The estrogen receptor is present in human megakaryocytes

Bleeding and mortality risk in patients implanted with mechanical prosthetic heart valves with and without thrombocytopenia. Insights from the nationwide PLECTRUM registry

Previous studies showed that mechanical prosthetic heart valve (MPHV) patients may develop thrombocytopenia, but its association with clinical outcomes has not been investigated. We enrolled 1,663 patients with available platelet count from the multicenter nationwide retrospective PLECTRUM registry to investigate the association of thrombocytopenia with all-cause mortality and major bleeding (MB) in patients implanted with MPHV. Thrombocytopenia was defined by platelet count <150 × 10⁹/L. Overall, 44.9% of patients were women and the mean age was 56.7 years. At baseline, 184 (11.1%) patients had thrombocytopenia. Patients with thrombocytopenia were more frequently men and elderly. Platelet count showed an age-dependent decline in men but not in women. We found an increased risk of death in patients with age ≥ 65 years, with a low anticoagulation quality, concomitant arterial hypertension, heart failure, a higher INR range, or with thrombocytopenia (OR 1.739, 95%CI 1.048-2.886, p = .032). At multivariable logistic regression, patients with age ≥65 years, concomitant AF and thrombocytopenia (OR 1.907, 95%CI 1.219-2.983, p = .005) had an increased risk of MBs. In MPHV patients, thrombocytopenia is associated with an increased risk of death and MB. There is a growing need for a sex- and age-specific threshold to define platelet count in adult patients.

Possible Risk of Thrombotic Events following Oxford-AstraZeneca COVID-19 Vaccination in Women Receiving Estrogen

People who receive the ChAdOx1 nCoV-19 vaccine, particularly perimenopausal women who are on birth control or postmenopausal women who take estrogen supplements, may experience thrombosis and thrombocytopenia. Estrogen and the ChAdOx1 nCoV-19 vaccine both have the potential to cause thrombus in different ways. Some postmenopausal women who are also taking estrogens may develop thrombosis and thrombocytopenia after receiving the ChAdOx1 nCoV-19 vaccine. Therefore, women are encouraged to stop taking drugs containing estrogen before receiving this vaccine. Furthermore, consuming fish oil can help reduce the risk of developing blood clots among women who are in the luteal phase and, thus, have high estrogen levels. In addition, ChAdOx1 nCoV-19's side effects in young women could be mitigated by administering it during the follicular phase.

Female platelets have distinct functional activity compared with male platelets: Implications in transfusion practice and treatment of trauma-induced coagulopathy

BACKGROUND

Females are hypercoagulable and have survival benefit in trauma-induced coagulopathy (TIC). The mechanism for this sex-specific hypercoagulability is unknown. Platelets and platelet function are central in providing hemostatic potential and are the largest contributor to clot strength. Ligands (adenosine diphosphate [ADP] and platelet-activating factor [PAF]) bind distinct platelet receptors to potentiate activation and aggregation. We hypothesize that female platelets have a differential response to ADP and PAF, resulting in greater aggregation and activation compared to males, and that estradiol pretreatment of male or female platelets enhances this activity.

METHODS

Platelets were collected from healthy volunteers: premenopausal/postmenopausal females (≤54 years, >54 years) and similarly aged males. Platelet aggregometry and flow cytometry (fibrinogen binding capacity) were examined. After treatment with ADP or PAF, platelet aggregation was assessed with Chronolog and activation assessed by CD41 receptor surface expression using flow cytometry. Aggregation and activation were again assessed after platelet pretreatment with estradiol.

RESULTS

Healthy volunteers included 12 premenopausal and 13 postmenopausal females and 18 similarly aged males. Female platelets (combined premenopausal and postmenopausal) had increased aggregation with ADP stimulation, as compared to male platelets. Male and female platelets had differential fibrinogen receptor expression, with female platelets (combined premenopausal and postmenopausal) demonstrating robust activation with ADP versus male platelets with PAF. In the presence of estradiol incubation, male platelets' activation with PAF approximated that of females (combined premenopausal and postmenopausal) and activation with PAF was enhanced in both male and female platelets.

CONCLUSION

Male and female platelets have differential response to stimuli, suggesting sex-dependent signaling and cellular activation. Female platelets have both increased aggregation and activation potential, and estradiol pretreatment feminizes male platelets to approximate female platelet activation with PAF. These findings offer potential explanation for sex-based differences in hemostatic potential in TIC and question whether donor sex of transfused platelets should be considered in resuscitation. Estradiol may also serve as a novel therapeutic adjunct in TIC.

Effects of Estrogens on Platelets and Megakaryocytes

In women, oral menopausal hormonal therapy (MHT) is associated with adverse effects including an increased incidence of thromboembolic events, classically attributed to an increase in several liver-derived coagulation factors due to hepatic first pass. While platelets are central players in thrombus constitution, their implication in women treated with estrogens remains incompletely characterized. Platelets and their medullar progenitors, megakaryocytes, express estrogen receptors (ER) that may explain, at least in part, a sensitivity to hormonal changes. The purpose of this review is to summarize our current knowledge of estrogen actions on platelets and megakaryocytes in mice following in vivo administration and in women using MHT.

Human cells involved in atherosclerosis have a sex

The influence of sex has been largely described in cardiovascular diseases. Atherosclerosis is a complex process that involves many cell types such as vessel cells, immune cells and endothelial progenitor cells; however, many, if not all, studies do not report the sex of the cells. This review focuses on sex differences in human cells involved in the atherosclerotic process, emphasizing the role of sex hormones. Furthermore, we report sex differences and issues related to the processes that determine the fate of the cells such as apoptotic and autophagic mechanisms. The analysis of the data reveals that there are still many gaps in our knowledge regarding sex influences in atherosclerosis, largely for the cell types that have not been well studied, stressing the urgent need for a clear definition of experimental conditions and the inclusion of both sexes in preclinical studies.

Age-related changes in platelet function are more profound in women than in men

Age is a risk factor for cardiovascular disease (CVD), however the effect of age on platelet function remains unclear. Ideally, platelet function should be assayed under flow and shear conditions that occur in vivo. Our study aimed to characterise the effect of age on platelet translocation behaviour using a novel flow-based assay that measures platelet function in less than 200 μl of blood under conditions of arterial shear. Blood from males (n = 53) and females (n = 56), ranging in age from 19–82 and 21–70 respectively were perfused through custom-made parallel plate flow chambers coated with immobilised human von Willebrand Factor (VWF) under arterial shear (1,500s⁻¹). Platelet translocation behaviour on VWF was recorded by digital-image microscopy and analysed. The study showed that aging resulted in a significant decrease in the number of platelet tracks, translocating platelets and unstable platelet interactions with VWF. These age related changes in platelet function were more profound in women than in men indicating that age and gender significantly impacts on platelet interactions with VWF.

Platelet reactivity and thrombogenicity in postmenopausal women

OBJECTIVE

Age-adjusted incidence of cardiovascular disease, including myocardial infarction, is significantly lower in premenopausal women than in men, which is thought to be caused by the cardioprotective effects of estrogen. However, there is a consistent increase in the incidence of coronary artery disease in postmenopausal women in comparison with premenopausal women. The protective benefit of hormone therapy has not been observed in postmenopausal women. It is unknown whether measures of platelet reactivity and clot strength contribute to the disproportionate incidence of cardiovascular disease between premenopausal and postmenopausal women.

METHODS

Fifty healthy volunteers, including 25 premenopausal women and 25 postmenopausal women, aged between 40 and 65 years were enrolled. Total estradiol and follicle-stimulating hormone levels were measured for confirmation of menopausal state and comparison testing. Platelet reactivity was assessed using light transmission aggregometry and P-selectin, and glycoprotein IIb/IIIa receptor expression was assessed using flow cytometry. Thrombelastography was used to measure clot strength, clotting time, and fibrinogen activity. Serum cholesterol, C-reactive protein, complete blood count, and comprehensive metabolic panel were also measured.

RESULTS

Platelet reactivity did not differ among menopausal states or hormone levels. Clotting time was increased in postmenopausal women (6.6 ± 2.0 vs. 7.8 ± 1.2 min, P = 0.013) and significantly correlated with estradiol levels (r = 0.68, P < 0.001). A significantly higher low-density lipoprotein cholesterol level was observed in postmenopausal women (P = 0.05). Mean C-reactive protein levels were numerically higher in the postmenopausal group.

CONCLUSIONS

The thrombotic risk profile between premenopausal and postmenopausal women is similar. However, improved management of cholesterol may be of clinical benefit. Large-scale studies are required to validate these findings.

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.

Platelet biology and response to antiplatelet therapy in women: implications for the development and use of antiplatelet pharmacotherapies for cardiovascular disease

Women are underrepresented in cardiovascular studies, even as their preponderance in the aging population steadily increases. Although concerns have been raised about the differential benefit of antiplatelet medications for women, the propensity for increased bleeding among women has also been recognized. A better understanding of the factors contributing to the observed sex-related differences in platelet biology is warranted. These factors include differences in the frequency and expression of genetic polymorphisms affecting platelet responsiveness to agonists (with and without antiplatelet therapies), which might be obtained through population-based studies and in large controlled clinical trials; inflammatory marker levels and their influence on atherothrombotic risk, and the role of specific hormones in mediating platelet activation and function. Knowledge gained about these mechanistic factors might inform the development of sex-specific antithrombotic treatment regimens that confer optimized safety and efficacy.

Climacteric lowers plasma levels of platelet-derived microparticles: a pilot study in pre- versus postmenopausal women

BACKGROUND

Climacteric increases the risk of thrombotic events by alteration of plasmatic coagulation. Up to now, less is known about changes in platelet- (PMP) and endothelial cell-derived microparticles (EMP).

METHODS

In this prospective study, plasma levels of microparticles (MP) were compared in 21 premenopausal and 19 postmenopausal women.

RESULTS

No altered numbers of total MP or EMP were measured within the study groups. However, the plasma values of CD61-exposing MP from platelets/megakaryocytes were higher in premenopausal women (5,364 × 10(6)/l, range 4,384-17,167) as compared to postmenopausal women (3,808 × 10(6)/l, range 2,009-8,850; p = 0.020). This differentiation was also significant for the subgroup of premenopausal women without hormonal contraceptives (5,364 × 10(6)/l, range 4,223-15,916; p = 0.047; n = 15). Furthermore, in premenopausal women, higher plasma levels of PMP exposing CD62P were also present as compared to postmenopausal women (288 × 10(6)/l, range 139-462, vs. 121 × 10(6)/l, range 74-284; p = 0.024). This difference was also true for CD63+ PMP levels (281 × 10(6)/l, range 182-551, vs. 137 × 10(6)/l, range 64-432; p = 0.015).

CONCLUSION

Climacteric lowers the level of PMP but has no impact on the number of EMP in women. These data suggest that PMP and EMP do not play a significant role in enhancing the risk of thrombotic events in healthy, postmenopausal women.

Pharmacogenetics of human cytosolic sulfotransferases

Cytosolic sulfotransferases (SULTs) are phase II detoxification enzymes that are involved in the biotransformation of a wide variety of structurally diverse endo- and xenobiotics, including many therapeutic agents and endogenous steroids. Single-nucleotide polymorphisms (SNPs) in SULTs have functional consequences on the translated protein. For the most part, these SNPs are fairly uncommon in the population, but some, most notably for SULT isoform 1A1, are commonly found and have been associated with cancer risk for a variety of tumor sites and also with response to therapeutic agents. SNPs in the hydroxysteroid sulfotransferase, SULT2A1, have been identified in African-American subjects and influence the ratio of plasma DHEA:DHEA-S. This modification could potentially influence cancer risk in steroidogenic tissues. SNPs in many SULTs are ethnically distributed, another factor that could influence SULT pharmacogenetics. Finally, genetic variation has also been identified in 3'-phosphoadenoside 5'-phosphosulfate synthetase (PAPPS), the enzymes responsible for producing the obligatory cosubstrate for all sulfotransferases. Taken together, this variability could substantially influence the disposition of drugs metabolized by SULTs. Elucidation of the basis and effect of variability in sulfation could greatly impact individualized therapy in the future.

Common genetic polymorphisms in the 5'-flanking region of the SULT1A1 gene: haplotypes and their association with platelet enzymatic activity

SULT1A1 is a phase II detoxification enzyme involved in the biotransformation of a wide variety of endogenous and exogenous phenolic compounds. Human platelet SULT1A1 enzymatic activity shows marked inter-individual variability and a common coding polymorphism, SULT1A1*1/*2, has been described that accounts for a proportion of this variability. We examined the 5'-flanking region of the SULT1A1 gene to determine if genetic variability in this portion of the gene influenced enzymatic activity. Direct sequencing revealed five common genetic polymorphisms (-624G>C, -396G>A, -358A>C, -341C>G and -294T>C) that were present at different allele frequencies in Caucasian, African-American and Chinese groups. Platelet SULT1A1 enzymatic activity was significantly correlated with individual promoter region polymorphisms and the associations were different between African-Americans and Caucasians. Haplotypes were constructed and platelet enzymatic activity according to haplotype was examined. The haplotypes were also significantly correlated with activity; haplotypes GAACT and GGACT (accounting for 13% and 5% of inter-individual variability in platelet activity, respectively) were important in Caucasians while haplotypes GAACC, GAACT and GGACC (accounting for 8%, 5% and 4% of variability) were significantly associated with activity in African-Americans. The coding region polymorphism, SULT1A1*1/*2 was in linkage disequilibrium with the promoter region polymorphisms and showed no effect on activity when examined in the context of the 5'-flanking region polymorphisms. These studies indicate that variation in the promoter region of the SULT1A1 gene exerts a significant influence on enzymatic activity.

Estrogen stimulates differentiation of megakaryocytes and modulates their expression of estrogen receptors alpha and beta

Estrogen has multifunctional effects influencing growth, differentiation, and function in many tissues. High-dose estrogen has been shown to produce anabolic skeletal effects in the skeleton of postmenopausal women with increased megakaryocyte (MK) population in the bone marrow, suggesting a possible role for these cells in bone remodelling. To investigate if estrogen stimulates megakaryocytopoiesis and affects on estrogen receptor (ER) expression, CD34(+) cells were cultured for 6, 9, and 14 days plus or minus low-dose or high-dose 17 beta estradiol (E). Cells were immunolocalised for CD61, CD41, ER alpha and beta. ER mRNA expression was assessed by RT-PCR. Cells formed more CD61 positive MK colonies with low- and high-dose E treatment (P < 0.001) at 6 and 9 days. CD41 expression was increased dose-dependently in MK (3- and 5-fold P < 0.001) at 9 days. E-stimulated ER alpha expression at 6 days (P < 0.001) whilst ER beta was dose-dependently increased only at 9 days (P < 0.01). ER alpha mRNA was increased at 6 days but not at 14 days whilst ER beta mRNA expression was only increased at 14 days with E treatment. These results demonstrate that E stimulates the colony forming potential of CD34(+) cells to a more megakaryocytic phenotype in vitro. This finding together with the stimulation of ER protein and mRNA expression adds to the increasing evidence for a role for MKs in estrogen-induced bone formation.

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

Changes in platelet functions could contribute to thrombotic risk associated with estrogen treatments. This study was designed to test the hypothesis that three clinically relevant estrogenic treatments affect platelet function comparably. Adult female pigs were ovariectomized and randomized to either no treatment or treatment with oral 17 beta-estradiol (2 mg/day), conjugated equine estrogen (0.625 mg/day), or raloxifene (60 mg/day) for 4 wk. Platelet turnover, aggregation, and secretion were assessed before and after treatment. Platelet turnover and mRNA increased significantly only in pigs treated with 17 beta-estradiol. Expression of estrogen receptors increased with ovariectomy and decreased with all treatments. Platelet aggregation and secretion of ATP, platelet-derived growth factor, and matrix metalloproteinase-2 increased with ovariectomy. All treatments reduced both aggregation and secretion. Expression of mRNA for constitutive endothelial nitric oxide synthase (eNOS), but not eNOS protein, increased with ovariectomy. Only eNOS mRNA decreased with all treatments, but only treatment with 17 beta-estradiol increased secretion of nitric oxide from intact platelets. Platelets from 17 beta-estradiol-treated animals caused relaxation of coronary arteries, which was sensitive to inhibition of nitric oxide. Although three different estrogenic treatments reversed increases in platelet aggregation caused by ovariectomy, only 17 beta-estradiol increased platelet RNA and release of platelet-derived nitric oxide. These differences reflect transcriptional and posttranscriptional regulation of protein synthesis in bone marrow megakaryocytes and circulating platelets.

Synthesis of osteoprotegerin and RANKL by megakaryocytes is modulated by oestrogen

To investigate the mechanisms by which megakaryocytes (MKs) may influence bone remodelling, CD34(+) cells were cultured for 6, 9 and 12 d with or without 17beta-oestradiol (E) and immunolocalized for osteoprotegerin (OPG), receptor activator of nuclear factor (NF)-kappaB ligand (RANKL) and CD61. Specific protein expression was measured quantitatively by image analysis. Fluorescence-based immunocytochemistry was used to co-localize OPG and RANKL with CD61. OPG and RANKL mRNA was assessed in CD61(+) cells with or without E at 24 and 48 h. At 6 d, OPG and RANKL expression was unchanged by E treatment. At 9 d, the E-treated cultures with maturing MKs showed a 1.72-fold (P < 0.01) increase in OPG expression and a 1.8-fold (P < 0.01) reduction in RANKL. Maximal OPG expression was seen at 12 d with a threefold induction of expression (P < 0.001), whilst RANKL levels were further suppressed by 2.3-fold compared with controls (P < 0.001). CD61 co-localized with OPG and RANKL. mRNA data were consistent with that of protein, with a 90-fold induction in OPG expression and a 34-fold suppression of RANKL expression by E (P < 0.001). Thus, E stimulates megakaryocytopoiesis and modulates OPG and RANKL expression, providing evidence that MKs may play a role in bone remodelling and, in particular, in E-induced changes in osteoclastogenesis and bone resorption.

Sex-specific changes in platelet aggregation and secretion with sexual maturity in pigs

Cardiovascular disease may begin early in adolescence. Platelets release factors contributing to vascular disease. Experiments were designed to test the hypothesis that hormonal transitions associated with sexual maturity differentially affect platelet aggregation and secretion in males and females. Platelets were collected from juvenile (2-3 mo) and sexually mature (adult; 5-6 mo) male and female pigs (n=8/group). Maturation was evidenced by increased weight of reproductive tissue and changes in circulating levels of gonadal hormones. Aggregation to ADP (10 microM) and collagen (6 microg/ml) and ATP secretion to 50 nM thrombin were determined by turbidimetric analysis and bioluminescence, respectively. Total platelet counts, platelet turnover, and mean platelet volume did not change with maturity. Platelet aggregation and ATP secretion decreased in females but increased in males with maturity, whereas total ATP content remained unchanged in platelets from females but increased in platelets from males. Platelet fibrinogen receptor, P-selectin expression, and receptors for sex steroids did not change with sexual maturation. Plasma C-reactive protein and brain-type natriuretic peptide also did not change. Results indicate that changes in platelet aggregation and secretion change with sexual maturity differently in females and males. These observations provide evidence on which clinical studies could be designed to examine platelet characteristics in human children and young adults.

Proplatelet formation of megakaryocytes is triggered by autocrine-synthesized estradiol

A matured megakaryocyte releases thousands of platelets through a drastic morphological change, proplatelet formation (PPF). The megakaryocyte/erythrocyte-specific transcription factor, p45 NF-E2, is essential for initiating PPF, but the factor regulating PPF has not been identified. Here we report that estradiol synthesized in megakaryocytes triggers PPF. We demonstrate that a key enzyme for steroid hormone biosynthesis, 3beta-hydroxysteroid dehydrogenase (3beta-HSD), is a target of p45 NF-E2, and rescues PPF of p45 NF-E2-deficient megakaryocytes. We also show that estradiol is synthesized within megakaryocytes, and that extracellular estradiol stimulates PPF, inhibition of 3beta-HSD activity blocks PPF, and estrogen receptor antagonists inhibit platelet production in vivo. We conclude that autocrine estradiol action regulates platelet production by triggering PPF.

Ovariectomy upregulates expression of estrogen receptors, NOS, and HSPs in porcine platelets

Platelets participate in normal and pathological thrombotic processes. Hormone replacement in postmenopausal women is associated with increase risk for thrombosis. However, little is known regarding how platelets are affected by hormonal status. Nitric oxide (NO) modulates platelet functions and is modulated by hormones. Therefore, the present study was designed to determine how loss of ovarian hormones changes expression of estrogen receptors and regulatory proteins for NO synthase (NOS) in platelets. Estrogen receptors (ER alpha and ER beta), NOS, heat shock proteins 70 and 90 (HSP70 and HSP90), caveolin-1, -2, and -3, calmodulin, NOS activity, and cGMP were analyzed in a lysate of platelets from gonadally intact and ovariectomized female pigs. Expression of ER beta and ER alpha receptors, endothelial NOS (eNOS), HSP70, and HSP90 increased with ovariectomy. NOS activity and cGMP also increased; calmodulin was unchanged. Caveolins were not detected. These results suggest that ovarian hormones influence expression of estrogen receptors and eNOS in platelets. Changes in estrogen receptors and NOS could affect platelet aggregation in response to hormone replacement.

Relationship of phenol sulfotransferase activity (SULT1A1) genotype to sulfotransferase phenotype in platelet cytosol

Sulfation catalysed by human cytosolic sulfotransferases is generally considered to be a detoxification mechanism. Recently, it has been demonstrated that sulfation of heterocyclic aromatic amines by human phenol sulfotransferase (SULT1A1) can result in a DNA binding species. Therefore, sulfation capacity has the potential to influence chemical carcinogenesis in humans. To date, one genetic polymorphism (Arg213His) has been identified that is associated with reduced platelet sulfotransferase activity. In this study, data on age, race, gender, SULT1A1 genotype and platelet SULT1A1 activity were available for 279 individuals. A simple colorimetric phenotyping assay, in conjunction with genotyping, was employed to demonstrate a significant correlation (r = 0.23, P < 0.01) of SULT1A1 genotype and platelet sulfotransferase activity towards 2-naphthol, a marker substrate for this enzyme. There was also a difference in mean sulfotransferase activity based on gender (1.28 nmol/min/mg, females; 0.94 nmol/min/mg, males, P = 0.001). DNA binding studies using recombinant SULT1A1*1 and SULT1A1*2 revealed that SULT1A1*1 catalysed N-hydroxy-aminobiphenyl (N-OH-ABP) DNA adduct formation with substantially greater efficiency (5.4 versus 0.4 pmol bound/mg DNA/20 min) than the SULT1A1*2 variant. A similar pattern was observed with 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5b]pyridine (N-OH-PhIP) (4.6 versus 1.8 pmol bound/mg DNA/20 min).

Effects of high-dose estrogen on murine hematopoietic bone marrow precede those on osteogenesis

High-dose estrogen both stimulates new medullary bone formation and suppresses hematopoiesis in mouse long bones. To determine whether the latter response is a direct consequence of the former, we compared the time course of estrogen's effects on osteogenesis and hematopoietic bone marrow. Flow cytometry was employed to measure hematopoietic subpopulations in bone marrow from femurs of female mice killed at different times after commencing 0.5 mg estradiol/wk to each animal. Estrogen markedly reduced the number of leucocytes (CD11a positive), which had already diminished by 75% after 4 days and had virtually disappeared by 18 days. Specific populations showed a similar pattern of decline after estrogen, including B lymphocytes, monocytes, and endothelial cells. In contrast, the osteogenic precursor population showed a marked increase after estrogen treatment, as assessed by assaying alkaline phosphatase-positive colony-forming units (fibroblastic) ex vivo. However, this rise did not reach significance until 8 days after estrogen administration, suggesting that it follows rather than precedes estrogen's effects on hematopoiesis. We conclude that estrogen does not suppress hematopoiesis in mouse long bones as a direct consequence of its effects on osteogenesis.

Human megakaryocytes and platelets contain the estrogen receptor β and androgen receptor (AR): testosterone regulates AR expression

Gender differences in vascular thromboses are well known, and there is evidence that platelets may be involved in these differences and that sex hormones affect platelet function. We characterized the expression of the estrogen receptor  (ER ), estrogen receptor β (ER β), progesterone receptor (PR), and androgen receptor (AR) in the megakaryocyte lineage. Megakaryocytes generated ex vivo from normal human CD34+ stem cells contained RNA for ER β and AR, which increased with cell differentiation. Platelets and human erythroleukemia (HEL) cells also contained ER β and AR transcripts. No ER  or PR messenger RNA or protein was detected in the megakaryocyte lineage. Immunofluorescence microscopy showed that ER β protein was present in glycoprotein (GP) IIb+ megakaryocytes and the HEL megakaryocytic cell line in a predominantly cytoplasmic location. AR showed a cytoplasmic and nuclear distribution in GPIIb+ and GPIIb− cells derived from CD34+ cells and in HEL cells. Western immunoblotting confirmed the presence of ER β and AR in platelets. Megakaryocyte and HEL AR expression was up-regulated by 1, 5, and 10 nmol/L testosterone, but down-regulated by 100 nmol/L testosterone. These findings indicate a regulated ability of megakaryocytes to respond to testosterone and suggest a potential mechanism through which sex hormones may mediate gender differences in platelet function and thrombotic diseases.

Human megakaryocytes and platelets contain the estrogen receptor β and androgen receptor (AR): testosterone regulates AR expression

Gender differences in vascular thromboses are well known, and there is evidence that platelets may be involved in these differences and that sex hormones affect platelet function. We characterized the expression of the estrogen receptor  (ER ), estrogen receptor β (ER β), progesterone receptor (PR), and androgen receptor (AR) in the megakaryocyte lineage. Megakaryocytes generated ex vivo from normal human CD34+ stem cells contained RNA for ER β and AR, which increased with cell differentiation. Platelets and human erythroleukemia (HEL) cells also contained ER β and AR transcripts. No ER  or PR messenger RNA or protein was detected in the megakaryocyte lineage. Immunofluorescence microscopy showed that ER β protein was present in glycoprotein (GP) IIb+ megakaryocytes and the HEL megakaryocytic cell line in a predominantly cytoplasmic location. AR showed a cytoplasmic and nuclear distribution in GPIIb+ and GPIIb− cells derived from CD34+ cells and in HEL cells. Western immunoblotting confirmed the presence of ER β and AR in platelets. Megakaryocyte and HEL AR expression was up-regulated by 1, 5, and 10 nmol/L testosterone, but down-regulated by 100 nmol/L testosterone. These findings indicate a regulated ability of megakaryocytes to respond to testosterone and suggest a potential mechanism through which sex hormones may mediate gender differences in platelet function and thrombotic diseases.

Oestrogens and wound healing

During the past few decades several studies have documented the deleterious impact of the menopause on bone mass and cardiovascular disease, and the reduction of risk in this area by HRT. However, the possible effects of the postmenopausal deficiency in ovarian hormones on skin and its repair post-injury, are less well documented. This review provides a survey of the literature that is available regarding the involvement and influence of oestrogens on the various phases of cutaneous repair - inflammation, proliferation and remodelling. Research carried out on the effects of oestrogens, both in terms of deficiency and replacement, on the process of wound healing in various animal models is described and discussed, together with the very limited work undertaken in humans. This area of research is of paramount clinical importance both in terms of financial cost and human suffering, since many chronic wounds such as venous ulcers, pressure sores and burns afflict the elderly population, of whom postmenopausal women comprise the majority. Clinically our aim should be to restore the integrity and function of wounded tissue as rapidly as possible after injury and it is generally believed that a better understanding of the effects of oestrogens on wound healing could lead to improved care of cutaneous wounds, and the treatment of not only the wound but of the postmenopausal woman as a whole.

Platelets: New Understanding of Platelet Glycoproteins and Their Role in Disease

This review covers new developments and their clinical implications in three areas: platelet antigen polymorphisms, inhibition of platelet glycoprotein IIb-IIIa, and autoimmune thrombocytopenia (ITP).

In Section I, Dr. Kunicki reviews platelet polymorphisms and their clinical implications. A current tabulation of the numerous platelet antigens, both those that are platelet specific and not platelet specific, are summarized. The immunogenic clinical implications of these polymorphisms are considered, including fetal and neonatal alloimmune thrombocytopenia, post transfusion purpura, and refractoriness to platelet transfusion. The functional relationship to hemostasis and thrombosis is also discussed, in particular whether one haplotype of the PIA1/PIA2 (HPA-1a/1b) polymorphism predisposes to myocardial infarction. Finally, novel investigations of polymorphisms will be considered, including hormonal induction of certain polymorphisms.

In Section II, Dr. Michelson reviews the newest generation of platelet inhibitors, those blocking glycoprotein IIB/IIIA, from the point of view of the hematologist who might be consulted about a patient receiving this form of treatment. The current use of available IIb-IIIa inhibitors and those in trial and the accepted and possible future indications for their use are addressed. The mechanism of action and actual and theoretical advantages and disadvantages of each inhibitor are explored. Scenarios that prompt consultation with a hematologist are presented, including management of bleeding, thrombocytopenia, and management of the patient requiring emergency surgery.

In Section III, Dr. Bussel reviews controversies in ITP, looking at both the current state of the art and the potential for the future. Case presentations are used to illustrate the issues in both children and adults. Three primary areas are addressed: 1) the diagnosis of ITP, 2) when and for which patient to recommend splenectomy, and 3) the management of the refractory splenectomized patient who still has a low platelet count and bleeding symptoms.

The current status of the platelet 5-HT(2A) receptor in depression

The author reviews the current status of the platelet serotonin (5-HT)(2A) receptor in depression. Considered are studies of receptor binding, and 5-HT-induced platelet activation and aggregation. 5-HT(2A) receptor density tends to increase in depression, although this more clearly relates to suicidality than depression per se. Indeed, data are consistent with the hypothesis that increased density of platelet 5-HT(2A) receptors may be a marker for increased risk of suicide. 5-HT-induced calcium mobilization is enhanced in unipolar depression; however, unlike in bipolar depression, baseline calcium levels are not. Despite inconsistencies, 5-HT-induced aggregation appears inhibited in depression. This may manifest as a relative inhibition, i.e. no change in aggregation response despite a higher density of 5-HT(2A) receptors. The inhibited aggregation response is state dependent, and acute phase proteins or components of the stress response may be factors. It is unclear if differences between depressed and normal subjects in disposition of 5-HT(2A) receptors are generally indicative of traits or states. Nonetheless, there is little evidence that the degree of departure from normal density or activity of platelet of 5-HT(2A) receptors reflects severity of depression.

Platelets: New Understanding of Platelet Glycoproteins and Their Role in Disease

This review covers new developments and their clinical implications in three areas: platelet antigen polymorphisms, inhibition of platelet glycoprotein IIb-IIIa, and autoimmune thrombocytopenia (ITP).

In Section I, Dr. Kunicki reviews platelet polymorphisms and their clinical implications. A current tabulation of the numerous platelet antigens, both those that are platelet specific and not platelet specific, are summarized. The immunogenic clinical implications of these polymorphisms are considered, including fetal and neonatal alloimmune thrombocytopenia, post transfusion purpura, and refractoriness to platelet transfusion. The functional relationship to hemostasis and thrombosis is also discussed, in particular whether one haplotype of the PIA1/PIA2 (HPA-1a/1b) polymorphism predisposes to myocardial infarction. Finally, novel investigations of polymorphisms will be considered, including hormonal induction of certain polymorphisms.

In Section II, Dr. Michelson reviews the newest generation of platelet inhibitors, those blocking glycoprotein IIB/IIIA, from the point of view of the hematologist who might be consulted about a patient receiving this form of treatment. The current use of available IIb-IIIa inhibitors and those in trial and the accepted and possible future indications for their use are addressed. The mechanism of action and actual and theoretical advantages and disadvantages of each inhibitor are explored. Scenarios that prompt consultation with a hematologist are presented, including management of bleeding, thrombocytopenia, and management of the patient requiring emergency surgery.

In Section III, Dr. Bussel reviews controversies in ITP, looking at both the current state of the art and the potential for the future. Case presentations are used to illustrate the issues in both children and adults. Three primary areas are addressed: 1) the diagnosis of ITP, 2) when and for which patient to recommend splenectomy, and 3) the management of the refractory splenectomized patient who still has a low platelet count and bleeding symptoms.

Hemostatic Factors and Ischemic Heart Disease Risk Among Postmenopausal Women

The following is a review of (largely) epidemiologic evidence on whether changes in plasma hemostatic concentrations occur with menopause and with postmenopausal hormone therapy which may have an impact on risk of ischemic heart disease. To date, only plasma fibrinogen has been positively associated with long-term risk of disease among women; however, data are sparse. Taken together, the evidence supports an impact of endogenous sex hormone levels on thrombotic potential and points to a modest increase in a number of plasma hemostatic factor levels at menopause. Results of studies of estrogen therapy are somewhat conflicting. Observational findings suggest that, except for possibly the Factor VII level, estrogen therapy may prevent the menopause-related rise in plasma hemostatic factors. In contrast, controlled experiments have found increased markers of thrombin generation with use of common formulations of estrogen therapy. The hemostatic effects found with oral preparations do not appear to occur with transdermal forms of estrogen although data are limited. Overall, the evidence shows menopause to have an impact on plasma levels of hemostatic factors which appears to be modified by use of oral estrogen. Whether these alterations in plasma levels have an impact on risk of ischemic heart disease among postmenopausal women remains to be demonstrated.

Biologic activity of tamoxifen at low doses in healthy women

BACKGROUND

Results of a clinical trial recently completed in the United States indicate that administration of tamoxifen (20 mg/day) to women at risk can reduce breast cancer incidence by approximately 50% but is associated with an increased risk of developing endometrial cancer and venous thromboembolic events. Since these adverse effects may be dose related, we investigated the effect of tamoxifen on several biomarkers when the drug was given at doses lower than those currently in use.

METHODS

In two sequential experiments, 127 healthy hysterectomized women aged 35-70 years were randomly assigned to one of the following four treatment arms: placebo (n = 31) or tamoxifen at 20 mg/day (n = 30) (first experiment); or tamoxifen at 10 mg/day (n = 34) or tamoxifen at 10 mg/ alternate days (n = 32) (second experiment). Baseline and 2-month measurements of the following parameters were compared: 1) total cholesterol (primary end point) and other surrogate markers of cardiovascular disease, e.g., low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, triglycerides, and lipoprotein(a); 2) blood cell count; 3) fibrinogen; 4) antithrombin III; 5) osteocalcin; and, 6) in a subgroup of 103 women, insulin-like growth factor-I (IGF-I), a possible surrogate marker for breast cancer.

RESULTS

After adjustment for the baseline values, there were reductions in circulating levels of total cholesterol and IGF-I of the same magnitude in all three tamoxifen treatment arms. A similar pattern was observed for most of the other parameters. In the placebo arm, fibrinogen level, which showed a decrease, was the only parameter exhibiting change.

CONCLUSIONS

Up to a 75% reduction in the conventional dose of tamoxifen (i.e., 20 mg/day) does not affect the activity of the drug on a large number of biomarkers, most of which are surrogate markers of cardiovascular disease. This study was hypothesis generating, and larger studies are warranted to assess the efficacy of tamoxifen at low doses.

The evolution of megakaryocytes to platelets

Megakaryocytes (MKs) arise from pluripotent stem cells by a process of cell division, endoreplication and maturation. Progressively, the MK cytoplasm is invaded by the demarcation membrane system speculated to delimit pre-formed platelets. One theory is that the passage of entire MKs (or fragments) into the blood stream is followed by their physical break-up into platelets in the pulmonary circulation. A second theory is that MKs produce beaded processes (proplatelets) which then separate into platelets. Functionally vital platelet receptors such as GPIIb-IIIa and GPIb-IX complexes are specific markers of the MK lineage. CD34 and CD4 are present in progenitors but progressively disappear as MKs mature. Stroma cells secrete cytokines, produce extracellular matrix proteins and mediate cellular contact interactions that regulate MK development. Studies on thrombopoietin and the use of transgenic mouse models are helping to clarify MK biology.