Effect of 18:1n-9, 20:5n-3, and 22:6n-3 on lipid accumulation and secretion by Atlantic salmon hepatocytes.
We have studied the effects of dietary FA on the accumulation and secretion of [3H]glycerolipids by salmon hepatocytes in culture. Atlantic salmon were fed diets supplemented with either 100% soybean oil (SO) or 100% fish oil (FO), and grew from an initial weight of 113 +/- 5 g to a final weight of 338 +/- 19 g. Hepatocytes were isolated from both dietary groups and incubated with [3H]glycerol in an FA-free medium; a medium supplemented with 0.75 mM of one of three FA-18:1 n-9, 20:5n-3, or 22:6n-3--or a medium supplemented with 0.75 mM of the sulfur-substituted FA analog tetradecylthioacetic acid (TTA), which cannot undergo beta-oxidation. Incubations were allowed to proceed for 1, 2, 6, or 24 h. The rate of the secretion of radioactive glycerolipids with no FA added was 36% lower from hepatocytes isolated from fish fed the FO diet than it was from hepatocytes isolated from fish fed the SO diet. Hepatocytes incubated with 18:1 n-9 secreted more [3H]TAG than when incubated with no FA, whereas hepatocytes incubated with 20:5n-3 or TTA secreted less labeled TAG than when incubated with no FA. This observation was independent of the feeding group. Hepatocytes incubated with 22:6n-3 secreted the highest amounts of total [3H]glycerolipids compared with the other treatments, owing to increased secretion of phospholipids and mono- and diacylglycerols (MDG). In contrast, the same amounts of [3H]TAG were secreted from these cells as from cells incubated in an FA-free medium. The lipid-lowering effect of FO is thus independent of 22:6n-3, showing that 20:5n-3 is the FA that is responsible for the lipid-lowering effect. The ratio of TAG to MDG in lipids secreted from hepatocytes to which 20:5n-3 or TTA had been added was lower than that in lipids secreted from hepatocytes incubated with 18:1 n-9 or 22:6n-3, suggesting that the last step in TAG synthesis was inhibited. Morphometric measurements revealed that hepatocytes incubated with 20:5n-3 accumulated significantly more cellular lipid than cells treated with 18:1n-9, 22:6n-3, TTA, or no treatment. The area occupied by mitochondria was also greater in these cells. The present study shows that dietary FO reduces TAG secretion from salmon hepatocytes and that 20:5n-3 mediates this effect.
Vegusdal
A
A
AKVAFORSK, Institute of Aquaculture Research, NO-1432 As, Norway. anne.vegusdal@akvaforsk.nlh.no
Gjøen
T
T
Berge
R K
RK
Thomassen
M S
MS
Ruyter
B
B
D000821:Animal Feed; D000818:Animals; D004042:Dietary Fats, Unsaturated / Q000494:pharmacology; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology*; D005395:Fish Oils / Q000494:pharmacology*; D005989:Glycerides / Q000378:metabolism; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism* / Q000648:ultrastructure; D050356:Lipid Metabolism; D008079:Lipoproteins, VLDL / Q000378:metabolism; D020317:Salmo salar / Q000378:metabolism*; D013024:Soybean Oil / Q000494:pharmacology*; D013440:Sulfides / Q000494:pharmacology
D004042:Dietary Fats, Unsaturated; D005231:Fatty Acids, Unsaturated; D005395:Fish Oils; D005989:Glycerides; D008079:Lipoproteins, VLDL; D013440:Sulfides; C062078:1-(carboxymethylthio)tetradecane; D013024:Soybean Oil