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PubMed1991

Thermotropic properties of phospholipid analogues.

To understand the structural bases for the polymorphism of phospholipids, it is often essential to study the properties of "unnatural" phospholipid analogues with modified polar headgroups and or backbone structures. While the thermodynamic characteristics of the "classical" hydrated-gel-to-liquid-crystalline phase transition often appear surprisingly insensitive to these aspects of phospholipid structure, the rich and diverse solid-phase polymorphism of phospholipids is in fact exquisitely sensitive to the nature of both the polar headgroup and the backbone moieties. The tendencies of different phospholipids to form nonlamellar phases at higher temperatures also depend strongly (and in a sometimes surprising manner) on fine details of the headgroup and backbone structures. These points are illustrated by discussions of how the structures of headgroup- and backbone-modified phospholipid analogues influence their proclivities to form distinct types of hydrated solid phases, dehydrated "crystralline" phases and nonlamellar phases.

Molecular Conformation↗
PubMed1995

Monolayer study of mixtures of diacetylenic phosphatidylcholine and phospholipids containing metal-chelating iminodiacetic acid headgroup.

The mixing behavior of polymerizable diacetylenic phosphatidylcholine (1) with two diacetylenic phospholipids containing the iminodiacetic acid (IDA) functionality in the headgroup region was studied at the air-water interface. All three phospholipids contained tricosa-10,12-diynoyl acyl chains. In phospholipid 2, the choline group (-CH2-CH2-NMe3) was replaced by an -CH2-CH2-N-(CH2-COOH)2 functionality. In phospholipid 3, the IDA unit was linked to the phosphate headgroup via a sulfonate linker, -CH2-CH2-OS(O2)-O-CH2-CH2-. Monolayers were prepared by mixing polymerizable 1,2 bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine (1) with metal-chelating IDA phospholipids (2, 3) on a 10 mM CuCl2 subphase. Studies of monolayer properties of mixtures of 2 and 3 with 1 demonstrated that mixtures of 2 with 1 had better mixing behavior than mixtures of phospholipids 1 and 3.

Chelating Agents↗
PubMed1980

A rapid and sensitive fluorometric assay of serum phospholipid.

A fluorometric assay of phospholipid in serum is presented. The reaction is based upon the binding of phospholipids with a fluorescent probe: 1-6-Diphenyl-1-3-5 hexatriene (DPH). The method is in very good agreement with other techniques for phospholipid estimation: phosphorus assay phospholipid extraction (Fiske and Subarrow), and enzymatic assay of phospholipid containing choline (Takayama). The correlation coefficient obtained was 0.81, when the proposed method was compared with the two other ones. Parameters influencing the reaction: DPH concentration, time and temperature of incubation are described. The normal range for human serum lies between 2.1 and 3.4 mmol/l. The sensitivity of the fluorometric assay is also sufficient for the determination of phospholipid in amniotic fluid and broncho-alveolar washings.

Amniotic Fluid↗
PubMed1987

Prevention by amiodarone of phospholipid depletion in isoproterenol-induced ischemia in rats.

This work was performed to study phospholipid metabolism in isoproterenol-induced ischemic heart and the possible protective effect of amiodarone (Am) and chlorpromazine (CPZ). Heart weight increased 24 h after subcutaneous injection of isoproterenol (40 mg/kg) whereas myocardial phospholipid content and creatine kinase activity decreased without modification of the cholesterol content. The phospholipid content was significantly correlated with creatine kinase activity (P less than 0.001). Phosphatidylcholine, phosphatidylethanolamine and cardiolipin decreased significantly (P less than 0.001) in the isoproterenol group whereas the lysophosphatidylcholine and lysophosphatidylethanolamine content increased. The lysophosphatidylcholine/phosphatidylcholine and lysophosphatidylethanolamine/phosphatidylethanolamine ratios consequently increased to a significant degree (P less than 0.01) suggesting indirectly the activation of phospholipases A in the ischemic myocardium. Free fatty acid content increased, indicating hydrolysis of phosphatidylcholine, phosphatidylethanolamine, lysophosphatidylcholine and lysophosphatidylethanolamine. Intravenous injection of Am (20 mg/kg) or intraperitoneal injection of CPZ (30 mg/kg) prior to isoproterenol injection provided complete protection against phospholipid depletion and against increase of the lysophosphatidylcholine/phosphatidylcholine and lysophosphatidylethanolamine/phosphatidylethanolamine ratios which returned to control values. Neither substance had any effect on the heart weight increase due to an edematous and inflammatory process. The total protection by both substances against phospholipid depletion was not sufficient to prevent the creatine kinase activity decrease. The improved phospholipid degradation in the ischemic myocardium is discussed in relation to the in vitro inhibitory effect of Am or CPZ on phospholipases A activity.

Amiodarone↗
PubMed1990

Comparison of membrane phospholipids of the rabbit and pig crystalline lens.

Crystalline lenses excised from 5-7-month-old rabbits and pigs were extracted for lipids with chloroform/methanol, 2/1 using the Folch method. The extracted crude lipids were analyzed at 202 MHz by 31P-NMR spectroscopy. Twelve membrane phospholipids were detected. Both rabbit and pig phospholipid profiles contained phosphatidylcholine (PC), lysophosphatidylcholine, phosphatidylcholine plasmalogen, phosphatidylethanolamine (PE), phosphatidylethanolamine plasmalogen (PE plas), phosphatidylserine, sphingomyelin (SPH), and an uncharacterized phospholipid. In addition, pig lens profiles contained lysophosphatidylethanolamine, phosphatidylinositol, cardiolipin and phosphatidylglycerol. The data indicate that these two animal models have significant differences in membrane phospholipid profiles. In each species, however, the bulk phospholipid component resides in the neutral phospholipids PC, PE, PE plas, and SPH.

Animals↗
PubMed1989

Schistosoma mansoni: synthesis and release of phospholipids, lysophospholipids, and neutral lipids by schistosomula.

Lipids in the two surface membranes of Schistosoma mansoni may play an important role in the parasite's defense against host immunity. In particular, lysophosphatidylcholine lyses erythrocytes attached to the parasite and alters the lateral mobilities of their membrane proteins and lipids (Golan et al. 1986). Here, we have studied the incorporation of radiolabeled precursors into the major lipid classes of schistosomula as well as into lipids released by schistosomula into the medium. Radiolabeled polar head groups (choline and ethanolamine) and fatty acid precursors (palmitate and oleate) were linearly incorporated into parasite phospholipids. Fatty acids were differentially incorporated into the various phospholipid classes, principally into phosphatidylcholine and, to a lesser extent, into phosphatidylethanolamine, lysophosphatidylcholine, and phosphatidylserine. The major neutral lipid class labeled, triglycerides, had a decrease in specific activity with time after pulse labeling and the specific activity of the phospholipids increased with time. Thus, triglycerides may provide acyl chains for phospholipid synthesis. Choline was incorporated into phosphatidylcholine and lysophosphatidylcholine, and ethanolamine into phosphatidylethanolamine and lysophosphatidylethanolamine. No evidence was found for phospholipid methylation or demethylation in schistosomula. Labeled lipids were linearly and selectively released into the medium. Triglycerides were released at the highest rate with measurable quantities of phosphatidylcholine, lysophosphatidylcholine, and phosphatidylethanolamine also observed. Monopalmitoylphosphatidylcholine was the only lysophosphatidylcholine present in the medium as demonstrated by reverse-phase chromatography of released choline-labeled lysophosphatidylcholine. These studies demonstrate that schistosomula synthesize phospholipids and neutral lipids and release some of them into the culture medium. In particular, they release a single molecular species of a potent biologically active molecule, monopalmitoylphosphatidylcholine, that may play a role in the parasite's evasion of the immune response.

Animals↗
PubMed1990

Acidic phospholipids directly inhibit DNA binding of mammalian DNA topoisomerase I.

Inhibition of mammalian DNA topoisomerase I by phospholipids was investigated using purified enzyme. Acidic phospholipids inhibited the DNA relaxation activity of topoisomerase I whereas neutral phospholipid, phosphatidylethanolamine, did not. Accumulation of a protein-DNA cleavable complex, an intermediate which is known to accumulate upon inhibition by a specific inhibitor camptothecin, did not occur. The filter binding assay revealed that the DNA binding activity of the enzyme was inhibited by acidic phospholipids. Moreover, direct binding of phosphatidylglycerol to topoisomerase I was demonstrated. These results indicated that the inhibitory effect of acidic phospholipids on topoisomerase I was due to the loss of the DNA binding of the enzyme as a result of direct interaction between phospholipids and the enzyme.

Animals↗
PubMed1996

Plasmalogen and anionic phospholipid dependence of the cardiac sarcolemmal sodium-calcium exchanger.

Although plasmalogens are the predominant phospholipids of cardiac sarcolemma, their physiological role has not been forthcoming. Since the cardiac sarcolemmal sodium-calcium exchanger has been proposed to be regulated by anionic phospholipids, the roles of plasmalogens and anionic phospholipids as regulators of the sodium-calcium exchanger were explored. Reconstituted sodium-calcium exchange activity in plasmalogen-containing proteoliposomes was 10-fold higher than that in control proteoliposomes comprised of only diacyl phospholipids. Additionally, exchange activity in plasmalogen-containing proteoliposomes was regulated by anionic phospholipids. Thus, plasmalogens provide a critical lipid environment in which anionic phospholipids serve as boundary lipids for the regulation of the trans-sarcolemmal sodium-calcium exchanger.

Amino Acid Sequence↗
PubMed1995

Abnormal lipoprotein phospholipid composition in patients with essential hypertension.

Vascular cell membranes from patients with essential hypertension (EH) and animals with genetic forms of hypertension have been found to have alterations in the content of free cholesterol and negatively charged phospholipids that may modify their function. Since membrane and lipoprotein lipids exchange freely, the lipid composition of lipoproteins may be an indirect measure of the content of vascular and other cells. To determine whether abnormalities are present in the lipid and phospholipid composition of lipoproteins from patients with EH, 30 EH (11 women; 19 men) and 20 normotensive control subjects were studied. Since significant gender differences were present in a number of parameters of lipoprotein composition, male and female data were examined separately. The EH group of both sexes tended to have higher plasma TG and VLDL + LDL and HDL2 lipid levels than their respective controls. Not only were the calcium-binding phospholipids phosphatidylinositol (PI) + phosphatidylserine (PS), and the membrane fluidizer phosphatidylethanolamine (PE) were significantly reduced in their VLDL + LDL, but all phospholipids (L, sphingomyelin (SPH), PI + PS, and PE) were significantly reduced in their neutral lipid content in both the HDL2 and HDL3 subfractions. These directional changes in lipoprotein FC and phospholipid in the EH women significantly increased the EH FC/PC (mol/mol) ratio in their plasma, a new cardiovascular risk factor, (EH 1.08 +/- 0.22 vs. control 0.86 +/0 0.08; P < 0.01) and lowered the SPH/PC ratio HDL2 and HDL3 in EH patients of both sexes. These findings showed that lipoproteins in normolipidemic EH women are relatively enriched in FC and in EH patients of both sexes depleted in certain phospholipids lacking in lipoproteins, their functional properties could be altered and vascular tone increased.

Aged↗
PubMed1984

Rat adrenal cycloheximide-sensitive factors and phospholipids in the control of acute steroidogenesis.

ACTH in vivo induces the formation of several steroidogenic factors in both cytosol and extramitochondrial particulate fractions of rat adrenal. Cycloheximide prevents the formation of these factors. Here we show the presence of a cytosolic steroidogenic component (C1) which is cycloheximide-sensitive and not ACTH-dependent. C1 is able to solubilize an ACTH-dependent steroidogenic factor (C2) from particulate fractions resulting in the release of the rat-limiting constraint of mitochondrial steroidogenesis. The thermolabile and trypsin-resistant factor C1 has an apparent mol.wt of 28,000 Daltons. In contrast, the cycloheximide-sensitive factor C2 from extra-mitochondrial fractions of ACTH-treated rats comigrates on Sephadex G-10 with phospholipids. Endogenous phospholipids isolated from particulate adrenal fractions of ACTH-treated rats or exogenous phospholipids will also stimulate steroidogenesis in vitro. Indeed, cytosolic solubilizing factor C1 enhances the exogenous phospholipid effect 3-4-fold. The results taken together suggest that C1 may be very similar to a well defined phospholipid exchange protein and C2 is itself a phospholipid. Both factors seem to be obligatory for the ACTH-induced steroidogenesis.

Adrenal Glands↗
PubMed1987

An update on the role of phospholipid metabolism in the action of steroidogenic agents.

Most steroidogenic agents which bind to cell surface receptors activate adenylate cyclase and/or phospholipase C. Activation of either signaling system may also be associated with rapid increases in de novo phospholipid synthesis, but it is at present uncertain whether this is a secondary or parallel event. Activation of phospholipase C leads to hydrolysis of phosphatidylinositol-4',5'-PO4 (PIP2) and generation of two second messengers, inositol-triphosphate and diacylglycerol (DAG), which mobilize Ca2+ and activate protein kinase C, respectively. Increases in de novo phospholipid synthesis lead to rapid increases in phosphatidic acid, DAG and C-kinase activity. The PIP2-phospholipase C system appears to initiate the steroidogenic response to certain agents, such as angiotensin-II, and this may be amplified by concomitant increases in phospholipid synthesis. With other agonists, the role of phospholipase C activation and de novo phospholipid (and DAG) synthesis is less certain. In some tissues, activation of protein kinase C by exogeneously added DAG analogues provokes an increase in steroidogenesis. However, this is not observed in other tissues, and it is uncertain whether this rules out involvement of the C-kinase system for steroidogenesis in these tissues, or whether endogenously produced DAG is a more effective activator of the relevant C-kinase system then exogenously added DAG analogues. The role of other potential intracellular signaling substances that may be derived from phospholipase C activation and de novo phospholipid synthesis is also at present uncertain, as are the interrelationships between these two phospholipid responses, cyclic nucleotides, and other steroidogenic factors.

Adenylyl Cyclases↗
PubMed1991

Histopathological findings in placentae from patients with intra-uterine fetal death and anti-phospholipid antibodies.

Anti-phospholipid antibodies are associated with first trimester abortions and late intra-uterine fetal death. The histopathology of 47 placentae from 45 women with intra-uterine fetal death, including 16 patients with anti-phospholipid antibodies, was studied in order to detect potential differences between placentae from women with and without these antibodies. Thirteen patients had systemic lupus erythematosus or lupus-like disease, including 6 women with anti-phospholipid antibodies. In placentae from patients with anti-phospholipid antibodies, a decrease in vasculo-syncytial membranes, fibrosis mainly in infarcted areas, hypovascular villi and thrombosis or infarction was seen significantly more often than in placentae from women without these antibodies. Of 17 placentae from 16 patients with anti-phospholipid antibodies, only 3 did not demonstrate signs of thrombosis or infarction. Thrombosis/infarction was significantly associated with a decrease in vasculo-syncytial membranes, fibrosis, hypovascular villi and an increase in syncytial knots. These findings are most likely to be the result of prolonged hypoxia due to thrombosis or infarction. It is concluded that thrombosis or infarctions are prominent features in placenta from patients with anti-phospholipid antibodies and intra-uterine fetal death. Consequently, antithrombotic treatment during pregnancy forms a rational approach in these patients.

Adult↗
PubMed1984

The interaction between factor VIII clotting antigen and phospholipids in genetic variants of hemophilia and von Willebrand's disease.

The interaction of factor VIII with phospholipids was investigated in 11 patients with mild and moderate hemophilia A, 7 patients with von Willebrand's disease and in 10 healthy people as controls. The addition of phospholipid vesicles containing phosphatidylserine and phosphatidylethanolamine to normal plasma and that of patients with von Willebrand's disease resulted in the loss of almost two thirds of the factor VIII clotting antigen (VIII:CAg) measurable by IRMA. Defective interaction of phospholipids with VIII:CAg was noted in some genetic variants of mild and moderate hemophilia A. Thus four of the five families tested showed decreased binding of VIII:CAg to phospholipids. One of the families tested belonged to a genetic variant with much more VIII:CAg than VIII:C, and it was in members of this family that the binding capacity was most reduced. The most probable explanations for the defective interaction with phospholipids is that molecular defects of VIII:CAg result in either decreased binding to phospholipids or might lead to a stronger binding between VIII:CAg and the von Willebrand factor (VIIIR:Ag) in the factor VIII complex and thereby preventing the normal separation of the complex.

Adult↗
PubMed1983

45Ca2+ uptake and phospholipid methylation in isolated rat liver microsomes.

The effects of glucagon, epinephrine and insulin on hepatic phospholipid methylation were studied. Glucagon, either injected into rats or added to perfused livers, stimulated methylation in subsequently isolated microsomes. Epinephrine also increased phospholipid methylation. Insulin by itself did not influence the rate of the reaction, but, when administered prior to glucagon, it blocked the effect of the latter. The possibility that the observed stimulation of phospholipid methylation might be causally linked to the reported stimulation by glucagon of 45Ca2+ uptake in subsequently isolated liver microsomes was examined. Both the substrate and the competitive inhibitor of the methylation reaction, S-adenosylmethionine and S-adenosylhomocysteine, had profound effect on the rate of phospholipid methylation, without having comparable effects on Ca2+ uptake. S-adenosylmethionine in increasing concentration stimulated methylation four-fold, while no significant changes in 45Ca2+ uptake were seen. S-adenosylhomocysteine did not inhibit 45Ca2+ uptake even at levels causing more than 95% decrease in methylation. In conclusion, while both phospholipid methylation and 45Ca2+ uptake seem to be hormonally controlled, the correlation between these two processes was not sufficient to support the notion that the changes in 45Ca2+ uptake are caused by the changes in phospholipid methylation.

Animals↗
PubMed1992

Metabolic regulations and biological functions of phospholipids in Escherichia coli.

Extensive genetic and biochemical studies in the last two decades have elucidated almost completely the framework of synthesis and turnover of quantitatively major phospholipids in E. coli. The knowledge thus accumulated has allowed to formulate a novel working model that assumes sophisticated regulatory mechanisms in E. coli to achieve the optimal phospholipid composition and content in the membranes. E. coli also appears to possess the ability to adapt phospholipid synthesis to various cellular conditions. Understanding of the functional aspects of E. coli phospholipids is now advancing significantly and it will soon be able to explain many of the hitherto unclear cell's activities on the molecular basis. Phosphatidylglycerol is believed to play the central role both in metabolism and functions of phospholipids in E. coli. The results obtained with E. coli should undoubtedly be helpful in the study of more complicated phospholipid metabolism and functions in higher organisms.

Animals↗
PubMed1991

Phospholipid metabolism of cultured Trichomonas vaginalis and Tritrichomonas foetus.

Trichomonas vaginalis and Tritrichomonas foetus grown in a fetal calf serum-based culture medium were exposed to radiolabeled phospholipids and lipid precursors to determine the extent to which these organisms can incorporate complex lipids and/or de novo synthesize their major membrane phosphoglycerides. Phosphatidylethanolamine and phosphatidylcholine were the dominant phospholipids (40-50% of extractable phospholipids), with acidic lipids, phosphatidylinositol, phosphatidylserine, phosphatidylglycerol and O-acylphosphatidylglycerol accounting for the remaining phosphoglycerides. T. vaginalis was rich in sphingomyelin while T. foetus lacks significant amounts of this lipid. Incubation with [32P]orthophosphate resulted in only modest incorporation into extractable phospholipids; the most striking observation being the failure to label choline-containing lipids (phosphatidylcholine, lysophosphatidylcholine and sphingomyelin). Phosphatidylethanolamine was heavily labeled with modest labeling observed in the acidic phosphoglycerides. [U-14C]Glucose failed to label choline-containing lipids in T. foetus but did so in T. vaginalis, with phosphatidylethanolamine again being heavily labeled. Choline, phosphorylcholine, ethanolamine, serine, inositol, glycerol and methionine were incorporated poorly or failed to label the expected phosphoglycerides in either of the trichomonads, demonstrating an impairment in synthesis. Intact phosphoglycerides, labeled in the fatty acyl groups, labeled most phospholipids indicating that turnover of membrane lipids can occur with respect to the acyl component of the phospholipids. Fluorescent probes attached to phosphoglyceride molecules support observations seen with radiolabeled phosphoglycerides. Though trichomonads are able to transacylate phosphoglycerides, it is evident that the trichomonads lack a variety of enzymatic activities necessary for de novo synthesis of complex phosphoglycerides and must rely on environmental sources to supply them.

Animals↗
PubMed1986

Changes in conformation of spin-labeled calmodulin by phospholipids.

Spin-labeled calmodulin was synthesized and the effects of phospholipids on its conformation were examined by ESR spectroscopy. Phosphatidylserine (0.1-1.0 mM) increased the signal intensity of the ESR spectrum of spin-labeled calmodulin and decreased the apparent rotational correlation time in the presence of 0.1 mM CaCl2. This change was reversed by addition of excess calcium, and in the absence of calcium phosphatidylserine did not change the spectrum, suggesting that the change in spin-labeled calmodulin brought about by phosphatidylserine was not induced by a hydrophobic interaction of the two, but by inhibition of the binding of calcium to calmodulin. L-Serine and O-phospho-L-serine had no effect on the ESR signals of spin-labeled calmodulin. The effects of various other phospholipids were also examined. Their inhibitory activities were in the order phosphatidic acid greater than phosphatidylserine greater than phosphatidylglycerol = phosphatidylinositol; phosphatidylethanolamine and phosphatidylcholine had no effect on the spectra. The effects of these phospholipids were dependent on their binding activities toward calcium. Furthermore, phosphatidic acid and phosphatidylserine at 1 mM reduced the activity of calmodulin-dependent phosphodiesterase by 16.4 and 8.7%, respectively. These findings indicate that spin-labeled calmodulin did not interact with the phospholipids by a hydrophobic interaction, but that calcium binding to spin-labeled calmodulin interfered with phosphatidic acid, phosphatidylserine, phosphatidylglycerol and phosphatidylinositol, and some of these phospholipids inactivated calmodulin. Thus the activity of calmodulin may be regulated in part by some phospholipids.

Binding Sites↗
PubMed1985

Studies on the enzymatic pathways of calcium ionophore-induced phospholipid degradation and arachidonic acid mobilization in peritoneal macrophages.

Exposure of mouse peritoneal macrophages to ionophore A23187 caused a rapid and extensive Ca2+-dependent phospholipid degradation and mobilization of arachidonic acid. Phosphatidylinositol, phosphatidylcholine and phosphatidylethanolamine all contributed to the arachidonic acid release, although the ethanolamine phospholipids incorporated [3H]arachidonic acid more slowly during the prelabeling period, particularly the plasmalogen form. Several enzymatic pathways could be positively identified as contributing to the ionophore-induced phospholipid degradation by the use of several different radiolabeled phospholipid precursors: (i) a phospholipase A-mediated deacylation, (ii) a phosphodiesterase (phospholipase C) reaction, rapidly generating diacylglycerol units from inositol phospholipids, and (iii) enzymatic processes generating diacylglycerol and CDP- and phosphocholine/ethanolamine from phosphatidylcholine/ethanolamine. The diacylglycerol formed was in part phosphorylated and in part hydrolyzed to monoacylglycerol, with retention of its arachidonic acid. These, and other, results indicate that the Ca2+-ionophore activates several apparently distinct phospholipid-degrading processes, in contrast to stimuli acting via cellular receptors.

Animals↗