Induction of chromatin damage and distribution of isochromatid breaks in human fibroblast cells exposed to heavy ions

mFISH analysis of chromosomal damage in bone marrow cells collected from CBA/CaJ mice following whole body exposure to heavy ions (56Fe ions)

To date, there is scant information on in vivo induction of chromosomal damage by heavy ions found in space (i.e. 56Fe ions). For radiation-induced response to be useful for risk assessment, it must be established in in vivo systems especially in cells that are known to be at risk for health problems associated with radiation exposure (such as hematopoietic cells, the known target tissue for radiation-induced leukemia). In this study, the whole genome multicolor fluorescence in situ hybridization (mFISH) technique was used to examine the in vivo induction of chromosomal damage in hematopoietic tissues, i.e. bone marrow cells. These cells were collected from CBA/CaJ mice at day 7 following whole-body exposure to different doses of 1 GeV/amu 56Fe ions (0, 0.1, 0.5 and 1.0 Gy) or (137)Cs gamma rays as the reference radiation (0, 0.5, 1.0 and 3.0 Gy, at the dose rate of 0.72 Gy/min using a GammaCell40). These radiation doses were the average total-body doses. For each radiation type, there were four mice per dose. Several types of aberrations in bone marrow cells collected from mice exposed to either type of radiation were found. These were exchanges and breaks (both chromatid- and chromosome-types). Chromosomal exchanges included translocations (Robertsonian or centric fusion, reciprocal and incomplete types), and dicentrics. No evidence of a non-random involvement of specific chromosomes in any type of aberrations observed in mice exposed to 56Fe ions or 137Cs gamma rays was found. At the radiation dose range used in our in vivo study, the majority of exchanges were simple. Complex exchanges were detected in bone marrow cells collected from mice exposed to 1 Gy of 56Fe ions or 3 Gy of 137Cs gamma rays only, but their frequencies were low. Overall, our in vivo data indicate that the frequency of complex chromosome exchanges was not significantly different between bone marrow cells collected from mice exposed to 56Fe ions or 137Cs gamma rays. Each type of radiation induced significant dose-dependent increases (ANOVA, P < 0.01) in the frequencies of chromosomal damage, including the numbers of abnormal cells. Based upon the linear-terms of dose-response curves, 56Fe ions were 1.6 (all types of exchanges), 4.3 (abnormal cells) and 4.2 (breaks, both chromatid- and chromosome-types) times more effective than 137Cs gamma rays in inducing chromosomal damage.

Lethal sectoring, genomic instability, and delayed division delay in HeLa S3 cells surviving alpha- or X-irradiation

Lethal sectoring (LS) is the process for survival in which lethal damage remaining in irradiated cells is eliminated as lethal sector (offspring without reproductive integrity). This process occurs through the postirradiation 1st to 4th divisions with the accompanying appearance of a clonogenic progenitor (clonogen) (clonogenic sectoring: CS). The features of LS or CS and genomic instability (GI) were explored by analyzing the pedigrees of HeLa cells surviving alpha- (0.45 Gy) or X-irradiation (3 Gy) (20% survival dose). Most (approximately 70%) of the lethal latent damage was eliminated from alpha-particle survivors through the 1st to 2nd divisions, but it persisted in X-ray survivors until the 2nd generation. Although the frequency of CS was similar to that of LS for alpha-irradiation, CS was higher than LS for X-irradiation. Nonlethal damage remaining in the clonogens led to an elevated incidence of delayed cell death in their progeny. The mean incidence was higher for alpha-particle (16.3%) than X-ray survivors (8.3%), indicating the greater potentiality for GI by alpha-particles. Evidence is available to suggest the intrinsic difference in the mechanisms of GI induction by these two radiations: the association of misrepaired clustered DNA damage (CD) with alpha-particles and unrepaired PLD with X-rays. A novel phenomenon, "delayed division delay (DDD)" was noticed, though occasionally (approximately 10% per cell), with the progeny during the postirradiation 1st-3rd generations. DDD was much longer in alpha- (mean: approximately 11 h) than X-irradiated cells (approximately 4 h). Supposedly DDD was triggered by delayed chromosome breakage. However, a significant shortening of cell-cycle time at the postirradiation 1st generation was recognized with X-ray survivors.

G2 chromatid damage and repair kinetics in normal human fibroblast cells exposed to low- or high-LET radiation

Radiation-induced chromosome damage can be measured in interphase using the Premature Chromosome Condensation (PCC) technique. With the introduction of a new PCC technique using the potent phosphatase inhibitor calyculin-A, chromosomes can be condensed within five minutes, and it is now possible to examine the early damage induced by radiation. Using this method, it has been shown that high-LET radiation induces a higher frequency of chromatid breaks and a much higher frequency of isochromatid breaks than low-LET radiation. The kinetics of chromatid break rejoining consists of two exponential components representing a rapid and a slow time constant, which appears to be similar for low- and high-LET radiations. However, after high-LET radiation exposures, the rejoining process for isochromatid breaks influences the repair kinetics of chromatid-type breaks, and this plays an important role in the assessment of chromatid break rejoining in the G2 phase of the cell cycle.

Chromosome Aberrations Induced by High-LET Radiations

Measurements of chromosome aberrations in peripheral blood lymphocytes are currently the most sensitive and reliable indicator of radiation exposure that can be used for biological dosimetry. This technique has been implemented recently to study radiation exposures incurred by astronauts during space flight, where a significant proportion of the dose is delivered by high-LET particle exposure. Traditional methods for the assessing of cytogenetic damage in mitotic cells collected at one time point after exposure may not be suitable for measuring high-LET radiation effects due to the drastic cell cycle perturbations and interphase cell death induced by this type of exposure. In this manuscript we review the recent advances in methodology used to study high-LET induced cytogenetic effects and evaluate the use of chemically-induced Premature Chromosome Condensation (PCC) as an alternative to metaphase analysis. Published data on the cytogenetic effects of in vitro exposures of high-LET radiation is reviewed, along with biodosimetry results from astronauts after short or long space missions.

Efficient repair of DNA damage induced by heavy ion particles in meiotic prophase I nuclei of Caenorhabditis elegans

The effects of heavy ion particle irradiation on meiosis and reproductive development in the nematode Caenorhabditis elegans were studied. Meiotic pachytene nuclei are significantly resistant to particle irradiation by the heavy ions carbon and argon, as well as to X-rays, but not UV, whereas diplotene to diakinesis stage oocytes and early embryonic cells are not. Chromosomal abnormalities appear in mitotic cells and in maturing oocytes irradiated with heavy ion particles during the diplotene to the early diakinesis stages, but not in oocytes irradiated during the pachytene stage. The pachytene nuclei of ced-3 mutants, which are defective in apoptosis, are similarly resistant to ionizing radiation, but pachytene nuclei depleted for Ce-atl-1 (ataxia-telangiectasia like 1) or Ce-rdh-1/rad-51 are more sensitive. Pachytene nuclei thus appear to effectively repair heavy ion-induced DNA damage by the meiotic homologous recombination system.