On the cholesteryl ester hydrolase activity in the microsomal and supernatant fractions of pigeon aorta

Cholesteryl ester hydrolysis in rat liver lysosomes: different response to female sex hormones

The regulation of the hydrolysis of cholesteryl oleate by female sex hormones was studied in the lysosomal fraction of rat liver. Cholesterol ester hydrolase activity was determined at pH 5.0 with an acetone-dissolved cholesteryl [1-14C]oleate substrate preparation. The administration of a single dose of progesterone decreased the enzyme activity during a 3- to 24-hr period following hormone injection. This effect was not correlated to changes in the lysosomal protein synthesis rate. The lysosomal hydrolysis of cholesteryl esters was also inhibited in a noncompetitive manner by the addition of progesterone at concentrations higher than 100 microM. The esterase failed to respond to the estradiol in vivo as well as in vitro. The findings of the present paper suggest that the lysosomal breakdown of cholesteryl esters in rat liver may be under selective hormonal regulation and that the inhibitory effect of progesterone on the enzyme activity might be, at least in part, responsible for the liver cholesterol ester accumulus produced by the administration of the hormone.

Substrate specificity of lysosomal cholesteryl ester hydrolase isolated from rat liver

The effect of various physicochemical forms of substrate on the activity of acid cholesteryl ester hydrolase isolated from rat liver lysosomes was studied. The amount of sodium taurocholate was varied in the substrate mixture which contained constant amounts of egg phosphatidylcholine (PC) and cholesteryl oleate. The resulting substrate forms produced were PC vesicles, PC vesicles with incorporated sodium taurocholate, mixed micelles, and mixed micelles together with free bile salt micelles. Gradually increasing amounts of sodium taurocholate activated cholesteryl oleate hydrolysis until the molar sodium taurocholate/PC ratio of ca. 0.6; thereafter hydrolytic activity decreased rapidly. The presence of sodium taurocholate micelles clearly inhibits cholesteryl oleate hydrolysis. We therefore propose that the activation observed at low bile salt concentrations depends on bile salt interaction with the substrate vehicle, whereas the inhibition observed at high bile salt concentrations depends on sodium taurocholate interacting with the enzyme. When comparing different phospholipid components in the supersubstrate, the enzyme activity was highest in the presence of dioleoyl PC and decreased when present with dipalmitoyl PC and egg PC. Egg lysoPC completely inhibited the enzyme activity. A net negative charge on the surface of the vesicle substrate increased cholesteryl ester hydrolase activity while a net positive charge on the surface inhibited the enzyme activity. Only part of the product inhibition of cholesteryl oleate hydrolase caused by Na-oleate was reversible when tested with bovine serum albumin present in the incubation mixture.

Properties of acid and neutral cholesterol ester hydrolases in rat and pigeon aortas

The activity of cholesterol ester hydrolase was measured in subcellular fractions from rat and pigeon aortas using a glycerol-dispersed cholesterol oleate substrate preparation. The specific activity of acid cholesterol ester hydrolase (assayed at pH 5) in adventitia tissue fractions was 40-50 fold greater than in media-intima fractions from rat aorta. Soluble and particulate subcellular fractions from rat aorta (media-intima) were observed to have cholesterol ester hydrolase activity with both an acid (pH 4.5-5) and a neutral (pH 7.5) pH optimum. A comparison of the subcellular distribution of acid cholesterol ester hydrolase with the lysosomal marker enzyme, N-acetylglucosaminidase, suggests that the acid hydrolase activity originated in aortic lysosomes; the neutral cholesterol ester hydrolase was predominantly soluble. Acid and neutral cholesterol ester hydrolases could also be distinguished on the basic of the effects of Mg Cl2 and NaCl on hydrolase activity and on rates of thermal denaturation. Both acid an neutral hydrolases from rat aorta (media-intima) were inhibited by chloroquine (half-maximal at 2-4 mM), and both hydrolases were characterized as having the same apparent affinity for the glycerol-dispersed cholesterol oleate substrate. Acid and neutral cholesterol ester hydrolases were also observed in preparations from pigeon aortas. The specific activity for both acid and neutral hydrolases was higher in atherosclerosis-susceptible White Carneau pigeon aortas in comparison to Show Racer pigeon aortas.

Effect of substrate properties on the activity of lysosomal cholesteryl ester hydrolase

The effects of the substrate properties on the catalytic activity of lysosomal cholesteryl ester hydrolase from rat liver have been examined with three standard substrate types: vesicle, micelle and emulsion. The pH optimum of the enzyme coincided to 4.5--5.0 with the substrate types employed. The apparent Km values were 15.3, 14.3 and 7.3 microM for vesicle, micelle and emulsion substrates, respectively. In the systems used in this study reaction products, cholesterol and oleic acid, and the nonionic surfactant Tween 80 and Triton X-100 Had an inhibitory effect. The emulsifier phosphatidylcholine and the charged phospholipid phosphatidic acid stimulated the activity. The mixed micelle of sodium taurocholate and phosphatidylcholine was the most potent substrate vehicle. With dipalmitoyl phosphatidylcholine vesicles the enzyme showed maximal activity at the gel-liquid-crystalline transition temperature of the phospholipid. The possible physiological significance of the lysosomal cholesteryl ester hydrolase is discussed with special reference to the form of the substrate.

Regression of naturally occurring atherosclerotic lesions in pigeon aorta by intestinal bypass surgery. Early changes in arterial cholesteryl ester metabolism

Early changes in cholesteryl ester metabolism of the aorta during the regression of naturally occurring atherosclerotic lesions in pigeon aorta by ileal bypass surgery were examined. Three months after surgery, there was a decrease (50%) in the content of cholesteryl esters in the aorta. Increases in the activity of cholesteryl ester hypdrolase in the lysosomal (P less than 0.05) and the supernatant (P less than 0.01) fractions of the aorta also occurred at this time. There were no differences in the activity of cholesteryl ester synthetase and in the plasma levels of cholesterol and triglycerides between the ileal bypass group and the controls. These results suggest that ileal bypass surgery decreases the level of cholesteryl esters in the aorta, probably because of enhanced cholesteryl ester hydrolysis.

Characterization of cholesterol ester hydrolase activities in rabbit and guinea pig aortas

Cholesterol ester hydrolase activity was determined in preparations of rabbit and guinea pig aorta utilizing micellar and glycerol-dispersed cholesterol oleate substrates. Both substrate preparations demonstrated an acid pH optimum of 4--5 for the soluble and particulate rabbit media cholesterol ester hydrolase, suggesting a lysosomal origin for this activity. Approximately one-fifth of the total recovered activity was particulate. Particulate media preparations from guinea pig aorta also demonstrated cholesterol ester hydrolase activity at acid pH values with a definite optimum at pH 5 for the glycerol-dispersed substrate. However, in contrast to the rabbit media enzyme, activity was also observed at neutral pH with another optimum at pH 7. The supernatant enzyme from guinea pig media exhibited only a single pH optimum of 7. Cholesterol ester hydrolase activity from either rabbit or guinea pig media was not influenced by preincubation with cyclic AMP, ATP and protein kinase. The addition of chloroquine resulted in the inhibition of both the rabbit and guinea pig enzyme. Cholesterol ester hydrolase activity from rabbit and guinea pig media was also inhibited by phenyl methane sulfonyl fluoride; activity measured at pH 7 (guinea pig) was more sensitive to inhibition than activity measured at pH 5 (guinea pig and rabbit).

Prostaglandin E2 biosynthesis and effect in pigeon aorta. Possible role in atherogenesis

This study for the first time examines the biosynthesis and effect of prostaglandin E2 (PGE2) in aorta during genetic atherosclerosis. Biosynthesis of PGE2 from [1-14C]arachidonic acid was investigated in the aorta of spontaneously atherosclerosis-susceptible White Carneau pigeons and was compared with that of the atherosclerosis-resistant Show Racer breed. Most of the PGE2 synthetase activity was located in the microsomes. The synthesis was linear up to an hour and was optimal at pH 7.4. The formation of PGE2 in the aorta in the White Carneau pigeons was significantly higher (P less than 0.01) than that in age-matched Show Racer pigeons. In vitro PGE2 strongly inhibited the cholesteryl ester hydrolase activity (51.6% inhibition at 4 X 10(-7) M concentration) in the supernatant fraction of the aorta. On the basis of (1) the increased formation of PGE2 in the aorta of atherosclerosis-susceptible pigeons and (2) its effect on specific enzymes that control cholesteryl ester concentration in aorta, it is hypothesized that PGE2 synthesized at a higher rate in damaged aorta has a significant role in cholesteryl ester accumulation during atherogenesis.

Effect of estrogens on the acitivities of cholesteryl ester synthetase and cholesteryl ester hydrolases in pigeon aorta

This study is the first to report the effect of conjugated equine estrogens on the acitivity of cholesteryl ester synthetase and cholesteryl ester hydrolases in the aorta. In spontaneously atherosclerosis-susceptible White Carneau pigeons, estrogens significantly decreased (P less 0.01) the activity of cholesteryl ester synthetase and increased (P less than 0.01) the cholesteryl ester hydrolase activity in the microsomal fraction of the aorta. There was no effect on the cholesteryl ester hydrolase activity in the supernatant fraction. The inhibition of cholesteryl ester synthesis and the stimulation of cholesteryl ester hydrolase might be responsible for the decreased content of cholesteryl esters noted in pigeon aorta after estrogen treatment.

Endothelial damage and thrombocyte adhesion in pigeon atherosclerosis

Scanning electron microscopy studies of spontaneously occurring atherosclerosis in pigeons reveal dramatic alterations in endothelial integrity. An irregular endothelium at the intimal cushion region of 5-week-old birds gives rise to extensive areas of pitted endothelium and subendothelial exposure. Thrombocytes, thrombocyte aggregates, and leukocytes are associated with the developing lesion.

Effect of prostaglandins E1 and F1alpha on the activities of cholesteryl ester synthetase and cholesteryl ester hydrolases of pigeon aorta in vitro

The in vitro effects of prostaglandins E1 and F1alpha on the activity of cholesteryl ester synthetase and cholesteryl ester hydrolase activities of the pigeon aorta were examined. It was found that prostaglandin E1 markedly inhibited the cholesteryl ester hydrolase activity in the supernatant fraction and slightly inhibited the cholesteryl ester synthetase activity. Prostaglandin F1alpha, however, modestly stimulated the cholesteryl ester hydrolase activity both in the microsomal and in the supernatant fraction of the aorta. These observations strongly warrant further studies on the role of prostaglandins in atherogenesis.

Effect of estrogens on the concentration and composition of arterial sterols and steryl esters in male white carneau pigeons

The effect of short-term (6 months) administration of conjugated equine estrogen (Premarin) on content and composition of the aortic sterols in male shite Carneau pigeons while they were on a cholesterol-free grain diet was investigated. Estrogen treatment resulted in a 38% increase (P less than 0.05) in free sterol concentration, with a 28.8% concomitant decrease (P less than 0.05) in the percent of cholesteryl esters. The total sterol concentration remained unchanged. This finding suggests that estrogens might influence the synthetic or hydrolytic (or both) processes that control the concentration of cholesteryl esters in the aorta. Fatty acid composition of steryl esters did not change significantly. The cholesterol content of plasma showed a mild reduction (14%) whereas the triglycerides increased significantly (30%).