digitonin and Hypercholesterolemia

Previous studies suggest that the steps of the CDP- choline pathway of phosphatidylcholine synthesis are tightly linked in a so-called metabolon. Evidence has been presented that only choline that enters cells through the choline transporter, and not phosphocholine administered to cells by membrane permeabilization, is incorporated into phosphatidylcholine. Here, we show that [(14)C]phosphocholine derived from the lysosomal degradation of [(14)C]choline-labeled sphingomyelin is incorporated as such into phosphatidylcholine in human and mouse fibroblasts. Low density lipoprotein receptor-mediated endocytosis was used to specifically direct [(14)C]sphingomyelin to the lysosomal degradation pathway. Free labeled choline was not found either intracellularly or in the medium, not even when the cells were energy-depleted. Deficiency of lysosomal acid phosphatases in mouse or alkaline phosphatase in human fibroblasts did not affect the incorporation of lysosomal [(14)C]sphingomyelin-derived [(14)C]phosphocholine into phosphatidylcholine, supporting our finding that phosphocholine is not degraded to choline prior to its incorporation into phosphatidylcholine. Inhibition studies and analysis of molecular species showed that exogenous [(3)H]choline and sphingomyelin-derived [(14)C]phosphocholine are incorporated into phosphatidylcholine via a common pathway of synthesis. Our findings provide evidence that, in fibroblasts, phosphocholine derived from sphingomyelin is transported out of the lysosome and subsequently incorporated into phosphatidylcholine without prior hydrolysis of phosphocholine to choline. The findings do not support the existence of a phosphatidylcholine synthesis metabolon in fibroblasts.

Topics: Alkaline Phosphatase; Animals; Cells, Cultured; Chromatography, High Pressure Liquid; Digitonin; Dose-Response Relationship, Drug; Endosomes; Fibroblasts; Humans; Hypercholesterolemia; Hypophosphatasia; Indicators and Reagents; Lipoproteins, LDL; Lysosomes; Mice; Niemann-Pick Diseases; Phosphatidylcholines; Phosphorylcholine; Sphingomyelins; Time Factors

A digitonin-containing affinity sorbent was prepared using a hydrophilic polymer carrier. The correlation was found between the polymer structure and crosslink. King degree, on the one hand, and the sorbent capacity to bind cholesterol, protein and lipoproteins--on the other. The sorbent was demonstrated to extract predominantly atherogenic lipoproteins from blood plasma.

Topics: Animals; Apolipoproteins; Arteriosclerosis; Cholesterol; Cholesterol, LDL; Cholesterol, VLDL; Digitonin; Hemoperfusion; Humans; Hypercholesterolemia; Lipoproteins, VLDL; Maleic Anhydrides; Polymers; Pyrrolidinones; Rabbits

Digitonin mixed in the diet was well tolerated by rats and cynomolgus monkeys (Macaca fascicularis), and prevented the expected rise in plasma cholesterol in monkeys fed a diet containing butter and cholesterol. Both digitonin and mildly hydrolyzed digitonin precipitated cholesterol dispersed in micellar suspensions and decreased intestinal absorption of cholesterol in rats, but only digitonin bound cholesterol in vitro. The hypocholesterolemic effect of digitonin may be secondary to decreased intestinal absorption of cholesterol associated with a disturbance in the micellar suspension of cholesterol in the intestinal content. Modification of other mechanisms that may be involved in membrane transport of cholesterol through the intestinal epithelium is not ruled out by the present findings.

Topics: Animals; Anticholesteremic Agents; Blood Chemical Analysis; Butter; Cholesterol, Dietary; Dietary Fats; Digitalis Glycosides; Digitonin; Female; Haplorhini; Hypercholesterolemia; Intestinal Absorption; Macaca fascicularis; Male; Micelles; Rats

Topics: Acetates; Adult; Carbon Radioisotopes; Cholesterol; Cycloheximide; Digitonin; Fasting; Humans; Hypercholesterolemia; In Vitro Techniques; Leukocytes; Lipids; Mevalonic Acid; Middle Aged; Sterols; Triglycerides