Rat brain CYP2B induction by nicotine is persistent and does not involve nicotinic acetylcholine receptors

Abstract

CYP2B is a drug-metabolizing enzyme expressed in the liver and brain that metabolizes a variety of centrally acting drugs (e.g. propofol, bupropion and nicotine), endogenous neurochemicals (e.g. serotonin and testosterone) and toxins (e.g. chlorpyrifos). Human CYP2B6 is found at higher levels in the brains of smokers, and 7-day nicotine treatment induces rat brain CYP2B while not altering hepatic CYP2B. We characterized the time course of rat brain CYP2B induction by nicotine and determined if nicotinic acetylcholine receptors (nAChRs) mediated this induction. Rats were treated once daily with 1 mg/kg nicotine base or saline s.c. for 1 or 7 days and sacrificed from 30 minutes to 7 days after the last injection. One-day nicotine treatment did not induce brain CYP2B, whereas 7-day nicotine treatment significantly increased CYP2B expression for up to 24 hours in the frontal cortex and brainstem; these levels returned to baseline by 7 days post-treatment. CYP2B activity was also higher at 24 hours in these regions. No change was seen in the cerebellar CYP2B levels or in vivo activity following nicotine treatment. Time of day of treatment and sacrifice altered the magnitude of brain CYP2B induction while chlorisondamine, an irreversible nAChR blocker, pre-treatment did not block CYP2B induction. Seven-day nicotine treatment resulted in an induction of rat brain CYP2B protein and in vivo activity for up to 24 hours, which would suggest greater local drug metabolism by brain CYP2B. Humans or animals exposed to nicotine may have altered therapeutic drug response, brain levels of neurotransmitters and/or neurotoxicity.