Effect of "marine" phospholipids omega-3 fatty acids on the composition of fatty acids of rat liver microsomal membrane under oxidative stress

As a result of experiments conducted the marine phospholipids preparation enriched by omega-3 fatty acids was defined to modify fatty acids content due to changes of fatty acids level change in the neutral lipids and phospholipids fractions. As well it was identified, that at the oxidative stress induced by administration of CCl4 the growth of arachidonic and docozahexaenoic acids in the neutral lipids fractions was observed if compare with the norm. At the same time, the presented fatty acids in the phospholipids fractions remained unchanged. At oxidative stress the phospholipids fraction reacts to levels of arachidonic and docozahexaenoic acids just only as a result of administrating phospholipids with omega-3 fatty acids. The most attractive is the change of correlation C20:4/C22:6--increasing at administration of CCl4 and decreasing both at phospolipids and vitamin E injection. Thus, at the oxidative stress the first reacting ones are the fatty acids of neutral lipids microsomal membranes.     

Influence of saturated long-chain N-acylethanolamines on lipid composition and heart contractility of isolated rat heart under ischemia-reperfusion

The heart contractility and changes of lipid composition of isolated rat heart (n = 26) under total ischemia and ischemia-reperfusion was studied. The effect of N-stearoyl-ethanolamine under these conditions was investigated. N-stearoyl-ethanolamine leads to remodelling of fatty acyl chain composition of myocardial phospholipids: to drastic fall of polyunsaturated fatty acyl chains (18:2w6, 20:3w6, 20:4w6, 22:5w3, 22:5w6, 22:6w3 and 22:6w6) and enhancement of 18:0. This can be caused by N-stearoyl-ethanolamine-induced suppression of polyunsaturated fatty acids synthesis. Naturally occurring minor lipids--N-acyl phosphatidylethanolamine and its derivative N-acylethanolamine were detected in isolated rat heart under ischemia-reperfusion. It is notable that approximately 12% of total N-acylethanolamines were composed by anandamide. Treatment of N-acyl phosphatidylethanolamine by phospholipase D with subsequent fatty acyl chain analysis demonstrates that fatty acid composition of both N-acyl chains of N-acyl phosphatidylethanolamine and free N-acylethanolamine are similar and their main fatty acyl chains are 16:0, 18:0 and 20:4w6. It was shown that exogenous N-stearoyl-ethanolamine did not alter the levels of endogenous N-acyl phosphatidylethanolamine and N-acylethanolamine, but caused the decrease of lyso-phosphatidylcholine and phosphatidylglycerol levels. The rate of heart contractility and heart relaxation was found to increase during the early period of reperfusion. N-stearoyl-ethanolamine prevents this alteration and exerts a negative inotropic effect. It is concluded that membrane protective properties of N-stearoyl-ethanolamine at least partly depend on its ability to inhibit decrease amount of arachidonic and docosahexaenoic acids, to modulate the fatty acyl chains of cardiac phospholipids and to decrease the level of lyso-phosphatidylcholine.     

Fatty acid incorporation is decreased in astrocytes cultured from alpha-synuclein gene-ablated mice

Because alpha-synuclein may function as a fatty acid binding protein, we measured fatty acid incorporation into astrocytes isolated from wild-type and alpha-synuclein gene-ablated mice. alpha-Synuclein deficiency decreased palmitic acid (16:0) incorporation 31% and arachidonic acid [20:4 (n-6)] incorporation 39%, whereas 22:6 (n-3) incorporation was unaffected. In neutral lipids, fatty acid targeting of 20:4 (n-6) and 22:6 (n-3) (docosahexaenoic acid) to the neutral lipid fraction was increased 1.7-fold and 1.6-fold, respectively, with an increase in each of the major neutral lipids. This was consistent with a 3.4- to 3.8-fold increase in cholesteryl ester and triacylglycerol mass. In the phospholipid fraction, alpha-synuclein deficiency decreased 16:0 esterification 39% and 20:4 (n-6) esterification 43% and decreased the distribution of these fatty acids, including 22:6 (n-3), into this lipid pool. alpha-Synuclein gene-ablation significantly decreased the trafficking of these fatty acids to phosphatidylinositol. This observation is consistent with changes in phospholipid fatty acid composition in the alpha-synuclein-deficient astrocytes, including decreased 22:6 (n-3) content in the four major phospholipid classes. In summary, these studies demonstrate that alpha-synuclein deficiency significantly disrupted astrocyte fatty acid uptake and trafficking, with a marked increase in fatty acid trafficking to cholesteryl esters and triacylglycerols and decreased trafficking to phospholipids, including phosphatidylinositol.     

OCCURRENCE OF OCTADECAPENTAENOIC ACID IN LIPIDS OF A COLD STENOTHERMIC ALGA,PRYMNESIOPHYTE STRAIN B1

The fatty acid composition of the prymnesiophyte strain B, a cold stenothermic microalga, was examined. The major fatty acids derived from the total lipids in this strain were myristic (14:0), palmitic (16:0), oleic (18:1ω9), linoleic (18:2ω6), octadecatetraenoic (18:4ω3), octadecapentaenoic (18:5ω3), and docosahexaenoic (22:6ω3) acids. Octadecapentaenoic acid (18:5ω3) was an unusual component and was characterized by mass spectrometry, infrared absorption spectrometry, and proton nuclear magnetic resonance spectrometry. Saturated fatty acids (14:0 and 16:0) and 18:5ω3 were distributed at significant levels in the major classes of galactolipids (monogalacto-syldiacylglycerol, digalactosyldiacylglycerol, and sulfoqui-novosyldiacylglycerol), phospholipids (phosphatidylcholine, phosphatidylglycerol, and phosphatidylethanolamine), and neutral lipids with the exception that phosphatidylethanolamine contained only trace amounts of 14:0. By contrast, 22:6ω3 was distributed in phospholipids and neutral lipids. A decrease in growth temperature from 5°C to 2°C was accompanied by a significant increase in levels of 18: 5ω3 and 18:4ω3 with a concomitant decrease in the level of saturated fatty acids, whereas the level of 22:6ω3 was scarcely changed. These results suggest that, in prymnesiophyte strain B, eighteen-carbon polyunsaturated fatty acids with more than three double bonds, 18:5ω3 in particular, serve as modulators of membrane fluidity. The potential role of 18:5ω3 as a specific marker for prym-nesiophytes is also discussed.     

Turnover of phospholipid fatty acyl chains in cultured neuroblastoma cells: involvement of deacylation-reacylation and de novo synthesis in plasma membranes

Cultured neuroblastoma cells (NIE-115) rapidly incorporated the essential fatty acid, linoleic acid (18:2 (n = 6), into membrane phospholipids. Fatty acid label appeared rapidly (2-10 min) in plasma membrane phospholipids without evidence of an initial lag. Specific activity (nmol fatty acid/mumol phospholipid) was 1.5-2-fold higher in microsomes than in plasma membrane. In these membrane fractions phosphatidylcholine had at least 2-fold higher specific activity than other phospholipids. With 32P as radioactive precursor, the specific activity of phosphatidylinositol was 2-fold higher compared to other phospholipids in both plasma membrane and microsomes. Thus a differential turnover of fatty acyl and head group moieties of both phospholipids was suggested. This was confirmed in dual-label (3H fatty acid and 32P), pulse-chase studies that showed a relatively rapid loss of fatty acyl chains compared to the head group of phosphatidylcholine; the opposite occurred with phosphatidylinositol. A high loss of fatty acyl chain relative to phosphorus indicated involvement of deacylation-reacylation in fatty acyl chain turnover. The patterns of label loss in pulse-chase experiments at 37 and 10 degrees C indicated some independent synthesis and modification of plasma membrane phospholipids at the plasma membrane. Lysophosphatidylcholine acyltransferase and choline phosphotransferase activities were demonstrated in isolated plasma membrane in vitro. Thus, studies with intact cells and with isolated membrane fractions suggested that neuroblastoma plasma membranes possess enzyme activities capable of altering phospholipid fatty acyl chain composition by deacylation-reacylation and de novo synthesis at the plasma membrane itself.     

Plasma and muscle phospholipids are involved in the metabolic response to long-distance migration in a shorebird

We studied: (1) concentrations and fatty acid compositions of plasma non-esterified fatty acids, neutral lipids, and phospholipids, and (2) fatty acid composition of flight muscle phospholipids in wintering, premigratory, and spring and fall migrating western sandpipers ( Calidris mauri). Plasma neutral lipid and phospholipid levels were elevated in migrants, reflecting high rates of fat deposition. An important role of phospholipids in fattening is suggested by the fact that the amount of fatty acids in plasma phospholipids was similar to, or in spring as much as twice, that of neutral lipids. Changes in the ratio of plasma neutral lipids to phospholipids may indicate seasonal changes in triacylglycerol stores of invertebrate prey. Monounsaturation and total unsaturation of plasma neutral lipids and phospholipids increased during migration. Muscle phospholipids were more monounsaturated in spring and fall, but total unsaturation was reduced in fall. Arachidonic acid [20:4(n-6)] was especially abundant in muscle phospholipids in winter (29%) and declined during migration (19-22%), contributing to a decline in the ratio of n-6 to n-3 fatty acids. The abundance of plasma phospholipids and variability of neutral lipid to phospholipid ratio indicates that measurement of plasma phospholipids will improve methods for assessment of fattening rates of birds. The functional significance of changes in muscle phospholipids is unclear, but may relate to depletion of essential n-6 fatty acids during exercise.     

Head group precursors modify phospholipid synthesis in Schistosoma mansoni

The two predominant phospholipids in schistosomula of Schistosoma mansoni are phosphatidylcholine (PC) and phosphatidylethanolamine (PE) which are found in a molar ratio of 0.52 (PE/PC). The incorporation of four fatty acids (arachidonic, myristic, oleic, and palmitic) and glycerol into phospholipids of schistosomula was measured. In two different media (one containing ethanolamine, the other without), all four fatty acids were predominantly incorporated into PC with a PE/PC ratio of approximately 0.1 in a 90-min label. After a 24-h chase, PC remained the predominant labeled phospholipid but the fatty acid-labeled PE/PC ratio increased slightly, the specific activity of labeled neutral lipids decreased, and the specific activity of labeled PE increased. Glycerol was incorporated with a ratio of 0.55 in the presence of ethanolamine but only 0.19 in its absence. Schistosomula also incorporate fatty acids into phosphatidylmonomethylethanolamine (PMME) and phosphatidyldimethylethanolamine (PDME) at rates intermediate to that into PE and PC in the presence of the respective head group precursor; this incorporation was inhibited by choline. Relative to PC, oleic acid is incorporated into PE, PMME, and PDME at rates higher than for palmitic acid. These results suggest that schistosomula possess acyltransferase(s) with head group specificity and that acyl chains are transferred from neutral lipids to phospholipids over time.     

The acyl composition of mammalian phospholipids: an allometric analysis

Data concerning the acyl composition of tissue phospholipids from mammal species, ranging in size from the shrew (7 g) to cattle (370 kg), has been collated from the literature and analysed allometrically. Phospholipids from heart, skeletal muscle, liver and kidney exhibited similar allometric trends whereby phospholipids had a significant decrease in unsaturation index (number of double bonds per 100 acyl chains) as species body size increased whilst there was no change in the percent of unsaturated acyl chains. Whilst total polyunsaturate content did not change with body mass, both heart and skeletal muscle phospholipids showed a significant allometric decrease in the omega-3 polyunsaturate content. The content of the highly polyunsaturated docosahexaenoic acid (22:6 n-3) in phospholipids showed significant and substantial allometric decline with increasing body mass in all four tissues (exponents ranged from -0.19 in liver to -0.40 in skeletal muscle). Brain phospholipids showed no allometric trends in acyl composition and were highly polyunsaturated in all species. These trends are discussed in light of the hypothesis that the relative content of polyunsaturated acyl chains in membranes, and especially docosahexaenoate (22:6 n-3), can act as a membrane pacemaker for metabolic activity.     

Docosahexaenoic acid: membrane properties of a unique fatty acid

Docosahexaenoic acid (DHA) with 22-carbons and 6 double bonds is the extreme example of an omega-3 polyunsaturated fatty acid (PUFA). DHA has strong medical implications since its dietary presence has been positively linked to the prevention of numerous human afflictions including cancer and heart disease. The PUFA, moreover, is essential to neurological function. It is remarkable that one simple molecule has been reported to affect so many seemingly unrelated biological processes. Although details of a molecular mode of action remain elusive, DHA must be acting at a fundamental level common to many tissues that is related to the high degree of conformational flexibility that the multiple double bonds have been identified to confer. One likely target for DHA action is at the cell membrane where the fatty acid is known to readily incorporate into membrane phospholipids. Once esterified into phospholipids DHA has been demonstrated to significantly alter many basic properties of membranes including acyl chain order and "fluidity", phase behavior, elastic compressibility, permeability, fusion, flip-flop and protein activity. It is concluded that DHA's interaction with other membrane lipids, particularly cholesterol, may play a prominent role in modulating the local structure and function of cell membranes.     

Astrocytes, Not Neurons, Produce Docosahexaenoic Acid (22:6ω-3) and Arachidonic Acid (20:4ω-6)

Elongated, highly polyunsaturated derivatives of linoleic acid (18:2 omega-6) and linolenic acid (18:3 omega-3) accumulate in brain, but their sites of synthesis are not fully characterized. To investigate whether neurons themselves are capable of essential fatty acid elongation and desaturation or are dependent upon the support of other brain cells, primary cultures of rat neurons and astrocytes were incubated with [1-14C] 18:2 omega-6, [1-14C]20:4 omega-6, [1-14C]18:3 omega-3, or [1-14C]20:5 omega-3 and their elongation/desaturation products determined. Neuronal cultures were routinely incapable of producing significant amounts of delta 4-desaturase products. They desaturated fatty acids very poorly at every step of the pathway, producing primarily elongation products of the 18- and 20-carbon precursors. In contrast, astrocytes actively elongated and desaturated the 18- and 20-carbon precursors. The major metabolite of 18:2 omega-6 was 20:4 omega-6, whereas the primary products from 18:3 omega-3 were 20:5 omega-3, 22:5 omega-3, and 22:6 omega-3. The majority of the long-chain fatty acids formed by astrocyte cultures, particularly 20:4 omega-6 and 22:6 omega-3, was released into the extracellular fluid. Although incapable of producing 20:4 omega-6 and 22:6 omega-3 from precursor fatty acids, neuronal cultures readily took up these fatty acids from the medium. These findings suggest that astrocytes play an important supportive role in the brain by elongating and desaturating omega-6 and omega-3 essential fatty acid precursors to 20:4 omega-6 and 22:6 omega-3, then releasing the long-chain polyunsaturated fatty acids for uptake by neurons.     

Synaptamide,endocannabinoid-like derivative of docosahexaenoic acid with cannabinoid-independent function

Docosahexaenoylethanolamide, the structural analog of the endogenous cannabinoid receptor ligand anandamide, is synthesized from docosahexaenoic acid (DHA) in the brain. Although docosahexaenoylethanolamide binds weakly to cannabinoid receptors, it stimulates neurite growth, synaptogenesis and glutamatergic synaptic activity in developing hippocampal neurons at concentrations of 10–100 nM. We have previously proposed the term synaptamide for docosahexaenoylethanolamide to emphasize its potent synaptogenic activity and structural similarity to anandamide. Synaptamide is subjected to hydrolysis by fatty acid amide hydrolase, and can be oxygenated to bioactive metabolites. The brain synaptamide content is dependent on the dietary DHA intake, suggesting an endogenous mechanism whereby diets containing adequate amounts of omega-3 fatty acids improve synaptogenesis in addition to well-recognized anti-inflammatory effects.     

Membrane lipids of Mycoplasma orale: lipid composition and synthesis of phospholipids.

Lipid composition of Mycoplasma orale was examined and compared with that of horse serum added to the growth medium. Ratios of cholesterol/cholesterol ester and sphingomyelin/phosphatidylcholine were much higher in M. orale than in the horse serum, indicating the organism incorporates selectively cholesterol and sphingomyelin. A distinct difference between the lipids from the two sources was that in phospholipids of M. orale almost all (greater than 95%) of the fatty acyl residues were saturated whereas nearly half of the residues were unsaturated in horse serum phospholipids. Approximately one third of M. orale phospholipids was phosphatidylglycerol, which was synthesized by the organism as was demonstrated by 32P-labeling experiment. Its acyl residues consisted mainly of C16:0 and were efficiently labeled with 14C-palmitate but not with 14C-acetate. These results clearly indicate the de novo synthesis of phosphatidylglycerol by M. orale is through acylation with exogenous saturated fatty acids. On the other hand, all the phosphatidylcholine and sphingomyelin of M. orale were derived from the medium. The 14C-labeling experiment demonstrates that no fatty acid synthesis takes place nor exogenous fatty acid can be incorporated so efficiently as phosphatidylglycerol, suggesting that extremely high proportion of saturated fatty acyl residues in these phospholipids is the consequence of saturation directed to the acyl chains of the incorporated phospholipids.     

Active labeling of phosphatidylcholines by [1-14C]docosahexaenoate in isolated photoreceptor membranes

Isolated bovine rod outer segments and photoreceptor disks actively incorporated [1-14C]docosahexaenoate (22:6) into phospholipids when incubated in the presence of CoA, ATP, and Mg2+. About 80% of the esterified fatty acid was in phosphatidylcholine (PC). Microsomal and mitochondrial fractions incorporated as much 22:6 as rod outer segments, but it was distributed among various phospholipids and neutral glycerides. The isolated photoreceptor membrane thus contains an acyl-CoA synthetase which activates the fatty acid and a docosahexaenoyl-CoA-lysophosphatidylcholine acyltransferase activity. The specific radioactivity of PC was higher in rod outer segments than in the other subcellular fractions. About 2/3 of the label in photoreceptor membrane PC was in its dipolyunsaturated molecular species and 1/3 in hexaenes. Dipolyunsaturated PCs showed high turnover rates of 22:6 in all three subcellular membranes, especially in mitochondria. Retinal membranes in vitro seem to take up free [14C]22:6 from the medium by simple diffusion or partition into the membrane lipid. The ability of these membranes to activate and esterify [1-14C]22:6 indicates that docosahexaenoate-containing molecular species of retina lipids, including those of photoreceptor membranes, are subject to acylation-deacylation reactions in situ.     

Lipid composition of Mycoplasma neurolyticum

The total lipid content of Mycoplasma neurolyticum comprises about 14% of the dry weight of the organisms and is about equally distributed between the phospholipid and the neutral-glycolipid fractions. The neutral lipids were identified as triglycerides, diglycerides, and cholesterol. The glycolipid fraction contained 1-O-beta-glucopyranosyl-d-2,3-diglyceride and 1-[O-beta-d-glycopyranosyl-(1-->6)-O-beta-d-glucopyranosyl]-d-2,3-diglyceride. The latter lipid is structurally identical to the diglucosyl diglyceride which occurs in Staphylococcus aureus. The phospholipids of the organism consist of a fully acylated glycerophosphoryl-glycerophosphoryl glycerol, phosphatidic acid, diphosphatidyl glycerol, phosphatidyl glycerol, and amino acyl esters of phosphatidyl glycerol. Phosphatidic acid and phosphatidyl glycerol account for greater than 90% of the phospholipids of organisms in the exponential phase of growth. The predominant fatty acids found in all of the acyl lipids were palmitic, stearic, and oleic acids.     

Isolation and composition of the carotenoid-containing oil droplets from cone photoreceptors.

A procedure for isolating the carotenoid-containing oil droplets of cone retinal photoreceptors of Gallus domesticus is described. The oil droplets, composed almost entirely of neutral lipids and carotenoids, have been separated into ten chromatographic components. Similar separations have been carried out on the total retinal neutral lipids for comparison. The neutral lipids represented 26.1% of the total retinal lipid. Cholesterol, cholesterol ester, mono-, di- and triacylglycerols represented 92.6% of the total neutral lipid. Each of these and other minor neutral lipid components were also present in the lipids extracted from the isolated oil droplets in correspondingly similar concentrations. However, the concentrations of carotenoids were greatly enriched in the neutral lipids of the oil droplets. Each of the major fatty acyl-containing neutral lipids from the chromatography of oil droplet lipids is greatly enriched in polyunsaturated fatty acids when compared with the corresponding component from the total neutral lipid chromatography. In the acylglycerols and free fatty acid fraction from the oil droplets, linoleic and arachidonic acid together represented 52-83% of the total polyunsaturated fatty acids present. The remainder was generally distributed about equally among six other acids. Except for the diacylglycerol fraction, linoleic acid was usually the most enriched acid in a specific oil droplet fraction when compared with any other polyunsaturated fatty acids. A similar pattern of polyunsaturated fatty acid enrichment observed in the fatty acids of the outer segment phospholipids relative to the corresponding total phospholipid fractions of this cone rich retina (Johnston, D. and Hudson, R.A. (1974) Biochim. Biophys. Acta 369, 269) suggest possible metabolic relationships between the oil droplet neutral lipids and the outer segment membrane phospholipids of the cone photoreceptors. A mechanism for the accumulation of the carotenoids in the oil droplets is also discussed.     

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

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

Docosahexaenoic,arachidonic, palmitic,and oleic acids are differentially esterified into phospholipids of frog retina

Docosahexaenoic acid (22:6n-3) is highly enriched in the retina. To determine if retinal cells take up and metabolize fatty acids in a specific manner, retinas from Rana pipiens were incubated for 3 h with an equimolar mixture of tritiated 22:6n-3, arachidonic acid (20:4n-6), palmitic acid, and oleic acid. The radiolabeling of retinal lipids was determined and compared to the endogenous fatty acid content of the lipids. The results showed that in most, but not all, cases, the relative labeling with the four precursor fatty acids was similar to their relative abundance in each glycerolipid. Thus, during retinal glycerolipid synthesis, either through de novo or acyl exchange reactions, fatty acids are incorporated in proportions reflecting their steady-state mass levels. Since other studies with labeled glycerol have shown greater differences between early labeling patterns and molecular species mass, the final incorporation we report may be due primarily to acyl exchange reactions.     

Complete retention of phospholipid acyl groups by mammalian cells in culture.

Radiolabeled phosphate, acetate, and glycerol are incorporated into strain L-fibroblast phospholipids. The acetate and glycerol specifically label the fatty acid and glycerol moieties, respectively, of the phospholipids. To study the metabolic fate of the various moieties of phospholipids, cells incubated with the above radiolabeled compounds were transferred to unlabeled medium, and the rate at which phospholipid radioactivity per 10(6) cells decreased was determined. The rate of decrease expected on the basis of cell division alone was estimated either by monitoring increases in cell number, or by measuring the rate at which radiolabeled DNA per 10(6) cells decreased. Both phospholipid phosphorus and glycerol are lost at a rate greater than can be accounted for by cell division alone. By contrast, nearly all phospholipid acyl chains were retained by the cell to the same extent as radiolabeled DNA. While presence of nonradioactive glycerol in the medium increased the rate at which glycerol was lost from phospholipid, the addition of exogenous fatty acid was without effect on the retention of phospholipid acyl groups. The acyl-glycerol bond of phosphatidylcholine is metabolically more labile than that of phosphatidylethanolamine. Together the data suggest that although L-fibroblast phospholipids undergo deacylation-reacylation reactions, the acyl chains do not equilibrate with either extracellular or intracellular pools of unesterified fatty acid.     

Role of the Blood-Brain Barrier in the Formation of Long-Chain ω-3 and ω-6 Fatty Acids from Essential Fatty Acid Precursors

Elongated, more highly polyunsaturated derivatives of linoleic acid (18:2 omega-6) and linolenic acid (18:3 omega-3) accumulate in brain, but their sites of synthesis and mechanism of entry are not well characterized. To investigate the role of the blood-brain barrier in this process, cultured murine cerebromicrovascular endothelia were incubated with [1-14C]18:2 omega-6 or [1-14C]18:3 omega-3 and their elongation/desaturation products determined. The major metabolite of 18:2 omega-6 was 20:4 omega-6, whereas the primary product from 18:3 omega-3 was 20:5 omega-3. Although these products were found primarily in cell lipids, they were also released from the cells and gradually accumulated in the extracellular fluid. Eicosanoid production was observed from the 20:4 omega-6 and 20:5 omega-3 that were formed. No 22:5 omega-6 or 22:6 omega-3 fatty acids were detected, suggesting that these endothelial cells are not the site of the final desaturation step. Although the uptake of 18:3 omega-3 and 18:2 omega-6 was nearly identical, 18:3 omega-3 was more extensively elongated and desaturated. Competition experiments demonstrated a preference for 18:3 omega-3 by the elongation/desaturation pathway. These findings suggest that the blood-brain barrier can play an important role in the elongation and desaturation of omega-3 and omega-6 essential fatty acids during their transfer from the circulation into the brain.     

Complex lipid metabolic remodeling is required for efficient hepatitis C virus replication

The hepatitis C virus (HCV) life cycle is tightly linked to the host cell lipid metabolism with the endoplasmic reticulum–derived membranous web harboring viral RNA replication complexes and lipid droplets as virion assembly sites. To investigate HCV-induced changes in the lipid composition, we performed quantitative shotgun lipidomic studies of whole cell extracts and subcellular compartments. Our results indicate that HCV infection reduces the ratio of neutral to membrane lipids. While the amount of neutral lipids and lipid droplet morphology were unchanged, membrane lipids, especially cholesterol and phospholipids, accumulated in the microsomal fraction in HCV-infected cells. In addition, HCV-infected cells had a higher relative abundance of phosphatidylcholines and triglycerides with longer fatty acyl chains and a strikingly increased utilization of C18 fatty acids, most prominently oleic acid (FA [18:1]). Accordingly, depletion of fatty acid elongases and desaturases impaired HCV replication. Moreover, the analysis of free fatty acids revealed increased levels of polyunsaturated fatty acids (PUFAs) caused by HCV infection. Interestingly, inhibition of the PUFA synthesis pathway via knockdown of the rate-limiting Δ6-desaturase enzyme or by treatment with a high dose of a small-molecule inhibitor impaired viral progeny production, indicating that elevated PUFAs are needed for virion morphogenesis. In contrast, pretreatment with low inhibitor concentrations promoted HCV translation and/or early RNA replication. Taken together our results demonstrate the complex remodeling of the host cell lipid metabolism induced by HCV to enhance both virus replication and progeny production.