Incorporation of polyunsaturated fatty acids into plasmalogens, compared to other phospholipids of cultured glioma cells, is more dependent on chain length than on selectivity between (n - 3) and (n - 6) families

In several tissues and cells, polyunsaturated fatty acids (PUFA) are esterified to plasmalogens (1-O-alk-1′-enyl-2-acyl-sn-glycero-3 phosphoethanolamine). Some studies have implicated selectivity for (n - 3) fatty acids, particularly of 20- and 22-carbons, over the (n - 6) family of fatty acids. We have investigated selectivity for esterification of both families of PUFA to plasmalogens in cultured C6 glioma cells. By 24 h, approx. 40% of cell-associated label from [1-¹⁴C]18:3(n - 3) was incorporated into plasmalogens and that label consisted almost exclusively of desaturation and chain elongation products [80% 20:5(n - 3) and 15% 22:5(n - 3)]. Relative incorporation of label from PUFA into plasmalogens was 20:5(n - 3) > 20:4(n - 6) > 18:3(n - 3) ≫ 18:2(n - 6); incorporation of unaltered 18-carbon chains was highly restricted. Cells incubated with [1-¹⁴C]18:3(n - 3) and 20-150 μM competing unlabeled fatty acids showed 20:5(n - 3) > 20:4(n - 6) ≥ 22:4(n - 6) > 18:3(n - 3) as inhibitors of plasmalogen labeling. Chase experiments in cells prelabeled with [1-¹⁴C]18:3(n - 3) for 2 h showed limited reduction of label in plasmalogen. Reduction of plasmalogen label did occur when (n - 3) or (n - 6) fatty acids were added to cells prelabeled for 48 h, accounting for losses of 20-35% compared to controls. Accordingly, little selectively occurs in esterification of plasmalogens from mixtures of (n - 3) and (n - 6) fatty acyl chains. Subsequent remodeling of (n - 3) acyl chains occurs, but is more dependent on acyl chain length than on selectivity between (n - 3) and (n - 6) families. Our data are consistent with a stable plasmalogen pool enriched in PUFA, but not specifically with (n - 3) fatty acids.