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Biomedical subjects

G Obe

Publications and source records attributed to G Obe.

At least 73 records · Page 4Linked to original sources
PubMed1994

Induction of chromosomal aberrations with benzon nuclease in Chinese hamster ovary (CHO) cells.

Benzon nuclease, an endonuclease originating from Serratia marcescens, was tested for its chromosome breaking activity in Chinese hamster ovary cells. Using a permeabilizing method with hypertonic glycerol, benzon nuclease induced chromosomal aberrations in an S-phase independent manner. The frequencies of polycentric chromosomes were correlated with the dose of the enzyme and the intercellular distribution of aberrations was overdispersed.

Animals↗
PubMed1993

Dosimetry in the space radiation field.

The results of dosimetric measurements are presented which were performed as part of a German experiment package flown onboard the Russian space station MIR. These results are compared to those of previous missions: the first United States Spacelab mission and the first German Spacelab mission. Detector packages consisting of plastic nuclear track detectors, nuclear emulsions, and thermoluminescence dosimeters were exposed in different sections of the Russian space station. The equivalent dose for the astronauts was calculated from the measurements to be 3.9 mSv. Before and after the flight venous blood was taken from the astronauts. Chromosomal aberrations in peripheral lymphocytes were analyzed. It was found that the radiation exposure during the spaceflight leads to an elevation of dicentric chromosomes, indicating a radiation burden of the astronauts.

Body Burden↗
PubMed1993

Scrape-loading: a simple method to induce chromosomal aberrations with restriction enzymes in CHO cells.

The restriction endonucleases AluI and EcoRI induce chromosomal aberrations in Chinese hamster ovary (CHO) cells when applied via scrape-loading. The frequencies of chromosomal aberrations induced by AluI are similar to the ones induced when the enzyme is applied by other methods to introduce it into cells (electroporation, glycerol, sorbitol). EcoRI produces lower frequencies of aberrations when applied via scrape-loading, as compared to the application in the presence of high concentrations of glycerol, which may reflect relaxed activities under the latter conditions.

Animals↗
PubMed1993

Chromatid-type aberrations induced by AluI in Chinese hamster ovary cells.

Treatment of CHO cells with AluI in the S-phase leads to chromatid-type aberrations whose frequencies are linearly correlated with dose. Treatment in the S-phase leads to fewer aberrations than treatment in the G1-phase, which is comparable to chromosomal aberration induction following X-irradiation in the G1- and S-phases. Treatment in the G1-phase leads to few chromatid-type interchanges, some of these may originate from DNA single-strand gaps induced by AluI in canonical structures of DNA and in DNA.RNA hybrids.

Animals↗
PubMed1993

Exposure of rats to a 50-Hz, 30-mT magnetic field influences neither the frequencies of sister-chromatid exchanges nor proliferation characteristics of cultured peripheral lymphocytes.

The issue of potential carcinogenic effects of extremely low-frequency (50/60-Hz) electric and magnetic fields (EMF) has developed almost completely from epidemiological studies suggesting a link between residential or occupational exposure to EMF and an elevated risk of various cancers. Concerning chromosome-altering effects of EMF, in vitro studies gave ambiguous results and only few in vivo studies have been done. In the present study, we investigated the effect of long-term exposure of rats to a 50-Hz, 30-mT magnetic field (MF) on cell proliferation and frequencies of sister-chromatid exchanges (SCE) in peripheral lymphocytes of rats following exposure to MF for 7 or 28 days. As a positive control, rats were treated with cyclophosphamide. In contrast to cyclophosphamide, MF exposure influenced neither SCE frequencies nor proliferation characteristics of cultured peripheral lymphocytes.

Animals↗
PubMed1992

Structure-activity relationships of epoxides: induction of sister-chromatid exchanges in V79 cells by enantiomeric epoxides.

Analysis of SCE frequencies in Chinese hamster V79 cells was used to investigate the influence of the stereoisomeric forms of epoxides in mammalian genotoxicity tests. The SCE-inducing potency of 12 pairs of (R)- and (S)-enantiomeric epoxides which differed in the degree of substitution of the oxirane ring was determined. Of these, 2 pairs of epoxides failed to induce SCE. Different SCE-inducing potencies between the (R)- and (S)-enantiomers were shown for 5 epoxides. This study demonstrates that stereoselectivity might play an important role in genotoxicity testing of chemicals with asymmetric C atoms.

Alkylation↗
PubMed1992

Chromosomal aberrations in human lymphocytes induced in vitro by very low doses of X-rays.

This paper presents results of a collaborative experiment between six laboratories which examined the yields of unstable chromosomal aberrations in human lymphocytes induced in vitro by X-rays over the dose range 0-300 mGy. The work included data points of nominal doses of 0, 3, 5, 6, 10, 20, 30, 50 and 300 mGy. Cells from 24 donors were examined and a total of about 300,000 metaphases were scored. The work was undertaken to determine the limits of sensitivity of the system taking into account variations in scoring data due to inter-donor sample and inter-laboratory effects. Despite the existence of these effects, aberration yields significantly in excess of control values were seen at doses greater than 20 mGy and these were consistent with a linear extrapolation from higher doses. Below 20 mGy the observed dicentric yields were generally lower than background, but not significantly so. Excess acentric aberrations, on the other hand, and centric rings, were higher than the controls but the increase was usually not significant. It is concluded that the statistical uncertainties are such that below 20 mGy this technique cannot distinguish between a linear or a threshold model.

Chromosome Aberrations↗
PubMed1992

Absence of adaptive response to low doses of X-rays in preimplantation embryos and spleen lymphocytes of an inbred mouse strain as compared to human peripheral lymphocytes: a cytogenetic study.

The adaptive response was studied in preimplantation embryos and spleen lymphocytes of a mouse inbred strain and in peripheral lymphocytes of three human donors, using chromosomal aberrations as the endpoint. Embryos were adapted to 0.05 Gy X-ray 50 h post-conception either in vitro or in vivo and challenged 6 h later. Chromosome aberrations of the 8----16 cell stage mitoses were scored. No adaptive response was seen in the embryos. Of 14 female mice studied, an adaptive response was seen in spleen lymphocytes of only one mouse. However, because variable chromosomal aberration levels were observed in lymphocytes of different donors, it is concluded that the adaptive response detected was merely a result of this heterogeneity. In human peripheral lymphocytes an adaptive response was seen in all three donors. It is speculated that the inbred mouse strain used is deficient in the adaptive response.

Adaptation, Physiological↗
PubMed1992

Modification of bleomycin-induced chromosome aberrations by hyperthermia and under energy depleting conditions in human peripheral lymphocytes.

Synergistic effects of bleomycin (BLM) and hyperthermia were studied in human peripheral lymphocytes (HPL). The frequencies of breaks produced by BLM were dependent on dose, incubation temperature, and treatment time. Heat alone did not induce chromosome aberrations. Synergistic effects of heat and BLM occurred at 43 degrees C, either when hyperthermia was for 60 min following treatment with BLM or when hyperthermia was for 30 min simultaneously with BLM treatment. At incubation temperatures below 43 degrees C as many dicentric chromosomes as chromosome breaks were found, but about twice as many dicentric chromosomes as chromosome breaks were found when cells were treated with BLM at 43 degrees C for 60 min. In all experiments with BLM chromosomal anomalies were overdispersed. Comparison with unstimulated HPL, heated after X-irradiation, suggested that heat inhibits repair of BLM-induced lesions to a smaller extent than X-ray-induced lesions. Experiments with sodium azide and 2-deoxyglucose led to the conclusion that cellular uptake of BLM is partly energy-dependent. Additionally, an energy-independent uptake of BLM, which could not be blocked by inhibitors, was apparent.

Azides↗
PubMed1992

Uptake of the restriction endonuclease AluI by Chinese hamster ovary cells measured by frequencies of induced chromosomal aberrations: effect of hypertonic concentrations of glycerol and sorbitol.

Chinese hamster ovary cells were exposed to the restriction endonuclease AluI in the presence of 2.2 M glycerol or 0.9 M sorbitol using different treatment regimens. Induced chromosomal aberrations were taken as indication for cellular uptake of AluI. The results indicate that cellular uptake of AluI is mediated by vesicles formed during transition of hypertonic to isotonic conditions. Addition of medium leads to breakdown of these vesicles and to liberation of AluI molecules which eventually may reach the chromatin.

Animals↗
PubMed1992

The restriction endonuclease AluI induces sister chromatid exchange in Chinese hamster ovary cells.

Chinese hamster ovary (CHO) cells were exposed to the restriction endonuclease AluI in the presence of 1.1 M glycerol. Chromosomal aberrations and sister chromatid exchange (SCE) were scored in first post-treatment metaphases following recovery times of 6-18 h. At all recovery times chromosomal aberrations were induced by the enzyme. In AluI-treated damaged cells significant elevations of SCE frequencies were found after recovery times of 12-18 h. These results indicate that SCE, unlike chromosomal aberrations, are induced only in late G1 and early S phase of the cell cycle. The lesions producing SCE are postulated as DNA single-strand breaks and gaps induced by AluI in canonical structures of DNA and in DNA-RNA hybrids.

Animals↗
PubMed1992

Role of lime in the generation of reactive oxygen species from betel-quid ingredients.

The role of lime in the formation of reactive oxygen species (ROS), i.e., O2-., H2O2, and OH., from betel-quid components (extracts of areca nut and catechu) was investigated in vitro using a chemiluminescence technique and an assay for oxidative DNA damage involving analysis of 8-hydroxy-2'-deoxyguanosine. Of the various areca-nut extracts, the catechin fraction, at alkaline pH, was shown to be the most active producer of ROS. The free Ca(OH)2 content and pH of lime samples (a component of betel quid and chewing tobacco) were highly correlated with the generation of ROS from areca-nut extract in vitro and with oxidative base damage to DNA in vitro. While Fe2+ had an enhancing effect on ROS formation, Mg2+ had a marked inhibitory effect. The cytogenetic effects of ROS generated in vivo were measured in Syrian golden hamsters in which the cheek pouch had been painted with lime and an areca-nut extract or catechu, singly or in combination. The frequency of micronucleated cells was increased only in animals that had received both the areca-nut extract and lime. The frequency of micronucleated cells in exfoliated oral mucosal cells from Indian chewers of betel quid with tobacco containing lime or of tobacco with lime was significantly higher than in a control (no habit) group. These studies demonstrate that addition of lime to betel quid constituents generates ROS, which induce cytogenetic damage in hamster cheek pouch and may contribute to the cytogenetic damage observed in the oral cavity of betel-quid chewers. These results implicate ROS in clastogenesis and probably in the etiology of oral cancer.

Animals↗
PubMed1991

Structure-activity relationships of epoxides: induction of sister-chromatid exchanges in Chinese hamster V79 cells.

Analysis of SCE frequencies in Chinese hamster V79 cells was used to investigate structure-activity relationships of epoxides in mammalian cells. For this purpose the SCE-inducing potency of 58 epoxides was determined. Of these, 16 failed to induce SCE in V79 cells. According to the substitution of the oxirane ring the results show general agreement with results obtained in the Ames test. Mono-substituted epoxides had the highest genotoxic potency compared to di- and tri-substituted epoxides. In detail, there are differences in genotoxic potency between bacteria and mammalian cells which can be explained by differences in the cellular uptake of the compounds and by detoxification reactions.

Animals↗
PubMed1991

Evaluation of frequency of micronucleated oral mucosa cells as a marker for genotoxic damage in chewers of betel quid with or without tobacco.

The frequency of micronucleated cells (MNC) derived from exfoliated human oral mucosal cells has been measured to assess genotoxic damage in chewers of betel quid with tobacco (BQT) and tobacco with lime (T). Significantly elevated frequencies of MNC were observed in the exposed groups (BQT = 4.83 +/- 0.70; T = 5.20 +/- 0.66 per 1000 cells) compared to the control group (C = 2.59 +/- 0.37) although the levels observed were lower than those reported in the literature. No correlation was seen between age, duration and frequency of habits and the frequency of MNC in the 2 habit groups. Clastogenic agents in betel quid possibly involved in micronucleus formation are discussed.

Age Factors↗
PubMed1991

The effect on lymphocyte chromosomes of additional radiation burden due to fallout in Salzburg (Austria) from the Chernobyl accident.

An investigation has been carried out to determine whether chromosome aberrations in peripheral blood lymphocytes reflect the elevated environmental dose of low-LET ionising radiation, mainly due to radiocesium from Chernobyl fallout, to the population living in Salzburg city. Sixteen volunteers were sampled 1 year after the Chernobyl accident. Two of these persons were also sampled before the accident, and then in 1988 and 1990. The radioactive environment of Salzburg city and the radiation burden of its inhabitants have been frequently determined before and after the accident. The Cs-137 content of the volunteers was measured by whole-body counting. The additional external plus internal radiation doses in the year 1987 to the tested individuals ranged between 15 and 68% of the former normal environmental burden. The aberration frequencies showed a sharp increase of about a factor 6 from the pre-Chernobyl dose rate (0.9. mGy/year) to the post-Chernobyl dose rate (about 2 mGy/year total) but then decreased again with higher additional dose. In the two persons analysed before and up to 4 years after the accident the aberration yield showed a significant increase from 1984/85 to 1987, a decrease in 1988 and a further decrease in 1990. If these last 2 values are plotted against additional dose they fit the curve of the pooled 1987 values. The dose-effect curves revealed the same tendency as we found in various previous investigations and support the assumption that repair enzymes could be triggered by a certain amount of damage to the DNA.

Adult↗
PubMed1991

Embryologic and cytogenetic effects of ethanol on preimplantation mouse embryos in vitro.

Ethanol and its primary metabolite acetaldehyde were studied in cultured preimplantation mouse embryos with respect to embryotoxicity, embryolethality, chromosome breaking activities, and ability to induce sister chromatid exchange (SCE). Analysis of differentiation and cell number of mouse morulae and blastocysts show that acetaldehyde is three orders of magnitude more toxic than ethanol, indicating that the metabolite is responsible for the embryotoxicity of ethanol in preimplantation embryos. Concentrations of ethanol that do not inhibit growth induce SCEs and chromosome aberrations. The SCE-inducing effect of ethanol disappears in the presence of 4-methylpyrazole (4-MP), an inhibitor of alcohol dehydrogenase (ADH). These data suggest that preimplantation embryos are able to convert ethanol to acetaldehyde and that ADH is the enzyme involved. It is, furthermore, shown histochemically that mouse oocytes as well as morulae and blastocysts are able to oxidize ethanol in the presence of NAD+.

Alcohol Dehydrogenase↗
PubMed1991

Modification of X-ray induced chromosome aberration frequency by pre- and postirradiation hyperthermia of human peripheral lymphocytes.

Human peripheral lymphocytes (HPL) were used to study the synergistic effects of hyperthermia and X-irradiation. The effects on the chromosome aberration frequencies of different combinations of heat and radiation exposure at different cell cycle phases were analysed at the first mitosis after irradiation. When unstimulated HPL were heated after irradiation with 2 and 3 Gy, respectively, the chromosomal aberration frequencies were significantly higher than following radiation exposure alone. Heat treatment during different phases of the cell cycle and irradiation during the G2 phase led to an increase in the aberration frequencies when the cells were heat-treated not later than 16 h before radiation. Furthermore we show that the number of breaks increased linearly with the duration of hyperthermia when HPL were heated for periods of 1-15 min at 45 degrees C 32 h before irradiation at 48 h after stimulation. Heat treatment alone during any phase of the cell cycle did not induce chromosome aberrations. The increased aberration frequencies are probably the result of inhibited repair of radiation-induced DNA strand breaks.

Cell Cycle↗