Phospholipid incorporation and metabolic conversion of n-3 polyunsaturatedfatty acids in the Y79 retinoblastoma cell line

The metabolic conversion of n-3 fatty acids was studied in the human Y79 re tinoblastoma cell line. Cultured cells were exposed to increasing concentra tions of either 18:3n-3, 22:5n-3, or 22:6n-3, and their phospholipid fatty acid composition was analyzed after 72 hr, Cells internalized the supplemen tal fatty acids and proceeded to their metabolic conversion. Supplemental 2 2:6n-3 was directly esterified into cell phospholipids, at levels typical f or normal neural retinas (41% by weight of phosphatidylethanolamine fatty a cids, and 24% of phosphatidylcholine fatty acids). In contrast, 18:3n-3 was mainly converted to 20:5n-3 and 22:5n-3, both of which appeared in cell ph ospholipids after exposure to low external concentrations of 18:3n-3 (10 mu g/ml). Y79 cells can proceed to the metabolic conversion of 18:3n-3 throug h elongation and Delta 6- and Delta 5-desaturation. When cells were exposed to high external concentrations of 18:3n-3 (30 mu g/ml), the supplemental fatty acid was directly incorporated, and its relative content increased in both phospholipid classes to the detriment of all other n-3 fatty acids. C ells cultured in the presence of 22.5n-3 did not incorporate 22.6n-3 into t heir phospholipids but did incorporate 20:5n-3 and 22:5n-3. The data sugges t that Y79 cells can proceed to the microsomal steps of n-3 metabolism, inv olving elongation, desaturation, and chain shortening of 22C fatty acids. A lthough Y79 cells avidly used supplemental 22.6n-3 for phospholipid incorpo ration at levels typical for normal photoreceptor cells, they failed to mat ch such levels through metabolic conversion of n-3 parent fatty acids. The terminal step of the very long-chain polyunsaturated fatty acid synthesis, consisting in Delta 6-desaturation followed by peroxisomal chain shortening of 24C-fatty acids, could be rate-limiting Y79 cells. (C) 2000 Wiley-Liss, Inc.