FAST TRANSMISSION OF ALTERATIONS IN PLASMA PHOSPHATIDYLCHOLINE SPHINGOMYELIN RATIO AND LYSE 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 compositio n are rapidly transmitted to the red blood cell membrane (RBCM) under in vivo conditions, the levels of major phospholipids in plasma, low d ensity 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 hypercholesterola emia. LDL apheresis induced a 30-70% decrease in plasma and LDL choles terol and total phospholipid levels within 23 h. Concomitantly, the pe rcentages of plasma phosphatidylcholine (PC) and the PC/sphingomyelin (SM) ratio were increased compared to initial values. The percentage o f plasma lyse 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 normolipi daemia and hypercholesterolaemia. LDL apheresis induced a rise by abou t 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 i n 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 i nduced by LDL apheresis are rapidly transmitted to the RBCM under in v ivo conditions, most probably as a result of phospholipid transfer bet ween both compartments. In addition, the percentages of LPC in plasma and LDL particles of patients with severe hypercholesterolaemia are ce rtainly below the levels of LPC reported to mediate biological effects of in vitro oxidized LDL.