Modelled microgravity does not modify the yield of chromosome aberrations induced by high-energy protons in human lymphocytes

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.

[Use of levosimendan after cardiac arrest by ventricular fibrillation: a case report]

We describe the case of a patient admitted in intensive care, after cardiac arrest by ventricular fibrillation treated by electrical defibrillation, that showed a serious deficit of the cardiac index and increase of the systemic vascular resistances. The patient was treated by levosimendan (Simdax): a starter dose of 12 microg/Kg in ten minutes and then a continuous perfusion of 0.1 microg/Kg/min. for 24 hours. He had a continuous amelioration of the clinical conditions and of the hemodynamics parameters. In the fifth day the patient was transferred to the Cardiology department and after 20 days he was discharged from hospital.

Early and delayed reproductive death in human cells exposed to high energy iron ion beams

The aim of this research was to determine the biological effectiveness for early and delayed effects of high energy, high linear energy transfer (LET) charged particles. Survival and delayed reproductive death were measured in AG1522 human fibroblast cells exposed to Fe-ion beams of energies between 0.2 and 1 GeV/n, 0.97 GeV/n Ti-ion and 0.49 GeV/n Si-ion beams. The cells were irradiated at the HIMAC accelerator in Chiba, Japan (0.2 and 0.5 GeV/n Fe and 0.49 GeV/n Si) and at the NASA Space Radiation Laboratory in Brookhaven, USA (1 GeV/n Fe and 0.97 GeV/n Ti ions). The dose-effect curves were measured in the dose range between 0.25 and 2 Gy. For comparison cells were exposed to 60Co gamma rays. Analysis of the dose-effect curves show that all the heavy ion beams induce inactivation and delayed reproductive death more effectively than 60Co gamma rays. The only exception is the 0.2 GeV/n Fe-ion beam at low doses. The progeny of the irradiated cells show delayed damage in the form of reproductive death with all the heavy ion beams with the 1 GeV/n Fe-ion beam being the most effective. The relative biological effectiveness at low doses of the iron beams is highest for LET values between 140 and 200 keV/micrometers with values of 1.6 and 3 for early and delayed reproductive death, respectively. Analysis of the fluence-effect curves shows that the cross-sections for early and delayed inactivation increase with increasing LET up to 442 keV/micrometers.

Chromosomal intrachanges induced by swift iron ions

We measured the induction of structural aberrations in human chromosome 5 induced by iron ions using the novel technique of multicolor banding in situ hybridization (mBAND). Human lymphocytes isolated from whole blood were exposed in vitro to 500 MeV/n (LET=200 keV/micrometers, doses 1 or 4 Gy) Fe nuclei at the HIMAC accelerator in Chiba (Japan). Chromosomes were prematurely condensed by calyculin A after 48 h in culture and slides were painted by mBAND. We found a frequency of 0.11 and 0.57 residual breakpoints per chromosome 5 after 1 and 4 Gy Fe-ions, respectively. Inter-chromosomal exchanges were the prevalent aberration type measured at both doses, followed by terminal deletions, and by intra-chromosomal exchanges. Among intra-chromosomal exchanges, intra-arm events were more frequent than inter-arm, but a significant number of intra-changes was associated to inter-changes involving the same chromosome after 4 Gy of iron ions. These events show that the complexity of chromosomal exchanges induced by heavy ions can be higher than expected by previous FISH studies.

Ground-based research with heavy ions for space radiation protection

Human exposure to ionizing radiation is one of the acknowledged potential showstoppers for long duration manned interplanetary missions. Human exploratory missions cannot be safely performed without a substantial reduction of the uncertainties associated with different space radiation health risks, and the development of effective countermeasures. Most of our knowledge of the biological effects of heavy charged particles comes from accelerator-based experiments. During the 35th COSPAR meeting, recent ground-based experiments with high-energy iron ions were discussed, and these results are briefly summarised in this paper. High quality accelerator-based research with heavy ions will continue to be the main source of knowledge of space radiation health effects and will lead to reductions of the uncertainties in predictions of human health risks. Efforts in materials science, nutrition and pharmaceutical sciences and their rigorous evaluation with biological model systems in ground-based accelerator experiments will lead to the development of safe and effective countermeasures to permit human exploration of the Solar System.

High LET-induced H2AX phosphorylation around the Bragg curve

We investigated the spatial distribution of the induction of the phosphorylated form of the histone protein H2AX (gamma-H2AX), known to be activated by DSBs. Following irradiation of human fibroblast cells with 600 MeV/nucleon silicon and 600 MeV/nucleon iron ions we observed the formation of gamma-H2AX aggregates in the shape of streaks stretching over several micrometers in an x/y plane. Polyethylene shielding was used to achieve a Bragg curve distribution with beam geometry parallel to the monolayer of cells. We present data that highlights the formation of immunofluorescent gamma-H2AX tracks showing the ion trajectories across the Bragg peak of irradiated human fibroblast cells. Qualitative analyses of these distributions indicated potentially increased clustering of DNA damage before the Bragg peak, enhanced gamma-H2AX distribution at the peak, and provided visual evidence of high-linear energy transfer particle traversal of cells beyond the Bragg peak in agreement with one-dimensional transport approximations. Spatial assessment of gamma-H2AX fluorescence may provide direct insights into DNA damage across the Bragg curve for high charge and energy ions including the biological consequences of shielding and possible contributors to bystander effects.

Fragmentation studies of relativistic iron ions using plastic nuclear track detectors

We measured fluence and fragmentation of high-energy (1 or 5 A GeV) 56Fe ions accelerated at the Alternating Gradient Synchrotron or at the NASA Space Radiation Laboratory (Brookhaven National Laboratory, NY, USA) using solid-state CR-39 nuclear track detectors. Different targets (polyethylene, PMMA, C, Al, Pb) were used to produce a large spectrum of charged fragments. CR-39 plastics were exposed both in front and behind the shielding block (thickness ranging from 5 to 30 g/cm2) at a normal incidence and low fluence. The radiation dose deposited by surviving Fe ions and charged fragments was measured behind the shield using an ionization chamber. The distribution of the measured track size was exploited to distinguish the primary 56Fe ions tracks from the lighter fragments. Measurements of projectile's fluence in front of the shield were used to determine the dose per incident particle behind the block. Simultaneous measurements of primary 56Fe ion tracks in front and behind the shield were used to evaluate the fraction of surviving iron projectiles and the total charge-changing fragmentation cross-section. These physical measurements will be used to characterize the beam used in parallel biological experiments.

Chromosome aberrations of clonal origin are present in astronauts' blood lymphocytes

Radiation-induced chromosome translocations remain in peripheral blood cells over many years, and can potentially be used to measure retrospective doses or prolonged low-dose rate exposures. However, several recent studies have indicated that some individuals possess clones of cells with balanced chromosome abnormalities, which can result in an overestimation of damage and, therefore, influence the accuracy of dose calculations. We carefully examined the patterns of chromosome damage found in the blood lymphocytes of twelve astronauts, and also applied statistical methods to screen for the presence of potential clones. Cells with clonal aberrations were identified in three of the twelve individuals. These clonal cells were present in samples collected both before and after space flight, and yields are higher than previously reported for healthy individuals in this age range (40-52 years of age). The frequency of clonal damage appears to be even greater in chromosomes prematurely condensed in interphase, when compared with equivalent analysis in metaphase cells. The individuals with clonal aberrations were followed-up over several months and the yields of all clones decreased during this period. Since clonal aberrations may be associated with increased risk of tumorigenesis, it is important to accurately identify cells containing clonal rearrangements for risk assessment as well as biodosimetry.

Distribution of breakpoints and fragment sizes in human chromosome 5 after heavy-ion bombardment

PURPOSE

To measure the location of heavy ion-induced residual breakpoints in human chromosome 5 and the size distribution of chromosome fragments involved in inter- or intrachromosomal exchanges.

MATERIALS AND METHODS

Human peripheral blood lymphocytes were exposed to 4 Gy accelerated 56Fe (iron) ions (500 MeV per nucleon (MeV n(-1)), linear energy transfer=200 keV microm(-1)). Cells were then stimulated to grow in vitro for 48 h, and chromosomes were prematurely condensed by calyculin A. Chromosome 5 was painted using high-resolution multicolour banding. The location of the observed residual breakpoints and the size of all chromosome 5 fragments involved in structural aberrations were measured using dedicated image analysis software.

RESULTS

Mapping of 283 breakpoints revealed a slight deviation from randomness, with an excess of breakpoints clustered in two small bands and an under representation of breaks at the telomeric end in the q-arm. Breakpoints per unit length were similar in p- and q-arms. The distribution of chromosome fragments has a maximum for very small fragments (< 10% of the chromosome size), indicating a severe fragmentation of chromosome 5 after heavy-ion bombardment. Only fragments < 40% of the chromosome size were involved in intrachromosomal exchanges (interstitial deletions or inversions), whereas fragments up to 75% of the whole chromosome 5 were found in interchromosomal exchanges.

CONCLUSIONS

Residual breakpoints after exposure to high-energy iron ions were not distributed randomly along chromosome 5, although the p- and q-arms displayed similar radiosensitivity. Large fragments are either restituted or misrejoined to other chromosome ends, whereas small intrachromosomal fragments can produce either inter- or intrachromosomal exchanges.

Chromosome intrachanges and interchanges detected by multicolor banding in lymphocytes: searching for clastogen signatures in the human genome

Genomic fingerprints of mutagenic agents would have wide applications in the field of cancer biology, epidemiology and prevention. The differential spectra of chromosomal aberrations induced by different clastogens suggest that ratios of specific aberrations can be exploited as biomarkers of carcinogen exposure. We have tested this hypothesis using the novel technique of multicolor banding in situ hybridization (mBAND) in human peripheral blood lymphocytes exposed in vitro to X rays, neutrons, heavy ions, or the restriction endonuclease AluI. In the heavy-ion-irradiated cells, we further analyzed aberrations in chromosome 5 using multicolor FISH (mFISH). Contrary to the expectations of biophysical models, our results do not support the use of the ratios of inter-/intrachromosomal exchanges or intra-/interarm intrachanges as fingerprints of exposure to densely ionizing radiation. However, our data point to measurable differences in the ratio of complex/simple interchanges after exposure to different clastogens. These data should be considered in current biophysical models of radiation action in living cells.

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.

Complex chromatid-isochromatid exchanges following irradiation with heavy ions?

We describe a peculiar and relatively rare type of chromosomal rearrangement induced in human peripheral lymphocytes that were ostensibly irradiated in G(0) phase of the cell cycle by accelerated heavy ions, and which, to the best of our knowledge, have not been previously described. The novel rearrangements which were detected using mFISH following exposure to 500 MeV/nucleon and 5 GeV/n 56Fe particles, but were not induced by either 137Cs gamma rays or 238Pu alpha particles, can alternatively be described as either complex chromatid-isochromatid or complex chromatid-chromosome exchanges. Different mechanisms potentially responsible for their formation are discussed.

Complex chromosomal rearrangements induced in vivo by heavy ions

It has been suggested that the ratio complex/simple exchanges can be used as a biomarker of exposure to high-LET radiation. We tested this hypothesis in vivo, by considering data from several studies that measured complex exchanges in peripheral blood from humans exposed to mixed fields of low- and high-LET radiation. In particular, we studied data from astronauts involved in long-term missions in low-Earth-orbit, and uterus cancer patients treated with accelerated carbon ions. Data from two studies of chromosomal aberrations in astronauts used blood samples obtained before and after space flight, and a third study used blood samples from patients before and after radiotherapy course. Similar methods were used in each study, where lymphocytes were stimulated to grow in vitro, and collected after incubation in either colcemid or calyculin A. Slides were painted with whole-chromosome DNA fluorescent probes (FISH), and complex and simple chromosome exchanges in the painted genome were classified separately. Complex-type exchanges were observed at low frequencies in control subjects, and in our test subjects before the treatment. No statistically significant increase in the yield of complex-type exchanges was induced by the space flight. Radiation therapy induced a high fraction of complex exchanges, but no significant differences could be detected between patients treated with accelerated carbon ions or X-rays. Complex chromosomal rearrangements do not represent a practical biomarker of radiation quality in our test subjects.

Chromosome aberration dosimetry in cosmonauts after single or multiple space flights

BACKGROUND AND AIMS

Cosmic radiation is one of the main hazards for manned space exploration. Uncertainty in radiation risk estimates for crews of long-term missions are very high, and direct biological measurements are necessary. We measured chromosomal aberrations in peripheral blood lymphocytes from 33 cosmonauts involved in space missions during the past 11 years.

METHODS

Blood lymphocytes from the cosmonauts were stimulated to grow in vitro and were harvested at their first mitosis. Slides were either stained with Giemsa stain for dicentrics analysis, or painted with whole-chromosome DNA probes for translocation analysis (FISH).

RESULTS

A statistically significant increase in the yield of chromosomal aberrations was measured following long-term space missions in lymphocytes from cosmonauts at their first flight. No significant changes in aberration frequencies were observed for short-term taxi flights. The increase in long-term missions was consistent with the values calculated from physical dosimetry data. However, for cosmonauts involved in two or more space flights, the yield of interchromosomal exchanges was not related to the total duration of space sojourn or integral absorbed dose. Indeed, the yield of aberrations at the end of the last mission was generally in the range of background frequencies measured before the first mission.

CONCLUSIONS

Chromosome aberration dosimetry can detect radiation damage during space flight, and biological measurements support the current risk estimates for space radiation exposure. However, for cosmonauts involved in multiple space missions the frequency of chromosomal aberrations is lower than expected, suggesting that the effects of repeated space flights on this particular endpoint are not simply additive. Changes in the immune system in microgravity and/or adaptive response to space radiation may explain the apparent increase in radioresistance after multiple space flights.

Chromosomal aberrations induced by high-energy iron ions with shielding

Biophysical models are commonly used to evaluate the effectiveness of shielding in reducing the biological damage caused by cosmic radiation in space flights. To improve and validate these codes biophysical experiments are needed. We have measured the induction of chromosomal aberrations in human peripheral blood lymphocytes exposed in vitro to 500 MeV/n iron ion beams (dose range 0.1-1 Gy) after traversing shields of different material (lucite, aluminium, or lead) and thickness (0-11.3 g/cm2). For comparison, cells were exposed to 200 MeV/n iron ions and to X-rays. Chromosomes were prematurely condensed by a phosphatase inhibitor (calyculin A) to avoid cell-cycle selection produced by the exposure to high-LET heavy-ion beams. Aberrations were scored in chromosomes 1, 2, and 4 following fluorescence in situ hybridization. The fraction of aberrant lymphocytes has been evaluated as a function of the dose at the sample position, and of the fluence of primary 56Fe ions hitting the shield. The influence of shield thickness on the action cross-section for the induction of exchange-type aberrations has been analyzed, and the dose average-LET measured as a function of the shield thickness. These preliminary results prove that the effectiveness of heavy ions is modified by shielding, and the biological damage is dependent upon shield thickness and material.

In vivo and in vitro measurements of complex-type chromosomal exchanges induced by heavy ions

Heavy ions are more efficient in producing complex-type chromosome exchanges than sparsely ionizing radiation, and this can potentially be used as a biomarker of radiation quality. We measured the induction of complex-type chromosomal aberrations in human peripheral blood lymphocytes exposed in vitro to accelerated H-, He-, C-, Ar-, Fe- and Au-ions in the LET range of approximately 0.4-1400 keV/micrometers. Chromosomes were analyzed either at the first post-irradiation mitosis, or in interphase, following premature condensation by phosphatase inhibitors. Selected chromosomes were then visualized after FISH-painting. The dose-response curve for the induction of complex-type exchanges by heavy ions was linear in the dose-range 0.2-1.5 Gy, while gamma-rays did not produce a significant increase in the yield of complex rearrangements in this dose range. The yield of complex aberrations after 1 Gy of heavy ions increased up to an LET around 100 keV/micrometers, and then declined at higher LET values. When mitotic cells were analyzed, the frequency of complex rearrangements after 1 Gy was about 10 times higher for Ar- or Fe- ions (the most effective ions, with LET around 100 keV/micrometers) than for 250 MeV protons, and values were about 35 times higher in prematurely condensed chromosomes. These results suggest that complex rearrangements may be detected in astronauts' blood lymphocytes after long-term space flight, because crews are exposed to HZE particles from galactic cosmic radiation. However, in a cytogenetic study of ten astronauts after long-term missions on the Mir or International Space Station, we found a very low frequency of complex rearrangements, and a significant post-flight increase was detected in only one out of the ten crewmembers. It appears that the use of complex-type exchanges as biomarker of radiation quality in vivo after low-dose chronic exposure in mixed radiation fields is hampered by statistical uncertainties.

Biological dosimetry in Russian and Italian astronauts

Large uncertainties are associated with estimates of equivalent dose and cancer risk for crews of long-term space missions. Biological dosimetry in astronauts is emerging as a useful technique to compare predictions based on quality factors and risk coefficients with actual measurements of biological damage in-flight. In the present study, chromosomal aberrations were analyzed in one Italian and eight Russian cosmonauts following missions of different duration on the MIR and the international space station (ISS). We used the technique of fluorescence in situ hybridization (FISH) to visualize translocations in chromosomes 1 and 2. In some cases, an increase in chromosome damage was observed after flight, but no correlation could be found between chromosome damage and flight history, in terms of number of flights at the time of sampling, duration in space and extra-vehicular activity. Blood samples from one of the cosmonauts were exposed in vitro to 6 MeV X-rays both before and after the flight. An enhancement in radiosensitivity induced by the spaceflight was observed.

M-FISH analysis of chromosome aberrations in human fibroblasts exposed to energetic iron ions in vitro

Confluent human fibroblast cells were exposed to 6 Gy gamma-rays or 200 MeV/nucleon Fe ions at 0.7 or 3 Gy. The cells were allowed to repair for 24 hours after exposure and chromosomes were collected using a premature chromosome condensation technique with calyculin-A. Chromosome aberrations were analyzed using the multicolor FISH (mFISH) technique that allows identification of both complex and truly incomplete exchanges. Results showed that both doses of the Fe ions produced higher ratios of complex to simple exchanges and lower ratio of complete to incomplete exchanges than the 6 Gy gamma-exposure. The ratios of aberration yields were similar for the two doses of Fe ions. After 0.7 Gy of Fe ions, most complex aberrations were found to involve three or four chromosomes, indicating this is the maximum number of chromosome domains traversed by a single Fe ion track.

Karyotypes of human lymphocytes exposed to high-energy iron ions

Chromosomal aberrations were analyzed using multicolor fluorescence in situ hybridization (mFISH) in human peripheral blood lymphocytes after in vitro exposure to gamma rays or accelerated (56)Fe ions (1 GeV/nucleon, 145 keV/microm) at Brookhaven National Laboratory (Upton, NY). Doses of 0.3 and 3 Gy were used for both radiation types. Chromosomes were prematurely condensed by a phosphatase inhibitor (calyculin A) to avoid the population selection bias observed at metaphase as a result of the severe cell cycle delays induced by heavy ions. A total of 1053 karyotypes (G(2) and M phases) were analyzed in irradiated lymphocytes. Results revealed different distribution patterns for chromosomal aberrations after low- and high-LET radiation exposures: Heavy ions induced a much higher fraction of cells with multiple aberrations, while the majority of the aberrant cells induced by low doses of gamma rays contained a single aberration. The high fraction of complex-type exchanges after heavy ions leads to an overestimation of simple-type asymmetrical interchanges (dicentrics) from analysis of Giemsa-stained samples. However, even after a dose of 3 Gy iron ions, about 30% of the cells presented no complex-type exchanges. The involvement of individual chromosomes in exchanges was similar for densely and sparsely ionizing radiation, and no statistically significant evidence of a nonrandom involvement of specific chromosomes was detected.

Kinetics of chromatid break repair in G2-human fibroblasts exposed to low- and high-LET radiations

The purpose of this study is to determine the kinetics of chromatid break rejoining following exposure to radiations of different quality. Exponentially growing human fibroblast cells AG1522 were irradiated with gamma-rays, energetic carbon (290 MeV/u), silicon (490 MeV/u) and iron (200 MeV/u, 600 MeV/u). Chromosomes were prematurely condensed using calyculin A. Prematurely condensed chromosomes were collected after several post-irradiation incubation times, ranging from 5 to 600 minutes, and the number of chromatid breaks and exchanges in G2 cells were scored. The relative biological effectiveness (RBE) for initial chromatid breaks per unit dose showed LET dependency having a peak at 55 keV/micrometers silicon (2.4) or 80 keV/micrometers carbon particles (2.4) and then decreased with increasing LET. The kinetics of chromatid break rejoining following low- or high-LET irradiation consisted of two exponential components. Chromatid breaks decreased rapidly after exposure, and then continued to decrease at a slower rate. The rejoining kinetics was similar for exposure to each type of radiation, although the rate of unrejoined breaks was higher for high-LET radiation. Chromatid exchanges were also formed quickly.

Influence of the shielding on the space radiation biological effectiveness

A research program in space radiobiology is described in this report. The program is focused on the effect of the shielding on the biological effects of heavy ions. Both experiments and models are included in the program. Experiments aim to determine genetic effects of heavy ions with or without shielding. Mathematical models, based on Monte Carlo codes, will be used to interpret the biological results. The final goal is to get a feasible model able to predict the radiation-induced biological damage in space, given the free-space radiation field and the space vessel shielding. The grant is supported by the Italian Space Agency (ASI), and involves Italian radiation biophysics groups (Universities of Milan and Naples, National Institute of Health in Rome), in collaboration with NASA (USA), NIRS (Japan), CERN (Switzerland), Brookhaven National Laboratories (USA), and TERA (Italy).

Cell inactivation by beryllium, boron and carbon ions at the low-energy irradiation facility of the Naples University

The 3MV HVEC TTT-3 Tandem accelerator at the University of Naples, already used for radiobiological studies with protons and alpha particles, was set up for irradiation of biological samples with low energy carbon, boron, and beryllium beams. Radiobiological characterisation and study of these ion beams is essential in hadrontherapy (correction of hadrotherapy) to understand, for example, the possible biological effect of the target fragmentation products. Furthermore in space radiation biology we need to know the biological effects of heavy ions, a component of cosmic radiation that can contribute to the radiobiological risk when long sojourns in space are concerned. V79 Chinese hamster cells were irradiated with the different ions and the resulting cell inactivation data are reported.

A model of radiation-induced myelopoiesis in space

Astronauts' radiation exposure limits are based on experimental and epidemiological data obtained on Earth. It is assumed that radiation sensitivity remains the same in the extraterrestrial space. However, human radiosensitivity is dependent upon the response of the hematopoietic tissue to the radiation insult. It is well known that the immune system is affected by microgravity. We have developed a mathematical model of radiation-induced myelopoiesis which includes the effect of microgravity on bone marrow kinetics. It is assumed that cellular radiosensitivity is not modified by the space environment, but repopulation rates of stem and stromal cells are reduced as a function of time in weightlessness. A realistic model of the space radiation environment, including the HZE component, is used to simulate the radiation damage. A dedicated computer code was written and applied to solar particle events and to the mission to Mars. The results suggest that altered myelopoiesis and lymphopoiesis in microgravity might increase human radiosensitivity in space.

Simultaneous exposure of mammalian cells to heavy ions and X-rays

Crews of space missions are exposed to a mixed radiation field, including sparsely and densely ionizing radiation. To determine the biological effectiveness of mixed high-/low-LET radiation fields, mammalian cells were exposed in vitro simultaneously to X-rays and heavy ions, accelerated at the HIMAC accelerator. X-ray doses ranged from 1 to 11 Gy. At the same time, cells were exposed to either 40Ar (550 MeV/n, 86 keV/micrometers), 28Si (100 MeV/n, 150 keV/micrometers), or 56Fe (115 MeV/n, 442 keV/micrometers) ions. Survival was measured in hamster V79 fibroblasts. Structural aberrations in chromosome 2 were measured by chemical-induced premature chromosome condensation combined with fluorescence in situ hybridization in isolated human lymphocytes. For argon and silicon experiments, measured damage in the mixed radiation field was consistent with the value expected using an additive function for low- and high-LET separated data. A small deviation from a simple additive function is observed with very high-LET iron ions combined to X-rays.

Chromosome aberrations in the blood lymphocytes of astronauts after space flight

Cytogenetic analysis of the lymphocytes of astronauts provides a direct measurement of space radiation damage in vivo, which takes into account individual radiosensitivity and considers the influence of microgravity and other stress conditions. Chromosome exchanges were measured in the blood lymphocytes of eight crew members after their respective space missions, using fluorescence in situ hybridization (FISH) with chromosome painting probes. Significant increases in aberrations were observed after the long-duration missions. The in vivo dose was derived from the frequencies of translocations and total exchanges using calibration curves determined before flight, and the RBE was estimated by comparison with individually measured physical absorbed doses. The values for average RBE were compared to the average quality factor (Q) from direct measurements of the lineal energy spectra using a tissue-equivalent proportional counter (TEPC) and radiation transport codes. The ratio of aberrations identified as complex was slightly higher after flight, which is thought to be an indication of exposure to high-LET radiation. To determine whether the frequency of complex aberrations measured in metaphase spreads after exposure to high-LET radiation was influenced by a cell cycle delay, chromosome damage was analyzed in prematurely condensed chromosome samples collected from two crew members before and after a short-duration mission. The frequency of complex exchanges after flight was higher in prematurely condensed chromosomes than in metaphase cells for one crew member.

Inactivation of human cells exposed to fractionated doses of low energy protons: relationship between cell sensitivity and recovery efficiency

Within the framework of radiation biophysics research in the hadrontherapy field, split-dose studies have been performed on four human cell lines with different radiation sensitivity (SCC25, HF19, H184B5 F5-1 M10, and SQ20B). Low energy protons of about 8 and 20 keV/micron LET and gamma-rays were used to study the relationship between the recovery ratio and the radiation quality. Each cell line was irradiated with two dose values corresponding to survival levels of about 5% and 1%. The same total dose was also delivered in two equal fractions separated by 1.5, 3, and 4.5 hours. A higher maximum recovery ratio was observed for radiosensitive cell lines as compared to radioresistant cells. The recovery potential after split doses was small for slow protons, compared to low-LET radiation. These data show that radiosensitivity may not be related to a deficient recovery, and suggest a possible involvement of inducible repair mechanisms.

Risk estimation based on chromosomal aberrations induced by radiation

The presence of a causal association between the frequency of chromosomal aberrations in peripheral blood lymphocytes and the risk of cancer has been substantiated recently by epidemiological studies. Cytogenetic analyses of crew members of the Mir Space Station have shown that a significant increase in the frequency of chromosomal aberrations can be detected after flight, and that such an increase is likely to be attributed to the radiation exposure. The risk of cancer can be estimated directly from the yields of chromosomal aberrations, taking into account some aspects of individual susceptibility and other factors unrelated to radiation. However, the use of an appropriate technique for the collection and analysis of chromosomes and the choice of the structural aberrations to be measured are crucial in providing sound results. Based on the fraction of aberrant lymphocytes detected before and after flight, the relative risk after a long-term Mir mission is estimated to be about 1.2-1.3. The new technique of mFISH can provide useful insights into the quantification of risk on an individual basis.

Rejoining of isochromatid breaks induced by heavy ions in G2-phase normal human fibroblasts

We reported previously that exposure of normal human fibroblasts in G2 phase of the cell cycle to high-LET radiation produces a much higher frequency of isochromatid breaks than exposure to gamma rays. We concluded that an increase in the production of isochromatid breaks is a signature of initial high-LET radiation-induced G2-phase damage. In this paper, we report the repair kinetics of isochromatid breaks induced by high-LET radiation in normal G2-phase human fibroblasts. Exponentially growing human fibroblasts (AG1522) were irradiated with gamma rays or energetic carbon (290 MeV/nucleon), silicon (490 MeV/nucleon), or iron (200 MeV/nucleon) ions. Prematurely condensed chromosomes were induced by calyculin A after different postirradiation incubation times ranging from 0 to 600 min. Chromosomes were stained with Giemsa, and aberrations were scored in cells at G2 phase. G2-phase fragments, the result of the induction of isochromatid breaks, decreased quickly with incubation time. The curve for the kinetics of the rejoining of chromatid-type breaks showed a slight upward curvature with time after exposure to 440 keV/microm iron particles, probably due to isochromatid-isochromatid break rejoining. The formation of chromatid exchanges after exposure to high-LET radiation therefore appears to be underestimated, because isochromatid-isochromatid exchanges cannot be detected. Increased induction of isochromatid breaks and rejoining of isochromatid breaks affect the overall kinetics of chromatid-type break rejoining after exposure to high-LET radiation.

Radiogenic transformation of human mammary epithelial cells in vitro

Cancer induction by space radiations is a major concern for manned space exploration. Accurate assessment of radiation risk at low doses requires basic understanding of mechanism(s) of radiation carcinogenesis. For determining the oncogenic effects of ionizing radiation in human epithelial cells, we transformed a mammary epithelial cell line (185B5), which was immortalized by benzo(a)pyrene, with energetic heavy ions and obtained several transformed clones. These transformed cells showed growth properties on Matrigel similar to human mammary tumor cells. To better understand the mechanisms of radiogenic transformation of human cells, we systematically examined the alterations in chromosomes and cancer genes. Among 16 autosomes examined for translocations, by using fluorescence in situ hybridization (FISH) technique, chromosomes 3, 12, 13, 15, 16, and 18 appeared to be normal in transformed cells. Chromosomes 1, 4, 6, 8, and 17 in transformed cells, however, showed patterns different from those in nontransformed cells. Southern blot analyses indicated no detectable alterations in myc, ras, Rb, or p53 genes. Further studies of chromosome 17 by using in situ hybridization with unique sequence p53 gene probe and a centromere probe showed no loss of p53 gene in transformed cells. Experimental results from cell fusion studies indicated that the transforming gene(s) is recessive. The role of genomic instability and tumor suppressor gene(s) in radiogenic transformation of human breast cells remains to be identified.

Relationship between radiation-induced aberrations in individual chromosomes and their DNA content: effects of interaction distance

PURPOSE

To study the effect of the interaction distance on the frequency of inter- and intrachromosome exchanges in individual chromosomes with respect to their DNA content. Assumptions: Chromosome exchanges are formed by misrejoining of two DNA double-strand breaks (DSB) induced within an interaction distance, d. It is assumed that chromosomes in G(0)/G(1) phase of the cell cycle occupy a spherical domain in a cell nucleus, with no spatial overlap between individual chromosome domains.

RESULTS

Formulae are derived for the probability of formation of inter-, as well as intra-, chromosome exchanges relating to the DNA content of the chromosome for a given interaction distance. For interaction distances <1 microm, the relative frequency of interchromosome exchanges predicted by the present model is similar to that by Cigarran et al. (1998) based on the assumption that the probability of interchromosome exchanges is proportional to the "surface area" of the chromosome territory. The "surface area" assumption is shown to be a limiting case of d-->0 in the present model. The present model also predicts that the probability of intrachromosome exchanges occurring in individual chromosomes is proportional to their DNA content with correction terms.

CONCLUSION

When the interaction distance is small, the "surface area" distribution for chromosome participation in interchromosome exchanges has been expected. However, the present model shows that for the interaction distance as large as 1 microm, the predicted probability of interchromosome exchange formation is still close to the surface area distribution. Therefore, this distribution does not necessarily rule out the formation of complex chromosomal aberrations by long-range misrejoining of DSB.

Dose--response of initial G2-chromatid breaks induced in normal human fibroblasts by heavy ions

PURPOSE

To investigate initial chromatid breaks in prematurely condensed G2 chromosomes following exposure to heavy ions of different LET.

MATERIAL AND METHODS

Exponentially growing human fibroblast cells AG1522 were irradiated with gamma-rays, energetic carbon (13 keV/ microm, 80 keV/microm), silicon (55 keV/microm) and iron (140 keV/microm, 185keV/microm, 440keV/microm) ions. Chromosomes were prematurely condensed using calyculin-A. Initial chromatid-type and isochromatid breaks in G2 cells were scored.

RESULTS

The dose response curves for total chromatid breaks were linear regardless of radiation type. The relative biological effectiveness (RBE) showed a LET-dependent increase, peaking around 2.7 at 55-80keV/microm and decreasing at higher LET. The dose response curves for isochromatid-type breaks were linear for high-LET radiations, but linear-quadratic for gamma-rays and 13 keV/microm carbon ions. The RBE for the induction of isochromatid breaks obtained from linear components increased rapidly between 13keV/microm (about 7) and 80keV/microm carbon (about 71), and decreased gradually until 440 keV/microm iron ions (about 66).

CONCLUSIONS

High-LET radiations are more effective at inducing isochromatid breaks, while low-LET radiations are more effective at inducing chromatid-type breaks. The densely ionizing track structures of heavy ions and the proximity of sister chromatids in G2 cells result in an increase in isochromatid breaks.

On the radiosensitivity of man in space

Astronauts' radiation exposure limits are based on experimental and epidemiological data obtained on Earth. It is assumed that radiation sensitivity remains the same in the extraterrestrial space. However, human radiosensitivity is dependent upon the response of the hematopoietic tissue to the radiation insult. It is well known that the immune system is affected by microgravity. We have developed a mathematical model of radiation-induced myelopoiesis which includes the effect of microgravity on bone marrow kinetics. It is assumed that cellular radiosensitivity is not modified by the space environment, but repopulation rates of stem and stromal cells are reduced as a function of time in weightlessness. A realistic model of the space radiation environment, including the HZE component, is used to simulate the radiation damage. A dedicated computer code was written and applied to solar particle events and to the mission to Mars. The results suggest that altered myelopoiesis and lymphopoiesis in microgravity might increase human radiosensitivity in space.

A biophysical model for estimating the frequency of radiation-induced mutations resulting from chromosomal translocations

Gene mutations can be induced by radiation as a result of chromosomal translocations. A biophysical model is developed to estimate the frequency of this type of mutation induced by low-LET radiation. Mutations resulting from translocations are assumed to be formed by misrejoining of two DNA double strand breaks (DSB), one within the gene and one on a different chromosome. The chromosome containing the gene is assumed to occupy a spherical territory and does not overlap spatially with other chromosomes. Misrejoining between two DSB can occur only if the two DSB are closer than an interaction distance at the time of their induction. Applying the model to mutations of the hprt gene induced in G0 human lymphocyte cells by low-LET radiation, it is calculated that mutations resulting from translocations account for about 14% of the total mutations. The value of the interaction distance is determined to be 0.6 micrometers by comparing with the observed frequency of translocations in the X-chromosome.

G2-chromosome aberrations induced by high-LET radiations

We report measurement of initial G2-chromatid breaks in normal human fibroblasts exposed to various types of high-LET particles. Exponentially growing AG 1522 cells were exposed to gamma rays or heavy ions. Chromosomes were prematurely condensed by calyculin A. Chromatid-type breaks and isochromatid-type breaks were scored separately. The dose response curves for the induction of total chromatid breaks (chromatid-type + isochromatid-type) and chromatid-type breaks were linear for each type of radiation. However, dose response curves for the induction of isochromatid-type breaks were linear for high-LET radiations and linear-quadratic for gamma rays. Relative biological effectiveness (RBE), calculated from total breaks, showed a LET dependent tendency with a peak at 55 keV/micrometer silicon (2.7) or 80 keV/micrometer carbon (2.7) and then decreased with LET (1.5 at 440 keV/micrometer). RBE for chromatid-type break peaked at 55 keV/micrometer (2.4) then decreased rapidly with LET. The RBE of 440 keV/micrometer iron particles was 0.7. The RBE calculated from induction of isochromatid-type breaks was much higher for high-LET radiations. It is concluded that the increased production of isochromatid-type breaks, induced by the densely ionizing track structure, is a signature of high-LET radiation exposure.

Calibration curves for biological dosimetry by fluorescence in situ hybridisation

Dose-response curves were measured for the induction of chromosomal aberrations in peripheral blood lymphocytes after acute exposure in vitro to 60Co gamma rays. Blood was obtained from four different healthy donors, and chromosomes were either observed at metaphase, following colcemid accumulation, or prematurely condensed by calyculin A. Cells were analysed in three different Italian laboratories. Chromosomes 1, 2, and 4 were painted, and simple-type interchanges between painted and non-painted chromosomes were scored in cells exposed in the dose range 0.1-3.0 Gy. The chemical-induced premature chromosome condensation method was also used combined with chromosome painting (chromosome 4 only) to determine calibration curves for high dose exposures (up to 20 Gy X rays). Calibration curves described in this paper will be used in our laboratories for biological dosimetry by fluorescence in situ hybridisation.

Event-related potentials in the elderly with new mild hypertension

Hypertension is a risk factor for cerebrovascular diseases (CVD) and cognitive impairment and the relative risk of CVD at every level of blood pressure (BP) is greater among the elderly. We submitted 20 elderly affected by new mild hypertension and 10 elderly normotensives to 24-hour ambulatory BP monitoring (ABPM), to evaluate their cognitive state using the Mini-Mental-State-Examination and to the recording of related acoustic evoked potentials (P300 and N2). We did not find significant differences for P300 latency between hypertensives and normotensives, while N2 latency recording showed a statistically significant protracted value in elderly hypertensives. In these patients we found a significant correlation between the N2 latency and systolic blood pressure values recorded by ABPM. These results demonstrated early functional alterations of cognitive state in elderly hypertensives, that are related to systolic blood pressure and future data might point to an earlier use of therapy.

High-LET radiation-induced aberrations in prematurely condensed G2 chromosomes of human fibroblasts

PURPOSE

To determine the number of initial chromatid breaks induced by low- or high-LET irradiations, and to compare the kinetics of chromatid break rejoining for radiations of different quality.

MATERIAL AND METHODS

Exponentially growing human fibroblast cells AG1522 were irradiated with gamma-rays, energetic carbon (290MeV/u), silicon (490MeV/u) and iron (200 and 600 MeV/u). Chromosomes were prematurely condensed using calyculin A. Chromatid breaks and exchanges in G2 cells were scored. PCC were collected after several post-irradiation incubation times, ranging from 5 to 600 min.

RESULTS

The kinetics of chromatid break rejoining following low- or high-LET irradiation consisted of two exponential components representing a rapid and a slow time constant. Chromatid breaks decreased rapidly during the first 10min after exposure, then continued to decrease at a slower rate. The rejoining kinetics were similar for exposure to each type of radiation. Chromatid exchanges were also formed quickly. Compared to low-LET radiation, isochromatid breaks were produced more frequently and the proportion of unrejoined breaks was higher for high-LET radiation.

CONCLUSIONS

Compared with gamma-rays, isochromatid breaks were observed more frequently in high-LET irradiated samples, suggesting that an increase in isochromatid breaks is a signature of high-LET radiation exposure.

X-rays vs. carbon-ion tumor therapy: cytogenetic damage in lymphocytes

PURPOSE

To measure chromosomal aberrations in peripheral blood lymphocytes from cancer patients treated with X-rays or carbon ions (C-ions).

METHODS AND MATERIALS

Blood samples from patients diagnosed for esophageal or uterine cervical cancer were obtained before, during, and at the end of the radiation treatment. The novel technique of interphase chromosome painting was used to detect aberrations in prematurely condensed chromosomes 2 and 4. The fraction of aberrant lymphocytes was measured as a function of the dose to the tumor volume. For comparison, blood samples were also exposed in vitro to X-rays or to carbon ions accelerated at the HIMAC.

RESULTS

C-ions were more efficient than X-rays in the induction of chromosomal aberrations in vitro. In patients with similar pathologies, tumor positions, and radiation field sizes, however, C-ions induced a lower fraction of aberrant lymphocytes than X-rays during the treatment. The initial slope of the dose-response curve for the induction of chromosomal aberrations during the treatment was correlated to the relative decrease in the number of white blood cells and lymphocytes during the treatment.

CONCLUSION

C-ions induce a lower level of cytogenetic damage in lymphocytes than X-rays, reducing the risk of bone marrow morbidity.

Inactivation of human normal and tumour cells irradiated with low energy protons

PURPOSE

To analyse the cell inactivation frequencies induced by low energy protons in human cells with different sensitivity to photon radiation.

MATERIALS AND METHODS

Four human cell lines with various sensitivities to photon irradiation were used: the SCC25 and SQ20B derived from human epithelium tumours of the tongue and larynx, respectively, and the normal lines M/10, derived from human mammary epithelium, and HF19 derived from a lung fibroblast. The cells were irradiated with y-rays and proton beams with linear energy transfer (LET) from 7 to 33 keV/microm. Clonogenic survival was assessed.

RESULTS

Survival curves are reported for each cell line following irradiation with gamma-rays and with various proton LETs. The surviving fraction after 2 Gy of gamma-rays was 0.72 for SQ20B cells, and 0.28-0.35 for the other cell lines. The maximum LET proton effectiveness was generally greater than that of gamma-rays. In particular there was a marked increase in beam effectiveness with increasing LET for the most resistant cells (SQ20B) whose 2 Gy-survival varied from 0.72 with gamma-radiation down to 0.37 with 30 keV/microm protons. The relative biological effectiveness (RBE(2 Gy gamma)) with the 30 keV/microm beam, evaluated as the ratio of 2 Gy to the proton dose producing the same inactivation level as that given by 2 Gy of gamma-rays, was 3.2, 1.8, 1.3 and 0.8 for SQ20B, M/10, SCC25, and HF19, respectively.

CONCLUSIONS

RBE for inactivation with high-LET protons increased with the cellular radioresistance to gamma-rays. The cell line with the greatest resistance to gamma-rays was the most responsive to the highest LET proton beam. A similar trend has also been found in studies reported in the literature with He, C, N ions with LET in the range 20-125 keV/microm on human tumour cell lines.

Complex-type chromosomal exchanges in blood lymphocytes during radiation therapy correlate with acute toxicity

The new method of chemical-induced premature chromosome condensation combined with fluorescence in situ hybridization was used to analyze chromosomal damage in peripheral blood mononuclear lymphocytes of patients undergoing radiation treatment for esophageal cancer with high-energy X-rays or accelerated carbon ions at the National Institute of Radiological Sciences (Chiba, Japan). Total number of aberrant cells correlated with radiation field size, but no correlation was found with acute toxicity. A high frequency of complex-type exchanges were also recorded. This aberration type presented a high individual variability, and correlated well with the acute morbidity. Cytogenetic analysis by interphase chromosome painting is proposed as a useful tool for monitoring normal tissue effects during radiotherapy.

Autonomic modulation of heart rate and blood pressure in normotensive offspring of hypertensive subjects

Predominant sympathetic cardiovascular modulation in the hyperkinetic phase of arterial hypertension has been well described. Less information is available on autonomic control in persons with a family history of arterial hypertension. To investigate this question, we selected 61 normotensive subjects (mean age 30.9 +/- 1.8 years) whose mother or father or both had arterial hypertension and 30 normotensive patients (mean age 30.1 +/- 1.4 years) whose parents had not had arterial hypertension (neither mother nor father) to undergo short-term power spectral analysis of RR interval and arterial pressure variabilities. The same recordings were used to determine baroreflex sensitivity or the alpha index by means of the transfer function. Normotensive offspring of hypertensive subjects had higher diastolic blood pressures (P < .05) and left ventricular mass index (P < .05) than did normotensive offspring of non-hypertensive subjects. They also had higher spectral densities of low frequency expressed in normalized units, both for R-R intervals (P < .05) and systolic pressure variabilities (P < .05); they also had a greater ratio of low-frequency to high-frequency powers of R-R interval variability (P < .05). No difference was observed between the two normotensive groups for baroreflex sensitivity. Our spectral data indicate that normotensive persons with a positive family history of arterial hypertension have lower parasympathetic modulation than those with a negative history. In normotensive persons with a family history of arterial hypertension, normal baroreflex sensitivity could be the mechanism that buffers the tendency for pressures to increase. The gradual loss of this regulatory mechanism may favor rising arterial pressures.

Chromatid break rejoining and exchange aberration formation following gamma-ray exposure: analysis in G2 human fibroblasts by chemically induced premature chromosome condensation

PURPOSE

To analyse the kinetics of chromatid break induction, rejoining, and misrejoining after y-irradiation in G2 phase human cells using premature chromosome condensation induced by calyculin A.

MATERIALS AND METHODS

Human fibroblast AG1522 cells were irradiated with gamma-rays and chromosomes were then prematurely condensed by calyculin A. The number of chromatid breaks and chromatid exchanges in G2 chromosomes were scored, and fitted curves were calculated.

RESULTS

Calyculin A induced premature chromosome condensation in cells immediately after irradiation. Kinetics of rejoining of chromatid breaks demonstrated two exponential components with rapid and slow time constants. Within 5 min after irradiation, the number of chromatid breaks fell rapidly to about one-half, then gradually decreased. Chromatid exchanges were formed very quickly, reaching a plateau within 20 min from exposure.

CONCLUSIONS

Chemically induced premature chromosome condensation technique allows a simple, rapid and precise analysis of chromatid breakage and rejoining. The rapid kinetic component was particularly well characterized.

Autonomic modulation and QT interval dispersion in hypertensive subjects with anxiety

Anxiety is associated with an increased risk of sudden death. QT dispersion is a marker of cardiac repolarization instability and is seen in conditions of high risk of sudden death. The purpose of this study was to evaluate autonomic nervous system control and QT dispersion in hypertensive subjects with anxiety symptoms. In a recent preliminary study, we observed that hypertensive individuals reporting high scores on a self-assessment anxiety scale had more marked left ventricular hypertrophy. In 105 hypertensive subjects divided into 3 groups according to severity of anxiety, we evaluated autonomic control by short-term power spectral analysis of RR and arterial pressure variability at rest (baseline) and during sympathetic stress (tilt test), left ventricular mass index, and heart rate-corrected QT (QTc) dispersion. At baseline, hypertensive subjects with higher anxiety symptom scores had significantly lower high-frequency RR values expressed in absolute terms (P<0.05) and in normalized units (P<0.05) than their counterparts without anxiety symptoms. Hypertensive subjects with anxiety also had a higher mean left ventricular mass index (P<0.001) and greater QTc dispersion (P<0.001). Both indexes and high frequency (P<0.05) correlated with severity of anxiety. These findings suggest that anxiety is associated with autonomic imbalance. This condition could favor an increase in left ventricular mass. Myocardial hypertrophy alone or combined with neuroautonomic imbalance may lead to QT dispersion.

Association between G2-phase block and repair of radiation-induced chromosome fragments in human lymphocytes

We have studied the induction of chromosomal aberrations in human lymphocytes exposed in G0 to X rays or carbon ions. Aberrations were analyzed in G0, G1, G2 or M phase. Analysis during the interphase was performed by chemically induced premature chromosome condensation, which allows scoring of aberrations in G1, G2 and M phase; fusion-induced premature chromosome condensation was used to analyze the damage in G0 cells after incubation for repair; M-phase cells were obtained by conventional Colcemid block. Aberrations were scored by Giemsa staining or fluorescence in situ hybridization (chromosomes 2 and 4). Similar yields of fragments were observed in G1 and G2 phase, but lower yields were scored in metaphase. The frequency of chromosomal exchanges was similar in G0 (after repair), G2 and M phase for cells exposed to X rays, while a lower frequency of exchanges was observed in M phase when lymphocytes were irradiated with high-LET carbon ions. The results suggest that radiation-induced G2-phase block is associated with unrejoined chromosome fragments induced by radiation exposure during G0.

Measurements of the equivalent whole-body dose during radiation therapy by cytogenetic methods

Estimates of equivalent whole-body dose following partial body exposure can be performed using different biophysical models. Calculations should be compared with biodosimetry data, but measurements are complicated by mitotic selection induced in target cells after localized irradiation. In this paper we measured chromosomal aberrations in peripheral blood lymphocytes during radiotherapy, and estimated the equivalent whole-body dose absorbed, by using the novel technique of interphase chromosome painting. Premature chromosome condensation was induced in stimulated lymphocytes by incubation in calyculin A, and slides were hybridized in situ with whole-chromosome DNA probes specific for human chromosomes 2 and 4. Reciprocal exchanges were used to estimate the equivalent whole-body dose, based on individual pre-treatment in vitro calibration curves. Equivalent whole-body dose increased as a function of the number of fractions, and reached a plateau at high fraction numbers. Chromosomal aberration yields were dependent on field size, tumour position and concurrent chemotherapy. Results suggest that interphase chromosome painting is a simple technique able to give a reliable estimate of the equivalent whole-body dose absorbed during therapeutic partial-body irradiation.

Left ventricular mass and heart rate variability in middle-aged and elderly salt-sensitive hypertensive subjects

Previous reports have shown that in salt-sensitive hypertension a high dietary salt intake can increase sympathetic activity. We evaluated the influence of the autonomic nervous system on myocardial hypertrophy by power spectral analysis of heart rate variability in middle-aged and elderly salt-sensitive hypertensive subjects. We compared autonomic nervous system activity in 32 salt-sensitive hypertensive patients (15 subjects with mean age, 42.4+/-2.4 years and 17 subjects with mean age, 74.6+/-1.6 years) and 20 age-matched normotensive controls. Power spectral analysis detects four spectral components: total power (TP), high-frequency (HF), low-frequency (LF) and very-low-frequency (VLF) power. In the elderly subjects we found an association between the left ventricular mass index (LVMI) and the following variables: very-low frequency (P<0.0001), 24-h urinary sodium excretion (P<0.0001) and diastolic blood pressure (DBP) (P<0.0001). In contrast, in middle-aged subjects we found a significant association between the LVMI and LF (P<0.001). In middle-aged, but not in elderly salt-sensitive hypertensive subjects, increased sympathetic activity correlated with the LVMI (P<0.0001). Our findings suggest an association between sympathetic hyperactivity and the LVMI in middle-aged subjects with salt-sensitive hypertension.

Chromosome aberrations induced by light ions: Monte Carlo simulations based on a mechanistic model

PURPOSE

To investigate the mechanisms underlying the induction of chromosome aberrations by ionizing radiation, focusing attention on DNA damage severity, interphase chromosome geometry and the distribution of DNA strand breaks.

METHODS

An ab initio biophysical model of aberration induction in human lymphocytes specific for light ions was developed, based on the assumption that 'complex lesions' (clustered DNA breaks) produce aberrations, whereas less severe breaks are repaired. It was assumed that interphase chromosomes are spatially localized and that chromosome break free-ends rejoin pairwise randomly; the unrejoining of a certain fraction of free-ends was assumed to be possible, and small fragments were neglected in order to reproduce experimental conditions. The yield of different aberrations was calculated and compared with some data obtained using Giemsa or FISH techniques.

RESULTS

Dose-response curves for dicentrics and centric rings (Giemsa) and for reciprocal, complex and incomplete exchanges (FISH) were simulated; the ratio between complex and reciprocal exchanges was also calculated as a function of particle type and LET. The results showed agreement with data from lymphocyte irradiation with light ions.

CONCLUSIONS

The results suggest that clustered DNA breaks are a critical damage type for aberration induction and that interphase chromosome localization plays an important role. Moreover, the effect of a given particle type is related both to the number of induced complex lesions and to their spatial distribution.

Theoretical and experimental tests of a chromosomal fingerprint for densely ionizing radiation based on F ratios calculated from stable and unstable chromosome aberrations

In the present study, F ratios for both stable chromosome aberrations, i.e. ratios of translocations to pericentric inversions, and unstable aberrations, i.e. dicentrics and centric rings, were measured using fluorescence in situ hybridization. F ratios for stable aberrations measured after exposure to low (2.89 Gy 60Co gamma rays) and high-LET (0.25 Gy 56Fe ions; 1.25 Gy 56Fe ions; 3.0 Gy 12C ions) radiation were 6.5 +/- 1.5, 4.7 +/- 1.6, 9.3 +/- 2.5 and 10.4 +/- 3.0, respectively. F ratios for unstable aberrations measured after low (2.89 Gy 60Co gamma rays) and high-LET (0.25 Gy 56Fe ions; 3.0 Gy 12C ions) radiations were 6.5 +/- 1.6, 6.3 +/- 2.3 and 11.1 +/- 3.7, respectively. No significant difference between the F ratios for low- and high-LET radiation was found. Further tests on the models for calculation of the F ratio proposed by Brenner and Sachs (Radiat. Res. 140, 134-142, 1994) showed that the F ratio may not be straightforward as a practical fingerprint for densely ionizing radiation.