Is oxidative stress involved in the developmental neurotoxicity of chlorpyrifos?

The increasing use of chlorpyrifos (CPF) has elicited concern about neuroto xic effects on the fetus and neonate. CPF targets a number of events specif ic to brain development, over and above the ability of its active metabolit e, CPF oxon, to inhibit cholinesterase. We used PC12 cells, a model system which displays many of the neurodevelopmental effects of CPF, in order to e xamine whether oxidative stress underlies the direct effects of CPF on deve lopment. Production of reactive oxygen species (ROS) was measured with a fl uorescent intracellular dye. When PC12 cell suspensions were treated acutel y with CPF for 10 min, ROS generation was increased in a concentration-depe ndent manner; CPF oxon was much less effective than the native compound. CP F also increased the ROS production in response to an acute sodium nitropru sside challenge, indicating sensitization of the cells to other oxidant str essors. Next, PC12 cells were grown in an undifferentiated state in the pre sence of CPF or CPF oxon for extended time periods, under conditions in whi ch CPF inhibits mitosis, and the cells were then washed and ROS production measured. Neither compound elicited a significant change in ROS production. Finally, differentiation was initiated with nerve growth factor and the ce lls were exposed continuously to CPF or CPF oxon over a 72 h period; under these conditions, CPF inhibits neurite outgrowth. When the cells were washe d and evaluated for ROS production, no significant differences were seen. T hese results indicate that CPF, but not CPF oxon, has the ability to elicit acute increases in ROS production. However, the effect disappears immediat ely once CPF exposure is terminated, possibly reflecting cellular defense m echanisms that lessen the impact of oxidant injury. (C) 2000 Elsevier Scien ce B.V. All rights reserved.