Current topic: the regulation of placental eicosanoid biosynthesis

Effect of calcium ionophore A23187 on prostaglandin synthase type 2 and 15-hydroxy-prostaglandin dehydrogenase expression in human chorion trophoblast cells

OBJECTIVE

Prostaglandins induce parturition in humans. Prostaglandin output is regulated by the synthetic and metabolic enzymes, prostaglandin synthase type 2 (PTGS2) and 15-hydroxyprostaglandin dehydrogenase (PGDH). The role of calcium in regulating PTGS2 and PGDH expression was investigated in chorion trophoblasts.

STUDY DESIGN

Cells were treated with calcium ionophore A23187 in the presence or absence of calcium chelators; changes in messenger ribonucleic acid expression were measured with real-time polymerase chain reaction and analyzed with analysis of variance. Protein expression was evaluated with Western blot and dual immunofluorescence.

RESULTS

A23187 stimulated PTGS2 and suppressed PGDH expression. Effects of A23187 were reversed by calcium chelators. PTGS2 had perinuclear and cytosolic distribution, whereas PGDH was cytosolic. Some cells expressed both enzymes, some neither enzyme, and some either PTGS2 or PGDH.

CONCLUSION

Chorion cells showed heterogeneity in the expression of PTGS2 and PGDH. Calcium influx regulates PTGS2 and PGDH expression, thereby promoting coordinated increased prostaglandin output in circumstances such as term and preterm labor.

Developmental maturation of primate placental trophoblast: placental cytosolic and secretory phospholipase A2 expression after estrogen suppression of baboons

We have demonstrated that the baboon placenta expressed the mRNAs and proteins for secretory and cytosolic phospholipase A2 (PLA2) enzymes and that cPLA2 expression increased with advancing gestation in association with the increase in placental estrogen production. To determine whether estrogen regulates placental PLA2 expression, as it does other aspects of syncytiotrophoblast functional differentiation, we compared sPLA2 and cPLA2 mRNA levels in placentas obtained on day 165 of gestation (term = day 184) from baboons that were untreated or treated during the second half of gestation with the aromatase inhibitor CGS 20267 or CGS 20267 and estradiol. Maternal saphenous and uterine vein estradiol levels were reduced (P < 0.05) by approximately 95% by treatment with CGS 20267 and restored by concomitant administration of CGS 20267 and estrogen. However, sPLA2 and cPLA2 mRNA levels expressed as a ratio of beta-actin were similar in whole villous placenta from baboons that were untreated or treated with CGS 20267 or CGS 20267 plus estrogen. PLA2 expression in an enriched fraction of nontrophoblast cells of the baboon placenta was also not altered by CGS 20267 treatment. Collectively these findings indicate that placental cPLA2 and sPLA2 expression is not estrogen-dependent. Because estrogen has been shown to regulate other aspects of placental steroidogenesis, we suggest that the regulatory role of estrogen on syncytiotrophoblast functional maturation is specific.

Effect of lipopolysaccharide on uterine contractions and prostaglandin production in pregnant rats

OBJECTIVE

Our aim was to evaluate the effect of lipopolysaccharide on prostaglandin production and on contraction of isolated myometrial strips from preterm pregnant rats.

STUDY DESIGN

Pregnant Wistar rats on day 17 of gestation were killed 3 hours after intraperitoneal injection of lipopolysaccharide (1.5 mg/kg) or vehicle, with or without pretreatment with indomethacin (5 mg/kg administered intraperitoneally) 1 hour beforehand. Concentrations of endotoxin in maternal serum and amniotic fluid, prostaglandin F2alpha and prostaglandin E2 in amniotic fluid, and progesterone in maternal serum were determined. Longitudinal uterine strips were prepared, placed in organ chambers with Krebs-Ringer solution, aerated with 95% oxygen and 5% carbon dioxide (37 degrees C, pH approximately 7.4), and equilibrated at 1g passive tension. Concentration-contraction relationships to oxytocin were determined. Samples of bathing solution were collected 10 minutes after the concentration of oxytocin was maximal. Prostaglandins and progesterone were measured by radioimmunoassay and endotoxin was measured by the Endospecy (Seikagaku Kogyo, Tokyo, Japan) kit.

RESULTS

Lipopolysaccharide treatment significantly increased the levels of prostaglandin F2alpha and prostaglandin E2 in amniotic fluid. Treatment with lipopolysaccharide inhibited the production and release of prostaglandin F2alpha and prostaglandin E2 that were activated by oxytocin in uterine strips and increased the sensitivity of strips to the contractile effect of oxytocin. Indomethacin did not affect the basal or the lipopolysaccharide-activated levels of endotoxin in serum and amniotic fluid and exerted a counteraction on lipopolysaccharide-induced increases in concentrations of prostaglandin F2alpha and prostaglandin E2 in amniotic fluid. Indomethacin counteracted oxytocin-activated production and release of prostaglandin F2alpha and prostaglandin E2 in uterine tissues after lipopolysaccharide administration without changing the sensitivity of uterine strips to oxytocin. Concentrations of progesterone were not changed after lipopolysaccharide, indomethacin, or their combined application, which suggests that the changes described were not associated with alterations in the levels of the hormone.

CONCLUSIONS

The activation of the uterine contractile system by prostaglandin and oxytocin during intra-amniotic infection may be one of the causes of preterm delivery. A combination of an oxytocin receptor antagonist and an inhibitor of cyclooxygenase may be beneficial in prevention or treatment of preterm labor.

Prostaglandins in selected reproductive tissues in preterm and full-term gestations

We investigated differences in maternal plasma and trophoblast prostaglandin metabolism associated with preterm births. Tissue prostaglandins (PGs) E2 and F2 alpha and the stable plasma PGF2 alpha metabolite, 13,14-dihydro-15-keto-PGF2 alpha, were measured in preterm (< 37 weeks) and term (< or = 37 weeks) births. Amnion PGE2 in preterm (106.1 +/- 15.7 ng/g wet weight tissue; x +/- SEM; n = 37) was lower than in term (176.6 +/- 22.7 ng/g wet weight; x +/- SEM; n = 34, P < 0.02). Placenta PGE2 was lower in preterm (34.7 +/- 19.7 ng/g wet weight; x +/- SEM) than in term (103.3 +/- 28.0 ng/g wet weight; x +/- SEM, P < 0.04). Preterm PGF2 alpha was consistently lower in the amnion (106.8 +/- 17.5 ng/g wet weight) and placenta (102.5 +/- 8.7 ng/g wet weight) than in term amnion (188.2 +/- 24.8 ng/g wet weight; P < 0.01) and placenta (128.9 +/- 7.8 ng/g wet weight; P < 0.03). Chorionic PGE2 and plasma PGF2 alpha metabolite followed this trend but did not reach significance. These findings suggest qualitative and quantitative differences in maternal and trophoblast eicosanoid metabolism between term and preterm parturition.

Cyclosporin A inhibits prostaglandin E2 production by fetal amnion cells in response to various stimuli

Use of cyclosporin A as part of an immunosuppressive regimen in pregnant transplant patients is not uncommon. Although successful pregnancies have been reported with the use of various immunosuppressive agents including cyclosporin A, the concern for fetal outcome still remains. Our purpose was to evaluate the effects of immunosuppressive cyclosporin A on prostaglandin E2 (PGE2) production by human fetal amnion. Amnion cells were isolated from term placentae obtained at elective cesarean section before the onset of labor. Cells were grown to confluence and then incubated for 16 hours with cyclosporin A (1-1000 ng/ml) in the presence and absence of interleukin 1 beta (IL-1 beta, 1 ng/ml), phorbol 12-myristate 13-acetate (PMA, 10(-7) M) and ionomycin (0.5 microM). PGE2 was measured by radioimmunoassay and cellular protein determined. IL-1 beta, PMA and ionomycin all stimulated amnion cell PGE2 production as expected. However, these stimulatory actions were attenuated by at least 50% when cells were co-incubated with cyclosporin A (1000 ng/ml). Concentrations of cyclosporin A tested included the therapeutic range (250-1000 ng/ml). Our results indicate that cyclosporin A does not stimulate amnion cell PGE2 production and is probably unrelated to preterm labor and delivery in allograft recipients.

Fetal fibronectin in cervicovaginal secretions as a predictor of preterm birth

OBJECTIVE

To determine whether fetal fibronectin detected in cervicovaginal secretions of patients with symptoms suggestive of preterm labour is a predictor for preterm birth.

DESIGN

A blind prospective observational study.

SETTING

A teaching hospital.

PARTICIPANTS

One hundred and forty-one women presenting to the delivery suite between 24 and 37 weeks of gestation (112 were between 24 and 34 weeks of gestation) with symptoms suggestive of preterm labour, with intact membranes and cervical dilation of < 2 cm.

INTERVENTION

Specimens of cervicovaginal secretions were collected from the ectocervix and posterior fornix. Fetal fibronectin levels were measured by an ELISA and samples were considered positive if the level of fetal fibronectin present was > or = 0.05 microgram/ml.

MAIN OUTCOME MEASURES

Gestation at birth and sampling-birth interval.

RESULTS

The preterm birth (before 37 weeks of gestation) rate in the population studied was 19.1%. Fetal fibronectin predicted preterm birth with sensitivity of 63%, specificity of 95.6%, positive predictive value of 77.3%, and negative predictive value of 91.6%. Analysis of the data from women at less than 34 weeks of gestation showed similar results. A negative test accurately excluded (97.9%) the chance of subsequent birth during the three weeks interval following sampling.

CONCLUSIONS

The presence of fetal fibronectin in the cervicovaginal secretions of women admitted with symptoms suggestive of preterm labour indicates a significant risk for subsequent preterm birth. The absence of fetal fibronectin in this group is a very strong indication that subsequent preterm birth is unlikely to occur. Fetal fibronectin test, if combined with clinical findings, has a potentially important role in clinical management of women with symptoms suggestive of preterm labour.

Intrauterine infection and the effects of inflammatory mediators on prostaglandin production by myometrial cells from pregnant women

OBJECTIVE

Our purpose was to evaluate the effects of known stimulants of prostaglandin production on cultured myometrial cells from women in labor with and without intrauterine infection.

STUDY DESIGN

Myometrial segments were obtained from 16 patients between 33 and 40 weeks' gestation who had been in labor for > or = 8 hours at cesarean delivery; 8 patients had clinical chorioamnionitis and 8 did not. Myometrial cells were isolated and grown in culture. Incubations were conducted with interleukin-1 beta, tumor necrosis factor-alpha, or epidermal growth factor. Prostaglandin E2, prostaglandin F2 alpha, and 6-keto-prostaglandin F1 alpha (the stable metabolite of prostacyclin) were measured by radioimmunoassay, and cellular protein was determined.

RESULTS

Cultured human myometrial cells from patients with and without prior intrauterine infection produced prostaglandins in response to interleukin-1 beta, tumor necrosis factor-alpha, and epidermal growth factor at a significantly increased rate (p<0.05 vs controls at and above 10 ng/ml of interleukin-1 beta, tumor necrosis factor-alpha, and epidermal growth factor). The major prostaglandin produced in response to each stimulant was 6-keto-prostaglandin F1 alpha; however, this response was attenuated in cells from patients with intrauterine infection.

CONCLUSIONS

Cultured human myometrial cells from patients with and without prior intrauterine infection respond to known stimulants of prostaglandin production. Prior intrauterine infection has no effect on baseline prostaglandin production, but the amount of prostacyclin produced as a response to cellular stimulants is decreased with prior intrauterine infection. This effect may have a role in regulating myometrial function in intrauterine infection.

Release of arachidonic acid metabolites by human fetal membranes: interrelationship between leukotriene B4 and prostaglandin E2

The objective of this study was to ascertain whether human fetal membranes metabolize arachidonic acid preferentially through the lipoxygenase rather than the cyclooxygenase pathway before labor and whether an interaction between lipoxygenase and cyclooxygenase products is present in these tissues. Reflected fetal membranes were obtained from 8 healthy women at term gestation who were delivered by elective repeat cesarean section before the onset of labor. Tissues were cultured either in the presence or in the absence of the calcium ionophore A23187 for 60 minutes. Leukotriene B4 (LTB4) and prostaglandin E2 (PGE2) were measured in culture medium by radioimmunoassays. Moreover, the effect of different concentrations of exogenously added LTB4 on PGE2 release was evaluated. The basal and stimulated output of LTB4 by tissues was significantly higher than that of PGE2. Addition of LTB4 significantly decreased PGE2 release by tissues. These findings suggest that in the above tissues: 1) the arachidonate lipoxygenase pathway is highly active before labor; 2) LTB4 might play a role in the regulation of PGE2 production.

The regulation of arachidonate lipoxygenase metabolite formation in cells derived from intrauterine tissues

Products of arachidonic acid (AA) metabolism via the lipoxygenase pathways may have key roles in the maintenance of pregnancy and the onset of labor. We have determined whether calcium ionophores can modulate the rate of biosynthesis within the uterus of five important arachidonate lipoxygenase metabolites, i.e. leukotriene B4 (LTB4), LTC4, 5-hydroxyeicosatetraenoic acid (5-HETE), 12-HETE, and 15-HETE. Amnion, chorion, and decidual cells were isolated, grown to confluence and incubated with ionomycin. The production of LTB4, LTC4, 5-HETE, 12-HETE, and 15-HETE was determined using specific radioimmunoassays. Cell-specific, concentration-related stimulatory actions of ionomycin on 5-HETE, 12-HETE, 15-HETE, and LTC4 but not LTB4 production were found. A23187 had effects similar to ionomycin. Hence elevation of intracellular calcium levels can result in enhanced intrauterine production of arachidonate lipoxygenase metabolites that may affect pregnancy outcome.

Regulation of utero-placental prorenin

Prorenin (Pro) is synthesized in a number of human utero-placental tissues, including chorion, decidua, villous placenta and probably mesenchymal cells. The release of Pro from these extra-renal tissues follows new protein synthesis and appears to utilize the constitutive secretory pathway. Unlike processing in the kidney, very little of the Pro is subsequently cleaved to the smaller product (active renin). Primary signals which regulate Pro include protein hormones and peptides (relaxin, endothelin, hCG), amines (epinephrine, norepinephrine, and related beta adrenergic agents), and eicosanoids. These agents increase the mRNA for prorenin at a time before peak secretory effects are noted. Other extracellular signals have negative regulatory effects. These include angiotensin, endotoxin and cytokines (TNF-alpha and interleukin-1 B). There is also evidence that glucocorticoid receptor activation has an inhibitory effects on Pro release in placenta. Second messengers involved in the regulation of Pro include cyclic AMP and protein kinase A (PKA), protein kinase C (PKC), and calcium. The possible biological effect(s) of the extracellular Pro are unknown but may be due to direct generation of angiotensin I. Since angiotensin-peptides have a number of trophic effect on both vascular and non-vascular tissues, regulation of utero-placental Pro by autocrine, paracrine or endocrine signalling may be critical in normal fetal and/or placental development.

Control of in vitro prostaglandin F2 alpha and E2 synthesis by caruncular and allantochorionic tissues from cows that calved normally and those with retained fetal membranes

High concentrations of PGF2 alpha and PGE2 are produced by the uterus during the early postpartum period in cows and may play an important role in both placental separation and uterine involution. In the present study, we have examined the hormonal and intracellular control mechanisms involved in PGF2 alpha and PGE2 secretion by caruncular and allantochorionic tissue in vitro. Tissue explants, obtained about 6 hr postpartum from cows that delivered normally (NFM, n = 10) or cows with retained fetal membranes (RFM, n = 4), were incubated for 6 hr and PGF2 alpha and PGE2 concentrations in the medium were determined by radioimmunoassay. Addition of oxytocin (100 microU/ml), platelet activating factor (PAF, 100 ng/ml) and epidermal growth factor (EGF, 100 ng/ml) had no effect on secretion of PGF2 alpha from the caruncle, but oxytocin and PAF did stimulate PGE2. There was no difference between groups of cows. All three substances stimulated PGF2 alpha from the allantochorion of NFM, but not RFM, cows and stimulated PGE2 secretion from the allantochorion of both groups of cows. Incubation of the tissues with cholera toxin (100 ng/ml), dibutyryl cyclic adenosine 3',5'-monophosphate (dibutyryl cAMP, 1 mM), calcium ionophore A23187 (5 microM) or phorbol ester 12-myristate-13 acetate (PMA, 100 nM) showed that PGF2 alpha secretion is essentially via the calcium-protein kinase C effector pathway. However, calcium-protein kinase C and cAMP second messenger systems appear to be involved in the secretion of PGE2. Prostaglandin secretion was sensitive to cycloheximide in both caruncular and allantochorionic tissues, suggesting that protein synthesis may be involved. In conclusion, these data show that in vitro PGF2 alpha secretion can be modulated by the agonists used only in allantochorion and is essentially via the calcium-protein kinase C effector pathway. PGE2 secretion can be modified in both caruncular and allantochorion tissues and involves both inositol triphosphate-diacylglycerol and cAMP second messenger systems.

Regulation of intrauterine prostaglandin biosynthesis: interactions between protein kinase C and interleukin 1 beta

Activation of protein kinase C with phorbol esters stimulates prostaglandin (PG) biosynthesis in many cell types whereas down-regulation of protein kinase C can suppress stimulatory responses. Interleukin-1 beta (IL-1 beta) can stimulate PG production by intrauterine tissues and may play a significant part in the mechanisms of preterm labor associated with intrauterine infection. Hence we have evaluated the effects of staurosporine and H7 (inhibitors of protein kinase C) on IL-1 beta stimulation of amnion, chorion and decidual prostaglandin E2 (PGE2) production. Staurosporine and H7 alone were without effect on PGE2 production by any cell type. However with minor exceptions both protein kinase C inhibitors enhanced the stimulatory actions of IL-1 beta on PGE2 production by all three cell types. Hence we believe that protein kinase C is closely linked to the regulation of intrauterine PG biosynthesis and that these links may have multiple layers of complexity.

Fetal fibronectin in patients at increased risk for premature birth

OBJECTIVE

The objective of this study was to evaluate fetal fibronectin as a screening test for subsequent preterm birth in asymptomatic pregnant women.

STUDY DESIGN

Eighty-seven pregnant women at increased risk for preterm birth underwent weekly sampling of cervicovaginal secretions beginning in the middle of the second trimester and continuing until delivery or until 34 weeks of gestation, with quantitative measurement for fetal fibronectin. In addition, assessment of cervical dilatation, uterine activity, and tocolytic therapy was performed with each sampling. Preterm birth was the specific outcome measured, and the correlation of fetal fibronectin with this outcome was determined.

RESULTS

Overall, 31% of the patients experienced a spontaneous preterm birth. As a predictor for delivery before 37 completed weeks of gestation, the presence of fetal fibronectin had a sensitivity of 92.6%, a specificity of 51.7%, a positive predictive value of 46.3%, and a negative predictive value of 93.9%. For delivery before 34 weeks, fetal fibronectin had a sensitivity of 92.3% and a negative predictive value of 97.8%. By means of logistic regression analysis a positive fetal fibronectin result was highly significantly correlated with preterm birth (odds ratio 3.8, p < 0.001) and more so than the presence of four or more uterine contractions per hour, tocolytic therapy, or cervical dilatation of > or = 2 cm. The addition of contractions, tocolytic therapy, or cervical dilatation to a positive fetal fibronectin result did not increase the predictive capacity of a positive fetal fibronectin alone.

CONCLUSION

Fetal fibronectin in the cervicovaginal secretions of asymptomatic patients has potential value as a screening test in the identification of patients at risk for preterm birth. This test had equally high sensitivity and negative predictive value for birth before 37 weeks.

Tumor necrosis factor alpha stimulates amnion prostaglandin biosynthesis primarily via an action on fatty acid cyclooxygenase

The purpose of this study was to determine how tumor necrosis factor alpha (TNF alpha) stimulates prostaglandin E2 production in human amnion. Amnion cells were isolated from term placentae and grown to confluence in culture. Incubations were conducted in quadruplicate wells for 16 hours with TNF alpha and protein synthesis inhibitors cycloheximide and actinomycin D, or arachidonic acid, acetylsalicylic acid (ASA), or staurosporine or H7 which inhibit protein kinase C activity. Prostaglandin E2 (PGE2) was measured by radioimmunoassay and cellular protein determined. The stimulatory action of TNF alpha on amnion PGE2 production was blocked by protein synthesis inhibitors, and the addition of arachidonic acid always enhanced the stimulatory properties of TNF alpha. TNF alpha consistently induced more rapid recovery from ASA treatment, and protein kinase C inhibition attenuated the stimulatory effects of TNF alpha. These results suggest that the stimulatory action of TNF alpha on amnion PGE2 production is likely at the level of induction of fatty acid cyclooxygenase activity and is partially dependent upon activation of protein kinase C.

Metabolism of arachidonic acid by caruncular and allantochorionic tissues in cows with retained fetal membranes (RFM)

The metabolism of arachidonic acid (AA) by caruncular and allantochorionic tissues and its regulation was studied in normal cows (n = 13) and those with retained fetal membranes (RFM; n = 9). Tissues were taken via the vagina about 6 hours postpartum and incubated for 6 hours in minimum essential medium containing tritiated AA alone or in the presence of oxytocin, platelet activating factor (PAF), epidermal growth factor (EGF) or ionophore calcium (A23187). The metabolites of AA were separated by reverse phase-high pressure-liquid chromatography. Tissue concentrations of prostaglandin F2 alpha (PGF2 alpha) and prostaglandin E2 (PGE2) and plasma 13,14-dihydro-15-keto-PGF2 alpha (PGFM) concentration were also measured by radioimmunoassay. For caruncular tissue, less thromboxane B2 (TXB2) and more 6-keto prostaglandin F1 alpha (PGIM) was synthesized in tissue from the animals with RFM than in the controls. Oxytocin, PAF, EGF and A23187 increased only PGIM production in the control animals; A23187 also decreased TBX2 synthesis. For the allantochorion, more PGE2, leukotriene B4 (LTB4) and PGIM and less TXB2, PGF2 alpha and hydroxyecosatetranoic acids (HETE) was synthesized in tissue from cows with RFM than from animals that delivered normally. All of the substances used in this study increased PGIM, PGF2 alpha and LTB4 and decreased TXB2 production by the allantochorionic tissue in control animals. The metabolism of AA by the allantochorionic tissue seems quantitatively under hormonal control. The metabolism of AA at the level of both maternal and fetal components of the placenta in cows with RFM differed from that seen in animals that expelled the membranes normally.