Comparison of the level of sister chromatid exchanges and chromosome aberrations induced by chemical mutagens in vitro and in vivo

The paper presents results of a study of a dose dependence of induction of SCE and chromosomal aberrations at the exposure of human lymphocytes in vitro and bone marrow cells of mice in vivo to 5 alkylating chemicals. The efficiency of SCE induction in vitro is found to be 300-30 times as high as that of arising of chromosomal aberrations. The same regularity is observed in experiments in vivo, but the ratio is reduced to 60-20 times.     

Reduced frequencies of Mitomycin-C induced sister chromatid exchanges in AKR Mice

Summary The frequencies of base-line and Mitomycin-C (MMC) induced sister chromatid exchanges (SCE) were surveyed in four inbred strains of mice. In contrast to the C57B1/6J, CBA/J, and A/J strains where frequencies of SCE increased linearly with increasing dose of MMC, levels of SCE were significantly lower in AKR/J mice at high MMC concentrations. At a dose of 5 mg/kg MMC, chromosomal aberrations were more frequent in bone marrow cells of AKR/J mice than in C57B1/6J mice. These observations suggest an altered response to DNA damage in the AKR mouse strain.     

Demonstration of spontaneous sister chromatid exchanges in vivo

The frequency of sister chromatid exchanges (SCEs) was examined as a function of bromodeoxyuridine (BUdR) concentration in vivo. Oneyear-old Wistar rats were continuously infused with BUdR through the tail vein for 24 h, sacrificed, and mitotic preparations prepared from femur bone marrow. It was observed that from the minimum concentration of BUdR which permitted accurate scoring (1.9 μg/g wt/h) to a BUdR concentration of 7 μg/g wt/h, SCE frequency remained constant. Above 7 μg BUdR/g wt/h SCE frequency increased, saturating at higher BUdR concentrations. The stability of SCE frequency at low BUdR concentrations is interpreted to indicate the existence of spontaneous SCEs in vivo.     

Dynamics of sister chromatid exchange after in vivo exposure to thiophosphamide

Thiophosphamide (T) was i.v. administered into New Zealand rabbit (4 mg/kg). The rate of SCE in blood lymphocytes was increased up to 21st day after T administration. There are two phases in dynamics curve of SCE--a rapid phase and a slow one. The rapid decrease of SCE's rate depends on cell mortality. The slow decrease of SCE rate is connected with reparation of chromosome damages and selection of cells in lymphopoietic tissue. It was demonstrated that the special class of cells with intermediate number of SCE exists in blood after T administration.     

In vivo sister chromatid differentiation and base line sister chromatid exchanges in Channa punctatus.

An in vivo system for differentially stained sister chromatids by incorporating 5' Bromo 2' deoxyuridine at two consecutive round of DNA replication has been developed in C. punctatus. The base line developed frequency of sister chromatid exchanges (SCEs) was found to be 0.038 SCE/chromosome. This low baseline frequency of SCEs could be useful in detecting genotoxicity of pollutants in aquatic medium.     

Dynamics of the frequencies of chemically induced sister chromatid exchanges in a series of cell generations

The number of sister chromatid exchanges (SCE) in a culture of human lymphocytes and the established cultures of Chinese hamster cells has been studied after the exposure to thiophosphamide and dipin at different stages of the cell cycle. The most pronounced effect is observed under the action of the mutagens at the G1 of the first cycle, prior to harvest. The SCE level becomes lower with the increase of the interval between the exposure to the mutagen and the time of 5-BUdR introduction. The number of SCEs per cell drops to the control level when the duration of the first interval is equal to that of the cell cycle. The results obtained prove the mutagen-induced impairments causing SCE formation to be repaired practically 100%, provided that at least one cycle of DNA replication took place.     

Micronuclei and sister chromatid exchanges induced by capsaicin in human lymphocytes

Escherichia coli has provided an important model system for understanding the molecular basis for genetic instabilities associated with repeated DNA. Changes in triplet repeat length during growth following transformation in E. coli have been used as a measure of repeat instability. However, very little is known about the molecular and biological changes that may occur on transformation. Since only a small proportion of viable cells become competent, uncertainty exists regarding the nature of these transformed cells. To establish whether the process of transformation can be inherently mutagenic for certain DNA sequences, we used a genetic assay in E. coli to compare the frequency of genetic instabilities associated with transformation with those occurring in plasmid maintained in E. coli. Our results indicate that, for certain DNA sequences, bacterial transformation can be highly mutagenic. The deletion frequency of a 106 bp perfect inverted repeat is increased by as much as a factor of 2 x 10(5) following transformation. The high frequency of instability was not observed when cells stably harboring plasmid were rendered competent. Thus, the process of transformation was required to observe the instability. Instabilities of (CAG).(CTG) repeats are also dramatically elevated upon transformation. The magnitude of the instability is dependent on the nature and length of the repeat. Differences in the methylation status of plasmid used for transformation and the methylation and restriction/modification systems present in the bacterial strain used must also be considered in repeat instability measurements. Moreover, different E. coli genetic backgrounds show different levels of instability during transformation.     

UV-light induced sister chromatid exchanges in xeroderma pigmentosum lymphocytes

Summary Cultured lymphocytes from 9 patients with clinically different types of xeroderma pigmentosum were exposed to ultraviolet light at 24 h. An increased rate of sister chromatid exchanges was observed in 6 patients (128–148% increase in three, 34–51% in three), but not in three patients with deSanctis-Cacchione syndrome (xeroderma pigmentosum with mental defect), compared to simultaneously cultured controls. A positive result could be useful as preliminary cytogenetic diagnostic test. The results are interpreted as an expression of UV-light induced chromosomal instability due to impaired DNA repair.     

Aging and sister chromatid exchange. IV. Reduced frequencies of mutagen-induced sister chromatid exchanges in vivo in mouse bone marrow cells with aging.

Induction of sister chromatid exchanges (SCE's) was examined in bone marrow cells of young and old C57BL/6J mice exposed to three different DNA-damaging agents (cyclophosphamide, mitomycin C, and doxorubicin). At low concentrations of all three mutagens, the levels of induced SCE's were similar in young and old cell populations. However, at higher mutagen concentrations, SCE induction was significantly reduced in old cell populations. Studies of mice aged 5 to 32 months revealed that induced SCE frequencies remain stable during early adulthood (5 to 12 months) and then begin to decline as a function of age. These results indicate that with aging there exists a gradual alteration of cellular response to DNA damage.     

Dose dependence of sister chromatid exchanges in human lymphocytes induced by in vitro α-particle irradiation

Exposure of human G₀ lymphocytes to high-LET particles under different conditions has been seen, unlike low-LET radiations, to be substantially effective in the induction of sister chromatid exchanges (SCE). However, whereas for fast neutrons a linear dose response of SCE has been determined, there is no sign of a dose-response relationship for α-particles. A likely reason for this lack of dose dependence may be the irradiation procedure. Therefore, a technique developed in our laboratory to ensure uniformity of irradiation with α-particles was used in the present study. Monolayers of 3 h-stimulated lymphocytes were exposed with α-particles from ²⁴¹Am. Underdispersion was found for the cell-to-cell variance of the number of SCE. The dose response of SCE was linear, with a yield of 3.4 SCE per cell and per Gray. Received: 26 April 1996 / Accepted in revised form: 24 July 1996     

In vivo sister chromatid differentiation and baseline sister chromatid exchanges in a mouse ascites tumour model.

Induction of differentially stained sister chromatids at G2/M and determination of baseline sister chromatid exchanges (SCEs) in ascites form of mouse sarcoma 180 cell line have been done by in vivo incorporation of 5-bromodeoxyuridine (BrdU) for two consecutive DNA replication cycles. The baseline SCE frequency is 6.24 at log phase of tumour growth.     

Increased rates of sister chromatid exchanges induced by the herbicide 2,4-D

The potential for genetic damage from widely used hormonic herbicides, such as 2,4-dichlorophenoxyacetic acid (2,4-D), continues to be of serious concern. The mutagenic effect as reflected by the rates of sister chromatid exchanges (SCE) was determined in cultured human lymphocytes. Data were based on the analysis of 50 cells for the control and each of the three treatments. A 50 micrograms/ml dosage caused a highly significant increase in SCE. Dosages of 100 and 250 micrograms/ml elevated the rate of SCE, but not significantly. Since 2,4-D biodegrades rapidly in soil and water, its continued use is not in serious question until safer compounds are available. However, the results of this study suggest that the danger of genetic damage from direct exposure to commercial samples of 2,4-D should not be ignored.     

The effect of sera on sister chromatid exchanges in vitro

To study viral effects on sister chromatid exchange (SCE), human diploid fibroblasts were infected with herpes simplex virus (HSV) of type-1 and type-2. Both types of virus produced remarkable chromosomal aberrations in the early phases of the infection, but neither of them caused an increase in the SCE frequency over the uninfected control level. Analysis of the breakpoints of chromatid deletions with respect to their association with SCE revealed that the chromatid deletions induced by HSV arose independently of the sites of SCE. It is probable that the genesis of virus-induced chromosomal aberrations is unrelated to the molecular processes that function in SCE formation.     

Statistical evaluation of sister chromatid exchanges

Summary Log-linear models are fitted to sister chromatid exchange (SCE) scores in order to test the significance of the differences in SCE scores observed between individuals or between experimental treatments. The analysis is performed at the level of chromosome groups. In each single test all measurements from all chromosome groups, both from the control and from the experimental sets, are utilized. By proceeding in this way full use is made of all the available information on the SCE scores at the level of chromosome groups and the shortcomings of the classical Student-t and chi-square tests are avoided.This work was supported by a grant Geconcerteerde Acties from the Belgian Government.     

The effects of high and low fluoride diets on the frequencies of sister chromatid exchanges

A recent report suggests that fluoride has mutagenic activity in mice. To examine the potential clastogenic effect of ingested fluoride, we examined the frequencies of baseline SCE and mitomycin C induced SCE as well as baseline chromsomal aberrations and cell-cycle kinetics in mice raised on high and low fluoride diets. The lack of significant differences in any of these parameters between the two groups of animals indicates that dietary fluoride is not clastogenic and supports the continued use of water fluoridation.     

DNA-protein cross-links and sister chromatid exchanges induced by dimethylarsinic acid in human fibroblasts cells

Biotransformation of inorganic arsenic to form both methylarsinic acid (MA) and dimethylarsinic acid (DMA) has traditionally been considered as a mechanism to facilitate the detoxification and excretion of arsenic. However, the methylation of inorganic arsenic as a detoxification mechanism has been questioned due to recent studies revealing an important role of organic arsenic in the induction of genetic damage. In a previous report a reduction of DNA migration after treatment of cells with DMA was described. In order to further evaluate the possible induction of protein-DNA adducts, an experiment was performed taking into account other parameters and modifications of the standard alkaline comet assay. In addition, the results obtained with the comet assay were compared with those obtained by analyzing the induction of sister chromatid exchanges (SCEs). SCE frequencies were significantly increased in treated cells in relation to controls (p<0.001). Furthermore, in the standard alkaline comet assay, as well as in the control assay for proteinase K treatment, a significant dose-dependent reduction in tail moment was observed. Nevertheless, the post-treatment with proteinase K induced the release of proteins joined to the DNA and consequently, a dose-dependent increment in DNA migration was observed (p<0.001). These results suggest that DNA-protein cross-links may be an important genotoxic effect induced by dimethylarsinic acid in human MRC-5 cells.     

Dynamics of the frequencies of sister chromatid exchange and chromosome aberrations in vivo

2.4 and 6 mg/kg thiophosphamide (T) was administered intravenously to New Zealand rabbits. A decrease in sister chromatid exchange (SCE) and chromosome aberration (CA) rate began immediately after the mutagenic action of T was over. The expected SCE rate was more than the investigated one. The difference between expected and investigated SCE rate increased with the dose of T. A calculation of SCE was based on the amount of the administered T, the rate of T removal and cell sensitivity to T. The death of cells with high number of SCE resulted in a fast decrease in SCE rate in the first 4 days. Reparative processes and cell proliferation in lymphocyte tissue resulted in a slow decrease in SCE rate after the 4th day. A number of nuclear cells in the blood was the smallest on the 4 th day, at the same time relative increase in CA rate was observed. The time of sampling and the dose of the substance tested should be taken into account for a more accurate estimation of mutagenic activity of some chemicals in in vivo cytogenetic tests.     

The effects of high and low fluoride diets on the frequencies of sister chromatid exchanges

A recent report suggests that fluoride has mutagenic activity in mice. To examine the potential clastogenic effect of ingested fluoride, we examined the frequencies of baseline SCE and mitomycin C induced SCE as well as baseline chromosomal aberrations and cell-cycle kinetics in mice raised on high and low fluoride diets. The lack of significant differences in any of these parameters between the two groups of animals indicates that dietary fluoride is not clastogenic and supports the continued use of water fluoridation.