Chlorpyrifos-oxon

Treatment of tubulin with 1.5 mM Chlorpyrifos-oxon (CPO) leads to protein aggregation. However, even at 1.5 μM Chlorpyrifos-oxon cross-linked trimers are apparent. Chlorpyrifos-oxon promotes isopeptide bond cross-linking of tubulin monomers to make multimers^[2].
In PC12 cells in culture, 24 hours of exposure to Chlorpyrifos at a concentration 10-fold below the concentration that inhibits AChE activity (3.0 μM) impaired neurite outgrowth while Chlorpyrifos-oxon inhibits neurite outgrowth at 1.0 nM^[3].

Chlorpyrifos-oxon (CPO) is rapidly detoxified by human liver microsomes via CYP-dependent deethylation and dearylation, and by glutathione-S-transferase. In addition, reactions with A-esterases such as paraoxonase 1 (PON 1) or B-esterases such as carboxylesterase and butyrylcholinesterase (BChE) in the liver may rapidly degrade or scavenge Chlorpyrifos-oxon^[1].
Chlorpyrifos-oxon (3 mg/kg, ip; once; wild-type mice) treatment shows the dimensions of microtubules from Chlorpyrifos-oxon-treated mice are about 60% of those from control mice. The microtubules from mice exposed to Chlorpyrifos-oxon have covalently modified amino acids and abnormal structure, suggesting disruption of microtubule function^[4].

References:
[1]. Florian Eyer, et al. Extreme variability in the formation of chlorpyrifos oxon (CPO) in patients poisoned by chlorpyrifos (CPF). Biochem Pharmacol. 2009 Sep 1;78(5):531-7.
[2]. Lawrence M Schopfer, et al. Chlorpyrifos oxon promotes tubulin aggregation via isopeptide cross-linking between diethoxyphospho-Lys and Glu or Asp: Implications for neurotoxicity. J Biol Chem. 2018 Aug 31;293(35):13566-13577.
[3]. Jie Gao, et al. Chlorpyrifos and chlorpyrifos oxon impair the transport of membrane bound organelles in rat cortical axons. Neurotoxicology. 2017 Sep;62:111-123.
[4]. Wei Jiang, et al. Mice treated with chlorpyrifos or chlorpyrifos oxon have organophosphorylated tubulin in the brain and disrupted microtubule structures, suggesting a role for tubulin in neurotoxicity associated with exposure to organophosphorus agents.