Metabolism of hexacosatetraenoic acid (C26:4,n-6) in immature rat brain.

Rat brain was recently found to contain polyenoic very-long-chain fatty acids (VLCFA) belonging to the n-3 and n-6 series with four, five and six double bonds and even-carbon chain lengths from 24 to 38 [Robinson, Johnson & Poulos (1990) Biochem. J. 265, 763-767]. In the present paper, the metabolism in vivo of hexacosatetraenoic acid (C26:4,n-6) was studied in neonatal rat brain. Rats were injected intracerebrally with [1-14C]C26:4,n-6 and the labelled metabolites were examined after 4 h. Radioactivity was detected mainly in non-esterified fatty acids, with smaller amounts in other neutral lipids and phospholipids. Radiolabelled fatty acid products included C28-36 tetraenoic and C26-28 pentaenoic VLCFA formed by elongation and desaturation of the substrate, and C14-24 saturated, C16-24 monoenoic, C18-24 dienoic, C18-22 trienoic and C20-24 tetraenoic fatty acids formed from released [1-14C]acetate either by synthesis de novo or by elongation of endogenous fatty acids. The data suggest that polyenoic VLCFA are synthesized in brain from shorter-chain precursor fatty acids and undergo beta-oxidation.     

Sensitivity to alcohol in mice with an altered brain fatty acid composition

Ethanol-induced sleep onset times, sleep times and blood alcohol levels upon awakening were measured in mice fed an essential fatty acid deficient, Purina Chow or unsaturated fat diet for nine months. These values in animals fed the essential fatty acid deficient and Purina Chow diets did not differ, but mice fed the unsaturated fat diet had longer sleep times and lower blood alcohol levels upon awakening than mice fed essential fatty acid deficient or Purina Chow diets. Crude brain mitochondrial fractions isolated from mice fed the essential fatty acid deficient diet had decreased levels of docosahexaenoic [22:6(n-3)] and increased levels of eicosatrienoic [20:3(n-9)], docosatrienoic [22:3(n-9)] and docosapentaenoic [22:5(n-6)] acids compared to mice fed the Purina Chow diet. The unsaturated fat diet decreased 22:6(n-3) and increased 22:5(n-6) compared to the Purina Chow dietary regimen. The longer sleep times and lower blood alcohol levels found in mice fed the unsaturated fat diet probably resulted from an artifact due to the obesity of the mice fed this diet and from the hinderance of obesity to the righting reflex (our measure of ethanol potency). We conclude that the alteration of several polyunsaturated fatty acid components in the brain has little or no influence on the sensitivity of the nervous system to alcohol.     

Hydrogen isotopic fractionations during desaturation and elongation associated with polyunsaturated fatty acid biosynthesis in marine macroalgae

Compound-specific hydrogen isotopic compositions (deltaD) of saturated, monounsaturated and polyunsaturated fatty acids have been determined for natural marine macroalgae including two brown algae (Heterokontophyta) and two red algae (Rhodophyta). deltaD values of individual fatty acids from four macroalgae exhibit a wide variation ranging from -189% to +48%. Generally, stearic (18:0), arachidic (20:0) and behenic acids (22:0) are much more enriched in D by up to approximately 180% relative to myristic (14:0), palmitic (16:0), octatetraenoic [18:4(n-3)] and eicosapentaenoic acids [20:5(n-3)]. Other fatty acids such as oleic [18:1(n-9)], lenoleic [18:2(n-6)] and linolenic acids [18:3(n - 3)] fall isotopically between these fatty acids. This wide deltaD variation of fatty acids is probably explained by the hydrogen isotopic fractionation during desaturation being much larger than that during elongation in the network of polyunsaturated fatty acid biosynthesis. A large hydrogen isotopic fractionation during desaturation may cause D-enrichment in the remaining hydrogen of the residual fatty acids, which could be controlled by the relative flux into their desaturates.     

Effects of long-term supplementation of eicosapentanoic and docosahexanoic acid on the 2-, 3-series prostacyclin production by endothelial cells.

We studied the effects of polyunsaturated fatty, acids such as arachidonic acid [20:4 (n-6)], eicosapentanoic acid [EPA, 20:5 (n-3)], and docosahexanoic acid [DHA, 22:6 (n-3)] on the changes of lipid profiles and prostacyclin production by cultured bovine aortic endothelial cells. The amounts of 6-keto-prostaglandin F1alpha(6-keto-PGF1alpha) and delta17-6-keto-PGF1alpha, non-enzymatic metabolites of prostacyclin (PGI2 and PGI3) in culture medium were measured by gas chromatography/selected ion monitoring. Endothelial cells were supplemented for five passages with arachidonic acid, EPA, or DHA, and the fatty acids of cell lipids and prostacyclin production in cultured medium were quantified. From the fatty acid analysis, the amounts of docosapentaenoic acid [22:5 (n-3)] were significantly increased in EPA-grown cells. In DHA-grown cells, the amounts of EPA were slightly increased compared to control cells. These cells produced similar amounts of PGI2 as the controls, but larger amounts of PGI3 under basal conditions. These findings suggest that EPA, docosapentaenoic acid, and DHA are interconverted to each other, and anti-aggregatory effects of EPA or DHA may be partially due to the stimulation of prostacyclin formation in endothelial cells.     

LIPID CLASS DISTRIBUTION OF HIGHLY UNSATURATED LONG CHAIN FATTY ACIDS IN MARINE DINOFLAGELLATES

The very long chain highly unsaturated C₂₈ fatty acids, octacosaheptaenoic [28:7(n-6)] and octacosaoctaenoic acid [28:8(n-3)], were found to be associated with phospholipids, obtained by fractionation of total lipid extracts into distinct lipid classes, in 4 and 6, respectively, of 16 examined dinoflagellates. An interfraction comparison of fatty acids associated with phospholipids and glycolipids has also shown that the phospholipid fractions contained the majority (over 75% in 12 of 16 strains) of docosahexaenoic acid [22:6(n-3)] and traces of tetracosanoic acid (24:0). By contrast, the highly unsaturated C₁₈ fatty acids octadecatetraenoic [18:4(n-3)] and octadecapentaenoic acid [18:5(n-3)] were primarily recovered from a chloroplast-associated glycolipid fraction comprised of monogalactosyldiacylglycerol, digalactosyldiacylglycerol, and sulfoquinovosyldiacylglycerol. In 12 of 16 strains, an interfraction comparison showed that over 90% of 18:5(n-3) was found to be associated with glycolipids. These findings indicate that the C₂₈ fatty acids are located and probably synthesized in the cytoplasm or in an organelle other than the chloroplast, possibly with 22:6(n-3) and 24:0 as precursors, whereas the C₁₈ fatty acids 18:4(n-3) and 18:5(n-3) are glycolipid constituents apparently synthesized within the chloroplast. The function(s) of these C₂₈ fatty acids as components of phospholipids in cellular membranes is currently unknown.     

Unique molecular species of phosphatidylcholine containing very-long-chain (C24-C38) polyenoic fatty acids in rat brain.

Rat brain has been shown to contain polyenoic very-long-chain fatty acids (VLCFA) belonging to the n-3 and n-6 series with four, five and six double bonds and even-carbon chain lengths from 24 to 38. These fatty acids are almost exclusively located in unusual molecular species of phosphatidylcholine at the sn-1 position of the glycerol backbone, whereas saturated, monoenoic and polyenoic fatty acids with less than 24 carbon atoms are present at the sn-2 position. Polyenoic VLCFA phosphatidylcholine in neonatal rat brain is enriched with n-6 pentaenoic and n-3 hexaenoic VLCFA with up to 36 carbon atoms, whereas the corresponding phospholipid in adult rat brain mainly contains n-6 tetraenoic and n-3 pentaenoic VLCFA with up to 38 carbon atoms. The total amount of polyenoic VLCFA associated with phosphatidylcholine is highest in the brain of immature animals. Polyenoic VLCFA phosphatidylcholine appears to be predominantly confined to nervous tissue in rats, and it is envisaged that this phospholipid is of physiological significance.     

Recycling of docosahexaenoic acid in rat retinas during n-3 fatty acid deficiency.

About 50% of the fatty acids in retinal rod outer segments is docosahexaenoic acid [22:6(n-3)], a member of the linolenic acid [18:3(n-3)] family of essential fatty acids. Dietary deprivation of n-3 fatty acids leads to only modest changes in 22:6(n-3) levels in the retina. We investigated the mechanism(s) by which the retina conserves 22:6(n-3) during n-3 fatty acid deficiency. Weanling rats were fed diets containing 10% (wt/wt) hydrogenated coconut oil (no n-3 or n-6 fatty acids), linseed oil (high n-3, low n-6), or safflower oil (high n-6, less than 0.1% n-3) for 15 weeks. The turnover of phospholipid molecular species and the turnover and recycling of 22:6(n-3) in phospholipids of the rod outer segment membranes were examined after the intravitreal injection of [2-3H]glycerol and [4,5-3H]22:6(n-3), respectively. Animals were killed on selected days, and rod outer segment membranes, liver, and plasma were taken for lipid analyses. The half-lives (days) of individual phospholipid molecular species and total phospholipid 22:6(n-3) were calculated from the slopes of the regression lines of log specific activity versus time. There were no differences in the turnover rates of phospholipid molecular species among the three dietary groups, as determined by the disappearance of labeled glycerol. Thus, 22:6(n-3) is not conserved through a reduction in phospholipid turnover in rod outer segments. However, the half-life of [4,5-3H]22:6(n-3) in the linseed oil group (19 days) was significantly less than in the coconut oil (54 days) and safflower oil (not measurable) groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Brain astrocyte synthesis of docosahexaenoic acid from n-3 fatty acids is limited at the elongation of docosapentaenoic acid

The phospholipids, particularly phosphatidylethanolamine, of brain gray matter are enriched with docosahexaenoic acid (22:6n-3). The importance of uptake of preformed 22:6n-3 from plasma compared with synthesis from the alpha-linolenic acid (18:3n-3) precursor in brain is not known. Deficiency of 18:3n-3 results in a compensatory increase in the n-6 docosapentaenoic acid (22:5n-6) in brain, which could be formed from the precursor linoleic acid (18:2n-6) in liver or brain. We studied n-3 and n-6 fatty acid incorporation in brain astrocytes cultured in chemically defined medium using delipidated serum supplemented with specific fatty acids. High performance liquid chromatography with evaporative light scattering detection and gas liquid chromatography were used to separate and quantify cell and media lipids and fatty acids. Although astrocytes are able to form 22:6n-3, incubation with 18:3n-3 or eicosapentaenoic acid (20:5n-3) resulted in a time and concentration dependent accumulation of 22:5n-3 and decrease in 22:6n-3 g/g cell fatty acids. Astrocytes cultured with 18:2n-6 failed to accumulate 22:5n-6. Astrocytes secreted cholesterol esters (CE) and phosphatidylethanolamine containing saturated and monounsaturated fatty acids, and arachidonic acid (20:4n-6) and 22:6n-3. These studies suggest conversion of 22:5n-3 limits 22:6n-3 synthesis, and show astrocytes release fatty acids in CE.     

Coexpression with beta(1)-subunit modifies the kinetics and fatty acid block of hH1(alpha) Na(+) channels

Voltage-gated cardiac Na(+) channels are composed of alpha- and beta(1)-subunits. In this study beta(1)-subunit was cotransfected with the alpha-subunit of the human cardiac Na(+) channel (hH1(alpha)) in human embryonic kidney (HEK293t) cells. The effects of this coexpression on the kinetics and fatty acid-induced suppression of Na(+) currents were assessed. Current density was significantly greater in HEK293t cells coexpressing alpha- and beta(1)-subunits (I(Na,alpha beta)) than in HEK293t cells expressing alpha-subunit alone (I(Na,alpha)). Compared with I(Na,alpha), the voltage-dependent inactivation and activation of I(Na,alpha beta) were significantly shifted in the depolarizing direction. In addition, coexpression with beta(1)-subunit prolonged the duration of recovery from inactivation. Eicosapentaenoic acid [EPA, C20:5(n-3)] significantly reduced I(Na,alpha beta) in a concentration-dependent manner and at 5 microM shifted the midpoint voltage of the steady-state inactivation by -22 +/- 1 mV. EPA also significantly accelerated channel transition from the resting state to the inactivated state and prolonged the recovery time from inactivation. Docosahexaenoic acid [C22:6(n-3)], alpha-linolenic acid [C18:3(n-3)], and conjugated linoleic acid [C18:2(n-6)] at 5 microM significantly inhibited both I(Na,alpha beta) and I(Na,alpha.) In contrast, saturated and monounsaturated fatty acids had no effects on I(Na,alpha beta). This finding differs from the results for I(Na,alpha), which was significantly inhibited by both saturated and unsaturated fatty acids. Our data demonstrate that functional association of beta(1)-subunit with hH1(alpha) modifies the kinetics and fatty acid block of the Na(+) channel.     

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

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

The pathway from arachidonic to docosapentaenoic acid (20:4n-6 to 22:5n-6) and from eicosapentaenoic to docosahexaenoic acid (20:5n-3 to 22:6n-3) studied in testicular cells from immature rats

The concentration-dependent metabolism of 1-(14)C-labelled precursors of 22:5n-6 and 22:6n-3 was compared in rat testis cells. The amounts of [(14)C]22- and 24-carbon metabolites were measured by HPLC. The conversion of [1-(14)C]20:5n-3 to [3-(14)C]22:6n-3 was more efficient than that of [1-(14)C]20:4n-6 to [3-(14)C]22:5n-6. At low substrate concentration (4 microM) it was 3.4 times more efficient, reduced to 2.3 times at high substrate concentration (40 microM). The conversion of [1-(14)C]22:5n-3 to [1-(14)C]22:6n-3 was 1.7 times more efficient than that of [1-(14)C]22:4n-6 to [1-(14)C]22:5n-6 using a low, but almost equally efficient using a high substrate concentration. When unlabelled 20:5n-3 was added to a cell suspension incubated with [1-(14)C]20:4n-6 or unlabelled 22:5n-3 to a cell suspension incubated with [1-(14)C]22:4n-6, the unlabelled n-3 fatty acids strongly inhibited the conversion of [1-(14)C]20:4n-6 or [1-(14)C]22:4n-6 to [(14)C]22:5n-6. In the reciprocal experiment, unlabelled 20:4n-6 and 22:4n-6 only weakly inhibited the conversion of [1-(14)C]20:5n-3 and [1-(14)C]22:5n-3 to [(14)C]22:6n-3. The results indicate that if both n-6 and n-3 fatty acids are present, the n-3 fatty acids are preferred over the n-6 fatty acids in the elongation from 20- to 22- and from 22- to 24-carbon atom fatty acids. In vivo the demand for 22-carbon fatty acids for spermatogenesis in the rat may exceed the supply of n-3 precursors and thus facilitate the formation of 22:5n-6 from the more abundant n-6 precursors.     

Fatty acid incorporation is decreased in astrocytes cultured from alpha-synuclein gene-ablated mice

Because alpha-synuclein may function as a fatty acid binding protein, we measured fatty acid incorporation into astrocytes isolated from wild-type and alpha-synuclein gene-ablated mice. alpha-Synuclein deficiency decreased palmitic acid (16:0) incorporation 31% and arachidonic acid [20:4 (n-6)] incorporation 39%, whereas 22:6 (n-3) incorporation was unaffected. In neutral lipids, fatty acid targeting of 20:4 (n-6) and 22:6 (n-3) (docosahexaenoic acid) to the neutral lipid fraction was increased 1.7-fold and 1.6-fold, respectively, with an increase in each of the major neutral lipids. This was consistent with a 3.4- to 3.8-fold increase in cholesteryl ester and triacylglycerol mass. In the phospholipid fraction, alpha-synuclein deficiency decreased 16:0 esterification 39% and 20:4 (n-6) esterification 43% and decreased the distribution of these fatty acids, including 22:6 (n-3), into this lipid pool. alpha-Synuclein gene-ablation significantly decreased the trafficking of these fatty acids to phosphatidylinositol. This observation is consistent with changes in phospholipid fatty acid composition in the alpha-synuclein-deficient astrocytes, including decreased 22:6 (n-3) content in the four major phospholipid classes. In summary, these studies demonstrate that alpha-synuclein deficiency significantly disrupted astrocyte fatty acid uptake and trafficking, with a marked increase in fatty acid trafficking to cholesteryl esters and triacylglycerols and decreased trafficking to phospholipids, including phosphatidylinositol.     

Incorporation into phospholipid classes and metabolism via desaturation and elongation of various 14C-labelled (n-3) and (n-6) polyunsaturated fatty acids in trout astrocytes in primary culture

The incorporation and metabolism of [1-14C]18:3(n-3), [1-14C]20:5(n-3), [1-14C]18:2(n-6), and [1-14C]20:4(n-6) were studied in primary cultures of trout brain astrocytes. There were no significant differences between the amounts of individual fatty acids incorporated into total lipid at 22 degrees C, with greater than 90% of all the fatty acids being incorporated into polar lipid classes. The distributions of 18:2(n-6), 18:3(n-3), and 20:5(n-3) in individual phospholipid classes at 22 degrees C were very similar, with 57-63 and 18-24% being incorporated into phosphatidylcholine and phosphatidylethanolamine, respectively. Approximately equal amounts of 20:4(n-6), approximately 30% of the total, were incorporated into each of phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol. The metabolism of the (n-3) fatty acids to longer-chain and more unsaturated species was significantly greater than that of (n-6) acids, but delta 4-desaturase activity was very low. A culture temperature of 10 degrees C increased the incorporation of all the fatty acids into total lipid and that of C20 fatty acids into polar lipid. At 10 degrees C, the incorporation of C20 fatty acids into phosphatidylethanolamine and phosphatidylinositol was increased, and the incorporation into phosphatidylcholine and phosphatidylserine was decreased. The distribution of C18 fatty acids was unchanged at the lower temperature, as was the desaturation and elongation of all the polyunsaturated fatty acids incorporated.     

Selective incorporation of various C-22 polyunsaturated fatty acids in Ehrlich ascites tumor cells

Three 14C-labeled 22-carbon polyunsaturated fatty acids, 7,10,13,16-[14C]docosatetraenoic acid (22:4(n-6)), 7,10,13,16,19-[14C]docosapentaenoic acid (22:5(n-3)), and 4,7,10,13,16,19-[14C]docosahexaenoic acid (22:6(n-3)), were compared with [3H]arachidonic acid (20:4(n-6] and [14C]linoleic acid (18:2(n-6)) to characterize their incorporation into the lipids of Ehrlich ascites cells. The relatively rapid incorporation of the labeled 22-carbon acids into phosphatidic acid indicated that substantial amounts of these acids may be incorporated through the de novo pathway of phospholipid synthesis. In marked contrast to 20:4(n-6), the 22-carbon acids were incorporated much less into choline glycerophospholipids (CGP) and inositol glycerophospholipids (IGP). No selective preference was apparent for the (n-3) or (n-6) type of fatty acids. The amounts of the acids incorporated into diacylglycerophosphoethanolamine were in the order of: 22:6(n-3) greater than 20:4(n-6) much greater than 22:5(n-3) greater than or equal to 22:4(n-6) greater than 18:2(n-6), whereas for alkylacylglycerophosphoethanolamine they were in the order of: 22:4(n-6) greater than 22:6(n-3) greater than 22:5(n-3) much greater than 20:4(n-6) greater than 18:2(n-6). Of the mechanisms possibly responsible for the selective entry of 22-carbon acids into ethanolamine glycerophospholipids, the most reasonable explanation was that the cytidine-mediated ethanolamine phosphotransferase may have a unique double selectivity: for hexaenoic species of diacylglycerol and for 22-carbon polyunsaturated fatty acid-containing species of alkylacylglycerol. The relative distribution of fatty acids between newly incorporated and already maintained lipid classes suggested that IGP may function in Ehrlich cells as an intermediate pool for the retention of polyunsaturated fatty acids in glycerolipids.     

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.     

The Zellweger syndrome: deficient conversion of docosahexaenoic acid (22:6(n-3)) to eicosapentaenoic acid (20:5(n-3)) and normal delta 4-desaturase activity in cultured skin fibroblasts

The metabolism of docosahexaenoic acid (22:6(n-3)) and adrenic acid (22:4(n-6)) was studied in cultured fibroblasts from patients with the Zellweger syndrome, X-linked adrenoleukodystrophy (X-ALD) and normal controls. It was shown that [4,5- 3H]22:6(n-3) is retroconverted to labelled eicosapentaenoic acid (20:5(n-3)) in normal and X-ALD fibroblasts, while this conversion is deficient in Zellweger fibroblasts. [U- 14C]Eicosapentaenoic acid (20:5(n-3)) is elongated to docosapentaenoic acid (22:5(n-3)) in all three cell lines. With [U- 14C]20:5(n-3) as the substrate, shorter fatty acids were not detected. With [4,5- 3H]22:6(n-3) as the substrate, labelled fatty acids were esterified in the phospholipid- and triacylglycerol-fraction to approximately the same extent in all three cell lines. [2- 14C]Adrenic acid (22:4(n-6)) was desaturated to 22:5(n-6) and elongated to 24:4(n-6) in all three cell lines and to the largest extent in the Zellweger fibroblasts. This agrees with the view that the delta 4-desaturase is not a peroxisomal enzyme. The observation that the retroconversion of 22:6(n-3) to 20:5(n-3) is deficient in Zellweger fibroblasts strongly suggest that the beta-oxidation step in the retroconversion is a peroxisomal function. Peroxisomal very-long-chain (lignoceroyl) CoA ligase is probably not required for the activation of 22:6(n-3), since the retroconversion to 20:5(n-3) is normal in X-ALD fibroblasts.     

Intestinal responsiveness to experimental colitis in young rats is altered by maternal diet

Increasing evidence suggests that fetal and neonatal nutrition impacts later health. Aims of the present study were to determine the effect of maternal dietary fat composition on intestinal phospholipid fatty acids and responsiveness to experimental colitis in suckling rat pups. Female rats were fed isocaloric diets varying only in fat composition throughout gestation and lactation. The oils used were high (8%) in n-3 [canola oil (18:3n-3)], n-6 (72%) [safflower oil (18:2n-6)], or n-9 (78%) [high oleic acid safflower oil (18:1n-9)] fatty acids, n = 6/group. Colitis was induced on postnatal day 15 by intrarectal 2,4-dinitrobenzene sulfonic acid (DNBS) administration with vehicle (50% ethanol) and procedure (0.9% saline) controls. Jejunal and colonic phospholipids and milk fatty acids were determined. The distal colon was assessed for macroscopic damage, histology, and MPO activity. The 18:2n-6 maternal diet increased n-6 fatty acids, whereas the 18:3n-3 diet increased n-3 fatty acids in milk and pup jejunal and colonic phospholipids. Maternal diet, milk, and pup intestinal n-6-to-n-3 fatty acid ratios increased significantly in order: high 18:3n-3 < high 18:1n-9 < high 18:2n-6. DNBS administration in pups in the high 18:2n-6 group led to severe colitis with higher colonic damage scores and MPO activity than in the 18:1n-9 and 18:3n-3 groups. High maternal dietary 18:3n-3 intake was associated with colonic damage scores and MPO activity, which were not significantly different from ethanol controls. We demonstrate that maternal dietary fat influences the composition of intestinal lipids and responsiveness to experimental colitis in nursing offspring.     

Adrenoleukodystrophy. The chain shortening of erucic acid (22:1(n-9)) and adrenic acid (22:4(n-6)) is deficient in neonatal adrenoleukodystrophy and normal in X-linked adrenoleukodistrophy skin fibroblasts

The metabolism of long chain unsaturated fatty acids was studied in cultured fibroblasts from patients with X-linked adrenoleukodystrophy (ALD) and with neonatal ALD. By using [14-14C] erucic acid (22:1(n-9)) as substrate it was shown that the peroxisomal beta-oxidation, measured as chain shortening, was impaired in cells from patients with neonatal ALD. The beta-oxidation of adrenic acid (22:4(n-6)), measured as acid-soluble products, was also reduced in the neonatal ALD cells. The peroxisomal beta-oxidation of [14-14C]erucic acid (22:1(n-9)) and [2-14C]adrenic acid (22:4(n-6)) was normal in cells from X-ALD patients. The beta-oxidation, esterification and chain elongation of [1-14C]arachidonic acid (20:4(n-6)) and [1-14C]eicosapentaenoic acid (20:5(n-3)) was normal in both X-linked ALD and in neonatal ALD. Previous studies suggest that the activation of very long chain fatty acids by a lignoceryl (24:0)-CoA ligase is deficient in X-linked ALD, while the peroxisomal beta-oxidation enzymes are deficient in neonatal ALD. The present results suggest that the peroxisomal very long-chain acyl-CoA ligase is not required for activation of unsaturated C20 and C22 fatty acids and that these fatty acids can be efficiently activated by the long chain acyl-(palmityl)-CoA ligase.     

Fatty acid utilisation and metabolism in caecal enterocytes of rainbow trout (Oncorhynchus mykiss) fed dietary fish or copepod oil

A combined fatty acid metabolism assay was employed to determine fatty acid uptake and relative utilisation in enterocytes isolated from the pyloric caeca of rainbow trout. In addition, the effect of a diet high in long-chain monoenoic fatty alcohols present as wax esters in oil derived from Calanus finmarchicus, compared to a standard fish oil diet, on caecal enterocyte fatty acid metabolism was investigated. The diets were fed for 8 weeks before caecal enterocytes from each dietary group were isolated and incubated with [1-14C]fatty acids: 16:0, 18:1n-9, 18:2n-6, 18:3n-3, 20:1n-9, 20:4n-6, 20:5n-3, and 22:6n-3. Uptake was measured over 2 h with relative utilisation of different [1-14C]fatty acids calculated as a percentage of uptake. Differences in uptake were observed, with 18:1n-9 and 18:2n-6 showing the highest rates. Esterification into cellular lipids was highest with 16:0 and C18 fatty acids, accounting for over one-third of total uptake, through predominant incorporation in triacylglycerol (TAG). The overall utilisation of fatty acids in phospholipid synthesis was low, but highest with 16:0, the most prevalent fatty acid recovered in intracellular phosphatidylcholine (PC) and phosphatidylinositol (PI), although exported PC exhibited higher proportions of C20/C22 polyunsaturated fatty acids (PUFA). Other than 16:0, incorporation into PC and PI was highest with C20/C22 PUFA and 20:4n-6 respectively. Recovery of labelled 18:1n-9 in exported TAG was 3-fold greater than any other fatty acid which could be due to multiple esterification on the glycerol 'backbone' and/or increased export. Approximately 20-40% of fatty acids taken up were beta-oxidised, and was highest with 20:4n-6. Oxidation of 20:5n-3 and 22:6n-3 was also surprisingly high, although 22:6n-3 oxidation was mainly attributed to retroconversion to 20:5n-3. Metabolic modification of fatty acids by elongation-desaturation was generally low at <10% of [1-14C]fatty acid uptake. Dietary copepod oil had generally little effect on fatty acid metabolism in enterocytes, although it stimulated the elongation and desaturation of 16:0 and elongation of 18:1n-9, with radioactivity recovered in longer n-9 monoenes. The monoenoic fatty acid, 20:1n-9, abundant in copepod oil as the homologous alcohol, was poorly utilised with 80% of uptake remaining unesterified in the enterocyte. However, the fatty acid composition of pyloric caeca was not influenced by dietary copepod oil.