Environmental levels of 6PPD and 6PPD-Q induced neurotoxicity in zebrafish: Insights from molecular dynamics simulation, neurotransmitters, and transcriptomic analysis

As emerging pollutants, N-(1,3-dimethylbutyl)-N’-phenyl-p-phenylenediamine (6PPD) and 6PPD-quinone (6PPD-Q) are considered to pose potential neurotoxicity. However, their long-term effects on nervous system of aquatic organisms are rarely understood. The neurotoxicity of 6PPD and 6PPD-Q was investigated in zebrafish at environmental levels (10 and 100 μg/L) with long-term exposure (28 days). Both 6PPD and 6PPD-Q could cross the blood-brain barrier (BBB) and accumulate in zebrafish brain. Moreover, 6PPD and 6PPD-Q induced abnormal behavior, caused brain morphological abnormalities and apoptosis, as well as suppressed antioxidant levels in zebrafish brain. The levels of γ-aminobutyric acid, dopamine, and acetylcholine were reduced by 0.44-, 0.46-, and 0.65-fold at 100 μg/L 6PPD-Q group. Molecular dynamics simulation proved that the conformation of tight junction proteins (ZO-1 and Occludin) was disrupted by 6PPD and 6PPD-Q and thus the permeability of BBB was increased. Transcriptomic revealed that both of them perturbed GABAergic and Cholinergic pathways and disrupted the synthesis, transport, and receptor binding of neurotransmitters by dysregulating genes, such as gabra4, gabbr1b, pik3r5, adcy1a, and abat. Bax/Bcl2 pathway was involved in 6PPD- and 6PPD-Q-induced apoptosis. These findings provide valuable insights into the neurotoxicity mechanisms of 6PPD and 6PPD-Q, contributing to their further ecological risk assessments.