Fatty acid utilisation and metabolism in caecal enterocytes of rainbow trout (Oncorhynchus mykiss) fed dietary fish or copepod oil.
A combined fatty acid metabolism assay was employed to determine fatty acid uptake and relative utilisation in enterocytes isolated from the pyloric caeca of rainbow trout. In addition, the effect of a diet high in long-chain monoenoic fatty alcohols present as wax esters in oil derived from Calanus finmarchicus, compared to a standard fish oil diet, on caecal enterocyte fatty acid metabolism was investigated. The diets were fed for 8 weeks before caecal enterocytes from each dietary group were isolated and incubated with [1-14C]fatty acids: 16:0, 18:1n-9, 18:2n-6, 18:3n-3, 20:1n-9, 20:4n-6, 20:5n-3, and 22:6n-3. Uptake was measured over 2 h with relative utilisation of different [1-14C]fatty acids calculated as a percentage of uptake. Differences in uptake were observed, with 18:1n-9 and 18:2n-6 showing the highest rates. Esterification into cellular lipids was highest with 16:0 and C18 fatty acids, accounting for over one-third of total uptake, through predominant incorporation in triacylglycerol (TAG). The overall utilisation of fatty acids in phospholipid synthesis was low, but highest with 16:0, the most prevalent fatty acid recovered in intracellular phosphatidylcholine (PC) and phosphatidylinositol (PI), although exported PC exhibited higher proportions of C20/C22 polyunsaturated fatty acids (PUFA). Other than 16:0, incorporation into PC and PI was highest with C20/C22 PUFA and 20:4n-6 respectively. Recovery of labelled 18:1n-9 in exported TAG was 3-fold greater than any other fatty acid which could be due to multiple esterification on the glycerol 'backbone' and/or increased export. Approximately 20-40% of fatty acids taken up were beta-oxidised, and was highest with 20:4n-6. Oxidation of 20:5n-3 and 22:6n-3 was also surprisingly high, although 22:6n-3 oxidation was mainly attributed to retroconversion to 20:5n-3. Metabolic modification of fatty acids by elongation-desaturation was generally low at <10% of [1-14C]fatty acid uptake. Dietary copepod oil had generally little effect on fatty acid metabolism in enterocytes, although it stimulated the elongation and desaturation of 16:0 and elongation of 18:1n-9, with radioactivity recovered in longer n-9 monoenes. The monoenoic fatty acid, 20:1n-9, abundant in copepod oil as the homologous alcohol, was poorly utilised with 80% of uptake remaining unesterified in the enterocyte. However, the fatty acid composition of pyloric caeca was not influenced by dietary copepod oil.
Oxley
Anthony
A
Institute of Marine Research, Matre Aquaculture Research Station, N-5984 Matredal, Norway. anthony.oxley@nifes.no
Tocher
Douglas R
DR
Torstensen
Bente E
BE
Olsen
Rolf E
RE
D000818:Animals; D001693:Biological Transport, Active; D002432:Cecum / Q000166:cytology / Q000378:metabolism; D033342:Copepoda / Q000737:chemistry; D004042:Dietary Fats, Unsaturated / Q000008:administration & dosage*; D020895:Enterocytes / Q000378:metabolism*; D005227:Fatty Acids / Q000737:chemistry / Q000378:metabolism*; D005395:Fish Oils / Q000008:administration & dosage / Q000737:chemistry; D066298:In Vitro Techniques; D015394:Molecular Structure; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D010084:Oxidation-Reduction; D010743:Phospholipids / Q000096:biosynthesis / Q000737:chemistry
D004042:Dietary Fats, Unsaturated; D005227:Fatty Acids; D005395:Fish Oils; D010743:Phospholipids