Maternal ingestion of acetylsalicylic acid inhibits fetal and neonatal prostacyclin and thromboxane in humans

Low-dose aspirin reduces hypoxia-induced sFlt1 release via the JNK/AP-1 pathway in human trophoblast and endothelial cells

Pre-eclampsia (PE) is a serious hypertensive disorder of pregnancy that remains a leading cause of perinatal and maternal morbidity and mortality worldwide. Placental ischemia/hypoxia and the secretion of soluble fms-like tyrosine kinase 1 (sFlt1) into maternal circulation are involved in the pathogenesis of PE. Although low-dose aspirin (LDA) has beneficial effects on the prevention of PE, the exact mechanisms of action of LDA, particularly on placental dysfunction, and sFlt1 release, have not been well investigated. This study aimed to determine whether LDA exists the protective effects on placental trophoblast and endothelial functions and prevents PE-associated sFlt1 release. First, we observed that LDA mitigated hypoxia-induced trophoblast apoptosis, showed positive effects on trophoblast cells migration and invasion activity, and increased the tube-forming activity of human umbilical vein endothelial cells (HUVECs). In addition, LDA decreased hypoxia-induced sFlt1 production, and the c-Jun NH₂ -terminal kinase/activator protein-1 (JNK/AP-1) pathway was shown to mediate the induction of sFlt1. Moreover, the transcription factor AP-1 was confirmed to regulate the Flt1 gene expression by directly binding to the Flt1 promoter in luciferase assays. The result of chromatin immunoprecipitation assays further demonstrated that LDA could directly decrease the expression of the transcription factor AP-1, and thus decrease sFlt1 production. Finally, the effects of LDA on sFlt1 production were proved in human placental explants. Taken together, our data show the protective effects of LDA against trophoblast and endothelial cell dysfunction and reveal that the LDA-mediated inhibition of sFlt1 via the JNK/AP-1 pathway may be a potential cellular/molecular mechanism for the prevention of PE.

Hematologic profile of neonates with growth restriction is associated with rate and degree of prenatal Doppler deterioration

OBJECTIVE

To examine the relationship between hematologic parameters at birth and prenatal progression of Doppler abnormalities in fetal growth restriction (FGR).

METHODS

The study was a secondary analysis of FGR patients (abdominal circumference < 5th percentile and umbilical artery pulsatility index (UA-PI) elevation) with at least three examinations prior to delivery. Prenatal progression was classified as rapid, moderate or slow based on the interval between diagnosis and delivery and the extent of UA, middle cerebral artery and ductus venosus Doppler abnormalities. Associations between diagnosis-to-delivery interval, Doppler Z-scores, progression and hematologic parameters at birth were examined.

RESULTS

Of 130 patients, 54 (41.5%) had rapid, 51 (39.2%) moderate and 25 (19.2%) slow deterioration, delivering within 4, 6 and 9 weeks of diagnosis, respectively. The strongest association of moderate and rapid deterioration was with a low platelet count (r2  = 0.37 and 0.70, respectively; P < 0.0001). In patients with moderate deterioration, platelet count correlated inversely with UA-PI (ρ = -0.44, P = 0.001) and was lowest when end-diastolic velocity was absent. With rapid progression, platelet count correlated inversely with nucleated red blood cell count (ρ = -0.51, P < 0.001) but no longer with UA-PI.

CONCLUSION

Our observations suggest a relationship between prenatal clinical progression of FGR and hematologic abnormalities at birth. Accelerating cardiovascular deterioration is associated with decreased platelet count, which can be explained by placental consumption or dysfunctional erythropoiesis and thrombopoiesis.

Aspirin in pregnancy

Aspirin, acetylsalicylic acid, is the most frequently consumed drug in pregnancy, taken mostly without a prescription because of headache or a minor ailment. Numerous preparations containing acetylsalicylic acid are freely available over the counter under a variety of proprietary names, and in many cases pregnant women and their doctors may be unaware that aspirin is being taken.

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.

PGE2/TXB2 imbalance in neonatal hypoxemic respiratory failure

BACKGROUND

An imbalance of vaso-constrictor and -dilator mediators has been implicated in the pathogenesis of the pulmonary hypertension accompanying neonatal hypoxemic respiratory failure (NHRF).

AIM

To characterize plasma PGE2, TXB2 and their ratio in normal newborns and in those with NHRF.

METHODS

Twenty newborns with NHRF received inhaled PGE1 (IPGE1) by jet nebulizer in doses of 25, 50, 150 and 300 ng/kg/min followed by weaning. Blood for PGE2 and TXB2 assay using EIA was available in 8 neonates with NHRF prior to IPGE1. Umbilical cord arterial samples were also obtained at delivery from 10 normal newborns to serve as controls.

RESULTS

Compared to normal newborns, those with NHRF had significantly lower PGE2/TXB2 ratios after controlling for preterm gestation (< 37 weeks) and postnatal age (p < 0.05). Notably, all subjects except one in the NHRF group had a value of < 1.0 (range 0.1-1.2) compared to a value of > 1.0 in all subjects in the Control group (range 1.1-5.2).

CONCLUSIONS

Lower PGE2/TXB2 ratio in subjects with NHRF compared with controls reflects a predominance of vaso-constrictor activity in these patients as the basis of pulmonary hypertension. Plasma PGE2/TXB2 ratio may have important implications for the diagnosis and treatment of NHRF.

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.

Umbilical cord serum levels of thromboxane B2 in term infants of women who participated in a placebo-controlled trial of low-dose aspirin

OBJECTIVE

Our aim was to quantify thromboxane B2 (TXB2) in umbilical cord serum of term infants of nulliparous, low-risk women who were randomly assigned to either placebo or low-dose (60 mg) aspirin (ASA) on a daily basis from 24 weeks' gestation through delivery as part of a randomized clinical trial for prevention of preeclampsia.

METHODS

Umbilical cord sera from 230 singleton, term infants whose mothers were involved in our low-dose ASA trial were assayed for TXB2, the stable metabolite of thromboxane A2, without knowledge of treatment or outcome data. The data were related to assigned treatment group, longitudinal pattern of maternal serum TXB2 levels, and other maternal and newborn characteristics. The data also were analyzed according to whether or not maternal serum levels of TXB2 at 29-31, 34-36, and delivery were reduced > or =50% compared to values prior to initiation of the trial.

RESULTS

Umbilical cord TXB2 levels (ng/ml, mean +/- SE) were significantly lower at term in the ASA group (36.1 +/- 3.3, n = 111) than in the placebo group (56.6 +/- 5.7, n = 119; P = 0.002). Umbilical cord TXB2 levels were correlated to those in maternal serum at delivery in the ASA group (r = 0.3441; P = 0.0005) but not in the placebo group (r = 0.0626; P = 0.53). Regardless of assigned treatment group, infants whose mothers had a > or =50% longitudinal reduction in serum TXB2 had lower umbilical cord TXB2 levels (39.2 +/- 3.6, n = 114) than infants whose mothers had <50% reductions in TXB2 (54.6 +/- 5.9, n = 116; P = 0.027). Birthweights of these infants correlated inversely (r = 0.1678, P = 0.017) with maternal serum TXB2 at delivery but not to umbilical cord TXB2 levels; the best correlation between birthweight and maternal serum TXB2 was noted in pregnancies assigned to receive placebo (r = -0.2558, P = 0.009).

CONCLUSIONS

Umbilical cord serum levels of TXB2 1) are reduced in instances of long-term maternal ingestion of ASA, 2) correlate well with maternal serum levels of TXB2 at delivery when there is evidence for consistent maternal use of ASA, but 3) do not correlate with maternal serum TXB2 levels when there is no evidence for frequent maternal ingestion of cyclooxygenase inhibitors. These data suggest that the capacity for platelet production of TXA2 in fetal and maternal compartments are regulated independently. Finally, there is an inverse relationship between maternal serum TXB2 levels at delivery and birthweight of newborn infants that is most evident among the pregnancies assigned to placebo and also among pregnancies in which there was little evidence to suggest a pattern of cyclooxygenase inhibitor use during pregnancy.

Administration of low-dose aspirin to mothers with small for gestational age fetuses and abnormal umbilical Doppler studies to increase birthweight: a randomised double-blind controlled trial

OBJECTIVE

To determine whether antenatal treatment (for > or = 14 days) with 100 mg aspirin daily, given to mothers with small for gestational age fetuses and abnormal umbilical Doppler, will increase birthweight.

DESIGN

Randomised, double-blind placebo controlled trial.

SETTING

A tertiary referral centre.

PARTICIPANTS

Ninety-nine women, of whom 65 were treated for > or = 14 days (32 with aspirin and 33 with placebo) and comprised the study group. The entry criteria were: singleton pregnancy with ultrasound evidence of a small for gestational age fetus (abdominal circumference < 10%); previous anatomy scan < 20 weeks and no evidence of fetal abnormality; gestation between 24 and 36 weeks; umbilical artery Doppler resistance index > 95% for gestation; no previous aspirin treatment in pregnancy; and no contra-indication to aspirin treatment.

RESULTS

The mean duration of treatment was 30 days for aspirin treated, and 29 for placebo. No difference was found in birthweight or other measures of fetal growth or newborn morbidity between those treated with aspirin or placebo. Compliance, assessed by thromboxane B2 analysis, showed almost complete suppression of thromboxane B2 in aspirin treated women.

CONCLUSION

Low-dose aspirin did not increase birthweight in pregnancies where the fetus has abnormal umbilical Doppler and is thought to be small for gestational age.

Drug actions in preeclampsia: aspirin, but not magnesium chloride or dihydralazine, differentially inhibits cultured human trophoblast release of thromboxane and prostacyclin without affecting angiotensin II, endothelin-1, or leukotriene B4 secretion

OBJECTIVE

We hypothesized that aspirin Mg++, and dihydralazine affect the release of vasoactive agents from cultured human placental trophoblast.

STUDY DESIGN

Cytotrophoblasts isolated from placentas of preterm or term deliveries of 14 healthy control women and 15 preeclamptic women were cultured in Dulbecco's modified Eagle's medium for 5 days in the presence or absence of either 0.1 mmol/L aspirin, 3 mmol/L magnesium chloride, or 136 ng/ ml dihydralazine. Vasoactive substances were quantitated by radioimmunoassay with mean +/- SEM percentage of untreated cells (= 100%) compared by the Mann-Whitney U test and analysis of variance.

RESULTS

Aspirin inhibited (p < 0.01) both thromboxane and prostacyclin on days 1 and 2 in culture but not on days 3 to 5 unless the Dulbecco's modified Eagle's medium was supplemented with arachidonic acid. Aspirin inhibition was greater (p < 0.01) for thromboxane in cells cultured 24 hours after preeclamptic pregnancy (preterm 29.9% +/- 6.8%, term 20.1% +/- 5.9%) compared with normal controls (preterm 66.3% +/- 10.6%, term 68.9% +/- 11.6%). Aspirin reduced (p < 0.01) the ratio of thromboxane to prostacyclin in media of cells from preeclampsia (untreated 27.8 +/- 7.2, aspirin 13.3 +/- 4.4), but aspirin had no effect on this ratio in cultures from control normal pregnancies (untreated 6.8 +/- 2.9, aspirin 4.8 +/- 1.1). Neither magnesium chloride nor dihydralazine affected trophoblast prostanoid production, and no drug altered the media levels of angiotensin II, endothelin-1, or leukotriene B4.

CONCLUSION

Aspirin selectively inhibits trophoblast prostanoid production. This inhibition depends on the availability of arachidonic acid and the presence or absence of preeclampsia. Magnesium and dihydralazine effects in pregnancy are not related to altered release of trophoblast vasoactive compounds.

Maternal serum thromboxane B2 reduction versus pregnancy outcome in a low-dose aspirin trial

OBJECTIVE

Our purpose was to determine whether in a low-dose aspirin trial a longitudinal decrease in maternal serum thromboxane B2 is associated with improvement in pregnancy outcomes.

STUDY DESIGN

A total of 606 healthy nulliparous women with singleton gestations were randomized at 24 weeks to either 60 mg of aspirin or a placebo. Maternal serum thromboxane B2 was measured at randomization, at 29 to 31 weeks, at 34 to 36 weeks, and at delivery. After delivery, and without knowledge of patient outcome or group assignment, patients were categorized as having had either a longitudinal twofold or greater (> or = 50%) or less than twofold reduction (< 50%) in thromboxane B2 from baseline levels at randomization.

RESULTS

Of 606 entrants, 92% had sufficient thromboxane B2 determinations to allow categorization. Whether patients were assigned to aspirin or placebo, birth weight was significantly greater in women who had a twofold or greater reduction in maternal serum thromboxane B2 levels. When the aspirin and placebo groups were combined, women with a twofold or greater reduction in thromboxane B2 levels had less preeclampsia, 1.9% (6/314) versus 5.7% (14/244) (p = 0.016), less preterm delivery (5.7% vs 10.7%, p = 0.032), fewer small-for-gestational-age newborns, 9 of 314 (2.95) versus 17 of 244 (7%) (p = 0.023), and a higher mean birth weight, 3314 gm versus 3121 gm (p = 0.0001).

CONCLUSION

Women with a twofold or greater longitudinal reduction in maternal serum thromboxane B2 had less preeclampsia and prematurity, fewer small-for-gestational-age newborns, and higher birth weights than women with less than a twofold reduction.

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.

Autacoids and control of human placental blood flow

1. Humans have a haemochorial, villous placenta. Uterine blood passes through maternal sinuses, bathing placental villi through which fetal blood circulates. Blood flow through each circulation is high and vascular resistance low. This haemodynamic situation is essential for efficient placental function. 2. The low placental vascular resistance is due to a lack of nervous influences together with pregnancy-induced changes promoting vasodilatation. Increases occur in output of the vasodilators prostacyclin and nitric oxide and also in membrane sodium pump activity. 3. Many autacoids are present in umbilical blood. Fetal vessels of the placenta develop intense vasoconstriction in the presence of some autacoids, such as thromboxane A2 and prostaglandins F2 alpha and E2, and respond weakly to others, such as angiotensin II and 5-hydroxytryptamine. Nevertheless, vasodilator influences predominate. 4. The diseases of pre-eclampsia and fetal growth retardation are associated with reduced output of nitric oxide and prostacyclin and with increased production of thromboxane A2 and endothelin-1. These changes promote vasoconstriction, increased vascular sensitivity to vasoconstrictor stimuli, platelet aggregation and intravascular coagulation, retarding blood flow and feto-placental growth. 5. Aspirin and glyceryl trinitrate have been investigated for possible therapeutic use in pre-eclampsia and fetal growth retardation. Improved drug therapy is likely as knowledge increases of the importance of autacoids in normal placental function and in the changes that occur during disease.

Secretion of lipid peroxides by the human placenta

OBJECTIVE

We attempted to determine whether the human placenta secretes lipid peroxides. If it does, then it could be a source of lipid peroxides in maternal blood.

STUDY DESIGN

In study 1 isolated human placental cotyledons (n = 7) were perfused serially for 20-minute intervals with control Krebs-Ringer-bicarbonate buffer gassed with 95% oxygen and 5% carbon dioxide and Krebs-Ringer-bicarbonate buffer with progressively increasing concentrations of t-butyl hydroperoxide added (10, 25, 50, and 100 mumol/L) to stimulate endogenous lipid peroxide production. In study 2 placental cotyledons (n = 6) were perfused serially for 20-minute intervals with control Krebs-Ringer-bicarbonate buffer, t-butyl hydroperoxide (100 mumol/L), low-dose aspirin (5 x 10(-5) mol/L), and low-dose aspirin plus t-butyl hydroperoxide. Maternal and fetal effluent samples were analyzed for lipid peroxides by hydrogen peroxide equivalents.

RESULTS

In study 1, compared with control Krebs-Ringer-bicarbonate perfusion, peroxide perfusion significantly increased, in a dose-response manner, placental lipid peroxide secretion. In study 2, aspirin completely blocked the ability of peroxide to increase the secretion of lipid peroxides. In both studies placental secretion of lipid peroxides was significantly greater toward the maternal side of the placenta than toward the fetal side.

CONCLUSIONS

(1) The human placenta secretes lipid peroxides primarily into the maternal effluent. (2) Exogenous peroxide stimulates endogenous lipid peroxide production, which is blocked by aspirin, suggesting cyclooxygenase is involved in lipid peroxide production. (3) The placenta could be a source of circulating lipid peroxides in pregnant women.

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.

Contractile responses of the human umbilical artery from pregnancies complicated by intrauterine growth retardation

The contractile properties of the umbilical artery to oxygen, U46619 (a stable thromboxane A2 mimetic) and 5-hydroxytryptamine (5-HT) were studied in normal term (> or = 37 weeks) and preterm (< 34 weeks) pregnancies, and in a group of pregnancies complicated by intrauterine growth retardation (IUGR). Isometric contractile responses in the preterm group to oxygen were reduced when compared with the term group, though no differences were found between these groups in the responses to either U46619 or 5-HT. In the IUGR group the responses to oxygen did not differ from gestationally matched normal pregnancies, though among those cases delivered preterm, the finding of absent end-diastolic flow velocity in the umbilical artery prior to delivery was associated with markedly diminished responses to oxygen. These data indicate the development of oxygen-induced contractions in the umbilical artery as pregnancy advances, which may fail to function in the severely growth-retarded fetus.

Low dose aspirin in hypertensive pregnant women: effect on pregnancy outcome and prostacyclin-thromboxane balance in mother and newborn

OBJECTIVE

To study the effect of daily treatment with 50 mg of aspirin (ASA) on the hypertensive pregnancy complications and on the production prostacyclin (PGI2) and thromboxane A2 (TxA2) in high risk pregnant women and their infants.

DESIGN

Placebo controlled prospective study.

SETTING

Departments of Obstetrics and Gynaecology, University of Helsinki, University of Oulu and Central Hospital of Middle Finland, Finland.

SUBJECTS

Two hundred and eight pregnant women with pre-existing hypertension or a history of severe preeclampsia in their previous pregnancy. Prostanoids were studied in a subgroup of 18 women.

INTERVENTIONS

The women were randomised to receive ASA (50 mg/day, n = 103) or placebo (n = 105) from the mean of 15 weeks gestational age to delivery. The exacerbation of pre-existing hypertension or the appearance of hypertension in previously normotensive women, the appearance of proteinuria and fetal growth were the main end points, but some other clinical characteristics were also recorded. Urinary excretion of PGI2 and TxA2 metabolites by mothers and infants and their production in umbilical arteries in vitro were also studied.

RESULTS

Two women (one in both groups) had miscarriages, and one pregnancy was terminated for fetal anencephaly (ASA group). In addition, seven women discontinued the treatment due to urticaria (two women in ASA group), increased activity of aspartate amino transferase in serum (one woman in both groups), or increased bleeding time (one woman in ASA group, two women in placebo group), and one woman in the placebo group was lost from follow-up. Thus the end points could be assessed in 97 women taking ASA and 100 women taking placebo. ASA did not diminish the rate of the rise of blood pressure without (12 vs 14, respectively) or with proteinuria (9 vs 11), but fetal haemodynamic disturbances as assessed by Doppler equipment (1/44 vs 6/45 women studied, P = 0.05) and need for treatment in neonatal intensive care unit (10 vs 21, P = 0.04) were more rare in ASA group. ASA tended to increase the birthweight of the newborn (3348 +/- 707 g vs 3170 +/- 665 g, mean +/- SD, P = 0.07), but two perinatal deaths occurred in ASA group. ASA prolonged the bleeding time of the mother (435 s, 210-998 s (geometric mean, range) vs 349 s, 210-690 s, P = 0.02), but caused no extra blood loss during delivery, nor affected neonatal hemostasis. In a subgroup of mothers (ASA, n = 10; placebo, n = 8), ASA inhibited more than 90% of platelet TxA2-production, and caused a 65 to 80% decrease in the urinary excretion of TxA2 metabolites, but no decrease in the urinary excretion of PGI2 metabolites.

CONCLUSIONS

ASA did not prevent the rise of maternal hypertension, but improved fetal haemodynamic performance and reduced the need of intensive neonatal care. It inhibited strongly maternal thromboxane A2 but not PGI2 production and thus shifted the balance between PGI2/TxA2 to the dominance of the vasodilatory, anti-aggregatory side.

A clinical trial of a slow-release formulation of acetylsalicylic acid in patients at risk for preeclampsia

The formation of thromboxane A2 (TXA2) in maternal and foetal cord serum was measured at birth in eight control patients and in 13 patients taking 100 mg of a slow-release formulation of acetylsalicylic acid. The serum concentrations of TXB2 (a stable end product of TXA2 hydrolysis) in both maternal and cord serum from patients who ingested the acetylsalicylic acid formulation were significantly lower (P < 0.01) than those in control subjects. Acetylsalicylic acid was not detected (< 30 ng ml-1) in maternal plasma from six mothers and in cord plasma from seven foetuses in the acetylsalicylic acid-treated group. The mean cord to maternal plasma concentration ratios for detectable acetylsalicylic acid and salicylate were 0.62 +/- 0.19 (s.d.) (n = 6) and 0.84 +/- 0.16 (n = 13), respectively. We conclude that low doses of acetylsalicylic acid given in a slow-release form to mothers during pregnancy cause depression of TXA2 formation in the foetal blood.

Low-dose aspirin therapy to prevent preeclampsia

OBJECTIVE

Our aim was to test the hypothesis that acetylsalicylate (aspirin) treatment reduces the incidence or severity of pregnancy-associated hypertension.

STUDY DESIGN

Patients were nulliparous, healthy, and with a singleton gestation at between 20 and 22 weeks' gestation. A sample size of 600 patients was calculated on the basis of p < or = 0.05 and 90% power of observation. A 2-week placebo-controlled "run-in" was used to select compliant patients. Randomization occurred at 24 weeks, with 60 mg of aspirin or placebo treatment from randomization to delivery.

RESULTS

Follow-up was maintained on 99% of the patients. The randomized patients had a 94% pill compliance index. At randomization, serum thromboxane medians were similar in both groups. Thromboxane B2 levels in the aspirin group decreased significantly from baseline at 29 to 31 weeks, 34 to 36 weeks, and at delivery as compared with an overall increase in the placebo group. Preeclampsia developed in five of 302 women (1.7%) who received aspirin versus 17 of 302 (5.6%) who received the placebo (p = 0.009). Preeclampsia was severe in one aspirin and in six placebo recipients (p = 0.06).

CONCLUSION

Daily ingestion of 60 mg of aspirin beginning at 24 weeks' gestation significantly reduced the occurrence of preeclampsia.

Acetylsalicylic acid inhibits anticardiolipin antibody-induced platelet-activating factor (PAF) synthesis

Enhanced endothelial cell PAF synthesis has been identified as a consequence of anticardiolipin antibody (ACA)-positive serum exposure. We proposed this observation as a contributing factor to thrombogenesis in women with the antiphospholipid syndrome. Since acetylsalicylic acid (ASA) is an accepted therapeutic alternative in these patients, we sought to determine if ASA would attenuate endothelial cell PAF production resulting from ACA exposure. Using primary, confluent monolayers of umbilical vein endothelial cells, experiments were performed to evaluate PAF synthesis after incubation with antibody-positive serum and ASA. Total PAF and its radyl-derivatives (1-alkyl- and 1-acyl-PAF) were quantified by tritiated acetate incorporation, phospholipid extraction, thin-layer chromatography and scintillation spectroscopy. ASA consistently decreased ACA-induced PAF synthesis (No ASA, 9573 +/- 443 vs 1mmol/L ASA, 4829 +/- 838 dpm/ml; p = 0.016) and the observed reduction was dose-dependent over a range of ASA concentrations (0.1, 1, 10 and 100 mmol/L; ANOVA, p = .00015). Reduced PAF synthesis was also observed in cultures exposed to ASA and incubated with antibody-negative serum. These observations suggest that in ACA-positive women, the antithrombotic effects of ASA may relate in part, to reduced endothelial cell PAF synthesis.

Low-dose aspirin in the prevention of preeclampsia and fetal growth retardation: rationale, mechanisms, and clinical trials

Preeclampsia is characterized by a functional imbalance between vascular prostacyclin and thromboxane A2 production. On the basis of the hypothesis that preeclampsia is at least partially caused by an increase in thromboxane A2, some studies attempted to correct this pathologic condition by pharmacologic manipulation with low-dose aspirin. The current literature suggests that the use of low-dose aspirin during pregnancy is safe with regard to congenital anomalies and fetal, neonatal, and maternal cardiovascular physiologic state and hemostasis. Aspirin at least partially corrects the pathologic increase in angiotensin II sensitivity that precedes the clinical development of preeclampsia. In addition, some clinical trials have demonstrated that low-dose aspirin is effective in reducing the incidence of preeclampsia and/or fetal growth retardation in selected high-risk women. Currently, large clinical trials are in progress to evaluate the effectiveness and side effects of the use of low-dose aspirin in preventing preeclampsia and/or fetal growth retardation. Until these studies have been completed, it will remain unclear whether antiplatelet therapy, such as low-dose aspirin, should be adopted for the prevention of either preeclampsia or fetal growth retardation.

Low dose aspirin in pregnancy: a clinical and biochemical study of effects on the newborn

Low dose Aspirin in pregnancy reduces the incidence of intra uterine growth retardation (IUGR) and pregnancy induced hypertension (PIH) in women at risk for these complications. To investigate if this drug, even in a low dose, could expose the newborn to hemorrhagic complications, we studied ten neonates whose mothers had been taking 50 mg/day of Aspirin from the 12th week of pregnancy until delivery and compared them with eight newborns whose mothers didn't take the drug. No hemorrhagic complications (emathemesis, ecchymoses or petechiae, subconjunctival hemorrhage, cephaloematomas etc.) were observed in the fetuses exposed to Aspirin or in the control group. No hemorrhagic lesions were found by ultrasound brain scan on the fourth day of life. Newborns exposed to Aspirin showed a significantly lower thromboxane concentration on the first day of life (median 73 ng/ml versus 217 ng/ml); however on the fourth day the level of serum thromboxane in the cases exposed reached the values of the unexposed ones (median 146 ng/ml versus 143 ng/ml). In conclusion low dose Aspirin in pregnancy can be considered a safe drug without and adverse effect on the newborn.

NSAIDs: maternal and fetal considerations

Nonsteroidal anti-inflammatory drugs (NSAIDs) gained popularity in the late 1970s. Inhibition of prostaglandin synthesis with indomethacin has been reported to be effective for prevention of labor and for treatment for symptomatic polyhydramnios. Concern about its possible constrictive effect on the fetal ductus arteriosus has limited its use in pregnancy. Maternal indomethacin therapy has also been associated with reduction in urine production in the fetus and with oligohydramnios. Obstetricians have discouraged pregnant women from taking analgesic doses of aspirin, mainly because of the availability of paracetamol (acetaminophen), which causes less gastric irritation, but also because of fear of maternal and fetal hemorrhage and of possible premature closure of the ductus. These fears largely derive from studies on patients taking large doses and from extrapolation from other NSAIDs. The likelihood that treatment with 60-75 mg/day of aspirin markedly reduces the incidence of preeclampsia and fetal intrauterine growth retardation makes it important to reexamine its use. This review describes the pharmacology and pharmacokinetics of aspirin with particular reference to pregnancy and considers teratogenesis, prolongation of pregnancy and labor, maternal bleeding, fetal and neonatal bleeding, possible effects on the ductus arteriosus and pulmonary circulation, and possible nonspecific effects on intelligence and breast feeding and acute toxicity in the neonate.

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).

Transfer of aspirin across the perfused human placental cotyledon

Pregnancy-induced hypertension is associated with a reduction in prostacyclin synthesis that is relative to normotensive pregnancy, whereas thromboxane A2 synthesis is unchanged or increased. The net effect is a decreased prostacyclin/thromboxane ratio that may result in the reduced fetal-placental blood flow seen in pregnancy-induced hypertension because thromboxane is known to constrict this circulation. Low-dose aspirin (acetylsalicylic acid), which is used to treat pregnancy-induced hypertension, selectively inhibits thromboxane synthesis and therefore may alter fetal-placental blood flow. We have investigated the transfer of acetylsalicylic acid in the perfused human placental cotyledon and its effects on fetal-placental perfusion pressure. Human placental cotyledons were perfused with tissue culture medium 199 plus 5% polyvinylpyrrolidone that was gassed with 95% oxygen/5% carbon dioxide at flow rates of 10 ml/min (maternal) and 4 ml/min (fetal). Acetylsalicylic acid (10(-5) mol/L) was added to the maternal circuit, and cotyledons were perfused for 1 hour with aliquots taken from a closed fetal circuit every 5 minutes. Acetylsalicylic acid was assayed by spectrofluorometry at 306/412 nm. Our data indicate an initial rapid transfer of acetylsalicylic acid during the first 5 minutes into the fetal-placental circulation, the concentration then decreased to a steady state at 0.4 x 10(-5) mol/L. Resting perfusion pressure of both maternal and fetal circulation did not change after the addition of acetylsalicylic acid to maternal perfusate and transfer to the fetal circulation.

Prevention of fetal growth retardation with low-dose aspirin: findings of the EPREDA trial

The efficacy of low-dose aspirin in preventing fetal growth retardation was tested in a randomised, placebo-controlled, double-blind trial. A secondary aim was to find out whether dipyridamole improves the efficacy of aspirin. 323 women at 15-18 weeks' amenorrhoea were selected at twenty-five participating centres on the basis of fetal growth retardation and/or fetal death or abruptio placentae in at least one previous pregnancy. They were randomly allocated to groups receiving placebo, 150 mg/day aspirin, or 150 mg/day aspirin plus 225 mg/day dipyridamole, for the remainder of the pregnancy. In the first phase of the trial all actively treated patients (n = 156) were compared with the placebo group (n = 73). Mean birthweight was significantly higher in the treated than in the placebo group (2751 [SD 670] vs 2526 [848] g; difference 225 g [95% CI 129-321 g], p = 0.029) and the frequency of fetal growth retardation in the placebo group was twice that in the treated group (19 [26%] vs 20 [13%]; p less than 0.02). The frequencies of stillbirth (4 [5%] vs 2 [1%]) and abruptio placentae (6 [8%] vs 7 [5%]) were also higher in the placebo than in the treated group. The benefits of aspirin treatment were greater in patients with two or more previous poor outcomes than in those with only one. In the second analysis, of aspirin only (n = 127) vs aspirin plus dipyridamole (n = 119), no significant differences were found. There was no excess of maternal or neonatal side-effects in the aspirin-treated patients.

Low-dose aspirin and vascular response in pregnant patients sensitive to angiotensin II

The angiotensin sensitivity test was performed in 25 high risk pregnant women before and after administration of low-dose aspirin (100 mg/day for 7 days). After aspirin administration there was a significant decrease in AII sensitivity in sensitive patients with no change in nonsensitive patients. Low-dose aspirin favorably affects sensitivity to AII in sensitive patients, thus indicating a reduced vascular reactivity as a consequence of this regimen.

Doppler ultrasound and aspirin in recognition and prevention of pregnancy-induced hypertension

Screening of 1226 nulliparous women by means of doppler uteroplacental flow-velocity waveforms in early pregnancy identified 148 (12%) as being at high risk of pregnancy-induced hypertension. After exclusions and refusals, 100 women were randomly allocated to groups receiving either low-dose aspirin (75 mg daily; 48 patients) or identical placebo (52 patients) for the remainder of the pregnancy. The difference between the aspirin and placebo groups in the frequency of pregnancy-induced hypertension (13% vs 25%) did not achieve significance, but there were significant differences in the frequencies of proteinuric hypertension (2% vs 19%) and hypertension occurring before 37 weeks' gestation (0% vs 17%). Fewer aspirin-treated than placebo-treated women had low birthweight babies (15% vs 25%), but this difference was not significant. The only perinatal death in the aspirin group followed a cord accident during labour, whereas the 3 perinatal deaths in the placebo group were all due to severe hypertensive disease. No maternal or neonatal side-effects were observed in either group.

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.

Low-dose aspirin therapy improves fetal weight in umbilical placental insufficiency

A randomized, placebo-controlled, double-blind trial was carried out to evaluate the fetal benefits of low-dose aspirin (150 mg/day) as a treatment of placental insufficiency during the last trimester of pregnancy. Forty-six women referred for study because there was concern about fetal welfare were found to have an elevated umbilical artery wave form systolic/diastolic ratio. Mothers with severe hypertension were excluded because fetal condition would not necessarily be the dominant determinant of obstetric decision making. A distinction was made between a high systolic/diastolic ratio (greater than 95th but less than 99.95th percentile) and an extreme systolic/diastolic ratio (greater than 99.95th percentile). There were 34 patients in the high ratio group and 12 in the extreme group. Aspirin therapy was associated with an increase in birth weight (mean difference 526 gm [p less than 0.02]), head circumference (1.7 cm [p less than 0.025]), and placental weight (136 gm [p less than 0.02]) in those patients with a high initial umbilical artery systolic/diastolic ratio. For the 12 women with an extreme initial systolic/diastolic ratio, aspirin therapy did not result in a significantly different pregnancy outcome.

Altered excretion of prostaglandin and thromboxane metabolites in pregnancy-induced hypertension

The renal and systemic metabolites (the latter as 2,3-dinor derivatives) of prostacyclin and thromboxane A2 were measured, along with renal prostaglandin E2 and kallikrein, in the urine of 15 patients with pregnancy-induced hypertension, 15 normotensive pregnant women matched for both age and gestational age, and 15 normotensive nonpregnant control women. Urinary excretion of all prostaglandin and thromboxane metabolites studied proved significantly higher in normotensive pregnant women than in controls. Prostaglandin E2, 6-keto-prostaglandin F1 alpha, and 2,3-dinor-6-keto-prostaglandin F1 alpha were significantly lower in pregnancy-induced hypertensive women than in normotensive pregnant women, whereas thromboxane B2 and 2,3-dinor-thromboxane B2 showed no significant differences in the two groups. A significant negative correlation (r = -0.636, p less than 0.01) was found between urinary 2,3-dinor-6-keto-prostaglandin F1 alpha and mean blood pressure in the two groups of pregnant women taken as a whole. These data indicate that, in pregnancy-induced hypertension, there is an imbalance between vasodilator and vasoconstrictor factors, not only in the kidneys, but also at the systemic vascular level. This imbalance, which may in itself produce vasoconstriction, may also potentiate the hypertensive effect of catecholamines and angiotensin II.

Low dose aspirin treatment in late pregnancy differentially inhibits cyclo-oxygenase in maternal platelets

Eighteen pregnant women were treated with aspirin, 37.5 mg once daily by mouth. Treatment was started two weeks before the expected date of delivery, and continued until delivery. Seventeen untreated women were studied concurrently. Platelet thromboxane (TX) production was determined by radioimmunoassay of TXB2 in serum from blood incubated for one hour with thrombin at 37 degrees C. Maternal blood was studied before treatment and at delivery. Fetal blood, from the cord, was studied at delivery. Prostacyclin (PGI2) production by rings of umbilical artery incubated in Hanks' solution at 37 degrees C for one hour was determined by radio-immunoassay of its hydrolysis product, 6-oxo-prostaglandin (PG) F1 alpha. Maternal and fetal blood from untreated women produced similar amounts of TXB2. Aspirin, in the dose regimen used, significantly inhibited TXB2 production in maternal but not in fetal blood, and did not impair PGI2 synthesis by umbilical artery rings. This differential effect on the cyclo-oxygenase of maternal platelets is probably due to the unusual kinetic properties of aspirin, and may prove therapeutically useful.