Neurofilaments degradation as an early molecular event in tri-ortho-cresyl phosphate (TOCP) induced delayed neuropathy

Tri-ortho-cresyl phosphate (TOCP), an organophosphorus ester, is capable of producing organophosphorus ester-induced delayed neuropathy (OPIDN) in human being and sensitive animals. In the present study, adult hens were treated with TOCP by gavage at single dosage of 750 mg/kg, and sacrificed by decapitation on the corresponding time points of 1, 5, 10, and 21 day post-dosing, respectively. The tibial nerves were dissected, homogenized, and centrifuged at 100,000 × g. The level of neurofilaments protein in both pellet and supernatant fractions was determined. Western blot analysis showed a nearly depletion of NF-M and a dramatic decrease of NF-L in both fractions of tibial nerves. These changes were observed within 24 h of TOCP administration and then followed by an obvious recovery. In contrast, a progressive reduction in NF-H was observed in tibial nerves of TCOP-treated hens throughout the period of experiment. With the reduction of NF-L level, the rate of NF-L degradation demonstrated a significant increase in both fractions of tibial nerves. Furthermore, the expression of μ-calpain in tibial nerves was increased following TOCP. Taken together, these results demonstrated that NFs changes occurred much earlier than the clinical appearance of ataxia in TOCP-induced delayed neuropathy, indicating that disruption of NF homeostasis in peripheral nerves might be an early molecular event in the development of OPIDN.