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

Effects of prostaglandin E1 on high density lipoprotein-phospholipid composition

Serum high-density phospholipids (HDL-phospholipids) composition was determined in rats treated with prostaglandin E1 (PGE1) and control group treated with isotonic saline. Total phospholipids and HDL-phospholipids levels at serum were found lower in rats treated with PGE1, than in controls. Considering the individual phospholipid classes of HDL, we observed that phosphatidylocholine (PC), phosphatidylinositol (PI) and diphosphatidylglycerol (DPG) serum concentrations were significantly higher in treated rats than in controls (P<0.001, P<0.005 and P<0.05 respectively). Furthermore, the serum concentrations of lysophosphatidylocholine (LPC) and phosphatidylserine (PS) were significantly lower in treated rats than in controls (P<0.01 and P<0.001 respectively). These findings suggest that PGE1 influences the composition of HDL-phospholipids and possibly modifies their action on lipid metabolism.

Effects of linoleic and gamma-linolenic acids (efamol evening primrose oil) on fatty acid-binding proteins of rat liver

We have studied the effects of Efamol evening primrose oil (EPO) on fatty acid-binding proteins (L-FABP) of rat liver. EPO contains 72% cis-linoleic acid and 9% cis-gamma linolenic acid. EPO has been clinically used for treatment of a number of diseases in humans and animals. EPO is also known to lower cholesterol level in humans and animals. Feeding of an EPO supplemented diet to rats (n = 9) for 2 months decreases the oleate binding capacity of purified L-FABP of rat liver whereas the palmitate binding activity was increased by 38%. However, EPO feeding did not alter the L-FABP concentrations significantly as measured by using the fluorescence fatty acid probe, dansylamino undecanoic acid. Endogenous fatty acid analysis of L-FABPs revealed significant qualitative and quantitative changes in fatty acid pattern after EPO feeding. EPO feeding decreased the endogenous palmitate level by 53% and oleate level by 64% in L-FABPs and also EPO feeding decreased the total endogenous fatty acid content from 62 nanomole per mg of protein to 42 nanomole per mg of L-FABP (n = 3).

Changes in serum lipids in rats treated with PGF2 alpha

Serum lipid concentrations were determined in rats treated with PGF2 alpha, PGE1, and controls. Administration of PGF2 alpha in rats influenced only the HDL lipid composition. HDL-cholesterol decreased while HDL-triglycerides increased. No significant difference was observed in the levels of serum total cholesterol, triglycerides, and phospholipids between animals treated with PGF2 alpha and controls. Reduced concentrations of serum lipid levels and especially of HDL-cholesterol, HDL-triglycerides, and HDL-phospholipids were found in the rats treated with PGE1. These results suggest that PGF2 alpha and PGE1 could modify serum lipid levels influencing lipoprotein metabolism.

Additive benefit of PGI2 and PGE1 (via different mechanisms?) on inhibition of activation of human vascular smooth muscle cells?

It seems likely that the antiplatelet action of antiaggregatory prostaglandins (PGE1, PGI2) is not the pivotal mechanism of action involved in clinical improvement of peripheral vascular disease. Based upon earlier results that both of these agents may have a certain effect on proliferation of vascular smooth muscle cells, we approached that question of an "optimal therapeutic regimen" going one step further. Patients having to undergo amputation were given a randomized "last choice" therapy with either PGI2 (once or twice a day, 6 h, 5 ng/kg/min i.v.), PGE1 (once or twice a day, 1 ng/kg/min i.a.) or a combination of both with a 6 h interval in between for 5 consecutive days. The ones who underwent surgery had a pathomorphological examination of vascular segments removed during amputation. The counting of activated smooth muscle cells indicates a significant drop induced by both of the PG's alone. A second infusion a day with the same compound, however, did not induce a further decrease in the activation state. In contrast administering the complimentary PG caused a comparable, significant decrease (p less than 0.01) in activation of smooth muscle cells in the intima and the media as well. It thus seems, that different mechanisms may be involved inducing additive therapeutic benefit. PGI2 is hypothesised to act predominantly by blocking PDGF-release and interference with PDGF, whereas PGE1 may have a more direct vascular action. From these findings, as well as the beneficial clinical results to be reported elsewhere, a combined therapy by the infusion scheme used may be the optimal one for a PG-therapy at the moment, based upon platelet and smooth muscle cell action.

Inhibitory effect of prostaglandin E2 on cholesterol ester accumulation in macrophages

The effects of prostaglandin E2 (PGE2) on the metabolism of beta-migrating very low density lipoprotein (beta-VLDL) in rat peritoneal macrophages were investigated. When cultured in vitro, macrophages apparently incorporated labelled beta-VLDL time-dependently until 12 h, when the incorporation appeared to reach a plateau. Labelled cholesterol ester in the macrophages increased rapidly until 2 h of incubation, did not change from 2 to 6 h, and then increased markedly until 28 h. Labelled free cholesterol in the macrophages increased until 12 h and then decreased until 28 h. Exogenously added PGE2 (10(-7) approximately 10(-5) M) inhibited the accumulation of labelled cholesterol ester between 6h and 28h with or without increasing the level of labelled free cholesterol. These results suggest that PGE2 prevented cholesterol ester accumulation by stimulating either hydrolysis of cholesterol ester or excretion of free cholesterol.

Regulation by thyrotropin of acyl-CoA: cholesterol acyltransferase in cultured thyroid cells

ACAT activity measured in microsomes of thyroid cells cultured for 4 days in the presence of TSH (1 mU/ml) was two or three times lower than that of the control cells cultured for the same period in the absence of TSH. The pool of cellular cholesterol which served as the ACAT substrate, was not exchangeable with exogenous cholesterol provided in the form of liposomes. However, the incubation of microsomes with liposomes made it possible to increase the cholesterol content in the microsomes by 35%, and this resulted in the activation of ACAT activity. Nevertheless, maximum activity measured after activation in the microsomes of the control cells remained higher than that of the microsomes of cells cultured in the presence of TSH. These findings would suggest that TSH acted by diminishing the cellular content in ACAT enzyme, as well as modifying the distribution of cholesterol in the intracellular membranes.

Chronic regulation by thyrotropin of arachidonic acid incorporation in cholesteryl esters of cultured thyroid cells

During short term incubations, radioactive arachidonic acid and palmitic acid were incorporated in the cholesteryl ester fraction of the lipids of cultured thyroid cells. Three times more arachidonic than palmitic acid was incorporated and the incorporation of both was dependent upon the culture conditions: the presence of 1 mU/ml thyrotropin in the culture medium during four days almost completely inhibited the subsequent incorporation of the two fatty acids in the cholesteryl ester fraction whereas the total cholesterol and cholesteryl ester content of the cells was not affected.

Prostacyclin modulates cholesteryl ester hydrolytic activity by its effect on cyclic adenosine monophosphate in rabbit aortic smooth muscle cells

We tested the hypothesis that prostacyclin (PGI2), 6-keto-prostaglandinF1 alpha(6-keto-PGF1 alpha), and several E series prostaglandins (PG) may affect the activity of cholesteryl ester (CE) hydrolase since our previous experiments indicated that smooth muscle cells (SMC) in neointima of injured rabbit aorta (a) acquire the capacity to produce PGI2 and (b) have increased lysosomal CE hydrolytic (acid cholesteryl ester hydrolase [ACEH])activity. Using cultured SMC from rabbit thoracic aorta, we demonstrated that PGI2, 6-keto-PGF1 alpha, and 6-keto-PGE1 enhanced ACEH activity fourfold. No significant effects on ACEH activity were observed with PGE1 or PGE2. Preincubation of SMC with an inhibitor of adenylate cyclase activity (dideoxyadenosine) abolished the effect of these PG on CE hydrolytic activity. Addition of dibutyryl cAMP to these SMC significantly increased ACEH activity. Although concentrations of PGI2 used significantly increased cAMP levels, proliferation of these SMC was not observed. In related experiments, we determined if the addition of PGI2, 6-keto-PGF1 alpha, or 6-keto-PGE1 to cultured aortic SMC would enhance the egress of unesterified cholesterol and CE from these SMC. A significant loss of total cholesterol from PG-treated SMC was observed at the end of 14 d. Results suggest that increased synthesis of PGI2 by neointimal SMC in the injured aortic wall may, at least in part, explain the changes in CE catabolism and accumulation following injury. These PG may also be important in CE metabolism and accumulation in human arteries.

Absence of effect of prostaglandins on cholesteryl ester metabolism of 3T3 mouse fibroblasts grown in tissue culture

This study examines the effect of prostaglandin E2 and 6-keto F1 alpha on the cholesteryl ester metabolism of cells grown in tissue culture. When 3T3 mouse fibroblasts were incubated with cationized low density lipoprotein (LDL) and 3H-labelled oleic and 14C-labelled linoleic acids a marked increase in cholesteryl ester content of cells was observed. Oleic acid was the preferred substrate for cholesterol esterification. However, the presence of prostaglandin E2 or 6-keto F1 alpha (up to 10 micrograms/ml) did not affect the cholesteryl ester content or the uptake of labelled fatty acids into cellular lipids. Following preincubation with cationized LDL and labelled fatty acids the cells were reincubated in normal medium with or without prostaglandins. The presence of PGE2 or 6KPGF1 alpha (up to 10 micrograms/ml) did not appreciably change the rate of removal of cholesteryl ester or labelled lipids. This indicates that these prostaglandins even when present in relatively large doses in the incubation medium do not affect lipid metabolism of cells grown in tissue culture.

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.