Interaction of Sesamin and Eicosapentaenoic Acid against Δ5 Desaturation and n-6/ n-3 Ratio of Essential Fatty Acids in Rat

Sesamin is a specific inhibitor of Δ5 desaturation, the conversion from dihomo-γ-linolenic acid (20: 3, n-6) to arachidonic acid (AA, 20: 4, n-6). Previously, we reported that sesamin inhibited Δ5 desaturation of n-6 fatty acids in rat hepatocytes but not that of n-3 fatty acids, from 20: 4 (n-3) to eicosapentaenoic acid (EPA, 20: 5, n-3). In this study, we investigated the interaction of sesamin and EPA on Δ5 desaturation of both series and the n-6/n-3 fatty acids ratio by measuring actural fatty acid contents in vivo. Rats were fed three types of dietary oils; 1) linoleic acid (LA, 18: 2, n-6): linolenic acid (LLA, 18: 3, n-3) = 3: 1, n-6/n-3 ratio of 3: 1 (LA group), 2) LA: LLA =1: 3, n-6/n-3 ratio of 1: 3 (LLA group), 3) LA: LLA: EPA =1: 0.5: 3, n-6/n-3 ratio of 1: 3.5 (EPA group) with or without sesamin (0.5% w/w) for 4 weeks. In all groups, sesamin administration increased the content of dihomo-γ-linolenic acid (20: 3, n-6) in the liver and decreased the Δ5 desaturation index of n-6 fatty acid, the ratio of 20: 4/20: 3 (n-6). On the contrary, the Δ5 desaturation index of n-3 fatty acid, the ratio of 20: 5 + 22: 5 + 22: 6/20: 4 (n-3), was increased by the administration of sesamin. These results suggest that sesamin inhibits the A5 desaturation of n-6 fatty acid, but not that of n-3 fatty acid in rat livers. Sesamin administration decreased incorporation of EPA (n-3) and simultaneously increased the AA (n-6) content in the liver. The n-6/n-3 ratio in the liver was increased by administering sesamin under n-3 rich conditions, i.e., the LLA and EPA groups.     

Lipid Content and fatty acid composition of algal communities in sea-ice and water from the Weddell Sea (Antarctica)

The lipid and fatty acid compositions of microalgae were investigated in sea-ice and water samples from six different habitats of the Weddell Sea (Antarctica). All sea-ice samples and ice-associated water contained high algal biomass dominated by centric and pennate diatoms. Cells partially filled with oil droplets and resting spores were found. In the cells from the ice platelet layer triacylglycerols formed the largest component of the lipids. The fatty acid composition of sea-ice microalgae was dominated by the 16:1(n-7), 16:0, 18:1(n-9) and 20:5 (n-3) fatty acids. Except 18:1, they are typical for diatom fatty acids. These fatty acids were most abundant in pieces of first year ice with a brown colouration (brown-ice) and in the water column directly below sea-ice (sub-ice water). The small amounts of non-diatom acids, as 22:6 (n-3) and 18:4 (n-3), clearly showed that the sea-ice communities were not purely composed of diatoms. The most striking difference, in comparison to the general fatty acid composition of diatoms, was the high proportion of the 18:1 fatty acid in all samples, which might be caused by detrital material or lipid accumulation within cells and resting spores. In general, no clear adaptation of the fatty acid composition to the Antarctic and sea-ice environment was found. The fatty acid composition of the particulate matter from the water column was totally different from all other samples dominated by the saturated fatty acids 16:0 and 18:0.     

Diets enriched in menhaden fish oil, seal oil, or shark liver oil have distinct effects on the lipid and fatty-acid composition of guinea pig heart

The purpose of this investigation was to determine whether diets supplemented with oils from three different marine sources, all of which contain high proportions of long-chain n-3 polyunsaturated fatty acids (PUFA), result in qualitatively distinct lipid and fatty acid profiles in guinea pig heart. Albino guinea pigs (14 days old) were fed standard, nonpurified guinea pig diets (NP) or NP supplemented with menhaden fish oil (MO), harp seal oil (SLO) or porbeagle shark liver oil (PLO) (10%, w/w) for 4-5 weeks. An n-6 PUFA control group was fed NP supplemented with corn oil (CO). All animals appeared healthy, with weight gains marginally lower in animals fed the marine oils. Comparison of relative organ weights indicated that only the livers responded to the diets, and that they were heavier only in the marine-oil fed guinea pigs. Heart total cholesterol levels were unaffected by supplementing NP with any of the oils, whereas all increased the triacylglycerol (TAG) content. The fatty-acid profiles of totalphospholipid (TPL), TAG and free fatty acid (FFA) fractions of heart lipids showed that feeding n-3 PUFA significantly altered the proportions of specific fatty-acid classes. For example, all marine-oil-rich diets were associated with increases in total monounsaturated fatty acids in TPL (p < 0.05), and with decreases in total saturates in TAG (p < 0.05). Predictably, the n-3 PUFA enriched regimens significantly increased the cardiac content of n-3 PUFA and decreased that of n-6 PUFA, although the extent varied among the diets. As a result, n-6/n-3 ratios were significantly lower in all myocardial lipid classes of marine-oil-fed guinea pigs. Analyses of the profiles of individual PUFA indicated that quantitatively, the fatty acids of the three marine oils were metabolized and/or incorporated into TPL, TAG and FFA in a diet-specific manner. In animals fed MO-enriched diets in which eicosapentaenoic acid (EPA) > docosahexacnoic acid (DHA), ratios of DHA /EPA in the hearts were 1.2, 2.2 and 1.5 in TPL, TAG and FFA, respectively. In SLO-fed guinea pigs in which dietary EPA DHA, ratios of DHA/EPA were 0.9, 3.4 and 2.1 in TPL, TAG and FFA, respectively. Feeding NP + PLO (DHA/EPA = 4.8), resulted in values for DHA/EPA in cardiac tissue of 2.1, 10.6 and 2.9 in TPL, TAG and FFA, respectively. In the TAG and FFA, proportions of n-3 docosapentaenoic acid (n-3 DPA) were equal to or higher than EPA in the SLO- and PLO-fed animals. The latter group exhibited the greatest difference between the DHA/n-3 DPA ratio in the diet and in cardiac TAG and FFA fractions (7, 3.4 and 3.1, respectively). Quantitative analysis indicated that 85% of the n-3 PUFA were in TPL, 7-11% were in TAG, and 2-6% were FFA. Specific patterns of distribution of EPA, DPA and DHA depended on the dietary oil. Both the qualitative and quantitative results of this study demonstrated that in guinea pigs, n-3 PUFA in different marine oils are metabolized and/or incorporated into cardiac lipids in distinct manners. In support of the concept that the diet-induced alterations reflect changes specifically in cardiomyocytes, we observed that direct supplementation of cultured guinea pig myocytes for 2-3 weeks with EPA or DHA produced changes in the PUFA profiles of their TPL that were qualitatively similar to those observed in tissue from the dietary study. The factors that regulate specific deposition of n-3 PUFA from either dietary oils or individual PUFA are not yet known, however the differences that we observed could in some manner be related to cardiac function and thus their relative potentials as health-promoting dietary fats.     

Heart phospholipid content and fatty acid composition in the rat after feeding different lipid supplemented diets.

The heart phospholipid content and fatty acid composition were examined in adult rats after four weeks of feeding lipid-supplemented diets (20 g % w/w) containing sunflower oil-lard (1:1) mixture (SL group) or margarine (M group). Our results showed a decreased cardiolipin content and distribution in both experimental groups and an increased lysophosphatidylcholine and phosphatidylcholine content and distribution in the SL group with a tendency to lower phosphatidylcholine/phospatidylethanolamine ratio in both experimental groups. In the SL group, the content of saturated fatty acids was higher and that of monounsaturated fatty acids was lower than in the control group. The M group showed inverse results. The content of saturated fatty acids was lower and that of monounsaturated was higher than in the control group. Polyunsaturated n-6 fatty acids were decreased in both experimental groups and n-3 fatty acids were increased in the M group. Feeding lipid-supplemented diets reduced n-6/n-3 and 20:4/22:6 ratios in the M group. The polyunsaturated/saturated fatty acid ratio was lower in the SL and higher in indicating the M group than in the control group. Our results are in agreement with the other reports indicating that the heart is sensitive to diet-induced lipid alterations.     

Effects of dietary n-3 fatty acids on characteristics and lipid composition of ovine sperm

The fatty acid composition of sperm affects the fertilization rate. The objective was to investigate the effects of dietary fish oil (as a source of n-3 fatty acids) on semen quality and sperm fatty acid composition in sheep. Eight Zandi fat-tailed rams were randomly allocated into two groups and fed either a control diet or a diet supplemented with fish oil. Both diets were isocaloric and isonitrogenous and were fed for 13 weeks, starting in the middle of the breeding season. Semen samples were collected weekly and their characteristics evaluated by standard methods, whereas samples collected at the start and end of the study were assessed (gas chromatography) for sperm lipid composition. Mean (±s.e.m.) sperm concentrations (4.3 × 109 ± 1.3 × 108 v. 3.9 × 109 ± 1.3 × 108 sperm/ml and percentages of motile (77.25 ± 3.34 v. 60.8 ± 3.34) and progressively motile sperm (74.13 ± 1.69 v. 62.69 ± 1.69) were significantly higher in the fish oil group than control. Dietary fish oil increased the proportion of docosahexaenoic acid (DHA, C22:6 n-3) in sperm fatty acid composition. We concluded that feeding fish oil as a source of n-3 fatty acids attenuated seasonal declines in semen quality in rams, perhaps through increased DHA in sperm.     

Effect of olive oil- and corn oil-enriched diets on the tissue mineral content in mice

The mineral content (zinc, iron, magnesium, and calcium) in the liver, spleen, and thymus of male Balb/C mice was analyzed. Animals were fed, over 21 d, diets enriched with corn oil (FCO diet) or olive oil (FOO diet) (5% addition to standard pellet, w/w). Olive oil with predominant oleic acid (C18:1, n-9) had a quite different composition than corn oil, in which linoleic acid (C18:2, n-6) prevails. The zinc and magnesium tissue concentrations were not changed in either group. The calcium concentration in liver as well as the calcium concentration in spleen increased in mice fed both the FCO and FOO diets. Furthermore, mice fed both the FOO and FCO diets had increased spleen iron concentration. Mice fed the FCO diet had increased thymus calcium concentration compared to controls. The results show the effect of diets with unsaturated, particularly polyunsaturated fatty acids, on the calcium and iron concentration in some organs.     

Effect of n-6 and n-3 polyunsaturated fatty acids ingestion on rat liver membrane-associated enzymes and fluidity

The influences of diets having different fatty acid compositions on the fatty-acid content, desaturase activities, and membrane fluidity of rat liver microsomes have been analyzed. Weanling male rats (35–45 g) were fed a fat-free semisynthetic diet supplemented with 10% (by weight) marine fish oil (FO, 12.7% docosahexaenoic acid and 13.8% eicosapentaenoic acid), evening primrose oil (EPO, 7.8% γ-linolenic acid and 70.8% linoleic acid) or a mixture of 5% FO-5% EPO. After 12 weeks on the respective diets, animals fed higher proportions of (n-3) polyunsaturated fatty acids (FO group) consistently contained higher levels of 20:3(n-6), 20:5(n-3), 22:5(n-3), and 22:6(n-3), and lower levels of 18:2(n-6) and 20:4(n-6), than those of the EPO (a rich source of (n-6) polyunsaturated fatty acids) or the FO + EPO groups. Membrane fluidity, as estimated by the reciprocal of the order parameter S_DPH, was higher in the FO than in the EPO or the FO + EPO groups, and the n-6 fatty-acid desaturation system was markedly affected.     

Unsaturated fatty acids differ between hepatic colorectal metastases and liver tissue without tumour in humans: Results from a randomised controlled trial of intravenous eicosapentaenoic and docosahexaenoic acids

IntroductionMediators derived from the n-6 polyunsaturated fatty acid (PUFA) arachidonic acid oxidation have been shown to have tumour promoting effects in experimental models, while n-3 PUFAs are thought to be protective. Here we report fatty acid concentrations in hepatic colorectal metastases compared to liver tissue without tumour in humans.MethodsTwenty patients with colorectal liver metastasis were randomized to receive a 72 h infusion of parenteral nutrition with or without n-3 PUFAs. Histological samples from liver metastases and liver tissue without tumour were obtained from 15 patients at the time of their subsequent liver resection (mean 8 days (range 4–12) post-infusion) and the fatty acid composition determined by gas chromatography.ResultsThere were no significant differences in fatty acid composition between the two intervention groups. When data from all patients were combined, liver tissue without tumour had a higher content of both n-3 and n-6 PUFAs and a lower content of oleic acid and total n-9 fatty acids compared with tumour tissue (p<0.0001, 0.0002,<0.0001 and <0.0001, respectively). The n-6/n-3 PUFA ratio was found to be higher in tumour tissue than tissue without tumour (p<0.0001).ConclusionsHepatic colorectal adenocarcinoma metastases have a higher content of n-9 fatty acids and a lower content of n-6 and n-3 PUFAs than liver tissue without tumour.     

Phosphatidylethanolamine methyltransferase: evidence for influence of diet fat on selectivity of substrate for methylation in rat brain synaptic plasma membranes

Male weanling rats were fed diets containing 20% (w/w) fat differing in fatty acid composition for 24 days. Synaptic plasma membranes were isolated from the brain and the fatty acid composition of phosphatidylethanolamine and phosphatidylcholine was determined. In vitro assays of phosphatidylethanolamine methyl-transferase activity were performed on fresh membrane samples to assess effect of dietary fat on the rate of phosphatidylethanolamine methylation for phosphatidylcholine synthesis via the phosphatidylethanolamine methyltransferase pathway. Dietary level of n-6 and ratio of n-6 to n-3 fatty acids influenced membrane phospholipid fatty acid composition and activity of the lipid-dependent phosphatidylethanolamine methyltransferase pathway. Rats fed a diet rich in n-6 fatty acids produced a high ratio of n-6/n-3 fatty acids in synaptosomal membrane phosphatidylethanolamine, and elevated rates of methylation of phosphatidylethanolamine to phosphatidylcholine by phosphatidylethanolamine methyltransferases, suggesting that the pathway exhibits substrate selectivity for individual species of phosphatidylethanolamine containing long-chain homologues of dietary n-6 and n-3 fatty acids (20:4(n-6), 22:4(n-6), 22:5(n-6) and 22:6(n-3). It may be concluded that diet alters the membrane content of n-6, n-3 and monounsaturated fatty acids, and that change in phosphatidylethanolamine species available for methylation to phosphatidylcholine alters the rate of product synthesis in vivo by the phosphatidylethanolamine methyltransferase pathway.     

Role of dietary oleic acid from two different sources on fatty acid composition of erythrocyte membrane and blood pressure in healthy subjects

This study has been undertaken to determine the effect of a diet enriched with olive oil (OO) and high-oleic sunflower oil (HOSO) on fatty acid composition of erythrocyte membrane phospholipids and blood pressure in healthy women. OO and HOSO were used as natural sources of monounsaturated fatty acids (MUFAs) in a random-order sequence over two 4-week periods with a 4-week washout period between both MUFA diets. HOSO diet resulted in significant increases in oleic [(18:1n-9) 8.6%, P < 0.001], eicosenoic [(20:1n-9) 33.3%, P < 0.05], arachidonic [(20:4n-6) 6.2%, P < 0.05], and docosapentaenoic [(22:5n-6) 56.0%, P < 0.001] acids, whereas OO diet besides increased the content of stearic acid [(18:0) 13.6%, P < 0.01] and long-chain polyunsaturated fatty acids (PUFAs) of the n-3 family (22:5n-3 and 22:6n-3), when compared with the baseline [a diet high in saturated fatty acids (SFAs) and low in MUFAs]. In contrast, there was a significant decrease in linoleic acid [(18:2n-6) 21.8%, P < 0.001] for both MUFA diets. Consistent with these data, dietary intake of OO significantly raised total PUFAs (7.2%, P < 0.05), the n-3 fatty acids (22.2%, P < 0.01) and the PUFAs/SFAs ratio (9.3%, P < 0.01), as well as decreased the ratio of cholesterol to phospholipids (26,1%, P < 0.001) versus HOSO-based diet. Interestingly, dietary OO, but not HOSO, was able to significantly reduce the systolic (3%, P < 0.05) and diastolic (4%, P < 0.05) blood pressures. Although both vegetable oils provided a similar content of MUFAs (mainly oleic acid), our findings rather indicate that OO has important benefits to modulate the fatty acid composition of membranes and the mechanisms involved in the regulation of blood pressure in human.     

Lipid and fatty acid composition during embryo and larval development of puye Galaxias maculatus Jenyns, 1842, obtained from estuarine, freshwater and cultured populations

Galaxias maculatus eggs and larvae obtained from broodfish captured either in an estuarine or a freshwater environment, as well as from cultured broodstock were analysed to compare their lipid and fatty acid profiles. Results showed a lower lipid content in embryos and larvae from estuarine populations than those from fresh water, denoting the influence of environmental conditions. The n-3:n-6 ratio was higher in eggs from estuarine and cultured populations, being in the range of marine fishes, whereas for eggs from freshwater fish was lower and typical of freshwater fishes. The polyunsaturated fatty acids (PUFA), particularly docosahexaenoic acid (22:6n-3) and eicosapentaenoic acid (20:5n-3), were higher in eggs and larvae of broodstock coming from culture or estuarine environments than in those from fresh water. Moreover, these fatty acids markedly increased after hatching in larvae coming from estuarine populations, suggesting the effect of the environment on fatty acid profiles to physiologically prepare the larvae to adapt to higher salinity conditions. Linoleic acid (18:2n-6) content was higher in fresh water fish and its reduction during embryo and larval development was accompanied by a significant increase of arachidonic acid (20:4n-6), which was not observed in embryos or larvae from broodstock fish from estuary or aquaculture origin. Both environment and diet of broodstock fish affected lipid and fatty acid composition of G. maculatus embryo and larvae as well as their changes during development.     

Role of fatty acids of (n-3) and (n-6) series on α-linolenic acid desaturation and chain elongation in HTC cells

Summary The desaturation and chain elongation of [1-¹⁴C] -linolenic acid were studied in HTC cells preincubated for 24 h in the presence of different unlabeled fatty acids of (n-3) and (n-6) series. After 24 h in the presence of [1-¹⁴C] -18:3, cells transformed this acid into labeled 20:5 and 22:5(n-3) through the desaturation-elongation pathway and into 20:3 and 22:3(n-3) by the elongation reactions. The preincubation of HTC cells with (n-3) fatty acids (-18:3, 20:5 and 22:6) produced an increase in the amount of [1-¹⁴C] -18:3 that remained in the cells without being metabolized and consequently, a decrease in the last product formed, the 22:5(n-3) was observed. Simultaneously, the desaturation-elongation products decreased significantly and those of the elongation pathway were not modified, except when the cells were pre-incubated with the last fatty acid of this family (22:6) which increased this metabolic route. Fatty acids of (n-6) series (-18:3, 20:3, 20:4 and 22:4) decreased the desaturation-elongation pathway and increased the elongation route from [1-¹⁴C] -18:3. From these results, it can be concluded that fatty acids of (n-3) family and intermediates of (n-6) series would impair the [1-¹⁴C] -18:3 metabolism at the 6 desaturation step. The fatty acid composition of the cells was also modified by the preincubation with (n-3) and (n-6) acids showing a decrease on 9 desaturation activity.     

Dietary manipulation with high marine fish oil intake of fatty acid composition and arachidonic acid metabolism in rat cerebral microvessels

Male weanling Wistar rats were maintained on one of two semisynthetic diets, differing only in the type of oil used: (i) 10% by weight marine fish oil (MFO group) containing 20% eicosapentaenoic acid (EPA) and 17% docosahexaenoic acid (DHA), or (ii) 10% by weight sunflower oil (SFO group). The control group was kept on standard diet for 4 weeks. Blood-free microvessels were isolated from brain cortex by a rapid micromethod, and their fatty acid composition was determined by gas chromatography. It was found that the proportion of n-3 fatty acids (including EPA and DHA) increased significantly in the microvessels of the MFO group, accompanied by a decrease of the n-6 fatty acid series. The changes in fatty acid composition of endothelial cells were not significant in the SFO group in comparison to the control. The amounts of lipoxygenase and cyclooxygenase metabolites were determined. Dietary fish oil decreased the percentage of total products of arachidonate by 50%, while the SFO diet had no effect on it. The amount of lipoxygenase products in the MFO group decreased significantly from 16931±3131 dpm to 6399±357 dpm/300 mg wet weight of brain. Significantly less PGF-1, PGF-2 and 12-hydroxyhepta-decatrienoic acid (HHT) were found in the capillaries of MFO treated animals, in comparison to the SFO group. The ratios of vasoconstrictor and vasodilator metabolites of arachidonate cascade were not modifed by the diets. Our results suggest that fish oil diet reduces the arachidonate cascade in cerebral microvessels. This effect may explain for the efficiency of n-3 fatty acids in vascular diseases.     

Reversibility of n-3 fatty acid deficiency-induced alterations of learning behavior in the rat: level of n-6 fatty acids as another critical factor

Rats fed a semipurified diet supplemented with 3% (w/w) safflower oil [Saf, n-3 fatty acid deficient, high linoleic acid (18:2n-6)] through two generations exhibit decreased correct response ratios in a brightness-discrimination learning test compared with rats fed 3% perilla oil [Per, high alpha-linolenic acid (18:3n-3)]. This is associated with a decreased DHA (22:6n-3)-to-arachidonic acid (20:4n-6) ratio in brain lipids. In the first set of experiments, dietary oil was shifted from Saf to a mixture of 2.4% safflower oil plus 0.6% DHA after weaning (Saf-DHA), but all parameters measured in the learning test were essentially unchanged. Brain 22:6n-3 content of the Saf-DHA group reached that of the Per group but the levels of 20:4n-6 and docosatetraenoic acid (22:4n-6) did not decrease to those of the Per group at the start of the test. In the second set of experiments, dietary oil was shifted to a mixture of 0.6% safflower oil plus 1.2% oleic acid (OA) plus 1.2% DHA (Saf-OA-DHA group) with 18:2n-6 content comparable to that of the Per group. The Saf-OA-DHA group exhibited a learning performance similar to that of the Per group; brain 22:6n-3, 20:4n-6, and 22:4n-6 contents were also comparable to those of the Per group. These results indicate that the altered learning behavior associated with a long-term n-3 fatty acid deficiency is reversed by supplementing 22:6n-3 after weaning, when the levels of competing n-6 fatty acids in the diet and brain lipids are limited.     

Dietary effects on brain fatty acid composition: the reversibility of n-3 fatty acid deficiency and turnover of docosahexaenoic acid in the brain, erythrocytes, and plasma of rhesus monkeys

Rhesus monkeys given pre- and postnatal diets deficient in n-3 essential fatty acids develop low levels of docosahexaenoic acid (22:6 n-3, DHA) in the cerebral cortex and retina and impaired visual function. This highly polyunsaturated fatty acid is an important component of retinal photoreceptors and brain synaptic membranes. To study the turnover of polyunsaturated fatty acids in the brain and the reversibility of n-3 fatty acid deficiency, we fed five deficient juvenile rhesus monkeys a fish oil diet rich in DHA and other n-3 fatty acids for up to 129 weeks. The results of serial biopsy samples of the cerebral cortex indicated that the changes of brain fatty acid composition began as early as 1 week after fish oil feeding and stabilized at 12 weeks. The DHA content of the phosphatidylethanolamine of the frontal cortex increased progressively from 3.9 +/- 1.2 to 28.4 +/- 1.7 percent of total fatty acids. The n-6 fatty acid, 22:5, abnormally high in the cerebral cortex of n-3 deficient monkeys, decreased reciprocally from 16.2 +/- 3.1 to 1.6 +/- 0.4%. The half-life (t 1/2) of DHA in brain phosphatidylethanolamine was estimated to be 21 days. The fatty acids of other phospholipids in the brain (phosphatidylcholine, -serine, and -inositol) showed similar changes. The DHA content of plasma and erythrocyte phospholipids also increased greatly, with estimated half-lives of 29 and 21 days, respectively. We conclude that monkey cerebral cortex with an abnormal fatty acid composition produced by dietary n-3 fatty acid deficiency has a remarkable capacity to change its fatty acid content after dietary fish oil, both to increase 22:6 n-3 and to decrease 22:5 n-6 fatty acids. The biochemical evidence of n-3 fatty acid deficiency was completely corrected. These data imply a greater lability of the fatty acids of the phospholipids of the cerebral cortex than has been hitherto appreciated.     

Modification of liver fatty acid metabolism in mice by n-3 and n-6 delta 6-desaturase substrates and products

The effects of dietary supplementation of either alpha-linolenic acid (18:3(n-3)) or stearidonic acid (18:4(n-3)) in combination with either linoleic acid (18:2(n-6)) or gamma-linolenic acid (18:3(n-6)) on liver fatty acid composition in mice were examined. Essential fatty acid deficient male C57BL/6 mice were separated into four groups of seven each and were fed a fat-free semi-purified diet supplemented with 1% (w/w) fatty acid methyl ester mixture (1:1), 18:2(n-6)/18:3(n-3), 18:2(n-6)/18:4(n-3), 18:3(n-6)/18:3(n-3), or 18:3(n-6)/18:4(n-3). After 7 days on the diets, fatty acid compositions in liver phosphatidylcholine and phosphatidylethanolamine fractions were analyzed. In groups fed 18:4(n-3) (18:2(n-6)/18:4(n-3) or 18:3(n-6)/18:4(n-3)) as compared to those fed 18:3(n-3) (18:2(n-6)/18:3(n-3) or 18:3(n-6)/18:3(n-3)), the levels of 20:4(n-3), 20:5(n-3) and 22:5(n-3) were increased, whereas those of 20:3(n-6) and 20:4(n-6) were decreased. When 18:3(n-6) replaced 18:2(n-6) as the source of n-6 acids, the levels of 18:3(n-6), 20:3(n-6), 20:4(n-6) and 22:5(n-6) were increased, whereas those of 20:4(n-3) and 20:5(n-3) were reduced. Replacing 18:3(n-3) by 18:4(n-3) reduced the (n-6)/(n-3) ratio by approx. 30%, whereas replacing 18:2(n-6) by 18:3(n-6) increased the (n-6)/(n-3) ratio by approx. 2-fold. These findings indicated that delta 6-desaturase products were metabolized more readily than their precursors. Both products also competed for the subsequent metabolic enzymes. However, the n-6 fatty acids derived from 18:3(n-6) were incorporated more favourably into liver phospholipids than n-3 fatty acids derived from 18:4(n-3).     

再投喂鱼油对瓦氏黄颡鱼肌肉脂肪酸组成的影响

为研究植物油替代鱼油对瓦氏黄颡鱼（Pelteobagrus vachelli）生长及肌肉脂肪组成的影响及重投喂鱼油对瓦氏黄颡鱼肌肉脂肪酸组成的影响,实验以大豆油分别替代饲料中的0（FO）、50（S1）、75（S2）和100%（SO）的鱼油配制等氮、等能的颗粒饲料,每组设置3个平行,养殖80d后,再投喂鱼油30d。结果表明,饲料中添加豆油不会显著影响瓦氏黄颡鱼的增重率、肝体指数和体成分（P>0.05）。随着饲料中大豆油含量的增加,S2和SO组肌肉中C18:1n-9、C18:2n-6和单不饱和脂肪酸比例显著增加（P < 0.05）,而C20:5n-3,C22:5n-3及n-3/n-6比例显著下降（P < 0.05）。再投喂鱼油30d后,SO组肌肉中C18:3n-6、C20:4n-6、Σ n-9、Σ n-6和S2组中C18:1n-9、Σ n-6比例显著下降（P < 0.05）,而S2和SO组肌肉中Σn-3多不饱和脂肪酸、C20:5n-3和C22:5n-3比例显著增加（P < 0.05）。在生产中,可采用先植物油饲料、后鱼油饲料的养殖方式提高瓦氏黄颡鱼肌肉品质（增加有益人类健康的多不饱和脂肪酸）。     

Screening of lipases for production of novel structured lipids from single cell oils

Lipids enriched in polyunsaturated fatty acids are very susceptible to oxidation, causing the formation of potentially harmful oxidized products. Hence, it is critical to keep the temperature as low as possible during reaction and storage. In this study, five commercial immobilized lipases were evaluated for their capability to produce novel structured lipids (SLs) enriched with medium-chain fatty acids (MCFAs) through acidolysis of single cell oil (SCO) with capric acid. Among the examined lipases, NS40086 and Lipozyme RM IM showed the highest incorporation degree. The acidolysis reactions resulted in an obvious variation in the fatty acids composition as well as their positional distribution. The obtained SLs contained (33.58 %–34.09 %) capric acid at sn-1, 3 positions with increasing the content of arachidonic acid at the sn-2 position up to (49.82 %–50.25 %). The NS40086 lipase displayed 1, 3 regiospecificity towards the TAG of SCO. The acidolysis reactions using NS40086 lipase resulted in a generation of 23 TAG molecular species containing capric acid. Moreover, the NS40086 lipase was more active than Lipozyme RM IM at relatively low temperatures (35 °C and 40 °C), which could be used effectively as a promising biocatalyst in lipid synthesis.     

Enzymatic fatty acid exchange in digalactosyldiacylglycerol

Six different lipases were screened for their ability of acidolysis between digalactosyldiacylglycerol (DGDG) and heptadecanoic acid in toluene. Lipases from Geotrichum candidum, Alcaligenes sp. and Penicillium camembertii did not catalyse the acidolysis reaction. Rhizopus arrhizus and Rhizomucor miehei (Lipozyme) catalysed the acidolysis but produced a mixture of DGMG, DGDG, acyl-DGMG and acyl-DGDG. The extra acyl group is bound to the primary hydroxyl of the digalactosyl moiety. Candida antarctica also catalysed the acidolysis but the TLC analysis showed bands with higher Rf values than acyl-DGDG, these probably being different tetra and higher esters. R. arrhizus lipase was the most promising enzyme under the conditions used, with no tetra esters being formed and giving the highest reaction rate of the enzymes investigated. Low water activity (0.06 or 0.11) and high fatty acid concentration (400 mM) increased the formation of acyl-DGDG whilst higher water activities (0.33 and 0.54) increased the amount of DGMG when R. arrhizus lipase was used as catalyst. At a water activity of 0.11 and a fatty acid concentration of 400 mM a yield of 24% modified DGDG was obtained. In this product the fatty acid originally present in the sn-1 position had been exchanged by heptadecanoic acid.     

Production of structured triacylglycerols by acidolysis catalyzed by lipases immobilized in a packed bed reactor

The aim of this work was to produce structured triacylglycerols (STAGs), with caprylic acid located at positions 1 and 3 of the glycerol backbone and docosohexaenoic acid (DHA) at position 2, by acidolysis of tuna oil and caprylic acid (CA) catalyzed by lipases Rd, from Rhizopus delemar, and Palatase 20000L from Mucor miehei immobilized on Accurel MP1000 in a packed bed reactor (PBR), working in continuous and recirculation modes. First, different lipase/support ratios were tested for the immobilization of lipases and the best results were obtained with ratios of 0.67 (w/w) for lipase Rd and 6.67 (w/w) for Palatase. Both lipases were stable for at least 4 days in the operational conditions. In the storage conditions (5 °C) lipases Rd and Palatase maintained constant activity for 5 months and 1 month, respectively.These catalysts have been used to obtain STAGs by acidolysis of tuna oil and CA in a PBR operating with recirculation of the reaction mixture through the lipase bed. Thus, STAGs with 52–53% CA and 14–15% DHA were obtained. These results were the basis for establishing the operational conditions to obtain STAGs operating in continuous mode. These new conditions were established maintaining constant intensity of treatment (IOT, lipase amount × reaction time/oil amount). In this way STAGs with 44–50% CA and 17–24% DHA were obtained operating in continuous mode. Although the compositions of STAGs obtained with both lipases were similar, Palatase required an IOT about four times higher than lipase Rd.To separate the acidolysis products (free fatty acids, FFAs, and STAGs) an extraction method of FFAs by water–ethanol solutions was tested. The following variables were optimized: water/ethanol ratio (the best results were attained with a water/ethanol ratio of 30:70, w/w), the solvent/FFA–STAG mixture ratio (3:1, w/w) and the number of extraction steps (3–5). In these conditions highly pure STAGs (93–96%) were obtained with a yield of 85%. The residual FFAs can be eliminated by neutralization with a hydroethanolic KOH solution to obtain pure STAGs. The positional analysis of these STAGs, carried out by alcoholysis catalyzed by lipase Novozym 435, has shown that CA represents 55% of fatty acids located at positions 1 and 3 and DHA represents 42% of fatty acids at position 2.