Effect of long-term application of snuff on the oral mucosa: an experimental study in the rat

Activation of PI3K/Akt/NF-kB Signaling Mediates Swedish Snus Induced Proliferation and Apoptosis Evasion in the Rat Forestomach: Modulation by Blueberry

BACKGROUND AND OBJECTIVES

The present study was undertaken to ascertain whether the modulatory effects of blueberries on cell proliferation induced by Swedish snus in the rat forestomach epithelium is mediated via abrogation of the PI3K/Akt/NFκB signaling axis that regulates cell fate decision.

METHODS

The transcript and protein expression of genes involved in cell cycle progression and apoptosis, as well as canonical PI3K/Akt/NF-κB signaling pathways, were analyzed by qRT-PCR, immunoblotting and ELISA. Expression profiling of noncoding RNAs (ncRNAs) that influence PI3K/Akt/NF-κB signaling was undertaken. TUNEL assay was performed using flow cytometry.

RESULTS

Administration of snus induced basal cell hyperplasia in the rat forestomach with increased cell proliferation and inhibition of apoptosis. This was associated with the activation of PI3K/Akt/NFκB signaling. Coadministration of blueberries significantly suppressed snus-induced hyperplasia. Analysis of the molecular mechanisms revealed that blueberries suppress the phosphorylation of Akt, NF-κB and IKKβ, prevent nuclear translocation of NF-κB and modulate the expression of microRNAs that influence PI3K/Akt/NF-κB signaling.

CONCLUSION

Taken together, the results of the current study provide compelling evidence that blueberries exert significant protective effects against snus-induced soft tissue changes in the rat forestomach epithelium mediated by inhibiting key molecular players in the PI3K/Akt/NF-κB signaling axis. Long-term studies on the impact of snus exposure on various cellular processes, signaling pathways, and the interplay between genetic and epigenetic mechanisms are however warranted. The results of this investigation may contribute to the development of protection against soft tissue changes induced by smokeless tobacco in the human oral cavity.

Inhibition by blueberries (bilberries) and extract from milk thistle of rat forestomach hyperplasia induced by oral smokeless tobacco (Swedish snus)

The aim of this study was to identify palatable additives which have a significant protective action against soft tissue changes in the oral cavity caused by Swedish smokeless tobacco ("snus"), and that satisfy existing legal requirements. Although the cancer risk from snus is extremely low, long term use may result in highly undesirable keratotic lesions and associated epithelial abnormalities in the oral cavity. The rat forestomach, which is vulnerable to the irritative action of non-genotoxic compounds like butylated hydroxyanisole, propionic acid as well as snus, was chosen as an experimental model. Studied toxicological endpoints included histopathology and cellular proliferation based on DNA incorporation of bromodeoxyuridine. After 6 weeks' exposure, blueberries (bilberries) and an extract from the common milk thistle were found to exert a highly significant inhibition of cell proliferation induced by snus in the rat forestomach epithelium, indicating a potential protection with respect soft tissue changes in the human oral cavity.

[Smokeless tobacco]

Use of smokeless tobacco (ST) (chewing tobacco and snuff) can lead to a number of consequences detrimental to health. ST rapidly delivers high doses of nicotine, which can lead to dependence and is also a source of carcinogenic nitrosamines. Changes usually develop in the mouth area where the ST is most often placed. Non-malignant oral lesions include leuko-oedema, hyperkeratotic lesions of the oral mucosa and localised periodontal disease. Oral premalignant lesions are leukoplakia, erythroplakia, submucosal fibrosis and lichen planus. Betel chewing, with or without tobacco, may increase the incidence of oral cancer. There is conflicting evidence with regard to snuff users about the risk of oral and gastro-oesophageal cancer. ST use is a risk factor for pancreatic cancer and may increase the risk of fatal myocardial infarction and ischemic stroke. During pregnancy, ST is associated with an increase in pre-eclampsia, preterm delivery and stillbirth. Nicotine replacement therapy and bupropion reduce withdrawal symptoms and tobacco craving during ST cessation. However, they have not been shown to help long-term abstinence. Information concerning the potential hazards of ST products should be incorporated into educational programmes to discourage its use and to help users to quit. Smokeless tobacco is not recommended to help smoking cessation.

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.

Smokeless tobacco-induced lamellar body abnormalities

OBJECTIVES

To compare the morphological changes and quantitative distribution of lamellar bodies (Lb) (membrane coating granules) in the hamster cheek pouch epithelium with smokeless tobacco (ST).

MATERIALS AND METHODS

Archives of experimental material from previously published studies [S. Ashrafi, A. Das, R. Worawongvasu, B. Mehdinejad and J. Waterhouse (1992) Scanning Microscopy6: 183] were utilized. Animals in experimental group received most ST (snuff) in their right pouch, 5 days weekly, for 24 months, while no snuff was given to control group. After 24 months, the epithelial tissues were processed for electron microscopic study. Volume densities of Lb were assessed by morphometry.

MAIN OUTCOME MEASURES

Densities of Lb in the two groups, experimental vs control.

RESULTS

In the control, Lb extruded their contents into the intercellular spaces of upper granular layers and in between the last granular cell layers and keratin layers to form a permeability barrier. Conversely, in the smokeless tobacco-treated epithelium, the majority of the Lb that were formed remained inside and accumulated within the granular cells, without extruding their contents into the intercellular spaces to form a lipid compound permeability barrier.

CONCLUSIONS

Commercial alkaline ST may have contributed to the abnormal accumulation of Lb in the granular cell layer and affected the extrusion process of Lb to form an incomplete permeability barrier in the oral epithelium.

Oral cancer after using Swedish snus (smokeless tobacco) for 70 years - a case report

Whereas the smoking habit has declined significantly in Sweden in recent decades, there has been a marked increase in the consumption of 'snus' (oral moist snuff). The use of this smokeless tobacco, exposing the user locally to carcinogenic nitrosamines, raises the question - will the increasing use of snuff eventually lead to a greater incidence of oral cancer? We report the case of a 90-year-old man who developed a localized squamous cell carcinoma in the gingival fold under the upper lip, at the exact place where he had regularly placed loose oral snuff for 70 years. Although this is a reminder of a prevailing cancer risk, the time frame indicates that the risk is slight. This is consistent with recent epidemiological reports regarding the minor risk of snuff-associated cancer in the Scandinavian countries.

Systemic and local effects of long-term exposure to alkaline drinking water in rats

Alkaline conditions in the oral cavity may be caused by a variety of stimuli, including tobacco products, antacids, alkaline drinking water or bicarbonate toothpaste. The effects of alkaline pH on oral mucosa have not been systematically studied. To assess the systemic (organ) and local (oral mucosal) effects of alkalinity, drinking water supplemented with Ca(OH)2 or NaOH, with pH 11.2 or 12 was administered to rats (n = 36) for 52 weeks. Tissues were subjected to histopathological examination; oral mucosal biopsy samples were also subjected to immunohistochemical (IHC) analyses for pankeratin, CK19, CK5, CK4, PCNA, ICAM-1, CD44, CD68, S-100, HSP 60, HSP70, and HSP90. At completion of the study, animals in the study groups had lower body weights (up to 29% less) than controls despite equal food and water intake, suggesting a systemic response to the alkaline treatment. The lowest body weight was found in rats exposed to water with the highest pH value and starting the experiment when young (6 weeks). No histological changes attributable to alkaline exposure occurred in the oral mucosa or other tissues studied. Alkaline exposure did not affect cell proliferation in the oral epithelium, as shown by the equal expression of PCNA in groups. The up-regulation of HSP70 protein expression in the oral mucosa of rats exposed to alkaline water, especially Ca(OH)2 treated rats, may indicate a protective response. Intercellular adhesion molecule-1 (ICAM-1) positivity was lost in 6/12 rats treated with Ca(OH)2 with pH 11.2, and loss of CD44 expression was seen in 3/6 rats in both study groups exposed to alkaline water with pH 12. The results suggest that the oral mucosa in rats is resistant to the effects of highly alkaline drinking water. However, high alkalinity may have some unknown systemic effects leading to growth retardation, the cause of which remains to be determined.

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.

Smokeless tobacco and oral cancer: an assessment of evidence derived from laboratory animals

No carcinogenic activity was observed when snuff was inserted into the cheek pouch of the hamster or spread over the oral mucosa. This negative result was obtained in a number of experiments whether snuff was applied once only and left in place for several months or inserted repeatedly for up to 2 years. In the rat, a few tumours were observed when snuff was inserted into the artificial lip canal. The insertion appeared to cause a considerable reaction in the surrounding tissue so it is plausible to assume that trauma plays an important role in the development of these tumours. An extract of snuff applied to the oral mucosa of the rat did not produce any tumours, but an extract enriched by the addition of 10 times the naturally-occurring amounts of NNN and NNK produced a few benign tumours at the site of application. A higher incidence of tumours was produced when an equivalent amount of an aqueous solution of these two nitrosamines was applied directly to the oral mucosa, suggesting, according to the authors, that snuff inhibits the carcinogenic activity of TSNAs. Initiation/promotion studies were carried out on snuff in the rat in order to explore further its carcinogenic potential. The results were consistent with the conclusion that snuff does not possess any promotional activity. No increase in tumour incidence was observed in mice when snuff was given in the diet at concentrations of 25% gradually decreasing to 5% in a 14 month study. A negative result was also obtained in the rat given snuff at a concentration of 5% for 18 months. In hamsters given snuff at a concentration of 20% for 2 years, forestomach tumours occurred. A comparable incidence of this type of tumour occurred in animals given 20% cellulose. The result of this study does not provide valid evidence of carcinogenicity. HSV and snuff applied orally in the hamster produced a high incidence of squamous cell carcinomas. The sustained high level of squamous cell hyperplasia generated by the experimental design could account for the development of these tumours. Despite the defects in some of the earlier studies, the sum total of this experimental work suggests that snuff is not carcinogenic to the oral mucosa of the hamster or the rat. It is also unlikely to cause tumours in other tissues in these species. These results give some degree of reassurance that snuff is not likely to be carcinogenic to the human oral mucosa. The interaction of snuff and HSV viruses is, at the moment, questionable and requires further investigation.

Expression of keratin 13, 14 and 19 in oral squamous cell carcinomas from Sudanese snuff dippers: lack of association with human papillomavirus infection

In stratified squamous epithelia, altered expression of keratins (Ks) is one possible marker of malignant potential. In the epithelium of the uterine cervix, presence of human papillomaviruses (HPVs) is increasingly regarded as a marker of risk for cervical cancer. However, a similar role in oral cancer and precancer remains controversial. To address these questions, formalin-fixed, paraffin-embedded oral carcinomas from Sudanese snuff dippers (n=14) and oral carcinomas from Sudanese (n=14), Swedish (n=19) and Norwegian (n=41) non-snuff dippers were examined by immunohistochemistry for expression of K types 13, 14 and 19 using monoclonal antibodies. HPV infection was searched for in all the carcinomas by in situ hybridization (ISH) using the cocktail HPV OmniProbe and the ViraType probe. Carcinomas from Sudanese (snuff dippers/non-snuff dippers) were also examined for HPV infection by polymerase chain reaction (PCR) using the general HPV primers GP5+/GP6+. For the oral carcinomas from snuff dippers, moderate to intense expression of K13 (71%; 10/14), K14 (86%; 12/14) and K19 (93%; 13/14) was found. For the oral carcinomas from non-snuff dippers, weak to moderate expression of K13 (64%; 47/74), K14 (43%; 32/74) and K19 (45%; 33/74) was found. HPV DNA was not detected in any of the carcinomas from three countries when examined by ISH. The Sudanese (from snuff dippers/non-snuff dippers) oral carcinomas were also negative for HPV DNA with the PCR. The present study shows that (i) there is a high level of expression of K13, K14 and K19 in oral carcinomas from snuff dippers compared to those from non-snuff dippers, (ii) this high level of expression may arise from dysregulation of keratinocyte proliferation and maturation caused by damaging effects of snuff, (iii) the HPV genome is not found in Sudanese (snuff dippers/non-snuff dippers), Swedish or Norwegian oral carcinomas, and (iv) this may suggest that these viruses do not play a prominent role in the aetiology of oral carcinomas from these countries.

Immunohistochemical detection of p53 in non-malignant and malignant oral lesions associated with snuff dipping in the Sudan and Sweden

Immunohistochemistry was used to examine the expression of p53 in pre-malignant oral lesions and oral squamous-cell carcinomas (SCCs) from Swedish and Sudanese snuff-dippers, as well as in pre-malignant oral lesions and oral SCCs from non-snuff-dippers from the Sudan, Sweden and Norway. Of the 14 SCCs from Sudanese snuff-dippers, 21% (3/14) expressed p53. Of the 14, 60 and 41 SCCs from non-snuff-dippers from the Sudan, Sweden and Norway, 64% (9/14), 65% (39/60) and 68% (28/41) expressed p53, respectively. A statistically significant difference in expression of p53 was found in SCCs from Sudanese snuff-dippers compared to those from non-snuff-dippers from all/or any of the 3 countries. None of the suspected pre-malignant oral lesions from Sudanese snuff dippers or non-snuff-dippers expressed p53. Only 2 out of the 15 oral fibro-epithelial hyperplastic lesions from Swedish snuff-dippers expressed p53. Some of the oral epithelial dysplastic lesions, as well as the carcinoma in situ lesions from Norwegian non-snuff-dippers, expressed p53, while the oral fibro-epithelial hyperplastic lesions did not. The low relative frequency of p53 expression found in oral SCCs from snuff-dippers compared to those from non-snuff-dippers might suggest differences in mechanisms of oncogenic action induced by snuff. Alternatively, the pathogenesis of malignant oral lesions from snuff-dippers may follow a p53-independent pathway. In view of the unusually high levels of the tobacco-specific nitrosamines (TSNA) found in the type of snuff used in the Sudan, investigations of p53 mutations or oncogenes are needed.

Assessment of p53 and Ki-67 expression in snuff-induced lesions

An immunohistochemical study of snuff-induced lesions with a monoclonal antibody (DO-7) specific to p53 mutant and wildtype antioncogene product demonstrated nuclear overexpression of the mutant protein in 45.9 nuclear profiles/mm2 epithelium (SEM 10.8; n = 15) compared with only 0.18 positively stained nuclear profiles/mm2 in the control group (SEM 0.18; n = 4). Furthermore, the biopsy material was also stained with the antibody Ki-67, which has been shown to be excellent for the estimation of the growth fraction in both normal and malignant human tissues. Ki-67 stained positive in 566.1 nuclear profiles/mm2 epithelium (SEM 85.0; n = 15) in the snuff-group compared with 20.2 nuclear profiles/mm2 (SEM 4.9; n = 4) in the control group. To the best of our knowledge, this is the first study showing overexpression of p53 protein and Ki-67 in snuff-induced lesions. The results may indicate that the p53 gene is involved in the initial events leading to subsequent malignant transformation of oral mucosa exposed to snuff. Furthermore, mutations of the p53 gene have been associated with increased cellular proliferation with greater risk of perpetuation of mutations and malignant transformation.

The effect of N-nitrosonornicotine on the buccal mucosa of Syrian hamsters

PURPOSE

The carcinogens in smokeless tobacco have been identified as the tobacco-specific nitrosamines and the effect of one of these, N-Nitrosonornicotine (NNN), on the buccal mucosa of the Syrian hamster was studied.

MATERIALS AND METHODS

Buccal pouches of 36 Syrian hamsters were painted five times per week for 24 weeks with 10 mg/mL 98% pure NNN in suspension with mineral oil. Animals were killed at 6, 8, 12, and 24 weeks.

RESULTS

At 6 weeks, the buccal pouch mucosa of the experimental animals appeared clinically more hyperemic than those of the controls. From 12 weeks onward, all experimental animals showed epithelial hyperplasia and inflammation on histologic examination. Three animals killed at 24 weeks showed mild epithelial dysplasia.

CONCLUSIONS

Exposure of Syrian hamster buccal mucosa to NNN, five times per week for 24 weeks, did not result in clinical or histologic cancerous changes. NNN may require other factors for cancer production, such as a cocarcinogen, a higher concentration, or a longer period of application.

Carcinoma of buccal mucosa in smokeless tobacco users: a preliminary study of the use of cytology for early detection

A type of smokeless tobacco, known as Maras powder, is widely used in lieu of cigarettes in the south-eastern region of Turkey. In the present study, we evaluated cytological smears obtained from the lesion of lower lip mucosa of 80 smokeless tobacco users. There were severe epithelial abnormalities in seven out of the 80 subjects. Punch biopsies from these cases disclosed dysplasia in three cases, carcinoma in situ in two, and carcinoma in the other two cases. There was mild dysplasia in two punch biopsies of the remaining 73 cases. Oral cancer in tobacco powder users appeared to be related to the length of use, as it was observed only in subjects with 15 or more years of exposure.

In vitro and animal studies of the role of viruses in oral carcinogenesis

The linkage of herpes simplex virus (HSV) and human papillomavirus (HPV) to the development of oral cancer has been studied. In spite of the presence of viral nucleic acids in some human oral cancer specimens, HSV alone is not carcinogenic in animals: repeated viral inoculation to mouse or hamster oral mucosa fails to produce tumours or histopathological evidence of malignancy. However, HSV demonstrates co-carcinogenicity in vivo: viral inoculation significantly enhances the oncogenic capacity of chemical carcinogens in the oral cavity of mice and hamsters. Though the detailed mechanisms of HSV cocarcinogenicity are unknown, HSV promotes the chemical carcinogen-induced activation of certain cellular proto-oncogenes and inactivation of p53 tumour suppressor gene. Human papillomaviruses type 16 (HPV-16) and 18 (HPV-18) demonstrate oncogenicity by transforming normal human oral keratinocytes in vitro. While normal cells exhibit a limited life-span, cells transformed by these viruses show immortality and altered morphology in comparison with their normal counterparts. The HPV-immortalised cells contain multiple copies of intact viral genome integrated into cellular chromosomes. These cells also express several viral-specific mRNAs including viral E6/E7 mRNAs. Notably, these cells contain low levels of p53 protein and overexpressed cellular myc proto-oncogene compared to their normal counterpart; however, the immortilised cell lines are non-tumorigenic in nude mice.

The prevalence of recurrent herpes labialis during an army hot weather exercise

A survey was performed on 1,062 of 2,500 (42%) Army personnel participating in a desert training exercise at Fort Irwin, California, in September 1983. The prevalence of recurrent herpes labialis (RHL) and chapped lips was observed during the third week of a four-week training period. Complexion, sex, lip protectant use, age, and time spent outdoors were obtained by observation and interview. Recurrent herpes labialis was found in 46 subjects (4%). Stratified analysis and stepwise logistic regression were used to identify risk factors associated with RHL and to determine the prevalence odds ratios (POR). Risk factors with statistically significant associations with RHL were lip protectant use (POR = 0.19), chapped lips (POR = 2.87), being female (POR = 5.00), and light complexion (POR = 2.48). These findings strongly support the use of lip protectants during prolonged exposure to hot, dry climates as a prophylaxis against recurrent herpes labialis. Additional studies should focus on excitatory factors of RHL; and clinical trials of the efficacy of the lip protectants to protect against RHL and chapped lips should be undertaken.

Nicotine-derived N-nitrosamines (TSNA) and their relevance in tobacco carcinogenesis

Biochemical studies and bioassays support the concept that the increased risk for cancer of the oral cavity in snuff dippers and cancer of the lung, upper aerodigestive tract, and pancreas in smokers is most likely associated with the exposure to tobacco-specific N-nitrosamines. The doses of TSNA required to induce tumors in the oral cavity in rats and tumors in the lungs of rats and hamsters are comparable to the total doses of TSNA to which a long-term snuff dipper, respectively a cigarette smoker, are exposed over 4 decades. The carcinogenic NNN and NNK are metabolized to highly reactive electrophiles which react with nucleophilic centers of DNA and with proteins. The DNA-adducts are known to cause miscoding which can activate K-ras proto-oncogenes. K-ras oncogenes have been detected in adenocarcinomas of the lung of smokers. TSNA also form globin adducts in the blood of laboratory animals as well as of snuff dippers and smokers. Such adducts are currently being evaluated for their significance as biochemical markers of exposure to TSNA. These biomarkers may also serve as indicators for the possible endogenous formation of TSNA in tobacco chewers and smokers. Additional research needs in TSNA carcinogenesis include the development of modified methods for the reduction of TSNA in tobacco and smoke, inhibition of TSNA carcinogenesis by nutrients and micro-nutrients and the testing of chemopreventive agents.

Evaluation of the evidence that tobacco-specific nitrosamines (TSNA) cause cancer in humans

Considerable evidence exists that TSNA may cause cancer in humans. Strong evidence suggests that the NNN and NNK in snuff are at least partially responsible for the excess of oral cancer among snuff dippers. Tobacco smoke, because it is a combustion product, is a far more complex matrix than is smokeless tobacco. Nonetheless, NNK is well established as a lung carcinogen in laboratory animals at levels similar to those experienced by heavy smokers. Although the epidemiology of the smoking/lung cancer association has been studied extensively and is well established as a causal relationship, few attempts have been made to determine the effective constituents in tobacco smoke, much less to quantify them and to reduce their levels in consumer products. More work is needed to determine TSNA uptake in smokers and users of smokeless tobacco and to determine the factors involved in the possible endogenous formation of TSNA and in their metabolic activation or inhibition of their formation. Exploratory work is in progress with various biological markers that may prove useful in quantifying the levels of TSNA exposure in humans. Epidemiologic evidence indicates that in addition to tobacco use other factors are causally related to the development of cancers of the oral cavity, lung and esophagus and that these factors (e.g., radon exposure in uranium miners who smoke) can act synergistically. Experimental investigation of some of these synergistic effects may prove to be a step in the direction of determining the proportion of various cancers that are likely to be attributable to various causes and ultimately to the various constituents of tobacco exposure.

Effect of repeated oral administration of tobacco snuff on natural killer-cell activity in the rat

The possible immune effect of oral snuff was investigated. In male adult rats, oral snuff given for 15 weeks significantly decreased NK-cell activity in peripheral blood against murine NK cell-sensitive target cells (YAC-1 lymphoma).

Modulatory effects of snuff, retinoic acid, and beta-carotene on DMBA-induced hamster cheek pouch carcinogenesis in relation to keratin expression

The hamster cheek pouch (HCP) serves as an excellent model system not only for the studies on initiation and promotion but also for the modulation of experimental oral carcinogenesis. In our studies, HCPs treated with 7,12-dimethylbenz[a]anthracene (DMBA) showed both cheek pouch and stomach papillomas. Utilizing this model system, we tested and compared the modulatory effects of snuff, retinoic acid, and beta-carotene on the incidence of tumors and the keratin expression pattern. HCPs treated with snuff, either alone or in combination with DMBA, resulted in stomach papillomas. HCPs treated with snuff showed no cheek pouch tumors, and those treated with snuff and DMBA showed only 10-15% tumor incidence. Both beta-carotene and retinoic acid showed a total inhibition of DMBA-induced carcinogenesis in the HCP as well as in the stomach. The keratin expression pattern showed alterations depending on the experimental conditions.

Snuff tumorigenesis: effects of long-term snuff administration after initiation with 4-nitroquinoline-N-oxide and herpes simplex virus type 1

The tumor promoting effects of snuff was studied in Lewis rats initiated with 4-nitroquinoline-N-oxide (4-NQO) and Sprague Dawley rats repeatedly inoculated with herpes simplex virus type 1 (HSV-1). The test substances were administered in a surgically created canal in the lower lips of the rats. There were 15 rats in each test group and 10 rats in the control group. In the groups treated with 4-NQO and 4-NQO + snuff, 8 and 12 tumors (5 and 9 malignant) were found, respectively. In the group subjected to HSV-1 only, 3 tumors were found (2 malignant), in the group subjected to snuff only, 4 tumors were found (3 malignant) and in the group subjected to the combination of HSV-1 and snuff, 13 tumors were found (7 malignant). In the control group only one malignancy was found. The study did not show any promoting effects of snuff in the oral cavity after initiation with 4-NQO. Neither was there any increase in the number of oral tumors in rats treated with HSV-1 and snuff. However, there was a marked increase in the number of malignant tumors outside the oral cavity in the group treated with HSV-1 and snuff, underlining the importance of interactions between these two agents in the development of malignant lesions.

Morphologic and immunohistochemical evidence of human papillomavirus capsid antigen in smokeless tobacco keratoses from juveniles and adults

Seventy-seven tissue samples from patients with either degree I, II, or III smokeless tobacco keratoses were examined. The tissues were evaluated for the presence of human papillomavirus (HPV) antigen by immunocytochemical staining. Capsid antigen could be identified in sixteen cases (20.78%). This investigation further supports the concept that smokeless tobacco-associated leukoplakias can be correlated with HPV infection.

An interpretative review of smokeless tobacco research in the United States: Part I

The first part of a two-part series reviewing the published literature of smokeless tobacco in the United States and concomitant health effects associated with its use. This article delineates the current status of its prevalence, behavioral psychosocial factors associated with use, and review of the negative health effects associated with regular use.

Effect of smokeless tobacco on the replication of herpes simplex virus in vitro and on production of viral lesions in hamster cheek pouch

Previous experiments have shown that combination of herpes simplex virus (HSV) infection and simulated snuff-dipping in hamster buccal pouches enhances the development of micro-invasive squamous cell carcinoma in cheek pouch epithelium. The effect has now been determined of water-extractable components of snuff (snuff-extract) on the growth and the cell-lysing activity of HSV. Various dilutions of snuff-extract in tissue culture medium significantly inhibited the growth of HSV in Vero cell monolayers by inhibiting the viral DNA replication. Moreover, HSV was inactivated and its cell-lysing activity lost when it was incubated with snuff-extract in cell-free condition. Snuff also had a similar anti-herpetic effect in vivo; HSV infection of pouch tissues followed by simulated snuff-dipping resulted in significant inhibition of viral growth. Thus snuff interferes with the DNA synthesis and cytolytic activity of HSV in vitro and in vivo, and this in turn, may increase its oncogenic capacity.

The reversibility of the snuff-induced lesion: an experimental study in the rat

Snuff lesions were induced in 30 rats. Ten of the snuff-exposed rats were killed immediately after 13 months snuff exposure, as were the 10 control animals. Ten rats were killed 1 month and 10 rats 4 months after the snuff administration had ceased. The rats exposed to snuff for 13 months exhibited hyperplastic, hyperorthokeratotic epithelium with focal mild atypia, focal ulcerations and marked subepithelial fibrosis. These changes were markedly reduced or absent in rats exposed to snuff and killed after a snuff-free interval of 1 or 4 months. Similar differences between the test-groups were seen in the epithelium lining the gingival sulcus of the lower incisors. This area seems to be more sensitive to chemical exposure than the oral mucosa proper as more severe microscopical changes were seen here. Snuff exposure results in the development of a hyperplastic, reactive, reversible lesion of the oral mucosa, suggesting that snuff predominantly has promoting activity when administered for a relatively short interval of time.

Forestomach carcinogens: possible mechanisms of action

A brief review indicates that a considerable number of compounds induce forestomach tumours in different species. Naturally occurring forestomach tumours are rare (an incidence of less than 1%) in rats and mice, but they do occur in hamsters with incidences up to 12%. Most forestomach carcinogens are known to be genotoxic, although a few non-genotoxic substances are also able to induce this type of tumour. The promoting and inhibiting action of substances in a two-stage forestomach tumour model is described. Morphologically the development of tumours is characterized by early lesions such as epithelial damage, hyperplasia and hyperkeratosis, which at a later stage progress to strong diffuse hyperplasia, dysplasia, papilloma and squamous-cell carcinoma. Possible mechanisms of action of non-genotoxic forestomach carcinogens are described, and the relevance to man is discussed. Since humans have no squamous epithelium in the stomach, the potential risk from non-genotoxic forestomach carcinogens involves exposure of the mouth, pharynx and oesophagus at dose levels that exert irritating action. It seems very unlikely that exposure to concentrations far below those having irritating potential is hazardous to man.

The reemergence of smokeless tobacco

Smokeless tobacco (snuff and chewing tobacco) is reemerging as a popular form of tobacco, particularly among male adolescents. In different regions of the United States, from 8 to 36 percent of male high-school students are regular users. The use of smokeless tobacco has been shown to cause oral-pharyngeal cancer. The strongest link is with cancers of the cheek and gum. White mucosal lesions (leukoplakia) are found in 18 to 64 percent of users, often at the site where the tobacco was held. Other associations have been suggested for cancers of the esophagus, larynx, and pancreas. Nitrosamines, found in high concentrations in smokeless tobacco, most likely have a role in its carcinogenicity. Other health problems include periodontal disease, acute elevations of blood pressure, and dependence. In early 1986, after action at the state level, Congress enacted a federal law requiring health-warning labels on packages of smokeless tobacco and a ban on electronic advertising. Other regulatory measures under consideration include raising state and federal excise taxes, tightening controls on advertising, and prohibiting sales to minors. In view of the recent growth of this problem, policy makers are taking the opportunity to intervene with preventive measures to protect a new generation of tobacco users.

Effect of excisional wounding on DMBA-induced hamster tongue carcinogenesis

The purpose of this study was to investigate histologically the effect of wounding on the hamster tongue after pretreatment with DMBA. The animals in which the tips of the tongues were pretreated with DMBA for 8 weeks, subsequently excised, and had no treatment or received applications of acetone, showed epithelial dysplasias. The animals which had the same pretreatment, excision, and received additional post-excision applications of DMBA for 9-13 days, developed squamous cell carcinomas. However, the animals which were pretreated with DMBA for 8 weeks but had no excision, did not show any pathologic changes, even though they received additional applications of DMBA for 9-13 days. The animals which received no pretreatment with DMBA for 8 weeks but had an excision, showed normal wound healing, even though they had a post-treatment with DMBA for 9-13 days. The results of the present study indicated that excisional wounding acted as a promotional stimulus in inducing the appearance of epithelial dysplasias or carcinomas of tongues initiated with the carcinogen DMBA.

Snuff-induced lesions in Finnish recruits

Snuff-induced lesions from 21 snuff users were studied clinically, histologically and by electron microscopy. Clinically most lesions appeared coarsely wrinkled, grayish white and slightly elevated. All lesions were found in the upper vestibular area. Histologically, epithelial thickening, acanthosis, vacuolation of surface cells and a slight subepithelial inflammatory reaction were seen. The electron microscopic findings revealed an intact basement lamina, increased tonofilament concentration moving up towards the surface of the epithelium, widening of intercellular spaces in the spinous cell layer and partial keratinization of surface cells. The salivary flow of resting saliva showed a slightly significant increase compared to controls. That of stimulated saliva was not significantly increased among snuff users.

Effect of snuff and herpes simplex virus-1 on rat oral mucosa: possible associations with the development of squamous cell carcinoma

The purpose of this investigation was to study the effect of snuff and experimentally induced herpes simplex virus type 1 (HSV-1) infection in Sprague-Dawley rats. It was demonstrated that it was possible to obtain 100% development of acute HSV-1 infection in the rat oral mucosa, but only 10% of latent reactive infection of the trigeminal ganglia. The rats were, therefore, acutely infected monthly with virus to simulate recurrence of latent infection. Virus was applied topically to the mucous membrane twice with an interval of one month. Snuff was administered between the virus applications and afterwards to half the virus-exposed animals. Sham-infected rats were given snuff during the same period (18 months). A fourth group of rats were left untreated. A complete post-mortem examination was performed. Two rats exposed to snuff and HSV-1 in combination developed squamous cell carcinoma of the oral cavity. It was also found that rats exposed to snuff alone or in combination with HSV-1 had a higher incidence of tumours or tumour-like conditions than control rats exposed to HSV-1 only. The incidence of malignant tumours was significantly higher in rats exposed to snuff or HSV-1 and snuff in combination than in control animals (p less than 0.05). The results of the study indicate that HSV-1 in combination with snuff exposure may be associated with the development of squamous cell carcinomas of the oral cavity.