Ultrastructure of Human Placental Tissue After 6h of Normoxic and Hypoxic Dual In Vitro Placental Perfusion

LPS from bovine serum albumin drives TNF-α release during ex-vivo placenta perfusion experiments, contaminates the perfusion system but can be effectively removed by oxidative cleaning

INTRODUCTION

The dual ex-vivo perfusion of human placental tissue is useful to study inflammatory pathways. We found significant TNF-α release in negative controls similar in concentration to lipopolysaccharide (LPS) stimulated placentas. The aim of the current study was to (i) identify sources driving TNF-α release and (ii) develop an approach to control for it.

METHOD

(i) To determine sources leading to TNF-α release, solutions frequently circulated through the perfusion system and perfusion media with different bovine serum albumin (BSA) quality were exposed to mouse macrophage cell lines (RAW264.7) and subsequently measured for TNF-α expression. (ii) To assess memory effects and validate cleaning procedures, sham perfusion experiments were conducted either in the presence or absence of exogenous LPS, in new tubing that was contaminated, cleaned and analyzed for the effectiveness of LPS removal. Oxidative and acid-base cleaning were tested for their effectiveness to reduce LPS contamination.

RESULTS

TNF-α release, observed in negative control experiments, was attributed to the use of LPS-contaminated BSA as well as inadequate cleaning of the perfusion system. Once introduced in the perfusion system, LPS accumulated and created a memory effect. Oxidative but not acid-base depyrogenation effectively reduced LPS levels to concentrations that were in accordance with FDA guidelines (<0.5 EU/mL) for medical equipment redeemed appropriate for re-use.

DISCUSSION

LPS contamination of the placenta perfusion model could have confounding effects on experimental outcomes leading to misinterpretation of data. To circumvent LPS contamination LPS-free BSA and oxidative depyrogenation cleaning techniques should be implemented in future placental perfusion studies.

Pathologic evaluation of normal and perfused term placental tissue

This study reports for the 1st time the incidence and interobserver variation of morphologic findings in a series of 34 term placentas from pregnancies with normal outcome used for perfusion studies. Histologic evaluation of placental tissue is challenging, especially when it comes to defining "normal tissue" versus "pathologic lesions." A scoring system for registration of abnormal morphologic findings was developed. Light microscopic examination was performed independently by 2 pathologists, and interobserver variation was analyzed. Findings in normal and perfused tissue were compared and selected findings were tested against success parameters from the perfusions. Finally, the criteria for frequent lesions with fair to poor interobserver variation in the nonperfused tissue were revised and reanalyzed. In the perfused tissue, the perfusion artefact "trophoblastic vacuolization," which is believed to represent dilated transtrophoblastic channels, was reproducible and significantly correlated to the perfusion marker "fetal leakage." In longer perfusions, microscopy of the perfused cotyledon revealed bacteria in the fetal vessels. This finding led to an adjustment in the perfusion protocol with addition of antibiotics to the medium. In the "normal" tissue, certain lesions were very frequent and showed only fair or poor interobserver agreement. Revised minimum criteria for these lesions were defined and found reproducible. This study has emphasized the value of pathologic examination as a supplement in placental perfusion models. Examination of the perfused cotyledon for trophoblastic vacuolization is recommended as an additional quality marker in perfusion models. The study also underlines the need for exact definitions of abnormality in frequent placental lesions.

Placental syncytiotrophoblast maintains a specific type of glycocalyx at the fetomaternal border: the glycocalyx at the fetomaternal interface in healthy women and patients with HELLP syndrome

Recent studies showed that considerable amounts of glycosaminoglycans are released into maternal blood during normal pregnancy and in hemolysis, elevated liver enzymes, and low platelets (HELLP) syndrome. Maternal endothelia and the syncytiotrophoblast layer have been discussed as a possible origin of these glycocalyx components. Our study aimed to visualize the glycocalyx on the syncytiotrophoblast by electron microscopy, to analyze its structure and composition by immunohistochemistry, and to determine potential differences between healthy women and women with HELLP syndrome. For electron microscopy, a cotyledon was fixed by perfusion of the intervillous space with a 2% lanthanum-nitrate glutaraldehyde solution followed by immersion fixation in the same fixative. For immunohistochemistry, sections of 16 placentas (HELLP patients/healthy women, n = 8 each) were stained with monoclonal antibodies against the main glycocalyx constituents syndecan 1, hyaluronic acid, and heparan sulfate. Semiquantitative evaluation of staining intensity focused on the apical surface of the syncytiotrophoblast and fetal intravillous endothelia as possible localizations of a placental glycocalyx. Electron microscopy revealed a glycocalyx of approximately 250 nm, covering the syncytiotrophoblast layer. This was found to contain large amounts of syndecan 1, but neither hyaluronic acid nor heparan sulfate as major components. Intravillous fetal endothelium did not express any of the investigated glycosaminoglycans. Healthy women and patients with HELLP showed no differences concerning glycocalyx composition and thickness of the syncytiotrophoblast. The composition of the "placental" glycocalyx differs from the adult and fetal vascular glycocalyx. Obviously, the human placental syncytiotrophoblast maintains a special kind of glycocalyx at the fetomaternal interface.

Reactivity of blood vessels in response to prostaglandin E2 in placentas from pregnancies complicated by fetal growth restriction

OBJECTIVE

The authors aimed to study the contractility responses of normal and fetal growth restriction (FGR) placentas to prostaglandin E(2) (PGE(2) ) and to correlate the results to subsequent placental histological analysis.

METHOD

A dual-perfused single cotyledon model was used. Placentas from pregnancies complicated by FGR and from normal pregnancies were obtained. Selected cotyledons were cannulated and dually perfused. Following stabilization, three concentrations of PGE(2) (0.05, 0.1, and 0.15 mg/mL) were administered to the fetal arterial side causing contraction/relaxation response. Fetal perfusion pressure was measured continuously during these contraction and relaxation phases. Following the perfusion experiments, the placentas were analyzed for fetal or maternal origin vascular lesions.

RESULTS

A total of 21 complete experiments were performed (16 normal, 5 FGR). In response to PGE(2) , FGR placentas exhibited lower change in the perfusion pressure and lower relaxation time constant. Basal perfusion pressure did not differ significantly between the two groups. Placental histopathology lesions, fetal or maternal origin, were more common in the FGR compared with the controls placentas, 80% versus 25%, respectively, P=  0.047.

CONCLUSIONS

The lower vascular reactivity in response to PGE(2) and the presence of fetal and maternal vascular placental lesions suggest a mechanism explaining the altered vascular supply in FGR.

Adapting in vitro dual perfusion of the human placenta to soluble oxygen tensions associated with normal and pre-eclamptic pregnancy

For decades, superoxic ex vivo dual perfusion of the human placental lobule has been used as a model to study the physiology and metabolism of the placenta. The aim of this study was to further develop the technique to enable perfusion at soluble oxygen concentrations similar to those in normal pregnancy (normoxia) and in pre-eclampsia (PE; hypoxia). Our design involved reducing the mean soluble oxygen tension in the maternal-side intervillous space (IVS) perfusate to 5-7% and <3% for normoxia and hypoxia, respectively, while providing a more ubiquitous delivery of perfusate into the IVS, using 22 maternal-side cannulae. We achieved quasi-steady states in [O₂](fetal venous (soluble)), which were statistically different between the two adaptations at t=150 to t=240 min of dual perfusion (2.1, 1.2, 2.8 and 0.4, 0.0, 1.5%; median, 25th, 75th percentiles, n=20 and 24 readings in n=5 and n=6 lobules, normoxic and hypoxic perfusion, respectively; P<0.001, Mann-Whitney U-test). Lactate dehydrogenase (LDH) levels in fetal and maternal venous outflow perfusates were unaffected by the adaptations. There was also no difference in tissue lactate release between the two adaptations. Glucose consumption from the fetal circulation and maternal-side 'venous' pyruvate release were higher under normoxic conditions, indicative of a greater metabolic flux through glycolysis. Furthermore, there was greater release of the hypoxic-sensitive marker, macrophage inflammatory protein-1α, into the maternal venous perfusate in the hypoxic model. Also, during hypoxic perfusion, we found that fetal-side venous placental growth factor (PlGF) levels were higher compared with normoxic perfusion. We conclude that these ex vivo adapted methods of placental perfusion provide a means of studying aspects of placental metabolism in relation to normal oxygenation and hypoxia-associated pregnancy disease.

In Vitro Models Using the Human Placenta to Study Fetal Exposure to Drugs

Over the recent years there has been a gradual rise in the use of pharmaceuticals during pregnancy. Knowledge on placental drug transfer and metabolism has increased during the past decades as well. Investigation of the transplacental transfer of any therapeutically useful drug is essential to the understanding of its metabolic processes and is a prerequisite for its use during pregnancy. The purpose of this review is to give insight on the various techniques that have been developed to evaluate transplacental transfer of drugs and xenobiotics.