Stereoselective metabolism of nicotine and tobacco-specific N-nitrosamines to 4-hydroxy-4-(3-pyridyl)butanoic acid in rats

Impact of Genetic Variants in the Nicotine Metabolism Pathway on Nicotine Metabolite Levels in Smokers

BACKGROUND

Nicotine metabolism is a major factor in nicotine dependence, with approximately 70% to 80% of nicotine metabolized to cotinine in Caucasians. Cotinine formation is catalyzed primarily by CYP2A6, which also converts cotinine to trans-3'-hydroxycotinine (3HC). The goal of the present study was to examine the effects of CYP2A6 deficiency on nicotine metabolism profiles in vivo and the importance of genetic variants in nicotine-metabolizing enzyme genes on urinary nicotine metabolites levels.

METHODS

Urine samples from 722 smokers who participated in the Singapore Chinese Health Study were analyzed using UPLC-MS/MS to detect nicotine and eight of its urinary metabolites, and a total of 58 variants in 12 genes involved in nicotine metabolism were investigated in 475 of these subjects with informative genotyping data.

RESULTS

Urine samples stratified by the ratio of 3HC/cotinine exhibited a 7-fold increase in nicotine-N'-oxide, a 6-fold increase in nicotine-Glucuronide (Gluc), and a 5-fold decrease in 3HC-Gluc when comparing the lower versus upper 3HC/cotinine ventiles. Significant (P < 0.0001) associations were observed between functional metabolizing enzyme genotypes and levels of various urinary nicotine metabolites, including CYP2A6 genotype and levels of nicotine, nicotine-Gluc, nicotine-N'-oxide and 3HC, UGT2B10 genotype and levels of cotinine, nicotine-Gluc and cotinine-Gluc, UGT2B17 genotype and levels of 3HC-Gluc, FMO3 genotype and levels of nicotine-N'-oxide, and CYP2B6 genotype and levels of nicotine-N'-oxide and 4-hydroxy-4-(3-pyridyl)-butanoic acid.

CONCLUSIONS

These data suggest that several pathways are important in nicotine metabolism.

IMPACT

Genotype differences in several nicotine-metabolizing enzyme pathways may potentially lead to differences in nicotine dependence and smoking behavior and cessation.

Metabolism and DNA Adduct Formation of Tobacco-Specific N-Nitrosamines

The tobacco-specific N-nitrosamines 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) always occur together and exclusively in tobacco products or in environments contaminated by tobacco smoke. They have been classified as "carcinogenic to humans" by the International Agency for Research on Cancer. In 1998, we published a review of the biochemistry, biology and carcinogenicity of tobacco-specific nitrosamines. Over the past 20 years, considerable progress has been made in our understanding of the mechanisms of metabolism and DNA adduct formation by these two important carcinogens, along with progress on their carcinogenicity and mutagenicity. In this review, we aim to provide an update on the carcinogenicity and mechanisms of the metabolism and DNA interactions of NNK and NNN.

Identification of an N'-Nitrosonornicotine-Specific Deoxyadenosine Adduct in Rat Liver and Lung DNA

The tobacco-specific nitrosamines N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) are considered to be two of the most important carcinogens in unburned tobacco and its smoke. They readily cause tumors in laboratory animals and are classified as "carcinogenic to humans" by the International Agency for Research on Cancer. DNA adduct formation by these two carcinogens is believed to play a critical role in tobacco carcinogenesis. Among all the DNA adducts formed by NNN and NNK, 2'-deoxyadenosine (dAdo)-derived adducts have not been fully characterized. In the study reported here, we characterized the formation of N⁶-[4-(3-pyridyl)-4-oxo-1-butyl]-2'-deoxyadenosine (N⁶-POB-dAdo) and its reduced form N⁶-PHB-dAdo formed by NNN 2'-hydroxylation in rat liver and lung DNA. More importantly, we characterized a new dAdo adduct N⁶-[4-hydroxy-1-(pyridine-3-yl)butyl]-2'-deoxyadenosine (N⁶-HPB-dAdo) formed after NaBH₃CN or NaBH₄ reduction both in vitro in calf thymus DNA reacted with 5'-acetoxy-N'-nitrosonornicotine and in vivo in rat liver and lung upon treatment with NNN. This adduct was specifically formed by NNN 5'-hydroxylation. Chemical standards of N⁶-HPB-dAdo and the corresponding isotopically labeled internal standard [pyridine-d₄]N⁶-HPB-dAdo were synthesized using a four-step method. Both NMR and high-resolution mass spectrometry data agreed well with the proposed structure of N⁶-HPB-dAdo. The new adduct coeluted with the synthesized internal standard under various LC conditions. Its product ion patterns of MS² and MS³ transitions were also consistent with the proposed fragmentation patterns. Chromatographic resolution of the two diastereomers of N⁶-HPB-dAdo was successfully achieved. Quantitation suggested a dose-dependent response of the levels of this new adduct in the liver and lung of rats treated with NNN. However, its level was lower than that of 2-[2-(3-pyridyl)-N-pyrrolidinyl]-2'-deoxyinosine, a previously reported dGuo adduct that is also formed from NNN 5'-hydroxylation. The identification of N⁶-HPB-dAdo in this study leads to new insights pertinent to the mechanism of carcinogenesis by NNN and to the development of biomarkers of NNN metabolic activation.

Tobacco Smoke Exposure Impairs Brain Insulin/IGF Signaling: Potential Co-Factor Role in Neurodegeneration

BACKGROUND

Human studies suggest tobacco smoking is a risk factor for cognitive impairment and neurodegeneration, including Alzheimer's disease (AD). However, experimental data linking tobacco smoke exposures to underlying mediators of neurodegeneration, including impairments in brain insulin and insulin-like growth factor (IGF) signaling in AD are lacking.

OBJECTIVE

This study tests the hypothesis that cigarette smoke (CS) exposures can impair brain insulin/IGF signaling and alter expression of AD-associated proteins.

METHODS

Adult male A/J mice were exposed to air for 8 weeks (A8), CS for 4 or 8 weeks (CS4, CS8), or CS8 followed by 2 weeks recovery (CS8+R). Gene expression was measured by qRT-PCR analysis and proteins were measured by multiplex bead-based or direct binding duplex ELISAs.

RESULTS

CS exposure effects on insulin/IGF and insulin receptor substrate (IRS) proteins and phosphorylated proteins were striking compared with the mRNA. The main consequences of CS4 or CS8 exposures were to significantly reduce insulin R, IGF-1R, IRS-1, and tyrosine phosphorylated insulin R and IGF-1R proteins. Paradoxically, these effects were even greater in the CS8+R group. In addition, relative levels of S312-IRS-1, which inhibits downstream signaling, were increased in the CS4, CS8, and CS8+R groups. Correspondingly, CS and CS8+R exposures inhibited expression of proteins and phosphoproteins required for signaling through Akt, PRAS40, and/or p70S6K, increased AβPP-Aβ, and reduced ASPH protein, which is a target of insulin/IGF-1 signaling.

CONCLUSION

Secondhand CS exposures caused molecular and biochemical abnormalities in brain that overlap with the findings in AD, and many of these effects were sustained or worsened despite short-term CS withdrawal.

Tobacco Smoke-Induced Hepatic Injury with Steatosis, Inflammation, and Impairments in Insulin and Insulin-Like Growth Factor Signaling

Background

Alcoholic liver disease (ALD) is associated with impairments in hepatic insulin and insulin-like growth factor (IGF) signaling through cell growth, survival, and metabolic pathways. Since not all heavy drinkers develop ALD, co-factors may be important. Epidemiologic data indicate that most heavy drinkers smoke tobacco and experimental data revealed that low-level nitrosamine exposures, including those from tobacco, can cause steatohepatitis with hepatic insulin/IGF resistance and exacerbate ALD. We hypothesize that cigarette smoke (CS) exposures also cause liver injury with impaired hepatic insulin/IGF signaling, and thereby contribute to ALD.

Methods

Adult male A/J mice were exposed to air for 8 weeks (A8), CS for 4 (CS4) or 8 (CS8) weeks, or CS for 8 weeks with 2 weeks recovery (CS8+R).

Results

CS exposures caused progressive liver injury with disruption of the normal hepatic chord architecture, lobular inflammation, apoptosis or necrosis, micro-steatosis, sinusoidal dilatation, and nuclear pleomorphism. Histopathological liver injury scores increased significantly from A8 to CS4 and then further to CS8 (P<0.0001). The mean histological grade was also higher in CS8+R relative to A8 (P<0.0001) but lower than in CS4, reflecting partial resolution of injury by CS withdrawal. CS exposures impaired insulin and IGF-1 signaling through IRS-1, Akt, GSK-3β, and PRAS40. Livers from CS8+R mice had normalized or elevated levels of insulin receptor, pYpY-Insulin-R, 312S-IRS-1, 473S-Akt, S9-GSK-3β, and pT246-PRAS40 relative to A8, CS4, or CS8, reflecting partial recovery.

Conclusion

CS-mediated liver injury and steatohepatitis with impairments in insulin/IGF signalling are reminiscent of the findings in ALD. Therefore, CS exposures (either first or second-hand) may serve as a co-factor in ALD. The persistence of several abnormalities following CS exposure cessation suggests that some aspects of CS-mediated hepatic metabolic dysfunction are not readily reversible.

Tobacco Smoke-Induced Brain White Matter Myelin Dysfunction: Potential Co-Factor Role of Smoking in Neurodegeneration

BACKGROUND

Meta-analysis studies showed that smokers have increased risk for developing Alzheimer's disease (AD) compared with non-smokers, and neuroimaging studies revealed that smoking damages white matter structural integrity.

OBJECTIVE

The present study characterizes the effects of side-stream (second hand) cigarette smoke (CS) exposures on the expression of genes that regulate oligodendrocyte myelin-synthesis, maturation, and maintenance and neuroglial functions.

METHODS

Adult male A/J mice were exposed to air (8 weeks; A8), CS (4 or 8 weeks; CS4, CS8), or CS8 followed by 2 weeks recovery (CS8 + R). The frontal lobes were used for histology and qRT-PCR analysis.

RESULTS

Luxol fast blue, Hematoxylin and Eosin stained histological sections revealed CS-associated reductions in myelin staining intensity and narrowing of the corpus callosum. CS exposures broadly decreased mRNA levels of immature and mature oligodendrocyte myelin-associated, neuroglial, and oligodendrocyte-related transcription factors. These effects were more prominent in the CS8 compared with CS4 group, suggesting that molecular abnormalities linked to white matter atrophy and myelin loss worsen with duration of CS exposure. Recovery normalized or upregulated less than 25% of the suppressed genes; in most cases, inhibition of gene expression was either sustained or exacerbated.

CONCLUSION

CS exposures broadly inhibit expression of genes needed for myelin synthesis and maintenance. These adverse effects often were not reversed by short-term CS withdrawal. The results support the hypothesis that smoking contributes to white matter degeneration, and therefore could be a key risk factor for a number of neurodegenerative diseases, including AD.

Extensive metabolic activation of the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in smokers

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent lung carcinogen present in both unburned tobacco and cigarette smoke. The sum of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its glucuronides, referred to as total NNAL, is an established urinary biomarker of human NNK uptake. Metabolic activation of NNK to DNA adducts proceeds via alpha-hydroxylation pathways, and 4-oxo-4-(3-pyridyl)butanoic acid (keto acid) and 4-hydroxy-4-(3-pyridyl)butanoic acid (hydroxy acid) are the principal end products of these pathways in rodents and primates. The purpose of this study was to determine NNK metabolic activation in smokers, as measured by the sum of keto acid and hydroxy acid, relative to total NNAL. To specifically identify NNK-derived keto acid and hydroxy acid, which are also formed from nicotine, we added [pyridine-D(4)]NNK to cigarettes that were originally low in NNK, and measured the deuterium-labeled metabolites in the urine of people who smoked these cigarettes. The total amount of [pyridine-D(4)]keto acid plus [pyridine-D(4)]hydroxy acid averaged 4.00 +/- 2.49 nmol/24 h, whereas the average amount of total [pyridine-D(4)]NNAL was 0.511 +/- 0.368 nmol/24 h. The results of this study show for the first time that NNK metabolic activation is a quantitatively significant pathway in smokers, accounting for approximately 86% of total urinary excretion of NNK metabolites. The large interindividual variation in the excreted [pyridine-D(4)]keto acid and [pyridine-D(4)]hydroxy acid among 20 smokers strongly supports our hypothesis that some smokers activate NNK more extensively than others and that the ratio between biomarkers of metabolic activation and detoxification at a given dose of NNK could be a potential indicator of cancer risk.

Identification of adducts formed in the reaction of 5'-acetoxy-N'-nitrosonornicotine with deoxyguanosine and DNA

N'-Nitrosonornicotine (NNN) is believed to play an important role as a cause of cancer in people who use tobacco products and is considered to be a human carcinogen. NNN requires metabolism to form DNA adducts, which are absolutely critical to its carcinogenic properties. Previous studies have identified cytochrome P450-catalyzed 2'- and 5'-hydroxylation of NNN as potential DNA adduct forming metabolic pathways. 5'-Hydroxylation is the more prevalent of these in monkeys and humans and is known to generate mutagenic intermediates, but the DNA adducts formed by this pathway have never been characterized. In this study, we used 5'-acetoxyNNN as a stable precursor to 5'-hydroxyNNN and investigated its esterase-catalyzed reactions with deoxyguanosine (dGuo) and DNA. Adducts resulting from carbocation and oxonium ion intermediates, produced by the spontaneous decomposition of 5'-hydroxyNNN, were identified. The carbocation pathway resulted in the formation of 2-[2-hydroxy-5-(3-pyridyl)pyrrolidin-1-yl]deoxyinosine (12) which was characterized by comparison to an independently synthesized standard. Treatment of 12 with NaBH(3)CN produced two diastereomers of 2-[2-(3-pyridyl)pyrrolidin-1-yl]deoxyinosine (14), and their absolute configurations at the 2-position were determined by comparison to synthetic standards. The oxonium ion pathway produced diastereomers of N(2)[5-(3-pyridyl)tetrahydrofuran-2-yl]dGuo (16), identified by comparison to synthetic standards. The absolute configuration at the 5-position was determined by establishing the stereochemistry of the enantiomers of 5-(3-pyridyl)-2-hydroxytetrahydrofuran at the 5-position and allowing these to react individually with dGuo. Treatment of 16 with NaBH(3)CN produced N(2)[4-hydroxy-4-(3-pyridyl)but-1-yl]dGuo (18) which was also synthesized independently. Using liquid chromatography-electrospray ionization-tandem mass spectrometry with selected reaction monitoring, we identified adducts 12 and 16 as products of the reactions of 5'-acetoxyNNN with dGuo. Similarly, adducts 14 and 18 were identified as products of the reaction of 5'-acetoxyNNN with DNA followed by NaBH(3)CN treatment and enzymatic hydrolysis. These results provide the first structural characterization of DNA adducts that can be formed by 5'-hydroxylation of NNN.

Acute and subacute effects of tobacco alkaloids, tobacco-specific nitrosamines and phenethyl isothiocyanate on N'-nitrosonornicotine metabolism in rats

N'-Nitrosonornicotine (NNN) was the first tobacco-specific nitrosamine (TSNA) identified as carcinogen in tobacco smoke, but no data exist on in vivo interactions between NNN and other tobacco alkaloids, TSNA or phenethyl isothiocyanate (PEITC) which have been demonstrated in various studies on 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Acute effects on NNN metabolism were tested in male Fischer F344 rats injected s.c. with 30nmol/kg body weight (bw) [5-(3)H]NNN either alone or simultaneously with 15mumol/kg bw nicotine, nornicotine, anatabine, or anabasine, 150mumol/kg bw cotinine, 3mumol/kg bw myosmine, or 300nmol/kg bw of either N'-nitrosoanatabine or N'-nitrosoanabasine. Another group of rats was fed a diet supplemented with PEITC at 1mumol/g diet starting 24h before NNN treatment. Within 24h more than 80% and about 10% of the radioactivity was excreted with urine and feces, respectively. Urinary metabolites were separated by reversed-phase radio-HPLC and identified by co-chromatography with UV standards. In two sets of experiments with control rats treated with NNN only, 4-hydroxy-4-(3-pyridyl)butanoic acid (hydroxy acid, 44.4/44.8%), 4-oxo-4-(3-pyridyl)butanoic acid (keto acid, 32.4/31.5%), NNN-N-oxide (5.0/3.8%), 4-(3-pyridyl)butane-1,4-diol (diol, 1.1/1.0%) and norcotinine (2.3/1.0%) were consistently detected besides unmetabolised NNN (4.7/3.3%). Co-treatment with nicotine, cotinine, nornicotine and PEITC shifted the contribution of the two major metabolites significantly in favor of hydroxy acid (108-113% of control) as compared to keto acid (86-90% of control). The same treatments also increased norcotinine (135-170% of control). These changes are consistent with a decreased metabolic activation of NNN. In subacute studies rats received NNN in drinking water for 4 weeks at a daily dose of 30 nmol/kg bw with or without nornicotine at 15 micromol/kg bw or myosmine at 3 micromol/kg bw. On the last day of the experiment all rats received [5-(3)H]NNN at 30 nmol/kg bw with a contaminated apple bite followed by collection of urine and feces for 18h. Most of the radioactivity, 87-96% of the dose, was recovered in urine and only minor amounts have been excreted in feces or persisted in blood. In urine of the NNN-control group keto acid (32.2%) and unmetabolised NNN (3.9%) were present in identical amounts as in the acute experiment whereas hydroxy acid (41.4% of total radioactivity in urine, 93% of acute NNN control) was reduced in expense of the minor NNN metabolites. Co-administration of nornicotine resulted in a small but significant rise of keto acid (107% of control) and a significant decrease in NNN-N-oxide (76% of control). After co-treatment with myosmine the increase of keto acid (104% of control) was even less but still significant whereas NNN-N-oxide and diol were significantly reduced to 72% and 79% of control, respectively. Our experiments with rats indicate significant mutual effects of some of the major tobacco alkaloids and most relevant TSNA. Further studies on the impact on smokers and the inhibitory effects of isothiocyanates are needed for a final risk assessment.

Metabolism of myosmine in Wistar rats

The alkaloid myosmine is present not only in tobacco products but also in various foods. Myosmine is easily nitrosated, yielding 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB) and the esophageal tobacco carcinogen N'-nitrosonornicotine. Due to its widespread occurrence, investigations on the metabolism and activation of myosmine are needed for risk assessment. Therefore, the metabolism of myosmine has been studied in Wistar rats treated with single oral doses of [pyridine-5-3H]myosmine at 0.001, 0.005, 0.5, and 50 micromol/kg body weight. Oral administration was achieved by feeding a labeled apple bite. Radioactivity was completely recovered in urine and feces within 48 h. At the two lower doses, 0.001 and 0.005 micromol/kg, a higher percentage of the radioactivity was excreted in urine (86.2 +/- 4.9% and 88.9 +/- 1.7%) as compared with the higher doses, 0.5 and 50 micromol/kg, where only 77.8 +/- 7.3% and 75.4 +/- 6.6% of the dose was found in urine. Within 24 h, urinary excretion of radioactivity was nearly complete with less than 4% of the total urinary output appearing between 24 and 48 h. The two major metabolites accounting for >70% of total radioactivity in urine were identified as 3-pyridylacetic acid (20-26%) and 4-oxo-4-(3-pyridyl)butyric acid (keto acid, 50-63%) using UV-diode array detection and gas chromatography-mass spectrometry measurements. 3-Pyridylmethanol (3-5%), 3'-hydroxymyosmine (2%) and HPB (1-3%) were detected as minor metabolites. 3'-Hydroxymyosmine is exclusively formed from myosmine and therefore might be used as a urinary biomarker for myosmine exposure in the future.

An analysis of the role of tobacco-specific nitrosamines in the carcinogenicity of tobacco smoke

Cigarette smoke is a complex mixture consisting of more than 4500 chemicals, including several tobacco-specific nitrosamines (TSNA). TSNA typically form in tobacco during the post-harvest period, with some fraction being transferred into mainstream smoke when a cigarette is burned during use. The most studied of the TSNA is 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). NNK has been shown to be carcinogenic in laboratory animals. Studies examining the carcinogenicity of NNK frequently are conducted by injecting rodents with a single dose of 2.5 to 10 mumol of pure NNK; the amount of NNK contained in all of the mainstream smoke from about 3700 to 14,800 typical U.S. cigarettes. Extrapolated to a 70-kg smoker, the carcinogenic dose of pure NNK administered to rodents would be equivalent to the amount of NNK in all of the mainstream smoke of 22 to 87 million typical U.S. cigarettes. Furthermore, extrapolating results from rodent studies based on a single injection of pure NNK to establish a causative role for NNK in the carcinogenicity of chronic tobacco smoke exposure in humans is not consistent with basic pharmacological and toxicological principles. For example, such an approach fails to consider the effect of other smoke constituents upon the toxicity of NNK. In vitro studies demonstrate that nicotine, cotinine, and aqueous cigarette "tar" extract (ACTE) all inhibit the mutagenic activity of NNK. In vivo studies reveal that the formation of pulmonary DNA adducts in mice injected with NNK is inhibited by the administration of cotinine and mainstream cigarette smoke. Cigarette smoke has been shown to modulate the metabolism of NNK, providing a mechanism for the inhibitory effects of cigarette smoke and cigarette smoke constituents on NNK-induced tumorigenesis. NNK-related pulmonary DNA adducts have not been detected in rodents exposed to cigarette smoke, nor has the toxicity of tobacco smoke or tobacco smoke condensate containing marked reductions in TSNA concentrations been shown to be reduced in any biological assay. In summary, there is no experimental evidence to suggest that reduction of TSNA will reduce the mutagenic, cytotoxic, or carcinogenic potential of tobacco smoke.

Metabolism and pharmacokinetics of N'-nitrosonornicotine in the patas monkey

N'-Nitrosonornicotine (NNN) is present in significant quantities in tobacco and tobacco smoke and is believed to play an important role as a cause of cancer in people who use tobacco products. Biomarkers of NNN uptake in humans such as urinary metabolites would be useful for assessing cancer risk. Previous studies, carried out almost exclusively in rodents, have characterized urinary metabolites of NNN, but none of these would be suitable as a biomarkers of NNN uptake in humans. Therefore, we studied NNN metabolism in the patas monkey. Monkeys were treated intravenously with [5-(3)H]NNN, which has tritium in the pyridine ring. Blood and urine samples were collected at timed intervals. Six urinary metabolites were observed by high-performance liquid chromatography (HPLC) and were identified by their spectral properties and/or comparison to appropriate standards as follows: metabolite (% of radioactivity eluting from HPLC +/- S.D., n = 3 monkeys); 4-hydroxy-4-(3-pyridyl)butyric acid (43.8 +/- 4.0); 4-oxo-4-(3-pyridyl) butyric acid (2.7 +/- 0.66); norcotinine (13.1 +/- 2.7); norcotinine-1N-oxide (16.5 +/- 1.3); 3'-hydroxynorcotinine (16.9 +/- 2.0); 3'-(O-beta-D-glucopyranuronosyl)hydroxynorcotinine (5.4 +/- 1.0); and unchanged NNN (0.63 +/- 0.15). The two major metabolites in serum were 4-hydroxy-4-(3-pyridyl)butyric acid and norcotinine. NNN was rapidly metabolized to 4-hydroxy-4-(3-pyridyl)butyric acid, whereas the formation of norcotinine and 3'-hydroxynorcotinine were somewhat delayed. The results of this study demonstrate substantial differences between NNN metabolism in the rodent and patas monkey. Metabolism of NNN to norcotinine and its derivatives was far more prevalent in the patas monkey than in the rat. 3'-Hydroxynorcotinine and its O-glucuronide may be formed from NNN via alpha-oximinonornicotine or isomyosmine. There was no evidence that it was formed via norcotinine, although this pathway could not be excluded. 3'-Hydroxynorcotinine could potentially be a biomarker of NNN uptake in humans.

Human urinary carcinogen metabolites: biomarkers for investigating tobacco and cancer

Measurement of human urinary carcinogen metabolites is a practical approach for obtaining important information about tobacco and cancer. This review presents currently available methods and evaluates their utility. Carcinogens and their metabolites and related compounds that have been quantified in the urine of smokers or non-smokers exposed to environmental tobacco smoke (ETS) include trans,trans-muconic acid (tt-MA) and S-phenylmercapturic acid (metabolites of benzene), 1- and 2-naphthol, hydroxyphenanthrenes and phenanthrene dihydrodiols, 1-hydroxypyrene (1-HOP), metabolites of benzo[a]pyrene, aromatic amines and heterocyclic aromatic amines, N-nitrosoproline, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol and its glucuronides (NNAL and NNAL-Gluc), 8-oxodeoxyguanosine, thioethers, mercapturic acids, and alkyladenines. Nitrosamines and their metabolites have also been quantified in the urine of smokeless tobacco users. The utility of these assays to provide information about carcinogen dose, delineation of exposed vs. non-exposed individuals, and carcinogen metabolism in humans is discussed. NNAL and NNAL-Gluc are exceptionally useful biomarkers because they are derived from a carcinogen- 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)- that is specific to tobacco products. The NNAL assay has high sensitivity and specificity, which are particularly important for studies on ETS exposure. Other useful assays that have been widely applied involve quantitation of 1-HOP and tt-MA. Urinary carcinogen metabolite biomarkers will be critical components of future studies on tobacco and human cancer, particularly with respect to new tobacco products and strategies for harm reduction, the role of metabolic polymorphisms in cancer, and further evaluation of human carcinogen exposure from ETS.

Automated in-tube solid-phase microextraction coupled with HPLC for the determination of N-nitrosamines in cell cultures

An automated in-tube solid-phase microextraction (SPME) HPLC analysis method for 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and several metabolites has been developed. NNK is one of the tobacco-specific N-nitrosamines (TSNA), which has been linked to cancers associated with the use of or exposure to tobacco products. In-tube SPME is an on-line extraction technique in which analytes are extracted and concentrated from the sample directly into a coated capillary by repeated draw/eject steps. In this study, a tailor-made polypyrrole (PPY)-coated capillary and several commercially available capillaries (capillary GC columns) were used to evaluate their extraction efficiencies for NNK and several metabolites in cell cultures. Compared with commercial capillaries that were currently used for in-tube SPME, the PPY-coated capillary showed better extraction efficiency for all of the compounds studied. After optimization of the extraction conditions, NNK and five metabolite compounds were analyzed in spiked cell cultures, confirming the applicability of the developed method. Excellent linearity was observed for all compounds (av R2 = 0.9942) and detection limits that ranged from 20 to 250 ng/mL. The average within-day and between day variations (% RSD) were 2.9 and 3.6%, respectively. This automated extraction and analysis method simplified the determination of the TSNA, requiring a total sample analysis time of only approximately 30 min.