Genotoxicity of nicotine and cotinine in the bacterial luminescence test

Cholinergic Receptor Modulation as a Target for Preventing Dementia in Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative condition characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) in the midbrain resulting in progressive impairment in cognitive and motor abilities. The physiological and molecular mechanisms triggering dopaminergic neuronal loss are not entirely defined. PD occurrence is associated with various genetic and environmental factors causing inflammation and mitochondrial dysfunction in the brain, leading to oxidative stress, proteinopathy, and reduced viability of dopaminergic neurons. Oxidative stress affects the conformation and function of ions, proteins, and lipids, provoking mitochondrial DNA (mtDNA) mutation and dysfunction. The disruption of protein homeostasis induces the aggregation of alpha-synuclein (α-SYN) and parkin and a deficit in proteasome degradation. Also, oxidative stress affects dopamine release by activating ATP-sensitive potassium channels. The cholinergic system is essential in modulating the striatal cells regulating cognitive and motor functions. Several muscarinic acetylcholine receptors (mAChR) and nicotinic acetylcholine receptors (nAChRs) are expressed in the striatum. The nAChRs signaling reduces neuroinflammation and facilitates neuronal survival, neurotransmitter release, and synaptic plasticity. Since there is a deficit in the nAChRs in PD, inhibiting nAChRs loss in the striatum may help prevent dopaminergic neurons loss in the striatum and its pathological consequences. The nAChRs can also stimulate other brain cells supporting cognitive and motor functions. This review discusses the cholinergic system as a therapeutic target of cotinine to prevent cognitive symptoms and transition to dementia in PD.

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.

Chemical fate and genotoxic risk associated with hypochlorite treatment of nicotine

Nicotine, the main alkaloid of tobacco, is a non- prescription drug to which all members of a tobacco-smoking society are exposed either through direct smoke inhalation or through second-hand passive 'smoking'. Nicotine is also commercially available in some pharmaceutical products and is used worldwide as a botanical insecticide in agriculture. Nicotine dynamics in indoor and outdoor environments as well as the human excretions and the manufacturing process are responsible for its entry in the environment through municipal and industrial wastewater discharges. The presence of nicotine in surface and ground waters points out that it survives a conventional treatment process and persists in potable-water supplies. Complete removal of nicotine is instead reported when additional chlorination steps are used. In this paper a simulation of STP chlorination of nicotine and a genotoxic evaluation of its main degradation products are reported. Under laboratory conditions removal of nicotine seems not to be due to mineralization but to transformation in oxidized and chlorinated products. The by-products have been isolated after fractionation by diverse chromatographic procedures and their structures determined using mass spectrometry and (1)H and (13)C NMR spectroscopy. Preliminary genotoxic SOS Chromotests with Escherichia coli PQ37 evidence no toxicity of the products.

Long-term nicotine replacement therapy: cancer risk in context

Nicotine replacement therapy (NRT) for up to 12 weeks is well established, safe and efficacious for fostering smoking cessation. Some smokers at a high risk of relapse may benefit from long-term use, and so long-term NRT safety and efficacy have become a paramount question for the FDA and others. Laboratory studies have indicated a carcinogenic potential of nicotine. Animal model studies reported in this issue of the journal by Maier and colleagues (beginning on page 1743) and Murphy and colleagues (beginning on page 1752), however, provide additional reassurance that NRT does not promote lung cancer. Very long-term studies of NRT effects do not yet exist and would be needed to definitively answer the question about NRT efficacy and cancer risk and some decision making will need to be made based on limited human data and experimental studies. The overall NRT safety question is complex and requires consideration of three contexts and comparator groups (long-term NRT/abstinence vs. smoking, long-term intermittent NRT/reduced smoking vs. smoking, and long-term NRT/abstinence vs. abstinence without long-term NRT). Although the data on these issues are insufficient, the first comparison seems intuitive and may be compelling enough to allow the FDA to approve a long-term indication for NRT. An important public health goal is to help smokers and their health care providers understand the implications of potential long-term NRT risks in the context of its potential benefits and the far greater risks of continued smoking.

An emulsion based microarray method to detect the toxin genes of toxin-producing organisms

Toxins produced by bacteria and fungi are one of the most important factors which may cause food contamination. The study of detection methods with high sensitivity and throughput is significant for the protection of food safety. In the present study, we coupled microarray with emulsion PCR and developed a high throughput detection method. Thirteen different gene sites which encode the common toxins of several bacteria and fungi were assayed in parallel in positive and maize samples. Conventional PCR assays were carried out for comparison. The results showed that the developed microarray method had high specificity and sensitivity. Two zearalenone-related genes were investigated in one of the ten maize samples obtained with this present method. The results indicated that the emulsion based microarray detection method was developed successfully and suggested its potential application in multiple gene site detection.

Thirdhand smoke: heterogeneous oxidation of nicotine and secondary aerosol formation in the indoor environment

Tobacco smoking is well-known as a significant source of primary indoor air pollutants. However, only recently has thirdhand smoke (THS) been recognized as a contributor to indoor pollution due to the role of indoor surfaces. Here, the effects of relative humidity (<10% RH and ∼ 45% RH) and substrate (cellulose, cotton, and paper) on secondary organic aerosol (SOA) formation from nicotine-ozone-NO(x) reactions are discussed. SOA formation from the sorbed nicotine-ozone reaction ([O(3)] = 55 ppb) varied in size distribution and number, depending on RH and substrate type, indicating the role of substrate and water interactions in SOA formation. This led to SOA yields from cellulose sorbed nicotine-ozone reaction of ∼ 1 and 2% for wet and dry conditions, respectively. SOA formation from nicotine-NO(x) reactions was not distinguishable from background levels. Simultaneously, cellulose sorbed nicotine-ozone reaction kinetics ([O(3)] = 55 ppb) were obtained and revealed pseudofirst-order surface rate constants of k(1) = (1 ± 0. 5) × 10(-3) and k(1) < 10(-4) min(-1) under <10% and ∼ 45% RH, respectively. Given the toxicity of some of the identified products and that small particles may contribute to adverse health effects, the present study indicates that exposure to THS ozonation products may pose additional health risks.

[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.

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.

Genotoxicity of benzene and its metabolites

The potential role of genotoxicity in human leukemias associated with benzene (BZ) exposures was investigated by a systematic review of over 1400 genotoxicity test results for BZ and its metabolites. Studies of rodents exposed to radiolabeled BZ found a low level of radiolabel in isolated DNA with no preferential binding in target tissues of neoplasia. Adducts were not identified by 32P-postlabeling (equivalent to a covalent binding index <0.002) under the dosage conditions producing neoplasia in the rodent bioassays, and this method would have detected adducts at 1/10,000th the levels reported in the DNA-binding studies. Adducts were detected by 32P-postlabeling in vitro and following high acute BZ doses in vivo, but levels were about 100-fold less than those found by DNA binding. These findings suggest that DNA-adduct formation may not be a significant mechanism for BZ-induced neoplasia in rodents. The evaluation of other genotoxicity test results revealed that BZ and its metabolites did not produce reverse mutations in Salmonella typhimurium but were clastogenic and aneugenic, producing micronuclei, chromosomal aberrations, sister chromatid exchanges and DNA strand breaks. Rodent and human data were compared, and BZ genotoxicity results in both were similar for the available tests. Also, the biotransformation of BZ was qualitatively similar in rodents, humans and non-human primates, further indicating that rodent and human genotoxicity data were compatible. The genotoxicity test results for BZ and its metabolites were the most similar to those of topoisomerase II inhibitors and provided less support for proposed mechanisms involving DNA reactivity, mitotic spindle poisoning or oxidative DNA damage as genotoxic mechanisms; all of which have been demonstrated experimentally for BZ or its metabolites. Studies of the chromosomal translocations found in BZ-exposed persons and secondary human leukemias produced by topoisomerase II inhibitors provide some additional support for this mechanism being potentially operative in BZ-induced leukemia.

Bacterial mutagenicity of some tobacco aromatic nitrogen bases and their mixtures

The first aim was to compare the genotoxicities of two tobacco-specific nitrosamines (TSNA), 4-(methylnitrosamino)-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) in two types of tests, the Salmonella reverse mutation assay (250-2000 microg per plate) and the Mutatox test (up to 1000 microg/ml) using dark mutant M-169 of Vibrio fischeri. The second aim was to assess the effects of single other tobacco chemicals and metabolites (nicotine (NIC), cotinine (COT), trans-3-hydroxycotinine (3HC), cotinine-N-oxide (CNO) and nicotine-N-oxide (NNO)) on the mutagenic responses at relative concentrations observed physiologically. The Salmonella strains were TA100, TA7004, TA7005, and TA7006, all showing missense backmutations that are characteristic of the TSNA. NNN was a direct mutagen to strains TA100, TA7004, and in the Mutatox test, and was not mutagenic in the presence of rat or hamster S9. NNK was mutagenic only in strain TA7004 with rat and hamster S9, but not in TA100, but was directly mutagenic in the Mutatox test. While all the other tobacco chemicals were not mutagenic alone to strains TA100 and TA7004 in the presence and absence of rat or hamster S9, the Mutatox test produced direct mutagenicity for COT, 3HC, and NNO, but not CNO. The latter was mutagenic in the Mutatox test with rat or hamster S9, but only rat S9 was effective for COT, NNO and 3HC. Inhibitory potentiations of NNN by NIC and COT were observed on strain TA7004, and by NIC on strain TA100. There were no interactions on NNK in the presence of S9 for strain TA7004 or TA100. In contrast, a complex inhibition and enhancement behavior occurred in the Mutatox test for each interaction, but no effects were observed for CNO on NNK without S9, and few for NIC on NNK with hamster S9. Compounds which showed no activity alone modulated the genotoxicity of two potent TSNAs in both types of tests.

Possible potentiation of toxins from Prevotella intermedia, Prevotella nigrescens, and Porphyromonas gingivalis by cotinine

BACKGROUND

Smoking is a recognized risk factor for the initiation and progression of periodontitis. However, the mechanism by which smoking induces its negative effects on the periodontium is not clear. This study aimed to test the hypothesis that synergy may occur between cotinine and bacterial products isolated from 3 putative periodontopathogens.

METHODS

A chick embryo toxin assay was used to investigate bacterial toxins (cell-free extracellular toxins and cell-free cell lysates) from 5 species with and without cotinine. A total of 9 putative periodontopathogens (3 species) and 2 non-oral controls (2 species) were studied. The periodontal species were: Prevotella intermedia (n = 4), Prevotella nigrescens (n = 4), and Porphyromonas gingivalis (n = 1). The control species tested were: Staphylococcus aureus (n = 1) and Escherichia coli (n = 1).

RESULTS

The toxicity kill was significantly greater than expected by simple addition alone (P <0.05, Fisher's exact test) between cotinine (800 ng/ml) and 1) the cell-free extracellular toxins of P. nigrescens MH1 and 2) the cell-free cell lysates of P. intermedia MH2. Synergy occurred with cotinine plus the cell-free extracellular toxins in all but 3 periodontal isolates, and the cell-free cell lysates in all but 2 periodontal isolates. Cotinine significantly (P <0.05, Fisher's exact test) enhanced the effects of cell-free extracellular toxins and cell lysates from one control species (E. coli), but not the other (S. aureus).

CONCLUSIONS

These findings indicate that synergy in an in vitro assay can occur between cotinine and toxins from putative periodontopathogens. This may be one important mechanism by which smoking increases the severity of periodontitis.

Induction of pulmonary CYP1A1 by nicotine

1. We have examined the catalytic activities (7-ethoxyresorufin O-deethylase [EROD] and 7-methoxyresorufin O-demethylase [MROD]), protein levels (Western blot analysis) and mRNA levels (Northern blot analysis) of cytochrome P4501A (CYP1A1 and CYP1A2) in the lung, liver and kidney following a single 2.5 mg/kg (15.4 micromol/kg) subcutaneous dose of nicotine to the female Sprague-Dawley rat. 2. Only in lung microsomes was EROD activity significantly induced by nicotine treatment. The activity increased 4.4-fold at 6 h after treatment relative to controls, peaked at 12 h at 14.7-fold the control activity and returned to near control level at 24 h. 3. In parallel with EROD activity, CYP1A1 immunoreactive protein abundance was altered significantly by nicotine treatment only in the lung, peaking at 12 h and decreasing towards control levels thereafter. 4. Following subcutaneous nicotine treatment, CYP1A1 mRNA was detectable in the lung at 6 and 12 h but not at 24 h, was slightly elevated in the kidney at 12 h and was detectable in the liver only at the 12-h point. CYP1A2 immunoreactive protein and its mRNA were detectable only in the liver, and their levels were not affected significantly by nicotine pretreatment. 5. Nicotine affected the binding of Hepa 1c1c7 cytosolic protein to a CYP1A1 xenobiotic response element in a gel mobility shift assay, suggesting involvement of the aryl hydrocarbon receptor and transcriptional activation in CYP1A1 induction by the chemical. 6. Inhaled nicotine also induced pulmonary EROD activity, and the induction by either inhaled or injected nicotine was more pronounced in the male than in the female rat. 7. The findings show that nicotine is a potent, rapid but transient inducer of CYP1A1 in the rat lung and suggest that the alkaloid is a likely contributor to CYP1A1 induction by cigarette smoke.

Janus carcinogens and mutagens

Janus carcinogens are carcinogenic agents that, under differing conditions of cell type or dose, can instead act as anticarcinogens. Studies by Haseman and Johnson [J.K. Haseman, F.M. Johnson, Analysis of rodent NTP bioassay data for anticarcinogenic effects, Mutat. Res. , 350 (1996) 131-142], have demonstrated that many chemicals that are carcinogenic for one tissue type can have anticarcinogenic action on another tissue type. As Magni et al. [G.E. Magni, R.C. von Borstel, S. Sora, Mutagenic action during meiosis and antimutagenic action during mitosis by 5-aminoacridine in yeast, Mutat. Res., 1 (1964) 227-230] have shown in 1964, this principle holds true for chemical mutagens as well, that is 9-aminoacridine is an antimutagen in the vegetative cell and a mutagen in the sporulating cell. The conclusion can be drawn that two established carcinogens, tobacco and ionizing radiation, are indeed Janus carcinogens. In their review of 'ambiguous carcinogens' (their name), Weinberg and Storer [A.M. Weinberg, J.B. Storer, Ambiguous carcinogens and their regulation, Risk Anal., 5 (1985) 151-156], pointed out that tobacco can be classified as an ambiguous carcinogen. The strong carcinogenicity and anticarcinogenicity of tobacco smoke and/or tobacco itself (i.e., chewing tobacco) may be due to components in the mixture, not that of a single carcinogenic chemical that also may be anticarcinogenic. Kondo [S. Kondo, Health Effects of Low-Level Radiation, Kinki Univ. Press, Osaka, Japan and Medical Physics Publishing, Madison, WI, 1995, 213 pp.] has compiled data that demonstrate that human populations who survive exposures to ionizing radiation generally live longer and have less cancer than unirradiated human populations, and this Janus phenomenon goes beyond the more trivial concept of increased sensitivity to radiation of rapidly dividing tumor cells. Thiabendazole is an interesting compound in that it is both aneugenic and antimutagenic, and yet it does not appear to be a carcinogen or a mutagen. It is discussed here because aneugenesis and antimutagenesis are at extremes of the mutagenic spectrum. In general, mutagenic or carcinogenic actions usually are at least partially understood at a molecular level, whereas antimutagenic and anticarcinogenic actions usually are not. It is possible there may be numerous specific mechanisms underlying the Janus activity of different chemicals.