ASYMMETRIC INCORPORATION OF DIETARY N-3 FATTY-ACIDS INTO MEMBRANE AMINOPHOSPHOLIPIDS OF HUMAN ERYTHROCYTES

Dietary supplementation with different classes of polyunsaturate fatty acids is known to result in their incorporation into cell membranes, but the effects of this on eicosanoid formation and other cell functio ns frequently does not correspond to the degree of alteration in total membrane fatty acids. This phenomenon may be related to the compartme ntalization of polyunsaturate fatty acids both within the organelles a nd within membranes. Aminophospholipids are asymmetrically distributed across the membrane bilayers of most human cells. These phospholipids are highly enriched in polyunsaturated fatty acids, and are known to have specific interactions with a number of membrane proteins. To dete rmine whether dietary n-3 fatty acids are preferentially incorporated into membrane lipids in a particular spatial pattern, we have utilized the nonpermeant aminophospholipid probe, trinitrobenzenesulfonic acid , to study the transmembrane molecular species distribution of human e rythrocyte ethanolamine phospholipids and phosphatidylserines before a nd at the end of 4 weeks of dietary supplementation with n-3 fatty aci ds. Selective incorporation of n-3 fatty acids occurred in the inner m embrane leaflet ethanolamine phospholipids, particularly into the alke nyl-acyl species. The n-3 species in phosphatidylserines, particularly 18:0 and 22:6 n-3 (sn-1 and sn-2, respectively), replaced n-6 and n-9 species. These data may provide a basis for different cell responses to n-3 fatty acid enrichment, and for different degrees of diet-induce d alteration in responses involving inner and outer membrane leaflet f unctions.