Modulation of gene expression in endothelial cells in response to high LET nickel ion irradiation

Ionizing radiation can elicit harmful effects on the cardiovascular system at high doses. Endothelial cells are critical targets in radiation-induced cardiovascular damage. Astronauts performing a long-term deep space mission are exposed to consistently higher fluences of ionizing radiation that may accumulate to reach high effective doses. In addition, cosmic radiation contains high linear energy transfer (LET) radiation that is known to produce high values of relative biological effectiveness (RBE). The aim of this study was to broaden the understanding of the molecular response to high LET radiation by investigating the changes in gene expression in endothelial cells. For this purpose, a human endothelial cell line (EA.hy926) was irradiated with accelerated nickel ions (Ni) (LET, 183 keV/mu m) at doses of 0.5, 2 and 5 Gy. DNA damage was measured 2 and 24 h following irradiation by gamma-H2AX foci detection by fluorescence microscopy and gene expression changes were measured by microarrays at 8 and 24 h following irradiation. We found that exposure to accelerated nickel particles induced a persistent DNA damage response up to 24 h after treatment. This was accompanied by a downregulation in the expression of a multitude of genes involved in the regulation of the cell cycle and an upregulation in the expression of genes involved in cell cycle checkpoints. In addition, genes involved in DNA damage response, oxidative stress, apoptosis and cell-cell signaling (cytokines) were found to be upregulated. An in silico analysis of the involved genes suggested that the transcription factors, E2F and nuclear factor (NF)-kappa B, may be involved in these cellular responses

Chromosome aberrations in human lymphocytes irradiated with heavy ions

Because of the increasing use of heavy ions in cancer therapy and for the planning of manned space travels, a realistic estimate of the health risks associated with particle exposure is indispensable. The standard method to quantify the exposed dose and to assess the health risks of radiation is the analysis of chromosome aberrations in peripheral blood lymphocytes at the first post-irradiation mitosis at one fixed time, 48 h, after in vitro stimulation. Using this procedure very low RBE values for high LET particles are reported. However, evidence is accumulating that high LET induced cell cycle delays and apoptosis may influence the aberration yield observable in metaphase cells. To address these questions, lymphocytes obtained from a healthy donor were irradiated with X-rays, C-, Fe- and Fe-like particles with LETs ranging from 2-3160 keV/microm and chromosome aberrations were measured in first cycle metaphase cells at multiple 3 h collection intervals from 48 to 84 h post-irradiation. In parallel, aberrations were determined in G2-phase cells and cell cycle progression as well as radiation-induced apoptosis were examined. Analysis of the data sets shows that high LET-induced apoptosis does not affect the observable aberration yield. However, a relationship between high LET induced cell cycle delays and the number of aberrations carried by a cell was found: the delayed entry of heavily damaged cells into mitosis results from a prolonged arrest in G2 and the delay is dose- and LET-dependent. Detailed statistical analysis of the frequency distributions of aberrations among cells revealed a correlation between the selective delay of heavily damaged cells and the number of particle hits per cell nucleus. Altogether, the data demonstrate that the application of the standard metaphase assay 48 h post-irradiation results in an underestimation of the RBE of high LET particles. Application of alternative cytogenetic approaches (G2-PCC analysis, the integration analysis) confirmed this conclusion

Intercomparison of Radiobiological RBE among Japanese Proton Therapy Facilities

PTCOG4

Production and distribution of aberrations in resting or cycling human lymphocytes following Fe-ion or Cr-ion irradiation: Emphasis on single track effects

In the present study we examined the cytogenetic effects of 177 MeV/u Fe-ions (LET = 335 keV/$\mu m$) and 4.1 MeV/u Cr-ions (LET = 3160 keV/$\mu m$) in human lymphocytes under exposure conditions that result on average in one particle hit per cell nucleus. In non-cycling (G0-phase) lymphocytes the induction and the repair of excess fragments was measured by means of the premature chromosome condensation (PCC) technique and the distribution of breaks among cells was analysed. The PCC-data were further compared with those reported recently for stimulated lymphocytes at the first post-irradiation mitosis. Our experiments show that a single nuclear traversal by a Fe-ion produced more initial chromatin breakage than one Cr-ion, but after 24 h of repair the number of excess fragments/cell was similar for both ion species. All distributions of aberrations were overdispersed. For low energy Cr-ions, where the track radius is smaller than the radius of the cell nucleus, the data could be well described by a Neyman type A distribution. In contrast, the data obtained for high energy Fe-ions were fitted with a convoluted Poisson–Neyman distribution to account for the fact that the dose is deposited not only in the cell actually traversed but also in neighbouring cells. By applying metaphase analysis a different picture emerged with respect to the aberration yield, i.e. more aberrations were detected in cells exposed to Fe-ions than in those irradiated with Cr-ions. Yet, as observed for non-cycling lymphocytes all aberration distributions generated for metaphase cells were overdispersed. The obtained results are discussed with respect to differences in particle track structure. Additionally, the impact of confounding factors such as apoptosis that affect the number of aberrations expressed in a cell population is addressed

Chromosome aberration measurements in mitotic and G2-PCC lymphocytes at the standard sampling time of 48 h underestimate the effectiveness of high-LET particles

The relationship between heavy-ion-induced cell cycle delay and the time-course of aberrations in first-cycle metaphases or prematurely condensed G(2)-cells (G(2)-PCC) was investigated. Lymphocytes of the same donor were irradiated with X-rays or various charged particles (carbon, iron, xenon, and chromium) covering an LET range of 2-3,160 keV/μm. Chromosome aberrations were measured in samples collected at 48, 60, 72, and 84 h postirradiation. Linear-quadratic functions were fitted to the data, and the fit parameters α and β were determined. At any sampling time, α values derived from G(2)-cells were higher than those from metaphases. The α value derived from metaphase analysis at 48 h increased with LET, reached a maximum around 155 keV/μm, and decreased with a further rise in LET. At the later time-points, higher α values were estimated for particles with LET > 30 keV/μm. Estimates of α values from G(2)-cells showed a similar LET dependence, yet the time-dependent increase was less pronounced. Altogether, our data demonstrate that heavily damaged lymphocytes suffer a prolonged G(2)-arrest that is clearly LET dependent. For this very reason, the standard analysis of aberrations in metaphase cells 48 h postirradiation will considerably underestimate the effectiveness of high-LET radiation. Scoring of aberrations in G(2)-PCC at 48 h as suggested by several authors will result in higher aberration yields. However, when particles with a very high-LET value (LET > 150 keV/μm) are applied, still a fraction of multiple damaged cells escape detection by G(2)-analysis 48 h postirradiation

Cell killing and chromosomal aberration induced by heavy-ion beams in cultured human tumor cells

12th International Congress of Radiation Researc