Cholesteryl Ester Synthesis in Normal and Atherosclerotic Aortas of Rabbits and Rhesus Monkeys

Abstract

The formation of cholesteryl ester in aortic tissue was studied using subcellular fractions from normal and atherosclerotic rabbit and rhesus monkey aortas. The properties of two enzyme systems capable of esterifying l-M C-oleic acid into cholesteryl ester in vitro were Investigated, and increased activity was demonstrated for both systems as a result of cholesterol feeding. Microsomal preparations were used to study the ATP, CoA-dependent esterification which involves two enzymes, fatty acyl CoA synthetase and fatty acyl CoA:cholesterol acyltransferase. The properties of both enzymes were investigated, and an increase of about fourfold in activity of the acryltransfrease was demonstrated in aortic microsomes as a result of cholesterol feeding for 3-6 months. Esterification of oleic acid into cholesteryl ester by aortic high-speed supernatant fractions at an acidic pH was also observed; the enzyme system involved did not require cofactors, and its activity greatly increased as a result of cholesterol feeding. Similar increases in the activity of both esterifying enzyme systems were found when normal and atherosclerotic rhesus monkey aortic fractions were compared. p-Chlorophenoxyisobutyrate (CPIB) and 2-methyl-2-[p-(l, 2, 3, 4-tetrahydro-l-naphthyl)-phenoxy]propionic acid (TPIA) produced inhibition of both cholesterol-esterifying enzyme systems. TPIA was a more effective inhibitor than CPIB on both enzyme systems by at least an order of magnitude. These studies suggest that increased intracellular synthesis of cholesteryl ester by aortic tissue may contribute to its accumulation in atherosclerosis.

Tissue-specific Expression and Cholesterol Regulation of Acylcoenzyme A:Cholesterol Acyltransferase (ACAT) in Mice

“…It is interesting that the mouse testis contains less ACAT mRNA than the other steroidogenic tissues and may explain the previous observation that, in contrast to rat adrenal and ovarian cells, mouse Leydig tumor cells contain little of their total cholesterol mass as cholesteryl esters (34). ACAT mRNA was also detected in tissues with a significant resident population of aorta supports the previous observations of ACAT activity in this tissue in rats (36,37) and further implies a role for this protein in the process of atherogenesis. In tissues that express high amounts of ACAT, another major species of approximately 9.5 kb in length was detected by Northern hybridization to total RNA.…”

Cellular cholesterol ester accumulation induced by free cholesterol-rich lipid dispersions.

“…In platelets, there are associated increases in sensitivity to aggregation by adenosine diphosphate and epinephrine (6), resistance to the aggregation inhibitor, prostaglandin El, and increases in the basal levels of adenylate cyclase (21). In both cell types, increases in membrane FC/P correlate with a decrease in membrane fluidity (19,22,23 The evidence suggests the concept that a significant amount of the EC which accumulates in human atherosclerosis is derived from the esterification of EC within cells (24)(25)(26). An equilibrium appears to be established based on the rate of FC esterification and the rate of EC hydrolysis (24,27).…”

Fish oil inhibits development of atherosclerosis in rhesus monkeys.

“…39 The incubation medium consisted of 40 pM (1-14 C) palmiryl-CoA, 2 mg/ml fatty acid-free bovine serum albumin (BSA) and 2 mM dithiothreitol in 0.1 M potassium phosphate buffer (pH 7.4). The aortic supernatants (20 n\) were assayed for 60 minutes at 37° C and the reaction was stopped by the addition of methanol.…”