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

The role of gender in the progression of renal disease

The rate of progression of certain renal diseases in animals is greater in men than in women. In various animal models of renal disease, investigators have concluded that the presence of testosterone explains the worse course in men compared with women, whereas in other diseases, estrogen seems to confer protection for women. The gender disparity in renal disease progression found in animals is seen in certain human renal diseases, including chronic renal disease, membranous nephropathy, immunoglobin A nephropathy, and polycystic kidney disease. In humans, the differences between the genders in renal disease progression cannot be fully explained by differences in blood pressure or serum cholesterol levels. The underlying mechanisms for this gender disparity are potentially related to differences between the sexes in glomerular structure, glomerular hemodynamics, diet, variations in the production and activity of local cytokines and hormones, and/or the direct effect of sex hormones on kidney cells. Further investigation into the contribution of gender to renal disease progression may aid us in developing strategies for slowing this pathological process.

Age-related changes in the activation of aortic cholesteryl ester hydrolases by protein kinases in rats

Age-related changes in the activities of acid and neutral cholesteryl ester hydrolases (ACEH and NCEH) and their activation by protein kinase A (PKA) and also by protein kinase C (PKC) were examined in the aortae of 4-, 8-, 12- and 20-week-old rats in relation to their aortic lipid and lipid peroxides and lipid contents. The physiological basal activity as well as total activities of the ACEH and NCEH activated by the two kinases, which were high in the aortae of the 4- and 8-week-old rats, decreased gradually with increasing age to about 40% (ACEH) and 50% (NCEH) by 20 weeks of age. The vitamin E intake and ad libitum-diet intake of the rats each modified the age-related decline of CEH activities. The aortic PKA and PKC activities were reflected by the CEH activities to some degree. The in vitro exposure of the aortic CEH to active oxygen (AO) generators revealed the PKC-mediated activation of CEH, which was inhibited by superoxide dismutase and catalase. These results suggested that the activities of ACEH and NCEH and their regulatory enzymes may be modulated by the dual effect of endogenous AO; an activation of CEH at low doses and an inactivation at high doses, or upon a long-term exposure in aging to a low level of endogenous AO.

Estrogens and atherosclerosis

Estrogens prevent heart disease in women and have also been shown to retard atherogenesis in animal models. Estrogens may act at several steps in the atherogenic process to prevent cardiovascular disease. Some of the benefits of estrogens can be ascribed to their ability to favorably alter the lipoprotein profile, i.e. increase high-density lipoprotein and decrease low-density lipoprotein, and also to their ability to prevent oxidative modification of low-density lipoprotein. Other beneficial effects of estrogens include direct actions on the vascular endothelium and vascular smooth muscle, leading to a decrease in the expression of adhesion molecules involved in monocyte adhesion to endothelial cells, and to a decrease in certain chemokines involved in monocyte migration into the subendothelial space. Estrogens may also affect the later stages of atherogenesis. Finally, estrogens may modify the behavior of atherosclerotic vessels by altering their reactivity and thereby promoting vasodilation, and this may also partly account for their ability to prevent clinical events due to cardiovascular disease.

The impact of gender on the progression of chronic renal disease

Observations in experimental animals and in humans have shown that the rate of progression of renal disease is influenced by gender. Deterioration of renal function in patients with chronic renal disease is more rapid in men than in women, independent of differences in blood pressure or serum cholesterol levels. In addition to genetically determined differences between the sexes in renal structure and function, sex hormones may directly influence many of the processes implicated in the pathogenesis of renal disease progression. Potential mechanisms include receptor-mediated effects of sex hormones on glomerular hemodynamics and mesangial cell proliferation and matrix accumulation as well as effects on the synthesis and release of cytokines, vasoactive agents, and growth factors. In addition, estrogens may exert potent antioxidant actions in the mesangial microenvironment, which may contribute to the protective effect of female gender.

Benzo(a)pyrene enhances atherosclerosis in White Carneau and Show Racer pigeons

Benzo(a)pyrene (BaP), a major environmental pollutant and component of cigarette smoke, is both carcinogenic and atherogenic in experimental models. We investigated the effect of long-term administration of BaP on atherogenesis in both atherosclerosis-susceptible White Carneau (WC) and atherosclerosis-resistant Show Racer (SR) pigeons. The number and size of arterial lesions in the brachiocephalic arteries in WC and SR females but not males were significantly enhanced after long-term dosing with BaP. Metabolic activation appears to be required for BaP atherogenicity, since benzo(e)pyrene (BeP), a noncarcinogenic analogue of BaP, did not enhance lesion development. Studies with 3H-BaP revealed no significant differences between male and female or between WC and SR pigeons in the arterial distribution of BaP and/or its metabolites. There were no consistent differences in blood pressure or plasma cholesterol levels between breeds or sexes. However, chronic administration of BaP did result in complete infertility in female birds, concomitant with grossly visible changes in ovarian appearance. These results clearly show that long-term dosing with BaP alters ovarian structure and function in treated birds, at the same time aggravating the development of arterial lesions. Thus, BaP-induced atherogenicity in female pigeons may be a consequence of an alteration in estrogen production or of antiestrogenic properties of BaP at the level of the arterial wall and may serve as a highly useful animal model to examine the well-known rapid development of atherosclerosis in postmenopausal women.

Ovarian sex steroids and atherosclerosis

Estrogens have been found to protect against atherosclerosis in a variety of animal models, and these antiatherogenic properties have been confirmed by epidemiological and clinical studies in women as well. Since the estrogen-induced changes of plasma lipid and lipoprotein levels do not fully account for the prevention of atherosclerosis, additional effects must be assumed. Experimental studies suggest various direct vascular actions. Estrogens enhance the endothelial degradation of low-density lipoprotein cholesterol, and preliminary data indicate antioxidative actions on low-density lipoprotein particles in macrophages. They suppress intimal proliferation and extracellular matrix production in the arterial wall and induce marked vasodilatation in systemic and coronary arteries. Adverse effects on hemostatic factors described with high doses and synthetic compounds are not evident during hormonal replacement in postmenopausal women, in whom an estradiol-induced inhibition of platelet aggregation may even have beneficial clinical effects. The role of progesterone and other progestogens in the progression of atherosclerosis is controversial. Despite a partial antagonism to estrogen-induced changes of plasma lipids, their addition to estrogens does not alter the anti-atherosclerotic properties, at least in animal experiments. The direct vascular actions of progestogens-although not as well documented-seem to be less pronounced than those of estrogens. The experimental data indicate that direct vascular effects play an important role in the antiatherogenic properties of ovarian sex steroids. However, the underlying cellular and molecular mechanisms remain largely unknown.

Effects of estrogen and progesterone on plasma lipoproteins and experimental atherosclerosis in the baboon (Papio sp.)

We determined the effect of estrogen and progesterone on plasma cholesterol and lipoprotein cholesterol concentrations and on arterial lesions in 24 ovariectomized and hysterectomized baboons fed a high-cholesterol/high-saturated-fat diet. These baboons were divided into four groups: untreated control (C); estrogen, 100 micrograms/kg/week injected i.m. (E); progesterone, 3 mg/kg/day (P); and estrogen plus progesterone (E + P). The treatment regimen continued for 18 months. Cholesterol levels in plasma and lipoproteins were measured before hormone treatment and at 3, 10, and 18 months of treatment. Postheparin plasma lipoprotein lipase (LPL) activity was also measured during the treatment. After 18 months of hormone treatment, baboons were necropsied and arterial lesions were measured. Hormone treatment significantly influenced plasma cholesterol (P greater than C greater than [E + P] greater than E) and very low density lipoprotein plus low density lipoprotein (VLDL + LDL) cholesterol (P greater than C greater than [E + P] greater than E), with very little effect on high density lipoprotein (HDL) cholesterol concentration. The E + P group had a significantly higher HDL cholesterol concentration than did the P group. The (VLDL + LDL)/HDL cholesterol ratios in the E and E + P groups were significantly lower than those in the P and C groups. LPL activities were significantly lower in the E group compared with those in the E + P and P groups. Hormone treatment significantly influenced lesions in four (innominate, carotid, iliac, and abdominal aorta) of seven arteries. The P group had the most fatty streaks, and the E + P group had the least.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of estradiol on low density lipoprotein uptake by bovine aortic endothelial cells

The means by which estrogen retards atherosclerosis cannot be explained solely by changes in circulating lipoprotein levels. We studied the effects of 17 beta-estradiol on the binding, incorporation, and degradation of low density lipoprotein (LDL) by cultured bovine aortic endothelial cells (BAEC). Estrogen receptors in the cytoplasm and nucleus of BAEC could be demonstrated by immunofluorescent staining. Estradiol was found not to affect surface binding of LDL to BAEC. However, at physiologic concentrations (50 pg/ml), estradiol did enhance LDL uptake by the BAEC (P less than 0.005). This enhancement was present but somewhat reduced at higher concentrations of estrogen (P less than 0.05). Only approximately 10% of incorporated LDL was trichloroacetic acid soluble, indicating a low rate of LDL degradation. The relative rate of LDL breakdown within the BAEC was not altered by estrogen. These results, showing estrogen stimulation of LDL uptake by the BAEC, do not clarify the protective effect of this hormone. It is speculated that estrogen may augment the cellular clearance of LDL.

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.

Effect of 17 beta estradiol on aortic cholesterol content and metabolism in cholesterol-fed rabbits

Administration of estrogen to cholesterol-fed rabbits dramatically retarded arterial lesion development despite its lack of effect on plasma cholesterol concentration and on lipoprotein patterns. Cholesteryl ester influx into the aortic wall was also much lower in the estrogen-treated animals and paralleled the aortic cholesterol content in treated and untreated animals; the fraction of aortic cholesteryl ester lost by efflux was the same in treated and untreated animals. The fraction of newly entered cholesteryl ester hydrolyzed by aorta was significantly reduced in the estrogen-treated animals. Low cholesteryl ester influx and relatively less hydrolysis of cholesteryl ester by the aorta may be indicative of reduced internalization of plasma cholesteryl ester by aortic cells, which may in turn account for the reduced atherogenesis in the estrogen-treated rabbits.

Cholesteryl ester hydrolysis in rat liver cytosol. Modulation by female sex hormones

The regulation of cholesterol ester hydrolase activity by female sex hormones was studied in cytosolic preparations from female rat liver. The investigation was undertaken in order to determine whether a reduction in the enzyme activity might be responsible for the increased content of esterified cholesterol found in rat liver after estradiol or progesterone treatments. The single injection of estradiol (0.75 mg/100 g) or progesterone (1.50 mg/100 g) produced respectively significant decreases and increases in sterol hydrolase activity. Both opposite effects were noted after a similar lag period of 3-4 hr and were of short duration. No alterations were observed in rats receiving short-term treatments. When hormones were added to the incubation medium, the activity of cholesterol ester hydrolase decreased progressively with increasing concentrations of hormones. Kinetic studies demonstrate that both estradiol and progesterone compete with the substrate (cholesteryl oleate) for the active center. The findings of the present paper exclude a direct relationship between hepatic hydrolytic activity and lipid deposition. However, they provide evidences that female sex hormones act as modulatory agents of the hydrolysis of cholesteryl esters in rat liver cytosol and suggest that other factors besides competitive inhibition are involved in such regulatory effects.

Regional differences in cholesterol content of aorta in response to experimental coarctation in spontaneously atherosclerosis-susceptible pigeons

The effect of experimental coarctation of the aorta at a site above the coeliac bifurcation (site of occurance of spontaneous atherosclerotic lesions) in White Carneau pigeons was examined. Cholesterol content of the aorta in the site where spontaneous atherosclerosis usually occurs (coeliac bifurcation = lesion site) was decreased in pigeons with aortic coarctation. On the other hand, in the region proximal to the site of coarctation which is usually free of atherosclerotic events cholesterol accumulation was increased. A decrease in percent composition of oleic acid (the major fatty acid which increases during atherosclerosis) was noted in the lesion site. These studies have shown regional differences in response of aorta to experimental coarctation in spontaneously atherosclerotic-susceptible pigeons and suggest that lowering of blood pressure at lesion site might decrease cholesterol accumulation and perhaps might retard subsequent atherogenic process.

The effect of oral contraceptives on mononuclear cell cholesteryl ester hydrolase activity

The influence of sex steroids on mononuclear cell cholesteryl ester hydrolase (CEH) activity in premenopausal women and women on combined estrogen-progestin oral contraceptives has been studied. In addition, plasma and mononuclear cell cholesterol and esters were measured along with plasma estrogen and progesterone levels. Mononuclear cell CEH activity in control women is highest on Day 20 of their menstrual cycle. The control women had significantly higher CEH activities than women on oral contraceptives. Plasma esters were higher in the oral contraceptive group. However, in mononuclear cells, free cholesterol but not cholesteryl esters were higher in women on oral contraceptives.

The characteristics and metabolism of a genetically hypercholesterolemic strain of rats (RICO)

A genetically hypercholesterolemic strain of rats was selectively bred, starting from an ordinary albino mutant of Rattus norvegicus. The new strain was given the designation RICO, standing for rats with increased cholesterol. In these animals, hypercholesterolemia is established, in both sexes, one day after weaning, and it increases progressively thereafter. It is due to elevated concentrations of LDL- and HDL-cholesterol. As in the ordinary rat, the HDL fraction makes up the main part of the serum cholesterol in the RICO rat. Metabolic studies revealed that in the RICO strain the overall rate of hepatic cholesterol synthesis is accelerated, as a result of higher than normal activity of 3-hydroxy-3-methylglutaryl-CoA reductase. The activity of cholesterol-7 alpha-hydroxylase is decreased in RICO rats, indicating a lower than normal rate of cholesterol catabolism. No difference was found between RICO and ordinary rats with respect to fecal excretion of bile acids and cholesterol.

Sterol and bile acid metabolism during development. 3. Occurrence of neonatal hypercholesterolemia in guinea pig and its possible relation to bile acid pool

The relationship of the changes in plasma cholesterol to bile acid pool was studied in the newborn guinea pig. Plasma cholesterol reached the maximum on the fifth day and gradually declined to adult levels. The cholesterol concentration in the high density lipoproteins (HDL) was higher in the newborn guinea pig than in the adult. Plasma triglycerides peaked on the third day and decreased markedly. The bile acid pool increased progressively after birth with a 13-fold increase at 5 days of age. While the hepatic triglycerides decreased sharply in the newborn guinea pig, hepatic cholesterol increased in the first 5 days and then decreased to adult levels. This study has described the occurrence of "neonatal hypercholesterolemia" in the guinea pig and its possible relationship to the low level of bile acid synthesis.

Effect of enhancement of cholesterol degradation during neonatal life of guinea pig on its subsequent response to dietary cholesterol

The effect of feeding cholestyramine to neonatal guinea pigs on their subsequent plasma cholesterol levels and response to dietary cholesterol were studied. Male neonatal guinea pigs were suckled for 6 days. One group was maintained on a 1.1% cholestyramine diet for 6 weeks and the control group weaned normally. Both groups of guinea pigs were then fed a standard diet of Guinea Pig Chow for 6 weeks. During the standard diet period bile acid and neutral sterol excretion rates were significantly higher in the group previously treated with cholestyramine than the control group despite the similarity in plasma cholesterol levels. When both groups of guinea pigs were subjected to a 0.5% cholesterol diet for 4 weeks, plasma cholesterol levels were significantly lower in the group previously treated with cholestyramine than the control group. The plasma cholesterol levels continued to be significantly lower in the group previously treated with cholestyramine after an additional four weeks on standard diet. These results suggest that stimulation of cholesterol catabolism in the neonatal period can influence the subsequent response to dietary cholesterol.

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.