The Induction of Gene Mutations and Micronuclei by Oxiranes and Siloranes in Mammalian Cells in vitro

Oxiranes and siloranes are candidate molecules for the development of composite materials with low shrinkage. Since some of these molecules are highly reactive, they could lead to adverse biological effects from underlying genetic mechanisms. Therefore, we analyzed the formation of micronuclei (chromosomal aberrations) and the induction of gene mutations (HPRT assay) in mammalian cells. The numbers of micronuclei induced by the oxirane di(cyclohexene-epoxidemethyl)ether (Eth-Ep) at low concentrations (10 μM) were about five-fold higher than controls. The related compound epoxy cyclohexyl methyl-epoxy cyclo-hexane carboxylate (Est-Ep) was less effective. The activity of diglycidylether of bisphenol A (BADGE) was even lower but similar to the most reactive silorane, di-3,4-epoxy cyclohexylmethyl-dimethyl-silane (DiMe-Sil). No induction of micronuclei was detected in the presence of a rat liver homogenate (S9). Est-Ep and Eth-Ep also induced gene mutations. Our analyses indicated low mutagenic potentials of siloranes; however, some oxiranes induced strong effects at two genetic endpoints.

Influence of DNA double‐strand break rejoining on clonogenic survival and micronucleus yield in human cell lines

PURPOSE

To examine the role of DNA double-strand break (DSB) rejoining in cell survival and micronucleus yield after 60Co gamma-irradiation.

MATERIALS AND METHOD

Thirteen human cell lines (six glioblastoma, five prostate, one melanoma, one squamous cell carcinoma) were irradiated with 60Co gamma-rays to doses of 0-10Gy for cell survival and micronucleus measurements and 0-100Gy for DSB rejoining. Measurements were performed using standard clonogenic, micronucleus and constant-field gel electrophoresis assays.

RESULTS

Radioresistance and micronucleus yield were positively correlated (r=0.74, p=0.004). A significant cell type-dependent correlation was demonstrated between total (0-20 h) DSB rejoining and cell survival (r=0.86, p=0.03 for glioblastomas; r=0.79, p=0.04 for other cell lines), with more resistant cell lines showing higher levels of DSB rejoining. No relationship was apparent between fast (0-2 h) or slow (2-20 h) DSB rejoining and clonogenic survival. While there was no relationship between total or slow DSB rejoining and micronucleus yield, a significant and cell type-specific correlation emerged between fast rejoining and micronucleus yield for the glioblastomas (r=0.89, p=0.04) and other cell lines (r=0.76, p=0.04). Cell lines with higher levels of DSB rejoining within 2 h of irradiation showed higher yields of micronuclei.

CONCLUSION

Fast DSB rejoining, possibly through interaction with slow DSB rejoining, appears to play an important role in the formation of micronuclei. However, total DSB rejoining reflects intrinsic radiosensitivity. Consideration of differences in DSB rejoining kinetics might contribute to a better understanding of the significance of cell survival and micronucleus data in the clinical and radiation protection setting.

Role of micronucleus-limited DNA in programmed deletion of mse2.9 during macronuclear development of Tetrahymena thermophila

Extensive programmed DNA rearrangements occur during the development of the somatic macronucleus from the germ line micronucleus in the sexual cycle of the ciliated protozoan Tetrahymena thermophila. Using an in vivo processing assay, we analyzed the role of micronucleus-limited DNA during the programmed deletion of mse2.9, an internal eliminated sequence (IES). We identified a 200-bp region within mse2.9 that contains an important cis-acting element which is required for the targeting of efficient programmed deletion. Our results, obtained with a series of mse2.9-based chimeric IESs, led us to suggest that the cis-acting elements in both micronucleus-limited and macronucleus-retained flanking DNAs stimulate programmed deletion to different degrees depending on the particular eliminated sequence. The mse2.9 IES is situated within the second intron of the micronuclear locus of the ARP1 gene. We show that the expression of ARP1 is not essential for the growth of Tetrahymena. Our results also suggest that mse2.9 is not subject to epigenetic regulation of DNA deletion, placing possible constraints on the scan RNA model of IES excision.

Genotoxicity biomarkers in Mytilus galloprovincialis: wild versus caged mussels

A biomonitoring programme of wild and caged mussels (Mytilus galloprovincialis) was carried out at four selected sites along the Ligurian coast: Cornigliano, Voltri, Zinola, and Sanremo (Italy). Mussels of a very narrow size range were left in situ for 30 days. Adult specimen of mussels from natural substrates were collected in the same areas. Animals from a mussel farm located in La Spezia were used as controls. Micronucleus frequency and DNA single strand breaks, evaluated by alkaline elution, were used as biomarkers of genotoxicity. Mussels were also analyzed for polycyclic aromatic hydrocarbons (PAH) and heavy metals (Hg and Cd). Different gradients of PAH and metal concentrations were detected in tissues of mussels from different samplings sites. A weak correlation was found between single strand breaks and PAH content while MN frequency correlated with Hg concentration (r = 0.28, P < 0.002). A clear distinction between the sites, allowing classification along a pollution gradient (Sanremo < Zinola < Voltri < Cornigliano) was demonstrated by the analysis of genotoxicity parameters. The obtained results suggested that the micronucleus assay compared with DNA damage determination by alkaline elution allow to better discriminate the selected sites. DNA damage expressed as constant of elution (k ml(-1) x 10(3)) ranges from 30 +/- 9.6 to 89.60 +/- 40.10, and micronuclei frequency from 1.78 +/- 1.04 to 24.4 +/- 12.9, in control animals and in mussels from the most polluted site, respectively. Wild mussels accumulated significant concentrations of chemicals and showed a higher induction of chromosomal damage than caged mussels, expressed as micronuclei frequency. Caged mussels showed higher level of DNA damage than wild mussels, probably as a result of recent exposure. DNA damage was higher in September than in May, as opposed to micronuclei frequency being higher in May than in September. Endogenous and exogenous factors, such as change of pollutant input levels or compositions, could be considered the cause of such variability.

Functional consequences of ATM sequence variants for chromosomal radiosensitivity

The ATM [for ataxia-telangiectasia (A-T) mutated] protein plays a key role in the detection and cellular response to DNA double-strand breaks. Several single-nucleotide polymorphisms (SNPs) have been described in the ATM gene; however, their association with cancer risk or radiosensitivity remains to be fully established. In this study, the functional consequences of specific ATM SNPs on in vitro radiosensitivity, as assessed by micronuclei (MN) formation, were measured in lymphoblastoid cell lines established from 10 breast cancer (BC) patients carrying different ATM missense SNPs, six A-T patients, six A-T heterozygotes (A-T het), and six normal individuals. The BC, A-T het, and A-T cell line groups showed significantly higher mean levels of MN formation after exposure to ionizing radiation (IR) than did the group containing normal cell lines, with similar levels in the BC and A-T het groups. Within the BC lines studied, the group composed of the six carrying the linked 2572T>C (858F>L) and 3161C>G (1054P>R) variants had a higher level of MN after IR exposure compared to that observed in the remaining four BC or in the normal cell lines. This increase was not related to the constitutive ATM mRNA level, which was similar in these BC and the normal cell lines. Our results indicate that alterations in the ATM gene, including the presence of heterozygous mutations and the 2572C and 3161G variant alleles, are associated with increased in vitro chromosomal radiosensitivity, perhaps by interfering with ATM function in a dominant-negative manner.

Anti-genotoxic effects of tea catechins against reactive oxygen species in human lymphoblastoid cells

Using the cytokinesis-block micronucleus assay in WIL2-NS cells, we investigated the effects of six tea constituents, (-)-epigallocatechin-3-O-gallate (EGCg), (-)-epicatechin-3-O-gallate (ECg), (-)-epigallocatechin (EGC), (-)-epicatechin (EC), (+)-catechin (+C) and gallic acid (GA), on chromosomal damage in two ways; induction by each component on its own and prevention against treatment of reactive oxygen species (ROS). None of the tea constituents induced chromosomal damage at <10 microM. On the other hand, EGCg, EGC, ECg, +C and GA prevented H(2)O(2)-induced chromosomal damage in a dose-dependent manner with a significant effect detected at 1 microM. Chromosomal damage induced by tert-butylhydroperoxide was apparently prevented by EGCg and ECg at 0.3 microM, but not by EGC and GA even at 10 microM, suggesting that the galloyl group linked to flavan-3-ol is needed for the observed protective effect. These results suggest that physiological concentration of tea constituents are not genotoxic but rather anti-genotoxic against ROS, although their preventive effects are slightly different depending on their chemical structure.

Telomere erosion and chromosomal instability in cells expressing the HPV oncogene 16E6

Progression to advanced-stage cervical carcinomas is characterized by a recurrent pattern of chromosomal rearrangements. Structural chromosome rearrangements are generated through the fusion of broken chromosome ends. These chromosome breaks may be induced by mutagenic agents such as ionizing radiation, or chromosome ends may be exposed through extensive telomere shortening. The human papilloma virus oncogene 16E6 induces telomerase activity in human keratinocytes, a model system for cervical tumor formation. The present study explores the relationship between 16E6 expression, telomerase activity, and chromosomal instability. We show that the frequency of anaphase bridges is dependent on the level of telomerase activity in 16E6/E7-expressing clones, and is the result of telomere shortening. High frequencies of anaphase bridges, associated with low telomerase activity, correlate with increased chromosome instability. Anaphase bridge formation is also associated with the presence of micronuclei, which are shown to contain unstable chromosomes frequently involved in rearrangements. As anaphase bridges are observed in both high and low telomerase 16E6/E7 clones, but not in hTERT-expressing control clones, expression of 16E6 in these immortalized clones is not sufficient to stabilize shortened telomeres completely. We suggest a model in which HPV-induced tumorigenesis may be dependent on persistent bridge-breakage-fusion cycles that allow for continued genomic rearrangements.

Investigation of genotoxic effect of ultrasound in cases receiving therapeutic ultrasound by using micronucleus method

In 1991, reported that therapeutic ultrasound (US) did not induce sister chromatid exchanges (SCEs) in patients whereas, in 1984, reported that each of 10 patients exposed to therapeutic US had a statistically significant increase in SCEs. The present study was planned to investigate if there was chromosomal damage resulting from therapeutic US by using a micronucleus (MN) method, and to counter the lack of reports in this area over the past 10 years. A total of 20 female volunteers were included in the study; 10 of them with low back pain (mechanical low back pain and facet syndrome) were treated with US and 10 healthy cases constituted the control group. Patients with low back pain received 10 sessions of US therapy at an intensity of 2 W/cm(2) and a frequency of 1 MHz for 10 min and patients in the control group received sham US therapy for 10 min. Peripheral blood taken before and after the fifth and tenth applications of US therapy was cultured for MN frequencies both for the treatment and the control groups. The scores of MN assessed before the therapy were compared with those at the end of the fifth session and the end of the tenth session in the treatment and the control groups. Pretreatment, end of the fifth session and end of the tenth session MN frequencies were compared between the treatment and the control groups. There was no statistically significant difference in MN frequencies between pretreatment and fifth session or pretreatment and tenth session in both groups. Nor was there any significant difference in the MN frequencies of the treatment and control groups between pretreatment, fifth session and tenth session evaluations. In conclusion, we observed that therapeutic US did not induce increases in MN frequency, which are a sign of cytogenetic damage.

Comparative evaluation of background micronucleus frequencies in domestic mammals

Exposure of human alimentation-destined animals to toxic substances can be an important risk factor for human health. Mutagenicity tests represent a good method for genotoxic effect evaluation of environmental pollutants. The micronucleus frequency in peripheral blood and bone marrow erythrocytes has been evaluated in four domestic Ungulate species (ox, sheep, swine and horse). For each species two or three groups of animals coming from Italy and other European countries were analysed and the results indicate a relatively low mean frequency of micronucleated erythrocytes (ME), both in peripheral blood and bone marrow. The comparison between these two frequencies in the four species studied shows that the ME frequency in sheep and horse is significantly higher in peripheral blood than in bone marrow, whereas in bovines it is higher in the bone marrow, and in swine the difference is not significant. These results could indicate that in ox and swine the spleen is involved in ME removal from the peripheral circulation, as is known for other species including man. Nevertheless, it cannot be excluded that the same occurs in the other two species, since they exhibit a relatively low peripheral blood ME frequency as well. Further studies on domestic mammals are needed to clarify the spleen function and verify the use of the peripheral blood micronucleus test for genotoxic biomonitoring. At present, the application of the micronucleus test to the bone marrow seems a more suitable method, but, being invasive, it can be used only as a control system of animal hygiene and health, in addition to the routine tests, rather than for biomonitoring.

Inactivation of hCDC4 can cause chromosomal instability

Aneuploidy, an abnormal chromosome number, has been recognized as a hallmark of human cancer for nearly a century; however, the mechanisms responsible for this abnormality have remained elusive. Here we report the identification of mutations in hCDC4 (also known as Fbw7 or Archipelago) in both human colorectal cancers and their precursor lesions. We show that genetic inactivation of hCDC4, by means of targeted disruption of the gene in karyotypically stable colorectal cancer cells, results in a striking phenotype associated with micronuclei and chromosomal instability. This phenotype can be traced to a defect in the execution of metaphase and subsequent transmission of chromosomes, and is dependent on cyclin E--a protein that is regulated by hCDC4 (refs 2-4). Our data suggest that chromosomal instability is caused by specific genetic alterations in a large fraction of human cancers and can occur before malignant conversion.

Spontaneous chromosome loss and colcemid resistance in lymphocytes from patients with myotonic dystrophy type 1

Myotonic Dystrophy type 1 (DM1) is one of the many inherited human diseases whose molecular defect is the expansion of a trinucleotide DNA sequence. DM1 shares with fragile X syndrome (FMR1), another "unstable triplet syndrome", several molecular features not present in the remaining triplet diseases. As FMR1 is also characterised by chromosome instability at the site of the expanded triplet, lymphocytes from DM1 patients and healthy donors were cultured for micronucleus (MN) analysis, in order to verify if DM1 is also prone to chromosome instability. A FISH analysis was also carried out to detect the presence of centromeric sequences in the observed MN. The data indicate that DM1 patients present a percentage of centromere-positive MN significantly higher than controls, suggesting that chromosome loss is the main mechanism underlying the origin of the increased spontaneous instability. To further assess the proneness to instability of cells of DM1 patients, cultures from patients and controls were treated in vitro with growing concentrations of two different mutagens: colcemid, a "pure" aneugen compound whose target is tubulin, and mytomicin C, a strong clastogen. The results show that the patient group is significantly less sensitive to colcemid. These data, together with FISH analysis, suggest the presence, in DM1 patients, of an already damaged tubulin, which becomes no more sensitive to the effect of colcemid and which could be the main defect underlying the aneugenic effects in DM1.

Micronuclei frequency in children exposed to environmental mutagens: a review

Cytogenetic monitoring has been traditionally used for the surveillance of populations exposed to genotoxic agents. In recent years sensitivity problems emerged in surveys of populations exposed to low levels of mutagens, and therefore alternative approaches have been explored. Biomonitoring studies in children are a promising field, since because of evident differences in the uptake, metabolism, distribution and excretion of mutagens this population seems to be more susceptible than adults. Further, the effect of major confounders such as cigarettes smoking, occupation, life-style, and dietary factors plays a minor role. Among cytogenetic assays, the micronucleus assay (MN) has several advantages and is increasingly used. A review was then carried out to synthesize the published data on the occurrence of MN in children and adolescents (age range 0-18 years), and to assess the impact of genotoxic exposure on MN frequency. Overall, 20 papers from international literature and 8 Russian papers were included. An effect of age was found within this age range, while the influence of gender on MN frequency was irrelevant. These results were confirmed by the re-analysis of data for 448 children selected from the HUMN database. An effect of chronic and infectious diseases on MN levels has been reported by various authors. Most studies describing the effect of exposure to genotoxic agents (ionizing radiation, chemicals, drugs, environmental tobacco smoke) found an increase of MN in exposed children. The limited number of published papers indicates that the conduct of properly designed studies on the effect of environmental pollutants in children may be difficult. This review confirmed the usefulness of MN assay in biomonitoring studies conducted in children, revealing that in many circumstances investigating children increases the sensitivity of the study, even with low dose exposures.

Chromosomal aberrations in Crepis capillaris cells detected by FISH

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

Inhibitory effect of local ischaemic preconditioning in total body irradiated rats

The aim of this study was to explore the relationship between local ischaemic preconditioning and the effectiveness of fractionated radiotherapy. The rat serum, bone marrow, and small intestine were examined for oxidative changes induced by total body irradiation with gamma rays with applied local ischaemic preconditioning immediately before irradiation. Serum concentrations of TBA-RS examined 12 hours after the last irradiation did not reveal any differences among the groups of animals analyzed. Twenty-four hours after the last dose of irradiation, the serum concentrations of TBA-RS varied in particular groups (P<0.0001). The concentration of triglycerides in the serum of local preconditioned ischaemia and irradiated animals showed a reversed shape similar to the TBA-RS fluctuation (P<0.003). The level of uric acid in the serum of animals treated only with radiation is slightly higher than the level of this acid in the serum of the local preconditioned ischaemia radiation group (P<0.58). The number of bone marrow polychromatic erythrocytes did not appear to differ substantially in both irradiated groups. At the first 12 hours after irradiation, the frequency of micronucleated polychromatic erythrocytes is significantly different in the bone marrow of both groups either in combination with ischaemic preconditioned radiation or with radiation alone (P<0.0002). In irradiated animals without ischaemic preconditioning, on the 3rd day after irradiation the number of crypts increased and in the next days decreased achieving the level of the control group on the 7th day. Irradiated rats with local ischaemic preconditioning did not reveal an increase in the number of crypts. The difference was statistically significant (P<0.05). These data indicate that the local ischaemic preconditioning modifies the radiation peroxidising effects through inhibition of free radical-dependent lipid peroxidation and, probably, other unrecognized mechanisms.

Micronuclei to detect in vivo chemotherapy damage in a p53 mutated solid tumour

Apoptosis induction and micronuclei formation were compared following cytotoxic treatments in two rat glioma differing in p53 integrity. In vitro, micronuclei emergence but not apoptosis was linked to the p53 mutated status. In vivo, micronuclei assays were more sensitive to evaluate DNA damage induced by chemotherapy in a p53-mutated solid tumour.

Micronuclei in peripheral blood lymphocytes as a possible cancer risk biomarker: a cohort study of occupationally exposed workers in Croatia

AIM

To describe the cohort of Croatian workers monitored for micronuclei in peripheral blood lymphocytes and validate predictive value of micronuclei for the risk of cancer development.

METHODS

Between 1985 and 1999, peripheral blood lymphocytes were analyzed with in vitro micronucleus assay in a cohort of 200 subjects occupationally exposed to genotoxic agents. The follow-up for cancer incidence and mortality was performed through the Croatian National Cancer Registry and records of occupational medicine physicians. Micronucleated cell frequency values were compared by Kruskal-Wallis test.

RESULTS

The median micronucleated cell frequency value in the cohort was 49 (range, 30-79) per thousand cells. Micronucleated cell frequency was significantly higher in men than in women, which could be attributed to the different distribution of exposures. Micronucleated cell frequency increased with age for both sexes. Smoking habit had no influence on micronucleated cell frequency. The follow-up identified four cases of cancer. Three of them belonged to the highest micronucleated cell frequency tertile.

CONCLUSION

Due to a small number of cancer cases, the predictive value of micronuclei for the risk of cancer development in the cohort of Croatian workers was not estimated, but 4 identified cases were more than expected in a similar non-exposed group. The Croatian cohort will contribute to the pooled analysis of the current European study of predictive value of micronuclei for the risk of cancer development.

An assessment of the genotoxicity of 2-hydroxy-1,4-naphthoquinone, the natural dye ingredient of Henna

2-Hydroxy-1,4-naphthoquinone (HNQ; Lawsone; CAS 83-72-7) is the principal natural dye ingredient contained in the leaves of Henna (Lawsonia inermis). Published genotoxicity studies on HNQ suggested it was a weak bacterial mutagen for Salmonella typhimurium strain TA98 or was more clearly mutagenic for strain TA 2637, both in the presence of metabolic activation. HNQ was unable to induce sex-linked recessive lethal mutations in Drosophila melanogaster. However, a small increase in micronucleus frequency was reported in the bone marrow of mice at a single mid-range dose level, 24h after intraperitoneal injection. In view of the wide use of Henna hair dyes it was deemed necessary to conduct a thorough investigation, under Good Laboratory Practice conditions, of the genotoxicity of HNQ. HNQ was non-mutagenic in bacterial (Ames test) or mammalian (V79 hprt) assays. It was borderline positive in a mouse lymphoma tk mutation assay and a chromosome aberration test (CHO cells), results that may reflect a similar clastogenic mechanism. Negative in vivo genotoxicity results were noted in the rat hepatocyte in vivo/in vitro UDS test, in peripheral lymphocytes (chromosome aberrations) of rats receiving repeated oral doses of HNQ at the MTD for 28 days, and in mouse and hamster bone marrow chromosome aberration tests. However small, but statistically significant increases in the incidence of bone marrow micronuclei were observed in two out of five tests at 72 h after dosing, but not at 24 or 48 h. There was evidence of haematotoxicity at 72 h, which may have been enhanced by the vehicle (DMSO) used in the positive tests. As erythropoiesis and administration of haematotoxic agents are known to induce small increases in the frequency of bone marrow micronuclei, typically at delayed sampling times, the data suggest that the positive 72 h response produced by HNQ is consistent with stimulation of haematopoiesis subsequent to haematological toxicity of HNQ, and not due to a DNA-reactive mechanism. Overall, the weight of evidence suggests that Henna and HNQ pose no genotoxic risk to the consumer.

Sister chromatid exchanges and micronuclei analysis in lymphocytes of men exposed to simazine through drinking water

In some cities of the autonomous community of Extremadura (south-west of Spain), levels of simazine from 10 to 30 ppm were detected in tap water. To analyse the possible effect of this herbicide, two biomarkers, sister chromatid exchanges (SCE) and micronuclei (MN), were used in peripheral blood lymphocytes from males exposed to simazine through drinking water. SCE and MN analysis failed to detect any statistically significant increase in the people exposed to simazine when compared with the controls. With respect to high frequency cells (HFC), a statistically significant difference was detected between exposed and control groups.

Oxidative stress in cultured cerebral endothelial cells induces chromosomal aberrations, micronuclei, and apoptosis

There is evidence accumulating that brain microvasculature is involved critically in oxidative stress-mediated brain damage. Cultured cerebral microvascular endothelial cells were used to demonstrate the cytotoxic and genotoxic effects elicited by hypoxia/reoxygenation and DMNQ treatment in vitro. In addition, the effect of glucose deprivation during oxidative insult was assessed. The parameters determined were: 1) chromosomal aberrations; 2) induction of micronuclei; and 3) apoptosis. Our results indicate that both the exposure of the cerebral endothelial cells to 24 hr of hypoxia followed by 4 hr of reoxygenation, and treatment with the redox cycling quinone DMNQ, increased markedly the occurrence of chromosomal aberrations and micronuclei. It was found that expression of p53 was induced by oxidative stress, particularly when glucose had been omitted from the culture medium. Aglycemic culture conditions in general exacerbated the cytotoxic effects of oxidative insults, as evidenced by the increase in apoptotic cells and the decrease in the mitotic index. Interestingly, neither an elevation of cell lysis nor an increase in necrosis has been observed during our experiments. In summary, our data indicate that oxidative stress exerts considerable genotoxic and cytotoxic effects on cerebral endothelial cells, which might contribute to the progression of tissue damage in the central nervous system.

Does a dose-response relationship reduce sensitivity to hidden bias?

It is often said that an important consideration in judging whether an association between treatment and response is causal is the presence or absence of a dose-response relationship, that is, larger ostensible treatment effects when doses of treatment are larger. This criterion is widely discussed in textbooks and is often mentioned in empirical papers. At the same time, it is well known through both important examples and elementary theory that a treatment may cause dramatic effects with no dose-response relationship, and hidden biases may produce a dose-response relationship when the treatment is without effect. What does a dose-response relationship say about causality? It is observed here that a dose-response relationship may or may not reduce sensitivity to hidden bias, and whether it has or has not can be determined by a suitable analysis using the data at hand. Moreover, a study without a dose-response relationship may or may not be less sensitive to hidden bias than another study with such a relationship, and this, too, can be determined from the data at hand. An example concerning cytogenetic damage among professional painters is used to illustrate.

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.

Association of HSP70 and genotoxic damage in lymphocytes of workers exposed to coke-oven emission

Heat shock proteins (Hsps) have been reported to protect cells, tissues, and organisms against damage from a wide variety of stressful stimuli. Whether they protect against deoxyribonucleic acid (DNA) damage in individuals exposed to environmental stresses and chemical carcinogens is unknown. In the study, we investigated the association between Hsp70 levels (the most abundant mammalian Hsp) and genotoxic damage in lymphocytes of workers exposed to coke-oven emission using Western dot blot and 2 DNA damage assays, the comet assay and the micronucleus test. The data show that there is a significant increase in Hsp70 levels, DNA damage score, and micronucleus rates in lymphocytes of workers exposed to coke-oven emission as compared with the control subjects. Furthermore, there was a significant negative correlation of Hsp70 levels with DNA damage scores in the comet assay (r = -0.663, P < 0.01) and with micronucleus rates (r = -0.461, P < 0.01) in the exposed group. In the control group, there was also a light negative correlation between Hsp70 with DNA damage and micronuclei rate (r = -0.236 and r = 0.242, respectively), but it did not reach a statistically significant level (P > 0.05). Our results show that individuals who had high Hsp70 levels generally showed lower genotoxic damage than others. These results suggest a role of Hsp70 in the protection of DNA from genotoxic damage induced by coke-oven emission.

Induction of micronuclei in wild-type and p53(+/-) transgenic mice by inhaled bromodichloromethane

Bromodichloromethane (BDCM) is commonly present in trace amounts in drinking water as a disinfection by-product. BDCM has been shown to be carcinogenic in mice and rats when given by gavage at relatively high doses. Genotoxic activity as well as induced regenerative cell proliferation may contribute to the carcinogenic potential of BDCM. The purpose of the current studies was to evaluate the ability of BDCM to induce micronuclei (MN) in bone marrow and blood of wild-type and p53(+/-) mice on the C57BL/6 and FVB/N genetic backgrounds using the inhalation route of exposure. Toxicity studies were being conducted in this laboratory with inhaled BDCM to select doses for longer-term cancer bioassays using wild-type and p53(+/-) transgenic mice on different genetic backgrounds. Bone marrow samples from these experiments were evaluated for the induction of MN after 1 and 3 weeks of exposure. Accumulation of MN in the peripheral blood was also evaluated at the 13-week time point of a cancer study with the p53(+/-) mice. For the 1-week time point, male C57BL/6 wild-type and p53(+/-) mice and FVB/N wild-type and p53(+/-) mice were exposed daily for 6h per day for 7 consecutive days to atmospheric BDCM concentrations of 0, 1, 10, 30, 100, or 150 ppm. In a second experiment, mice were exposed daily for 6h per day for 3 weeks to atmospheric BDCM concentrations of 0, 0.5, 1, 3, 10, or 30 ppm. Resulting levels of polychromatic erythrocytes (PCE) containing MN were assessed in the bone marrow. For all of the 1- and 3-week exposure groups, the only statistically significant increase in the percentage of bone marrow PCE cells containing MN was in the 1-week 100 ppm BDCM exposure group in the FVB/N wild-type mice (control 0.26% versus exposed 1.16%). C57BL/6 p53(+/-) mice and FVB/N p53(+/-) mice were exposed daily for 6 h per day for 13 weeks to atmospheric BDCM concentrations of 0, 0.5, 3, 10, or 15 ppm. MN were quantified in samples of peripheral blood. Statistically significant increases in the percentage of peripheral blood NCE cells containing MN were seen at the highest BDCM exposure group of 15 ppm in both the C57BL/6 p53(+/-) strain (control 0.36% versus exposed 0.67%) and the FVB/N p53(+/-) strain (control 0.36% versus exposed 0.86%). These data indicate weak induction of MN by BDCM, but only at high atmospheric concentrations relative to normal environmental exposures and with extended periods of exposure. Although comparisons are difficult because responses were negative or marginal, the p53 genotype or the genetic background did not appear to substantially alter susceptibility to the genotoxic effects of BDCM.

Cytogenetic alterations in lymphocytes of Alzheimer's disease and Parkinson's disease patients

We investigated the presence of cytogenetic alterations in peripheral blood lymphocytes of Alzheimer's disease (AD) and Parkinson's disease (PD) patients. Detection of spontaneous structural and/or numerical chromosome damage has been assessed by micronucleus (MN) assay coupled with fluorescence in situ hybridization (FISH). The cytogenetic investigation was performed on 22 AD patients, 18 PD patients, and 20 controls. The spontaneous frequencies of micronuclei (MN) in human lymphocytes of both AD and PD patients were significantly higher than in controls. The majority of MN was composed of whole chromosomes in AD patients, while a prevalence of MN arising from chromosome breakage was observed in PD patients. Different molecular mechanisms underlie cytogenetic alterations observed in peripheral lymphocytes of AD and PD patients.

Micronuclei, nucleoplasmic bridges and nuclear buds induced in folic acid deficient human lymphocytes-evidence for breakage-fusion-bridge cycles in the cytokinesis-block micronucleus assay

We have validated the analysis of nucleoplasmic bridges (NPBs) and nuclear buds as biomarkers of genomic instability within the cytokinesis-block micronucleus assay in long-term lymphocyte cultures. Lymphocytes from 20 subjects were cultured in medium containing 12-120 nM folic acid for 9 days. Binucleate cells were scored for micronuclei (MN), NPBs and nuclear budding on day nine after 24h incubation in the presence of the cytokinesis inhibitor cytochalasin-B. Folic acid concentration was correlated significantly (P<0.0001) and negatively (r=-0.63 to -0.74) with all these markers of chromosome damage. Chromosome damage was minimised at 60-120 nM folic acid, which is greater than the concentration of folate normally observed in plasma (<30 nM). Current evidence suggests that (a) NPBs originate from dicentric chromosomes in which the centromeres have been pulled to the opposite poles of the cell at anaphase and are therefore, indicative of chromosome rearrangement and (b) that the nuclear budding process is the mechanism by which cells remove amplified DNA and is therefore a marker of gene amplification. The strong correlation between micronucleus formation, nuclear budding and NPBs (r=0.75-0.77, P<0.001) is supportive of the hypothesis that folic acid deficiency causes genomic instability and gene amplification by the initiation of breakage-fusion-bridge (BFB) cycles. These results also suggest that the CBMN assay may be a useful model for the study of the BFB cycle which may be one of the key mechanisms for the hypermutability phenotype required for the rapid evolution of cancer cells.

Oxidative damage and cytogenetic analysis in leukocytes of Parkinson's disease patients

BACKGROUND

Postmortem studies suggest excessive free radical toxicity in the substantia nigra of patients with PD. Increased lipid peroxidation and oxidative DNA damage have been reported in the CNS. Markers of oxidative stress have been identified in the blood of patients with PD.

OBJECTIVE

To assess the presence of spontaneous chromosome and primary or oxidative DNA damage in peripheral blood leukocytes of patients with untreated PD.

METHODS

Patients with de novo PD (20) and control subjects (16), matched for age, sex, and smoking habits, underwent cytogenetic analysis using the human lymphocyte micronucleus assay coupled with the fluorescence in situ hybridization technique and the Comet assay.

RESULTS

Compared with controls, patients with PD showed an increase in the incidence of spontaneous micronuclei (p < 0.001); single strand breaks (p < 0.001); and oxidized purine bases (p < 0.05). Fluorescence in situ hybridization analysis showed micronuclei harboring acentric fragments.

CONCLUSIONS

There is chromosomal, primary DNA damage and oxidative DNA damage demonstrable in lymphocytes of patients with untreated PD.

Jam packed genomes--a preliminary, comparative analysis of nucleomorphs

There are two ways eukaryotic cells can permanently acquire chloroplasts. They can take up a cyanobacterium and turn it into a chloroplast or they can engulf an alga that already has a chloroplast. The second method is far more common and there are at least seven major groups of protists that have obtained their chloroplasts, this way. In most cases little remains of the engulfed alga apart from its chloroplast, but in two groups, the cryptomonads and chlorarachniophytes, a small remnant nucleus of the engulfed alga is still present. These tiny nuclei, called nucleomorphs, are the smallest and most compact eukaryotic genomes known and recently the nucleomorph of the cryptomonad alga Guillardia theta, was completely sequenced (551 kilobases). The nucleomorph of the chlorarachniophyte Bigellowiella natans (380 kilobases), is also being sequenced and is about half complete. We discuss some of the similarities and differences that are emerging between these two nucleomorph genomes. Both genomes contain just three chromosomes that encode mainly housekeeping genes and a few proteins for chloroplast functions. The bulk of nucleomorph gene coding capacity, therefore, appears to be devoted to self perpetuation and creating gene and protein expression machineries to make a small number of essential chloroplast proteins. We discuss reasons why both nucleomorphs are extraordinarily compact and why their gene sequences are evolving rapidly.

Effects of heavy metal contamination of soils on micronucleus induction in Tradescantia and on microbial enzyme activities: a comparative investigation

The aim of this study was to investigate correlation between genotoxic effects and changes of microbial parameters caused by metal contamination in soils. In total, 20 soils from nine locations were examined; metal contents and physicochemical soil parameters were measured with standard methods. In general, a pronounced induction of the frequency of micronuclei (MN) in the Tradescantia micronucleus (Trad-MN) assay was seen with increasing metal concentration in soils from identical locations. However, no correlations were found between metal contents and genotoxicity of soils from different locations. These discrepancies are probably due to differences of the physicochemical characteristics of the samples. Also, the microbial parameters depended on the metal content in soils from identical sampling locations. Inconsistent responses of the individual enzymes were seen in soils from different locations, indicating that it is not possible to define a specific marker enzyme for metal contamination. The most sensitive microbial parameters were dehydrogenase and arylsulfatase activity, biomass C, and biomass N. Statistical analyses showed an overall correlation between genotoxicity in Tradescantia on the one hand and dehydrogenase activity, biomass C, and the metabolic quotient on the other hand. In conclusion, the results of the present study show that the Trad-MN assay is suitable for the detection of genotoxic effects of metal contamination in soils and furthermore, that the DNA-damaging potential of soils from different origin cannot be predicted on the basis of chemical analyses of their metal concentrations.

UV-A induces persistent genomic instability in human keratinocytes through an oxidative stress mechanism

Ultraviolet-A (UV-A, 320 to 400 nm) radiation comprises 95% of the solar ultraviolet radiation (UVR) reaching the earth's surface. It has been associated experimentally and epidemiologically with malignant melanoma. In this study we investigated whether UV-A radiation can induce a persistent, heritable hypermutability in mammalian cells similar to that observed following ionising radiation (IR). Using the immortalized human skin keratinocyte cell line HaCaT we found that UV-A radiation does lead to a continuing reduction in plating efficiency, an increased "spontaneous" mutant fraction, and an increase in micronucleus formation up to 21 d after initial exposure. Reversal of these effects using catalase may indicate a role for hydrogen peroxide in this phenomenon. These results add to the significance of UV-A radiation as a risk factor in skin carcinogenesis.

Computerized automated morphometric assay including frequency estimation of pentachlorophenol induced nuclear anomalies (micronucleus) in catfish Heteropneustes fossilis

An in vivo study of the effects of pentachlorophenol was carried out with a pre-acclimatized fish species, Heteropneustes fossilis, using four sub-lethal concentrations, 0.1, 0.2, 0.3 and 0.4 ppm, and three sampling times, 48, 72 and 96 h. Cytogenetic preparations were stained by the haematoxylin-eosin technique. The incidence of micronuclei was scored by a manual and an automated method. Small-sized micronuclei appeared in the cytoplasm in addition to the main nucleus. The frequency of micronucleated erythrocytes peaked at 4 days (96 h) exposure. The percentage of single micronuclei increased with longer exposures. The Mann-Whitney U test showed all micronuclei frequencies were significantly different from control (P<0.05). No statistical difference was observed between scores obtained by the manual and automated methods. A linear relationship between the percentage of micronucleated erythrocytes and dose was confirmed at all levels. Computer image analysis of morphological variations of erythrocytes indicated a 1:5 ratio of micronuclei and main nucleus accompanied by a reduction in cell volume by 600 dot units. Pentachlorophenol-mediated genotoxicity was confirmed in this fish for the first time. Possible consequences of genotoxicity and cytotoxicity are discussed.

[Comparative study of the effect of synthetic pyrethroids on the induction of genetic changes in mice somatic and sex cells depending on the exposure route]

Synthetic pyrethroid insecticides are widely used in the protection of fruits and vegetables as well as in the public hygiene due to their strong neurotoxic activity against insects. The induction of genetic changes in somatic and sex cells in male mice after different routes of exposure to permethrin and fenvalerate was studied. The male 8-10 weeks old mice were intraperitoneally exposed to 20 and 40 mg/kg bw of fenvalerate and 125 and 250 mg/kg bw of permethrin. Another groups of mice were exposed per os to fenvalerate and permethrin in the doses of 50, 100 and 200, 400 mg/kg bw respectively. For the sperm anomalies testing the exposure was repeated for five consecutive days followed by the 35 days waiting period after which the gonads were removed and spermatozoa prepared from the epididymis. The changed spermatozoa were counted in the smears after staining in the 0.5% eosin Y solution and the results compared with the number of normal cells. For the testing of the effect of pyrethroids on the micronuclei frequency in the bone marrow cells the tested substances were administered twice in 24 hours intervals and the bone marrow was sampled after 6 and 24 hours from the femur bone. The polychromatic erythrocytes and the presence of micronuclei were evaluated in the bone marrow smears. The results showed the difference in the action of the pyrethroids on the genetic material of the tested cells and the effect of the route of exposure. Permethrin induced the lesions in the sex cells regardless the route of exposure, however a substantial increase in the micronuclei frequency in the bone marrow was observed after oral exposure only. No signs of cytotoxicity accompanied the sperm anomalies and micronuclei induction. Fenvalerate induced changes in sperm cells after intraperitoneal exposure only. No increase in the micronuclei frequency in the polychromatic erythrocytes of the bone marrow was observed after per os or intraperitoneal exposure. The intraperitoneal exposure to this pyrethroid resulted in cytotoxicity in both bone marrow and sex cells.

Induction of micronuclei in mice exposed to static magnetic fields

The aim of this experiment was to investigate whether static magnetic fields (SMFs) have cytogenetic effects in mouse bone marrow cells. The frequency of micronuclei was significantly increased by exposure of mice to 3.0 T for 48 and 72 h and 4.7 T for 24, 48 and 72 h. The increase in micronucleus frequency was dose dependent at all times. Micronucleus frequency at 4.7 T was higher than at 3.0 T. We consider that the increased numbers of micronuclei may be attributable to a stress reaction caused by SMFs or a direct clastogenic/spindle disturbance effect of SMFs.

Chronic long-term nitrate therapy: possible cytogenetic effect in humans?

Nitrates act as donors of nitric oxide (NO), a molecule with a recognized potential for genotoxicity. In order to assess whether chronic long-term nitrate therapy may increase genotoxicity, we evaluated chromosomal damage in peripheral lymphocytes of 27 ischaemic patients undergoing chronic nitrate treatment for vertical line4 years (7.9 +/- 3.1, mean +/- SD) and 18 age- and sex-matched subjects without any previous nitrate treatment. At the same time, after treatment in vitro with 0-20 microM sodium nitroprusside as NO donor, micronucleus induction and cell proliferation were also evaluated using blood from six different healthy donors. The results showed that the frequency of structural chromosomal aberrations was not significantly higher in the drug-treated group than the control [2.1 +/- 1.4 versus 1.6 +/- 1.2 (mean +/- SD); P = 0.23]. The frequency of micronucleated lymphocytes was higher in the nitrate group than in the control group (6.5 +/- 4.6 versus 3.5 +/- 2.9, P=0.01). In vitro treatment indicated a dose-dependent increase in the frequency of micronucleated lymphocytes with increasing SNP concentrations. Cytotoxicity and cell cycle delay, with a statistically significant difference with respect to control culture, were also observed. Our results suggest a possible genotoxic activity of nitrate therapy. Further studies focusing on the possible link between nitrate therapy and genotoxicity are warranted at this point.

The application of spectral karyotyping (SKY) and fluorescent in situ hybridization (FISH) technology to determine the chromosomal content(s) of micronuclei

DNA loss by the process of micronucleation is associated with aging, cancer and environmental exposure. The primary aim of this study was to identify the chromosomal origin of the DNA excluded into micronuclei (MN). This was achieved using a novel application of SKY and FISH technologies. Cytochalasin B (Cyt B)-treated lymphocyte cultures from three females (aged 28, 42 and 72) were analyzed. SKY revealed that the majority of MN (89.8, 82.9, and 97.6% in the 28-, 42- and 72-year-old (y.o.), respectively) had a uniform, single color, suggesting that they were comprised of DNA from a single chromosome. Using a pancentromeric probe, most of the MN (82% in 28 y.o., 69% in 42 y.o. and 80% in 72 y.o.) had one centromere signal present. Overall, the confirmation studies (using FISH with chromosome-specific WCP) were in agreement with the SKY chromosomal assignments for 71.1% of the MN. Although the SKY analysis showed that all of the 23 chromosomes (22 autosomes and the X chromosome) could be present in the MN, overall, the X chromosome was seen most frequently. DNA from the X chromosome was seen in 50.6% of MN in the 42 y.o. individual, whereas in the 28 and 72 y.o. it was seen in 12.2 and 7.1% of MN, respectively. This difference (P<0.0001) in the frequencies of X chromosome exclusion into MN among individuals was independently confirmed using a single whole chromosome painting probe (WCP) for the X chromosome. SKY also showed variation in the frequency of autosomal exclusion into MN between chromosomes and between females. Collectively, this study supports the hypothesis that the majority of MN contain DNA from a single, monocentric chromosome. The use of SKY technology for the identification of the chromosomal content(s) of MN provides an opportunity for expansion of our knowledge of the chromosomal changes that accompany MN formation.

Loss of poly(ADP-ribose) polymerase-1 causes increased tumour latency in p53-deficient mice

PARP-1-deficient mice display a severe defect in the base excision repair pathway leading to radiosensitivity and genomic instability. They are protected against necrosis induced by massive oxidative stress in various inflammatory processes. Mice lacking p53 are highly predisposed to malignancy resulting from defective cell cycle checkpoints, resistance to DNA damage-induced apoptosis as well as from upregulation of the iNOS gene resulting in chronic oxidative stress. Here, we report the generation of doubly null mutant mice. We found that tumour-free survival of parp-1(-/-)p53(-/-) mice increased by 50% compared with that of parp- 1(+/+)p53(-/-) mice. Tumour formation in nude mice injected with oncogenic parp-1(-/-)p53(-/-) fibroblasts was significantly delayed compared with parp-1(+/+)p53(-/-) cells. Upon gamma-irradiation, a partial restoration of S-phase radiosensitivity was found in parp-1(-/-)p53(-/-) primary fibroblasts compared with parp-1(+/+)p53(-/-) cells. In addition, iNOS expression and nitrite release were dramatically reduced in the parp-1(-/-)p53(-/-) mice compared with parp-1(+/+)p53(-/-) mice. The abrogation of the oxydated status of p53(-/-) cells, due to the absence of parp-1, may be the cause of the delay in the onset of tumorigenesis in parp-1(-/-)p53(-/-) mice.

Sister chromatid exchanges and micronuclei in lymphocytes of operating room personnel occupationally exposed to enfluorane and nitrous oxide

The objective of this article is to assess whether occupational exposure to anesthetics increases genotoxic risk. We investigated two cytogenetic biomarkers, sister chromatid exchanges (SCE) and micronuclei (MN), in the peripheral blood lymphocytes of 46 anesthesiologists (24 men), working in operating rooms and mostly exposed to enfluorane and nitrous oxide, and 66 controls (35 men), not exposed to chemicals and living in the same area. Contrary to what was expected, a lower frequency of SCE was found in male anesthesiologists than in controls. Smoking status was found to be positively associated with SCE frequency in each group, while no relation to age was evident. On the contrary, MN frequency was significantly higher in female, but not male, anesthesiologists than in controls. Age and smoking status did not modify the association. No relationship between MN frequency and duration of employment was found in anesthesiologists. Smoking status and mean number of cigarettes smoked per day in smokers were not associated with MN frequency in either anesthesiologists or in controls. MN analysis seems to be a sensitive index of possible genotoxic effects of occupational exposure to anesthesiologists, and women appear to be more susceptible to these effects than men.

Mitochondrial genotypes and radiation-induced micronucleus formation in human osteosarcoma cells in vitro

We investigated whether or not the mitochondrial genotypes affect radiation-induced micronucleus (MN) formation. For that purpose, the rho+, KT1 and rho0 human osteosarcoma cell lines were used, which carry the wild-type mitochondrial DNA (mtDNA), the tRNALys mutant mtDNA and no mtDNA, respectively. Despite no significant difference in the clonogenic radiosensitivity, the rho+, KT1 and rho0 cells exhibited high, intermediate and low radiosensitivities, respectively, to the MN induction in cytokinesis-blocked binucleated cells. Such differential MN inductions were correlated with high, intermediate and low levels of cellular ATP in the rho+, KT1 and rho0 cells, respectively, but not exactly with ROS production. Antimycin A that inhibits the respiratory complex III reduced the rate of radiation-induced MN induction in the rho+ and KT1, but not rho0 cells. Thus, the functional status of the mtDNA to produce ATP appears to play a significant role for radiation-induced MN.

Mutagen sensitivity of human lymphoblastoid cells with a BRCA1 mutation in comparison to ataxia telangiectasia heterozygote cells

Our previous results indicated a close relationship between the presence of a BRCA1 mutation in lymphocytes and hypersensitivity for the induction of micronuclei by gamma irradiation and hydrogen peroxide (H(2)O(2)). Comparative investigations with the comet assay (single-cell gel electrophoresis) suggested a normal rate of damage removal and pointed to a disturbed fidelity of DNA repair as a direct or indirect consequence of a BRCA1 mutation. We now wanted to see whether similar results could be obtained with lymphoblastoid cell lines (LCLs) and whether such permanent cells are suitable as a model for the investigation of mechanisms involved in mutagen sensitivity. Our results show that LCLs with a BRCA1 mutation are also hypersensitive to the chromosome-damaging effects of gamma irradiation or H(2)O(2), as revealed by the micronucleus test. Interestingly, LCLs heterozygous for an ataxia telangiectasia (AT) mutation have similar characteristics as BRCA1 cells with respect to the induction and repair of DNA damage induced by either gamma irradiation or H(2)O(2). However, caffeine enhanced the induction of micronuclei by gamma irradiation only in normal and heterozygous AT cells but not in BRCA1 cells, thus indicating a difference in the pathways leading to mutagen sensitivity in cells with a BRCA1 or an AT mutation. Our results suggest that caffeine could be useful in discriminating AT heterozygotes from carriers of a BRCA1 mutation, as well as BRCA1 mutation carriers from normal individuals.

Induction and time-dependent accumulation of micronuclei in peripheral blood of transgenic p53+/- mice, Tg.AC (v-Ha-ras) and parental wild-type (C57BL/6 and FVB/N) mice exposed to benzene by inhalation

In this study, we determined the induction and time-dependent accumulation of micronuclei in the peripheral blood of transgenic C57BL/6 p53+/- mice (p53+/- mice), FVB/N Tg.AC v-Ha-ras mice (Tg.AC mice) and their isogenic parental strains, FVB/N and C57BL/6 following inhalation exposure to benzene. Our objective was to determine the impact of p53 heterozygosity in p53+/- mice and the v-Ha-ras transgene in Tg.AC mice on micronuclei induction following exposure to inhaled benzene. A flow cytometric technique that distinguishes micronucleated red blood cells (MN-RBC) from micronucleated reticulocytes (MN-RET) was used. Mice were exposed to 0, 100 or 200 p.p.m. benzene using three different exposure regimens that resulted in an equal weekly cumulative exposure (3000 p.p.m.x hours) to benezene: 100 p.p.m. for 6 h/day, 5 days/week, Monday to Friday (M-F); 100 p.p.m. for 10 h/day, 3 days/week, Monday, Wednesday, Friday (MWF); and 200 p.p.m. for 5 h/day, 3 days/week MWF. Significant elevations of MN-RBC and MN-RET were observed from 1 week exposure in all of the benzene-exposed groups that increased in a time-dependent manner for up to 13 weeks exposure. Fewer MN-RBC and MN-RET were induced in the 200 p.p.m. benzene exposure group than in mice exposed to 100 p.p.m. The reduction in the frequency of MN-RBC in the 200 p.p.m.x5 h benzene exposure group is probably due to metabolic saturation resulting in a lower bone marrow dose (concentration x time) than in the 100 p.p.m. exposure groups. No differences were observed in the frequency of MN-RBC or MN-RET in Tg.AC compared with the FVB/N isogenic controls. At certain time points the frequency of micronuclei was less in the heterozygous p53+/- mice than determined in the wild-type C57BL/6 isogenic parental strain. These results indicate that the heterozygous state in p53+/- mice, but not the v-Ha-ras transgene in Tg.AC mice can influence the induction of micronuclei by benzene.

Chromosomal composition of micronuclei in mouse NIH 3T3 cells treated with acrylamide, extract of Tripterygium hypoglaucum (level) hutch, mitomycin C and colchicine, detected by multicolor FISH with centromeric and telomeric DNA probes

The chromosomal composition of micronuclei (MN) induced by the model mutagens mitomycin (MMC) and colchicine (COL) as well as by acrylamide (AA) and the traditional Chinese medicine Tripterygium hypoglaucum (level) hutch (THH) in NIH 3T3 cells was analyzed by multicolor fluorescence in situ hybridization (FISH) using DNA probes for the centromere repeated minor satellite DNA and the telomeric hexamer repeat (TTAGGG). The majority of MN (78.6%) from treatment with MMC (0.1 microg/ml) did not show centromeric signals, reflecting the clastogenic action of MMC. Following treatment with COL (0.1 microg/ml), 74.5% of the MN showed centromeric signals and several telomeric signals, indicating that MN induced by this well-known aneugen were mainly composed of whole chromosomes. After treatment with AA (100, 200 and 400 microg/ml) both MN containing whole chromosomes and MN containing acentric fragments were found to increase in a dose-dependent manner, demonstrating that AA is not only a clastogen but also an aneugen. THH induced a high frequency of MN harboring whole chromosomes at all concentrations tested (5, 10 and 20 microl/ml) and produced a dose-dependent increase in fragment-containing MN, indicating that THH has both aneugenic and clastogenic potential.

Micronuclei and gene mutations in transgenic big Blue((R)) mouse and rat fibroblasts after exposure to the epoxide metabolites of 1, 3-butadiene

1,3-Butadiene (BD) is a commodity compound and by-product in the manufacture of synthetic rubber that elicits a differential carcinogenic response in rodents after chronic exposure. Mice are up to approximately 1000-fold more sensitive to the tumorigenicity of inhaled BD than rats, thereby confounding human risk assessment analyses. Rodent transgenic in vivo and in vitro models have been recently utilized for generating genetic toxicology data in support of risk assessment studies. However, studies have not been extended to investigate multiple endpoints of genetic damage using in vitro transgenic models. The goal of this study was to evaluate possible differences in the production of genetic damage in transgenic Big Blue((R)) mouse (BBM1) and rat (BBR1) fibroblasts exposed to three predominant epoxide metabolites of BD. Analyses of cytotoxicity, micronucleus (MN) formation, cII mutant frequency (MF) and apoptosis were assessed after in vitro exposure of BBM1 and BBR1 cells exposed to various concentrations of butadiene monoepoxide (BMO), diepoxybutane (DEB) and butadiene diolepoxide (BDE). Both BMO and DEB reduced cell survival in BBM1 and BBR1 cells. However, BDE decreased cell survival only in BBM1 cells at the concentrations evaluated. Concentration-dependent increases in the formation of MN was observed in both BBM1 and BBR1 cells, with DEB being the most potent followed by BDE and then BMO. The dose-response for mutations induced at the cII locus was essentially equal after DEB exposure of BBM1 and BBR1 fibroblasts. In contrast, the cII MF was significantly increased only in BBM1 cells after exposure to either BMO or BDE. These data demonstrate a differential genetic response for gene mutations but not for MN formation in transgenic BBM1 and BBR1 fibroblasts and suggest a rodent species-specific difference in the persistence of DNA damage that results in gene mutations. In addition, apoptosis was observed in BBR1 cells but not in BBM1 cells when treated with any of the three BD epoxide metabolites. This response may partially explain the differential response to mutations induced by BMO and BDE. These data offer insight into specific differences in mouse and rat cells with respect to their response to BD epoxide metabolites. Such data may help to explain the different tumorigenicity results observed in rodent BD carcinogenicity studies.

Effects on the immune system associated with living near a pesticide dump site

In this paper, we report results of the second phase of a larger study designed to evaluate the effects on the immune system of living near a Superfund site containing organochlorine pesticides, volatile organic compounds, and metals. Phase II was conducted to determine whether living near the site, consisting of six locations in Aberdeen, North Carolina, is associated with higher plasma organochlorine levels, immune suppression, or DNA damage. Each of 302 residents of Aberdeen and neighboring communities provided a blood specimen, underwent a skin test, and answered a questionnaire. Blood specimens were analyzed for organochlorine pesticides, immune markers, and micronuclei. Of 20 organochlorines tested, only DDE was detected in the blood of participants (except for one individual). Age-adjusted mean plasma DDE levels were 4.05 ppb for Aberdeen residents and 2.95 ppb (p = 0.01) for residents of neighboring communities. Residents of 40-59 years of age who lived within a mile of any site, but particularly the Farm Chemicals site, had higher plasma DDE levels than residents who lived farther away. Residents who lived near the Farm Chemicals site before versus after 1985 also had higher plasma DDE levels. Overall, there were few differences in immune markers between residents of Aberdeen and the neighboring communities. However, residents who lived closer to the dump sites had statistically significantly lower mitogen-induced lymphoproliferative activity than residents who lived farther away (p < 0.05). Residential location was not consistently associated with frequency of micronuclei or skin test responses. Although some statistically significant differences in immune markers were noted in association with residential location, the magnitude of effects are of uncertain clinical importance.

No evidence of increased chromosomal aberrations and micronuclei in lymphocytes from nonfamilial thyroid cancer patients prior to radiotherapy

The relationship between the presence of high frequencies of chromosomal aberrations in peripheral lymphocytes and predisposition to cancer has been suggested for some cancer diseases. In nonfamilial thyroid cancer, the few reports available are equivocal. The aim of this study was to assess the possible chromosomal instability in peripheral blood lymphocytes from 22 patients suffering from nonfamilial thyroid cancer. For this purpose, 2 classic cytogenetic assays, the chromosomal aberrations assay and cytokinesis-blocked micronucleus assay, were chosen. The frequency of chromosomal aberrations excluding gaps (%) was 1.68 +/- 1.39 (mean value +/- SD) for the patients group versus 2.20 +/- 1.87 for the control group. The frequency of binucleated lymphocytes with micronuclei ( per thousand) was 5.41 +/- 3.51 (mean value +/- SD) for the patients group versus 5.37 +/- 3.21 for the control group. The results obtained revealed no significant differences between both groups. The present study reinforces the idea that constitutional chromosomal instability in peripheral blood lymphocytes is not visible in nonfamilial thyroid carcinomas.

Chromosome painting reveals specific patterns of chromosome occurrence in mitomycin C- and diethylstilboestrol-induced micronuclei

Cultures of human blood lymphocytes from three subjects were incubated with the clastogen mitomycin C (MMC, 500 ng/ml) and the aneugen diethylstilboestrol (DES, 80 microM) 23 h before harvesting, to induce formation of micronuclei (MN) and numerical and structural alterations in metaphase chromosomes. We used fluorescence in situ hybridization (FISH) with painting probes for all human chromosomes to determine which chromosomes had contributed material to the induced MN. MMC treatment induced an approximately 18-fold increase in MN and led to a significant increase in hypodiploidy and structural chromosome aberrations in metaphase preparations. Undercondensation of pericentromeric heterochromatin of chromosomes 9 and 1 occurred in 20-75% of metaphases and FISH disclosed an abundance of material from these chromosomes in induced MN (62-69% from chromosome 9 and 7-12% from chromosome 1). DES treatment of lymphocytes induced a seven-fold increase in MN frequency and four-fold increase in the frequency of numerical aberrations; structural aberrations were not significantly increased. FISH analysis showed that material from all chromosomes was present in DES-induced MN, with material from chromosome 1 present in 16% of MN and material from each other chromosomes being present in 2-10% of MN. Material from chromosomes 14, 19 and 21 was significantly more frequent material from chromosome Y significantly less frequent in DES-treated cells than in controls. The findings of the MMC studies indicate that the heterochromatin block of chromosome 9 is a specific target for MMC-induced undercondensation, which induces a preferential occurrence of chromosome 9 material in MN. DES, in contrast, does not trigger heterochromatin decondensation and fails to induce such a significant appearance of material of particular chromosomes in MN.

A cytogenetic study on the teaching staff of a polluted school with a questionable increased incidence of malignancies

Exposure to pollutants, in particular polychlorinated biphenyls (PCB), was established at a school built in 1966. Because of a statistically conspicuous increased frequency of breast cancer observed in the teachers of the school this study was performed to ascertain whether the teachers in the polluted school have an increased level of micronucleated cells (MN) or sister chromatid exchanges (SCE) as an expression of a raised cytogenetic risk. Teachers in a directly adjacent school served as one control group and those from a school about 30 km away as a second one. Each teacher had to answer a questionnaire and after venous blood samples had been taken, the number of MN and SCE in peripheral lymphocytes were determined. For the teachers in the polluted school, in addition, the length of stay in the building during the last month and year was recorded. Thereby no correlation with the number of MN and SCE was proven. In comparison with the two control groups, neither the number of MN nor SCE was increased in the teachers of the polluted school. Even if their predictive value for cancer risk assessment is disputed, MN and SCE have a high rating as standard procedures in the proof of an exposure to genotoxic agents. This study thus does not provide any evidence that, for the teachers in the polluted school, a relevant exposure to genotoxic agents exists.

Long-term monitoring of sister chromatid exchanges and micronucleus frequencies in pharmacy personnel occupationally exposed to cytostatic drugs

OBJECTIVES

Many antineoplastic drugs were found to have carcinogenic, mutagenic and teratogenic potential. The aim of this study was to carry out cytogenetic and internal dose monitoring of hospital pharmacy personnel regularly involved in the preparation of cytostatic agents, in order to test possible cytostatics-induced genotoxic effects due to occupational exposure under routine working conditions, and in cases of accidental contamination.

METHODS

Platinum in whole blood and anthracyclines in plasma were measured to assess internal exposure to cytostatics. The level of cytogenetic damage was determined in peripheral blood lymphocytes with the micronucleus test and the sister chromatid exchange assay. Five series of monitoring were performed over a period of 2 years.

RESULTS

No significant differences in the mean frequencies of sister chromatid exchanges (SCE) and micronuclei (MN) were found between occupationally exposed probands and controls (9.9 +/- 1.4 vs 10.1 +/- 1.2 SCEs/cell and 21.2 +/- 7.2 vs 23.3 +/- 7.5 MN/2000 binucleated (BN) cells, n = 16). Significant elevations of SCE or MN were detected in seven out of 12 cases of accidental contamination at the workplace, whereas no increase in platinum in blood and anthracyclines in plasma was observed in these probands. Two cases of non-reported contamination were identified by measurement of epirubicin in plasma. Smoking was found to increase the SCE significantly. No correlation between individual SCE scores and MN scores was observed.

CONCLUSIONS

Our findings support a transient increase in SCE or MN after relevant exposure to cytostatic drugs in cases of accidental contamination. The lack of significant differences in SCE and MN between hospital pharmacy personnel and unexposed controls, points to high standards of safety at the corresponding workplaces.

Genotoxic effects of allyl isothiocyanate (AITC) and phenethyl isothiocyanate (PEITC)

Two isothiocyanates (ITCs) commonly found in human diet, allyl isothiocyanate (AITC) and phenethyl isothiocyanate (PEITC), were tested for genotoxic effects in a battery of assays: Salmonella/microsome assay with TA 98 and TA 100, differential DNA repair assay with E. coli and micronucleus (MN) induction assay with human derived Hep G2 cells. Albeit to a different degree, both ITCs induced genotoxic effects in all test systems. AITC was more genotoxic in bacterial test systems than in Hep G2 cells; in contrast, the effect of PEITC was stronger in Hep G2 cells. In in vivo assays with E. coli indicators in which mice were exposed to relatively high doses of the compounds (90 and 270 mg/kg), AITC induced moderate but significant effects; PEITC failed to induce significant effects in any of the organs. To find out the reason for the weak genotoxicity of AITC and PEITC under in vivo test conditions, we exposed E. coli indicator cells to the test substances in the absence or presence of rat liver homogenate (with and without cofactors), bovine serum albumin (BSA) and human saliva. All of them markedly attenuated the genotoxicity of AITC and PEITC, implying that the test substances are detoxified by direct non-enzymatic binding to proteins. Additional experiments carried out on the mechanistic aspects of AITC and PEITC-induced genotoxicity showed that the compounds induce the formation of thiobarbituric acid reactive substances (TBARS) in Hep G2 cells. Furthermore, in in vitro assays with E. coli, radical scavengers reduced the differential DNA damage induced by AITC and PEITC. The latter two findings give a clue that reactive oxygen species might be involved in the genotoxic effect of the ITCs. Although ITCs have been repeatedly advocated as very promising anticancer agents, the data presented here indicate that the compounds are genotoxic, and probably carcinogenic, in their own right.