Specific accumulation of docosahexaenoic acid (22∶6n−3) in brain lipids during development of juvenile turbotScophthalmus maximus L.

The changes in the lipid class and the fatty acid compositions of total lipids and individual glycerophospholipids which occur in brain during development of juvenile turbot (Scophthalmus maximus L.) were investigated. Fish were sampled during a 10-week period immediately following weaning from a live feed to a pellet diet. During this period, brain dry weight increased over 6-fold. The percentages of protein, cholesterol and galactolipids increased in brain during development, presumably reflecting increased membrane maturation and myelination processes. The percentages of docosahexaenoic acid (DHA; 22∶6n−3) were low at the beginning of the study period. However, DHA specifically accumulated in juvenile turbot brain during development. The percentages of DHA increased in total lipid, total diradyl glycerophosphocholine (GPC), total diradyl glycerophosphoethanolamine (GPE), phosphatidylserine (PS) and phosphatidylinositol (PI) reaching 26.1%, 25.8%, 40.8%, 47.1% and 17.9% of the total fatty acids, respectively, by the end of the 10-week period. The percentages of other n−3 polyunsaturated fatty acids (PUFA) and n−6 PUFA generally decreased during this period, as did that of monoenes; the percentages of saturated fatty acids remained relatively constant. Non-linear regression analysis showed that the increase in DHA in total lipid, GPC, GPE and PS fitted 1st order rate kinetics (plus offset) allowing maximum values for the percentages of DHA in each lipid class to be estimated.     

The lipid composition of selected tissues from a Mediterranean monk seal,Monachus monachus

The lipid composition of blubber, brain, muscle and heart from a Mediterranean monk sealMonachus monachus (an endangered species) were examined to allow comparisons with more common species of seals. Only neutral lipids (mainly triacylglycerols) were detectable in the blubber lipids, whereas polar lipids predominated in the heart and in the brain. Neutral and polar lipids comprised almost equal proportions in both liver and muscle. Choline glycerophospholipids (CGP) were the major polar lipids, followed by ethanolamine glycerophospholipids (EGP) in the liver, heart and muscle. Cerebrosides accounted for 28.8% of the brain lipids. All lipid classes of the liver contained high levels (31–47%) of polyunsaturated fatty acids (PUFA), with the exception of phosphatidylserine. The total proportion of n−6 PUFA exceeded that of n−3 PUFA in all lipid classes of the liver, due mainly to the high levels of 20∶4n−6. The highest level of 20∶4n−6 occurred in phosphatidylinositol, where it comprised 32.4% of the total fatty acids. The CGP and EGP of the brain contained lower levels of PUFA than those of the liver, muscle and heart. Alkenyl ethers accounted for 35.8% of the total long-chain moieties in brain EGP. The fatty acid composition of blubber triacylglycerols differed from those of the lipid classes from other tissues in that it had a very low ratio of n−6 to n−3 PUFA (0.3) as a result of a lower content of 20∶4n−6.     

Composition of the phospholipids and their fatty acids in the ROC-1 oligodendroglial cell line

ROC-1 cells are a hybrid of C−6 rat glioma and rat oligodendroglia cells. Biochemically these cells resemble the oligodendroglia parent, but their lipid composition is unknown. The phospholipid composition in mole % was: cardiolipin, 1.0; phosphatidylglycerol, 1.2; ethanolamine glycerophospholipids, 27.6; phosphatidylinositol, 5.8; lysophosphatidylethanolamine, 0.8; phosphatidylserine, 5.6; choline glycerophospholipids, 43.7; sphingomyelin, 13.7; phosphatidylinositol-4-monophosphate, 0.8; and lysophosphatidylcholine, 0.6. The choline and ethanolamine plasmalogens made up 7.2 and 18.4% of the total phospholipids, respectively. The phospholipid composition reflects that of both parental cells. The cells had moderate to high levels of 20∶3n−9 indicating n−6 series fatty acid deficiency. The phosphatidylinositol had very high 20∶3n−9 levels with a 20∶3n−9/20∶4n−6 ratio of 2.1 compared to 0.44 and 0.58 for ethanolamine glycerophospholipids (EtnGpl) and choline glycerophospholipids (ChoGpl) respectively. The saturated/polyenoic fatty acid ratios were 0.40 for EtnGpl, 3.38 for ChoGpl and 1.48 for phosphatidylinositol.     

Liver and intestinal fatty acid-binding protein expression increases phospholipid content and alters phospholipid fatty acid composition in L-cell fibroblasts

Although fatty acid-binding proteins (FABP) differentially affect fatty acid uptake, nothing is known regarding their role(s) in determining cellular phospholipid levels and phospholipid fatty acid composition. The effects of liver (L)- and intestinal (I)-FABP expression on these parameters were determined using stably transfected L-cells. Expression of L- and I-FABP increased cellular total phospholipid mass (nmol/mg protein) 1.7- and 1.3-fold relative to controls, respectively. L-FABP expression increased the masses of choline glycerophospholipids (ChoGpl) 1.5-fold, phosphatidylserine (PtdSer) 5.6-fold, ethanolamine glycerophospholipids 1.4-fold, sphingomyelin 1.7-fold, and phosphatidylinositol 2.6-fold. In contrast, I-FABP expression only increased the masses of ChoGpl and PtdSer, 1.2- and 3.1-fold, respectively. Surprisingly, both L- and I-FABP expression increased ethanolamine plasmalogen mass 1.6- and 1.1-fold, respectively, while choline plasmalogen mass was increased 2.3- and 1.7-fold, respectively. The increase in phospholipid levels resulted in dramatic 48 and 33% decreases in the cholesterol-to-phospholipid ratio in L- and I-FABP expressing cells, respectively. L-FABP expression generally increased polyunsaturated fatty acids, primarily by increasing 20∶4n−6 and 22∶6n−3, while decreasing 18∶1n−9 and 16∶1n−7. I-FABP expression generally increased only 20∶4n−6 proportions. Hence, expression of both I- and L-FABP differentially affected phospholipid mass, class composition, and acyl chain composition. Although both proteins enhanced phospholipid synthesis, the effect of L-FABP was much greater, consistent with previous work suggesting that these two FABP differentially affect lipid metabolism.     

Fatty acid composition of brain glycerophospholipids in peroxisomal disorders

This paper shows for the first time the differential fatty acid composition of ethanolamine plasmalogens (EP) and phosphatidylethanolamine (PE) in the brains of 12 patients with disorders of peroxisomal biogenesis and compares the results to normal values for the age. Other important glycerophospholipids (GPL), such as phosphatidylserine (PS) and phosphatidylcholine (PC), are also included in this study. GPL were separated by two-dimensional thin-layer chromatography, and their fatty acid composition was determined by capillary column gas-liquid chromatography. Total brain GPL were slightly decreased in peroxisomal disorders (27.98±2.95 μmol/g in the patients against 34.5±6.21 μmol/g in age-matched controls, P=0.005), and the distribution of the different GPL classes was much altered. In confirmation of known data, EP were very much decreased (2.18±1.3 μmol/g in the patients against 6.9±2.3 μmol/g in controls) at the expense of PE, which was increased (8.58±2.17 μmol/g in the patients against 5.97±0.58 μmol/g in controls, P<0.005). PS and PC were both significantly decreased (P=0.0001 and P=0.037, respectively). The polyunsaturated fatty acid (PUFA) composition of all the GPL fractions was markedly abnormal. In absolute terms, docosahexaenoic acid (22∶6n−3) was drastically decreased in all GPL classes (always at the P<0.0001 level) while arachidonic acid (20∶4n−6) was increased in PE and PS (P<0.001 in both cases). In the alkenyl acyl form, EP, 22∶6n−3, and 20∶4n−6 were both very significantly decreased (P<0.0001), although the former was always the most affected. The myelin PUFA adrenic acid (22∶4n−6) was decreased in EP (P<0.0001) and slightly increased in PS (P<0.05). The changes found confirm that 22∶6n−3 deficiency is a predominant defect in the brain in peroxisomal disorders.     

Lipid composition of the pineal organ from rainbow trout (Oncorhynchus mykiss)

The lipid composition of the pineal organ from the rainbow trout (Oncorhynchus mykiss) was determined to establish whether the involvement of this organ in the control of circadian rhythms is reflected by specific adaptations of lipid composition. Lipid comprised 4.9% of the tissue wet weight and triacylglycerols were the major lipid class present (47% of total lipid). Phosphatidylcholine (PC) was the principal polar lipid, and smaller proportions of other phospholipids and cholesterol were also present. Plasmalogens contributed 11% of the ethanolamine glycerophospholipids (EGP). No cerebrosides were detected. The fatty acid composition of triacylglycerols was generally similar to that of total lipids in which saturated, monounsaturated and polyunsaturated fatty acids (PUFA) were present in almost equal proportions. Each of the polar lipid classes had a specific fatty acid composition. With the exception of phosphatidylinositol (PI), in which 20∶4n−6 comprised 27.4% of the total fatty acids, 22∶6n−3 was the principal PUFA in all lipid classes. The proportion of 20∶5n−3 never exceeded 6.0% of the fatty acids in any lipid class. The predominant molecular species of PC were 16∶0/22∶6n−3 and 16∶0/18∶1, which accounted for 33.2 and 28.5%, respectively, of the total molecular species of this phospholipid. Phosphatidylethanolamine (PE) contained the highest level of di-22∶6n−3 (13.0%) of any phospholipid. There was also 4.9% of this molecular species in phosphatidylserine (PS) and 4.1% in PC. In PE, the species 16∶0/22∶6, 18∶1/22∶6 and 18∶0/22∶6 totalled 45.1%, while in PS 18∶0/22∶6 accounted for 43.9% of the total molecular species. The most abundant molecular species of PI was 18∶0/20∶4n−6 (37.8%). The lipid composition of the pineal organ of trout, and particularly the molecular species composition of PI, is more similar to the composition of the retina than that of the brain. Molecular species are abbreviated as follows: e.g., 16∶0/22∶6 PC is 1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine.     

Influence of dietary fatty acids on the glycerophospholipid composition in organs of cod (gadus morhua)

Cod (mean start weight of 26 g) were fed three diets for 15 months, each based on a dry pellet coated at a level of 9g/100 g with soybean oil, capelin oil or sardine oil. The fatty acid compositions of neutral lipids and four glycerophospholipids of white muscle, liver, gills and heart were determined. The fatty acid composition of dietary lipids influenced the composition of neutral lipids in all organs. Linoleic acid (18∶2n−6) from soybean oil was selectively incorporated into phosphatidylcholine of the four tissues. Similar levels of 20∶5n−3 and 22∶6n−3 in phosphatidylcholine and phosphatidylethanolamine were found in all organs from cod fed capelin oil and sardine oil in spite of highly differentiated feed fatty acid levels. The polyunsaturated fatty acid (PUFA) composition of phosphatidylinositol was least influenced by dietary lipids. The preferred monoenic fatty acid in phospholipids of cod was 18∶1n−9, independent of dietary intake, whereas the longer chain monoenoic acids seemed to be preferentially catabolized. The results suggest that 20∶4n−6 as well as 20∶5n−3 and 22∶6n−3 fatty acids are essential for cod.     

Lipid components and enzymatic hydrolysis of lipids in muscle of Chinese freshwater fish

The lipid and fatty acid composition of muscle of 10 species of freshwater fish obtained from a market of Shanghai City was examined. Total lipids (TL) ranged over 0.9–4.7% of muscle for all samples. The content of triacylglycerol (TG) in muscle ranged over 0.2–3.4% and that of polar lipids (PL) was 0.5–1.3%. Differences of TL content were dependent on TG contents. The predominant important fatty acids (>10% of the total fatty acids in TL) were 16∶0 and 18∶1n−9 with some 16∶1n−7, 18∶2n−6, and 22∶6n−3. The polyunsaturated fatty acids (PUFA) content was 10.2–43.4%, and especially Chinese sea bass contained above 20% of 22∶6n−3 in the total fatty acids. There were higher levels of PUFA such as 20∶5n−3 and 22∶6n−3 in PL than in neutral lipids. Muscle of the silver carp was stored at 20°C, and changes of lipid classes during storage were examined. Free fatty acids increased, and PL decreased during storage. This phenomenon was inhibited by heating the muscle, suggesting that lipid hydrolysis by phospholipase occurred in silver carp muscle.     

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

The effects of different dietary oils on the fatty acid compositions of liver phospholipids and the desaturation and elongation of [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 oliver 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−9, 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 Δ6 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 Δ5 desaturation. Only the BO diet significantly affected the desaturation of [1-¹⁴C]18:2n−6, increasing recovery of radioactivity in both Δ6- and Δ5-desaturation products. In conclusion, dietary BO, enriched in γ-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.     

Major clofibrate effects on liver and plasma lipids are independent of changes in polyunsaturated fatty acid composition induced by dietary fat

The effects of clofibrate on the content and composition of liver and plasma lipids were studied in mice fed for 4 wk on diets enriched in n−6 or n−3 polyunsaturated fatty acids (PUFA) from sunflower oil (SO) or fish oil (FO), respectively; both oils were fed at 9% of the diet (dry weight basis). Only FO was hypolipidemic. Both oil regimes led to slightly increased concentrations of phospholipids (PL) and triacylglycerols (TG) in liver as compared with a standard chow diet containing 2% fat. Clofibrate promoted hypolipidemia only in animals fed SO. Its main effect was to enlarge the liver, such growth increasing the amounts of major glycerophospholipids while depleting the TG. SO and FO consumption changed the proportion of n−6 or n−3 PUFA in liver and plasma lipids in opposite ways. After clofibrate action, the PUFA of liver PL were preserved better than in the absence of oil supplementation. However, most of the drug-induced changes (e.g., increased 18∶1n−9 and 20∶3n−6, decreased 22∶6/20∶5 ratios) occurred inrrespective of lipids being rich in n−6 or n−3 PUFA. The concentration of sphingomyelin (SM), a minor liver lipid that virtually lacks PUFA, increased with the dietary oils, decreased with clofibrate, and changed its fatty acid composition in both situations. Thus. oil-increased SM had more 22∶0 and 24∶0 than clofibrate-decreased SM, which was significantly richer in 22∶1 and 24∶1.     

Lipid composition and prostaglandin synthesis in mouse lung microsomes: Alterations following the ingestion of menhaden oil

Three groups of male mice were fed a normal diet or a semisynthetic diet containing either 10% hydrogenated coconut oil (CO group) or 10% menhaden oil (MO group) for two wk. The synthetic diet altered the fatty acid composition of lung microsomal lipids. Mice ingesting menhaden oil contained greater amounts of eicosapentaenoic acid (20∶5 n−3), docosapentaenoic acid (22∶5 n−3) and docosahexaenoic acids (22∶6 n−3) and decreased amounts of n−6 fatty acids such as arachidonic and adrenic. Synthesis of prostaglandin E₂ and prostaglandin F_2α from exogenous arachidonic acid was significantly depressed in n−3 fatty acid-enriched lung microsomes. These studies indicated that dietary fish oil not only alters the fatty acid composition of lung microsomes but also lowers the capacity of lungs to synthesize prostaglandins from arachidonic acid.     

Microsomal desaturation-elongation of linoleic acid following parenteral feeding with lipid emulsions in the rat

The effect of total parenteral nutrition (TPN) with lipid emulsion to supply either 27.5% or 2% total calories on in vitro desaturation-elongation of 18∶2(n−6) by liver microsomes was studied in the rat. The emulsion lipid contained ca. 50% 18∶2(n−6) plus 8% 18∶3(n−3) or 77% 18∶2(n−6) plus 0.5% 18∶3(n−3). The reaction rate was influenced by the in vitro substrate concentration and inhibited above 50 μmol 18∶2(n−6)/mg microsomal protein. At maximum rates of desaturation-elongation, the formation of triene and tetraene (n−6) fatty acids was reduced in rats given either of the two emulsions. The rate of (n−6) pentaene formation was increased in rats given the emulsion with low 18∶3(n−3) but not in rats given the emulsion with 8% 18∶3(n−3). Analyses of the microsomal lipid indicated increased free cholesterol in all rats that received TPN. Esterified cholesterol was increased only in rats given 27.5% TPN calories as lipid. Microsomal total phospholipids and phospholipid class distributions were not altered by TPN. The data are consistent with reports of reduced levels of long-chain desaturation-elongation metabolites of 18∶2(n−6) in tissue phospholipids following infusion of parenteral lipid. The data suggest that the mechanism may include alterations in other metabolic pathways such as cholesterol, in addition to desaturase enzyme activities, and may be influenced by both the quantity and fatty acid composition of the lipid infused.     

The effect of a fish oil diet on the fatty acid composition of individual phospholipids and eicosanoid production by rat platelets

When rats were fed a diet containing chow or fish oil for six weeks, the platelet phospholipid content and percent distribution were similar. In the fish oil fed animals there was a 54, 40, 41, and 24% reduction, respectively, in the levels of 20∶4(n−6) in the choline-, ethanolamine-, inositol-and serine-containing glycerophospholipids. Dietary fish oil increased the total (n−3) polyunsaturated fatty acid content in all lipids. This effect was most pronounced in the ethanolamine glycerophospholipids which now contained 26, 11, and 4 nmols of 20∶5(n−3), 22∶5(n−3), and 22∶6(n−3) in 10⁹ cells. Ionophore A23187 stimulation of platelets from the chow fed rats resulted in the synthesis of 7, 64, and 3.5 nmols of 12-hydroxy-5,8,10-heptadecatrienoic acid, 12-hydroxy-5,8,10,14-eicosatetraenoic acid and 12-hydroxy-5,8,10,14,17-eicosapentaenoic acid, respectively, from 1×10⁹ cells. The values from animals fed fish oil were 4, 18, and 27 nmol/10⁹ platelets. It was not possible to detect any lipoxygenase products from 22∶5(n−3) or 22∶6(n−3), even though both acids are readily metabolized by lipoxygenase when added directly to platelets. These findings suggest that 22-carbon (n−3) fatty acids are not liberated when phospholipases are activated by calcium mobilization.     

Infant cerebellar gray and white matter fatty acids in relation to age and diet

There is little evidence as to the fatty acid composition of the cerebellum in infancy and it remains uncertain whether milk diet can influence its composition. We therefore examined cerebellar gray and white matter of infants less than 6 mon old who had died unexpectedly. The fatty acid content of 33 gray and 21 white matter specimens from infants born at term and 6 gray and 5 white matter specimens from pretern infants was assessed by gas chromatographic/mass spectrometric analysis. Infants were grouped according to whether they had received human or manufactured formula milk. Whereas cerebellar cortex docosahexaenoic acid (DHA, 22∶6n−3) concentrations were significantly lower (P<0.01) in the formula-fed than breast-fed infants, no differences existed between the term (n=10) and preterm (n=5) Scientific Milk Adaptation (SMA) formula-fed infants. Cerebellar white matter DHA concentrations were similarly lower (P<0.01) in the SMA formula-fed infants (n=8) than in an age-matched breast-fed group. Low concentrations of cerebellar white matter lignoceric (24∶0) and nervonic acid (24∶1n−9) in two 7-wk-old preterm infants appeared to correlated with postgestational rather than chronological age. Dietary long-chain polyunsaturated fatty acids particularly DHA, are probably essential for normal development of the infant cerebellum.     

Trans-monoenoic and polyunsaturated fatty acids in phospholipids of aVibrio species of bacterium in relation to growth conditions

AVibrio species of bacterium known to contain the polyunsaturated fatty acid 20∶5n−3 was grown in both freshwater and seawater media at 5 and 20°C and examined for adaptive changes in lipid composition. Phosphatidylethanolamine (PE) and phosphatidylglycerol (PG), together with a smaller proportion of nonesterified fatty acids (NEFA), comprised almost all the lipid under all growth conditions examined. Temperature had a more pronounced effect than the salinity of the medium on lipid composition. The proportion of PE in total lipid was always higher at 5 than at 20°C. Conversely, the proportion of NEFA was lower at 5 than 20°C whereas that of PG was not altered. The levels of saturated fatty acids in total lipid, PE and PG were all decreased by growth at 5°C. No differences were observed with respect to growth temperature in the levels ofcis 16∶1n−7, the principal monoenoic fatty acid in both PE and PG.Trans 16∶1n−7 was found to comprise 12.8–15.2% of fatty acids in PE and PG of bacteria grown at 5°C but only 4.4–8.5% of phospholipid fatty acids in bacteria cultured at 20°C. Regardless of medium composition, a reduction in growth temperature from 20 to 5°C also caused the proportions of 20∶5n−3 to increase from around 0.8 to 4.4% in PE and from around 4 to 20% in PG. The simultaneous occurrence oftrans 16∶1n−7 and 20∶5n−3 is unique to thisVibrio species of bacterium. The increased proportions of both these fatty acids with decreasing temperature suggest that they have a role in retailoring biomembrane phospholipids during temperature acclimation of the bacterium.     

Lipid and fatty acid composition of different fractions from rat urinary transitional epithelium

The phospholipid composition of rat urinary transitional epithelium (TE) and the fatty acid composition of microsomal, mitochondrial, cytosolic, and plasma membrane (PM) subcellular fractions were investigated. PM marker enzymes and electron microscopy analysis were used to characterize the PM fraction, which showed a distinctive lipid composition compared to the general profile of PM from different sources. The levels of cholesterol and sphingomyelin were not enriched in the PM fraction; on the other hand, the increased amounts of glycosphingolipids and phosphatidylserine, and the decreased level of phosphatidylcholine followed the general features of a PM profile. This differential PM lipid composition may reflect the unique morphology of this mammal TE, consisting of concave plaques with an asymmetrical membrane unit. The distribution of the double bond across the PM indicated a higher unsaturation of the inner relative to the outer part of the PM hemileaflet. In addition, the presence of 20∶3n−9 nonessential fatty acid in a normal TE may represent a characteristic fatty acid metabolism of this epithelium. The authors wish to dedicate this work to the memory of the late Professors Benito Monis, who participated in the generation of this research and whose working hypothesis remains a source of fruitful inspiration.     

Effects of dietary fats on fatty acid composition and Δ5 desaturase in normal and diabetic rats

We have studied the effect of various diets on the phospholipid fatty acid composition andin vitro Δ5 desaturase activity of hepatic microsomes derived either from the normal or streptozotocin-induced diabetic rat. The diets studied were the standard rat chow diet and a basal fat-free diet supplemented either with 20 percent saturated fat, 20 percent unsaturated fat, or 20 percent menhaden oil. Phospholipid fatty acid composition analysis revealed that the normal rat fed the saturated fat or menhaden oil diet had significantly decreased arachidonate levels, consistent with decreased Δ5 desaturase activities and decreased 18∶2n−6 intake. On the contrary, the unsaturated fat diet decreased dihomo-γ-linolenate and increased arachidonate levels, without increased Δ5 desaturase activity. Streptozotocininduced diabetes resulted in decreased arachidonate and Δ5 desaturase activity. The unsaturated fat diet fed to the diabetic rat also failed to correct this decreased Δ5 desaturase activity. The unsaturated fatty acids in this diet also displaced a substantial amount of n−3 fatty acids in both normal and diabetic microsomes, due to the competition between these two fatty acid families for incorporation into the membrane phospholipids. Conversely, the menhaden oil diet fed to the normal and diabetic rats displaced n−6 fatty acids, reduced Δ5 desaturase activity, and enhanced 22∶6n−3 incorporation into diabetic microsomes.     

The lipids of slugs and snails: Evolution,diet and biosynthesis

There is a considerable gap in current knowledge of the lipid composition of snails and slugs, both of which belong to the phylum Mollusca. We have therefore analyzed the sterol and fatty acid compositions of three species of slugs and three species of snails. The sterols of slugs included eight different sterols: cholesterol contributed 76–85% of the total sterols, brassicasterol accounted for 4–13%; other sterols we identified were lathosterol, 24-methylene cholesterol, campesterol, stigmasterol, sitosterol and sitostanol. In contrast, snails contained two additional sterols, desmosterol and cholestanol. Of the polyunsaturated fatty acids in slugs, linoleic (18∶2n−6) and arachidonic acids (20∶4n−6) were the major n−6 fatty acids, while linolenic (18∶3n−3) and eicosapentaenoic acids (20∶5n−3) were the predominant n−3 fatty acids. Docosahexaenoic acid (22∶6n−3), the end product in the n−3 fatty acid synthetic pathway and an important membrane fatty acid of mammals, fish and birds, was absent in both slugs and snails. However, the analogous product of n−6 fatty acid synthesis, 22∶5n−6, was found in both snails and slugs. This raises speculation about preference for n−6 fatty acid synthesis in these species. Our data show the unique sterol and fatty acid compositions of slugs and snails, as well as similarities and differences in sterol composition between the two. The results between the two land mollusks are contrasted with those of marine mollusks, such as oysters, clams and scallops.     

Effects of dietary n−3 fatty acid-enriched chicken eggs on plasma and tissue cholesterol and fatty acid composition of rats

The purpose of this study was to examine the effects of feeding n−3 polyunsaturated fatty acid (PUFA)-enriched chicken eggs on plasma and liver cholesterol levels and fatty acid composition in rats. Eggs were collected from laying hens fed diets containing 10% flax seed (Hn−3), 12% sunflower seed (Hn−6), or wheat and soybean meal control (CON). Yolk powders were prepared and fed at the 15% level to weanling female Sprague-Dawley rats for 28 days. Consumption of n−3 PUFA-enriched yolks significantly reduced both plasma and liver total cholesterol. Liver total lipids and phospholipids of rats fed Hn−3 diet were enriched with linolenic, eicosapentaenoic, and docosahexaenoic acids with a concomitant reduction of arachidonic acid in liver phospholipids. The plasma cholesterol of rats fed yolk powders enriched with n−6 PUFA (mainly linoleic acid) was reduced to the same extent as in those fed the n−3 enriched, but the liver cholesterol was significantly increased, indicating differential effects of dietary n−3 and n−6 PUFA. The results demonstrated that the cholesterolemic and tissue lipid modulating properties of chicken eggs could be modified in a favorable way by altering the fatty acid composition of yolk lipids through manipulation of laying hen diets.     

Effect of fish oil on the fatty acid composition of human milk and maternal and infant erythrocytes

To examine the effect of fish oil supplementation on the fatty acid (FA) composition of human milk and maternal and infant erythrocytes, five lactating women were supplemented with 6 g of fish oil daily for 21d. Usual maternal diets contained 1,147 mg of total n−3 FA, with 120 mg from very long-chain (>C₁₈) n−3 FA. Supplementation increased dietary levels to 3,092 mg of total n−3 FA and 2,006 mg of very long-chain n−3 FA. Milk samples were collected daily, prior to fish oil ingestion, and at 4-h intervals on days 1, 7, 14 and 21. Milk n−3 FA content increased within 8 h and reached steady state levels within one week. The n−6 fatty acid content decreased. Erythrocyte eicosapentaenoic acid content increased from 0.24% to 1.4% (P<0.01) in mothers and from 0.11% to 0.70% (P<0.05) in infants. Docosapentaenoic acid increased from 1.4% to 2.2% (P<0.05) in mothers and from 0.30% to 0.78% (P<0.01) in infants. There was no significant change in docosahexaenoic acid or n−6 fatty acid content. Maternal platelet aggregation responses were variable. No differences in milk or plasma tocopherol levels were noted. Based on a paper presented at the Symposium on Milk Lipids held at the AOCS Annual Meeting, Baltimore, MD, April 1990.