Showing papers on "Sister chromatid exchange published in 2001"

Chromosome Instability and Defective Recombinational Repair in Knockout Mutants of the Five Rad51 Paralogs

Abstract: The Rad51 protein, a eukaryotic homologue of Escherichia coli RecA, plays a central role in both mitotic and meiotic homologous DNA recombination (HR) in Saccharomyces cerevisiae and is essential for the proliferation of vertebrate cells. Five vertebrate genes, RAD51B, -C, and -D and XRCC2 and -3, are implicated in HR on the basis of their sequence similarity to Rad51 (Rad51 paralogs). We generated mutants deficient in each of these proteins in the chicken B-lymphocyte DT40 cell line and report here the comparison of four new mutants and their complemented derivatives with our previously reported rad51b mutant. The Rad51 paralog mutations all impair HR, as measured by targeted integration and sister chromatid exchange. Remarkably, the mutant cell lines all exhibit very similar phenotypes: spontaneous chromosomal aberrations, high sensitivity to killing by cross-linking agents (mitomycin C and cisplatin), mild sensitivity to gamma rays, and significantly attenuated Rad51 focus formation during recombinational repair after exposure to gamma rays. Moreover, all mutants show partial correction of resistance to DNA damage by overexpression of human Rad51. We conclude that the Rad51 paralogs participate in repair as a functional unit that facilitates the action of Rad51 in HR.

A review of the genotoxicity of marketed pharmaceuticals

Abstract: Information in the 1999 Physician’s Desk Reference as well as from the peer-reviewed published literature was used to evaluate the genotoxicity of marketed pharmaceuticals. This survey is a compendium of genotoxicity information and a means to gain perspective on the inherent genotoxicity of structurally diverse pharmaceuticals. Data from 467 marketed drugs were collected. Excluded from analysis were anti-cancer drugs and nucleosides, which are expected to be genotoxic, steroids, biologicals and peptide-based drugs. Of the 467 drugs, 115 had no published gene-tox data. This group was comprised largely of acutely administered drugs such as antibiotics, antifungals, antihistamines decongestants and anesthetics. The remaining 352 had at least one standard gene-tox assay result. Of these, 101 compounds (28.7%) had at least one positive assay result in the pre-ICH/OECD standard four-test battery (bacterial mutagenesis, in vitro cytogenetics, mouse lymphoma assay (MLA), in vivo cytogenetics). Per assay type, the percentage of positive compounds was: bacterial mutagenesis test, 27/323 (8.3%); in vitro cytogenetics 55/222 (24.8%); MLA 24/96 (25%); in vivo cytogenetics 29/252 (11.5%). Of the supplemental genetic toxicology test findings reported, the sister chromatid exchange (SCE) assay had the largest percentage of positives 17/39 (43.5%) and mammalian mutagenesis assays (excluding MLA) had the lowest percentage of positives 2/91 (2.2%). The predictive value of genetic toxicology findings for 2-year bioassay outcomes is difficult to assess since carcinogenicity can occur via non-genotoxic mechanisms. Nevertheless, the following survey findings were made: 201 drugs had both gene-tox data and rodent carcinogenicity data. Of these, 124 were negative and 77 were equivocal or positive for carcinogenicity in at least 1 gender/1 species. Of the 124 non-carcinogens, 100 had no positive gene-tox findings. Of the remaining 24, 19 were positive in in vitro cytogenetics assays. Among the 77 compounds that exhibited equivocal or positive effects in carcinogenesis studies, 26 were positive in gene-tox assays and 51 were negative. Of the 51 negatives, 47 had multiple negative gene-tox assay results suggesting that these are probably non-genotoxic carcinogens. Statistical analyses suggested that no combination of gene-tox assays provided a higher predictivity of rodent carcinogenesis than the bacterial mutagenicity test itself.

Fission yeast Rad50 stimulates sister chromatid recombination and links cohesion with repair

Abstract: To study the role of Rad50 in the DNA damage response, we cloned and deleted the Schizosaccharo myces pombe RAD50 homologue The deletion is sensitive to a range of DNA-damaging agents and shows dynamic epistatic interactions with other recombination?repair genes We show that Rad50 is necessary for recombinational repair of the DNA lesion at the mating-type locus and that rad50 shows slow DNA replication We also find that Rad50 is not required for slowing down S phase in response to hydroxy urea or methyl methanesulfonate (MMS) treatment Interestingly, in rad50 cells, the recombination frequency between two homologous chromosomes is increased at the expense of sister chromatid recombination We propose that Rad50, an SMC-like protein, promotes the use of the sister chromatid as the template for homologous recombinational repair In support of this, we found that Rad50 functions in the same pathway for the repair of MMS-induced damage as Rad21, the homologue of the Saccharomyces cerevisiae Scc1 cohesin protein We speculate that Rad50 interacts with the cohesin complex during S phase to assist repair and possibly re-initiation of replication after replication fork collapse

Platinum(II) and palladium(II) complexes with 2-acetylpyridine thiosemicarbazone: cytogenetic and antineoplastic effects.

Abstract: The effect of three novel complexes of Pt(II) and three complexes of Pd(II) with 2-acetylpyridine thiosemicarbazone (HAcTsc) on sister chromatid exchange (SCE) rates and human lymphocyte proliferation kinetics on a molar basis was studied. Also, the effect of Pt(II) and Pd(II) complexes against leuk

Evaluation of Chromosomal Aberrations, Micronuclei, and Sister Chromatid Exchanges in Hospital Workers Chronically Exposed to Ionizing Radiation

Abstract: Cytogenetic analysis was performed in peripheral blood lymphocytes from hospital workers chronically exposed to ionizing radiation in comparison to matched non-exposed individuals. The accumulated absorbed doses calculated for the radiation workers ranged from 9.5 to 209.4 mSv. The endpoints used were chromosomal aberrations (CA), micronuclei (MN), and sister chromatid exchanges (SCE). The frequencies of CA/100 cells observed for the exposed group were significantly (P=0.018) higher than in the control group: 3.2 and 2.6, respectively. Similarly, the mean numbers of SCE per cell were statistically higher (P=0.025) in the exposed group (6.2) in comparison with the control group (5.8). In the case of micronuclei analysis, no significant (P=0,06) difference between both groups was found, but these data should be cautiously interpreted since an increase in the frequencies of MN was found for radiation workers (3.0 MN/100 cells), compared to the control group (2.6 MN/100 cells) and this increase occur in parallel to CA and SCE frequencies. The difference between the results could be explained by the nature of CA and MN generation. The increased frequencies of CA and SCE in radiation workers indicate the cumulative effect of low-level chronic exposure to ionizing radiation, and the relevance of conducting cytogenetic analysis in parallel to physical dosimetry in the working place.

Chromosome aberrations and sister chromatid exchanges in cultured human lymphocytes treated with sodium metabisulfite, a food preservative.

Abstract: The aim of this study was to investigate the ability of sodium metabisulfite (SMB) which is used as an antimicrobial substance in food, to induce chromosome aberrations (CA) and sister chromatid exchanges (SCE) in human lymphocytes. SMB-induced CAs and SCEs at all concentrations (75, 150 and 300 microg/ml) and treatment periods (24 and 48h) dose-dependently. However, SMB decreased the replication index (RI) and the mitotic index (MI) at the concentrations of 150 and 300 microg/ml for 24 and 48h treatment periods. This decrease was dose-dependent as well.

Cytogenetic effects of 900 MHz (GSM) microwaves on human lymphocytes

Abstract: The cytogenetic effects of 900 MHz radiofrequency fields were investigated with the chromosome aberration and sister chromatid exchange frequency methods. Three different modes of exposure (continuous, pseudo-random and dummy burst) were studied for different power outputs (0, 2, 8, 15, 25, 50 W). The specific absorption rates varied between 0 and 10 W/kg. We investigated the possible effects of the 900 MHz radiation alone as well as of combined exposure to the chemical or physical mutagens mitomycin C and X-rays. Overall, no indication was found of a mutagenic, and/or co-mutagenic/synergistic effect of this kind of nonionizing radiation.

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

Abstract: 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 0.05). Sex (F=4.18; 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 ∼10% of interphase cells from the centenarians males, that is six times more often than in the younger control men (∼1.6%). The frequency of X signal loss (∼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 (∼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

Termini of human chromosomes display elevated rates of mitotic recombination.

Abstract: The strand-specific in situ hybridization technique of CO-FISH was used to probe telomeres of human mitotic cells in order to determine the spontaneous frequency of crossover. This approach allowed the detection of recombinational crossovers occurring anywhere along the length of individual chromosomes, including reciprocal events taking place between sister chromatids. Although the process of sister chromatid exchange (SCE) is the most prominent type of recombination in somatic mammalian cells, our results show that SCEs accounted for less than a third of the recombinational events revealed by CO-FISH. It is concluded that chromosomal regions near the termini of chromosome arms undergo extraordinarily high rates of spontaneous recombination, producing terminal crossovers whose small size precludes detection by standard cytogenetic methods. That similar results were observed for transformed epithelial cells, as well as primary fibroblasts, suggests that the phenomenon is a common characteristic of human cells. These findings are noteworthy because, although telomeric and subtelomeric DNA is known to be preferentially involved in certain types of recombination, the tips of somatic mammalian chromosomes have not previously been identified as preferred sites for crossover. Implications of these results are discussed in terms of limitations imposed on CO-FISH for its proposed use in directional hybridization mapping.

Saccharomyces cerevisiae rad51 mutants are defective in DNA damage-associated sister chromatid exchanges but exhibit increased rates of homology-directed translocations.

Abstract: Saccharomyces cerevisiae Rad51 is structurally similar to Escherichia coli RecA. We investigated the role of S. cerevisiae RAD51 in DNA damage-associated unequal sister chromatid exchanges (SCEs), translocations, and inversions. The frequency of these rearrangements was measured by monitoring mitotic recombination between two his3 fragments, his3-Delta5' and his3-Delta3'::HOcs, when positioned on different chromosomes or in tandem and oriented in direct or inverted orientation. Recombination was measured after cells were exposed to chemical agents and radiation and after HO endonuclease digestion at his3-Delta3'::HOcs. Wild-type and rad51 mutant strains showed no difference in the rate of spontaneous SCEs; however, the rate of spontaneous inversions was decreased threefold in the rad51 mutant. The rad51 null mutant was defective in DNA damage-associated SCE when cells were exposed to either radiation or chemical DNA-damaging agents or when HO endonuclease-induced double-strand breaks (DSBs) were directly targeted at his3-Delta3'::HOcs. The defect in DNA damage-associated SCEs in rad51 mutants correlated with an eightfold higher spontaneous level of directed translocations in diploid strains and with a higher level of radiation-associated translocations. We suggest that S. cerevisiae RAD51 facilitates genomic stability by reducing nonreciprocal translocations generated by RAD51-independent break-induced replication (BIR) mechanisms.

Correlation between lead exposure indicators and sister chromatid exchange (SCE) frequencies in lymphocytes from inorganic lead exposed workers.

Abstract: Inorganic lead exposure was studied in 31 volunteers employed in storage battery plant. The genotoxicity of lead was measured in terms of sister chromatid exchange (SCE). Erythrocyte δ-aminolevulinic acid dehydrogenase (ALAD) activity, urinary δ-aminolevulinic acid (U-ALA), and blood lead levels (PbBs) were also determined to evaluate some possible relations between these lead exposure indicators and the observed SCE frequencies. Blood lead concentration of 36.31 μg/dl was determined as an average level in the workers. Consequently decreased ALAD activity in erythrocytes and increased U-ALA excretion was observed in statistically higher PbBs when compared with the control group. A statistically significant correlation was observed between the PbBs and SCE frequencies (p < 0.05). Moreover, the correlation between U-ALA excretion and SCE frequencies (p < 0.01) was relatively higher than the correlation between PbBs and SCE frequencies. These results might indicate a possible mechanism of ALA mediation in the genotoxic effects of lead.

Resveratrol, a naturally occurring polyphenol, induces sister chromatid exchanges in a Chinese hamster lung (CHL) cell line

Abstract: We tested the genotoxicity of 3,5,4'-trihydroxystilbene (resveratrol), a polyphenolic phytoalexin found in grapes, in a bacterial reverse mutation assay, in vitro chromosome aberration (CA) test, in vitro micronucleus (MN) test, and sister chromatid exchange (SCE) test. Resveratrol was negative in the strains we used in the bacterial reverse mutation assay (S. typhimurium TA98 and TA100 and E. coli WP2uvrA) in the absence and presence of a microsomal metabolizing system. It induced structural CAs at 2.5-20 microg/ml and showed weak aneuploidy induction in a Chinese hamster lung (CHL) cell line. It induced MN cells and polynuclear and karyorrhectic cells after 48h treatments in the in vitro MN test. In the SCE test, resveratrol caused a clear cell-cycle delay; at 10 microg/ml, the cell cycle took twice as long as it did in the control. Resveratrol induced SCEs dose-dependently at up to 10 microg/ml, at which it increased SCE six-fold, and the number was almost as large as mitomycin C, a strong SCE inducer. No second mitoses were observed at 20 microg/ml even after 54h. Cell cycle analysis by FACScan indicated that resveratrol caused S phase arrest, and 48h treatment induced apoptosis. Our results suggest that resveratrol may preferentially induce SCE but not CA, that is, it may cause S phase arrest only when SCEs are induced.

Role of RAD51 in sister-chromatid exchanges in mammalian cells

Abstract: To measure the impact of the RAD51 pathway on Sister-Chromatid Exchanges (SCE), we used hamster cells expressing either the wild-type MmRAD51, which stimulates, or the dominant negative SMRAD51, which inhibits, gene conversion without affecting cell viability of untreated as well as γ-rays irradiated cells. We show that MmRAD51 did not affect the rate of spontaneous SCE while it strongly stimulated spontaneous recombination between tandem repeats. No spontaneous recombinant was detected when expressing SMRAD51 while spontaneous SCE were only slightly diminished. After treatment by an alkylating agent (MNU), MmRAD51 stimulated MNU-induced recombination whereas no recombinant was detected when expressing SMRAD51. MNU induced SCE in all cell lines, even in the SMRAD51 expressing lines, but the induction of SCE was slightly more efficient in lines expressing MmRAD51 and less efficient in lines expressing SMRAD51. Thus, in mammalian cells, the RAD51-dependent gene conversion pathway drastically affects recombination between intrachromosomal tandem repeats, whereas it only partially participates in SCE formation, measured at a chromosomal level. These results show that RAD51-gene conversion can participate in induced SCE but that alternative pathways should exist.

Preliminary study of cytogenetic damage in personnel exposed to anesthetic gases

Abstract: Occupational exposure to anesthetic gases is associated with various adverse health effects. Genetic material has been shown to be a sensitive target of numerous harmful agents. The aim of this study was to examine whether chromosomal damage could serve to indicate exposure to anesthetics. A group of 43 hospital workers of three professions (anesthesiologists, technicians and operating room nurses) and 26 control subjects were examined for chromosome aberrations, sister chromatid exchanges and micronucleus frequency. The exposed groups matched in duration of exposure to anesthetics, but not in age. An equal ratio between women and men was possible in all groups except nurses. Likewise, the ratio between smokers and non-smokers was also not comparable. An increase in chromosome damage was found in all exposed groups. While the increase in sister chromatid exchange frequency was not significant, chromosome aberrations and micronucleus frequency increased significantly, showing higher rates in women. The results suggest that the micronucleus test is the most sensitive indicator of changes caused by anesthetic gases. The observed difference between sexes with respect to exposure risk call for further, targeted investigations.

The C-terminal domain of the Bloom syndrome DNA helicase is essential for genomic stability

Abstract: Bloom syndrome is a rare cancer-prone disorder in which the cells of affected persons have a high frequency of somatic mutation and genomic instability. Bloom syndrome cells have a distinctive high frequency of sister chromatid exchange and quadriradial formation. BLM, the protein altered in BS, is a member of the RecQ DNA helicase family, whose members share an average of 40% identity in the helicase domain and have divergent N-terminal and C-terminal flanking regions of variable lengths. The BLM DNA helicase has been shown to localize to the ND10 (nuclear domain 10) or PML (promyelocytic leukemia) nuclear bodies, where it associates with TOPIIIα, and to the nucleolus. This report demonstrates that the N-terminal domain of BLM is responsible for localization of the protein to the nuclear bodies, while the C-terminal domain directs the protein to the nucleolus. Deletions of the N-terminal domain of BLM have little effect on sister chromatid exchange frequency and chromosome stability as compared to helicase and C-terminal mutations which can increase SCE frequency and chromosome abnormalities. The helicase activity and the C-terminal domain of BLM are critical for maintaining genomic stability as measured by the sister chromatid exchange assay. The localization of BLM into the nucleolus by the C-terminal domain appears to be more important to genomic stability than localization in the nuclear bodies.

Genotoxic effects of styrene-7,8-oxide in human white blood cells: comet assay in relation to the induction of sister-chromatid exchanges and micronuclei.

Abstract: Styrene is used in the production of plastics, resins and rubber. The highest human exposures to styrene take place by inhalation during the production of fiberglass reinforced plastics. Styrene is metabolized mainly in the liver to styrene-7,8-oxide (SO), its principal in vivo mutagenic metabolite. In this study, human peripheral white blood cells were exposed to several SO concentrations (10–200 μM) in order to evaluate its genotoxic properties by means of comet assay, sister-chromatid exchanges (SCE) and cytokinesis-blocked micronucleus (MN) test, in addition to determine its clastogenic or aneugenic properties by combining MN with fluorescence in situ hybridization (FISH) procedures. Our results show that SO induces DNA damage, SCE and MN in human leukocytes in vitro at concentrations above 50 μM, and that there is a strong relationship between DNA damage, as measured by the comet assay, and cytogenetic damage induced by SO at the doses employed. SO shows preferently a clastogenic activity and produces a cytostatic effect at high doses, reflected by the significant decrease of the calculated proliferation indices. A good dose-effect relationship is obtained in the three tests performed at the concentration range assayed.

Deceleration of carcinogenic potential by adaptation with low dose gamma irradiation.

Abstract: Animals that have been exposed to a very low dose of radiation are known to have many physiological benefits. Very low dose of ionizing radiation also induces mechanisms whereby cell or tissue become better fit to cope with subsequent exposures of high doses. This phenomenon of low dose radiation is termed 'adaptive response'. This response has been reported to be true in many biological systems and confirmed by experiments on chromosomal and chromatid aberrations, micronucleus formation, sister chromatid exchange tests, DNA mutation and cell survival study and using many other biological end points, although there are quite a few exceptions. The adaptation induced by low doses of radiation has been attributed to the induction of an efficient chromosome break repair mechanism at molecular and biochemical level. It is also substantiated in whole animal systems. When mice are initially conditioned with very small adapting doses, incidence of a challenging dose induced thymic lymphoma is recorded, with delayed latency and reduced frequency. Similarly, appearance of a transplanted barcl-95 thymic tumor has been delayed when mice are preconditioned with a small dose of radiation. Appearance and development of a tumour following transplantation of in vitro irradiated barcl-95 tumour cells with a small dose of 1 cGy are also delayed and volume of the tumour is reduced. Latency period of radiation-induced leukemia is modified by prior treatment with an adapting dose of radiation. Neoplastic transformation of several human cultured cells is also significantly decreased by prior low dose exposure of radiation compared to non-exposed cells. These results indicate that an earlier exposure to a small dose of radiation also reduces the radiation-induced carcinogenesis. Various aspects of molecular mechanism underlying the radio-adaptation have been explained. However, the mechanism underlying the inhibition of carcinogenesis by low dose radiation is yet to be fully resolved.

Bloom helicase is involved in DNA surveillance in early S phase in vertebrate cells

Abstract: Bloom syndrome (BS) is a recessive human genetic disorder characterized by short stature, immunodeficiency and an elevated risk of malignancy. The gene mutated in BS, BLM, encodes a RecQ-type DNA helicase. BS cells have mutator phenotypes such as hyper-recombination, chromosome instability and an increased frequency of sister chromatid exchange (SCE). To define the primary role of BLM, we generated BLM−/− mutants of the chicken B-cell line DT40. In addition to characteristics of BLM−/− cells reported previously by the other group, they are hypersensitive to genotoxic agents such as etoposide, bleomycin and 4-nitroquinoline-1-oxide and irradiation with the short wave length of UV (UVC) light, whereas they exhibit normal sensitivity to X-ray irradiation and hydroxyurea. UVC irradiation to BLM−/− cells during G1 to early S phase caused chromosomal instability such as chromatid breaks and chromosomal quadriradials, leading to eventual cell death. These results suggest that BLM is involved in surveillance of base abnormalities in genomic DNA that may be encountered by replication forks in early S phase. Such surveillance would maintain genomic stability in vertebrate cells, resulting in the prevention of cellular tumorigenesis.

Hemoglobin adducts and sister chromatid exchanges in hospital workers exposed to ethylene oxide: effects of glutathione S-transferase T1 and M1 genotypes.

Abstract: Ethylene oxide (EtO) is a genotoxic carcinogen with widespread uses as an industrial chemical intermediate and sterilant. We examined the effects of glutathione S-transferase T1 ( GSTT1 ) and M1 ( GSTM1 ) genotypes on the levels of N -(2-hydroxyethyl)valine (HEV) adducts in the erythrocytes and sister chromatid exchange (SCE) in lymphocytes from a group of 58 operators of sterilizers that used EtO and nonexposed workers from nine hospitals in the United States and one hospital in Mexico City. Cumulative exposure to EtO was estimated during the 4-month period before the collection of blood samples. Results showed that EtO exposure was significantly associated with the levels of HEV adducts and SCE after adjusting for cigarette smoking and other potential confounders. A significantly higher HEV adduct level (0.17 ± 0.03 versus 0.08 ± 0.01, mean ± SE; P = 0.02) but lower SCE frequency (5.31 ± 0.39 versus 6.21 ± 0.17; P = 0.04) was observed in subjects with homozygous deletion of the GSTT1 gene (null genotype) as compared with those with at least one copy of the gene (positive genotype). In multiple regression analysis, the GSTT1 -null genotype was associated with an increase in HEV adduct level (β = 1.62; P = 0.02) and a decrease in SCE frequency (β = −1.25; P = 0.003) after adjusting for age, gender, race, education, cigarette smoking, and EtO exposure status. The inverse SCE- GSTT1 relationship remained unchanged when SCE was further examined in relation to HEV adducts as an indicator of the internal EtO dose. The GSTM1 genotype was not associated with the level of either HEV adduct or SCE. These data indicate that the GSTT1 -null genotype is associated with increased formation of EtO-hemoglobin adducts in relation to occupational EtO exposure, suggesting that individuals with homozygous deletion of the GSTT1 gene may be more susceptible to the genotoxic effects of EtO. The unexpected finding of decreased SCEs, which is less clear, may be attributed to the nonchemical specificity of this end point and the lack of expression of the GSTT1 enzyme in lymphocytes.

Variant metabolizing gene alleles determine the genotoxicity of benzo[a]pyrene.

Abstract: Understanding the mechanisms involved with genetic susceptibility to environmental disease is of major interest to the scientific community. We have conducted an in vitro study to elucidate the involvement of polymorphic metabolizing genes on the genotoxicity of benzo[a]pyrene (BP). Blood samples from 38 donors were treated with BP and the induction of sister chromatid exchanges (SCE) and chromosome aberrations (CA) were evaluated. The latter is based on the tandem-probe fluorescence in situ hybridization (FISH) assay. The data indicate that the induction of genotoxicity was clearly determined by the inherited variant genotypes for glutathione-S-transferase (GSTM1) and microsomal epoxide hydrolase (EH). In a comparison of the two biomarkers, the CA biomarker shows a more definite association with the genotypes than does SCE. For example, the presence of the GSTM1 null genotype (GSTM1 0/0) is responsible for the highest level and significant induction of CA, irrespective of the presence of other genotypes in the different donors. This effect is further enhanced significantly by the presence of the excessive activation EH gene allele (EH4 * ) and decreased by the reduced activation EH gene allele (EH3 * ). Overall, the modulation of genotoxicity by the susceptibility genotypes provides support of their potential involvement in environmental cancer. Furthermore, the data indicate that the variant enzymes function independently by contributing their metabolic capability toward the expression of biologic activities. Therefore, studies like this one can be used to resolve the complexity of genetic susceptibility to environmental disease in human.

Cytological effects of 60 Hz magnetic fields on human lymphocytes in vitro: sister‐chromatid exchanges, cell kinetics and mitotic rate

Abstract: Incubation for 72 h of human peripheral blood cultures in the presence of 60 Hz sinusoidal magnetic fields (MF) at magnetic flux densities of 1.0, 1.5, and 2.0 mT led to stimulation of lymphocyte proliferation but had no influence on the frequency of sister-chromatid exchanges (SCE). The cytotoxic potential of MF combined with the mutagen Mitomycin-C also was analyzed. An opposite effect between MF exposure and Mitomycin-C treatment in terms of cell kinetics and mitotic rate was found, whereas no variation in SCE frequency was observed for this coexposure condition.

The protection of Vitamin E and selenium against carbon tetrachloride-induced genotoxicity in ovine peripheral blood lymphocytes.

Abstract: The protective effect of Vitamin E and selenium was studied for the possibility of decreasing the chromosome aberrations (CA), micronuclei (MN) and sister chromatid exchanges (SCE) induced by carbon tetrachloride (CCl4) in ovine peripheral lymphocytes cultured in vitro. The cultures of lymphocytes from two healthy lambs were treated with carbon tetrachloride at concentrations of 2, 4, 8, and 16 μg/ml for the last 48 h of cultivation and subsequently with the same doses of CCl4 and Vitamin E and selenium. A possible metabolic modification in carbon tetrachloride genotoxicity was detected with the application of S9 fraction for 2 h. No positive clastogenic effect of CCl4, and subsequently no protective effect of either antioxidant was obtained in the CA assay. In the MN assay for 48 h, an increase and, respectively, a decrease in the frequency of MN was found in cultures treated with CCl4 alone and in cultures treated concurrently with CCl4, Vitamin E and selenium at concentrations of 8 and 16 μg/ml ( P and P ). High statistical significance was achieved in SCE assay after the treatment of ovine peripheral lymphocytes with CCl4 at all concentrations tested (P

Evaluation of genotoxic potential of synthetic progestins-norethindrone and norgestrel in human lymphocytes in vitro.

Abstract: The genotoxicity study of two widely used contraceptive synthetic progestins, i.e. norgestrel and norethindrone was carried out on human lymphocyte chromosomes using chromosomal aberrations (CA), sister chromatid exchanges (SCE) and cell growth kinetics as parameters. The study was carried out both in the presence as well as in the absence of metabolic activation (S9 mix). The lymphocytes were exposed to three different concentrations of the drugs (20, 40 and 75 μg/ml for norethindrone and 10, 25 and 50 μg/ml for norgestrel) for three different durations (24, 48 and 72 h). The drug norethindrone was found to be non-genotoxic at any concentration and at any exposure duration either in the presence or in the absence of S9 mix. But another drug norgestrel was found to affect the genetic material. It induces CA, SCE at significant level, and inhibits lymphocyte proliferation at 25 and 50 μg/ml of concentrations only. In the presence of S9 mix the values obtained for CA, SCE and mitotic index (MI) were more significant. A time and dose relationship was also observed. It was concluded that norgestrel itself and possibly its metabolites are potent mutagens beyond a particular dose in human lymphocytes.

INCENP loss from an inactive centromere correlates with the loss of sister chromatid cohesion.

Abstract: Inactive centromeres of stable dicentric chromosomes provide a unique opportunity to examine the resolution of sister chromatid cohesion in mitosis. Here we show for the first time that inactive centromeres are composed of heterochromatin, as defined by the presence of heterochromatin protein HP1(Hs alpha). We then show that both the inner centromere protein (INCENP) and its binding partner Aurora-B/AIM-1 kinase can also be detected at the inactive centromere. Thus, targeting of the chromosomal passengers is not dependent upon the presence of an active centromere/kinetochore. Furthermore, we show that the association of INCENP with the inactive centromere correlates strictly with the state of cohesion between sister chromatids: loss of cohesion is accompanied by loss of detectable INCENP. These results are consistent with recent suggestions that one function of the chromosomal passenger proteins may be to regulate sister chromatid separation in mitosis.

Induction and persistence of micronuclei, sister-chromatid exchanges and chromosomal aberrations in splenocytes and bone-marrow cells of rats exposed to ethylene oxide.

Abstract: Studies on the induction and persistence of ethylene oxide (EO) induced chromosomal alterations in rat bone-marrow cells and splenocytes following in vivo exposure were carried out. Rats were exposed to ethylene oxide either chronically by inhalation (50-200ppm, 4 weeks, 5 days/week, 6h/day) or acutely by intraperitoneal injection (i.p.) at dose levels of 50-100ppm.Spontaneous- and induced-frequencies of micronuclei (MN), sister-chromatid exchanges (SCEs) and chromosomal aberrations were determined in rat bone-marrow cells, and in splenocytes following in vitro mitogen stimulation. Unstable chromosomal aberrations were studied in whole genome using standard Giemsa staining technique and fluorescence in situ hybridisation using probe for chromosome #2 was employed to detect chromosome translocations. Following chronic exposure, the cytogenetic analyses were carried out at days 5 and 21 in rat splenocytes, to study the induction and persistence of sister-chromatid exchanges. Following chronic exposure, ethylene oxide was effective in inducing SCEs, and markedly cells with high frequency SCEs were observed and they in-part persisted until day 21 post-exposure. However, no significant effect was observed in rat splenocytes for induction of MN and chromosomal aberrations. Following acute exposure, both SCEs and MN were increased significantly in rat bone-marrow cells as well as splenocytes.In conclusion, this study indicates that ethylene oxide at the concentrations employed by intraperitoneal injection or inhalation in adult rats is mutagenic and can induce both SCEs and MN.

Genotoxic action of the sesquiterpene lactone centratherin on mammalian cells in vitro and in vivo.

Abstract: Centratherin is a sesquiterpene lactone known for its antimicrobial, anti-inflammatory, and trypanocidal activities. The aim of this study was to determine the clastogenic and cytotoxic potential of centratherin in human lymphocytes and in mice. Human lymphocytes in culture were submitted to either continuous treatment or treatment during G(2) phase of the cell cycle. After continuous treatment the 0.2 microg/ml concentration induced a significant increase in total of chromosomal aberrations (CA) and sister chromatid exchange compared to control, and it reduced the mitotic index (MI). In the treatment during G(2) phase, centratherin induced a significant increase in the frequency of CA for all concentrations tested (0.1, 0.3, and 0.5 microg/ml). In the in vivo test system all three concentrations tested in mice (3.3, 6.7, and 13.3 mg/kg b.w.) induced a significant increase in CA compared to the negative control. On the basis of these results, centratherin showed clastogenic and cytotoxic activity on in vitro and in vivo mammalian systems.

Evaluation of phytotoxicity and genotoxicity of uranyl nitrate in Allium assay system.

Abstract: Uranyl nitrate inhibited root growth of Allium cepa at > or = 25 microM concentration. Fluorimetric analysis of metal uptake indicated the entry and accumulation of uranium into the root cell. Uranyl nitrate was neither clastogenic nor aneugenic as it failed to induce micronuclei significantly, but between 25 and 100 microM concentration, it increased significantly the frequency of sister chromatid exchange over that of control, implying its genotoxicity that possibly interfered with DNA replication and/or repair process.