Regional and cellular induction of nicotine-metabolizing CYP2B1 in rat brain by chronic nicotine treatment

doi:10.1016/S0006-2952(00)00281-1

Biochemical Pharmacology

Volume 59, Issue 12, June 2000, Pages 1501-1511

https://doi.org/10.1016/S0006-2952(00)00281-1 Get rights and content

Abstract

In the rat, nicotine is metabolized to cotinine primarily by hepatic cytochrome P450 (CYP) 2B1. This enzyme is also found in other organs such as the lung and the brain. Hepatic nicotine metabolism is unaltered after nicotine exposure; however, nicotine may regulate CYP2B1 in other tissues. We hypothesized that nicotine induces its own metabolism in brain by increasing CYP2B1. Male rats were treated with nicotine (0.0, 0.1, 0.3, or 1.0 mg base/kg in saline) s.c. daily for 7 days. CYP2B1 mRNA and protein were assayed in the brain and liver by reverse transcriptase-polymerase chain reaction (RT-PCR), immunoblotting, and immunocytochemistry. In control rats, CYP2B1 mRNA and protein expression were brain region- and cell-specific. CYP2B1 was not induced in the liver, but CYP2B1 mRNA and protein showed dose-dependent, region- and cell-specific patterns of induction across brain regions. At 1.0 mg nicotine/kg, the largest increase in protein was in the brain stem (5.8-fold, P < 0.05) with a corresponding increase in CYP2B1 mRNA (7.6-fold, P < 0.05). Induction of CYP2B1 was also observed in the frontal cortex, striatum, and olfactory tubercle. Immunocytochemistry showed that induction was restricted principally to neurons. These data indicate that nicotine may alter its own metabolism in the brain through transcriptional regulation, perhaps contributing to central tolerance to the effects of nicotine. CYP2B1 and its human homologue CYP2B6 also activate tobacco smoke procarcinogens such as NNK [4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone]. Highly localized increases in CYP2B could result in increased mutagenesis. These data suggest roles for nicotine-induced CYP2B in central metabolic tolerance, nicotine-induced neurotoxicity, neuroplasticity, and carcinogenesis.

Section snippets

Animals

Four groups (N = 6 per group) of adult male Wistar rats (250–300 g; Charles River) were injected s.c., once per day, for 7 days with 0, 0.1, 0.3, or 1.0 mg nicotine base/kg body weight, in the form of nicotine bitartrate (Sigma) in sterile saline adjusted to pH 7.4. The doses used in this study provided a range that was both behaviorally and pharmacologically relevant. This range included doses at which rats develop nicotine tolerance (0.4 mg/kg over 12 days, continuous infusion, e.g. Ref. 25),

CYP2B in untreated rat brain

On immunoblots we found a single immunoreactive band in brain that comigrated with induced hepatic CYP2B1; this band was not detected when the antibody was preadsorbed with expressed rat CYP2B1 protein (inset, Fig. 1 A), providing evidence that we were measuring CYP2B1 in these studies [38]. Immunoreactive protein was detected in all brain regions examined (Fig. 1). The level of CYP2B1 was much lower than that found in rat liver (approximately 80-fold less than in untreated rat liver, and

Discussion

In this study we have shown that CYP2B1 protein and mRNA are expressed variably across rat brain regions and specific cell types. In addition, we demonstrated that nicotine, a CYP2B1 substrate, can induce CYP2B1 and, hence, its own metabolism. The induction occurred in rat brain, but not in rat liver, and the pattern of induction was brain region- and cell type-specific. The cell-type specific induction occurred both in cells that normally have detectable CYP2B1 and in those that either

Acknowledgements

We would like to thank Ms. Yvette Grybowski for her technical assistance. This work was funded by MRC Grant MT14173 and the Centre for Addictions and Mental Health.

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Regional and cellular induction of nicotine-metabolizing CYP2B1 in rat brain by chronic nicotine treatment

Abstract

Section snippets

Animals

CYP2B in untreated rat brain

Discussion

Acknowledgements

Neuroscience

Biochem Pharmacol

Toxicol Appl Pharmacol

Neuroscience

Front Neuroendocrinol

Neuroscience

Pharmacol Biochem Behav

Biochem Pharmacol

Anal Biochem

Biochem Pharmacol

Biochem Pharmacol

Trends Pharmacol Sci

Biochem Pharmacol

Biochem Pharmacol

Neuroscience

Brain Res

Biochem Pharmacol

Neuroscience

Arch Biochem Biophys

Cancer Lett

Eur J Cancer

Brain Res

Cytochrome P450-dependent biotransformation of drugs and other xenobiotic substrates in neural tissue

Drug Metab Rev

Regional distribution of cytochrome P450 2D1 in the rat central nervous system

J Comp Neurol

Molecular modeling of mammalian CYP2B isoforms and their interaction with substrates, inhibitors and redox partners

Xenobiotica

Expression analysis of the mixed function oxidase system in rat brain by the polymerase chain reaction

Mol Cell Biochem

Regional distribution and expression modulation of cytochrome P-450 and epoxide hydrolase mRNAs in the rat brain

Mol Pharmacol

A major role for CYP2A6 in nicotine C-oxidation by human liver microsomes

J Pharmacol Exp Ther

Role of human cytochrome P4502A6 in C-oxidation of nicotine

Drug Metab Dispos

Metabolism of nicotine by rat liver cytochromes P-450. Assessment utilizing monoclonal antibodies to nicotine and cotinine

Drug Metab Dispos