IPPD-induced growth inhibition and its mechanism in zebrafish

N-isopropyl-N-phenyl-1,4-phenylenediamine (IPPD) is used as a ubiquitous antioxidant worldwide, it is an additive in tire rubber easily discharged into the surrounding environment. At present, there is no study concerning the subacute toxicity of IPPD on fish. We used zebrafish embryos (2 h post-fertilization) exposed to IPPD for 5 days at concentrations of 0, 0.0012, 0.0120 and 0.1200 mg/L to investigate its toxic effects of embryonic development, disruption of growth hormone/insulin-like growth factor (GH/IGF) and hypothalamic-pituitary-thyroid (HPT) axis. The results showed that IPPD exposure decreased hatchability, weakened movement ability, reduced body length, and caused multiple types of deformities in zebrafish embryos. The expression of genes involved to GH/IGF and HPT axis were altered after exposure to IPPD in zebrafish larvae. Meanwhile, exposure to IPPD significantly decreased thyroxine (T4) and 3,5,3'-triiodothyronine (T3) contents in larvae, which indicated that HPT axis was in a disturbed state. Moreover, treatment of IPPD decreased the enzymatic activities of superoxide dismutase (SOD) and catalase (CAT) as well as levels of glutathione (GSH). While the contents of malondialdehyde (MDA) were elevated after exposure to IPPD. The present study thus demonstrated that IPPD induced oxidative stress, caused developmental toxicity and disrupted the GH/IGF and HPT axis of zebrafish, which could be responsible for developmental impairment and growth inhibition.