In vitro and in vivo effects of chlorpyrifos on glutathione peroxidase and catalase in developing rat brain

Preliminary findings of a study on the role of oxidative stress in the developmental neurotoxicity of chlorpyrifos (CPF) indicates that in vitro exposure to 1-100 microM CPF or 1-100 nM CPF-oxon had no effect on the activity of glutathione peroxidase (GSHpx) in brain homogenates from postnatal day (PN) 21 rats, or on the activity of purified GSHpx. A single high-dose acute injection of 45 mg/kg CPF to PN19 rats also did not significantly alter GSHpx activity at PN21, in spite of extensive (72%) brain acetylcholinesterase (AChE) inhibition. However, catalase activity was significantly reduced by 28%. PN21 pups exposed maternally to a lower effective dose of CPF throughout development (dams injected with 50 mg/kg every 3 days) also had normal GSHpx activity, but a 30% increase in H2O2-independent NADPH consumption. Brain catalase activity in these rats was significantly increased by 24%. These preliminary data suggest that specific GSHpx activity is not altered by in vitro or in vivo exposures to CPF-oxon or CPF, but catalase and an unknown H2O2-independent NADPH-consuming factor were affected differentially depending on the type and timing of exposure.