Developmental neurotoxicity of organophosphates targets cell cycle and apoptosis, revealed by transcriptional profiles in vivo and in vitro.
Developmental organophosphate exposure reduces the numbers of neural cells, contributing to neurobehavioral deficits. We administered chlorpyrifos or diazinon to newborn rats on postnatal days 1-4, in doses straddling the threshold for barely-detectable cholinesterase inhibition, and evaluated gene expression in the cell cycle and apoptosis pathways on postnatal day 5. Both organophosphates evoked transcriptional changes in 20-25% of the genes in each category; chlorpyrifos and diazinon targeted the same genes, with similar magnitudes of change, as evidenced by high concordance. Furthermore, the same effects were obtained with doses above or below the threshold for cholinesterase inhibition, indicating a mechanism unrelated to anticholinesterase actions. We then evaluated the effects of chlorpyrifos in undifferentiated and differentiating PC12 cells and found even greater targeting of cell cycle and apoptosis genes, affecting up to 40% of all genes in the pathways. Notably, the genes affected in undifferentiated cells were not concordant with those in differentiating cells, pointing to dissimilar outcomes dependent on developmental stage. The in vitro model successfully identified 60-70% of the genes affected by chlorpyrifos in vivo, indicating that the effects are exerted directly on developing neural cells. Our results show that organophosphates target the genes regulating the cell cycle and apoptosis in the developing brain and in neuronotypic cells in culture, with the pattern of vulnerability dependent on the specific stage of development. Equally important, these effects do not reflect actions on cholinesterase and operate at exposures below the threshold for any detectable inhibition of this enzyme.
Department of Pharmacology & Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA. t.slotkin@duke.edu
Theodore A
TA
Slotkin
Frederic J
FJ
Seidler
D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000187:drug effects*; D001921:Brain / Q000187:drug effects* / Q000254:growth & development* / Q000378:metabolism / Q000473:pathology; D002453:Cell Cycle / Q000187:drug effects*; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D004390:Chlorpyrifos / Q000633:toxicity; D002800:Cholinesterase Inhibitors / Q000633:toxicity; D003976:Diazinon / Q000633:toxicity; D015870:Gene Expression / Q000187:drug effects; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000473:pathology*; D020258:Neurotoxicity Syndromes / Q000209:etiology* / Q000378:metabolism; D010755:Organophosphates / Q000633:toxicity*; D016716:PC12 Cells / Q000166:cytology / Q000187:drug effects; D051381:Rats; D014158:Transcription, Genetic / Q000187:drug effects
D002800:Cholinesterase Inhibitors; D010755:Organophosphates; D004390:Chlorpyrifos; D003976:Diazinon