Journal article
In vitro-in vivo correlations of human ( s)-nicotine metabolism
Biochemical pharmacology, Vol.50(4), pp.565-570
1995
Handle:
https://hdl.handle.net/2376/114076
PMID: 7646564
Abstract
The profile of (
S)-nicotine metabolism in human liver microsomes was examined at concentrations approaching
in vivo conditions (10 μM). At such concentrations, no (
S)-nicotine
N-1′-oxygenation was seen, and thus
C-oxidation to the (
S)-nicotine
Δ
1′,5′-iminium ion was the sole product observed in the metabolic profile in the presence of the human liver microsomes. For simplicity of analysis, the (
S)-nicotine
Δ
1′,5′-iminium ion formed was converted to (
S)-cotinine in the presence of exogenously added aldehyde oxidase. To explain the lack of (
S)-nicotine
N-1′-oxygenation at low (
S)-nicotine concentrations, inhibition of flavin-containing monooxygenase (FMO) activity by (
S)-cotinine was examined. Although (
S)-cotinine was observed to inhibit pig FMO1 (
K
i
= 675
μM), partially purified cDNA-expressed adult human liver FMO3 was not inhibited by (
S)-cotinine. We therefore concluded that the kinetic properties of the nicotine
N′- and
C-oxidases were responsible for the metabolic product profile observed. Kinetic constants were determined for individual human liver microsomal preparations from low (10 μM) and high (500 μM) (
S)-nicotine concentrations by monitoring (
S)-cotinine formation with HPLC. The mean
K
m
app
and
V
max for formation of (
S)-cotinine by the microsomes examined were 39.6 μM and 444.3 pmol· min
−1 · (mg protein)
−1, respectively. The formation of (
S)-cotinine was strongly dependent on the previous drug administration history of each subject, and among the highest rates for (
S)-cotinine formation were those of the barbiturate-pretreated subjects. The rate of (
S)-cotinine formation at low (10 μM) concentration correlated well with immunoreactivity for cytochrome P450 2A6 (
r = 0.89).
In vitro-in vivo correlation of the results suggests that the low amount of (
S)-nicotine
N-1′-oxygenation and the large amount of (
S)-cotinine formed in human smokers (i.e. 4 and 30% of a typical dose, respectively) are determined primarily by the kinetic properties of the human monooxygenase enzyme systems. However, additional non-hepatic monooxygenase(s) contributes to (
S)-nicotine metabolism.
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Details
- Title
- In vitro-in vivo correlations of human ( s)-nicotine metabolism
- Creators
- Clifford E Berkman - Seattle Biomedical Research Institute, Seattle, WA 98109 U.S.ASang B Park - Seattle Biomedical Research Institute, Seattle, WA 98109 U.S.ASteven A Wrighton - Lilly Research Laboratories, Eli Lilly & Company, Indianapolis, IN 46285, U.S.AJohn R Cashman - Seattle Biomedical Research Institute, Seattle, WA 98109 U.S.A
- Publication Details
- Biochemical pharmacology, Vol.50(4), pp.565-570
- Publisher
- Elsevier Inc
- Identifiers
- 99900547720301842
- Language
- English
- Resource Type
- Journal article