Accelerated heavy particles and the lens. III. Cataract enhancement by dose fractionation

For a number of biological end points it has been shown that, in contrast to low linear energy transfer (LET) radiation, dose fractionation of high-LET radiation does not result in a reduction in overall effectiveness. Studies were conducted to determine the effect of fractionating the exposures to heavy ion doses on the development of cataracts. Rat eyes were exposed to single doses of 1, 5, and 25 cGy of 570 MeV/amu40Ar ions and to 2, 4, and 10 Gy of 250 kVp X rays. These were compared to unirradiated controls and eyes which were exposed to the same total dose delivered in four fractions over 12 h. While in all cases fractionation of the exposure to X rays produced significant reduction in cataractogenic potential, fractionating doses of 40Ar ions caused a dose- and stage-dependent enhancement in the development of cataracts.     

Effects of heavy ion to the primary [correction of rimary] culture of mouse brain cells.

To investigate effects of low dose heavy particle radiation to CNS system, we adopted mouse neonatal brain cells in culture being exposed to heavy ions by HIMAC at NIRS and NSRL at BNL. The applied dose varied from 0.05 Gy up to 2.0 Gy. The subsequent biological effects were evaluated by an induction of apoptosis and neuron survival focusing on the dependencies of the animal strains, SCID, B6, B6C3F1, C3H, used for brain cell culture, SCID was the most sensitive and C3H the least sensitive to particle radiation as evaluated by 10% apoptotic criterion. The LET dependency was compared with using SCID and B6 cells exposing to different ions (H, C, Ne, Si, Ar, and Fe). Although no detectable LET dependency was observed in the high LET (55-200 keV/micrometers) and low dose (<0.5 Gy) regions. The survivability profiles of the neurons were different in the mouse strains and ions. In this report, a result of memory and learning function to adult mice after whole-body and brain local irradiation at carbon ion and iron ion.     

Relative biological effectiveness of high-energy iron ions for micronucleus formation at low doses

Dose-response curves for micronucleus (MN) formation were measured in Chinese hamster V79 and xrs6 (Ku80(-)) cells and in human mammary epithelial MCF10A cells in the dose range of 0.05-1 Gy. The Chinese hamster cells were exposed to 1 GeV/nucleon iron ions, 600 MeV/nucleon iron ions, and 300 MeV/nucleon iron ions (LETs of 151, 176 and 235 keV/microm, respectively) as well as with 320 kVp X rays as reference. Second-order polynomials were fitted to the induction curves, and the initial slopes (the alpha values) were used to calculate RBE. For the repair-proficient V79 cells, the RBE at these low doses increased with LET. The values obtained were 3.1 +/- 0.8 (LET = 151 keV/microm), 4.3 +/- 0.5 (LET = 176 keV/microm), and 5.7 +/- 0.6 (LET = 235 keV/microm), while the RBE was close to 1 for the repair-deficient xrs6 cells regardless of LET. For the MCF10A cells, the RBE was determined for 1 GeV/nucleon iron ions and was found to be 5.5 +/- 0.9, slightly higher than for V79 cells. To test the effect of shielding, the 1 GeV/nucleon iron-ion beam was intercepted by various thicknesses of high-density polyethylene plastic absorbers, which resulted in energy loss and fragmentation. It was found that the MN yield for V79 cells placed behind the absorbers decreased in proportion to the decrease in dose both before and after the iron-ion Bragg peak, indicating that RBE did not change significantly due to shielding except in the Bragg peak region. At the Bragg peak itself with an entrance dose of 0.5 Gy, where the LET is very high from stopping low-energy iron ions, the effectiveness for MN formation per unit dose was decreased compared to non-Bragg peak areas.     

Effects of carbon-ion radiation on the postnatal development of mice and on the yield of white spots in the mid-ventrum and tail tips

Pregnant female C57BL/10JHir mice were irradiated whole-body at 9 days of gestation with a single acute dose of carbon-ion radiation. The average linear energy transfer (LET) of the carbon ions was 50 keV/microm within a spread-out Bragg peak (SOBP). The effects were studied by scoring changes in the postnatal development of the mice as well as in the pigmentation of the cutaneous coats and tail tips of their offspring 22 days after birth. The percentage of live births was reduced in mice exposed to carbon ions at doses greater than 0.5 Gy. The survival to day 22 was also reduced in mice exposed to carbon ions at doses greater than 0.75 Gy. Moreover, the body weight at day 22 was reduced in mice exposed to carbon ions at doses greater than 0.1 Gy. A comparison of the survival to day 22 after exposure to carbon ions with our previous results for 60Co gamma rays indicated that carbon ions were twice as effective as gamma rays. White spots were found in the mid-ventrum as well as in the tail tips of offspring exposed to carbon ions in utero. The frequency and the size of the white spots in the mid-ventrum and in the tail tips increased as the dose increased. Carbon ions appear to be slightly more effective than the gamma rays used in our previous study. In the ventral white spots, no melanocytes were observed in the epidermis, dermis and hair follicles. These results indicate that prenatal exposure to carbon ions has a greater effect on the postnatal development and survival of mice than does exposure to gamma rays, and that the relative biological effectiveness is greater than that for effects on melanocyte development.     

Cataractogenic action of accelerated carbon ions with energies of 300 MeV/nucleon

The influence of carbon ions of 300 MeV/nucleon on the incidence of lenticular opacity has been studied on mice. The cataractogenic efficiency of low carbon ion doses (0.003 to 0.5 Gy) is higher than that of gamma-radiation. The threshold dose of carbon ions is 0.05 Gy. The RBE ratios vary from 30.4 to 11.1 as the period of the postirradiation observation increases from 20 to 50 weeks.     

Neoplastic transformation in vitro by mixed beams of high-energy iron ions and protons

The radiation environment in space is complex in terms of both the variety of charged particles and their dose rates. Simulation of such an environment for experimental studies is technically very difficult. However, with the variety of beams available at the National Space Research Laboratory (NSRL) at Brookhaven National Laboratory (BNL) it is possible to ask questions about potential interactions of these radiations. In this study, the end point examined was transformation in vitro from a preneoplastic to a neoplastic phenotype. The effects of 1?GeV/n iron ions and 1?GeV/n protons alone provided strong evidence for suppression of transformation at doses ≤5?cGy. These ions were also studied in combination in so-called mixed-beam experiments. The specific protocols were a low dose (10?cGy) of protons followed after either 5-15?min (immediate) or 16-24?h (delayed) by 1?Gy of iron ions and a low dose (10?cGy) of iron ions followed after either 5-15?min or 16-24?h by 1?Gy of protons. Within experimental error the results indicated an additive interaction under all conditions with no evidence of an adaptive response, with the one possible exception of 10?cGy iron ions followed immediately by 1?Gy protons. A similar challenge dose protocol was also used in single-beam studies to test for adaptive responses induced by 232?MeV/n protons and (137)Cs γ radiation and, contrary to expectations, none were observed. However, subsequent tests of 10?cGy of (137)Cs γ radiation followed after either 5-15?min or 8?h by 1?Gy of (137)Cs γ radiation did demonstrate an adaptive response at 8?h, pointing out the importance of the interval between adapting and challenge dose. Furthermore, the dose-response data for each ion alone indicate that the initial adapting dose of 10?cGy used in the mixed-beam setting may have been too high to see any potential adaptive response.     

Increased content of zinc and iron in human cataractous lenses

The purpose of the study was to examine the zinc and iron content of human lenses in different types of cataract and to investigate the possible influence of diabetes on the zinc and iron content of the lens. Iron and zinc of 57 human lenses (28 corticonuclear cataracts and 29 mature cataracts with a mean age of 70.6±16.1 and 74.7±11.1 yr, 41 nondiabetics and 16 diabetics) were determined by atomic absorption spectroscopy. The zinc content of human lenses was significantly increased in mature cataracts compared to corticonuclear cataracts (0.51±0.33 vs 0.32±0.20 μmol/g dry mass, p=0.012). The iron content of mature cataracts was also higher than in corticonuclear cataracts (0.11±0.09 vs 0.07±0.05 μmol/g dry mass, p=0.071). Furthermore, a significant increase of the lens zinc content could be observed with increasing lens coloration (light brown 0.33±0.17 vs dark brown 0.52±0.35 μmol/g dry mass, p=0.032). Diabetic patients seem to have both increased zinc and iron contents in the lens compared to nondiabetic subjects (zinc: 0.45±0.42 vs 0.40±0.22 μmol/g dry mass; iron: 0.12±0.10 vs 0.08±0.05 μmol/g dry mass). These data suggest a possible influence of the lens zinc and iron content on the development of lens opacification. Especially advanced forms of cataract and dark brown colored lenses show significantly increased zinc and iron content.     

mFISH analysis of chromosomal damage in bone marrow cells collected from CBA/CaJ mice following whole body exposure to heavy ions (<Superscript>56</Superscript>Fe 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 ¹³⁷Cs γ 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 γ 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 γ 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 γ 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 γ rays in inducing chromosomal damage.     

Detection of genomic instability in offspring of male mice chronically exposed to gamma-radiation by the "adaptive response" test

The genomic instability (GI) in somatic cells of the progeny (F1 generation) of male mice chronically exposed to low-dose gamma-radiation was studied by comparative analysis of chromosome damage. BALB/C male mice exposed to 0.1 Gy (0.01 Gy/day) and 0.5 Gy (0.01 and 0.05 Gy/day) were mated with unirradiated females 15 days after irradiation. For comparison of radiosensitivity, two-month-old males, the descendants of irradiated and unirradiated animals, were subjected to irradiation with a dose of 1.5 Gy (0.47 Gy/min) from a 60Co source. GI was revealed by the standard scheme of adaptive response. The experiments indicated that, by using the test "adaptive response", it is possible to detect the transition of gamma-radiation-induced genomic instability in sex cells of male parent into somatic cells of mice (F1 generation) either from changes in radiosensitivity or by the absence of the adaptive response induced by a standard scheme.     

Truly incomplete and complex exchanges in prematurely condensed chromosomes of human fibroblasts exposed in vitro to energetic heavy ions

Confluent human fibroblast cells (AG1522) were irradiated with gamma rays, 490 MeV/nucleon silicon ions, or iron ions at either 200 or 500 MeV/nucleon. The cells were allowed to repair at 37 degrees C for 24 h after exposure, and a chemically induced premature chromosome condensation (PCC) technique was used to condense chromosomes in the G2 phase of the cell cycle. Incomplete and complex exchanges were analyzed in the irradiated samples. To verify that chromosomal breaks were truly unrejoined, chromosome aberrations were analyzed using a combination of whole-chromosome specific probes and probes specific for the telomere region of the chromosome. Results showed that the frequency of unrejoined chromosome breaks was higher after irradiation with the heavy ions of high LET, and consequently the ratio of incomplete to complete exchanges increased steadily with LET up to 440 keV/microm, the highest LET included in the present study. For samples exposed to 200 MeV/nucleon iron ions, chromosome aberrations were analyzed using the multicolor FISH (mFISH) technique, which allows identification of both complex and truly incomplete exchanges. Results of the mFISH study showed that 0.7 and 3 Gy iron ions produced similar ratios of complex to simple exchanges and incomplete to complete exchanges; these ratios were higher than those obtained after exposure to 6 Gy gamma rays. After 0.7 Gy of iron ions, most complex aberrations were found to involve three or four chromosomes, which is a likely indication of the maximum number of chromosome domains traversed by a single iron-ion track.     

Induction of cytogenetic adaptive response in spermatogonia and spermatocytes by pre-exposure of mouse testis to low-dose (12)C(6+) ions

To investigate the effects of pre-exposure of mouse testis to low-dose (12)C(6+) ions on cytogenetics of spermatogonia and spermatocytes induced by subsequent high-dose irradiation, the testes of outbred Kun-Ming strain mice were irradiated with 0.05Gy of (12)C(6+) ions as the pre-exposure dose, and then irradiated with 2Gy as challenging dose at 4h after per-exposure. Poly(ADP-ribose) polymerase (PARPs) activity and PARP-1 protein expression were respectively measured by using the enzymatic and Western blot assays at 4h after irradiation; chromosomal aberrations in spermatogonia and spermatocytes were analyzed by the air-drying method at 8h after irradiation. The results showed that there was a significant increase in the frequency of chromosomal aberrations and significant reductions of PARP activity and PARP-1 expression level in the mouse testes irradiated with 2Gy of (12)C(6+) ions. However, pre-exposure of mouse testes to a low dose of (12)C(6+) ions significantly increased PARPs activity and PARP-1 expression and alleviated the harmful effects induced by a subsequent high-dose irradiation. PARP activity inhibitor 3-aminobenzamide (3-AB) treatment blocked the effects of PARP-1 on cytogenetic adaptive response induced by low-dose (12)C(6+) ion irradiation. The data suggest that pre-exposure of testes to a low dose of heavy ions can induce cytogenetic adaptive response to subsequent high-dose irradiation. The increase of PARP-1 protein induced by the low-dose ionizing irradiation may be involved in the mechanism of these observations.     

Effects of very low fluences of high-energy protons or iron ions on irradiated and bystander cells

In space, astronauts are exposed to radiation fields consisting of energetic protons and high atomic number, high-energy (HZE) particles at very low dose rates or fluences. Under these conditions, it is likely that, in addition to cells in an astronaut's body being traversed by ionizing radiation particles, unirradiated cells can also receive intercellular bystander signals from irradiated cells. Thus this study was designed to determine the dependence of DNA damage induction on dose at very low fluences of charged particles. Novel techniques to quantify particle fluence have been developed at the NASA Space Radiation Biology Laboratory (NSRL) at Brookhaven National Laboratory (BNL). The approach uses a large ionization chamber to visualize the radiation beam coupled with a scintillation counter to measure fluence. This development has allowed us to irradiate cells with 1 GeV/nucleon protons and iron ions at particle fluences as low as 200 particles/cm(2) and quantify biological responses. Our results show an increased fraction of cells with DNA damage in both the irradiated population and bystander cells sharing medium with irradiated cells after low fluences. The fraction of cells with damage, manifest as micronucleus formation and 53BP1 focus induction, is about 2-fold higher than background at doses as low as ～0.47 mGy iron ions (～0.02 iron ions/cell) or ～70 μGy protons (～2 protons/cell). In the irradiated population, irrespective of radiation type, the fraction of damaged cells is constant from the lowest damaging fluence to about 1 cGy, above which the fraction of damaged cells increases with dose. In the bystander population, the level of damage is the same as in the irradiated population up to 1 cGy, but it does not increase above that plateau level with increasing dose. The data suggest that at fluences of high-energy protons or iron ions less than about 5 cGy, the response in irradiated cell populations may be dominated by the bystander response.     

Relative cataractogenic effects of X rays, fission-spectrum neutrons, and 56Fe particles: a comparison with mitotic effects

The eyes of Sprague-Dawley rats were irradiated with doses of 2.5-10 Gy 250-kVp X rays, 1.25-2.25 Gy fission-spectrum neutrons (approximately 0.85 MeV), or 0.1-2.0 Gy 600-MeV/A 56Fe particles. Lens opacifications were evaluated for 51-61 weeks following X and neutron irradiations and for 87 weeks following X and 56Fe-particle irradiations. Average stage of opacification was determined relative to time after irradiation, and the time required for 50% of the irradiated lenses to achieve various stages (T50) was determined as a function of radiation dose. Data from two experiments were combined in dose-effect curves as T50 experimental values taken as percentages of the respective T50 control values (T50-% control). Simple exponential curves best describe dose responsiveness for both high-LET radiations. For X rays, a shallow dose-effect relationship (shoulder) up to 4.5 Gy was followed at higher doses by a steeper exponential dose-effect relationship. As a consequence, RBE values for the high-LET radiations are dose dependent. Dose-effect curves for cataracts were compared to those for mitotic abnormalities observed when quiescent lens epithelial cells were stimulated mechanically to proliferate at various intervals after irradiation. Neutrons were about 1.6-1.8 times more effective than 56Fe particles for inducing both cataracts and mitotic abnormalities. For stage 1 and 2 cataracts, the X-ray Dq was 10-fold greater and the D0 was similar to those for mitotic abnormalities initially expressed after irradiation.     

Persistence of apoptosis and inflammatory responses in the heart and bone marrow of mice following whole-body exposure to 28Silicon (28Si) ions

It has been well established that the bone marrow (BM) is a radiosensitive tissue, but the radiosensitivity of the heart is poorly understood. In this study, we investigated the comparative effects of ²⁸Silicon (²⁸Si) ions (one type of heavy ion found in space) on tissue from the heart and the BM of exposed mice. We gave adult male CBA/CaJ mice a whole-body exposure to a total dose of 0, 0.1, 0.25, or 0.5 Gy of 300 MeV/nucleon (n) ²⁸Si ions, using a fractionated schedule (two exposures, 15 days apart that totaled each selected dose). The heart and BM were collected from 5 mice per treatment group at various times up to 6 months post-irradiation. In each mouse, we obtained tissue lysates from the heart and from the total population of BM cells for measuring the levels of cleaved poly (ADP-ribose) polymerase (cleaved PARP, a marker of apoptotic cell death) and the levels of activated nuclear factor-kappa B (NF-κB) and selected NF-κB-regulated cytokines known to be involved in inflammatory responses. Our data showed that, up to 6 months post-irradiation, the levels of apoptotic cell death and inflammatory responses in tissues from the heart and BM collected from exposed mice were statistically higher than those in sham controls. Hence, these findings are suggestive of chronic apoptotic cell death and inflammation in both tissues after exposure to ²⁸Si ions. In summary, our data are indicative of a possible association between exposure to ²⁸Si ions during space flight and long-term health risk.     

A murine model for bone loss from therapeutic and space-relevant sources of radiation.

Cancer patients receiving radiation therapy are exposed to photon (gamma/X-ray), electron, and less commonly proton radiation. Similarly, astronauts on exploratory missions will be exposed to extended periods of lower-dose radiation from multiple sources and of multiple types, including heavy ions. Therapeutic doses of radiation have been shown to have deleterious consequences on bone health, occasionally causing osteoradionecrosis and spontaneous fractures. However, no animal model exists to study the cause of radiation-induced osteoporosis. Additionally, the effect of lower doses of ionizing radiation, including heavy ions, on general bone quality has not been investigated. This study presents data developing a murine model for radiation-induced bone loss. Female C57BL/6 mice were exposed to gamma, proton, carbon, or iron radiation at 2-Gray doses, representing both a clinical treatment fraction and spaceflight exposure for an exploratory mission. Mice were euthanized 110 days after irradiation. The proximal tibiae and femur diaphyses were analyzed using microcomputed tomography. Results demonstrate profound changes in trabecular architecture. Significant losses in trabecular bone volume fraction were observed for all radiation species: gamma, (-29%), proton (-35%), carbon (-39%), and iron (-34%). Trabecular connectivity density, thickness, spacing, and number were also affected. These data have clear implications for clinical radiotherapy in that bone loss in an animal model has been demonstrated at low doses. Additionally, these data suggest that space radiation has the potential to exacerbate the bone loss caused by microgravity, although lower doses and dose rates need to be studied.     

Effect of radiation dose on the recovery of aerobic and anaerobic bacteria from mice

The presence of aerobic and anaerobic bacteria in the blood, spleen, and liver was investigated in mice that were exposed to 7, 8, 9, or 10 Gy 60Co radiation. Microorganisms were detected more often in animals exposed to higher doses of radiation. The number of mice that were culture positive and the number of isolates in one site increased with increasing dose. Bacteria were recovered in mice killed at various times after radiation, in 3 of 100 mice exposed to 7 Gy, in 13 of 100 irradiated with 8 Gy, in 23 of 90 exposed to 9 Gy, and in 34 of 87 irradiated with 10 Gy. The predominant organisms recovered were Escherichia coli, anaerobic Gram-positive cocci, Proteus mirabilis, Staphylococcus aureus, and Bacteroides spp. Escherichia coli and anaerobes were more often isolated in animals exposed to 10 Gy, while S. aureus was more often recovered in those irradiated with 9 Gy. These data demonstrate a relationship between the dose of radiation and the rate of infection due to enteric aerobic and anaerobic bacteria.     

Combined action of X-rays and nonylphenol on mouse sperm

The aim of this study was to assess the effects of 2-weeks’ X-ray and/or nonylphenol (NP) exposure on male mice’s sperm count and quality. Pzh:SFIS mice were exposed to X-rays (0.05 Gy, 0.10 Gy, 0.20 Gy) or to nonylphenol (25 mg/kg bw, 50 mg/kg bw, 100 mg/kg bw) or to both agents (0.05 Gy + 25 mg/kg bw NP, 0.10 Gy + 50 mg/kg bw NP). At 24 h and 5 weeks after the end of exposure the sperm count, morphology and frequency of DNA damage in the male germ cells were estimated. Each agent alone diminished sperm count and morphology. The dose of 0.05 Gy of X-rays decreased the frequency of DNA damage. Combined exposure to lower doses of both agents significantly improved sperm morphology and decreased the level of DNA damage compared to one agent alone. Combined exposure to higher doses reduced the frequency of DNA damage compared to the effect of the appropriate dose of NP. Results of combined exposure to low doses of both agents suggest that 0.05 Gy of X-rays stimulate the DNA damagecontrol system and in consequence repair of DNA caused by X-rays and NP. It may be correlated with increased antioxidant capacity.     

Repair of DNA damage induced by accelerated heavy ions in mammalian cells proficient and deficient in the non-homologous end-joining pathway

Human and rodent cells proficient and deficient in non-homologous end joining (NHEJ) were irradiated with X rays, 70 keV/microm carbon ions, and 200 keV/microm iron ions, and the biological effects on these cells were compared. For wild-type CHO and normal human fibroblast (HFL III) cells, exposure to iron ions yielded the lowest cell survival, followed by carbon ions and then X rays. NHEJ-deficient xrs6 (a Ku80 mutant of CHO) and 180BR human fibroblast (DNA ligase IV mutant) cells showed similar cell survival for X and carbon-ion irradiation (RBE = approximately 1.0). This phenotype is likely to result from a defective NHEJ protein because xrs6-hamKu80 cells (xrs6 cells corrected with the wild-type KU80 gene) exhibited the wild-type response. At doses higher than 1 Gy, NHEJ-defective cells showed a lower level of survival with iron ions than with carbon ions or X rays, possibly due to inactivation of a radioresistant subpopulation. The G(1) premature chromosome condensation (PCC) assay with HFL III cells revealed LET-dependent impairment of repair of chromosome breaks. Additionally, iron-ion radiation induced non-repairable chromosome breaks not observed with carbon ions or X rays. PCC studies with 180BR cells indicated that the repair kinetics after exposure to carbon and iron ions behaved similarly for the first 6 h, but after 24 h the curve for carbon ions approached that for X rays, while the curve for iron ions remained high. These chromosome data reflect the existence of a slow NHEJ repair phase and severe biological damage induced by iron ions. The auto-phosphorylation of DNA-dependent protein kinase catalytic subunits (DNA-PKcs), an essential NHEJ step, was delayed significantly by high-LET carbon- and iron-ion radiation compared to X rays. This delay was further emphasized in NHEJ-defective 180BR cells. Our results indicate that high-LET radiation induces complex DNA damage that is not easily repaired or is not repaired by NHEJ even at low radiation doses such as 2 Gy.     

Influence of ionizing radiation, application of iron ions and their chelate complexes on the oxidative status of blood serum of rats

Influence of ionizing radiation, ions of iron and their chelate complexes on the oxidative status of blood serum of rats has been investigated. Animals were irradiated by gamma-rays 60Co at a dose of 4 Gy. Ions of iron and iron chelates with nitrilotriacetic acid and citric acid were introduced into animals intra-abdominally at a doze of 10 mg of iron on 1 kg of body weight. The oxidative status of blood serum was determined according to the estimated content of oxidizing peroxide equivalents which oxidize ferrous iron in ferric iron with the subsequent estimation of ferric iron by means of xylenol orange. We also estimated the total content of iron in blood serum using ferrozine as an indicator. The oxidative status was defined 24 and 96 hours after irradiation and 2 hours after introduction of iron ions and their chelates. The research conducted has shown that the concentration of oxidizing peroxide equivalents in serum and the total iron concentration increase 1.47 times and 1.63 times correspondingly 24 hours after irradiation. The increase in the content of oxidizing peroxide equivalents and iron owing to Fenton's reaction can lead to the appearance of OH* radical and raise the level of damage of nuclear and membrane structures in irradiated cells. 2 hours after introduction of iron ions and their chelates, the content of oxidizing peroxide equivalents increased in the blood serum of irradiated and non-irradiated rats, and the maximum effect was observed when introducing ferrous iron and its chelate with citric acid.     

Chromosomes lacking telomeres are present in the progeny of human lymphocytes exposed to heavy ions

High-charge and energy (HZE) nuclei represent one of the main health risks for human space exploration, yet little is known about the mechanisms responsible for the high biological effectiveness of these particles. We have used in situ hybridization probes for cross-species multicolor banding (RxFISH) in combination with telomere detection to compare yields of different types of chromosomal aberrations in the progeny of human peripheral blood lymphocytes exposed to either high-energy iron ions or gamma rays. Terminal deletions showed the greatest relative variation, with many more of these types of aberrations induced after exposure to accelerated iron ions (energy 1 GeV/nucleon) compared with the same dose of gamma rays. We found that truncated chromosomes without telomeres could be transmitted for at least three cell cycles after exposure and represented about 10% of all aberrations observed in the progeny of cells exposed to iron ions. On the other hand, the fraction of cells carrying stable, transmissible chromosomal aberrations was similar in the progeny of cells exposed to the same dose of densely or sparsely ionizing radiation. The results demonstrate that unrejoined chromosome breaks are an important component of aberration spectra produced by the exposure to HZE nuclei. This finding may well be related to the ability of such energetic particles to produce untoward late effects in irradiated organisms.