Correlation of the sister chromatid exchange level with chromosome aberrations induced by chemical mutagens in vivo

The data on the dose dependencies of the induction of sister chromatid exchanges (SCE) and chromosomal aberrations during exposure of mouse bone marrow cells in vivo to 5 alkylating substances are provided. The efficacy of SCE induction was found to be higher than that of chromosomal aberrations. It was established that SCE induced by chemical mutagens in vivo and in vitro are more sensitive and stable tests than chromosomal aberrations.     

Chromosomal damage induced by maleic hydrazide in mammalian cells in vitro and in vivo

The induction of sister-chromatid exchanges (SCE) and chromosomal aberrations (Ch.Ab.) by the herbicide maleic hydrazide (MH) has been investigated in Chinese hamster ovary (CHO) cells grown in vitro and in bone marrow cells of mice treated in vivo. MH induces SCE and Ch.Ab. in CHO cells without metabolic activation; however, no induction of SCE was found in the in vivo experiments.     

Induction of chromosomal damage in mammalian cells in vitro and in vivo by sulfapyridine or 5-aminosalicylic acid.

Sulfapyridine (SP) and 5-aminosalicylic acid (5-ASA) are the two primary metabolites of the anti-inflammatory drug salicylazosulfapyridine (SASP). These two metabolites were studied for induction of chromosomal damage in mammalian cells, in vitro and in vivo, in an attempt to understand better the genetic effects produced by SASP in humans and laboratory mice. To this end, SP and 5-ASA were tested for induction of sister-chromatid exchanges (SCE) and chromosomal aberrations (Abs) in Chinese hamster ovary (CHO) cells in vitro. In addition, they were tested in vivo for induction of micronuclei (MN) in mouse bone marrow polychromatic erythrocytes (PCE). SP gave positive results in the in vitro SCE test and the in vivo MN test, and negative results in the in vitro Abs test. 5-ASA was negative in all three tests. These results indicate that it is the SP metabolite of SASP that is necessary for the induction of chromosomal damage reported to occur in humans and mice after treatment with SASP.     

Quantitative evaluation of the effectiveness of the formation of sister chromatid exchanges and chromosome aberrations as affected by chemical mutagens

Dose curves of five chemicals were studied to compare the efficiency of SCE and chromosomal aberration induction by different chemical mutagens. SCEs were found to increase linearly with the dose, whereas chromosomal aberrations--nonlinearly. Using regression coefficients obtained from the dose curves it was found that the efficiency of the studied chemical mutagens in induction of SCEs is 100-300 times as high as that in the induction of chromosomal aberrations.     

Ratio of the frequency of chromosome aberrations and sister chromatid exchanges to the dose of the mutagenic exposure to cyclophosphamide in vivo and in vitro

Cyclophosphamide (CP) and its metabolites were used to compare the rate of chromosomal aberrations (CA) and sister chromatid exchange (SCE) in the rabbit lymphocytes in vivo and in vitro. The dose-dependent increase of cytogenetic effects rate appeared to be of linear and exponential dependence for SCE and CA, respectively, both in vivo and in vitro. The regression equation coefficients coincided in in vivo and in vitro experiments.     

Chromosome damage induced in human lymphocytes by 5-methoxypsoralen and 8-methoxypsoralen plus UV-A

The induction of structural chromosome aberrations and sister chromatid exchanges (SCE) was studied in human lymphocytes in vitro after treatment with the two bifunctional furocoumarins 5-methoxypsoralen (5-MOP) and 8-methoxypsoralen (8-MOP) in the presence of UV-A. The results show that both psoralens induce a dose-dependent increase in the SCE rate as well as in structural chromosome aberrations. 5-MOP was 2.0-2.5 times more effective for the induction of chromosome breaks and had a slightly stronger effect with respect to SCE induction. A significant influence on proliferation kinetics could be observed only with 5-MOP plus UV-A.     

The induction of chromosomal aberrations and SCE by visible light in combination with dyes. I. The effect of hypoxia during light exposure in unsynchronized Chinese hamster ovary cells, sensitized with acridines

A comparison has been made between the ability of different acridine compounds to act as sensitizers for visible light (400-700 nm) induced chromosomal aberrations and sister-chromatid exchanges (SCE) in unsynchronized Chinese hamster ovary (CHO) cells. Cells were treated for 20 min with acridines (0.1-5.0 microgram/ml), washed free of excess dye and subsequently exposed to visible light (2 x 40 W/8 W m-2) either in air or in nitrogen for 5-15 min. The 4 acridines tested, proved to be effective sensitizers for the induction of both chromosomal aberrations and SCE by visible light. The most pronounced effect was observed when the light exposure of the fluorochrome-pretreated cells was performed in air. Hypoxic conditions during light exposure reduced the effect dramatically, especially in the case of induced chromosomal aberrations. The order of efficiency for the induction of both chromosomal aberrations and SCE was acridine orange greater than acridine yellow greater than proflavine greater than 3,6-diamino-10-methylacridine. The results are discussed in terms of S-independent versus S-dependent mechanisms for inducing chromosomal alterations and the potential involvement of oxygen-derived free radicals in this process.     

Evaluation of the mutagenic potential of the hair dye N-methyl-amino-2-nitro-4-N',N'-bis-(2-hydroxyethyl)-aminobenzene in a battery consisting of Drosophila and mammalian cytogenetic assays

The compound N-methyl-amino-2-nitro-4-N', N'-bis(2-hydroxyethyl)-aminobenzene was tested for mutagenic activity in the sex-linked recessive lethal test with Drosophila melanogaster, the induction of chromosomal aberrations and sister-chromatid exchanges (SCEs) with Chinese hamster ovary (CHO) cells in vitro, and the micronucleus test with mouse bone-marrow cells in vivo. Consistently negative results were obtained with the 3 tests. The SCE tests gave positive results with prolonged treatments. It is concluded that reliable decisions about mutagenic activity cannot be based on the induction, in vitro, of SCEs alone.     

Role of homologous recombination in the alpha-particle-induced bystander effect for sister chromatid exchanges and chromosomal aberrations

The bystander effect for sister chromatid exchanges (SCEs) and chromosomal aberrations was examined in hamster cell lines deficient in either DNA-PKcs (V3 cells, deficient in nonhomologous end joining, NHEJ) or RAD51C (irs3 cells, deficient in homologous recombination, HR). Cells synchronized in G0/G1 phase were irradiated with very low fluences of alpha particles such that < 1% of the nuclei were traversed by an alpha particle. Wild-type cells showed a prominent bystander response for SCE induction; an even greater effect was observed in V3 cells. On the other hand, no significant induction of SCE was observed in the irs3 RAD51C-deficient bystander cells irradiated at various stages in the cell cycle. Whereas a marked bystander effect for chromosomal aberrations occurred in V3 cells, the induction of chromosomal aberrations in irs3 bystander cells was minimal and similar to that of wild-type cells. Based on these findings, we hypothesize that HR is essential for the induction of SCE in bystander cells; however, HR is unable to repair the DNA damage induced in NHEJ-deficient bystander cells that leads to either SCE or chromosomal aberrations.     

Comparison of the cytogenetic effects of cyclophosphamide on monkey lymphocytes in vivo and in vitro

The comparative in vivo and in vitro study of chromosomal aberrations and SCE induced by cyclophosphamide (CP) in macaca rhesus lymphocytes was performed. The dose of mutagenic exposure for quantitative estimation of effects was determined as a product of concentration of alkylating CP metabolites on the exposure time. The mutagenic effect caused by the same doses of CP (CP metabolites) appeared similar in vivo and in vitro. This suggests that the results obtained in adequate in vitro mutagen-testing experiments may be quantitatively extrapolated for the in vivo conditions.     

The mouse splenocyte assay, an in vivo/in vitro system for biological monitoring: studies with X-rays, fission neutrons and bleomycin.

A modified mouse splenocyte culture system was standardized after testing different mitogens (i.e., phytohemagglutinin (PHA), concanavalin A (Con A)). The mitotic index was determined for comparison between different mitogens. Following selection of appropriate mitogen (PHA 16, Flow), a series of experiments were conducted to evaluate the application of a cytokinesis-block for scoring micronuclei and assays for chromosomal aberrations produced by treatment in G0 and G2 for the purposes of biological dosimetry following in vivo and/or in vitro exposure to X-rays, fission neutrons and bleomycin. In the X-irradiation studies, the frequencies of micronuclei and chromosomal aberrations (i.e., dicentrics and rings) increased in a dose-dependent manner. These data could be fitted to a linear-quadratic model. No difference was observed between irradiation in vivo and in vitro, suggesting that measurement of dicentrics and micronuclei in vitro after X-irradiation can be used as an in vivo dosimeter. Following in vivo irradiation with 1 MeV fission neutrons and in vitro culturing of mouse splenocytes, linear dose-response curves were obtained for induction of micronuclei and chromosomal aberrations. The lethal effects of neutrons were shown to be significantly greater than for a similar dose of X-rays. The relative biological effectiveness (RBE) was 6-8 in a dose range of 0.25-3 Gy for radiation-induced asymmetrical exchanges (dicentrics and rings), and about 8 for micronuclei in a dose range of 0.25-2 Gy. Furthermore, the induction of chromosomal aberrations by bleomycin was investigated in mouse G0 splenocytes (in vitro) and compared with X-ray data. Following bleomycin treatment (2 h) a similar pattern of dose-response curve was obtained as with X-rays. In this context a bleomycin rad equivalent of 20 micrograms/ml = 0.50 Gy was estimated.     

Induction of chromosomal aberrations and SCE by camptothecin, an inhibitor of mammalian topoisomerase I

The induction of chromosomal aberrations and sister-chromatid exchanges (SCE) was studied in human lymphocyte cultures treated with camptothecin (CM), an inhibitor of mammalian topoisomerase I. While no chromosome-type aberrations were found in G1-treated cells, instead there was a dose-dependent induction of chromatid-type aberrations. These types of chromosomal alteration were not induced during the treatment itself but during the S phase, as CM is not efficiently removed with the normal washing procedure after treatment.     

Mutagenic activity of anticancer agent cis-dichlorodiammine platinum-II.

cis-Dichlorodiamminoplatinum-II (cis-DDP) has been widely used as an anticancer chemotherapeutic agent. The mutagenicity of cis-DDP was investigated in vitro and in vivo using sister-chromatid exchange analysis and the analysis of chromosomal aberrations. Parallel human lymphocyte cultures were incubated with and without the addition of BrdU at 4 concentrations of cis-DDP. Significant increases in SCE rate were observed at 0.25 micrograms/ml and higher, showing a clear dose-response relation between SCE rate and cis-DDP concentration. A significant increase in chromosome breakage and tetraradial figures was observed in BrdU free cultures treated with cis-DDP again showing a dose dependency. Analysis of the distribution of cells in the first, second and third division in cis-DDP treated cultures demonstrated the depressing effect of the drug on mitotic activity. In vivo analysis of SCE and chromosome aberrations in mouse showed that 13.85 mg/kg i.p. of cis-DDP produces significant increases in the rate of SCE and chromosome aberrations in bone-marrow cells.     

Mutagenicity of methyl 2-benzimidazolecarbamate, diethylstilbestrol and estradiol: structural chromosomal aberrations, sister-chromatid exchanges, C-mitoses, polyploidies and micronuclei

Methyl 2-benzimidazolecarbamate (MBC), diethylstilbestrol (DES) and estradiol were tested with regard to their ability to induce C-mitoses, polyploidies, micronuclei, structural chromosomal aberrations and sister-chromatid exchanges (SCE) in human peripheral lymphocytes in vitro. The compounds did not induce structural chromosomal aberrations either in the presence or absence of metabolic activation. MBC and estradiol were negative in the SCE test. DES induced SCE rates which were not even twice the control level and which were independent of dose and of metabolic activation. All compounds induced C-mitoses, polyploidies and micronuclei. The micronuclei are interpreted as resulting from errors in the anaphase distribution of chromosomes by spindle disturbances rather than from structural chromosomal aberrations.     

Effects of various cyclophosphamide concentrations in vivo on sister chromatid exchanges (SCE) and chromosome aberrations of Chinese hamster bone marrow cells

Summary The in vivo SCE formation and the induction of chromosome aberrations in the bone marrow of Chinese hamsters (Cricetulus griseus) were studied after various concentrations of cyclophosphamide, and the sensitivity of the two test methods was compared. The administration of 1.0, 5.0, 13.3, 25.0, and 40.0 mg/kg body weight induced a dose-dependent increase in SCE. The frequency of chromosome aberration, however, was not increased significantly with doses of 1.0 and 5.0 mg/kg body weight. Only with doses of more than 13.3 mg is a significant induction of chromosome aberrations seen. Therefore the SCE test system seems to be 10 times more sensitive than the induction of chromosome aberrations in the same cell type.This work is a part of the M.D. thesis of G. Roszinsky-Köcher, to whom offprint requests should be sent     

Multiple genotoxic activities of ptaquiloside in human lymphocytes: aneugenesis, clastogenesis and induction of sister chromatid exchange

Ptaquiloside, a norsesquiterpene glycoside from bracken (Pteridium aquilinum), is a known carcinogen towards animals. Its genotoxicity is mainly attributed to its DNA-alkylating and clastogenic properties. This study analyses various modes of genotoxic action of ptaquiloside in human mononuclear blood cells. The alkaline comet assay was performed on cells exposed to 5μg/ml ptaquiloside for 5, 10, 20, 30, 40 or 50min. Tail length was used as a DNA-damage parameter. Assays to determine structural and numerical chromosomal aberrations and sister-chromatid exchange were conducted on cells exposed to 5, 10 or 20μg/ml ptaquiloside for 48h. The tail length showed maximum DNA damage at 20-30min, diminishing onwards. Highly significant (p<0.001) dose-dependent increases in structural and numerical chromosomal aberrations and SCE were observed in response to ptaquiloside. These results indicate that ptaquiloside is not only a DNA-alkylating agent, but expresses its genotoxicity through multiple mechanisms including clastogenesis, aneugenesis and the mechanism underlying SCE induction, which is not entirely understood. Recent studies support the role played by aneuploidy in oncogenesis, highlighting the importance of this endpoint for mutagenicity screening. SCE are thought to represent the long-term effects of mutagens and are an important genotoxicity biomarker. The present results also agree with data from epidemiological studies and from animal in vivo studies, further supporting the hypothesis that ptaquiloside may represent a significant threat to human health.     

Quantitative comparison of the cytogenetic effect of thiophosphamide during in vivo and in vitro action on monkey lymphocytes

Mutagenic in vivo and in vitro effects were compared quantitatively by the investigation of sister chromatid exchange (SCE) rate and chromosomal aberrations caused by thiophosphamide in macaca rhesus lymphocytes. The integral of thiophosphamide concentration in the blood or culture fluid by a certain time period was used for the estimation of the dose of mutagenic exposure. It was shown that the dose-response relationships and corresponding regression coefficients were similar when the in vivo and in vitro results were compared. The data obtained indicate the possibility for quantitative extrapolation of the results obtained in vitro on the entire organism.     

Comparative effectiveness in the induction of sister chromatid exchanges and chromosome aberrations

The dose curves for 5 chemicals were studied to compare the efficiency of induction of SCEs and chromosomal aberrations by "polycentric" mutagens. The number of SCEs was found to increase linearly with the dose while that of chromosomal aberrations--nonlinearly. The efficiency of SCEs induction by these mutagens was found to be 25-50 times as high as in the induction of chromosomal aberrations. Division of alkylating mutagens into "monocentric" and "polycentric" is shown to be useful. It reflects their different efficiency in damaging one or simultaneously two DNA strands. The correlation between SCEs and formation of aberrations of the chromatid type is stated.     

Bimodal distribution of sensitivity to SCE induction by diepoxybutane in human lymphocytes. I. Correlation with chromosomal aberrations

We carried out a cross-sectional analysis of sister-chromatid exchanges (SCEs) and chromosomal aberrations induced by diepoxybutane (DEB) in lymphocyte cultures from 58 normal blood donors. DEB-induced SCE frequencies were measured in all subjects and chromosomal aberrations in 18. Analysis of variance was used to assess the contributions of exposure to organic solvents, age, smoking history, alcohol and coffee consumption, and red and white blood cell counts to variations in DEB-induced SCEs. In 10 individuals, the epoxide-detoxifying enzyme, glutathione (GSH)-S-transferase mu, was also measured. We observed a bimodal distribution of DEB-induced SCEs in the study population. Approx. 24% of the individuals were twice as sensitive to the induction of SCEs by DEB as the remaining 76%. Lymphocytes from persons sensitive to SCE induction by DEB contained a 4.4-fold increase in the number of DEB-induced chromatid deletions and exchanges. Within sensitive and resistant groups, significant interindividual variations in DEB-induced SCE frequencies were noted. Cigarette smoking was weakly associated with lower SCE frequencies within each group. Genetic deficiency in GSH-S-transferase mu was not correlated with increased sensitivity to SCE induction by DEB. Sensitivity to induction of SCEs by DEB can be rapidly determined and may be a marker of sensitivity to the induction of genotoxicity by certain classes of mutagens.     

Disparate effects of 5-bromodeoxyuridine on sister-chromatid exchanges and chromosomal aberrations in Bloom syndrome fibroblasts

The existence of a high frequency of spontaneous sister-chromatid exchanges (SCEs) in Bloom syndrome (BS) has thus far been supported by data on a small number of BS cell lines. To examine the cause of baseline SCEs more broadly, the frequencies of SCEs, as well as chromosomal aberrations (CAs) in 4 additional BS fibroblast strains were compared, under different assay and cell culture conditions, with those of normal cells in the range of approximately 0.9-90% 5-bromodeoxyuridine (BrdUrd) substitution into template DNA. SCEs at low levels of BrdUrd substitution were detected by an extremely sensitive immunofluorescent technique. From approximately 0.9% to 4.5% BrdUrd substitution, the SCE frequency in BS cells remained constant, at a level (40/cell) 8 times higher than that of normal cells. As BrdUrd substitution increased further, the SCE frequency in BS cells increased almost linearly, reaching 70-100 per cell at approximately 90% substitution, while the SCE increment in control fibroblasts was less than 5 per cell. Analysis of SCEs in 3 successive replication cycles similarly revealed that the SCE increment in BS cells depended on BrdUrd only at a high BrdUrd substitution level. In contrast to data on SCEs, CA induction by incorporated BrdUrd in BS cells was only slightly higher than that in normal cells. Thus, BS cells are extremely sensitive to BrdUrd for SCE induction, but much less so for CA induction.