An approach based on a combination of toxicological experiments and in silico predictions to investigate the adverse outcome pathway (AOP) of paraquat neuro-immunotoxicity

Paraquat (PQ) exposure is strongly associated with neurotoxicity. However, studies investigating the mechanism of PQ neurotoxicity have varied in toxicity assessment endpoints, making it challenging to understand the early neurotoxic effects of PQ. In this study, we developed an adverse outcome pathway (AOP) to investigate PQ-induced neuro-immunotoxicity from an immunological perspective, using a combination of traditional toxicology methods and computer simulations. In this study, we confirmed in vivo that PQ exposure can lead to early synapse loss and that this change in brain micromechanisms leads to cognitive dysfunction in mice. We confirmed both in vitro and in vivo that synapse loss is caused by excessive activation of the complement C1q/C3-CD11b pathway, which mediates microglial phagocytosis dysfunction. The interaction between PQ and C1q was then validated by molecular simulation docking. Our findings extend the AOP framework related to PQ neurotoxicity from a neuro-immunotoxic perspective, highlighting C1q activation as the initiating event for PQ-induced neuro-immunotoxicity. In addition, downstream complement cascades induce abnormal microglial phagocytosis, resulting in reduced synaptic density and subsequent non-motor dysfunction. These findings deepen our understanding of PQ neurotoxicity and provide a theoretical basis for ecological risk assessment of PQ.