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Purpose: To analyse lymphocyte chromosomes from astronauts of MIR and EUROMIR missions. Materials and methods: Peripheral lymphocytes from seven astronauts before and after space flights were cultured and analysed for structural chromosomal aberrations. Results: Chromosome-type but not chromatid-type aberrations were significantly elevated after space flights when compared to pre-flight values. In one astronaut two rogue cells were found. Conclusions: Overall the frequencies of aberrations were found to be correlated with estimated absorbed cosmic radiation doses. [ABSTRACT FROM AUTHOR]

Purpose : To estimate the frequencies of dicentric chromosomes in peripheral lymphocytes of astronauts on missions to Mars. Materials and methods: Calculations of expected frequencies of dicentrics are based on dose estimations and lymphocyte biology. Results : Frequencies of dicentrics are predicted to be 10-40 times higher than the background level. Conclusions : Stressing the importance of careful mission planning and optimized shielding of transfer vehicle to Mars. [ABSTRACT FROM AUTHOR]

Purpose: By extending to other animal models the experiments on irradiated rabbit testes performed by the German Albers-Schönberg and Frieben and inspired by the preliminary observations of Regaud on spermatogenesis after irradiation, Bergonié and Tribondeau established a link between radiosensitivity and proliferation as a 'law' in 1906. Although it is still popular and taken as one of the founding laws of radiation oncology, it was early considered as a 'first approximation'. Conclusions: More than 100 years later, one tribute paid to these pioneers should be to at least avoid mixing notions like radiosensitivity, proliferation, differentiation, stem cells that they deeply contributed to define and to re-read their works in their original version in order to better understand what the technological and conceptual advances really are today. [ABSTRACT FROM AUTHOR]

Purpose: Risk assessment of radiation exposure during long-term space missions requires the knowledge of the relative biological effectiveness (RBE) of space radiation components. Few data on gene transcription activation by different heavy ions are available, suggesting a dependence on linear energy transfer. The transcription factor Nuclear Factor κB (NF-κB) can be involved in cancerogenesis. Therefore, NF-κB activation by accelerated heavy ions of different linear energy transfer (LET) was correlated to survival. Materials and methods: NF-κB-dependent gene induction after exposure to heavy ions was detected in stably transfected human embryonic kidney 293 cells (HEK-pNF-κB-d2EGFP/Neo cells carrying a neomycin resistance), using the destabilized Enhanced Green Fluorescent Protein (d2EGFP) as reporter. Results: Argon (LET 272 keV/μm) and neon ions (LET 91 keV/μm) had the highest potential to activate NF-κB, resulting in a RBE of 8.9 in comparison to 150 kV X-rays. The RBE for survival also reached its maximum in this LET range, with a maximal value of 2. Conclusions: NF-κB might be involved in modulating survival responses of cells hit by heavy ions in the LET range of 91-272 keV/μm and could therefore become a factor to be considered for risk assessment of radiation exposure during space travel. [ABSTRACT FROM AUTHOR]

Purpose: Quantitative analysis of cancer risk of ionising radiation as a function of dose-rate. Materials and methods: Non-tumour dose, Dnt, defined as the highest dose of radiation at which no statistically significant tumour increase was observed above the control level, was analysed as a function of dose-rate of radiation. Results: An inverse correlation was found between Dnt and dose-rate of the radiation. Dnt increased 20-fold with decreasing dose-rate from 1--10−−8 Gy/min for whole body irradiation with low linear energy transfer (LET) radiation. Partial body radiation also showed a dose-rate dependence with a 5- to 10-fold larger Dnt as dose rate decreased. The dose-rate effect was also found for high LET radiation but at 10-fold lower Dnt levels. Conclusions: The cancer risk of ionising radiation varies 1000-fold depending on the dose-rate of radiation and exposure conditions. This analysis explains the discrepancy of cancer risk between A-bomb survivors and radium dial painters. [ABSTRACT FROM AUTHOR]

Purpose: The tardigrade Richtersius coronifer has previously been shown to tolerate very high doses of low linear energy transfer (low-LET) radiation (gamma rays). The purpose of this study was to extend our knowledge on radiation tolerance in this species by investigating the dose-response to high-LET radiation in terms of protons. Materials and methods: Dehydrated tardigrades of the species R. coronifer were irradiated with 2.55 MeV (megaelectronvolts) protons at doses ranging from 500 gray (Gy) to 15,000 Gy, to investigate the dose-viability relationship. In addition, a focused proton microbeam was utilised to determine the areal mass distribution, using the ion beam analytical technique STIM (Scanning Transmission Ion Microscopy). Results: The experiment suggests that R. coronifer is unaffected by doses of proton irradiation up to 10,000 Gy, but shows very little viability at higher doses. The STIM analysis revealed that the thickness of the dehydrated tardigrades exceeds 150 μm, and that a fraction of the protons may not be fully absorbed. Conclusion: Our results are in line with previous studies of exposure to high-LET radiation in tardigrades, indicating that these animals are equally or even more tolerant to high-LET compared to low-LET gamma radiation. The physiological background to this remarkable result is currently unknown, but deserves investigation. [ABSTRACT FROM AUTHOR]

Purpose : To characterize the ultraviolet (UV) sensitivity and establish the UV-induced DNA damage profile of cells of four Deinococcus radiodurans strains. The investigated strains differ in their radiation susceptibility, leading to a classification into a UV-sensitive (UVS78 and 1R1A) and a UV-resistant class (wild type strain R1 and 262). Materials and methods : Deinococcus radiodurans cells were exposed in suspension to monochromatic 254 nm (UV-C) and polychromatic UV radiations; the surviving fraction was determined by assessing the ability of the bacteria to form colonies. The UV-induced DNA lesions were measured quantitatively using an accurate and highly specific assay that involves the combination of high performance liquid chromatography (HPLC) with tandem mass spectrometry detection. Results : Analysis of the DNA photoproducts showed that the TC (6‐4) photoproduct and the TT and TC cyclobutane dimers were the major lesions induced by UV-C and UV-(>200 nm)-radiation. The UV-sensitive class was approx. 10 times more susceptible to UV-C and UV-(>200 nm)-radiations than the resistant class. Interestingly, the survival curves of all investigated strains become similar with longer UV wavelengths in the UV-(>315 nm)-radiation range. This observation suggests that the repair mechanisms of the UV-resistant class are not specifically effective for damage produced by UV of the >315 nm range. However, the initial amount of DNA photoproducts produced upon irradiation was found to be the same in resistant and sensitive strains for each wavelength range. Conclusion : Compared to mammalian cells, the DNA of Deinococcus radiodurans cells is less susceptible to the photo-induced formation of thymine cyclobutane dimers as inferred from comparative analysis. The ongoing investigations may contribute to a better understanding of the mechanism of DNA photoprotection against the direct effects of UV radiation. This may be of interest in the present context of a possible continuous decrease in the ozone layer thickness. [ABSTRACT FROM AUTHOR]

The aim was to evaluate the effect of modelled microgravity on radiation-induced chromosome aberrations (CAs). G0 peripheral blood lymphocytes were exposed to 60 MeV protons or 250?kVp X-rays in the dose range 0?–?6?Gy, and allowed to repair DNA damage for 24?h under either normal gravity or microgravity modelled by the NASA-designed rotating-wall bioreactor. Cells were then stimulated to proliferate by phytohaemagglutinin (PHA) under normal gravity conditions and prematurely condensed chromosomes were harvested after 48?h. CAs were scored in chromosomes 1 and 2 by fluorescence in-situ hybridization. Proliferation gravisensitivity was examined by cell growth curves and by morphological evaluation of mitogen-induced activation. Cell replication rounds were monitored by bromodeoxyuridine labelling. Modelled microgravity markedly reduced PHA-mediated lymphocyte blastogenesis and cell growth. However, no significant differences between normal gravity and modelled microgravity were found in the dose?–?response curves for the induction of aberrant cells or total interchromosomal exchange frequency. Rotating-wall bioreactor-based microgravity reproduced space-related alterations of mitogen stimulation in human lymphocytes but did not affect the yield of CAs induced by low- linear energy transfer radiation. [ABSTRACT FROM AUTHOR]

Purpose : It is important to develop simple experimental models to assess the induction of DNA damage and study the different factors involved under controlled conditions. This paper describes the cytogenetic analysis carried out in Chinese hamster cells (CHO) sequentially exposed to very low doses of X-rays. Materials and methods : CHO cells were cultured for 14 passages. Irradiation treatment was performed once per passage, and three irradiation doses were employed: 2.5, 5.0 and 10.0 mSv. Results : Sequential irradiation of CHO cells did not increase the yield of chomatid- or chromosome-type aberrations. However, a significant increase of achromatic lesions (gaps) was found after the first or second X-ray dose, with all three irradiation doses employed. Conclusions : The variation in the frequency of gaps as well as that in the mitotic index during the 14 cycles of radiation could be an indication of the induction of genomic instability. According to this, continuous rises and falls in the frequency of gaps as well as in the mitotic index reflects the simultaneous induction of endogenous DNA damage, cell death and cell survival. [ABSTRACT FROM AUTHOR]

Purpose: To investigate how cell-cycle delays in human peripheral lymphocytes affect the expression of complex chromosome damage in metaphase following high- and low-LET radiation exposure. Materials and methods: Whole blood was irradiated in vitro with a low and a high dose of 1 GeV u[sup -1] iron particles, 400MeV u[sup -1] neon particles or γ-rays. Lymphocytes were cultured and metaphase cells were collected at different time points after 48-84h in culture. Interphase chromosomes were prematurely condensed using calyculin-A, either 48 or 72 h after exposure to iron particles or γ-rays. Cells in first division were analysed using a combination of FISH whole-chromosome painting and DAPI/Hoechst 33258 harlequin staining. Results: There was a delay in expression of chromosome damage in metaphase that was LET- and dose-dependant. This delay was mostly related to the late emergence of complex-type damage into metaphase. Yields of damage in PCC collected 48h after irradiation with iron particles were similar to values obtained from cells undergoing mitosis after prolonged incubation. Conclusion: The yield of high-LET radiation-induced complex chromosome damage could be underestimated when analysing metaphase cells collected at one time point after irradiation. Chemically induced PCC is a more accurate technique since problems with complicated cell-cycle delays are avoided. [ABSTRACT FROM AUTHOR]

Purpose: To compare the occurrence of cytogenetically abnormal rogue cells, characterized by a high frequency of chromosometype aberrations, in people exposed to ionizing radiation and in non-exposed subjects. Materials and methods: Data on rogue cells from a total of nine cytogenetic studies on radiation-exposed populations and controls were collected from three laboratories in the United Kingdom, France and Finland. The studies were conducted on first-division metaphases of peripheral blood lymphocytes. Solid Giemsastained, G- or R-banded and FISH chromosome-painted material was included. Results: Rogue cells were found both from controls and from exposed subjects. The highest incidence of these cells was observed in a control group of young trainees (1:400), whereas the lowest incidence of rogue cells (1:36 500) was demonstrated in a follow-up study of people accidentally exposed to high levels of ionizing radiation. Rogue cells were found to be distributed non-randomly among individuals; the highest individual frequency was 1 in 50 analysed metaphases. Conclusions: The origin of rogue cells is still unclear. The incidence of rogue cells showed a large variability between studies and individuals. No correlation between long-term radiation exposure and the occurrence of rogue cells was demonstrated. Although the presence of rogue cells in astronauts after a 6 month space flight may be attributable to high-LET radiation, the frequencies were not remarkable when compared with those in the other studies in this review. [ABSTRACT FROM AUTHOR]

Presents an index of authors submitting papers for volume 27 of the 'International Journal of Radiation Biology.' Topics covered; Titles of the papers.

Purpose : To measure clonogenic death of Chinese hamster V79 cells following exposure to a defined number of 4.3 MeV alpha particles (track-averaged LET 105 keV/ mu m). Materials and methods : Cells were irradiated at the radiobiological facility installed at the TTT-3 Tandem accelerator in Naples by using a 'Biostack' approach, which allows the positions of incident tracks relative to cells to be carefully determined. Subcellular structure was identified by fluorescence microscopy, while tracks were visualized by LR-115 solid state nuclear track detectors. Results : Particle hits in the cytoplasm did not significantly affect cell survival, yet survival probability decreased exponentially as a function of the number of nuclear traversals. Measured probability of surviving to exactly one 4.3 MeV alpha -particle traversal in the cell nucleus was 0.67 0.10. Inactivation cross-section was substantially higher than expected from conventional survival curves. However, folding of the data with Poisson statistics showed that survival level expected if a mean of one alpha -particle goes through a nucleus is higher than the measured value after exactly one particle traversal. Conclusions : V79 cells have about 67% probability to survive a single alpha -particle traversal in the cell nucleus. Single-particle survival curves are consistent with conventional dose-survival relationships, once Poisson distribution of traversals is taken into account. [ABSTRACT FROM AUTHOR]