In-vitro secretion of prostanoids by placental villous cytotrophoblasts in pre-eclampsia

Bioactive lipid mediators in plasma are predictors of preeclampsia irrespective of aspirin therapy

There are few early biomarkers to identify pregnancies at risk of preeclampsia (PE) and abnormal placental function. In this cross-sectional study, we utilized targeted ultra-performance liquid chromatography-ESI MS/MS and a linear regression model to identify specific bioactive lipids that serve as early predictors of PE. Plasma samples were collected from 57 pregnant women prior to 24-weeks of gestation with outcomes of either PE (n = 26) or uncomplicated term pregnancies (n = 31), and the profiles of eicosanoids and sphingolipids were evaluated. Significant differences were revealed in the eicosanoid, (±)11,12 DHET, as well as multiple classes of sphingolipids; ceramides, ceramide-1-phosphate, sphingomyelin, and monohexosylceramides; all of which were associated with the subsequent development of PE regardless of aspirin therapy. Profiles of these bioactive lipids were found to vary based on self-designated race. Additional analyses demonstrated that PE patients can be stratified based on the lipid profile as to PE with a preterm birth linked to significant differences in the levels of 12-HETE, 15-HETE, and resolvin D1. Furthermore, subjects referred to a high-risk OB/GYN clinic had higher levels of 20-HETE, arachidonic acid, and Resolvin D1 versus subjects recruited from a routine, general OB/GYN clinic. Overall, this study shows that quantitative changes in plasma bioactive lipids detected by ultra-performance liquid chromatography-ESI-MS/MS can serve as an early predictor of PE and stratify pregnant people for PE type and risk.

The Road to Low-Dose Aspirin Therapy for the Prevention of Preeclampsia Began with the Placenta

The road to low-dose aspirin therapy for the prevention of preeclampsia began in the 1980s with the discovery that there was increased thromboxane and decreased prostacyclin production in placentas of preeclamptic women. At the time, low-dose aspirin therapy was being used to prevent recurrent myocardial infarction and other thrombotic events based on its ability to selectively inhibit thromboxane synthesis without affecting prostacyclin synthesis. With the discovery that thromboxane was increased in preeclamptic women, it was reasonable to evaluate whether low-dose aspirin would be effective for preeclampsia prevention. The first clinical trials were very promising, but then two large multi-center trials dampened enthusiasm until meta-analysis studies showed aspirin was effective, but with caveats. Low-dose aspirin was most effective when started <16 weeks of gestation and at doses >100 mg/day. It was effective in reducing preterm preeclampsia, but not term preeclampsia, and patient compliance and patient weight were important variables. Despite the effectiveness of low-dose aspirin therapy in correcting the placental imbalance between thromboxane and prostacyclin and reducing oxidative stress, some aspirin-treated women still develop preeclampsia. Alterations in placental sphingolipids and hydroxyeicosatetraenoic acids not affected by aspirin, but with biologic actions that could cause preeclampsia, may explain treatment failures. Consideration should be given to aspirin's effect on neutrophils and pregnancy-specific expression of protease-activated receptor 1, as well as additional mechanisms of action to prevent preeclampsia.

Placental Production of Eicosanoids and Sphingolipids in Women Who Developed Preeclampsia on Low-Dose Aspirin

Low-dose aspirin, which selectively inhibits thromboxane synthesis, is now standard of care for the prevention of preeclampsia in at risk women, but some women still develop preeclampsia despite an aspirin regimen. To explore the "aspirin failures," we undertook a comprehensive evaluation of placental lipids to determine if abnormalities in non-aspirin sensitive lipids might help explain why some women on low-dose aspirin develop preeclampsia. We studied placentas from women with normal pregnancies and women with preeclampsia. Placental villous explants were cultured and media analyzed by mass spectrometry for aspirin-sensitive and non-aspirin-sensitive lipids. In women who developed severe preeclampsia and delivered preterm, there were significant elevations in non-aspirin-sensitive lipids with biologic actions that could cause preeclampsia. There were significant increases in 15- and 20-hydroxyeicosatetraenoic acids and sphingolipids: D-e-C_18:0 ceramide, D-e-C_18:0 sphingomyelin, D-e-sphingosine-1-phosphate, and D-e-sphinganine-1-phosphate. With regard to lipids sensitive to aspirin, there was no difference in placental production of thromboxane or prostacyclin, but prostaglandins were lower. There was no difference for isoprostanes, but surprisingly, anti-inflammatory omega 3 and 6 PUFAs were increased. In total, 10 of 30 eicosanoids and 5 of 42 sphingolipids were abnormal in women with severe early onset preeclampsia. Lipid changes in women with mild preeclampsia who delivered at term were of lesser magnitude with few significant differences. The placenta produces many aspirin-sensitive and non-aspirin-sensitive lipids. Abnormalities in eicosanoids and sphingolipids not sensitive to aspirin might explain why some aspirin-treated women develop preeclampsia.

Review: maternal and placental antioxidant response to preeclampsia - impact on vasoactive eicosanoids

The abnormally developed placenta is believed to be the pathophysiological cause of preeclampsia (PE). The resulting malperfusion of the placenta in PE can be associated with fluctuations in oxygen levels, leading to oxidative stress. How then do the placenta and the circulatory system of the mother adapt and respond to the increased oxidative challenge associated with PE? Many antioxidant systems have been shown to be upregulated or downregulated in the placenta and/or the maternal circulation during PE. Such altered antioxidant response can lead to increased lipid peroxidation. Oxidation of arachidonoyl residues in phospholipids generates bioactive lipids such as F2-isoprostanes, which are known vasoconstrictors. The consequences of changes in antioxidant status can also affect signal transduction and enzymatic pathways related to eicosanoid synthesis.

Pathophysiology of preeclampsia: links with implantation disorders

The phenomenon of implantation anchors the embryo into the uterine wall and produces a hemochorial placenta that maintains the pregnancy and fetal growth. Implantation and placentation are intimately linked and cannot be dissociated either in time or in space. Preeclampsia is characterized by hypertension and proteinuria. It is secondary to an anomaly of the invasion of the uterine spiral arteries by extra-villous cytotrophoblast cells, associated with local disruptions of vascular tone, of immunological balance and inflammatory status, and sometimes with genetic predispositions. Preeclampsia is a disease of early pregnancy, a form of incomplete spontaneous abortion, but is expressed late in pregnancy. Aspirin may play a favorable role in implantation which is related to the genesis of preeclampsia and some cases of intra-uterine growth restriction. The most important points in obtaining a preventive effect from low-dose aspirin during the pregnancy are early treatment (before 13 weeks of gestation) and the prescription of a sufficient dose (more than 100 mg per day).

Endothelium and hypertensive disorders in pregnancy

Pregnancy-induced hypertension is one of the complications that obstetricians fear most due to its sudden appearance, its changing clinical presentation, its rapid evolution, and its association with high fetal and maternal morbidity and mortality. Because of these reasons, preeclampsia has been studied widely. But although the search for answers to many questions about its etiopathogenesis and physiopathology has led to numerous researches, after many years of studies and efforts there still exist obscure and enigmatic aspects about them. Today, various risk factors for the development of this entity have been identified, and a combination of different hypotheses has been proposed to try to find an approximation to the real solution for this problem, which could probably lead to better therapeutic management.

Eicosanoids in preeclampsia

Preeclampsia is characterized by an imbalance between two cyclooxygenase metabolites of arachidonic acid, thromboxane and prostacyclin, that favors thromboxane. Because of the biologic actions of these two eicosanoids, this imbalance might explain major clinical symptoms of preeclampsia, such as hypertension, platelet aggregation and reduced uteroplacental blood flow. In the maternal circulation, this imbalance is primarily manifested by decreased production of prostacyclin by endothelial cells. Platelet thromboxane synthesis is only increased in severe preeclampsia. In the placenta and in leukocytes, the imbalance is exacerbated by increased production of thromboxane coupled with decreased production of prostacyclin in both mild and severe preeclampsia. Longitudinal measurements of urinary metabolites of thromboxane and prostacyclin reveal that the thromboxane/prostacyclin imbalance predates the onset of clinical symptoms of preeclampsia. The imbalance between thromboxane and prostacyclin is most likely caused by oxidative stress, which is manifest in preeclampsia by increased lipid peroxidation and decreased antioxidant protection. Oxidative stress may drive this imbalance because lipid peroxides activate the cyclooxygenase enzyme to increase thromboxane synthesis, but at the same time they inhibit prostacyclin synthase to decrease prostacyclin synthesis. Low-dose aspirin therapy (50-150 mg/day) has been considered for the prevention of preeclampsia because it selectively inhibits thromboxane synthesis. Several studies reported dramatic decreases in the incidence of preeclampsia with low-dose aspirin therapy. However, two large multicenter studies reported only modest decreases, which dampened enthusiasm. The two large studies were "intent to treat" studies which included patients who were noncompliant and who discontinued the use of aspirin. In one of the studies for which compliance statistics were available only 53% of the aspirin group had a compliance rate greater than 75%, which raises a question as to whether the effectiveness of aspirin was being tested. Low-dose aspirin therapy should not yet be dismissed for the prevention of preeclampsia, but be reconsidered with emphasis on compliance using doses of aspirin in the range of 100-150 mg/day combined with antioxidants.

In vitro migration of cytotrophoblasts through a decidual endothelial cell monolayer: the role of matrix metalloproteinases

Deficient trophoblast invasion is a major feature of pre-eclampsia. In vitro studies suggest that in normal pregnancy, maternal cells may play a role in controlling trophoblast invasion, although the exact nature of the regulatory interactions between these cells is not fully understood. To examine the effect of maternal-placental cell interactions on matrix metalloproteinase (MMP) secretion and endovascular cytotrophoblast migration in normal pregnancy and in pre-eclampsia, we performed co-culture experiments using cytotrophoblasts from normal pregnancies, together with decidual endothelial cells from both normal and preeclamptic pregnancies. Cells were incubated on semi-permeable membranes with or without phorbol 12-myristate 13-acetate (PMA). Results showed that third trimester cytotrophoblasts are migratory under basal conditions and display a different MMP profile from decidual endothelial cells. Co-culture did not damage either cell type and resulted in reduced latent MMP-9 secretion and reduced cytotrophoblast migration. Although PMA upregulated MMPs in decidual endothelial cells, it had no effect on cytotrophoblast MMP secretion. PMA, however, reduced cytotrophoblast migration. Pre-eclamptic decidual endothelial cells showed reduced MMP-1 secretion, but overall were not different in co-culture from normal endothelial cells. This study demonstrates the effectiveness of a bilayer co-culture model to study maternal-foetal cell interactions and provides evidence that maternal cells may contribute to the control of endovascular cytotrophoblast invasion.

Modulation of prostacyclin and thromboxane secretion by cytotrophoblasts from normal and pre-eclamptic human pregnancies

We and others have previously observed an imbalance in cytotrophoblast secretion of the vasoactive prostanoids prostacyclin and thromboxane A(2) in pre-eclampsia. To examine the effects of potential modulators of this imbalance, cytotrophoblasts isolated from normal and pre-eclamptic pregnancies were incubated in the presence of lipopolysaccharide, the calcium ionophore A23187, tumour necrosis factor alpha, or interleukin 1beta, with or without the cyclo-oxygenase inhibitor, indomethacin. Further incubations included the drugs tranylcypromine, a prostacyclin synthetase inhibitor (0.1, 10 microM ), or the thromboxane synthetase inhibitor, pirmagrel (0.001, 1 microM ). Results showed that cytotrophoblasts from pre-eclamptic pregnancies had increased thromboxane production and significant stimulation of prostacyclin production by lipopolysaccharide and calcium ionophore. Lipopolysaccharide stimulated thromboxane production in normal cytotrophoblasts, while indomethacin almost completely inhibited production of both prostanoids. Tranylcypromine mildly inhibited prostacyclin production in normal cytotrophoblasts only, whereas pirmagrel strongly inhibited thromboxane production in a dose-related manner, with reciprocal increase in prostacyclin production occurring in cytotrophoblasts from pre-eclamptic pregnancies. This study confirmed that cytotrophoblasts from pre-eclamptic women had increased thromboxane production and showed that pirmagrel, at the relatively low dose of 0.001 microM, was able to normalize the imbalance of thromboxane and prostacylin production and may therefore warrant further investigation as a treatment for pre-eclampsia.

Thromboxane A(2) limits differentiation and enhances apoptosis of cultured human trophoblasts

Prostanoids influence differentiation in diverse cell types. Altered expression of cyclooxygenase and prostaglandins has been implicated in the pathophysiology of placental dysfunction, which results in preeclampsia and fetal growth restriction. We hypothesized that prostanoids modulate differentiation and apoptosis in cultured human trophoblasts. Villous cytotrophoblasts were isolated from term human placentas and cultured in serum-free medium. The level of human chorionic gonadotropin was used as a marker of biochemical differentiation of primary trophoblasts, and syncytia formation was used as a marker of morphologic differentiation. Of the prostanoids tested, we found exposure to thromboxane A(2) hindered both biochemical and morphologic differentiation of cultured trophoblasts. As expected, human chorionic gonadotropin levels in the media were elevated in a concentration-dependent manner in the presence of the thromboxane synthase inhibitor, sodium furegrelate, or the thromboxane A(2) receptor blocker SQ 29,548. Furthermore, thromboxane A(2) enhanced trophoblast apoptosis, determined using terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining, cell morphology, and a concentration-dependent increase in p53 expression. We conclude that thromboxane A(2) hinders differentiation and enhances apoptosis in cultured trophoblasts from term human placenta. We speculate that thromboxane may contribute to placental dysfunction by restricting differentiation and enhancing apoptosis in human trophoblasts.

Hypoxia attenuates PGE(2)but increases prostacyclin and thromboxane production in human term villous trophoblast

Prostanoids have been proposed to play a major role in the regulation of uteroplacental blood flow. We examined the effect of hypoxia on the production of prostaglandin E(2)(PGE(2)) thromboxane B(2)(TXB(2)), and prostacyclin (measured as 6-keto-PGF(1alpha)) by human term trophoblast cells and villous placental explants. Explants (n=8) and purified trophoblast cells (n=5) were incubated for 24-72 h under either normoxic (21 per cent O(2)) or hypoxic (2 per cent O(2)) conditions. In trophoblast monolayer cultures, hypoxia attentuated PGE(2)production rates to 52+/-9.4 per cent (mean+/-sem, P< 0.05) but recovered to control rates within 48 h. In villous explants, PGE(2)production was significantly decreased after 48 and 72 h of hypoxia versus the normoxic control, accompanied by increased production of 6-keto-PGF(1alpha)to 173.9+/-26.7 per cent after 48 h. TXB(2)production was increased to 172.3+/-25.9 per cent and 653.2+/-135.7 per cent (P< 0.05) control after 48 and 72 h of hypoxia, respectively. These results were confirmed in villous explants (n=3) cultured in the presence of exogenous 10 microm arachidonic acid. Hypoxia had no significant effect on TXB(2)and 6-keto-PGF(1alpha)in trophoblast cells. In summary, our findings suggest that hypoxia could be responsible for abnormal profiles of prostanoid production commonly observed in women with pre-eclampsia. These results indicate a putative link between hypoxia and compromised placental perfusion.

In vitro human decidual endothelial cell thromboxane secretion in preeclampsia is not abnormal

OBJECTIVES

The aims of this study were to describe levels of thromboxane secretion by decidual endothelial cells from normal pregnancies and to determine whether decidual endothelial cell secretion of thromboxane, implicated in the causation of the hypertension and vasoconstriction of preeclampsia, is increased in this disorder.

METHODS

We measured thromboxane generation by cultured decidual endothelial cells from 13 normal pregnancies (NDEC) and 13 pregnancies complicated by preeclampsia (PEDEC), compared with a control population of 6 normal human umbilical vein endothelial cells (HUVEC). Responses to stimulation by bacterial lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF-alpha), and interleukin-1 beta (IL-1 beta) were examined.

MAIN OUTCOME MEASURES

Thromboxane B2 levels in supernatants of cultured endothelial cells.

RESULTS

The level of secretion over 24 h in culture by NDEC [14 (7-26) pg/10(6) cells] was approximately 25% that of HUVEC [63 (49-70) pg/10(6) cells]. Levels achieved in response to all stimuli examined were consistently lower in NDEC than in HUVEC (p < 0.01). Proportional stimulation by LPS and TNF-alpha was comparable in HUVEC and NDEC, whereas NDEC displayed a greater increase (25-fold) than HUVEC (10-fold) in response to IL-1 beta (p < 0.01). There were no significant differences between decidual endothelial cells from normotensive and preeclamptic women in basal secretion of thromboxane or in responses to the stimuli examined.

CONCLUSIONS

In vitro thromboxane secretion by decidual endothelial cells is lower than that of HUVEC, and responsiveness to specific stimuli may be quantitatively different. These findings emphasize the importance of examining endothelial cells from the involved maternal vascular bed if intrauterine vascular pathophysiological events are to be clarified. No significant differences were noted in decidual endothelial cell thromboxane secretion between normal and preeclamptic subjects.

Hemodynamic and renal effects of U-46619, a TXA2/PGH2 analog, in late-pregnant rats

The vasoconstrictor effects of pressor agents are attenuated during pregnancy. Thromboxane A2 (TXA2) is produced in great quantities during hypertension in pregnancy, and therefore it is important to know whether pregnancy modifies the pressor effects of TXA2. The TXA2 analog U-46619 was infused in anesthetized, acutely prepared and conscious, chronically prepared late-pregnant and nonpregnant female rats to examine its systemic hemodynamic and renal effects. Mean arterial pressure (MAP) and total peripheral resistance (TPR) were lower in anesthetized pregnant than nonpregnant rats (P < 0.01). The infusion of U-46619 into the aortic arch resulted in elevation of MAP only in pregnant rats, due to a greater elevation of TPR (60 +/- 17%) compared with nonpregnant rats (36 +/- 6%, P < 0.05). The pressor effect of intravenously infused U-46619 was also enhanced in conscious pregnant versus nonpregnant rats, and the increase in renal vascular resistance was undiminished. U-46619 increased hematocrit and plasma protein concentration more during pregnancy, which suggested greater reduction of plasma volume. The urinary excretion of sodium (-1.49 +/- 0.25 vs. -0.54 +/- 0.24 micromol/min) and water was reduced more in pregnant than nonpregnant rats during U-46619 (P < 0.01). Thus the MAP and renal effects of the TXA2 analog are exaggerated during pregnancy in the rat.

Expression of endothelial (type III) nitric oxide synthase in cytotrophoblastic cell lines: regulation by hypoxia and inflammatory cytokines

Expression of endothelial nitric oxide synthase (eNOS) has been localized to the villous syncytiotrophoblasts suggesting that NO release from these cells could prevent platelet adhesion and aggregation in the intervillous space. Hypoxia- or inflammation-dependent changes in the release of this vasoactive substance may result in thrombus formation and altered vascular resistance which occur in the placental bed of pre-eclamptic patients. To evaluate the influence of low-oxygen tension and inflammation on eNOS production in the trophoblast steady-state eNOS mRNA and protein levels were investigated in cytotrophoblastic BeWo and Jeg-3 cells cultured at 3.5 per cent oxygen and/or in the presence of the pro-inflammatory cytokines IL-1 and TNF-alpha. By RT-PCR and immunocytochemistry we demonstrate that BeWo cells produce eNOS mRNA and protein while eNOS polypeptide was undetectable in JEG-3 cells. In BeWo cells addition of both cytokines decreases eNOS mRNA and protein abundancies within 24 h of incubation while each substance alone had no effect. Compared to controls, the amount of eNOS transcripts was found to be elevated at low-oxygen tension, however, cNOS protein was downregulated after 24 h in the hypoxic environment, as shown by immunocytochemistry and Western blot analysis. Forskolin and methotrexate, which induce biochemical differentiation/ growth arrest in choriocarcinoma cells, stimulate eNOS mRNA and protein synthesis, but cannot overcome the decline of eNOS polypeptide levels during hypoxic incubation. It is speculated that acute hypoxia and inflammation impair eNOS/NO production of the trophoblast in vivo, which might contribute to pathological conditions of gestational diseases.

Serum from women with preeclampsia partially corrects the abnormal in vitro prostacyclin secretion of preeclamptic villous cytotrophoblasts but not that of prostaglandin E2 or endothelin-1

OBJECTIVE

This study was conducted (1) to determine in vitro placental villous cytotrophoblast secretion of prostacyclin, prostaglandin E2, and endothelin-1, (2) to examine the effect of serum from normal and preeclamptic women on secretion of these vasoactive substances, and (3) to determine whether responses to these sera by cytotrophoblasts from preeclamptic pregnancies are different from those of normal pregnancies.

STUDY DESIGN

Cytotrophoblasts isolated from human placentas collected at cesarean section from normal and preeclamptic women were incubated for 20 hours in 20% (vol/vol) sera from preeclamptic or gestational age-matched normal pregnant women. Levels of prostacyclin (measured as 6-keto-prostaglandin F1alpha), prostaglandin E2, and endothelin-1 were measured in cytotrophoblast supernatants.

RESULTS

In normal pregnancy sera preeclamptic cytotrophoblasts secreted significantly lower amounts of prostacyclin and prostaglandin E2 but higher amounts of endothelin-1 than did normal cytotrophoblasts. In preeclamptic sera the abnormality of prostacyclin secretion by preeclamptic cytotrophoblasts was partially corrected, but there was no effect on prostaglandin E2 or endothelin-1 secretion. Preeclamptic sera had no effect on secretion by normal cytotrophoblasts.

CONCLUSIONS

The differences between normal and preeclamptic cytotrophoblasts in prostacyclin, PGE2, and endothelin-1 secretion and in response to preeclamptic serum suggest altered arachidonic acid metabolism in preeclampsia.

Ischaemic cerebral injury, intrauterine growth retardation, and placental infarction

Two hundred and twenty-five consecutive autopsies performed on fetuses >20 weeks' gestation were reviewed, and 37 growth-retarded stillborn fetuses without multiple congenital abnormalities or evidence of intrauterine infection were identified. Histological evidence of ischaemic cerebral injury was found in 31 of the 37 cases and placental infarction was seen in 26 of 36 placentas. Of the 31 cases with cerebral ischaemia, 24 had placental infarcts. Twenty-six of 27 stillborn fetuses >26 weeks' gestation showed histological evidence of cerebral ischaemia. It was concluded that in the group of growth-retarded fetuses studied, there was a high incidence of both cerebral and placental ischaemic abnormality.

The expression and activity of prostaglandin H synthase-2 is enhanced in trophoblast from women with preeclampsia

Preeclampsia is associated with altered biosynthesis of vasoactive prostanoids in placental villi. The two isozymes of prostaglandin H synthase (PGHS) are essential for prostanoid synthesis. We tested the hypothesis that PGHS-2 expression is elevated in trophoblast from preeclamptic women, compared with trophoblast from healthy women. Using immunofluorescent staining, we demonstrated a higher PGHS-2 expression in villi from preeclampsia, compared with normal pregnancy. Cytotrophoblasts cultured from placentas of preeclamptic women expressed higher levels of PGHS-2 compared with cytotrophoblasts from normal placentas. This enhanced expression of PGHS-2 correlated with increased media levels of both thromboxane and prostaglandin E2, two products of PGHS activity. The increased prostanoid production by trophoblast from preeclamptic women was markedly reduced by NS-398, a specific inhibitor of PGHS-2. We conclude that both expression and activity of PGHS-2 are enhanced in trophoblasts from preeclamptic women compared with trophoblast from normal pregnancies. The increased production of prostanoids may contribute to the clinical syndrome of preeclampsia. Our data suggest that a selective inhibitor of PGHS-2 might provide a therapeutic alternative to prophylactic low-dose aspirin in modifying the prostanoid profile in preeclampsia.