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.