Sister Chromatid Exchange Levels Research Articles

Sister chromatid exchanges in workers employed in car-painting workshops.

Car painting workers are exposed to a number of potentially genotoxic agents. The frequencies of sister chromatid exchanges (SCEs) were determined in a group of 22 workers involved in painting repaired cars in small workshops. An occupationally non-exposed age-matched group served as controls. There was a significant difference (P < 0.001) in the mean SCE levels in exposed (7.81 +/- 1.50) and non-exposed (4.92 +/- 0.10) groups. Smoking habit was the other factor most influencing SCE levels. Among both the exposed workers and the controls, smokers had a higher SCE frequency than non-smokers.

Mutagenic risk in psoriatic patients before and after 8-methoxypsoralen and long-wave ultraviolet radiation

Sister-chromatid exchange (SCE) analysis was carried out in different age groups prior to and after therapy with 8-Methoxypsoralen (8-MOP) followed by exposure of the patient to long-wave UV-A (PUVA) and compared to control. The SCE frequencies were increased significantly in PUVA-treated patients as compared to their pre-treatment SCE levels and to controls. A significant increase in SCEs was found in smoking PUVA-treated patients as compared to non-smoking PUVA-treated patients. This study indicates a detectable chromosome-damaging effect of PUVA therapy on its human users.

Altered DNA ligase III activity in the CHO EM9 mutant

Delayed joining of DNA strand breaks and a high spontaneous level of sister-chromatid exchanges (SCEs) are characteristics of the mutant cell strain EM9 of Chinese hamster ovary (CHO) cells. The introduction of the human gene XRCC1 into EM9 cells reverts the phenotypic properties of EM9 to those of the wild type. We have investigated both DNA ligase activities and a protein which stimulates DNA ligase activity in mutant EM9 cells, XRCC1-transfectant H9T3-7-1 cells and wild-type AA8 cells. Our results, which demonstrate both a decreased DNA ligase activity in EM9 cells using poly(rA)· oligo(dT) as substrate and a decreased ability of DNA ligase III to form a covalent DNA ligase III-adenylate intermediate with AMP, clearly indicate an altered DNA ligase III activity in the mutant. Furthermore, the AMP-binding capacity of DNA ligase III and its enzymatic activity with the synthetic polymer were restored after transfection of EM9 with the human XRCC1 gene. Immunoblotting data suggest that the XRCC1 gene does not code for DNA ligase III. IN conclusion, the data indicate that the EM9 cell strain has an altered DNA ligase III activity that can be restored by the XRCC1 gene product.

Sister chromatid exchange frequencies in lymphocytes of oral cancer patients seem to be influenced by drinking habits.

Sister chromatid exchange (SCE) values were determined in the lymphocytes of 24 oral cancer patients before therapy and in the lymphocytes of 24 control persons standardized with respect to sex, age and smoking habits. Oral cancer patients showed significantly elevated SCE values (mean 7.82 versus 6.42). In both groups the highest SCE values were found in the subgroups with the highest alcohol consumption. A significant correlation between SCE and gamma-glutamyltranspeptidase (GGT) values by Spearman correlation analysis was detected in the combined group (cancer patients and control persons) (n = 32, r = 0.40, P = 0.023). The SCE values in the oral cancer patients were weakly correlated (Pearson) to DNA adduct levels (n = 22, r = 0.39, P = 0.068) and DNA single-strand breakage frequencies (n = 12, r = 0.56, P = 0.054) in lymphocytes. The correlation (Pearson) between SCE values and DNA strand breakage values in lymphocytes was significant (n = 10, r = 0.67, P = 0.036) in smoking cancer patients. The increase of SCE values with respect to alcohol drinking habits underlines epidemiologic findings that alcohol is an important co-carcinogen in many cancers, especially in oral cancers. Because of the influences on SCE and adduct levels in lymphocytes, alcohol drinking habits should be controlled as broadly as possible in biomarker studies.

Some substrates and inhibitors of cytosolic epoxide hydrolase induce sister-chromatid exchanges in mammalian cells, but do not induce gene mutations in Salmonella typhimurium and V79 cells

Trans-stilbene oxide, trans-β-methylstyrene, 7,8-oxide, trans-β-ethylstyrene, 7,8-oxide, trans-β-propylstyrene 7,8-oxide and 4-fluorochalcone oxide were investigated for genotoxic activity in bacterial and mammalian cells, in the absence of external xenobiotic-metabolising systems. All compounds strongly enhanced the frequency of sister-chromatid exchanges (SCE) in cultured human lymphocytes. None of them was mutagenic in Salmonella typhimurium (reversion of the his − strains TA98, TA100 and TA104). The limit of detection was 1 20,000 to 1 10 6 of the activity of the positive control, benzo[ a]pyrene 4,5-oxide, depending on the compound and the bacterial strain. Trans-β-methylstyrene 7,8-oxide and 4-fluorochalcone oxide were additionally tested for induction of SCE and gene mutations in the same target cells, namely Chinese hamster V79 cells. Their influence on the level of SCE was similar to that observed in human lymphocytes, whilst gene mutations (at the hprt locus) were not induced. The four investigated styrene oxide derivatives are known to be excellent substrates for a mammalian enzyme, cytosolic epoxide hydrolase (cEH). 4-Fluorochalcone oxide is a potent selective inhibitor of this enzyme and is structurally similar to the investigated styrene oxide derivatives. These properties of the test compounds however cannot explain the observed discrepancies in the results, since the genetic end point (SCE versus gene mutations) was decisive, and SCE were induced in cEH-proficient human lymphocytes as well as in cEH-deficient V79 cells.

Sensitivity of lymphocytes from vulcanizers to the in vitro induction of sister chromatid exchanges.

Spontaneous frequencies of sister chromatid exchanges (SCEs) and SCEs induced in vitro by chemicals with different mechanisms of action such as mitomycin C, 4-nitroquinoline oxide, and 3-aminobenzamide were examined in phytohemagglutinin-stimulated peripheral blood lymphocytes from a group of workers in a rubber plant and a control group, both of which had been analyzed for levels of spontaneous SCEs 2 years earlier. An interindividual variability in the induction of SCEs was found after in vitro treatments with the different mutagens, which did not correlate with occupational exposure. This variability in the sensitivity to the induction of SCEs might be correlated to genetic differences among individuals, which have to be taken into account in environmental monitoring programs.

Measurement of chromosomal aberrations, sister chromatid exchange, hprt mutations, and DNA adducts in peripheral lymphocytes of human populations at increased risk for cancer

Using a multidisciplinary approach, we have measured various indicators of DNA damage in peripheral lymphocytes of human populations potentially at increased risk for cancer. Sister chromatid exchanges (SCE) and polycyclic aromatic hydrocarbon (PAH)-DNA adducts were evaluated in a group of firefighters; chromosomal aberrations and hprt mutations were evaluated in a group of cancer patients undergoing radioimmunoglobulin therapy (RIT); SCE and acrolein-modified DNA were measured in cancer chemotherapy patients and in pharmacists preparing chemotherapy prescriptions; and SCE and PAH-DNA adducts are being measured in U.S. army troops stationed in Kuwait. Our results indicate that both SCE and PAH-DNA adduct levels were not elevated in firefighters, but that other factors such as smoking status and race were risk factors for increased SCE and PAH-DNA adducts. RIT was found to increase background rates of chromosome-type aberrations and frequencies of hprt mutations and there was a strong correlation between levels of therapy-induced chromosome damage sustained in vivo and in vitro sensitivity to radiation-induced chromosome damage. Peripheral blood lymphocytes of cancer patients treated with cyclophosphamide showed higher levels of SCE and had a higher incidence of acrolein adducts in DNA. Lymphocytes from pharmacists preparing antineoplastic drugs were found to acquire increased in vitro sensitivity to SCE induction by phosphoramide mustard with increased lifetime duration of drug handling. A prospective, longitudinal study was performed to identify environmental factors that modulate genetic damage in breast cancer patients. Women with benign breast masses and no apparent disease served as controls. Mutant frequency, cloning efficiency, and chromosomal aberration frequency did not differ significantly among the three groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Okadaic acid, a ptotein phosphatase inhibitor, induces sister-chromatid exchanges depending on the presence of bromodeoxyuridine

Okadaic acid (OA), a potent tumor promoter and an inhibitor of protein phosphatase 1 and 2A, induced sister-chromatid exchanges (SCEs) in human lymphoblastoid cells and Chinese hamster ovary cells at low concentrations of 2–10 nM, when the cells were grown for two cell cycles in the presence of OA and bromodeoxyuridine (BrdUrd). Prolonged treatment with OA prior to addition of BrdUrd did not induce SCEs, indicating an essential role of BrdUrd. A similar important role of BrdUrd in SCE induction has been reported in the cases of benzamide (BA) (Natarajan et al., 1981) and camptothecin (CPT) (Zhao et al., 1992), which are inhibitors of poly(ADP-ribose)polymerase and DNA topoisomerase I (topo I), respectively. Unlike many DNA-damaging agents, they are required to be present during S phase along with BrdUrd in the medium and/or in the parental DNA as BrdUMP. Thus OA, like BA and CPT, is a new type of SCE inducer. Exposing cells to a combined treatment with OA, BA and CPT, a significantly higher level of SCEs was induced than that expected if the numbers of SCE caused by these three inhibitors were additive, while no such synergistic increase was seen in every combination of two agents. Since both phosphorylation and poly(ADP-ribosyl)ation have been known to modify topo I activity, the results suggest a common involvement of topo I for SCE formation by OA, BA and CPT. In addition to SCE induction, OA resulted in an increase of mitotic cells which were characterized by a marked chromosome condensation. OA also induced chromosome fragmentation/pulverization in human lymphoblastoid cells and fragmented nuclei in Chinese hamster cells.

Inhibitory Effects of Sizofiran on Anticancer Agent‐ or X‐Ray‐induced Sister Chromatid Exchanges and Mitotic Block in Murine Bone Marrow Cells

The inhibitory effects of a biological response modifier (BRM), sizofiran, on sister chromatid exchanges (SCEs) in the bone marrow cells of mice treated with various anticancer agents or irradiation were investigated. Sizofiran (10 mg/kg i.m.) inhibited SCEs induced by mitomycin C (2 mg/kg i.v.), adriamycin (20 mg/kg i.v.) and cyclophosphamide (20 mg/kg i.v.) by about 20%, respectively. Analysis of the SCEs in vivo after irradiation plus sizofiran indicated that SCE levels were significantly lower than those observed in mice exposed to irradiation without sizofiran. Moreover, the effects of sizofiran were dependent on the timing of administration. Our results indicated that sizofiran should be administered simultaneously or soon after irradiation in order to minimize damage. Sizofiran also markedly restored the bone marrow cell mitosis which had been suppressed by anticancer agents, and this action was closely correlated with the prevention of increase in SCEs. These results indicate that in addition to immunopotentiating activity, sizofiran may play a role in preventing chromosomal damage induced by cancer chemotherapy and radiotherapy.

Sister chromatid exchange in Waldenström's macroglobulinemia

Results on sister chromatid exchange (SCE) frequency and interchromosomal distribution in bone marrow and peripheral blood cultures from patients with Waldenström's macroglobulinemia are reported. PHA-stimulated bone marrow cultures showed increased SCE frequencies in all 12 patients examined. The increase was particularly high in two cases (17.07 and 16.77 SCE/cell, respectively) and, in one of them, a very high SCE level was found in PHA-stimulated peripheral blood culture (40.81 SCE/cell). In LPS-stimulated cultures, increased SCE levels were observed in some patients. Comparison between SCE frequency in bone marrow cell cultures with either mitogen showed a significant increase in PHA-stimulated cultures. Analysis of the interchromosomal SCE distribution revealed significant differences with respect to the control values; however, these differences were variable in the different patients. In pooled data of PHA-stimulated bone marrow cultures, there were differences between expected and observed SCEs in chromosomes 1 and 2 and in B, E, F, and G chromosome groups. Results of cell cycle modifications are also reported.

Genotoxic evaluation of ammonium inactivated aflatoxin B 1 in mice fed with contaminated corn

Aflatoxin B 1 (AFB 1) is a major contaminant in different agricultural products including maize. In an attempt to reduce this problem and the hazards to human health, an AFB 1 inactivating system with ammonia has been developed. In this work we evaluated the efficiency of the system in mice using micronucleus (MN) and sister chromatid exchange (SCE) analysis. Four groups of animals were fed during 8 weeks with a special diet mainly composed of maize: (1) uncontaminated; (2) uncontaminated/ inactivated; (3) contaminated/inactivated; and (4) contaminated. We evaluated MN at weekly intervals in peripheral blood, and in weeks 4 and 8 SCE frequencies were quantified in bone marrow cells. The results showed that animals fed with AFB 1 contaminated/inactivated maize had a 45% lower level of induced cytogenetic damage than those animals fed with AFB 1 contaminated, but not inactivated maize. A residual amount of AFB 1 after the inactivating treatment and the reconversion back to AFB 1 in the organism may account for the remaining increased levels of SCE and MN.

Characterisation of methotrexate-resistant clones

Three methotrexate (MTX)-resistant clones M1, M2 and M3 have been isolated from Chinese hamster V79 cells and characterised for aneuploidy, chromosomal aberrations, sister-chromatid exchange (SCE) mutation and transfection. Amplification of the dihydrofolate reductase (DHFR) gene in these clones has been established from (a) direct measurement of DHFR activity, (b) existence of double minute chromosomes and (c) homogeneously staining region (HSR) in chromosome number 2 by G-banding technique. Clone M1 on further exposure to gradually increasing concentrations of MTX gave rise to two more clones M4 and M5, resistant to 1200 nM and 2400 nM MTX, respectively. The levels of folate reductase activity in clones M4 and M5 were 21.90 units per 10 7 cells and 33.30 units per 10 7 cells, whereas the value was 13.90 units per 10 7 cells in clone M1 and 1.1 units per 10 7 cells in normal V79 cells. Increased chromosomal aberrations were observed in each of these clones in comparison to those in normal V79 cells. There was a correlation between the increase in DHFR activity and the increase in the level of background SCE as well as the increase in aneuploidy. However, background mutation frequency at the HGPRT locus remained unaffected though transfection frequency decreased.

DNA crosslinking, sister chromatid exchange and cytotoxicity of N-2-chloroethylnitrosoureas tethered to minor groove binding peptides.

Chloroethylnitrosoureas (CENU) are clinically important chemotherapeutic agents whose mechanism of action involves the formation of interstrand DNA crosslinks via an ethane bridge between N1-G and N3-C. CENU generally alkylate G at the N7- and O6-positions, with the latter lesion being the precursor to the interstrand crosslink. In previous studies, we reported the synthesis of CENU appended by a C2H4 linker to the N-terminus of DNA minor groove binding dipeptides (lex, information reading peptides) based on N-methylpyrrole-carboxamide subunits. Because of the dipeptide structure, these CENU-lex's react with DNA at adenines associated with lex equilibrium binding sites. No other CENU has been reported to yield A adducts. The biological evaluation of these CENU-lex's show that they are somewhat less cytotoxic than their simpler counterparts. In addition, in vitro studies show that the minor groove binding CENU-lex's afford a lower level of sister chromatid exchange (SCE) in 9L cells that are sensitive to CENU. There is no difference between CENU-lex in SCE induction in 9L-2 cells that are resistant to CENU. Formation of DNA interstrand crosslinks from the CENU-lex's is lower than for their nonaffinity binding analogs in low ionic strength buffer, but similar in the same buffer containing 200 mM NaCl. Salt inhibits crosslinking for all CENU, but distamycin, a competitive inhibitor of lex minor groove binding, uniquely enhances crosslinks for the CENU-lex's. These results are consistent with the novel minor groove adduction being a 'detoxification' pathway for the CENU-lex's since this lesion is formed at the expense of the cytotoxic major groove interstrand crosslink.

Factors affecting zero background frequency of sister-chromatid exchange in mosquito cells

A background level of sister-chromatid exchange (SCE) is found in mammalian cells. However, in the somatic cells of Drosophila melanogaster, there was no spontaneous SCE if a minimum concentration of bromodeoxyuridine (BrdU) was used. In this communication we report that in a mosquito (Aedes albopictus) cell line (C6/36), some cells also have no background SCE (0-SCE). Subclones of high (44%) or low (12%) frequency of 0-SCE cells were obtained, but none of them contained 100% 0-SCE cells. Increasing frequency of SCE/cell concomitant with decreasing frequency of 0-SCE cells was observed by raising the BrdU concentration in the culture medium during the first cell cycle, culturing cells at lower density and depleting reduced glutathione (GSH) with buthionine sulfoximine. Since these mosquito cells contain much higher level of GSH than Chinese hamster ovary (CHO) cells, and feeding cells with BrdU increased GSH in mosquito cells but decreased GSH in CHO cells, we speculate that GSH may play a role in the low or non-existent background SCE and in the high resistance to many DNA damaging agents of mosquito cells.

Stationary cell cultures as a tool for gerontological studies.

Studies of cellular and molecular mechanisms of aging are currently often carried o u t on cells senescing not only in vivo but also in vitro (Hayflick’s model), that is, altering with increasing of population doubling level in culture. However, some data suggest that in some cases the results obtained with this model are not in accord with those of in vivo aging studies. Furthermore, such experiments, as a rule, are comparable in labor-consuming character with routine studies in laboratory animals. In fact, Hayflick himself suggests that cells in vivo never realize their proliferative potential and never reach phase 111. In other words, an organism never ages because of a cell’s limitation, called “Hayflick’s limit.” It ages, we believe,’ because of an accumulation of various kinds of damage in cells due to restriction of cell proliferation during the formation (the differentiation process) of populations of specialized resting cells or very slowly dividing cells. The rate of any type of damage accumulation in the cell population (not in a single cell!) has to depend on the ratio of the rates of three processes: (1) cell proliferation, ( 2 ) spontaneous appearance of damage, and (3) damage repair. Thus, during cell proliferation a “dilution” of the damage occurs. Our data2 demonstrating a direct relation between the average proliferative activity of a cell line or strain and the average DNA molecular weight support this hypothesis. With all this in mind we suppose that it is more advisable to study cellular aging mechanisms using the “stationary phase aging” model.‘ The model is based on the assumption that in cells of stationary cultures various changes similar to those in cells of aging organisms have to appear. Last year we and other investigators obtained many experimental results confirming this assumption. “Age” changes at different levels (accumulation of DNA breaks and DNA protein cross-links, DNA demethylation, changes in spontaneous sister chromatid exchange level, plasma membrane changes, nuclear structure modulations, and decreased rate of mitogenstimulated cell cycling and of cell colony-forming ability a.0.) were shown to occur in stationary cell cultures. These experiments can be carried out in nearly any type of cell including normal and transformed human and animal cells, plant cells, bacteria, mycoplasmas, yeasts, and the like. In particular, we now study the phenomenon of stationary phase aging and the possibility of modulating this kind of cell aging by geroprotectors (physical or chemical factors that retard aging) and geropromoters (factors that accelerate aging) in cyanobacteria cultures. ‘Thus, an evolutionary approach to analysis of the data is provided. Moreover, changes in stationary cell cultures become detectable very soon, as a rule in 2-3 weeks after beginning the experiment. All of these data suggest that the stationary phase aging model is a good alternative to the Hayflick model.

A cytogenetic study of men environmentally and occupationally exposed to airborne pollutants

The level of sister-chromatid exchanges (SCE), high-frequency cells (HFC), chromosomal aberrations (CA) as well as the proliferation rate index (PRI) were measured in peripheral blood lymphocytes from three groups of volunteers. The environmentally exposed donors were residents from the vicinity of a coke factory; the occupationally exposed persons were cokery workers, while rural region inhabitants served as a control group. Compared with the control group, statistically significant increases of SCE and HFC, as well as decreased cell kinetics (PRI) were observed for both occupationally and environmentally exposed groups. The effect was especially pronounced when only smokers were taken into account. A statistically significant increase of CA was observed in the environmentally exposed group when CA including gaps (CA + G) were evaluated. The proportion of HFC was found to be the most sensitive method to detect genetic effects on the tested human population. This study demonstrates the usefulness of all 4 biomarkers (SCE, HFC, CA and PRI) in monitoring populations exposed to ambient pollution and clearly indicates effects from residential as well as occupational exposure to industrial air pollutants.

Effects of amino acids on sister-chromatid exchanges

The effects of 10 amino acids on sister-chromatid exchange (SCE) frequency in human peripheral blood lymphocytes (PBL) and six amino acids on the SCE frquency in root tip cells of Hordeum vulgare were studied. Alanine (Ala), glycine (Gly), phenylalanine (Phe), valine (Val), histidine (His) and serine (Ser) induced a significant increase in SCE in PBL but threonine (Thr), isoleucine (Ile), lysine (Lys) and arginine (Arg) did not. Ala, Gly, Thr, Ile and Val induced a significant increase in SCE in root tip cells of Hordeum vulgare but Lys did not. The effect of Lys and bromodeoxyuridine (BrdU) on SCE levels in PBL and the interaction between them were also studied. The results show that Lys can inhibit the SCE induced by BrdU.

Baseline frequency of sister-chromatid exchanges in 142 persons of the general Korean population

Baseline frequencies of sister-chromatid exchange (SCE) were measured in lymphocytes of 142 healthy Koreans ranging in age from newborn infants to the fifties. The overall mean frequency of SCE was 8.78±0.24/cell. However, highly significant differences were found between individuals. The mean SCE values of the newborn babies and small children less than 10 years old were significantly lower than those of other age groups. No age effect was, however, observed in adolescent and adult subjects. Females had statistically higher SCE levels than males. The mean SCE frequencies of smokers, measured in male subjects more than 10 years old, were slightly, but statistically significantly, higher than those of non-smokers.

Baseline and phosphoramide mustard-induced sister-chromatid exchanges in pharmacists handling anti-cancer drugs

Determinations of baseline and mutagen-induced sister-chromatid exchanges (SCE) have been used as indicators of previous mutagen exposure in several human populations. Mutagen-induced SCE is based on the premise that a genetic outcome may depend not only on a present exposure, but also on a cell's “memory” of previous exposure. The genotoxicity of some anti-cancer drugs including cyclophosphamide (CP) has been studied by determining baseline and mutagen-induced SCE in peripheral blood lymphocytes in treated cancer patients. This study examined the in vivo genotoxic effects of occupational exposure to anti-cancer drug handling by relating baseline and phosphoramide mustard (PM) -induced SCE levels with duration of anti-cancer drug handling as a surrogate for anti-cancer drug exposure dose. The mean baseline SCE for the population was 5.19 ± 0.17 and was not correlated with duration of drug handling. However, a strong correlation was demonstrated between inducible SCE values and life-time duration of drug handling with r = 0.63 ( p < 0.0001 for low-dose PM challenge (0.1 mg/ml PM) and r = 0.67 ( p < 0.0001) for high-dose PM challenge (0.25 mg/ml PM). A similar relationship was seen for PM-induced SCE and duration of anti-cancer drug handling for the workers' present job with correlations obtained being r = 0.63 ( p < 0.0001) for low-dose PM and r = 0.59 ( p < 0.0001) for high dose PM. The short-lived nature of the baseline SCE lesion is discussed as a limitation in population surveillance studies, as it reflects primarily recent mutagen exposure and persists only for days to weeks after exposure. The induced SCE measure is postulated to provide an integrating dosimeter of remote previous exposure, improving upon the current limitation of the baseline SCE measure and allowing the “unmasking” of previous exposure in a provocative framework.

On the distribution of spontaneous SCE in human peripheral blood lymphocytes

Sister-chromatid exchanges (SCE), phenomena of incompletely understood mechanism or significance, are often enumerated as a measure of genotoxicity, as their frequency is clearly elevated by exposure to many, if not most, chemical mutagens and carcinogens (Latt et al., 1984). However, SCE arise spontaneously, and in fairly large numbers per cell on average, in the absence of known genotoxin exposure. Statistical tests to determine whether SCE levels are elevated in a population or in an individual are based on underlying assumptions regard-