Dislocation of chromatin elements in prophase induced by diethylstilbestrol: a novel mechanism by which micronuclei can arise

The ecogenotoxic plant biomonitoring of a long-term polluted area in central Slovakia

The aim of the study was to analyze, update, and complete the results of research in the field of in situ phytoindication of environmental genotoxicity near the aluminum plant in Žiar nad Hronom in central Slovakia. The authors focused on two methodologies: pollen abortivity assay of native flora and Trad-MCN assay. Comparison of changes in responses of living systems to changes in precipitation was conducted, and it suggests that there is an existence of an impact from a dilution effect to the plants. Also, the gradual increase of pollen abortivity in the 1990s and its decrease from 2009 were observed in a majority of species of wild flora. On an annual basis, abortivity has declined, although it has risen up slightly within each season. Despite a gradual decrease in the micronucleus frequency, the study area is still influenced by the ecogenotoxic factors. Pollen analysis of native flora and introduced Tradescantia plants indicates the long-time presence of ecogenotoxicity in this region due to the presence of aluminum plant.

Next-Generation Magnetic Nanocomposites: Cytotoxic and Genotoxic Effects of Coated and Uncoated Ferric Cobalt Boron (FeCoB) Nanoparticles In Vitro

Metal nanoparticles (NPs) have unique physicochemical properties and a widespread application scope depending on their composition and surface characteristics. Potential biomedical applications and the growing diversity of novel nanocomposites highlight the need for toxicological hazard assessment of next-generation magnetic nanomaterials. Our study aimed to evaluate the cytotoxic and genotoxic properties of coated and uncoated ferric cobalt boron (FeCoB) NPs (5-15 nm particle size) in cultured normal human dermal fibroblasts. Cell proliferation was assessed via ATP bioluminescence kit, and DNA breakage and chromosomal damage were measured by alkaline comet assay and micronucleus test. Polyacryl acid-coated FeCoB NPs [polyacrylic acid (PAA)-FeCoB NPs) and uncoated FeCoB NPs inhibited cell proliferation at 10 μg/ml. DNA strand breaks were significantly increased by PAA-coated FeCoB NPs, uncoated FeCoB NPs and l-cysteine-coated FeCoB NPs (Cys-FeCoB NPs), although high concentrations (10 μg/ml) of coated NPs (Cys- and PAA-FeCoB NPs) showed significantly more DNA breakage when compared to uncoated ones. Uncoated FeCoB NPs and coated NPs (PAA-FeCoB NPs) also induced the formation of micronuclei. Additionally, PAA-coated NPs and uncoated FeCoB NPs showed a negative correlation between cell proliferation and DNA strand breaks, suggesting a common pathomechanism, possibly by oxidation-induced DNA damage. We conclude that uncoated FeCoB NPs are cytotoxic and genotoxic at in vitro conditions. Surface coating of FeCoB NPs with Cys and PAA does not prevent but rather aggravates DNA damage. Further safety assessment and a well-considered choice of surface coating are needed prior to application of FeCoB nanocomposites in biomedicine.

Biogenesis of Micronuclei

The presence of micronuclei in a cell is an indicator of DNA damage and genetic instability. In this review, mechanisms of emergence of micronuclei, their functional activity, and pathways of elimination are discussed. It is supposed that morphological and functional varieties of micronuclei as well as their degradation pathways can be determined by the chromosomal material localized inside these cell structures.

Cytotoxic and genotoxic effects on gingival fibroblasts from static magnetic fields produced by dental magnetic attachments

OBJECTIVE

To investigate cytotoxic and genotoxic effects of static magnetic field (SMF) produced by dental magnetic attachments on human gingival fibroblasts in vitro.

BACKGROUND

Magnetic attachments have numerous roles in dental prosthesis fixation, but few reports evaluate possible biological effects of static magnetic field (SMF) on human gingival tissues, particular genotoxic effects.

MATERIALS AND METHODS

The Dyna (500-gr breakaway force) and Steco (173-gr breakaway force) dental magnetic attachments were embedded into autopolymerising acrylic resin in four different configurations each, including single and double magnets. Gingival biopsy was performed on 28 individuals during third molar extraction, and each sample was divided into two pieces for culture under SMF exposure or as a control. In total, seven test and seven control gingival fibroblast cultures were performed for each group resulting in 56 gingival fibroblast cultures. The test culture flasks were placed atop the magnet-embedded resin blocks. After cultures were terminated, mitotic index (MI) and micronucleus (MN) rates were analysed at a p = 0.05 significance level by Wilcoxon's test; intergroup differences were analysed with a Kruskal-Wallis test.

RESULTS

There was no significant difference in intragroup or intergroup MI rates. The double Dyna (p = 0.023) and double Steco (p = 0.016) groups had statistically significant intragroup differences in the MN rates. There were no statistically significant differences in MN rates in intergroup analyses.

CONCLUSION

In particular, higher magnetic fields from dental magnetic attachments might be toxic genetically to human gingival fibroblasts. However, there is need for further investigations from different aspects to detect any genotoxicity.

Oxidative stress and nucleic acid oxidation in patients with chronic kidney disease

Patients with chronic kidney disease (CKD) have high cardiovascular mortality and morbidity and a high risk for developing malignancy. Excessive oxidative stress is thought to play a major role in elevating these risks by increasing oxidative nucleic acid damage. Oxidative stress results from an imbalance between reactive oxygen/nitrogen species (RONS) production and antioxidant defense mechanisms and can cause vascular and tissue injuries as well as nucleic acid damage in CKD patients. The increased production of RONS, impaired nonenzymatic or enzymatic antioxidant defense mechanisms, and other risk factors including gene polymorphisms, uremic toxins (indoxyl sulfate), deficiency of arylesterase/paraoxonase, hyperhomocysteinemia, dialysis-associated membrane bioincompatibility, and endotoxin in patients with CKD can inhibit normal cell function by damaging cell lipids, arachidonic acid derivatives, carbohydrates, proteins, amino acids, and nucleic acids. Several clinical biomarkers and techniques have been used to detect the antioxidant status and oxidative stress/oxidative nucleic acid damage associated with long-term complications such as inflammation, atherosclerosis, amyloidosis, and malignancy in CKD patients. Antioxidant therapies have been studied to reduce the oxidative stress and nucleic acid oxidation in patients with CKD, including alpha-tocopherol, N-acetylcysteine, ascorbic acid, glutathione, folic acid, bardoxolone methyl, angiotensin-converting enzyme inhibitor, and providing better dialysis strategies. This paper provides an overview of radical production, antioxidant defence, pathogenesis and biomarkers of oxidative stress in patients with CKD, and possible antioxidant therapies.

Micronuclei as a biological endpoint for genotoxicity: A minireview

The in vitro micronucleus assay has now been applied in many laboratories. This endpoint is useful in biomonitoring or ecotoxicology, as a sensitivity measure of human cells in cancer treatment and also to replace or supplement other in vitro genotoxicity assays. Learning more about the mechanisms of micronucleus formation allows conclusions about its biological significance. It has been demonstrated that disturbance of the mitotic apparatus (spindle, kinetochores) as well as impaired function of topoisomerase II can be involved in micronucleus formation. In addition, the roles of changes in DNA-conformation that are induced by alterations in the status of cytosine-methylation and of the cellular DNA repair capacity have been shown. The fate of micronucleus-containing cells is not known: the cells may theoretically be cytostatic and micronucleus-formation may therefore be a way of the organism to eliminate genetic damage or the cells may survive the loss of that chromosomal material and develop into transformed cells. Published data and ideas of selected areas within this field are reviewed.

Assessment of the genotoxic potential of contaminated estuarine sediments in fish peripheral blood: laboratory versus in situ studies

Juvenile Senegalese soles (Solea senegalensis) were exposed to estuarine sediments through 28-day laboratory and in situ (field) bioassays. The sediments, collected from three distinct sites (a reference plus two contaminated) of the Sado Estuary (W Portugal) were characterized for total organic matter, redox potential, fine fraction and for the levels of metals, polycyclic aromatic hydrocarbons (PAHs) and organochlorines, namely polychlorinated biphenyls (PCBs) and dichloro diphenyl tricholoethane plus its main metabolites (DDTs). Genotoxicity was determined in whole peripheral blood by the single-cell gel electrophoresis (SCGE or "comet") assay and by scoring erythrocytic nuclear abnormalities (ENA). Analysis was complemented with the determination of lipid peroxidation in blood plasma by the thiobarbituric acid reactive substances (TBARS) protocol and cell type sorting. The results showed that exposure to contaminated sediments induced DNA fragmentation and clastogenesis. Still, laboratory exposure to the most contaminated sediment revealed a possible antagonistic effect between metallic and organic contaminants that might have been enhanced by increased bioavailability. The laboratory assay caused a more pronounced increase in ENA whereas a very significant increase in DNA fragmentation was observed in field-tested fish exposed to the reference sediment, which is likely linked to increased lipid peroxidation that probably occurred due to impaired access to food. Influence of natural pathogens was ruled out by unaltered leukocyte counts. The statistical integration of data correlated lipid peroxidation with biological variables such as fish length and weight, whereas the genotoxicity biomarkers were more correlated to sediment contamination. It was demonstrated that laboratory and field bioassays for the risk assessment of sediment contamination may yield different genotoxicity profiles although both provided results that are in overall accordance with sediment contamination levels. While field assays may provide more ecologically relevant data, the multiple environmental variables may produce sufficient background noise to mask the true effects of contamination.

Multiple origins of spontaneously arising micronuclei in HeLa cells: direct evidence from long-term live cell imaging

Although micronuclei (MNi) are extensively used to evaluate genotoxic effects and chromosome instability, the most basic issue regarding their origins has not been completely addressed due to limitations of traditional methods. Recently, long-term live cell imaging was developed to monitor the dynamics of single cell in a real-time and high-throughput manner. In the present study, this state-of-the-art technique was employed to examine spontaneous micronucleus (MN) formation in untreated HeLa cells. We demonstrate that spontaneous MNi are derived from incorrectly aligned chromosomes in metaphase (displaced chromosomes, DCs), lagging chromosomes (LCs) and broken chromosome bridges (CBs) in later mitotic stages, but not nuclear buds in S phase. However, most of bipolar mitoses with DCs (91.29%), LCs (73.11%) and broken CBs (88.93%) did not give rise to MNi. Our data also show directly, for the first time, that MNi could originate spontaneously from (1) MNi already presented in the mother cells; (2) nuclear fragments that appeared during mitosis with CB; and (3) chromosomes being extruded into a minicell which fused with one of the daughter cells later. Quantitatively, most of MNi originated from LCs (63.66%), DCs (10.97%) and broken CBs (9.25%). Taken together, these direct evidences show that there are multiple origins for spontaneously arising MNi in HeLa cells and each mechanism contributes to overall MN formation to different extents.

Origin of nuclear buds and micronuclei in normal and folate-deprived human lymphocytes

Micronuclei are formed from chromosomes and chromosomal fragments that lag behind in anaphase and are left outside daughter nuclei in telophase. They may also be derived from broken anaphase bridges. Nuclear buds, micronucleus-like bodies attached to the nucleus by a thin nucleoplasmic connection, have been proposed to be generated similarly to micronuclei during nuclear division or in S-phase as a stage in the extrusion of extra DNA, possibly giving rise to micronuclei. To better understand these phenomena, we have characterized the contents of 894 nuclear buds and 1392 micronuclei in normal and folate-deprived 9-day cultures of human lymphocytes using fluorescence in situ hybridization with pancentromeric and pantelomeric DNA probes. Such information has not earlier been available for human primary cells. Surprisingly, there appears to be no previous data on the occurrence of telomeres in micronuclei (or buds) of normal human cells in general. Our results suggest that nuclear buds and micronuclei have partly different mechanistic origin. Interstitial DNA without centromere or telomere label was clearly more prevalent in nuclear buds (43%) than in micronuclei (13%). DNA with only telomere label or with both centromere and telomere label was more frequent in micronuclei (62% and 22%, respectively) than in nuclear buds (44% and 10%, respectively). Folate deprivation especially increased the frequency of nuclear buds and micronuclei harboring telomeric DNA and nuclear buds harboring interstitial DNA but also buds and micronuclei with both centromeric and telomeric DNA. According to the model we propose, that micronuclei in binucleate lymphocytes primarily derive from lagging chromosomes and terminal acentric fragments during mitosis. Most nuclear buds, however, are suggested to originate from interstitial or terminal acentric fragments, possibly representing nuclear membrane entrapment of DNA that has been left in cytoplasm after nuclear division or excess DNA that is being extruded from the nucleus.

Genomic damage in chronic renal failure--potential therapeutic interventions

In end-stage renal failure, genomic damage is enhanced. This has been shown both in the predialysis and dialysis phase by various biomarkers, such as micronuclei frequency and single cell gel electrophoresis in lymphocytes as well as with 8-hydroxy-2'-deoxyguanosine in leukocytes. There are also data about mitochondrial DNA deletions and chromosomal abnormalities. Genomic damage may be induced by a multitude of toxic factors and mutagens, in particular via enhanced generation of reactive oxygen species. In in vitro studies, incubation of tubular cells with various AGEs (carboxymethyllysine-BSA, AGE-BSA, and methylglyoxal-BSA) and angiotensin II resulted in a marked DNA damage. Coincubation with various antioxidants as well as the angiotensin II receptor blocker, candesartan, suppressed the toxic action. Moreover, an improved uremic state by daily hemodialysis ameliorated the genomic damage in lymphocytes, as compared to patients on conventional hemodialysis.

Genomic damage in end-stage renal failure: potential involvement of advanced glycation end products and carbonyl stress

In patients with chronic renal failure, genomic damage has been shown by numerous biomarkers, such as micronuclei frequency and comet assay (single-cell gel electrophoresis) in peripheral lymphocytes, 8-hydroxy 2'-deoxyguanosine (8-OH-dG) content in leukocytes, mitochondrial DNA deletions in skeletal muscle tissue and hair follicles, as well as in DNA repair mechanisms in freshly isolated lymphocytes after ultraviolet light exposure. In the pathogenesis of DNA damage--besides genetic influences, enhanced reactive oxygen species (ROS), and lipid peroxidation-the genotoxic potential of advanced glycation end products (AGEs) and reactive carbonyl compounds deserve special attention. In fact, reactions of glucose with DNA can lead to mutagenic DNA AGEs. In vitro, incubation of tubulus cells with various AGEs and methylglyoxal induces DNA damage, which is suppressed by antioxidants. This underlines the role played by oxidative stress in DNA damage.

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.

Dose-rate effects for apoptosis and micronucleus formation in gamma-irradiated human lymphocytes

We have compared dose-rate effects for gamma-radiation-induced apoptosis and micronucleus formation in human lymphocytes. Long-term assessment of individual radiation-induced apoptosis showed little intraindividual variation but significant interindividual variation. The effectiveness of radiation exposure to cause apoptosis or micronucleus formation was reduced by low-dose-rate exposures, but the reduction was apparent at different dose rates for these two end points. Micronucleus formation showed a dose-rate effect when the dose rate was lowered to 0.29 cGy/min, but there was no accompanying cell cycle delay. A further increase in the dose-rate effect was seen at 0.15 cGy/min, but was now accompanied by cell cycle delay. There was no dose-rate effect for the induction of apoptosis until the dose rate was reduced to 0.15 cGy/min, indicating that the mechanisms or signals for processing radiation-induced lesions for these two end points must be different at least in part. There appear to be two mechanisms that contribute to the dose-rate effect for micronucleus formation. One of these does not affect binucleate cell frequency and occurs at dose rates higher than that required to produce a dose-rate effect for apoptosis, and one affects binucleate cell frequency, induced only at the very low dose rate which coincidentally produces a dose-rate effect for apoptosis. Since the dose rate at which cells showed reduced apoptosis as well as a further reduction in micronucleus formation was very low, we conclude that the processing of the radiation-induced lesions that induce apoptosis, and some micronuclei, is very slow in quiescent and PHA-stimulated lymphocytes, respectively.

Induction of genotoxic effects and modulation of the intracellular calcium level in syrian hamster embryo (SHE) fibroblasts caused by ochratoxin A

The mycotoxin ochratoxin A (OTA) is a naturally occuring contaminant of food. The genotoxic status of OTA is still controversial because contradictory results were obtained in various microbial and mammalian gene mutation assays. In this study, OTA was investigated to examine its potency to induce micronuclei (MN) in SHE cells. The SHE-micronucleus assay revealed that OTA induces MN in a dose- and time-dependent manner. The results of kinetochore analysis revealed that mainly clastogenic events are involved in OTA genotoxicity. Induction of mitotic disturbances can be closely related to changes of the intracellular calcium concentration ([Ca2+]i). The investigated time course of OTA-induced [Ca2+]i changes revealed that the obtained signal is a short spike signal resembling physiological responses. In the absence of extracellular calcium, a long-lasting signal indicates possible damage to intracellular calcium stores or channels. Our data show that the OTA-induced [Ca2+]i rise is caused by Ca2+ -release from intracellular stores as well as Ca2+ influx from extracellular area. Finally, the influence of the changed intracellular calcium level on the actin cytoskeleton was investigated. Visualization of the actin filaments revealed time- and concentration-dependent effects. Cell shrinkage and depolymerized filaments were observed. We conclude that OTA disrupts actin filaments by a direct irreversible binding to actin.

Biological effects of a bifunctional DNA cross-linker. II. Generation of micronuclei and attached micronuclear-like structures

Madin-Darby bovine kidney (MDBK) cells were treated with the bifunctional DNA cross-linker, L-7, to examine the generation of micronuclei and other nuclear abnormalities. The preceding paper demonstrates that L-7 treatment induces the formation of triradial and quadriradial chromosomes in MDBK cells. These chromosomes are believed to result from interduplex DNA cross-links formed between G-C rich centromeric satellite DNA regions on non-sister chromatids. Treatment produces a majority of centromere-positive micronuclei. In addition, many daughter cells remain attached by chromatin bridges which are sometimes beaded with micronuclei. Up to 15% of cell nuclei become lobular and fused with numerous micronuclear-like structures attached to their membranes. These attached structures are classified as attached micronuclear-like structures (AMNLS). Fluorescence in situ hybridization (FISH) using a centromeric satellite sequence was performed on treated cells. Hybridization reveals that intercellular bridges are composed of centromeric sequences and initiate at centromeric foci in daughter cells. Furthermore, the majority of junctions between AMNLS and nuclei contain an enhancement of centromeric signal. The frequency of AMNLS appears dependent on the concentration of L-7 and the duration of treatment. Similar results were found for the generation of cross-linked chromosome products in the previous paper. We suggest that AMNLS result from the abnormal mitotic segregation of cross-linked chromosome products.

Mitotic centromere-associated kinesin is important for anaphase chromosome segregation

Mitotic centromere-associated kinesin (MCAK) is recruited to the centromere at prophase and remains centromere associated until after telophase. MCAK is a homodimer that is encoded by a single gene and has no associated subunits. A motorless version of MCAK that binds centromeres but not microtubules disrupts chromosome segregation during anaphase. Antisense-induced depletion of MCAK results in the same defect. MCAK overexpression induces centromere-independent bundling and eventual loss of spindle microtubule polymer suggesting that centromere-associated bundling and/or depolymerization activity is required for anaphase. Live cell imaging indicates that MCAK may be required to coordinate the onset of sister centromere separation.

Toxic effects of griseofulvin: disease models, mechanisms, and risk assessment

Griseofulvin (GF) has been in use for more than 30 years as a pharmaceutical drug in humans for the treatment of dermatomycoses. Animal studies give clear evidence that it causes a variety of acute and chronic toxic effects, including liver and thyroid cancer in rodents, abnormal germ cell maturation, teratogenicity, and embroyotoxicity in various species. No sufficient data from human studies are available at present to exclude a risk in humans: therefore, attempts were made to elucidate the mechanisms responsible for the toxic effects of GF and to address the question whether such effects might occur in humans undergoing GF therapy. It is well documented that GF acts as a spindle poison and its reproductive toxicity as well as the induction of numerical chromosome aberrations and of micronuclei in somatic cells possibly may result from disturbance of microtubuli formation. Likewise, a causal relationship between aneuploidy and cancer has been repeatedly postulated. However, a critical survey of the data available on aneuploidogenic chemicals revealed insufficient evidence for such an association. Conceivably, other mechanisms may be responsible for the carcinogenic effects of the drug. The induction of thyroid tumors in rats by GF is apparently a consequence of the decrease of thyroxin levels and it is unlikely that such effects occur in GF-exposed humans. The appearance of hepatocellular carcinomas (HCC) in mice on GF-supplemented diet is preceded by various biochemical and morphological changes in the liver. Among these, hepatic porphyria is prominent, it may result from inhibition of ferrochelatase and (compensatory) induction of ALA synthetase. GF-induced accumulation of porphyrins in mouse liver is followed by cell damage and necrotic and inflammatory processes. Similar changes are known from certain human porphyrias which are also associated with an increased risk for HCC. However, the porphyrogenic effect of GF therapy in humans is moderate compared with that in the mouse model, although more detailed studies should be performed in order to clarify this relationship on a quantitative basis. A further important effect of GF-feeding in mice is the formation of Mallory bodies (MBs) in hepatocytes. These cytoskeletal abnormalities occur also in humans, although under different conditions; their appearance is associated with the induction of liver disease and HCC. Chronic liver damage associated with porphyria and MB formation, enhanced cell proliferation, liver enlargement, and enzyme induction all may contribute to the hepatocarcinogenic effect of GF in mice. In conclusion, further investigation is required for adequate assessment of health risks to humans under GF therapy.

Induction of micronuclei in Syrian hamster embryo cells: comparison to results in the SHE cell transformation assay for National Toxicology Program test chemicals

Sixteen chemicals currently being tested in National Toxicology Program (NTP) carcinogenicity studies were evaluated in the Syrian hamster embryo (SHE) cell in vitro micronucleus assay. Results from these studies were compared to the results from the SHE cell transformation assay for the same chemicals The overall concordance between induction of micronuclei and transformation of SHE cells was 56%, which is far lower that the 93% concordance between these two tests reported previously by Fritzenschaf et al. (1993; Mutation Res. 319, 47-53). The difference between our results appears to be due to differences in the types of chemicals in the two studies. Overall, there is good agreement between the SHE cell micronucleus and transformation assays for mutagenic chemicals, but, as our study highlights, the SHE cell transformation assay has the added utility of detecting nonmutagenic carcinogens. The utility of a multi-endpoint assessment in SHE cells for carcinogen screening is discussed.

A critical evaluation of centromeric labeling to distinguish micronuclei induced by chromosomal loss and breakage in vitro

The in vitro micronucleus assay in conjunction with CREST-staining and fluorescence in situ hybridization (FISH) with centromere-specific DNA probes is being increasingly utilized for the detection of clastogenic and aneuploidy-inducing agents. Although potentially powerful techniques, both methods have unique characteristics that can influence sample processing and the interpretation of results. In this article, the use of the CREST and the FISH modifications of the in vitro micronucleus assay have been used to characterize the origin of the micronuclei induced by cyclophosphamide, 4,4'-methylene-bis(2-chloroaniline), 4-nitroquinoline N-oxide and ionizing radiation in metabolically competent MCL-5 cells or a derived cell line lacking metabolic activation. Using these results and our previous experiences with these techniques, a detailed comparison including the strengths and limitations of each technique as well as potential problems in performing each assay and in analyzing the data is discussed. In spite of their limitations, our results to date indicate that CREST-staining as well as FISH with centromere-specific DNA probes can be used to accurately distinguish micronuclei formed from chromosome loss from those originating from chromosome breakage and that these techniques can be valuable complements to the in vitro micronucleus assay.

Analysis of DES-induced micronuclei in binucleated rat fibroblasts: comparison between FISH with a rat satellite I probe and immunocytochemical staining with CREST serum

The usefulness of fluorescence in situ hybridization (FISH) with rat satellite I DNA was compared with immunocytochemical staining with CREST serum for the analysis of the content of micronuclei from primary rat fibroblasts. We analyzed micronuclei induced in vitro by the aneugenic compound diethylstilbestrol (DES) or the clastogenic compound mitomycin C (MMC). Since a centromeric probe was not available for the rat, we isolated rat satellite I DNA by PCR with primers designed on the basis of the known rat satellite I DNA sequence. The PCR products obtained as well as the cloned PCR products showed hybridization to the centromeric regions of a large number of chromosomes, but not of chromosome 1, 19, 20, X and Y. Clone 18-5 was further analyzed and was shown to contain at least 4 repeats of the rat satellite I family. This probe, which hybridizes in the centromeric region of 34 of the 42 chromosomes, was used throughout the study as a probe for the FISH analysis of the micronuclei. For the immunocytochemical staining, the commonly used commercial anti-centromeric antibodies could not be used because of the weakness of the fluorescent signals given. Consequently, CREST serum of a single patient was used, which showed bright and distinct signals on the kinetochores of each chromosome. After treatment of the cells with the aneugen DES an increase in centromere (FISH) and kinetochore (CREST) positive micronuclei was found, whereas after treatment with the clastogen MMC, the percentage of centromere-positive micronuclei was similar to that observed in controls. Analysis of a large number of DES-induced micronuclei showed that the immunocytochemical method is equally as or slightly less sensitive for the detection of chromosomes in micronuclei and we therefore recommend FISH with probe 18-5 for the detection of chromosome loss in rat cells.

Detection of aneuploidy-inducing carcinogens in the Syrian hamster embryo (SHE) cell transformation assay

As evidenced by the recent report of the Commission of the European Communities (CEEC) project (Detection of Aneugenic Chemicals-CEEC project, 1993), there currently is a great deal of effort towards developing and validating assays to detect aneuploidy-inducing chemicals. In this report, we describe the utility of the Syrian hamster embryo (SHE) cell transformation assay for detecting carcinogens with known or suspected aneuploidy-inducing activity. The following carcinogens were tested: asbestos, benomyl, cadmium chloride, chloral hydrate, diethylstilbestrol dipropionate, and griseofulvin. Thiabendazole, a noncarcinogen, was also tested. Chemicals of unknown or inconclusive carcinogenicity data, colcemid, diazepam, econazole nitrate, and pyrimethamine were also evaluated. All of the above chemicals except thiabendazole induced a significant increase in morphological transformation (MT) in SHE cells. Based on these results as well as those published in the literature previously, the SHE cell transformation assay appears to have utility for detecting carcinogens with known or suspected aneuploidy-inducing ability.

Induction of micronuclei by stilbene-type and steroidal estrogens in Syrian hamster embryo and ovine seminal vesicle cells in vitro

The induction of micronuclei (MN) is a known effect of the carcinogenic estrogen diethylstilbestrol (DES). We have now tested the time course and dose dependence of MN induction by DES and its analogs 3',3"-DES, indenestrol A (IA), indenestrol B (IB) or by the steroidal estrogen 17 beta-estradiol (E2) and by the clastogenic compound 4-nitroquinoline-N-oxide (NQO) in two primary mammalian cell culture systems. All compounds induced MN in Syrian hamster embryo and ovine seminal vesicle cells with compound-specific time courses and dose dependences. DES induced a maximum MN frequency 12 h post treatment, whereas with all other estrogens the highest MN frequency was observed 3-6 h after removal of the compound. The maximum MN frequency after NQO treatment occurred at 24 h or later. Of the stilbene estrogens tested, only DES caused an increase of the mitotic index. Further characterization of the MN by indirect immunofluorescence microscopy using CREST antikinetochore antibodies revealed that 92-99% of the DES-induced MN but only 0-2% of the NQO-induced MN contained CREST-reactive kinetochores. Since kinetochore-positive MN are indicative of whole chromosomes/chromatids and kinetochore-negative MN of acentric chromosomal fragments, our findings support the view that DES acts as a pure aneuploidogen and NQO as a pure clastogen in the two cell systems. In the case of 3',3"-DES, IA, IB and E2, 41-68% of the induced MN contained CREST-reactive kinetochores. As the time courses of MN induction are not compatible with those of clastogenic agents, it is proposed that these estrogens induce MN containing chromatids/chromosomes with altered kinetochore structures.

Effect of indanyl analogues of diethylstilboestrol on morphological transformation of Syrian hamster embryo fibroblasts and micronuclei in vitro

Two analogues of the carcinogenic oestrogen diethylstilboestrol (DES), indenoestrol A (IA) and indenoestrol B (IB), have been studied with respect to their genotoxic and cell transforming properties in mammalian cells. The conformation and oestrogenicity of IA and IB are very similar, but they differ with respect to their ease of peroxidation and the resulting reactive intermediates: only IA is readily converted to a p-quinone. Both DES derivatives caused morphological transformation of Syrian hamster embryo (SHE) fibroblasts with similar efficiency at concentrations (1 to 10 mum) that did not affect cloning efficiency. In addition, IA and IB (5 to 50 mum) induced micronuclei in the same cell system. These micronuclei were detectable as early as 1-3 hr after a 5-hr treatment with IA or IB. Such a time course is characteristic of compounds that cause mitotic disturbances. Indomethacin, an inhibitor of prostaglandin H synthase (the enzyme responsible for oxidation of DES in target cells), did not affect the frequency of micronuclei induced by IA or by IB. From these data we conclude that peroxidative metabolism resulting in quinone formation is not a prerequisite for the genotoxicity of these compounds. In addition to DES and several of its analogues the indanyl derivatives now also have been shown to be active in both of these short-term assays, suggesting that the in vitro micronucleus formation and morphological cell transformation are causally related events.

Prostaglandin-H synthase containing cell lines as tools for studying metabolism and toxicity of xenobiotics

Prostaglandin-H synthase (PHS) can oxidize many xenobiotics and carcinogens (chemicals) in vitro and has been suggested to serve as an alternative metabolic activation enzyme, particularly in tissues low in monooxygenase activity. This article briefly describes types of PHS-catalyzed xenobiotic oxidations and discusses its determinants in cells. Methods employed for studying the involvement of PHS in the bioactivation of chemicals are reviewed with special emphasis on a cell culture system derived from ram seminal vesicles which has been used in studies on the metabolism and the genotoxicity of diethylstilbestrol.

Cell-cycle dependent micronucleus formation and mitotic disturbances induced by 5-azacytidine in mammalian cells

5-Azacytidine was originally developed to treat human myelogenous leukemia. However, interest in this compound has expanded because of reports of its ability to affect cell differentiation and to alter eukaryotic gene expression. In an ongoing attempt to understand the biochemical effects of this compound, we examined the effects of 5-azacytidine on mitosis and on micronucleus formation in mammalian cells. In L5178Y mouse cells, 5-azacytidine induced micronuclei at concentrations at which we and others have already reported its mutagenicity at the tk locus. Using CREST staining and C-banding studies, we showed that the induced micronuclei contained mostly chromosomal fragments although some may have contained whole chromosomes. By incorporating BrdU into the DNA of SHE cells, we determined that micronuclei were induced only when the compound was added while the cells were in S phase. Microscopically visible effects due to 5-azacytidine treatment were not observed until anaphase of the mitosis following treatment or thereafter. 5-Azacytidine did not induce micronuclei via interference with formation of the metaphase chromosome arrangement in mitosis, a common mechanism leading to aneuploidy. Supravital UV microscopy revealed that chromatid bridges were observed in anaphase and, in some cases, were sustained into interphase. In the first mitosis after 5-azacytidine treatment we observed that many cells were unable to perform anaphase separation. All of these observations indicate that 5-azacytidine is predominantly a clastogen through its incorporation into DNA.

Cytogenetic changes in primary, immortalized and malignant mammalian cells

Some chromosomes in transformed rat cells and somatic cell hybrids fail to display the presence of kinetochore proteins as detected by antikinetochore antibodies. Such chromosomes (K- chromosomes) may constitute a novel mechanism for the genesis of aneuploidy. We have analyzed primary, immortalized and malignant mammalian cells for the presence of kinetochore proteins and micronuclei. Our results suggest a correlation of the K- chromosome and micronucleus frequency with the variability in chromosome number. Upon in situ hybridization with the minor satellite and alpha satellite sequences some K- chromosomes showed a signal. This indicates that the observed lack of kinetochores is not necessarily due to a lack of centromeric DNA. We conclude that dislocated K- chromosomes may become incorporated into micronuclei which are prone to loss. Such events would be associated with the generation of aneuploidy.

SEMV cell cultures: a model for studies of prostaglandin-H synthase-mediated metabolism and genotoxicity of xenobiotics

Many xenobiotics and carcinogens are oxidized in vitro by prostaglandin-H synthase (PHS) in the presence of arachidonic acid or lipid peroxides. PHS has been suggested to serve as an alternative metabolic activation enzyme to the cytochrome P-450 isoenzymes, particularly in tissues low in monooxygenase activity. This article briefly describes PHS-catalyzed oxidations and reviews methods available for investigating the involvement of PHS in mediating the toxicity of certain chemicals. Since in vivo systems impose certain limitations on such studies, particular emphasis is placed on a specialized cell system which can serve as a model for investigating the PHS-dependent bioactivation of xenobiotics, its determinants and toxicological significance. This is exemplified by experiments conducted with the carcinogenic estrogen diethylstilbestrol (DES) in cell cultures derived from ram seminal vesicles which express PHS but lack monooxygenase activity. DES is oxidized by PHS in seminal vesicle (SEMV) cells and DES can induce micronuclei in this model; both processes are inhibited by indomethacin. These data support the hypothesis that PHS-dependent oxidation of DES plays a role in its genotoxicity.

Genotoxicity studies of benzofuran dioxetanes and epoxides with isolated DNA, bacteria and mammalian cells

1,2-Dioxetanes, very reactive and high energy molecules, are involved as labile intermediates in dioxygenase-activated aerobic metabolism and in physiological processes. Various toxicological tests reveal that dioxetanes are indeed genotoxic. In supercoiled DNA of bacteriophage PM2 they induce endonuclease-sensitive sites, most of them are FPG protein-sensitive base modifications (8-hydroxyguanine, formamidopyrimidines). Pyrimidine dimers and sites of base loss (AP sites) which were probed by UV endonuclease and exonuclease III are minor lesions in this system. While the alkyl-substituted dioxetanes do not show any significant mutagenic activity in different Salmonella typhimurium strains, heteroarene dioxetranes such any significant mutagenic activity in different Salmonella typhimurium strains, heteroarene dioxetanes such as benzofuran and furocoumarin dioxetanes are strongly mutagenic in S. typhimurium strain TA100. DNA adducts formed with an intermediary alkylating agent appear to be responsible for the mutagenic activity of benzofuran dioxetane. We assume that the benzofuran epoxides, generated in situ from benzofuran dioxetanes by deoxygenation are the ultimate mutagens of the latter, since benzofuran epoxides are highly mutagenic in the S. typhimurium strain TA100 and they form DNA adducts, as detected by the 32P-postlabelling technique. Our results imply that the type of DNA damage promoted by dioxetanes is dependent on the structural feature of dioxetanes. Furthermore, the direct photochemical DNA damage by energy transfer, i.e., pyrimidine dimers, plays a minor role in the genotoxicity of dioxetanes. Instead, photooxidation dominates in isolated DNA, while radical damage and alkylation prevail in the cellular system.

High capacity in vitro micronucleus assay for assessment of chromosome damage: results with quinolone/naphthyridone antibacterials

A high capacity in vitro micronucleus assay was developed to evaluate the ability of selected 6-fluorinated quinolone and naphthyridone antibacterial compounds to induce micronuclei (MN) in vitro in V79 Chinese hamster lung cells. Log-phase cells in six-well cluster dishes were exposed for 3 h in the absence of S9 to 34 compounds. After treatment, cells were refed with media containing cytochalasin B, incubated for 16 h, and harvested for cell-cycle kinetics (CCK) and MN analyses. The quinolones tested were grouped according to the substituent at the 8-position. All 4 compounds having a halogen substitution at position 8, five of the six 8-trifluoromethyl quinolones, and all eight 8-methoxy-substituted compounds induced a significant increase in MN. Only 5 of the 10 naphthyridone compounds tested, having a variety of substituents at the 7-position, were inducers of MN and the overall magnitude of the response was less than with the quinolones. The minimum clastogenic concentration for the quinolones ranged from 4 to 400 micrograms/ml and for the naphthyridones this range was from 22.5 to 100 micrograms/ml. In the groups examined, napthyridone compounds were less likely than quinolones to induce in vitro MN, particularly when the substituent at the 7-position in the naphthyridone contains some bulk (methyl groups) around the amine side-chain. Most of the quinolones tested induced MN, irrespective of the substituents at positions 7 or 8.

Diethylstilboestrol: II, pharmacology, toxicology and carcinogenicity in experimental animals

Diethylstilboestrol (DES) exerts several toxic effects in experimental animals, by mechanisms which are still unclear. The genotoxicity of the drug has been attributed to a quinone metabolite and is mainly clastogenic, including sister chromatid exchange, unscheduled DNA synthesis, chromosomal aberrations, disruption of mitotic spindle and aneuploidy. There is evidence that genotoxic effects may occur also transplacentally. Intrauterine and early postnatal exposure to DES can cause a variety of dysplasias. In the offspring of female mice exposed to DES during pregnancy, histological changes are observed in the vaginal and cervical epithelium, the endometrium, the ovary, the testis and the epididymis. Prenatal exposure of rats to DES led to decreased litter size and to urethrovaginal cloaca, penile and testicular hypoplasia, and cryptorchidism. Vaginal ridging, vaginal adenosis, testicular hypoplasia and cryptorchidism have been observed in rhesus monkeys following prenatal exposure. There is sufficient evidence that diethylstilboestrol is carcinogenic in experimental animals, after either prenatal or postnatal exposure. Mice show a similar type of carcinogenicity to that observed in humans, target organs being vagina, cervix, uterus, ovary, mammary gland and testis. In rats, prenatal exposure to DES produces mostly mammary and pituitary tumours, but also some tumours of the vagina. Hamsters develop tumours of vagina, cervix, endometrium, epididymis, testis, liver and kidney. DES induces ovarian papillary carcinomas in dogs, and malignant uterine mesotheliomas in squirrel monkeys. Some experimental evidence points to the possibility of a transgenerational carcinogenic effect, since prenatal treatment of mice with DES is followed by an increased incidence of uterine and ovarian carcinomas in the second-generation descendants. Experimental results could have been used to predict the adverse effects of DES observed in humans in the early 1970s: DES had been reported to be carcinogenic in mice in the 1930s, while experiments in the 1960s had provided evidence that exposure during pregnancy could result in an increased cancer risk in the progeny.

5-azacytidine induces micronuclei in and morphological transformation of Syrian hamster embryo fibroblasts in the absence of unscheduled DNA synthesis

It is known that 5-azacytidine (5-AC) induces tumors in several organs of rats and mice. The mechanisms of these effects are still poorly understood although it is known that 5-AC can be incorporated into DNA. Furthermore, it can inhibit DNA methylation. The known data on its clastogenic and/or gene mutation-inducing potential are still controversial. Therefore, we have investigated the kinds of genotoxic effects caused by 5-AC in Syrian hamster embryo (SHE) fibroblasts. Three different endpoints (micronucleus formation, unscheduled DNA synthesis (UDS) and cell transformation) were assayed under similar conditions of metabolism and dose at target in this cell system. 5-AC induces morphological transformation of SHE cells, but not UDS. Therefore, 5-AC does not seem to cause repairable DNA lesions. Furthermore, our studies revealed that 5-AC is a potent inducer of micronuclei in the SHE system. Immunocytochemical analysis revealed that a certain percentage of these contain kinetochores indicating that 5-AC may induce both clastogenic events and numerical chromosome changes.

Interphase cytogenetics of the ICF syndrome

Interphase behaviour of centromeric heterochromatin of chromosomes 1 and 16 has been investigated in lymphocytes and fibroblasts of patients with ICF syndrome and of normal subjects with non-isotopic in situ hybridization, using the satellite II-related probe pHuR 195. We found evidence for interphase somatic pairing in ICF lymphocytes with a frequency higher than that found in normal cells. Lymphocytes of ICF patients showed nuclear protrusions and micronuclei and these nuclear abnormalities consistently involved a hybridization signal. Somatic pairing was also present in fibroblasts, but with frequencies similar in normal and ICF subjects. The fibroblasts do not have the major chromosomal abnormalities found in lymphocytes. The degree of heterochromatin condensation in fibroblasts was lower than that in lymphocytes and we postulate that the more decondensed state of chromocentres in the fibroblasts could be the reason for the absence of the major chromosomal abnormalities.

Testicular toxicity and mutagenicity of steroidal and non-steroidal estrogens in the male mouse

The mutagenicity and toxicity of diethylstilbestrol (DES), 17 beta-estradiol and zeranol on the male mouse germ cells were investigated with meiotic micronucleus assays in vivo and in vitro, sperm-head abnormality test and morphometry. Further, the developmental effects of DES on testicular morphology were explored. Micronucleus induction was observed at 10(-7) M concentration of DES and 17 beta-estradiol in vitro, but other treatments yielded negative results. The micronucleus assay in vivo revealed a small number of micronuclei in early haploid spermatids 17 days after a single subcutaneous injection of DES 50 mg/kg, whereas estradiol and zeranol gave negative results. The sperm-head abnormality rates were significantly elevated 5 weeks after treatments with high doses of DES, 17 beta-estradiol and zeranol, and testicular morphometry revealed transient changes in the volume densities of testicular tissue components. Prenatal and neonatal estrogen administration resulted in permanent alterations in seminiferous epithelium and dilatation of the rete testis, but did not affect micronucleus or sperm-head abnormality rates. The mutagenicity and toxicity of hormones in the mouse testis paralleled the hormonal activity of these compounds. Early estrogenization was the most sensitive toxicity test, followed by in vitro meiotic micronucleus induction, whereas the sperm-head abnormality assay and morphological analysis did not reveal subtle changes.