Phosphatidylcholine metabolism in human endothelial cells: modulation by phosphocholine

Phosphatidylcholine is the principal phospholipid in mammalian tissues, and a major source for the production of arachidonic acid. In this study, the effect of exogenous phosphocholine, a precursor of phosphatidylcholine biosynthesis, on the metabolism of phosphatidylcholine in human umbilical vein endothelial cells was investigated. Incubation of endothelial cells with exogenous phosphocholine at concentrations of 1 to 5 mM was found to inhibit choline uptake and its subsequent incorporation into phosphatidylcholine. Phosphocholine appeared to inhibit choline uptake in a competitive manner. Since phosphatidylcholine is metabolized mainly by the action of phospholipase A₂, with the release of arachidonic acid and other fatty acids, the effect of phosphocholine on arachidonic acid release in endothelial cells was also examined. The induction of arachidonic acid release by ATP was enhanced in cells treated with 1 mM phosphocholine. In vitro assays of phospholipase A₂ activity in cells incubated with phosphocholine, however, did not produced any significant change in the activity of this enzyme. The results of this study show that phosphocholine modulates the biosynthesis and catabolism of phosphatidylcholine in an indirect manner.     

Phospholipid molecular species in human umbilical artery and vein endothelial cells

Molecular species of several phospholipid classes and subclasses were quantitatively determined in human umbilical artery and vein endothelial cells. Both types of endothelial cells were similar in phospholipid class composition, whereas they were markedly different in phospholipid subclass and molecular species composition. The amounts of two ether subclasses in phosphatidylcholine and phosphatidylethanolamine were higher in artery endothelial cells than those in vein endothelial cells. The relative content of alkylacyl subclass in phosphatidylcholine, a precursor of platelet-activating factor, was about three times higher in artery endothelial cells than in vein endothelial cells. In artery endothelial cells, arachidonic acid was in highest amounts in alkenylacyl phosphatidylethanolamine, followed by diacyl phosphatidylcholine, diacyl phosphatidylethanolamine, and phosphatidylinositol. In the vein endothelial cells, arachidonic acid was highest in phosphatidylinositol, followed by diacyl phosphatidylethanolamine, diacyl phosphatidylcholine, and alkenylacyl phosphatidylethanolamine. Artery endothelial cells had higher amounts of molecular species containing arachidonic acid than vein endothelial cells in all phospholipid classes and subclasses. These differences are thought to reflect the functional differences of artery and vein endothelial cells.     

Phospholipid turnover during phagocytosis in human polymorphonuclear leucocytes

We have previously observed that the phagocytosis of zymosan particles coated with complement by human polymorphonuclear leucocytes is accompanied by a time- and dose-dependent inhibition of phosphatidylcholine synthesis by transmethylation [García Gil, Alonso, Sánchez Crespo & Mato (1981) Biochem. Biophys. Res. Commun. 101, 740–748]. The present studies show that phosphatidylcholine synthesis by a cholinephosphotransferase reaction is enhanced, up to 3-fold, during phagocytosis by polymorphonuclear cells. This effect was tested by both measuring the incorporation of radioactivity into phosphatidylcholine in cells labelled with [Me-¹⁴C]choline, and by assaying the activity of CDP-choline:diacylglycerol cholinephosphotransferase. The time course of CDP-choline:diacylglycerol cholinephosphotransferase activation by zymosan mirrors the inhibition of phospholipid methyltransferase activity previously reported. The extent of incorporation of radioactivity into phosphatidylcholine induced by various doses of zymosan correlates with the physiological response of the cells to this stimulus. This effect was specific for phosphatidylcholine, and phosphatidyl-ethanolamine turnover was not affected by zymosan. The purpose of this enhanced phosphatidylcholine synthesis is not to provide phospholipid molecules rich in arachidonic acid. The present studies show that about 80% of the arachidonic acid generated in response to zymosan derives from phosphatidylinositol. A transient accumulation of arachidonoyldiacylglycerol has also been observed, which indicates that a phospholipase C is responsible, at least in part, for the generation of arachidonic acid. Finally, isobutylmethylxanthine and quinacrine, inhibitors of phosphatidylinositol turnover, inhibit both arachidonic acid generation and phagocytosis, indicating a function for this pathway during this process.     

Antioxidant modulation of oxidant-stimulated uptake and release of arachidonic acid in eicosapentaenoic acid-supplemented human lymphoma U937 cells

Omega-3 polyunsaturated fatty acids (PUFA) are increasingly finding use as treatments for a variety of medical conditions. PUFA supplementation can, however, result in increased oxidative stress causing elevated turnover rate of membrane phospholipids, impairment of membrane integrity and increased formation of inflammatory mediators. The aim of this study was to determine which antioxidant compounds were most effective in ameliorating the stimulation of phospholipid turnover by oxidative stress. U937 cells were supplemented with eicosapentaenoic acid and either ascorbic acid, alpha-tocopherol, beta-carotene or astaxanthin prior to being challenged with oxidant. Although all antioxidants were found to be effective in decreasing oxidant-stimulated peroxide formation, only alpha-tocopherol significantly decreased oxidant-stimulated release of 3H-labeled arachidonic acid (AA), while ascorbic acid markedly increased release. All antioxidants except alpha-tocopherol decreased oxidant-stimulated 3H-AA uptake. Our data suggest that antioxidants are not equally effective in combating the effects of oxidative stress upon membrane phospholipid turnover, and that optimal protection will require mixtures of antioxidants.     

Lipid composition and metabolism in megakaryocytes at different stages of maturation

The lipid composition and metabolism of isolated guinea pig megakaryocyte subgroups at various stages of maturation were investigated. Three groups were studied: 1) 67% of megakaryocytes in Group A were immature; 2) Group B was heterogeneous and contained both immature and mature subgroups of megakaryocytes; 3) 92% of megakaryocytes in Group C were mature. Lipid composition was determined by thin-layer chromatography, lipid-phosphorus, and gas-liquid chromatography. Cholesterol, ceramide, and de novo fatty acid synthesis were evaluated with [14C]acetate. [14C]Glycerol was used to assess de novo phospholipid synthesis. 14C-Labeled fatty acids were used to evaluate fatty acid uptake. The phospholipid and cholesterol content was found to be four times greater in mature megakaryocytes than that in immature megakaryocytes, which paralleled the protein content and volume of mature and immature cells. The cholesterol-phospholipid ratio was similar and there were no differences in the phospholipid species in the three groups. Phospholipid and cholesterol synthesis were established in immature megakaryocytes and persisted at about the same level in mature megakaryocytes. The uptake of arachidonic and palmitic acids also occurred primarily in immature cells, while the de novo synthesis of palmitic acid occurs predominantly in mature megakaryocytes. There was an inverse relationship between the uptake of exogenous palmitic acid and fatty acid synthesis, but the uptake of palmitic acid primarily inhibited fatty acid synthesis in mature megakaryocytes. There were differences in the acylation of phospholipid species with arachidonic acid in megakaryocytes at different stages of maturation since the acylation of phosphatidylcholine occurred primarily in immature megakaryocytes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increased levels of a particular phosphatidylcholine species in senescent human dermal fibroblasts in vitro

Plasma membranes are essential components of living cells, and phospholipids are major components of cellular membranes. Here, we used liquid chromatography/mass spectrometry to investigate changes in the membrane phospholipid content that occur in association with aging. Our results indicate that the levels of a particular species of phosphatidylcholine comprised of stearic acid and arachidonic acid increased with age. To determine the reason for the increased levels of this particular phosphatidylcholine, we examined the effect of highly unsaturated fatty acids, such as arachidonic acid and eicosapentaenoic acid, on cellular aging. Applied arachidonic acid was incorporated into phosphatidylcholine molecules, but neither arachidonic acid nor other related unsaturated fatty acids had any effect. We conclude that increased levels of this distinctive phosphatidylcholine are a result of in vitro senescence.     

Metabolism of n-3 polyunsaturated fatty acids and modification of phospholipids in cultured rabbit aortic smooth muscle cells

The metabolism of the linolenic acid family (n-3) of fatty acids, e.g., linolenic, eicosapentaenoic, and docosahexaenoic acids, in cultured smooth muscle cells from rabbit aorta was compared to the metabolism of linoleic and arachidonic acids. There was a time-dependent uptake of these fatty acids into cells for 16 hr (arachidonic greater than docosahexaenoic, linoleic, eicosapentaenoic greater than linolenic), and the acids were incorporated mainly into phospholipids and triglycerides. Eicosapentaenoic and arachidonic acids were incorporated more into phosphatidylethanolamine and phosphatidylinositol plus phosphatidylserine and less into phosphatidylcholine than linolenic and linoleic acids. Docosahexaenoic acid was incorporated into phosphatidylethanolamine more than linolenic and linoleic acids and into phosphatidylinositol plus phosphatidylserine less than eicosapentaenoic and arachidonic acids. Added linolenic acid accumulated mainly in phosphatidylcholine and did not decrease the arachidonic acid content of any phospholipid subfraction. Elongation-desaturation metabolites of linoleic acid did not accumulate. Cells treated with eicosapentaenoic acid accumulated both eicosapentaenoic and docosapentaenoic acids mainly in phosphatidylethanolamine and the arachidonic acid content was decreased. Added docosahexaenoic acid accumulated mainly in phosphatidylethanolamine and decreased the content of both arachidonic and oleic acids. The following conclusions are drawn from these results. The three n-3 fatty acids are utilized differently in phospholipids. The arachidonic acid content of phospholipids is reduced by eicosapentaenoic and docosahexaenoic acids, but not by linolenic acid. Smooth muscle cells have little or no desaturase activity, but have significant elongation activity for polyunsaturated fatty acids.     

Transfer of arachidonic acid from phosphatidylcholine to phosphatidylethanolamine during storage of human platelets for 5 days

Human platelets are routinely stored for 5 days prior to transfusion, but they deteriorate during storage. Since very little information is available concerning the effect of storage on platelet phospholipid metabolism, the biosynthesis and remodelling of platelet phospholipids were studied. Platelets were incubated separately with [14C]glycerol, [14C]arachidonic acid, or a mixture of [14C]glycerol and [3H]arachidonic acid, and stored in a platelet storage medium at 22 degrees C. Maximum glycerol uptake (20%) was attained after 6 h. [14C]Glycerol was incorporated into phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol, and to a much lesser extent phosphatidylserine, under storage conditions for 5 days. The distribution of the initial arachidonic acid uptake was not as would be expected based on the molar composition of endogenous phospholipids. The arachidonic acid (75%) which was taken up within 10 min of incubation distributed 55% into the phosphatidylcholine and only 14% into the phosphatidylethanolamine; the molar composition is actually 18% phosphatidylcholine and 47% phosphatidylethanolamine. During storage, there was a continuous transfer of the radiolabelled arachidonic from phosphatidylcholine to phosphatidylethanolamine until, after 5 days, the distribution of arachidonic acid was identical to the endogenous distribution. In contrast, no change in the glycerol incorporation pattern was detected during storage. This suggested that the mechanism for arachidonic acid redistribution was not through exchange of polar head groups, but through acyl transfer of arachidonic acid from phosphatidylcholine to phosphatidylethanolamine.     

Fatty acid changes in liver and plasma lipid fractions after safflower oil was fed to rats deficient in essential fatty acids

1. Fatty acid patterns of liver and plasma triglycerides, phospholipids and cholesteryl esters were determined at intervals during 24hr. after essential fatty acid-deficient rats were given one feeding of linoleate (as safflower oil). 2. Liver triglyceride, phospholipid and cholesteryl ester fatty acid compositions did not change up to 7hr. after feeding. Between 7 and 10hr., linoleic acid began to increase in all fractions, but arachidonic acid did not begin to rise in the phospholipid until 14-19hr. after feeding. 3. Oleic acid and eicosatrienoic acid in liver phospholipid began to decline at about the time that linoleic acid increased, i.e. about 9hr. before arachidonic acid began to increase. 4. Changes in linoleic acid, arachidonic acid and eicosatrienoic acid in phosphatidylcholine resembled those of the total phospholipid. Phosphatidylethanolamine had a higher percentage content of arachidonic acid before the linoleate was given than did phosphatidylcholine, and after the linoleate was given the fatty acid composition of this fraction was little changed. 5. The behaviour of the plasma lipid fatty acids was similar to that of the liver lipids, with changes in linoleic acid, eicosatrienoic acid and arachidonic acid appearing at the same times as they occurred in the liver. 6. The results indicated that linoleic acid was preferentially incorporated into the liver phospholipid at the expense of eicosatrienoic acid and oleic acid. The decline in these fatty acids apparently resulted from their competition with linoleic acid for available sites in the phospholipids rather than from any direct replacement by arachidonic acid.     

Activation of phospholipase hydrolysis in the process of oxidative cell damage]

Effect of tert-butyl hydroperoxide toxic action on phospholipase A2 activity and the changes in phospholipid composition from mastocytoma P815 cells were investigated. Oxidative damage of tumor cell membranes was accompanied by the release of arachidonic acid from membrane phospholipids and the accumulation of lysophosphatidylcholine, the product of phospholipase A2 reaction and a potent detergent. Tert-butyl hydroperoxide also increased relative contents of sphingomyelin, phosphatidylserine and phosphatidic acid in tumor cell membranes. It is possible that phospholipase A2 activation and the changes of phospholipid molecular species contents may cause the damage of cell membrane stability.     

Acyltransferase-catalyzed cleavage of arachidonic acid from phospholipids and transfer to lysophosphatides in lymphocytes and macrophages

The cleavage of fatty acyl moieties from phospholipids was compared in intact cells and homogenates of mouse lymphocytes (thymocytes, spleen cells) and macrophages. Liberation of free arachidonic acid during incubations of intact cells was only detectable in the presence of albumin. Homogenization of prelabeled thymocytes and further incubation of these homogenates at 37 degrees C resulted in a pronounced decrease of phospholipid degradation and cleavage of arachidonoyl residues, while further incubation of homogenates from prelabeled macrophages produced a greatly increased phospholipid degradation. Homogenates of macrophages but not those of thymocytes contain substantial activities of phospholipase A2 detectable using exogenous radiolabeled substrates. These findings indicate that in thymocytes cleavage of arachidonic acid from phosphatidylcholine is an active process that is not catalyzed by phospholipase A2. Addition of CoA and lysophosphatidylethanolamine to prelabeled thymocyte homogenates induced a fast breakdown of phosphatidylcholine and transfer of arachidonic acid to phosphatidylethanolamine, as in seen during incubations of intact thymocytes or macrophages. The transfer is restricted to arachidonic acid and does not require addition of ATP. Sodium cholate, a known inhibitor of the acyl-CoA:lysophosphatide acyltransferase, completely inhibited this transfer reaction. These results suggest that the CoA-mediated, ATP-independent breakdown of phosphatidylcholine and transfer of arachidonic acid is catalyzed by the acyl-CoA:lysophosphatide acyltransferase operating in reverse.     

Surfactant peptides stimulate uptake of phosphatidylcholine by isolated cells

To determine whether small hydrophobic surfactant peptides (SP-B and SP-C) participate in recycling of pulmonary surfactant phospholipid, we determined the effect of these peptides on transfer of 3H- or 14C-labelled phosphatidylcholine from liposomes to isolated rat alveolar Type II cells and Chinese hamster lung fibroblasts. Both natural and synthetic SP-B and SP-C markedly stimulated phosphatidylcholine transfer to alveolar Type II cells and Chinese hamster lung fibroblasts in a dose- and time-dependent fashion. Effects of the peptides on phospholipid uptake were dose-dependent, but not saturable and occurred at both 4 and 37 degrees C. Uptake of labelled phospholipid into a lamellar body fraction prepared from Type II cells was augmented in the presence of SP-B. Neither SP-B nor SP-C augmented exchange of labelled plasma membrane phosphatidylcholine from isolated Type II cells or enhanced the release of surfactant phospholipid when compared to liposomes without SP-B or SP-C. Addition of native bovine SP-B and SP-C to the phospholipid vesicles perturbed the size and structure of the vesicles as determined by electron microscopy. To determine the structural elements responsible for the effect of the peptides on phospholipid uptake, fragments of SP-B were synthesized by solid-phase protein synthesis and their effects on phospholipid uptake assessed in Type II epithelial cells. SP-B (1-60) stimulated phospholipid uptake 7-fold. A smaller fragment of SP-B (15-60) was less active and the SP-B peptide (40-60) failed to augment phospholipid uptake significantly. Like SP-B and SP-C, surfactant-associated protein (SP-A) enhanced phospholipid uptake by Type II cells. However, SP-A failed to significantly stimulate phosphatidylcholine uptake by Chinese hamster lung fibroblasts. These studies demonstrate the independent activity of surfactant proteins SP-B and SP-C on the uptake of phospholipid by Type II epithelial cells and Chinese hamster lung fibroblasts in vitro.     

Measles-virus-persistent infection in BGM cells. Modification of the incorporation of [3H]arachidonic acid and [14C]stearic acid into lipids.

In BGM cells chronically infected with measles virus, although the composition of the phospholipids is unaltered, the fatty acid composition is modified. Uninfected, lytic and persistently infected cells were labelled with [3H]arachidonic acid and [14C]stearic acid and their metabolic fate analysed. No difference in the total incorporation was observed in the different systems. However, the [14C]stearic acid and [3H]arachidonic acid were incorporated up to 2-fold and 13-fold respectively greater into the neutral lipid of persistently infected compared with that of uninfected cells. Both radioactive fatty acids were specifically accumulated in the triacylglycerol and non-esterified fatty acids fractions. Lytically infected cells were similar to uninfected cells. Although there was no significant difference in the incorporation of radioactivity into the total phospholipid in either system, there was a large decrease in [3H]arachidonic acid incorporated into phosphatidylethanolamine and to a lesser extent phosphatidylcholine and phosphatidylinositol in persistently infected cells. [14C]Stearic acid incorporation was also reduced in phosphatidylcholine and phosphatidylethanolamine fractions of persistently infected cells.     

Altered arachidonic acid biosynthesis and antioxidant protection mechanisms in Schwann cells grown in elevated glucose

In cultured Schwann cells, elevated glucose induces alterations in arachidonic acid metabolism that cause a decrease in the content of glycerophospholipid arachidonoyl-containing molecular species (ACMS). This could result from decreased de novo arachidonic acid biosynthesis, or increased arachidonic acid release from phospholipids. Incorporation of radioactive 8,11,14-eicosatrienoic acid into ACMS was lower for cells grown in 30 mm versus 5 mm glucose, consistent with a decrease in delta5 desaturase activity. However, neither basal arachidonic acid release from prelabeled cells nor stimulated generation of arachidonic acid in the presence of the reacylation inhibitor, thimerosal, the phosphotyrosine phosphatase inhibitor, bipyridyl peroxovanadium, or both together, were altered by varying the glucose concentrations, indicating that arachidonic acid turnover did not contribute to ACMS depletion. Free cytosolic NAD+ /NADH decreased, whereas NADP+ /NADPH remained unchanged for cells grown in elevated glucose, implying that decreased desaturase activity is a result of metabolic changes other than cofactor availability. Schwann cells in elevated glucose were susceptible to oxidative stress, as shown by increased malondialdehyde, depleted glutathione levels, and reduced cytosolic superoxide dismutase activity. Glutathione-altering compounds had no effect on ACMS levels, in contrast to N -acetylcysteine and alpha-lipoic acid, which partly corrected ACMS depletion in phosphatidylcholine. These findings suggest that in the Schwann cell cultures, a high glucose level elicits oxidative stress and weakens antioxidant protection mechanisms which could decrease arachidonic acid biosynthesis and that this deficit can be partly corrected by treatment with exogenous antioxidants.     

Compartmentation of phosphorylated precursors of phospholipid biosynthesis in cultured neuroblastoma cells

The continuous turnover of membrane phospholipids requires a steady supply of biosynthetic precursors. We evaluated the effects of decreasing extracellular Na+ concentration on phospholipid metabolism in cultured neuroblastoma (N1E 115) cells. Incubating cultures with 145 to 0 mM NaCl caused a concentration-dependent inhibition of [32P]phosphate uptake into the water-soluble intracellular pool and incorporation into phospholipid. Phospholipid classes were differentially affected; [32P]phosphate incorporated into phosphati-dylethanolamine (PE) and phosphatidylcholine (PC) was consistently less than into phosphatidylinositol (PI) and phosphatidylserine (PS). This could not be attributed to decreased phospholipid synthesis since under identical conditions, there was no effect on arachidonic acid or ethanolamine incorporation, and choline utilization for PC synthesis was increased. The effect of Na+ was highly specific since reducing phosphate uptake to a similar extent by incubating cultures in a phosphate-deficient medium containing Na+ did not alter the relative distribution of [32P]phosphate in phospholipid. Of several cations tested only Li+ could partially (50%) replace Na+. Incubation in the presence of ouabain or amiloride had no effect on [32P]phosphate incorporation into phospholipid. The differential effects of low Na+ on [32P]phosphate incorporation into PI relative to PC and PE suggests preferential compartmentation of [32P]phosphate into ATP in pools used for phosphatidic acid synthesis and relatively less in ATP pools used for synthesis of phosphocholine and phosphoethanolamine, precursors of PC and PE, respectively. This suggestion of heterogeneous and distinct pools of ATP for phospholipid biosynthesis, and of potential modulation by Na+ ion, has important implications for understanding intracellular regulation of metabolism.     

Changes in arachidonic acid content of X-irradiated human lymphocytes and plasma membrane fractions

The 14C-arachidonic acid content of pre-labelled human lymphocytes was followed during in vitro incubation in untreated and X-irradiated cells. Loss of about 35-40 per cent of the incorporated radioactivity was found already at 10 minutes after irradiation as detected in whole cells, phospholipid, free fatty acid and phosphatidylcholine fractions of plasma membranes. When pulse labeling with 14C-arachidonic acid was performed at various intervals after in vitro irradiation, the uptake of precursor by irradiated cells did not differ from untreated ones. At the same time the activity of phospholipid, free fatty acid and phosphatidylcholine fractions was approximately 50 per cent lower compared to the control, then it increased gradually reaching the control level.     

Unsaturated Fatty Acids Esterified in 2-Acyl-1-Lysophosphatidylcholine Bound to Albumin Are More Efficiently Taken up by the Young Rat Brain than the Unesterified Form

The aim of the present study was to investigate whether unsaturated 2-acyl-lysophosphatidylcholine bound to plasma albumin is a relevant delivery form of unsaturated fatty acids to the developing brain. Twenty-day-old rats were perfused for 30 s with labeled palmitic, oleic, linoleic, and arachidonic acids in either their unesterified form or esterified in 2-acyl-lysophosphatidylcholine labeled on the choline and fatty acid moieties. Both forms were bound to albumin. Incorporation in brain lipid classes was followed within 1 h. The brain uptake of the unesterified fatty acids reached a plateau at 5-15 min and was maximal for arachidonic acid (0.45% of the perfused dose). The brain uptake of palmitoyl-lysophosphatidylcholine was similar to that of palmitic acid, whereas that of other lysophosphatidylcholines increased with the degree of unsaturation (rate and maximal uptake) and was six- to 10-fold higher than that of the corresponding unesterified fatty acid. 2-Acyl-lysophosphatidylcholines were taken up without prior hydrolysis and reacylated into doubly labeled phosphatidylcholine, which was the most labeled lipid class, whereas lipid distribution of the unesterified fatty acid was more diversified. Partial hydrolysis of 2-acyl-lysophosphatidylcholine occurred in the brain tissue, and redistribution of the fatty acyl moiety into other phospholipid classes was also observed and was the highest for arachidonic acid. In this case, the percentage of esterification of this fatty acid in phosphatidylinositol (expressed as a percentage of the total lipid fraction) was relatively lower than that observed when the unesterified form was used.(ABSTRACT TRUNCATED AT 250 WORDS)     

The action of digitonin on rat liver mitochondria. Phospholipid content

1. The amount and types of phospholipid and the fatty acid composition of the various phospholipids were examined in intact rat liver mitochondria, in mitochondria devoid of their outer membrane (preparation A) and in very small pieces derived from the disruption of the inner-membrane complexes (preparation B). The latter two preparations were obtained by digitonin treatment and carry out oxidative phosphorylation. 2. The ratio mug.atoms of phospholipid P/mg. of protein was 0.163 for intact mitochondria, decreased to 0.118 on removal of the outer membrane and increased markedly to 0.292 on disruption of the inner-membrane complex. 3. Examination of the various types of phospholipid present showed that the molar proportions cardiolipin:phosphatidylcholine:phosphatidylethanolamine were approx. 1:6:6 for intact mitochondria and 1:3:3 for preparations A and B. 4. There was a correlation between the recovery of cardiolipin and adenosine triphosphatase activity in the conversion of intact mitochondria into preparations A and B. 5. The fatty acid contents of the various types of phospholipid purified by thin-layer chromatography were identical in all three preparations. Our results show a considerably higher content of arachidonic acid and lower content of oleic acid for phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol than have previously been reported for mitochondrial phospholipids.     

Leukotrienes stimulate phosphatidylcholine secretion in cultured type II pneumocytes

We previously reported that arachidonic acid stimulates secretion of phosphatidylcholine in cultures of type II pneumocytes and, based on studies with cyclooxygenase and lipoxygenase inhibitors, suggested that this effect was mediated by lipoxygenase products of arachidonic acid metabolism (Gilfillan, A.M. and Rooney, S.A. (1985) Biochim. Biophys. Acta 833, 336-341). We have now examined the effect of leukotrienes on phosphatidylcholine secretion in type II cells as well as the effect of a leukotriene antagonist, FPL55712, on the stimulatory effect of arachidonic acid. Leukotrienes C4, D4 and E4 stimulated phosphatidylcholine secretion and this effect was dependent on concentration in the range 10(-12)-10(-6) M. Leukotriene E4 was the most stimulatory, followed by D4 and C4. Leukotriene B4 had no effect. Incubation of the cells with 10(-7) M leukotriene E4 for 90 min resulted in a 107% increase in the rate of phosphatidylcholine secretion. Incubation with 10(-6) M leukotrienes D4 and C4 for the same period resulted in 81% and 63% stimulation, respectively. The leukotrienes had no effect on cellular phosphatidylcholine synthesis or on lactate dehydrogenase release. The stimulatory effects of leukotrienes E4 and D4 were abolished by FPL55712. Similarly, the stimulatory effect of 6 X 10(-6) M arachidonic acid on phosphatidylcholine secretion was reduced from 74% to 25% by 10(-5) M FPL55712. Thus, the stimulatory effect of arachidonic acid on surfactant phospholipid secretion in type II cells is mediated at least in part by leukotrienes.     

Influence of septic shock upon phosphatidylcholine remodeling mechanism in rat lung

Septic shock in rats lead to pulmonary disorders associated with alterations of phospholipid metabolism. The ratio between phosphatidylcholine and lysophosphatidylcholine is lowered both in lung tissue and in pulmonary surfactant because enzymes of phosphatidylcholine remodeling mechanism are distinctly affected by septic shock. Specific activity of phospholipase A2 is enhanced 5-fold while specific activities of lysolecithin acyltransferase and lysolecithin : lysolecithin acyltransferase are only slightly increased or remain unchanged. Beyond that, palmitic acid content of lung tissue phosphatidylcholine is significantly reduced and replaced mainly by arachidonic acid. The release of this fatty acid by action of phospholipase A2 may lead via intermediates to the generation of potent mediators such as prostaglandins, thromboxane or slow-reacting substance.