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Minireview: Estrogen and Mouse Models of Atherosclerosis

Department of Pathology and Laboratory Medicine, University of North Carolina, Chapel Hill, North Carolina 27599-7525

Address all correspondence and requests for reprints to: Dr. Nobuyo Maeda, Department of Pathology and Laboratory Medicine, University of North Carolina, Chapel Hill, North Carolina 27599-7525. E-mail: nobuyo{at}med.unc.edu.

	Abstract

Top Abstract Introduction Atheroprotection by Estrogen in... Atheroprotection by Estrogen in... E2 and Estrogen Receptors... E2 and NO in... E2 and Inflammation in... Summary and Considerations for... References

 
The use of hormone replacement therapy for coronary heart disease prevention in humans has been an area of intense controversy. The atheroprotective qualities of estrogens have been challenged recently by several negative results of randomized clinical trials in postmenopausal women. However, the inhibitory effects of estrogens on atherogenesis are well documented in numerous animals, including atherosclerotic mouse models, but the detailed mechanisms of this protection are not understood. In this minireview, we will focus on the considerable success that has been achieved in demonstrating the atheroprotective effects of 17ß-estradiol in apolipoprotein E and low-density lipoprotein receptor-deficient mice and the use of these atherosclerotic mouse models in pharmacological and genetic study designs to investigate antiatherogenic mechanisms of estrogens. Mouse models of atherosclerosis should prove beneficial to understanding the cellular and molecular mechanisms of estrogen-mediated atheroprotection and aid the development of improved therapies to confer the benefits and reduce the risks associated with hormone replacement therapy.

	Introduction

Top Abstract Introduction Atheroprotection by Estrogen in... Atheroprotection by Estrogen in... E2 and Estrogen Receptors... E2 and NO in... E2 and Inflammation in... Summary and Considerations for... References

 
CARDIOVASCULAR DISEASES resulting from atherosclerosis, such as myocardial infarction and stroke, are the principal causes of death in Western society (1). Coronary heart disease (CHD) is rare, and the incidence of CHD complications is much lower in premenopausal women than in men or postmenopausal women of similar age. After menopause, however, the gender difference is lost and the incidence of CHD complications in women gradually approaches that of men. In addition, menopause adversely affects several risk factors for coronary heart disease (2). These observations strongly support a cardioprotective role for endogenous estrogen (17ß-estradiol or E2) through an attenuating effect on atherogenesis and suggest a potential benefit of hormone replacement therapy (HRT). In the United States, the most common HRT formulation is conjugated equine estrogen (CEE) and the progestin medroxyprogesterone acetate (MPA). If HRT prevented CHD and its complications, it would have a large public health benefit and would outweigh any increase in risk for breast cancer or venous thromboembolism. However, the use of HRT to prevent heart disease has been an area of controversy in recent years. A large body of observational data demonstrates an association between HRT use and a 30–50% reduction in CHD risk in postmenopausal women (3). However, observational studies by design are subject to biases that may overestimate benefits and underestimate risks. Thus, recent findings from randomized, placebo-controlled trials not only do not support any cardiovascular benefit of CEE plus MPA use but also demonstrate a surprising increase in the risk of CHD events within the first year of therapy (4, 5, 6).

In 1998, the Heart and Estrogen/Progestin Replacement Study (HERS; Ref. 4), a secondary prevention trial, was reported. In this study, a total of 2763 women with established CHD were randomly assigned to either placebo or HRT. There was no difference in CHD complications (myocardial infarction or CHD death) between study arms by yr 4, but significantly more CHD events occurred during yr 1 in the treatment group compared with the placebo group. These findings were supported by The Estrogen Replacement Atherosclerosis (ERA) trial (5), a second randomized secondary prevention trial, in which postmenopausal HRT did not alter the progression of existing coronary artery atherosclerosis as assessed by angiography. Recently, the first randomized primary prevention trial of postmenopausal HRT, the Women’s Health Initiative (WHI; Ref. 6), was terminated when women receiving active drug had an increased risk of CHD events, stroke, and invasive breast cancer.

Several misunderstandings have contributed to the controversy regarding the effects of estrogens on the vasculature. First, combination estrogen-progestin replacement therapy, or HRT, and estrogen-alone replacement therapy, or ERT, are not alike. The coadministration of certain types of progestins may oppose the cardioprotective effects of estrogens. For example, in the Postmenopausal Estrogen/Progestin Interventions (PEPI) trial (7), coadministration of MPA with CEE diminished the beneficial increases in high-density lipoprotein, whereas micronized progesterone did not. In cynomologous monkeys, the addition of MPA to CEE treatment, at a dose that attained the desired antagonist effect on the endometrium, attenuated all of the reduction in coronary artery atherosclerosis observed with CEE alone (8). It is important to note that the estrogen-alone arm of the WHI trial (the HERS and ERA trials only compared combination HRT with placebo) has not been halted, suggesting that estrogen alone may be safer than a combination of estrogen and progestin. Second, all estrogens are not alike. CEEs are a mixture of sulfate esters of estrone, equiline, 17-hydroequilin, and other related steroids. The exact composition and precisely how each estrogen contributes to the drug’s overall effectiveness are not known. The results of the HERS, ERA, and WHI trials refer to the use of CEE and cannot be generalized to treatments with E2 or other regimens. Indeed unopposed micronized E2 has been shown to reduce the progression of subclinical carotid atherosclerosis in younger women at earlier stages of disease development than those in the ERA trial (9). Third, the route of administration may be an important determinant of the effects of estrogen on CHD risk. Unlike oral formulations, transdermal administration of estrogens bypasses the effects on the liver, resulting in fewer beneficial effects on serum lipid concentrations (10) but avoiding the induction of angiotensinogen (11) and C-reactive protein, a marker of inflammation associated with atherosclerotic disease (12).

In contrast to the findings of randomized controlled trials of HRT in humans, an atheroprotective benefit of estrogen is strongly supported by research using animal models of atherosclerosis (Tables 1 and 2). Animal studies not only reduce bias through complete randomization but also allow elucidation of the cellular and molecular mechanisms of atheroprotection by estrogen through direct access to vascular tissue for histological and molecular analyses. In recent years, the mouse has become a key animal model to advance the understanding of the pathogenesis of atherosclerosis. In this minireview, we will focus on the use of mice with targeted inactivation of one or more genes to investigate the major components of the atheroprotective mechanism of E2, the primary endogenous estrogen.

	Atheroprotection by Estrogen in Animal Models

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A strong argument for the atheroprotective effect of estrogen is the near-consistent observation that estrogen treatment in animal models of atherosclerosis inhibits the development of the atherosclerotic plaque or lesion. These effects have been reviewed recently in great detail (14). Studies using diet-induced hypercholesterolemic rabbits and monkeys over the last decade are listed in Table 1. These studies have used several common formulations of estrogen, including E2, alone or with a progestin, through both oral and parenteral routes, and in gonadectomized females as well as males (Table 1). The magnitude of protection varies from a 35% to an 80% reduction in lesion size or cholesterol content measured in aortic and coronary arteries. Furthermore, the addition of a progestin has either no effect or attenuates the effect of estrogen.

	Atheroprotection by Estrogen in Atherosclerotic Mice

Top Abstract Introduction Atheroprotection by Estrogen in... Atheroprotection by Estrogen in... E2 and Estrogen Receptors... E2 and NO in... E2 and Inflammation in... Summary and Considerations for... References

 
With the advent of gene targeting in mice to modify genes in a predetermined manner, the mouse has become a key animal model to advance the understanding of the genes and pathways involved in atherogenesis (15). Mice with targeted inactivation of the apolipoprotein E (Apoe) gene and the low-density lipoprotein (LDL) receptor (Ldlr) gene, under appropriate conditions, spontaneously develop atherosclerosis that simulates simple and complex human atherosclerotic lesions. The predictable development of lesions in Apoe^-/- and Ldlr^-/- mice; the animal’s small size, short generation time, relative ease of care; and, most importantly, the availability of genetically defined inbred and mutant strains to reduce genetic bias have resulted in mice becoming the most widely used experimental model of atherosclerosis (15).

Studies of estrogen treatment in atherosclerotic mice have consistently demonstrated a dramatic inhibitory effect of E2 on lesion initiation and progression in ovariectomized females in a dose-dependent manner. These studies uniformly employed sc implanted E2-releasing or control pellets at varying doses of hormone (0.17–28 µg/d) and attained serum levels of E2 within the physiological range (Table 2). Lesion size was assessed most commonly at the aortic sinus or by an en face preparation. When treated with E2, plaques rarely progressed beyond small and uncomplicated fatty streaks consisting almost entirely of macrophage-derived foam cells. These studies demonstrate that E2 targets atherogenesis at early stages of lesion development. Most studies have focused on female mice but E2 appears to be equally efficacious in males. For example, Nathan et al. (16) showed that orchidectomy increased lesion size in Ldlr^-/- males, and both exogenous E2 and testosterone reduced lesion size. However, coadministration of an aromatase inhibitor removed the atheroprotective effect of exogenous testosterone. The authors concluded that testosterone, at least in part, attenuates atherosclerosis as a result of conversion to estradiol by aromatase. E2 treatment has also been shown to reduce lesion size and prevent calcified cartilaginous metaplasia in the aorta of streptozotocin-induced hyperglycemic Apoe^-/- males (17).

Estrogen treatment was associated with a reduction in total plasma cholesterol in several (8, 18, 19, 20, 21), but not all (22, 23, 24, 25, 26, 27), animal studies. However, reduction of atherosclerosis was not always accompanied by a reduction in plasma cholesterol, suggesting that estrogen possesses an atheroprotective effect beyond an effect on plasma lipids presumably at the level of the vessel wall. In addition, high physiologic doses (8.3 µg/d) of E2 reduced both atherosclerosis and plasma cholesterol in Apoe^-/- females, whereas lower doses (1.6 µg/d) of E2 reduced lesion size fully without a change in total plasma cholesterol (28). Two other studies of estrogen treatment in atherosclerotic mice reported little to no correlation between lesion size and plasma cholesterol levels (29, 30), suggesting that estrogen inhibits the development of atherosclerosis independent of lipid changes in animals.

An exception to the atheroprotective effect of E2 in mice is the human B100, cholesterol ester transfer protein (CETP) double-transgenic atherosclerotic mouse model, in which oral administration of 17-ethinyl estradiol resulted in an increase in LDL-cholesterol and atherosclerosis (31). In addition to using a different estrogen formulation and route of administration from other studies in Apoe^-/- and Ldlr^-/- mice, this study did not employ ovariectomy and used an atherosclerotic diet containing cholate instead of normal chow. Nevertheless, the authors point out that, although estrogen-treated transgenic B100xCETP mice had total plasma cholesterol 2–3 times higher than untreated Apoe^-/- mice, lesion development was much smaller by comparison, suggesting that estrogen in this model has positive and negative effects toward reducing the amount of lesion expected at this level of hypercholesterolemia.

	E2 and Estrogen Receptors in Atherosclerosis

Top Abstract Introduction Atheroprotection by Estrogen in... Atheroprotection by Estrogen in... E2 and Estrogen Receptors... E2 and NO in... E2 and Inflammation in... Summary and Considerations for... References

 
The primary effects of E2 on atherogenesis are believed to require changes in gene expression (genomic), although short-term, transcription-independent (nongenomic) effects of E2 have been described (10). Long-term, genomic effects of E2 that modify atherosclerotic pathways can be studied by using atherosclerotic mouse models crossbred with mice carrying additional mutations (15). Thus, in a series of experiments, we and others have evaluated the effects of E2 treatment in atherosclerotic mice by administering exogenous E2 to mice doubly deficient for apolipoprotein E (Apoe^-/-) and genes that are likely play a role in the atheroprotective mechanism of estrogens (Table 2).

The long-term effects of E2 are generally ascribed to transcriptional modulation of target genes through estrogen receptors (ERs). Two ERs, ER and ERß, have been characterized (32, 33), and both are expressed in vascular cell types important in atherogenesis, including endothelial cells and vascular smooth muscle cells (VSMC; Ref. 10). Two lines of knockout mice for ER have been generated: one in Chapel Hill, North Carolina (ER_CH^-/-; Ref. 34) and the other in Strasbourg, France (ER_ST^-/-; Ref. 35). Their phenotypes differ slightly, as will be discussed later. Two lines of ERß-deficient mice (ERß^-/-) also exist (35, 36), but they appear to be phenotypically identical. To determine the relative contribution of each receptor to E2-mediated atheroprotection, we crossed ER_CH^-/- and ERß^-/- mice with Apoe^-/- mice (ER_CH^-/-Apoe^-/- and ERß^-/-Apoe^-/-, respectively) and treated them with hormone for 3 months. E2 reduced lesion size in Apoe^-/- females more than 80%, but the inhibitory effect of E2 on atherosclerotic lesion progression was almost completely abrogated in ER_CH^-/-Apoe^-/- mice (37). Lesion size in E2-treated ER_CH^-/-Apoe^-/- females was only slightly, but not significantly, smaller than control-treated ER_CH^-/-Apoe^-/- females. Thus, this result demonstrates that ER is a major mediator of the atheroprotective effects of E2. Plasma lipid-lowering effects of E2 were also eliminated in ER_CH^-/- Apoe^-/- females. In contrast, E2 treatment inhibited atherosclerotic lesion progression equally in ERß^-/-Apoe^-/- and Apoe^-/- females, demonstrating that E2 is fully atheroprotective in the absence of ERß (Hodgin, J. B., J. H. Krege, L. E. Senkbeil, O. Smithies, and N. Maeda, manuscript in preparation). Evidence suggests ER and ERß preferentially heterodimerize (38) and, with ligand binding, may confer distinct transcriptional activities apart from homodimerized ER or ERß. Our findings in E2-treated ER_CH^-/-Apoe^-/- and ERß^-/-Apoe^-/- mice also demonstrate that an ER·ERß heterodimer is not required for atheroprotection by E2 and establish ER as crucial for the inhibition of lesion initiation and progression in Apoe^-/- mice. Atheroprotective effects of dietary soy, a source of phytoestrogenic isoflavones (plant-derived estrogenic compounds), in Apoe^-/- mice are also mediated mainly through ER but not ERß (Adams, M. R., D. L. Golden, T. C. Register, M. S. Anthony, J. B. Hodgin, N. Maeda, and J. K. Williams, submitted manuscript).

We noted, however, that the atherosclerotic lesions of E2-treated ER_CH^-/-Apoe^-/- mice contained fewer fibrous caps and other advanced lesion characteristics compared with lesions in control ER_CH^-/-Apoe^-/- mice, although lesion size was large and not significantly different between the two groups (37). This observation suggests the possibility that ERß may play an important protective role in the maturation of plaques, although it is clearly not involved in early stages of atherosclerosis development. Alternatively, the residual protective effect may be mediated by a splice variant produced in low amounts in ER_CH^-/- mice. Pendaries et al. (39) demonstrated that ER_CH^-/- mice, but not ER_ST^-/- mice, retain E2-mediated increases in the basal production of endothelial nitric oxide (NO) and that an alternative ER splice variant lacking a functional AF-1 domain at the N terminus is expressed in the aorta of ER_CH^-/- mice.

In carotid, aortic, and iliac arteries of normolipidemic, ovariectomized rabbits, rats, and monkeys, E2 reduces neointimal and medial growth (a result of VSMC proliferation and extracellular matrix deposition) by 60% or better after injury to the endothelium by balloon catheter or passage of a fine wire (reviewed in Ref. 14). ER^-/- and ERß^-/- mice have also been used to clarify the roles of ERs in the protective mechanism of E2 after vascular injury. The first two such studies (40, 41), using a fine wire to denude carotid endothelial cells, demonstrated that E2 protects against vascular injury in normolipidemic ER_CH^-/- and ERß^-/- mice. In a follow-up study in ER_ST^-/- mice that completely lack any form of ER, E2 was no longer protective (42). Thus, the activity of the alternative ER splice variant in ER_CH^-/- mice is sufficient to confer complete protection by E2 against vascular injury in this model. Because VSMC proliferation is an important step in atherosclerosis, the underlying cellular and molecular mechanisms of the mechanical response-to-injury may have important implications for atherogenesis. However, the response to acute mechanical injury that causes intimal and medial cell growth and the response to cholesterol-induced chronic injury that results in atherosclerotic plaque development may well be separable. Indeed, a recent study (43) using five inbred strains of mice demonstrated that the genes dictating susceptibility to injury-induced neointimal hyperplasia are distinct from those that determine susceptibility to diet-induced atherosclerosis. The effects of estrogen in atherosclerotic mouse models after vascular injury has not been tested.

	E2 and NO in Atherosclerosis

Top Abstract Introduction Atheroprotection by Estrogen in... Atheroprotection by Estrogen in... E2 and Estrogen Receptors... E2 and NO in... E2 and Inflammation in... Summary and Considerations for... References

 
The atheroprotective effects of E2 in the vasculature have been widely attributed to its ability to increase the bioavailability of NO. Physiological levels of E2 stimulate endothelial NO synthase (eNOS) mRNA and protein expression through long-term, receptor-dependent mechanisms and up-regulate eNOS activity through short-term, nongenomic mechanisms (10). NO has many potentially atheroprotective functions, such as inhibition of leukocyte adhesion and VSMC proliferation, in addition to vasodilation and blood pressure reduction (44). In fact, the absence of eNOS in Apoe^-/- mice results in hypertension and increased atherosclerotic lesion size (45). To test whether the protective effects of exogenous E2 are mediated by eNOS, we gonadectomized both female and male mice deficient in eNOS and apolipoprotein E (eNOS^-/-Apoe^-/-) and treated them with E2 for 3 months. Contrary to our expectation, E2 dramatically reduced lesion size, more than 75%, compared with control-treated eNOS^-/-Apoe^-/- mice (46). The degree of reduction by E2 was similar to that in Apoe^-/- mice, demonstrating that the powerful atheroprotective effects of exogenous E2 do not depend on the presence of eNOS. In addition, E2 treatment modestly, but significantly, reduced blood pressure regardless of the presence of eNOS. These findings are consistent with an earlier study (47) demonstrating that pharmacological inhibition of NO production did not influence atheroprotection by exogenous E2 in Apoe^-/- mice. Unexpectedly, however, ovariectomy alone reversed the hypertensive and proatherogenic effects of the lack of eNOS in eNOS^-/-Apoe^-/- females (46). Orchidectomy produced the same effects in eNOS^-/-Apoe^-/- males. Taken together, it appears that endogenous sex hormones cause significant damage to the vasculature in the absence of eNOS. In contrast, eNOS has little effect in the absence of endogenous sex hormones. When both are present, however, eNOS and endogenous sex hormones interact and confer highly significant vascular protective effects. Thus, in terms of their dependency upon eNOS, the vascular protective effects of E2 given sc are different from the effects of endogenous sex hormones.

	E2 and Inflammation in Atherosclerosis

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Other studies have explored the possibility that E2 protects against atherosclerosis by targeting cellular and molecular components of inflammation. Macrophage-derived foam-cell accumulation is an essential part of atherosclerotic plaque initiation and progression. In addition, cells of the immune system have been thought to play an important regulatory role. Elhage et al. (48) examined the effect of E2 treatment on Apoe^-/- mice that lack mature T and B lymphocytes due to a deficiency in recombinase activator gene 2, or rag-2 (Rag-2^-/-Apoe^-/-), and found that E2 treatment failed to reduce lesion size in Rag-2^-/-Apoe^-/- females. The authors suggested that the T and B cells of the immune system are required for the atheroprotective effects of E2. In a separate study (49), the role of IL-6, a multifunctional cytokine, was investigated by the treatment of doubly deficient IL-6^-/-Apoe^-/- mice with E2. E2 was fully atheroprotective in IL-6^-/-Apoe^-/- mice, demonstrating that IL-6 does not constitute a target for the inhibition of atheroprogression by E2.

	Summary and Considerations for the Future

Top Abstract Introduction Atheroprotection by Estrogen in... Atheroprotection by Estrogen in... E2 and Estrogen Receptors... E2 and NO in... E2 and Inflammation in... Summary and Considerations for... References

 
Exogenous administration of the natural estrogen E2 dramatically inhibits atherogenesis in atherosclerotic mouse models. These studies have demonstrated that the antiatherogenic effect of E2 is primarily mediated through ER and independent of ERß, at least at early stages of plaque formation. Additionally, atheroprotection by exogenous E2 does not require eNOS or IL-6, but may involve modulation of immunoinflammatory components of atherogenesis. Other potential vascular targets for the early atheroprotective effects of E2 include, but are not limited to, endothelial permeability to LDL (26), LDL oxidation (50), cytokine and cell adhesion molecule expression (51, 52), macrophage cholesterol homeostasis (53), and other vasoactive substances released by the vessel wall such as prostacyclin and angiotensin II as well as their receptors (54, 55). Creating unique mouse models to test potential target genes and pathways of E2-mediated atheroprotection is an informative although arduous process.

A principle issue confronting the use of mouse models of atherosclerosis to investigate the cardiovascular effects of estrogens is to reconcile study findings with findings from human studies. Unlike E2 treatment in mice, human studies demonstrate no protection and an increased risk of cardiovascular harm with HRT. However, oral formulations of CEE combined with a progestin, as has been employed in human trials, are not equivalent to sc administration of E2 alone. Furthermore, most of the trials in humans have used women with preexisting disease. The majority of animal studies demonstrating the protective effects of estrogen are on the formation of new lesions. It is therefore important to note that, in three of four studies in animals with preexisting lesions (56, 57, 58, 59), reduced or no protective effect of E2 treatment was observed, suggesting that inhibitory effects of estrogen may be lost once atherosclerotic lesions are established. The effect of E2 on established atherosclerotic lesions in mouse models has yet to be addressed. Additionally, the effect of E2 in the setting of acute vascular injury in atherosclerotic mice should be addressed. Finally, human trials have used myocardial infarction and CHD death as study endpoints, reflecting late thrombotic events. Plaque rupture and subsequent thrombosis, which precipitate clinical events including myocardial infarction, are very rare in atherosclerotic mouse models. The generation of such models and treatment with estrogens would help clarify the role of estrogens in this clinically important stage of atherosclerosis.

The HERS, ERA, and WHI trials have demonstrated that the long-term use of the most common HRT formulation confers health risks that outweigh any benefits. The divergent results of these trials and studies using animal models have not only highlighted the need to understand the differences in replacement therapy formulations, route of administration, and timing of pharmacological intervention, but also the need to understand the vascular effects of estrogens at the cellular and molecular levels. In the future, specific hormonal therapies for CHD may be found in the use of selective estrogen receptor modulators, or SERMS (examples of these include synthetically produced compounds, such as tamoxifen and raloxifene, or plant-derived phytoestrogens), which may confer the benefits of HRT without the risks. In fact, secondary analysis of a recent study (60) of raloxifene in postmenopausal women with CHD demonstrated a reduced risk of cardiovascular events after 4 yr of treatment without an increase in events during the first year other than an increase in venous thromboembolic events. Mouse models of atherosclerosis should prove invaluable toward this end.

	Acknowledgments

 
We thank Margaret and Felix Hicken for critical review of this manuscript.

	Footnotes

 
Studies in our laboratory were supported by NIH Grants HL-42630, GM-20069, HL-62845, and HL-49277.

Abbreviations: Apoe, Apolipoprotein E gene; CEE, conjugated equine estrogen; CHD, coronary heart disease; E2, 17ß-estradiol; eNOS, endothelial NO synthase; ER, estrogen receptor; ERA, Estrogen Replacement Atherosclerosis; ERT, estrogen-alone replacement therapy; HERS, Heart and Estrogen/Progestin Replacement Study; HRT, hormone (estrogen-progestin) replacement therapy; LDL, low-density lipoprotein; Ldlr, low-density lipoprotein receptor gene; MPA, medroxyprogesterone acetate; NO; nitric oxide; VSMC, vascular smooth muscle cell; WHI, Women’s Health Initiative.

Received August 13, 2002.

Accepted for publication September 19, 2002.

	References

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1. Ross R 1999 Atherosclerosis–an inflammatory disease. N Engl J Med 340:115–126[Free Full Text]
2. Mosca L 1998 Estrogen and atherosclerosis. J Investig Med 46:381–386[Medline]
3. Grady D, Rubin SM, Petitti DB, Fox CS, Black D, Ettinger B, Ernster VL, Cummings SR 1992 Hormone therapy to prevent disease and prolong life in postmenopausal women. Ann Intern Med 117:1016–1037
4. Hulley S, Grady D, Bush T, Furberg C, Herrington D, Riggs B, Vittinghoff E 1998 Randomized trial of estrogen plus progestin for secondary prevention of coronary heart disease in postmenopausal women. Heart and Estrogen/progestin Replacement Study (HERS) Research Group. JAMA 280:605–613[Abstract/Free Full Text]
5. Herrington DM, Reboussin DM, Brosnihan KB, Sharp PC, Shumaker SA, Snyder TE, Furberg CD, Kowalchuk GJ, Stuckey TD, Rogers WJ, Givens DH, Waters D 2000 Effects of estrogen replacement on the progression of coronary-artery atherosclerosis. N Engl J Med 343:522–529[Abstract/Free Full Text]
6. Writing Group for the Women’s Health Initiative Investigators 2002 Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results from the Women’s Health Initiative randomized controlled trial. JAMA 288:321–333[Abstract/Free Full Text]
7. The Writing Group for the PEPI Trial 1995 Effects of estrogen or estrogen/progestin regimens on heart disease risk factors in postmenopausal women. The Postmenopausal Estrogen/Progestin Interventions (PEPI) Trial. JAMA 273:199–208[Abstract]
8. Adams MR, Register TC, Golden DL, Wagner JD, Williams JK 1997 Medroxyprogesterone acetate antagonizes inhibitory effects of conjugated equine estrogens on coronary artery atherosclerosis. Arterioscler Thromb Vasc Biol 17:217–221[Abstract/Free Full Text]
9. Hodis HN, Mack WJ, Lobo RA, Shoupe D, Sevanian A, Mahrer PR, Selzer RH, Liu Cr C, Liu Ch C, Azen SP 2001 Estrogen in the prevention of atherosclerosis. A randomized, double-blind, placebo-controlled trial. Ann Intern Med 135:939–953[Abstract/Free Full Text]
10. Mendelsohn ME, Karas RH 1999 The protective effects of estrogen on the cardiovascular system. N Engl J Med 340:1801–1811[Free Full Text]
11. Schunkert H, Danser AH, Hense HW, Derkx FH, Kurzinger S, Riegger GA 1997 Effects of estrogen replacement therapy on the renin-angiotensin system in postmenopausal women. Circulation 95:39–45[Abstract/Free Full Text]
12. Giltay EJ, Gooren LJ, Emeis JJ, Kooistra T, Stehouwer CD 2000 Oral ethinyl estradiol, but not transdermal 17ß-estradiol, increases plasma C-reactive protein levels in men. Thromb Haemost 84:359–360[Medline]
13. Ross R 1995 Cell biology of atherosclerosis. Annu Rev Physiol 57:791–804[CrossRef][Medline]
14. Holm P 2001 Effect of estrogen on development of atherosclerosis. A review of experimental animal studies. Dan Med Bull 48:146–160[Medline]
15. Knowles JW, Maeda N 2000 Genetic modifiers of atherosclerosis in mice. Arterioscler Thromb Vasc Biol 20:2336–2345[Abstract/Free Full Text]
16. Nathan L, Shi W, Dinh H, Mukherjee TK, Wang X, Lusis AJ, Chaudhuri G 2001 Testosterone inhibits early atherogenesis by conversion to estradiol: critical role of aromatase. Proc Natl Acad Sci USA 98:3589–3593[Abstract/Free Full Text]
17. Tse J, Martin-McNaulty B, Halks-Miller M, Kauser K, DelVecchio V, Vergona R, Sullivan ME, Rubanyi GM 1999 Accelerated atherosclerosis and premature calcified cartilaginous metaplasia in the aorta of diabetic male Apo E knockout mice can be prevented by chronic treatment with 17ß-estradiol. Atherosclerosis 144:303–313[CrossRef][Medline]
18. Haarbo J, Leth-Espensen P, Stender S, Christiansen C 1991 Estrogen monotherapy and combined estrogen-progestogen replacement therapy attenuate aortic accumulation of cholesterol in ovariectomized cholesterol-fed rabbits. J Clin Invest 87:1274–1279
19. Bjarnason NH, Haarbo J, Byrjalsen I, Kauffman RF, Christiansen C 1997 Raloxifene inhibits aortic accumulation of cholesterol in ovariectomized, cholesterol-fed rabbits. Circulation 96:1964–1969[Abstract/Free Full Text]
20. Buko VU, Lukivskaya O, Naruta E, Popov Y, Chirkin A, Chirkina I, Oettel M, Romer W, Hubler D 2001 Antiatherogenic effects of 17ß-estradiol and 17-estradiol and its derivative J811 in cholesterol-fed rabbits with thyroid inhibition. Climacteric 4:49–57[Medline]
21. Williams JK, Adams MR, Klopfenstein HS 1990 Estrogen modulates responses of atherosclerotic coronary arteries. Circulation 81:1680–1687[Abstract/Free Full Text]
22. Sulistiyani, Adelman SJ, Chandrasekaran A, Jayo J, St Clair RW 1995 Effect of 17-dihydroequilin sulfate, a conjugated equine estrogen, and ethynylestradiol on atherosclerosis in cholesterol-fed rabbits. Arterioscler Thromb Vasc Biol 15:837–846[Abstract/Free Full Text]
23. Hanke H, Hanke S, Finking G, Muhic-Lohrer A, Muck AO, Schmahl FW, Haasis R, Hombach V 1996 Different effects of estrogen and progesterone on experimental atherosclerosis in female versus male rabbits. Quantification of cellular proliferation by bromodeoxyuridine. Circulation 94:175–181[Abstract/Free Full Text]
24. Haines CJ, James AE, Panesar NS, Ngai TJ, Sahota DS, Jones RL, Chang AM 1999 The effect of percutaneous oestradiol on atheroma formation in ovariectomized cholesterol-fed rabbits. Atherosclerosis 143:369–375[CrossRef][Medline]
25. Adams MR, Kaplan JR, Manuck SB, Koritnik DR, Parks JS, Wolfe MS, Clarkson TB 1990 Inhibition of coronary artery atherosclerosis by 17ß estradiol in ovariectomized monkeys. Lack of an effect of added progesterone. Arteriosclerosis 10:1051–1057[Abstract/Free Full Text]
26. Wagner JD, Clarkson TB, St. Clair RW, Schwenke DC, Shively CA, Adams MR 1991 Estrogen and progesterone replacement therapy reduces low density lipoprotein accumulation in the coronary arteries of surgically postmenopausal cynomolgus monkeys. J Clin Invest 88:1995–2002
27. Wagner JD, Schwenke DC, Zhang L, Applebaum-Bowden D, Bagdade JD, Adams MR 1997 Effects of short-term hormone replacement therapies on low-density lipoprotein metabolism in cynomologus monkeys. Arterioscler Thromb Vasc Biol 17:1128–1134[Abstract/Free Full Text]
28. Elhage R, Arnal JF, Pieraggi MT, Duverger N, Fievet C, Faye JC, Bayard F 1997 17ß-Estradiol prevents fatty streak formation in apolipoprotein E-deficient mice. Arterioscler Thromb Vasc Biol 17:2679–2684[Abstract/Free Full Text]
29. Bourassa PA, Milos PM, Gaynor BJ, Breslow JL, Aiello RJ 1996 Estrogen reduces atherosclerotic lesion development in apolipoprotein E-deficient mice. Proc Natl Acad Sci USA 93:10022–10027[Abstract/Free Full Text]
30. Marsh MM, Walker VR, Curtiss LK, Banka CL 1999 Protection against atherosclerosis by estrogen is independent of plasma cholesterol levels in LDL receptor-deficient mice. J Lipid Res 40:893–900[Abstract/Free Full Text]
31. Zuckerman SH, Evans GF, Schelm JA, Eacho PI, Sandusky G 1999 Estrogen-mediated increases in LDL cholesterol and foam cell-containing lesions in human ApoB100xCETP transgenic mice. Arterioscler Thromb Vasc Biol 19:1476–1483[Abstract/Free Full Text]
32. Walter P, Green S, Greene G, Krust A, Bornert JM, Jeltsch JM, Staub A, Jensen E, Scrace G, Waterfield M, Chambon P 1985 Cloning of the human estrogen receptor cDNA. Proc Natl Acad Sci USA 82:7889–7893[Abstract/Free Full Text]
33. Kuiper GG, Enmark E, Pelto-Huikko M, Nilsson S, Gustafsson JA 1996 Cloning of a novel receptor expressed in rat prostate and ovary. Proc Natl Acad Sci USA 93:5925–5930[Abstract/Free Full Text]
34. Lubahn DB, Moyer JS, Golding TS, Couse JF, Korach KS, Smithies O 1993 Alteration of reproductive function but not prenatal sexual development after insertional disruption of the mouse estrogen receptor gene. Proc Natl Acad Sci USA 90:11162–11166[Abstract/Free Full Text]
35. Dupont S, Krust A, Gansmuller A, Dierich A, Chambon P, Mark M 2000 Effect of single and compound knockouts of estrogen receptors (ER) and ß (ERß) on mouse reproductive phenotypes. Development 127:4277–4291[Abstract]
36. Krege JH, Hodgin JB, Couse JF, Enmark E, Warner M, Mahler JF, Sar M, Korach KS, Gustafsson JA, Smithies O 1998 Generation and reproductive phenotypes of mice lacking estrogen receptor ß. Proc Natl Acad Sci USA 95:15677–15682[Abstract/Free Full Text]
37. Hodgin JB, Krege JH, Reddick RL, Korach KS, Smithies O, Maeda N 2001 Estrogen receptor is a major mediator of 17ß-estradiol’s atheroprotective effects on lesion size in Apoe(-/-) mice. J Clin Invest 107:333–340[Medline]
38. Pettersson K, Grandien K, Kuiper GG, Gustafsson JA 1997 Mouse estrogen receptor ß forms estrogen response element-binding heterodimers with estrogen receptor . Mol Endocrinol 11:1486–1496[Abstract/Free Full Text]
39. Pendaries C, Darblade B, Rochaix P, Krust A, Chambon P, Korach KS, Bayard F, Arnal JF 2002 The AF-1 activation-function of ER may be dispensable to mediate the effect of estradiol on endothelial NO production in mice. Proc Natl Acad Sci USA 99:2205–2210[Abstract/Free Full Text]
40. Karas RH, Hodgin JB, Kwoun M, Krege JH, Aronovitz M, Mackey W, Gustafsson JA, Korach KS, Smithies O, Mendelsohn ME 1999 Estrogen inhibits the vascular injury response in estrogen receptor ß-deficient female mice. Proc Natl Acad Sci USA 96:15133–15136[Abstract/Free Full Text]
41. Iafrati MD, Karas RH, Aronovitz M, Kim S, Sullivan Jr TR, Lubahn DB, O’Donnell Jr TF, Korach KS, Mendelsohn ME 1997 Estrogen inhibits the vascular injury response in estrogen receptor -deficient mice. Nat Med 3:545–548[CrossRef][Medline]
42. Pare G, Krust A, Karas RH, Dupont S, Aronovitz M, Chambon P, Mendelsohn ME 2002 Estrogen receptor- mediates the protective effects of estrogen against vascular injury. Circ Res 90:1087–1092[Abstract/Free Full Text]
43. Kuhel DG, Zhu B, Witte DP, Hui DY 2002 Distinction in genetic determinants for injury-induced neointimal hyperplasia and diet-induced atherosclerosis in inbred mice. Arterioscler Thromb Vasc Biol 22:955–960[Abstract/Free Full Text]
44. Moncada S, Higgs A 1993 The L-arginine-nitric oxide pathway. N Engl J Med 329:2002–2012[Free Full Text]
45. Knowles JW, Reddick RL, Jennette JC, Shesely EG, Smithies O, Maeda N 2000 Enhanced atherosclerosis and kidney dysfunction in eNOS(-/-)Apoe(-/-) mice are ameliorated by enalapril treatment. J Clin Invest 105:451–458[Medline]
46. Hodgin JB, Knowles JW, Kim HS, Smithies O, Maeda N 2002 Interactions between endothelial nitric oxide synthase and sex hormones in vascular protection in mice. J Clin Invest 109:541–548[CrossRef][Medline]
47. Elhage R, Bayard F, Richard V, Holvoet P, Duverger N, Fievet C, Arnal JF 1997 Prevention of fatty streak formation of 17ß-estradiol is not mediated by the production of nitric oxide in apolipoprotein E-deficient mice. Circulation 96:3048–3052[Abstract/Free Full Text]
48. Elhage R, Clamens S, Reardon-Alulis C, Getz GS, Fievet C, Maret A, Arnal JF, Bayard F 2000 Loss of atheroprotective effect of estradiol in immunodeficient mice. Endocrinology 141:462–465[Abstract/Free Full Text]
49. Elhage R, Clamens S, Besnard S, Mallat Z, Tedgui A, Arnal J, Maret A, Bayard F 2001 Involvement of interleukin-6 in atherosclerosis but not in the prevention of fatty streak formation by 17ß-estradiol in apolipoprotein E-deficient mice. Atherosclerosis 156:315–320[CrossRef][Medline]
50. Sack MN, Rader DJ, Cannon 3rd RO 1994 Oestrogen and inhibition of oxidation of low-density lipoproteins in postmenopausal women. Lancet 343:269–270[CrossRef][Medline]
51. Caulin-Glaser T, Watson CA, Pardi R, Bender JR 1996 Effects of 17ß-estradiol on cytokine-induced endothelial cell adhesion molecule expression. J Clin Invest 98:36–42[Medline]
52. Frazier-Jessen MR, Kovacs EJ 1995 Estrogen modulation of JE/monocyte chemoattractant protein-1 mRNA expression in murine macrophages. J Immunol 154:1838–1845[Abstract]
53. St Clair RW 1997 Effects of estrogens on macrophage foam cells: a potential target for the protective effects of estrogens on atherosclerosis. Curr Opin Lipidol 8:281–286[Medline]
54. Nickenig G, Baumer AT, Grohe C, Kahlert S, Strehlow K, Rosenkranz S, Stablein A, Beckers F, Smits JF, Daemen MJ, Vetter H, Bohm M 1998 Estrogen modulates AT1 receptor gene expression in vitro and in vivo. Circulation 97:2197–201[Abstract/Free Full Text]
55. Mikkola T, Viinikka L, Ylikorkala O 1998 Estrogen and postmenopausal estrogen/progestin therapy: effect on endothelium-dependent prostacyclin, nitric oxide and endothelin-1 production. Eur J Obstet Gynecol Reprod Biol 79:75–82[CrossRef][Medline]
56. Williams JK, Anthony MS, Honore EK, Herrington DM, Morgan TM, Register TC, Clarkson TB 1995 Regression of atherosclerosis in female monkeys. Arterioscler Thromb Vasc Biol 15:827–836[Abstract/Free Full Text]
57. Clarkson TB, Anthony MS, Morgan TM 2001 Inhibition of postmenopausal atherosclerosis progression: a comparison of the effects of conjugated equine estrogens and soy phytoestrogens. J Clin Endocrinol Metab 86:41–47[Abstract/Free Full Text]
58. Bjarnason NH, Haarbo J, Byrjalsen I, Alexandersen P, Kauffman RF, Christiansen C 2001 Raloxifene and estrogen reduces progression of advanced atherosclerosis—a study in ovariectomized, cholesterol-fed rabbits. Atherosclerosis 154:97–102[CrossRef][Medline]
59. Hanke H, Kamenz J, Hanke S, Spiess J, Lenz C, Brehme U, Bruck B, Finking G, Hombach V 1999 Effect of 17-ß estradiol on pre-existing atherosclerotic lesions: role of the endothelium. Atherosclerosis 147:123–132[CrossRef][Medline]
60. Barrett-Connor E, Grady D, Sashegyi A, Anderson PW, Cox DA, Hoszowski K, Rautaharju P, Harper KD 2002 Raloxifene and cardiovascular events in osteoporotic postmenopausal women: four-year results from the MORE (Multiple Outcomes of Raloxifene Evaluation) randomized trial. JAMA 287:847–857[Abstract/Free Full Text]
61. Adams MR, Anthony MS, Manning JM, Golden DL, Parks JS 2000 Low-dose contraceptive estrogen-progestin and coronary artery atherosclerosis of monkeys. Obstet Gynecol 96:250–255[Abstract/Free Full Text]
62. Clarkson TB, Anthony MS, Jerome CP 1998 Lack of effect of raloxifene on coronary artery atherosclerosis of postmenopausal monkeys. J Clin Endocrinol Metab 83:721–726[Abstract/Free Full Text]

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