Systematic in vivo (Zebrafish) and in vitro study on nanoplastics-induced AChE inhibition

Nanoplastics (NPs) are emerging environmental contaminants posing risks to aquatic organisms and human health. This study integrated in vivo (zebrafish) and in vitro (purified enzyme) approaches to systematically investigate the neurotoxic effects of polystyrene nanoplastics (PS-NPs) on brain acetylcholinesterase (AChE) activity and elucidate underlying mechanisms. Zebrafish exposed to PS-NPs (0.02, 0.2, 2 mg·L⁻¹) for up to 28 days exhibited concentration- and time-dependent suppression of brain AChE activity, disruption of the antioxidant defense system (altered SOD/CAT, increased ROS/MDA), and neurohistopathological damage. Vitamin E intervention significantly attenuated both AChE decline and oxidative stress markers. In vitro experiments revealed that PS-NPs directly inhibited purified AChE activity. Spectroscopic analyses (UV-Vis, CD, fluorescence) confirmed PS-NP-induced intrinsic fluorescence quenching, changes in amino acid microenvironments, and secondary-structure rearrangements consistent with a more compact enzyme conformation, likely impeding substrate access. This study is the first to demonstrate that PS-NPs suppress AChE activity via two synergistic mechanisms: oxidative stress induction and direct perturbation of AChE molecular conformation. Our findings advance the mechanistic understanding of nanoplastic neurotoxicity, providing a theoretical basis for developing early-warning indicators and risk assessment frameworks for emerging plastic pollutants.