Smokeless tobacco use and oral epithelial dysplasia

Clinicopathologic evaluation of lesions associated with tobacco usage

INTRODUCTION

Tobacco usage in different forms is the single most common etiological factor responsible for oral cancers. The aim of the present study was to record various mucosal lesions associated with tobacco usage and to ascertain the prevalence of dysplasia in them by histopathological evaluation and to compare the extent of dysplastic features seen among patients associated with a habit of smoked and smokeless form of tobacco.

MATERIALS AND METHODS

Seventy-six patients with the clinical diagnosis of tobacco related lesions (Leukoplakia, Erythroplakia, Nicotina stomatitis, Tobacco pouch keratosis) were selected. A detailed description of the clinical presentation of the lesion was noted and the patients were subjected to incisional biopsy followed by a histopathological evaluation.

RESULTS

Showed dysplastic changes in 50 cases (65.8%) ranging from mild dysplasia in 27 cases (35.5%), moderate dysplasia in 17 cases (22.4%) and 6 cases (7.9%) showed severe dysplasia. Moderate to severe dysplasia was 1.83 times more likely to occur with smokeless tobacco usage when compared to smoked form. Data obtained from this study reveals that patients with a duration of tobacco usage more than 10 years were 2.17 times more likely to have moderate to severe dysplasia (p = 0.154).

CONCLUSION

Thus, the study highlights the role of oral physicians in detecting oral mucosal lesions and screening high-risk patients on a regular basis and also reaffrms the importance of public education, stressing the risk factors for oral cancers.

Receptor-mediated tobacco toxicity: acceleration of sequential expression of alpha5 and alpha7 nicotinic receptor subunits in oral keratinocytes exposed to cigarette smoke

Tobacco products and nicotine alter the cell cycle and lead to squamatization of oral keratinocytes (KCs) and squamous cell carcinoma. Activation of nicotinic acetylcholine receptors (nAChRs) elicits Ca(2+) influx that varies in magnitude between different nAChR subtypes. Normal differentiation of KCs is associated with sequential expression of the nAChR subtypes with increasing Ca(2+) permeability, such as alpha5-containing alpha3 nAChR and alpha7 nAChR. Exposure to environmental tobacco smoke (ETS) or an equivalent concentration of nicotine accelerated by severalfold the alpha5 and alpha7 expression in KCs, which could be abolished by mecamylamine and alpha-bungarotoxin with different efficacies, suggesting the following sequence of autoregulation of the expression of nAChR subtypes: alpha3(beta2/beta4) > alpha3(beta2/beta4)alpha5 > alpha7 > alpha7. This conjecture was corroborated by results of quantitative assays of subunit mRNA and protein levels, using nAChR-specific pharmacologic antagonists and small interfering RNAs. The genomic effects of ETS and nicotine involved the transcription factor GATA-2 that showed a multifold increase in quantity and activity in exposed KCs. Using protein kinase inhibitors and dominant negative and constitutively active constructs, we characterized the principal signaling cascades mediating a switch in the nAChR subtype. Cumulative results indicated that the alpha3(beta2/beta4) to alpha3(beta2/beta4)alpha5 nAChR transition predominantly involved protein kinase C, alpha3(beta2/beta4)alpha5 to alpha7 nAChR transition-Ca(2+)/calmodulin-dependent protein kinase II and p38 MAPK, and alpha7 self-up-regulation-the p38 MAPK/Akt pathway, and JAK-2. These results provide a mechanistic insight into the genomic effects of ETS and nicotine on KCs and characterize signaling pathways mediating autoregulation of stepwise overexpression of nAChR subtypes with increasing Ca(2+) permeability in exposed cells. These observations have salient clinical implications, because a switch in the nAChR subunit composition can bring about a corresponding switch in receptor function, leading to profound pathobiologic effects observed in KCs exposed to tobacco products.

Inhibition of nitric oxide-induced apoptosis by nicotine in oral epithelial cells

Development of oral cancer is clearly linked to the usage of smokeless tobacco. The molecular mechanisms involved in this process are however not well understood. Toward this goal, we investigated the effect of smokeless tobacco exposure on apoptosis of oral epithelial cells. Exposure of oral epithelial cells to smokeless tobacco extract (STE) induces apoptosis in a dose-dependent manner, until a threshold level of nicotine is achieved upon which apoptosis is inhibited. 1 mM of nicotine is able to inhibit apoptosis significantly induced by STE in these oral cells. Exposure of cells to nicotine alone has no effect on apoptosis, but nicotine inhibits apoptosis induced by other agents present in STE. In this study we show that, the anti-apoptotic action of nicotine is specifically associated with down-regulation of nitric oxide (NO) production. Using specific inducers of NO, we have demonstrated that inhibition of apoptosis by nicotine is through down-regulation of NO production. Further, we observed that nicotine clearly acts as a sink of NO radicals, shown using peroxynitrite generator (SIN-1) in conjunction or absence of radical scavengers. Nicotine thus causes most damage in transformed epithelial cells as depicted by accumulation of nitrotyrosine in a 3-NT ELISA assay. Inhibition of apoptosis is a hallmark in tumor progression and propels development of cancer. It may further result in functional loss of apoptotic effector mechanisms in the transformed cells. Thus, our data clearly indicates that inhibition of NO-induced apoptosis by nicotine may lead to tobacco-induced oral carcinogenesis, and implies careful development of modalities in tobacco cessation programs.

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.

Tobacco harm reduction: an alternative cessation strategy for inveterate smokers

According to the Centers for Disease Control and Prevention, about 45 million Americans continue to smoke, even after one of the most intense public health campaigns in history, now over 40 years old. Each year some 438,000 smokers die from smoking-related diseases, including lung and other cancers, cardiovascular disorders and pulmonary diseases. Many smokers are unable--or at least unwilling--to achieve cessation through complete nicotine and tobacco abstinence; they continue smoking despite the very real and obvious adverse health consequences. Conventional smoking cessation policies and programs generally present smokers with two unpleasant alternatives: quit, or die. A third approach to smoking cessation, tobacco harm reduction, involves the use of alternative sources of nicotine, including modern smokeless tobacco products. A substantial body of research, much of it produced over the past decade, establishes the scientific and medical foundation for tobacco harm reduction using smokeless tobacco products. This report provides a description of traditional and modern smokeless tobacco products, and of the prevalence of their use in the United States and Sweden. It reviews the epidemiologic evidence for low health risks associated with smokeless use, both in absolute terms and in comparison to the much higher risks of smoking. The report also describes evidence that smokeless tobacco has served as an effective substitute for cigarettes among Swedish men, who consequently have among the lowest smoking-related mortality rates in the developed world. The report documents the fact that extensive misinformation about ST products is widely available from ostensibly reputable sources, including governmental health agencies and major health organizations. The American Council on Science and Health believes that strong support of tobacco harm reduction is fully consistent with its mission to promote sound science in regulation and in public policy, and to assist consumers in distinguishing real health threats from spurious health claims. As this report documents, there is a strong scientific and medical foundation for tobacco harm reduction, and it shows great potential as a public health strategy to help millions of smokers.

Diagnosis and management of suspicious lesions of the oral cavity

Oral lesions associated with premalignant changes and malignancy present in diverse ways. This article discusses the clinical characteristics of such lesions enabling clinicians to identify classical features.Additionally, an effort is made to familiarize clinicians with the significance of red and white lesions, especially those having a high index of suspicion for oral cancer, and to alert clinicians when a biopsy is mandatory.

Smokeless tobacco and oral cancer: a review of the risks and determinants

Smokeless tobacco has been associated with oral cancer for many decades. The purpose of this article is to review research relevant to this association, including epidemiologic studies, studies of putative carcinogens such as tobacco-specific nitrosamines (TSNAs) and other contaminants, and possible cancer inhibitors. Epidemiologic studies addressing this issue primarily consist of case-control studies. They show that the use of chewing tobacco and moist snuff is associated with very low risks for cancers of the oral cavity and related structures (relative risks [RR] from 0.6 to 1.7). The use of dry snuff is associated with higher RRs, ranging from 4 to 13, while the RRs from smokeless tobacco, unspecified as to type, are intermediate (RR = 1.5 to 2.8). With regard to TSNAs, historical levels in American moist snuff products were higher than those in their Swedish counterparts, but levels in contemporary products are uniformly low. TSNA levels in chewing tobacco have always been low, but levels in dry snuff have been higher, including some very high levels in current products. In general, smokeless tobacco users are not exposed to significant levels of cadmium, lead, benzo(a)pyrene, polonium-210, and formaldehyde, when compared with concentrations of these compounds in foods. Finally, low oral cancer risk from smokeless tobacco use may be influenced by the presence of cancer inhibitors, mainly anti-oxidants, in smokeless tobacco products.

A receptor-mediated mechanism of nicotine toxicity in oral keratinocytes

Smoking and smokeless tobacco cause morbidity that originates from the epithelium lining of the skin and upper digestive tract. Oral keratinocytes (OKC) express nicotinic acetylcholine receptors (nAChRs) that bind nicotine (Nic). We studied the mechanism of the receptor-mediated toxicity of tobacco products on OKC. Preincubation of normal human OKC with Nic altered the ligand-binding kinetics of their nAChRs, suggesting that the nAChRs underwent structural changes. This hypothesis was confirmed by the finding that exposure of OKC to Nic causes transcriptional and translational changes. Through RT-PCR and immunoblotting, we found a 1.5- to 2.9-fold increase in the mRNA and protein levels of alpha3, alpha5, alpha7, beta2, and beta4 nAChR subunits. Exposure of OKC to Nic also changed the mRNA and protein levels of the cell cycle and cell differentiation markers Ki-67, PCNA, p21, cyclin D1, p53, filaggrin, loricrin, and cytokeratins 1 and 10. The nicotinic antagonist mecamylamine prevented these changes, which indicates that the Nic-induced changes in the expression of both the nAChR and the cell cycle and cell differentiation genes resulted from pharmacologic stimulation of nAChRs with Nic. To establish the relevance of these findings to the pathobiologic effects of tobacco products in vivo, we studied the above parameters in the oral tissue of rats and mice after their exposure for 3 weeks to environmental cigarette smoke or drinking water containing equivalent concentrations of Nic that are pathophysiologically relevant. The changes of the nAChRs and the cell cycle and cell differentiation genes were similar to those found in vitro. The results of indirect immunofluorescence assay of tissue specimens validated these findings. Thus, some pathobiologic effects of tobacco products in oral tissues may stem from Nic-induced alterations of the structure and function of keratinocyte nAChRs responsible for the physiologic regulation of the cell cycle by the cytotransmitter acetylcholine.

Choline acetyltransferase, acetylcholinesterase, and nicotinic acetylcholine receptors of human gingival and esophageal epithelia

A non-neuronal cholinergic system that includes neuronal-like nicotinic acetylcholine receptors (nAChRs) has recently been described in epithelial cells that line the skin and the upper respiratory tract. Since the use of nicotine-containing products is associated with morbidity in the upper digestive tract, and since nicotine may alter cellular functions directly via nAChRs, we sought to identify and characterize a non-neuronal cholinergic system in the gingival and esophageal epithelia. mRNA transcripts for alpha3, alpha5, alpha7, and beta2 nAChR subunits, choline acetyltransferase, and the asymmetric and globular forms of acetylcholinesterase were amplified from gingival keratinocytes (KC) by means of polymerase chain-reactions. These proteins were visualized in the gingival and esophageal epithelia by means of specific antibodies. Variations in distribution and intensity of immunostaining were found, indicating that the repertoire of cholinergic enzymes and receptors expressed by the cells changes during epithelial maturation, and that an upward concentration gradient of free acetylcholine exists. Blocking of the nAChRs with mecamylamine resulted in reversible loss of cell-to-cell adhesion, and shrinking and rounding of cultured gingival KC. Activation of the receptors with acetylcholine or carbachol caused stretching and peripheral ruffling of the cytoplasmic aprons, and formation of new intercellular contacts. These results demonstrate that both the keratinizing epithelium of attached gingiva and the non-keratinizing epithelium lining the upper two-thirds of the esophageal mucosa possess a non-neuronal cholinergic system. The nAChRs expressed by these epithelia are coupled to regulation of cell adhesion and motility, and may provide a target for the deleterious effects of nicotine.

Oral cancer in a tobacco-chewing US population--no apparent increased incidence or mortality

OBJECTIVE

Smokeless tobacco use is an accepted risk factor for oral cancer in the United States, but the major proof of this is based largely on a single epidemiologic (case-control) comparison of women, whereas the chewing of tobacco is predominantly a habit of men. The present investigation sought to compare gender-specific oral cancer mortality and incidence rates in West Virginia, the state with the highest per capita consumption of smokeless tobacco, with rates from other states and with the US average rates. It was hypothesized that the cancer rates for West Virginia males would be significantly greater than the US average and greater than the rates for states with less smokeless tobacco consumption.

STUDY DESIGN

Data from the West Virginia Cancer Registry for the years 1993 through 1995 were compared with data from contemporary Surveillance and Epidemiology End Results for the US (with respect to incidence) and from the Center for Disease Control and Prevention's National Center for Health Statistics (with respect to mortality).

RESULTS

The average annual incidence rates (per 100,000 population) for oral/pharyngeal cancer in West Virginia males and females were 13.4 and 5.1, respectively; these compared with rates of 15.4 and 5.7 for the US. The average annual mortality rates (per 100,000 population) for the disease in West Virginia males and females were 4.2 and 1.6, respectively; these compared with 4.4 and 1.5 for the US. West Virginia oral/pharyngeal mortality rates for both genders were statistically significantly lower than US rates throughout the years 1950 through 1980. Among other potential oral cancer etiologic factors, the very low prevalence of alcohol abuse in West Virginia seemed to be relevant.

CONCLUSIONS

The hypothesis was not confirmed by data analysis. West Virginia is the state with the highest per capita consumption of smokeless tobacco, yet it has less oral/pharyngeal cancer than the US average. The authors strongly urge additional and improved epidemiologic evaluation of the oral cancer risk of smokeless tobacco use in US males.

Effect of snuff and smoking on tenascin expression in oral mucosa

We have shown, by using two monoclonal antibodies (143DB7 and 100EB2), that the expression of the extracellular matrix protein tenascin (Tn) is increased in the connective tissue of biopsies taken from snuff users' and tobacco smokers' oral mucosa. In normal oral mucosa Tn was seen to underlie the epithelium as a thin delicate band. The most increase in Tn reaction was observed in snuff users' mucosa while the immunoreaction in smokers' mucosa was less conspicuous. Often the most prominent Tn reaction took place in association with round cell inflammatory infiltration, indicating epithelial irritation. Tn has been shown to take part in epithelial-mesenchymal interactions during embryogenesis, wound healing and tumorigenesis. Here, a superficial epithelial irritant has been shown to cause conspicuous alterations not only in the epithelial cell layers but also in the underlying connective tissue by increasing its Tn content. As a result of our findings we suggest a further link for Tn in a dynamic epithelial-mesenchymal interplay by virtue of this marked connective tissue reaction in snuff users' and smokers' oral mucosa.

Tobacco use and cancer. A reappraisal

With approximately six million users, smokeless tobacco has received considerable scrutiny as a risk factor for oral cancer. We review the relationship between smokeless tobacco use, keratosis, and oral cancer. Several features of smokeless tobacco keratosis, including the natural history, clinical presentation, and biologic behavior, differentiate it from other leukoplakias that exhibit greater malignant potential. Previous research has demonstrated that the relative risk of oral cancer with smokeless tobacco use is 4.2, about half of the risk from smoking (relative risk = 10 to 15). Mortality data from populations with sustained high-frequency smokeless tobacco use do not support the mistaken prediction of an epidemic of oral cancer with increasing smokeless tobacco use. In fact, the risks of smokeless tobacco use compare so favorably with those of smoking that smokers who switch to smokeless tobacco reduce their risks for all tobacco-related illnesses including oral cancer. Although some criticize this proposal as less than an ideal solution for the nation's smokers, full adoption of this strategy would eventually save over 400,000 lives each year.

Planning a spit tobacco cessation intervention: identification of beliefs associated with addiction

We examine the relationship between beliefs regarding spit tobacco (ST) use and addiction among 473 male college athletes who currently use ST. Beliefs were assessed using methods prescribed by the Theory of Reasoned Action. Independent associations between beliefs and addiction, defined by self-reported amount of ST used per week, were found via multivariate polychotomous regression modeling. We found that with increasing addiction level, athletes were significantly more likely to believe that "ST helps me relax," "ST keeps me alert," "ST tastes good," and "ST is addicting." All athletes believed that clinicians, parents, and girlfriends do not approve of their ST use, but that male peers, coaches, and professional athletes are fairly indifferent about it. To increase quit rates, highly addicted ST users may require an intensive cessation program including nicotine replacement to overcome symptoms of withdrawal, oral substitutes for the enjoyable taste of ST, and the support of male peers and athletes who influence their social norms.

The prevalence of oral lesions in smokeless tobacco users and an evaluation of risk factors

BACKGROUND

The widespread use of smokeless tobacco (ST) has prompted concern in regard to the development of oral lesions in long-term users.

METHODS

For inclusion in the current study, a subject must have used an ST product, either snuff or chewing tobacco, for at least 6 months. The subjects were recruited by advertising, and none was referred for the evaluation of an oral lesion. The following were performed on all subjects: assessment of exposure to ST, cigarettes, and alcohol; examination of the oral cavity; a biopsy, if an oral lesion was found; and analysis of a blood sample for beta-carotene. The dietary intake of most of the subjects was analyzed.

RESULTS

Of the 347 ST users, all of whom were white male subjects, 45 (13.0%) had an oral lesion. Thirty-five of the lesions were hyperkeratosis and 10 were epithelial dysplasia.

CONCLUSIONS

Snuff exposure was associated significantly with the presence of an oral lesion (P < 0.0001). A decreased vitamin C intake also was found among the ST users with oral lesions (P < 0.01). The ST users with epithelial dysplasia, as compared with those with hyperkeratotic lesions, were slightly older, had a lower intake of vitamin C (P < 0.05), and were more likely to have used chewing tobacco than snuff.

Histopathology of smokeless tobacco lesions in professional baseball players. Associations with different types of tobacco

We examined 142 biopsy specimens of smokeless tobacco-associated oral mucosal lesions from 133 professional baseball players. Four types of epithelial change were observed in the specimens: hyperparakeratosis, hyperorthokeratosis, pale surface staining, and basal cell hyperplasia. These types of epithelial change were associated with the type of smokeless tobacco used (snuff or chewing tobacco) but not with the duration (years) or amount (hours per day) of use. The thickness of hyperkeratosis in a specimen correlated directly with the amount of smokeless tobacco use. The use of snuff was more frequently associated with development of oral mucosal lesions than was the use of chewing tobacco, and snuff appeared to cause a greater variety and severity of epithelial change than did chewing tobacco.

Comparison of oral carcinomas in smokeless tobacco users and nonusers

Biopsy reports of squamous cell carcinoma (SCC) and verrucous carcinoma (VC) were retrospectively evaluated to determine the prevalence of smokeless tobacco (ST) use and to ascertain if any clinical or histologic differences existed when comparing ST users with nonusers. Of the 874 SCC cases, 12 patients (1.4%) were ST users as compared with 7.7% (10 of 129) of the VC patients. The carcinomas in ST users, either SCC or VC, were diagnosed at a later age and were more likely to occur in the buccal mucosa/vestibule area. The SCCs in ST users were more often histologically well differentiated. Because of the anatomic site predilection, it appears probable that ST use is a causative factor in the development of some cases of oral carcinoma.

Reduction of Langerhans cells in smokeless tobacco-associated oral mucosal lesions

Localized absence of epithelial Langerhans cells (LC) has been shown to affect systemic immune responses, allow microbial colonization and play a possible role in carcinogenesis. Because use of smokeless tobacco is associated with abnormal oral mucosal changes and development of carcinoma, we examined lesion and control specimens from 17 current users of smokeless tobacco to determine whether lesions showed changes in LC number or antigen expression. We identified LC by immunohistochemistry with antibodies to the antigens T6, HLA-DR, HLA-DQ, and HLA-DP. Lesion specimens contained fewer LC (means of 6 LC/mm and 10 LC/mm2) than did the corresponding control specimens (means of 14 LC/mm and 30 LC/mm2), and in each pair of lesion and autologous control specimens the reduction in LC was on average 58% (range, 3% to 95%). There were no apparent differences between lesion and control specimens in the number of LC expressing each of the four marker antigens. Reductions in LC occurred in all types of smokeless tobacco-associated lesions, regardless of increased epithelial thickness or changes in keratinization. Our data indicate that smokeless tobacco reduces the number of Langerhans cells at its site of contact with the oral mucosa.

Evaluation of risk factors in smokeless tobacco-associated oral lesions

Smokeless tobacco (ST) users and nonusers were recruited to evaluate the contribution of various risk factors (ST use, cigarettes, alcohol, and diet) in the development of oral mucosal lesions. Ninety-eight ST users with no lesion, 29 ST users with an oral lesion, and 33 nonusers were enrolled in the study. ST users with lesions, when compared with users with no lesion, were more likely to have used snuff than chewing tobacco (p = 0.01) and to have used more ST (p less than 0.01). Alcohol consumption, dietary intake of beta-carotene, and serum levels of beta-carotene were not related to an increased risk of lesion development. Our findings showed that the only significant risk factor for ST-associated oral lesions was the extent of ST exposure. Of 127 ST users, 29 (22.8%) had an oral lesion at the time of examination. Of these lesions, 23 (79.3%) were hyperkeratotic and 6 (20.7%) were epithelial dysplasia.

Reversibility of snuff dippers' lesion in Swedish moist snuff users: a clinical and histologic follow-up study

The purpose of this study was to assess possible reversibility of oral mucosal changes, associated with the use of Swedish moist snuff, after change of habit. Biopsies from a total material of 252 regular snuff users, 184 using loose snuff and 68 using portion-bag packed snuff, were screened microscopically to identify histopathologic epithelial changes in addition to, or differing from, those generally seen as a result of snuff use. The main basis for selection of these variables were the criteria of epithelial dysplasia as defined by WHO and the eight histologic features, which have been reported to be the most important discriminators to separate cases with leukoplakia that subsequently developed carcinoma, from those that did not. Twenty-nine subjects, 3 showing Degree 2 lesions, 21 Degree 3 lesions and 5 Degree 4 lesions, all of them loose snuff users were identified. All the 29 users were re-examined clinically and histologically after 3-6 months. The rebiopsy was always secured from the same mucosal area as the original biopsy. At follow-up, 20 subjects had either stopped their snuff habit or changed to portion-bags and changed placement of the quid. All of them showed a healthy mucosa at the previous biopsy site and normal tissue in the histologic examination of the rebiopsies. Seven subjects had changed to portion-bags and variably reduced their daily exposure to snuff. At follow-up they presented with less pronounced clinical changes and the rebiopsies showed evidence of reduced epithelial changes. One major conclusion from this study is that tissue changes, clinically as well as histologically, are reversible following cessation of snuff habit.(ABSTRACT TRUNCATED AT 250 WORDS)