The metabolism of 7,10,13,16,19-docosapentaenoic acid to 4,7,10,13,16,19-docosahexaenoic acid in rat liver is independent of a 4-desaturase

Mechanisms involved in the differential reduction of omega-3 and omega-6 highly unsaturated fatty acids by structural heart disease resulting in "HUFA deficiency"

The causes of reduced levels of omega-3 and omega-6 highly unsaturated fatty acids ("HUFA deficiency") in heart failure remain unresolved. HUFA profiles were examined in the serum of 331 patients with failing versus nonfailing heart disease. Arachidonic acid was positively correlated (P < 0.001) with eicosapentaenoic acid (EPA) (r = 0.40) and docosahexaenoic acid (DHA) (r = 0.53) and negatively with palmitic (r = 0.42), palmitoleic (r = 0.38), and oleic acid (r = 0.48). Delta-5 desaturase activity was reduced (P < 0.01) in heart failure patients with low ejection fraction, dilatation, increased wall stress, and reduced heart rate variability (SDNN). In these patients, the reduced (P < 0.01) HUFA and increased palmitic (P < 0.01) and oleic acid (P = 0.05) arose from separate influences involving reduced cardiac contractility (arachidonic acid and palmitic acid predicted by ejection fraction) and chamber dilatation (DHA and oleic acid predicted by end-diastolic diameter). A low DHA (0.2%-0.9% versus 1.4%-3.1%) was associated (P < 0.025) with atrial dilatation (44 ± 8 mm versus 40 ± 8 mm). Equidirectional but less pronounced effects on HUFA were induced by sympathetic activation and (or) insulin resistance (fat and sugar fed to deoxycorticosterone acetate (DOCA)-salt rats) but not by compensated cardiac overload alone (DOCA-salt or aortic constriction), or reduced fatty acid oxidation (CPT-1 inhibition). Based on administration of omega-3 HUFA (OMACOR), dilatation is identified as a target for 1-2 g omega-3 HUFA·day(-1). Interventions for reduced arachidonic acid remain to be explored.

Towards a whole-body systems [multi-organ] lipidomics in Alzheimer's disease

Preclinical and clinical evidence suggests that docosahexaenoic acid (DHA), an omega-3 fatty acid derived from diet or synthesized in the liver, decreases the risk of developing Alzheimer's disease (AD). DHA levels are reduced in the brain of subjects with AD, but it is still unclear whether human dementias are associated with dysregulations of DHA metabolism. A systems biological view of omega-3 fatty acid metabolism offered unexpected insights on the regulation of DHA homeostasis in AD [1]. Results of multi-organ lipidomic analyses were integrated with clinical and gene-expression data sets to develop testable hypotheses on the functional significance of lipid abnormalities observed and on their possible mechanistic bases. One surprising outcome of this integrative approach was the discovery that the liver of AD patients has a limited capacity to convert shorter chain omega-3 fatty acids into DHA due to a deficit in the peroxisomal d-bifunctional protein. This deficit may contribute to the decrease in brain DHA levels and contribute to cognitive impairment.

The front-end desaturase: structure, function, evolution and biotechnological use

Very long chain polyunsaturated fatty acids such as arachidonic acid (ARA, 20:4n-6), eicosapentaenoic acid (EPA, 20:5n-3), docosapentaenoic acid (DPA, 22:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) are essential components of cell membranes, and are precursors for a group of hormone-like bioactive compounds (eicosanoids and docosanoids) involved in regulation of various physiological activities in animals and humans. The biosynthesis of these fatty acids involves an alternating process of fatty acid desaturation and elongation. The desaturation is catalyzed by a unique class of oxygenases called front-end desaturases that introduce double bonds between the pre-existing double bond and the carboxyl end of polyunsaturated fatty acids. The first gene encoding a front-end desaturase was cloned in 1993 from cyanobacteria. Since then, front-end desaturases have been identified and characterized from a wide range of eukaryotic species including algae, protozoa, fungi, plants and animals including humans. Unlike front-end desaturases from bacteria, those from eukaryotes are structurally characterized by the presence of an N-terminal cytochrome b₅-like domain fused to the main desaturation domain. Understanding the structure, function and evolution of front-end desaturases, as well as their roles in the biosynthesis of very long chain polyunsaturated fatty acids offers the opportunity to engineer production of these fatty acids in transgenic oilseed plants for nutraceutical markets.

Supranutritional selenium level affects fatty acid composition and oxidative stability of chicken breast muscle tissue

A total of 128 broilers were used to investigate the effect of selenium (Se) on fatty acid (FA) composition and oxidative stability of lipids in the breast muscle tissue. There were 4 replicates of 4 dietary treatments: T1 (basal diet with no added Se), T2 (T1 with 0.15 mg Se added per kg diet), T3 (T1 with 0.3 mg Se added per kg diet) and T4 (T1 with 3.0 mg Se added per kg diet). A yeast source was used for added Se. Breast muscle tissue was collected from two chickens per replicate pen for the determination of Se concentration by ICP-MS, FA profile by GC and lipid oxidation using thiobarbituric acid reactive substances method. Addition of supranutritional Se levels to chicken diets leads to the production of Se-enriched meat. Consumption of 100 g of breast meat from chickens fed diets supplemented with 0.15, 0.3 and 3 mg Se per kg of diet can provide 26, 41 and 220 μg of Se, respectively. Long-chain polyunsaturated fatty acids namely C20:3n-6, C20:4n-6, C20:5n-3, C22:5n-3 and C22:6n-3 increased linearly (p = 0.047, p < 0.001, p = 0.023, p = 0.003 and p = 0.002, respectively) as the Se inclusion levels in the diets increased. At slaughter, a linear decrease in lipid oxidation (p = 0.019) was observed with Se addition, possibly attributed to the antioxidant properties of Se. Addition of supranutritional Se to chicken diets, at levels well below those causing toxicity, leads to production of Se-enriched meat, protection of health-promoting long-chain FA like C20:5n-3 and C22:6n-3 and protection of meat quality from oxidation at day 1 after slaughter.

Echium acanthocarpum hairy root cultures, a suitable system for polyunsaturated fatty acid studies and production

Background

The therapeutic and health promoting role of highly unsaturated fatty acids (HUFAs) from fish, i.e. eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) are well known. These same benefits may however be shared by some of their precursors, the polyunsaturated fatty acids (PUFAs), such as stearidonic acid (SDA, 18:4 n-3). In order to obtain alternative sources for the large-scale production of PUFAs, new searches are being conducted focusing on higher plants oils which can contain these n-3 and n-6 C18 precursors, i.e. SDA and GLA (18:3n-6, γ-linolenic acid).

Results

The establishment of the novel Echium acanthocarpum hairy root cultures represents a powerful tool in order to research the accumulation and metabolism of fatty acids (FAs) in a plant particularly rich in GLA and SDA. Furthermore, this study constitutes the first example of a Boraginaceae species hairy root induction and establishment for FA studies and production. The dominant PUFAs, 18:2n-6 (LA, linoleic acid) and 18:3n-6 (GLA), accounted for about 50% of total FAs obtained, while the n-3 PUFAs, 18:3n-3 (ALA, α-linolenic acid) and 18:4n-3 (SDA), represented approximately 5% of the total. Production of FAs did not parallel hairy root growth, and the optimal productivity was always associated with the highest biomass density during the culture period. Assuming a compromise between FA production and hairy root biomass, it was determined that sampling times 4 and 5 gave the most useful FA yields. Total lipid amounts were in general comparable between the different hairy root lines (29.75 and 60.95 mg/g DW), with the major lipid classes being triacylglycerols. The FAs were chiefly stored in the hairy roots with very minute amounts being released into the liquid nutrient medium.

Conclusions

The novel results presented here show the utility and high potential of E. acanthocarpum hairy roots. They are capable of biosynthesizing and accumulating a large range of polyunsaturated FAs, including the target GLA and SDA fatty acids in appreciable quantities.

Testes of obese rats are highly responsive to n-3 long-chain fatty acids

The present study investigated whether fatty acid compositions of testes are affected by the obese condition and dietary n-3 long-chain fatty acid (LCFA) intake. Male lean and obese Zucker rats were fed a 15 % (w/w, total diet) fat diet containing either 0 or 5·0 % (w/w, total fatty acids) n-3 LCFA for 8 weeks. Reproductive organ weights, sperm morphology and fatty acid composition of phosphatidylcholine (PC), and phosphatidylethanolamine (PE) of testes were analysed. The obese rats had significantly (P < 0·0001) smaller epididymides and seminal vesicles, larger prostates and abundant underdeveloped testes compared with lean rats. Diet treatment did not affect the sex organ weights. The effect of genotype on fatty acid composition was minor in PC and PE except for DHA (22 : 6n-3). The n-3 LCFA diet significantly (P < 0·0001) elevated 22 : 6n-3 and reduced arachidonic acid (20 : 4n-6) and DPA (22 : 5n-6) in testicular PC and PE of lean and obese rats compared with the control diet. The acylation of dietary n-3 LCFA into 22 : 6n-3 was 2-fold higher in obese rat testes than in lean rats fed the same diet. Underdeveloped testes had 70 % less 22 : 5n-6 in PC and PE than normal-size testes. Results indicate that testicular fatty acid composition is sensitive to dietary fat modulations and especially obese rats responded more to dietary n-3 LCFA than their lean counterparts. The selective reduction in 22 : 5n-6 in underdeveloped testes indicates that 22 : 5n-6 is important in male reproduction in rats and requires further study to define the role of elongation and desaturation in testicular development.

Efficient synthesis of the very-long-chain n-3 fatty acids, tetracosahexaenoic acid (C24:6n-3) and tricosahexaenoic acid (C23:6n-3)

Tetracosahexaenoic acid (C(24):6n-3, THA, 3) is an essential biosynthetic precursor in mammals of docosahexaenoic acid (C(22):6n-3, DHA, 1), the end-product of the metabolism of n-3 fatty acids. THA 3 is present in commercially valuable fishes, such as flathead flounder. Tricosahexaenoic acid (C(23):6n-3, TrHA, 2), an odd-numbered-chain fatty acid, has been identified from marine organisms such as the dinoflagellate, Amphidinium carterae. To date, few studies have examined THA 3 and TrHA 2 due to difficulties in detecting and identifying these compounds, so their chemical and biological properties remain poorly characterized. Only one methodology for the chemical synthesis of THA 3 has been presented, and no method for the synthesis of TrHA 2 has been reported. We report here the efficient synthesis of THA 3 in four steps in 56% overall yield, and the synthesis of TrHA 2 in six steps in 48% overall yield. We also present the synthesis of Δ(2)-THA 4, an intermediate of β-oxidation of THA 3 to DHA 1, in three steps in 73% overall yield.

Altered essential fatty acid metabolism and composition in rat liver, plasma, heart and brain after microalgal DHA addition to the diet

To investigate the effect of docosahexaenoic acid (DHA) without other highly unsaturated fatty acids (HUFA) on n-3 and n-6 essential fatty acid (EFA) metabolism and fatty acid composition in mammals, a stable isotope tracer technique was used in adult rats fed diets with or without 1.3% of algal DHA in a base diet containing 15% of linoleic acid and 3% of alpha-linolenic acid over 8 weeks. The rats were administered orally a mixed oil containing 48 mg/kg body weight of deuterated linoleic and alpha-linolenic acids and euthanized at 4, 8, 24, 96, 168, 240, 360 and 600 h after administration of the isotopes. Fatty acid compositions and the concentrations of deuterated precursors and their respective metabolites were determined in rat liver, plasma, heart and brain as a function of time. DHA, docosapentaenoic acid and eicosapentaenoic acid in the n-3 EFA family were significantly increased in all organs tested in the DHA-fed group, ranging from 5% to 200% greater in comparison with the control group. The accumulation of the metabolites, deuterated-DHA and deuterated-docosapentaenoic acid n-6 was greatly decreased by 1.5- to 2.5-fold in the dietary DHA group. In summary, feeding preformed DHA led to a marked increase in n-3 HUFA content of rat organs at the expense of n-6 HUFA and also prevented the accumulation of newly synthesized deuterated end products. This is the first study which has isolated the effects of DHA on the de novo metabolism on both the n-6 and n-3 EFA pathways.

Influence of dietary sesamin, a bioactive compound on fatty acids and expression of some lipid regulating genes in Baltic Atlantic salmon (Salmo salar L.) juveniles

The effects of inclusion of sesamin / episesamin in Baltic Atlantic salmon (Salmo salar L.) diets based on vegetable oils were studied. The study was designed as a dose response study with two control diets, one diet based on fish oil (FO) and one diet based on a mixture of linseed and sunflower oil (6:4 by vol.) (MO). As experimental diets three different levels of inclusion of sesamin / episesamin (hereafter named sesamin) to the MO based diet and one diet based on sesame oil and linseed oil (SesO) (1:1 by vol.) were used. The dietary oils were mirrored in the fatty acid profile of the white muscle. Sesamin significantly decreased the levels of 18:3n-3 in the white muscle phospholipid (PL) fraction of all groups fed sesamin, no significant differences were found in the triacylglycerol fraction (TAG). Slightly increased levels of docosahexaenoic acid (22:6n-3, DHA) in PL and TAG were found in some of the sesamin fed groups. Sesamin significantly affected the expression of peroxisome proliferator-activated receptor alpha, scavenger receptor type B and hormone sensitive lipase, in agreement with previous studies on rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar L.) hepatocytes published by our group. No significant effects on toxicological response measured as ethoxyresorufin O-deethylase activity was found. The total cytochrome P450 enzymes were significantly higher in MO 0.29 and SesO group. The amount of alpha- and gamma-tocopherols in liver and the amount of gamma-tocopherol in white muscle were significantly lower in fish fed the FO diet compared to the MO diet, but no difference after inclusion of sesamin was found in this study. Increased inclusion of sesamin increased the levels of sesamin and episesamin in the liver, but did not affect the amounts in white muscle.

Deficient liver biosynthesis of docosahexaenoic acid correlates with cognitive impairment in Alzheimer's disease

Reduced brain levels of docosahexaenoic acid (C22:6n-3), a neurotrophic and neuroprotective fatty acid, may contribute to cognitive decline in Alzheimer's disease. Here, we investigated whether the liver enzyme system that provides docosahexaenoic acid to the brain is dysfunctional in this disease. Docosahexaenoic acid levels were reduced in temporal cortex, mid-frontal cortex and cerebellum of subjects with Alzheimer's disease, compared to control subjects (P = 0.007). Mini Mental State Examination (MMSE) scores positively correlated with docosahexaenoic/α-linolenic ratios in temporal cortex (P = 0.005) and mid-frontal cortex (P = 0.018), but not cerebellum. Similarly, liver docosahexaenoic acid content was lower in Alzheimer's disease patients than control subjects (P = 0.011). Liver docosahexaenoic/α-linolenic ratios correlated positively with MMSE scores (r = 0.78; P<0.0001), and negatively with global deterioration scale grades (P = 0.013). Docosahexaenoic acid precursors, including tetracosahexaenoic acid (C24:6n-3), were elevated in liver of Alzheimer's disease patients (P = 0.041), whereas expression of peroxisomal d-bifunctional protein, which catalyzes the conversion of tetracosahexaenoic acid into docosahexaenoic acid, was reduced (P = 0.048). Other genes involved in docosahexaenoic acid metabolism were not affected. The results indicate that a deficit in d-bifunctional protein activity impairs docosahexaenoic acid biosynthesis in liver of Alzheimer's disease patients, lessening the flux of this neuroprotective fatty acid to the brain.

Unraveling algal lipid metabolism: Recent advances in gene identification

Microalgae are now the focus of intensive research due to their potential as a renewable feedstock for biodiesel. This research requires a thorough understanding of the biochemistry and genetics of these organisms' lipid-biosynthesis pathways. Genes encoding lipid-biosynthesis enzymes can now be identified in the genomes of various eukaryotic microalgae. However, an examination of the predicted proteins at the biochemical and molecular levels is mandatory to verify their function. The essential molecular and genetic tools are now available for a comprehensive characterization of genes coding for enzymes of the lipid-biosynthesis pathways in some algal species. This review mainly summarizes the novel information emerging from recently obtained algal gene identification.

Linseed oil in the maternal diet increases long chain-PUFA status of the foetus and the newborn during the suckling period in pigs

Linseed oil, being rich in 18 : 3n-3, represents an alternative source of n-3 PUFA in the maternal diet. However, little is known about the effect of this oil on the long chain n-3 PUFA composition of offspring, which are required for normal growth and maturation of numerous organs. The main objective of the experiment was therefore to investigate fatty acid composition of tissues from sows at the end of gestation and from piglets during the first week of postnatal life in response to maternal dietary linseed oil intake. Sows received either a lard (LAR)-based diet or a linseed oil (LSO)-based diet during gestation and lactation. Fatty acid composition was evaluated in sow plasma, placenta and milk, and in different tissues of piglets on days 0, 3, 7, 21 and 32. The LSO diet increased the proportions of n-3 PUFA and especially 22 : 6n-3 in the placenta. The carcass of LSO piglets at birth contained greater proportions of 20 : 5n-3, 22 : 5n-3 and 22 : 6n-3. The LSO sow milk exhibited greater proportions of 18 : 3n-3 compared with the LAR sow milk. The piglets suckling LSO sows had greater proportions of 18 : 3n-3, 20 : 5n-3 and 22 : 5n-3 in plasma and carcass. The proportions of 22 : 5n-3 and 22 : 6n-3 were greater in the brain of LSO piglets than in that of LAR piglets during the suckling period. In conclusion, LSO in the maternal diet during gestation and lactation increases 22 : 6n-3 concentrations in the placenta and in the foetus carcass, and it maintains 22 : 6n-3 concentrations in the brain during the first week of postnatal life.

Omega-3 fatty acids in cancer, the protectors of good and the killers of evil?

Omega-3 fatty acids have been implicated in cancer prevention and treatment. Conventional chemotherapeutics are considered "double-edged swords", as they kill the cancer cells but also strike the healthy cells causing severe morbidity and sometimes also mortality. Could omega-3 fatty acids in this setting work as a "sword and shield" instead, by being cytotoxic to cancer cells, but at the same time protect healthy cells from these deleterious effects? In addition, may our current diet with decreased omega-3/omega-6 ratio contribute to the increased cancer incidence, and could an omega-3 enriched diet be used as a preventive measure against cancer? Here, we seek answers to these questions by reviewing the effects of omega-3 fatty acids, particularly DHA, on various cancers with emphasis on a cancer of neural origin, neuroblastoma. Results from preventive and therapeutic animal as well as human studies together with mechanisms behind the observed toxicity are summarized.

Elevated production of docosahexaenoic acid in females: potential molecular mechanisms

Observational evidence suggests that in populations consuming low levels of n-3 highly unsaturated fatty acids, women have higher blood levels of docosahexaenoic acid (DHA; 22:3n-6) as compared with men. Increased conversion of alpha-linolenic acid (ALA; 18:3n-3) to DHA by females has been confirmed in fatty acid stable isotope studies. This difference in conversion appears to be associated with estrogen and some evidence indicates that the expression of enzymes involved in synthesis of DHA from ALA, including desaturases and elongases, is elevated in females. An estrogen-associated effect may be mediated by peroxisome proliferator activated receptor-alpha (PPARalpha), as activation of this nuclear receptor increases the expression of these enzymes. However, because estrogens are weak ligands for PPARalpha, estrogen-mediated increases in PPARalpha activity likely occur through an indirect mechanism involving membrane-bound estrogen receptors and estrogen-sensitive G-proteins. The protein kinases activated by these receptors phosphorylate and increase the activity of PPARalpha, as well as phospholipase A(2) and cyclooxygenase 2 that increase the intracellular concentration of PPARalpha ligands. This review will outline current knowledge regarding elevated DHA production in females, as well as highlight interactions between estrogen signaling and PPARalpha activity that may mediate this effect.

Role of Elovl4 protein in the biosynthesis of docosahexaenoic acid

The disk membranes of retinal photoreceptor outer segments and other neuronal and reproductive tissues are enriched in docosahexaenoic acid (DHA, 22:6n3), which is essential for their normal function and development. The fatty acid condensing enzyme Elongation of Very Long chain fatty acids-4 (ELOVL4) is highly expressed in retina photoreceptors as well as other tissues with high 22:6n3 content. Mutations in the ELOVL4 gene are associated with autosomal dominant Stargardt-like macular dystrophy (STGD3) and results in synthesis of a truncated protein that cannot be targeted to the endoplasmic reticulum (ER), the site of fatty acid biosynthesis. Considering the abundance and essential roles of 22:6n3 in ELOVL4-expressing tissues (except the skin), it was proposed that the ELOVL4 protein may be involved in 22:6n3 biosynthesis. We tested the hypothesis that the ELOVL4 protein is involved in 22:6n3 biosynthesis by selectively silencing expression of the protein in the cone photoreceptors derived cell line 661 w and showed that the ELOVL4 protein is not involved in DHA biosynthesis from the short chain fatty acid precursors 18:3n3 and 22:5n3.

The key roles of elongases and desaturases in mammalian fatty acid metabolism: Insights from transgenic mice

In mammalian cells, elongases and desaturases play critical roles in regulating the length and degree of unsaturation of fatty acids and thereby their functions and metabolic fates. In the past decade, a great deal has been learnt about these enzymes and the first part of this review summarizes our current knowledge concerning these enzymes. More recently, several transgenic mouse models lacking either an elongase (Elovl3(-/-), Elovl4(-/-), Elovl5(-/-), Elovl6(-/-)) or a desaturase (Scd-1(-/-), Scd-2(-/-), Fads2(-/-)) have been developed and the second part of this review focuses on the insights gained from studies with these mice, as well as from investigations on cell cultures.

Do FADS genotypes enhance our knowledge about fatty acid related phenotypes?

Several physiological processes, such as visual and cognitive development in early life, are dependent on the availability of long-chain polyunsaturated fatty acids (LC-PUFAs). Furthermore, the concentration of LC-PUFAs in phospholipids has been associated with numerous complex diseases like cardiovascular disease, atopic disease and metabolic syndrome. The level and composition of LC-PUFAs in the human body is mainly dependent on their dietary intake or on the intake of fatty acid precursors, which are endogenously elongated and desaturated to physiologically active LC-PUFAs. The delta-5 and delta-6 desaturase are the most important enzymes in this reaction cascade. In the last few years, several studies have reported an association between single nucleotide polymorphisms (SNPs) in the two desaturase encoding genes (FADS1 and FADS2) and the concentration of omega-6 and omega-3 fatty acids. This shows that beside nutrition, genetic factors play an important role in the regulation of LC-PUFAs as well. This review focuses on current knowledge of the impact of FADS genotypes on LC-PUFA and lipid metabolism and discusses their influence on infant intellectual development, neurological conditions, metabolic disease as well as cardiovascular disease.

Early and sustained enrichment of serum n-3 long chain polyunsaturated fatty acids in dogs fed a flaxseed supplemented diet

A study was conducted in dogs to assess n-3 long chain polyunsaturated fatty acid incorporation after feeding an alpha-linolenic (ALA)-rich flaxseed supplemented diet (FLX) for 84 days. Serum total phospholipids (PL), triacylglycerol (TG), and cholesteryl esters (CE) were isolated at selected times and fatty acid methyl esters were analyzed. Increased LA was seen in the FLX-PL fraction after 28 days and an expected decrease in PL-AA. Enrichment of ALA, eicosapentaenoic acid (EPA) and docosapentaenoic acid n-3 (DPAn-3) in the FLX-group occurred early on (day 4) in both PL and TG fractions but no docosahexaenoic acid (DHA) was found, consistent with data from other species including humans. In contrast, no accumulation of DPAn-3 was seen in serum-CE, suggesting that this fatty acid does not participate in reverse-cholesterol transport. The accumulation of DPAn-3 in fasting PL and TG fractions is likely due to post-absorptive secretion after tissue synthesis. Because conversion of DPAn-3 to DHA occurs in canine neurologic tissues, this DPAn-3 may provide a circulating reservoir for DHA synthesis in such tissues. The absence of DPAn-3 in serum-CE suggests that such transport may be unidirectional. Although conversion of DPAn-3 to DHA is slow in most species, one-way transport of DPAn-3 in the circulation may help conserve this fatty acid as a substrate for DHA synthesis in brain and retinal tissues especially when dietary intakes of DHA are low.

Transgenic expression of n-3 fatty acid desaturase (fat-1) in C57/BL6 mice: Effects on glucose homeostasis and body weight

The fat-1 gene, derived from Caenorhabditis elegans, encodes for a fatty acid n-3 desaturase. In order to study the potential metabolic benefits of n-3 fatty acids, independent of dietary fatty acids, we developed seven lines of fat-1 transgenic mice (C57/BL6) controlled by the regulatory sequences of the adipocyte protein-2 (aP2) gene for adipocyte-specific expression (AP-lines). We were unable to obtain homozygous fat-1 transgenic offspring from the two highest expressing lines, suggesting that excessive expression of this enzyme may be lethal during gestation. Serum fatty acid analysis of fat-1 transgenic mice (AP-3) fed a high n-6 unsaturated fat (HUSF) diet had an n-6/n-3 fatty acid ratio reduced by 23% (P < 0.025) and the n-3 fatty acid eicosapentaenoic acid (EPA) concentration increased by 61% (P < 0.020). Docosahexaenoic acid (DHA) was increased by 19% (P < 0.015) in white adipose tissue. Male AP-3-fat-1 line of mice had improved glucose tolerance and reduced body weight with no change in insulin sensitivity when challenged with a high-carbohydrate (HC) diet. In contrast, the female AP-3 mice had reduced glucose tolerance and no change in insulin sensitivity or body weight. These findings indicate that male transgenic fat-1 mice have improved glucose tolerance likely due to increased insulin secretion while female fat-1 mice have reduced glucose tolerance compared to wild-type mice. Finally the inability of fat-1 transgenic mice to generate homozygous offspring suggests that prolonged exposure to increased concentrations of n-3 fatty acids may be detrimental to reproduction.

Novel plasma phospholipid biomarkers of autism: mitochondrial dysfunction as a putative causative mechanism

Autism is a neurological disorder that manifests as noticeable behavioral and developmental abnormalities predominantly in males between the ages of 2 and 10. Although the genetics, biochemistry and neuropathology of this disease have been extensively studied, underlying causal factors to this disease have remained elusive. Using a longitudinal trial design in which three plasma samples were collected from 15 autistic and 12 non-autistic age-matched controls over the course of 1 year, universal and unambiguous alterations in lipid metabolism were observed. Biomarkers of fatty acid elongation and desaturation (poly-unsaturated long chain fatty acids (PUFA) and/or saturated very long chain fatty acids (VLCFA)-containing ethanolamine phospholipids) were statistically elevated in all autistic subjects. In all 8 of the affected/non-affected sibling pairs, the affected sibling had higher levels of these biomarkers than the unaffected sibling. Exposure of neurons, astrocytes and hepatocytes in vitro to elevated extracellular glutamate levels resulted in lipid biomarker changes indistinguishable from those observed in autistic subjects. Glutamate stress also resulted in in vitro decreased levels of reduced glutathione (GSH), methionine and cysteine, in a similar way to the decreases we observed in autism plasma. Impaired mitochondrial fatty acid oxidation, elevated plasma VLCFAs, and glutamate toxicity as putative causal factors in the biochemistry, neuropathology, and gender bias in autism are discussed.

Alzheimer's disease as homeostatic responses to age-related myelin breakdown

The amyloid hypothesis (AH) of Alzheimer's disease (AD) posits that the fundamental cause of AD is the accumulation of the peptide amyloid beta (Aβ) in the brain. This hypothesis has been supported by observations that genetic defects in amyloid precursor protein (APP) and presenilin increase Aβ production and cause familial AD (FAD). The AH is widely accepted but does not account for important phenomena including recent failures of clinical trials to impact dementia in humans even after successfully reducing Aβ deposits. Herein, the AH is viewed from the broader overarching perspective of the myelin model of the human brain that focuses on functioning brain circuits and encompasses white matter and myelin in addition to neurons and synapses. The model proposes that the recently evolved and extensive myelination of the human brain underlies both our unique abilities and susceptibility to highly prevalent age-related neuropsychiatric disorders such as late onset AD (LOAD). It regards oligodendrocytes and the myelin they produce as being both critical for circuit function and uniquely vulnerable to damage. This perspective reframes key observations such as axonal transport disruptions, formation of axonal swellings/sphenoids and neuritic plaques, and proteinaceous deposits such as Aβ and tau as by-products of homeostatic myelin repair processes. It delineates empirically testable mechanisms of action for genes underlying FAD and LOAD and provides "upstream" treatment targets. Such interventions could potentially treat multiple degenerative brain disorders by mitigating the effects of aging and associated changes in iron, cholesterol, and free radicals on oligodendrocytes and their myelin.

Alpha-linolenic acid and its conversion to longer chain n-3 fatty acids: benefits for human health and a role in maintaining tissue n-3 fatty acid levels

There is little doubt regarding the essential nature of alpha-linolenic acid (ALA), yet the capacity of dietary ALA to maintain adequate tissue levels of long chain n-3 fatty acids remains quite controversial. This simple point remains highly debated despite evidence that removal of dietary ALA promotes n-3 fatty acid inadequacy, including that of docosahexaenoic acid (DHA), and that many experiments demonstrate that dietary inclusion of ALA raises n-3 tissue fatty acid content, including DHA. Herein we propose, based upon our previous work and that of others, that ALA is elongated and desaturated in a tissue-dependent manner. One important concept is to recognize that ALA, like many other fatty acids, rapidly undergoes beta-oxidation and that the carbons are conserved and reused for synthesis of other products including cholesterol and fatty acids. This process and the differences between utilization of dietary DHA or liver-derived DHA as compared to ALA have led to the dogma that ALA is not a useful fatty acid for maintaining tissue long chain n-3 fatty acids, including DHA. Herein, we propose that indeed dietary ALA is a crucial dietary source of n-3 fatty acids and its dietary inclusion is critical for maintaining tissue long chain n-3 levels.

Novel fatty acid desaturase 3 (FADS3) transcripts generated by alternative splicing

Fatty acid desaturase 1 and 2 (FADS1 and FADS2) code for the key desaturase enzymes involved in the biosynthesis of long chain polyunsaturated fatty acids in mammals. FADS3 shares close sequence homology to FADS1 and FADS2 but the function of its gene product remains unknown. Alternative transcripts (AT) generated by alternative splicing (AS) are increasingly recognized as an important mechanism enabling a single gene to code for multiple gene products. We report the first AT of a FADS gene, FADS3, generated by AS. Aided by ORF Finder, we identified putative coding regions of eight AT for FADS3 with 1.34 kb (classical splicing), 1.14 (AT1), 0.77 (AT2), 1.25 (AT3), 0.51 (AT4), 0.74 (AT6), and 1.11 (AT7). In addition we identified a 0.51 kb length transcript (AT5) that has a termination codon within intron 8-9. The expression of each AT was analyzed in baboon neonate tissues and in differentiated and undifferentiated human SK-N-SH neuroblastoma cells. FADS3 AT are expressed in 12 neonate baboon tissues and showed reciprocal increases and decreases in expression changes in response to human neuronal cell differentiation. FADS3 AT, conserved in primates and under metabolic control in human cells, are a putative mediator of LCPUFA biosynthesis and/or regulation.

Highly purified eicosapentaenoic acid prevents the progression of hepatic steatosis by repressing monounsaturated fatty acid synthesis in high-fat/high-sucrose diet-fed mice

Eicosapentaenoic acid (EPA) is a member of the family of n-3 polyunsaturated fatty acids (PUFAs) that are clinically used to treat hypertriglyceridemia. The triglyceride (TG) lowering effect is likely due to an alteration in lipid metabolism in the liver, but details have not been fully elucidated. To assess the effects of EPA on hepatic TG metabolism, mice were fed a high-fat and high-sucrose diet (HFHSD) for 2 weeks and were given highly purified EPA ethyl ester (EPA-E) daily by gavage. The HFHSD diet increased the hepatic TG content and the composition of monounsaturated fatty acids (MUFAs). EPA significantly suppressed the hepatic TG content that was increased by the HFHSD diet. EPA also altered the composition of fatty acids by lowering the MUFAs C16:1 and C18:1 and increasing n-3 PUFAs, including EPA and docosahexaenoic acid (DHA). Linear regression analysis revealed that hepatic TG content was significantly correlated with the ratios of C16:1/C16:0, C18:1/C18:0, and MUFA/n-3 PUFA, but was not correlated with the n-6/n-3 PUFA ratio. EPA also decreased the hepatic mRNA expression and nuclear protein level of sterol regulatory element binding protein-1c (SREBP-1c). This was reflected in the levels of lipogenic genes, such as acetyl-CoA carboxylase alpha (ACCalpha), fatty acid synthase, stearoyl-CoA desaturase 1 (SCD1), and glycerol-3-phosphate acyltransferase (GPAT), which are regulated by SREBP-1c. In conclusion, oral administration of EPA-E ameliorates hepatic fat accumulation by suppressing TG synthesis enzymes regulated by SREBP-1 and decreases hepatic MUFAs accumulation by SCD1.

Relationship between abnormal sperm morphology induced by dietary zinc deficiency and lipid composition in testes of growing rats

The present study investigated the effect of dietary Zn deficiency during sexual maturation on sperm integrity and testis phospholipid fatty acid composition. Male weanling Sprague-Dawley rats were randomised into four dietary groups for 3 weeks: Zn control (ZC; 30 mg Zn/kg); Zn marginally deficient (ZMD; 9 mg Zn/kg); Zn deficient (ZD; < 1 mg Zn/kg); pair fed (PF; 30 mg Zn/kg) to the ZD group. Morphology of cauda epididymal sperm and lipid profiles of testis phospholipids were analysed. The rats fed the ZD diet had a lower testis weight (P < 0.02). Seminal vesicles and prostate weight were also lower in the ZD and PF groups. Rats fed the ZD diet, but not the ZMD diet, had 34-35 % more abnormal spermatozoa and 24 % shorter sperm tail length than the ZC and PF rats (P < 0.001). Testis cholesterol concentration was higher in the ZD rats compared with the ZC and PF rats (P < 0.04). Testes were highly enriched with n-6 fatty acids by showing n-6 : n-3 fatty acid ratios of 27:1 in phosphatidylcholine (PC) and 23:1 in phosphatidylethanolamine (PE). The dominant fatty acid in testes was docosapentaenoic acid (22 : 5n-6), comprising 15 and 24 % of PC and PE, respectively. This fatty acid was significantly lower in the ZD rats, whereas 18 : 2n-6 was higher compared with the rats in the other diet groups. These results demonstrate that severe Zn deficiency adversely affects sperm integrity and modulates testis fatty acid composition by interrupting essential fatty acid metabolism. This suggests that Zn deficiency-associated abnormal testicular function is perhaps preceded by altered membrane fatty acid composition, especially of a major fatty acid, 22 : 5n-6.

An alternate pathway to long-chain polyunsaturates: the FADS2 gene product Delta8-desaturates 20:2n-6 and 20:3n-3

The mammalian Delta6-desaturase coded by fatty acid desaturase 2 (FADS2; HSA11q12-q13.1) catalyzes the first and rate-limiting step for the biosynthesis of long-chain polyunsaturated fatty acids. FADS2 is known to act on at least five substrates, and we hypothesized that the FADS2 gene product would have Delta8-desaturase activity. Saccharomyces cerevisiae transformed with a FADS2 construct from baboon neonate liver cDNA gained the function to desaturate 11,14-eicosadienoic acid (20:2n-6) and 11,14,17-eicosatrienoic acid (20:3n-3) to yield 20:3n-6 and 20:4n-3, respectively. Competition experiments indicate that Delta8-desaturation favors activity toward 20:3n-3 over 20:2n-6 by 3-fold. Similar experiments show that Delta6-desaturase activity is favored over Delta8-desaturase activity by 7-fold and 23-fold for n-6 (18:2n-6 vs 20:2n-6) and n-3 (18:3n-3 vs 20:3n-3), respectively. In mammals, 20:3n-6 is the immediate precursor of prostaglandin E1 and thromboxane B1. 20:3n-6 and 20:4n-3 are also immediate precursors of long-chain polyunsaturated fatty acids arachidonic acid and eicosapentaenoic acid, respectively. These findings provide unequivocal molecular evidence for a novel alternative biosynthetic route to long-chain polyunsaturated fatty acids in mammals from substrates previously considered to be dead-end products.

Rapid beta-oxidation of eicosapentaenoic acid in mouse brain: an in situ study

Analyses of brain phospholipid fatty acid profiles reveal a selective deficiency and enrichment in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), respectively. In order to account for this difference in brain fatty acid levels, we hypothesized that EPA is more rapidly beta-oxidized upon its entry into the brain. Wild-type C57BL/6 mice were perfused with either (14)C-EPA or (14)C-DHA via in situ cerebral perfusion for 40s, followed by a bicarbonate buffer to wash out the residual radiolabeled polyunsaturated fatty acid (PUFA) in the capillaries. (14)C-PUFA-perfused brains were extracted for chemical analyses of neutral lipid and phospholipid fatty acids. Based on the radioactivity in aqueous, total lipid, neutral lipid and phospholipid fractions, volume of distribution (V(D), microl/g) was calculated. The V(D) between (14)C-EPA- and (14)C-DHA-perfused samples was not statistically different for total lipid, neutral lipids or total phospholipids. However, the V(D) of (14)C-EPA in the aqueous fraction was 2.5 times higher than that of (14)C-DHA (p=0.025), suggesting a more extensive beta-oxidation than DHA. Furthermore, radiolabeled palmitoleic acid, a fatty acid that can be synthesized de novo, was detected in brain phospholipids from (14)C-EPA but not from (14)C-DHA-perfused mice suggesting that beta-oxidation products of EPA were recycled into endogenous fatty acid biosynthetic pathways. These findings suggest that low levels of EPA in brain phospholipids compared to DHA may be the result of its rapid beta-oxidation upon uptake by the brain.

Transcriptional regulation of hepatic fatty acid metabolism

The liver is a major site of fatty acid synthesis and degradation. Transcriptional regulation is one of several mechanisms controlling hepatic metabolism of fatty acids. Two transcription factors, namely SREBP1-c and PPARalpha, appear to be the main players controlling synthesis and degradation of fatty acids respectively. This chapter briefly presents fatty acid metabolism. The first part focuses on SREBP1-c contribution to the control of gene expression relevant to fatty acid synthesis and the main mechanisms of activation for this transcriptional program. The second part reviews the evidence for the involvement of PPARalpha in the control of fatty acid degradation and the key features of this nuclear receptor. Finally, the third part aims at summarizing recent advances in our current understanding of how these two transcription factors fit in the regulatory networks that sense hormones or nutrients, including cellular fatty acids, and govern the transcription of genes implicated in hepatic fatty acid metabolism.

Impact of PUFA on early immune and fetal development

It has recently been reported that the increased prevalence in childhood allergy may be linked to deviations in fetal immune development. One reason may be impaired nutrient supply. Hence, a well-differentiated placenta together with an optimal fetal nutrition via the mother are important prerequisites for the establishment of a functional immune system with normal immune responses. Fatty acids and their derivatives can influence both the early immune development and immune maturation by regulating numerous metabolic processes and the gene expression of important proteins such as enzymes and cytokines. The present review summarises the impact of nutritional fatty acids on the development of the immune system as well as the fetal development. It describes the mechanisms of action of PUFA, trans fatty acids and conjugated linoleic acids in programming the fetus with regard to its risk of acquiring atopic diseases in childhood.

Neurological benefits of omega-3 fatty acids

The central nervous system is highly enriched in long-chain polyunsaturated fatty acid (PUFA) of the omega-6 and omega-3 series. The presence of these fatty acids as structural components of neuronal membranes influences cellular function both directly, through effects on membrane properties, and also by acting as a precursor pool for lipid-derived messengers. An adequate intake of omega-3 PUFA is essential for optimal visual function and neural development. Furthermore, there is increasing evidence that increased intake of the long-chain omega-3 PUFA, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), may confer benefits in a variety of psychiatric and neurological disorders, and in particular neurodegenerative conditions. However, the mechanisms underlying these beneficial effects are still poorly understood. Recent evidence also indicates that in addition to the positive effects seen in chronic neurodegenerative conditions, omega-3 PUFA may also have significant neuroprotective potential in acute neurological injury. Thus, these compounds offer an intriguing prospect as potentially new therapeutic approaches in both chronic and acute conditions. The purpose of this article is to review the current evidence of the neurological benefits of omega-3 PUFA, looking specifically at neurodegenerative conditions and acute neurological injury.

Lipids and infant formulas

The ultimate goal in the design of infant formula is to achieve the outcome seen in breast fed infants. This review of lipids in infant formulas for term infants begins by referring to the lipid composition of human milk, and relates that to differences in lipid digestion and metabolism which exist between breast fed and formula fed infants and which may significantly influence fatty acid bioavailability.

Recommendations are made for the lipid content and fatty acid composition of term infant formulas (especially for lauric, linoleic, α-linolenic, long chain 20 and 22C n-3 and n-6 polyunsaturated fatty acids and thetransfatty acids).

Further research is required to define more clearly the long term nutritional, growth and developmental effects of structured lipids in formulas for term infants. More information is required on the differential handling of LCPUFA and other fatty acids at the organ and cellular level. There is a need for large (multi-centre) randomized studies to determine the short and long term functional effects of LCPUFA supplementation. Further research and development is required to determine a commercial source of LCPUFA which is safe, effective and economic. Further information is required on the short and long term effects of cholesterol intake during infancy, and in particular its relationship to LCPUFA metabolism. Long term studies should be initiated to determine the relationship of infant diet (especially saturated fatty acid and cholesterol intake) to the development of cardiovascular disease.

Peripheral ethanolamine plasmalogen deficiency: a logical causative factor in Alzheimer's disease and dementia

Although dementia of the Alzheimer's type (DAT) is the most common form of dementia, the severity of dementia is only weakly correlated with DAT pathology. In contrast, postmortem measurements of cholinergic function and membrane ethanolamine plasmalogen (PlsEtn) content in the cortex and hippocampus correlate with the severity of dementia in DAT. Currently, the largest risk factor for DAT is age. Because the synthesis of PlsEtn occurs via a single nonredundant peroxisomal pathway that has been shown to decrease with age and PlsEtn is decreased in the DAT brain, we investigated potential relationships between serum PlsEtn levels, dementia severity, and DAT pathology. In total, serum PlsEtn levels were measured in five independent population collections comprising >400 clinically demented and >350 nondemented subjects. Circulating PlsEtn levels were observed to be significantly decreased in serum from clinically and pathologically diagnosed DAT subjects at all stages of dementia, and the severity of this decrease correlated with the severity of dementia. Furthermore, a linear regression model predicted that serum PlsEtn levels decrease years before clinical symptoms. The putative roles that PlsEtn biochemistry play in the etiology of cholinergic degeneration, amyloid accumulation, and dementia are discussed.

Estradiol Favors the Formation of Eicosapentaenoic Acid (20:5n-3) and n-3 Docosapentaenoic Acid (22:5n-3) from Alpha-Linolenic Acid (18:3n-3) in SH-SY5Y Neuroblastoma Cells

Whether neurosteroids regulate the synthesis of long chain polyunsaturated fatty acids in brain cells is unknown. We examined the influence of 17-beta-estradiol (E2) on the capacity of SH-SY5Y cells supplemented with alpha-linolenic acid (ALA), to produce eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA). Cells were incubated for 24 or 72 h with ALA added alone or in combination with E2 (ALA + E2). Fatty acids were analyzed by gas chromatography of ethanolamine glycerophospholipids (EtnGpl) and phosphatidylcholine (PtdCho). Incubation for 24 h with ALA alone increased EPA and DPA in EtnGpl, by 330 and 430% compared to controls (P < 0.001) and DHA by only 10% (P < 0.05). Although DHA increased by 30% (P < 0.001) in ALA + E2-treated cells, the difference between the ALA and ALA + E2 treatments were not significant after 24 h (Anova-1, Fisher's test). After 72 h, EPA, DPA and DHA further increased in EtnGpl and PtdCho of cells supplemented with ALA or ALA + E2. Incubation for 72 h with ALA + E2 specifically increased EPA (+34% in EtnGpl, P < 0.001) and DPA (+15%, P < 0.001) compared to ALA alone. Thus, SH-SY5Y cells produced membrane EPA, DPA and DHA from supplemental ALA. The formation of DHA was limited, even in the presence of E2. E2 significantly favored EPA and DPA production in cells grown for 72 h. Enhanced synthesis of ALA-elongation products in neuroblastoma cells treated with E2 supports the hypothesis that neurosteroids could modulate the metabolism of PUFA.

l-Carnitine increases liver α-tocopherol and lowers liver and plasma triglycerides in aging ovariectomized rats

The objective of this study was to determine whether dietary L-carnitine can influence the status of alpha-tocopherol, retinol and selected lipid parameters in aging ovariectomized rats, an animal model for the menopausal state. Fourteen Fisher-344 female rats 18 months old were acclimated for 4 weeks and ovarectomized. Seven rats per treatment were assigned to either a control group fed ad libitum AIN-93M diet or a carnitine group fed the same diet supplemented with L-carnitine. After an 8-week feeding period, blood and selected tissues were taken for analyses. No differences were noted in food intake, body weight, or organ weights due to L-carnitine. Dietary carnitine significantly increased liver alpha-tocopherol and tended to increase plasma alpha-tocopherol (P<.09). No changes in alpha-tocopherol were observed in other tissues including the brain, lungs and retroperitoneal fat. Retinol levels in plasma and tissues were not affected by supplemental L-carnitine. Significant decreases in liver and plasma triglyceride (TG) levels were noted, suggesting increased utilization of fatty acids. No differences were observed in the fatty acid profile of tissues. The results provide evidence that dietary supplementation of L-carnitine enhances the alpha-tocopherol status and improves the utilization of fat leading to lowering of the liver and plasma levels of TG in aging ovariectomized rats. Whether supplemental L-carnitine may be of benefit to postmenopausal women in lowering plasma TG and improving the antioxidant status remains to be studied.

Extremely limited synthesis of long chain polyunsaturates in adults: implications for their dietary essentiality and use as supplements

There is considerable interest in the potential impact of several polyunsaturated fatty acids (PUFAs) in mitigating the significant morbidity and mortality caused by degenerative diseases of the cardiovascular system and brain. Despite this interest, confusion surrounds the extent of conversion in humans of the parent PUFA, linoleic acid or α-linolenic acid (ALA), to their respective long-chain PUFA products. As a result, there is uncertainty about the potential benefits of ALA versus eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA). Some of the confusion arises because although mammals have the necessary enzymes to make the long-chain PUFA from the parent PUFA, in vivo studies in humans show that ≈5% of ALA is converted to EPA and <0.5% of ALA is converted to DHA. Because the capacity of this pathway is very low in healthy, nonvegetarian humans, even large amounts of dietary ALA have a negligible effect on plasma DHA, an effect paralleled in the ω6 PUFA by a negligible effect of dietary linoleic acid on plasma arachidonic acid. Despite this inefficient conversion, there are potential roles in human health for ALA and EPA that could be independent of their metabolism to DHA through the desaturation – chain elongation pathway.

Analysis of long-chain ω-3 fatty acid content in fish-oil supplements

BACKGROUND

Omega-3 polyunsaturated fatty acids (long-chain omega-3 PUFA) have proved to be beneficial in atherosclerosis, arrhythmia and hypertriglyceridemia in several studies, which has led national and international societies to recommend an intake of 1 g/d long-chain omega-3 PUFA for anti-atherosclerotic and antiarrhythmic purposes or 2-4 g/d for a lipid lowering effect. Numerous preparations are marketed for supplementing western diet, which is low in long-chain omega-3 PUFA. Since these preparations vary in their long-chain omega-3 PUFA content, we tested nine commercially available products for their fatty acid composition.

METHODS

Nine commercially available omega-3 fatty acid supplements were analyzed using capillary gas chromatography to determine their fatty acid content.

RESULTS

The nine preparations showed huge differences, up to 63.7 +/- 1.58 mol% (P = 0.002), in their longchain omega-3 fatty acid content. Most of them failed to achieve the daily recommended dose of 1 g, even when administered at the highest dosage according to the manufacturer's recommendations. Eight of the preparations contained either equal or significantly greater amounts of long-chain omega-3 PUFA than denoted by the manufacturer; one preparation did not provide any information. The highest percentage of DHA and EPA was detected in Omacor(95.80 +/- 0.63%) and Percucor (76.8 +/- 7.109%).

CONCLUSION

Administering long-chain omega-3 fatty acid preparations may result in huge differences in terms of the actual amount ingested. It is therefore advisable to use the most standardized and purified products available.

Competition between 24:5n-3 and ALA for Δ6 desaturase may limit the accumulation of DHA in HepG2 cell membranes

The use of Delta 6 desaturase (D6D) twice in the conversion of alpha-linolenic acid (ALA; 18:3n-3) to docosahexaenoic acid (DHA; 22:6n-3) suggests that this enzyme may play a key regulatory role in the synthesis and accumulation of DHA from ALA. We examined this using an in vitro model of fatty acid metabolism to measure the accumulation of the long-chain metabolites of ALA in HepG2 cell phospholipids. The accumulation of ALA, eicosapentaenoic acid (20:5n-3), docosapentaenoic acid (22:5n-3), and 24:5n-3 in cell phospholipids was linearly related to the concentration of supplemented ALA over the range tested (1.8-72 microM). The accumulation of the post-D6D products of 22:5n-3, 24:6n-3 and DHA, in cell phospholipids was saturated at concentrations of >18 microM ALA. Supplementation of HepG2 cells with preformed DHA revealed that, although the accumulation of DHA in cell phospholipids approached saturation, the level of DHA in cell phospholipids was significantly greater compared with the accumulation of DHA from ALA, indicating that the accumulation of DHA from ALA was not limited by incorporation. The parallel pattern of accumulation of 24:6n-3 and DHA in response to increasing concentrations of ALA suggests that the competition between 24:5n-3 and ALA for D6D may contribute to the limited accumulation of DHA in cell membranes.

Metabolic pathway that produces essential fatty acids from polymethylene-interrupted polyunsaturated fatty acids in animal cells

Sciadonic acid (20:3 Delta-5,11,14) and juniperonic acid (20:4 Delta-5,11,14,17) are polyunsaturated fatty acids (PUFAs) that lack the Delta-8 double bond of arachidonic acid (20:4 Delta-5,8,11,14) and eicosapentaenoic acid (20:5 Delta-5,8,11,14,17), respectively. Here, we demonstrate that these conifer oil-derived PUFAs are metabolized to essential fatty acids in animal cells. When Swiss 3T3 cells were cultured with sciadonic acid, linoleic acid (18:2 Delta-9,12) accumulated in the cells to an extent dependent on the concentration of sciadonic acid. At the same time, a small amount of 16:2 Delta-7,10 appeared in the cellular lipids. Both 16:2 Delta-7,10 and linoleic acid accumulated in sciadonic acid-supplemented CHO cells, but not in peroxisome-deficient CHO cells. We confirmed that 16:2 Delta-7,10 was effectively elongated to linoleic acid in rat liver microsomes. These results indicate that sciadonic acid was partially degraded to 16:2 Delta-7,10 by two cycles of beta-oxidation in peroxisomes, then elongated to linoleic acid in microsomes. Supplementation of Swiss 3T3 cells with juniperonic acid, an n-3 analogue of sciadonic acid, induced accumulation of alpha-linolenic acid (18:3 Delta-9,12,15) in cellular lipids, suggesting that juniperonic acid was metabolized in a similar manner to sciadonic acid. This PUFA remodeling is thought to be a process that converts unsuitable fatty acids into essential fatty acids required by animals.