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In order to study in vivo the effect of modified high density lipoprotein (HDL) on the movement of free cholesterol to liver cells and bile, we injected i.v. into rats, native or malondialdehyde modified HDL labelled with [14C]cholesterol. Bile analysis indicated that the contribution of labelled cholesterol to bile acid secretion was diminished in the group receiving MDA-modified HDL when compared to control group. On the other hand, the liver analysis revealed higher radioactivity in the treated group. A separation of liver cells into parenchymal, endothelial, and kupffer at 90 min after the injection of MDA-modified HDL or native HDL indicated that the endothelial cell uptake of labelled free cholesterol from MDA-modified HDL was 2.6-fold higher than for native HDL. It is suggested that liver endothelial cells may be involved in the protection against atherogenoic oxidized lipoprotein. However, with regard to our finding, the uptake of cholesterol from modified HDL was detrimental to bile acid secretion.Copyright 1995, 1999 Academic Press, Inc.

Lipid peroxidation was measured by the thio-barbituric assay for malondialdehyde (MDA). A small amount of MDA was formed when medial cells from guinea pig aorta were grown in tissue culture. The polyunsaturated fatty acids 8,11,14-eicosatrienoic acid, 5,8,11,14-eicosatetraenoic acid, and 7,10,13,16-docosatetraenoic acid generated significant amounts of MDA in a time-dependent manner when they were added to cultures of medial cells and fibroblasts. MDA or its precursor remained within the cell and did not accumulate in the media. Indomethacin enhanced MDA formation from polyunsaturated fatty acid. Alpha-Tocopherol, alpha-tocopherolquinone, and 2,6-di-tert-butyl-4-methylphenol (BHT) inhibited MDA formation when a polyunsaturated fatty acid was incubated with the pro-oxidant cumene hydroperoxide. Menadione had no effect on MDA formation in the cumene hydroperoxide system. Alpha-Tocopherol and alpha-tocopherolquinone inhibited MDA formation when they were added to cells in culture. Menadione had no effect on MDA formation in tissue culture. Anti-oxidant effects which were time-dependent showed that intracellular MDA was generated from a lipid peroxide precursor during the thiobarbituric acid assay. Relative plating efficiency was measured in medial cells and fibroblasts. Alpha-Tocopherolquinone and alpha-tocopherol enhanced the extent of cell proliferation. Alpha-Tocopherolquinone overcame the inhibitory effect of a polyunsaturated fatty acid on the extent of cell proliferation. Menadione was cytotoxic. Thus antioxidant data support the hypothesis that the extent of cell proliferation is controlled in part by lipid peroxidation.

Acyl coenzyme A:1-acyl-sn-glycero-3-phosphorylcholine acyltransferase (EC 2.3.1.23) is capable of forming lipid bilayer vesicles from its soluble substrates lysophosphatidylcholine (LPC) and oleoyl CoA. This suggested a purification method in which rat liver microsomes are first washed with deoxycholate to increase specific activity of the endogenous acyltransferase approximately fivefold, then solubilized by the detergent effect of excess LPC and oleoyl CoA in 1:1 stoichiometric ratios. As the LPC is converted to phosphatidylcholine by acyl group transfer, the detergent effect is lost and lipid vesicles containing the enzyme activity are produced. Other microsomal proteins are excluded from the vesicles. The vesicles may be separated by density gradient flotation and are found to contain acyltransferase with a specific activity of 9–10 µmol/mg/min. This reflects a purification of approximately 140-fold, about ten times greater than achieved in previous studies.

The utilization of millimolar concentrations of [2-14C]acetone and the production of acetone from acetoacetate were studied in perfused livers from 48-h starved rats. We devised a procedure for determining, in a perfused liver system, the first-order rate constant for the decarboxylation of acetoacetate (0.29 +/- 0.09 h-1, S.E., n = 8). After perfusion of livers with [2-14C]acetone, labeled acetate was isolated from the perfusion medium and characterized as [1-14C]acetate. No radioactivity was found in lactate or 3-hydroxybutyrate. After 90 min of perfusion with [2-14C]acetone, the specific activity of acetate was 30 +/- 4% (n = 13) of the initial specific activity of acetone. We conclude that, in perfused livers from 2-day starved rats, acetone metabolism occurs for the most part via free acetate.