Ex vivo dual perfusion of an isolated human placenta cotyledon: Towards protocol standardization and improved inter-centre comparability

Fetus Exposure to Drugs and Chemicals: A Holistic Overview on the Assessment of Their Transport and Metabolism across the Human Placental Barrier

BACKGROUND

The placenta exerts a crucial role in fetus growth and development during gestation, protecting the fetus from maternal drugs and chemical exposure. However, diverse drugs and chemicals (xenobiotics) can penetrate the maternal placental barrier, leading to deleterious, adverse effects concerning fetus health. Moreover, placental enzymes can metabolize drugs and chemicals into more toxic compounds for the fetus. Thus, evaluating the molecular mechanisms through which drugs and chemicals transfer and undergo metabolism across the placental barrier is of vital importance. In this aspect, this comprehensive literature review aims to provide a holistic approach by critically summarizing and scrutinizing the potential molecular processes and mechanisms governing drugs and chemical transfer and metabolism across the placental barrier, which may lead to fetotoxicity effects, as well as analyzing the currently available experimental methodologies used to assess xenobiotics placental transfer and metabolism.

METHODS

A comprehensive and in-depth literature review was conducted in the most accurate scientific databases such as PubMed, Scopus, and Web of Science by using relevant and effective keywords related to xenobiotic placental transfer and metabolism, retrieving 8830 published articles until 5 February 2024. After applying several strict exclusion and inclusion criteria, a final number of 148 relevant published articles were included.

RESULTS

During pregnancy, several drugs and chemicals can be transferred from the mother to the fetus across the placental barrier by either passive diffusion or through placental transporters, resulting in fetus exposure and potential fetotoxicity effects. Some drugs and chemicals also appear to be metabolized across the placental barrier, leading to more toxic products for both the mother and the fetus. At present, there is increasing research development of diverse experimental methodologies to determine the potential molecular processes and mechanisms of drug and chemical placental transfer and metabolism. All the currently available methodologies have specific strengths and limitations, highlighting the strong demand to utilize an efficient combination of them to obtain reliable evidence concerning drug and chemical transfer and metabolism across the placental barrier. To derive the most consistent and safe evidence, in vitro studies, ex vivo perfusion methods, and in vivo animal and human studies can be applied together with the final aim to minimize potential fetotoxicity effects.

CONCLUSIONS

Research is being increasingly carried out to obtain an accurate and safe evaluation of drug and chemical transport and metabolism across the placental barrier, applying a combination of advanced techniques to avoid potential fetotoxic effects. The improvement of the currently available techniques and the development of novel experimental protocols and methodologies are of major importance to protect both the mother and the fetus from xenobiotic exposure, as well as to minimize potential fetotoxicity effects.

Variability in perfusion conditions and set-up parameters used in ex vivo human placenta models: A literature review

The ex vivo human placenta perfusion model has proven to be clinically relevant to study transfer- and fetal exposure of various drugs. Although the method has existed for a long period, the setup of the perfusion model has not been generalized yet. This review aims to summarize the setups of ex vivo placental perfusion models used to examine drug transfer across the placenta to identify generalized properties and differences across setups. A literature search was carried out in PubMed September 26, 2022. Studies were labeled as relevant when information was reported, between 2000 and 2022, on the setups of ex vivo placental perfusion models used to study drug transfer across the placenta. The placenta perfusion process, and the data extraction, was divided into phases of preparation, control, drug, and experimental reflecting the chronological timeline of the different phases during the entire placental perfusion process. 135 studies describing an ex vivo human placental perfusion experiment were included. Among included studies, the majority (78.5%) analyzed drug perfusion in maternal to fetal direction, 18% evaluated bi-directional drug perfusion, 3% under equilibrium conditions, and one study investigated drug perfusion in fetal to maternal direction. This literature review facilitates the comparison of studies that employ similar placenta perfusion protocols for drug transfer studies and reveals significant disparities in the setup of these ex vivo placental perfusion models. Due to interlaboratory variability, perfusion studies are not readily comparable or interchangeable. Therefore, a stepwise protocol with multiple checkpoints for validating placental perfusion is needed.

Placental transfer of tofacitinib in the ex vivo dual-side human placenta perfusion model

Tofacitinib is a small molecule Janus kinase (JAK) inhibitor, introduced to the European market in 2017, for the treatment of rheumatoid arthritis, psoriatic arthritis and ulcerative colitis. In the treatment of women with autoimmune diseases, pregnancy is a relevant issue, as such diseases typically affect women in their reproductive years. Currently, there is limited data on the use of tofacitinib during pregnancy. To estimate the extent of placental transfer in the absence of clinical data, we conducted ex vivo dual-side perfused human placental cotyledon perfusions. Term placentas were perfused for 180 min with tofacitinib (100 nM, added to the maternal circuit) in a closed-closed configuration. At the end of the perfusions, drug concentrations in the maternal and fetal reservoirs were near equilibrium, at 35.6 ± 5.5 and 24.8 ± 4.7 nM, respectively. Transfer of tofacitinib was similar to that observed for the passive diffusion marker antipyrine (100 µg/mL, added to the maternal reservoir). Final antipyrine maternal and fetal concentrations amounted to 36.9 ± 3.0 and 36.7 ± 1.3 µg/mL, respectively. In conclusion, in the ex vivo perfused placenta tofacitinib traverses the placental barrier rapidly and extensively. This suggests that substantial fetal tofacitinib exposure will take place after maternal drug dosing.

Placental disposition of cannabidiol: An ex vivo perfusion study

OBJECTIVE

In the absence of safety data in humans, the use of cannabidiol (CBD) is not recommended during pregnancy. Yet >50% of pregnancies in women with epilepsy are unintended, making fetal exposure to CBD possible. As a small-molecule, highly lipid-soluble drug, CBD is likely to be distributed into the placenta and cross it. To estimate the placental distribution profile of CBD and its potential short-term placental effects, we conducted an ex vivo perfusion study in human placentas.

METHODS

Placentas were obtained from healthy women undergoing cesarean deliveries. Selected cotyledons were cannulated and perfused for 180 min with a CBD-containing medium (250 ng/mL, .796 μmol·L-1 ; representative of a low therapeutic concentration; n = 8). CBD concentrations were determined at 180 min in the medium and placental tissue using liquid chromatography-tandem mass spectrometry. A customized gene panel array was used to analyze the expression of selected genes in the perfused placental cotyledons as well as in placentas perfused with 1000 ng/mL CBD (3.18 μmol·L-1 ; high therapeutic concentration; n = 8) and in those exposed to the vehicle.

RESULTS

CBD was sequestered in the placental tissue, exhibiting significant variability across samples (median = 5342 ng/g tissue, range = 1066-9351 ng/g tissue). CBD concentrations in the fetal compartment were one fifth of those measured in the maternal compartment (median = 59 ng/mL, range = 48-72 ng/mL vs. 280 = ng/mL, range = 159-388 ng/mL, respectively; p < .01). Placental gene expression was not significantly altered by CBD.

SIGNIFICANCE

The placenta acts as a depot compartment for CBD, slowing down its distribution to the fetus. This phenomenon might yield flatter but prolonged fetal CBD levels in vivo. The attenuated transplacental CBD transfer does not imply that its use by pregnant women is safe for the fetus. Only pregnancy registries and neurocognitive assessments would establish the risk of being antenatally exposed to CBD.

Asymmetrical Transport of Thyroxine Across Human Term Placenta

Background: Fetal development is crucially dependent on thyroid hormone (TH). Maternal-to-fetal transfer of TH is a prerequisite for fetal TH availability, particularly in the first half of pregnancy. The mechanisms of transplacental transport of TH, however, are yet poorly understood. We, therefore, investigated the TH transport processes across human placentas using an ex vivo perfusion system. Methods: Intact cotyledons from term placentas of uncomplicated pregnancies were cannulated within 30 minutes after delivery and the maternal and fetal circulations were re-established. One hundred nanomolar thyroxine (T4) was added to either the maternal or fetal circulation and perfusions run up to three hours during which samples were taken from both circulations at different time points. Variables included addition of iopanoic acid (IOP) to block activity of the deiodinase type 3 (D3) and bovine serum albumin (BSA) to trap released T4. T4 and 3,3',5'-triiodothyronine concentrations in the perfusates were measured by radioimmunoassays. Results: Maternal-to-fetal transfer was slow, with T4 barely detectable in the fetal circulation unless D3 was blocked by IOP. Fetal T4 was detected after three hours perfusion (10.6 ± 0.6 nM) when BSA (34 g/L) was added in the fetal circulation to trap the released T4. In contrast, fetal-to-maternal transfer of T4 was rapid and maternal T4 increased to 43.6 ± 5.5 nM. Conclusions: Maternal-to-fetal T4 transport is limited, whereas fetal-to-maternal transport is rapid indicating that T4 transport across human term placenta is an asymmetrical process. With the high D3 activity, our observations are compatible with a protective role of the placental barrier. Future studies should reveal how the placenta exerts its gatekeeper function in ensuring optimal TH passage to the fetus.

Human-Based New Approach Methodologies in Developmental Toxicity Testing: A Step Ahead from the State of the Art with a Feto-Placental Organ-on-Chip Platform

Developmental toxicity testing urgently requires the implementation of human-relevant new approach methodologies (NAMs) that better recapitulate the peculiar nature of human physiology during pregnancy, especially the placenta and the maternal/fetal interface, which represent a key stage for human lifelong health. Fit-for-purpose NAMs for the placental-fetal interface are desirable to improve the biological knowledge of environmental exposure at the molecular level and to reduce the high cost, time and ethical impact of animal studies. This article reviews the state of the art on the available in vitro (placental, fetal and amniotic cell-based systems) and in silico NAMs of human relevance for developmental toxicity testing purposes; in addition, we considered available Adverse Outcome Pathways related to developmental toxicity. The OECD TG 414 for the identification and assessment of deleterious effects of prenatal exposure to chemicals on developing organisms will be discussed to delineate the regulatory context and to better debate what is missing and needed in the context of the Developmental Origins of Health and Disease hypothesis to significantly improve this sector. Starting from this analysis, the development of a novel human feto-placental organ-on-chip platform will be introduced as an innovative future alternative tool for developmental toxicity testing, considering possible implementation and validation strategies to overcome the limitation of the current animal studies and NAMs available in regulatory toxicology and in the biomedical field.

Contribution of the ex vivo placental perfusion model in understanding transplacental immunoglobulin G transfer

INTRODUCTION

The acquisition of humoral immunity in utero is essential for the fetus. The crucial protein, which is responsible for this part of immunity, is immunoglobulin-G (IgG). Immune functions of IgGs are mediated via the interaction of the crystallizable fragment (Fc) region of IgG with specific Fc γ receptors (FcγRs). However, an atypical FcγR, the neonatal Fc receptor (FcRn), is a key regulator of IgG transfer across the human placenta. During the last four decades ex vivo placental perfusion studies have contributed significantly to the study of mechanisms of IgG transfer across the multicellular placental barrier.

METHOD

A PubMed search was conducted by using specific keywords: placenta, perfusion and IgG to review manuscripts using human placental perfusion to study the transplacental transfer of IgG. Relevant studies found in reference lists of these manuscripts were also added to the review, and references were included that supported or gave nuance to the discussion of the mechanisms of IgG kinetics in the placenta.

RESULTS AND DISCUSSION

We found twenty publications on the study of transplacental transfer of IgG using human ex vivo placental perfusion, by research groups with partly different settings. This review summarizes knowledge about placental IgG transfer, with a strong focus on the contributions from ex vivo placental perfusion studies.