Recommendations and quality criteria for micronucleus studies with humans

A Double Fluorescent Staining Method Increases the Sensitivity of the Cytokinesis-Block Micronucleus Assay

The micronucleus test is one of the most popular genotoxicity assays. In order to avoid underestimation of micronuclei frequencies by counting non-replicating cells, the cytokinesis-blocked micronucleus test has been developed. In this technique, only binucleated cells are scored. One underestimated problem is the potential difficulty in discriminating binucleated from mononucleated cells when using DAPI staining, i.e., the possibility that two neighboring mononucleated cells could be mistaken for a binucleated one. The new protocol presented here comprises the addition of acridine orange in order to stain the cytoplasm (in addition to DAPI to stain nuclei and micronuclei). This new technique can increase the sensitivity of the cytokinesis-blocked micronucleus test and avoid underestimation of micronuclei frequencies, an important issue when high doses are employed.

Micronuclei as genotoxicity endpoint applied in the co-culture of two mammalian cell lines

There has been a shift from traditional animal models towards alternative methods. While 2D cell culture has a decade long tradition, more advances methods like 3D cultures, organoids, and co-culture techniques, which better mimic in vivo conditions, are not yet well established in every research area. Genotoxicity assessment is an integral part of toxicological testing or regulatory approval of pharmaceuticals and chemicals. The micronucleus assay is now a standard method in this context. In this systematic literature review, we aim to describe the state of the art of the application of co-cultures of two mammalian cell lines for micronucleus assessment. We summarized the cell types used, methods for co-culture, disease models and agents, as well as the application of additional genotoxicity endpoints and viability tests. Airway system cells were the most frequent, followed by macrophage-like cells, liver cells, and various others. Co-culture techniques involve either direct physical contact or separation by porous membranes. Within a limited number of investigations using other genotoxicity assays like the comet and γH2AX assays in parallel, the micronucleus assay performed well. Overall, the micronucleus test demonstrating its suitability in disease models and for a more complex substance testing beyond simple 2D cultures, encouraging a more widespread use in co-culture systems in the future.

Impact of indoor air pollution on DNA damage and chromosome stability: a systematic review

Indoor air pollution is becoming a rising public health problem and is largely resulting from the burning of solid fuels and heating in households. Burning these fuels produces harmful compounds, such as particulate matter regarded as a major health risk, particularly affecting the onset and exacerbation of respiratory diseases. As exposure to polluted indoor air can cause DNA damage including DNA sd breaks as well as chromosomal damage, in this paper, we aim to provide an overview of the impact of indoor air pollution on DNA damage and genome stability by reviewing the scientific papers that have used the comet, micronucleus, and γ-H2AX assays. These methods are valuable tools in human biomonitoring and for studying the mechanisms of action of various pollutants, and are readily used for the assessment of primary DNA damage and genome instability induced by air pollutants by measuring different aspects of DNA and chromosomal damage. Based on our search, in selected studies (in vitro, animal models, and human biomonitoring), we found generally higher levels of DNA strand breaks and chromosomal damage due to indoor air pollutants compared to matched control or unexposed groups. In summary, our systematic review reveals the importance of the comet, micronucleus, and γ-H2AX assays as sensitive tools for the evaluation of DNA and genome damaging potential of different indoor air pollutants. Additionally, research in this particular direction is warranted since little is still known about the level of indoor air pollution in households or public buildings and its impact on genetic material. Future studies should focus on research investigating the possible impact of indoor air pollutants in complex mixtures on the genome and relate pollutants to possible health outcomes.

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.

Use of micronucleus cytome assays with buccal cells for the detection of genotoxic effects: A systematic review and meta-analysis of occupational exposures to metals

Micronucleus (MN) assays with buccal cells are at present widely used to investigate occupational exposures to genotoxic carcinogens. This article describes their use for the monitoring of metal exposed workers. We found in total 73 relevant articles, in the majority (97 %) increased MN and/or other nuclear anomalies were reported. Most studies were realized in South East Asia and South America. A variety of different occupations was studied including welders, electroplaters, painters, workers in battery recycling and production, tannery workers, dental technicians, miners, workers in foundries and smelters, and also subjects working in waste recycling, glass, aluminum and steel production. In many investigations the effects increased with the duration of the working period. The quality of individual studies was evaluated with a quality score tool. The number of cells was in most studies sufficient and DNA-specific stains were used. However, many studies have shortcomings, e.g. they focused solely on MN formation and did not evaluate anomalies, which provide additional information about the stability of the genetic material and acute cytotoxic effects. Only 35 % of the investigations contain quantitative information about exposures to metals and other toxicants. In 6 of these studies, correlations were observed between the concentrations of specific metals (As, Pb, Cr, Cd) in body fluids and MN frequencies. Taken together, the available data indicate that the MN assay can be used to detect chromosomal damage in metal exposed groups; furthermore, it enables also comparisons between subgroups differing in regard to their exposure and allows an estimation of the efficiency of protective measures. The exposure of workers to metals is currently controlled with chemical analytical measurements only, MN assays with buccal cells could contribute to further improve the safety at workplaces as they reflect the biological consequences including synergistic and antagonistic interactions between toxicants.

Mobile phone specific radiation disturbs cytokinesis and causes cell death but not acute chromosomal damage in buccal cells: Results of a controlled human intervention study

Several human studies indicate that mobile phone specific electromagnetic fields may cause cancer in humans but the underlying molecular mechanisms are currently not known. Studies concerning chromosomal damage (which is causally related to cancer induction) are controversial and those addressing this issue in mobile phone users are based on the use of questionnaires to assess the exposure. We realized the first human intervention trial in which chromosomal damage and acute toxic effects were studied under controlled conditions. The participants were exposed via headsets at one randomly assigned side of the head to low and high doses of a UMTS signal (n = 20, to 0.1 W/kg and n = 21 to 1.6 W/kg Specific Absorption Rate) for 2 h on 5 consecutive days. Before and three weeks after the exposure, buccal cells were collected from both cheeks and micronuclei (MN, which are formed as a consequence of structural and numerical chromosomal aberrations) and other nuclear anomalies reflecting mitotic disturbance and acute cytotoxic effects were scored. We found no evidence for induction of MN and of nuclear buds which are caused by gene amplifications, but a significant increase of binucleated cells which are formed as a consequence of disturbed cell divisions, and of karyolitic cells, which are indicative for cell death. No such effects were seen in cells from the less exposed side. Our findings indicate that mobile phone specific high frequency electromagnetic fields do not cause acute chromosomal damage in oral mucosa cells under the present experimental conditions. However, we found clear evidence for disturbance of the cell cycle and cytotoxicity. These effects may play a causal role in the induction of adverse long term health effects in humans.

Micronuclei and other nuclear anomalies in exfoliated urothelial cells and urinary 8-hydroxy-deoxyguanosine levels among Turkish hairdressers

Hairdressers are constantly occupationally exposed to many chemicals have the potential to cause allergies and carcinogenic effects, act as skin and eye irritants and induce oxidative stress and DNA damage. This study aimed to evaluate occupation-induced genotoxicity based on the presence of micronucleus (MN) and other nuclear anomalies in urothelial cells and measure oxidative DNA damage based on the 8-hydroxy-2'-deoxyguanosine level in the urine of Turkish hairdressers. Originality of this study comes from that there was no study on MN and other nuclear anomalies frequencies and oxidative DNA damage in urine samples of hairdressers in the literature. The mean±standard deviation frequency (‰) of micronucleated (MNed) cells was higher in the hairdresser group (n=56) (4.81±7.87, p<0.001) than in the control group (n=56) (0.93±1.85). Nuclear buds were not observed in either group. While the frequency of basal cells was higher in the control group (446.6±106.21) than in the hairdresser group (367.78±101.51, p<0.001), the frequency of binuclear, karyolytic, pycnotic and karyorrhectic cells were higher in the hairdresser group (0.41±0.80, p<0.001; 438.02±118.27, p<0.001; 0.43±0.76, p<0.001; and 47.27±28.40, p<0.001) than in the control group (0.04±0.27, 358.57±95.71, 0.05±0.23 and 24.41±14.50). Condensed chromatins were observed only in the hairdresser group. Specific gravity adjusted 8-hydroxy-2'-deoxyguanosine level was statistically lower in the hairdresser group (908.21±403.25 ng/mL-SG) compared to the control group (1003.09±327.09 ng/mL-SG) (p=0.024). No significant correlation was found between the 8-hydroxy-2'-deoxyguanosine level and the frequency MN. The amount of formaldehyde released during Brazilian keratin treatment was higher than the American Conference of Governmental Industrial Hygienists -Threshold Limit Value (ACGIH-TLV; 0.1 ppm). Similarly, the amount of ethyl acetate released in three salons was above the recommended limit (400 ppm). These findings suggest that hairdressers have an increased risk of genotoxicity and cytotoxicity owing to occupational exposure, regardless of age, working hours, smoking and alcohol consumption.

Are Cytomorphogenetic Events Correlated with Oral Mucosal Lesions Induced by Crack Cocaine Use? A Systematic Review

The aim of this systematic review was to answer the question of whether crack cocaine can induce cellular and molecular alterations and whether such alterations are somehow related to clinical lesions in the oral mucosa. The searches were undertaken in three electronic databases and conducted based on the PRISMA 2020 statement. Eleven studies published between 1994 and 2020 were analyzed. The quality of the included studies was assessed by two independent reviewers (TGP and DAR) through a confounder's categorization methodology, in which final ratings were attributed (strong, moderate or weak) for each study. From 11 studies included, 7 evaluated the cellular/molecular impact of the addiction in a total of 492 individuals and compared to a control (non-exposure) group (n = 472). The main tests used for cellular alteration were MN and AgNORs. Cells from crack cocaine groups exhibited increased proliferation and MN counting. Only four studies evaluated the prevalence of oral lesions. All of them showed that individuals exposed to crack cocaine presented an increased number of oral lesions. Most studies showed good quality. In conclusion, our results demonstrate that crack use may induce changes at the cellular and molecular level and also exhibit an increased number of oral lesions. However, a correlation between such changes and oral mucosa lesions still needs further investigation and elucidation through other clinical studies in humans.

Cytogenetic changes in oral mucosa cells from individuals submitted to oral human immunodeficiency virus pre-exposure prophylaxis use

OBJECTIVE

The objective of this study was to evaluate cytogenetic changes in individuals submitted to oral human immunodeficiency virus pre-exposure prophylaxis use through the micronucleus test in oral mucosa.

METHODS

This study consisted of 37 individuals, of whom 17 comprised the pre-exposure prophylaxis group and 20 comprised the control group. A total of 2,000 cells per slide were analyzed for the determination of micronuclei, binucleation, nuclear buds, and cytotoxicity parameters: pyknosis, karyolysis, and karyorrhexis (KR), in a double-blind manner. The repair index was also evaluated in this setting.

RESULTS

In the mutagenicity parameters, the pre-exposure prophylaxis group showed increased frequencies of micronuclei (p=0.0001), binucleation (p=0.001), and nuclear buds (p=0.07). Regarding the cytotoxicity parameters, there was an increase with a statistical difference (p≤0.05) in the karyorrhexis frequency (p=0.001). Additionally, the repair system efficiency decreased in the pre-exposure prophylaxis group.

CONCLUSION

These results indicate that individuals undergoing pre-exposure prophylaxis use have geno- and cytotoxicity in oral mucosal cells.

Protective Effects of Micronutrient Supplements, Phytochemicals and Phytochemical-Rich Beverages and Foods Against DNA Damage in Humans: A Systematic Review of Randomized Controlled Trials and Prospective Studies

Accumulation of deoxyribonucleic acid (DNA) damage diminishes cellular health, increases risk of developmental and degenerative diseases, and accelerates aging. Optimizing nutrient intake can minimize accrual of DNA damage. The objectives of this review are to: 1) assemble and systematically analyze high-level evidence for the effect of supplementation with micronutrients and phytochemicals on baseline levels of DNA damage in humans, and 2) use this knowledge to identify which of these essential micronutrients or nonessential phytochemicals promote DNA integrity in vivo in humans. We conducted systematic literature searches of the PubMed database to identify interventional, prospective, cross-sectional, or in vitro studies that explored the association between nutrients and established biomarkers of DNA damage associated with developmental and degenerative disease risk. Biomarkers included lymphocyte chromosome aberrations, lymphocyte and buccal cell micronuclei, DNA methylation, lymphocyte/leukocyte DNA strand breaks, DNA oxidation, telomere length, telomerase activity, and mitochondrial DNA mutations. Only randomized, controlled interventions and uncontrolled longitudinal intervention studies conducted in humans were selected for evaluation and data extraction. These studies were ranked for the quality of their study design. In all, 96 of the 124 articles identified reported studies that achieved a quality assessment score ≥ 5 (from a maximum score of 7) and were included in the final review. Based on these studies, nutrients associated with protective effects included vitamin A and its precursor β-carotene, vitamins C, E, B1, B12, folate, minerals selenium and zinc, and phytochemicals such as curcumin (with piperine), lycopene, and proanthocyanidins. These findings highlight the importance of nutrients involved in (i) DNA metabolism and repair (folate, vitamin B12, and zinc) and (ii) prevention of oxidative stress and inflammation (vitamins A, C, E, lycopene, curcumin, proanthocyanidins, selenium, and zinc). Supplementation with certain micronutrients and their combinations may reduce DNA damage and promote cellular health by improving the maintenance of genome integrity.

Do hairdressers comprise a high risk group for genotoxicity? A systematic review

BACKGROUND AND OBJECTIVES

Nowadays, hair dye products are widely used for aesthetic purposes, in which it generates chemical exposure to customers and, mainly, hairdressers. The aim of this systematic review was designed to elucidate the following question: are hair dye products able to induce DNA damage in hairdressers?

METHODS

Studies were included in our analyses if they met the following criteria: (1) studies measuring genetic damage in vivo; (2) studies published in English; (3) studies that provided data clearly presented in scientific standards.

RESULTS

Full manuscripts from 13 studies were carefully selected in this setting. Our results demonstrate that hair dye products may contain chemical agents able to induce DNA strand breaks or chromosome damage since the majority of studies demonstrated positive findings for genotoxicity. A total of 7 studies (out of 13) had strong or moderate rates in the quality assessment. The type of genotoxicity assay and sample selection criteria time influenced the outcome.

CONCLUSION

In summary, our results reveal that hairdressers are occupationally exposed to genotoxic agents. Such findings are very important for protecting these professionals who are continuously exposed to chemicals for long periods.

Genomic Instability and Cytotoxicity Evaluation of Two Communities Exposed to Pesticides in the Mexicali Valley by the L-CBMN Assay

The continuous biomonitoring of a population directly or indirectly exposed to pesticides could be an additional tool for decision makers to improve their health conditions. In this work, we performed biomonitoring on two groups of people from the Mexicali Valley who were continuously exposed to pesticides using the cytokinesis-block micronucleus cytome assay (L-CBMN) to evaluate cytotoxic and genotoxic damage in human peripheral blood lymphocytes. The study groups comprised 14 indigenous Cucapah with non-vegetarian habits (NV group) from Ejido el Mayor (32.12594°, -115.27265°) and 21 lacto-ovo vegetarian (LOV) persons from the Seventh-day Adventist Church of Ejido Vicente Guerrero (32.3961°, -115.14023°). The L-CBMN assay determines the nuclear division index (NDI), apoptosis, necrosis, micronuclei (MNs), nuclear buds (NBUDs), and nucleoplasmic bridges (NPBs). Our results show that, regardless of diet or daily habits, both the studied groups presented with cytogenotoxic damage compared with non-exposed pesticide individuals, without modifications to the nuclear division index. In the rest of the evaluated biomarkers, the NV group exhibited greater cytotoxic and genotoxic damage than the LOV group. Nevertheless, individuals practicing a lacto-ovo vegetarian diet (LOV) showed lower damage than those with non-vegetarian habits (NV), suggesting a better antioxidant response that helps decrease the genotoxic damage due to the enhanced intake of folates and antioxidants from a plant-based diet.

Empirical relationship between chromosomal damage and airborne particulate matter: A systematic review and meta-analysis of studies in exposed populations

Ambient particulate matter (PM) has gained significant attention as an environmental risk factor for human health. Although the association between ambient PM and micronucleus (MN) induction has been investigated, the quantitative association of PM and genomic instability is inconclusive. We conducted a systematic review and meta-analysis to study the association between PM exposure and MN endpoint. Four databases were systematically searched for studies published up to November 2022, to find papers investigating the relationship between ambient PM and MN induction. Random effect models were conducted to estimate the overall effect based on the Ratio of Means (RoM) with 95% confidence intervals (95% CIs). Subgroup analysis, funnel plot, and Egger and Begg tests, were also performed. Twenty-three studies across nine countries, including 4450 participants, were included. A meta-RoM of 2.13 for MN (95% CI 1.63-2.79) was observed for individuals exposed to ambient PM compared to non-exposed. A significant difference in the subgroup test was found for buccal cells (3.16, 95% CI 2.20-4.52) and low economy level (3.61, 95% CI 1.44-9.01). Our meta-analysis suggests the presence of an association between PM exposure and the frequency of MN and identified the kind of cells and economic status as possible effect modifiers. The use of effective methods, such as the MN assay, enables identification of early genetic damage in humans, which in turn may anticipate the risk of developing respiratory diseases, including lung cancer.

A machine learning method for improving the accuracy of radiation biodosimetry by combining data from the dicentric chromosomes and micronucleus assays

A large-scale malicious or accidental radiological event can expose vast numbers of people to ionizing radiation. The dicentric chromosome (DCA) and cytokinesis-block micronucleus (CBMN) assays are well-established biodosimetry methods for estimating individual absorbed doses after radiation exposure. Here we used machine learning (ML) to test the hypothesis that combining automated DCA and CBMN assays will improve dose reconstruction accuracy, compared with using either cytogenetic assay alone. We analyzed 1349 blood sample aliquots from 155 donors of different ages (3-69 years) and sexes (49.1% males), ex vivo irradiated with 0-8 Gy at dose rates from 0.08 Gy/day to ≥ 600 Gy/s. We compared the performances of several state-of-the-art ensemble ML methods and found that random forest generated the best results, with R2 for actual vs. reconstructed doses on a testing data subset = 0.845, and mean absolute error = 0.628 Gy. The most important predictor variables were CBMN and DCA frequencies, and age. Removing CBMN or DCA data from the model significantly increased squared errors on testing data (p-values 3.4 × 10-8 and 1.1 × 10-6, respectively). These findings demonstrate the promising potential of combining CBMN and DCA assay data to reconstruct radiation doses in realistic scenarios of heterogeneous populations exposed to a mass-casualty radiological event.

Clinical Prospective Assessment of Genotoxic and Cytotoxic Effects of Fluoride Toothpaste and Mouthwash in Buccal Mucosal Cells

Background: Fluorides are an essential component of oral hygiene products used to prevent dental decay. Therefore, a question arises about the potential harms of joint use of fluoridated toothpaste and mouthwashes regarding the increased amount of fluoride in the oral mucosa. Methods: This prospective, double-blinded parallel randomized clinical trial was conducted using a buccal micronucleus cytome assay (BMCyt assay). Forty-one participants were randomly assigned to the two groups. All participants used the same kinds of toothpaste for 12 weeks, designed explicitly for this study (non-fluoride, 1050 ppm F, and 1450 ppm F each for 4 weeks). Simultaneously, during the 3 months of the research, one group used mouthwash with fluoride (450 ppm) and another without fluoride. The buccal mucosal sampling was taken before using the tested products and after 4, 8, and 12 weeks of their use. Results: The frequency of micronuclei and the majority of other scored endpoints from the BMCyt assay showed no statistically significant differences within and between the studied groups. Comparing two groups, only statistically significant increases in the number of cells with nuclear buds (p = 0.048) and karyorrhexis (p = 0.020) at four weeks of usage were observed in the group that used mouthwash with fluoride. Conclusion: On the basis of the results, it can be concluded that simultaneous application of fluoridated toothpaste and fluoride mouthwash does not lead to cytogenetic damage in buccal mucosal cells.