Cholesterol oxidation derivatives and arterial endothelial damage

Transport of cholesterol autoxidation products in rabbit lipoproteins

Radiolabeled pure [4-14C]cholesterol was kept at 60 degrees C under air to autoxidize for 5 weeks, after which approximately 12% cholesterol oxidation products were formed. The mixture, suspended in gelatin, was given to rabbits by gastric gavage. Rabbits were killed 4, 24, and 48 h after treatment. Cholesterol and its autoxidation products were separated by thin-layer chromatography into 5 fractions and radioactivities of each fraction were measured. Percentages of each fraction of cholesterol oxidation products and cholesterol in the original mixture before administration and in the rabbit sera after administration were similar, suggesting that the rates of absorption of cholesterol oxidation products are not significantly different from that of cholesterol. Lipoproteins were fractionated by ultracentrifugation into VLDL, LDL and HDL. Radioactivities of each fraction in lipoproteins separated by thin layer chromatography showed that fractions containing cholestane-3 beta,5 alpha,6 beta-triol, 7 alpha- and 7 beta-hydroxycholesterol and 7-ketocholesterol were more selectively transported in VLDL, whereas most of the 25-hydroxycholesterol was present in LDL. HDL contained only minute amounts of cholesterol oxidation products.

Accumulation of cholesteryl ester and lipid droplets in macrophages after uptake of cholesterol-rich necrotic products

The prevalence of degenerated cells in the thickened intima of cholesterol-fed animals suggested that necrotic regions might become a focus for lesion development by attracting histiocytes or monocytes. We propose that cholesterol-rich necrotic products scavenged by macrophages incite the accumulation of cholesteryl ester and the formation of cholesteryl ester droplets. The feasibility of this hypothesis was tested with readily available materials, namely, lung macrophages and plasma membrane vesicles (PMV) released from dying cholesterol-rich and normal hepatocytes. PMV from cholesterol-rich hepatocytes contained 30-fold more cholesteryl ester than PMV from normal hepatocytes. Degradation of 125I-PMV to trichloroacetic acid-soluble products by macrophages was fourfold higher than that of 125I-acetylated low density lipoprotein (acetyl-LDL) at 100 micrograms/ml of ligand in the incubation medium. Within this concentration range, degradation of PMV increased almost linearly with increasing concentrations of PMV, while the degradation of acetyl-LDL followed a saturation curve. Cholesterol-rich PMV increased the cholesteryl ester content of macrophages fourfold and augmented the incorporation of oleate threefold relative to normal PMV. These studies were extended to aortic smooth muscle cells. As with hepatocyte-PMV, smooth muscle cell-PMV was internalized and degraded by macrophages. The results suggested that cholesterol-rich necrotic materials could play a significant role in atherogenesis.

Action of cholestane-3 beta,5 alpha,6 beta-triol on rats with particular reference to the aorta

Cholestane-3 beta,5 alpha,6 beta-triol, administered orally to rats in different doses and for varying lengths of times, effected toxic cell damage on aortic smooth muscle cells and endothelium. Cholesterol, applied in the same doses, did not lead to appreciable alterations of the aorta. After parenteral application of lipids with simultaneous administration of cholestane-triol there were no demonstrable fat deposits in the damaged aortic wall with angiotensin II (AII) induced hypertension. Thus, there was no recognizable influence of hypertension on increased fat passage in the arterial wall, or any action of lipids to enhance the permeability of vessels. However, the hypertension had an exacerbating effect in so far as in animals with AII-induced blood pressure rise alterations of the media were more pronounced after cholestane-triol, although we were unable to rule out a primary effect of AII. A potentiation of the cholestane-triol action by simultaneous application of cholesterol demonstrated for the rabbit did not occur in rats. Blood content was lowered mostly by cholestane-triol, also by cholesterol. HDL-cholesterol was little affected; almost no influence was observed in triglycerides. The strong cytotoxic action of cholestane-triol underlines its health-damaging role. Due to its action on the aorta of the rat, despite the animal's resistance to arteriosclerosis, involvement of this cholesterol derivative in the pathogenesis of arteriosclerotic alterations can not be excluded.