Antioxidant protection of LDL by physiologic concentrations of estrogens is specific for 17-beta-estradiol

The Roles of Androgens in Humans: Biology, Metabolic Regulation and Health

Androgens are an important and diverse group of steroid hormone molecular species. They play varied functional roles, such as the control of metabolic energy fate and partition, the maintenance of skeletal and body protein and integrity and the development of brain capabilities and behavioral setup (including those factors defining maleness). In addition, androgens are the precursors of estrogens, with which they share an extensive control of the reproductive mechanisms (in both sexes). In this review, the types of androgens, their functions and signaling are tabulated and described, including some less-known functions. The close interrelationship between corticosteroids and androgens is also analyzed, centered in the adrenal cortex, together with the main feedback control systems of the hypothalamic-hypophysis-gonads axis, and its modulation by the metabolic environment, sex, age and health. Testosterone (T) is singled out because of its high synthesis rate and turnover, but also because age-related hypogonadism is a key signal for the biologically planned early obsolescence of men, and the delayed onset of a faster rate of functional losses in women after menopause. The close collaboration of T with estradiol (E2) active in the maintenance of body metabolic systems is also presented Their parallel insufficiency has been directly related to the ravages of senescence and the metabolic syndrome constellation of disorders. The clinical use of T to correct hypoandrogenism helps maintain the functionality of core metabolism, limiting excess fat deposition, sarcopenia and cognoscitive frailty (part of these effects are due to the E2 generated from T). The effectiveness of using lipophilic T esters for T replacement treatments is analyzed in depth, and the main problems derived from their application are discussed.

Crosstalk between high-density lipoproteins and endothelial cells in health and disease: Insights into sex-dependent modulation

Atherosclerotic cardiovascular disease is the leading cause of death worldwide. Intense research in vascular biology has advanced our knowledge of molecular mechanisms of its onset and progression until complications; however, several aspects of the patho-physiology of atherosclerosis remain to be further elucidated. Endothelial cell homeostasis is fundamental to prevent atherosclerosis as the appearance of endothelial cell dysfunction is considered the first pro-atherosclerotic vascular modification. Physiologically, high density lipoproteins (HDLs) exert protective actions for vessels and in particular for ECs. Indeed, HDLs promote endothelial-dependent vasorelaxation, contribute to the regulation of vascular lipid metabolism, and have immune-modulatory, anti-inflammatory and anti-oxidative properties. Sex- and gender-dependent differences are increasingly recognized as important, although not fully elucidated, factors in cardiovascular health and disease patho-physiology. In this review, we highlight the importance of sex hormones and sex-specific gene expression in the regulation of HDL and EC cross-talk and their contribution to cardiovascular disease.

Estrogens and the regulation of glucose metabolism

The main estrogens: estradiol, estrone, and their acyl-esters have been studied essentially related to their classical estrogenic and pharmacologic functions. However, their main effect in the body is probably the sustained control of core energy metabolism. Estrogen nuclear and membrane receptors show an extraordinary flexibility in the modulation of metabolic responses, and largely explain gender and age differences in energy metabolism: part of these mechanisms is already sufficiently known to justify both. With regard to energy, the estrogen molecular species act essentially through four key functions: (1) Facilitation of insulin secretion and control of glucose availability; (2) Modulation of energy partition, favoring the use of lipid as the main energy substrate when more available than carbohydrates; (3) Functional protection through antioxidant mechanisms; and (4) Central effects (largely through neural modulation) on whole body energy management. Analyzing the different actions of estrone, estradiol and their acyl esters, a tentative classification based on structure/effects has been postulated. Either separately or as a group, estrogens provide a comprehensive explanation that not all their quite diverse actions are related solely to specific molecules. As a group, they constitute a powerful synergic action complex. In consequence, estrogens may be considered wardens of energy homeostasis.

Gender, race and cardiac rehabilitation in the United States: is there a difference in care?

Coronary heart disease is the leading cause of death within the United States, involving both genders and among all races and ethnic populations. Cardiac rehabilitation (CR) has been shown to significantly improve morbidity and mortality, and these benefits extend to individuals of both genders and all ages with coronary heart disease. Despite this, referral and participation rates remain surprisingly low. Furthermore, women and minorities have even lower referral rates than do their male and white counterparts. Over the course of this article, we will review CR referral and participation among women, as well as racial and ethnic minorities in the United States. We will also examine barriers to CR participation among these subgroups.

Effects of diabetes and ovariectomy on rat hippocampus (a biochemical and stereological study)

Oxidative stress is one of the main reasons of both menopause and diabetes. So, it plays crucial role in the pathogeneses of that condition and disease. Therefore, the objective of the present study was to investigate the effects of menopause and diabetes upon the hippocampus using a rat model. Adult female Sprague Dawley rats (n = 24) were allocated randomly as follows; control (C group) ovariectomized (O group), diabetic (D group) and ovariectomy plus diabetic groups (DO group) (n = 6; in each group), respectively. For evaluating the results, tissue biochemistry and stereological analysis were made. Biochemistry results (lipid peroxidase (LPO); catalase (CAT); superoxide dismutase (SOD); total glutatyon (GSH); and myeloperoxidase (MPO) values) in Group C-DO were determined as 12.27, 21.88, 23.08 and 29.90 nmol/gr tissue; 59.3, 70.06, 69.7 and 78.1 mmol/min/mg tissue; 174.2, 156.4, 159.7 and 154.6 mmol/min/mg tissue; 3.63, 3.61, 4.21 and 3.97 nmol/mg tissue; and 5.05, 5.68, 5.58 and 6.19 µmol/min/mg tissue, respectively. Moreover, both menopause and diabetes led to change of lipid profiles. There were significant differences between the control and other groups (Group C and D-DO) (p < 0.01) and among experimental groups (p < 0.01) in terms of neuron number. When the volumes of the hippocampus were compared, there were no significant differences between the all groups (P > 0.05). At this point, we suggested that diabetes could aggravate deleterious effects of ovariectomy.

Are there endogenous estrone fatty acyl esters in human plasma or ovarian follicular fluid?

BACKGROUND

Estrone and its sulfated esters are the most abundant estrogens in blood in men and in women after the menopause. However, previous studies on the esterification of estrone with fatty acids have yielded conflicting results, some studies reporting high nanomolar concentrations of estrone fatty acyl esters in plasma.

METHODS

We developed an estrone radioimmunoassay (RIA) method to determine endogenous concentrations of estrone and after saponification, applied it to male and female plasma. In addition, the concentration of estrone fatty acyl esters in ovarian follicular fluid was analyzed by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS).

RESULTS

By estrone RIA, we did not find measurable amounts of estrone fatty acyl esters in male or female plasma, except for one premenopausal woman who had the highest plasma concentration of nonesterified estrone. The concentration of hydrolyzed estrone fatty acyl esters determined by LC-MS/MS in follicular fluid obtained from women undergoing ovarian stimulation was below the limit of quantification of <10 pmol/l (<2.7 ng/l).

CONCLUSIONS

In contrast to previous data by others, our study suggests that estrone fatty acyl esters are in most cases not detectable in plasma of healthy men or healthy nonpregnant women.

Fatty acid esters of steroids: synthesis and metabolism in lipoproteins and adipose tissue

At the end of the last century ideas concerning the physiological role of the steroid fatty acid ester family were emerging. Estrogens, fatty acylated at C-17 hydroxyl group and incorporated in lipoproteins were proposed to provide antioxidative protection to these particles. A large number of studies involving non-estrogenic adrenal steroids, and their fatty acylated forms, demonstrated their lipoprotein-mediated transport into cells and subsequent intracellular activation, suggesting a novel transport mechanism for lipophilic steroid derivatives. After these important advances the main focus of interest has shifted away from C-19 and C-21 steroids to fatty acylated estrogens. However, interest in their lipoprotein-mediated transport has decreased because only minute amounts of these derivatives were detected in circulating lipoproteins, and their antioxidative activity remained unconfirmed under physiological circumstances. It now appears that the overwhelming majority of estradiol in postmenopausal women resides in adipose tissue, most of it in esterified form. This is poorly reflected in plasma levels which are very low. Recent data suggest that estrogen fatty acid esters probably represent a storage form. The future focus of investigation is likely to be on firstly, the enzymatic mechanisms regulating the esterification and de-esterification of estradiol and other steroids residing in adipose tissue and secondly, on the role of insulin and other hormones in the regulation of these enzymatic mechanisms. Thirdly, as a large proportion of fatty acid esterified C-19 and C-21 non-estrogenic steroids is transported in lipoproteins and as they are important precursors of androgens and estrogens, this field should be investigated further.

Oxidative status and cardiovascular risk in women: Keeping pink at heart

Although cardiovascular disease (CVD) has always been perceived as a pathology regarding essentially males, incidence and death from cardiovascular events dramatically increase after menopause in women. Obviously, while many aspects of CVD are similar in both sexes, it is now clear that there are significant differences as well. Exploration of these gender-related differences in CVD might provide a basis for the development of new strategies in the management of patients with CVD from a gender point of view. In particular, a growing amount of data suggested the possible major role of oxidative stress in female patients and the possibility to integrate this new biomarker in future study evaluating CVD risk in women.

Changes of markers of oxidative stress during menstrual cycle

The levels of urinary hydrogen peroxide and thiobarbituric acid reactive substances have been compared during the menstrual cycle of 12 regularly menstruating women. Higher level of both indices of oxidative stress (normalized with respect to creatinine content) were found in the luteal phase of the cycle. These results give further evidence for the usefulness of urinary hydrogen peroxide and thiobarbituric acid reactive substances as potential biomarkers of oxidative stress and for the antioxidant action of estrogens.

Scavenger receptor of class B expressed by osteoblastic cells are implicated in the uptake of cholesteryl ester and estradiol from LDL and HDL3

Lipoproteins transport many vitamins and hormones that have been shown to be necessary for bone formation. However, the metabolism of LDL and HDL3 by bone-forming osteoblastic cells remains unknown. Here we report that osteoblastic cells express scavenger receptors of class B that are implicated in the uptake of cholesterol and estradiol from LDL and HDL3.

INTRODUCTION

The bone tissue is continuously remodeled, and its integrity requires a balance between osteoclastic bone resorption and osteoblastic bone formation. Recent studies have reported the importance of triglyceride-rich lipoproteins for the delivery of lipophilic vitamins necessary for normal bone metabolism. However, the ability of osteoblastic cells to process low- and high-density lipoproteins (LDL and HDL3) and the receptors involved remain unknown.

MATERIALS AND METHODS

Binding, competition, degradation, and selective uptake assays with LDL and HDL3 radiolabeled in their protein and lipid moieties or with [3H]estradiol were conducted on human osteoblasts (MG-63 cell line and primary cultures of human osteoblasts [hOB cells]) and on mouse osteoblasts (MC3T3-E1 cell line and primary cultures of murine osteoblasts [mOB cells]). The expression of scavenger receptors (SRs) by osteoblastic cells was determined by RT-PCR and Western immunoblotting, and cellular localization was assessed by sucrose gradient fractionation.

RESULTS

Osteoblastic cells were able to bind, internalize, and degrade HDL3 and LDL and are capable of selectively taking up cholesteryl esters (CEs) from these lipoproteins. Also, we provide evidence that osteoblastic cells express SR-BI, SR-BII, and CD36 (SR-Bs receptors) and that these receptors are localized in membrane lipid rafts or caveolin-rich membranes. The selective uptake of CE from LDL and HDL3 by osteoblastic cells was strongly inhibited by the known SR-B ligand oxidized LDL, indicating that SR-B receptors are responsible for the selective uptake. Finally, estradiol carried by LDL and HDL3 was selectively transferred to the osteoblastic cells also through SR-B receptors.

CONCLUSIONS

Overall, our results suggest a novel mechanism for the routing of cholesterol and estradiol to osteoblasts involving the metabolism of LDL and HDL3 by SR-B receptors.

No effect of menstrual cycle on LDL oxidizability and particle size

OBJECTIVES

Premenopausal women have a lower incidence of cardiovascular disease than men, but this female advantage disappears after menopause, suggesting that female sex hormones exert some cardioprotective effects. One of the mechanisms proposed to explain this cardioprotection is the antioxidant properties of estrogens. The aim of this work was to assess whether fluctuations in ovarian hormones, particularly 17beta-estradiol (E(2)), during the menstrual cycle were associated with changes in the low-density lipoprotein (LDL) particle size, fatty acyl composition, alpha-tocopherol content and in vitro oxidizability.

METHODS

Twenty-eight healthy premenopausal women (mean age: 32.2 years) participated in the study. Blood was drawn on days 3 (menstrual phase), 14 (follicular phase) and 22 (luteal phase) of the menstrual cycle for plasma determinations and LDL isolation. Plasma E(2), progesterone, follicle-stimulating hormone and luteinizing hormone were determined by immunoassay. LDL oxidation by Cu(2+)- and 2,2'-azobis (2-amidinopropane) was measured by the formation of conjugated dienes, LDL particle size by quasi-elastic light scattering, fatty acyl composition by gas chromatography, alpha-tocopherol by reversed phase HPLC. A within-subjects analysis of variance was performed to determine significant differences of the variables over the course of a subject's menstrual cycle.

RESULTS

The LDL oxidizability indices (lag time before the onset of propagation and the maximal oxidation rate) did not change during the menstrual cycle. The LDL particle size (24.8+/-1.7 nm diameter), alpha-tocopherol (11.7+/-3.7 nmol/mg LDL protein) and fatty acyl composition also remained constant.

CONCLUSIONS

The LDL physicochemical properties and oxidizability are not affected by menstrual cycle phase.

Fatty acid esterification of lipoprotein-associated estrone in human plasma and follicular fluid

Estrogen fatty acid esters constitute a unique family of extremely hydrophobic hormonal derivatives which are exclusively transported in lipoprotein particles in plasma. In estradiol, the fatty acyl residues are conjugated at the 17beta-hydroxyl of the steroid D-ring, leaving the phenolic 3-hydroxyl group unsubstituted and, therefore, preserving antioxidative efficacy. The 17beta-fatty acid derivative of estradiol is proposedly an even more efficient antioxidant protecting LDL and HDL than the parent steroid. Previous studies have established that the enzyme lecithin:cholesterol acyltransferase which catalyzes the fatty acid esterification of 3beta-hydroxyl group of cholesterol, also catalyzes the formation of estrogen 17beta-esters. Estrone, the principal estrogen in the postmenopausal female, has a keto group at carbon-17 and has been thought unable to form fatty acid esters. However, we detected hydrophobic derivatives of estrone following incubations with human plasma and ovarian follicular fluid. These derivatives accumulated in HDL and LDL during incubation showing chemical characteristics similar to estrone-3-fatty acid esters. Liquid chromatographic-mass spectrometric analyses established the presence of unhydrolyzed estrone esters consisting of different fatty acid species, the major one being estrone-3-linoleate, in human HDL particles following incubation of estrone with plasma. These extremely hydrophobic estrone conjugates could, in theory, represent a storage form of this estrogen.

Effects of estrogen-only therapy on LDL oxidation in women with hysterectomy: Does paraoxonase genotype play a role?

OBJECTIVES

This study investigated the effects of estrogen-only therapy on lipid profile (through susceptibility of low density lipoproteins to oxidation) and on oxidant-antioxidant parameters in surgical menopausal women. PON genotypes are also evaluated considering that they may be associated with the personal differences observed in antioxidant effects induced by estrogen.

METHODS

Thirty women who had undergone hysterectomy+bilateral ovariectomy in the last 3 years, with causes other than malignancy were included and given estrogen-only (Premarin-Wyeth Inc. 0.625 mg/day/6 months, equine conjugated estrogen). Blood samples were collected at baseline, first and sixth month of treatment. Serum (total antioxidant activity-TAO and PON activity), erythrocyte (TBARS and catalase activity), LDL and Cu2+ induced ox-LDL (TBARS and diene levels) samples were evaluated and PON1 192 polymorphisms were determined by PCR amplification & restriction enzyme digestion.

RESULTS

At the sixth month, a higher TAO activity (p=0.016) and a lower eTBARS (p=0.028) were detected compared to the basal values. LDL and Cu induced ox-LDL TBARS levels at the sixth month of treatment were significantly (p=0.012 and 0.026, respectively) lower compared to the pretreatment values. Baseline eTBARS (p=0.007), LDL TBARS (p=0.044) and eCAT (p=0.033) activities were significantly higher in homozygote Q allele carriers compared to subjects with R allele. LDL TBARS and Cu2+ induced ox-LDLTBARS of QQ subjects (p=0.018 and 0.050) as well as LDL TBARS of QR subjects (p=0.044) showed a significant decrease with estrogen-only treatment.

CONCLUSIONS

Our study drives the attention to PON polymorphism in postmenopausal women who have risk for atherosclerosis. Although our data is limited, this study is the first that focuses on the role of PON genotypes in antiatherosclerotic effects of estrogen-only and provides important points for further studies.

Estrogen A-ring structure and antioxidative effect on lipoproteins

The oxidative modification of lipoprotein particles is an important step in atherogenesis. Estrogens are known to be powerful antioxidants independently of their binding to the estrogen receptors and the hormonal functions. We explored the structural determinants for the antioxidant activity of a large number of estrogen derivatives (n=43) in an aqueous lipoprotein solution in vitro by monitoring formation of conjugated dienes. Our results indicate that estrogen derivatives with an unsubstituted A-ring phenolic hydroxyl group with one or two adjacent methoxy groups provide strongest antioxidant protection of low density lipoprotein (LDL) and high density lipoprotein (HDL). The electron donating methoxy groups may enhance the antioxidant effect by weakening the phenolic OH bond and providing stability to the formed phenoxyl radical. With some exceptions, compounds completely lacking unsubstituted hydroxyl groups in the A-ring exhibited no antioxidant effect, e.g. the most hydrophilic "tetrol" compound with three unsubstituted A-ring hydroxyl groups had no antioxidant effect. Moreover, additional hydroxyl groups in the B-, C- or D-ring seemed to weaken the antioxidant effect. Accordingly, both the presence of unsubstituted hydroxyl groups and adjacent substituents, as well as the lipophilicity of the derivatives determine the antioxidant activity of estrogen derivatives in aqueous lipoprotein solutions.

Regulation of Low-Density Lipoprotein Receptor Activity by Estrogens and Phytoestrogens in a HepG2 Cell Model

BACKGROUND/AIMS

Estrogen treatment is thought to lower low-density lipoprotein (LDL) cholesterol levels by increasing clearance through hepatic LDL receptors. This study aimed to determine the effect of estrogens and phytoestrogens on LDL receptor activity in a human hepatoma cell line, HepG2.

METHODS

HepG2 cells in culture were incubated for 24 h with estrogen or phytoestrogen and LDL receptor activity was measured by examining the cellular binding of colloidal gold-labelled LDL.

RESULTS

17Beta-estradiol significantly increased LDL receptor activity whereas estriol had negligible effects. Incubation with the isoflavonoids, formononetin, biochanin A and daidzein, caused significant elevations in receptor activity at concentrations above 40 microM. Coumestrol, a coumestan with a high level of estrogenic activity, caused a 3-fold increase in receptor activity at a concentration of 50 microM. Of the phytoestrogenic mammalian lignans enterolactone and enterodiol, only enterolactone displayed the ability to significantly upregulate LDL receptor activity at 50 microM.

CONCLUSION

This study suggests that the LDL receptor-stimulating effect of natural estrogens is mainly due to estradiol and that the cholesterol-lowering effect of diets high in phytoestrogens may be due in part to their ability to increase hepatic LDL receptor activity.

The effect of estrogens and phytoestrogenic lignans on macrophage uptake of atherogenic lipoproteins

The present study examined the effect of estrogens and compounds with estrogenic activity on the uptake of atherogenic lipoproteins into macrophages, thought to be the initiating step in the development of atherosclerotic lesions. Isolated low density lipoprotein (LDL) and lipoprotein(a) (Lp(a)) were radiolabelled with (3)H-cholesterol linoleate, and incubated with J774 macrophages for 24 hours in the presence of pharmacological doses of estrogens and phytoestrogens. At a concentration of 0.1 microM, the estrogen 17beta-estradiol significantly reduced LDL uptake by macrophages by 14% (p < 0.05), but estrone did not have any effect. At 10 microM, both estrogens significantly reduced macrophage LDL uptake, but the phytoestrogenic-lignans enterodiol and enterolactone had no effect on LDL uptake. Lp(a) uptake into cells was significantly reduced by both estrone and estradiol, and by enterolactone and enterodiol at concentrations of 10 microM (p < 0.01), with enterodiol being most effective. The results of this study suggest that the uptake of these structurally similar lipoproteins is regulated differently. Macrophage Lp(a) uptake appears more phytoestrogen sensitive than does LDL uptake.

One site on the apoB-100 specifically binds 17-beta-estradiol and regulates the overall structure of LDL

The major protein component (apoB-100) of low-density lipoprotein (LDL) is known as a multipotential molecule the several functional regions of which can all be affected by key structural modifications driven by specific domains. Based on our previous report on structural and conformational modifications of apoB-100 in the presence of 17-beta-estradiol (E2), we characterized the interaction between E2 and the apoB-100 and further explored the induced alterations in terms of the structural arrangement of the whole LDL particle. We report evidence for the existence on apoB-100 of a single specific and saturable binding site for E2, the occupancy of which modifies the overall structure of the protein, inducing an increase in the alpha-helix fraction. As a consequence, the structure of the LDL particle is deeply perturbed, with a change in the arrangement of both the outer shell and lipid core and an overall volume shrinkage. The evidence of a regulation of apoB-100 structure by a physiological ligand opens new perspectives in the study of the biological addressing of the LDL particle and suggests a novel rationale in the search for mechanisms underlying the beneficial role of E2 in decreasing the risk of early lesions in atherosclerosis.

Current status of estrogen receptors

Increasing knowledge on structure and function of estrogen receptors is providing information on the mechanism of action of estrogen agonists, as well as antagonists, and in understanding their tissue-selective action. However, there are still many factors associated with estrogen response which are poorly understood. Therefore, the task of designing a tissue-selective estrogen for use as a pharmaceutical in estrogen-dependent disorders remains an uncertain game. This review provides information on the current status of estrogen receptors for a better understanding.

Estradiol reduces F2alpha-isoprostane production in cultured human endothelial cells

Free radical-generated F(2alpha)-isoprostanes are a group of compounds with vasoconstrictor properties. To investigate whether estradiol exerts antioxidant actions modifying F(2alpha)-isoprostane production, cultured human umbilical vein endothelial cells were exposed to estradiol and other compounds and F(2alpha)-isoprostanes were measured in culture medium. Exposure to 1 and 10 nM estradiol for 24 h reduced F(2alpha)-isoprostane production by 36 and 49%, respectively (P < 0.001 vs. control). Exposure to antiestrogens alone (ICI-182780 or EM-652) slightly reduced F(2alpha)-isoprostanes (P < 0.05 vs. control), but much less than exposure to estradiol (P < 0.05). ICI-182780 reversed the estradiol-induced reduction of F(2alpha)-isoprostane concentration (P < 0.05). Along with time-course analysis, these results suggest that estradiol effects were mediated through estrogen receptor-dependent and -independent mechanisms. Progestogens alone (progesterone or medroxyprogesterone acetate) did not modify F(2alpha)-isoprostane production at any of the tested concentrations (1, 10, and 100 nM). Progesterone completely reversed estradiol-induced reduction of F(2alpha)-isoprostane production (P < 0.05 vs. control and estradiol), but medroxyprogesterone acetate did not (P < 0.05 vs. control).

Inhibition of low-density lipoprotein oxidation by the pure antiestrogens ICI 182780 and EM-652 (SCH 57068)

OBJECTIVE

The use of modulators of estrogen receptors activation is receiving increasing interest in menopausal medicine. Pure antiestrogens define a group of compounds exhibiting universal antagonistic properties. Nevertheless, we cannot disregard the possibility that they may still have some agonistic actions. Because estradiol (E2) has antioxidant properties, we tested the antioxidant capacity of two pure antiestrogens, ICI 182780 and EM-652 (SCH 57068).

DESIGN

The ability of both compounds to protect isolated low-density lipoproteins against copper-induced oxidation in vitro was used as an index of their antioxidant properties.

RESULTS

When compared with control (vehicle alone), ICI 182780 and EM-652 significantly increased the lag time of low-density lipoprotein oxidation when present at concentrations of 10 and 0.5 microM or greater, respectively. When compared with estrogens, ICI 182780 was as effective as E2 at the lower concentrations tested (0.1 and 1 microM) but less effective at higher concentrations. EM-652 had similar antioxidant potency as E2 but exerted maximal effects at lower concentration. Combined exposure to E2 and each of the antiestrogens resulted in a higher antioxidant effect than that of antiestrogen alone. Another estrogen (estrone), and selective estrogen-receptor modulators, such as tamoxifen and hydroxytamoxifen, displayed an antioxidant potency that was close to ICI 182780 but lower than EM-652. Progestogens, such as progesterone or medroxyprogesterone acetate, had no antioxidant effect.

CONCLUSIONS

Both ICI 182780 and EM-652 exhibited potent antioxidant activity, which could have important biological implications.

Lipophilic oestrogen derivatives contained in lipoprotein particles

Steroid fatty acid esters constitute a unique family of lipophilic hormones carried exclusively in circulating lipoproteins. Our studies have focused on the formation of 17beta fatty acid esters of labelled oestradiol in in vitro incubations with human ovarian follicular fluid and plasma and demonstrated the accumulation of these labelled derivatives in lipoprotein particles. The oestradiol esters are formed in a reaction catalysed by lecithin : cholesterol acyltransferase in association with high-density lipoprotein particles and they can be transferred to low-density lipoprotein particles in a process mediated by cholesteryl ester transfer protein. Using a novel quantitative method for the determination of oestradiol esters their endogenous concentrations in follicular fluid and in early and late pregnancy plasma have been determined. In addition, using labelled genistein and its chemically synthesized fatty acid esters, we also demonstrated that phytoestrogen derivatives could be incorporated in lipoprotein particles. Both oestradiol and genistein contain aromatic hydroxyl groups which cause them to exert powerful antioxidant activity in lipid-aqueous systems in vitro. The physiological role of the steroidal fatty acid esters remains to be elucidated. In theory, the hormonal esters might form a reservoir constituted by esterified hormones stored in lipoprotein particles and perhaps in fat tissue, or they might use lipoproteins as vehicles for endocrine transport, or they could act as antioxidant protection of the lipoprotein particles. Enzyme systems necessary for the formation of lipophilic oestrogen and phytoestrogen derivatives as well as for their incorporation in lipoprotein particles are present in human body fluids. Because of their water-insolubility, steroid fatty acid esters are carried exclusively by circulating lipoproteins. These esters can provide antioxidant protection for lipoprotein particles.

Estrogen and Alzheimer's disease: the story so far

The ovarian hormone estrogen has long been used to treat the physical symptoms of menopause and to aid in the prevention of osteoporosis in postmenopausal women. Cumulative evidence from basic science and clinical research suggests that estrogen also plays a significant neuromodulatory and neuroprotective role. The numerous estrogenic effects in the brain include the modulation of synaptogenesis, increased cerebral blood flow, mediation of important neurotransmitters and hormones, protection against apoptosis, anti-inflammatory actions, and antioxidant properties. These multiple actions in the central nervous system support estrogen as a potential treatment for the cognitive decline associated with Alzheimer's disease (AD), the most common form of dementia. Evidence from epidemiological studies supports enhanced cognitive function in women with AD taking estrogen replacement therapy (ERT) as well as a reduced risk for developing AD in healthy women receiving ERT. Additional clinical evidence suggests that estrogen may modulate specific cognitive functions such as working memory and verbal learning and memory. However, results from more recent controlled trials have not consistently shown a beneficial effect of estrogen on the cognitive function of women with AD. Future research should focus on examining the influence of multiple potential mediators of ERT including the route of estrogen administration, form of estrogen (conjugated estrogens vs estradiol), duration of treatment, opposed versus unopposed estrogen and the use of estrogen analogues. Further, sensitive neuropsychological measures may provide more detailed information concerning the specific effects of estrogen on cognitive function. These important issues must be addressed in order to establish the role of estrogen for the prevention and treatment of AD in women.

Reactive carbonyls from tobacco smoke increase arterial endothelial layer injury

We hypothesized that reactive carbonyls generated from smoke exposure cause increased arterial low-density lipoprotein (LDL) accumulation and endothelial layer permeability. In addition, we hypothesized that estrogen supplementation was protective against chronic environmental tobacco smoke (ETS) exposure to the artery wall. Quantitative fluorescence microscopy was used to determine artery injury after exposure. For our chronic studies, ovariectomized rats treated with subcutaneous placebo or 17beta-estradiol pellets were exposed to ETS or filtered air for 6 wk. ETS exposure increased carotid artery LDL accumulation more than fourfold compared with filtered air exposure, an effect largely mediated by increased permeability. No protective effect of estradiol was observed. Acute ETS exposure of a buffer solution containing LDL resulted in a more than sixfold increase in the highly reactive carbonyl glyoxal. Perfusion of this solution through carotid arteries resulted in a 105% increase in permeability. Moreover, perfusion of glyoxal alone caused a 50% increase in carotid artery permeability. This endothelial damage and changes in lipid accumulation may serve as an initiating event in atheroma formation in individuals exposed to ETS.

Pro-oxidant and antioxidant potential of catecholestrogens against ferrylmyoglobin-induced oxidative stress

Ferryl heme proteins may play a major role in vivo under certain pathological conditions. Catecholestrogens, the estradiol-derived metabolites, can act either as antioxidants or pro-oxidants in iron-dependent systems. The aim of the present work was (1) to determine the effects of ferrylmyoglobin on hepatocyte cytotoxicity, and (2) to assess the pro/antioxidant potential of a series of estrogens (phenolic, catecholic and stilbene-derived) against ferrylmyoglobin induced lipid peroxidation in rat hepatocytes. Cells were exposed to metmyoglobin plus hydrogen peroxide to form ferrylmyoglobin in the presence of the transition metal chelator diethylentriaminepentaacetic acid. Results showed that ferrylmyoglobin induced an initial oxidative stress, mainly reflected in an early lipid peroxidation and further decrease in GSH and ATP. However, cells gradually adapted to this situation, by recovering the endogenous ATP and GSH levels at longer incubation times. Phenolic and stilbene-derived estrogens inhibited ferrylmyoglobin-induced lipid peroxidation to different degrees: diethylstilbestrol>estradiol>resveratrol. Catecholestrogens at concentrations higher than 1 microM also inhibited lipid peroxidation with similar efficacy. The ability of estrogens to reduce ferrylmyoglobin to metmyoglobin may account for their antioxidant activity. In contrast, physiological concentrations (100 pM-100 nM) of the catecholestrogens exerted pro-oxidant activities, 4-hydroxyestradiol being more potent than 2-hydroxyestradiol. The implications of these interactions should be considered in situations where local myoglobin or hemoglobin microbleeding takes place.

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.

Quantitative Determination of Estradiol Fatty Acid Esters in Human Pregnancy Serum and Ovarian Follicular Fluid

Background: Lipophilic estradiol derivatives carried by lipoprotein particles in blood may mediate antioxidant or endocrine effects. We developed a new quantitative method to determine the concentration of circulating lipophilic estradiol fatty acid esters in human early- and late-pregnancy serum and in ovarian follicular fluid.

Methods: After extraction from serum or follicular fluid, estradiol fatty acid esters were separated from nonesterified estradiol by Sephadex LH-20 column chromatography. The estradiol ester fraction was hydrolyzed by saponification and further purified by several chromatographic steps. The hydrolyzed estradiol esters were measured by time-resolved fluoroimmunoassay.

Results: The average estradiol fatty acid ester concentration in serum increased 10-fold during pregnancy, from 40.4 pmol/L (expressed as pmol/L estradiol; range, 25.0–64.2 pmol/L) in early pregnancy (n = 8) to 404 pmol/L (196–731 pmol/L) in late pregnancy (n = 10). The ratio of estradiol ester to nonesterified estradiol remained relatively constant during pregnancy, at 0.4–0.6%. In 10 follicular fluid samples, the mean estradiol ester concentration was 106 nmol/L (56.9–262 nmol/L). Compared with serum, a greater proportion of estradiol in follicular fluid (3.0–10%) was in the esterified form.

Conclusion: The new method provides a means to measure circulating estradiol fatty acid ester concentrations in human pregnancy serum.

The use of hormone replacement therapy in postmenopausal women with type 2 diabetes

In healthy postmenopausal women, estrogen or hormone replacement therapy (ERT or HRT) can alleviate menopausal symptoms and prevent osteoporosis and may also protect against cardiovascular disease (CVD). In addition to improving lipid metabolism, there are reports that estrogen also improves parameters regulating carbohydrate metabolism, including insulin resistance, in healthy women. Therefore, it is likely that ERT or HRT would also benefit women with type 2 diabetes, not only in relieving menopausal symptoms but also in improving the metabolic abnormalities associated with diabetes and in preventing cardiovascular disease.

The pharmacokinetics and efficacy of different estrogens are not equivalent

In the next decade many women will turn to the medical community for advice on maintaining or improving health after menopause. Estrogen replacement therapy, with or without progestins, alleviates menopausal symptoms, prevents or manages osteoporosis, and reduces the increased cardiovascular disease risk that results from estrogen deficiency caused by ovarian decline. Although several estrogen replacement products are available, the pharmacokinetics and efficacy of these products may vary depending on either the estrogen formulation or the route of administration, or both. For example, oral estrogens, which elicit a marked hepatic response, induce greater beneficial effects on serum lipoproteins than transdermal estrogens, which circumvent first-pass liver metabolism. Oral conjugated estrogens and transdermal estradiol increase bone density and prevent bone loss. This article summarizes the studies comparing estrogen formulations and discusses the differential effects of various estrogen products that promote postmenopausal health.

The endosomal-lysosomal system of neurons in Alzheimer's disease pathogenesis: a review

A prominent feature of brain pathology in Alzheimer's disease is a robust activation of the neuronal lysosomal system and major cellular pathways converging on the lysosome, namely, endocytosis and autophagy. Recent studies that identify a disturbance of the endocytic pathway as one of the earliest known manifestation of Alzheimer's disease provide insight into how beta-amyloidogenesis might be promoted in sporadic Alzheimer's disease, the most prevalent and least well understood form of the disease. Primary lysosomal dysfunction has historically been linked to neurodegeneration. New data now directly implicate cathepsins as proteases capable of initiating, as well as executing, cell death programs in certain pathologic states. These and other studies support the view that the progressive alterations of lysosomal function observed during aging and Alzheimer's disease contribute importantly to the neurodegenerative process in Alzheimer's disease.

Lipoproteins and low-dose estradiol replacement therapy in post-menopausal Type 2 diabetic patients: the effect of addition of norethisterone acetate

AIMS

Low-dose continuous oestrogen/progestogen may increase patient compliance long-term but the cardioprotective effects in diabetes are unknown. The aim of this study was to compare the effect of low-dose oral oestrogen (1 mg, 17-beta-estradiol) treatment with oestrogen (1 mg 17-beta-estradiol) in combination with low-dose (0.5 mg) continuous norethisterone acetate (NETA) on lipoproteins in Type 2 diabetic patients.

METHODS

Thirty-four post-menopausal Type 2 diabetic patients in moderate control (mean haemoglobin A1c 7.7%) who had a serum oestradiol level of < 50 pg/ml were examined over a 6-month period. Serum lipids, and lipoprotein composition of very low density lipoprotein (VLDL), low density lipoprotein (LDL) and high density lipoprotein (HDL) were measured. Serum lipoprotein(a) was determined by an ELISA method, LDL fatty acids by gas-liquid chromatography and LDL oxidizability by thiobarbituric acid reactive substances (TBARS assay). Cholesteryl ester transfer protein (CETP), and cell cholesterol were measured.

RESULTS

There was a reduction in serum cholesterol on both treatments but no significant difference between treatment groups. LDL cholesterol decreased by 17% in each group. There was a no significant difference between the groups in serum VLDL or HDL cholesterol or serum triglycerides during the study. The change in lipoprotein(a) during the study was not significantly different between the groups. There was no significant difference in 4 h LDL oxidizability between groups. Although CETP increased with time in both groups there was no significant difference in the change between the groups.

CONCLUSION

In this small study, the addition of continuous low-dose NETA did not reduce the potentially beneficial effects of low-dose 17-beta-estradiol on the progression of atherosclerosis in diabetes.

Smoking and cardiovascular disease

Mainstream and ETS exposure are strong risk factors for cardiovascular disease in men and women. The relationships between smoking and cardiovascular disease result from multiple mechanisms that interact to contribute to atherosclerosis, vascular injury, thrombosis, and vascular dysfunction. We are only now beginning to understand how smoking contributes to the genesis and progression of cardiovascular disease. Because of the complexity of the interactions between nicotine and the components of MSS, ETS, and sidestream smoke with the vasculature, it will take a great deal of time and effort to fully unravel the mechanisms by which smoking contributes to cardiovascular disease. In addition, cardiovascular risk in female smokers is complicated by hormonal variables that may contribute to greater relative risk. It is important that health care providers, educators, and policy makers recognize the changing patterns of smoking and the impact of smoking on cardiovascular disease, and continue campaigns aimed at enhancing smoking cessation in the general population and in teens. Rigorous research is needed on the changing cultural, psychosocial, and environmental factors that influence tobacco use to improve our understanding of racial/ethnic smoking patterns, and identify strategic tobacco control opportunities. The capacity of tobacco control efforts to keep pace with patterns of tobacco use and cessation depends on timely recognition of emerging prevalence and cessation patterns and the resulting development of appropriate community-based programs to address the factors involved. Smoking trends today will determine how heavy the health burden of cardiovascular disease and others will be among communities tomorrow. Programs that aim at early intervention and reflect cultural diversity will be the cornerstone in the battle against tobacco use. Continued interest in research, educational, and prevention efforts are needed to help curb the risk of cardiovascular disease from smoking in men and women.

Gender differences in response to a hypercholesterolemic diet in hamsters: effects on plasma lipoprotein cholesterol concentrations and early aortic atherosclerosis

Gender is a strong predictor of coronary heart disease (CHD) susceptibility and reports indicate that males are more likely to develop CHD compared to age-matched premenopausal females. To test whether similar gender differences exist in hamsters, 16 male and 16 female F1B Golden Syrian hamsters, aged 10 weeks, were fed a hypercholesterolemic nonpurified diet (HCD) containing 10% coconut oil and 0.05% cholesterol for 12 weeks. Plasma lipid and lipoprotein cholesterol concentrations, LDL oxidative susceptibility, LDL tocopherol concentrations, LDL fatty acid composition, LDL particle size, plasma estradiol and testosterone concentrations, and early aortic atherosclerosis were analyzed. Female hamsters had significantly lower plasma total cholesterol and nonhigh-density lipoprotein cholesterol (nonHDL-C) and greater high-density lipoprotein cholesterol (HDL-C) concentrations compared to male hamsters (-15, -33, and 33%; respectively). Female hamsters had significantly greater LDL particle size (4%), LDL 22:6 (21%) fatty acid, and rate of LDL oxidation (34%) compared to male hamsters. Female hamsters had a significantly higher concentration of plasma estradiol (49%) compared to male hamsters. Female hamsters also had significantly less early aortic atherosclerosis compared to male hamsters (-77%). In female hamsters, aortic fatty streak formation was significantly associated with plasma nonHDL-C (r = 0.76, P<0.0007), LDL particle size (r = -0.66, P<0.005), plasma TC (r = 0.68. P<0.004), and lag phase of LDL oxidation (r = 0.84. P<0.02). In male hamsters, aortic fatty streak formation was significantly associated with plasma nonHDL-C (r = 0.52, P<0.04), plasma TC (r = 0.55, P<0.03), plasma TG (r = 0.79, P<0.0003), and LDL 22:6 (r = -0.78, P<0.03) with no association with any measures of LDL oxidation susceptibility. This study demonstrates that female hamsters have an improved plasma lipoprotein cholesterol profile, larger LDL particle size, and less early aortic atherosclerosis compared to male hamsters fed the same HCD.

Antioxidant protection of lipoproteins containing estrogens: in vitro evidence for low- and high-density lipoproteins as estrogen carriers

Some recent studies have reported that low-density lipoprotein (LDL) isolated from estrogen-treated postmenopausal women exhibited increased oxidation resistance ex vivo. However, the underlying mechanisms responsible for this effect are not clear. We explored the possibility that lipophilic derivatives of 17beta-estradiol (E(2)) could be incorporated into LDL and high-density lipoprotein (HDL) particles inhibiting lipoprotein oxidation. Introduction of small amounts of esterified E(2) into lipoproteins by means of incubation of free E(2) and E(2) 17-stearate in plasma did not result in any antioxidant effect. Using an artificial transfer system (Celite dispersion), larger amounts of E(2) esters could be incorporated into lipoproteins. Concentrations ranging between 0.27 and 1.38 molecules/LDL particle for E(2) 17-stearate and between 0.36 and 1.93 molecules/LDL particle for E(2) 17-oleate resulted in increased Cu(2+)-induced oxidation resistance of LDL as indicated by statistically significant lag time prolongations. Significant prolongations of lag times were also observed for HDL following incorporation of E(2) esters using Celite as transfer system. Our results suggest that free E(2) can be esterified and incorporated into lipoproteins during incubation in plasma. However, incorporation of supraphysiologic concentrations of E(2) esters into lipoproteins by means of the artificial transfer system was required in order to reduce their oxidation susceptibility.