[en] Thioguanine resistant CHO cells (HPRT^-) were stably cotransfected with pSV2-gpt and πH3-CD2 vectors using the calcium phosphate coprecipitation technique. The effects of single low doses of ionizing radiation were studied in a CD2⁺ CHO clone. The CD2⁺ phenotype responsible for binding sheep erythrocytes and rosette formation, was not affected by X-rays doses in the range 2-6 cGy. However, after 10 Gy of X-irradiation, 50% of the cells lost the CD2⁺ phenotype. These results suggest that this CD2⁺ clone might be a very sensitive indicator of very low X-ray doses. The implications of the phenotypic changes, observed after very low doses of irradiation, are discussed. (author)

[en] The radiosensitization of exponentially-growing V79-171 cells whose DNA has been substituted by bromodeoxy-uridine (BrdU) in place of thymidine is decreased if acetone is present during irradiation. Acetone, at a concentration of 1 mol dm^-3, removes the majority of the increase in double-strand breaks (dsbs) caused by BrdU substitution, but only removes approximately half of the increase in cell killing. The decrease in cell radiosensitization coincides with the removal of the additional dsbs. The protection afforded by acetone against dsbs is assumed to be due to its ability to scavenge hydrated electrons, thought to be the active species causing the increased DNA damage in the presence of BrdU. (Author)

[en] The effects of exogenously added nerve growth factor (NGF) on reaggregation cultures of foetal rat brain cells after X-irradiation with 2 Gy were studied. Irradiation caused decreased protein and DNA levels, which was not prevented by NGF. The activities of the cholinergic marker enzymes choline acetyl transferase and acetylcholine esterase were increased in irradiated cultures. However, no difference in the activities of these enzymes was found between irradiated and unirradiated NGF-treated cultures. Irradiation did not affect the activity of the marker enzyme for oligodendrocytes (2',3'-cyclic nucleotide 3'-phosphodiesterase), but caused an increase in the astrocyte marker (glutamine synthetase) activity. This effect on astrocytes was prevented by NGF. (Author)

[en] The protraction of total body irradiation (TBI) to a continuous low dose-rate (LDR) has been investigated for its effect on donor marrow engraftment in murine bone marrow transplant (BMT) models of varying histocompatibility. The data suggest that radiation damage repair during LDR irradiation in an immunocyte target cell population is mainly responsible for enhanced graft rejection thus rendering protracted TBI less effective for application in clinical allogeneic BMT. (Author)

[en] The survival of E. coli K12 strain AB1157 and the isogenic repair-deficient mutant E. coli AB2480 (recA13, uvrA6) was measured after γ-irradiation in the presence of various alcohols as well as after incubation and subsequent removal of the alcohols before irradiation. The authors conclude that alcohols protect predominantly by OH radical scavenging. The comparatively small protection of cell survival by the more hydrophobic alcohols can be attributed to the sensitizing effect of these alcohols. (author)

[en] Only a small percentage of the DNA damage set by ionizing radiation in the living cell manifests itself as lethal. It is now increasingly accepted that clustered lesions may constitute the kind of damage that the repair enzymes cannot adequately deal with. The question is raised as to whether damage amplification reactions (radical transfer reactions) may contribute to these clustered lesions, and examples of such damage amplification reactions are given. In one example a purine is involved. With 2'-deoxy adenosine and 2'-deoxy guanosine it is shown that these purine nucleosides undergo unexpected radical reactions. Evidence for the radical transfer from the purine to the sugar moiety is provided by the formation of the 5'-aldehydes. These products have been assayed with 2-thiobarbituric acid (TBA), a reagent commonly applied to the detection of malonaldehyde. TBA-reactive material has also been assayed in γ-irradiated DNA, about one-third of this is free malonaldehyde, while the major part of the TBA-reactive material remains bound to the DNA. In contrast, bleomycin-treated DNA yields practically no free malonaldehyde, and the major TBA-reactive products are identified as the thymine and adenine base propenals. (Author)

[en] A non-homogeneous target model of nucleosome particle for track structure calculations and biophysical modelling of radiation-induced DNA damage was developed together with a sampling method for non-homogeneous targets. The model allows one to distinguish energy deposited in the histone core, primary hydration shell and nucleosome DNA. Illustrative results for low energy electrons are presented and compared with results obtained with simpler models of a nucleosome particle. (author)

[en] A colony-forming assay of human skin fibroblast radiosensitivity was established in our laboratory and applied to primary skin biopsies from 12 women belonging to an unselected group of patients who received postmastectomy radiotherapy 10-12 years prior to this study. The aim was to investigate the relationship between in vitro radiosensitivity and the occurrence of subcutaneous fibrosis after radiotherapy. Early generations of normal skin fibroblasts in exponential growth were irradiated at room temperature at a high dose-rate to estimate the surviving fraction of colony-forming cells after single doses ranging from 1 to 8 Gy. A linear-quadratic cell survival curve was fitted to the data and from these fits the surviving fraction at 3.5 Gy (SF_3.5) was estimated. Replicate experiments of different cell generations were made to validate the assay, and the between-patients variability was significantly larger than the assay variability for both SF₂(p=0.002) and SF_3.5(p=0.04). Patients were treated in the period 1978-1982 with a dose per fraction between 2.7 and 3.9 Gy, a total of 12 fractions at two fractions per week. They were evaluated with respect to the occurence of marked subcutaneous fibrosis in a total of 36 independent treatment fields. In each treatment field the total dose and dose per fraction at the relevant dosimetric reference depth as well as the length of follow-up were recorded. (Author)

[en] To date, there has been no effective therapy to counter incorporated radionuclides of strontium. In an endeavour to solve this problem, we have synthesized and evaluated various N,N'-distributed derivatives of 1,4,10,13-tetraoxa-7,16-diaza-cyclooctadecane (cryptand 2.2) for their ability to mobilize ⁸⁵Sr²⁺. These ligands are water soluble and have a relatively low acute i.v. toxicity, as demonstrated by their evaluation in rat and mouse. The di-sodium-calcium complex and tetra-sodium salt of the cryptand (2.2) dimalonate have exerted a remarkable decorporation effectiveness for ⁸⁵Sr²⁺ in extracellular space. The tetra-potassium salt of the cryptand (2.2) dimalonate has a moderate effect, while no mobilization activity can be detected with the cryptand (2.2) that does not have a side chain substituent. Animals were initially given ⁸⁵SrCl₂ either i.p. or into the lung, then the compounds were administered 30-60 min later using an alternative route. The degree of decorporation achieved a 80-95% of the initial body burden (ibb) compared with the control values of 20-30%. The agents are resorbed easily from the lung, and the radiostrontium deposition in bone was inhibited strongly by a decorporation agent. The success of the treatment, however is dependent upon the speed with which decorporation therapy commences. (Author)

[en] We have found that F9 murine teratocarcinoma cells undergo morphological changes and internucleosomal DNA fragmentation characteristic of apoptosis after exposure to ionizing radiation. We studied the time course, radiation dose-response, and the effects of protein and RNA synthesis inhibitors on this process. The response is dose dependent in the range 2-12 Gy. Internucleosomal DNA fragmentation can be detected as early as 6 h postirradiation and is maximal by 48 h. Cycloheximide, a protein synthesis inhibitor, and 5,6-dichloro-1-β-D-ribofuranosylbenzimidazole, an RNA synthesis inhibitor, both induced internucleosomal DNA fragmentation in the unirradiated cells and enhanced radiation-induced DNA fragmentation. F9 cells can be induced to differentiate into cells resembling endoderm with retinoic acid. After irradiation, differentiated F9 cells exhibit less DNA fragmentation than stem cells. This indicates that ionizing radiation can induce apoptosis in non-lymphoid tumours. We suggest that embryonic tumour cells may be particularly susceptible to agents that induce apoptosis. (Author)