Control of lecithin biosynthesis in erythrocyte membranes

Lipid nutrition: "In silico" studies and undeveloped experiments

This review examines lipids and lipid-binding sites on proteins in relation to cardiovascular disease. Lipid nutrition involves food energy from ingested fatty acids plus fatty acids formed from excess ingested carbohydrate and protein. Non-esterified fatty acids (NEFA) and lipoproteins have many detailed attributes not evident in their names. Recognizing attributes of lipid-protein interactions decreases unexpected outcomes. Details of double bond position and configuration interacting with protein binding sites have unexpected consequences in acyltransferase and cell replication events. Highly unsaturated fatty acids (HUFA) have n-3 and n-6 motifs with documented differences in intensity of destabilizing positive feedback loops amplifying pathophysiology. However, actions of NEFA have been neglected relative to cholesterol, which is co-produced from excess food. Native low-density lipoproteins (LDL) bind to a high-affinity cell surface receptor which poorly recognizes biologically modified LDLs. NEFA increase negative charge of LDL and decrease its processing by "normal" receptors while increasing processing by "scavenger" receptors. A positive feedback loop in the recruitment of monocytes and macrophages amplifies chronic inflammatory pathophysiology. Computer tools combine multiple components in lipid nutrition and predict balance of energy and n-3:n-6 HUFA. The tools help design and execute precise clinical nutrition monitoring that either supports or disproves expectations.

Balancing proportions of competing omega-3 and omega-6 highly unsaturated fatty acids (HUFA) in tissue lipids

People eating different balances of omega-3 and omega-6 nutrients develop predictably different proportions of competing highly unsaturated fatty acids (HUFA) in their tissue lipids. While epidemiological studies have associated wide differences in HUFA balance with disease severity, some clinical studies that did not examine wide differences failed to confirm the association. We examined the degree to which the relative amount of arachidonic acid, the major precursor of omega-6 eicosanoids, differs among people who have widely different dietary intakes of omega-3 and omega-6 nutrients. Gas chromatographic analyses of human blood samples describe the balance among n-3 and n-6 HUFA for different individuals. The proportion of the omega-6 arachidonic acid, from which potent eicosanoids are formed, is not constant. It ranges from 30% to 70% of HUFA while the competing n-3 HUFA range from 60% to 10% of HUFA. Significant differences in clinical outcomes between control and intervention groups have been seen when using dietary interventions that shift the balance of n-3 and n-6 nutrients far enough to create a biologically significant difference in the HUFA balance.

Using a fingertip whole blood sample for rapid fatty acid measurement: method validation and correlation with erythrocyte polar lipid compositions in UK subjects

It is well accepted that n-3 long-chain PUFA intake is positively associated with a range of health benefits. However, while benefits have been clearly shown, especially for CVD, the mechanisms for prevention/benefit are less understood. Analysis of plasma and erythrocyte phospholipids (PL) have been used to measure the status of the highly unsaturated fatty acids (HUFA), especially EPA (20 : 5n-3) and DHA (22 : 6n-3), although the time and complexity of the process places limitations on the sample numbers analysed. An assay has been developed using whole blood, collected by finger prick, and stored on absorbant paper, subjected to direct methylation and fatty acids quantified by automated GC. Tests on fatty acid stability show that blood samples are stable when stored at - 20°C for 1 month although some loss of HUFA was seen at 4°C. A total of fifty-one patients, including twenty-seven who consumed no fatty acid supplements, provided a blood sample for analysis. Concentrations of all major fatty acids were measured in erythrocyte PL and whole blood. The major HUFA, including EPA, DHA and arachidonic acid (ARA; 20 : 4n-6), as well as the ARA:EPA ratio and the percentage n-3 HUFA/total HUFA all showed good correlations, between erythrocyte PL and whole blood. Values of r2 ranged from 0.48 for ARA to 0.95 for the percentage of n-3 HUFA/total HUFA. This assay provides a non-invasive, rapid and reliable method of HUFA quantification with the percentage of n-3 HUFA value providing a potential blood biomarker for large-scale nutritional trials.

Substrate preferences of a lysophosphatidylcholine acyltransferase highlight its role in phospholipid remodeling

An important enzyme involved in phospholipid turnover is the acyl-CoA: lysophosphatidylcholine acyltransferase (LPCAT). Here, we report characterization of a newly discovered human LPCAT (LPCAT3), which has distinct substrate preferences strikingly consistent with a role in phosphatidylcholine (PtdCho) remodeling and modulating fatty acid composition of PtdCho. LPCAT3 prefers lysophosphatidylcholine (lysoPtdCho) with saturated fatty acid at the sn-1 position and exhibits acyl donor preference towards linoleoyl-CoA and arachidonoyl-CoA. Furthermore, LPCAT3 is active in mediating 1-O-alkyl-sn-glycero-3-phosphocholine acylation with long chain fatty acyl-CoAs to generate 1-O-alkyl-phosphatidylcholine, another very important constitute of mammalian membrane systems. These properties are precisely the known attributes of LPCAT previously ascribed to the isoform involved in Lands' cycle, and thus strongly suggest that LPCAT3 is involved in phospholipids remodeling to achieve appropriate membrane lipid fatty acid composition.

Discovery of a lysophospholipid acyltransferase family essential for membrane asymmetry and diversity

All organisms consist of cells that are enclosed by a cell membrane containing bipolar lipids and proteins. Glycerophospholipids are important not only as structural and functional components of cellular membrane but also as precursors of various lipid mediators. Polyunsaturated fatty acids comprising arachidonic acid or eicosapentaenoic acid are located at sn-2 position, but not at sn-1 position of glycerophospholipids in an asymmetrical manner. In addition to the asymmetry, the membrane diversity is important for membrane fluidity and curvature. To explain the asymmetrical distribution of fatty acids, the rapid turnover of sn-2 position was proposed in 1958 by Lands [Lands WE (1958) Metabolism of glycerolipides: A comparison of lecithin and triglyceride synthesis. J Biol Chem 231:883-888]. However, the molecular mechanisms and biological significance of the asymmetry remained unknown. Here, we describe a putative enzyme superfamily consisting mainly of three gene families, which catalyzes the transfer of acyl-CoAs to lysophospholipids to produce different classes of phospholipids. Among them, we characterized three important enzymes with different substrate specificities and tissue distributions; one, termed lysophosphatidylcholine acyltransferase-3 (a mammalian homologue of Drosophila nessy critical for embryogenesis), prefers arachidonoyl-CoA, and the other two enzymes incorporate oleoyl-CoAs to lysophosphatidylethanolamine and lysophosphatidylserine. Thus, we propose that the membrane diversity is produced by the concerted and overlapped reactions with multiple enzymes that recognize both the polar head group of glycerophospholipids and various acyl-CoAs. Our findings constitute a critical milestone for our understanding about how membrane diversity and asymmetry are established and their biological significance.

Membrane Lipid Alterations in Hemoglobinopathies

The red blood cell (RBC) membrane is a complex mixture of lipids and proteins. Hundreds of phospholipid molecular species spontaneously arrange themselves in a lipid bilayer and move rapidly in the plane as well as across the bilayer in a dynamic but highly organized fashion. Areas enriched in certain lipids determine proper protein function. Phospholipids are asymmetrically distributed across the lipid bilayer with phosphatidylserine (PS) exclusively on the inside. Both the composition and organization of the RBC membrane is well maintained. Alterations lead to apoptosis during erythropoiesis or early demise of the cell in the circulation. The mechanisms that govern the maintenance of the lipid bilayer are only recently being unraveled at the individual protein level. Oxidized lipids are rapidly repaired using fatty acids taken up from plasma to maintain membrane integrity. Several isoforms of a RBC acyl-Coenzyme A (CoA) synthase have been reported, as well as the first member of a family of lysophospholipid acylCoA acyltransferases. Phospholipid asymmetry is maintained by the recently identified RBC amino-phospholipid translocase. These enzymes, essential in maintaining membrane lipid organization, are affected by oxidant stress or an increase in cytosolic calcium. Normal lipid composition and organization is lost in subpopulations of RBC in hemoglobinopathies such as sickle cell disease and thalassemia. Despite elaborate antioxidant systems, lipids and membrane proteins, including those that maintain lipid organization, are damaged in these cells. This in turn leads to improper repair of damaged RBC membranes and altered interactions of RBCs with other blood cells and plasma components that play a role in the pathology that defines these disorders. The altered lipid bilayer in RBCs in hemoglobinopathies leads to premature removal (anemia) and imbalance in hemostasis, and plays a role in vaso-occlusive crisis in sickle cell disease. Lipid breakdown products of PS-exposing cells result in vascular dysfunction, including acute chest syndrome in sickle cell disease. In summary, altered membrane lipids play an important role in the pathology of hemoglobinopathies and characterization of the proteins involved in lipid turnover will elucidate the pathways that maintain plasma membrane organization and cellular viability.

Erythrocyte PAF-acetylhydrolase activity in various stages of chronic kidney disease: effect of long-term therapy with erythropoietin

BACKGROUND

Erythrocytes represent an important component of the antioxidant capacity of blood, comprising, in particular, intracellular enzymes, including platelet-activating factor acetylhydrolase (PAF-AH) and glutathione peroxidase (Gpx). We evaluated the erythrocyte PAF-AH and Gpx activities in various stages of chronic kidney disease (CKD), and further investigated whether erythropoietin (EPO) administration in these patients has any influence on the enzyme activities.

METHODS

Thirty-six patients (19 men and 17 women) with CKD (stages 1 to 5) participated in the study. Thirteen of them presented with CKD stage 1 to 2 (group I), whereas 23 patients presented with CKD stage 3 to 5 and randomized into two groups (i.e., groups II and III). Patients of group II (N= 11) were administered EPO subcutaneously, 50 units per kg once per week. In group III (N= 12), EPO was initiated only when the hemoglobin (Hb) levels decreased during follow-up to less than 9 g/dL. All patients were seen on an outpatient basis at 2 and 4 months. Fifteen normolipidemic age- and sex-matched healthy volunteers also participated in the study and were used as controls. The PAF-AH and Gpx activities were determined in isolated washed erythrocytes.

RESULTS

The erythrocyte-associated PAF-AH and Gpx activities were higher in all CKD patient groups at baseline compared to controls, the groups II and III exhibiting significantly higher enzyme activities compared with group I. In all studied populations, both enzyme activities were negatively correlated with the creatinine clearance values. Importantly, the PAF-AH and Gpx activities were progressively decreased during the follow-up in patients not treated with EPO (group III), a phenomenon not observed in patients receiving EPO (group II), or in patients of group I. This reduction in enzyme activities was positively correlated with the decrease in the creatinine clearance values in patients of group III.

CONCLUSION

Significant alterations in the erythrocyte-associated PAF-AH and Gpx activities related to the disease stage are observed in CKD patients. Administration of EPO prevented the reduction in enzyme activities observed during the progression of the renal insufficiency, thus preserving the erythrocyte defense mechanisms against oxidative stress.

Docosahexaenoic acid is superior to eicosapentaenoic acid as the essential fatty acid for growth of grouper, Epinephelus malabaricus

Juvenile grouper (Epinephelus malabaricus) were fed seven experimental diets, one control diet and one reference diet for 12 wk to determine the dietary requirement of grouper for docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids. Each of the seven diets contained 1 g/100 g DHA and EPA in various combinations and 9 g/100 g tristearin. The control diet contained 1 g/100 g trilinolenin and trilinolein (3:1, wt/wt), and no supplemental EPA or DHA. The reference diet contained only natural oils from a mixture of cod liver oil, linseed oil and safflower oil at a ratio of 2:1:1 (wt/wt/wt). Significant differences (P < 0.05) in growth were observed among the dietary treatments but not in survival rate or relative liver weight. Only the diet with the highest DHA/EPA ratio (3:1) promoted significantly greater growth than the control diet. Purified EPA and DHA did not perform better in promoting growth than did the impure EPA and DHA oils. Enhanced growth was observed when the dietary DHA/EPA ratio was greater than 1, indicating that DHA was superior to EPA in promoting fish growth. Neutral lipid (NL) was the predominant lipid fraction (>70%) in both liver and muscle. Tissue NL/polar lipid did not differ among groups except the reference diet group that had a higher ratio (P < 0.05). DHA and EPA levels in the grouper tissues, especially muscle, were highly reflective of dietary levels of DHA and EPA, indicating that direct incorporation was likely. In addition, the 20:1(n-9), concentration in NL fractions seems to be an appropriate indicator of dietary essential fatty acid deficiency in grouper.

Involvement of calcium-independent phospholipase A2 in uterine stromal cell phospholipid remodelling

The role of Ca2+-independent phospholipase A2 (iPLA2) in arachidonic (AA) and docosahexaenoic (DHA) acid incorporation and phospholipid remodelling in rat uterine stromal cells (UIII cells) was studied. Incorporation of AA and DHA into UIII cell phospholipids was Ca2+-independent. Bromoenollactone (BEL), a potent inhibitor of iPLA2, reduced lysophosphatidylcholine level and AA incorporation into phospholipids by approximately 20%. DHA incorporation was not affected by BEL, indicating that the pathways for AA and DHA incorporation are partially different. In control cells, the transfer of AA occurred mainly from diacyl-glycerophosphocholine (GroPCho) to alkenylacyl-glycerophosphoethanolamine (GroPEtn) and to a lesser extent from diacyl-GroPCho to diacyl-GroPEtn. [3H]DHA was redistributed from diacyl-GroPCho and alkylacyl-GroPEtn to alkenylacyl-GroPEtn. BEL treatment inhibited completely the redistributrion of AA within diacyl-GroPCho and diacyl -GroPEtn and reduced the [3H]DHA content of diacyl-GroPEtn, indicating that a BEL-sensitive iPLA2 controls the redistribution of polyunsaturated fatty acids to diacyl-GroPEtn. In contrast the redistribution of radioactive AA and DHA to alkenylacyl-GroPEtn was almost insensitive to BEL. The analysis of substrate specificity and BEL sensitivity of iPLA2 activity indicates that UIII cells exhibit at least two isoforms of iPLA2, one of which is BEL-sensitive and quite selective of diacyl species, and another one that is insensitive to BEL and selective for alkenylacyl-GroPEtn. Taken together, these results suggest that several iPLA2 participate independently in the remodelling of UIII cell phospholipids.

Platelet-activating factor acetylhydrolases in health and disease

The platelet-activating factor (PAF) acetylhydrolases catalyze hydrolysis of the sn-2 ester bond of PAF and related pro-inflammatory phospholipids and thus attenuate their bioactivity. One secreted (plasma) and four intracellular isozymes have been described. The intracellular isozymes are distinguished by differences in primary sequence, tissue localization, subunit composition, and substrate preferences. The most thoroughly characterized intracellular isoform, Ib, is a G-protein-like complex with two catalytic subunits (alpha1 and alpha2) and a regulatory beta subunit. The beta subunit is a product of the LIS1 gene, mutations of which cause Miller-Dieker lissencephaly. Isoform II is a single polypeptide that is homologous to the plasma PAF acetylhydrolase and has antioxidant activity in several systems. Plasma PAF acetylhydrolase is also a single polypeptide with a catalytic triad of amino acids that is characteristic of the alpha/beta hydrolases. Deficiency of this enzyme has been associated with a number of pathologies. The most common inactivating mutation, V279F, is found in >30% of randomly surveyed Japanese subjects (4% homozygous, 27% heterozygous). The prevalence of the mutant allele is significantly greater in patients with asthma, stroke, myocardial infarction, brain hemorrhage, and nonfamilial cardiomyopathy. Preclinical studies have demonstrated that recombinant plasma PAF acetylhydrolase can prevent or attenuate pathologic inflammation in a number of animal models. In addition, preliminary clinical results suggest that the recombinant enzyme may have pharmacologic potential in human inflammatory disease as well. These observations underscore the physiological importance of the PAF acetylhydrolases and point toward new approaches for controlling pathologic inflammation.

Relationship between arachidonate--phospholipid remodeling and apoptosis

Our previous studies reveal that three structurally distinct inhibitors of the enzyme CoA-independent transacylase, including the antiproliferative alkyllysophospholipid ET-18-O-CH3, induce programmed cell death (apoptosis) in the promyelocytic cell line HL-60. The objective of the current study was to better elucidate the mechanism responsible for apoptosis. CoA-IT is an enzyme believed to be responsible for the remodeling of long chain polyunsaturated fatty acids like arachidonate between the phospholipids of mammalian cells. The chronic (24-48 h) treatment of HL-60 cells with all three CoA-IT inhibitors resulted in the inhibition of the remodeling of labeled arachidonate from choline- into ethanolamine-containing phospholipid molecular species. GC-MS analysis of the fatty acids in phospholipids revealed that CoA-IT inhibitor treatment induced a marked loss of arachidonate-containing phosphatidylethanolamine and an increase in arachidonate-containing phosphatidylcholine. This redistribution was specific to arachidonate since the mass distribution of linoleic acid in glycerolipids was not affected. In spite of the dramatic redistribution of arachidonate, the total cellular arachidonate content was not altered nor was the relative distribution of total phospholipid classes. The increase of arachidonate in phosphatidylcholine was specifically due to an increase in 1-acyl-2-arachidonoyl-sn-glycero-3-phosphocholine species, whereas the loss of arachidonate in PE was from both 1-acyl- and 1-alk-1-enyl-2-arachidonoyl-sn-glycero-3-phosphoethanolamine species. The incubation of cells with exogenous arachidonic acid or ethanolamine did not reverse the inhibition of proliferation induced by CoA-IT inhibitor treatment. Incubation with CoA-IT inhibitors also induced the characteristic cytoplasmic and nuclear changes associated with apoptosis as assessed by transmission electron microscopy and DNA fragmentation as determined by flow cytometry. Taken together, these data show that apoptosis in HL-60 cells, induced by blocking arachidonate-phospholipid remodeling, is correlated with a redistribution of arachidonate in membrane phospholipids and suggest that such alterations represent a signal which controls the capacity of cells to proliferate.

Changes in plasma phospholipids in the presence and absence of erythrocytes 31P-NMR time-course studies

Whole human blood and plasma were incubated at 37 degrees C and 31P-NMR spectra were acquired from aliquots of plasma dissolved in sodium cholate. The narrow resonances of phospholipids were well resolved, allowing identification and accurate quantification of the various phospholipid classes. During the course of plasma incubation, the rate of increase in 2-lysphosphatidylcholine (2-LysoPtdCho) corresponded closely to the rate of decrease in phosphatidylcholine. However, little or no change was observed in the sphingomyelin concentrations. The rate of cholesteryl ester formation in plasma was also determined using HPLC and was observed to be similar to the rate of 2-LysoPtdCho increase in plasma; this is consistent with the rate of acyl transfer from phosphatidylcholine to free cholesterol catalysed by lecithin:cholesterol acyltransferase. However, during the course of whole blood incubation, the rate of 2-LysoPtdCho increase in plasma was significantly lower than the rate of 2-LysoPtdCho production during incubation of plasma alone (31 +/- 4 micromol x 1(-1) x h(-1) and 80 +/- 8 micromol x 1(-1) x h(-1), respectively). The difference between the rates can be attributed to the action of enzymes present in blood cells including those in the erythrocytes that catalyse acylation or hydrolysis of 2-LysoPtdCho.

Density-associated changes in platelet-activating factor acetylhydrolase activity and membrane fluidity of human erythrocytes

Platelet-activating factor acetylhydrolase is known to degrade oxidatively fragmented phospholipids which are similar in structure to platelet-activating factor. We examined changes of acetylhydrolase activity during in vivo aging of human erythrocytes and tried to assess its role in maintaining the membrane properties of erythrocytes. Higher-density erythrocytes are enriched with older cells. Erythrocytes obtained from seven healthy colleagues were separated into four density fractions by centrifugation in discontinuous Percoll density gradients. Both membrane and cytosolic acetylhydrolase decreased with increasing erythrocyte density. Membrane and cytosolic acetylhydrolase activities in the lightest fraction were 2.0 +/- 1.0 (SD) nkat/g protein and 362 +/- 58 pkat/g protein, respectively, and these values were significantly higher than those in the densest fraction: 1.3 +/- 0.7 nkat/g protein and 286 +/- 70 pkat/g protein, respectively. Membrane acyltransferase activity also decreased with red cell density and the average values in the lightest and densest fractions were 51.2 +/- 23.6 and 27.0 +/- 20.2 mukat/g protein, respectively. Generation of thiobarbituric acid-reactive substances induced by t-butyl hydroperoxide treatment decreased with increasing cell density, and the inhibition of acetylhydrolase with diisopropylfluorophosphate resulted in enhanced peroxide-induced lipid oxidation, particularly in lower-density fractions. There was no significant change in basal levels of thiobarbituric acid-reactive substances in red cell membrane. Membrane fluidity was evaluated by fluorescence recovery after photo-bleaching and it decreased as erythrocyte density increased. We conclude that the activity of the deacylation/reacylation cycle maintained by acetylhydrolase and acyltransferase is gradually reduced during in vivo aging of erythrocytes. This may be connected with decreases of polyunsaturated fatty acids and membrane fluidity in old erythrocytes.

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.

Effects of high alpha-linolenate and linoleate diets on erythrocyte deformability and hematological indices in rats

Rats were fed either a high alpha-linolenate diet or a high linoleate diet from weaning to 4 mon of age. Soybean oil was used as a control. Phospholipid compositions of erythrocytes from the three dietary groups were not significantly different. However, the difference in the alpha-linolenate (18:3n-3)/linoleate (18:2n-6) ratio of the diets was reflected in the n-3/n-6 ratios of the 20 and 22 carbon highly unsaturated fatty acids except for docosahexaenoic acid (22:6n-3) in the phospholipids. Despite the significant differences in the fatty acid compositions of phospholipids, no measurable differences were detectable in erythrocyte deformability, whole blood viscosity and hematological indices of the three dietary groups. These results indicate that the beneficial effects of the high alpha-linolenate diet, as compared with the high linoleate diet, are exerted without significant changes in these parameters.

Quantitative effects of dietary polyunsaturated fats on the composition of fatty acids in rat tissues

A method combining data on fatty acid composition into subsets is used to illustrate general relative competitive selectivities in the metabolic and transport events that maintain fatty acid compositions in tissue lipids and to minimize differences among tissues or species in the amount of individual fatty acids. Fatty acid compositions of triglycerides and phospholipids in several tissues of the rat were maintained with simple relationships between the exogenous n-3 and n-6 dietary polyunsaturated fatty acids and the endogenous n-7 and n-9 types of fatty acid. The general pattern of fatty acids in triglycerides was similar for liver, plasma and adipose tissue, averaging about 30% as saturated acids, 67% as 16- and 18-carbon unsaturated acids and only about 2% as 20- and 22-carbon highly unsaturated acids. The tissues maintained a linear relationship between the amount of 18-carbon polyunsaturated fatty acids in the diet and in the tissue triglycerides, with the proportionality constant for 18:3n-3 being 60% of that for 18:2n-6. The total phospholipids of liver, plasma and red blood cells maintained about 45% of the fatty acids in the form of saturated fatty acids and 20-30% as 20- and 22-carbon highly unsaturated fatty acids irrespective of very different proportions of n-3, n-6 and n-9 types of fatty acids. In all three tissues, the 20-carbon highly unsaturated fatty acids of the n-3, n-6 and n-9 type were maintained in a competitive hyperbolic relationship with apparent EC50 values for dietary 18:2n-6 and 18:3n-3 near 0.1% of dietary calories. The consistent quantitative relationships described in this study illustrate an underlying principle of competition among fatty acids for a limited number of esterification sites. This approach may be useful in predicting the influence of diet upon tissue levels of the substrates and antagonists of eicosanoid biosynthesis.

Effects of estrogen-induced hyperlipidemia on the erythrocyte membrane in chicks

The effects of estrogen-induced hyperlipidemia on plasma lipid peroxidation, fatty acid composition and osmotic fragility of erythrocytes in chickens were studied. Young male chickens implanted with estrogen for three wk developed a marked hyperlipidemia. Plasma levels of triglyceride, cholesterol and phospholipid were elevated 68-, four- and 24-fold, respectively, over controls. There was also a two-fold increase in plasma lipid peroxidation measured by the thiobarbituric acid test. Vitamin E supplement (1,000 IU/kg diet) reduced the plasma lipid peroxidation to the control level, but had no effect on the plasma lipid content. Estrogen-induced hyperlipidemia resulted in changes in the fatty acid composition of membrane lipids of erythrocytes. The major changes were an increase in oleic acid from 10.0% to 14.2% and a decrease in linoleic acid from 31.3% to 26.0%. The erythrocytes with an altered membrane fatty acid composition were found to have an increased osmotic fragility. It was apparent that there was a direct correlation between the oleic acid content and the osmotic fragility of erythrocytes.

Phase I trial of the thioether phospholipid analogue BM 41.440 in cancer patients

BM 41.440 (1-hexadecylmercapto-2-methoxymethyl-rac-glycero-3-phosphocholine) is a new thioether phospholipid, which has been shown to possess antineoplastic, antimetastatic, anti-invasive and immunomodulating properties in several tumor models. The mechanism whereby this compound exerts its direct antineoplastic effect is thought to be related to specific interference with the normal phospholipid metabolism, preferentially of neoplastic cells. BM 41.440 was evaluated in a multicenter phase I study in patients (pts) with refractory cancers. In phase I A, 34 pts were orally treated with doses ranging from 0.5 to 7.0 mg/kg body weight (bw). Three different formulations were tested. The maximum-tolerated dose (MTD) was ca. 5 mg/kg bw. The limiting side effects were nausea and vomiting. There was no evidence for systemic toxicities like myelosuppression, nephro-, neuro-, hepatotoxicity or hematological side effects. The current phase I B is designed to determine the MTD of BM 41.440 administered orally on a daily schedule for at least eight weeks. So far, 19 pts have entered this trial at dose levels ranging from 1.0 to 5.0 mg/kg bw/day. Some pts receiving 1.0 and 2.5 mg/kg bw/day, respectively, have been treated, up to now, for more than nine months. Clinical progress was followed with at-least-weekly blood counts, chemistry profiles, urine analysis, liver function tests and recordings of side effects. Tumor parameters were evaluated at eight-week intervals. In parallel, pharmacokinetic investigations were performed in some pts in phase I A and IB. First results on tolerability and therapeutic efficacy of the long-term BM 41.440 treatment are reported in this intermediate evaluation.

Pharmacokinetics of the thioether phospholipid analogue BM 41.440 in rats

BM 41.440 (1-hexadecylmercapto-2-methoxymethyl-rac-glycero-3-phosphocholine) is a cytotoxic thioether phospholipid analogue that recently has entered phase I trials in cancer patients. The objective of this study was to evaluate the pharmacokinetics of this compound in female rats after administration of a single oral dose (15 mg/kg body weight [bw] ). Furthermore, BM 41.440 serum concentrations were determined under a daily oral treatment of up to 13 weeks. Blood samples were obtained via permanent catheters from the femoral arteries before and after drug administration for a total of 120 hr. Urine was collected in 24 hr-intervals for 120 hr; the volume was measured, and aliquots were stored at -20 C until analytical determination of the thioether derivative. BM 41.440 was assayed in serum and urine by means of a specific, newly developed reverse-phase high pressure liquid chromatography technique. Mean maximum serum concentrations (1.7 micrograms/ml, n = 4 animals) were attained after seven hr. A terminal half-life of ca. 27 hr was calculated from the rate constant for the terminal elimination phase (lambda z approximately 0.026/hr). The mean serum BM 41.440 concentration-time-area-under-the-curve was 52.9 mg X hr/l. The ratio of total body clearance to absorption fraction was 4.7 ml/min X kg bw. Only a small amount of the drug was found in the urine. The quantity excreted in the urine during a 24 hr-interval never exceeded 1.5% of the administered dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of dietary trans-octadecenoate among acyl-CoA and other lipid fractions of rat liver and heart

Groups of rats were fed diets containing 10% of either corn oil, partially hydrogenated soybean oil, or a mixture of the two. The partially hydrogenated oil contained a high level of trans-octadecenoate and a low level of linoleate, and all diets were adjusted to contain similar levels of cis-octadecenoate. The fatty acid compositions of five tissue lipid fractions from liver and heart (non-esterified fatty acids, acyl-CoA, diacylglycerols, triacylglycerols and phospholipids) were analyzed to measure the effect of the dietary supply on the accumulation of trans-octadecenoates and other fatty acids at different steps of glycerolipid synthesis. Although trans-octadecenoate was increased in all of the lipid fractions when the dietary supply was increased, the accumulation did not exceed 15% of the acyl chains in any of the lipid pools even when the dietary trans acid accounted for 46% of the fatty acids supplied in the diet. The trans-octadecenoate accumulated in a similar manner in the lipids of both liver and heart, and the amounts found in the acyl-CoA esters of both tissues were relatively low compared to the diet. A high dietary supply of trans-octadecenoate appeared to diminish the relative content of stearate in the acyl-CoA and phospholipid fractions. The level of cis-octadecenoate maintained in tissue phospholipids was similar to that in the acyl-CoA fractions, whereas the trans-octadecenoate content in phospholipids more closely resembled that in the diacylglycerols. Normal proportions of arachidonate were maintained in the tissue phospholipids during high intake of trans acids, even though lower levels were observed in the acyl-CoA and diacylglycerols of liver.

Ether phospholipids as inhibitors of the arachidonoyl-CoA: 1-acyl-sn-glycero-3-phosphocholine acyltransferase in macrophages

1-Alkylglycerophosphatide analogs which are known to activate macrophages to enhanced tumor cytotoxicity are structurally closely related to 1-acyl-sn-glycero-3-phosphocholine. In this study we have examined the influence of some of these compounds and of platelet-activating factor (PAF-acether, 1-0-alkyl-2-0-acetyl-sn-glycero-3-phosphocholine) on the arachidonoyl-CoA: 1-acyl-sn-glycero-3-phosphocholine acyltransferase (EC 2.3.1.23) in homogenate of bone-marrow-derived murine macrophages. This enzyme is suggested to be involved in the control of the availability of the icosanoid precursor, arachidonic acid. Kinetic experiments revealed apparent Km and V values for 1-palmitoyl-sn-glycero-3-phosphocholine of 6.0 microM and 16.10 nmol/mg protein per min, respectively. When the 1-palmitoyl-sn-glycero-3-phosphocholine concentration was equal to Km, the enzyme was dose-dependently inhibited by 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine with a 50% inhibition at 30 microM. The kinetic parameters in the presence of 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (K'm = 10.0 microM, V' = 11.40 nmol X mg-1 X min-1) suggest that this alkyl phospholipid is a mixed-type inhibitor. All other alkyl analogs tested (1-O-methyl-2-O-octadecyl-rac-glycerol-3-phosphocholine, racemic PAF-acether, L-PAF-acether, D-1-O-hexadecyl-sn-glycero-3-phosphocholine, 1-O-octadecyl-rac-glycero-3-phosphocholine) inhibited the enzyme to various degrees. Arachidonic acid transfer to the 1-alkylglycerophosphatide analogs themselves could be ruled out under the assay conditions used. Therefore, we conclude that the arachidonoyl-CoA: 1-acyl-sn-glycero-3-phosphocholine acyltransferase can be inhibited by synthetic and naturally occurring ether phospholipids in homogenate of bone-marrow-derived murine macrophages.

Fatty acid composition of plasma and erythrocyte phospholipids in preterm infants

Erythrocyte and plasma phospholipid fatty acids were determined in preterm babies at 0, 6 and 10 weeks. There were highly significant changes in fatty acid composition between birth and 6 weeks in both plasma and erythrocyte phospholipids, the changes being more numerous and quantitatively greater in phosphatidyl choline. There was little further change by 10 weeks. Linoleic acid increased by approximately 100% at 6 weeks in plasma phosphatidyl ethanolamine and 200% in phosphatidyl choline. In erythrocyte phosphatidyl ethanolamine, linoleic acid increased by approximately 150% at 6 weeks and in phosphatidyl choline increased 170%. Arachidonic acid decreased by 54%. The essential fatty acid status of the preterm babies studied using contemporary feeding regimes was satisfactory and by 6 weeks phospholipid fatty acid profiles were comparable with published data for normal healthy breast-fed infants.

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.

Modification by clofibric acid of acyl composition of glycerolipids in rat liver. Possible involvement of fatty acid chain elongation and desaturation

Administration of p-chlorophenoxyisobutyric acid (clofibric acid) to rats induced a marked change in acyl composition of hepatic glycerolipids; a considerable increase in the proportion of octadecenoic acid (18:1) was accompanied by a marked decrease in the proportion of octadecadienoic acid (18:2). Among the glycerolipids, the changes in the proportions of 18:1 and 18:2 were the most marked in phosphatidylcholine. The change in the acyl composition of phosphatidylcholine paralleled the change in free fatty acid composition in microsomes. The treatment of rats with clofibric acid resulted in a 2.3-fold increase in activity of microsomal palmitoyl-CoA chain elongation and a 4.8-fold increase in activity of stearoyl-CoA desaturation. The activities of acyl-CoA synthetase, 1-acylglycerophosphate acyltransferase and 1-acylglycerophosphorylcholine acyltransferase in hepatic microsomes were increased approx. 3-, 1.7- and 3.6-times, respectively, by the treatment of rats with clofibric acid. These findings are discussed with respect to the role of fatty acid modification systems in the regulation of acyl composition of phosphatidylcholine.

Acyl-CoA synthase and acyltransferase activity in developing skeletal muscle membranes

Enzymes participating in the activation and esterification of fatty acids for complex lipid biosynthesis were characterized in neonatal and adult rabbit skeletal muscle membranes. The activity of acyl-CoA synthase was 1.4-1.6-fold greater in neonatal vs. adult sarcoplasmic reticulum for the fatty acid substrates linoleic (2.6 vs. 1.61 nmol 18:2-CoA/min per mg), stearic (0.94 vs. 0.66 nmol 18:0-CoA/min per mg) and palmitic (2.43 vs. 1.51 nmol 16:0-CoA/min per mg) acids. Enzyme activity was identical between neonate and adult for coenzyme A, ATP and linoleic acid concentration dependence. Glycerol-3-phosphate acyltransferase activity was 6-fold greater in neonatal than adult sarcoplasmic reticulum for both linoleoyl-CoA (1.4 vs. 0.22 nmol 18:2/min per mg) and stearoyl-CoA (1.1 vs. 0.13 nmol 18:0/min per mg) donor substrates, whereas lysophosphatidylcholine acyltransferase activity was similar. Enriched fractions of sarcolemmal membranes possessed the highest activity for lysophosphatidylcholine acyltransferase activity, being 2-4-fold greater than sarcoplasmic reticulum. In contrast to sarcoplasmic reticulum, lysophosphatidylcholine acyltransferase activity was 2-3-fold greater in neonatal compared to adult sarcolemma for lineoleic (18.9 vs. 8.5 nmol 18:2/min per mg) and the stearic (2.8 vs. 0.68 nmol 18:0/min per mg) acid incorporation. The greater capacity of neonatal membranes for acylation by the de novo pathway is in accord with the requirements for neonatal muscle to effect high rates of triacylglycerol and phospholipid synthesis essential for oxidative metabolism and membrane synthesis during postnatal development and growth.

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.

Fatty acid activation and transfer in blood cells of patients with muscular dystrophy

Two membrane-bound enzymes, concerned in repair of erythrocyte membranes, have been investigated in patients with muscular dystrophy. The activation of long-chain fatty acids is normal in erythrocytes from Duchenne patients, but increases two-fold in cells from myotonic dystrophy patients (congenital form). This alteration is not present in leucocytes. In all leucocytes tested palmitate was the preferred substrate while palmitoleate and linoleate were activated at a lower rate. In the erythrocytes the 3 fatty acids were activated at the same rate. Carnitine palmitoyltransferase was not significantly altered in erythrocytes of both groups of patients.

Interaction of plasma lipoproteins with erythrocytes. I. Alteration of erythrocyte morphology

Intact erythrocytes incubated in the presence of low density lipoproteins (LDL) undergo a time-dependent morphologic transformation from biconcave discs to spherocytes within 4 h. No shape change is observed when erythrocytes are incubated with high density lipoproteins (HDL). The LDL-induced change in erythrocyte morphology occurs without concomitant leakage of hemoglobin from the cell or depletion of intracellular ATP; no change in the distribution of the major lipids of the erythrocyte membranes was detected. The alteration of morphology does require attachment of LDL to the erythrocyte surface. The LDL-induced morphologic alteration is inhibited by HDL, but not by serum albumin. HDL prevent the attachment of LDL to the cell membrane; however, the HDL subfractions, HDL2 and HDL3, are only partially effective. These data suggest that normal erythrocyte morphology and cell function may depend on the concentration and composition of the circulating lipoproteins.

Erythrocyte spectrin alteration induced by low-density lipoprotein

Addition of human plasma low-density lipoproteins (LDL) to intact human erythrocytes induces the erythrocytes to undergo morphologic transition from biconcave disks to echinocytes and spherocytes. The transformation is time-dependent. Two hours are required before echinocytes are detected by scanning electron microscopy. After two hours, LDL also decrease the phosphate content of spectrin by 40% relative to the control, suggesting that these lipoproteins modulate cell shape by influencing phosphorylation-dephosphorylation of a membrane-associated cytoskeletal protein. LDL do not induce depletion of intracellular adenosine triphosphate (ATP), nor do they inhibit cyclic adenosine monophosphate-independent protein kinases which phosphorylate spectrin. LDL stimulate membrane-bound phosphatases by a factor of two, thereby reducing the amount of phosphate covalently bound to membrane proteins. The observed effects are specific for LDL. High-density lipoproteins (HDL) do not stimulate dephosphorylation of spectrin or alter erythrocyte morphology. However, HDL protect the erythrocytes against LDL-induced alterations. These data suggest that the circulating lipoproteins have a role in maintaining erythrocyte morphology by regulating the extent of phosphorylation of spectrin.