Title: Chlorpyrifos induces apoptosis in rat cortical neurons that is regulated by a balance between p38 and ERK/JNK MAP kinases.

Authors: Caughlan, Anne; Newhouse, Kathleen; Namgung, Uk; Xia, Zhengui

Published In Toxicol Sci, (2004 Mar)

Abstract: Chlorpyrifos, an acetylcholinesterase (AChE) inhibitor, is a widely used organophosphate pesticide. Recent concern has focused on its neurotoxicity that is not attributable to AChE inhibition. Here, we report that chlorpyrifos and chlorpyrifos-oxon, but not 3,5,6-trichloro-2-pyridinol (TCP; the breakdown product of chlorpyrifos and chlorpyrifos-oxon), induce apoptosis in primary cortical neurons cultured from embryonic day 17 or newborn rats. It is generally agreed that chlorpyrifos-oxon is approximately three orders of magnitude more potent than chlorpyrifos in inhibition of brain acetylcholinesterase activity. However, our data demonstrate that chlorpyrifos-oxon is only slightly more potent than chlorpyrifos in inducing apoptosis. This indicates that chlorpyrifos-induced apoptosis may occur independently of AChE inhibition, although AChE activity was not measured in this study. Furthermore, chlorpyrifos activates the ERK1/2 and p38 MAP kinases. Surprisingly, blocking ERK1/2 activation by the MEK inhibitor SL327 caused a small but statistically significant inhibition of apoptosis, while blocking p38 with SB202190 significantly accelerated apoptosis induced by chlorpyrifos. This suggests a pro- and anti-apoptotic role for ERK1/2 and p38, respectively. Although chlorpyrifos did not stimulate total JNK activity, it caused a sustained activation of a sub-pool of JNK in the nucleus and stimulated phosphorylation of c-Jun, a downstream target of JNK. Transient expression of a dominant negative c-Jun mutant inhibited chlorpyrifos-induced apoptosis, suggesting a role for JNK and JNK-mediated transcription in this cell death. Together, our data suggest apoptosis as a novel toxic endpoint of chlorpyrifos neurotoxicity in the brain that may be independent of AChE inhibition. Furthermore, activation of the ERK1/2 and JNK MAP kinases contributes to, while activation of the p38 MAP kinase counteracts chlorpyrifos-induced apoptosis in cortical neurons.

PubMed ID: 14691213

MeSH Terms: Animals; Animals, Newborn; Apoptosis/drug effects*; Blotting, Western; Cell Nucleus/drug effects; Cell Nucleus/ultrastructure; Cells, Cultured; Cerebral Cortex/cytology*; Cerebral Cortex/drug effects; Chlorpyrifos/analogs & derivatives*; Chlorpyrifos/toxicity*; Embryo, Mammalian/cytology; Embryo, Mammalian/physiology; Female; Herbicides/toxicity; Immunohistochemistry; Insecticides/toxicity*; JNK Mitogen-Activated Protein Kinases*; MAP Kinase Kinase 4; Mitogen-Activated Protein Kinase Kinases/genetics*; Mitogen-Activated Protein Kinases/genetics*; Neurons/drug effects*; Pregnancy; Proto-Oncogene Proteins c-jun/biosynthesis; Pyridones/toxicity; Rats; Rats, Sprague-Dawley; Signal Transduction/drug effects; Tetrazolium Salts; Thiazoles; Transfection; p38 Mitogen-Activated Protein Kinases