Bacterial mutagenicity of some tobacco aromatic nitrogen bases and their mixtures

Transcriptional Response of Mycobacterium tuberculosis to Cigarette Smoke Condensate

Smoking is known to be an added risk factor for tuberculosis (TB), with nearly a quarter of the TB cases attributed to cigarette smokers in the 22 countries with the highest TB burden. Many studies have indicated a link between risk of active TB and cigarette smoke. Smoking is also known to significantly decrease TB cure and treatment completion rate and increase mortality rates. Cigarette smoke contains thousands of volatile compounds including carcinogens, toxins, reactive solids, and oxidants in both particulate and gaseous phase. Yet, to date, limited studies have analyzed the impact of cigarette smoke components on Mycobacterium tuberculosis (Mtb), the causative agent of TB. Here we report the impact of cigarette smoke condensate (CSC) on survival, mutation frequency, and gene expression of Mtb in vitro. We show that exposure of virulent Mtb to cigarette smoke increases the mutation frequency of the pathogen and strongly induces the expression of the regulon controlled by SigH—a global transcriptional regulator of oxidative stress. SigH has previously been shown to be required for Mtb to respond to oxidative stress, survival, and granuloma formation in vivo. A high-SigH expression phenotype is known to be associated with greater virulence of Mtb. In patients with pulmonary TB who smoke, these changes may therefore play an important, yet unexplored, role in the treatment efficacy by potentially enhancing the virulence of tubercle bacilli.

Genotoxic effect induced by dried nicotiana tabacum leaves from tobacco barns (kiln-houses) in chinese hamster lung fibroblast cells (V79)

Nicotiana tabacum is the most cultivated tobacco species in the state of Rio Grande do Sul, Brazil. Workers who handle the plant are exposed to the leaf components during the harvesting process and when separating and classifying the dried leaves. In addition to nicotine, after the drying process, other components may be found including tobacco-specific nitrosamines, polycyclic aromatic hydrocarbons, as well as pesticides residues. The objective of this study was to examine the genotoxicity attributed to the aqueous extract of dried tobacco leaves obtained from tobacco barns using Chinese hamster lung fibroblast cells (V79) as a model system by employing alkaline comet assay, micronucleus (MN) and Ames test. MTT assay was used to assess cytotoxicity and establish concentrations for this study. Data demonstrated cell viability > 85% for concentrations of 0.625-5 mg/ml while the comet assay indicated a significant increase in DNA damage at all concentrations tested. A significant elevation of MN and nuclear buds (NBUD) was found for 5 mg/ml compared to control and other dry tobacco leaves concentrations (0.625-2.5 mg/ml). Mutagenicity was not found using the Salmonella/Microsome test (TA98, TA100, and TA102 strains) with and without metabolic activation. The concentration of inorganic elements was determined employing the PIXE technique, and 13 inorganic elements were detected. Using CG/MS nicotine amounts present were 1.56 mg/g dry tobacco leaf powder. Due to the observed genotoxicity in V79 cells, more investigations are needed to protect the health of tobacco workers exposed daily to this complex mixture of toxic substances present in dry tobacco leaves.

Smoking causes induction of micronuclei and other nuclear anomalies in cervical cells

INTRODUCTION

Smoking is an independent cause of cervical cancer, which is the 4th most common malignancy in women. It is currently not known if tobacco consumption causes chromosomal damage (which is a hallmark of human cancer) in cervical cells and if age and the hormonal status have an impact on tobacco induced genetic instability in the cervix.

METHODS

We conducted a study with pre- and post-menopausal women smokers and never-smokers (25/group). Smokers consumed 30 light/medium cigarettes/day and were matched with the non-smoking group. Cervical cells were analyzed for induction of micronuclei (MN) which are caused by structural/numerical chromosomal aberrations; additionally, other nuclear anomalies reflecting genomic instability and cytotoxicity were scored. Furthermore, the frequencies of basal cells were recorded which reflect the mitotic activity of the mucosa.

RESULTS

MN and other abnormalities were increased in both groups of smokers. The effects were most pronounced in postmenopausal smokers (i.e. 2-fold higher) compared to premenopausal smokers. Also the number of basal cells (indicative for cell proliferation) was clearly enhanced in older women. Tar and nicotine had no detectable impact on chromosomal damage but a clear association with pack-years was observed.

CONCLUSIONS

Smoking increased chromosomal instability, cytotoxicity and induced cell divisions in cervical mucosa cells of pre- and post-menopausal women. The effects were more pronounced in the latter group indicating a higher risk for diseases (including cancer) that are causally related to DNA damage.

Mode-of-action analysis of the effects induced by nicotine in the in vitro micronucleus assay

Nicotine's genotoxic potential has been extensively studied in vitro. While the results of mammalian cell-based studies have inferred that it can potentially damage chromosomes, in general and with few exceptions, adverse DNA effects have been observed primarily at supraphysiological concentrations in nonregulatory assays that provide little information on its mode-of-action (MoA). In this study, a modern-day regulatory genotoxicity assessment was conducted using a flow cytometry-based in vitro micronucleus (MN) assay, Good Laboratory Practice study conditions, Chinese hamster ovary cells of known provenance, and acceptance/evaluation criteria from the current OECD Test Guideline 487. Nicotine concentrations up to 3.95 mM had no effect on background levels of DNA damage; however, concentrations above the point-of-departure range of 3.94-4.54 mM induced increases in MN and hypodiploid nuclei, indicating a possible aneugenicity hazard. Follow-up experiments designed to elucidate nicotine's MoA revealed cellular vacuolization, accompanying distortions in microtubules, inhibition of tubulin polymerization, centromere-positive DNA, and multinucleate cells at MN-inducing concentrations. Vacuoles likely originated from acidic cellular compartments (e.g., lysosomes). Remarkably, genotoxicity was suppressed by chemicals that raised the luminal pH of these organelles. Other endpoints (e.g., changes in phosphorylated histones) measured in the study cast doubt on the biological relevance of this apparent genotoxicity. In addition, three major nicotine metabolites, including cotinine, had no MN effects but nornicotine induced a nicotine-like profile. It is possible that nicotine's lysosomotropic properties drive the genotoxicity observed in vitro; however, the potency and mechanistic insights revealed here indicate that it is likely of minimal physiological relevance for nicotine consumers. Environ. Mol. Mutagen. 2019. © 2019 The Authors. Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.

Evaluation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) mutagenicity using in vitro and in vivo Pig-a assays

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a genotoxic carcinogen found in tobacco and tobacco smoke. Several in vitro and in vivo assays have been used for evaluating the genotoxicity of tobacco smoke and tobacco smoke constituents like NNK, yet it is not clear which in vitro assays are most appropriate for extrapolating the in vitro responses of these test agents to animal models and humans. The Pig-a gene mutation assay can be performed in vitro, in laboratory animals, and in humans, a potential benefit in estimating in vivo responses from in vitro data. In the current study we used Pig-a as a reporter of gene mutation both in vitro, in L5178Y/Tk+/- cells, and in vivo, in Sprague-Dawley rats. NNK significantly increased Pig-a mutant frequency in L5178Y/Tk+/- cells, but only at concentrations of 100 μg/ml and greater, and only in the presence of S9 activation. Pig-a mutations in L5178Y/Tk+/- cells were detected in 80% of the NNK-induced mutants, with the predominate mutation being G→A transition; vehicle control mutants contained deletions. In the in vivo study, rats were exposed to NNK daily for 90 days by inhalation, a common route of exposure to NNK for humans. Although elevated mutant frequencies were detected, these responses were not clearly associated with NNK exposure, so that overall, the in vivo Pig-a assays were negative. Thus, while NNK induces mutations in the in vitro Pig-a assay, the in vivo Pig-a assay has limited ability to detect NNK mutagenicity under conditions relevant to NNK exposure in smokers.

Reprint of: cancer "causation" by infections--individual contributions and synergistic networks

The search for infectious agents playing a role in human carcinogenesis and their identification remain important issues. This could provide clues for a broader spectrum of cancers preventable by vaccination and accessible to specific therapeutic regimens. Yet, the various ways of interacting among different factors functioning synergistically and their different modes of affecting individual cells should bring to question the validity of the term "causation". It also should put a word of caution into all attempts to summarize criteria for "causality" of infectious agents in cancer development. At least in the opinion of these authors, we would be much better off avoiding these terms, replacing "causal factor" by "risk factor" and grading them according to their contribution to an individual's cancer risk.

Toxicological assessment of kretek cigarettes: Part 2: kretek and American-blended cigarettes, smoke chemistry and in vitro toxicity

Two commercial kretek cigarettes typical for the Indonesian market and a reference kretek cigarette were compared to the American-blended reference cigarette 2R4F by smoke chemistry characterization and in vitro cytotoxicity and mutagenicity assessments. Despite the widely diverse designs and deliveries of the selected kretek cigarettes, their smoke composition and in vitro toxicity data present a consistent pattern when data were normalized to total particulate matter (TPM) deliveries. This confirms the applicability of the studies' conclusions to a wide range of kretek cigarette products. After normalization to TPM delivery, nicotine smoke yields of kretek cigarettes were 29-46% lower than that of the 2R4F. The yields of other nitrogenous compounds were also much lower, less than would be expected from the mere substitution of one third of the tobacco filler by clove material. Yields of light molecular weight pyrolytic compounds, notably aldehydes and hydrocarbons, were reduced, while yields of polycyclic aromatic hydrocarbons were unchanged and phenol yield was increased. The normalized in vitro toxicity was lowered accordingly, reflecting the yield reductions in gas-phase cytotoxic compounds and some particulate-phase mutagenic compounds. These results do not support a higher toxicity of the smoke of kretek cigarettes compared to American-blended cigarettes.

Cancer "causation" by infections--individual contributions and synergistic networks

The search for infectious agents playing a role in human carcinogenesis and their identification remain important issues. This could provide clues for a broader spectrum of cancers preventable by vaccination and accessible to specific therapeutic regimens. Yet, the various ways of interacting among different factors functioning synergistically and their different modes of affecting individual cells should bring to question the validity of the term "causation". It also should put a word of caution into all attempts to summarize criteria for "causality" of infectious agents in cancer development. At least in the opinion of these authors, we would be much better off avoiding these terms, replacing "causal factor" by "risk factor" and grading them according to their contribution to an individual's cancer risk.

A core in vitro genotoxicity battery comprising the Ames test plus the in vitro micronucleus test is sufficient to detect rodent carcinogens and in vivo genotoxins

In vitro genotoxicity testing needs to include tests in both bacterial and mammalian cells, and be able to detect gene mutations, chromosomal damage and aneuploidy. This may be achieved by a combination of the Ames test (detects gene mutations) and the in vitro micronucleus test (MNvit), since the latter detects both chromosomal aberrations and aneuploidy. In this paper we therefore present an analysis of an existing database of rodent carcinogens and a new database of in vivo genotoxins in terms of the in vitro genotoxicity tests needed to detect their in vivo activity. Published in vitro data from at least one test system (most were from the Ames test) were available for 557 carcinogens and 405 in vivo genotoxins. Because there are fewer publications on the MNvit than for other mammalian cell tests, and because the concordance between the MNvit and the in vitro chromosomal aberration (CAvit) test is so high for clastogenic activity, positive results in the CAvit test were taken as indicative of a positive result in the MNvit where there were no, or only inadequate data for the latter. Also, because Hprt and Tk loci both detect gene-mutation activity, a positive Hprt test was taken as indicative of a mouse-lymphoma Tk assay (MLA)-positive, where there were no data for the latter. Almost all of the 962 rodent carcinogens and in vivo genotoxins were detected by an in vitro battery comprising Ames+MNvit. An additional 11 carcinogens and six in vivo genotoxins would apparently be detected by the MLA, but many of these had not been tested in the MNvit or CAvit tests. Only four chemicals emerge as potentially being more readily detected in MLA than in Ames+MNvit--benzyl acetate, toluene, morphine and thiabendazole--and none of these are convincing cases to argue for the inclusion of the MLA in addition to Ames+MNvit. Thus, there is no convincing evidence that any genotoxic rodent carcinogens or in vivo genotoxins would remain undetected in an in vitro test battery consisting of Ames+MNvit.

Potent mutagenicity of 3-methylindole requires pulmonary cytochrome P450-mediated bioactivation: a comparison to the prototype cigarette smoke mutagens B(a)P and NNK

3-Methylindole (3MI) is a preferential pneumotoxicant found in cigarette smoke. A number of lung-expressed human cytochrome P450 enzymes, including 1A1, 2F1, and 2A13, catalyze the metabolism of 3MI to reactive intermediates that fragment DNA, measured with the Comet assay to assess DNA damage, in a cytochrome P450-dependent manner in primary normal human lung cells in culture, but the mutagenesis of 3MI has been controversial. In the present study, the mutagenic potential of 3MI was compared to the prototypical cigarette smoke carcinogens benzo(a)pyrene (B(a)P) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). 3MI, B(a)P, and NNK were incubated with the Salmonella typhimurium strain TA98, which is known to detect the most common subtype of cigarette smoke-induced mutagenicity, frameshift mutations in DNA, and with Salmonella typhimurium strain TA100, which detects base pair substitution mutants, with five sources of P450-mediated bioactivation: rat liver S9, human lung microsomes, recombinant CYP2A13, purified CYP2F3, and recombinant CYP1A1. Only B(a)P was mutagenic in TA100, and it was bioactivated by human lung microsomes and rat liver S9 sources of P450s. However, with the TA98 strain, CYP1A1, CYP2A13, CYP2F3, and human lung microsomes bioactivated 3MI to highly mutagenic intermediates, whereas neither human nor rat liver S9 subcellular fractions formed mutagenic intermediates from 3MI. Quantitative Western blot analysis verified that all three respiratory enzymes were present in human lung microsomes in widely varying amounts. These results indicate that metabolism of 3MI by human lung-expressed cytochrome P450 enzymes but not hepatic P450s elicits equivalent or higher mutagenicity than the prototype cigarette smoke mutagens B(a)P and NNK and indicates that 3MI is a likely human pulmonary carcinogen.

[Effects of nicotine with special consideration given to tumorigenesis in the head and neck region]

BACKGROUND

Tumorigenesis is based on initiation, promotion, and progression, whereas tobacco smoke is a decisive predisposing factor for squamous cell carcinomas of the upper aerodigestive tract. A variety of tobacco smoke compounds is known to potentially initiate tumors, but the alkaloid nicotine is generally considered to induce addiction only. However, there is growing evidence that nicotine may also contribute to early stages of tumorigenesis. In the present study, a possible direct genotoxic potential of nicotine is investigated.

MATERIAL AND METHODS

Lymphatic tissue of the tonsilla palatina of eight donors was harvested during surgery and incubated with nicotine. DNA damage was measured with the comet assay.

RESULTS

Genotoxic effects of nicotine could be demonstrated.

DISCUSSION

The results suggest a direct contribution of nicotine to tumor initiation and carcinogenesis.

Genotoxicity testing of four food preservatives and their combinations in the Drosophila wing spot test

In this study, four food preservatives (sodium nitrate, sodium nitrite, potassium nitrate and potassium nitrite) and there five combinations at a concentration of 25mM have been evaluated for genotoxicity in the somatic mutation and recombination test (SMART) of Drosophila melanogaster. Three-day-old larvae trans-heterozygous including two linked recessive wing hair mutations (multiple wing hairs and flare) were fed at different concentrations of the test compounds (25, 50, 75 and 100mM) in standard Drosophila Instant Medium. Wings of the emerging adult flies were scored for the presence of spots of mutant cells, which can result from either somatic mutation or mitotic recombination. Also lethal doses of food preservatives used were determined in the experiments. A positive correlation was observed between total mutations and the number of wings having mutation. In addition, the observed mutations in each wing were classified according to the size and type of the mutation. For the evaluation of genotoxic effects, the frequencies of spots per wing in the treated series were compared to the control group, which is distilled water. Chemicals used were ranked as sodium nitrite, potassium nitrite, sodium nitrate and potassium nitrate according to their genotoxic and toxic effects. Moreover, the genotoxic and toxic effects produced by the combined treatments were considerably increased, especially when the four chemicals were mixed. The present study shows that correct administration of food preservatives/additives may have a significant effect on human health.

The pharmacological actions of nicotine on the gastrointestinal tract

Increasing use of tobacco and its related health problems are a great concern in the world. Recent epidemiological findings have demonstrated the positive association between cigarette smoking and several gastrointestinal (GI) diseases, including peptic ulcer and cancers. Interestingly, smoking also modifies the disease course of ulcerative colitis (UC). Nicotine, a major component of cigarette smoke, seems to mediate some of the actions of cigarette smoking on the pathogenesis of GI disorders. Nicotine worsens the detrimental effects of aggressive factors and attenuates the protective actions of defensive factors in the processes of development and repair of gastric ulceration. Nicotine also takes part in the initiation and promotion of carcinogenesis in the GI tract. In this regard, nicotine and its metabolites are found to be mutagenic and have the ability to modulate cell proliferation, apoptosis, and angiogenesis during tumoriogenesis through specific receptors and signalling pathways. However, to elucidate this complex pathogenic mechanism, further study at the molecular level is warranted. In contrast, findings of clinical trials give promising results on the use of nicotine as an adjuvant therapy for UC. The beneficial effect of nicotine on UC seems to be mediated through multiple mechanisms. More clinical studies are needed to establish the therapeutic value of nicotine in this disease.

Effect of nicotine, cotinine and phenethyl isothiocyanate on 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) metabolism in the Syrian golden hamster

The effect of nicotine, cotinine and phenethyl isothiocyanate (PEITC) on metabolism of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) was studied in the Syrian golden hamster. Urinary metabolite profiles were determined in 24 h urine after a single subcutaneous (s.c.) administration of [5-(3)H]NNK (80 nmol/kg, s.c.). Co-administration of either a 500-fold higher dose of nicotine (40 micromol/kg, s.c.) or a 5000-fold higher dose of cotinine (400 micromol/kg, s.c.) significantly (P<0.001) reduced metabolic activation of NNK by alpha-hydroxylation to 85 and 71% of control, respectively. Co-administration of a 300-fold higher dose of PEITC (1 micromol/g diet) slightly reduced alpha-hydroxylation of NNK (94% of control). Metabolism of NNK by reduction to 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) was increased by nicotine (155%), and significantly increased by cotinine (670%, P<0.001) and PEITC (219%, P<0.01). Detoxification of NNAL by glucuronidation was also increased by all three test agents. Detoxification of NNK and NNAL by N-oxidation was marginally increased by nicotine, reduced by PEITC, and significantly reduced by cotinine. The urinary metabolite profiles suggest that nicotine, which occurs in concentrations up to 30000-fold higher than NNK in mainstream cigarette smoke, and cotinine, its proximal metabolite, may have a significant protective effect against in vivo metabolic activation of NNK.