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 phospholipids in plasma are transmitted into red blood cell membrane (RBCM) phospholipids, molecular species of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were analyzed after reduction of apo B containing lipoproteins through low density lipoprotein (LDL) apheresis in patients with severe hypercholesterolemia. As compared to the control, 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 after the procedure, the sum of species of plasma and RBCM PC plus PE with 20:4 were reduced. Two days after apheresis major species of plasma diacyl-PC reapproached preapheresis values while, in contrast, the composition of plasma alkenylacyl(plasmalogen)-PE was distinctly altered. In plasmalogen-PE of RBCM similar modifications were induced by the apheresis as in the same subgroup in plasma. In vitro experiments using vesicles with plasmalogen-PE labeled at sn-2 with either [14C]20:4 or a fluorescent pyrenedecanoyl residue indicated fast incorporation of the subgroup into the RBCM. In contrast, diacyl-PE was not taken up by 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 those of the RBCM suggest that erythrocytes play an important role in the homeostasis of fatty acids bound to plasma phospholipids in vivo.

Transfer of phosphatidylcholine, phosphatidylethanolamine and sphingomyelin from low- and high-density lipoprotein to human platelets.

Following a 1 h incubation of human platelets with low-density lipoprotein (LDL) labelled in the apoprotein fraction (125I-apoB) or in phospholipid fractions [14C-labelled phosphatidylcholine (PC), phosphatidylethanolamine (PE) or sphingomyelin (SM)], the percentage of total 14C associated with the cells was about 3-fold higher than the percentage of 125I. Differences in temperature sensitivity also indicated differential interactions of phospholipids and apoprotein with platelets. In order to assess the amount of [14C]phospholipid transferred from LDL or high-density lipoprotein (HDL) to the cells, the quantity of bound lipoproteins was estimated by adding an excess of unlabelled lipoprotein, or by selectively degrading LDL- and HDL-associated [14C]PC and [14C]PE with phospholipase C. Incubation of platelets with LDL or HDL containing pyrenedecanoic acid-labelled PC or SM (py-PC, py-SM) increased pyrene monomer fluorescence, indicating incorporation of the phospholipids into platelets. With HDl as donor, incorporation of py-SM was greater than uptake of py-PC. Pretreating platelets with elastase dose-dependently inhibited uptake of py-SM and py-PC. Treatment of cells with phospholipase C indicated that the uptake of [14C]PC by platelets, and not the binding of lipoproteins to the cells, was partially inhibited by elastase. In conclusion, LDL and HDL rapidly deliver SM, PC and PE to platelets. Incorporation of LDL-derived phospholipids into platelets is unlikely to be mediated by endocytosis of lipoprotein particles. The uptake of the two choline-containing phospholipids appears to require the presence of specialized platelet membrane protein(s).

Fast transmission of alterations in plasma phosphatidylcholine/sphingomyelin ratio and lyso phosphatidylcholine levels into changes of red blood cell membrane phospholipid composition after low density lipoprotein apheresis.

In order to evaluate whether changes in plasma phospholipid composition are rapidly transmitted to the red blood cell membrane (RBCM) under in vivo conditions, the levels of major phospholipids in plasma, low density and high density lipoproteins (LDL and HDL) as well as in RBCM were determined before (pre), directly after (post) and 2 days after (48 h post) LDL apheresis in six patients with severe hypercholesterolaemia. LDL apheresis induced a 30-70% decrease in plasma and LDL cholesterol and total phospholipid levels within 2-3 h. Concomitantly, the percentages of plasma phosphatidylcholine (PC) and the PC/sphingomyelin (SM) ratio were increased compared to initial values. The percentage of plasma lyso PC (LPC) determined before apheresis in the patients was 30% lower with respect to the mean level of LPC in a normolipidaemic control. For LPC of LDL no differences were observed between normolipidaemia and hypercholesterolaemia. LDL apheresis induced a rise by about one third in the percentage of plasma LPC. At 48 h post, plasma LPC levels reapproached pre-apheresis levels, while the percentages of PC and the PC/SM ratio remained elevated. The pattern of changes induced by apheresis in plasma PC, SM and LPC levels was mimicked by changes in RBCM phospholipids. Strong positive relationships were noted for PC, SM and PC/SM as determined at pre, post and 48 h post between plasma and RBCM. In summary, changes in plasma PC, LPC, and PC/SM ratios as induced by LDL apheresis are rapidly transmitted to the RBCM under in vivo conditions, most probably as a result of phospholipid transfer between both compartments.(ABSTRACT TRUNCATED AT 250 WORDS)