Towards a more comprehensive evaluation of a genotoxic hazard in man

Frequency of micronucleated exfoliated cells in oral lichen planus

OBJECTIVE

The purpose of this study was to determine the frequency of micronucleated exfoliated cells (MEC) in atrophic and erosive oral lichen planus (OLP).

MATERIALS AND METHODS

Twenty-two patients with atrophic and/or erosive OLP participated in this study. Lesions were scored ranging from 0 (no lesion) to 5 (large erosion) according to the severity and assessed for MEC. Exfoliated cells were obtained by swabbing the lesions and normal-appearing mucosa adjacent to the lesions. Swabbing was also performed in age-sex-matched normal individuals. Five hundred exfoliated cells were screened for nuclear anomalies including micronuclei, karyorhexis, pycnosis, and chromatid clumping.

RESULTS

The severity score of OLP ranged from 2 to 4 with the average of 2. The frequency of MEC in OLP patients was 3.79% and 0.37% in the lesions and normal-appearing mucosa, respectively. In normal individuals, the frequency of MEC was also 0.37%. Using a paired t-test, it was found that the MEC frequency in the OLP lesions was significantly elevated (p<0.01) as compared to that in normal-appearing mucosa adjacent to lesions and that in normal individuals. There were no statistically significant differences in the MEC frequency of the three severity scores as analyzed by Kruskal-Wallis one way analysis of variance on ranks (p>0.05).

CONCLUSION

This study revealed an increase in micronuclei in OLP lesions. The results indicate genotoxic damage in atrophic and erosive OLP.

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

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

Anticlastogenic activity of beta-carotene against cyclophosphamide in mice in vivo

beta-Carotene (BC), a natural food colourant and an antioxidant, acts as an antimutagen/anticarcinogen in several test systems. The anticlastogenic activity of BC against cyclophosphamide (CP) was studied in bone marrow cells of mice in vivo. Seven days' oral priming with BC (2.7 and 27 mg/kg b.w.) followed by an acute treatment with cyclophosphamide (25 mg/kg b.w.; i.p.) inhibited clastogenicity. The values of chromosomal aberrations and micronucleated polychromatic erythrocytes were consistently lower than the sum of the expected values of BC and CP given individually. This antagonistic response indicates anticlastogenic activity of BC against CP.

Prevention of adverse effects of food browning

Amino-carbonyl interactions of food constituents encompass those changes commonly termed browning reactions. Such reactions are responsible for deleterious post-harvest changes during processing and storage and may adversely affect the appearance, organoleptic properties, nutritional quality, and safety of a wide spectrum of foods. A growing area of concern is nutritional carcinogenesis, in which nutritionally linked cancer has been associated with amino-carbonyl reaction products. Specific practical and theoretical approaches to prevent adverse effects of food browning include: (1) modification and removal of primary reactants and endproducts in the browning reaction; (2) prevention of deleterious browning reactions through the use of antioxidants; (3) blocking of in vivo toxicant formation from browning products by means of dietary modulation; (4) accurate estimation of low levels of browning products in whole foods and their removal through antibody complexation; and (5) stimulation of inactivation in vivo toxicants from browning products by use of amino acids and sulfur-rich proteins.

Bronchial micronuclei as a marker of an early stage of carcinogenesis in the human tracheobronchial epithelium

In the bronchial epithelium, smoking initiates a multistep process that first appears histologically as premalignant squamous metaplasia/dysplasia, a biological predecessor of squamous-cell lung cancer. Reflecting chromosomal damage from a carcinogenic insult, micronuclei may reveal earlier events in the carcinogenic sequence. We prospectively evaluated and correlated micronucleus count, histology (index of metaplasia) and smoking exposure in 35 consecutive subjects (9 active smokers, 10 previous smokers and 16 never-smokers) undergoing diagnostic bronchoscopy. Samples for micronuclei and histological evaluation were taken from the main carinal mucosa in each subject for site-specific comparisons. The median and mean micronucleus counts per 1,000 cells were significantly higher in active smokers than in non-smokers (subjects who had never smoked and previous smokers): median counts were 3.7 vs. 1.4, p = 0.03; mean counts were 4.7 vs. 1.9, p = 0.01. There was no significant difference, however, in micronucleus counts between subjects who had never smoked and previous smokers. Bronchial metaplasia and smoking history were not associated. Our findings suggest that micronuclei are a readily quantitated, early intermediate-endpoint marker for detecting tobacco-initiated tracheobronchial carcinogenesis.

Antigenotoxic activity of carotenoids in carcinogen-exposed populations

Although epidemiological studies suggest the presence of anticarcinogenic agents in the diet, it is difficult to obtain actual proof for the activity of such agents in humans. One approach is to develop and validate potential quantifiable indicators of antigenotoxic/anticarcinogenic agents which can be used in humans belonging to populations at elevated risk for cancer. This paper provides evidence that the exfoliated cell micronucleus test (MEC test) can be used (i) to provide a quantifiable marker for the amount of chromosomal breakage occurring in target tissues of carcinogen-exposed populations; (ii) to indicate the capacity of beta-carotene, alone or in combination with vitamin A, to prevent such damage; and (iii) to predict the response of other biological indicators of cancer risk, such as oral leukoplakias, in individuals receiving oral supplementation with beta-carotene/vitamin A (although the dose and time to response may differ for these endpoints). Future extensions of this approach include establishing the levels of beta-carotene required for antigenotoxic activity in a carcinogen's target tissue by concurrently measuring MEC frequencies and beta-carotene levels in exfoliated cells. In summary, early indications are that the MEC assay is an effective indicator for antigenotoxic agents in carcinogen-exposed individuals and that beta-carotene and vitamin A can suppress such genotoxic activity in at least some populations.

Remission of oral leukoplakias and micronuclei in tobacco/betel quid chewers treated with beta-carotene and with beta-carotene plus vitamin A

Fishermen from Kerala (India) who chewed tobacco-containing betel quids daily (17.2 +/- 9.6 quids per day) and had well-developed oral leukoplakias with elevated frequencies of micronucleated cells participated in a short-term intervention trial. Beta-carotene (180 mg/week) (Group I), beta-carotene (180 mg/week) plus vitamin A (100,000 IU/week) (Group II), and placebo (Group III) capsules were given twice weekly for 6 months under strict supervision. The remission of oral leukoplakias, the inhibition of new leukoplakias, and the reduction of micronucleated oral mucosal cells were recorded at the 3rd and 6th months of the trial period. After 3 months, the frequency of micronucleated cells was significantly reduced in Group I (from 4.09% to 1.1% in areas of leukoplakia, and from 4.1% to 1.0% in the normal mucosa). At this time, remission of oral leukoplakias did not differ significantly from that observed in the placebo group. After 6 months of treatment, remission of leukoplakias in Group I (14.8%) and Group II (27.5%) differed significantly from that seen in Group III (3.0%). The development of new leukoplakias during the 6-month period was strongly inhibited in Group II (7.8%), and to a lesser degree in Group I (14.8%), as compared to Group III (21.2%). During the trial period, all participants continued to chew tobacco-containing betel quids in their accustomed manner. Thus, remission and inhibition of new oral leukoplakias and reduction of micronucleated mucosal cells occurred in the groups receiving beta-carotene and beta-carotene plus vitamin A during the continuous presence of carcinogens derived from tobacco and areca nut.

In vivo chromosomal instability in ataxia-telangiectasia homozygotes and heterozygotes

The exfoliated cell micronucleus test was used to monitor in vivo chromosomal instability in a population comprised of five ataxia-telangiectasia (A-T) homozygotes and seven obligate heterozygotes (parents of A-T patients). This assay was previously validated as a procedure for quantifying non-invasively carcinogen-induced chromosomal aberrations occurring in vivo in epithelial tissues of both the oral cavity and the urinary bladder. The procedure involved taking air-dried smears of three sites in the oral cavity of each examined individual. Desquamated urinary bladder cells were collected by centrifugation of freshly voided urine samples. Frequencies of exfoliated cells in these preparations were determined and compared with control values (individuals with no genetic chromosomal instability and no known carcinogen exposure) for these sites. Exfoliated cell micronucleus (MEC) frequencies were elevated 5- to 14-fold in samples from the A-T homozygotes. This elevation in MEC frequency occurred for both the oral cavity and urinary bladder. Five out of the seven obligate A-T heterozygotes had an elevated MEC frequency in samples from the oral cavity. In addition, all examined urine samples from A-T heterozygotes contained an elevated percentage of micronucleated cells. These data suggest that this assay is suitable for in vivo monitoring of groups of individuals in which genetically produced chromosomal damage occurs. The possibility of A-T heterozygote detection with this simple procedure is of particular significance, since such individuals are believed to comprise up to 1% of the general population, and have been identified as being at elevated risk for cancer.

Relationship between cellular levels of beta-carotene and sensitivity to genotoxic agents

The usefulness of an in vitro test system to predict the inhibitory effect of beta-carotene on the genotoxic activity of carcinogens/mutagens was explored. To facilitate the comparison of data obtained from cultured cells (CHO) and from exfoliated human cells, endpoints were used which can be quantitated in both cell systems: the frequency of micronuclei for estimating the effect of genotoxic agents, and cellular levels of beta-carotene as a protective agent. In CHO cells, beta-carotene inhibited the clastogenic and micronucleus-forming effect of methyl methanesulfonate (MMS) and 4-nitroquinoline-1-oxide (4NQO), but had no protective action against gallic acid, tannic acid, and aqueous extract of areca nut or H2O2. The extent of inhibition depended on the ratio of beta-carotene to MMS. Doses of beta-carotene which exerted a protective effect in vitro ranged from approximately 2 to 5 ng per 10(6) CHO cells. Comparable levels of beta-carotene were previously found to reduce the frequency of micronucleated exfoliated cells from the buccal mucosa of tobacco and areca-nut chewers (Stich et al., 1984b).

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.

Beta-carotene levels in exfoliated mucosa cells of population groups at low and elevated risk for oral cancer

Beta-carotene was estimated in exfoliated oral mucosa cells in groups of individuals at various risks for oral cancer. Approximately 4 X 10(6) exfoliated cells were collected from each subject by brushing the oral mucosa. Cell pellets were hydrolyzed with pronase and then with KOH/methanol. Beta-carotene was extracted with hexane, separated by reverse-phase HPLC, and detected at 450 nm. Mean beta-carotene levels in exfoliated cells were 0.08 ng/10(6) cells for 56 heavy consumers of alcoholic beverages (150 g or more per week), 1.36 ng/10(6) cells for 28 Seventh Day Adventists (all abstainers from alcohol, tobacco and meat consumption), 1.39 ng/10(6) cells for 55 lacto-vegetarians of the International Society for Krishna Consciousness (ISKC) (abstainers from alcohol and tobacco), and 1.08 ng/10(6) cells for 61 representatives of a "Western" life-style pattern (64% consumed the equivalent of at least one bottle of wine or 7 bottles of beer per week, and all were non-smokers). If the heavy alcohol consumers (males) are matched to non-drinking males of comparable age, the mean beta-carotene values are 0.08 ng versus 1.24 ng/10(6) cells. The possible involvement of the low levels of beta-carotene in the mucosa of heavy alcohol drinkers in increased sensitivity towards the carcinogenic and genotoxic activity of cigarette smoking plus alcohol ingestion is discussed.