Transfer of arachidonic acid from phosphatidylcholine to phosphatidylethanolamine during storage of human platelets for 5 days

Human platelets are routinely stored for 5 days prior to transfusion, but they deteriorate during storage. Since very little information is available concerning the effect of storage on platelet phospholipid metabolism, the biosynthesis and remodelling of platelet phospholipids were studied. Platelets were incubated separately with 14C]glycerol, 14C]arachidonic acid, or a mixture of 14C]glycerol and 3H]arachidonic acid, and stored in a platelet storage medium at 22 degrees C. Maximum glycerol uptake (20%) was attained after 6 h. 14C]Glycerol was incorporated into phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol, and to a much lesser extent phosphatidylserine, under storage conditions for 5 days. The distribution of the initial arachidonic acid uptake was not as would be expected based on the molar composition of endogenous phospholipids. The arachidonic acid (75%) which was taken up within 10 min of incubation distributed 55% into the phosphatidylcholine and only 14% into the phosphatidylethanolamine; the molar composition is actually 18% phosphatidylcholine and 47% phosphatidylethanolamine. During storage, there was a continuous transfer of the radiolabelled arachidonic from phosphatidylcholine to phosphatidylethanolamine until, after 5 days, the distribution of arachidonic acid was identical to the endogenous distribution. In contrast, no change in the glycerol incorporation pattern was detected during storage. This suggested that the mechanism for arachidonic acid redistribution was not through exchange of polar head groups, but through acyl transfer of arachidonic acid from phosphatidylcholine to phosphatidylethanolamine.