ALTERATIONS IN THE HDL SYSTEM AFTER RAPID PLASMA-CHOLESTEROL REDUCTION BY LDL-APHERESIS

Changes in high density lipoprotein (HDL) subfraction structure and composition were analyzed during and after extracorporeal removal of apo B containing lipoproteins in seven familial hypercholesterolemic (FH) patients. After the apheretic procedure, carried out with dextran-sulfate-cellulose columns, the plasma levels of very low density lipoproteins (VLDL), low density lipoproteins (LDL), and HDL decreased by 72%, 50%, and 19%, respectively. The free cholesterol to esterified cholesterol ratio in plasma increased, with a 26% drop in the lecithin: cholesterol acyl transferase (LCAT) activity. In the ensuing 24 hours, VLDL, HDL, and LCAT activity approached the pretreatment levels. During this phase, possibly as a consequence of increased cholesterol esterification and exchange of cholesteryl esters for triglycerides between HDL and VLDL, HDL2a particles were detected in plasma. However, these metabolic changes did not result in clearcut modifications in the HDL2-HDL3 subfraction distribution. These findings clearly demonstrate that rapid changes in the plasma VLDL-LDL levels affect several processes involved in the HDL metabolism, but confirm that the HDL system, in spite of a considerable plasticity, displays a marked stability of the HDL2-HDL3 subfraction distribution

ALTERATIONS IN HIGH-DENSITY LIPOPROTEIN SUBFRACTIONS DURING POSTPRANDIAL LIPIDEMIA INDUCED BY FAT WITH AND WITHOUT ETHANOL

1. Serum lipid and apolipoprotein levels, distribution and composition of high-density lipoprotein (HDL) subfractions and lecithin:cholesterol acryltransferase activity were analysed in nine normolipidaemic subjects, in whom a hypertriglyceridaemic state was induced by the acute administration of ethanol (40 g) plus fat (70 g) or of fat only. 2. Triglyceride (TG) levels increased by 180% 4-6 h after fat plus ethanol intake, the hypertriglyceridaemic response being inversely correlated with the basal HDL 2 mass (r = -0.82). Serum apolipoprotein (apo) B levels rose by 8%, HDL-cholesterol decreased by 10% and HDL-TG increased by 57% at 6-8 h. 3. When ethanol was omitted, serum cholesterol and TG rose by 6% and 70%, respectively; both apo AI and apo B levels went up by 8%, whereas HDL-cholesterol rose progressively (15%) at 12 h. 4. The flotation rates of both HDL 2 and HDL 3 increased, reaching a maximum 6-8 h after ethanol plus fat intake. These changes were due to an increase in TG and phospholipid contents, whereas cholesteryl esters and proteins decreased. 5. The alterations in HDL are attributable to the increase in TG-rich lipoproteins, to the stimulated cholesterol esterification (+15%) and to an enhanced transfer of newly formed cholesteryl esters to apo-B-containing lipoproteins in exchange for TG. 6. Changes in HDL properties were evident only when ethanol was given concomitantly with fat. 7. These findings suggest that in the postprandial phase lipoprotein changes may occur, which facilitate an improved removal of cholesterol from tissues