Role of lipoprotein-X in the pathogenesis of cholestatic hypercholesterolemia: uptake of lipoprotein-X and its effect on 3-hydroxy-3-methylglutaryl coenzyme A reductase and chylomicron remnant removal in human fibroblasts, lymphocytes, and in the rat

• Published in: The Journal of clinical investigation Vol. 74; no. 3; pp. 867 - 879
• Main Authors: WALLI, A. K, SEIDEL, D
• Format: Journal Article
• Language: English
• Published: Ann Arbor, MI American Society for Clinical Investigation 01.09.1984
• Subjects: Animals; Biological and medical sciences; Biological Transport; Cells, Cultured; Cholestasis - complications; Chylomicrons - blood; Disorders of blood lipids. Hyperlipoproteinemia; Fibroblasts - metabolism; Humans; Hydroxymethylglutaryl CoA Reductases - metabolism; Hypercholesterolemia - complications; Kinetics; Lipoprotein-X - metabolism; Lipoproteins, LDL - blood; Liver - metabolism; Male; Medical sciences; Metabolic diseases; Monocytes - metabolism; Rats; Rats, Inbred Strains; Skin - metabolism; Tissue Distribution; Human; Vertebrata; X-Lipoprotein; Mammalia; Hypercholesterolemia; Rat; Rodentia; Cholostasis; Etiopathogenesis; Lipids; Metabolic diseases
• ISSN: 0021-9738; 1558-8238
• DOI: 10.1172/jci111504

Cholestasis is accompanied by the appearance of lipoprotein-X (LP-X) in plasma. This lipoprotein has a high content of unesterified cholesterol and phospholipids and appears to be ineffective in suppressing the enhanced hepatic cholesterogenesis of cholestasis. Its role as a possible causative factor for cholestatic hypercholesterolemia was investigated. When 125I-LP-X was injected into rats, it disappeared rapidly from the circulation. Calculated on the basis of gram wet weight, spleen took up more LP-X than liver. Prior ligation of the bile duct reduced the uptake in spleen. Experiments with isolated perfused rat liver showed that nonparenchymal cells (NPC) took up over eightfold more 125I-LP-X than hepatic parenchymal cells (PC). Incubation of PC, NPC, human lymphocyte suspensions, or fibroblast cultures with LP-X showed that NPC bound more LP-X than PC or fibroblasts. Lymphocytes took up 20-fold more LP-X than PC and the activity of 3-hydroxy-3-methylglutaryl Coenzyme A (HMG-CoA) reductase was depressed by LP-X. Lymphocytes isolated from cholestatic patients showed low activity of this enzyme. The activity was increased by LP-X in isolated perfused livers, but suppressed in isolated microsomes. LP-X competitively inhibited the uptake of chylomicron remnants in isolated perfused livers and hepatocytes. In contrast, degradation of LDL by perfused livers, which were isolated from ethinyl estradiol-treated rats or human fibroblast cultures, remained unchanged in the presence of LP-X. The results indicate that cholesterol transported by LP-X is mainly taken up by the cells of the reticuloendothelial system. It increases the activity of hepatic HMG-CoA reductase and suppresses remnant uptake, thus emphasizing a major role of LP-X in cholestatic hypercholesterolemia.