In vitro testing of an indirect mutagen (cyclophosphamide) with human leukocyte cultures. Activation by a non-enzymatic hydroxylation system (Udenfriend system).
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Ascorbic Acid↗
Biomedical subjects
G Obe
Publications and source records attributed to G Obe.
Molecular mechanisms involved in the production of chromosomal aberrations. I. Utilization of Neurospora endonuclease for the study of aberration production in G2 stage of the cell cycle.
Chinese hamster ovary cells (CHO) were X-irradiated in G2 stage of the cell cycle and immediately treated, in the presence of inactivated Sendai virus, with Neurospora endonuclease (E.C. 3.1.4.), an enzyme which is specific for cleaving single-stranded DNA. With this treatment, the frequencies of all types of chromosome aberrations increased when compared to X-irradiated controls. These results are interpreted as due to the conversion of some of the X-ray induced single-stranded DNA breaks into double-strand breaks by this enzyme. Similar enhancement due to this enzyme was found following treatment with methyl methanesulfonate (MMS) and bleomycin, but not following UV and mitomycin C. Addition of Micrococcus endonuclease and Neurospora endonuclease to the cells did not alter the frequencies of aberrations induced by UV. The introduction of enzymes with specific DNA-repair function offers possibilities to probe into the molecular events involved in the formation of structural chromosome aberrations induced by different classes of physical and chemical mutagens.
Bleomycin↗
Testing in vitro of an indirect mutagen (cyclophosphamide) with human leukocyte cultures: Activation by liver perfusion and by incubation with crude liver homogenate.
The indirect mutagen cyclophosphamide was tested in human whole blood cultures with respect to chromosome-breaking activities and suppression of mitotic indices after activation by liver perfusion and crude liver homogenates with and without cofactors. Both methods produced nearly the same effects, with the exception of liver homogenate without cofactors which had only weak metabolic activities.
Animals↗
Acetaldehyde induces cross-links in DNA and causes sister-chromatid exchanges in human cells.
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Acetaldehyde↗
Differential chromosomal radiosensitivity within the first G1-phase of the cell cycle of early-dividing human leukocytes in vitro after stimulation with PHA.
Human leukocyte cultures were irradiated with 200 RX-rays before the addition of phytohemagglutinin (PHA) in the Go-stage and at different times up to 25 h within the first G1-phase of the cell cyle after the addition of PHA. The results of the analysis of chromosomal aberrations show that the frequencies of dicentric chromosomes increase significantly when leukocytes leave the Go-stage, reaching a miximum yield of aberrations about halfway through the first G1-phase. After that, toward the end of the G1-phase, the frequencies of dicentric chromosomes decrease again to a level similar to that found in the Go-stage. Different possible explanations for the differential chromosomal radiosensitivity of human leukocytes within the first post-stimulation G1-phase are discussed.
Chromosome Aberrations↗
Chromosomal damage by alcohol in vitro and in vivo.
Alcohol has no damaging effects on human chromosomes in vitro. The chromosomes of alcoholics, however, show a significant elevation of aberrations. Alcohol inhibits cellular and cell free RNA synthesis. One possible reason for the mutagenic activity of alcohol in vivo may be an inhibition of cellular repair.
Adult↗
Suppressive activity by fluoride on the induction of dominant lethals with trenimon in spermatozoa of Phryne cincta (Nematocera, Diptera).
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Animals↗
In vitro testing of an indirect mutagen (cyclophosphamide) with human leukocyte cultures: activation with liver microsomes and use of a dialysis bag.
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Cells, Cultured↗
The human leukocyte test system. X. higher sensitivity to X-irradiation in the G0 stage of the cell cycle of early as compared to late replicating cells.
Leukocyte cultures were set up with X-irradiated whole blood (200 R). Cells starting with their DNA synthesis between 25 and 35 h after cultureinitiation ("early replicating cells") were pulse-labeled with tritiated thymidine ([3H]TdR). Mitoses were collected with colcemid in adjacent intervals from 36 up to 72 h after culture initiation. At fixation times of 50, 56, 62, and 72 h enough mitoses for a determination of the frequencies of chromosomal aberrations (dicentric and ring chromosomes) were found. After that the preparations were processed for autoradiography. All mitoses analyzed for chromosomal aberrations were re-analyzed for labeling, and the frequencies of chromosomal aberrations in labeled (="late replicating cells") mitoses were compared. At all fixation times, higher frequencies of dicentric chromosomes were found in labeled as compared to unlabeled mitoses, indicating a higher sensitivity of early replicating cells to X-irradiation in the G0 stage of the cell cycle.
Chromosome Aberrations↗
Chromosomal damage in epileptics on monotherapy with carbamazepine and diphenylhydantoin.
We analyzed the leukocyte chromosomes of 10 epileptic probands on monotherapy with carbamazepine (CP), of 14 epileptic probands on monotherapy with diphenylhydantoin (DPH) and of 20 clinically normal probands (controls, CO). In the CP and in the DPH group we found a significant elevation of exchange-type aberrations as compared to the CO group. In the CP group we found predominantly chromatid translocations, in the DPH group exclusively dicentric chromosomes.
Adolescent↗
Effects of inhibitors of DNA, RNA and protein synthesis on frequencies and types of premature chromosome condensation from X-ray induced micronuclei.
Cells containing X-ray induced micronuclei were treated for a few hours before fixation with inhibitors of DNA synthesis (cytosine arabinoside; azathioprine; thymidine; trenimon), of RNA synthesis (actinomycin D; ethidium bromide), and of protein synthesis (puromycin). Only the inhibitors of DNA synthesis lead to a significant suppression of the frequencies of mitoses with micronucleus derived premature chromosome condensation (PCC). We tend to interprete the result as follows: Micronuclei that are in the G1 phase of their cell cycles are accumulated at the G1/S border or in the early S phase of their cell cycles under the influence of the inhibitors of the DNA synthesis. Micronuclei blocked in this way cannot be induced to undergo PCC and seem to disappear from the cells.
Azathioprine↗
The human leukocyte test system. IX. DNA synthesis and mitoses in PHA-stimulated 2-day cultures set up with Eagle's mimimal essential medium (MEM).
In human leukocyte cultures set up with Eagle's MEM and stimulated with Difco's PHA M, DNA synthesis and mitotic indices were analyzed by means of 3(H)-thymidine autoradiography and cell counting from 23 up to 52 h after culture initiation. Considerable amounts of DNA synthesis and mitoses were found in this time span. This resembles the results found with Ham's F-10 medium. However, the DNA synthesis pattern and the distribution of mitotic indices a higher yield of asynchrony in Eagle's MEM as compared with Ham's F-10 cultures. Proportions of first, second, and third mitoses at 72 h culture time were determined with different methods.
Culture Media↗
The human leukocyte test system. VIII. DNA synthesis and mitoses in 3-day cultures stimulated with pokeweed mitogen.
In human leukocyte cultures set up with Ham's F-10 medium and stimulated with pokeweed mitogen (PWM), DNA synthesis and mitotic indices were analyzed by means of (3H)TdR autoradiography and cell counting. The results show a very similar pattern of DNA synthesis and mitotic indices to that found in cultures set up with TC medium 199 and stimulated with phytohemagglutinin (Obe et al., 1975 a).
Chromosome Aberrations↗
Cytogenetic investigations in a new case of Bloom's syndrome.
Cytogenetic studies of an 8-year-old caucasian girl with typical but mild manifestation of Bloom's syndrome showed a characteristic increase of homologous chromatid translocations and prematurely condensed chromosomes. The average frequency of sister chromatid exchanges (SCE) in lymphocytes with 133 was much higher than in skin fibroblasts with 49. The inter- and intrachromosomal distributions of SCE in lymphocytes were analyzed.
Abnormalities, Multiple↗
The effect of sodium fluoride on DNA synthesis, mitotic indices and chromosomal aberrations in human leukocytes treated with trenimon in vitro.
Human leukocyte cultures were set up with Ham's F-10 medium and stimulated with PHA-M. Treatment of the cells in G1 from 15-20 h with 0.5 X 10(-6) M Trenimon resulted in a considerable cell cycle delay, as measured by [3H]-TdR autoradiography and determination of mitotic indices. Under these conditions only few cells incorporated the tracer at the same time as most cells did in untreated cultures. However, this did not lead to a mitotic activity at the same time as obtained in controls. Most of the treated cells started their DNA synthesis and mitotic activities with a delay of around 20 h, as compared with the controls. Continuous treatment of the cells with 10(-3) M NaF had no effect on [3H]TdR labelling or mitotic indices in otherwise untreated cultures, but led to an impressive effect on DNA synthesis in Trenimon-treated cultures, without a considerable effect on the mitotic indices. This finding could be explained as due to a lower alkylation in cellular DNA in the presence of NaF. More cells can start with their DNA synthesis, although they are, like Trenimon-treated cultures, incapable of completing it normally. Analysis of the effect of NaF on chromosome aberrations induced by Trenimon revealed that pre-, simultaneous and post-treatments significantly enhanced the frequency of undamaged mitoses. Continuous fluoride treatment also protected the cells from Trenimon-induced damage, but the effect was not significant, possibly because of heavily damaged mitoses which appeared under these conditions. We interpret our findings as an indication of a real anti-mutagenic activity of NaF.
Chromosome Aberrations↗
Analysis of intercellular distributions of chromatid aberrations.
59 intercellular distributions of chemically induced and spontaneous chromatid aberrations were analyzed for goodness of fit in respect of the Poisson (PD), the geometrical (GD), and the negative binomial distributions (NBD). The data are excellently described by the NBD. This distribution can be deduced from a model out of the queueing theory and is based on the hypothesis of restitution. Estimators are obtained for the ratio of restitution and induction processes involved in the origin of chromosomal aberrations.
Alkylating Agents↗
The human leulocyte test system. VII. Further investigations concerning micronucleus-derived premature chromosome condensation.
Premature chromosome condensation (PCC) from X-ray induced micronuclei shows a dose-effect relationship in human leukocytes in vitro. Preparations at different culture times without colcemide treatment reveal complex variations of the frequencies of micronuclei and PCC correlated with the fixation time. The positions of PCC patches in the metaphase plate and the frequencies of different PCC types (S and G2) ar independent on the X-ray dose. The latter indicates that the slowing down of the micronuclei in the cell cycle, which is the reason for the formation of PCC, may be an outcome rather of a regulatory phenomenon than of an unspecific physiological damage of the chromatin included in the micronuclei. This is especially evident from labeling experiments with tritiated thymidine, showing that the extent of asynchrony between main nuclei and micronuclei is independent on the X-ray dose. Labeling experiments with tritiated uridine reveal a X-ray dose dependent suppression of RNA synthesis in cells with main nuclei and micronuclei. THE S-phase nature of "pulverized" PCC patches could be verified by incorporation of tritiated thymidine in aound 50%. Staining of centromeric heterochromatin in micronuclei reveal a frequency of micronuclei with centromeric heterochromatin resembling the frequency of G2-phase PCC found in mitoses.
Cell Nucleus↗
Chromosomal damage in chronic alcohol users.
First in vitro mitoses were analysed from the peripheral leukocytes of 22 chronic alcohol users and of 18 controls. The frequency of exchange aberrations of the chromatid and chromosome type were significantly higher in the alcohol as compared with the control group. The results indicate an indirect or direct mutagenic activity of alcohol in vivo.
Adult↗