Exposure to nicotine and a tobacco-specific carcinogen increase with duration of use of smokeless tobacco

BACKGROUND

Smokeless tobacco is an efficient delivery vehicle for nicotine and can contain significant amounts of carcinogens. However, few studies have examined factors that might moderate levels of nicotine or carcinogen exposure.

AIMS

To determine the effect of duration of smokeless tobacco use on the uptake of nicotine and a tobacco-specific carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK).

METHODS

Questionnaires on use of smokeless tobacco were administered, and urine samples from 212 smokeless tobacco users were analysed for biomarkers of uptake of nicotine and NNK. The biomarkers were cotinine and total 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL). Male smokeless tobacco users were recruited for studies designed to investigate methods of reducing smokeless tobacco use. The questionnaire and biomarker data were obtained at baseline, prior to reduction.

RESULTS

Levels of cotinine (p<0.001) and total NNAL (p<0.001) were significantly correlated with duration (in years) of use of smokeless tobacco products. Median cotinine and total NNAL were 2.4 and 2.1 times higher, respectively, in the > or = 21 years of use than in the 0-5 years of use category.

CONCLUSIONS

Smokeless tobacco users adjust their intensity of use with experience in order to increase their nicotine dose, resulting in a corresponding increase in exposure to NNK, a powerful carcinogen. These results indicate the importance of educating smokeless tobacco users about the effects of prolonged use of these products.

Effects of glucosinolate-rich broccoli sprouts on urinary levels of aflatoxin-DNA adducts and phenanthrene tetraols in a randomized clinical trial in He Zuo township, Qidong, People's Republic of China

Residents of Qidong, People's Republic of China, are at high risk for development of hepatocellular carcinoma, in part due to consumption of aflatoxin-contaminated foods, and are exposed to high levels of phenanthrene, a sentinel of hydrocarbon air toxics. Cruciferous vegetables, such as broccoli, contain anticarcinogens. Glucoraphanin, the principal glucosinolate in broccoli sprouts, can be hydrolyzed by gut microflora to sulforaphane, a potent inducer of carcinogen detoxication enzymes. In a randomized, placebo-controlled chemoprevention trial, we tested whether drinking hot water infusions of 3-day-old broccoli sprouts, containing defined concentrations of glucosinolates, could alter the disposition of aflatoxin and phenanthrene. Two hundred healthy adults drank infusions containing either 400 or < 3 micromol glucoraphanin nightly for 2 weeks. Adherence to the study protocol was outstanding; no problems with safety or tolerance were noted. Urinary levels of aflatoxin-N(7)-guanine were not different between the two intervention arms (P = 0.68). However, measurement of urinary levels of dithiocarbamates (sulforaphane metabolites) indicated striking interindividual differences in bioavailability. An inverse association was observed for excretion of dithiocarbamates and aflatoxin-DNA adducts (P = 0.002; R = 0.31) in individuals receiving broccoli sprout glucosinolates. Moreover, trans, anti-phenanthrene tetraol, a metabolite of the combustion product phenanthrene, was detected in urine of all participants and showed a robust inverse association with dithiocarbamate levels (P = 0.0001; R = 0.39), although again no overall difference between intervention arms was observed (P = 0.29). Understanding factors influencing glucosinolate hydrolysis and bioavailability will be required for optimal use of broccoli sprouts in human interventions.

Metabolites of a tobacco-specific lung carcinogen in the urine of elementary school-aged children

Limited data are available in the literature on carcinogen uptake by children exposed to environmental tobacco smoke (ETS). In this study, we quantified metabolites of the tobacco-specific lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in the urine of elementary school-aged children participating in the School Health Initiative: Environment, Learning, Disease study, a school-based investigation of the environmental health of children. The metabolites of NNK are 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its glucuronide (NNAL-Gluc). We also measured cotinine and its glucuronide (total cotinine). Urine samples were collected from 204 children. Seventy (34.3%) of these had total cotinine > or =5 ng/ml. NNAL or NNAL-Gluc was detected in 52 of 54 samples with total cotinine > or =5 ng/ml and in 10 of 20 samples with total cotinine < 5 ng/ml. Levels of NNAL plus NNAL-Gluc and total cotinine were significantly higher when exposure to ETS was reported than when no exposure was reported. However, even when no exposure to ETS was reported, levels of NNAL, NNAL-Gluc, and NNAL plus NNAL-Gluc were higher than in children with documented low exposure to ETS, as determined by cotinine levels < 5 ng/ml. Levels of NNAL, NNAL-Gluc, and cotinine were not significantly different in samples collected twice from the same children at 3-month intervals. Levels of NNAL plus NNAL-Gluc in this study were comparable with those observed in our previous field studies of adults exposed to ETS. There was a 93-fold range of NNAL plus NNAL-Gluc values in the exposed children. The results of this study demonstrate widespread and considerable uptake of the tobacco-specific lung carcinogen NNK in this group of elementary school-aged children, raising important questions about potential health risks. Our data indicate that objective biomarkers of carcinogen uptake are important in studies of childhood exposure to ETS and cancer later in life.

Consumption of watercress fails to alter coumarin metabolism in humans

Watercress is an excellent source of phenethyl isothiocyanate (PEITC), an effective inhibitor of nitrosamine carcinogenesis in rodents. The mechanism of inhibition is believed to be due in part to inhibition of cytochrome P450 (P450) enzymes. P450 2A6 is a catalyst for the metabolic activation of several nitrosamines. In this study, we investigated the effect of watercress consumption on coumarin 7-hydroxylation, a P450 2A6-specific reaction, in a group of 15 nonsmoking, healthy volunteers. The urinary excretion of 7-hydroxycoumarin (7OHC) was determined. For 6 of the 15 subjects, watercress consumption decreased the amount of 7OHC excreted in the first 2 h following coumarin administration. However, the mean 0- to 2-h excretion of 7OHC for all 15 subjects was not significantly lowered by the consumption of watercress, 2.8 +/- 0.78 versus 3.1 +/- 0.53 mg (+/-S.D.). The mean 7OHC excreted from 2 to 4 h (1.1 +/- 0.50 mg) was significantly higher (P = 0.027) during watercress consumption than before (0.77 +/- 0.22 mg), suggesting a delay in coumarin metabolism. Total excretion of 7OHC was unaffected by watercress consumption. Therefore, under the conditions of our study, PEITC and other constituents of watercress had at most a marginal inhibitory effect on P450 2A6-catalyzed coumarin 7-hydroxylation.

Metabolites of a tobacco-specific lung carcinogen in nonsmoking women exposed to environmental tobacco smoke

BACKGROUND

Environmental tobacco smoke (ETS) is associated with lung cancer in nonsmokers. Most epidemiologic studies find a higher risk for lung cancer in nonsmoking women married to smokers than in those married to nonsmokers. We measured metabolites of a tobacco-specific lung carcinogen in urine from healthy, nonsmoking women exposed to ETS.

METHODS

We recruited women and their partners through advertisements. Couples completed questionnaires on smoking history and demographics, and both partners provided 100 mL of urine; 23 women had male partners who smoked in the home (i.e., exposed women), and 22 women had male partners who did not smoke (i.e., unexposed women). Urine samples were analyzed for nicotine, for cotinine, for 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its glucuronide (NNAL-Gluc), as well as for creatinine. NNAL and NNAL-Gluc are metabolites of the tobacco-specific lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Unpaired Student's t tests were conducted on log-transformed values. All statistical tests are two-sided.

RESULTS

Urinary levels of nicotine, cotinine, NNAL, and NNAL-Gluc were statistically significantly higher in exposed women than in unexposed women. Geometric means for these compounds in exposed versus unexposed women, respectively, were as follows: nicotine, 0.050 nmol/mg of creatinine (95% confidence interval [CI] = 0.033 to 0.076) versus 0.008 nmol/mg of creatinine (95% CI = 0.004 to 0.014); cotinine, 0.037 nmol/mg of creatinine (95% CI = 0.022 to 0.061) versus 0.007 nmol/mg of creatinine (95% CI = 0.004 to 0.011); NNAL, 0.013 pmol/mg of creatinine (95% CI = 0.007 to 0.024) versus 0.004 pmol/mg of creatinine (95% CI = 0.002 to 0.007); and NNAL-Gluc, 0.027 pmol/mg of creatinine (95% CI = 0.016 to 0.045) versus 0.004 pmol/mg of creatinine (95% CI = 0.003 to 0.006).

CONCLUSIONS

Nonsmoking women exposed to ETS take up and metabolize the tobacco-specific lung carcinogen NNK, which could increase their risk of lung cancer. Within couples, the NNAL plus NNAL-Gluc level in exposed women compared with that of their smoking partners averaged 5.6%. Notably, epidemiologic studies have estimated the excess risk for lung cancer in nonsmoking women exposed to ETS as 1%-2% of that in smokers.

Formation and metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol enantiomers in vitro in mouse, rat and human tissues

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) is a major metabolite of the tobacco-specific lung carcino- gen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). NNAL has a chiral center at the 1-position, but little is known about the stereochemical aspects of its metabolic formation from NNK or its further metabolism. We investigated the metabolism of NNK to enantiomers of NNAL in microsomes and cytosol from male F-344 rat liver and lung, female A/J mouse liver and lung, and human liver, as well as in red blood cells from rats, mice and humans. In all systems, (S)-NNAL was the predominant enantiomer formed, ranging from 90 to 98% in the rodent tissues and averaging 64, 90 and >95% in human liver microsomes, liver cytosol and red blood cells, respectively. In rat liver microsomes, (R)- and (S)-NNAL were metabolized at similar rates by alpha-hydroxylation, considered to be the major metabolic activation pathway of NNAL. Pyridine-N-oxidation and adenosine dinucleotide phosphate adduct formation also occurred at similar rates from both enantiomers, while reoxidation to NNK was favored with (S)-NNAL as substrate. In rat lung microsomes, (S)-NNAL was more rapidly metabolized than (R)-NNAL by all oxidative pathways. In human liver microsomes, there were no significant differences in the rates of alpha-hydroxylation, pyridine-N-oxidation and reoxidation to NNK between the two enantiomers. The results of this study demonstrate that (S)-NNAL, the more tumorigenic enantiomer in mice, is preferentially formed from NNK in rodent and human tissues, and is a substrate for oxidative metabolism in rodent and human tissue microsomes.

Enantiomeric composition of N'-nitrosonornicotine and N'-nitrosoanatabine in tobacco

The tobacco-specific nitrosamines N'-nitrosonornicotine (NNN) and N'-nitrosoanatabine (NAT) are found in substantial quantities in unburned tobacco. Although this has been documented in many previous studies, no data are available on the enantiomeric composition of these nitrosamines, which both have a chiral center at their 2'-positions. We used chiral stationary phase gas chromatography with nitrosamine-selective detection to determine the enantiomeric composition of NNN and NAT in moist snuff, chewing tobacco, and cigarette tobacco. (S)-NNN comprised 75.0 +/- 8.83% (SD) (n = 12) of total NNN while (S)-NAT comprised 82.6 +/- 1.44% (n = 12) of total NAT. Levels of the (S)-enantiomers of NNN and NAT were generally similar to those of the corresponding secondary amines, nornicotine and anatabine, suggesting a precursor to product relationship. Nitrosation of (S)-nicotine at pH 7.0 produced >99% (S)-NNN. These results suggest that nornicotine is a significant precursor of NNN in tobacco. The results of this study provide new insights into the structures and precursors of tobacco-specific nitrosamines in tobacco products.

A tobacco-specific carcinogen in the fetus

A tobacco-specific carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), and its metabolite, 4-[(methylnitrosamino)-1-(3-pyridyl)but-1-yl]beta-O-D-glucosiduronic+ ++ acid (NNAL-Gluc), have been found in the urine of newborns whose mothers smoked during pregnancy. We set out to determine whether this carcinogen is present in the fetus in early pregnancy. Cell-free amniotic fluid (AF) was obtained through routine amniocentesis for prenatal genetic studies from groups of smokers and non-smokers. NNAL and NNAL-Gluc were quantified by previously published methods. A history of smoking was confirmed by assays for cotinine plus N-beta-D-glucosiduronosyl-(S)-(-) cotinine inner salt (cotinine-Gluc) in AF. NNAL was detected in the AF of 11/21 (52.4%) of smokers and in 2/30 (6.7%) of non-smokers, a statistically significant difference (p=0.0006). There was not convincing evidence of NNAL-Gluc in the AF. This study documents for the first time that the tobacco-specific carcinogen NNAL is present in the fetus in early pregnancy. Further rigorous epidemiological studies are needed to determine whether the offspring of smoking mothers have an increased lifetime risk of cancer.

Determination of r-7,t-8,9,c-10-tetrahydroxy-7,8,9, 10-tetrahydrobenzo[a]pyrene in human urine by gas chromatography/negative ion chemical ionization/mass spectrometry

r-7,t-8,9,c-10-Tetrahydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene (trans-anti-BaP-tetraol) is the major hydrolysis product of r-7, t-8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE), the principal ultimate carcinogen of the environmental pollutant benzo[a]pyrene (BaP). As part of a program to establish activation/detoxification profiles of urinary metabolites of BaP in humans, we developed a method for quantifying trans-anti-BaP-tetraol. Urine was collected from three groups of individuals exposed to BaP: psoriasis patients treated with a coal tar-containing ointment, steel workers, and smokers. [(2)H(12)]-trans-anti-BaP-tetraol was added to the urine as an internal standard. The urine was treated with beta-glucuronidase and sulfatase, and then the BaP-tetraols were enriched by reverse-phase and phenylboronic acid solid-phase extraction. The resulting fraction was treated with sodium hydride and methylmethane sulfonate to convert BaP-tetraols to the corresponding tetramethyl ethers (BaP-TME). The mixture was purified by normal-phase HPLC and analyzed by gas chromatography/negative ion chemical ionization/mass spectrometry with selected ion monitoring. [(13)CH(3)](4)-trans-anti-BaP-TME was used as an external standard. Ions at m/z 376, 380, and 388 were monitored for quantitation of trans-anti-BaP-TME, [(13)CH(3)](4)-trans-anti-BaP-TME, and [(2)H(12)]-trans-anti-BaP-TME, respectively. The instrumental detection limit was approximately 1 fmol of trans-anti-BaP-TME. trans-anti-BaP-tetraol (as trans-anti-BaP-TME) was detected in 20 of 20 individuals receiving coal tar therapy (mean, 16 fmol/mL of urine), 13 of 13 exposed steel workers (mean, 4.1 fmol/mL of urine), and nine of 21 cigarette smokers (mean, 0.5 fmol/mL of urine). The means in these groups were significantly different (P < 0.0001). The urine of steel workers was also analyzed for cis-anti-BaP-tetraol and cys-syn-BaP-tetraol, but neither was found. The results of this study provide a quantitative method for determination of parts per trillion levels of trans-anti-BaP-tetraol in human urine. Ultimately, this method can be employed as part of a phenotyping approach for assessing BaP metabolites in human urine.

Effects of watercress consumption on urinary metabolites of nicotine in smokers

The effects of watercress consumption on the metabolism of nicotine in smokers were examined. Watercress is a rich source of phenethyl isothiocyanate (PEITC), an effective chemopreventive agent for cancers of the lung and esophagus induced in rodents by nitrosamines, including the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone. PEITC is believed to inhibit nitrosamine carcinogenesis in rodents by inhibiting specific cytochrome P450 (P450) enzymes. Among the P450s involved in the activation of these nitrosamines are members of the 2A family. P450 2A6 is believed to be involved in the metabolism of both nicotine and its major metabolite cotinine. Therefore, we hypothesized that watercress consumption might inhibit nicotine and cotinine metabolism in smokers. The urine samples analyzed in this study were the same ones that we used in an earlier study (S. S. Hecht et al., Cancer Epidemiol. Biomark. Prev., 4: 877-884, 1995), in which we showed that watercress consumption increased levels of two metabolites of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone: NNAL and its glucuronide NNAL-Gluc. This increase was attributed either to inhibition of cytochromes P450 or induction of glucuronidation. In the present study, we quantified urinary nicotine and seven of its metabolites. There were no effects of watercress consumption on levels of nicotine, cotinine, trans-3'-hydroxycotinine, 4-oxo-4-(3-pyridyl)butanoic acid, or 4-hydroxy-4-(3-pyridyl)butanoic acid, indicating either that watercress ingestion has little effect on the oxidative metabolism of nicotine (presumably by P450 2A6 or other P450 enzymes) or that these enzymes are not important for nicotine and cotinine metabolism in smokers. However, watercress consumption resulted in a significant increase compared to baseline levels of the glucuronides of cotinine (25%, P = 0.031) and trans-3'-hydroxycotinine (33%, P = 0.043) during the period when it was consumed and in a nonsignificant increase in levels of the glucuronide of nicotine. These levels returned to baseline values after the watercress consumption period. There was a correlation between increases in levels of the glucuronides of trans-3'-hydroxycotinine and NNAL in the same subjects, suggesting the involvement of a common enzyme. Thus, the results of this study suggest that PEITC or another component of watercress induces UDP-glucuronosyltransferase activity in humans.

Stereochemistry of metabolites of a tobacco-specific lung carcinogen in smokers' urine

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a tobacco-specific lung carcinogen, is believed to be important as a causative agent for lung cancer in smokers. NNK is extensively metabolized to its carbonyl reduction product 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), which, in turn, can be glucuronidated, producing [4-methylnitrosamino)-1-(3-pyridyl)but-1-yl]-beta-O-D-glucosiduronic+ ++ acid (NNAL-Gluc). Metabolism of NNK to NNAL produces a chiral center. A recent study demonstrated that (R)-NNAL is more tumorigenic in mice than (S)-NNAL and that these enantiomers have substantially different metabolic pathways. Therefore, it is important to determine the stereochemistry of NNAL and NNAL-Gluc in smokers. In this study, we used chiral stationary phase-gas chromatography-nitrosamine-selective detection with confirmation by liquid chromatography-tandem mass spectrometry to determine the stereochemistry of NNAL and NNAL-Gluc in smokers' urine. The two methods agreed well. The results of analyses of urine samples from 30 smokers demonstrated that the enantiomeric distribution of NNAL in urine was 54% (R) and 46% (S) +/- 7.0 (SD), whereas the diastereomeric distribution of NNAL-Gluc was 68% (R) and 32% (S) +/- 8.1. These results conclusively demonstrate that both (R)- and (S)-NNAL are formed metabolically from NNK in smokers. These data are essential for furthering our understanding of the role of NNK as a cause of lung cancer in smokers.

Metabolites of a tobacco-specific carcinogen in urine from newborns

BACKGROUND

Cigarette smoking during pregnancy can result in fetal exposure to carcinogens that are transferred from the mother via the placenta, but little information is available on fetal uptake of such compounds. We analyzed samples of the first urine from newborns whose mothers did or did not smoke cigarettes for the presence of metabolites of the potent tobacco-specific transplacental carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK).

METHODS

The urine was collected and analyzed for two metabolites of NNK, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its glucuronide (NNAL-Gluc). Gas chromatography and nitrosamine-selective detection, with confirmation by mass spectrometry, were used in the analyses, which were performed without knowledge of the origin of the urine samples.

RESULTS

NNAL-Gluc was detected in 22 (71%) of 31 urine samples from newborns of mothers who smoked; NNAL was detected in four of these 31 urine samples. Neither compound was detected in the 17 urine samples from newborns of mothers who did not smoke. The arithmetic mean level of NNAL plus NNAL-Gluc in the 27 newborns of smokers for which both analytes were quantified was 0.14 (95% confidence interval [CI] = 0.083-0.200) pmol/mL. The levels of NNAL plus NNAL-Gluc in the urine from these babies were statistically significantly higher than those in the urine from newborns of nonsmoking mothers (geometric means = 0.062 [95% CI = 0.035-0.110] and 0.010 [considered as not detected; no confidence interval], respectively; two-sided P<.001). NNAL plus NNAL-Gluc levels in the 18 positive urine samples in which both analytes were quantified ranged from 0.045 to 0.400 pmol/mL, with an arithmetic mean level of 0.20 (95% CI = 0.14-0.26) pmol/mL, about 5%-10% of the levels of these compounds detected in the urine from adult smokers.

CONCLUSIONS

Two metabolites of the tobacco-specific transplacental carcinogen NNK can be detected in the urine from newborns of mothers who smoked cigarettes during pregnancy.

Quantitation of urinary metabolites of a tobacco-specific lung carcinogen after smoking cessation

We quantified urinary levels of two metabolites of the tobacco-specific lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in people who had stopped smoking: 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its O-glucuronide, 4-[(methylnitrosamino)-1-(3-pyridyl)but-1-yl]-beta-O-D-glucosiduronic acid (NNAL-Gluc). Twenty-seven people completed the study. Thirteen used the nicotine patch starting at the quit date, whereas the others used no patch. Two 24-h urine samples were collected on 2 consecutive days before smoking cessation; blood was also obtained. Beginning at their quit date, subjects provided 24-h urine samples on days 7, 21, 42, 70, 98, and 126, and some subjects also provided samples at later times. The urine was analyzed for NNAL, NNAL-Gluc, nicotine plus nicotine-N-glucuronide, and cotinine plus cotinine-N-glucuronide. Some blood samples were also analyzed for NNAL. The decline of urinary NNAL and NNAL-Gluc after smoking cessation was much slower than expected. This was clearly demonstrated by comparison with cotinine and nicotine levels in urine. One week after smoking cessation, 34.5% of baseline NNAL plus NNAL-Gluc was detected in urine, whereas the corresponding values for cotinine and nicotine were 1.1 and 0.5%, respectively. Even 6 weeks after cessation, 7.6% of the original levels of NNAL plus NNAL-Gluc remained. In some subjects, NNAL plus NNAL-Gluc were detected 281 days after cessation. The distribution half-life for NNAL and NNAL-Gluc was 3-4 days, whereas the elimination half-life was 40-45 days. Total body clearance of NNAL was estimated to be 61.4 +/- 35.4 ml/min, and volume of distribution in the beta-phase was estimated to be 3800 +/- 2100 liters, indicating substantial distribution into the tissues. Parallel studies in rats treated chronically or acutely with NNK in the drinking water support the conclusion that NNAL has a large volume of distribution. There was no effect of the nicotine patch on levels of NNAL plus NNAL-Gluc, indicating that NNK is not formed endogenously from nicotine. The results of this study demonstrate that NNAL and NNAL-Gluc are slowly cleared from the body after smoking cessation, indicating the presence of a high-affinity compartment where NNK, NNAL, and/or NNAL-Gluc are retained or sequestered and slowly released.

A metabolite of the tobacco-specific lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in the urine of hospital workers exposed to environmental tobacco smoke

We analyzed the urine of nonsmoking hospital workers exposed to environmental tobacco smoke for [4-(methylnitrosamino)-1-(3-pyridyl)but-1-yl]-beta-O-D-glucosiduronic acid (NNAL-Gluc), a metabolite of the tobacco-specific lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone. Samples were collected three times on a single day from nine workers. Quantitative analysis was carried out by combined gas chromatography-nitrosamine-selective detection. The identity of NNAL-Gluc was confirmed by combined gas chromatography-tandem mass spectrometry. The results demonstrated the presence of NNAL-Gluc in the urine of the exposed subjects. The mean level of NNAL-Gluc +/- SD was 0.059 +/- 0.028 pmol/ml urine (23 pg/ml urine); range, 0.005-0.11 pmol/ml urine. Levels of NNAL-Gluc per milliliter of urine correlated with those of cotinine (r = 0.51; P = 0.029). These results demonstrate for the first time that NNAL-Gluc, a metabolite of the lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, is present in the urine of nonsmokers exposed to environmental tobacco smoke under field conditions.

Differences in the urinary metabolites of the tobacco-specific lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in black and white smokers

Incidence and mortality rates for lung cancer in the United States are significantly greater in blacks than in whites. This disparity cannot be explained by differences in smoking behavior. We hypothesize that the observed racial differences in risk may be due to differences in the metabolic activation or detoxification of the tobacco-specific lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). To test this, different biomarkers of NNK exposure and metabolism, including the urinary metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and the presumed detoxification product [4-(methylnitrosamino)-1-(3-pyridyl)but-1-yl]-beta-O-D-glucosiduronic acid (NNAL-Gluc), were examined along with questionnaire data on lifestyle habits and diet in a metabolic epidemiological study of 34 black and 27 white healthy smokers. Results demonstrated that urinary NNAL-Gluc:NNAL ratios, a likely indicator of NNAL glucuronidation and detoxification, were significantly greater in whites than in blacks (P < 0.02). In addition, two phenotypes were apparent by probit analysis representing poor (ratio < 6) and extensive (ratio > or = 6) glucuronidation groups. The proportion of blacks falling into the former, potentially high-risk group was significantly greater than that of whites (P < 0.05). The absolute levels of urinary NNAL, NNAL-Gluc, and cotinine were also greater in blacks than in whites when adjusted for the number of cigarettes smoked. None of the observed racial differences could be explained by dissimilarities in exposure or other sociodemographic or dietary factors. Also, it is unlikely that the dissimilarities are due to racial differences in preference for mentholated cigarettes, because chronic administration of menthol to NNK-treated rats did not result in either increases in urinary total NNAL or decreases in NNAL-Gluc:NNAL ratios. Altogether, these results suggest that racial differences in NNAL glucuronidation, a putative detoxification pathway for NNK, may explain in part the observed differences in cancer risk.

Effects of indole-3-carbinol on the metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in smokers

Indole-3-carbinol (I3C) is a component of the human diet, occurring as a conjugate in certain cruciferous vegetables. I3C protects against carcinogenesis in a variety of animal models by modifying carcinogen metabolism. In mice, I3C decreases lung tumor formation by the tobacco-specific nitrosamine 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) by enhancing its hepatic clearance (M. A. Morse et al., Cancer Res., 50: 2613-2617, 1990). In this study, our goal was to determine whether I3C would have similar effects on NNK metabolism in smokers as it did in mice. Thirteen women took 400 mg of I3C on 5 consecutive days and maintained constant smoking habits during this period. Their urine was analyzed before and after the I3C treatment period for two metabolites of NNK: 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its glucuronide (NNAL-Gluc). I3C treatment resulted in decreased levels of urinary NNAL, NNAL-Gluc, and NNAL plus NNAL-Gluc, and increased NNAL-Gluc:NNAL ratio in 10 of the 13 women. The mean decreases in NNAL (-0.27 +/- 0.09 pmol/mg creatinine, -23.4%) and NNAL plus NNAL-Gluc (-0.43 +/- 0.16 pmol/mg creatinine, -10.9%) were statistically significant as was the increase in NNAL-Gluc:NNAL ratio (1.1 +/- 0.5, 39.9%). These changes in urinary metabolites of NNK were consistent with those seen in mice treated with I3C and NNK; they suggest that I3C increased hepatic metabolism of NNK in our smokers. This is the first study to examine the effects of I3C on metabolism of an exogenous carcinogen in humans.

Evidence for endogenous formation of tobacco-specific nitrosamines in rats treated with tobacco alkaloids and sodium nitrite

Carcinogenic tobacco-specific nitrosamines are present in tobacco products and are believed to play a significant role in human cancers associated with tobacco use. Additional amounts of tobacco-specific nitrosamines could be formed endogenously. We tested this hypothesis by treating rats with nicotine and sodium nitrite and analyzing their urine. Initially, we treated groups of rats with (S)-nicotine (60 micromol/kg) and NaNO2 (180 micromol/kg), (S)-nicotine alone, NaNO2 alone or 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK, 12 nmol/kg) by gavage twice daily for 4 days. We collected urine and analyzed for two metabolites of NNK; 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol and its glucuronide. We did not detect these metabolites in the urine of rats treated with nicotine alone or nicotine plus NaNO2, indicating that endogenous conversion of nicotine to NNK did not occur. However, the urine did contain N'-nitrosonornicotine (NNN), N'-nitrosoanabasine (NAB) and N'-nitrosoanatabine (NAT). Analysis of the (S)-nicotine used in this experiment demonstrated that it contained trace amounts of nornicotine, anabasine and anatabine. In a second experiment, we used an identical protocol to compare the endogenous nitrosation of this (S)-nicotine with that of synthetic (R,S)-nicotine, which did not contain detectable amounts of nornicotine, anabasine or anatabine. NNN (0.53 x 10(-3)% of nicotine dose), NAB (0.68%) and NAT (2.1%) were detected in the urine of the rats treated with the (S)-nicotine and NaNO2. NNN (0.47 x 10(-3)% of dose), but not NAB or NAT, was present in the urine of the rats treated with synthetic (R,S)-nicotine and NaNO2. NNN probably formed via nitrosation of metabolically formed nornicotine. These results demonstrate for the first time that endogenous formation of tobacco-specific nitrosamines occurs in rats treated with tobacco alkaloids and NaNO2. The potential significance of the results with respect to nitrosamine formation in people who use tobacco products or nicotine replacement therapy is discussed.

Analysis of human urine for pyridine-N-oxide metabolites of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, a tobacco-specific lung carcinogen

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent pulmonary carcinogen in rodents and is believed to be a causative factor for lung cancer in smokers. NNK also may be involved in oral cancer etiology in users of smokeless tobacco products. Pyridine-N-oxidation of NNK and its major metabolite, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), produces NNK-N-oxide and NNAL-N-oxide, respectively, which are detoxification products of NNK metabolism and are excreted in the urine of rodents and primates. Our goal is to develop a panel of urinary biomarkers to assess the metabolic activation and detoxification of NNK in humans. In this study, we developed methodology to analyze human urine for NNK-N-oxide and NNAL-N-oxide. The key step in the method was conversion of the N-oxides to NNK and NNAL by treatment with Proteus mirabilis. The resulting samples were then analyzed essentially by methods that we have described previously. 4-(Methylnitrosamino)-4-(3-pyridyl-N-oxide)-1-butanol (iso-NNAL-N-oxide) was used as internal standard. Levels of NNAL-N-oxide in smokers' urine ranged from 0.06 to 1.4 pmol/mg creatinine, mean +/- SD 0.53 +/- 0.36 pmol/mg creatinine. Its presence was confirmed by high performance liquid chromatography-electrospray ionization-tandem mass spectrometry. NNK-N-oxide was not detected in smokers' urine. Levels of NNAL-N-oxide in the urine of smokeless tobacco users ranged from 0.02 to 1.2 pmol/mg creatinine, mean +/- SD 0.41 +/- 0.35 pmol/mg creatinine. The amounts of NNAL-N-oxide in urine were less than 20% of those of [4-(methylnitrosamino)-1-(3-pyridyl)but-1-yl]-beta-O-D-glucosiduronic acid (NNAL-Gluc) and were approximately 50% as great as those of free NNAL. These results demonstrate that pyridine-N-oxidation is a relatively minor detoxification pathway of NNK and NNAL in humans. The method was applied to analysis of urine from 11 smokers who consumed a diet containing watercress. In an earlier study (S.S. Hecht et al., Cancer Epidemiol., Biomarkers & Prev., 4: 877-884, 1995), we showed that consumption of watercress, a source of phenethyl isothiocyanate (PEITC), caused an increase in urinary excretion of NNAL plus NNAL-Gluc. This was attributed to inhibition of alpha-hydroxylation of NNK by PEITC, as seen in rodents in which PEITC also inhibits the pulmonary carcinogenicity of NNK. However, PEITC also could have inhibited pyridine-N-oxidation of NNK and NNAL. The urine of these smokers was analyzed for NNAL-N-oxide. The results demonstrated that watercress consumption had no effect on levels of NNAL-N-oxide in urine, supporting the conclusion that PEITC does inhibit the metabolic activation of NNK in humans.

Inhibitory effects of 6-phenylhexyl isothiocyanate on 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone metabolic activation and lung tumorigenesis in rats

This study examined the effects of 6-phenylhexyl isothiocyanate (PHITC) on lung tumorigenesis in F344 rats induced by the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Two biomarkers of NNK metabolism, 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB)-releasing hemoglobin adducts and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its glucuronide (NNAL-Gluc) in urine, were also quantified during the course of the tumor induction experiment. Rats were divided into groups as follows: (1) NNK, 2 p.p.m. in drinking water, 60 rats; (2) NNK, 2 p.p.m. in drinking water and PHITC, 1 micromol/g NIH-07 diet, 60 rats; (3) PHITC, 1 micromol/g NIH-07 diet, 20 rats; (4) control, 20 rats. PHITC was added to the diet for 1 week prior to and during 111 weeks of NNK treatment. There were no effects of PHITC on body weight, mortality, blood chemistry or hematology. Seventy percent of the rats treated with NNK had adenoma or adenocarcinoma of the lung. In the rats treated with NNK plus PHITC, the total percent incidence of lung tumors was 26% (P < 0.01 compared with NNK). PHITC had no effect on the total incidence of exocrine pancreatic tumors induced by NNK. The rats treated with PHITC and NNK had significantly lower levels of HPB-releasing hemoglobin adducts throughout the course of the bioassay than did those treated with NNK alone and significantly higher levels of NNAL plus NNAL-Gluc excreted in urine at two time points during the bioassay. These results demonstrate that near lifetime administration of PHITC to rats strongly inhibits the metabolic activation and lung tumorigenicity of NNK.

Complete inhibition of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced rat lung tumorigenesis and favorable modification of biomarkers by phenethyl isothiocyanate

Phenethyl isothiocyanate (PEITC), which occurs in certain cruciferous vegetables, was tested for its ability to inhibit lung tumorigenesis in rats induced by the tobacco-specific nitrosamine 4-(methylnitrosamino-1-(3-pyridyl)-1-butanone (NNK) in a study involving virtually lifelong administration of both compounds. In addition, two biomarkers of NNK metabolism [4-hydroxy-1-(3-pyridyl)-1-butanone-releasing hemoglobin adducts and 4-(methylnitrosamino-1-3-pyridyl-1-butanol and its glucuronide in urine] were quantified in randomly selected rats during the course of the study. The rats were assigned to groups as follows: NNK, 2 ppm in drinking water, 60 rats; NNK, 2 ppm in drinking water and PEITC, 3 micromol/g NIH-07 diet, 60 rats; PEITC, 3 micromol/g NIH-07 diet, 20 rats; and untreated controls, 20 rats. NNK was added to the drinking water for 111 weeks and PEITC to the diet for 1 prior to NNK administration and then throughout the 111-week course of treatment. There were no significant differences in body weights or survival among the groups. There were no significant effects of PEITC on blood chemistry or hematology. NNK induced lung tumors (adenoma and/or adenocarcinoma) in 70% of the rats. In the group treated with NNK plus PEITC, 5% of the rats had lung tumors, which was not different from that of control rats. PEITC also appeared to inhibit progression of benign to malignant pancreatic tumors. At intervals during the study, blood was withdrawn from selected rats, and 4-hydroxy-1-(3-pyridyl)-1-butanone-releasing hemoglobin adducts, which are formed upon metabolic activation of NNK, were quantified. The hemoglobin adducts were significantly repressed throughout the study in the rats treated with NNK plus PEITC compared to those treated with NNK. The 24-h urine sample of several rats was analyzed for 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol glucuronide. A 4-6-fold increase in the sum of these metabolites was observed in the rats treated with NNK plus PEITC compared to those treated with NNK. This is also consistent with inhibition of metabolic activation of NNK by PEITC. Collectively, the results of this study provide strong evidence for the efficacy of PEITC as a chemopreventive agent against NNK-induced pulmonary carcinogenesis in rats and indicate that two biomarkers of NNK metabolism, measurable in tobacco consumers, can be modulated in a predictable way by PEITC administration.

Metabolites of a tobacco-specific nitrosamine, 4-(methylnitrosamino)- 1-(3-pyridyl)-1-butanone (NNK), in the urine of smokeless tobacco users: relationship between urinary biomarkers and oral leukoplakia

Two metabolites of the carcinogenic tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone were quantified in the urine of smokeless tobacco users. The metabolites are 4-(methylnitrosamino) -1-(3-pyridyl)-1-butanol (NNAL) and [4-(methylnitrosamino)-1-(3-pyridyl) but-1-yl]-beta-O-D-glucosiduronic acid (NNAL-Gluc). The study population consisted of 47 male nonsmokers, of whom 23 were snuff dippers, 13 were tobacco chewers, 3 were users of both products, and 8 were nonusers. The levels of NNAL-Gluc in urine ranged from 0.14-30.3 pmol/mg creatinine with a mean +/- SD of 3.47 +/- 5.86, whereas the levels of NNAL ranged from 0.02-8.73 pmol/mg creatinine with a mean +/- SD of 0.92 +/- 1.59. The mean levels of NNAL-Gluc and NNAL were not significantly different from those measured in a previous study of smokers. The levels of NNAL-Gluc were significantly higher in snuff dippers than in tobacco chewers. The ratio of NNAL-Gluc:NNAL was higher in snuff dippers than in tobacco chewers or smokers. There was no indication of two phenotypes of the NNAL-Gluc:NNAL ratio in smokeless tobacco users, in contrast to previous observations in smokers. Of the 39 smokeless tobacco users in this study, 16 presented with oral leukoplakia. When the total levels of NNAL-Gluc, NNAL, or NNAL-Gluc + NNAL were divided into tertiles, there was a significant association between the presence of leukoplakia and increasing levels of these metabolites; a similar relationship was found between urinary cotinine and leukoplakia. The results of this study demonstrate that there is significant uptake of carcinogenic nitrosamines in smokeless tobacco users, and that such products are not harmless alternatives to cigarettes. Moreover, the urinary biomarkers NNAL-Gluc, NNAL, and cotinine were associated with the presence of leukoplakia, which provides biochemical support for the role of smokeless tobacco products as a cause of oral leukoplakia.

Gastric carcinogenesis: 2-chloro-4-methylthiobutanoic acid, a novel mutagen in salted, pickled Sanma hiraki fish, or similarly treated methionine

The customary salting and pickling of fish in high risk gastric cancer regions were modeled to explore the relevant causative chemicals. The fish Sanma hiraki was treated with sodium chloride and sodium nitrite at pH 3. Previously, it had been found that an extract of the treated fish was mutagenic in Salmonella typhimurium TA 1535 without S9 and also that it induced glandular stomach cancer upon gavage to rats. We now demonstrate that the mutagenicity was enhanced by preincubation of the raw meat for several days before salt-nitrite treatment. HPLC techniques showed that three mutagens were present in the fish extract. One of the mutagens was found to be stable over the pH range of 1.0-9.0. This mutagen was purified by silica gel solid phase extraction, followed by a series of reverse phase HPLC steps, and was characterized by low and high resolution MS, NMR, and FT-IR. While N-nitroso compounds were generally believed to be associated with gastric carcinogenesis, it was unexpectedly found that the mutagen has the novel structure 2-chloro-4-methylthiobutanoic acid (CMBA). Based on the structure, it seemed likely that methionine might be the precursor, and this was, indeed, proven. Both salt and nitrite are essential factors for forming this mutagen. The yield of CMBA was linear for chloride concentrations from 0 to 800 mM NaCl. Of 20 amino acids reacted with nitrite and chloride at pH 3, only methionine generated a mutagen for S. typhimurium TA 1535. Tryptophan gave a product mutagenic in S. typhimurium TA 100 and TA 98, but not TA 1535, and in the case of tyrosine, the mutagen was active only for TA 100. These results suggest an important role for salt in gastric carcinogenesis and provide new approaches for exploring the formation of mutagens/carcinogens for specific target organs.

Effects of watercress consumption on metabolism of a tobacco-specific lung carcinogen in smokers

Epidemiological studies indicate that vegetable consumption protects against lung cancer in humans, but the protective constituents have not been identified. Phenethyl isothiocyanate (PEITC), which is release upon chewing of watercress (nasturtium officinale), is a chemopreventive agent against lung cancer induced by the tobacco-specific lung carcinogen 4- (methylnitrosamino)-1-(3-pyridyl-1-butanone (NNK) in rats and mice. PEITC inhibits the carcinogenicity of NNK by inhibiting its metabolic activation and thereby increasing the levels of detoxified metabolites excreted in urine. In this study, our goal was to determine whether watercress consumption would modify NNK metabolism in smokers. Eleven smokers maintained constant smoking habits and avoided cruciferous vegetables and other sources of isothiocyanates throughout the study. They donated 24-h urine samples on 3 consecutive days (baseline period). One to 3 days later, they consumed 2 ounces (56.8 g) of watercress at each meal for 3 days and donated 24-h urine samples on each of these days (watercress consumption period). One and 2 weeks later, they again donated 24-h urine samples on 2-3 consecutive days (follow-up periods). The samples were analyzed for two metabolites of NNK; 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and [4-methylnitrosamino)-1-(3-pyridyl)but-1-yl]-beta-omega-D-glucosiduro nic acid (NNAL- Gluc). NNAL-Gluc is believed to be a detoxification product of NNK. The urine samples were also analyzed for PEITC-NAC, a metabolite of PEITC. Minimum exposure to PEITC during the watercress consumption period averaged 19-38 mg/day. Seven of the 11 subjects had increased levels of urinary NNAL plus NNAL-Gluc on days 2 and 3 of the watercress consumption period, compared to the baseline period. Overall, the increase in urinary NNAL plus NNAL-Gluc in this period was significant [mean +/- SD 0.924 +/- 1.12 nmol/24 h (33.5%); P < 0.01]. Urinary levels of NNAl plus NNAL-Gluc returned to near baseline levels in the follow-up periods. The percentage of increase in urinary NNAL plus NNAL-Gluc during days 2 and 3 of the watercress consumption period correlated with intake of PEITC during this period, as measured by total urinary PEITC-NAC (r = 0.62; P = 0.04). The results of this study support our hypothesis that PEITC inhibits this oxidative metabolism of NNK in humans, as seen in rodents, and support further development of PEITC as a chemopreventive agent against lung cancer. This is the first study to report an effect of vegetable consumption on metabolism of a lung carcinogen in humans.

Intraindividual and interindividual differences in metabolites of the tobacco-specific lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in smokers' urine

This study describes quantitation in smokers' urine of two metabolites of the tobacco-specific lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). The metabolites are 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), which is also a lung carcinogen, and its O-glucuronide (NNAL-Gluc), a presumed detoxification product of NNK. Using updated methodology, levels of NNAL, NNAL-Gluc, and cotinine were determined in the urine of 61 smokers. The NNAL-Gluc: NNAL ratio, a potential marker for NNK detoxification potential, varied 16-fold in this group. Two phenotypes of this ratio were apparent; one ranging from 0 to 6 and found in 85% of the smokers and a second ranging from 6 to 11. The short-term and long-term consistency of the ratio was investigated. Studies carried out over a 4-5 day period indicated that the NNAL-Gluc: NNAL ratio was reasonably stable. Subjects who donated urine samples on two occasions separated by 4-16 months were classified in the same group (ratio range, 0-6 or 6-11) each time. Different urine collection protocols appeared to have little influence on the NNAL-Gluc: ratio. Thus, intraindividual differences in the NNAL-Gluc:NNAL ratio were generally small, whereas interindividual differences were large. Amounts of NNAL, NNAL-Gluc, and cotinine excreted by smokers were constant in 24-h samples obtained over a 3-day period of constant cigarette intake and controlled diet. Levels of NNAL, NNAL-Gluc, and NNAL plus NNAL-Gluc correlated with cotinine in a study of 61 smokers without controlled diet or smoking (r = 0.58; P < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Uptake and metabolism of carcinogenic levels of tobacco-specific nitrosamines by Sudanese snuff dippers

It was recently reported that toombak, a type of snuff used in the Sudan, contained unusually high levels of tobacco-specific nitrosamines. To estimate the internal dose of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) received by individuals who use this type of tobacco, urine from a group of users was analyzed for 2 metabolites of NNK, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its O-glucuronide, NNAL-Gluc. NNK is a strong lung carcinogen believed to contribute to human lung cancer. NNAL is also a lung carcinogen. NNAL and NNAL-Gluc were analyzed by gas chromatography with a nitrosamine selective detector. The average levels detected were 0.39 +/- 0.14 (SD) nmol/ml urine (n = 7) and 0.88 +/- 0.50 nmol/ml urine (n = 7), respectively. In a 24-h period, these individuals would excrete from 0.12 to 0.44 mg of these two metabolites (expressed per mg NNAL). Therefore, assuming chronic toombak use, the minimum daily dose of NNK to which these users were exposed was 0.12-0.44 mg. This is the highest documented uptake of a nonoccupational carcinogen. Two diastereomers of NNAL-Gluc were present in all urine samples analyzed. Previously, these two diastereomers were identified in the urine of an NNK-treated patas monkey but only one was detected in the urine of NNK-treated rats. The level of the 4-hydroxy-1-(3-pyridyl)-1-butanone releasing hemoglobin adduct was also quantified in these individuals. This adduct is believed to be a measure of NNK activation. The levels ranged from 68 to 323 fmol/g hemoglobin [mean, 148 +/- 104 (SD)]. The wide range of adduct levels which were observed suggests that despite similar levels of NNK exposure, there are significant differences in the ability of individuals in this population to activate NNK, as well as potential differences in their cancer risk.

Biomarkers for human uptake and metabolic activation of tobacco-specific nitrosamines

Tobacco-specific nitrosamines are a group of carcinogens formed from nicotine and related tobacco alkaloids. Two of these compounds, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine, are believed to be involved as causative agents for cancers of the lung, oral cavity, esophagus, and pancreas associated with the use of tobacco products. The goal of the studies described here is to develop biomarkers which will allow us to understand the uptake, metabolic activation, and detoxification of these carcinogens in humans. Two metabolites of NNK, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol and its glucuronide, have been identified and quantified in human urine. These metabolites allow assessment of NNK uptake in smokers, tobacco chewers, and people exposed to environmental tobacco smoke. NNK and N'-nitrosonornicotine form hemoglobin and DNA adducts upon metabolic activation by alpha-hydroxylation. These adducts release 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB) upon hydrolysis. The released 4-hydroxy-1-(3-pyridyl)-1-butanone can be quantified by gas chromatography-mass spectrometry. A subset of smokers and most tobacco chewers have hemoglobin adduct levels which are higher than detected in nonsmokers. 4-Hydroxy-1-(3-pyridyl)-1-butanone-releasing DNA adducts are higher in lung tissue from smokers than from nonsmokers. These data indicate that some smokers and tobacco chewers are capable of metabolically activating NNK or N'-nitrosonornicotine to intermediates which bind to cellular macromolecules and are, therefore, at potentially higher risk for cancer development. The application of these biomarkers to studies on cancer induction by tobacco products is discussed.

A tobacco-specific lung carcinogen in the urine of men exposed to cigarette smoke

BACKGROUND

Environmental tobacco smoke has been classified by the Environmental Protection Agency as a carcinogen causally associated with lung cancer in adults, but there have been no reports of lung carcinogens or their metabolites in the body fluids or tissues of nonsmokers exposed to environmental tobacco smoke.

METHODS

Five male nonsmokers were exposed to sidestream cigarette smoke generated by machine smoking of reference cigarettes for 180 minutes on each of two days, six months apart. Sidestream smoke is the smoke that originates from the smoldering end of a cigarette between puffs. Twenty-four-hour urine samples were collected before and after exposure. The urine samples were analyzed for 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its glucuronide, which are metabolites of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a powerful lung carcinogen in rodents. NNAL is also a lung carcinogen in rodents.

RESULTS

The urinary excretion of the metabolites increased after exposure to sidestream smoke in all the men. The mean (+/- SD) amount of NNAL and NNAL glucuronide was significantly higher after exposure than at base line (33.9 +/- 20.0 vs. 8.4 +/- 11.2 ng per 24 hours [127 +/- 74 vs. 31 +/- 41 pmol per day], P < 0.001) and was correlated with urinary cotinine excretion (r = 0.89, P < 0.001). The nicotine concentrations in the air to which the men were exposed were comparable to those in a heavily smoke-polluted bar.

CONCLUSIONS

Nonsmokers exposed to sidestream cigarette smoke take up and metabolize a lung carcinogen, which provides experimental support for the proposal that environmental tobacco smoke can cause lung cancer.

Identification of 4-(methylnitrosamino)-1-[3-(6-hydroxypyridyl)]-1-butanone as a urinary metabolite of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in rodents

A previously unknown urinary metabolite of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) was identified as 4-(methylnitrosamino)-1-[3-(6-hydroxypyridyl)]-1-butanone (6-hydroxyNNK). The metabolite was initially isolated from rat urine. On the basis of its MS and NMR, it was either a 4- or 6-hydroxypyridyl derivative of NNK. Model compounds were synthesized to distinguish between these possibilities; the results indicated that the metabolite was 6-hydroxyNNK. This was confirmed by independent synthesis; the spectral and chromatographic properties of 6-hydroxyNNK were the same as those of the metabolite. F-344 rats and A/J mice treated with 100 mg/kg NNK excreted approximately 1% of urinary metabolites as 6-hydroxyNNK; it was not detected as a sulfate or glucuronide conjugate. This is the first example of a pyridyl-hydroxylated metabolite of a tobacco-specific nitrosamine. On the basis of comparison to published data on other pyridine derivatives, 6-hydroxyNNK may be formed by bacterial metabolism. The potential utility of 6-hydroxyNNK as a dosimeter of human uptake of NNK is discussed.

Tobacco-specific nitrosamine adducts: studies in laboratory animals and humans

This paper describes quantitation of human hemoglobin and DNA adducts of the carcinogenic tobacco-specific nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN). NNK and NNN are believed to be involved in cancers of the lung, esophagus, oral cavity, and pancreas in people who use tobacco products. The adduct dosimetry method employs GC-MS for quantitation of 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB) released by mild base hydrolysis of hemoglobin or acid hydrolysis of DNA as a biochemical marker of the pyridyloxobutylation metabolic activation pathway. Approximately 22% of smokers (n = 101) had elevated levels of HPB released from hemoglobin (range, 200-1600 fmole/g Hb). Adduct levels in snuff dippers ranged from 200-1800 fmole/g Hb. HPB levels in nonsmokers were generally below the detection limit. Acid hydrolysis of lung and tracheal DNA obtained at autopsy and analysis for released HPB revealed levels ranging up to 50 fmole/mg DNA in smokers; the adduct was not detected in nonsmokers. These findings are consistent with data generated in studies of adduct formation by NNK in rats. The biological significance of the HPB-releasing DNA pyridyloxobutylation pathway was compared to that of the DNA methylation pathway in the A/J mouse. These studies demonstrated that the persistence of O6-methylguanine in lung DNA is critical for tumorigenesis by NNK and that pyridyloxobutylation enhances both persistence of O6-methylguanine and tumorigenesis by acetoxymethylmethylnitrosamine. In the rat, the relative roles of methylation and pyridyloxobutylation in lung tumorigenesis by NNK are not as clearly defined.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that a hemoglobin adduct used for dosimetry of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone is a carboxylic ester

Hemoglobin adducts of the carcinogenic tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) release 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB) upon mild base or acid hydrolysis. HPB has been detected in hydrolysates of hemoglobin from smokers and snuff dippers and has been proposed as a dosimeter of exposure to and metabolic activation of NNK in people exposed to tobacco products. In this study, labeling experiments were carried out with [18O]NaOH that provide strong evidence that the globin adduct that releases HPB upon hydrolysis is a carboxylic ester. Globin was isolated from rats treated with [5-3H]NNK. This globin was reacted with NaCNBH3, followed by hydrolysis at room temperature with 0.2 N NaOH. Analysis of the products demonstrated the presence of 4-hydroxy-1-(3-pyridyl)-1-butanol, but not HPB. These results demonstrate that the adduct in globin has a free carbonyl group and is not a Schiff base. This sequence of reactions was then carried out with [18O]NaOH under conditions that were shown to result in incorporation of 18O if nucleophilic displacement at C-4 had occurred. Analysis by GC-MS of the 4-hydroxy-1-(3-pyridyl)-1-butanol formed in this experiment demonstrated that there was no incorporation of 18O. These results are consistent only with the hydrolysis of an ester by a BAC2 mechanism. Therefore, the adduct releasing HPB upon mild base hydrolysis must be a 4-(3-pyridyl)-4-oxobutyl ester of aspartate, glutamate, or a terminal carboxylate.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolites of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in smokers' urine

Metabolites of the tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, a potent pulmonary carcinogen, have been quantified in the urine of 11 smokers. They were not detected in nonsmokers' urine. The metabolites, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol and its glucuronide, were detected in quantities of 0.23-1.0 and 0.57-6.5 micrograms/24 h, respectively. The results of this study provide the first evidence for metabolites of tobacco-specific nitrosamines in human urine.

Metabolism of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in the patas monkey: pharmacokinetics and characterization of glucuronide metabolites

The metabolism of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) was examined in the patas monkey, in order to provide further information about NNK metabolic pathways in primates. Female patas monkeys were given i.v. injections of [5-3H]NNK, and metabolites in serum and urine were analyzed by HPLC. Metabolism by alpha-hydroxylation of NNK was rapid and extensive, and the products of this pathway, 4-hydroxy-4-(3-pyridyl)butyric acid and 4-oxo-4-(3-pyridyl) butyric acid, accounted for a relatively large proportion of serum and urinary metabolites at all time points. This is significant because the formation of these products is associated with modification of DNA by NNK. The other major metabolic pathway was carbonyl reduction to 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), which detected both unconjugated and diastereomeric O-glucuronides. One of these glucuronides had been previously identified in rat urine, but the other diastereomer, which was the more prevalent of the two in serum and urine, had not been observed in studies of NNK metabolism in rodents. It was characterized by its spectral properties, by enzymatic hydrolysis to NNAL, and by derivatization of the released NNAL enantiomer with (R)-(+)-alpha-methylbenzylisocyanate. The two NNAL glucuronides accounted for 15-20% of the urinary metabolites in monkeys given 0.1 micrograms/kg NNK, which is similar to a smoker's dose, suggesting their use as dosimeters of NNK exposure in humans. Pharmacokinetic parameters were consistent with those observed in previous studies of nitrosamines, and varied predictably with body weight of five species. The results of this study have provided new insights relevant to assessing human metabolism of NNK.

Carcinogen biomarkers related to smoking and upper aerodigestive tract cancer

Smoking is the major cause of upper aerodigestive tract cancers. Among the many constituents of tobacco smoke, polynuclear aromatic hydrocarbons and tobacco-specific nitrosamines are strongly implicated as causative factors for these cancers. The probability that these compounds will induce cancer in a given individual will depend on that person's ability to metabolically activate or detoxify them. Chronic production of DNA damage by these metabolically activated carcinogens is consistent with current concepts of carcinogenesis in which multiple genetic changes, such as activation of oncogenes or inactivation of tumor suppressor genes, appear to be critical. Chemopreventive agents which decrease the level of DNA damage should therefore decrease the risk for cancer. Biomarkers such as carcinogen-DNA adducts, carcinogen-hemoglobin adducts, and urinary metabolites of carcinogens will indicate the amount of metabolically activated carcinogen which may damage DNA in an individual and can therefore be used as an index of risk. Selected biomarkers are discussed in this paper. These biomarkers of internal dose have great potential for application in chemoprevention trials.

DNA and hemoglobin adducts as markers of metabolic activation of tobacco-specific carcinogens

Lung cancer is now the leading cause of excess mortality among smokers in the United States. The ability to identify smokers with the greatest risk of developing lung cancer would be an important step in reducing lung cancer mortality. Tobacco-specific nitrosamines such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and N'-nitrosonornicotine are important carcinogens in tobacco smoke. These carcinogens require metabolic activation to exert their carcinogenic effects. Methods are described for the measurement of DNA and hemoglobin adducts formed by the metabolites of these nitrosamines. Preliminary evidence is presented that shows that a subpopulation of smokers have elevated levels of DNA and hemoglobin adducts of tobacco-specific nitrosamines. Further work is in progress to test the hypothesis that smokers with elevated levels of tobacco-specific nitrosamine adducts are at increased risk of developing lung cancer.

Evidence that a hemoglobin adduct of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone is a 4-(3-pyridyl)-4-oxobutyl carboxylic acid ester

Hemoglobin adducts of the carcinogenic tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) release 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB) upon mild base or acid hydrolysis. HPB has been detected in hydrolysates of human hemoglobin and has been proposed as a dosimeter of exposure to and metabolic activation of NNK in people exposed to tobacco products. In this study, labeling experiments were carried out with Na18OH which provide strong evidence that the globin adduct which releases HPB upon base hydrolysis is a carboxylic acid ester. Globin was isolated from rats treated with NNK. This globin was reacted with NaCNBH3, followed by hydrolysis at room temperature with 0.2 N NaOH. Analysis of the products demonstrated the presence of 4-hydroxy-1-(3-pyridyl)-1-butanol (7), but not HPB. These results demonstrate that the adduct in globin has a free carbonyl group and is not a Schiff base. This sequence of reactions was then carried out with Na18OH, under conditions which would have resulted in incorporation of 18O into 7 if nucleophilic displacement at carbon 4 of the adduct had occurred. Analysis of the products by GC-MS showed no detectable incorporation of 18O into 7. These results demonstrate that the globin adduct which releases HPB upon base hydrolysis is a 4-(3-pyridyl)-4-oxobutyl carboxylic ester. Consistent with this conclusion, a model ester, alpha-methyl beta-[4-(3-pyridyl)-4-oxobutyl] N-(carbobenzyloxy)-L-aspartate (13), hydrolyzed in base and acid in a manner similar to that observed with globin from NNK-treated rats.

Hemoglobin adducts as biomarkers of exposure to and metabolic activation of carcinogenic tobacco-specific nitrosamines

The carcinogenic tobacco-specific nitrosamines N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) form hemoglobin adducts in laboratory animals and humans. These adducts release 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB) upon mild base hydrolysis. HPB released from human hemoglobin can be quantified by gas chromatography-mass spectrometry. It is the only available biochemical marker for determination of exposure to, and metabolic activation of, carcinogens present only in tobacco. Levels of HPB were highest in snuff-dippers, followed by smokers and nonsmokers. Large interindividual variations in adduct levels were observed. The relationship between HPB levels in globin and DNA of rats treated with NNK has been investigated in order to aid in interpretation of the data from humans. These studies have provided the initial database for understanding the metabolic activation of tobacco-specific nitrosamines in humans.

Mass spectrometric analysis of tobacco-specific nitrosamine-DNA adducts in smokers and nonsmokers

A gas chromatography, negative ion chemical ionization mass spectrometry (GC-NICI-MS) based assay for tobacco-specific nitrosamine adducts of DNA is described. The assay is based on the observation that acid hydrolysis of DNA from animals treated with tobacco-specific nitrosamines releases 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB). HPB and the internal standard [4,4-D2]HPB are derivatized with pentafluorobenzoyl chloride and the resulting HPB-pentafluorobenzoate is purified by high-performance liquid chromatography prior to GC-NICI-MS analysis. DNA from human peripheral lung and tracheobronchial tissue, collected at autopsy, was analyzed for acid-released HPB. The mean HPB level (fmol/mg of DNA) for peripheral lung DNA was 11 +/- 16 (SD, n = 9) for smokers and 0.9 +/- 2.3 (n = 8) for nonsmokers. Mean adduct levels in tracheobronchus were 16 +/- 18 (n = 4) for smokers and 0.9 +/- 1.7 (n = 4) for nonsmokers. These are the first measurements of tobacco-specific nitrosamine-DNA adducts in humans. Further studies comparing the levels of DNA and globin adducts will provide a better understanding of the metabolic activation of tobacco-specific nitrosamines in humans and may provide a more accurate indication of an individual's risk of developing tobacco-related cancer.

Evaluation of cysteine adduct formation in rat hemoglobin by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and related compounds

The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) forms hemoglobin adducts in rats. Upon mild base treatment, 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB) is released from this globin. HPB has been suggested as a dosimeter for exposure to and metabolic activation of tobacco-specific nitrosamines. The purpose of this study was 2-fold: (a) to determine whether cysteine adducts of NNK were precursors to HPB, and (b) to determine to what extent cysteine adducts accounted for the material bound to globin that is not released upon mild base hydrolysis. The chemistry of cysteine adduct formation was investigated by reacting N-acetyl-L-cysteine with three model compounds for pyridyloxobutylation by metabolically activated NNK: 4-(carbethoxynitrosamino)-1-(3-pyridyl)-1-butanone (1); 4-oxo-4-(3-pyridyl)-1-butylmethanesulfonate (2); and 4-iodo-1-(3-pyridyl)-1-butanone (3). Five adducts were isolated and characterized by their spectral properties and by independent syntheses: two diastereomers of N-acetyl-S-[1-methyl-3-oxo-3-(3-pyridyl)propyl]-L-cysteine (7a,b), N-acetyl-S-[4-oxo-4-(3-pyridyl)-1-butyl]-L-cysteine (9), and two diastereomers of N-acetyl-S-(2-[2-(3-pyridyl)]-2,3,4,5-tetrahydrofuranyl)-L-cystein e (11a,b). Only 11a,b produced HPB upon mild base treatment; however, the chemistry of this adduct did not support its role as a major precursor to HPB released upon base treatment of globin. The formation of adducts in rat hemoglobin was then examined by reacting it with tritium-labeled 1 [( 5-3H]1) or tritium-labeled 4-oxo-4-(3-pyridyl)-1-butyl p-toluenesulfonate [( 5-3H]4). The results demonstrated that the amino acids corresponding to 7a,b were present in hemoglobin reacted with [5-3H]1, accounting for 72% of the bound tritium. Amino acids corresponding to 9 were not detected in this globin. In contrast, hemoglobin reacted with [5-3H]4 contained the amino acid corresponding to 9 (15% of bound tritium), but not those corresponding to 7a,b. These results indicated that the alpha, beta-unsaturated ketone, 1-(3-pyridyl)-2-buten-1-one (5), played a major role in the hemoglobin binding of 1, but not of 4. Cysteine adducts were not detected in globin isolated from rats treated with [5-3H]NNK. The results of this study provide insights into the mechanisms of cysteine adduct formation in vitro by pryidyloxobutylating agents and indicate that these adducts are not formed in NNK-treated rats.

Mass spectrometric analysis of tobacco-specific nitrosamine hemoglobin adducts in snuff dippers, smokers, and nonsmokers

Hemoglobin adducts of the carcinogenic tobacco-specific nitrosamines 4-(methylnitrosamino)-1(3-pyridyl)-1-butanone and N'-nitrosonornicotine were quantified in blood samples collected from snuff dippers, smokers, and nonsmokers. Mild base treatment of hemoglobin adducted by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone or N'-nitrosonornicotine releases 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB). HPB was enriched by solvent partitioning and derivatized to its pentafluorobenzoate. After purification by high performance liquid chromatography, HPB-pentafluorobenzoate was analyzed by capillary column gas chromatography with detection by negative ion chemical ionization mass spectrometry and selected ion monitoring. [4,4-D2]HPB was used as internal standard. The detection limit for HPB-pentafluorobenzoate was approximately 100 amol/injection or 5 fmol/g hemoglobin. Mean adduct levels (fmol HPB/g hemoglobin) were 517 +/- 538 (SD) in snuff dippers, 79.6 +/- 189 in smokers, and 29.3 +/- 25.9 in nonsmokers. Adduct levels in snuff dippers and in a subgroup of smokers were higher than would have been predicted solely based on estimates of exposure to tobacco-specific nitrosamines. The results of this study provide the first measurements of tobacco-specific nitrosamine hemoglobin adducts in humans and suggest new approaches to understanding the metabolic activation of 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone and N'-nitrosonornicotine in humans.

Investigations of metabolic precursors to hemoglobin and DNA adducts of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone

Levels of DNA and/or hemoglobin pyridyloxobutylation were compared in A/J mice or F344 rats treated with a single dose of [5-3H]4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone ([5-3H]NNK), [5-3H]4-hydroxy-1-(3-pyridyl)-1-butanone ([5-3H]4-HPB) or [5-3H]4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanone ([5-3H]NNKOAc), a compound that generates the proposed pyridyloxobutylating agent in situ upon esterase hydrolysis. The lung and liver DNA samples isolated from A/J mice treated with the various compounds were subjected to acid hydrolysis and the hydrolysates were analyzed for the presence of [5-3H]4-HPB. No detectable levels were found in the lung DNA isolated from [5-3H]4-HPB-treated animals, whereas significant amounts of [5-3H]4-HPB were released from lung and liver DNA isolated from [5-3H]NNK- and [5-3H]NNKOAc-treated mice. The levels of total binding and [5-3H]4-HPB released from the globin isolated from these animals showed a similar trend. That is, low binding levels were detected in the globin isolated from [5-3H]4-HPB-treated animals and significantly higher levels of binding were detected in the globin from the [5-3H]NNKOAc- and [5-3H]NNK-treated animals. Comparable findings were obtained in the rat experiments. These studies clearly demonstrate that methyl hydroxylation of NNK leads to a species that is capable of reacting covalently with nucleophiles in DNA and protein. Thus, the levels of 4-HPB released from DNA and globin can be attributed to the activation of NNK and not to the direct binding of 4-HPB.

Approaches to the development of assays for interaction of tobacco-specific nitrosamines with haemoglobin and DNA

The tobacco-specific, nicotine-derived nitrosamines 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) are among the most important carcinogens in tobacco and tobacco smoke. Treatment of Fischer 344 rats with these carcinogens resulted in alkylation of haemoglobin and DNA by the 4-(3-pyridyl)-4-oxobutyl group formed during their metabolism. This alkyl group can be detached from globin or DNA under mild hydrolytic conditions as 4-hydroxy-1-(3-pyridyl)-1-butanone, which appears to be a potentially useful dosimeter for human exposure to, and activation of, tobacco-specific nitrosamines.

Formation of hemoglobin adducts upon treatment of F344 rats with the tobacco-specific nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and N'-nitrosonornicotine

[5-3H]4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone ([5-3H]NNK), [C3H3]NNK, and [5-3H]N'-nitrosonornicotine ([5-3H]NNN) were administered to F344 rats by i.p. injection. Levels of tritium present per milligram globin, 24 h after treatment were 720 fmol (0.1% of dose) for [5-3H]NNK, 640 fmol for [C3H3]NNK, and 370 fmol for [5-3H]NNN. Tritium was detectable in globin 7-8 weeks after treatment with [5-3H]NNK or [5-3H]NNN. Approximately 10-15% of the bound tritium in the globin of rats treated with [5-3H]NNK was released upon incubation of the globin with dilute NaOH or HCl. The released material was identified as 4-hydroxy-1-(3-pyridyl)-1-butanone; it was detectable in globin for 6 weeks (t1/2 = 9.1 days) after administration of [5-3H]NNK. 4-Hydroxy-1-(3-pyridyl)-1-butanone was also formed upon NaOH treatment of globin isolated from rats injected with [5-3H]NNN or [5-3H]4-(carbethoxynitrosamino)-1-(3-pyridyl)-1-butanone. The formation of 4-hydroxy-1-(3-pyridyl)-1-butanone under these conditions is consistent with a mechanism by which 4-(3-pyridyl)-4-oxobutyldiazohydroxide is produced upon metabolic alpha-hydroxylation of NNK or NNN and binds to globin of hemoglobin, yielding an adduct which is readily hydrolyzed by acid or base. Support for this mechanism was obtained by in vitro experiments. Levels of 4-hydroxy-1-(3-pyridyl)-1-butanone released upon base treatment of globin were 50 times greater after incubation of rat hemoglobin with [5-3H]4-(carbethoxynitrosamino)-1-(3-pyridyl)-1-butanone than with either [5-3H]NNK or [5-3H]4-hydroxy-1-(3-pyridyl)-1-butanone. The results of this study suggest methods that might be applicable for assessing the molecular dosimetry of NNK and NNN in individuals exposed to tobacco and tobacco smoke.

Investigations on the molecular dosimetry of tobacco-specific N-nitrosamines

Approaches for assessing molecular dosimetry of 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) in humans by measurement of haemoglobin or DNA adducts are discussed. NNK and NNN form haemoglobin adducts in Fischer 344 rats. Acid or base hydrolysis of the globin gives 4-hydroxy-1-(3-pyridyl)-1-butanone, which can be detected in rat blood up to six weeks after injection of NNK; it may be a useful marker for assessing uptake and metabolic activation of NNK and NNN in tobacco consumers. NNK and its major metabolite, 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanol (NNAI), methylated DNA of rat liver, lung and nasal mucosa to similar extents. NNAI is formed in human tissues from NNK, but immunoassays for O6-methyldeoxyguanosine (O6-medGuo) in exfoliated oral cells from snuff-dippers have been negative. NNK is also expected to form pyridyloxobutyl adducts in DNA; 32P-postlabelling assays for these adducts are being developed and appear to hold promise for detecting NNK- or NNN-DNA adducts in vivo.

Effects of butylated hydroxyanisole on the tumorigenicity and metabolism of N-nitrosodimethylamine and N-nitrosopyrrolidine in A/J mice

Female A/J mice were maintained on NIH-07 diet or on NIH-07 diet containing butylated hydroxyanisole (BHA, a mixture of 2- and 3-tert-butyl-4-hydroxyanisole), 5 mg/g, for 1 week prior to and during 10 weeks of treatment with N-nitrosodimethylamine (NDMA) or N-nitrosopyrrolidine (NPYR), administered in the drinking water. Twenty weeks after nitrosamine treatment ended, mice were sacrificed and lung adenomas were counted. BHA inhibited NDMA tumorigenesis but enhanced NPYR tumorigenesis. Treatment of A/J mice for three weeks with BHA (5 mg/g) added to semisynthetic diet increased whole lung microsomal alpha-hydroxylation of NDMA and NPYR, as measured by aldehyde production, and increased lung and hepatic glutathione-S-transferase activities. No evidence was found for formation of S-methylglutathione in incubations with NDMA and hepatic supernatants obtained from BHA treated or control mice. Four h after gavage of NDMA, levels of 7-methylguanine in the lung DNA of mice treated with BHA were higher than in the lung DNA of control mice, but levels of O6-methylguanine in the two groups were the same. The results of this study indicate that BHA treatment increases the microsomal metabolic alpha hydroxylation of both NDMA and NPYR, but has differential effects on their tumorigenic activities.

High-performance liquid chromatographic analysis of metabolites of the nicotine-derived nitrosamines, N'-nitrosonornicotine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone

An improved high-performance liquid chromatographic system was developed for separation of 11 metabolites of the nicotine-derived nitrosamines N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). The new system employed a 5-microns octadecylsilane bonded column eluted with aqueous sodium acetate-methanol gradients of varying pH. Analysis times were typically 30 min for NNN metabolites and 50 min for NNK metabolites, compared to 80 and 90 min, respectively, when 10-microns columns were used. The E and Z isomers of all nitrosamine-containing metabolites of NNK were separated. The chromatographic behavior of the 11 metabolites as well as NNN and NNK was studied between pH 4.0 and 7.5. The retention times of several metabolites were altered significantly as a function of pH. The results of the pH study provide valuable additional criteria for metabolite identification as well as optimized conditions for their separation. Applications of the system to the metabolism of [2'-14C]NNN in cultured rat esophagus and [carbonyl-14C]NNK in rat liver slices are presented.

Quantitative analysis of catechol and 4-methylcatechol in human urine

A method was developed for the quantitative analysis of catechol and 4-methylcatechol in human urine. [U-14C]Catechol was used as in internal standard. Urine was treated with beta-glucuronidase and sulphatase, acidified and extracted with ether. The ether extract was silylated and analysed by glass capillary gas chromatography. Catechol and 4-methylcatechol occurred in urine primarily as conjugates. Levels of catechol and 4-methylcatechol in the urine of nonsmokers on unrestricted diets were 10 +/- 7.3 (mean +/- 1 SD) and 3.4 +/- 2.3 mg/24 hr, respectively. Nonsmokers on uniform restricted diets, in which the intake of plant-derived products was limited, excreted 4.4 +/- 1.2 mg catechol and 8.1 +/- 1.7 mg 4-methylcatechol/24 hr. Smokers on the same restricted diet excreted 6.8 +/- 3.0 mg catechol and 6.1 +/- 2.6 mg 4-methylcatechol/24 hr. These results indicate that diet is a major factor in determining urinary catechol levels and that the contribution of smoking is comparatively small. Catechol and 4-methylcatechol appear to have different dietary precursors.