Metabolism of red-cell lipids. I. Incorporation in vitro of fatty acids into phospholipids from mature erythrocytes

Antitumor Lipids--Structure, Functions, and Medical Applications

Cell proliferation and metastasis are considered hallmarks of tumor progression. Therefore, efforts have been made to develop novel anticancer drugs that inhibit both the proliferation and the motility of tumor cells. Synthetic antitumor lipids (ATLs), which are chemically divided into two main classes, comprise (i) alkylphospholipids (APLs) and (ii) alkylphosphocholines (APCs). They represent a new entity of drugs with distinct antiproliferative properties in tumor cells. These compounds do not interfere with the DNA or mitotic spindle apparatus of the cell, instead, they incorporate into cell membranes, where they accumulate and interfere with lipid metabolism and lipid-dependent signaling pathways. Recently, it has been shown that the most commonly studied APLs inhibit proliferation by inducing apoptosis in malignant cells while leaving normal cells unaffected and are potent sensitizers of conventional chemo- and radiotherapy, as well as of electrical field therapy. APLs resist catabolic degradation to a large extent, therefore accumulate in the cell and interfere with lipid-dependent survival signaling pathways, notably PI3K-Akt and Raf-Erk1/2, and de novo phospholipid biosynthesis. They are internalized in the cell membrane via raft domains and cause downstream reactions as inhibition of cell growth and migration, cell cycle arrest, actin stress fibers collapse, and apoptosis. This review summarizes the in vitro, in vivo, and clinical trials of most common ATLs and their mode of action at molecular and biochemical levels.

Phospholipid content, expression and support of thrombin generation of neonatal platelets

AIM

Newborns have, despite low clotting factors and poor in vitro platelet function, a well functioning haemostasis. We investigated whether phospholipids (PL) in neonatal platelets differ from those in adult platelets in their exposure on the platelet surface, and their effect on thrombin generation.

METHODS

The effect of newborn and adult platelets on thrombin generation (TG) was measured by means of calibrated automated thrombography (CAT), and in a purified system. In addition, clotting times were measured. Phosphatidylserine (PS)-exposure was measured by flow cytometry. The amount of PL was determined by means of mass-spectrometry (Materials and Methods section in Supporting Information online).

RESULTS

In comparison with adults the clotting times in platelet-rich plasma of newborns were less shortened by adding calciumionophore. No differences in the support of TG between neonatal and adult platelets were found by means of CAT. In the purified system, TG was increased by ionophor-stimulated platelets but no difference was evident between newborn and adult platelets. Flow cytometric analysis showed no difference between adult and newborn platelets. Results of mass-spectrometry showed a very similar pattern of phospholipid-content of adult and newborn platelets.

CONCLUSION

Our results do not provide any evidence that a different phospholipid-expression of neonatal platelets may alter TG in neonates.

In vivo turnover of 1,2-dipalmitoylphosphatidylcholine and sphingomyelin in rabbit erythrocytes

The in vivo turnover of both 1,2-dipalmitoylphosphatidylcholine (DPPC) and sphingomyelin (SM) in rabbit erythrocytes was studied. DPPC, either 14C-labelled in the fatty acyl chain at the 2-position of the glycerol moiety or 3H-labelled in the choline's methyl group, and [N-methyl-14C]SM (bovine) were introduced into the membrane of freshly isolated rabbit erythrocytes by using phospholipid transfer proteins. Thereafter, the labelled erythrocytes were reinjected into the bloodstream of the animal. Analysis of blood samples shows that both labels disappear from the circulating cells with the same rate, resulting in a half-time value of about 6.4-6.6 days. This result demonstrates that the loss of DPPC from the cells is due to transfer of intact molecules to the plasma and that a deacylation process is of no or minor importance as mechanism of renewal of DPPC. Labelled sphingomyelin, introduced into the rabbit erythrocyte membrane in a similar way, disappears from the circulating red cell with a half-time value of 15.5 days. This accounts for a daily replacement of the total SM pool by 3.2%.

The effects of dietary oils on the fatty acid composition and osmotic fragility of rat erythrocytes

The present study was carried out to investigate the effect of different dietary oils representing special fatty acids which varied in chain length, position and number of double bonds on fatty acid composition of erythrocyte membranes and on the osmotic fragility of rat erythrocytes after incubation in NaCl solutions of different concentrations. For this purpose all animals were initially fed a control diet (CO) containing 10% coconut oil and 0.4% safflower oil for 28 days. After that 10 groups of 10 animals each were switched to test diets for another 20 days in which 50% or 100% of the coconut oil was exchanged for one of the following oils: olive oil (OO 5, OO 10), safflower oil (SFO 5, SFO 10), evening primrose oil (EPO 5, EPO 10), linseed oil (LO 5, LO 10) or salmon oil (SLO 5, SLO 10). The results show that the fatty acid composition of rat erythrocyte membranes was affected by the fatty acid composition of the dietary fats. Rats fed OO 10, EPO 10, LO 5 and LO 10 had a slightly lower concentration of saturated fatty acids (SFA) in erythrocyte membranes than control rats. Groups fed olive oil showed the highest level of monounsaturated fatty acids (MUFA) in the erythrocyte membrane. This increase in MUFA at the expense of SFA and (n-6) polyunsaturated fatty acids (PUFA) was most pronounced with respect to 18:1 and occurred in a dose-dependent fashion. Rats fed SFO, EPO or LO had higher linoleic acid levels in the erythrocyte membrane than control rats. This increase in 18:2 (n-6) was mainly at the expense of 18:1 and occurred in a dose-dependent fashion. The proportion of 20:4 (n-6) did not remarkably change feeding diets with (n-6) PUFA-rich oils. The (n-3) PUFA concentration in the erythrocyte membranes considerably increased, whereas (n-6) PUFA decreased feeding linseed oil or salmon oil rich in (n-3) PUFA. Linseed oil and salmon oil caused similar changes in the membrane, which were more pronounced in rats fed salmon oil than in rats fed linseed oil. The osmotic fragility of erythrocytes was also influenced by dietary oil, respectively fatty acid pattern of the erythrocytes. In almost all NaCl solutions erythrocytes from rats fed the dietary oils were less resistant to hemolysis than those from control rats. These changes became statistically apparent feeding EPO 5, LO 5, LO 10 and SLO 5.

Glycerophosphocholine release in human erythrocytes. 1H spin-echo and 31P-NMR evidence for lysophospholipase

The direct techniques of 1H spin-echo and 31P-NMR spectroscopy made it possible to monitor the release of glycerophosphocholine from lysophosphatidylcholine in lysates from human red blood cells. Thus, the existence of a lysophospholipase in human erythrocytes was confirmed using a new more direct method. No evidence for a phospholipase A2 activity in the haemolysates was found with the same approach; since this enzyme is present in leukocytes, the absence of activity helped verify the purity of the erythrocyte preparation. The lysophospholipase may constitute, with the earlier described glycerophosphocholine phosphodiesterase activity, a metabolic unit for the removal of haemolytic lysophosphatidylcholine which is formed in the erythrocyte membranes as well as taken up from the plasma.

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)

Plasma and red blood cell fatty acid values as indexes of essential fatty acids in the developing organs of infants fed with milk or formulas

The dietary requirement of n-6 and n-3 fatty acids for normal biochemical and functional development of the central nervous system (CNS) is an important, unresolved issue in infant nutrition. High levels of arachidonic acid (AA; 20:4n-6) and docosahexaenoic acid (DHA; 22:6n-3) are found in the CNS and are important to normal learning and visual function. Dietary fatty acids may be desaturated and elongated to AA and DHA, respectively, but may also be oxidized for energy. Synthesis of AA and DHA in the young infant, therefore, depends on adequate desaturase enzyme activity, as well as an adequate supply of dietary 18:2n-6, 18:3n-3, and energy. Levels of AA and DHA are lower in the plasma and red blood cell (RBC) lipids of infants fed formula rather than human milk and are not increased with increased formula 18:2n-6 or 18:3n-3 supply. The decline in AA and DHA in infants fed formula becomes evident in the order plasma phospholipid greater than RBC phosphatidylcholine greater than RBC phosphatidylethanolamine. As in infants, piglets fed formula rather than natural milk have lower plasma and RBC AA and DHA concentrations. Despite lower levels in the plasma and RBC, analyses of CNS lipids demonstrated adequate AA and DHA in piglets fed formula with greater than 7% kcal 18:2n-6 and greater than 0.3% kcal 18:3n-3. This finding suggests that circulating lipid fatty acids are not specific indexes of organ deficiency. The rapid decrease in circulating lipid AA and DHA concentrations experienced by premature infants during early postnatal parenteral and enteral nutrition, however, may be related to oxidation of 18:2n-6 and 18:3n-3, rather than equilibrium of circulating lipids with the dietary fatty acids. Arachidonic acid and DHA may be conditionally essential nutrients for these infants because of oxidation of 18:2n-6 and 18:3n-3 for energy during periods of negative energy balance.

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.

Palmitate binding to and efflux kinetics from human erythrocyte ghost

At 0 degrees C, pH 7.3, palmitate (PA) binds to human erythrocyte ghosts suspended in 0.2% bovine serum albumin (BSA) solution with molar ratios of PA to BSA, v, between 0.2 and 1.3. The binding depends on the water phase PA concentration, measured in equilibrium experiments, using BSA-filled ghosts as semipermeable bags. The saturable binding has a capacity of 19.4 +/- 7.5 nmol g-1 packed ghosts (7.2 x 10(9) cells) and Kd = 13.5 +/- 5 nM. PA exchange efflux kinetics to 0.2% BSA is recorded from ghosts without and with 0.2% BSA with a resolution time of about 1 s. Data are analyzed in terms of compartmental models. Using BSA-free ghosts the kinetics is essentially monoexponential. The rate constant is 0.0287 +/- 0.0022 s-1. Using ghosts with BSA, the kinetics is biexponential with widely different rate constants. Extrapolated zero-time values reflect, according to additional investigations, 'instantaneous' release of PA from the outer surface of the ghosts. Analyses of the biexponential curve up to about 55% tracer efflux assign unequivocally values to three model parameters. (1) k1, the dissociation rate constant of the PA-BSA complex is (1.47 +/- 0.03) x 10(-3) s-1 and (2.56 +/- 0.08) x 10(-3) s-1 and (4.08 +/- 0.13) x 10(-3) s-1 at v = 0.2, 0.6 and 1.4, respectively. (2) k3*, the overall rate constant of PA transport from the inside of the ghost membrane to the medium is 0.0269 +/- 0.0020 s-1 independent of v. (3) Qkin, the ratio of PA on the inside of the membrane to PA on BSA within the ghosts is v dependent and smaller than a corresponding ratio Qeq measured in equilibrium by a value corresponding to PA on the outer surface. This fraction is released with a rate constant, k5, which is of the order of 1 s-1. The data suggest a maximum PA transport capacity, Jmax, of 2 pmol min-1 cm-2, 0 degrees C, pH 7.3.

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.

Fatty acid composition of erythrocyte membrane lipid obtained from children suffering from kwashiorkor and marasmus

The fatty acid composition of erythrocyte membrane (EM) lipids obtained from normal, kwashiorkor, and marasmic children was analyzed by gas chromatography. The proportion of palmitic acid (16:0) was lower and of oleic acid (18:1) higher in the kwashiorkor group than in the control group. The marasmic group showed lower proportions of eicosatrienoic acid (20:3) and arachidonic acid (20:4) and a higher proportion of oleic acid (18:1) than the control group. A significant difference was found between the marasmic and kwashiorkor groups with respect to arachidonic acid (20:4), which showed a lower proportion in the former group than the latter. The ratio of arachidonic acid to linoleic acid (20:4/18:2) was markedly lower in the marasmic group than the control group, suggesting a possible impairment in the conversion of linoleic acid to arachidonic acid in marasmic children. The ratio of unsaturated fatty acids to saturated fatty acids was markedly elevated in the kwashiorkor group over that of control group, indicating increased fluidity of EM in kwashiorkor. It is suggested that the altered membrane fatty acid composition reflects deranged lipid metabolism and affects the physical and physiological properties of EM and could contribute to changes in the activities of several red blood cell membrane-bound enzymes reported earlier in kwashiorkor children.

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.

Plasma and cellular zinc levels and membrane lipid composition in streptozotocin diabetic rats

1. Lipid and zinc analyses were conducted on liver mitochondrial and microsomal membranes as well as erythrocyte ghosts from streptozotocin (STZ) treated animals. 2. In STZ animals, analysis of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) fatty acids revealed an increase in palmitic acid and a corresponding decrease in stearic acid. 3. Polyunsaturated fatty acids were also affected, with an increase in 18:2, decrease in 20:4 and an increase in 22:6 in STZ animals compared to controls. 4. The change in fatty acid composition was observed in all three membrane fractions. 5. Plasma zinc levels in STZ animals were elevated while no difference was observed in membrane bound zinc. 6. Thus, while there appears to be both altered trace metal as well as membrane lipid metabolism in STZ treated animals, membrane bound zinc does not seem to be affected.

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.

Uptake of exogenous and endogenous eicosapentaenoic acid by cultured human mononuclear cells

1. Peripheral blood mononuclear cells from eight healthy volunteers were cultured, with or without concanavalin A (Con A), in a medium containing (ml/l) 100 normal autologous serum, 100 experimental autologous serum or 100 heterologous (fetal calf) serum. 2. The control and experimental autologous sera were obtained from the volunteers, before and after 15 d supplementation with 15 g fish oil (MaxEPA)/d to provide 1.5 g eicosapentaenoic acid (EPA; 20:5n-3)/d. The sera were frozen at -20 degrees. The level of EPA increased from trace quantities in the control autologous serum to 14.3% w/w free fatty acids and between 6.9 and 8.1% w/w lipoprotein phospholipids in the experimental autologous serum. The heterologous fetal calf serum was enriched with EPA, complexed with bovine serum albumin, to provide a final concentration of 15 micrograms/ml. All culture medium contained 10 ml fresh autologous serum/l and cells were obtained from the volunteers for the culture studies about 60 d after the end of EPA supplementation. 3. Portions of cells were removed from culture at 36, 48 and 72 h for phospholipid fatty acid analysis. 4. The level of EPA in phospholipids of cells cultured with exogenous EPA in fetal calf serum was increased significantly (P less than 0.05) at all sampling times, both with and without Con A. By 48 h the levels had peaked at 15.8 (SE 2.7) and 18.4 (SE 4.5)% w/w respectively. 5. Resting cells, i.e. with no Con A present, failed to accumulate EPA when cultured in the experimental autologous serum containing 8.6% w/w total lipids as endogenous EPA.(ABSTRACT TRUNCATED AT 250 WORDS)

Acyl-CoA synthetase activity in Plasmodium knowlesi-infected erythrocytes displays peculiar substrate specificities

In its blood stages the malaria parasite, Plasmodium, displays very high lipid metabolism. We present evidence for an abundant long-chain acyl-CoA synthetase (EC 6.2.1.3) activity in Plasmodium knowlesi-infected simian erythrocytes. The activity was found to be 20-fold higher in the schizont-infected (the last parasite stage) than in control erythrocytes. The cosubstrate requirements of the enzyme were similar to those previously reported for acyl-CoA synthetases from other sources. Among the separated reaction products of oleyl-CoA synthetase, only PPi and oleyl-CoA were inhibitory, with Ki over 350 microM. The fatty acid specificity of the parasite acyl-CoA synthetase activity was fairly marked and depended on the unsaturation state of the substrate. The tested fatty acids displayed similar Vmax, whereas their Km ranged from 11 (palmitate) to 59 microM (arachidonate). Finally, experiments involving heat inactivation and separation on hydroxyapatite excluded the presence of a specific arachidonyl-CoA synthetase identical to those present in other cells. On the other hand, fatty acid competition experiments evidenced the existence of at least two distinct enzymatic sites for fatty acid activation in P. knowlesi-infected simian erythrocytes: one is specific for saturated fatty acids and the other for polyunsaturated species, whereas oleate could be activated at both sites.

Phospholipid organization in monkey erythrocytes upon Plasmodium knowlesi infection

The phospholipid organization in monkey erythrocytes upon Plasmodium knowlesi infection has been studied. Parasitized and nonparasitized erythrocytes from malaria-infected blood were separated and pure erythrocyte membranes from parasitized cells were isolated using Affi-Gel beads. In this way, the phospholipid content and composition of the membrane of nonparasitized cells, the erythrocyte membrane of parasitized cells and the parasite could be determined. The phospholipid content and composition of the erythrocyte membranes of nonparasitized and parasitized cells and erythrocytes from chloroquine-treated monkeys cured from malaria, were the same as in normal erythrocytes. The phospholipid content of the parasite increased during its development, but its composition remained unchanged. Three independent techniques, i.e., treatment of intact cells with phospholipase A2 and sphingomyelinase C, fluorescamine labeling of aminophospholipids and a phosphatidylcholine-transfer protein-mediated exchange procedure have been applied to assess the disposition of phospholipids in: erythrocytes from healthy monkeys, nonparasitized and parasitized erythrocytes from monkeys infected with Plasmodium knowlesi, and erythrocytes from monkeys that had been cured from malaria by chloroquine treatment. The results obtained by these experiments do not show any abnormality in phospholipid asymmetry in the erythrocyte from malaria-infected (splenectomized) monkeys, neither in the nonparasitized cells, nor in the parasitized cells at any stage of parasite development. Nevertheless, a considerable degree of lipid bilayer destabilization in the membrane of the parasitized cells is apparent from the enhanced exchangeability of the PC from those cells, as well as from their increased permeability towards fluorescamine.

Highly unsaturated phospholipid molecular species of rat erythrocyte membranes: selective incorporation of arachidonic acid into phosphoglycerides containing polyunsaturation in both acyl chains

This study describes for the first time the complete molecular species composition and turnover of [3H]arachidonic acid in various glycerophospholipid classes of rat erythrocytes, a model system that has been extensively used to investigate numerous membrane phenomena. Quantitative analysis of the individual molecular species of the choline, ethanolamine, serine, and inositol glycerophospholipid classes was possible by preparing their diradylglycerobenzoate derivatives that can be quantitated by on-line uv detection in conjunction with high-performance liquid chromatography; turnover of the molecular species containing arachidonate was evaluated in erythrocytes labeled with [3H]arachidonic acid. A unique observation was the significant amounts of 22:6-20:4, 20:4-20:4, and 18:2-20:4 species observed in the diacyl fractions of phosphatidylethanolamine and phosphatidylserine. Moreover, the analysis of the specific radioactivities of individual phospholipid species from erythrocytes incubated with [3H]arachidonic acid demonstrated a selective incorporation of arachidonic acid into the most highly unsaturated molecular species in all of the phospholipid classes examined. Although the 22:6-20:4, 20:4-20:4, and 18:2-20:4 species represented only 4.5% of the total mass of the diacyl phosphoglycerides, these species accounted for a major portion (37%) of the arachidonic acid incorporated into the phospholipids. These results demonstrate the existence of unique populations of phospholipid molecules in rat erythrocytes with a high degree of unsaturation that exhibit a very rapid metabolic turnover rate.

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.

Effect of erythropoietin on the interchange of cholesterol and phospholipid between erythrocyte membrane and plasma

Ep enhanced the exchange of unesterified cholesterol from plasma to the RBC membrane and vice versa. Similar to unesterified cholesterol, the exchange of phospholipids from plasma to the RBC membrane and vice versa in starved rats increased on the administration of Ep. But, unlike cholesterol exchange, the hormone favored phospholipid transport from the RBC membrane to plasma more significantly than from plasma to the RBC membrane.

Flip-flop rates of individual molecular species of phosphatidylcholine in the human red cell membrane

Trace amounts of four different, well-defined species of phosphatidyl[N-methyl-14C]choline ([14C]PC), differing in their fatty acyl constituents, were introduced exclusively into the outer membrane leaflet of the intact erythrocyte by using a PC-specific phospholipid transfer protein. The rate of transbilayer equilibration of these probe molecules was calculated from the time-dependent decay in specific radioactivity of the PC pool in the outer monolayer, which was discriminated from that in the inner leaflet by treating the intact cells with phospholipase A2 in the presence of sphingomyelinase C. At 37 degrees C, 1,2-dipalmitoyl-, 1,2-dioleoyl-, 1-palmitoyl-2-linoleoyl- and 1-palmitoyl-2-arachidonoyl-PC revealed halftime values for the rate of their transbilayer equilibration of 26.3 +/- 4.4, 14.4 +/- 3.5, 2.9 +/- 1.7 and 9.7 +/- 1.6 h, respectively.

Erythrocyte membrane acyl:CoA synthetase activity

The presence of long-chain acyl:CoA synthetases in mammalian microsomes and mitochondria has been established previously [(1971) Biochim. Biophys. Acta 231, 32-47]. The presence of a plasma membrane-associated enzyme was investigated in human erythrocyte ghost plasma membranes, where an enzyme exhibiting high activity, and with a preferred substrate of 18 carbon chain length, was discovered. The results are consistent with the presence of a single enzyme. The effect of the degree of unsaturation of the fatty acid substrates was not as pronounced as that arising from the length of the carbon chain. The pattern of substrate preference of the enzyme was omega 3 polyenoics greater than omega 6 polyenoics greater than omega 9 monoenoics greater than saturated fatty acids. This may relate to the similar substrate preference pattern exhibited by the fatty acyl desaturase enzymes. However, the role played by long-chain acyl:CoA synthetase in erythrocyte metabolism is uncertain, but may relate to the transportation of polyenoic fatty acids in the circulation.

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.

Murine erythrocytes contain high levels of lysophospholipase activity

Murine erythrocytes were found to be unique in the high levels of lysophospholipase activity in the cytosol of these cells. The specific activity of the enzyme in the cytosol of the murine cells is 10-times higher than in the cytosol of rabbit erythrocytes and approximately three orders of magnitude higher than those in the red cells of rat, man, pig and ox.

Partial requirements for in vitro survival of human red blood cells

Some of the requirements for survival of human red blood cells were studied in vitro at 25 and 37 degrees C for 1--2 weeks. During the first week at 25 degrees C in Krebs-Ringer bicarbonate medium with glucose, the cells at 2--5% hematocrit (HCT) maintained normal K+, Na+, and water contents with negligible hemolysis. After six days ion gradients decreased, preceded by decline of ATP. With adenosine, ATP was maintained for 1--2 weeks. Sustained in vitro survival of human red blood cells at 25 or 37 degrees C requires constant pHo and sufficient substrates to support a glycolytic carbon flux as well as a nitrogen flux via nucleotide turnover. In Earle's salts buffered with HEPES and supplemented with glucose, Eagle's essential vitamins, albumin, and antibiotics, suspensions at 0.1% HCT exhibited constant pH at 7.39 +/- 0.03 for at least two weeks at 37 degrees C. With glucose alone, ATP declined steadily to negligible levels despite constant pHo, but 0.1 mM adenine supported ATP for one week. Also, several amino acids partially prevented the decline of reduced glutathione during the first week at 37 degrees C. These results and current knowledge of red cell metabolism suggest a new defined medium for experiments requiring long term incubations, and extend the characterization of human red cell in vitro survival to a time period not previously studied.

Selective changes in fatty acid composition of phosphatidylserine in rat erythrocyte membrane induced by nitrate

The relationship between nitrate which is formed from inhaled nitrogen dioxide, a common air pollutant, and changes in fatty acid metabolism of phosphatidylserine in rat erythrocytes has been examined. When erythrocytes were incubated at 37 degrees C for 60 min with fatty acid, the incorporation rate of [1-14C]arachidonic acid and [9,10-3H]palmitic acid into phosphatidylserine was 15% (80 pmol/h per mumol lipid phosphorus) and 20% (12 pmol/h per mumol lipid phosphorus) of those into phosphatidylethanolamine, respectively. By the addition of 1.0 mM sodium nitrate or 0.5 microM ionophore A23187 to the incubation mixture, the rate of incorporation of both arachidonic acid and palmitic acid into phosphatidylethanolamine was stimulated 1.45-fold. On the other hand, the incorporation of palmitic acid into phosphatidylserine was little affected, while that of arachidonic acid was stimulated 1.35-fold. An increase in arachidonic acid of phosphatidylserine was also found by the addition of nitrate or ionophore A23187. This increase was dependent on the concentration of extracellular calcium and observed by the addition of other chaotropic anions in the order SCN- greater than ClO4- greater than NO3-. It seems likely, therefore, that nitrate causes changes in erythrocyte membranes to facilitate calcium uptake. Increasing the concentration of intracellular calcium may cause stimulation of acyl-CoA:lysophospholipid acyltransferase and/or endogenous phospholipase A2.

Transbilayer movement of various phosphatidylcholine species in intact human erythrocytes

Phosphatidylcholine specific phospholipid exchange protein was used to introduce (14C)-labeled phosphatidylcholine of different fatty acyl compositions into the intact human erythrocyte. Hydrolysis by a combination of phospholipase A2 and sphingomyelinase was applied to prove that originally all newly introduced phosphatidylcholine resided in the outer monolayer. Subsequently the erythrocytes were reincubated at 37 degrees C, and redistribution of the introduced (14C)phosphatidylcholine was monitored by applying the combination of phospholipases after different times of incubation. In the situation where 20% of the native erythrocyte phosphatidylcholine had been replaced by phosphatidylcholine from (14C)choline-labeled rat liver microsomal membranes, a slow translocation of the (14C)microsomal phosphatidylcholine was found, with a half-time of transbilayer equilibration of 10.8 hr. Furthermore, the transbilayer movement of probe amounts of (14C)dipalmitoyl-phosphatidylcholine, (14C)egg phosphatidylcholine and (14C)soybean phosphatidylcholine was studied under conditions whereby the fatty acyl composition of the bulk erythrocyte phosphatidylcholine remained unchanged. In correlation to the increasing unsaturation of the probe, half-times for the transbilayer equilibration were calculated to be 26.9, 12.8, and 8.1 hr, respectively.

Altered phospholipid composition and changed fatty acid pattern of the various phospholipid fractions of red cell membranes of cystic fibrosis children with pancreatic insufficiency

After two-dimensional thin-layer chromatography, it appears that the phospholipid composition of the erythrocyte membranes of cystic fibrosis children, compared with healthy ones, is changed by an increase of the phosphatidyl inositol content. The plasmalogen concentration of the membrane phospholipids is the same for both groups. The fatty acid pattern of the various red cell membrane phospholipid fractions was determined by gas chromatography (Tables II, III and IV), and significant changes were observed in the cystic fibrosis patients (Table V). Phosphatidyl choline and ethanolamine (non-plasmalogen forms) especially show strikingly abnormal fatty acid patterns similar to those in the various plasma lipid fractions.

Asymmetry in the renewal of molecular classes of phosphatidylcholine in the rat-erythrocyte membrane

1. Rat-blood phospholipids were labeled in vivo with [32P]phosphate. The erythrocytes were treated with phospholipase A2 plus sphingomyelinase to discriminate between the labeling patterns of the phospholipids from the inner and outer layer of the membrane. 2. The specific activities of the more unsaturated classes of phosphatidylcholine were higher in the outer layer of the erythrocyte membrane than in the inner layer. The disaturated class, however, had the highest specific activity in the inner layer. 3. After incubating 32P-labeled erythrocytes in unlabeled plasma, the labeling pattern recovered in the molecular classes of plasma phosphatidylcholine was very similar to that of the phosphatidylcholines in the outer layer of the erythrocyte membrane. 4. It is proposed that the exchange of phosphatidylcholines between plasma and the outer layer of the erythrocyte is mainly responsible for the renewal of the unsaturated phosphatidylcholines of the erythrocyte, and that the acylation activity of the erythrocyte is directed towards the formation of disaturated phosphatidylcholines at the inside of the membrane.

Incorporation of deuterium-labeled cis- and trans-9-octadecenoic acids in humans: plasma, erythrocyte, and platelet phospholipids

The objective of this study was to follow the uptake and distribution of oleic and elaidic acids into human erythrocytes, platelets, and plasma phospholipids. The use of dual and triple labeling methodology permitted a precise comparison of elaidic and oleic acid utilization. Elaidic acid (EI) was selectively concentrated in all the plasma phospholipids except for lysophosphatidylcholine. Three times more elaidic than oleic acid (OI) accumulated in the 1-acyl position of phosphatidylcholine, as determined by hydrolysis with phospholipase A2. Rapid incorporation and removal of elaidate were observed for all samples. These results support the concept that enzymes responsible for acylation of phospholipids are sensitive to double bond configuration and the physical properties of the fatty acid moieties. Labeled fatty acid levels in red cell and platelet phospholipids were much lower than for plasma phospholipids, indicating a relatively slow rate for the in vivo incorporation of fatty acids into blood cell membrane phospholipids. No isotope effect was found when oleic acid labeled with deuterium on the double bond was used.

Synthesis of phospholipids in mitochondria and other membrane fractions of rabbit reticulocytes

1. Reticulocytosis of 40-50% was obtained in rabbits by daily bleeding. Reticulocytes (plus erythrocytes) were subfractionated into plasma membrane fraction, mitochondria and the post-mitochondrial fraction. 2. In all fractions, fatty acids were incorporated into phospholipids. This process was ATP dependent and represented acylation of lysophospholipids. 3. Incorporation of fatty acids into lysophosphatidic and phosphatidic acids occurred only in the presence of sn-glycerol 3-phosphate and was observed in mitochondria and the post-mitochondrial fraction. It represents a two-step acylation of sn-glycerol 3-phosphate. 4. Incorporation of phosphorylcholine from CDPcholine into phosphatidylcholine was observed in the mitochondrial and the post-mitochondrial fractions. This activity was correlated with NADPH-cytochrome c reductase and was probably connected with the remnants of the endoplasmic reticulum.

The transposition of molecular classes of phosphatidylcholine across the rat erythrocyte membrane and their exchange between the red cell membrane and plasma lipoproteins

1. The molecular composition of phosphatidylcholine is similar in the inner and the outer layer of the rat erythrocyte membrane. 2. The rate of exchange of the various molecular classes of phosphatidylcholine between rat plasma and the red cell membrane does not depend on the degree of unsaturation of the different classes. 3. The transposition of the molecular classes of phosphatidylcholine between the inner and the outer layer of the rat erythrocyte membrane is more pronounced for the more unsaturated classes.

Phospholipase activity of sea urchin sperm: its possible involvement in membrane fusion

Phospholipase activity of egg-water treated Arbacia punctulata and Lytechinus variegatus sperm was shown to result from the sequential action of phospholipase A and lysophospholipase. A transient burst of phospholipase A activity followed induction of the acrosome reaction with egg water. The time of appearance suggested an acrosomal localization of the enzyme. The peak activity of phospholipase A correlated with initiation of sperm-egg fusion, suggesting a role for sea urchin sperm phospholipase A in membrane fusion and/or egg activation during fertilization.

Dual-labeled technique for human lipid metabolism studies using deuterated fatty acid isomers

Two deuterated fatty acids, elaidated2 and oleate-d4, were fed simultaneously to a human subject as a mixture of trielaidin-d6 and triolein-d12. Periodically, blood samples were drawn, and red blood cells were separated from the plasma. Red blood cells and plasma lipids were fractionated and analyzed by combined gas chromatography--multiple ion mass spectroscopy. Dual deuterium-labeling allows rate and extent of fatty acid incorporation to be followed in various plasma and red cell neutral and phospholipid fractions. Maximum amount of deuterated fat varied from 4% in cholescurred in either 6-, 8-, or 12-hr samples; generally, less than 1% labeled fatty acids could be detected in 72-hr samples. Because the method is based on dual-labeling, differences in the relative incorporation of both fatty acid isomers can be compared directly. Differences in rates of incorporation, rates of removal, and extent of incorporation of labeled fatty acids into blood plasma can also be determined reliably. Our experimental labeling of fats with deuterium permits for the first time the metabolism of two fatty acid isomers to be compared simultaneously in human subjects. This new method should be applicable to a variety of other lipid metabolic studies.

Topological asymmetry of phospholipid metabolism in rat erythrocyte membranes. Evidence for flip-flop of lecithin

1. The distribution of phospholipids between inside and outside of rat erythrocyte membranes was studied by incubating the cells with phospholipase A2 from Naja naja venom and sphingomyelinase from Staphylococcus aureus. 2. Choline-containing phospholipids were found to comprise the majority of the outer layer of the membrane. 3. The incorporation of radioactive fatty acids into phospholipids occurred predominantly at the inside of the membrane. 4. Exchange of phospholipids between red cell membranes and plasma lipoproteins occurred at the outside of the membrane. 5. Indications were found for a rather slow flip-flop of lecithin across the membrane.

Role of dietary iron and fat on vitamin E deficiency anemia of infancy

Thirty-five infants weighing less than 1500 g at birth were fed four commercial formulas (A-D) varying in polyunsaturated fatty acid composition (32 per cent linoleic acid in A and B and 12 per cent linoleic acid in C and D) and in iron content (smaller than 1.0 in A and B; 12 to 12 mg per liter in B and D). Infants receiving formula B showed significantly lower hemoglobins (p smaller than 0.01) and higher reticulocyte counts (p smaller than 0.005) than infants fed the other three formulas. Infants receiving the two formulas with higher concentrations of unsaturated fatty acids (A and B) showed significantly greater hydrogen-peroxide-induced hemolysis (p smaller than 0.001) than those given diets containing lower amounts. Infants in groups A and B also had lower serum tocopherol concentrations. Infant red-cell membranes are altered by the increased amounts of polyunsaturated fatty acids and iron in the diet. It appears that the development of vitamin E deficiency anemia occurs in infants receiving iron supplementation.