The effect of hormone replacement therapy on Ca2+ mobilization and P-selectin (CD62P) expression in platelets examined under flow cytometry

Monitoring platelet function in marine mammals: Intracellular Ca2+ mobilization as a biomarker of platelet activation

Platelet functionality plays a crucial role in marine mammals. Alterations in platelet function can result from stress, pathologies, or exposure to xenobiotics, among others. The early detection of platelet function abnormalities is essential in these species to prevent advanced pathology and mitigate potential risks. Our main objective was to establish a range of physiological values of platelet function in bottlenose dolphins (Tursiops truncatus), beluga whales (Delphinapterus leucas), sea lions (Otaria flavescens) and walruses (Odobenus rosmarus). Intraplatelet Ca2+ mobilization using adenosine diphosphate (ADP) as a platelet agonist was used as a platelet function biomarker, adapting the methodology previously described by us in dolphins (Felipo-Benavent et al., 2022) to the rest of the species. The assay was also adapted to a seal (Phoca vitulina). Numerical indicators of intraplatelet Ca2+ mobilization kinetics were established, and statistical analyses were performed to compare the effects of species, sex, age, aquarium and species. Significant differences were observed between species, being the platelets of the sea lions the more reactive to the agonist. This work demonstrates the usefulness of this assay in the diagnosis or monitoring of animals with hemostatic diseases, showing two clinical cases in which intraplatelet calcium mobilization values were altered in marine mammals suffering haemorrhages. This assay may also serve as a means to monitor environmental changes and their potential impact on the health of marine mammal populations.

Flow cytometric kinetic assay of calcium mobilization in whole blood platelets of bottlenose dolphins (Tursiops truncatus)

Marine mammals may suffer alterations in platelet function and hemostasia due to multiple pathologies, environmental conditions (including stress) or exposure to different contaminants that induce platelet activation. Detecting early alterations in platelet function in these animals could be an especially relevant diagnostic tool in these species because they typically do not show signs of weakness or disease until the pathology is in advanced state, in order to avoid attracting predators in natural conditions. The study of early markers of platelet activation is relevant for the detection, monitoring and therapy of inflammation and hemostasis disorders. Flow cytometry provides a convenient method to evaluate platelet activation by following the kinetics of intracellular Ca²⁺ , using sensitive fluorescent indicators that can be loaded into intact cells. In order to study intraplatelet Ca²⁺ mobilization in marine mammals, we have adapted a kinetic assay of human platelet activation to study platelet activation in whole-blood samples of bottlenose dolphins (Tursiops truncatus) using the Ca²⁺ -sensitive dye Fluo-4AM and a clone of the platelet-specific antibody CD41-PE that recognizes dolphin platelets. This no-wash, no-lyse protocol provides a simple and sensitive tool to assess in vitro the time course and intensity of signal-transduction responses to platelet agonists under near-physiological conditions. The adaptation of this technique to marine mammals represents a methodological advance for basic and clinical veterinary applications but also for general environmental studies on these species.

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.

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.