Coexposure to Inhaled Aldehydes or Carbon Dioxide Enhances the Carcinogenic Properties of the Tobacco-Specific Nitrosamine 4-Methylnitrosamino-1-(3-pyridyl)-1-butanone in the A/J Mouse Lung

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

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

Face Mask as a Versatile Sampling Device for the Assessment of Personal Exposure to 54 Toxic Compounds in Environmental Tobacco Smoke

Exposure to environmental tobacco smoke (ETS), which contains hundreds of toxic compounds, significantly increases the risk of developing many human diseases, including lung cancer. The most common method of assessing personal exposure to ETS-borne toxicants is by sampling sidestream smoke generated by a smoking machine through a sorbent tube or filter, followed by solvent extraction and instrumental analysis. However, the ETS sampled may not truly represent the ETS in the ambient environment, due to complicating factors from the smoke released by the burning end of the cigarette and from the absorption of the chemicals in the respiratory tract of the smoker. In this study, we developed and validated an alternative air sampling method involving breathing through a face mask to simultaneously determine personal exposure to 54 ETS-borne compounds, including polycyclic aromatic hydrocarbons, aromatic amines, alkaloids, and phenolic compounds in real smoking scenarios. The newly developed method was used to evaluate the risk associated with exposure to ETS released from conventional cigarettes (CCs) and that from novel tobacco products such as e-cigarettes (ECs) and heated tobacco products (HTPs), with the observation of cancer risk associated with exposure to ETS released from CCs significantly higher than that from ECs and HTPs. It is anticipated that this method offers a convenient and sensitive way to collect samples for assessing the health impacts of ETS exposure.

Smoking-Associated Exposure of Human Primary Bronchial Epithelial Cells to Aldehydes: Impact on Molecular Mechanisms Controlling Mitochondrial Content and Function

Chronic obstructive pulmonary disease (COPD) is a devastating lung disease primarily caused by exposure to cigarette smoke (CS). During the pyrolysis and combustion of tobacco, reactive aldehydes such as acetaldehyde, acrolein, and formaldehyde are formed, which are known to be involved in respiratory toxicity. Although CS-induced mitochondrial dysfunction has been implicated in the pathophysiology of COPD, the role of aldehydes therein is incompletely understood. To investigate this, we used a physiologically relevant in vitro exposure model of differentiated human primary bronchial epithelial cells (PBEC) exposed to CS (one cigarette) or a mixture of acetaldehyde, acrolein, and formaldehyde (at relevant concentrations of one cigarette) or air, in a continuous flow system using a puff-like exposure protocol. Exposure of PBEC to CS resulted in elevated IL-8 cytokine and mRNA levels, increased abundance of constituents associated with autophagy, decreased protein levels of molecules associated with the mitophagy machinery, and alterations in the abundance of regulators of mitochondrial biogenesis. Furthermore, decreased transcript levels of basal epithelial cell marker KRT5 were reported after CS exposure. Only parts of these changes were replicated in PBEC upon exposure to a combination of acetaldehyde, acrolein, and formaldehyde. More specifically, aldehydes decreased MAP1LC3A mRNA (autophagy) and BNIP3 protein (mitophagy) and increased ESRRA protein (mitochondrial biogenesis). These data suggest that other compounds in addition to aldehydes in CS contribute to CS-induced dysregulation of constituents controlling mitochondrial content and function in airway epithelial cells.

Acrolein Increases the Pulmonary Tumorigenic Activity of the Tobacco-Specific Nitrosamine 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)

Tobacco smoke is a complex mixture of more than 7000 chemicals, of which many are toxic and/or carcinogenic. Many hazard assessments of tobacco have focused on individual chemical exposures without consideration of how the chemicals may interact with one another. Two chemicals, the human carcinogen 4-methylnitrosamino-1-(3-pyridyl)-1-butanone (NNK) and a possible human carcinogen, acrolein, were hypothesized to interact with one another, possibly owing to the additive effects of DNA adduct formation or influence on the repair of mutagenic DNA adducts. To test our hypothesis that coexposure to NNK and acrolein is more carcinogenic than either chemical alone, A/J mice were exposed to NNK (i.p., 0, 2.5, or 7.5 μmol in saline) in the presence or absence of inhaled acrolein (15 ppmV). While the single 3 h exposure to acrolein alone did not induce lung adenomas, it significantly enhanced NNK's lung carcinogenicity. In addition, mice receiving both NNK and acrolein had more adenomas with dysplasia or progression than those receiving only NNK, suggesting that acrolein may also increase the severity of NNK-induced lung adenomas. To test the hypothesis that the interaction was due to effects on DNA adduct formation and repair, NNK- and acrolein pulmonary DNA adduct levels were assessed. There was no consistent effect of the coexposure on NNK-derived DNA adducts, and acrolein DNA adducts were not elevated above endogenous levels. This study supports the hypothesis that tobacco smoke chemicals combine to contribute to the carcinogenic potency of tobacco smoke, and the mechanism of interaction cannot be explained by alterations of DNA adduct levels.

Comparison of tobacco and alcohol consumption in young and older patients with oral squamous cell carcinoma: a systematic review and meta-analysis

OBJECTIVE

To compare the proportion of young (up to 45 years of age) and older (over 45 years of age) oral squamous cell carcinoma (OSCC) patients who report tobacco and alcohol consumption.

METHODS

Observational studies reporting tobacco and alcohol consumption among young and older OSCC patients were selected in a two-phase process. Search strategies were conducted on five main electronic databases and complemented by grey literature. The risk of bias was assessed using the Joanna Briggs Institute's Critical Appraisal Checklist for Studies Reporting Prevalence Data. Synthesis of results was calculated with the software R Statistics version 4.0.2 (The R Foundation).

RESULTS

From 6675 records identified, 38 studies met the eligibility criteria and were selected for qualitative synthesis and meta-analysis, encompassing 2439 young and 13,393 older patients. Tobacco smoking was reported by 39.5% (confidence interval (CI) = 31.7% to 47.9%, I² = 78%) of the young patients and 48.4% (CI = 37.8% to 59.2%, I² = 94%) of the older patients. Alcohol consumption was reported by 30.9% (CI = 22.7% to 40.5%, I² = 83%) of the young and 45.8% (CI = 35.6% to 56.5%, I² = 95%) of the older patients (P < 0.05).

CONCLUSION

The comparison in the proportion of individuals reporting tobacco and alcohol consumption demonstrated that these habits were more prevalent in the older group (48.4% and 45.8% respectively) than in the young group (39.5% and 30.9%, respectively).

CLINICAL RELEVANCE

As a significant proportion of patients with OSCC reported no habits, novel risk factors for OSCC need to be investigated in further research.

LC-MS/MS Quantitation of Formaldehyde-Glutathione Conjugates as Biomarkers of Formaldehyde Exposure and Exposure-Induced Antioxidants: A New Look on an Old Topic

Humans are continuously exposed to formaldehyde via both endogenous and exogenous sources. Prolonged exposure to formaldehyde is associated with many human diseases, such as lung cancer and leukemia. The goal of this study is to develop biomarkers to measure formaldehyde exposure, which could be used to predict the risk of associated diseases. As glutathione (GSH) is well-known for its crucial role in the detoxification of a wide variety of xenobiotics, including formaldehyde, we rigorously quantitated in this study the conjugates formed when formaldehyde reacted with GSH using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) coupled with an isotope dilution method. The results showed for the first time that (S)-1-(((R)-2-amino-3-(carboxymethylamino)-3-oxopropylthio)methyl)-5-oxopyrrolidine-2-carboxylic acid (PGF) and thioproline-glycine (SPro-Gly) are major metabolites in both nonenzymatic reactions and formaldehyde-exposed human cells. In particular, over 35% of the formaldehyde from external sources was found to convert to SPro-Gly in the exposed cells. Interestingly, data showed that these exposure-induced adducts exhibited good antioxidative properties, which can protect cells from hydrogen peroxide mediated oxidative insult. It is anticipated that the findings of this study could shed light on developing PGF and SPro-Gly as dietary supplements and on the development of noninvasive methods to assess health risks associated with formaldehyde exposure.

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.