Synthesis and removal of different cholesterol esters by aortic smooth muscle cells in culture

Cholestyramine treatment in early life. Immediate and delayed effects on arterial cholesteryl ester metabolizing enzymes in the rabbit

Feeding of cholestyramine-enriched diet to weaned normocholesterolemic rabbits resulted in: lowering of plasma cholesterol and distinctly decreased activity of aortic acyl-CoA cholesterol acyl transferase with no changes in aortic acid and neutral cholesteryl esterase activity. At 9 weeks after cessation of cholestyramine treatment enhanced activity of both aortic esterases were noted despite normalization of plasma cholesterol. No evidence for the presence of plasma factor influencing esterases activity was found in lipoprotein-free serum from cholestyramine-treated animals. These studies show that cholestyramine treatment in early life causes immediate and delayed changes in rabbit arterial cholesteryl ester metabolizing enzymes.

Chlorpromazine inhibits arterial ACAT and reduces arterial cholesterol and cholesteryl ester accumulation in cholesterol-fed rabbits

Rabbits were fed an atherogenic diet concurrently with chlorpromazine for 2 weeks (10 mg/kg/day in the diet) or 12 weeks (20 mg/kg/day given orally in a single capsule). After 2 weeks, arterial acyl CoA: cholesterol acyltransferase (ACAT) activity tended to be reduced by chlorpromazine treatment with no affect on net arterial cholesterol. After 12 weeks of treatment, arterial ACAT activity was significantly reduced and was paralleled by a reduction in net arterial cholesterol, a reduction in the esterified cholesterol/unesterified cholesterol ratio, and a reduction in lipid staining intensity as determined histologically with oil red O staining of aortic cross sections. Paradoxically, there was no histological evidence for a reduction in the size of atheromatous lesions with chlorpromazine treatment as determined by morphometric analysis of tissue cross sections. The results support the hypothesis that the increased esterification of cholesterol that characteristically accompanies the atherogenic process serves as a biochemical trapping mechanism for cholesterol entering the vessel wall and suggest that regulation of the enzyme in vivo can reduce the net accumulation of arterial cholesterol.

Accumulation and loss of cholesterol esters in monkey arterial smooth muscle cells exposed to normal and hyperlipemic serum lipoproteins

The effects of high low and very low density lipoprotein fractions from normal or hyperlipemic rhesus monkey serum on the accumulation or removal of cholesterol esters from rhesus monkey smooth muscle cells in tissue culture were determined. Serum or serum lipoproteins were labeled with [14C] free cholesterol and adjusted to the same free cholesterol level in the incubation medium. Of the two normal lipoproteins examined, the LDL fraction caused more esterification than the HDL. Cells incubated in hyperlipemic serum showed a 2-fold stimulation in esterification as compared to cells in normal serum. This was contributed by hyperlipemic VLDL and LDL and led to a concomitant increase in cellular cholesterol ester content. Both hyperlipemic LDL and HDL stimulated esterification when compared to their normal counterparts. Cholesterol ester removal was examined by incubating the serum or lipoprotein fractions with cells enriched in cholesterol ester through a prior exposure to hyperlipemic serum. The cells incubated in normal or hyperlipemic HDL or lipoprotein-deficient serum had the lowest cholesterol ester content. Thus, the lipoprotein fractions which caused the lowest levels of cholesterol esterification were also the most efficient in the removal of cellular cholesterol esters.

Intralysosomal hydrolysis of cholesterol esters of varying fatty acid composition in cultured human skin fibroblasts

Intralysosomal accumulation of low density lipoprotein-cholesterol ester was achieved during incubation of cultured human skin fibroblasts in the presence of chloroquine and the subsequent hydrolysis of the cholesterol ester was studied after removal of chloroquine. The fall in the ratio of cholesterol linoleate to cholesterol oleate during recovery from chloroquine inhibition suggested preferential hydrolysis of cholesterol linoleate. To verify this assumption, low density lipoprotein (labeled with [3H] cholesterol linoleate, oleate, palmitate or stearate) was sequestered in the lysosomes as described above. The rate of hydrolysis of the different cholesterol esters was determined 24 and 48 h after removal of chloroquine from the medium and was found to be similar for the four cholesterol esters studied. These findings indicate that enrichment in cholesterol oleate in atheromatous lesions does not result from preferential hydrolysis of intralysosomal cholesterol linoleate, but rather could be due to preferential utilization of oleic acid for the esterification in the cytoplasm of free cholesterol released from the lysosomal compartment.

Removal of fatty acid labelled cholesterol ester, phospholipid and triglyceride from atherosclerotic rabbit aorta in vitro

An organ culture technique was used to investigate the removal of fatty acids incorporated into various lipid fractions in intimal segments of atherosclerotic rabbit aorta. Segments of aorta were pulse-labelled in vitro with [9,10-3H]oleic acid and [1-14C]linoleic acid for 24 h. The incubation medium was replaced with non-radioactive medium and the removal of the endogenously labelled phospholipid, triglyceride and cholesterol ester was followed for a further period of 10 days. Fatty acids incorporated into phospholipid and triglyceride were removed rapidly from the aortic intima, with fractional half-times of 4--5 days. Cholesterol ester fatty acids were removed more slowly from the aortic intima with fractional half-times of 9--12 days. When the removal rate of oleic acid incorporated into phospholipid, triglyceride and cholesterol ester was compared with that of linoleic acid incorporated into the same lipid fractions, no difference between removal of the two fatty acids could be detected with respect to any of the 3 lipid fractions.