Effect of cytochrome P450 1A induction on oxidative damage in rat brain.

Polycyclic and halogenated aromatic hydrocarbons (PAHs and HAHs) can enhance the generation of reactive oxygen species (ROS) by inducing cytochrome P450 1A (CYP 1A) in vivo and in vitro. While the brain is vulnerable to oxidative injury, whether or not CYP 1A induction in the brain can produce measurable levels of oxidative damage has not been reported. The objective of this study was to investigate the effect of this induction on oxidative damage to the CNS. Time course changes in rat brain CYP 1A activity were determined by measurement of ethoxyresorufin O-deethylase (EROD) activity in whole brain homogenates. Three days after exposure of rats to five daily injections of 3-methylcholanthrene (3-MC) an approximately sevenfold increase in EROD activity was observed. Hepatic levels were increased 60-100 fold. This increase in CYP 1A activity was not accompanied by increased protein or lipid oxidation as measured by tryptophan fluorescence and TBAR formation, or decreased glutamine synthetase (GS) activity. These findings indicate that if increased CYP 1A activity in the brain following 3-MC treatment leads to increased ROS generation, the increase is insufficient to overwhelm the endogenous antioxidant defense system, produce detectable oxidative damage, and alter glutamate homeostasis.