Though little attention has been given to the possibility that glial cells may represent a target for the developmental neurotoxicity of organophosphorus (OP)
insecticides, recent evidence, obtained in particular with
chlorpyrifos (CP), suggests that developmental exposure to this compound may indeed target astrocytes. To substantiate and expand these observations, we carried out a series of in vitro studies utilizing fetal rat astrocytes and a human
astrocytoma cell line, 1321N1 cells, to investigate the effect of the OPs CP,
diazinon (DZ) and
parathion (P), their
oxygen analogs
chlorpyrifos oxon (CPO),
diazoxon (DZO) and
paraoxon (PO), and their metabolites
3,5,6-trichloro-2-pyridinol (TCP), 2-isopropyl-6-methyl-4-pyrimidol (
IMP) and para-
nitrophenol (PNP), on cell proliferation. In fetal rat astrocytes and
astrocytoma cells maintained in serum, CP, DZ, P, CPO, DZO, and PO induced a concentration-dependent inhibition in [(3)H]
thymidine incorporation with a very similar potency (IC(50) between 45 and 57 microM). Among the other metabolites, PNP was the most potent (IC(50)=70-80 microM), while TCP and
IMP were much less effective (IC(50)>100 microM). Cytotoxicity appears to account only for a small part of the effect on
DNA synthesis. OP
insecticides and their oxons were three- to six-fold more potent in inhibiting [(3)H]
thymidine incorporation when cells were synchronized in the G(0)/G(1) phase of the cell cycle and re-stimulated by
carbachol or
epidermal growth factor. These results suggest that OP
insecticides and their oxons affect astroglial cell proliferation and that the transition from the G(0)/G(1) to the S/G(2) phase of the cell cycle may be particularly sensitive to the action of these compounds.