Melatonin improves mouse oocyte quality from 2-ethylhexyl diphenyl phosphate-induced toxicity by enhancing mitochondrial function.

2-Ethylhexyl diphenyl phosphate (EHDPP) is a representative organophosphorus flame retardant (OPFR) that has garnered attention due to its widespread use and potential adverse effects. EHDPP exhibits cytotoxicity, genotoxicity, developmental toxicity, and endocrine disruption. However, the toxicity of EHDPP in mammalian oocytes and the underlying mechanisms remain poorly understood. Melatonin is a natural free radical scavenger that has demonstrated cytoprotective properties. In this study, we investigated the effect of EHDPP on mouse oocytes in vitro culture system and evaluated the rescue effect of melatonin on oocytes exposed to EHDPP. Our results indicated that EHDPP disrupted oocyte maturation, resulting in the majority of oocytes arrested at the metaphase I (MI) stage, accompanied by cytoskeletal damage and elevated levels of reactive oxygen species (ROS). Nevertheless, melatonin supplementation partially rescued EHDPP-induced mouse oocyte maturation impairment. Results of single-cell RNA sequencing (scRNA-seq) analysis elucidated potential mechanisms underlying these protective effects. According to the results of scRNA-seq, we conducted further tests and found that EHDPP primarily disrupts mitochondrial distribution and function, kinetochore-microtubule (K-MT) attachment, DNA damage, apoptosis, and histone modification, which were rescued upon the supplementation of melatonin. This study reveals the mechanisms of EHDPP on female reproduction and indicates the efficacy of melatonin as a therapeutic intervention for EHDPP-induced defects in mouse oocytes.