Oral contraceptive treatment decreases arterial low density lipoprotein degradation in female cynomolgus monkeys

Ischemic heart disease in women and the role of hormone therapy

The prevalence of ischemic heart disease (IHD) has been increasing among the women in developed countries. The well recognized IHD excess in men has often obscured the fact that IHD is the leading cause of death in women. Women have atypical symptoms of IHD that lead to a delay in the diagnosis and an overall poor prognosis. Women have a delay in the onset of IHD due to the beneficial effects of their sex hormones. Postmenopausal women lose this beneficial effect of estrogen and undergo significant changes in their lipid profile, arterial pressure, glucose tolerance, and vascular reactivity that increase their risk for development of IHD. Recently there has been considerable interest in the sex hormones and their role in IHD in women. The general belief that hormone replacement therapy (HRT) has an overall beneficial effect on cardiovascular disease (CVD) in women and hence decreases CVD mortality and morbidity has not been shown in the recent multicenter prospective studies. With the availability of various types of estrogen and progestins, physicians prescribing these agents should take into consideration their varying effects on the cardiovascular system. Risk factor modifications should include diet, weight loss, regular exercise, smoking cessation and adequate control of hypertension (HTN), diabetes (DM) and hyperlipidemia. In the appropriate setting, treatment with proven beneficial agents like aspirin, beta-blockers, angiotensin converting enzyme (ACE) inhibitors and statins will help decrease the burden of IHD in women.

Reproductive hormones and cardiovascular disease mechanism of action and clinical implications

The bulk of the experimental data suggest beneficial effects of estrogen (both premenopausal use of OCs and postmenopausal use of ERT-HRT). An intriguing finding from the monkey studies is that social subordination, which induces estrogen deficiency in female monkeys, accelerates atherosclerosis premenopausally and predicts extent of postmenopausal atherosclerosis. This effect can be inhibited by exogenous estrogen, premenopausally. The results suggest that more effort on detecting and regulating premenopausal ovarian dysfunction may be justified. A complication in understanding estrogen action may be the result of varying extents of arterial damage. For example, primary prevention studies in both postmenopausal animals and women have provided strong evidence of atheroprotection with a variety of estrogens. In contrast, the results of secondary prevention studies [10,12] have in general suggested little cardioprotection with either ERT or HRT. Studies in rabbits suggest the antiatherogenic effect of estrogen may not be present when the endothelium is damaged [64]. The state of the endothelium may be critical for some estrogen actions. For those effects of estrogen that require the ER, be it ERalpha or ERbeta, the presence of the receptor may vary with age, disease state, or type of hormone therapy. If continuous combined HRT therapy decreases ER in the artery as it does in the uterus, this may eliminate those estrogen actions requiring the ER, but not others. Older women who have not been exposed to estrogens for many years may be more sensitive to some estrogen effects, and may need lower doses of ERT-HRT. Recent reports suggest that lower doses of estrogens maintain beneficial effects on lipoproteins and coagulation factors [95], while also requiring lower doses of progestogens to protect the uterus [96]. These beneficial findings are very promising in light of the improvements in CHD risk and decreased stroke risk reported with low-dose estrogens [5]. It ill be interesting to see if CRP is increased with lower doses of estrogens and whether these changes are associated with increased early risk of CHD. Perhaps older women with CHD are also more obese, may have diabetes, and may be more susceptible to inflammatory and thrombotic effects of higher doses of estrogens. There are many questions left unanswered. It is hoped that some of the answers may come from the WHI, which is a large prospective trial assessing ERT and HRT. The age range is also relatively large and may be able to determine if older women respond differently than younger women. Some initial data from the WHI have been made available suggesting a small increased risk in the first 2 years and a trend for decreasing risk in the last months of the first 2 years [34]. Just recently, the CEE + MPA arm of the study was stopped early by the data and-safety monitoring board as the overall health risks exceeded benefits with increases in both breast cancer and CVD [97]. The remainder of the study groups including an estrogen-only arm, are expected to continue until 2005.

Effect of dienogest-containing oral contraceptives on lipid metabolism

In a double-blind, controlled, randomized, four-arm, bicentric clinical study, the effect of four oral contraceptives (OCs) on lipid metabolism was investigated. Four groups composed of 25 volunteers each (mean age 26.1 +/- 4.5 years; body mass index 21.9 +/- 2.8 kg/m(2)) were treated for six cycles with monophasic combinations containing 21 tablets with either 30 microg ethinyl estradiol (EE) + 2 mg dienogest (DNG) (30 EE/DNG), 20 microg EE + 2 mg DNG (20 EE/DNG), 10 microg EE + 2 mg estradiol valerate (EV) + 2 mg DNG (EE/EV/DNG), or 20 microg EE + 100 microg levonorgestrel (LNG; EE/LNG). The study was completed by 91 women. Blood samples were taken by venipuncture after at least 12 h fasting on Days 21-26 of the control cycle and Days 18-21 of the first, third, and sixth treatment cycle. There were clear differences between the effects of EE/LNG and the formulations containing estrogens and DNG. Although EE/LNG did not change the triglycerides levels, a significant increase was observed during treatment with the DNG-containing preparations. Although EE/LNG significantly reduced HDL-CH and HDL(2)-CH, there was a nonsignificant increase with the DNG-containing OCs. No change was observed in the levels of HDL(3)-CH. A significant rise in apolipoprotein A1 occurred during intake with the three DNG-containing formulations, but not with EE/LNG. In contrast to the women treated with combinations of estrogens and DNG, apolipoprotein B rose significantly in the women in the EE/LNG group. Lipoprotein (a) was significantly reduced by 30 EE/DNG and EE/LNG and remained unaltered with 20 EE/DNG and EE/EV/DNG. Altogether, the changes in lipid metabolism caused by the DNG-containing formulations appeared to be more favorable than those observed with EE/LNG. In OCs with DNG, the EE dose does not seem to play a major role with respect to the effect on lipids.

Chronic estradiol treatment attenuates stiffening, glycoxidation, and permeability in rat carotid arteries

Aging-related changes in vascular stiffening and permeability are associated with cardiovascular disease. We examined the interaction of estradiol on the aging process in vascular tissue from rats by assessing the changes in endothelial layer permeability, arterial compliance, and glycoxidative damage levels. We isolated carotid arteries from ovariectomized (OVX) rats that underwent 1 yr of estrogen treatment with subcutaneous pellets and a subsequent 1 mo of cessation of treatment. Endothelial layer permeability and arterial compliance were determined using quantitative fluorescence microscopy. Endothelial layer permeability was reduced with estradiol treatment (estrogen groups, 2.58 +/- 0.21 ng dextran x min(-1) x cm(-2) vs. nonestrogen groups, 4.01 +/- 0.30 ng dextran x min(-1) x cm(-2); P < 0.05). Additionally, arteries from animals treated with estradiol had an increased compliance index (estrogen groups, 82.9 +/- 3.8 mm2. Torr vs. nonestrogen groups, 69.3 +/- 3.2 mm2. Torr; P < 0.05). Estradiol treatment also reduced levels of pentosidine, which is a specific marker of glycoxidative damage (estrogen groups, 0.11 +/- 0.03 pmol pentosidine/nmol collagen vs. nonestrogen groups, 0.20 +/- 0.03 pmol pentosidine/nmol collagen; P < 0.05). These results indicate that estradiol has multiple chronic vasculoprotective effects on the artery wall to maintain normal vascular wall function.

Preclinical profiles of progestins used in formulations of oral contraceptives and hormone replacement therapy

Progestins used in oral contraceptive formulations available in the United States include norgestimate, desogestrel, norethindrone, norethindrone acetate, and levonorgestrel. Progestins used in the United States in continuous and intermittent formulations of hormone replacement therapy are norgestimate, medroxyprogesterone acetate, and norethindrone acetate. The chemical structure of a progestin determines its relative binding affinity for the progesterone and androgen receptors, as well as the sex hormone binding globulin in human serum, and determines its clinical profile. Overall, the properties of levonorgestrel or norethindrone acetate in this regard differ from norgestimate and are more conducive to androgenic stimulation. Estrogen replacement offers cardioprotective effects in postmenopausal women. Progestins are added to hormone replacement therapy to counteract the well-known increased risk of endometrial hyperplasia associated with the use of unopposed estrogen. Animal models show that for some parameters, including improvement of lipid profiles, progestins can diminish the cardioprotective effect of estrogen. Initial animal studies of norgestimate combined with estrogen do not show an attenuation of estrogenic effects.

Sex hormones and vascular reactivity

It is increasingly recognized that sex steroids have, among many other effects, the ability to cause vasodilation. The vasodilatory effects of estradiol have been the best documented and described. At low concentrations, estradiol has the ability to improve impaired endothelium dependent (nitric oxide mediated) relaxation in estrogen deficient subjects. At high concentrations, estradiol causes vasodilation principally by endothelium independent mechanisms, in a gender independent fashion, which appear to involve a number of pathways such as ATP-dependent K+ channels. Testosterone also has ability, at higher doses, to cause vasodilation of the coronary circulation, in a gender independent fashion. The mechanisms of sex steroid-induced vasodilation are reviewed in this article.

Psychosocial factors, sex differences, and atherosclerosis: lessons from animal models

OBJECTIVE

Premenopausal women, compared with men, are relatively spared from coronary heart disease and the underlying atherosclerosis. Our purpose has been to elucidate the reason for this difference and to explore the role of behavioral factors in this phenomenon.

METHODS

Studies employed socially housed cynomolgus macaques (Macaca fascicularis) fed an atherogenic diet and subjected to behavioral observations. Ovariectomy, with or without hormone replacement, was used to test specific hypotheses about estrogen's role in the protection of females from atherosclerosis and coronary heart disease.

RESULTS

Female macaques, like women, are resistant to atherosclerosis. However, this resistance is modified by social status-dominant monkeys develop little atherosclerosis, whereas subordinates resemble males in the amount of lesion that occurs. Subordinate females also are characterized by hypercortisolemia, behavioral dysfunction, and impaired ovarian function; the resulting low concentrations of circulating estrogen perhaps explain their accelerated atherosclerosis. Notably, atherosclerosis is exacerbated in ovariectomized monkeys but is suppressed in association with pregnancy, a hyperestrogenic state. Moreover, exogenous estrogen (an oral contraceptive) inhibits atherosclerosis in premenopausal social subordinates.

CONCLUSIONS

To the extent that our results apply to women, they highlight the potential importance of behavioral stressors and their effects on estrogen activity in the premenopausal development of atherosclerosis. The triad of hypercortisolism, ovarian impairment, and psychiatric morbidity found in monkeys also occurs in women and may represent a high-risk state for disorders of the cardiovascular system and perhaps, other estrogen-sensitive tissues.

Transfer of low density lipoprotein into the arterial wall and risk of atherosclerosis

The aim of the review is to summarize the present knowledge on determinants of transfer of low density lipoprotein (LDL) into the arterial wall, particularly in relation to the risk of development of atherosclerosis. The flux of LDL into the arterial wall (in moles of LDL per surface area per unit of time) has two major determinants, i.e. the LDL concentration in plasma and the arterial wall permeability. LDL enters the arterial wall as intact particles by vesicular ferrying through endothelial cells and/or by passive sieving through pores in or between endothelial cells. Estimates in vivo of the LDL permeability of a normal arterial wall vary between 5 and 100 nl/cm2/h. In laboratory animals, the regional variation in the arterial wall permeability predicts the pattern of subsequent dietary induced atherosclerosis. Moreover, mechanical or immunological injury of the arterial wall increases the LDL permeability and is accompanied by accelerated development of experimental atherosclerosis. This supports the idea that an increased permeability to LDL, like an increased plasma LDL concentration, increases the risk of atherosclerosis. Hypertension, smoking, genetic predisposition, atherosclerosis, and a small size of LDL may all increase the arterial wall permeability to LDL and in this way increase the risk of accelerated development of atherosclerosis. The hypothesis that atherosclerosis risk can be reduced by improving the barrier function of the arterial wall towards the entry of LDL remains to be investigated; agents which directly modulate the LDL permeability of the arterial wall in vivo await identification.

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

This study was designed to determine the effect of several hormone replacement therapies on LDL size, density, heterogeneity, and composition in surgically postmenopausal cynomolgus monkeys fed an atherogenic diet. Groups (n = 5 each) of ovariectomized cynomolgus monkeys were untreated (control), or treated with conjugated equine estrogens, medroxyprogesterone acetate (progesterone), combined estrogen-progesterone, or tamoxifen for 9 weeks. There were no differences among treatment groups in total plasma, LDL, or HDL cholesterol or triglyceride concentrations. Plasma LDL were isolated by ultracentrifugation and size exclusion chromatography and subfractionated by density gradient centrifugation for subsequent chemical analysis. Estrogen treatment was associated with significantly smaller (measured as LDL molecular weight, 3.9 +/- 0.2 g/mu mol) and denser plasma LDL (1.034 g/ml peak density) compared with control (4.5 +/- 0.1 g/mu mol; 1.030 g/ml peak density) or progesterone-treated animals (4.6 +/- 0.2; 1.029 g/ml peak density). LDL from the estrogen group were relatively enriched in protein and triglyceride and poor in cholesteryl ester and apolipoprotein F (apoE) compared to the control group. Triglyceride enrichment with estrogen treatment occurred predominantly in the lighter, larger LDL subfractions (d = 1.015-1.025 g/ml), which were reduced in concentration (26 +/- 10 mg cholesterol/dl) compared to control (61 +/- 19 mg/dl) or progesterone treated animals (67 +/- 16 mg/dl). Combined estrogen-progesterone or tamoxifen treatment resulted in changes in LDL that followed the same trend as those observed with estrogen treatment. We conclude that short-term estrogen treatment of ovariectomized cynomolgus monkeys results in changes in plasma LDL size, density, and composition while having no apparent effect on overall plasma lipid concentrations.

Effects of estrogens on lipoprotein metabolism and cardiovascular disease in women

Estrogen use is associated with protection from cardiovascular disease in postmenopausal women. This benefit appears to be magnified among women with pre-existing heart disease. The possible bias of intrinsically better health in women using estrogen has not been ruled out in observational studies. Therefore, two double-blind randomized clinical trials are underway in postmenopausal women. One in women with coronary disease is known as HERS (Heart Estrogen-progestin Replacement Study) and another in predominantly healthy women is the WHI (Women's Health Initiative). Several mechanisms of estrogen mediated protection from cardiovascular disease have been identified including increased HDL, lower LDL, lower VLDL-cholesterol/triglyceride ratio, increased clearance of intermediate density lipoprotein (IDL) and LDL via an upregulated LDL receptor, diminished penetration and degradation of LDL in the arterial wall, an inhibition of LDL oxidation by various estrogens and a reversal of inappropriate acetylcholine (EDRF)-mediated vasoconstriction in arteriosclerotic vessels. The predominating mechanism is not known, but estrogen replacement therapy is both likely to be beneficial to female health, pending randomized trials, as well as a tool to understand mechanisms of prevention of coronary artery disease.