Fatty acid metabolism in Atlantic salmon (Salmo salar L.) hepatocytes and influence of dietary vegetable oil

Isolated hepatocytes from Atlantic salmon (Salmo salar), fed diets containing either 100% fish oil or a vegetable oil blend replacing 75% of the fish oil, were incubated with a range of seven (14)C-labelled fatty acids. The fatty acids were [1-(14)C]16:0, [1-(14)C]18:1n-9, 91-(14)C]18:2n-6, [1-(14)C]18:3n-3, [1-(14)C]20:4n-6, [1-(14)C]20:5n-3, and [1-(14)C]22:6n-3. After 2 h of incubation, the hepatocytes and medium were analysed for acid soluble products, incorporation into lipid classes, and hepatocytes for desaturation and elongation. Uptake into hepatocytes was highest with [1-(14)C]18:2n-6 and [1-(14)C]20:5n-3 and lowest with [1-(14)C]16:0. The highest recovery of radioactivity in the cells was found in triacylglycerols. Of the phospholipids, the highest recovery was found in phosphatidylcholine, with [1-(14)C]16:0 and [1-(14)C]22:6n-3 being the most prominent fatty acids. The rates of beta-oxidation were as follows: 20:4n-6>18:2n-6=16:0>18:1n-9>22:6n-3=18:3n-3=20:5n-3. Of the fatty acids taken up by the hepatocytes, [1-(14)C]16:0 and [1-(14)C]18:1n-9 were subsequently exported the most, with the majority of radioactivity recovered in phospholipids and triacylglycerols, respectively. The major products from desaturation and elongation were generally one cycle of elongation of the fatty acids. Diet had a clear effect on the overall lipid metabolism, with replacing 75% of the fish oil with vegetable oil resulting in decreased uptake of all fatty acids and reduced incorporation of fatty acids into cellular lipids, but increased beta-oxidation activity and higher recovery in products of desaturation and elongation of [1-(14)C]18:2n-6 and [1-(14)C]18:3n-3.     

Studies on polyenoic acid incorporation into human platelet lipid stores: interactions with linoleic and arachidonic acids

Several polyunsaturated fatty acids (C18-C22 acids) have been compared in their uptake by human platelets and their acylation into glycerophospholipid subclasses. This was also studied in the presence of linoleic and/or arachidonic acids, the main fatty acids of plasma free fatty acid pool. Amongst C20 fatty acids, dihomogamma linolenic acid (20:3(n-6)), 5,8,11-icosatrienoic acid (20:3(n-9)) and arachidonic acid (20:4(n-6)) were better incorporated. The uptake of 5,8,11,14,17-icosapentaenoic acid (20:5(n-3)) was significantly lower and comparable to that of C22 fatty acids (7,10,13,16-docosatetraenoic acid (22:4(n-6)) and 4,7,10,13,16,19-docosahexaenoic acid (22:6(n-3)) and linoleic acid (18:2(n-6)). In this respect, linolenic acid (18:3(n-3)) appeared the poorest substrate. The bulk of each acid was acylated into glycerophospholipids although the presence of linoleic and/or arachidonic acids diverted a part towards neutral lipids. This was prominent for 18:3(n-3) and C22 fatty acids. The glycerophospholipid distribution of each acid differed substantially and was not affected by the presence of linoleic and or arachidonic acids, except for 18:3(n-3) and 22:6(n-3) that were strongly diverted towards phosphatidylethanolamine (PE) at the expense of phosphatidylcholine (PC). The main features were an efficient acylation of 20:3(n-9) into phosphatidylinositol (PI) followed by 20:3(n-6) and 20:4(n-6), then by 20:5(n-3) and 22:4(n-6), and finally 22:6(n-3) and C18 fatty acids. This was reciprocal to the acylation into PE and to a lesser extent into PC which remained the main storage species in all cases. We conclude that human platelets may exhibit a certain specificity for taking up polyunsaturated fatty acids both in terms of total uptake and glycerophospholipid subclass distribution. Also the presence of polyunsaturated fatty acids of normal plasma, like linoleic and arachidonic acids, may interact specifically with such an uptake and distribution.     

The influence of dietary essential fatty acids on uterine C20 and C22 fatty acid composition.

The effect of dietary fatty acids on uterine fatty acid composition was studied in rats fed control diet or semi-synthetic diet supplemented with 1.5 microliter/g/day evening primrose oil (EPO) or fish oil (FO). Diet-related changes in uterine lipid were detected within 21 days. Changes of 2- to 20-fold were detected in the uterine n-6 and n-3 essential fatty acids (EFA) and in certain saturated and monounsaturated fatty acids. The FO diet was associated with higher uterine C20 and C22 n-3, and the EPO diet, with higher uterine n-6 fatty acid. High uterine C18:2 n-6 was detected in neutral lipid (NL) of rats fed high concentrations of this fatty acid, but there was little evidence of selective incorporation or retention of C18:2 n-6 by uterine NL. The incorporation of EFA into uterine phospholipids (PL) was greater than NL EFA incorporation, and uterine PL n-3/n-6 ratios showed greater diet dependence. Tissue/diet fatty acid ratios in NL and PL also indicated preferential incorporation/synthesis of C16:1 n-9, and C16:0, and there was greater incorporation of C12:0 and C14:0 into uteri of rats fed EPO and FO. Replacement of 50-60% of arachidonate with n-3 EFA in uterine PL may inhibit n-6 EFA metabolism necessary for uterine function at parturition.     

Double bond localization in minor homoallylic fatty acid methyl esters using acetonitrile chemical ionization tandem mass spectrometry

Double bond position in natural fatty acids is critical to biochemical properties, however, common instrument-based methods cannot locate double bonds in fatty acid methyl esters (FAME), the predominant analysis form of fatty acids. A recently described mass spectrometry (MS) method for locating double bonds in FAME is reported here for the analysis of minor (<1%) components of real FAME mixtures derived from three natural sources; golden algae (Schizochytrium sp.), primate brain white matter, and transgenic mouse liver. Acetonitrile chemical ionization tandem MS was used to determine double bond positions in 39 FAME, most at concentrations well below 1% of all fatty acid methyl esters. FAME identified in golden algae are 14:1n-6, 14:3n-3, 16:1n-7, 16:2n-6, 16:3n-6, 16:3n-3, 16:4n-3, 18:2n-7, 18:3n-7, 18:3n-8, 18:4n-3, 18:4n-5, 20:3n-7, 20:4n-3, 20:4n-5, 20:4n-7, 20:5n-3, and 22:4n-9. Additional FAME identified in primate brain white matter are 20:1n-7, 20:1n-9, 20:2n-7, 20:2n-9, 22:1n-7, 22:1n-9, 22:1n-13, 22:2n-6, 22:2n-7, 22:2n-9, 22:3n-6, 22:3n-7, 22:3n-9, 22:4n-6, 24:1n-7, 24:1n-9, and 24:4n-6. Additional FAME identified in mouse liver are 26:5n-6, 26:6n-3, 28:5n-6, and 28:6n-3. The primate brain 22:3n-7 and algae 18:4n-5 are novel fatty acids. These results demonstrate the usefulness of the technique for analysis of real samples. Tables are presented to aid in interpretation of acetonitrile CIMS/MS spectra.     

Comparison of 20-, 22-, and 24-carbon n-3 and n-6 polyunsaturated fatty acid utilization in differentiated rat brain astrocytes

Astrocytes convert n-6 fatty acids primarily to arachidonic acid (20:4n-6), whereas n-3 fatty acids are converted to docosapentaenoic (22:5n-3) and docosahexaenoic (22:6n-3) acids. The utilization of 20-, 22- and 24-carbon n-3 and n-6 fatty acids was compared in differentiated rat astrocytes to determine the metabolic basis for this difference. The astrocytes retained 81% of the arachidonic acid ([(3)H]20:4n-6) uptake and retroconverted 57% of the docosatetraenoic acid ([3-(14)C]22:4n-6) uptake to 20:4n-6. By contrast, 68% of the eicosapentaenoic acid ([(3)H]20:5n-3) uptake was elongated, and only 9% of the [3-(14)C]22:5n-3 uptake was retroconverted to 20:5n-3. Both tetracosapentaenoic acid ([3-(14)C]24:5n-3) and tetracosatetraenoic acid ([3-(14)C]24:4n-6) were converted to docosahexaenoic acid (22:6n-3) and 22:5n-6, respectively. Therefore, the difference in the n-3 and n-6 fatty acid products formed is due primarily to differences in the utilization of their 20- and 22-carbon intermediates. This metabolic difference probably contributes to the preferential accumulation of docosahexaenoic acid in the brain.     

Fatty acids of some algae from the Bohai Sea.

The fatty acid compositions of 22 species of marine macrophytes, belonging to the Ceramiales, Cryptonemiales, Nemalionales, Laminariales, Chordariales, Scytosiphonales, Desmarestiales, Dictyosiphonales, Fucales, Dictyotales and Ulvales and collected from the Bohai Sea, were determined by capillary gas chromatography. The contents of polyunsaturated fatty acids (FAs) in the Bohai Sea algae, in comparison with the same species from the Yellow Sea were found to be lower. Red algae had relatively high levels of the acids 16:0, 18:1(n-7), 18:1(n-9), 20:5(n-3) and 20:4(n-6), and those examined were rich in C(20) PUFAs, these chiefly being arachidonic and eicosapentaenoic acids. The major FAs encountered in the Phaeophyta were 14:0, 16:0, 18:1(n-9), 18:2(n-6), 18:3(n-3), 18:4(n-3), 20:4(n-6) and 20:5(n-3). C(18)PUFAs are of greater abundance in the brown algae than in the red algae examined. All three green algae from the Ulvales had similar fatty acid patterns with major components, 16:0, 16:4(n-3), 18:1(n-7), 18:2(n-6), 18:3(n-3), and 18:4(n-3). They contained 16:3(n-3) and more 16:4(n-3), were rich in C(18)PUFAs, chiefly 18:3(n-3) and 18:4(n-3) and had 18:1(n-7)/18:1(n-9) ratios higher than 1.     

The levels of essential unsaturated fatty acids in human milk on the 3rd, 4th, 5th, and 6th days after labour

The composition of fatty acids in human milk lipids was determined in 41 women on the 3rd, 4th, 5th and 6th days after labour by the method of gas chromatography. In these investigations no significant differences were demonstrated in the fatty acids in the lipid fractions between these consecutive days. The level of polyunsaturated fatty acids of the n-6 and n-3 groups was about 11.9-13.6%, including linoleic acid (18:2, n-6) about 7.7-9.8%, and alpha-linolenic acid (18:3, n-3) about 0.7-1%. In the analysis group of n-6 fatty acids the determined acids were: linoleic acid (18:2, n-6), gamma-linolenic acid (18:3, n-6), eicosadienoic acid (20:2, n-6), eicosatrienoic acid (20:3, n-6), arachidonic acid (20:4, n-6), docosahexaenoic acid (22:6, n-6). From the group of n-3 acids the identified ones were: alpha-linolenic acid (18:3, n-3), eicosapentaenoic acid (20:5, n-3), docosapentaenoic acid (22:5, n-3) and docosahexaenoic acid (22:6, n-3). The obtained quotients of fatty acids n-6 through n-3 on the consecutive days were: 7.2:1-7.8:1, indicating a too low level of the n-3 acids in the investigated milk. The acids prevailing in human milk lipids were: oleic (18:1, n-9) and palmitic (16:0) which accounted for 37-39% and 25-26% respectively. The polyunsaturated to saturated fatty acid ratio (P:S) ranged from 0.28 to 0.33.     

Evidence for peroxisomal retroconversion of adrenic acid (22:4(n-6)) and docosahexaenoic acids (22:6(n-3)) in isolated liver cells

The intracellular localization of the oxidation of [2-14C]adrenic acid (22:4(n-6)) and [1-14C]docosahexaenoic acid (22:6(n-3)) was studied in isolated liver cells. The oxidation of 22:4(n-6) was 2-3-times more rapid than the oxidation of 22:6(n-3), [1-14C]arachidonic acid (20:4(n-6)) or [1-14C]oleic acid (18:1). (+)-Decanoylcarnitine and lactate, both known to inhibit mitochondrial beta-oxidation, reduced the oxidation of 18:1 distinctly more efficiently than with 22:4(n-6) and 22:6(n-3). In liver cells from rats fed a diet containing partially hydrogenated fish oil, the oxidation of 22:6(n-6) and 22:6(n-3) was increased by 30-40% compared with cells from rats fed a standard pellet diet. With 18:1 as substrate, the amount of fatty acid oxidized was very similar in cells from animals fed standard pellets or partially hydrogenated fish oil. Shortened fatty acids were not produced from [5,6,8,9,11,12,14,15-3H]arachidonic acid. In hepatocytes from rats starved and refed 20% fructose, a large fraction of 14C from 22:4 was recovered in 14C-labelled C14-C18 fatty acids. Oxidation of 22:4 thus caused a high specific activity of the extramitochondrial pool of acetyl-CoA. The results suggest that 22:4(n-6) and to some extent 22:6(n-3) are oxidized by peroxisomal beta-oxidation and by this are retroconverted to arachidonic acid and eicosapentaenoic acid.     

Fatty acid composition of Ruditapes decussatus spat fed on different microalgae diets

The fatty acid composition of the Ruditapes decussatus spat fed on three different microalgal diets during 4 weeks was determined. The fatty acid pattern of each diet was also analysed. The diets used were Isochrysis galbana, clone T-ISO, Tetraselmis suecica, and Phaeodactylum tricornutum. The fatty acid composition of the spat was usually well correlated with that of the diet supplied. Major differences among spat cultures were found in 14:0, 16:0, 16:1n-9, 16:1n-7, 18:1n-9, 18:2n-6, 18:3n-3, 18:4n-3, 20:5n-3, 22:5n-6 and 22:6n-3 fatty acids. These differences were correlated with the particular fatty acid content of each diet supplied. It has been shown that R. decussatus spat have a very low capacity to elongate and desaturate linolenic acid to n-3 PUFA, so when 20:5n-3 or 22:6n-3 were not present in the diet, they were also absent, at least in measurable amounts, in the clams. The absence of any of the “essential” fatty acids, 20:5n-3 in T-ISO or 22:6n-3 in Tetraselmis, did not limit spat growth, so their role as “essential” fatty acids might be a matter for discussion. Finally, the nutritive value of each diet was discussed in terms of its fatty acid composition.     

On the singular, dual, and multiple positional specificity of manganese lipoxygenase and its G316A mutant

Abstract manganese lipoxygenase (Mn-LO) oxygenates 18:3n-3 and 18:2n-6 to bis-allylic 11S-hydroperoxy fatty acids, which are converted to 13R-hydroperoxy fatty acids. Other unsaturated C(16)-C(22) fatty acids, except 17:3n-3, are poor substrates, possibly because of ineffective enzyme activation (Mn(II)-->Mn(III)) by the produced hydroperoxides. Our aim was to determine whether unsaturated C(16)-C(22) fatty acids were oxidized by Mn(III)-LO. Mn(III)-LO oxidized C(16), C(19), C(20), and C(22) n-3 and n-6 fatty acids. The carbon chain length influenced the position of hydrogen abstraction (n-8, n-5) and oxygen insertion at the terminal or the penultimate 1Z,4Z-pentadienes. Dilinoleoyl-glycerophosphatidylcholine was oxidized by Mn-LO, in agreement with a "tail-first" model. 16:3n-3 was oxidized at the bis-allylic n-5 carbon and at positions n-3, n-7, and n-6. Long fatty acids, 19:3n-3, 20:3n-3, 20:4n-6, 22:5n-3, and 22:5n-6, were oxidized mainly at the n-6 and the bis-allylic n-8 positions (in ratios of approximately 3:2). The bis-allylic hydroperoxides accumulated with one exception, 13-hydroperoxyeicosatetraenoic acid (13-HPETE). Mn(III)-LO oxidized 20:4n-6 to 15R-HPETE ( approximately 60%) and 13-HPETE ( approximately 37%) and converted 13-HPETE to 15R-HPETE. Mn(III)-LO G316A oxygenated mainly 16:3n-3 at positions n-7 and n-6, 19:3n-3 at n-10, n-8, and n-6, and 20:3n-3 at n-10 and n-8. We conclude that Mn-LO likely binds fatty acids tail-first and oxygenates many C(16), C(18), C(20), and C(22) fatty acids to significant amounts of bis-allylic hydroperoxides.     

Dietary LC-PUFA and environmental salinity modulate the fatty acid biosynthesis capacity of the euryhaline teleost thicklip grey mullet (Chelon labrosus)

The capacity to biosynthesise long-chain (≥C20) polyunsaturated fatty acids (LC-PUFA) depends upon the complement and function of key enzymes commonly known as fatty acyl desaturases and elongases. The presence of a Δ5/Δ6 desaturase enabling the biosynthesis of docosahexaenoic acid (22:6n-3, DHA) through the “Sprecher pathway” has been reported in Chelon labrosus. Research in other teleosts have demonstrated that LC-PUFA biosynthesis can be modulated by diet and ambient salinity. The present study aimed to assess the combined effects of partial dietary replacement of fish oil (FO) by vegetable oil (VO) and reduced ambient salinity (35 ppt vs 20 ppt) on the fatty acid composition of muscle, enterocytes and hepatocytes of C. labrosus juveniles. Moreover, the enzymatic activity over radiolabelled [1-¹⁴C] 18:3n-3 (α-linolenic acid, ALA) and [1-¹⁴C] 20:5n-3 (eicosapentaenoic acid, EPA) to biosynthesise n-3 LC-PUFA in hepatocytes and enterocytes, and the gene regulation of the C. labrosus fatty acid desaturase-2 (fads2) and elongation of very long chain fatty acids protein 5 (elovl5) in liver and intestine was also investigated. Recovery of radiolabelled products including stearidonic acid (18:4n-3, SDA), 20:5n-3, tetracosahexaenoic acid (24:6n-3, THA) and 22:6n-3 in all treatments except FO35-fish, provided compelling evidence that a complete pathway enabling the biosynthesis of EPA and DHA from ALA is present and active in C. labrosus. Low salinity conditions upregulated fads2 in hepatocytes and elovl5 in both cell types, regardless of dietary composition. Interestingly, FO20-fish showed the highest amount of n-3 LC-PUFA in muscle, while no differences in VO-fish reared at both salinities were found. These results demonstrate a compensatory capacity of C. labrosus to biosynthesise n-3 LC-PUFA under reduced dietary supply, and emphasise the potential of low salinity conditions to stimulate this pathway in euryhaline fish.     

Fatty Acid Composition of Porcine Muscle and Adipose Tissue Lipids as Affected by Anatomical Location and Cod Liver Oil Supplementation of the Diet

In pigs fed a standard pig mash the contents of polyunsaturated fatty acids (PUFAs) of both the n-6 and n-3 series were significantly higher in the dark red mm adductores compared to the light coloured m longissimus lumborum. Perirenal fat had a higher concentration of saturated fatty acids (14:0,16:0, 18:0) than backfat, and a lower concentration of monounsaturated fatty acids, such as 16:ln-7 and 18:ln-9. Daily supplementation of 50 ml cod liver oil, rich in n-3 PUFAs, during the fourth and third week before slaughter led to a 1.4 to 1.7 times increase in the contents of n-3 PUFAs in muscles and fat depots. There was no difference between the incorporation of n-3 PUFAs in dark and light muscles. Perirenal fat contained more 20:5n-3 (EPA) and 22:6n-3 (DHA), but less 20:ln-9 (eicosenoic acid) than the backfat, after cod liver oil supplementation rich in these 3 fatty acids. Supplementation of cod liver oil reduced the n-6/n-3 fatty acid ratio in all anatomical locations examined.     

Sex differences in the metabolism of essential fatty acids studied in isolated rat liver cells

The triacylglycerol synthesis from exogenous linoleic acid (18:2(n-6], linolenic acid (18:3(n-3], dihomogammalinolenic acid (20:3(n-6], eicosapentaenoic acid (20:5(n-3] and oleic acid (18:1(n-9] was observed to be significantly increased in isolated liver cells from female rats compared with males. The rate of fatty acid oxidation and phospholipid biosynthesis was concomitantly more important in male cells. With the C22-polyenoic fatty acids, adrenic acid (22:4(n-6] and docosahexaenoic acid (22:6(n-3), only a minor sex-related difference in fatty acid metabolism was found.     

(n-7) and (n-9) cis-Monounsaturated fatty acid contents of 12 Brassica species

cis-Vaccenic acid or cis-11-octadecenoic acid, a C18:1 (n-7) isomer of oleic acid (C18:1 (n-9)) has been found in several oilseeds. It is synthesized from palmitic acid (C16:0) via production of C16:1 (n-7) by a Delta9 desaturase and elongation by an elongase giving C18:1 (n-7). In this study, the fatty acid composition of 12 Brassica species was analyzed by GC-FID and confirmed by GC-MS. All species contained C18:1 (n-7), C20:1 (n-7) and C22:1 (n-7) fatty acid isomers, suggesting that C18:1 (n-7) was elongated. The levels of these fatty acids varied according to the species. C18:1(n-7)) represented from 0.4% to 3.3% of the total relative fatty acid contents of the seeds. The contents of C20:1(n-7) and C22:1(n-7) levels were lower than C18:1(n-7) contents; the relative fatty acid composition varied from 0.02% to 1.3% and from below the limit of detection to 1.3% for C20:1 (n-7) and C22:1 (n-7), respectively. The ratios of (n-7)/(n-9) ranged from 2.8% to 16.7%, 0.6% to 29.5% and 0% to 2.6% for C18:1, C20:1 and C22:2, respectively. Using statistical similarities or differences of the C18:1 (n-7)/(n-9) ratios for chemotaxonomy, the surveyed species could be arranged into three groups. The first group would include Brassica napus, B. rapa, and B. tournefortii with Eruca sativa branching only related to B. napus. The second group would include B. tournefortii, Raphanus sativus and Sinapis alba. The last group would include B. juncea, B. carinata and B. nigra with no similarity/relationship between them and between the other species. Results suggested that the level of C20:1 (n-7) influenced the levels of all monounsaturated fatty acids with chain length higher than 20 carbons. On the other hand, palmitoleic acid (C16:1) levels, C16:1 being the parent of all (n-7) fatty acids, had no statistically significant correlation with the content of any of the fatty acids of the (n-7) or (n-9) family.     

Effect of frozen storage on fatty acid composition and changes in lipid content of Scomberomorus commersoni and Carcharhinus dussumieri

Investigated were the changes in fatty acid composition, oxidation and enzymatic deterioration of lipids in frozen (−30°C) fish fillets from the Persian Gulf. The narrow barred Spanish mackerel ( Scomberomorus commersoni ) and white cheek shark ( Carcharhinus dussumieri ) were tested with storage times of 0, 1, 2, 3, 4, 5 and 6 months at −18°C. Statistical results showed that the major fatty acids among the saturated and monounsaturated fatty acids of each fish species were palmitic (C16:0) and oleic (C18:1n-9) acids, respectively. Both linoleic acid (C18:2n-6) and arachidonic acid (AA) (C20:4n-6) were predominant in total n-6 polyunsaturated fatty acids in both mackerel and shark. The EPA (eicosapentaenoic acid; C20:5 n-3) and DHA (docosahexaenoic acid; C22:6 n-3) acids were the major fatty acids among total n-3 acids in both fishes. During frozen storage, the PUFA (40.1 and 23.94%), n-3 (48 and 42.83%), ω 3/ ω 6 (41.36 and 50%), PUFA/SFA (56 and 42.23%) and EPA + DHA/C16 (55.55 and 46.66%) contents decreased in S. commersoni and C. dussumieri , respectively. Also peroxide, thiobarbituric acid (TBA) and free fatty acid (FFA) values significantly increased (P < 0.01) with the time of storage.     

Assimilation and biosynthesis of lipids in Arctic Calanus species based on feeding experiments with a C labelled diatom

The dominant Arctic Ocean and North Atlantic copepods Calanus hyperboreus, Calanus glacialis, and Calanus finmarchicus were collected in the Greenland Sea and fed ¹³C labelled diatom Thalassiosira weissflogii to follow the transfer and assimilation of carbon, lipid, and individual fatty acids and alcohols. The diatom was grown with ¹³C for 3 to 5 days and fed then to the copepods. During the feeding period of 14 days, total carbon increased in the copepodite stages V of C. hyperboreus and C. finmarchicus, whereas carbon remained almost constant in C. glacialis females. However, total lipid increased in all species and stages. Highest lipid accumulation occurred in C. hyperboreus in which nearly all lipids were exchanged already after 11 days of feeding. In the other species lipid accumulation made up between 22% (C. finmarchicus) and 45% of total lipid (C. glacialis). The proportion of wax esters was high ranging from 76% of total lipid in C. glacialis to 92% in C. finmarchicus. The fatty acid composition of the alga was dominated by 16:1(n-7), 16:0, 20:5(n-3), and 22:6(n-3). The composition of the copepods was similar because of feeding already on diatoms in the field. In addition, the monounsaturated fatty acids and alcohols, 20:1(n-9) and 22:1(n-11), were major components of the copepod lipids. During the feeding period the highest ¹³C labelling was always found in the C₁₆ polyunsaturated fatty acids and in the 16:1(n-7) alcohol. Because these components occurred only in trace amounts in the copepods they totally originated from the diet explaining the high labelling. It is noteworthy that the 16:1(n-7) alcohol originated only from the corresponding dietary and not from the abundant internal fatty acid. The long-chain monounsaturated fatty acids and alcohols, 20:1(n-9) and 22:1(n-11), are not existent in phytoplankton and have to be produced de novo. They were less labelled in the smaller species but highly ¹³C enriched in C. hyperboreus. Although dietary fatty acids were generally retained by the copepods it seems that fatty acids or even lipids were selectively accumulated and turned over due to bodily requirements, and thus, essential polyunsaturated fatty acids were preferentially retained. During feeding mixing, accumulation, and exchange of internal and dietary fatty acids and alcohols occurred as well as utilisation of lipids from both sources for metabolic requirements. The differences in lipid assimilation fit to the different life strategies of the copepods.     

Polyunsaturated fatty acid biosynthesis from [1-14C]20:3 n-6 acid in rat cultured Sertoli cells. Linoleic acid effect

Primary culture is a suitable system to study lipid metabolism and polyunsaturated fatty acid biosynthesis. Sertoli cell-enriched preparations were used to determine the fatty acid composition after 5 and 7 days in culture (serum free) as well as the uptake and metabolism of [1-14C]eicosa-8,11,14-trienoic acid. The addition of unlabeled linoleic acid (0.2 and 2.0 microg/ml) was also evaluated. Fatty acid methyl esters derived from cellular lipids were analyzed by gas liquid chromatography and radiochromatography. After 5 days in culture, cells had significantly less 18:2, 20:4, 22:5 and 24:5 and more 18:3, 20:3, 22:4 and 24:4 n-6 fatty acids than non-cultured cells. On day 7, an additional increment in 22:4 n-6 and a decrease in linoleic, gamma-linoleic and 24:4 n-6 fatty acids were observed. The presence of linoleic acid (low dose) produced a significant decrease in saturated and monounsaturated acids and an increase in 18:2, 20:4 and 22:5 n-6 fatty acids. At a high concentration almost all fatty acids belonging to 18:2 n-6 increased significantly. The drop in 20:4 n-6/20:3 n-6 ratio was considered as an indirect evidence of a Delta 5 desaturase activity depression. This assumption was corroborated by studying the transformation of [1-14C]eicosa-8,11,14-trienoic acid into 20:4, 22:4, 22:5, 24:4 and 24:5 n-6 fatty acids. We conclude that Sertoli cells after 7 days in culture evidenced changes in the fatty acid profile similar to those described under fat deprivation. The addition of linoleic acid reverted this pattern and indicated that the Delta 5 desaturase activity is a limiting step in the polyunsaturated fatty acid biosynthesis.     

Interactions of saturated, n-6 and n-3 polyunsaturated fatty acids to modulate arachidonic acid metabolism

Anti-thrombotic effects of omega-3 (n-3) fatty acids are believed to be due to their ability to reduce arachidonic acid levels. Therefore, weanling rats were fed n-3 acids in the form of linseed oil (18:3n-3) or fish oil (containing 20:5n-3 and 22:6n-3) in diets containing high levels of either saturated fatty acids (hydrogenated beef tallow) or high levels of linoleic acid (safflower oil) for 4 weeks. The effect of diet on the rate-limiting enzyme of arachidonic acid biosynthesis (delta 6-desaturase) and on the lipid composition of hepatic microsomal membrane was determined. Both linseed oil- or fish oil-containing diets inhibited conversion of linoleic acid to gamma-linolenic acid. Inhibition was greater with fish oil than with linseed oil, only when fed with saturated fat. delta 6-Desaturase activity was not affected when n-3 fatty acids were fed with high levels of n-6 fatty acids. Arachidonic acid content of serum lipids and hepatic microsomal phospholipids was lower when n-3 fatty acids were fed in combination with beef tallow but not when fed with safflower oil. Similarly, n-3 fatty acids (18:3n-3, 20:5n-3, 22:5n-3, and 22:6n-3) accumulated to a greater extent when n-3 fatty acids were fed with beef tallow than with safflower oil. These observations indicate that the efficacy of n-3 fatty acids in reducing arachidonic acid level is dependent on the linoleic acid to saturated fatty acid ratio of the diet consumed.     

Alteration in Fatty Acid Composition of Adult Rat Brain Capillaries and Choroid Plexus Induced by a Diet Deficient in n-3 Fatty Acids: Slow Recovery After Substitution with a Nondeficient Diet

Wistar rats were fed for three generations with a semisynthetic diet containing either 1.5% sunflower oil (940 mg% of C18:2n-6, 6 mg% of C18:3n-3) or 1.9% soya oil (940 mg% of C18:2n-6, 130 mg% of C18:3n-3). At 60 days of age, the male offspring of the third generation were killed. The fatty acyl composition of isolated capillaries and choroid plexus was determined. The major changes noted in the fatty acid profile of isolated capillaries were a reduction (threefold) in the level of docosahexaenoic acid and, consequently, a fourfold increase in docosapentaenoic acid in sunflower oil-fed animals. The total percentage of polyunsaturated fatty acids was close to that in the soya oil-fed rats, but the ratio of n-3/n-6 fatty acids was reduced by threefold. In the choroid plexus, the C22:6n-3 content was also reduced, but by 2.6-fold, whereas the C22:5n-6 content was increased by 2.3-fold and the ratio of n-3/n-6 fatty acids was reduced by 2.4-fold. When the diet of sunflower oil-fed rats was replaced with a diet containing soya oil at 60 days of age, the recovery in content of n-6 and n-3 fatty acids started immediately after diet substitution; it progressed slowly to reach normal values after 2 months for C22:6n-5 and 2.5 months for C22:6n-3. The recovery in altered fatty acids of choroid plexus was also immediate and very fast. Recovery in content of C22:5n-6 and C22:6n-3 was complete by 46 days after diet substitution.     

Influence of testosterone on polyunsaturated fatty acid biosynthesis in Sertoli cells in culture

Sertoli cells play a central role in spermatogenesis, its development and regulation. They are target cells for androgen action in the seminiferous tubules. The Sertoli cell is considered to be the most important cell type in the testis with regard to essential fatty acid metabolism. We studied the response to testosterone of cultured Sertoli cells from immature rats by determining the fatty acid composition of total cellular lipids as well as by the biosynthesis of polyunsaturated fatty acids. Fatty acid methyl esters were analysed by gas liquid chromatography and radiochromatography. Two doses of testosterone were tested (150 and 300 ng ml(-1)). Significant differences were found in fatty acids derived from total cellular lipids after 8 days in culture in the presence of testosterone (300 ng ml(-1), for 48 h). Compared to controls, the hormone produced a significant increase of 16:1 and 18:1 n-9, and of 18:2 n-6, and a decrease of 20:4 and 22:5 n-6 in total cellular lipids. The decrease in the n-6 fatty acid ratios 20:4/20:3, 20:4/18:2 and 24:5/24:4, and the increase in 18:1n-9/18:0 and 16:1n-9/16:0 ratios were taken as an indirect signal of testosterone effects on Delta5, Delta6 and Delta9 desaturase activities. The drop in Delta5 and Delta6 desaturase activities was corroborated by analysing the transformation of [1-14C]20:3 n-6 into its higher homologues. We concluded that testosterone modifies the fatty acid pattern of cultured Sertoli cells, and this hormone is involved in polyunsaturated fatty acid biosynthesis, modulating Delta5 and Delta6 desaturases activity.