 degrees C for 5 min or by papain digestion. Therefore, it seems likely that the identified lipids are specifically associated with a protein receptor and are preferentially labeled either because of the location or reactivity of the nitrene generated on the photoaffinity probe.

Affinity Labels↗

Membrane lipid changes in laminectomized and traumatized cat spinal cord.

Free fatty acid (FFA), diacylglycerol (acyl2Gro), icosanoid, phospholipid, and cholesterol levels were measured in samples of cat spinal cord (L2) that were frozen in situ with vertebrae intact, at various times after laminectomy, and at various times after laminectomy with compression trauma to the spinal cord. Tissue samples either were grossly dissected into gray and white portions prior to FFA and acyl2Gro analysis or were used whole for the other lipid types. Gray matter total FFA and acyl2Gro values were abnormally high in samples frozen with vertebrae intact and in those frozen 10 min after laminectomy. This indicates that the surgical procedures resulted in some perturbation of spinal cord lipid metabolism. If the experimental animals were allowed to recover for 90 min after laminectomy, the gray matter FFA and acyl2Gro levels were greatly reduced. Compression of the spinal cord with a 170-g weight for 1, 3, or 5 min (following 90 min of recovery after laminectomy) caused significant elevations of total FFA, acyl2Gro, icosanoids, and phosphatidic acid and significant decreases in ethanolamine plasmalogens and cholesterol. Among the total FFA, arachidonic acid was found to have the largest relative increase. Comparisons of gray and white matter demonstrate that, in general, changes in white matter FFA and acyl2Gro were similar to those seen in gray matter. However, the increases in white matter levels of FFA and acyl2Gro were delayed, occurring after the elevations in gray matter. For some FFA (e.g., arachidonate), the rise in white matter occurred as gray matter levels were decreasing. This suggests that the initial alteration in spinal cord lipid metabolism after trauma was in gray matter but, with time, spread radially into white matter.

Animals↗