(S)-N'-Nitrosonornicotine, a constituent of smokeless tobacco, is a powerful oral cavity carcinogen in rats

Human cancer genomes harbor the mutational signature of tobacco-specific nitrosamines NNN and NNK

Tobacco usage is linked to multiple cancer types and accounts for a quarter of all cancer-related deaths. Tobacco smoke contains various carcinogenic compounds, including polycyclic aromatic hydrocarbons (PAH), though the mutagenic potential of many tobacco-related chemicals remains largely unexplored. In particular, the highly carcinogenic tobacco-specific nitrosamines NNN and NNK form pre-mutagenic pyridyloxobutyl (POB) DNA adducts. In the study presented here, we identified genome-scale POB-induced mutational signatures in cell lines and rat tumors, while also investigating their role in human cancer. These signatures are characterized by T>N and C>T mutations forming from specific POB adducts damaging dT and dC residues. Analysis of 2,780 cancer genomes uncovered POB signatures in ∼180 tumors; from cancer types distinct from the ones linked to smoking-related signatures SBS4 and SBS92. This suggests that, unlike PAH compounds, the POB pathway may contribute uniquely to the mutational landscapes of certain hematological malignancies and cancers of the kidney, breast, prostate and pancreas.

An update on the formation in tobacco, toxicity and carcinogenicity of N'-nitrosonornicotine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone

The tobacco-specific nitrosamines N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) are considered 'carcinogenic to humans' by the International Agency for Research on Cancer (IARC) and are believed to be important in the carcinogenic effects of both smokeless tobacco and combusted tobacco products. This short review focuses on the results of recent studies on the formation of NNN and NNK in tobacco, and their carcinogenicity and toxicity in laboratory animals. New mechanistic insights are presented regarding the role of dissimilatory nitrate reductases in certain microorganisms involved in the conversion of nitrate to nitrite that leads to the formation of NNN and NNK during curing and processing of tobacco. Carcinogenicity studies of the enantiomers of the major NNK metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and the enantiomers of NNN are reviewed. Recent toxicity studies of inhaled NNK and co-administration studies of NNK with formaldehyde, acetaldehyde, acrolein and CO2, all of which occur in high concentrations in cigarette smoke, are discussed.

Molecularly imprinted polymer sheathed mesoporous silica tube as SPME fiber coating for determination of tobacco-specific nitrosamines in water

Tobacco-specific nitrosamines (TSNAs) are probably carcinogenic disinfection byproducts eliciting health risk concerns. The determination and surveillance of TSNAs in water is still cumbersome due to the lack of advanced sample preparation methods. Herein, we prepared a solid phase microextraction (SPME) fiber coated with the molecularly imprinted polymer (MIP) sheathed mesoporous silica tube (MST) composite material, and developed a highly efficient, selective, and sensitive method for the determination of five TSNAs in water. Benefiting from the TSNAs-specific recognition of MIP and the increased specific surface area derived from MST, the MIP@MST fiber exhibited excellent extraction performance for TSNAs, which was much superior to the commercially available SPME fibers. By coupling to high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), the outstanding analytical merits such as low method detection limits (ranging 0.1-6.7 ng L-1) and good reproducibility (intra-fiber and inter-fiber relative standard deviations ranging 4.1 %-11.6 % and 3.5 %-12.2 %, respectively) were achieved with the consumption of 8 mL water sample and 100 μL methanol solvent in 50 min. The feasibility of the SPME-HPLC-MS/MS method was demonstrated in tap water and chloraminated source water, with relative recoveries for the five TSNAs ranging from 85.2 % to 108.5 %. In result, none of the TSNAs were found in the tap water samples, while 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-Butanol (NNAL) were detected in the chloraminated source water samples. The rapid and convenient SPME-HPLC-MS/MS method developed in this study offers a powerful tool for monitoring TSNAs in water.

From cultivation to cancer: formation of N-nitrosamines and other carcinogens in smokeless tobacco and their mutagenic implications

Tobacco use is a major cause of preventable morbidity and mortality globally. Tobacco products, including smokeless tobacco (ST), generally contain tobacco-specific N-nitrosamines (TSNAs), such as N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-butanone (NNK), which are potent carcinogens that cause mutations in critical genes in human DNA. This review covers the series of biochemical and chemical transformations, related to TSNAs, leading from tobacco cultivation to cancer initiation. A key aim of this review is to provide a greater understanding of TSNAs: their precursors, the microbial and chemical mechanisms that contribute to their formation in ST, their mutagenicity leading to cancer due to ST use, and potential means of lowering TSNA levels in tobacco products. TSNAs are not present in harvested tobacco but can form due to nitrosating agents reacting with tobacco alkaloids present in tobacco during certain types of curing. TSNAs can also form during or following ST production when certain microorganisms perform nitrate metabolism, with dissimilatory nitrate reductases converting nitrate to nitrite that is then released into tobacco and reacts chemically with tobacco alkaloids. When ST usage occurs, TSNAs are absorbed and metabolized to reactive compounds that form DNA adducts leading to mutations in critical target genes, including the RAS oncogenes and the p53 tumor suppressor gene. DNA repair mechanisms remove most adducts induced by carcinogens, thus preventing many but not all mutations. Lastly, because TSNAs and other agents cause cancer, previously documented strategies for lowering their levels in ST products are discussed, including using tobacco with lower nornicotine levels, pasteurization and other means of eliminating microorganisms, omitting fermentation and fire-curing, refrigerating ST products, and including nitrite scavenging chemicals as ST ingredients.

Mass Spectrometry-Based Metabolic Profiling of Urinary Metabolites of N'-Nitrosonornicotine (NNN) in the Rat

The tobacco-specific nitrosamine N'-nitrosonornicotine (NNN) and its close analogue 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK) are classified as "carcinogenic to humans" (Group 1) by the International Agency for Research on Cancer. The currently used biomarker to monitor NNN exposure is urinary total NNN (free NNN plus its N-glucuronide). However, total NNN does not provide information about the extent of metabolic activation of NNN as related to its carcinogenicity. Targeted analysis of the major metabolites of NNN in laboratory animals recently led to the identification of N'-nitrosonornicotine-1N-oxide (NNN-N-oxide), a unique metabolite detected in human urine that is specifically formed from NNN. To further investigate NNN urinary metabolites that hold promise as new biomarkers for monitoring NNN exposure, uptake, and/or metabolic activation, we conducted a comprehensive profiling of NNN metabolites in the urine of F344 rats treated with NNN or [pyridine-d4]NNN. Using our optimized high-resolution mass spectrometry (HRMS)-based isotope-labeling method, 46 putative metabolites were identified with robust MS evidence. Out of the 46 candidates, all known major NNN metabolites were identified and structurally confirmed by comparing them to their isotopically labeled standards. More importantly, putative metabolites considered to be exclusively formed from NNN were also identified. The two new representative metabolites─4-(methylthio)-4-(pyridin-3-yl)butanoic acid (23, MPBA) and N-acetyl-S-(5-(pyridin-3-yl)-1H-pyrrol-2-yl)-l-cysteine (24, Py-Pyrrole-Cys-NHAc) ─were identified by comparing them to synthetic standards that were fully characterized by nuclear magnetic resonance and HRMS. They are hypothesized to be formed by NNN α-hydroxylation pathways and thus represent the first potential biomarkers to specifically monitor the uptake plus metabolic activation of NNN in tobacco users.

Quantitative measurement of harmful and potentially harmful constituents, pH, and moisture content in 16 commercial smokeless tobacco products

Smokeless tobacco products expose adult and youth tobacco users to various addictive and carcinogenic constituents that can cause long-term nicotine dependence and oral cancers. In this study, nicotine, benzo[a]pyrene (B[a]P), N'-nitrosonornicotine (NNN), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), acetaldehyde, crotonaldehyde, formaldehyde, moisture, and pH levels in 16 smokeless tobacco products were measured on a wet-weight basis (wwb). In addition, change in analytical variability with increasing replicate measurements was assessed. Total nicotine in the products varied from 6.2 to 35.5 mg/g. The percentage of total nicotine in the unprotonated form ranged from 0.1 to 62%; whereas, product moisture varied from 7.4 to 57%. The quantities of harmful and potentially harmful constituents (HPHCs) range from 0.46 to 179.9 ng/g for B [a]P, 270-12206 and 81-20716 ng/g for NNN and NNK, respectively, and 0.33-6.85 and 0.13-5.67 μg/g for acetaldehyde and formaldehyde, respectively. This study shows wide variation in smokeless tobacco product HPHC quantities. The results also show that analytical variability stabilizes after seven replicate measurements.

Toxicity of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in early development: A wide-scope metabolomics assay in zebrafish embryos

The tobacco-specific nitrosamine 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a carcinogenic and ubiquitous environmental pollutant for which toxic activity has been thoroughly investigated in murine models and human tissues. However, its potential deleterious effects on vertebrate early development are yet poorly understood. In this work, we characterized the impact of NNK exposure during early developmental stages of zebrafish embryos, a known alternative model for mammalian toxicity studies. Embryos exposed to different NNK concentrations were monitored for lethality and for the appearance of malformations during the first five days after fertilization. LC-MS based untargeted metabolomics was subsequently performed for a wide-scope assay of NNK-related metabolic alterations. Our results revealed the presence of not only the parental compound, but also of two known NNK metabolites, 4-Hydroxy-4-(3-pyridyl)-butyric acid (HPBA) and 4-(Methylnitrosamino)-1-(3-pyridyl-N-oxide)-1-butanol (NNAL-N-oxide) in exposed embryos likely resulting from active CYP450-mediated α-hydroxylation and NNK detoxification pathways, respectively. This was paralleled by a disruption in purine and pyrimidine metabolisms and the activation of the base excision repair pathway. Our results confirm NNK as a harmful embryonic agent and demonstrate zebrafish embryos to be a suitable early development model to monitor NNK toxicity.

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.

Assessment of the Exposure to Tobacco-Specific Nitrosamines and Minor Tobacco Alkaloids in Users of Various Tobacco/Nicotine Products

Tobacco-specific nitrosamines (TSNAs), in particular, the human carcinogens 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN), are important toxicants in tobacco and also (as contaminants) in nicotine products. In a clinical study comprising a period of 74 h under confinement, we investigated the exposure to NNK, NNN, N'-nitrosoanabasine (NAB), and N'-nitrosoanatabine (NAT) as well as to the minor tobacco alkaloids anabasine (AB) and anatabine (AT) by measuring suitable biomarkers in habitual users of combustible cigarettes (CCs), electronic cigarettes (ECs), heated tobacco products (HTPs), oral tobacco (OT), and nicotine replacement therapy products (NRTs). Non-users (NU) of any tobacco/nicotine products served as the (negative) control group. Smokers exhibited the highest levels for all biomarkers measured, except for AB in urine, which was found to be highest in OT users. Somewhat elevated levels compared to NU, EC, and NRT groups were also observed in the users of HTPs. In the users of tobacco-containing products (CC, HTP, and OT), most frequently the biomarkers significantly correlated with the dose markers such as daily consumption, urinary nicotine equivalents (Nequ), and plasma cotinine (CotP). In conclusion, except for smokers (CC) and OT users, exposure of users of ECs, HTPs, and NRTs to TSNAs as well as the minor tobacco alkaloids AB and AT is marginal and statistically not distinguishable from that of NU. Finally, our results for NNN in the saliva provide preliminary evidence for the formation of NNN from the precursor nornicotine in the presence of thiocyanate as a catalyst. The latter hypothesis requires experimental verification.

Smokeless tobacco and cigarette smoking: chemical mechanisms and cancer prevention

Tobacco products present a deadly combination of nicotine addiction and carcinogen exposure resulting in millions of cancer deaths per year worldwide. A plethora of smokeless tobacco products lead to unacceptable exposure to multiple carcinogens, including the tobacco-specific nitrosamine N'-nitrosonornicotine, a likely cause of the commonly occurring oral cavity cancers observed particularly in South-East Asian countries. Cigarettes continue to deliver a large number of carcinogens, including tobacco-specific nitrosamines, polycyclic aromatic hydrocarbons and volatile organic compounds. The multiple carcinogens in cigarette smoke are responsible for the complex mutations observed in critical cancer genes. The exposure of smokeless tobacco users and smokers to carcinogens and toxicants can now be monitored by urinary and DNA adduct biomarkers that may be able to identify those individuals at highest risk of cancer so that effective cancer prevention interventions can be initiated. Regulation of the levels of carcinogens, toxicants and nicotine in tobacco products and evidence-based tobacco control efforts are now recognized as established pathways to preventing tobacco related cancer.

Separation of N'-nitrosonornicotine isomers and enantiomers by supercritical fluid chromatography tandem mass spectrometry

N'-nitrosonornicotine (NNN) is one of the most prevalent and toxic tobacco-specific nitrosoamines. A chiral center at its 2'-position results in R and S enantiomers, the partial double bond character of the NN = O group also results in E and Z isomers, therefore, NNN can form a total of four absolute configurations (E-(R)-NNN, E-(S)-NNN, Z-(R)-NNN, and Z-(S)-NNN). This study investigated the resolution of R/S enantiomers and E/Z isomers of NNN by supercritical fluid chromatography tandem mass spectrometry (SFC-MS/MS). The baseline separation of E/Z-(R,S)-NNN isomers/enantiomers was accomplished through the optimization of chiral columns and co-solvents. Due to the lack of single standard of E/Z isomers, only R-NNN (sum of E-(R)-NNN and Z-(R)-NNN) and S-NNN (sum of E-(S)-NNN and Z-(S)-NNN) were further examined. Through the comprehensive optimization of SFC-MS/MS conditions, R-NNN and S-NNN were separated with a run time of 5 min, the developed method was validated, and its applicability to the determination of NNN enantiomers in burley tobacco samples was demonstrated. This study could be applied to preparative separation of single enantiomer and/or isomer of NNN, and could provide potential benefits to biologic activity studies on these enantiomers and isomers.

Investigation of 2'-Deoxyadenosine-Derived Adducts Specifically Formed in Rat Liver and Lung DNA by N'-Nitrosonornicotine Metabolism

The International Agency for Research on Cancer has classified the tobacco-specific nitrosamines N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) as "carcinogenic to humans" (Group 1). To exert its carcinogenicity, NNN requires metabolic activation to form reactive intermediates which alkylate DNA. Previous studies have identified cytochrome P450-catalyzed 2'-hydroxylation and 5'-hydroxylation of NNN as major metabolic pathways, with preferential activation through the 5'-hydroxylation pathway in some cultured human tissues and patas monkeys. So far, the only DNA adducts identified from NNN 5'-hydroxylation in rat tissues are 2-[2-(3-pyridyl)-N-pyrrolidinyl]-2'-deoxyinosine (Py-Py-dI), 6-[2-(3-pyridyl)-N-pyrrolidinyl]-2'-deoxynebularine (Py-Py-dN), and N⁶-[4-hydroxy-1-(pyridine-3-yl)butyl]-2'-deoxyadenosine (N⁶-HPB-dAdo) after reduction. To expand the DNA adduct panel formed by NNN 5'-hydroxylation and identify possible activation biomarkers of NNN metabolism, we investigated the formation of dAdo-derived adducts using a new highly sensitive and specific liquid chromatography-nanoelectrospray ionization-high-resolution tandem mass spectrometry method. Two types of NNN-specific dAdo-derived adducts, N⁶-[5-(3-pyridyl)tetrahydrofuran-2-yl]-2'-deoxyadenosine (N⁶-Py-THF-dAdo) and 6-[2-(3-pyridyl)-N-pyrrolidinyl-5-hydroxy]-2'-deoxynebularine (Py-Py(OH)-dN), were observed for the first time in calf thymus DNA incubated with 5'-acetoxyNNN. More importantly, Py-Py(OH)-dN was also observed in relatively high abundance in the liver and lung DNA of rats treated with racemic NNN in the drinking water for 3 weeks. These new adducts were characterized using authentic synthesized standards. Both NMR and MS data agreed well with the proposed structures of N⁶-Py-THF-dAdo and Py-Py(OH)-dN. Reduction of Py-Py(OH)-dN by NaBH₃CN led to the formation of Py-Py-dN both in vitro and in vivo, which was confirmed by its isotopically labeled internal standard [pyridine-d₄]Py-Py-dN. The NNN-specific dAdo adducts Py-THF-dAdo and Py-Py(OH)-dN formed by NNN 5'-hydroxylation provide a more comprehensive understanding of the mechanism of DNA adduct formation by NNN.

Mass Spectrometric Quantitation of Apurinic/Apyrimidinic Sites in Tissue DNA of Rats Exposed to Tobacco-Specific Nitrosamines and in Lung and Leukocyte DNA of Cigarette Smokers and Nonsmokers

Metabolic activation of the carcinogenic tobacco-specific nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) results in formation of reactive electrophiles that modify DNA to produce a variety of products including methyl, 4-(3-pyridyl)-4-oxobutyl (POB)-, and 4-(3-pyridyl)-4-hydroxybutyl adducts. Among these are adducts such as 7-POB-deoxyguanosine (N7POBdG) which can lead to apurinic/apyrimidinic (AP) sites by facile hydrolysis of the base-deoxyribonucleoside bond. In this study, we used a recently developed highly sensitive mass spectrometric method to quantitate AP sites by derivatization with O-(pyridin-3-yl-methyl)hydroxylamine (PMOA) (detection limit, 2 AP sites per 108 nucleotides). AP sites were quantified in DNA isolated from tissues of rats treated with NNN and NNK and from human lung tissue and leukocytes of cigarette smokers and nonsmokers. Rats treated with 5 or 21 mg/kg bw NNK for 4 days by s.c. injection had 2-6 and 2-17 times more AP sites than controls in liver and lung DNA (p < 0.05). Increases in AP sites were also found in liver DNA of rats exposed for 10 and 30 weeks (p < 0.05) but not for 50 and 70 weeks to 5 ppm of NNK in their drinking water. Levels of N7POBG were significantly correlated with AP sites in rats treated with NNK. In rats treated with 14 ppm (S)-NNN in their drinking water for 10 weeks, increased AP site formation compared to controls was observed in oral and nasal respiratory mucosa DNA (p < 0.05). No significant increase in AP sites was found in human lung and leukocyte DNA of cigarette smokers compared to nonsmokers, although AP sites in leukocyte DNA were significantly correlated with urinary levels of the NNK metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL). This is the first study to use mass spectrometry based methods to examine AP site formation by carcinogenic tobacco-specific nitrosamines in laboratory animals and to evaluate AP sites in DNA of smokers and nonsmokers.

Quantitative Liquid Chromatography-Nanoelectrospray Ionization-High-Resolution Tandem Mass Spectrometry Analysis of Acrolein-DNA Adducts and Etheno-DNA Adducts in Oral Cells from Cigarette Smokers and Nonsmokers

Cigarette smoking is an important source of human exposure to toxicants and carcinogens and contributes significantly to cancer morbidity and mortality worldwide. Acrolein, a widespread environmental pollutant, is present in relatively high amounts in cigarette smoke and can react directly with DNA to form DNA adducts, which serve as important biomarkers for the assessment of exposure to acrolein and its potential role in smoking related cancer. Etheno-DNA adducts are promutagenic DNA lesions that can derive from exogenous chemicals as well as endogenous sources, including lipid peroxidation. In this study, we developed a combined method for the quantitation of (6R/S)-3-(2'-deoxyribos-1'-yl)-5,6,7,8,-tetrahydro-6-hydroxypyrimido[1,2-a]purine-10(3H)-one (α-OH-Acr-dGuo), (8R/S)-3-(2'-deoxyribos-1'-yl)-5,6,7,8,-tetrahydro-8-hydroxypyrimido[1,2-a]purine-10(3H)-one (γ-OH-Acr-dGuo), 1,N6-etheno-dAdo (εdAdo), and 3,N4-etheno-dCyd (εdCyd) adducts in oral rinse and cytobrush DNA from smokers and nonsmokers by liquid chromatography-nanoelelctrospray ionization-high-resolution tandem mass spectrometry (LC-NSI-HRMS/MS). For oral rinse samples, there was a statistically significant difference between the levels of α-OH-Acr-dGuo, γ-OH-Acr-dGuo, εdAdo, and εdCyd in smokers (12.1 ± 17.9, 163 ± 227, 182 ± 568, and 194 ± 400 adducts/109 nucleotides, respectively) and nonsmokers (1.85 ± 2.08, 5.95 ± 4.23, 7.69 ± 11.7, and 6.07 ± 10.9 adducts/109 nucleotides, respectively). For cytobrush samples, there was a statistically significant difference between the levels of γ-OH-Acr-dGuo and εdAdo in smokers (259 ± 540 and 82.9 ± 271 adducts/109 nucleotides, respectively) and nonsmokers (7.37 ± 5.09 and 16.2 ± 30.2 adducts/109 nucleotides, respectively) but not for α-OH-Acr-dGuo and εdCyd. Our results demonstrate that oral mucosa cells are an excellent source of material for evaluating DNA adducts to be used as biomarkers of tobacco smoke exposure and molecular changes potentially related to cancer.

Comparison of tobacco-specific nitrosamine levels in smokeless tobacco products: High levels in products from Bangladesh

Bangladesh exhibits the second highest rate of smokeless tobacco (SLT) product usage in the world, and this has been associated with the high upper aerodigestive tract cancer incidence in this country. The goal of the present study was to examine the levels of the highly carcinogenic tobacco-specific nitrosamines (TSNAs) in Bangladeshi SLT products and compare these levels to that observed in SLT brands from southeast Asia and the USA. The levels of TSNAs and nicotine were determined by LC-MS/MS in twenty-eight SLT brands and several tobacco additives from Bangladesh, as well as several SLT brands from India, Pakistan and the USA. The levels of N-nitrosonornicotine (NNN), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), N-nitrosoanatabine (NAT) and N-nitrosoanabasine (NAB) in Bangladeshi SLT brands ranged from 1.1-59, 0.15-34, 0.79-45, and 0.037-13 μg/g SLT powder, respectively. The mean levels of the highly carcinogenic TSNAs (NNN+NNK) were 7.4-, 2.4-, and 63-fold higher in Bangladeshi SLT products as compared to SLT brands from the USA, India and Pakistan, respectively; these trends were also observed for NAT and NAB. Similar mean levels of nicotine were observed in the Bangladeshi brands (31 mg/g powder) versus brands from the USA (25 mg/g powder) and India (20 mg/g powder); they were 3-fold higher than brands from Pakistan (10 mg/g powder). Gul SLT brands exhibited the highest pH and the highest levels of unprotonated nicotine. The high levels of TSNAs in Bangladeshi SLT brands may be an important factor contributing to the high rates of upper aerodigestive tract cancer in Bangladesh.

Use of Electronic Cigarettes in Smoke-Free Spaces by Smokers: Results from the 2014-2015 Population Assessment on Tobacco and Health Study

Background: Smoke-free air policies exist to protect users and nonusers from exposure to tobacco smoke. Although electronic nicotine delivery systems (ENDS) may expose passerby to nicotine and particulate matter, few US states regulate indoor use of ENDS. The purpose of this study was to investigate reported rationales for ENDS use and reported ENDS use in public smoke-free places by dual cigarette/ENDS users. Methods: A population of ENDS/cigarette co-users (n = 2051) was drawn from Wave 2 of the Population Assessment of Tobacco and Health (PATH) dataset (2014–2015). Harm reduction beliefs and cessation behavior of co-users were investigated as predictors of ENDS use in public smoke-free places using logistic regression. Results: Fifty-eight percent of dual users reported past 30-day ENDS use in public smoke-free places. Reported use of ENDS to cut down on cigarette smoking (OR: 2.38, 95% CI: 1.86, 3.05), as an alternative to quitting tobacco (OR: 1.71, 95% CI: 1.37, 2.13), or because of belief that ENDS help people to quit cigarettes (OR: 1.52, 95% CI: 1.20, 1.92) were significantly associated with increased odds of ENDS use in smoke-free places. Conclusions: Beliefs that ENDS were useful as cessation tools or posed modified risk to users and nonusers were associated with elevated odds of use ENDS in locations where conventional tobacco is prohibited. Due to limitations in the survey instrument, in-home ENDS use could not be directly assessed in this analysis. However, these self-reported findings suggest that use of ENDS in public places where cigarette use is prohibited is prevalent enough to be of concern for future regulation and enforcement efforts.

Oral Health Effects of Combusted and Smokeless Tobacco Products

The oral cavity is usually the first part of a consumer's body exposed to the constituents of tobacco products or their emissions. Consequently, the oral cavity is a frequent site for carcinogenic, microbial, immunologic, and clinical effects of tobacco use. This article summarizes 5 presentations on various aspects of oral health affected by combusted or noncombusted tobacco products from a recent conference, "Oral Health Effects of Tobacco Products: Science and Regulatory Policy," sponsored by the American Association for Dental Research and the Food and Drug Administration.

Effects of the Tobacco Carcinogens N'-Nitrosonornicotine and Dibenzo[a,l]pyrene Individually and in Combination on DNA Damage in Human Oral Leukoplakia and on Mutagenicity and Mutation Profiles in lacI Mouse Tongue

In previous studies, we showed that the topical application of dibenzo[a,l]pyrene (DB[a,l]P), also known as dibenzo[def,p]chrysene, to the oral cavity of mice induced oral squamous cell carcinoma. We also showed that dA and dG adducts likely account for most of the mutagenic activity of DB[a,l]P in the oral tissues in vivo. Here we report for the first time that the oral treatment of lacI mice with a combination of tobacco smoke carcinogens, DB[a,l]P and N'-nitrosonornicotine (NNN), induces a higher fraction of mutations than expected from a simple sum of their induced individual mutation fractions, and a change in the mutational profile compared with that expected from the sum of the individual agents. The mutational profile of the combination of agents resembled that of the P53 gene in human head and neck cancers more than that of either of the individual agents, in that the percentage of the major class of mutations (GC > AT transitions) is similar to that seen in the P53 gene. A preliminary study was performed to understand the origin of the unexpected mutagenesis observations by measuring specific DNA adducts produced by both NNN and DB[a,l]P in human oral leukoplakia cells. No significant differences in the expected and observed major adduct levels from either agent were observed between individual or combined treatments, suggesting that additional adducts are important in mutagenesis induced by the mixture. Taken together, the above observations support the use of this animal model not only to investigate tobacco smoke-induced oral cancer but also to study chemoprevention.

Determination of tobacco alkaloid enantiomers using reversed phase UPLC/MS/MS

Nʹ-Nitrosonornicotine (NNN), a carcinogenic tobacco-specific Nʹ-nitrosamine (TSNA), is on the FDA list of harmful and potentially harmful constituents (HPHCs). Nornicotine, a product of the demethylation of nicotine, is the immediate alkaloid precursor for NNN formation. Nicotine, nornicotine and NNN are optically active. The accumulation of the isomers of nicotine, nornicotine, and NNN impacts their biological activity. In this paper, we report the determination of tobacco alkaloid enantiomers (including nicotine, nornicotine, anabasine, and anatabine) in samples of different tobacco lines using a reversed phase ultra-performance liquid chromatography-tandem mass spectrometer (UPLC/MS/MS) method. Current method demonstates excellent detection capability for all alkaloid enantiomers, with correlation coefficients (r²) > 0.996 within their linear dynamic ranges. The limit of detection (LOD) and limit of quantitation (LOQ) of all analytes are less than 10 ng/mL and 30 ng/mL, respectively. In addition, their recovery and coefficient of variation (CV%) are within 100–115% and 0.2–3.7%, respectively. The method validated in this paper is simple, fast, and sensitive for the quantification of alkaloid enantiomers in tobacco leaf and has been applied to investigations of tobacco alkaloid enantiomer ratios in different tobacco lines and tobacco products.

Mass Spectrometric Quantitation of Pyridyloxobutyl DNA Phosphate Adducts in Rats Chronically Treated with N'-Nitrosonornicotine

The tobacco-specific carcinogens N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) require metabolic activation to exert their carcinogenicity. NNN and NNK are metabolized to the same reactive diazonium ions, which alkylate DNA forming pyridyloxobutyl (POB) DNA base and phosphate adducts. We have characterized the formation of both POB DNA base and phosphate adducts in NNK-treated rats and the formation of POB DNA base adducts in NNN-treated rats. However, POB DNA phosphate adducts in NNN-treated rats are still uncharacterized. In this study, we quantified the levels of POB DNA phosphate adducts in tissues of rats chronically treated with ( S)-NNN or ( R)-NNN for 10, 30, 50, and 70 weeks during a carcinogenicity study. The highest amounts of POB DNA phosphate adducts were observed in the esophagus of the ( S)-NNN-treated rats, with a maximum level of 5400 ± 317 fmol/mg DNA at 50 weeks. The abundance of POB DNA phosphate adducts in the esophagus was consistent with the results of the carcinogenicity study showing that the esophagus was the primary site of tumor formation from treatment with ( S)-NNN. Compared to the ( R)-NNN group, the levels of POB DNA phosphate adducts were higher in the oral mucosa, esophagus, and liver, while lower in the nasal mucosa of the ( S)-NNN-treated rats. Among 10 combinations of all isomers of POB DNA phosphate adducts, Ap(POB)C and combinations with thymidine predominated across all the rat tissues examined. In the primary target tissue, esophageal mucosa, Ap(POB)C accounted for ∼20% of total phosphate adducts in the ( S)-NNN treatment group throughout the 70 weeks, with levels ranging from 780 ± 194 to 1010 ± 700 fmol/mg DNA. The results of this study showed that POB DNA phosphate adducts were present in high levels and persisted in target tissues of rats chronically treated with ( S)- or ( R)-NNN. These results improve our understanding of DNA damage during NNN-induced carcinogenesis. The predominant POB DNA phosphate isomers observed, such as Ap(POB)C, may serve as biomarkers for monitoring chronic exposure of tobacco-specific nitrosamines in humans.

Metabolic Activation and Carcinogenesis of Tobacco-Specific Nitrosamine N'-Nitrosonornicotine (NNN): A Density Function Theory and Molecular Docking Study

N'-nitrosonornicotine (NNN) is one of the tobacco-specific nitrosamines (TSNAs) that exists widely in smoke and smokeless tobacco products. NNN can induce tumors in various laboratory animal models and has been identified by International Agency for Research on Cancer (IARC) as a human carcinogen. Metabolic activation of NNN is primarily initiated by cytochrome P450 enzymes (CYP450s) via 2'-hydroxylation or 5'-hydroxylation. Subsequently, the hydroxylating intermediates undergo spontaneous decomposition to generate diazohydroxides, which can be further converted to alkyldiazonium ions, followed by attacking DNA to form various DNA damages, such as pyridyloxobutyl (POB)-DNA adducts and pyridyl-N-pyrrolidinyl (py-py)-DNA adducts. If not repaired correctly, these lesions would lead to tumor formation. In the present study, we performed density functional theory (DFT) computations and molecular docking studies to understand the mechanism of metabolic activation and carcinogenesis of NNN. DFT calculations were performed to explore the 2'- or 5'- hydroxylation reaction of (R)-NNN and (S)-NNN. The results indicated that NNN catalyzed by the ferric porphyrin (Compound I, Cpd I) at the active center of CYP450 included two steps, hydrogen abstraction and rebound reactions. The free energy barriers of the 2'- and 5'-hydroxylation of NNN are 9.82/8.44 kcal/mol (R/S) and 7.99/9.19 kcal/mol (R/S), respectively, suggesting that the 2'-(S) and 5'-(R) pathways have a slight advantage. The free energy barriers of the decomposition occurred at the 2'-position and 5'-position of NNN are 18.04/18.02 kcal/mol (R/S) and 18.33/19.53 kcal/mol (R/S), respectively. Moreover, we calculated the alkylation reactions occurred at ten DNA base sites induced by the 2'-hydroxylation product of NNN, generating the free energy barriers ranging from 0.86 to 4.72 kcal/mol, which indicated that these reactions occurred easily. The docking study showed that (S)-NNN had better affinity with CYP450s than that of (R)-NNN, which was consistent with the experimental results. Overall, the combined results of the DFT calculations and the docking obtained in this study provide an insight into the understanding of the carcinogenesis of NNN and other TSNAs.

Electronic nicotine delivery systems: Oral health implications and oral cancer risk

There is a paucity of evidence surrounding the potential detrimental effects of electronic nicotine delivery systems (ENDS) for both systemic and oral health. The effects of conventional cigarettes on the development of oral cancer are well known; however, the role of ENDS in oral carcinogenesis is yet to be elucidated. Furthermore, the exponential rise of the use of ENDS by the general public means that dental healthcare providers are more likely to encounter questions on their safety in the oral cavity, and on their effectiveness as a smoking cessation aid. Herein, we review the most up to date literature on the systemic and oral health complications of ENDS. Moreover, evidence-based recommendations on the use of ENDS as a smoking cessation tool within the dental setting are discussed.

Tobacco carcinogen research to aid understanding of cancer risk and influence policy

Education regarding the health effects associated with tobacco use has made important progress worldwide over the last few decades. Still, tobacco remains a significant cause of cancer and other diseases. As a result, significant worldwide morbidity and mortality is still attributable to tobacco use in modern times. Research into tobacco products, the carcinogens they contain, and how users metabolize them is an important benefit to the advancement of research aimed at reducing harm associated with tobacco use. This review summarizes the use of this type of research to study tobacco users’ risk of developing cancer, especially head and neck cancer. In addition, we discuss the use of tobacco research to provide support for increasing levels of federal regulation of tobacco products.

Level of Evidence

4.

Presence of the Carcinogen N'-Nitrosonornicotine in Saliva of E-cigarette Users

Many harmful constituents are present in e-cigarettes at much lower levels than in cigarette smoke, and the results of analysis of urinary biomarkers in e-cigarette users are consistent with these findings. However, understanding the health effects of chronic exposures to e-cigarette aerosols may require thinking beyond these comparisons. In this study, we investigated the endogenous formation of the tobacco-specific oral and esophageal carcinogen N'-nitrosonornicotine (NNN) in e-cigarette users. Salivary NNN, nornicotine, and nicotine as well as urinary tobacco biomarkers, including total NNN, were analyzed in 20 e-cigarette users, 20 smokers, and 19 nonsmokers. Nornicotine and NNN levels in e-cigarettes used by the study participants were also analyzed. The mean of NNN in saliva of e-cigarette users was 14.6 (±23.1) pg/mL, ranging from nonquantifiable (below the limit of quantitation, LOQ) to 76.0 pg/mL. In smokers, salivary NNN ranged from below LOQ to 739 pg/mL, with 80% of smokers having salivary NNN in the range of levels found in e-cigarette users. Consistent with a previous report, very low levels of urinary total NNN were present in only 5 out of 20 e-cigarette users (ranging from 0.001 to 0.01 pmol/mL urine). Only trace levels of NNN were found in e-cigarette liquids. Together, our findings demonstrate that NNN is formed endogenously in e-cigarette users. While the overall exposure to NNN in e-cigarette users is dramatically lower than in smokers, the known carcinogenic potency of NNN warrants further investigations into the potential consequences of its endogenous formation. Salivary NNN, rather than urinary total NNN, which accounts for only 1-3% of the NNN dose, should be used to monitor e-cigarette users' exposure to this carcinogen.

A comprehensive methodology for the chiral separation of 40 tobacco alkaloids and their carcinogenic E/Z-(R,S)-tobacco-specific nitrosamine metabolites

The predominant enantiomer of nicotine found in nature is (S)-nicotine and its pharmacology has been widely established. However, pharmacologic information concerning individual enantiomers of nicotine-related compounds is limited. Recently, a modified macrocyclic glycopeptide chiral selector was found to be highly stereoselective for most tobacco alkaloids and metabolites. This study examines the semi-synthetic and native known macrocyclic glycopeptides for chiral recognition, separation, and characterization of the largest group of nicotine-related compounds ever reported (tobacco alkaloids, nicotine metabolites and derivatives, and tobacco-specific nitrosamines). The enantioseparation of nicotine is accomplished in less than 20s for example. All liquid chromatography separations are mass spectrometry compatible for the tobacco alkaloids, as well as their metabolites. Ring-closed, cyclized structures were identified and separated from their ring-open, straight chain equilibrium structures. Also, E/Z-tobacco-specific nitrosamines and their enantiomers were directly separated. E/Z isomers also are known to have different physical and chemical properties and biological activities. This study provides optimal separation conditions for the analysis of nicotine-related isomers, which in the past have been reported to be ineffectively separated which can result in inaccurate results. The methodology of this study could be applied to cancer studies, and lead to more information about the role of these isomers in other diseases and as treatment for diseases.

Tobacco-related carcinogenesis in head and neck cancer

Head and neck cancer (head and neck squamous cell carcinoma (HNSCC)) is a devastating disease. Patients require intensive treatment that is often disfiguring and debilitating. Those who survive are often left with poor speech articulation, difficulties in chewing and swallowing, and cosmetic disfigurement, as well as loss of taste. Furthermore, given that HNSCC survivors are frequently disabled and unable to return to work, the economic and societal costs associated with HNSCC are massive. HNSCC is one of many cancers that are strongly associated with tobacco use. The risk for HNSCC in smokers is approximately ten times higher than that of never smokers, and 70-80% of new HNSCC diagnoses are associated with tobacco and alcohol use. Tobacco products have been used for centuries; however, it is just within the last 60-70 years that we have developed an understanding of their damaging effects. This relatively recent understanding has created a pathway towards educational and regulatory efforts aimed at reducing tobacco use. Understanding the carcinogenic components of tobacco products and how they lead to HNSCC is critical to regulatory and harm reduction measures. To date, nitrosamines and other carcinogenic agents present in tobacco products have been associated with cancer development. The disruption of DNA structure through DNA adduct formation is felt to be a common mutagenic pathway of many carcinogens. Intense work pertaining to tobacco product constituents, tobacco use, and tobacco regulation has resulted in decreased use in some parts of the world. Still, much work remains as tobacco continues to impart significant harm and contribute to HNSCC development worldwide.

High Level of Tobacco Carcinogen-Derived DNA Damage in Oral Cells Is an Independent Predictor of Oral/Head and Neck Cancer Risk in Smokers

Exposure to tobacco-specific nitrosamines (TSNA) and polycyclic aromatic hydrocarbons (PAH) is recognized to play an important role in the development of oral/head and neck squamous cell cancer (HNSCC). We recently reported higher levels of TSNA-associated DNA adducts in the oral cells of smokers with HNSCC as compared with cancer-free smokers. In this study, we further investigated the tobacco constituent exposures in the same smokers to better understand the potential causes for the elevated oral DNA damage in smokers with HNSCC. Subjects included cigarette smokers with HNSCC (cases, n = 30) and cancer-free smokers (controls, n = 35). At recruitment, tobacco/alcohol use questionnaires were completed, and urine and oral cell samples were obtained. Analysis of urinary 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and N'-Nitrosonornicotine (NNN; TSNA biomarkers), 1-hydroxypyrene (1-HOP, a PAH), cotinine, 3'-hydroxycotinine, and the nicotine metabolite ratio (NMR) were performed. Cases and controls differed in mean age, male preponderance, and frequency of alcohol consumption (but not total alcoholic drinks). Univariate analysis revealed similar levels of NNN, 1-HOP, and cotinine between groups but, as reported previously, significantly higher DNA adduct formation in the cases. Multiple regression adjusting for potential confounders showed persistent significant difference in DNA adduct levels between cases and controls [ratio of geometric means, 20.0; 95% CI, 2.7-148.6). Our cohort of smokers with HNSCC demonstrates higher levels of TSNA-derived oral DNA damage in the setting of similar exposure to nicotine and tobacco carcinogens. Among smokers, DNA adduct formation may act as a predictor of eventual development of HNSCC that is independent of carcinogen exposure indicators. Cancer Prev Res; 10(9); 507-13. ©2017 AACRSee related editorial by Johnson and Bauman, p. 489.

Use of rodent data for cancer risk assessment of smokeless tobacco in the regulatory context

To support risk management decisions, information from different fields has been integrated in this presentation to provide a realistic quantitative cancer risk assessment of smokeless tobacco. Smoking among Swedish men is currently below 10%, while about 20% use a special smokeless tobacco (snus) as a substitute for cigarettes. Epidemiological data and molecular biomarkers demonstrate that rodent bioassays with tobacco specific nitrosamines (TSNA) overestimate cancer risk from snus by more than one order of magnitude. The underlying reasons are discussed. DNA damage constitutes a necessary, although not sufficient prerequisite for cancer initiation. Individuals who have not used tobacco exhibit DNA lesions identical with those induced by TSNA. No increase above this adduct background can be shown from snus, and extensive epidemiological studies in Sweden have failed to demonstrate elevated cancer risks even in long term users. A "bench mark" for acceptable risk of 1/10(6) derived from rodent data has been suggested when regulating snus. By relating similarly derived estimates for some food contaminants, the implementation even of a limit of 1/10(4) may be unrealistic. The management of smokeless tobacco products has rarely been based on a scientifically sound risk assessment, where attention is given to the outstandingly higher hazards associated with smoking.

Plausible Roles for RAGE in Conditions Exacerbated by Direct and Indirect (Secondhand) Smoke Exposure

Approximately 1 billion people smoke worldwide, and the burden placed on society by primary and secondhand smokers is expected to increase. Smoking is the leading risk factor for myriad health complications stemming from diverse pathogenic programs. First- and second-hand cigarette smoke contains thousands of constituents, including several carcinogens and cytotoxic chemicals that orchestrate chronic inflammatory responses and destructive remodeling events. In the current review, we outline details related to compromised pulmonary and systemic conditions related to smoke exposure. Specifically, data are discussed relative to impaired lung physiology, cancer mechanisms, maternal-fetal complications, cardiometabolic, and joint disorders in the context of smoke exposure exacerbations. As a general unifying mechanism, the receptor for advanced glycation end-products (RAGE) and its signaling axis is increasingly considered central to smoke-related pathogenesis. RAGE is a multi-ligand cell surface receptor whose expression increases following cigarette smoke exposure. RAGE signaling participates in the underpinning of inflammatory mechanisms mediated by requisite cytokines, chemokines, and remodeling enzymes. Understanding the biological contributions of RAGE during cigarette smoke-induced inflammation may provide critically important insight into the pathology of lung disease and systemic complications that combine during the demise of those exposed.

Analysis of N'-nitrosonornicotine enantiomers in human urine by chiral stationary phase liquid chromatography-nanoelectrospray ionization-high resolution tandem mass spectrometry

We have developed a chiral stationary phase liquid chromatography-nanoelectrospray ionization-high resolution tandem mass spectrometry (LC-NSI-HRMS/MS) method to investigate the enantiomeric composition of low parts per trillion amounts of the carcinogen N'-nitrosonornicotine (NNN) in the urine of cigarette smokers and smokeless tobacco users. (S)-NNN is the major enantiomer in tobacco and is more carcinogenic than (R)-NNN in rats, but no data are available on the enantiomeric composition of NNN in humans. The method used [13C6]NNN as an internal standard and [pyridine-D4]nornicotine to monitor possible artifactual formation of NNN, which was found to be less than 2% of the quantified NNN. The enantiomeric composition of NNN (20.5±27.1fmol/mL urine) in 20 cigarette smokers was 67±5% (S)-NNN while that in 10 smokeless tobacco users (67.1±56.7 fmol/mL urine) was 56±3% (S)-NNN. These results demonstrate that the highly carcinogenic (S)-NNN is the major enantiomer in human urine, and that the enantiomeric composition of NNN in human urine is remarkably similar to that in cigarette smoke and smokeless tobacco. This is the first study to combine chiral stationary phase separations with nanoelectrospray ionization and high resolution tandem mass spectrometry to quantify trace levels of enantiomeric metabolites in human urine.

Tobacco Use and Cancer Risk in the Agricultural Health Study

Background: Cigarettes are well known to cause cancer, but less is known about the risks of other tobacco products and use of more than one product.Methods: We examined cancer incidence in relation to exclusive use of six tobacco products [cigarettes, other combustibles (pipe, cigar, cigarillo), and smokeless tobacco (chewing tobacco, snuff)] in the Agricultural Health Study. We also examined the added cancer risks associated with use of cigarettes and other tobacco products.Results: In our study population of 84,015, ever use of smokeless tobacco was higher than the general United States population, whereas cigarette use was lower and other combustible product use was about the same. The strongest associations for exclusive ever use were for lung cancer [cigarettes HR = 15.48; 95% confidence interval (CI), 11.95-20.06; other combustible tobacco HR = 3.44; 95% CI, 1.53-7.71; smokeless tobacco HR = 2.21; 95% CI, 1.11-4.42]. Compared with exclusive cigarette smokers, cigarette smokers who additionally ever-used another combustible product had higher risks of smoking-related cancers (HR = 1.16; 95% CI, 1.04-1.30), especially among those who smoked cigarettes for more than 15 years.Conclusions and Impact: Cigarette smokers who additionally ever used smokeless tobacco had cancer risks similar to exclusive cigarette smokers. Users of cigarettes and other combustible tobacco may have higher risks of certain cancers than exclusive cigarette users. Cancer Epidemiol Biomarkers Prev; 26(5); 769-78. ©2016 AACR.

Transcriptome profiling in oral cavity and esophagus tissues from (S)-N'-nitrosonornicotine-treated rats reveals candidate genes involved in human oral cavity and esophageal carcinogenesis

Recently, we have shown that (S)-N'-Nitrosonornicotine [(S)-NNN], the major form of NNN in tobacco products, is a potent oral cavity and esophageal carcinogen in rats. To determine the early molecular alterations induced by (S)-NNN in the oral and esophageal mucosa, we administered the carcinogen to rats in the drinking water for 10 wk and global gene expression alterations were analyzed by RNA sequencing. At a false discovery rate P-value < 0.05 and fold-change ≥2, we found alterations in the level of 39 genes in the oral cavity and 69 genes in the esophagus. Validation of RNA sequencing results by qRT-PCR assays revealed a high cross-platform concordance. The most significant impact of exposure to (S)-NNN was alteration of genes involved in immune regulation (Aire, Ctla4, and CD80), inflammation (Ephx2 and Inpp5d) and cancer (Cdkn2a, Dhh, Fetub B, Inpp5d, Ly6E, Nr1d1, and Wnt6). Consistent with the findings in rat tissues, most of the genes were deregulated, albeit to different degrees, in immortalized oral keratinocytes treated with (S)-NNN and in non-treated premalignant oral cells and malignant oral and head and neck squamous cells. Furthermore, interrogation of TCGA data sets showed that genes deregulated by (S)-NNN in rat tissues (Fetub, Ly6e, Nr1d1, Cacna1c, Cd80, and Dgkg) are also altered in esophageal and head and neck tumors. Overall, our findings provide novel insights into early molecular changes induced by (S)-NNN and, therefore, could contribute to the development of biomarkers for the early detection and prevention of (S)-NNN-associated oral and esophageal cancers. © 2016 Wiley Periodicals, Inc.

Biomarkers of Tobacco Exposure: Summary of an FDA-Sponsored Public Workshop

Since 2009, the FDA Center for Tobacco Products (CTP) has had the authority to regulate the manufacturing, distribution, and marketing of tobacco products in order to reduce the death and disease caused by tobacco use. Biomarkers of exposure pertain to actual human exposure to chemicals arising from tobacco use and could play an important role across a number of FDA regulatory activities, including assessing new and modified-risk tobacco products and identifying and evaluating potential product standards. On August 3-4, 2015, FDA/CTP hosted a public workshop focused on biomarkers of exposure with participants from government, industry, academia, and other organizations. The workshop was divided into four sessions focused on: (i) approaches to evaluating and selecting biomarkers; (ii) biomarkers of exposure and relationship to disease risk; (iii) currently used biomarkers of exposure and biomarkers in development; and (iv) biomarkers of exposure and the assessment of smokeless tobacco and electronic nicotine delivery systems. This article synthesizes the main findings from the workshop and highlights research areas that could further strengthen the science around biomarkers of exposure and help determine their application in tobacco product regulation. Cancer Epidemiol Biomarkers Prev; 26(3); 291-302. ©2016 AACR.

Assessment of tobacco specific nitrosamines (TSNAs) in oral fluid as biomarkers of cancer risk: A population-based study

BACKGROUND

Smoke-free laws are expected to reduce smoking habits and exposure to secondhand smoke. The objective of this study was the measurement of tobacco specific carcinogens (TSNAs) in oral fluid to assess the most suitable biomarker of cancer risk associated with tobacco smoke.

METHODS

TSNAs, N'-nitrosonornicotine (NNN), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), as well as nicotine and cotinine were measured in oral fluid samples from 166 smokers and 532 non-smokers of the adult population of Barcelona, Spain. A simple method with an alkaline single liquid-liquid extraction with dichloromethane/isopropanol was used and lower limits of quantification for cotinine, NNN, NNK and NNAL were set at 0.10ng/mL, 1.0, 2.0 and 0.50pg/mL respectively. The NNN/cotinine ratio was also calculated.

RESULTS

NNN was the most abundant TSNA present in oral fluid with a significant difference between smokers and non-smokers (mean concentrations of 118 and 5.3pg/mL, respectively, p<0.001). NNK and NNAL were detectable in fewer samples. NNN and cotinine concentrations had a moderate correlation within both groups (Spearman's rank correlation coefficient of 0.312, p<0.001 in smokers and 0.279, p=0.022 in non-smokers). NNN/cotinine ratio was significantly higher (p<0.001) in non-smokers than in smokers, in line with equivalent findings for the NNAL/cotinine ratio in urine.

CONCLUSIONS

TSNAs are detectable in oral fluid of smokers and non-smokers. NNN is the most abundant, in line with its association with esophageal and oral cavity cancers. The NNN/cotinine ratio confirms the relative NNN increase in second hand smoke. Findings provide a new oral fluid biomarker of cancer risk associated with exposure to tobacco smoke.

Conversion of nornicotine to 6-hydroxy-nornicotine and 6-hydroxy-myosmine by Shinella sp. strain HZN7

Nornicotine is a natural alkaloid produced by plants in the genus Nicotiana and is structurally related to nicotine. Importantly, nornicotine is the direct precursor of tobacco-specific nitrosamine N'-nitrosonornicotine, which is a highly potent human carcinogen. Microbial detoxification and degradation of nicotine have been well characterized; however, until now, there has been no information on the molecular mechanism of nornicotine degradation. In this study, we demonstrate the transformation of nornicotine by the nicotine-degrading strain Shinella sp. HZN7. Three transformation products were identified as 6-hydroxy-nornicotine, 6-hydroxy-myosmine, and 6-hydroxy-pseudooxy-nornicotine by UV spectroscopy, high-resolution mass spectrometry, nuclear magnetic resonance, and Fourier transform-infrared spectroscopy analyses. The two-component nicotine dehydrogenase genes nctA1 and nctA2 were cloned, and their product, NctA, was confirmed to be responsible for the conversion of nornicotine into 6-hydroxy-nornicotine as well as nicotine into 6-hydroxy-nicotine. The 6-hydroxy-nicotine oxidase, NctB, catalyzed the oxidation of 6-hydroxy-nornicotine to 6-hydroxy-myosmine, and it spontaneously hydrolyzed into 6-hydroxy-pseudooxy-nornicotine. However, 6-hydroxy-pseudooxy-nornicotine could not be further degraded by strain HZN7. This study demonstrated that nornicotine is partially transformed by strain HZN7 via nicotine degradation pathway.

Contribution of Nicotine and Nornicotine toward the Production of N'-Nitrosonornicotine in Air-Cured Tobacco (Nicotiana tabacum)

N'-Nitrosonornicotine (6) is a potent and organ-specific carcinogen found in tobacco and tobacco smoke in substantial amounts. Nicotine (1) and nornicotine (2) are proposed to be the precursors of 6 in tobacco. Since 1 can be rapidly demethylated to 2 in tobacco, to distinguish between the direct formation of 6 from these potential precursors is difficult. A gas chromatography/thermal energy analyzer method using two columns in series was developed to separate the enantiomers of 6, N'-nitrosoanabasine (7), and N'-nitrosoanatabine (8). Tobacco lines with different combinations of three nicotine demethylases inhibited were grown in the field. Air-cured leaves were analyzed for the enantiomeric composition of four main alkaloids and their corresponding tobacco-specific nitrosamines. The percentage of (R)-6 of total 6 varied from 7% to 69% in mutant lines. The measured 6 had the same enantiomeric composition as 2, rather than 1, even when the level of 2 was reduced to 0.6% of 1 in a triple mutant line. The pattern of the enantiomeric composition of 1, 2, and 6 demonstrated that the direct formation of 6 from 1, if it occurs, is negligible in air-cured tobacco. Since (S)-6 is more highly carcinogenic than its R form, the reduction of (S)-2 should be a priority for the reduction of 6.

Proceedings of the 2015 National Toxicology Program Satellite Symposium

The 2015 Annual National Toxicology Program Satellite Symposium, entitled "Pathology Potpourri" was held in Minneapolis, Minnesota, at the American College of Veterinary Pathologists/American Society for Veterinary Clinical Pathology/Society of Toxicologic Pathology combined meeting. The goal of this symposium is to present and discuss diagnostic pathology challenges or nomenclature issues. Because of the combined meeting, both laboratory and domestic animal cases were presented. This article presents summaries of the speakers' talks, including challenging diagnostic cases or nomenclature issues that were presented, along with select images that were used for audience voting and discussion. Some lesions and topics covered during the symposium included hepatocellular lesions, a proposed harmonized diagnostic approach to rat cardiomyopathy, crop milk in a bird, avian feeding accoutrement, heat exchanger in a tuna, metastasis of a tobacco carcinogen-induced pulmonary carcinoma, neurocytoma in a rat, pituicytoma in a rat, rodent mammary gland whole mounts, dog and rat alveolar macrophage ultrastructure, dog and rat pulmonary phospholipidosis, alveolar macrophage aggregation in a dog, degenerating yeast in a cat liver aspirate, myeloid leukemia in lymph node aspirates from a dog, Trypanosoma cruzi in a dog, solanum toxicity in a cow, bovine astrovirus, malignant microglial tumor, and nomenclature challenges from the Special Senses International Harmonization of Nomenclature and Diagnostic Criteria Organ Working Group.

DNA Adduct Formation from Metabolic 5'-Hydroxylation of the Tobacco-Specific Carcinogen N'-Nitrosonornicotine in Human Enzyme Systems and in Rats

N'-Nitrosonornicotine (NNN) is carcinogenic in multiple animal models and has been evaluated as a human carcinogen. NNN can be metabolized by cytochrome P450s through two activation pathways: 2'-hydroxylation and 5'-hydroxylation. While most previous studies have focused on 2'-hydroxylation in target tissues of rats, available evidence suggests that 5'-hydroxylation is a major activation pathway in human enzyme systems, in nonhuman primates, and in target tissues of some other rodent carcinogenicity models. In the study reported here, we investigated DNA damage resulting from NNN 5'-hydroxylation by quantifying the adduct 2-(2-(3-pyridyl)-N-pyrrolidinyl)-2'-deoxyinosine (py-py-dI). In rats treated with NNN in the drinking water (7-500 ppm), py-py-dI was the major DNA adduct resulting from 5'-hydroxylation of NNN in vivo. Levels of py-py-dI in the lung and nasal cavity were the highest, consistent with the tissue distribution of CYP2A3. In rats treated with (S)-NNN or (R)-NNN, the ratios of formation of (R)-py-py-dI to (S)-py-py-dI were not the expected mirror image, suggesting that there may be a carrier for one of the unstable intermediates formed upon 5'-hydroxylation of NNN. Rat hepatocytes treated with (S)- or (R)-NNN or (2'S)- or (2'R)-5'-acetoxyNNN exhibited a pattern of adduct formation similar to that of live rats. In vitro studies with human liver S9 fraction or human hepatocytes incubated with NNN (2-500 μM) demonstrated that py-py-dI formation was greater than the formation of pyridyloxobutyl-DNA adducts resulting from 2'-hydroxylation of NNN. (S)-NNN formed more total py-py-dI adducts than (R)-NNN in human liver enzyme systems, which is consistent with the critical role of CYP2A6 in the 5'-hydroxylation of NNN in human liver. The results of this study demonstrate that the major DNA adduct resulting from NNN metabolism by human enzymes is py-py-dI and provide potentially important new insights into the metabolic activation of NNN in rodents and humans.

Analysis of Tobacco-Specific Nitrosamines in the Common Smokeless Tobacco Afzal in Oman

OBJECTIVES

There is a lack of awareness regarding the carcinogenicity of Afzal, an illegal smokeless tobacco product (STP) widely used among the Omani youth. Previous research has shown that certain types of tobacco-specific nitrosamines (TSNAs) are associated with oral and lung cancers. This study therefore aimed to assess levels of four common TSNAs in a randomly selected sample of Afzal.

METHODS

This study was carried out at Sultan Qaboos University in Muscat, Oman, between April and September 2013. A random sample of Afzal was analysed for four types of TSNAs using high-performance liquid chromatography-tandem mass spectrometry. The four types of TSNAs analysed were 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK), N-nitrosonornicotine (NNN), N-nitrosoanatabine (NAT) and N-nitrosoanabasine (NAB). As a reference product, a sample of laboratory-manufactured American moist snuff (Centers for Disease Control and Prevention, Atlanta, Georgia, USA) was also used to confirm the accuracy and precision of the analysis.

RESULTS

The analysis revealed total TSNA levels of 3.573 μg/g in the Afzal sample. Mean levels of NNN, NNK, NAT and NAB were 1.205, 1.015, 0.809 and 0.545 μg/g, respectively.

CONCLUSION

Levels of the two most abundant TSNAs (NNN and NNK) found in the Afzal sample exceeded international regulatory limits. Afzal users therefore need to be educated regarding the potential health risks associated with their STP use. Stricter implementation of current legislation is recommended to reduce the availability and usage of Afzal in Oman.

Analysis of O(6)-[4-(3-Pyridyl)-4-oxobut-1-yl]-2'-deoxyguanosine and Other DNA Adducts in Rats Treated with Enantiomeric or Racemic N'-Nitrosonornicotine

(S)-N'-Nitrosonornicotine [(S)-NNN] and racemic NNN are powerful oral and esophageal carcinogens in the F344 rat, whereas (R)-NNN has only weak activity. Tumor formation in these tissues of rats treated with racemic NNN was far greater than the sum of the activities of the individual enantiomers. We hypothesized that metabolites of (R)-NNN enhanced levels of DNA adducts produced by (S)-NNN. A test of that hypothesis necessitated the development of a novel liquid chromatography-nanoelectrospray ionization-high resolution tandem mass spectrometry method for the analysis of O(6)-[4-(3-pyridyl)-4-oxobut-1-yl]-2'-deoxyguanosine (O(6)-POB-dGuo), a highly mutagenic DNA adduct not previously quantified in rats treated with NNN. The new method, with a limit of detection of 6.5 amol for diluted standard and 100 amol for DNA samples, was applied in this study. Groups of nine F344 rats were treated with doses as follows: 7 ppm (R)-NNN, 7 ppm (S)-NNN, and 14 ppm racemic NNN; 14 ppm (R)-NNN, 14 ppm (S)-NNN, and 28 ppm racemic NNN; or 28 ppm (R)-NNN, 28 ppm (S)-NNN, and 56 ppm racemic NNN for 5 weeks, and tissues were analyzed for DNA adducts. We found statistically significant, but modest, synergistic enhancement of levels of O(6)-POB-dGuo in the esophagus but not the oral cavity of rats treated with racemic NNN (low and median doses only) compared to the sum of the amounts formed in these tissues of rats treated with (S)-NNN or (R)-NNN. There was no synergy in the formation of other POB-DNA adducts of NNN in oral cavity and esophagus, nor was there any evidence for synergy in nasal respiratory and olfactory epithelium, lung, or liver. Our results provide the first quantitation of O(6)-POB-dGuo in DNA from tissues of rats treated with NNN and evidence for synergy in DNA adduct formation as one possible mechanism by which (R)-NNN enhances the carcinogenicity of (S)-NNN in rats.

Combined analysis of N'-nitrosonornicotine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol in the urine of cigarette smokers and e-cigarette users

A liquid chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI(+)-MS/MS) method for the analysis of the tobacco-specific carcinogens N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and their glucuronides (total NNN and total NNAL) in human urine was developed. The method has excellent accuracy and intra-day and inter-day precision, and limits of quantitation of 0.015 and 0.075pmol/mL urine, respectively, for total NNN and total NNAL. A unique aspect of this method is internal assessment of possible artifactual formation of NNN by inclusion of the monitor amine [pyridine-D4]nornicotine. We found that artifactual formation of NNN comprised only 2.5% of the measured amounts of total NNN in urine of cigarette smokers, under our conditions using ammonium sulfamate as an inhibitor of nitrosation. The method was applied to urine samples from cigarette smokers and e-cigarette users. Levels of total NNN and total NNAL in the urine of cigarette smokers averaged 0.060±0.035pmol/mL and 2.41±1.41pmol/mL urine, (N=38), respectively, which were both significantly greater than in the urine of 27 e-cigarette users.

Quantitative analysis of 3'-hydroxynorcotinine in human urine

INTRODUCTION

Based on previous metabolism studies carried out in patas monkeys, we hypothesized that urinary 3'-hydroxynorcotinine could be a specific biomarker for uptake and metabolism of the carcinogen N'-nitrosonornicotine in people who use tobacco products.

METHODS

We developed a method for quantitation of 3'-hydroxynorcotinine in human urine. [Pyrrolidinone-(13)C4]3'-hydroxynorcotinine was added to urine as an internal standard, the samples were treated with β-glucuronidase, partially purified by solid supported liquid extraction and quantified by liquid chromatography-electrospray ionization-tandem mass spectrometry.

RESULTS

The method was accurate (average accuracy = 102%) and precise (coefficient of variation = 5.6%) in the range of measurement. 3'-Hydroxynorcotinine was detected in 48 urine samples from smokers (mean 393±287 pmol/ml urine) and 12 samples from individuals who had stopped smoking and were using the nicotine patch (mean 658±491 pmol/ml urine), but not in any of 10 samples from nonsmokers.

CONCLUSIONS

Since the amounts of 3'-hydroxynorcotinine found in smokers' urine were approximately 50 times greater than the anticipated daily dose of N'-nitrosonornicotine, we concluded that it is a metabolite of nicotine or one of its metabolites, comprising perhaps 1% of nicotine intake in smokers. Therefore, it would not be suitable as a specific biomarker for uptake and metabolism of N'-nitrosonornicotine. Since 3'-hydroxynorcotinine has never been previously reported as a constituent of human urine, further studies are required to determine its source and mode of formation.

Evidence supporting product standards for carcinogens in smokeless tobacco products

Smokeless tobacco products sold in the United States vary significantly in yields of nicotine and tobacco-specific nitrosamines (TSNA). With the passage of the Family Smoking Prevention and Tobacco Control Act, the Food and Drug Administration now has the authority to establish product standards. However, limited data exist determining the relative roles of pattern of smokeless tobacco use versus constituent levels in the smokeless tobacco product in exposure of users to carcinogens. In this study, smokeless tobacco users of brands varying in nicotine and TSNA content were recruited from three different regions in the U.S. Participants underwent two assessment sessions. During these sessions, demographic and smokeless tobacco use history information along with urine samples to assess biomarkers of exposure and effect were collected. During the time between data collection, smokeless tobacco users recorded the amount and duration of smokeless tobacco use on a daily basis using their diary cards. Results showed that independent of pattern of smokeless tobacco use and nicotine yields, levels of TSNA in smokeless tobacco products played a significant role in carcinogen exposure levels. Product standards for reducing levels of TSNA in smokeless tobacco products are necessary to decrease exposure to these toxicants and potentially to reduce risk for cancer.

Implications of acetaldehyde-derived DNA adducts for understanding alcohol-related carcinogenesis

Among various potential mechanisms that could explain alcohol carcinogenicity, the metabolism of ethanol to acetaldehyde represents an obvious possible mechanism, at least in some tissues. The fundamental principle of genotoxic carcinogenesis is the formation of mutagenic DNA adducts in proliferating cells. If not repaired, these adducts can result in mutations during DNA replication, which are passed on to cells during mitosis. Consistent with a genotoxic mechanism, acetaldehyde does react with DNA to form a variety of different types of DNA adducts. In this chapter we will focus more specifically on N2-ethylidene-deoxyguanosine (N2-ethylidene-dG), the major DNA adduct formed from the reaction of acetaldehyde with DNA and specifically highlight recent data on the measurement of this DNA adduct in the human body after alcohol exposure. Because results are of particular biological relevance for alcohol-related cancer of the upper aerodigestive tract (UADT), we will also discuss the histology and cytology of the UADT, with the goal of placing the adduct data in the relevant cellular context for mechanistic interpretation. Furthermore, we will discuss the sources and concentrations of acetaldehyde and ethanol in different cell types during alcohol consumption in humans. Finally, in the last part of the chapter, we will critically evaluate the concept of carcinogenic levels of acetaldehyde, which has been raised in the literature, and discuss how data from acetaldehyde genotoxicity are and can be utilized in physiologically based models to evaluate exposure risk.

An analytical study on the common type of smokeless tobacco available in the Iranian market

Background:

The use of smokeless tobacco is considered as a risk factor for oral cancer.

Objectives:

The current study aimed to chemically analyze, separate and measure the existing substances in a type of chewing tobacco.

Materials and Methods:

In the current descriptive study, the investigated sample was a type of smokeless tobacco, known as BT, manufactured in India. First steam distillation method and Clevenger machine were used to separate and extract the essential oil of the sample. The presence of the desired compounds was evaluated in the essential oil, using gas chromatography (GC) and then gas chromatography coupled to mass spectrometry (GC/MS) analysis.

Results:

Based on the results obtained by the applied technique, the presence of carcinogenic compounds, N-nitrosomethyl-vinylamine (162 µg/g), N-nitrosonornicotine (6.3 µg/g), and Acetaldehyde (117 µg/g) was confirmed in the sample.

Conclusions:

Chemical analysis of the sample confirmed the existence of carcinogenic compounds.

It is time to regulate carcinogenic tobacco-specific nitrosamines in cigarette tobacco

The Family Smoking Prevention and Tobacco Control Act gives the U.S. Food and Drug Administration power to regulate tobacco products. This commentary calls for immediate regulation of the carcinogenic tobacco-specific nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) in cigarette tobacco as a logical path to cancer prevention. NNK and NNN, powerful carcinogens in laboratory animals, have been evaluated as "carcinogenic to humans" by the International Agency for Research on Cancer. NNK and NNN are present in the tobacco of virtually all marketed cigarettes; levels in cigarette smoke are directly proportional to the amounts in tobacco. The NNK metabolite NNAL, itself a strong carcinogen, is present in the urine of smokers and nonsmokers exposed to secondhand smoke. Some of the highest levels of NNK and NNN are found in U.S. products. It is well established that factors such as choice of tobacco blend, agricultural conditions, and processing methods influence levels of NNK and NNN in cigarette tobacco and cigarette smoke. Therefore, it is time to control these factors and produce cigarettes with 100 ppb or less each of NNK and NNN in tobacco, which would result in an approximate 15- to 20-fold reduction of these carcinogens in the mainstream smoke of popular cigarettes sold in the United States.

Tobacco-specific N-nitrosamine exposures and cancer risk in the Shanghai Cohort Study: remarkable coherence with rat tumor sites

The tobacco-specific nitrosamines N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) are potent carcinogens for the rat esophagus and lung, respectively. Consistent with the animal carcinogenicity data, we previously reported a remarkably strong association between prospectively measured urinary total NNN, a biomarker of human NNN intake, and the risk of developing esophageal cancer among smokers in the Shanghai Cohort Study. We also demonstrated that urinary total 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), a biomarker of exposure to the lung carcinogen NNK, is strongly associated with the risk of lung, but not esophageal cancer in smokers. In this study, we investigated the potential relationship between NNN intake and lung cancer risk in the same cohort. The prospectively collected urine samples from lung cancer cases and matching controls selected for this study, all current smokers, have been previously analyzed for total NNAL, cotinine (a biomarker of nicotine intake) and phenanthrene tetraol (PheT) (a biomarker of exposure to polycyclic aromatic hydrocarbons). Urinary levels of total NNN were not associated with the risk of lung cancer: odds ratios (95% confidence intervals) associated with the second and third tertiles of total NNN, relative to the lowest tertile, were 0.82 (0.36-1.88) and 1.02 (0.39-2.89), respectively (p for trend = 0.959), after adjustment for self-reported smoking history, urinary cotinine and PheT. The results of this study reaffirm the previously reported specificity of urinary total NNN and total NNAL as predictors of esophageal and lung cancer risks, respectively, in smokers, and demonstrate remarkable coherence between rat target tissues of these carcinogens and susceptibility to cancer in smokers.