Showing papers on "Sister chromatid exchange published in 1990"
TL;DR: The cloning and function of the human XRCC1 gene is described, which is the first mammalian gene isolated that affects cellular sensitivity to ionizing radiation and appears to be missing approximately 100 bp of transcribed sequence, including 26 nucleotides of coding sequence.
Abstract: We describe the cloning and function of the human XRCC1 gene, which is the first mammalian gene isolated that affects cellular sensitivity to ionizing radiation. The CHO mutant EM9 has 10-fold-higher sensitivity to ethyl methanesulfonate, 1.8-fold-higher sensitivity to ionizing radiation, a reduced capacity to rejoin single-strand DNA breaks, and a 10-fold-elevated level of sister chromatid exchange compared with the CHO parental cells. The complementing human gene was cloned from a cosmid library of a tertiary transformant. Two cosmid clones produced transformants that showed approximately 100% correction of the repair defect in EM9 cells, as determined by the kinetics of strand break repair, cell survival, and the level of sister chromatid exchange. A nearly full-length clone obtained from the pcD2 human cDNA expression library gave approximately 80% correction of EM9, as determined by the level of sister chromatid exchange. Based on an analysis of the nucleotide sequence of the cDNA insert compared with that of the 5' end of the gene from a cosmid clone, the cDNA clone appeared to be missing approximately 100 bp of transcribed sequence, including 26 nucleotides of coding sequence. The cDNA probe detected a single transcript of approximately 2.2 kb in HeLa polyadenylated RNA by Northern (RNA) blot hybridization. From the open reading frame and the positions of likely start sites for transcription and translation, the size of the putative XRCC1 protein is 633 amino acids (69.5 kDa). The size of the XRCC1 gene is 33 kb, as determined by localizing the endpoints on a restriction endonuclease site map of one cosmid clone. The deduced amino acid sequence did not show significant homology with any protein in the protein sequence data bases examined.
402 citations
Journal Article•
TL;DR: The results indicate that GSH S-transferase mu, a proposed marker of cancer susceptibility, is also a marker of susceptibility to the induction of cytogenetic damage by a certain class of mutagens.
Abstract: The identification of genetic traits that predispose individuals to environmentally induced cancers is one of the most important problems in cancer risk assessment. Genetic deficiency in the mu-isozyme of the glutathione (GSH) S-transferases (EC 2.5.1.18) has recently been associated with increased lung cancer risk. To test whether this association could arise from a metabolically mediated sensitivity to mutagenic substrates, cytogenetic damage in lymphocytes from 21 isozyme-deficient and 24 nondeficient individuals was induced. Cells were treated with trans-stilbene oxide, an excellent substrate for GSH S-transferase mu, or cis-stilbene oxide, a poor substrate for the isozyme. Sister chromatid exchange induction was measured as an indicator of cytogenetic damage. A trimodal distribution of trans-stilbene oxide-induced sister chromatid exchanges was observed in the population, including resistant, moderate, and highly sensitive groups. Glutathione S-transferase mu deficiency was associated with both moderate and high sensitivity to trans-stilbene oxide-induced damage but had no effect on cis-stilbene oxide-induced sister chromatid exchange. The results indicate that GSH S-transferase mu, a proposed marker of cancer susceptibility, is also a marker of susceptibility to the induction of cytogenetic damage by a certain class of mutagens. The differential effects of the cis- and trans-isomers of stilbene oxide illustrate that the stereoselectivity of GSH S-transferase mu toward various alkene epoxide substrates can be an important factor affecting individual sensitivity to DNA-damaging epoxides.
136 citations
TL;DR: In vitro cytogenetic testing was conducted at four laboratories, each using a standard protocol to evaluate coded chemicals with and without exogenous metabolic activation, and it is concluded that this protocol is effective and reproducible in detecting ABS and SCE.
Abstract: Forty-two chemicals were tested for their ability to induce cytogenetic change in Chinese hamster ovary cells using assays for chromosome aberrations (ABS) and sister chromatid exchanges (SCE). These chemicals were included in the National Toxicology Program's evaluation of the ability of four in vitro short-term genetic toxicity assays to distinguish between rodent carcinogens and noncarcinogens. The conclusions of this comparison are presented in Zeiger et al. [Zeiger E, Haseman JK, Shelby MD, Margolin BH, Tennant RW (1990): [Environ Molec Mutagen 16(Suppl 18): 1-14]. The in vitro cytogenetic testing was conducted at four laboratories, each using a standard protocol to evaluate coded chemicals with and without exogenous metabolic activation. Most chemicals were tested in a single laboratory; however, two chemicals, tribromomethane and p-chloroaniline, were tested at two laboratories as part of an interlaboratory comparison. Four chemicals (C.I. basic red 9 HCl, 2-mercaptobenzothiazole, oxytetracycline HCl, and rotenone) were tested for SCE in one laboratory and in a different laboratory for ABS. Tetrakis(hydroxymethyl)phosphonium sulfate was tested at one laboratory and the chloride form was tested at a different laboratory. Twenty-five of the 42 chemicals tested induced SCE. Sixteen of these also induced ABS; all chemicals that induced ABS also induced SCE. There was approximately 79% reproducibility of results in repeat tests, thus, we conclude that this protocol is effective and reproducible in detecting ABS and SCE.
122 citations
Journal Article•
TL;DR: Experimental evidence suggests that this adduct is derived from a metabolic pathway that includes the formation of 9-hydroxy-B(a)P, and was significantly elevated above concurrent controls up to 14 days.
Abstract: Male CD rats were injected with single i.p. doses of benzo( a )pyrene (B( a )P), and peripheral blood lymphocytes (PBLs), livers, and lungs were removed at various times after administration. DNA adducts were analyzed in each tissue by 32P postlabeling with nuclease P1 enhancement. Sister chromatid exchange frequencies were concomitantly measured in cultured whole blood. B( a )P-DNA adducts were observed in all three tissues from animals sacrificed between 1 and 56 days after injection. Maximal adduction levels occurred at about 4 days after administration, followed by a gradual loss of adducts over the period examined. The apparent half-lives of total DNA adducts were 15 days in liver, 17 days in PBLs, and 22 days in lung. Induced sister chromatid exchanges were linearly related to the amount of DNA adducts remaining in the PBLs at the time of harvest up to 56 days and were significantly elevated above concurrent controls up to 14 days.
One of the major adducts found in each tissue was N 2-{10β-[7β,8α,9α-trihydroxy-7,8,9,10-tetrahydrobenzo( a )pyrene]yl}deoxyguanosine. An additional novel major adduct was found in the liver DNA and is derived from the further metabolism of B( a )P- trans -7,8-dihydrodiol. A second major novel B( a )P adduct was found in the DNA of lung tissues and accounts for about 40% of the total adducts present. Experimental evidence suggests that this adduct is derived from a metabolic pathway that includes the formation of 9-hydroxy-B( a )P.
95 citations
Journal Article•
TL;DR: It is suggested that drug-induced stabilization of topoisomerase II-DNA complexes stimulates induction of sister chromatid exchanges, which consequently lead to cell death, and further studies show that the time course of VP-16-induced cytotoxicity correlated better with theTime course of sister Chromatid exchange formation than with protein-cross-linked DNA strand break formation.
Abstract: Mutant Chinese hamster V79 cells selected for alterations in poly(ADP-ribose) metabolism were shown to be resistant to epipodophyllotoxin (VP-16)-induced cytotoxicity. Cell lines ADPRT 54 and ADPRT 351 have reduced activity of poly(ADP-ribose) polymerase. N2, N3, and N4 cell lines grow in the absence of nicotinamide, with total NAD levels 1.5-3% of those found in parental V79 cells grown in complete medium. When grown in complete medium, the mutant cell lines are 2.3- to 9.6-fold resistant to VP-16-induced cytotoxicity. All of the cell lines respond to VP-16 treatment by formation of protein-cross-linked DNA strand breaks. Upon drug removal, all the cell lines reverse the DNA strand breaks at similar rates. Our studies show a clear dissociation between induction of DNA strand breaks and cytotoxicity. However, there is a good correlation between drug-induced sister chromatid exchanges and cytotoxicity. Thus, N3 cells, with low levels of VP-16-induced sister chromatid exchanges, show reduced levels of cytotoxicity relative to parental V79 cells, despite the fact that both cell lines show similar levels of VP-16-induced protein-cross-linked DNA strand breaks. Additional studies show that the time course of VP-16-induced cytotoxicity correlated better with the time course of sister chromatid exchange formation than with protein-cross-linked DNA strand break formation. These studies provide strong support for the proposal that VP-16-induced cytotoxicity involves the induction of sister chromatid exchanges. Thus, we suggest that drug-induced stabilization of topoisomerase II-DNA complexes stimulates induction of sister chromatid exchanges, which consequently lead to cell death.
78 citations
TL;DR: Genotoxicity of nicotine was evaluated employing Chinese hamster ovary cells and was genotoxic at the concentration, comparable to the saliva levels of nicotine achieved during tobacco chewing.
72 citations
TL;DR: It is concluded that the fumigants studied here may be less likely to express genotoxicity in terms of SCEs or chromosome aberrations than ethylene oxide or phosphine given a single short-term in vivo exposure.
Abstract: In preparation for a human study of worker exposure to grain fumigants and pesticides, we decided to screen commonly used fumigants for genotoxic effects in vitro. This research strategy was employed to test the possibility that structurally simple chemicals might have similar genotoxic properties in vivo and in vitro. As a first step, we designed our in vitro protocol to mimic to the extent possible, a single in vivo exposure of lymphocytes to fumigants. Go lymphocytes were treated with different doses of carbon tetrachloride, carbon disulfide, methyl bromide, chloropicrin, and melathion with and without addition of rat liver homogenate for 1/2 hour, washed free of toxicant, and stimulated with PHA. After culture, the prepared slides were studied for chromosome aberrations and SCEs. Malathion, methyl bromide, and chloropicrin significantly induced SCEs without S-9. Carbon disulfide alone required S-9 for significant SCE induction. Chromosome aberrations were significantly increased by malathion and methyl bromide. Carbon tetrachloride failed to induce SCEs or chromosome aberrations with or without S-9. We concluded from these preliminary studies and other comparable work that the fumigants studied here may be less likely to express genotoxicity in terms of SCEs or chromosome aberrations than ethylene oxide or phosphine given a single short-term in vivo exposure. The final design of our human study was altered to focus on seasonal worker exposure rather than on a single exposure event.
65 citations
Journal Article•
TL;DR: The results indicate that tartrazine is more clastogenic than curcumin, and sister chromatid exchanges and chromosomal aberrations induced byCurcumin and Tartrazine following acute and chronic exposure via the diet.
Abstract: Sister chromatid exchanges (SCEs) and chromosomal aberrations induced by curcumin (a natural dye) and tartrazine (a synthetic dye) were studied on bone marrow cells of mice and rats following acute and chronic exposure via the diet. Except for two low concentrations in the curcumin and one low concentration in the tartrazine treated series a significant increase in SCEs was observed in all the concentrations of the two dyes tested. Except for two high concentrations during the 9 months treatment no significant increase in chromosomal aberrations was observed in the curcumin treated series, whereas tartrazine showed a significant increase in chromosomal aberrations in some of the higher concentrations in all the series tested. The results indicate that tartrazine is more clastogenic than curcumin.
59 citations
TL;DR: The activities of vanadium oxide, vanadyl sulfate and ammonium metavanadate in inducing sister chromatid exchange and chromosomal aberrations were assayed in Chinese hamster ovary cells and induced CAb in the cells at doses closely equivalent to the TC50.
55 citations
TL;DR: It is shown that paracetamol reduces DNA synthesis by a specific inhibition of ribonucleotide reductase by electron paramagnetic resonance, and added to crude cell extracts of HU-resistant cells also immediately destroys this radical.
Abstract: Effects of paracetamol have been studied in a hydroxyurea (HU)-resistant mouse mammary tumour cell line TA3H2, shown to overproduce the small subunit of ribonucleotide reductase. These TA3H2 cells were much more resistant than the TA3H (wild-type) cells towards the inhibitory effect of paracetamol on cell growth, IC50 0.55 mM paracetamol for the wild-type compared to 2.7 mM for the HU-resistant cells. The reduced cell growth was due to an inhibition of replicative DNA synthesis, judged from an increased percentage of cells in S-phase measured by flow cytometry. Furthermore, in the wild-type cells, the increase in the number of cells in S phase was already observed at 0.1 mM while in the HU-resistant cell line this effect was first seen at 3.0 mM paracetamol. HU inhibits ribonucleotide reductase by destroying a tyrosyl free radical located on the small subunit of the enzyme. By electron paramagnetic resonance we demonstrate that paracetamol added to crude cell extracts of HU-resistant cells also immediately destroys this radical. These results show that paracetamol reduces DNA synthesis by a specific inhibition of ribonucleotide reductase. A concentration-dependent induction of sister chromatid exchanges was found both with paracetamol (1.0-10 mM) and HU (0.3-3 mM) in wild-type cells whereas no such increase was observed in HU-resistant cells. Paracetamol (1 mM for 2 h) also increased the number of chromosomal aberrations CAs in wild-type cells (i.e. chromatid breaks and chromatid exchanges). The frequency of CAs was not increased in HU-resistant cells at paracetamol concentrations up to 10 mM.(ABSTRACT TRUNCATED AT 250 WORDS).
51 citations
TL;DR: It is suggested that the exposure level is too low to increase SCE in human lymphocytes in vivo, and smokers, both the workers and the controls, had a higher SCE frequency than non-smokers.
Abstract: Sister chromatid exchange (SCE) was studied in the lymphocytes of 27 agricultural workers occupationally exposed to several pesticides and 28 matched controls from el Maresme, an agricultural area near Barcelona. Comparison between both groups with the t-test did not reveal significant differences. These negative findings suggest that, possibly, the exposure level is too low to increase SCE in human lymphocytes in vivo. Our results indicate that smokers, both the workers and the controls, had a higher SCE frequency than non-smokers, in agreement with previous data reported by different authors.
TL;DR: The structural basis of the induction of sister chromatid exchanges and chromosomal aberrations in Chinese hamster ovary cells was investigated by the CASE (Computer Automated Structure Evaluation) method, on artificial‐intelligence‐based system.
Abstract: The structural basis of the induction of sister chromatid exchanges (SCE) and chromosomal aberrations (Cvt) in Chinese hamster ovary cells was investigated by the CASE (Computer Automated Structure Evaluation) method, on artificial-intelligence-based system. Using the relevant National Toxicology Program data bases CASE identified a set of structural determinants responsible for the induction of SCE and another one for Cvt.
A comparison between the structural determinants associated with SCE and Cvt revealed an overlap of only 22.6%, while the overlap between SCE and the determinants of mufagenicity in Salmonella is 54.5%. This indicates a) that the structural bases of the two phenomena differ and b) that it is likely that SCE, but not Cvt, involves a significant electrophilic/DNA-damaging component.
TL;DR: Treatment of human lymphocytes with vanadium pentoxide was not found to increase the frequency of structural chromosomal aberrations (CA) and sister-chromatid exchanges (SCE), but V2O5 significantly increased polyploid cell frequency and the mitotic index was significantly decreased.
TL;DR: Benomyl decreased the number of female rats with implants but did not cause any dominant lethals and was also shown to induce sister chromatid exchanges and micronuclei but not chromosome aberrations.
Abstract: Benomyl (methyl-1-[butylcarbamoyl]-2-benzimidazole carbamate), a benzimidazole derivative fungicide, was tested in the Ames test for point mutations; in human lymphocyte cultures for cell division disturbances, chromosomal aberrations, and SCE; in rat bone marrow cells in vivo for micronuclei; and in rats in vivo for dominant lethals. Benomyl was negative in the Ames test. In human lymphocytes, benomyl at concentrations of 0.5, 1.0, and 2.0 micrograms/ml decreased the number of cells undergoing third division whereas at the concentrations of 0.25 to 4.0 micrograms/ml it strongly increased the number of aneuploid cells. Benomyl was also shown to induce sister chromatid exchanges and micronuclei but not chromosome aberrations. Benomyl decreased the number of female rats with implants but did not cause any dominant lethals.
Journal Article•
TL;DR: 6-TG-resistant cells, selected by growth in 6-TG, exhibited cross-resistance to MNU but not to methyl methanesulfonate, confirming that a common pathway of tolerance is responsible for resistance to 6- TG and O6-methylguanine.
Abstract: The biochemical and genetic characteristics of a clone of Chinese hamster ovary cells displaying resistance to N-methyl-N-nitrosourea (MNU) and 6-thioguanine (6-TG) were analyzed. The initial level of 7-methylguanine, 3-methyladenine, and O6-methylguanine formation and the repair rates for these alkylated bases were the same in the resistant and in the parental cell line, indicating that the resistance to alkylation damage is not due to differences in DNA alkylation. After exposure for 24 or 48 h to 6-TG (0.6 µg/ml) in culture medium, the resistant clone incorporated 1.6-fold more 6-TG into DNA than the parental cells and, in contrast to them, was able to replicate the DNA containing the base analogue during the following 24 h. These data are in agreement with the hypothesis that resistant cells tolerate both O6-methylguanine and 6-TG present in DNA. The tolerance to MNU and 6-TG also included chromosomal damage induced by these two agents, and MNU-resistant cells incurred less sister chromatid exchanges after treatment with either MNU or 6-TG. 6-TG-resistant cells, selected by growth in 6-TG, exhibited cross-resistance to MNU but not to methyl methanesulfonate, confirming that a common pathway of tolerance is responsible for resistance to 6-TG and O6-methylguanine.
TL;DR: The cellular effects of the antioxidants butylated hydroxyanisole andbutylated hydroxytoluene were studied in a battery of in vitro tests and no evidence of genotoxicity was obtained.
TL;DR: VE appeared to inhibit the generation of oxidants by activated phagocytes, whereas BC scavenged oxidants generated by the myeloperoxidase/H2O2/halide system.
Abstract: Sixty asymptomatic cigarette smokers were randomly allocated into three treatment groups. Smokers in Group 1 received 900 international units of Vitamin E (VE) daily for 6 wk, whereas 40 mg of beta-carotene (BC) daily was administered to those in Group 2 for the same period. Subjects in Group 3 were treated with a matched placebo. Plasma levels of VE and BC as well as circulating leukocyte counts, sister chromatid exchanges (SCEs), and the luminol-enhanced chemiluminescence (LECL) responses of blood phagocytes activated with phorbol myristate acetate (PMA) and FMLP with cytochalasin B (FMLP/CB) were measured prior to the administration of the anti-oxidants/placebo after 4 and 6 wk of supplementation and 12 wk after cessation of treatment. SCEs and leukocyte counts remained unchanged throughout the trial in all three treatment groups. Administration of VE for 4 wk was accompanied by decreased FMLP/CB-activated (p < 0.005) and PMA-activated (p < 0.005) LECL responses. However, with PMA as stimulant, the inh...
TL;DR: The dose-response relationship for the induction of SCE by X-rays increased linearly with doses up to 100 cGy in both 3T3 and 10T1/2 cells, then declined, reaching nearly background levels after 400 cGy.
Abstract: SummaryWe examined the dose—response relationships for the induction of cell killing, chromosomal aberrations and sister chromatid exchanges (SCE) by 220 kV X-rays and 5·3 MeV alpha particles from a 238Pu source. The cells were irradiated in density-inhibited, confluent cultures. The D0 values for the X-ray and alpha particle survival curves were 1·7 Gy and 0·7 Gy, and the extrapolation numbers 2·5 and 1·0, respectively, for mouse 3T3 cells. Chromosomal aberrations increased linearly with dose for alpha-radiation and roughly with the square of dose for X-rays in 3T3 cells. At 37 per cent survival, 1·0 chromosomal aberration per cell was induced by X-rays and 1·7 per cell by alpha-radiation, but the fraction of cells without aberrations was similar. In confluent holding recovery experiments there was a 50 per cent reduction in X-ray-induced aberrations during the first 4 h of confluent holding. No decline in alpha-induced aberrations was observed with holding times up to 24 h. The dose—response relationshi...
TL;DR: It is shown that sister chromatid exchanges frequencies are an indicator of DNA damage induced in human lymphocytes in vitro by a low‐level pulsed electromagnetic field.
Abstract: We analyzed sister chromatid exchanges (SCE) frequencies as an indicator of DNA damage induced in human lymphocytes in vitro by a low-level pulsed electromagnetic field.
We studied the effect of low-level pulsed electromagnetic fields on human chromosomes with the cytogenetic assay of sister chromatid exchange (SCE) analysis. After the human peripheral lymphocyte cultures were exposed in vitro to the electromagnetic field at different intensities, no significant differences were observed when comparing with the control group as to the number of SCE.
TL;DR: 1,3-butadiene is genotoxic in vivo but is a weak in vitro genotoxin, according to sister chromatid exchange and micronucleus induction results, which paralleled the chronic bioassays which showed mice to be more susceptible than rats to 1, 3- butadiene carcinogenicity.
Abstract: 1,3-Butadiene and two major genotoxic metabolites 3,4-epoxybutene (EB) and 1,2:3,4-diepoxybutane (DEB) were used as model compounds to determine if genetic toxicity findings in animal and human cells can aid in extrapolating animal toxicity data to man. Sister chromatid exchange (SCE) and micronucleus induction results indicated 1,3-butadiene was genotoxic in the bone marrow of the mouse but not the rat. This paralleled the chronic bioassays which showed mice to be more susceptible than rats to 1,3-butadiene carcinogenicity. However, 1,3-butadiene did not induce unscheduled DNA synthesis (UDS) in the rat or mouse hepatocytes following in vivo exposure. Likewise, UDS in rat and mouse hepatocytes in vitro was not induced by EB or DEB. Salmonella typhimurium gene mutation (Ames) tests of 1,3-butadiene using strains TA1535, TA97, TA98, and TA100 and employing rat, mouse, and human liver S9 metabolic systems were barely 2-fold above background only in strain TA1535 at 30% 1,3-butadiene in air with induced and uninduced rat S9 and mouse S9 (uninduced). 1,3-Butadiene was negative in in vitro SCE studies in human whole blood lymphocytes cultures treated in the presence of rat, mouse, or human liver S9 metabolic activation. In general, 1,3-butadiene is genotoxic in vivo but is a weak in vitro genotoxin.
TL;DR: Because the analysis revealed that each of the cytogenetic assays responds to a different set of structural features associated with carcinogenicity, it can be concluded that the assays can be included in a battery of tests to improve predictivity.
Abstract: Two independent analyses were carried out to compare the induction of sister chromatid exchanges and of chromosomal aberrations as predictors of carcinogenicity. Using both a classical and a Bayesian approach, as well as by analysis of the structural fragments generated by CASE, an artificial intelligence system, it is included that individually neither of these tests is a satisfactory predictor of carcinogenicity. However, because the analysis revealed that each of the cytogenetic assays responds to a different set of structural features associated with carcinogenicity, it can be concluded that the assays can be included in a battery of tests to improve predictivity.
TL;DR: In relation to non-smokers, smokers exposed to vinyl chloride show significant increases in sister-chromatid exchange frequencies, and the problem of correlating the results of the chromosome aberration assay with micronucleus and sister- chromosomes exchange frequencies is discussed.
Abstract: The mutagenic effects of vinyl chloride monomer in man were studied in the lymphocyte culture with 3 methods: the chromosome aberration assay, the micronucleus assay and the sister-chromatid exchange method. Compared with control, values obtained by these tests are increased in workers occupationally exposed to vinyl chloride. In relation to non-smokers, smokers exposed to vinyl chloride show significant increases in sister-chromatid exchange frequencies. The problem of correlating the results of the chromosome aberration assay with micronucleus and sister-chromatid exchange frequencies is discussed.
TL;DR: SCE mediated by rat MEC is better correlated with carcinogenecity in rat than L.I., SCE, and in vivo carcinogen ECity for the 5 PAHs, while BA was significantly less effective (30% reduction).
Abstract: Five polycyclic aromatic hydrocarbons (PAHs) of different carcinogenic activities were evaluated for their effects on DNA synthesis ({sup 3}HTdR labeling index (L.I.)) of rat and human mammary epithelial cells (MEC) and for their effects on chromosomes in MEC-mediated sister chromatid exchange (SCE) assays. When compared with DMSO-treated cells, exposures of rat MEC to the two most potent carcinogens, i.e., 7,12-dimethylbenz(a)anthracene (DMBA) and benzo(a)pyrene (B(a)P), resulted in a 45-62% reduction in the L.I. of rat MEC. Another carcinogen, 20-methylcholanthrene (MCA), produced a 35-48% reduction in L.I., while the noncarcinogenic PAHs, 1,2-benzanthracene (BA) and benzo(e)pyrene (B(e)P), showed no effect. Similarly, exposures of human MEC to DMBA and B(a)P resulted in a 50-90% depression in L.I. while BA was significantly less effective. When co-cultivated with Chinese hamster V-79 cells in the presence of PAH, both rat and human MEC can activate and release the active metabolites to induce SCE in V-79 cells. Comparing depression of L.I., SCE, and in vivo carcinogenicity for the 5 PAHs, SCE mediated by rat MEC is better correlated with carcinogenicity in rat than L.I. depression.
TL;DR: Flow cytometric analysis of the temperature-sensitive mutants exhibiting chromosomal instability indicated that many of the mutants were arrested in the S or S to G2 phases of the cell cycle at the nonpermissive temperature, accompanied by a decrease in the rate of DNA synthesis.
Abstract: Twenty-five temperature-sensitive (ts) mutants were isolated from Chinese hamster CHO-K1 cells after mutagenization withN-methyl-N′-nitro-N-nitrosoguanidine. Of 13 complementation groups identified, nine exhibited chromosomal instability at a nonpermissive temperature. They were classified into three major classes according to inducibility of sister chromatid exchange (SCE) and/or chromosomal aberration (CA): class 1 resulted in predominant SCEs, class 2 manifested both SCEs and CAs, and class 3 exhibited higher induction of CAs. Flow cytometric analysis of the mutants exhibiting chromosomal instability indicated that many of the mutants were arrested in the S or S to G2 phases of the cell cycle at the nonpermissive temperature, accompanied by a decrease in the rate of DNA synthesis. These results imply that ts defects are related to some points in DNA replication and might be responsible for the induction of SCEs and/or CAs at the nonpermissive temperature.
TL;DR: The persistence of chromosomal abnormalities in the form of replicating minutes and exchange configurations, even 1114 days after exposure to the gas, may indicate a residual effect on T-cell precursors.
Abstract: Frequencies of chromosomal abnormalities, sister chromatid exchanges, and replicative index were assessed following peripheral lymphocyte culture in 129 individuals from Bhopal, India. Of these, 83 persons (40 male and 43 female) had been exposed directly to the methyl isocyanate (MIC) gas after the accident at the Union Carbide plant on December 2 and 3, 1984. The remaining 46 samples were taken from age-matched unexposed persons in the same city. Chromosome aberrations were recorded at first cycle metaphase (M1) and sister chromatid exchanges, at second cycle metaphase (M2), following standard schedule. The frequency of chromosomal aberrations was, in general, higher in individuals from the exposed populations, with the females showing a higher incidence. Nondisjunction of chromosomes or laggard was rare. The frequencies of sister chromatid exchanges and depression in mitotic and replicative indices could not be related to exposure or sex. The persistence of chromosomal abnormalities in the form of replicating minutes and exchange configurations, even 1114 days after exposure to the gas, may indicate a residual effect on T-cell precursors.
TL;DR: The mutagenic activity of methylglyoxal was assayed in vitro in human lymphocytes both in the presence and in the absence of metabolic activation (S9 mix) and positive results were obtained for all the genetic endpoints analysed.
Abstract: The mutagenic activity of methylglyoxal (MG) was assayed in vitro in human lymphocytes [induction of chromosomal aberrations (CAs), sister chromatid exchanges (SCEs) and micronuclei] both in the presence and in the absence of metabolic activation (S9 mix). The Ames/microsome test was performed with the Salmonella typhimurium strains considered more responsive (TA102 and TA104). Positive results were obtained for all the genetic endpoints analysed. In human lymphocytes the activity of MG is decreased by the presence of S9 mix. In the in vivo studies, the metaphase analysis in the ileum and duodenum cells of mice treated per os with MG (400 and 600 mg/kg body wt) gave negative results for CA induction, while only a weak increase of SCE in duodenum cells at the higher dose was obtained. Dimethylhydrazine (25 mg/kg body wt), as positive control, was clearly active in inducing both CAs and SCEs in the same intestinal tissues.
TL;DR: Findings indicate the possible risk of cytogenetic damage for staff working in unscavenged rooms and a significant increase in the percentage of chromosome aberration was observed.
Abstract: Summary
The study in a group of 24 (11 anaesthetists and 13 support staff) was planned to ascertain the cytogenetic risk in a group of theatre personnel who worked in various city hospitals. Their exposure in terms of duration of service vary from 3–30 years. The control group (n = 24) consisted of people with different occupations matched for possible confounding variables. Cytogenetic risk was assessed in terms of chromosome aberration and sister chromatid exchange in 72-hour lymphocyte cultures. A significant increase in the percentage of chromosome aberration was observed. The sister chromatid exchange was double that of the baseline value in 20% of the exposed individuals. These findings indicate the possible risk of cytogenetic damage for staff working in unscavenged rooms.
01 Jan 1990
TL;DR: Current methods for introducing restriction enzymes into cells, and the effects of restriction enzymes on the induction of DNA double-strand breaks, chromosome aberrations, and sister chromatid exchange (SCE) are reviewed.
Abstract: Bacterial restriction endonucleases recognize specific, short (4–8 base pair) nucleotide sequences in DNA. They bind at or near these sequences, then cleave DNA to generate either blunt-end or cohesive-end double-strand breaks. The role of DNA double-strand breaks in chromosome damage has long been a matter of some controversy (see Bryant 1988). By introducing restriction endonucleases into cells and examining their cytogenetic effects, investigators have now been able to define a more precise role for DNA double-strand breaks in chromosome damage and repair. In this report we review current methods for introducing restriction enzymes into cells, and the effects of restriction enzymes on the induction of DNA double-strand breaks, chromosome aberrations, and sister chromatid exchange (SCE).
TL;DR: Results show that dicamba is capable of inducing DNA damage since it significantly increases the unwinding rate of rat liver DNA in vivo and also induces UDS in HPBL in vitro in the presence of exogenous metabolic activation (S‐9 mix).
Abstract: The genotoxic effects of the herbicide dicamba have been studied by measuring 1) the unwinding rate of liver DNA from intraperitoneally (i.p.) treated rats (fluorimetric assay); 2) DNA repair as unscheduled DNA synthesis (UDS) induced in cultured human peripheral blood lymphocytes (HPBL); and 3) sister chromatid exchanges (SCE) in HPBL. Results show that dicamba is capable of inducing DNA damage since it significantly increases the unwinding rate of rat liver DNA in vivo and also induces UDS in HPBL in vitro in the presence of exogenous metabolic activation (S-9 mix). Furthermore, dicamba causes a very slight increase in SCE frequency in HPBL in vitro.
TL;DR: Comparison of the DNA alkylation products produced by CNU and ENU treatment of 9L cells suggests that the formation of the intrastrand crosslink N7-bis(guanyl)ethane and the interstrand crosslink 1-(3- deoxycytidyl)-2-(1-deoxyguanosinyl)ethanes by CNu is responsible for the increased effectiveness of CNU treatment at both induction of SCEs and cytotoxicity.
Abstract: The induction of sister-chromatid exchanges (SCEs) and cytotoxicity in 9L cells treated with monofunctional and bifunctional alkylating agents has been investigated. Three classes of monofunctional and bifunctional agents were studied: nitrosoureas, mustards and epoxides. Independent of class the bifunctional agents were 55–630-fold more effective at inducing SCEs and 300–2400-fold more effective at inducing cellular cytotoxicity than the corresponding monofunctional agents. Comparing the induction of SCEs and cytotoxicity by these agents showed that these two cellular responses to DNA damage are highly correlated. The extent of DNA alkylation in cells treated with 1-ethyl-1-nitrosourea (ENU) or 1-(2-chloro-ethyl)-1-nitrosourea (CNU) was similar indicating that the increased effectiveness of CNU to induce SCEs and cytotoxicity was not due to increased DNA alkylation. Molecular dosimetry calculations indicate that for CNU and ENU treatment of 9L cells there are 116 and 8500 alkylations per SCE induced and 2.6 × 10 4 and 4.6 × 10 6 alkylations at the dose required to reduce survival of 9L cells by 90%. Comparison of the DNA alkylation products produced by CNU and ENU treatment of 9L cells suggests that the formation of the intrastrand crosslink N 7 -bis(guanyl)ethane the interstrand crosslink 1-(3-deoxycytidyl)-2-(1-deoxyguanosinyl)ethane by CNU is responsible for the increased effectiveness of CNU treatment at both induction of SCEs and cytotoxicity.