Estrogen replacement in menopausal women: Recent and current prospective studies, the WHI and the KEEPS

GENDER MEDICINE/VOL. 3, NO. 4, 2 0 0 6

CSD Grand Rounds

Estrogen Replacement in Menopausal Women: Recent and Current Prospective Studies, the WHI and the KEEPS S. M i t c h e l l H a r m a n , MD, P h D Dr. Mitch Harman attended Downstate Medical School and completed his internship and residency at Yale University. Shortly thereafter, he joined the National Institute of Aging (NIA), where he was the Section Chief of the Division of Endocrinology and, toward the end of his tenure, the Clinical Director of the NIA. On leaving the NIA in 2000, Dr. Harman became Director and President of the Kronos Longevity Research Institute in Phoenix, Arizona. The institute is now engaged in a seminal study to address unanswered questions about hormone replacement therapy, in particular whether estrogen treatment initiated within 3 years of menopause slows atherosclerosis progression.

ABSTRACT In the wake of the Women's Health Initiative (WHI) trials, m a n y questions have yet to be resolved regarding the use of h o r m o n e replacement therapy (HRT) in postmenopausal women, primarily whether HRT's cardioprotective effects outweigh a possible increase in breast cancer risk. Several factors, including differences in HRT regimens, the duration of follow-up, and study participants' ages, m a y have contributed to the widely different conclusions of the WHI trials in comparison to the observational studies. A woman's risk of dying from heart disease is roughly 10 times greater than her risk of dying from breast cancer. Soon after menopause, the rate of heart disease accelerates rapidly, whereas the rate of breast cancer increases slowly. Estrogens have been found to reduce coronary heart disease and to have favorable effects on lipid profiles. The risks of adverse health effects must be balanced against the benefits associated with HRT. Further research into the timing of estrogen replacement treatment m a y be crucial to the prevention of cardiovascular disease.

INTRODUCTION Most clinicians are aware of the current controversy regarding the use of h o r m o n e replacement therapy (HRT) in postmenopausal w o m e n pursuant to the Women's Health Initiative (WHI) trials. Some mistakenly believe that this question has already been answered and that HRT should not be prescribed to postmenopausal women. This article considers the m a n y issues that remain to be resolved on this highly significant topic for women. W h a t was known about HRT before the W H I results of 2002? To begin, one might ask, "What did we k n o w about HRT in w o m e n before the publication of the WHI results in 2002?" What we thought we knew was that HRT prevents or abolishes hot flashes. That it prevents or improves vaginal atrophy. That it prevents or slows b o n e loss and reduces the inciBased on a presentation to the Georgetown University Center for the Study of Sex Differences in Health, Aging and Disease (CSD), September 14, 2006.

Accepted for publication November 16, 2006. Gend Med. 2006;3:254-269.

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he Women's Health Initiative trials were conceived because hormone replacement therapy was formerly based either on small trials examining intermediate end points, such as lipids, or on observational studies in which women were not randomized.

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dence of osteoporotic fractures. That it reduces the risk of heart disease. Moreover, there were data that showed improved blood flow to the brain, possible reduction in Alzheimer's disease, possible reduction of the risk of colon cancer, and, in some more or less anecdotal data, improved quality of life. Much positive t h o u g h t surrounded HRT, and the n u m b e r of prescriptions written for menopausal w o m e n were increasing logarithmically.

H o w w a s the WHI conceived? The WHI trials were conceived because what we knew about HRT was based either on small studies examining intermediate end points, such as lipids, or on observational trials in which w o m e n were not randomized. It was important to study HRT because of its association with the risk of heart disease. W o m e n previously believed t h e y h a d a m u c h greater chance of dying from breast cancer t h a n from heart disease. The real statistics are quite different. A woman's chance of dying from heart disease is currently ~45%, 1 t h o u g h we do expect this percentage will decline with the widespread use of statins and the rollout of national campaigns (such as the one l a u n c h e d by the National Heart, Lung, and Blood Institute to increase women's awareness of their risk of heart disease and the benefits of exercise and improved diet). In contrast, the actual risk of dying from breast cancer is ~4%2; that is, the risk of dying from breast cancer is only a t e n t h of the risk of heart disease. These statistics are significant because the use of HRT in menopausal w o m e n has implications for the risk of both heart disease and breast cancer. Therefore, if HRT significantly protects w o m e n from heart disease, a small increase in

the risk of breast cancer would be tolerable, because the overall risk-benefit ratio would favor HRT. On the other hand, if there is no protection from heart disease or, worse, if there is an increase in the risk of heart disease, t h e n the breast cancer risk becomes paramount and the risk-benefit ratio reverses. This is the crux of the question.

woman's chance of dying from heart disease A is currently ~45%; in contrast, the actual risk of dying from breast cancer is ~4%. Thus, the risk of dying from breast cancer is only a tenth of the risk of heart disease.

W h e n you consider the early phase of the menopausal period, the mortality rate from heart disease and the mortality rate from breast cancer are almost equal ( F i g u r e 1). Soon thereafter, the rate of heart disease accelerates rapidly, whereas the rate of breast cancer continues to increase slowly until the seventh decade of life. After age 65, the risk of heart disease dwarfs the risk of breast cancer. Thus, if you had an intervention that reduced the risk of heart disease by 40%, you would achieve an enormous gain in years of h e a l t h y life span. Therefore, the issue of whether or not to employ HRT in menopausal w o m e n has vast public health implications.

hormone replacement therapy in Briskecause menopausal women has implications for the of both heart disease and breast cancer, the issue of whether or not to use it has huge public health implications.

W h a t is the evidence that estrogens are cardioprotective? Epidemiologic observations suggest t h a t estrogens reduce coronary heart disease (CHD) by 40% to 50% t h r o u g h multiple plausible mechanisms. 5 These include favorable effects on lipid profiles, antioxidant effects by decreas-

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Age (y) Figure 1. Mean mortality rates (deaths/lOO,OOO/y) for the years 1995 to 1998" and 1994 to 1998t due to heart disease, stroke, and some common cancers, by decade in adult women aged 45 to _>85 years. The alternative heart disease rate in women taking hormone replacement therapy (HRT) depicts the projected mortality rate if HRT were to provide an overall 40% reduction beginning ~5 years after menopause. Sources: *Eberhardt et a13; tRies et al, eds. 4 ing lipid oxidation, vascular effects directly on the endothelium of the arterial wall, upregulation of nitric oxide synthase resulting in vasodilatation, inhibition of platelet aggregation, increases in prostacyclin levels by increasing cyclooxygenase-2 activity, decreases in cell adhesion molecules (several of the cell adhesion molecules are inhibited by estrogens), and decreases in key inflammatory factors, most notably, tumor necrosis factor-or, interleukin-6, m e m b r a n e cofactor protein-i, and fibrinogen. All these positive effects associated with an estrogen-replete state would be expected to protect against heart disease. In one HRT study of w o m e n taking 0.62S or 1.2S mg of conjugated equine estrogens (CEE) daily along with S mg of medroxyprogesterone acetate (MPA), total and low-density lipoprotein 256

cholesterol were reduced to nearly the same extent as that of w o m e n treated with simvastatin (10 mg daily). 6 HRT elevated high-density lipoprotein cholesterol to a greater extent than did simvastatin in this study. Additionally, simvastatin lowered triglyceride levels, whereas HRT tended to raise them. However, HRT was more effective than simvastatin at reducing Lp(a) lipoprotein, which is considered a major risk factor for CHD. In another study, flow-mediated vasodilatation in the endothelium nearly doubled in menopausal w o m e n treated with 0.62S mg of CEE compared with age-matched untreated menopausal women. 7 This effect was negated by the addition of 2.S mg of MPA. In fact, at a higher dose of S m g of MPA, this effect was nearly reversed. These and other findings suggest that certain progestins m a y actually work

S.M Harman

against the vasodilatation effects of estrogens in the endothelium.

strogen-associated effects that would be Einclude expected to protect against heart disease favorable lipid profiles; antioxidant effects; increases in nitric oxide synthase, prostacyclin, and vasodilatory effects; and decreases in platelet aggregation, cell adhesion molecules, and key inflammatory factors.

A risk-ratio analysis of several large observational studies of w o m e n taking HRT for m a n y years, including estrogen replacement therapy (ERT) alone or combined estrogen+progestin, strongly suggested that HRT is highly cardioprotective ( F i g u r e 2). The relative risk in these trials primarily favored cardioprotection; on average, there was a 40% to 50% reduction in CHD events over time in w o m e n w h o took HRT after menopause. The best of these observational studies is the Nurses' Health Study (NHS). Because all of the w o m e n studied were nurses and this population was essentially middle class with good accessibility to health care, the NHS did not have m a n y of the confounds associated with disparities in health care. In addition, the statistical group at Harvard Medical School and School of Public Health performed sophisticated statistical corrections for various potentially confounding factors and still realized approximately a 40% reduction in events after 18 years of follow-up. 2°

he relative risk in most observational trials was primarily on the side of cardioprotection; there was approximately a 40% reduction in coronary heart disease events over time in women who used hormone replacement therapy after menopause.

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What are the inherent biases present in observational studies? The caveats for interpreting the NHS data are the same biases inherent in observational stud-

ies in general. A selection bias could exist that skews the interpretation of the results. For example, healthier w o m e n m a y tend to take HRT, whereas w o m e n with more health problems m a y be less likely to obtain HRT prescriptions. There is also a prevention bias: monitoring and t r e a t m e n t are likely to be more intensive in w o m e n who are prescribed HRT t h a n in those w h o are not, and thus other health issues m a y be detected, which would lead to measures being taken that reduce their risk of heart disease. A compliance bias m a y exist as well: patients with better adherence m a y have better outcomes overall because t h e y tend to take better care of their health; that is, w o m e n w h o continue to take HRT m a y be taking other beneficial steps to maximize their health. There is also what is k n o w n as a survivor bias: w o m e n w h o become ill and develop heart disease are more likely to stop taking their HRT. In addition, there is a prevalence-incidence bias, in which early adverse effects of treatment are not observed if the user dies or becomes ill before being admitted to the cohort. These are all potential biases that could skew the results of a n o n r a n d o m i z e d study so that taking estrogen appears markedly cardioprotective when, in reality, it is not.

Health Risks Associated with HRT Studies suggest that HRT prescribed for 10 to 15 years increases the risk of breast cancer by 20% to 30%. 21,22 However, it is important to note that because the risk of death from breast cancer is ~4 in 100 w o m e n in the general female population, 2 a 30% increase caused by HRT translates into a breast cancer mortality risk of 1.3 × 4 = 5.2%, or 1.2 additional w o m e n in 100 overall. Women who have a uterus are generally prescribed HRT with a progestin, because unopposed estrogens would markedly increase the risk of endometrial cancer. There is some evidence that the addition of a progestin m a y augm e n t breast cancer risk by an additional 10% or so. 22 HRT is also associated with a small increase in risk for venous thromboembolism (VTE), ~2 additional cases in 10,000 women23,24; however, the mortality rate is low. In some studies, HRT

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RelativeRisk Figure 2. Relative risks of incident coronary heart disease (CHD) or CHD mortality, with 95% CIs when provided, in hormone replace therapy users versus nonusers from 13 reports of observational (nonrandomized) population studies. has been associated with an increase in the relative risk of stroke, and there appears to be an increase in the risk of cholelithiasis and gallstones. These risks all must be balanced against the benefits associated with HRT.

biases inherent in observational studp otential ies could skew the results so that taking hormone replacement therapy appears markedly cardioprotective when, in reality, it is not.

In the NHS, the risk of breast cancer was increased by ~30% with CEE therapy; with CEE plus MPA, the risk was somewhat higher. 21 In the group that took CEE at a dose of 0.62S mg, there was a 44% increase in the risk of stroke. 25 With the lower CEE dose of 0.3 mg, the increase in the risk of stroke disappeared. Thus, there m a y be a dose-response relationship between ERT and the risk of thromboembolic disease

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and stroke. Most important, in the NHS there was approximately a 37% reduction in the risk of overall mortality w h e n comparing current users with past users, and almost a S0% reduction in the risk of mortality from CHD compared with past users or nonusers. 26

What were the results of the Heart and Estrogen-progestln Replacement Study (HERS)? The generally beneficial outcomes of the previously mentioned observational studies prompted the National Institutes of Health (NIH) to plan and support randomized, blinded, controlled trials to investigate the clinical effects of HRT. One of the best k n o w n trials, HERS was a secondary prevention study in which menopausal w o m e n w h o had had a d o c u m e n t e d CHD--with either a heart attack, coronary artery bypass graft, angioplasty, or an angiogram showing at least a S0% narrowing of the coronary arteries--were randomized to receive HRT (0.62S mg of CEE

S.M Harman

and 2.5 mg of MPA) or placebo. 27 Their m e a n age was 67 years. Although a significant increase in VTE and a borderline significant increase in gallbladder disease were observed, this study showed no significant effects on the incidence of cancer, stroke, or mortality. For w o m e n w h o already had CHD, the HERS trial concluded that no cardiovascular benefit was obtained by treatment with HRT. It is always important to bear in mind, however, that this study examined a specific HRT regimen, which m a y or m a y not have any relevance to other HRT regimens.

or women who already had coronary heart FReplacement disease, the Heart and Estrogen-progestin Study concluded that no cardiovascular benefit was obtained by treatment with hormone replacement therapy.

W h a t w a s the outcome of the W H I estrogen + progestln trlal? The HERS trial did not address the cardioprotective benefits of HRT in w o m e n who have not had a CHD event. The WHI study trials were designed to address this question by focusing on primary, rather t h a n secondary, prevention. These were randomized, double-blinded, placebocontrolled trials intended as primary prevention in w o m e n 50 to 79 years of age. The trials were planned for an 8.5-year duration and included an estrogen+progestin group (0.625 mg CEE and 2.5 mg of MPA in w o m e n with a uterus) and an estrogen-alone group (0.625 mg CEE alone in w o m e n w h o had undergone hysterectomies). The n u m b e r of participants was remarkable: in the estrogen plus progesterone study, there were 8500 w o m e n taking estrogen+ progestin and 8100 w o m e n receiving placebo. The unopposed CEE trial numbers were somewhat smaller but still substantial: 5300 w o m e n were taking estrogen alone and 5400 received placebo. These NIH-funded studies cost about half a billion dollars over an 8-year period. The end points were cardiovascular events including new myocardial infarctions and stroke, b o t h of

which are solid clinically. In addition, there were secondary cardiac end points and some secondary clinical events including fractures, cancers, VTE, and stroke.

ather than exhibiting any clear cardiovascuRcoronary lar protection, we were shocked to find that heart disease increased 24% in the Women's Health Initiative estrogen+progestin group.

The m e a n age of w o m e n in the estrogen+ progestin group was 63 years. Approximately 5000 w o m e n were between the ages of 50 and 59 years, 7500 were between ages 60 and 69, and almost 3600 were over the age of 70. They were slightly overweight, with a body mass index of 28.5. Six percent were current HRT users; 20% were past HRT users. The great majority (74%) had never used HRT before entry in the study. W h e n the placebo group was compared with the HRT-treated group, the n u m b e r of deaths was about equal; the risk ratio for death was 0.98. Fractures were reduced by ~24%. The risk of colon cancer was also significantly reduced, whereas the risk of breast cancer increased by 26%; this latter increase was not statistically significant. The risk of deep vein thrombophlebitis and p u l m o n a r y embolism taken as a combined variable was increased 2-fold. Similarly to the NHS finding, a 40% increase in the risk of stroke was observed. All these risk factors were consistent with previous observational studies. W h a t was shocking was that, rather t h a n exhibiting any clear cardiovascular protection, CHD increased 24% in the WHI estrogen+progestin group, t h o u g h this effect narrowly missed statistical significance. Because this effect on heart disease was totally unexpected, concerns were raised, and the US Food and Drug Administration (FDA) quickly changed its HRT guidelines to conclude that estrogen in h e a l t h y postmenopausal w o m e n did not protect against heart disease. The FDA warned physicians to stop prescribing HRT to menopausal w o m e n except to treat symptoms for a few m o n t h s if

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absolutely necessary. The current FDA guidelines specify use of the lowest dose for the shortest possible time period for the relief of symptoms. 28 That is where we are today.

he US Food and Drug Administration warned Treplacement physicians to stop prescribing hormone therapy to menopausal women except for a few months to treat symptoms if absolutely necessary. The current guidelines are: the lowest dose for the shortest possible time period for the relief of symptoms.

How could ERT increase CHD events? In a large retrospective case-control study in which most w o m e n were taking 17[3-estradiol either orally or transdermally, the w o m e n taking oral HRT had a 3.S-fold increase in their odds ratio for thromboembolic disease compared with the w o m e n receiving HRT transdermally. 29 There was no excess risk of thromboembolic disease associated with transdermal ERT. The authors concluded that ERT augments blood coagulation if it is taken by m o u t h but not if it is used transdermally. Because CHD events involve d o t formation as a critical element in their etiology, this effect of oral ERT may contribute to the increase in CHD events. W h e n estrogens are synthesized in a woman's ovary, they are released directly into the systemic circulation. In this large blood pool, the estrogens are rapidly diluted. Throughout the menstrual cycle, the concentration of estrogens varies between 20 and 200 pg/mL. In contrast, when a w o m a n takes ERT orally, the estrogens move into the intestines and are taken up into the portal circulation. The liver is then exposed to very high quantities of estrogens. Oral ERT is associated with decreases in antidotting factors such as antithrombin III, tissue factor pathway inhibitor, and protein C, and with increases in several thrombotic markers such as prothrombotic complex F1 and F2, ot thrombin-antithrombin complexes, and the D-dimer, as well as with an increase in C-reactive protein (CRP). The liver is not normally exposed to such high quantities of estrogens except during preg-

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nancy, w h e n the placenta makes huge a m o u n t s of estrogens resulting in high levels in the liver. From an evolutionary perspective, the effects of oral ERT on thrombotic factors should not be surprising given that during pregnancy, the increased t e n d e n c y for blood to clot is beneficial w h e n a w o m a n delivers, because she has a better chance of surviving if she does not continue to bleed. In contrast, the increased tendency to clot is probably harmful for a 6S-yearold w o m a n w h o already has plaque in her coronary arteries. The increase in CRP observed with oral ERT also m a y contribute to the increase in CHD, because CRP has recently been identified as an i n f l a m m a t o r y risk factor for CHD in women, 3°,31 most likely because inflamm a t i o n plays a major role in atherosclerosis.

n a large retrospective case-control study, it was Iconcluded that estrogen augments clotting,

increasing the risk of thromboembolism if taken by mouth but not if used transdermally.

Alternatively, if you receive ERT through a skin patch, the estrogens are absorbed into systemic circulation, in a similar fashion to ovarian secretion. This difference in route of administration between oral and transdermal formulations m a y explain w h y no notable increases in thrombotic markers or decreases in antithrombin III and other anticlotting factors have been observed in w o m e n receiving transdermal ERT.

Is the WHI the last word on the value of HRT in cardiovascular protection? There are two ways of approaching the WHI results. One is to say, "All the previous trials were observational and thus biased. We n o w know that HRT is not cardioprotective because we have completed randomized, controlled, b l i n d e d trials, w h i c h is the gold standard m e t h o d in clinical study design, in a very large n u m b e r of women. The data are incontrovertible. Let's move on." On the other hand, if we accept this approach, t h e n we are stuck with a gigantic paradox. We have m a n y good reasons

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to believe that estrogens should protect against CHD, b o t h from biochemical determinations in small trials and from large observational studies. N o w the questions become, " W h y are the results from the WHI so different?"; " W h y the paradox?"; and "Are there critically important differences in the study designs that could explain the widely different conclusions?"

Differences in HRT Regimen The HRT regimens used in the WHI and observational studies were not very different. HRT consisted mainly of CEE alone or CEE in combination with MPA at similar doses. It is important to note, however, that the wealth of animal studies s h o w i n g cardioprotective effects of estrogens utilized 1713-estradiol, which is the major circulating estrogen in humans. Thus, this difference in HRT regimen m a y possibly contribute to the differences observed between the WHI and experimental studies.

Differences in Duration of Follow-Up In the observational studies, w o m e n were followed, on average, between 10 to 1S years; in fact, some w o m e n were followed for as long as 18 to 20 years. In contrast, the w o m e n in the WHI were not followed nearly as long. This is a potentially important difference. We know that CHD events begin to accelerate S to 10 years after the onset of menopause. It m a y take as much as S years for fatty streaks to form mature plaques. If HRT only prevents new plaque formation, then a w o m a n m a y need >S years to detect significant degrees of protection against heart disease events. The data for cumulative risk from the estrogenalone WHI trial are highly suggestive of a durationof-treatment effect because the ERT group's cumulative CHD rate appears to diverge from placebo as a function of time. W h e n you calculate the event rates year by year in this study (ie, the events in 1000 w o m e n per year) for the first 3 to 4 years, there is no difference between the ERT and placebo groups ( F i g u r e 3). However, if you pool the data from years 6 to 8+, in which there are 14,633 women-years and 71 events, the unadjusted hazard ratio during this late period is markedly reduced, with a value of 0.41 in the ERT

group. This analysis raises the possibility that the cardioprotective effects of HRT would become visible if the study had continued longer.

nalysis of lhehazard ratio in years 6 to 8+ of A the Women s Health Initiative estrogenalone trial raises file possibility lhat the cardioprotective effects of hormone replacement therapy would become visible if file study had continued longer.

Differences in Study Participant Age In most of the observational studies, w o m e n began to take ERT around the time of menopause, which is, on average, $1 years of age, because that is w h e n w o m e n typically receive prescriptions for ERT. They stop menstruating, have symptoms, and visit their doctors, w h o prescribe ERT In contrast, in the WHI h o r m o n e trials, w o m e n were, on average, 63 years of age, which is 12 years after the typical onset of menopause. Furthermore, the WHI was underpowered to assess the cardioprotective effects of HRT in w o m e n at the time of menopause because it studied relatively few w o m e n aged 4S to SS years. It is possible that the age of the population receiving ERT m a y be an important difference. In this regard, it is worth noting that the vast majority of cardiovascular studies of ERT are performed in animals that have not been exposed long term to an estrogen-deficient state, which m a y be significant, considering the mean age of w o m a n entering the WHI.

How could the timing of ERT be important in cardiovascular disease? To achieve primary prevention of atherosclerosis, it is imperative that fatty streaks are prevented from progressing over the years to form plaques, especially mature "at-risk" plaques. Many of the k n o w n effects of estrogens (eg, vasodilatation and maintenance of favorable lipid profiles) could potentially prevent or slow this progression ( F i g u r e 4). However, once a mature plaque is formed with a necrotic core

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n most observational studies, women started Iofestrogen replacement therapy around the time menopause (51 years of age), whereas in the Women's Heallh Initiative estrogen-alone study, women began taking estrogen at the mean age of 63 years.

and fibrous cap, there is infiltration by round cells, monocytes, and macrophages with inflammation, which t h e n fosters the breakdown of the fibrous cap by cell-derived metalloproteinases. Once the fibrous cap begins to break down, a clot can rapidly form, resulting in an adverse cardiovascular event. Thus, in the presence of mature plaques, estrogens m a y have adverse effects on the vasculature, because oral ERT increases the t e n d e n c y toward thrombosis. This is known as the timing hypothesis, 33 which raises a n u m b e r of questions: "Do a s y m p t o m a t i c

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w o m e n already have significant mature plaques by the time they are 5, 10, or more years after the onset of menopause?" and "Could subclinical atherosclerosis have a major impact on the cardiovascular effects of ERT?" Interestingly, based on a study of accumulation of coronary calcium in asymptomatic women, 34 it seems likely that -30% to 3S% of the w o m e n in the WHI trials had at-risk plaques in their arteries before they ever took the first dose of ERT.

Support for the Timing Hypothesis Additional support for the timing hypothesis comes from a series of primate studies undertaken by Tom Clarkson and colleagues. 35-37 Monkeys were fed a healthy diet up until the point of ovariectomy. Then they were divided into two ovariectomized groups and fed an atherogenic diet. One group received vehide while the other received ERT. The monkeys that received ERT had a 70% reduction in plaque area at the time of

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Vascular Biologist's Definition of Primary Prevention

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Figure 4. Atherosclerosis prevention/protection versus putative adverse effects of estrogens on coronary heart disease (CHD) events. (A) Progression of early atherosclerosis (fatty streak) lesions found most commonly in women at age of menopausal transition to mature plaque, with thickening of intima and media, and formation of fibrous cap, a process generally taking place over several years and hypothetically susceptible to slowing by beneficial effects of estrogen on lipid profile and vascular biology. (B) Further progression to "at-risk" plaque with necrotic zone and infiltrating inflammatory cells. Rapid (hours) progression to CHD event may occur when cells secrete matrix metalloproteinase-9 (MMP-9) (in response to estrogen?), leading to disruption of fibrous cap and exposure of thrombogenic plaque material to blood in arterial lumen, with clot formation assisted by oral estrogen-induced procoagulative state, resulting in coronary occlusion. Modified from a slide provided by TB Clarkson, DVM 263

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any of the known effects of estrogens (eg, asodilatation, favorable lipid profiles) could attenuate the progression of atherosclerosis. Under the conditions of mature plaque formation, however, estrogens may have adverse effects on the vasculature, because oral estrogen replacement therapy increases the tendency toward thrombosis. This is known as the timing hypothesis.

autopsy compared with the vehicle (control) group, indicating the cardioprotective effects of ERT. In a third group, the ovariectomized monkeys were treated with vehicle and provided with an atherogenic diet for the first 3 years, after which ERT was added and their diet was switched back to a healthy diet. The extent of plaque area was similar to the animals that never received ERT. This strongly suggests that no cardioprotective benefits of ERT occur after prolonged exposure to an estrogen-deficient state. The timing hypothesis is further supported b y the discrepancy between the cardioprotective effects observed in the NHS, in which the mean age of the population was 51 years, and the adverse cardiovascular effects observed in the HERS and WHI, in which the population had been exposed to an estrogen-deficient state for a mean of 12 and 16 years, respectively. W h e n age is considered in the WHI estrogen-alone study, the older the woman, the less beneficial effects she will receive from ERT. Similarly, in the WHI estrogen+progestin trial, time since m e n o p a u s e is associated with a worsening of cardiovascular disease risk in the treated versus placebo groups. If y o u construct, using linear regression, the best straight line connecting risk ratios for w o m e n <10, 10 to 19, and _>20 years since m e n o p a u s e and extrapolate that line to the time of menopause, there is approximately a 40% reduction in CHD risk in the HRT group c o m p a r e d with the placebo control group ( F i g u r e 5). Interestingly, this reduction in CHD is similar to what is observed in the NHS. In the WHI estrogen-alone trial (unopposed CEE in w o m e n w h o had had a hysterectomy), w o m e n were followed for about 1-1/2 to 2 years

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longer than in the estrogen+progestin study. The risk of stroke increased by 40%, and the risk of t h r o m b o e m b o l i c disease increased by 30%. There was no increase in breast cancer risk in the absence of MPA and, not surprisingly, fractures were reduced b y ~30%. Although no significant cardioprotective effects were observed overall, w h e n the data were stratified by age, a 44% reduction in CHD was observed in the 50to 59-year-old age group. Moreover, in this age group, there were no significant increases in stroke, t h r o m b o e m b o l i c disease, or breast cancer risk. These findings are further supported by Kaplan-Meier estimates of cumulative hazard from the WHI estrogen-alone study. 39 After year 3, the placebo group had a higher risk for CHD than did the ERT group in the youngest women. Additionally a m o n g the 50- to 59-year-old women, the risk of having to undergo coronary artery bypass grafting or angioplasty was reduced by half in the ERT group compared with the placebo group. In contrast, among the oldest w o m e n (aged 70-79 years), the risk of CHD was higher in the ERT group than in the placebo group, and there were no differences in the n u m b e r of w o m e n having to undergo coronary artery bypass grafting or angioplasty between groups. Taken together, these findings lend added support to the timing hypothesis.

he Kronos Early Estrogen Prevention Study

Treplacement (KEEPS) will test the hypothesis that hormone therapy will result in cardiovascular

protection because of a window of opportunity in early menopause.

H o w will the KEEPS trial address the WHI controversy? Given the continuing controversy over the interpretation of the WHI h o r m o n e trial results, a group of women's health investigators, including this author, developed the Kronos Early Estrogen Prevention Study (KEEPS) to test the hypothesis that HRT will result in cardiovascular protection because of a window of opportuni-

S . M Harman

Subgroup

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ty in early m e n o p a u s e . 4° W o m e n aged 42 to 58 years, at least 6 m o n t h s but n o m o r e t h a n 36 m o n t h s postmenopausal, a n d in good general h e a l t h with a n o r m a l m a m m o g r a m , will be studied. We do n o t h a v e the k i n d of b u d g e t or n u m bers t h a t will enable us to observe significant n u m b e r s of cardiovascular events, so we h a v e c h o s e n to assess atherosclerosis progression b y imaging. Our e n d p o i n t s are i n t i m a - m e d i a thickness of the carotid artery a n d c o r o n a r y artery c a l c i u m as i n d i c a t e d b y x - r a y t o m o g r a p h y ( T a b l e ) . A variety of risk factors i n c l u d i n g lipids, i n f l a m m a t o r y factors, c o a g u l a t i o n indicators, a n d h o r m o n e s will be m e a s u r e d over a follow-up period of 4 years. Of the 720 w o m e n r a n d o m ized, we anticipate t h a t 450 will c o m p l e t e the study. We will also c o m p a r e HRT regimens b y e x a m i n i n g CEE 0.45 m g h e a d - t o - h e a d w i t h t r a n s d e r m a l 17]3-estradiol 0.05 mg. W o m e n will be r a n d o m i z e d to o n e or t h e o t h e r estrogen or to placebo. We will be using a progestin, b u t n o t MPA. Because a " n a t u r a l " m i c r o n i z e d progester o n e will be a d m i n i s t e r e d orally 12 clays a m o n t h , the w o m e n will cycle. This is a n o t h e r i m p o r t a n t difference b e t w e e n the WHI a n d our study. We believe cyclic exposure to progester o n e will be safer t h a n a c o n s t a n t progestin regimen. To date, we h a v e 314 w o m e n r a n d o m i z e d a n d >300 in active screening. Our h o p e is t h a t KEEPS will shed f u r t h e r light o n the c o n t r o v e r s y s u r r o u n d i n g t h e cardiovascular effects of HRT, as well as fuel n e w research studies t h a t will m o r e closely e x a m i n e this crucial h e a l t h question.

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Chartbook. Hyattsville, Md: National Center for Health Statistics; 2001:189,192. 4. Ries LA, Eisner MP, Kosary CL, et al, eds. SEER Cancer Statistics Review, 1973-1998. Bethesda, Md: National Cancer Institute; 2001. 5. Hodis HN, Mack WJ, Lobo R. Postmenopausal hormone replacement therapy as antiatherosclerotic therapy. Curr Atheroscler Rep. 2002;4:52-58. 6. Darling GM, Johns JA, McCloud PI, Davis SR. Estrogen and progestin compared with simvastatin for hypercholesterolemia in postmenopausal women. N Engl J Med. 1997;337:595-601. 7. Wakatsuki A, Okatani Y, Ikenoue N, Fukaya T. Effect of medroxyprogesterone acetate on endotheliumdependent vasodilation in postmenopausal women receiving estrogen. Circulation. 2001;104: 17731778. 8. Stampfer MJ, Willett WC, Colditz GA, et al. A prospective study of postmenopausal estrogen therapy and coronary heart disease. N Engl J Med. 1985;313:1044-1049. 9. Wilson PW, Garrison RJ, Castelli WP. Postmenopausal estrogen use, cigarette smoking, and cardiovascular morbidity in women over 50. The Framingham Study. N Engl JMed. 1985;313: 10381043. 10. Bush TL, Barrett-Connor E, Cowan LD, et al. Cardiovascular mortality and noncontraceptive use of estrogen in women: Results from the Lipid Research Clinics Program Follow-up Study. Circulation. 1987;75:1102-1109. 11. Petitti DB, Perlman JA, Sidney S. Noncontraceprive estrogens and mortality: Long-term followup of women in the Walnut Creek Study. Obstet Gynecol. 1987;70:289-293. 12. Boysen G, Nyboe J, Appleyard M, et al. Stroke incidence and risk factors for stroke in Copenhagen, Denmark. Stroke. 1988; 19:1345-1353. 13. Criqui MH, Suarez L, Barrett-Connor E, et al. Postmenopausal estrogen use and mortality. Results from a prospective study in a defined, homogeneous community. Am J Epidemiol. 1988; 128:606-614. 14. Henderson BE, Paganini-Hill A, Ross RK. Estrogen replacement therapy and protection from acute myocardial infarction [published correction appears in Am l Obstet Gynecol. 1988;159:1574]. Am J Obstet Gynecol. 1988;159:312-317.

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25. Grodstein F, Manson JE, Colditz GA, et al. A prospective, observational study of postlnenopausal hormone therapy and primary prevention of cardiovascular disease. Ann Intern Med. 2000; 133:933-941. 26. Grodstein F, Stalnpfer MJ, Colditz GA, et al. Postlnenopausal hormone therapy and mortality. N Engl JMed. 1997;336:1769-1775. 27. Hulley S, Grady D, Bush T, et al, for the Heart and Estrogen/progestin Replacement Study (HERS) Research Group. Randomized trial of estrogen plus progestin for secondary prevention of coronary heart disease in postlnenopausal women. JAMA. 1998;280:605-613. 28. US Food and Drug Administration. FDA Fact Sheet. FDA approves new labeling and provides new advice to postmenopausal women who use or who are considering using estrogen and estrogen with progestin. January 8, 2003. Available at: http://www, fda.gov/oc/factsheets/WHI.htlnl. 29. Scarabin PY, Oger E, Plu-Bureau G, for the EStrogen and THronlboEinbolisnl Risk Study Group. Differential association of oral and transderinal oestrogen-replacelnent therapy with venous thronlboenlbolisln risk. Lancet. 2003;362:428-432. 30. Pal JK, Pischon T, MaJ, et al. Inflammatory markers and the risk of coronary heart disease in men and women. N Engl J Med. 2004;351:2599-2610. 31. Hu P, Greendale GA, Palla SL, et al. The effects of hormone therapy on the markers of inflammation and endothelial function and plasma matrix inetalloproteinase-9 level in postlnenopausal women: The postlnenopausal estrogen progestin intervention (PEPI) trial. Atherosclerosis. 2006; 185: 347-352. 32. Anderson GL, Lilnacher M, Assaf AR, et al, for the Women's Health Initiative Steering Committee. Effects of conjugated equine estrogen in postmenopausal w o m e n with hysterectomy: The Women's Health Initiative randomized controlled trial. JAMA. 2004;291:1701-1712. 33. Mendelsohn ME, Karas RH. Molecular and cellular basis of cardiovascular gender differences. Science. 2005;308:1583-1587. 34. Raggi P, Callister TO,, Cooil B, et al. Identification of patients at increased risk of first unheralded acute myocardial infarction by electron-bealn computed tolnography. Circulation. 2000;101:850-855.

S.M. Harman

35. Clarkson TB, Anthony MS, Jerome CR Lack of effect of raloxifene on coronary artery atherosclerosis of postrnenopausal monkeys. ] Clin Endocrinol Netab. 1998;83:721-726. 36. Adams MR, Register TC, Golden DL, et al. Medroxyprogesterone acetate antagonizes inhibitory effects of conjugated equine estrogens on coronary artery atherosclerosis. Arterioscler Thromb Vasc Biol. 1997;17:217-221. 37. Williams JK, Anthony MS, Honore EK, et al. Regression of atherosclerosis in female monkeys. Arterioscler Thromb Vasc Biol. 1995;15:827836.

38. Manson JE, Hsia J, Johnson KC, et al, for the Women's Health Initiative Investigators. Estrogen plus progestin and the risk of coronary heart disease. N Engl J Ned. 2003;349:523-534. 39. Hsia J, Langer RD, Manson JE, et al, for the Women's Health Initiative Investigators. Conjugated equine estrogens and coronary heart disease: The Women's Health Initiative [published correction appears in Arch Intern Ned. 2006;166: 759]. Arch Intern Ned. 2006;166:357-365. 40. Kronos Longevity Research Institute. The Kronos Early Estrogen Prevention Study (KEEPS). Available at: http://www.keepsstudy.org/.

Address c o r r e s p o n d e n c e to: M i t c h H a r m a n , MD, PhD, Kronos L o n g e v i t y Research Institute, 2390 E. C a m e l b a c k , Suite 440, Phoenix, AZ 85016. Email: m i t c h ' h a r m a n @ k r ° n ° s i n s t i t u t e ' ° r g

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