The Plasma Cholesterol: Cholesterol-Ester Cycle
Three years ago, at the V International Symposium on Atherosclerosis (l), we have presented evidence that both LDL and HDL are metabolic products of the core and surface domains of triglyceride-rich lipoproteins. The data can be summarized as follows: Triglyceride-rich lipoproteins (chylomicrons and VLDL) are primary secretory products of intestinal and hepatic cells. In the plasma, the two lipoproteins interact with lipoprotein lipases at luminal surfaces of endothelial cells and deliver triglyceride-fatty acids to tissues. The reaction leaves behind a triglyceride-depleted lipoprotein that contains non-hydrolyzable core lipids (cholesterol esters) and residual triglycerides. As well, the post-lipolysis particles remain with excess of surface constituents, phospholipids, free cholesterol and apoproteins. Our experiments indicated that the metabolism of non-triglyceride molecules in chylomicrons and VLDL is best described along two pathways: a core pathway, and a surface pathway (2, 3). Along the core pathway, the lipoprotein cholesterol ester and residual triglyceride molecules together with apo B and sufficient quantities of phospholipids and free cholesterol form remnant particles or LDL (4). Along the surface pathway, HDL precursors are formed (4, 5). These precursors are converted to spherical HDL by the activity of the LCAT system and accumulation of cholesterol ester molecules.
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- 3.Eisenberg S, Chacjek T, Deekelbaum RJ (1981) The plasma origin of low density and high density lipoproteins. In: Parnow B, Carlson L (eds) Metabolie Risk Factors in Ischemic CV Disease, Raven Press, NY, pp 56–67Google Scholar
- 6.Perret BP, Eisenberg S, Chajek-Shaul T, Deckelbaum RJ, Olivecrona T (1982) Free cholesterol distribution during in vitro lipolysis of rat plasma very low density lipoprotein. Lack of a role for blood and heart cells. Submitted for publicationGoogle Scholar
- 7.Glomset JA, Norum KR (1973) The metabolic role of lecithin: cholesterol acyltransferase: Perspective from pathology. Adv Lipid Res 11: 1–65Google Scholar
- 12.Eisenberg S (1982) The plasma cholesterol ester transfer reaction. Evaluation of an experimental system and mechanism of transfer between high density (HDL) and very low density (VLDL) lipoproteins. Submitted for publicationGoogle Scholar
- 13.Deckelbaum R, Eisenberg S, Oschry Y, Olivecrona T (1982) Reverse modification of human plasma low density lipoprotein toward triglyceride rich precursors: A mechanism for losing excess cholesterol ester. J Biol Chem. In pressGoogle Scholar
- 14.Deckelbaum RJ, Eisenberg S, Oschry Y, Blum C (1981) Abnormal high density lipoproteins in abetalipoproteinemia. Relevance to normal HDL formation (Abstract) Arteriosclerosis 1:392Google Scholar
- 15.Oschry Y, Eisenberg S. Rat plasma lipoproteins. Re-evaluation of a lipoprotein system in an animal devoid of cholesterol ester transfer activity. J Lipid Res. In pressGoogle Scholar