Non-uniform distribution of sister chromatid exchanges in human lymphocytes

To test whether sister chromatid exchange (SCE) scores on human chromosomes have a uniform distribution, simulated SCE scores were generated and compared with observed scores using log-linear models. The analysis was performed at the level of the chromosome groups. Using this method we first tested whether the number of SCEs was distributed uniformly, i.e. proportional to the relative length of the chromosomes. Refinements of this hypothesis were made by considering a variable region around a first SCE to be inert for other SCEs and by making the occurrence of an SCE on a chromosome dependent on the occurrence of another SCE on the same chromosome. In further analyses it was tested whether the number of SCEs was proportional to the number of G bands on a chromosome, or to the DNA content of the chromosomes. None of the tested hypotheses fitted the observed data, establishing the non-uniform distribution of these events.     

Spontaneous level of sister chromatid exchanges in patients with tuberous sclerosis and Recklinghausen's neurofibromatosis

It is shown that the average number of sister chromatid exchanges (SCE) per one cell in patients with tuberous sclerosis as well as in those with Recklinghausen's neurofibromatosis do not differ from the control. But the non-parametric methods of analysis have revealed differences in the spontaneous level of SCE is patients with tuberous sclerosis, while no such differences were revealed in patients with Recklinghausen's neurofibromatosis.     

The frequency and distribution of sister chromatid exchanges in human chromosomes

Summary A detailed procedure is described for a rapid detection of phosphoglucomutase-2 (=phosphopentomutase; PGM-2) on Cellogel following electrophoresis of extracts of human red blood cells and other tissues, including cultured fibroblasts and various types of primate-rodent somatic hybrid cells.The present study indicated that there is only one locus for phosphopentomutase in man. The data from a selected panel of 20 independent clones of man-mouse somatic cell hybrids, investigated for the presence of human chromosomes and for the presence or absence of human PGM-2 favored the assignment of the human PGM-2 locus to chromosome 4.     

Analysis of the frequency and distribution of sister chromatid exchanges in cultured human lymphocytes

Summary Lymphocytes from 20 normal subjects (11 male and 9 female) were examined for the frequency and location of sister chromatid exchanges (SCE) by the BrdU—Giemsa method. The mean frequency of SCE was 6.37 with little significant variation. One subject had a high number of exchanges in chromosome 1 while the remainder showed a random distribution of exchanges between chromosomes. The frequency of exchanges generally increased with chromosome length. However, chromosome 1, 2 and the B group had more exchanges than expected while the E, F and G groups had less than expected. The distribution of exchanges in chromosomes 1, 2 and the B group was non-random with a concentration of exchanges below the centromere and to a lesser extent on the distal portion of the long arm. The majority of exchanges appeared to occur at the junction between the dark and light G bands. It is suggested that the concentration of exchanges may reflect differences in BrdU incorporation along the length of the chromosome.     

Fenvalerate-induced chromosome aberrations and sister chromatid exchanges in the bone marrow cells of mice in vivo

To investigate whether subjects with low-acid states are exposed to increased genetic risk with respect to controls, we evaluated mutagenicity and presence of clastogenic factors (CF) in the gastric juice of chronic atrophic gastritis and omeprazole-treated patients. Mutagenic gastric juice was found in 8/15 (53%) chronic atrophic gastritis patients, 8/11 (73%) omeprazole-treated patients, and 2/13 (15%) healthy control subjects. The mean mutagenicity ratio of omeprazole-treated patients (1.52+/-0.48/0.1 ml gastric juice) was significantly higher than those of either controls (1.07+/-0.15; P<0.01) or chronic atrophic gastritis patients (1.16+/-0.21; P<0.05). Only chronic atrophic gastritis patients showed an increased clastogenic index with respect to healthy controls (2.67+/-2.13 versus 0.38+/-0.51; P<0.001). These findings expand our knowledge of gastric disease risk factors, and indicate that there may well be a risk of mucosal DNA damage arising from the presence of mutagenic and CF in the gastric juice.     

Fenvalerate-induced chromosome aberrations and sister chromatid exchanges in the bone marrow cells of mice in vivo

Fenvalerate, a synthetic pyrethroid insecticide, is commonly used in agriculture and other domestic applications due to its high insecticidal activity and low mammalian-, avian- and phyto-toxicities. However, the genotoxic effect of fenvalerate is highly equivocal. In the present study the genotoxic effects of fenvalerate was evaluated using structural chromosome aberration (CA) and sister chromatid exchange (SCE) assays in mice. Out of the three doses (5, 10 and 20 mg/kg) tested, statistically significant increase in CA was found following intra peritoneal (i.p.) treatment of 20 mg/kg of fenvalerate for 24 h (P<0.01) and 48 h (P<0.05) only. Neither the acute doses of 5 and 10 mg/kg, nor the sub-acute dose (5×4 mg/kg) of fenvalerate could induce any significant effect. All the three acute doses induced significant increase in the frequency of SCEs (P<0.01) in the bone marrow cells, which showed a significant dose-response correlation (r=0.9541, P<0.05). With certain reservations to possible impurities, from the present findings technical grade fenvalerate may be considered as a weak clastogen and a potent inducer of SCEs in mice.     

The effects of boric acid on sister chromatid exchanges and chromosome aberrations in cultured human lymphocytes

The aim of this study was to determine the possible genotoxic effects of boric acid (BA) (E284), which is used as an antimicrobial agent in food, by using sister chromatid exchange (SCEs) and chromosome aberration (CAs) tests in human peripheral lymphocytes. The human lymphocytes were treated with 400, 600, 800, and 1000 μg/mL concentrations of BA dissolved in dimethyl sulfoxide (DMSO), for 24 h and 48 h treatment periods. BA did not increase the SCEs for all the concentrations and treatment periods when compared to control and solvent control (DMSO). BA induced structural and total CAs at all the tested concentrations for 24 and 48 h treatment periods. The induction of the total CAs was dose dependent for the 24 h treatment period. However, BA did not cause numerical CAs. BA showed a cytotoxic effect by decreasing the replication index (RI) and mitotic index (MI). BA decreased the MI in a dose-dependent manner for the 24 h treatment period.     

Induction of sister chromatid exchanges in human cells by fluorescent light.

The Brd-U differential staining technique was utilized to examine the induction of sister-chromatid exchanges (SCE) by fluorescent ligt in human fetal lung fibroblasts (IMR-90). Exposure of these cells in media to fluorescent light resulted in an increase in SCE frequencies from a background level of 8.5 SCE/cell to 20.5 SCE/cell. Cellular replication kinetics were also inhibited by fluorescent light exposure. Exposure of cells to fluorescent light in phosphate buffered saline (PBS) resulted in a two-fold increase in SCE levels and incresed inhibition of cell replication, indicating that culture media may have a protective effect. Determinations of SCE frequencies with blocking filters indicated that the fluorescent light wavelengths responsible for SCE induction were in the near-ultraviolet spectrum between 300 and 390 nm. Culturing cell sin media that had been exposed to fluorescent light resulted in a significant increase in SCE levels, 14.5 ± 1.5 vs. 7.5 ± 0.65, demonstrating the contribution of media photoproducts to SCE induction. The role of media photoproducts was further reinforced by finding a significant decline in fluorescent light induced SCE in cells cultured in medium deficient in three known photosensitizers (phenol red, tetracycline and riboflavin) for 2–3 weeks prior to exposure.Since SCE have been shown to be a sensitive indicator of DNA damage, these results indicate that fluorescent light can induce genetic damage in human cells. These findings are also of importance to investigators culturing cells in laboratories with fluorescent illumination.     

Spontaneous chromosome aberrations in human somatic cells

Conclusion In conclusion it is necessary to say that at present, we cannot consider whether there may be a geographical difference in frequency of spontaneous chromosome aberrations in somatic cells. For that purpose, a very abundant experimental material is required, as well as an improvement in methodology: what causes the difference in the results of various investigators; what methodical principles should be used for collection of data.Important factors in the differences of frequencies of spontaneous chromosome aberrations are likely to be the conditions of cultivation and making the preparations, as well as the methods of scoring the chromosome aberrations. The international standardisation of the cultivation conditions and of the estimates of chromosome aberrations is needed for the further study of the rate and reasons of the spontaneous mutation process in somatic cells.     

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.     

Induction of structural chromosome aberrations and sister chromatid exchanges in human lymphocytes in vitro by aristolochic acid

The medicinal use of Aristolochia clematitis has been known for some time. The main active agent of this medicinal plant is aristolochic acid, a nitrophenanthrenecarbonic acid. Very recently, however, the Federal Health Office withdrew the licence for all drugs containing aristolochic acid, because of the well-founded suspicion that aristolochic acid may be a very potent carcinogen. We investigated the induction of structural chromosome aberrations and sister chromatid exchanges (SCEs) by aristolochic acid in human lymphocytes in vitro. Cells were treated with the agent tested throughout culture time and during the G0 phase of the cell cycle. We tested concentrations over a range of 1 to 20 micrograms/ml. Both treatment conditions resulted in an increased aberration frequency. The induction of gaps and breaks as well as the induction of SCEs showed a dose-dependent increase. The number of SCEs per metaphase was enhanced by a factor of 2 to 3. If conventional cytogenetic methods had been applied in time, one would have recognized the mutagenic risk of aristolochic acid earlier.     

Individual variability in the level of spontaneous sister chromatid exchanges

The contribution of genetic factors to spontaneous level of the sister chromatid exchanges (SCE) has been determined on the basis of the twin method of study. A close relation is shown to exist between the SCE tests in the group of the monozygotic twins which is a result of the common genotype. The SCE test with late BUdR introduction is under rigid genetic control.     

Relationship of spontaneous chromosome instability and sister chromatid exchanges in Fanconi's anemia

The frequency of spontaneous instability of lymphocyte chromosomes of the first 2 mitoses, the rate of sister chromatid exchanges (SCEs), and the proliferative kinetics of lymphocytes were studied in a 6-year-old girl with Fanconi's anemia (FA) and in 4 healthy donors. The frequencies of aberrant cells and the total number of chromosome breaks in the FA patient decreased with cell transition from the first to the second mitosis. The FA lymphocytes had a slower proliferative kinetics and the level of SCEs was higher as compared with control. The probability of chromatid deletions at the sites of SCEs localization and in the dark and light stained chromatids was unequal. 33.8% of chromatid breaks were associated with SCEs. The data point to the relationship between SCEs and spontaneous chromosome instability in AF cells.     

Positional control of the distribution of spontaneous sister chromatid exchanges along mouse chromosomes]

The use of a new method having combined C-band staining and differential staining of sister chromatids allowed to determine a pattern of distribution of spontaneous sister chromatid exchanges (SCE) along cytologically marked chromosomes 1, 2 and 6 of house mouse. All chromosomes displayed the same pattern of SCE distribution: SCEs are most frequent in the middle part of the chromosome arm and rather rare near the centromere and the telomere. It has been suggested that this pattern of distribution is positional, rather chromatin-specific. The chromosome 1 carrying paracentric inversion with breakpoints in the middle part of the arm and just near the telomere has the same pattern of SCE distribution as normal chromosome 1. Double insertion of homogeneously staining regions in the middle part of the chromosome 1 produces increase in the SCE number per chromosome proportional to the physical length of the insertion. In contrast to meiotic recombination, interference between SCEs is not detected. No evidence for existence of the hot-spots of SCE on the junctions between C-positive and C-negative regions, as well as between G-bands and R-bands, has been produced.     

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.     

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.     

Ultrasonic induction of sister chromatid exchanges in human lymphocytes

Summary We analyzed sister chromatid exchange (SCE) frequencies as an indicator of DNA damage induced in human lymphocytes by real-time ultrasound. A range of exposure times and intensities was tested in a series of blind, randomized, in vitro experiments under spatial and sonographic conditions simulating exposure of a gravid abdomen and uterus. Our studies showed small but consistent effects of ultrasound on SCE frequencies, for each experiment. Differences between matched control and exposed means were significantly different from zero. X ² tests for homogeneity indicated no significant differences among either the means or the total distributions of the controls, nor among each of the separate dose levels. Consequently, experiments were pooled, and X ² analysis indicated significant differences both among distributions and among means of SCE frequencies for controls versus exposed cells (P(0.001). The pooled control mean was also significantly different from each of the pooled dose means. Correcting for multiple comparisons gave identical results for the paired comparisons of means except for the 20-min level which was borderline (0.025P(0.01). We conclude that the well-established value of clinical ultrasonography warrants its continued use; however, minimizing the numbers and lengths of exposure per patient would seem prudent, pending further information on clinical implications of our results.Supported in part by NIH-HD82855 and HD 11021 and a National Foundation Summer Science Research Grant for Medical Students, 8-80-22     

Changes in the level of sister chromatid exchanges in cultured Chinese hamster cells undergoing limited proliferation

"Stationary phase ageing" of cultured Chinese hamster cells (when proliferation rate decreases and in the stationary growth phase) produces an increase in the frequency of spontaneous sister chromatid exchanges (SCE). Thiophosphamide-induced (24 h) frequency of SCE increases from 2-day to 5-day "age" and later (in the stationary phase) is practically the same. The "stationary ageing" cultured cells are suggested to be used as a model system for studying molecular-genetic age changes.