Developmental toxicity and transcriptome analysis of equine estrogens in developing medaka (Oryzias latipes) using nanosecond pulsed electric field incorporation

Equine estrogens (EQs) are steroidal hormones isolated from the urine of pregnant mares and are used in the formulation of human medications. This study initially investigated the embryonic developmental toxicity of equilin (Eq) and equilenin (Eqn) in medaka (Oryzias latipes). Malformations were observed in embryos exposed to nominal concentrations of 1 and 10 mg/L of Eq and Eqn. Delayed hatching was observed at 1 mg/L of Eq. To further investigate the molecular mechanism of developmental toxicity caused by Eq and Eqn, transcriptome and bioinformatics analyses were performed. Among 2016 and 3855 total differentially expressed genes (DEGs), 1117 DEGs overlapped between Eq. (55.4 % of total DEGs) and Eq. (29.0 % of total DEGs). Gene ontology indicated effects in terms related to blood circulation and cell junctions. Pathway analyses using DEGs revealed that both Eq and Eqn treatments at 10 mg/L affected various KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways, such as neuroactive ligand-receptor interaction, mitogen-activated protein kinase signaling, retinol metabolism, and cytokine-cytokine receptor interaction. These results suggest that the disruption of these KEGG pathways is involved in the developmental toxicity of EQs in medaka embryos.

Medaka (Oryzias latipes) Embryo as a Model for the Screening of Compounds That Counteract the Damage Induced by Ultraviolet and High-Energy Visible Light

Continuous overexposure to sunlight increases its harmful effects on the skin. For this reason, there is a growing need to characterize economic models more representative of the negative effects and counteracting responses that irradiation causes on human skin. These models will serve for the screening of protective compounds against damage caused by ultraviolet (UV) and high energy visible light (HEV). Therefore, two common in vitro models employed for sunlight irradiation studies, namely human keratinocyte HaCat culture and reconstructed human epidermis (RHE), were compared with the medaka fish embryo model, traditionally used in other scientific disciplines. Using suberythemal doses of UVA and HEV to determine the level of Reactive Oxygen Species (ROS) generation and thymine dimers formed by UVB, we show that medaka embryo responds with a lower damage level, more comparable to human skin, than the other two models, probably due to the protective mechanisms that work in a complete organism. In the same way, the protective effects of antioxidant compounds have the greatest effect on medaka embryos. Taken together, these findings suggest that medaka embryos would be a good alternative in vitro model for sunlight effect studies, and for the screening of molecules with counteracting capacity against the damage caused by UV and HEV.

Potential mechanisms underlying embryonic developmental toxicity caused by benzo[a]pyrene in Japanese medaka (Oryzias latipes)

Polycyclic aromatic hydrocarbons (PAHs), such as benzo[a]pyrene (BaP), are widely distributed in air, water, and sediments; however, limited data are available regarding their potential adverse effects on the early life stages of fish. In this study, we evaluated the embryonic teratogenicity and developmental toxicity of BaP in Japanese medaka (Oryzias latipes) using a nanosecond pulsed electric field (nsPEF) technique and predicted their molecular mechanisms via transcriptome analysis. The gas chromatography/mass spectrometry analyses revealed that the BaP was efficiently incorporated into the embryos by nsPEF treatment. The embryos incorporating BaP presented typical teratogenic and developmental effects, such as cardiovascular abnormalities, developmental abnormalities, and curvature of backbone. DNA microarray analysis revealed several unique upregulated genes, such as those involved in cardiovascular diseases, various cellular processes, and neural development. Furthermore, the gene set enrichment and network analyses found several genes and hub proteins involved in the developmental effects of BaP on the embryos. These findings suggest a potential mechanism of teratogenicity and developmental toxicity caused by exposure to BaP. The nsPEF and transcriptome analyses in combination can be effective for evaluating the potential effects of chemical substances on medaka embryos.