Differential effects of 17beta-estradiol, conjugated equine estrogen, and raloxifene on mRNA expression, aggregation, and secretion in platelets

Sex dimorphisms in coagulation: Implications in trauma-induced coagulopathy and trauma resuscitation

Trauma-induced coagulopathy (TIC) is one of the leading causes of preventable death in injured patients. Consequently, it is imperative to understand the mechanisms underlying TIC and how to mitigate this mortality. An opportunity for advancement stems from the awareness that coagulation demonstrates a strong sex-dependent effect. Females exhibit a relative hypercoagulability compared to males, which persists after injury and confers improved outcomes. The mechanisms underlying sex dimorphisms in coagulation and its protective effect after injury have yet to be elucidated. This review explores sex dimorphisms in enzymatic hemostasis, fibrinogen, platelets, and fibrinolysis, with implications for resuscitation of patients with TIC.

Estradiol provokes hypercoagulability and affects fibrin biology: A mechanistic exploration of sex dimorphisms in coagulation

BACKGROUND

Sex dimorphisms in coagulation are well established, with female-specific hypercoagulability conferring a survival benefit in the setting of trauma-induced coagulopathy (TIC). The mechanism behind these phenomena remains to be elucidated. We hypothesize that estradiol provokes a hypercoagulable profile and alters clot proteomics and fibrin crosslinking.

METHODS

Whole blood was collected from healthy adult volunteers (n = 30). A battery of thrombelastography (TEG) assays (native, kaolin, platelet-mapping, functional fibrinogen), whole blood thrombin generation, proteomics, and clot structure architecture (via analysis of fibrin crosslinks and fluorescent fibrinogen-visualized clots) were performed after pre-treatment of the blood with physiologic concentrations of beta-estradiol. In addition, a prospective study of coagulation through the menstrual cycle was conducted by collecting blood from women on peak and nadir estrogen days in the standard 28-day menstrual cycle.

RESULTS

On TEG, in females, estradiol provoked a hypercoagulable phenotype, specifically a shorter time to clot formation and greater thrombin generation, greater rate of clot propagation and functional fibrinogen, higher clot strength, and diminished clot fibrinolysis. In both males and females, estradiol increased platelet hyperactivity. Similar changes were seen in time to clot formation and clot strength in vivo during peak estrus of the menstrual cycle. On proteomic analysis, in both males and females, estradiol was associated with increases in abundance of several procoagulant and antifibrinolytic proteins. Crosslinking mass spectrometry analysis showed addition of estradiol increased the abundance of several FXIII crosslinks within the FIBA alpha chain in both sexes. Fluorescent fibrinogen analysis revealed a trend toward increased fiber resolvability index after addition of estradiol.

CONCLUSION

Estradiol provokes a hypercoagulable phenotype, affecting time to clot formation, clot propagation, clot strength, clot fibrinolysis, and clot structure. In sum, these data highlight the role of estradiol is driving female-specific hypercoagulability and highlights its potential role as a therapeutic adjunct in resuscitation of TIC.

Human versus non-human sex steroid use in hormone replacement therapies part 1: Preclinical data

Prior to 2002, hormone replacement therapy (HRT) was considered to be an important component of postmenopausal healthcare. This was based on a plethora of basic, epidemiological and clinical studies demonstrating the health benefits of supplementation with human sex steroids. However, adverse findings from the Women's Health Initiative (WHI) studies that examined the 2 major forms of HRT in use in the US at that time - Premarin (conjugated equine estrogens; CEE) and Prempro (CEE + medroxyprogesterone acetate; MPA), cast a shadow over the use of any form of HRT. Here we review the biochemical and physiological differences between the non-human WHI study hormones - CEE and MPA, and their respective human counterparts 17β-estradiol (E₂) and progesterone (P₄). Preclinical data from the last 30 years demonstrate clear differences between human and non-human sex steroids on numerous molecular, physiological and functional parameters in brain, heart and reproductive tissue. In contrast to CEE supplementation, which is not always detrimental although certainly not as optimal as E₂ supplementation, MPA is clearly not equivalent to P₄, having detrimental effects on cognitive, cardiac and reproductive function. Moreover, unlike P₄, MPA is clearly antagonistic of the positive effects of E₂ and CEE on tissue function. These data indicate that minor chemical changes to human sex steroids result in physiologically distinct actions that are not optimal for tissue health and functioning.

Bioidentical menopausal hormone therapy: registered hormones (non-oral estradiol ± progesterone) are optimal

The many advantages of registered bioidentical sex hormones over registered, conventional, non-bioidentical menopausal hormone therapy (MHT) are considered. The transdermal route of estrogen administration avoids excess venous thromboembolic and ischemic stroke events. There is some indication that conjugated equine estrogens are more thrombogenic and most likely induce some hypertensive responses; estradiol might also be superior to conjugated equine estrogens (CEE) in terms of global cardiovascular health. The most valid evidence presently suggests that CEE-only treatment does not increase the risk of breast cancer and even may reduce it. But its combination with a synthetic progestogen (mainly medroxyprogesterone acetate) is a critical issue since it seems to be primarily associated with an increased incidence of breast cancer, however similar to or lower than that associated with some common lifestyle factors. Though not yet proven in a randomized, controlled trial, MHT continuously combining oral micronized progesterone with transdermal estradiol can presently be considered as the optimal MHT. It is not only safer than custom-compounded bioidentical hormones but also than oral conventional MHT and has the best breast profile; registered products for such optimal MHT are available around the world and must be preferred.

Hormone therapy and risk of cardiovascular outcomes and mortality in women treated with statins

Objective

This work aims to study the effects of hormone therapy (HT) on the risk of cardiovascular outcomes and all-cause mortality in women treated with statins.

Methods

We included women aged 40 to 74 years and living in Sweden who filled a first statin prescription between 2006 and 2007. Women were categorized as HT users or as nonusers. Information on dispensed drugs, comorbidity, cardiovascular outcomes, and all-cause mortality was obtained from national health registers.

Results

A total of 40,958 statin users—2,862 (7%) HT users and 38,096 nonusers—were followed for a mean of 4.0 years. In total, 70% of the women used statins as primary prevention. Among HT users, there were five cardiovascular deaths per 10,000 person-years. The corresponding rate among nonusers was 18, which yielded a hazard ratio of 0.38 (95% CI, 0.12-1.19). The all-cause mortality rates were 33 and 87, respectively, and the hazard ratio was 0.53 (95% CI, 0.34-0.81). There were no associations with cardiovascular events. A similar pattern was found for both primary and secondary prevention.

Conclusions

HT is associated with a reduced risk of all-cause mortality in women treated with statins. Although confounding factors, such as lifestyle and disease severity, might have influenced the results, HT does not seem to be detrimental to statin-treated women.

Longitudinal effects of menopausal hormone treatments on platelet characteristics and cell-derived microvesicles

Activated platelets serve as a catalyst for thrombin generation and a source of vasoactive and mitogenic factors affecting vascular remodeling. Oral menopausal hormone treatments (MHT) may carry greater thrombotic risk than transdermal products. This study compared effects of oral and transdermal MHT on platelet characteristics, platelet proteins, and platelet-derived microvesicles (MV) in recently menopausal women. Platelets and MV were prepared from blood of a subset of women (n = 117) enrolled in the Kronos Early Estrogen Prevention Study prior to and after 48 months of treatment with either oral conjugated equine estrogen (0.45 mg/day), transdermal 17β-estradiol (50 µg/day), each with intermittent progesterone (200 mg/day for 12 days a month), or placebo pills and patch. Platelet count and expression of platelet P-selectin and fibrinogen receptors were similar across groups. An aggregate measure of 4-year change in vasoactive and mitogenic factors in platelet lysate, by principle component analysis, indicated significantly lower values in both MHT groups compared to placebo. Increases in numbers of tissue factor positive and platelet-derived MV were significantly greater in the transdermal compared to placebo group. MHT was associated with significantly reduced platelet content of vasoactive and mitogenic factors representing a potential mechanism by which MHT may affect vascular remodeling. Various hormonal compositions and doses of MHT could differentially regulate nuclear transcription in bone marrow megakaryocytes and non-genomic pathways in circulating platelets thus determining numbers and characteristics of circulating MV. Thrombotic risk associated with oral MHT most likely involves liver-derived inflammatory/coagulation proteins rather than circulating platelets per se.

Ovariectomy differential influence on some hemostatic markers of mice and rats

Rodent ovariectomy is an experimental method to eliminate the main source of sexual steroids. This work explored for the first time the ovariectomy temporal changes induced in the hemostatic coagulation markers: prothrombin time (PT), activated partial thromboplastin time (aPTT), thrombin time (TT), and fibrinogen concentration (FIB) along with uterine weight on adult female CD1 mice and Wistar rats. Uterine weight (Uw) was assessed before ovariectomy (control), and 1, 3, 5, 7, 9, 16, and 21 days after surgery. PT, aPTT, TT and FIB were estimated the same days, using reported standard techniques. Ovariectomy decreased Uw, since day 1; and from day 10 to 21 reached the lowest values for both species. After day 1, mice hemostatic parameters changed (PT +10%, P<0.05; aPTT +53%, P<0.05; TT −24%, P<0.05; FIB +67%, P<0.05). Rats showed significant changes only in TT and FIB (TT −13%, P<0.001; FIB +65%, P<0.001). Neither mice PT, aPTT and TT, recovered control values after 21 days. In the rats from day 5 to 16 aPTT diminished (18–23%, P<0.05) recovering to control values on day 21, TT after 9 days and PT on day 16. In both species, FIB returned to its control values after 9 days. Ovariectomy differentially altered the PT hemostatic parameter of mice and rats indicating a non-equivalence among both species behaviour for experimental studies of blood coagulation.

Differential effects of oral and transdermal menopausal hormone therapy on prostacyclin and thromboxane in platelets

Abstract Menopausal hormone therapies (MHT) may increase thrombotic risk but modulate endothelial function and reduce development of vascular lesions. This study compared effects of MHT on prostanoid-modulated adenosine triphosphate (ATP) secretion from platelets in relationship with endothelial reactive hyperemia (RH) index and carotid intima medial thickness (CIMT). Participants were healthy, recently menopausal women of the Kronos Early Estrogen Prevention Study (KEEPS) randomized to one of three treatments: oral conjugated equine estrogen (oCEE, 0.45 mg/day), transdermal 17β-estradiol (tE2, 50 μg/day) each with intermittent oral progesterone or placebo pills and patch (PL). Prostacyclin and thromboxane A2 were assessed by quantification of their stable metabolites (6-keto-prostaglandin F1α, 6-k-PGF1α; thromboxane B2, TXB2), using ELISA. Dense granule ATP secretion from activated platelets was determined by bioluminescence; RH and CIMT were determined by fingertip tonometry and ultrasound, respectively. After 48 months of treatment, platelet content of 6-k-PGF1α and TXB2 was significantly lower in oCEE compared to the PL. Inhibition of ATP secretion by exogenous activation of cAMP associated with platelet 6-k-PGF1α (r = -0.41, P = 0.04) and TXB2 (r = 0.71, P = 0.0005) only in the oCEE group. Serum and platelet content of 6-k-PGF1α and TXB2 associated positively in the PL and tE2 groups. Serum 6-k-PGF1α positively associated with RH in the oCEE group (r = 0.73, P = 0.02), while serum TXB2 positively associated with CIMT in the tE2 group (r = 0.64, P = 0.01). Thus, oCEE and tE2 differentially affect prostanoid-mediated platelet secretory pathways but alone would not account for an increased thrombotic risk for oral MHT. Furthermore, platelet-derived prostanoids may contribute to RH and vascular remodeling in healthy menopausal women.

Sex-specific risk of cardiovascular disease and cognitive decline: pregnancy and menopause

Understanding the biology of sex differences is integral to personalized medicine. Cardiovascular disease and cognitive decline are two related conditions, with distinct sex differences in morbidity and clinical manifestations, response to treatments, and mortality. Although mortality from all-cause cardiovascular diseases has declined in women over the past five years, due in part to increased educational campaigns regarding the recognition of symptoms and application of treatment guidelines, the mortality in women still exceeds that of men. The physiological basis for these differences requires further research, with particular attention to two physiological conditions which are unique to women and associated with hormonal changes: pregnancy and menopause. Both conditions have the potential to impact life-long cardiovascular risk, including cerebrovascular function and cognition in women. This review draws on epidemiological, translational, clinical, and basic science studies to assess the impact of hypertensive pregnancy disorders on cardiovascular disease and cognitive function later in life, and examines the effects of post-menopausal hormone treatments on cardiovascular risk and cognition in midlife women. We suggest that hypertensive pregnancy disorders and menopause activate vascular components, i.e., vascular endothelium and blood elements, including platelets and leukocytes, to release cell-membrane derived microvesicles that are potential mediators of changes in cerebral blood flow, and may ultimately affect cognition in women as they age. Research into specific sex differences for these disease processes with attention to an individual's sex chromosomal complement and hormonal status is important and timely.

Sex, stroke, and inflammation: the potential for estrogen-mediated immunoprotection in stroke

Stroke is the third leading cause of death and the primary cause of disability in the developed world. Experimental and clinical data indicate that stroke is a sexually dimorphic disease, with males demonstrating an enhanced intrinsic sensitivity to ischemic damage throughout most of their lifespan. The neuroprotective role of estrogen in the female brain is well established, however, estrogen exposure can also be deleterious, especially in older women. The mechanisms for this remain unclear. Our current understanding is based on studies examining estrogen as it relates to neuronal injury, yet cerebral ischemia also induces a robust sterile inflammatory response involving local and systemic immune cells. Despite the potent anti-inflammatory effects of estrogen, few studies have investigated the contribution of estrogen to sex differences in the inflammatory response to stroke. This review examines the potential role for estrogen-mediated immunoprotection in ischemic injury.

Testosterone alters maternal vascular adaptations: role of the endothelial NO system

Sex steroid hormones estradiol and progesterone play an important role in vascular adaptations during pregnancy. However, little is known about the role of androgens. Plasma testosterone (T) levels are elevated in preeclampsia, mothers with polycystic ovary, and pregnant African American women, who have endothelial dysfunction and develop gestational hypertension. We tested whether increased T alters vascular adaptations during pregnancy and whether these alterations depend on endothelium-derived factors, such as prostacyclin, endothelium-derived hyperpolarizing factor, and NO. Pregnant Sprague Dawley rats were injected with vehicle (n=12) or T propionate [0.5 mg/Kg per day from gestation day 15-19; n=12] to increase plasma T levels 2-fold, similar to that observed in preeclampsia. Telemetric blood pressures and endothelium-dependent vascular reactivity were assessed with wire-myograph system. Phospho-endothelial NO synthase and total endothelial NO synthase were examined in mesenteric arteries. Mean arterial pressures were significantly higher starting from gestation day19 until delivery in T-treated dams. Endothelium-dependent relaxation responses to acetylcholine were significantly lower in mesenteric arteries of T-treated dams (pD(2) [-log EC(50)]=7.05±0.06; E(max)=89.4±1.89) compared with controls (pD(2)=7.38±0.04; E(max)=99.9±0.97). Further assessment of endothelial factors showed NO-mediated relaxations were blunted in T-treated mesenteric arteries (E(max)=42.26±5.95) compared with controls (E(max)=76.49±5.06); however, prostacyclin- and endothelium-derived hyperpolarizing factor-mediated relaxations were unaffected. Relaxation to sodium nitroprusside was unaffected with T-treatment. Phosphorylations of endothelial NO synthase at Ser(1177) were decreased and at Thr(495) increased in T-treated mesenteric arteries without changes in total endothelial NO synthase levels. In conclusion, increased maternal T, at concentrations relevant to abnormal clinical conditions, cause hypertension associated with blunting of NO-mediated vasodilation. T may induce the increased vascular resistance associated with pregnancy-induced hypertension.

Chronic estradiol treatment reduces platelet responses and protects mice from thromboembolism through the hematopoietic estrogen receptor α

Although estrogens are known to have a deleterious effect on the venous thrombosis risk and a preventive action on the development of arterial atheroma, their effect on platelet function in vivo remains unclear. Here, we demonstrate that a chronic high physiologic level of estradiol (E2) in mice leads to a marked decrease in platelet responsiveness ex vivo and in vivo compared with ovariectomized controls. E2 treatment led to increased bleeding time and a resistance to thromboembolism. Hematopoietic chimera mice harboring a selective deletion of estrogen receptors (ERs) α or β were used to demonstrate that the effects of E2 were exclusively because of hematopoietic ERα. Within ERα the activation function-1 domain was not required for resistance to thromboembolism, as was previously shown for atheroprotection. This domain is mandatory for E2-mediated reproductive function and suggests that this role is controlled independently. Differential proteomics indicated that E2 treatment modulated the expression of platelet proteins including β1 tubulin and a few other proteins that may impact platelet production and activation. Overall, these data demonstrate a previously unrecognized role for E2 in regulating the platelet proteome and platelet function, and point to new potential antithrombotic and vasculoprotective therapeutic strategies.

The structures and inhibitory effects of Buame [N-(3-hydroxy-1,3,5(10)-estratrien-17β-yl)-butylamine] and Diebud [N,N'-bis-(3-hydroxy-1,3,5(10)-estratrien-17β-yl)-1,4-butanediamine] on platelet aggregation

Compounds with estrogenic effects that also inhibit platelet aggregation might be useful in reducing thrombotic events associated with estrogenic therapy. In this study, two aminoestrogens, Buame [N-(3-hydroxy-1,3,5(10)-estratrien-17β-yl)-butylamine] and Diebud [N,N'-bis-(3-hydroxy-1,3,5(10)-estratrien-17β-yl)-1,4-butanediamine], were synthesized and characterized using common analytical methods and spectrophotometric analyses. The location and orientation of these molecules on the estrogenic receptor α (ERα) were also evaluated. Platelet inhibitory effects were elucidated ADP-induced platelet aggregation and ADP- and collagen-induced ATP release. Molecular docking demonstrated that Buame can reach and bind to the ERα in the ligand binding domain (LBD) similar to 17β-estradiol (co-crystallized ligand). On the other hand, Diebud binds only to the surface of ERα due to its high molecular volume compared to 17β-estradiol and Buame.

Primary Prevention of Cardiovascular Disease with HRT

Prevention of cardiovascular disease has increasingly important health implications as our population ages. Menopause is associated with the development of cardiovascular risk factors and there are many plausible biological mechanisms through which estrogen may confer cardiovascular protection. Despite a wealth of observational data to support the use of estrogen, large randomized controlled trials failed to demonstrate a benefit. It is now becoming clearer that the beneficial cardiovascular effects of estrogen are greatest in younger women and those closest to menopause. This has led to the development of the timing hypothesis. Use of age-appropriate estrogen doses is crucial to maximize cardiovascular benefits while minimizing risk of adverse effects such as venous thromboembolism and stroke.

A novel role for tamoxifen in the inhibition of human platelets

Tamoxifen, a selective estrogen receptor (ER) modulator (SERM), is widely used therapeutically for the treatment and prevention of breast cancer, but its use is associated with an increased risk of thrombosis. The mechanism of this adverse effect is still unclear. Arterial thromboses mostly consist of platelets that are adherent to ruptured endothelial surfaces. Several lines of evidence reported that tamoxifen stimulates platelet activation using different methodologies. In our preliminary study, tamoxifen exhibited potent antiplatelet activity in washed human platelets. The aim of this study was to examine the signal transduction pathways of tamoxifen in platelet activation. In this study, tamoxifen (3∼7 μmol/L) exhibited more potent activity in inhibiting platelet aggregation stimulated by collagen than other agonists (ie, thrombin). Tamoxifen inhibited collagen-stimulated platelet activation accompanied by relative Ca(+2) mobilization, thromboxane A(2) (TxA(2)) formation, and phospholipase C (PLC)γ2, protein kinase C (PKC), and mitogen-activated protein kinase (MAPK) phosphorylation (ie, p38 MAPK and extracellular signal-regulated kinase 1/2), but not hydroxyl radical (OH(•)) formation. However, tamoxifen did not increase nitric oxide (NO) release or vasodilator-stimulated phosphoprotein (VASP) phosphorylation in washed platelets. Furthermore, neither ICI 182,780, a pure ER antagonist, nor ODQ, an inhibitor of guanylate cyclase, significantly reversed the tamoxifen-mediated inhibition of platelet aggregation. In conclusion, this study demonstrates for the first time that tamoxifen possesses potent antiplatelet activity, the mechanism of which may be involved in the inhibition of the PLCγ2-PKC-p38 MAPK-TxA(2) cascade, thereby leading to the inhibition of platelet activation. In our study, the direct inhibition of platelet activation by tamoxifen possibly may provide new insights into understanding its cardiovascular effects.

Sex-based differences in vascular function

Cardiovascular disease is the leading cause of morbidity and mortality for both men and women in the USA. However, there are differences between the sexes in age-dependent onset, severity, symptoms and outcomes. Basic research into the causes of sex-dependent differences in cardiovascular disease is ongoing and includes investigation into genetic variation in expression and distribution of receptors for the sex steroids; specificity of natural and synthetic ligands that activate the sex steroid receptors; and intracellular mechanisms that are activated by the receptors in all components of the vessel wall and blood elements, which integrate to regulate vascular tone, vascular repair and remodeling in health and disease. In this era of personalized medicine, basic research into mechanisms of sex differences in vascular function will result in improved prevention, detection and treatment of cardiovascular disease in both men and women.

Inhibitory signaling of 17β-estradiol in platelet activation: the pivotal role of cyclic AMP-mediated nitric oxide synthase activation

Arterial thromboses are mostly composed of platelets adherent to ruptured endothelial surfaces. Platelets are anucleated cells; therefore, they represent an excellent and unique model to selectively investigate the signaling pathways mediating the nongenomic effects of estrogen. The aim of this study was to examine the signal transduction pathways of 17β-estradiol in preventing platelet activation. In this study, 17β-estradiol (5~10 μM) exhibited more-potent activity of inhibiting platelet aggregation stimulated by collagen than other agonists (i.e., thrombin). 17β-Estradiol-inhibited collagen-stimulated platelet activation accompanied by [Ca(2+)]i mobilization, thromboxane A₂ (TxA₂) formation, and phospholipase C (PLC)γ2, protein kinase C (PKC), and p38 mitogen-activated protein kinase (MAPK) phosphorylation. 17β-Estradiol markedly increased cyclic AMP and cyclic GMP levels, nitric oxide (NO) release, vasodilator-stimulated phosphoprotein (VASP) phosphorylation, and endothelial nitric oxide synthase (eNOS) expression. SQ 22536, an inhibitor of adenylate cyclase, markedly reversed the 17β-estradiol-mediated effects (i.e., platelet aggregation, and PLCγ2, VASP, and eNOS phosphorylation). Furthermore, ICI 182,780, a pure estrogen receptor antagonist, also reversed the 17β-estradiol-mediated effects on platelet aggregation and eNOS activation. In conclusion, the most important findings of this study demonstrate for the first time that the inhibitory effect of 17β-estradiol in platelet activation involves activation of the cyclic AMP-eNOS/NO-cyclic GMP pathway, resulting in inhibition of PLCγ2 and p38 MAPK activation, which may lower the incidence of cardiovascular events in postmenopausal women.

Aggregation and microparticle production through toll-like receptor 4 activation in platelets from recently menopausal women

Bacterial infection may increase risk for thrombosis and atherosclerosis. Human platelets express toll-like receptor 4 (TLR4), the receptor for gram-negative bacterial lipopolysaccharide (LPS). Experiments were designed to evaluate direct, acute effects of TLR4 activation on aggregation, secretion, and generation of prothrombogenic microparticles in vitro on platelets derived from healthy women at risk for development of cardiovascular disease because of their hormonal status. Platelet-rich plasma from recently menopausal women was incubated with ultrapure Escherichia coli LPS in the absence or presence of antibodies that neutralize the human TLR4. Incubating platelets with LPS (100 ng/mL) for 5 minutes decreased aggregation and dense granule adenosine triphosphate secretion induced by thrombin receptor agonist peptide (TRAP) but not by adenosine diphosphate or collagen. The antibody to TLR4 blocked this effect of LPS. TLR4 activation increased phosphorylation of p38 mitogen-activated protein kinase and decreased production of prothrombotic phosphatidylserine and P-selectin-positive microparticles in response to TRAP. Therefore, acute, direct activation of TLR4 reduces platelet reactivity to TRAP stimulation in vitro. Increased thrombotic and cardiovascular risk with bacterial infection most likely reflects the sum of TLR4 activation on other blood and vascular cells to release proinflammatory cytokines/chemokines, which indirectly affect platelet reactivity.

Effects of raloxifene on platelet functions in patients with postmenopausal osteoporosis

Many studies have addressed the effects of estrogenic compounds on platelet function. Raloxifene is a selective estrogen receptor modulator (SERM), which is currently used for the treatment of postmenopausal osteoporosis. At present, there are no clinical data about the effects of raloxifene on platelet function. The purpose of this study was to determine if raloxifene at therapeutic doses affects platelet function in patients with postmenopausal osteoporosis. The effects of raloxifene on platelet function were investigated using a commercial platelet function analyzer (PFA-100) with collagen epinephrine and collagen adenosine 5'-diphosphate (ADP) cartridges. We studied platelet function of 30 patients with postmenopausal osteoporosis before and 15 days after initiation of raloxifene 60 mg/daily. Closure times did not differ significantly between samples obtained before (117.8 +/- 20.5 s) and after raloxifene therapy (106.5 +/- 25.4 s) in collagen/epinephrine cartridges (P > 0.05). There was also no statistically significant difference in mean closure times with collagen/ADP cartridges at baseline (86.2 +/- 18.5 s) and after raloxifene therapy (84.4 +/- 13.8 s) (P > 0.05). Platelet counts (278.3 +/- 72.9 vs. 262.4 +/- 56.7 109/L, P > 0.05) and mean platelet volumes (8.9 +/- 1 vs. 9.1 +/- 1 fL, P > 0.05) were not different before and after raloxifene therapy. Although estrogen related compounds do affect platelet function, there is suggestive data in our study that raloxifene in therapeutic dose exhibit no effect on platelet function in patients with postmenopausal osteoporosis.

Circulating microparticles and endogenous estrogen in newly menopausal women

BACKGROUND

Estrogen modulates antithrombotic characteristics of the vascular endothelium and the interaction of blood elements with the vascular surface. A marker of these modulatory activities is formation of cell-specific microparticles. This study examined the relationship between blood-borne microparticles and endogenous estrogen at menopause.

METHODS

Platelet activation and plasma microparticles were characterized from women being screened (n = 146) for the Kronos Early Estrogen Prevention Study. Women were grouped according to serum estrogen (< 20 pg/ml; low estrogen, n = 21 or > 40 pg/ml; high estrogen, n = 11).

RESULTS

Age, body mass index, blood pressure and blood chemistries were the same in both groups. No woman was hypertensive, diabetic or a current smoker. Platelet counts, basal and activated expression of P-selectin on platelet membranes were the same, but activated expression of glycoprotein IIb/IIIa was greater in the high-estrogen group. Numbers of endothelium-, platelet-, monocyte- and granulocyte-derived microparticles were greater in the low-estrogen group. Of the total numbers of microparticles, those positive for phosphatidylserine and tissue factor were also greater in the low-estrogen group.

CONCLUSION

These results suggest that, with declines in endogenous estrogen at menopause, numbers of procoagulant microparticles increase and thus may provide a means to explore mechanisms for cardiovascular risk development in newly menopausal women.

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 beta predominates in circulating platelets. Estrogenic treatment in ovariectomized animals decreased platelet aggregation and adenosine triphosphate (ATP) secretion. However, acute exposure to 17beta-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.

Pilot study of sex differences in chemokine/cytokine markers of atherosclerosis in humans

BACKGROUND

Atherogenic processes increase in women after menopause, when the risk of cardiovascular adverse events approaches that observed in age-matched men. In experimental animals, ovariectomy increases the platelet content of mitogenic cytokines, such as platelet-derived growth factor (PDGF), which when released into the blood or site of vascular injury, contribute to atherogenic processes.

OBJECTIVE

Experiments were designed to assess the sex distribution of inflammatorychemokines/cytokines, which may be released from platelets in the serum of middle-aged women and men in whom the extent of atherosclerotic coronary disease was defined by coronary arterial calcification (CAC).

METHODS

Blood was obtained from healthy white individuals recruited from the Mayo Clinic database. CAC was assessed by 64-slice computed tomography. Plasma cholesterol, lipids, and high-sensitivity C-reactive protein were analyzed by the Mayo Clinic Department of Laboratory Medicine and Pathology. Serum cytokines were determined using cytokine arrays. Cytokine expression was measured using dot blot analysis.

RESULTS

Of the 16 individuals (11 women, 5 men) who agreed to participate in the study, 1 woman was premenopausal, 1 was taking oral contraceptives, and 1 was receiving menopausal hormone therapy. One woman had an active infection and was eliminated from the study. CAC was detected in only 2 of the 11 women (scores of 46 and 56 Agatston units [AU]) but in 3 of the 5 men (scores of 3, 123, and 609 AU). Correcting for all other risk factors, expression of the chemokine RANTES (regulated on activation, normal, T-cell expressed and secreted; CCL5 [CC chemokine ligand 5]) was 100.98% greater in women than in men, and PDGF-BB was 55.30% greater in women than in men.

CONCLUSIONS

This small pilot study found that the circulating chemokines/cytokines RANTES and PDGF-BB showed sex-disparate distribution between the women and men studied, and did not appear related to the degree of CAC.

Vascular actions of estrogens: functional implications

The impact of estrogen exposure in preventing or treating cardiovascular disease is controversial. But it is clear that estrogen has important effects on vascular physiology and pathophysiology, with potential therapeutic implications. Therefore, the goal of this review is to summarize, using an integrated approach, current knowledge of the vascular effects of estrogen, both in humans and in experimental animals. Aspects of estrogen synthesis and receptors, as well as general mechanisms of estrogenic action are reviewed with an emphasis on issues particularly relevant to the vascular system. Recent understanding of the impact of estrogen on mitochondrial function suggests that the longer lifespan of women compared with men may depend in part on the ability of estrogen to decrease production of reactive oxygen species in mitochondria. Mechanisms by which estrogen increases endothelial vasodilator function, promotes angiogenesis, and modulates autonomic function are summarized. Key aspects of the relevant pathophysiology of inflammation, atherosclerosis, stroke, migraine, and thrombosis are reviewed concerning current knowledge of estrogenic effects. A number of emerging concepts are addressed throughout. These include the importance of estrogenic formulation and route of administration and the impact of genetic polymorphisms, either in estrogen receptors or in enzymes responsible for estrogen metabolism, on responsiveness to hormone treatment. The importance of local metabolism of estrogenic precursors and the impact of timing for initiation of treatment and its duration are also considered. Although consensus opinions are emphasized, controversial views are presented to stimulate future research.

Selective estrogen receptor modulation influences atherosclerotic plaque composition in a rabbit menopause model

OBJECTIVE

Osteoporosis trials suggest raloxifene decreased cardiovascular events in women with pre-existing atherosclerosis. We assessed the hypothesis that selective estrogen receptor modulation induces plaque stability in "menopausal" animals.

METHODS AND RESULTS

Atherosclerosis was induced in 42 ovariectomized New Zealand white rabbits by cholesterol feeding and mechanical injury. Animals were imaged by magnetic resonance imaging (MRI) for baseline atherosclerosis, and randomized to control (OVX (ovariectomized control group), n=12), raloxifene 35-60 mg/kg/day by diet admixture (RLX (raloxifene therapy group), n=24), or immediate sacrifice (n=6) for immunohistopathologic correlation of MRI. Six months later, rabbits underwent repeat MRI then sacrifice for micro-computed tomography (microCT) and molecular analysis. Unlike OVX, RLX reduced atheroma volume. Analysis for lesion inflammation revealed reductions in COX-2 (cyclooxygenase-2), MMP-1 (matrix metalloproteinase-1), MCP-1 (monocyte chemoattractant protein-1) expression and macrophage infiltration in RLX versus OVX with concomitant upregulation of estrogen receptor alpha (ERalpha). microCT showed similar total vascular calcification between groups, but calcifications in RLX were less nodular with better radial organization (mean calcific arc angle 63+/-7 degrees versus 33+/-6 degrees in OVX), the predicted result of a 53% increase in BMP-2 (bone-morphogenetic protein-2).

CONCLUSIONS

Raloxifene treatment results in reduced lesion volume, enhanced mechanical stability of vascular calcification, and less inflamed lesions characterized by less macrophage infiltration and reduced COX-2, MMP-1 and MCP-1 expression.

17Beta-estradiol increases basal but not bradykinin-stimulated release of active t-PA in young postmenopausal women

Angiotensin-converting enzyme inhibition potentiates basal and bradykinin-stimulated tissue-type plasminogen activator (t-PA) release to a greater extent in women than in men. This study tested the hypothesis that 17beta-estradiol enhances the effect of angiotensin-converting enzyme inhibition on t-PA release in young postmenopausal women. We conducted a double-blind, prospective, crossover study in 14 young postmenopausal women (mean age 48.2+/-2.3 years) who were randomized to receive 17beta-estradiol (1 mg/d) or matching placebo for 4 weeks. At the end of each treatment period, we measured the effect of intraarterial infusion of bradykinin, methacholine, and nitroprusside on forearm blood flow and net t-PA release, before and during intraarterial enalaprilat (0.33 microg/min/100 mL forearm volume). 17Beta-estradiol significantly reduced baseline venous plasminogen activator inhibitor-1 antigen (4.4+/-1.4 versus 10.4+/-2.5 ng/mL, P=0.001) and t-PA antigen (5.5+/-0.6 versus 7.5+/-1.3 ng/mL, P=0.022) compared with placebo. 17Beta-estradiol increased basal forearm vascular release of active t-PA compared with placebo (1.2+/-0.3 IU/mL/min versus 0.4+/-0.1 IU/mL/min respectively, P=0.032), without increasing t-PA antigen release (P=0.761). Enalaprilat significantly increased basal net t-PA antigen release (from -0.8+/-1.0 to 3.2+/-1.2 ng/min/100 mL, P=0.012), but not the release of active t-PA, during either placebo or 17beta-estradiol. Enalaprilat potentiated bradykinin-stimulated vasodilation and t-PA antigen and activity release similarly during placebo and 17beta-estradiol treatment. 17Beta-estradiol treatment does not alter the effect of angiotensin-converting enzyme inhibition on basal t-PA antigen or on bradykinin-stimulated t-PA antigen or activity release. 17Beta-estradiol increases basal release of active t-PA in young postmenopausal women, consistent with enhanced vascular fibrinolytic function.

17Beta-oestradiol partially attenuates the inhibition of nitric oxide synthase-3 by advanced glycation end-products in human platelets

1. Diabetes mellitus predisposes to and female sex protects against arterial thrombosis. The aim of the present study was to determine whether advanced glycation end-products (AGE), which accumulate in diabetes, impair platelet function through effects on platelet nitric oxide (NO) generation and whether this can be prevented by 17beta-oestradiol. 2. Aggregation responses of human platelet-rich plasma to ADP were determined in the absence or presence of 200 mg/L AGE-modified albumin (AGE-albumin), 10(-5) mol/L 17beta-oestradiol and 10(-5) mol/L ICI 182 780 (the pure oestrogen receptor antagonist). 3. Intraplatelet cGMP, an index of bioactive NO, was measured by radioimmunoassay and expression of nitric oxide synthase (NOS)-3, phosphoserine-1177-NOS-3 and O-glycosylated NOS-3 was quantified by western blotting in response to these same treatments. 4. Advanced glycation end-products-albumin increased platelet aggregatory responses to ADP. This increase was largely prevented by 17beta-oestradiol. Advanced glycation end-products-albumin decreased and 17beta-oestradiol increased intraplatelet NO-attributable cGMP and 17beta-oestradiol attenuated the AGE-albumin-induced decrease in NO-attributable cGMP. Despite no effect on NOS-3 expression, AGE-albumin decreased and 17beta-oestradiol increased phosphoserine-1177-NOS-3 and 17beta-oestradiol largely prevented the decrease in phosphoserine-1177-NOS-3 induced by AGE-albumin. Alone, AGE-albumin increased O-glycosylation of NOS-3 by N-acetylglucosamine, an effect largely inhibited by 17beta-oestradiol. 5. In conclusion, AGE-albumin inhibits platelet NO biosynthesis through effects on serine phosphorylation and O-glycosylation of platelet NOS-3 and this may explain, at least in part, the increase in platelet aggregability induced by AGE-albumin. These effects of AGE-albumin are largely prevented by 17beta-oestradiol. These actions may contribute to the effects of diabetes and sex on arterial thrombosis in vivo.

Ageing, oestrogen, platelets and thrombotic risk

1. Adverse thrombotic cardiovascular events increase in women coincident with the onset of menopause. 2. Age past menopause may be an important variable in defining the benefit/risk of hormone treatments. 3. Few studies have examined hormonal status as a variable of ageing using a polygenomic approach of both humoral and cellular components of the coagulation system. 4. Longitudinal studies of a global set of platelet functions that define procoagulant activity (i.e. adhesion, aggregation, secretion and thrombin production) in individuals with documented hormonal status are needed to better understand how hormonal changes associated with ageing impact thrombotic risk.

Selective estrogen receptor modulators and risk for coronary heart disease

Coronary heart disease (CHD) is the leading cause of death in women in most countries. Atherosclerosis is the main biological process determining CHD. Clinical data support the notion that CHD is sensitive to estrogens, but debate exists concerning the effects of the hormone on atherosclerosis and its complications. Selective estrogen receptor modulators (SERMs) are compounds capable of binding the estrogen receptor to induce a functional profile distinct from estrogens. The possibility that SERMs may shift the estrogenic balance on cardiovascular risk towards a more beneficial profile has generated interest in recent years. There is considerable information on the effects of SERMs on distinct areas that are crucial in atherogenesis. The complexity derived from the diversity of variables affecting their mechanism of action plus the differences between compounds make it difficult to delineate one uniform trend for SERMs. The present picture, nonetheless, is one where SERMs seem less powerful than estrogens in atherosclerosis protection, but more gentle with advanced forms of the disease. The recent publication of the Raloxifene Use for The Heart (RUTH) study has confirmed a neutral effect for raloxifene. Prothrombotic states may favor occlusive thrombi at sites occupied by atheromatous plaques. Platelet activation has received attention as an important determinant of arterial thrombogenesis. Although still sparse, available evidence globally suggests neutral or beneficial effects for SERMs.

The effects of estrone, estradiol and estriol on platelet aggregation induced by adrenaline and adenosine diphosphate

The impact of estrogens on the cardiovascular system and their ability to regulate platelet functions remains controversial. Changes in platelet functions could contribute to thrombotic risk associated with estrogen treatments. Here, we investigated the effects of various forms of estrogen, including estrone (E1), estradiol (E2) and estriol (E3), on platelet aggregation induced by standard agonists (adrenaline and adenosine diphosphate). Platelet-rich plasma (PRP) was prepared from citrated blood donated by 25 normal volunteers. The study on platelet aggregation was carried out in 96-well flat-bottom microtitre plates and assessed using a microplate reader. For studying the effects of each estrogen, PRP was preincubated with 1, 10 and 100 nM of E1, E2 and E3 at 37 degrees C for 20 min, and then coincubated with normal saline (control untreated PRP), adrenaline (ADR) or adenosine diphosphate (ADP) in the microplate. Platelet aggregation was then measured every minute for 8 min. None of the estrogens (E1, E2 and E3) affected platelet aggregation in untreated PRP. Interestingly, only E1 and E3 can synergize the increased platelet aggregation by either ADR or ADP, while the effects of E2 on the increased platelet aggregation by either ADR or ADP depended on internal factors such as endogenous estradiol and platelet aggregated state. Thus, for the rational use of these internal factors for estrogen use, especially E2, in clinical applications, such as hormone replacement therapy, may need evaluation of thrombotic risk.

In vivo effects of lipopolysaccharide and TLR4 on platelet production and activity: implications for thrombotic risk

Gram-negative bacteria release LPS, which activates Toll-like-receptor-4 (TLR4) in the host, initiating an inflammatory response to infection. Infection increases risk for thrombosis. Platelets contribute to defense from infection and to thrombosis. Experiments were designed to determine whether LPS, through TLR4 signaling, affects platelet phenotype. Platelet responses in wild-type (WT) mice and mice that lack the TLR4 gene (dTLR4) were compared following a single nonlethal injection of LPS (0.2 mg/kg iv). Compared with WT mice, mice without TLR4 had fewer circulating platelets with lower RNA content and were less responsive to thrombin-activated expression of P-selectin but were equally sensitive to aggregation or ATP secretion. One week following the LPS injection, the time it takes for the circulating platelet pool to turnover, the number of circulating platelets, thrombin-induced expression of P-selectin, and collagen-activated aggregation were increased comparably in both groups of mice. Therefore, the change of the platelet pool to an activated phenotype 1 wk after a single exposure to LPS appears to arise from a process that is independent of TLR4. The persistence of the effect 1 wk after the injection suggests that the changes reflect an action of LPS on megakaryocytes and their platelet progeny rather than on circulating platelets, which would have been cleared.

Estrogen therapy and thrombotic risk

Post-menopausal hormone therapy increases the risk for venous thrombosis, and possibly myocardial infarction (MI) and ischemic stroke. However, most women using hormone therapy do not suffer thrombosis, and to date our ability to identify women at risk is limited. Thrombosis, arterial or venous, has 2 requisites: a vascular anomaly and a response of the hemostasis system to the anomaly. Consequently, experimental approaches to understand the pathophysiology of thrombosis require definition of vascular anatomy and function as well as characteristics of the blood within the context of genetic background, lifestyle choices and environmental exposures, which influence gene expression. Defining interactions among factors that affect individual propensity to thrombosis will allow physicians to better identify at-risk individuals, for example a woman contemplating estrogen therapy for symptoms of menopause, and prevent adverse thrombotic events.

Lipoprotein-associated proteins involved in platelet signaling

Platelets and lipoproteins are both key elements in the development of atherosclerosis and thrombosis. Based on their density, five classes of lipoproteins have been identified which all influence platelets via distinct mechanisms. The activation of platelets starts with binding of apolipoproteins to different platelet receptors and is followed by the activation of signaling pathways resulting in activation or inhibition of platelet functions like aggregation or secretion. In addition to apolipoproteins, lipoproteins are also associated to a large amount of proteins, enzymes and lipids that also can induce platelet activation or inhibition. This review provides a summary of the activation of signaling pathways after platelet-lipoprotein interactions initiated by lipoprotein-associated proteins and lipids.

Cellular mechanisms underlying the cardiovascular actions of oestrogens

Although pre-menopausal women enjoy relative cardiovascular protection, hormone (oestrogen±progestin)-replacement therapy has not shown cardiovascular benefits in post-menopausal women, suggesting that the effects of oestrogens on the cardiovascular system are much more complex than previously expected. Endothelial cells, smooth muscle cells, cardiac myocytes and fibroblasts, the cellular components of blood vessels and the heart, play important roles in cardiovascular health and disease. During the development and progression of cardiovascular disease, changes occur both in the structure and function of these cells, resulting in a wide range of abnormalities, which affect growth, death and physiological function. These cells contain functional oestrogen receptors and are targets for oestrogen action. This review focuses on recent studies on the effects of oestrogen on cardiovascular cell function. Oestrogens, particularly 17β-oestradiol, exert multiple effects on cardiovascular cells, and these effects may contribute to the gender-associated protection against cardiovascular diseases.

Platelet characteristics change with aging: role of estrogen receptor beta

Estrogen receptor beta (betaER) is the predominant estrogen receptor in platelets. Experiments were designed to define phenotypic changes in platelets with aging following deletion of betaER (betaERKO). Blood was collected from wild-type and betaERKO female mice at 4-7 (young) and 24-25 (aged) months of age. In young animals, total number of platelets, number of platelets containing RNA (reticulated platelets), aggregation, dense body adenosine triphosphate secretion, and alpha granular secretion were the same in both groups. With aging, total number of platelets decreased but reticulated platelets increased in betaERKO mice; aggregation and dense granule adenosine triphosphate secretion decreased whereas basal expression of fibrinogen receptors increased with age in wild-type and betaERKO mice. Basal expression of P-selectin and annexin V binding increased with aging only in betaERKO mice; thrombin did not increase expression in these mice. Therefore, deletion of betaER is associated with specific platelet functions, which are expressed only with age-associated reproductive senescence.

Estrogenic regulation of tissue factor and tissue factor pathway inhibitor in platelets

Oral estrogen treatment increases thrombotic risk. Tissue factor (TF), tissue factor pathway inhibitor (TFPI), and platelet interaction with leukocytes are important determinants of thrombogenesis. Therefore, the present study was designed to define and compare platelet TF and TFPI mRNA and adhesion protein expression in platelets derived from animals treated with different types of oral estrogens. Ovariectomized pigs were treated with 17beta-estradiol (2 mg/day), conjugated equine estrogen (CEE; 0.625 mg/day), or raloxifene (60 mg/day) for 4 wk. Compared with intact animals, ovariectomy and treatment differentially affected populations of leukocytes: neutrophils decreased whereas lymphocytes increased significantly 4 wk after ovariectomy and with 17beta-estradiol and CEE treatments; eosinophils increased only with 17beta-estradiol treatment. Content of TF protein increased in platelets from 17beta-estradiol- and raloxifene-treated pigs, whereas TF mRNA was detected only in platelets from 17beta-estradiol- and CEE treated pigs. TFPI mRNA increased in platelets after ovariectomy and estrogen treatment. Only a trace of TFPI protein was detected, but a higher-molecular-mass protein was observed in all treatment groups. Expression of CD40 and CD40 ligand increased with ovariectomy and decreased with 17beta-estradiol and CEE treatments more than with raloxifene. The ratio of activated to basal P-selectin expression decreased with ovariectomy and increased with raloxifene treatments. These results suggest that estrogenic formulations may affect individual thrombotic risk by different mechanisms that regulate TF and platelet-leukocytic interactions. These studies provide the rationale for evaluation of interactions among platelets and TF and TFPI expression on thrombin generation during estrogen treatment in humans.