Search PubMed⌕ Search

Biomedical subjects

C Streffer

Publications and source records attributed to C Streffer.

At least 73 records · Page 4Linked to original sources
PubMed1996

Do DNA double-strand breaks induced by Alu I lead to development of novel aberrations in the second and third post-treatment mitoses?

Several authors have reported that ionizing radiation can give rise to novel aberrations several mitotic divisions after the exposure. At our institute this phenomenon has been observed in mouse preimplantation embryos. This cell system is uniquely well suited for such investigations because the first three cell divisions show a high degree of synchrony. Thus the expression of chromosomal aberrations at the first, second and third mitosis after irradiation can be scored unambiguously. To investigate whether DNA double-strand breaks may be the lesions responsible for the delayed expression of chromosomal aberrations, we have studied the frequencies of aberrations in the first, second and third mitosis after treatment of one-cell mouse embryos with the restriction enzyme Alu I. Embryos were permeabilized with Streptolysin-O. The results indicate that the induction of double-strand breaks does not lead to novel aberrations in the third post-treatment mitosis. Several embryos scored at the second mitosis showed very high numbers of aberrations, indicating that Alu I may remain active in the cells for a period of one cell cycle. After treatment with Streptolysin-O alone, enhanced aberration frequencies were observed in the third post-treatment mitosis, suggesting that membrane damage has a delayed effect on the cellular integrity.

Animals↗
PubMed1996

Malformations after radiation exposure of preimplantation stages.

Our studies have shown that, contrary to the opinion in most textbooks, it is possible to increase the number of malformed fetuses in one of our mouse strains (originally "Heiligenberger Stamm", meanwhile HLG/Zte) by radiation exposure of zygotes or of subsequent preimplantation stages. The malformation affected most pronouncedly is gastroschisis, a defect occurring at a frequency of 1 to 4% in the controls. The observed increase is strain specific (C57Bl mice or (HLGxC57Bl)F1 hybrids do not react in the same way), it is accompanied by an increased frequency of chromosomal aberrations in skin fibroblasts and of modified protein patterns in liver, kidney, and skin cells of day 19 fetuses. The most probable explanation seems to be the assumption that radiation exposure of preimplantation stages increases a defect with a genetic predisposition in a specific way and labelizes the genome of subsequent cell generations making these cells more susceptible for noxes acting on the fetus.

Abdominal Muscles↗
PubMed1996

Analysis of the relationship between radiosensitivity and cell age in proliferating mouse spleen lymphocytes.

The radiosensitivity of the first cell cycle in mouse lymphocytes was compared to that of the later cell cycles by means of analysis of chromatid-type aberrations. A nearly pure population of first-division metaphases (M1) was obtained when lymphocytes were harvested 28 h after stimulation. When the cells were fixed at 52 h of culture time, approximately 90% of the metaphases were composed of M2 and M3 or later cells. After irradiation with X rays 24 or 48 h after stimulation, metaphases were scored from sequential samplings. Generally, no significant differences in aberration frequencies were found between cells irradiated at the two times, indicating that the radiosensitivity of mouse lymphocytes does not vary with their age in culture after stimulation with phytohemagglutinin. Significantly different aberration yields were observed at different sampling times, emphasizing the necessity of sequential samplings when analyzing aberrations in cells irradiated during asynchronous growth.

Animals↗
PubMed1995

Heterogeneity in the fractionation sensitivities of human tumor cell lines: studies in a three-dimensional model system.

PURPOSE: Current concepts to optimize the therapeutic gain of radiotherapy by hyperfractionation assume that human tumors are less sensitive to fractionation than late reacting normal tissues. The aim of this study was to investigate the extent of the intercell line heterogeneity of fractionation sensitivity of a wide variety of human tumor cell lines in a three-dimensional model system under fully oxic conditions using schedules with one to eight fractions. Biological characteristics of the tumors that correlate with fractionation sensitivity should be identified. METHODS AND MATERIALS: A total of 21 cell lines from human tumors maintained as multicellular spheroids consisting of 1000-1500 cells were given fractionated irradiation within a total treatment time of maximally 50 h. Complete dose-spheroid control curves were determined for each fractionation scheme. The spheroid control data were adequately described by the linear quadratic model assuming Poisson statistics. In addition, the induction of a G2 block by a fractionated test dose of seven 3 Gy fractions given at 6-h intervals was determined in spheroid cells using flow cytometry of propidium bromide stained cell nuclei. RESULTS: The fractionation sensitivities of human tumor cells in multicellular spheroids could be characterized by alpha/beta values, ranging from 2.8-37 Gy in dependence on the cell line. The log normally distributed alpha/beta values were positively correlated with the percentage increase in G2/M phase after the fractionated test dose compared to the controls (r = 0.72, p < 0.01), and were associated with the degree of tumor differentiation (p = 0.01, ANOVA F-test). No significant correlation between the log (alpha/beta) values and the surviving fractions at 2 Gy (SF2) or the total doses with 2 Gy per fraction necessary to control 50% of the spheroids (SCD50) was observed. Despite the intercell line variability of the alpha/beta values, the SCD50 values of the different cell lines, given with one and eight fractions or one fraction and 2 Gy per fraction, were closely associated (Spearman rank correlation coefficients: r = 0.89 or r = 0.90, p < 0.0001). CONCLUSION: Human tumor cell lines showed a marked heterogeneity in the fractionation sensitivity when irradiated as multicellular spheroids and assayed in situ using the spheroid control end point. Therefore, the therapeutic gain of altered fractionation also depends on those biological characteristics of each individual tumor that affects its fractionation sensitivity. Parameters that correlate with fractionation sensitivity of the tumor lines in the spheroid system were identified as grade of tumor differentiation and percentage increase in G2/M cells at the end of an eight-fraction schedule.

Humans↗
PubMed1995

Image processing algorithms for the automated micronucleus assay in binucleated human lymphocytes.

The frequency of micronuclei in binucleated lymphocytes (cytochalasin B assay) may serve as a biological dosimeter after radiation exposure. The automation of the micronucleus assay in binucleated human lymphocytes has been considerably advanced in recent years. In our studies for this purpose the detection of binucleated cells (BNCs) and the scoring of micronuclei (MN) was divided into two parts. First, detection of BNCs was feasible with low microscopic magnification (x 100). The positions of classified BNCs were stored. Second, after an automatic change of microscope objective, the stored BNCs were automatically analyzed in sequence at high microscopic magnification (x 630) for occurrence of MN. For both phases of image analysis we used empirical methods based on mathematical morphology. The system is able to recognize nearly 65% of BNCs with false positive decisions of 6% and about 75% of the MN with false positive decisions of 7%.

Algorithms↗
PubMed1995

No indications of an enhanced UV-light-induced unscheduled DNA synthesis in splenocytes of mice following a low-dose irradiation in vivo or in vitro.

One of the open questions regarding the adaptive response to ionizing radiation is whether it can be induced in G0 lymphocytes. In the majority of experiments in which an adaptive response in G0 lymphocytes was observed, the adapting dose was applied in vivo. In order to investigate whether there is some in vivo component of adaptive response, mouse splenocytes of the C57BL/6 strain were irradiated with 0.1 Gy x-rays either in vivo or in vitro, and their UV-light-induced unscheduled DNA synthesis (UDS) levels were determined autoradiographically. An augmented UV-light-induced UDS following an adapting dose applied in vivo has previously been described by several authors in splenocytes of C57BL/6 mice, indicating that the adapting dose enhanced the DNA repair capacity of lymphocytes. In the present investigation, however, no evidence of an adaptive response could be seen regardless of whether the adapting dose was given in vivo or in vitro. Those results present a further indication for the fact that the adaptive response to ionizing radiation is not always inducible, even in lymphocytes of an inbred mouse strain in which its existence has been reported before.

Adaptation, Physiological↗
PubMed1995

Application of a multiple fixation regimen to study the adaptive response to ionizing radiation in lymphocytes of two human donors.

The majority of experiments studying the adaptive response using chromosomal aberrations have been performed with proliferating lymphocytes. It is known that lymphocytes have variable cell cycle transit times and it has been pointed out that in such cases aberration scores obtained from a single harvest are not very meaningful because cells harvested together in metaphase at any one time after irradiation were in different parts of the cell cycle at the time of irradiation. The scored sample will thus always contain a mixture of cells having different radiosensitivities and any variations of cell proliferation will influence the aberration score. In order to get a more representative aberration score a multiple fixation regimen was applied to lymphocytes of two human donors. Cells receiving the adapting + challenging and the challenging dose were fixed at three intervals after the challenge. In lymphocytes of donor 1 no adaptive response was seen at any fixation time in two experiments. In lymphocytes of donor 2, however, a reduction of aberration frequencies was seen, but at different fixation times in the two experiments. In a third experiment, no adaptive response was detected. It is concluded that the response observed at some fixation times in lymphocytes of donor 2 is rather a result of some phenomenon associated with variations of cell cycle kinetics than of induced radiation resistance.

Adaptation, Physiological↗
PubMed1995

Changes in S-phase fraction and micronucleus frequency as prognostic factors in radiotherapy of cervical carcinoma.

Twenty-five patients with cervical carcinoma were treated with combined external beam and high dose rate afterloading radiotherapy. Biopsies obtained at different time points in the course of therapy were analysed with respect to cell proliferation and cytogenetic damage. The fraction of cells with an S-phase DNA-content as well as the frequency of micronuclei were determined. These two parameters were then related to treatment outcome, in particular patient survival. Neither S-phase fraction nor the micronucleus frequency before radiotherapy were predictive of treatment outcome in this small group of patients. However, when changes in response to therapy were considered, patients whose S-phase fraction decreased and patients whose micronucleus frequency increased tended to have a better prognosis. Although statistical significance was not achieved with either criterion alone, when applied together the combination predicted patient survival quite reliably; the 5-year survival rate of those patients who showed a decrease in S-phase fraction as well as an increase in micronucleus frequency was about 90% in contrast to less than 30% for the non-responders (p < 0.03).

Aged↗
PubMed1995

Radiation induced G1-block and p53 status in six human cell lines.

Considerable attention has recently been focused on the fact that the tumor suppressor protein p53 is involved in the cellular response to radiation. In its wild-type form the protein appears to control a cell cycle checkpoint, preventing entry into S-phase following DNA damage. A number of authors observed a radiation induced G1-block in cells expressing wild-type p53, but not in p53 mutant cells. We obtained similar results with four human tumour cell lines as well as two strains of human fibroblasts, whose p53 status was ascertained at the protein as well as DNA levels. In addition to cell cycle delays in exponentially growing cell cultures, we have studied the possible role of the p53 in the transition from quiescence to active proliferation. Cells were irradiated after 6 days of serum-starvation and labelled with BrdU at different times after addition of fresh medium. Entry into S-phase was found to be delayed by several hours in the p53 wild-type cells, but no such effect was observed in the p53 mutants. Where a delay occurred, it was roughly proportional to the X-ray dose. Although it remains to be clarified, whether the cells were delayed only in G1 or also in G0, it is interesting to note that entry into S-phase can be delayed by irradiation in a quiescent state immediately before serum-stimulation, provided the cells are wild-type with respect to p53. Certain differences in the cell cycle response of transformed and untransformed cells were noted.

Antimetabolites↗
PubMed1995

Metabolic imaging in tumours by means of bioluminescence.

A bioluminescence technique involving single photon imaging was used to quantify the spatial distribution of the metabolites ATP, glucose and lactate in cryosections of various solid tumours and normal tissue. Each section was covered with an enzyme cocktail linking the metabolite in question to luciferase with light emission proportional to the metabolite concentration. The photons emitted are imaged directly through a microscope and an imaging photon counting system. In some cases, good agreement was observed between the distribution of relatively high concentrations of ATP and glucose in viable cell regions of the periphery, while the reverse was seen in more necrotic tumour centres with comparatively high lactate levels. In general, lactate was distributed more diffusely over the sections while ATP was more highly localised and glucose assumed an intermediate pattern. In contrast to the large degree of heterogeneity seen in tumours, distribution patterns of metabolites were much more homogeneous in normal tissue, such as heart muscle. Mean values for metabolite levels in cryosections using bioluminescence are in good agreement with those obtained from the same tumour by conventional methods.

Adenocarcinoma↗
PubMed1995

Protein alterations in the skin of the mouse with radiation-induced gastroschisis.

We have used two-dimensional gel electrophoresis to analyse proteins in the skin of mouse foetuses with and without gastroschisis after X-irradiation of embryos during the one-cell stage. An increased phosphorylation of two proteins and a shift in one glycoprotein were observed in the skin of irradiated foetuses with gastroschisis compared with the unirradiated normal controls. These protein changes are specifically associated with this malformation. We discuss the results in terms of mutations related to the irradiation of the one-cell embryo.

Abdominal Muscles↗
PubMed1995

Evidence for quiescent S- and G2-phase cells in human colorectal carcinomas: a flow cytometric study with the Ki-67 antibody.

The expression of certain antigens specific for proliferating cells can be determined simultaneously with cell cycle distribution by means of two-dimensional flow cytometry. In this way, a tumour's growth potential is characterized more precisely than with any one parameter alone. Here we describe such simultaneous measurements of DNA content and labelling with the Ki-67 antibody that distinguishes between cycling and non-cycling cells. Having overcome a number of technical problems we were able to analyse material from 29 biopsies of human colorectal tumours. In a number of cases, Ki-67 negative cells were found with a DNA-content of G0/1 only, whereas all cells with an S- or G2-phase DNA-content were Ki-67 positive. There were other cases in which cells with an S- and G2-phase DNA-content had obviously become quiescent (Ki-67 negative), sometimes even outnumbering the proliferating (Ki- 67 positive) cells in the respective compartments of the cycle. Generally, however, when Ki-67 negative and positive subpopulations were analysed separately it was found that the former had a significantly lower (S + G2)-phase fraction than the latter. There was evidence for a correlation between Ki-67 index and (S + G2)-phase fraction at least in the subgroup of aneuploid tumours. Neither of the two parameters was correlated with stage according to Duke's classification or tumour size. However, a positive correlation was found between the fraction of unlabelled S- and G2-phase cells and tumour size as reflected in the T category.

Adult↗
PubMed1995

Micronucleus determination as a means to assess radiation exposure.

Radiation accidents require an easy to perform and rapid determination of the radiation response of the victim(s) affected by the exposure. Micronuclei in cytochalasin B blocked lymphocytes are able to serve this purpose. Micronuclei are particularly useful when it comes to screening many exposed people after a more or less homogeneous whole body exposure with a high dose rate. There are problems, as is the case for most biological indicators, with partial body (especially when it is due to internal emitters), chronic and fractionated exposure.

Dose-Response Relationship, Radiation↗
PubMed1995

Cell cycle-dependent expression of Ki-67 antigen in human melanoma cells subjected to irradiation and/or hyperthermia.

The proliferation of human melanoma cells in vitro during the first 3 days after irradiation and/or hyperthermia was followed by two-parameter flow cytometry combining cell cycle analysis on the basis of DNA content with Ki-67 antibody labeling. It was found that cells arrested or delayed in the S and G2 phases of the cell cycle were Ki-67-positive in spite of the antigen's very short half-life. Thus Ki-67 staining failed to reflect those changes in cell proliferation which typically occur in the course of a fractionated radiotherapy as well as those expected in the case of hyperthermia or a combined treatment.

Cell Cycle↗
PubMed1995

[Radiation effects of exposure during prenatal development].

The embryo and fetus are very radiosensitive during the total prenatal development period. The quality and extent of radiation effects depend strongly on the developmental stage at which the exposure occurs. During the preimplantation period radiation exposure can cause death of the embryo after radiation doses of 0.2 Gy and higher. Malformations are only observed in very rare cases when genetic predispositions exist. Macroscopic-anatomical malformations are induced only after irradiation during the major organogenesis. On the basis of experimental data with mammals it is assumed that a radiation dose of about 0.2 Gy doubles the malformation risk. Studies in humans give rise to the assumption that the human embryo is more radioresistant than the embryos of mice and rats. Radiation exposure during the major organogenesis and the early fetal period lead to disturbances in the growth and developmental processes. During early fetogenesis (week 8-15 post corruption) high radiosensitivity exists for the development of the central nervous system. Radiation doses of 1 Gy cause severe mental retardation in about 50% of exposed fetuses. Analysis of the dose-effect curves shows that there is probably a dose-effect curve with a threshold for this effect. It must be taken into account that radiation exposure during the fetal period also induces cancer. The studies, however, do not allow quantitative estimate of this radiation risk at present. It is therefore generally assumed that the risk is about the same level as for children.

Abnormalities, Radiation-Induced↗
PubMed1994

Protein patterns in tissues of fetuses with radiation-induced gastroschisis.

We have used two-dimensional gel electrophoresis coupled with computer-assisted data analysis to monitor protein expression in the liver of mouse fetuses with and without gastroschisis after X-irradiation of embryos during the 1-cell stage. A significantly higher frequency of changes in protein expression was observed in liver from irradiated fetuses with gastroschisis than from irradiated fetuses without gastroschisis. It was found that the frequency of abnormal protein patterns in the malformed fetuses is higher by approximately a factor of 2. Two proteins showed changes simultaneously in liver, kidney and/or skin of one individual fetus. The changes in protein expression probably result from mutations induced by the radiation exposure of the embryos at the 1-cell stage of prenatal development. We discuss these results in terms of increased mutation frequencies in irradiated fetuses with gastroschisis.

Abdomen↗
PubMed1994

Metabolic studies and neurotoxicity in tumors and brain of mice after hypoxic cell sensitizers.

PURPOSE: The effects of the radiosensitizers RK-28 and RP-170, both 2-nitroimidazole nucleoside analogues, and KU-2285, a fluorinated 2-nitroimidazole, as well as etanidazole (ETA) on glucose metabolism in mouse tumors and brain were studied to assess their degree of neurotoxicity. METHODS AND MATERIALS: Adult male C57Bl mice received differing doses of the above sensitizers IP. Blood, brain, and tumor samples were removed at various times and the levels of glycolytic metabolites determined. Glucose uptake and phosphorylation in brain was measured by the 2-deoxyglucose method of Sokoloff et al. (6). RESULTS: RP-170 showed neither signs of toxicity nor significant alterations in glucose metabolism in brain or tumor at doses up to 4 g/kg b.w. up to 4 h. By contrast, RK-28 was extremely neurotoxic at a dose of 1 g/kg b.w. with a high degree of lethality, resulting in a highly significant increase in the brain glucose level from 0.38 mumol/g to 2.20 mumol/g (p < 0.001) 2 h after administration, whereas that in the tumor was decreased. KU-2285 and ETA were significantly (p < 0.01) less toxic than RK-28 at this dose, as reflected in a lower increase in the brain glucose level (0.60 mumol/g), although KU-2285 approached that of RK-28 (1.43 mumol/g; p < 0.01) after 2 h following a dose of 2 g/kg b.w. However, in contrast to the other sensitizers, KU-2285 concomitantly also resulted in a highly significant continuous increase (p < 0.01) in tumor glucose levels. Labeled 3H-2-deoxyglucose studies showed that RP-170 neither markedly affected the uptake of total radioactivity into the brain nor its degree of phosphorylation whereas, KU-2285 (2 g/kg) and RK-28 (1 g/kg) decreased uptake by approximately 50% and phosphorylation approximately 3 and 4-fold, respectively. At doses of 1 g/kg, ETA and KU-2285 showed no significant changes in these parameters. This indicates a decreased level of neurotoxicity. CONCLUSION: Since the adult brain relies solely on glucose metabolism for its energy supply, interference to this pathway may be instrumental in the development of neurotoxicity, thus, underlining the need for such metabolic studies to assess the level of toxicity by radiosensitizers.

Adenosine Triphosphate↗