Acylation of docosahexaenoic acid into phospholipids by intact human neutrophils

Docosahexaenoic acid was not only acylated into phospholipids but also into triacylglycerols by intact human neutrophils. The distribution of radiolabeled docosahexaenoic acid among individual phospholipids was dependent on the incubation time. [1-14C]Docosahexaenoic acid at all concentrations (1 to 8 microM) was acylated mainly into phosphatidic acid after 1-2 min incubation, and the radioactivity of phosphatidic acid started to decline after a longer period of incubation, suggesting the participation of docosahexaenoyl-phosphatidic acid in the synthesis of other glycerolipids. It was acylated primarily into phosphatidylcholine (PC) and phosphatidylethanolamine (PE) after a 2-hr incubation. The labeled phosphatidic acid may be rapidly deacylated and the 22:6(n-3) moiety is then reacylated into other lysophospholipids. The low levels of [14C]22:6(n-3) in 1,2-diacylglycerol suggest that the deacylation-reacylation cycle may be a major pathway in the formation of [14C]22:6(n-3)-PC and -PE in intact neutrophils. This n-3 fatty acid was a relatively poor substrate for acylation into phosphatidylinositol as compared to arachidonic acid and eicosapentaenoic acid. However, the patterns of distribution of all three polyunsaturated fatty acids among the diacyl- and ether-linked class compositions of PC and PE were similar. These data suggest the potential of increasing the content of docosahexaenoic acid of membrane lipids in neutrophils by dietary supplement of this fatty acid.