Formula alpha-linolenic (18:3(n - 3)) and linoleic (18:2(n - 6)) acid influence neonatal piglet liver and brain saturated fatty acids, as well as docosahexaenoic acid (22:6(n - 3)).

Saturated fatty acids can be synthesized de novo and play a role in determining properties of structural membranes. The effect of dietary essential fatty acids, linoleic acid (18:2(n - 6)) and alpha-linolenic acid (18:3(n - 3)), on the saturated fatty acid content of membrane phospholipid has not previously been considered in newborn nutrition. The studies report the effect of low (1% fatty acids) or high (4%) formula 18:3(n - 3) with low (16%) or high (30-35%) formula 18:2(n - 6) on the saturated and unsaturated fatty acid composition of liver and brain structural lipid of piglets fed formula from birth for 15 days. A significant inverse relationship between the formula % 18:3(n - 3), but not 18:2(n - 6), and the liver phospholipid palmitic acid (16:0) was found. This may indicate a possible effect of dietary 18:3(n - 3) on de novo synthesis of 16:0 and requires further investigation. Monounsaturated fatty acids in both liver and brain were significantly lower in response to high 18:3(n - 3) and to high 18:2(n - 6) plus low 18:1(n - 9) in the formula. Liver phospholipid and brain total lipid % docosahexaenoic acid (22:6(n - 3)) were significantly higher when formula containing 4% rather than 1% 18:3(n - 3) was fed, suggesting that 1% 18:3(n - 3) may limit tissue (n - 3) fatty acid accretion. These results suggest that future studies of essential fatty acid requirements, specifically 18:3(n - 3), should consider possible influences on the saturated fatty acids which also play a functional role in tissue structural lipids.     

The Fatty Acid Profile Analysis of Cyperus laxus Used for Phytoremediation of Soils from Aged Oil Spill-Impacted Sites Revealed That This Is a C18:3 Plant Species

The effect of recalcitrant hydrocarbons on the fatty acid profile from leaf, basal corm, and roots of Cyperus laxus plants cultivated in greenhouse phytoremediation systems of soils from aged oil spill-impacted sites containing from 16 to 340 g/Kg total hydrocarbons (THC) was assessed to investigate if this is a C18:3 species and if the hydrocarbon removal during the phytoremediation process has a relationship with the fatty acid profile of this plant. The fatty acid profile was specific to each vegetative organ and was strongly affected by the hydrocarbons level in the impacted sites. Leaf extracts of plants from uncontaminated soil produced palmitic acid (C16), octadecanoic acid (C18:0), unsaturated oleic acids (C18:1-C18:3), and unsaturated eichosanoic (C20:2-C20:3) acids with a noticeable absence of the unsaturated hexadecatrienoic acid (C16:3); this finding demonstrates, for the first time, that C. laxus is a C18:3 plant. In plants from the phytoremediation systems, the total fatty acid contents in the leaf and the corm were negatively affected by the hydrocarbons presence; however, the effect was positive in root. Interestingly, under contaminated conditions, unusual fatty acids such as odd numbered carbons (C15, C17, C21, and C23) and uncommon unsaturated chains (C20:3n6 and C20:4) were produced together with a remarkable quantity of C22:2 and C24:0 chains in the corm and the leaf. These results demonstrate that weathered hydrocarbons may drastically affect the lipidic composition of C. laxus at the fatty acid level, suggesting that this species adjusts the cover lipid composition in its vegetative organs, mainly in roots, in response to the weathered hydrocarbon presence and uptake during the phytoremediation process.     

Similarities and differences in lipid metabolism of chloroplasts isolated from 18:3 and 16:3 plants

Photosynthetically active chloroplasts retaining high rates of fatty acid synthesis from [1-¹⁴C]acetate were purified from leaves of both 16:3 (Solanum nodiflorum, Chenopodium album) and 18:3 plants (Amaranthus lividus, Pisum sativum). A comparison of lipids into which newly synthesized fatty acids were incorporated revealed that, in 18:3 chloroplasts, enzymic activities catalyzing the conversion of phosphatidate to diacylglycerol and of diacylglycerol to monogalactosyl diacylglycerol (MGD) were significantly less active than in 16:3 chloroplasts. In contrast, labeling rates of MGD from UDP-[¹⁴C]gal were similar for both types of chloroplasts.

The composition and positional distribution of labeled fatty acids within the glycerides synthesized by isolated 16:3 and 18:3 chloroplasts were similar and in each case only a C18/C16 diacylglycerol backbone was synthesized. In nodiflorum chloroplasts, C18:1/C16:0 MGD assembled de novo was completely desaturated to the C18:3/C16:3 stage.

Whereas newly synthesized C18/C18 MGD could not be detected in any of these chloroplasts if incubated with [¹⁴C]acetate after isolation, chloroplasts isolated from acetate-labeled leaves contained MGD with labeled C18 fatty acids at both sn-1 and sn-2 positions. Taken together, these results provide further evidence on an organellar level for the operation of pro- and eucaryotic pathways in the biosynthesis of MGD in different groups of plants.

     

C18:3-GM1a induces apoptosis in Neuro2a cells: enzymatic remodeling of fatty acyl chains of glycosphingolipids

GM1a [Gal beta1-3GalNAc beta1-4(NeuAc alpha2-3)Gal beta1-4Glc beta1-1Cer] is known to support and protect neuronal functions. However, we report that alpha-linolenic acid-containing GM1a (C18:3-GM1a), which was prepared using the reverse hydrolysis reaction of sphingolipid ceramide N-deacylase, induced apoptosis in neuronal cells. Intranucleosomal DNA fragmentation, chromatin condensation, and caspase activation, all typical features of apoptosis, were observed when mouse neuroblastoma Neuro2a cells were cultured with C18:3-GM1a but not GM1a containing stearic acid (C18:0) or oleic acid (C18:1). The phenotype of Neuro2a cells induced by C18:3-GM1a was similar to that evoked by lyso-GM1a. However, lyso-GM1a caused a complete disruption of lipid microdomains of Neuro2a cells and hemolysis of sheep erythrocytes, whereas C18:3-GM1a did neither. C18:3-GM1a, but not lyso-GM1a, was found to be abundant in lipid microdomains after the removal of loosely bound GM1a by BSA. The activation of stress-activated protein kinase/c-Jun N-terminal kinase in Neuro2a cells was observed with lyso-GM1a but not C18:3-GM1a. These results indicate that the mechanism of apoptosis induced by C18:3-GM1a is distinct from that caused by lyso-GM1a. This study also clearly shows that fatty acid composition of gangliosides significantly affected their pharmacological activities when added to the cell cultures and suggests why naturally occurring gangliosides do not possess polyunsaturated fatty acids as a major constituent.     

Changes in C12:0, C18:1, C18:2 and C20:2 fatty acid content in wheat treated with resistance inducers and infected by powdery mildew

This work presents a global investigation of total fatty acid (FA) content in wheat in relation to treatment with four inducers of resistance and to powdery mildew infection. Linolenic acid (C18:3), linoleic acid (C18:2) and palmitic acid (16:0) were the most abundant FAs in wheat leaves. We investigated the effect of the following inducers of resistance: Iodus40, heptanoyl salicylic acid (HSA), Milsana and trehalose on FA accumulation. Previous studies established that lipid metabolism is altered by these compounds, and we therefore aimed to characterise their impact at the FA level. During a time course experiment, content (quantitative analysis) and percentage (qualitative analysis) of FAs were compared in treated plants and in controls, as well as in plants inoculated with Blumeria graminis f. sp. tritici (i) and non-inoculated (ni) plants. No change in C18:3 content was observed. C18:1 in Iodus 40-treated (ni) plants showed a quantitative 1.2-fold increase. Lauric acid (C12:0) content quantitatively increased after Iodus 40 (2.8-fold), Milsana (4.8-fold) and trehalose (4.0-fold) treatment in (i) plants. However, eicosadienoic acid (C20:2) quantitatively decreased in (ni) plants after Iodus 40 (1.5-fold) and Milsana (2.3-fold) treatment. The amount of C18:2 increased (1.6-fold) after HSA treatment in (i) plants. All these variations in FA content were correlated with variations in the corresponding relative percentages. Our work provides the first evidence for alterations in C12:0, C18:1, C18:2 and C20:2 FA content caused by four resistance inducers. We also compared the amount and percentage of each FA in untreated (i) and (ni) plants. In (i) plants, eicosadienoic acid (C20:2) increased and C18:2 decreased slightly. The potential involvement of these FAs during induced resistance and infection is discussed.     

Carbohydrate, glycolipid, and lipid components from the photobiont (Scytonema sp.) of the lichen, Dictyomema glabratum

The photobiont of the lichen, Dictyonema glabratum (Scytonema sp.), was isolated and cultivated in a soil-extract medium and submitted to chemical analysis. Successive extractions with CHCl3-MeOH, aqueous MeOH, and H2O gave rise to solutions of lipids (25%), low-molecular-weight carbohydrates (22%), and polysaccharides (4%), respectively. TLC of the lipid extract showed the presence of glycolipids, which were further purified and examined by NMR spectroscopy and GC-MS. Monogalactosyldiacylglycerol (1%), digalactosyldiacylglycerol (0.8%), trigalactosyldiacylglycerol (0.4%), and sulfoquinovosyldiacylglycerol (0.5%) were identified. The most abundant fatty acid ester in each fraction was palmitic (C16:0), but a great variation of the ester composition from one to another was found. Others present were those of C12:0, C14:0, C15:0, C16:1, C17:0, C18:0, C18:1, C18:2, C18:3, C22:0, C22:2, and C24:0. The lipid extract was also subjected to acid methanolysis, which gave rise to dodecane, 2-Me-heptadecane, 2,6-Me2-octadecane, and 8-Me-octadecane, methyl esters of C14:0, C15:0, C16:0, C16:1, C17:0, C18:0, C18:1, C18:2, C20:0, and C24:0 fatty acids, and the dimethyl ester of decanedioic acid. The polysaccharide had mainly Glc, Gal, and Man, with small amounts of 3-O-methylrhamnose and 2-O-methylxylose, both found in plants, and unexpectedly, some of the units were beta-galactofuranose, typical of fungal, but not cyanobacterial polysaccharides. The low-molecular-weight carbohydrates showed mannose as the main free reducing sugar, which differs from Nostoc sp. and Trebouxia sp. photobionts.     

Whole-body beta-oxidation of 18:2omega6 and 18:3omega3 in the pig varies markedly with weaning strategy and dietary 18:3omega3

Segregated early weaning (SEW) into a cleaner nursery increases food intake and growth in pigs, presumably because of reduced immune stimulation compared with conventionally reared, nonsegregated pigs (NSW). The aim of the present study was to evaluate the oxidation of linoleic acid (18:2omega6) and alpha-linolenic acid (18:3omega3) in SEW and NSW pigs. Pigs consumed a control or high 18:3omega3 diet (omega6 PUFA/omega3 PUFA; 21.3 vs. 2.5, respectively) and were weaned at either 14 days old into a SEW nursery or at 21 days old into a conventional NSW nursery. The major acute-phase protein of pigs but not haptoglobin increased in 35-day-old NSW pigs. NSW pigs had 15-25% lower carcass 18:2omega6 and 20-30% lower carcass 18:3omega3 (% composition) at 49 days old. Between 35- and 49-days-old, NSW pigs had a higher whole-body oxidation of 18:2omega6 (40-120%) and 18:3omega3 (30-80%). The high 18:3omega3 diet decreased the whole-body oxidation of 18:2omega6 by 73% and of 18:3omega3 by 63% in NSW pigs. We conclude that moderately cleaner housing SEW significantly decreases 18:2omega6 and 18:3omega3 oxidation in pigs.     

A mutant of Arabidopsis deficient in c(18:3) and c(16:3) leaf lipids

Leaf tissue of a mutant of Arabidopsis thaliana contains reduced levels of both 16:3 and 18:3 fatty acids and has correspondingly increased levels of the 16:2 and 18:2 precursors due to a single recessive nuclear mutation. The kinetics of in vivo labeling of lipids with [¹⁴C]acetate and quantitative analysis of the fatty acid compositions of individual lipids suggests that reduced activity of a glycerolipid n-3 desaturase is responsible for the altered lipid composition of the mutant. The effects of the mutation are most pronounced when plants are grown at temperatures above 26°C but are relatively minor below 18°C, suggesting a temperature-sensitive enzyme. Since the desaturation of both 16- and 18-carbon fatty acids is altered, it appears that the affected enzyme lacks specificity with respect to acyl group chain length and that it is located in the chloroplast where 16:3-monogalactosyldiglyceride is synthesized. Because the degree of unsaturation of all the major glycerolipids was similarly affected by the mutation, it is inferred that either the affected desaturase does not exhibit head group specificity or there is substantial transfer of trienoic acyl groups between different lipid classes. Both chloroplast and extrachloroplast lipids are equally affected by the mutation. Thus, either the desaturase is located both outside and inside the chloroplast, or 18:3 formed inside the chloroplast is reexported to other cellular sites.     

Rates and products of long-chain Fatty Acid synthesis from [1-C]acetate in chloroplasts isolated from leaves of 16:3 and 18:3 plants

Chloroplasts highly active in the synthesis of long-chain fatty acids from [1-¹⁴C]acetate were prepared from leaves of Solanum nodiflorum, Chenopodium quinoa, Carthamus tinctorius, and Pisum sativum. These preparations were used to test whether the various additions to incubation media found to stimulate the synthesis of particular lipid classes in vitro by Spinacia oleracea chloroplasts were applicable generally. Chloroplasts from 18:3 plants incorporated a greater proportion of radioactivity into unesterified fatty acids under control conditions than did those from 16:3 plants. Supplying exogenous sn-glycerol 3-phosphate or Triton X-100 to chloroplasts increased the synthesis of glycerolipids in all cases and accentuated the capacity of chloroplasts from 18:3 plants to accumulate phosphatidic acid rather than the diacylglycerol accumulated by chloroplasts from 16:3 plants. The UDP-galactose-dependent synthesis of labeled diacylgalactosylglycerol was much less active in incubations of chloroplasts from 18:3 plants also containing sn-glycerol 3-phosphate and Triton X-100 compared with similar incubations from 16:3 plants. Exogenous CoA stimulated total fatty acid synthesis in all chloroplast preparations and the further addition of ATP diverted radioactivity from the unesterified fatty acid to acyl-CoA. The results have been discussed in terms of the two pathway hypothesis for lipid synthesis in leaves.     

Dietary trans-18:1 raises plasma triglycerides and VLDL cholesterol when replacing either 16:0 or 18:0 in gerbils

To compare the relative impact of trans-18:1 with the two main dietary saturated fatty acids it replaces, plasma lipid response was assessed in Mongolian gerbils fed diets rich in 16:0 (24%en),18:0 (10%en), or trans-18:1 (4 or 6%en). The diets were designed such that the 18:0-rich diet substituted 7%en as 18:0 for 16:0, whereas 4%en and 6%en from trans-18:1 was substituted for 16:0 in the two trans diets. The control group was fed a diet formulated according to the fatty acid balance of American Heart Association (AHA), but provided 40%en as fat. Gerbils (n = 10 per dietary group) were fed one of the five diets for 8 weeks. The control diet, with 4 times the polyunsaturated fatty acids (PUFA) content and a P:S ratio about 10 times greater than the test diets, resulted in the lowest plasma TC, LDL cholesterol (LDL-C) and VLDL cholesterol (VLDL-C). Among the test diets, plasma TC and TG were lowest with the 18:0-rich diet. TC in gerbils fed the 16:0-rich diet and 4%en-trans were 20% higher than the 18:0-rich diet, while the 6%en-trans diet was 35% higher. VLDL-C was significantly higher in the 6%en-trans diet compared to all other groups at 8 weeks. Both trans fatty acid diets elevated plasma TG approximately 2- and 3-fold, respectively, compared to the 16:0-rich and 18:0-rich diets at 8 weeks. Further, plasma TG continued to rise over time with trans fatty acids compared to 16:0 or 18:0. Thus, in the fatty acid-sensitive gerbil, impaired TG metabolism represents a major aspect of the hyperlipemia caused by trans fatty acid substitution for major saturated fatty acids.     

The Effect of Light Intensity, Day Length, and Temperature on Fatty Acid Synthesis and Desaturation in Vicia faba L.

Some effects of light intensity, day length, and temperatureon the fatty acid composition of the major glycerolipids ofleaves of Vicia faba L. (cv. Giant Windsor) were observed. Increasinglight intensity caused an increase in the relative concentrationsof 16 : 1 in PG and 18 : 3 in MGDG and DGDG. Increasing daylength during growth (and continuous illumination of leaf tissue)had no effect on 16 : 1 in PG but caused a decrease in the 18: 3 content of PG, PC, MGDG, and DGDG. Since the quantitiesof these lipids increased under these conditions, the decreasewas not due to photodestruction but to the differences in therelative rates of biosynthesis and desaturation of fatty acids.Incubation of leaf tissue in the dark for 4 d had little effecton the fatty acid composition of MGDG, DGDG, and PG. Temperaturealso controls fatty acid synthesis and desaturation. Above theoptimum growth temperature (20 °C), the 18 : 3 content ofMGDG, DGDG, PG, and PC decreased. In mature leaf tissue, thedegree of unsaturation of MGDG may be modified upward in responseto temperature changes. When plants were grown at 30 °Cand transferred to 20 °C the level of 18 : 3 in MGDG ofthe leaf tissue increased to levels found in plants grown onlyat 20 °C. The level of 18 : 3 in MGDG does not decreaseas rapidly when plants grown at 20 °C were transferred to30 °C. This suggests that the lower temperature induceddesaturation of 18 : 2 to 18 : 3.     

13种微藻的脂肪酸组成分析

分析了13种微藻(包括7种绿藻,5种杂色藻和1种红藻)的总脂含量和脂肪酸组成,结果表明,不同门类微藻的脂肪酸组成差异较大:绿藻的脂肪酸组成以C16和C18为主;杂色藻类的脂肪酸组成相近,金藻门含有14:0、16:0、18:1、18:4等特征脂肪酸,三角褐指藻主要的脂肪酸为14:0、16:0、16:1、16:3和20:5,而粉核油球藻的脂肪酸以14:0、16:0、20:5为主;紫球藻的脂肪酸组成以16:0、20:4和20:5为主。在测试的13种微藻中,杜氏盐藻的亚麻酸含量最高,占总脂肪酸的60.9%;等鞭金藻的十八碳四烯酸含量最高,占总脂肪酸的19.6%;紫球藻和粉核油球藻中花生四烯酸与二十碳五烯酸(EPA)含量分别占总脂肪酸的17.1%和20.9%。     

Metabolism of 18:2(n - 6), 18:3(n - 3), 20:4(n - 6) and 20:5(n - 3) by the fungus Gaeumannomyces graminis: identification of metabolites formed by 8-hydroxylation and by w2 and w3 oxygenation.

The present study was aimed at developing a cell-free preparation of Gaeumannomyces graminis to biosynthesize w2-hydroxy, w3-hydroxy and related metabolites of essential fatty acids. 14C-labelled linoleic acid (18:2(n - 6)), linolenic acid (18:3(n - 3)), arachidonic acid (20:4(n - 6)) and eicosapentaenoic acid (20:5(n - 3)) were incubated with the cytosolic and microsomal fractions and NADPH. Significant metabolism was only found in the cytosol. The main products were purified by high-performance liquid chromatography and identified by gas chromatography-mass spectrometry (GC-MS). 18:2(n - 6) was metabolized mainly to 8-hydroxy-9,12-octadecadienoic acid (8-HODE), while the w2 and the w3 alcohols were formed in relatively small amounts. The absolute configuration of the 8-hydroxyl was found to be R by ozonolysis of the diastereoisomeric (-)-menthoxycarbonyl derivative of 8-HODE and GC-MS analysis. In analogy, 18:3(n - 3) was converted to 8-hydroxy-9,12,15-octadecatrienoic acid and to smaller amounts of the 15,16-diol (15,16-DiHODE). In contrast, 8-hydroxy metabolites of 20:4(n - 6) or 20:5(n - 3) could not be detected. 20:4(n - 6) was efficiently converted to 18(R)-hydroxyeicosatetraenoic acid (18(R)-HETE) and 19(R)-HETE and to traces of 17-HETE, while 20:5(n - 3) was mainly metabolized to the 17,18-diol (17,18-DiHETE) and to smaller amounts of the w2 alcohol. In conclusion, the cytosol of G. graminis can be used for stereoselective biosynthesis of some hydroxy metabolites of essential fatty acids.     

Biosynthesis of digalactosyldiacylglycerol in plastids from 16:3 and 18:3 plants

Intact chloroplasts isolated from leaves of eight species of 16:3 and 18:3 plants and chromoplasts isolated from Narcissus pseudonarcissus L. flowers synthesize galactose-labeled mono-, di-, and trigalactosyldiacylglycerol (MGDG, DGDG, and TGDG) when incubated with UDP-[6-³H]galactose. In all plastids, galactolipid synthesis, and especially synthesis of DGDG and TGDG, is reduced by treatment of the organelles with the nonpenetrating protease thermolysin. Envelope membranes isolated from thermolysin-treated chloroplasts of Spinacia oleracea L. (16:3 plant) and Pisum sativum L. (18:3 plant) or membranes isolated from thermolysin-treated chromoplasts are strongly reduced in galactolipid:galactolipid galactosyltransferase activity, but not with regard to UDP-Gal:diacylglycerol galactosyltransferase. For the intact plastids, this indicates that thermolysin treatment specifically blocks DGDG (and TGDG) synthesis, whereas MGDG synthesis is not affected. Neither in chloroplast nor in chromoplast membranes is DGDG synthesis stimulated by UDP-Gal. DGDG synthesis in S. oleracea chloroplasts is not stimulated by nucleoside 5′-diphospho digalactosides. Therefore, galactolipid:galactolipid galactosyltransferase is so far the only detectable enzyme synthesizing DGDG. These results conclusively suggest that the latter enzyme is located in the outer envelope membrane of different types of plastids and has a general function in DGDG synthesis, both in 16:3 and 18:3 plants.     

Determination of structure and composition of suberin from the roots of carrot, parsnip, rutabaga, turnip, red beet, and sweet potato by combined gas-liquid chromatography and mass spectrometry

Suberin from the roots of carrots (Daucus carota), parsnip (Pastinaca sativa), rutabaga (Brassica napobrassica), turnip (Brassica rapa), red beet (Beta vulgaris), and sweet potato (Ipomoea batatas) was isolated by a combination of chemical and enzymatic techniques. Finely powdered suberin was depolymerized with 14% BF₃ in methanol, and soluble monomers (20-50% of suberin) were fractionated into phenolic (<10%) and aliphatic (13-35%) fractions. The aliphatic fractions consisted mainly of ω-hydroxyacids (29-43%), dicarboxylic acids (16-27%), fatty acids (4-18%), and fatty alcohols (3-6%). Each fraction was subjected to combined gas-liquid chromatography and mass spectrometry. Among the fatty acids very long chain acids (>C₂₀) were the dominant components in all six plants. In the alcohol fraction C₁₈, C₂₀, C₂₂, and C₂₄ saturated primary alcohols were the major components. C₁₆ and C₁₈ dicarboxylic acids were the major dicarboxylic acids of the suberin of all six plants and in all cases octadec-9-ene-1, 18-dioic acid was the major component except in rutabaga where hexadecane-1, 16-dioic acid was the major dicarboxylic acid. The composition of the ω-hydroxyacid fraction was quite similar to that of the dicarboxylic acids; 18-hydroxy-octadec-9-enoic acid was the major component in all plants except rutabaga, where equal quantities of 16-hydroxyhexadecanoic acid and 18-hydroxyoctadec-9-enoic acid (42% each) were found. Compounds which would be derived from 18-hydroxyoctadec-9-enoic acid and octadec-9-ene-1, 18-dioic acid by epoxidation, and epoxidation followed by hydration of the epoxide, were also detected in most of the suberin samples. The monomer composition of the six plants showed general similarities but quite clear taxonomic differences.     

Sterols and fatty acids of an antarctic sea ice diatom, Stauroneis amphioxys

Unialgal clonal cultures of the diatom Stauroneis amphioxys Gregory, isolated from sea ice of the Indian Ocean sector ofthe Southern Ocean, were grown at 3° and 20°. The relative abundances offatty acids, sterols and phytol for the two cultures are comparable. The two sterols observed [24-methylcholesta-5,22E-dien-3β-ol (79%) and cholesterol (21%)] did not vary with culture temperature. The-major fatty acid composition is typical ofmost diatoms. A pronounced change of ratio with temperature occurred with the pair 16:4 Δ6, 9, 12, 15 and 16:3 Δ6, 9, 12 followed by 18:4 Δ6, 9, 12, 15:18:3 Δ9,12,15 and 20:5 Δ5,8,11,14,17:20:4 Δ8,11,14,17; thus the relative abundances of 16:4, 18:4, 20:5 and 22:6 increase at the lower growth temperature. The total amounts of unsaturated acids do not change with temperature suggesting an effect on the final desaturase step. No cryoprotective role for such changes in lipid composition was inferred.     

Effect of diets enriched in Delta6 desaturated fatty acids (18:3n-6 and 18:4n-3), on growth, fatty acid composition and highly unsaturated fatty acid synthesis in two populations of Arctic charr (Salvelinus alpinus L.)

This study aimed to test the hypothesis that diets containing relatively high amounts of the Delta6 desaturated fatty acids stearidonic acid (STA, 18:4n-3) and gamma-linolenic acid (GLA, 18:3n-6), may be beneficial in salmonid culture. The rationale being that STA and GLA would be better substrates for highly unsaturated fatty acid (HUFA) synthesis as their conversion does not require the activity of the reputed rate-limiting enzyme, fatty acid Delta6 desaturase. Duplicate groups of two Arctic charr (Salvelinus alpinus L.) populations with different feeding habits, that had been reported previously to show differences in HUFA biosynthetic capacity, were fed for 16 weeks on two fish meal based diets containing 47% protein and 21% lipid differing only in the added lipid component, which was either fish oil (FO) or echium oil (EO). Dietary EO had no detrimental effect on growth performance and feed efficiency, mortalities, or liver and flesh lipid contents in either population. The proportions of 18:2n-6, 18:3n-3, 18:3n-6, 18:4n-3, 20:3n-6 and 20:4n-3 in total lipid in both liver and flesh were increased by dietary EO in both populations. However, the percentages of 20:5n-3 and 22:6n-3 were reduced by EO in both liver and flesh in both strains, whereas 20:4n-6 was only significantly reduced in flesh. In fish fed FO, HUFA synthesis from both [1-(14)C]18:3n-3 and [1-(14)C]20:5n-3 was significantly higher in the planktonivorous Coulin charr compared to the demersal, piscivorous Rannoch charr morph. However, HUFA synthesis was increased by EO in Rannoch charr, but not in Coulin charr. In conclusion, dietary EO had differential effects in the two populations of charr, with HUFA synthesis only stimulated by EO in the piscivorous Rannoch morph, which showed lower activities in fish fed FO. However, the hypothesis was not proved as, irrespective of the activity of the HUFA synthesis pathway in either population, feeding EO resulted in decreased tissue levels of n-3HUFA and 20:4n-6. This has been observed previously in salmonids fed vegetable oils, and thus the increased levels of Delta6 desaturated fatty acids in EO did not effectively compensate for the lack of dietary HUFA.     

Purification of stearidonic acid (18:4(n-3)) and hexadecatetraenoic acid (16:4(n-3)) from algal fatty acid with lipase and medium pressure liquid chromatography

Stearidonic acid (18:4(n-3)) and hexadecatetraenoic acid (16:4(n-3)) are included in some edible marine algae such as Undaria pinnatifida and Ulva pertusa with relatively high compositions (up to 40%) of total fatty acids. In order to prepare 16:4(n-3) and 18:4(n-3) enriched fatty acid concentrates, we screened for a suitable lipase which concentrates these acids by the removal of other fatty acids in the selective esterification reaction reported by Shimada et al. (Shimada et al. (1997), J. Am. Oil Chem. Soc., 74, 1465-1470). In combination with the lipase reaction and reversed-phase medium pressure liquid chromatography, we purified 18:4(n-3) and 16:4(n-3) to more than 95% purity.     

Alternate pathways in the desaturation and chain elongation of linolenic acid, 18:3(n-3), in cultured glioma cells.

Cultured C6 glioma cells rapidly incorporate and metabolize the essential fatty acids, 18:2(n-6) and 18:3(n-3), to 20- and 22-carbon polyunsaturated fatty acids. Using several deuterated fatty acid substrates we have obtained data that suggest alternate pathways, one possibly involving delta 8-desaturation, may exist in glioma cells for formation of 20:5(n-3) and 22:6(n-3) from 18:3(n-3). With 18:3(n-3)-6,6,7,7-d4 practically no 18:4(n-3)-6,7-d2 or 20:4(n-3)-8,9-d2 was detected whereas 20:3(n-3)-8,8,9,9-d4 accounted for 3.4% and delta 5,11,14,17-20:4-8,8,9,9-d4 for 21.1% of the total deuterated fatty acids recovered in phospholipids after a 16 h incubation; 20:5(n-3)-8,9-d2, 22:5(n-3)-10,11-d2, and 22:6(n-3)-10,11-d2 accounted for 42.4%, 13.2%, and 2.8% of deuterated acyl chains, respectively. When added exogneously, 20:3-8,8,9,9,-d4 was extensively converted to delta 5,11,14,17-20:4(n-3)-8,8,9,9-d4 (45%) and 20:5(n-3)-8,9-d2 (24%); a small amount (4%) of 18:3(n-3)-d4 also was detected. Both 20:4(n-3)-8,9-d2 and 18:4(n-3)-12,13,15,16-d4 were also converted to 20:5(n-3) and 22:6(n-3) with 8 and 0% of the respective original deuterated substrate remaining after 16 h. A possible pathway for 18:3(n-3) metabolism in glioma cells is described whereby an initial chain elongation step is followed by successive delta 5 and delta 8 desaturation reactions resulting in 20:5(n-3) formation and accounting for the ordered removal of deuterium atoms. Alternatively, extremely effective retroconversion may occur to chain shorten 20:3(n-3)-d4 to 18:3(n-3)-d4 followed by rapid conversion through the classical desaturation and chain elongation sequence.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of the conversion rates of alpha-linolenic acid (18:3(n - 3)) and stearidonic acid (18:4(n - 3)) to longer polyunsaturated fatty acids in rats.

The delta 6-desaturase reaction is regarded to be the rate-limiting step in the conversion of linoleic acid (18:2(n - 6)) to arachidonic acid (20:4(n - 6)). The same is probably also the case with the conversion of alpha-linolenic acid (18:3(n - 3)) to eicosapentaenoic acid (20:5(n - 3)). However, there are very few in vivo studies that directly compared the conversion rate between 18:3(n - 3) and stearidonic acid (18:4(n - 3)), which is the delta 6-desaturated product of 18:3(n - 3). We compared this rate by feeding rats on a lipid-free diet supplemented with lard (9%, w/w) and 18:3(n - 3) ethyl ester (1%) diet or on a diet containing lard (9%) and 18:4(n - 3) ethyl ester (1%). A lard (10%)-supplemented diet was used as the control diet. The fatty acid compositions of total phospholipids, triglycerides and free fatty acids of both liver and plasma were measured after 1 or 3 weeks on different diets. The molar ratio of 20:5(n - 3) of most lipid fractions was about 2-fold higher in rats fed the 18:4(n - 3)-supplemented diet than in rats fed the 18:3(n - 3)-supplemented diet. 18:4(n - 3) was found in the liver lipid fraction in only a very small amount, even in the 18:4(n - 3)-supplemented groups. Thus, desaturation at C-6 is suggested to be the rate-limiting step in the conversion of 18:3(n - 3) to 20:5(n - 3).