Zebrafish embryos as a teratogenicity screening tool to reduce potential birth defects

Teratogens play a crucial role in the development of birth defects, making effective screening vital for prevention and management. This study aimed to develop an optimized zebrafish embryo-based platform for teratogenicity screening and further evaluate its findings with established clinical and animal data. Zebrafish embryos [6-8 h post-fertilization (hpf)] were exposed to 19 different test solutions, including nine known teratogens and ten non-teratogens, in 96-well plates, and mortality and morphological abnormalities were assessed at 48, 72, and 96 hpf. The half-lethal concentration (LC₅₀) and half-effective concentration (EC₅₀) were calculated from the counts of dead and abnormal embryos, respectively. The teratogenicity index (TI), defined as LC₅₀/EC₅₀, was used to classify the chemicals. Of the tested compounds, eight were identified as teratogenic, nine as non-teratogenic, and two outliers due to solubility constraints in this assessment. Notably, extending the exposure duration to 96 hpf provided a more accurate assessment of teratogenicity compared to shorter exposures. Eight teratogenic substances exhibited a TI greater than 3, while (-)-thalidomide did not yield a definitive TI due to low solubility. Among the non-teratogenic chemicals, nine had a TI below 3, with ajmaline also lacking a precise TI due to solubility constraints. These findings suggest that using a 6-8 hpf to 96 hpf exposure window and establishing a TI threshold of 3 can facilitate reliable teratogenicity risk assessment. Furthermore, the phenotypes observed in zebrafish embryos were consistent with typical teratogenic malformations documented in clinical and animal studies. This study demonstrates that the refined zebrafish embryo teratogenicity testing method coupled with the TI, can be an effective tool for assessing teratogenic risk.