Potentiation of genotoxicity by concurrent application of compounds found in betel quid: arecoline, eugenol, quercetin, chlorogenic acid and Mn2+

Ultrastructural findings in the oral mucosa of betel chewers

Eighteen biopsies of the oral mucosa of northern Thai hilltribe betel chewers were studied histologically and by transmission and scanning electron microscopy (TEM, SEM). Clinically, varying stages of epithelial atrophy and one case of submucous fibrosis were observed. Histologically, epithelial atrophy with marked reduction of the rete pegs, hyperortho- and/or parakeratosis, and subepithelial edema and inflammatory changes were the prominent findings. On the ultrastructural level, cytoplasmic projections of the basal cells into the subepithelial stroma were seen. The basal membrane frequently revealed gaps; the interepithelial space was widened and unusual microvilli were observed on cell surfaces (SEM). Intercellularly, cristalloid material of unknown origin was also seen. The subepithelial connective tissue was characterized by dense bundles of collagen fibres adjacent to which masses of amorphous material were located. While some of the ultrastructural findings in the epithelium of betel chewers are indicative of early dysplastic changes, the nature of the juxta-epithelial stromal alterations is still unknown. Current hypotheses regarding the etiology of oral submucous fibrosis are briefly discussed.

Influence of caffeine on arecoline-induced SCE in mouse bone-marrow cells in vivo

The effect of exposure of mice for 5, 10 and 15 days to arecoline or/and caffeine on the frequency of sister-chromatid exchanges (SCEs) in bone-marrow cells was evaluated by using the fluorescence plus Giemsa technique. There was a significant increase in the frequency of SCEs after exposure to either arecoline or caffeine. When these two alkaloids were given in combination, the SCE frequency-enhancing effect was additive. The implications of coffee/tea drinking and betel chewing on oral cancer are discussed.

Activation of rutin by human oral bacterial isolates to the carcinogen-mutagen quercetin

Oral streptococci, isolated from the mouths of 2 healthy subjects, hydrolysed innocuous rutin, a flavonoid glycoside, to its genotoxic aglycon quercetin, in vitro. The isolates were identified as Streptococcus milleri. The glycosidase, rutinase, was studied in cell-free extracts derived from one of the isolates, grown anaerobically in batch cultures by the use of a bioassay, the Ames test, in which S-9 was replaced by the cell-free extracts. This streptococcal rutinase was: constitutive, partly inducible, cytosolic, most active for rutin and most active at pH 6.5. Type-culture collection strains of other oral streptococci (Streptococcus salivarius ATCC 25975 and Streptococcus mutans strain 6715-10) showed no capacity for rutin degradation. A hypothesis for a novel role of the oral microflora in a disease process other than caries and periodontal disease, namely intra-oral cancer, is presented. The possibility of a bacterial liberation of the genotoxic quercetin in situ could be but one example of its involvement in the local carcinogenic process.

Application of the micronucleus test to exfoliated cells of high cancer risk groups: tobacco chewers

Powdered tobacco (Khaini tobacco) with the addition of lime is commonly used by the residents of Bihar, India. The tobacco/lime mixture is usually placed on the inner side of the lower lip within the gingivolabial groove. About 42% of the users keep it at the front, the rest move the tobacco towards the left or right side within the oral cavity. Carcinomas (so-called "Khaini cancers") develop mainly at the site where the tobacco is in close contact with the mucosa. Scrapings of the mucosa were taken at sites where the tobacco is kept, then smears were prepared, stained with the Feulgen reaction and fast green, and screened for micronuclei which indicate the occurrence of chromosome aberrations in the dividing cell population of the basal layer. An elevated frequency of cells with micronuclei was found in the oral mucosa of all 27 examined Khaini tobacco users (Munda and Santal tribes) compared to that of non-chewers of similar ethnic background and dietary habits. The induction of micronucleated mucosa cells seems to be due to genotoxic agents released from the tobacco/lime mixture. In vitro, an aqueous extract of the Khaini tobacco elicits chromosome aberrations and micronuclei in cultured human fibroblasts and Chinese hamster ovary (CHO) cells. No chromosome-damaging effect was observed following the application of lime or calcium hydroxide (Ca(OH)2). The micronucleus test on exfoliated cells can provide evidence of carcinogen exposure in the tissue from which cancers will develop. This approach combines all the advantages of in vitro short-term tests for genotoxic and carcinogenic agents with those of using an intact organism with all its defence mechanisms.

Inhibition of mutagenicity of a model nitrosation reaction by naturally occurring phenolics, coffee and tea

Several plant phenolics, one instant coffee, one instant decaffeinated coffee, one roasted coffee, one Japanese tea, one black Indian tea, and one Chinese tea were examined for their inhibitory properties on mutagenicity resulting from the nitrosation of methylurea. Mutagenicity was estimated as the number of his+ revertants per survivor of Salmonella typhimurium TA1535 which was exposed in suspension to the nitrosation mixtures and the modulating agents for 20 min. Tannic acid, gallic acid and chlorogenic acid suppressed the mutagenicity of the model nitrosation system at concentrations similar to or even lower than ascorbic acid. The three tested coffees and three tested teas exerted an inhibitory effect on the mutagenicity of the test system at doses at which they are consumed.

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.