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Analytisch-biologisches Forschungslabor, D-80336 München, Germany
| Abstract |
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Total dietary BaP intake, as calculated from questionnaire data, did not correlate with any of the PAH biomarkers (r < 0.1). Subjects living in the suburbs tended to have higher BaP-protein adduct levels than subjects living in the city.
Our findings suggest that diet and smoking are major sources for PAH exposure of persons not occupationally exposed to PAH, whereas the influence of ETS exposure is negligible. The lack of correlation between the dietary PAH intake and the PAH biomarkers may be due to the inaccuracy of the estimate for the dietary PAH intake.
| Introduction |
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Biomonitoring is an especially valuable method to provide exposure data on multimedia environmental contaminants such as PAH (6 , 7) . Various urinary PAH metabolites such as 1-OHP, 1-OHP-glucuronide, monohydroxy-phenanthrenes, and BaP (after chemical reduction of the BaP metabolites in urine) have been used as PAH biomarkers in nonoccupationally exposed subjects. The effective dose can be determined by measuring the adducts formed by the ultimate carcinogen of BaP (r-7,t-8-dihydroxy-t-9,t-10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene, BPDE) with cellular macromolecules such as DNA and proteins. In addition to numerous biomonitoring studies with workers exposed to PAH (for review see Refs. 7 and 8 ), the effect of smoking, diet, automobile traffic, and ETS on the PAH adduct levels has been investigated using DNA of WBCs. BPDE also forms covalent adducts with albumin (9) and hemoglobin (10) , both of which can be used as surrogate biomarkers for the internal exposure dose to the ultimate carcinogen BPDE (11) . BaP-albumin adduct studies with nonoccupationally exposed subjects have been performed using ELISA (12, 13, 14, 15) , GC-MS (16) , and HPLC with fluorescence detection (17) . Similarly, BaP hemoglobin adducts have been investigated with GC-MS (16 , 18, 19, 20) . Smoking was found to increase the BaP protein adduct levels in most of the studies (12 , 13 , 15 , 17 , 19) . ETS exposure was reported to significantly increase BaP albumin adduct levels in one study (12) , but not in other studies (13 , 21) . Exposure to PAH from ambient air (traffic exhaust) had no, or only a marginal, effect on the BaP adduct levels (18 , 21) . Elevated BaP-hemoglobin adduct levels were found in winter compared with summer (22) .
The purpose of our investigation was to elucidate the influence of smoking, exposure to ETS, and diet on the exposure to PAH in healthy, nonoccupationally exposed subjects. The extent of exposure to PAH was determined by measuring the PAH biomarkers urinary 1-OHP six times per subject and the BaP adducts with albumin and hemoglobin once during the 8-month study period.
| Materials and Methods |
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Dietary BaP Intake.
On the basis of published data (2
, 23, 24, 25, 26, 27, 28, 29)
, the following
BaP concentrations of food products were used for estimating the BaP
intake from the reported food consumption data (µg/kg): cereals and
bread, 0.2; leafy vegetables, 5.0; root vegetables and fruits, 0.2;
meat and sausages, 3.0; fish, 1.0; and dairy products, 0.5.
Biological Samples.
Twenty-four-h urine samples were collected after voiding the first
morning urine until the following morning (including the first morning
urine). The sample was stored in a cooling box until it was returned to
the laboratory. In the laboratory, pH and volume were determined within
2 h, before the sample was divided into several fractions and
frozen at -20°C.
Blood samples were drawn into EDTA-tubes and separated by centrifugation (500 x g, 10 min, 10°C) into plasma and erythrocytes. The blood fractions were stored until analysis at -20°C.
| Analytical Methods |
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Hemoglobin Adducts of BaP.
Washed erythrocytes from 10 ml of blood were lysed with 20 ml of
bidestilled water and centrifuged (13,000 x g, 45 min,
4°C). The hemoglobin concentration in the supernatant was determined
spectrophotometrically (31)
. After adding the internal
standard (BT II-2) to 200 mg of hemoglobin, the protein was digested
with Pronase (16 h, 37°C) to destroy the tertiary structure and the
adducts were hydrolyzed (pH 11, 2 h, 80°C). The aqueous
hydrolysate was applied to an Extrelut 20-column (1.5 x 23 cm, 80
ml; Merck) and eluted with 40 ml of ethyl acetate. The solvent was
removed with a rotary evaporator and finally in a nitrogen stream. The
dry residue was dissolved in 1 ml of water/methanol (80:20, v/v) and
injected into the HPLC. The further steps were performed as described
for the albumin adducts of BaP (see above and Ref. 30
).
The LOD for the hemoglobin adducts of BaP was 0.007 fmol/mg, and the
recovery rate was 55 ± 17% (n = 69). All 69
samples from the second visit were run in duplicate, with a coefficient
of variation of 30%.
Urinary 1-OHP.
1-OHP was determined according to a published method (32)
.
Briefly, to 10 ml of urine, 20 ml of 0.1 M acetate buffer
(pH 5.0) and 13 µl of ß-glucuronidase/arylsulfatase (Boehringer
Mannheim) were added and incubated for 5 h at 37°C in the dark.
The solution was applied to a Sepak C18 cartridge (Varian GmbH,
Darmstadt, Germany) and eluted with 2 ml of methanol. After the
addition of 2 ml of 20 mM potassium dihydrogenphosphate, 20
µl were injected into the HPLC system (Model 2510 pump system, Model
9090 autosampler, and Model 4270 integrator; Varian GmbH), equipped
with a column oven and a fluorescence detector (Model FP-920; Jasco,
Groß-Umstadt, Germany). A C18-guard column and a C18-analytical
column (4.6 x 250 mm; Symmetry, Waters, Milford, MA) were used.
The retention time for 1-OHP was 19.5 min. The calibration curve (10
points) was constructed with spiked urine samples (0.05- 0.5 µg/l).
The recovery rate was 94%, and the LOD was 0.01 µg/l. All urine
samples (69 subjects x 6 time points - 5 missing
samples = 409) were run in duplicate, with a coefficient of
variation of 8%.
Cotinine in Plasma.
Cotinine in plasma was determined by a RIA (33
, 34)
. The
LOD was 1 µg/l. All 409 plasma samples were run in duplicate, with a
coefficient of variation of 10%.
Cotinine in Urine.
Cotinine in urine was determined by GC with a nitrogen-selective
detector according to a published method (35)
. The LOD was
1 µg/l. About 40% of the 409 urine samples were run in duplicate,
with a coefficient of variation of 5%.
Thiocyanate in Plasma.
Thiocyanate in plasma was determined photometrically according to a
published method (36)
. The method was adapted to
microtiter plate scale. The difference of the absorbance after adding
iron(III)nitrate (formation of a red-colored complex) and
after the addition of mercury-(II)nitrate (formation of a colorless
complex) was measured at a wavelength of 492 nm.
Nicotine and 3-Ethenylpyridine on Personal Samplers.
Nicotine and 3-ethenylpyridine were sampled on passive diffusion
samplers (37)
worn by the nonsmoking subjects over 5 or 7
days and analyzed as reported (37)
. The LOD was 0.01
µg/m3
for both compounds using GC with
nitrogen-selective detection.
Statistical Methods.
Differences between the three groups according to smoking status
(nonsmokers, passive smokers, smokers) were tested with the Students
t test. The associations between the PAH biomarkers
(dependent variables) and urinary cotinine or BaP intake with the diet
(independent variables) were analyzed by linear regression. All
calculations and tests were performed with the SPSS 8.0 software
package (SPSS ASC GmbH, Erkrath, Germany).
| Results |
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Exposure to Tobacco Smoke.
As expected, the biomarkers of tobacco smoke exposure (thiocyanate in
plasma, cotinine in plasma and urine) are significantly elevated in
smokers compared with nonsmokers. The ratio (smokers:all nonsmokers) is
about 300 for cotinine in plasma or urine and about 4 for thiocyanate
in plasma.
Nonsmokers classified as ETS exposed (passive smokers) reported significantly longer ETS exposure durations (2.43 versus 0.52 h/day) and significantly higher ETS exposure intensities (3.31 versus 0.67) compared with the nonexposed or only marginally ETS-exposed nonsmokers. The personal samplers of the passive smokers showed higher exposure to nicotine (0.730 versus 0.184 µg/m3) and 3-ethenylpyridine (0.121 versus 0.041 µg/m3) than those of the unexposed nonsmokers. Cotinine levels in plasma (1.32 versus 0.71 ng/ml) and urine (12.3 versus 2.3 µg/24 h) were also significantly higher in passive smokers than in unexposed nonsmokers. There was no significant difference in the plasma thiocyanate levels between these two groups (19.6 versus 22.0 µmol/l).
PAH Biomarkers in Relation to Tobacco Smoke Exposure.
In Table 2
, the means, SEs, and the ranges of the PAH biomarkers urinary 1-OHP,
BaP-hemoglobin adducts, and BaP-albumin adducts for the various study
groups are shown. Smokers excreted significantly higher amounts of
1-OHP than nonsmokers (0.346 versus 0.157 µg/24 h). The
determination of BaP-hemoglobin adducts revealed one sample (a
nonsmoker) that was below the LOD of 0.007 fmol/mg, whereas for the
BaP-albumine adduct measurements, 13 samples of the 27 smokers (48.1%)
and 29 samples of the 42 nonsmokers (69.0%) were below the LOD of 0.01
fmol/mg. Within the group of nonsmokers, the percentage of undetectable
samples for BaP-albumin adducts was 16 of the 23 unexposed nonsmokers
(69.6%) and 13 of the 19 passive smokers (68.4%). The means of the
BaP-albumin adducts was significantly elevated in smokers compared with
nonsmokers (0.042 versus 0.020 fmol/mg), whereas the
BaP-hemoglobin adducts tended to be higher in smokers compared with
nonsmokers (0.105 versus 0.068 fmol/mg; not significant). No
significant differences between passive smokers and unexposed
nonsmokers were observed for urinary 1-OHP (0.140 versus
0.171 µg/24 h), BaP-hemoglobin adducts (0.049 versus 0.083
fmol/mg), and BaP-albumin adducts (0.021 versus 0.019
fmol/mg).
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PAH Biomarkers in Relation to Urban or Suburban Residence.
The subjects were classified as "urban" or "suburban" according
to the postal code of their home address. Urban residence means that
the subject lives in the city of Munich, whereas suburban residence was
within a radius of 1560 km of the city center. In Fig. 3
, the PAH biomarkers for all subjects divided into urban and suburban
groups are shown. The significant effect of smoking on all three
biomarkers is visible. Furthermore, the BaP adduct levels with
hemoglobin and albumin tended to be higher in subjects with suburban
residences. This effect reached borderline significance
(P = 0.056) for BaP-albumin adducts of all subjects. No
difference in urinary 1-OHP excretion was observed between subjects
residing in the suburb or city (Fig. 3
).
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| Discussion |
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Smoking.
The mainstream smoke of a filter cigarette contains about 10 ng of BaP
(3
, 4)
. Smoking, on average, 18 cigarettes/day, as the
smokers in this study did (Table 1)
, would result in a smoking-related
BaP intake of 180 ng/day. We found 2-fold increased PAH biomarker
levels in smokers compared with nonsmokers (Table 2)
. The effect of
smoking was significant for urinary 1-OHP (P < 0.001)
and BaP-albumin adducts (P < 0.05), but did not reach
statistical significance in the case of BaP-hemoglobin adducts
(P = 0.12). Furthermore, we observed a significant
correlation between the extent of smoking (measured as the urinary
excretion of cotinine) and urinary 1-OHP (r = 0.76;
P < 0.01) and BaP-albumin adducts (r =
0.44; P < 0.05; Fig. 1
). There was no significant
correlation between urinary cotinine and BaP-hemoglobin adducts
(r = 0.19, P = 0.35). These findings
confirm other reports on the effect of smoking on PAH biomarkers. Van
Rooij et al. (5)
reported urinary excretion of
1-OHP of 0.090.13 µmol/mol creatinine for nonsmokers and 0.240.34
µmol/mol creatinine for smokers. These levels are higher than in our
study when converted to daily excretion rates, assuming a creatinine
excretion of 1.5 g/day (nonsmokers, 0.260.38 µg/24 h; smokers,
0.690.98 µg/24 h). Van Rooij et al. (5)
reported a correlation coefficient between urinary 1-OHP excretion and
the average number of cigarettes per day of r = 0.67
(P = 0.001), which is in good agreement with our
reported correlation with urinary cotinine (r = 0.76;
Fig. 1
) and with daily cigarette consumption (r = 0.59,
P < 0.01). In another study (41)
, the
difference in 1-OHP excretion between occupationally exposed smokers
and nonsmokers (foundry workers) was insignificant, whereas the
difference in the not occupationally exposed control group was of
borderline significance (P = 0.06). Pastorelli et
al. (22)
reported two times higher levels of urinary
1-OHP in smokers compared with nonsmokers. Sithisarankul et
al. (42)
reported a concentration of
1-OHP-glucuronide of 1.04 pmol/ml for smokers and 0.55 pmol/ml for
nonsmokers (P = 0.001), a ratio similar to that in our
study. The correlation with daily cigarette consumption was weaker than
in our study (r = 0.34)
Melikian et al. (19)
observed significantly
higher BaP-hemoglobin adducts in 10 smokers (mean, 2.6; range, 1.27.8
fmol/mg) than in 10 nonsmokers (mean, 0.97; range, 0.71.3 fmol/mg).
It is noteworthy that the BaP adduct levels in our study were at least
one order of magnitude lower. In a study with 44 smokers (lung cancer
patients), Pastorelli et al. (16)
found
detectable levels of BaP-hemoglobin adducts (LOD, 0.05 fmol/mg) in only
six subjects (13.6%). The median for all 44 samples was 0.025 fmol/mg
(half the detection level). In our study, comprising subjects with low
to moderate traffic exposure, only one subject had a BaP-hemoglobin
level below the detection level of 0.007 fmol/mg (Table 2)
. The median
was 0.064 fmol/mg for smokers and 0.046 fmol/mg for nonsmokers,
comparable with the values reported by Pastorelli et al.
(16)
. In an earlier study, Pastorelli et al.
(18)
reported median BaP-hemoglobin adduct levels of
0.1
fmol/mg and
0.26 fmol/mg for newspaper vendors with low and extensive
traffic exposure, respectively. The difference was not significant. In
a recent publication (22)
, the same group reported
significantly lower adduct levels in summer (mean, 0.031 fmol/mg) than
in winter (mean, 0.14 fmol/mg). No effect of smoking and diet was
found.
The smokers in our study had significantly elevated BaP-albumin adduct
levels compared with the nonsmokers (Table 2)
. Thirteen samples
(48.1%) from the smokers and 29 samples (69.0%) of the nonsmokers
were below the LOD (0.01 fmol/mg). The percentage of undetectable
samples for unexposed and ETS-exposed nonsmokers was similar (69.6 and
68.4%, respectively; Table 2
). Elevated BaP-albumin adduct levels in
smokers have also been reported in other studies (12
, 15
, 17
, 43)
. However, adduct levels in smokers/nonsmokers determined by
ELISA were several orders of magnitude higher than in our investigation
(Table 2)
: 14.2/7.23 fM BaP equivalents/100 µg (15)
,
0.80/0.41 fmol/µg (12)
, 5.78/4.67 fmol/µg (medians;
Ref. 13
). It can only be assumed that the antibodies used
in the ELISA are selective for PAH rather than specific for BaP. Using
HPLC with fluorescence detection, Tas et al.
(17)
found median BaP-albumin adduct levels of 1.62
fmol/mg for smokers and 1.39 fmol/mg for nonsmokers. Also, these levels
were almost two orders of magnitude higher than those in our study,
suggesting probably an unspecific detection of the BaP-tetrol. In the
study of Pastorelli et al. (16)
, in which
GC-MS-NICI was applied for adduct determination, 24 of 44 smokers
(56.8%) had undetectable (LOD, 0.05 fmol/mg) BaP-albumin adduct
levels. The median of all 44 samples was 0.11 fmol/mg, which is about
7-fold higher than the median for smokers in our study (0.015 fmol/mg).
Part of the discrepancy could be due to more intense smoking in the
Italian study group compared with ours.
Passive Smoking.
Indoor air concentrations of BaP in smoking and nonsmoking homes are
reported to be 1.0 ng/m3
and 0.4
ng/m3, respectively (44)
. In
commercial buildings, mean BaP concentrations of 1.07
ng/m3 and 0.39 ng/m3 in
smoking and nonsmoking environments, respectively, have been found
(45)
. Therefore, the additional ETS-related BaP exposure
is about 0.6 ng/m3. Assuming a daily ETS exposure
duration of about 3 h (Table 2
; Refs. 46
and
47
), a respiration rate of 1 m3/h
would result in a maximum intake of 1.8 ng BaP/day due to passive
smoking, which accounts for about 1% of the overall daily BaP intake
in nonsmokers. It is, therefore, not surprising that we found no
influence of exposure to ETS on any of the three PAH biomarkers (Table 2
and Fig. 2
).
The evidence from the BaP adduct measurement is limited due to the fact
that for a major part of the samples the adduct levels were at or below
the LOD (Table 2)
. On the other hand, the 1-OHP measurements, in our
view, provide strong evidence because for each subject six independent
samples were analyzed and the concentrations were well above the LOD in
all samples.
We took great effort to determine the extent of exposure to ETS:
(a) nonsmokers were selected either to be not or only
marginally exposed to ETS or to be regularly exposed to ETS at home, at
work, or in leisure time; (b) the subjects were asked to
keep records of their ETS exposure in terms of duration and intensity
during 6 weeks; (c) the nonsmokers also wore personal
samplers for nicotine and 3-ethenylpyridine during the 6 weeks; and
(d) cotinine in plasma and urine, suitable biomarkers for
ETS exposure (48
, 49) , were measured on six different
occasions. No association between plasma thiocyanate and passive
smoking was observed (Table 2)
. This confirms an earlier report in the
literature (50)
, suggesting that plasma thiocyanate is not
a suitable biomarker for determining exposure to ETS. Friedman et
al. (51)
found that only about 2% of the variation
in serum thiocyanate concentration is explained by passive smoking.
There was satisfactory consistency between the other ETS exposure
markers, both objectively measured and subjectively reported, except
for plasma cotinine. The reason for this is probably the fact that for
all nonsmokers the plasma cotinine concentration was at or below the
LOD of 1 µg/l for at least one time point. Taken together, we are
confident that our assessment of the extent of exposure to ETS is
reliable and that there is no measurable effect of real-life passive
smoking on urinary 1-OHP or on BaP adduct levels with hemoglobin or
albumin.
Diet.
The method of choice for determining the BaP intake from food seems to
be the "duplicate meal" approach. Using this method, daily BaP
intakes of 123 ng (24)
and 176 ng (6)
were
found. We estimated a mean dietary BaP intake of 500600 ng/day for
the various subgroups in our study (Table 1)
, which is clearly higher
than the values found with the duplicate meal method but corresponds
with some of the reported ranges in the literature (8)
. A
reason for the large variations of the BaP intake estimates is
certainly the heterogenous array of cooking styles and foodstuffs used
(24)
. With the limitations described above, it is
comprehensible that we found no correlation of the estimated BaP
intake with the diet and any of the PAH biomarkers.
In general, it can be stated that although diet is recognized as the most important source of PAH exposure for nonoccupationally exposed nonsmokers (5 , 6 , 52) , only weak associations between the estimated PAH intake from the diet and various PAH biomarkers were found. We believe that the inaccuracy of the estimate for the PAH intake is the major reason for this observation.
Ambient Air.
We looked for a possible effect of urban or city residence on the
concentrations of the PAH biomarkers. Unexpectedly, we observed a trend
for higher BaP adduct levels with hemoglobin and albumin for subjects
living in the suburbs, whereas the place of residence had no influence
on the urinary excretion of 1-OHP (Fig. 3
). The smoking behavior is not
responsible for this result. Presently, we have no reasonable
explanation for this finding.
Pastorelli et al. (18)
found significantly
increased BaP-hemoglobin adducts in traffic-exposed, nonsmoking
newspaper vendors compared with their unexposed counterparts (median,
0.3 versus
0.1 fmol/mg). In smokers, no influence of
exposure to traffic was observed (0.27 versus 0.26 fmol/mg).
Nielsen et al. (21) found elevated BaP-albumin adduct levels in subjects living in rural areas compared with urban areas of Denmark (4.54 versus 3.54 fmol/µg, determined by ELISA). The difference was not significant. Interestingly, significantly higher DNA adduct levels (determined by 32P-postlabeling) in lymphocytes of the urban subjects were observed (21) . Protein and DNA adducts did not correlate in this study. DNA adduct levels in lymphocytes were also found to increase from rural controls to bus drivers working in the dormitory, suburban and center of Copenhagen (53) .
In a study with 130 pregnant women living in urban, suburban, and rural areas of the county of Aarhus, Denmark, Autrup and Vestergaard (43) found about similar levels of BaP-albumin adducts (determined with an ELISA) in subjects from urban and rural parts, whereas subjects living in the suburbs had significantly lower adduct levels. Because the samples were collected in November/December, the authors speculated that differences in domestic heating sources were responsible for these findings.
Conclusion.
In conclusion, our results show that smoking increases the PAH exposure
of nonoccuptionally exposed persons by a factor of two, whereas passive
smoking does not measurably increase the overall PAH burden. We suggest
that diet is, by far, the most important source for PAH intake in
nonsmokers, although, probably due to the inaccuracy of the intake
estimates, we were not able to find an association between the dietary
PAH intakes and the levels of the PAH biomarkers. Our results further
indicate that PAH exposure through ambient air might be of some
importance. Part of the interindividual variation in the PAH biomarkers
is certainly due to the genetic polymorphism in metabolic activation
and detoxification pathways (for review see Ref. 54
). The
influence of the genetic polymorphism in this study is presently under
investigation in our laboratory. Finally, the levels of the BaP-protein
adducts that we measured are partly much lower than those reported by
others also using GC-MS-NICI.
| Footnotes |
|---|
1 We thank the Forschungsgesellschaft Rauchen und
Gesundheit, Hamburg for funding this work. ![]()
2 To whom requests for reprints should be
addressed, at Analytisch-biologisches Forschungslabor, Goethestrasse
20, 80336 München, Germany. Fax: 49-89-5328039; E-mail: abf{at}compuserve.com ![]()
3 The abbreviations used are: PAH, polycyclic
aromatic hydrocarbon; BaP, benzo(a)pyrene; 1-OHP,
1-hydroxypyrene; BPDE, benzo[a]pyrene diolepoxide;
ETS, environmental tobacco smoke; LOD, limit of detection; GC-MS, gas
chromatography-mass spectroscopy; HPLC, high-performance liquid
chromatography; NICI, negative ion chemical ionization. ![]()
Received 9/23/99; revised 12/31/99; accepted 1/17/00.
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