Acetylcholinesterase (AChE) inhibition has been described as the main mechanism of organophosphate (OP)-evoked toxicity. OPs represent a human health threat, because chronic exposure to low doses can damage the developing brain, and acute exposure can produce long-lasting damage to adult brains, despite post-exposure medical countermeasures. Although the main mechanism of OP toxicity is AChE inhibition, several lines of evidence suggest that OPs also act by other mechanisms. We hypothesized that rat neural progenitor cells extracted on embryonic day 14.5 would be affected by constant inhibition of AChE from chronic exposure to OP or pyridostigmine (a reversible AChE blocker) during differentiation. In this work, the OP paraoxon decreased cell viability in concentrations >50 μM, as measured with the MTT assay; however, this effect was not dose-dependent. Reduced viability could not be attributed to blockade of AChE activity, since treatment with 200 µM pyridostigmine did not affect cell viability, even after 6 days. Although changes in protein expression patterns were noted in both treatments, the distribution of differentiated phenotypes, such as the percentages of neurons and glial cells, was not altered, as determined by flow cytometry. Since paraoxon and pyridostigmine each decreased neurite outgrowth (but did not prevent differentiation), we infer that developmental patterns may have been affected.
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This work was supported by the following NIH Grants: NINDS SNRP U54NS083924 (AHM), NIMHD RTRN Small Grant U54RR022762 (AHM), NIMHD 8G12MD007583 RCMI Biomedical Proteomics Facility (NMB), NIMHD 8G12MD007583 RCMI Neural Glial Facility (PAF). The authors wish to thank Madeline Rodriguez and Sheila Lopez for their valuable research contribution during the preparation of this manuscript and the Proteomics Center at the University of Texas Medical Branch for the mass spectrometry service. HU acknowledges grant support from Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brazil. CAT and PDN acknowledge fellowship support from FAPESP. SLBO was supported by CNPq.
Conflict of interest
The authors declare that they have no conflict of interest.
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