Neuroprotective effect of nano-carboxymethyl chitosan from Doryteuthis sibogae against rotenone-induced Parkinson’s disease in the zebrafish model

This study investigates the neuroprotective effects of N-carboxymethyl chitosan (N-CMC) against rotenone (ROT)-induced Parkinson's disease (PD) in a zebrafish (ZF) model. In vivo experiments revealed that ROT-exposed ZF larvae exhibited reduced locomotor activity, increased edge preference, and impaired touch response, while N-CMC treatment significantly improved these behavioral parameters. The reactive oxygen species (ROS) levels in ROT-exposed larvae were elevated (37.75 %) but decreased with N-CMC treatment (30.28 %). Apoptosis was also reduced from 38.87 % in ROT-exposed larvae to 16.52 % with N-CMC treatment. In vitro studies using the N2A cell line confirmed N-CMC’s neuroprotective effects. In adult ZF, ROT exposure decreased locomotion, and N-CMC treatment reversed these effects, as demonstrated through ToxTrac analysis. Novel Tank and Light/Dark tests showed significant behavioral improvements with N-CMC. Neurotransmitter analysis indicated increased dopamine, GABA, and glutamate levels in ROT-exposed ZF, which were moderated with N-CMC treatment. Gene expression analysis of gap43, syn2a, and tuba1b showed upregulation in ROT-exposed ZF, while N-CMC treatment downregulated these genes. Antioxidant assays demonstrated that ROT decreased SOD, CAT, and GSH levels in the brain, while N-CMC treatment increased these antioxidant levels by 1.3-fold, 7.5-fold, and 1.3-fold, respectively. Histopathology revealed neuronal degeneration in ROT-exposed ZF brains, but N-CMC treatment protected the neuronal loss. This study is the first to explore the neuroprotective and antioxidant properties of N-CMC in a ZF model, indicating its potential therapeutic benefits over conventional ROT-based treatments for PD.