Low Doses of Nicotine and Ethanol Induce CYP2E1 and Chlorzoxazone Metabolism in Rat Liver
- Departments of 1Pharmacology (L.A.H., A.L.M., E.M.S., R.F.T.) and2Psychiatry (E.M.S.), 3Centre for Addiction and Mental Health (E.M.S., R.F.T.), University of Toronto, Toronto, Ontario, Canada
- Rachel F. Tyndale, Department of Pharmacology, 1 King's College Circle, University of Toronto, Toronto, ON, Canada M5S 1A8. E-mail: r.tyndale{at}utoronto.ca
Abstract
The use of ethanol and nicotine is strongly linked; 80 to 95% of heavy alcohol users are also smokers. In humans, cigarette smoking significantly enhances CYP2E1 activity, as measured by increased metabolism of chlorzoxazone in vivo. CYP2E1 metabolizes ethanol and can generate toxic intermediates. CYP2E1 also bioactivates tobacco smoke and other procarcinogens and several hepatotoxins. We hypothesized that, like ethanol, nicotine increases CYP2E1 activity. Rats were treated once daily with saline, ethanol (0.3, 1.0, and 3.0 g/kg p.o.), or nicotine bitartrate (0.1, 0.3, and 1.0 mg base/kg s.c.) for 7 days. After ethanol or nicotine administration, immunostaining for CYP2E1 was increased in the centrilobular regions of rat liver. Western blot analyses revealed that hepatic CYP2E1 levels were increased by ethanol (1.6–2.4-fold) and nicotine (1.3–1.7-fold). In vitro chlorzoxazone 6-hydroxylation analyses demonstrated elevatedVmax values (compared with saline-treated animals) by using hepatic microsomes from high-dose ethanol (2.27 ± 0.12 versus 1.18 ± 0.23 nmol/mg/min, p < 0.001) or nicotine-treated rats (2.35 ± 0.04 versus 1.32 ± 0.55 nmol/mg/min, p < 0.005), with no change in affinity. The magnitude of enhanced chlorzoxazone metabolism by microsomes from drug-treated animals is consistent with the observed increase in CYP2E1 protein by immunoblot. These data suggest that nicotine may increase CYP2E1-induced toxicity and contribute to cross-tolerance in smokers and people treated with nicotine (e.g., smokers, patients with Alzheimer's disease, ulcerative colitis, neuropsychiatric motor disorders).
Footnotes
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This work was supported by the Canadian Institutes for Health Research (Grant MT14173), National Institute on Drug Abuse (Grant DA 06889), and the Center for Addiction and Mental Health. L.A.H. was supported by scholarships from the Canadian Institutes for Health Research, the Natural Sciences and Engineering Council of Canada, the Center for Addiction and Mental Health, and the Ontario Ministry of Training, Colleges and Universities.
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A preliminary report of this study was presented at the following conferences and published in abstract form: Howard LA, Miksys S, and Tyndale RF (2000) Chronic nicotine and ethanol induce CYP2E1 in rat brain and liver in vivo, 13thInternational Symposium on Microsomes and Drug Oxidations, Abstract 207, p 161; and Howard LA, Miksys S, Zhang W, Sellers E, and Tyndale RF (2001) Chronic in vivo nicotine treatment increases CYP2E1, American Society for Pharmacology and Experimental Therapeutics at Experimental Biology 2001, Abstract 5045.
- Abbreviations:
- CYP
- cytochrome P450
- ADH
- alcohol dehydrogenase
- ALD
- alcoholic liver disease
- CZN
- chlorzoxazone
- PBS
- phosphate-buffered saline
- 6-OH-CZN
- 6-hydroxychlorzoxazone
- DDC
- diethyldithiocarbamate
- PCR
- polymerase chain reaction
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- Received April 3, 2001.
- Accepted July 26, 2001.
- The American Society for Pharmacology and Experimental Therapeutics
