Effect of raloxifene on aortic elasticity in healthy postmenopausal women

Effect of raloxifene on aortic elasticity in healthy postmenopausal women Nicholas A. Tritos, MD, DSc,b Lois Goepfert, RN,a Kraig V. Kissinger, RT (MR),a George Katsimaglis, MD,a Warren J. Manning, MD,a,c and Peter G. Danias, MD, PhDa Boston, MA

Background The effect of raloxifene on aortic elasticity in healthy postmenopausal women is unknown. The purpose of the present study was to examine the effect of raloxifene on aortic elasticity and cardiovascular structure and function in healthy postmenopausal women. Methods A randomized, crossover, double-blind, placebo-controlled clinical trial was performed. Fourteen healthy postmenopausal women received treatment with raloxifene 60 mg daily and matching placebo for 8 weeks with an 8-week washout period in between the 2 treatment periods. Cardiovascular magnetic resonance imaging was used to assess ascending thoracic and abdominal aortic elasticity and cardiovascular structure and function (left ventricular volumes, ejection fraction, and mass and mitral annular displacement) before and at the end of each treatment period. Results

Administration of raloxifene had no significant effect on either heart rate or systemic blood pressure. Raloxifene treatment was associated with a small decrease of the ascending aorta wall thickness (pretreatment 2.4 F 0.3 vs posttreatment 2.2 F 0.2 mm, P = .01). Consequently, there was an increase in the Young’s elastic modulus after raloxifene treatment at the ascending thoracic aorta but not the abdominal aorta. There were no significant differences in aortic compliance or any cardiac indexes after raloxifene treatment.

Conclusions Raloxifene administration in healthy postmenopausal women over an 8-week period may decrease the aortic wall thickness but has no significant effects on aortic compliance or cardiac structure and function. (Am Heart J 2005;150:1212.e1- 1212.e6.) Although hormone replacement therapy in postmenopausal women does not decrease cardiovascular disease risk, estrogens have favorable vascular effects, in part by increasing arterial and arteriolar compliance.1-5 Raloxifene is a nonsteroidal selective estrogen receptor modulator used for prevention and treatment of osteoporosis.6,7 In a small study, raloxifene administration led to increased brachial artery diameter in postmenopausal women.8 Raloxifene has also been shown to increase plasma nitric oxide levels, decrease plasma endothelin-1 levels, and improve flow-mediated vasodilation.9 However, the effects of raloxifene in larger arteries in humans are unknown. Besides having direct vascular effects, raloxifene decreases both plasma cholesterol levels and cholesterol deposition in the aortic wall of experimental animals.10 In postmenopausal women, raloxifene administration From the aCardiovascular Division, bDivision of Endocrinology, and cDepartments of Medicine and Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA. Submitted November 17, 2004; accepted February 16, 2005. Reprint requests: Peter G. Danias, MD, PhD, Beth Israel Deaconess Medical Center, 330 Brookline Avenue, Boston, MA 02215. E-mail: [email protected] 0002-8703/$ - see front matter n 2005, Mosby, Inc. All rights reserved. doi:10.1016/j.ahj.2005.02.020

leads to a decrease in total and low-density lipoprotein serum cholesterol, as well as a decrease in serum fibrinogen, lipoprotein (a), and homocysteine.11-13 We hypothesized that administration of raloxifene may improve aortic elasticity in postmenopausal women and sought to characterize the effects of raloxifene administration on cardiac structure and function. Cardiovascular magnetic resonance (CMR) imaging can most accurately measure small changes in the aortic lumen crosssectional area with very high spatial and temporal resolution and thus is uniquely suited for the evaluation of the elastic properties of large arteries.14,15

Methods Study protocol The study was a randomized, crossover, double-blind, placebo-controlled clinical trial evaluating aortic elasticity in 18 postmenopausal women who were allocated to receive either raloxifene 60 mg daily or matching placebo for 8 weeks (F3 days). The study was reviewed and approved by the hospital committee on clinical investigation and all subjects provided written informed consent before participation. Subjects had a CMR study of the thoracic and abdominal aorta to determine aortic elasticity before initiation of any treatment and after each treatment period. Thus, each participating subject underwent 4 CMR examinations on 4 different days

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(within 6 months) at the same time of the day, before and after therapy with either raloxifene or placebo. An 8-week (F3 days) washout period was introduced between the first and second treatment periods, both in subjects randomized to raloxifene followed by placebo and in those allocated to placebo followed by raloxifene. All CMR studies were performed at 8:00 am to avoid possible diurnal influence on aortic elasticity.16 Subjects were also asked to avoid any alcoholic or caffeine-containing beverages for at least 24 hours before the CMR study.

Subjects Eighteen healthy postmenopausal women (at least 1 year after last menstrual period) who had not received hormone replacement therapy for at least 6 months before participation were enrolled. Subjects were excluded from participation if they had any one of the following: cardiac illnesses sufficiently severe to affect aortic elasticity (including moderate or severe valvular heart disease, prosthetic heart valves, congestive heart failure, or history of myocardial infarction); significant systemic illness (including renal insufficiency, nephrotic syndrome, hepatic insufficiency, malignancies, diabetes mellitus, or hypertension); current smoking; use of cardiovascular medications or any hormone therapy; history of prior thromboembolism; or contraindication to CMR (due to electronic pacemakers/defibrillators, metal ocular or cochlear implants, surgical vascular or neurosurgery clips, arrhythmia, or claustrophobia). All interested subjects were screened before participation and a 12-lead electrocardiogram, serum chemistries including electrolytes, urea nitrogen, creatinine, glucose, liver function tests (serum aspartate aminotransferase and alanine aminotransferase), and a complete blood count were obtained. Subjects with significant abnormalities in any of these screening tests were excluded from participation. All subjects were asked to return all study medication bottles with any remaining study medication, and pill counts were obtained to assess compliance.

Imaging protocol Cardiovascular magnetic resonance imaging studies were performed using a 1.5-T whole-body scanner (Gyroscan NT/ACS, Philips Medical Systems, Best, The Netherlands) equipped with advanced cardiac software and enhanced gradient hardware (Powertrack 6000, Philips Medical Systems). A 5-element phase array coil was used as the radio frequency receiver for imaging of the thoracic aorta and the body coil was used for imaging of the abdominal aorta. After initial scout images to identify the heart, aorta, and kidneys, oblique transverse images were obtained perpendicular to the long axis of the aorta at the sinotubular junction of the ascending thoracic aorta and immediately cephalad to the renal arteries (abdominal aorta). Imaging was performed using a fast steady-state free precession imaging sequence with the following imaging parameters: field of view 400
400 mm, matrix 224
256, echo time (TE) = 1.6 milliseconds, repetition time (TR) = 3.2 milliseconds, flip angle of 608, and slice thickness of 10 mm. With this sequence, an in-plane spatial resolution of 1.8
1.8 mm was obtained with a temporal resolution of 30 phases per cardiac cycle. At both ascending thoracic and abdominal aortas, phase-contrast scans were also obtained using a retrospectively electrocardiogram-gated sequence with the following imaging parameters: field of view

210
300 mm, matrix 96
128, TE = 6.5 milliseconds, TR = 15 milliseconds, flip angle of 308, and slice thickness of 6 mm, velocity encoding set at 300 cm/s. A fast-field echo scan was also obtained at the same levels using the following parameters: field of view 384
384 mm, matrix 192
256, TE = 1.8 milliseconds, TR = 20 milliseconds, flip angle of 308, and slice thickness of 8 mm. Finally, to determine aortic wall thickness, a high-resolution black blood image was obtained at the ascending thoracic aorta using a turbo spin-echo sequence with a dual inversion pulse with the following parameters: field of view 320
400 mm, matrix 336
512, TE = 20 milliseconds, TR equal to the R-R interval in milliseconds, turbo spin echo factor = 12, flip angle of 908, and slice thickness of 6 mm. For the steady-state free precession and turbo spin-echo images, we used breath holding to minimize respiratory motion artifacts (breath-hold duration of 10-12 seconds). For the fast-field echo and phasecontrast sequences, respiratory motion compensation was accomplished by measuring multiple signal averages (number of signal averages = 4). During the examination, blood pressure was noninvasively measured using an automated sphygmomanometer (Dinamap, GE Medical Systems, Madison, Wis), with the cuff placed at the calf. At least 5 measurements were obtained during the magnetic resonance examination. The 2 extreme values were disregarded and the mean of the remaining values was used as the systolic and diastolic blood pressure in measurements of vascular elasticity.

Data analysis Image analysis was performed off-line at a dedicated analysis workstation (EasyVision 5, Philips Medical Systems) by an observer blinded to subject identity and treatment allocation. To minimize interobserver variation, a single observer used the semiautomated software to trace the contour of the aorta at the ascending aorta and abdominal levels for all phases, including the phase-contrast, steady-state free precession, and fast-field echo scans. The area within each contour (representing the cross-sectional area of the aorta) was calculated, and the maximal and minimal aortic diameter/area were determined and used in the calculations of aortic elasticity. A single observer also measured the aortic wall thickness by manually taking 3 measurements about the aortic circumference. The mean value was used for the data analysis.

Aortic elasticity We assessed vascular elasticity with the following parameters: Arterial compliance. Arterial compliance (AC) is defined as the absolute volume increase within an arterial segment during the cardiac cycle divided by the arterial pulse pressure. The AC per unit length (1 mm) is

  AC ¼ p D2s  D2d =f4½Ps  Pd g where D s and D d are the systolic and diastolic diameters of the artery and P s and P d are the systolic and diastolic blood pressures, respectively. Arterial compliance is measured in mm2/kPa (1 kPa = 7.6 mm Hg). Stiffness index. Stiffness index (SI) is defined as the natural logarithm of the ratio of systolic to diastolic blood pressure divided by the circumferential arterial strain (CAS), which is the

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Table I. Demographic characteristics of the study population Age (y) Height (m) Weight (kg) Body surface area (m2) Body mass index (kg/m2) Ethnic background White Black Hispanic Asian Other

57 F 10 1.5 F 0.1 67 F 21 1.6 F 0.3 25.5 F 6.2 11 (79) 2 (14) 0 1 (7) 0

Values are presented as mean F SD or n (%), as appropriate.

fractional increase in arterial diameter during the cardiac cycle. Thus, SI is a unitless quantity and considered to be relatively independent of blood pressure:

SI ¼ ln½Ps =Pd =CAS

;

where

CAS ¼ ½Ds  Dd =Dd

Pressure-strain elastic modulus. Pressure-strain elastic modulus (E p) is defined as the arterial pulse pressure divided by the CAS

Ep ¼ ½Ps  Pd =CAS and is measured in kPa. Young’s elastic modulus. Young’s elastic modulus (YEM) is defined as the ratio of stress (force per unit area) to strain and measures arterial stiffness controlling for vessel wall thickness:

YEM ¼ ðR=WT ÞfðPs  Pd =CAS g where R is the outer arterial radius and WT is the wall thickness (intima plus media). Young’s elastic modulus is measured in kPa. Left ventricular endocardial contours for end-diastolic and end-systolic short-axis images and epicardial contours at the end-diastolic images were manually traced by a single experienced observer blinded to subject identity and treatment allocation. Volumetric assessment of mass, end-diastolic and end-systolic volumes, ejection fraction, stroke volume, and cardiac output were derived for the left ventricle. Mitral annular displacement was measured from single-slice 4-chamber and 2-chamber views at end diastole and end systole by measuring the in-plane systolic displacement of the septal and lateral wall (4-chamber view) and anterior and inferior (2-chamber view) mitral annulus.

Statistical analysis Sample size calculations suggested that a sample size of 14 subjects would provide 90% power to detect a 15% difference in aortic elasticity between the raloxifene and placebo treatments using paired t test analysis with the significance level set at .05. We recruited 18 subjects to account for an expected 20% attrition rate. Statistical analysis was performed using the SPSS software version 10.0 (SPSS Inc, Chicago, Ill) on a personal computer. Paired t test was used to compare differences in aortic elasticity pretreatment and posttreatment between the raloxifene and

Table II. Systemic blood pressure and heart rate before and after treatment with placebo and raloxifene Systolic Diastolic blood pressure blood pressure (mm Hg) (mm Hg) Preplacebo Postplacebo Preraloxifene Postraloxifene

136 136 134 135

F F F F

Heart rate (beat/min)

21 P = NS 58 F 12 P = NS 66 F 10 P = NS 18 59 F 10 63 F 8 17 P = NS 58 F 7 P = NS 63 F 6 P = NS 18 57 F 8 63 F 6

placebo groups. All comparisons were 2-tailed and a P value of b.05 was considered as statistically significant.

Results Eighteen subjects signed informed consent. However, 1 subject had blood chemistry abnormalities that precluded her from participating, and 2 withdrew before any imaging was performed. One subject participated only in the first treatment period and had only 2 (pretreatment and posttreatment) magnetic resonance imaging examinations. Fourteen subjects successfully completed the entire study protocol and were included in the analysis. The demographic characteristics of the study population are shown in Table I. Subjects tolerated both raloxifene and placebo well. Only 1 subject reported mild vaginal spotting during the treatment with raloxifene, but she regarded this as a mild side effect and continued participating after consulting her gynecologist. Compliance with both treatment regimens was excellent with 92% of treatment periods having V5 difference between the actual number of pills returned and those expected. Treatment with raloxifene had no significant effect on heart rate and systolic or diastolic arterial blood pressure (Table II). There were no significant differences between the pretreatment and posttreatment measurements for both placebo and raloxifene treatments ( P = NS for all comparisons). Analysis of the measured values of the aortic crosssectional areas, wall thickness, and indexes of aortic elasticity of the ascending thoracic and abdominal levels are presented in Table III. After raloxifene treatment, the aortic wall thickness was slightly decreased compared with pretreatment (posttreatment 2.2 F 0.2 vs pretreatment 2.4 F 0.3 mm, P = .01). Accordingly, YEM, which is dependent on vessel wall thickness, was significantly higher in the postraloxifene versus preraloxifene images (postraloxifene 92 F 39 vs preraloxifene 69 F 36, P = .04). There were no other significant differences in any of the measured elasticity indices or cross-sectional areas between the preraloxifene and postraloxifene or placebo images. Treatment with raloxifene had no effect on cardiac structure and function. Left ventricular end-diastolic

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Table III. Differences in aortic dimensions and elasticity measures before and after the 8-week treatment (raloxifene or placebo) based on the measured (actual) maximal and minimal aortic cross-sectional areas calculated from the phase-contrast scans Preplacebo Ascending thoracic aorta Maximal cross-sectional area (mm2) Minimal cross-sectional area (mm2) Wall thickness (mm) AC (mm2 kPa1 mm1)
103 SI E p (kPa) YEM Abdominal aorta Maximal cross-sectional area (mm2) Minimal cross-sectional area (mm2) AC (mm2 kPa1 mm1)
103 SI E p (kPa) YEM

7.7 6.3 2.4 2.7 9.7 118 75

F 1.1 F 1.0 F 0.2 F 2.1 F 4.3 F 54 F 37

2.8 2.0 1.4 5.0 59 22

F F F F F F

0.5 0.4 0.6 2.1 20 9

Postplacebo

126 124 124 126

F F F F

37 32 31 36

45 44 41 46

F F F F

23 13 14 22

0.65 0.64 0.67 0.65

F F F F

0.07 0.05 0.07 0.06

95 97 93 95

F F F F

26 31 31 33

Preraloxifene

7.8 F 1.3 6.6 F 1.0 2.4 F 0.3 2.2 F 1.5 12 F 5.7 145 F 68 95 F 49

NS NS NS NS NS NS NS

7.8 F 1.3 6.4 F 1 2.4 F 0.3 2.7 F 1.7 9.2 F 4.0 111 F 54 69 F 36

2.8 2.0 1.5 4.6 56 21

NS NS NS NS NS NS

2.9 2.0 1.5 5.3 63 23

F F F F F F

Table IV. Left ventricular volumes, ejection fraction, and mass before and after treatment with placebo and raloxifene End-diastolic volume (mL) Preplacebo Postplacebo Preraloxifene Postraloxifene End-systolic volume (mL) Preplacebo Postplacebo Preraloxifene Postraloxifene Ejection fraction Preplacebo Postplacebo Preraloxifene Postraloxifene Mass (g) Preplacebo Postplacebo Preraloxifene Postraloxifene

P

P = NS P = NS

P = NS P = NS

P = NS P = NS

P = NS P = NS

volume, end-systolic volume, ejection fraction, and mass were identical in the pre– versus post–placebo and raloxifene treatments (Table IV). The mitral valve annular displacement was also similar in the preraloxifene versus postraloxifene treatments (data not shown).

Discussion Vascular and aortic elasticity may serve as early markers of atherosclerosis and have been shown to be abnormal in patients with coronary artery17,18 or peripheral vascular disease,19 as well as in those with risk factors for coronary disease, including hypertension,20-23 smoking,24 and diabetes mellitus,20,21 as well as in diseases that are

0.5 0.5 0.6 1.5 20 9

F F F F F F

0.7 0.4 0.9 3.1 37 15

Postraloxifene

P

7.9 F 1.2 6.6 F 1.0 2.2 F 0.2 2.3 F 1.4 11.1 F 5.2 134 F 61 92 F 40

NS NS .01 NS NS NS .04

2.8 F 0.5 2.0 F 0.5 1.4 F 0.5 5.0 F 2.5 60 F 29 24 F 12

NS NS NS NS NS NS

associated with high prevalence of vascular disease such as chronic renal failure.25 In the current study, we sought to assess the effect or raloxifene on aortic elasticity in healthy postmenopausal women and found a small but significant decrease in the wall thickness and an increase in YEM of the ascending thoracic aorta with an 8-week treatment. We found no effect on systemic arterial blood pressure and indexes of left ventricular structure and function and no effect on most indexes of aortic elasticity. These findings suggest that short-term raloxifene treatment likely has no major effect on cardiac structure and function but may affect large vessel wall thickness. The lack of adverse effects of raloxifene administration on cardiovascular structure and function in postmenopausal women is of particular importance in view of the adverse effects of estrogenprogestin replacement therapy on cardiovascular morbidity in the Women’s Health Initiative study.26 Selective estrogen receptor modulators, including raloxifene, have been suggested to have favorable cardiovascular effects in experimental models by decreasing lipid deposition in the aortic wall in experimental models of vascular injury and atherosclerosis.10,27-29 Raloxifene may both exert an antiproliferative effect and induce apoptosis in vascular smooth muscle cells in vitro.30,31 To date, there are no data in humans to suggest that a similar effect may occur either in patients with atherosclerosis or in healthy individuals. Although we cannot completely exclude the possibility of a spurious difference because of multiple comparisons, the possibility of a short-term direct effect of raloxifene on large vessel wall thickness is quite intriguing. In a blinded analysis, small inaccuracies of the measuring technique would tend to attenuate, rather than falsely increase, a measurement difference and thus should not be

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considered as a possible explanation in this study. Although the effect of raloxifene on cardiovascular morbidity and mortality in humans is unknown, current data suggest favorable effects on serum lipoproteins, coagulation markers, and endothelial function.7-9,11-13 In addition to exerting direct hepatic effects, raloxifene has direct actions on vascular endothelium and smooth muscle.8,9 Our study did not include investigation of any biochemical or hematologic parameters possibly associated with raloxifene administration, including serum lipid profiles, and therefore, we cannot provide any mechanistic explanations. Such data should be obtained in future studies that should also serve to confirm our findings. The elastic properties of large arteries are determined by several factors, including smooth muscle hypertrophy and tone, matrix collagen deposition, vascular wall elastin-collagen ratio, and glycosaminoglycan content.32,33 Previous studies have suggested that hormone replacement therapy may improve the elastic properties of large and medium arteries, although this finding has not been demonstrated in all studies.1-5,34-39 In addition, progesterone administration has shown no demonstrated effect on arterial elasticity.40 To our knowledge, there are no published data in humans assessing the effect of raloxifene or other selective estrogen receptor modulators on aortic structure or elastic properties. Our findings suggest a lack of significant effect of raloxifene administration on aortic elasticity in healthy postmenopausal women when administered for 2 months at the currently approved dose for prevention and therapy for osteoporosis. Our study cannot exclude an effect on aortic elasticity of a higher raloxifene dose or longer treatment duration. As our study had adequate power to detect a 15% difference in indexes of aortic elasticity between raloxifene and placebo treatment periods, it cannot exclude a smaller treatment effect. In addition, we did not examine the effects of raloxifene on the elastic properties of small- and medium-sized arteries. However, the lack of any effect on any of the hemodynamic parameters assessed (heart rate and blood pressure) makes it less likely that raloxifene would have any significant effect on functional parameters of the cardiovascular system after a 2-month administration. In conclusion, our findings suggest that raloxifene administration in healthy postmenopausal women at the currently approved dose for prevention and therapy for osteoporosis over a 2-month period may decrease the aortic wall thickness but has no significant effects on aortic compliance, cardiac structure and function, heart rate, or systemic blood pressure. This study was supported by a grant from Eli Lilly and Co and in part by grant RR 01032 to the Beth Israel Deaconess Medical Center General Clinical Research Center from the National Institutes of Health.We thank

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the staff of the General Clinical Research Center of the Beth Israel Deaconess Medical Center for their excellent care of the participating subjects.

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