Chromosome aberrations: past, present and future

Comparison between two FISH techniques in the in vitro study of cytogenetic markers for low-dose X-ray exposure in human primary fibroblasts

This work is about the setup of an in vitro system to report low-dose of X-rays as measured as cytogenetic damage. Q- and multicolor FISH (m-FISH), for telomere length and chromosome instability analysis, respectively, were compared to evaluate their sensitivity in the low-dose range in human primary fibroblasts. No telomere length modulation was observed up to 1 Gy in cycling fibroblasts, though reported for high doses, by that frustrating the purpose of using it as a low-exposure marker. To date the m-FISH is the best setup for the assessment of the chromosome structural damage: it allows stable and instable aberrations to be detected all over the karyotype. Stable ones such as balanced translocations, are not eliminated due to cell-cycle as unstable ones, so they are considered transmissible markers for retrospective dosimetry. The induction of chromosome damage showed a clear dependence on dose delivered; unstable aberrations were demonstrated after doses of 0.1 Gy, and stable aberrations after doses higher than 0.5 Gy. Summarizing, q-FISH is unfit to report low exposures while m-FISH provides better results: unstable aberrations are sensible short-term reporters, while stable ones long report exposures but with a higher induction threshold.

Evaluation of phytotoxicity and genotoxicity of nitrobenzene with a battery of Vicia faba assay system

Nitrobenzene (NB) is an important organic compound intermediate that is used widely in industry. In the present study, to evaluate the phytotoxicity and genotoxicity of NB on plants, Vicia faba was exposed to increasing concentrations of NB (5 mg L(-1) , 10 mg L(-1) , 25 mg L(-1) , 50 mg L(-1) , and 100 mg L(-1) ). The data revealed that germination rate and radicle length of V. faba seedlings were promoted by low NB concentrations and short exposure periods, whereas these parameters were inhibited at greater NB concentrations and longer exposures. When assessed by mitotic index, micronucleus, and chromosomal aberration assays, NB showed dose-dependent genotoxicity at 0 mg L(-1) to 50 mg L(-1).

Cytotoxicity and mutagenicity of cola and grape flavored soft drinks in bone marrow cells of rodents

Due to the large consumption of soft drinks in Brazil and worldwide in recent years and considering that some of the components present in their composition pose potential risks to human health, the aim of this study was to evaluate the cytotoxic and mutagenic potential of specific cola and grape-flavored soft drink brands. Bone marrow cells of Wistar rats were initially treated by gavage with one single dose of Cola or Grape soft drink, which was next offered ad libitum (instead of water) for 24 hours. A negative control treatment was performed by administering one single dose of water and a positive control administering cyclophosphamide intraperitoneally. Statistical analysis showed that the Cola and Grape soft drinks studied were not cytotoxic. However, the Cola soft drink proved mutagenic in this experiment treatment time. Therefore, this study serves as a warning about the consumption of Cola-flavored soft drink and for the need for further subchronic and chronic studies on soft drinks in order to evaluate the long term mutagenic and cytotoxic effects of these substances.

Effects of pneumonia and malnutrition on the frequency of micronuclei in peripheral blood of pediatric patients

The aim of this study was to evaluate the effects of bacterial pneumonia and malnutrition on the frequency of micronuclei (MN) in peripheral blood of pediatric patients through flow cytometric analysis. The study was an analytical case-control study carried out on 35 malnourished children with bacterial pneumonia and 20 well-nourished children with bacterial pneumonia, in addition to 20 healthy children as controls. Complete physical examination including; anthropometric measurement, Chest roentgenograms were done for all cases. Assessment of MN was done by FACSCalibur flow cytometry. The frequency of micronucleated reticulocytes (MN-RETs) was higher both in the malnourished children with pneumonia and well-nourished children with pneumonia than the controls. Within the malnourished children with pneumonia, patients with kwashiorkor had more micronucleated mature erythrocytes (MN-RBCs) and MN-RETs than patients with marasmus.

IN CONCLUSION

Pneumonia is associated with an increased frequency of MN and this increment is more pronounced in children with severe malnutrition especially kwashiorkor group.

Effect of thiol compounds on bleomycin-induced DNA and chromosome damage in human cells

Non-protein thiols are considered radioprotectors, preventing DNA damage by ionizing radiation. As bleomycin (BLM) is a radiomimetic agent it was proposed that thiols may prevent DNA damage produced by this antibiotic. However, results obtained with thiols and BLM-combined treatments in living cells are contradictory. The goal of this work was to assess the influence of five non-protein thiols of different electrical charge and chemical composition, on the DNA damage, DNA repair, chromosomal aberrations and cell killing induced by BLM. We found that, at the chromosomal level and cell killing, Glutathione, β-Mercaptoethanol and cysteine showed a protective effect, while ditiothreitol and cysteamine increased them, whereas at the DNA level all thiols potentiated the DNA damage induced by BLM, most probably due to a reactivation of the BLM complex.

Anticlastogenic effect of diosgenin on 7,12-dimethylbenz(a)anthracene treated experimental animals

The present investigation explores the anticlastogenic effect of diosgenin on 7,12-dimethylbenz(a)anthracene (DMBA) treated clastogenesis. The frequency of bone marrow micronucleated polychromatic erythrocytes (MnPCEs), chromosomal aberrations (CA), deoxyribonucleic acid (DNA) damage as cytogenetic markers and the levels of lipid peroxidation by-products, activities of enzymatic antioxidant and the status of detoxification agents were performed to assess the anticlastogenic effects of diosgenin on DMBA treated hamsters. Intraperitoneal injection of DMBA (30 mg/kg bw) leads to clastogenesis in hamster. Elevated MnPCEs frequencies, CA, DNA damage, enhanced lipid peroxidation by products, declined antioxidant activities and detoxification cascade were observed in DMBA treated hamsters. Oral pretreatment with diosgenin (80 mg/kg bw) daily for a period of five days significantly reduced the frequency of MnPCEs, CA, DNA damage and normalized the levels of lipid peroxidation by products with increased activities of antioxidants and detoxification agents in DMBA alone treated hamsters. Outcome of the present study revealed that diosgenin has potent anticlastogenic effects on DMBA treated hamsters.

Mutagenicity of diagnostic and therapeutical doses of radiopharmaceutical iodine-131 in Wistar rats

Iodine-131 ((131)I) is a radioisotope used for the diagnosis and treatment of thyroidal disorders such as hyperthyroidism and cancer. During its decay, (131)I emits beta particles and gamma rays; its physical half-life is 8 days, and it is accumulated preferentially in the thyroid tissue. This study aimed to evaluate the cytotoxicity and mutagenicity of diagnostic and therapeutic doses of (131)I using bone marrow cells of rats treated in vivo in a test system with a single dose by gavage. Concentrations of 5, 25, 50 and 250 μCi in 1 ml of water were used, and after 24 h, the animals were killed. Also, a concentration of 25 μCi/ml of water was used, and the animals were killed after 5 days. The results showed that no concentration of (131)I was cytotoxic and that all concentrations were mutagenic. As a result, there was no statistically significant difference detected by the χ(2) test in the induction of chromosomal aberrations between the different doses. Thus, the present study demonstrated a significant increase in chromosomal aberration in bone marrow cells exposed to (131)I regardless of the dose or the treatment time.

Structural alerts for predicting clastogenic activity of pro-oxidant flavonoid compounds: quantitative structure-activity relationship study

Flavonoids have been reported to exert multiple biological effects that include acting as pro-oxidants at very high doses. The authors determined a structural alert to identify the clastogenic activity of a series of flavonoids with pro-oxidant activity. The methodology was based on a quantitative structure-activity relationship (QSAR) study. Specifically, the authors developed a virtual screening method for a clastogenic model using the topological substructural molecular design (TOPS-MODE) approach. It represents a useful platform for the automatic generation of structural alerts, based on the calculation of spectral moments of molecular bond matrices appropriately weighted, taking into account the hydrophobic, electronic, and steric molecular features. Therefore, it was possible to establish the structural criteria for maximal clastogenicity of pro-oxidant flavonoids: the presence of a 3-hydroxyl group and a 4-carbonyl group in ring C, the maximal number of hydroxyl groups in ring B, the presence of methoxyl and phenyl groups, the absence of a 2,3-double bond in ring C, and the presence of 5,7 hydroxyl groups in ring A. The presented clastogenic model may be useful for screening new pro-oxidant compounds. This alert could help in the design of new and efficient flavonoids, which could be used as bioactive compounds in nutraceuticals and functional food.

In vitro evaluation of the genotoxic and cytotoxic effects of artesunate, an antimalarial drug, in human lymphocytes

Artesunate is one of the main antimalarial drugs used in several countries. It is a semisynthetic compound derived from artemisinin, a substance extracted from the Chinese plant, Artemisia annua L. Despite the widespread use of artesunate as an antimalarial drug, there is a lack of data regarding its genotoxic effects in human lymphocytes. Therefore, in this study, we used the comet assay and micronucleus test to evaluate the possible genotoxic effects of artesunate in cultured human lymphocytes. In addition, cell death by necrosis and apoptosis was also assessed. Cells exposed to different concentrations of artesunate showed a significant concentration-dependent increase (P < 0.05) in DNA damage index and micronuclei frequency. A significant increase in the frequency of apoptotic and necrotic cells was also observed. Our results showed that artesunate is a genotoxic and cytotoxic compound in cultured human lymphocytes.

Chromatin dynamics during cell cycle mediate conversion of DNA damage into chromatid breaks and affect formation of chromosomal aberrations: biological and clinical significance

The formation of diverse chromosomal aberrations following irradiation and the variability in radiosensitivity at different cell-cycle stages remain a long standing controversy, probably because most of the studies have focused on elucidating the enzymatic mechanisms involved using simple DNA substrates. Yet, recognition, processing and repair of DNA damage occur within the nucleoprotein complex of chromatin which is dynamic in nature, capable of rapid unfolding, disassembling, assembling and refolding. The present work reviews experimental work designed to investigate the impact of chromatin dynamics and chromosome conformation changes during cell-cycle in the formation of chromosomal aberrations. Using conventional cytogenetics and premature chromosome condensation to visualize interphase chromatin, the data presented support the hypothesis that chromatin dynamic changes during cell-cycle are important determinants in the conversion of sub-microscopic DNA lesions into chromatid breaks. Consequently, the type and yield of radiation-induced chromosomal aberrations at a given cell-cycle-stage depends on the combined effect of DNA repair processes and chromatin dynamics, which is cell-cycle-regulated and subject to up- or down-regulation following radiation exposure or genetic alterations. This new hypothesis is used to explain the variability in radiosensitivity observed at various cell-cycle-stages, among mutant cells and cells of different origin, or among different individuals, and to revisit unresolved issues and unanswered questions. In addition, it is used to better understand hypersensitivity of AT cells and to provide an improved predictive G2-assay for evaluating radiosensitivity at individual level. Finally, experimental data at single cell level obtained using hybrid cells suggest that the proposed hypothesis applies only to the irradiated component of the hybrid.

In vitro genotoxicity of rocuronium bromide in human peripheral lymphocytes

Rocuronium bromide (RB), an aminosteroid type neuromuscular blocking agent, acts by reducing or inhibiting the depolarising effect of acetylcholine on the terminal disc of the muscle cell. To our knowledge, there is no adequate information on the genotoxic effects of RB, up to now. In the present study, possible genotoxic effects of RB have been determined by means of sister chromatid exchange (SCE), chromosome aberration (CA) and micronucleus (MN) analyses in human peripheral blood lymphocytes. The human peripheral blood lymphocytes were exposed to three different concentrations of RB (60, 80 and 100 μg/mL) for 24- and 48-h. In this study, RB increased the frequency of CAs, however, did not increase the frequency of SCEs. RB did not decrease the proliferation index (PI) and mitotic index (MI). Accordingly, RB increased the frequency of micronucleus (MN) but did not decrease the nuclear division index (NDI). Findings from this study suggest that rocuronium bromide is clastogenic but not cytotoxic to cultured human peripheral blood lymphocytes.

FISH in analysis of gamma ray-induced micronuclei formation in barley

A micronucleus test in combination with fluorescent in situ hybridization (FISH) using telomere-, centromere-specific probes and 5S and 25S rDNA was used for a detailed analysis of the effects of gamma ray irradiation on the root tip meristem cells of barley, Hordeum vulgare (2n = 14). FISH with four DNA probes was used to examine the involvement of specific chromosomes or chromosome fragments in gamma ray-induced micronuclei formation and then to explain their origin. Additionally, a comparison of the possible origin of the micronuclei induced by physical and chemical treatment: maleic hydrazide (MH) and N-nitroso-N-methylurea (MNU) was done. The micronuclei induced by gamma ray could originate from acentric fragments after chromosome breakage or from whole lagging chromosomes as a result of a dysfunction of the mitotic apparatus. No micronuclei containing only centromeric signals were found. An application of rDNA as probes allowed it to be stated that 5S rDNA–bearing chromosomes are involved in micronuclei formation more often than NOR chromosomes. This work allowed the origin of physically- and chemically-induced micronuclei in barley cells to be compared: the origin of micronuclei was most often from terminal fragments. FISH confirmed its usefulness in the characterization of micronuclei content, as well as in understanding and comparing the mechanisms of the actions of mutagens applied in plant genotoxicity.

Protective effect of hawthorn extract against genotoxicity induced by methyl methanesulfonate in human lymphocytes

The preventive effect of hawthorn (Crataegus microphylla) fruit extract against genotoxicity induced by methyl methanesulfonate (MMS) has been investigated in human cultured blood lymphocytes. Peripheral blood samples were collected from human volunteers at 0 (10 minutes before), and at 1 and 2 hours after a single oral ingestion of 1 g hawthorn powder extract. At each time point, the whole blood was treated in vitro with MMS (200 µmol) at 24 hours after cell culture, and then the lymphocytes were cultured with mitogenic stimulation to determine the micronuclei in cytokinesis-blocked binucleated cells. The lymphocytes treated with hawthorn and MMS to exhibit a significant decreasing in the incidence of micronucleated binucleated cells, as compared with similarly MMS-treated lymphocytes from blood samples collected at 0 hour. The maximum protection and decreasing in frequency of micronuclei (36%) was observed at 1 hour after ingestion of hawthorn extract. The high performance liquid chromatography (HPLC) analysis showed that hawthorn contained chlorogenic acid, epicatechin and hyperoside. It is obvious that hawthorn, particularly flavonoids constituents with antioxidative activity, reduced the oxidative stress and genotoxicity induced by toxic compounds. This set of data may have an important application for the protection of human lymphocyte from the genetic damage and side effects induced by chemicals hazardous in people.

Influence of DMSO on Carbon K ultrasoft X-rays induced chromosome aberrations in V79 Chinese hamster cells

Ultrasoft X-rays have been shown to be very efficient in inducing chromosomal aberrations in mammalian cells. The present study was aimed to evaluate the modifying effects of DMSO (a potent scavenger of free radicals) on the frequencies of chromosome aberrations induced by soft X-rays. Confluent held G1 Chinese hamster cells (V79) were irradiated with Carbon K ultrasoft X-rays in the presence and absence of 1M DMSO and frequencies of chromosome aberrations in the first division cells were determined. DMSO reduced the frequencies of exchange types of aberrations (dicentrics and centric rings) by a factor of 2.1-3.5. The results indicate that free radicals induced by ultrasoft X-rays contribute to a great extent to the induction of chromosome aberrations. The possible implications of these results in interpreting the mechanisms involved in the high efficiency of ultrasoft X-rays in the induction of chromosome aberrations are discussed.

BRCA1 role in the mitigation of radiotoxicity and chromosomal instability through repair of clustered DNA lesions

Oxidatively-induced clustered DNA lesions are considered the signature of any ionizing radiation like the ones human beings are exposed daily from various environmental sources (medical X-rays, radon, etc.). To evaluate the role of BRCA1 deficiencies in the mitigation of radiation-induced toxicity and chromosomal instability we have used two human breast cancer cell lines, the BRCA1 deficient HCC1937 cells and as a control the BRCA1 wild-type MCF-7 cells. As an additional control for the DNA damage repair measurements, the HCC1937 cells with partially reconstituted BRCA1 expression were used. Since clustered DNA damage is considered the signature of ionizing radiation, we have measured the repair of double strand breaks (DSBs), non-DSB bistranded oxidative clustered DNA lesions (OCDLs) as well as single strand breaks (SSBs) in cells exposed to radiotherapy-relevant γ-ray doses. Parallel measurements were performed in the accumulation of chromatid and isochromatid breaks. For the measurement of OCDL repair, we have used a novel adaptation of the denaturing single cell gel electrophoresis (Comet assay) and pulsed field gel electrophoresis with Escherichia coli repair enzymes as DNA damage probes. Independent monitoring of the γ-H2AX foci was also performed while metaphase chromatid lesions were measured as an indicator of chromosomal instability. HCC1937 cells showed a significant accumulation of all types of DNA damage and chromatid breaks compared to MCF-7 while BRCA1 partial expression contributed significantly in the overall repair of OCDLs. These results further support the biological significance of repair resistant clustered DNA damage leading to chromosomal instability. The current results combined with previous findings on the minimized ability of base clusters to induce cell death (mainly induced by DSBs), enhance the potential association of OCDLs with breast cancer development especially in the case of a BRCA1 deficiency leading to the survival of breast cells carrying a high load of unrepaired DNA damage clusters.

Genotoxic effects of a particular mixture of acetamiprid and alpha-cypermethrin on chromosome aberration, sister chromatid exchange, and micronucleus formation in human peripheral blood lymphocytes

The genotoxic effects of a particular mixture of acetamiprid (Acm, neonicotinoid insecticide) and alpha-cypermethrin (alpha-cyp, pyrethroid insecticide) on human peripheral lymphocytes were examined in vitro by chromosomal aberrations (CAs), sister chromatid exchange (SCE), and micronucleus (MN) tests. The human peripheral lymphocytes were treated with 12.5 + 2.5, 15 + 5, 17.5 + 7.5, and 20 + 10 microg/mL of Acm+alpha-cyp, respectively, for 24 and 48 h. The mixture of Acm+alpha-cyp induced the CAs and SCEs at all concentrations and treatment times when compared with both the control and solvent control and these increases were concentration-dependent in both treatment times. MN formation was significantly induced at 12.5 + 2.5, 15 + 5, 17.5 + 7.5, microg/mL of Acm+alpha-cyp when compared with both controls although these increases were not concentration-dependent. Binuclear cells could not be detected sufficiently in the highest concentration of the mixture (20 + 10 microg/mL) for both the 24- and 48-h treatment times. Mitotic index (MI), proliferation index (PI) and nuclear division index (NDI) significantly decreased because of the cytotoxic and cytostatic effects of the mixture, at all concentrations for two treatment periods. Significant decreases in MI and PI were concentration dependent at both treatment times. The decrease in NDI was also concentration-dependent at 48-h treatment period. In general, Acm+alpha-cyp inhibited nuclear division more than positive control, mitomycin C (MMC) and showed a higher cytostatic effect than MMC. Furthermore, in this article, the results of combined effects of Acm+alpha-cyp were compared with the results of single effects of Acm or alpha-cyp (Kocaman and Topaktas,2007,2009, respectively). In conclusion, the particular mixture of Acm+alpha-cyp synergistically induced the genotoxicity/cytotoxicity in human peripheral blood lymphocytes.

Comparison of chromosomal aberrations frequency and polymorphism of GSTs genes in workers occupationally exposed to cytostatics or anaesthetics

Authors compared the incidence of chromosomal aberrations (CAs) of workers occupationally exposed to cytostatics (group EXP1) or anaesthetics (group EXP2) in relationship to polymorphism of GSTM1, GSTP1 and GSTT1 genes. The cytogenetic analysis for chromosomal aberrations frequency and for polymorphisms of genes the PCR and PCR-RFLP method were used. Statistically higher frequency of total CAs was detected in both exposed groups: group EXP1 1.90±1.34%; Mann-Whitney U-test, p=0.001; group EXP2 2.53±1.46%, p=0.0008) as compared to control (1.26±0.93%). In group EXP2 was detected statistically higher frequency of aberrations CSA-type as compared to CTA-type. In xenobiotic metabolizing genes for GST higher frequency of total CAs and constituent types chromatid-type aberrations (CTAs) and chromosome-type aberrations (CSAs) of genes GSTM1 and GSTT1 with null genotype was detected. Statistically significant difference was detected only in CSA-type of aberrations in GSTT1 gene. In gene GSTP1 was not detected any difference in frequency of aberrations in presence of the variant allele. Presented results point out importance of individual susceptibility in evaluation of genotoxic agents of anaesthetics or cytostatics.

Origin of nuclear and chromosomal alterations derived from the action of an aneugenic agent--Trifluralin herbicide

Trifluralin is a herbicide capable of interfering in mitotic cell division due to either microtubule depolymerization or alteration in the concentration of calcium ions within the cell. The aim of this study was to investigate the effects of trifluralin in Allium cepa meristematic cells, evaluating the induction mechanisms of the chromosomal and nuclear aberrations. In this study, A. cepa root tips were submitted for 24h treatment to several concentrations of this herbicide and 48 h recovery post-treatment. The results showed that some concentrations of trifluralin can lead to a mitotic index inhibition, besides inducing chromosomal and nuclear alterations throughout the mitotic cycle. Some of the alterations found seem to be resulting from the herbicide action in different phases and in more than one consecutive cell cycle.

Effect of occupational exposure to multiple pesticides on translocation yield and chromosomal aberrations in lymphocytes of plant workers

Employees handling pesticides are simultaneously exposed to different active substances. Occurring multiple chemical exposures may pose a higher risk than it could be deduced from studies evaluating the effect of a single substance. This study comprised 32 pesticide plantworkers exposed to carbofuran, chlorpyrifos, metalaxyl, and dodine and an equal number of control subjects. Groups were matched by age (43.8 +/- 10.16 vs 41.8 +/- 7.42, respectively), sex (14 females; 18 males), and smoking (11 smokers; 21 nonsmokers). Chromosome aberration and translocation frequencies were determined using a standard aberration assay and fluorescent in situ hybridization (FISH) by applying painting probes for chromosomes 1, 2, and 4. Although significant, an observed increase in chromatid breaks (5.2 +/- 2.49) compared to controls (2.1 +/- 0.87), p(PostHoc) = 0.000001 is biologically irrelevant. Genomic frequency of translocations was also significantly elevated (exposed 0.0165 +/- 0.0070; control 0.0051 +/- 0.0023, P(PostHoc) = 0.000004). The distribution of translocations among chromosomes 1, 2, and 4 did not differ from control subjects. It corresponded to the distribution of DNA content among selected chromosomes indicating randomness of DNA damage. A good translocation yield correlation within years spent in pesticide production indicates that multiple pesticide exposure may pose a risk to genome integrity. However, for more accurate health risk assessments, the use of probes for some other groups of chromosomes should be considered.

Effect of N-metylcarbamate pesticide bendiocarb on cattle lymphocytes after in vitro exposure

Bendiocarb is a carbamate broad-spectrum insecticide used to control disease vectors such as mosquitoes and flies, as well as household and agricultural pests. Nowadays, only few papers reporting cytogenetic or possible genotoxic effect of this insecticide on mammalian cells are available. In the present study 24-hour exposure to bendiocarbamate at concentrations ranging from 20 to 160 μg/ml was used for investigation of unstable chromosomal aberrations (CA), sister chromatid exchanges (SCE) and stable chromosomal aberration induction in cultured bovine peripheral lymphocytes. The slight but no significant increase of chromatide breaks frequency was observed after the exposure of lymphocytes to 80 μg/ml of bendiocarb. At the highest concentration added to the cell cultures (160 μg/ml) mitotic index decrease was shown in both donors (p < 0.05; p < 0.01). Both statistically significant elevation of SCEs (p < 0.05) and a reduction of proliferative indices (PI) (p < 0.01) were shown at a dose of 80 μg/ml. By means of two fluorescent-labelled whole chromosome-painting probes, stable aberrations such as bovine chromosome 1 and 5 translocation as well as numerical aberrations (polyploidies, heteroploidies) were visualised under fluorescent microscope in some examined metaphases.

Detection of intergenomic chromosome rearrangements in irradiated Triticum aestivum--Aegilops biuncialis amphiploids by multicolour genomic in situ hybridization

The frequency and pattern of irradiation-induced intergenomic chromosome rearrangements were analysed in the mutagenized (M0) and the first selfed (M1) generations of Triticum aestivum L. - Aegilops biuncialis Vis. amphiploids (2n = 70, AABBDDUbUbMbMb) by multicolour genomic in situ hybridization (mcGISH). mcGISH allowed the simultaneous discrimination of individual Ae. biuncialis genomes and wheat chromosomes. Dicentric chromosomes, fragments, and terminal translocations were most frequently induced by gamma-irradiation, but centric fusions and internal exchanges were also more abundant in the treated plants than in control amphiploids. Rearrangements involving the Ub genome (Ub-type aberrations) were more frequent than those involving the Mb genome (Mb-type aberrations). This irradiation sensitivity of the Ub chromosomes was attributed to their centromeric or near-centromeric regions, since Ub-type centric fusions were significantly more abundant than Mb-type centric fusions at all irradiation doses. Dicentrics completely disappeared, but centric fusions and translocations were well transmitted from M0 to M1. Identification of specific chromosomes involved in some rearrangements was attempted by sequential fluorescence in situ hybridization with a mix of repeated DNA probes and GISH on the same slide. The irradiated amphiploids formed fewer seeds than untreated plants, but normal levels of fertility were recovered in their offspring. The irradiation-induced wheat - Ae. biuncialis intergenomic translocations will facilitate the successful introgression of drought tolerance and other alien traits into bread wheat.

Cytogenetic study of Ascaris trypsin inhibitor in cultured human lymphocytes with metabolic activation

The trypsin inhibitor (ATI) isolated from gastrointestinal nematode Ascaris suum was tested in vitro for induction of chromosome aberrations and sister chromatid exchanges (SCE). Genotoxicity assessment of purified ATI was carried out on metaphase plates received from peripheral blood lymphocyte macroculture (48 h test of structural chromosome aberrations and 72 h test of SCE) with exogenous metabolic activation. ATI was tested in dose of 25, 50 and 100 microg per ml of culture. Kinetics of cell divisions were determined by the replication index (RI). The mitotic index (MI) was expressed as a number of metaphases per 1000 nuclei analysed. Analysis of chromosome aberrations showed that higher doses of ATI (50 and 100 microg/ml) significantly increased the frequency of chromosome aberrations (mainly of chromatid gaps and breaks) compared to the negative control. All concentrations of ATI caused a statistically significant reduction in the MI and RI. In comparison with the negative control, a significant increase in the SCE frequency was observed in all applied doses of ATI. Thus, in the presence of S9 activation, the Ascaris trypsin inhibitor showed potential clastogenic activity and inhibition of the dynamics of lymphocyte divisions.

Determination of genotoxic effects of copper sulphate and cobalt chloride in Allium cepa root cells by chromosome aberration and comet assays

We used the anaphase-telophase chromosome aberration and comet (Single Cell Gel Electrophoresis, SCGE) assays to evaluate the genotoxic effects of copper sulphate (CS) and cobalt chloride (CC) chemicals prepared in two concentrations (EC(50), 2xEC(50)), using methyl methanesulfonate (MMS) as a positive control and untreated cells as a negative control. In Allium root growth inhibition test, EC(50) values for CS and CC are 1.5 and 5.5 ppm, respectively. Mitotic index (MI) decreased in all concentrations tested of CS and CC compared to the control at each exposure time. The bridge, stickiness, vagrant chromosomes, fragments, c-anaphase and multipolarity chromosome aberrations were observed in anaphase-telophase cells. The total chromosome aberrations were more frequent with an increasing in the exposure time and the concentrations of both chemicals. The genotoxicity of CS and CC in Allium cepa root cells was analyzed using a mild alkaline comet assay at pH 12.3, which allows the detection of single strand breaks. In all the concentrations, CS and CC induced a significant increase (P<0.05) in DNA damage. No significant difference was found between positive control (300+/-5.81) and 3 ppm CS (280+/-4.61). The methods used are applicable for biological monitoring of environmental pollutants.

Advances in the biophysical and molecular bases of radiation cytogenetics

PURPOSE

For more than 70 years radiation cytogenetics has continued to be a topic of major concern in relation to the action of radiation on living cells. To date, diverse cytogenetic findings have developed into orderly, quantitative interpretations and have stimulated numerous biophysical models. However, it is generally agreed that any one of the models used alone is still unable to explain all aspects of the observed chromosomal effects. In this review, a large number of radiation-induced chromosome aberration findings from the literature are reassessed with special attention given to the reaction kinetics and the relevant molecular processes.

CONCLUSION

It is now clear that DNA double-strand breaks (DSB) are an integral component of radiation-induced chromosome aberration. At the nexus of the maintenance of genome integrity, cells are equipped with excellent systems to repair DSB, notably non-homologous end-joining (NHEJ) and homologous recombination repair (HRR). These repair mechanisms are strictly regulated along with the DNA turnover cycle. NHEJ functions in all phases of the cell cycle, whereas HRR has a supplementary role specifically in S/G2 phase, where homologous DNA sequences are available in close proximity. The repair pathways are further regulated by a complex nuclear dynamism, where DSB are sensed and large numbers of repair proteins are recruited and assembled to form a repair complex involving multiple DSB. Considering such DSB repair dynamism, radiation-induced chromosome aberrations could be well understood as DSB-DSB pairwise interactions associated with the NHEJ pathway in all phases of the cell cycle and misrepair of a single DSB associated with the complementary HRR pathway in late S/G2 phase.

Genotoxic effects of X-rays on keratinized mucosa cells during panoramic dental radiography

OBJECTIVES

The aim of this study was to evaluate the genotoxic effects of X-rays on epithelial gingival cells during panoramic dental radiography using a differentiated protocol for the micronucleus test.

METHODS

40 healthy individuals who underwent this procedure for diagnostic purposes on request from their dentists agreed to participate in this study. All of them answered a questionnaire before the examination. Epithelial gingival cells were obtained from the keratinized mucosa of the upper dental arcade by gentle scraping with a cervical brush immediately before exposure and 10 days later. Cytological preparations were stained according to the Feulgen-Rossenbeck reaction, counterstained with fast green 1% for 1 min and analysed under a light microscope. Micronuclei, nuclear projections (broken eggs) and degenerative nuclear alterations (pyknosis, karyolysis, karyorrhexis and condensed chromatin) were scored.

RESULTS

The frequency of micronuclei was significantly higher after exposure (P < 0.05), as were the frequencies of nuclear alterations indicative of apoptosis (P < 0.001).

CONCLUSIONS

These results indicate that X-ray radiation emitted during panoramic dental radiography induces a genotoxic effect on epithelial gingival cells that increases the frequency of chromosomal damage and nuclear alterations indicative of apoptosis.

Styrene Metabolism, Genotoxicity, and Potential Carcinogenicity

This report reviews styrene biotransformation, including minor metabolic routes, and relates metabolism to the genotoxic effects and possible styrene-related carcinogenicity. Styrene is shown to require metabolic activation in order to become notably genotoxic and styrene 7,8-oxide is shown to contribute quantitatively by far the most (in humans more than 95%) to the genotoxicity of styrene, while minor ring oxidation products are also shown to contribute to local toxicities, especially in the respiratory system. Individual susceptibility depending on metabolism polymorphisms and individual DNA repair capacity as well as the dependence of the nonlinearity of the dose-response relationships in the species in question and the consequences for risk evaluation are analyzd.

The type and yield of ionising radiation induced chromosomal aberrations depend on the efficiency of different DSB repair pathways in mammalian cells

In order to evaluate the relative role of two major DNA double strand break repair pathways, i.e., non-homologous end joining (NHEJ) and homologous recombination repair (HRR), CHO mutants deficient in these two pathways and the parental cells (AA8) were X-irradiated with various doses. The cells were harvested at different times after irradiation, representing G2, S and G1 phase at the time of irradiation, The mutant cell lines used were V33 (NHEJ deficient), Irs1SF, 51-D1 (HRR deficient). In addition to parental cell line (AA8), a revertant of V33, namely V33-155 was employed. Both types of mutant cells responded with increased frequencies of chromosomal aberrations at all recovery times in comparison to the parental and revertant cells. Mutant cells deficient in NHEJ were more sensitive in all cell stages in comparison to HRR deficient mutant cells, indicating NHEJ is the major repair pathway for DSB repair through out the cell cycle. Both chromosome and chromatid types of exchange aberrations were observed following G1 irradiation (16 and 24 h recovery). Interestingly, configurations involving both chromosome (dicentrics) and chromatid exchanges were encountered in G1 irradiated V33 cells. This may indicate that unrepaired DSBs accumulate in G1 in these mutant cells and carried over to S phase, where they are repaired by HRR or other pathways such as B-NHEJ (back up NHEJ), which appear to be highly error prone. Both NHEJ and HRR, which share some of the same proteins in their pathways, are involved in the repair of DSBs leading to chromosomal aberrations, but with a major role of NHEJ in all stages of cell cycle.

Genotoxic effects of white fluorescent light on human lymphocytes in vitro

Sources of light beams such as white fluorescent light, are present in our daily life to meet the needs of life in the modern world. This study was conducted with the objective of determining the possible genotoxic, cytotoxic and aneugenic effects caused by this agent in different stages of the cell cycle (G0/early G1, S, and late G2), using different cytogenetic parameters (sister chromatid exchanges--SCE, chromosome aberrations--CA, and detection of aneugenic effects) in lymphocytes from temporary cultures of human peripheral blood. WFL showed a genotoxic effect in vitro, expressed by an increase in the frequency of SCE's, regardless of the cell cycle stage. However, no increase in the frequency of CAs was observed. In addition, disturbances in cell cycle kinetics and chromosomal segregation were also observed. Taken together, such data may contribute to a better understanding and a different management in the use of phototherapy for some pathological conditions.

Protective effect of hawthorn extract against genotoxicity induced by cyclophosphamide in mouse bone marrow cells

The preventive effect of hawthorn (Crataegus microphylla) fruit extract was investigated in mouse bone marrow cells against genotoxicity induced by cyclophosphamide. Mice were orally (gavages) pretreated with solutions of hawthorn extract which was prepared at five different doses (25, 50, 100, 200 and 400mg/kg b.w.) for seven consecutive days. Mice were injected intraperitoneally on the seventh day with cyclophosphamide (50mg/kg b.w.) and killed after 24h for the evaluation of micronucleated polychromatic erythrocytes (MnPCEs) and the ratio of PCE/(PCE+NCE) (polychromatic erythrocyte/polychromatic erythrocyte+normochromatic erythrocyte). All of five doses of extract significantly reduced MnPCEs induced by cyclophosphamide (P<0.0001). Hawthorn extract at dose 100mg/kg b.w. reduced MnPCEs 2.5 time and also completely normalized PCE/(PCE+NCE) ratio. Hawthorn extract exhibited concentration-dependent antioxidant activity on 1,1-diphenyl-2-picryl hydrazyl free radical. Hawthorn contains high amounts of phenolic compounds; the HPLC analysis showed that it contained chlorogenic acid, epicatechin and hyperoside. It is obvious that hawthorn, particularly flavonoids constituents with antioxidative activity, reduced the oxidative stress and genotoxicity induced by cyclophosphamide in mouse bone marrow cells.

Assessment of the genotoxicity of imidacloprid and metalaxyl in cultured human lymphocytes and rat bone-marrow

Imidacloprid and metalaxyl are two pesticides that are widely used in agriculture, either separately, or in combination. These agents were studied for their possible genotoxic effects with respect to the following cytogenetic end-points: (1) in vitro micronucleus (MN) formation and sister-chromatid exchange (SCE) induction in human lymphocytes and (2) in vivo micronucleus induction in polychromatic erythrocytes (PCEs) of the rat bone-marrow. The results of the MN analysis indicate that MN frequencies after treatment with both pesticides, separately or as a mixture, do not significantly differ from those in the controls except after treatment with metalaxyl alone at 50 microg/ml (p<0.05). The results of the SCE analysis show that SCE frequencies after treatment with imidacloprid do not differ significantly from those in the controls. A statistically significant increase (p<0.05) in SCE frequency resulted from treatments with metalaxyl at 5, 10 and 100 microg/ml and with the combination of imidacloprid and metalaxyl at 100 and 200 microg/ml. Finally, the in vivo micronucleus assay with rat bone-marrow polychromatic erythrocytes showed a statistically significant effect upon separate treatments with imidacloprid and metalaxyl at doses of 300 mg/kg body weight (b.w.) (p<0.01) or upon combined treatment with 200 mg/Kg b.w. (p<0.001) and 400 mg/kg b.w. (p<0.05).

Automatic extraction of structural alerts for predicting chromosome aberrations of organic compounds

We use the topological sub-structural molecular design (TOPS-MODE) approach to formulate structural alert rules for chromosome aberration (CA) of organic compounds. First, a classification model was developed to group chemicals as active/inactive respect to CA. A procedure for extracting structural information from orthogonalized TOPS-MODE descriptors was then implemented. The contributions of bonds to CA in all the molecules studied were then generated using the orthogonalized classification model. Using this information we propose 22 structural alert rules which are ready to be implemented in expert systems for the automatic prediction of CA. They include, among others, structural alerts for N-nitroso compounds (ureas, urethanes, guanidines, triazines), nitro compounds (aromatic and heteroaromatic), alkyl esters or phosphoric acids, alkyl methanesulfonates, sulphonic acids and sulphonamides, epoxides, aromatic amines, azaphenanthrene hydrocarbons, etc. The chemico-biological analysis of some of the structural alerts found is also carried out showing the potential of TOPS-MODE as a knowledge generator.