Biochemical characterization of acyl-CoA:diacylglycerol acyltransferase2 from the diatom Phaeodactylum tricornutum and its potential effect on LC-PUFAs biosynthesis in planta.

BACKGROUND: Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), belonging to ω-3 long-chain polyunsaturated fatty acids (ω3-LC-PUFAs), are essential components of human diet. They are mainly supplemented by marine fish consumption, although their native producers are oleaginous microalgae. Currently, increasing demand for fish oils is insufficient to meet the entire global needs, which puts pressure on searching for the alternative solutions. One possibility may be metabolic engineering of plants with an introduced enzymatic pathway producing ω3-LC-PUFAs. RESULT: In this study we focused on the acyl-CoA:diacylglycerol acyltransferase2b (PtDGAT2b) from the diatom Phaeodactylum tricornutum, an enzyme responsible for triacylglycerol (TAG) biosynthesis via acyl-CoA-dependent pathway. Gene encoding PtDGAT2b, incorporated into TAG-deficient yeast strain H1246, was used to confirm its activity and conduct biochemical characterization. PtDGAT2b exhibited a broad acyl-CoA preference with both di-16:0-DAG and di-18:1-DAG, whereas di-18:1-DAG was favored. The highest preference for acyl donors was observed for 16:1-, 10:0- and 12:0-CoA. PtDGAT2b also very efficiently utilized CoA-conjugated ω-3 LC-PUFAs (stearidonic acid, eicosatetraenoic acid and EPA). Additionally, verification of the potential role of PtDGAT2b in planta, through its transient expression in tobacco leaves, indicated increased TAG production with its relative amount increasing to 8%. Its co-expression with the gene combinations aimed at EPA biosynthesis led to, beside elevated TAG accumulation, efficient accumulation of EPA which constituted even 25.1% of synthesized non-native fatty acids (9.2% of all fatty acids in TAG pool). CONCLUSIONS: This set of experiments provides a comprehensive biochemical characterization of DGAT enzyme from marine microalgae. Additionally, this study elucidates that PtDGAT2b can be used successfully in metabolic engineering of plants designed to obtain a boosted TAG level, enriched not only in ω-3 LC-PUFAs but also in medium-chain and ω-7 fatty acids.

Factors impacting the microbial production of eicosapentaenoic acid.

The increasing applications for eicosapentaenoic acid (EPA) and the potential shortfall in supply due to sustainability and contamination issues related with its conventional sources (i.e., fish oils; seafood) led to an extensive search for alternative and sustainable sources, as well as production processes. The present mini-review covers all the steps involved in the production of EPA from microorganisms, with a deeper focus on microalgae. From production systems to downstream processing, the most important achievements within each area are briefly highlighted. Comparative tables of methodologies are also provided, as well as additional references of recent reviews, so that readers may deepen their knowledge in the different issues addressed. KEY POINTS: • Microorganisms are more sustainable alternative sources of EPA than fish. • Due to the costly separation from DHA, species that produce only EPA are preferable. • EPA production can be optimised using non-genetic and genetic tailoring engineering.

Dual stress factors adaptive evolution for high EPA production in Schizochytrium sp. and metabolomics mechanism analysis.

Eicosapentaenoic acid (EPA) is a vital É·-3 polyunsaturated fatty acid (PUFA) for human body with various physiological functions. In this study, we proposed an adaptive evolutionary strategy based on high-temperature and high-oxygen two-factor stress to increase the EPA production capacity of Schizochytrium. High-temperature stress was used to increase EPA yield, and high oxygen was implemented to continuously stimulate cell growth and lipid accumulation. The biomass and EPA production of ALE-D50 reached 35.33 g/L and 1.54 g/L, which were 43.85% and 71.11% higher than that of the original strain, respectively. Lower in vivo reactive oxygen species levels indicated that the evolved strain possessed stronger antioxidant activity. Liquid chromatography-mass spectrometry metabolomics showed that enhanced glucose consumption and glycolysis metabolism, as well as a weakened tricarboxylic acid cycle and reduced amino acid metabolic tributaries in the evolved strain, might be associated with increased growth and EPA synthesis. Finally, the lipid production and EPA production in a fed-batch fermentation were further increased to 48.93 g/L and 3.55 g/L, improving by 54.30% and 90.86%, respectively. This study provides a novel pathway for promoting EPA biosynthesis in Schizochytrium.

Plastidial acyl carrier protein Δ9-desaturase modulates eicosapentaenoic acid biosynthesis and triacylglycerol accumulation in Phaeodactylum tricornutum.

The unicellular marine diatom Phaeodactylum tricornutum accumulates up to 35% eicosapentaenoic acid (EPA, 20:5n3) and has been used as a model organism to study long chain polyunsaturated fatty acids (LC-PUFA) biosynthesis due to an excellent annotated genome sequence and established transformation system. In P. tricornutum, the majority of EPA accumulates in polar lipids, particularly in galactolipids such as mono- and di-galactosyldiacylglycerol. LC-PUFA biosynthesis is considered to start from oleic acid (18:1n9). EPA can be synthesized via a series of desaturation and elongation steps occurring at the endoplasmic reticulum and newly synthesized EPA is then imported into the plastids for incorporation into galactolipids via an unknown route. The basis for the flux of EPA is fundamental to understanding LC-PUFA biosynthesis in diatoms. We used P. tricornutum to study acyl modifying activities, upstream of 18:1n9, on subsequent LC-PUFA biosynthesis. We identified the gene coding for the plastidial acyl carrier protein Δ9-desaturase, a key enzyme in fatty acid modification and analyzed the impact of overexpression and knock out of this gene on glycerolipid metabolism. This revealed a previously unknown role of this soluble desaturase in EPA synthesis and production of triacylglycerol. This study provides further insight into the distinctive nature of lipid metabolism in the marine diatom P. tricornutum and suggests additional approaches for tailoring oil composition in microalgae.

Metabolic and molecular evidence for long-chain PUFA biosynthesis capacity in the grass carp Ctenopharyngodon idella.

There is a growing interest to understand the capacity of farmed fish species to biosynthesise the physiologically important long-chain (≥C20) n-3 and n-6 polyunsaturated fatty acids (LC-PUFAs), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and arachidonic acid (ARA), from their C18 PUFA precursors available in the diet. In fish, the LC-PUFA biosynthesis pathways involve sequential desaturation and elongation reactions from α-linolenic acid (ALA) and linoleic acid (LA), catalysed by fatty acyl desaturases (Fads) and elongation of very long-chain fatty acids (Elovl) proteins. Our current understanding of the grass carp (Ctenopharyngodon idella) LC-PUFA biosynthetic capacity is limited despite representing the most farmed finfish produced worldwide. To address this knowledge gap, this study first aimed at characterising molecularly and functionally three genes (fads2, elovl5 and elovl2) with putative roles in LC-PUFA biosynthesis. Using an in vitro yeast-based system, we found that grass carp Fads2 possesses ∆8 and ∆5 desaturase activities, with ∆6 ability to desaturase not only the C18 PUFA precursors (ALA and LA) but also 24:5n-3 to 24:6n-3, a key intermediate to obtain DHA through the "Sprecher pathway". Additionally, the Elovl5 showed capacity to elongate C18 and C20 PUFA substrates, whereas Elovl2 was more active over C20 and C22. Collectively, the molecular cloning and functional characterisation of fads2, elovl5 and elovl2 demonstrated that the grass carp has all the enzymatic activities required to obtain ARA, EPA and DHA from LA and ALA. Importantly, the hepatocytes incubated with radiolabelled fatty acids confirmed the yeast-based results and demonstrated that these enzymes are functionally active.

Biocatalytic regio- and stereoselective access to ω-3 endocannabinoid epoxides with peroxygenase from oat flour.

The biocatalytic epoxidation of ethanolamides of ω-3 fatty acids EPA and DHA, regarded as biologically active ω-3 endocannabinoids, in the presence of a peroxygenase-containing preparation from oat flour was investigated. Good regio- and steroselectivity toward the formation of the epoxide on the terminal double bond in the chain was observed with both these fatty acid derivatives and chiral monoepoxides 1 or 2 in 74% optical purity and 51-53% yields were isolated and spectroscopically characterized. The use of acetone as cosolvent in the reaction medium allowed to increase the concentration of starting substrates up to 40 mM and to further improve the selectivity in the epoxidation of DHA-EA. Due to the easy availability of the enzymatic preparation, the method offers a valuable strategy for the access to oxyfunctionalized derivatives of fatty acids.

Characterization of ω3 fatty acid desaturases from oomycetes and their application toward eicosapentaenoic acid production in Mortierella alpina.

ω3 Polyunsaturated fatty acids are currently obtained mainly from fisheries; thus, sustainable alternative sources such as oleaginous microorganisms are required. Here, we describe the isolation, characterization, and application of 3 novel ω3 desaturases with ω3 polyunsaturated fatty acid-producing activity at ordinary temperatures (28 °C). First, we selected Pythium sulcatum and Plectospira myriandra after screening for oomycetes with high eicosapentaenoic acid/arachidonic acid ratios and isolated the genes psulω3 and pmd17, respectively, which encode ω3 desaturases. Subsequent characterization showed that PSULω3 exhibited ω3 desaturase activity on both C18 and C20 ω6 polyunsaturated fatty acids while PMD17 exhibited ω3 desaturase activity exclusively on C20 ω6 polyunsaturated fatty acids. Expression of psulω3 and pmd17 in the arachidonic acid-producer Mortierella alpina resulted in transformants that produced eicosapentaenoic acid/total fatty acid values of 38% and 40%, respectively, at ordinary temperatures. These ω3 desaturases should facilitate the construction of sustainable ω3 polyunsaturated fatty acid sources.

Autotrophic vs. Heterotrophic Cultivation of the Marine Diatom Cyclotella cryptica for EPA Production.

Recently, the marketable value of ω-3 fatty acid, particularly eicosapentaenoic acid (EPA), increased considering their health effects for human consumption. Microalgae are considered a valuable and "green" source of EPA alternative to fish oils, but considerable efforts are necessary for their exploitation at an industrial level. Due to the high operation costs of photoautotrophic microalgae cultivation, heterotrophic growth represents a promising economic solution. Marine diatoms are the major ecological producers of ω-3 fatty acids. Few species of diatoms are capable to grow in the dark using organic carbon sources. The marine diatom Cyclotella cryptica was cultivated for 14 days under photoautotrophic and heterotrophic conditions to define the effects on growth parameters, lipid production, total fatty acids and EPA content. Photoautotrophic conditions led to a total EPA production of 1.6% of dry weight, 12.2 mg L-1 culture and productivity of 0.9 mg L-1 day-1. The heterotrophy cultures reported a total EPA production of 2.7% of dry cell weight, 18 mg L-1 culture, a productivity of 1.3 mg L-1 day-1, which are promising values in the prospective of improving culture parameters for the biotechnological exploitation of dark cultivation. C. cryptica could be a potential candidate for the heterotrophic production of EPA, also considering its robustness, capacity to resist to bacterial contaminations and plasticity of lipid metabolism.

Transcriptomics and Metabolomics Analyses Provide Novel Insights into Glucose-Induced Trophic Transition of the Marine Diatom Nitzschia laevis.

Diatoms have important ecological roles and are natural sources of bioactive compounds. Nitzschia laevis is a member of marine diatoms that accumulates high-value products including fucoxanthin and eicosapentaenoic acid (EPA). In this study, physiological data showed that comparing to autotrophic growth, mixotrophic cultivation with glucose supplementation led to a decrease of chlorophyll and fucoxanthin content in N. laevis, and an increase of biomass density and EPA yield. To further examine the metabolic barriers for fucoxanthin and EPA biosynthesis, comparative transcriptomic and metabolome analyses were conducted, with a focus on the genes related to carotenoids biosynthesis and fatty acid metabolism. The results indicated that phytoene desaturase (PDS) and zeta-carotene isomerase (ZISO) could be the rate-limiting enzymes in carotenoid biosynthesis. The transcription regulation of 3-ketoacyl-CoA synthase (KCS) and elongation of very long chain fatty acids protein (EVOVL) are important contributors associated with polyunsaturated fatty acids (PUFAs) accumulation. Furthermore, we also investigated the glucose-associated regulatory genes using weighted gene co-expression network analysis, and identified potential hub genes linked with cell cycle, carbohydrate metabolism, purine biosynthesis, and lipid metabolism. This study offers a high-quality transcriptome resource for N. laevis and provides a molecular framework for further metabolic engineering studies on fucoxanthin and EPA production.

Microalgae n-3 PUFAs Production and Use in Food and Feed Industries.

N-3 polyunsaturated fatty acids (n-3 PUFAs), and especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are essential compounds for human health. They have been proven to act positively on a panel of diseases and have interesting anti-oxidative, anti-inflammatory or anti-cancer properties. For these reasons, they are receiving more and more attention in recent years, especially future food or feed development. EPA and DHA come mainly from marine sources like fish or seaweed. Unfortunately, due to global warming, these compounds are becoming scarce for humans because of overfishing and stock reduction. Although increasing in recent years, aquaculture appears insufficient to meet the increasing requirements of these healthy molecules for humans. One alternative resides in the cultivation of microalgae, the initial producers of EPA and DHA. They are also rich in biochemicals with interesting properties. After defining macro and microalgae, this review synthesizes the current knowledge on n-3 PUFAs regarding health benefits and the challenges surrounding their supply within the environmental context. Microalgae n-3 PUFA production is examined and its synthesis pathways are discussed. Finally, the use of EPA and DHA in food and feed is investigated. This work aims to define better the issues surrounding n-3 PUFA production and supply and the potential of microalgae as a sustainable source of compounds to enhance the food and feed of the future.

Application of the cbh1 promoter in Mortierella alpina and optimization of induction conditions.

Mortierella alpina has gained remarkable interest due to its high capacity for arachidonic acid (AA) production and potential for eicosapentaenoic acid (EPA) production recently. However, the development of genetically modified strains is limited by lacking inducible promoters, which can express genes conditionally. Here the inducible promoter of cellobiohydrolase (Pcbh1) was utilized in M. alpina and the gene oPpFADS17 encoding ω-3 fatty acid desaturase was selected as the reporter gene. Under conditions with inducer, expression of this gene enables M. alpina to produce EPA at room temperature, while no EPA was detected without inducer. We then optimized the induction conditions. The results demonstrated that the optimal induction condition was broth medium with 1% avicel as the inducer and 5% glucose as extra carbon source and the transcription level of the reporter gene was increasing with the extension of induction time. Successful application of Pcbh1 in M. alpina would significantly contribute to the steerable system to construct engineered strains for industrial production of microbial oils. SIGNIFICANCE AND IMPACT OF THE STUDY: Mortierella alpina is a commercial strain for production of polyunsaturated fatty acids. Genetic engineering strategies based on M. alpina require the development of inducible promoters to regulate gene expression conditionally at specific times. However, available inducible promoters for M. alpina were limited. In this study, we explore the feasibility of inducible cbh1 promoter in M. alpina and determined the optimal induction condition, which accelerates the genetic manipulation of M. alpina. Besides, high transcriptional levels of the reporter gene under the control of Pcbh1 showed that Pcbh1 is a strong inducible promoter for M. alpina.

Novel Vibrio spp. Strains Producing Omega-3 Fatty Acids Isolated from Coastal Seawater.

Omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs), such as eicosapentaenoic acid (EPA) (20:5n-3) and docosahexaenoic acid (DHA) (22:6n-3), are considered essential for human health. Microorganisms are the primary producers of omega-3 fatty acids in marine ecosystems, representing a sustainable source of these lipids, as an alternative to the fish industry. Some marine bacteria can produce LC-PUFAs de novo via the Polyunsaturated Fatty Acid (Pfa) synthase/ Polyketide Synthase (PKS) pathway, which does not require desaturation and elongation of saturated fatty acids. Cultivation-independent surveys have revealed that the diversity of microorganisms harboring a molecular marker of the pfa gene cluster (i.e., pfaA-KS domain) is high and their potential distribution in marine systems is widespread, from surface seawater to sediments. However, the isolation of PUFA producers from marine waters has been typically restricted to deep or cold environments. Here, we report a phenotypic and genotypic screening for the identification of omega-3 fatty acid producers in free-living bacterial strains isolated from 5, 500, and 1000 m deep coastal seawater from the Bay of Biscay (Spain). We further measured EPA production in pelagic Vibrio sp. strains collected at the three different depths. Vibrio sp. EPA-producers and non-producers were simultaneously isolated from the same water samples and shared a high percentage of identity in their 16S rRNA genes, supporting the view that the pfa gene cluster can be horizontally transferred. Within a cluster of EPA-producers, we found intraspecific variation in the levels of EPA synthesis for isolates harboring different genetic variants of the pfaA-KS domain. The maximum production of EPA was found in a Vibrio sp. strain isolated from a 1000 m depth (average 4.29% ± 1.07 of total fatty acids at 10 °C, without any optimization of culturing conditions).

Two-stage pH control combined with oxygen-enriched air strategies for the highly efficient production of EPA by Mortierella alpina CCFM698 with fed-batch fermentation.

Dissolved oxygen and pH are critical factors influencing cell growth and metabolism. In our previous work, we constructed the recombinant strain Mortierella alpina CCFM698, which has the ability to produce EPA at room temperature. However, our experiments showed that the dissolved oxygen produced by the aeration and agitation of the fermenter was insufficient for cell growth and EPA synthesis by this recombinant strain. Moreover, the optimum pH for cell growth was incompatible with that of EPA accumulation. This study introduced a combined strategy of two-stage pH control with oxygen-enriched air in fed-batch fermentation to facilitate both cell growth and EPA production in M. alpina CCFM698. After 10 days of fermentation in a 7.5 L tank, the biomass production reached 41.2 g/L, with a lipid content of 31.5%, and EPA accounting for 26.7% of total lipids. The final EPA production reached 3.47 g/L, which is the highest yet achieved by M. alpina. This study reveals the critical role of dissolved oxygen and pH control for EPA production of M. alpina, and provides an easy and efficient strategy for industrial production of EPA.

Genome-wide sequencing and metabolic annotation of Pythium irregulare CBS 494.86: understanding Eicosapentaenoic acid production.

BACKGROUND: Pythium irregulare is an oleaginous Oomycete able to accumulate large amounts of lipids, including Eicosapentaenoic acid (EPA). EPA is an important and expensive dietary supplement with a promising and very competitive market, which is dependent on fish-oil extraction. This has prompted several research groups to study biotechnological routes to obtain specific fatty acids rather than a mixture of various lipids. Moreover, microorganisms can use low cost carbon sources for lipid production, thus reducing production costs. Previous studies have highlighted the production of EPA by P. irregulare, exploiting diverse low cost carbon sources that are produced in large amounts, such as vinasse, glycerol, and food wastewater. However, there is still a lack of knowledge about its biosynthetic pathways, because no functional annotation of any Pythium sp. exists yet. The goal of this work was to identify key genes and pathways related to EPA biosynthesis, in P. irregulare CBS 494.86, by sequencing and performing an unprecedented annotation of its genome, considering the possibility of using wastewater as a carbon source. RESULTS: Genome sequencing provided 17,727 candidate genes, with 3809 of them associated with enzyme code and 945 with membrane transporter proteins. The functional annotation was compared with curated information of oleaginous organisms, understanding amino acids and fatty acids production, and consumption of carbon and nitrogen sources, present in the wastewater. The main features include the presence of genes related to the consumption of several sugars and candidate genes of unsaturated fatty acids production. CONCLUSIONS: The whole metabolic genome presented, which is an unprecedented reconstruction of P. irregulare CBS 494.86, shows its potential to produce value-added products, in special EPA, for food and pharmaceutical industries, moreover it infers metabolic capabilities of the microorganism by incorporating information obtained from literature and genomic data, supplying information of great importance to future work.

Low-linoleic acid diet and oestrogen enhance the conversion of α-linolenic acid into DHA through modification of conversion enzymes and transcription factors.

Conversion of α-linolenic acid (ALA) into the longer chain n-3 PUFA has been suggested to be affected by the dietary intake of linoleic acid (LA), but the mechanism is not well known. Therefore, the purpose of this study was to evaluate the effect of a low-LA diet with and without oestrogen on the fatty acid conversion enzymes and transcription factors. Rats were fed a modified American Institute of Nutrition-93G diet with 0% n-3 PUFA or ALA, containing low or high amounts of LA for 12 weeks. At 8 weeks, the rats were injected with maize oil with or without 17ß-oestradiol-3-benzoate (E) at constant intervals for the remaining 3 weeks. Both the low-LA diet and E significantly increased the hepatic expressions of PPAR-α, fatty acid desaturase (FADS) 2, elongase of very long chain fatty acids 2 (ELOVL2) and ELOVL5 but decreased sterol regulatory element binding protein 1. The low-LA diet, but not E, increased the hepatic expression of FADS1, and E increased the hepatic expression of oestrogen receptor-α and ß. The low-LA diet and E had synergic effects on serum and liver levels of DHA and on the hepatic expression of PPAR-α. In conclusion, the low-LA diet and oestrogen increased the conversion of ALA into DHA by upregulating the elongases and desaturases of fatty acids through regulating the expression of transcription factors. The low-LA diet and E had a synergic effect on serum and liver levels of DHA through increasing the expression of PPAR-α.

Production of eicosapentaenoic acid (EPA, 20:5n-3) in transgenic peanut (Arachis hypogaea L.) through the alternative Δ8-desaturase pathway.

An important alternative source of fish oil is its production by plants through metabolic engineering. To produce eicosapentaenoic acid (EPA, 20:5n-3) in peanut through the alternative Δ8-pathway, a plant expression vector containing five heterologous genes driven by the constitutive 35S promoter respectively, namely, ∆9-elongase (Isochrysis galbana), ∆8-desaturase (Euglena gracilis), ∆5-desaturase (Mortierella alpina), ∆15-desaturase (Arabidopsis thaliana) and ∆17-desaturase (Phytophthora infestans) were transferred into peanut through Agrobacterium-mediated transformation method. The gas chromatography results indicated that the average content of EPA in the leaves of the transgenic lines was 0.68%, and the highest accumulation of EPA in an individual line reached 0.84%. This finding indicates that it is feasible to synthesize EPA in peanut through metabolic engineering and lays the foundations for the production of very-long-chain polyunsaturated fatty acids (VLCPUFAs) in peanut seeds.

Biosynthesis of Nutraceutical Fatty Acids by the Oleaginous Marine Microalgae Phaeodactylum tricornutum Utilizing Hydrolysates from Organosolv-Pretreated Birch and Spruce Biomass.

Polyunsaturated fatty acids (PUFAs) are essential for human function, however they have to be provided through the diet. As their production from fish oil is environmentally unsustainable, there is demand for new sources of PUFAs. The aim of the present work was to establish the microalgal platform to produce nutraceutical-value PUFAs from forest biomass. To this end, the growth of Phaeodactylum tricornutum on birch and spruce hydrolysates was compared to autotrophic cultivation and glucose synthetic media. Total lipid generated by P. tricornutum grown mixotrophically on glucose, birch, and spruce hydrolysates was 1.21, 1.26, and 1.29 g/L, respectively. The highest eicosapentaenoic acid (EPA) production (256 mg/L) and productivity (19.69 mg/L/d) were observed on spruce hydrolysates. These values were considerably higher than those obtained from the cultivation without glucose (79.80 mg/L and 6.14 mg/L/d, respectively) and also from the photoautotrophic cultivation (26.86 mg/L and 2.44 mg/L/d, respectively). To the best of our knowledge, this is the first report describing the use of forest biomass as raw material for EPA and docosapentaenoic acid (DHA) production.

Intravenous Lipid Emulsions to Deliver Bioactive Omega-3 Fatty Acids for Improved Patient Outcomes.

Lipids used in intravenous nutrition support (i.e., parenteral nutrition) provide energy, building blocks, and essential fatty acids. These lipids are included as emulsions since they need to be soluble in an aqueous environment. Fish oil is a source of bioactive omega-3 fatty acids (eicosapentaenoic acid and docosahexaenoic acid). Lipid emulsions, including fish oil, have been used for parenteral nutrition for adult patients post-surgery (mainly gastrointestinal). This has been associated with alterations in biomarkers of inflammation and immune defense, and in some studies, a reduction in length of intensive care unit and hospital stay. These benefits, along with a reduction in infections, are emphasized through recent meta-analyses. Perioperative administration of fish oil may be superior to postoperative administration, but this requires further exploration. Parenteral fish oil has been used in critically ill adult patients. Here, the influence on inflammatory processes, immune function, and clinical endpoints is less clear. However, some studies found reduced inflammation, improved gas exchange, and shorter length of hospital stay in critically ill patients if they received fish oil. Meta-analyses do not present a consistent picture but are limited by the small number and size of studies. More and better trials are needed in patient groups in which parenteral nutrition is used and where fish oil, as a source of bioactive omega-3 fatty acids, may offer benefits.

Genetically Engineered Oil Seed Crops and Novel Terrestrial Nutrients: Ethical Considerations.

Genetically engineered (GE) organisms have been at the center of ethical debates among the public and regulators over their potential risks and benefits to the environment and society. Unlike the currently commercial GE crops that express resistance or tolerance to pesticides or herbicides, a new GE crop produces two bioactive nutrients (eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)) that heretofore have largely been produced only in aquatic environments. This represents a novel category of risk to ecosystem functioning. The present paper describes why growing oilseed crops engineered to produce EPA and DHA means introducing into a terrestrial ecosystem a pair of highly bioactive nutrients that are novel to terrestrial ecosystems and why that may have ecological and physiological consequences. More importantly perhaps, this paper argues that discussion of this novel risk represents an opportunity to examine the way the debate over genetically modified crops is being conducted.

Defatted Microalgae-Mediated Enrichment of n-3 Polyunsaturated Fatty Acids in Chicken Muscle Is Not Affected by Dietary Selenium, Vitamin E, or Corn Oil.

Background: We previously showed enrichments of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) in broiler chicks fed defatted microalgae. Objectives: The aims of this study were to determine 1) if the enrichments affected meat texture and were enhanced by manipulating dietary corn oil, selenium, and vitamin E concentrations and 2) how the enrichments corroborated with hepatic gene expression involved in biosynthesis and oxidation of EPA and DHA. Methods: Day-old hatching Cornish Giant cockerels (n = 216) were divided into 6 groups (6 cages/group and 6 chicks/cage). Chicks were fed 1 of the 6 diets: a control diet containing 4% corn oil, 25 IU vitamin E/kg, and 0.2 mg Se/kg (4CO), 4CO + 10% microalgae (defatted Nannochloropsis oceanica; 4CO+ MA), 4CO+ MA - 2% corn oil (2CO+MA), 2CO+MA + 75 IU vitamin E/kg (2CO+MA+E), 2CO+MA + 0.3 mg Se/kg (2CO+MA+Se), and 2CO+MA+E + 0.3 mg Se/kg (2CO+MA+E+Se). After 6 wk, fatty acid profiles, DHA and EPA biosynthesis and oxidation, gene expression, lipid peroxidation, antioxidant status, and meat texture were measured in liver, muscles, or both. Results: Compared with the control diet, defatted microalgae (4CO+MA) enriched (P < 0.05) DHA and EPA by ≤116 and 24 mg/100 g tissue in the liver and muscles, respectively, and downregulated (41-76%, P < 0.01) hepatic mRNA abundance of 4 cytochrome P450 (CYP) enzymes (CYP2C23b, CYP2D6, CYP3A5, CYP4V2). Supplemental microalgae decreased (50-82%, P < 0.05) lipid peroxidation and improved (16-28%, P < 0.05) antioxidant status in the liver, muscles, or both. However, the microalgae-mediated enrichments in the muscles were not elevated by altering dietary corn oil, vitamin E, or selenium and did not affect meat texture. Conclusion: The microalgae-mediated enrichments of DHA and EPA in the chicken muscles were associated with decreased hepatic gene expression of their oxidation, but were not further enhanced by altering dietary corn oil, vitamin E, or selenium.