Induction of chromosome aberrations and sister-chromatid exchanges by caprolactam in vitro

Caprolactam (CAP) induced chromosome aberrations in whole-blood cultures of human lymphocytes at 50 mM without metabolic activation (24-h treatment) and at 200 mM in the presence of rat liver S9 mix (1-h treatment). CAP also produced a dose-dependent increase in polyploid cells, the effect being statistically significant at 25 and 50 mM without S9 mix and at 100 and 200 mM with S9 mix. Without metabolic activation, there was an increase in hypodiploid cells at 50 mM and hyperdiploid cells at 12.5 mM. In Chinese hamster ovary cells, CAP produced a marginal elevation of sister-chromatid exchanges at 125 mM in the presence of S9 mix (4-h treatment). The results show that CAP is able to induce cytogenetic changes in vitro at very high toxic concentrations.     

Relationship of DNA repair to chromosome aberrations, sister-chromatid exchanges and survival during liquid-holding recovery in X-irradiated mammalian cells

The repair of X-ray induced DNA single strand breaks and DNA—protein cross-links was investigated in stationary phase, contact-inhibited mouse cells by the alkaline-elution technique. Approx. 90% of X-ray induced single strand breaks were rejoined during the first hour of repair, whereas most of the remaining breaks were rejoined more slowly during the next 5 h. At early repair times, the number of residual non-rejoined sungle strand breaks was approx. proportional to the X-ray dose. DNA—protein cross-links were removed at a slower rate (T1/2 approx. 10–12 h). Cells were held in stationary growth for various periods of time after irradiation before subculture at low density to score for colony survival (potentially lethal damage repair), chromosome aberrations in the first mitosis, and sister-chromatid exchanges in the second mitosis. Both cell killing and the frequency of chromosome aberrations decreased during the first several hours of recovery, reaching a minimum level by 6 h; this decrease correlated temporally with the repair of the slowly rejoining DNA-strand breaks. Relatively few sister-chromatid exchanges were observed when the cells were subcultured immediately after X-ray. The exchange frequency rose to maximum levels after a 4-h recovery interval, and returned to control levels after 12 h of recovery. The possible relationship of DNA repair to these changes in survival, chromosome aberrations, and sister-chromatid exchanges during liquid-holding recovery is discussed.     

Induction of chromosome aberrations and sister-chromatid exchanges in CHO-K1 cells by o-phenylphenol

o-Phenylphenol (OPP), is used in Japan as a fungicide in food additives for citrus fruits. The induction of chromosome aberrations and sister-chromatid exchanges (SCEs) by OPP in cultured Chinese hamster ovary (CHO-K1) cells was studied. Cells were exposed to various concentrations of OPP ranging from 50 to 175 micrograms/ml for 3 h, and further incubated for 27 and 42 h. These incubation periods are almost equal to 2 and 3 cell cycles. SCEs and chromosome aberrations were induced by OPP at concentrations of 100, 125 and 150 micrograms/ml after the incubation for 27 h. For chromosome aberrations, chromatid breaks and exchanges there was a dose-dependent increase. Diplochromosomes due to endoreduplication were also caused by the same concentrations of OPP in a dose-dependent manner. After incubation for 42 h, chromosome aberrations were also increased by OPP at concentrations of 100 and 125 micrograms/ml, but the frequencies of SCEs were not significantly different from those of the control. These results suggest that OPP has a cytogenetic toxicity, and that the DNA damage resulting in SCEs induced by OPP is relatively short-lived and can be repaired during the longer incubation time.     

Effect of recombinant interferon-alpha on streptonigrin-induced chromosome aberrations and sister-chromatid exchanges in hamster cells

The effect of recombinant interferon-alpha-2a (rIFN-alpha-2a) on the induction of chromosomal aberrations (CAs) and sister-chromatid exchanges (SCEs) by the radiomimetic antibiotic streptonigrin (SN, 250 ng/ml, 20 min, 37 degrees C) in Chinese hamster ovary (CHO) cells was investigated. Recombinant IFN-alpha-2a (4500-45,000 IU/ml) was added to the cell cultures 30 min before SN and left in the culture medium until the end of SN treatment or until cell harvesting. A statistically significant increase in the frequency of CAs and SCEs was observed following treatment with SN (P < 0.05), whereas treatments with rIFN-alpha-2a alone did not produce any significant increase of CAs and SCEs over control values. Low rIFN-alpha-2a doses produced a reduction in the frequency of CAs and an increase in the yield of SCEs induced by SN, while high doses of the cytokine caused an increase in the yield of CAs and a reduction in the frequency of SCEs induced by the antibiotic. In addition, rIFN-alpha-2a caused a marked inhibition (around 50%) on the yield of SN-induced chromatid-type aberrations in the G(2) phase of the cell cycle. It is suggested that the inhibitory effect of rIFN-alpha-2a on the SN-induced chromosome damage is due to the stimulation of DNA synthesis and repair by the cytokine. On the other hand, our results give further support to our previous hypothesis that the induction of CAs and SCEs by SN is based on different mechanisms.     

Effects of caffeine on chromosome aberrations and sister-chromatid exchanges induced by mitomycin C in BrdU-labeled human chromosomes.

The BrdU-Hoechst staining technique has been used in analyzing the effect of caffeine (CAF) on chromosome aberrations and sister-chromatid exchanges (SCEs) induced by mitomycin C (MC). CAF increased the frequency of SCE in MC-treated chromosomes in all specimens. The combination of MC and CAF caused a remarkable increase in all types of chromosome aberrations, but the most startling effect was the appearance of many cells with multiple aberrations (shattered chromosomes). The BrdU-Hoechst technique showed that the shattered chromosomes did not appear in cells that had replicated only once, but did occur in cells which replicated twice in the presence of MC and CAF. The large majority of chromatid breaks observed did not involve areas common to SCE; and the SCE frequency significantly increased in spite of the existence of multiple breaks. This indicates that very few of the breaks are incomplete exchanges and that the mechanism for formation of SCE might be different from that of chromosome breaks. In another experiment, monofunctional-MC (M-MC) had a small effect on SCE rates, though it induced shattered chromosomes with CAF post-treatment. Possible differences in the mechanisms leading to SCE and chromosome breaks are discussed.     

Analysis of chromosome aberrations and sister-chromatid exchanges in human lymphocytes exposed in vitro to Hydergine.

Hydergine (dihydroergotoxine mesylate, Sandoz) was examined for its capability to induce chromosome damage and sister-chromatid exchanges (SCEs) in human lymphocyte in vitro. For the chromosome-aberration study, cultures set up from 6 individuals were divided into 5 groups: negative control, positive control (caffeine, 0.5 mg/ml), and Hydergine (0.1, 0.25 and 0.5 micrograms/ml). For the SCE examination, which used 8 individuals, 4 cultures were made per person in the following way: negative control, positive control (mitomycin C, 0.1 microgram/ml), and Hydergine (0.1 and 0.5 micrograms/ml). Lymphocytes were cultivated for 72 h, being exposed to the respective treatments during the final 24 h. The results showed that Hydergine induced no chromosome damage in human lymphocytes in vitro.     

Chromosomal aberrations and sister-chromatid exchanges in workers exposed to styrene

Few studies exist about chromosomal damage in workers occupationally exposed to styrene. In the present study, chromosomal aberrations and SCEs were analyzed from cultures of peripheral lymphocytes of workers employed in 6 different reinforced-plastics industries with styrene air exposure levels ranging from 30 to 400 mg/mc. A control group was selected on the base of sex, age and smoking habit. We examined 50-h cultures (for chromosomal-aberrations) and 72-h cultures (for SCEs) for each individual.All workers exposed to styrene, as compared with controls, showed significantly increased frequencies of chromosomal aberrations, while SCEs were significantly increased at 4 of the 6 plants. High SCE values appeared with styrene air concentrations higher than 200 mg/mc.Apart from the possible presence and role of other interfering chemicals in the various plants, chromosomal aberrations seem to be more sensitive than SCEs for the detection of chromosomal damage caused by exposure to low doses of styrene.     

Chromosomal aberrations and sister-chromatid exchanges in workers exposed to styrene

Few studies exist about chromosomal damage in workers occupationally exposed to styrene. In the present study, chromosomal aberrations and SCEs were analyzed from cultures of peripheral lymphocytes of workers employed in 6 different reinforced-plastics industries with styrene air exposure levels ranging from 30 to 400 mg/mc. A control group was selected on the base of sex, age and smoking habit. We examined 50-h cultures (for chromosomal-aberrations) and 72-h cultures (for SCEs) for each individual. All workers exposed to styrene, as compared with controls, showed significantly increased frequencies of chromosomal aberrations, while SCEs were significantly increased at 4 of the 6 plants. High SCE values appeared with styrene air concentrations higher than 200 mg/mc. Apart from the possible presence and role of other interfering chemicals in the various plants, chromosomal aberrations seem to be more sensitive than SCEs for the detection of chromosomal damage caused by exposure to low doses of styrene.     

Effects of vanillin on sister-chromatid exchanges and chromosome aberrations induced by mitomycin C in cultured Chinese hamster ovary cells

Effects of vanillin on the induction of sister-chromatid exchanges (SCEs) and structural chromosome aberrations by mitomycin C (MMC) were investigated in cultured Chinese hamster ovary cells. Vanillin induced neither SCEs nor chromosome aberrations by itself. However, an obvious increase in the frequency of SCEs was observed when MMC-treated cells were cultured in the presence of vanillin. The effect of vanillin was S-phase-dependent. On the contrary, the frequency of cells with chromosome aberrations was significantly decreased by the post-treatment with vanillin at G2 phase.     

Acrylonitrile-induced sister-chromatid exchanges and DNA single-strand breaks in adult human bronchial epithelial cells

The ability of acrylonitrile to induce cytotoxicity, sister-chromatid exchanges and DNA single-strand breaks was studied in cultured human bronchial epithelial cells. The toxic effect as determined by cloning efficiency was observed at a dose of 600 micrograms/ml but not at doses of both 150 and 300 micrograms/ml. The frequency of sister-chromatid exchange in untreated cells was 3.7 +/- 1.3 per cell. In contrast, cells treated with acrylonitrile at 150 and 300 micrograms/ml exhibited 6.6 +/- 1.3 and 10.7 +/- 1.7 sister-chromatid exchanges per metaphase, respectively. DNA single-strand breaks were induced by acrylonitrile at dose levels of 200 and 500 micrograms/ml. The genotoxic effects on human bronchial epithelial cells that were directly exposed to acrylonitrile are of interest in relation to evidence for the higher lung cancer incidence of acrylonitrile workers in epidemiological studies.     

Plant extracts induce chromosome aberrations and sister-chromatid exchanges in Chinese hamster ovary cells and human lymphocytes

Effects of extracts from Vicia faba were compared with those of Zea mays for the induction of sister-chromatid exchanges (SCEs) and of chromosome aberrations (CAs) in Chinese hamster ovary (CHO) cells. CA induction by the maize extract was also tested in human lymphocytes. The extracts from roots and leaves of Vicia faba induced CAs and SCEs in CHO cells. The extracts from maize leaves also induced SCEs and CAs in CHO cells, and CAs in human lymphocytes. Maize extracts were more potent in inducing SCEs than Vicia extracts and the SCE- and CA-inducing capacity of maize extracts decreased during preincubation before addition to cells.     

Cytogenetic effects of pulsing electromagnetic field on human lymphocytes in vitro: chromosome aberrations, sister-chromatid exchanges and cell kinetics

Exposure of human lymphocyte cultures to a pulsing electromagnetic field (PEMF; 50 Hz, 1.05 mT) for various durations (24, 48 and 72 h) resulted in a statistically significant suppression of mitotic activity and a higher incidence of chromosomal aberrations. Furthermore, the shorter exposure times (24 and 48 h) did not cause a significant delay in cell turnover (cell proliferation index) or an increase in the baseline frequency of sister-chromatid exchanges (SCE). However, cultures continuously exposed to PEMF for 72 h exhibited significant reduction of the cell proliferation index (CPI) and an elevation of SCE rate. These results suggest that exposure to PEMF may induce a type of DNA lesions that lead to chromosomal aberrations and cell death but not to SCE, except probably at longer exposure times.     

Relationships among cytotoxicity, lysosomal breakdown, chromosome aberrations, and DNA double-strand breaks

Certain chemicals that are either weak or non-carcinogens had been previously shown to induce DNA single-strand breaks in rat hepatocytes, but only at cytotoxic doses. In contrast, stronger carcinogens induced DNA single-strand breaks at non-toxic doses. This report shows that the strong carcinogens and mutagens cadmium sulfate, sodium dichromate, dimethyl sulfate, and N-methyl-N'-nitro-N-nitrosoguanidine all induce DNA single-strand breaks at non-toxic concentrations, but that they also induce DNA double-strand breaks at concentrations that are closely correlated with cytotoxicity. Some weak carcinogens produced DNA single- and double-strand breaks, but only at acutely cytotoxic concentrations. We suggest that the DNA double-strand breaks result from a cell-mediated process such as release of DNAase from lysosomes or other cellular compartments, that might occur during cellular response to acutely toxic damage. Experiments with N-dodecyl imidazole (NDI), a lysosomal detergent, show that lysosomal breakdown alone is only a weak inducer of DSBs, but that lysosomal breakdown in combination with prior chemical damage produced by MNNG synergistically induces DNA DSBs in BHK cells. N-Dodecyl imidazole also induces chromosomal aberrations in CHO cells at concentrations which cause cytotoxicity, cell cycle delay, and lysosomal breakdown. These results all suggest that chemical toxicity leads to limited lysosomal breakdown that induces DNA DSBs and chromosomal aberrations. Cells that have been sublethally damaged and that can repair these damages and survive could become transformed by the DNA-damaging mechanisms associated with carcinogenesis.     

Production of chromosome aberrations, micronuclei, and sister-chromatid exchanges by 24-keV epithermal neutrons in human G0 lymphocytes

The induction of chromosome aberrations, micronuclei and sister-chromatid exchanges in human G0 lymphocytes by 24-keV epithermal neutrons has been measured. Positive linear dose responses were obtained for the 3 end points, with a tendency to saturation at higher dose for SCE production. In all cases, the responses to 24-keV neutrons were characteristic of high-LET radiations.     

Low pH leads to sister-chromatid exchanges and chromosomal aberrations,and its clastogenicity is S-dependent

The effect of low pH on sister-chromatid exchanges (SCE), chromosomal aberrations (CA), and the cell cycle were investigated in Chinese hamster cells. The cells were treated in media over the pH range 7.2–5.4 during 24-h continuous or 3-h pulse treatments. In Chinese hamster ovary K1 cells, slight increases in SCE frequency were induced by 3-h pulse treatment with a 28-h recovery time. In Chinese hamster V79 379A cells, similar slight increases in SCE frequency were observed with both treatments. A severe delay in the cell cycle was noted in both cell types. DNA analysis with flow cytometry indicated that the cell cycle delay occured in S phase. CA were observed in the first metaphase. Multiple fixation times over a 27-h period were used to determine whether or not CA could be induced in cells exposed to low pH medium in more than one part of the cell cycle. Only a few chromatid gaps were induced when the cells were fixed at 0–9 h after the 3-h treatment, most probably representing cells that were treated in their G2 or late S phase. CA were induced in cells fixed between 12 and 27 h after the 3-h treatment. These cells were most probably treated in early S phase, in G1, or in the previous G2/M. These results suggest that low pH clastogenicity is S-dependent.