An automated flow cytometric micronucleus assay for human lymphocytes

Potentials of cytokinesis blocked micronucleus assay in radiation triage and biological dosimetry

The measurement of micronucleus (MN) in the cytokinesis-block arrested binucleated cells has been extensively used as a biomarker in many radiation biology applications in specific biodosimetry. Following radiation casualties, medical management of exposed individuals begins with triage and biological dosimetry. The cytokinesis blocked micronucleus (CBMN) assay is the alternate for the gold standard dicentric chromosome assay in radiation dose assessment. In recent years, the CBMN assay has become well-validated and emerged as a method of choice for evaluating occupational and accidental exposures scenario. It is feasible due to its cost-effective, simple, and rapid dose assessment rather than a conventional chromosome aberration assay. PubMed search tool was used with keywords of MN, biodosimetry, radiotherapy and restricted to human samples. Since Fenech and Morely developed the assay, it has undergone many technical and technological reforms as a biomarker of various applications. In this review, we have abridged recent developments of the CBMN assay in radiation triage and biodosimetry, focusing on (a) the influence of variables on dose estimation, (b) the importance of baseline frequency and reported dose-response coefficient values among different laboratories, (c) inter-laboratory comparison and (d) its limitations and means to overcome them.

The potential for complete automated scoring of the cytokinesis block micronucleus cytome assay using imaging flow cytometry

The lymphocyte Cytokinesis-Block Micronucleus (CBMN) assay was originally developed for the measurement of micronuclei (MN) exclusively in binucleated (BN) cells, which represent the population of cells that can express MN because they completed nuclear division. Recently the assay has evolved into a comprehensive cytome method to include biomarkers that measure chromosomal instability and cytotoxicity by quantification of nuclear buds (NBUDs), nucleoplasmic bridges (NPBs) and apoptotic/necrotic cells. Furthermore, enumeration of mono- and polynucleated cells allows for computation of the nuclear division index (NDI) to assess mitotic activity. Typically performed by manual microscopy, the CBMN cytome assay is laborious and subject to scorer bias and fatigue, leading to inter- and intra-scorer variability. Automated microscopy and conventional flow cytometry methods have been developed to automate scoring of the traditional and cytome versions of the assay. However, these methods have several limitations including the requirement to create high-quality microscope slides, lack of staining consistency and sub-optimal nuclear/cytoplasmic visualization. In the case of flow cytometry, stripping of the cytoplasmic membrane makes it impossible to measure MN in BN cells, calculate the NDI or to quantify apoptotic or necrotic cells. Moreover, the absence of cellular visualization using conventional flow cytometry, makes it impossible to quantify NBUDs and NPBs. In this review, we propose that imaging flow cytometry (IFC), which combines high resolution microscopy with flow cytometry, may overcome these limitations. We demonstrate that by using IFC, images from cells in suspension can be captured, removing the need for microscope slides and allowing visualization of intact cytoplasmic membranes and DNA content. Thus, mono-, bi- and polynucleated cells with and without MN can be rapidly and automatically identified and quantified. Finally, we present high-resolution cell images containing NBUDs and NPBs, illustrating that IFC possesses the potential for completely automated scoring of all components of the CBMN cytome assay.

Radiation signature on exposed cells: Relevance in dose estimation

The radiation is considered as a double edged sword, as its beneficial and detrimental effects have been demonstrated. The potential benefits are being exploited to its maximum by adopting safe handling of radionuclide stipulated by the regulatory agencies. While the occupational workers are monitored by personnel monitoring devices, for general publics, it is not a regular practice. However, it can be achieved by using biomarkers with a potential for the radiation triage and medical management. An ideal biomarker to adopt in those situations should be rapid, specific, sensitive, reproducible, and able to categorize the nature of exposure and could provide a reliable dose estimation irrespective of the time of the exposures. Since cytogenetic markers shown to have many advantages relatively than other markers, the origins of various chromosomal abnormalities induced by ionizing radiations along with dose-response curves generated in the laboratory are presented. Current status of the gold standard dicentric chromosome assay, micronucleus assay, translocation measurement by fluorescence in-situ hybridization and an emerging protein marker the γ-H2AX assay are discussed with our laboratory data. With the wide choice of methods, an appropriate assay can be employed based on the net.

In vitro primary human lymphocyte flow cytometry based micronucleus assay: simultaneous assessment of cell proliferation, apoptosis and MN frequency

In order to minimise the number of positive in vitro cytogenetic results which are not confirmed in rodent carcinogenicity tests, biological systems that are p53 and DNA repair proficient should be recommended. Moreover, an appropriate cytotoxicity parameter for top dose selection should be considered. Recent International Conference on Harmonisation draft S2 and Organisation for Economic Co-operation and Development (OECD) 487 guideline accepted the in vitro micronucleus test (MNT) as a valid alternative method for in vitro chromosome aberration test within the in vitro cytogenetic test battery. Since mitosis is a prerequisite for expression of the micronuclei, it is compulsory to demonstrate that cell division occurred, and if possible, to identify the cells that completed mitosis. The OECD guideline recommends the use of a cytokinesis block for the assessment of proliferation in primary T-lymphocytes. The work presented in this manuscript was initiated to develop a novel flow cytometry-based primary human lymphocyte MNT method. This new assay is based on a three-step staining procedure: carboxyfluorescein succinimidyl ester as a proliferation marker, ethidium monoazide for chromatin of necrotic and late apoptotic cells discrimination and 4,6-diaminodino-2-phenylindole as a DNA marker. The proof of principle of the method was performed using genotoxic and non-genotoxic compounds: methyl methanesulfonate, mitomycin C, vinblastine sulphate, cyclophosphamide, sodium chloride and dexamethasone. It has been shown that the new flow cytometry-based primary human lymphocyte MNT method is at least equally reliable method as the standard Cytochalasin B MNT. However, further validation of the assay using a wide selection of compounds with a variety of mechanisms of action is required, before it can be used for regulatory purposes. Moreover, a miniaturisation of the technology may provide an additional advantage for early drug development.

A flow cytometry based in vitro micronucleus assay in TK6 cells--validation using early stage pharmaceutical development compounds

The micronucleus test (MNT) is a well established test for detecting clastogenic and aneugenic compounds. Despite the assay's advantages, the MNT may produce false positive and false negative results in some conditions. This fact may be related to the underestimation of apoptosis or necrosis, the p53 status of the cell system or the cytotoxicity assay, and the top dose selection. The purpose of our studies was to contribute to the validation efforts of the flow cytometry based MNT. To identify the most reliable cytotoxicity assay for the top dose selection five parameters for relative survival were tested: relative cell count, relative population doubling, trypan blue supravital staining, relative ratio of scored nuclei to latex beads, and ethidium monoazide staining. For all compounds the least sensitive method was the relative cell count and the most reliable was the nuclei/beads ratio. The comparative evaluation of micronuclei induction in TK6 cells, analyzed with microscopy and flow cytometry, was performed with reference compounds and internal Novartis early development compounds with positive, weak positive, equivocal, and negative genotoxic effects. Our data document a good correlation between the MNT results obtained by flow cytometry and by microscopy. The results confirm that the method may be applied for routine testing in the pharmaceutical industry for the tested group of compounds, including compounds which require metabolic activation. However, further validation and miniaturization may be required.

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.

Antineoplastic Drugs as a Potential Risk Factor in Occupational Settings: Mechanisms of Action at the Cell Level, Genotoxic Effects, and Their Detection Using Different Biomarkers

U članku je prikazana osnovna podjela antineoplastičnih lijekova prema mehanizmima djelovanja na razini stanice. Objašnjeni su mehanizmi genotoksičnosti najvažnijih vrsta lijekova koji se primjenjuju u okviru uobičajenih protokola za liječenje zloćudnih novotvorina. Navedena je važeća klasifikacija antineoplastika prema kancerogenom potencijalu, podaci o mutagenom potencijalu te je prikazana njihova podjela u skladu s anatomsko-terapijsko-kemijskim sustavom klasifikacije. Sustavno su prikazani najvažniji rezultati svjetskih i hrvatskih istraživanja na populacijama radnika izloženih antineoplasticima, provedenih u razdoblju 1980.-2009. s pomoću četiri najčešće primjenjivane metode: analize izmjena sestrinskih kromatida, analize kromosomskih aberacija, mikronukleus-testa i komet-testa. Objašnjena su osnovna načela navedenih metoda te raspravljene njihove prednosti i nedostaci. Biološki pokazatelji daju važne podatke o individualnoj osjetljivosti profesionalno izloženih ispitanika koji mogu poslužiti unaprjeđenju postojećih uvjeta rada i upravljanju rizicima pri izloženosti genotoksičnim agensima. Na osnovi prednosti i nedostataka citogenetičkih metoda zaključeno je da je mikronukleus-test, koji podjednako uspješno dokazuje klastogene i aneugene učinke, jedna od najboljih metoda dostupnih za otkrivanje štetnih djelovanja antineoplastičnih lijekova koji su u aktivnoj primjeni.

Sulforaphane induces cell-cycle arrest and apoptosis in cultured human lung adenocarcinoma LTEP-A2 cells and retards growth of LTEP-A2 xenografts in vivo

Sulforaphane (1), a glucosinolate-derived isothiocyanate found in the cruciferous vegetable broccoli, is considered an anticarcinogenic component. In the present study, the proliferation and apoptosis induction in human lung adenocarcinoma LTEP-A2 cells by 1 was investigated. Compound 1 caused G(2)/M-phase arrest (p < 0.05) and increase of apoptotic cell fraction (p < 0.05) in a time- and dose-dependent manner. Intraperitoneal injection of 1 significantly inhibited growth of LTEP-A2 xenografts in nude mice, and 9 days after tumor cell implantation with 100 mg/kg intraperitoneal injection of 1, the average tumor weights in 1-treated mice was >70% lower than that of the control mice.

In vitro micronucleus assay scored by flow cytometry provides a comprehensive evaluation of cytogenetic damage and cytotoxicity

This laboratory has previously reported on the development of a flow cytometry-based method for scoring in vitro micronuclei in mouse lymphoma (L5178Y) cells [S.L. Avlasevich, S.M. Bryce, S.E. Cairns, S.D. Dertinger, In vitro micronucleus scoring by flow cytometry: differential staining of micronuclei versus apoptotic and necrotic chromatin enhances assay reliability, Environ. Molec. Mutagen. 47 (2006) 56-66]. With this method, necrotic and mid/late stage apoptotic cells are labeled with the fluorescent dye ethidium monoazide. Cells are then washed, stripped of their cytoplasmic membranes, and incubated with RNase plus a pan-nucleic acid dye (SYTOX Green). This process provides a suspension of free nuclei and micronuclei that are differentially stained relative to chromatin associated with dead/dying cells. The current report extends this line of investigation to include the human cell line TK6. Additionally, methods are described that facilitate simultaneous quantitative analysis of cytotoxicity, perturbations to the cell cycle, and what we hypothesize is aneuploidization. This comprehensive cytogenetic damage assay was evaluated with the following diverse agents: etoposide, ionizing radiation, methyl methanesulfonate, vinblastine, ethanol, and staurosporine. Cells were harvested after 30h of continuous treatment (in the case of chemicals), or following graded doses of radiation up to 1Gy. Key findings include the following: (1) Significant discrepancies in top dose selection were found for five of the six agents studied when relative survival measurements were based on Coulter counting versus flow cytometry. (2) Both microscopy- and flow cytometry-based scoring methods detected dose-dependent micronucleus formation for the four genotoxic agents studied, whereas no significant increases were observed for the presumed non-genotoxicants ethanol and staurosporine when top dose selection was based on flow cytometric indices of cytotoxicity. (3) SYTOX and ethidium monoazide fluorescence signals conveyed cell cycle and cell death information, respectively, and appear to represent valuable aids for interpreting micronucleus data. (4) The frequency of hypodiploid nuclei increased in response to each of the genotoxic agents studied, but not following exposure to ethanol or staurosporine. Collectively, these results indicate that a comprehensive assessment of genotoxicity and other test article-induced toxicities can be acquired simultaneously using a simple two-color flow cytometry-based technique.

In vitro micronucleus scoring by flow cytometry: differential staining of micronuclei versus apoptotic and necrotic chromatin enhances assay reliability

The in vitro micronucleus test has received considerable attention in recent years for its use in drug safety assessment and toxicological research. The less tedious nature of the assay relative to chromosome aberration analyses is a driving force, and explains why many chemical and drug safety programs have adopted the endpoint. Development of a high-throughput micronucleus scoring system would further enhance the utility of the assay for lead optimization and other early drug development work. Although several variations of a flow cytometric (FCM) method for scoring cell-culture-derived micronuclei (MN) have been described in the literature, they have been unable to distinguish true MN from apoptotic and necrotic chromatin (Nüsse M and Marx K 1997: Mutat Res 392: 109-115). Here, we report advances to this methodology whereby a sequential staining procedure is used to differentially label these types of sub-2n particles. With the use of ethidium monoazide (EMA), the chromatin of dead and dying cells is labeled. After a photoactivation step that covalently binds EMA to chromatin, cytoplasmic membranes are digested and resulting lysates are incubated with RNase plus a pan-nucleic acid dye (SYTOX Green). This process provides a suspension of free nuclei and sub-2n particles that are labeled with either SYTOX or SYTOX and EMA. Preliminary studies with heat-shocked L5178Y mouse cells demonstrated that EMA stains necrotic and mid- through late-stage apoptotic cells. Importantly, the sequential labeling procedure provided reliable micronucleus enumeration, even when cultures contained high percentages of dead cells. Subsequently, experiments with the following diverse genotoxicants were performed: hydroxyurea, methyl methanesulfonate, benzo[a]pyrene, etoposide, cyclophosphamide, and vinblastine. Additionally, the nongenotoxicants sucrose, tributyltin methoxide, and dexamethasone were tested up to 5 mg/ml, or to cytotoxic concentrations. FCM data were found to correspond closely with microscopy-based measurements. Collectively, these data suggest that this sequential EMA/SYTOX staining procedure provides reliable, high-throughput enumeration of in vitro MN.

A mixture of isothiocyanates induces cyclin B1- and p53-mediated cell-cycle arrest and apoptosis of human T lymphoblastoid cells

As with other candidate chemopreventive agents, most of our knowledge on the biological effects of isothiocyanates (the many sulfur-containing metabolites found in cruciferous vegetables) comes from studies of single natural or synthetic compounds. To investigate whether the biological/chemopreventive effects of administration of single isothiocyanates can differ from those of a mixture of isothiocyanates, we tested the effects of a mixture of four different isothiocyanates on cell-cycle progression and apoptosis in human T leukemia Jurkat cells, and identified some of the molecular pathways triggered by the mixture. The mixture affected critical points of the cell cycle via modulation of the expression of cyclin B1. Moreover, it induced apoptosis, mediated by an increase in p53 and bax (expression of bcl-2 was unaffected). Comparison of the data with those previously obtained with the single isothiocyanates under identical experimental conditions provides evidence that the quantitative effects of a single, specific isothiocyanate can be significantly different from those of an isothiocyanate mixture at realistic doses.

The effect of 835.62 MHz FDMA or 847.74 MHz CDMA modulated radiofrequency radiation on the induction of micronuclei in C3H 10T(1/2) cells

To determine if radiofrequency (RF) radiation induces the formation of micronuclei, C3H 10T(1/2) cells were exposed to 835.62 MHz frequency division multiple access (FDMA) or 847.74 MHz code division multiple access (CDMA) modulated RF radiation. After the exposure to RF radiation, the micronucleus assay was performed by the cytokinesis block method using cytochalasin B treatment. The micronuclei appearing after mitosis were scored in binucleated cells using acridine orange staining. The frequency of micronuclei was scored both as the percentage of binucleated cells with micronuclei and as the number of micronuclei per 100 binucleated cells. Treatment of cells with cytochalasin B at a concentration of 2 microg/ml for 22 h was found to yield the maximum number of binucleated cells in C3H 10T(1/2) cells. The method used for the micronucleus assay in the present study detected a highly significant dose response for both indices of micronucleus production in the dose range of 0.1-1.2 Gy and it was sensitive enough to detect a significant (P > 0.05) increase in micronuclei after doses of 0.3 Gy in exponentially growing cells and after 0.9 Gy in plateau-phase cells. Exponentially growing cells or plateau-phase cells were exposed to CDMA (3.2 or 4.8 W/kg) or FDMA (3.2 or 5.1 W/kg) RF radiation for 3, 8, 16 or 24 h. In three repeat experiments, no exposure condition was found by analysis of variance to result in a significant increase relative to sham-exposed cells either in the percentage of binucleated cells with micronuclei or in the number of micronuclei per 100 binucleated cells. In this study, data from cells exposed to different RF signals at two SARs were compared to a common sham-exposed sample. We used the Dunnett's test, which is specifically designed for this purpose, and found no significant exposure-related differences for either plateau-phase cells or exponentially growing cells. Thus the results of this study are not consistent with the possibility that these RF radiations induce micronuclei.

Micronuclei induction, cell cycle delay and apoptosis as markers of cellular stress caused by ursodeoxycholic acid in human lymphocytes

Ursodeoxycholic acid (UDCA) is a bile acid (BA) used for cholesterol gallstone dissolution. Since epidemiological evidence indicates that BAs can be involved in the etiology of colorectal cancer, we investigated the effects of UDCA and its physiologically produced taurine conjugate tauroursodeoxycholic acid (TUDCA) on human lymphocyte cultures in terms of genetic damage in the form of micronuclei (MN) production, cell cycle modifications and induction of apoptosis. With respect to controls, treatment with UDCA (from 10 microg/ml) caused a dose-related increase in MN, whereas TUDCA caused no significant increase (up to 1000 microg/ml). Fluorescence in situ hybridization (FISH) analysis using pancentromeric probes suggested that UDCA exerts aneugenic activity. Bromodeoxyuridine/Hoechst flow cytometry showed that both BA significantly inhibit cell cycle progression (UDCA at 100 microg/ml, and TUDCA, more markedly at 300-1000 microg/ml). Neither UDCA nor TUDCA affected induction of apoptosis, as evaluated by the Annexin-V-Fluos assay. We conclude that UDCA is potentially genotoxic. However, taking into account the characteristics of other physiological BA, our findings are in line with the concept that long-term UDCA treatment may be safely administered. The multi-assay approach reported here could be useful in the toxicological evaluation of newly developed BA analogs as candidates for pharmacological use.

Flow cytometric analysis of genetic damage, effect on cell cycle progression, and apoptosis by thiophanate-methyl in human lymphocytes

Flow cytometric technique was used to study the effects of the fungicide Thiophanate-methyl on cell proliferation, micronucleus induction, and apoptosis in human peripheral blood lymphocytes treated in vitro. In particular, a combined approach of flow cytometry and fluorescence in situ hybridization (FISH) with a pancentromeric alpha-satellite probe was used to evaluate the mechanism of micronucleus induction by Thiophanate-methyl. Flow sorted micronuclei (MN) induced in human lymphocytes by Thiophanate-methyl were analyzed by FISH and the results were compared with results from FISH analysis on MN in binucleated cells. It could be shown that most MN induced by Thiophanate-methyl did not reveal any centromeric signal, thus demonstrating clastogenic action of this fungicide. Moreover, it was found that as a function of the concentration of Thiophanate-methyl, cellular proliferation was delayed and the frequency of apoptotic cells was increased.

Flow cytometric analysis of micronuclei in cell cultures and human lymphocytes: advantages and disadvantages

Flow cytometric techniques are described to quantify micronucleus (MN) induction in cell cultures and human lymphocytes. The advantages and disadvantages of these techniques are discussed. Because a suspension of nuclei and MN has to be prepared for flow cytometric measurements, care has to be taken to avoid unspecific debris that can influence the results. Using additional flow cytometric parameters, most of the unspecific particles in the suspension can, however, be gated out. Apoptotic cells and apoptotic bodies can overlap the MN during measurement, it is, therefore, proposed not to use the technique if apoptosis is induced by the respective treatment. Advantages of the automated flow cytometric techniques are that results can be obtained in short time intervals, the frequency of MN and the DNA distribution of MN can be measured simultaneously and flow sorting can be used for a further analysis of MN using other techniques.

The in vitro micronucleus test: a multi-endpoint assay to detect simultaneously mitotic delay, apoptosis, chromosome breakage, chromosome loss and non-disjunction

Genotoxicity testing aims to detect a large range of genetic damage endpoints and evaluate such results in context of cell survival. The cytokinesis block micronucleus test offers the advantage to provide simultaneously information on both cell cycle progression and chromosome/genome mutations. Indeed, 1. frequencies of cytokinesis-blocked binucleated cells (and polynucleated) are good estimators of the mitotic rate; 2. frequencies of apoptotic figures in mononucleated and binucleated cells provide a measure for cell death before or after cell division; 3. combination of fluorescence in situ hybridization (FISH) for centromere/telomeres and micronucleus scoring allows discrimination between clastogenic and aneugenic events; 4. detection of FISH signals for chromosome specific sequences in both macronuclei and micronuclei, discriminates between aneuploidy due to chromosome non-disjunction or to chromosome loss. The cytokinesis block in vitro micronucleus test is thus a cytogenetic multi-test providing mechanistic information with a simple, rapid, objective, microscopical analysis.

Analysis of mitomycin C-induced micronuclei in lymphocytes from malnourished infected children

The purpose of this study was to determine if peripheral blood lymphocytes from malnourished children with gastrointestinal or respiratory bacterial infection show increased frequencies of Mitomycin C (MMC)-induced micronuclei as compared to well-nourished, infected children. The results indicate that cells from malnourished, infected children had greater chromosome damage. This may indicate that such children would be more susceptible to environmental damage and malignant transformation. Micronucleus frequencies were analyzed in binucleate cells produced by the cytokinesis block method; the overall micronucleus frequency was significantly higher in binucleate cells from malnourished, infected children. The mean micronucleus frequency in MMC-free cultures was 4.3/1000 in malnourished infected children and 1.0/1000 in well-nourished infected children. In MMC-exposed cultures the mean induced micronucleus frequency was 32.6 +/- 6.1 vs. 12.9 +/- 2.3; 68.6 +/- 12.1 vs. 21.0 +/- 5.1, and 88.1 +/- 16.2 vs. 41.7 +/- 5.0 for malnourished and well-nourished children at 20, 40, and 60 ng/ml MMC, respectively. The number of binucleated cells with more than one micronucleus was also higher in malnourished, infected children at all doses tested, including cells with two micronuclei in MMC-free cultures from malnourished, infected children. This increase was not found in peripheral blood lymphocytes from well-nourished infected children.

Automated scoring of micronuclei in binucleated human lymphocytes

Manual and automatic scoring of micronuclei (MN) in binucleated human lymphocytes (BNC) were compared after irradiation of whole blood samples. The blood samples were irradiated with X-ray doses (1, 2 or 3 Gy) and stained with Giemsa. The preparation technique was optimized in such a way that acceptable conditions (cell density, contrast) were obtained for both scoring procedures. To estimate the quality of automatic micronucleus detection, two researchers who had different experience in scoring MN (6 months and 5 years) analysed the samples independently from each other. Automatic scoring was carried out with a digital image analysis system and the recognition procedure was divided into two parts. The BNC positions were detected with low microscope magnification (100x), and the recognition of micronuclei within the cytoplasm of the classified BNC was carried out at high magnification (630x). A fuzzy logic classification system as well as two different segmentation steps (preclassification and postclassification) made it possible that about 94% of all automatically recognized BNC were classified correctly). On the other hand, the classification system was optimized in such a way that false positive decisions were minimized (95% of automatically recognized micronuclei were classified correctly). Failure to recognize micronuclei (8.5%-25% false negatives) was mainly due to extremely small micronuclei, poor contrast with respect to the cytoplasm, and aggregation of micronuclei especially at higher doses.

Flow cytometric detection of micronuclei by combined staining of DNA and membranes

A new staining method is presented for flow cytometric measurement of micronuclei (MN) in cell cultures and human lymphocytes using membrane-specific fluorescent dyes in addition to DNA staining. Several combinations of fluorescent membrane and DNA dyes were studied for a better discrimination of MN from debris in a suspension of nuclei and micronuclei. For staining of membranes, the lipophilic dyes 2-hydroxyethyl-7,12,17-tris(methoxyethyl)porphycene (HEPn) and 1,6-diphenyl-1,3,5-hexatriene (DPH) were used in combination with ethidium bromide (EB), proflavine (PF), and Hoechst 33258 (HO). Due to their spectral properties, HO or EB combined with HEPn were not as suitable for the discrimination of MN from debris as was HEPn in combination with PF. With HEPn in combination with PF, however, additional noise was found at low fluorescence intensities, probably due to free fluorescent dye molecules in the solution. The optimal simultaneous staining of membranes and DNA was obtained using a combination of DPH and EB. The induction of MN in Chinese hamster and mouse NIH-3T3 cells by UV-B illumination was studied with this new staining technique. UV-B illumination (280-360 nm) induced MN in both cell lines. Chinese hamster cells were found to be more sensitive to these wavelengths. Illumination with wavelengths above 360 nm did not induce MN in either cell line. The results obtained from human lymphocytes using the combination of EB and DPH were comparable to the results obtained with the combination of EB and HO.

Flow cytometric analysis of micronuclei in the CD2+/- subpopulation of human lymphocytes enriched by magnetic separation

An improved flow cytometric method for the scoring of micronuclei in human lymphocytes irradiated in vitro is presented. Because, especially in cultivated human lymphocytes, unspecific DNA-containing debris from dying cells can influence the measured frequency of micronuclei, a preselection of CD2 + population was performed before preparation of the suspension of micronuclei and nuclei. Magnetic separation using anti-CD2 antibody-conjugated magnetic beads were used for this purpose. The results obtained by this improved flow cytometric technique were compared with results obtained by microscopic scoring using the CB technique. No correlation was found when the individual values in unirradiated controls were compared, due mainly to the presence of DNA-containing particles from fragmented cell nuclei and other unspecific debris. The averaged data from nine dose-effect curves simultaneously analysed by both techniques showed a linear-quadratic dose dependence with alpha and beta's that were similar for flow cytometry and for microscopic scoring. Only the constant term was higher for the flow cytometric results. A correlation between both techniques applied to individual data at doses > 0.2 Gy could also be demonstrated. It is concluded that a dose estimation of man exposed to low doses of ionizing radiation can at present not be improved by the flow cytometric technique.

Aneugen-induced micronuclei (MN) in human lymphocytes may be discerned using image analysis techniques when cell-cycle stage is taken into account

We show that for the in vitro cytochalasin-B human lymphocyte micronucleus (MN) test, the quantification of the DNA content of MN and the difference in DNA content between the two macronuclei in the binucleate cells without MN, as measured by image analysis, gives a first estimation of the aneugenic potential of a test compound. Cultures of isolated human lymphocytes were exposed either to gamma-rays as a clastogen or to carbendazim (MBC) as an aneugen. The lymphocytes were stained with Feulgen stain and the MN were analyzed for DNA content with a Magiscan 2A image analyzer. The mean DNA content of MN induced by MBC were statistically higher than gamma-irradiation-induced MN. It was demonstrated that in culture the lymphocytes, as well as the MN, are in different stages of the cell cycle, but this will not affect the discriminating power of the MN DNA content when only G1 cells are considered, or when DNA content of the MN is expressed relative to the total genome. The identification of G1 and G2 cell populations from image analysis data was performed by extrapolation of DNA content data from G1- and G2-sorted lymphocytes with a FacStar plus flow sorter. It was demonstrated that in MBC-treated cells the DNA rearrangement between the macronuclei in binucleates without MN was on the average higher than in gamma-irradiated and untreated cells, which points to aneugenic effects of MBC without the formation of MN. In contrast to DNA content measurements, the area of the MN is not a reliable measure for discriminating clastogens from aneugens.

Scoring of radiation-induced micronuclei in cytokinesis-blocked human lymphocytes by automated image analysis

The micronucleus assay in human lymphocytes is, at present, frequently used to assess chromosomal damage caused by ionizing radiation or mutagens. Manual scoring of micronuclei (MN) by trained personnel is very time-consuming, tiring work, and the results depend on subjective interpretation of scoring criteria. More objective scoring can be accomplished only if the test can be automated. Furthermore, an automated system allows scoring of large numbers of cells, thereby increasing the statistical significance of the results. This is of special importance for screening programs for low doses of chromosome-damaging agents. In this paper, the first results of our effort to automate the micronucleus assay with an image-analysis system are represented. The method we used is described in detail, and the results are compared to those of other groups. Our system is able to detect 88% of the binucleated lymphocytes on the slides. The procedure consists of a fully automated localization of binucleated cells and counting of the MN within these cells, followed by a simple and fast manual operation in which the false positives are removed. Preliminary measurements for blood samples irradiated with a dose of 1 Gy X-rays indicate that the automated system can find 89% +/- 12% of the micronuclei within the binucleated cells compared to a manual screening.

A new combined integral-light and slit-scan data analysis system (DAS) for flow cytometry

Flow cytometry using list mode parameters such as fluorescence emission, light scatter and size on one hand and different slit-scan parameters on the other hand needs a fast, flexible, efficient and easy-to-use data analysis software. A new software package (data analysis system, DAS) has been developed that integrates data analysis for conventional (integral-light) flow cytometry and for slit-scan flow cytometry. The requirements, design and some examples are discussed and an implementation for IBM-compatible computers is presented. Special attention is directed to the handling of different data types from one-parameter histograms to multiparameter slit-scan data files. The package can be used as an interpreting programming language or as an interactive menu-driven command line interpreter with a large number of graphic, mathematical and statistical functions. DAS is not limited to use in flow cytometry only, but multidimensional data analysis, from astronomy to economics, can be done as well.

Biological and biophysical techniques to assess radiation exposure: a perspective

Biological dosimeters measure biologically relevant effects of radiation exposure that are in some sense an estimate of effective dose, whereas biophysical indicators serve as surrogates of absorbed dose in a manner analogous to conventional thermoluminescent dosimeters (TLD). The biological and biophysical dosimeters have the potential to play an important role in assessing unanticipated or occupational radiation exposures. For example, where the exposure is large and uncertain (i.e. radiation accidents), accurate dose information can help in deciding the most appropriate therapy and medical treatment. Another useful area is that of lifetime accumulated dose determination, and the ability to distinguish between and integrate the exposures from natural and anthropogenic (medical X-rays, indoor radon, natural background radiation, occupational and non-occupational exposures). Also, the possibility to monitor individual response and differences in inherent or induced radiation sensitivity may have important implications for radiation protection. More commonly, this type of dosimetry could be used for routine monitoring to detect and quantify unsuspected exposure, for regulatory purposes or for epidemiological studies of the long-term effects of radiation exposure (e.g. in Japanese A-bomb survivors or in the population surrounding Chernobyl). This review is a comparative study of the existing techniques and their future prospects. It summarizes the sensitivity, reproducibility, limiting dose, dose-rate, energy, LET response, sources of variability and uncertainty, and other practical aspects of each bio-indicator. The strengths and weaknesses of each approach are evaluated on the basis of common criteria for particular applications, and are summarized for each assay both in the text and in tabular form, for convenience. It is clear that no single indicator qualifies to reliably measure occupational exposures at the current levels of sensitivity conventional dosimetry services provide. Most of the bio-techniques are applicable to the detection of relatively high radiation exposures at relatively short times after exposure. Some of the bio-indicators have been identified that are, or offer future prospects for becoming, appropriate bio-indicators for dosimetry needs. However, all methods are subject to biological and other variables that are presently uncontrolled, and represent a major source of uncertainty. These include variations in background signals not directly associated with radiation exposure, inter- and intra-individual variability of radiation response, and genetic and environmental effects. Although these factors contribute to the lack of confidence in biological dosimetry, promising bio-indicators may be applied to large populations to establish the inherent variability and confounding factors that limit quantitative data collection and analysis, and reduce reliability and reproducibility.