Cytotoxicity of organophosphate anticholinesterases

  • C. J. Cao
  • R. J. Mioduszewski
  • D. E. Menking
  • J. J. Valdes
  • E. J. Katz
  • M. E. Eldefrawi
  • A. T. Eldefrawi
Cellular And Molecular Toxicology

Summary

Organophosphate (OP) anticholinesterases were found to modulate metabolic activities of human neuroblastoma cells and hepatocytes, which was detectable by the Cytosensor® microphysiometer. The nerve gas ethyl-S-2-diisopropylaminoethyl methylphosphorothiolate (VX), at 10 µM, produced significant reduction in cell metabolism within 2 min, as measured by changes in the acidification rate of the medium. The reduction was dose-and time-dependent and irreversible after 4 h of exposure. Two alkaline degradation products of VX produced no cytotoxicity. Exposure for 24 h to 3 µM VX caused 36% and 94% irreversible loss of metabolism in hepatocytes and neuroblastoma cells, respectively. The insecticides parathion and chlorpyrifos stimulated hepatocyte metabolism but inhibited neuroblastoma cells. Their oxons were more active. Exposure of neuroblastoma cells for 4 h to VX, parathion, paraoxon, diisopropylfluorophosphate or chlorpyrifos gave an LC50 of 65, 775, 640, 340, or 672 µM, respectively, whereas 24 h gave an LC50 of 0.7, 3.7, 2.5, 29, and 31 µM, respectively. Preincubation of hepatocytes with phenobarbital enhanced their response to parathion and VX due to metabolic bioactivation. Atropine partially blocked the effects of VX and paraoxon on both cell types, which suggests the involvement of a muscarinic receptor as the target for cytotoxicity. There was no correlation between OP in vivo neurotoxicity and in vitro cytotoxicity. It is suggested that the former results from their cholinesterase inhibition, while the latter results from action on different targets and requires much higher concentrations.

Key words

bioactivation enzyme induction hepatocytes human cell cultures in vitro cytotoxicity media acidification rate microphysiometer neuroblastoma cells organophosphate anticholinesterases 

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Copyright information

© Society for In Vitro Biology 1999

Authors and Affiliations

  • C. J. Cao
    • 1
  • R. J. Mioduszewski
    • 2
  • D. E. Menking
    • 2
  • J. J. Valdes
    • 2
  • E. J. Katz
    • 1
  • M. E. Eldefrawi
    • 1
  • A. T. Eldefrawi
    • 1
  1. 1.Department of Pharmacology and Experimental TherapeuticsUniversity of Maryland School of MedicineBaltimore
  2. 2.Research and Technology DirectorateEdgewood Research Development and Engineering Center, Aberdeen Proving GroundAberdeen

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