Dose-response study of the carcinogenicity of tobacco-specific N-nitrosamines in F344 rats

Nicotine, Humectants, and Tobacco-Specific Nitrosamines (TSNAs) in IQOS Heated Tobacco Products (HTPs): A Cross-Country Study

Heated Tobacco Products (HTPs) purport to reduce exposure to tobacco-related toxicants compared to combustible cigarettes. This cross-sectional study examined the content of nicotine, two humectants (propylene glycol (PG) and vegetable glycerin (VG)), and four tobacco-specific nitrosamines (TSNAs: NNN, NNK, NAT, and NAB) in the tobacco filler of a popular HTP brand (IQOS). Non-menthol and menthol IQOS sticks were purchased from nine countries between 2017 and 2020 and were classified into two versions ("Bold" and "Light") using Philip Morris's flavor descriptors. The average nicotine concentration was 4.7 ± 0.5 mg/stick, and the highest nicotine concentration was found in products from Japan (5.1 ± 0.2 mg/stick). VG was the dominant humectant found in all sticks, with an average concentration of (31.5 ± 2.3 mg/stick). NNN, NNK, and NAT were substantially higher in the "Bold" sticks than the "Light" sticks. Significant differences between countries for TSNAs were also observed: the NAT and NAB contents were the highest in the "Light" products from Canada (192.5 ± 24.1 and 22.9 ± 1.0 ng/stick, respectively); the NNK concentration was the highest in the "Bold" products from Poland (64.8 ± 7.9 ng/stick); and the highest NNN concentrations were observed in the "Bold" products from South Africa (488.9 ± 26.7 ng/stick). As NNN and NNK are known human carcinogens, and as humectants like PG and VG can degrade into toxic carbonyl compounds upon heating, monitoring the concentration of these chemicals in HTPs is important for protecting users' health and ensuring compliance with regulations.

A chemometric experimental design with three-step stacking capillary electrophoresis for analysis of five tobacco-specific nitrosamines in cigarette products

Tobacco-specific nitrosamines (TSNAs) as carcinogens endanger our health and life from cigarette products. However, the safe range of TSNAs levels in commercial cigarette products has not yet been established. For the purpose of safety and supervision, a three-step stacking approach including field amplified sample injection (FASI), sweeping, and analyte focusing by micelle collapse (AFMC), was developed for the simultaneous determination of five TSNAs levels in cigarette products. This approach also involved aspects of chemometric experimental design, including fractional factorial design and central composite design. After the multilevel optimization of the experimental design, the five TSNAs were well separated. The LOD (S/N = 3) values of the N´-nitrosonornicotine (NNN), N´-nitrosoanatabine (NAT), N´-nitrosoanabasine (NAB), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in the FASI-sweeping-AFMC CE approach were 1.000 ng/mL, 0.500 ng/mL, 0.125 ng/mL, 1.000 ng/mL, and 0.500 ng/mL respectively. The results of relative standard deviation (RSD) and relative error (RE) were all less than 3.35%, demonstrating good precision and accuracy. Finally, this novel approach was further applied to monitor three commercial cigarette products, and a range of 250.1-336.6 ng/g for NNN, 481.6-526.7 ng/g for NAT, 82.2-247.6 ng/g for NAB, 167.7-473.7 ng/g for NNAL, and 39.4-246.7 ng/g for NNK could be observed among these. Based on these results, the novel CE stacking strategy was successfully applied for the analysis of five TSNAs levels in cigarette products and could serve as a tool for assays of quality control of nitrosamines.

The Effect of Tobacco Smoke N-Nitrosamines, NNK and NDEA, and Nicotine, on DNA Mismatch Repair Mechanism and miRNA Markers, in Hypopharyngeal Squamous Cell Carcinoma: An In Vivo Model and Clinical Evidence

Deregulation of the DNA mismatch repair (MMR) mechanism has been linked to poor prognosis of upper aerodigestive tract cancers. Our recent in vitro data have provided evidence of crosstalk between deregulated miRNAs and MMR genes, caused by tobacco smoke (TS) N-Nitrosamines, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), in hypopharyngeal cells. Here, we explored whether chronic exposure to TS components can affect MMR mechanism and miRNA profiles in hypopharyngeal mucosa. Using a mouse model (C57Bl/6J wild type) of in vivo 14-week exposure to NNK (0.2 mmol/L) and N-Nitrosodiethylamine (NDEA; 0.004 mmol/L), with or without nicotine (0.02 μmol/L), we provide direct evidence that TS components can promote dysplasia, significant downregulation of Msh2 and Mlh1 genes and deregulation of miR-21, miR-155, miR-34a, and miR-451a. By analyzing eight human specimens from tobacco smokers and eight controls, we provide clinical evidence of a significant reduction in hMSH2 and hMLH1 mRNAs in hypopharyngeal squamous cell carcinoma (HSCC). In summary, deregulation of the MMR mechanism and miRNAs is caused by chronic exposure to TS-related N-Nitrosamines, with or without nicotine, in the early stages of upper aerodigestive tract carcinogenesis, and can also be detected in human HSCC. Thus, we encourage future studies to further elucidate a possible in vivo dose-dependent effect of individual or combined N-Nitrosamines, NNK and/or NDEA, and nicotine, on the MMR mechanism and their clinical testing to elaborate prognosis and risk assessment.

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.

Noxious Combination of Tobacco Smoke Nitrosamines with Bile, Deoxycholic Acid, Promotes Hypopharyngeal Squamous Cell Carcinoma, via NFκB, In Vivo

Tobacco smoking is the most known risk factor for hypopharyngeal cancer. Bile reflux has recently been documented as an independent risk factor for NFκB-mediated hypopharyngeal squamous cell carcinoma. However, the carcinogenic effect of tobacco smoke on the hypopharynx and its combination with bile has not yet been proven by direct evidence. We investigated whether in vivo chronic exposure (12-14 weeks) of murine (C57Bl/6J) hypopharyngeal epithelium to tobacco smoke components (TSC) [N-nitrosamines; 4-(N-Methyl-N-Nitrosamino)-1-(3-pyridyl)-1-butanone (0.2 mmol/L), N-nitrosodiethylamine (0.004 mmol/L)], as the sole drinking fluid 5 days per week, along with topically applied (two times/day) bile [deoxycholic acid (0.28 mmol/L)], can accelerate a possible TSC-induced neoplastic process, by enhancing NFκB activation and the associated oncogenic profile, using histologic, IHC, and qPCR analyses. We provide direct evidence of TSC-induced premalignant lesions, which can be exacerbated by the presence of bile, causing invasive carcinoma. The combined chronic exposure of the hypopharynx to TSC with bile causes advanced NFκB activation and profound overexpression of Il6, Tnf, Stat3, Egfr, Wnt5a, composing an aggressive phenotype. We document for the first time the noxious combination of bile with a known risk factor, such as tobacco smoke nitrosamines, in the development and progression of hypopharyngeal cancer, via NFκB, in vivo. The data presented here encourage further investigation into the incidence of upper aerodigestive tract cancers in smokers with bile reflux and the early identification of high-risk individuals in clinical practice. This in vivo model is also suitable for large-scale studies to reveal the nature of inflammatory-associated aerodigestive tract carcinogenesis and its targeted therapy.

PREVENTION RELEVANCE

Early assessment of bile components in refluxate of tobacco users can prevent the chronic silent progression of upper aerodigestive tract carcinogenesis. This in vivo model indicates that bile reflux might have an additive effect on the tobacco-smoke N-nitrosamines effect and could be suitable for large-scale studies of diagnostic and therapeutic interventions.

Determination of 4-(Methylnitrosamino)-1-(3-Pyridyl)-1-Butanone (NNK) arising from tobacco smoke in airborne particulate matter

The most important tobacco-specific nitrosamine found in cigarette smoke and formed in ageing smoke after cigarettes are extinguished is 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). It is formed from nitrosation of nicotine, under particular conditions both in indoor and outdoor environments. NNK has been classified as a potent lung carcinogen which is expected to be found primarily in the particle-phase and to be stable in particulate matter. In this study tests have been carried out to show that a bisulfate-treated filter is more efficient than an untreated filter to collect both nicotine and NNK, and that the latter is stable in outdoor particulate matter. To characterize NNK in the outdoor environment, airborne samples were collected from 11 cities in USA, UK, Hong Kong and Malta with characteristics varying from low to high population densities and from urban to suburban to rural, and with desert characteristics and distinct climates. It has been shown that airborne particle + gas phase nicotine and particle-phase NNK behave in a linearly correlated manner. A seasonal analysis was carried out on a subset of data available from five sites in California, where the load of NNK in PM10 is driven by long range transport of the air masses passing over densely populated cities. In the winter season, the load of NNK in PM is higher than in summer in a statistically significant manner. The contamination of PM with NNK shows variability, but is observed at all sites. This paper highlights the potential risk of chronic exposure to NNK in particulate matter by the inhalation pathway.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone-Induced Histone Acetylation via α7nAChR-Mediated PI3K/Akt Activation and Its Impact on γ-H2AX Generation

A typical tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is known as a strong carcinogen. We previously reported that metabolized NNK induced histone H2AX phosphorylation (γ-H2AX), a DNA damage-induced histone modification. In this study, we found that NNK globally acetylated histone H3, which affected γ-H2AX generation. Human lung adenocarcinoma A549 was treated with several doses of NNK. NNK induced dose-dependent global histone H3 acetylation (Ac-H3), at 2 to 12 h after the treatment, independent of the cell cycle. The Ac-H3 pattern was not affected by CYP2A13 overexpression unlike γ-H2AX, indicating no requirement of NNK metabolism to induce Ac-H3. Immunofluorescence staining of Ac-H3 was uniform throughout the nucleus, whereas γ-H2AX was formed as foci and did not coincide with Ac-H3. Nicotinic receptor antagonist methyllycaconitine inhibited Ac-H3 and also γ-H2AX. Phosphoinositide-3-kinase (PI3K)/Akt inhibitors, LY294002, wortmannin, and GSK690693, also suppressed both Ac-H3 and γ-H2AX, whereas KU-55933, an inhibitor of ataxia telangiectasia mutated (ATM) upstream of γ-H2AX, inhibited γ-H2AX but not Ac-H3. These results suggested that binding of NNK to the nicotinic acetylcholine receptor (α7nAChR) activated the PI3K/Akt pathway, resulting in Ac-H3. The activated pathway leading to Ac-H3 enhanced γ-H2AX, suggesting that NNK-induced DNA damage is impacted by the α7nAChR-mediated signal transduction pathway.

Tobacco-Specific Nitrosamines in the Tobacco and Mainstream Smoke of Commercial Little Cigars

Cigars are among the broad variety of tobacco products that have not been as extensively studied and characterized as cigarettes. Small cigars wrapped in a tobacco-containing sheet, commonly referred to as little cigars, are a subcategory that are similar to conventional cigarettes with respect to dimensions, filters, and overall appearance. Tobacco-specific nitrosamines (TSNAs) are carcinogens in the tobacco used in both little cigars and cigarettes. This study uses a validated high-performance liquid chromatography-electrospray tandem mass spectrometry (LC-MS/MS) method to measure the TSNAs 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) in the tobacco filler and the nonintense International Organization for Standardization smoking regimen, ISO 3308, and the newer ISO 20778 Cigarette Intensive (CI) smoking regimen mainstream smoke of 60 commercial little cigars. Tobacco filler NNK and NNN quantities ranged from 26 to 2950 and 1440 to 12 100 ng/g tobacco, respectively. NNK and NNN by the ISO nonintense smoking regimen ranged from 89 to 879 and 200 to 1540 ng/cigar, respectively; by the CI regimen, NNK and NNN ranged from 138 to 1570 and 445 to 2780 ng/cigar, respectively. The average transfer (%) for NNK and NNN from tobacco filler to mainstream smoke was 24% and 36% by the ISO nonintense and CI smoking regimens, respectively. By the ISO nonintense and CI smoking regimens, mainstream smoke NNK and NNN yields showed a moderate to strong correlation (ISO nonintense, R2 = 0.60-0.68, p < 0.0001; CI, R2 = 0.78-0.81, p < 0.0001) with tobacco filler NNK and NNN quantities. In addition, the mainstream smoke NNK and NNN yields of little cigars were determined to be 3- to 5-fold higher compared to previously tested commercial cigarettes. The mainstream smoke NNK and NNN yields have wide variation among commercial little cigars and suggest that, despite design similarities to cigarettes, machine-smoke yields of carcinogenic TSNAs are higher in little cigars.

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.

Innovative Approaches for Estimating the Levels of Tobacco-Specific Nitrosamines in Cured Tobacco Samples

Tobacco-specific nitrosamines (TSNAs), mainly the 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), are known carcinogens. Part of the NNK found in smoke is provided from matrix-bound NNK, and its determination is extremely relevant. However, the reference extraction procedure of matrix-bound NNK is time-consuming and labor-intensive and has a limited analytical capacity. Three different methodologies were proposed to predict matrix-bound NNK: simple linear regression (LR) with soluble NNK; multiple linear regression (MLR) considering soluble NNK and characteristic parameters of the samples; and orthogonal partial least-squares (O-PLS) regression using high-throughput screening by flow injection analysis coupled to high-resolution mass spectrometry (HTS-FIA-HRMS) data. Simple linear regression showed a high influence of matrix and leaf origin. Although an existing linearity trend has been observed ( R2 = 0.62) for the global model, higher correlation values were achieved for matrix and country segregation models. Multiple linear regression predicted matrix-bound NNK with more satisfactory efficiency than simple linear regression models. The coefficients of determination were 0.87 and 0.94 for flue-cured Virginia and air-cured Burley, respectively. However, this method has a limited application, since previous information about the sample is required. The proposed method based on HTS-FIA-HRMS and O-PLS has shown the most suitable performance in the prediction of matrix-bound NNK, with errors comparable to the reference method, and a higher throughput. In addition, this approach allows to determine other soluble nitrosamines, namely N'-nitrosoanatabine, N'-nitrosoanabasine, and N-nitrosonornicotine, with relative percentage errors between 5.25 and 11.98%. Therefore, the third approach is the best method for a large number of cured tobacco for accuracy in determination of TSNAs.

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.

Cigarette Filter Ventilation and its Relationship to Increasing Rates of Lung Adenocarcinoma

The 2014 Surgeon General's Report on smoking and health concluded that changing cigarette designs have caused an increase in lung adenocarcinomas, implicating cigarette filter ventilation that lowers smoking machine tar yields. The Food and Drug Administration (FDA) now has the authority to regulate cigarette design if doing so would improve public health. To support a potential regulatory action, two weight-of-evidence reviews were applied for causally relating filter ventilation to lung adenocarcinoma. Published scientific literature (3284 citations) and internal tobacco company documents contributed to causation analysis evidence blocks and the identification of research gaps. Filter ventilation was adopted in the mid-1960s and was initially equated with making a cigarette safer. Since then, lung adenocarcinoma rates paradoxically increased relative to other lung cancer subtypes. Filter ventilation 1) alters tobacco combustion, increasing smoke toxicants; 2) allows for elasticity of use so that smokers inhale more smoke to maintain their nicotine intake; and 3) causes a false perception of lower health risk from "lighter" smoke. Seemingly not supportive of a causal relationship is that human exposure biomarker studies indicate no reduction in exposure, but these do not measure exposure in the lung or utilize known biomarkers of harm. Altered puffing and inhalation may make smoke available to lung cells prone to adenocarcinomas. The analysis strongly suggests that filter ventilation has contributed to the rise in lung adenocarcinomas among smokers. Thus, the FDA should consider regulating its use, up to and including a ban. Herein, we propose a research agenda to support such an effort.

Tobacco-Specific Nitrosamines in the Tobacco and Mainstream Smoke of U.S. Commercial Cigarettes

Tobacco-specific nitrosamines (TSNAs) are N-nitroso-derivatives of pyridine-alkaloids (e.g., nicotine) present in tobacco and cigarette smoke. Two TSNAs, N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), are included on the Food and Drug Administration's list of harmful and potentially harmful constituents (HPHCs) in tobacco products and tobacco. The amounts of four TSNAs (NNK, NNN, N-nitrosoanabasine (NAB), and N'-nitrosoanatabine (NAT)) in the tobacco and mainstream smoke from 50 U.S. commercial cigarette brands were measured from November 15, 2011 to January 4, 2012 using a validated HPLC/MS/MS method. Smoke samples were generated using the International Organization of Standardization (ISO) and Canadian Intense (CI) machine-smoking regimens. NNN and NAT were the most abundant TSNAs in tobacco filler and smoke across all cigarette brands, whereas NNK and NAB were present in lesser amounts. The average ratios for each TSNA in mainstream smoke to filler content is 29% by the CI smoking regimen and 13% for the ISO machine-smoking regimen. The reliability of individual TSNAs to predict total TSNA amounts in the filler and smoke was examined. NNN, NAT, and NAB have a moderate to high correlation (R2 = 0.61-0.98, p < 0.0001), and all three TSNAs individually predict total TSNAs with minimal difference between measured and predicted total TSNA amounts (error < 7.4%). NNK has weaker correlation (R2 = 0.56-0.82; p < 0.0001) and is a less reliable predictor of total TSNA quantities. Tobacco weight and levels of TSNAs in filler influence TSNA levels in smoke from the CI machine-smoking regimen. In contrast, filter ventilation is a major determinant of levels of TSNAs in smoke by the ISO machine-smoking regimen. Comparative analysis demonstrates substantial variability in TSNA amounts in tobacco filler and mainstream smoke yields under ISO and CI machine-smoking regimens among U.S. commercial cigarette brands.

Tobacco carcinogen induces both lung cancer and non-alcoholic steatohepatitis and hepatocellular carcinomas in ferrets which can be attenuated by lycopene supplementation

Early epidemiologic studies have reported that tobacco smoking, which is causally associated with liver cancer, is an independent risk factor for non-alcoholic fatty liver diseases (NAFLD). Lycopene from tomatoes has been shown to be a potential preventive agent against NAFLD and hepatocellular carcinoma (HCC). In the present study, we investigated whether the tobacco carcinogen 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) induces lesions in both lungs and livers of ferrets with or without lycopene intervention. Male ferrets (6 groups, n = 8-10) were treated either with NNK (50 mg/kg BW, i.p., once a month for four consecutive months) or saline with or without dietary lycopene supplementation (2.2 and 6.6 mg/kg BW/day, respectively) for 26 weeks. Results demonstrate that NNK exposure results in higher incidences of lung tumors, HCC and steatohepatitis (which is characterized by severe inflammatory cell infiltration with concurrent fat accumulation in liver, hepatocellular ballooning degeneration and increased NF-κB expression), as well as elevations in bilirubin and AST levels in ferrets. Lycopene supplementation at two doses prevented NNK-induced expressions of α7 nicotinic acetylcholine receptor in the lung and NF-κB and CYP2E1 in the liver and attenuated the NNK-induced mortality and pathological lesions in both the lungs and livers of ferrets. The present study provided strong experimental evidence that the tobacco carcinogen NNK can induce both HCC and steatohepatitis in the ferrets and can be a useful model for studying tobacco carcinogen-associated NAFLD and liver cancer. Furthermore, lycopene could provide potential benefits against smoke carcinogen-induced pulmonary and hepatic injury.

Association between Glucuronidation Genotypes and Urinary NNAL Metabolic Phenotypes in Smokers

BACKGROUND

The most abundant and potent carcinogenic tobacco-specific nitrosamine in tobacco and tobacco smoke is 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). In vivo, NNK is rapidly metabolized to both the (R)- and (S)-enantiomers of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), which possesses similar carcinogenic properties as NNK. The major detoxification pathway for both NNAL enantiomers is glucuronidation by UDP-glucuronosyltransferase (UGT) enzymes including UGT2B10 and UGT2B17. The goal of the present study was to directly examine the role of UGT genotypes on urinary levels of NNAL glucuronides in smokers.

METHODS

NNAL-N-Gluc, (R)-NNAL-O-Gluc, (S)-NNAL-O-Gluc, and free NNAL were simultaneously and directly quantified in the urine of smokers by LC/MS analysis. Genotypes were determined by TaqMan assay using genomic DNA.

RESULTS

The functional knockout polymorphism in the UGT2B10 gene at codon 67 (Asp>Tyr) was significantly (P < 0.0001) associated with a 93% decrease in creatinine-adjusted NNAL-N-Gluc. The polymorphic whole-gene deletion of the UGT2B17 gene was associated with significant (P = 0.0048) decreases in the levels of creatinine-adjusted (R)-NNAL-O-Gluc, with a 32% decrease in the levels of urinary (R)-NNAL-O-Gluc/(S)-NNAL-O-Gluc among subjects with the UGT2B17 (*2/*2) genotype as compared to subjects with the UGT2B17 (*1/*1) genotype.

CONCLUSIONS

These results suggest that functional polymorphisms in UGT2B10 and UGT2B17 are associated with a reduced detoxification capacity against NNAL and may therefore affect individual cancer risk upon exposure to tobacco.

IMPACT

This is the first report to clearly demonstrate strong genotype-phenotype associations between both the UGT2B10 codon 67 Asp<Tyr genotype and urinary NNAL-N-Gluc levels and between the UGT2B17 copy number variant and urinary (R)-NNAL-O-Gluc levels in smokers. Cancer Epidemiol Biomarkers Prev; 25(7); 1175-84. ©2016 AACR.

Assessing exposure to tobacco-specific carcinogen NNK using its urinary metabolite NNAL measured in US population: 2011-2012

Carcinogenic tobacco-specific nitrosamines (TSNAs) such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) are found only in tobacco and derived products. Food and Drug Administration of the United States (US FDA) lists NNK as one of the 93 harmful and potentially harmful constituents (HPHCs) found in tobacco products and tobacco smoke. The aim of this study was to use the urinary concentration of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), a major metabolite of NNK, to quantitatively estimate exposure to NNK in the US general population. In 2011-2012, the Centers for Disease Control and Prevention's National Health and Nutrition Examination Survey (NHANES) collected urine and serum samples from a representative sample of US residents. We used a serum cotinine cutoff of 10 ng/ml with combination of questionnaire data to select non-users from cigarette users and used self-reported data to determine different tobacco product user groups. We estimated the absorbed total daily dose of NNK using a probabilistic method based on a two-compartment model. The geometric mean (GM) for the daily dose of NNK among smokers aged 12-16 years was significantly higher than that for non-users at the same age stage exposed to second-hand smoke (SHS) (P<0.001). Among those exposed to SHS, the GM for daily dose of NNK in young children (6-11 years) was nearly three times of those for adults in the age range 21-59 years. Among cigarette users, non-Hispanic Whites had the highest NNK daily dose and Mexican Americans had the lowest levels. Exclusive snuff or chewing product users had significantly higher daily dose of NNK than did cigarette smokers. Our study found that the maximum daily dose of NNK for children aged from 6 to 11 years and that for a significant percentage of cigarette users, chewing product and snuff users were higher than an estimated provisional "reference" risk level.

Serum-based protein biomarkers for detection of lung cancer

Lung cancer is one of the most common cancers in terms of both incidence and mortality.The major reasons for the increasing number of deaths from lung cancer are late detection and lack of effective therapies. To improve our understanding of lung cancer biology, there is urgent need for blood-based, non-invasive molecular tests to assist in its detection in a cost-effective manner at an early stage when curative interventions are still possible. Recent advances in proteomic technology have provided extensive, high throughput analytical tools for identification, characterization and functional studies of proteomes. Changes in protein expression patterns in response to stimuli can serve as indicators or biomarkers of biological and pathological processes as well as physiological and pharmacological responses to drug treatment, thus aiding in early diagnosis and prognosis of disease. However, only a few biomarkers have been approved by the FDA to date for screening and diagnostic purposes. This review provides a brief overview of currently available proteomic techniques, their applications and limitations and the current state of knowledge about important serum biomarkers in lung cancer and their potential value as prognostic and diagnostic tools.

Quantitative analysis of five tobacco-specific N-nitrosamines in urine by liquid chromatography-atmospheric pressure ionization tandem mass spectrometry

A liquid chromatography tandem mass spectrometry (LC/MS/MS) method was developed and validated for the determination of five total tobacco-specific N-nitrosamines (TSNA), including free and conjugated forms in urine. The limits of detection for 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol, N'-nitrosonornicotine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, N'-nitrosoanatabine and N'-nitrosoanabasine were 0.6, 0.6, 10.0, 0.4 and 0.4 pg/mL, respectively, with a linear calibration range of up to 20,000 pg/mL. Intra- and inter-day precision for TSNA measurements ranged from 0.82 to 3.67% and from 2.04 to 7.73% respectively. For total TSNAs, the β-glucuronidase amount was optimized for hydrolysis time and yield. Different liquid chromatography columns and mobile phases with different pH conditions were evaluated. The validated method was then applied to 50 smoker and 30 nonsmoker urine samples. Our results suggest that this sensitive and relatively simple analytical method is suitable for application to epidemiological investigations of health risks associated with the exposure to tobacco smoke or secondhand smoke in both smokers and nonsmokers.

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.

A non-surgical method for induction of lung cancer in Wistar rats using a combination of NNK and high dietary fats

Lung cancer is one of the most common malignant neoplasms all over the world. Smoking and a number of constituents of tobacco are responsible for development of lung tumours; however, the deleterious effects of tobacco-derived carcinogen, nitrosamine 4-(methylnitrosoamino)-1-(3-pyridyl)-1-butanone (nicotine-derived nitrosamine ketone (NNK)) remain unmatched. We report the development of a novel rodent model by administering multiple doses of NNK to male Wistar rats and feeding them with high-fat and low-protein diet. Tumour cells in lungs were observed in approximately 98 % rats after 8 months of NNK treatment, as evident by histopathological analysis. This rodent model showed slow progression of lung tumours which has helped us to assess early indicators of oxidative damage in lungs by studying the levels of lipid peroxidation and antioxidant parameters. LPO was elevated by 46.94 %, SOD, CAT, GSH and GR activity was decreased by 48.67 %, 22.04 %, 21.46 % and 20.85 %, respectively in serum of NNK treated rats when compared with control. These findings suggest that increased oxidative stress can represent a risk factor for the development of chronic disease in early future. This new animal model is an attempt to greatly facilitate studies of the pathophysiology, biochemistry and therapy of lung cancer.

Mechanisms for nicotine in the development and progression of gastrointestinal cancers

Long-term smoking is major risk factor for a variety of cancers, including those of the gastrointestinal (GI) tract. Historically, nicotine and its derivatives are well known for their role in addiction, and have more recently been documented for their carcinogenic role in a number of human cancers. The cellular and molecular pathways activated by nicotine mimic physiological and environmental carcinogenesis in cancers throughout the GI tract potentiating cancer growth and/or inducing the formation of cancer on their own. Thus, it is important to unlock the carcinogenic mechanisms induced by nicotine in these systems, and underscore nicotine's potential as an environmental hazard. This review outlines the specific pathways demonstrated to mediate nicotine's carcinogenic mechanism in the GI tract. The abundance of cell and animal evidence calls for increased epidemiologic and case-control evaluation of nicotine's role in cancer.

Development of a method for the determination of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol in urine of nonsmokers and smokers using liquid chromatography/tandem mass spectrometry

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) is an efficient biomarker of tobacco-specific carcinogen 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). The ability to monitor biomarker concentrations is very important in understanding potential cancer risk. An analytical method using molecularly imprinted polymer (MIP) column coupled with liquid chromatography/tandem mass spectrometry (LC-MS/MS) for the determination of total NNAL in human urine was developed and validated. The combination of MIP column extraction and LC-MS/MS can provide a high sensitive and relatively simple analytical method. The limit of detection (LOD) was 0.30 pg/ml and analysis time was 6min. The method has been applied to urine samples of 36 nonsmokers and 207 smokers. NNAL was found to be significantly higher in the urine of smokers compared with nonsmokers. Compared with smokers with blended cigarettes, Chinese virginia cigarettes smokers had low urinary NNAL levels. There was a direct association between the 24-h mouth-level exposure of carcinogen NNK from cigarette smoking and the concentration of NNAL in the urine of smokers. However, there was not a positive correlation between urinary total NNAL levels in 24 h and tar. Total urinary NNAL is a valuable biomarker for monitoring exposure to carcinogenic NNK in smokers and in nonsmokers. A prediction model of cigarette smoke NNK and urinary average NNAL levels in 24 h was established (y=2.8987x-245.38, r²=0.9952, n=204).

A novel application of the Margin of Exposure approach: segregation of tobacco smoke toxicants

This paper presents a rationale for utilising a Margin of Exposure (MOE) approach to the segregation of tobacco smoke toxicants for risk assessment and management purposes. Future regulatory frameworks and product modifications aimed at tobacco harm reduction could utilise data that segregate toxicants using associations with specific diseases caused by cigarette smoking together with an indication of their relative contribution to that disease. Compounds with MOEs >10,000 accompanied by appropriate narrative are considered "low priority for risk management actions". This paper applies the MOE model to representative examples of tobacco smoke toxicants associated with respiratory tract carcinogenesis and other respiratory diseases. A multiplicity of published dose response data on individual toxicants has been used to determine the range of possible MOE values, thus demonstrating the consistency of the relationships. Acetaldehyde, acrolein, acrylonitrile, cadmium, ethylene oxide, formaldehyde and isoprene all segregate with MOEs <10,000 and should be considered as high priority for exposure reduction research whereas benzo(a)pyrene and vinyl chloride segregate with an MOE >10,000 and therefore may be considered as a low priority. 1,3-Butadiene, m-/p-cresols, NNK and NNN are assumed to segregate with high priority although additional data would be required to complete a full MOE assessment.

Lung cancer and environmental chemical exposure: a review of our current state of knowledge with reference to the role of hormones and hormone receptors as an increased risk factor for developing lung cancer in man

Lung cancer is a dominant cause of cancer mortality. The etiology of lung cancer is mainly related to cigarette smoking, airborne genotoxic carcinogens, and arsenic, but its sex-specific incidence suggests that other mechanisms, such as hormones, may also be involved in the process of carcinogenesis. A number of agents commonly present in the living environment can have dual biological effects: not only are they genotoxic / carcinogenic, but they are also hormonally active as xenoestrogens. This dualism may explain sex-specific differences reported in both types and incidence of lung cancer. In a novel approach to investigate the complexity of lung cancer, etiology, including systems biology, will be used as a tool for a simultaneous interpretation of measurable environmental and biological parameters. Using this approach, the etiology of human lung cancer can be more thoroughly investigated using the available data from oncology and environmental health. The information gained could be applied in the introduction of preventive measures, in personalized medicine, and in more relevant legislation, which should be adjusted to reflect the current knowledge on the complex environmental interactions underlying this life-threatening disease.

Formation and distribution of NNK metabolites in an isolated perfused rat lung

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a lung-specific tobacco carcinogen. Metabolism is critical to its elimination given its lipophilic nature. Although NNK can be metabolized through detoxification pathways that safely eliminate it from the body, it can also be bioactivated, resulting in the formation of potentially carcinogenic DNA adducts. The isolated perfused rat lung (IPRL) system was used to determine the effect of NNK perfusate concentration (0.1 and 1.2 microM) on the formation and distribution of metabolites, the level of individual DNA adducts, and total covalent binding in the lung. Coadministration of the chemopreventive agent phenethyl isothiocyanate (PEITC; 20 microM) was also examined to determine its effect on NNK metabolism. NNK was readily metabolized in the IPRL system. In the 0.1 muM perfusions approximately 55% of metabolites formed were through detoxification pathways, whereas roughly 30% were the result of bioactivation pathways. An increase in NNK concentration increased the percentage of unmetabolized NNK and decreased the apparent metabolic clearance in the lung, but the metabolite profiles remained similar between concentrations. The addition of PEITC reduced the formation of oxidative metabolites and increased 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) formation and the percentage of unmetabolized NNK. PEITC also significantly decreased the formation of DNA adducts in the lung tissue. The level of O(2)-[4-(3-pyridyl)-4-oxobut-1-yl]thymidine (O(2)-POB-dThd) and O(6)-[4-(3-pyridyl)-4-oxobut-1-yl]-2'-deoxyguanosine (O(6)-POB-dGuo) decreased by 70 to 75%, and that of O(6)-methylguanine (O(6)-methyl-Gua) and 7-[4-(3-pyridyl)-4-oxobut-1-yl]guanine (7-POB-Gua) decreased by 40 to 45%. Pyridylhydroxybutyl-DNA adducts were not detected in any of the treatment groups. Thus, the IPRL system is useful in determining pulmonary metabolism and DNA adduct formation separate from other metabolizing organs.

Identification of adducts formed in the reactions of 5'-acetoxy-N'-nitrosonornicotine with deoxyadenosine, thymidine, and DNA

N'-Nitrosonornicotine (NNN) is the most prevalent of the carcinogenic tobacco-specific nitrosamines found in all tobacco products. Previous studies have demonstrated that cytochrome P450-mediated 5'-hydroxylation of NNN is a major metabolic pathway leading to mutagenic products, but to date, DNA adducts formed by this pathway have been only partially characterized, and there have been no studies reported on adducts formed with bases other than dGuo. Because adducts with dAdo and dThd have been identified in the DNA of the livers of rats treated with the structurally related carcinogen N-nitrosopyrrolidine, we investigated dAdo and dThd adduct formation from 5'-acetoxyNNN (3), a stable precursor to 5'-hydroxyNNN (2). Reaction of 3 with dAdo gave diastereomeric products, which were identified by their spectral properties and LC-ESI-MS/MS-SRM analysis as N(6)-[5-(3-pyridyl)tetrahydrofuran-2-yl]dAdo (9). This adduct was further characterized by NaBH(3)CN reduction to N(6)-[4-hydroxy-4-(3-pyridyl)but-1-yl]dAdo (17). A second dAdo adduct was identified, after NaBH(3)CN treatment, as 6-[2-(3-pyridyl)pyrrolidin-1-yl]purine-2'-deoxyriboside (18). Reaction of 3 with dThd, followed by NaBH(3)CN reduction, gave O(2)-[4-(3-pyridyl)-4-hydroxybut-1-yl]thymidine (11). Adducts 9, 11, 17, and 18 were all identified by LC-ESI-MS/MS-SRM comparison to synthetic standards. The reaction of 3 with calf thymus DNA was then investigated. The DNA was enzymatically hydrolyzed to deoxyribonucleosides, and the resulting mixture was treated with NaBH(3)CN and analyzed by LC-ESI-MS/MS-SRM. Adducts 11, 17, and 18, as well as the previously identified dGuo adducts, were identified. The results of this study provide a more comprehensive picture of DNA adduct formation by the quantitatively important 5'-hydroxylation pathway of NNN and will facilitate investigation of the presence of these adducts in laboratory animals treated with NNN or in people who use tobacco products.

Repair kinetics of specific types of nitroso-induced DNA damage using the comet assay in human cells

The comet assay is sensitive and can detect DNA damage frequencies less than 1 in 10(7) bases. We have previously shown that several types of DNA damage associated with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a tobacco-specific pro-mutagen, can be investigated with some specificity using this technique. Little is known about their repair. We verified the ability of the comet assay to quantify the repair kinetics of specific types of damage in normal fibroblasts, e.g., dimethylsulfate-induced 7-methylguanines (7-mG) and UVB-induced cyclobutane pyrimidine dimers. The time course, formation and repair, of DNA damage after acute doses of NNK reactive metabolites, were then compared in normal human cells (fibroblasts and lymphocytes) and in cells proficient for activating NNK (U937 and NCI-H23). NNK can be activated in cells into reactive metabolites that can either methylate or pyridyloxobutylate DNA. The 7-mG generated by methylation gave post-treatment patterns that were sufficiently different between cell types to conclude that repair of 7-mG in U937 cells was fast, repair in lymphocytes was slow, and repair in NCI-H23 cells and fibroblasts displayed intermediate rates. Pyridyloxobutylation generated formamidopyrimidine (fapy) glycosylase (fpg)-sensitive sites that could be the fapy form of 7-pyridyloxobutylguanines produced in cells. For this type of adducts, the post-treatment patterns of adduct frequency as a function of time depended even more clearly on the cell type: fibroblasts and NCI-H23 cells showed an initial rapid increase in fpg-sensitive damage frequency that did not occur in lymphocytes and U937 cells. This increase seemed associated with p53 proficiency in fibroblasts. Our results show that repair kinetics can be investigated with the comet assay and that differences between cell types can be observed with that technique. But it seems that pro-mutagen activation and/or the way a type of adducts is formed can affect the quantification of the repair.

Induction of lung lesions in Wistar rats by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and its inhibition by aspirin and phenethyl isothiocyanate

Background

The development of effective chemopreventive agents against cigarette smoke-induced lung cancer could be greatly facilitated by suitable laboratory animal models, such as animals treated with the tobacco-specific lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). In the current study, we established a novel lung cancer model in Wistar rats treated with NNK. Using this model, we assessed the effects of two chemopreventive agents, aspirin and phenethyl isothiocyanate (PEITC), on tumor progression.

Methods

First, rats were treated with a single-dose of NNK by intratracheal instillation; control rats received iodized oil. The animals were then sacrificed on the indicated day after drug administration and examined for tumors in the target organs. PCNA, p63 and COX-2 expression were analyzed in the preneoplastic lung lesions. Second, rats were treated with a single-dose of NNK (25 mg/kg body weight) in the absence or presence of aspirin and/or PEITC in the daily diet. The control group received only the vehicle in the regular diet. The animals were sacrificed on day 91 after bronchial instillation of NNK. Lungs were collected and processed for histopathological and immunohistochemical assays.

Results

NNK induced preneoplastic lesions in lungs, including 33.3% alveolar hyperplasia and 55.6% alveolar atypical dysplasia. COX-2 expression increased similarly in alveolar hyperplasia and alveolar atypical dysplasia, while PCNA expression increased more significantly in the latter than the former. No p63 expression was detected in the preneoplastic lesions. In the second study, the incidences of alveolar atypical dysplasia were reduced to 10%, 10% and 0%, respectively, in the aspirin, PEITC and aspirin and PEITC groups, compared with 62.5% in the carcinogen-treated control group. COX-2 expression decreased after dietary aspirin or aspirin and PEITC treatment. PCNA expression was significantly reduced in the aspirin and PEITC group.

Conclusion

(1) A single dose of 25 mg/kg body weight NNK by intratracheal instillation is sufficient to induce preneoplastic lesions in Wistar rat lungs. (2) COX-2 takes part in NNK-induced tumorigenesis but is not involved in proliferation. (3) Aspirin and PEITC have protective effects in the early stages of tumor progression initiated by NNK.

Kinetics of O(6)-methyl-2'-deoxyguanosine repair by O(6)-alkylguanine DNA alkyltransferase within K-ras gene-derived DNA sequences

O(6)-Methyl-2'-deoxyguanosine (O(6)-Me-dG) is a potent mutagenic DNA adduct that can be induced by a variety of methylating agents, including tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). O(6)-Me-dG is directly repaired by the specialized DNA repair protein, O(6)-alkylguanine DNA alkyltransferase (AGT), which transfers the O(6)-alkyl group from the modified guanine to a cysteine thiol within the active site of the protein. Previous investigations suggested that AGT repair of O(6)-alkylguanines may be sequence-dependent as a result of flanking nucleobase effects on DNA conformation and energetics. In the present work, a novel high-performance/pressure liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-ESI+-MS/MS)-based approach was developed to analyze the kinetics of AGT-mediated repair of O(6)-Me-dG adducts placed at different sites within the double-stranded DNA sequence representing codons 8-17 of the K-ras protooncogene, 5'-G1TA G2TT G3G4A G5CT G6G7T G8G9C G10TA G11G12C AAG13 AG14T-3', where G5, G6, G7, G8, G9, G10, or G11 was replaced with O(6)-Me-dG. The second guanine of K-ras codon 12 (G7 in our numbering system) is a major mutational hotspot for G --> A transitions observed in lung tumors of smokers and in neoplasms induced in laboratory animals by exposure to methylating agents. O(6)-Me-dG-containing duplexes were incubated with human recombinant AGT protein, and the reactions were quenched at specific times. Following acid hydrolysis to release purines, isotope dilution HPLC-ESI-MS/MS was used to determine the amounts of O(6)-Me-G remaining in DNA. The relative extent of demethylation for O(6)-Me-dG adducts located at G5, G6, G7, G8, G9, G10, or G11 following a 10 s incubation with AGT showed little variation as a function of sequence position. Furthermore, the second-order rate constants for the repair of O(6)-Me-dG adducts located at the first and second positions of the K-ras codon 12 (5'-G6G7T-3') were similar (1.4 x 10(7) M(-1) s(-1) vs 7.4 x 10(6) M(-1) s(-1), respectively), suggesting that O(6)-Me-dG repair by AGT is not the determining factor for K-ras codon 12 mutagenesis following exposure to methylating agents. The new HPLC-ESI-MS/MS assay developed in this work is a valuable tool which will be used to further explore the role of local sequence environment and endogenous DNA modifications in shaping mutational spectra of NNK and other methylating agents.

Development of a quantitative liquid chromatography/electrospray mass spectrometric assay for a mutagenic tobacco specific nitrosamine-derived DNA adduct, O6-[4-Oxo-4-(3-pyridyl)butyl]-2'-deoxyguanosine

Liquid chromatography with electrospray tandem mass spectrometry (LC/ESI-MS/MS) was employed to quantify O6-[4-oxo-4-(3-pyridyl)butyl]-2'-deoxyguanosine (O6-pobdG), a mutagenic adduct formed by pyridyloxobutylating nitrosamines. Selected reaction monitoring (SRM) of the neutral loss of the sugar from protonated molecules of the adduct, [M + H - 116]+, was utilized for detection of O6-pobdG in pyridyloxobutylated DNA from both in vitro and in vivo sources. Quantitation was based on isotope dilution with synthetic O6-[1,2,2-2H3-4-oxo-4-(3-pyridyl)butyl]-2'-deoxyguanosine. The detection limits in this study were less than 5 fmol of pure standard and 50 fmol in 1.5 mg of DNA. This method was validated by comparing adduct levels measured with the LC/ESI-MS/MS method to those obtained with radiochemical methods in DNA alkylated with the model pyridyloxobutylating agent, [5-3H]4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanone ([5-3H]NNKOAc). The pyridyloxobutyl 2'-deoxyguanosine adduct coeluting with the deuterated standard disappeared when NNKOAc-treated DNA had been reacted with the repair protein, O6-alkylguanine-DNA alkyltransferase. This result confirms that the coeluting peak is solely O6-pobdG. Preliminary studies with liver DNA isolated from NNKOAc-treated mice demonstrated that this method can be used to quantify O6-pobG in DNA from in vivo sources. The improved sensitivity and specificity of adduct detection afforded by this LC/ESI-MS/MS method will allow us to explore the role of O6-pobdG in the toxicological properties of pyridyloxobutylating nitrosamines.

Environmental tobacco smoke in the workplace: markers of exposure, polymorphic enzymes and implications for disease state

Studies focusing directly on tobacco smoke have tended to center on the differences in effect between smokers and non-smokers and many hundreds of such studies have been performed. In this review, we examine the current literature specifically concerning workplace exposure to environmental tobacco smoke (ETS) and its impact on individuals, particularly non-smokers and never smokers. The paper deals with quantifying and minimizing ETS exposures in a working environment, the effect of polymorphisms and other genetic factors that influence health outcomes after exposure to ETS and the association of occupational ETS exposure to disease-specific biomarkers.

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

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

Induction of esophageal carcinogenesis by diethylnitrosamine and assessment of the promoting effect of ethanol and N-nitrosonornicotine: experimental model in mice

It is known that some nitrosamines preferably affect particular organs because of their organospecificity. Diethylnitrosamine (DEN) is one of the most powerful nitrosamines for experimentally inducing esophagus cancer. The present study aimed to evaluate the rate and type of epithelial lesions induced by DEN in mice. We also assessed the role of alcohol and N-nitrosonornicotine (NNN) as promoters of this carcinogenesis. A total of 208 female mice (Mus musculus) were allocated to five experimental groups: group 1, water only (controls); group 2, DEN + water; group 3, DEN + NNN; group 4, DEN + 6% alcohol solution; group 5, DEN + NNN + 6% alcohol solution. Animals in groups 2, 3, 4 and 5 received DEN (0.04 ml/l) three times per week, and during the following 4 days they received the other solutions. NNN was provided at a final concentration of 30 mg/l. The overall experimental period was 180 days. At the end of this time, the animals were killed and their esophagus was dissected for macro- and microscopic analysis. There was no significant difference in relation to the size of the esophagus and to the average DEN intake by the animals (p > 0.05). A statistically significant difference (p < 0.0001) was observed between controls and all other experimental groups. There was no significant difference among experimental groups treated with carcinogens (p > 0.05). The average incidence of cancer was 85.4%. The experimental model used in the present study is a very potent indicator of esophagus cancer. Owing to the high incidence for cancer observed in the present study, it was not possible to assess the effect of alcohol and NNN as inducers for the development of esophageal cancer.

DNA adduct formation from tobacco-specific N-nitrosamines

Tobacco-specific N-nitrosamines are a group of carcinogens derived from the tobacco alkaloids. They are likely causative factors for cancers of the lung, esophagus, pancreas, and oral cavity in people who use tobacco products. The most carcinogenic tobacco-specific nitrosamines in laboratory animals are 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), and N'-nitrosonornicotine (NNN). DNA adduct formation from NNK and NNN has been studied extensively and is reviewed here. NNK is metabolically activated by cytochromes P450 to intermediates which methylate and pyridyloxobutylate DNA. The resulting adducts have been detected in cells and tissues susceptible to NNK carcinogenesis in rodents. The methylation and pyridyloxobutylation pathways are both important in carcinogenesis by NNK. NNK also induces single strand breaks and increases levels of 8-oxodeoxyguanosine in DNA of treated animals. NNAL, which like NNK is a potent pulmonary carcinogen, is also metabolically activated to methylating and pyridyloxobutylating intermediates. NNN pyridyloxobutylates DNA in its rat target tissues, esophagus and nasal mucosa. Methyl and pyridyloxobutyl DNA adducts are detected in human tissues. The methyl adducts most likely result in part from exposure of smokers to NNK, but these adducts are also detected in non-smokers. Some of the methyl adducts detected in non-smokers may be due to environmental tobacco smoke exposure. There are also potential dietary and endogenous sources of these adducts. Pyridyloxobutyl DNA adducts in human tissues result mainly from exposure to tobacco-specific N-nitrosamines. In laboratory animals, DNA adduct formation and carcinogenicity of tobacco-specific N-nitrosamines are closely correlated in many instances, and it is likely that similar relationships will hold in humans.

Volatile nitrosamines and tobacco-specific nitrosamines in the smoke of Thai cigarettes: a risk factor for lung cancer and a suspected risk factor for liver cancer in Thailand

In Thailand, smoking of commercial cigarettes and of handmade cigarettes has drastically increased in recent decades. Cancer of the lung and of the upper aero-digestive tract have also increased in Thailand as they have in many other countries. It is our working hypothesis that the increase of primary cancer of the liver, especially of cholangiocarcinoma in the north-eastern provinces of Thailand is associated with the use of tobacco in men infested with the liver fluke Opisthorchis viverrini (OV). Bioassays have shown that volatile nitrosamines and tobacco-specific nitrosamines induce cholangiocarcinoma in laboratory animals and that the hepatocarcinogenic action of nitrosodimethylamine in hamsters is significantly increased by infestation with the liver fluke OV. The endogenous formation of nitrosamines is significantly increased by OV infestation. This report presents analytical data on the concentration of volatile nitrosamines and tobacco-specific nitrosamines in mainstream smoke of nine leading brands of commercially produced Thai cigarettes which represent approximately 85% of the market share in Thailand. Observed ranges (ng/cigarette) were 8.5-31.9 for nitrosodimethylamine, 8.8-49.6 for nitrosopyrrolidine and 4.2-18.9 for nitrosodi-n-butylamine. These values are exceptionally high compared with the smoke of light and blended cigarettes from North America and Western Europe. Among the tobacco-specific nitrosamines, the range was 28-730 for nitrosonornicotine and 16-370 for 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone. There was a correlation between volatile and tobacco-specific nitrosamines, and tar and nicotine deliveries in the mainstream smoke. The analytical data are in line with the rate for lung cancer and support our working hypothesis that nitrosamines, and especially the tobacco-specific nitrosamines, are associated with the increased risk for primary liver cancer among those Thai people who smoke cigarettes and also carry OV infestation.

A qualitative and quantitative risk assessment of snuff dipping

The presence of highly carcinogenic tobacco-specific nitrosamines (TSNA) in snuff has been a matter of serious concern. However, the levels of TSNA in such products may differ by orders of magnitude depending on origin and manner of processing, and the mere presence of such agents at low levels does hardly constitute a meaningful prerequisite for classifying all types of snuff as human carcinogens. Reviewing available epidemiological evidence, a wide discrepancy is found for estimated cancer risk associated with snuff dipping derived from on one hand previous investigations conducted in the United States and on the other from recent extensive Swedish epidemiological studies. In spite of the fact that approximately 20% of all grown-up Swedish males use moist snuff, it has not been possible to detect any significant increase in the incidence of cancer of the oral cavity or pharynx-the prevalence of which by international standards remains low in this country. Further, there is insufficient evidence for a causal link between the use of Swedish snuff and increased risk for cardiovascular disease. Dissimilarities in the content of TSNA in oral snuff products may represent one important reason for the different outcomes of the epidemiological surveys conducted in the United States and Sweden. Bioassays using pure TSNA in rodents appear to give exaggerated risk estimates for humans, a discrepancy that could be ascribed to species-related differences in the relation between exposure and DNA target dose and/or adduct repair rates, as well as to the presence of anticarcinogens in snuff. Although a small risk cannot be excluded, the use of smokeless tobacco products low in TSNA which now are available on the market entails a risk that at any rate is more than 10 times lower than that associated with active smoking. Nevertheless, due to the decisive role of potent TSNA in determining possible cancer risks in users of smokeless tobacco, and due to the fact that large variations in the concentrations may occur, adequate control measures should be taken to keep the levels of these nitrosamines in smokeless tobacco products as low as is technically feasible.

DNA damage in the nasal passageway: a literature review

The purpose of this review is to provide a compilation of work examining DNA damage in the nasal cavity. There are numerous methods to identify and quantify damage to DNA and the diversity of methods and toxicologic endpoints is illustrated by the range of studies presented here. There are a large number of independent studies measuring endpoints in the upper respiratory tract; however, with regard to toxicant induced DNA damage in the nasal passageway, the effects of two compounds, 4-(N-Methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and formaldehyde (HCHO), appear to have been extensively characterized. The body of work on NNK and formaldehyde have provided insights into molecular mechanisms of DNA damage and repair and induced cell replication and its relationship to nasal cancer. With new technologies and molecular techniques, the sensitivity to enable evaluations of the minute quantities of nasal tissue available in test species and human biopsy impact the study of the nasal-toxicant interactions. As methods used to characterize DNA damage increase in sensitivity, the importance of both exogenous and endogenous sources of DNA damage, steady-state levels of cellular damage, repair, and resulting mutations, low-dose exposure assessments and inter-species extrapolation will become increasingly complex. Additional studies of DNA damage in the nasal passage will undoubtedly challenge future estimations of risk and impact what are perceived to be acceptable levels of exposure to known and predicted carcinogens. The aim of this paper is to provide to the interested scientist literature relevant to the effects of agents on nasal DNA, so that areas of insufficient information can be identified and used to further develop and expand the knowledge base for nasal DNA toxicant interactions.

Risk factors for adrenal cancer: an exploratory study

Adrenal cancer is a heterogeneous group of neoplasms with unknown etiology. In search of risk factors, we conducted a case-control study based on data from the 1986 National Mortality Followback Survey, which included a questionnaire sent to the next of kin of almost 20,000 deceased adults (age > or = 25 year) in the United States. Information was obtained on a large number of items, including use of cigarettes, alcohol, oral contraceptives (OCs), height and weight and food consumption patterns. A total of 176 subjects who died of adrenal cancer (88 men and 88 women) and 352 controls (176 men and 176 women) who died of causes unrelated to smoking, drinking or OCs (for female controls) were included in the study. Although information on histologic type was not available, most cases were estimated from incidence surveys to be adrenocortical carcinoma, with a small percentage being malignant pheochromocytoma or neuroblastoma. An increased risk was associated with heavy smoking (> or = 25 cigarettes/day) among men (odds ratio [OR] = 2.0, 95% confidence interval [CI] 1.0-4.4) but not women. No clear association was seen for alcohol use, height and weight or food consumption patterns in either sex. Among women, increased risks were found for ever users of OCs (OR = 1.8, 95% CI 1.0-3.2) and especially those who used them before age 25 (OR = 2.5, 95% CI 1.2-5.5). When the analysis was restricted to subjects with spousal respondents, more pronounced risks were seen for ever users of OCs and for those who used OCs before age 25. Our findings suggest that cigarette smoking and use of OCs may increase the risk of adrenal cancer, but additional studies are needed with more detailed information on risk factors and histologic type of adrenal cancer.

Synthesis of tobacco-specific N-nitrosamines and their metabolites and results of related bioassays

Tobacco-specific N-nitrosamines (TSNA) are the most abundant, strong carcinogens in tobacco smoke. Seven TSNA have been identified in tobacco products: N'-nitrosonornicotine (NNN), N'-nitrosoanabasine (NAB), N'-nitrosoanatabine (NAT), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), 4-(methylnitrosamino)-4-(3-pyridyl)-1-butanol (iso-NNAL), and 4-(methylnitrosamino)-4-3-pyridyl)butyric acid (iso-NNAC). The syntheses of these compounds are reviewed. The syntheses of 14C- and 3H-labeled NNK as well as metabolites of NNK and NNN are also discussed. Comparative assays for lung tumorigenesis in female A/J mice were carried out for six of the TSNA and for two related compounds, N-nitrosodimethylamine (NDMA) and N-nitrosopyrrolidine (NPYR). They yielded the following ranking of potency: NDMA > NNK > NNAL > NPYR > NNN > NAB. Iso-NNAL and iso-NNAC were inactive. These results are also compared with previous assays of TSNA carcinogenicity in rats and hamsters.

The biological significance of tobacco-specific N-nitrosamines: smoking and adenocarcinoma of the lung

In the U.S., there has been a steeper rise of the incidence of lung adenocarcinoma than of squamous cell carcinoma of the lung among cigarette smokers. Since 1950, the percentage of all cigarettes sold that had filter tips increased from 0.56 to 92% in 1980 and to 97% in 1990. The tobacco of the filter cigarettes is richer in nitrate than that of the nonfilter cigarettes manufactured in past decades. Because the smoker of cigarettes with lower nicotine yield tends to smoke more intensely and to inhale the smoke more deeply than the smoker of plain cigarettes, the peripheral lung is exposed to higher amounts of nitrogen oxides, nitrosated compounds, and lung-specific smoke carcinogens. It is our working hypothesis that more intense smoking, deeper inhalation of the smoke, and higher smoke delivery of the organ-specific lung carcinogen NNK to the peripheral lung are major contributors to the increased risk of cigarette smokers for lung adenocarcinoma. Bioassay data and biochemical studies in support of this concept are discussed.

Effects of K-ras gene mutations in the development of lung lesions induced by 4-(N-methyl-n-nitrosamino)-1-(3-pyridyl)-1-butanone in A/J mice

The relationship between the development of peripheral lung lesions induced by tobacco-specific 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and K-ras gene mutation in A/J mice, and the correlations between histological alterations and the course of lung lesion development after NNK treatment and K-ras gene mutation were investigated. The acquisition of a selective growth advantage by the lung lesions with mutations was also examined using immunohistochemical labeling with bromodeoxyuridine. Thirty female 5 weeks old A/J mice were each injected intraperitoneally with a single dose of NNK (100 mg/kg body weight) and subdivided into 6 groups according to the time after NNK treatment. The lung lesions were characterized histologically as alveolar/bronchiolar hyperplasia, adenoma and adenocarcinoma, and point mutations in codons 12 and 61 of the K-ras gene were detected by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) and dideoxy sequencing methods. K-ras gene mutations were identified in 7 (58.3%) of 12 hyperplasias, 42(75.0%) of 56 adenomas and 3 (75.0%) of 4 adenocarcinomas. The most frequent K-ras gene mutation was a G-to-A transition at the second base of codon 12 and this accounted for 86.5% of all the mutations detected. Neither the frequency of activation of this gene nor the specific mutation was affected by the time after NNK treatment and there was no positive correlation between the proliferative activity of lung lesions and the presence of K-ras gene mutations. Thus, K-ras gene mutation is closely associated with the development of NNK-induced peripheral lung lesions in A/J mice, but it plays no role in the selective growth advantage of these lesions.

Dose-response relationships for carcinogens

Biotransformation of chemical carcinogens involves both metabolic activation and detoxication. The molecular dose present on DNA as adducts represents a balance between these two pathways (formation) and DNA repair. All of these are enzymatic processes subject to saturation. When none of the pathways is saturated, linear molecular dosimetry is expected, whereas if metabolic activation is saturated, a supralinear response occurs. If detoxication or DNA repair is saturated, a sublinear response occurs. With chronic exposure, steady-state concentrations of DNA adducts develop and these follow the same patterns. With several alkylating agents, multiple adducts are formed. The extent of formation is chemically defined, but different DNA repair pathways can be involved for different adducts. By understanding the molecular dose and biology of each adduct and comparing these to the dose-response for tumor induction, it may be possible to identify the most appropriate biomarkers for risk assessment. Recently, endogenous DNA adducts identical to those induced by known human carcinogens have been identified. These endogenously formed adducts may play an important role in human carcinogenesis.

Tobacco-specific nitrosamines in some Nigerian cigarettes

Ten popular brands of cigarettes on the Nigerian market were analyzed for tobacco-specific nitrosamines (TSNA) in tobacco and in mainstream smoke, as well as nitrate in tobacco. TSNA was analyzed using a gas chromatography/thermal energy analyzer (GC-TEA), while nitrate was determined spectrophotometrically as nitrite following on-line reduction with copper, diozatization with sulfanilamide and coupling with N-(1-naphthyl) ethylene diamine to form an azo dye. In mainstream smoke, the concentration of NNN, NAB/NAT and NNK were respectively, between 8 and 90 ng, 10 and 65 ng, and between 15 and 72 ng/cigarette. Preformed NNN ranged between 64 and 565 ng/cigarette, while preformed NAB/NAT and NNK ranged respectively from 109 to 476 ng/cigarette, and from 55 to 317 ng/cigarette. Nitrate levels ranged between 1.5 and 6.1 mg/g tobacco. In general, the results indicate that the TSNA content of Nigerian cigarettes are within the range found for European and American cigarettes.