Need for research on estrogen receptor function: Importance for postmenopausal hormone therapy and atherosclerosis

Background: Cardiovascular disease is the leading cause of morbidity and mortality in men and women worldwide. Although rare in premenopausal women, its incidence rises sharply after menopause, indicating atheroprotective effects of endogenous estrogens.Objective: This review discusses the differential effects of estrogen receptor function on atherosclerosis progression in pre- and postmenopausal women, including aspects of gender differences in vascular physiology of estrogens and androgens.Methods: Recent advances in the understanding of the pathogenesis of atherosclerosis, estrogen receptor function, and hormone therapy are reviewed, with particular emphasis on clinical and molecular issues.Results: Whether hormone therapy can improve cardiovascular health in postmenopausal women remains controversial. Current evidence suggests that the vascular effects of estrogen are affected by the stage of reproductive life, the time since menopause, and the extent of subclinical atherosclerosis. The mechanisms of vascular responsiveness to sex steroids during different stages of atherosclerosis development remain poorly understood in women and men.Conclusion: In view of the expected increase in the prevalence of atherosclerotic vascular disease worldwide due to population aging, research is needed to determine the vascular mechanism of endogenous and exogenous sex steroids in patients with atherosclerosis. Such research may help to define new strategies to improve cardiovascular health in women and possibly also in men.     

Genetic and pharmacologic strategies to determine the function of estrogen receptor α and estrogen receptor β in cardiovascular system

Background: The biological functions of estrogens extend beyond the female and male reproductive tract, affecting the cardiovascular and renal systems. Traditional views on the role of postmenopausal hormone therapy (HT) in protecting against heart disease, which were challenged by clinical end point studies that found adverse effects of combined HT, are now being replaced by more differentiated concepts suggesting a beneficial role of early and unopposed HT that does not include a progestin.Objective: We reviewed recent insights, concepts, and research results on the biology of both estrogen receptor (ER) subtypes, ERα and ERβ, in cardiac and vascular tissues. Knowledge of these ER subtypes is crucial to understanding gender and estrogen effects and to developing novel, exciting strategies that may have a profound clinical impact.Methods: This review focuses on in vivo studies and includes data presented at the August 2007 meeting of the American Physiological Society as well as data from a search of the MEDLINE and Ovid databases from January 1986 to November 2007. Search results were restricted to English-language publications, using the following search terms: estrogen, estrogen receptor α, estrogen receptor β, estrogen receptor α agonist, estrogen receptor α antagonist, estrogen receptor β agonist, estrogen receptor β antagonist, PPT, DPN, heart, vasculature, ERKO mice, BERKO mice, transgenic mice, and knockout mice.Results: Genetic mouse models and pharmacologic studies that employed selective as well as nonselective ER agonists support the concept that both ER subtypes confer protective effects in experimental models of human heart disease, including hypertension, cardiac hypertrophy, and chronic heart failure.Conclusions: Genetic models and novel ligands hold the promise of further improving our understanding of estrogen action in multiple tissues and organs. These efforts will ultimately enhance the safety and efficacy of HT and may also result in new applications for synthetic female sex hormone analogues.     

Estrogen receptors in the kidney: Lessons from genetically altered mice

Background: Sex differences in human and animal models of kidney disease suggest that estrogen receptor (ER)-mediated events may modulate these processes. Genetically altered mice lacking one or both ERs provide a powerful tool to study these phenomena.Objective: This article examines sex differences in the kidney, particularly the role of ERs.Methods: To identify pertinent studies in genetically altered mice, a literature search was conducted on the MEDLINE database from January 1966 to July 2007, using the search terms estrogen receptor, kidney, and mice. Our group examined the effect of the ER-α knockout genotype on the kidney in streptozotocin-induced diabetes mellitus and compensatory kidney growth after uninephrectomy.Results: Female mice lacking ERa had reduced renal growth, including glomerular enlargement after 2 weeks of streptozotocin-induced diabetes mellitus and compensatory kidney growth 48 hours after uninephrectomy.Conclusion: ER-mediated events influence kidney growth and disease in female mice.     

Cardiovascular Health Maintenance in Aging Individuals: The Implications for Transgender Men and Women on Hormone Therapy

ObjectiveTo review screening guidelines for cardiometabolic disease in aging patients and review literature describing the effect of hormone therapy (HT) on several key cardiometabolic processes to inform providers caring for older transgender individuals.MethodsA traditional literature review was performed using PubMed and Google Scholar databases.ResultsThe risk of cardiovascular disease increases with age. Exogenous sex hormones may interact with hormone-dependent metabolic pathways and affect some biochemical assays, but they do not necessarily impact clinical outcomes. While long-term HT is associated with an increased risk of some adverse cardiovascular outcomes, modern treatment regimens minimize this risk.ConclusionScreening for cardiometabolic derangements and risk reduction are important for all aging individuals. Currently, there is insufficient evidence to propose separate screening recommendations for transgender individuals on long-term HT. Aging transgender men and women should be monitored for cardiovascular disease in much the same way as their cisgender counterparts.     

Estrogen,inflammation, and platelet phenotype

Background: Although exogenous estrogenic therapies increase the risk of thrombosis, the effects of estrogen on formed elements of blood are uncertain.Objective: This article examines the genomic and nongenomic actions of estrogen on platelet phenotype that may contribute to increased thrombotic risk.Methods: To determine aggregation, secretion, protein expression, and thrombin generation, platelets were collected from experimental animals of varying hormonal status and from women enrolled in the Kronos Early Estrogen Prevention Study.Results: Estrogen receptor β predominates in circulating platelets. Estrogenic treatment in ovariectomized animals decreased platelet aggregation and adenosine triphosphate (ATP) secretion. However, acute exposure to 17β-estradiol did not reverse decreases in platelet ATP secretion invoked by lipopolysaccharide. Thrombin generation was positively correlated to the number of circulating microvesicles expressing phosphatidylserine.Conclusion: Assessing the effect of estrogen treatments on blood platelets may lead to new ways of identifying women at risk for adverse thrombotic events with such therapies.     

Gender, sex hormones, and vascular tone

The greater incidence of hypertension and coronary artery disease in men and postmenopausal women compared with premenopausal women has been related, in part, to gender differences in vascular tone and possible vascular protective effects of the female sex hormones estrogen and progesterone. However, vascular effects of the male sex hormone testosterone have also been suggested. Estrogen, progesterone, and testosterone receptors have been identified in blood vessels of human and other mammals and have been localized in the plasmalemma, cytosol, and nuclear compartments of various vascular cells, including the endothelium and the smooth muscle. The interaction of sex hormones with cytosolic/nuclear receptors triggers long-term genomic effects that could stimulate endothelial cell growth while inhibiting smooth muscle proliferation. Activation of plasmalemmal sex hormone receptors may trigger acute nongenomic responses that could stimulate endothelium-dependent mechanisms of vascular relaxation such as the nitric oxide-cGMP, prostacyclin-cAMP, and hyperpolarization pathways. Additional endothelium-independent effects of sex hormones may involve inhibition of the signaling mechanisms of vascular smooth muscle contraction such as intracellular Ca2+ concentration and protein kinase C. The sex hormone-induced stimulation of the endothelium-dependent mechanisms of vascular relaxation and inhibition of the mechanisms of vascular smooth muscle contraction may contribute to the gender differences in vascular tone and may represent potential beneficial vascular effects of hormone replacement therapy during natural and surgically induced deficiencies of gonadal hormones.     

Methoxyestradiols mediate the antimitogenic effects of estradiol on vascular smooth muscle cells via estrogen receptor-independent mechanisms

Estrogen receptors (ERs) are widely held to mediate the ability of 17 beta-estradiol (estradiol) to attenuate injury-induced proliferation of vascular smooth muscle cells (VSMCs) leading to vascular lesions. However, recent findings that estradiol prevents injury-induced vascular lesion formation in knock-out mice lacking either ER alpha or ER beta seriously challenge this concept. Here we report that the local metabolism of estradiol to methoxyestradiols, endogenous metabolites of estradiol with no affinity for ERs, is responsible for the ER-independent inhibitory effects of locally applied estradiol on rat VSMC growth. These finding imply that local vascular estradiol metabolism may be an important determinant of the cardiovascular protective effects of circulating estradiol. Thus, interindividual differences, either genetic or acquired, in the vascular metabolism of estradiol may define a given female's risk of cardiovascular disease and influence the cardiovascular benefit she receives from estradiol replacement therapy in the postmenopausal state. These findings also imply that nonfeminizing estradiol metabolites may confer cardiovascular protection in both women and men.     

Serotonergic and noradrenergic receptors in the rat brain: modulation by chronic exposure to ovarian hormones

Noradrenergic (alpha 1 and beta) and serotonergic (5HT1 and 5HT2) receptors were assayed in the brains of ovariectomized female rats treated for 2 weeks with estrogen, progesterone or a combination of both hormones. Estrogen treatment resulted in a decrease in the number of 5HT1 and beta adrenergic receptors, with a concomitant increase in 5HT2 receptors. Progesterone alone caused a smaller increase in 5HT2 receptors, a similar decrease in 5HT1 and had no significant effect on noradrenergic receptors. When given with estrogen, progesterone blocked the estrogen effect on 5HT2 receptors but did not inhibit the estrogen-mediated decrease in 5HT1 and beta adrenergic receptors. alpha 1 adrenergic receptors were not affected by any of the hormone treatment paradigms. beta adrenergic and 5HT2 receptors are often implicated in antidepressant action, and the modulation of these two receptor types by ovarian hormones might be relevant to hormone-linked affective changes such as premenstrual tension and post-partum depression.     

The protective role of estrogen and estrogen receptors in cardiovascular disease and the controversial use of estrogen therapy

Epidemiologic studies have previously suggested that premenopausal females have reduced incidence of cardiovascular disease (CVD) when compared to age-matched males, and the incidence and severity of CVD increases postmenopause. The lower incidence of cardiovascular disease in women during reproductive age is attributed at least in part to estrogen (E2). E2 binds to the traditional E2 receptors (ERs), estrogen receptor alpha (ERα), and estrogen receptor beta (ERβ), as well as the more recently identified G-protein-coupled ER (GPR30), and can exert both genomic and non-genomic actions. This review summarizes the protective role of E2 and its receptors in the cardiovascular system and discusses its underlying mechanisms with an emphasis on oxidative stress, fibrosis, angiogenesis, and vascular function. This review also presents the sexual dimorphic role of ERs in modulating E2 action in cardiovascular disease. The controversies surrounding the clinical use of exogenous E2 as a therapeutic agent for cardiovascular disease in women due to the possible risks of thrombotic events, cancers, and arrhythmia are also discussed. Endogenous local E2 biosynthesis from the conversion of testosterone to E2 via aromatase enzyme offers a novel therapeutic paradigm. Targeting specific ERs in the cardiovascular system may result in novel and possibly safer therapeutic options for cardiovascular protection.     

Selected contribution: estrogen receptor-alpha gene transfer inhibits proliferation and NF-kappaB activation in VSM cells from female rats.

Epidemiological studies have demonstrated that hormone replacement therapy with estrogen (E2) or E2 plus progesterone in postmenopausal women decreases the age-associated risk of cardiovascular disease by 30-50%. Treatment of vascular smooth muscle (VSM) cells with physiological concentrations of E2 has been shown to inhibit growth factor-stimulated cell proliferation. In this study, we tested the hypothesis that E2 inhibits the age-associated increase in VSM cell proliferation by inhibiting nuclear factor (NF)-kappaB pathway. We investigated the effects of E2 treatment and adenovirus-mediated estrogen receptor (ER)-alpha gene transfer on cell proliferation and NF-kappaB activation using VSM cells cultured from 3-mo-old and 24-mo-old Fischer 344 female rats. Our results demonstrate that VSM cell proliferation was significantly increased (P < 0.05) in aged compared with young adult female rats. Treatment of VSM cells with physiological concentrations of E2 inhibited VSM cell proliferation, and this inhibition was significantly greater (P < 0.05) in cells from aged female rats compared with young adults. The inhibitory effects of E(2) on cell proliferation in aged female rats were significantly potentiated by overexpression of the human ER-alpha gene into VSM cells. Constitutive and interleukin (IL)-1beta-stimulated NF-kappaB activation was significantly greater (P < 0.05) in VSM cells from aged compared with young female rats. E2 treatment of VSM cells from aged female rats inhibited both constitutive and IL-1beta-stimulated NF-kappaB activation. ER-alpha gene transfer into VSM cells from aged female rats further augmented the inhibitory effects of E2. In conclusion, our data demonstrate that constitutive and IL-1beta-stimulated NF-kappaB activation is increased in VSM cells from aged female rats due to loss of E2 and this can be restored back to normal levels by ER-alpha gene transfer and E2 treatment. In addition, increased NF-kappaB signaling may be responsible for increased incidence of cardiovascular disease in postmenopausal females.     

Postmenopausal hormone therapy and cognition

This article is part of a Special Issue "Estradiol and cognition".Prior to the publication of findings from the Women's Health Initiative (WHI) in 2002, estrogen-containing hormone therapy (HT) was used to prevent age-related disease, especially cardiovascular disease, and to treat menopausal symptoms such as hot flushes and sleep disruptions. Some observational studies of HT in midlife and aging women suggested that HT might also benefit cognitive function, but randomized clinical trials have produced mixed findings in terms of health and cognitive outcomes. This review focuses on hormone effects on cognition and risk for dementia in naturally menopausal women as well as surgically induced menopause, and highlights findings from the large-scale WHI Memory Study (WHIMS) which, contrary to expectation, showed increased dementia risk and poorer cognitive outcomes in older postmenopausal women randomized to HT versus placebo. We consider the ‘critical window hypothesis’, which suggests that a window of opportunity may exist shortly after menopause during which estrogen treatments are most effective. In addition, we highlight emerging evidence that potential adverse effects of HT on cognition are most pronounced in women who have other health risks, such as lower global cognition or diabetes. Lastly, we point towards implications for future research and clinical treatments.     

Regulation of mitochondrial respiratory chain structure and function by estrogens/estrogen receptors and potential physiological/pathophysiological implications

It is well known that the biological and carcinogenic effects of 17beta-estradiol (E2) are mediated via nuclear estrogen receptors (ERs) by regulating nuclear gene expression. Several rapid, non-nuclear genomic effects of E2 are mediated via plasma membrane-bound ERs. In addition, there is accumulating evidence suggesting that mitochondria are also important targets for the action of estrogens and ERs. This review summarized the studies on the effects of estrogens via ERs on mitochondrial structure and function. The potential physiological and pathophysiological implications of deficiency and/or overabundance of these E2/ER-mediated mitochondrial effects in stimulation of cell proliferation, inhibition of apoptosis, E2-mediated cardiovascular and neuroprotective effects in target cells are also discussed.     

Impact of triglycerides on lipid and lipoprotein biology in women

Background: Because atherosclerosis, a leading cause of morbidity and mortality in women, is thought of as a sterol (cholesterol and noncholesterol sterol)-mediated disease, plasma triglyceride (TG) levels (the concentration of all TG trafficked within all of the lipoproteins per dL of plasma), TG biology, and TG pathobiology historically have been ignored or frequently misunderstood in both risk assessment and treatment decisions.Objectives: This review presents information on the importance of TG (chemical name, triacylglycerol) in atherogenesis and the relationship of TG to gender, adiposopathy (the pathophysiological transformation of functional adipose tissue into an organ with pathogenic endocrine and immune responses), insulin resistance, sterol-trafficking lipoproteins, and overall vascular health. In addition, this review seeks to explain the complexities of lipid homeostasis and how it is influenced by lipid-modulating medications, reproductive hormones, and selective estrogen receptor modulators (SERMs).Methods: Using peer-reviewed materials published in English from the extensive libraries of the authors, this narrative review references key epidemiologic, basic science lipid/lipoprotein publications as well as efficacy trials of lipid-modulating, hormonal, and SERM therapies.Results: TG are associated with insulin resistance; the metabolic syndrome; increased atherogenic lipo-proteins; and rheologic, inflammatory, and coagulation abnormalities. TG can be influenced by lifestyle and multiple medications used by women, including hormonal therapies. Several studies, but not all, support sex differences in TG.Conclusions: Through effects on sterol-trafficking lipoproteins, TG have a significant influence on atherosclerotic cardiovascular disease risk in menopausal women. TG-rich lipoproteins are affected by lipid-modulating drugs, estrogen therapy, estrogen-progestogen therapy, and SERMs.     

Vasoprotective activity of standardized Achillea millefolium extract

We investigated the effects of Achillea millefolium extract in vitro on the growth of primary rat vascular smooth muscle cells (VSMCs) as well as the potential involvement of estrogen receptors (ERs) in this process. In addition, the ability of A. millefolium extract to modulate the NF-κB pathway was tested in human umbilical vein endothelial cells (HUVECs). The fingerprinting of the extract was carried out by HPLC-DAD and LC-MSⁿ and main constituents were flavonoids (10%) and dicaffeolylquinic acid derivatives (12%). The extract enhanced VSMC growth at least in part by acting through ERs and impaired NF-κB signaling in HUVECs. The various compounds may act with different mode of actions thus contributing to the final effect of the extract. Our findings support some of the traditional uses of A. millefolium, and suggest potential modes of action as related to its effects on vascular inflammation. Therefore, A. millefolium may induce novel potential actions in the cardiovascular system.     

Menopausal Hormone Therapy and Chronic Disease Risk in the Women’S Health Initiative: is Timing Everything?

ObjectiveThis review provides a comprehensive overview of the most recent findings from the Women’s Health Initiative (WHI) hormone therapy (HT) trials and highlights the role of age and other clinical risk factors in risk stratification.MethodsWe review the findings on cardiovascular disease, cancer outcomes, all-cause mortality, and other major endpoints in the two WHI HT trials (conjugated equine estrogens [CEEs, 0.625 mg/day] with or without medroxyprogesterone acetate [MPA, 2.5 mg/day]).ResultsThe hazard ratio (HR) for coronary heart disease (CHD) was 1.18 (95% confidence interval [CI], 0.95 to 1.45) in the CEE + MPA trial and 0.94 (95% CI, 0.78 to 1.14) in the CEE-alone trial. In both HT trials, there was an increased risk of stroke and deep vein thrombosis and a lower risk of hip fractures and diabetes. The HT regimens had divergent effects on breast cancer. CEE + MPA increased breast cancer risk (cumulative HR, 1.28; 95% CI, 1.11 to 1.48), whereas CEE alone had a protective effect (cumulative HR, 0.79; 95% CI, 0.65 to 0.97). The absolute risks of HT were low in younger women (ages 50 to 59 years) and those who were within 10 years of menopause onset. Furthermore, for CHD, the risks were elevated for women with metabolic syndrome or high low-densitylipoprotein cholesterol concentrations but not in women without these risk factors. Factor V Leiden genotype was associated with elevated risk of venous thromboembolism on HT.ConclusionHT has a complex pattern of benefits and risks. Women in early menopause have low absolute risks of chronic disease outcomes on HT. Use of HT for management of menopausal symptoms remains appropriate, and risk stratification will help to identify women in whom benefits would be expected to outweigh risks. (Endocr Pract. 2014;20:1201-1213)     

A component of Premarin® enhances multiple cognitive functions and influences nicotinic receptor expression

In women, ovarian hormone loss at menopause has been related to cognitive decline, and some studies suggest that estrogen-containing hormone therapy (HT) can mitigate these effects. Recently, the Women's Health Initiative study found that conjugated equine estrogens, the most commonly prescribed HT, do not benefit cognition. Isolated components of conjugated equine estrogens (tradename Premarin^®) have been evaluated in vitro, with delta^8,9-dehydroestrone (?⁸E1) and equilin showing the strongest neuroprotective profiles. It has not been evaluated whether ?⁸E1 or equilin impact cognition or the cholinergic system, which is affected by other estrogens and known to modulate cognition. Here, in middle-aged, ovariectomized rats, we evaluated the effects of ?⁸E1 and equilin treatments on a cognitive battery and cholinergic nicotinic receptors (nAChR). Specifically, we used ¹²⁵I-labeled epibatidine binding to assay brain nicotinic receptor containing 4α and 2β subunits (α4β2-nAChR), since this nicotinic receptor subtype has been shown previously to be sensitive to other estrogens. ?⁸E1 enhanced spatial working, recent and reference memory. ?⁸E1 also decreased hippocampal and entorhinal cortex α4β2-nAChR expression, which was related to spatial reference memory performance. Equilin treatment did not affect spatial memory or rat α4β2-nAChR expression, and neither estrogen impacted ⁸⁶Rb⁺ efflux, indicating lack of direct action on human α4β2 nAChR function. Both estrogens influenced vaginal smear profiles, uterine weights, and serum luteinizing hormone levels, analogous to classic estrogens. The findings indicate that specific isolated Premarin^® components differ in their ability to affect cognition and nAChR expression. Taken with the works of others showing ?⁸E1-induced benefits on several dimensions of health-related concerns associated with menopause, this body of research identifies ?⁸E1 as a new avenue to be investigated as a potential component of HT that may benefit brain health and function during aging.     

A component of Premarin® enhances multiple cognitive functions and influences nicotinic receptor expression

In women, ovarian hormone loss at menopause has been related to cognitive decline, and some studies suggest that estrogen-containing hormone therapy (HT) can mitigate these effects. Recently, the Women's Health Initiative study found that conjugated equine estrogens, the most commonly prescribed HT, do not benefit cognition. Isolated components of conjugated equine estrogens (tradename Premarin^®) have been evaluated in vitro, with delta^8,9-dehydroestrone (∆⁸E1) and equilin showing the strongest neuroprotective profiles. It has not been evaluated whether ∆⁸E1 or equilin impact cognition or the cholinergic system, which is affected by other estrogens and known to modulate cognition. Here, in middle-aged, ovariectomized rats, we evaluated the effects of ∆⁸E1 and equilin treatments on a cognitive battery and cholinergic nicotinic receptors (nAChR). Specifically, we used ¹²⁵I-labeled epibatidine binding to assay brain nicotinic receptor containing 4α and 2β subunits (α4β2-nAChR), since this nicotinic receptor subtype has been shown previously to be sensitive to other estrogens. ∆⁸E1 enhanced spatial working, recent and reference memory. ∆⁸E1 also decreased hippocampal and entorhinal cortex α4β2-nAChR expression, which was related to spatial reference memory performance. Equilin treatment did not affect spatial memory or rat α4β2-nAChR expression, and neither estrogen impacted ⁸⁶Rb⁺ efflux, indicating lack of direct action on human α4β2 nAChR function. Both estrogens influenced vaginal smear profiles, uterine weights, and serum luteinizing hormone levels, analogous to classic estrogens. The findings indicate that specific isolated Premarin^® components differ in their ability to affect cognition and nAChR expression. Taken with the works of others showing ∆⁸E1-induced benefits on several dimensions of health-related concerns associated with menopause, this body of research identifies ∆⁸E1 as a new avenue to be investigated as a potential component of HT that may benefit brain health and function during aging.     

Estrogens and the diabetic kidney

Background: Across all ages, the incidence and rate of progression of most nondiabetic renal diseases are markedly higher in men compared with age-matched women. These observations suggest that female sex may be renoprotective. In the setting of diabetes, however, this female protection against the development and progression of renal disease is diminished.Objective: This review aimed to summarize our current understanding of sex differences in the development and progression of diabetic renal disease, and of the contribution of sex hormones, particularly estrogens, to the pathophysiology of this disease. We also attempted to answer why female sex does not protect the diabetic kidney.Methods: Using terms such as gender, sex, diabetes, diabetic nephropathy, estrogens, and sex hormones, the PubMed database was searched for English-language articles; targeted searches were conducted using terms such as gender/sex differences in diabetic renal disease. No restrictions were imposed on publication dates.Results: Although the existing data regarding the sex differences in the incidence and progression of diabetic renal disease are inconclusive, the undisputed fact is that women with either type 1 or type 2 diabetes mellitus exhibit a much higher incidence of renal disease compared with nondiabetic women. It is conceivable that the loss of female sex as a renoprotective factor in diabetes may be related to the abnormal regulation of sex hormone concentrations. Both clinical and experimental data suggest that diabetes may be associated with an imbalance in estradiol concentrations. Supplementation with 17β-estradiol or administration of selective estrogen receptor modulators reduces the incidence of diabetes and attenuates the progression of diabetic renal disease.Conclusions: Serum concentrations of ovarian hormones may provide a new means for predicting future risk of renal complications in diabetes. Exogenous steroid hormones may be an effective treatment for attenuating the progression of diabetic nephropathy.