Chlorpyrifos-oxon, an active metabolite of Chlorpyrifos, is a potent phosphorylating agent that significantly inhibits AChE activity and induces cross-linking between tubulin subunits, thereby disrupting microtubule function [4].

Treatment with 1.5 mM Chlorpyrifos-oxon (CPO) induces aggregation in tubulin proteins. Remarkably, at a concentration as low as 1.5 μM, Chlorpyrifos-oxon still facilitates the formation of cross-linked trimers. This compound enhances the cross-linking of tubulin monomers through isopeptide bonds, resulting in the formation of multimers[2]. In the context of cultured PC12 cells, exposure to Chlorpyrifos at a concentration 10 times lower than that required to inhibit acetylcholinesterase (AChE) activity (3.0 μM) adversely affects neurite outgrowth. Conversely, Chlorpyrifos-oxon exhibits its inhibitory effect on neurite extension at an even lower concentration of 1.0 nM[3].

Chlorpyrifos-oxon (CPO) undergoes rapid detoxification in human liver microsomes through CYP-dependent deethylation and dearylation, as well as glutathione-S-transferase activity. Additionally, it is efficiently degraded or scavenged by liver enzymes, including A-esterases like paraoxonase 1 (PON 1) and B-esterases such as carboxylesterase and butyrylcholinesterase (BChE). Moreover, when wild-type mice are treated with Chlorpyrifos-oxon (3 mg/kg, ip; once), it significantly affects microtubule integrity, reducing their size to approximately 60% compared to those in control mice, indicating altered amino acid covalency and compromised microtubule structure, which suggests a disruption of their function[1][4].