
Cancer Epidemiology Biomarkers & Prevention Vol. 9, 1205-1209, November 2000
© 2000 American Association for Cancer Research
Weekly Patterns in Smoking Habits and Influence on Urinary Cotinine and Mutagenicity Levels: Confounding Effect of Nonsmoking Policies in the Workplace
Roel Vermeulen,
Hillion Wegh,
Rob P. Bos and
Hans Kromhout1
Environmental and Occupational Health Group, Institute of Risk Assessment Sciences, Utrecht University, 3508 TD Utrecht, the Netherlands [R. V., H. W., H. K.], and Department of Pharmacology and Toxicology, University Medical Center St Radboud, University of Nijmegen, 6500 HB Nijmegen, the Netherlands [R. V., R. P. B.]
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Abstract
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Lifestyle factors such as smoking have been shown to influence urinary
mutagenicity. Therefore, these factors have to be considered carefully
when evaluating occupational genotoxic exposures. We investigated
day-to-day variability in active and passive tobacco smoke exposure by
studying urinary cotinine levels and determined their influence on
observed urinary mutagenicity. Urinary cotinine was assessed for 105
subjects employed in the rubber manufacturing industry in the
Netherlands on Sunday, Wednesday, and Thursday. Urinary mutagenicity
was measured by the Salmonella typhimurium strain YG1041
with metabolic activation for the Sunday urine sample and a
pooled weekday urine sample. A sharp decrease in urinary cotinine
concentration was observed during the week compared to Sunday for
smokers (39%; P < 0.01) and nonsmokers (23%).
Different smoking habits on Sunday resulted in higher regression
coefficients for categorical proxies for smoking habits and urinary
mutagenicity levels. However, regression coefficients for urinary
cotinine and urinary mutagenicity were similar for the Sunday and
weekday urine samples (ß = 0.29 and ß = 0.28,
respectively). Consequently, these estimates were used to adjust
urinary mutagenicity for tobacco smoke intake. Cotinine-adjusted
urinary mutagenicity levels were comparable between smokers and
nonsmokers, and a similar increase in urinary mutagenicity of 39% and
34%, respectively, was observed for both smokers and nonsmokers due to
occupational genotoxic exposures or other changes in lifestyle factors.
These results indicate that the introduction of nonsmoking policies in
the workplace has reduced exposure to mainstream and environmental
tobacco smoke, resulting in a temporal variation in lifestyle-related
mutagenicity. Therefore, adequate adjustment for daily tobacco smoke
exposure is a necessity when using the urinary mutagenicity assay to
evaluate possible genotoxic exposures in the workplace.
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Introduction
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Urinary mutagenicity is often used as a biomarker of exposure to
study the genotoxic effect of occupational exposures
(1, 2, 3, 4)
. Because of the nonselective character of the
urinary mutagenicity assay, the assay has been found particularly
useful in occupational settings with exposure to complex mixtures
(5, 6, 7, 8, 9)
. However, the nonselective character of the assay
makes it prone to confounding factors such as smoking and diet
(10, 11, 12, 13)
. Therefore, these factors have to be considered
carefully, especially when genotoxic exposures are low
(10)
. Because of the influence of lifestyle factors on
urinary mutagenicity, large variations in background mutagenicity
levels can be expected between subjects. Therefore, when comparing
occupationally exposed and nonexposed groups, large samples are needed
to ensure random distribution of confounding lifestyle factors. Another
approach that has been used to control for variation in mutagenicity
due to lifestyle factors is the use of the subjects as their own
internal control. In this approach, the increment in urinary
mutagenicity between urine samples collected before and after suspected
mutagenic exposure is studied (14)
. The underlying
assumption in this approach is that confounding lifestyle factors do
not significantly change within subjects over time. However,
differences exist in activity patterns during the weekend and weekdays
such as more frequent visits to restaurants and bars and an increased
number of active smokers in the personal environment. These factors
have been shown to influence the exposure to
MS2
and ETS (15
, 16)
.
The aim of the present investigation was to study the day-to-day
variability in active and passive smoking by studying urinary cotinine
levels and to determine their influence on observed urinary
mutagenicity. Urinary mutagenicity was measured by the Salmonella
typhimurium strain YG1041 with metabolic activation. S9 mix from
aroclor induced rat livers was used as metabolic activation
system to detect indirect mutagenic compounds or metabolites in urine.
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Materials and Methods
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Subjects
After completion of a survey, subjects (n = 116)
were randomly selected based on their reported smoking habits and
external genotoxic exposure profile from a group of 225 male subjects
participating on a voluntary basis in a large exposure survey among
nine companies in the rubber manufacturing industry in the Netherlands
(17)
. Subjects were employed full time. All companies but
one had a strict nonsmoking policy at the workplace, allowing smoking
only during breaks in designated areas in the company.
Spot urine samples were collected on Sunday, Wednesday, and Thursday at
approximately the same time of day (around 4 p.m.), stored
in polyethylene containers, and kept at -20°C until use. Information
regarding smoking status (yes/no) and average number of cigarettes
smoked per day (0, 110, >10) was obtained by a self-administered
questionnaire completed before the survey and by assessing urinary
cotinine levels.
Analytical Procedures
Cotinine.
Cotinine in urine was quantified by high-performance liquid
chromatography according to the method of Barlow et al.
(18)
, using the modifications described by Parviainen and
Barlow (19)
. Urine samples with undetectable cotinine
levels (limit of detection, 25 nmol/liter) were arbitrarily assigned a
value of one-half of the detection limit. Creatinine levels were
used to estimate urinary dilution by using a colometric test based on
the Jaffé reaction between creatinine and sodium picrate.
Cotinine levels were expressed in micrograms/gram of creatinine.
Mutagenic Activity.
Urine samples collected on Wednesday and Thursday were pooled for each
subject before mutagenicity analysis. A volume corresponding to 0.5
mmol of creatinine of the Wednesday and Thursday urine sample was
pooled, resulting in a volume corresponding to 1 mmol of creatinine.
Urine aliquots corresponding to 1.0 mmol of creatinine from the Sunday
urine sample and a pooled weekday urine sample were neutralized to pH
7.0 and extracted with XAD-2 resin (6-cm3
bed volume). After the urine was passed through the resin, the column
was washed with distilled water, and the adsorbed material was eluted
with 10 ml of acetone. After evaporation at 40°C under nitrogen, the
residue was dissolved in 2.5 ml of DMSO (14
, 20)
. Urine
extracts were assayed for mutagenic activity with the S.
typhimurium bacteria strain YG1041 with S9 mix of aroclor
induced rat liver (20
, 21)
. Mutagenic activity was
calculated based on the dose-response curves acquired at different dose
levels. The slope of the linear component was used as an estimate of
the mutagenic potency (22)
. Urinary mutagenic activity
levels were expressed in revertants/gram of creatinine.
Statistical Methods
Urinary cotinine and mutagenicity levels for both smokers and
nonsmokers were log-normally distributed. Therefore, the natural
logarithm of the cotinine concentration and mutagenic activity was used
in all statistical procedures.
Intra- and interindividual variance components of urinary cotinine
based on the Wednesday and Thursday urine samples were estimated using
a one-way nested random effects ANOVA model. The influence of smoking
habits and urinary cotinine levels on the mutagenic activity in urine
was studied in separate linear regression models. Mean urinary cotinine
concentration was calculated for the pooled weekday urine sample based
on the cotinine levels of the Wednesday and Thursday urine samples. All
statistical analyses were performed using SAS version 6.12 software
(23)
.
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Results
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Of the 116 subjects, 105 subjects (90.5%) had complete data
concerning smoking habits, urinary cotinine (Sunday, Wednesday, and
Thursday urine samples), and mutagenic activity levels (Sunday urine
sample and a pooled weekday urine sample). No systematic
differences in smoking habits, urinary cotinine, and mutagenic activity
levels were observed for subjects with incomplete data
(n = 11) or for those with complete data
(n = 105). Consequently, the results presented
in this study are based on these 105 subjects. Subjects were all male,
with a mean age of 37.9 ± 9.0 years.
A large statistically significant difference (P < 0.0001,
t test) in mean urinary cotinine concentration between
smokers and nonsmokers was observed for Sunday and weekday urine
samples (Table 1
; Fig. 1
). Furthermore, a clear dose-response relationship was found between the
average number of cigarettes smoked per day and urinary cotinine levels
for smokers on Sunday. However, this dose-response relationship was not
found for the weekday samples, in which almost no difference in mean
urinary cotinine levels was observed for the different categories of
average number of cigarettes smoked per day.
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Table 1 Mean urinary cotinine concentration (micrograms/gram of creatinine) and
intra- and interindividual cotinine variability by smoking status and
average number of cigarettes smoked per day
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Fig. 1. Geometric mean and 95% upper confidence limit of urinary cotinine
concentration (in micrograms/gram of creatinine) by smoking status and
sampling day.
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Analyses of the inter- and intraindividual variability in urinary
cotinine levels of Wednesday and Thursday samples revealed an overall
higher interindividual variability. Hence, the ratio (
) of the
intra- and interindividual variability for all smoking categories was
well below 1, indicating that the observed cotinine levels were
predominantly influenced by the individual. It is noteworthy that this
phenomenon was more pronounced for smokers than for nonsmokers.
Smoking status (yes/no), categories of average number of
cigarettes smoked per day, and urinary cotinine levels were clearly
associated with urinary mutagenicity, with only minor differences in
the explained proportion of the total variance for the different
proxies used for smoking habits in these models (Table 2)
. However, an overall larger proportion of the total variability in
urinary mutagenicity was explained by the proxies of smoking habits for
weekday urine samples than for Sunday urine samples. Observed
regression coefficients for smoking status and categories of average
number of cigarettes smoked per day were higher for Sunday urine
samples than for pooled weekday urine samples, with the exception of
light smoking (110 cigarettes/day). Regression coefficients observed
for the relationship between urinary cotinine levels and urinary
mutagenicity for the Sunday and pooled weekday urine samples were
practically identical (ß = 0.29 and ß = 0.28,
respectively).
View this table:
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Table 2 Relationship between smoking status, average number of cigarettes
smoked per day, and the natural logarithm of urinary cotinine levels
and urinary mutagenicity levels on Sunday and weekdays
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In Table 3
, mean urinary mutagenicity levels of the Sunday and pooled weekday
samples are presented. Smokers had, on average, a 5-fold higher urinary
mutagenicity level than nonsmokers. Furthermore, both smokers and
nonsmokers showed elevated levels of urinary mutagenicity when Sunday
and pooled weekday urine samples were compared, with an increase of
28% for nonsmokers and 14% for smokers. However, cotinine-adjusted
urinary mutagenicity levels (based on the observed relationship between
urinary cotinine and urinary mutagenicity), revealed an almost
identical increment in urinary mutagenicity for nonsmokers and smokers
(34% and 39%, respectively). Hence, the observed levels of
cotinine-adjusted urinary mutagenicity were almost similar for smokers
and nonsmokers.
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Discussion
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Smoking is almost invariably the most important confounder or
effect modifier in studies focusing on occupational and environmental
genotoxic exposures. To control for tobacco smoke intake, several
exposure indices have been used, including, for example, the number of
cigarettes smoked and several biochemical tests for plasma or saliva
thiocyanate, expired carbon monoxide, and carboxyhemoglobin
(24
, 25)
. These exposure proxies have been found
unsuitable because of a lack of sensitivity and specificity
(26)
. Cotinine, one of the major metabolites of nicotine,
has been considered as the most accurate biochemical indicator of
exposure to MS and ETS (26
, 27)
. Accordingly, urinary
cotinine has been used in several studies to quantify the influence of
tobacco smoke on urinary mutagenicity (9
, 10
, 28)
.
However, other lifestyle factors such as diet have been shown to
influence urinary mutagenicity as well (10)
. Because no
biochemical indicators are available to control for all lifestyle
factors, another approach has been advocated. In this approach, the
studied subjects are used as their own internal control. The underlying
assumption in this approach is that mutagenic exposure from other
sources (lifestyle-related mutagenicity) does not vary temporarily
(14)
. However, due to the introduction of strict
nonsmoking policies at indoor workplaces in the Netherlands in the
1990s, this underlying assumption could possibly be refuted with regard
to MS and ETS exposure. All companies but one in the present study had
strict nonsmoking policies allowing smoking only at designated times
and areas of the company.
We investigated the cotinine levels in urine collected on Sunday,
Wednesday, and Thursday and observed a statistically significant
decrease (P < 0.01, t test) for smokers in
both unadjusted and creatinine-adjusted urinary cotinine levels during
the week when compared to Sunday. Nonsmokers showed a similar downward
trend, but the decrease did not reach statistical significance.
Nevertheless, both downward trends in urinary cotinine levels suggest a
decrease in both active and passive intake of tobacco smoke during the
week compared to the weekend. Interestingly, heavy smokers (>10
cigarettes/day) showed a larger decrease in cotinine concentrations
than light smokers (110 cigarettes/day), resulting in comparable
cotinine concentrations during the week. Heavy smokers were probably
more affected by nonsmoking policies in the workplace, resulting in a
tobacco smoke intake comparable to that of light smokers during
weekdays.
The low ratio of intraindividual:interindividual variability among
active and passive smokers indicated a high degree of interindividual
variability in cotinine concentration. Other investigators have
found similar results, which presumably represent intersubject
differences in nicotine metabolism and inhalation patterns (29
, 30)
. However, because of the approximately 20-h half-life of
cotinine, urinary cotinine levels of Wednesday and Thursday samples
could potentially have been autocorrelated and thereby have resulted in
an underestimation of the intraindividual variability
(31)
.
Regression analysis between several qualitative estimates of MS
exposure and urinary mutagenicity showed a clear relationship between
active smoking and urinary mutagenicity. However, the observed
association between urinary cotinine and urinary mutagenicity also
implicates a relationship between passive smoking and urinary
mutagenicity. Stratified analyses for smokers and nonsmokers revealed
no significant difference in the observed regression coefficients (data
not shown). Therefore, the overall observed relationship between
urinary cotinine and urinary mutagenicity was used to adjust for MS and
ETS exposure.
In the presented study, urinary mutagenicity on Sunday was used as an
estimate of mutagenic exposure due to lifestyle factors, whereas
urinary mutagenicity on weekdays was used as a measure of mutagenic
exposure due to lifestyle factors and occupational exposure. The
difference between these two measures would therefore yield an estimate
of the mutagenic activity due to occupational genotoxic exposure.
Adjustment of urinary mutagenicity levels for urinary cotinine
concentrations revealed comparable background mutagenicity levels due
to lifestyle factors other than tobacco smoke for smokers and
nonsmokers, indicating adequate adjustment for tobacco smoke intake.
Increases in mutagenicity due to workplace exposure or other changes in
lifestyle factors, such as diet, were similar for smokers and
nonsmokers after adjustment for MS and ETS exposure. Without adjustment
for MS and ETS exposure, a different conclusion would have been
reached. It is worth noting that adjusted urinary mutagenicity levels
for smokers, although statistically nonsignificant, were still slightly
elevated compared with those for nonsmokers. This could have been
caused either by inadequate adjustment of urinary mutagenicity for
cotinine levels or by smoking-induced enzyme systems leading to higher
urinary mutagenicity levels due to mutagenic exposures from other
sources (32, 33, 34)
.
These results indicate that the introduction of nonsmoking policies in
the workplace has reduced exposure to tobacco smoke by active and
passive smoking, resulting in a temporal variation in lifestyle-related
mutagenicity. Therefore, adequate adjustment for daily tobacco smoke
exposure is a necessity when using the urinary mutagenicity assay to
evaluate possible genotoxic exposures in the workplace.
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Acknowledgments
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S. typhimurium strain YG1041 was kindly provided by
Drs. T. Nohmi and M. Watanabe (Division of Mutagenesis, National
Institute of Genetics and Mutagenesis, Tokyo, Japan). We also thank
Prof. B. Brunekreef (Environmental and Occupational Health Group,
Utrecht University, Utrecht, the Netherlands) for valuable comments on
the manuscript.
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Footnotes
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1 To whom requests for reprints should be
addressed. Present address: Environmental and Occupational Health
Group, Institute of Risk Assessment Sciences, Utrecht University, P. O.
Box 238, 6700 AE Wageningen, the Netherlands. Phone: 31-317-484147;
Fax: 31-317-485278; E-mail: h.kromhout{at}vet.uu.nl 
2 The abbreviations used are: MS, mainstream
smoke; ETS, environmental tobacco smoke. 
Received 2/ 2/00;
revised 8/25/00;
accepted 9/ 5/00.
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