Content uploaded by Elmar Richter
Author content
All content in this area was uploaded by Elmar Richter on Oct 28, 2021
Content may be subject to copyright.
Carcinogenesls vol.15 no.5
pp.
1061-1064, 1994
Nicotine inhibits the metabolic activation of the tobacco-specific
nitrosamine 4-(methylnitrosamino)-l-(3-pyridyl)-l-butanone in rats+
E.Richter and A.R.Tricker1
Walther Straub-Insritut fflr Pharmakologie und Toxikologie, Ludwig-
Maximilians-UniversitSt MOnchen, Nussbaumstrasse 26, D-80336 Mflnchen
and 'Analytisch-biologisches Forschungslabor
Prof.
Dr med. Adlkofer,
Goethestrasse 20, D-80336 MQncben, Germany
The effect of
nicotine
on the metabolism of the tobacco-specific
nitrosamine 4-(methylnitrosamino)-l-(3-pyridyI)-l-butanone
(NNK) was studied in rats. [1-14C]NNK was s.c. injected at
a dose of 0.08 /unol/kg. Co-administration of a 500-fold higher
dose of nicotine (40 /unol/kg) did not reduce the overall
urinary excretion of radioactivity. However, the metabolic
pattern in 24 h urine was significantly changed. Metabolites
resulting from NNK activation by a-hydroxylation were
significantly (P <
0.001)
reduced to 72% of the control.
Detoxification to iV-oxides and the glucuronide of 4-(methyI-
nitrosamino)-l-(3-pyridyl)-l-butanol increased to 155%
(P < 0.01) and 188% (P < 0.01) of the control respectively.
These results suggest that nicotine, which occurs in concen-
trations up to 30 000-fold higher than NNK in mainstream
smoke of cigarettes may have a protective effect against
metabolic activation of NNK.
Introduction
The tobacco-specific nitrosamine 4-{methylnitrosamino)-l-
(3-pyridyl)-l-butanone (NNK*) has been suggested to be involved
in the induction of lung cancer in smokers (1,2). NNK is a po-
tent pulmonary carcinogen and also induces tumors of the nasal
mucosa, exocrine pancreas and liver in rats (1-3). Together with
A^-nitrosonornicotine (NNN), it may be involved in the etiology
of oral cancer in users of smokeless tobacco products (2).
NNK requires metabolic activation for expression of its
carcinogenicity. Studies in rodents conclusively demonstrate that
hydroxylation of the methylene and methyl carbons adjacent to
the A'-nitroso group (so-called a-hydroxylation) are the key
metabolic processes leading to the initiation of carcinogenesis
(1,4-9).
As shown in Figure
1
the common urinary metabolite
from these two reactions is 4-oxo-(3-pyridyl)butyric acid (keto
acid).
The product of NNK carbonyl reduction, 4-(methyl-
nitrosamino)-l-(3-pyridyl)-l-butanol (NNAL) is also a rodent
carcinogen (4,10). NNAL undergoes a-hydroxylation in a similar
way to NNK resulting in the formation of the common urinary
metabolite, 4-hydroxy-(3-pyridyl)butyric acid (hydroxy acid).
Detoxification pathways include glucuronidation of NNAL and
pyridine-A'-oxidation of both NNK and NNAL. All these
•Abbreviations: NNK, 4-(in(^lrdtiosarrdrio)-l-{3-pyrklyI)-l-butanone; NNN,
yV'-nitrosonomicotine; NNAL, 4-{mediylnitrosamirwH-(3-pyTidyI)-l-butanol;
hydroxy acid, 4-hydroxy-(3-pyridyl)butyric acid; keto acid, 4-oxo-(3-pyridyl)-
butyric acid; NNAL-GIuc, [4-{methylnitrosamino)-l-(3-pyridyl)-but-l-yl]-/3-
O-D-glucopyranosiduronic acid; NNAL-N-oxide, 4-{methylnitrosamino)-l-
(3-pyridyWV^Hide)-l-butanoJ; NNK-Moxide, 4^ir«hylnitrosamire>H-(3-pyridyl)-
JV-oxideH-butanone; HPB, 4-hydroxy-<3-pyridyI)-l-butanorje.
+Dedicated to Professor Dr R.Preussmarm on the occasion of his 65th birthday.
metabolic pathways have been demonstrated not only in rodent
species (1,4,10-13), but also in primates (14-16) and in human
tissues
(17 —
19).
In humans the presence of hemoglobin and DNA
adducts formed from NNK and/or NNN has been reported (20,
21).
Recendy, the NNK metabolites NNAL and its glucuronide
have been detected in 24 h urine of smokers (22).
The tobacco alkaloid nicotine, quantitatively the main component
of cigarette smoke, is present at 3000- to 30 000-fold higher
concentrations than NNK in the mainstream and sidestream
smoke (23,24). In rat oral tissue, nicotine inhibits the metabolic
activation of NNK when present at 100-fold higher concentrations
dian NNK (25). For the rabbit olfactory-specific cytochrome
P450 isozyme NMa, nicotine is a competitive inhibitor of NNK
a-hydroxylation (26). The only in vivo study using a NNK dose
far in excess of that of
nicotine
did not show any effect of nicotine
on NNK activation
(27).
Therefore, we investigated the metabolism
of NNK in the rat when given togedier widi a 500-fold higher
dose of nicotine.
Materials and methods
Chemicals
[1-MC]NNK with a sp. act. of 29 mCi/mmol was obtained from Chemsyn
Science Laboratories (Lenexa, KS). NNK metabolite standards were a gift from Dr
D.Hoffmann (American Health Foundation, Valhalla, NY). (-)Nicotine,
0-glucuronidase (type DC) and thimerosal (sodium ethylmercurithiosalicylate)
were obtained from Sigma Chemie GmbH (Tauflrirchen, Germany). All other
chemicals, which were of either HPLC or analytical grade, were purchased from
Merck (Darmstadt, Germany).
Animals
Male Wistar rats (85-110 g) from the breeding colony of the University of
Gomngen were housed in stainless sted metabolism cages in a fully air-conditioned
room (18 ± 1°C; 60 ± 5% humidity). The day-night cycle was 12 h (light
from 7 a.m.). The animals had unrestricted access to Alma H 1003 Laboratory
chow (F.Botzenhardt KG, Kempten, Germany) and drinking water. The animal
experiments were officially approved by the Government of Upper Bavaria
(AZ 211-2531-53/92).
Collection of rat urine
Groups of eight rats were administered 0.4 ml of saline with either
[
1-14C]NNK
(8 nmol = 1.66 pg) alone or [1-14C]NNK plus nicotine (4 ^mol = 650 /ig) by
s.c. injection. Urine was collected over 24 h time intervals for 2 days in
polyethylene vials containing a few grains of thimerosal. Aliquots of 100 and
500 itl from the first and second day of the experiment respectively were used
for total 14C determination. The remaining urine was cenlrifuged and the
supernatant stored at -20°C until analysis by HPLC.
HPLC analysis
Urine samples from the first 24 h of the experiment were chromatographed on
a 4.6 x 250 mm UChrosorb* RP18 SelectB column (Merck) by elution with
a gradient of 100% A for 0.5 min, linear to 80% A/20% B in 20 min and linear
to 20% A/80% B in 2 min (A: 20 mM Tris buffer, pH 7.2; B: acetonkrile) at
a flow rate of 0.7 ml/min. Detection of 14C was performed by solid-phase
radioactivity monitoring (Ramona, Raytest, Straubenhardt, Germany). Radioactive
metabolites were identified by co-chromatography with unlabeled reference
compounds detected by UV at 234 and 254 nm (UVD 160, Gynkotek, Germering
Germany). The O-ghicuronide of NNAL was further characterized by co-injecting
the purified radioactive compound obtained in a previous study (12) and by
treatment of urine with 0-glucuronidase (13).
Suaistical analysis
Reported values represent means ± standard error. Statistical analysis was
performed by the two-sided Mest for independent samples.
© Oxford University Press1061
E.Rkhter and A.R.Tricker
>T NNAL-Qfcic
HPBhy*cny»dd
Fig. 1. Metabolic scheme of NNK. Structures in brackets are hypothetical intermediates (13).
Results
The urinary excretion of NNK was studied in rats s.c. injected
with ~ 80 nmol/kg NNK either alone or in combination with
—
40 /imol/kg nicotine. This represents a 500-fold higher dose
of nicotine than NNK. In excess of 98% of the total urinary
excretion occurred within the first 24 h with no difference
between NNK only (72.4 ± 2.9%) and NNK plus nicotine
(74.8 ± 2.1%) treated rats.
Figure 2 shows typical HPLC profiles of
the
urinary metabolites
of [1-I4C]NNK obtained from rats treated with or without a
500-fold excess of
nicotine.
Peaks I and II co-eluted with hydroxy
acid and 4-oxo-4-(3-pyridyl)butyric acid (keto acid) resulting from
a-hydroxylation of NNK and NNAL respectively (Figure 1).
Peak in corresponds to [4-(methylnitrosamino)-l-(3-pyridyl)-
but-l-yl]-/3-OD-glucopyranosiduronic acid (NNAL-Gluc). Peaks
IV and V co-eluted with 4-(methylnitrosamino)-l-(3-pyridyl-
Ak)xide)-l-butanol (NNAL-A^-oxide) and 4-<methylnitrosamino)-
l-(3-pyridyl-A^-oxide)-l-butanone (NNK-N-oxide). 4-Hydroxy-
l-(3-pyridyl)-butanol (diol), 4-oxo-l-(3-pyridyl)-l-butanone (HPB)
and NNAL were occasionally detected. Of
these
three metabolites,
only NNAL exceeded 2% of the radioactivity in five and two
of eight samples of 24 h urine of the NNK only and NNK plus
nicotine-treated rats respectively.
Figure 3 shows the pattern of
the
five major NNK metabolites
in 24 h urine. Nicotine treatment significantly reduced the
formation of hydroxy acid and keto acid to
75%
(P < 0.001) and
69%
(P < 0.001) of
the
control respectively. The detoxification
products NNAL-Gluc and NNAL-N-oxide were significantly
increased by 188% (P < 0.01) and 163% (P < 0.001) of the
control
respectively
by co-administration of
nicotine.
The formation
of NNK-N-oxide was also increased 124% but the difference did
not reach statistical significance. In Table I the results are
presented as total amounts excreted in 24 h urine.
Discussion
Cigarette smoke contains several thousand different components,
of which nicotine is quantitatively the most abundant. Nicotine
occurs in concentrations 3000- to 30 000-fold higher than NNK
in mainstream cigarette smoke (23,24). As such, nicotine was
chosen as the first candidate with which to study the in vivo
inhibition of NNK metabolism. Previous in vitro studies have
shown that nicotine is a potent competitive inhibitor of NNK
a-hydroxylation in hamster lung (28), rat oral tissue (25) and
in rabbit nasal olfactory and respiratory microsomes (26). The
effect of multiple-dose exposure to nicotine on the in vivo
metabolism of NNK in rats (27) and in vitro pulmonary
metabolism of NNK in hamsters (29) has also been studied. In
both studies, 0.002% nicotine was administered in drinking water
for 14 days. After nicotine pretreatment, no inhibition of
in
vivo
metabolic activation of NNK was observed in rats given a single
i.v. dose of 0.4 mmol NNK/kg body wt (27). Contrary to this
finding, nicotine pretreatment of hamsters induced pulmonary
a-hydroxylation in lung explants (29). In both studies, the nicotine
dose was 2000- to 20 000-fold lower than that of NNK.
In the reported study, the nicotine dose was 500-fold higher
than that of NNK. Subcutaneous injection of both nicotine and
NNK was chosen as the route of administration. Following s.c.
injection, NNK is first transported to the lung, which is considered
to be the primary site of NNK metabolism. Previous studies using
N-nitrosodibutylamine have shown a high first-pass metabolism
in the lung following either s.c. or i.v. administration (30).
Numerous studies with isolated perfused rat lung (31) as well
as different in
vitro
preparations of rat lung (5,9,11,32—36) have
demonstrated extensive metabolism of NNK by a-hydroxylation,
N-oxidation and reduction to NNAL in this organ. Quantitative
comparison of urinary NNK metabolites in Wistar rats clearly
shows nicotine inhibition of the metabolic activation of this
1062
Nicotine Inhibition of NNK metabolism
21.0
15.0
II. 1
5.0
I.I
CPS
• i i i • i
c
iiNNK control
IV V
vwJW-WlVw*\v
1UTable I. Effect of nicotine on excretion of NNK metabolites in 24 h urine1
21
15
11
5
1
I
I
I
1
• -
CPS
1 1 1 1—I 1 T i i
NNK
1
+ nicotine
L
i
i i i
HC
1
III
15.11
Time (min)
Fig. 2. HPLC analysis of metabolites in the urine of rats 24 h following s.c.
administration of [1-14C]NNK at 80 nmol/kg with or without nicotine at
40 /tmol/kg. Labeling of radioactive peaks—hydroxy acid (I), keto acid (Tf),
NNAL-Gluc (III), NNAL-W-oxide (IV) and NNK-Ak>xide (V)—refers to
peaks co-eluting wim authentic standards added as UV markers.
o 40-
t
"S
30-
M-
o
^ 20-
c
IV
o
a 10-
f
•
1
T m
1 •
I
•
1 • 1
NNK control
NNK + nicotine
**
1
is A
III
Hydroxy
acidKeto
acid
NNALglu-
NNAL NNK
curonide N-oxide N-oxide
F^.
3. Effect of nicotine on die metabolite pattern in 24 h urine following
s.c. administration of [1-MC]NNK at 80 nmol/kg with or without nicotine at
40 /tmol/kg. Values are die mean ± SE of eight samples. Asterisks indicate
a statistically significant difference to the group given only NNK at
*P < 0.01 and **P <
0.001.
tobacco-specific nitrosamine (Table I). The largest suppression
was observed for the keto acid, which results from a-hydroxylation
of NNK (Figure 1). This decrease was not compensated by
Metabolitepmol detected in urine (% of urinary metabolites)
Hydroxy acid
Keto acid
NNAL-Gluc
NNAL-A'-oxide
NNK-Moxide
£ of alphab
£ of N-oxxtes
NNAL-Gluc + NNALC
Total
NNK
668 db 17
1332 ± 50
118 ± 20
441 ± 38
320 ± 37
2021 ± 57
720 ± 79
161 ± 21
2902 ±104
(22.4)d
(44.7)
(3.9)
(13.3)
(10.6)
(67.8)
(23.8)
(6.2)
(96.9)
NNK
502
919
222
719
397
1462
1116
296
2874
+
±
±
±
±
±
±
±
nicotine
24
35
26
27
54
41
68
41
105
(17.6)***
(31.9)***
(7.6)**
(23.0)***
(13.5)
(50.8)***
(38.5)**
(10.1)*
(99.3)
•Groups of eight male Wistar rats were administered [1-14C]NNK at a dose
of 80 nmol/kg wim or wimout nicotine at a dose of 40 /imol/kg. Urine was
collected for 24 h and analyzed for urinary metabolites of NNK as indicated
in the text.
'including hydroxy acid, keto acid, diol (detected in one sample from each
experiment) and HPB (detected in four and five samples from experiments
wim NNK and NNK + nicotine respectively).
"^NNAL was detected in five and six samples from experiments with NNK
and NNK + nicotine respectively.
dMean ± SE of eight samples. Values labeled are statistically significandy
different from the NNK group at *P < 0.05, **P < 0.01 and
••*/> <
0.001.
a comparable increase in NNK-ALoxide formation. Therefore,
the in vivo equilibrium existing between NNK and NNAL
as described by Adams et al. (15) is shifted in favor of
NNAL. The urinary excretion of hydroxy acid resulting from
a-hydroxylation of NNAL was also reduced. The excretion
of NNAL and its detoxification products, NNAL-Gluc and
NNAL-A'-oxide, expressed as total urinary excretion of I4C
nearly doubled from 19.9 ± 1.5% in control rats to
35.1 ± 1.0% in rats treated with nicotine.
Whether nicotine specifically inhibits metabolic activation of
NNK by a-hydroxylation at either the methylene or methyl
carbon atom adjacent to the N-nitroso group or both sites
simultaneously, cannot be determined from the present results.
Methylene hydroxylation produces methanediazohydroxide,
which can methylate DNA bases in vivo. Methyl hydroxylation
yields 4-(3-pyridyl)-4-oxobutanediazohydroxide, which pyridyl-
oxobutylates DNA. Which of these two pathways plays the
predominant role in the proposed carcinogenic effect of NNK
in humans is unknown (37). The extent of pyridyloxobutylation
of DNA by NNK can be estimated by measuring HPB released
by alkaline hydrolysis of hemoglobin (38). This HPB-releasing
adduct is also formed by NNN (39) and has been quantified in
tobacco users, since it is considered to be a surrogate marker
for the uptake and activation of both NNN and NNK (20). Such
studies show a < 3-fold difference in HPB-releasing hemoglobin
adduct levels in smokers and nonsmokers (20,40,41). The results
of the present study clearly show that nicotine inhibits NNK
a-hydroxylation, the required metabolic step in the formation
of HPB-releasing adducts.
Additional comparative studies need to be performed with
NNN, both NNN and NNK in combination and with a higher
nicotine dose relative to both nitrosamines to determine the full
extent of nicotine inhibition of tobacco-specific nitrosamine
metabolism. Furthermore, the mechanisms of nicotine inhibition
of NNK metabolism and both hemoglobin and tissue adduct
formation need to be studied.
1063
E.RJchter and A.R.Tricker
Acknowledgements
We extend special thanks to D.Hoffmann for providing reference compounds
and Christiana Oehlmann for expert technical assistance. This work was supported
by a grant from the Forschungsrat Rauchen und Gesundheh.
References
1.
Hecht.S.S. and Hoffmann.D. (1988) Tobacco-specifk njtrosamines, an
important group of carcinogens in tobacco and tobacco smoke.
Carcinogenesis,
9, 875-884.
2.
Hecht.S.S. and Hoffmann.D. (1989) The relevance of tobacco-specific
nitrosamines to human cancer. Cancer Surv., 8, 273—294.
3.
Rivenson.A., Hoffmann,D., Prokopczyk,B., Amin.S. and Hecht.S.S. (1988)
Induction of lung and exocrine pancreas tumors in F344 rats by tobacco-specific
and Areca-dcrivcd Mnhrosamines. Cancer Res., 48, 6912-6917.
4.
Castonguay.A., Tjalve.H. and Hecht.S.S. (1983) Tissue distribution of the
tobacco-specific carcinogen 4-(memylnitrosamino)-l-(3-pyridyl)-l-butanone
and its metabolites in F344 rats. Cancer Res., 43, 630-638.
5.
Bdinsky.S.A., FoteyJ.F., White.C.M., Anderson.M.W. and Maronpot, R.R.
(1990) Dose—response relationship between C^-methylguanine formation in
Clara cells and induction of pulmonary neoplasia in the rat by
4-(nWrrylnitrc)samino)-l-(3-pyridyI)-l-butanone. CancerRes., 50, 3772-3780.
6. Hecht.S.S., Trushin.N., Castonguay.A. and Rivenson,A. (1986) Comparative
tumorigenicity and DNA methylation in F344 rats by 4-(methylnitrosamino)-
l-(3-pyridyl)-l-butanone and A^-nitrosodimethylamine. Cancer Res., 46,
489-502.
7.
Hecht.S.S., Spratt.T.E. and Trushin.N. (1988) Evidence for 4-(3-pyridyl)-
4-oxobutylatk>n of DNA in F344 rats treated with the tobacco-specific
nitrosamines 4-(methylnitrosamino)-l-(3-pyridyl)-l-butanone and A^nhroso-
nomicotine. Carcinogenesis, 9,
161
—
165.
8. Peterson.L.A. and Hecht.S.S. (1991) O*-Methylguanine is a critical
determinant of 4-(memylnitrosamino)-l-(3-pyridyl)-l-butanone tumorigenesis
in A/J mouse lung. Cancer Res., 51, 5557-5564.
9. Belinsky.S.A., Devereux.T.R., White,C.M., FoleyJ.F., Maronpot.R.R. and
Anderson.M.W. (1991) Role of Clara cells and type n cells in the development
of pulmonary tumors in rats and mice following exposure to a tobacco-specific
nitrosamine. Exp. Lung Res., 17, 263-278.
10.
Castonguay.A., Lin.D., Stoner.G.D., Radok.P., Furuya.K., Hecht.S.S.,
Schut.H.A.J. and Klaunig,J.E. (1983) Comparative carcinogenicity in A/J
mice and metabolism by cultured mouse peripheral lung of A^-mtrosonornicotine,
4-(memylnhTosamino)-l-(3-pyridyl)-l-butanone, and their analogues. Cancer
Res.,
43, 1223-1229.
11.
Bdinsky.S.A., White.C.M., Trushin.N. and Hecht.S.S. (1989) Cell specificity
for die pulmonary metabolism of tobacco-specific nitrosamines in the Fischer
rat. Carcinogenesis, 10, 2269-2274.
12.
SchulzeJ., Richter.E., Binder.U. and Zwickenpflug.W. (1992) Biliary
excretion of 4-(methylnitrosamino)-l-(3-pyridyl)-l-butanone in die rat.
Carcinogenesis, 13, 1961-1965.
13.
Morse.M.A., Eldind^C.I., Toussaint.M., Amin.S.G. andChung,F.-L. (1990)
Characterization of a glucuronide metabolite of 4-(methylrutrosamino)-
l-(3-pyridyl)-l-butanone (NNK) and its dose-dependent excretion in the urine
of mice and rats. Carcinogenesis, 11, 1819-1823.
14.
Castonguay.A., Tjalve.H., Trushin.N., D'Argy.R. and Sperber.G. (1985)
Metabolism and tissue distribution of tobacco-specific nitrosamines in die
marmoset monkey
(CaUithrix
jacchus). Carcinogenesis, 6, 1543—1550.
15.
AdamsJ.D., Lavoie.EJ., O'Mara-Adams.KJ., Hoffinann.D., Carey.K.D.
and Marshall.M.V. (1985) Pharmacolrinetics of A^-nitrosonornicotine and
4-(methylnitrosaniino)-l-(3-pyridyl)-l-butanone in laboratory animals. Cancer
Lett., 28,
195-201.
16.
Hecht,S.S., Trushin,N., Reid-Quinn,C.A., Burak,E.S., Jones,A.B., Southers,
J.L., Gombar.C.T., Carmella.S.G., Anderson.L.M. and RiceJ.M. (1993)
Metabolism of the tobacco-specific nitrosamine 4-(methylnitrosamino)-
l-(3-pyridyl)-l-butanone in the patas monkey: pharmacokinetics and
characterization of glucuronide metabolites. Carcinogenesis, 14, 229-236.
17.
CastonguayA, Stoner.G.D., Schut,H.AJ. and Hecht,S.S. (1983) Metabolism
of tobacco-specific A'-nitrosammes by cultured human tissues. Proc. NatL
Acad.
Sd. USA, 80, 6694-6697.
18.
Smith.T.J., Guo.Z., Gonzalez.F.J., Guengerich.F.P., Stoner.G.D. and
Yang.C.S.
(1992) Metabolism of 4-(methyuiitrosamino)-l-(3-pyridyl)-
1-butanone
in human lung and liver microsomes and cytochromes P-450
expressed in hepatoma cells. CancerRes., 52, 1757-1763.
19.
Yamazaki.H., Inui.Y., Yun,C.-H., Guengerich.F.P. and Shimada.T. (1992)
Cytochrome P450 2E1 and 2A6 enzymes as major catalysts for metabolic
activation of ALaitrosodialkylamines and tobacco-related nitrosamines in human
liver microsomes. Carcinogenesis, 13, 1789-1794.
20.
Carmella,S.G., Kagan.S.S., Kagan.M., Foiles.P.G., Palladino.G.,
Quart.A.M., Quart.E. and Hecht.S.S. (1990) Mass spectrometric analysis
of tobacco-specific nitrosamine hemoglobin adducts in snuff-dippers, smokers,
and non-smokers. Cancer Res., 50, 5438-5445.
21.
Foiles.P.G., Akerkar.S.A., Carmella.S.G., Kagan.M., Stoner.G.D.,
ResauJ.H. and Hecht.S.S. (1991) Mass spectrometric analysis of tobacco-
specific nitrosamine DNA adducts in smokers and nonsmokers. Chem. Res.
Toxicol., 4, 364-368.
22.
Carmella.S.G., Akerkar.S. and Hecht.S.S. (1993) Metabolites of
the
tobacco-
specific nitrosamine 4-{methylnitrosamino)-l-(3-pyridyl)-l-butanone in
smokers' urine. CancerRes., 53, 721-724.
23.
AdamsJ.D., O'Mara-Adams.K.J. and Hoffmann.D. (1987) Toxic and
carcinogenic agents in undiluted mainstream smoke and sidestream smoke
of different types of cigarettes. Carcinogenesis, 8,
729—731.
24.
Tricker.A.R., Ditrich.C. and Preussmann.R. (1991) W-Nitroso compounds
in cigarette tobacco and their occurrence in mainstream tobacco smoke.
Carcinogenesis, 12,
257-261.
25.
Murphy,S.E. and Heiblum.R. (1990) Effect of nicotine and tobacco-specific
nitrosamines on the metabolism of A^-nitrosonomicotine and 4-(methyl-
nitrosamino)-l-(3-pyridyl)-l-butanone by rat oral tissue.
Carcinogenesis,
11,
1663-1666.
26.
HongJ.-Y., Ding.X., Smith.T.J., Coon.M.J. and Yang.C.S. (1992)
Metabolism of 4-(methylnitrosamino)-l-(3-pyridyl)-l-butanone (NNK), a
tobacco-specific carcinogen, by rabbit nasal microsomes and cytochrome P450s
NMa and NMb. Carcinogenesis, 13, 2141-2144.
27.
Prokopczyk.G., Adams,J.D., LeVoie.E.J. and Hoffmann.D. (1987) Effect
of snuff and nicotine on DNA methylation and 4-(methylnitrosamino>-
K3-pyrklyl)-l-butanone. Carcinogenesis, 8, 1395-1397.
28.
Schuller.H.M., Castonguay.A., Orloff.M. and Rossignol.G. (1991)
Modulation of the uptake and metabolism of 4-(methylnitrosamino)-
l-(3-pyridyl)-l-butanone by nicotine in hamster lung. Cancer Res., 51,
2009-2014.
29.
Charest.M., Rossignol.G. and Castonguay.A. (1989) In vitro and in vivo
modulation of die bioactivation of 4-(methylnitrosamino)-l-(3-pyridyl)-
1-butanone
in hamster lung tissues. Chem.-Biol. Interactions, 71, 265 -278.
30.
Feng,X.-C. and Richter.E. (1989) The role of extrahepatic organs in the first
pass metabolism of A'-nitrosodibutylamine. Arch. Toxicol. Suppl., 13,
227-229.
31.
Foth.H., Schulze.J. and Richter.E. (1991) NNK metabolism by isolated
perfused rat lung. IARC Tech. Report, 11, P29.
32.
Doerr-O'Rourke.K., Trushin.N., Hecht.S.S. and Stoner.G.D. (1991) Effect
of phenethyl isothiocyanate on the metabolism of die tobacco-specific
nitrosamine 4-(methylnitrosamino)-l-(3-pyridyl)-l-butanone by cultured rat
lung tissue. Carcinogenesis, 12,
1029
—
1034.
33.
Guo.Z., Smith.T.J., Thomas.P.E. and Yang.C.S. (1991) Metabolic activation
of 4-(methylnitrosamino)-l-(3-pyridyl)-l-butanone as measured by DNA
alkylation in vitro and its inhibition by isothiocyanates. Cancer Res., 51,
4798-4803.
34.
Peterson.L.A., Mathew.R. and Hecht.S.S. (1991) Quantitation of microsomal
alpha-hydroxylation of the tobacco-specific nitrosamine, 4-(methylnitrosamino)-
l-(3-pyridyl)-l-butanone. CancerRes., 51, 5495-5500.
35.
Peterson.L.A., Mathew.R., Murphy.S.E., Trushin.N. and Hecht.S.S. (1991)
In vivo and in vitro persistence of pyridyloxobutyl DNA adducts from
4-(methylnitrosamino)-l-(3-pyridyl)-l-butanone. Carcinogenesis, 12,
2069-2072.
36.
Guo.Z.Y., Smith.TJ., Thomas.P.E. and Yang.C.S. (1992) Metabolism of
4-(rriethylnitrosarnino)-l-{3-pyridyl)-l-butanone by inducible and constitutive
cytochrome P450 enzymes in rats. Arch. Biochem. Biophys., 298, 279-286.
37.
Hecht.S.S., Lin.D., Castonguay.A. and Rivenson.A. (1987) Effects of
a-deuterium substitution on die tumorigenicity of 4-(methylnitrosamino)-
l-<3-pyridyi)-l-butanone in F344 rats. Carcinogenesis, 8, 291-294.
38.
Murphy.S.E., Paloraino.A., Hecht.S.S. and Hoffmann.D. (1990)
Dose—response study of DNA and hemoglobin adduct formation by
4-(methylnitrosamino)-l-(3-pyridyl)-l-butanone in F344 rats. Cancer Res.,
50,
5446-5452.
39.
Carmella,S.G. and Hecht,S.S. (1987) Formation of hemoglobin adducts upon
treatment of F344 rats with the tobacco-specific nitrosamines 4-(methyl-
nitrosamino)-l-(3-pyridyI)-l-butanone and Ar-nilrosonomicotine.
Cancer
Res.,
47,
2626-2630.
40.
Falter,B., Kutzer.C. and Richter.E. (1994) Bkmxmitoring of hemoglobin
adducts: aromatic amines and tobacco-specific nitrosamines. CUn. Invest.,
in press.
41.
Richter.E., Schaffler.G., Malone.A. and SchulzeJ. (1992) Tobacco-specific
nitrosamines—metabolism and biological monitoring of exposure to tobacco
products. CUn. Invest., 70, 290-294.
Received on
July
6,
1993;
revised
on
December
15, 1993;
accepted
on
December
23,
1993
1064
