Murray D. Mitchell

Infection and labor. IV: Cachectin-tumor necrosis factor in the amniotic fluid of women with intraamniotic infection and preterm labor

A growing body of evidence supports a causal link between subclinical intrauterine infection and preterm labor. The mechanisms responsible for the onset of parturition in this setting have not been elucidated. The conventional view has been that bacterial products increase prostaglandin biosynthesis by intrauterine tissues and this, in turn, leads to the onset of labor. An alternative or complementary mechanism is that microbial products activate the host monocyte-macrophage system and that cytokines released during this process signal the initiation of parturition by stimulating prostaglandin biosynthesis by intrauterine tissues. This study was conducted to determine if cachectin-tumor necrosis factor is present in the amniotic fluid of women with intraamniotic infection and whether this cytokine can alter the rate of prostaglandin biosynthesis by intrauterine tissues. Amniotic fluid from 54 women was assayed for tumor necrosis factor. Tumor necrosis factor was not detectable in the amniotic fluid of women without intraamniotic infection regardless of the presence or absence of term or preterm labor. On the other hand, the amniotic fluid of 11 of 15 women with preterm labor and intraamniotic infection had measurable tumor necrosis factor. This cytokine stimulated prostaglandin E2 biosynthesis by amnion cells in monolayer culture in a dose-dependent fashion. These data support the concept that macrophage activation is involved in the onset of human parturition in the setting of infection. We propose that the host (fetus and/or mother) signals the onset of parturition through the secretion of inflammatory cytokines released in response to bacterial invasion.

Immunoglobulin G fractions from patients with antiphospholipid antibodies cause fetal death in BALB/c mice: A model for autoimmune fetal loss

We determined whether purified immunoglobulin G from patients with antiphospholipid antibodies causes fetal loss in pregnant mice. Sera were obtained from nonpregnant parous women (group 1) and nonpregnant women with antiphospholipid antibodies and a history of fetal loss (group 2). Pregnant BALB/c mice were given an intraperitoneal injection of 15 mg of IgG on day 8 of pregnancy. Typically, mice treated with IgG from antiphospholipid antibodies aborted within 48 hours. When animals were sacrificed on days 9 to 15, the uterus of each animal was inspected for the presence of live, dead, or resorbing fetuses. In contrast to mice injected with control IgG or saline solution, each mouse injected with IgG from antiphospholipid antibodies aborted and no live fetuses were found (p less than 0.05). Histologic examination of the uteroplacental interface showed decidual necrosis in the mice treated with IgG containing antiphospholipid antibodies, and immunofluorescent studies also showed prominent intravascular decidual IgG and fibrin deposition. We conclude that IgG from antiphospholipid antibodies of women with fetal loss causes fetal loss in BALB/c mice. It appears that the fetal loss is mediated by IgG binding in the maternal decidual vasculature.

Interleukin-1 stimulates prostaglandin biosynthesis by human amnion

The purpose of these studies was to determine if Interleukin-1 (IL-1) alters the rate of prostaglandin biosynthesis by human amnion. Primary monolayer cultures of amnion cells were established from women undergoing elective cesarean section before the onset of labor. Natural purified and recombinant human IL-1 alpha and IL-1 beta were incubated with amnion cells in culture, and prostaglandin E2 (PGE2) biosynthesis was measured by radioimmunoassay in cell-free media. A concentration-dependent increase in PGE2 production by amnion cells occurred in response to natural purified and recombinant IL-1 preparations. No differences in the parameters of the dose-response curves between the two IL-1 gene products could be determined (p greater than 0.05). Indomethacin blocked the effect of IL-1 in prostaglandin biosynthesis by human amnion. Interleukin-1, a fever mediator, could serve as a signal for the initiation of labor in cases of intrauterine or systemic infection.

Interleukin-6 stimulates prostaglandin production by human amnion and decidual cells

The effects of interleukin-6 on prostaglandin production by cells from two key sources on intrauterine prostaglandin, i.e. amnion and decidua, have been evaluated. Interleukin-6 induced a concentration-related increase in prostaglandin production by amnion and decidual cells. The concentrations of interleukin-6 required for this stimulatory action are within the range measured in amniotic fluid of women with intrauterine infections and preterm labor. Hence, interleukin-6 may contribute to the mechanism of preterm labor under these conditions.

Prostaglandin biosynthesis by human decidual cells: Effects of inflammatory mediators

There is substantial evidence that decidual activation, in association with infection, is linked with the onset of both preterm and term labor. We therefore undertook the present study to evaluate prostaglandin production and its potential regulation by inflammatory mediators in human decidual cells in primary monolayer culture. Upon attaining confluence, the cells were incubated with endotoxin, interleukin 1 alpha (IL1 alpha), interleukin 1 beta (IL1 beta); or tumor necrosis factor (TNF). Production of prostaglandin (PG) E2 and PGF2 alpha was determined using specific radioimmunoassays. Endotoxin and these cytokines all induced significant concentration-dependent increases in PGE2 and PGF2 alpha production. Our results suggest that term human decidual cells are responsive to endotoxin and cytokines and that generation of these substances in the decidua or nearby (eg. in response to infection) will lead to increased prostaglandin production and uterine contractions.

Maternal plasma level of endothelin is increased in preeclampsia

Endothelin is a potent vasoconstrictor that is reportedly increased in conditions characterized by endothelial damage. Maternal plasma endothelin levels were compared between 27 women with preeclampsia (23 without and 4 with the hemolysis, elevated liver enzymes, and low platelet count syndrome) and 14 women with normotensive pregnancies. The mean +/- SEM plasma endothelin values were significantly higher in patients with preeclampsia uncomplicated by the hemolysis, elevated liver enzymes, and low platelet count syndrome (5.48 +/- 0.30 fmol/ml vs 3.86 +/- 0.28, p less than 0.001). In addition, the preeclamptic group with the hemolysis, elevated liver enzymes, and low platelet count syndrome had significantly higher endothelin levels than those without the syndrome (8.30 +/- 1.62 fmol/ml vs 5.48 +/- 0.30, p less than 0.05). There was no correlation between plasma endothelin values and either systolic or diastolic blood pressure. We conclude that plasma endothelin levels are significantly increased in women with preeclampsia and particularly in those with the hemolysis, elevated liver enzymes, and low platelet count syndrome, suggesting an association with widespread endothelial damage.

Cytokine abundance in placental tissues: Evidence of inflammatory activation in gestational membranes with term and preterm parturition ☆ ☆☆ ★

OBJECTIVES This study of the changes in cytokine concentrations in gestational tissues from women with term and preterm labor was undertaken to assess the extent of inflammatory activation associated with spontaneous labor and delivery. STUDY DESIGN Extracts of amniotic, chorionic-decidual, and placental tissues from women delivered at term before labor (n = 15), at term after labor (n = 15), and preterm (n = 31) were assayed for interleukin 1beta, interleukin 6, and interleukin 8. RESULTS In amniotic tissues of women delivered by spontaneous labor at term the median interleukin-6, interleukin-8, and interleukin-1beta concentrations were 3.8 to 5.4 times those of tissues from women delivered at term without labor (P <.05, Mann-Whitney U test). Interleukin-6 and interleukin-8 concentrations were also significantly increased (3. 3-4 times) in chorionic-decidual tissues. Marked increases (approximately 3-6 times) in the concentrations of all 3 cytokines were observed in both amniotic and chorionic-decidual tissues from women with preterm deliveries with respect to those from women with term deliveries after labor. Cytokine concentrations were significantly correlated within amniotic tissues from both women with term delivery after labor and women with preterm delivery and also in preterm chorionic-decidual tissues but not preterm placental tissues. Concentrations of cytokines in the tissues of women delivered preterm were not significantly affected by mode of delivery, treatment with antibiotics, or twin birth. In preterm tissues with evidence of intrauterine infection only amniotic interleukin-1beta concentrations were significantly elevated (P <. 05). Little or no labor-related change in cytokine concentrations was seen within placental tissues. CONCLUSIONS Increased cytokine abundance in gestational membranes associated with labor supports the view that an inflammatory process is involved in both term and preterm labor. This process does not, however, appear to be evident in the villous placenta.

Prostaglandin concentrations in amniotic fluid of women with intra-amniotic infection and preterm labor

This study was undertaken to examine the effects of intrauterine infection and preterm labor on the amniotic fluid concentrations of prostaglandins in women with premature rupture of the membranes. Amniotic fluid was obtained from four groups of patients with premature rupture of the membranes: group 1, patients without labor or infection; group 2, patients with labor but without infection; group 3, patients with an intra-amniotic infection but without labor; group 4, patients with both infection and labor. Prostaglandins E2 and F2a were measured by radioimmunoassays. Preterm labor, in the absence of infection, was not associated with significant increases in amniotic fluid concentrations of prostaglandins. Women with preterm labor and intra-amniotic infections had higher amniotic fluid concentrations of prostaglandins than women with preterm labor in the absence of infection or women with intra-amniotic infection in the absence of labor. These observations are compatible with the participation of prostaglandins in the mechanisms of onset of preterm labor associated with intra-amniotic infection.

Transfer of bisphenol A across the human placenta

OBJECTIVE The objective of the investigation was to study placental transfer and conjugation of bisphenol A (BPA) across the human placenta. STUDY DESIGN Human placentae obtained from healthy term singleton pregnancies were utilized in a dual recirculating model of ex vivo placental perfusion. Seven placentae were perfused with BPA (10 ng/mL) added to the maternal perfusate for 180 minutes. Antipyrine and fluorescein isothiocyanate dextran were used as positive and negative controls, respectively, to validate integrity of the circuits. Concentrations of BPA and its conjugates were determined by liquid chromatography-mass spectrometry. RESULTS The transfer percentage for antipyrine and BPA were 25.5 +/- 1.13% and 27.0 +/- 1.88%, respectively, and the transfer index for BPA was 1.1 +/- 0.09 after 180 minutes of perfusion. Only 3.2 +/- 1.6% of BPA in the fetal compartment was in the conjugated form. CONCLUSION Bisphenol A at low environmentally relevant levels can transfer across the human placenta, mainly in active unconjugated form.

Bacterial endotoxin and tumor necrosis factor stimulate prostaglandin production by human decidua

The purpose of these studies was to determine the effect of bacterial endotoxin and tumor necrosis factor (TNF) on prostaglandin (PG) secretion by human decidua. Decidual explants were established from women undergoing elective cesarean sections before the onset of labor. Escherichia Coli endotoxin and purified human recombinant TNF (rh TNF) were incubated with decidual explants. PGF2 alpha and PGE2 biosynthesis was measured by radioimmunoassay. A significant increase in the release of all PGs into the media occurred in response to LPS and TNF. In the setting of an extraamniotic infection, bacterial and host secretory products (TNF) could trigger the onset of labor, activating the decidua to produce PGs.