Long-term dual perfusion of isolated human placental lobules with improved oxygenation for infectious diseases research

Infectious and environmental placental insults: from underlying biological pathways to diagnostics and treatments

Because the placenta is bathed in maternal blood, it is exposed to infectious agents and chemicals that may be present in the mother's circulation. Such exposures, which do not necessarily equate with transmission to the fetus, may primarily cause placental injury, thereby impairing placental function. Recent research has improved our understanding of the mechanisms by which some infectious agents are transmitted to the fetus, as well as the mechanisms underlying their impact on fetal outcomes. However, less is known about the impact of placental infection on placental structure and function, or the mechanisms underlying infection-driven placental pathogenesis. Moreover, recent studies indicate that noninfectious environmental agents accumulate in the placenta, but their impacts on placental function and fetal outcomes are unknown. Critically, diagnosing placental insults during pregnancy is very difficult and currently, this is possible only through postpartum placental examination. Here, with emphasis on humans, we discuss what is known about the impact of infectious and chemical agents on placental physiology and function, particularly in the absence of maternal-fetal transmission, and highlight knowledge gaps with potential implications for diagnosis and intervention against placental pathologies.

A review of ex vivo placental perfusion models: an underutilized but promising method to study maternal-fetal interactions

Studying the placenta can provide information about the mechanistic pathways of pregnancy disease. However, analyzing placental tissues and manipulating placental function in real-time during pregnancy is not feasible. The ex vivo placental perfusion model allows observing important aspects of the physiology and pathology of the placenta, while maintaining its viability and functional integrity, and without causing harm to mother or fetus. In this review, we describe and compare setups for this technically complex model and summarize outcomes from various published studies. We hope that our review will encourage wider use of ex vivo placental perfusion, which in turn would generate more knowledge to improve pregnancy outcomes.

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

Since the full development of the ex vivo dual perfusion model of the human placenta cotyledon, the technique has provided essential insight into how nutrients, lipids, gases, immunoglobulins, endocrine agents, pharmaceuticals, chemicals, nanoparticles, micro-organisms and parasites might traverse the maternofetal barrier. Additionally, the model has been instrumental in gaining a better understanding of the regulation of vascular tone, endocrinology and metabolism within this organ. The human placenta is unique amongst species in its anatomy and transfer modalities. This orthologous diversity therefore requires an appropriate consideration of placental transfer rates of compounds, particles and micro-organisms specific to humans. Different research centres have adapted this model with a wide variation in perfusion parameters, including in the establishment of perfusion, perfusate composition, gassing regime, cannulation method, flow rates, perfused tissue mass, and also in the application of quality control measures. The requirement to harmonise and standardise perfusion practice between centres is largely driven by the need to obtain consistency in our understanding of placental function, but also in the qualification of the model for acceptance by regulatory agencies in drug and toxicology testing. A pilot study is proposed, aiming to describe how existing inter-centre variation in perfusion methodology affects placental metabolism, protein synthesis, oxygen consumption, the materno-fetal transfer of key molecular markers, and placental structure.

Nanoparticle mediated increased insulin-like growth factor 1 expression enhances human placenta syncytium function

INTRODUCTION

Placental dysfunction is an underlying cause of many major obstetric diseases and treatment options for complications like fetal growth restriction (FGR) are limited .We previously demonstrated nanoparticle delivery of the human insulin-like growth factor 1 (hIGF1) transgene under control of the trophoblast-specific PLAC1 promoter maintains normal fetal growth in a surgically-induced FGR mouse model. However, uptake by human placental syncytiotrophoblast has yet to be determined.

METHODS

An ex vivo human placenta perfusion model, term placenta villous fragments, and other in vitro syncytiotrophoblast models were used to determine nanoparticle uptake, transgene expression, and functional responses under oxidative stress conditions.

RESULTS

In the ex vivo perfusion, fluorescence from a Texas-Red conjugated nanoparticle increased in maternal perfusate upon nanoparticle addition and declined by the conclusion of the experiment (P < 0.001. Fluorescent histology confirmed localization in the syncytiotrophoblasts. No Texas-Red fluorescence was detected in the fetal perfusate. Transgene expression of hIGF1 in differentiated BeWo cells, isolated primary trophoblasts and fragments was increased compared to untreated (55,000-fold, P = 0.0003; 95-fold, P = 0.003; 400-fold, P < 0.001, respectively). Functionally, increased hIGF1 expression in villous fragments resulted in translocation of glucose transporter 1 to the syncytiotrophoblast cell membrane and under conditions of oxidative stress in BeWo cells, protected against increased cell death (P < 0.01) and decreased mitochondrial activity (P < 0.01).

CONCLUSION

The current study confirms that our nanoparticle is capable of uptake in human placental syncytium which results in enhanced transgene expression, functional changes to cellular activity and protection against increased oxidative stress.

Placenta-on-a-chip: a novel platform to study the biology of the human placenta

OBJECTIVE

Studying the biology of the human placenta represents a major experimental challenge. Although conventional cell culture techniques have been used to study different types of placenta-derived cells, current in vitro models have limitations in recapitulating organ-specific structure and key physiological functions of the placenta. Here we demonstrate that it is possible to leverage microfluidic and microfabrication technologies to develop a microengineered biomimetic model that replicates the architecture and function of the placenta.

MATERIALS AND METHODS

A "Placenta-on-a-Chip" microdevice was created by using a set of soft elastomer-based microfabrication techniques known as soft lithography. This microsystem consisted of two polydimethylsiloxane (PDMS) microfluidic channels separated by a thin extracellular matrix (ECM) membrane. To reproduce the placental barrier in this model, human trophoblasts (JEG-3) and human umbilical vein endothelial cells (HUVECs) were seeded onto the opposite sides of the ECM membrane and cultured under dynamic flow conditions to form confluent epithelial and endothelial layers in close apposition. We tested the physiological function of the microengineered placental barrier by measuring glucose transport across the trophoblast-endothelial interface over time. The permeability of the barrier study was analyzed and compared to that obtained from acellular devices and additional control groups that contained epithelial or endothelial layers alone.

RESULTS

Our microfluidic cell culture system provided a tightly controlled fluidic environment conducive to the proliferation and maintenance of JEG-3 trophoblasts and HUVECs on the ECM scaffold. Prolonged culture in this model produced confluent cellular monolayers on the intervening membrane that together formed the placental barrier. This in vivo-like microarchitecture was also critical for creating a physiologically relevant effective barrier to glucose transport. Quantitative investigation of barrier function was conducted by calculating permeability coefficients and metabolic rates in varying conditions of barrier structure. The rates of glucose transport and metabolism were consistent with previously reported in vivo observations.

CONCLUSION

The "Placenta-on-a-Chip" microdevice described herein provides new opportunities to simulate and analyze critical physiological responses of the placental barrier. This system may be used to address the major limitations of existing placenta model systems and serve to enable research platforms for reproductive biology and medicine.

Optimising sample collection for placental research

Biobanks provide an important repository of samples for research purposes. However, for those samples to reflect the in vivo state, and for experimental reliability and reproducibility, careful attention to collection, processing and storage is essential. This is particularly true for the placenta, which is potentially subjected to stressful conditions during delivery, and sample collection may be delayed owing to routine postpartum inspection by clinical staff. In addition, standardisation of the collection procedure enables samples to be shared among research groups, allowing larger datasets to be established. Here, we provide an evidence-based and experts' review of the factors surrounding collection that may influence data obtained from the human placenta. We outline particular requirements for specific techniques, and propose a protocol for optimal sample collection. We recognise that the relevance of these factors, and of the sample types collected to a particular study will depend on the research questions being addressed. We therefore anticipate that researchers will select from the protocol to meet their needs and resources available. Wherever possible, we encourage researchers to extend their collection to include additional samples that can be shared on an international collaborative basis, with appropriate informed consent, to raise the quality, as well as quantity, of placental research.

Ex vivo perfusion of mid-to-late-gestation mouse placenta for maternal-fetal interaction studies during pregnancy

Ex vivo perfusion systems offer a reliable, reproducible method for studying acute physiological responses of an organ to various environmental manipulations. Unlike in vitro culture systems, the cellular organization, compartmentalization and three-dimensional structure of ex vivo-perfused organs are maintained. These particular parameters are crucial for the normal physiological function of the placenta, which supports fetal growth through transplacental exchange, nutritional synthesis and metabolism, growth factor promotion and regulation of both maternally and fetally derived molecules. The perfusion system described here, which can be completed in 4-5 h, allows for integrated, physiological studies of de novo synthesis and metabolism and transport of materials across the live mouse placenta, not only throughout a normal gestation period but also following a variety of individual or combined genetic and environmental perturbations compromising placental function.

Placental transfer and metabolism: an overview of the experimental models utilizing human placental tissue

Over the decades several ex vivo and in vitro models which utilize delivered human placenta have been developed to study various placental functions. The use of models originating from human placenta to study transplacental transfer and related mechanisms is an attractive option because human placenta is relatively easily available for experimental studies. After delivery placenta has served its purpose and is usually disposed of. The purpose of this review is to give an overview of the use of human placental models for the studies on human placental transfer and related mechanisms such as transporter functions and xenobiotic metabolism. Human placental perfusion, the most commonly used continuous cell lines, primary cells and tissue culture, as well as subcellular fractions are briefly introduced and their major advantages and disadvantages are discussed.

[Contributions of the ex vivo human perfused placenta in the study of placental transfer of drugs]

Perfused human placental lobule was developed during the 1970s. Only this model respects the anatomical features of the human placenta. This approach allows different technical conditions (concentrations of drugs…) without ethical problems. Limitations of this ex vivo model are detailed in this review, also its recent contributions in better understanding of placental passage of drugs.

Advancing fetal brain MRI: targets for the future

Fetal MRI is becoming an increasingly powerful imaging tool for studying brain development in vivo. Until recently, the application of advanced magnetic resonance imaging techniques was limited by motion in the nonsedated fetus. Extensive research efforts currently underway are focusing on the development of dedicated magnetic resonance imaging sequences and sophisticated postprocessing techniques that are revolutionizing our ability to study the healthy and compromised fetus. The ongoing refinement of these magnetic resonance imaging techniques will undoubtedly lead to the development of cornerstone biomarkers that will provide healthcare caregivers with vital, and currently lacking, information upon which to counsel parents effectively, and base rational decisions regarding the timing and type of novel medical and surgical interventions currently on the horizon.

Experimental methods to study human transplacental exposure to genotoxic agents

Human placenta differs more than any other organ between species. This is the primary reason to develop models utilizing human tissue to study placental functions. There are no major ethical restrictions using human placenta for scientific studies. Also, the size of human placenta enables a great number of different parameters to be studied in one placenta. The most important cell types considering transplacental transfer, are the trophoblasts differentiating into syncytiotrophoblasts facing maternal circulation, and endothelial cells of fetal vessels. Primary trophoblasts are difficult to culture and do not grow in monolayer thus inhibiting studies on the polarized functions of transport. Several cell lines originating from trophoblasts have been developed, of which BeWo cells seem most useful for transport studies, because they grow in a tight monolayer. Placental tissue can also be retained as explant cultures, although the trophoblast viability is very restricted despite of culture conditions. Cotyledons of human placenta can be retained viable in an isolated organ perfusion. Perfused placental tissue stays viable longer than placental tissue in tissue culture. Although human placental perfusion is the most tedious experimental method to study placental functions, there are several good reasons to develop it further: transplacental transfer and molecular mechanisms of genotoxic compounds can be studied. Placental perfusion is the only experimental method that retains fully the structure of placenta for polarized transport. Furthermore, perfusion of placentas from mothers, who smoke, use illegal drugs or have a disease, allows studies on the impact of such factors on fetal exposure to genotoxic agents.

L’IRM fonctionnelle pour l’étude de la fonction placentaire

Placental insufficiency, a process due to either poor placental perfusion or permeability, may lead to progressive deterioration in placental function and materno-fetal morbidity. Advances in MR contrast media pharmacokinetic studies of transit through tissues and dynamic MRI allow to characterize organs microcirculation in vivo. Placental function assessment might be achieved using analysis of dynamic contrast enhanced MRI of tracers. A murine model of placental assessment has been constructed. Herein, principles, results and limitations of such techniques are discussed as well as their potential interest and weaknesses in humans.

Gene transfer to human placenta ex vivo: a novel application of dual perfusion of human placental cotyledon

OBJECTIVE

The purpose of this study was to determine whether the transfer of a marker gene in dual recirculating human placental perfusion is feasible and whether the transgene production is detectable by X-Gal histochemistry.

STUDY DESIGN

Four term human placentas were perfused for 9 to 16 hours in a dual perfusion chamber. At the beginning of each experiment, an adenoviral vector that carried beta-galactosidase gene was added to the maternal perfusate that was entering the intervillous space; at the end, the placental tissues were analyzed for beta-galactosidase activity by X-Gal staining.

RESULTS

Adenovirus-mediated gene transfer resulted in a 0.5% to 1% gene transfer efficiency in placental trophoblastic cells after 9 hours of perfusion, whereas the gene transfer efficiency was much higher, to 5% after 16 hours of perfusion. When postperfusion tissue explant cultures were analyzed for beta-galactosidase expression 56 hours after the perfusion, the transfection rate was as high as 11%.

CONCLUSION

Perfused human placenta can be efficiently transfected with adenoviral vectors, and the expression of the transgene can be detected in the trophoblastic cells. This system can be used for the optimization and analysis of gene transfer conditions to human placenta without any risk to the fetus.

Villous trophoblasts cultured on semi-permeable membranes form an effective barrier to the passage of high and low molecular weight particles

An effective in vitro model of the placental villous syncytium cultured on semi-permeable substrata is essential for studies of infectious pathogen transmission from mother to fetus. Current models using amniotic membranes or thinner artificial membranes show significant leakage, suggesting disruption of tight junctions or the presence of gaps between syncytial units. Such disruption and discontinuity of trophoblast cultures are probably the result of high stromal cell contamination, poor viability and lack of proliferation in culture. We have successfully cultured confluent layers of tight-junctioned syncytium on semi-permeable insert membranes using highly viable purified cytotrophoblasts and an alternating multiple seeding and differentiation technique. Using criteria including transepithelial diffusion of high and low molecular weight substances, electrical resistance and directional secretion of the matrix metalloproteinase, MMP-9, we demonstrate that these cultures form effective and functional physical barriers that can be maintained for up to 1 month.

Transport of viruses through fetal membranes: an in vitro model of perinatal transmission

A model system for perinatal transmission of viral infections was developed and transport of infectious virus particles through fetal membranes was investigated. Viruses of different families known to cause serious intrauterine infections were selected, including relevant and model viruses: the DNA-viruses HSV-1 and -2 as well as the animal herpes viruses BHV-1 and SHV-1, the RNA-virus BVDV as a model for hepatitis C virus, HIV-1 and -2, and PPV as a model for parvovirus B19. Migration of infectious virus from the maternal to the fetal side of the membrane could be detected as early as 20 min after the start of incubation. A peak of virus migration was observed after 1-2 hr. 0.02-1% of HSV-1 and 0.03-0.2% of HSV-2 were transported from the maternal side of the membrane to the fetal side. Only 0.01% of PPV migrated to the fetal side, whereas no transport of BVDV was observed. HIV-1 (1.4%) and HIV-2 (0.8%) seemed to be transported at higher rates. The concept of an active transport of infectious virus is compatible with the kinetics of penetration of the fetal membrane. The question of whether different receptors for the individual viruses on the cellular surface account for differences in virus transport will require further investigation. The fetal membrane acts as a protective barrier for the fetus, reducing greatly infectious titers or even preventing completely penetration of virus.

Protein transport across the in vitro perfused human placenta

PROBLEM

Placental transport of various proteins present in human serum, such as immunoglobulins (IgG, IgA), specific anti-tetanus IgG (anti-TT-IgG), and tetanus toxoid-antigen (TT-AG), was investigated. In addition, the transport of IgG modified with biotin (IgG-BT) and 14C-bovine serum albumin (14C-BSA, a permeability marker for macromolecules), was assessed.

METHOD OF STUDY

During the perfusion of an isolated cotyledon from human term placenta the perfusate was recirculated on both maternal and fetal sides. After an initial stabilisation phase of 2 hr (control phase), media on both sides were exchanged and perfusion was continued comparing two different conditions (experimental phase). In the first group (control experiments [A, n = 3]), no test proteins were added during the experimental phase (4-6 hr). In the second group (B, n = 5), during the experimental phase (6 hr) the maternal perfusion medium contained IgG (Sandoglobuline, 6-10 g/L), anti-TT-IgG (21-25 mg/L), TT-AG (0.19-0.24 mg/L), and IgA (0.13-0.19 g/L). IgG-BT (2 g/L) and 14C-BSA (30-40 nCi/ml) were added to the medium on the maternal side. IgGs and TT-AG were determined by specific enzyme-linked immunosorbent assay.

RESULTS

Both groups showed stable metabolic conditions with constant rates of glucose consumption, lactate production, and hormone (human chorionic gonadotropin, human placental lactogen) release observed throughout the experiment. Washout levels of endogenous IgG and IgA observed in the maternal circuit at the end of the control period were 5 and 1000 times higher than in the fetal circuit. In the experimental phase these levels remained constant at 50-80% of control levels with no change in the last 4 hr of perfusion (group A). In group B, with addition of extra proteins, trace amounts of IgG-BT, IgA, and 14C-BSA were detectable in the fetal circuit within 1 hr, with no significant further increase in circulating levels in the following 4 hr of the perfusion. In contrast, the detection of IgGs in the fetal circuit was delayed by 2 hr; thereafter, a continuous linear increase was observed for all IgGs. TT-AG in fetal perfusate was below the detection limit. TT-AG was found on the fetal side only after ultrafiltration of samples obtained at the end of the experiment. For permeability comparison, the ratio between concentrations on the fetal and maternal side multiplied by 100 ([F:M] x 100), as detected after 6 hr of perfusion, was assessed (n = 5, mean +/- SD). Labelling of IgG with biotin (IgG-BT) reduced its placental transfer by a factor 10 (0.04 +/- 0.01) when compared with the natural IgG (0.49 +/- 0.08) or the specific antibody (anti-TT-IgG). The relative fetal-to-maternal ratio found for TT-AG (0.48 +/- 0.12) was similar to anti-TT-IgG (0.46 +/- 0.11), and approximately 4 and 50 times that of 14C-BSA (0.12 +/- 0.03) and IgA (0.01 +/- 0.01), respectively. Considering that the molecular weights of TT-AG and anti-TT-IgG were at least twice that of BSA and similar to IgA, the difference in transfer suggests a specific mechanism of transport.

CONCLUSIONS

Compared with other proteins there is a significantly increased transfer of IgGs across the in vitro perfused human placenta from the maternal to the fetal side, indicating a specific transport mechanism. The similarity in transfer of anti-TT-IgG and tetanus antigen may suggest the transport as antibody-antigen complex.

Production of granulocyte colony-stimulating factor by the human placenta at various stages of development

The human placenta is capable of producing a variety of haematopoietic growth factors in vitro. It is not clear, however, whether the placenta produces such factors in vivo and if so, whether placental production of haematopoietic growth factors has a physiological role in fetal haematopoietic development. As a step toward making this determination, we assessed whether the onset of placental production of granulocyte colony-stimulating factor (G-CSF), in vivo, coincides with the onset of granulocytopoiesis in the developing fetus. To make this assessment, we obtained human placentae between 10 weeks of gestation and term and studied production of G-CSF in several ways. First, we sought to determine whether the onset of production of G-CSF mRNA in the placenta immediately precedes the appearance of neutrophil development in the fetus. Second, we assessed the effect of gestational age on the capacity of the placenta to generate G-CSF in vitro, by incubating cubes of placenta, with or without including interleukin-1 alpha (IL-1 alpha) in the culture media, and quantifying G-CSF in the cell culture supernatants 24 h later. Third, we assessed the rate of G-CSF production by the placenta, by perfusing two normal, term placentae using a membrane-oxygenator system, and quantifying G-CSF, at intervals, in the perfusates. We found: (1) no evidence that placental production of G-CSF is involved in regulating granulocytopoiesis in the fetus, (2) that the healthy placenta contains little or no G-CSF mRNA in vivo, (3) the placenta at term has a far greater capacity to produce G-CSF, when stimulated, than does the placenta before term, and (4) that although the placenta does not normally produce G-CSF in vivo, it has the capacity of generating very large quantities of G-CSF continuously over at least several days.