Effects of dietary supplementation of rapeseed oil on metabolism of [1‐¹⁴C]18∶1n−9, [1‐¹⁴C]20∶3n−6, and [1‐¹⁴C]20∶4n−3 in atlantic salmon heaptocytes

Abstract

Atlantic salmon were fed fish meal-based diets supplemented with either 100% fish oil (FO) or 100% rapeseed oil (RO) from an initial weight of 85 g to a final average weight of 280 g. The effects of these diets on the capacity of Atlantic salmon hepatocytes to elongate, desaturate, and esterify [1-14C] 18:1n-9 and the immediate substrates for the delta5 desaturase, [1-14C] 20:3 n-6 and [1-14C] 20:4n-3, were investigated. Radiolabeled 18:1n-9 was mainly esterified into cellular TAG, whereas the more polyunsaturated FA, [1-14C] 20:3n-6 and [1-14C] 20:4n-3, were primarily esterified into cellular PL. More of the elongation product, [1-14C] 20:1n-9, was produced from 18:1n-9 and more of the desaturation and elongation products, 22:5n-6 and 22:6n-3, were produced from [1-14C]20:3n-6 and [1-14C] 20:4n-3, respectively, in RO hepatocytes than in FO hepatocytes. Further, we studied whether increased addition of [1-14C]18:1n-9 to the hepatocyte culture media would affect the capacity of hepatocytes to oxidize 18:1n-9 to acid-soluble products and CO2. An increase in exogenous concentration of 18:1 n-9 from 7 to 100 microM resulted in a nearly twofold increase in the amount of 18:1n-9 that was oxidized. The conversion of 20:4n-3 and 20:3n-6 to the longer-chain 22:6n-3 and 22:5n-6 was enhanced by RO feeding in Atlantic salmon hepatocytes. The increased capacity of RO hepatocytes to produce 22:6n-3 was, however, not enough to achieve the levels found in FO hepatocytes. Our data further showed that there were no differences in the hepatocyte FA oxidation capacity and the lipid deposition of carcass and liver between the two groups.

Regulation of the Omega-3 Fatty Acid Biosynthetic Pathway in Atlantic Salmon Hepatocytes

“…There was also a tendency to higher production of 18:4n-3 in the high OA groups than in the high DHA groups. These results are in agreement with previous studies showing that vegetable oil can stimulate elongase and desaturase activity and/or gene expression [10,16,20,44,45]. No differences were found in DHA production between the four groups.…”

“…This FA is the most abundant FA in rapeseed oil, which is the most common oil substitute in today’s aquaculture. The capacity for conversion of ALA to EPA and DHA, and the gene expression of the elongases, the Δ5- and Δ6fad activities in salmon is increased when fed high dietary levels of vegetable oils, while FOs depressed the capacities [6,18–20]. Similar results have been found by Zheng et al [21], showing that EPA suppressed LC-PUFA synthesis in salmon cells and also suppressed the activity of the salmon Δ6fad promoter.…”

Issues of Fish Consumption for Cardiovascular Disease Risk Reduction

“…The impact of these changes of aquafeed ingredients on the composition of the fish and ultimately the impacts on the health of the consumers have not yet been explored in great detail. There is apparently some capacity for LC n -3 production from vegetable oils [58,59,60] in some fish, so this potential remains to be explored and developed.…”

Sustainability issues related to feeding salmonids: a Canadian perspective

“…Several studies have reported that most salmonids held in freshwater potentially have the ability to convert C18: 3n‐3 (α‐linolenic acid) from vegetable oil into the corresponding C20:5 n‐3 (EPA) and C22:6 n‐3 (DHA) in vivo by an alternating succession of desaturation and elongation (Ruyter & Thomassen ; Nakamura & Nara ; Moya‐Falcón et al . , ; Farrell et al . ; Codabaccus et al .…”