Prostaglandin endoperoxide H synthase type 1 and type 2 messenger ribonucleic acid in human fetal tissues throughout gestation and in the newborn infant

Inflammation-induced preterm lung maturation: lessons from animal experimentation

Intrauterine inflammation, or chorioamnionitis, is a major contributor to preterm birth. Prematurity per se is associated with considerable morbidity and mortality resulting from lung immaturity but exposure to chorioamnionitis reduces the risk of neonatal respiratory distress syndrome (RDS) in preterm infants. Animal experiments have identified that an increase in pulmonary surfactant production by the preterm lungs likely underlies this decreased risk of RDS in infants exposed to chorioamnionitis. Further animal experimentation has shown that infectious or inflammatory agents in amniotic fluid exert their effects on lung development by direct effects within the developing respiratory tract, and probably not by systemic pathways. Differences in the effects of intrauterine inflammation and glucocorticoids demonstrate that canonical glucocorticoid-mediated lung maturation is not responsible for inflammation-induced changes in lung development. Animal experimentation is identifying alternative lung maturational pathways, and transgenic animals and cell culture techniques will allow identification of novel mechanisms of lung maturation that may lead to new treatments for the prevention of RDS.

The Promise of Prostaglandins: Have They Fulfilled Their Potential as Therapeutic Targets for the Delay of Preterm Birth?

OBJECTIVE

The elucidation some 30 years ago by Sir Mont Liggins that the activation of the hypothalamic-pituitary-adrenal-placental axis in fetal sheep led to elevated maternal prostaglandin (PG) concentrations and the initiation of labor provided hope that targeting PG synthesis or action would lead to effective tocolysis and lowering of the human preterm birth rate. This was the "promise of PGs."

METHODS AND RESULTS

Although early trials showed that nonsteroidal anti-inflammatory drugs (NSAIDs), which inhibit PG H synthase (PGHS), delayed preterm birth by 48 hours, other trials revealed an association between NSAIDs and adverse fetal effects, including oligohydramnios, patent ductus arteriosus, necrotizing enterocolitis, intraventricular hemorrhage, and persistent pulmonary hypertension of the newborn (PPHN). Hope was revived when studies in the mid 1990s demonstrated that much of the PGs synthesized by intrauterine tissues at preterm labor were derived from the inducible isoenzyme PGHS-2. Unfortunately, administration of specific PGHS-2 inhibitors led to the same adverse fetal effects displayed by the mixed PGHS-1 and -2 NSAIDs, causing interest in the promise of PGs to wane. This led to the development of new strategies for specific PG inhibition or antagonism. One of these is the application of a specific PGF2alpha receptor blocker, Theratechnologies (THG)113.31. THG113.31 decreases the in vitro contractile activity of mouse, sheep, and human myometrium in response to exogenous PGF2alpha, delays lipopolysaccharide (LPS)-induced preterm birth in mice, and lowers uterine electromyographic activity and delays preterm birth in sheep administered RU486. There have been no observable maternal or fetal side effects with its use.

CONCLUSION

By developing new strategies based on other therapeutic targets, the promise of PGs may once again offer hope for delaying preterm birth.

Effects of intrauterine infection or inflammation on fetal lung development

1. Intrauterine infection or inflammation is common in cases of preterm birth. Preterm infants are at risk of acute respiratory distress as a result of lung immaturity; evidence of exposure to infection and/or inflammation before birth is associated with a reduced risk of neonatal respiratory distress syndrome (RDS). Experimentally induced intrauterine inflammation or infection in sheep causes a precocious increase in pulmonary surfactant in the preterm lungs that improves preterm lung function, consistent with the reduced risk of RDS in human infants exposed to infection and/or inflammation before birth. 2. The effects of intrauterine inflammation on fetal lung development appear to result from direct action of proinflammatory stimuli within the lungs rather than by systemic signals, such as the classical glucocorticoid-mediated lung maturation pathway. However, paracrine and/or autocrine production and/or metabolism of glucocorticoids in fetal lung tissue may occur as a result of inflammation-induced changes in the expression of 11β-hydroxysteroid dehydrogenase (types 1 and 2). 3. Likely candidates that mediate inflammation-induced surfactant production by the preterm lung include prostaglandin E₂ and/or other arachidonic acid metabolites. Intrauterine inflammation induces the expression of enzymes responsible for prostaglandin production in fetal lung tissue. Inhibition of prostaglandin production prevents, at least in part, the effects of inflammation on fetal lungs. 4. Our experiments are identifying mechanisms of surfactant production by the preterm lungs that may be exploited as novel therapies for preventing respiratory distress in preterm infants. Elucidation of the effects of inflammation on the fetal lungs and other organs will allow more refined approaches to the care of preterm infants exposed to inflammation in utero.

Antiprostaglandin Drugs

Prostaglandins create conditions favorable for activation and stimulation of labor and are key components in the process of both normal and preterm labor. Antiprostaglandins may be useful in the prevention of preterm labor because they inhibit prostaglandin synthetase and reduce prostaglandin formation. The antiprostaglandin indomethacin has been the most studied as a tocolytic agent, but its success is limited because of fetal and neonatal complications associated with prolonged use. More recently, the cyclooxygenase-2 specific agents have been investigated because of their improved side effect profile. This article discusses the process of prostaglandin production and inhibition and reviews and critiques the available literature investigating the efficacy and safety of indomethacin and the newer cyclooxygenase-2 agents.

Delay of preterm birth in sheep by THG113.31, a prostaglandin F2alpha receptor antagonist

OBJECTIVE

A novel prostaglandin F2alpha receptor antagonist, THG113.31, was tested for the suppression of uterine contractility and delay of preterm labor in sheep.

STUDY DESIGN

We determined the tocolytic effectiveness of THG113.31 on contractions that were stimulated in vitro by prostaglandin F2alpha and E2 in longitudinal and circular myometrial strips. We also tested the ability of THG113.31 in vivo to lower uterine electromyographic activity that was induced by the progesterone receptor blocker, RU486, and to delay preterm birth.

RESULTS

THG113.31 suppressed the amplitude of prostaglandin F2alpha, but not prostaglandin E2-induced contractions of both circular and longitudinal myometrium (P<.01). The times to delivery after RU486 were 34.8+/-1.1 hours (saline solution) and 41.9+/-0.5 hours (THG113.31; P<.001) or an average delay of 7.1 hours. There were no changes in fetal blood gases (PaO2 , PaCO2 , pH, or SaO2) because of THG113.31. Fetal cortisol levels rose in each group, and fetal and maternal prostaglandin E2 and F2alpha metabolite concentrations rose similarly in both groups.

CONCLUSION

THG113.31 specifically suppresses prostaglandin F2alpha-induced myometrial contractility and delays delivery.

Cortisol infusion decreases renin, but not PGHS-2, EP2, or EP4 mRNA expression in the kidney of the fetal sheep at days 109-116

Renal prostaglandins (PG), renin, and cortisol are necessary for normal kidney development and function during fetal life. We examined the effects of cortisol infusion before completion of nephrogenesis (d 109-116 gestation; 2.0-3.0 mg hydrocortisone succinate/24 h) on the renal mRNA expression of PGHS-2, the PGE(2) receptors, EP(2) and EP(4), and renin in fetal sheep. Cortisol infusion raised plasma cortisol levels to 42.8 +/- 6.0 nmol/L compared with saline infusion levels of 1.5 +/- 0.5 nmol/L (p < 0.001), but had no effect on fetal body weight, proportional kidney mass, or blood gases. Cortisol decreased significantly the relative expression of renin mRNA (saline: 0.93 +/- 0.06 units; cortisol: 0.32 +/- 0.03 units, p < 0.05), however it had no effect upon the expression of PGHS-2, EP(2), or EP(4) mRNA in fetal sheep kidney. Although there is substantial evidence that PGE(2) acting through either the EP(2) or EP(4) receptor stimulates renin synthesis in the adult kidney, our results have demonstrated that before the completion of nephrogenesis, cortisol down-regulation of renin mRNA expression is independent of any change in the expression of PGHS-2, EP(2), or EP(4) mRNA expression. During nephrogenesis, the insensitivity of PGHS-2, EP(2), and EP(4) expression to down-regulation by cortisol may permit continued PG regulation of renal development and urine formation.

Prostaglandin endoperoxide H synthase inhibitors and other tocolytics in preterm labour

Preterm delivery (<37 weeks of gestation) is the major obstetrical complication in developed countries, yet attempts to delay labour and prolong pregnancy have largely been unsuccessful. One of the many reasons it is so difficult to prevent preterm birth is that the nature of preterm labour changes as a function of gestational age, maternal lifestyle factors or infection, to list a few of the reasons. The inhibitors of prostaglandin endoperoxide H synthase (PGHS), known as the Non-steroidal Antiinflammatory Drugs, have been viewed with interest as tocolytics with promising effectiveness under most conditions of preterm labour. Three isoforms of PGHS exist; the first two, PGHS-1 and -2, have been studied for their catalytic activity, X-ray crystallographic structure, and physiological roles in the adult and the foetus. Mixed inhibitors and isoform-specific inhibitors of PGHS have been developed, and their roles in delaying preterm labour are examined and compared to other tocolytics.

Bacterially-induced preterm labor and regulation of prostaglandin-metabolizing enzyme expression in mice: the role of toll-like receptor 4

Toll-like receptor 4 (TLR-4) is a critical mediator of the cellular response to lipopolysaccharide. Our purpose was to examine the role of TLR-4 in parturition and in the regulation of expression of prostaglandin synthase (cyclooxygenase [COX]-1 and COX-2) and 15-hydroxyprostaglandin dehydrogenase (PGDH) following exposure to heat-killed Escherichia coli (HKE) in pregnant mice. Inbred TLR-4-mutant C3H/HeJ mice and inbred normal C3HeB/FeJ mice on Day 14.5 of a 19- to 20-day gestation received intrauterine injection of either HKE or sterile vehicle (PBS). Preterm or term delivery was recorded for these animals. Tissues (myometrium, decidual caps, placentas, fetal membranes, and fetuses) were collected after injection of sterile vehicle or 5 x 109 HKE bacteria (n = 5 mice per strain per treatment per time point). The COX-1, COX-2, and PGDH gene expression was determined by semiquantitative reverse transcription-polymerase chain reaction. We found that 5 x 109 HKE induced preterm delivery in 100% of TLR-4-normal mice but in 0% of TLR-4-mutant mice. The HKE exposure up-regulated expression of COX-2, but not of COX-1, in maternal tissues in both mouse strains. The prostaglandin-catabolizing enzyme PGDH was down-regulated in myometrium, fetal membranes, and fetuses in control mice, but no change was observed in TLR-4-mutant mice after HKE treatment. These results demonstrate that a functional TLR-4 is essential for HKE-induced preterm labor and PGDH down-regulation but is not essential for HKE-induced COX-2 gene up-regulation. The TLR-4 may mediate bacterially induced preterm labor via regulation of prostaglandin degradation rather than prostaglandin synthesis.