Changes in Platelet ATP Secretion and Aggregation during Pregnancy and in Preeclampsia

Overexpression of facilitative glucose transporter-3 and membrane procoagulation in maternal platelets of preeclamptic pregnancy

BACKGROUND

Preeclampsia (PE) is a hypertensive disorder during pregnancy that results in significant adverse maternal and neonatal outcomes. Platelet activation is present in PE and contributes to the thrombo-hemorrhagic states of the disorder. However, the mechanisms that initiate and/or sustain platelet activation in PE are ill-defined.

OBJECTIVES

We aimed to characterise this mechanism and the procoagulant potentials of platelets in PE.

METHODS

In this quantitative observational study, we analyzed platelet procoagulant membrane dynamics in patients with PE (n = 21) compared with age-matched normotensive pregnancies (n = 20), gestational hypertension (n = 10), and non-pregnant female controls (n = 19). We analyzed fluorescently labeled indicators of platelet activation, bioenergetics, and procoagulation (phosphatidylserine exposure and thrombin generation), coupled with high-resolution imaging and thrombelastography. We then validated our findings using flow cytometry, immunoassays, classical pharmacology, and convolutional neural network analysis.

RESULTS

PE platelets showed significant ultra-structural remodeling, are more extensively preactivated than in healthy pregnancies and can circulate as microaggregates. Preactivated platelets of PE externalized phosphatidylserine and thrombin formed on the platelet membranes. Platelets' expression of facilitative glucose transporter-1 increased in all pregnant groups. However, PE platelets additionally overexpress glucose transporter-3 to enhance glucose uptake and sustain activation and secretion events. Although preeclampsia platelets exposed to subendothelial collagen showed incremental activation, the absolute hemostatic response to collagen was diminished, and likely contributed to greater blood loss perioperatively.

CONCLUSIONS

We revealed 2 bioenergetic mediators in the mechanism of sustained platelet procoagulation in preeclampsia. Although glucose transporter-1 and glucose transporter-3 remain elusive antiprocoagulant targets, they may be sensitive monitors of PE onset and progression.

A new decade awaits sticky platelet syndrome: where are we now, how do we manage and what are the complications?

INTRODUCTION

Sticky platelet syndrome is a less known platelet function disorder with a familiar occurrence and likely genetic background. Clinically, it is characterized by an increased risk of venous and arterial thromboembolic events and obstetric placenta-mediated complications. The increased aggregation after low-dose ADP and/or epinephrine is its distinctive laboratory feature. Though described for almost 40 years, several issues regarding its etiology, involved pathomechanisms, genetic background, optimal diagnostic and treatment approach remain controversial.

AREAS COVERED

The work aims to summarize published studies, the actual definition of the syndrome, and point out its drawbacks. A literature search on Medline, Embase, and archives from EHA congresses was performed (terms: 'sticky platelet syndrome' - 'platelet hyperreactivity' - 'platelet hyperaggregability'). The authors added in their unpublished data. The introductory overview of the present understanding is followed by the discussion of the pathophysiologic, diagnostic, and therapeutic problems.

EXPERT OPINION

Despite the growing evidence provided by case reports and series, the lack of robust studies limits the decision-making on diagnostics and management. The diagnostic issues, particularly the standardization of light transmission aggregometry, represent the crucial problem for the broader acceptance of the syndrome.

Changes in Maternal Platelet Physiology during Gestation and Their Interaction with Trophoblasts

Upon activation, maternal platelets provide a source of proinflammatory mediators in the intervillous space of the placenta. Therefore, platelet-derived factors may interfere with different trophoblast subtypes of the developing human placenta and might cause altered hormone secretion and placental dysfunction later on in pregnancy. Increased platelet activation, and the subsequent occurrence of placental fibrinoid deposition, are linked to placenta pathologies such as preeclampsia. The composition and release of platelet-derived factors change over gestation and provide a potential source of predicting biomarkers for the developing fetus and the mother. This review indicates possible mechanisms of platelet-trophoblast interactions and discusses the effect of increased platelet activation on placenta development.

Platelet activation and placenta-mediated adverse pregnancy outcomes: an ancillary study to the Effects of Aspirin in Gestation and Reproduction trial

BACKGROUND

Platelet activation may play a role in the pathophysiology of placenta-mediated obstetrical complications, as evidenced by the efficacy of aspirin in preventing preeclampsia, but published data regarding the relationship between biomarkers for platelet activation and adverse obstetrical outcomes are sparse. In particular, it is unknown whether prepregnancy biomarkers of platelet activation are associated with adverse pregnancy outcomes.

OBJECTIVE

This study aimed to determine the following: (1) whether maternal plasma concentrations of platelet factor 4 are associated with risk of placenta-mediated adverse obstetrical outcomes, and (2) whether these associations are modified by low-dose aspirin.

STUDY DESIGN

This ancillary study included measurement of platelet factor 4 among 1185 of 1228 women of reproductive age enrolled in the Effects of Aspirin in Gestation and Reproduction trial with available plasma samples, with relevant outcomes assessed among 584 women with pregnancies lasting at least 20 weeks' gestation. We measured platelet factor 4 in plasma samples obtained at the prepregnancy study visit (before randomization to low-dose aspirin or placebo), 12 weeks' gestation, and 28 weeks' gestation. The primary outcome was a composite of hypertensive disorders of pregnancy, placental abruption, and small-for-gestational-age infant. We estimated the relative risks (RRs) and 95% confidence intervals (CIs) for the association between platelet factor 4 and the composite and individual outcomes at each time point using log-binomial regression that was weighted to account for potential selection bias and adjusted for age, body mass index, education, income, and smoking. To evaluate the potential effect modification of aspirin, we stratified the analyses by aspirin treatment assignment.

RESULTS

During follow-up, 95 women experienced the composite adverse obstetrical outcome, with 57 cases of hypertensive disorders of pregnancy, 35 of small for gestational age, and 6 of placental abruption. Overall, prepregnancy platelet factor 4 was positively associated with the composite outcome (third tertile vs first tertile; relative risk, 2.36; 95% confidence interval, 1.38-4.03) and with hypertensive disorders of pregnancy (third tertile vs first tertile; relative risk, 2.14; 95% confidence interval, 1.08-4.23). In analyses stratified by treatment group, associations were stronger in the placebo group (third tertile vs first tertile; relative risk, 3.36; 95% confidence interval, 1.42-7.93) than in the aspirin group (third tertile vs first tertile; relative risk, 1.78; 95% confidence interval, 0.90-3.50).

CONCLUSION

High concentrations of platelet factor 4 before pregnancy are associated with increased risk of placenta-mediated adverse pregnancy outcomes, particularly for hypertensive disorders of pregnancy. Aspirin may mitigate the increased risk of these outcomes among women with higher plasma concentrations of preconception platelet factor 4, but low-dose aspirin nonresponders may require higher doses of aspirin or alternate therapies to achieve obstetrical risk reduction.

Maternal Platelets—Friend or Foe of the Human Placenta?

Human pregnancy relies on hemochorial placentation, including implantation of the blastocyst and deep invasion of fetal trophoblast cells into maternal uterine blood vessels, enabling direct contact of maternal blood with placental villi. Hemochorial placentation requires fast and reliable hemostasis to guarantee survival of the mother, but also for the neonates. During human pregnancy, maternal platelet count decreases gradually from first, to second, and third trimester. In addition to hemodilution, accelerated platelet sequestration and consumption in the placental circulation may contribute to a decline of platelet count throughout gestation. Local stasis, turbulences, or damage of the syncytiotrophoblast layer can activate maternal platelets within the placental intervillous space and result in formation of fibrin-type fibrinoid. Perivillous fibrinoid is a regular constituent of the normal placenta which is considered to be an important regulator of intervillous hemodynamics, as well as having a role in shaping the developing villous trees. However, exaggerated activation of platelets at the maternal-fetal interface can provoke inflammasome activation in the placental trophoblast, and enhance formation of circulating platelet-monocyte aggregates, resulting in sterile inflammation of the placenta and a systemic inflammatory response in the mother. Hence, the degree of activation determines whether maternal platelets are a friend or foe of the human placenta. Exaggerated activation of maternal platelets can either directly cause or propagate the disease process in placenta-associated pregnancy pathologies, such as preeclampsia.

L-NAME-induced Preeclampsia: correction of functional disorders of the hemostasis system with Resveratrol and Nicorandil

Introduction. Preeclampsia is a formidable disease of the second half of pregnancy, leading to severe complications, including disability and even death. Many authors have recognized the correlation between the severity of preeclampsia and the degree of disturbances in the hemostasis system. In this regard, the objective of this study was to assess inhibition of platelet aggregation and the possibility of its correction with resverаtrol and nicorandil.

Materials and methods. The study was performed on 250 mature white Wistar female rats weighing 250–300 g. The platelet aggregation induced by ADP, collagen, ristomycin, adrenaline was determined, as well as PTT, TT, aPTT, fibrinogen, and the clotting time.

Results and discussion. Introduction of resverаtrol and nicorandil resulted in a decrease in thrombocyte aggregation capacity from 53.8 ± 2.60% to 22.1 ± 1.25% and 37.1 ± 1.79%, respectively, when using ADP as an inducer. The clotting time was from 841 ± 42 s up to 1135 ± 33 s and 1034 ± 26 s, respectively. In addition, there was an increase in temporal parameters of plasma-coagulation hemostasis and a decrease in plasma fibrinogen content. The use of glibenclamide resulted in partial cancellation of the positive effects of resverаtrol and nicorandil, with an increase in platelet aggregation to 28.9 ± 1.8% and 43.9 ± 1.2% when using ADP as an inducer and a decrease in the thrombosis time to 988 ± 26 s and 950 ± 22 s, respectively.

Conclusion. In animals with experimental preeclampsia, there were disturbances in the hemostasis system, comparable to those in the clinical situation. The use of resverаtrol and nicorandil leads to a pronounced correction of hemostasis parameters. The positive effects of the studied pharmacological agents are mediated by several mechanisms, including K+ATP channels.

Platelet function in preeclampsia - a systematic review and meta-analysis

Preeclampsia is a serious pregnancy-related complication. Platelets are potentially important in the pathogenesis of preeclampsia, and platelet function analyses may prove as sensitive preeclampsia biomarkers. This study aimed to systematically review and summarise the literature on platelet function markers in preeclampsia. This systematic review was conducted according to PRISMA and registered in PROSPERO. Relevant studies were identified through PubMed and Embase on 15/08/17. As platelet function markers platelet activation, platelet aggregation and platelet adhesion markers were included. If possible, relevant data were extracted for each marker to perform a meta-analysis of the mean difference between women with and without preeclampsia. All 69 included articles underwent quality rating. Some platelet activation markers, especially p-selectin and mean platelet volume (MPV), were significantly increased comparing the two groups of women, while others were not. The meta-analysis demonstrated that, overall, women with preeclampsia had significantly higher MPV than in women without preeclampsia. No significant difference was found regarding platelet aggreg`ation comparing the two groups. Platelet adhesion was investigated in noneof the included studies. In conclusion, further studies are warranted to investigate platelet activation markers future role as predictive markers in preeclampsia. MPV is suggested as the most promising biomarker for evaluating platelet function in preeclampsia.

Placental hemostasis and sterile inflammation: New insights into gestational vascular disease

Activation of the coagulation and inflammatory systems are physiologically occurring during pregnancy. However, excess activation of either system is well documented in gestational vascular diseases (GVD). GVD are placenta-mediated pregnancy complications and a major cause of feto-maternal morbidity and mortality. The causal relevance of excess coagulation and inflammatory responses for GVD remains largely unknown. Deciphering the causal relationship of excess coagulation and inflammation in GVD may allow conceptualizing new therapeutic approaches to combat GVD. Platelet activation and procoagulant extracellular vesicles (EVs) provide a link between coagulation and inflammation and their activation or generation in GVD is well established. As recently shown EVs cause sterile placental inflammation by activating maternal platelets that release ATP and activate purinergic receptor signaling and NLRP3 inflammasome in the embryonic trophoblast. This thrombo-inflammatory mechanism suggests a novel link between coagulation activation and sterile inflammation in GVD. These findings highlight a role of anti-platelet therapies in GVD. In addition, targeting the inflammasome alone or in combination with platelet inhibition may provide a new therapeutic strategy in GVD.

Characterization of five marker levels of the hemostatic system and endothelial status in normotensive pregnancy and pre-eclampsia

OBJECTIVES

Pre-eclampsia is associated with changes in the hemostatic system and endothelial status. Urinary 11-dehydrothromboxane B2/creatinine (11-DTXB2/Cr) is a marker for platelet activation and vascular constriction, thrombin-antithrombin complex (TAT) for thrombin formation, serum thrombomodulin (TM) for endothelial damage, and beta-thromboglobulin (beta-TG) and platelet factor 4 (PF-4) for platelet activation and releasing reaction. The present study attempted to evaluate these five markers in normotensive pregnancy and pre-eclampsia.

METHODS

These five markers were simultaneously measured in urine and blood samples from 25 women who were not pregnant (group 1, controls), 31 women with normotensive pregnancy (group 2, second controls), 22 women with mild pre-eclampsia (group 3), and 21 women with severe pre-eclampsia (group 4). The average gestational age was 36 wk.

RESULTS

The 11-DTXB2/Cr, TAT, and beta-TG levels were significantly higher (P < 0.01) in groups 2, 3, and 4 than in group 1. The TM and beta-TG levels were significantly higher (P < 0.05) in group 3 than in group 2. The TM, beta-TG, and PF-4 levels were increased significantly (P < 0.05-0.01) in group 4 compared to those in groups 1, 2, and 3.

CONCLUSION

Platelet aggregation, vascular constriction, and thrombin formation (detected by 11-DTXB2/Cr and TAT) may be markedly enhanced even in group 2, but further enhancement may be relatively slight in groups 3 and 4. In contrast, endothelial damage (determined by TM) and platelet release of PF-4 may not increase significantly in group 2, but they may increase in group 4. Platelet-release of beta-TG may be enhanced in groups 2, 3, and 4. Endothelial damage and platelet-releasing reaction (detected by PF-4 and beta-TG) may be significantly more enhanced in group 4 than in group 3.

The levels of five markers of hemostasis and endothelial status at different stages of normotensive pregnancy

BACKGROUND

Urinary 11-dehydrothromboxane B(2)/creatinine (11-DTXB(2)/Cr) is a marker for in vivo platelet activation and vascular constriction, blood thrombomodulin (TM) for endothelial damage and associated thrombosis, thrombin-antithrombin complex (TAT) for thrombin formation, and beta-thromboglobulin (beta-TG) and platelet factor 4 (PF-4) for in vivo platelet activation and releasing reaction. Little is known about the quantitative relationship among them during pregnancy. The present study investigated levels of five markers at different stages of normotensive pregnancy.

METHODS

Subjects were 17 healthy non-pregnant women (Group 1, control) and 67 women carrying single fetuses in normotensive pregnancy. Of the pregnant women, 17 were in the 20th week of gestation (Group 2), 20 were in their 30th week (Group 3), and 30 were in their 36th week (Group 4). Urinary and circulating blood levels of 11-DTXB(2)/Cr, TM, TAT, beta-TG, and PF-4 were measured simultaneously.

RESULTS

The 11-DTXB(2)/Cr and TAT levels showed elevated values at the 20th and 30th weeks of gestation, and markedly elevated values at the 36th week, whereas the TM level remained constant throughout pregnancy. The beta-TG and PF-4 levels maintained stable values at the 20th week, but showed elevated values at the 30th and 36th weeks.

CONCLUSIONS

Platelet aggregation, vascular constriction, and thrombin formation (detected by 11-DTXB(2)/Cr and TAT) appear to be enhanced as early as the 20th week of gestation, continuously enhanced by the 30th week, and markedly enhanced by the 36th week. Platelet activation and releasing reaction (determined by beta-TG and PF-4) gradually enhanced from the 30th to 36th weeks. In contrast, endothelial damage and associated thrombosis (detected by TM) were minimal throughout pregnancy. Investigating these markers of hemostasis and endothelial function in normotensive pregnancy may provide insights into related disease states.