REVERSIBLE REDUCTION OF PHOSPHOLIPID BOUND ARACHIDONIC-ACID AFTER LOW-DENSITY-LIPOPROTEIN APHERESIS - EVIDENCE FOR RAPID INCORPORATION OF PLASMALOGEN PHOSPHATIDYLETHANOLAMINE INTO THE RED-BLOOD-CELL MEMBRANE

In order to evaluate whether acute changes in fatty acids bound to pho spholipids in plasma are transmitted into red blood cell membrane (RBC M) phospholipids, molecular species of phosphatidylcholine (PC) and ph osphatidylethanoiamine (PE) were analyzed after reduction of apo B con taining lipoproteins through low density lipoprotein (LDL) apheresis i n patients with severe hypercholesterolemia. As compared to the contro l, increases and decreases in molecular species with arachidonic acid (20:4) and with linoleic acid (18:2), respectively, at sn-2 of plasma diacyl-PC were seen in the patients before the apheresis. Directly aft er the procedure, the sum of species of plasma and RBCM PC plus PE wit h 20:4 were reduced. Two days after apheresis major species of plasma diacyl-PC reapproached preapheresis values while, in contrast, the com position of plasma alkenylacyl(plasmalogen)-PE was distinctly altered. In plasmalogen-PE of RBCM similar modifications were induced by the a pheresis as in the same subgroup in plasma. In vitro experiments using vesicles with plasmalogen-PE labeled at sn-2 with either [C-14]20:4 o r a fluorescent pyrenedecanoyl residue indicated fast incorporation of the subgroup into the RBCM. In contrast, diacyl-PE was not taken up b y the RBCM. In conclusion, apo B containing lipoproteins are partially responsible for the supply of phospholipids with arachidonic acid to RBCM, in particular by means of the fast incorporation of plasmalogen- PE. The transmission of changes induced by apheresis in plasma into th ose of the RBCM suggest that erythrocytes play an important role in th e homeostasis of fatty acids bound to plasma phospholipids in vivo.