Incorporation of arachidonic,dihomogamma linolenic and eicosapentaenoic acids into cultured V79 cells

The uptake and distribution of three common dietary polyunsaturated fatty acids was studied using Chinese hamster lung fibroblasts (V79 cells). Treatment of V79 cells with arachidonic (20∶4), eicosapentaenoic (20∶5) and dihomogammalinolenic (20.3) acids for 24 hr produced a marked uptake of 20∶3 and 20∶4, both of which were assimilated to a considerably greater degree than 20∶5. All polyunsaturated fatty acids were incorporated primarily into phospholipids; however, there were considerable differences in their distribution into individual phospholipid species. Although 20∶4 was incorporated primarily into phosphatidylcholine, 20∶3 entered largely into phosphatidylethanolamine and phosphatidylglycerol, and 20∶5 was distributed about equally between phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol. A marked conversion of 20∶3 to 20∶4 was found after 24 hr and, in several phospholipids, there was as much derived-radiolabeled 20∶4 as there was radiolabeled 20∶3. There was little evidence of 20∶4 and 20∶5 metabolism. V79 cells undergo substantial changes in phospholipid fatty acid composition following supplementation with these polyunsaturated fatty acids; however, these fatty acids are assimilated to different degrees and their distribution among cellular phospholipids is distinct, suggesting incorporation via independent mechanisms.     

Incorporation of arachidonic acid and eicosapentaenoic acid into phospholipids by polymorphonuclear leukocytes in vitro

The present study demonstrated that the patterns of the incorporation of [1-¹⁴C] arachidonic acid and [1-¹⁴C] eicosapentaenoic acid into individual phospholipids by polymorphonuclear leukocytes were similar. However, human leukocytes exhibited higher activity than guinea pig periotoneal leukocytes in the formation of arachidonoyl- and eicosapentaenoyl-phosphatidic acid. Cells from both origins showed a decrease of label in phosphatidylcholine accompanied by an increase of label in phosphatidylethanolamine after a longer period (30–120 min) of incubation, suggesting that part of the arachidonoyl or eicosapentaenoyl moiety in phosphatidylethanolamine may be derived from that of phosphatidylcholine. The observed difference between human cells and elicited cells in the time-course of the incorporation of both fatty acids into phosphatidylcholine and phosphatidylethanolamine appears to be due to different contents of the diacyl and ether-linked class compositions of these phospholipids in cells from different origins. Both labeled fatty acids were incorporated more rapidly into the diacyl-linked class, but were retained to a greater extent in alkylacyl-phosphatidyl-choline and alkenylacyl-phosphatidylethanolamine. The data suggest that, in addition to alkylacyl-phosphatidylcholine and phosphatidylinositol, alkenylacyl-phosphatidylethanolamine may be an important endogenous source of arachidonic acid and eicosapentaenoic acid in stimulated human leukocytes.     

Differential effects of eicosapentaenoic acid and docosahexaenoic acid on human skin fibroblasts

To better understand the mode of action of ω3 fatty acids in cell membranes, human foreskin fibroblasts were grown in serum-free medium supplemented with 50 μM oleic acid linoleic acid, eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA), and the effects on membrane composition, fluorescence polarization and enzyme activities were followed. The cells were enriched with EPA and DHA up to 7 and 13% of total lipids, respectively, of which >95% was associated with phospholipids. In addition, the concentration of 22∶5n−3 increased with both EPA and DHA to 7.5, and 2.1% of the total fatty acids, respectively. When compared to controls (oleic acid), cells treated with DHA showed a decrease in cholesterol, phospholipids, arachidonic acid (AA) and free cholesterol/phospholipid ratio (P<0.05). In the presence of EPA, only decreases in AA and cholesterol were significant (P<0.05). Membrane fluidity, assessed by fluorescence anisotropy, was increased 16% in cells enriched with DHA (P<0.05), but showed no change with EPA or linoleic acid. There was an increase in membrane-associated 5′-nucleotidase (+27%) and adenylate cyclase (+19%) activities (P<0.05), in DHA-enriched, but not in EPA-enriched cells, when compared with oleate controls. The studies show that incorporation of DHA, but not EPA, into cell membranes of fibroblasts alters membrane biophysical characteristics and function. We suggest that these two major n−3 fatty acids of fish oils have differential effects on cell membranes, and this may be related to the known differences in their physiological effects.     

Incorporation of linolenic-1-C14 acid into eicosapentaenoic and docosahexaenoic acids in fish

Following intraperitoneal injection of methyl linolenate-1-C¹⁴ into kelp bass,Paralablax clathratus, the highly polyunsaturated fatty acids of their body fats were concentrated by low temperature crystallization from acetone, and eicosapentaenoic and docosahexaenoic acids were isolated from the concentrate by reversed-phase chromatography and hydrogenated. The resulting arachidic and behenic acids were degraded stepwise to margaric acid, and the distribution of activity was determined. The results indicate that the injected linolenic acid was converted to eicosapentaenoic acid and the latter incorporated into docosahexaenoic acid. A probable conversion pathway is linolenic acid→6,9,12,15-octadecatetraenoic acid→8,11,14,17-eicosatetraenoic acid→5,8,11,14,17-eicosapentaenoic acid→7,10,13,16,-19-docosapentaenoic acid→4,7,10,13,16,19-docosahexaenoic acid. Supported by a training grant from the National Heart Institute, Bethesda, Md. This paper based partially on work performed under Contract AT(04-1)GEN-12 between the Atomic Energy Commission and the University of California.     

Comparison of linoleic acid and eicosapentaenoic acid incorporation into human breast cancer cells

To gain some insight into the mechanisms involved in the opposing effects of linoleic acid (LA) and eicosapentaenoic acid (EPA) on the growth and invasiveness of MDA-MB-435 human breast cancer cells, the dynamics of the uptake by cells and the incorporation of [¹⁴C]LA and [¹⁴C]EPA into major lipid and phospholipid pools, as well as the effects of unlabeled EPA or LA on the uptake and distribution of [¹⁴C]LA or [¹⁴C]EPA, respectively, were examined. Cells were exposed to [¹⁴C]LA (1.28 μg/mL) or [¹⁴C]EPA (1.0 μg/mL) and unlabeled EPA or LA, respectively, at 0, 1, 4 and 16 μg/mL for 24 h in serum-free media. The uptake of each fatty acid (FA) was linear over time and was not affected by the presence of the opposing FA. For both FA, 80–90% was incorporated into the phospholipid fraction with the remaining 10–20% in neutral lipids. The relative distribution profile of [¹⁴C]LA among the phospholipid classes indicated a preferential incorporation into phosphatidylcholine (65%), whereas [¹⁴C]EPA was mostly found in phosphatidylethanolamine (58%). In the presence of unlabeled EPA or LA at various concentrations, corresponding dose-dependent shifts of [¹⁴C]LA or [¹⁴C]EPA from the phospholipid to the neutral lipid pool were noted, which did not alter the relative distribution of the FA among the phospholipid classes. Exogenous exposure to EPA or LA increased its content in membrane phospholipids while concurrently decreasing LA or EPA content, respectively, in a dose-dependent manner. Arachidonic acid content of membrane phospholipids remained constant. The divergent distribution profiles of LA and EPA within the phospholipid compartment provides some insight into the mechanisms of their opposing effects on MDA-MB-435 cell growth and invasiveness. Also, the effects of LA and EPA on the uptake and distribution of their opposing FA shed some light on the mechanisms mediating their competitive effects.     

Polyenoic acid metabolism in cultured human skin fibroblasts

The incorporation of [1-¹⁴C]linoleic acid, and [1-¹⁴C]linoleic acid into cellular lipids of cultured human skin fibroblasts was studied. Cultured cells took up both labeled fatty acids at nearly the same rate and incorporated them into a variety of lipid classes. At the end of 1 hr incubation with [1-¹⁴C]linoleic acid, radioactivity was found in the triacylglycerol (TG) and choline phosphoglyceride (CPG) pools preferentially. Incorporation into the TG fraction decreased rapidly, while the uptake into CPG, serine phosphoglyceride (SPG), and ethanolamine phosphoglyceride (EPG) fractions increased progressively with longer incubation times. Similar results were obtained with [1-¹⁴C]linoleic acid as precursor. At the end of 24 hr, desaturation and chain elongation of 18∶3 n−3 was more extensive than conversion of 18∶2 n−6 to higher polyenoic acids. During pulse-chase experiments with either fatty acid precursor, the incorporated radioactivity was progressively lost from cellular lipids, particularly from the TG and CPG fractions, but continued to increase in the SPG and EPG pools. The similar labeling pattern of cellular phospholipids with linoleic or linolenic acids, and data from pulse-chase studies suggest that a direct transfer of fatty acids from CPG to EPG is a likely pathway in fibroblast cultures. Incorporation into the EPG pool during the pulse-chase experiments paralleled extensive desaturation and elongation of linoleic acid into 20∶4 n−6, and 22∶4 n−6; and of linolenic acid into 22∶5 n−3 and 22∶6 n−3.     

Incorporation of alpha-linolenic acid and linoleic acid into human respiratory epithelial cell lines

Animal and human studies designed to examine the effects of α-linolenic acid (ALA) and linoleic acid (LA) supplementation on the fatty acid composition of plasma and tissues have demonstrated a marked difference in incorporation into phospholipids of these 18-carbon precursors of the long-chain polyunsaturates. Whereas tissue phospholipid levels are linearly related to dietary ALA and LA, the levels of tissue LA can be 10-fold higher than tissue ALA even when dietary levels are equivalent. There is some dispute whether this disparity is due to ALA being more rapidly metabolized to its products or substantially oxidized by the liver, or whether LA but not ALA is readily incorporated into cellular phospholipids. We examined the level of incorporation of polyunsaturated fatty acids into human respiratory epithelial cell lines (A549, 16HBE) by determining the dose-dependent incorporation of ALA and LA as free fatty acid (5–150 μg FFA/mL). Cell membrane phospholipid ALA and LA were both increased up to ∼20–30% total fatty acids, with a concomitant decrease predominantly in monounsaturated membrane fatty acids, before significant toxicity was observed (50 μg/mL). Our data support the concept that rather than any inherent inability by human cells to incorporate ALA into membrane phospholipids, the lack of ALA content in human and animal tissues in vivo is due to the rapid metabolism or oxidation of this fatty acid in the liver.     

Comparison of the clearances of serum chylomicron triglycerides enriched with eicosapentaenoic acid or oleic acid

Rat mesenteric lymph chylomicrons containing triglycerides enriched with either [¹⁴C]oleic acid (OA) or [¹⁴C]-eicosapentaenoic acid (EPA) were prepared by ultracentrifugation of lymph samples collected for 6 hr after a single duodenal infusion of an emulsion containing either fatty acid. These chylomicrons were injected into the jugular vein of recipient rats and, at various time intervals, blood was drawn and serum was assayed for radioactivity. In separate animals, serum lipoprotein fractions were separated by ultracentrifugation, and the redistribution of labeled fatty acid among circulating lipoproteins was determined by liquid scintillation spectrometry. When the early disappearance rates (10 min) of either total serum radioactivity or specifically the chylomicron fraction were compared, there were no differences between the groups receiving OA-or EPA-enriched chylomicrons. However, disappearance rates of EPA-enriched chylomicrons were slower than those of OA-enriched chylomicrons from 25 to 90 min. The small but significant differences in the disappearance rates for the longer time periods cannot be ascertained without further studies. At 5 min after injection of either type of chylomicron, the d<1.006 g/ml lipoprotein fraction of serum chylomicrons and very low density lipoproteins contained almost 90% of the original radioactivity. By 240 min, when less than 2% of the radioactivity remained, this radioactivity in the d<1.006 g/ml fraction was 43–46%, with concomitant increases in the low and high density lipoprotein fractions and in the lipoprotein-free serum. Deceased.     

Incorporation of eicosapentaenoic and docosahexaenoic acids into groundnut oil by lipase-catalyzed ester interchange

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were incorporated into groundnut oil by interesterification with a 1,3-specific lipase fromMucor miehei. The resultant EPA and DHA concentrations of the groundnut oil were 9.5 and 8.0%, respectively.     

The differential effect of eicosapentaenoic acid and oleic acid on lipid synthesis and VLDL secretion in rabbit hepatocytes

The suppression of plasma very low density lipoprotein (VLDL) triglyceride levels by dietary fish oils rich in polyunsaturated n−3 fatty acids has been attributed to decreased hepatic VLDL secretion. To investigate the effect of n−3 fatty acids on lipid metabolism and VLDL secretion in a tissue culture system, we incubated rabbit hepatocytes with oleic acid and eicosapentaenoic acid (EPA) and examined [³H]glycerol and [¹⁴C]fatty acid incorporation into hepatocyte triglyceride and phospholipid and into media VLDL. Glycerol incorporation studies showed that EPA failed to stimulate VLDL triglyceride secretion from hepatocytes as occurred with oleic acid (P<0.05). Oleic acid preferentially enhanced hepatocyte triglyceride synthesis while EPA stimulated significantly phospholipid synthesis (P<0.01). Varying the relative concentrations of oleic acid and EPA at a constant total fatty acid concentration corroborated preferential triglyceride synthesis from oleic acid. Synthesis shifted predominantly to phospholipids with increasing concentrations of EPA and lower levels of oleic acid. Incorporation of the [¹⁴C]fatty acids (800 μM) followed similar patterns: 87% of [¹⁴C]oleic acid was incorporated into hepatocyte triglyceride and 44% of [¹⁴C]EPA was assimilated in hepatocyte phospholipid (p<0.001). Fatty acids at trace concentrations (53 nM) showed a more divergent pattern of lipid incorporation: 60% of [¹⁴C]oleic acid was incorporated into triglyceride while 91% of [¹⁴CEPA was incorporated into phospholipid (p<0.001). We conclude that in primary rabbit hepatocyte culture, which appears to be a useful model to study lipid metabolism and VLDL secretion, EPA is avidly incorporated into phospholipid while oleic acid predominantly becomes esterified in triglyceride. In addition, EPA, unlike oleic acid, fails to stimulate hepatocyte VLDL secretion. These divergent effects on hepatocyte lipid metabolism are, at least in part, likely to be responsible for fish oil induced suppression of plasma triglycerides.     

Trifluoperazine increases fatty acid turnover in phospholipids in cultured human fibroblasts

A 24-hr pretreatment of cultured human fibroblasts with trifluoperazine induced a marked increase in incorporation of saturated (stearic, palmitic) and unsaturated (oleic, arachidonic) fatty acids into phospholipids (1.5- to 2-fold for 5.10⁻⁵ M trifluoperazine). Concomitantly, incorporation into cholesteryl esters was strongly inhibited (20% of control for 5.10⁻⁵ M trifluoperazine). The drug did not change the phospholipid composition of treated cells. The effect of trifluoperazine on oleic acid incorporation into phospholipids was time-dependent and reached a maximum after a six-hr preincubation with the drug. Trifluoperazine also induced an increase in the rate of chase of oleic acid from the different phospholipid classes. In vitro preincubation of cell-free extracts with trifluoperazine resulted in activation of phospholipid acyltransferases, whereas cholesterol acyltransferase activity was decreased. The rapid effect of trifluoperazine together with its effect on a cell-free system suggests a direct action of this amphiphilic drug on the acyltransferase activities, probably by modification of the structural organization of cellular membranes.     

Acid-catalyzed condensation of oleic acid into estolides and polyestolides

Oleic acid, when treated with 1.0 equivalent of perchloric acid at 50°C, produced a 76% yield of polyestolide. The concentration of mineral acid greatly affected the rate of estolide formation, with increased rates under high acid concentrations. Over a range of temperatures from room temperature to 100°C, reaction rates increased at higher temperatures. However, high acid concentrations and temperatures produced undesirable side products, primarily lactones. Other acids catalyze the condensation of oleic acid to form estolide with the following relative rates: HClO₄ >H₂SO₄>p-toluenesulfonic>BF₃·Et₂O> montmorillonite K-10>HCl>H₃PO₄, HNO₃. Addition of water impedes the formation of estolide.     

Differential utilization of eicosapentaenoic acid and docosahexaenoic acid in human plasma

It has recently been shown that the ω3 fatty acid status in humans can be predicted by the concentration of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids in plasma phospholipids [Bjerve, K.S., Brubakk, A.M., Fougner, K.J., Johnsen, H., Midjthell, K., and Vik, T. (1993)Am. J. Clin. Nutr., in press]. In countries with low intake of ω3 fatty acids, the level of EPA in plasma phospholipids is often only about one-fifth the concentration of DHA. The purpose of this study was to investigate whether this difference in the concentration of these two fatty acids was due to a selective loss of EPA relative to DHA or to a lower dietary intake of EPA. Seven female volunteers ingested four grams of MaxEPA daily for 2 wk and in the following 4 wk they ate a diet almost completely devoid of the long-chain ω3 fatty acids. The concentrations of the ω3 fatty acids in the plasma cholesteryl esters, triglycerides and phospholipids and the high density lipoprotein phospholipids were examined at weekly intervals throughout the study. There was a more rapid rise in the concentration of EPA than in DHA levels in the supplementation period in all lipid fractions, but there was a disproportionate rise in DHA relative to EPA in the plasma lipids compared with the ratio in the supplement. In the depletion phase there was a rapid disappearance of EPA from all fractions, such that pre-trial levels were reached by one week post-supplementation. The disappearance of DHA was slower, particularly for the plasma phospholipids: at 4 wk post-supplementation, the DHA concentration in this fraction was still 40% above the pre-trial value. It is suggested that the low plasma EPA values relative to DHA are the result of increased β-oxidation of EPA and/or low dietary intake, rather than a rapid conversion of EPA to DHA. One practical result of this experiment is that, compared with DHA, the maintenance of increased EPA levels in plasma (and therefore tissues) would require constant inputs of EPA due to its more rapid loss from the plasma.     

Application of water mimics on preparation of eicosapentaenoic and docosahexaenoic acids containing glycerolipids

To obtain enhanced incorporation of highly unsaturated fatty acids and recovery of glycerolipid products, organic solvents with high dielectric constants (water mimics) were substituted for part of the essential water for lipase activation to study their effect on acidolysis and transesterification. In acidolysis/transesterification of fish oil triglycerides and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), Lipozyme IM-60 with ethylene glycol as a water mimic enhanced the incorporation of EPA and suppressed the hydrolysis of synthesized glycerolipid. On the other hand, transesterification between soy phosphatidylcholine and EPA was enhanced by a water and propylene glycol combination. In a nonaqueous medium that contained appropriate amounts of water and organic solvents (water mimics), Lipozyme IM-60 increased transesterification of EPA into soy phosphatidylcholine. Simultaneously, the recovered glycerolipid products showed decreased hydrolysis of newly synthesized EPA- and DHA-containing glycerolipids.     

Lipase-catalyzed incorporation of oleic acid into melon seed oil

The ability of lipase PS30 (Pseudomonas sp.) to modify the fatty acid profile of melon seed oil by incorporation of oleic acid (18:1n-9) was investigated. The transesterification was carried out in hexane in an orbital shaking water bath at 55°C for 24 h with methyl oleate (70% pure) as acyl donor. Oleic acid content increased from 13.5% to 53%, and linoleic acid (18:2n-6) content decreased from 65% to 33%. The incorporation of oleic acid into melon seed oil by Pseudomonas sp. lipase helped balance the fatty acid profile of the oil in terms of monounsaturated (18:1n-9) and essential fatty acids (18:2n-6).     

Lipid synthesis in cultured human embryonic fibroblasts

We describe here the pathways by which human embryonic fibroblasts synthesize lipids. In these studies, we quantitated the phospholipids by their phosphorus content and by their acyl components. These determinations defined both the chemical composition of the cellular membranes as well as their metabolic turnover. Using radiolabeled precursors, we have shown (a) synthesis of the glycerol moiety via glycolysis and the action of glycerokinase, (b) utilization of both exogenously added and endogenously synthesized fatty acids, (c) synthesis de novo of phosphatidyl choline and phosphatidyl ethanolamine from their base precursors, and (d) the methylation of phosphatidyl ethanolamine yielding phosphatidyl choline. Dividing cells synthesized phosphoglyceride more rapidly than cells in the stationary phase. However, considerable turnover of cellular lipid did occur in the stationary phase.     

The effect of eicosapentaenoic acid consumption on human neutrophil chemiluminescence

The effect of eicosapentaenoic acid (EPA) on the inflammatory potential of neutrophils was investigated by supplementing the diets of 12 subjects with 2.16 g of EPA or 12 g of olive oil per day for 4 weeks in a double blind crossover study. Neutrophil function as assessed by luminol enhanced chemiluminescence responses to plateletactivating factor (PAF) and formyl-methionyl-leucyl-EPA but not after olive oil consumption in the subjects who consumed EPA first. In contrast, EPA had no significant effect on neutrophil chemiluminescence in the subjects who consumed olive oil first. Dietary supplementation with EPA inhibits neutrophil responses to inflammatory mediators such as PAF while other fatty acids appear to modify the effects of EPA. Based on a paper presented at the Third International Conference on Platelet-Activating Factor and Structurally Related Alkyl Ether Lipids, Tokyo, Japan, May 1989.     

The relative incorporation of arachidonic and eicosapentaenoic acids into human platelet phospholipids

The incorporation of arachidonic acid (AA) as compared to eicosapentaenoic acid (EPA) into human platelet phospholipids was tested by incubating washed platelets with a known mixture of [³H]AA and [¹⁴C]EPA. Following incubation, the platelet lipids were extracted, the individual phospholipids—phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylinositol (PI) and phosphatidylethanolamine (PE)—were separated by thin layer chromatography, and their corresponding [³H]/[¹⁴C] ratios were determined. Based on a [³H]/[¹⁴C] ratio of unity for the substrate mixture, the PC, PS, PI and PE exhibited ratios of 0.55, 0.93, 1.12 and 0.74, respectively, which were significantly different from 1.00 in all instances except in the case of PS. These results indicate that PC and PE selectively incorporated EPA, while PI showed preference toward AA. These selectivities may account partly for the differing AA/EPA mass ratios that have been observed among the individual phospholipids of human subjects consuming fish oils.     

Incorporation of exogenous docosahexaenoic acid into various bacterial phospholipids

Incorporation of exogenous docosahexaenoic acid (DHA) into bacterial phospholipids was examined as a method for DHA-linked phospholipid production. The cultivation of 23 bacterial strains in medium with DHA showed that an eicosapentaenoic acid-producing bacteriumShewanella sp. strain SCRC-2738 (strain SCRC-2738),Bacillus subtilis W23,B. cereus, an Antarctic marine bacterium strain S-7 (strain S-7), photosynthesis bacterium (PSB)Rhodopseudomonas capsulatus utilized for the production of larval marine fish,Pseudomonas aeruginosa, Staphylococcus aureus, Serratia marcescens andEscherichia coli K12 all incorporated DHA into their polar lipids. The polar lipids of the strain SCRC-2738, strain S-7, PSB andE. coli K12 were identified to be phospholipids. DHA was localized at thesn-2 position in the phospholipids of the four strains. Incorporation of exogenous DHA into their phospholipids produced an increase in saturated fatty acids and a decrease in monounsaturated fatty acids exceptE. coli K12. The strain SCRC-2738 incorporated the largest amount of DHA into their phospholipids among the tested bacterial strains in this study: DHA was 16% of the total fatty acids in the phosphatidylethanolamine (PE) and 29% in the phosphatidylglycerol (PG). In the PSB, incorporated DHA was 12% of the total fatty acids in the PE, 10% in the PG and phosophatidylcholine so that the PSB was nutritionally fortified.     

Selectivity in incorporation,utilization and retention of oleic and linoleic acids by human skin fibroblasts

Fetal human fibroblasts were grown in culture medium containing 10% fetal bovine serum supplemented with [1-¹⁴C] linoleate or [1-¹⁴C] oleate. At all concentrations of exogenous fatty acids, the incorporation of oleate was greater than that of linoleate. With increased medium fatty acid concentrations, linoleate in triacylglycerol (TAG) could be increased from 13 to 75% of the total incorporated; at each concentration, relatively more linoleate than oleate was in TAG. When the cells were exposed to exogenous oleate/linoleate mixtures, the composition of the mixture determined the extent of incorporation of both fatty acids. When the mixture was primarily linoleate, scarce oleate was used preferentially for phospholipids (PL); no such specificity for scarce linoleate was observed. Addition of exogenous fatty acids resulted in a shift of previously incorporated¹⁴C fatty acids from phospholipid into TAG; retention of oleate in PL was greater than that of linoleate. Incorporation of oleate into phospholipids was also higher than that of linoleate from exogenous fatty acid mixtures which were 80% saturated. It is suggested that normal human fibroblasts have adapted to the low levels of exogenous polyunsaturated fatty acids in culture media by increased use of oleate in phospholipid. Even when the cells aresupplemented with linoleate, the preferential use of oleate in phospholipid groups is retained. Presented in part at the ASBC Meeting, Dallas, april 1979.