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

Cytoskeletal influences on nuclear shape in granulocytic HL-60 cells

BACKGROUND

During granulopoiesis in the bone marrow, the nucleus differentiates from ovoid to lobulated shape. Addition of retinoic acid (RA) to leukemic HL-60 cells induces development of lobulated nuclei, furnishing a convenient model system for nuclear differentiation during granulopoiesis. Previous studies from our laboratory have implicated nuclear envelope composition as playing important roles in nuclear shape changes. Specifically noted were: 1) a paucity of lamins A/C and B1 in the undifferentiated and RA treated cell forms; 2) an elevation of lamin B receptor (LBR) during induced granulopoiesis.

RESULTS

The present study demonstrates that perturbation of cytoskeletal elements influences nuclear differentiation of HL-60 cells. Because of cytotoxicity from prolonged exposure to cytoskeleton-modifying drugs, most studies were performed with a Bcl-2 overexpressing HL-60 subline. We have found that: 1) nocodazole prevents RA induction of lobulation; 2) taxol induces lobulation and micronuclear formation, even in the absence of RA; 3) cytochalasin D does not inhibit RA induced nuclear lobulation, and prolonged exposure induces nuclear shape changes in the absence of RA.

CONCLUSIONS

The present results, in the context of earlier data and models, suggest a mechanism for granulocytic nuclear lobulation. Our current hypothesis is that the nuclear shape change involves factors that increase the flexibility of the nuclear envelope (reduced lamin content), augment connections to the underlying heterochromatin (increased levels of LBR) and promote distortions imposed by the cytoskeleton (microtubule motors creating tension in the nuclear envelope).

Apoptosis may contribute to false-positive results in the in vitro micronucleus test performed in extreme osmolality, ionic strength and pH conditions

Conditions in which clastogens produce positive responses have been increasingly challenged, and several situations have been described in which clastogenic responses would be considered not to be relevant. For example, extreme culture conditions lead to high variations of pH, osmolality or ionic strength. Apoptosis is induced in extreme culture conditions and contributes to false-positive results in the in vitro micronucleus test performed with CTLL-2 cells. These cells can enter apoptosis when exposed to apoptosis stimuli or after IL-2 deprivation, whereas the CTLL-2 Bcl2 cell line is protected from apoptosis due to the over-expression of the apoptosis inhibitor Bcl2 in bcl2-transfected CTLL-2 cells. The two cell lines were treated in extreme culture conditions of either pH or osmolality or were submitted to high ionic strength. The apoptosis level was measured in parallel with the in vitro micronucleus test using the annexin V-FITC method. Data obtained in the two cell lines suggested that apoptosis caused by extreme culture condition induces the formation of micronucleated cells, which leads to false-positive results in the in vitro micronucleus test.

Resolution of anaphase bridges in cancer cells

Chromosomal instability is a key step in the generation of the cancer cell karyotype. An indicator of unstable chromosomes is the presence of chromatin bridges during anaphase. We examined in detail the fate of anaphase bridges in cultured oral squamous cell carcinoma cells in real-time. Surprisingly, chromosomes in bridges typically resolve by breaking into multiple fragments. Often these fragments give rise to micronuclei (MN) at the end of mitosis. The formation of MN is shown to have important consequences for the cell. We found that MN have incomplete nuclear pore complex (NPC) formation and nuclear import defects and the chromatin within has greatly reduced transcriptional activity. Thus, a major consequence of the presence of anaphase bridges is the regular sequestration of chromatin into genetically inert MN. This represents another source of ongoing genetic instability in cancer cells.

Progesterone prevents radiation-induced apoptosis in breast cancer cells

Sex steroid hormones play an essential role in the control of homeostasis in the mammary gland. Although the involvement of progesterone in cellular proliferation and differentiation is well established, its exact role in the control of cell death still remains unclear. As dysregulation of the apoptotic process plays an important role in the pathogenesis of breast cancer, we investigated the regulation of apoptosis by progesterone in various breast cancer cell lines. Our results show that progesterone treatment protects against radiation-induced apoptosis. This prevention appears to be mediated by the progesterone receptor and is unrelated to p53 status. There is also no correlation with the intrinsic hormonal effect on cell proliferation, as the presence of cells in a particular phase of the cell cycle. Surprisingly, progesterone partly allows bypassing of the irradiation-induced growth arrest in G(2)/M in PgR+ cells, leading to an increase in cell proliferation after irradiation. One consequence of this effect is a higher rate of chromosome damage in these proliferating progesterone-treated cells compared to what is observed in untreated irradiated cells. We propose that progesterone, by inhibiting apoptosis and promoting the proliferation of cells with DNA damage, potentially facilitates the emergence of genetic mutations that may play a role in malignant transformation.

An assessment of the genotoxicity and human health risk of topical use of kojic acid [5-hydroxy-2-(hydroxymethyl)-4H-pyran-4-one]

Kojic acid (KA), a natural substance produced by fungi or bacteria, such as Aspergillus, Penicillium or Acetobacter spp, is contained in traditional Japanese fermented foods and is used as a dermatological skin-lightening agent. High concentrations of KA (>or=1000 microg/plate) were mutagenic in S. typhimurium strains TA 98, TA 100, TA 1535, TA102 and E. coli WP2uvrA, but not in TA 1537. An Ames test following the "treat and plate" protocol was negative. A chromosome aberration test in V79 cells following a robust protocol showed only a marginal increase in chromosome aberrations at cytotoxic concentrations after prolonged (>or=18 h) exposure. No genotoxic activity was observed for hprt mutations either in mouse lymphoma or V79 cells, or in in vitro micronucleus tests in human keratinocytes or hepatocytes. All in vivo genotoxicity studies on KA doses were negative, including mouse bone marrow micronucleus tests after single or multiple doses, an in vivo/in vitro unscheduled DNA synthesis (UDS) test, or a study in the liver of the transgenic Muta(TM) Mouse. On the basis of pharmacokinetic studies in rats and in vitro absorption studies in human skin, the systemic exposure of KA in man following its topical application is estimated to be in the range of 0.03-0.06 mg/kg/day. Comparing these values with the NOAEL in oral subchronic animal studies (250 mg/kg/day), the calculated margin of safety would be 4200- to 8900-fold. Comparing human exposure with the doses that were negative for micronuclei, UDS and gene mutations in vivo, the margins of safety are 16000 to 26000-fold. In conclusion, the topical use of KA as a skin lightening agent results in minimal exposure that poses no or negligible risk of genotoxicity or toxicity to the consumer.

Lack of genotoxicity of potassium iodate in the alkaline comet assay and in the cytokinesis-block micronucleus test. Comparison to potassium bromate

Iodine could be added to the diet of human population in the form of iodide or iodate but iodate had not been adequately tested for genotoxicity and carcinogenicity. In the present study, genotoxic effects of potassium iodate were evaluated in vitro using the alkaline comet assay and the cytokinesis-block micronucleus assay on CHO cells and compared to halogenate salt analogues potassium bromate and chlorate and also to their respective reduced forms (potassium iodide, bromide and chloride). The results showed that the comet assay failed to detect the presence of DNA damage after a treatment of cells by potassium iodate for concentrations up to 10 mM. This absence of primary DNA damage was confirmed in the cytokinesis-block micronucleus assay. In the same way, results showed that potassium chlorate as well as potassium iodide, bromide and chloride did not induced DNA damage in the alkaline comet assay for doses up to 10 mM. By contrast, potassium bromate exposure led to an increase in both DNA damage and frequency of micronucleated cells. The repair of bromate-induced DNA damage was incomplete 24 h after the end of treatment. These results seem to indicate that potassium bromate would induce DNA damage by several mechanisms besides oxidative stress.

Effect of cyanidin 3-O-beta-glucopyranoside on micronucleus induction in cultured human lymphocytes by four different mutagens

The anthocyanin cyanidin 3-O-beta-glucopyranoside (Cy-g) is reported to be one of the most effective antioxidants, but little is currently known regarding its potential chemopreventive properties. In this study, we evaluated the ability of Cy-g to protect cultured human lymphocytes from micronucleus (MN) induction by four different mutagens: ethyl methanesulfonate (EMS), colchicine (COL), H(2)O(2), and mitomycin C (MMC). To gain insight into the mechanisms of action of Cy-g, the cultures were treated with the compound before, during, and after treatment with the mutagens; in addition, the cultures were evaluated for the induction of apoptosis. When used by itself, up to 100 microg/ml of Cy-g was nongenotoxic, while 100 microg/ml Cy-g reduced the replicative index of the cells by nearly 50%. In addition, Cy-g was able to reduce the frequency of micronuclei induced by EMS, COL, and H(2)O(2) using all three treatment protocols, but it had no significant effect on MN induction by MMC in any of the protocols. Apoptosis was produced in the cultures treated with Cy-g alone and was increased under conditions in which Cy-g produced anti-genotoxic effects, suggesting that Cy-g mediated-apoptosis may remove highly damaged cells. However, increases in apoptosis were found under conditions in which Cy-g was not significantly anti-genotoxic, indicating that the increases in apoptosis were not sufficient to account for the anti-genotoxicity of Cy-g. Taken together, our findings indicate that Cy-g possesses anti-genotoxic activity in vitro, which suggests its potential use as a chemopreventive agent.

Toxicological characterization of the new water cleaning product and its waste by-product

Water extracts genotoxicity of the coagulant produced from industrial waste (red mud and waste base) and its waste mud remained after waste water treatment by the coagulation/flocculation process were studied. Tests were conducted in order to confirm nontoxicity of this new product prior to commercial production and usage and also to recommend a safe way for a handling and disposal of the remaining waste material. The toxicity investigation included (i) determining frequency of the cell survival, (ii) the Ames assays, (iii) micronucleus assay, and (iv) cell proliferation kinetics (expressed as mitotic index). These techniques were also employed in toxicity testing of the different concentrations of metal salts, zinc chloride, and lead nitrate in this case since these two elements were present in high concentrations in the waste water intended for the purification with the new coagulant. Mixture of metal salts in the concentrations that represent maximum allowed values for water extracts of technological waste was also tested. Two strains of Salmonella typhimurium, TA98, and TA100 were used for determining cytotoxicity and for the Ames test, while the cytogenetic investigations were performed on human peripheral blood lymphocytes. Water extracts of the coagulant and its waste mud did not induce a significant increase of the micronuclei in human peripheral blood lymphocytes. They also did not disturb lymphocyte proliferation kinetics in vitro. As regards lead nitrate it proved not to be cytotoxic on bacterial strains in the tested concentration range (1-100 mg/L), whereas zinc chloride showed cytotoxic effect for the concentrations above 25 mg/L. The Ames test results for the noncytotoxic concentrations of these metals were negative. Comparing to the negative control a significantly higher number of the micronuclei was determined after the treatment of the whole blood with 100 mg/L of zinc chloride, as well as with 10 and 100 mg/L of lead nitrate. A linear, dose dependent increase was obtained for both salts. Similar results were obtained on the basis of the mitotic index.

Fish as bioindicators to assess the effects of pollution in two southern Brazilian rivers using the Comet assay and micronucleus test

Industrial effluents, agricultural runoff, and municipal wastewaters contain unknown substances and complex mixtures that are released into the environment and can lead to contamination of surface and subsurface waters. In the present report, we have used the alkaline Comet assay and the micronucleus (MN) test to detect the genotoxicity due to multiple sources of pollution in the peripheral blood of two native estuarine fish (mullet and sea catfish) and evaluated possible interactive genotoxic effects from multiple contaminants and the seasonal variation of the genotoxicity. Mullet and sea catfish were captured in the Tramandai and Mampituba Rivers in the southern Brazilian state of Rio Grande do Sul. Reference animals were obtained from the Armazem lagoon. Fish captured in the two estuaries during the four seasons over a period of 2 years had increased levels of DNA damage and MN frequencies relative to the reference fish. In general, the alkaline Comet assay was more sensitive to the genotoxicity of the river contaminants than the MN test. The Comet assay demonstrated significant differences in fish captured at different seasons and at the two river sites, while the MN test showed significant differences only for the annual average for mullet from both sites and fish from the control site. The increases in DNA damage appear to be related to the increase in the number of people in the towns close to the study areas during the warm spring and summer seasons. Although no specific cause-effect relationships were established, comparison of the chemical contaminants and physical variations in the rivers with the genotoxicity data indicate that there may be some association between hydrocarbons, metals, pH, and water temperature and the level of damaged cells observed in mullet and sea catfish from the Tramandai and Mampituba estuaries.

Report from the in vitro micronucleus assay working group

At the Washington "2nd International Workshop on Genotoxicity Testing" (25-26 March 1999) current methodologies and data for the in vitro micronucleus test were reviewed. As a result, guidelines for the conduct of specific aspects of the protocol were developed. Agreement was achieved on the following topics: choice of cells, slide preparation, analysis of micronuclei, toxicity, use of cytochalasin-B, number of doses, and treatment/harvest times [Environ. Mol. Mutagen. 35 (2000) 167]. Because there were a number of important in vitro micronucleus validation studies in progress, it was not possible to design a definitive, internationally harmonized protocol at that time. These studies have now been completed and the data were reviewed at the Plymouth "3rd International Workshop on Genotoxicity Testing" (28-29 June 2002). Data from studies coordinated by the French Society of Genetic Toxicology, Japanese collaborative studies, European pharmaceutical industry validation studies, along with data from Lilly Research Laboratories were used to prepare conclusions on the main aspects of the in vitro micronucleus protocol. In this paper, the consensus agreements on the protocol for performing the in vitro micronucleus assay are presented. The major recommendations concern: 1. Demonstration of cell proliferation: both cell lines and lymphocytes can be used, but demonstration of cell proliferation in both control and treated cells is compulsory for the acceptance of the test. 2. Assessment of toxicity and dose range finding: assessment of toxicity should be performed by determining cell proliferation, e.g. increased cell counts (CC) or population doubling (PD) without cytochalasin-B, or e.g. cytokinesis-block proliferation index with cytochalasin-B; and by determining other markers for cytotoxicity (confluency, apoptosis, necrosis) which can provide valuable additional information. 3. Treatment schedules for cell lines and lymphocytes. 4. Choice of positive controls: without S9-mix both a clastogen (e.g. mitomycin C or bleomycin) and an aneugen (e.g. colchicine) should be included as positive controls and a clastogen that requires S9 for activity when S9-mix is used (e.g. dimethylnitrosamine, or cyclophosphamide in those cell types that cannot activate this agent directly). 5. Duplicate cultures and number of cells to be scored. 6. Repeat experiments: in lymphocytes, for each experiment blood from 2 different healthy young and non-smoking donors should be compared. In cell lines, the experiments need only to be repeated if the first one is negative. 7.

STATISTICS

statistical significance should not be the sole factor for determining positive results. Biological meaning should serve as a guideline. Examples of statistical analyses are given.

Induction of micronuclei by Zearalenone in Vero monkey kidney cells and in bone marrow cells of mice: protective effect of Vitamin E

Zearalenone (ZEN) is a non-steroidal estrogenic mycotoxin mainly produced by Fusarium graminaerum, found as a world-wide contaminant mainly of corn and wheat. Previous studies have demonstrated that among several other effects on animals and humans, ZEN also displays hepatotoxicity, immunotoxicity and nephrotoxicity. ZEN is mainly known as a hormonal disrupter due to its estrogenic activities and consequent toxicity for reproduction. Furthermore, mutagenic and genotoxic proprieties of ZEN were disclosed recently, the molecular mechanisms of which are not yet well understood. In the present study, the genotoxic potential of ZEN was evaluated using genotoxicity tests: the 'cytokinesis block micronucleus assay' in Vero monkey kidney cells and the 'in vivo mouse bone marrow micronucleus assay'. In cultured cells treated with 5, 10 and 20 microM ZEN, the frequency of binucleated micronucleated cells (BNMN) was assessed in 1000 binucleated cells and in mice given oral doses of 10, 20 and 40 mg/kg bw, the frequency of polychromatic erythrocytes micronucleated (PCEMN) in bone marrow cells was assessed in 2000 polychromatic erythrocytes (PCE). The potential prevention of ZEN-induced effects by 25 microM Vitamin E (Vit E) was also evaluated. In vivo, doses of 10, 20 and 40 mg/kg bw ZEN representing, respectively 2, 4 and 8% of the LD50 (LD50 of ZEN in mice is 500 mg/kg bw), were administered to animals either with or without pre-treatment with Vit E (216.6 mg/kg bw) in order to evaluate its preventive potential.ZEN was found to induce micronuclei (MN) in a dose-dependent manner in cultured Vero cells as well as in mouse bone marrow cells. The present data emphasise the likely clastogenic pathway among the molecular mechanisms that underlay the ZEN-induced genotoxicity. Vit E was found to prevent partially-from 30 to 50%-these toxic effects, most likely acting either as a structural analogue of ZEN or as an antioxidant.

Implication of nitro group reduction in the mutagenic and chromosome damaging activities of 22 new 5-nitroisoquinolines by the Salmonella mutagenicity test and the cytokinesis-blocked micronucleus assay

The mutagenic (MUT) and chromosome-damaging (CHR) activities of 22 potential antimalarial drugs (5-nitroisoquinoline derivatives) were evaluated by the Salmonella test and the cytokinesis-blocked micronucleus assay (CBMN). The Salmonella mutagenicity test was performed with and without metabolic activation (S9 mix) in S. typhimurium strains TA100 and YG1042 (an overproducing nitroreductase and O-acetyltransferase TA100 strain). The CBMN was carried out on human lymphocytes without metabolic activation. Four concentrations were tested: 1, 10, 100 and 1000 ng/ml. MUT was expressed as minimal mutagenic concentrations (MMC, microM) and CHR was expressed as minimal chromosome-damaging concentrations (MCDC, nM) to compare both activities. All the 5-nitroisoquinoline compounds were mutagenic in TA100. MMC ranged from 0.1 to 52.9 microM in TA100. A statistically significant decrease in MMC was observed in YG1042 (8 x 10(-3) to 3.5 microM), implicating reduction of the nitro group. Modulation of MUT by S9 mix was not significant in TA100 and YG1042. CHR was detected in 13 products for at least one concentration. Among the chromosome-damaging compounds, the MCDC ranged from 2.9 x 10(-3) to 3.6 nM. No relationship was found between MUT and CHR, suggesting two distinct pathways of DNA damage.

Intra- and inter-laboratory variation in the scoring of micronuclei and nucleoplasmic bridges in binucleated human lymphocytes. Results of an international slide-scoring exercise by the HUMN project

One of the objectives of the HUman MicroNucleus (HUMN) project is to identify the methodological variables that have an important impact on micronucleus (MN) or micronucleated (MNed) cell frequencies measured in human lymphocytes using the cytokinesis-block micronucleus assay. In a previous study we had shown that the scoring criteria used were likely to be an important variable. To determine the extent of residual variation when laboratories scored cells from the same cultures using the same set of standard scoring criteria, an inter-laboratory slide-scoring exercise was performed among 34 laboratories from 21 countries with a total of 51 slide scorers involved. The results of this study show that even under these optimized conditions there is a great variation in the MN frequency or MNed cell frequency obtained by individual laboratories and scorers. All laboratories ranked correctly the MNed cell frequency in cells from cultures that were unirradiated, or exposed to 1 or 2Gy of gamma rays. The study also estimated that the intra-scorer median coefficient of variation for duplicate MNed cell frequency scores is 29% for unexposed cultures and 14 and 11% for cells exposed to 1 and 2Gy, respectively. These values can be used as a standard for quality or acceptability of data in future studies. Using a Poisson regression model it was estimated that radiation dose explained 67% of the variance, while staining method, cell sample, laboratory, and covariance explained 0.6, 0.3, 6.5, and 25.6% of the variance, respectively, leaving only 3.1% of the variance unexplained. As part of this exercise, nucleoplasmic bridges were also estimated by the laboratories; however, inexperience in the use of this biomarker of chromosome rearrangement was reflected in the much greater heterogeneity in the data and the unexplained variation estimated by the Poisson model. The results of these studies indicate clearly that even after standardizing culture and scoring conditions it will be necessary to calibrate scorers and laboratories if MN, MNed cell and nucleoplasmic bridge frequencies are to be reliably compared among laboratories and among populations.

Assessment of the potential genotoxic risk of Phyllantus orbicularis HBK aqueous extract using in vitro and in vivo assays

Phyllanthus orbicularis HBK is an endemic Cuban plant whose aqueous extract has been proposed as an effective drug for the treatment of viral diseases. In addition, antimutagenic properties of this extract have also been reported. In the present study, the genotoxicity of this plant extract was assessed using different in vitro and in vivo assays. Results from SOS gene induction, gene reversion and conversion, and SMART assays clearly show that P. orbicularis aqueous extract does not induce either primary DNA damage or mutation. Additionally, no statistically significant difference was found in the percentage of chromosomal aberrations in Chinese hamster ovarian (CHO) cells treated with the plant extract. On the contrary, micronuclei and abnormal anaphase were induced by this extract in CHO cells. This genotoxic effect was related to a high cytotoxicity. Single spots were detected in the SMART assay. These results point to a possible aneugenic effect of the P. orbicularis aqueous extract at cytotoxic doses which are much higher than those seen by their antiviral and antimutagenic activities.

Acentromeric micronuclei are increased in peripheral blood lymphocytes of untreated cancer patients

Increased micronucleated cell rates, dicentric chromosomes, and other chromosomal damages have been reported in lymphocytes of cancer patients prior to the initiation of chemotherapy, and/or radiotherapy. The cause of these chromosomal damages in these lymphocytes remains unclear. In the present work, we investigated whether these micronuclei mainly reflect structural or numerical chromosomal aberrations by applying the cytokinesis-blocked micronucleus (CBMN) assay in combination with fluorescent in situ hybridization (FISH) of a DNA centromeric probe on blood samples of 10 untreated cancer patients (UCPs), and 10 healthy subjects (HSs). Micronucleated binucleated lymphocyte rate was significantly increased in patients (mean+/-S.D.: 19.0 per thousand +/-14.1 versus 9.2 per thousand +/-4.6 in controls). Trinucleated cytokinesis-blocked cells were not significantly higher in patients than in controls. Acentromeric, centromeric, and multicentromeric micronucleus levels were two-fold higher in patients than in controls, but the difference was significant only with acentromeric micronuclei. The percentage of micronuclei containing one or more centromeres averaged 69.2, and 71.5% in patients, and controls, respectively. The percentage of micronuclei containing several centromeres was 44.7% in patients, and 54.6% in controls. Among centromere-positive micronuclei, the percentage of micronuclei containing several centromeres averaged 59.7% in patients, and 75.4% in controls. These results indicate that genetic instability in peripheral blood lymphocytes of UCPs occurs because of enhanced chromosome breakage. However, a substantial proportion of this genetic instability occurs because of defects in chromosome segregation.

Importance of detecting numerical versus structural chromosome aberrations

The aim is to review briefly the key questions related to aneuploidy/polyploidy and to compare the advantages and disadvantages of the in vitro micronucleus test to assess aneuploidy/polyploidy in vitro. The key questions that will be addressed, concern the importance of polyploidy for health, and cancer in particular, the mechanisms leading to aneuploidy and polyploidy, and the survival of aneuploid/polyploid cells. The recently recognised contribution of numerical chromosome changes to carcinogenesis triggered the development and the implementation of tests specifically aiming at the detection of aneugens in the test battery for mutagenicity and carcinogenicity. The validation of the in vitro micronucleus test in combination with the identification of in vitro divided cells with the cytokinesis-block methodology and of centromeres with pancentromeric or chromosome specific centromeric probes fluorescence in situ hybridisation (FISH) provides a sensitive, easy to score and powerful test which allows assessment of cell proliferation, the discrimination between chromosome breaks, chromosome loss and chromosome non-disjunction and polyploidy. Moreover, classic histology permits the estimation of necrosis and apoptosis on the same slide. The cytokinesis-blocked micronucleus assay could be considered as a multi-endpoint test for genotoxic responses to clastogens/aneugens. This methodology has also shown to be capable of identifying threshold values for the induction of chromosome loss and/or non-disjunction by microtubule inhibitors, data which are particularly important for risk calculations. Similar approaches were conducted in vivo on bone marrow in mice and rats (except for identification of chromosome non-disjunction), and are in development for gut in mice.

Spontaneous and induced aneuploidy, considerations which may influence chromosome malsegregation

Aneuploidy plays a major role in the production of human birth defects and is becoming increasingly recognised as a critical event in the etiology of a wide range of human cancers. Thus, the detection of aneuploidy and the characterisation of the mechanisms which lead to chromosome malsegregation is an important area of genotoxicological research. As an aid to aneuploidy research, methods have been developed to analyse the mechanisms of chromosome malsegregation and to investigate the role of aneuploidy in tumour progression. The presence of aneuploid cells is a common characteristic of many of tumour cell types as illustrated by the wide range of chromosome number changes detected in post-menopausal breast tumours. To investigate the time of occurrence of aneuploidy during tumour progression, we have studied the chromosome number status of Syrian hamster dermal (SHD) cells cultures progressing to morphological transformation. The production of both polyploid and aneuploid cells is a common feature of progressing cells in this model. The elevation of both progression to morphological transformation and aneuploid frequencies can be produced by exposure to a diverse range of carcinogens and tumour promoters. Analysis of the genotoxic activity of the hormone 17-beta oestradiol demonstrated its ability to induce both chromosome loss and non-disjunction in human lymphoblastoid cells implicating aneugenic activity in hormone related cancers. Mutations in the p53 tumour suppressor gene introduced into human fibroblasts produced modifications in chromosome separation at mitosis which may lead to the production of both aneuploidy and polyploid cells. Our studies indicate that the production of aneuploid cells can be influenced by both endogenous and exogenous factors and occur throughout the progression of normal cells to a malignant phenotype.

Photogenotoxicity of mammalian cells: a review of the different assays for in vitro testing

During the past several years, phototoxicity has been studied at the molecular level, and these studies have provided new insights in the field of DNA lesion characterization, DNA repair and cell response to ultraviolet (UV)-induced stress. The development of new antibiotics and antiinflammatory drugs has highlighted the necessity to develop the assessment of phototoxicity in the safety evaluation of new chemical compounds. This paper aims at reviewing the known molecular mechanisms of the cellular response to UV-induced stress, the in vitro methods that can be proposed and used to screen for toxicity of sunlight and the photosensitization process resulting from the activation of drugs by light. UV sources, biological systems and endpoints of interest in that particular objective are listed. Phototoxic effects span from the cytotoxic-apoptotic effect to the induction of primary DNA damage, DNA repair and a variety of stress genes acting on the cell cycle and the fate of the cell. Ultimately, it can lead to the induction of hereditary DNA modification. A variety of assays are proposed to specifically address all these particular consequences of UV-induced toxicity.

Cytogenetic analysis of embryos generated from in vitro matured mouse oocytes reveals an increase in micronuclei due to chromosome fragmentation

PURPOSE

(i) To determine the prevalence of micronuclei in the cytoplasm of embryos generated from in vitro matured oocytes. (ii) Assess whether micronuclei presence are the result of chromosome fragmentation or the loss of whole chromosomes.

METHODS

In vitro fertilization was performed on mature oocytes generated from superovulated mice (control) and in vitro matured mouse oocytes. Fertilized oocytes were cultured to the two-cell stage and fixed to slides. Micronuclei assessment was performed after staining with Giemsa. Centromere assessment was made using immunofluorescent staining (CREST) of the centromeric kinetochores.

RESULTS

Micronuclei were observed in 2% (4/197) of control two-cell embryos and 36.2% (46/127) of two-cell embryos generated from in vitro matured oocytes (P < 0.02). Centromeres were not detected in micronuclei from either group.

CONCLUSIONS

A significant increase in micronuclei was observed in embryos generated from in vitro matured oocytes. The lack of accompanyingcentromeres would suggest the micronuclei are the result of chromosome fragmentation.

Aneuploidy induced in lymphocytes of parents of trisomic 21 children

A possible predisposition to aneuploidy in trisomic 21 individuals, their parents, and a control group was evaluated. Peripheral blood lymphocytes from those three groups were used to study the induction of micronuclei (MN) by mitomycin C, cyclophosphamide, and quercetin. Induced MN were further analysed by C-banding and CREST antibody. Trisomic 21 individuals have spontaneous frequencies of MN significantly higher than their parents and the control group. Quercetin without metabolic activation induces MN in trisomic 21 and their parents at a significantly higher level than in control group. The group of the parents of trisomic 21 individuals exhibits higher frequencies of induced MN by mitomycin C and cyclophosphamide than controls. Mitomycin C significantly induced CREST-positive-MN in ten of the sixteen parents evaluated. The results obtained seem to suggest a unique behaviour for the parents of trisomic 21 patients consisting in an increased susceptibility to chromosome loss in the presence of clastogenic genotoxicants, suggesting a higher predisposition to aneuploidy.

Malsegregation as a possible mechanism of aneuploidy induction by metal salts in MRC-5 human cells

Many aneugenic compounds are known to affect one or more components of the mitotic apparatus leading to an erroneous migration of chromosomes. Malsegregation occurs when a chromosome (or a chromatid) fails to migrate and remains at the metaphase plate. Nondisjunction implies the lack of dissociation between sister chromatids and the migration of both together to the same pole. The aim of the present study was to provide evidence that the aneugenic effect of some metal salts is the consequence of malsegregation at anaphase and that it is not caused by nondisjunction mechanisms. The frequencies of lagging chromosomes at anaphase-telophase of mitosis, hypoploid metaphases, and kinetochore-positive micronuclei induced by cadmium chloride, potassium dichromate, and cacodilic acid (dimethylarsinic acid) in MRC-5 human cells were compared. The data indicate that all the tested compounds are able to induce aneuploidy in MRC-5 human cells. Positive, statistically significant correlations were found when kinetochore-positive micronuclei, hypoploidy, and lagging chromosome frequencies were compared. The results suggest that malsegregation is the main mechanism involved in the induction of aneuploidy by metal salts in MRC-5 cells.

Cytogenetic damage in human lymphocytes following GMSK phase modulated microwave exposure

The present study investigated, using in vitro experiments on human lymphocytes, whether exposure to a microwave frequency used for mobile communication, either unmodulated or in presence of phase only modulation, can cause modification of cell proliferation kinetics and/or genotoxic effects, by evaluating the cytokinesis block proliferation index and the micronucleus frequency. In the GSM 1800 mobile communication systems the field is both phase (Gaussian minimum shift keying, GMSK) and amplitude (time domain multiple access, TDMA) modulated. The present study investigated only the effects of phase modulation, and no amplitude modulation was applied. Human peripheral blood cultures were exposed to 1.748 GHz, either continuous wave (CW) or phase only modulated wave (GMSK), for 15 min. The maximum specific absorption rate (approximately 5 W/kg) was higher than that occurring in the head of mobile phone users; however, no changes were found in cell proliferation kinetics after exposure to either CW or GMSK fields. As far as genotoxicity is concerned, the micronucleus frequency result was not affected by CW exposure; however, a statistically significant micronucleus effect was found following exposure to phase modulated field. These results would suggest a genotoxic power of the phase modulation per se.

Micronuclei in peripheral blood lymphocytes and buccal epithelial cells of Polish farmers exposed to pesticides

In this biomonitoring study, we investigated whether an occupational exposure to a complex mixture of chemical pesticides produced a significant increase of micronuclei (MN) in both peripheral blood lymphocytes and buccal cells. Forty-nine male workers exposed to pesticides, from an agricultural area of Malopolska Region in Southern Poland, together with 50 men from the same area without indication of exposure to pesticides that served as controls, were used in this investigation. No statistically significant differences in the frequencies of cytogenetic damage were detected between exposed and control individuals, for either type of cells. The multiple linear regression analysis in the case of lymphocytes indicated that the studied cytogenetic endpoints were inversely influenced by alcohol; whilst a negative binomial regression, in the case of buccal cells, indicated that the MN values were directly influenced by the ingestion of red meat. An inverse negative relationship between the cytokinesis-block proliferation index and age, and a significant increase of miscarriages due to the exposure to pesticides were also observed.

The induction of micronuclei in vitro by unpolymerized resin monomers

Components of resin materials may damage DNA, leading to genetic alterations in mammalian cells. Here, monomers were analyzed for the induction of chromosomal aberrations indicated by micronuclei induced in V79 cells. A dose-related increase in the numbers of micronuclei was observed with triethyleneglycol dimethacrylate (TEGDMA), 2-hydroxyethyl methacrylate (HEMA), and glycidyl methacrylate (GMA). These effects were reduced, however, by a metabolically active microsomal fraction from rat liver. The very low activity of Bis-GMA and UDMA and the elevated numbers of micronuclei caused by high concentrations of methyl methacrylate and bisphenol A were associated with cytotoxicity. Our findings provide evidence for the induction of micronuclei by TEGDMA, HEMA, and GMA under physiological conditions, indicating clastogenic activity of these chemicals in vitro. Since it has been shown that TEGDMA also caused gene mutations and DNA sequence deletions in mammalian cells, the activity of this substance should be analyzed in vivo.

Non-disjunction and chromosome loss in gamma-irradiated human lymphocytes: a fluorescence in situ hybridization analysis using centromere-specific probes

Centromere-specific DNA probes for chromosomes 4, 7 and 18 were used to simultaneously analyze chromosome loss, non-disjunction, breaks within the labeled region, and nucleoplasmic bridges induced by gamma rays in binucleated human lymphocytes. The doses used were 0, 1, 2 and 4 Gy, and approximately 1000 cells were scored per dose. Micronucleus frequency increased in a linear-quadratic fashion. For chromosome loss, significant increases were observed at 2 and 4 Gy, whereas for non-disjunction significant increases were observed at 1 Gy; thus non-disjunction allowed us to detect the effects of radiation at a lower dose than chromosome loss. The use of centromere-specific probes allowed discrimination between the clastogenic and aneugenic effects of ionizing radiation. The analysis of chromosome loss, not taking fragmented signals into account, ensures the detection of an aneugenic effect, which was not possible using pancentromeric probes. The frequency of chromosome breakage within the labeled regions was higher in nuclei than in micronuclei, suggesting an increase in the engulfment of chromosomal material by nuclei as a consequence of the presence of cytochalasin B in the cultures. Chromatin filaments connecting main nuclei, the so-called nucleoplasmic bridges, were observed in irradiated samples, and are a manifestation of rearranged chromosomes producing anaphase bridges.

Genotoxic ability of cadmium, chromium and nickel salts studied by kinetochore staining in the cytokinesis-blocked micronucleus assay

The aneugenic and clastogenic ability of cadmium chloride(II), cadmium sulfate(II), nickel chloride(II), nickel sulfate(II), chromium chloride(III) and potassium dichromate(IV) have been evaluated through kinetochore-stained micronucleus test. Traditional genotoxicity assays evaluate DNA damage, gene mutations and chromosome breakage. However, these tests are not adequate to detect aneugenic agents that do not act directly on DNA. Staining kinetochores in the cytokinesis-blocked micronucleus assay is a useful way to discriminate between clastogens and aneuploidogens and may allow a rapid identification of aneuploidy-inducing environmental compounds. Human diploid fibroblasts (MRC-5) were employed. All compounds increased micronuclei frequency in a statistically significant way. However, increases in kinetochore-positive micronuclei frequencies were higher than in kinetochore-negative ones. The present work demonstrates the genotoxic ability of the cadmium and chromium salts studied. Aneugenic as well as clastogenic ability could be observed with this assay. Nickel salts, as it was expected because of their known weak mutagenicity, showed lower genotoxic effects than the other metal salts studied. As the test employed only allows the detection of malsegregation, it is proposed that this mechanism is at least one of those by which the tested metal salts induced aneuploidy. On the other hand, visualization of kinetochores in all experiments suggests that the compounds studied did not act by damaging these structures.

Mechanisms involved in the induction of aneuploidy: the significance of chromosome loss

The induction of aneuploidy by physical and chemical agents using different test systems was evaluated. The effect of X-rays, caffeine, acetaldehyde, ethanol, diethylstilbestrol, propionaldehyde, and chloral hydrate was studied by chromosome counting in Chinese hamster embryonic diploid cells. Aneugenic ability of cadmium chloride, cadmium sulfate, potassium dichromate, chromium chloride, nickel chloride, and nickel sulfate was assessed by means of anaphase-telophase analysis in Chinese hamster ovary cells. Chromosome counting in human fibroblasts (MRC-5 cell line) was employed to evaluate the effect of cacodilic acid, cadmium chloride, cadmium sulfate, and potassium dichromate. Finally, the induction of kinetochore-positive and kinetochore negative micronuclei by cadmium chloride, cadmium sulfate, potassium dichromate, chromium chloride, and nickel chloride was studied using CREST antibodies. When the effect of different agents was determined by chromosome counting, an increase of hypoploid but not of hyperploid cells was observed. Anaphase-telophase analysis showed that metal salts increased the frequency of lagging chromosomes. This finding has been confirmed by the increment of kinetochore-positive micronuclei using CREST antibodies. Therefore, chromosome loss could be considered as the main cause of induced aneuploidy.

The in vitro micronucleus technique

The study of DNA damage at the chromosome level is an essential part of genetic toxicology because chromosomal mutation is an important event in carcinogenesis. The micronucleus assays have emerged as one of the preferred methods for assessing chromosome damage because they enable both chromosome loss and chromosome breakage to be measured reliably. Because micronuclei can only be expressed in cells that complete nuclear division a special method was developed that identifies such cells by their binucleate appearance when blocked from performing cytokinesis by cytochalasin-B (Cyt-B), a microfilament-assembly inhibitor. The cytokinesis-block micronucleus (CBMN) assay allows better precision because the data obtained are not confounded by altered cell division kinetics caused by cytotoxicity of agents tested or sub-optimal cell culture conditions. The method is now applied to various cell types for population monitoring of genetic damage, screening of chemicals for genotoxic potential and for specific purposes such as the prediction of the radiosensitivity of tumours and the inter-individual variation in radiosensitivity. In its current basic form the CBMN assay can provide, using simple morphological criteria, the following measures of genotoxicity and cytotoxicity: chromosome breakage, chromosome loss, chromosome rearrangement (nucleoplasmic bridges), cell division inhibition, necrosis and apoptosis. The cytosine-arabinoside modification of the CBMN assay allows for measurement of excision repairable lesions. The use of molecular probes enables chromosome loss to be distinguished from chromosome breakage and importantly non-disjunction in non-micronucleated binucleated cells can be efficiently measured. The in vitro CBMN technique, therefore, provides multiple and complementary measures of genotoxicity and cytotoxicity which can be achieved with relative ease within one system. The basic principles and methods (including detailed scoring criteria for all the genotoxicity and cytotoxicity end-points) of the CBMN assay are described and areas for future development identified.

The induction of micronuclei in V79 cells by the root canal filling material AH plus

The in vitro micronucleus test (MNT) is an alternative to the chromosomal aberration assay for the detection of chromosomal mutations. Here, the epoxy resin-based root canal filling material AH Plus, the compounds paste A and paste B were tested for cytotoxicity and the induction of micronuclei in V79 cells. Paste A is the epoxy-resin-containing compound. AH Plus was tested immediately after mixing and after a setting time of 24 h. The materials were eluted in dimethyl sulfoxide (DMSO) and physiologic saline for 24 h. DMSO eluates of the mixed material, paste A and paste B clearly reduced the viability of V79 cells, but eluates prepared with physiological saline were at least 10-100-fold less toxic. Likewise, freshly mixed AH Plus was mutagenic in a dose-dependent manner in V79 cells after elution in dimethyl sulfoxide only. The numbers of micronuclei were about 7-fold higher in treated cell cultures compared with untreated controls. No mutagenicity was observed with DMSO and physiological saline eluates of mixed AH Plus set for 24 h. DMSO eluates of paste A induced effects similar to the freshly mixed AH Plus, and paste B was not effective. Therefore, we provide evidence for the induction of chromosomal mutations by freshly mixed AH Plus under experimental conditions.

Cytogenetic biomonitoring of Spanish greenhouse workers exposed to pesticides: micronuclei analysis in peripheral blood lymphocytes and buccal epithelial cells

In the present study, we evaluate whether or not occupational exposure to a complex mixture of pesticides results in a significant increase of micronuclei (MN) in both peripheral blood lymphocytes and buccal cells. Sixty four greenhouse workers from Almería (Southeastern Spain), together with 50 men from the same area, without indication of exposure to pesticides, that served as controls were used in this investigation. The results obtained indicate that there are no statistically significant differences in the MN frequencies between the two groups. Each donor was assessed for the presence or absence of glutathione S-transferase M1 (GSTM1) and glutathione S-transferase T1 (GSTT1), to look for relationships between the genotypes and the cytogenetic reponses. According to the GSTT1 genotype, there is a difference between both groups only for the cytokinesis-block proliferation index (CBPI). Neither GSTM1 nor smoking habit and age showed any effect in the overall analysis.

Report from the In Vitro Micronucleus Assay Working Group

At the Washington International Workshop on Genotoxicity Test Procedures (March 25-26, 1999), the current methodologies and data for the in vitro micronucleus test were reviewed. From this, guidelines for the conduct of specific aspects of the protocol were developed. Because there are a number of important in vitro micronucleus validation studies in progress, it was not possible to design a definitive, internationally harmonized protocol at this time. Agreement was achieved on the following topics: Cells. The choice of cells is flexible, yet the choice of cell type should be justified and take into consideration doubling time, spontaneous frequency of micronuclei, and genetic background. Slide preparation. A fixation method that preserves the cytoplasm and cytoplasmic boundaries, and minimizes clumping should be used. Use of fluorescent DNA-specific dyes is encouraged for better detection of small micronuclei. Analysis. Micronuclei should have a diameter less than one-third of the main nucleus, and should be clearly distinguishable from the main nucleus. In the cytokinesis-block method, binucleated cells selected for analysis should have two clearly distinguishable main nuclei. Cells where the main nucleus(ei) is undergoing apoptosis should not be scored for micronuclei because the assumed micronuclei may have been the result of nuclear fragmentation during the apoptotic process. Toxicity. Cytotoxicity can be measured by various methods including cell growth, cell counts, nucleation (i.e., percent binucleated), division/proliferation index, confluence. A majority of the group recommended that the highest concentration should induce at least 50% cytotoxicity (by whatever measure is selected). Cytochalasin B. There is much debate regarding the use of cytochalasin B. For human lymphocytes, the use of cytochalasin B (6 microg/ml [lymphocytes cultured from whole blood cells] and 3-6 microg/ml [isolated lymphocyte cultures]) is recommended. For cell lines, because there were no definitive data showing a clear advantage or disadvantage of the use of cytochalasin B for a variety of chemicals, the majority opinion of the group was that at this time, the use of cytochalasin B for cell lines is considered optional. Further studies (many chemicals of a variety of potencies, tested both with and without cytochalasin B) are clearly needed to resolve this issue. Number of doses. At least three concentrations should be scored for micronuclei. Treatment/harvest times. At this time, there are not enough data to define the most appropriate treatment/harvest times. Following the principles of the in vitro metaphase assay (with or without metabolic activation), it was agreed that there was a need for a short treatment followed by a recovery time in the absence of test chemical, there was a need for a long treatment (maybe with and without recovery time), and ideally, treatment should cover cells in different cell cycle stages.

Phyllanthus orbicularis aqueous extract: cytotoxic, genotoxic, and antimutagenic effects in the CHO cell line

The present work evaluates the cytotoxic, genotoxic, and antimutagenic effects of Phyllanthus orbicularis (plant of genus Phyllantus) aqueous extract in Chinese hamster ovary (CHO) cells. P. orbicularis aqueous extracts are used in Cuban traditional medicine for their antiviral activity against Hepatitis B virus and A and B flu virus. The cytotoxicity of the extract was tested by means of colony-forming ability and growth-inhibition assays as well as by measuring the mitotic index. Apoptosis induction and cell-cycle kinetics were analyzed by cytofluorimetric methods. Chromosome aberration assays were performed to study the genotoxic and antimutagenic activity of the extract. Results show that doses of up to 100 microg/ml of the extract did not induce any cytotoxic effects. Cell survival and mitotic index decreased significantly at doses higher than 100 microg/ml as a function of dose as well as of treatment time. Moreover, continuous treatments of up to 18 h induced the appearance of a significant number of apoptotic cells. Following a 3-h exposure to a dose of 750 microg/ml, cells accumulated significantly in G(2)-M phase and remained blocked in G(1-) and G(2)-M phases after several posttreatments in fresh growth medium. The aqueous extract alone did not induce chromosome aberrations but, in combined treatment with H(2)O(2), significantly reduced H(2)O(2)-induced chromosome aberrations. Flow cytometric analysis of DCFH intracellular oxidation showed that the extract decreased the oxidizing power of H(2)O(2.) This ability could possibly explain the extract's antigenotoxic activity. Absence of cytotoxicity at the lower tested doses and the antimutagenic properties of the extract stimulate the interest in studying possible new pharmaceutical uses of P. orbicularis.

Micronucleus assay and lymphocyte mitotic activity in risk assessment of occupational exposure to microwave radiation

The effects of radiofrequency electromagnetic radiation (RFR) on the cell kinetics and genome damages in peripheral blood lymphocytes were determined in lymphocytes of 12 subjects occupationally exposed to microwave radiation. Results showed an increase in frequency of micronuclei (MN) as well as disturbances in the distribution of cells over the first, second and third mitotic division in exposed subjects compared to controls. According to previous reports micronucleus assay can serve as a suitable indicator for the assessment of exposure to genotoxic agents (such as RFR) and the analysis of mitotic activity as an additional parameter for the efficient biomonitoring.

Necrosis, apoptosis, cytostasis and DNA damage in human lymphocytes measured simultaneously within the cytokinesis-block micronucleus assay: description of the method and results for hydrogen peroxide

A method is described for the inclusion of apoptotic and necrotic cells in the cell counts obtained in the cytokinesis-block micronucleus (CBMN) assay, which is conventionally used solely for the assessment of chromosome breakage, chromosome loss and frequency of dividing cells. The morphological criteria for the recognition and discrimination between necrotic, apoptotic and viable cells are described. Using this comprehensive method we have evaluated the cytotoxic and genotoxic effects of hydrogen peroxide (0-100 microM) in lymphocytes exposed in RPMI 1640 medium. The results obtained indicated significant (P < 0.05) correlations between hydrogen peroxide concentration and the frequency of micronucleated cells (r = 0.39), necrotic cells (r = 0.73), apoptotic cells (r = -0.26) and binucleated cells (r = -0.55). Almost similar results were obtained using the cytosine arabinoside modification of the CBMN assay, which enables excision-repaired sites to be converted to micronuclei. Some of the above end-points were significantly (P < 0.05) correlated with each other (necrosis and apoptosis, R = -0.39; necrosis and micronucleated cell frequency, R = 0.46; necrosis and binucleated cells, R = -0.78; apoptosis and binucleated cells, R = 0.32). It was therefore necessary to use multiple regression analysis to identify the main event induced by hydrogen peroxide, which was necrosis (beta = 0.57, P = 0.0001) and not micronucleus formation (beta = 0. 15, P = 0.1332). Using an ELISA assay we showed that hydrogen peroxide did not induce 8-hydroxydeoxyguanosine. Our data show that the proposed comprehensive test system may provide a better procedure for classifying potential toxic chemicals and enable discrimination between agents that primarily induce cytotoxic effects as opposed to genotoxic effects. The integration of apoptosis and necrosis into the micronucleus assay may also be of practical use in radiosensitivity studies.

A cytogenetic study of nuclear power plant workers using the micronucleus-centromere assay

A cytogenetic study was performed in 215 nuclear power plant workers occupationally exposed to radiation using the micronucleus-centromere assay for peripheral blood lymphocytes. As control population served administrative staff with yearly doses below 1 mSv. The increase of the micronucleus frequency with age, observed in the non-smoking control population, is mainly due to an enhanced number of centromere-positive micronuclei, pointing to an increased chromosome loss. No differences in the number of micronuclei, centromere-positive and centromere-negative micronuclei between smokers and non-smokers are observed. An analysis of the micronucleus data vs. the dose accumulated over the 10 years preceding the venepuncture shows no significant clastogenic or aneuploidogenic effects of the exposure in the studied population which is representative for workers in the nuclear industry at present. According to the linear fits to our data an increase of the micronucleus frequency pro rata 0.5 per 1000 binucleated cells per year, related to the centromere-negative micronuclei, may be expected for workers with the maximal tolerable dose of 20 mSv/year.

The application of the micronucleus test in Chinese hamster V79 cells to detect drug-induced photogenotoxicity

Recent reports on the photochemical carcinogenicity and photochemical genotoxicity of fluoroquinolone antibacterials led to an increasing awareness for the need of a standard approach to test for photochemical genotoxicity. In this study the micronucleus test using V79 cells was adapted to photogenotoxicity testing. Results of using different UVA/UVB relationships enabled us to identify a suitable irradiation regimen for the activation of different kinds of photosensitizers. Using this regimen, 8-methoxypsoralen and the fluoroquinolones lomefloxacin, grepafloxacin and Bay Y 3118 were identified to cause micronuclei and toxicity upon photochemical activation. Among the phenothiazines tested, chlorpromazine and 2-chlorophenothiazine, were positive for both endpoints, whereas triflupromazine was only slightly photoclastogenic in the presence of strong phototoxicity. Among the other potential human photosensitizers tested (oxytetracycline, doxycycline, metronidazole, emodin, hypericin, griseofulvin), only hypericin was slightly photogenotoxic. Photochemical toxicity in the absence of photochemical genotoxicity was noted for doxycycline and emodin. With the assay system described, it is possible to determine photochemical toxicity and photochemical genotoxicity concomitantly with sufficient reliability.

Induction of micronuclei in V79 cells by fractions of roofing asphalt fume condensate

More than 50,000 workers in the United States are exposed to roofing asphalt fumes that may pose genotoxic and potential carcinogenic hazards. The Type III roofing asphalt is most frequently used in roof-application. Results of our previous studies showed that fume condensates of Type III roofing asphalts induced micronuclei (MN) in vitro in cultured V79 cells and DNA adduct formation in vivo in rat lung cells. In this study, the genotoxicity of whole fume condensates (WFC) of Type III roofing asphalt and its five chemical fractions (A, B, C, D and E) was determined by the micronucleus assay using V79 cells. Linear regressions were determined for the dose response of MN frequencies and percent of binucleated and multinucleated cells (MTC) following the treatment. Results showed that the numbers of micronucleated cells in cultures treated with Type III roofing asphalt WFC and its fractions B, C, D and E were significantly higher than that in the control culture, and that the slopes of the linear regression line for fractions B and C were greater than those for the WFC and fractions D and E. A clear dose response of binucleated cells was also induced by the WFC and fractions B and C. These findings indicate that: (1) WFC and all fractions, except fraction A, induced MN formation in cultured V79 cells; (2) fractions B and C possess the highest genotoxic activity; (3) the roofing asphalt WFC contains chemicals or chemical classes that induce not only chromosomal aberrations but also binucleation in V79 cells.

Comparison of spontaneous and idoxuridine-induced micronuclei by chromosome painting

Fluorescence in situ hybridisation (FISH) technique with chromosome specific library (CSL) DNA probes for all human chromosomes were used to study about 9000 micronuclei (MN) in normal and idoxuridine (IUdR)-treated lymphocyte cultures of female and male donors. In addition, MN rates and structural chromosome aberrations were scored in Giemsa-stained chromosome spreads of these cultures. IUdR treatment (40 microg/ml) induced on the average a 12-fold increase of the MN rate. Metaphase analysis revealed no distinct increase of chromosome breaks but a preferential decondensation at chromosome 9q12 (28-79%) and to a lower extend at 1q12 (8-21%). Application of FISH technique with CSL probes to one male and one female untreated proband showed that all human chromosomes except chromosome 12 (and to a striking high frequency chromosomes 9, X and Y) occurred in spontaneous MN. In cultures containing IUdR, the chromosomal spectrum found in MN was reduced to 10 chromosomes in the male and 13 in the female proband. Eight chromosomes (2, 6, 12, 13, 14, 15, 17 and 18) did not occur in MN of both probands. On the contrary chromosomes 1 and especially 9 were found much more frequently in the MN of IUdR-treated cultures than in MN of control cultures. DAPI-staining revealed heterochromatin signals in most of the IUdR-induced MN. In an additional study, spontaneous and IUdR-induced MN were investigated in lymphocytes of another female donor using CSL probes only for chromosomes 1, 6, 9, 15, 16 and X. The results confirmed the previous finding that chromosomes 1 and 9 occur very often in MN after IUdR-treatment. The results indicate that decondensation of heterochromatic regions on chromosomes 1 and 9 caused by IUdR treatment strongly correlates with MN formation by these chromosomes.

Low persistence of radiation-induced centromere positive and negative micronuclei in cultured human cells

The micronucleus (MN) assay is widely used both in genetic toxicology and in the biomonitoring of human populations. Lymphocytes, cell lines, and bone marrow and epithelial cells are usually employed as target systems in such studies. However, little effort has been done to assess the persistence of MN in highly proliferative cells. To study the behaviour of MN containing whole chromosomes or acentric fragments, we have performed a time course experiment on the persistence of gamma-ray (3 Gy) induced MN in a human lymphoblastoid cell line. The frequency and content of MN were analyzed 1, 3, 7, 14, and 56 days after irradiation by pancentromeric fluorescence in situ hybridization (FISH). We observed a clear induction of both centromere positive and negative MN at completion of the first mitotic division. The frequency of both types of MN drastically declined to basal levels 7 days after irradiation with an identical kinetics. We therefore conclude that centromere positive and negative MN are highly unstable upon cell division, indicating that the MN assay could not be a good biomarker of DNA damage induced by acute treatments in highly proliferative cells. The implication of our findings in biomonitoring and in genotoxicity studies is discussed.

Genotoxic evaluation of the antimicrobial drug, trimethoprim, in cultured human lymphocytes

The antimicrobial drug, trimethoprim, was evaluated for genotoxicity in human peripheral blood lymphocyte cultures set-up from two healthy donors. Sister-chromatid exchanges (SCE) and micronuclei (MN) were scored as genetic endpoints. The treatment was done using different trimethoprim concentrations ranging from 1 to 100 microg/ml. From our results, we can conclude that this drug is able to induce both cytotoxic and moderate genotoxic effects, as revealed by the increases seen in SCE and MN frequencies in cultures from the two donors and, at least, at one of the concentrations tested.

Important variables that influence base-line micronucleus frequency in cytokinesis-blocked lymphocytes-a biomarker for DNA damage in human populations

The cytokinesis-block micronucleus (CBMN) assay has been adopted by numerous laboratories as a means for rapidly assessing base-line chromosome damage (breakage and loss) in human populations. However, the appropriate implementation of this assay requires a thorough understanding of both experimental variables and biological factors that can have impact on micronucleus (MN) frequency. The paper describes, with the help of experimental data the from the author's laboratory as well as other data, the impact of these variables. With regards to experimental variables, the scoring of micronuclei on slides by different technicians has been identified as an important factor; however, the use of different culture media, namely RPMI 1640 and McCoy's medium, did not have a significant effect on base-line frequencies. The paper also describes results showing that the MN index in cytokinesis-blocked cells, measured once every three months over a 12-month period for 53 healthy subjects, remains constant and the data measured on these occasions were significantly and positively correlated (R=0.477 to 0.684, P<0. 0001) with each other thus indicating the reliability and intra-individual variability of the assay over time. Inter-individual variation for males and female subjects has been estimated for each decade of age between 20 and 80 years; the difference between the 25th and 75th percentile of MN frequency varied between 1.4 fold and 2.3 fold and the minimum and maximum values for MN frequency varied by a factor of 4.7 and 12.5 depending on the age group. Age and gender are the most important demographic variables impacting on the MN index with MN frequencies in females being greater than those in males by a factor of 1.2 to 1.6 depending on the age group. For both sexes, MN frequency was significantly and positively correlated with age (R=0.62 in males and R=0.65 in females) and the slope of the regression line in males was 0.314 (P<0.0001) and in females it was 0.517 (P<0.0001). The main dietary factors influencing the MN index in subjects who are not folate deficient are plasma B12 (R=-0.315, P=0.0127) and plasma homocysteine (R=0.415, P=0.0086). In addition, it was proposed that the MN index is likely to be influenced by the propensity of an individual's cells to undergo apoptosis when damaged so that one might expect the MN frequency to be negatively correlated with apoptotic rate although this has yet to be tested. The above indicates the importance of maintaining an international network of scientists working with the CBMN assay to ensure appropriate quality control and for the development of standard experimental and documentation protocols. The human micronucleus (HUMN) project launched in 1997 is briefly described and proposed as the vehicle for these activities.

Development and validation of the in vivo alkaline comet assay for detecting genomic damage in marine flatfish

Biomonitoring is an important subject within environmental sciences. Biomonitoring tests are required to be quick, relatively inexpensive, accurate, and reproducible. No genetic test currently fulfils all of these requirements. The chromosome aberration and sister chromatid exchange tests are very time consuming, the DNA adduct technique is rather expensive, and the micronucleus test has not inconclusively proven its use as a reliable monitoring tool. This work is focused on the validation of the comet assay as a candidate for monitoring marine ecosystems. For the comet assay, this work deals with the effectiveness of tissue dissociation, storage of cells in lysing buffer and in liquid nitrogen, different electrophoretic conditions, neutralisation and fixation of slides, interindividual variation between samples, and responsiveness of four tissue types to ethyl methanesulphonate (EMS). The main conclusions are: (i) dissociation of solid tissues in a phosphate buffer supplemented with 200 mM N-t-butyl-alpha-phenylnitrone provides cells with an acceptable background DNA damage; (ii) freezing of cells or tissues in liquid nitrogen generally leads to an increase in DNA breakage, especially for liver, gill and kidney tissue; (iii) storage of slides in the lysing solution for up to one week gives minor changes in comet tails; (iv) differences in protocols for neutralisation and fixation may influence the results; (v) high intra- and interindividual variations in comets (length and DNA content) may obscure the interpretation of comet results; (vi) blood, gill, liver and kidney all showed a statistically significant increase of DNA damage after exposure to 50 mg EMS/l; (vii) electrophoresis at low voltage for longer periods is to be preferred to high voltage and short electrophoresis times. The simplicity and sensitivity of the comet assay make it an adequate test system for biomonitoring of chronic low level exposure. However, protocols and experimental conditions have to be chosen carefully.

Genetic toxicology

Systems for testing genetic toxicology are components of carcinogenic and genetic risk assessment. Present routine genotoxicity-testing is based on at least 20 years of development during which many different test systems have been introduced and used. Today, it is clear that no single test is capable of detecting all genotoxic agents. Therefore, the usual approach is to perform a standard battery of in-vitro and in-vivo tests for genotoxicity. Work-groups of the European Union (EU), the Organization for Economic Co-operation and Development (OECD), and, very recently, the work-group of the International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) have defined such standard battery tests. These and some currently used supplementary or confirmatory tests are briefly discussed here. Additional test systems for the assessment of genotoxic and carcinogenic hazard and risk are seriously needed. These tests must be more relevant to man than are current assays and less demanding in respect of cost, time and number of animals. Another aspect for reassessment derives from the actual situation in the pharmaceutical industry. Companies have to prepare for the world economy of the 21st century. Therefore, pharmaceutical research is speeding up tremendously by use of tools such as genomics, combinatorial chemistry, high throughput screening and proteomics. Toxicology and genotoxicology need to re-evaluate their changing environment and must find ways to respond to these needs. In conclusion, genetic toxicology needs to answer questions coming from two major directions: hazard and risk identification and high throughput testing.