Participation of carnitine palmitoyltransferase in the synthesis of dipalmitoylphosphatidylcholine in rat alveolar type II cells

We have investigated the role of carnitine palmitoyltransferase (EC 2.3.1.21) in pulmonar type II pneumocyte, a lung cell responsible for the synthesis of surface active lipids. Adult type II pneumocytes were isolated from rat lung and purified by differential adherence. When these lung cells were incubated with radioactive palmitate, the percentage of radioactivity recovered into dipalmitoylphosphatidylcholine (DPPC), a major surface active lipid, was almost 60% with respect to total phosphatidylcholine (PC) molecular species. Cellular lysates from type II pneumocytes contained detectable amount of carnitine palmitoyltransferase (CPT) activity (1 nmol/min/mg). Most of the CPT activity found in these cells could be inhibited by incubating them for 60 min with 5 M tetradecylglycidic acid (TDGA), a specific and irreversible CPT inhibitor of the malonyl-CoA sensitive CPT isoform (CPT I). TDGA treatment of adult type II pneumocytes caused a significant reduction in the incorporation of radioactive palmitate into PC, though this effect did not seem to be specific for DPPC. TDGA affected the incorporation of radioactive palmitate at the sn2 rather than the sn1 position of the glycerol backbone of PC. The incorporation of radioactive palmitate into DPPC was also observed when these lung cells were incubated with palmitate-labeled palmitoyl-L-carnitine. Our data suggest that type II pneumocyte CPT may play an important role in remodelling PC fatty acid composition and hence DPPC synthesis.     

Composition and metabolism of phospholipids of human leukocytes

Human mononuclear (MN) and polymorphonuclear (PMN) leukocytes were analyzed for their phospholipid, triglyceride, cholesterol and fatty acid content. The phospholipid/cholesterol ratio was 1.24 for both cels. MN cells contain more phosphatidylcholine (PC), but less phosphatidylserine (PS), phosphatidylethanolamine (PE) and sphingomyelin (SPH) than PMN cells when expressed as percent of total phospholipid. When expressed on the basis of lipid content per cell, MN cells contain less PS, PE and SPH but more triglyceride than PMN cells. PMN cells incorporate palmitic, stearic, linoleic and linolenic acids into their phospholipids, triglycerides or cholesterol esters. The incorporation into triglycerides was highest for all fatty acids. Of the phospholipids, the incorporation was highest into PC. Labeled fatty acids also were found in proteins which had been delipidized by exhaustive extraction with organic solvents. These represent tightly or covalently bound fatty acids. The incorporation of [³H]palmitic acid into this protein fraction is stimulated by insulin.     

Role of triglycerides in endothelial cell arachidonic acid metabolism

Arachidonic acid was incorporated into triglycerides by cultured bovine endothelial cells in a time- and concentration-dependent manner. At 75 microM or higher, more arachidonic acid was incorporated into triglycerides than into phospholipids. The triglyceride content of the cells increased as much as 5.5-fold, cytoplasmic inclusions appeared, and arachidonic acid comprised 22% of the triglyceride fatty acids. Triglyceride turnover occurred during subsequent maintenance culture; there was a 60% decrease in the radioactive arachidonic acid contained in triglycerides and a 40% decrease in triglyceride content in 6 hr. Most of the radioactivity was released into the medium as free fatty acid. The turnover of arachidonic acid, but not oleic acid in cellular triglycerides, decreased when supplemental fatty acid was added to the maintenance medium. Incorporation and turnover of radioactive arachidonic acid in triglycerides also was observed in human skin fibroblasts, 3T3-L1 cells, and MDCK cells. Other fatty acids were incorporated into triglycerides by the endothelial cells; the amounts after a 16-hr incubation with 50 microM fatty acid were 20:3 greater than 20:4 greater than 18:1 greater than 18:2 greater than 22:6 greater than 16:0 greater than 20:5. These findings indicate that triglyceride formation and turnover can play a role in the fatty acid metabolism of endothelial cells and that arachidonic acid can be stored in endothelial cell triglycerides.     

Ethynylestradiol alters lipid composition and phosphatidylethanolamine metabolism in red blood cells

Treatment of female rats with ethinylestradiol at a dose of 60 micrograms/rat, daily for 21 days, produced marked changes in red blood cell lipids. Cholesterol was decreased by 22% and total phospholipids were increased by 13%, resulting in a 31% decrease in the cholesterol to phospholipid ratio. The mass distribution of phosphatidylcholine and phosphatidylethanolamine relative to total phospholipids was unchanged. Whereas control red cells incorporated preferentially fatty acids in phosphatidylcholine, ethinylestradiol stimulated their incorporation specifically in phosphatidylethanolamine, where increases occurred with palmitic acid (+75%), oleic acid (+68%) and arachidonic acid (+31%). Incorporation in phosphatidylcholine was unaffected with any of the 3 fatty acids. The stimulation of fatty acid incorporation in phosphatidylethanolamine is likely to reflect an estrogen-dependent increase in turnover rate of fatty acids in this phospholipid. Such alterations in lipid composition and fatty acid incorporation in red cell phospholipids may have significant effects on membrane function.     

Role of carnitine and carnitine palmitoyltransferase as integral components of the pathway for membrane phospholipid fatty acid turnover in intact human erythrocytes.

The deacylation and reacylation process of phospholipids is the major pathway of turnover and repair in erythrocyte membranes. In this paper, we have investigated the role of carnitine palmitoyltransferase in erythrocyte membrane phospholipid fatty acid turnover. The role of acyl-L-carnitine as a reservoir of activated acyl groups, the buffer function of carnitine, and the importance of the acyl-CoA/free CoA ratio in the reacylation process of erythrocyte membrane phospholipids have also been addressed. In intact erythrocytes, the incorporation of [1-14C]palmitic acid into acyl-L-carnitine, phosphatidylcholine, and phosphatidylethanolamine was linear with time for at least 3 h. The greatest proportion of the radioactivity was found in acyl-L-carnitine. Competition experiments using [1-14C]palmitic and [9,10-3H]oleic acid demonstrated that [9,10-3H]oleic acid was incorporated preferentially into the phospholipids and less into acyl-L-carnitine. When an erythrocyte suspension was incubated with [1-14C]palmitoyl-L-carnitine, radiolabeled palmitate was recovered in the phospholipid fraction, and the carnitine palmitoyltransferase inhibitor, 2-tetradecylglycidic acid, completely abolished the incorporation. ATP depletion decreased incorporation of [1-14C]palmitic and/or [9,10-3H]oleic acid into acyl-L-carnitine, but the incorporation into phosphatidylcholine and phosphatidylethanolamine was unaffected. In contrast, ATP depletion enhanced the incorporation into phosphatidylcholine and phosphatidylethanolamine of the radiolabeled fatty acid from [1-14C]palmitoyl-L-carnitine. These data are suggestive of the existence of an acyl-L-carnitine pool, in equilibrium with the acyl-CoA pool, which serves as a reservoir of activated acyl groups. The carnitine palmitoyltransferase inhibition by 2-tetradecylglycidic acid or palmitoyl-D-carnitine caused a significant reduction of radiolabeled fatty acid incorporation into membrane phospholipids, only when intact erythrocytes were incubated with [9,10-3H]oleic acid. These latter data may be explained by the differences in rates and substrates specificities between acyl-CoA synthetase and the reacylating enzymes for palmitate and oleate, which support the importance of carnitine palmitoyltransferase in modulating the optimal acyl-CoA/free CoA ratio for the physiological expression of the membrane phospholipids fatty acid turnover.     

Lipid composition of liver peroxisomes isolated from untreated and clofibrate-treated mice and rats

Peroxisomes were isolated from liver tissue of control and clofibrate-treated adult male NMRI mice and Sprague-Dawley rats. Phospholipids, cholesterol, triglycerides and free fatty acids were measured in the peroxisomes. The fatty acid profiles of the phosphatidylethanolamine, the phosphatidylcholine, the triglyceride and the free fatty acid fractions were also analyzed. Phosphatidylethanolamine was the dominating phospholipid in peroxisomes from untreated animals. The fatty acid profiles of phosphatidylethanolamine, free fatty acids and triglycerides were similar for untreated mice and rats but differences between the species were observed in the pattern derived from phosphatidylcholine. Phosphatidylcholine was the most abundant phospholipid after clofibrate treatment. Clofibrate treatment caused an increase in the concentrations of phospholipids and unsaturated long-chain fatty acids and a decrease in the concentrations of triglycerides, free fatty acids, cholesterol and shorter saturated fatty acids.     

t-Butyl hydroperoxide alters fatty acid incorporation into erythrocyte membrane phospholipid

Because the ability of cells to replace oxidized fatty acids in membrane phospholipids via deacylation and reacylation in situ may be an important determinant of the ability of cells to tolerate oxidative stress, incorporation of exogenous fatty acid into phospholipid by human erythrocytes has been examined following exposure of the cells to t-butyl hydroperoxide. Exposure of human erythrocytes to t-butyl hydroperoxide (0.5-1.0 mM) results in oxidation of glutathione, formation of malonyldialdehyde, and oxidation of hemoglobin to methemoglobin. Under these conditions, incorporation of exogenous [9,10-3H]oleic acid into phosphatidylethanolamine is enhanced while incorporation of [9,10-3H]oleic acid into phosphatidylcholine is decreased. These effects of t-butyl hydroperoxide on [9,10-3H]oleic acid incorporation are not affected by dissipating transmembrane gradients for calcium and potassium. When malonyldialdehyde production is inhibited by addition of ascorbic acid, t-butyl hydroperoxide still decreases [9,10-3H]oleic acid incorporation into phosphatidylcholine but no stimulation of [9,10-3H]oleic acid incorporation into phosphatidylethanolamine occurs. In cells pre-treated with NaNO2 to convert hemoglobin to methemoglobin, t-butyl hydroperoxide reduces [9,10-3H]oleic acid incorporation into phosphatidylcholine by erythrocytes but does not stimulate [9,10-3H]oleic acid incorporation into phosphatidylethanolamine. Under these conditions oxidation of erythrocyte glutathione and formation of malonyldialdehyde still occur. These results indicate that membrane phospholipid fatty acid turnover is altered under conditions where peroxidation of membrane phospholipid fatty acids occurs and suggest that the oxidation state of hemoglobin influences this response.     

Dietary control of triglyceride and phospholipid synthesis in rat liver slices.

1. The effect of dietary manipulation on the synthesis of triglycerides and phospholipids was investigated by determining the incorporation of labeled long-chain fatty acid or glycerol into these lipids in liver slices derived from normally fed, fasted, and fat-free refed rats. 2. Triglyceride synthesis was affected markedly by the dietary regime of the animal; the lowest rates were measured with fasted rats, and the highest ones with fat-free refed rats. 3. In contrast to triglyceride synthesis, phospholipid synthesis occured at virtually constant rates regardless of the dietary conditions. 4. Addition of large amounts of fatty acid to the incubation mixture resulted in a marked stimulation of triglyceride synthesis, whereas phospholipid synthesis was affected to a much smaller extent. 5. These results indicate that the synthesis of triglycerides and that of phospholipids are controlled independently, and that the availability of fatty acid in the cell contributes to the control of triglyceride synthesis.     

Effect of propionyl-L-carnitine treatment on membrane phospholipid fatty acid turnover in diabetic rat erythrocytes

In this work we have examined the effect of the oral administration of propionyl-L-carnitine (PLC) on the membrane phospholipid fatty acid turnover of erythrocytes from streptozotocin-induced diabetic rats. A statistically significant reduction in radioactive palmitate, oleate, and linoleate, but not arachidonate, incorporation into membrane phosphatidylcholine (PC) of diabetic rat erythrocytes with respect to control animals was found. Changes in radioactive fatty acid incorporation were also found in diabetic red cell phosphatidylethanolamine (PE), though they were not statistically significant. Oral propionyl-L-carnitine (PLC) treatment of diabetic rats partially restored the ability of intact red cells to reacylate membrane PC with palmitate and oleate, and reacylation with linoleate was fully restored. The analysis of the membrane phospholipid fatty acid composition revealed a consistent increase of linoleate levels in diabetic rat red cells, and a modest decrease of palmitate, oleate and arachidonate. The phospholipid fatty acid composition of diabetic red blood cells was not affected by the PLC treatment. Lysophosphatidylcholine acyl-CoA transferase (LAT) specific activity measured with either palmitoyl-CoA or oleyl-CoA was significantly reduced in diabetic erythrocyte membranes in comparison to controls. In addition LAT kinetic parameters of diabetic erythrocytes were altered. The reduced LAT activity could be partially corrected by PLC treatment of diabetic rats. Our data suggest that the impaired erythrocyte membrane physiological expression induced by the diabetic disease may be attenuated by the beneficial activity of PLC on the red cell membrane phospholipid fatty acid turnover.Abbreviations LAT lysophosphatidylcholine acyl-CoA transferase - PC phosphatidylcholine - PE phosphatidylethanolamine - PLC propionyl-L-carnitine - STZ streptozotocin     

Preferential incorporation of eicosanoid precursor fatty acids into human umbilical vein endothelial cell phospholipids

We have examined the preferential incorporation of specific fatty acids into phospholipid classes of cultured human umbilical vein endothelial cells. Pulse-labeling of human umbilical vein endothelial cell phospholipids with radiolabeled fatty acids and inhibition of radiolabeled fatty acid incorporation by competition with excess, unlabeled fatty acids in pair-wise combinations revealed two distinct classes of esterification systems into human umbilical vein endothelial cell phospholipids. The eicosanoid precursor fatty acids, including arachidonate, 8,11,14-eicosatrienoate (ETA) and 5,8,11,14,17-eicosapentaenoate (EPA), exhibited high affinity incorporation into total phospholipids, whereas other fatty acids, including docosahexaenoate and monohydroxy eicosatetraenoates, showed low affinity incorporation. The relative degree of incorporation of eicosanoid precursor fatty acids into phospholipid classes was phosphatidylcholine (PC) greater than phosphatidylethanolamine (PE) greater than phosphatidylinositol (PI) greater than phosphatidylserine (PS). The specific activity of [14C]arachidonic acid-labeled PI was two times higher than that of any other radiolabeled phospholipids. When competitive incorporation of eicosanoid precursor fatty acids into phospholipid classes was studied, they were found to be acylated into different phospholipid classes at different rates. Although eicosanoid precursor fatty acids were not preferentially incorporated into PC, arachidonic acid was preferentially incorporated into the other phospholipids and exhibited particular selectivity in comparison with the other eicosanoid precursor fatty acids for incorporation into PI. These results demonstrate that human umbilical vein endothelial cells possess selective incorporation mechanisms for specific fatty acids into various phospholipids via the deacylation-reacylation pathway.     

Fatty acid composition and incorporation of arachidonic acid into phospholipids of hemocytes from the tobacco hornworm Manduca sexta

The fatty acid compositions were determined for total lipids, triacylglycerols, phospholipids and four phospholipid fractions, including phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine/phosphatidylinositol (PS/PI) and cardiolipin (CA) obtained from hemocytes and cell-free serum from second day, fifth instar larvae of the tobacco hornworm Manduca sexta and the standard Manduca rearing medium. The hemocyte fatty acid profiles were considerably different from the profiles of the medium the insects were reared on and from the profiles of the cell-free serum. Hemocyte neutral lipids had lower proportions of polyunsaturated fatty acids than phospholipids. The fatty acid profiles of PC, PE, PS/PI and CA differ from each other and from the total lipid profiles, indicating selective fatty acid incorporation into hemocyte phospholipid species. Studies with radioactive arachidonic acid similarly indicated selective incorporation of polyunsaturated fatty acids into hemocyte lipids. Under our in vitro conditions, >40% of the total radioactivity was incorporated into hemocyte lipids. About 93% of the incorporated radioactivity was found in phospholipids. Within phospholipids. most of the radioactivity was associated with PC (46%), and less with PE (28%) and PS/PI (21%). Very little radioactivity was recovered in CA (0.9%).     

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.     

Involvement of phospholipids in triglyceride biosynthesis by developing soybean cotyledons

The incorporation of phospholipids specifically labeled with glycerol-2³H and acyl-¹⁴C by whole cell tissues of developing soybean cotyledons (Glycine max L.) reveals that phosphatidylinositol, phosphatidylcholine, phosphatidylethanolamine, N-acylphosphatidylethanolamine, and phosphatidic acid can be metabolized to diglyceride. The diglyceride formed may be recylced into phospholipid or acylated to triglyceride. Diglyceride from phosphatidic acid and phosphatidylethanolamine is used readily in triglyceride biosynthesis compared to the other phospholipids. Incorporation of N-acylphosphatidylethanolamine having [9-10-³H(N)]oleic acid esterified at sn-3 in cotyledons shows rapid acyltransfer of ³H into triglyceride and therefore N-acylphosphatidylethanolamine appears to participate in triglyceride biosynthesis as an acyl donor. These studies emphasize phospholipid metabolism in developing soybean cotyledons is a dynamic process which plays a key role in triglyceride formation.     

Pathways for the incorporation of exogenous fatty acids into phosphatidylethanolamine in Escherichia coli

Two distinct pathways for the incorporation of exogenous fatty acids into phospholipids were identified in Escherichia coli. The predominant route originates with the activation of fatty acids by acyl-CoA synthetase followed by the distribution of the acyl moieties into all phospholipid classes via the sn-glycerol-3-phosphate acyltransferase reaction. This pathway was blocked in mutants (fadD) lacking acyl-CoA synthetase activity. In fadD strains, exogenous fatty acids were introduced exclusively into the 1-position of phosphatidylethanolamine. This secondary route is related to 1-position fatty acid turnover in phosphatidylethanolamine and proceeds via the acyl-acyl carrier protein synthetase/2-acylglycerophosphoethanolamine acyltransferase system. The turnover pathway exhibited a preference for saturated fatty acids, whereas the acyl-CoA synthetase-dependent pathway was less discriminating. Both pathways were inhibited in mutants (fadL) lacking the fatty acid permease, demonstrating that the fadL gene product translocates exogenous fatty acids to an intracellular pool accessible to both synthetases. These data demonstrate that acyl-CoA synthetase is not required for fatty acid transport in E. coli and that the metabolism of exogenous fatty acids is segregated from the metabolism of acyl-acyl carrier proteins derived from fatty acid biosynthesis.     

Microbial Assimilation of Hydrocarbons: Phospholipid Metabolism

An analysis of the turnover of the major phospholipids of Micrococcus cerificans growing or nongrowing cultures. The turnover rates of (14)C-PE and (14)C-PE were 61.5% of the total phospholipid, exhibited no significant rate of turnover in either growing or nongrowing cultures. The turnover rates of PE-(14)C and PE-(32)P were 3.2% per hr and 1.2% per hr, respectively. Phosphatidylglycerol (PG) exhibited a turnover rate of 11% and 7.7% per hr for (14)C and (32)P, respectively, indicating an extremely slow metabolism. PG metabolism was examined in greater detail, and the data indicated a preferential 75% incorporation of glycerol-1,3-(14)C into the unacylated portion of the PG molecule. The turnover of cardiolipin (CL) was extremely slow in growing cells whereas nongrowing cells exhibited a 30% and 36% increase per hr for (14)C-Cl and (14)C-CL, respectively. Glycerol-1,3-(14)C was not converted to phospholipid fatty acid carbon; all radioactivity appeared only in the water-soluble backbone of the phospholipids. The kinetics of assimilation of hexadecane-1-(14)C into cellular lipids is presented. Radioactivity in neutral lipid increased approximately sevenfold over the growth cycle, whereas radioactivity in phospholipid increased 50-fold during the same time period. The incorporation of radioactive fatty acids derived from the direct oxidation of hexadecane-1-(14)C demonstrated differential kinetics of assimilation into PE, PG, and CL. The results indicated a rapid turnover of phospholipid fatty acids in M. cerificans growing at the expense of hexadecane.     

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.     

The effect of corticotropin on phospholipid metabolism in isolated adrenocortical cells.

Trypsin-dispersed cat adrenocortical cells were incubated at 37 degrees C in modified Eagle's medium containing [14C]arachidonic acid of sodium [14C]-acetate and then in non-radioactive medium. Radioactive incorporation was obtained in all phospholipids, with the greatest amount of radioactivity in phosphatidylcholine, followed by phosphatidylethanolamine, phosphatidyl-serine, and phosphatidylinositol. Concentrations of individual phospholipids generally paralleled the relative amounts of corresponding radiolabeled phospholipids, although the percentage of phosphatidylinositol was considerably lower than its radioactive counterpart, resulting in a high specific activity of this particular phospholipid. Although a potently steroidogenic concentration of corticotropin failed to enhance release of label from any particular phospholipid, analysis of specific activity showed that corticotropin stimulation was accompanied by an increased turnover of phosphatidylinositol and phosphatidic acid. These studies demonstrate that isolated cortical cells have the capacity to synthesize phospholipids from radioactive precursors. The finding that the acute effects of corticotropin are associated with changes in specific phospholipids, including phosphatidylinositol and phosphatidic acid, conforms to the general pattern observed in other secretory systems.     

Effects of Short- and Long-Term Protriptyline Treatment on Phospholipid Metabolism in Rat Brain

Wistar rats were injected intraperitoneally with 10 mg/kg of protriptyline according to one of the following schedules: a single dose or daily for 4 days (short-term), or daily for 2 or 13 weeks (long-term). Total lipid, total phospholipid, and individual phospholipid contents in the brain were determined. Further, the incorporation of 32P into individual phospholipids in vivo and the fatty acid composition of phosphatidylethanolamine in the brains of rats treated with protriptyline for 13 weeks were studied. Three alternative phases of changes of total and individual phospholipid contents in the brain during 13 weeks of experimentation were distinguished. An increase of phospholipid contents after 4 days, a decrease after 2 weeks, and a further increase after 13 weeks of protriptyline administration were found. However, phosphatidylinositol and phosphatidic acid levels after 13 weeks of protriptyline administration were diminished. The decrease of specific radioactivity of phosphatidylethanolamine, phosphatidylcholine, and phosphatidylserine and the increase of phosphatidylinositol, phosphatidic acid, and sphingomyelin in rats treated with the drug for a longer period of time were noted. No greater differences in fatty acid composition of phosphatidylethanolamine in the brains of the same group of rats were observed as compared to control. These results indicate that during long-term treatment with protriptyline the contents of lipids and phospholipids in rat brain are altered. The modification of the biological function of phospholipids in brain cell membranes is suggested.     

Palmitoyl-L-carnitine, a metabolic intermediate of the fatty acid incorporation pathway in erythrocyte membrane phospholipids

In this paper we report that palmitoyl-L-carnitine can be a metabolic intermediate of the fatty acid incorporation pathway into erythrocyte membrane phosphatidylcholine, and phosphatidylethanolamine. Phospholipid acylation was evaluated by measuring the incorporation of radioactive [1-14C]-palmitoyl-L-carnitine in membrane erythrocyte ghost phospholipids in the presence or absence of CoA. CoA highly stimulated the incorporation of [1-14C]-palmitic acid into both the phospholipids examined, although the incorporation was also evident in the absence of added CoA. Incorporation of [1-14C]-palmitic acid into phosphatidylcholine was greater than into phosphatidylethanolamine. 2-Bromo-palmitoyl-CoA, an irreversible inhibitor of the erythrocyte carnitine palmitoyltransferase, inhibited the acylation process.     

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.