Effects of pyriproxyfen on zebrafish brain mitochondria and acetylcholinesterase

Pyriproxyfen is an insecticide used worldwide that acts as a biomimetic of juvenile hormone. This study investigated metabolic and synaptic impairments triggered by pyriproxyfen using zebrafish acetylcholinesterase (zbAChE) and mitochondria as markers. A brain zbAChE assay was performed in vitro and in vivo covering a range of pyriproxyfen concentrations (0.001-10 μmol/L) to assess inhibition kinetics. Docking simulations were performed to characterize inhibitory interactions. Zebrafish male adults were acutely exposed to 0.001, 0.01 and 0.1 μg/mL pyriproxyfen for 16 h. Mitochondrial respiration of brain tissues was assessed. ROS generation was estimated using H₂DCF-DA and MitoSOX. Calcium transport was monitored by Calcium Green™ 5 N. NO synthesis activity was estimated using DAF-FM-DA. Brain acetylcholinesterase showed an in vivo IC₂₀ of 0.30 μmol/L pyriproxyfen, and an IC₅₀ of 92.5 μmol/L. The inhibitory effect on zbAChE activity was competitive-like. Respiratory control of Complex I/II decreased significantly after insecticide exposure. The MitoSOX test showed that O₂^- generation had a pyriproxyfen dose-dependent effect. Brain tissue lost 50% of Ca²⁺ uptake capacity at 0.1 μg/mL pyriproxyfen. Ca²⁺ release showed a clear mitochondrial impairment at lower pyriproxyfen exposures. Thus, Ca²⁺ transport imbalance caused by pyriproxyfen may be a novel deleterious mechanism of action. Overall, the results showed that pyriproxyfen can compromise multiple and interconnected pathways: (1) zbAChE impairment and (2) the functioning of the electron transport chain, ROS generation and calcium homeostasis in zebrafish brain mitochondria. Considering the many similarities between zebrafish and human, more caution is needed when pyriproxyfen is used in both urban and agricultural pest control.