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The aim of this study was to assess relationships between the fatty acid contents of plasma and erythrocyte phospholipids and those in liver, heart, brain, kidney and quadriceps muscle in rats.To obtain a wide range of tissue omega-3 (n-3) long chain polyunsaturated fatty acids (LCPUFA) we subjected weanling rats to dietary treatment with the n-3 LCPUFA precursor, alpha linolenic acid (ALA, 18:3 n-3) for 3 weeks. With the exception of the brain, we found strong and consistent correlations between the total n-3 LCPUFA fatty acid content of both plasma and erythrocyte phospholipids with fatty acid levels in all tissues. The relationships between eicosapentaenoic acid (EPA, 20:5n-3) and docosapentaenoic acid (DPA, 22:5 n-3) content in both blood fractions with levels in liver, kidney, heart and quadriceps muscle phospholipids were stronger than those for docosahexaenoic acid (DHA, 22:6 n-3). The strong correlations between the EPA+DHA (the Omega-3 Index), total n-3 LCPUFA and total n-3 PUFA contents in both plasma and erythrocyte phospholipids and tissues investigated in this study suggest that, under a wide range of n-3 LCPUFA values, plasma and erythrocyte n-3 fatty acid content reflect not only dietary PUFA intakes but also accumulation of endogenously synthesized n-3 LCPUFA, and thus can be used as a reliable surrogate for assessing n-3 status in key peripheral tissues.

 If accepted for publication, we encourage authors to link from the preprint to their formal publication via its Digital Object Identifier (DOI). Millions of researchers have access to the formal publications on ScienceDirect, and so links will help your users to find, access, cite, and use the best available version.  Authors can update their preprints on arXiv or RePEc with their accepted manuscript . Please note: Cell Press, The Lancet, and some society-owned titles have different preprint policies. Information on these is available on the journal homepage.  Preprints should not be added to or enhanced in any way in order to appear more like, or to substitute for, the final versions of articles. ABSTRACT 17This study examined the effects of substituting fish oil and fish meal with a blend of 18 alpha-linolenic acid (ALA, 18:3 n-3) rich vegetable oils (14%, w/w) and defatted poultry 19 meal (34%, w/w) in a formulated diet, on growth and tissue fatty acid profiles in 20 barramundi fingerlings. Results indicated that on average, while the ALA levels of the 21 barramundi liver and fillet increased with increasing dietary ALA, there was no 22 corresponding increase in the levels of the omega-3 (n-3) long chain polyunsaturated 23 fatty acid (LCPUFA). Compared to fish consuming a commercial feed, which contained 24 fish meal and fish oil, fish on the ALA diets grew slower, had a lower feed intake and 25 lower n-3 LCPUFA levels in the tissues. Hepatic mRNA expression of Δ6 desaturase 26 (FADS2) and elongase (ELOVL5/2) were ~10 fold and ~3 fold higher, respectively, in all 27 the ALA dietary groups, relative to those fed the commercial feed. However, the level of 28 expression of the two genes was not different between fish fed differing ALA levels. 29These data demonstrate that increasing the ALA level of the diet is not an appropriate 30 strategy for replacing marine sources of n-3 LCPUFA in barramundi. It was also noted, 31 however, that within the different ALA dietary groups there was a large amount of 32 variation between individual fish in their tissue DHA levels, suggesting a significant 33 heterogeneity in their capacity for conversion of ALA and/or retention of n-3 LCPUFA. 34When dietary ALA intakes were greater than 0.8%en, tissue DHA levels were inversely 35 related to ALA intake, suggesting that high intake of dietary ALA may inhibit DHA 36 synthesis.

Barramundi is a commercially farmed fish in Australia. To examine the potential for barramundi to metabolise dietary -linolenic acid (ALA, 18:3 n-3), the existence of barramundi desaturase enzymes was examined. A putative fatty acid Δ6 desaturase was cloned from barramundi liver and expressed in yeast. Functional expression revealed Δ6 desaturase activity with both the 18 carbon (C18) and C24 n-3 fatty acids, ALA and 24:5 n-3 as well as the C18 n-6 fatty, linoleic acid (LA, 18:2 n-6).Metabolism of ALA was favoured over LA. The enzyme also had Δ8 desaturase activity which raises the potential for synthesis in barramundi of omega-3 (n-3) long chain polyunsaturated fatty acids (LCPUFA) from ALA via a pathway that bypasses the initial Δ6 desaturase step. Findings from this study not only provide molecular evidence for the fatty acid desaturation pathway in the barramundi and also highlight the importance of taking extracellular fatty acid levels into account when assessing enzyme activity expressed in Saccharomyces cerevisiae.