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Biomedical subjects

C Streffer

Publications and source records attributed to C Streffer.

At least 55 records · Page 3Linked to original sources
PubMed1997

A fast autofocus unit for fluorescence microscopy.

In this paper a fast autofocus unit is introduced for fluorescence microscopy based on image content information. The module, an electronic board with several differentiators and integrators, is designed for high-speed autofocusing and is directly coupled to the output of the video camera. A Leitz MPV II fluorescence microscope with x, y, z stepping motors was used as basic equipment. The microscope images were focused by using an intensified target camera with a following analogue-digital converter and a PC. Thus one obtains a focus value for the current image within one video cycle. Furthermore, it is possible to process three different focus functions (weighted intensity, first derivative and second derivative) simultaneously. The flexibility to select a certain focus function or a combination of these functions allows the use of the analogue detector for various cell types and fluorescent dyes. In order to test the experimental set-up we use three different kinds of biological specimen (lymphocytes, fibroblasts and comet cells) which are distinguished by large differences in their morphological structure. Successful focusing is carried out in more than 95% of cases (investigation of several hundred different cells). The focusing procedure is almost finished after 1-2 s.

Algorithms↗
PubMed1997

Detection of chromosome 2 and chromosome 7 within X-ray- or colchicine-induced micronuclei by fluorescence in situ hybridization.

The occurrence of chromosome 2 and chromosome 7 within micronuclei of binucleated lymphocytes induced by X-rays or colchicine was scored using the whole chromosome painting technique. The observed frequency of involvement in micronucleus formation was compared with the yield that would be expected theoretically, when the random participation of each chromosome is assumed. No difference was observed between the expected and observed inclusion of chromosome 2 or chromosome 7 into micronuclei after X-ray exposure (2.5 Gy). This was also the case for chromosome 2, but not for chromosome 7 after colchicine treatment (0.04/0.06 microgram/ml); chromosome 7 was detected approximately 1.5 times more frequently in micronucleus formation than would be expected from the assumption of a random distribution.

Aneuploidy↗
PubMed1997

Correlation of radiation-induced micronucleus frequency with clonogenic survival in cells of one diploid and two tetraploid murine tumor cell lines of the same origin.

Whether the micronucleus assay can be used as a predictive tool to estimate the intrinsic cellular radiosensitivity depends on whether the results correlate with clonogenic survival. In the present study we investigated the influence of the ploidy on the correlation of the two assays by comparing cells of one diploid and two tetraploid murine tumor cell lines of different radiosensitivities. A definite correlation between survival and micronucleus frequency is evident for all three cell lines investigated. The rank order of the frequency of micronucleus expression correlates with that of clonogenic survival in the cell lines studied. No influence of DNA content on the radiosensitivity and the relationship between the micronucleus frequency and clonogenic survival could be observed. Thus our results are promising for the clinical application of the micronucleus assay as a predictive measure of radiosensitivity. However, it is necessary to consider such factors such as cell proliferation kinetics which may influence the correlation between micronucleus frequency and clonogenic survival.

Animals↗
PubMed1997

Health impacts of large releases of radionuclides. Biological effects of prenatal irradiation.

After large releases of radionuclides, exposure of the embryo or fetus can take place by external irradiation or uptake of radionuclides. The embryo and fetus are radiosensitive throughout prenatal development. The quality and extent of radiation effects depend on the developmental stage. During the preimplantation period (one to 10 days postconception, p.c.), a radiation exposure of at least 0.2 Gy can cause the death of the embryo. Malformations are only observed in rare cases when genetic predispositions exist. Macroscopic, anatomical malformations are induced only after irradiation during the major organogenesis (two to eight weeks p.c.). A radiation dose of about 0.2 Gy is a doubling dose for the malformation risk, as extrapolated from experiments with rodents. The human embryo may be more radioresistant. During early fetogenesis (8-15 weeks p.c.) a high radiosensitivity exists for the development of the brain. Radiation doses of 1.0 Gy cause severe mental retardation in about 40% of the exposed fetuses. It must be taken into account that a radiation exposure during the fetal period can also induce cancer. It is generally assumed that the risk exists at about the same level as for children.

Abnormalities, Radiation-Induced↗
PubMed1996

Genetic analysis of the cause of gastroschisis in the HLG mouse strain.

An inbred mouse strain HLG shows a high incidence of gastroschisis after X-ray exposure to the zygotes. About 11% of the fetuses display this malformation after irradiation with 1 Gy. The C57BL-strain does not show the increased frequency of gastroschisis after radiation-exposure to the zygotes. The genetic background of this malformation was investigated in a backcross of HLG x C57BL females to HLG males. The pregnant HLG x C57BL females were irradiated in a stage in which the (HLG x C57BL) x HLG [BC1] embryos were in the 1-cell stage. The frequency of gastroschisis in the BC1 generation was compared with a genetic model of a single recessive mutation with 11% penetrance. This frequency does not fit a single-locus inheritance. The number of loci involved was estimated to be about two or three. HLG mouse strain may be a valuable animal model in the study of polygenic traits.

Abdominal Muscles↗
PubMed1996

A genetic characterization of differences in the sensitivity to radiation-induced malformation frequencies in the mouse strains Heiligenberger, C57BI, and Heiligenberger x C57BI.

We studied the frequency of malformations induced in two mouse strains (Heiligenberger, C57B1/6J) by exposure to x-rays 3 h after conception. Whereas there was a high number of malformed fetuses in Heiligenberger mice (mostly gastroschises) on day 19 of pregnancy, C57B1 did not respond to radiation exposure shortly after conception with an increased frequency of malformed fetuses. Cross-breeding of both strains revealed that no statistically significant increase in radiation-induced malformations was obtained in the F1 fetuses when the father was Heiligenberger and the mother C57B1. In the opposite case (Heiligenberger mother, C57B1 father) a small but statistically significant increase was observed.

Abnormalities, Radiation-Induced↗
PubMed1996

Effects of cell cycle specific exposure to 3H-thymidine or 3H-arginine on development and cell proliferation of mouse embryos.

One-cell mouse embryos were exposed to either 3H-thymidine (100 or 200 kBq/ml) or 3H-arginine (2.5 to 50 kBq/ml) for 2 h either in G1, S or G2 phase. 3H-Arginine affected embryonic development and cell proliferation in an activity-dependent way irrespective of the cell cycle stage exposed, whereas 3H-thymidine was effective only at higher activities and only after exposure during S phase.

Animals↗
PubMed1996

Automated scoring of micronuclei in binucleated human lymphocytes.

Manual and automatic scoring of micronuclei (MN) in binucleated human lymphocytes (BNC) were compared after irradiation of whole blood samples. The blood samples were irradiated with X-ray doses (1, 2 or 3 Gy) and stained with Giemsa. The preparation technique was optimized in such a way that acceptable conditions (cell density, contrast) were obtained for both scoring procedures. To estimate the quality of automatic micronucleus detection, two researchers who had different experience in scoring MN (6 months and 5 years) analysed the samples independently from each other. Automatic scoring was carried out with a digital image analysis system and the recognition procedure was divided into two parts. The BNC positions were detected with low microscope magnification (100x), and the recognition of micronuclei within the cytoplasm of the classified BNC was carried out at high magnification (630x). A fuzzy logic classification system as well as two different segmentation steps (preclassification and postclassification) made it possible that about 94% of all automatically recognized BNC were classified correctly). On the other hand, the classification system was optimized in such a way that false positive decisions were minimized (95% of automatically recognized micronuclei were classified correctly). Failure to recognize micronuclei (8.5%-25% false negatives) was mainly due to extremely small micronuclei, poor contrast with respect to the cytoplasm, and aggregation of micronuclei especially at higher doses.

Automation↗
PubMed1996

Comet assay study of DNA damage and repair of tumour cells following boron neutron capture irradiation with fast d(14) + Be neutrons.

We compared the amount of radiation-induced DNA damage and the extent of DNA repair in human melanoma cells (MeWo) using the 'comet assay' after neutron, boron neutron capture and X-irradiation. Using a colony-forming assay it was shown earlier that lethal effects in tumour cells treated with fast neutrons may be increased by the neutron capture reaction 10B(n, alpha)7Li. The effectiveness of boron neutron capture in killing tumour cells depends on the number of 10B atoms delivered to the tumour, the subcellular distribution of 10B and the thermal neutron fluence at the side of the tumour. Using the 'comet assay' the DNA damage of fast neutrons (mean energy 5.8 MeV) was shown to be significantly greater than for the same absorbed dose of X-rays. The presence of 600 ppm 10B (boric acid H5 10BO3) in the cell medium during irradiation with d(14) + Be neutrons in a phantom enhances the DNA damage by 20% compared with neutron irradiation alone. After DNA damage induction by neutrons and neutron capture of boron, the DNA repair capacity of the MeWo cells is significantly reduced in comparison with X-irradiation resulting in proportionally more residual DNA damage after 180 min of repair time.

Boron Neutron Capture Therapy↗
PubMed1996

Induction of DNA double-strand breaks by ionizing radiation at the c-myc locus compared with the whole genome: a study using pulsed-field gel electrophoresis and gene probing.

Ionizing radiation-induced double-strand breaks (dsb) in a human colon carcinoma-derived cell line COLO320HSR were determined from the fragment size distribution of non-specifically labelled DNA and Sfi I restriction enzyme-digested DNA uniformly labelled with a c-myc probe. The dose-effect relation for the induction of DNA dsb was linear with no significant difference between slopes for the curves in the whole genome (7.2 +/- 0.3 x 10(-9) dsb/bp/Gy) and in the 130 kbp restriction fragments containing c-myc (6.5 +/- 0.5 x 10(-9) dsb/bp/Gy). The size distribution of the c-myc fragments showed deviations from the random-breakage model, indicating heterogeneity of dsb induction at this locus.

DNA↗
PubMed1996

Micronuclei in lymphocytes of children from the vicinity of Chernobyl before and after 131I therapy for thyroid cancer.

The present study addresses the monitoring of children from the Belorussian and Ukrainian Republics exposed to the fall-out of the Chernobyl accident. Micronucleus analysis has been performed on 56 children from different areas. The micronucleus frequencies in individuals as well as in regional groups were comparable with controls, except for three donors. Such results had to be expected, taking into account that at least 7 years have passed since the accident. Most of the children whose micronucleus frequencies were determined are suffering from thyroid cancer and were treated by radioiodine (131I) therapy. We studied the effect of in vitro exposure with 131I on micronucleus induction and that proliferative ability of lymphocytes. The present investigation indicates that micronuclei can be usefully employed to detect individual exposures to the incorporated radionuclide within several days after the intake of the radionuclide in a dose range of around 65-390 mGy (effective dose).

Adolescent↗
PubMed1996

Automated cell cycle analysis with fluorescence microscopy and image analysis.

Automatic cell cycle analysis (DNA histograms) is usually performed with flow cytometry. In cases when only few cells are available, the DNA content has to be measured with a fluorescence microscope combined with sensitive camera systems (SIT, MCP, cooled CCDs) and a frame grabber for image analysis. The fluorescent cells are observed on the monitor of the image analyser. The DNA content of specific cells of interest is calculated after an interactive selection via mouse click on the monitor screen. It is desirable to automate this time-consuming procedure by a computer "cell-finding' and "cell-measurement' system, which is comparable in speed and measurement accuracy with manual scoring. A software program, based on image analysis, was designed for the automated cell finding, the cell measurement, and finally the interactive DNA data evaluation. The system has already been used to determine cell cycle stages in which specific manipulations of a lymphocyte culture were required. However, the system is also able to determine, automatically, DNA distributions of different kinds of cell (different leucocytes) within one sample, as long as the automatic recognition software can distinguish between them by morphological differences.

Algorithms↗
PubMed1996

Comet assay studies indicate that caffeine-mediated increase in radiation risk of embryos is due to inhibition of DNA repair.

It is well known that under specific conditions caffeine is able to enhance radiation risk of mammalian cells by a factor of approximately 1.5-2. Various mechanisms are discussed in the literature as possible explanations for this interaction. Inhibition of DNA repair plays a crucial role in the discussion, although direct evidence for this assumption is difficult to obtain. We used the "comet assay' in order to analyse the significance of repair inhibition by caffeine in the two-cell stage of mammalian gestation. Our data show that at the concentration necessary for increasing radiation risk (2 mM), caffeine effectively inhibits the restitution of radiation-damaged DNA.

Animals↗
PubMed1996

A comparison of the physiological effects of RSU1069 and RB6145 in the SCCVII murine tumour.

The physiological and therapeutic effects of the bioreductive agent RSU1069 (80 mg/kg i.p.) and its prodrug RB6145 (240 mg/kg i.p.) were investigated in the SCCVII tumour. Using laser Doppler flowmetry it was found that RSU1069 produced a significant 30% reduction in tumour blood flow 30 min after administration, while RB6145 had no effect. Tumour oxygenation, measured with an Eppendorf oxygen electrode, was unchanged by either agent except for a reduction in values less than 2.5 mmHg at 30 min after injection. Neither agent significantly altered tumour energy metabolism, assessed by 31P magnetic resonance spectroscopy. Both agents significantly increased tumour glucose content by a factor of 1.6-1.7 at 30 min after injection, but had no effect on glucose-6-phosphate or lactate levels. Tumour growth was significantly delayed by heating (42.5 degrees C, 60 min), and although neither RSU1069 nor RB6145 alone had any effect on tumour growth they produced a similar enhancement of the tumour response to heat. The therapeutic effects are consistent with the known conversion in vivo of one third of the pro-drug RB6145 to its active product RSU1069, however the physiological effects of the two agents in the SCCVII tumour are not identical.

Animals↗