Genotoxicity of 'gudakhu', a tobacco preparation. II. In habitual users

Relationship between type of smokeless tobacco & risk of cancer: A systematic review

BACKGROUND & OBJECTIVES

Causative linkages of smokeless tobacco (SLT) use with oral potentially malignant disorders and cancers of oral cavity, oesophagus and pancreas have been reported. Published meta-analyses have provided pooled risk estimates for major cancers caused by SLT, both on global and regional levels. This systematic review was aimed at summarizing the available studies on occurrence and mortality risk of common cancers due to various SLT products.

METHODS

PubMed and Google Scholar databases were systematically searched from 1985 till January 2018 for observational studies on SLT and cancer. The included studies were evaluated and data were extracted and reviewed.

RESULTS

The review included 80 studies providing 121 risk estimates for various cancers. Majority of the studies from South-East Asian Region (SEAR) and Eastern Mediterranean Region (EMR) showed a significant positive association of SLT use with oral [odds ratio (OR) ranging from 1.48 to 27.4] and oesophageal cancers (OR between 2.06 and 12.8), while studies from European Region (EUR) reported a positive association with pancreatic cancer (OR between 1.6 and 2.1). Cancer-related mortality was evaluated in a few reports with higher risk of mortality for lung (OR between 2.0 and 9.1), cervical (OR 2.0) and prostate (OR 2.1) cancers. A wide variation was noted in the association of various cancers and specific SLT products based on their nature, methods of use and inherent toxicity. The majority of chewing tobacco products displayed higher risk for oral and oesophageal cancers while the same was not observed for snus.

INTERPRETATION & CONCLUSIONS

This review emphasizes on the significantly positive association of SLT use with oral and oesophageal cancers in SEAR and EMR and pancreatic cancer in EUR. Mortality estimates for SLT-associated cancers need further analysis. Risk analysis for cancers of other sites in SLT users also requires multicentric well-designed studies.

Assessment of micronuclei frequency in individuals with a habit of tobacco by means of exfoliated oral buccal cells

AIMS AND OBJECTIVES

To study the genotoxic effects of tobacco on the exfoliated buccal epithelial cells in patients with oral precancerous lesions (OPLs) and Patients with tobacco habit but without oral precancerous lesion(habit controls) by using micronucleus assay as well as the quantification and detection of the biomarkers in these premalignant lesions which will be helpful in finding those patients who are at higher risk for malignant transformation.

MATERIALS AND METHODS

Forty samples were collected from the right and left side of buccal epithelial cells obtained from 20 individuals, i.e., 10 patients with habit control and 10 patients with OPLs. Statistical analysis was performed by the Statistical Package for the Social Sciences version 21.0 Unpaired t-test was performed to determine the micronucleated cell (MNC) and micronuclei (MN) frequencies in individuals; significance was set at P > 0.05.

RESULTS

There was an increase in both the MNC and MN frequency from habit controls to OPLs, indicating that the number of cells with chromosomal damage and extent of chromosomal damage in each cell was high in OPLs.

CONCLUSION

The MN count can be used as a noninvasive tool for early detection, educating patients, screening a large population, and to check the risk for malignancy, which in turn may help in treatment planning.

Involvement of various molecular events in cellular injury induced by smokeless tobacco

Smokeless tobacco (ST) consumption is implicated in the pathogenesis of oral diseases, including cancer. However, its pathological effect in other organs is not well understood. In the present study, the effect of aqueous extract of smokeless tobacco (AEST) prepared from "gutkha" (a form of ST) on the xenobiotic drug-metabolizing enzymes, histopathological changes, and damage to the genetic material in lung, liver, and kidney of rats was evaluated. Animals were orally administered AEST at a low dose (L-AEST, 96 mg/kg body wt/day) for 2 (L-AEST(2)) and 28 weeks (L-AEST(28)) and at a high dose (H-AEST, 960 mg/kg body wt/day) for 2 weeks (H-AEST(2)). Real-time PCR and immunohistological studies showed that administration of L-AEST(2) did not induce the expression of phase I cytochrome P450s (CYP1A1, 1A2, and 2E1) and phase II mu-glutathione-s-transferase (GST-mu) drug-metabolizing enzymes in lung, liver, and kidney. Although H-AEST(2) administration significantly induced both gene and protein expression of CYP1A1, 1A2, and 2E1 in all of the above organs, it mildly expressed the phase II detoxifying enzyme, GST-mu, in type I and type II epithelial cells of lung and in proximal tubular cells of kidney. L-AEST(28) enhanced the gene and protein expression of CYP1A1, 1A2, and 2E1 in lung, liver, and kidney in a differential manner and induced the expression of GST-mu in lung and kidney. L-AEST(28) induced the micronuclei formation in the peripheral blood mononuclear cells, TNF-alpha in plasma, and myeloperoxidase activity in the organs. L-AEST(28) significantly enhanced Bax, p53, and NF-kappaB and decreased Bcl-2 gene expressions differentially in an organ-specific manner. The differential changes in these organs due to AEST might be due to their different physiological functions and variable sensitivities toward the metabolites of AEST, which create a microenvironment favorable for AEST-induced pathogenesis. This study broadens the insight into the different molecular mechanisms in various organs, which appear to be deregulated due to AEST. Understanding these processes may help in clinical treatment planning strategies for tobacco-related diseases.

The effect of maras powder on DNA methylation and micronucleus formation in human buccal tissue

The plant powder "maras powder" (MP) has been used widely instead of cigarettes in the southeastern region of Turkey. The aim of this study was to assess the impacts of MP and cigarette smoking on the methylation and micronuclei (MN) formation in buccal cells of humans with a comparison to blood lymphocytes. DNA samples from 80 subjects (40 MP users, 20 tobacco smokers, 20 healthy volunteers) were analyzed for their genomic methylation status using Hpa II and Msp I digestions followed by a simple gel electrophoresis and ethidium bromide staining. A densitometric method was developed to measure the methylation in genomic DNA samples and the results were evaluated using a software program designed for this purpose. Buccal epithelial cells were collected from the same groups and examined for MN formation. The results indicated that a general genomic hypomethylation was present in almost all of the samples that were obtained from MP users and tobacco smokers. This hypomethylation was significant in MP users compared to smokers and healthy volunteers. The percentage of cells containing MN was 1.93 in MP users, 0.95 in healthy volunteers, and 1.82 in smokers. The MN frequency was significantly higher in MP users and smokers than in healthy volunteers. There was no statistical difference between smokers and MP users. Evidence indicates that MP usage induces DNA hypomethylation and increase frequency of MN formation.

Clinical, pathological, cellular and molecular lesions caused by oral smokeless tobacco - a review

While carcinogenicity of smokeless tobacco (ST) to humans is well established the oral lesions that precede development of cancer are less well characterized. The clinical appearances of ST-associated lesions are variable. Epidemiological studies show a strong significant association of risk with chronic daily use but population differences are noted because of various commercial products in use. Morphological features observed are some what different to oral lesions caused by smoking and oral dysplasia in ST-associated lesions is less common. Effects of ST on oral keratinocytes observed in vitro include alterations in cell proliferation, apoptosis and activation of inflammatory markers. Genetic aberrations caused by ST include activation of ras, uncommon in smokers but mutational hot spots in p53 encountered are similar to those in smokers.

Smoking and smokeless tobacco-associated human buccal cell mutations and their association with oral cancer--a review

Reported herein are the results of a structured literature review that was undertaken to (a) determine if human buccal (mouth) cell changes are associated with smoking and smokeless ("chewing") tobacco, (b) tabulate different buccal cell alterations that have been reported, (c) delineate buccal cell assays that have been used successfully, (d) determine whether buccal cell changes correlate with oral cancer as defined in clinicopathologic investigations, and (e) assess the feasibility of developing a high-throughput buccal cell assay for screening smokers for the early detection of oral cancer. The results of the studies reported herein have established that diverse buccal cell changes are associated with smoking and smokeless tobacco. This review documents also that buccal cells have been collected in a noninvasive manner, and repetitively for serial studies, from different sites of the mouth (e.g., cheek, gum, and tongue) and from normal tissue, preneoplastic lesions (leukoplakia), and malignant tumors. Tobacco-associated genetic mutations and nongenetic changes have been reported; a partial listing includes (a) micronuclei, (b) bacterial adherence, (c) genetic mutations, (d) DNA polymorphisms, (d) carcinogen-DNA adducts, and (e) chromosomal abnormalities. Clinical studies have correlated buccal cell changes with malignant tumors, and some oral oncologists have reported that the buccal cell changes are practical biomarkers. Summarily, the literature has established that buccal cells are useful not only for characterizing the molecular mechanisms underlying tobacco-associated oral cancers but also as exfoliative cells that express diverse changes that offer promise as candidate biomarkers for the early detection of oral cancer.

Influence of smokeless tobacco exposure on detoxification status and chromosomal damage in male and female habitues

In India, a large number of tobacco chewers and masheri users are chronically exposed to tobacco genotoxicants. Detoxification processes involving cellular glutathione (GSH) and glutathione S-transferases (GST) determine the outcome of exposure to environmental mutagens including those present in tobacco. Hence, in this study, GSH levels, GST activity, GSTM1 genotype and cytogenetic damage were determined using lymphocytes from 114 smokeless tobacco habitues and controls. The study groups comprised of male tobacco chewers, female masheri users, and age- and sex-matched controls. Irrespective of the tobacco habit, GSH levels and GST activity were higher in females than in males. In both the groups of habitues, GSH levels were similar to those in controls, while a significant reduction in GST activity was observed in tobacco chewers only. The frequency of cytogenetic alterations was significantly elevated in both the groups of habitues with respect to controls. However, break-type aberrations were more frequent in tobacco chewers while gaps were commonly observed in masheri users. Differences in the nature of chromosomal alterations in the two groups of habitues appeared to be related to variation in total tobacco exposure and gender-related differences in the efficacy of the GSH/GST detoxification system.