Phospholipid molecular species, β-oxidation, desaturation and elongation of fatty acids in Atlantic salmon hepatocytes: Effects of temperature and 3-thia fatty acids

We have investigated the effects of a 3-thia fatty acid (TTA) and of temperature on the fatty acid (FA) metabolism of Atlantic salmon (Salmo salar). One experiment investigated the activity of the peroxisomal β-oxidation enzyme, acyl-CoA oxidase (ACO), and the incorporation of TTA into phospholipid (PL) molecular species. Salmon hepatocytes in culture were incubated either without TTA (control♠) or with 0.8 mM TTA (TTA♠) in a short term (48 h) temperature study at 5 °C and at 12 °C. TTA was incorporated into the four PL classes studied: phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI) and phosphatidylserine (PS). TTA was preferentially esterified with 18:1, 16:1, 20:4 and 22:6 in the PLs. Hepatocytes incubated with TTA had higher ACO activity at 5 °C than at 12 °C. In a second experiment salmon were fed a diet based on fish meal–fish oil without any TTA added (control) or a fish meal–fish oil diet supplemented with 0.6% TTA for 8 weeks at 12 °C and 20 weeks at 5 °C. At the end of the feeding trial, hepatocytes from fish acclimated to high or low temperatures were isolated from both dietary groups and incubated with either [1-14C]18:1 n-9 or [1-14C]20:4 n-3 at 5 °C or 12 °C. Radiolabelled 18:1 n-9 was mainly esterified into neutral lipids (NL), whereas [1-14C]20:4 n-3 was mainly esterified into PL at both temperatures. The rate of elongation of [1-14C]18:1 n-9 to 20:1 n-9 was twice as high in hepatocytes from fish fed the control diet than it was in hepatocytes from fish fed the TTA diet, at both temperatures. The amount of [1-14C]20:4 n-3 converted to 22:6 n-3 was approximately the same in hepatocytes from the two dietary groups, but there was a tendency to higher production of 22:6 n-3 at the lower temperature. Oxidation of [1-14C]18:1 n-9 to acid soluble products (ASP) and CO2 was approximately 10-fold greater in hepatocytes kept at 5 °C than in those kept at 12 °C and the main oxidation products formed were acetate, oxaloacetate and malate.