4-phenylbutyric acid mitigates triphenyl phosphate developmental neurotoxicity via the ER stress–autophagy–apoptosis axis in zebrafish embryos

Although environmental monitoring data for 4-phenylbutyric acid (4-PBA) remain limited, its potential co-occurrence with triphenyl phosphate (TPhP) in aquatic systems cannot be excluded, given its applications in agriculture and pharmaceuticals. The combined effects of these compounds on early neurodevelopment in organisms such as zebrafish remain largely unexplored. Here, zebrafish embryos were exposed from 2 h post-fertilisation (hpf) to TPhP, then co exposure to environmentally plausible 4-PBA (0.5 μM). Light–dark locomotion, high-light avoidance, and light–dark preference assays revealed that TPhP disrupted photomotor behaviors, whereas 4-PBA co-treatment partly restored normal activity. Morphological endpoints showed that TPhP-dependent delays in hatching, reduced body length, tachycardia, and ocular abnormalities; partly of these defects were significantly rescued by 4-PBA. Transgenic Tg (sox10: EGFP) imaging demonstrated that TPhP altered neural-crest patterning, an effect again rescued by 4-PBA. At the molecular level, TPhP activated the PERK–eIF2α–CHOP arm of endoplasmic-reticulum (ER) stress, increased reactive oxygen species (ROS) production, up-regulated autophagy and apoptosis markers, and disturbed dopamine/GABA homeostasis. Co-exposure to 4-PBA inhibited ER-stress gene expression, normalized ROS levels, suppressed excessive autophagy and apoptosis, and restored neurotransmitter balance. Collectively, these findings support a model in which the ER-stress–autophagy–apoptosis axis is a key contributor of TPhP-induced neurotoxicity and provide first evidence that a chemical chaperone can alleviate pollutant-mediated developmental damage in an aquatic vertebrate model.