DIFFERENTIAL INCORPORATION OF FATTY-ACIDS INTO AND PEROXIDATIVE LOSS OF FATTY-ACIDS FROM PHOSPHOLIPIDS OF HUMAN SPERMATOZOA

Intact human sperm incorporated radiolabelled fatty acids into membran e phospholipids when incubated in medium containing bovine serum album in as a fatty acid carrier. The polyunsturated fatty acids were prefer entially incorporated into the plasmalogen fraction of phospholipid. U ptake was linear with time over 2 hr; at this time sufficient label wa s available to determine the loss of fatty acids under conditions of s pontaneous lipid peroxidation. Loss of the various phospholipid types, the loss of the various fatty acids from these phospholipids, and the overall loss of fatty acids were all first order. The loss of saturat ed fatty acids was slow with first order rate constant k(1) = 0.003 hr (-1); for the polyunsaturated fatty acids, arachidonic and docosahexae noic acids, k(1) = 0.145 and 0.162 hr(-1), respectively. The rate of l oss of fatty acids from the various phospholipid types was dependent o n the type, with loss from phosphatidylethanolamine being the most rap id. Among the phospholipid types, phosphatidylethanolamine was lost at the greatest rate. Analysis of fatty acid loss through oxidation prod ucts was determined for radiolabelled arachidonic acid. Under conditio ns of spontaneous lipid peroxidation at 37 degrees C under air in the absence of albumin, free arachidonic acid was found in the medium, alo ng with minor amounts of hydroxylated derivative. All the hydroperoxy fatty acid remained in the cells. In the presence of albumin, all the hydroperoxy fatty acid was found in the supernatant bound to albumin; none could be detected in the cells. Albumin is known as a very potent inhibitor of lipid peroxidation in sperm; its action may be explained , based on these results, as binding the damaging hydroperoxy fatty ac ids. These results also indicate that a phospholipase A(2) may act in peroxidative defense by excising a hydroperoxy acyl group from phospho lipid and providing the hydroperoxy fatty acid product as substrate to glutathione peroxidase. This formulation targets hydroperoxy fatty ac id as a key intermediate in peroxidative degradation. (C) 1995 Wiley-L iss, Inc.