Polyunsaturated fatty acid metabolism in retinal and cerebral microvascular endothelial cells

Docosahexaenoic acid (22:6n-3), an n-3 essential fatty acid derived from elongation and desaturation of linolenic acid (18:3n-3), is found in abundant proportion in the brain and the retina. It is generally assumed that the liver is the major source of 22:6n-3 for these organs, although some retinal and cerebral cells, such as retinal pigment epithelium (Wang and Anderson, 1993. Biochemistry. 32:13703-13709) and brain astrocytes (Moore et al. 1991. J. Neurochem. 56:518-524) have the ability to produce 22:6n-3. The aim of the present study was to determine whether retinal and cerebral microvascular endothelium could synthesize 22:6n-3. After incubation of both cultured bovine retinal and rat cerebral endothelial cells with [3-14C] 22:5n-3 in presence of serum, radioactivity was primarily recovered in 20:5n-3, indicating active retroconversion reactions in both tissues. However, 22:6n-3, 24:5n-3, and 24:6n-3 were also labeled. All of these metabolites were released in the medium as free fatty acids. Retinal endothelial cells preferentially released labeled 24-carbon metabolites, whereas cerebral endothelial cells released relatively more 20:5n-3 and 22:6n-3. With heat-inactivated serum or no serum, both endothelial cell preparations showed relatively higher retroconversion levels. However, in serum-deprived cells, the elongation/desaturation pattern was affected in retinal cells only, with an accumulation of 24:5n-3 relative to a decrease of 24:6n-3 and 22:6n-3. Fatty acid composition analyses revealed a decrease in long-chain polyunsaturated n-6 and n-3 fatty acids in retinal cells maintained in inactivated serum compared to normal serum, while no change was found in cerebral cells. Taken together, these results suggest that 1) the synthesis of 22:6n-3 by both retinal and cerebral endothelial cells is independent of a delta4-desaturase; 2) retinal and cerebral endothelia could be a source of 22:6n-3 for the retina and the brain, respectively; and 3) retinal endothelial delta6-desaturase, which converts 24:5n-3 to 24:6n-3, could be stimulated by serum components.     

Fatty acyl desaturation in isolated hepatocytes from Atlantic salmon (Salmo salar): stimulation by dietary borage oil containing gamma-linolenic acid

The effects of different dietary oils on the fatty acid compositions of liver phospholipids and the desaturation and elongation or [1-14C]18:3n-3 and [1-14C]18:2n-6 were investigated in isolated hepatocytes from Atlantic salmon. Atlantic salmon smolts were fed diets containing either a standard fish oil (FO) as a control diet, a 1:1 blend of Southern Hemisphere marine oil and tuna orbital oil (MO/TO), sunflower oil (SO), borage oil (BO), or olive oil (OO) for 12 wk. The SO and BO diets significantly increased the percentages of 18:2n-6, 18:3n-6, 20:2n-6, 20:3n-6, and total n-6 polyunsaturated fatty acids (PUFA) in salmon liver lipids in comparison with the FO diet. The BO diet also increased the percentage of 20:4n-6. Both the SO and BO diets significantly reduced the percentages of all n-3 PUFA in comparison with the FO diet. The OO diet significantly increased the percentages of 18:1n-3, 18:2n-6, total monoenes, and total n-6 PUFA in liver lipids compared to the FO diet, and the percentages of all n-3 PUFA were significantly reduced. With [1-14C]18:3n-3, the recovery of radioactivity in the products of delta 6 desaturation was significantly greater in the hepatocytes from salmon fed SO, BO, and OO in comparison with the FO diet. The BO diet also increased the recovery of radioactivity in the products of delta 5 desaturation. Only the BO diet significantly affected the desaturation of [1-14C]18:2n-6, increasing recovery of radioactivity in both delta 6- and delta 5-desaturation products. In conclusion, dietary BO, enriched in gamma-linolenic acid (18:3n-6), significantly increased the proportions of both 20:3n-6 and 20:4n-6 in salmon liver phospholipids and also significantly increased the desaturation of both 18:2n-6 and 18:3n-3 in salmon hepatocytes. The possible relationships between dietary fatty acid composition, tissue phospholipid fatty acid composition, and desaturation/elongation activities are discussed.     

Modifying the n-3 fatty acid content of the maternal diet to determine the requirements of the fetal and suckling rat

During perinatal development, docosahexaenoic acid (22:6n-3) accumulates extensively in membrane phospholipids of the nervous system. To evaluate the n-3 fatty acid requirements of fetal and suckling rats, we investigated the accumulation of 22:6n-3 in the brain and liver of pup rats from birth to day 14 postpartum when their dams received increasing amounts of dietary 18:3n-3 (from 5 to 800 mg/100 g diet) during the pregnancy-lactation period. The fatty acid composition of brain and liver phospholipids of pups, as well as that of dam's milk, was determined. At birth, 22:6n-3 increased regularly to reach the highest level when the maternal diet contained 800 mg 18:3n-3/100 g. On days 7 and 14 postpartum, brain 22:6n-3 plateaued at a maternal dietary supply of 200 mg/100 g. Docosapentaenoic acid (22:5n-6) had the opposite temporal pattern. The unusually high concentration of eicosapentaenoic acid (20:5n-3) in liver and dam's milk observed at the highest 18:3n-3 intake suggests an excessive dietary supply of this fatty acid. All these data suggest that the n-3 fatty acid requirements of the pregnant rat are around 400 mg 18:3n-3 and those of the lactating rat at 200 mg (i.e., 0.9 and 0.45% of dietary energy, respectively). The values of 18:3n-3 and 22:6n-3 milk content which allowed brain 22:6n-3 to reach a plateau value in suckling pups were 1% of total fatty acids and 0.9% (colostrum) to 0.2% (mature milk), respectively. These levels are similar to those recommended for infant formulas.     

Dietary modulation of phase 1 and phase 2 activities with benzo(a)pyrene and related compounds in the intestine but not the liver of the channel catfish, Ictalurus punctatus

EPA, DHA, C15SCH2COOH (n-3), C15SCH2COOH (n-6) and C18SCH2COOH (n-3) are extensively incorporated into phospholipids and triacylglycerol in rat hepatocytes after 24 h incubation with 80 microM fatty acid/derivative. Only traces of polyunsaturated 3-oxa fatty acids (C15OCH2COOH, C18OCH2COOH) were incorporated. C15-S-butyric acid (n-3) is a stronger inhibitor of delta6-desaturase in rat liver-microsomes than C15SCH2COOH (n-3), C15-S-propionic acid (n-3), EPA and DHA. It inhibits delta5-desaturase in a similar manner to EPA and DHA. Arachidonic acid and C15SCH2COOH, (n-6) are better substrates for PGH-synthase than EPA and C15SCH2COOH, (n-3), showing the inhibitory effect of the n-3 bond. The n-3 polyunsaturated fatty acids, including the sulfur-substituted fatty acid derivatives, are poor substrates for PGH-synthase. However, they inactivate the PGH-synthase activity at least as efficiently as arachidonic acid. C15SCH2COOH (n-3), C15S(CH2)2COOH (n-3) and C18SCH2COOH (n-3) induce peroxisomal beta-oxidation more than EPA and DHA.     

Liver microsomal membrane fluidity and microsomal desaturase activities in adult spontaneously hypertensive rats

OBJECTIVE: The purpose of the present study was to investigate liver microsomal membrane fluidity simultaneously with membrane fatty acid composition and desaturase activities in spontaneously hypertensive rats (SHR). DESIGN AND METHODS: The membrane fluidity was determined, after electron spin resonance (ESR) measurement, in SHR compared with normotensive Wistar-Kyoto (WKY) rats, by calculating the order parameter S from ESR spectra of 5-nitroxide stearate and 10-nitroxide stearate, used as spin-labelled fatty acids. Desaturase activities were measured by incubating SHR and WKY rat liver microsomes with [14C]-radiolabeled fatty acids as substrates for desaturation reactions. The fatty acid composition of liver microsomal membranes was determined by gas-liquid chromatography. RESULTS: Whereas no significant difference between S of 5-nitroxide stearate was observed for SHR and WKY rats, S of 10-nitroxide stearate was significantly lower in SHR than it was in WKY rat microsomal membrane, indicating that the core microsomal membrane fluidity was higher in SHR. Significant differences between fatty acid compositions were observed for SHR and WKY rat microsomal membranes. Delta9 and n-6 delta6 microsomal desaturase activities were significantly lower in SHR. CONCLUSION: These results suggest that the higher liver core microsomal membrane fluidity observed in SHR might be dependent on the increased proportion of mono-unsaturated fatty acids. Such observed modifications and the alterations in delta9 and n-6 delta6 desaturase activities suggest that an impaired polyunsaturated fatty acid biosynthesis is related to changes in microsomal membrane fluidity in hypertension.     

Fasting increases tissue uptake and interconversion of plasma unesterified linoleic acid in guinea pigs

A large part of the arachidonic acid (20:4 n-6) pools in some extrahepatic tissues can be formed by local interconversion of linoleic acid (18:2 n-6) taken up as free fatty acid (FFA) from blood in both rats and guinea pigs. This study investigates the rate of uptake and interconversion of unesterified 14C-18:2 by different tissues in fasted guinea pigs. The initial half-life of 14C-18:2 in plasma was 5.8 s. The average concentration of plasma FFA was 551.3 nmol ml-1 and of plasma FFA-18:2 was 67.3 nmol ml-1. The total amount of 20:4 formed in the liver was 1.8 +/- 0.3 nmol min-1, which was lower than that in the gastrointestinal tract (3.1 nmol min-1), bone marrow (6.0 nmol min-1) and lung (2.1 nmol min-1). Due to the fast turnover and higher concentration of plasma FFA-18:2 in the fasting state, the retained 18:2 in tissue lipids was 5.8-25.6-fold higher than that in fed guinea pigs [L. Zhou et al. Biochim. Biophys. Acta 1349 (1997) 197-210]. The total delta 6-desaturase products both in liver and in extrahepatic tissues were also increased, 3.8-fold in liver, 7.2-fold in upper small intestine, 6.0-fold in colon, and 6.5-fold in bone marrow. The increased rate of tissue uptake of FFA during fasting is thus linked to an increased local interconversion of plasma FFA-18:2, which is an important source of 20:4 in some extrahepatic tissue in guinea pigs.     

Essential fatty acid metabolism in cardiomyocytes grown in media enriched with different N-6/N-3 fatty acid combinations

We have evaluated the effects of three different 18:3n-6, 20:5n-3 and 22:6n-3 fatty acid combinations on essential fatty acid (EFA) metabolism in rat cultured cardiomyocytes. The desaturating/elongating activities for linoleic (LA) and alpha-linolenic acid (ALA) were evaluated by radiolabeling the cells with 1-[14C]LA or 1-[14C]ALA and the fatty acid pattern of cardiomyocytes was assessed by gas chromatography. LA and ALA conversion to more unsaturated metabolites was reduced by increasing respectively n-3 and n-6 fatty acid concentration in the media. The all three combinations used reduced the saturated and increased the polyunsaturated fatty acid content of cardiomyocytes. The n-6/n-3 fatty acid ratio did not change compared to control cells in cardiomyocytes receiving the highest amount of 18:3n-6 and the lowest amounts of n-3 fatty acids. This combination may be suitable for modifying EFA desaturating/elongating activities without altering the physicochemical parameters which are related to the correct balance between n-6 and n-3 fatty acid content.     

Correlation of suppressed linoleic acid metabolism with the hypocholesterolemic action of eritadenine in rats

The dose-dependent effects of dietary eritadenine on the metabolism of linoleic acid and on the plasma cholesterol concentration were investigated to clarify the mechanism of the hypocholesterolemic action of eritadenine in rats. Rats were fed control or eritadenine-supplemented (2 to 20 mg/kg) diets for 14 d. Eritadenine supplementation significantly decreased both the plasma cholesterol concentration and the 20:4n-6/18:2n-6 ratio of liver microsomal and plasma phosphatidylcholine (PC) in a dose-dependent manner. Eritadenine was also found to decrease the activity of delta 6 desaturase in liver microsomes; there was significant correlation between the delta 6-desaturase activity and the 20:4n-6/18:2n-6 ratio in the PC of liver microsomes (r = 0.989, P < 0.001) or plasma (r = 0.986, P < 0.001). Certain plasma PC molecular species, as represented by 16:0-18.2, were increased by eritadenine in a dose-dependent manner, and certain plasma PC molecular species, as represented by 18:0-20:4, were conversely decreased by eritadenine. There was a significant correlation between the plasma total cholesterol concentration and the proportion of the sum of plasma PC molecular species which contain 18:1 or 18:2 in the sn-2 position. These results support the idea that the suppression of linoleic acid metabolism by eritadenine might be associated with the hypocholesterolemic action of eritadenine.     

Differences in fatty acid composition of immature and mature articular cartilage in humans and sheep

Chondrocytes are imbedded in an avascular, highly charged extracellular matrix which could form a barrier to the transfer of dietary essential fatty acids (EFA) to chondrocytes. A study was designed to assess the composition of immature and mature joint cartilage with respect to essential and nonessential fatty acids relevant to EFA deficiency. Cartilage and muscle samples were obtained from human fetus, infant and adult cadavers, and from fetal and mature sheep. Lipid extracts were prepared and the fatty acid composition determined. In human and sheep joint cartilage, linoleic acid (LA; 18:2n-6) content was lower, and n-9 eicosatrienoic acid (ETrA; 20:3n-9) and arachidonic acid (AA; 20:4n-6) were higher in fetuses compared to mature subjects. An intermediate pattern was seen in infant cartilage. n-3 Fatty acids tended to be higher in fetal than in mature cartilage in humans and in sheep. In human muscle (and in other noncartilaginous comparison tissues), similar differences between fetuses and adults were seen in LA and AA, but not in ETrA. In fetal sheep muscle, very low LA, reduced AA and raised ETrA levels compared to mature sheep muscle were seen. However, although the pattern is characteristic of EFA deficiency, the abundance of n-6 EFA in liver and spleen of human fetuses and of n-3 EFA in liver and spleen of fetal sheep suggests that placental transfer of EFA is not likely to be limiting. During fetal development, the metabolism of fatty acids is distinctive and differs between the species. ETrA appears to be a readily measurable component of some tissues at certain stages of development when its presence in tissues does not indicate EFA deficiency.     

Expression of a cyanobacterial delta 6-desaturase gene results in gamma-linolenic acid production in transgenic plants

Gamma-linolenic acid (GLA), a nutritionally important fatty acid in human and animal diets, is not produced in oil seed crops. Many oil seed plants, however, produce significant quantities of linoleic acid, a fatty acid that could be converted to GLA by the enzyme delta 6-desaturase if it were present. As a first step to producing GLA in oil seed crops, we have cloned a cyanobacterial delta 6-desaturase gene. Expression of this gene in transgenic tobacco resulted in GLA accumulation. Octadecatetraenoic acid, a highly unsaturated, industrially important fatty acid, was also found in transgenic tobacco plants expressing the cyanobacterial delta 6-desaturase. This is the first example of engineering the production of 'novel' polyunsaturated fatty acids in transgenic plants.     

Effects of dietary fatty acids on eicosanoid-generating capacity, fatty acid composition and chemotactic activity of rainbow trout (Oncorhynchus mykiss) leucocytes

Rainbow trout, Oncorhynchus mykiss, were maintained on isocalorific diets in which either sunflower, menhaden or Fosol oils were used as the dietary source of fatty acids. At intervals over a period of 6 months, head kidney leucocytes were isolated and used for the analysis of their fatty acid composition and eicosanoid-generating capacity. Major changes in fatty acid composition were apparent within 4 weeks on the diets, with fish fed sunflower oil diets showing a 2.1-fold increase in total n-6 fatty acids and a 2.3-fold decrease in n-3 fatty acids, compared with the original basal levels. By week 8 the fatty acid composition changes were greater in the sunflower-fed fish, but thereafter remained relatively stable to the end of the experiment at week 24. Leucocytes from the fish maintained for > 8 weeks on the sunflower oil containing diet produced significantly lower percentages of 5-series lipoxygenase products derived from eicosapentaenoic acid including 12-hydroxyeicosapentaenoic acid, leukotriene B5 and lipoxin A5 compared with those cells from fish fed either menhaden or Fosol based diets. Unlike the fatty acid composition, differences in lipoxygenase product profiles between the dietary groups increased throughout the experiment and by week 24 the arachidonic acid/eicosapentaenoic acid derived product ratios were approx. 14:1 in the sunflower oil-fed fish compared with approx. 1:1.5 in the menhaden oil-fed fish. A functional consequence of these differing ratios was seen in the ability of supernatants containing these products to cause the in vitro locomotion of trout neutrophils. Supernatants from sunflower oil-fed fish were less chemo-attractive than supernatants from menhaden or Fosol oil-fed fish.     

Addition of triglycerides with arachidonic acid or docosahexaenoic acid to infant formula has tissue- and lipid class-specific effects on fatty acids and hepatic desaturase activities in formula-fed piglets

The effects of including triglycerides with arachidonic [20:4(n-6)] or docosahexaenoic acid [22:6(n-3)] in formula on plasma chylomicron, LDL and HDL, liver, heart, kidney and brain (n-6) and (n-3) fatty acids were investigated in formula-fed piglets. Piglets were fed formula with (in % total fatty acids) 20% 18:2(n-6) and 2% 18:3(n-3) without or with 0.8% 20:4(n-6) or 0.3% 22:6(n-3) from birth to 18 d. The effects of adding 20:4(n-6) or 22:6(n-3) to the formula differed among different tissues and lipids, with the brain showing resistance to change. Piglets fed formula with 20:4(n-6) had significantly higher plasma, heart and kidney phospholipid and triglyceride, and liver triglyceride 20:4(n-6), but lower plasma and tissue phospholipid 18:2(n-6) than piglets fed formula without 20:4(n-6). Supplementation with 22:6(n-3), in contrast, had no effect on plasma or tissue 18:2(n-6). Higher 22:6(n-3) in liver phospholipid (30-92% greater) and triglyceride (200% greater) in piglets fed formula with 22:6(n-3) rather than without 22:6(n-3) was accompanied by lower 20:4(n-6) in liver phosphatidylethanolamine (mean +/- SEM, 8.6 +/- 0.4 and 10.5 +/- 0.4% fatty acids, respectively), but higher 20:4(n-6) in triglyceride (5.2 +/- 0.4 and 11.5 +/- 0.5%, respectively), and higher liver, heart and kidney phospholipid 20:5(n-3). These results indicate competitive interaction between dietary 20:4(n-6) and tissue 18:2(n-6), and between dietary 20:4(n-6) and tissue 20:5(n-3), rather than 22:6(n-3). The results also show that even at low intakes, dietary 22:6(n-3) or 20:4(n-6) supplementation alters the tissue phospholipid 20:4(n-6) to 20:5(n-3) balance. Studies on the physiologic effects of dietary 20:4(n-6) and 22:6(n-3) supplementation should consider the different sensitivity among tissues to dietary fatty acids.     

Fatty acid carbon isotope ratios in humans on controlled diets

Carbon stable isotope ratios for six serum fatty acids (FA) are reported for human subjects on controlled fat diets to determine the range of natural isotope abundance and to demonstrate the leveling effect of a well-controlled diet. Twenty-nine subjects were randomly assigned to one of three controlled diets containing high, medium, or low fat. Diets were consumed for 8 wk. Serum samples were collected at baseline (0), 5, 6, 7, and 8 wk. FA were extracted and methylated. Isotope ratios were analyzed by high-precision gas chromatography combustion-isotope ratio mass spectrometry. At baseline, mean delta 13C for 16:0b, 16:1a, 18:0a, 18:1c,18:2n-6d and 20:4n-6bc were -24.1, -21.7, -21.6, -25.6, -29.6, and -25.0/1000, respectively, with an average standard deviation of 1.9/1000. Most delta 13C decreased during the diet period and appeared to have stabilized by week 5 at -25.3, -21.9, -22.3, -26.5, -30.1, and -24.5/1000, respectively. Between-subjected variability decreased from 1.74 to 1.20/1000 on the controlled diets. Measurement variability was 0.53/1000. The within-subject variability during weeks 5-8 was 0.57/1000 (range of 0.32-0.84/1000), showing a minimum biological fluctuation on controlled diets. There was no diet group effect on delta 13C of serum FA. Except for 18:2, the delta 13C of experimental diets was lower than that of serum FA, consistent with observations in animals. These data show that carbon isotope ratios stabilize in response to controlled diets within 5 wk, reflecting the isotope ratio of their dietary source, and establish isotope ratio fluctuations for endogenous compounds for future studies.     

Osteomalacia of renal origin disclosing Gougerot-Sj?gren syndrome

We examined the delta 4 (n-6) desaturation and the fatty acid composition of liver microsomes in the insulin-dependent spontaneously diabetic Wistar Bio-Breeding (BB) rat. The desaturation of adrenic acid to n-6 docosapentaenoic acid was decreased in the normo- and hyperglycemic diabetic rats. Insulin treatment with 1.0 IU. 100 g body weight-1 twice a day for 2 days restored the reduced activity during the hypoglycemic period. The pattern of responses was similar to that of linoleic acid delta 6 and dihomo-gamma-linolenic acid delta 5 desaturases, with a non-parallel relationship between the desaturation system and the glycemia. The microsomal fatty acid composition of BB rat liver reflected only partially to the delta 4 desaturation at different states of glycemia. Factors other than impaired desaturation system are involved in the fatty acid metabolism of spontaneously diabetic rats.     

Effect of diet on the fatty acid and molecular species composition of dog retina phospholipids

Dogs were born to mothers fed commercial diets low or enriched in n-3 fatty acids and raised on those diets until they were about 50 d old. Retinas were removed, lipids were extracted, and total phospholipids were analyzed for fatty acid and molecular species composition. Animals from the low n-3 group had significantly lower retinal levels of 22:6n-3 and higher levels of n-6 fatty acids, especially 20:4n-6 and 22:5n-6. There was no difference in the retinal levels of 18:2n-6, and only small differences were found in saturated and monounsaturated fatty acids. The most dramatic differences in molecular species occurred in 22:6n-3-22:6n-3 (4.7 vs. 0.8%) and 18:0-22:6n-3 (27.6 vs. 14.4%); total molecular species containing 22:6n-3 were significantly lower in the low n-3 group (45.5 vs. 24.0%). Molecular species containing 20:4n-6 and 22:5n-6 were greater in the low n-3 animals (13.0 vs. 25.7%), as were molecular species containing only saturated and monounsaturated fatty acids (40.8 vs. 35.4%). These results show that modest differences in the amount of n-3 fatty acids in the diets of dogs can have profound effects on the fatty acid and molecular species composition of their retinas.     

Changes in plasma and colonic mucosa fatty acid profiles in rats with ulcerative colitis induced by trinitrobenzene sulfonic acid

Polyunsaturated fatty acids have a key role in the pathogenesis of inflammatory bowel disease since some of the arachidonic acid-derived eicosanoids have been found to be increased in inflamed intestinal mucosa in the acute phase of human disease. The aim of this study was to prospectively assess plasma and colon mucosa fatty acid patterns in rats with experimental ulcerative colitis. Twenty rats were treated with trinitrobenzene sulfonic acid and 20 with NaCl; two groups were killed after one week and two after two weeks to evaluate colon damage. Plasma was obtained by aortic puncture and colonic mucosa was scraped off and the fatty acid pattern was determined by gas-liquid chromatography. Total, saturated, and monounsaturated plasma fatty acids were significantly higher in both periods of ulcerative colitis as compared to controls. Plasma n-6 fatty acids were increased after treatment, but no significant changes were observed concerning to n-3 fatty acids. With regard to colon mucosa, saturated and monounsaturated fatty acids did not change because of the disease; however, n-6 fatty acids decreased in the first week and increased in the second week and n-3 fatty acids were increased. Changes on the fatty acid distribution in plasma did not parallel to those of colonic mucosa except for 22:6(n-3). We have also found that experimental ulcerative colitis induced by trinitrobenzene sulfonic acid reproduces many of the features related to changes in plasma and colon mucosa fatty acids observed in the human disease.     

Long-term supplementation of culture medium with essential fatty acids alters alpha-linolenic acid uptake in Caco-2 clone TC7

We investigated the influence of four different culture media: 20% fetal bovine serum (FBS), 5% FBS, 5% FBS supplemented with 10 mg x L(-1) linoleic acid (18:2(n-6)) or alpha-linolenic acid (18:3(n-3)) on alpha-linolenic acid apical uptake in clone TC7 of human intestinal Caco-2 cell line. Neither cellular viability nor cell monolayer integrity and permeability were altered by the four culture conditions. Our results show that the different culture media led to changes in alpha-linolenic acid maximal rate of uptake (Vmax) but did not alter the apparent transport constant (Km). Reducing FBS concentration from 20% to 5% increased significantly the rate of alpha-linolenic acid uptake, which was further increased by supplementation of the medium with 18:2(n-6) or 18:3(n-3). Supplementation with essential fatty acids led to a marked enrichment of brush-border membrane phospholipids in polyunsaturated fatty acids of the corresponding series and decreased significantly the levels of monounsaturated fatty acids. Saturated fatty acids, unsaturation index, and cholesterol/fatty acid ratios were unchanged. No clear relation could be established between the changes in membrane lipid composition and the alterations of alpha-linolenic acid uptake. These results indicate a weak influence of membrane lipid composition in the modulation of the uptake. Therefore, the increase of uptake following long-term supplementation of TC7 cells with essential fatty acids could be attributed to an increase of the expression of membrane protein(s) involved in the apical uptake of long-chain fatty acids. This remains to be established.     

Fatty acid composition in maternal milk and plasma during supplementation with cod liver oil

OBJECTIVE: We investigated how cod liver oil influences the amount of essential fatty acids in mothers' breast milk. DESIGN AND INTERVENTION: Lactating mothers (n =22) were randomized into four groups 3-8 weeks after parturition. They were supplemented for 14 days with 0, 2.5, 5 and 10 ml cod liver oil (7.7 g eicosapentaenoic acid (EPA, 20:5n-3), 10.2 g docosahexaenoic acid (DHA, 22:6n-3) and 22.9 g n-3 fatty acids in total per 100 ml). RESULTS: In maternal plasma phospholipids there was an increase in the content of EPA and DHA in the group supplemented with 10 ml cod liver oil daily (P < or = 0.05). DHA concentrations in breast milk pre-supplementation ranged from 0.15 to 1.56 wt% and increased in all supplemented groups (P< or =0.05). The concentration of EPA in breast milk increased in the groups supplemented with 5 or 10 ml cod liver oil (P< or =0.05), whereas the concentration of arachidonic acid (AA, 20:4n-6) did not change in any of the supplemented groups. Total intake of DHA adjusted to body mass index (BMI), correlated to DHA concentrations in plasma (r = 0.49, P = 0.02) and breast milk (r = 0.45, P = 0.04). The concentration of tocopherol did not change during the supplementation period, neither in plasma nor in breast milk. CONCLUSION: Dietary intake of DHA is reflected in the concentration of DHA in breast milk, without affecting the concentration of AA or tocopherol.     

Fatty acid composition of human brain phospholipids during normal development

The fatty acid composition of phosphatidylethanolamine (PE), ethanolamine plasmalogens (EPs), phosphatidylserine (PS), phosphatidylcholine (PC), and sphingomyelin was studied in 22 human forebrains, ranging in age from 26 prenatal weeks to 8 postnatal years. Phospholipids were separated by two-dimensional TLC, and the fatty acid methyl esters studied by capillary column GLC. Docosahexaenoic acid (22:6n-3) increased with age in PE and PC, whereas arachidonic acid (20:4n-6) remained quite constant. In EP, 22:6n-3 increased less markedly than 20:4n-6, adrenic (22:4n-6) and oleic (18:1n-9) acids being the predominant fatty acids during postnatal age. In PS, 18:1n-9 increased dramatically throughout development, and 20:4n-6 and 22:4n-6 increased only until approximately 6 months of age. Although 22:6n-3 kept quite constant during development in PS, its percentage decreased due to the accretion of other polyunsaturated fatty acids (PUFAs). As a characteristic myelin lipid, sphingomyelin was mainly constituted by very long chain saturated and monounsaturated fatty acids. Among them, nervonic acid (24:1n-9) was the major very long chain fatty acid in Sp, followed by 24:0, 26:1n-9, and 26:0, and its accretion after birth was dramatic. As myelination advanced, 18:1n-9 increased markedly in all four glycerophospholipids, predominating in EP, PS, and PC. In contrast, 22:6n-3 was the most important PUFA in PE in the mature forebrain.     

Isolation of the Pichia pastoris PYC1 gene encoding pyruvate carboxylase and identification of a suppressor of the pyc phenotype

It has been reported that both n-3 and n-6 octadecatrienoic acids can increase hepatic fatty acid oxidation activity. It remains unclear, however, whether different enzymes in fatty acid oxidation show a similar response to n-3 and n-6 octadecatrienoic acids. The activity of hepatic fatty acid oxidation enzymes in rats fed an oil mixture rich in alpha-linolenic acid (18:3n-3) and borage oil rich in gamma-linolenic acid (18:3n-6) was therefore compared to that in rats fed an oil mixture rich in linoleic acid (18:2n-6) and a saturated fat (palm oil) in this study. Linseed oil served as the source of 18:3n-3 for the oil mixture rich in this octadecatrienoic acid and contained 30.6% 18:3n-3 but not 18:3n-6. Borage oil contained 25.7% 18:3n-6 and 4.5% 18:3n-3. Groups of seven rats each were fed diets containing 15% various fats for 15 d. The oxidation rate of palmitoyl-CoA in the peroxisomes was higher in rats fed a fat mixture rich in 18:3n-3 (3.03 nmol/min/mg protein) and borage oil (2.89 nmol/min/mg protein) than in rats fed palm oil (2.08 nmol/min/mg protein) and a fat mixture rich in 18:2n-6 (2.15 nmol/min/mg protein). The mitochondrial palmitoyl-CoA oxidation rate was highest in rats fed a fat mixture rich in 18:3n-3 (1.93 nmol/min/mg protein), but no significant differences in this parameter were seen among the other groups (1.25-1.46 nmol/min/mg protein). Compared to palm oil and fat mixtures rich in 18:2n-6, a fat mixture rich in 18:3n-3 and borage oil significantly increased the hepatic activity of carnitine palmitoyltransferase and acyl-CoA oxidase. Compared to palm oil and a fat mixture rich in 18:2n-6, a fat mixture rich in 18:3n-3, but not fats rich in 18:3n-6, significantly decreased 3-hydroxyacyl-CoA dehydrogenase activity. Compared to palm oil and a fat mixture rich in 18:2n-6, borage oil profoundly decreased mitochondrial acyl-CoA dehydrogenase activity, but a fat mixture rich in 18:3n-3 increased it. 2,4-Dienoyl-CoA reductase activity was significantly lower in rats fed palm oil than in other groups. Compared to other fats, borage oil significantly increased delt3,delta2-enoyl-CoA isomerase activity. Activity was also significantly higher in rats fed 18:2n-6 oil than in those fed palm oil. It was confirmed that both dietary 18:3n-6 and 18:3n-3 increased fatty acid oxidation activity in the liver. These two dietary octadecatrienoic acids differ considerably, however, in how they affect individual fatty acid oxidation enzymes.