A study of tobacco carcinogenesis. XIV. Effects of N'-nitrosonornicotine and N'-nitrosonanabasine in rats

Impact of Marijuana Use on Lung Health

The widespread use of marijuana in the context of increasing legalization has both short- and long-term health implications. Although various modes of marijuana use-smoked, vaped, or ingested-may lead to a wide scope of potential systemic effects, we focus here on inhalational use of marijuana as the most common mode with the lung as the organ that is most directly exposed to its effects. Smoked marijuana has been associated with symptoms of chronic bronchitis and histopathologic changes in airway epithelium, but without consistent evidence of long-term decline in pulmonary function. Its role in immunomodulation, both for risk of infection and protection against a hyperinflammatory host response to infection, has been suggested in animal models and in vitro without conclusive extrapolation to humans. Marijuana smoke contains carcinogens like those found in tobacco, raising concern about its role in lung cancer, but evidence is mixed and made challenging by concurrent tobacco use. Vaping may offer a potential degree of harm reduction when compared with smoking marijuana with reduction of exposure to several toxins, including carbon monoxide, and reduction in chronic respiratory symptoms. However, these potential benefits are counterbalanced by risks including vaping-associated lung injury, potentially more intense drug exposure, and other yet not well-understood toxicities. As more states legalize marijuana and the federal government considers changing this from a Schedule I to a Schedule III controlled substance, we anticipate an increase in prospective medical studies concerning the risks related to marijuana use. This review is based on currently available data concerning the impact of inhaled marijuana on lung health.

Development and Validation of LC-MS/MS Method for the Determination of 1-Methyl-4-Nitrosopiperazine (MNP) in Multicomponent Products with Rifampicin-Analytical Challenges and Degradation Studies

Rifampicin is an essential medicine for treating and preventing tuberculosis (TB). TB is a life-threatening infectious disease and its prevention and treatment are public health imperatives. In the time of a global crisis of nitrosamine contamination of medicinal products, patient safety and a reduction in the number of drug recalls at the same time are crucial. In this work, the LC-MS/MS method was developed for the determination of the 1-methyl-4-nitrosospiperazine (MNP), a genotoxic nitrosamine impurity in various products containing rifampicin at a 5.0 ppm limit level according to Food and Drug Administration (FDA). Extraction with neutralization was necessary due to the matrix and solvent effect associated with the complexity of the rifampicin product. The developed method was validated in accordance with regulatory guidelines. Specificity, accuracy, precision, limit of detection, and limit of quantification parameters were evaluated. The recovery of the MNP was 100.38 ± 3.24% and the intermediate precision was 2.52%. The contamination of MNP in Rifampicin originates in the manufacturing process of the drug. Furthermore, the results of the forced degradation experiments show that the formation of MNP is possible by two mechanisms: through degradation of rifampicin and the oxidation of 1-amino-4-methyl-piperazine. This article points out that it is necessary to monitor and describe degradation products and the mechanism of degradation of potentially affected active pharmaceutical ingredient (API) with respect to the formation of nitrosamines during stress testing, as it was done in the following work for rifampicin in multicomponent products.

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.

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.

Prominent Stereoselectivity of NNAL Glucuronidation in Upper Aerodigestive Tract Tissues

Tobacco specific nitrosamines (TSNAs) are among the most potent carcinogens found in cigarettes and smokeless tobacco products. Decreases in TSNA detoxification, particularly 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), have been associated with tobacco-related cancer incidence. NNK is metabolized by carbonyl reduction to its major carcinogenic metabolite, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), which is detoxified by glucuronidation at the nitrogen within the pyridine ring or at the chiral alcohol to form four glucuronide products: (R)-NNAL-O-Gluc, (S)-NNAL-O-Gluc, (R)-NNAL-N-Gluc, (S)-NNAL-N-Gluc. Stereoselective NNAL-Gluc formation and the relative expression of NNAL-glucuronidating UGTs (1A4, 1A9, 1A10, 2B7, 2B10, 2B17) were analyzed in 39 tissue specimens from the upper aerodigestive tract (esophagus (n = 13), floor of mouth (n = 4), larynx (n = 9), tongue (n = 7), and tonsil (n = 6)). All pooled tissue types preferentially formed (R)-NNAL-O-Gluc in the presence of racemic-NNAL; only esophagus exhibited any detectable formation of (S)-NNAL-O-Gluc. For every tissue type examined, UGT1A10 exhibited the highest relative expression levels among the NNAL-O-glucuronidating UGTs, ranging from 36% (tonsil) to 49% (esophagus), followed by UGT1A9 > UGT2B7 > UGT2B17. UGT1A10 also exhibited similar or higher levels of expression as compared to both NNAL-N-glucuronidating UGTs, 1A4 and 2B10. In a screening of cells expressing individual UGT enzymes, all NNAL glucuronidating UGTs exhibited some level of stereospecific preference for individual NNAL enantiomers, with UGTs 1A10 and 2B17 forming primarily (R)-NNAL-O-Gluc. These data suggest that UGTs 1A10 and 2B17 may be important enzymes in the detoxification of TSNAs like NNK in tissues of the upper aerodigestive tract.

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.

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.

Clusterin induced by N,N'-Dinitrosopiperazine is involved in nasopharyngeal carcinoma metastasis

Nasopharyngeal carcinoma (NPC) has a high metastatic clinicopathological feature. As a carcinogen factor, N,N'-Dinitrosopiperazine (DNP) is involved in NPC metastasis, but its precise mechanism has not been fully elucidated. Herein, we showed that DNP promotes NPC metastasis through up-regulating anterior clusterin (CLU). DNP was found to increase CLU, matrix metalloproteinases (MMP) 9 and vascular endothelial growth factor (VEGF) expression and activity, further DNP-increased MMP-9 and VEGF expression was through up-regulating CLU. We also found that DNP increased the binding of CLU with MMP-9 or VEGF. DNP induced the motility and invasion of NPC cell, which was inhibited by siRNA-CLU. The clinical investigation showed that CLU, MMP-9 and VEGF were positively correlated with the tumor-node -metastasis (TNM) classification. These results indicate that DNP may promote NPC tumor metastasis through up-regulating CLU, MMP-9 and VEGF expression. Therefore, DNP-increased CLU expression may be an important factor of NPC-high metastasis, and CLU may serve as a biomarker for NPC metastasis.

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

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

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.

(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.

Insecticides of Natural Origin, Other than Pyrethrum and Nicotine

This chapter gives a detailed overview on the history, use and toxicology of substances of biological origin such as plant extracts (rotenone, azadirachtin, quassin, anabasin) and fermentation products from soil microorganisms (avermectins and spinosins) that are more or less widely used as insecticides in plant protection products or biocides but may also play a role in public health to prevent spread of infectious diseases or even to cure them.

Smoking and reproduction: the oviduct as a target of cigarette smoke

The oviduct is an exquisitely designed organ that functions in picking-up ovulated oocytes, transporting gametes in opposite directions to the site of fertilization, providing a suitable environment for fertilization and early development, and transporting preimplantation embryos to the uterus. A variety of biological processes can be studied in oviducts making them an excellent model for toxicological studies. This review considers the role of the oviduct in oocyte pick-up and embryo transport and the evidence that chemicals in both mainstream and sidestream cigarette smoke impair these oviductal functions. Epidemiological data have repeatedly shown that women who smoke are at increased risk for a variety of reproductive problems, including ectopic pregnancy, delay to conception, and infertility. In vivo and in vitro studies indicate the oviduct is targeted by smoke components in a manner that could explain some of the epidemiological data. Comparisons between the toxicity of smoke from different types of cigarettes, including harm reduction cigarettes, are discussed, and the chemicals in smoke that impair oviductal functioning are reviewed.

Determination of carcinogenic tobacco-specific nitrosamines in mainstream smoke from U.S.-brand and non-U.S.-brand cigarettes from 14 countries

Tobacco-specific nitrosamines (TSNAs) comprise one of the major classes of carcinogenic compounds in mainstream cigarette smoke. As part of collaborative efforts between the World Health Organization and the U.S. Centers for Disease Control and Prevention (CDC) to reduce tobacco use and resulting disease, the CDC examined carcinogenic TSNA levels from cigarettes obtained from selected countries around the world. Using a modern, high-throughput liquid chromatography/mass spectrometry/mass spectrometry method under stringent quality control protocols, we determined the carcinogenic TSNA levels in mainstream smoke from a globally marketed brand, Marlboro, and from local top-selling cigarette brands from 14 countries. The levels of carcinogenic TSNAs in mainstream smoke collected using a 35-ml puff volume, 60-s puff interval, and 2-s puff duration correlated well (R=0.79, p<.0001) with previously reported levels in the corresponding tobacco filler. Marlboro cigarettes purchased in 10 countries had significantly higher carcinogenic TSNA levels in mainstream smoke than did local-brand cigarettes from the same country. In only one country, Brazil, were the carcinogenic TSNA levels in mainstream smoke from Marlboro cigarettes significantly lower than in the locally popular brand. However, carcinogenic TSNA levels in mainstream smoke from Brazilian Marlboro cigarettes were usually lower than those in mainstream smoke from the Marlboros purchased in the other 13 countries, suggesting a reason for the difference. The wide range of mainstream smoke carcinogenic TSNA levels measured in the present study (8.7-312 ng/cigarette) suggest that manufacturers can lower the carcinogenic TSNA levels and that, for similar filter ventilation, carcinogenic TSNA levels in the tobacco filler of a cigarette are a useful indicator of the corresponding levels in mainstream smoke.

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.

Oral cancer after using Swedish snus (smokeless tobacco) for 70 years - a case report

Whereas the smoking habit has declined significantly in Sweden in recent decades, there has been a marked increase in the consumption of 'snus' (oral moist snuff). The use of this smokeless tobacco, exposing the user locally to carcinogenic nitrosamines, raises the question - will the increasing use of snuff eventually lead to a greater incidence of oral cancer? We report the case of a 90-year-old man who developed a localized squamous cell carcinoma in the gingival fold under the upper lip, at the exact place where he had regularly placed loose oral snuff for 70 years. Although this is a reminder of a prevailing cancer risk, the time frame indicates that the risk is slight. This is consistent with recent epidemiological reports regarding the minor risk of snuff-associated cancer in the Scandinavian countries.

N-Nitrosation of myosmine yields HPB (4-hydroxy-1-(3-pyridyl)-1-butanone) and NNN (N-nitrosonornicotine)

N-Nitrosonornicotine (NNN) is formed by synthetic or biological N-nitrosation of the tobacco alkaloid nornicotine. Following metabolic activation of NNN, DNA and protein adducts are formed releasing 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB), an actual biomarker to differentiate between tobacco smokers and passive smokers. NNN and HPB can be prepared in a new one-step reaction by N-nitrosation of the nicotinoid myosmine which has been found not only in tobacco but also in nut products. The reaction was tested also in human gastric juice. The formation rate of NNN and HPB depends on the pH value in the reaction solutions. This is important under the aspect of myosmine uptake by humans from other biological sources and subsequent biological activation. The new reaction pathway indicates that human exposure to nicotinoid nitrosation products seems to be not restricted exclusively to tobacco.

A study of tobacco carcinogenesis, LIII: carcinogenicity of N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in mink (Mustela vison)

In an earlier study, young male and female mink (Mustela vison) were found to be highly susceptible to the carcinogenic effect of N'-nitrosonornicotine (NNN). In this follow-up study we tested (i) the importance of the age of the animals with regard to the carcinogenic effect of NNN, (ii) the carcinogenic activity of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and (iii) the combined carcinogenic effect of NNN plus NNK. (I) In the previous study, the latency of nasal tumor induction by NNN (11.9 mM) averaged 84 +/- 40 weeks upon twice weekly applications, starting at the age of 3 weeks and continuing for 38 weeks. In this bioassay, giving NNN in 28 weeks but starting at the age of 3 months, it took, on the average, 97 +/- 29 weeks to induce malignant nasal tumors, primarily esthesioneuroepithelioma with invasion of the brain. (ii) NNK (6.3 mM), given by s.c. injection, induced nasal carcinoma with invasion of the forebrain after 77 +/- 39 weeks. (iii) NNN (11.9 mM) plus NNK (6.3 mM) led to the same type of carcinoma but at an accelerated pace, namely after 71 +/- 57 weeks. This study supports the earlier observation that tobacco-specific N-nitrosamines induce malignant tumors of the nasal cavity with invasion of the brain, dependent to some degree on the age of the mink at first application. NNK appears to be a stronger carcinogen than NNN in mink which follows the observations made with mice, rats and hamsters. It is suggested that combined administration of NNN with NNK induces a stronger carcinogenic effect than NNN or NNK given alone.

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.

Tobacco-specific N-nitrosamines and Areca-derived N-nitrosamines: chemistry, biochemistry, carcinogenicity, and relevance to humans

Nicotine and the minor tobacco alkaloids give rise to tobacco-specific N-nitrosamines (TSNA) during tobacco processing and during smoking. Chemical-analytical studies led to the identification of seven TSNA in smokeless tobacco (< or = 25 micrograms/g) and in mainstream smoke of cigarettes (1.3 micrograms TSNA/cigarette). Indoor air polluted by tobacco smoke may contain up to 24 pg/L of TSNA. In mice, rats, and hamsters, three TSNA, N'-nitrosonornicotine (NNN), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), are powerful carcinogens; two TSNA are moderately active as carcinogens; and two TSNA appear not to be carcinogenic. The TSNA are procarcinogens, agents that require metabolic activation. The active forms of the carcinogenic TSNA react with cellular components, including DNA, and with hemoglobin (Hb). The Hb adducts in chewers and smokers serve as biomarkers for the uptake and metabolic activation of carcinogenic TSNA and the urinary excretion of NNAL as free alcohol and as glucuronide for the uptake of TSNA. The review presents evidence that strongly supports the concept that TSNA contribute to the increased risk for cancer of the upper digestive tract in tobacco chewers and for the increased risk of lung cancer, especially pulmonary adenocarcinoma, in smokers. The high incidence of cancer of the upper digestive tract especially among men on the Indian subcontinent has been causally associated with chewing of betel quid mixed with tobacco. In addition to the TSNA, the betel quid chewers are exposed to four N-nitrosamines that are formed during chewing from the Areca alkaloids, two of these N-nitrosamines are carcinogens. The article also reviews approaches toward the reduction of the carcinogenic potency of smokeless tobacco, betel quid-tobacco mixtures, and cigarette smoke. Although the safest way to reduce the risk for tobacco-related cancers is to refrain from chewing and smoking, modifications of smokeless tobacco and of cigarettes are indicated to lead to less toxic products. Another more recent approach for reducing the carcinogenic effect of tobacco products is the application of chemopreventive agents, primarily of micronutrients. Future aspects in tobacco carcinogenesis, especially as it relates to TSNA, are expected in the field of molecular biochemistry and in biomarker studies, with the goal of identifying those tobacco and betel quid chewers and tobacco smokers who are at especially high risk for cancer.

A study of tobacco carcinogenesis. LI. Relative potencies of tobacco-specific N-nitrosamines as inducers of lung tumours in A/J mice

Tobacco-specific N-nitrosamines (TSNA) are formed from nicotine and the minor Nicotiana tabacum alkaloids during tobacco processing and tobacco smoking. The TSNA are the most abundant strong carcinogens in smokeless tobacco and in smoke. In this comparative study six TSNA and two major volatile N-nitrosamines of cigarette smoke are assayed for their relative tumorigenicities in strain A/J female mice and for their potential to induce lung tumors. N-nitrosodimethylamine was the most potent inducer of lung adenoma in the A/J mouse model followed in order of decreasing potencies by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol, N-nitrosopyrrolidine, N'-nitrosonornicotine and N'-nitrosoanabasine. 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol and 4-(methylnitrosamino)-4-(3-pyridyl)butyric acid were inactive. The relative tumorigenic activities of the tobacco-specific nitrosamines in strain A/J mice compare well with the available data for their relative tumorigenic activities in F344 rats and Syrian golden hamsters.

Effects of tobacco-specific nitrosamines and snuff extract on cell proliferation and activities of ornithine decarboxylase and aryl hydrocarbon hydroxylase in mouse tongue primary epithelial cell cultures

Tobacco and its related compounds, including snuff, have been implicated in oral cancers. Tobacco-specific nitrosamines have been shown to be the causative agents present in tobacco and its related compounds. Both, N-nitrosonornicotine (NNN) and its butanone derivative (NNK) are carcinogenic in animals. In our in vitro studies using embryonic mouse tongue epithelial cells, NNN is linked to an increase in [3H]dT uptake along with a concomitant increase in ornithine decarboxylase and aryl hydrocarbon hydroxylase activities. NNK, the more potent compared to NNN, causes a further increase in [3H]dT uptake, cell count and ornithine decarboxylase activity. However, aryl hydrocarbon hydroxylase behaves differently in cultures treated with NNK compared to those treated with NNN. Snuff extract has an overall inhibitory effect on cell count, [3H]dT uptake, and ornithine decarboxylase and aryl hydrocarbon hydroxylase activities when administered either alone or in combination with NNN and NNK. How the inhibitory effect of snuff in the presence of tobacco-specific nitrosamines is involved in oral carcinogenesis should be further investigated.

Tumorigenic activity of the tobacco-specific nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), 4-(methylnitrosamino)-4-(3-pyridyl)-1-butanol (iso-NNAL) and N'-nitrosonornicotine (NNN) on topical application to Sencar mice

The tumor-initiating activities of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), 4-(methylnitrosamino)-4-(3-pyridyl)-1-butanol (iso-NNAL) and N'-nitrosonornicotine (NNN) were evaluated on the skin of female SENCAR mice. A total initiator dose of 28 mumol/mouse of each nitrosamine was applied in 10 subdoses administered every second day. Promotion commenced 10 days after the last initiator dose and consisted of twice weekly application of 2.0 micrograms of tetradecanoylphorbol acetate for 20 weeks. NNK induced a 79% incidence of skin tumors with an average of 1.6 tumors/mouse and a 59% incidence of lung adenomas. In contrast, iso-NNAL and NNN were not active as tumor initiators in either the skin or lung of mice. The tumorigenic activity of NNK on SENCAR mouse skin was evaluated at several doses. At a total initiator dose of 28 and 5.6 mumol/mouse, NNK exhibited significant activity (P less than 0.005) inducing a 59% and 24% incidence of skin tumors, respectively. In this dose response bioassay, NNK at a total initiator dose of 28 mumol induced a 63% incidence (P less than 0.005) of lung adenomas. The numbers of lung adenomas induced at the lower doses employed were not significant. NNK, at a total initiation dose of 1.4 mumol, did not exhibit significant tumorigenic activity (P greater than 0.05). Analysis of DNA from the skin of mice treated with NNK using HPLC with fluorescence detection failed to detect O6- and N-methylguanine (O6-MG and N7-MG) adducts. These data indicate that NNK can exert a contact carcinogenic effect and suggest that mechanisms other than DNA methylation may be involved in its activation to a tumorigenic agent in mouse skin.

Structure-activity relations in carcinogenesis by N-nitroso compounds

For a large number of N-nitroso compounds a comparison of their carcinogenic effects in rats and Syrian golden hamsters has been made. Nitrosamines, which require metabolic activation, and nitrosoalkylamides, which do not, produce quite different tumor responses. There are also large differences in the types of tumor induced in rats and in hamsters. In all the studies doses of the various compounds, equimolar to the extent that was possible, are administered orally. Continuous doses (in drinking water or food) often produce a response different from that after administration of the same compound in pulsed doses (by gavage), even though the same total dose is delivered. Continuous doses of nitrosamines are usually more effective than pulsed doses, but with the nitrosoalkylureas, the reverse is more generally the case. Rat and hamster liver is a common target of many nitrosamines, but rarely of nitrosamides. The most common site of tumor induction in rats by N-nitroso compounds is the esophagus, but the hamster esophagus never responds. The pancreas duct of the hamster is a common target of nitrosamines containing a beta-oxygenated propyl group, but pancreas duct tumors are never seen in rats. Nitrosomethyl-n-alkylamines (with an even numbered carbon chain) induce bladder tumors in rats and hamsters. Many nitrosoalkylureas induce tumors of the nervous system in rats, as well as a great variety of other tumors. In hamsters, nitrosoalkylureas give rise only to tumors of the forestomach and spleen, but no tumors of the nervous system. The similar carcinogenic actions of certain groups of N-nitroso compounds can be related to their generation, directly or by metabolism, of similar simple moieties having certain organs as their target.

Influence of ethyl alcohol on the carcinogenic activity of N-nitrosonornicotine

The present paper describes an experiment designed to investigate the effects of the combined action of different doses of N-nitrosonornicotine (NNN) and ethyl alcohol in BDVI rats. Dose-response relationships of NNN was clearly shown. Ethyl alcohol did not appear to increase, to a great degree, the tumour incidence of NNN. However, ethyl alcohol did shorten the tumour latency period in the groups given NNN in alcoholic solution. In addition, an infiltration of the olfactory tumours to the brain was observed more frequently in both males and females given the high dose of NNN in alcoholic solution.

The reemergence of smokeless tobacco

Smokeless tobacco (snuff and chewing tobacco) is reemerging as a popular form of tobacco, particularly among male adolescents. In different regions of the United States, from 8 to 36 percent of male high-school students are regular users. The use of smokeless tobacco has been shown to cause oral-pharyngeal cancer. The strongest link is with cancers of the cheek and gum. White mucosal lesions (leukoplakia) are found in 18 to 64 percent of users, often at the site where the tobacco was held. Other associations have been suggested for cancers of the esophagus, larynx, and pancreas. Nitrosamines, found in high concentrations in smokeless tobacco, most likely have a role in its carcinogenicity. Other health problems include periodontal disease, acute elevations of blood pressure, and dependence. In early 1986, after action at the state level, Congress enacted a federal law requiring health-warning labels on packages of smokeless tobacco and a ban on electronic advertising. Other regulatory measures under consideration include raising state and federal excise taxes, tightening controls on advertising, and prohibiting sales to minors. In view of the recent growth of this problem, policy makers are taking the opportunity to intervene with preventive measures to protect a new generation of tobacco users.

Tissue-specific inhibition of [3H]thymidine incorporation into DNA by carcinogenic N-nitrosamines

The N-nitrosamines N-nitrosodimethylamine (DMN), N'-nitrosonornicotine (NNN) and 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) were injected intraperitoneally 24 h before sacrifice in F344 rats and C57BL mice in doses of 297 mumoles/kg b.w. and 148 mumoles/kg b.w., respectively. 2 h before sacrifice, the animals were given an intraperitoneal injection of [3H]thymidine. The results showed that the examined N-nitrosamines inhibited the incorporation of [3H]thymidine into DNA in a few tissues of the rats and the mice. The results indicated that the N-nitrosamines exerted a tissue-specific inhibition of the [3H]thymidine incorporation in the tissues reported to be involved in the biotransformation of these substances. The observed inhibitory effects on the incorporation of [3H]thymidine by DMN, NNN and NNK were also correlated to a considerable extent to the reported sites of carcinogenicity. The present study indicates that measurements of [3H]thymidine incorporation into DNA in various tissues of experimental animals is a useful short-term bioassay to evaluate the potential tissue-specific carcinogenicity of the N-nitrosamines. The method may also be useful as a complement to other short-term in vivo tests in the screening of potential genotoxicity of several other chemicals.

Experimental studies on mutagenic and carcinogenic effects of tobacco chewing

The alcoholic extract of the chewing (Pandharpuri) variety of tobacco (Nicotiana tabacum) was subjected to mutagenicity and tumorigenicity studies. The extract was found to be mutagenic in strain TA 98 of Salmonella typhimurium in the presence of S 9 mixture. It also induced 8 AZG-resistant mutation in V 79 Chinese hamster cells. Administration of tobacco extract to male Swiss mice by gavage or mixed with diet resulted in an increased incidence of lung/liver tumors. Further, an additive effect of tobacco extract and hexachlorocyclohexane on liver tumor induction was observed.

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

Tobacco and tobacco smoke contain relatively high amounts of four tobacco-specific N-nitrosamines. Of these, N-nitrosonornicotine (NNN), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and N'-nitrosoanatabine (NAT) were bioassayed at three dose levels by subcutaneous injections into male and female F344 rats in 60 subdoses amounting in total to 9,3, and 1 mmol/kg. Compared with the solvent control group (trioctanoin), both NNN and NNK induced significant numbers of tumors of the nasal cavity (P less than 0.01) at all three dose levels in both male and female rats. Significant numbers of tumors were also induced by NNK in the lung at all three dose levels and in the liver at the highest dose level (P less than 0.05). In addition to nasal tumors NNN also induced esophageal tumors at a significant rate in male rats at the high and medium dose levels and in female rats at the high level (P less than 0.05); NAT was inactive at the three doses tested. Bioassays at lower dose levels as well as biochemical studies are strongly indicated for NNN and NNK since these nitrosamines occur in relatively high amounts in both chewing tobacco and tobacco smoke.

Comparative carcinogenicity in F344 rats and Syrian golden hamsters of N'-nitrosonornicotine and N'-nitrosonornicotine-1-N-oxide

N'-Nitrosonornicotine (NNN) or N'-nitrosonornicotine-1-N-oxide (NNN-1-N-oxide), one of its metabolites, was added to the drinking water (0.012% for 36 weeks) of groups of male and female F344 rats or to the drinking water (0.016% for 31 weeks) of groups of male and female Syrian golden hamsters. All rats treated with NNN had died after 12 months but 50% of those treated with NNN-1-N-oxide survived for 22 months. NNN induced esophageal tumors in 23/24 rats and nasal cavity tumors in 21/24 rats. NNN-1-N-oxide induced esophageal tumors in 10/24 rats and nasal cavity tumors in 18/24 rats. There was no difference in survival rates among hamsters treated with either NNN or NNN-1-N-oxide. NNN induced tracheal tumors in 2/20 hamsters and nasal cavity tumors in 4/20 hamsters. NNN-1-N-oxide did not induce respiratory tract tumors in hamsters. These results demonstrate that NNN-1-N-oxide is less carcinogenic than NNN in F344 rats and Syrian golden hamsters.

Inhibition by alcohols of the localization of radioactive nitrosonornicotine in sites of tumor formation

Oral administration of ethanol, n-butanol, or t-butanol to mice 20 minutes before injection of carbon-14-labeled nitrosonornicotine inhibited the localization of radioactivity in bronchial and salivary duct epithelium and in the liver. Localization of radioactivity in the nasal epithelium and esophagus was not significantly reduced. These alcohols therefore may selectively inhibit tumor formation in three of the five sites where this carcinogen typically acts.

Nicotine intake by snuff users

Blood nicotine and cotinine concentrations were measured in 27 volunteers before and after taking snuff. Within 10 minutes after snuffing blood nicotine concentrations were comparable to those obtained after the 10 minutes or so that it takes to smoke a cigarette. Nicotine intake from snuffing was related to the experience of the snuffer. In daily and occasional snuffers increases in plasma nicotine concentrations averaged 77.7 and 12.3 nmol/l (12.6 and 2.0 ng/ml) respectively, while the novices showed no appreciable increase. The increase shown by thea daily snuffers was comparable to the average increase of 62.3 nmol/l (10.1 ng/ml) obtained from a single cigarette by a group of heavy smokers. The peak nicotine concentrations in the daily snuffers were also similar to the peak values in 136 heavy smokers--222.6 and 226-3 nmol/l (36.1 and 36.7 ng/ml), respectively. Unusual multiple-dose snuffing produced massive increases in plasma nicotine to concentrations that have never been recorded in smokers. The similarity of the concentrations produced by regular daily snuffing and regular daily smoking suggests that the plasma nicotine concentration has some controlling influence over the self-regulation of these two quite different forms of tobacco use. The rapid absorption of nicotine from snuff confirms its potential as an acceptable and relatively harmless substitute for smoking.

Snuff dipping and oral cancer among women in the southern United States

A case-control study in North Carolina involving 255 women with oral and pharyngeal cancer and 502 controls revealed that the exceptionally high mortality from this cancer among white women in the South is primarily related to chronic use of snuff. The relative risk associated with snuff dipping among white nonsmokers was 4.2 (95 per cent confidence limits, 2.6 to 6.7), and among chronic users the risk approached 50-fold for cancers of the gum and buccal mucosa--tissues that come in direct contact with the tobacco powder. In the absence of snuff dipping, oral and pharyngeal cancer resulted mainly from the combined effects of cigarette smoking and alcohol consumption. The carcinogenic hazard of oral snuff is of special concern in view of the recent upswing in consumption of smokeless tobacco in the United States.

Alpha-hydroxylation of N-nitrosopyrrolidine and N'-nitrosonornicotine by human liver microsomes

The environmental carcinogens N-nitrosopyrrolidine (NPYR) and N'-nitrosonornicotine (NNN) were incubated with human liver microsomes to test for the presence of enzymes catalyzing alpha-hydroxylation, which is likely to be an activation mechanism for these compounds. Both nitrosamines underwent alpha-hydroxylation; rates were higher for NPYR than for NNN, as observed in rats. The results indicate that both NPYR and NNN can be metabolically activated by human liver microsomes.