Retroconversion and delta 4 desaturation of docosatetraenoate (22:4(n-6)) and docosapentaenoate (22:5(n-3)) by human cells in culture

Updates to the n-3 polyunsaturated fatty acid biosynthesis pathway: DHA synthesis rates, tetracosahexaenoic acid and (minimal) retroconversion

N-3 polyunsaturated fatty acids (PUFA) and the numerous families of lipid mediators derived from them collectively regulate numerous biological processes. The mechanisms by which n-3 PUFA regulate biological processes begins with an understanding of the n-3 biosynthetic pathway that starts with alpha-linolenic acid (18:3n-3) and is commonly thought to end with the production of docosahexaenoic acid (DHA, 22:6n-3). However, our understanding of this pathway is not as complete as previously believed. In the current review we provide a background of the evidence supporting the pathway as currently understood and provide updates from recent studies challenging three central dogma of n-3 PUFA metabolism. By building on nearly three decades of research primarily in cell culture and oral dosing studies, recent evidence presented focuses on in vivo kinetic modelling and compound-specific isotope abundance studies in rodents and humans that have been instrumental in expanding our knowledge of the pathway. Specifically, we highlight three main updates to the n-3 PUFA biosynthesis pathway: (1) DHA synthesis rates cannot be as low as previously believed, (2) DHA is both a product and a precursor to tetracosahexaenoic acid (24:6n-3) and (3) increases in EPA in response to DHA supplementation are not the result of increased retroconversion.

Is essential fatty acid interconversion an important source of PUFA in humans?

Humans can obtain pre-formed long-chain PUFA from the diet and are also able to convert essential fatty acids (EFA) to longer-chain PUFA. The metabolic pathway responsible for EFA interconversion involves alternating desaturation and carbon chain elongation reactions, and carbon chain shortening by peroxisomal β-oxidation. Studies using stable isotope tracers or diets supplemented with EFA show that capacity for PUFA synthesis is limited in humans, such that DHA (22 : 6n-3) synthesis in men is negligible. PUFA synthesis is higher in women of reproductive age compared with men. However, the magnitude of the contribution of hepatic PUFA synthesis to whole-body PUFA status remains unclear. A number of extra-hepatic tissues have been shown to synthesise PUFA or to express genes for enzymes involved in this pathway. The precise function of extra-hepatic PUFA synthesis is largely unknown, although in T lymphocytes PUFA synthesis is involved in the regulation of cell activation and proliferation. Local PUFA synthesis may also be important for spermatogenesis and fertility. One possible role of extra-hepatic PUFA synthesis is that it may provide PUFA in a timely manner to facilitate specific cell functions. If so, this may suggest novel insights into the effect of dietary PUFA and/or polymorphisms in genes involved in PUFA synthesis on health and tissue function.

Supplementation with plant-derived oils rich in omega-3 polyunsaturated fatty acids for lamb production

In this report, an overview of the health benefits of omega-3 long-chain (≥C20) polyunsaturated fatty acids (n-3 LC-PUFA) and recent progress in using alpha linolenic acid (ALA) rich sources derived from oilseeds to enhance productive performance, n-3 PUFA profiles and sensory properties of lamb for human consumption is reviewed. Omega-3 LC-PUFA can prevent mental health issues and chronic human disorders including cancer, cardiovascular and inflammatory diseases. The median amount of n-3 LC-PUFA consumption is generally lacking in Western diets. More attention is now being paid to the use of innovative nutritional strategies to improve PUFA content in ruminants, which could subsequently increase the content of health-benefitting n-3 LC-PUFA for human consumption. The richest sources of dietary n-3 LC-PUFA are derived from marine products, while forage and oilseeds such as flaxseed, canola, and their oils are abundant in ALA. Numerous studies have shown that dietary ALA increases n-3 LC-PUFA levels of edible tissues. However, other studies concluded that ALA rich supplementation led to no differences in tissue FA profiles because of extensive biohydrogenation of dietary ALA, limited conversion from ALA to n-3 LC-PUFA and low incorporation of n-3 LC-PUFA into edible tissues. Generally, the inclusion of ALA rich sources in lamb diets potentially increases ALA content in lamb. It is proposed that supplementing ruminants with ALA-rich sources at or below 6% can promote n-3 PUFA profiles in lamb and is unlikely to have negative effects on feed intake, growth, carcass and sensory properties.

Metabolic fate of docosahexaenoic acid (DHA; 22:6n-3) in human cells: direct retroconversion of DHA to eicosapentaenoic acid (20:5n-3) dominates over elongation to tetracosahexaenoic acid (24:6n-3)

Docosahexaenoic acid (22:6n-3) supplementation in humans causes eicosapentaenoic acid (20:5n-3) levels to rise in plasma, but not in neural tissue where 22:6n-3 is the major omega-3 in phospholipids. We determined whether neuronal cells (Y79 and SK-N-SH) metabolize 22:6n-3 differently from non-neuronal cells (MCF7 and HepG2). We observed that (13) C-labeled 22:6n-3 was primarily esterified into cell lipids. We also observed that retroconversion of 22:6n-3 to 20:5n-3 was 5- to 6-fold greater in non-neural compared to neural cells and that retroconversion predominated over elongation to tetracosahexaenoic acid (24:6n-3) by 2-5-fold. The putative metabolic intermediates, (13) C-labeled 22:5n-3 and (13) C-labeled 24:5n-3, were not detected in our assays. Analysis of the expression of enzymes involved in fatty acid beta-oxidation revealed that MCF7 cells abundantly expressed the mitochondrial enzymes CPT1A, ECI1, and DECR1, whereas the peroxisomal enzyme ACOX1 was abundant in HepG2 cells, thus suggesting that the initial site of 22:6n-3 oxidation depends on the cell type. Our data reveal that non-neural cells more actively metabolize 22:6n-3 to 20:5n-3 via channeled retroconversion, while neural cells retain 22:6n-3.

Effect of double-muscling in Belgian Blue young bulls on the intramuscular fatty acid composition with emphasis on conjugated linoleic acid and polyunsaturated fatty acids

The effect of double-muscling (DM) genotype (double-muscling, mh/mh; heterozygous, mh/+; normal, +/+) of Belgian Blue (BB) young bulls on the intramuscular fatty acid composition, in particular conjugated linoleic acid (CLA) and polyunsaturated fatty acids (PUFA) was examined in five different muscles. The relative fatty acid composition showed only minor differences between muscles within genotypes. However, the DM genotype had a large effect on both the intramuscular total fatty acid content and on the relative fatty acid composition. Across muscles, the mh/mh animals had a lower total fatty acid content compared with the +/+animals (907 v: 2656 mg/100 g muscle;P< 0·01) and a higher PUFA proportion in total fatty acids (27·5 v 11·3 g/100 g total fatty acids;P< 0001), resulting in a higher PUFA/saturated fatty acid ratio (0·55 v 0·18;P< 0·01) and a lower n-6/n-3 ratio (5·34 v. 6·17;P< 0·01). The heterozygous genotype was intermediate between the two homozygous genotypes. The relative CLA content was similar in the mh/mh and +/+ genotypes and approximated 0·4 to 0·5 g/100 g total fatty acids. From the data it is further suggested that differences in the metabolism of the n-3 and n-6 fatty acids could exist between DM genotypes.

Anti-proliferative effects of a new docosapentaenoic acid monoacylglyceride in colorectal carcinoma cells

N-3 polyunsaturated fatty acids (n-3 PUFAs) have been shown to inhibit the induction and progression of many tumor types. However, the anticancer effect of n-3 PUFA monoglyceride on colorectal cancer has yet to be assessed. The aim of the present study was to determine the anti-tumorigenic effects of docosahexaenoic acid monoglyceride (MAG-DHA), eicosapentaenoic acid monoglyceride (MAG-EPA) and docosapentaenoic acid (22:5n-3) monoglyceride (MAG-DPA) in colorectal carcinoma cells. Our results demonstrate that MAG-DHA, MAG-EPA and MAG-DPA all decreased cell proliferation and induced apoptosis in HCT116 cells, with MAG-DPA having the higher anti-proliferative and pro-apoptotic effects in vitro. In a HCT116 xenograft mouse model, oral administration of MAG-DPA significantly inhibited tumor growth. Furthermore, MAG-DPA treatments decreased NFκB activation leading to a reduction in Bcl-2, CyclinD1, c-myc, COX-2, MMP9 and VEGF expression levels in tumor tissue sections. Altogether, these data provide new evidence regarding the mode of action of MAG-DPA in colorectal cancer cells.

Lipidomics of essential fatty acids and oxygenated metabolites

Polyunsaturated fatty acids in mammals may be oxygenated into a myriad of bioactive products through di- and monooxygenases, products that are rapidly degraded to control their action. To evaluate the phenotypes of biological systems regarding this wide family of compounds, a lipidomics approach in function of time and compartments would be relevant. The current review takes into consideration most of the diverse oxygenated metabolites of essential fatty acids at large and their immediate degradation products. Their biological function and life span are considered. Overall, this is a fluxolipidomics approach that is emerging.

A short-term n-3 DPA supplementation study in humans

PURPOSE

Despite the detailed knowledge of the absorption and incorporation of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) into plasma lipids and red blood cells (RBC) in humans, very little is known about docosapentaenoic acid (DPA, 22:5 n-3). The aim of this study was to investigate the uptake and incorporation of pure DPA and EPA into human plasma and RBC lipids.

METHODS

Ten female participants received 8 g of pure DPA or pure EPA in randomized crossover double-blinded manner over a 7-day period. The placebo treatment was olive oil. Blood samples were collected at days zero, four and seven, following which the plasma and RBC were separated and used for the analysis of fatty acids.

RESULTS

Supplementation with DPA significantly increased the proportions of DPA in the plasma phospholipids (PL) (by twofold) and triacylglycerol (TAG) fractions (by 2.3-fold, day 4). DPA supplementation also significantly increased the proportions of EPA in TAG (by 3.1-fold, day 4) and cholesterol ester (CE) fractions (by 2.0-fold, day 7) and of DHA in TAG fraction (by 3.1-fold, day 4). DPA proportions in RBC PL did not change following supplementation. Supplementation with EPA significantly increased the proportion of EPA in the plasma CE and PL fractions, (both by 2.7-fold, day 4 and day 7) and in the RBC PL (by 1.9-fold, day 4 and day 7). EPA supplementation did not alter the proportions of DPA or DHA in any lipid fraction. These results showed that within day 4 of supplementation, DPA and EPA demonstrated different and specific incorporation patterns.

CONCLUSION

The results of this short-term study suggest that DPA may act as a reservoir of the major long-chain n-3 fatty acids (LC n-3 PUFA) in humans.

Do omega-6 and trans fatty acids play a role in complex regional pain syndrome? A pilot study

OBJECTIVES

The study aims to compare the omega-6 (n-6) and omega-3 (n-3) highly unsaturated fatty acids (HUFA), and trans fatty acid (trans FA) status of Complex Regional Pain Syndrome (CRPS) patients to pain-free controls.

DESIGN

Case control study. Setting. The setting was at a multidisciplinary rehabilitation center.

PATIENTS

Twenty patients that met the Budapest research diagnostic criteria for CRPS and 15 pain-free control subjects were included in this study. Outcome Measures. Fasting plasma fatty acids were collected from all participants. In CRPS patients, pain was assessed using the McGill Pain Questionnaire-Short Form. In addition, results from the perceived disability (Pain Disability Index), pain-related anxiety (Pain Anxiety Symptom Scale Short Form), depression (Center for Epidemiologic Studies Depression Scale Short Form), and quality of life (Short Form-36 [SF-36]) were evaluated.

RESULTS

Compared with controls, CRPS patients demonstrated elevated concentrations of n-6 HUFA and trans FA. No differences in n-3 HUFA concentrations were observed. Plasma concentrations of the n-6 HUFA docosatetraenoic acid were inversely correlated with the "vitality" section of the SF-36. Trans FA concentrations positively correlated with pain-related disability and anxiety.

CONCLUSION

These pilot data suggest that elevated n-6 HUFA and trans FA may play a role in CRPS pathogenesis. These findings should be replicated, and more research is needed to explore the clinical significance of low n-6 and trans FA diets with or without concurrent n-3 HUFA supplementation, for the management of CRPS.

Retinal very long-chain PUFAs: new insights from studies on ELOVL4 protein

Compared with other mammalian tissues, retina is highly enriched in PUFA. Long-chain PUFA (LC-PUFA; C18-C24) are essential FAs that are enriched in the retina and are necessary for maintenance of normal retinal development and function. The retina, brain, and sperm also contain very LC-PUFA (VLC-PUFA; >C24). Although VLC-PUFA were discovered more than two decades ago, very little is known about their biosynthesis and functional roles in the retina. This is due mainly to intrinsic difficulties associated with working on these unusually long polyunsaturated hydrocarbon chains and their existence in small amounts. Recent studies on the FA elongase elongation of very long chain fatty acids-4 (ELOVL4) protein, however, suggest that VLC-PUFA probably play some uniquely important roles in the retina as well as the other tissues. Mutations in the ELOVL4 gene are found in patients with autosomal dominant Stargardt disease. Here, we review the recent literature on VLC-PUFA with special emphasis on the elongases responsible for their synthesis. We focus on a novel elongase, ELOVL4, involved in the synthesis of VLC-PUFA, and the importance of these FAs in maintaining the structural and functional integrity of retinal photoreceptors.

Short-term docosapentaenoic acid (22 : 5n-3) supplementation increases tissue docosapentaenoic acid, DHA and EPA concentrations in rats

The metabolic fate of dietary n-3 docosapentaenoic acid (DPA) in mammals is currently unknown. The aim of the present study was to determine the extent of conversion of dietary DPA to DHA and EPA in rats. Four groups of male weanling Sprague–Dawley rats (aged 5 weeks) were given 50 mg of DPA, EPA, DHA or oleic acid, daily for 7 d by gavage. At the end of the treatment period, the tissues were analysed for concentrations of long-chain PUFA. DPA supplementation led to significant increases in DPA concentration in all tissues, with largest increase being in adipose (5-fold) and smallest increase being in brain (1·1-fold). DPA supplementation significantly increased the concentration of DHA in liver and the concentration of EPA in liver, heart and skeletal muscle, presumably by the process of retroconversion. EPA supplementation significantly increased the concentration of EPA and DPA in liver, heart and skeletal muscle and the DHA concentration in liver. DHA supplementation elevated the DHA levels in all tissues and EPA levels in the liver. Adipose was the main tissue site for accumulation of DPA, EPA and DHA. These data suggest that dietary DPA can be converted to DHA in the liver, in a short-term study, and that in addition it is partly retroconverted to EPA in liver, adipose, heart and skeletal muscle. Future studies should examine the physiological effect of DPA in tissues such as liver and heart.

Selective polyunsaturated fatty acids enrichment in phospholipids from neuronal-derived cell lines

Most studies aimed at exploring the molecular and cellular properties of plasma membranes in neural tissues make use of cell lines. However, cell membrane lipid composition of cell lines is notably different from that of brain tissues where they presumably derive from. Using septal-derived SN56 cells and hippocampal-derived HT22 cells, we demonstrated that cell lines exhibit lower contents of saturated (18:0) and long polyunsaturated fatty acids (PUFA; 20:4n-6 and especially 22:6n-3), as well as higher monounsaturated fatty acid contents (mainly 18:1n-9), compared to mouse brain. Also, cell lines exhibited higher contents of sterol esters and lower contents of cholesterol and phospholipids, especially phosphatidylethanolamine and phosphatidylserine. We have also evaluated the effects of different (n-3/n-6) PUFA enrichments on fatty acid and phospholipid contents in these cell lines. Our results show that enrichment of culture medium with 22:6n-3 and 20:4n-6 in a 70/30 proportion during 48 h, using fat-free bovine serum albumin as vehicle, successfully readjusted fatty acid profiles in cell line-polar lipids to values found in natural nerve cells. Interestingly, no differences in cell survival were observed upon enrichment. The generalization of these methodologies would allow a more feasible adaptation of cellular models to the study of in vivo nerve physiology.

The Influence of long-chain polyunsaturated fatty acids on total lipid fatty acid composition of a canine mastocytoma cell line

Cutaneous mast cells are considered as key immune effectors in the pathogenesis of canine atopic dermatitis (CAD). These cells release immediate-phase and late-phase mediators of inflammation. Dietary fatty acids are incorporated in cellular membranes and seem to influence mediator production and release. A dietary intervention with n6- and n3-fatty acids is thought to alleviate clinical symptoms in atopic dogs. The purpose of this study was to examine the effects of n6- and n3-fatty acids on the fatty acid composition of canine mastocytoma cells (C2) as a possible model for CAD. The C2 was cultured in a basic medium called Dulbecco's modified Eagle's medium (DEH) or with additional 14 mum linoleate (C18:2n6, DEH-LA), gamma-linolenate (C18:3n6, DEH-GLA), arachidonate (C20:4n6, DEH-AA), alpha-linolenate (C18:3n3, DEH-LnA), eicosapentaenoate (C20:5n3, DEH-EPA) or docosahexaenoate (C22:6n3, DEH-DHA). Cell growth was examined for 11 days in all media. Cell growth increased from days 1 to 8 and decreased thereafter in all media conditions. The fatty acids supplied did not influence cell growth. The cells were harvested after 8 days for fatty acid analysis. The fatty acid composition was determined by gas chromatography after extraction and trans-esterification of the lipids. The added fatty acids increased the concentration of these fatty acids in C2 differently (LA 4.9-fold, GLA 6.9-fold, AA 6-fold, LNA 9.3-fold, EPA 6.5-fold and DHA 8.4-fold). Furthermore, elongated and Delta6-desaturated products of the corresponding fatty acids were significantly elevated. However, Delta5-desaturated products were not measurable. These results let us assume that C2 has no measurable activity of the Delta5-desaturase. In case the low activity of Delta5-desaturase is one of the mechanisms underlying the pathogenesis of CAD, C2 seems to be an adequate model for investigations in CAD.

Alterations of mast cell mediator production and release by gamma-linolenic and docosahexaenoic acid

The purpose of our investigations was to evaluate the supposed beneficial effects of gamma-linolenic (GLA) and docosahexaenoic acid (DHA) in a canine mastocytoma cell line (C2) as a model for canine atopic dermatitis. Cells were cultured in a basic medium (DEH) and in DEH supplemented with 14.3 microM GLA (DEH-GLA) or 14.3 microM DHA (DEH-DHA) for 8 days. Chymase and tryptase activity, as well as histamine and prostaglandin (PG)E(2) release were measured. To stimulate histamine and PGE(2) release, cells were incubated with the wasp venom peptide mastoparan (50 microM) for 30 min. GLA increased tryptase activity and decreased histamine release after C2 stimulation. DHA diminished PGE(2) production in activated C2. These results support the prescription of GLA- and DHA-enriched diets to reduce inflammatory signs in canine atopic dermatitis.

A review of the safety of DHA45-oil

Polyunsaturated fatty acids (PUFAs), such as docosahexaenoic acid (DHA), are natural constituents of the human diet; however, dietary intakes of these fatty acids are below recommended values. The main dietary source of DHA is fatty fish, with lesser amounts provided by shellfish, marine mammals, and organ meats. The addition to traditional food products of refined oils produced by marine microalgae represents potential sources of supplemental dietary DHA. DHA45-oil is manufactured through a multi-step fermentation and refining process using a non-toxigenic and non-pathogenic marine protist. Comprising approximately 45% DHA, and lesser concentrations of palmitic acid and docosapentaenoic acid, DHA45-oil is intended for use in foods as a dietary source of DHA. The safety of DHA45-oil was evaluated in various genotoxicity and acute, subchronic, and reproductive toxicity studies. DHA45-oil produced negative results in genotoxicity assays and demonstrated a low acute oral toxicity in mice and rats. Dietary administration of DHA45-oil to rats in subchronic and one-generation reproductive studies produced results consistent with those observed in oral studies using high concentrations of omega-3 PUFAs from fish or other microalgal-derived oils. The results of these studies, as well as those of various published metabolic, toxicological, and clinical studies with DHA-containing oils, support the safety of DHA45-oil as a potential dietary source of DHA.

Effects of essential fatty acid deficiency and supplementation with docosahexaenoic acid (DHA; 22:6n-3) on cellular fatty acid compositions and fatty acyl desaturation in a cell culture model

The desaturation of [1-(14)C] 18:3n-3 to docosahexaenoic acid (DHA; 22:6n-3) is enhanced in an essential fatty acid deficient cell line (EPC-EFAD) in comparison with the parent cell line (EPC) from carp. In the present study, the effects of DHA on lipid and fatty acid compositions, and the metabolism of [1-(14)C]18:3n-3 were investigated in EPC-EFAD cells in comparison with EPC cells. DHA supplementation had only relatively minor effects on lipid content and lipid class compositions in both EPC and EPC-EFAD cells, but significantly increased the amount of DHA, 22:5n-3, eicosapentaenoic acid (EPA; 20:5n-3), total n-3 polyunsaturated fatty acids (PUFA), total PUFA and saturated fatty acids in total lipid and total polar lipid in both cell lines. Retroconversion of supplemental DHA to EPA was significantly greater in EPC cells. Monounsaturated fatty acids, n-9 and n-6PUFA were all decreased in total lipid and total polar lipid in both cell lines by DHA supplementation. The incorporation of [1-(14)C]18:3n-3 was greater into EPC-EFAD compared to EPC cells but DHA had no effect on the incorporation of [1-(14)C]18:3n-3 in either cell line. In contrast, the conversion of [1-(14)C]18:3n-3 to tetraenes, pentaenes and total desaturation products was similar in the two cell lines and was significantly reduced by DHA supplementation in both cell lines. However, the production of DHA from [1-(14)C]18:3n-3 was significantly greater in EPC-EFAD cells compared to EPC cells and, whereas DHA supplementation had no effect on the production of DHA from [1-(14)C]18:3n-3 in EPC cells, DHA supplementation significantly reduced the production of DHA from [1-(14)C] 18:3n-3 in EPC-EFAD cells. Greater production of DHA in EPC-EFAD cells could be a direct result of significantly lower levels of end-product DHA in these cells' lipids compared to EPC cells. Consistent with this, the suppression of DHA production upon DHA supplementation was associated with increased cellular and membrane DHA concentrations in EPC-EFAD cells. However, an increase in cellular DHA content to similar levels failed to suppress DHA production in DHA-supplemented EPC cells. A possible explanation is that greatly increased levels of EPA, derived from retroconversion of the added DHA, acts to offset the suppression of the pathway by DHA by stimulating conversion of EPA to DHA in DHA-supplemented EPC cells.

Incorporation and metabolism of trans 20:5 in endothelial cells. Effect on prostacyclin synthesis

To study the ability of long-chain trans fatty acids (FA) to be incorporated and metabolized into endothelial cells, bovine aortic endothelial cells were incubated with medium enriched eicosapentaenoic acid (EPA) bound to albumin (M2) or one of its geometrical isomers: 20:5 5c,8c,11t,14c,17c (M3), 20:5 5c,8c,11c,14c,17t (M4), or 20:5 5c,8c,11t,14c,17t (M5). After 48 h of incubation, supernatant and cells were harvested and their lipids were analyzed, including prostacyclin synthesis. EPA and 22:5n-3 of endothelial cells incubated with M2 were, respectively, three and two times higher than in control cells (incubated in M1, without any fatty acid added), whereas 22:6n-3 increased only in the supernatant, suggesting its release after biosynthesis. However, 18:2n-6 and 22:4n-6 decreased (about 30%). Trans 20:5 isomers represented 4.7, 3.9, and 5.2% of total phospholipid FA in endothelial cells incubated with M3, M4, and M5, respectively. They were elongated into trans 22:5 and trans 24:5, as revealed by gas chromatography-mass spectrometry and gas chromatography-Fourier transform infrared analysis. In cells incubated with M2, M3, M4, and M5, prostacyclin synthesis was inhibited by 49.0, 62.5, 60.5, and 72.0%, respectively. This effect may be due to less available arachidonic acid in the cells and to a competition between EPA isomers and AA at the level of cyclooxygenase pathway, as it was demonstrated that 20:5 delta17t was metabolized by this enzyme.

Dietary trans fatty acids affect docosahexaenoic acid concentrations in plasma and liver but not brain of pregnant and fetal rats

The aim of the present study was to investigate the maternal-fetal transport, incorporation, and effects on liver delta-6 fatty-acid desaturase activity of dietary trans fatty acids in pregnant rats. Three groups of six rats each were fed three experimental diets containing approximately 0%, 15%, and 30% of trans fatty acids but containing the same proportion of linoleic (18:2 n-6) and a-linolenic (18:3 n-3) acids for 10 wk. On d 20 of pregnancy, the animals from each group were killed. We determined the fatty acid profiles in plasma, brain, and liver microsomes of pregnant rats, as well as in placenta and fetal liver and brain. No changes were found in the number of fetuses of the pregnant rats. Trans fatty acids were incorporated in high concentrations in placenta and in maternal and fetal tissues, except brain, strongly elevating the linoleic acid proportion and lowering that of docosahexaenoic acid. The delta-6 fatty-acid desaturase activity in the liver microsomes of the pregnant rats was inhibited by trans isomers. In conclusion, high intakes of trans fatty acids partially inhibit liver delta-6 fatty-acid desaturase in pregnant rats, which may explain, in part, the low concentrations of docosahexaenoic acid in pregnant and fetal tissues. However, the fatty acid composition of both fetal and pregnant rat brain remains mostly unaffected regardless of the dietary trans fatty acid content.

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.

Bioequivalence of dietary alpha-linolenic and docosahexaenoic acids as sources of docosahexaenoate accretion in brain and associated organs of neonatal baboons

The dietary bioequivalence of alpha-linolenic (LNA) and docosahexaenoic acids (DHA) as substrates for brain and retinal n-3 fatty acid accretion during the brain growth spurt is reported for neonatal baboons who consumed a long-chain-polyunsaturate free commercial human infant formula with a n-6/n-3 ratio of 10:1. Neonates received oral doses of 13C-labeled fatty acids (LNA*) or (DHA*) at 4 wk of age, and at 6 wk brain (occipital cortex), retina, retinal pigment epithelium, liver, erythrocytes, and plasma were analyzed. In the brain, 1.71% of the preformed DHA* dose was detected, whereas 0.23% of the LNA* dose was detected as DHA*, indicating that preformed DHA is 7-fold more effective than LNA-derived DHA as a source for DHA accretion. In LNA*-dosed animals, DHA* was greater than 60% of labeled fatty acids in all tissues except erythrocytes, where docosapentaenoic acid was 55%. Estimates using dietary LNA levels as tracees indicate that brain turnover of DHA is less than 5% per week between weeks 4 and 6 of life. For retina and retinal pigment epithelium, preformed DHA was at levels 12-fold and 15-fold greater than LNA-derived DHA. Liver, plasma, and erythrocytes ratios were 27, 29, and 51, respectively, showing that these pools do not parallel tissue metabolism of a single dose of omega-3 fatty acids. The distributions of labeled fatty acids for LNA*-dosed animals were similar, in the order DHA > DPA > EPA > LNA, except for erythrocytes where docosapentaenoic acid predominated. These are the first direct measurements of the bioequivalence of DHA and LNA in neonatal primate brain and associated tissues.

Analysis of the putative role of 24-carbon polyunsaturated fatty acids in the biosynthesis of docosapentaenoic (22:5n-6) and docosahexaenoic (22:6n-3) acids

The recent literature on the putative involvement of a single cycle of peroxisomal beta-oxidation of 24:5n-6 and 24:6n-3 polyunsaturated fatty acids in the biosynthesis of the respective docosapentaenoic (22:5n-6) and docosahexaenoic (22:6n-3) fatty acids is critically reviewed. Present evidence suggests that in vitro data in support of the above proposition is an artifact of a low 2,4-dienoyl-CoA reductase activity due to depletion of NADPH resulting from incubation conditions. Kinetic studies with radiolabeled precursors in cell cultures have shown lower initial rates of labeling of 24:6n-3 than that of 22:6n-3, indicating that 24:6n-3 is an elongation product of 22:6n-3 rather than its precursor. Analysis of other literature data supports the proposal that 22:5n-6 and 22:6n-3 are synthesized in mitochondria via channeled carnitine-dependent pathways involving separate n-6- and n-3-specific desaturases. It is proposed that impaired peroxisomal function in some peroxisomal disorders is a secondary consequence of defective mitochondrial synthesis of 22:6n-3; moreover, some disorders of peroxisomal beta-oxidation show normal or increased 22:5n-6 concentrations, indicating that 22:5n-6 is synthesized by independent desaturases without peroxisomal involvement.

Metabolic aspects of trans fatty acids

The consumption of trans isomers of unsaturated fatty acids has been associated withuntoward metabolic effects. Several clinical investigations demonstrated that trans fatty acids increase plasma LDL-cholesterol and lipoprotein (a) and reduce HDL-cholesterol concentrations. These alterations of plasma lipid profiles indicate an atherogenic effect of trans fatty acids. Both in preterm infants and in healthy children aged 1-15 years, we found blood plasma arachidonic acid (C20:4omega-6) levels and the product/substrate ratios of arachidonic acid synthesis (C20:4omega-6/C18:2omega-6) inversely correlated to the level of the principal trans fatty acid, trans octadecaenoic acid (C18:1omega-9/7, trans), which is compatible with a dose-dependent inhibition of arachidonic acid synthesis by trans fatty acids. Moreover, in premature infants trans fatty acids in blood plasma correlated inversely with birth weight in an observational study, indicating that trans fatty acids may impair early human growth. It appears desirable to limit the dietary intake of trans fatty acids. The major dietary sources of trans fatty acids are partially hydrogenated vegetable and fish oils. Refinement of the industrial technology of partial hydrogenation and appropriate food labelling may lead to a considerably decrease of human exposure to trans fatty acids.

Modification of odd-chain length unsaturated fatty acids by hepatocytes of rainbow trout (Oncorhynchus mykiss) fed diets containing fish oil or olive oil

Hepatocytes isolated from rainbow trout fed on diets containing either fish oil or olive oil were incubated with individual odd-chain length unsaturated fatty acids (19:1n-9, 19:2n-6, 19:3n-3, 21:2n-6, 21:3n-6, 21:4n-6, 21:3n-3, and 21:5n-3) to examine whether these fatty acids were substrates for modification by desaturation and elongation. All odd-chain length fatty acids were readily assimilated into the lipids of hepatocytes from both dietary groups of fish, but their conversion to longer-chain, more unsaturated derivatives was more pronounced with cells from trout fed olive oil. Thus, the conversion of 19:2n-6 and 21:2n-6 to 21:3n-6 and 21:4n-6, and of 19:3n-3 to 21:4n-3 and 21:5n-3, was most obvious in cells from the olive oil group, as was the conversion of 21:3n-6 and 21:3n-3 to 21:4n-6 and 21:4n-3, respectively. Elongation of 19:1n-9 to 21:1n-9 and 23:1n-9 occurred in cells from both groups. No 23:6n-3 was detectable as a product of 19:3n-3 or 21:3n-3. However, this fatty acid was a major product formed by cells from fish fed olive oil presented with 21:5n-3. Cells from both groups of fish incorporated 21:4n-6 and 21:5n-3 into their lipids largely without modification but chain-shortened around 40, 23, and 19% of the incorporated 21:2n-6, 21:3n-3, and 19:1n-9, respectively. The results demonstrate that odd-chain length unsaturated fatty acids can act as substrates for the desaturation, elongation, and chain-shortening systems of trout hepatocytes.

On the molecular etiology of decreased arachidonic (20:4n-6), docosapentaenoic (22:5n-6) and docosahexaenoic (22:6n-3) acids in Zellweger syndrome and other peroxisomal disorders

Alterations in the metabolism of arachidonic (20:4n-6), docosapentaenoic (22:5n-6), and docosahexaenoic (22:6n-3) acids and other polyunsaturated fatty acids in Zellweger syndrome and other peroxisomal disorders are reviewed. Previous proposals that peroxisomes are necessary for the synthesis of 22:6n-3 and 22:5n-6 are critically examined. The data suggest that 22:6n-3 is biosynthesized in mitochondria via a channelled carnitine-dependent pathway involving an n-3-specific delta-4 desaturase, while 20:4n-6, 20:5n-3 and 22:5n-6 are synthesized by both mitochondrial and microsomal systems; these pathways are postulated to be interregulated as compensatory-redundant systems. Present evidence suggests that 22:6n-3-containing phospholipids may be required for the biochemical events involved in successful neuronal migration and developmental morphogenesis, and as structural cofactors for the functional assembly and integration of a variety of membrane enzymes, receptors, and other proteins in peroxisomes and other subcellular organelles. A defect in the mitochondrial desaturation pathway is proposed to be a primary etiologic factor in the clinicopathology of Zellweger syndrome and other related disorders. Several implications of this proposal are examined relating to effects of pharmacological agents which appear to inhibit steps in this pathway, such as some hypolipidemics (fibrates), neuroleptics (phenothiazines and phenytoin) and prenatal alcohol exposure.

Dietary marine algae promotes efficient deposition of n-3 fatty acids for the production of enriched shell eggs

Two experiments were conducted to investigate the usefulness of a natural golden marine algae (MA) as a poultry ration supplement for the production of shell eggs rich in n-3 fatty acids (n-3 FA). This MA is unique due to a high concentration of docosahexaenoic acid (DHA; C22:6n-3) and the absence of other n-3 FA normally present in marine oils such as menhaden oil (MO). In the first experiment, 60 24-wk-old Single Comb White Leghorn (SCWL) hens were divided among four dietary treatments, including a typical corn-soybean control (CON); 1.5% MO, supplying 233 mg eicosapentaenoic acid (EPA) and 155 mg DHA per d; 2.4% MA, supplying 200 mg DHA/d; and 4.8% MA, supplying 400 mg DHA/d. A second experiment using 96 56-wk-old SCWL was conducted using the same diets. In both experiments, eggs were collected weekly for 4 wk for determination of egg production parameters and yolk FA content. Each week, yolk samples were extracted, methyl estered, and quantified using gas chromatography. Transient depression in egg and yolk weights were noted early in Experiment 1 in response to dietary 4.8% MA. Although egg and yolk weights were not affected in Experiment 2, egg production was significantly reduced in the 4.8% MA treatment. Egg production was unaffected due to diet or week in Experiment 1. In both experiments, yolk polyunsaturated profiles were significantly influenced by diet. Dietary n-3 FA supplementation significantly increased yolk total N-3 FA with concomitant reductions in yolk n-6 FA. Although hens fed MO were supplied predominantly EPA, the principal yolk FA deposited was DHA. Marine algae also promoted efficient yolk DHA deposition with the highest yolk DHA concentrations attained in eggs from hens fed 4.8% MA. These data indicate that utilization of MA as a direct source of dietary n-3 FA may provide an efficient alternative to current sources of n-3 FA available for the production of poultry products rich in n-3 FA.

Docosapentaenoic acid (22:5,n-3): metabolism and effect on prostacyclin production in endothelial cells

Eicosapentaenoic acid (EPA, 20:5,n-3) and docosahexaenoic acid (DHA, 22:6, n-3), the two main fatty acids of fish oil, have been shown to inhibit prostacyclin production and to be actively interconverted, leading to the accumulation of docosapentaenoic acid (DPA, 22:5,n-3) in endothelial cell phospholipids. We have investigated the effect of supplementing endothelial cells with DPA on their capacity to produce prostacyclin. We found that endothelial cells incubated for 22 h with 25 microM DPA bound to albumin (fatty acid/albumin ratio of 1.3) produced two-fold less prostacyclin compared to control cells when stimulated with endogenous arachidonic acid-mobilizing agents such as bradykinin and calcium ionophore A23187. Since the formation of prostacyclin from 0.1-15 microM exogenous arachidonic acid was also reduced, it is suggested that prostacyclin inhibition observed in DPA-treated cells might not proceed from a reduction of arachidonic acid availability only. Such an inhibition was already observed after 1 h incubation of the cells with DPA, and with 2-20 times lower DPA concentrations. The inhibition might depend on EPA which was formed by retroconversion of DPA.

Utilization of precursor essential fatty acids in culture by skin fibroblasts from schizophrenic patients and normal controls

Based on the lower levels of long-chain polyunsaturated analogs of essential fatty acids (EPUFAs) in plasma membrane phospholipids of red blood cells, brain and cultured skin fibroblasts from schizophrenic patients, a defective utilization (uptake, conversion to EPUFAs and incorporation into membrane phospholipids) of precursor EFAs has been suggested. Utilization of radiolabeled linoleic (LA, 18:2(n-6)) and alpha-linolenic (ALA, 18:3(n-3)) acids was studied in cultured skin fibroblasts from patients with established schizophrenia and at the first episode of psychosis, and normal controls. Uptake and incorporation of both the EFAs were similar in fibroblasts from both groups of patients studied compared with normal controls. However, although the utilization of LA into arachidonic acid (AA, 20:4n-6) was similar in patients and controls, the utilization of eicosapentaenoic acid (EPA, 20:5(n-3)) into docosahexaenoic acid (DHA, 22:6(n-3)) was significantly lower in first-episode psychotic patients (patients, 96.33 +/- 27.16 versus normals, 161.66 +/- 26.33 nmoles per mg total protein; P = < 0.001). This data indicates that the level of delta 6- as well as delta 5-desaturase may be normal. However, the levels of delta 4-desaturase may be lower in fibroblasts from schizophrenic patients even at the first episode of psychosis.

Biosynthesis of docosahexaenoic acid in human cells: evidence that two different delta 6-desaturase activities may exist

It has been proposed that synthesis of docosahexaenoic acid (22:6(n-3) in rat hepatocytes occurs by a route independent of delta 4-desaturase, which involves delta 6-desaturation and retroconversion (Voss A., Reinhart M., Sankarappa S. and Sprecher H. (1991) J. Biol. Chem. 266, 19995-20000). However, most cells exhibit these enzymatic activities and nevertheless synthesize low to undectectable amounts of 22:6(n-3). Moreover, there are few data on the occurrence of this pathway in human cells. In the present work, we have analysed the biosynthetic pathway of 22:6(n-3) in human Y-79 retinoblastoma and Jurkat T-cells. Y-79 cells were supplemented with 18:3(n-3) and 20:5(n-3) or incubated with [1-14C]18:3(n-3) and [1-14C]20:5(n-3) and lipids analysed by argentation TLC, reverse-phase TLC and GLC-mass spectrometry. Pulse-chase experiments revealed that synthesis of 22:6(n-3) from 20:5(n-3) in Y-79 cells occurred through two successive elongations, followed by a delta 6-desaturation of 24:5(n-3) to 24:6(n-3) and retroconversion to 22:6(n-3). Incubation of Y-79 cells with [1-14C]18:3(n-3) in medium containing 50 microM trans-9,12-18:2, a potent inhibitor of delta 6-desaturase, caused a reduction of 22:6(n-3) synthesis mainly by interfering with the desaturation of 18:3(n-3). However, when [1-14C]20:5(n-3) was used as precursor, synthesis of 22:6(n-3) was depressed to a lesser extent and mainly by reduction of 24:6(n-3) retroconversion. Neuronal differentiation of Y-79 cells caused a great increase in delta 6-desaturase activity on 18:3(n-3), though the amount of 22:6(n-3) synthesized did not change or diminish, suggesting the existence of a particular delta 6-desaturase involved in the synthesis of 22:6(n-3). The existence of a distinctive delta 6-desaturase activity could also explain why Jurkat cells growing in serum-free medium showed a near 3-fold increase in the synthesis of pentaenes from 18:3(n-3) and, at the same time, a large decrease in the synthesis of 22:6(n-3). The verification of the involvement of two delta 6-desaturase activities in 22:6(n-3) synthesis would have important implications for the formulation of the nutritional requirements of this fatty acid during development.

Docosapentaenoic acid (22:5, n-3), an elongation metabolite of eicosapentaenoic acid (20:5, n-3), is a potent stimulator of endothelial cell migration on pretreatment in vitro

Endothelial cell (EC) migration plays an important role in wound repair of blood vessels. We have previously reported that eicosapentaenoic acid (EPA; 20:5, n-3) pretreatment stimulates migration of ECs but not smooth muscle cells. In the present study, we used the modified Boyden chamber technique to investigate whether the stimulative effect of EPA pretreatment on EC migration is caused by EPA itself or by some metabolites of EPA. When ECs were treated with EPA (5 micrograms/ml) for 2 days, EPA was predominantly elongated to docosapentaenoic acid (DPA; 22:5, n-3), with little docosahexaenoic acid (DHA; 22:6, n-3) being formed. Direct pretreatment of ECs with DPA (0.01-1.0 microgram/ml) resulted in a dose-dependent increase in migration in response to fetal bovine serum. Moreover, maximum stimulation of EC migration by DPA pretreatment (0.5 microgram/ml) was achieved at a concentration one-tenth of that required for maximal stimulation by EPA pretreatment (5.0 micrograms/ml), indicating that DPA is a potent stimulator of EC migration. We have demonstrated by lipid analysis that direct DPA pretreatment (0.5 microgram/ml) sufficiently increased the absolute quantity of phospholipids of ECs. Cyclooxygenase inhibitor and lipoxygenase inhibitor did not abolish the stimulative effect of DPA pretreatment on EC migration. In contrast to EC migration, DPA pretreatment had no effect on smooth muscle cell migration. Together these data suggest that the stimulative effect of EPA on EC migration occurs via DPA, and that DPA may act as a powerful anti-atherogenic factor.

Studies on the metabolism of [1-14C]5.8.11-eicosatrienoic (Mead) acid in rat hepatocytes

The oxidation, esterification and formation of chain elongated and desaturated products of [1-14C]5,8,11-eicosatrienoic (Mead) acid was studied. Liver cells from essentially fatty acid deficient (EFAD) and control rats were used. The metabolism of [1-14C]20:4, n-6 and [1-14C]20:5, n-3 were studied under the same experimental conditions. More 20:3, n-9 than 20:4, n-6 and 20:5, n-3 was oxidised both in EFAD and control cells. 20:3, n-9 was elongated to [14C]22:3, n-9 in both cell types and significant amounts of [14C]22:4, n-9 were formed in EFAD cells. Less 20:3, n-9 was esterified in phospholipids and more in triacylglycerol than observed with 20:4, n-6 and 20:5, n-3 in both cell types. 20:3, n-9 was mainly esterified in phosphatidylcholine and little was esterified in phosphatidylethanolamine compared to 20:4, n-6 and 20:5, n-3. In comparison, 20:3, n-9 was rather efficiently esterified in phosphatidylinositol as 18:0-20:3. [14C]22:4, n-9 formed from 20:3, n-9 in EFAD hepatocytes was esterified in triacylglycerol, not in phospholipids, unlike [14C]22:5, n-6 and [14C]22:6, n-3 which were mainly esterified in phospholipids.

N-3 and n-6 fatty acid metabolism in undifferentiated and differentiated human intestine cell line (Caco-2)

Metabolism of n-6 and n-3 fatty acids in the undifferentiated and differentiated human adenocarcinoma colon cell line (Caco-2) was studied. In cells incubated with either 18:2n-6 or 18:3n-3, no significant amounts of long chain n-6 and n-3 metabolites were found. Incubation with either 18:3n-6 or 18:4n-3 raised significantly the levels of 20:3n-6 and 20:4n-3, respectively. In the undifferentiated cells, significant proportions of 20:3n-6 and 20:4n-3 were further delta 5-desaturated to form 20:4n-6 and 20:5n-3, respectively. Incubation with either 20:4n-6 or 20:5n-3 raised the levels of their direct elongation products, 22:4n-6 and 22:5n-3, respectively. Incubation with 22:4n-6 or 22:5n-3 increased the levels of 20:4n-6 and 20:5n-6. These results suggest that delta 6-desaturation in the Caco-2 cells is less active in comparison with elongation, delta 5-desaturation and retro-conversion. These enzymes were modulated by the state of differentiation, and appeared to be non-specific to n-3 and n-6 fatty acids. When cells were incubated with 18:3n-6 and 18:4n-3 concomitantly, the levels of incorporation of total n-6 fatty acids into cellular lipids were greater than those of the n-3 fatty acids, whereas the ratios of 20+22 carbon metabolites to 18-carbon precursor favored n-3 over n-6 fatty acids. These results suggest that n-3 and n-6 fatty acids were not metabolized identically in Caco-2 cells.

Interconversions and distinct metabolic fate of eicosapentaenoic, docosapentaenoic and docosahexaenoic acids in bovine aortic endothelial cells

The anti-aggregatory activity of endothelial cells being affected by eicosapentaenoic (EPA, 20:5(n-3)) and docosahexaenoic (DHA, 22:6(n-3)) acids, the two main polyunsaturated fatty acids of fish oil, these fatty acids, as well as their intermediary, docosapentaenoic acid (DPA, 22:5(n-3)), were investigated with respect to their metabolism. Primary cultured bovine aortic endothelial cells were supplemented for 22 h at 37 degrees C with either n-3 fatty acid, and the fatty acids of cell media, of cell lipid classes, and of choline and ethanolamine glycerophospholipids (PC and PE) were quantified. Endothelial cells converted each of the three fatty acids into the two others. They were found esterified in cell lipids and partly released in cell media, the respective parts varying according to the fatty acid. For instance, half of the DPA formed from EPA and two third of the EPA formed from DPA were released in the media. Moreover, the DHA formed from EPA and DPA was not esterified but released in media. In addition, the esterified counterparts were found in either PC or PE, depending on whether they were added or formed by conversions. It is concluded that EPA, DPA and DHA are actively interconverted each others, and differ substantially in terms of distribution between media and cells, and within phospholipid classes.

Very long chain fatty acids in higher animals--a review

Fatty acids with greater than 22 carbon atoms (very long chain fatty acids, VLCFA) are present in small amounts in most animal tissues. Saturated and monoenoic VLCFA are major components of brain, while the polyenoic VLCFA occur in significant amounts in certain specialized animal tissues such as retina and spermatozoa. Biosynthesis of VLCFA occurs by carbon chain elongation of shorter chain fatty acid precursors while beta-oxidation takes place almost exclusively in peroxisomes. Mitochondria are unable to oxidize VLCFA because they lack a specific VLCFA coenzyme A synthetase, the first enzyme in the beta-oxidation pathway. VLCFA accumulate in the tissues of patients with inherited abnormalities in peroxisomal assembly, and also in individuals with defects in enzymes catalyzing individual reactions along the beta-oxidation pathway. It is believed that the accumulation of VLCFA in patient tissues contributes to the severe pathological changes which are a feature of these conditions. However, little is known of the role of VLCFA in normal cellular processes, and of the molecular basis for their contribution to the disease process. The present review provides an outline of the current knowledge of VLCFA including their biosynthesis, degradation, possible function and involvement in human disease.

Diversity in the ability of cultured cells to elongate and desaturate essential (n-6 and n-3) fatty acids

Essential fatty acids (EFAs) cannot be synthesized by mammalian cells. Once taken in with the diet, they can undergo desaturations/saturations and chain elongations/shortenings to yield a variety of polyunsaturated fatty acids of the same family. Cells in vitro from a variety of tissues are capable of processing EFAs to varying extents. Conversion of the parent EFAs, linoleic (LA, n-6) and alpha-linolenic (LNA, n-3) acids, to the 20-carbon polyunsaturated fatty acids, arachidonic (AA, n-6) and eicosapentanoic (EPA, n-3), requires chain elongation and delta 6 and delta 5 desaturations. AA and EPA are required by many tissues for optimal biological function and are precursors of biologically active eicosanoid hormones. All cultured cells are able to elongate exogenous LA and LNA, and most can perform delta 5 desaturation, so delta 6 desaturation is the limiting step in AA and EPA production. Longer fatty acids that have more double bonds than AA or EPA are less frequently produced due to a deficiency in delta 4 desaturating ability. The process of retroconversion (chain shortening) is less extensively studied, but evidence from a variety of cells suggests that this type of metabolic conversion is normally active. The example of MCF-7 (human breast cancer cell line) and MCF-10A cells (human noncancerous breast cell line) is discussed in order to emphasize the diversity in EFA processing ability of cultured cells. Under identical culture conditions, MCF-10A cells perform extensive desaturations, elongations, and retroconversions, whereas MCF-7 cells can only elongate and retroconvert exogenous EFAs. Given the great diversity in the ability of cultured cells to process EFAs, no conclusions can be drawn regarding the mechanisms responsible for the effects of exogenous EFAs on a particular cell until that cell's EFA processing patterns have been evaluated.

Relationships between the fatty acid status and insulinemic indexes in obese children

The relationship between the fatty acid (FA) status and indices of insulin secretion in young obese subjects at risk of developing insulin resistance and its complications was investigated. In 12 subjects (8-14 years) at first diagnosis of obesity the FA composition of total plasma and circulating and erythrocyte phospholipids was related to basal and peak insulinemia and the insulinemic area resulting from a standard oral glucose tolerance test. Negative correlations were shown between both delta-6-desaturation products and 20:5 n-3 levels and insulinemic values. On the contrary, circulating total saturated and monounsaturated FA and erythrocyte phospholipid products of delta-5- and delta-4-desaturation positively correlate with insulinemic indices. The observed relationships could be markers of developing insulin resistance and suggest the possibility of a dietary intervention.

n-3 and n-6 fatty acid processing and growth effects in neoplastic and non-cancerous human mammary epithelial cell lines

The type rather than the amount of dietary fat may be more important in breast carcinogenesis. While animal studies support this view, little is known about the effects of essential fatty acids (EFAs) at the cellular level. The MCF-7 breast cancer and the MCF-10A non-cancerous human mammary epithelial cell lines are compared in terms of growth response to EFAs and ability to incorporate and process the EFAs. Eicosapentaenoic (EPA, n-3) and docosahexaenoic (DHA, n-3) acids, presented bound to albumin, inhibited the growth of MCF-7 cells by as much as 50% in a dose-dependent manner (6-30 microM) in medium containing 0.5% serum. alpha-Linolenic (LNA, n-3) and arachidonic (AA, n-6) acids inhibited growth less extensively, while linoleic acid (LA, n-6) had no effect. In contrast, MCF-10A cells were not inhibited by any of the EFAs at levels below 24 microM. The differential effects of AA, EPA and DHA on MCF-7 and MCF-10A cells support a protective role of highly unsaturated essential fatty acids against breast cancer. The EFAs were primarily incorporated into phosphoglycerides. MCF-7 cells showed chain elongations and possibly delta 8 desaturation, but no AA was formed from LA, nor EPA or DHA from LNA. In contrast, MCF-10A cells desaturated and elongated the exogenous EFAs via all the known pathways. These findings suggest defects in the desaturating enzymes of MCF-7 cells. LNA, DHA and AA presented to MCF-7 cells in phospholipid liposomes inhibited growth as extensively as albumin-bound free acids, but were less extensively incorporated, suggesting different mechanisms of inhibition for the two methods.

Formation of 22 and 24 carbon 6-desaturated fatty acids from exogenous deuterated arachidonic acid is activated in THP-1 cells at high substrate concentrations

Deuterated arachidonic acid (AA, [2H8]20:4 n-6) 1-25 microM, is converted to other fatty acids, as evaluated by gas chromatography-mass spectrometry, in THP-1 cells. The major products, in the 1 to 10 microM range, are 22:4 (elongated) and 20:3 (reduced in 5). At 25 microM, 24:4, 24:5 and 22:5 accumulate, with [2H8]/[2H0] ratios higher than in AA. At high AA concentration preferential conversion to elongated fatty acids with 5 unsaturations, through a 6 desaturase takes place and the 4-desaturated 22:5 appears to be formed through beta-oxidation of 24:5.

In vivo metabolism of [1-14C]linolenic acid (18:3(n-3)) and [1-14C]eicosapentaenoic acid (20:5(n-3)) in a marine fish: time-course of the desaturation/elongation pathway

The metabolism (via the desaturation/elongation pathways) of [1-14C]18:3(n-3) and [1-14C]20:5(n-3) in a marine fish, gilthead sea bream (Sparus aurata L.), were investigated over 8 days to determine the time-courses for the production of delta 6 and delta 5-desaturase products and 22:6(n-3). Fish were starved for 1 week prior to, and during, the period of the experiment. The recovery of radioactivity from [1-14C]20:5(n-3) in tissue lipids exceeded that of [1-14C]18:3(n-3) at all time points. The recoveries of both fatty acids decreased by 85-89% between days 2 and 8, indicating that substantial loss of radioactivity due to beta-oxidation occurred. Incorporation of 18:3(n-3) and 20:5(n-3) was predominantly into triacylglycerol but during the time-course of the experiment there were decreased percentages of radioactivity from both labelled fatty acids recovered in triacylglycerol with concomitant increased percentages recovered in phospholipids indicating preferential oxidation of fatty acids in triacylglycerol and/or redistribution of incorporated fatty acids. Recovery of radioactivity in 22:6(n-3) was 10-fold greater with [1-14C]20:5(n-3) than with [1-14C]18:3(n-3). However, there were few consistently significant trends in the levels of components of the desaturation/elongation pathways during the time-course of the experiment. In particular, the relative recovery of radioactivity in 22:6(n-3) did not increase during the experiment with either substrate. Substantial amounts of radioactivity were found in 24:5(n-3) and 24:6(n-3), particularly after injection with [1-14C]20:5(n-3), indicating that the conversion of 20:5(n-3) to 22:6(n-3) in sea bream may occur by a pathway utilizing delta 6-desaturase activity rather than by a delta 4-desaturation.

Abnormal plasma lipids of patients with Retinitis pigmentosa

Retinitis pigmentosa (RP) is a hereditary retinal degeneration of unknown etiology, resulting in progressive night blindness, loss of peripheral vision, abnormal retinal pigmentation and reduced electroretinographic response. Docosahexaenoic acid (22:6 omega 3) is found in high concentration in the rod outer segment membranes of the retina. Previous reports of low 22:6 omega 3 in blood lipids or phospholipids in RP patients prompted us to evaluate the complete fatty acid (FA) profiles of plasma phospholipids (PL), cholesteryl esters, triglycerides (TG) and nonesterified fatty acids (NEFA) in ten patients with RP. In the PL fraction, we found significantly depressed levels of 22:6 omega 3, 22:5 omega 3, total omega 3, 22:5 omega 6, 22:4 omega 6 and total omega 6 polyunsaturated FA (PUFA), and elevated total saturated acids. Plasma TG showed normal levels of PUFA, normal total saturated FA and total monounsaturated FA. The NEFA fraction showed significant elevation in total saturated FA with depressed total omega 6 PUFA. Evidence is accumulating mulating that RP is associated with abnormal PUFA and lipid metabolism.

Regulation of rat pulmonary endothelial cell interleukin-6 production by bleomycin: effects of cellular fatty acid composition

Previous studies have shown upregulation of lung cell interleukin-6 (IL-6) production in bleomycin-induced pulmonary fibrosis. To further elucidate the regulatory mechanisms governing this disease, the effects of bleomycin on the production of the pleiotropic cytokine, IL-6, were investigated in lung endothelial cells. Rat pulmonary artery endothelial cells were treated with bleomycin at doses previously shown to be effective in upregulating cytokine production in these cells, and the conditioned media was collected and assayed for IL-6 activity. The results show that these endothelial cells constitutively produced IL-6 and that bleomycin increased the production in a time- and dose-dependent manner. Feeding rats diets deficient in n-6 fatty acids is known to ameliorate bleomycin-induced lung fibrosis. In order to examine if fatty acids could modulate IL-6 production in vitro, cells were lipid depleted and then supplemented with 18:1n-9, 18:2n-6, or 18:3n-3 fatty acids, and the effects of bleomycin on IL-6 production reexamined. This regimen resulted in significant depletion of arachidonate in the 18:1n-9 and 18:3n-3 supplemented cells, which was associated with significantly reduced IL-6 production relative to the 18:2n-6-supplemented cells, both constitutively and when stimulated with bleomycin. Preincubation with indomethacin did not significantly inhibit the production of IL-6 by all three groups of cells, nor did supplementation with a stable prostacyclin analog increase IL-6 production. These results suggest that endothelial cell IL-6 production is not directly dependent on prostacyclin or other cyclooxygenase metabolites but may require or be upregulated by 18:2n-6 and/or metabolites derived from it.(ABSTRACT TRUNCATED AT 250 WORDS)

Peroxisomal beta-oxidation of polyunsaturated long chain fatty acids in human fibroblasts. The polyunsaturated and the saturated long chain fatty acids are retroconverted by the same acyl-CoA oxidase

The metabolism of the C22 unsaturated fatty acids erucic acid (22:1(n-9)), adrenic acid (22:4(n-6)), docosapentaenoic acid (22:5(n-3)) and docosahexaenoic acid (22:6(n-3)) was studied in cultured fibroblasts from patients with acyl-CoA oxidase deficiency, the Zellweger syndrome, X-linked adrenoleukodystrophy (X-ALD) and normal controls. [3-14C] 22:4 (n-6) and [3-14C] 22:5 (n-3) were shortened (retroconverted) to [1-14C] 20:4 (n-6) and [1-14C] 20:5 (n-3), respectively, in normal and X-ALD fibroblasts. In Zellweger and acyl-CoA oxidase deficient fibroblasts these reactions were deficient. Since the retroconversion is normal in X-ALD fibroblasts peroxisomal very long chain (lignoceryl) CoA ligase is probably not required for the activation of C22 unsaturated fatty acids. The present work with fibroblasts from patients with a specific acyl-CoA oxidase deficiency, previously shown to have a deficient peroxisomal clofibrate-inducible acyl-CoA oxidase, and which accumulate 24:0 and 26:0 fatty acids, supports the view that this enzyme is responsible for the chain-shortening of docosahexaenoic acid (22:6(n-3)), erucic acid (22:1(n-9)), docosapentaenoic acid (22:5(n-3)), and adrenic acid (22:4(n-6)) as well.