Application of the micronucleus test to exfoliated epithelial cells from the oral cavity of beedi smokers, a high-risk group for oral cancer

The primary sites for occurrence of oral cancer include the buccal mucosa, tongue, alveolus, palate, lip and the floor of the mouth. In this study, an attempt was made to estimate the cytogenetic damage in different regions of the oral mucosa in people habituated to smoking beedi,which is one of the major forms of tobacco consumption in India and believed to be a major risk factor for oral cancer. By using the micronucleus assay on exfoliated cells from the buccal mucosa, palate and tongue of beedi smokers, we examined an early cellular response to the effect of beedi smoking. A total number of 50 randomly selected male subjects were included in the study. Case and control groups (smokers and non-smokers, respectively) comprised 25 subjects each. The difference in mean micronucleated cell count between cases and controls was significant (P <0.01) for buccal mucosa and palate, but not for tongue. The correlation between age and micronucleus cell count was weak for both cases (r=0.27) and controls (r=0.36).

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.

Low dose induction of micronuclei by lindane

Environmental contaminants possessing hormonal activity have long been suspected of playing a role in cancer causation. What is unclear is whether such agents elicit their effects through genotoxic and/or epigenetic mechanisms. gamma-Hexachlorocyclohexane (gamma-HCH, lindane) was tested in the 10(-12)-10(-4) M range. Chromosomal damage in MCF-7 breast cells and PC-3 prostate cells was assessed using the cytokinesis block micronucleus assay. Micronuclei (MNi) were scored in 1000 binucleate cells per treatment. Cell viability and cell cycle kinetics were also assessed, along with immunocytochemical and quantitative gene expression analyses of CDKN1A (P21WAF1/CIP1), BCL-2 and BAX. Following 24 h treatment, lindane (10(-12)-10(-10) M) induced increases (up to 5-fold) in MNi in both cell lines. Increases in MNi occurred in the absence of DNA single-strand breaks or cytotoxicity and, compared with benzo[a]pyrene and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, at low concentrations. Lindane induced more MNi than the alpha or beta stereoisomers of HCH. Low dose lindane (10(-12)-10(-10) M) significantly elevated the percentage of MCF-7 cells staining positive for Bcl-2 and of PC-3 cells staining positive for Bax. Only high dose lindane (10(-4) M) disrupted cell cycle kinetics with increases in percentage of cells in G1 and decreases in percentage of cells in G2/M. Despite a comparable high dose lindane induction of cell cycle arrest, marked increases in expression of P21WAF1/CIP1 were observed only in MCF-7 cells, although in PC-3 cells a significant increase (P < 0.0005) in the percentage of cells staining positive for p21Waf1/Cip1 was seen. These results suggest that 'environmental' concentrations of lindane can induce a number of subtle alterations in breast and prostate cells in the absence of cytotoxicity.

[Cytogenetic changes of the bone marrow in massive blood loss and their correction with mexidol]

The citogenetic lesions were evaluated in the marrow erythroblasts of 45 anesthetized white nonlinear male rats, weight--200-300 g who were subjected to an acute blood loss with a 1-hour arterial hypotension (ABR = 40 mm Hg); the micronucleus tests was made use of. Two stages of the increase of polychromatophilic erythrocytes with micronuclei in the marrow of the animals, who underwent a massive blood loss, were registered: stage 1--an incomplete marrow ischemia with a subsequent arterial hypotension and with a reliably confirmed formation of cytogenetic lesions in the marrow polychromatophilic erythrocytes; stage 2--the reperfusion period contributed to a 1.7-fold increase of polychromatophilic erythrocytes with micronuclei versus the previous stage. Mexidole, when used at 50 mg/kg prior to blood reinfusion, decreased the quantity of polychromatophilic erythrocytes with micronuclei to the basic level, which is indicative of reversibility and instability of cytogenetics impairments in the marrow cells of animals observed in the early post-resuscitation period.

Effects of a Diet High in Fish Oil (MaxEPA) on the Formation of Micronucleated Erythrocytes in Blood and on the Number of Atypical Acinar Cell Foci Induced in Rat Pancreas by Azaserine

The present study was performed to investigate the influence of fish oil on the genotoxic effects of azaserine, using the formation of micronucleated erythrocytes as a measure for the degree of initiating potency and the number and size of putative preneoplastic pancreatic atypical acinar cell foci (AACF) as a measure for the actual number of initiated cells. Male Wistar rats were treated twice i.p. with 30 mg azaserine per kg body weight to induce AACF. During the initiation/early promotion phase the rats were maintained on diets containing 5 wt% vegetable oil (safflower and high-oleic sunflower oil), 25 wt% vegetable oil, 25 wt% fat (15% vegetable oil + 10 wt% fish oil), or 25 wt% fat (5% vegetable oil + 20 wt% fish oil), respectively. One day after carcinogen treatment, the numbers of micronucleated polychromatic erythrocytes were determined in blood smears obtained from 10 animals per group. Each high-fat diet resulted in higher percentages of micronucleated polychromatic erythrocytes than the low-fat diet. Dietary fish oil did not significantly influence the number of micronucleated cells. Two weeks after carcinogen treatment, the diets containing fish oil were replaced by the diet containing 25% vegetable oil, and the animals were further maintained for about 14 wk. Pancreatic tissue slides were microscopically evaluated for the number and size of AACF. Dietary fish oil caused an increase in the number and size of AACF, although a clear dose-effect relationship was absent. It was concluded that a high level of dietary fish oil, when given during the induction/early promotion phase, enhances azaserine-induced pancreatic carcinogenesis in rats.

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.

Preimplantation mouse embryo development as a target of the pesticide methoxychlor

Effects of methoxychlor (MXC) and estradiol-17beta (E) were studied in mouse preimplantation embryos. Pregnant mice received s.c. injections of sesame oil only, 10 microg E, or 0.5 mg purified (95%) MXC on Days 2-4 of pregnancy (plug = Day 1). Another group received a single dose of 2.5 microg E on Day 2 only. Based on the average weight of pregnant females, 10 microg of estradiol was equivalent to 0.33 mg/kg of bw, 2.5 microg of estradiol was equivalent to 0.082 mg/kg of bw, and the 0.5-mg dose of MXC was equivalent to 16.5 mg/kg of bw. All embryos were collected for analyses on Day 4. MXC and both estradiol-17beta doses suppressed embryonic development to blastocyst, decreased embryo cell numbers, and caused abnormal blastocyst formation. The high estradiol-17beta dose significantly increased the percent degenerating embryos and caused a tube-locking effect, with retention of embryos in the oviduct. In contrast to estradiol-17beta, MXC at the dose used in this study did not alter tubal transport of embryos. Also in contrast to estradiol-17beta, MXC increased the percentage of nuclear fragmentation and micronuclei. In preimplantation embryos, MXC and estradiol-17beta both suppressed embryo development. MXC effects were, however, different from those of estradiol-17beta, indicating a difference in mechanism of action, possibly due to cytotoxicity and induction of apoptosis.

A unifying model for reconstructing radiosensitivity from micronucleus formation, apoptosis and abnormal morphology

At present micronucleus data cannot predict cellular radiosensitivity. The inclusion of data from apoptosis and abnormal morphology has not entirely resolved this problem. Here, we assess the probability of cell death arising from events other than micronucleation, apoptosis and abnormal morphology (i.e. lesions not detected by these damage assays) P(oe), for its ability to reflect intrinsic cellular radiosensitivity. Analysis of data from 17 cell lines used in two separate studies, spanning a wide range of radiosensitivity (0.09</=SF2</=0.70), confirmed our previous observation that cell death due to undetected lesions depends on the irradiation dose and is cell type-specific. We further demonstrate that P(oe) accounts for inter-cell line differences in translating irradiation damage into cell death. Data from any two of micronucleus formation, apoptosis and abnormal cell morphology, fitted to the P(oe) model, adequately predict clonogenic survival, and measurement of additional damage endpoints is not required. The P(oe) model may benefit patient selection in situations where colony formation of primary tumour cultures fails to arrive at estimates of radiosensitivity.

Inhibitory effect of chlorophyllin on the frequency of micronuclei induced by sodium nitrite in mice

In this report the potency of chlorophyllin (CHL) was evaluated to prevent two types of damage produced by nitrite in mice: the increase of micronucleated polychromatic erythrocytes (MNPE) and the bone marrow toxicity, measured as the index of polychromatic erythrocytes/normochromatic erythrocytes (PE/NE). The study was done in eight groups of male mice. The first three groups were administered orally for 4 days with sodium nitrite (10, 15 and 20 mg/kg), the daily administration with nitrite was followed by an intraperitoneal administration of CHL (4 mg/kg), three more groups were administered with the same amounts of nitrite, a seventh group of mice was treated with distilled water while another was treated with CHL (4 mg/kg). Our study produced two main results: (a) no bone marrow injury was induced by any of the tested chemicals, as indicated with the PE/NE index, and (b) CHL protected (as high as 44%) the MNPE produced in nitrite treated mice.

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.

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.

Curcumin disrupts mitotic spindle structure and induces micronucleation in MCF-7 breast cancer cells

The dietary phytochemical curcumin possesses anti-inflammatory, -oxidant, and cytostatic properties, and exhibits significant potential as a chemopreventative agent in humans. Although many cell types are arrested in the G2/M-phase of the cell cycle after curcumin treatment, the mechanisms by which this occurs are not well understood. The purpose of this study was to examine the effects of curcumin on the cell cycle of MCF-7 breast cancer cells to determine whether growth arrest is associated with structural changes in cellular organization during mitosis. For this purpose, MCF-7 breast cancer cells were treated with 10-20 microM curcumin, and the effects on cell proliferation and mitosis studied. Structural changes were monitored by immunolabeling cells with antibodies to a number of cytoplasmic and nuclear proteins, including beta-tubulin, NuMA, lamins A/C and B1, lamin B receptor, and centromere antigens. At the concentrations used, a single dose of curcumin does not induce significant apoptosis, but is highly effective in inhibiting cell proliferation for over 6 days. During the first 24-48 h of treatment, many cells are arrested in M-phase, and DNA synthesis is almost completely inhibited. Remarkably, arrested mitotic cells exhibit monopolar spindles, and chromosomes do not undergo normal anaphase movements. After 48 h, most cells eventually leave M-phase, and many form multiple micronuclei instead of individual daughter nuclei. These observations indicate that the curcumin-induced G2/M arrest previously described for MCF-7 cells is due to the assembly of aberrant, monopolar mitotic spindles that are impaired in their ability to segregate chromosomes. The production of cells with extensive micronucleation after curcumin treatment suggests that at least some of the cytostatic effects of this phytochemical are due to its ability to disrupt normal mitosis, and raises the possibility that curcumin may promote genetic instability under some circumstances.

Persistence of micronuclei in lymphocytes of cancer patients after radiotherapy

To verify the applicability of the micronucleus (MN) yield in peripheral blood lymphocytes (PBLs) as a quantitative biodosimeter for monitoring in vivo ionizing radiation damage, we applied the cytokinesis-blocked micronucleus assay in PBLs of cancer patients treated with partial-body radiotherapy. Dosimetric information on these 13 patients represented a wide range in the number of fractions, cumulative tumor dose, total integral dose, and equivalent total-body absorbed dose. We found in PBLs of these patients that (1) the MN yield increased linearly with the equivalent total-body absorbed dose (r = 0.8, P = 0.002), (2) the distributions of the MN yields deviated significantly from Poisson, and (3) there was a general decline in MN yields with increasing length of follow-up, but with considerable variation between individuals. The average rate of decline was found to be linear and was correlated with the equivalent total-body absorbed dose (r = 0.7, P = 0.007). Further, at 19-75 months of follow-up time, seven patients showed higher MN yields than their respective levels before radiotherapy, indicating the persistence of radiation-induced residual cytogenetic damage. Our findings suggest that the MN yield in human PBLs offers a reliable acute and perhaps chronic biodosimeter for in vivo radiation dose estimation. After the completion of radiotherapy, the persistence of elevated MN yield in PBLs is a reflection of the surviving population of radiation-induced genetically aberrant cells.

Enhanced frequency of micronuclei in individuals exposed to arsenic through drinking water in West Bengal, India

In West Bengal, India arsenic in ground water has been found to be above the maximum permissible limit in seven districts covering an area of 37,493km2. In the present study, evaluation of the micronuclei (MN) formation in oral mucosa cells, urothelial cells and peripheral blood lymphocytes was carried out in the symptomatic individuals exposed to arsenic through drinking water. Forty five individuals with cutaneous signs of arsenicism from four affected districts (368.11 microg/l of As in drinking water) were considered as the exposed group and 21 healthy individuals with no symptoms of arsenic poisoning and residing in two unaffected districts (5.49 microg/l of As) were considered as controls. The exposed and control groups had similar age distribution and socioeconomic status. Standardised questionnaires were utilised and medical examination was conducted to ascertain exposure history, sociodemographic characteristics, diet, health, medication, addiction and chief symptoms in the study participants. Arsenic exposure was confirmed by measuring the arsenic content in the drinking water, nails, hair and urine samples from the volunteers. Arsenic contents in the urine, nail and hair in the exposed group were 24.45 microg/l, 12.58 and 6.97 microg/g, respectively which were significantly high in comparison to corresponding control group values of 4.88 microg/l, 0.51 and 0.34 microg/g, respectively. Exposed individuals showed a statistically significant increase in the frequency of MN in oral mucosa, urothelial cells and lymphocytes (5.15, 5.74 and 6.39/1000 cells, respectively) when compared with the controls (0.77, 0.56 and 0.53/1000 cells, respectively). Thus, the above results indicate that the symptomatic individuals exposed to arsenic through drinking water in this region have significant cytogenetic damage.

Micronuclei in cervical smears and peripheral blood lymphocytes from women with and without cervical uterine cancer

Cervical cancer represents the second most common malignant neoplasia in women world-wide. In Mexico, cervical cancer is the most common female malignancy. It has been recently seen an increased frequencies of micronuclei (MN) lymphocytes and cervical epithelial cells of cervical cancer patients. The aim of this hospital-based unmatched case-control study was to investigate the association between progressive stages in development of cervical cancer and frequency of micronucleated cells in the cervical epithelium and peripheral lymphocytes of 40 women, grouped by disease stage. Women at the Obstetrics and Gynecology Hospital of the Instituto Mexicano del Seguro Social (IMSS) in Monterrey, Mexico were diagnosed and classified on the bases of the Papanicolaou (PAP) smear and colposcopy/biopsy into control, low-grade squamous intraepithelial lesions (LGSIL), high-grade squamous intraepithelial lesions (HGSIL), and invasive groups. Analysis of the MN data in both cell types revealed (a) homogeneity among women within each of the four groups with regard to MN frequency, (b) in general, a correlation between MN frequency and grade of cervical lesion, and (c) a positive linear trend between the MN frequency and increased cervical cancer risk. In conclusion, we suggest that MN are a useful biomarker of cancer risk. Nonetheless, these results should be validated by other researchers.

[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.

Analyses of micronuclei in exfoliated epithelial cells from individuals chronically exposed to arsenic via drinking water in inner Mongolia, China

The groundwater in Bayingnormen (Ba Men), located in Central West Inner Mongolia, China, is naturally contaminated with arsenic at concentrations ranging from 50 microg/L to 1.8 mg/L. Various adverse health effects in this region, including cancer, have been linked to arsenic exposure via drinking water. A pilot study was undertaken to evaluate frequencies of micronuclei (MN), as measures of chromosomal alterations, in multiple exfoliated epithelial cell types from residents of Ba Men chronically exposed to arsenic via drinking water. Buccal mucosal cells, airway epithelial cells in sputum, and bladder urothelial cells were collected from 19 residents exposed to high levels of arsenic in drinking water (527.5 +/- 24 microg/l), and from 13 control residents exposed to relatively low levels of arsenic in drinking water (4.4 +/- microg/L). Analytical results from these individuals revealed that MN frequencies in the high-exposure group were significantly elevated to 3.4-fold over control levels for buccal and sputum cells, and to 2.7-fold over control for bladder cells (increases in MN frequency significant at p < .001 for buccal cells; p < .01 for sputum cells; p < .05 for bladder cells). When smokers were excluded from high-exposure and control groups the effects of arsenic were observed to be greater, although only in buccal and sputum cells; approximately 6-fold increases in MN frequency occurred in these tissues. The results indicate that residents of Ba Men chronically exposed to high levels of arsenic in drinking water reveal evidence of genotoxicity in multiple epithelial cell types; higher levels of induced MN were observed in buccal and sputum cells than in bladder cells.

Sex chromosome loss, micronuclei, sister chromatid exchange and aging: a study including 16 centenarians

In the present study we analysed the possible effect of age, sex and smoking on the mean values of micronucleus (MN) and sister chromatid exchange (SCE) frequencies on peripheral blood obtained from 38 subjects ranging in age from 16 to 63 years and 16 centenarians. The mean number of binucleated cells with micronuclei varied in function of age and sex (as demonstrated by the analysis of covariance (F=13.13; P<0.001), particularly evident was the increment observed in women with increasing age (interaction age/sex: F=5.53; P<0.05). Smoking habits had no effects on MN frequency (F=0.36; P>0.05). Sex (F=4.18; P<0.05) and smoking habits (F=14.64; P<0.001) influenced significantly SCE per cell frequencies, but age had no effects on them (F=2.45; P>0.05). The age-associated increase of sex chromosome loss was studied using fluorescence in situ hybridisation (FISH) on interphase nuclei. The loss of Y signals was observed in approximately 10% of interphase cells from the centenarians males, that is six times more often than in the younger control men (approximately 1.6%). The frequency of X signal loss (approximately 1.7%) in young women was similar to that observed in male controls of the same age but the incidence of the X chromosome aneuploidy in centenarian females was appreciably higher (approximately 22%) than that found for the Y chromosome in males. These results were correlated with the data on MN formation and a positive correlation between the percentage of aneuploid cells (FISH) and MN values was observed (r=0.50; P<0.05).

Induction of micronuclei in mouse polychromatic erythrocytes by the administration of non-radioactive CsCl by the oral and intraperitoneal route

In the present study, we describe the effects of the concentration and route of administration of non-radioactive cesium chloride (CsCl) in inducing micronuclei in mouse bone marrow polychromatic erythrocytes (PCEs). When the dose of 500mg/kg body weight was administered perorally (p.o.), no significant incidence of micronuclei was detected. However, when the same dose was administered intraperitoneally (i.p.), a significant induction of micronuclei in PCEs was observed compared to control. At the dose of 1000mg/kg, both routes were efficient, with no significant difference in micronucleus frequencies. We conclude that both the p.o. and i.p. routes are efficient in inducing micronuclei, with the i.p. route being more efficient when lower CsCl doses are used.

Inhibitory effect of naringin on the micronuclei induced by ifosfamide in mouse, and evaluation of its modulatory effect on the Cyp3a subfamily

Naringin (Nar) is a flavonone found in high amount in grapefruit. In in vitro studies to determine its antimutagenicity results have been both positive and negative. On the other hand, an increase in the bioavailability of some medicaments have been observed when these are ingested together with grapefruit. It has been suggested that the effect may be related to the inhibition of the human enzyme Cytochrome P450 (CYP) 3A4 by Nar, an enzyme with a high aminoacid sequence homology with the Cyp3a in mouse. The present study was designed for three main purposes: (1) to determine whether Nar has a genotoxic effect in mouse in vivo. This was evaluated by measuring the rate of micronucleated polychromatic erythrocytes (MNPE); (2) to determine its antigenotoxic and its anticytotoxic potential on the damage produced by ifosfamide (Ifos). The first study was done by scoring the rate of MNPE, and the second one by establishing the index polychromatic erythrocytes/normochromatic erythrocytes (PE/NE); and (3) to explore whether its antigenotoxic mechanism of action is related to an inhibitory effect of Nar on the expression of the Cyp3a enzyme, an effect which could avoid the biotransformation of Ifos. A single oral administration was used for all groups in the experiment: three groups were given different doses of Nar (50, 250, and 500 mg/kg), other groups received the same doses of Nar plus an administration of Ifos (60 mg/kg), another group treated with distilled water and another with Ifos (60 mg/kg) were used as negative and positive controls, respectively. The micronuclei and the cell scoring were made in blood samples taken from the tail of the animals at 0, 24, 48, 72, and 96 h. The results showed that Nar was neither genotoxic nor cytotoxic with the doses tested, but Ifos produced an increase in the rate of MNPE at 24 and 48 h. The highest value was 24+/-1.57 MNPE per thousand cells at 48 h. The index PE/NE was significantly reduced by Ifos at 24 and 48 h. Concerning the antigenotoxic capacity of Nar, a significant decrease was observed in the MNPE produced by Ifos at the three tested doses. This effect was dose-dependent, showing the highest reduction in MNPE frequency (54.2%) at 48 h with 500 mg/kg of Nar. However, no protection on the cytotoxicity produced by Ifos was observed. Immunoblot analysis was used to assess the Cyp3a expression in liver and intestinal microsomes from mouse exposed orally to Nar. An induction in the Cyp3a protein was observed in both intestinal and hepatic microsomes from treated mice. This induction correlated with an increase in erythromycin N-demethylase activity. These data suggest that other mechanism(s) are involved in the antigenotoxic action of naringin.

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.

[Micronucleus frequency is increased in bone marrow erythrocytes from offspring of male mice exposed to chronic low-dose gamma irradiation]

The micronucleus frequency in bone marrow erythrocytes from the F1 progeny of male mice exposed to chronic low-dose gamma-irradiation was determined. Male BALB/c mice were irradiated with 10, 25 and 50 cGy at dose rates of 1, 5, and 15 cGy/day and mated with unirradiated females on day 15 after irradiation. The obtained offspring had an elevated micronucleus frequency in bone marrow erythrocytes at the age of 2 months. This suggests the transmission of genome instability from damaged germ-line cells of irradiated male parents to somatic cells of the progeny.

Frequency of oral mucosa micronuclei in gas station operators after introducing methanol

Methanol has been proposed in different countries as an alternative automotive fuel to be used as an additive to, or replacement for, gasoline or ethanol. Utilization of methanol is increasing exposure to low levels of methanol vapors in the environment and more specifically in occupational settings such as gas stations. Pump operators are exposed to relatively high levels of fuel vapors, the consequences of which have not been fully examined. In this study, the micronucleus assay in squamous oral cells was performed on pump operators of 28 gas stations in three different periods in the city of São Paulo, Brazil. The frequency of micronuclei (MN) was evaluated before and 1 year after a mixed fuel called MEG, which contains 33% methanol, 60% ethanol and 7% gasoline, was introduced. The third evaluation, 3 years later, represents a period where the number of cars using alcohol fuel had decreased drastically and the pump operator exposure to MEG became very low. The frequency of MN observed in 76 employees in 1992 (mean = 3.62 +/- 0.39) was significantly increased (P < 0.001) as compared with 76 operators exposed in 1989 (mean = 1.41 +/- 0.26) and 129 exposed in 1995 (mean = 1.20 +/- 0.15). These differences were also significant when compared with control groups not exposed professionally to motor fuel. These findings could indicate a mutagenic hazard of the MEG occurring in those with occupational exposure.

Inclusion of micronuclei in non-divided mononuclear lymphocytes and necrosis/apoptosis may provide a more comprehensive cytokinesis block micronucleus assay for biomonitoring purposes

Human biomonitoring of early genetic effects requires accurate, sensitive and, if possible, easy and not too time-consuming methodologies to assess mutations. One of the most promising methodologies at the present time is the cytokinesis block micronucleus (MN) assay (CBMN), which detects both chromosome breakage and chromosome loss in once-divided binucleated (BN) cells. Many studies have been published with this methodology, but before its extensive application is recommended, it is necessary to evaluate its strengths and limitations. Recently, Fenech et al. reviewed the advantages of the CBMN assay for biomonitoring purposes. However, up to now information present in mononucleated (MONO) cells has rarely been taken into account, although it might be complementary to that assessed in BN cells. Indeed, MONO cells should indicate damage which was present in vivo before the start of culture and BN cells may contain pre-existing micronuclei (MNi) plus lesions which are expressed as MNi during in vitro culture. To address this question, the objectives of this paper were as follows. (i) To situate the CBMN assay in a historical and mechanistic perspective. (ii) To consider whether impaired mitotic capacity in vitro may be responsible for false negative biomonitoring studies if MN in MONO cells are not taken into account in the CBMN test. The following factors were considered: division delay for repair and mitotic block, in vitro apoptosis and necrosis of damaged cells, mitotic slippage and correlation between MN expression in vitro versus in vivo. (iii) To analyse the factors which may cause a negative result in the CBMN assay in biomonitoring when exposure to specific genotoxins is evident. The specific effects of aneugens and of adaptive responses to chronic low level exposure were examined. (iv) To compare the sensitivity of MONO and BN cells in relation to the genotoxic mechanism. (v) To propose an adequate sampling scheme to study MN in both MONO and BN cells. It was concluded that a more comprehensive assessment of DNA damage may be achieved if the CBMN assay includes measures of: (i) MNi in MONO cells; (ii) MNi in BN cells; (iii) apoptotic cells; (iv) necrotic cells. It is probable that the 24 h post-phytohaemagglutinin time point may be the optimal time to assess the frequency of MNi in MONO cells, apoptotic cells and necrotic cells. It is also practical to include these measures when scoring MNi in BN cells after cytokinesis block.

Computerized video time-lapse analysis of apoptosis of REC:Myc cells X-irradiated in different phases of the cell cycle

Asynchronous rat embryo cells expressing Myc were followed in 50 fields by computerized video time lapse (CVTL) for three to four cycles before irradiation (4 Gy) and then for 6-7 days thereafter. Pedigrees were constructed for single cells that had been irradiated in different parts of the cycle, i.e. at different times after they were born. Over 95% of the cell death occurred by postmitotic apoptosis after the cells and their progeny had divided from one to six times. The duration of the process of apoptosis once it was initiated was independent of the phase in which the cell was irradiated. Cell death was defined as cessation of movement, typically 20-60 min after the cell rounded with membrane blebbing, but membrane rupture did not occur until 5 to 40 h later. The times to apoptosis and the number of divisions after irradiation were less for cells irradiated late in the cycle. Cells irradiated in G(1) phase divided one to six times and survived 40-120 h before undergoing apoptosis compared to only one to two times and 5-40 h for cells irradiated in G(2) phase. The only cells that died without dividing after irradiation were irradiated in mid to late S phase. Essentially the same results were observed for a dose of 9.5 Gy, although the progeny died sooner and after fewer divisions than after 4 Gy. Regardless of the phase in which they were irradiated, the cells underwent apoptosis from 2 to 150 h after their last division. Therefore, the postmitotic apoptosis did not occur in a predictable or programmed manner, although apoptosis was associated with lengthening of both the generation time and the duration of mitosis immediately prior to the death of the daughter cells. After the non-clonogenic cells divided and yielded progeny entering the first generation after irradiation with 4 Gy, 60% of the progeny either had micronuclei or were sisters of cells that had micronuclei, compared to none of the progeny of clonogenic cells having micronuclei in generation 1. However, another 20% of the non-clonogenic cells had progeny with micronuclei appearing first in generation 2 or 3. As a result, 80% of the non-clonogenic cells had progeny with micronuclei. Furthermore, cells with micronuclei were more likely to die during the generation in which the micronuclei were observed than cells not having micronuclei. Also, micronuclei were occasionally observed in the progeny from clonogenic cells in later generations at about the same time that lethal sectoring was observed. Thus cell death was associated with formation of micronuclei. Most importantly, cells irradiated in late S or G(2) phase were more radiosensitive than cells irradiated in G(1) phase for both loss of clonogenic survival and the time of death and number of divisions completed after irradiation. Finally, the cumulative percentage of apoptosis scored in whole populations of asynchronous or synchronous populations, without distinguishing between the progeny of individually irradiated cells, underestimates the true amount of apoptosis that occurs in cells that undergo postmitotic apoptosis after irradiation. Scoring cell death in whole populations of cells gives erroneous results since both clonogenic and non-clonogenic cells are dividing as non-clonogenic cells are undergoing apoptosis over a period of many days.

Micronucleus frequencies in exfoliated buccal cells in normal mucosa, precancerous lesions and squamous cell carcinoma

OBJECTIVE

To assess the value of micronuclei in the characterization of precancerous lesions of the oral cavity with reference to their likelihood of progressing to malignant lesions.

STUDY DESIGN

The frequency of micronuclei was determined in exfoliated cells from normal oral mucosa, a preneoplastic condition (leukoplakia) and precancerous lesions with and without dysplasia, squamous cell carcinomas and sites of previous carcinomas that had been removed.

RESULTS

Average micronucleus frequencies were increased in precancerous lesions as compared to normal mucosa and further increased in carcinomas, suggesting that micronuclei are a biomarker of neoplastic progression in this type of cancer. With all samples, micronucleus frequencies were systematically higher when cells were collected by vigorous than by light scraping, suggesting a decreasing gradient from basal to superficial layers of mucosa. The micronucleus frequency did not vary with the sex or age of patients, while it did vary with the anatomic site of the lesions.

CONCLUSION

Although the gradual increase in micronucleus counts from normal mucosa to precancerous lesions to carcinomas suggests a link of this biomarker with neoplastic progression, the large overlapping of data prevents its use as a predictor of progression of precancerous lesions to malignancy in individual patients.

[The correlation analysis between frequency of micronucleated cells of exfoliated oral mucosa cells and oral mucosa cells in different grading of oral leukoplakia lesions]

OBJECTIVE

To provide evidence for using micronucleated cells of exfoliated oral mucosa cells in diagnosis and treatment of oral leukoplakias and chemopreventive studies of oral cancer.

METHODS

Micronuclei of exfoliated oral mucosa cells and oral mucosa cells in 119 patients comprising 59 simple hyperplasia, 32 mild and moderate oral leukoplakia and 28 severe oral leukoplakia and oral squamous carcinoma by Feulgen stain method were examined, and micronuclei of exfoliated oral mucosa cells in 100 normal persons were also examined.

RESULTS

Frequency of micronucleated cells of exfoliated oral mucosa cells in oral leukoplakia lesions was higher than that of normal persons. Frequency of micronucleated cells of exfoliated oral mucosa cells had a positive correlation with oral leukoplakia lesions(r = 0.9997, P < 0.001) and with frequency of micronucleated cells of oral mucosa cells (P < 0.001).

CONCLUSIONS

Frequency of micronucleated cells of exfoliated oral mucosa cells are useful markers to the clinician to predict oral leukoplakia behaviour and prognosis and substitute for frequency of micronucleated cells of oral mucosa cells as intermediate endpoint in chemopreventive trials.

Effects of 50 Hz EMF exposure on micronucleus formation and apoptosis in transformed and nontransformed human cell lines

Effects of applying extremely low-frequency electromagnetic fields (ELF-EMF) for different durations (24, 48, and 72 h) and different field intensities (0.1-1.0 mT) on micronucleus (MN) formation and induction of apoptosis were examined in a human squamous cell carcinoma cell line (SCL II) and in a human amniotic fluid cell line (AFC). A statistically significant increase of MN frequency and of induction of apoptosis in SCL II cells after 48-h and 72-h continuous exposure to 50 Hz magnetic field (MF) (0.8 and 1.0 mT) was found. However, exposure of AFC cells to EMF of different intensities and for different exposure times showed no statistically significant differences when compared with controls. These results demonstrate that different human cell types respond differently to EMF. Dose-dependent induction of apoptosis and genotoxic effects, resulting in increased micronucleus formation, could be demonstrated in the transformed cell line, whereas the nontransformed cell line did not show statistically significant effects. These findings suggest that EMF could be a promotor but not an initiator of carcinogenic effects.

Evaluation of micronucleated lymphocytes, constitutional karyotypes and anti-p53 antibodies in 21 children with various malignancies

The implication of environmental carcinogens in childhood cancer is still unknown. To assess a possible link between DNA damage and alterations of the tumor suppressor gene p53, blood samples of 21 children with malignancies were examined for the presence of micronuclei in lymphocytes using the cytokinesis blocked micronucleus assay (CBMA). The constitutional karyotypes were analyzed for chromosome abnormalities and the presence of anti-p53 antibodies in blood sera was evaluated by an enzyme-linked immuno sorbent assay (ELISA). A control group of 20 children was also included. The rates of micronucleated cells were 5.1 per thousand+/-3.9 and 2.4 per thousand+/-2.3 for the cancer and control groups, respectively. The difference between the groups were statistically significant (P<0.05 by the Mann-Withney rank sum test). Two children in the cancer group showed extensive chromosome breakage in lymphocytes. The sera of two other children from the cancer group and of one child from the control group contained anti-p53 antibodies. Chromosome breakage and anti-p53 antibodies from the five children were associated with increased micronucleated cell rates. The results of the present study suggest that genotoxic events can occur in the lymphocytes of children with a cancerous state.

Spontaneous micronuclei in peripheral blood erythrocytes from 54 animal species (mammals, reptiles and birds): part two

The normal numbers of micronucleated erythrocytes (MNE) observed in peripheral blood samples differ among species. This depends on the effectiveness of the spleen (or the rest of the reticuloendothelial system) to withdraw them from circulation. In our previous report, we assessed the number of MNE in the peripheral blood of 35 mammalian species. Here we show the results observed in 54 species including mammals, reptiles and birds. We obtained 212 peripheral blood samples from different species. In 14 species, only one individual was studied. Slides were stained with acridine orange. The total number of MNE (normo and polychromatic) in 10,000 erythrocytes per animal are shown. The species that display the higher MNE were: ocelote, lynx, owl, gray squirrel, hedgehog, lion, orange fronted parakeet and common barn owl. For this reason, these species could be tested as monitors for genotoxic events. Another interesting observation was that in the gray squirrel, we found the highest values of MNE in the smaller (younger) animals when compared with the larger (older) of the same species.

The use of cryopreserved lymphocytes in assessing inter-individual radiosensitivity with the micronucleus assay

PURPOSE

The feasibility of using cryopreserved lymphocytes to detect inter-individual differences in chromosomal radiosensitivity was investigated. Typically, such studies are conducted with fresh blood samples but, in a clinical setting, when availability of samples is unpredictable, this is not always convenient. The sensitivity of 23 normal healthy donors, 11 breast cancer patients who had shown severe acute skin reactions to radiotherapy and seven ataxia telangiectasia (A-T) heterozygotes was determined.

MATERIALS AND METHODS

Thawed lymphocytes were exposed to high (HDR) or low dose rate (LDR) gamma irradiation (3.5 Gy) in Go, stimulated with PHA, treated with cytochalasin-B 24 h later and then harvested at 90 h for the determination of micronucleus (MN) yields in binucleate cells.

RESULTS

Each normal donor was tested one to three times. Mean MN yields were 76.1 +/- 9.3/100 cells at HDR and 44.5 +/- 5.3 at LDR, giving an LDR sparing effect of 39.6 +/- 9.3%. A relatively high proportion of tests failed to yield sufficient binucleate cells for analysis. Inter-experimental variability was also high and it was not possible to demonstrate inter-individual differences in sensitivity in spite of the use of an internal control sample from a single normal donor in each experiment. There was a small but significant increase in radiation-induced MN in the breast cancer patients compared with the normals at LDR (but not at HDR), but a complete overlap with the normal range. There was no increase in sensitivity in the A-T heterozygotes at HDR. The LDR samples failed because the LDR protocol reduced proliferation rates, and radiation-induced mitotic inhibition in this group was higher than in normals.

CONCLUSIONS

In comparison with previous experience with fresh blood samples, the use of frozen lymphocytes is not as satisfactory because: (1) experimental failures are higher; (2) inter-experiment variability is higher: (3) dose-rate sparing is lower, suggesting poorer repair; and (4) the ability to discriminate between breast cancer cases and normals is probably lower.

The 2-phenylbenzotriazole-type water pollutant PBTA-2 has cytochalasin B-mimetic activity

The 2-phenylbenzotriazole (PBTA)-type water pollutant, 2-[2-(acetylamino)-4-[N-(2-cyanoethyl)ethylamino]-5-methoxyphenyl]-5- amino-7-bromo-4-chloro-2H-benzotriazole (PBTA-2), has been recently identified in samples from the Nishitakase River in Kyoto, Japan, and shows potent mutagenic activities in Salmonella typhimurium in the presence of a microsomal metabolizing system (S9 mix). In the present study, we conducted the in vitro micronucleus (MN) test on PBTA-2 in the absence and presence of S9 mix in two Chinese hamster cell lines, CHL and V79-MZ. In the MN test, PBTA-2 was weakly positive in CHL cells and strongly positive in V79-MZ cells. Because the positive results were accompanied by a statistically significant increase in the number of polynuclear (PN) and/or mitotic (M) cells, we examined treated cells in metaphase to see if numerical chromosome aberrations were being induced. We found that PBTA-2 induces polyploidy in both CHL and V79-MZ cells. A detailed analysis of MN preparations showed that in CHL cells, PBTA-2 predominantly induces equal-sized binucleated cells. Rhodamine phalloidin staining revealed that PBTA-2 causes actin filament abnormalities in both cell lines similar to those caused by cytochalasin B. Cytochalasin B induced PN cells predominantly and dose dependently, and almost all the cells were equal-sized and binucleate. The results suggest that PBTA-2 has cytochalasin B-mimetic activity, although agents affecting actin filaments, such as cytochalasins, phallotoxins and chloropeptide, have been derived only from molds so far. This study also suggests that our MN test protocol may be used to identify chemicals that have cytochalasin B-mimetic activity as well as those that induce numerical aberrations.

Genotoxicity of paraquat: micronuclei induced in bone marrow and peripheral blood are inhibited by melatonin

The ability of melatonin to influence paraquat-induced genotoxicity was tested using micronucleated polychromatic erythrocytes as an index of damage in both bone marrow and peripheral blood cells of mice. Melatonin (10 mg/kg) or an equal volume of saline were administered intraperitoneally (ip) to mice 30 min prior to an ip injection of paraquat (20 mg/kgx2), and thereafter at 6-h intervals until the conclusion of the study (72 h). The number of the micronucleated polychromatic erythrocytes increased after paraquat administration both in peripheral blood and bone marrow cells. Melatonin administration to paraquat-treated mice significantly reduced micronuclei formation in both peripheral blood and bone marrow cells; these differences were apparent at 24, 48 and 72 h after paraquat administration. The induction of micronuclei was time-dependent with peak values occurring at 24 and 48 h. The reduction in paraquat-related genotoxicity by melatonin is likely due in part to the antioxidant activity of the indole. We did not observe effects of melatonin over paraquat in paraquat+melatonin groups incubated at 0, 60 and 120 min. Mitomycin C, which was used as a positive control, also caused the expected large rises in micronuclei in both bone marrow and peripheral blood cells at 24, 48 and 72 h after its administration.

Frequency of radiation-induced micronuclei in neuronal cells does not correlate with clonogenic survival

It is generally assumed that radiation-induced micronuclei (MN) in cytokinesis-blocked cells are an expression of cellular radiosensitivity. Therefore, radiosensitive cells should have a high frequency of MN and radioresistant cells should show lower levels. We have irradiated cells of a panel of 13 neuronal cell lines of widely differing radiosensitivity [human neuroblastomas: N2alpha, SHSY5Y, SK-N-SH, KELLY and SK-N-BE(2c); murine neuroblastomas: OP-6 and OP-27; human glioblastomas: G120, G60, G28, G112, G44 and G62] and compared their radiation response using the micronucleus and standard clonogenic assays. It was found that micronucleus frequency was much higher in some of the radioresistant cell lines (N2alpha, G28, G120 and G44; SF2 >/= 0.60). These cell lines showed a high frequency of more than 0.32 MN per gray of (60)Co gamma radiation per binucleated cell. On the other hand, the more radiosensitive cell lines (OP-27 and SK-N-SH, SF2 </= 0.27) produced 0.08 +/- 0.01 and 0.04 +/- 0.01 MN per gray, respectively. OP-6, SK-N-BE(2c), G112, G62, G60 and KELLY cells constituted an intermediate group and displayed a micronucleus formation index between 0.10 and 0.24 MN per gray per binucleated cell. SHSY5Y cells showed no detectable formation of MN. In two groups [OP-6, SK-N-BE(2c), G112, G62, N2alpha and G28 or G120, G60, OP-27 and SK-N-SH], the more resistant cell lines produced more MN per unit dose. Another group [OP-6, SK-N-BE(2c), G112, G62, G44 and G120] showed no correlation between micronucleus formation and radiosensitivity. We conclude that the relationship between cell survival and micronucleus formation is not straightforward and that it would be simplistic to translate micronucleus frequency into radiosensitivity.

[Correlation between the duration of radiation adaptive response in bone marrow cells of mice and the dose of gamma-irradiation in vivo]

The dependence between the adaptive response and adaptive dose was studied on the basis of cytogenetic damage in polychromatic erythrocytes of bone marrow cells in mice after a low dose gamma-irradiation in vivo. The adaptive response to doses of 0.1 and 0.2 Gy was found to be retained for at least two months after irradiation. However, the adaptive dose of 0.4 Gy did not induce prolonged adaptive response.

Effects of TNF-alpha/colchicine combined treatment on Burkitt lymphoma cells: molecular and ultrastructural changes

Tumour necrosis factor alpha (TNF-alpha) kills Daudi cells (Human Burkitt Lymphoma), inducing either necrosis or apoptosis without DNA fragmentation. Therefore, we were interested in studying the molecular and ultrastructural events occurring when the nucleus is more accessible and cells are blocked in mitosis, following colchicine treatment. In fact, as early as after 1 h treatment a typical ladder pattern was shown by means of DNA gel electrophoresis. In parallel the quantitative analysis of the different morphological patterns observed gave evidence of an increased percentage of primary necrosis after 6 h treatment, and a higher incidence of cells in late apoptosis as well as in secondary necrosis after 24 h treatment. Our findings show that Daudi cells respond to the combined treatment with an increased formation of micronuclei and nuclear alterations which follow a number of early mitochondrial changes and result in enhanced cell death. These data imply that TNF-alpha-induced apoptosis of Daudi cells can be triggered by mitochondrial changes and is somehow related to microtubule organization.

Origin of microcells in the human sarcoma cell line HT-1080

The aim of this study was to investigate the development of microcells in the human sarcoma cell line HT-1080 after interference with thiophosphamidum. We found that damaged interphase macrocells located at the projection of the nucleolus may form one or several microcells. The micronuclei of the microcells intensively incorporate the thymidine analogue 5-bromo-2'-deoxyuridine and strongly express argyrophilic nucleolar organiser region proteins. At an early phase of the development, the micronuclei contain fragmented DNA, but in subsequent phases, the micronuclei accumulate polymeric DNA, simultaneously with an increase in their size. After desintegration of the damaged macrocell, the microcells appear in the intercellular space. The microcells can enter mitosis and they strongly express the lung resistance protein. Electron microscopic observations suggest that coiled bodies are involved in the development of the microcells. Since the observed path of microcell formation differs from apoptotic cell fragmentation into apoptotic bodies, we propose a new term for this microcell development: sporosis. We suggest that self-renewal of the tumour stem cells is likely based on sporosis.

Stage-specific apoptosis, developmental delay, and embryonic lethality in mice homozygous for a targeted disruption in the murine Bloom's syndrome gene

Bloom's syndrome is a human autosomal genetic disorder characterized at the cellular level by genome instability and increased sister chomatid exchanges (SCEs). Clinical features of the disease include proportional dwarfism and a predisposition to develop a wide variety of malignancies. The human BLM gene has been cloned recently and encodes a DNA helicase. Mouse embryos homozygous for a targeted mutation in the murine Bloom's syndrome gene (Blm) are developmentally delayed and die by embryonic day 13.5. The fact that the interrupted gene is the homolog of the human BLM gene was confirmed by its homologous sequence, its chromosomal location, and by demonstrating high numbers of SCEs in cultured murine Blm-/- fibroblasts. The proportional dwarfism seen in the human is consistent with the small size and developmental delay (12-24 hr) seen during mid-gestation in murine Blm-/- embryos. Interestingly, the growth retardation in mutant embryos can be accounted for by a wave of increased apoptosis in the epiblast restricted to early post-implantation embryogenesis. Mutant embryos do not survive past day 13.5, and at this time exhibit severe anemia. Red blood cells and their precursors from Blm-/- embryos are heterogeneous in appearance and have increased numbers of macrocytes and micronuclei. Both the apoptotic wave and the appearance of micronuclei in red blood cells are likely cellular consequences of damaged DNA caused by effects on replicating or segregating chromosomes.

Micronucleus formation in human amnion cells after exposure to 50 Hz MF applied horizontally and vertically

Micronucleus (MN) induction as a genotoxic effect of extremely-low-frequency electromagnetic fields (ELF-EMF, 50 Hz, 1 mT) was studied in human amniotic fluid cells (AFC) after continuous exposure to magnetic fields (MF), oriented horizontally and vertically with respect to the surface of the culture medium, at different time points. To compare the effectiveness of different exposure systems, a Helmholtz-coil system and a so-called Merritt-coil system was used. A statistically significant increase in MN frequency could be detected in exposed cells compared to controls after 72 h continuous exposure to MF applied vertically in the Merritt-coil system, while no effect was found after exposure in the Helmholtz-coil system. Furthermore, a significant increase in MN induction occurred after 24, 48 and 72 h exposure to MF applied horizontally in the Helmholtz-coil system in comparison to controls, whereas horizontally MF generated in the Merritt-coil system induced no genotoxic effects. To exclude suppression of indirect EMF-induced DNA-lesions, we studied MN formation in the presence of N-Acetyl-p-aminophenol (APAP, Paracetamol(R)), which is an inhibitor of DNA-repair mechanisms. We found a dose-dependent increase of MN formation in APAP-treated AFC cells, but no significant further increase in MN frequency after additional MF exposure. Therefore we conclude, that EMF-induced MN formation is not caused by directly or indirectly induced clastogenic mechanisms. The obtained results show that the orientation of MF with respect to the cell culture dish and the physical condition of the exposure system is of major importance for the induction of micronuclei in certain cell types. Therefore, the reason for inconsistent results published in the literature may be caused by the variability of exposure systems, the exposure conditions and the cell types used.

Antigenotoxic effects of cimetidine against benzene induced micronuclei in mouse bone marrow erythrocytes

An in vivo micronucleus assay using Balb/C male mice was used to examine antigenotoxic effects of cimetidine (CM) on benzene (BZN) induced genotoxic effects. CM not only has therapeutic and immunomudolatory role, but it has also been shown to protect bone marrow stem cells from radiation induced clastogenic effects. Therefore, in the present study we attempt to investigate the protective effects and possible mechanisms involved in the effects of CM. An 8-week-old male Balb/C mice (22+/-4 g weight) were treated with different doses of BZN (400, 600 and 800 mg/kg body weight), i.p. and sampled at 24, 48 and 72 h after treatment by cervical dislocation. Various doses of CM (10, 15, 30 mg/kg) were used in association with BZN and 1-2 h prior to BZN treatment. Results show that BZN effectively induced micronuclei in polychromatic erythrocytes (PCEs). Application of CM led to a significant reduction of micronuclei in PCEs, i.e. 2-fold after 10 mg/kg and 3-fold after 30 mg/kg CM treatment. Results also indicate CM was more effective when used in combination with BZN. Therefore, results indicate that CM could reduce clastogenic effects of BZN. Although further investigations are needed to reveal the mechanistical background behind the effect, the most probable mechanism involved might be free radical scavenging. This mechanism might be associated with amplification of glutathione system and cytochrome P-450 inhibition.

Radiation-induced acute immediate nuclear abnormalities in oral cancer cells: serial cytologic evaluation

OBJECTIVE

To evaluate the dose-response relationship of nuclear abnormalities in tumor cells collected by serial scrape smears from oral cancer patients on fractionated radiotherapy.

STUDY DESIGN

The study included 31 patients with squamous cell carcinoma of the oral cavity treated by radiotherapy (60 Gy in 25 fractions; 2.4 Gy per fraction). Serial scrape smears were taken from each tumor before treatment and after delivery of various fractions, usually 2 (4.8 Gy), 5 (12.0 Gy), 8 (19.2 Gy) or 12 (28.8 Gy). The smears were stained by Giemsa stain and evaluated by light microscopy, and the number of micronucleated, binucleated, nuclear budded and multinucleated cells were scored. Their relation to cumulative dose was analyzed by Kruskal-Wallis one-way analysis of variance. The results were expressed in terms of 1,000 mononucleated cells.

RESULTS

Even before treatment, most of the tumors showed various abnormally nucleated cells, and, despite the high intertumoral variation (as indicated by the high variance), all of them showed statistically significant dose-related increases. The mean values before treatment and after irradiation with 28.8 Gy, respectively, were 2.8 and 19.5 (P < .0001) for micronucleated cells, 1.5 and 8.5 (P < .000001) for nuclear budded cells, 8.2 and 35.5 (P < .0001) for binucleated cells, and 3.7 and 16.8 (P < .0001) for multinucleated cells. When the different types of nuclear abnormalities were combined and analyzed as "abnormally nucleated cells," the mean count before treatment and after 28.8 Gy were 7.9 and 44.9 (P < .00001), respectively.

CONCLUSION

The study showed that radiation-induced micronucleation, multinucleation, binucleation and nuclear budding in oral cancer cells has statistically significant dose-related increases that become evident in the initial few days of radiotherapy and that they can be differentiated well by cytology. This dose-response relationship and the high intertumoral variations suggest that serial assay of these changes has potential use for radiosensitivity prediction.

Further characterization of the radiosensitivity of the scid mouse

PURPOSE

To further characterize the radiation response of the scid mutation.

MATERIALS AND METHODS

X-ray induced chromosomal aberrations and cell killing were analysed using various in vivo or in vitro cell systems.

RESULTS

Using low LET X-irradiation a reverse dose-rate effect was found for killing of differentiated and differentiating spermatogonia and the chromosomal hyperradiosensitivity of scid mice was extended to the meiotic prophase. Most striking was the observation made in vitro with synchronized established cell lines that, contrary to the situation in wild-type cells, scid cells display high levels of both chromatid- and chromosome type aberrations when irradiated during the G1-phase of the cell cycle. A time-course for induction of micronucleated polychromatic erythrocytes (MPCE) was determined for scid mice using flow analysis. No significant differences with wild-type mice were recorded. The chromosomal radiosensitivity at the G1 stage in scid cells was 4.3 times higher than in control CB-17 cells whereas G2 sensitivity differed only by a factor of 1.3.

CONCLUSIONS

The reportedly normal radiosensitivity for MPCE in scid mice together with previous findings of hypo- or normal radiation sensitivity of scid cells could be explained by the induction of highly lethal chromatid-type damage at the G1 stage of the cell cycle leading to selective elimination of aberration-carrying cells. The differences in chromosomal radiosensitivity between wild-type and scid for the G1 and G2 stage of the cell cycle correlate with variation in the rates of DNA double-strand break (dsb) repair in scid cells during the cell cycle found by others.

Proliferative activity and micronucleus frequency after radiation of lung cancer cells as assessed by the cytokinesis-block method and their relationship to clinical outcome

We previously proposed a new assay using the cytokinesis-block micronucleus (MN) technique to estimate the fraction of cells undergoing mitosis in vitro [dividing fraction (DF)], potential doubling time (Tpot), and radiosensitivity (in terms of MN frequency) of human tumors. In the present study, we applied this technique to primary lung cancers to evaluate their biological characteristics, and the assay results for the proliferative activity were compared with the treatment outcome. Tumor tissues were disaggregated to single cells, which were cultured in the presence of cytochalasin B after (or without) radiation. At intervals, the proportion of multinucleate cells (its maximum value is the DF), the average number of nuclei/cell, and MNs in binucleate cells were scored. The Tpot was the extrapolated time for the nuclei:cell ratio to reach 2.0. Of the 71 tumor samples obtained, the DF and Tpot were evaluable in 61 (86%), and the MN frequency was evaluable in 52 (73%). The median DF and Tpot values were 23% and 7.7 days, respectively, for adenocarcinoma (n = 41), 26% and 8.9 days for squamous cell carcinoma (n = 13), 27% and 6.5 days for large cell carcinoma (n = 3), and 30% and 7.0 days for small cell carcinoma (n = 4). There was no significant difference in the mean DF or Tpot values according to the histological type or disease stage. The mean MN frequency after 2 Gy of radiation (minus the 0 Gy frequency) was 0.15 for adenocarcinoma, 0.17 for squamous cell carcinoma, 0.16 for large cell carcinoma, and 0.20 for small cell carcinoma. The MN frequency after radiation was positively correlated with both the DF and the baseline (at 0 Gy) MN frequency. In non-small cell lung cancer, a DF above the median was associated with an increased recurrence rate after operation, and the Tpot was correlated with the time until relapse in patients who developed recurrence. Although the clinical significance of the MN frequency needs to be clarified in future studies, the DF and Tpot determined by this assay appear to be good parameters of tumor proliferative activity.

Micronuclei and fluctuating asymmetry in brown trout (Salmo trutta): complementary methods to biomonitor freshwater ecosystems

In this work we measured both micronuclei number in kidney erythrocytes and fluctuating asymmetry in wild brown trout (Salmo trutta), caught in different fluvial ecosystems of Asturias (northern Spain) characterized by different levels of anthropic influence. Brown trout samples from rivers with high anthropic influence possessed significantly higher averages of both micronuclei and fluctuating asymmetry than brown trout samples from less anthropic-influenced rivers. These findings demonstrated the sensitivity of the micronucleus test in kidney erythrocytes to biomonitor freshwater ecosystems. The positive association found between micronuclei average and fluctuating asymmetry at the populational level suggests that fluctuating asymmetry tests could be potential indicators of environmental threat. Variation of fish asymmetry with ageing indicates that fluctuating asymmetry surveys of wild populations should be carried out in trouts of the same age class.

Interferon alpha reduces the level of radiation-induced micronuclei in mouse bone marrow cells

The effect of natural mouse interferon alpha (IFN-alpha) on production of micronuclei (MN) in bone marrow cells of whole-body gamma-irradiated mice (in sublethal dose of 0.5 Gy from 60Co source) was studied. It was shown that free interferon alpha (IFN-alpha(F)) and IFN-alpha encapsulated into liposomes (IFN-alpha(L)), when injected intraperitoneally to mice prior to their irradiation, reduced substantially the frequency of gamma-ray-induced micronuclei in polychromatic erythrocytes (MN-PCE) of the bone marrow of these mice. The antimutagenic effect of IFN-alpha(F), as registered by the micronucleus test, was observed in bone marrow cells of mice irradiated 24 h after injection. For IFN-alpha(L), the decrease in MN frequency in PCE of mice was observed 48-72 h after administration of the preparation.

Hypothermia induces micronuclei in mouse bone marrow cells

We investigated the effect of hypothermia on micronucleus induction in mouse bone marrow cells. Reserpine, which was negative in an in vitro chromosome aberration test, was administered intraperitoneally at 1, 5, 10, 100, and 1000 mg/kg to mice to induce hypothermia. Doses of 10-1000 mg/kg decreased rectal temperature to less than 33.3 degrees C from 24 h to 96 h after dosing and produced a statistically significant (p < 0.01) increase in micronucleated polychromatic erythrocyte frequencies (4.0-12.0/1000). When mice that were administered reserpine at 50, 100, or 200 mg/kg were exposed to an environmental temperature of 30 degrees C for 40 h to keep their body temperature within normal range, the frequency of micronucleated erythrocytes did not increase, while it did without increased environmental temperature. In addition, relatively large micronuclei (diameter of micronucleus > or = 1/4 diameter of cytoplasm) accounted for approximately 50% of the induced micronuclei. The results suggest that the low body temperature of less than 33 degrees C for 40 h induced micronuclei in bone marrow cells, and one possible mechanism was disturbance of the mitotic apparatus.

Comparative cytology of the oral cavities of snuff users

OBJECTIVE

To determine the effects of smokeless tobacco (snuff) on the epithelium of the oral cavity.

STUDY DESIGN

Cytologic smears were taken from the oral cavities of 22 snuff users and 19 control subjects. The samples were stained with the Papanicolaou method and accessed for cellularity, anucleated cells, micronuclei and broken egg nuclei.

RESULTS

An average of 7,624 cells per slide were found in the user group and 1,348 in the control. An average of 3,619 (47.5%) anucleated cells in the user group and 33.1 (2.5%) in the control were found per slide. Users with lesions had a significantly higher rate of anucleation than those without lesions. A total of 216 micronuclei were found in the user group and 46 in the control group. The broken egg nucleus was commonly found in both groups. The broken egg phenomenon is described as a nucleus that is in two portions and connected by a thin band of Feulgen-negative material.

CONCLUSION

The regular use of snuff causes loss of cell cohesion, hyperkeratosis and an increased incidence of micronuclei. The relationship of these conditions to the development of oral cancer is unclear. The most likely anomaly that may be associated with carcinogenesis is the micronucleus.

Micronuclei in exfoliated bladder cells among individuals chronically exposed to arsenic in drinking water

Inorganic arsenic is an established cause of lung and skin cancer. Epidemiological evidence from Taiwan suggests that arsenic causes more fatal internal cancers, with the highest relative risks reported for bladder cancer. We conducted a cross-sectional biomarker study in a Chilean male population chronically exposed to high (70 subjects) and low (55 subjects) arsenic levels in their drinking water (average concentrations, 600 and 15 micrograms As/liter, respectively). A fluorescent version of the exfoliated bladder cell micronucleus (MN) assay was used employing fluorescence in situ hybridization with a centromeric probe to identify the presence (MN+) or absence (MN-) of whole chromosomes within micronuclei, thereby determining the mechanism of arsenic-induced genotoxicity in vivo. We divided the study population into quintiles by urinary arsenic levels and found an exposure-dependent increase in micronucleated cell prevalence in quintiles 2-4 (urinary arsenic, 54-729 micrograms/liter). The largest increase appeared when quintile 4 was compared to quintile 1 [prevalence ratio, 3.0; 95% confidence interval (CI), 1.9-4.6]. The prevalence of MN+ increased to 3.1-fold in quintile 4 (95% CI, 1.4-6.6), and the prevalence of MN-increased to 7.5-fold in quintile 3 (95% CI, 2.8-20.3), suggesting that chromosome breakage was the major cause of MN formation. Prevalences of total MN, MN+, and MN- returned to baseline levels in quintile 5 (urinary arsenic, 729-1894 micrograms/liter), perhaps due to cytostasis or cytotoxicity. These results add additional weight to the hypothesis that ingesting arsenic-contaminated water enhances bladder cancer risk and suggest that arsenic induces genetic damage to bladder cells at drinking water levels close to the current United States Maximum Contaminant Level of 50 micrograms/liter for arsenic.