Oral lesions, genotoxicity and nitrosamines in betel quid chewers with no obvious increase in oral cancer risk

A link between the generation of areca nut-related N-nitrosamines in the saliva, the induction of genotoxic damage in the oral mucosa, as judged by an increase in micronucleated exfoliated cells (MEC), and a low incidence of oral cancer was studied in 2 population groups characterized by their habit of chewing quids without tobacco: Guamanians, who chew areca nuts (Areca catechu) with or without the addition of betel leaf (Piper betle); Taiwanese, who use areca nut, betel leaf or inference and slaked lime. The levels of N-nitrosoguvacoline (NG) in the saliva of chewers of fresh green areca nuts were very high (70.8 ng/ml) as compared to those reported for individuals using the more complex Indian betel quids (0.91 ng/ml or 5.6 ng/ml). None of the other areca nut-related nitrosamines (N-nitrosoguvacine (NGC), 3-(methylnitrosamino)propionitrile (MNPN) and 3-(methylnitrosamino)propionaldehyde (MNPA)) were detected in the saliva of Taiwanese betel quid chewers. The addition of slaked lime to the areca nut enhances the formation of NG during a chewing session. The frequency of MEC did not increase in the oral mucosa of areca nut chewers who do not use slaked lime, but showed a small but significant elevation in individuals using lime-containing quids. The elevation of MEC in Taiwanese, who are at low risk for oral cancer, is relatively small as compared to that found in chewers of Indian betel quids (pan), who show a highly elevated oral cancer risk. The results seem to suggest that NG may play only a minor role, if any, in the etiology of oral cancer among betel quid chewers.     

Tobacco (Kretek) Smoking,Betel Quid Chewing and Risk of Oral Cancer in a Selected Jakarta Population

Purpose: This study aimed to determine the association between tobacco consumption (kretek) and betel quidchewing with oral cancer risk. Materials and Methods: A total of 81 cases of oral cancers were matched with162 controls in this hospital-based study. Information on sociodemographic characteristics and details of riskhabits (duration, frequency and type of tobacco consumption and betel quid chewing) were collected. Associationbetween smoking and betel quid chewing with oral cancer were analysed using conditional logistic regression.Results: Slightly more than half of the cases (55.6%) were smokers where 88.9% of them smoked kretek. Afteradjusting for confounders, smokers have two fold increased risk, while the risk for kretek consumers and thosesmoking for more than 10 years was increased to almost three-fold. Prevalence of betel quid chewing among casesand controls was low (7.4% and 1.9% respectively). Chewing of at least one quid per day, and quid combinationof betel leaf, areca nut, lime and tobacco conferred a 5-6 fold increased risk. Conclusions: Smoking is positivelyassociated with oral cancer risk. A similar direct association was also seen among betel quid chewers.     

Chromosome-damaging activity of saliva of betel nut and tobacco chewers

Saliva of volunteers chewing betel quid, cured betel nut (Areca catechu), betel leaves (Piper betle), a mixture of quid ingredients (dried betel nut flakes, catechu, cardamon, lime, copra and menthol) and Indian tobacco was collected and examined for its genotoxic activity. Chromosome aberrations (chromatid breaks and chromatid exchanges) in Chinese hamster ovary (CHO) cells were used to estimate the genotoxic effect. No detectable levels of clastogenic activity were observed in the saliva of non-chewing individuals. After 5 min of chewing betel quid, betel nut, betel leaves, quid ingredients and Indian tobacco, the saliva samples showed relatively potent clastogenic activities. The addition of transition metals Mn²⁺ and Cu²⁺ to the saliva samples of betel nut and Indian tobacco chewers enhanced their clastogenic activities, whereas Fe³⁺ increased the clastogenicity of the betel nut saliva but decreased the genotoxic effect of the saliva of Indian tobacco chewers. After removal of the betel quid or its components from the mouth, the clastogenic activity disappeared within 5 min. The western-type chewing tobacco did not produce a genotoxic activity in the saliva of chewers. A possible association between the genotoxicity in the saliva of betel quid chewers and the development of oral, pharyngeal and esophageal carcinomas is discussed.     

Cytotoxic Effects of Betel Quid and Areca Nut Aqueous Extracts on Mouse Fibroblast,Human Mouth-Ordinary-Epithelium 1 and Human Oral Squamous Cell Carcinoma Cell Lines

Background: Betel quid chewing is more common among the older generation in rural areas of Malaysia. Oral cancer in Asia has been associated with the habit of chewing betel quid and areca nut. Objective:  This study aims to investigate the cytotoxic effects of betel quid and areca nut extracts on the fibroblast (L929), mouth-ordinary-epithelium 1 (MOE1) and oral squamous cell carcinoma (HSC-2) cell lines. Methods: L929, MOE1 and HSC-2 cells were treated with 0.1, 0.2 and 0.4 g/ml of betel quid and areca nut extracts for 24, 48 and 72 h. MTT assay was performed to assess the cell viability. Results: Both extracts, regardless of concentration, significantly reduced the cell viability of L929 compared with the control (P<0.05). Cell viability of MOE1 was significantly enhanced by all betel quid concentrations compared with the control (P<0.05). By contrast, 0.4 g/ml of areca nut extract significantly reduced the cell viability of MOE1 at 48 and 72 h of incubation. Cell viability of HSC-2 was significantly lowered by all areca nut extracts, but 0.4 g/ml of betel quid significantly increased the cell viability of HSC-2 (P<0.05). Conclusion: Areca nut extract is cytotoxic to L929 and HSC-2, whereas the lower concentrations of areca nut extract significantly increased the cell viability of MOE1 compared to the higher concentration and control group. Although betel quid extract is cytotoxic to L929, the same effect is not observed in MOE1 and HSC-2 cell lines. Further investigations are needed to clarify the mechanism of action.     

Elevated frequency of micronucleated cells in the buccal mucosa of individuals at high risk for oral cancer: betel quid chewers

The micronucleus test was applied to buccal mucosa cells of 2 population groups at high risk for oral cancer: Khasis of the northeastern hill region of India, who eat raw betel nuts together with betel leaves and lime, and residents of the state of Orissa (India), who chew betel quids consisting mainly of perfumed tobacco, dried betel nut, betel leaf, lime and several spices. Micronuclei were scored on Feulgen/fast green-stained smear preparations of exfoliated cells obtained by scraping the surface of the buccal mucosa. All 17 raw betel nut eaters and all 20 chewers of betel quids had significantly elevated frequencies of micronucleated mucosa cells over nonchewing controls of comparable ethnic background and dietary habits. The frequencies of micronucleated exfoliated cells were higher at the site within the oral cavity where the quid was kept compared to those at the opposite buccal wall. The micronuclei frequency was lower among individuals chewing a raw betel nut, betel leaf and lime mixture compared to those using tobacco,-betel nut-, lime- and betel leaf-containing quids. Micronuclei frequencies in exfoliated human cells seem to represent a useful 'internal dosimeter' for estimating exposure to genotoxic, and by implication, carcinogenic agents in the tissue from which cancers will develop.     

Promoting activity of betel quid ingredients and their inhibition by retinol

Ingredients of betel quids, which have been linked to the high incidence of precancerous oral lesions and oral cancers, were examined for their promoting activity. Aqueous extracts were tested using the bovine papillomavirus (BPV) DNA transformation assay, which consists of cultured C3H/10T1/2 cells transfected with the plasmid pdPBV-1 as targets, and the frequency of transformed foci as endpoints. Areca nut extracts enhanced the formation of BPV DNA-induced transformed foci approximately tenfold. No promoting activity was detected in two samples of chewing tobacco examined. The addition of retinol to the areca nut extract inhibited its tumour promoting effect in a dose-dependent manner, completely abolishing the promoting activity at a dose of 10(-6) M. The experimental results are compared with epidemiological data on oral cancer incidences among chewers of different areca nut/tobacco mixtures and with the chemopreventive effect of vitamin A administered to betel quid chewers.     

Ortho- and meta-tyrosine formation from phenylalanine in human saliva as a marker of hydroxyl radical generation during betel quid chewing

The habit of betel quid chewing, common in South-East Asia andthe South Pacific islands, is causally associated with an increasedrisk of oral cancer. Reactive oxygen species formed from polyphenolicbetel quid ingredients and lime at alkaline pH have been implicatedas the agents responsible for DNA and tissue damage. To determinewhether hydroxyl radical (HO) is generated in the human oralcavity during chewing of betel quid, the formation of o- andm-tyrosine from L-phenylalanine was measured, Both o- and m-tyrosinewere formed in vitro in the presence of extracts of areca nutand/or catechu, transition metal ions such as Cu²⁺ and Fe²⁺and lime or sodium carbonate (alkaline pH). Omission of anyof these ingredients from the reaction mixture significantlyreduced the yield of tyrosines. Hydroxyl radical scavengerssuch as ethanol, D-mannitol and dimethylsulfoxide inhibitedthe phenylalanine oxidation in a dose-dependent fashion. Fivevolunteers chewed betel quid consisting of betel leaf, arecanut, catechu and slaked lime (without tobacco). Their saliva,collected after chewing betel quid, contained high concentrationsof p-tyrosine, but no appreciable amounts of o- or m-tyrosine.Saliva samples from the same subjects after chewing betel quidto which 20 mg phenylalanine had been added contained o- andm-tyrosine at concentrations ranging from 1010 to 3000 nM andfrom 1110 to 3140 nM respectively. These levels were significantlyhigher (P< 0.005) than those of subjects who kept phenylalaninein the oral cavity without betel quid, which ranged from 14to 70 nM for o-tyrosine and from 10 to 35 nM for m-tyrosine.These studies clearly demonstrate that the HO radical is formedin the human oral cavity during betel quid chewing and is probablyimplicated in the genetic damage that has been observed in oralepithelial cells of chewers.     

Different impact from betel quid, alcohol and cigarette: risk factors for pharyngeal and laryngeal cancer

The risks of betel quid chewing with or without tobacco, alcohol drinking and cigarette smoking have been well explored in the oral cavity but not in the pharynx and larynx. We conducted a case-control study to investigate the association of these three risk factors to cancers of the pharynx and larynx in Taiwan. A total cases of 148 pharyngeal cancer, 128 laryngeal cancer and 255 hospital controls, all men, were recruited. Betel quid chewing was a significant independent risk factor (adjusted odds ratio [aOR] = 7.7; 95% confidence interval [CI] = 4.1-15.0) similar to that of alcohol drinking (aOR = 6.6; 95% CI = 3.5-13.0) for pharyngeal cancer, but not for laryngeal cancer (aOR = 1.3; 95% CI = 0.7-2.5) on which cigarette smoking (aOR = 7.1) exerts a stronger significant independent risk than alcohol drinking (aOR = 3.8). For pharyngeal cancers, chewers who consumed >20 quid/day, chewed with inflorescence in the quid or swallowed the betel quid juice were at higher risks; significant dose-response effects were found in daily quantity of drinking and chewing, and cumulative quantity of drinking. Synergistic effects from the 3 risk factors existed both on the pharynx (aOR = 96.9) and the larynx (aOR = 40.3), and attributed for 93.1% and 92.9% respectively. Our study is the first evidence to show that betel quid chewing without tobacco has different impact on the pharynx (digestive tract) and the larynx (airway), and supports the concept that exposure quantity and direct mucosal contact with the betel quid juice may contribute to carcinogenesis. Our results show an important insight into the impact of betel quid chewing on other sites of the digestive tract other than the oral cavity.     

A study of betel quid carcinogenesis. 1. On the in vitro N-nitrosation of arecoline

Betel quid chewing is strongly associated with cancer of theoral cavity. Extracts of betel quid are tumorigenic in the experimentalanimal, but thus far, not a single carcinogen has been detectedin the tobacco free quid. This study is based on the hypothesisthat during chewing, arecoline, the major alkaloid of the betelnut, gives rise to carcinogenic N-nitros-amines. In vitro experimentsreported here have shown that N-nitrosation of arecoline leadsto N-nitrosoguvacoline (NG), 3-(methylnitrosamino)propionitrile(MNPN) and 3-(methyI-nitrosoamino)propionaldehyde. Although,according to an earlier study, NG is most likely not carcinogenic,MNPN is suspected to be a relatively strong animal carcinogenbased on bioassays with its lower homologue. The conditionsprevailing in the oral cavity of betel quid chewers are likelyto favor the formation of these three nitrosamines.     

Chewing areca nut, betel quid, oral snuff, cigarette smoking and the risk of oesophageal squamous-cell carcinoma in South Asians: a multicentre case-control study

Oesophageal cancer remains an important public health problem worldwide. This multicentre matched case-control study examined the chewing areca nut alone, betel quid with tobacco, oral snuff (snuff dipping) and cigarette smoking as the risk factors for oesophageal squamous-cell carcinoma. We enrolled 91 cases of oesophageal squamous-cell carcinoma and 364 matched controls from three tertiary-care hospitals in Karachi, Pakistan. A structured questionnaire was used to collect the data through face-to-face interview of the participants. Multivariable conditional logistic regression model showed that after adjusting for the effect of ethnicity, ever chewed areca nut alone (adjusted matched odds ratio (mOR(adj))=3.7; 95% confidence interval (CI): 1.6-8.5), ever chewed betel quid with tobacco (mOR(adj)=12.8; 95% CI: 6.3-26.2), ever practiced snuff dipping (mOR(adj)=4.3; 95% CI: 1.6-11.7) and ever smoked cigarettes (mOR(adj)=2.9; 95% CI: 1.4-5.9) were significantly and independently associated with oesophageal squamous-cell carcinoma status. The adjusted summary population attributable risk (PAR) percent for all four substances together was 67.0. Furthermore, despite incomplete synergy, there was manifold increase in the risk of oesophageal squamous-cell carcinoma, if the respondents ever smoked cigarettes and ever chewed betel quid with tobacco (mOR(adj)=21.4; 95% CI: 6.3-72.4) or if they ever smoked cigarettes and ever practiced snuff dipping (mOR(adj)=14.4; 95% CI: 2.3-91.1). The adjusted PAR (%) was higher for the dual practice of smoking cigarettes and chewing betel quid with tobacco (64.3) than the dual practice of smoking cigarettes and snuff dipping (32.2). Public awareness to curtail the addiction to these substances may result in a substantial reduction in the incidence of oesophageal squamous-cell carcinoma and related mortality in this and similar settings.     

Betel quid not containing tobacco and oral cancer: a report on a case-control study in Papua New Guinea and a meta-analysis of current evidence

Smoking and betel quid chewing are associated with increased risk of oral cancer but few studies have reported on associations in populations where betel quid does not contain tobacco. We conducted a case-control study in Papua New Guinea and a systematic review. Our case-control study recruited 143 cases with oral cancer and 477 controls. We collected information on smoking and betel quid chewing. Current smoking was associated with an increased risk of oral cancer with an adjusted odds ratio (OR) for daily smokers of 2.63 (95% confidence intervals (95% CI) 1.32, 5.22) and amongst heaviest smokers of 4.63 (95% CI 2.07, 10.36) compared to never-smokers. Betel chewing was associated with increased risk of oral cancer with an adjusted OR for current chewers of 2.03 (95% CI 1.01, 4.09) and in the heaviest chewers of 2.47 (95% CI 1.13, 5.40) compared to nonchewers. The OR in those who both smoked tobacco and chewed betel quid was 4.85 (95% 1.10, 22.25), relative to those who neither smoked nor chewed. The systematic review identified 10 previous studies that examined risk of oral cancer associated with betel quid chewing that controlled for smoking in populations where betel quid did not contain tobacco. In studies that reported results for non-smokers the combined OR was 2.14 (95% CI 1.06, 4.32) in betel quid chewers and in studies that adjusted for smoking the combined OR was 3.50 (95% CI 2.16, 5.65) in betel quid chewers. Preventive efforts should discourage betel quid chewing as well as smoking.     

The Risk of Oral Cancer among Different Categories of Exposure to Tobacco Smoking in Sri Lanka

Background: The global incidence of oral squamous cell carcinoma (OSCC) is on the rise with no improvement seen in survival rates. Tobacco consumption varies depending on geographic location, ethnicity and culture. The present case-controlled study aimed to determine the relative risk of OSCC for different tobacco consumption patterns in a selected Sri Lankan population. Methods: One hundred and five patients with histopathologically confirmed OSCC attending the National Cancer Institute (Apeksha Hospital) of Sri Lanka and 210 age and gender-matched controls from the community responded to an interviewer-administered questionnaire regarding their smoking and betel-quid chewing (with/ without smokeless tobacco) habits were included in the study. The odds ratios (OR) and 95% confidence intervals (CI) were calculated. p<0.05 was considered as statistically significant. Results: The overall risk of OSCC increased 2.93-fold for smokers. Those smoking two packets of cigarettes or more per day (OR=5.56; 95% CI-2.822-10.984; p=0.000) had more than double the risk of OSCC than those smoking 1-2 packets per day. Smoking for more than 20 years had a 3.4-fold risk of OSCC. Consumption of betel quid containing tobacco (smokeless tobacco) had a 4.26-fold higher risk for OSCC (OR=4.26; 95% CI-2.21-8.21; p=0.000), and the risk increased when all four ingredients (betel leaf, slaked lime, areca nut, and tobacco) were consumed together (OR=4.26; 95% CI-2.34-7.74; p=0.000). The combined effect from concurrent smoking and betel chewing emerged as the highest risk for OSCC (OR=15.34) which significantly exceeded the risks evident for the two habits practised in isolation from each other. Conclusions: Use of smokeless tobacco, consumption of all four ingredients together, duration of smoking, the number of cigarettes smoked per day and combined consumption of betel quid and smoking are significant risk factors in the development of OSCC among Sri Lankans.     

Effect of lime composition on the formation of reactive oxygen species from areca nut extract in vitro

Lime, representative of that used by betel quid chewers, was collected in a region of Papua New Guinea where the incidence of oral cancer is high. The free calcium hydroxide content and pH of 25 lime samples were highly correlated with the generation of reactive oxygen species from areca nut extract in vitro, and DNA damage in vitro, measured as 8-hydroxy-2'-deoxyguanosine. Fe2+ and Mg2+ levels in the lime samples were too low to modify formation of reactive oxygen species, but hydrogen peroxide formation was almost entirely inhibited by addition of Mg2+ to the reaction mixture. These results suggest that the calcium hydroxide content of lime in the presence of areca nut is primarily responsible for the formation of reactive oxygen species which might cause oxidative damage in the DNA of buccal mucosa cells of betel quid chewers.     

Oral submucous fibrosis: review on aetiology and pathogenesis

Data from recent epidemiological studies provide overwhelming evidence that areca nut is the main aetiological factor for OSF. A clear dose-dependent relationship was observed for both frequency and duration of chewing areca nut (without tobacco) in the development of OSF. Commercially freeze dried products such as pan masala, Guthka and mawa (areca and lime) have high concentrates of areca nut per chew and appear to cause OSF more rapidly than by self prepared conventional betel quid that contain smaller amounts of areca nut. It is logical to hypothesise that the increased collagen synthesis or reduced collagen degradation as possible mechanisms in the development of the disease. There are numerous biological pathways involved in the above processes and, it is likely that the normal regulatory mechanisms are either down regulated or up regulated at different stages of the disease. Among the chemical constituents, alkaloids from areca nut are the most important biologically whilst tannin may have a synergistic role. These chemicals appear to interfere with the molecular processes of deposition and/or degradation of extracellular matrix molecules such as collagen. In vitro studies on human fibroblasts using areca extracts or chemically purified arecoline support the theory of fibroblastic proliferation and increased collagen formation that is also demonstrable histologically in human OSF tissues. The copper content of areca nut is high and the possible role of copper as a mediator of fibrosis is supported by the demonstration of up regulation of lysyl oxidase in OSF biopsies. It has been postulated that areca nut may also induce the development of the disease by increased levels of cytokines in the lamina propria. Increased and continuous deposition of extracellular matrix may take place as a result of disruption of the equilibrium between matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinases (TIMP). Current evidence implicates collagen-related genes in the susceptibility and pathogenesis of OSF. The individual mechanisms operating at various stages of the disease-initial, intermediate and advanced-need further study in order to propose appropriate therapeutic interventions.     

Betel quid not containing tobacco and oral leukoplakia: a report on a cross-sectional study in Papua New Guinea and a meta-analysis of current evidence

Leukoplakia is an asymptomatic, potentially malignant change in the oral mucosa. Previous studies have reported that smoking and betel quid chewing are associated with increased risk of leukoplakia; few studies have reported on these associations in populations where betel quid does not contain tobacco. We conducted a case-control study nested in a cross-sectional study in Papua New Guinea and a systematic review of studies that included chewers of betel quid without tobacco. Our study recruited 1,670 adults. We recorded betel quid chewing and smoking. The prevalence of leukoplakia was 11.7%. In the nested case-control study of 197 cases and 1,282 controls, current betel chewing was associated with increased risk of leukoplakia with an adjusted odds ratio for current chewers of 3.8 (95% CI 1.7, 8.4) and in the heaviest chewers of 4.1 (95% CI 1.8, 9.1) compared to non-chewers. Current smoking was associated with an increased risk of leukoplakia with an adjusted odds ratio for current smokers of 6.4 (95% CI 4.1, 9.9) and amongst heaviest smokers of 9.8 (95% CI 5.9, 16.4) compared to non-smokers. The systematic review identified 5 studies examining risk of leukoplakia associated with betel quid chewing in populations where betel quid did not contain tobacco and that controlled for smoking. In studies that adjusted for smoking, the combined random effect odds ratio was 7.9 (95% CI 4.3, 14.6) in betel quid chewers. The results of this study and systematic review of similar studies provide evidence of the role of betel quid not containing tobacco and leukoplakia.     

Tobacco-specific and betel nut-specific N-nitroso compounds: occurrence in saliva and urine of betel quid chewers and formation in vitro by nitrosation of betel quid

In order to evaluate exposure of betel quid chewers to N-nitrosocompounds, saliva and urine samples were collected from chewersof betel quid with or without tobacco, from tobacco chewers,from cigarette smokers and from people with no such habit, andwere analysed for the presence of N-nitrosamines by gas chromatographycoupled with Thermal Energy Analyzer and alkaloids derived frombetel nut and tobacco by capillary gas chromatography fittedwith nitrogen-phosphorous selective detector. The levels ofthe betel nut-specific nitrosamines, N-nitrosoguvacoline andN-nitrososoguvacine (the latter being detected for the firsttime in saliva), ranged from 0 to 7.1 and 0 to 30.4 ng/ml, respectively.High levels of tobacco-specific nitrosamines were detected inthe saliva of chewers of betel quid with tobacco and in thatof chewers of tobacco, ranging from 1.6 to 59.7 (N'-nitrosonornicotine),1.0 to 51.7 (N'-nitrosoanatabine) and 0 to 2.3 [4-(methyl-nitrosamino)-1-(3-pyridyl)-l-butanone]ng/ml. Urinary concentrations of certain N-nitrosamino acids,including N-nitrosoproline, were determined as a possible indexof exposure to nitroso compounds and their precursors in thestudy groups: no clear difference was observed. The betel nut-specificalkaloid, arecoline, was present at high levels in the salivaof betel quid chewers with or without tobacco. Nicotine andcotinine were also detected in saliva and urine of chewers oftobacco and of betel quid with tobacco. In order to assess whetherN-nitroso compounds are formed in vivo in the oral cavity duringchewing or in the stomach after swallowing the quids, the levelsof N-nitroso compounds in betel quid extracts were determinedbefore and after nitrosation at pH 7.4 and 2.1. The resultsindicate that N-nitroso compounds could easily be formed invivo. The possible role of N-nitroso compounds in the causationof cancer of the upper alimentary tract in betel quid chewersis discussed.     

Mutagenicity of betel quid and its ingredients using mammalian test systems

The mutagenic potential of betel quid and its ingredients (knowncolloquially as PAN) were tested in two short term mutagenicityassays, the micronucleus test and a mammalian gene mutationtest. Betel quid with tobacco, tobacco, betel nut and one ofits alkaloids arecoline were positive in both tests. Extractsof betel quid and arecaidine (a metabolite of arecoline presentin Betel nut) were negative. The data presented correlate wellwith our previous tumorigenicity data on these compounds.     

A review of betel quid chewing, oral cancer and precancer in Mainland China

On the Chinese mainland, betel quid (BQ) chewing is common in the Hunan and Hainan provinces. The BQ chewing habit in Hunan consists of dried husks and betel nuts, which are sold as industrially packaged, areca nut-based products. In Hainan, the fresh nut is chewed. Tobacco is not added. Reported prevalence of BQ chewing in Hunan province is high (64.5-82.7%). Oral diseases associated with BQ chewing are oral submucous fibrosis (OSF), oral leukoplakia (OL) and oral cancer. Reported prevalence of OSF among BQ chewers ranges from 0.9% to 4.7%. People most commonly affected are between the ages of 30 and 39 years, and 40 and 49 years. The reported prevalence of OL in Hainan ranges from 2.1% to 2.5%. In BQ chewers who also smoke, the reported prevalence is 20.3%. The prevalence of OL in Hunan province ranges from 0.1% to 0.5%. The prevalence of oral cancer among BQ chewers is low, ranging from 0.02% to 0.05%. In cases of OSF, reported prevalence is 2.6% and 1.2%. Presently, data on prevalence of BQ chewing in southern provinces of Mainland China is limited. BQ chewing habits, however, seem to differ between geographic areas. Future case-control studies are necessary to evaluate the risk for oral cancer and other associated oral mucosal diseases resulting from variations in BQ chewing habits.     

The precancer risk of betel quid chewing,tobacco use and alcohol consumption in oral leukoplakia and oral submucous fibrosis in southern Taiwan

In areas where the practise of betel quid chewing is widespread and the chewers also often smoke and drink alcohol, the relation between oral precancerous lesion and condition to the three habits is probably complex. To explore such association and their attributable effect on oral leukoplakia (OL) and oral submucous fibrosis (OSF), a gender-age-matched case-control study was conducted at Kaohsiung, southern Taiwan. This study included 219 patients with newly diagnosed and histologically confirmed OL or OSF, and 876 randomly selected community controls. All information was collected by a structured questionnaire through in-person interviews. A preponderance of younger patients had OSF, while a predominance of older patients had OL. Betel quid chewing was strongly associated with both these oral diseases, the attributable fraction of OL being 73.2% and of OSF 85.4%. While the heterogeneity in risk for areca nut chewing across the two diseases was not apparent, betel quid chewing patients with OSF experienced a higher risk at each exposure level of chewing duration, quantity and cumulative measure than those who had OL. Alcohol intake did not appear to be a risk factor. However, cigarette smoking had a significant contribution to the risk of OL, and modified the effect of chewing based on an additive interaction model. For the two oral premalignant diseases combined, 86.5% was attributable to chewing and smoking. Our results suggested that, although betel quid chewing was a major cause for both OL and OSF, its effect might be difference between the two diseases. Cigarette smoking has a modifying effect in the development of oral leukoplakia.     

A study of betel quid carcinogenesis. II. Formation of N-nitrosamines during betel quid chewing

In model studies, nitrosation of the major areca alkaloid, arecoline, leads to the formation of N-nitrosoguvacoline, 3-(methylnitrosamino)propionitrile (MNPN), 3-(methylnitrosamino)propionaldehyde and two unknown N-nitrosamines. MNPN is a strong carcinogen in Fischer 344 rats. After subcutaneous injection of 1.1 mmol MNPN in 60 doses, all 15 male and 15 female rats developed tumours within 24 weeks; multiple tumours occurred in 26 of the rats. Eighty-seven percent of the animals had tumours of the oesophagus, 70% had nasal cavity tumours, 37% had tumours of the tongue, 7% tumours of the pharynx and 7% tumors of the forestomach. At the dose used, male and female rats showed no significant difference in tumour incidence or site of tumours. The formation of MNPN during betel quid chewing, although likely, has not yet been proven, while the areca-derived N-nitrosamine, N-nitrosoguvacoline (NG), has been found in the saliva of betel quid chewers at levels of 2.2-348 micrograms/L. N-Nitrosoguvacoline levels were higher in the saliva of chewers who used betel quid together with tobacco. The saliva of these chewers also contained tobacco-specific N-nitrosamines.