Chitosan-based delivery of fish codon-optimised Caenorhabditis elegans FAT-1 and FAT-2 boosts EPA and DHA biosynthesis in Sparus aurata

Omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA) are essential fatty acids required in healthy balanced diets for humans. To induce sustained production of n-3 LC-PUFA in gilthead seabream (Sparus aurata), chitosan-tripolyphosphate (TPP) nanoparticles encapsulating plasmids expressing fish codon-optimised Caenorhabditis elegans FAT-1 and FAT-2 were intraperitoneally administered every 4 weeks (3 doses in total, each of 10 μg plasmid per g of body weight). Growth performance and metabolic effects of chitosan-TPP complexed with pSG5 (empty plasmid), pSG5-FAT-1, pSG5-FAT-2 and pSG5-FAT-1 + pSG5-FAT-2 were assessed 70 days post-treatment. Tissue distribution analysis showed high expression levels of fish codon-optimised FAT-1 and FAT-2 in the liver (> 200-fold). Expression of fat-1 and fat-1 + fat-2 increased weight gain. Fatty acid methyl esters assay revealed that co-expression of fat-1 and fat-2 increased liver production and muscle accumulation of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and total n-3 LC-PUFA, while decreased the n-6/n-3 ratio. Co-expression of fat-1 and fat-2 downregulated srebf1 and genes encoding rate-limiting enzymes for de novo lipogenesis in the liver, leading to decreased circulating triglycerides and cholesterol. In contrast, FAT-2 and FAT-1 + FAT-2 upregulated hepatic hnf4a, nr1h3 and key enzymes in glycolysis and the pentose phosphate pathway. Our findings demonstrate for the first time efficient and sustained production of EPA and DHA in animals after long-term treatment with chitosan-TPP-DNA nanoparticles expressing FAT-1 and FAT-2, which enabled the production of functional fish rich in n-3 LC-PUFA for human consumption.