Developmental neurotoxicity of chlorpyrifos in vivo and in vitro: effects on nuclear transcription factors involved in cell replication and differentiation

Chlorpyrifos is a widely used organophosphate insecticide that is a suspect ed developmental neurotoxin. Although chlorpyrifos exerts some effects thro ugh cholinesterase inhibition, recent studies suggest additional, direct ac tions on developing cells. We assessed the effects of chlorpyrifos on nucle ar transcription factors involved in cell replication and differentiation u sing in vitro and in vivo models. HeLa nuclear protein extracts were incuba ted with the labeled consensus oligonucleotides for AP-1 and Spl transcript ion factors in the presence and absence of chlorpyrifos. In concentrations previously shown to affect cell development, chlorpyrifos reduced AP-1, but not Spl DNA-binding activity. Next, chlorpyrifos was incubated with PC12 c ells either during cell replication or after initiation of differentiation with NGF. Chlorpyrifos evoked stage-specific interference with the expressi on of the transcription factors: Spl was reduced in replicating and differe ntiating cells, whereas AP-1 was affected only during differentiation. Fina lly, neonatal rats were given apparently subtoxic doses of chlorpyrifos eit her on postnatal days 1-4 or 11-14 and the effects were evaluated in the fo rebrain (an early-developing, cholinergic target region) and cerebellum (la te-developing region, poor in cholinergic innervation). Again, chlorpyrifos evoked stage-specific changes in transcription factor expression and bindi ng activity, with greater effects on Spl during active neurogenesis, and ef fects on AP-1 during differentiation. The changes were present in both fore brain and cerebellum and were gender-specific. These results indicate that chlorpyrifos interferes with brain development, in part by multiple alterat ions in the activity of transcription factors involved in the basic machine ry of cell replication and differentiation Noncholinergic actions of chlorp yrifos that are unique to brain development reinforce the need to examine e ndpoints other than cholinesterase inhibition. (C) 2000 Elsevier Science B. V. All rights reserved.