Effect of fatty acid modification on prostacyclin production by cultured human endothelial cells

Accumulation of (n-9)-eicosatrienoic and docosatrienoic acids in human fibroblast phospholipids

An essential fatty acid (EFA) deficiency-like profile of fatty acids has been observed in HF-1 human skin fibroblasts cultured at clonal densities in MCDB 110 and 0.4% fetal bovine serum (FBS). The profile was characterized by an accumulation of 16:1n-7, 18:1n-9, 20:3n-9 and 22:3n-9, a reduction of n-6 fatty acids and a reduction in total polyunsaturated fatty acids (PUFA). The fatty acid composition of sphingomyelin (SPH), phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylinositol (PI) and phosphatidylethanolamine (PE) was determined and, except for SPH, each displayed an EFA deficiency-like profile. The triene to tetraene ratio (20:3n-9/20:4n-6) ranged from 5.3 in PI to 0.9 in PE. In addition, the highest percentage of 20:3n-9 was present in the PI and the highest percentage of 22:3n-9, in PE. Other human fibroblasts (normal, transformed and at different population doubling number levels [PDL]) were grown under the same conditions and were found to display triene to tetraene ratios (20:3n-9/20:4n-6) in total cellular lipids ranging from 0.7 to 4.5. The accumulation of 20:3n-9 and 22:3n-9 is due primarily to the existence of a basal nutrient medium (MCDB 110) that allows for the rapid clonal growth of human fibroblasts at reduced serum levels (0.4%). This culture procedure can be exploited to further elucidate various aspects of lipid metabolism in human fibroblasts.

Effects of dietary corn oil and salmon oil on lipids and prostaglandin E2 in rat gastric mucosa

Three groups of male rats were fed either a corn oil-enriched diet (17%, w/w), a salmon oil-enriched diet (12.5%) supplemented with corn oil (4.5%) or a low-fat diet (4.4%) for eight wk to investigate the possible relationships between dietary fatty acids and lipid composition, and prostaglandin E2 level and phospholipase A2 activity in the rat gastric mucosa. High-fat diets induced no important variation in total protein, phospholipid and cholesterol contents of gastric mucosa. Compared with a low-fat diet, corn oil produced a higher n-6/n-3 ratio in mucosal lipids, whereas this ratio was markedly lowered by a fish oil diet. In comparison with the low-fat diet, the production of prostaglandin E2(PGE2) in gastric mucosa of rats fed salmon oil was significantly decreased by a factor of 2.8. In the corn oil group, PGE2 production tended to decrease, but not significantly. In comparison with the low-fat diet, both specific and total gastric mucosal phospholipase A2 activities were increased (+ 18 and 23%, respectively) in the salmon oil group; they were unchanged in the corn oil group. It is suggested that the decrease of gastric PGE2 in rats fed fish oil is not provoked by a decrease in phospholipase A2 activity but may be the result of the substitution of arachidonic acid by n-3 PUFA or activation of PGE2 catabolism.

Modification of upper gastrointestinal prostaglandin synthesis by dietary fatty acids

The effects of dietary oils on gastric, duodenal mucosa and liver were investigated in a rat model. Unsaturated fatty acid profiles and in vitro prostaglandin (PG) synthesis (PGE2, PGF2 alpha, 6-oxo-PGF1 alpha and thromboxane B2), were measured after 14 days of dietary oil supplements. There were no significant differences in prostanoid synthesis between rats fed coconut oil (high saturated fat content) and standard diet. After fish oil supplement, tissue eicosapentaenoic acid and docosahexaenoic acid levels were higher, arachidonic acid levels were lower, and prostanoid synthesis was reduced in both stomach and duodenum. After corn oil and evening primrose oil, linoleic acid levels were variably increased, but there were no significant differences in arachidonic acid or prostanoid synthesis. Dihomogamma-linolenic acid levels were slightly increased after evening primrose oil. Dietary incorporation of fatty acids into gastroduodenal tissue is not uniform. When incorporated, fatty acids can modify prostaglandin synthesis.

Polyunsaturated fatty acids and protection of newborn rats from oxygen toxicity

To test whether polyunsaturated fatty acids (PUFA) might be associated with protection against oxygen toxicity in newborn experimental animals, we performed two series of experiments. In the first series, adult female rats were fed one of three diets--regular Rat Chow, a high-PUFA (safflower oil-based) diet, or a low-PUFA (palm oil-based) diet--for several weeks before and throughout pregnancy and lactation. Newborn offspring of the three diet groups had similar antioxidant enzyme activities and surfactant development. Offspring of dams fed the high-PUFA diet had total lung lipid fatty acids characterized by increased linoleic acid (18:2 omega 6) and arachidonic acid (20:4 omega 6) and a significantly increased PUFA/saturated fatty acid ratio, compared with offspring of dams fed the regular diet or low-PUFA diet; associated with this increased PUFA pattern was markedly superior survival (80 of 84 (95%) vs 56 of 84 (67%) for regular-diet offspring, P less than 0.01) after 7 days in greater than 95% oxygen. Conversely, offspring born to dams fed the low-PUFA diet had decreased lung PUFA content and inferior tolerance to prolonged high O2 exposure (survival 38 of 84 (45%)). In the second experimental series, the postnatal provision of high PUFA rat milk to offspring born to dams fed the low-PUFA diet (via "cross-nurturing" by high-PUFA diet dams) rapidly increased their lung lipid PUFA and improved their hyperoxic survival (44 of 50 vs 25 of 50 for low-PUFA diet newborn animals kept with their low-PUFA mother rats, P less than 0.01). These studies suggest that increasing lung lipid PUFA can confer a protective effect against the toxic effects of hyperoxia on the newborn animal lung.

Preferential incorporation of eicosanoid precursor fatty acids into human umbilical vein endothelial cell phospholipids

We have examined the preferential incorporation of specific fatty acids into phospholipid classes of cultured human umbilical vein endothelial cells. Pulse-labeling of human umbilical vein endothelial cell phospholipids with radiolabeled fatty acids and inhibition of radiolabeled fatty acid incorporation by competition with excess, unlabeled fatty acids in pair-wise combinations revealed two distinct classes of esterification systems into human umbilical vein endothelial cell phospholipids. The eicosanoid precursor fatty acids, including arachidonate, 8,11,14-eicosatrienoate (ETA) and 5,8,11,14,17-eicosapentaenoate (EPA), exhibited high affinity incorporation into total phospholipids, whereas other fatty acids, including docosahexaenoate and monohydroxy eicosatetraenoates, showed low affinity incorporation. The relative degree of incorporation of eicosanoid precursor fatty acids into phospholipid classes was phosphatidylcholine (PC) greater than phosphatidylethanolamine (PE) greater than phosphatidylinositol (PI) greater than phosphatidylserine (PS). The specific activity of [14C]arachidonic acid-labeled PI was two times higher than that of any other radiolabeled phospholipids. When competitive incorporation of eicosanoid precursor fatty acids into phospholipid classes was studied, they were found to be acylated into different phospholipid classes at different rates. Although eicosanoid precursor fatty acids were not preferentially incorporated into PC, arachidonic acid was preferentially incorporated into the other phospholipids and exhibited particular selectivity in comparison with the other eicosanoid precursor fatty acids for incorporation into PI. These results demonstrate that human umbilical vein endothelial cells possess selective incorporation mechanisms for specific fatty acids into various phospholipids via the deacylation-reacylation pathway.

Functional heterogeneity of vascular endothelial cells

This review has highlighted some of the well-described differences in endothelial cells derived from different sites of the vascular tree. In presenting a select group of endothelial properties, there was no intention to imply that these are the only properties of endothelial cells that exhibit heterogeneity. Nonetheless, having described endothelial heterogeneity in regard to a number of defined properties, we are left with persistent questions including: Are these divergent properties of endothelial cells fixed? Alternatively, can we alter the properties of endothelial cells by affecting the signals from the environment? A number of reports strongly suggest that endothelial cells are capable of acquiring new properties. Stewart and Wiley investigated the role of the neural tissue environment on the differentiation of brain capillary endothelial cells. These authors transplanted ectopic sites, i.e. vascular segments of brain from very young quail embryos to chick coeliac cavity, and a quail somites to chick brain ventricles. The distinctive morphology of quail cells provided a cell marker to differentiate host from graft. The results of this study demonstrated that mesenteric or somatic vessels growing into grafted brain developed functional, structural and histochemical features specific for neural capillaries. Conversely, capillaries in mesodermal tissue that had been grafted to the brain were devoid of the neural capillary characteristics, indicating that brain vessels do not form a barrier when they are made to vascularize non-neural tissue. Milici and Carley reported that bovine adrenal capillary cells cultured on plastic exhibited occasional diaphragmed fenestrations and no transendothelial channels. However, if these same cells were cultured on a basement membrane (matrix) laid down by MDCK cells (a canine nephron epithelial cell line), the cells responded by increasing the number of diaphragmed fenestrations and transendothelial channels. This cell culture study supported an earlier whole animal study in which the importance of the epithelium and/or epithelial basal lamina in the maintenance of endothelial ultrastructure was demonstrated in a developmental study of rat intestinal capillaries. In this earlier study, it was noted that epithelial development coincided with the formation of fenestrations by the endothelium. Enzymatic activities of endothelial cells can also be altered by environmental signals. For example, primary cerebral microvascular endothelial cells exhibit barrier features and are enriched in gamma-glutamyl transpeptidase activity, yet rapidly lose the activity when subcultured.(ABSTRACT TRUNCATED AT 400 WORDS)

Selective internalization of arachidonic acid by endothelial cells

The asymmetric distribution of phospholipids in bovine endothelial-cell membranes was probed with 2,4,6-trinitrobenzenesulphonate and purified phospholipase A2. The data suggest that phosphotidylethanolamine is primarily located in the inner lipid bilayer, as reported for other cell types. Stearic acid is taken up by the endothelial cells and is randomly distributed among the membrane phospholipids. In contrast, the polyunsaturated fatty acids (arachidonic, eicosatrienoic and eicosapentaenoic acids) have initial incorporation into the phosphatidylcholine fraction. These fatty acids then undergo a time-dependent transfer from phosphatidylcholine to phosphatidylethanolamine. Thus we propose that endothelial cells possess a mechanism for the selective internalization of polyunsaturated fatty acids.

Influence of environmental medium on fatty acid composition of human cells: leukocytes and fibroblasts

Fibroblasts in culture and leukocytes have been widely used to study fatty acid and lipoprotein cellular metabolism. The present investigations were designed to study the role of nutritional and environmental factors on lipid metabolism in these two types of cells. Leukocytes freshly isolated from human blood and fibroblasts cultured in media enriched in human serum (HS) have relatively similar fatty acid distributions. However, more important differences are observed in fibroblasts cultured in media enriched with HS or with fetal bovine serum (FBS). It is obvious that the quantity and quality of fatty acids are very different in FBS and HS, but intracellular regulation ensures relative homogeneity of saturated (SFA) and monounsaturated fatty acids (MUFA) in the cells, particularly in phospholipids. The first modifications induced by different media (FBS or HS) are detected on cellular growth; the differences seem to be due more to the fatty acid (FA) quantitative supply than to the FA quality of each culture medium. The major modifications in FA composition induced by different culture media concern the polyunsaturated fatty acids (PUFA) of phospholipids, especially the n-6 family. The intracellular linoleic acid level depends on the level in the medium, but intracellular n-6 metabolite levels depend both on the level in the medium and on the growth state of the cells. The n-3 family seems to be less affected by the quality of the medium in our experiment, and the cells maintain a stable docosahexaenoic acid (22:6n-3) level. A higher content of the n-3 family in the medium induces a higher level of eicosa- or docosapentaenoic acid, rather than docosahexaenoic acid itself.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell biology of endothelial cells

Endothelial cells are a source of physiologically important molecules synthesized therein and secreted to the blood and/or to the subendothelial extracellular matrix. These molecules participate in formation of platelet and fibrin thrombi (e.g., von Willebrand factor and tissue factor) and contribute to antithrombotic properties of the endothelium (e.g., prostacyclin, thrombomodulin, and heparan sulfate). Endothelial cells synthesize and secrete plasminogen activator and inhibitors. They are the source of molecules regulating the growth of other cells; they synthesize angiotensin-converting enzyme, and bind lipoproteins and hormones. Finally, they are the target for, and participant in, immune reactions. Thus, endothelial cells constitute not only the first barrier between the blood and the extravascular space but also serve as a source of molecules influencing the structural and functional integrity of the circulation.

Pathways of arachidonic acid liberation in thrombin and calcium ionophore A23187-stimulated human endothelial cells: respective roles of phospholipids and triacylglycerol and evidence for diacylglycerol generation from phosphatidylcholine

Cultured endothelial cells from human umbilical vein were incubated for 20 h at 37 degrees C in the presence of [U-14C]arachidonic acid. Around 60-70% of the radioactive fatty acid was incorporated into cell lipids and was predominantly found in phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol and triacylglycerol (39%, 33%, 13% and 6.5% of total incorporated radioactivity, respectively). Stimulation of the cells with human thrombin (2 U/ml) or calcium ionophore A23187 (5 microM) promoted the release into supernatants of arachidonic acid, 6-ketoprostaglandin F1 alpha, prostaglandins E2 and F2 alpha, in decreasing order of importance. The amount of secreted material was 4-fold higher with A23187, compared to thrombin. Parallel to the liberation process, phosphatidylcholine underwent a rapid decrease of radioactivity with both agonists, suggesting the involvement of a Ca2+-dependent phospholipase A2. Phosphatidylethanolamine displayed a minor decrease with A23187, whereas some reacylation was observed at 10 min with thrombin. Phosphatidylinositol was non-significantly affected in thrombin-stimulated cells, whereas A23187 promoted an early but minor decrease, followed by resynthesis. In contrast to A23187, thrombin was also able to promote a significant hydrolysis of triacylglycerol, which might thus be implicated in the process of arachidonate liberation. Finally, radioactive phosphatidic acid and diacylglycerol appeared in endothelial cells, in response to the two agonists. However, diacylglycerol formation did not parallel that of phosphatidic acid, especially with A23187. Determination of the 14C/3H ratio of the different lipids upon cell labelling with both [14C]arachidonic acid and [3H]palmitic acid revealed that diacylglycerol and phosphatidic acid are hardly derived from inositol-phospholipid breakdown by phospholipase C. Other possible pathways involving for instance phospholipase C splitting of phosphatidylcholine are discussed.

Docosahexaenoic acid metabolism and effect on prostacyclin production in endothelial cells

Bovine aortic endothelial cultures readily take up docosahexaenoic acid (DHA). Most of the DHA was incorporated into phospholipids, primarily in ethanolamine and choline phosphoglycerides, and plasmalogens accounted for 34% of the DHA contained in the ethanolamine fraction after a 24-h incubation. The retention of DHA in endothelial phospholipids was not greater than other polyunsaturated fatty acids and unlike arachidonic and eicosapentaenoic acids, DHA did not continue to accumulate in the ethanolamine phosphoglycerides after the initial incorporation. About 15% of the [14C(U)]DHA uptake was retroconverted to docosapentaenoic and eicosapentaenoic acids in 24 h. Some of the newly incorporated [14C(U)]DHA was released when the cells were incubated subsequently in a medium containing serum and albumin. The released radioactivity was in the form of free fatty acid and phospholipids and after 24 h, 11% was retroconverted to docosapentaenoic and eicosapentaenoic acids. Total DHA uptake was decreased only 10% by the presence of a 100 microM mixture of physiologic fatty acids, but as little as 10 microM docosatetraenoic acid reduced DHA incorporation into phospholipids by 25%. DHA was not converted to prostaglandins or lipoxygenase products by the endothelial cultures. When DHA was available, however, less arachidonic acid was incorporated into endothelial phospholipids, and less was converted to prostacyclin (PGI2). Enrichment of the endothelial cells with DHA also reduced their capacity to subsequently produce PGI2. These findings indicate that endothelial cells can play a role in DHA metabolism and like eicosapentaenoic acid, DHA can inhibit endothelial PGI2 production when it is available in elevated amounts.

Incorporation and redistribution of arachidonic acid in diacyl and ether phospholipids of bovine aortic endothelial cells

The present experiments characterized the incorporation and redistribution of arachidonic acid in diacyl and ether phospholipids of bovine aortic endothelial cells. Confluent cultures were either continuously labeled or pulse labeled with [14C]arachidonic acid. Major lipid classes and ether-linked subclasses of phosphatidyl-ethanolamine (PE) and phosphatidylcholine (PC) were separated by high-performance liquid chromatography and thin-layer chromatography. During continuous labeling, total incorporation of arachidonic acid reached a peak at 8 h and was essentially constant up to 24 h. After 8 h, net label in total PC declined, whereas that in total PE continued to rise. In pulse labeling experiments radioactivity in diacyl PC continuously declined with concomitant increases in both diacyl- and alkenylacyl PE. The data demonstrate that transfer of arachidonic acid from diacyl PC to both diacyl- and alkenylacyl PE occurs in endothelial cells. In contrast to previous observations in platelets, transfer of arachidonic acid to alkenylacyl PE did not require agonist stimulation. This pathway may contribute to the enrichment of endothelial cell PE with arachidonic acid with the potential for subsequent metabolism to prostacyclin.

Phospholipid fatty acid composition of pulmonary airway epithelial cells: potential substrates for oxygenation

To determine possible substrates for airway epithelial lipoxygenase and cyclooxygenase activities, we examined the amounts and distributions of fatty acids in phospholipids of human, dog and sheep airway epithelial cells. We found that the cells contained significant levels of n-6 and n-3 fatty acids in species-specific amounts: dog cells were relatively enriched in the n-6 series and poor in n-3, while sheep cells were enriched in the n-3 series and poor in n-6. Despite differences in fatty acid content, cells from each species expressed a constant phospholipid composition and distributed their n-6 and n-3 fatty acids in a stereotyped fashion among phospholipid classes. The analysis shows that the species differences in oxygenation activities reported previously are paralleled by heterogeneity in potential substrates.

Composition and incorporation of [3H]arachidonic acid into molecular species of phospholipid classes by cultured human endothelial cells

Based on quantitative high-performance liquid chromatographic analyses of molecular species in selected phospholipid subclasses from culture human umbilical vein endothelial cells, the relative degree of unsaturation was ethanolamine plasmalogens greater than phosphatidylethanolamine greater than phosphatidylcholine. A total of 36 different molecular species were identified in the phosphatidylcholine fraction. Interestingly, the phosphatidylcholine contained a significant amount (11.7%) of the dipalmitoyl species, a lipid normally associated with lung surfactant. The arachidonoyl-containing molecular species of phosphatidylserine/inositol were labeled to the highest extent and the ethanolamine plasmalogens contained the lowest specific radioactivity after incubating [3H]arachidonic acid with human endothelial cells for 4 h. Within each phospholipid subclass the arachidonoyl species where both acyl groups of the phospholipid are unsaturated (20:4-20:4, 18:2-20:4 + 16:1-20:4, and 18:1-20:4) had higher specific radioactivities, after labeling with [3H]arachidonic acid, than those that contained saturated aliphatic chains (16:0-20:4 and 18:0-20:4). This indicates that the unsaturated species have higher turnover rates.

12-Hydroxyeicosatetraenoic acid reduces prostacyclin production by endothelial cells

12-Hydroxyeicosatetraenoic acid (12-HETE), a lipoxygenase product released by activated platelets and macrophages, reduced prostacyclin (PGI2) formation in bovine aortic endothelial cultures by as much as 70%. Maximal inhibition required 1 to 2 h to occur and after 2 hr, a concentration of 1 microM 12-HETE produced 80% of the maximum inhibitory effect. 5-HETE and 15-HETE also inhibited PGI2 formation. The inhibition was not specific for PGI2; 12-HETE reduced the formation of all of the radioactive eicosanoids synthesized from [1-14C]arachidonic acid by human umbilical vein endothelial cultures. Inhibition occurred in the human cultures when PGI2 formation was elicited with arachidonic acid, ionophore A23187 or thrombin. These findings suggest that prolonged exposure to HETEs may compromise the antithrombotic and vasodilator properties of the endothelium by reducing its capacity to produce eicosanoids, including PGI2.

Neurochemical coupled actions of transmitters in the microvasculature of the brain

The discovery that monoamine nerves end on the central microvessels of the choroid plexus, pia-arachnoid and parenchyma has prompted an intense investigation as to their physiological and neuropathological roles. The source of the monoamine fibers to the pial vessels and choroid plexus was shown to be the superior cervical ganglion. Ganglionic stimulation causes vasoconstriction or vasodilation of pial vessels, an event depending upon the functional ratio of alpha to beta adrenergic receptors. Moreover, stimulation of the superior cervical ganglion evokes an inhibition of cerebrospinal fluid formation in choroid plexus. The locus coeruleus is the site of adrenergic nerve supply to the parenchymal capillaries and stimulation of this nucleus increases capillary permeability to small molecules and water. Neurotransmitter receptors (adrenergic, histamine, adenosine, dopamine, prostacyclin, prostaglandins and specific amino acids or neuropeptides) have been identified on microvessels and in many instances these transmitter actions are coupled to cyclic AMP synthesis. Moreover, cyclic AMP has been shown to increase the rate of capillary endothelial pinocytosis and produce brain edema. In small vessels containing smooth muscle cells cyclic AMP production improves cerebral blood flow via an initiation of vasodilatory processes. The presence of receptors for serotonin and acetylcholine have likewise been demonstrated to occur on cerebral microvessels. Limited information is available as to the receptor coupled actions of these two transmitters, but cholinergic mechanisms may act to restrict catecholamine-induced formation of cyclic AMP. Altered sensitivity of microvessels to neurotransmitters has been demonstrated following conditions of stroke, hypertension, aging, diabetes and X-irradiation.

Metabolism of platelet activating factor (1-alkyl-2-acetyl-sn-glycero-3-phosphocholine) and 1-alkyl-2-acetyl-sn-glycerol by human endothelial cells

The metabolism of platelet activating factor (1-[1,2-3H]alkyl-2-acetyl-sn-glycero-3-phosphocholine) and 1-[1,2-3H]alkyl-2-acetyl-sn-glycerol was studied in cultures of human umbilical vein endothelial cells. Human endothelial cells deacetylated 1-[1,2-3H]alkyl-2-acetyl-sn-glycero-3-phosphocholine to the corresponding lyso compound (1-[1,2-3H]alkyl-2-lyso-sn-glycerol-3-phosphocholine) and a portion was converted to 1-[1,2-3H]alkyl-2-acyl(long-chain)-sn-glycero-3-phosphocholine. Lyso platelet activating factor (lyso-PAF) (1-[1,2-3H]alkyl-2-lyso-sn-glycero-3-phosphocholine) was detected in the media very early during the incubation and the amount remained higher than the level of the lyso product observed in the cells. Cellular levels of 1-[1,2-3H]alkyl-2-lyso-sn-glycero-3-phosphocholine were significantly higher than the acylated product (1-[1,2-3H]alkyl-2-acyl(long-chain)-sn-glycero-3-phosphocholine) at all times during the 60-min incubation period, which suggests that the ratio of acetylhydrolase to acyltransferase activities is greater in endothelial cells than in most other cells. When endothelial cells were incubated with 1-[1,2-3H]alkyl-2-acetyl-sn-glycerol, a known precursor of PAF, 1-[1,2-3H]alkyl-sn-glycerol was the major metabolite formed (greater than 95% of the 3H-labeled metabolites during 20- and 40-min incubations). At least a portion of the acetate was removed from 1-[1,2-3H]alkyl-2-acetyl-sn-glycerol by a hydrolytic factor released from the endothelial cells into the medium during the incubations. Only negligible amounts of the total cellular radioactivity (0.2%) was incorporated into platelet activating factor (1-[1,2-3H]alkyl-2-acetyl-sn-glycero-3-phosphocholine); therefore, it is unlikely that the previously observed hypotensive activity of 1-alkyl-2-acetyl-sn-glycerols can be explained on the basis of the conversion to platelet activating factor (1-alkyl-2-acetyl-sn-glycero-3-phosphocholine) by endothelial cells. Results of this investigation indicate that endothelial cells play an important role in PAF catabolism. Undoubtedly, the endothelium is important in the regulation of PAF levels in the vascular system.

Increasing the thermosensitivity of a mammary tumor (CA755) through dietary modification

Disruption of the integrity of tumor cellular membranes has been proposed as an initiating event in hyperthermic cell death. Thermosensitivity measured by the shift in the harmonic mean of tumor regrowth delay of CA755 mammary adenocarcinomas grown in the hind legs of male BDF1, mice increased 22% when the hosts were fed a diet enriched in polyunsaturated fatty acids. Although the diet elicited the anticipated increase in tumor membrane phospholipid polyunsaturated fatty acids, the proportion of total unsaturated fatty acids decreased and the proportion of membrane-rigidifying saturated fatty acids increased. Concomitantly, the concentrations of cholesterol and phospholipid phosphorus increased and the ratio of phosphatidylethanolamine to phosphatidylcholine decreased, presumably to counter the effect of the change in the fatty acid pattern. In host liver membranes, the diet-mediated increase in proportion of polyunsaturated fatty acids was not accompanied by an increase in the proportion of rigidifying saturated fatty acids. Instead, the homeoviscous adaptation consisted of decreases in monounsaturated fatty acids and cholesterol concentration and an increase in the phosphatidylethanolamine-phosphatidylcholine ratio. Addition of a natural inhibitor of cholesterol biosynthesis to the polyunsaturated fatty acid enriched-diet reversed the diet-mediated increase in the phosphatidylethanolamine-phosphatidylcholine ratio of host liver membranes. Tumor membrane lipids from hosts fed the combined dietary factors were characterized by the formentioned rigidifying increase in saturated fatty acids and compensatory decrease in the phosphatidylethanolamine-phosphatidylcholine ratio. The inhibitor reversed the compensatory increases in cholesterol and phospholipid phosphorus concentrations. As a consequence the thermosensitivity of tumors bearing this perturbed membrane was increased.

Eicosapentaenoic acid utilization by bovine aortic endothelial cells: effects on prostacyclin production

We have investigated whether the presence of other fatty acids in physiologic amounts will influence the effects of eicosapentaenoic acid on cellular lipid metabolism and prostaglandin production. Eicosapentaenoic acid uptake by cultured bovine aortic endothelial cells was time and concentration dependent. At concentrations between 1 and 25 microM, most of the eicosapentaenoic acid was incorporated into phospholipids and of this, 60-90% was present in choline phosphoglycerides. Eicosapentaenoic acid inhibited arachidonic acid uptake and conversion to prostacyclin (prostaglandin I2) but was not itself converted to eicosanoids. Only small effects on the uptake of 10 microM eicosapentaenoic acid occurred when palmitic, stearic or oleic acids were added to the medium in concentrations up to 75 microM. In contrast, eicosapentaenoic acid uptake was reduced considerably by the presence of linoleic, n-6 eicosatrienoic, arachidonic or docosahexaenoic acids. Although a 100 microM mixture of palmitic, stearic, oleic and linoleic acid (25:10:50:15) had little effect on the uptake of 10 or 20 microM eicosapentaenoic acid, less of this acid was channeled into endothelial phospholipids. However, the fatty acid mixture did not prevent the inhibitory effect of eicosapentaenoic acid on prostaglandin I2 formation in response to either arachidonic acid or ionophore A23187. An 8 h exposure to eicosapentaenoic acid was required for the inhibition to become appreciable and, after 16 h, prostaglandin I2 production was reduced by as much as 60%. These findings indicate that the capacity of aortic endothelial cells to produce prostaglandin I2 is decreased by continuous exposure to eicosapentaenoic acid. Even if the eicosapentaenoic acid is present as a small percentage of a physiologic fatty acid mixture, it is still readily incorporated into endothelial phospholipids and retains its inhibitory effect against endothelial prostaglandin I2 formation. Therefore, these actions may be representative of the in vivo effects of eicosapentaenoic acid on the endothelium.

Docosatetraenoic acid in endothelial cells: formation, retroconversion to arachidonic acid, and effect on prostacyclin production

Cultured bovine aortic endothelial cells convert arachidonic acid to docosatetraenoic acid and also take up docosatetraenoic acid from the extracellular fluid. After a 24-h incubation with biosynthetically prepared [3H]docosatetraenoic acid, about 20% of the cellular fatty acid radioactivity was converted to arachidonic acid. Furthermore, in pulse-chase experiments, the decrease in phospholipid docosatetraenoic acid content was accompanied by an increase in arachidonic acid, providing additional evidence for retroconversion. These findings suggest that one possible function of docosatetraenoic acid in endothelial cells is to serve as a source of arachidonic acid. The endothelial cells can release docosatetraenoic acid when they are stimulated with ionophore A23187, but they do not form appreciable amounts of eicosanoids from docosatetraenoic acid. Enrichment of the endothelial cells with docosatetraenoic acid reduced their capacity to produce prostacyclin (PGI2) in response to ionophore A23187. This may be related to the fact that docosatetraenoic acid enrichment caused a 40% reduction in the arachidonic acid content of the inositol phosphoglycerides. In addition, less prostacyclin was formed when the enriched cells were incubated with arachidonic acid, suggesting that docosatetraenoic acid also may act as an inhibitor of prostaglandin synthesis in endothelial cells.

Morphological alterations in cultured endothelial cells induced by arachidonic acid

The addition of arachidonic acid (20:4), but not other fatty acids, including the structurally similar eicosapentaenoic acid (20:5), induced specific morphological changes in cultured endothelial cells derived from bovine aorta and pulmonary artery. Cells exhibited a time- and dose-dependent change from their normal, epithelioid morphology to become elongated, polygonal, and spindle-shaped. Cells isolated from aorta appeared more sensitive to these changes than those from pulmonary artery. The effect was observed as early as 12 h after exposure to 20:4, required 48 h for maximal expression, and could be reversed in 2-5 h after change to normal media. The morphological alteration was not observed in cells treated with leukotrienes or PGE2. When cells were pretreated with ibuprofen, aspirin, or indomethacin to block prostaglandin synthesis and then exposed to 20:4, the dose-response effect was shifted to the left. This increased sensitivity to 20:4 suggests either a direct effect of 20:4 on cell morphology or an indirect effect due to metabolites of 20:4 which are not dependent on the cyclooxygenase pathway.

Regulation of intracellular arachidonate in normal and stressed endothelial cells

The uptake of arachidonate and stearate from serum-free media by endothelial cells was investigated over a 48 h period. Arachidonate was rapidly incorporated into both the phospholipids and triacylglycerols. Triacylglycerol incorporation reached a maximum at 2 h and then rapidly declined with a concomitant increase in phospholipid incorporation. High initial arachidonate incorporation into phosphatidylcholine was followed by a partial transfer of that arachidonate to phosphatidylethanolamine. In contrast, stearate was slowly incorporated into all of the phospholipids and was not incorporated into the triacylglycerols. Cells stimulated with A23187 for 24 h cleaved stearate from all the phospholipids equally, whereas more arachidonate was cleaved from phosphatidylethanolamine than from the other phospholipids. Released arachidonate was both metabolized and reacylated into the triacylglycerols. Our results suggest that triacylglycerols serve as a modulator of intracellular arachidonate concentrations in endothelial cells.

Changes in serum influence the fatty acid composition of established cell lines

The fatty acid composition of different kinds of commercially available serum used to supplement cell culture media differs widely. As compared with fetal bovine serum, horse and bovine calf serum have a very high content of linoleic acid (18:2) and are low in arachidonic acid (20:4). (Fatty acids are abbreviated as number of carbon atoms:number of double bonds). Swine serum contains substantial amounts of both 18:2 and 20:4. Only fetal bovine serum contains more than 1% docosahexaenoic acid (22:6). Considerable differences in fatty acid composition occur when cells are grown in media containing any of these different serum supplements. The 18:2 and 20:4 content of 3T3 mouse fibroblast phospholipids is highest when the medium contains horse serum, intermediate with bovine calf serum, and lowest with swine or fetal bovine serum. Likewise, the highest phospholipid 18:2 content in Madin-Darby canine kidney cells (MDCK) occurs when the medium contains horse serum. With MDCK cells, however, growth in swine serum produces the highest 20:4 content. The 3T3 cell phospholipids accumulate more than 1% 22:6 only when the medium contains fetal bovine serum, whereas in no case do the MDCK cell phospholipids accumulate appreciable amounts of 22:6. The fact that the cellular fatty acid composition is likely to change should be taken into account when changes are contemplated in the serum used to grow established cell lines.

Effects of membrane lipid unsaturation on the interactions of insulin and multiplication stimulating activity with endothelial cells

Modification of plasma membrane fatty acyl composition has resulted in major changes in insulin binding and insulin action in several cell types. In the present study, endothelial cells, which in vivo are directly bathed by the changing fatty acid and insulin environment of the bloodstream, were grown in media enriched in specific saturated, monounsaturated and polyunsaturated fatty acids. These media conditions resulted in major and specific alteration in fatty acyl unsaturation of both neutral lipids and phospholipids of the endothelial cells. Despite the extensive fatty acyl changes, the lipid-modified cells demonstrated no change in the binding of insulin or the insulin-like growth factor, multiplication stimulating activity, and little alteration in insulin-induced down-regulation of the insulin receptor, or in cell processing of insulin. We suggest that the insulin receptor of the endothelial cell responds in a different manner than other cell types to similar alterations of membrane fatty acyl composition.

Prostacyclin production by confluent and non-confluent human endothelial cells in culture

Prostacyclin (PGI2) production by cultured human umbilical vein endothelial cells was examined by platelet bioassay and by radioimmunoassay of its stable metabolite 6-oxo-prostaglandin F1 alpha (6-oxo-PGF1 alpha). Confluent cultures produced PGI2 in a burst of activity approx. 20 min after changing the growth medium. This occurred in either normal, serum-supplemented growth medium or in balanced salt solution. The mechanical action of changing the growth medium did not appear to be responsible for this burst of PGI2 production. PGI2 production by non-confluent cultures decreased as cell density increased towards confluence. Supplementing the growth medium with arachidonic acid did afford some protection against decreased PGI2 production, whilst the use of conditioned media potentiated this effect. Reduction of cell density by passaging confluent cultures further demonstrated the inverse relationship between PGI2 production and cell density. These results are discussed in relation to the control of PGI2 production in cultured endothelial cells.

Phosphatidylcholine is the major phospholipid providing arachidonic acid for prostacyclin synthesis in thrombin-stimulated human endothelial cells

Upon incubation for 24 hours with [3H]arachidonic acid (AA, 1 mu Ci/ml), cultured endothelial cells from human umbilical vein incorporated one half of the added radioactivity, mostly into phospholipids (83% of the total cell radioactivity). Distribution of the label between the various phospholipid classes was found to reflect the distribution of endogenous AA. Stimulation with human thrombin (2 U/ml) promoted a rapid release of radioactive material into supernatants, which contained essentially 6-keto-prostaglandin F1 alpha and non-converted AA. This process levelled off at 10 min, at which time phosphatidylcholine displayed a decrease accounting for 3.7% of the total cell radioactivity. Phosphatidylinositol also appeared significantly diminished, but this decrease was almost 2.5 fold less than that observed in phosphatidylcholine. It is concluded that AA availability for prostacyclin biosynthesis is mostly regulated by a phospholipase A2.

Streptozotocin-induced diabetes in the neonatal rat: Effect on plasma lipids and aortic prostaglandin synthesis in adult life

The effect of streptozotocin (STZ)-induced diabetes in neonatal male rats on plasma lipids and aortic 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) synthesis in adult life was investigated. A reduction (62% of control) in aortic 6-keto-PGF1 alpha was observed only after maturity, at 17, but not 8, weeks of age. In contrast to STZ-induced diabetes in adult rats, who experience marked elevations in both plasma triglyceride (TG) levels (up to 13-fold) and total cholesterol (CH) levels (2-fold), plasma TG levels were never elevated and plasma total CH levels were significantly elevated (37%) only at 17 weeks of age. Thus, the reduction in aortic 6-keto-PGF1 alpha synthesis was dissociated from alterations in plasma TG levels in adult male rats with diabetes of neonatal origin. A significant elevation (0.31 to 0.48) in the proportion of linoleate (a competitive inhibitor of prostacyclin synthesis) to arachidonate in aortic phospholipids was also found. The results suggest that the reduced aortic synthesis of 6-keto-PGF1 alpha occurring in diabetic rats was not related to hypertriglyceridemia, but may have been related to hypercholesterolemia or altered ratios of linoleate to arachidonate in aortic phospholipids.

Prostaglandin I3 is formed in vivo in man after dietary eicosapentaenoic acid

Greenland Eskimos who live on a traditional marine diet rich in long chain omega 3-polyunsaturated fatty acids have a low incidence of cardiovascular disease and myocardial infarction. In their plasma and platelet lipids, arachidonic acid, the precursor of dienoic prostanoids, is partly replaced by eicosapentaenoic acid (C20:5, omega 3; EPA), the precursor of trienoic prostanoids. Studies with an Eskimo diet or a Western diet supplemented with sea fish or fish oil rich in EPA resulted in an 'Eskimo-like' pattern of plasma and platelet lipids. Moreover, less reactive platelets, a reduced ex vivo formation of proaggregatory thromboxane A2 and a blunted circulatory response to pressor hormones were reported. These favourable functional effects may be induced by a shift of prostanoid formation from the dienoic to the trienoic series. We show here that the major urinary metabolite of endogenous prostaglandin I3 is present in subjects that have ingested either cod liver oil (approximately 4 g EPA per day) or mackerel (approximately 10-15 g EPA per day). Our studies provide the first direct evidence for in vivo formation of prostaglandin I3 in man.

Fatty acid composition in native and cultured human endothelial cells

Endothelial cells from human umbilical veins were isolated by collagenase treatment. Cells were cultured in the presence of either 20% fetal bovine serum (FBS) or 20% human serum (HS). At confluency, endothelial cell lipids were labeled with tracer concentrations of tritiated arachidonic acid, then extracted and separated into lipid subclasses by thin layer chromatography. The fatty acid composition of each lipid class was determined by glass capillary gas-liquid chromatography analysis and compared to that of cells freshly isolated from the cord (NC cells). The fatty acid compositions differed only in phospholipids. Polyunsaturated fatty acids (PFAs), arachidonic, and linoleic acids were depleted in FBS cell phospholipids and replaced by both stearic and oleic acids. No significant difference could be observed between NC cell and HS cell phospholipids. We conclude that PFAs might be decreased in FBS cells because of the relative paucity of PFAs in FBS as compared to HS. It seems therefore more convenient to cultivate endothelial cells in the presence of HS, especially in respect to their phospholipid content of arachidonic acid, which is the physiological reservoir for prostacyclin synthesis.

Specific effect of dietary saturated fat on rat aortic 6-keto-PGF1 alpha synthesis

The effect of dietary lard and corn oil-supplementation on rat aortic 6-keto-PGF1 alpha synthesis from both exogenous and endogenous arachidonic acid was investigated. Only lard-supplementation resulted in any change when compared to rats fed normal chow. Lard-supplementation resulted in both a significant increase in the conversion of exogenous arachidonic acid to 6-keto-PGF1 alpha and a significant decrease in the ratio of linoleate to arachidonate in aortic phospholipids. Basal aortic synthesis of 6-keto-PGF1 alpha from endogenous arachidonic acid was not different for any group. We conclude that at least for the aortic conversion of exogenous arachidonic acid to 6-keto-PGF1 alpha the level of inhibitor linoleic acid in tissue phospholipids may be important.

Intralipid alters macrophage membrane fatty acid composition and inhibits complement (C2) synthesis

Intralipid (IL) is a soybean oil emulsion commonly used as a parenteral nutrient. IL is taken up by macrophages. These cells are a site of synthesis of several of the proteins in the complement system, a major mediator of the humoral system. These studies were undertaken to determine whether IL has an effect on the production of the second (C2) and the fourth (C4) components of complement by guinea pig and human macrophages in vitro. Guinea pig macrophages incubated with IL, in concentrations from 5 to 40 mg/dl, produced significantly decreased amounts of C2 and C4 when compared with controls (decreases from 40% at 5 mg/dl to 60% at 40 mg/dl). Human macrophages incubated in IL, 19 or 38 mg/dl, also produced significantly decreased amounts of C2 when compared to controls (decreases were 45 and 50% at 19 and 38 mg/dl, respectively). The maximum concentration of IL used in these studies did not significantly affect cell viability, or the production of lysozyme or β‐glucosaminidase. For human macrophages, which were studied more thoroughly, the inhibition of C2 production was reversible. C2 levels returned to normal after removal of IL. Cells stimulated with opsonized zymosan produced levels of C2 comparable to stimulated control cells, despite the continued presence of IL within the cells. Human macrophages incubated with arachidonic acid, in addition to IL, produced C2 as well as control cells did. Thus, IL appears to have a selective, reversible effect on C2 production. It is possible that a general increase in fat metabolism, in response to the ingestion of IL, nonspecifically consumed arachidonic acid, decreasing its availability as a substrate for a cell product important in production of C2. Since the effects on C2 production were seen with concentrations of IL commonly seen in plasma of infants receiving IL intravenously, these studies have implications for the clinical use of oil emulsions in parenteral nutrition.

Arachidonic acid availability and prostacyclin production by cultured human endothelial cells

When human umbilical vein endothelial cultures were grown in the presence of supplemental arachidonic acid, the cell phospholipids became enriched with arachidonic acid. Prostacyclin (PGI2) accumulated in the medium during supplementation with arachidonic acid. The capacity of these enriched cultures to produce PGI2 when subsequently incubated with either arachidonic acid or thrombin was reduced by as much as 90%, but release of arachidonic acid from the cell lipids in response to thrombin stimulation was not inhibited. Refractory cultures completely recovered the capacity to form PGI2 within 18 hours after removal of the medium containing supplemental arachidonic acid. However, recovery was prevented by cycloheximide. When enrichment with arachidonic acid was done in the presence of ibuprofen, a reversible cyclooxygenase inhibitor, PGI2 did not accumulate in the medium during supplementation, and the subsequent capacity of the cultures to produce PGI2 in response to thrombin increased by 70% to 240%. By contrast, the capacity of these supplemented cultures to convert added arachidonic acid to PGI2 did not increase. Therefore, the enhancement in thrombin-stimulated PGI2 production when the cultures are supplemented with arachidonic acid probably is due to the larger amount of arachidonic acid available in the intracellular lipid substrate pools, rather than to an activation of the PGI2 synthetic pathway. These findings suggest that changes in the arachidonic acid content of the endothelial cell lipids may modulate the capacity of the endothelium to produce PGI2 in response to stimulation.

Fatty acid composition of serum lipids in fasting ponies

Alterations in the fatty acid distribution of total lipid extracts and 4 of the major lipid subclasses of serum in ponies fasted overnight and for 4 and 7 days were determined. Although increases in 16:0, 16:1, and 18:3 omega 3 were observed, decreased amounts of 18:0 and 18:2 omega 6 combined to cause no significant change in the saturated to unsaturated fatty acid ratio in the total extracts. Phospholipid became somewhat preferentially enriched in saturated fatty acids due to a decrease in 18:1, although this response was variable. The free fatty acid and triglyceride fractions both showed increases in relative amounts of 18:3 omega 3 and a decrease in 18:0 and a concomitant change in the saturated to unsaturated fatty acid ratio. This endogenous alteration was most likely due to the mobilization of an increased proportion of polyunsaturated fatty acids from tissue sites with their subsequent incorporation into triglyceride by the liver. It probably reflects the type of forage diet on which the animals had been maintained prior to the study. The fatty acid composition of the cholesteryl ester fractions was unchanged during fasting but contained appreciable amounts of the 18:2 omega 6 fatty acid.

Increased arachidonic acid content in platelet phospholipids from diabetic patients

Platelet abnormalities have been suggested to be linked with vascular diseases. Diabetes mellitus has a high incidence of vascular complications. In the present study gas-liquid chromatography analyses were carried out to investigate the fatty acid composition in platelet phospholipids of Type-2 (non-insulin-dependent) diabetic patients. Fatty acid composition in platelet phospholipids was different between diabetics and age-matched control subjects. Arachidonic acid increased significantly (p less than 0.01), and both eicosatrienoic acid and eicosapentaenoic acid decreased in diabetes mellitus. A good correlation was found between fatty acid content of platelet phospholipids and that of plasma total lipids in the fatty acids examined, except for arachidonic acid. The levels of arachidonic acid in diabetic platelet phospholipids was disproportionately high to these in plasma total lipids. These results suggest that the system for arachidonic acid incorporation into platelet phospholipids is specifically accelerated in the diabetic metabolic state.