| Ameliorating the Developmental Neurotoxicity of Chlorpyrifos: A Mechanisms-Based Approach in PC12 Cells Theodore A. Slotkin, Emiko A. MacKillop, Ian T. Ryde, and Frederic J. Seidler Department of Pharmacology & Cancer Biology, Duke University Medical Center, Durham, North Carolina, USA Abstract
Background: Organophosphate developmental neurotoxicity involves multiple mechanisms converging on neural cell replication and differentiation. Objectives: 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. Key words: adenylyl cyclase, brain development, chlorpyrifos, cholinergic antagonists, neurotoxicity, nicotine, organophosphate insecticides, oxidative stress, theophylline, vitamin E. Environ Health Perspect 115:1306–1313 (2007) . doi:10.1289/ehp.10194 available via http://dx.doi.org/ [Online 14 June 2007]
Address correspondence to T.A. Slotkin, Box 3813 DUMC, Duke University Medical Center, Durham, NC 27710 USA. Telephone: (919) 681-8015. Fax: (919) 684-8197. E-mail: t.slotkin@duke.edu This research was supported by grant ES10356 from the National Institutes of Health. T.A.S. and F.J.S. have served as expert witnesses on behalf of governmental entities, corporations, and/or individuals. The authors declare they have no competing financial interests. Received 26 February 2007 ; accepted 14 June 2007.
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