Diastereomer-selective developmental toxicity of cis- and trans-permethrin in zebrafish (Danio rerio) embryos: AI-assisted analysis of seizure-like behaviors.

Permethrin (PM) has been widely used to control insect pests, including mosquitoes, flies, scabies, and mites. Its use for agricultural purposes is strongly restricted because of its high toxicity to aquatic organisms. Nevertheless, PM continues to be detected in aquatic environments, and formulations containing different diastereomeric ratios of cis-PM and trans-PM (40:60 or 25:75) are still used in the field. In this study, the developmental toxicities associated with the diastereomeric properties of PM were evaluated using zebrafish (Danio rerio) embryos. Although neither PM diastereomer significantly affected survival or hatching rates, cis-PM induced dose-dependent developmental toxicity in zebrafish embryos, including reductions in body length and eye area, as well as yolk sac abnormalities, whereas trans-PM did not cause noticeable morphological alterations. Regarding cardiotoxicity, both cis-PM and trans-PM increased heart rate, while cis-PM additionally elevated stroke volume and ejection fraction. Neither PM diastereomer showed severe toxicity toward liver development; however, only cis-PM caused pronounced neurological disorders, including significant reductions in midbrain and hindbrain area, decreased locomotor activity, and seizure-like events identified using AI-assisted analysis. In addition, cis-PM produced more pronounced region-specific apoptotic responses and increased reactive oxygen species generation compared with trans-PM. Furthermore, oxidative stress- and estrogen-related genes were downregulated in cis-PM-treated embryos. Taken together, these findings demonstrate that cis-PM exerts stronger developmental toxicity in zebrafish embryos than trans-PM, particularly with respect to brain development and behavioral abnormalities, including seizure-like events.