Failure of Endotoxin to Cross the Chorioamniotic Membranes in Vitro

Abstract

We have previously reported the detection of endotoxin in the amniotic fluid of patients with gram-negative intra-amniotic infection. Endotoxin or lipopolysaccharide (LPS) is a potent biologic product capable of inducing prostaglandin release from several cell types, and therefore may be involved in the onset of human parturition in the setting of intra-amniotic infection. The experiments outlined in this report were designed to determine whether endotoxin crosses chorioamniotic membranes in vitro. Chorioamniotic membranes obtained at the time of elective cesarean section were placed in Ussing chambers used for transport experiments. Endotoxin was placed in one chamber, and serial timed samples were taken from both chambers for endotoxin quantification, which was performed with the limulus amebocyte gel clot assay. Blue dextran was used to exclude the presence of large defects. Bromophenol blue was used to demonstrate membrane permeability to low-molecular weight substances. Endotoxin failed to cross the chorioamniotic membranes in all experiments (n = 11).

Prevention of Inflammatory Activation of Human Gestational Membranes in an Ex Vivo Model Using a Pharmacological NF-κB Inhibitor

“…This response occurs in the constituent cells that comprise the tissues without the requirement for leukocyte recruitment and activation. Since LPS does not cross the membranes to any significant extent (16), this implies that amniotic fluid cytokine concentrations can be increased in response to decidual activation, presumably via a paracrine cascade of mediators released within the various layers of the membranes leading to secretion from the amnion into the amniotic cavity. This finding may illuminate how elevated fetal cytokine levels and fetal inflammatory response syndrome can occur even in the absence of any identifiable pathogen in fetal fluids.…”

“…Under these circumstances, it is likely that detrimental fetal responses occur primarily in response to exposure to elevated cytokine concentrations, rather than to direct exposure to the pathogen (14,15). Since the membranes present an effective barrier to endotoxin and most cytokines (16,17), the source of cytokines in amniotic fluid is presumed to be the fetal membranes or fetal leukocytes.…”

Endotoxin-Neutralizing Antimicrobial Proteins of the Human Placenta

“…Recent studies suggest that the amnion epithelial cell monolayer may provide an effective barrier against entry of microbial pathogens to the nutrient-rich amniotic fluid (64), and may partially explain why the rate of amniotic fluid infections associated with chorioamnionitis is not higher (65,66). Moreover, bacterial LPS fails to cross the chorioamniotic membranes, possibly due to the presence of LPS-binding proteins (67). We speculate, therefore, that the failure of both microbial pathogens and bacterial LPS to cross the placental membranes may be attributed in part to the antimicrobial and endotoxin-neutralizing potential of histone H2A and H2B proteins coating the epithelial surface of the placenta.…”

Effect of Salmonella Endotoxin Administered to the Pregnant Sheep at 133–142 Days Gestation on Fetal Oxygenation, Maternal and Fetal Adrenocorticotropic Hormone and Cortisol, and Maternal Plasma Tufnor Necrosis Factor α Concentrations1

“…It is uncertain whether endotoxins in the maternal system reach the fetus since there is little information available concerning movement of endotoxin across the placenta in any species. 32 p_ Labeled E. coli endotoxin was shown to cross the placenta of the rabbit [34,35], but in vitro studies using human chorioamnionic membranes failed to detect movement of LPS across fetal membranes [36]. It has also been shown that the fetus is generally less sensitive to LPS than is the adult [37].…”