ARACHIDONIC-ACID OF PLATELET PHOSPHOLIPIDS IS DECREASED AFTER EXTRACORPOREAL REMOVAL OF PLASMA LOW-DENSITY LIPOPROTEINS IN PATIENTS WITH FAMILIAL HYPERCHOLESTEROLEMIA

Platelet phospholipid composition was analyzed before and after extrac orporeal removal of low density lipoproteins (LDL) by LDL apheresis in six patients with familial hypercholesterolemia. Elevated levels of t otal plasma cholesterol and the portion of plasma cholesterol carried by LDL were reduced by 56 and 66% after LDL apheresis. Platelet choles terol contents remained unaffected. While the phosphatidylcholine (PC) :sphingomyelin (SM) ratio in plasma lipoproteins was increased by 22% following apheresis, the same parameter was lowered by 14% in platelet s. LDL apheresis induced decreases in the percentages of distinct mole cular species containing arachidonic acid in platelet diacyl subgroups of PC, phosphatidylinositol (PI) and phosphatidylserine (PS) as well as in alkenylacyl (plasmalogen) phosphatidylethanolamine (PE). Directl y after apheresis, the percentages of molecular species with arachidon ic acid of diacyl PC, diacyl PI and alkenylacyl PE were reduced by 20, 23 and 8%, respectively, Two days after the procedure, total arachido nic acid of diacyl PC: diacyl PS and alkenylacyl PE was lowered by 11, 20 and 8%. Overall, the amount of phospholipid bound arachidonic acid was reduced by 16% after apheresis (from 79.1 to 66.4 nmol/10(8) plat elets). The results are thus in agreement with previous data indicatin g decreased phospholipid bound arachidonic acid in red blood cells aft er apheresis (Engelman B, Brautigam C, Kulschar R et al. Biochim Bioph ys Acta 1994;1196:154). Urinary 2,3-dinor thromboxane B-2, an estimate of platelet thromboxane A(2) (TXA(2)) production, tended to be decrea sed following the procedure. The percentage change in the TXA(2) metab olite was positively related to the magnitude of change induced by aph eresis in phospholipid bound arachidonic acid. In summary, the results suggest that in patients with hypercholesterolemia, the level of plas ma LDL is an important determinant of the arachidonic acid content of several platelet phospholipids. (C) 1997 Elsevier Science Ireland Ltd.