Does the developmental neurotoxicity of chlorpyrifos involve glial targets? Macromolecule synthesis, adenylyl cyclase signaling, nuclear transcription factors, and formation of reactive oxygen in C6 glioma cells

The widespread use of chlorpyrifos (CPF) has raised major concerns about it s potential to cause fetal or neonatal neurobehavioral damage, even at dose s that do not evoke acute toxicity. CPF has been shown to inhibit replicati on of brain cells, to elicit alterations in neurotrophic signaling governin g cell differentiation and apoptosis, and to evoke oxidative stress. Howeve r, the specific cell types targeted by CPF have not been clarified, an issu e of vital importance in establishing the boundaries of the critical period in which the developing brain is vulnerable. In the current study, we eval uated the effects of CPF on C6 glioma cells, a well-established glial model . In undifferentiated C6 cells, CPF inhibited DNA synthesis in a concentrat ion-dependent manner, with greater potency than had been seen previously wi th neuronal cell lines. Just as found after in vivo CPF treatment or with n euronal cell lines, the effects on cell replication were independent of cho linergic stimulation, as cholinergic antagonists did not block CPF-induced inhibition. CPF interfered with cell signaling mediated through adenylyl cy clase at the level of G-protein function; the effects again were greater in undifferentiated C6 cells but were still delectable in differentiating cel ls. In contrast, differentiation enhanced the ability of CPF to elicit the formation of reactive oxygen species and to evoke deficits in Sp1, a nuclea r transcription factor essential for differentiation. These results indicat e that glial-type cells are targeted by CPF through the same multiple mecha nisms that have been demonstrated for the effects of CPF on brain developme nt in vivo. Because glial development continues long after the conclusion o f neurogenesis, and given that CPF targets events in both glial cell replic ation and the later stages of differentiation, the vulnerable period for de velopmental neurotoxicity of CPF is likely to extend well into childhood. ( C) 2001 Elsevier Science B.V. All rights reserved.