Effects of hormone replacement modalities on low density lipoprotein composition and distribution in ovariectomized cynomolgus monkeys

Estrogen receptor genotypes, menopausal status, and the lipid effects of tamoxifen

Tamoxifen induces important changes in serum lipid profiles in some women; however, little information is available to predict which women will experience improved lipid profiles during tamoxifen therapy. As part of a multicenter prospective observational trial in 176 breast cancer patients, we tested the hypothesis that tamoxifen-induced lipid changes were associated with genetic variants in candidate target genes (CYP2D6, ESR1, and ESR2). Tamoxifen lowered low-density lipoprotein cholesterol (P<0.0001) by 23.5 mg/dl (13.5-33.5 mg/dl) and increased triglycerides (P=0.006). In postmenopausal women, the ESR1-XbaI and ESR2-02 genotypes were associated with tamoxifen-induced changes in total cholesterol (P=0.03; GG vs GA/AA) and triglycerides (P=0.01; gene-dose effect), respectively. In premenopausal women, the ESR1-XbaI genotypes were associated with tamoxifen-induced changes in triglycerides (P=0.002; gene-dose effect) and high-density lipoprotein (P=0.004; gene-dose effect). Our results suggest that estrogen receptor genotyping may be useful in predicting which women would benefit more from tamoxifen.

Chronic Treatment with Physiological Doses of Estradiol Affects the GH-IGF-1 Axis and Fat Metabolism in Young and Middle-aged Ovariectomized Rats

Estrogen deficiency may be partly responsible for the metabolic syndrome and the condition may be reversible with hormone replacement therapy. However, after the heart and estrogen/progestin replacement study and the women's health initiative study the prospect of HRT on CVD has changed dramatically. As the pituitary and the liver are targets for estrogen action we assessed the effect of ovariectomy (OVX) and long-term (3 months) estradiol (E2) treatment by means of subcutaneously (s.c.) implanted silastic capsules on pituitary and liver function in young and middle-aged female rats. Our results demonstrate that triglyceride serum levels increased, whereas insulin-like growth factor-1 (IGF-1), high density lipoprotein cholesterol (HDL), and glucose levels decreased during the transition from young to middle-age. E2 treatment increased dose-independently growth hormone (GH) secretion. IGF-1 levels were increased upon OVX in middle-aged rats and the high dose of E2 decreased IGF-1 concentrations in both age groups. Cholesterol concentrations increased after OVX and were attenuated by E2 administration in middle-aged rats. Both, low density lipoprotein cholesterol (LDL) and HDL levels raised after castration and both parameters decreased in response to E2 in young and middle-aged rats. Glucose serum concentrations decreased after E2 treatment in all animals. Taken together, our results clearly demonstrate that the pituitary and the liver metabolism of middle-aged rats remain susceptible to the influence of OVX and E2 treatment.

Estradiol and progesterone treatments change the lipid profile in naturally menopausal rats from different age groups

The effect of estradiol and progesterone therapy in serum and liver on the lipid profile of naturally menopausal albino rats of the Wistar strain of different age groups (12,18 and 24 months) have been measured and compared with the age matched groups. Three months old rats were used as young controls. The aged rats were administered subcutaneous injection of 17-beta-estradiol (0.1 microg/g body weight), progesterone (2.5 microg/g body weight) and similar concentrations of both in combined treatment for 1 month and the level of triglycerides (TG), total lipids (TL), total cholesterol (TC), high density lipoprotein (HDL), low density lipoprotein (LDL) and very low density lipoprotein (VLDL) were measured in serum and liver of 3, 12, 18 and 24 months old control as well as treated groups. The results show that TG, HDL, VLDL levels were increased significantly by 71%, 155%, 54%, respectively in liver of 24 months old rats by combination treatment when compared with age matched control animals. The levels of TL, TC and LDL were decreased by 20%, 31%, and 30%, respectively in serum of 12 months old rats in combination treatment group. The effect was more significant in 12 and 24 months old female rats with administration of estrogen and combined (EP) treatments. The results indirectly suggest that hormone replacement therapy (HRT) can reduce the risk of cardiovascular disease (CVD) thereby playing a cardio-protective role by restoring lipid and hormone levels to the similar levels as found in young female animals.

Norgestimate and medroxyprogesterone acetate do not attenuate the atheroprotective effects of 17beta-estradiol in ovariectomized, apolipoprotein E-deficient mice

OBJECTIVE

To determine whether progestins counteract the cardioprotective effects of estrogen.

DESIGN

Controlled animal study.

SETTING

Academic laboratory environment.

ANIMAL(S)

Female apolipoprotein E-deficient mice.

INTERVENTION(S)

Mice were randomly assigned to groups receiving a sham operation plus placebo pellet, bilateral gonadectomy plus placebo pellet, or gonadectomy plus one of nine combinations of estrogen/progestin SC pellets.

MAIN OUTCOME MEASURE(S)

Total plasma cholesterol, body weight, fat depot weight, uterine weight and size, and the cross-sectional area of fatty streaks in the aortic sinus were measured in each animal.

RESULT(S)

After 8 weeks of treatment, plasma cholesterol levels were significantly higher only in the ovariectomized and sham-operated animals that received placebo pellets. No differences in plasma cholesterol were observed relative to the type or amount of progestin administered. There was a reduction in fatty streaks in all of the hormone treatment groups as compared with both the ovariectomized and sham-operated animals that received placebo pellets.

CONCLUSION(S)

There were no significant differences in lesion area in response to estrogen alone or to estrogen plus the different types and doses of progestins.

Cholesterol-fed ovariectomized monkeys are good animal models for human atherosclerosis of postmenopausal women

Although it is well known that the incidence of atherosclerosis is markedly increased in postmenopausal women, antiatherosclerotic effects of estrogen replacement therapies are not clear. One of the reasons for this is due to the lack of appropriate animal models for atherosclerosis of postmenopausal women. Therefore, we attempted to develop an animal model for atherosclerosis of postmenopausal women and examined the antiatherosclerotic effects of estrogen replacement therapy. Adult ovariectomized Japanese monkeys were fed 2% cholesterol diet alone (C-group) or in combination with conjugated estrogen (CE-group) for 30 months. The serum estradiol-17beta levels of the CE-group were varied between 10 and 204.5 ng/dl during treatment. In the C-group, the serum total cholesterol levels were increased from 110 to 270 mg/dl, and atheroma was first observed after 3-months treatment with angioscopy. In the CE-group, the levels of the serum total cholesterol during treatment were 30% lower than those of the C-group, and the aortic lesions were first observed after 12-months treatment with angioscopy. The aortic intimal thickness of the CE-group was 58% of the C-group. This finding showed good agreement with the angioscopic observation. The aortic lesions were of a fibromuscular type in both groups. In conclusion, a cholesterol-fed ovariectomized monkey is an appropriate animal model for atherosclerosis of postmenopausal women. Furthermore, angiofiberscopic and histopathological observations suggested that estrogen replacement therapy was valid for atherosclerosis of postmenopausal women.

17beta-estradiol affects in vivo the low density lipoprotein composition, particle size, and oxidizability

The aim of this study was to explore the possible modifications induced by 17beta-estradiol (E(2)) in vivo on low-density lipoprotein (LDL) lipid composition, particle size, and oxidizability. For this purpose, women were recruited from an in vitro fertilization program, ranging their plasma E(2) levels from less than 12 pg/ml to more than 2000 pg/ml at the end of the treatment. The LDL lipid constituents were analyzed by thin layer chromatography and image analysis, and the LDL diameter was calculated from the lipid data. The results showed that high plasma E(2) levels were associated with smaller LDL particles, with lower amounts of free and esterified cholesterol and an increased relative content of alpha-tocopherol. The hormonal treatment produced a remodelation of the LDL acyl composition, rendering a lipoprotein enriched in saturated fatty acids, with a poorer polyunsaturated fatty acid content. These alterations in the physicochemical properties of LDL paralleled changes in the susceptibility of LDL to in vitro oxidation induced by both Cu(2+) and the peroxyl radical generator, 2,2'-azobis (2-amidinopropane), these changes being mainly reflected in a reduced maximum oxidation rate. The in vivo changes in the physicochemical properties of LDL induced by E(2) could explain some of the antiatherogenic actions of estrogens.

Effect of estrogen-progestin replacement therapy on plasma lipids and lipoproteins in postmenopausal women

Serum levels of cholesterol (Chol), triglycerides (TG), low-density lipoprotein cholesterol (LDL) high-density lipoprotein cholesterol (HDL), both apolipoproteins A1 and B (Apo A1, Apo B), follicle-stimulating hormone (FSH) luteinizing hormone (LH), estradiol (E2), progesterone (P), testosterone (T) and steroid hormone binding globulin (SHBG) were measured in postmenopausal women, before and after four different estrogen-progestin replacement therapies. Each woman was her own control to avoid genetic or socioeconomic differences. Our results showed that serum E2 and TG significantly increased and serum FSH, LH, LDH, Apo B, and Chol significantly decreased after all treatments. Serum P and T did not significantly change after any of the treatments. HDL, Apo A1 and SHBG significantly increased in the groups treated with medroxiprogesterone acetate (MPA) but not in the group treated with Norgestrel. We conclude that estrogen-progestin replacement therapy in postmenopausal women leads to profound and beneficial changes in plasma lipids and lipoproteins and that treatments with cyclic or continuous MPA could provide greater protection against coronary heart disease (CHD).

Consumption of soy protein reduces cholesterol absorption compared to casein protein alone or supplemented with an isoflavone extract or conjugated equine estrogen in ovariectomized cynomolgus monkeys

Dietary intake of soy protein is associated with reductions in plasma cholesterol. Isoflavones are thought to be active components of soy and responsible for the beneficial effects because of their structural similarities to estrogen. The purposes of this study were to determine if i) soy protein or a semipurified soy extract, rich in isoflavones, is responsible for improving the lipid profile and ii) altered intestinal cholesterol metabolism is one mechanism for hypocholesterolemic effects. Ovariectomized adult female cynomolgus monkeys (40) were assigned to groups fed diets containing i) casein-lactalbumin (CAS) ii) intact soy protein (SOY), iii) CAS plus an isoflavone-rich semipurified soy extract similar in isoflavone content as SOY (ISO) or iv) CAS plus conjugated equine estrogen (CEE) for 20 wk. Cholesterol absorption was determined using the fecal isotope ratio method. Bile acid excretion was measured using the 3alpha-hydroxysteroid dehydrogenase assay. The SOY group had significantly lower total- and VLDL + LDL-cholesterol compared to the other three groups and significantly higher HDL-cholesterol compared to the CAS and CEE groups. Cholesterol absorption was significantly lower in the SOY group compared to the other groups, but bile acid excretion was not significantly affected. The hypocholesterolemic effect of soy protein appears to be mediated in part by decreased cholesterol absorption. The semipurified soy extract, rich in isoflavones, added to casein protein did not have lipid-lowering effects. Other components of soy such as saponins, phytic acid or the amino acid composition may be involved in the hypocholesterolemic effects seen in this study.

Effects of menopause and hormone replacement therapy on plasma lipids, lipoproteins and LDL-receptor activity

A cross-sectional study of ninety six women was conducted to examine the effect of menopause and hormone replacement therapy (HRT) on plasma lipids, lipoproteins and oxidation of low density lipoproteins. The sample consisted of 26 premenopausal women, 26 postmenopausal women taking no replacement hormones and 43 postmenopausal women on hormone replacement therapy. Postmenopausal women not taking replacement hormones had significantly higher plasma cholesterol, low density lipoprotein (LDL) cholesterol and lipoprotein[a] (Lp[a]) levels compared to premenopausal women or postmenopausal women on HRT [6.00 +/- 0.15, 5.36 +/- 0.17 (P < 0.01), 5.63 +/- 0.13 (P < 0.05) mmol/l, respectively for total cholesterol; 4.13 +/- 0.15, 3.64 +/- 0.15 (P < 0.05), 3.82 +/- 0.12 (P < 0.05) mmol/l, respectively for LDL-cholesterol; 48.19 +/- 9.90, 26.59 +/- 5.53 (P < 0.03), 25.12 +/- 4.62 (P < 0.03) mg/dl, respectively for Lp[a]]. The differences in LDL cholesterol concentrations were inversely related to changes in LDL receptor activity (r = -0.27, P < 0.01). HRT use was found to be associated with a significantly smaller LDL particle size. Plasma triglyceride was significantly higher in women on HRT (1.16 +/- 0.07 mmol/l) than in the premenopausal group (0.96 +/- 0.07) or postmenopausal group not using HRT (0.87 +/- 0.06). There were no differences in LDL oxidation between the groups when LDL was oxidised in the presence of copper. Nor was there any difference in the uptake of copper-oxidised or macrophage-modified LDL into J774 macrophages. These results confirm the effect of menopause and exogenous hormones on plasma lipids and lipoproteins, and suggest that HRT modifies the activity of the LDL receptor. Hormone replacement did not appear to protect LDL from oxidation.

Aortic plaque size and endometrial response in cholesterol-fed rabbits treated with estrogen plus continuous or sequential progestin

ERT is associated with a reduced incidence of coronary risk and cardiac events in postmenopausal women, but increases the risk of endometrial hyperplasia and carcinoma. Combined estrogen and progestin therapy protects the endometrium; however, its effects on heart disease risk factors are not completely known. In our study, 56 ovariectomized New Zealand White rabbits in 7 groups received a 0.5% cholesterol diet for 12 weeks. Controls were not treated with hormones. All other animals received (per kilogram body weight per week) intramuscular injections of either 0.3 mg estrogen (estradiol valerate) alone, 8.3 mg progestin (hydroxyprogesterone caproate) alone, estrogen and progestin continuously in 3 different dosages (0.3 and 8.3 mg; 1 and 8.3 mg; or 1 and 2.8 mg; estrogen and progestin, respectively), or 1 mg estrogen with 25 mg progestin sequentially in 2-week cycles. Eight non-ovariectomized animals served as further controls for endometrial analysis. Morphometric analysis of plaque size in the aortic arch showed that estrogen monotherapy, and the 3 combined therapies with 1 mg estrogen, significantly reduced intimal thickening (P<0.05). The application of progestin alone had no effect on plaque size. The endometrium was enlarged by 3-fold after estrogen treatment, and was decreased by half after progestin treatment, compared with control uteri (P<0.05). In all groups with combined hormone regimens, endometrial size was not significantly different from control uteri. However, these uteri showed more inflammatory reactions, especially when higher doses of hormones were given. In this animal model, doses of progestin that are able to successfully reduce the proliferative effect of estrogen on endometrium do not diminish the desirable antiatherosclerotic properties of estrogen.

Intact dietary soy protein, but not adding an isoflavone-rich soy extract to casein, improves plasma lipids in ovariectomized cynomolgus monkeys

The dietary consumption of soy protein has been linked to a reduction in coronary heart disease and improvements in a number of related risk factors. Recent investigations have focused on isoflavone components of soy protein. The purpose of this study was to examine plasma lipids and lipoproteins, particularly LDL, with the intake of intact soy protein or casein-lactalbumin diets with and without a semipurified extract of soy, rich in isoflavones. Sixty ovariectomized cynomolgus monkeys were assigned to one of three groups fed diets containing the following: 1) casein-lactalbumin as the protein source (CAS; n = 20); 2) CAS plus a semipurified extract of soy, rich in isoflavones (ISO; n = 20); or 3) intact soy protein (SOY; n = 20) for 12 wk. Lipoproteins were fractionated by combined ultracentrifugation and HPLC. Isolated LDL particles were further subfractionated by dividing the LDL peak into three fractions for compositional analyses. The SOY group had significantly lower plasma total cholesterol, VLDL plus IDL cholesterol and LDL cholesterol, and significantly less HDL cholesterol than the CAS group. LDL particles from the SOY group had a significantly less cholesteryl ester than the CAS group. The semipurified extract of soy, rich in isoflavones, added to casein-lactalbumin protein did not have the same effects as intact soy protein on plasma lipids and lipoproteins. Other components of soy protein, either alone or in combination with isoflavones, may be involved in the effects seen in this study.

Sex steroids increase cholesterol 7alpha-hydroxylase mRNA in nonhuman primates

One mechanism that may account for our prior observation that oral contraceptives decrease the hepatic cholesterol concentration independently of the low-density lipoprotein (LDL) receptor in sexually intact nonhuman primates is that sex hormones increase biliary cholesterol secretion by increasing hepatic mRNA abundance for cholesterol 7alpha-hydroxylase, the rate-limiting enzyme in the conversion of cholesterol into bile acids. To examine the independent effect of estrogen, progestin, and combined estrogen and progestin on the hepatic cholesterol concentration and cholesterol 7alpha-hydroxylase mRNA abundance, 34 ovariectomized adult female cynomolgus monkeys were fed a moderately atherogenic diet for 12 weeks with either oral conjugated equine estrogen ([CEE] n = 8), medroxyprogesterone acetate ([MPA] n = 9), or combined CEE + MPA (n = 9) and compared with a control group (n = 8) that did not receive exogenous sex hormones. After 12 weeks, hepatic cholesterol was significantly lower in CEE-treated (6.2 +/- 1.2 mg/g liver) and CEE + MPA-treated (6.4 +/- 0.9 mg/g liver) animals compared with the control (12.6 +/- 1.9 mg/g liver) and MPA-treated (14.6 +/- 1.6 mg/g liver) groups. Hepatic cholesterol 7alpha-hydroxylase mRNA abundance was significantly increased in CEE-treated (0.553 +/- 0.08 pg/microg RNA), MPA-treated (0.734 +/- 0.12 pg/microg RNA), and CEE + MPA-treated (0.487 +/- 0.07 pg/microg RNA) animals compared with the controls (0.318 +/- 0.03 pg/microg RNA). There was no significant difference in the plasma LDL cholesterol concentration and hepatic LDL receptor mRNA abundance between the groups. These data support but do not prove the hypothesis that low-dose oral estrogen induces an increase in cholesterol 7alpha-hydroxylase mRNA abundance, which is correlated with biliary cholesterol secretion and may result in depletion of hepatic cholesterol.

The effect of hormone replacement therapy on the oxidation of low density lipoprotein in postmenopausal women

The oxidative modification of low density lipoprotein (LDL) is important in the pathogenesis of atherosclerosis, and oestrogen has been shown to inhibit copper and cell mediated oxidation of LDL in vitro. We have investigated the effect of oral and transdermal oestrogens (oestradiol valerate 1 mg, conjugated equine oestrogens 0.625 mg and patches releasing 50 microg oestradiol daily), oestrogen implants (oestradiol 50 mg) and oral combined oestrogen and progestogen (oestradiol valerate 2 mg with medroxyprogesterone acetate 5 mg and oestradiol valerate 2 mg with norethisterone acetate 1 mg), on the susceptibility of LDL to oxidation in postmenopausal women (total n = 56). Oxidation of LDL was initiated by the addition of copper ions, and monitored by measurement of conjugated dienes. Changes in fasting serum levels of total cholesterol, LDL, HDL and triglycerides were also evaluated, as were changes in LDL composition. Total cholesterol decreased by 5.5% (P < 0.05) with CEE, 6.8% with oestradiol implants (P < 0.05), 9.3% with oestradiol + MPA (P < 0.01) and 10% with oestradiol + norethisterone (P < 0.05). There were reductions in LDL with oral oestradiol valerate (7.8%) (P < 0.05), CEE (13.8%) (P < 0.01) and oestradiol combined with MPA (12.7%) (P < 0.05). HDL increased by 7.1% (P < 0.01) and 6.3% (P < 0.05), with oestradiol valerate and CEE respectively, and decreased by 9% (P < 0.05) with implants and by 14.7% with oestradiol combined with norethisterone (P < 0.01). Triglycerides were significantly increased with CEE (14.9%) and reduced with oestradiol implants (15.2%) (both P < 0.05). While there was no change in the ratio of 'cholesterol ester' to 'free cholesterol' within LDL with any of the HRT preparations, a reduction in total cholesterol and cholesterol ester content of LDL occurred with transdermal oestradiol and a reduction in free cholesterol occurred with oestradiol plus MPA. Although we found a small but significant decrease in plasma hydroperoxide concentration four weeks after insertion of the oestradiol implant from 1.17 +/- 0.06 to 1.03 +/- 0.04 micromol/l (P < 0.05), we found no significant change in the lag time to oxidation, or in the maximum rate of propagation of the reaction, after treatment with any of the above forms of hormone replacement therapy. This study does not therefore support the role of oestrogens as antioxidants in vivo.

Effects of contraceptive estrogen and progestin on the atherogenic potential of plasma LDLs in cynomolgus monkeys

This study was designed to determine the effect of oral contraceptive treatment (estrogen and progestin), alone or in combination, on LDL composition and atherogenic potential in cynomolgus monkeys fed an atherogenic diet. Groups (n = 8 each) of monkeys were untreated (control) or treated with ethinyl estradiol (EE), levonorgestrel (LNG); or triphasic oral contraceptive (EE+LNG) for 1.5 years before plasma LDLs were isolated for characterization. Total plasma cholesterol concentrations were unaffected by the treatments. LDL particle size (measured as LDL molecular weight, g/mumol) was significantly smaller, in the EE (4.61 +/- 0.09) and EE+LNG (4.43 +/- 0.09) treatment groups compared with the control (4.99 +/- 0.09) or LNG (5.29 +/- 0.17) groups and contained fewer molecules of free and esterified cholesterol. Both the EE and EE+LNG groups had significantly less cholesterol and apolipoprotein B distributed in the d = 1.015 to 1.025 g/mL subfraction and correspondingly more in the d = 1.025 to 1.035 g/mL subfraction of LDL compared with the control and LNG groups. The apolipoprotein E content (molecules/particle) of LDL was significantly less in the EE (0.35 +/- 0.1) and EE+LNG (0.28 +/- 0.1) groups compared with the control (0.86 +/- 0.2) and LNG (0.99 +/- 0.2) groups, and this trend was apparent in all three LDL subfractions. The atherogenic potential of LDL was tested using an in vitro binding assay to arterial proteoglycans. Twice as much LDL bound to arterial proteoglycans in the LNG group (11.3 +/- 1.8% of total LDL cholesterol in the incubation) compared with the control (6.4 +/- 1.9%), EE (5.5 +/- 1.5%), or EE+LNG (5.2 +/- 1.2%) groups. We conclude that EE and EE+LNG treatment alters the composition of LDL toward a less atherogenic particle that is smaller and more dense, contains less cholesterol and less apolipoprotein E, and is less reactive with arterial proteoglycans compared with LNG treatment. The inclusion of EE in the triphasic oral contraceptive treatment was sufficient to negate the potentially atherogenic effects of LNG on LDL composition.

Effects of short-term hormone replacement therapies on low-density lipoprotein metabolism in cynomologus monkeys

Estrogen replacement therapy reduces the risk of coronary heart disease in women and decreases the extent of atherosclerosis in monkeys. In our previous studies, estrogen treatment decreased arterial LDL degradation and accumulation, thus indicating one mechanism by which estrogen inhibits the progression of atherosclerosis. The influence of progestins on these processes remains nuclear. The objective of this study was to determine the effects of oral estrogen (conjugated equine estrogens) and progestin (medroxyprogesterone acetate) alone or in combination on arterial LDL metabolism after 12 weeks of atherogenic stimulus. This relatively short period of treatment was chosen to determine effects on arterial LDL metabolism before substantial subendothelial macrophage accumulation. In contrast to previous studies (16 to 18 weeks of treatment), when macrophages were present in the intima, neither estrogen nor progestin (nor their combination) had any effect on any index of arterial LDL metabolism. These results suggest that estrogen may preferentially reduce LDL metabolism in macrophages with little effect on cells of the normal artery. In contrast to arterial LDL metabolism, hepatic LDL uptake was significantly increased in animals treated with estrogen or estrogen plus progestin. Despite the increased LDL uptake by the liver, hepatic lipid content was significantly decreased by approximately 50% in both estrogen and estrogen-plus-progestin treatment compared with control and progestin-treated animals. The decrease in hepatic cholesterol content in hypothesized to be due to increased biliary secretion of cholesterol.

Dietary soy protein and estrogen replacement therapy improve cardiovascular risk factors and decrease aortic cholesteryl ester content in ovariectomized cynomolgus monkeys

Estrogen replacement therapy (ERT) decreases the progression of coronary artery atherosclerosis in monkeys. Dietary soy protein also retards the progression of atherosclerosis relative to animal proteins such as casein. Soy protein contains weakly estrogenic compounds called isoflavones or phytoestrogens that may be responsible for the cardioprotective effects. This study was designed as a 2 x 2 factorial to determine the magnitude of soy protein's effects on cardiovascular risk factors relative to casein and lactalbumin, with or without estradiol treatment. Ovariectomized female monkeys were randomized to four treatment groups based on past dietary cholesterol consumption, their origin, and past reproductive history, and studied for 7 months. The animals were divided into (1) a group fed casein and lactalbumin as the protein source (n = 14), (2) a group fed casein and lactalbumin as the protein source plus 17 beta-estradiol (E2) (n = 13), (3) a group fed soybean protein isolate as the protein source (n = 11), and (4) a group fed soybean protein isolate as the protein source plus E2 (n = 10). Soy protein compared with casein consumption resulted in a significant improvement in plasma lipid and lipoprotein concentrations, a significant improvement in insulin sensitivity and glucose effectiveness as determined by minimal-model analyses, and a decrease in arterial lipid peroxidation. E2-treated monkeys had a significant reduction in fasting insulin levels and insulin to glucose ratios, total body weight, and amounts of abdominal fat, and had smaller low-density lipoprotein (LDL) particles. In addition, E2 treatment resulted in a significant reduction (P = .001) in aortic cholesteryl ester content. A similar trend (P = .14) was found for soy protein compared with casein. There also was a significant interaction (P = .02) with soy and E2, such that animals consuming soy protein +E2 had the least arterial cholesteryl ester content. These results suggest that both ERT and dietary soybean protein have beneficial effects on cardiovascular risk factors. Interestingly, the two treatments affected different risk factors and together resulted in the greatest reduction in arterial cholesterol content. Further studies are needed to determine the active component of the soy protein and to assess its long-term effects on the cardiovascular system and other organ systems (such as the bones and reproductive system).

Esterified estrogens with and without methyltestosterone decrease arterial LDL metabolism in cynomolgus monkeys

Although both epidemiological and experimental evidence suggests that estrogen replacement therapy reduces the risk of coronary heart disease, the mechanisms for this beneficial effect are largely unknown. Furthermore, the addition of progestins or androgens to estrogen replacement therapy is of concern. The objective of this study was to examine the effects of esterified estrogens alone or in combination with an androgen on arterial LDL metabolism and early atherogenesis in ovariectomized female cynomolgus monkeys. Arterial LDL metabolism was assessed by using dual-labeled LDL that was injected 24 hours before necropsy. Arterial LDL degradation was reduced by 64% to 84% and cholesteryl ester content was decreased by approximately 50% in the thoracic aorta in both treatment groups compared with controls. In addition, aortic lipid peroxidation products, as assessed by thiobarbituric acid reaction, were significantly lower in animals treated with esterified estrogens, with a similar trend for combined estrogen-androgen treatment. Both treatments also reduced plasma concentrations of apoB-containing lipoproteins, reduced LDL particle size, and increased total-body LDL catabolism. The combination of decreased arterial LDL metabolism, decreased arterial lipid peroxidation, and improved plasma lipoprotein metabolism may explain some of the protective effects of estrogens on coronary heart disease and indicate that beneficial actions extend to a combination of estrogen and androgen.