Inactivation of CYP2A6 and CYP2A13 during nicotine metabolism

Research output: Contribution to journalArticle

44 Citations (Scopus)

Abstract

Nicotine is the major addictive agent in tobacco. The primary catalyst of nicotine metabolism in humans is CYP2A6. However, the closely related enzyme CYP2A13 is a somewhat better catalyst. CYP2A13 is an extrahepatic enzyme that is an excellent catalyst of the metabolic activation of the tobacco-specific carcinogen 4-(methylnitrosamine)-1-(3-pyridyl)-1-butanone (NNK). Here we report that both CYP2A6 and CYP2A13 were inactivated during nicotine metabolism. Inactivation of both enzymes was dependent on NADPH and increased with time and concentration. Alternate substrates for CYP2A6 and CYP2A13 protected these enzymes from inactivation. Inactivation of CYP2A13 was irreversible upon extensive dialysis and seems to be mechanism-based. The KI of CYP2A13 inactivation by nicotine was 17 μM, the rate of inactivation, k inact, was 0.1 min-1, and the t1/2 was 7 min. However, the loss in enzyme activity occurred after nicotine metabolism was complete, suggesting that a secondary or possible tertiary metabolite of nicotine may be responsible. [5-3H]Nicotine metabolism by CYP2A13 was monitored by radioflow high-pressure liquid chromatography during the course of enzyme inactivation; the major product was the Δ 1′(5′)iminium ion. However, cotinine was a significant metabolite even at short reaction times. The metabolism of the nicotine Δ1′(5′)iminium ion to cotinine did not require the addition of aldehyde oxidase. CYP2A13 catalyzed this reaction as well as further metabolism of cotinine to 5′-hydroxycotinine, trans-3′- hydroxycotinine, and N-(hydroxymethyl)-norcotinine as enzyme inactivation occurred. Studies are on-going to identify the metabolite responsible for nicotine-mediated inactivation of CYP2A13.

Original languageEnglish (US)
Pages (from-to)295-303
Number of pages9
JournalJournal of Pharmacology and Experimental Therapeutics
Volume316
Issue number1
DOIs
StatePublished - Jan 1 2006

Fingerprint

Nicotine
Cotinine
Enzymes
Tobacco
Aldehyde Oxidase
Ions
Butanones
NADP
Carcinogens
Dialysis
High Pressure Liquid Chromatography

Cite this

Inactivation of CYP2A6 and CYP2A13 during nicotine metabolism. / von Weymarn, Linda B; Brown, Kathryn M.; Murphy, Sharon E.

In: Journal of Pharmacology and Experimental Therapeutics, Vol. 316, No. 1, 01.01.2006, p. 295-303.

Research output: Contribution to journalArticle

@article{4bbc2c70ce024277b7803b7eac8b9d51,
title = "Inactivation of CYP2A6 and CYP2A13 during nicotine metabolism",
abstract = "Nicotine is the major addictive agent in tobacco. The primary catalyst of nicotine metabolism in humans is CYP2A6. However, the closely related enzyme CYP2A13 is a somewhat better catalyst. CYP2A13 is an extrahepatic enzyme that is an excellent catalyst of the metabolic activation of the tobacco-specific carcinogen 4-(methylnitrosamine)-1-(3-pyridyl)-1-butanone (NNK). Here we report that both CYP2A6 and CYP2A13 were inactivated during nicotine metabolism. Inactivation of both enzymes was dependent on NADPH and increased with time and concentration. Alternate substrates for CYP2A6 and CYP2A13 protected these enzymes from inactivation. Inactivation of CYP2A13 was irreversible upon extensive dialysis and seems to be mechanism-based. The KI of CYP2A13 inactivation by nicotine was 17 μM, the rate of inactivation, k inact, was 0.1 min-1, and the t1/2 was 7 min. However, the loss in enzyme activity occurred after nicotine metabolism was complete, suggesting that a secondary or possible tertiary metabolite of nicotine may be responsible. [5-3H]Nicotine metabolism by CYP2A13 was monitored by radioflow high-pressure liquid chromatography during the course of enzyme inactivation; the major product was the Δ 1′(5′)iminium ion. However, cotinine was a significant metabolite even at short reaction times. The metabolism of the nicotine Δ1′(5′)iminium ion to cotinine did not require the addition of aldehyde oxidase. CYP2A13 catalyzed this reaction as well as further metabolism of cotinine to 5′-hydroxycotinine, trans-3′- hydroxycotinine, and N-(hydroxymethyl)-norcotinine as enzyme inactivation occurred. Studies are on-going to identify the metabolite responsible for nicotine-mediated inactivation of CYP2A13.",
author = "{von Weymarn}, {Linda B} and Brown, {Kathryn M.} and Murphy, {Sharon E}",
year = "2006",
month = "1",
day = "1",
doi = "10.1124/jpet.105.091306",
language = "English (US)",
volume = "316",
pages = "295--303",
journal = "Journal of Pharmacology and Experimental Therapeutics",
issn = "0022-3565",
publisher = "American Society for Pharmacology and Experimental Therapeutics",
number = "1",

}

TY - JOUR

T1 - Inactivation of CYP2A6 and CYP2A13 during nicotine metabolism

AU - von Weymarn, Linda B

AU - Brown, Kathryn M.

AU - Murphy, Sharon E

PY - 2006/1/1

Y1 - 2006/1/1

N2 - Nicotine is the major addictive agent in tobacco. The primary catalyst of nicotine metabolism in humans is CYP2A6. However, the closely related enzyme CYP2A13 is a somewhat better catalyst. CYP2A13 is an extrahepatic enzyme that is an excellent catalyst of the metabolic activation of the tobacco-specific carcinogen 4-(methylnitrosamine)-1-(3-pyridyl)-1-butanone (NNK). Here we report that both CYP2A6 and CYP2A13 were inactivated during nicotine metabolism. Inactivation of both enzymes was dependent on NADPH and increased with time and concentration. Alternate substrates for CYP2A6 and CYP2A13 protected these enzymes from inactivation. Inactivation of CYP2A13 was irreversible upon extensive dialysis and seems to be mechanism-based. The KI of CYP2A13 inactivation by nicotine was 17 μM, the rate of inactivation, k inact, was 0.1 min-1, and the t1/2 was 7 min. However, the loss in enzyme activity occurred after nicotine metabolism was complete, suggesting that a secondary or possible tertiary metabolite of nicotine may be responsible. [5-3H]Nicotine metabolism by CYP2A13 was monitored by radioflow high-pressure liquid chromatography during the course of enzyme inactivation; the major product was the Δ 1′(5′)iminium ion. However, cotinine was a significant metabolite even at short reaction times. The metabolism of the nicotine Δ1′(5′)iminium ion to cotinine did not require the addition of aldehyde oxidase. CYP2A13 catalyzed this reaction as well as further metabolism of cotinine to 5′-hydroxycotinine, trans-3′- hydroxycotinine, and N-(hydroxymethyl)-norcotinine as enzyme inactivation occurred. Studies are on-going to identify the metabolite responsible for nicotine-mediated inactivation of CYP2A13.

AB - Nicotine is the major addictive agent in tobacco. The primary catalyst of nicotine metabolism in humans is CYP2A6. However, the closely related enzyme CYP2A13 is a somewhat better catalyst. CYP2A13 is an extrahepatic enzyme that is an excellent catalyst of the metabolic activation of the tobacco-specific carcinogen 4-(methylnitrosamine)-1-(3-pyridyl)-1-butanone (NNK). Here we report that both CYP2A6 and CYP2A13 were inactivated during nicotine metabolism. Inactivation of both enzymes was dependent on NADPH and increased with time and concentration. Alternate substrates for CYP2A6 and CYP2A13 protected these enzymes from inactivation. Inactivation of CYP2A13 was irreversible upon extensive dialysis and seems to be mechanism-based. The KI of CYP2A13 inactivation by nicotine was 17 μM, the rate of inactivation, k inact, was 0.1 min-1, and the t1/2 was 7 min. However, the loss in enzyme activity occurred after nicotine metabolism was complete, suggesting that a secondary or possible tertiary metabolite of nicotine may be responsible. [5-3H]Nicotine metabolism by CYP2A13 was monitored by radioflow high-pressure liquid chromatography during the course of enzyme inactivation; the major product was the Δ 1′(5′)iminium ion. However, cotinine was a significant metabolite even at short reaction times. The metabolism of the nicotine Δ1′(5′)iminium ion to cotinine did not require the addition of aldehyde oxidase. CYP2A13 catalyzed this reaction as well as further metabolism of cotinine to 5′-hydroxycotinine, trans-3′- hydroxycotinine, and N-(hydroxymethyl)-norcotinine as enzyme inactivation occurred. Studies are on-going to identify the metabolite responsible for nicotine-mediated inactivation of CYP2A13.

UR - http://www.scopus.com/inward/record.url?scp=29244464299&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=29244464299&partnerID=8YFLogxK

U2 - 10.1124/jpet.105.091306

DO - 10.1124/jpet.105.091306

M3 - Article

VL - 316

SP - 295

EP - 303

JO - Journal of Pharmacology and Experimental Therapeutics

JF - Journal of Pharmacology and Experimental Therapeutics

SN - 0022-3565

IS - 1

ER -