Docosahexaenoic acid-containing phospholipid molecular species in brains of vertebrates.

The fatty acid composition of phospholipids and the contents of docosahexaenoic acid (DHA)-containing diacyl phosphatidylcholine and diacyl phosphatidylethanolamine molecular species were determined from brains of five fresh-water fish species from a boreal region adapted to 5 degrees C, five fresh-water fish species from a temperate region acclimated to 5 degrees C, five fresh-water fish species from a temperate region acclimated to 20 degrees C, and three fresh water fish species from a subtropic region adapted to 25-26 degrees C, as well as six mammalian species and seven bird species. There was little difference in DHA levels of fish brains from the different thermal environments; mammalian and bird brain phospholipids contained a few percentage points less DHA than those of the fish investigated. Molecular species of 22:6/22:6, 22:6/20:5, 22:6/20:4, 16:0/22:6, 18:0/22:6, and 18:1/22:6 were identified from all brain probes, and 16:0/22:6, 18:0/22:6, and 18:1/22:6 were the dominating species. Cold-water fish brains were rich in 18:1/22:6 diacyl phosphatidylethanolamine (and, to a lesser degree, in diacyl phosphatidylcholine), and its level decreased with increasing environmental/body temperature. The ratio of 18:0/22:6 to 16:0/22:6 phosphatidylcholine and phosphatidylethanolamine was inversely related to body temperature. Phospholipid vesicles from brains of cold-acclimated fish were more fluid, as assessed by using a 1, 6-diphenyl-1,3,5-hexatriene fluorescent probe, than those from bird brains, but the fluidities were almost equal at the respective body temperatures. It is concluded that the relative amounts of these molecular species and their ratios to each other are the major factors contributing to the maintenance of proper fluidity relationships throughout the evolutionary chain as well as helping to maintain important brain functions such as signal transduction and membrane permeability.

Health benefits of docosahexaenoic acid (DHA)

Docosahexaenoic acid (DHA) is essential for the growth and functional development of the brain in infants. DHA is also required for maintenance of normal brain function in adults. The inclusion of plentiful DHA in the diet improves learning ability, whereas deficiencies of DHA are associated with deficits in learning. DHA is taken up by the brain in preference to other fatty acids. The turnover of DHA in the brain is very fast, more so than is generally realized. The visual acuity of healthy, full-term, formula-fed infants is increased when their formula includes DHA. During the last 50 years, many infants have been fed formula diets lacking DHA and other omega-3 fatty acids. DHA deficiencies are associated with foetal alcohol syndrome, attention deficit hyperactivity disorder, cystic fibrosis, phenylketonuria, unipolar depression, aggressive hostility, and adrenoleukodystrophy. Decreases in DHA in the brain are associated with cognitive decline during aging and with onset of sporadic Alzheimer disease. The leading cause of death in western nations is cardiovascular disease. Epidemiological studies have shown a strong correlation between fish consumption and reduction in sudden death from myocardial infarction. The reduction is approximately 50% with 200 mg day(-1)of DHA from fish. DHA is the active component in fish. Not only does fish oil reduce triglycerides in the blood and decrease thrombosis, but it also prevents cardiac arrhythmias. The association of DHA deficiency with depression is the reason for the robust positive correlation between depression and myocardial infarction. Patients with cardiovascular disease or Type II diabetes are often advised to adopt a low-fat diet with a high proportion of carbohydrate. A study with women shows that this type of diet increases plasma triglycerides and the severity of Type II diabetes and coronary heart disease. DHA is present in fatty fish (salmon, tuna, mackerel) and mother's milk. DHA is present at low levels in meat and eggs, but is not usually present in infant formulas. EPA, another long-chain n-3 fatty acid, is also present in fatty fish. The shorter chain n-3 fatty acid, alpha-linolenic acid, is not converted very well to DHA in man. These longchain n-3 fatty acids (also known as omega-3 fatty acids) are now becoming available in some foods, especially infant formula and eggs in Europe and Japan. Fish oil decreases the proliferation of tumour cells, whereas arachidonic acid, a longchain n-6 fatty acid, increases their proliferation. These opposite effects are also seen with inflammation, particularly with rheumatoid arthritis, and with asthma. DHA has a positive effect on diseases such as hypertension, arthritis, atherosclerosis, depression, adult-onset diabetes mellitus, myocardial infarction, thrombosis, and some cancers.

Ether lipid composition and molecular species alterations in carp brain (Cyprinus carpio L.) during normoxic temperature acclimation.

Carp (Cyprinus carpio L.) whole brain was used to investigate the thermal acclimation changes under normoxic conditions of three-subclasses (alkenylacyl-, alkylacyl- and diacyl-subclasses) of choline glycerophospholipids (CGP), ethanolamine glycerophospholipids (EGP) and inositol glycerophospholipids (IGP) as well as their acyl chain profiles and molecular species composition. The alkenylacyl subclass of CGP and IGP and the alkylacyl subclass of CGP and EGP varied significantly during summer (25 degrees C) acclimation compared to winter (5 degrees C). The levels of alkenylacyl and alkylacyl-CGP, alkylacyl-EGP and alkenylacyl-IGP were 17.3-, 3.7-, 3.5- and 1.3-fold higher in the summer, respectively, while the alkenylacyl EGP was moderately lower. The levels of diacyl subclasses from CGP and IGP were considerably lower in the summer to compensate for the higher proportion of alkenylacyl and alkylacyl subclasses. Significant changes of ether phospholipids and the reorganization of the molecular species composition of all lipid subclasses may be associated with the "fine tuning" of the physical properties of the cellular membranes in carp brain due to temperature acclimation. The overall acyl chain profile of the three subclasses of carp brain phospholipids showed differences in composition depending upon the subclass of the individual phospholipid. Generally the polyunsaturated fatty acid (PUFA) chain composition increased relative to monounsaturated fatty acid (MUFA) and saturated fatty acids (SFA) during winter acclimation. Docosahexaenoic acid (DHA) was richer in the winter compared to summer. However, no DHA was found in ether-containing species of IGP from either winter or summer, except for 2% in alkylacyl-IGP during the summer. The above observations suggest that the content of ether phospholipids (alkenylacyl and alkylacyl) as well as the reorganization of the molecular species composition of all phospholipids may serve to maintain a functional fluid-crystalline state to preserve the signaling functions in carp brain.

Dietary alpha-linolenic acid increases the biosynthesis of the choline glycerophospholipids from [14C]CDPcholine in rat liver and kidney but not in brain.

The effect of feeding rats for 30 days with diets containing high levels of linoleic acid (sunflower oil, SO) or alpha-linolenic acid (perilla oil, PO) was studied in the liver, kidney and brain. The PO group showed a higher labeling of choline glycerophospholipids (CGP) in liver and kidney but no difference with the SO group in ethanolamine glycerophospholipids (EGP) labeling. The brain displayed the lowest incorporation of both precursors and no difference between the two diets. Analyses of brain CGP and EGP fatty acid composition showed that in the PO group the ratio n-6/n-3 was lower than in the SO group, mainly as a consequence of lower levels of n-6 fatty acids. The mole % of docosahexaenoate (DHA) in these lipids was the same for both groups and only triacylglycerols (TAG) displayed a higher DHA. Therefore, at least in the brain, the magnitude of fatty acid changes observed in CGP and EGP for the PO group does not affect the uptake/incorporation of the precursors into phospholipids.

Changes in ether-linked phospholipids in rat kidney by dietary alpha-linolenic acid in vivo.

We investigated the effects of perilla oil containing a high level of alpha-linolenic acid on in vivo phospholipid metabolism, particularly three subclasses of choline glycerophospholipids (CGP) and ethanolamine glycerophospholipids (EGP), in rat kidney. After three weeks of feeding, a significantly lower proportion (by 35%) of the alkylacyl subclass of CGP was found in the perilla oil, as compared to corn oil-fed animals. The alkylacyl species of EGP was also higher in the perilla oil than in the corn oil-fed animals. These alterations were accompanied by a remarkably lower proportion of arachidonic acid and a higher level of eicosapentaenoic acid (EPA) in all six subclasses of CGP and EGP in the perilla oil-fed animals. The levels of linoleic acid were even higher in the diacyl subclasses of CGP and EGP in the perilla oil group, suggesting that desaturase and elongase enzymes prefer n-3 to n-6 fatty acids as substrates for diacyl species. These data are useful in defining the effects of alpha-linolenic acid on the biosynthesis of renal phospholipids and on the replacement of n-6 with n-3 fatty acids in the six CGP and EGP subclasses.

The Thrombostat system. A useful method to test antiplatelet drugs and diets.

UNLABELLED: The use of platelet inhibitory drugs, like aspirin, has resulted in a significant reduction of thrombotic complications in primary and secondary prevention of heart attacks. To find more effective substances or better drug combinations, inhibition of primary hemostasis in vitro (Thrombostat system) was investigated, with different drugs and fish diet, using small samples (1 ml) of anticoagulated (Na- citrate 3.8%, 1/9) human blood. RESULTS: 1. In the presence of 1 mM aspirin, which had no effect on bleeding volume, only 0.6 nM iloprost were necessary to show a 50% inhibition, in contrast to 2.5 nM without aspirin. 2. At aspirin concentrations of 1 mM, 50% inhibition of primary hemostasis could be achieved with 20 microM SIN-1, or with 7 microM SIN-1 together with iloprost (500 pM). The same effect was seen only with very high doses of SIN-1 (1000 microM) alone. 3. For 50% inhibition of primary hemostasis in vitro, RGDS concentrations were reduced from 250 microM to 160 microM when blood was pretreated with 1 mM aspirin and to 75 microM when 500 pM iloprost were added additionally. 4. Japanese fishermen (eating 270 g fish/day) demonstrated significantly longer in-vivo bleeding times and in-vitro bleeding volumes (6.49 min/224 microliters), respectively, as compared to Japanese farmers (90 g fish/day, 4.85 min/137 microliters). 5. In Japanese subjects in-vivo bleeding times correlated with in-vitro bleeding volumes (0.69). The Thrombostat system proved to be a sensitive method to detect synergistic effects of various antiplatelet drugs in vitro and of a platelet inhibitory diet ex vivo.

Structural order of membranes and composition of phospholipids in fish brain cells during thermal acclimatization.

A comparison of the structural orders of membranes of a mixed brain-cell population isolated from Cyprinus carpio L. acclimated to either summer (23-25 degrees C) or winter (5 degrees C) revealed a high degree of compensation (80%) for temperature, as assayed by electron spin resonance spectroscopy. The cells rapidly forget their thermal history and adjust the physical properties of the membranes when shifted to the other extreme of temperature either in vivo or in vitro. Phospholipids separated from both types of animals exhibit only around 10% compensation. Arachidonic and docosahexaenoic acids are the major polyunsaturated fatty acids in the brains, but the fatty acid composition of the brain total phospholipids does not vary with adaptation to temperature. Separation of phosphatidylcholines and phosphatidylethanolamines into molecular species revealed a 2- to 3-fold accumulation of 18:1/22:6, 18:1/20:4, and 18:1/18:1 species in the latter; 18:0/22:6 showed an opposite tendency. Molecular species composition of phosphatidylcholines did not vary with the temperature. The same trends of changes were seen with brains of freshwater fish from subtropical (Catla catla L.) or boreal (Acerina cernua) regions. It is concluded that the gross amount of docosahexaenoic acid (22:6) plays only a minor role in adjusting the membrane physical properties to temperature. Factors other than lipids might be involved in the adaptation processes. Due to their specific molecular architecture, molecules such as 18:1/22:6, 18:1/20:4, or 18:1/18:1 phosphatidylethanolamine might prevent the contraction of membranes in the cold and may provide an environment for some other components involved in the temperature regulation of physical properties of nerve cell membranes.

Influence of dietary fish oil on the relative synthesis of triacylglycerol and phospholipids in rat liver in vivo.

The influence of dietary fish oil containing n-3 polyunsaturated fatty acids on the biosynthesis of triacylglycerol relative to total individual phospholipids was studied in rat liver in vivo. The dietary lipid (10% by weight of diet) was either sunflower oil enriched in linoleic acid (SO group) or MaxEPA fish oil/sunflower oil, 9:1 by weight (FO group) enriched in eicosapentaenoic acid (EPA, 20:5n-3) plus docosahexaenoic acid (DHA, 22:6n-3). After a 3-week feeding period, the triacylglycerol content (in mumol/g liver) was 44% lower in the FO group relative to the SO animals. The in vivo incorporation of [3H]glycerol into individual hepatic lipids resulted in triacylglycerol/total phospholipid radioactivity ratios of 2.1 and 0.9 for the SO and FO groups, respectively. These results indicate an inhibitory effect of dietary EPA/DHA on triacylglycerol relative to phospholipid synthesis from intermediary 1,2-diacylglycerol in rat liver in vivo. This metabolic alteration was accompanied by a substantially lower amount (in mumol/g liver) of arachidonic acid and higher levels of EPA plus DHA in the triacylglycerol, choline glycerophospholipid (CGP), and ethanolamine glycerophospholipid (EGP) of the FO group. A moderately higher labelling of the EGP from [3H]glycerol was observed in the FO as compared to the SO group (as evidenced by CGP/EGP radioactivity ratios of 1.3:1 and 1.8:1, respectively). The present study provides in vivo evidence for a dampening effect of dietary fish oil on the synthesis of liver triacylglycerol relative to phospholipid and a moderate alteration of de novo synthesis of individual phospholipids.

Effects of dietary n - 3 fatty acids on mass changes and [3H]glycerol incorporation in various glycerolipid classes of rat kidney in vivo.

The effects of dietary fish oil containing n - 3 polyunsaturated fatty acids on triacylglycerol synthesis and phospholipid metabolism (including the alkylacyl subclass of choline glycerophospholipids (CGP)) was studied in rat kidney in vivo. After a 3 week feeding period, the triacylglycerol content (in mumol/g kidney) was 47% lower in the fish oil group relative to animals given sunflower oil. This alteration was accompanied by a substantially lower amount of arachidonic acid (20:4(n - 6)) and higher level (mumol/g tissue) of eicosapentaenoic acid (20:5(n - 3)) plus docosahexaenoic acid (22:6(n - 3)) in the triacylglycerol, CGP, and ethanolamine glycerophospholipids (EGP) of the fish oil group. The labelling of triacylglycerol relative to phospholipid from [3H]glycerol following i.p. administration was 49% lower in the fish oil as compared to the sunflower oil group, indicating a suppression of renal triacylglycerol synthesis relative to phospholipid synthesis. Modest differences in the labelling of CGP and EGP were found. A moderate and significantly lower proportional labelling (by 35%) of the alkylacyl subclass of CGP was observed in the fish oil as compared to the sunflower oil animals. These findings may have relevance to eicosanoid and platelet activating factor (PAF) biosyntheses as well as renal function and pathophysiology.

The effect of long-term consumption of fish oil on platelet-activating factor synthesis in rat renal microsomes.

The effect of consuming eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA) on platelet-activating factor (PAF) biosynthesis by renal acetyl-CoA: 1-O-alkyl-sn-glycero-3-phosphocholine (lysoPAF) acetyltransferase activity was compared in rats fed diets containing fish oil (FO) or sunflower oil (SO) for 11 months. Microsomes from the FO group exhibited a significantly lower formation of [14C]PAF from [1-14C]acetyl-CoA in the absence of exogenously-added lysoPAF. There were no differences between the two groups in the generation of radioactive acylacetyl-glycerophosphocholine (GPC) upon incubation of microsomes without added lysoPAF. Upon addition of lysoPAF, the microsomal synthesis of PAF, but not acylacetyl-GPC, rose considerably. Furthermore, PAF synthesis via microsomal acetyltransferase activity in the FO-fed animals was only 40% that of the SO groups. These findings may bear potential relevance in terms of reducing PAF synthesis in association with renal pathophysiology.

Altered acyl chain compositions of alkylacyl, alkenylacyl, and diacyl subclasses of choline and ethanolamine glycerophospholipids in rat heart by dietary fish oil.

The effects of dietary fish oil containing n - 3 polyunsaturated fatty acids on the fatty acid compositions of the alkylacyl and alkenylacyl species of choline glycerophospholipids (CGP) and ethanolamine glycerophospholipids (EGP) were studied in rat heart and compared with the corresponding diacylglycerophospholipids. After a 7 week feeding period, all phospholipid classes from the fish oil group exhibited much higher levels of the n - 3 polyunsaturated fatty acids including eicosapentaenoic acid (20:5(n - 30)), docosapentaenoic acid (22:5(n - 3)) and docosahexaenoic acid (22:6(n - 3)), as well as lower levels of the n - 6 series (18:2, 20:4, 22:4 and 22:5), relative to animals given sunflower seed oil-enriched in 18:2(n - 6). However, the docosahexaenoic acid rather than eicosapentaenoic acid provided a much greater contribution to the n - 3 accumulation (fish oil group) in the ether-containing CGP, as indicated by the 20:5(n - 3)/22:6(n - 3) molar ratios of 0.32, 0.26 and 0.56 in the alkylacyl, alkenylacyl and diacyl classes, respectively. In addition to accumulating very high levels of docosahexaenoic acid (e.g., 47.2 mol% of fatty acids in alkenylacylglycerophosphoethanolamine of fish oil group), both ether-linked classes of EGP exhibited significantly higher levels of docosapentaenoic acid than the diacylglycerophosphoethanolamine (GPE) and all classes of CGP. These findings may bear relevance to possible beneficial effects of dietary fish oil on pathophysiological states (including myocardial ischemia) in cardiac tissue and their mediation via platelet-activating factor, 1-alkyl-2-acetylglycerophosphocholine (PAF) and arachidonic acid (20:4(n - 6))-derived eicosanoids.