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.

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.

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.

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.

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.

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.

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.

Single Cell Oil (SCO)-Based Bioactive Compounds: I-Enzymatic Synthesis of Fatty Acid Amides Using SCOs as Acyl Group Donors and Their Biological Activities.

Fatty acid amides (FAAs) are of great interest due to their broad industrial applications. They can be synthesized enzymatically with many advantages over chemical synthesis. In this study, the fatty acid moieties of lipids of Cunninghamella echinulata ATHUM 4411, Umbelopsis isabellina ATHUM 2935, Nannochloropsis gaditana CCAP 849/5, olive oil, and an eicosapentaenoic acid (EPA) concentrate were converted into their fatty acid methyl esters and used in the FAA (i.e., ethylene diamine amides) enzymatic synthesis, using lipases as biocatalysts. The FAA synthesis, monitored using in situ NMR, FT-IR, and thin-layer chromatography, was catalyzed efficiently by the immobilized Candida rugosa lipase. The synthesized FAAs exhibited a significant antimicrobial activity, especially those containing oleic acid in high proportions (i.e., derived from olive oil and U. isabellina oil), against several human pathogenic microorganisms, insecticidal activity against yellow fever mosquito, especially those of C. echinulata containing gamma-linolenic acid, and anticancer properties against SKOV-3 ovarian cancer cell line, especially those containing EPA in their structures (i.e., EPA concentrate and N. gaditana oil). We conclude that FAAs can be efficiently synthesized using microbial oils of different fatty acid composition and used in specific biological applications.

Production of Algal Biomass and High-Value Compounds Mediated by Interaction of Microalgal Oocystis sp. KNUA044 and Bacterium Sphingomonas KNU100.

There is growing interest in the production of microalgae-based, high-value by-products as an emerging green biotechnology. However, a cultivation platform for Oocystis sp. has yet to be established. We therefore examined the effects of bacterial culture additions on the growth and production of valuable compounds of the microalgal strain Oocystis sp. KNUA044, isolated from a locally adapted region in Korea. The strain grew only in the presence of a clear supernatant of Sphingomonas sp. KNU100 culture solution and generated 28.57 mg/l/d of biomass productivity. Protein content (43.9 wt%) was approximately two-fold higher than carbohydrate content (29.4 wt%) and lipid content (13.9 wt%). Oocystis sp. KNUA044 produced the monosaccharide fucose (33 µg/mg and 0.94 mg/l/d), reported here for the first time. Fatty acid profiling showed high accumulation (over 60%) of polyunsaturated fatty acids (PUFAs) compared to saturated (29.4%) and monounsaturated fatty acids (9.9%) under the same culture conditions. Of these PUFAs, the algal strain produced the highest concentration of linolenic acid (C18:3 ω3; 40.2%) in the omega-3 family and generated eicosapentaenoic acid (C20:5 ω3; 6.0%), also known as EPA. Based on these results, we suggest that the application of Sphingomonas sp. KNU100 for strain-dependent cultivation of Oocystis sp. KNUA044 holds future promise as a bioprocess capable of increasing algal biomass and high-value bioactive by-products, including fucose and PUFAs such as linolenic acid and EPA.

Optimizing Eicosapentaenoic Acid Production by Grafting a Heterologous Polyketide Synthase Pathway in the Thraustochytrid Aurantiochytrium.

Eicosapentaenoic acid (EPA) is an essential nutritional supplement for human health. The most prominent dietary source of EPA is fish oil, which is unsustainable because of the decline in fishery resources and serious environmental pollution. Alternatively, a heterologous polyketide synthase pathway for EPA biosynthesis was assembled in Thraustochytrid Aurantiochytrium. A 2A peptide-based facile assembly platform that can achieve multigene expression as a polycistron was first established. The platform was then applied to express the EPA biosynthetic gene cluster from Shewanella japonica in Aurantiochytrium. In the shake flask fermentation, the lipid and PUFA yields of the mutant were increased by 26.9 and 36.0%, respectively, and led to about 5-fold increase of the EPA yield. The final EPA titer reached 2.7 g/L in fed-batch fermentation. This study provides a novel metabolic engineering strategy to regulate the EPA ratio in microalgal oil for human nutritional supplementation.

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.

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).

Integrated metabolomic and transcriptomic analyses identify critical genes in eicosapentaenoic acid biosynthesis and metabolism in the sea urchin Strongylocentrotus intermedius.

Gonads are the only edible part of the sea urchin and have great potential as a health-promoting food for human consumption. Polyunsaturated fatty acids (PUFAs) are important necessary nutrients that determine not only the nutritional value of sea urchins but guarantee their normal growth and reproduction. However, the information on the molecular mechanisms of PUFA biosynthesis and metabolism in this species remains elusive. In this study, we used Strongylocentrotus intermedius as our model species and conducted integrated metabolomic and transcriptomic analyses of potentially critical genes involved in PUFA biosynthesis and metabolism during gonad growth and development, mainly focusing on eicosapentaenoic acid (EPA). We found six differentially accumulated metabolites associated with PUFA in the metabolomic analysis. More differentially expressed genes (DEGs) were related to PUFA in testis than ovary (1823 DEGs in testis and 1499 DEGs in ovary). We verified 12 DEGs by RNA-Seq results and found that Aldh7a1, Ecm3, Fads2, and Hsd17b12 genes had similar expression patterns in EPA concentration during gonad growth and development. In contrast, the other DEGs were downregulated and we inferred that EPA or PUFA may be metabolized as energy during certain periods. Our metabolic and genetic data will facilitate a better understanding of PUFA regulation networks during gonad growth and development in S. intermedius.

Identification and Functional Characterization of Two Novel Fatty Acid Genes from Marine Microalgae for Eicosapentaenoic Acid Production.

Marine microalgae such as Isochrysis sp. and Pavlova sp. are the predominant source of polyunsaturated fatty acids (PUFAs) such as eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3). EPA biosynthesis pathway is predominant in lower eukaryotes, and its biosynthetic gene expressions are not well established. Till date, the C18 elongation enzymes for EPA biosynthesis have not been identified from lower eukaryote. In the present study, we describe the identification of two microalgal genes Δ6-elongase and Δ5-desaturase involved for EPA biosynthesis. By PCR-based technique, a novel elongase gene (Δ6Elo-Iso) was isolated from Isochrysis sp., and 654 bp of full-length sequence was identified, which catalysed the conversion of SDA into ETr in E. coli. The identified gene displayed unique substrate specificity for both n-3 and n-6 C18-substrates for Δ6-elongation, with no activity towards Δ9-elongase. In addition, a novel Δ5-desaturase gene (Δ5Des-Pav) was isolated from Pavlova sp. and found an ORF of 1149 bp in length, which was capable of converting ETr into EPA in omega-3 pathway. For the first time, the heterologous expressions of two novel microalgal genes were successfully expressed in Escherichia coli. EPA production from E. coli is being considered as an alternative and economic source for industrial and pharmaceutical sectors.

Mapping and Validating QTL for Fatty Acid Compositions and Growth Traits in Asian Seabass.

Asian seabass is an important food fish species. While improving growth, increasing the nutritional value is important, omega-3 fatty acids are indispensable to human health. Identifying and validating DNA markers associated with traits is the first step towards marker-assisted selection (MAS). We quantified 13 different fatty acids and three growth traits in 213 F2 Asian seabass from a family at the age 270 days post hatch, and screened QTL for these traits. The content of total fatty acids in 100 g flesh was 2.57 ± 0.80 g, while the proportions of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) were 16.96 ± 2.20% and 5.42 ± 0.90%, respectively. A linkage map with 2424 SNPs was constructed and used for QTL mapping. For fatty acid compositions, 14 significant QTL were identified on three linkage groups (LG5, LG11 and LG14), with phenotypic variance explained (PVE) from 12.8 to 24.6%. Thirty-nine suggestive QTL were detected on 16 LGs. Two significant QTL for EPA were identified on LG5 and LG14, with PVE of 15.2% and 15.1%, respectively. No significant QTL was identified for DHA. For growth traits, six significant and 13 suggestive QTL were identified on two and seven LGs, respectively. Only a few significant QTL for fatty acids overlapped with previously mapped QTL for these traits, suggesting that most QTL detected in a family are family-specific and could only be used in MAS in the family per se. To facilitate population-wide molecular breeding, more powerful methods (e.g. GWAS) should be used to identify SNPs for genomic selection.

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.

CRISPR/Cas9-mediated ablation of elovl2 in Atlantic salmon (Salmo salar L.) inhibits elongation of polyunsaturated fatty acids and induces Srebp-1 and target genes.

Atlantic salmon can synthesize polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic acid (20:5n-3), arachidonic acid (20:4n-6) and docosahexaenoic acid (22:6n-3) via activities of very long chain fatty acyl elongases (Elovls) and fatty acyl desaturases (Fads), albeit to a limited degree. Understanding molecular mechanisms of PUFA biosynthesis and regulation is a pre-requisite for sustainable use of vegetable oils in aquafeeds as current sources of fish oils are unable to meet increasing demands for omega-3 PUFAs. By generating CRISPR-mediated elovl2 partial knockout (KO), we have shown that elovl2 is crucial for multi-tissue synthesis of 22:6n-3 in vivo and that endogenously synthesized PUFAs are important for transcriptional regulation of lipogenic genes in Atlantic salmon. The elovl2-KOs showed reduced levels of 22:6n-3 and accumulation of 20:5n-3 and docosapentaenoic acid (22:5n-3) in the liver, brain and white muscle, suggesting inhibition of elongation. Additionally, elovl2-KO salmon showed accumulation of 20:4n-6 in brain and white muscle. The impaired synthesis of 22:6n-3 induced hepatic expression of sterol regulatory element binding protein-1 (srebp-1), fatty acid synthase-b, Δ6fad-a, Δ5fad and elovl5. Our study demonstrates key roles of elovl2 at two penultimate steps of PUFA synthesis in vivo and suggests Srebp-1 as a main regulator of endogenous PUFA synthesis in Atlantic salmon.

Methyl-end desaturases with ∆12 and ω3 regioselectivities enable the de novo PUFA biosynthesis in the cephalopod Octopus vulgaris.

The interest in understanding the capacity of aquatic invertebrates to biosynthesise omega-3 (ω3) long-chain (≥C20) polyunsaturated fatty acids (LC-PUFA) has increased in recent years. Using the common octopus Octopus vulgaris as a model species, we previously characterised a ∆5 desaturase and two elongases (i.e. Elovl2/5 and Elovl4) involved in the biosynthesis of LC-PUFA in molluscs. The aim of this study was to characterise both molecularly and functionally, two methyl-end (or ωx) desaturases that have been long regarded to be absent in most animals. O. vulgaris possess two ωx desaturase genes encoding enzymes with ∆12 and ω3 regioselectivities enabling the de novo biosynthesis of the C18 PUFA 18:2ω6 (LA, linoleic acid) and 18:3ω3 (ALA, α-linolenic acid), generally regarded as dietary essential for animals. The O. vulgaris ∆12 desaturase ("ωx2") mediates the conversion of 18:1ω9 (oleic acid) into LA, and subsequently, the ω3 desaturase ("ωx1") catalyses the ∆15 desaturation from LA to ALA. Additionally, the O. vulgaris ω3 desaturase has ∆17 capacity towards a variety of C20 ω6 PUFA that are converted to their ω3 PUFA products. Particularly relevant was the affinity of the ω3 desaturase towards 20:4ω6 (ARA, arachidonic acid) to produce 20:5ω3 (EPA, eicosapentaenoic acid), as supported by yeast heterologous expression, and enzymatic activity exhibited in vivo when paralarvae were incubated in the presence of [1-14C]20:4ω6. These results confirmed that several routes enabling EPA biosynthesis are operative in O. vulgaris whereas ARA and docosahexaenoic acid (DHA, 22:6ω3) should be considered essential fatty acids since endogenous production appears to be limited.

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.