A stereologic study of postmature placentas fixed by dual perfusion

Gestation-Specific Changes in the Anatomy and Physiology of Healthy Pregnant Women: An Extended Repository of Model Parameters for Physiologically Based Pharmacokinetic Modeling in Pregnancy

BACKGROUND

In the past years, several repositories for anatomical and physiological parameters required for physiologically based pharmacokinetic modeling in pregnant women have been published. While providing a good basis, some important aspects can be further detailed. For example, they did not account for the variability associated with parameters or were lacking key parameters necessary for developing more detailed mechanistic pregnancy physiologically based pharmacokinetic models, such as the composition of pregnancy-specific tissues.

OBJECTIVES

The aim of this meta-analysis was to provide an updated and extended database of anatomical and physiological parameters in healthy pregnant women that also accounts for changes in the variability of a parameter throughout gestation and for the composition of pregnancy-specific tissues.

METHODS

A systematic literature search was carried out to collect study data on pregnancy-related changes of anatomical and physiological parameters. For each parameter, a set of mathematical functions was fitted to the data and to the standard deviation observed among the data. The best performing functions were selected based on numerical and visual diagnostics as well as based on physiological plausibility.

RESULTS

The literature search yielded 473 studies, 302 of which met the criteria to be further analyzed and compiled in a database. In total, the database encompassed 7729 data. Although the availability of quantitative data for some parameters remained limited, mathematical functions could be generated for many important parameters. Gaps were filled based on qualitative knowledge and based on physiologically plausible assumptions.

CONCLUSION

The presented results facilitate the integration of pregnancy-dependent changes in anatomy and physiology into mechanistic population physiologically based pharmacokinetic models. Such models can ultimately provide a valuable tool to investigate the pharmacokinetics during pregnancy in silico and support informed decision making regarding optimal dosing regimens in this vulnerable special population.

Clarification and 3-D visualization of immunolabeled human placenta villi

We report here the successful 3D visualization of human placenta villous structures on the order of ∼1 mm³ by a combination of immunolabeling, rapid tissue clarification and laser scanning confocal microscopy. The resultant image sets exhibit a complex arrangement of villi and their contained vasculature that mirrors their arrangement in situ.

Bidirectional Transfer Study of Polystyrene Nanoparticles across the Placental Barrier in an ex Vivo Human Placental Perfusion Model

BACKGROUND

Nanoparticle exposure in utero might not be a major concern yet, but it could become more important with the increasing application of nanomaterials in consumer and medical products. Several epidemiologic and in vitro studies have shown that nanoparticles can have potential toxic effects. However, nanoparticles also offer the opportunity to develop new therapeutic strategies to treat specifically either the pregnant mother or the fetus. Previous studies mainly addressed whether nanoparticles are able to cross the placental barrier. However, the transport mechanisms underlying nanoparticle translocation across the placenta are still unknown.

OBJECTIVES

In this study we examined which transport mechanisms underlie the placental transfer of nanoparticles.

METHODS

We used the ex vivo human placental perfusion model to analyze the bidirectional transfer of plain and carboxylate modified polystyrene particles in a size range between 50 and 300 nm.

RESULTS

We observed that the transport of polystyrene particles in the fetal to maternal direction was significantly higher than for the maternal to fetal direction. Regardless of their ability to cross the placental barrier and the direction of perfusion, all polystyrene particles accumulated in the syncytiotrophoblast of the placental tissue.

CONCLUSIONS

Our results indicate that the syncytiotrophoblast is the key player in regulating nanoparticle transport across the human placenta. The main mechanism underlying this translocation is not based on passive diffusion, but is likely to involve an active, energy-dependent transport pathway. These findings will be important for reproductive toxicology as well as for pharmaceutical engineering of new drug carriers.

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.

Kinetics of silica nanoparticles in the human placenta

The potential medical applications of nanoparticles (NPs) warrant their investigation in terms of biodistribution and safety during pregnancy. The transport of silica NPs across the placenta was investigated using two models of maternal-foetal transfer in human placenta, namely, the BeWo b30 choriocarcinoma cell line and the ex vivo perfused human placenta. Nanotoxicity in BeWo cells was examined by the MTT assay which demonstrated decreased cell viability at concentrations >100 µg/mL. In the placental perfusion experiments, antipyrine crossed the placenta rapidly, with a foetal:maternal ratio of 0.97 ± 0.10 after 2 h. In contrast, the percentage of silica NPs reaching the foetal perfusate after 6 h was limited to 4.2 ± 4.9% and 4.6 ± 2.4% for 25 and 50 nm NPs, respectively. The transport of silica NPs across the BeWo cells was also limited, with an apparent permeability of only 1.54 × 10(-6) ± 1.56 × 10(-6) cm/s. Using confocal microscopy, there was visual confirmation of particle accumulation in both BeWo cells and in perfused placental tissue. Despite the low transfer of silica NPs to the foetal compartment, questions regarding biocompatibility could limit the application of unmodified silica NPs in biomedical imaging or therapy.

[Fetal and neonatal complications related to prolonged pregnancy]

OBJECTIVE

To evaluate fetal and neonatal outcomes related to prolonged pregnancy.

METHODS

This study is based on Pubmed search, Cochrane library and HAS recommendations.

RESULTS

The risk of fetal complications including macrosomia (6 %), oligohydramnios (10 %-15 %), abnormal fetal heart rate pattern and meconium-stained fluid is increased in prolonged pregnancy (≥ 41(+0) weeks). The rate of stillbirth was estimated between 1.6 ‰ and 3.0 ‰ live births according to countries in post-term pregnancies (≥ 42(+0) weeks). The risk of umbilical cord pH less than 7.10, Apgar score at five minutes inferior to 7, ICU admissions and perinatal asphyxia is increased in post-term infants (≥ 42(+0) weeks) compared with term infants. The risk of neurologic complications including neonatal convulsion, hypoxic ischemic encephalopathy, cerebral palsy, developmental deviations and epilepsy in childhood is increased in post-term infants. The risk of meconium aspiration syndrome, neonatal sepsis, and birth trauma including shoulder dystocia and bone fracture is increased in post-term infants. The rate of perinatal mortality increases in post-term infants. The perinatal mortality in post-term infants could be explained by perinatal asphyxia and meconium aspiration syndrome.

CONCLUSIONS

The risk of perinatal complications and mortality are increased in prolonged pregnancy.

Stereologic examination of placentas from mothers who smoke during pregnancy

OBJECTIVE

Structural changes in the placenta might contribute to the lower birth weight seen among infants born to mothers who smoke cigarettes. In this study, a morphologic examination and a stereologic quantitation of placentas from mothers who smoked cigarettes and who did not smoke cigarettes during pregnancy were performed.

STUDY DESIGN

Twenty-five placentas from mothers who did not smoke cigarettes, 15 placentas from mothers who smoked 5 to 10 cigarettes per day, 16 placentas from mothers who smoked 11 to 20 cigarettes per day, and 16 placentas from mothers who smoked >20 cigarettes per day were delivered at term after normal pregnancies and were fixed by dual perfusion. The volume and the surface area of villi, the trophoblast volume, and the volume and the surface area and length of villous capillaries were estimated. A measurement of the concentration of cadmium in serum was used to assess the validity of information concerning smoking habits.

RESULTS

No differences were shown in the total volume of placenta between the groups. The estimated volume and surface area and the calculated lengths for villous capillaries were significantly reduced in all 3 groups of smokers. A significant increase of the trophoblast volume was observed in the mothers who smoked cigarettes.

CONCLUSION

Cigarette smoking during pregnancy influences the placental vasculature. The reduced dimensions of fetal capillaries in villi may affect the placental blood flow, and the diminished area for exchange of gases and nutrients between the mother and the fetus will increase the risk of fetal undernourishment.

A quantitative study on the effects of maternal smoking on placental morphology and cadmium concentration

The aim of this study was to quantify the effects of maternal cigarette smoking on placental morphology, paying particular attention to variables known to be influential in facilitating oxygen diffusion. Structural quantities were estimated by stereological analyses of placental samples drawn from non-smoking and smoking women whose smoking habits were assessed both subjectively (from volunteered cigarette consumption) and objectively (by determining levels of plasma cotinine, a major metabolite of nicotine). Concentrations of placental cadmium were also measured. In the smoking group, maternal and fetal haematocrits were elevated and mean birthweight was reduced. Within placentae, the most significant alterations were increases in cadmium levels, the relative volumes of maternal intervillous space, the relative surface areas of fetal capillaries and decreases in the relative and absolute volumes of fetal capillaries. Findings indicate that changes in capillary volume are the result of a decrease in mean capillary diameter rather than total length. The mean thickness of the trophoblast component of the villous membrane was also increased in the smoking group. Although increased haematocrits suggest that fetuses of smoking mothers suffer hypoxic stress, these morphological changes are likely to compromise, rather than assist, transplacental oxygen transfer. This is in marked contrast to the adaptive changes seen in pregnancies associated with preplacental hypoxia and suggests that other factors might be compromising the fetoplacental unit. Finally, although the morphological changes associated with maternal smoking seem to be the result of an all-or-none, rather than dose-dependent, effect, the available evidence is not conclusive.

Stereology and its impact on our understanding of human placental functional morphology

The new stereology permits the objective, quantitative description of morphology by efficient and design-based methods. Applications to placentas in normal and abnormal pregnancies have proved of great value for challenging earlier misconceptions and interpreting better the processes of growth, morphogenesis, adaptation, and functioning at the whole-organ level. This contribution reviews the essential features of the stereological approach, identifies useful structural quantities, and provides examples of their application in various experiments of nature. We focus particularly on normal gestation and the effects of pregnancies associated with high altitude, maternal diabetes mellitus, preeclampsia, and maternal smoking.