Characterization of epithelial oral dysplasia in non-smokers: First steps towards precision medicine

OBJECTIVES

Tobacco usage is the strongest risk factor in the development of oral squamous cell carcinoma (OSCC), which mandates careful screening for oral cancers in smokers. However, there are indications that oral potentially malignant lesions, such as oral epithelial dysplasia (OED), in non-smokers (NS) have a higher cancer risk than those in smokers. Without tobacco as an etiology, the development of these lesions in NS may suggest genetic susceptibility. The increasing incidence of OSCC in NS calls for a better understanding of the natural history of OED in NS as compared to that of smokers.

MATERIALS AND METHODS

Patients from a population-based longitudinal study with more than 10 years of follow up were analyzed. Of the 455 patients with primary OED (233 mild and 212 moderate dysplasia), 139 were NS and 306 were smokers. Demographic and habit information, clinical information (lesion site, size and appearance; toluidine blue and fluorescent visualization), microsatellite analysis for loss of heterozygosity (LOH) and outcome (progression) were compared between the two groups.

RESULTS AND CONCLUSIONS

The majority of patients with OED were smokers. Of these, more were males, non-Caucasians and heavy drinkers. A significantly higher number of OED in NS were in the tongue, whereas a significantly higher number of OED in smokers were in the floor of mouth (FOM). OED in NS showed a greater than 2-fold increase in cancer progression. Strikingly, OED located in the FOM in NS showed a 38-fold increase in cancer progression as compared to those in smokers.

Dysplasia Should Not Be Ignored in Lichenoid Mucositis

Oral lichen planus is categorized as a potentially malignant condition by the World Health Organization; however, some argue that only lichen planus with dysplasia have malignant potential. Many pathologists call lichen planus with dysplasia "dysplasia with lichenoid mucositis (LM)" or "LM with dysplasia." Previous research has shown that certain high-risk patterns of loss of heterozygosity (LOH) in dysplastic lesions are associated with significantly increased cancer risk. However, LM without dysplasia lacks such molecular patterns, supporting the hypothesis that LM, by itself, is not potentially malignant and that only those with dysplasia have malignant potential. To further investigate the premalignant nature of LM with dysplasia, this study compared the rate of malignant progression of dysplasia with LM with that of dysplasia without LM. Patients from a population-based prospective cohort study with >10 y of follow-up were analyzed. Study eligibility included a histological diagnosis of a primary low-grade dysplasia with or without LM. A total of 446 lesions in 446 patients met the selection criteria; 373 (84%) were classified as dysplasia without LM, while 73 (16%) were classified as dysplasia with LM. Demographic and habit information, clinical information, and outcome (progression) were compared between the 2 groups. Forty-nine of 373 cases of dysplasia (13%) progressed compared to 8% (6/73) of dysplasia with LM. However, the difference was not statistically different ( P = 0.24). The 3- and 5-y rate of progression did not differ between the groups (6.7% and 12.5% for dysplasia without LM and 2.9% and 6.6% for those with LM; P = 0.36). Progression was associated with nonsmoking, location at a high-risk site, and diagnosis of moderate dysplasia regardless of whether LM was present or not. Dysplasia with or without LM had similar cancer risk, and dysplasia should not be discounted in the presence of LM.

Comparison of HPV infection, p53 mutation and allelic losses in post-transplant and non-posttransplant oral squamous cell carcinomas

BACKGROUND

Oral squamous cell carcinoma (SCC) is increasingly found in transplant recipients, although little is known of the natural history of the disease or the mechanism underlying this increase.

METHODS

In this article we describe the history of development of 5 oral post-transplant SCCs (PSCCs) and compare their genetic profiles to 34 non-posttransplant SCCs (NPSCCs).

RESULTS

Of the five patients with PSCCs, 3 had bone marrow transplants and two, kidney. All three PSCCs from bone marrow recipients were preceded locally by graft-vs.-host disease (GVHD). Two of the GVHD were biopsied and demonstrated dysplasia. Similar frequencies of loss of heterozygosity (LOH) occurred in PSCCs and NPSCCs at 3p, 9p, 17p and 8p, with lower frequencies in PSCCs at 4q (39% vs. 0%), 11q (53% vs. 20%) and 13q (45% vs. 20%), although the latter were not significantly different. Only 1 PSCC had a p53 mutation, compared to historical values of 40-60% for NPSCC. Interestingly, human papillomavirus (HPV) DNA was detected in 3 (60%) PSCCs, in comparison to only 4 (12%) of the 34 NPSCCs (P = 0.0346).

CONCLUSIONS

Dysplasia in oral GVHD may be a strong indicator of cancer risk and should not be regarded as reactive changes to lichenoid mucosites. The low level of p53 mutation and increased HPV infection support the involvement of HPV in the development of PSCC, while the similarity in LOH patterns suggests that other aspects of carcinogenesis may be comparable in these two types of SCCs.

Loss of heterozygosity: a potential tool in management of oral premalignant lesions?

Oral leukoplakia, a heterogeneous group of lesions, demonstrates a varying degree of risk for cancer progression. Histology (presence and degree of dysplasia), the current gold standard for assessing this risk, is reasonably effective in judging the malignant risk of high-grade pre-invasive lesions. It is, however, a poor predictor for lesions without dysplasia, or with minimal dysplasia, as only a few of these lesions will progress to cancer. This poses an enormous dilemma for clinicians as to whether these lesions should be aggressively treated or not. Recent studies show that loss of specific chromosomal regions (loss of heterozygosity, LOH) that contain known or presumptive tumor suppressor genes is an early predictor of subsequent progression of oral premalignant lesions. Incorporation of LOH findings into staging of oral premalignancy could improve our ability to identify and manage high-risk premalignant lesions, particularly those with relatively benign histology but high-risk genetic changes (high-risk LOH pattern).

Impact of localized treatment in reducing risk of progression of low-grade oral dysplasia: molecular evidence of incomplete resection

Currently, there is no consensus on the appropriate treatment for low-grade oral dysplasia. This is mainly due to the difficulty in predicting outcome for this heterogeneous group of lesions. In this study, we constructed a detailed clinical history of 66 mild and moderate dysplasias in order to determine how treatment affected outcome, and to evaluate the effect of treatment on lesions with different genetic profiles, which are defined by patterns of loss of heterozygosity (LOH) associated with low, intermediate and high risk of progression [Clin. Cancer Res., 6, 357-62, 2000]. The results showed that although treatment guided by clinical removal of leukoplakia reduced cancer progression risk in all three risk groups, the amount of reduction in our study group did not reach statistical significance. To assess whether completeness of lesion removal was a major factor in recurrence, repeat biopsies at the primary sites were analyzed for persistent LOH status on chromosomes 3p, 4q, 8p, 9p, 11q, 13q and 17p. Strikingly, eight of 17 cases judged clinically removed contained the same molecular clones in the initial and subsequent biopsies, suggesting incomplete removal. When molecular information was included in the assessment of lesion removal, treatment significantly reduced the risk of progression for cases with intermediate (P=0.043) and high risk (P=0.001) genetic profiles, but not cases with low-risk profiles. A 9.1-fold decrease in progression risk was observed for those with high-risk profile. Altogether, these data suggest the use of molecular profiles to guide the treatment of low-grade dysplasia. Our data also suggest that currently an inadequate margin may in part be responsible for the high rate of recurrence, especially in high-risk lesions.

Increased genetic damage in oral leukoplakia from high risk sites: potential impact on staging and clinical management

BACKGROUND

Two staging systems for oral leukoplakias have been proposed to better predict prognosis. Although one system includes site as an independent determinant, its use is controversial.

METHODS

Recent studies have shown that loss of heterozygosity (LOH) in oral premalignancies is associated with risk of progression. The authors analyzed 127 oral dysplasias for LOH on 3 chromosome arms (3p, 9p, and 17p). The lesions included 71 from the floor of mouth, ventrolateral tongue, and soft palate complex (designated high risk [HR] sites) and 56 from the rest of the oral cavity (low risk [LR] sites).

RESULTS

Dysplasias from HR sites contained significantly higher LOH frequencies than LR sites (percentage with any loss, P = 0.0004; percentage with multiple losses, P = 0.0001; percentage loss on each of the arms, P < 0.05). Loss on 3p and/or 9p, a pattern associated with a 24-fold increased risk of progression (Rosin MP, Cheng X, Poh C, Lam WL, Huang Y, Lovas J, et al. Use of allelic loss to predict malignant risk for low-grade oral epithelial dysplasia. Clin Cancer Res 2000;6:357-62) was more frequent among HR lesions (P = 0.0005). Loss of heterozygosity frequencies were elevated at HR sites among both genders and among smokers and nonsmokers. For different histologic groups, LOH frequencies were elevated for HR sites in mild dysplasias (P < 0.05) and moderate dysplasias (marginal significance, P = 0.06), but not in severe dysplasias/carcinoma in situ.

CONCLUSIONS

Anatomic location of mild and moderate oral dysplasias in Western populations may be an important diagnostic indicator because lesions at HR sites have a greater tendency to include genetic alterations associated with elevated risk of progression.

A high frequency of allelic loss in oral verrucous lesions may explain malignant risk

Verrucous carcinoma (VC), a variant of squamous cell carcinoma (SCC), is distinct from SCC in morphology and behavior. The underlying genetic changes involved in the development of VC and its precursor verrucous hyperplasia (VH) are unknown. This study determined whether chromosomal regions frequently lost during the development of SCC are also lost in the VH/VC variant. Twenty-five VH and 17 VC were analyzed for loss of heterozygosity (LOH) at 19 loci on 7 chromosome arms using microsatellite analysis. These data were compared with those from 47 reactive hyperplasias, 92 dysplasias (54 low- and 38 high-grade), and 41 SCCS: The results showed that VC/VH shared many of the losses present in dysplasia/SCC but differed in two aspects. First, VC/VH showed early acquisition of loss, compared with a gradual accumulation of losses from dysplasias to SCC. The LOH pattern of VH was similar to that of high-grade dysplasia and sharply different from reactive hyperplasia. The loss in VH often involved multiple arms (in 60% of VH vs 0% of reactive lesions). Only a marginal elevation of loss was observed at 9p (p = 0.06) and 4q (p = 0.05) from VH to VC because of the high degree of loss already present in VH. Second, a strikingly lower frequency of loss at 17p was noted in VH/VC compared with dysplasia/SCC and may indicate human papillomavirus (HPV) involvement. The finding of high-risk LOH profiles in VH may partly account for the high-progression risk seen for VH and also has potentially important clinical implications. The difficult pathological diagnosis of VH/VC from reactive hyperplasia frequently requires repeated biopsies and results in delay in diagnosis and significantly increased mortality/morbidity. Microsatellite analysis might facilitate this differential diagnosis.

Use of allelic loss to predict malignant risk for low-grade oral epithelial dysplasia

One of the best approaches to identifying genetic changes critical to oral cancer progression is to compare progressing and nonprogressing oral premalignant lesions. However, such samples are rare, and they require long-term follow-up. The current study used the large archive network and clinical database in British Columbia to study loss of heterozygosity (LOH) in cases of early oral premalignancies, comparing those with a history of progression to carcinoma in situ or invasive cancer and those without a history of progression (referred to as nonprogressing cases). Each of 116 cases was analyzed for LOH at 19 microsatellite loci on seven chromosome arms (3p, 4q, 8p, 9p, 11q, 13q, and 17p). The progressing and nonprogressing cases showed dramatically different LOH patterns of multiple allelic losses. An essential step for progression seems to involve LOH at 3p and/or 9p because virtually all progressing cases showed such loss. However, LOH at 3p and/or 9p also occurred in nonprogressing cases. Individuals with LOH at 3p and/or 9p but at no other arms exhibit only a slight increase of 3.8-fold in relative risk for developing cancer. In contrast, individuals with additional losses (on 4q, 8p, 11q, or 17p), which appeared uncommon in nonprogressing cases, showed 33-fold increases in relative cancer risk. In conclusion, analysis of LOH at 3p and 9p could serve as an initial screening for cancer risk of early premalignancies. Follow-up investigation for additional losses would be essential for predicting cancer progression.

High frequency of allelic loss in dysplastic lichenoid lesions

Oral lichen planus (OLP) is a common mucosal condition that is considered premalignant by some, whereas others argue that only lichenoid lesions with epithelial dysplasia are at risk of progressing into oral carcinoma. A recent study from this laboratory used microsatellite analysis to evaluate OLP for loss of heterozygosity (LOH) at loci on three chromosomal arms (3p, 9p, and 17p) (Am J Path 1997;Vol151:Page323-Page327). Loss on these arms is a common event in oral epithelial dysplasia and has been associated with risk of progression of oral leukoplakia to cancer. The data showed that, although dysplastic epithelium demonstrated a high frequency of LOH (40% for mild dysplasia), a significantly lower frequency of LOH was noted in OLP (6%), which is even lower than that in hyperplasia (14%). Such results do not support OLP as a lesion at risk for malignant transformation. As a second step of the research, we determined LOH frequencies in 61 dysplastic lichenoid lesions (mild 35; moderate 19; severe 7) using the same microsatellite markers and compared these results with data obtained from the first study and from 13 normal mucosal specimens. Dysplastic lichenoid lesions showed a high frequency of loss (54% for lichenoid lesions with mild dysplasia), but values did not differ significantly from those observed in dysplasia of similar degree without lichenoid appearance. None of the normal mucosa demonstrated LOH. Epithelial dysplasia is a sign of malignant risk, independent of lichenoid changes. Such results suggest that pathologists should search for dysplasia carefully in lesions that otherwise qualify as OLP and that caution should be used when discounting dysplasia as being merely a reactive condition in lichenoid lesions.

Local tumor recurrence or emergence of a new primary lesion? A molecular analysis

The distinction between a new primary oral tumor and recurrence may bear significant prognostic implications. Currently, this differentiation relies mainly on tumor location: when both lesions are at or near the same site, the new one is regarded as a recurrence; when the two are at different sites, the second lesion is regarded as a new primary. Recent investigations using molecular analysis have demonstrated that some oral squamous cell carcinomas (SCC) arising from different sites show the same clonogenical changes. In this case report, we studied the clonality of three SCC (one primary, two apparent recurrences) from the right lateral tongue of a young, non-smoking woman by using microsatellite analysis for loss of heterozygosity. The results showed that while the first two tumors were clonogenically similar, the third tumor was clonogenically different and was consistent with the development of a new primary. This result indicates that location of tumors alone is not always reliable in determining whether a new tumor is a recurrence or a new primary lesion.

The use of exfoliative cell samples to map clonal genetic alterations in the oral epithelium of high-risk patients

Although it is widely accepted that clonal genetic alterations are an essential component of tumor progression, little is known of the distribution of such changes in high-risk lesions or how such clones are altered over time. We explored the feasibility of using exfoliative cells collected by scraping the mucosal surface to detect allelic loss in oral lesions of 22 patients (14 squamous cell carcinomas, 2 carcinomas in situ, and 6 dysplasias). The data show that the patterns of allelic loss observed in these samples closely represent those observed in biopsies of the same region. Furthermore, early indications are that this approach can be used to detect recurrent outgrowth of clones of altered cells in patients after therapy.

Molecular analysis of oral lichen planus. A premalignant lesion?

Oral lichen planus (OLP) is a common mucosal condition that is considered premalignant by some, although others argue that only lichenoid lesions with dysplasia are precancerous. To address the question of whether OLP without dysplasia is premalignant, we used microsatellite analysis to examine 33 cases of OLP for allelic loss at nine loci located on chromosomes 3p, 9p, and 17p. Loss of heterozygosity (LOH) on these three arms occurs frequently in oral tumors, and the presence of these alterations in premalignant lesions suggests that they may play an important role in tumor progression. Results were compared with those observed in oral dysplasias (10 mild, 11 moderate, 16 severe/carcinoma in situ), 22 oral squamous cell carcinomas, and 29 reactive lesions. LOH was present in 6% of OLP, 14% of reactive lesions, 40% of mild dysplasia, 46% of moderate dysplasia, 81% of severe dysplasia/carcinoma in situ, and 91% of squamous cell carcinomas. LOH was detected on only a single arm in OLP and reactive lesions but occurred on more than one chromosome in dysplasia and cancer, and the frequency of this multiple loss correlated significantly with increasing degrees of dysplasia and progression into squamous cell carcinoma (P = 0.0028). Although these findings do not support OLP as a lesion at risk for malignant transformation, such results need to be confirmed by use of other genetic markers as OLP may undergo malignant transformation through genetic pathways different from those of oral dysplasia.

Rejoining of DNA double-strand breaks after the introduction of chromosome 11 into a radiosensitive bladder carcinoma cell line

Insertion of a normal chromosome 11 into tumour cell lines can protect against a sensitivity to irradiation and oxidative stress. A possible mechanism underlying this effect is that there is a correction of a defect in the rejoining of double-strand breaks (dsb) by the chromosome insertion. In order to explore this hypothesis, three cell lines were evaluated for their ability to rejoin dsb: (1) a bladder carcinoma cell line ('parent') previously shown to be sensitive to irradiation and radical generating species; (2) a derivative of this cell line into which a normal chromosome 11 had been inserted by microcell fusion ('hybrid') showing corrected radiosensitivity; and (3) a 'revertant' cell line that had spontaneously lost the insert and reverted to the radiosensitive phenotype. Nuclear extracts from the 3 lines were isolated and evaluated for their capacity to rejoin plasmid (pUC18) DNA broken at defined restriction sites (SalI, EcoRI, KpnI, SmaI) in the lacZ gene. The extent of rejoining was determined by gel electrophoresis and the fidelity of rejoining determined by expression of the lacZ gene in E. coli DH5 alpha bacteria. Results suggest there is no difference between the 'parent', 'hybrid' and 'revertant' nuclear extracts in the fidelity and the total extent of rejoining, regardless of the type of break. However, there is an alteration in the distribution of rejoined products. Nuclear extracts from 'hybrid' cells tend to rejoin linear DNA into circular monomers with a greater efficiency than extracts from both 'parent' and 'revertant' cells. This alteration in distribution is observed when 3'- or 5'-protruding ends are rejoined but not in the rejoining of blunt ends. The results suggest that loci on chromosome 11 are involved in the rejoining of dsb, affecting the relative amount of the different rejoined products. Whether this alteration plays a role in the 'parent' cell's radiosensitivity is yet to be determined.

Micronucleus frequencies in urothelial cells of catheterized patients with chronic bladder inflammation

Epidemiological studies suggest an association between chronic inflammation and increased risk for cancer, although the mechanism underlying this relationship is unresolved. In the present study, we test the hypothesis that DNA damage is induced in the epithelium of tissues during such inflammation by products of activated inflammatory cells. Individuals on long-term indwelling urinary catheterization were used as a study population. These individuals have chronic bladder inflammation and, as a population, an increased risk for bladder cancer. Urine of 29 patients and 26 age-matched non-catheterized controls was collected and micronucleus (MN) frequencies were determined in exfoliated urothelial cells in the urinary sediments. The urine from the catheterized group had large numbers of white blood cells (mean count, 26.6 +/- 3.6 cells per high-power field), indicating the presence of a chronic bladder infection and an inflammatory reaction. In contrast, white blood cells were not present in urine from individuals in the control group. There was no significant difference in MN frequencies in the 2 groups (mean frequencies, controls: 0.098 +/- 0.030%; catheterized: 0.140 +/- 0.025%, p = 0.13). These data imply that chromosomal damage does not always occur during chronic inflammation. Although the reasons for this observation are yet to be determined, possible explanations include the pathophysiology of the inflammatory reaction and the influence of vitamins, non-steroidal anti-inflammatory drugs and the catheter itself in protection against inflammatory cell-mediated DNA damage.

Elevation of interferon beta-inducible proteins in ataxia telangiectasia cells

The recently cloned ATM gene has been shown to bear considerable homology to phosphatidylinositol 3 kinases and, therefore, its product may function in signal transduction. In this study, we report constitutively elevated levels of two IFN-beta-inducible proteins, ubiquitin cross-reactive protein (UCRP), and low molecular weight protein (LMP2), in human fibroblasts with the inherited disease ataxia telangiectasia (AT). Using immunoblotting, it was found that a M(r) 15,000 band representing free UCRP was hardly detectable in normal cells, while it was the predominant band in AT cells. Similarly, the expression of a M(r) 23,000 protein, LMP2 was found to be higher in AT cells than in normal cells. Culturing three successive passages of the AT cell line in the presence of different concentrations of neutralizing antibodies against IFN-beta caused partial and complete reduction, respectively, of the free UCRP and LMP2 signals to normal levels. These results indicate that UCRP and LMP2 pools may be basally elevated in AT cells due to constitutive activation of the IFN-beta induction pathway and are in keeping with the recently reported constitutive activation of the NF-kappaB transcriptional activator in AT cells.

Partial allelotype of carcinoma in situ of the human bladder

Carcinoma in situ (CIS) of the urinary bladder is an aggressive lesion that frequently progresses to an invasive tumor, yet the underlying molecular changes in this lesion are largely unknown. In this study, we microdissected 31 cases of CIS and examined them for loss of heterozygosity (LOH) on 13 chromosomal arms. Twenty-nine microsatellite markers were chosen for this analysis based on their location in regions previously shown to be frequently lost in primary transitional cell carcinoma of the bladder. LOH of chromosome 9 was a frequent event in these samples, occurring in 77% of these lesions, with 19 of 31 cases showing deletion on the 9p arm (61%) and 17 of 28 cases displaying LOH on 9q (61%). Fine mapping at 9p21 demonstrated that CIS also displayed a high frequency of homozygous deletion surrounding the p16INK4A locus, like superficial papillary tumors, the other form of noninvasive lesion found in the bladder. However, loss of 14q (70%) was frequent in CIS yet extremely rare in papillary lesions (9%). Other chromosomal arms showing frequent LOH included 8p (65%), 17p (60%), 13q (56%), 11p (54%), and 4q (52%), whereas slightly lower frequencies of loss were observed for 11q (36%), 4p (32%), 3p (31%), 18q (29%), and 5q (20%). CIS lesions already possess many of the genetic alterations displayed by invasive transitional cell carcinomas, potentially accounting for the aggressive nature of these lesions.

High prevalence of expression of p53 oncoprotein in oral carcinomas from India associated with betel and tobacco chewing

A recent study reported a low prevalence of p53 expression (11%) in oral squamous cell carcinomas (SCCs) from South Asia, in contrast to a high prevalence (averaging 52%) in other studies. It was proposed that the different aetiologies for oral SCCs in the South Asia population, i.e. betel and tobacco chewing in combination with smoking and alcohol consumption as compared to smoking and alcohol consumption alone in other populations, may account for the low prevalence of p53 expression. To confirm this hypothesis, we examined p53 expression immunohistochemically in 23 cases of oral SCC from patients in Southern India. Thirteen of the 23 SCCs (56.5%) demonstrated nuclear p53 staining. The expression of p53 was strongly correlated with the number of tobacco-containing quids chewed per day (r = 0.8). These data support the hypothesis that carcinogens derived from tobacco and betel chewing may induce p53 mutations, which in turn are involved in the development of oral cancer.

A protective effect of chromosome 11 against DNA damage by TPA-activated neutrophils but not TPA acting alone

Evidence from animal models suggests that 12-O-tetrade-canoylphorbol-13-acetate (TPA) is capable of inducing genetic damage within a tissue, although the mechanism underlying this response is unknown. A favoured hypothesis is that the TPA is acting either by stimulating cells in the tissue directly to generate DNA damaging agents or by recruiting inflammatory cells to the tissue and stimulating them to release such agents. These agents include reactive oxygen species, such as hydrogen peroxide and superoxide anion, as well as products generated during lipid peroxidation and arachidonic acid metabolism. It is not known whether significant alterations occur in the sensitivity of cells to TPA during the process of tumourigenesis. In this paper the capacity of TPA to induce chromosomal breakage (measured by micronuclei induction) was found to be elevated in bladder tumour cell lines compared to two normal cultures, a primary epithelial culture and a fibroblast culture. This effect was observed when cells were exposed to TPA directly or co-cultured with TPA-activated neutrophils isolated from human blood. In addition, we present evidence that loci on chromosome 11 may be involved in altering the response of cells to TPA. When chromosome 11 was inserted into a bladder tumour cell line, a reduction in sensitivity to TPA-activated neutrophils was observed. The chromosome insert did not protect against damage induced by direct treatment with TPA alone. In another scenario, fibroblasts from a patient with ataxia telangiectasia, a syndrome localized to chromosome 11, were shown to have an elevated sensitivity to the chromosome damaging action of TPA-activated neutrophils, but not to TPA alone. These results suggest that some of the alterations occurring in a tissue during tumourigenesis could have a significant impact on the responsiveness of cells to genetic damage by TPA. They also suggest that the damage induced by TPA in a cell may be different if a neutrophil is present.

Localized induction of micronuclei in the oral mucosa of xeroderma pigmentosum patients

Xeroderma pigmentosum (XP) patients are predisposed not only to skin cancers but also to tumors on the tip of the tongue. Although this enhanced risk has been attributed to a defect in the repair of DNA damage induced by ultraviolet rays from sunlight there is a lack of data showing that DNA damage is occurring in vivo at these sites. In order to determine whether a relationship exists between exposure to ultraviolet light and the level of chromosomal breakage occurring in epithelial tissue in XP patients, the exfoliated cell micronucleus test was applied to different sites in the oral cavities of four XP patients: the right and left buccal mucosa, the dorsal tip of the tongue and the palate. Six Egyptian controls were sampled concurrently. Micronucleus (MN) frequencies were higher in XP patients than in controls for all sites except the palate, where technical difficulties were encountered. In addition, an unequal distribution of the frequency of micronucleated cells was found in the different sample sites of the oral cavity in the XP patients, with the greatest elevation in frequencies among cells collected from the dorsal tip of the tongue. In contrast, the frequency of micronucleated cells did not vary significantly in samples from different sites obtained from the controls. These data suggest that the complex interplay of host and environmental factors can affect MN frequencies when this endpoint is used to quantify in vivo genotoxic damage in a tissue.

Inflammation, chromosomal instability, and cancer: the schistosomiasis model

Evidence is accumulating in support of a role for reactive oxygen species in the etiology of cancer. Inflammatory cells, such as neutrophils, macrophages, and eosinophils, are an important endogenous source of oxygen radicals. Stimulation of these cells by tumor promoters or by foreign bodies (parasites, bacteria, etc.) causes the release of reactive oxygen species. Laboratory studies have shown that genetic damage and neoplastic transformation are induced in vitro in cells cocultured with activated inflammatory cells. We have recently begun to study the role of inflammatory reactions in inducing genetic damage in a human population. This paper describes our initial studies of Egyptian patients infected with Schistosoma haematobium. This infection induces chronic inflammation and irritation in the urinary bladder and is associated with increased cancer at this site. We describe a recently completed population study that shows that infected individuals have elevated levels of genetic damage in their bladders, as measured by the exfoliated cell micronucleus test. Treatment that kills the parasite also reduces the micronucleus frequencies. We also explore the hypothesis that altered sensitivity of clones of cells in these patients to reactive oxygen species could be a force that drives the development of neoplasia by facilitating clonal expansion. Evidence is presented for the possible involvement of loci on chromosome 11 in controlling the level of chromosomal breakage caused by oxidative damage. We have shown that bladder carcinoma cells are sensitive to micronucleus induction by promoter-activated neutrophils and that they can be protected from this damage by insertion of a normal chromosome 11. Further work is in progress to define the source of chromosomal breakage in schistosomiasis patients and to begin to develop an understanding of the host factors protecting bladder cells in these individuals from genetic damage.

Involvement of inflammatory reactions and elevated cell proliferation in the development of bladder cancer in schistosomiasis patients

Schistosoma haematobium infection is strongly associated with urinary bladder cancer. Although numerous explanations have been proposed for this association, the nature of this relationship remains unresolved. This paper explores the hypothesis that inflammation and elevated cell proliferation play a major role in the development of bladder cancer in infected patients, possibly by increasing the level of genetic instability in the urothelium. The paper details in vivo and in vitro studies being done in our laboratories to test this hypothesis. These studies include population studies in which chromosomal breakage in the bladder of infected individuals is assayed using the micronucleus (MN) test on exfoliated urothelial cells. The approach also includes parallel studies in Vancouver with patients with long-term catheter drainage, a population with many similarities to schistosomiasis patients. In the in vitro studies we are co-incubating bladder cells with activated neutrophils or experimental conditions simulating inflammation. These studies show that inflammatory cells when activated can induce micronuclei in bladder cells and that this response is associated with loci on chromosome 11, a chromosome commonly altered during bladder carcinogenesis. A final approach being used is to assay chromosomal change (MN frequencies and numerical chromosome alterations) and level of proliferation (expression of proliferating cell nuclear antigen) in archival biopsies from schistosomiasis patients. Preliminary results show that a dysregulation of cell proliferation is occurring during cystitis in these patients. The extent to which this alteration affects the level of chromosomal breakage is yet to be determined.

Response of fibroblast cultures from ataxia-telangiectasia patients to reactive oxygen species generated during inflammatory reactions

Cells from patients with ataxia-telangiectasia (AT) are more sensitive than cells from normal individuals to a number of compounds which induce DNA damage via oxygen-derived free radical attack. We tested the hypothesis that AT cells would show a sensitivity to reactive oxygen species (ROS) generated by activated inflammatory cells. AT cells were exposed to neutrophils activated with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or to xanthine/xanthine oxidase (X/XO), an enzyme system which generates superoxide and hydrogen peroxide. Induced micronuclei (MN) frequencies (corrected for spontaneous MN frequencies) were significantly higher in AT cell cultures than in cultures from normal individuals (comparison of MN frequencies of AT vs. normal cultures: for treatment with activated neutrophils, P = 0.003; for X/XO, P = 0.05). The comet assay was used to determine whether the elevated chromosomal damage in the treated AT cells was due to a difference in strand breakage or its rejoining. X/XO treatment was used in studies of single-stranded (SS) DNA breakage, and X-ray treatment for double-stranded (DS) DNA damage. AT and normal cells showed no significant differences in the initial levels of SS (P = 0.29) or DS (P = 0.91) DNA damage. Likewise, they exhibited similar rejoining kinetics (rejoining half-time for SS = 10 min, for DS = 30 min). These data support the involvement of the AT loci in determining a cell's ability to deal with oxidative stress, although the mechanism underlying this effect has yet to be resolved. The data also suggest that AT patients are at elevated risk of sustaining DNA damage in tissues undergoing inflammatory reactions.

A sensitivity to oxidative stress is linked to chromosome 11 but is not due to a difference in single strand DNA breakage or repair

Defects in loci on chromosome 11 have been associated with tumourigenicity, anchorage-independent growth, metastasis and radiosensitive DNA repair in tumour cells. The introduction of normal chromosome 11 into these cells suppresses these responses. In the present study we tested two hypotheses: (1) that microcell fusion of normal chromosome 11 into bladder-carcinoma cells (A1698) can protect the cells against chromosomal damage by oxidative stress; and (2) that insertion of normal chromosome 11 corrects a single-strand (SS) DNA-repair defect. Cultures of A1698 (termed parent) and its microcell-mediated hybrid (termed hybrid) were exposed for 1 h to xanthine/xanthine oxidase (X/XO) or co-incubated with human neutrophils activated with 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Micronucleus frequencies (an indication of chromosomal damage) were significantly higher in parent cultures after treatment than in hybrid (P < 0.0001). The level of single-strand DNA breakage and its repair was assayed in X/XO-treated cultures with the alkaline comet assay. There was no significant difference between parent and hybrid in the amount of SS DNA breakage at treatment (P > 0.1) or after 20 min of repair (P > 0.1). The data support the involvement of a defect in chromosome 11 leading to sensitivity to oxidative stress and suggest this defect is not in the initial amount or rate of rejoining of SS DNA breakage.

Genetic alterations in carcinogenesis and chemoprevention

Laboratory and clinical studies suggest that genetic change is intrinsically involved in the development of cancer and that this change occurs in humans throughout carcinogenesis, in both early and late stages. Therefore, the quantification of the level of genetic change in human epithelial tissues may serve as a marker for cancer risk. The micronucleus test has been used to quantify the level of site-specific chromosomal breakage occurring in epithelial tissues of individuals at elevated risk for cancer. These studies include individuals exposed to carcinogens, patients who have chromosome-breakage syndromes, and individuals with premalignant lesions. As a counterpart to this approach, the assay has been used to study the suppression of this breakage with chemopreventive agents, some of which occur naturally in the diet. These agents include beta-carotene, retinyl palmitate, 13-cis-retinoic acid, riboflavin, canthaxanthin, and folic acid. Not all of these agents were effective. The success of the treatment depended on both the agent being used and the population being studied. The results of these studies suggest that successful intervention with chemopreventive agents will depend on tailoring treatment regimens to specific populations. The micronucleus test can be used along with other biological end points to obtain an early indication of the efficacy of chemopreventive agents in altering biological changes associated with carcinogenesis in tissues of high-risk individuals.

Reduction in chromosomal damage in schistosomiasis patients after treatment with praziquantel

Schistosoma haematobium infection is the most common health problem in Egypt. It is strongly associated with the development of urinary bladder carcinoma. The aim of this study was to determine whether infection with this parasite resulted in an increase of chromosomal breakage in the exfoliated urothelial cells. Urine samples were collected from 211 Egyptian male farmers and schoolchildren with Schistosoma haematobium ova in their urine. 66 samples were suitable for scoring. Accordingly, 66 non-infected males attending the same village clinic were included in the study as a control group. The urine was centrifuged and the urothelial cells present in the sediment were assayed for the presence of micronuclei, a quantitative indicator of chromosomal breakage. Micronucleus frequencies were significantly higher in the infected group (mean frequency, 0.84 +/- 0.69%) than among controls (mean frequency, 0.12 +/- 0.21%, p < 0.001). There was a trend towards an increase in micronucleus frequencies in infected individuals who smoked (17 of the 66 subjects) compared with those who were non-smokers, although this effect was not significant (p > 0.05). Bladder infection was associated with a 6.1-fold increase in micronucleus frequencies among non-smokers. In this study, patients were treated with praziquantel, an anti-schistosomal agent. Out of the 66 studied patients, only 37 gave scoreable samples after treatment. The mean micronucleus frequencies were reduced significantly (before treatment, 0.80 +/- 0.70%, after treatment, 0.19 +/- 0.23%, p < 0.001), thus supporting a direct involvement of the infection in increased chromosomal breakage in the urothelium.

The use of the micronucleus test on exfoliated cells to identify anti-clastogenic action in humans: a biological marker for the efficacy of chemopreventive agents

Laboratory and epidemiological studies support the hypothesis that cancer incidence in human populations can be reduced by supplementing high-risk individuals with chemopreventive agents. Many candidate agents have been identified, too many to be assayed in long-term clinical trials. As an alternate approach, intermediate markers are currently being evaluated as short-term screens for the activity of chemopreventive agents in humans. These markers quantify cellular and molecular changes of biological significance to the process of carcinogenesis. One such marker is the micronucleus test on exfoliated cells. This assay has been used to quantify chromosomal breakage occurring in the human oral cavity, esophagus, cervix, lung, nasal cavity and urinary bladder. Intervention trials on high-risk populations have shown that supplementation with chemopreventive agents can modulate this breakage. This article will review the evidence in support of the use of this assay as a biological marker for the efficacy of a chemopreventive regime. Basic problem areas in the design and conduct of this assay in humans will also be discussed, as will the future potential of the assay.

Chromosomal damage in urothelial cells from Egyptians with chronic Schistosoma haematobium infections

The most common cancer in Egypt is urinary-bladder carcinoma, which is strongly associated with infection with Schistosoma haematobium. The object of this study was to determine whether infection with this parasite resulted in an increase in chromosomal breakage in the urothelium. Urine samples were collected from 37 Egyptian farmers with S. haematobium ova in their urine and from 32 non-infected males attending the same village clinic. The urine was centrifuged and the urothelial cells present in the sediment were assayed for the presence of micronuclei, a quantitative indicator of chromosomal breakage. Micronucleus frequencies were significantly higher in the infected group (mean frequency, 0.97 +/- 0.12%) than among controls (mean frequency, 0.12 +/- 0.04%, p less than 0.001). There was a trend towards an increase in micronucleus frequencies in infected individuals who smoked (10 of the 37 subjects) compared with those who were non-smokers, although this effect was not significant (p = 0.12). Bladder infection was associated with a 6.8-fold increase in micronucleus frequencies among non-smokers. In a pilot study, 11 patients were treated with praziquantel, an anti-schistosomal agent. Mean micronucleus frequencies were reduced significantly (before treatment, 1.27 +/- 0.16%; after treatment, 0.30 +/- 0.16%, p less than 0.001), thus supporting a direct involvement of the infection in increased chromosomal breakage in the urothelium.

Response of fibroblast cultures from ataxia-telangiectasia patients to oxidative stress

The object of this study was to determine whether ataxia-telangiectasia (AT) cells are more sensitive than normal cells to reduced oxygen species generated either during normal cell processes or resulting from metabolism of xenoblotics. To test this hypothesis four AT and four normal fibroblast cultures were exposed to hydrogen peroxide (H2O2) and the induction of micronucleated cells was assayed. AT cultures responded to the H2O2 treatment with a greater increase in micronucleus frequencies than that observed in normal cultures (P less than 0.01). At time course study showed that an elevation in micronucleus frequencies occurred earlier in AT cultures (significant increase by 1.5 h after treatment) than in normal cultures, possibly indicating a G2-phase sensitivity of AT cells to H2O2. The addition of an aqueous extract of areca nut to the cultures, as an example of exogenous stress, induced a greater frequency of micronucleated cells in AT cultures than in the normal cultures. These results suggest that the AT syndrome may serve as a model for investigating the role of reduced oxygen species in cancer.

Variations in the uptake of beta-carotene in the oral mucosa of individuals after 3 days of supplementation

Variations in the response of individuals to beta-carotene supplementation were studied by measuring the accumulation of beta-carotene in oral mucosa cells. Beta-carotene was administered orally to 178 individuals for 3 consecutive days, exfoliated oral mucosa cells were collected by brushing the entire oral mucosa on the 7th day following supplementation, and the beta-carotene content was measured by HPLC analysis of the pronase-treated cells. The rise in beta-carotene levels in the oral mucosa following supplementation varied considerably. Significant differences in mean beta-carotene levels in the oral mucosa were observed in 4 population groups. After supplementation, beta-carotene levels increased by factors of 10.3 (100 Mile House), 7.8 (Williams Lake), 6.9 (Lytton) and 3.4 (Vancouver), respectively. This difference in mean beta-carotene values is due to there being different proportions of weak and strong responders in the various population groups. Neither peak levels nor increases in beta-carotene levels were correlated with base-line concentrations of beta-carotene in the pre-supplementation samples. A second supplementation was given to 54 individuals several months after the initial supplementation. Of 17 weak responders in the first supplementation study, 10 (58.8%) individuals again showed only a small increase. A time-course study revealed that low responders showed no significant changes in beta-carotene levels over the 21 days following supplementation. Particular attention should be paid to weak responders when results of intervention trials using beta-carotene are interpreted.

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.

Clastogenic activity in urine of individuals with urinary bladder infections

The object of this study was to determine whether an elevation in chromosome-damaging (clastogenic) activity occurred in the urine of individuals with bladder infections. Urine samples were collected from 18 patients with chronic (long-term) bladder infections (CBI). Organic material was extracted from urine by preparative reversed-phase high-pressure liquid chromatography and assayed for chromosome-damaging activity in Chinese Hamster Ovary (CHO) cell cultures. Clastogenic activity was present in these urine extracts at levels significantly above those observed in control individuals (P less than 0.001). These levels were comparable to those observed in smoker's urine. In addition, 2 of 4 individuals with acute (short-term) bladder infection (ABI) showed a significant elevation in clastogenic activity in their urine samples (P = 0.025). This study indicates that clastogenic components can be produced during bacterial infections in the urinary bladder and supports a direct involvement of urinary tract infections in the development of bladder cancer.

Heterogeneity of chromosomal breakage levels in epithelial tissue of ataxia-telangiectasia homozygotes and heterozygotes

The objective of this study was to obtain an estimate of the frequency distribution of spontaneous chromosomal breakage occurring in vivo in oral epithelia of 20 ataxia-telangiectasia patients (A-T homozygotes) and 26 parents (A-T obligate heterozygotes). Samples of exfoliated cells were obtained from each individual by swabbing the oral cavity and preparing air-dried slides. The percentage of exfoliated cells with micronuclei (MEC frequency) was used as an in vivo indicator for the amount of chromosomal breakage occurring in the tissue. As a population group, MEC frequencies of the A-T patients differed significantly from controls (mean for A-T patients, 1.51; for controls, 0.29; P less than 0.01). However, the values observed in individual patients ranged from MEC frequencies 10- to 12-fold above control values, to frequencies overlapping the upper values observed in the controls. Similarly, MEC frequencies observed among the A-T heterozygotes differed significantly from controls (mean for A-T heterozygotes, 1.02, mean for controls, 0.29; P less than 0.01). However, only 16 of the 26 individuals sampled had MEC frequencies greater than 0.5%, the 90th percentile for controls (compared with 16 of the 20 A-T patients examined). Of the A-T patients 11 had been previously assigned to complementation groups on the basis of sensitivity to x-irradiation. Seven of the patients belonged to group A and had MEC frequencies ranging from 0.3% to 1.9% with the remaining patients belonging to group C with MEC frequencies of 0.2% to 0.9%. The data presented in this paper suggest that although levels of spontaneous breakage in epithelial tissues of A-T patients and A-T obligate heterozygotes are often significantly elevated, this is not the case in all individuals.

Use of exfoliated cells to study tissue-specific levels of beta-carotene in humans

This study was designed to explore the feasibility of using exfoliated cells to study beta-carotene incorporation into different epithelial tissues in humans. Exfoliated cells were collected from the oral cavities (by brushing the oral mucosa) and from the urogenital tracts (by centrifuging urine samples) of 36 females and basal levels of beta-carotene (without oral supplementation) were determined. Beta-carotene levels in cells from the two sites differed significantly, although a weak correlation was observed. As a second aspect of the study, 10 of these females were given oral supplementation with beta-carotene (90 mg twice weekly for 4 weeks). Beta-carotene levels increased significantly in both exfoliated urogenital tract (6.8-fold) and oral mucosa (5-fold) cells. However, the supplemented levels remained significantly different for the two types of cells. Beta-carotene levels did not change in individuals receiving a placebo treatment (n = 7). These studies suggest that exfoliated cells collected from different sites may be of value in quantifying tissue levels of beta-carotene during cancer intervention trials.

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.

Use of intermediate endpoints in quantitating the response of precancerous lesions to chemopreventive agents

A current area of emphasis in cancer research is the determination of whether cancer can be prevented through the use of naturally occurring chemopreventive agents such as beta-carotene. A major area of concern in the design of long-term, large-scale population studies to ascertain the efficacy of such chemopreventive agents lies in the paucity of biological data on the activity of these agents in man. The studies described in this paper were performed to determine whether a series of short-term markers could be used in chemopreventive trials as indicators of the possible success of a chemopreventive regime. Three such markers are described. The first involves the measurement of genotoxic damage in the target tissues of carcinogen-exposed individuals by using the micronucleus test on exfoliated cells. This end point has been successfully used to demonstrate a reduction in carcinogen damage (micronuclei production) in the oral cavity of individuals in population groups at elevated risk for oral cancer (tobacco and betel quid users in the Philippines, snuff users in the Northwest Territories). The second marker involves the determination of DNA adducts in exfoliated cells of carcinogen-exposed individuals by the use of DNA postlabelling procedure. The final marker discussed involves a chemical determination of the levels of a chemopreventive agent in target tissues of individuals receiving a supplement in the diet. In this case, the example described is beta-carotene in exfoliated cells of carcinogen-exposed individuals. These three markers may be combined to determine whether a chemopreventive agent reaches a target tissue, affects DNA adduct formation, and prevents genotoxic damage.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

The effect of nass use and smoking on the risk of oral leukoplakia

The results of a survey of a population with a high incidence of oral cancer are presented in this paper. A remarkably high proportion (41%) of the men surveyed used nass, which is a mixture of tobacco, lime, ash, and cotton oil. The prevalence of oral leukoplakia, lesions thought to be a precursor of oral cancer, was high in persons who used nass (12%) and who smoked cigarettes (15%), and highest among those men who both used nass and smoked (21%). It has been shown that nass use increases the frequency of micronucleated cells in the exfoliated sublingual cells. The clastogenic and genotoxic effect of nass revealed in the study could be attributed to the presence of tobacco-specific N-nitroso compounds. However, the results of chemical analysis, which has shown that nass contains relatively low levels of these compounds, suggest that the relatively strong genotoxic activity of nass could primarily be associated with other chemicals, possibly oxidized phenolics. Despite the uncertainty as to which of the chemicals contained in nass are involved in the etiology of oral cancer and what exactly are the mechanisms of nass-induced carcinogenesis, the results of this study suggest that in populations where nass is widely used, oral leukoplakia and, most probably, oral cancer are conditions that could be prevented by the elimination of nass use and cigarette smoking.

Evidence for chromosome instability in vivo in Bloom syndrome: increased numbers of micronuclei in exfoliated cells

The incidence of exfoliated epithelial cells containing micronuclei was determined in two small human populations, one homozygous and the other heterozygous for the Bloom syndrome gene (bl). The objectives of the study were two: to learn whether the chromosome instability featured so prominently by Bloom syndrome (BS) cells proliferating in vitro also occurs in vivo, and as part of a broad survey of various cancer-prone populations, to determine whether estimating micronucleus frequencies in exfoliated cell samples might be useful for identifying individuals with genetically determined chromosome instability. Eight individuals homozygous (bl/bl) for the BS gene, i.e., persons with the clinical syndrome, were examined, along with 11 obligate heterozygotes (bl/+), parents of affected persons. Exfoliated cells were obtained from two sites, the oral cavity and the urinary tract. Striking and statistically highly significant elevations in the frequencies of cells with micronuclei were observed in cells from both sites in bl/bl individuals compared to that in bl/+ (P less than 0.001) and in a control population, indicating that chromosome instability occurs in vivo in BS. In contrast, micronucleus frequencies at either site did not differ significantly between bl/+ individuals and the control population. This survey, in combination with similar earlier ones of populations predisposed to cancer not on a genetic basis but because of exposure to some environmental carcinogen, suggests that the exfoliated cell micronucleus test identifies individuals whose somatic genetic material has, for either genetic or environmental reasons, been damaged in a way that produces chromosome breakage and rearrangement.

Use of the micronucleus test to monitor the effect of vitamin A, beta-carotene and canthaxanthin on the buccal mucosa of betel nut/tobacco chewers

The frequency of exfoliated cells with micronuclei in buccal swabs was used to estimate the protective effect of vitamin A, beta-carotene and canthaxanthin (4,4'-diketo-beta-carotene) on the buccal mucosa of betel (areca) nut/tobacco chewers. Micronuclei were scored on exfoliated cells taken by swabbing and stained with the Feulgen reaction and fast green. The betel (areca) nut/tobacco chewers served as their own controls. Prior to the administration of vitamin A and beta-carotene, the examined betel quid chewers had elevated frequencies of micronucleated buccal mucosa cells, averaging 4.03% +/- 1.24 SD (n = 26) and 3.43% +/- 1.22 SD (n = 25), respectively. The frequency of micronucleated buccal mucosa cells in non-chewers and non-smokers was 0.51% (n = 52). Following a 9-week ingestion of vitamin A (150,000 IU/week) and beta-carotene (180 mg/week in 6 capsules), the frequency of micronucleated cells decreased significantly (p less than 0.001) to 1.70% and 1.16%, respectively. No significant shift in the frequencies of micronucleated cells was observed following the intake of canthaxanthin (180 mg/week in 6 capsules) for 9 weeks or that of a placebo. The lack of protective activity of canthaxanthin, which is a good trapper of oxygen singlets but cannot be converted into vitamin A, suggests that vitamin A and beta-carotene exert their inhibitory effect on the formation of micronuclei by a mechanism not involving the scavenging of free radicals. The efficacy of beta-carotene as an inhibitor of micronucleated cell formation, the lack of toxicity, and its availability from a multitude of dietary sources should focus attention on this carotenoid as a promising chemopreventive agent.

Reduction with vitamin A and beta-carotene administration of proportion of micronucleated buccal mucosal cells in Asian betal nut and tobacco chewers

The frequency of micronuclei in cells scraped from inside the human cheek is a measure of chromosome breakage in earlier cell divisions, and it can be increased tenfold by carcinogenic stimuli. Supplementation for 3 months of the diet of 40 rural Filipino betel chewers with sealed capsules of retinol (100 000 IU/week) and beta-carotene (300 000 IU/week) was associated with a threefold decrease (from 4.2% to 1.4%) in the mean proportion of cells with micronuclei. This proportion decreased in 37 of the 40 supplemented subjects and no large increases were seen in any subjects. In 11 unsupplemented betel chewers in a nearby cluster of houses the mean proportion of micronuclei did not change (4.3% before and 4.8% three months later). This suggests the possibility that in this population an increase in the dietary intake of retinol and/or carotene may reduce the incidence of oral cancer, which is an important neoplasm in many parts of Asia.

Micronuclei in exfoliated human cells as a tool for studies in cancer risk and cancer intervention

The use of the micronucleus test on exfoliated cells as an approach to identify genotoxic damage in human tissues which are targets for organ-specific carcinogens and from which carcinomas will develop, is described. Chromosomal damage by carcinogens to dividing basal cells of the epithelium results in the production of micronuclei in the daughter cells which migrate up through the epithelium and are exfoliated. Exfoliated cells can be readily obtained from several tissues, including the oral buccal mucosa (scrapings of oral cells), bronchi (sputum), urinary bladder and ureter (centrifugation of urine), cervix (smears) and esophagus (imprints from biopsies). The micronucleus test on exfoliated cells has been successfully used to: (1) recognize population groups at an elevated risk for cancer of the oral cavity or urinary bladder; (2) estimate synergistic or additive effects of carcinogen exposure (cigarette smokers plus drinkers of alcoholic beverages); (3) pinpoint the site within an organ from which most carcinomas will develop (oral cancers among 'inverted' smokers in the Philippines). The possibility that this assay may also serve as a rapid monitor for chemopreventive agents is suggested by a preliminary trial on the effect of vitamin A/beta--carotene dietary supplementation among 33 betel quid chewers in the Philippines. These individuals received sealed capsules of retinol (100,000 IU/week) and beta-carotene (300,000 IU/week) for a 3-month period. At the end of this time, the frequencies of micronucleated buccal mucosa cells were reduced from an average of 4.2% to 1.4%. No changes were observed in micronucleus frequencies among 11 betel quid chewers not receiving vitamin pills. Non- chewers of betel quid in this population had a micronucleus frequency of 0.5%.

The influence of pH on the convertogenic activity of plant phenolics

The genotoxicity of plant phenolics, including pyrogallol, gallic acid, resorcinol and catechin, and a water extract and tannin fraction of betel nut (Areca catechu) was examined at pH levels ranging from 5 to 10. Strain D7 of Saccharomyces cerevisiae was used since the cells can withstand a wide range of pH levels without any loss of viability. At alkaline pH ranges, the examined phenolics and betel nut extracts induced mitotic conversion, whereas they lacked this capacity at acid pH levels. This phenomenon may be due to the rapid autoxidation of phenolics under alkaline conditions, which leads to the generation of H2O2 and free radicals. The results indicate that plant phenolics may pose a genotoxic hazard during chewing of lime-containing betel quid and tobacco which causes the salivary pH to rise above 8.