Ameliorating the developmental neurotoxicity of chlorpyrifos: a mechanisms-based approach in PC12 cells.
BACKGROUND
Organophosphate developmental neurotoxicity involves multiple mechanisms converging on neural cell replication and differentiation.


OBJECTIVE
We evaluated mechanisms contributing to the adverse effects of chlorpyrifos (CPF) on DNA synthesis, cell number and size, and cell signaling mediated by adenylyl cyclase (AC) in PC12 cells, a neuronotypic cell line that recapitulates the essential features of developing mammalian neurons.


RESULTS
In undifferentiated cells, cholinergic receptor antagonists had little or no protective effect against the antimitotic actions of CPF; however, when nerve growth factor was used to evoke differentiation, the antagonists showed partial protection against deficits in cell loss and alteration in cell size elicited by CPF, but were ineffective in preventing the deterioration of AC signaling. Nicotine, which stimulates nicotinic acetylcholine receptors but also possesses a mixture of prooxidant/antioxidant activity, had adverse effects by itself but also protected undifferentiated cells from the actions of CPF and had mixed additive/protective effects on cell number in differentiating cells. The antioxidant vitamin E also protected both undifferentiated and differentiating cells from many of the adverse effects of CPF but worsened the impact on AC signaling. Theophylline, which prevents the breakdown of cyclic AMP, was the only agent that restored AC signaling to normal or supranormal levels but did so at further cost to cell replication.


CONCLUSIONS
Our results show definitive contributions of cholinergic hyperstimulation, oxidative stress, and interference with AC signaling in the developmental neurotoxicity of CPF and point to the potential use of this information to design treatments to ameliorate these adverse effects.
Slotkin
Theodore A
TA
Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA. t.slotkin@duke.edu
MacKillop
Emiko A
EA
Ryde
Ian T
IT
Seidler
Frederic J
FJ
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D000931:Antidotes / Q000494:pharmacology*; D000975:Antioxidants / Q000494:pharmacology; D001285:Atropine / Q000494:pharmacology; D001921:Brain / Q000196:embryology; D049109:Cell Proliferation / Q000187:drug effects; D004390:Chlorpyrifos / Q000633:toxicity*; D002800:Cholinesterase Inhibitors / Q000633:toxicity*; D004247:DNA / Q000378:metabolism; D007306:Insecticides / Q000633:toxicity*; D008464:Mecamylamine / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D018733:Nicotinic Antagonists / Q000494:pharmacology; D019384:Nucleic Acid Synthesis Inhibitors / Q000633:toxicity*; D018384:Oxidative Stress / Q000187:drug effects; D016716:PC12 Cells; D051381:Rats; D013806:Theophylline / Q000494:pharmacology; D014810:Vitamin E / Q000494:pharmacology