Pre-validation study of alternative developmental toxicity test using mouse embryonic stem cell-derived embryoid bodies

Fluorene-9-bisphenol affects the terminal differentiation of mouse embryonic bodies

Fluorene-9-bisphenol (BHPF) has recently attracted interest as it is increasingly used in industrial settings as a substitute for Bisphenol A (BPA). However, the effects of BHPF exposure on embryonic stem cell (ESC) self-renewal, pluripotency, and differentiation remain poorly understood. This study investigates the impacts of BHPF on mouse embryonic stem cells (mESCs) and embryonic bodies (EBs). Our results reveal that BHPF exposure leads to a morphological shift in mESCs, reducing the percentage of dome-shaped colonies and indicating loss of self-renewal and pluripotency. BHPF exposure also appeared to affect the early stages of EB formation and their growth dynamics, with a reduction in EB numbers and an increase in their size. Subsequent gene expression analysis revealed that BHPF exposure led to increased expression of the inflammatory gene Il6, indicating a potential stress response. Furthermore, BHPF affected the terminal differentiation pathway, modulating the expression of 16 genes associated with distinct cell types, including lymphatic endothelium, keratinocyte epithelium, pancreatic beta cells, macrophages, monocytes, T-cells, neurons, retinal ganglion cells, nephrons proximal tubule cells, and cardiomyocytes. These findings offer insights into the impact of BHPF on ESC biology and suggest potential implications for developmental and neurodegenerative disorders. Future work should focus on elucidating the underlying mechanisms of BHPF-mediated effects on stem cell function. This may offer new perspectives for understanding the health impacts of environmental exposure to BHPF.

Mitochondrial dynamics when mitochondrial toxic chemicals exposed in 3D cultured mouse embryonic stem cell

Mitochondria need to use considerable energy for the intracellular organelles that produce ATP. They are abundant in the cells of organs, such as muscles, liver, and kidneys. The heart, which requires a lot of energy, is also rich in mitochondria. Mitochondrial damage can induce cell death. Doxorubicin, acetaminophen, valproic acid, amiodarone, and hydroxytamoxifen are representative substances that induce mitochondrial damage. On the other hand, the effects of this substance on the progress of cardiomyocyte-differentiating stem cells have not been investigated. Therefore, a 3D cultured embryonic body toxicity test was performed. The results confirmed that the cytotoxic effects on cardiomyocytes were due to mitochondrial damage in the stage of cardiomyocyte differentiation. After drug treatment, the cells were raised in the embryoid body state for four days to obtain the ID50 values, and the levels of mRNA expression associated with the mitochondrial complex were examined. The mitochondrial DNA copy numbers were also compared to prove that the substance affects the number of mitochondria in EB-state cardiomyocytes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-022-00161-1.

Effects of Decamethylcyclopentasiloxane on Reproductive Systems in Female Rats

The female reproductive system becomes fertile through the action of hormones involved in the hypothalamic-pituitary-ovarian axis. On the other hand, estrogen-like endocrine disruptors released into the environment come into contact with humans by various routes and affect the reproductive system. Exposure to these chemicals can cause problems with the reproductive process, from egg ovulation to implantation, or cause female reproductive diseases. These reproductive problems cause infertility. Decamethylcyclopentasiloxane (D5) is used for lubrication in silicone polymers, households, and personal care products. In the case of D5, it is discharged through factory wastewater and can bioaccumulate. Therefore, it accumulates in the human body. In this study, D5 was administered orally for four weeks to determine the effects of D5 on the reproductive process. As a result, D5 increases the number of follicles in the ovary and suppresses the expression of genes related to the growth of follicles. In addition, it increases the gonadotropin hormone, inducing estradiol enhancement and progesterone reduction. Because of these changes in the reproductive system when exposed to D5, the industry should reconsider using D5.

Genes Involved in DNA Repair and Mitophagy Protect Embryoid Bodies from the Toxic Effect of Methylmercury Chloride under Physioxia Conditions

The formation of embryoid bodies (EBs) from human pluripotent stem cells resembles the early stages of human embryo development, mimicking the organization of three germ layers. In our study, EBs were tested for their vulnerability to chronic exposure to low doses of MeHgCl (1 nM) under atmospheric (21%O₂) and physioxia (5%O₂) conditions. Significant differences were observed in the relative expression of genes associated with DNA repair and mitophagy between the tested oxygen conditions in nontreated EBs. When compared to physioxia conditions, the significant differences recorded in EBs cultured at 21% O₂ included: (1) lower expression of genes associated with DNA repair (ATM, OGG1, PARP1, POLG1) and mitophagy (PARK2); (2) higher level of mtDNA copy number; and (3) higher expression of the neuroectodermal gene (NES). Chronic exposure to a low dose of MeHgCl (1 nM) disrupted the development of EBs under both oxygen conditions. However, only EBs exposed to MeHgCl at 21% O₂ revealed downregulation of mtDNA copy number, increased oxidative DNA damage and DNA fragmentation, as well as disturbances in SOX17 (endoderm) and TBXT (mesoderm) genes expression. Our data revealed that physioxia conditions protected EBs genome integrity and their further differentiation.

Cytotoxicity evaluation and mechanism of endocrine-disrupting chemicals by the embryoid body test

Endocrine-disrupting chemicals (EDCs) are a structurally diverse class of synthetic and natural compounds. EDCs can cause non-communicable diseases such as obesity, type 2 diabetes, thyroid disorders, neurodevelopmental disease, hormone-dependent cancers, and reproductive disorders. The embryoid body test (EBT) is a developmental toxicity test method that determines the size of embryoid bodies (EBs) and the viability of mouse embryonic stem cells (mESCs) and fibroblasts (3T3 cells). The present study used the EBT to perform cytotoxicity evaluations of 10 EDCs and assessed the mechanistic relationship between endoplasmic reticulum (ER) stress and cytotoxicity. According to the statistical analysis and prediction model results, methylparaben, butylparaben, propylparaben, ethylparaben, triclosan, octylphenol, methoxychlor, bisphenol A, and diethylstilbestrol were classified as cytotoxic, but trichloroacetic acid was non-toxic. Classification accuracy was 90%. The mechanistic study showed that the cytotoxicities of butylparaben, propylparaben, octylphenol, and triclosan were induced by ER stress. The mRNA expressions of BiP, CHOP, and ATF4 were significantly higher following treatments with four EDCs compared to those after the control treatment. Compared to the control treatment, the mRNA levels of XBP1u and XBP1s increased significantly after butylparaben and propylparaben treatments, but did not increase with octylphenol and triclosan treatments. These results indicate that the EBT can be applied as an alternative toxicity test when evaluating the cytotoxicity of EDCs.

Pluripotent stem cell assays: Modalities and applications for predictive developmental toxicity

This manuscript provides a review focused on embryonic stem cell-based models and their place within the landscape of alternative developmental toxicity assays. Against the background of the principles of developmental toxicology, the wide diversity of alternative methods using pluripotent stem cells developed in this area over the past half century is reviewed. In order to provide an overview of available models, a systematic scoping review was conducted following a published protocol with inclusion criteria, which were applied to select the assays. Critical aspects including biological domain, readout endpoint, availability of standardized protocols, chemical domain, reproducibility and predictive power of each assay are described in detail, in order to review the applicability and limitations of the platform in general and progress moving forward to implementation. The horizon of innovative routes of promoting regulatory implementation of alternative methods is scanned, and recommendations for further work are given.

Pre-validation of an alternative test method for prediction of developmental neurotoxicity

Exposure to neurodevelopmental toxicants can cause permanent brain injury. Hance, determining the neurotoxicity of unknown substances is essential for the safety of substance. As an alternative method to animal studies, developmental neurotoxicity test (DNT) and the first discriminant function (DF) were established in previous study. This study aimed to increase the predictability of the DNT method and perform a mobility test. Two endpoints of 29 newly investigated substances were used to establish a second-generation DF (2nd GDF). As two endpoints, the half-inhibitory concentration of the cell viability (IC₅₀) was determined using a cell counting kit-8 assay. The half-inhibitory concentration of differentiation (ID₅₀) was determined by measuring the green fluorescent protein (GFP) intensity in 46C cells. The substances were treated dose-dependently to measure IC₅₀ and ID₅₀. The 2nd GDF classified 29 chemicals accurately as toxic and non-toxic. Four participants of three independent laboratories were enrolled to test the mobility. The results of the test set were highly accurate in reproducibility (100% of accuracy, sensitivity, and specificity) and mobility (accuracy 93.33%, sensitivity 90.91%, and specificity 100%). In conclusion, the protocol is transferable, reproducible, and accurate. Therefore, this could be a standardizing method for determining a neurotoxicant as an alternative for animal experiments.

Stem Cell Based Preclinical Drug Development and Toxicity Prediction

Stem cell based toxicity prediction plays a very important role in the development of the drug. Unexpected adverse effects of the drugs during clinical trials are a major reason for the termination or withdrawal of drugs. Methods for predicting toxicity employ in vitro as well as in vivo models; however, the major drawback seen in the data derived from these animal models is the lack of extrapolation, owing to interspecies variations. Due to these limitations, researchers have been striving to develop more robust drug screening platforms based on stem cells. The application of stem cells based toxicity testing has opened up robust methods to study the impact of new chemical entities on not only specific cell types, but also organs. Pluripotent stem cells, as well as cells derived from them, can be evaluated for modulation of cell function in response to drugs. Moreover, the combination of state-of-the -art techniques such as tissue engineering and microfluidics to fabricate organ- on-a-chip, has led to assays which are amenable to high throughput screening to understand the adverse and toxic effects of chemicals and drugs. This review summarizes the important aspects of the establishment of the embryonic stem cell test (EST), use of stem cells, pluripotent, induced pluripotent stem cells and organoids for toxicity prediction and drug development.

Establishment of a developmental neurotoxicity test by Sox1-GFP mouse embryonic stem cells

Developmental toxicity tests have been generated by applying the embryonic stem cell tests at the European Centre for the Validation of Alternative Methods, or by using the embryoid body test in our laboratory. This study was undertaken to explore novel developmental neurotoxicity (DNT) assay, using a Sox1-GFP cell line (mouse embryonic stem cells with an endogenous Sox1-GFP reporter). The expression of Sox1, a marker for neuroepithelial cells, is detected by green fluorescence, and the fluorescence intensity is a critical factor for achieving neuronal differentiation. Sox1-GFP cells cultured for 24 h were exposed to eleven neurotoxicants and four non-neurotoxicants. CCK-8 assays were performed to determine IC₅₀ values after 48 h of chemical treatment. The fluorescence intensity of GFP was measured 4 days after treating the cells, and it was observed to decrease after exposure to neurotoxicants at higher concentrations, thereby indicating that the neuronal differentiation of Sox1-GFP cells is inhibited by the chemicals. Taken together, the results obtained in this study provide a model for DNT using embryonic stem cells, which may be applied to evaluate the toxicity of new chemicals or new drug candidates.

Comparative assessment of toxic responses in 3D embryoid body differentiation model and mouse early embryos treated with 5-hydroxytryptophan

Pluripotent stem cells recapitulate in vitro the early developmental stages and are considered promising cell models for predictive developmental toxicity studies. To investigate the consistency between adverse drug effects on early development and the early stages of embryonic stem cell differentiation in three-dimensional (3D) in vitro culture, the toxic responses to 5-hydroxytryptophan (5-HTP; 0.5-2 mM) were evaluated in early mouse embryos and the embryoid body (EB) differentiation model. 3D architectures, developmental and differentiation dynamics and the cell death rates were analyzed in early mouse embryos (E2.5-E5.5) and EBs at 1 and 6 days of differentiation using a combination of confocal immunofluorescence microscopy with high content imaging analysis and quantitative gene expression analysis. Comparative analysis of toxic responses in early embryos and EBs revealed a similar dose- and stage-dependent decrease in the 5-HTP toxic effects during development and differentiation. The integral toxic responses in the early embryos and EBs were significantly dependent on their 3D architecture and cellular composition. Treatment with 5-HTP (1 mM and above) induced developmental arrest, growth inhibition, and increased cell death in the early embryos without the trophoblasts (E2.5) and those with impaired trophoblasts and in early EBs, whereas later embryos and EBs were more resistant due to the protection of the extraembryonic tissues. This study demonstrates that the EB differentiation model is a relevant 3D-model of early mammalian development and can be useful for the predictive evaluation of toxic and teratogenic effects in embryos at the preimplantation and early post-implantation developmental stages.