Role of the microtubule cytoskeleton in gravisensing Chara rhizoids

Docosahexaenoic acid and arachidonic acid are deposited in large amounts in the developing central nervous system, and concentrations are particularly high in synaptic plasma membrane and retina ethanolamine phospholipids. Arachidonic acid and docosahexaenoic acid are present in human milk. The precursors linoleic [18:2(n-6)] and alpha-linolenic [18:3(n-3)] acid, but not arachidonic acid or docosahexaenoic acid, are present in formulas. Desaturation and elongation of 18:2(n-6) and 18:3(n-3) to arachidonic acid and docosahexaenoic acid, respectively, depend on the dietary content and ratio of 18:2(n-6) and 18:3(n-3), but appropriate levels and ratios of 18:2(n-6) and 18:2(n-3) for formula are not well defined. The effect of formula with 1 or 4% fatty acids 18:3(n-3) and 16, 30 or 35% fatty acids 18:2(n-6) on synaptic plasma membrane and retina ethanolamine phospholipid fatty acids was therefore studied in piglets, with reference to piglets fed milk. Piglets fed 4% fatty acids 18:3(n-3), but not those fed 1% fatty acids 18:3(n-3), had similar central nervous system docosahexaenoic acid levels but had significantly lower brain weights than piglets fed sow milk. Synaptic plasma membrane and retina arachidonic acid were lower in piglets fed the formulas with 4% rather than 1% fatty acids 18:3(n-3). The dietary 18:3(n-3) content, rather than the 18:2(n-6) to 18: 3(n-3) ratio, seemed more important for deposition of docosahexaenoic acid in brain. However, synaptic plasma membrane and retina docosahexaenoic acid levels were further reduced in piglets fed 1% fatty acids 18:3(n-3) (0.4% energy) with 30% rather than with 16% fatty acids 18:2(n-6). The need for further study of upper limits of dietary 18:3(n-3) during development is suggested.     

Essential fatty acid metabolism in cardiomyocytes grown in media enriched with different N-6/N-3 fatty acid combinations

We have evaluated the effects of three different 18:3n-6, 20:5n-3 and 22:6n-3 fatty acid combinations on essential fatty acid (EFA) metabolism in rat cultured cardiomyocytes. The desaturating/elongating activities for linoleic (LA) and alpha-linolenic acid (ALA) were evaluated by radiolabeling the cells with 1-[14C]LA or 1-[14C]ALA and the fatty acid pattern of cardiomyocytes was assessed by gas chromatography. LA and ALA conversion to more unsaturated metabolites was reduced by increasing respectively n-3 and n-6 fatty acid concentration in the media. The all three combinations used reduced the saturated and increased the polyunsaturated fatty acid content of cardiomyocytes. The n-6/n-3 fatty acid ratio did not change compared to control cells in cardiomyocytes receiving the highest amount of 18:3n-6 and the lowest amounts of n-3 fatty acids. This combination may be suitable for modifying EFA desaturating/elongating activities without altering the physicochemical parameters which are related to the correct balance between n-6 and n-3 fatty acid content.     

Fatty acyl desaturation in isolated hepatocytes from Atlantic salmon (Salmo salar): stimulation by dietary borage oil containing gamma-linolenic acid

The effects of different dietary oils on the fatty acid compositions of liver phospholipids and the desaturation and elongation or [1-14C]18:3n-3 and [1-14C]18:2n-6 were investigated in isolated hepatocytes from Atlantic salmon. Atlantic salmon smolts were fed diets containing either a standard fish oil (FO) as a control diet, a 1:1 blend of Southern Hemisphere marine oil and tuna orbital oil (MO/TO), sunflower oil (SO), borage oil (BO), or olive oil (OO) for 12 wk. The SO and BO diets significantly increased the percentages of 18:2n-6, 18:3n-6, 20:2n-6, 20:3n-6, and total n-6 polyunsaturated fatty acids (PUFA) in salmon liver lipids in comparison with the FO diet. The BO diet also increased the percentage of 20:4n-6. Both the SO and BO diets significantly reduced the percentages of all n-3 PUFA in comparison with the FO diet. The OO diet significantly increased the percentages of 18:1n-3, 18:2n-6, total monoenes, and total n-6 PUFA in liver lipids compared to the FO diet, and the percentages of all n-3 PUFA were significantly reduced. With [1-14C]18:3n-3, the recovery of radioactivity in the products of delta 6 desaturation was significantly greater in the hepatocytes from salmon fed SO, BO, and OO in comparison with the FO diet. The BO diet also increased the recovery of radioactivity in the products of delta 5 desaturation. Only the BO diet significantly affected the desaturation of [1-14C]18:2n-6, increasing recovery of radioactivity in both delta 6- and delta 5-desaturation products. In conclusion, dietary BO, enriched in gamma-linolenic acid (18:3n-6), significantly increased the proportions of both 20:3n-6 and 20:4n-6 in salmon liver phospholipids and also significantly increased the desaturation of both 18:2n-6 and 18:3n-3 in salmon hepatocytes. The possible relationships between dietary fatty acid composition, tissue phospholipid fatty acid composition, and desaturation/elongation activities are discussed.     

Fatty acid composition of human brain phospholipids during normal development

The fatty acid composition of phosphatidylethanolamine (PE), ethanolamine plasmalogens (EPs), phosphatidylserine (PS), phosphatidylcholine (PC), and sphingomyelin was studied in 22 human forebrains, ranging in age from 26 prenatal weeks to 8 postnatal years. Phospholipids were separated by two-dimensional TLC, and the fatty acid methyl esters studied by capillary column GLC. Docosahexaenoic acid (22:6n-3) increased with age in PE and PC, whereas arachidonic acid (20:4n-6) remained quite constant. In EP, 22:6n-3 increased less markedly than 20:4n-6, adrenic (22:4n-6) and oleic (18:1n-9) acids being the predominant fatty acids during postnatal age. In PS, 18:1n-9 increased dramatically throughout development, and 20:4n-6 and 22:4n-6 increased only until approximately 6 months of age. Although 22:6n-3 kept quite constant during development in PS, its percentage decreased due to the accretion of other polyunsaturated fatty acids (PUFAs). As a characteristic myelin lipid, sphingomyelin was mainly constituted by very long chain saturated and monounsaturated fatty acids. Among them, nervonic acid (24:1n-9) was the major very long chain fatty acid in Sp, followed by 24:0, 26:1n-9, and 26:0, and its accretion after birth was dramatic. As myelination advanced, 18:1n-9 increased markedly in all four glycerophospholipids, predominating in EP, PS, and PC. In contrast, 22:6n-3 was the most important PUFA in PE in the mature forebrain.     

Effect of diet on the fatty acid and molecular species composition of dog retina phospholipids

Dogs were born to mothers fed commercial diets low or enriched in n-3 fatty acids and raised on those diets until they were about 50 d old. Retinas were removed, lipids were extracted, and total phospholipids were analyzed for fatty acid and molecular species composition. Animals from the low n-3 group had significantly lower retinal levels of 22:6n-3 and higher levels of n-6 fatty acids, especially 20:4n-6 and 22:5n-6. There was no difference in the retinal levels of 18:2n-6, and only small differences were found in saturated and monounsaturated fatty acids. The most dramatic differences in molecular species occurred in 22:6n-3-22:6n-3 (4.7 vs. 0.8%) and 18:0-22:6n-3 (27.6 vs. 14.4%); total molecular species containing 22:6n-3 were significantly lower in the low n-3 group (45.5 vs. 24.0%). Molecular species containing 20:4n-6 and 22:5n-6 were greater in the low n-3 animals (13.0 vs. 25.7%), as were molecular species containing only saturated and monounsaturated fatty acids (40.8 vs. 35.4%). These results show that modest differences in the amount of n-3 fatty acids in the diets of dogs can have profound effects on the fatty acid and molecular species composition of their retinas.     

Linoleic acid enhances the secretion of plasminogen activator inhibitor type 1 by HepG2 cells

This study was undertaken in order to assess whether triglycerides and/or their fatty acids directly influence the secretion of plasminogen activator inhibitor type 1 (PAI-1) in HepG2 cells. To this end, subconfluent HepG2 cells were incubated with triglyceride-rich particles (TGRP) isolated from Intralipid for 16 h, and PAI-1 levels were determined in conditioned medium using a specific ELISA. TGRP (1 to 6 mg triglycerides/ml) concentration-dependently increased PAI-1 secretion by cells, concomitantly with significant increases in intracellular triglyceride (TG) levels. Fatty acid analysis indicated that the incubation of cells with 3 mg of TG per ml of TGRP induced significant accumulation of 18:2 n-6 (linoleic acid, LA) and 18:3 n-3 (linolenic acid) reflecting the fatty acid composition at the added triglycerides. We then tested the comparative effects on PAI-1 secretion by HepG2 cells of LA and 18:1 n-9 (oleic acid, OA). LA, as a bovine serum albumin (BSA) complex, concentration-dependently (1 to 35 mumol/L) increased the secretion of PAI-1 by cells, whereas OA-BSA only minimally affected it at the highest concentration used (35 mumol/L). Incorporation of LA into cell pools, in the presence of increasing concentration of the FA in the medium, was studied by the use of a preparation containing [14C]LA. LA accumulated in all lipid classes including diacylglycerol, the incorporated LA being converted into arachidonic acid (AA) as assessed by HPLC radiochromatography of the fatty acid methyl esters. It is concluded that PAI-1 secretion in HepG2 cells is modulated by triacylglycerols and by linoleic acid and/or its metabolic products.     

Net transfer and incorporation of yolk n-3 fatty acids into developing chick embryos

The effect of egg yolk fatty acid composition on the uptake and utilization of essential n-6 and n-3 fatty acids by the developing chick embryo was studied. Eggs were enriched with n-9, n-3, or n-6 fatty acids by incorporating sunflower seed high in oleic acid (C18:1 n-9), flax seed rich in linolenic acid (C18:3 n-3), or sunflower seed high in linoleic acid (C18:2 n-6) into the laying hen diets. Fertile eggs were collected and incubated. The fatty acid composition of eggs and newly hatched chicks were compared. Feeding diets containing flax seed increased (P < .05) total n-3 fatty to 528.4 mg compared with 53.9 and 39.3 mg for eggs from hens fed diets with high oleic acid or regular sunflower seed, respectively. Levels of C18:2 n-6 and monounsaturated fatty acids were higher in eggs from hens fed diets containing regular or high oleic acid sunflower seeds. Dietary fat did not influence the total lipid content of the egg yolk or total lipids of chick tissues. The fatty acid composition of the hatched progeny was significantly altered by egg yolk lipids. However, the percentage incorporation of essential n-6 and n-3 fatty acids into the progeny increased when yolk sources of these fatty acids were low. The developing chick embryo appeared to preferentially take up docosahexaenoic acid and arachidonic acid from the yolk lipids. Evidence also suggests that conversion of C18:2 n-6 and C18:2 n-3 to longer chain n-3 or n-6 fatty acids occurs during the incubation period.     

Polyunsaturated fatty acid metabolism in retinal and cerebral microvascular endothelial cells

Docosahexaenoic acid (22:6n-3), an n-3 essential fatty acid derived from elongation and desaturation of linolenic acid (18:3n-3), is found in abundant proportion in the brain and the retina. It is generally assumed that the liver is the major source of 22:6n-3 for these organs, although some retinal and cerebral cells, such as retinal pigment epithelium (Wang and Anderson, 1993. Biochemistry. 32:13703-13709) and brain astrocytes (Moore et al. 1991. J. Neurochem. 56:518-524) have the ability to produce 22:6n-3. The aim of the present study was to determine whether retinal and cerebral microvascular endothelium could synthesize 22:6n-3. After incubation of both cultured bovine retinal and rat cerebral endothelial cells with [3-14C] 22:5n-3 in presence of serum, radioactivity was primarily recovered in 20:5n-3, indicating active retroconversion reactions in both tissues. However, 22:6n-3, 24:5n-3, and 24:6n-3 were also labeled. All of these metabolites were released in the medium as free fatty acids. Retinal endothelial cells preferentially released labeled 24-carbon metabolites, whereas cerebral endothelial cells released relatively more 20:5n-3 and 22:6n-3. With heat-inactivated serum or no serum, both endothelial cell preparations showed relatively higher retroconversion levels. However, in serum-deprived cells, the elongation/desaturation pattern was affected in retinal cells only, with an accumulation of 24:5n-3 relative to a decrease of 24:6n-3 and 22:6n-3. Fatty acid composition analyses revealed a decrease in long-chain polyunsaturated n-6 and n-3 fatty acids in retinal cells maintained in inactivated serum compared to normal serum, while no change was found in cerebral cells. Taken together, these results suggest that 1) the synthesis of 22:6n-3 by both retinal and cerebral endothelial cells is independent of a delta4-desaturase; 2) retinal and cerebral endothelia could be a source of 22:6n-3 for the retina and the brain, respectively; and 3) retinal endothelial delta6-desaturase, which converts 24:5n-3 to 24:6n-3, could be stimulated by serum components.     

Tumor necrosis factor-induced release of endogenous fatty acids analyzed by a highly sensitive high-performance liquid chromatography method

A highly sensitive method to determine agonist-induced release of endogenous fatty acids from cells in culture was developed using high-performance liquid chromatography and fluorescence detection. Fatty acids were selectively derivatized with 1-pyrenyldiazomethane and separated on a LC18 reversed phase column using an acetonitrile-water gradient. The detection limit was approx. 20 fmol and the recovery of the complete method using oleic acid was 93-98%. Tumor necrosis factor alpha (TNF-alpha) increased the extracellular release of endogenous arachidonic acid (20:4n-6) from 21 to 153 pmol/well per 4 h using 2.7 x 10(6) WEHI fibrosarcoma cells. In cells preincubated with 50 microM 20:4n-6, the corresponding figures were 463 and 3379 pmol 20:4n-6/well. Simultaneously, nearly equimolar amounts of 22:4n-6 were released together with slightly lower amounts of 24:4n-6, 16:0, 16:1n-9, and 18:1n-9. Analysis of cell lipid fatty acids showed that phosphatidylcholine was the major source of the released fatty acids. TNF-alpha increased the intracellular concentration of unesterified 20:4n-6 and 22:4n-6 by 368% and 451%, respectively. This suggests that released 20:4n-6 is rapidly chain elongated to 22:4n-6. The results indicate that the present method facilitates studies on agonist-induced release of endogenous fatty acids, and that TNF-induced fatty acid release seems to be less selective for 20:4n-6 than previously reported.     

Ontogenesis of lipids in chick embryo retina

PURPOSE: The effects of embryonic development on lipid composition in the retina were studied in 7, 11, 15, and 18-day-old chick embryos and newly hatched chicks. METHODS: The proportions of phospholipids, free and esterified cholesterol, diacylglycerides, and free fatty acids were determined using the Iatroscan TLC/FID procedure. Gas chromatography and mass spectrometry were used to determine the fatty acid composition. RESULTS: The major phospholipid species were phosphatidylethanolamine, phosphatidylcholine, phosphatidylserine, phosphatidylinositol, lysophosphatidylcholine, and sphingomyelin. Concentrations of the analyzed components have been related to the chronology of concrete stages of retinal development. The fatty acid composition of the total lipids, (n-6):(n-3) and saturated: unsaturated fatty acid ratios, and other parameters are reported. The proportions of total saturated and total monounsaturated fatty acids decreased very little from day 7 to hatching, whereas total polyunsaturated fatty acids nearly doubled over the same period. The increase in C18:2(n-6) from day 11 onwards was not followed by a similar increase in C20:4(n-6), hence the C20:4 to C18:2 ratio decreased with age. CONCLUSIONS: The cholesterol:phospholipid ratio decreased from day 7 to day 15 and increased from day 15 to hatching. High proportions of esterified cholesterol, very probably originating in the retinal pigment epithelium, were also recorded. Total saturated and monounsaturated fatty acids decreased, while polyunsaturated fatty acids increased during the period of initial retinal growth.     

Fatty acids suppress voltage-gated Na+ currents in HEK293t cells transfected with the alpha-subunit of the human cardiac Na+ channel

Studies have shown that fish oils, containing n-3 fatty acids, have protective effects against ischemia-induced, fatal cardiac arrhythmias in animals and perhaps in humans. In this study we used the whole-cell voltage-clamp technique to assess the effects of dietary, free long-chain fatty acids on the Na+ current (INa,alpha) in human embryonic kidney (HEK293t) cells transfected with the alpha-subunit of the human cardiac Na+ channel (hH1alpha). Extracellular application of 0.01 to 30 microM eicosapentaenoic acid (EPA, C20:5n-3) significantly reduced INa,alpha with an IC50 of 0.51 +/- 0.06 microM. The EPA-induced suppression of INa,alpha was concentration- and voltage-dependent. EPA at 5 microM significantly shifted the steady-state inactivation relationship by -27.8 +/- 1.2 mV (n = 6, P < 0.0001) at the V1/2 point. In addition, EPA blocked INa,alpha with a higher "binding affinity" to hH1alpha channels in the inactivated state than in the resting state. The transition from the resting state to the inactivated state was markedly accelerated in the presence of 5 microM EPA. The time for 50% recovery from the inactivation state was significantly slower in the presence of 5 microM EPA, from 2.1 +/- 0.8 ms for control to 34.8 +/- 2.1 ms (n = 5, P < 0.001). The effects of EPA on INa,alpha were reversible. Furthermore, docosahexaenoic acid (C22:6n-3), alpha-linolenic acid (C18:3n-3), conjugated linoleic acid (C18:2n-7), and oleic acid (C18:1n-9) at 5 microM and all-trans-retinoic acid at 10 microM had similar effects on INa,alpha as EPA. Even 5 microM of stearic acid (C18:0) or palmitic acid (C16:0) also significantly inhibited INa, alpha. In contrast, 5 microM EPA ethyl ester did not alter INa,alpha (8 +/- 4%, n = 8, P > 0.05). The present data demonstrate that free fatty acids suppress INa,alpha with high "binding affinity" to hH1alpha channels in the inactivated state and prolong the duration of recovery from inactivation.     

Intestinal absorption of polyunsaturated phosphatidylcholine in the rat

The mechanism of intestinal absorption of polyunsaturated phosphatidylcholine in an oil medium was studied with 1,2-di-[9,10,12,13-3H4]linoleoyl-sn-glycero-3-phospho-[N-14CH3]-choline, 1-[1-14C]linoleoyl-2-[9,10,12,13-3H4]-linoleoyl- and 1-[9,10,12,13-3H4]linoleoyl-2-[1-14C]linoleoyl-sn-glycero-3-phosphocholine, especially with regard to the stability of the ester bonds in position 1 and 2 of the phospholipid molecule. The absorption rate, as measured by the disappearance from the gastro-intestinal tract, was comparatively rapid in the first 6 - 8 h, but then became considerably slower. After 24 h more than 90% of the applied radioactivity was absorbed from the intestinal tract. Respiratory 14CO2 from the degradation of the unsaturated acyl moiety in position 2 is produced much more rapidly than that from the acyl group attached to the 1-position of the glycerophosphocholine backbone. Analyses of the liver phosphatidylcholine by specific enzymatic hydrolysis with phospholipase A2, 6 h after the application, showed that in the isolated PC 9 times more labelled fatty acids from the original 1-position were present than from the corresponding 2-position. In rats with lymph fistula it was shown that more than 90% of the acyl moieties of the administered 1,2-di-[9,10,12,-13-3H4]linoleoyl-[N-14CH3] glycerophosphocholine was transported by the chylomicrons. About one half of the 14C choline radioactivity of the glycerophosphocholine backbone was found in the chylomicrons and the other half in the liver. The 3H radioactivity distribution in the chylomicrons amounted to 25% in the phosphatidylcholine fraction and 75% in the neutral lipids. Positional specific analyses of the phosphatidylcholine present in chylomicrons confirmed the fact that the 1-position remained practically intact while the 2-position underwent considerable exchange with unlabelled fatty acids. Analysis of the liver of the animals with lymph fistula indicated that it was practically free of the 3H radioactivity derived from the acyl moieties but contained a high percentage of the 14C radioactivity of the choline group. The methyl groups of choline were oxidized only to a very small extent. These results demonstrate that during the absorption process, about one half of the absorbed polyunsaturated phosphatidylcholine is hydrolyzed to 1-acyl-lysophosphatidylcholine and reacylated again to phosphatidylcholine upon entering the mucosa cell, while the other half is completely hydrolyzed to free fatty acids and glycerophosphocholine or its hydrolysis products. The fatty acids released are utilized for the reassembly of triacylglycerides and phosphatidylcholine found in the chylomicrons.     

Inhibition of icosanoid production in MC/9 mouse mast cells by n-3 polyunsaturated fatty acids isolated from edible marine algae

The effects of two polyunsaturated fatty acids, 18:4n-3 and 16:4n-3 purified from the marine algae, Undaria pinnatifida and Ulva pertusa, on icosanoid production in MC/9 mouse mast cells were assessed. Both fatty acids suppressed the production of leukotriene B4 (LTB4), leukotriene C4 (LTC4), and 5-hydroxyeicosatetraenoic acid (5-HETE). The order of the suppressive activity for the two marine algae-derived fatty acids and three other common polyunsaturated fatty acids was as follows; 22:6n-3 = 18:4n-3 = 18:3n-3 > 20:5n-3 = 16:4n-3 for LTB4; 22:6n-3 = 18:4n-3 = 18:3n-3 > 16:4n-3 > 20:5n-3 (no suppression) for LTC4; 22:6n-3 = 18:4n-3 > 18:3n-3 > 20:5n-3 = 16:4n-3 for 5-HETE.     

Uneven distribution of desmosterol and docosahexaenoic acid in the heads and tails of monkey sperm

Previously we demonstrated high concentrations of desmosterol and docosahexaenoic acid (DHA, 22:6 n-3) in monkey testes and sperm. Desmosterol, a cholesterol precursor, is not present elsewhere in the body. High concentrations of DHA are found elsewhere only in the retina and brain. To examine the distribution of these compounds in the heads and tails of sperm, we separated them and determined their sterol, fatty acid, and phospholipid molecular species composition. Desmosterol predominated in tails (134.4 vs. 1.7 microg/10(9) cells in heads). The cholesterol content was also greater in the tails (66.2 vs. 30.3 microg/10(9) cells in heads). Sperm tails had more polyunsaturated fatty acids than the heads (34.1 vs. 12.1% of total fatty acids) which resulted mainly from the higher contents of DHA (19.6 vs. 1.1%) and arachidonic acid (20:4 n-6) (6.4 vs. 1.6%) in the tails. These differences in fatty acid composition occurred mainly in phospholipids: phosphatidyl choline and phosphatidyl ethanolamine for n-3 fatty acids and phosphatidyl serine and cardiolipin for n-6 fatty acids. Fifteen phospholipid molecular species were identified. Sperm tails had more molecular species containing unsaturated fatty acids than the heads. Our results reveal the large differences in membrane lipid composition between the heads and tails of sperm. Most (99%) of the desmosterol and DHA in sperm is located in the tail. These differences may be responsible for the different functions of these two components of sperm. The large number of double bonds in DHA, six, and in desmosterol, two, may contribute to the membrane fluidity necessary for the motility of the sperm tails.     

Incorporation of polyunsaturated fatty acids into phospholipids of hemocytes from the tobacco hornworm, Manduca sexta

We examined the incorporation of four radioactive fatty acids, 18:1n-9, 18:2n-6, 20:4n-6 and 20:5n-3, into cellular lipids of hemocytes from tobacco hornworms, Manduca sexta. Most of the radioactivity associated with 18:1n-9 was recovered from triacylglycerols (TGs), and the radioactivity associated with 18:2n-6 was heavily incorporated into phospholipids (PLs) and TGs. Most of the radioactivity associated with the two eicosanoid-precursor polyunsaturated fatty acids (PUFAs), 20:4n-6 and 20:5n-3, was incorporated into PLs. The incorporated fatty acids were redistributed among the lipid classes during 2 h incubations. The two C20 PUFAs were moved from PLs to TGs. While 18:2n-6 underwent little change, 18:1n-9 was redistributed from TGs to PLs. Within PLs, each of the fatty acids were incorporated into phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PtG) and phosphatidylserine/inositol (PS/PI). The incorporation patterns changed over time, indicating that the incorporated fatty acids were redistributed among the four PL fractions. The radioactivity associated with 18:1n-9 was mostly recovered from the sn-1 position of PC (59%) and PE (83%). Most of the radioactivity associated with 18:2n-6 was found in the sn-2 position of PC (88%) and PE (67%). Over 90% of the radioactivity associated with 20:5n-3 was recovered from the sn-2 position of PC and PE. Incorporation of 20:4n-6 differed from 20:5n-3 because more radioactivity was recovered from the sn-2 position of PC (93%) than PE (69%). These findings are in line with the general background of lipid biochemistry, from which incorporation of 20:4n-6 into PE marks a notable departure: 31% of the radioactivity associated with this acid was recovered from the sn-1 position of PE. These findings indicate that hemocytes from the tobacco hornworm elaborate a fatty acid incorporation system, which exhibits specificity with respect to fatty acid structure and lipid class.     

Arachidonic acid inhibits lipogenic gene expression in 3T3-L1 adipocytes through a prostanoid pathway

This report examines the effect of polyunsaturated fatty acids (PUFA) on lipogenic gene expression in cultured 3T3-L1 adipocytes. Arachidonic acid (20:4, n-6) and eicosapentaenoic acid (20:5, n-3) suppressed mRNAs encoding fatty acid synthase (FAS) and S14, but had no effect on beta-actin. Using a clonal adipocyte cell line containing a stably integrated S14CAT fusion gene, oleic acid (18:1, n-9), arachidonic acid (20:4, n-6) and eicosapentaenoic acid (20:5, n-3) inhibited chloramphenicol acetyltransferase (CAT) activity with an ED50 of 800, 50, and 400 microM, respectively. Given the high potency of 20:4, n-6, its effect on adipocyte gene expression was characterized. Arachidonic acid suppressed basal CAT activity, but did not affect glucocorticoid-mediated induction of S14CAT expression. The effect of 20:4, n-6 on S14CAT expression was blocked by an inhibitor of cyclooxygenase implicating involvement of prostanoids. Prostaglandins (PGE2 and PGF2alpha at 10 microM) inhibited CAT activity through a pertussis toxin-sensitive Gi/Go-coupled signalling cascade. Our results suggest that 20:4, n-6 inhibits lipogenic gene expression in 3T3-L1 adipocytes through a prostanoid pathway. This mechanism of control differs from the polyunsaturated fatty acid-mediated suppression of hepatic lipogenic gene expression.     

Modifying the n-3 fatty acid content of the maternal diet to determine the requirements of the fetal and suckling rat

During perinatal development, docosahexaenoic acid (22:6n-3) accumulates extensively in membrane phospholipids of the nervous system. To evaluate the n-3 fatty acid requirements of fetal and suckling rats, we investigated the accumulation of 22:6n-3 in the brain and liver of pup rats from birth to day 14 postpartum when their dams received increasing amounts of dietary 18:3n-3 (from 5 to 800 mg/100 g diet) during the pregnancy-lactation period. The fatty acid composition of brain and liver phospholipids of pups, as well as that of dam's milk, was determined. At birth, 22:6n-3 increased regularly to reach the highest level when the maternal diet contained 800 mg 18:3n-3/100 g. On days 7 and 14 postpartum, brain 22:6n-3 plateaued at a maternal dietary supply of 200 mg/100 g. Docosapentaenoic acid (22:5n-6) had the opposite temporal pattern. The unusually high concentration of eicosapentaenoic acid (20:5n-3) in liver and dam's milk observed at the highest 18:3n-3 intake suggests an excessive dietary supply of this fatty acid. All these data suggest that the n-3 fatty acid requirements of the pregnant rat are around 400 mg 18:3n-3 and those of the lactating rat at 200 mg (i.e., 0.9 and 0.45% of dietary energy, respectively). The values of 18:3n-3 and 22:6n-3 milk content which allowed brain 22:6n-3 to reach a plateau value in suckling pups were 1% of total fatty acids and 0.9% (colostrum) to 0.2% (mature milk), respectively. These levels are similar to those recommended for infant formulas.     

Dietary modulation of phase 1 and phase 2 activities with benzo(a)pyrene and related compounds in the intestine but not the liver of the channel catfish, Ictalurus punctatus

EPA, DHA, C15SCH2COOH (n-3), C15SCH2COOH (n-6) and C18SCH2COOH (n-3) are extensively incorporated into phospholipids and triacylglycerol in rat hepatocytes after 24 h incubation with 80 microM fatty acid/derivative. Only traces of polyunsaturated 3-oxa fatty acids (C15OCH2COOH, C18OCH2COOH) were incorporated. C15-S-butyric acid (n-3) is a stronger inhibitor of delta6-desaturase in rat liver-microsomes than C15SCH2COOH (n-3), C15-S-propionic acid (n-3), EPA and DHA. It inhibits delta5-desaturase in a similar manner to EPA and DHA. Arachidonic acid and C15SCH2COOH, (n-6) are better substrates for PGH-synthase than EPA and C15SCH2COOH, (n-3), showing the inhibitory effect of the n-3 bond. The n-3 polyunsaturated fatty acids, including the sulfur-substituted fatty acid derivatives, are poor substrates for PGH-synthase. However, they inactivate the PGH-synthase activity at least as efficiently as arachidonic acid. C15SCH2COOH (n-3), C15S(CH2)2COOH (n-3) and C18SCH2COOH (n-3) induce peroxisomal beta-oxidation more than EPA and DHA.     

First-trimester growth restriction and fetal aneuploidy: the effect of type of aneuploidy and gestational age

Changes in the proportions of the various lipid components in spermatozoa were investigated throughout the reproductive period (24-72 wk of age) of male chickens. Sperm motility and in vivo fertility were also measured, and correlation coefficients with the lipid values were determined. The proportion of total phospholipid (PL) increased to reach a maximum value at 39 wk and decreased significantly thereafter. The relative content of free cholesterol and triacylglycerols showed no change in spermatozoa during aging or in relation to fertility values; free fatty acids and cholesterol esters increased continuously with age. Of the various PL classes, phosphatidylserine and phosphatidylcholine displayed a pattern of changes with age positively and negatively, respectively, in relation to the changes of fertility. The proportion of phosphatidylethanolamine had significantly decreased by the end of the reproductive period. The proportions of C16:0, C18:0, and C18:1n-9 within the PL of the spermatozoa increased with age, and those of C20:4n-6, C22:4n-6, and C22:6n-3 decreased. Positive correlations were found between fertility and total PLs, phosphatidylserine, and PL-bound C20:4n-6 and C22:4n-6; a negative correlation was found between fertility and phosphatidylcholine. Motility was positively correlated with the level of PL and negatively with that of free cholesterol; it was also positively correlated with the levels of C22:4n-6 and C22:6n-3 and negatively with those of C16:0, C18:0, and C18:1n-9. The results suggest that the lipid and fatty acid compositions of spermatozoa may be important predictors of fertility.     

Relationships between serum lipids, platelet membrane fatty acid composition and platelet aggregation in type 2 diabetes mellitus

In order to gain further insight into the mechanism of platelet dysfunction frequently reported in diabetes we investigated circulating fatty acids, lipid composition of platelet membrane and platelet function in Type 2 diabetic patients. In these subjects, percentages of C16 : 1n-7 and C18 : 1n-9 in serum phospholipid fraction and of C16 : 1n-7 in serum cholesterol ester fraction were decreased. Moreover, the content of C20 : 4n-6 in serum cholesterol esters was altered in Type 2 diabetic subjects: C18 : 0 and C20 : 3n-6 were increased but C20 : 4n-6 content was similar to controls. Aggregation in vitro did not differ from controls but aggregation in vivo was increased in Type 2 diabetic subjects. No correlation was observed between metabolic parameters -i.e., HbA1, blood glucose, serum triglycerides and total cholesterol, circulating fatty acids and fatty acid content of platelet membrane. A negative linear correlation was found between aggregation in vivo and C20 : 4n-6 content of platelet membrane. Moreover, a U shaped relationship was observed between platelet aggregation in vitro and C20 : 4n-6 content of platelet membrane suggesting that C20 : 4n-6 level should be tightly controlled otherwise platelet hyperreactivity may occur. These results indicate that despite a normal mean C20 : 4n-6 content in the platelet membrane, regulation of C20 : 4n-6 metabolism is less strictly controlled in Type 2 diabetes mellitus and confirm the importance of arachidonic acid platelet content in the regulation of platelet aggregability.