Using fluorescence for improvement of the quantitative analysis of micronucleus in cell culture

Does cone-beam computed tomography examination increase the micronuclei frequency in the oral mucosa exfoliated cells? A systematic review and meta-analysis

OBJECTIVE

This systematic review (SR) with meta-analysis aimed to evaluate the frequency of micronuclei in the oral mucosa exfoliated cells after cone-beam computed tomography (CBCT) examination.

METHODS

We performed language-independent computer-assisted data searches using PubMed databases, Cochrane, Embase, Web of Science all databases, and Google Scholar. The literature on micronucleus (MN) frequency of clinical trials before and after CBCT examination was included. The frequency of MN in exfoliated cells of the human oral mucosa was the primary outcome of the study. All statistical analyses were performed with R (version 4.1.0), RStudio (version 2022.02.2 + 485) software, and Meta packages (version 5.2-0). Two reviewers independently assessed the quality of the included studies by the EPHPP (Effective Public Health Practice Project) Modified scale with minor modifications. The heterogeneity of the data was analyzed using I² statistics, in which I² > 50% was considered substantial heterogeneity.

RESULTS

A total of 559 articles were selected through the search strategy. After screening titles and abstracts, nine full-text manuscripts were assessed for eligibility, and six observational studies were included in the meta-analysis. The present study showed a significant increase in MN frequency of human oral mucosal exfoliated cells 10 days after CBCT examination compared to baseline (SMD = - 0.56, 95%-CI = - 0.99 ~ - 0.13, p = 0.01). Because of the high heterogeneity among the studies (I² = 72%), after removing one study that was the main source of heterogeneity, excluding the study (I² = 47%), the common-effect model was chosen, and the meta-analysis also showed that the frequency of MN in human oral mucosa exfoliated cells increased significantly 10 days after CBCT examination (SMD =  - 0.35, 95%-CI =  - 0.59 ~  - 0.11, p = 0.004).

CONCLUSION

This review suggested that CBCT examination increases the frequency of micronuclei in oral mucosal exfoliated cells.

Plant Cytogenetics in the Micronuclei Investigation-The Past, Current Status, and Perspectives

Cytogenetic approaches play an essential role as a quick evaluation of the first genetic effects after mutagenic treatment. Although labor-intensive and time-consuming, they are essential for the analyses of cytotoxic and genotoxic effects in mutagenesis and environmental monitoring. Over the years, conventional cytogenetic analyses were a part of routine laboratory testing in plant genotoxicity. Among the methods that are used to study genotoxicity in plants, the micronucleus test particularly represents a significant force. Currently, cytogenetic techniques go beyond the simple detection of chromosome aberrations. The intensive development of molecular biology and the significantly improved microscopic visualization and evaluation methods constituted significant support to traditional cytogenetics. Over the past years, distinct approaches have allowed an understanding the mechanisms of formation, structure, and genetic activity of the micronuclei. Although there are many studies on this topic in humans and animals, knowledge in plants is significantly limited. This article provides a comprehensive overview of the current knowledge on micronuclei characteristics in plants. We pay particular attention to how the recent contemporary achievements have influenced the understanding of micronuclei in plant cells. Together with the current progress, we present the latest applications of the micronucleus test in mutagenesis and assess the state of the environment.

The smokeless tobacco habit and DNA damage: A systematic review and meta-analysis

BACKGROUND

The aim of this systematic review was to evaluate the frequency of micronuclei or other DNA damage in the oral mucosa of adults that have smokeless tobacco habits compared to adults that not have these habits.

MATERIAL AND METHODS

We searched PubMed, Scopus, Web of Science, LILACS, BBO and Cochrane Library and SIGLE. We also surveyed gray literature. We included only clinical trials that compare the frequency of micronuclei or other DNA damage in the oral mucosa of adults that have smokeless tobacco habits compared to adults that not have these habits. Quality assessments of the selected trials were evaluated by two independent reviewers, using the Effective Public Health Practice Project - (EPHPP) with modifications.

RESULTS

After the database screening and removal of duplicates, 2574 studies were identified. After title screening, 172 studies remained, and this number was reduced to 25 after careful examination of the abstracts. The standardized mean difference of the frequency of micronuclei between groups was 1.88, with a 95% confidence interval of 1.40 to 2.36 (p < 0.00001). In all analyses heterogeneity was detected.

CONCLUSIONS

Despite the heterogeneity of studies, the frequency of micronuclei was significant bigger in adults who have the smokeless tobacco habit when compared to those not have this habit. The same occurred with the frequency of binucleated cells, karyolisis and karyorrhexis.

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.

Analysis of the Genotoxic Effects of Mobile Phone Radiation using Buccal Micronucleus Assay: A Comparative Evaluation

INTRODUCTION

Micronucleus (MN) is considered to be a reliable marker for genotoxic damage and it determines the presence and the extent of the chromosomal damage. The MN is formed due to DNA damage or chromosomal disarrangements. The MN has a close association with cancer incidences. In the new era, mobile phones are constantly gaining popularity specifically in the young generation, but this device uses radiofrequency radiation that may have a possible carcinogenic effect. The available reports related to the carcinogenic effect of mobile radiation on oral mucosa are contradictory.

AIM

To explore the effects of mobile phone radiation on the MN frequency in oral mucosal cells.

MATERIALS AND METHODS

The subjects were divided into two major groups: low mobile phone users and high mobile phone users. Subjects who used their mobile phone since less than five years and less than three hours a week comprised of the first group and those who used their mobile since more than five years and more than 10 hours a week comprised of the second group. Net surfing and text messaging was not considered in this study. Exfoliated buccal mucosal cells were collected from both the groups and the cells were stained with DNA-specific stain acridine orange. Thousand exfoliated buccal mucosal cells were screened and the cells which were positive for micronuclei were counted. The micronucleus frequency was represented as mean±SD, and unpaired Student t-test was used for intergroup comparisons.

RESULTS

The number of micronucleated cells/ 1000 exfoliated buccal mucosal cells was found to be significantly increased in high mobile phone users group than the low mobile phone users group. The use of mobile phone with the associated complaint of warmth around the ear showed a maximum increase in the number of micronucleated cells /1000 exfoliated buccal mucosal cells.

CONCLUSION

Mobile phone radiation even in the permissible range when used for longer duration causes significant genotoxicity. The genotoxicity can be avoided to some extent by the regular use of headphones.

A combination of micronucleus assay and fluorescence in situ hybridization analysis to evaluate the genotoxicity of formaldehyde

A genotoxic effect of formaldehyde (FA), particularly micronucleus (MN) induction, has been shown in several previous studies. The aim of the present study was to assess the frequency of micronuclei and to identify the type of chromosomal damage in Tunisian staff members working in the Pathologic Anatomy Laboratory of Farhat Hached hospital (Sousse, Tunisia) who were exposed to FA. Assessment of chromosomal damage was performed in peripheral lymphocytes of 31 FA-exposed employees compared with 31 control employees working in the administrative department of the same hospital. The clastogenic/aneugenic effect of FA was evaluated using the standard MN assay in combination with fluorescence in situ hybridization (FISH) using pan-centromeric probes. The mean level of exposure to FA was 3.4 ppm. The results showed a significant increase of MN frequency in lymphocytes of exposed workers compared with the control group (25.35 ± 6.28 ‰ vs. 7.08  ± 4.62 ‰, p < 0.05). As assessed by FISH, the frequency of centromeric micronuclei (C+MN) was greater in exposed subjects than in controls (18.38 ± 5.94 ‰ vs. 5.03 ± 3.64 ‰). Among the C+MN, the frequency of MN containing one centromere (C1+MN) was significantly greater in pathologists and anatomists than in controls (15.35 ± 6.0 ‰ vs. 3.33 ± 2.74 ‰, p < 0.05). The results showed an effect of sex and time of FA exposure with significantly increased frequencies of all end points measuring aneuploidy (C+MN, C1+MN, and Cx+MN [more then one MN]). The increased frequency of C1+MN observed in the exposed group may suggest a slight aneugenic effect of FA exposure.

FISH in analysis of gamma ray-induced micronuclei formation in barley

A micronucleus test in combination with fluorescent in situ hybridization (FISH) using telomere-, centromere-specific probes and 5S and 25S rDNA was used for a detailed analysis of the effects of gamma ray irradiation on the root tip meristem cells of barley, Hordeum vulgare (2n = 14). FISH with four DNA probes was used to examine the involvement of specific chromosomes or chromosome fragments in gamma ray-induced micronuclei formation and then to explain their origin. Additionally, a comparison of the possible origin of the micronuclei induced by physical and chemical treatment: maleic hydrazide (MH) and N-nitroso-N-methylurea (MNU) was done. The micronuclei induced by gamma ray could originate from acentric fragments after chromosome breakage or from whole lagging chromosomes as a result of a dysfunction of the mitotic apparatus. No micronuclei containing only centromeric signals were found. An application of rDNA as probes allowed it to be stated that 5S rDNA–bearing chromosomes are involved in micronuclei formation more often than NOR chromosomes. This work allowed the origin of physically- and chemically-induced micronuclei in barley cells to be compared: the origin of micronuclei was most often from terminal fragments. FISH confirmed its usefulness in the characterization of micronuclei content, as well as in understanding and comparing the mechanisms of the actions of mutagens applied in plant genotoxicity.

Fluorescent stains for quantification of DNA by confocal laser scanning microscopy in 3-D

Confocal microscopy requires the use of fluorophores to visualize structures of interest within a specimen. To perform reliable measurements of the intensity of fluorescence, the stain should be specific, penetrate well into tissue sections, and bind stoichiometrically. Furthermore, emission must be linear with respect to DNA content and brightness, and fluorescence should be stable. Confocal microscopy is used to determine DNA ploidy and to analyze texture of nuclei, which is accomplished in three dimensions, because nuclei can be measured within the original tissue context. For this purpose the sample must be stained with a DNA binding fluorophore with the properties described above. Stains with different properties have been developed for different applications. We review here the advantages and disadvantages of these different stains for analyzing DNA ploidy and nuclear texture using three-dimensional microscopy. We conclude that SYBR green I and TO-PRO-3 are the most suitable stains for this purpose at present.

Multicolour FISH in an analysis of chromosome aberrations induced by N-nitroso-N-methylurea and maleic hydrazide in barley cells

The present study is a rare example of a detailed characterization of chromosomal aberrations by identification of individual chromosomes (or chromosome arms) involved in their formation in plant cells by using fluorescent in situ hybridization (FISH). In addition, the first application of more than 2 DNA probes in FISH experiments in order to analyse chromosomal aberrations in plant cells is presented. Simultaneous FISH with 5S and 25S rDNA and, after reprobing of preparations, telomeric and centromeric DNA sequences as probes, were used to compare the cytogenetic effects of 2 chemical mutagens: N-nitroso-N-methylurea (MNU) and maleic hydrazide (MH) on root tip meristem cells of Hordeum vulgare (2n=14). The micronucleus (MN) test combined with FISH allowed the quantitative analysis of the involvement of specific chromosome fragments in micronuclei formation and thus enabled the possible origin of mutagen-induced micronuclei to be explained. Terminal deletions were most frequently caused by MH and MNU. The analysis of the frequency of micronuclei with signals of the investigated DNA probes showed differences between the frequency of MH- and MNU-induced micronuclei with specific signals. The micronuclei with 2 signals, telomeric DNA and rDNA (5S and/or 25S rDNA), were the most frequently observed in the case of both mutagens, but with a higher frequency after treatment with MH (46%) than MNU (37%). Also, 10% of MH-induced micronuclei were characterized by the presence of only telomere DNA sequences, whereas there were almost 3-fold more in the case of MNU-induced micronuclei (28%). Additionally, by using FISH with the same probes, an attempt was made to identify the origin of chromosome fragments in mitotic anaphase.

Genotoxicity screening: the slow march to the future

Genetic toxicology testing in drug discovery and development is slowly moving into the age of high-throughput screening (HTS). This has been helped by the development of new tools, as well as validation studies and data analysis to support their use in hit-to-lead or lead optimisation decisions. This review provides an overview of the current genetic toxicology methodologies and a few HTS methodologies. Comparisons are made between the predictivity of carcinogenesis that can be achieved in screening strategies as well as by the battery of regulatory tests. The importance of false-positive and false-negative calls at different stages in development is considered. There is a good prospect that in genetic toxicology, as in other areas of ADME-Tox, HTS will reduce the growing costs of carrying compounds with undesirable characteristics too far along the drug development process.