Concurrent endoplasmic reticulum stress and demyelination in DEHP-exposed zebrafish larvae at the early developmental stages.

Di-ethylhexyl phthalate (DEHP) is an endocrine disruptor with established neurotoxic as well as potential neurodegenerative effects. The myelin sheath plays a crucial role in maintaining the health of the nervous system, whereas demyelination contributes to the onset of brain diseases. This study investigated the effect of DEHP on the neurological development with special reference to endoplasmic reticulum (ER) stress, inflammation, and concurrently with demyelination and cellular apoptotic development in zebrafish larvae. Results indicated that DEHP exposure can lead to demyelination through ER stress and inflammation, as evident from the decreased expression of myelin basic protein (Mbp) in both the brain and spinal cord of zebrafish larvae analyzed through immunofluorescent assay. The mRNA expression of axon marker nfl significantly increased, while tuba1a was decreased with DEHP exposure. Western blotting analysis revealed that ER stress markers such as phosphorylated inositol-requiring enzyme 1 alpha (p-Ire1α), activating transcription factor 4 (Atf4), binding immunoglobulin protein (Bip), phosphorylated e-IF2 alpha (p-eIF2α), CCAAT/enhancer-binding protein homologous protein (Chop), and inflammatory markers (nuclear factor kappa B subunit p65; Nf-κb p65), ionized calcium-binding adaptor molecule 1 (Iba1), and glial fibrillary acid protein (Gfap), were significantly upregulated on exposure to DEHP. Scototaxis, a behavioral assay, showed an altered anxiety-like behaviour in DEHP-treated larvae. Oxidative stress markers, such as superoxide dismutase (SOD), catalase, and monoamine oxidase (MAO) were also elevated. Apoptotic cells were observed in DEHP-treated zebrafish larvae in acridine orange staining. Overall, the DEHP exposure to zebrafish larvae caused myelin sheath degeneration and axonal dysfunction due to the generation of ER stress and inflammation.