Thromboxane and prostacyclin production by different compartments of the human placental villus

Pregnancy-specific expression of protease-activated receptor 1: a therapeutic target for prevention and treatment of preeclampsia?

Neutrophils extensively infiltrate maternal blood vessels in preeclampsia. This could explain why multiple organs are affected in this enigmatic disorder. Lipid peroxides produced by the placenta are probably the first factors that activate neutrophils as they circulate through the intervillous space, but then a second factor specific to pregnancy comes into play, protease-activated receptor 1. The only time neutrophils express protease-activated receptor 1 is during pregnancy. This means that neutrophils can be activated by a mechanism specific to pregnancy, that is, by proteases. Two proteases that are elevated in preeclampsia and activate protease-activated receptor 1 are matrix metalloproteinase-1 and neutrophil elastase. There is an 8-fold increase in vascular protease-activated receptor 1 expression in women with preeclampsia, and protease-activated receptor 1 is also expressed on the placenta, a pregnancy-specific tissue. The question arises if the pregnancy-specific expression of protease-activated receptor 1 is essential to the pathophysiology of preeclampsia. Protease activation of protease-activated receptor 1 in neutrophils of women with normal pregnancies causes activation of RhoA kinase. RhoA kinase phosphorylates nuclear factor-kappa B causing its translocation from the cytosol into the nucleus, increasing the expression of inflammatory genes. This signaling pathway is blocked by inhibition of either protease-activated receptor 1 or RhoA kinase activity. In contrast, neutrophils obtained from preeclamptic women are already activated, with nuclear factor-kappa B localized in the nucleus. Surprisingly, inhibition of either protease-activated receptor 1 or RhoA kinase results in an efflux of nuclear factor-kappa B from the nucleus back into the cytoplasm. Cyclooxygenase-2 seems to be a downstream mediator between protease-activated receptor 1 and RhoA kinase because aspirin inhibits the nuclear translocation of nuclear factor-kappa B and inhibits neutrophil production of superoxide, thromboxane, and tumor necrosis factor alpha. Currently, low-dose aspirin is the standard of care to prevent preeclampsia in high-risk women. Generally, the actions of low-dose aspirin are attributed to selective inhibition of maternal platelet thromboxane production. However, a recent study showed that beneficial effects extend to the placenta, where aspirin corrected the imbalance of increased thromboxane and reduced prostacyclin and oxidative stress. Selective inhibition of placental thromboxane is possible because thromboxane and prostacyclin are compartmentalized. Thromboxane is produced by trophoblast cells and prostacyclin by endothelial cells, so as aspirin crosses the placenta, its levels decline, sparing prostacyclin. Placental oxidative stress is attenuated because cyclooxygenase-2 inhibition decreases the generation of reactive oxygen species to decrease the formation of isoprostanes. The clinical manifestations of preeclampsia can be explained by protease activation of protease-activated receptor 1 in different tissues. In neutrophils, it can account for their activation and inflammatory response. In vascular tissue, protease-activated receptor 1 activation leads to enhanced vascular reactivity to angiotensin II to cause hypertension. In the placenta, it leads to oxidative stress, increased soluble fms-like tyrosine kinase, and thromboxane production. Activation of protease-activated receptor 1 on endothelial cells causes contraction, leading to edema and proteinuria, and activation on platelets leads to coagulation abnormalities. As proteases that activate protease-activated receptor 1 are elevated in the circulation of women with preeclampsia, consideration should be given to the inhibition of protease-activated receptor 1 as a treatment. Recently, The Food and Drug Administration (FDA) approved a protease-activated receptor 1 inhibitor, creating an opportunity to test whether protease-activated receptor 1 inhibition can prevent and/or treat preeclampsia, but a standard dose of aspirin might be just as effective by blocking its downstream actions.

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.

Human Placental Vascular Reactivity in Health and Disease: Implications for the Treatment of Pre-eclampsia

Adequate development of the placenta is essential for optimal pregnancy outcome. Pre-eclampsia (PE) is increasingly recognized to be a consequence of placental dysfunction and can cause serious maternal and fetal complications during pregnancy. Furthermore, PE increases the risk of neonatal problems and has been shown to be a risk factor for cardiovascular disease of the mother later in life. Currently, there is no adequate treatment for PE, mainly because its multifactorial pathophysiology remains incompletely understood. It originates in early pregnancy with abnormal placentation and involves a cascade of dysregulated systems in the placental vasculature. To investigate therapeutic strategies it is essential to understand the regulation of vascular reactivity and remodeling of blood vessels in the placenta. Techniques using human tissue such as the ex vivo placental perfusion model provide insight in the vasoactive profile of the placenta, and are essential to study the effects of drugs on the fetal vasculature. This approach highlights the different pathways that are involved in the vascular regulation of the human placenta, changes that occur during PE and the importance of focusing on restoring these dysfunctional systems when studying treatment strategies for PE.

Peroxisome proliferator-activated receptor gamma blunts endothelin-1-mediated contraction of the uterine artery in a murine model of high-altitude pregnancy

The environmental hypoxia of high altitude (HA) increases the incidence of intrauterine growth restriction (IUGR) approximately threefold. The peroxisome proliferator-activated receptor γ (PPAR-γ), a ligand-activated nuclear receptor that promotes vasorelaxation by increasing nitric oxide and downregulating endothelin-1 (ET-1) production, has been implicated in IUGR. Based on our prior work indicating that pharmacologic activation of the PPARγ pathway protects against hypoxia-associated IUGR, we used an experimental murine model to determine whether such effects may be attributed to vasodilatory effects in the uteroplacental circulation. Using wire myography, ex vivo vasoreactivity studies were conducted in uterine arteries (UtA) isolated from pregnant mice exposed to hypoxia or normoxia from gestational day 14.5 to 18.5. Exposure to troglitazone, a high-affinity PPARγ agonist-induced vasorelaxation in UtA preconstricted with phenylephrine, with HA-UtA showing increased sensitivity. Troglitazone blunted ET-1-induced contraction of UtA in hypoxic and normoxic dams equivalently. Immunohistological analysis revealed enhanced staining for ET-1 receptors in the placental labyrinthine zone in hypoxic compared to normoxic dams. Our results suggest that pharmacologic PPAR-γ activation, via its vasoactive properties, may protect the fetal growth under hypoxic conditions by improving uteroplacental perfusion and thereby justify further investigation into PPARγ as a therapeutic target for IUGR in pregnancies complicated by hypoxia.

Chronic Methylmercury Exposure Induces Production of Prostaglandins: Evidence From A Population Study and A Rat Dosing Experiment

Methylmercury (MeHg) is a well-known environmental neurotoxicant affecting millions worldwide who consume contaminated fishes and other food commodities. Exposure to MeHg has been shown to associate positively with some chronic diseases including cardiovascular diseases, but the mechanism is poorly characterized. MeHg had been shown to affect prostaglandin (PG) regulations in in vitro studies, but neither in vivo nor human studies investigating the effects of MeHg on PG regulations has been reported. Thus, the current study aimed to investigate the association between MeHg exposure and serum PG concentrations in a cross-sectional study among human adults followed by a validation investigation on the cause-effect relationship using a rat model. First, a total of 121 women were recruited from two cities: Wanshan and Leishan in Guizhou, China. Statistical analysis of the human data showed a positive association between blood total mercury (THg) levels and serum concentrations of PGF2α, 15-deoxy-PGJ2, and PGE2 after adjusting for site effects. In the animal study, adult female Sprague-Dawley rats were dosed with 40 μg MeHg/kg body weight/day for 12 weeks. Serum 15-deoxy-PGJ2 and 2,3 d-6-keto-PGF1α concentrations were found to increase significantly after 6 and 10 weeks of MeHg dosing, respectively, while serum PGF2α concentration increased significantly after 12 weeks of MeHg dosing. Combined results of our human and rat studies have shown that chronic MeHg exposure induced dysregulation of PG metabolism. As PGs are a set of mediators with very diverse functions, its abnormal production may serve as the missing mechanistic link between chronic MeHg exposure and various kinds of associated clinical conditions including neurodegeneration and cardiovascular diseases.

Chronic glucocorticoid exposure potentiates placental chorionic plate artery constriction: implications for aberrant fetoplacental vascular resistance in fetal growth restriction

Fetal growth restriction (FGR) is a serious pregnancy complication, resulting in significant perinatal morbidity and mortality. Increased vascular resistance in the fetoplacental circulation is a hallmark of FGR and is associated with enhanced vasoconstriction of the resistance arteries in the placenta, the chorionic plate arteries (CPAs). Although the cause is unknown, FGR is associated with excess exposure to glucocorticoids (GCs), key mediators of vascular resistance in the systemic circulation. We hypothesized that GCs alter CPA reactivity, thereby contributing to the altered blood flow dynamics seen in FGR. We aimed to examine the acute and chronic effects of GCs on CPA reactivity and the operational mechanisms. Glucocorticoid receptors were highly expressed by CPA. 11β-Hydroxysteroid isoenzyme type 2 was detected within the endothelium, whereas 11β-hydroxysteroid isoenzyme type 1 was absent. Acute GC treatment significantly attenuated U46619-induced constriction. This effect was reversed by cotreatment with mifepristone or an endothelial NOS inhibitor. In contrast, chronic GC treatment potentiated U46619 constriction in a dose-dependent manner, which was partially abolished by mifepristone cotreatment. Similar effects were observed using a novel nonsteroidal glucocorticoid receptor-specific agonist. Chronic treatment with GCs altered the expression of several vasoactive factors, including thromboxane and bradykinin receptors, prokineticin-1, cyclooxygenase-2, and endothelial NOS. In summary, acute and chronic GC treatment exerts contrasting effects on CPA vasoreactivity. These opposing effects are consistent with temporal actions in other vascular beds and reflect activation of distinct nongenomic and genomic pathways. Chronic exposure to elevated GCs may contribute to the raised vascular resistance observed in the fetoplacental circulation in FGR.

Contractility of placental vascular smooth muscle cells in response to stimuli produced by the placenta: roles of ACE vs. non-ACE and AT1 vs. AT2 in placental vessel cells

Our previously published work has shown that non-ACE angiotensin II (Ang II) generating system is dominate in the placenta and may play a critical role in regulation of placental vascular contractile function. In the present study, using a collagen gel contraction assay we further studied contractility of placental vascular smooth muscle cells (VSMCs) in response to factors produced by preeclamptic (PE) placentas. Placental VSMCs/type-1 collagen gels were incubated with PE placental conditioned medium in the presence or absence of inhibitors or receptor blockers. Captopril (an ACE inhibitor), chymostatin (a non-ACE chymase inhibitor), losartan (an AT1 receptor blocker) and PD123,319 (an AT2 receptor blocker) were used to study the specific ACE vs. non-ACE and AT1 vs. AT2 effects on placental VSMC contractility, respectively. Our results showed that chymostatin, but not captopril, and PD123,319, but not losartan, significantly attenuated placental VSMC/collagen gel contraction, p<0.01, respectively. The inhibitory effects of chymostatin and PD123,319 were dose-dependent. Our results suggest that chymase, a non-ACE Ang II generating enzyme, may contribute significantly to Ang II generated in the placenta vascular tissue and that the AT2 receptor may play an important role in the regulation of Ang II induced contractility of placental VSMCs. These results provide new insights into Ang II generation and Ang II receptor regulation of vessel contractile function in the placental vasculature. These results also suggest the potential role of increased chymase activity and altered AT2 receptor function in placental related pregnancy disorders such as preeclampsia and IUGR.

Predominant basal directional release of thromboxane, but not prostacyclin, by placental trophoblasts from normal and preeclamptic pregnancies

OBJECTIVE

To investigate apical and basal releases of thromboxane (TX) and prostacyclin (PGI2) by trophoblasts (TCs) from normal and preeclamptic (PE) placentas.

METHODS

TCs isolated from normal and PE placentas were incubated in cell culture inserts for 48h. Medium from the upper (apical) and the lower (basal) chambers were then collected separately and measured for TX and PGI2 by their stable metabolites of TXB2 and 6-keto PGF1alpha by ELISA. Apical and basal releases of TX and PGI were also examined with apical exposure of TCs to arachidonic acid (AA)+/-aspirin at different concentrations. Villous tissue expressions for PGI synthase, TX synthase and TX (TP) receptor were examined by immunohistochemistry.

RESULTS

(1) TXB2, but not 6-keto PGF1alpha, concentrations were significantly higher in the lower than in the upper chambers with both normal and PE TCs (p<0.01); (2) apical exposure of TCs to AA resulted in a significant increase in TX release towards both the upper and the lower chambers in normal TCs (p<0.01), but only a significant increase in the upper chamber in PE TCs (p<0.01); (3) aspirin could attenuate AA-induced TX release both in the upper and the lower chambers in normal, but not in PE, TCs (p<0.01), respectively; (4) there were no differences in 6-keto PGF1alpha productions both in normal and PE TCs treated with AA+/-aspirin; (5) intense staining of TX synthase and TP receptor was seen in syncytiotrophoblast layer, villous core vessels and stromal cells in preeclamptic placental tissue sections.

CONCLUSION

Predominant basal release of TX together with intense staining of TX synthase and TP receptor in trophoblasts, stromal cells and villous core vessels are found in placentas from PE. We speculate if predominant basal release of TX by TCs occurs in vivo as we found in our in vitro culture condition, basal released TX may play a significant role in increased placental vasoconstriction such as in PE.

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.

Heterogeneity of microvascular endothelial cells isolated from human term placenta and macrovascular umbilical vein endothelial cells

The present study compares some phenotypic and physiologic characteristics of microvascular and macrovascular endothelial cells from within one human organ. To this end microvascular endothelial cells from human full-term placenta (PLEC) were isolated using a new method and compared with macrovascular human umbilical vein endothelial cells (HUVEC) and an SV40-transformed placental venous endothelial cell line (HPEC-A2). PLEC were isolated by enzymatic perfusion of small placental vessels, purified on a density gradient and cultured subsequently. Histological sections of the enzyme-treated vessels showed a selective removal of the endothelial lining in the perfused placental cotyledons. The endothelial identity of the cells was confirmed by staining with the endothelial markers anti-von Willebrand factor, Ulex europaeus lectin and anti-QBEND10. The cells internalized acetylated low-density lipoprotein and did not show immunoreactivity with markers for macrophages, smooth muscle cells and fibroblasts. The spindle-shaped PLEC grew in swirling patterns similar to that described for venous placental endothelial cells. However, scanning electron microscopic examination clearly showed that PLEC remained elongated at the confluent state, in contrast to the more polygonal phenotype of HPEC-A2 and HUVEC that were studied in parallel. The amount of vasoactive substances (endothelin-1,2, thromboxane, angiotensin II, prostacyclin) released into the culture medium and the proliferative response to cytokines was more similar to human dermal microvessels (MIEC) derived from non-fetal tissue than to HUVEC. Potent mitogens such as vascular endothelial growth factors (VEGF121, VEGF165) and basic fibroblast growth factor (FGF-2) induced proliferation of all endothelial cell types. Placental growth factors PIGF-1 and PIGF-2 effectively stimulated cell proliferation on PLEC (142 +/- 7% and 173 +/- 10%) and MIEC (160 +/- 20% and 143 +/- 28%) in contrast to HUVEC (9 +/- 8% and 15 +/- 20%) and HPEC-A2 (15 +/- 7% and 24 +/- 6%) after 48 h incubation time under serum-free conditions. These data support evidence for (1) the microvascular identity of the isolated PLEC described in this study, and (2) the phenotypic and physiologic heterogeneity of micro- and macrovascular endothelial cells within one human organ.

Oxidative stress reproduces placental abnormalities of preeclampsia

OBJECTIVE

The activities of placental superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), but not catalase, are lower than normal in preeclampsia, which could contribute to the uncontrolled placental production of lipid peroxides and thromboxane (TX). Oxidative stress, hyperlipidemia and increased iron levels in the maternal compartment in preeclampsia could be responsible for these placental changes by causing oxidative stress in the placenta.

METHODS

We tested this possibility in vitro by exposing a trophoblast-like cell line, ED27, to a combination of linoleic acid (LA, 90 microM) and an oxidizing solution composed of hypoxanthine, xanthine oxidase and ferrous sulfate (OxLA) for 6 days. For these studies, the cells were treated with dexamethasone (10-8 M) for the first 72 hr. This was done to differentiate the cells into a phenotype more like syncytiotrophoblast cells as evidenced by production of beta-human chorionic gonadotropin (beta-hCG).

RESULTS

After 6 days of exposure to OxLA, the activities of SOD and GSH-Px were significantly decreased as compared to exposure to LA alone. In contrast, catalase activity was increased by OxLA. The OxLA-induced decreases in SOD and GSH-Px activities were attenuated by deferoxamine, an iron chelator, suggesting a role for Fe2+ in the decreased activities. Compared to LA, OxLA significantly increased TX secretion and lipid peroxidation in cells and media at 2, 4 and 6 days. Deferoxamine inhibited the OxLA-induced increase in lipid peroxidation, but not the increase in TX. Isolation of trophoblast cells and villous core tissue from term placentas verified that antioxidant enzyme activity was localized primarily to the trophoblast cell compartment lending validity to the in vitro findings.

CONCLUSIONS

These data mimic the changes in placental SOD, GSH-Px, catalase, TX and lipid peroxidation that occur in preeclampsia suggesting that maternal hyperlipidemia and increased iron levels may be responsible for placental oxidative stress and abnormalities in antioxidants and thromboxane.

Effect of ethanol on thromboxane and prostacyclin production in the human placenta

Fetal alcohol syndrome (FAS) is frequently associated with intrauterine growth retardation (IUGR). One cause of ethanol-induced IUGR is thought to be related to increased pressor activity in the human placenta, resulting in decreased oxygenation and nutrient transport to the fetus. Thus, we have investigated the effect of ethanol on paracrine substances, such as thromboxane and prostacyclin, that act as vasoregulators within the intrauterine tissues. In these studies we have utilized the perfused single human cotyledon system to study the effect of ethanol on placental prostanoid production. We assessed the effect of longer (240 min) and more acute (60 min) exposure to ethanol on release of thromboxane B(2) (TxB(2)) and 6-keto-prostaglandin F(1 alpha) (6-keto-PGF(1 alpha)) at the maternal and fetal sides of the placenta. Thromboxane was increased by both longer and shorter ethanol exposure, especially on the fetal side of the placenta. Prostacyclin was essentially unchanged with exposure to ethanol. The thromboxane:prostacyclin ratio also tended to increase with both 60- and 240-min ethanol exposure, but a statistically significant increase was seen only at a few time points. In the 60-min ethanol exposure, an increase in thromboxane was observed both during and following exposure to ethanol. The increase in the thromboxane milieu observed with ethanol exposure may lead, at least in part, to the IUGR which is frequently associated with FAS. Prevention of this effect of ethanol on thromboxane production might be a beneficial intervention for FAS.

U46619-mediated vasoconstriction of the fetal placental vasculature in vitro in normal and hypertensive pregnancies

OBJECTIVES

To measure in-vitro responses to the thromboxane A2 (TxA2) mimetic U46619 in the fetal placental vasculature of human placentae from normotensive women and those with pre-eclampsia. Furthermore, to compare fetal vascular responses to endothelin-1,5-hydroxytryptamine, potassium chloride (KCl) and prostacyclin (PGI2) in placentae from normal or pre-eclamptic pregnancies.

METHODS

Single placental lobules of intact placentae were bilaterally perfused in situ (fetal and maternal) with constant flows of Krebs' solution. Changes in fetal arterial perfusion pressure during intra-arterial infusion of vasoactive agents were recorded. Fetal placental vasoconstrictor concentration response curves were obtained to U46619 (0.01-300 nmol/l), endothelin-1 (0.4-160 nmol/l), KCl (3-300 mmol/l) and 5-hydroxytryptamine (0.03-30 mumol/l). In addition, vasodilator concentration response curves were obtained for PGI2 (1.2-350 nmol/l) in the fetal placental circulation during submaximal increases in perfusion pressure with prostaglandin F2 alpha (PGF2 alpha; 0.7-2.0 mumol/l).

RESULTS

The maximum increase in perfusion pressure caused by U46619 in placentae from normotensive women was 194 +/- 25 mmHg. The maximum response to U46619 was significantly reduced in the placentae from women with pre-eclampsia (104 +/- 21 mmHg). In contrast, there were no differences in constrictor responses to endothelin-1,5-hydroxytryptamine and KCl, or in dilator responses to PGI2 in placentae obtained from either normotensive women or those with pre-eclampsia.

CONCLUSION

TxA2 receptor-mediated vasoconstriction is reduced in the fetal vasculature of placentae from women with pre-eclampsia, possibly to compensate for the increased levels of TxA2 seen in these conditions.

Impaired antioxidant activity in women with pre-eclampsia

OBJECTIVE

To investigate antioxidant activity of sera and the plasma blood levels of two potent antioxidant in women with pre-eclampsia and normotensive pregnancies.

STUDY DESIGN

The antioxidant activity of sera and the blood levels of ascorbic acid and alpha-tocopherol were assayed in women with normal pregnancies (n = 33), mild pre-eclampsia (n = 8), and severe pre-eclampsia (n = 16) between 20 and 40 weeks' gestation. Ascorbic acid and alpha-tocopherol concentrations were analyzed by high-performance liquid chromatography. Antioxidant activity of sera was measured as the percent inhibition of spontaneous autoxidation of a standard brain homogenate.

RESULTS

Plasma levels of ascorbic acid in women with mild and severe pre-eclampsia were significantly lower than normal pregnancies (P < 0.05). Sera alpha-tocopherol levels were significantly decreased only in severe pre-eclampsia (P < 0.05). Sera antioxidant activity were significantly decreased in mild (73%) and severe (51%) pre-eclampsia compared with normal (86%) pregnancies (P = 0.02, P = 0.000, respectively).

CONCLUSIONS

In women with pre-eclampsia, sera antioxidant activity and antioxidant level of plasma are decreased when compared with normotensive pregnancies. Impaired antioxidant activity and the reduction of antioxidant levels which increase the level of lipid peroxidation products may cause peroxidative damage of vascular endothelium and result in clinical symptoms of pre-eclampsia.

Antiphospholipid antibodies and reproduction: the antiphospholipid antibody syndrome

In women who have a diagnosis of APS (both clinical and laboratory criteria) the chance for successful pregnancy is reduced. In these cases, treatment appears to be a clear option, particularly in the case of prior thromboembolic events. The current preference of treatment for women with RPL and aPL antibodies is subcutaneous heparin and aspirin. This treatment should begin with a positive pregnancy test and continue postpartum. It is unclear, at this time, what treatment, if any, is required for women who do not meet all the criteria for diagnosis of APS, but who are known to have aPL antibodies. In some cases, these women were tested because of a prior false-positive test for syphilis, with subsequent identification of aPL antibodies. More recently, women undergoing IVF were tested and found to have an increased incidence of aPL antibodies. It was suggested that aPL antibodies are associated with infertility and failure to implant. However, a summary of published reports indicate that positive aPL antibodies in patients undergoing IVF do not influence ongoing pregnancy rates. This subject, however, remains an area of active investigation because aPL antibodies were shown to interact with the syncytiotrophoblast and cytotrophoblast layers and could, theoretically, after implantation.

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.

Aspirin induces increased expression of both prostaglandin H synthase-1 and prostaglandin H synthase-2 in cultured human placental trophoblast

OBJECTIVE

We tested the hypothesis that aspirin affects trophoblast like other epithelial cells do, by inhibiting prostanoid production, inducing prostaglandin H synthase-2 expression, and enhancing secretion of 15-hydroxyeicosatetraenoic acid.

STUDY DESIGN

Cytotrophoblast from placentas (n = 15) of uncomplicated singleton pregnancies were cultured in medium 199 for 4 to 72 hours in the presence or absence of aspirin.

RESULTS

Aspirin (10(-4) M) inhibited (p < 0.01) average trophoblast prostaglandin E2 release by 60% and thromboxane B2 by 86%. Western immunoblotting showed the prostaglandin H synthase-1 was constitutively expressed in cytotrophoblast, and aspirin treatment caused a twofold increase in prostaglandin H synthase-1 expression. Prostaglandin H synthase-2 was also constitutively expressed in untreated cytotrophoblast but at lower levels than prostaglandin H synthase-1. Aspirin enhanced prostaglandin H synthase-2 expression in trophoblast cultures, but prostaglandin H synthase-2 contributed a range of only 10% to 33% (n = 4) of the total cellular prostaglandin H synthase protein pool even after aspirin induction. The increased prostaglandin H synthase expression depended on both transcription and translation because actinomycin D and cycloheximide each inhibited the increased prostaglandin H synthase protein expression after aspirin treatment. The aspirin induction of prostaglandin H synthase was accompanied by decreased release of 15-hydroxyeicosatetraenoic acid.

CONCLUSIONS

Trophoblast differs from other cells studied because aspirin enhances expression of both prostaglandin H synthase-1 and prostaglandin H synthase-2 isozymes while decreasing, instead of increasing, the secretion of 15-hydroxyeicosatetraenoic acid. The aspirin effects on prostaglandin H synthase synthesis and 15-hydroxyeicosatetraenoic acid release in trophoblast suggest that the mechanisms of action for aspirin in the prophylaxis of preeclampsia may be more diverse than simply altering platelet thromboxane production.

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

Villous trophoblasts isolated from term placentae of normal pregnancies, and pregnancies complicated by chronic hypertension or pre-eclampsia, were examined over 7 days in primary culture. Low levels of prostaglandin E2 and prostacyclin (measured as 6-keto prostaglandin Fl alpha) were secreted by trophoblast cells from all three clinical groups. Secretion was maximal at day 1 and decreased exponentially thereafter. Thromboxane secretion also fell sequentially from day 1. Thromboxane secretion by pre-eclamptic trophoblasts was three to four times that of cells from normal or chronically hypertensive subjects. Prostanoid secretion by isolated cultured cytotrophoblasts was not dependent on aggregation or morphological alteration, nor related to changes in progesterone or human chorionic gonadotrophin production. Because the local maternal circulation is exposed to substances secreted by this cell population, thromboxane could be the trigger for vasoconstriction and coagulation found within the maternal uteroplacental circulation in pre-eclampsia.

Pre-eclampsia and gestational age differently alter binding of endothelin-1 to placental and trophoblast membrane preparations

The aim of the study was to compare the binding of endothelin-1 (ET-1) to membranes from placental tissue and trophoblast cells in normal and pre-eclamptic pregnancies. Plasma membranes from placental tissue and trophoblastic cells were prepared from 15 control and 18 pre-eclamptic pregnancies at either preterm (weeks 31-36) or term (weeks 37-40). ET-1 binding to tissue membranes was measured by a radioreceptor assay. In addition, binding of 56 nmol/l [125I]ET-1 to plasma membranes of trophoblastic cells was determined. In pre-eclampsia, placental membranes bound less (P < 0.01) ET-1 owing to fewer (P < 0.01) receptors at preterm than in the corresponding preterm controls. In contrast, binding of [125I]ET-1 to plasma membranes of trophoblast cells was higher (P < 0.01) in pre-eclampsia at both gestational stages than in the controls. Incubation of trophoblast cells with hydralazine reduced binding by 70%. We conclude that pre-eclampsia is associated with changes in the binding of ET-1 to its placental receptors. Moreover, the data suggest that pre-eclampsia affects non-trophoblast cells in the opposite manner to the trophoblast.

Reductions in platelet force development by cardiopulmonary bypass are associated with hemorrhage

Quantitative assessment of platelet dysfunction after cardiopulmonary bypass (CPB) and prediction of excessive microvascular bleeding remain elusive goals. We used a sensitive instrument capable of simultaneously measuring the force generated by platelets during plasma clot retraction and global clot strength. We hypothesized that CPB would significantly reduce these two variables. Platelet-rich plasma was obtained from eight patients undergoing aortocoronary revascularization prior to induction, after 90 min of CPB, and after protamine administration. Platelet force development was measured using a standardized technique that controlled for platelet number and permitted clot formation in the presence of heparin. Despite the presence of a measurable elastic modulus, platelet force development during bypass was abolished. Peak platelet force development after CPB was significantly lower than before CPB (5255 +/- 955 dynes vs 11,600 +/- 780 dynes, P = 0.01). The percent recovery (after/before bypass) of peak platelet force development inversely correlated with tube thoracostomy drainage during the first 24 h after placement (rs = -0.71, P = 0.048). This study demonstrates that CPB has dramatic effects on platelet force development. The correlation between the percent recovery of peak platelet force development and blood loss supports the clinical relevance of this measurement.

Aspirin inhibits both lipid peroxides and thromboxane in preeclamptic placentas

Preeclampsia is a hypertensive disorder of human pregnancy that is a leading cause of premature delivery and fetal growth retardation. It is characterized by hypertension, reduced uteroplacental blood flow, proteinuria, and edema. Preeclampsia is associated with an imbalance of increased thromboxane and decreased prostacyclin, as well as with an imbalance of increased lipid peroxides and decreased antioxidants. Low-dose aspirin (ASA) therapy (60-150 mg/day) is being evaluated for the prevention of preeclampsia. The rationale for this is that low-dose ASA selectively inhibits thromboxane synthesis without affecting prostacyclin synthesis. We hypothesized that ASA might also inhibit the synthesis of lipid peroxides. The purpose of this study was to examine the effects of aspirin on lipid peroxide, thromboxane, and prostacyclin production rates in placentas obtained from women with preeclampsia. Placentas were obtained from five preeclamptic women. Placental tissues (350 mg) were incubated in Dulbecco's Modified Eagles Medium (DMEM) for 48 h, alone and with varying concentrations of aspirin: 1 x 10(-6) M, 1 x 10(-5) M, 5 x 10(-5) M, 1 x 10(-4) M, and 5 x 10(-4) M. Samples were collected at 0, 2, 6, 16, 28, and 48 h of incubation, and analyzed for thromboxane and prostacyclin by RIA of their stable metabolites, thromboxane B2 and 6-keto-PGF1 alpha, and for lipid peroxides by peroxide equivalents. As compared to control, an aspirin concentration of 5 x 10(-5) M significantly inhibited (p < 0.05) both lipid peroxides (3.15 +/- 0.49 vs. 1.90 +/- 0.31 pmol/microgram/h) and thromboxane (0.66 +/- 0.11 vs. 0.32 +/- 0.10 pg/microgram/h), but not prostacyclin (0.24 +/- 0.05 vs. 0.17 +/- 0.02 pg/microgram/h, p > 0.05). Lower aspirin doses (1 x 10(-6) M, 1 x 10(-5) M) had no effect, whereas higher doses (1 x 10(-4) M and 5 x 10(-4) M) inhibited all three compounds. We conclude that aspirin inhibits lipid peroxides, as well as thromboxane and prostacyclin, in preeclamptic placentas. The inhibitory effects are dose dependent. Low-dose aspirin (5 x 10(-5) M) selectively inhibits lipid peroxides and thromboxane without affecting prostacyclin. We speculate that the selective inhibitory effect of low-dose aspirin may account for its effectiveness in the prevention of preeclampsia.

Control of vascular resistance in the maternal and feto-placental arterial beds

This review aims to provide a comprehensive summary of the mechanisms involved in the physiological adaptation of the vasculature to pregnancy. Profound changes occur both systemically and in discrete circulations in the mother, but it is debatable which factors are responsible. Similarly, whilst the feto-placental circulation must be substantially controlled by humoral mechanisms, the exact role of each potential contributor is not known. In view of the hitherto unappreciated and very important role of the endothelium-derived vasodilator, nitric oxide, in the control of peripheral vascular resistance, considerable emphasis will be placed on the many recent investigations in this area.

Differentiation and growth on a fibrin matrix modulate the cyclooxygenase expression and thromboxane production by cultured human placental trophoblasts

Preeclampsia is associated with altered placental production of several end-products of cyclooxygenase activity. Thromboxane (TX) is one of these end-products, and trophoblast is a source of villous thromboxane. We cultured term trophoblast in the presence or absence of fibrin to study how differentiation and epithelial-matrix interactions regulate cyclooxygenase expression. The cellular trophoblast present during the first 24 h of culture on uncoated plastic produced TXB2, but little or no TX was produced in cultures grown longer than 24 h when differentiation into syncytial trophoblast occurred. Growth of cells on a fibrin matrix enhanced cellular trophoblast TX production five-fold. Medium containing 10 mumol/l arachidonic acid maximized thromboxane production in cells cultured for less than 24 h, regardless of growth surface, but this medium had little or no effect on TX production by cultures grown for more than 24 h. In contrast, exogenous arachidonic acid enhanced prostaglandin E2 (PGE2) production by both cellular and syncytial trophoblast. Cytochemical staining indicated that changes in cyclooxygenase content occurred with trophoblast differentiation. Western immunoblot analysis of cells cultured in the presence or absence of a fibrin matrix showed cyclooxygenase was induced under both growth conditions. Detectable cyclooxygenase protein disappeared beyond 24 h in cells grown on uncoated plastic. In contrast, cells grown beyond 24 h on fibrin showed sustained expression of cyclooxygenase by Western immunoblotting, and this enzyme protein expression correlated with increased PGE2 production by the differentiated trophoblast.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical localization of thromboxane synthase in human intrauterine tissues

Uterine tissues are known to be able to synthesize thromboxane A2 (TXA2), but there is little information about the nature of cells actually responsible for its production. In this study human placenta, fetal membranes, umbilical cord and pregnant myometrium were investigated immunohistochemically. The avidin-biotin method for a monoclonal antibody against human thromboxane synthase (Tü 300) was applied on frozen tissue sections. In placenta, fetal membranes and umbilical cord, staining was positive for Hofbauer cells and fibroblasts. Further, in sections of placenta, capillary endothelium showed antigenicity for TX synthase. Leiomyocytes in the umbilical cord vessels contained the enzyme as well. Preparations of pregnant myometrium were shown to express TX synthase in leiomyocytes, endothelial cells and connective tissue cells. Amnion, trophoblast and decidua did not possess antigenicity for this enzyme. Since TXA2 plays an important role for the regulation of vascular tone and aggregation of platelets and may stimulate myometrial contractions during parturition, the abundance of TX synthase in pregnancy-specific tissues confirms previous in vivo and in vitro observations. Further, TXA2 synthesized by Hofbauer cells may be involved in immunological reactions during pregnancy, and the number and level of activation of Hofbauer cells may be closely related to the initiation of labour. Thromboxane production by the endothelium lining the fetal vessels points to its regulatory role for the blood flow in the fetoplacental unit.

Quantitative assessment of platelet function and clot structure in patients with severe coronary artery disease

The prothrombotic state of patients with coronary artery disease (CAD) can be attributed partially to platelet activity. Management of such patients is hindered by a lack of techniques to assess hemostatic function. This study used a sensitive technique to monitor platelet function by measuring platelet force development during clot retraction. This technique allowed simultaneous measurement of clot elastic modulus on the same sample. Fibrin mass-length ratio (mu), fibrinopeptide A, D-Dimer, von Willebrand's factor, thromboxane A2, platelet aggregation studies, and bleeding times also were performed. Fourteen patients with CAD were compared with 10 healthy volunteers. Despite more than 95% suppression of thromboxane B2 and prolongation bleeding times in patients taking aspirin, force development remained significantly elevated over healthy control patients (8,279 +/- 476 dynes versus 4,857 +/- 380 dynes, p < 0.0006). Patients not taking aspirin had normal bleeding times and force development of 19,110 +/- 3,700 dynes. Clot elastic moduli were enhanced in patients with CAD whether taking or not taking aspirin. Adenosine diphosphate and ristocetin-induced platelet aggregation were insensitive to the effect of aspirin in patients with CAD. Fibrinopeptide A, von Willebrand's factor, and D-Dimer levels were significantly elevated, and fibrin mass-length ratios were significantly larger in patients with CAD. Therefore, despite aspirin therapy, patients with severe CAD have evidence of persistent platelet activation and rigid clot structure. Monitoring of platelet force development may prove useful in delineating enhanced platelet function.

Peroxide induces vasoconstriction in the human placenta by stimulating thromboxane

OBJECTIVE

Placental lipid peroxides and thromboxane are abnormally increased in preeclampsia. Thromboxane is a potent vasoconstrictor of the placental vasculature. Peroxides stimulate cyclooxygenase (prostaglandin H synthase), and thereby could increase thromboxane, to cause vasoconstriction in the placenta. This study was performed to test the hypothesis that peroxides would produce vasoconstriction in the human placenta by stimulating thromboxane production.

STUDY DESIGN

Isolated human placental cotyledons were perfused for 20-minute intervals with 100 mumol/L t-butyl hydroperoxide alone, and during and after perfusion with low-dose aspirin (5 x 10(-5) mol/L) (n = 6) or the thromboxane receptor blocker SQ 29,548 (n = 2). Krebs-Ringer-bicarbonate buffer gassed with 95% oxygen and 5% carbon dioxide was used for the perfusion buffer. Perfusion pressure was monitored continuously, and effluent flow rates were measured during each experimental treatment. Maternal and fetal effluent samples were analyzed for thromboxane B2 and 6-keto-prostaglandin F1 alpha.

RESULTS

Compared with control Krebs-Ringer-bicarbonate buffer perfusion, peroxide perfusion significantly increased (p < 0.05) vascular resistance (14 +/- 2 vs 25 +/- 3 mm Hg.min/ml, mean +/- SE, respectively), thromboxane B2 secretion (fetal 0.20 +/- 0.04 vs 1.65 +/- 0.26 ng/min, maternal 4.8 +/- 1.5 vs 8.1 +/- 2.1 ng/min) and 6-keto-prostaglandin F1 alpha secretion (fetal 21 +/- 5 vs 60 +/- 1.8 pg/min, maternal nondetectable). Peroxide perfusion increased the thromboxane B2/6-keto-prostaglandin F1 alpha ratio threefold on the fetal side. Subsequent perfusion with aspirin significantly blocked the peroxide-induced vasoconstriction (13 +/- 1 mm Hg.min/ml during aspirin + peroxide) and the peroxide-induced increase in the secretion of thromboxane B2 (fetal 0.52 +/- 0.12 ng/min, maternal 2.0 +/- 0.3 ng/min) and 6-keto-prostaglandin F1 alpha (fetal 30 +/- 8 pg/min). After perfusion with aspirin the thromboxane B2/6-keto-prostaglandin F1 alpha ratio declined. When the thromboxane receptor blocker was used instead of aspirin, maternal and fetal secretion rates of thromboxane were still significantly increased by peroxide perfusion, but there was no change in perfusion pressure or vascular resistance.

CONCLUSIONS

(1) Peroxide induces placental vasoconstriction coincident with increased secretion of thromboxane; (2) low-dose aspirin blocks both increased thromboxane secretion and vasoconstriction, whereas a thromboxane receptor antagonist allows increased thromboxane secretion but prevents peroxide induced vasoconstriction; (3) therefore, peroxide induces vasoconstriction by stimulating thromboxane synthesis.

Differential mRNA expression and production of interleukin-6 in placental trophoblast and villous core compartments

PROBLEM

Interleukin-6 (IL-6) is a pleiotropic protein that functions as an immunoregulatory peptide, growth factor, and endocrine hormone. IL-6 has been shown to be produced in whole placental tissue and isolated trophoblast (TC). In addition, the villous core (VC) compartment of the placenta contains cell types (fibroblasts, macrophages) capable of IL-6 production. Consequently, the present study was designed to determine the relative contribution of the TC and VC compartments to placental IL-6 production.

METHOD

The VC and TC compartments from term pregnancies were separated using CR-Dispase digestion and Percoll density gradient centrifugation. The VC, TC, and whole placental tissues were cultured in Dulbecco's modified Eagle's medium over a 28-h period. Relative IL-6 mRNA expression was determined by dot blot analysis and secreted IL-6 protein was determined by enzyme-linked immunosorbent assays.

RESULTS

All three tissues demonstrated linear production of IL-6 protein over the culture period. At 28 h, whole placental tissue produced the most IL-6 (5.1 ng +/- 0.8 ng/microgram/protein) followed by TC (4.0 ng +/- 1.3 ng/micrograms) and VC (0.55 ng +/- 0.24 ng/microgram). Although production rates of IL-6 were 8.4-fold higher in TC compared to VC (P < .05), steady-state IL-6 mRNA expression was 3.5-fold higher in freshly isolated VC compared to TC (P < .0001) and 13-fold higher in VC compared to TC (P < .01) after 24 h in culture.

CONCLUSIONS

These results demonstrate that: (1) the placenta can produce large quantities of immunoreactive IL-6 in vitro, (2) TC produce significantly more IL-6 than VC although both compartments contribute to placental IL-6 production, (3) placental IL-6 production and secretion are probably posttranscriptionally regulated since steady-state IL-6 mRNA expression in VC and TC compartments did not correlate with IL-6 production.

Study of thromboxane and prostacyclin metabolism in an in vitro model of first-trimester human trophoblast

OBJECTIVES

The purpose of our study was to establish an in vitro tissue culture system to study eicosanoid metabolism in first-trimester trophoblastic tissue. Thromboxane A2, a potent vasoconstrictor, and prostacyclin, a potent vasodilator, were analyzed to evaluate their production in early pregnancy.

STUDY DESIGN

Trophoblastic tissue was obtained via transabdominal chorionic villous sampling from 33 pregnancies at 9 to 12 weeks' gestation for cytogenetic diagnosis. Initially, tissue obtained from the cytogenetics lab was morphologically consistent with villous core cells. Through altering cell density and passage, the cells became morphologically consistent with cytotrophoblasts. The cell lines were exposed to arachidonic acid (50 mumol/L) and aspirin (1 to 100 mumol/L) for 24 hours. Thromboxane B2 and 6-keto prostaglandin F2 alpha were measured by radioimmunoassay.

RESULTS

Villous core cells and cytotrophoblasts increased production of thromboxane A2 and prostacyclin in the presence of arachidonic acid (p < 0.002). The villous core cells produced more thromboxane A2 and prostacyclin than cytotrophoblasts (p < 0.02). A significant inhibition of both thromboxane A2 and prostacyclin production was seen in the presence of 100 mumol/L aspirin in both cell types (p < 0.05).

CONCLUSIONS

This model may be useful for studying placental function in the first trimester because individual placental compartments can be evaluated in tissue culture. At the cellular level we were not able to detect a preferential decrease in thromboxane A2 production in the presence of aspirin (1 to 100 mumol/L).

Placental lipid peroxides and thromboxane are increased and prostacyclin is decreased in women with preeclampsia

OBJECTIVE

There is an imbalance of increased thromboxane and decreased prostacyclin in placentas of women with preeclampsia, but this may not be the only imbalance. There is also an abnormal increase in serum lipid peroxides in preeclamptic women. Lipid peroxides are toxic compounds that damage cells and inhibit prostacyclin synthesis. The following study examined lipid peroxides to determine if they were also increased in placentas of preeclamptic women.

STUDY DESIGN

Placental tissue for nine normal and eight preeclamptic women were frozen in liquid nitrogen immediately after delivery. Frozen tissue samples (1 gm) were homogenized and analyzed for lipid peroxides by malondialdehyde and hydrogen peroxide equivalents and for thromboxane and prostacyclin by radioimmunoassay of their stable metabolites, thromboxane B2 and 6-keto prostaglandin F1 alpha.

RESULTS

Lipid peroxides were significantly higher in preeclamptic placentas than in normal placentas by both analytic methods (49 +/- 5 vs 31 +/- 1 nmol/gm for malondialdehyde and 5.3 +/- 0.3 vs. 3.2 +/- 0.3 mumol/gm for hydrogen peroxide equivalent; mean +/- SE; p < 0.01, respectively). Thromboxane was significantly higher and prostacyclin significantly lower in preeclamptic placentas than in normal placentas (213 +/- 23 vs 158 +/- 14 ng/gm for thromboxane and 24 +/- 3 vs 53 +/- 7 ng/gm for prostacyclin, p < 0.05). The thromboxane/prostacyclin and lipid peroxides/prostacyclin ratios were threefold higher in preeclamptic placentas than in normal placentas.

CONCLUSION

Placental levels of both lipid peroxides and thromboxane are increased and prostacyclin decreased in preeclampsia. We speculate that abnormally increased levels of lipid peroxides in preeclamptic placentas may be a cause of decreased prostacyclin.

Eicosanoid production and transfer in the placenta of the diabetic pregnancy

The metabolism of arachidonic acid (AA) and the transfer of its metabolites was determined in in vitro perfused placental tissue from normal pregnancies and those complicated by maternal insulin-dependent diabetes mellitus (IDDM). 14C-labelled AA was recirculated in the fetal circulation for 60 min while 3H-AA was recirculated in the maternal circulation. Placental effluent was subjected to high performance liquid chromatography (HPLC) and analysis of dual-label scintillation counts. Placentae from IDDM pregnancies converted 3-6 times more radiolabelled AA to eicosanoids than did normal placentae. In addition, the transfer of eicosanoids into the opposing circulation was doubled in placentae from IDDM pregnancies compared to normal placentae. The predominant direction of eicosanoid transfer in both groups of placentae was in the fetal-to-maternal direction. The relative amounts of eicosanoids produced was also altered in placentae from IDDM pregnancies. Increased amounts of thromboxane (Tx) B2 and hydroxyeicosatetraenoic acids (HETEs) were present in both circulations of placentae from IDDM pregnancies. Levels of 6-keto prostaglandin F1a (6KPGF1a) were significantly reduced in both circulations in placentae from IDDM pregnancies. Thus, the ratio of TxA2 to PGI2 and the ratio of HETEs to PGI2 were both significantly increased in placentae from IDDM pregnancies. These results suggest an imbalance in eicosanoid production which may be relevant to abnormal placental structure and function in IDDM pregnancies.

Aspirin differentially affects thromboxane and prostacyclin production by trophoblast and villous core compartments of human placental villi

Low-dose aspirin has been used as prophylactic treatment for preeclampsia and fetal growth retardation, but the physiologic mechanisms for the beneficial effect of this therapy are unknown. We studied the effects of aspirin on eicosanoid production by different compartments of normal term human placental villi. Duplicate parallel incubations (n = 7) of whole villi, villous core tissues, and trophoblast were established on Millicell platform dishes in minimum essential medium in the presence or absence of 1 x 10(-4) or 1 x 10(-5) mol/L aspirin. Production rates of thromboxane A2 and prostacyclin were estimated by radioimmunoassay of their stable hydrolysis products, thromboxane B2 and 6-keto-prostaglandin F1 alpha, respectively. Our results indicate that 1 x 10(-4) mol/L aspirin inhibits thromboxane production in whole villi and villous core tissues denuded of their trophoblast layer but not in isolated trophoblast cells. The same concentration of aspirin also inhibits prostacyclin production in the isolated villous core but not in whole villi and not in isolated trophoblast. We conclude that aspirin can selectively inhibit thromboxane production in whole placental villi and differentially affects thromboxane and prostacyclin production by the trophoblast and villous core compartments.

High glucose levels decrease proliferation of cultured human fetal cells from placenta

We used the placenta as a source of undifferentiated cells to study the effect high glucose levels can have on human fetal cell proliferation in vitro. Cells were subcultured in a modified minimum essential medium with 10% fetal bovine serum containing either 5.5 mmol/L (100 mg/dl) D-glucose (control), 11 mmol/L (200 mg/dl) D-glucose, or 22 mmol/L (400 mg/dl) D-glucose. Cells grown in mannitol-containing media were used as controls for osmolality. After 3 and 7 days' growth in different media, the labeling index was determined by autoradiographic analysis, and cell numbers were determined with a Coulter counter. The labeling indices for cells grown 3 days in 11 or 22 mmol/L D-glucose were 89% (p less than 0.002) and 84% (p less than 0.001), respectively, of control cells grown in 5.5 mmol/L D-glucose. After 7 days' growth, the labeling indices of cells grown in 11 or 22 mmol/L D-glucose were 84% (p less than 0.002) and 70% (p less than 0.001), respectively, of cells grown in 5.5 mmol/L D-glucose media. There was a significant decrease in the number of cells present at both 3 and 7 days in cultures grown in 22 mmol/L D-glucose compared with control. We conclude that a few day's exposure to high glucose levels can have an effect on proliferation of human placental cells in vitro. We suggest that a glucose effect on proliferation of other cells derived from the products of conception might be one mechanism contributing to abnormal development in some pregnancies of diabetic women.

Increased placental progesterone may cause decreased placental prostacyclin production in preeclampsia

Placentas obtained from women with preeclampsia produce more thromboxane and less prostacyclin than normal. They also produce more progesterone than normal. This study tested whether a progesterone concentration equivalent to that in the medium after in vitro incubation of placentas from women with preeclampsia (greater than or equal to 1.5 x 10(-5) mol/L) could cause an imbalance of increased thromboxane and decreased prostacyclin production by normal placentas. Fresh term placental tissues were incubated for 48 hours in the absence or presence of various concentrations of progesterone and/or estradiol. Prostacyclin and thromboxane were determined by radioimmunoassay of their stable metabolites, 6-keto-prostaglandin F1 alpha and thromboxane B2. A progesterone concentration of 1.5 x 10(-5) mol/L significantly (p less than 0.001) inhibited prostacyclin production, compared with control, but lower concentrations did not. Estradiol at concentrations present in the medium after incubation of either normal or preeclamptic placental tissue did not significantly affect prostacyclin production, nor did it prevent progesterone at 1.5 x 10(-5) mol/L from inhibiting prostacyclin. Thromboxane production was not affected by either progesterone or estradiol.

CONCLUSION

In vitro addition of progesterone at a concentration equivalent to that in the medium after incubation of preeclamptic placentas inhibited prostacyclin production by normal placentas to a rate characteristic of preeclampsia. However, it did not increase thromboxane.

SPECULATION

Increased trophoblast progesterone in preeclampsia may act by a paracrine mechanism to inhibit prostacyclin synthesis in placental vasculature. Progesterone's selective inhibition of prostacyclin without affecting thromboxane may be due to the compartmentalization of thromboxane production to trophoblast and stroma and prostacyclin production to placental vasculature.