Metabolism of n-3 and n-6 fatty acids in Atlantic salmon liver: stimulation by essential fatty acid deficiency.
Oxidation, esterification, desaturation, and elongation of [1-14C]18:2n-6 and [1-14C]18:3n-3 were studied using hepatocytes from Atlantic salmon (Salmo salar L.) maintained on diets deficient in n-3 and n-6 polyunsaturated fatty acids (PUFA) or supplemented with n-3 PUFA. For both dietary groups, radioactivity from 18:3n-3 was incorporated into lipid fractions two to three times faster than from 18:2n-6, and essential fatty acids (EFA) deficiency doubled the incorporation. Oxidation to CO2 was very low and was independent of substrate or diet, whereas oxidation to acid-soluble products was stimulated by EFA deficiency. Products from 18:2n-6 were mainly 18:3n-6, 20:3n-6, and 20:4n-6, with minor amounts of 20:2n-6 and 22:5n-6. Products from 18:3n-3 were mainly 18:4n-3, 20:5n-3, and 22:6n-3, with small amounts of 20:3n-3. The percentage of 22:6n-3 in the polar lipid fraction of EFA-deficient hepatocytes was fourfold higher than in n-3 PUFA-supplemented cells. This correlated well with our other results obtained after abdominal injection of [1-14C]18:3n-3 and [1-14C]18:2n-6. In hepatocytes incubated with [4,5-3H]-22:6n-3, 20:5n-3 was the main product. This retroconversion was increased by EFA deficiency, as was peroxisomal betaoxidation activity. This study shows that 18:2n-6 and 18:3n-3 can be elongated and desaturated in Atlantic salmon liver, and that this conversion and the activity of retroconversion of very long chain PUFA is markedly enhanced by EFA deficiency.
Ruyter
B
B
AKVAFORSK, Institute of Aquaculture Research, As Norway. bente.ruyter@akvaforsk.nlh.no
Thomassen
M S
MS
D000818:Animals; D002250:Carbon Radioisotopes; D004041:Dietary Fats / Q000032:analysis; D005227:Fatty Acids / Q000032:analysis; D005228:Fatty Acids, Essential / Q000172:deficiency*; D015525:Fatty Acids, Omega-3 / Q000378:metabolism*; D043371:Fatty Acids, Omega-6; D005231:Fatty Acids, Unsaturated / Q000378:metabolism*; D050356:Lipid Metabolism; D008055:Lipids / Q000032:analysis; D008099:Liver / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D010171:Palmitoyl Coenzyme A / Q000378:metabolism; D020675:Peroxisomes / Q000378:metabolism; D020317:Salmo salar / Q000254:growth & development / Q000378:metabolism*; D014316:Tritium
D002250:Carbon Radioisotopes; D004041:Dietary Fats; D005227:Fatty Acids; D005228:Fatty Acids, Essential; D015525:Fatty Acids, Omega-3; D043371:Fatty Acids, Omega-6; D005231:Fatty Acids, Unsaturated; D008055:Lipids; D014316:Tritium; D010171:Palmitoyl Coenzyme A