Antiatherogenic effect of estrogen abolished by balloon catheter injury in cholesterol-clamped rabbits

The purpose of this study was to investigate the importance of an intact endothelial cell layer for the direct antiatherogenic effect of estrogen on the arterial wall. Thirty rabbits were bilaterally ovariectomized and subjected to mechanical injury of the endothelium by balloon catheterization of the upper thoracic aorta. Immediately after the operation, treatment was initiated with either 17 beta-estradiol or placebo given intramuscularly. All rabbits were clamped at a similar plasma cholesterol level from 1 week before the operation until the experiment was terminated 13 weeks later. In the undamaged aorta, ie, the aortic arch, the lower thoracic aorta, and the upper abdominal aorta, the estrogen-treated rabbits had one third (P = .06), one sixth (P = .002), and one seventh (P = .001), respectively, the accumulation of cholesterol of the placebo-treated rabbits. In the upper thoracic aorta that had been subjected to mechanical injury of the endothelium, however, aortic cholesterol accumulation was not significantly different between the two groups. Similar results were obtained by histological evaluation of the aortic tissues. Immunohistochemical staining with antibodies against macrophages, smooth muscle cells, and T lymphocytes revealed no significant differences in the intimal distribution of cells between estrogen- and placebo-treated rabbits, except for a higher number of T lymphocytes per unit intimal area of the undamaged aortic arch (P < .0005) in the estrogen-treated-rabbits than the placebo-treated rabbits. This is the first study to demonstrate that the antiatherogenic effect of estrogen is abolished by balloon catheter injury in cholesterol-clamped rabbits. These results may indicate that an intact endothelial cell layer is crucial for the direct antiatherogenic effect of estrogen on the arterial wall.     

Raloxifene inhibits aortic accumulation of cholesterol in ovariectomized, cholesterol-fed rabbits

BACKGROUND: The beneficial effect of long-term hormone replacement therapy in terms of a decreased risk of cardiovascular disease is now generally accepted. Raloxifene, a selective estrogen receptor modulator, has demonstrated hypolipidemic properties while leaving the endometrium unstimulated. METHODS AND RESULTS: For our study of the effects of raloxifene on atherosclerosis, 75 rabbits were ovariectomized and treated with either raloxifene, 17beta-estradiol, or placebo; 25 rabbits were sham operated and treated with placebo. After 45 weeks, the raloxifene group had two thirds of the aortic atherosclerosis, as evaluated by the cholesterol content of the proximal inner part of the aorta, found in the placebo group (placebo, 577+/-55.1 nmol/mg protein; raloxifene, 397+/-53.6 nmol/mg protein; P<.05); the estrogen group had one third of the aortic atherosclerosis in the placebo group (estrogen, 177+/-32.1 nmol/mg protein; P<.001). The sham-operated group (473+/-59.6 nmol/mg protein) was not significantly different from placebo. These effects were only partly explained by the changes in serum lipids and lipoproteins, and treatment with both estrogen and raloxifene independently predicted the response in aorta cholesterol. Because plasma levels of total raloxifene were low relative to clinical values in postmenopausal women, dose-response data for raloxifene are required. CONCLUSIONS: Our findings indicate that raloxifene hydrochloride has a potentially important antiatherogenic effect, analogous to that observed with estrogen in this model.     

Gender gap in aortic cholesterol accumulation in cholesterol-clamped rabbits: role of the endothelium and mononuclear-endothelial cell interaction

BACKGROUND: The purpose of the present study was to investigate plasma lipid-independent mechanisms for the sex difference in the development of atherosclerosis. METHODS AND RESULTS: In the first experiment, 20 male and 20 female rabbits were balloon-injured in the middle thoracic aorta and maintained at the same plasma cholesterol level of approximately 25 mmol/L by use of individualized cholesterol feeding for 13 weeks. In the undamaged aorta, female rabbits had accumulated less than half the amount of cholesterol found in male rabbits (P<0.05). In the balloon-injured aorta, cholesterol accumulation was 3- to 4-fold higher than in the undamaged aorta, with no difference between groups. When cholesterol accumulation data for the balloon-injured aorta were separately assessed for blue (deendothelialized) and white (reendothelialized) tissue, blue tissue surprisingly revealed a reverse gender gap, ie, a significantly higher accumulation of cholesterol in females than in males (P<0.05). White tissue, which constituted the majority of the balloon-injured area, showed no difference in aortic cholesterol accumulation between groups. In the second experiment, 6 male and 6 female rabbits were fed standard rabbit pellets and 6 male and 6 female rabbits were fed a 0.5% cholesterol-enriched chow for 2 weeks. Mononuclear cell binding was 5-fold higher in aortic segments from hypercholesterolemic than from normocholesterolemic rabbits (P<0. 001). In hypercholesterolemic rabbits, cell binding was significantly lower in female than in male rabbits (P<0.05) and showed higher values in atherosclerosis-prone regions. These differences were not found in normocholesterolemic animals. CONCLUSIONS: The present results suggest that female atheroprotection is independent of sex differences in plasma cholesterol but vitally dependent on the state of the arterial endothelium and involves mononuclear-endothelial cell adhesion as an early step.     

Immunosorbent assay based on recombinant hemagglutinin protein produced in a high-efficiency mammalian expression system for surveillance of measles immunity

Raloxifene has been shown to have estrogen agonist effects on bone and cholesterol metabolism while having estrogen antagonist effects on mammary gland and uterus. Reported here are the results of a study to determine whether raloxifene had the estrogen agonist effect of inhibiting coronary artery atherogenesis and to compare its effects with those of traditional conjugated equine estrogens (CEE) treatment. Ovariectomized (surgically postmenopausal) cynomolgus monkeys were fed a moderately atherogenic diet and treated with a placebo, raloxifene (1 mg/kg x day), raloxifene (5 mg/kg x day), or CEE (Premarin) at a dose that mimicked that of 0.625 mg/day in women. The effects of raloxifene on plasma lipid concentrations were generally comparable to those reported in postmenopausal women treated with raloxifene: reductions in low density lipoprotein cholesterol concentrations and no significant effects on high density lipoprotein cholesterol. We found no evidence that raloxifene had an estrogen agonist effect on coronary arteries. Treatment with CEE resulted in about a 70% reduction in coronary artery plaque size relative to that in the placebo group, whereas neither the low nor the high dose of raloxifene had an effect on coronary artery plaque size. The low dose raloxifene group had about 2 times more atherosclerosis and the high dose group had about 3 times more atherosclerosis than the CEE group.     

Estrogen increases low-density lipoprotein receptor-independent catabolism of apolipoprotein B in hyperlipidemic rabbits

Estrogen has been reported to increase the catabolism of low-density lipoprotein (LDL) apolipoprotein (apo) B by increasing LDL receptor activity. To determine the effect of estrogen on LDL receptor-independent pathways, paired turnover studies of native LDL and chemically modified LDL (methyl-LDL) were performed before and during estrogen administration in female New Zealand rabbits consuming a diet containing 0.5% (wt/wt) cholesterol. Rabbits were matched by plasma cholesterol concentration and assigned randomly to receive estrogen (estradiol cypionate 0.5 mg/kg/wk) or placebo. The residence time of both the native LDL apo B tracer and the methyl-LDL apo B tracer in plasma was decreased by estrogen but not by placebo. Multicompartmental modeling of the paired, double-labeled turnover studies indicated that an increase in fractional catabolic rate (FCR) of the fast-turnover pool, a kinetically distinct LDL subpopulation in plasma, accounted for the observed decrease in residence time in plasma for both tracers. These data support the hypothesis that, in addition to any effect on the LDL receptor, estrogen promotes the activity of LDL receptor-independent pathways.     

Gender differences in intima-media permeability to low-density lipoprotein at atherosclerosis-prone aortic sites in rabbits. Lack of effect of 17 beta-estradiol

Premenopausal women are protected from coronary heart disease, and premenopausal nonhuman primates are protected from atherosclerosis, the underlying cause of coronary heart disease. Estrogen is thought to account for this protection in females, and part of this protection is independent of the effects on risk factors, including lipoprotein levels. This study considered the hypothesis that reduced intima-media permeability to low-density lipoproteins (LDL) may account for the protection from atherosclerosis and coronary heart disease in premenopausal females and that this effect might be mediated by estrogen. Intima-media permeability to LDL was determined in male and female rabbits made hypercholesterolemic by feeding them 0.5% cholesterol for 8 days. The diet of half of the female rabbits was supplemented with 17 beta-estradiol (4 mg/d) during cholesterol feeding and the preceding 4 weeks. Estrogen treatment in the female rabbits did not influence the intima-media permeability to LDL. However, intima-media permeability to LDL for branch sites of the abdominal aorta and aortic arch (regions highly susceptible to atherosclerosis) was 43% and 38% lower, respectively, in male rabbits than in female rabbits: (2.93 +/- 0.39 microL/h/g, (n = 8), vs 6.28 +/- 0.86 microL/h/g, (n = 16), P < .001, and 4.69 +/- 0.28 microL/h/g, (n = 8) vs 7.57 +/- 0.75 microL/h/g, (n = 16), P < .02). In contrast, intima-media permeability to LDL in 7 of 8 aortic sites relatively resistant to atherosclerosis did not differ between male and female rabbits. These data suggest that the protection from atherosclerosis associated with female sex and estrogen is mediated by mechanism(s) other than reduction in intima-media permeability to LDL.     

Conjugated equine estrogens inhibit progression of atherosclerosis but have no effect on intimal hyperplasia or arterial remodeling induced by balloon catheter injury in monkeys

OBJECTIVES: This study sought to determine the effects of estrogen treatment on atherosclerosis progression and the proliferative and structural responses of the atherosclerotic arteries to injury. BACKGROUND: Estrogen treatment suppresses the intimal response to arterial injury in nonatherosclerotic rodents and rabbits and inhibits the in vitro proliferation of smooth muscle cells. However, the effect of estrogen on the response of atherosclerotic arteries to transmural injury, as occurs in balloon catheter angioplasty in humans, is unknown. METHODS: Forty-six ovariectomized cynomolgus monkeys were fed an atherogenic diet for 30 months; 25 received 175 microg/day of conjugated equine estrogens, and 21 served as untreated control animals. All animals underwent balloon catheter injury of the left iliac artery. Subsets of animals underwent a necropsy study at 4, 7, 14 and 28 days after injury; injured and contralateral (uninjured) arteries were pressure-fixed and evaluated morphometrically. RESULTS: Estrogen treatment resulted in a 37% decrease (p < 0.05) in atherosclerosis (plaque area) in the uninjured artery. In response to injury, arterial cell proliferation increased at days 4 and 7, and intimal area was increased two- to threefold at day 28 (p < 0.05). Although estrogen treatment resulted in a trend toward decreased arterial cell proliferation at day 4, there was evidence of increased cell proliferation in both media and intima at day 7 (p < 0.05). However, there was no effect of estrogen treatment on intimal area or indexes of arterial remodeling in the injured artery at day 28 (p > 0.4). CONCLUSIONS. In contrast to previous studies of nonatherosclerotic animals, the results indicate that in the circumstance of transmural injury to arteries of primates with preexisting atherosclerosis, estrogen does not suppress arterial neointimal or structural responses to injury.     

The effect of intermittent carbon monoxide exposure on experimental atherosclerosis in the rabbit

(1) Twenty-four female New Zealand White rabbits were fed commercial diet plus 2% cholesterol. Twelve of these animals were exposed to carbon monoxide for 4 hours per day, seven days per week for 10 weeks. The carbon monoxide exposure was such that the mean blood carboxy-haemoglobin was raised to approximately 20% during each exposure period. Twelve control animals breathed atmospheric air under the same conditions of confinement as the carbon monoxide-exposed group. (2) No significant differences in the plasma levels of cholesterol, triglycerides or glutamate oxalacetate transaminase were observed between the two groups during the experiment. (3) When the animals were sacrificed at the end of the experiment no significant differences were observed between the two groups in the aortic content of triglycerides, cholesterol or phospholipids. (4) The extent of coronary artery atherosclerosis was statistically significantly higher in the carbon monoxide group than in the control group. (5) Ultracentrifugal analysis of plasma lipoproteins revealed that there was significantly more cholesterol in the d less than l.006 fraction from the CO-exposed rabbits. (6) These findings, are discussed with particular reference to the claim that the causal agent in tobacco smoke associated arterial disease is carbon monoxide.     

Effect of long-term treatment with synthetic oestrogens on plasma lipids and arterial vessels in male rabbits (author's transl)

The effects of long-term treatment with synthetic oestrogens (Retalon retard, Sanabo Ltd., Wien, 5 mg/kg i.m. at weekly intervals) were investigated in 12 male rabbits and compared with the data obtained in 9 saline-treated control animals. After 6 months of treatment the oestrogen group showed significantly higher plasma phospholipid (p less than 0.005) and cholesterol (p less than 0.01) concentrations than the control group. However, histological examination of various important arterial vessels (the aorta and the coronary, cerebral, limb and renal arteries) revealed no pathological changes indicative of premature atherosclerosis in either the oestrogen group or in the control group. It is concluded that long-term treatment with synthetic oestrogens does not result in a higher incidence of atherosclerosis in rabbits.     

Anti-atherosclerotic effect of E5324, an inhibitor of acyl-CoA:cholesterol acyltransferase, in Watanabe heritable hyperlipidemic rabbits

E5324, n-butyl-N'-[2-[3-(5-ethyl-4-phenyl-1H-imidazol-1-yl)propoxy]-6- methylphenyl]urea, a novel and potent inhibitor of acyl-CoA:cholesterol acyltransferase (ACAT), was evaluated for its anti-atherosclerotic and lipid-lowering effects in Watanabe heritable hyperlipidemic (WHHL) rabbits. At 3 months of age, 40 male WHHL rabbits were divided into 4 groups. The rabbits were fed a standard rabbit chow (control group), or standard rabbit chow containing E5324 (0.1% or 0.02%) or 1% probucol for 16 weeks. Even the high dose of E5324 did not lower the plasma total cholesterol levels throughout the experiment. Probucol slightly reduced the plasma cholesterol levels, and showed anti-atherosclerotic activity, i.e., reductions of atherosclerotic plaque formation and cholesterol content in the aorta. Although E5324 did not lower plasma cholesterol, atherosclerotic plaque formation in the aortic arch and thoracic aorta was reduced (by about 34% and 41%, respectively, at the high dose; P < 0.05). Cholesterol content in the aortic arch and thoracic aorta was also reduced (by about 59% and 62% at the high dose, respectively) compared with the control. These results suggest that E5324 acts directly on the arterial wall through ACAT inhibition, and prevents the progression of atherosclerosis in WHHL rabbits.     

Preservation of endogenous antioxidant activity and inhibition of lipid peroxidation as common mechanisms of antiatherosclerotic effects of vitamin E, lovastatin and amlodipine

OBJECTIVES: We sought to document the common mechanisms of the antiatherogenic effects of the cholesterol-lowering hydroxy-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor lovastatin, the dihydropyridine Ca2+ blocker amlodipine and the antioxidant vitamin E. BACKGROUND: Vitamin E, HMG-CoA reductase inhibitors and Ca2+ blockers each inhibit atherosclerosis in hypercholesterolemic animals. METHODS: New Zealand White rabbits were fed regular chow (Group A), chow with 1% cholesterol (Group B), 1% cholesterol diet plus lovastatin (Group C), 1% cholesterol diet plus vitamin E (Group D) or 1% cholesterol diet plus amlodipine (Group E) for 12 weeks. The extent of aortic atherosclerosis was measured by planimetry of the sudanophilic area. Malondialdehyde (MDA) and superoxide dismutase (SOD) in blood were measured as indexes of lipid peroxidation and antioxidant activity, respectively. RESULTS: Group A rabbits showed no atherosclerosis, whereas Group B rabbits had 17.4 +/- 9.3% (mean +/- SD) of the aorta covered with atherosclerosis, and Groups C, D and E rabbits had significantly less atherosclerosis. Plasma SOD activity was lower in Group B than in Group A (6.9 +/- 1.1 vs. 12.8 +/- 1.5 U/ml, p < 0.01) and was preserved in the groups given lovastatin, vitamin E or amlodipine with a high cholesterol diet. The serum MDA level was higher in Group B rabbits than Group A rabbits (12.1 +/- 2.6 vs. 1.2 +/- 0.1 nmol/ml, p < 0.01) and increased minimally in rabbits given lovastatin, vitamin E or amlodipine with a high cholesterol diet. In in vitro experiments, both lovastatin and amlodipine preserved SOD activity and reduced the oxidizability of low density lipoproteins by rabbit leukocytes. CONCLUSIONS: This study suggests that a reduction in lipid peroxidation and preservation of SOD may be common mechanisms of antiatherosclerotic effects of lovastatin, vitamin E and amlodipine.     

Cytokine production by dengue virus antigen-responsive human T lymphocytes in vitro examined using a double immunocytochemical technique

In rabbits, the pulmonary artery and the aorta are susceptible to atherosclerosis. However, susceptibility of the pulmonary artery, compared with the aortic arch, to atherosclerosis and the relationship between the accumulation of cholesterol during the early stages of atherogenesis and the development of atheromatous lesions for these arterial regions remain to be clarified. Cholesterol concentrations for the pulmonary artery and aorta were measured in normal rabbits and in rabbits fed a 0.5% cholesterol diet for 8, 12, and 16 days and 17 weeks. In normal rabbits, the rank order of arterial cholesterol concentrations was pulmonary artery>aortic arch>descending thoracic aorta, with concentrations of total and nonesterified cholesterol 17% and 25% (both P<.05) greater, respectively, for the pulmonary artery than for the descending thoracic aorta. Rank order remained the same during 16 days of cholesterol feeding, but differences between arterial regions were exaggerated. After rabbits were fed cholesterol for 16 days, total and esterified cholesterol concentrations were 57% and 920% (both P<.01) greater, respectively, for the pulmonary artery than for the descending thoracic aorta, with much smaller differences between the aortic regions. In contrast, after rabbits were fed cholesterol for 17 weeks, concentrations of total, esterified, and nonesterified cholesterol were similar for the pulmonary artery and aortic arch, but these forms of cholesterol were increased 100%, 130%, and 53% (all P<.03), respectively, for the aortic arch compared with the descending thoracic aorta. Cholesterol concentrations for the pulmonary artery were positively associated with those for the aortic regions during the first 16 days of cholesterol feeding, but for rabbits fed cholesterol for 17 weeks the associations were either negative or absent. These results indicate that relative rates of cholesterol accumulation in the pulmonary artery and aorta differ at different stages of atherogenesis and suggest that the balance between processes that deliver cholesterol to, and remove cholesterol from, the artery may change in different ways in these arterial regions during atherogenesis.     

Effect of estrogen and progesterone on the expression of hepatic and extrahepatic sterol 27-hydroxylase in baboons (Papio sp)

Sterol 27-hydroxylase plays an important role in cholesterol metabolism in hepatic and extrahepatic tissues. To determine whether female sex steroid hormones influence its expression, we measured plasma and hepatic 27-hydroxycholesterol, hepatic mRNA levels, activity of sterol 27-hydroxylase, and adrenal mRNA levels of this enzyme in baboons (n = 6 per group) treated with placebo, estrogen, estrogen + progesterone, and progesterone. We also measured hepatic cholesterol concentration and hepatic acyl coenzyme A:cholesterol acyltransferase (ACAT) activity to determine their relationship with hepatic sterol 27-hydroxylase activity. Plasma 27-hydroxycholesterol concentration was increased by estrogen and estrogen + progesterone and was negatively correlated with plasma (P = .090) and LDL (P = .026) cholesterol concentrations. Similarly, hepatic sterol 27-hydroxylase activity was increased by estrogen and estrogen + progesterone and was negatively correlated with plasma (P = .056) and LDL (P = .052) cholesterol concentrations but was positively correlated with hepatic and plasma 27-hydroxycholesterol concentrations (P < .001). Hepatic ACAT activity was increased by progesterone (P < .004) and was positively correlated with plasma (P = .002) and LDL (P = .009) cholesterol concentrations but was negatively correlated with hepatic sterol 27-hydroxylase activity (P = .035). Hepatic and adrenal gland mRNA levels for sterol 27-hydroxylase were increased by estrogen alone or in combination with progesterone (P < .05). Hepatic sterol 27-hydroxylase activity was positively correlated with hepatic mRNA levels (P < .001), an observation suggesting that estrogen increases the activity of sterol 27-hydroxylase by increasing its synthesis. Hepatic cholesterol concentration was not influenced by the hormone treatment. These observations suggest that estrogen alone or in combination with progesterone increases the synthesis of sterol 27-hydroxylase in hepatic and extrahepatic tissues, and the increased activity of hepatic sterol 27-hydroxylase resulting from the increased synthesis is associated with a hypolipidemic effect on plasma LDL levels. Furthermore, progesterone alone increases the hepatic ACAT activity, but given in combination with estrogen progesterone does not have the same effect on hepatic ACAT activity. The effect of estrogen on hepatic ACAT activity may be mediated by sterol 27-hydroxylase and its effect on cholesterol metabolism (decreased cholesterol synthesis and increased output of cholesterol in the bile) in liver.     

Genetic factors in the development of atherosclerosis]

Atherosclerosis is a complex multifactorial disease of the arterial wall, dependent on genetic disposition and multiple other risk factors. There are probably several candidate genes, that determine the individual susceptibility of the vessel wall to develop atherosclerosis. In recent years, a growing number of gene polymorphisms, associated with an elevated risk of myocardial infarction, has been identified. These genes and gene clusters play a crucial role in lipid metabolism, regulation of blood pressure and clotting. In contrast to rare monogenetic diseases with severe clinical signs and symptoms (e.g. familial hypercholesterolemia), genetic polymorphisms are relatively frequent. Due to their frequency, there is a high probability that one individual carries several alleles predisposing to coronary heart disease. Genetic polymorphisms become clinically important by interacting with lifestyle, environmental factors or endogenous metabolic disorders. We have recently established an animal model of rabbits, which may prove useful in the search for new genes predisposing to or protecting from atherosclerosis. Rabbits with high atherosclerotic response (HAR) show more than 70% atherosclerotic involvement of the aorta when fed a high cholesterol diet. In contrast, rabbits with low atherosclerotic response (LAR) show less than 20% atherosclerosis in spite of comparably high plasma cholesterol levels. Preliminary studies indicate that macrophages of LAR rabbits have a high scavenger receptor activity and high apolipoprotein E expression and thus appear to be very efficient in uptake and elimination of modified lipoproteins. This may result in a more efficient removal of cholesterol from the arterial wall and thus protect the animals from developing atherosclerosis. Today we are only at the beginning of understanding the complexity of gene interaction in atherosclerosis. Further identification of genetic factors of atherosclerosis will no doubt lead to a more efficient and economic prevention of coronary heart disease in the future.     

beta-VLDL hypercholesterolemia relative to LDL hypercholesterolemia is associated with higher levels of oxidized lipoproteins and a more rapid progression of coronary atherosclerosis in rabbits

The accumulation of the oxidized apolipoprotein, apoB-100, containing lipoproteins in the arterial wall and the progression of coronary atherosclerotic lesions in rabbits with beta-VLDL and LDL hypercholesterolemia was compared. In New Zealand White (NZW) rabbits on a 0.125% cholesterol diet, LDL cholesterol levels increased from 14 +/- 1 mg/dL (mean +/- SEM; n = 9) to 170 +/- 34 mg/dL (n = 10, P = .0002). On 0.5% cholesterol, LDL cholesterol levels were similar, but beta-VLDL cholesterol levels increased from 60 +/- 4 mg/dL (n = 10) to 550 +/- 75 mg/dL (n = 8; P < .0001). In Watanabe heritable hyperlipidemic (WHHL) rabbits, LDL cholesterol levels were 2.3-fold higher (n = 13; P < .0001) than in NZW rabbits on 0.5% cholesterol, whereas their beta-VLDL cholesterol levels were 3.7-fold lower (P < .0001), resulting in similar total cholesterol levels. At 2 months, mean intimal areas of lesions in the coronary arteries of NZW rabbits on 0.125% cholesterol were 0.13 +/- 0.045 mm2 (n = 4; mean +/- SEM) and were 5.8-fold, (n = 4; P = .016) and 2.0-fold (n = 6; P = NS versus 0.125% cholesterol and P = .014 versus 0.5% cholesterol) higher in NZW rabbits on 0.5% cholesterol and in WHHL rabbits, respectively. At 5 months, mean intimal areas were 0.47 +/- 0.088 mm2 (n = 6) in NZW rabbits on 0.125% cholesterol and were 4.5-fold (n = 4; P = .0001) and 2.0-fold (n = 7; P = .012 and P = .0019) higher in rabbits on 0.5% cholesterol and in WHHL rabbits, respectively. Levels of oxidized apoB-100 containing lipoproteins (both beta-VLDL and LDL) in the lesions correlated with mean intimal area (r = .88; n = 31; P < .0001) of those lesions and with the plasma levels of total beta-VLDL/LDL (r = .72; P < .0001). Levels of oxidized apoB-100 containing lipoproteins in the arterial wall correlate with progression of hypercholesterolemia-induced coronary atherosclerotic lesions. Plasma levels of beta-VLDL relative to similar increases in LDL result in a more pronounced accumulation of oxidized apoB-100 containing lipoproteins in the arterial wall and in the plasma and a more rapid progression of coronary atherosclerosis.     

Prolonged fasting in humans results in diminished plasma choline concentrations but does not cause liver dysfunction

The potential antiatherogenic actions of the angiotensin II receptor antagonist, losartan were investigated in apolipoprotein (apo) E deficient mice, an animal model with severe hypercholesterolemia and extensive atherosclerosis. In these animals accelerated atherosclerosis is associated with increased lipid peroxidation which may play a crucial role in the build up of the atherosclerotic lesions. Administration of losartan (25mg/kg/d) to the apo E deficient mice for a 3-month period increased the plasma renin activity 3.5-fold compared to the placebo group. Losartan increased the resistance of LDL to CuSO4-induced oxidative modification as shown by a significant reduction in the LDL content of malondialdehyde by 55% compared to placebo, as well as by the prolongation of the lag time required for LDL oxidation, from 60 min in the placebo-treated mice to more than 140 min in the losartan-treated mice. Losartan reduced significantly the mean atherosclerotic lesion area by 80% compared to the placebo group. We conclude that losartan inhibits LDL lipid peroxidation in the apo E deficient mice and this effect may have an important role in the attenuation of the accelerated atherosclerosis.     

Arterial reactivity is enhanced in genetic males taking high dose estrogens

OBJECTIVES: We sought to assess whether high dose estrogen treatment is associated with enhanced arterial reactivity in genetic males. BACKGROUND: Although estrogens have been shown to enhance arterial reactivity in women, and are thereby thought to confer cardiovascular benefit, the vascular effects of long-term estrogen therapy in genetic males is unknown. METHODS: We studied the arterial physiology of 30 genetic males--15 male to female transsexuals receiving long-term high dose estrogen therapy and 15 healthy male control subjects matched for age, smoking history and vessel size. Using external vascular ultrasound, brachial artery diameter was measured at rest, after flow increase (causing endothelium-dependent dilation [EDD]) and after nitroglycerin (GTN), an endothelium-independent dilator. Blood pressure, cholesterol and testosterone levels were also measured in each subject. RESULTS: Total testosterone and free testosterone index levels were lower in the transsexuals compared with the control subjects (p < 0.001). In contrast, EDD was significantly higher in the transsexuals than in the control males (mean [+/-SD] 7.1 +/- 3.1% vs. 3.2 +/- 2.8%, p = 0.001), as was the GTN response (21.2 +/- 6.7% vs. 14.6 +/- 3.3%, p = 0.002). Total and high density lipoprotein cholesterol, blood pressure levels and baseline vessel size were similar in the two groups. On multivariate analysis, enhanced EDD was associated independently with estrogen therapy (p = 0.02) and with low total cholesterol (p = 0.04). An enhanced GTN response was also significantly associated with estrogen therapy (p = 0.03). CONCLUSIONS: Long-term treatment with high dose estrogens is associated with enhanced arterial reactivity in genetic males, which may be due to the effects of estrogen excess or androgen deprivation, or both.     

Cholesterol mobilization and regression of atheroma in cholesterol-fed rabbits induced by large unilamellar vesicles

The antiatherogenic properties of repeated injections of egg phosphatidylcholine large unilamellar vesicles (LUVs) of 100 nm diameter were tested in an experimental model for atherosclerosis. Forty eight rabbits were divided into two diet groups fed standard rabbit chow or fed a cholesterol-enriched diet (0.5% by weight) to induce the formation of atherosclerotic lesions. Prior to the initiation of LUV therapy, the cholesterol diet was ceased and all animals were returned to standard rabbit chow. The treatment protocol consisted of a total of 10 bolus injections of vesicles, at a phospholipid dose of 300 mg/kg body weight or the equivalent volume of saline, with one injection given to each animal every 10 days. LUV injections brought about a large movement of cholesterol into the blood pool and resulted in a significant reduction in the cholesterol content as well as the degree of surface plaque involvement of aortic tissue in atherosclerotic animals. Most notably, the thoracic aorta of LUV-treated animals exhibited a 48% reduction in tissue cholesterol content per gram of protein compared to saline-treated controls. Histochemical analyses revealed that aortas from animals receiving the repeated injections of LUVs displayed less cholesterol deposits in lesions, and a moderate reduction in intimal-to-medial thickness. This regression of atheroma, induced by LUV therapy, was observed even though animals possessed persistent elevated plasma cholesterol levels after the cholesterol-enriched diet was ceased. These results suggest that repeated injections of LUVs, working with endogenous HDL, may be a useful therapy in the management of atherosclerosis.     

Effects of 17 alpha-dihydroequilenin sulfate on atherosclerotic male and female rhesus monkeys

OBJECTIVES: Our purpose was to determine the effects of 17 alpha-dihydroequilenin on plasma lipid and lipoprotein, glucose, and insulin concentrations; coronary artery vasomotor function; and reproductive organ and mammary gland proliferation in atherosclerotic male and female rhesus macaques. STUDY DESIGN: Fifty adult female and 33 adult male rhesus macaques were randomized to treatment by lifetime dietary cholesterol exposure and ratio of total plasma cholesterol to high-density lipoprotein cholesterol. The female treatment groups were intact female controls (n = 9), ovariectomized controls (n = 16), ovariectomized plus 0.3 mg/kg/day 17 alpha-dihydroequilenin (n = 17) and ovariectomized plus subcutaneous estradiol (n = 7). The male treatment groups were control (n = 16) and 1.25 mg/kg/day 17 alpha-dihydroequilenin (n = 17). Treatment lasted 5 weeks. Longitudinal assessments of plasma lipid and lipoprotein and glucose and insulin concentrations were performed. Coronary artery vasomotor function was assessed by quantitative coronary angiography 1 week after initiation of treatment. Morphologic and immunohistochemical assessments of proliferation index values of reproductive organs and mammary glands were done at necropsy. RESULTS: 17 alpha-Dihydroequilenin prevented endothelium-dependent vasoconstriction in males (p < 0.05) and ovariectomized females (p < 0.08). 17 alpha-Dihydroequilenin treatment increased plasma apolipoprotein A-1 concentrations (p < 0.05) and lowered fasting insulin concentrations (p < 0.05) without changing fasting plasma glucose concentrations in males. 17 alpha-Dihydroequilenin had no other effects on plasma lipid and lipoprotein concentrations in either males or females. It had no trophic effects on uterus, endometrium, or breast. There was no effect on either prostatic or testicular weight. CONCLUSION: 17 alpha-Dihydroequilenin may represent a single-agent hormone therapy for reduction of ischemic hear disease risk for both menopausal women and men. It has no apparent trophic effects on reproductive organs or mammary glands of female and male rhesus macaques.     

Protection from procarbazine-induced testicular damage by hormonal pretreatment does not involve arrest of spermatogonial proliferation

The purpose of the present study was to reexamine the relationship between alcohol and atherosclerosis. Two experiments were performed: The first contained three groups of New Zealand White (NZW) female rabbits. The control group was fed a cholesterol-containing liquid diet and the other two groups were fed the same diet with either 20% or 30% of the calories supplied by alcohol. The second experiment had two treatments: one control group and another group fed a 10% alcohol diet. In experiment 1, alcohol at the 20% and 30% levels increased VLDL and LDL but not HDL compared with levels in control rabbits. Hepatic mRNA levels of apolipoprotein (apo) A-I, apoB, and 7 alpha-hydroxylase were not affected by alcohol. However, the LDL-receptor mRNA was decreased to half of control values by either 20% or 30% alcohol. Lesion areas and aortic cholesterols were significantly increased in the 20% and 30% alcohol-treated groups. Also, significant correlations were found between plasma cholesterol levels and total lesion area or lesion cholesterol contents. In experiment 2, the 10% alcohol-treated rabbits showed no differences in circulating lipoproteins, LDL-receptor mRNA, or lesion formation above that observed in controls. These experiments suggest that alcohol substituted at 20% or 30% of the dietary calories induces hypercholesterolemia and more aortic atherosclerotic lesions. The alcohol-induced accumulation of VLDL and LDL was accompanied by low hepatic LDL-receptor mRNA levels, suggesting that alcohol may affect LDL-receptor expression and rates of lipoprotein clearance, but more experiments are needed to evaluate this possibility.