This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Williams, J. K. Articles by Adams, M. R. Search for Related Content PubMed PubMed Citation Articles by Williams, J. K. Articles by Adams, M. R.

(Arteriosclerosis, Thrombosis, and Vascular Biology. 1997;17:403-408.)
© 1997 American Heart Association, Inc.

Articles

Tamoxifen Inhibits Arterial Accumulation of LDL Degradation Products and Progression of Coronary Artery Atherosclerosis in Monkeys

J. Koudy Williams; Janice D. Wagner; Zhang Li; Deborah L. Golden; Michael R. Adams

the Comparative Medicine Clinical Research Center, Bowman Gray School of Medicine of Wake Forest University, Winston-Salem, NC.

Correspondence to J. Koudy Williams, DVM, Department of Comparative Medicine, Bowman Gray School of Medicine, Medical Center Blvd, Winston-Salem, NC 27157-1040.

	Abstract

Top Abstract Introduction Methods Results Discussion References

 
Estrogen replacement therapy reduces the risk of coronary heart disease in postmenopausal women and inhibits progression of coronary artery atherosclerosis in monkeys. Tamoxifen is a nonsteroidal compound with mixed estrogen agonist and antagonist properties. Its antagonist activity is useful in chemotherapy of breast cancer and may have protective effects on plasma lipid concentrations, but its effects on atherogenesis have not been defined. The goal of this study was to examine the effect of tamoxifen on plasma lipids, arterial and hepatic LDL metabolism, and progression of coronary artery atherosclerosis in surgically postmenopausal female monkeys. Thirty-five monkeys were fed an atherogenic diet containing 1.3 mg·kg^-1·d^-1 tamoxifen (equivalent to the usual dose of 20 mg/d given to women). Thirty-one monkeys were fed the same atherogenic diet with no tamoxifen. Ten monkeys from each treatment group were fed the test diets for 12 weeks to examine the short-term effects of tamoxifen on arterial LDL metabolism. The rest of the monkeys were fed the test diets for 3 years to study the long-term effects of tamoxifen on development of atherosclerosis. In the short term, tamoxifen inhibited the rate of arterial accumulation of LDL degradation products overall (P=.03) and decreased hepatic cholesterol content (P=.003). In the long term, tamoxifen increased plasma concentrations of triglycerides (0.60±0.67 versus 0.23±0.02 mmol/L, P=.001) and reduced average LDL molecular weight (5.3±0.2 versus 4.8±0.1 g/µmol, P=.004) but had no effects on plasma total, LDL, or HDL cholesterol concentrations. Coronary artery atherosclerosis (intimal area, mean±SEM) was 0.25±0.06 mm² in control monkeys and 0.12±0.03 mm² in tamoxifen-treated monkeys (P=.057). We conclude that tamoxifen has antiatherogenic effects that may be modulated in part through direct effects on arterial LDL metabolism.

Key Words: atherosclerosis • cynomolgus monkeys • females • lipids • LDL cholesterol • tamoxifen

	Introduction

Top Abstract Introduction Methods Results Discussion References

 
There is increased interest in the effects of tissue-selective estrogens on disease prevention. Tamoxifen is a mixed estrogen receptor agonist/antagonist that, because of its estrogen antagonist activity, is useful in the treatment of breast cancer. Tamoxifen reduces recurrence and the risk of new primary cancer developing in the contralateral breast by 40%.^{1 2} The possibility of using tamoxifen to prevent development of breast cancer in women with a family history of the disease is being considered^{3 4} but must be weighed along with recent evidence that tamoxifen increases the risk of endometrial cancer, suggesting that tamoxifen has estrogenic properties at other tissue sites.^{5 6}

Data from studies of postmenopausal women with breast cancer indicate that tamoxifen may reduce the risk of cardiovascular disease.⁷ These data suggest that tamoxifen functions primarily as an estrogen agonist in the cardiovascular system. However, the effects of tamoxifen on plasma lipids and lipoproteins are inconsistent and are based almost entirely on studies in women with breast cancer.^{8 9 10 11 12} Because cardiovascular disease is the most common cause of death in postmenopausal women,¹³ the effect of tamoxifen on cardiovascular disease is central to the risk-benefit analysis of the use of estrogen agonist/antagonists in women. Thus, there is a need to clearly define the impact of tamoxifen on cardiovascular risk factors and progression of atherosclerotic disease.

The effects of tamoxifen on plasma lipids are difficult to study in a human population because of confounding risk factors (eg, breast cancer, hypertension, dietary changes, smoking, and stress). Furthermore, it is difficult and often impractical or unethical to measure direct effects of treatments, such as tamoxifen, on atherogenesis. Therefore, a well-characterized monkey model of atherosclerosis was used to examine the effects of tamoxifen on plasma lipid profiles, arterial LDL metabolism, and subsequent development of coronary artery atherosclerosis.

	Methods

Top Abstract Introduction Methods Results Discussion References

 
Subjects
Seventy adult female cynomolgus macaques (Macaca fascicularis) were imported from Indonesia (Institut Pertanian Bogor) and fed monkey chow (High Protein Monkey Chow, Ralston Purina Co) during a 3-month quarantine period. The monkeys were then fed a moderately atherogenic diet containing 0.28 mg cholesterol per calorie with 40% of calories from fat¹⁴ for a 1-month dietary challenge to stratify animals into four groups with similar TPC and HDL-C concentrations. After the challenge period, the animals were again fed monkey chow until the treatment part of the study began.

One monkey from each group was ovariectomized and then started the treatment part of the study, during which the monkeys were fed the same atherogenic diet as during the challenge period with either no treatment (postmenopausal controls) or tamoxifen (Nolvadex, ICI Pharma) at a dose of 1.3 mg/d, which is equivalent to the usual human dose of 20 mg/d. Monkeys were fed the atherogenic diet with or without hormone treatment for 12 weeks (n=10 monkeys per group, short-term experiments) or 34 months (n=25 monkeys per group, long-term experiments). Monkeys were housed in social groups of four until 1 week before the study began. Four animals from the long-term control group died of causes unrelated to their treatment, leaving 21 monkeys in that treatment group and a total of 66 monkeys in the study.

Femoral catheterizations and ovariectomies were done while the animals were anesthetized with ketamine hydrochloride (10 mg/kg body wt) and butorphanol (0.05 mg/kg body wt), and blood sampling and body measurements were obtained while animals were sedated with ketamine hydrochloride (10 to 15 mg/kg body wt). All procedures involving animals were conducted in compliance with state and federal laws, standards of the Department of Health and Human Services, and guidelines established by the Institutional Animal Care and Use Committee.

Plasma Lipids and Tamoxifen Concentrations
Blood samples were taken from tranquilized monkeys after an overnight fast at weeks 3 and 4 of the dietary challenge and (1) at weeks 4, 7, and 11 of the experimental period during the short-term studies or (2) at 3-month intervals during the long-term study for determinations of TPC,¹⁵ triglycerides,¹⁶ and HDL-C.¹⁷ Plasma LDL-C concentrations were determined by ultracentrifugation (to separate the LDL-C fraction) and high-performance liquid chromatography¹⁸ and then quantified.¹⁹ Average molecular weight of the LDL-C fraction was determined at week 9 by including a trace amount of iodinated LDL of known molecular weight.²⁰ Plasma concentrations of tamoxifen metabolites were measured by methods described previously.²¹ Data reported here for short-term and long-term studies are the mean of all values during the treatment phase of the experiment.

Short-term Studies
Arterial LDL Metabolism
Forty-eight hours before necropsy, radiolabeled LDL was injected intravenously as described below. Whole-body LDL FCR and arterial and hepatic LDL degradation rates, amount of undegraded LDL, and total accumulation of LDL degradation products were then determined (see below).^{22 23}

LDL particles for labeling and reinjection were isolated from pooled blood obtained from a group of ovariectomized female monkeys consuming the same atherogenic diet. Blood was collected in tubes containing aprotinin and D-phenylalanyl-L-prolylarginine chloromethyl ketone (PPACK) at final concentrations of 25 kallikrein inhibitory units/mL and 1 µmol/L, respectively, to limit degradation of apolipoprotein B by proteolysis and 1 mg/mL Na₂EDTA to prevent oxidation. The serine protease inhibitor phenylmethylsulfonyl fluoride and the antioxidant butylated hydroxytoluene were added to isolated plasma at final concentrations of 0.5 and 0.5 mmol/L, respectively.

The LDL (1.020 to 1.063 g/mL) was isolated by differential ultracentrifugation followed by exhaustive dialysis against buffer (0.9% NaCl/0.01% EDTA, pH 7.4). LDL protein was determined with BSA as a standard. Each LDL preparation was first labeled with ¹³¹I by use of 1,3,4,6-tetrachloro-3,6-diphenylglycouril (Iodo-gen), then coupled to ¹²⁵I-TC. Specific activities for the doubly labeled LDL averaged 454±59 and 150±64 cpm/ng protein for ¹²⁵I-TC and ¹³¹I, respectively (mean±SEM), for the 10 preparations. Trichloroacetic acid–soluble radioactivities (10% final concentration of trichloroacetic acid) averaged 3.6±0.3% for ¹²⁵I-TC and 0.7±0.2% for ¹³¹I, and radioactivities extractable in chloroform/methanol averaged 3.6±0.2% and 3.5±1.0%, respectively. Before injection, LDL preparations were sterilized by filtration (0.45-µm Millipore filter).

After the monkeys had consumed the atherogenic diet for 12 weeks, doubly labeled LDL (2.79±0.26x10⁹ cpm ¹²⁵I and 5.02±0.60x10⁸ cpm ¹³¹I) were injected through an indwelling femoral venous catheter 48 hours before necropsy. Subsequent blood samples were collected in tubes containing EDTA (1 mg/mL final concentration) from the arterial catheter at 3, 10, 20, 40, and 60 minutes and 2, 4, 6, 20, 24, and 48 hours after injection to determine the plasma decay of labeled LDL. The FCR of LDL by the whole body was calculated from coefficients and exponents determined by the biexponential equation fitted from the decay of protein-bound radioactivity in the plasma.^{22 23}

After the final (48-hour) blood sample was collected, the animals were transported to the necropsy laboratory, where sodium pentobarbital (30 mg/kg IV) was administered to attain surgical anesthesia. An infusion of Ringer's solution was initiated via an 18-gauge needle inserted into the left ventricle. The monkeys were then euthanized with an intravenous injection of sodium pentobarbital (80 mg/kg). A 1-cm longitudinal incision was made in the abdominal vena cava for drainage of blood from the cardiovascular system. The following arteries and their adventitia were removed: thoracic and abdominal aorta, right common iliac artery, common carotid arteries and carotid bifurcations, and left anterior descending and left circumflex coronary arteries. These were placed in modified Karnovsky's solution for 24 hours to provide adequate fixation for radiolabeled LDL.

Analysis of LDL Degradation
Accumulation of radioactivity from ¹²⁵I-TC represents both undegraded LDL and products of LDL degradation. The arterial ¹²⁵I-TC radioactivity (in cpm/g) was normalized by the area under the curve of protein-bound ¹²⁵I-TC radioactivity in plasma during the metabolic experiment (in [cpm/µL]xhours) to express the arterial ¹²⁵I-TC radioactivity in a form independent of the plasma LDL concentration and amount of labeled LDL injected.²²

The rates of LDL degradation and the calculated concentration of undegraded LDL were determined as described previously.^{23 24} Because the [¹³¹I]iodotyrosine released during cellular degradation is leached from arteries during fixation in modified Karnovsky's solution, the remaining ¹³¹I radioactivity represents undegraded LDL. The ¹²⁵I-TC representing LDL degraded by the artery can then be determined by subtracting the arterial ¹³¹I radioactivity from the total arterial ¹²⁵I-TC radioactivity, taking into account the relative activities of these two isotopes in plasma LDL at the time of necropsy.

Arterial LDL degradation was first calculated in fractional terms and expressed as FCR_artery. FCR_artery was calculated as the product of the whole-body FCR determined from the plasma decay curve^{22 23} and the ratio of LDL degradation products per gram of artery to the LDL degraded by the whole body (dose injected multiplied by the fraction of the dose irreversibly degraded by the whole body).^{22 23 25}

Degradation of LDL in absolute terms (in µg LDL-C·g artery^-1·h^-1) was calculated by multiplying FCR_artery by the total amount of LDL-C in plasma, which was calculated as the product of the plasma LDL-C concentration and the plasma volume.²³

Lipid Content
Lipid extracts of samples of thoracic, aortic, and hepatic tissue were prepared by the method of Folch et al.²⁶ Triglyceride and total and free cholesterol concentrations were then determined enzymatically as described by Carr et al.²⁷ Cholesteryl ester content was determined as the difference between measured total and free cholesterol.

Long-term Studies
Atherosclerosis Evaluation
Monkeys were sedated with ketamine hydrochloride (15 mg/kg body wt IM) for transport to the necropsy laboratory. Monkeys were euthanized and prepared for processing of tissues as in the short-term studies. The heart was removed after the whole-body perfusion with Ringer's solution and connected to the heart perfusion apparatus. The heart was perfused for 1 hour with 10% neutral buffered formalin at 100 mm Hg.

To study the extent and severity of coronary artery atherosclerosis, 15 tissue blocks (each 3 mm long) were cut perpendicular to the long axis of the arteries. Five blocks each were taken from the left circumflex, left anterior, and right coronary arteries.

The tissue blocks were dehydrated through increasing concentrations of ethanol and embedded in paraffin. Two 5-µm sections were cut from each block and stained with either hematoxylin and eosin or Verhoeff–van Gieson's stain. Sections stained with Verhoeff–van Gieson's stain were projected by a projection microscope onto a digitizer plate. The component parts of the artery were traced with a handheld stylus and computer-assisted digitizer. The intimal area was used as the measure of atherosclerosis extent. Intimal area is the area between the internal elastic lamina and luminal surface of each coronary artery section.

Statistical Analyses
Data are presented as mean±SEM. Outcome variables for the short-term and long-term studies were compared between groups by a Student's t test and normalized to equalize variance when necessary. Arterial LDL metabolism outcomes were evaluated with repeated-measures ANOVA.

	Results

Top Abstract Introduction Methods Results Discussion References

 
Plasma concentrations of 4-hydroxytamoxifen (a primary active metabolite of tamoxifen) in the monkeys in both the short-term and long-term studies were 5±1 ng/mL, which is similar to those found in women taking 20 mg tamoxifen daily.²¹

Short-term Studies
Short-term treatment with tamoxifen did not significantly alter plasma concentrations of TPC, HDL-C, LDL-C, or LDL molecular weight (all P>.05, Table 1). Tamoxifen increased the plasma concentrations of triglycerides (P=.01). LDL degradation differed among arterial sites (P=.001), but tamoxifen decreased arterial accumulation of LDL degradation products overall (P=.03). The treatment effects on arterial accumulation of LDL degradation products were greatest at the thoracic aorta (P=.03) and carotid bifurcation (P=.04), followed by the abdominal aorta (P=.06), the coronary arteries (P=.18), and the common carotid artery (P=.43) (Fig 1). There was a tendency for a tissue site–by-treatment interaction (P=.07). Similar trends were found for undegraded LDL, but these changes were not statistically significant (P>.05). After 12 weeks of treatment, progression of atherosclerosis as measured by intimal area was minimal (Table 2). However, tamoxifen treatment resulted in reduced cholesteryl ester content in the thoracic aorta (P=.04).

View this table: [in this window] [in a new window]   Table 1. Effect of Short-term Tamoxifen Treatment on Plasma Lipoprotein Cholesterol Distribution in Surgically Postmenopausal Cynomolgus Monkeys

View larger version (19K): [in this window] [in a new window]   Figure 1. Arterial LDL degradation rates for samples from coronary and common carotid arteries, thoracic and abdominal aortas, and carotid bifurcation for control (open bars) and tamoxifen-treated (solid bars) monkeys. Group-by–tissue site ANOVA: effect of treatment, P=.03; effect of site, P=.001; and treatment by site, P=.07.

View this table: [in this window] [in a new window]   Table 2. Effect of Short-term Tamoxifen Treatment on LDL Metabolism in Surgically Postmenopausal Cynomolgus Monkeys

There was a slight increase in whole-body FCR (P>.05) as well as a trend toward increased hepatic LDL accumulation (P=.11) in the tamoxifen-treated group. Also, there was a decrease in total hepatic cholesterol content (P=.003, Table 2), which was due entirely to a decrease in cholesteryl ester. Furthermore, there was a significant decrease in hepatic triglyceride concentrations (P=.001, Table 2).

Long-term Studies
Long-term tamoxifen treatment did not result in significant changes in plasma concentrations of TPC, HDL-C, or LDL-C (P>.05, Table 3). However, tamoxifen increased plasma concentrations of triglycerides (P=.0001) and reduced LDL molecular weight (P=.004). The coronary arteries of tamoxifen-treated monkeys had less atherosclerosis than the untreated controls, but this was of borderline statistical significance (P=.057, Fig 2).

View this table: [in this window] [in a new window]   Table 3. Effects of Long-term Tamoxifen Treatment on Plasma Lipoprotein Cholesterol Distribution

View larger version (17K): [in this window] [in a new window]   Figure 2. Atherosclerosis extent (intimal area, mm2) in the coronary arteries of ovariectomized cynomolgus monkeys given no hormone replacement (control) or monkeys fed tamoxifen in the diet (Tamoxifen).

There were no treatment effects on body weight, blood pressure, or glucose/insulin ratios (all P>.05).

	Discussion

Top Abstract Introduction Methods Results Discussion References

 
The major findings of the study were that tamoxifen (1) reduced arterial accumulation of LDL degradation products, (2) altered hepatic cholesterol metabolism, and (3) reduced progression of coronary artery atherosclerosis.

Tamoxifen is an estrogen agonist/antagonist that is currently prescribed to several hundred thousand breast cancer patients in the United States.^{1 2 3 4 28 29} Trials of tamoxifen as an adjuvant therapy have been so encouraging that its long-term use has been recommended in women with breast cancer as well as for women at high risk of developing breast cancer.^{8 9} The effect of tamoxifen on breast cancer is thought to be primarily antiestrogenic through blockade of estrogen receptors in breast tissue, although tamoxifen has estrogenic properties in other organs.²⁸

Whether tamoxifen has estrogenic (ie, beneficial) effects on the risk of coronary heart disease remains uncertain. The data available concerning the effects of tamoxifen on plasma lipids are inconsistent and are based almost entirely on studies of women with breast cancer. Generally, tamoxifen has been shown to reduce TPC by 10% and LDL-C by 20% in women with breast cancer.^{8 9 10} However, the effect of tamoxifen on HDL-C and triglycerides has been variable.^{8 9 11 12 30 31} The only data available from non–breast cancer patients are from a pilot study that included premenopausal subjects in its design. In that study, tamoxifen had little effect on TPC, HDL-C, and triglycerides.³ The results of our study confirm that tamoxifen has minimal, if any, plasma TPC- and LDL-C–lowering effects or plasma HDL-C–elevating effects. In the present study, there was careful control of the dietary constituents and dose of tamoxifen, and healthy animals without other coronary heart disease risk factors were used. Taken together with the results of other studies, we conclude that tamoxifen probably has minimal effects on TPC, HDL-C, and LDL-C. On the other hand, it is important to note that the variance in results between previous studies and ours could be due to some species differences in cholesterol metabolism that may exist between monkeys and humans. However, the increase in plasma concentrations of triglycerides and reduction of LDL size indicate that tamoxifen has estrogen agonist activity on plasma lipoprotein metabolism.

Short-term Effects of Tamoxifen
The major short-term effects of tamoxifen observed in our study were on arterial and hepatic LDL metabolism. Tamoxifen significantly reduced arterial accumulation of LDL degradation products, consistent with an estrogenic effect on arterial wall LDL metabolism.^{22 23 32} The effect was most pronounced in the thoracic aorta and carotid bifurcation, probably because those sites had the greatest amount of LDL degradation. We have seen more consistent effects of sex hormones at different arterial sites in past studies.^{22 23} However, accumulation of LDL degradation products was measured after 16 to 18 weeks of atherogenic diet and treatment in these studies, which supports the notion that longer treatment results in greater LDL accumulation and more consistent results. Furthermore, atherosclerosis develops first in the aorta and carotid bifurcation, which could explain why an effect of tamoxifen on arterial accumulation of LDL degradation products is more prominent at this early time point.

The exact mechanism by which tamoxifen reduced arterial accumulation of LDL degradation products was not tested directly in this study. However, the trend toward a higher FCR and LDL accumulation suggests that upregulation of hepatic LDL receptors by tamoxifen diverted LDL to the liver, and this could contribute to a reduction in the delivery of LDL to arterial tissues.

Tamoxifen had a tendency to lower plasma LDL-C in the present study, and it significantly reduced LDL molecular weight. Altered hepatic metabolism of LDL (possibly through tamoxifen-associated regulation of the LDL receptor) may have contributed to a selective removal of large LDL particles.³³ Also, the significant reduction of hepatic cholesterol content may result in reduced production of large LDL particles.³⁴ In previous studies, LDL molecular weight has been positively correlated with atherosclerosis progression.³⁵ A reduction in LDL molecular weight is favorable with respect to atherosclerosis in monkeys and has been consistently associated with estrogen treatment in monkeys^{22 23 32} and in women.³⁶ Small LDL has been associated with increased risk of coronary heart disease in many studies in humans, and more recent studies have shown that in normolipidemic men, small LDL also may be associated with decreased risk of CHD.³⁷

Long-term Effects of Tamoxifen
Long-term treatment with tamoxifen inhibited progression of coronary artery atherosclerosis. Inhibition of atherosclerosis was independent of the effects of tamoxifen on TPC, HDL-C, and LDL-C concentrations. However, the effects of tamoxifen on progression of atherosclerosis may be due in part to its inhibitory effects on arterial LDL accumulation. These results are consistent with an estrogenic effect on progression of atherosclerosis. Adams et al³⁸ reported that subcutaneous administration of estradiol inhibited progression of atherosclerosis by 50%. In the present study, tamoxifen also inhibited progression of atherosclerosis by about 50%. However, it is difficult to compare the relative estrogenic properties of tamoxifen and estradiol because these two studies were done independently. Regardless of the relative potency, it seems likely from these experiments that tamoxifen has "estrogenic" effects on progression of atherosclerosis.

Results of the present experiment indicate that tamoxifen may inhibit progression of atherosclerosis in part by inhibiting accumulation of LDL degradation products in the artery wall. Although they were not examined in this study, one can speculate that tamoxifen may have other direct effects on the arterial wall that relate to its estrogen agonist properties. Several studies have implicated estrogens as modulators of the expression of inflammatory mediators and growth factors thought to be important in atherogenesis. Estrogen modulates the expression of interleukin-1,^{38 39} platelet-derived growth factor-A,⁴⁰ tumor necrosis factor-,⁴¹ and interleukin-6.⁴² Recent evidence indicates that estrogen inhibits the expression of nuclear factor-B, a transcription factor that regulates the expression of many genes, in monkey aorta.⁴³

Sex hormones also may influence the initiation of atherosclerosis by modulating arterial production of nitric oxide. Available evidence indicates that estrogen may augment nitric oxide production or inhibit its breakdown in arteries.^{44 45 46} Long-term supplementation of L-arginine (the precursor of nitric oxide) has been associated with reduced development of atherosclerosis in rabbits.⁴⁷ Although this hypothesis was not addressed in the present study, it is reasonable to speculate that tamoxifen (like estrogen) may modulate nitric oxide activity and affect progression of atherosclerosis through this mechanism.

The selective estrogenic effects of tamoxifen on certain tissues (eg, bone and cardiovascular tissue) raise interesting questions about the role of the estrogen receptor in disease processes. Evidence is accumulating that implicates several molecular processes in the tissue selectivity of various estrogens. Gene transcription associated with estrogen receptor binding depends greatly on cell type, ligand-specific effects on receptor conformation, and structure of the promoter region of the target gene. For example, as recently described, estrogen inhibits the transcription of interleukin-6 (which plays a major role in the pathogenesis of osteoporosis) by binding estrogen receptors and interacting directly with other transcription factors.⁴⁸ Furthermore, cell-specific, direct (receptor-independent) effects on cellular function may be involved. Although the mechanism(s) involved in the effects of tamoxifen on atherogenesis remain to be determined, it is now apparent that agents that function primarily as estrogens in one cell or tissue type can function primarily as antiestrogens in another.

Tamoxifen and Coronary Heart Disease
One could conclude from these studies that tamoxifen may reduce the risk of coronary heart disease in women taking this drug. This may be true, and in many ways tamoxifen might serve as a useful alternative to traditional hormone replacement therapy. There are data that estrogen agonist/antagonists prevent loss of bone density in rats⁴⁹ and thus may reduce the risk of osteoporosis. Therefore, tamoxifen might reduce the risk of breast cancer, coronary heart disease, and osteoporosis. However, results of recent studies indicate that long-term treatment (2 years) of women with tamoxifen increases their risk of developing an aggressive form of endometrial cancer.^{5 6} Therefore, the widespread use of tamoxifen as an alternative to traditional hormone replacement is problematic.

The cardiovascular effects of other estrogen agonist/antagonist agents, such as droloxifene and raloxifene, have not been evaluated from the standpoint of cardiovascular protection. Furthermore, it is not clear whether these other estrogen agonist/antagonist agents have effects similar to those of tamoxifen on breast tissue, uterus, or bone. These selective effects on different organ systems would most likely have important implications for these agents as therapeutic approaches to the prevention and treatment of coronary heart disease in postmenopausal women.

	Selected Abbreviations and Acronyms

 

FCR = fractional catabolic rate FCRartery = fraction of plasma LDL pool degraded·h-1·g artery-1 HDL-C = HDL cholesterol LDL-C = LDL cholesterol TC = tyramine cellobiose TPC = total plasma cholesterol

	Acknowledgments

 
This study was supported in part by grants HL-49085 (Dr Williams) and P01-HL-45666 from the National Heart, Lung, and Blood Institute (project 2 to Dr Adams) and by grant KO1-RR-00072 (Dr Wagner), National Center for Research Resources, all from the National Institutes of Health, Bethesda, Md. The authors thank Jamie Fox for technical assistance and Karen Potvin Klein for editorial comments.

Received December 28, 1995; revision received June 19, 1996;

	References

Top Abstract Introduction Methods Results Discussion References

 

1. Early Breast Cancer Triallists' Collaborative Group. Systemic treatment of early breast cancer by hormonal, cytotoxic, or immune therapy. Lancet. 1992;339:1-15.[Medline] [Order article via Infotrieve]
2. Bonadonna G, Valagussa P, Brambilla C, Moliterni A, Zambitti M, Ferrari LS. Adjuvant and neoadjuvant treatment of breast cancers with chemotherapy and endocrine therapy. Semin Oncol. 1991;18:515-524.[Medline] [Order article via Infotrieve]
3. Powles TJ. The case for clinical trials of tamoxifen for prevention of breast cancer. Lancet. 1992;340:1145-1147.[Medline] [Order article via Infotrieve]
4. Fugh-Berman A, Epstein S. Tamoxifen: disease prevention or disease substitution? Lancet. 1992;340:1143-1145.[Medline] [Order article via Infotrieve]
5. Neven P, De Muylder X, Van Belle Y, Vanderick G, De Muylder E. Hysteroscopic follow-up during tamoxifen treatment. Eur J Obstet Gynecol Reprod Biol. 1990;35:235-238.[Medline] [Order article via Infotrieve]
6. Fornander T, Rutqvist IE, Sjoberg HE, Blomqvist L, Mattson A, Glas V. Long-term adjuvant tamoxifen in early breast cancer: effect on bone mineral density in postmenopausal women. J Clin Oncol. 1990;8:1019-1024.[Abstract]
7. McDonald CC, Stewart HJ, the Scottish Breast Cancer Committee. Fatal myocardial infarction in the Scottish adjuvant tamoxifen trial. Br Med J. 1993;303:435-437.
8. Love RR, Mazess RB, Barden HS, Newcomb PA, Jordan VC. Bone mineral density in women with breast cancer treated with adjuvant tamoxifen for at least two years. Breast Cancer Res Treat. 1988;12:297-302.[Medline] [Order article via Infotrieve]
9. Cuzick J, Wang DY, Bulbrook RD. The prevention of breast cancer. Lancet. 1986;1:83-86.[Medline] [Order article via Infotrieve]
10. Dewer JA, Horobin JM, Preece PE, Tavendale R, Tunstall-Pedoe H, Wood RAB. Long term effects of tamoxifen on blood lipid values in breast cancer. Br Med J. 1992;305:225-226.
11. Bagdade JD, Wolter J, Subbaiah PV, Ryan W. Effects of tamoxifen on plasma lipids and lipoprotein composition. J Clin Endocrinol Metab. 1990;70:1132-1135.[Abstract]
12. Ingram D. Tamoxifen use, estrogen binding and serum lipids in postmenopausal women with breast cancer. Austr N Z J Surg. 1990;60:673-675.
13. Barrett-Connor E, Bush TL. Estrogen and coronary heart disease in women. JAMA. 1991;265:1861-1867.[Abstract]
14. Adams MR, Williams JK, Kaplan JR. Effects of androgens on coronary artery atherosclerosis and atherosclerosis-related impairment of vascular responsiveness. Arterioscler Thromb Vasc Biol. 1995;15:562-570.[Abstract/Free Full Text]
15. Allain CC, Poon LS, Chan CSG, Richmond W, Fu PC. Enzymatic determination of total serum cholesterol. Clin Chem. 1974;20:470-475.[Abstract]
16. Fossati P, Principe L. Serum triglycerides determined colorimetrically with an enzyme that produces hydrogen peroxide. Clin Chem. 1982;28:2077-2080.[Abstract/Free Full Text]
17. Lipid Research Clinics Program. Manual of Laboratory Operations: Lipid and Lipoprotein Analysis. Bethesda, Md: National Institutes of Health; 1974. US Dept of Health, Education, and Welfare publication NIH 75-628.
18. Carroll RM, Rudel LL. Lipoprotein separation and low density lipoprotein molecular weight determination using high performance gel-filtration chromatography. J Lipid Res. 1983;24:200-207.[Abstract]
19. Auerbach BJ, Parks JS, Applebaum-Bowden D. A rapid and sensitive micro-assay for the enzymatic determination of plasma and lipoprotein cholesterol. J Lipid Res. 1990;31:738-742.[Abstract]
20. Rudel LL, Sawyer JK, Parks JS. Heterogeneity of low density lipoproteins in atherosclerosis: nonhuman primate species and diet comparisons. In: Proceedings of the Workshop on Lipoprotein Heterogeneity. Rockville, Md: National Heart, Lung, and Blood Institute; 1986:263-278. US Dept of Health and Human Services publication NIH 87-2646.
21. Langan-Fahey SM, Tormey DC, Jordan VC. Tamoxifen metabolites in patients on long term adjuvant therapy for breast cancer. Eur J Cancer. 1990;26:883-888.
22. Wagner JD, Clarkson TB, St Clair RW, Schwenke DC, Shively CA, Adams MR. Estrogen and progesterone replacement therapy reduces LDL accumulation in the coronary arteries of surgically postmenopausal cynomolgus monkeys. J Clin Invest. 1991;88:1995-2002.
23. Wagner JD, St Clair RW, Schwenke DC, Shively CA, Adams MR, Clarkson TB. Regional differences in arterial low density lipoprotein metabolism in surgically postmenopausal cynomolgus monkeys: effects of estrogen and progesterone therapy. Arterioscler Thromb. 1992;12:717-726.[Abstract/Free Full Text]
24. Schwenke DC, Carew TE. Quantification in vivo of increased LDL content and rate of LDL degradation in the normal rabbit aorta occurring at sites susceptible to early atherosclerotic lesions. Circ Res. 1988;62:699-710.[Abstract/Free Full Text]
25. Carew TC, Pittman RC, Marchand ER, Steinberg D. Measurement in vivo of irreversible degradation of low density lipoprotein in the rabbit aorta: predominance of intimal degradation. Arteriosclerosis. 1984;4:214-224.[Abstract/Free Full Text]
26. Folch J, Lees M, Sloane Stanley GH. A simple method for the isolation and purification of total lipids from animal tissues. J Biol Chem. 1957;224:497-509.
27. Carr TP, Andresen CJ, Rudel LL. Enzymatic determination of triglyceride, free cholesterol, and total cholesterol in tissue lipid extracts. Clin Biochem. 1993;26:39-42.[Medline] [Order article via Infotrieve]
28. Legha SS. Tamoxifen in the treatment of breast cancer. Ann Intern Med. 1988;109:219-228.
29. Jordan VC. Long-term adjuvant tamoxifen therapy for breast cancer. Lancet. 1986;1:83-86.
30. Bruning PF, Bonfrer JM, Hart AA, de Jong-Bakker D, Linders D, van Lood J, Nooyen WJ. Tamoxifen, serum lipoproteins and cardiovascular risk. Br J Cancer. 1988;58:497-499.[Medline] [Order article via Infotrieve]
31. Thangaraju M, Kumar K, Gandhirajan R, Sachdanandam P. Effect of tamoxifen on plasma lipids and lipoproteins in postmenopausal women with breast cancer. Cancer. 1994;73:659-663.[Medline] [Order article via Infotrieve]
32. Wagner JD, Adams MR, Schwenke DC, Clarkson TB. Oral contraceptive treatment decreases arterial LDL degradation in female cynomolgus monkeys. Circ Res. 1993;72:1300-1307.[Abstract/Free Full Text]
33. Walsh BW, Schiff I, Rosner B, Greenberg L, Ravnikar V, Sacks FM. Effects of postmenopausal estrogen replacement on the concentrations and metabolism of plasma lipoproteins. N Engl J Med. 1991;325:1196-1204.[Abstract]
34. Parks JS, Gebre AK. Studies on the effect of dietary fish oil on the physical and chemical properties of low density lipoproteins in cynomolgus monkeys. J Lipid Res. 1991;32:305-315.[Abstract]
35. Rudel LL, Parks JS, Johnson FL, Babiak J. Low density lipoproteins in atherosclerosis. J Lipid Res. 1986;27:465-474.[Medline] [Order article via Infotrieve]
36. Campos H, Sacks FM, Walsh BW, Schiff I, O'Hanesian MA, Krauss RM. Differential effects of estrogen on low-density lipoprotein subclasses in healthy postmenopausal women. Metabolism. 1993;42:1153-1158.[Medline] [Order article via Infotrieve]
37. Eriksson M, Berglund L, Rudling M, Henriksson P, Angelin B. Effects of estrogen on low density lipoprotein metabolism in males: short-term and long-term studies during hormonal treatment of prostatic carcinoma. J Clin Invest. 1989;84:802-810.
38. Adams MR, Kaplan JR, Manuck SB, Koritnik DR, Parks JS, Wolfe MS, Clarkson TB. Inhibition of coronary artery atherosclerosis by 17-beta estradiol in ovariectomized monkeys: lack of an effect of added progesterone. Arteriosclerosis. 1990;10:1051-1057.[Abstract/Free Full Text]
39. Polan ML, Loukides J, Nelson P, Carding S, Diamond M, Walsh A, Bottomly K. Progesterone and estradiol modulate interleukin-1 beta messenger ribonucleic acid levels in cultured human peripheral monocytes. J Clin Endocrinol Metab. 1989;69:1200-1206.[Abstract]
40. Shanker G, Sorci-Thomas M, Adams MR. Estrogen modulates the inducible expression of platelet-derived growth factor mRNA by monocyte/macrophages. Life Sci. 1995;56:499-507.[Medline] [Order article via Infotrieve]
41. Loy RA, Loukides JA, Polan ML. Ovarian steroids modulate human monocyte tumor necrosis factor alpha messenger ribonucleic acid levels in cultured human peripheral monocytes. Fertil Steril. 1992;58:733-739.[Medline] [Order article via Infotrieve]
42. Stein B, Yang MX. Repression of the interleukin-6 promoter by estrogen receptor is mediated by NF-B and C/EBPß. Mol Cell Biol. 1995;15:4971-4979.[Abstract]
43. Register TC, Bora TA, Adams MR. Estrogen inhibits activation of arterial NF-kB transcription factor in early diet-induced atherogenesis. Circulation. 1995;92(suppl I):I-628. Abstract.
44. Miller VM, Gisclard V, Vanhoutte PM. Modulation of endothelium-dependent and vascular smooth muscle responses by oestrogens. Phlebology. 1988;3(suppl 1):63-69.
45. Schray-Utz B, Zeiher AM, Busse R. Expression of constitutive NO synthase in cultured endothelial cells is enhanced by 17-beta estradiol. Circulation. 1993;88(suppl I):I-80. Abstract.
46. Mendelsohn ME, Karas RH. Estrogen and the blood vessel wall. Curr Opin Cardiol. 1994;9:619-626.[Medline] [Order article via Infotrieve]
47. Cooke JP, Singer AH, Tsao P, Zera P, Rowan RA, Billingham ME. Antiatherogenic effects of L-arginine in the atherosclerotic rabbit. J Clin Invest. 1992;90:1168-1172.
48. Pottratz ST, Bellido T, Mocharla H, Crabb D, Manolagas SC. 17ß-Estradiol inhibits expression of human interleukin-6 promoter-reporter constructs by a receptor-dependent mechanism. J Clin Invest. 1994;93:944-950.
49. Turner RT, Wakley GK, Hannon KS, Bell NH. Tamoxifen prevents the skeletal effects of hormone deficiency in rats. J Bone Miner Res. 1987;2:449-456.[Medline] [Order article via Infotrieve]

This article has been cited by other articles:

				D. J. Grainger and P. M. Schofield Tamoxifen for the Prevention of Myocardial Infarction in Humans: Preclinical and Early Clinical Evidence Circulation, November 8, 2005; 112(19): 3018 - 3024. [Full Text] [PDF]

				Y. Suarez, C. Fernandez, D. Gomez-Coronado, A. J. Ferruelo, A. Davalos, J. Martinez-Botas, and M. A. Lasuncion Synergistic upregulation of low-density lipoprotein receptor activity by tamoxifen and lovastatin Cardiovasc Res, November 1, 2004; 64(2): 346 - 355. [Abstract] [Full Text] [PDF]

				P. de Medina, B. L. Payre, J. Bernad, I. Bosser, B. Pipy, S. Silvente-Poirot, G. Favre, J.-C. Faye, and M. Poirot Tamoxifen Is a Potent Inhibitor of Cholesterol Esterification and Prevents the Formation of Foam Cells J. Pharmacol. Exp. Ther., March 1, 2004; 308(3): 1165 - 1173. [Abstract] [Full Text] [PDF]

				T. Simon, P. Boutouyrie, J.M. Simon, B. Laloux, C. Tournigand, A.I. Tropeano, S. Laurent, and P. Jaillon Influence of Tamoxifen on Carotid Intima-Media Thickness in Postmenopausal Women Circulation, December 3, 2002; 106(23): 2925 - 2929. [Abstract] [Full Text] [PDF]

				K. J. Ho and J. K. Liao Nonnuclear Actions of Estrogen Arterioscler. Thromb. Vasc. Biol., December 1, 2002; 22(12): 1952 - 1961. [Abstract] [Full Text] [PDF]

				K. J. Ho and J. K. Liao Non-nuclear Actions of Estrogen: New Targets for Prevention and Treatment of Cardiovascular Disease Mol. Interv., July 1, 2002; 2(4): 219 - 228. [Abstract] [Full Text] [PDF]

				T. S Mikkola and T. B Clarkson Estrogen replacement therapy, atherosclerosis, and vascular function Cardiovasc Res, February 15, 2002; 53(3): 605 - 619. [Abstract] [Full Text] [PDF]

				T. C. Register, C. S. Carlson, and M. R. Adams Serum YKL-40 Is Associated with Osteoarthritis and Atherosclerosis in Nonhuman Primates Clin. Chem., December 1, 2001; 47(12): 2159 - 2161. [Full Text] [PDF]

				S. E. Reis, J. P. Costantino, D. L. Wickerham, E. Tan-Chiu, J. Wang, and M. Kavanah Cardiovascular Effects of Tamoxifen in Women With and Without Heart Disease: Breast Cancer Prevention Trial J Natl Cancer Inst, January 3, 2001; 93(1): 16 - 21. [Abstract] [Full Text] [PDF]

				P. Bausero, M.-H. Ben-Mahdi, J.-P. Mazucatelli, C. Bloy, and M. Perrot-Applanat Vascular endothelial growth factor is modulated in vascular muscle cells by estradiol, tamoxifen, and hypoxia Am J Physiol Heart Circ Physiol, November 1, 2000; 279(5): H2033 - H2042. [Abstract] [Full Text] [PDF]

				C. K. Osborne and S. A. W. Fuqua Selective Estrogen Receptor Modulators: Structure, Function, and Clinical Use J. Clin. Oncol., September 17, 2000; 18(17): 3172 - 3186. [Abstract] [Full Text] [PDF]

				L. Mosca The Role of Hormone Replacement Therapy in the Prevention of Postmenopausal Heart Disease Arch Intern Med, August 14, 2000; 160(15): 2263 - 2272. [Abstract] [Full Text] [PDF]

				D. M. Herrington, B. E. Pusser, W. A. Riley, T. Y. Thuren, K. B. Brosnihan, E. A. Brinton, and D. B. MacLean Cardiovascular Effects of Droloxifene, a New Selective Estrogen Receptor Modulator, in Healthy Postmenopausal Women Arterioscler. Thromb. Vasc. Biol., June 1, 2000; 20(6): 1606 - 1612. [Abstract] [Full Text] [PDF]

				D. Grainger, D. Mosedale, J. Metcalfe, and E. Bottinger Dietary fat and reduced levels of TGFbeta1 act synergistically to promote activation of the vascular endothelium and formation of lipid lesions J. Cell Sci., January 7, 2000; 113(13): 2355 - 2361. [Abstract] [PDF]

				D. C. Schwenke, J. D. Wagner, and M. R. Adams In vitro lipid peroxidation of LDL from postmenopausal cynomolgus macaques treated with female hormones J. Lipid Res., February 1, 1999; 40(2): 235 - 244. [Abstract] [Full Text]

				C. K. Osborne Tamoxifen in the Treatment of Breast Cancer N. Engl. J. Med., November 26, 1998; 339(22): 1609 - 1618. [Full Text] [PDF]

				T. B. Clarkson and M. S. Anthony Lack of Effect of Raloxifene on Coronary Atherosclerosis of Postmenopausal Monkeys--Authors' Response J. Clin. Endocrinol. Metab., August 1, 1998; 83(8): 3002 - 3004. [Full Text]

				J. K. Williams, E. K. Honore, and M. R. Adams Contrasting Effects of Conjugated Estrogens and Tamoxifen on Dilator Responses of Atherosclerotic Epicardial Coronary Arteries in Nonhuman Primates Circulation, September 16, 1997; 96(6): 1970 - 1975. [Abstract] [Full Text]

This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles