Radiation-induced human chromosome aberrations. II. Human in vitro irradiation compared to in vitro and in vivo irradiation of marmoset leukocytes

Whole blood cultures from humans and from the New World primate, Saguinus fuscicollis, were irradiated with various doses of 250 kV X-rays. The resulting centric ring plus dicentric aberration yields were fitted to the three models, Y = a+bD, Y = a+bD+cD², and Y = a+cD², by least squares regression. In both instances the best fit was to the model Y = a+bD+cD², with coefficients of the one- and two-track components for human and marmoset being: b = (0.78 ± 0.09)·10⁻³, c = (5.92 ± 0.31)·10⁻⁶, and b = (1.11 ± 0.36)·⁻³, c = (7.7 ± 1.7)·10⁻⁶, respectively.     

Mutagenic effectiveness of 14.1 MeV neutrons and 200 kV X-rays at the dumpy complex locus of Drosophila melanogaster.

The effectiveness of 14.1 MeV neutrons relative to 200 kV X-rays for the induction of the various kinds of dumpy mutation in mature sperm of Drosophila melanogaster was investigated. The estimated RBE values are: 0.52 for all complete mutations; 0.64 for the (olv, ov) types; 0.33 for the (ol, lv, o, v, c) types; 0.33 for all fractional mutations. These data lend support to the thesis that (1) complete dumpy mutations of the olv and ov types are more frequently associated with chromosomal aberrations than those of the ol, lv, o, v and c types, and (2) fractional mutations and complete mutations of the (ol, lv, o, v, c) types are most probably point mutational events.     

Comparative study of gamma-ray and high-energy carbon ion irradiation on negative gravitaxis inEuglena gracilisZ

The effects of ⁶⁰Co gamma-ray and 290 MeV/amu carbon ion irradiation on negative gravitaxis was studied in the photosynthetic flagellate Euglena gracilis strain Z in a dose-response dependent manner. Cells were exposed to the doses (0-200 Gy for water). The negative gravitaxis was quantified by the r-value observed in a recently developed biomonitoring system. The present results demonstrate the inhibitory effects of gamma-rays and 290 MeV/amu carbon ions on negative gravitaxis of the Euglena gracilis strain Z. The 290 MeV/amu carbon ions had a greater impact at a low dose (<40 Gy) than the ⁶⁰Co gamma-rays.     

Chromosomal rearrangements induced in mouse spermatogonia by 14.5-MeV neutrons

Inbred CBA male mice were irradiated with 14.5-MeV neutrons. Three acute doses, 75, 150 and 250 rad, and one chronic dose, 250 rad, were given. The percentages of affected spermatocytes as counted from reciprocal translocations which had been induced in spermatogonia were 0.7, 0.8 and 1.6 respectively for the acute series and 2.2 after chronic exposure. The data could be fitted to a linear or concave curvilinear regression line. There seemed to be a slight increase of damage with dose, even if the percentages were generally lower than those reported earlier for fast neutrons with energies around 1 MeV. The existence of dose-rate effects is discussed, and the conclusion drawn so far is that there seems to be no such effect either for 1-MeV fast neutrons or 14.5-MeV high energy neutrons. The term “reversed dose-rate effect”, as used earlier, relates to another phenomenon. The difference between the point estimates for the chronic and acute 250 rad series is not significant. The effectiveness of neutrons with energies around 14 MeV versus neutrons with energies around 1 MeV is discussed.     

Studies on the induction of translocations in mouse spermatogonia. IV. Effects of acute gamma-irradiation

The rate of induction of reciprocal translocations by 56–816 R exposures of mouse spermatogonia to acute γ-irradiation (95 R/min) was determined by cytological examination of descendant spermatocytes. The dose-response relationship did not differ significantly from linearity and had a regression coefficient of 1.8·10⁻⁴ per R with respect to translocations per spermatocyte. Further analysis at exposures below 816 R (considered less likely to produce distortion) showed that the quadratic regression of best fit had too small a square-law component to account for the very low frequency of translocations obtained after chronic γ-exposures in a previous experiment. The possibility is discussed that there is some extra factor, besides the diminution of the square-law component, which operates to reduce the yield after protracted exposures.     

The regulation of human exposure to mutagens amidst scientific controversy

Human peripherial lymphocytes were irradiated with different doses of 15.0-MeV neutrons. The frequency of different aberration types was determined and the dose-response relation was calculated. The data were fitted by least-squared regression analysis to different models. The dicetric, dicentric+centric ring, and different acentric data gave the best fit to the linear quadratic model. The RBE of 15.0-MeV neutrons versus 220 kV X-rays decreased significantly with increasing dose.     

Relative biological effectiveness of x-rays and fast neutrons in inducing translocations in mouse spermatogonia

The dose-response relationships for inducing translocations in the spermatogonia of mice were studied, and they were compared for 200 kVp X-rays and 2 MeV fast neutrons. The dose response for fast neutrons was markedly convex; more precisely, the response obtained was linear in the dose range from 24 to 94 rad with a regression coefficient of 11.36·10^?4, but decreased for a further increase in dose up to 267 rad. On the other hand, that for X-rays showed a linear dose-response relationship from 48 to 672 rad with a regression coefficient of 2.69·10^?4. The relative biological effectiveness for inducing translocations in the spermatogonia of mice was compared for the linear parts of the dose response in both types of radiation, and the relative biological effectiveness (RBE) value was 4.22.     

Chromosome aberrations induced in human peripheral blood lymphocytes using heavy particles from 10 B (n, ) 7 Li reaction

The relationship between α-particle dose and chromosome aberration yield was studied in human peripheral blood leukocytes cultured in vitro. The α-irradiation was produced from thermal neutron capture by boron, according to the nuclear reaction ¹⁰B (n, α)⁷Li. Blood samples containing 49 μg ¹⁰B per ml were exposed to the thermal neutrons in a reactor at a flux density of 2·10⁷n/cm²s. By subtracting the rad dose due to the reactor radiations alone from that due to both boron capture and the reactor radiations, the rad dose rate of heavy particles was estimated. The dicentric yield appeared to follow a linear response up to about 18 rad and then showed signs of “saturation”. Comparison with 250 kV X-ray data (doses up to 510 rad) gave an RBE of 22.97.     

Light dependency of resistance to ionizing radiation in Euglena gracilis

The resistance of Euglena gracilis strains Z (wild type) and SM-ZK (chloroplast-deficient mutant) to ionizing radiation was investigated. The colony forming ability of E. gracilis strain Z was higher than that of strain SM-ZK after 60Cogamma-irradiation. For both strains, the resistance of light-grown cells was higher than that of dark-grown cells, suggesting that the light conditions during culture contribute to the radiation resistance of E. gracilis. The comet assay showed that the ability of rejoining DNA double-strand breaks (dsb) was much higher in the light-grown cells. These results suggest that E. gracilis possesses a light-induced repair system to cope with DNA dsb.     

High yields of isochromatid breaks and successive formation of chromosome exchanges may lead to reproductive cell death following high-LET irradiation

To clarify the relationship between cell death and chromosomal aberrations following exposure to heavy-charged ion particles beams, exponentially growing Human Salivary Gland Tumor cells (HSG cells) were irradiated with various kinds of high energy heavy ions; 13 keV/μm carbon ions as a low-LET charged particle radiation source, 120 keV/μm carbon ions and 440 keV/μm iron ions as high-LET charged particle radiation sources. X-rays (200 kVp) were used as a reference. Reproductive cell death was evaluated by clonogenic assays, and the chromatid aberrations in G2/M phase and their repairing kinetics were analyzed by the calyculin A induced premature chromosome condensation (PCC) method. High-LET heavy-ion beams introduced much more severe and un-repairable chromatid breaks and isochromatid breaks in HSG cells than low-LET irradiation. In addition, the continuous increase of exchange aberrations after irradiation occurred in the high-LET irradiated cells. The cell death, initial production of isochromatid breaks and subsequent formation of chromosome exchange seemed to be depend similarly on LET with a maximum RBE peak around 100–200 keV/μm of LET value. Conversely, un-rejoined isochromatid breaks or chromatid breaks/gaps seemed to be less effective in reproductive cell death. These results suggest that the continuous yield of chromosome exchange aberrations induced by high-LET ionizing particles is a possible reason for the high RBE for cell death following high-LET irradiation, alongside other chromosomal aberrations additively or synergistically.     

X-ray induction of dominant lethals in late spermatids and mature spermatozoa of Drosophila melanogaster: the role of oxygenation

The role of oxygenation in determining the sensitivity to the induction of dominant lethals was examined in late spermatids and mature spermatozoa of Drosophila melanogaster. 0–2-h-old or 7-day-old Oregon-K males were irradiated with different X-ray exposures in nitrogen, air or in oxygen and the frequencies of dominant lethals induced in these stages were studied. The results obtained confirm and extend Sobels' earlier observations and the interpretation derived therefrom namely, that under normal conditions in air, mature spermatozoa are characterised by a higher degree of oxygenation than late spermatids and this difference is sufficient to explain the differential response of these stages. Similar Oxygen-Enhancement-Ratios(OERs) (of about 2) were obtained for both the cell stages. The present data also revealed that late spermatids are significantly less sensitive than mature spermatozoa to the X-ray-induction of dominant lethals in a nitrogen atmosphere. A plausible mechanism is suggested to explain this observation.     

Influence of waste water from the paper industry and UV-B radiation on the photosynthetic efficiency of Euglena gracilis

The green flagellate Euglena gracilis has been used as a model organism to elucidate the possible large-scale and short-term effects of waste substances from the pulp and paper industry on photosynthetic efficiency (PE). Different concentrations of waste substances before and after treatment in a cleaning system were studied. The uncleaned sample at concentrations up to 1:10 and the cleaned sample at concentrations up to 1:5 showed stimulating effects on the PE after 7 days of incubation compared to the control. The effects of waste substances on the PE of E. gracilis were also studied in combination with short-term studies (20 and 40 min) of ultraviolet-B radiation (UV-B, 280–320 nm). It was shown that increasing concentrations of the uncleaned sample had continuously stimulating effects on the PE and worked protectively against UV-B radiation. The cleaned sample exhibited no effects, or negative effects, on the PE of E. gracilis together with UV-B radiation compared to the experiments with only UV-B radiation. At the concentration 1:1 of the cleaned sample an increase in the PE was detected due to the high concentration of the coloured substances and a decrease in the UV-B penetration. PE revealed itself to be highly sensitive for detecting toxic effects on E. gracilis and is thus very promising for use in regular toxicity tests of waste water from pulp and paper industry. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effect of beam shape on physical parameters of head and neck simultaneous-integrated boost intensity-modulated radiation therapy

Aim

To evaluate the influence of the beam shape created by X-rays with “flat beams” and without “flattening-filter-free [FFF] beams” a flattening filter, and the isocenter locations for FFF beams on the treatment of a large irradiated volume for tumours.

An Effective Method for Detection and Analysis of DNA Damage Induced by Heavy-Ion Beams

We have developed an efficient system to detect and analyze DNA mutations induced by heavy-ion beams in Arabiopsis thaliana. In this system, a stable transgenic Arabidopsis line that constitutively expresses a yellow fluorescent protein (YFP) by a single-copy gene at a genomic locus was constructed and irradiated with heavy-ion beams. The YFP gene is a target of mutagenesis, and its loss of function or expression can easily be detected by the disappearance of YFP signals in planta under microscopy. With this system, a ¹²C⁶⁺-induced mutant with single deletion and multiple base changes was isolated.     

Variability of Wax Ester Fermentation in Natural and Bleached Euglena gracilis Strains in Response to Oxygen and the Elongase Inhibitor Flufenacet

ABSTRACT. Euglena gracilis is able to synthesize adenosine triphosphate under anaerobic conditions through a malonyl-independent fatty acid synthesis leading to wax ester fermentation. Mitochondrial fatty acid synthesis uses acetyl-CoA and propionyl-CoA as C2- and C3-donors for de novo synthesis of even- and odd-numbered fatty acids, respectively. Euglena' s wax ester fermentation has only been described in the E. gracilis strain 1224-5/25 Z. Here we investigate eight E. gracilis strains isolated in 1932–1958 from different localities in Europe and two bleached substrains of E. gracilis 1224-5/25, obtained by treatment with streptomycin and ofloxacin, and examine their anaerobic growth, wax ester fermentation, and wax ester composition. Under ambient oxygen levels, all strains accumulated wax esters in concentrations between 0.3% and 3.5% of the dry weight, but the strains revealed marked differences in wax ester accumulation with respect to anaerobic growth. Most fermenting strains tested showed increased wax ester synthesis under anaerobic conditions as well as the increased synthesis of odd-numbered fatty acids and alcohols suggesting an activation of the mitochondrial fatty acid biosynthesis pathway. Addition of the elongase inhibitor flufenacet to the growth medium specifically reduced the accumulation of odd-numbered fatty acids and alcohols and tended to increase the overall yield of anaerobic wax esters.     

ATR signaling cooperates with ATM in the mechanism of low dose hypersensitivity induced by carbon ion beam

Little work has been done on the mechanism of low dose hyper-radiosensitivity (HRS) and later appeared radioresistance (termed induced radioresistance (IRR)) after irradiation with medium and high linear energy transfer (LET) particles. The aim of this study was to find out whether ATR pathway is involved in the mechanism of HRS induced by high LET radiation. GM0639 cells and two ATM deficient/mutant cells, AT5BIVA and AT2KY were irradiated by carbon ion beam. Thymidine block technique was developed to enrich the G2-phase population. Radiation induced early G2/M checkpoint was quantitatively assess with dual-parameter flow cytometry by detecting the cells positive for phospho-histone H3. The involvement of ATR pathway in HRS/IRR response was detected with pretreatment of specific inhibitors prior to carbon ion beam. The link between the early G2/M checkpoint and HRS/IRR under carbon ion beam was first confirmed in GM0639 cells, through the enrichment of cell population in G2-phase or with Aurora kinase inhibitor that attenuates the transition from G2 to M phase. Interestingly, the early G2/M arrest could still be observed in ATM deficient/mutant cells with an effect of ATR signaling, which was discovered to function in an LET-dependent manner, even as low as 0.2 Gy for carbon ion radiation. The involvement of ATR pathway in heavy particles induced HRS/IRR was determined with the specific ATR inhibitor in GM0639 cells, which affected the HRS/IRR occurrence similarly as ATM inhibitor. These data demonstrate that ATR pathway may cooperate with ATM in the mechanism of low dose hypersensitivity induced by carbon ion beam.     

Responses of the photosynthetic flagellate,Euglena gracilis,to hypergravity

Motility and orientation has been studied in the unicellular photosynthetic flagellate, Euglena gracilis, using real time image analysis capable of tracking up to 200 cells simultaneously in the slow rotating centrifuge microscope (NIZEMI) which allows one to observe the cells' swimming behavior during centrifugation accelerations between 1 g and 5 g. At 1 g the cells show a weak negative gravitaxis, which increases significantly at higher accelerations up to about 3 g. Though most cells were capable of swimming even against an acceleration of 4.5 g, the degree of gravitaxis decreased and some of the cells were passively moved downward by the acceleration force; this is true for most cells at 5 g. The velocity of cells swimming against 1 g is about 10% lower than that of cells swimming in other directions. The velocity decreases even more drastically in cells swimming against higher acceleration forces than those at 1 g. The degree of gravitactic orientation drastically decreases after short exposure to artificial UV radiation which indicates that gravitaxis may be due to an active physiological perception rather than a physical effect such as an asymmetry of the center of gravity within the cell. Offprint requests to: D.-P. Häder     

低剂量率下高线性能量转移碳离子束辐照人类唾液腺细胞的存活效应

利用日本千叶重离子医用加速器 HIMAC 提供的碳离子束,对人类唾液腺细胞 (HSG) 在剂量率为 0.5 Gy/h 的低剂量率条件下进行了辐照,运用标准的克隆形成法得到了 3 种不同剂量平均线性能量转移 (LET) 碳离子束辐照 HSG 细胞的剂量存活效应 . 与先前 HSG 细胞在治癌剂量率 (1~5 Gy/min) 下对相近剂量平均 LET 碳离子束辐照的剂量存活效应数据相比, HSG 细胞对高 LET 碳离子束辐射表现出明显的剂量率效应 . 为在相同条件下得到碳离子束对 HSG 细胞的相对生物学效应 (RBE) ,利用 60Co-γ射线在剂量率为 0.5 Gy/h 的条件下辐照了 HSG 细胞,得到该细胞系对低 LET 射线响应的剂量存活效应 . 与先前在治癌剂量率下得到的 RBE 值相比,低剂量率条件下得到的 RBE 值总体减小 . 由实验发现的剂量率效应及低剂量率条件下 RBE 值的减小,表明由高 LET 碳离子束造成的辐射损伤在低剂量率条件下也存在着显著的修复效应 . 据此,对辐射造成细胞致死的原因进行了探讨 .     

The stoichiometry of ion fluxes during Sr2+-induced oscillations in mitochondria

A quantitative study of H⁺, K⁺, Sr²⁺ and succinate fluxes in Sr²⁺-induced oscillatory state of rat liver mitochondria is presented. It was shown that oscillation of succinate content in mitochondria occurs synchronously with oscillations of the cation fluxes. Total charge transferred across the membrane by the registered cations and the succinate-anion is equal to zero. Passive H⁺-influx has been calculated at all stages of the oscillatory cycle. The conclusion is made that electroneutral 2 H⁺/Sr²⁺ exchange is periodically induced in mitochondria. A value of (2 ± 0.2) · 10^-7 mol Sr²⁺/min per mg protein. has been determined for Sr²⁺ by this type of exchange.