Overview of in vitro models in developmental toxicology

Morphometric-Assisted Prediction of Developmental Toxicity Using Stem Cell-Based Embryo Models in Microwells

Congenital abnormalities cause ≈3% of fetal defects and premature deaths in Europe, often due to maternal exposure to toxicants. To mitigate the ethical and logistical challenges of animal studies, stem cell-based models are being exploredthat offer scalable readouts at various stages of embryogenesis. However, most current in vitro models are limited in complexity, throughput, automation compatibility or real-time spatio-temporal read-outs. In this study, a scalable, automated platform capable of imaging and quantifying morphological features such as shape, size, texture, and marker intensity is presented. Using a microwell screening platform, XEn/EpiCs, a peri-implantation stage embryo model that mimics eXtraembryonic Endoderm and Epiblast co-development, is robustly generated and used to screen a library of 38 reported compounds. Unlike conventional cytotoxicity assays, this approach also evaluates development-disrupting morphological changes, termed "morphotoxicity", thereby offering complementary insights that may improve the prediction of developmental toxicity across cell types. This pilot study shows thathigh doses of compoundslike retinoic acid, caffeine, ampyrone, and dexamethasone, significantly disrupt XEn/EpiC development, causing morphotoxic effects with or without affecting cell viability. Together, thisstudy highlights the importance of complementing cytotoxicity assessments with morphotoxicity read-outs, emphasizing its potential to enhance the evaluation of teratogenic risks in toxicity tests.

How to use an in vitro approach to characterize the toxicity of airborne compounds

As part of the development of new approach methodologies (NAMs), numerous in vitro methods are being developed to characterize the potential toxicity of inhalable xenobiotics (gases, volatile organic compounds, polycyclic aromatic hydrocarbons, particulate matter, nanoparticles). However, the materials and methods employed are extremely diverse, and no single method is currently in use. Method standardization and validation would raise trust in the results and enable them to be compared. This four-part review lists and compares biological models and exposure methodologies before describing measurable biomarkers of exposure or effect. The first section emphasizes the importance of developing alternative methods to reduce, if not replace, animal testing (3R principle). The biological models presented are mostly to cultures of epithelial cells from the respiratory system, as the lungs are the first organ to come into contact with air pollutants. Monocultures or cocultures of primary cells or cell lines, as well as 3D organotypic cultures such as organoids, spheroids and reconstituted tissues, but also the organ(s) model on a chip are examples. The exposure methods for these biological models applicable to airborne compounds are submerged, intermittent, continuous either static or dynamic. Finally, within the restrictions of these models (i.e. relative tiny quantities, adhering cells), the mechanisms of toxicity and the phenotypic markers most commonly examined in models exposed at the air-liquid interface (ALI) are outlined.

Development and gene expression of C57BL/6 mouse embryo palate shelves in rotary organ culture

The aim of the present study was to improve methods for the suspension culture of mouse palatal shelves by comparing the expression of platelet-derived growth factor receptor (PDGFR)-α in palatal shelves in vivo, to that in vitro. The palatal shelves of C57BL/6 mouse embryos were obtained on gestation days (GDs) 13.5, 14.5, 15.0 and 15.5 for in vivo experiments. The palatal shelves were removed and observed under a stereomicroscope to investigate palatal development. For in vitro experiments, the palatal shelves were dissected under a stereomicroscope on GD 13.5 and then subjected to rotary culture for 0, 24, 36 or 48 h. The expression of PDGFR-α at different time points was detected by immunohistochemical staining and western blot analysis. Both methods of analysis displayed PDGFR-α expression in mesenchymal and epithelial cells at GD 13.5, 14.5, 15.0 and 15.5, in vivo and in vitro. The level of PDGFR-α expression peaked on GD 14.5. The expression of PDGFR-α in palatal shelves in in vitro rotary culture was consistent with that in vivo. Therefore, the novel technique of palatal rotary organ culture presented in the current study could provide a good model for studying the mechanism of pathological palatal fusion in vitro. Additionally, the present study further confirmed that PDGFR-α gene expression was associated with the development of palatal shelves.

A method for electroporation to study gene function in mammary gland development

To reveal the specific functions of various genes during embryonic development, the manipulation of genes using techniques such as electroporation is of fundamental importance for providing direct evidence concerning function or downstream activation of signaling networks. In vitro embryo culture and electroporation are useful techniques to introduce foreign genes, for developmental biology studies. Among the various mammalian culture techniques, Trowell culture is suitable for studies of embryonic mammary gland development because of its stability and ease of use in conjunction with electroporation technique application. The manipulation of gene expression using electroporation is a useful technique for the functional analysis of a particular gene. In this protocol, full steps for electroporation and in vitro embryo culture have been described for use in embryonic mammary gland development research.