Micronucleus Assay: The State of Art, and Future Directions.

During almost 40 years of use, the micronucleus assay (MN) has become one of the most popular methods to assess genotoxicity of different chemical and physical factors, including ionizing radiation-induced DNA damage. In this minireview, we focus on the position of MN among the other genotoxicity tests, its usefulness in different applications and visibility by international organizations, such as International Atomic Energy Agency, Organization for Economic Co-operation and Development and International Organization for Standardization. In addition, the mechanism of micronuclei formation is discussed. Finally, foreseen directions of the MN development are pointed, such as automation, buccal cells MN and chromothripsis phenomenon.

[Micronucleus test of human oral buccal epithelium: problems, progress and prospects].

The articles by russian and foreign authors for the period from 2000 to 2012, devoted to the problems of application, analysis and interpretation of the results of micronucleus test in human buccal epithelium has been analyzed in the review. Nuclear abnormality founding in the cells of the oral mucosa has been described. The paper summarizes works devoted to the analysis of the influence of the micronucleus test methods (painting, taking scrapings) to its results. Modern opinions about the factors of different etiology (sex, age, genotype, psycho-physiological characteristics, immune status, diseases of different etiology, man-made pollution, climatic and geographical conditions, ionizing and nonionizing radiation, chemical compounds (drugs, dietary supplements, androgenic steroids, etc.), dental fillings, occupational exposures, alcohol, using tobacco blends) inducing the estimation of nuclear aberration has been summarized as a scheme. The problems and unresolved issues related to the peculiarities of micronucleus test has been noted.

Micronucleus assay with urine derived cells (UDC): a review of its application in human studies investigating genotoxin exposure and bladder cancer risk.

The first micronucleus (MN) study with urine derived cells (UDC) appeared 30 years ago. So far, 56 investigations have been published with this method and it was shown that it can be used for the detection of chromosomal damage caused by environmental and lifestyle factors as well as by occupational exposures and certain diseases This approach may be also useful as a diagnostic tool for the detection and prognosis of bladder cancer. The test system has been improved in the last years, i.e., it was shown that, apart from MN also other nuclear anomalies can be evaluated in UDC which are found in other types of epithelial cells as well (e.g., in oral and nasal cells) and are indicative for acute toxicity (pyknosis, karyorrhexis, karyolysis, condensed chromatin) and genomic instability (nuclear buds, binucleates). Furthermore, an improved protocol with Carnoy I fixation and Papanicolaou stain was developed which enables the discrimination between cells which originate from the cervix and those from the urothelium. The evaluation of the currently available results indicates that exposures and health conditions which are associated with increased cancer rates in the bladder (and possibly also in other organs) lead to positive results in MN-UDC assays and a limited number of studies indicate that this method may be equally sensitive as other more frequently used human biomonitoring assays. The major shortcoming of the UDC-MN method is the lack of standardization; the evaluation of the current data shows that a variety of staining and fixation methods are used and that the numbers of evaluated cells vary over a broad range. These inconsistencies may account for the large inter-laboratory variations of the background frequencies. In order to improve the reliability of the method, further standardization and validation is required. Therefore an international program should be initiated in which a similar strategy could be used as in previous validation/standardization projects concerning MN-cytome assays with lymphocytes and buccal cells.

Flow cytometric analysis of micronuclei in mammalian cell cultures: past, present and future.

The relative simplicity of the in vitro micronucleus (MNvit) endpoint has made it amenable to several automated scoring approaches. Flow cytometry is one such scoring platform that has been successfully employed. This review describes the origins of the MNvit assay, as well as the evolution and properties of flow cytometry-based scoring systems. While the current state-of-the-art methods acquire micronucleus (MN) frequency data very efficiently, it is becoming clear that they also endow the assay with high information content. For instance, simultaneous with MN frequency determinations, several additional endpoints are acquired that provide insights into cytotoxicity, cell cycle perturbations and, in the event of MN induction, information about genotoxic mode of action. This review concludes with a discussion regarding data gaps and also recommendations for additional work that is needed to more fully realise the potential of flow cytometric MNvit scoring.

The HUMN and HUMNxL international collaboration projects on human micronucleus assays in lymphocytes and buccal cells--past, present and future.

The International Human Micronucleus (HUMN) Project (www.humn.org) was founded in 1997 to coordinate worldwide research efforts aimed at using micronucleus (MN) assays to study DNA damage in human populations. The central aims were to (i) collect databases on baseline MN frequencies and associated methodological, demographic, genetic and exposure variables, (ii) determine those variables that affect MN frequency, (iii) establish standardised protocols for performing assays so that data comparisons can be made more reliably across laboratories and countries and (iv) evaluate the association of MN frequency with disease outcomes both cross-sectionally and prospectively. In the first 10 years of the HUMN project, all of these objectives were achieved successfully for the MN assay using the cytokinesis-block micronucleus (CBMN) assay in human peripheral blood lymphocytes and the findings were published in a series of papers that are among the most highly cited in the field. The CBMN protocol and scoring criteria are now standardised; the effect of age, gender and smoking status have been defined, and it was shown prospectively using a database of almost 7000 subjects that an increased MN frequency in lymphocytes predicts cancer risk. More recently in 2007, the HUMN coordinating group decided to launch an equivalent project focussed on the human MN assay in buccal epithelial cells because it provides a complementary method for measuring MN in a tissue that is easily accessible and does not require tissue culture. This new international project is now known as the human MN assay in exfoliated cells (HUMN(xL)). At present, a database for >5000 subjects worldwide has been established for the HUMN(xL) project. The inter-laboratory slide-scoring exercise for the HUMN(xL) project is at an advanced stage of planning and the analyses of data for methodological, demographic, genetic, lifestyle and exposure variables are at a final stage of completion. Future activities will be aimed at (i) defining the genetic variables that affect MN frequencies, (ii) validation of the various automated scoring systems based on image analysis, flow cytometry and laser scanning cytometry, (iii) standardisation of protocols for scoring micronuclei (MNi) in cells from other tissues, e.g. erythrocyte and nasal cells and (iv) prospective association studies with pregnancy complications, developmental defects, childhood cancers, cardiovascular disease and neurodegenerative diseases.

State of the art survey of the buccal micronucleus assay--a first stage in the HUMN(XL) project initiative.

The study of DNA damage in exfoliated buccal cells is a minimally invasive method for monitoring populations for exposure to genotoxic agents. The presence of micronuclei (MN) and other nuclear anomalies within these cells has been shown to be associated with genetic defects in genome maintenance, accelerated ageing, genotoxic damage and some degenerative diseases. To identify important information gaps regarding these biomarkers, a new initiative was launched within the framework of the HUman MicroNucleus (HUMN) collaborative programme, the HUMN(XL) project ('XL' designating eXfoLiated cell). An invitation to join the project was sent out together with a questionnaire to all laboratories that have published on the buccal micronucleus assay. Overall, 188 messages were delivered and 58 laboratories from 25 countries agreed to participate (43 contributing data). The questionnaire was designed to collect methodological information regarding the laboratory's performance of the assay and to assess the extent and type of epidemiological data that are routinely collected. The results provide an overview of the most commonly used methods for buccal cell collection and preparation, slide preparation, staining, scoring criteria and an evaluation of epidemiological data, including demographics, genetic background, gender, health status, occupation, exposure, lifestyle and dietary habit. According to this survey, a potential base of 15 103 subjects can be included in future pooled analyses. A number of protocol discrepancies emerged, implying that method standardization is a major priority. The results of this survey will contribute to (i) identify technical and epidemiological key variables that impact on buccal MN frequency in human populations, (ii) drive the design of future intra- and interlaboratory validation studies and (iii) determine the role of MN frequency and other biomarkers, in monitoring genomic damage and predicting cancer and other degenerative diseases.

The micronucleus assay in human buccal cells as a tool for biomonitoring DNA damage: the HUMN project perspective on current status and knowledge gaps.

The micronucleus (MN) assay in exfoliated buccal cells is a useful and minimally invasive method for monitoring genetic damage in humans. This overview has concluded that although MN assay in buccal cells has been used since the 1980s to demonstrate cytogenetic effects of environmental and occupational exposures, lifestyle factors, dietary deficiencies, and different diseases, important knowledge gaps remain about the characteristics of micronuclei and other nuclear abnormalities, the basic biology explaining the appearance of various cell types in buccal mucosa samples and effects of diverse staining procedures and scoring criteria in laboratories around the world. To address these uncertainties, the human micronucleus project (HUMN; see http://www.humn.org) has initiated a new international validation project for the buccal cell MN assay similar to that previously performed using human lymphocytes. Future research should explore sources of variability in the assay (e.g. between laboratories and scorers, as well as inter- and intra-individual differences in subjects), and resolve key technical issues, such as the method of buccal cell staining, optimal criteria for classification of normal and degenerated cells and for scoring micronuclei and other abnormalities. The harmonization and standardization of the buccal MN assay will allow more reliable comparison of the data among human populations and laboratories, evaluation of the assay's performance, and consolidation of its world-wide use for biomonitoring of DNA damage.

Chromosomal aberrations in Crepis capillaris cells detected by FISH.

Crepis capillaris (2n=6) is an excellent plant for the assay of chromosome aberrations after mutagenic treatment. It has simple karyotype: three pairs of morphologically distinct and relatively large chromosomes. The frequency of structural chromosome aberrations and micronuclei in root meristem cells has been used for evaluation of the genotoxicity of chemicals and environmental pollutants. The introduction of fluorescence in situ hybridization method allows more detailed detection and localization of chromosomal rearrangements not only in mitotic but also in interphase nuclei. We demonstrate a few examples of the detection of chromosomal aberrations using rDNA and telomeric sequences as probes for in situ hybridization to C. capillaris chromosomes.

Achievements by CSGMT/JEMS.MMS: the Collaborative Study Group for the Micronucleus Test in the Mammalian Mutagenesis Study Group of the Environmental Mutagen Society of Japan.

The Collaborative Study Group for the Micronucleus Test (CSGMT) is one of the task groups in the Mammalian Mutagenesis Study Group (MMS) of the Environmental Mutagen Society of Japan (JEMS). It was established in 1982 and has made efforts to understand what the micronucleus test is, what are the advantages and disadvantages of the test as an in vivo detection system for mutagens/carcinogens, and to establish a standard protocol applicable to numerous chemicals. Members of the CSGMT have published more than 75 papers as part of collaborative studies and have contributed to the understanding of the nature of the micronucleus test and to setting guidelines for testing of medicinal and other chemicals. The CSGMT held some workshops to share up-to-date knowledge and techniques on the micronucleus test. Through workshops and collaborative studies, the CSGMT contributed to the maintaining of a high standard of knowledge and techniques among Japanese researchers of the micronucleus test. This paper reviews achievements made by the CSGMT until now.

Micronuclei as an index of cytogenetic damage: past, present, and future.

The workshop was designed to present what is known about the production of micronuclei, what protocols are now accepted or proposed internationally, what new results have been obtained, and what new methods and protocols are likely to be forthcoming. This report is designed to convey the flavour of the workshop and to provide the essence of the new information. After the workshop an effort was made to determine what single protocol would satisfy the requirements set for the micronucleus test by as many regulatory agencies as possible. The result, reported here, includes the requirements of six regulatory authorities in Canada, the European Economic Community, the Organization for Economic Co-operation and Development, Japan, and the United States.