(n−3) and (n−6) polyunsaturated fatty acids in the phosphoglycerides of salt-secreting epithelia from two marine fish species

Fatty acid analyses were carried out on phosphoglycerides isolated from microsomal fractions of the rectal gland of the dogfish,Scyliorthinus canicula, and gills of the cod,Gadus morhua. Ratios of (n−3)/(n−6) polyunsaturated fatty acids were ca. 10 for phosphatidylcholine, (PC), phosphatidylethanolamine (PE) and phosphatidylserine (PS) from cod gills, reflecting high concentrations of 20∶5 (n−3) and 22∶6(n−3). The ratio for phosphatidylinositol (PI) from cod gills was 1.3, reflecting high concentrations of 20∶4(n−6) as well as (n−3) polyunsaturates. PC, PE and PS from rectal glands all had much lower (n−3)/(n−6) ratios than in cod gills, reflecting higher concentrations of 20∶4(n−6), but the lowest ratio was again present in PI. The latter phospholipid had high concentrations of 18∶0 in both tissues. The relative constancy of the fatty acid composition of PI in the two salt-secreting tissues and its similarity to mammalian phospholipids is considered to reflect its specialized role in biomembranes.     

The effect of borage oil consumption on the composition of individual phospholipids in human platelets

The effect of supplementation with borage oil containing γ-linolenic acid (GLA, 18∶3n−6) on the levels and fattya cid compositions of individual human platelet phospholipids was evaluated. For this purpose, male volunteers were given an average daily intake of 5.23 g of GLA (as borage oil) for 42 days, after which the supplement was withdrawn for an additional 42-day period. No significant differences were found in the relative amounts of the choline phospholipids (PC), ethanolamine phospholipids (PE), phosphatidylserine (PS), phosphatidylinositol (PI), and sphingomyelin (SPH) at days 0, 22, 43, 64, and 85. However, marked differences were observed in the fatty acid compositions of all the phospholipids including a marked, and reversible, rise in the level of dihomo-γ-linolenic acid (DGLA, 20∶3n−6), without a significant elevation in arachidonic acid (AA, 20∶4n−6) and decreases in n−3 polyunsaturated fatty acids. In the case of PC, a net rise in DGLA of 1.8 mol% was observed by day 22 (from 2.1 to 3.9 mol%). The DGLA/AA ratios at day 43 exhibited considerable variability across phospholipids with PC>PS>PE=PI; the PC, PE, PS, and PI accounted for 67.6, 16.7, 12.9, and 2.6%, respectively, of the total DGLA in platelet phospholipids. Interestingly, despite the lack of DGLA in SPH, this phospholipid exhibited a marked enrichment in nervonic acid (NA, 24∶1n−9) from 16.2 to 24.7 mol% upon borage oil consumption. The observed alterations may represent biochemical strategies for adaptation to dietary fatty acid modifications and the regulation of platelet membrane functioning.     

Effects of dietary saturated fat on erucic acid induced myocardial lipidosis in rats

Male Sprague-Dawley rats were fed for one week diets containing 20% by weight fat/oil mixtures with different levels of erucic acid (22∶1n−9) (∼2.5 or 9%) and total saturated fatty acids (∼8 or 35%). Corn oil and high erucic acid rapeseed (HEAR) oil were fed as controls. The same hearts were evaluated histologically using oil red O staining and chemically for cardiac triacylglycerol (TAG) and 22∶1n−9 content in cardiac TAG to compare the three methods for assessing lipid accumulation in rat hearts. Rats fed corn oil showed trace myocardial lipidosis by staining, and a cardiac TAG content of 3.6 mg/g wet weight in the absence of dietary 22∶1n−9. An increase in dietary 22∶1n−9 resulted in significantly increased myocardial lipidosis as assessed histologically and by an accumulation of 22∶1n−9 in heart lipids; there was no increase in cardiac TAG except when HEAR oil was fed. An increase in saturated fatty acids showed no changes in myocardial lipid content assessed histologically, the content of cardiac TAG or the 22∶1n−9 content of TAG at either 2.5 or 9% dietary 22∶1n−9. The histological staining method was more significantly correlated to 22∶1n−9 in cardiac TAG (r=0.49;P<0.001) than to total cardiac TAG (r=0.40;P<0.05). The 22∶1n−9 content was highest in cardiac TAG and free fatty acids. Among the cardiac phospholipids, the highest incorporation was observed into phosphatidylserine, followed by sphingomyelin. With the addition of saturated fat, the fatty acid composition showed decreased accumulation of 22∶1n−9 and increased levels of arachidonic and docosahexaenoic acids in most cardiac phospholipids, despite decreased dietary concentrations of their precursor fatty acids, linoleic and linolenic acids.     

Composition and structure of triacylglycerols in brown adipose tissue of rats fed fish oil

This study examines the incorporation of highly unsaturated n−3 fatty acids (HUFA) into triacylglycerols (TAG) of brown adipose tissue (BAT), and their effect on the positional distribution of saturated (SFA) and of unsaturated (UFA) 16- or 18-carbon fatty acids. To this end, rats were fed a fish oil diet for up to four weeks. The stereospecific analysis of TAG was based on generation ofsn-1,2- andsn-2,3-acylglycerols by Grignard degradation, followed by synthesis of phosphatidic acid and specific hydrolysis with phospholipase A₂. From the end of the first week of fish oil feeding, a steady-state in the fatty acid composition of TAG in BAT was reached. HUFA concentration increased 30-fold, mainly at the expense of n−9 UFA and of SFA. The amount of SFA decreased selectively at position 3, where these fatty acids were progressively replaced by n−3 HUFA. By contrast, the amount of UFA decreased at all positions, and their positional distribution was not affected. About 60% of HUFA was incorporated at position 3. Nearly twice as much 22∶6n−3 was incorporated into TAG than had been previously observed in white adipose tissue (WAT) [Leray, C., Raclot, T., and Groscolas, R. (1993)Lipids 28, 279–284]. At the steady-state, the distribution of HUFA was characterized by high proportions of 22∶6n−3 and 20∶5n−3 in position 3. Moreover, in each position of TAG, a steady level was reached rapidly (within 1 wk). It is concluded that, during fish-oil feeding, fatty acids in TAG of BAT show characteristic time-course changes that lead to a characteristic composition and a tissue-specific positional distribution. This suggests that adipose tissue has its own specificity in controlling the build-up of TAG stores, which is likely to be regulated by the specificity of acylating enzymes as well as molecular rearrangements.     

Accumulation of (n−9)-eicosatrienoic and docosatrienoic acids in human fibroblast phospholipids

An essential fatty acid (EFA) deficiency-like profile of fatty acids has been observed in HF-1 human skin fibro-blasts cultured at clonal densities in MCDB 110 and 0.4% fetal bovine serum (FBS). The profile was characterized by an accumulation of 16∶1n−7, 18∶1n−9, 20∶3n−9 and 22∶3n−9, a reduction of n−6 fatty acids and a reduction in total polyunsaturated fatty acids (PUFA). The fatty acid composition of sphingomyelin (SPH), phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylinositol (PI) and phosphatidylethanolamine (PE) was determined and, except for SPH, each displayed an EFA deficiency-like profile. The triene to tetraene ratio (20∶3n−9/20∶4n−6) ranged from 5.3 in PI to 0.9 in PE. In addition, the highest percentage of 20∶3n−9 was present in the PI and the highest percentage of 22∶3n−9, in PE. Other human fibroblasts (normal, transformed and at different population doubling number levels [PDL] were grown under the same conditions and were found to display triene to tetraene ratios (20∶3n−9/20∶4n−6) in total cellular lipids ranging from 0.7 to 4.5. The accumulation of 20∶3n−9 and 22∶3n−9 is due primarily to the existence of a basal nutrient medium (MCDB 110) that allows for the rapid clonal growth of human fibroblasts at reduced serum levels (0.4%). This culture procedure can be exploited to further elucidate various aspects of lipid metabolism in human fibroblasts. Fatty acids are abbreviated as number of carbon atoms: number of double bonds, followed by an n-number to designate the position of the first double bond with respect to the methyl carbon. Thus, Mead acid is 20∶3n−9 and its elongation product is 22∶3n−9.     

Acylation of docosahexaenoic acid into phospholipids by intact human neutrophils

Docosahexaenoic acid was not only acylated into phospholipids but also into triacylglycerols by intact human neutrophils. The distribution of radiolabeled docosahexaenoic acid among individual phospholipids was dependent on the incubation time. [1-¹⁴C]Docosahexaenoic acid at all concentrations (1 to 8 μM) was acylated mainly into phosphatidic acid after 1–2 min incubation, and the radioactivity of phosphatidic acid started to decline after a longer period of incubation, suggesting the participation of docosahexaenoyl-phosphatidic acid in the synthesis of other glycerolipids. It was acylated primarily into phosphatidylcholine (PC) and phosphatidylethanolamine (PE) after a 2-hr incubation. The labeled phosphatidic acid may be rapidly deacylated and the 22∶6(n−3) moiety is then reacylated into other lysophospholipids. The low levels of [¹⁴C]22∶6(n−3) in 1,2-diacylglycerol suggest that the deacylation-reacylation cycle may be a major pathway in the formation of [¹⁴C]22∶6(n−3)-PC and-PE in intact neutrophils. This n−3 fatty acid was a relatively poor substrate for acylation into phosphatidyl-inositol as compared to arachidonic acid and eicosapentaenoic acid. However, the patterns of distribution of all three polyunsaturated fatty acids among the diacyl-and ether-linked class compositions of PC and PE were similar. These data suggest the potential of increasing the content of docosahexaenoic acid of membrane lipids in neutrophils by dietary supplement of this fatty acid.     

On the specificity of a phospholipase A2 purified from the 106,000×g pellet of bovine brain

Assessment has been made of the specificity of a purified phospholipase A₂ from the 106,000×g pellet (microsomal fraction) of bovine grey matter which shows strong activity toward phosphatidylinositol (PI). In the first series of experiments involving the utilization as substrates of PI with different¹⁴C- or³H-labeled fatty acids in the 2-position, the purified phospholipase A₂ most readily removed 16∶0 palmitic acid, followed by 18∶0 stearic acid, 18∶1 oleic acid and 20∶4 arachidonic acid. In the second series of experiments, the purified phospholipase A₂ showed preferential action toward PI (100%) compared to phosphatidylcholine (PC, 62.5%), phosphatidic acid (PA, 32.6%), phosphatidylethanolamine (PE, 25.1%) and phosphatidylserine (PS, 21.5%), where each phosphoglyceride was labeled in the 2-position with [1-¹⁴C] oleic acid. In the third series of experiments, fatty acids were shown to cause inhibition of action of the purified phospholipase A₂ on 1-acyl, 2-[1-¹⁴C] oleoyl PI in the order 20∶4>18∶1>18∶0>16∶0 which is the reverse order to that just noted. In the final series of experiments, the addition of the phosphoglycerides PC, PE, PS and PA in amounts of 5 or 10 μM caused either no inhibition (PE, 2%), slight inhibition (PC, 15%) or reasonably significant inhibition (PA, 20% and PS, 40%) of action of the purified phospholipase A₂ on 1-acyl, 2-[1-¹⁴C]-oleoyl PI. The pattern of specificity observed for the purified phospholipase A₂ combined with its microsomal location are the expected properties of a phospholipase A₂ that might function in a deacylation-reacylation cycle for modifying the fatty acid distribution in PI.     

New findings in the fatty acid composition of individual platelet phospholipids in man after dietary fish oil supplementation

Nine healthy male volunteers were given 15 Max EPA fish oil capsules providing 2.67 g of eicosapentaenoic acid (EPA, 20∶5ω3) and 1.72 g of docosahexaenoic acid (DHA, 22∶6ω3) daily for 3 wk. Measurements were taken at baseline, at the end of the fish-oil period, and at 2 and 6 wk postsupplementation. The effect of fish oil on plasma lipids and the fatty acid composition of individual platelet phospholipids was studied. In general, the proportions of 20∶5ω3 and 22∶6ω3 in platelet phosphoglycerides were substantially increased mainly at the expense of arachidonic acid (AA, 20∶4ω6). A large and significant increase in the relative EPA content of phosphatidylcholine (PC) (P<0.001) and phosphatidylethanolamine (PE) (P<0.001) was noted at the end of the 3 wk supplementation. We have also shown for the first time a small but significant (P<0.001) incorporation of EPA in phosphatidylserine (PS). Incorporation of DHA was also detected in PC, PE and PS, whereas the relative AA content of these phospholipids was significantly reduced. Fish oil supplementation led to a significant increase of 22∶5ω3 in PS and decreases of 20∶3ω6 in PC and 22∶4ω6 in PE. Postsupplementation measurements showed a gradual return of all fatty acids to baseline levels. The fatty acid composition of the phosphatidylinositol (PI) fraction remained unchanged throughout the trial period. We conclude that in humans ω3 fatty acids are incorporated into platelet membrane phospholipid subclasses with a high degree of specificity.     

Occurrence of n−5 monounsaturated fatty acids in jujube pulp lipids

The pulp lipids of jujube (Zizyphus jujuba var.inermis) fruit have been shown by chromatographic, spectrometric and chemical analyses to contain a series ofcis-monoenoic fatty acids with n−5 unsaturation as major acyl moieties. The total concentration of these n−5 fatty acids, such as 14∶1n−5, 16∶1n−5 and 18∶1n−5, ranged from 22 to 54% of total fatty acids in the pulp lipids of 11 different sources. The main component of the n−5 homologues was 16∶1n−5 in all cases. Other monoenoic acids with n−7 unsaturation, namely palmitoleic (cis-9-hexadecenoic) acid andcis-vaccenic (cis-11-octadecenoic) acid, as well as with n−9 unsaturation, namely oleic acid, were also identified. In the seed lipids of jujube fruit, none of the n−5 monoenoic acids could be detected. Thus the jujube pulp lipids are characterized by the predominance of n−5 monoenoic acid isomers.     

Fatty acid composition of subcellular particles from sheep platelets and topological distribution of phosphatidylethanolamine fatty acids in the plasma membrane

The fatty acid composition of individual phospholipids in subcellular fractions of sheep platelets and the asymmetrical distribution of phosphatidylethanolamine (PE) fatty acyl chains across the plasma membrane were examined. The main fatty acids of total lipid extracts were oleic (18∶1; 32–41%), linoleic (18∶2, 10–17%), stearic (18∶0; 13–15%), palmitic (16∶0; 11–15%) and arachidonic (20∶4; 8–12%) acids, with a saturated/unsaturated ratio of about 0.4. Each phospholipid class had a distinct fatty acid pattern. Sphingomyelin (SM) showed the highest degree of saturation (50%), with large proportions of behenic (22∶0), 18∶0 and 16∶0 acids. The main fatty acid in PE, phosphatidylserine (PS) and phosphatidylcholine (PC) was 18∶1n−9. Our findings suggest that fatty acids are asymmetrically distributed between thecholineversus the non-choline phospholipids, and also between plasma membranes and intracellular membranes. The transbilayer distribution of PE fatty acids in plasma membranes from non-stimulated sheep platelets was investigated using trinitrobenzenesulfonic acid (TNBS). A significant degree of asymmetry was found, which is a new observation in a non-polar cell. The PE molecules from the inner monolayer contained higher amounts of 18∶2 and significantly less 18∶1 and 20∶5 than those found in the outer monolayer, although no major differences were detected in the transbilayer distribution of total unsaturatedversus saturated PE acyl chains.     

Composition and seasonal variation of fatty acids of <Emphasis Type="Italic">Diplodus vulgaris</Emphasis> L. from the Adriatic Sea

Muscle tissue from the common two-banded sea bream Diplodus vulgaris L. originating from the Adriatic Sea, Croatia, was analyzed. The FA composition of neutral (TAG) and polar (PE, PC, PI/PS) lipid classes was determined, as well as the lipid and water contents during winter and summer periods. Both the total lipid and water contents were higher in the winter period. We identified 16 different FA. The major constituents of the total FA in both seasons were saturates: palmitic (16∶0) and stearic acids (18∶0); monoenes: oleic (18∶1n−9) and palmitoleic acids (16∶1n−7); and polyunsaturates: arachidonic acid (20∶4n−6), EPA (20∶5n−3), and DHA (22∶6n−3), but their amounts and ratios differed significantly between the two seasons and between lipid fractions. The FA composition showed a noticeable pattern of seasonality that reflected fluctuations mainly in TAG. The diminution of the monounsaturated FA content in the summer was clearly followed by an increase in PUFA content. Diplodus vulgaris is a good source of natural n−3 PUFA and would therefore be suitable for inclusion in highly unsaturated low-fat diets.     

Changes in liver fatty acid unsaturation after partial hepatectomy in the rat

The purpose of this study was to assess changes in the degree of fatty acid unsaturation in rat liver after partial hepatectomy. This is the first study in which liver fatty acid unsaturation has been analyzed over a long period of regeneration until day 28 after operation. The relationship between changes in unsaturation and fatty acid composition in the regenerating liver were also investigated in this study. Proton nuclear magnetic resonance spectroscopy revealed significantly elevated levels of unsaturation with a maximum on day 5 after partial hepatectomy, compared with untreated controls (11.72±0.55 vs. 11.05±0.26%, P<0.05). No significant changes in unsaturation were found in day 1 regenerating liver, which is rich in absolute amounts of fatty acids. Based on gas-liquid chromatography, the relative amounts of oleic acid (18∶1n−9) and linoleic acid (LA; 18∶2n−6) were increased, while polyunsaturated fatty acids such as arachidonic acid (20∶4n−6) and docosahexaenoic acid (DHA; 22∶6n−3) were decreased on day 1. On the other hand, on day 5 of regeneration, while most fatty acids were returning to their preoperative control levels, only DHA was higher than the control value (7.69±0.58 vs. 5.57±0.37%, P<0.001). The high levels of unsaturation on day 5 were found to be partly due to the increase in DHA. The findings suggest that some significant signals are transmitted during the regeneration process owing to alterations in the membrane structure by the high levels of fatty acid unsaturation and the increase in DHA levels on day 5 after partial hepatectomy.     

Dietary cod liver oil decreases arachidonic acid in rat gastric mucosa and increases stress-induced gastric erosions

The purpose of this study was to examine the influence of long-term feeding of dietary fat rich in either n−3 or n−6 fatty acids on the availability of arachidonic acid (20∶4n−6) in major phospholipids of gastric mucosa in rats. Three groups of male Wistar rats were fed either a standard diet, a cod liver oil-enriched diet (10% by weight), or a corn oil-enriched diet (10% by weight) for 8 mon. Dietary cod liver oil significantly reduced the level of 20∶4n−6 in phosphatidylcholine (PC) and in phosphatidylethanolamine (PE) of gastric mucosa. The loss of 20∶4n−6 was compensated for by eicosapentaenoic acid (20∶5n−3) in PC, whereas the decrease in 20∶4n−6 in PE corresponded to the increase in three n−3 fatty acids: 20∶5n−3, docosapentaenoic acid (22∶5n−3), and docosahexaenoic acid (22∶6n−3). The level of 20∶5n−3 was higher than the level of 22∶6n−3 both in PC and PE of mucosa in rats fed cod liver oil. Diets supplemented with corn oil increased the level of 18∶2n−6 but decreased the monoene fatty acids 16∶1 and 18∶1n−7 in PC but not in PE of gastric mucosa. The 20∶4n−6 levels of both PC and PE were markedly reduced by dietary cod liver oil, to about one-third of control levels. Similar changes were also observed in the stomach wall. Gastric erosions were observed in all rats exposed to restriction stress, but this form of stress induced twice the number of erosions in rats fed fish oil compared to control rats or rats fed corn oil. We conclude that a diet rich in fish oil altered the balance between n−6 and n−3 fatty acids in major gastric mucosal phospholipids, markedly reduced the availability of 20∶4n−6, and increased the incidence of gastric erosions induced by restriction or emotional stress.     

Trans fatty acids. 2. Fatty acid composition of the brain and other organs in the mature female pig

Female pigs were fed from three wk of age and up to two years a diet containing partially hydrogenated fish oil (PHFO, 28%trans monoenoic fatty acids), partially hydrogenated soybean oils (PHSBO, 36%trans fatty acids) or lard. No consistent differences were found between PHFO and PHSBO with regard to incorporation oftrans fatty acids in organ lipids, buttrans incorporations were highly organ-specific. Notrans fatty acids were detected in brain phosphatidylethanolamine (PE). The incorporation of monoenoictrans isomers, as a percentage of totalcis + trans, in other organs was highest in subcutaneous adipose tissue and liver mitochondria PE, followed by blood lipids with the lowest level in heart PE. The percentage oftrans isomers compared with that of dietary lipids was consistently lower for 20∶1, compared with 18∶1 in organs from PHFO-fed pigs. The only effect of dietarytrans fatty acids on the fatty acid pattern of brain PE was an increased level of 22∶5n−6. Heart PE and total serum lipids of pigs fed the hydrogenated fats contained higher levels of 18∶2n−6, and these lipids of the PHFO-fed group also contained slightly elevated amounts of 20∶3n−6, 18∶3n−3 and 20∶5n−3. Liver mitochondria PE of the PHFO group also contained higher levels of 20∶3n−6 and 22∶5n−6. Dietarytrans fatty acids caused a consistent decrease of saturated fatty acids compensated by increased levels of monoenes. Thus, it may be concluded that dietary long-chaintrans fatty acids in PHFO behaved similarly metabolically to 18∶1-trans in PHSBO in pigs, without noticeable influence on brain PE composition and with moderate to slight effects on the fatty acid profile of the other organs.     

Dietary manipulation of macrophage phospholipid classes: Selective increase of dihomogammalinolenic acid

Because alterations in the dietary content of fatty acids are an important method for modulating macrophage eicosanoid production, we have quantitated the levels of n−6 and n−3 polyunsaturated fatty acids in peritoneal macrophage individual phospholipids from mice fed diets (3 wk) with either safflower oil (SAF), predominantly containing 18∶2n−6, borage (BOR) containing 18∶2n−6 and 18∶3n−6, fish (MFO) containing 20∶5n−3 and 22∶6n−3, and borage/fish mixture (MIX) containing 18∶2n−6, 18∶3n−6, 20∶5n−3 and 22∶6n−3. Dietary n−3 fattya cids were readily incorporated into macrophage phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI). The increase in n−3 fatty acid levels was accompanied by a decrease in the absolute levels of 18∶2n−6, 20∶4n−6 and 22∶4n−6 in PC, PE and PS. Interestingly, PI 20∶4n−6 levels were not significantly lowered (P>0.05) in MIX and MFO macrophages relative to SAF and BOR. These data demonstrate the unique ability of this phospholipid to selectively maintain its 20∶4n−6 levels. In BOR and MIX animals, 20∶3n−6 levels were significantly increased (P<0.05) in all phospholipids relative to SAF and MFO. The combination of borage and fish oils (MIX diet) produced the highest 20∶3n−6/20∶4n−6 ratio in all phospholipids. These data show that the macrophage eicosanoid precursor levels of 20∶3n−6, 20∶4n−6 and n−3 acids can be selectively manipulated through the use of specific dietary regimens. This is noteworthy because an increase in phospholipid levels of 20∶3n−6 and 20∶5n−3, while concomitantly reducing 20∶4n−6, may have therapeutic potential in treating inflammatory disorders.     

Molecular species composition of glycerophospholipids from white matter of human brain

The molecular species composition of the major glycerophospholipids from white matter of human brain were determined by high-performance liquid chromatography of the 3,5-dinitrobenzoyl derivatives of the corresponding diradylglycerols. In phosphatidylcholine (PC) and phosphatidylserine (PS), molecular species containing only saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA) comprised 85.7 and 82.4% of the respective totals, with 18∶0/18∶1 predominant in PS and 16∶0/18∶1 in PC. These molecular species were also abundant in phosphatidylethanolamine (PE), but in this phospholipid species containing polyunsaturated fatty acids (PUFA), largely 18∶0/22∶6n−3 and 18∶0/20∶4n−6, accounted for over half the total; 18∶1/18∶1 was also abundant in PE. In contrast, 1-O-alk-1′-enyl-2-acylsn-glycero-3-phosphoethanolamine (GPE) had much more SFA- and MUFA-containing species, predominantly 16∶0a/18∶1, 18∶0a/18∶1 and 18∶1a/18∶1, with low amounts of species containing 20∶4n−6 and 22∶6n−3. In alkenylacyl GPE, 22∶4n−6 was the major PUFA and 16∶0a/22∶4n−6 and 18∶1a/22∶4n−6 the main PUFA-containing species. There was six times more 22∶6n−3, twice as much 20∶4n−6 and half the amount of 22∶4n−6 in PE as compared to alkenylacyl GPE. Molecular species are abbreviated as follows:e.g., 16∶0/18∶1 PE is 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine; the corresponding alkenylacyl species, 1-O-hexadec-1′-enyl-2-oleoyl-sn-glycero-3-phosphoethanolamine is 16∶0a/18∶1.     

Alterations in fatty acid composition of tissue phospholipids in the developing retinal dystrophic rat

Alterations in lipid composition occur in the retinal pigment epithelium and photoreceptor cells of the Royal College of Surgeons (RCS) dystrophic rat, a model for inherited retinal degeneration. With respect to lipid composition of nonretinal tissues, the developmental timing of lipid alterations and the incidence of dystrophy are unknown. We determined the fatty acid composition in choline phosphoglycerides (ChoGpl) and ethanolamine phosphoglycerides (EtnGpl) in the brain, liver, and retina from dystrophic RCS rats and from their nondystrophic congenics (controls) at the ages of 3 and 6 wk. At 3 wk, the fatty acid compositions were specific to individual phospholipid classes without any difference between dystrophic and nondystrophic tissues. In plasma phospholipids, there was an age-related increase in the relative contents of monounsaturated and n-3 polyunsaturated fatty acids, with only minor differences between dystrophic and nondystrophic rats. At 6 wk, the fatty acid compositions in ChoGpl and EtnGpl from dystrophic brain and retina were significantly different from those of nondystrophics. The effect of strain on developmental changes in brain fatty acid composition was significant for 18∶0 and 22∶6n−3 in EtnGpl and for 16∶0, 18∶0, 18∶1n−9, and 20∶4n−6 in ChoGpl. The brain ChoGpl fatty acid composition in nondystrophic rats was similar at 6 wk to that of normal rats, and there were almost no postweaning changes in the dystrophics. In retinal phospholipids, the effect of dystrophy was to increase the 20∶4n−6 content in EtnGpl and to decrease 22∶6n−3 in ChoGpl. The 18∶2n−6 and 22∶6n−3 contents in dystrophic liver ChoGpl were also significantly affected, while no difference was observed in the EtnGpl fraction. The dystrophy affected the phospholipid fatty acid developmental changes in a tissue- and class-specific manner. Fatty acid metabolism could be selectively altered in neural and nonneural tissues of developing dystrophic RCS rats.     

Linolenic acid deficiency: Changes in fatty acid patterns in female and male rats raised on a linolenic acid-deficient diet for two generations

Rats were fed for two generations a purified, linolenic acid-deficient diet in which the only source of lipid was purified methyl linoleate. This diet contained about 38 mg linolenic acid/kg diet. Control rats were given the same diet supplemented with methyl linolenate (2,500 mg/kg diet). Male and female rats ranged in age from weanling pups to adults. Lipids were extracted from liver, brain, kidney, spleen, heart, muscle, gastrointestinal tract, lung, ovary, testis, adrenal, plasma, erythrocytes, retina, and adipose tissue. Fatty acids of major phospholipid classes (choline phosphoglycerides, ethanolamine phosphoglycerides, and mixed serine phosphoglycerides plus inositol phosphoglycerides) or of total lipid extracts were measured by gas liquid chromatography. Growth rates and organ weights were similar in control and linolenic acid-deficient rats. The major effect of the deficiency was to lower the proportions of n−3 fatty acids, especially 22∶6 n−3, in all the organs analyzed. Docosahexaenoic acid (22∶6 n−3) was mainly replaced by 22∶5 n−6 in deficient rats. The greatest changes in composition were found in brain, heart, muscle, retina, and liver.     

Metabolism and incorporation into glycerolipids of exogenous 18∶3(n−3) and 18∶3(n−6) by MDCK cells

The extent to which exogenous 18∶3(n−3) and 18∶3(n−6) were desaturated and elongated and the degree to which they and their derivatives altered the unsaturation index of cell glycerolipids were compared using clone 4 MDCK cells grown in lipid- and serum-free medium. Despite differences in the degree of unsaturation of the individual polyunsaturated fatty acids produced from 18∶3(n−3) or 18∶3(n−6), the unsaturation index of phospholipids increased similarly from 0.7 in control cells grown in serum- and lipid-free medium to ca. 1.6 in those supplemented with fatty acid. The added fatty acids had little effect on cell growth. The conversion of 18∶3(n−6) to 20∶3(n−6) and 20∶4(n−6) was more rapid than that of 18∶3(n−3) to 20∶4(n−3) and 20∶5(n−3). No significant quantities of 20∶3(n−3) or 18∶4(n−3) were noted. When both 18∶3 isomers were supplied simultaneously, marked differences in the amounts of some species of n−3 and n−6 polyunsaturated fatty acids were observed. The presence of 18∶3(n−6) and/or its derivatives suppressed levels of 20∶4(n−3) and 20∶5(n−3), perhaps through inhibition of the Δ6 and Δ5 desaturases responsible for their synthesis from 18∶3(n−3). Similarly 18∶3(n−3), and/or its longer more unsaturated derivatives, diminished the formation of 20∶4(n−6) from 18∶3(n−6). No marked effect on the products derived from elongation alone were observed.     

Dietary fatty acids,membrane transport,and oxidative sensitivity in human erythrocytes

This study examined effects of dietary n−3 fatty acids on age-related changes in erythrocyte anion transport and susceptibility to oxidation. Blood was drawn from healthy adult volunteers before and after six weeks' supplementation (nine/group) with 4.0 g/day of safflower oil (containing 2.9 g n−6 fatty acids) or fish oil (containing 1.2 g long-chain n−3 fatty acids). Following density separation of young and old erythrocytes, membrane anion transport and cell membrane lipid composition were measured. Oxidative damage was measured in erythrocyte ghosts exposed to a free radical generator. Fish oil significantly increased 16∶0 and 20∶5n−3 in ghosts of both young and old cells, and 22∶5n−3 and 22∶6n−3 in old cells alone. Safflower oil increased 16∶0, 18∶0, 18∶1n−9, and 22∶5n−6 in ghosts of young cells only. The age-dependent increase in membrane anion transport (P<0.01) was decreased by dietary fish oil supplementation, but not by safflower oil supplementation. Safflower oil and fish oil increased the susceptibility of both young and old erythrocytes to oxidative damage by free radical generation (P<0.001).