Definition of the pathway for membrane phospholipid fatty acid turnover in human erythrocytes

Influence of a hyperlipidic diet on the composition of the non-membrane lipid pool of red blood cells of male and female rats

Background and objectives. Red blood cells (RBC) are continuously exposed to oxidative agents, affecting their membrane lipid function. However, the amount of lipid in RBCs is higher than the lipids of the cell membrane, and includes triacylglycerols, which are no membrane components. We assumed that the extra lipids originated from lipoproteins attached to the cell surface, and we intended to analyse whether the size and composition of this lipid pool were affected by sex or diet. Experimental design. Adult male and female Wistar rats were fed control or cafeteria diets. Packed blood cells and plasma lipids were extracted and analysed for fatty acids by methylation and GC-MS, taking care of not extracting membrane lipids. Results. The absence of ω3-PUFA in RBC extracts (but not in plasma) suggest that the lipids extracted were essentially those in the postulated lipid surface pool and not those in cell membrane. In cells' extracts, there was a marked depletion of PUFA (and, in general, of insaturation). Fatty acid patterns were similar for all groups studied, with limited effects of sex and no effects of diet in RBC (but not in plasma) fatty acids. Presence of trans fatty acids was small but higher in RBC lipids, and could not be justified by dietary sources. Conclusions. The presence of a small layer of lipid on the RBC surface may limit oxidative damage to the cell outer structures, and help explain its role in the transport of lipophilic compounds. However, there may be other, so far uncovered, additional functions for this lipid pool.

Analytical investigation of bilayer lipid biosensor based on graphene

Graphene is another allotrope of carbon with two-dimensional monolayer honeycomb. Owing to its special characteristics including electrical, physical and optical properties, graphene is known as a more suitable candidate compared to other materials to be used in the sensor application. It is possible, moreover, to use biosensor by using electrolyte-gated field effect transistor based on graphene (GFET) to identify the alterations in charged lipid membrane properties. The current article aims to show how thickness and charges of a membrane electric can result in a monolayer graphene-based GFET while the emphasis is on the conductance variation. It is proposed that the thickness and electric charge of the lipid bilayer (LLP and QLP) are functions of carrier density, and to find the equation relating these suitable control parameters are introduced. Artificial neural network algorithm as well as support vector regression has also been incorporated to obtain other models for conductance characteristic. The results comparison between analytical models, artificial neural network and support vector regression with the experimental data extracted from previous work show an acceptable agreement.

A 'soft spot' for drug transport: modulation of cell stiffness using fatty acids and its impact on drug transport in lung model

The impact of a polyunsaturated fatty acid, arachidonic acid (AA), on membrane fluidity of epithelial cells and subsequent modulation of the drug transport was investigated. Membrane fluidity was assessed using molecular force microscopy. Calu-3 human bronchial epithelial cells were cultured on Transwell® inserts and the cell stiffness was assessed in the absence of fatty acids or in the presence of 30 μM AA. The morphology of the epithelial cells was distinctly different when AA was present, with the cell monolayer becoming more uniform. Furthermore the cell stiffness and variation in stiffness was lower in the presence of AA. In the fat-free medium, the median cell stiffness was 9.1 kPa which dropped to 2.1 kPa following exposure to AA. To further study this, transport of a common β2-agonist, salbutamol sulphate (SS) was measured in the presence of AA and in a fat free medium. The transport of SS was significantly higher when AA was present (0.61 ± 0.09 μg versus 0.11 ± 0.003 μg with and without AA respectively). It was evidenced that AA play a vital role in cell membrane fluidity and drug transport. This finding highlights the significance of the dietary fatty acids in transport and consequentially effectiveness of medications used to treat pulmonary diseases such as asthma.

Separation of intact plasmalogens and all other phospholipids by a single run of high-performance liquid chromatography

Plasmalogens are a unique subclass of glycerophospholipids characterized by the presence of a vinyl ether bond at the sn-1 position of the glycerol backbone, and they are found in high concentration in cellular membranes of many mammalian tissues. However, separation of plasmalogens as intact phospholipids has not been reported. This article describes a high-performance liquid chromatographic method that can separate intact ethanolamine plasmalogens (pl-PEs) and choline plasmalogens (pl-PCs) as well as all other phospholipid classes usually found in mammalian tissues by a single chromatographic run. The separation was obtained using an HPLC diol column and a gradient of a hexane/isopropanol/water system containing 1% acetic acid and 0.08% triethylamine. The HPLC method allowed a clear separation of plasmalogens from their diacyl analogues. The HPLC method, as applied to the study of peroxidation in human erythrocytes by a hydroperoxide, demonstrated that pl-PEs were targeted twice as much as their diacyl analogues.

The cell membrane as a biosensor of oxidative stress induced by radiation exposure: a multiparameter investigation

The role of biological membranes as a target in biological radiation damage remains unclear. The present study investigates how the biochemical and biophysical properties of a simple biological model, i.e. human erythrocyte membranes, are altered after exposure to relatively low doses of (60)Co gamma rays. Lipid peroxidation increased in the hours after radiation exposure, based on measurements of MDA and on the lipid peroxidation index after parinaric acid incorporation. Protein carbonyl content also increased rapidly after radiation exposure. An imbalance between the radiation-mediated oxidative damages and the antioxidant capacity of the erythrocytes was observed in the hours after radiation exposure. Antioxidant enzyme activities, mainly catalase and glutathione peroxidase, were found to decrease after irradiation. The development of a radiation-induced oxidative stress probably explains the reorganization of the fatty acid pattern 72 h after radiation exposure. The phosphatidylethanolamine (PE) fatty acids of the (n-3) and (n-6) series decreased, while the PE saturated fatty acid content increased. All these modifications may be involved in the variation of the biophysical properties of the membranes that we noted after radiation exposure. Specifically, we observed that the lipid compartment of the membrane became more fluid while the lipid-protein membrane interface became more rigid. Taken together, these findings reinforce our understanding that the cell membrane is a significant biological target of radiation. Thus the role of the biological membrane in the expression and course of cell damage after radiation exposure must be considered.

Differential in vitro effects of ethanol on glycerolipid acylation and biosynthesis in rat reticulocytes

Earlier reports have shown that, in human and rat red blood cells (RBC), ethanol modulates acylation reaction sin several membrane glycerolipid components. Little is known, however, about the kinetics and the mechanisms involved in the acylation changes. In the present study, we show that short-term in vitro exposure of intact rat reticulocytes to ethanol differentially modifies within minutes the incorporation of [3H]oleic acid in glycerolipids. A concentration-dependent inhibition of acyl incorporation was measured in phosphatidylcholine (PC) and phosphatidylethanolamine (PE). This effect did not involve inhibition of the corresponding acyltransferase activities and is likely to be due to ethanol-dependent decreases in phospholipase activities. In contrast, ethanol markedly stimulated [3H]oleic acid incorporation in phosphatidic acid (PA), diacylglycerol (DG) and, to a lesser extent, in triacylglycerol (TG). To determine the mechanisms of the latter increases, reticulocytes were pulsed with [14C]glycerol and assayed as a function of time for labeled biosynthetic precursors and products. We observed a very close correlation between time courses and amplitudes of the ethanol stimulation of acylation and biosynthesis reactions, suggesting that stimulation of acylation in PA, DG and TG is causally related at least partly to their increased biosynthesis. Further studies revealed that increases in glycerolipid acylation and biosynthesis in reticulocytes were: (a) readily reversible upon ethanol withdrawal; (b) detectable for clinically relevant concentration (50 mM) of ethanol; and (c) associated with concomitant increases in cell resistance to hemolysis. These changes may be relevant to the development of tolerance to ethanol.

Studies on the extraction of phospholipids from erythrocyte membranes in the rat

The effects of choice of solvent and period of extraction on recovery of phospholipid classes extracted from rat erythrocyte membranes were investigated. For extraction of phosphatidylserine (PS) the best recovery was achieved using chloroform-methanol (2:1, v/v), for diacyl phosphatidylethanolamine (PE) acetone-isopropanol (3:2, v/v), and for extraction of plasmalogen PE, phosphatidylcholine (PC) and sphingomyelin (SM) using hexane-isopropanol (3:2, v/v). Using hexane-isopropanol (3:2, v/v), boiling during the extraction increased the recovery of some of the individual phospholipid classes whereas mechanical treatment of the sample had only a slight effect. Furthermore, the fatty acid composition of PS and PE varied most with different extraction conditions and the phospholipid classes PC and SM were extracted more readily from rat erythrocyte membranes than PS, diacyl and plasmalogen PE.

Changes in plasma and erythrocyte fatty acids in patients fed enteral formulas containing different fats

Critically ill hospital patients were fed enteral formulas containing different fat substrates. Seven patients received formula X, which contained 28 g of structured triglycerides and menhaden oil to provide 7.6 g of medium-chain fatty acids, 2.5 g linoleic acid, 1.3 g eicosapentaenoic acid, and 0.4 g docosahexaenoic acid per 1000 mL of formula. Six patients received formula Y consisting of 36.8 g of medium-chain triglycerides and corn and soy oils providing 14.3 g medium-chain fatty acids and 11.7 g linoleic acid per 1000 mL. Feeding of formula X increased plasma total phospholipid levels of eicosapentaenoic acid on days 7 and 14 and docosahexaenoic acid levels on day 14. Plasma levels of linoleic acid were reduced in formula-X-fed in comparison to formula-Y-fed patients, whereas arachidonic acid was maintained in both groups during feeding. As a result of these changes, the patients receiving formula X had decreased ratios of arachidonic acid:eicosapentaenoic acid in plasma. Formula Y feeding did not alter eicosapentaenoic acid and docosahexaenoic acid levels in the plasma. In the erythrocyte, formula X feeding resulted in a threefold increase in eicosapentaenoic acid from mean baseline levels of 0.4 +/- 0.4% to a mean value of 1.2 +/- 0.9% at day 7. The formula X feeding decreased linoleic acid levels on days 7 and 14, whereas levels of arachidonic acid and docosahexaenoic acid remained constant. Formula Y feeding did not affect any of the parameters measured for erythrocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes of membrane phospholipid composition of human erythrocytes in hyperlipidemias. II. Increases in distinct molecular species of phosphatidylethanolamine and phosphatidylcholine containing arachidonic acid

The molecular species composition of red blood cell diacyl-phosphatidylcholine (PC), diacyl-phosphatidylethanolamine (PE) and alkenylacyl-PE (plasmalogen PE) has been analyzed in normolipidemic and hyperlipidemic donors. In all three phospholipid subclasses the percentages of the species 16:0/20:4 were increased in hyperlipidemic patients. In diacyl-PE, 18:1/20:4 was also elevated. No changes were observed in the other quantitatively important molecular species containing arachidonic acid at sn-2, namely 18:0/20:4. The rise in 16:0/20:4 in diacyl-PC and diacyl-PE of hyperlipidemic donors was accompanied by a fall in molecular species with linoleic acid (18:2) at sn-2 (in particular 18:1/18:2). In alkenylacyl-PE the elevation of 16:0/20:4 was compensated by a decrease in species with docosatetraenoic acid (22:4) at sn-2 in particular by a fall in 16:0/22:4. Among all donors, the percentages of 16:0/20:4 in diacyl-PC and PE were positively associated with plasma total cholesterol levels. The changes in molecular species composition of PC and PE in hyperlipidemia are expected to alter the function of erythrocyte membrane transport proteins and--if present also in other cell types--to affect eicosanoid metabolism.

Acyl-trafficking in membrane phospholipid fatty acid turnover: the transfer of fatty acid from the acyl-L-carnitine pool to membrane phospholipids in intact human erythrocytes

In this work we have investigated the transfer of radioactive palmitic acid between membrane phospholipids and acyl-L-carnitines in intact human erythrocytes. During the incubation period of labeled erythrocyte in non-defatted bovine serum albumin, radioactivity in phosphatidylcholine and phosphatidylethanolamine increased. On the contrary, a decrease of radioactivity in erythrocyte palmitoyl-L-carnitine was observed. 2-Tetradecylglycidic acid, an irreversible erythrocyte carnitine palmitoyltransferase inhibitor, abolished any radioactivity changes in both phospholipids and palmitoyl-L-carnitine. Similar findings were obtained by using erythrocytes labeled with radioactive oleic acid. Our data suggest that in human erythrocytes a carnitine palmitoyltransferase-catalyzed acyl transfer from acyl-L-carnitine to phospholipids, rather than a previously described fatty acid transfer from phosphatidylcholine to phosphatidylethanolamine, is operative.

The effect of dietary zinc deficiency on the lipid composition of the rat erythrocyte membrane

The effect of dietary zinc deficiency in the rat on the lipid composition of the erythrocyte membrane was determined. Weanling male Wistar rats were fed an egg white-based diet containing less than 1.0 mg Zn/kg diet ad libitum. Control rats were either pair-fed or ad libitum-fed the basal diet supplemented with 100 mg Zn/kg diet. A zinc refed group was fed the -Zn diet until day 18 and then pair-fed the +Zn diet until day 21. The voluntary feed restriction associated with dietary zinc deficiency resulted in erythrocyte membranes that had depressed phospholipid/protein and elevated cholesterol/phospholipid ratios. Similarly, all feed restricted groups had elevated 22-carbon n-3 polyunsaturated fatty acids (PUFA) and depressed 22-carbon n-6 PUFA concentrations in alkenyl-acyl and diacyl glycerophosphoethanolamine, phosphatidylserine and phosphatidylcholine; they also had depressed 24:2n-6 levels in sphingomyelin. The relative concentrations of phospholipids in the membrane was similar between -Zn and +Zn (ad libitum) groups; however, the -Zn group had significantly less phosphatidyl-serine relative to +Zn (pair-fed) controls.

Fast translocation of phosphatidylcholine to the outer membrane leaflet after its synthesis at the inner membrane surface in human erythrocytes

The translocation rate of [14C]phosphatidylcholine to the outer membrane leaflet of human erythrocytes after its primary synthesis from lysophosphatidylcholine by acylation with 14C-labeled oleic or palmitic acid in the inner leaflet has been measured by following the time-dependent increase of cleavability of 14C-labeled phospholipids by external phospholipase A2 (5 min, 37 degrees C). Immediately after a short acylation time period of 10 min about 20% of the newly synthesized [14C]phosphatidylcholine are already detectable in the outer leaflet. After an incubation of 1 h at 37 degrees C following 10 min of acylation the fractions of labeled and native phosphatidylcholine accessible to the lipase are identical, which demonstrates that [14C]phosphatidylcholine has attained the same asymmetric distribution as its endogenous analogue. The calculated halftime of the outward translocation is about 20 min and its activation energy is low, 30 kJ/mol. Translocation is inhibited by a 5 min treatment with phenylglyoxal following acylation. A fast translocation is not observed for newly synthesized phosphatidylethanolamine. Results suggest a selective, protein-mediated outward translocation of newly synthesized phosphatidylcholine.

Inhibition of arachidonic acid incorporation into erythrocyte phospholipids by peracetic acid and other peroxides. Role of arachidonoyl-CoA: 1-palmitoyl-sn-glycero-3-phosphocholine acyl transferase

To explore possible mechanisms of the arachidonic acid deficiency of the red blood cell membrane in alcoholics, we compared the effect of ethanol and its oxidized products, acetaldehyde and peracetic acid, with other peroxides on the accumulation of [14C]arachidonate into RBC membrane lipids in vitro. Incubation of erythrocytes with 50 mM ethanol or 3 mM acetaldehyde had no effect on arachidonate incorporation. Pretreatment of erythrocytes with 10 mM hydrogen peroxide, 0.1 mM cumene hydroperoxide or 0.1 mM t-butyl hydroperoxide had little effect on [14C]arachidonate incorporation in the absence of azide. However, pretreatment of cells with N-ethylmaleimide, 0.1 mM peracetic acid or performic acid, with or without azide, inhibited arachidonate incorporation into phospholipids but not neutral lipids. In chase experiments, peracetate also inhibited transfer of arachidonate from neutral lipids to phospholipids. To investigate a possible site of this inhibition of arachidonate transfer into phospholipids by percarboxylic acids, we assayed a repair enzyme, arachidonoyl CoA: 1-palmitoyl-sn-glycero-3-phosphocholine acyl transferase (EC 2.3.1.23). As in intact cells, phospholipid biosynthesis was inhibited more by N-ethylmalemide and peracetic acid than by hydrogen peroxide, cumene hydroperoxide, and t-butyl hydroperoxide. Peracetic acid was the only active inhibitor among ethanol and its oxidized products studied and may deserve further examination in ethanol toxicity.

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.

Erythrocyte membrane lipid alterations in undernourished cerebral palsied children during high intakes of a soy oil-based enteral formula

Five undernourished children with severe cerebral palsy (CP) were tube-fed sufficient volumes of Isocal to allow rapid weight gain. Isocal provided, on average, 88% of their daily energy intake for at least 25 days. The purpose of our study was to correct the undernutrition and to analyze the major erythrocyte phospholipids before and after feeding periods for possible feeding and disease-related differences. The fatty acid profiles of erythrocyte membranes from CP children were compared with those from 12 healthy children and with the fatty acid composition of the formula. There were no clinical or biochemical indications of essential fatty acid deficiency. The feeding of a soy oil-based formula increased the proportions of 18:2n-6 in the phospholipids. The increases occurred predominantly in phosphatidylcholine followed by phosphatidylethanolamine. Despite such large dietary intakes of soy oil, no changes were observed in the phospholipid concentrations of 20:4n-6, 18:3n-3, 20:5n-3, or in the C22n-6 and C22n-3 fatty acids. These findings are consistent with an inhibition of the delta 6 desaturase by high dietary linoleate.

In vitro kinetics of the oxidative reactivity of nitrate and nitrite in the rat erythrocyte

Isolated rat erythrocytes were incubated in the presence of nitrate and nitrite. Glucose, lactate, reduced glutathione, methaemoglobin, malondialdehyde and Na+/K+ membrane exchange were investigated. Nitrite induced a strong methaemoglobinaemia and a net depletion of reduced glutathione in the intracellular medium associated with membrane lipid peroxidation. This oxidative reactivity induced by nitrate and nitrite altered the cell's ionic flux.

Translocation of oleic acid across the erythrocyte membrane. Evidence for a fast process

To clarify divergent views concerning the mechanism of fatty acid translocation across biomembranes this issue was now investigated in human erythrocytes. Translocation rates of exogenously inserted radioactive oleic acid across the membrane of native cells were derived from the time-dependent increase of the fraction of radioactivity becoming non-extractable by albumin. No accumulation of non-extractable unesterified oleic acid occurred. The rate of transfer was markedly suppressed by SH-reagents and by ATP-depletion. The suppression, however, resulted from a mere decrease of incorporation of oleic acid into phospholipids and was not accompanied by an increase of non-extractable unesterified oleic acid. These findings were reconcilable with the concept of a slow, possibly carrier-mediated fatty acid transfer as well as a very fast presumably, diffusional process not resolvable by the albumin extraction procedure. This ambiguity was resolved by using resealed ghosts, which are unable to incorporate oleic acid into phospholipids. In such ghosts all of the oleic acid inserted into the membrane remains extractable by albumin even after prolonged incubation. On the other hand, ghosts containing albumin accumulated non-extractable oleic acid. The rate of accumulation was beyond the time resolution of the albumin extraction procedure at 4 degrees C. Oleic acid uptake into albumin-containing ghosts became kinetically resolvable when the fatty acid was added as a complex with albumin. Correspondingly, time-resolvable release of oleic acid, originally complexed to internal albumin, into an albumin-containing medium was demonstrated at 4 degrees C. Rate and extent of these redistributions of oleic acid were dependent on the concentrations of internal and external albumin. This indicates limitation by the dissociation of oleic acid from albumin and not its translocation across the membrane. Translocation of oleic acid, which is probably a simple diffusive flip-flop process, must therefore occur with a half-time of less than 15 s. These findings raise doubts on the physiological role of presently discussed concepts of a carrier-mediated translocation of fatty acids across plasma membranes.

Polyunsaturated fatty acids, prostaglandins, and schizophrenia

Psychotic disorders, particularly schizophrenia, are associated with clinical phenomena that can be explained by disturbances in polyunsaturated fatty acid and prostaglandin metabolism. Previous studies of PUFA, PG synthesis, PGE1 receptor activity and aggregation responses in platelets, and clinical treatment trials suggest a role for PGE in the pathophysiology of schizophrenia. Since a decrease in PGE1 activity can be associated with an increase of dopamine release, a deficiency of PGE1 is consistent with the dopamine hypothesis of schizophrenia. State-of-the-art assay and clinical trial methodology should clarify the role of PUFA metabolism in schizophrenia.

Alteration of erythrocyte lipid composition following total parenteral nutrition in the rat

Rats were infused continuously for 7 days with a complete total parenteral nutrition (TPN) solution in which 27.5% total calories were given as a parenteral lipid emulsion containing soybean oil (Liposyn) or safflower oil (Intralipid) emulsified with egg phospholipid (PL). Compared to sham-operated rats fed chow, the erythrocyte membranes from rats given TPN with lipid emulsion had increased cholesterol and PL but normal molar cholesterol:PL ratios. The fatty acid changes in sphingomyelin and phosphatidylcholine, in particular, suggested replacement of endogenous PL with the exogenous egg PL infused with the emulsion. The changes in membrane lipid composition were accompanied by greater resistance of the cells from rats given TPN to osmotic lysis in vitro.

Effect of a hyperlipidic diet on lipid composition, fluidity, and (Na+-K+)ATPase activity of rat erythrocyte membranes

Feeding rats a hyperlipidic diet in which animals were offered daily a variety of high-energy food resulted in a significant increase of serum free fatty acids and a decrease of phospholipids with respect to controls. On the contrary, there were no significant differences in erythrocyte membrane total lipid composition between the two groups. Erythrocyte membranes showed a significant decrease in saturated fatty acid content and a significant increase in (n-6) polyunsaturated fatty acid content; (n-3) polyunsaturated fatty acids significantly decreased. Membrane fluidity, investigated by fluorescence polarization of diphenylhexatriene, significantly increased in the erythrocyte membranes of the experimental group. These results seem compatible with the decreased saturated/unsaturated fatty acid ratio. A significant decrease of (Na+-K+)ATPase activity occurred in erythrocyte membranes of the experimental group rats with respect to the controls.

Acylation and deacylation of phospholipids in isolated bovine rod outer segments

Isolated bovine rod outer segments (ROS) were incubated under different conditions with radiolabeled fatty acid-Coenzyme A (CoA) compounds, fatty acids and phospholipids in order to further investigate the rates, mechanisms and function of phospholipid metabolism within that organelle. ROS contain acyl CoA synthetase, acyl transferase, acyl CoA hydrolase, and phospholipase A activities. Although different radiolabeled fatty acid CoAs were esterified to the major ROS phospholipids (phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine) at the same rate, different free fatty acids were esterified at different rates. There was no correlation between these estimates of in vitro rates of incorporation of fatty acids and the fatty acid composition of ROS phospholipids. Both the deacylation of radiolabeled phospholipids (phospholipase A activity) and the acylation of endogenous phospholipids (acyl transferase activity) were maximally stimulated when ATP, CoA, Mg2+ and Ca2+ were present, and both processes were stimulated by pro-oxidizing conditions and exposure to light. Under phospholipase A-stimulatory conditions, there was preferential hydrolysis of polyenoic fatty acids from endogenous ROS phospholipids. Both the acylation and deacylation reactions were primarily at the sn-2 position of ROS phospholipids.

Altered acylation of erythrocyte phospholipids in alcoholism

The composition and metabolism of erythrocyte lipids were studied in 10 chronic alcoholic patients within 48 hr after discontinuation of alcohol intake and in 10 nonalcoholic control subjects. Chronic alcoholism produced no change in contents of cholesterol, total phospholipids, and proportions of phosphatidylcholine and phosphatidylethanolamine in erythrocyte phospholipids. The mean values of the rates of acylation of phosphatidylcholine and phosphatidylethanolamine with oleic acid were increased respectively by 59% (p less than 0.001) and 38% (p less than 0.05) as compared with the controls. There was no correlation between acylation rates and mean cellular volumes. Increases in acylation rates normalized over several weeks after alcohol withdrawal and were not related to a direct effect of alcohol on the intact erythrocyte, suggesting that these alterations result from ethanol-induced changes in the membrane during erythrocyte formation. The increased rates of acylation might modify the remodeling of the lipid matrix and thereby the membrane function.

Effect of hypothyroidism on the lipid composition of rat plasma and erythrocyte membranes

The effect of hypothyroidism on plasma and erythrocyte membrane lipid components has been investigated. This pathological state is accompanied by a) a cholesterol increase of about 60% in plasma, and at the same time a 22% reduction in erythrocyte membranes; b) 44% and 30% phospholipid level decreases in both plasma and red cell membranes, respectively; and c) almost unaffected phospholipid and fatty acid compositions of both plasma and erythrocyte membranes. All changes were corrected by treatment of the hypothyroid rats with triiodothyronine for two days. These findings suggest that in hypothyroid rats a reduced transfer of cholesterol from plasma to erythrocyte membrane probably takes place. This could explain, at least in part, the increased hematic cholesterol level observed in hypothyroid animals. In red cell membranes, the simultaneous decrease in cholesterol and phospholipid levels does not alter the cholesterol/phospholipid molar ratio, thus avoiding their abnormal function.

Changes in the fatty acid composition of plasma and red blood cell membrane during the first hours of life in human neonates

The objective of this work was to examine the changes in the fatty acid profiles of plasma lipid fractions and red blood cell membrane phospholipids in newborn infants during the first 6-8 h of life. Methyl esters of fatty acids from plasma free fatty acids and phospholipids and from membrane phosphatidylethanolamine, phosphatidylcholine and sphingomyelin for cord blood (n = 20) and venous blood (n = 19) were analyzed by GLC. Important changes were observed in plasma fatty acids. Palmitic and palmitoleic acid increased from birth to 6-8 h of age for both free fatty acids and phospholipids. Palmitic acid also increased in membrane phosphatidylcholine and phosphatidylethanolamine. In the former, stearic acid declined whereas oleic and docosatetraenoic acids increased. Phosphatidylethanolamine and sphingomyelin were less affected than phosphatidylcholine probably because the internal location of the two first fractions in erythrocyte membrane. Polyunsaturated fatty acids dropped slightly during the first hours of life in most lipid fractions. This may be a consequence of the interruption of placental fatty acid supply and the limited capacity of the newborn to desaturate their essential fatty acid tissue stores.

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.

Modulation of human erythrocyte shape and fatty acids by diet

A semi-synthetic diet (Vivonex) was administered via nasogastric tube to three cystic fibrosis patients with pancreatic exocrine deficiency for 14 days to gain weight. Dietary essential fatty acids were provided as safflower oil, which constituted 1.3% of total calories. Plasma and red blood cells were analyzed for the content and composition of lipids at the start of the diet and at days 7 and 14 of the dietary period, and the results were correlated with the morphology of the cells. Feeding Vivonex to the patients led to an essential fatty acid deficiency, which was manifested in a 50% decrease in the linoleic acid content of the phosphatidylcholine of plasma and red blood cells at days 7 and 14 and in a 20% decrease in the linoleic acid content of red cell phosphatidylethanolamine at day 14. There was no significant alteration in the levels or composition of the other phospholipid classes and in the free cholesterol/phospholipid ratio. The decrease in the linoleic acid content of the erythrocytes was accompanied by a dramatic increase in the proportion of cells as echinocytes. We conclude that restricted linoleic acid availability in cystic fibrosis patients causes a change in red blood cell shape either directly by decreasing the linoleoylphosphatidylcholine content of the membrane or indirectly by affecting enzyme activity.

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.

Membrane solubility of ethanol in chronic alcoholism. The effect of ethanol feeding and its withdrawal on the protection by alcohol of rat red blood cells from hypotonic hemolysis

Membranes from ethanol-fed rats are resistant to the in vitro effects of ethanol on membrane structure and function. We have proposed that the resistance arises from adaptive changes in membrane composition which lower the solubility (partition coefficient) of ethanol in these membranes. The partition of ethanol (and other alcohols and anesthetics) into red blood cells protects the cells from hypotonic hemolysis. Here, we show that the protection by alcohols and anesthetics of red blood cells from ethanol-fed rats is greatly attenuated. This finding indicates that the membrane solubility of these agents is lowered in chronic alcoholism and thus explains the resistance to the acute effects of ethanol. The protection from hemolysis decreases over 2 weeks of ethanol-feeding and returns to normal values within 1 day after ethanol withdrawal. These changes are associated with a parallel increase in total and free serum cholesterol during ethanol feeding and a return to normal values within a day after withdrawal. However, we find only a slight increase in the cholesterol/phospholipid ratio of the red blood cell membranes during the development of ethanol tolerance. In rats fed a cholesterol and saturated fat diet, the increase in serum cholesterol is also associated with an attenuation of the protection from hypotonic hemolysis.

Transport of fatty acids across the membrane of human erythrocyte ghosts

Human erythrocyte ghosts were used for studying the mechanism of uptake and membrane transport of fatty acids. Hemoglobin-free ghosts were prepared and loaded with substrates such as CoA and/or ATP, and their ability for transporting and activating radiolabelled palmitic acid was tested further. Uptake of radiolabelled palmitic acid by CoA- and ATP-loaded ghosts exceeded that observed with ghosts loaded only with ATP, the latter being greater than that measured with non-loaded ghosts. Acyl-CoA was synthesized in CoA- and ATP-loaded ghosts upon incubation with radiolabelled palmitic acid. Both CoA and ATP were needed within the ghosts to permit acyl-CoA synthesis, suggesting that the acyl-CoA synthetase is located in and is bound to the inner layer of the membrane. The rate of acyl-CoA synthesis was saturable with increasing concentration of palmitic acid in the incubation mixture, and kinetic parameters were calculated. The rate of acyl-CoA synthesis in CoA- and ATP-loaded ghosts upon incubation with radiolabelled palmitic acid was markedly decreased when increasing albumin concentration in the incubation medium up to a molar ratio albumin/fatty acid of one to one. It is not easy to distinguish experimentally fatty acids located in the outer layer and the inner layer of the membrane and the data of this paper suggest that acyl-CoA synthesis by an enzyme located in the inner layer could be used as a measure of the acyl groups which have been translocated across the membrane of erythrocyte ghosts.

Preparation of inside-out vesicles from erythrocyte membranes inactivates the pathway for oleic acid incorporation into phospholipid

The pathway for membrane phospholipid fatty acid turnover in situ may be important in the regulation of the composition and turnover of the lipid microenvironment of membrane proteins. This pathway has been characterized further by studying the activation and incorporation of [9,10(n)-3H]oleic acid and transesterification of [1-14C]oleoyl-CoA into membrane phospholipids by isolated erythrocyte membrane ghosts and inside-out vesicles derived from these ghosts. Erythrocyte ghosts and sealed vesicles of defined orientation prepared from them have been widely employed in studies of the function of membrane proteins, particularly those which mediate the transport of ions and sugars. Preparation of inside-out vesicles from ghosts by exposure to alkaline hypotonic conditions results in elution of some membrane proteins but no loss of membrane phospholipid. Compared to ghosts, the ability of inside-out vesicles to activate and incorporate [9,10(n)-3H]oleic acid into phospholipid is diminished by over 90% and the ability of inside-out vesicles to transesterify [1-14C]oleoyl-CoA to phospholipid is diminished by over 50%. These findings indicate that exposure of erythrocyte membranes to the alkaline hypotonic conditions required for inside-out vesicle preparation results in loss or inactivation of both acyl-CoA ligase and acyl-CoA-lysophospholipid acyltransferase activities. This lability of the enzymes for in situ phospholipid fatty acid turnover should be considered in the design and interpretation of studies concerned with elucidation of the relationship between phospholipid fatty acid turnover and the regulation of membrane protein function in this membrane preparation.

Composition and metabolism of fatty acids in phospholipids of density-separated red cells of rats

Fatty acid compositions of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) and the rates of fatty acid esterification to these phospholipids (PL) were measured in intact rat red cell populations of different ages separated by density gradient centrifugation in order to clarify changes in membrane lipids of red blood cells during in vivo aging. Fatty acid compositions of PC and PE altered progressively as red cells became denser. Changes in unsaturated fatty acids occurred predominantly at the 2-position of PC and PE and those in saturated fatty acids at both positions. The esterification rates of 5 major fatty acids decreased as red cells became denser and those of oleic acid, linoleic acid and arachidonic acid to both PC and PE of fraction I cells (oldest cells) were 37-51% those of fraction IV cells (youngest cells). Reduction in the rates of fatty acid esterification appeared to occur in the course of red cell maturation because reticulocyte-enriched cell fractions showed 4.5-14.5 times higher rates of linoleic acid and arachidonic acid esterifications to PC and PE.

Minireview. Roles of turnover and repair of macromolecules and supramolecular structural components

Macromolecules and supramolecular structural components that are incorrectly synthesized or are damaged by radiation or by reactive chemicals are either repaired or selectively degraded and resynthesized. In addition, turnover rates for macromolecules and supramolecular structures can be elevated by alternation of fasting and feeding periods and can be influenced by metabolic regulatory mechanisms which are governed by steady-state concentrations of labile macromolecules.

Formation of diacylglycerol and degradation of phosphatidylinositol induced in rat lymphocytes by non-esterified oleic or linoleic acid

Rat spleen lymphocytes were incubated for 3 h with [14C]arachidonic acid in foetal calf serum. It was found that arachidonic acid distributed into phospholipids in the order phosphatidylcholine greater than phosphatidylethanolamine greater than phosphatidylinositol. After labelling with arachidonic acid the lymphocytes were washed, and incubated for up to 2 h with non-radioactive palmitic, oleic or linoleic acid dissolved in ethanol. The presence of ethanol or palmitic acid during a 2 h post-incubation had little effect on the amount of radioactivity found in different lipid fractions. Both oleic acid and linoleic acid, however, brought about an accumulation (up to 8-fold) of radioactivity in the diacylglycerol fraction. These fatty acids also brought about a change of radioactivity in several phospholipids, notably in phosphatidylinositol, which lost more than 50% of its counts during the 2 h incubation. Although maximum effects were seen at 2 h, diacylglycerol radioactivity was increased by 100% within 5 min after adding the fatty acids. The minimum concentration of fatty acids used (50 microM) gave an almost maximum response. The results indicate that unsaturated fatty acids may activate phosphatidylinositol phosphodiesterase in lymphocytes, as they do in brain. The possibility that a phospholipase A is activated is discussed. Possible implications for any experiments in which cells are incubated with fatty acids are pointed out.

Acylation of lysoglycerophospholipids by adrenal membranes

1. Substantial differences were found in the acyl donor and lyso-acceptor specificities among subcellular membranes and with respect to different regions of the adrenal gland. 2. In the presence of Mg2+-ATP and CoASH, adrenal microsomes were actively transferring arachidonate to lysophospholipids with acyl acceptor specificity in the order: 1-acyl-GPI greater than 1-acyl-GPC greater than 1-acyl-GP. However, when oleoyl-CoA was used, acyl acceptor specificity for the microsomal transferases was in the order: 1-acyl-GPC greater than 1-acyl-GP greater than 1-acyl-GPI. 3. Mitochondrial membranes had very low acyl transfer activity and they preferred 1-acyl-GPC over other lyso-acceptors. 4. The chromaffin granules were apparently lacking this type of activity.