State of art of micronuclei assay in exfoliative cytology as a clinical biomarker of genetic damage in oral carcinogenesis: A systematic review and meta-analysis

Oral squamous cell carcinoma (OSCC) is the most common oral malignancy, often preceded by oral potentially malignant disorders (OPMDs). Currently, no clinical biomarker exists to predict malignancy, necessitating OPMD follow-up. Habits and environmental factors, such as smoking, and alcohol consumption, influence OSCC onset. Increased micronuclei (MNs) formation has been observed in the development of OSCC. Non-invasive diagnostic tests like exfoliative cytology offer painless and regular monitoring options. This study evaluates the impact of tobacco, alcohol, and pesticide exposure on MNs occurrence in exfoliative cytology-collected oral mucosal cells, assessing their potential as non-invasive biomarker for OSCC development prediction and monitoring in high-risk patients. Despite results from this meta-analysis supporting the existence of a stepwise increase from controls to patients with OPMD to OSCC, the translation of these findings into clinical practice is limited due to intra- and inter-individual heterogeneity, as well as methodological variability in MNs quantification. Various factors contribute to this heterogeneity, including demographic variables, methodological variability of different laboratories, staining techniques, sample collection location, and patient characteristics. All these points were discussed to provide further insights and improve standardization for future studies.

Objectives and achievements of the HUMN project on its 26th anniversary

Micronuclei (MN) are a nuclear abnormality that occurs when chromosome fragments or whole chromosomes are not properly segregated during mitosis and consequently are excluded from the main nuclei and wrapped within nuclear membrane to form small nuclei. This maldistribution of genetic material leads to abnormal cellular genomes which may increase risk of developmental defects, cancers, and accelerated aging. Despite the potential importance of MN as biomarkers of genotoxicity, very little was known about the optimal way to measure MN in humans, the normal ranges of values of MN in healthy humans and the prospective association of MN with developmental and degenerative diseases prior to the 1980's. In the early 1980's two important methods to measure MN in humans were developed namely, the cytokinesis-block MN (CBMN) assay using peripheral blood lymphocytes and the Buccal MN assay that measures MN in epithelial cells from the oral mucosa. These discoveries greatly increased interest to use MN assays in human studies. In 1997 the Human Micronucleus (HUMN) project was founded to initiate an international collaboration to (i) harmonise and standardise the techniques used to perform the lymphocyte CBMN assay and the Buccal MN assay; (ii) establish and collate databases of MN frequency in human populations world-wide which also captured demographic, lifestyle and environmental genotoxin exposure data and (iii) use these data to identify the most important variables affecting MN frequency and to also determine whether MN predict disease risk. In this paper we briefly describe the achievements of the HUMN project during the period from the date of its foundation on 9th September 1997 until its 26th Anniversary in 2023, which included more than 200 publications and 23 workshops world-wide.

Cytogenetic Effects in Children Exposed to Air Pollutants: A Systematic Review and Meta-Analysis

The aim of this systematic review and meta-analysis was to assess the association between exposure to ambient air pollutants and micronuclei (MN) frequency in children. This work was performed according to the Cochrane Collaboration and the PRISMA guidelines and recommendations. Articles published before November 2021 were identified by an advanced search on PubMed/MEDLINE, Scopus and Web of Science databases. A critical appraisal using a specific tool was conducted to assess the quality of each included study. All analyses were carried out by using the Review Manager (RevMan) 5.4 software (The Cochrane Collaboration, London, UK). One hundred and forty-five references were firstly identified, and, at the end of selection process, 13 studies met the inclusion criteria. Six studies carried out a direct evaluation through the use of air samplers, whereas the other ones accessed environmental databases (n = 2) or used other tools (n = 3). In two cases, exposure was not directly investigated, with children sampled in two different areas with well-known different levels of pollution. The overall effect size (ES) was 1.57 ((95% CI = 1.39; 1.78), p-value < 0.00001) (total evaluated subjects: 4162), which highlighted a statistically significant association between outdoor air pollution and MN frequency in children. As a high MN frequency has been associated with a number of pathological states and a higher risk of developing chronic degenerative diseases, our results should be taken into consideration by policy makers to design and implement interventions aimed at reducing the introduction of pollutants in the atmosphere as well as at minimizing the exposure extent, particularly in children.

Recommendations and quality criteria for micronucleus studies with humans

Micronucleus (MN) analyses in peripheral blood lymphocytes and exfoliated cells from different organs (mouth, nose, bladder and cervix) are at present the most widely used approaches to detect damage of genetic material in humans. MN are extranuclear DNA-containing bodies, which can be identified microscopically. They reflect structural and numerical chromosomal aberrations and are formed as a consequence of exposure to occupational, environmental and lifestyle genotoxins. They are also induced as a consequence of inadequate intake of certain trace elements and vitamins. High MN rates are associated with increased risk of cancer and a range of non-cancer diseases in humans. Furthermore, evidence is accumulating that measurements of MN could be a useful tool for the diagnosis and prognosis of different forms of cancer and other diseases (inflammation, infections, metabolic disorders) and for the assessment of the therapeutic success of medical treatments. Recent reviews of the current state of knowledge suggest that many clinical studies have methodological shortcomings. This could lead to controversial findings and limits their usefulness in defining the impact of exposure concentrations of hazardous chemicals, for the judgment of remediation strategies, for the diagnosis of diseases and for the identification of protective or harmful dietary constituents. This article describes important quality criteria for human MN studies and contains recommendations for acceptable study designs. Important parameters that need more attention include sufficiently large group sizes, adequate duration of intervention studies, the exclusion of confounding factors which may affect the results (sex, age, body mass index, nutrition, etc.), the evaluation of appropriate cell numbers per sample according to established scoring criteria as well as the use of proper stains and adequate statistical analyses.

Micronuclei and upper body cancers (head, neck, breast cancers) a systematic review and meta-analysis

A systematic review and a meta-analysis were performed on 19 studies on head and neck cancer (HNC) and 21 studies on breast cancer (BC) to evaluate the application of micronucleus (MN) assay as a predictive and prognostic test for cancer risk. In these studies the MN test was applied in peripheral lymphocytes and buccal cells of patients and healthy subjects with family history of cancer. The meta-analysis on MN applied in buccal cells of HNC patients was performed on two subgroups of studies. A significant increase of MN frequency in patients compared to healthy controls was observed for the subgroup on oral cancer (243 cases/370 controls, meta-MR = 4.71 95 %CI:2.75-8.06) and HNC (204 patients/163 controls metaMR=2.28 95 %CI:2.02-2.58). A metaMR = 3.27 (95 %CI:1.41-7.59) was obtained for MN applied in peripheral lymphocytes on HNC (160 cases/160 controls). For BC, the analysis of MN in peripheral lymphocytes showed significantly higher values in patients (n = 761) than in controls (n = 788) (meta-MR1.90 95 % CI:1.44-2.49). No statistically significant increase of baseline MN was detected in studies on groups of healthy subjects with BC family history (n = 224) or with BRCA1/2 mutations (n = 101) with respect to the controls. After ex-vivo challenge with ionizing radiation, the meta-analysis revealed a slightly statistically significant increase in MN only in BC patients (n = 614) compared to controls (n = 622)(meta-MR = 1.11 95 %CI:1.02-1.21); no increase was observed in healthy subjects with BC family history carrying or not BRCA1/2 mutations. Significant difference between BC patients (n = 183) and controls (n = 165) was observed by the meta-analysis of data on MN in buccal cells (MR = 3.89 95 %CI:1.54-9.78). The MN assay in buccal cells has some perspective of clinical application in HNC.

Buccal micronucleus cytome assay: Inter-laboratory scoring exercise and micronucleus and nuclear abnormalities frequencies in different populations from Brazil

The Buccal Micronucleus Cytome Assay (BMCyt) has become an important biomonitoring tool for assessing cytogenetic damage in many studied populations. Each laboratory applies protocols that vary according to the method of collecting and preparing samples. Besides, Brazil is a country of great territorial extensions that received immigrants from various parts of the world with different genetic backgrounds. Therefore, the present study aimed to evaluate the inter-laboratory variation in scoring the same set of slides using the more comprehensive scoring criteria, to standardize the BMCyt protocol, to observe the basal alterations in populations of different Brazilian regions and to compare it with other places around the world. Our results showed that a valuable number of laboratories participated, ten laboratories from different regions of the country, for the validation of the BMCyt in human biomonitoring studies, resulting in the 804 healthy individuals. This was possible because we observed: a range of measures needs to be considered, such as the baseline frequency of DNA damage and cell death in non-exposed individuals; age when grouped showed an influence on DNA damage, although when evaluated by group we did not see an influence; association between smoking habit and all endpoints of the BMCyt (except karyolytic cells) was evident; the basal MN frequency, in the majority of groups, follows those around the world; and the BMCyt was confirmed as a good health status biomarker. We emphasize the need for constant discussions on the parameters of cell death due to greater difficulty among the analyzers.

Micronuclei, inflammation and auto-immune disease

Auto-immune diseases (AUD) are characterized by an immune response to antigenic components of the host itself. The etiology of AUD is not well understood. The available evidence points to an interaction between genetic, epigenetic, environmental, infectious and life-style factors. AUD are more prevalent in women than in men; sex hormones play a crucial role in this sex bias. Micronuclei (MN) emerged as a new player in the induction of AUD, based on the capacity of DNA-sensors to detect self-DNA that leaks into the cytoplasm from disrupted MN and induce the cGAS-STING pathway triggering an innate auto-immune response and chronic inflammation. It was found that inflammation can induce MN and MN can induce inflammation, leading to a vicious inflammation-oxidative-DNA damage-MN-formation-chromothripsis cycle. MN originating from sex chromosome-loss may induce inflammation and AUD. We performed a systematic review of studies reporting MN in patients with systemic or organ-specific AUD. A meta-analysis was performed on lymphocyte MN in diabetes mellitus (10 studies, 457 patients/290 controls) and Behcet's disease (3 studies, 100 patients/70 controls) and for buccal MN in diabetes mellitus (11 studies, 507 patients/427 controls). A statistically significant increase in patients compared to controls was found in the meta-analyses providing an indication of an association between MN and AUD. A 36%-higher mean-MRi in buccal cells (3.8+/-0.7) was found compared to lymphocytes (2.8+/-0.7)(P = 0.01). The meta-MRi in lymphocytes and buccal cells (1.7 and 3.0 respectively) suggest that buccal cells may be more sensitive. To assess their relative sensitivity, studies with measurements from the same subjects would be desirable. It is important that future studies (i) investigate, in well-designed powered studies, the prospective association of MN-formation with AUD and (ii) explore the molecular mechanisms by which chromosome shattering in MN and the release of chromatin fragments from MN lead to the formation of auto-antibodies.

Genomic Instability in Exfoliated Buccal Cells among Cement Warehouse Workers

BACKGROUND

Workers in cement warehouses of Kerala are enduring long-standing exposure to cement dust, which is considered genotoxic.

OBJECTIVE

To evaluate the extent of genotoxicity and cytotoxicity caused due to exposure of cement dust among those working in cement warehouses.

METHODS

The study included 82 cement warehouse workers and 82 age-matched individuals with no exposure to cement dust. Exfoliated buccal micronucleus cytome assay (BMCyt) was performed to analyze the genotoxic and cytotoxic effects caused by inhalation of cement dust.

RESULTS

The frequency of various genotoxic and cytotoxic end markers (micronucleated cells [2-fold increase, p<0.001], nuclear buds [4-fold increase, p<0.001], binucleated cells [4-fold increase, p<0.001], karyorrhectic cells [2-fold increase, p<0.001], pyknotic cells [3-fold increase, p<0.001], and karyolytic cells [2-fold increase, p<0.001]) were higher in the exposed workers compared with unexposed group. Increase of these parameters represented an increased level of chromosomal damage, nuclear disintegration and increased cell death among exposed group compared with unexposed group.

CONCLUSION

Continuous exposure to cement dust results in increased frequency of nuclear aberrations and cellular apoptosis. This may lead to defects in genome maintenance, accelerated ageing, increased chance of oral cancer and neurodegenerative disorders in those occupationally exposed to cement dust.

Genomic Instability Decreases in HIV Patient by Complementary Therapy with Rosmarinus officinalis Extracts

Genomic instability is associated with increased oxidative stress in patients with human immunodeficiency virus (HIV). The aim of this study was to determine the effect of intake of methanolic and aqueous extracts of Rosmarinus officinalis on genomic instability in HIV patients. We studied 67 HIV patients under pharmacological treatment with ATRIPLA who were divided into three groups: group 1, patients under ATRIPLA antiretroviral therapy; group 2, patients with ATRIPLA and rosemary aqueous extract (4 g/L per day); and group 3, patients with ATRIPLA and rosemary methanolic extract (400 mg/day). The genomic instability was evaluated through the buccal micronucleus cytome assay. Oral epithelial cells were taken at the beginning and 1 and 4 months later. The groups that received the pharmacological therapy with ATRIPLA and the complementary therapy with R. officinalis extracts showed a decrease in the number of cells with micronuclei and nuclear abnormalities compared with the group that only received ATRIPLA. The complementary therapy with R. officinalis decreased the genomic instability in HIV patients.

In vivo assessment of genotoxicity in buccal cells of children undergoing tooth restoration

OBJECTIVES

Whereas dental materials came in direct or close contact with oral tissue, it is a great concern about the biocompatibility of those materials. This study was performed to evaluate possible DNA damage to buccal cells exposed to dental materials.

METHODS

This prospective, longitudinal clinical study was conducted over a three months period. Class II restorations were placed in 60 young patients with no previous filling using one of three tested dental materials (two glass ionomers; Ketac Molar and Ionofil Molar and one compomer material; Twinky Star). DNA damage was analysed by micronucleus assays, in buccal exfoliated epithelial cells.

RESULTS

In patients treated with Ketac Molar, a significant frequency of micronuclei (p = 0.027) and binucleated cells in samples taken 30 days following restoration (p = 0.029) was confirmed. In patients treated with Twinky Star, a statistically significant increase in the number of binucleated cells in samples taken after 7 and 30 days following restoration (p = 0.001 and p < 0.001, respectively) was observed. In all samples collected 90 days after treatment, there was no statistical difference in the number of any cell changes.

CONCLUSION

In this study long-term biocompatibility of tested materials was confirmed. Glass ionomers and compomers are widely used materials in paediatric dentistry, and this study has proved their safety for usage in children.

Age related micronuclei frequency ranges in buccal and nasal cells in a healthy population

BACKGROUND

Micronuclei (MNs) are extranuclear DNA-containing bodies and determining MN frequencies is a measure of genomic instability. An age-related increase in MN frequencies in lymphocytes has been quantified, but this effect has not yet been measured in nasal and buccal cells.

METHODS

We determined the effect of age on the MN frequency distributions in buccal and nasal cells among a sample of a general adult population in Switzerland. To maximize the power to detect an effect of age in our population study, we recruited preferentially younger and older working age adults. We harvested buccal and nasal cells from 32 young (19-36 year) and 33 working age (47-71 years) participants. The collected cells were washed, centrifuged, and stained (Feulgen) before microscopic manual counting in 2000 cells. Based on these results, we developed an age-dependent background MN frequency chart to help interpret an individual's MN frequency score as an early signal for the effect of genotoxic exposure.

RESULTS

MN frequencies were respectively 0.53‰ and 0.47‰ for buccal and nasal among the younger and 0.87‰ and 1.03‰ in the older working age group. This corresponded to a multiplicative slope of 14% and 20% per 10 years of age for buccal and nasal cells, respectively.

CONCLUSION

Based on our study results, we are able to propose an approach for interpreting an individual's MN screening results.

Micronucleus Cytome Assays in Human Lymphocytes and Buccal Cells

The micronucleus (MN) assay, applied in different surrogate tissues, is one of the best validated cytogenetic techniques for evaluating chromosomal damage in humans. The cytokinesis-block micronucleus cytome assay in peripheral blood lymphocytes (L-CBMNcyt) is the most frequently used method in biomonitoring human populations to evaluate DNA damage caused by exposure to genotoxic agents, micronutrient deficiency or excess and genetic instability. Furthermore, recent scientific evidence suggests an association between an increased MN frequency in lymphocytes and risk of cancer and other age-related degenerative diseases. The micronucleus cytome assay applied in buccal exfoliated cells (BMNCyt), provides a complementary method for measuring DNA damage and cytotoxic effects in an easily accessible tissue not requiring ex vivo/in vitro culture. The protocol for L-CBMNcyt described here, refers to the use of ex vivo whole blood method, involving 72 h of culture with the block of cytokinesis starting at 44 h. BMNCyt protocol reports the established method for sample collection, processing, slide preparation and scoring.

Evaluation of Pb-210 in urine and frequency of micronuclei in exfoliated cells as indicators of exposure to cigarettes

This study aimed at analyzing the frequency of micronuclei (MN) in exfoliated cells as well as the levels of Pb-210 in urine samples to evaluate the association between the smoking habit and toxic stress of transitional epithelial cells. The frequency of MN was scored from Giemsa-stained slides while exchange resin and beta counting techniques were employed to measure the concentrations of this radioisotope. Urine samples of smokers had levels of Pb-210 up to 158.65 mBq L^-1. For nonsmokers, the median was below the detection limit (45 mBq L^-1). The analyses of mononucleated cells showed a significant increase of the frequency of MN in smokers when compared to nonsmokers. Statistical tests showed a tight relation between the cigarette consumption and the increase of the frequency of MN, rather than with the levels of Pb-210 present in smoke particles. The results indicate the usefulness of the methodology for the evaluation of human health risks related to chronic contamination with Pb-210.

The micronucleus test for the oral mucosa: global trends and new questions

This study reviews global trends in the publication of papers on the micronucleus test of the exfoliated cells of the oral mucosa in mammals as an approach for environmental biomonitoring. This test has been widely used due to its precision for the detection of chromosome damage. Our temporal analysis showed a significant increase (p < 0.05) in the publication of papers on the oral mucosa over the past 33 years. Brazil was the country that published most papers (24% of the total), followed by India (16%), the USA (10%), Mexico (7%), and Turkey (6%). A further 30 countries contributed the other 37% of the papers. Overall, 99% of the micronucleus studies involved human subjects, and only 1% involved other mammals. As many wild mammals are subject to the same environmental pressures as humans, in particular chemical pollution, it seems likely that many species are equally susceptible to genotoxicogical damage. We emphasize the importance of applying this technique to the analysis of the oral mucosa of wild mammals, as well as the evaluation of its effectiveness, as observed in humans, and the expansion of the available approaches to the monitoring of environmental quality.

Inter-laboratory consistency and variability in the buccal micronucleus cytome assay depends on biomarker scored and laboratory experience: results from the HUMNxl international inter-laboratory scoring exercise

The buccal micronucleus cytome (BMNcyt) assay in uncultured exfoliated epithelial cells from oral mucosa is widely applied in biomonitoring human exposures to genotoxic agents and is also proposed as a suitable test for prescreening and follow-up of precancerous oral lesions. The main limitation of the assay is the large variability observed in the baseline values of micronuclei (MNi) and other nuclear anomalies mainly related to different scoring criteria. The aim of this international collaborative study, involving laboratories with different level of experience, was to evaluate the inter- and intra-laboratory variations in the BMNcyt parameters, using recently implemented guidelines, in scoring cells from the same pooled samples obtained from healthy subjects (control group) and from cancer patients undergoing radiotherapy (treated group). The results indicate that all laboratories correctly discriminated samples from the two groups by a significant increase of micronucleus (MN) and nuclear bud (NBUD) frequencies and differentiated binucleated (BN) cells, associated with the exposure to ionizing radiation. The experience of the laboratories was shown to play an important role in the identification of the different cell types and nuclear anomalies. MN frequency in differentiated mononucleated (MONO) and BN cells showed the greatest consistency among the laboratories and low variability was also detected in the frequencies of MONO and BN cells. A larger variability was observed in classifying the different cell types, indicating the subjectivity in the interpretation of some of the scoring criteria while reproducibility of the results between scoring sessions was very good. An inter-laboratory calibration exercise is strongly recommended before starting studies with BMNcyt assay involving multiple research centers.

Micronucleus Assay: An Early Diagnostic Tool to Assess Genotoxic Changes in Patients with Tobacco Use, Oral Leukoplakia and Oral Submucous Fibrosis

Introduction

Micronuclei (MNi) are acentric chromatid or chromosome fragments produced via genetic damage through genotoxic agents contained in tobacco and betel nut. Evidently, the various Oral Potentially Malignant Disorders (OPMDs) like oral lichen Planus, oral leukoplakia and Oral Submucous Fibrosis (OSMF) demonstrate MNi, as a substantiation of genetic damage. As these changes can be easily appreciated in oral exfoliated cells, an exfoliated cell based MNi assay might be utilized as handy and non invasive biomonitoring tool for gauging the genetic damage and hence the propensity for malignant transformation in OPMDs. To this end, MNi are definitely easier to evaluate when compared to chromosome aberrations.

Aim

To compare the MNi frequency in normal mucosa, in individuals using various tobacco forms without oral leukoplakia, individuals using various tobacco forms with oral leukoplakia, and areca nut chewers with OSMF, using three different stains.

Materials and Methods

Oral exfoliated cells from 50 cases of normal mucosa (Group I), 50 cases of tobacco chewing people without Oral Leukoplakia (Group II), 50 cases of people with Oral Leukoplakia (Group III) and 50 cases of areca nut chewers with OSMF (Group IV) were taken. MNi frequencies were compared in these groups using three different stains i.e., Papanicolaou (PAP) stain, May Grunwald Giemsa (MGG) stain and Feulgen stain. The data between cases (Group II, III and IV) and control groups (Group I) was analyzed by Kruskal-Wallis Test. The comparison between two independent groups was done by Mann-Whitney U test and interstain comparison between cases and control was done by Wilcoxon Signed Rank Test and the individual p-value was obtained.

Results

A significant increase in the count was observed during transition of normal mucosa to OPMDs. The best stain for detecting MNi was PAP stain followed by MGG stain and Feulgen stain.

Conclusion

The higher mean MNi count for PAP stain and MGG stain could be attributed to nonspecific staining. Further study using a larger sample size on quantitative assessment of MNi count in various OPMDs is warranted.

Biomonitoring of agricultural workers exposed to pesticide mixtures in Guerrero state, Mexico, with comet assay and micronucleus test

The aim of this study was to evaluate the genotoxic effect of pesticides in exfoliated buccal cells of workers occupationally exposed in Guerrero, Mexico, using the comet assay and the micronucleus test. The study compared 111 agricultural workers in three rural communities (Arcelia 62, Ajuchitlan 13, and Tlapehuala 36), with 60 non-exposed individuals. All the participants were males. The presence of DNA damage was investigated in the exfoliated buccal cells of study participants with the comet assay and the micronucleus (MN) test; comet tail length was evaluated in 100 nuclei and 3000 epithelial cells of each individual, respectively; other nuclear anomalies such as nuclear buds, karyolysis, karyorrhexis, and binucleate cells were also evaluated. Study results revealed that the tail migration of DNA and the frequency of MN increased significantly in the exposed group, which also showed nuclear anomalies associated with cytotoxic or genotoxic effect. No positive correlation was noted between exposure time and tail length and micronuclei frequencies. No significant effect on genetic damage was observed as a result of age, smoking, and alcohol consumption. The MN and comet assay in exfoliated buccal cells are useful and minimally invasive methods for monitoring genetic damage in individuals exposed to pesticides. This study provided valuable data for establishing the possible risk to human health associated with pesticide exposure.

Frequency of micronucleus in oral epithelial cells after exposure to mate-tea in healthy humans

OBJECTIVES

The aim of this study was to evaluate the possibility of technique simplification for cytology slides in order to evaluate the frequency of micronuclei (FMic) and conduct a experiment looking to know the FMic of oral epithelial cells of healthy volunteers exposed to mate tea (Ilex paraguarariensis).

MATERIAL AND METHODS

This is a laboratorial and nonrandomized trial (quasi-experiment), where the nonusers subjects were exposed to mate-tea, consumed in the traditional way, two drinks, two times a day for a single week. Two cytology of exfoliated epithelial cells were obtained before and after the mate tea exposition.

RESULTS

The sample was composed by 10 volunteers. The age ranged from 18 to 33 years (Mean 23; SD5.5). The use of mate tea did not showed significant variation in the FMic (Wilcoxon Signed Ranks Test p= .24).

CONCLUSIONS

The proposed technique simplification showed to be reliable, without losses when compared to the conventional technique and with the advantage of eliminate toxic substances, becoming simple and practical tool for research in dentistry. The acute exposure to mate tea did not induce an increase of FMic in exfoliated buccal cells of healthy nondrinkers and nonsmokers subjects and may not have genotoxic effect. More human studies are needed before a conclusion can be made on the oral carcinogenic risk of mate tea to humans.

Cytogenetic analysis of oral mucosa cells, induced by chlorhexidine, essential oils in ethanolic solution and triclosan mouthwashes

OBJECTIVES

The aim of this study was to evaluate DNA damage and cytokinetic defects, proliferative potential and cell death caused by the frequent use of mouthrinses containing chlorhexidine, triclosan and essential oils in ethanolic solution, compared to a placebo mouthwash.

STUDY DESIGN

This double-blind, prospective, randomized clinical trial included 80 Caucasian patients. Subjects were divided into four groups: Group I used a mouthrinse, Triclosan; Group II used physiological saline; Group III used chlorhexidine; Group IV a mouthrinse with essential oils in ethanolic solution. All subjects used the mouthrinses for two weeks (15 ml, twice a day, rinsing for 30s). Two cell samples per subject were collected, before and after mouthrinse use (on day 0 and day 15). Samples were processed as follows: cell collection from cheeks with a cytobrush; cell centrifuge; slide preparation, fixation and staining; and fluorescent microscope analysis. 2000 exfoliated cells were screened for nuclear abnormalities, particularly the presence of micronuclei by means of cytome assay.

RESULTS

No significant differences between study times (before and after use of mouthwash) were identified for any of the variables studied (p>0.05). Differences between mouthrinse groups were also compared but no significant differences were found (p>0.05).

CONCLUSIONS

This study did not observe any genotoxic effect resulting from mouthrinse use.

Nicotine derived genotoxic effects in human primary parotid gland cells as assessed in vitro by comet assay, cytokinesis-block micronucleus test and chromosome aberrations test

Genotoxic effects of nicotine were described in different human cells including salivary gland cells. Based on the high nicotine concentration in saliva of smokers or patients using therapeutic nicotine patches, the current study was performed to evaluate the genotoxic potential of nicotine in human salivary gland cells. Therefore, primary salivary gland cells from 10 patients undergoing parotid gland surgery were exposed to nicotine concentrations between 1 μM and 1000 μM for 1 h in the absence of exogenous metabolic activation. The acinar phenotype was proven by immunofluorescent staining of alpha-amylase. Genotoxic effects were evaluated using the Comet assay, the micronucleus test and the chromosome aberration test. Cytotoxicity and apoptosis were determined by trypan blue exclusion test and Caspase-3 assay. Nicotine was able to induce genotoxic effects in all three assays. The chromosome aberration test was the most sensitive and increases in numerical and structural (chromatid-type and chromosome-type) aberrations were seen at ≥1 μM, whereas increases in micronuclei frequency were detected at 10 μM and DNA damage as measured in the Comet assay was noted at >100 μM. No cytotoxic damage or influence of apoptosis could be demonstrated. Nicotine as a possible risk factor for tumor initiation in salivary glands is still discussed controversially. Our results demonstrated the potential of nicotine to induce genotoxic effects in salivary gland cells. These results were observed at saliva nicotine levels similar to those found after oral or transdermal exposure to nicotine and suggest the necessity of careful monitoring of the use of nicotine in humans.

Micronucleus evaluation of exfoliated buccal epithelial cells using liquid-based cytology preparation

OBJECTIVE

Micronuclei (MN) are biomarkers that can be applied to buccal epithelial cells to assess populations occupationally exposed to potentially carcinogenic agents. Liquid-based cytology (LBC) is a way to improve and refine the results obtained by this test.

STUDY DESIGN

Exfoliated buccal cells were collected from 40 subjects (20 construction workers from the Barretos Cancer Hospital and 20 administrative staff from the same institution). LBC and three stains (Feulgen/fast green, Papanicolaou and Giemsa) were used to prepare the slides. Student's t test was applied for statistical comparisons of the data. A p value of <0.05 was considered statistically significant.

RESULTS

Regardless of the stain employed, the frequency of MN was greater in the case group (Feulgen/fast green: 5.15; Papanicolaou: 29; Giemsa: 26) than in the control group (Feulgen/fast green: 2.30; Papanicolaou: 17; Giemsa: 15).

CONCLUSIONS

Using LBC to prepare slides and evaluate the frequency of MN potentially serves as a screening option for more comprehensive studies of cancer risk among populations occupationally exposed to potentially carcinogenic agents. In addition, the residual fluid enables the preparation of slides for DNA-specific stains that can be compared to those with Papanicolaou stain.

The HUMNxl scoring criteria for different cell types and nuclear anomalies in the buccal micronucleus cytome assay - an update and expanded photogallery

The buccal micronucleus cytome assay is a minimally invasive cytological and interphase cytogenetic technique for measuring DNA damage and cell death biomarkers in the oral epithelium. In this report we provide an updated and more comprehensive version of the cellular and nuclear scoring criteria used in the assay accompanied with a photogallery of the various cell types and nuclear anomalies. These detailed scoring criteria complement previous published protocols of this assay and form the basis for guiding intra- and inter-laboratory slide scoring comparisons. The scoring criteria update described in this paper is the outcome of ongoing efforts of the HUMN and HUMNxl projects (www.humn.org) to standardize the application of micronucleus assay for use in human biomonitoring and to update procedures as knowledge on mechanisms and technical capability improvements.

A comparative study for selectivity of micronuclei in oral exfoliated epithelial cells

BACKGROUND

Micronucleus (MN) represents small, additional nuclei formed by the exclusion of chromosome fragments or whole chromosomes lagging at mitosis. MN rates, therefore, indirectly reflect chromosome breakage or impairment of the mitotic apparatus. During the last few decades, micronuclei ("MNi") in oral exfoliated epithelial cells are widely used as biomarkers of chromosomal damage, genome instability and cancer risk in humans. However, until now only little attention has been given to the effect of different staining procedures on the results of these MN assays.

AIM

To compare the MNi frequencies in oral exfoliated epithelial cells using three different stains, i.e.,Feulgen stain, Papanicolaou stain (Pap) and hemotoxylin and eosin stain (H and E).

MATERIALS AND METHODS

Oral exfoliated cells from 45 cases of potentially malignant disorders (15 oral submucous fibrosis, 15 lichen planus and 15 leukoplakia) and 15 controls with healthy mucosa, were taken and MNi frequencies (No. of MNi/1000 cells) were compared using three different stains.

RESULTS

Mean MNi frequency in cases was found to be 3.8 with Feulgen stain, 16.8 with PAP and 25.9 with H and E. In controls, mean MNi frequency was 1.6 with Feulgen stain, 7.7 with PAP and 9.6 with H and E stain. Statistically significant value (P < 0.01) were observed when the three stains were compared together using Kruskal Walli's ANOVA test.

CONCLUSION

Feulgen being a DNA-specific stain gave the least counts, although statistically significant results from the comparison of MNi frequency between cases and controls were obtained with all the three stains.

The frequency of granulocytes with spontaneous somatic mutations: a wide distribution in a normal human population

Germ-line mutation rate has been regarded classically as a fundamental biological parameter, as it affects the prevalence of genetic disorders and the rate of evolution. Somatic mutation rate is also an important biological parameter, as it may influence the development and/or the course of acquired diseases, particularly of cancer. Estimates of this parameter have been previously obtained in few instances from dermal fibroblasts and lymphoblastoid cells. However, the methodology required has been laborious and did not lend itself to the analysis of large numbers of samples. We have previously shown that the X-linked gene PIG-A, since its product is required for glycosyl-phosphatidylinositol-anchored proteins to become surface bound, is a good sentinel gene for studying somatic mutations. We now show that by this approach we can accurately measure the proportion of PIG-A mutant peripheral blood granulocytes, which we call mutant frequency, ƒ. We found that the results are reproducible, with a variation coefficient (CV) of 45%. Repeat samples from 32 subjects also had a CV of 44%, indicating that ƒ is a relatively stable individual characteristic. From a study of 142 normal subjects we found that log ƒ is a normally distributed variable; ƒ variability spans a 80-fold range, from less than 1×10⁻⁶ to 37.5×10⁻⁶, with a median of 4.9×10⁻⁶. Unlike other techniques commonly employed in population studies, such as comet assay, this method can detect any kind of mutation, including point mutation, as long as it causes functional inactivation of PIG-A gene. Since the test is rapid and requires only a small sample of peripheral blood, this methodology will lend itself to investigating genetic factors that underlie the variation in the somatic mutation rate, as well as environmental factors that may affect it. It will be also possible to test whether ƒ is a determinant of the risk of cancer.

Micronucleus assay in human cells: lymphocytes and buccal cells

The micronucleus (MN) assay, applied in different surrogate tissues, is one of the best validated cytogenetic techniques for evaluating chromosomal damage in humans. The cytokinesis-block micronucleus cytome assay (CBMNcyt) in peripheral blood lymphocytes is the most frequent method in biomonitoring human populations to evaluate exposure to genotoxic agents, micronutrient deficiency, or excess and genetic instability. Furthermore recent scientific evidence suggests an association between an increased MN frequency in lymphocytes and risk of cancer and other age-related degenerative diseases. The micronucleus cytome assay applied in buccal exfoliated cells (BMNCyt) provides a complementary method for measuring DNA damage and cytotoxic effects in an easily accessible tissue not requiring in vitro culture. The protocol for CBMNcyt described here refers to the use of ex vivo whole blood involving 72 h of culture with the block of cytokinesis at 44 h. BMNCyt protocol reports the established method for sample processing, slide preparation, and scoring.

Cytological changes in the oral mucosa after use of a mouth rinse with alcohol. A prospective double blind control study

AIM

The aim of this preliminary study was to detect cytological changes in the oral mucosa after using a mouth wash with alcohol.

MATERIAL AND METHODS

A prospective double-blind, controlled study was performed, for 6 months. Group 1 consisted of 30 subjects who used a mouth rinse with 26.9% of alcohol [Listerine] and Group 2 consisted of 30 subjects who used a mouth rinse with the same ingredients but with no alcohol. We obtained three cytological samples from the oral mucosa. The presence of cytological atypia, binucleation and karyorrhesis, and type of cells were studied. We also used a fluorescent in situ hybridization technique (FISH) in 15 samples in each group, for the micronucleus.

RESULTS

We found no clinical mucosal alteration after using the mouth wash at the end of the study in either group. We observed no cytological differences between the groups at the end of the study (p>0.05). Regarding the study of the micronucleus by FISH, we observed no significant difference between the groups (p>0.05).

CONCLUSIONS

Our results showed no cytological alteration in patients using a mouth rinse with alcohol, but these findings should be considered preliminary results, to be confirmed in a greater sample of patients.

DNA and oxidative damages decrease after ingestion of folic acid in patients with type 2 diabetes

BACKGROUND AND AIMS

Type 2 diabetes mellitus (T2DM) is a chronic degenerative disease that promotes autoxidation of sugars, leading to the production of reactive oxygen species. This damage occurs especially at the level of cellular proteins, carbohydrates, lipids and DNA, thus playing an important role in the pathogenesis of late complications of T2DM. We investigated the effect of folic acid on DNA and oxidative damage in patients with T2DM.

METHODS

We studied 30 individuals diagnosed with T2DM and 30 control individuals without disease. Individuals with T2DM were prescribed 5 mg of folic acid, taken orally three times daily for 1 month. Samples were taken 15 and 30 days after treatment. DNA damage was determined using the micronucleus test in oral mucosa and oxidative stress by quantifying 8-hydroxy-2'-deoxyguanosine (8-OHdG) as well as by quantifying total lipid peroxides.

RESULTS

Individuals with T2DM had a higher number of micronuclei as well as higher levels of 8-OHdG and lipid peroxides than the control group (p = 0.001). Individuals with T2DM showed a significant reduction in the number of micronuclei and the concentration of 8-OHdG and lipid peroxides over time with folic acid intake.

CONCLUSIONS

A positive correlation exists between oxidative stress produced by T2DM and DNA damage, so the use of an antioxidant such as folic acid in DM2 therapy is advisable for delaying complications due to T2DM-induced oxidative stress and DNA damage.

Micronuclei assay in exfoliated buccal cells from individuals exposed to arsenic in Argentina

Drinking arsenic (As)-laden water for a long time affects a population's health and leads to chronic hydroarsenicism, which is associated with an increased incidence of different types of cancer. To determine the potential genotoxic risk associated with different degrees of environmental exposure to inorganic As by way of drinking water, micronuclei (MN) frequency in exfoliated buccal cells was evaluated in Argentina among rural populations of Santiago del Estero and urban populations of Buenos Aires. The exposed group in Santiago del Estero (La Firmeza and Santos Lugares localities) showed a significant increase in MN frequency in epithelial cells compared with controls (Monte Quemado and Urutau localities) (p = 0.0005). With regard to the Buenos Aires groups, Navarro individuals (the exposed group) exhibited a significant difference compared with controls (Ciudad Autónoma de Buenos Aires) (p = 0.0002). Comparison of MN frequencies between Santiago del Estero and Buenos Aires individuals showed that genotoxic effects of As in drinking water exhibit variation between rural and urban groups, probably due to individual susceptibility being an important incidence factor. The results clearly show that MN assay in buccal mucosa cells is an ideal methodology with which to measure potential genetic risk related to environmental As exposure in humans.

The in vitro MN assay in 2011: origin and fate, biological significance, protocols, high throughput methodologies and toxicological relevance

Micronuclei (MN) are small, extranuclear bodies that arise in dividing cells from acentric chromosome/chromatid fragments or whole chromosomes/chromatids lagging behind in anaphase and are not included in the daughter nuclei at telophase. The mechanisms of MN formation are well understood; their possible postmitotic fate is less evident. The MN assay allows detection of both aneugens and clastogens, shows simplicity of scoring, is widely applicable in different cell types, is internationally validated, has potential for automation and is predictive for cancer. The cytokinesis-block micronucleus assay (CBMN) allows assessment of nucleoplasmic bridges, nuclear buds, cell division inhibition, necrosis and apoptosis and in combination with FISH using centromeric probes, the mechanistic origin of the MN. Therefore, the CBMN test can be considered as a "cytome" assay covering chromosome instability, mitotic dysfunction, cell proliferation and cell death. The toxicological relevance of the MN test is strong: it covers several endpoints, its sensitivity is high, its predictivity for in vivo genotoxicity requires adequate selection of cell lines, its statistical power is increased by the recently available high throughput methodologies, it might become a possible candidate for replacing in vivo testing, it allows good extrapolation for potential limits of exposure or thresholds and it is traceable in experimental in vitro and in vivo systems. Implementation of in vitro MN assays in the test battery for hazard and risk assessment of potential mutagens/carcinogens is therefore fully justified.

Assessment of genotoxic effects and changes in gene expression in humans exposed to formaldehyde by inhalation under controlled conditions

Forty-one volunteers (male non-smokers) were exposed to formaldehyde (FA) vapours for 4 h/day over a period of five working days under strictly controlled conditions. For each exposure day, different exposure concentrations were used in a random order ranging from 0 up to 0.7 p.p.m. At concentrations of 0.3 and 0.4 p.p.m., four peaks of 0.6 or 0.8 p.p.m. for 15 min each were applied. During exposure, subjects had to perform bicycle exercises (∼80 W) four times for 15 min. Blood samples, exfoliated nasal mucosa cells and nasal biopsies were taken before the first and after the last exposure. Nasal epithelial cells were additionally sampled 1, 2 and 3 weeks after the end of the exposure period. The alkaline comet assay, the sister chromatid exchange test and the cytokinesis-block micronucleus test were performed with blood samples. The micronucleus test was also performed with exfoliated nasal mucosa cells. The expression (mRNA level) of the glutathione (GSH)-dependent formaldehyde dehydrogenase (FDH, identical to alcohol dehydrogenase 5; ADH5; EC 1.2.1.46) was measured in blood samples by quantitative real-time reverse transcription-polymerase chain reaction with TaqMan probes. DNA microarray analyses using a full-genome human microarray were performed on blood samples and nasal biopsies of selected subgroups with the highest FA exposure at different days. Under the experimental conditions of this study, inhalation of FA did not lead to genotoxic effects in peripheral blood cells and nasal mucosa and had no effect on the expression of the FDH gene. Inhalation of FA did also not cause alterations in the expression of genes in a microarray analysis with nasal biopsies and peripheral blood cells.

Use of nasal cells in micronucleus assays and other genotoxicity studies

Genotoxicity experiments with exfoliated nasal mucosa cells are a promising minimally invasive approach for the detection of DNA-damaging compounds in ambient air. Results of single cell gel electrophoresis (SCGE) assays with individual cells and organ cultures from bioptic material show that DNA damage caused by compounds such as nitrosamines, polycyclic aromatic hydrocarbons and pesticides can be detected. Biochemical studies indicate that enzymes involved in the metabolism of environmental mutagens are represented in nasal cells. Several protocols for experiments with nasal cells have been developed and it was shown that formaldehyde, metals, styrene and crystalline silica induce DNA damage in SCGE and/or in micronucleus studies; furthermore, it was also found that polluted urban air causes DNA instability in nasal epithelial cells. Comparisons of these data with results obtained in lymphocytes and buccal cells indicate that nasal cells are in general equally sensitive. Broad variations in the baseline levels, differences of results obtained in various studies as well as the lack of information concerning the impact of confounding factors on the outcome of experiments with these cells indicate the need for further standardisation of the experimental protocols.

Reflections on the development of micronucleus assays

These are personal reflections on the development of methods to use micronuclei as a measure of genetic damage and their use in research and in toxicology by four people who have been intimately involved with this work, a personal rather than a comprehensive history. About 6000 papers have been published using such methods in many tissues in vivo or in cultured cells of many organisms from plants to humans, but the majority of the work has been on mammalian erythrocytes and human lymphocytes, the areas in which we have worked primarily. Although this is by no means a complete history, those working in the field may be interested in some of the personal events that lie behind the development and acceptance of methods that are now standard.