n−3 polyunsaturated fatty acids and coronary thrombosis

Studies of Greenland Eskimos showed that a very high intake of marine n?3 fatty acids markedly inhibited platelet reactivity and suggested that intake of these fatty acids might prevent coronary thrombosis. Later studies with lower, more practical doses of n?3 fatty acids also have shown a platelet inhibitory effect of n?3 fatty acids, albeit fairly marginal. Furthermore, n?3 fatty acids have little effect on measures of blood coagulability and may slightly decrease fibrinolysis. In animal models, n?3 fatty acids often have been shown to inhibit thrombosis, but again the doses have tended to be very high. Finally, there has been little effect of (low-dose) n?3 fatty acids in clinical trials in humans on the incidence of myocardial infarction. Overall, there is little evidence for a major antithrombotic effect of practical doses of n?3 fatty acids on coronary thrombosis. This does not exclude a beneficial effect of n?3 fatty acids on coronary heart disease as suggested from clinical trials, but the major effect may be antiarrhythmic rather than antithrombotic.     

Effect of dietary n−6 and n−3 polyunsaturated fatty acids on peroxidizability of lipoproteins in steers

The susceptibility of major plasma lipoproteins to lipoperoxidation was studied in relation to the FA composition of their neutral and polar lipids in steers given PUFA-rich diets. Two trials used, respectively, 18 (“sunflower” experiment, S) or 24 (“linseed” experiment, L) crossbred Salers x Charolais steers. Each involved three dietary treatments over a 70-d period: a control diet (CS or CL diets) consisting of hay and concentrate, or the same diet supplemented with oilseeds (4% diet dry matter) fed either as seeds (SS or LS diets) or continuously infused into the duodenum (ISO or ILO diets). Compared with control diets, ISO and ILO treatments tended to decrease the resistance time of LDL and HDL classes to peroxidation, mainly owing to the enrichment of their polar and neutral lipids with PUFA. With diets SS and LS, sensitivity of major lipoprotein classes (LDL, light and heavy HDL) was not affected because ruminal hydrogenation of dietary PUFA decreased their incorporation into lipoparticles. ISO and ILO treatments induced a more important production of conjugated dienes and hydroperoxides generated by peroxidation in the three lipoprotein classes due to the higher amounts of PUFA esterified in lipids of the core and the hydrophilic envelope of particles. The production of malondialdehyde (MDA) increased in steers fed linseed supplements, indicating that MDA production did not occur with linoleic acid provided by sunflower oil supplements. Thus, plasma peroxidation of PUFA generates toxic products in steers fed diets supplemented with PUFA and can be deleterious for the health of the animal during long-term treatment.     

Supplementation and delivery of n−3 fatty acids through spray-dried milk reduce serum and liver lipids in rats

Indian diets comprising staples such as cereals, millets, and pulses provide 4.8 energy % from linoleic acid (18∶2n−6) but fail to deliver adequate amounts of n−3 FA. Consumption of long-chain n−3 PUFA such as EPA (20∶5n−3) and DHA (22∶6n−3) is restricted to those who consume fish. The majority of the Indian population, however, are vegetarians needing additional dietary sources of n−3 PUFA. The present work was designed to use n−3 FA-enriched spray-dired milk powder to provide n−3 FA. Whole milk was supplemented with linseed oil to provide α-linolenic acid (LNA, 18∶3n−3), with fish oil to provide EPA and DHA, or with groundnut oil (GNO), which is devoid of n−3 PUFA, and then spray-dired. Male Wistar rats were fed the spray-dired milk formulations for 60 d. The rats given formulations containing n−3 FA showed significant increases (P<0.001) in the levels of LNA or EPA/DHA in the serum and in tissue as compared with those fed the GNO control formulation. Rats fed formulations containing n−3 FA had 30–35% lower levels of serum total cholesterol and 25–30% lower levels of serum TAG than control animals. Total cholesterol and TAG in the livers of rats fed the formulations containing n−3 FA were lower by 18–30% and 11–18%, respectively, compared with control animals. This study showed that spray-dried milk formulations supplemented with n−3 FA are an effective means of improving dietary n−3 FA intake, which may decrease the risk factors associated with cardiovascular disease.     

Paradoxical effect of n−3-containing vegetable oils on long-chain n−3 fatty acids in rat heart

Flaxseed, echium, and canola oils contain α-linolenic acid (18∶3n−3, ALA) in a range of concentrations. To examine their effect on elevating cardiac levels of long-chain n−3 FA, diets based on these n−3-containing vegetable oils were fed to rats for 4 wk. Sunflower oil, which contains little ALA, was a comparator. Despite canola oil having the lowest ALA content of the three n−3-containing vegetable oils, it was the most potent for elevating DHA (22∶6n−3) levels in rat hearts and plasma. However, the relative potencies of the dietary oils for elevation of EPA (20∶5n−3) in heart and plasma followed the same rank order as their ALA content, i.e., flaxseed>echium>canola>sunflower oil. This paradox may be explained by lower ALA intake leading to decreased competition for Δ6 desaturase activity between ALA and the 24∶5n−3 FA precursor to DHA formation.     

Effects of dietary supplementation of saturated fatty acids and of n−6 or n−3 polyunsaturated fatty acids on plasma and red blood cell membrane phospholipids and deformability in weanling guinea pigs

The fatty acid composition of plasma cholesteryl esters, plasma phospholipids, red blood cell (RBC) membrane phosphatidylcholine (corresponding to the outer membrane leaflet), and phosphatidylethanolamine (corresponding to the inner membrane leaflet) was investigated in weanling guinea pigs fed with diets of cacao (saturated fatty acids), sunflower oil [n−6 polyunsaturated fatty acids (PUFA)] or fish oil (n−3 PUFA) for 20 wk. RBC deformation was measured by means of a cell-transit analyzer (filtration) and a cone-plate rheoscope. The contents of saturated fatty acids in plasma phospholipids and RBC membrane leaflets were similar in all three groups. Diets with sunflower oil resulted in a high content of linoleic acid in plasma cholesteryl esters and in the outer leaflet of RBC membranes. Fatty acids of fish oil were mainly incorporated in plasma phospholipids and in the inner leaflet of RBC membranes. The arachidonic acid content was high in all groups in the plasma phospholipids and in the inner leaflet. The n−6 and n−3 PUFA were mainly incorporated in the inner leaflet. In all groups the polyunsaturated/saturated fatty acid ratio and the total PUFA content were similar in the inner RBC membrane. The RBC filtration times and the RBC deformation indices were not affected by the dietary treatment.     

Effects of dietary n−3 polyunsaturated fatty acids on T-Cell membrane composition and function

Dietary n−3 PUFA have been shown to attenuate T-cell-mediated inflammation, in part, by suppressing T-cell activation and proliferation. n−3 PUFA have also been shown to promote apoptosis, another important mechanism for the prevention of chronic inflammation by maintaining T-cell homeostasis through the contraction of populations of activated T cells. Recent studies have specifically examined Fas death receptor-mediated activation-induced cell death (AICD), since it is the form of apoptosis associated with peripheral T-cell deletion involved in immunological tolerance and T-cell homeostasis. Data from our laboratory indicate that n−3 PUFA promote AICD in T helper 1 polarized cells, which are the mediators of chronic inflammation. Since Fas and components of the deathinducing signaling complex are recruited to plasma membrane microdomains (rafts), the effect of dietary n−3 PUFA on raft composition and resident protein localization has been the focus of recent investigations. Indeed, there is now compelling evidence that dietary n−3 PUFA are capable of modifying the composition of T-cell membrane microdomains (rafts). Because the lipids found in membrane microdomains actively participate in signal transduction pathways, these results support the hypothesis that dietary n−3 PUFA influence signaling complexes and modulate T-cell cytokinetics in vivo by altering T-cell raft composition.     

Influence of dietary supplementation with long-chain n−3 or n−6 polyunsaturated fatty acids on blood inflammatory cell populations and functions and on plasma soluble adhesion molecules in healthy adults

Greatly increasing the amounts of flaxseed oil [rich in α-linolenic acid (ALNA)] or fish oil (FO); [rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] in the diet can decrease inflammatory cell functions and so might impair host defense. The objective of this study was to determine the effect of dietary supplementation with moderate levels of ALNA, γ-linolenic acid (GLA), arachidonic acid (ARA), DHA, or FO on inflammatory cell numbers and functions and on circulating levels of soluble adhesion molecules. Healthy subjects aged 55 to 75 yr consumed nine capsules per day for 12 wk. The capsules contained placebo oil (an 80∶20 mix of palm and sunflowerseed oils) or blends of placebo oil with oils rich in ALNA, GLA, ARA, or DHA or FO. Subjects in these groups consumed 2 g ALNA; approximately 700 mg GLA, ARA, or DHA; or 1 g EPA plus DHA (720 mg EPA+280 mg DHA) daily from the capsules. Total fat intake from the capsules was 4 g per day. None of the treatments affected inflammatory cell numbers in the bloodstream; neutrophil and monocyte phagocytosis or respiratory burst in response to E. coli; production of tumor necrosis factor-α, interleukin-1β, and interleukin-6 in response to bacterial lipopolysaccharide; or plasma concentrations of soluble intercellular adhesion molecule-1. In contrast, the ALNA and FO treatments decreased the plasma concentrations of soluble vascular cell adhesion molecule-1 (16 and 28% decrease, respectively) and soluble E-selectin (23 and 17% decrease, respectively). It is concluded that, in contrast to previous reports using higher amounts of these fatty acids, a moderate increase in consumption of long-chain n−6 or n−3 polyunsaturated fatty acids does not significantly affect inflammatory cell numbers or neutrophil and monocyte responses in humans and so would not be expected to cause immune impairment. Furthermore, we conclude that moderate levels of ALNA and FO, which could be incorporated into the diet, can decrease some markers of endothelial activation and that this mechanism of action may contribute to the reported health benefits of n−3 fatty acids.     

n−3 fatty acids and revascularization procedures

Largely initiated by studies among Greenland Eskimos in the early 1970s, great attention has been given to the possible effects of the very long chain n?3 polyunsaturated fatty acids (PUFA) in a variety of cardiovascular disease states. A series of possibly positive effects on pathogenetic mechanisms in cardiovascular disease has evolved from laboratory studies in cell cultures and animals as well as in humans, focusing mainly on eicosanoid metabolism with reduced activities of platelets and leucocytes, reduced plasma triglycerides and, antiarrhythmic effects in the myocardium. A rationale for a positive effect of very long chain n?3 PUFA in the secondary prophylaxis after revascularization procedures obviously also exists. The positive clinical effects based on prospectively randomized trials are summarized as follows. After coronary artery bypass grafting (CABG), the SHOT study showed statistically significant reduction in angiographic vein graft occlusion in 610 patients after 1 yr with supplementation of 3.4 g/d of highly concentrated very long chain n?3 PUFA. The reduction in occlusion rates was significantly related to the change in the n?3 PUFA concentration in serum phospholipids during the study period with the occlusion rate in the upper quartile of such changes at only ～50% of that in the lower quartile. These results were also clearly related to the presence of angina pectoris and occurrence of myocardial infarction after 1 yr. Several studies were conducted in patients after percutaneous transluminal coronary angioplasty (PTCA). By 1993, two meta-analyses indicated a positive effect on the restenosis rate, a significant problem after otherwise successful PTCA. During the late 1990s, three large prospective randomized placebo-controlled angiographic studies were conducted with very long n?3 PUFA 5.1–8.0 g/d, all with completely negative results. Today, therefore, very long chain n?3 PUFA supplementation cannot be recommended to reduce the incidence of restenosis after PTCA. All studies were performed without stenting of the coronary lesion. In the very special revascularization procedure of heart transplantation, evolving hypertension and accelerated atherosclerosis have been major clinical problems. In other studies, positive effects by supplementation with very long chain n?3 PUFA (3.4–5.7 g/d) were obtained on the surrogate end points coronary vasoreactivity to acetylcholine and hypertension, respectively. On the basis of the presently available literature from clinical studies, recommendations for supplementation with very long chain n?3 PUFA can be given to patients after venous CABG (up to 3.4 g/d), and after heart transplantation (3.4–5.7 g/d) but not to patients after traditional PTCA. In fact, data from substudies suggested the possibility that large doses (5.1 g/d) of very long chain n?3 PUFA might be contraindicated because they induce a proinflammatory state in patients under oxidative stress.     

Metabolism of n−3 and n−6 fatty acids in Atlantic salmon liver: Stimulation by essential fatty acid deficiency

Oxidation, esterification, desaturation, and elongation of [1-¹⁴C]18∶2n−6 and [1-¹⁴C]18∶3n−3 were studied using hepatocytes from Atlantic salmon (Salmo salar I.) maintained on diets deficient in n−3 and n−6 polyunsaturated fatty acids (PUFA) or supplemented with n−3 PUFA. For both dietary groups, radioactivity from 18∶3n−3 was incoporated into lipid fractions two to three times faster than from 18∶2n−6, and essential fatty acids (FFA) deficiency doubled the incorporation. Oxidation to CO₂ was very low and was independent of substrate or diet, whereas oxidation to acid-soluble products was stimulated by EFA deficiency. Products from 18∶2n−6 were mainly 18∶3n−6, 20∶3n−6, and 20∶4n−6, with minor amounts of 20∶2n−6 and 22∶5n−6. Products from 18∶3n−3 were mainly 18∶4n−3, 20∶5n−3, and 22∶6n−3, with small amounts of 20∶3n−3. The percentage of 22∶6n−3 in the polar lipid fraction of EFA-deficient hepatocytes was fourfold higher than in n−3 PUFA-supplemented cells. This correlated well with our other results obtained after abdominal injection of [1-¹⁴C]18∶3n−3 and [1-¹⁴C]18∶2n−6. In hepatocytes incubated with [4,5-³H]-22∶6n−3, 20∶5n−3 was the main product. This retrocon-version was increased by EFA deficiency, as was peroxisomal β-oxidation activity. This study shows that 18∶2n−6 and 18∶3n−3 can be elongated and desaturated in Atlantic salmon liver, and that this conversion and the activity of retroconversion of very long chain PUFA is markedly enhanced by FFA deficiency.     

Effects of diets enriched in n−6 or n−3 fatty acids on cholesterol metabolism in older rats chronically fed a cholesterol-enriched diet

Hypocholesterolemic effects in older animals after long-term feeding are unknown. Therefore, aged rats (24 wk of age) fed a conventional diet were shifted to diets containing 10% perilla oil [PEO; oleic acid+linoleic acid+α-linolenic acid; n−6/n−3, 0.3; polyunsaturated fatty acid/saturated fatty acid (P/S), 9.6], borage oil [oleic acid+linoleic acid+α-linolenic acid; n−6/n−3, 15.1; P/S, 5.3], evening primrose oil (FPO; linoleic acid+γ-linolenic acid; P/S, 10.5), mixed oil (MIO; oleic acid+linoleic acid+γ-linolenic acid+α-linolenic acid; n−6/n−3, 1.7; P/S, 6.7), or palm oil (PLO; palmitic acid+oleic acid+linoleic acid; n−6/n−3, 25.3; P/S, 0.2) with 0.5% cholesterol for 15 wk in this experiment. There were no significant differences in the food intake and body weight gain among the groups. The liver weight in the PEO (n−6/n−3, 0.3) group was significantly higher than those of other groups in aged rats. The serum total cholesterol and very low density lipoprotein (VLDL) +intermediate density lipoprotein (IDL)+low density lipoprotein (LDL)-cholesterol concentrations of the PLO (25.3) group were consistently higher than those in the other groups. The serum high density lipoprotein cholesterol concentrations of the PEO (0.3) and EPO groups were significantly lower than in the other groups at the end of the 15-wk feeding period. The liver cholesterol concentration of the PLO (25.3) group was significantly higher than those of other groups. There were no significant differences in the hepatic LDL receptor mRNA level among the groups. Hepatic apolipoprotein (apo) B mRNA levels were not affected by the experimental conditions. The fecal neutral steroid excretion of the PLO (25.3) group tended to be low compared to the other groups. The results of this study demonstrate that both n\t-6 fatty acid and n\t-3 fatty acids such as \gg-linolenic acid and \ga-linolenic acid inhibit the increase of serum total cholesterol and VLDL+IDL+LDL-cholesterol concentrations of aged rats in the presence of excess cholesterol in the diet compared with dietary saturated fatty acid.     

Effect of species and genotype on the efficiency of enrichment of poultry meat with n−3 polyunsaturated fatty acids

The effect of poultry species (broiler or turkey) and genotype (Wrolstad or BUT T8 turkeys and Ross 308 or Cobb 500 broilers) on the efficiency with which dietary long-chain n−3 PUFA were incorporated into poultry meat was determined. Broilers and turkeys of both genotypes were fed one of six diets varying in FA composition (two replicates per genotype x diet interaction). Diets contained 50 g/kg added oil, which was either blended vegetable oil (control), orpartially replaced with linseed oil (20 or 40 g/kg diet), fish oil (20 or 40 g/kg diet), or a mixture of the two (20 g linseed oil and 20 g fish oil/kg diet). Feeds and samples of skinless breast and thigh meat were analyzed for FA. Worlstad dark meat was slightly more responsive than BUT T8 (P=0.046) to increased dietary 18∶3 concentrations (slopes of 0.570 and 0.465, respectively). The Ross 308 was also slightly more responsive than the Cobb 500 (P=0.002) in this parameter (slopes of 0.557 and 0.449). There were no other significant differences between the genotypes. There was some evidence (based on the estimates of the slopes and their associated standard errors) that white turkey meat was more responsive than white chicken meat to 20∶5 (slopes of 0.504 and 0.289 for turkeys and broilers, respectively). There was no relationship between dietary 18∶3 n−3 content and meat 20∶5 and 22∶6 contents. If birds do convert 18∶3 to higher FA, these acids are not then deposited in the edible tissues.     

Induction of apoptosis and apoptotic mediators in balb/C splenic lymphocytes by dietary n−3 and n−6 fatty acids

The present study was designed to investigate the effect of diatery n−6 and n−3 polyunsaturated fatty acids (PUFA) on anti-CD3 and anti-Fas antibody-induced apoptosis and its mediators in mouse spleen cells. Nutritionally adequate semipurified diets containing either 5% w/w corn oil (n−6 PUFA) or fish oil (n−3 PUFA) were fed to weanling female Balb/C mice, and 24 wk later mice were sacrificed. In n−3 PUFA-fed mice, serum and splenocyte lipid peroxides were increased by 20 and 28.3% respectively, compared to n−6 PUFA-fed mice. Further, serum vitamin F levels were decreased by 50% in the n−3 PUFA-fed group, whereas higher anti0Fas- and anti-CD3-induced apoptosis (65 and 66%) and necrosis (17 and 25%), compared to the n−6 PUFA-fed group, were found when measured with Annexin V and propidium iodide staining, respectively. In addition, decreased Bcl-2 and increased Fas-ligand (Fas-L) also were observed in the n−3 PUFA-fed group compared to the n−6 PUFA-fed group. No difference in the ratio of splenocyte subsets nor their Fas expression was observed between the n−3 PUFA-fed and n−6 PUFA-fed groups, whereas decreased proliferation of splenocytes was found in n−3 PUFA-fed mice compared to n−6 PUFA-fed mice. In conclusion, our results indicate that dietary n−3 PUFA induces higher apoptosis by increasing the generation of lipid peroxides and elevating Fas-L expression along with decreasing Bcl-2 expression. A reduced proliferative response of immune cells also was observed in n−3 PUFA-fed mice.     

Polyunsaturated n−3 fatty acids and the development of atopic disease

The relationship between polyunsaturated long-chain fatty acids and atopy has been discussed for decades. Higher levels of the essential fatty acids linoleic acid and α-linolenic acid and lower levels of their longer metabolites in plasma phospholipids of atopic as compared to nonatopic individuals have been reported by several, but not all, studies. Largely similar findings have been reported in studies of cell membranes from immunological cells from atopics and nonatopics despite differences in methodology, study groups, and definitions of atopy. An imbalance in the metabolism of the n−6 fatty acids, particularly arachidonic acid and dihomo-γ-linolenic acid, leading to an inappropriate synthesis of prostaglandin (PG) E₂ and PGE₁ was hypothesized early on but has not been corroborated. The fatty acid composition of human milk is dependent on the time of lactation not only during a breast meal but also the time of the day and the period of lactation. This explains the discrepancies in reported findings regarding the relationship between milk fatty acids and atopic disease in the mother. Prospective studies show disturbances in both the n−6 and n−3 fatty acid composition between milk from atopic and nonatopic mothers. Only the composition of long-chain polyunsaturated n−3 fatty acids was related to atopic development in the children, however. A relationship between lower levels of n−3 fatty acids, particularly eicosapentaenoic acid (20∶5 n−3), and early development of atopic disease is hypothesized.     

Dietary n−3 polyunsaturated fatty acids increase T-lymphocyte phospholipid mass and acyl-CoA binding protein expression

Dietary flaxseed oil, which is enriched in α-linolenic acid, and fish oil, which is enriched inEPA and DHA, possess anti-inflammatory properties when compared with safflower oil, which is enriched in linoleic acid. The influence of flaxseed oil and fish oil feeding on lipid metabolism in T-lymphocytes is currently unknown. This study directly compared the effects of feeding safflower oil, flaxseed oil, and fish oil for 8 wk on splenic T-lymphocyte proliferation, phospholipid mass, and acyl-CoA binding protein expression in the rat. The data show that both flaxseed oil and fish oil increased acyl-CoA binding protein expression and phosphatidic acid mass in unstimulated T-lymphocytes when compared with safflower oil feeding. Fish oil feeding increased cardiolipin mass, whereas flaxseed oil had no effect. After stimulation, flaxseed oil and fish oil blunted T-lymphocyte interleukin-2 production and subsequent proliferation, which was associated with the lack of incraased acyl-CoA binding protein expression. The results reported show evidence for a novel mechanism by which dietary flaxseed oil and fish oil suppress T-lymphocyte proliferation via changes in acyl-CoA binding protein expression and phospholipid mass.     

Different kinetic in incorporation and depletion of n−3 fatty acids in erythrocytes and leukocytes of mice

n−3 PUFA are well known for their anti-inflammatory effects. However, there has been only limited study on the kinetics of incorporation and depletion of n−3 PUFA in immune cells. In the present study we investigated the incorporation and depletion of n−3 PUFA in erythrocytes and leukocytes in mice during a 6-wk feeding period. Over the first 3-wk period (the incorporation period) the mice were fed a special diet with a high n−3/n−6 PUFA ratio. In the following 3-wk period (the depletion period) the mice were fed a standard chow diet. A linear incease of the concentration of EPA and DHA in erythrocyte membranes was observed during the incorporation period, whereas a stagnation was observed after the second week for leukocytes. The level of EPA did not fall to the background level after the depletion period, and the level of DHA was kept almost constant during the depletion period in the erythrocyte membranes. In leukocytes the concentration of both EPA and DHA decreased during the depletion period, but did not reach the background level after the 3-wk depletion. In conclusion, the kinetics of EPA and DHA in the different cells are different. The rate of incorporation is faster than that of depletion for n−3 PUFA. More n−3 PUFA can be incorporated into leukocytes in comparison with erythrocytes. The ratio of n−3/n−6 PUFA is more important than the amount of n−3 FA in changing the FA compositions of membrane lipids.     

Whole-body utilization of n−3 PUFA in n−6 PUFA-deficient rats

We evaluated the utilization of α-linolenic acid (18∶3n−3) in growing rats consuming a diet deficient in n−6 PUFA. After 90 d, whole-body 18∶3n−3 accumulation was 55% lower, total n−3 PUFA accumulation was 21% lower, and 18∶3n−3 disappearance was 14% higher in n−6 PUFA-deficient rats. Part of the reduction of whole-body 18∶3n−3 in n−6 PUFA-deficient rats was due to the 25% increase in net conversion of 18∶3n−3 to long-chain n−3 PUFA. Despite adequate 18∶3n−3 intake, n−6 PUFA deficiency decreased the accumulation of 18∶3n−3 and total n−3 PUFA.     

Effects of ψ-linolenic acid and docosahexaenoic acid in formulae on brain fatty acid composition in artificially reared rats

This study evaluated the effects of dietary supple-mentation with ψ-linolenic acid (GLA, 18∶3n−6) and docosahexaenoic acid (DHA, 22∶6n−3) on the fatty acid composition of the neonatal brain in gastrostomized rat pups reared artificially from days 5–18. These pups were fed rat milk substitutes containing fats that provided 10% linoleic acid and 1% α-linolenic acid (% fatty acids) and, using a 2×3 factorial design, one of two levels of DHA (0.5 and 2.5%), and one of three levels of GLA (0.5, 1.0, and 3.0%). A seventh artificially reared groups served as a reference group and was fed 0.5% DHA and 0.5% arachidonic acid (AA, 20∶4n−6); these levels are within the range of those found in rat milk. The eighth group, the suckled control group, was reared by nursing dams fed a standard American Institute of Nutrition 93M chow. The fatty acid composition of the phosphatidylethanolamine, phosphatidyl-choline, and phosphatidylserine/phosphatidylinositol membrane fractions of the forebrain on day 18 reflected the dietary composition in that high levels of dietary DHA resulted in increases in DHA but decreases in 22∶4n−6 and 22∶5n−6 in brain. High levels of GLA increased 22∶4n−6 but, in contrast to previous findings with high levels of AA, did not decrease levels of DHA. These results suggest that dietary GLA, during development, differs from high dietary levels of AA in that it does not lead to reductions in brain DHA.     

Changes of the transcriptional and fatty acid profiles in response to n−3 fatty acids in SH-SY5Y neuroblastoma cells

Synthesis of docosahexaenoic acid (DHA) from its metabolic precursors contributes to membrane incorporation of this FA within the central nervous system. Although cultured neural cells are able to produce DHA, the membrane DHA contents resulting from metabolic conversion do not match the high values of those resulting from supplementation with preformed DHA. We have examined whether the DHA precursors down-regulate the incorporation of newly formed DHA within human neuroblastoma cells. SH-SY5Y cells were incubated with gradual doses of alpha-linolenic acid (alpha-LNA), EPA, or docosapentaenoic acid (DPA), and the incorporation of DHA into ethanolamine glycerophospholipids was analyzed as a reflection of synthesizing activity. The incorporation of EPA, DPA, and preformed DHA followed a dose-response saturating curve, whereas that of DHA synthesized either from alpha-LNA, EPA, or DPA peaked at concentrations of precursors below 15-30 microM and sharply decreased with higher doses. The mRNA encoding for six FA metabolism genes were quantified using real-time PCR. Two enzymes of the peroxisomal beta-oxidation, L-bifunctional protein and peroxisomal acyl-CoA oxidase, were expressed at lower levels than fatty acyl-CoA ligase 3 (FACL3) and delta6-desaturase (delta6-D). The delta6-D mRNA slightly increased between 16 and 48 h of culture, and this effect was abolished in the presence of 70 microM EPA. In contrast, the EPA treatment resulted in a time-dependent increase of FACL3 mRNA. The terminal step of DHA synthesis seems to form a "metabolic bottleneck," resulting in accretion of EPA and DPA when the precursor concentration exceeds a specific threshold value. We conclude that the critical precursor- concentration window of responsiveness may originate from the low basal expression level of peroxisomal enzymes.     

The electrophysiologic basis for the antiarrhythmic and anticonvulsant effects of n−3 polyunsaturated fatty acids: Heart and brain

The n?3 polyunsaturated fatty acids (PUFA) have been shown to be antiarrhythmic in animals and probably in humans. PUFA stabilize the electrical activity of isolated cardiac myocytes by modulating sarcolemmal ion channels, so that a stronger electrical stimulus is required to elicit an action potential and the refractory period is markedly prolonged. Inhibition of voltage-dependent sodium currents, which initiate action potentials in excitable tissues, and of the L-type calcium currents, which initiate release of sarcoplasmic calcium stores, thus increasing cytosolic free calcium concentrations and activating the contractile proteins in myocytes, appears at present to be the probable major antiarrhythmic mechanisms of PUFA. Because the ion channels in neurons have channel proteins essentially homologous to those in the heart, the n?3 fatty acids would appear to be likely to affect the electrical activity in the brain in a manner similar to their effects in the heart, and accumulating evidence supports this notion. Evidence of important beneficial neurological effects of dietary n?3 PUFA are emerging with more likely to be discovered.     

The metabolism and n−6/n−3 ratio of essential fatty acids in rats: Effect of dietary arachidonic acid and a mixture of sesame lignans (sesamin and episesamin)

In this study, we examined the effect of dietary arachidonic acid (AA) and sesame lignans on the content and n-6/n-3 ratio of polyunsaturated fatty acid (PUFA) in rat liver and the concentrations of triglyceride (TG) and ketone bodies in serum. For 4 wk, rats were fed two types of dietary oils: (i) the control oil diet groups (CO and COS): soybean oil/perilla oil=5∶1, and (ii) the AA-rich oil group (AO and AOS): AA ethyl esters/palm oil/perilla oil=2∶∶1, with (COS and AOS) or without (CO and AO) 0.5% (w/w) of sesame lignans. Dietary AA and sesame lignans significantly affected hepatic PUFA metabolism. AA content and n-6/n-3 ratio in the liver were significantly increased in the AO group, despite the dietary total of n-6 PUFA being the same in all groups, while AOS diet reduced AA content and n-6/n-3 ratio to a level similar to the CO and COS groups. These results suggest that (i) dietary AA considerably affects the hepatic profile and n-6/n-3 ratio of PUFA, and (ii) dietary sesame lignans reduce AA content and n-6/n-3 ratio in the liver. In the AO group, the concentration of acetoacetate was significantly increased, but the ratio of β-hydroxybutyrate/acetoacetate was decreased. On the other hand, the AO diet increased the concentration of TG in serum by almost twofold as compared to other groups. However, the AOS diet significantly reduced serum IG level as compared to the AO group. In addition, the AOS diet signicantly increased the acetoacetate level, but reduced the β-hydroxybutyrate/acetoacetate ratio. These results suggest that dietary sesame lignans promote ketogenesis and reduce PUFA esterification into TG. This study resulted in two findings: (i) sesame lignans inhibited extreme changes of the n-6/n-3 ratio by reducing hepatic PUFA content, and (ii) the reduction of hepatic PUFA content may have occurred because of the effects of sesame lignans on PUFA degradation (oxidation) and esterification.