Levels of (S)-N'-nitrosonornicotine in U.S. tobacco products

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.

Variation of Benzo[a]pyrene, NNN, and NNK Levels in 16 Commercial Smokeless Tobacco Products

This study examined the variation of benzo[a]pyrene (B[a]P), N'-nitrosonornicotine (NNN), and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) levels in 16 smokeless tobacco products from several different product subcategories obtained at two different locations and at two different procurement times. B[a]P quantities range from 0.6 to 160 ng/g on a wet-weight basis, whereas NNN and NNK quantities range from 276 to 10473 ng/g and 79 to 28882 ng/g, respectively. The B[a]P, NNN, and NNK quantities vary widely among various smokeless tobacco product categories and among various brands within each product subcategory. Dry snuff products contain the highest B[a]P, NNN, and NNK quantities, whereas loose and portioned snus products contain the lowest B[a]P, NNN, and NNK levels. In general, variation of B[a]P, NNN, and NNK levels across four sets of each product brand purchased six months apart and at two different locations show statistically significant differences (p < 0.05), although with a much narrower product set-to-set variability.

Associations between microbial communities and key chemical constituents in U.S. domestic moist snuff

BACKGROUND

Smokeless tobacco (ST) products are widely used throughout the world and contribute to morbidity and mortality in users through an increased risk of cancers and oral diseases. Bacterial populations in ST contribute to taste, but their presence can also create carcinogenic, Tobacco-Specific N-nitrosamines (TSNAs). Previous studies of microbial communities in tobacco products lacked chemistry data (e.g. nicotine, TSNAs) to characterize the products and identify associations between carcinogen levels and taxonomic groups. This study uses statistical analysis to identify potential associations between microbial and chemical constituents in moist snuff products.

METHODS

We quantitatively analyzed 38 smokeless tobacco products for TSNAs using liquid chromatography with tandem mass spectrometry (LC-MS/MS), and nicotine using gas chromatography with mass spectrometry (GC-MS). Moisture content determinations (by weight loss on drying), and pH measurements were also performed. We used 16S rRNA gene sequencing to characterize the microbial composition, and additionally measured total 16S bacterial counts using a quantitative PCR assay.

RESULTS

Our findings link chemical constituents to their associated bacterial populations. We found core taxonomic groups often varied between manufacturers. When manufacturer and flavor were controlled for as confounding variables, the genus Lactobacillus was found to be positively associated with TSNAs. while the genera Enteractinococcus and Brevibacterium were negatively associated. Three genera (Corynebacterium, Brachybacterium, and Xanthomonas) were found to be negatively associated with nicotine concentrations. Associations were also investigated separately for products from each manufacturer. Products from one manufacturer had a positive association between TSNAs and bacteria in the genus Marinilactibacillus. Additionally, we found that TSNA levels in many products were lower compared with previously published chemical surveys. Finally, we observed consistent results when either relative or absolute abundance data were analyzed, while results from analyses of log-ratio-transformed abundances were divergent.

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.

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.

Novel Pathways and Mechanism of Nicotine-Induced Oral Carcinogenesis

BACKGROUND

Smokeless Tobacco (SLT) contains 9 times more nicotine than Smoked Tobacco (SMT). The carcinogenic effect of nicotine is intensified by converting nicotine-to-nicotine-derived Nitrosamines (NDNs).

METHODS

A review of the literature was conducted with a tailored search strategy to unravel the novel pathways and mechanisms of nicotine-induced oral carcinogenesis.

RESULTS

Nicotine and NDNs act on nicotinic Acetylcholine Receptors (nAChRs) as agonists. Nicotine facilitates cravings through α4β2nAChR and α7nAChR, via enhanced brain dopamine release. Nicotine binding to nAChR promotes proliferation, migration, invasion, chemoresistance, radioresistance, and metastasis of oral cancer cells. Nicotine binding to α7nAChR on keratinocytes triggers Ras/Raf-1/MEK1/ERK cascade promoting anti-apoptosis and pro-proliferative effects. Furthermore, the nicotine-enhanced metastasis is subdued on nAChR blockade through reduced nuclear localization of p-EGFR.

CONCLUSION

Protracted exposure to nicotine/NDN augments cancer-stimulatory α7nAChR and desensitizes cancer inhibitory α4β2nAChR. Since nAChRs dictate both addictive and carcinogenic effects of nicotine, it seems counterintuitive to designate nicotine just as an addictive agent devoid of any carcinogenicity.

Spatial, temporal, and demographic patterns in prevalence of chewing tobacco use in 204 countries and territories, 1990-2019: a systematic analysis from the Global Burden of Disease Study 2019

BACKGROUND

Chewing tobacco and other types of smokeless tobacco use have had less attention from the global health community than smoked tobacco use. However, the practice is popular in many parts of the world and has been linked to several adverse health outcomes. Understanding trends in prevalence with age, over time, and by location and sex is important for policy setting and in relation to monitoring and assessing commitment to the WHO Framework Convention on Tobacco Control.

METHODS

We estimated prevalence of chewing tobacco use as part of the Global Burden of Diseases, Injuries, and Risk Factors Study 2019 using a modelling strategy that used information on multiple types of smokeless tobacco products. We generated a time series of prevalence of chewing tobacco use among individuals aged 15 years and older from 1990 to 2019 in 204 countries and territories, including age-sex specific estimates. We also compared these trends to those of smoked tobacco over the same time period.

FINDINGS

In 2019, 273·9 million (95% uncertainty interval 258·5 to 290·9) people aged 15 years and older used chewing tobacco, and the global age-standardised prevalence of chewing tobacco use was 4·72% (4·46 to 5·01). 228·2 million (213·6 to 244·7; 83·29% [82·15 to 84·42]) chewing tobacco users lived in the south Asia region. Prevalence among young people aged 15-19 years was over 10% in seven locations in 2019. Although global age-standardised prevalence of smoking tobacco use decreased significantly between 1990 and 2019 (annualised rate of change: -1·21% [-1·26 to -1·16]), similar progress was not observed for chewing tobacco (0·46% [0·13 to 0·79]). Among the 12 highest prevalence countries (Bangladesh, Bhutan, Cambodia, India, Madagascar, Marshall Islands, Myanmar, Nepal, Pakistan, Palau, Sri Lanka, and Yemen), only Yemen had a significant decrease in the prevalence of chewing tobacco use, which was among males between 1990 and 2019 (-0·94% [-1·72 to -0·14]), compared with nine of 12 countries that had significant decreases in the prevalence of smoking tobacco. Among females, none of these 12 countries had significant decreases in prevalence of chewing tobacco use, whereas seven of 12 countries had a significant decrease in the prevalence of tobacco smoking use for the period.

INTERPRETATION

Chewing tobacco remains a substantial public health problem in several regions of the world, and predominantly in south Asia. We found little change in the prevalence of chewing tobacco use between 1990 and 2019, and that control efforts have had much larger effects on the prevalence of smoking tobacco use than on chewing tobacco use in some countries. Mitigating the health effects of chewing tobacco requires stronger regulations and policies that specifically target use of chewing tobacco, especially in countries with high prevalence.

FUNDING

Bloomberg Philanthropies and the Bill & Melinda Gates Foundation.

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.

Variability of TSNA in U.S. Tobacco and Moist Smokeless Tobacco Products

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Incoming tobaccos have extremely variable nitrosamine content.

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Blending reduces the variation in tobacco products, but it is still considerable.

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Few, if any, U.S. moist smokeless tobacco products meet the proposed FDA standard.

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Products must be targeted well below the proposed standard to consistently meet it.

Tobacco-specific nitrosamines (TSNAs) have been of concern to the public health community for decades and their reduction through agricultural practices, plant breeding, and tobacco processing has also been a decades-long industry effort. Despite those efforts, TSNAs, though lower, continue to be constituents of concern in tobacco products. This paper examines the TSNA levels of dark air-cured, dark fire-cured, and burley tobaccos purchased in the United States by U.S. Smokeless Tobacco Company LLC (USSTC) and of nine finished USSTC moist smokeless tobacco products. TSNA values of the incoming purchased tobaccos and the finished products showed considerable variability. For the incoming tobaccos, the coefficient of variation was generally more than 100 % for each tobacco type and for each of the measured TSNAs. The relative TSNA variability of the finished tobacco products was also considerable, averaging approximately 25 %. It was also found that the measured values for the finished products averaged well above the proposed FDA NNN proposed product standard of 1.0 μg/g dry weight. Because of the large variability in NNN values, products would have to average well below FDA’s proposed product standard to be consistently compliant.

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.

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.

Regulation of toxic contents of smokeless tobacco products

Effective regulation of contents of tobacco products is one of the primary milestones to reduce negative health effects associated with the use of smokeless tobacco (SLT) products. As per the available sources, testing of some SLT products has been done on ad hoc basis, but there is a lack of comprehensive and periodic analysis of these products. In addition, the available results indicate huge variations among the levels of pH, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, N-nitrosonornicotine, benzo[a]pyrene, heavy metals and nicotine within different products as well as within different brands of the same product. This review was aimed to throw light on the variations and gaps in testing of SLT products and emphasize the need for strong policy regulation for monitoring the chemical constituents of these products.

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.

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.

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.

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.

Non-cigarette tobacco and the lung

Cigarette smoking is known to cause a wide range of damaging health outcomes; however, the effects of non-cigarette tobacco products are either unknown or perceived as less harmful than cigarettes. Smokeless tobacco, cigar smoking, and waterpipe smoking have increased in usage over the past few decades. Some experts believe that their use is reaching epidemic proportions. Factors such as a perception of harm reduction, targeted advertising, and unrecognized addiction may drive the increased consumption of non-cigarette tobacco products. In particular, the need for social acceptance, enjoyment of communal smoking activities, and exotic nature of waterpipe smoking fuels, in part, its popularity. The public is looking for "safer" alternatives to smoking cigarettes, and some groups advertise products such as smokeless tobacco and electronic cigarettes as the alternatives they seek. Though it is clear that cigar and waterpipe tobacco smoking are probably as dangerous to health as cigarette smoking, there is an opinion among users that the health risks are less compared to cigarette smoking. This is particularly true in younger age groups. In the cases of smokeless tobacco and electronic cigarettes, the risks to health are less clear and there may be evidence of a harm reduction compared to cigarettes. In this article, we discuss commonly used forms of non-cigarette tobacco products, their impacts on lung health, and relevant controversies surrounding their use.

Awareness and use of non-conventional tobacco products among U.S. students, 2012

BACKGROUND

Increasing diversity of the tobacco product landscape, including electronic cigarettes (e-cigarettes), hookah, snus, and dissolvable tobacco products (dissolvables), raises concerns about the public health impact of these non-conventional tobacco products among youth.

PURPOSE

This study assessed awareness, ever use, and current use of non-conventional tobacco products among U.S. students in 2012, overall and by demographic and tobacco use characteristics.

METHODS

Data from the 2012 National Youth Tobacco Survey, a nationally representative survey of U.S. middle and high school students, were analyzed in 2013. Prevalence of awareness, ever use, and current use of e-cigarettes, hookah, snus, and dissolvables were calculated overall and by sex, school level, race/ethnicity, and conventional tobacco product use, including cigarettes, cigars, or smokeless tobacco (chewing tobacco, snuff, or dip).

RESULTS

Overall, 50.3% of students were aware of e-cigarettes; prevalence of ever and current use of e-cigarettes was 6.8% and 2.1%, respectively. Awareness of hookah was 41.2% among all students, and that of ever and current use were 8.9% and 3.6%, respectively. Overall awareness; ever; and current use of snus (32%, 5.3%, 1.7%, respectively) and dissolvables (19.3%, 2.0%, 0.7%, respectively) were generally lower than those of e-cigarettes or hookah. Conventional tobacco product users were more likely to be aware of and to use non-conventional tobacco products.

CONCLUSIONS

Many U.S. students are aware of and use non-conventional tobacco products. Evidence-based interventions should be implemented to prevent and reduce all tobacco use among youth.

Estimating the harms of nicotine-containing products using the MCDA approach

BACKGROUND

An international expert panel convened by the Independent Scientific Committee on Drugs developed a multi-criteria decision analysis model of the relative importance of different types of harm related to the use of nicotine-containing products.

METHOD

The group defined 12 products and 14 harm criteria. Seven criteria represented harms to the user, and the other seven indicated harms to others. The group scored all the products on each criterion for their average harm worldwide using a scale with 100 defined as the most harmful product on a given criterion, and a score of zero defined as no harm. The group also assessed relative weights for all the criteria to indicate their relative importance.

FINDINGS

Weighted averages of the scores provided a single, overall score for each product. Cigarettes (overall weighted score of 100) emerged as the most harmful product, with small cigars in second place (overall weighted score of 64). After a substantial gap to the third-place product, pipes (scoring 21), all remaining products scored 15 points or less.

INTERPRETATION

Cigarettes are the nicotine product causing by far the most harm to users and others in the world today. Attempts to switch to non-combusted sources of nicotine should be encouraged as the harms from these products are much lower.

Clinical and biochemical studies support smokeless tobacco's carcinogenic potential in the human oral cavity

In 2007, the International Agency for Research on Cancer presented compelling evidence that linked smokeless tobacco use to the development of human oral cancer. Although these findings imply vigorous local carcinogen metabolism, little is known about levels and distribution of phase I, II, and III (drug egress) enzymes in human oral mucosa. In this study here, we integrated clinical data, and imaging and histopathologic analyses of an oral squamous cell carcinoma that arose at the site of smokeless tobacco quid placement in a patient. Immunoblot and immunohistochemical (IHC) analyses were used to identify tumor and normal human oral mucosal smokeless tobacco-associated metabolic activation and detoxification enzymes. Human oral epithelium contains every known phase I enzyme associated with nitrosamine oxidative bioactivation with approximately 2-fold interdonor differences in protein levels. Previous studies have confirmed approximately 3.5-fold interdonor variations in intraepithelial phase II enzymes. Unlike the superficially located enzymes in nonreplicating esophageal surface epithelium, IHC studies confirmed that oral mucosal nitrosamine metabolizing enzymes reside in the basilar and suprabasilar region, which notably is the site of ongoing keratinocyte DNA replication. Clearly, variations in product composition, nitrosamine metabolism, and exposure duration will modulate clinical outcomes. The data presented here form a coherent picture consistent with the abundant experimental data that link tobacco-specific nitrosamines to human oral cancer.

Quantitation of pyridyloxobutyl-DNA adducts in tissues of rats treated chronically with (R)- or (S)-N'-nitrosonornicotine (NNN) in a carcinogenicity study

We quantified DNA adducts resulting from 2'-hydroxylation of enantiomers of the tobacco-specific nitrosamine N'-nitrosonornicotine (NNN) in tissues of male F-344 rats after 10, 30, 50, and 70 weeks of treatment with 14 ppm in the drinking water. These rats were in subgroups of a carcinogenicity study in which (S)-NNN was highly tumorigenic in the oral cavity and esophagus, while (R)-NNN was relatively weakly active. DNA adducts were quantified by liquid chromatography-electrospray ionization-tandem mass spectrometry in six tissues: oral mucosa, esophageal mucosa, nasal respiratory mucosa, nasal olfactory mucosa, liver, and lung. O²-[4-(3-Pyridyl)-4-oxobut-1-yl]thymidine (O²-POB-dThd, 7) and 7-[4-(3-pyridyl)-4-oxobut-1-yl]-2'-deoxyguanosine (7-POB-dGuo, 8), the latter as 7-[4-(3-pyridyl)-4-oxobut-1-yl]guanine (7-POB-Gua, 11), were detected at each time point in each tissue. In the target tissues for carcinogenicity, oral mucosa and esophageal mucosa, levels of 7-POB-Gua (11) and O²-POB-dThd (7) were similar, or 11 predominated, while in all other tissues at all time points for both enantiomers, 7 was clearly present in greater amounts than 11. Total measured DNA adduct levels in esophageal mucosa and oral mucosa were higher in rats treated with (S)-NNN than (R)-NNN. The highest adduct levels were found in the nasal respiratory mucosa. DNA adducts generally persisted in all tissues without any sign of substantial decreases throughout the 70 week time course. The results of this study suggest that inefficient repair of 7-POB-dGuo (8) in the rat oral cavity and esophagus may be important in carcinogenesis by NNN and support the development of these DNA adducts as potential biomarkers of NNN metabolic activation in people who use tobacco products.

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

Currently, smokeless tobacco products are being proposed as an alternative mode of tobacco use associated with less harm. All of these products contain the tobacco-specific carcinogen N'-nitrosonornicotine (NNN). The major form of NNN in tobacco products is (S)-NNN, shown in this study to induce a total of 89 benign and malignant oral cavity tumors in a group of 20 male F-344 rats treated chronically with 14 p.p.m. in the drinking water. The opposite enantiomer (R)-NNN was weakly active, but synergistically enhanced the carcinogenicity of (S)-NNN. Thus, (S)-NNN is identified for the first time as a strong oral cavity carcinogen in smokeless tobacco products and should be significantly reduced or removed from these products without delay in order to prevent debilitating and deadly oral cavity cancer in people who use them.