Showing papers in "International Journal of Radiation Biology in 1987"
TL;DR: Using methods derived from Maxam and Gilbert sequencing procedures and DNA fragment 32P-labelled at one end, it has been shown that the alkali-labile sites in DNA induced by radiation are strongly dependent on the DNA base sequence.
Abstract: Application of modern methods of organic chemistry and recombinant DNA technologies has provided new insights in the field of DNA radiation damage and its repair. An overview of the chemical nature of the lesions inflicted on DNA by ionizing radiation is presented. The structures of 29 different DNA modified base or sugar residues are shown in comprehensive formation schemes. A fraction of radiation-induced modified bases is spontaneously released from the DNA chain during irradiation. Another part remains attached to the DNA chain backbone and for its characterization mild formic acid or enzymatic hydrolysis have been used. Starting from the chemical formulae of the altered base residues, the specific repair enzymes and their modes of action are discussed. Various glycosylases and endonucleases have been purified to homogeneity, and in some cases the gene which encodes the protein cloned. Using methods derived from Maxam and Gilbert sequencing procedures and DNA fragment 32P-labelled at one end, it has been shown that the alkali-labile sites in DNA induced by radiation are strongly dependent on the DNA base sequence. Enzymatic methods have been used to analyse the DNA base defects produced by gamma-irradiation of cells under in vivo conditions. Structures of modified bases were the same as those observed when DNA was irradiated in aqueous solution.
384 citations
TL;DR: The Chemical Basis of Radiation Biology as discussed by the authors was the first publication of a journal dedicated to the study of radiation biology and related studies in physics, chemistry and medicine, Vol. 52, No. 6, pp. 976-976.
Abstract: (1987). The Chemical Basis of Radiation Biology. International Journal of Radiation Biology and Related Studies in Physics, Chemistry and Medicine: Vol. 52, No. 6, pp. 976-976.
314 citations
TL;DR: In this article, atoms, radiation and radiation protection are discussed in the International Journal of Radiation Biology and Related Studies in Physics, Chemistry and Medicine: Vol. 51, No. 5, pp. 951-951.
Abstract: (1987). Atoms, Radiation and Radiation Protection. International Journal of Radiation Biology and Related Studies in Physics, Chemistry and Medicine: Vol. 51, No. 5, pp. 951-951.
185 citations
TL;DR: Using the neutral filter elution technique, the induction of DNA double-strand breaks (dsb) has been measured in 250 kVp X-irradiated V79-379A Chinese hamster cells irradiated under air or nitrogen, and there is no general correlation between induced dsb and lethal effect.
Abstract: SummaryUsing the neutral filter elution technique, the induction of DNA double-strand breaks (dsb) has been measured in 250 kVp X-irradiated V79-379A Chinese hamster cells irradiated under air or nitrogen. The dose–effect curves for induced dsb were curvilinear, mirroring cell survival curves, such that there was an approximately linear relationship between induced dsb and lethal lesions (− ln (cell survival)) which was independent of oxygen. With cells irradiated with 2·3 MeV neutrons or 238Pu α-particles the correlations between lethal events and dsb, although also approximately linear, do not match those for X-rays. With neutrons there is approximately a 2·5-fold reduction in the level of dsb induction per lethal event. Thus either the apparently linear relationships found are spurious, and there is no general correlation between induced dsb and lethal effect, or there are qualitative differences between neutron, α-particle and X-ray induced dsb that give them differing probabilities of cell kill.
120 citations
TL;DR: Ataxia-telangiectasia cells (AT2BE) and normal fibroblasts exhibited similar dsb rejoining capacity following α-irradiation, but showed marked differences in the rejoining kinetics of dsb induced by γ-rays or bleomycin.
Abstract: The rejoining of DNA double strand breaks (dsb) induced by 60Co gamma-rays, 241Am alpha-particles or bleomycin was measured by neutral filter elution. In agreement with their colony-forming ability, ataxia-telangiectasia cells (AT2BE) and normal fibroblasts exhibited similar dsb rejoining capacity following alpha-irradiation, but showed marked differences in the rejoining kinetics of dsb induced by gamma-rays or bleomycin.
117 citations
TL;DR: 2,5-Me2THF can be regarded as a model for the sugar moiety of DNA where the C(4')-radical is known to lead to DNA strand breakage and the possible role of cellular thiols in the repair of the C (4') DNA radical is discussed.
Abstract: Thiyl radicals (RS) formed by the reaction of radiolytically generated OH radicals with thiols, e.g. 1,4-dithiothreitol (DTT), react with cis- and trans-2,5-dimethyltetrahydrofuran by abstracting an H atom in the alpha-position to the ether function (k approximately equal to 5 X 10(3) dm3 mol-1 s-1). The so-formed planar ether radical is 'repaired' by the thiol (k = 6 X 10(8) dm3 mol-1 s-1) thereby regenerating a cis- or trans-2,5-dimethyltetrahydrofuran molecule. In this reaction a thiyl radical is reproduced. Thus trans-2,5-Me2THF from cis-2,5-Me2THF and vice versa are formed in a chain reaction: at a dose rate of 2.8 X 10(-3) Gys-1 and a trans-2,5-Me2THF concentration of 1 X 10(-2) mol dm-3 using DTT as the thiol, G(cis-2,5-Me2THF) = 160 has been found. The chain reaction is very sensitive to impurities and also to disulphides such as those radiolytically formed. 2,5-Me2THF can be regarded as a model for the sugar moiety of DNA where the C(4')-radical is known to lead to DNA strand breakage. The possible role of cellular thiols in the repair of the C(4') DNA radical, and also the conceivable role of thiyl radicals inducing DNA strand breakage, are discussed.
108 citations
TL;DR: Chinese hamster ovary cells grown in vitro were treated with bleomycin or irradiated with high doses of 60Co gamma rays and DNA strand breaks in single cells were analysed by using the newly introduced microelectrophoretic technique.
Abstract: SummaryChinese hamster ovary cells grown in vitro were treated with bleomycin or irradiated with high doses of 60Co gamma rays (200 and 400 Gy). DNA strand breaks in single cells were analysed by using our newly introduced microelectro-phoretic technique. Bleomycin seems to act in a selective manner so that in some cells the DNA is heavily degraded while in others there is only moderate or no measurable damage. In contrast, a uniform response was found after gamma irradiation. To achieve the same magnitude of DNA fragmentation as in the most severely bleomycin-damaged cells, irradiation with more than 200 Gy is required. Some 8000 double-strand breaks per cell are produced by 200 Gy which will convert the molecular weight of the DNA to the range of 108–109 dalton, and free migration of DNA fragments occurs during electrophoresis. We include also a detailed study of the DNA migration pattern following doses of 0–100 Gy gamma rays.
106 citations
TL;DR: The results demonstrate the high reactivity of both fatty acid peroxyl radicals and the flavone antioxidants in aqueous solution.
Abstract: SummaryLinoleic acid peroxyl radicals (LOO·) can be viewed as model intermediates occurring during lipid peroxidation processes. Formation and reactions of these species were investigated in aqueous alkaline solution using the technique of pulse radiolysis combined with kinetic spectroscopy. Irradiation of linoleic acid in N2O/O2-saturated solutions leads to a mixture of peroxyl radical isomers, whereas reaction of 13-hydroperoxylinoleic acid (13-LOOH) with azide radicals in N2O-saturated solution produces 13-LOO· radicals specifically. These peroxyl radicals cannot be observed directly, but their reactions with the two flavonols, kaempferol and quercetin, acting as radical-scavenging antioxidants, produced strongly absorbing aroxyl radicals (ArO·). The same aroxyl radicals were generated by ·OH and N·3 with rate constants exceeding 109 dm3 mol−1 s−1. Applying a reaction scheme that includes competing generation and decay reactions of both LOO· and ArO· radicals, we derived individual rate constants for L...
88 citations
TL;DR: The results of this study suggest that exposure of chick embryos to a 50 Hz magnetic field causes abnormal development, and that no abnormalities are induced below a threshold between 0.9 and 1 A/m.
Abstract: SummaryChick embryos were exposed to sinusoidally oscillating 50 Hz magnetic fields during their first 2 days of development. In the first series of experiments magnetic field strengths of 0·1, 0·3, 1 and 10 A/m were used. The percentage of abnormal embryos (%AE) was 16 per cent in the sham-exposed control group. %AE was increased at 1 A/m (29 per cent) and 10 A/m (32 per cent), but not at 0·1 A/m (16 per cent) or 0·3 A/m (14 per cent). In the second series of experiments field strengths of 0·4, 0·6, 0·9 and 1·35 A/m were used. %AE was 17 per cent in the control group, 10 per cent at 0·4 A/m, 19 per cent at 0·6 A/m, 17 per cent at 0·9 A/m and 36 per cent at 1·35 A/m. Only the 1·35 A/m group was significantly different from the controls. The results of this study suggest that exposure of chick embryos to a 50 Hz magnetic field causes abnormal development, and that no abnormalities are induced below a threshold between 0·9 and 1 A/m.
82 citations
TL;DR: In this paper, the authors performed an analogous study with alpha-particles at comparable dose rates, and found that alpha was substantially more effective than gamma-rays, both for cell inactivation and for neoplastic transformation at high and low dose rates.
Abstract: The findings of Hill et al. (1984) on the greatly enhanced transformation frequencies at very low dose rates of fission neutrons induced us to perform an analogous study with alpha-particles at comparable dose rates. Transformation frequencies were determined with gamma-rays at high dose rate (0.5 Gy/min), and with alpha-particles at high (0.2 Gy/min) and at low dose rates (0.83-2.5 mGy/min) in the C3H 10T1/2 cell system. alpha-particles were substantially more effective than gamma-rays, both for cell inactivation and for neoplastic transformation at high and low dose rates. The relative biological effectiveness (RBE) for cell inactivation and for neoplastic transformation was of similar magnitude, and ranged from about 3 at an alpha-particle dose of 2 Gy to values of the order of 10 at 0.25 Gy. In contrast to the experiments of Hill et al. (1984) with fission neutrons, no increased transformation frequencies were observed when the alpha-particle dose was protracted over several hours.
81 citations
TL;DR: The kinetics of repair of sublethal damage in mouse lung was studied after fractionated doses of 137Cs gamma-rays and results imply that treatments with multiple fractions per day that involve the lung will not be limited by the necessity for interfraction intervals much longer than 6 h.
Abstract: SummaryThe kinetics of repair of sublethal damage in mouse lung was studied after fractionated doses of 137Cs γ-rays. A wide range of doses per fraction (1·7–12 Gy) was given with interfraction intervals ranging from 0·5 to 24 h. The data were analysed by a direct method of analysis using the incomplete repair model. The half-time of repair (T1/2) was 0·76 h for the pneumonitis phase of damage (up to 8 months) and 0·65 h for the later phase of damage up to 12 months. The rate of repair was dependent on fraction size for both phases of lung damage and was faster after large dose fractions than after small fractions. The T1/2 was 0·6 h (95 per cent c.1. 0·53, 0·69) for doses per fraction greater than 5 Gy and 0·83 h (95 per cent c.1. 0·76, 0·92) for doses per fraction of 2 Gy. Repair was nearly complete by 6 h, at least for the pneumonitis phase of damage. To the extent that extrapolation of these data to humans may be valid, these results imply that treatments with multiple fractions per day that involve t...
TL;DR: The use of SO4.- to mimic, to some extent, the effects of direct energy deposition in DNA may assist in the understanding of the resulting molecular processes relevant to radiobiological studies.
Abstract: Using the technique of pulse radiolysis it has been demonstrated that the interaction of SO4.- with deoxynucleosides (k approximately less than 2 X 10(8)-2.3 X 10(9) dm3 mol-1 s-1) in aqueous solution at pH 7.0 results in the formation of the corresponding one-electron oxidized radicals which either deprotonate or hydrate to yield OH adducts. Based upon the ease of oxidation of the deoxynucleosides, dG, dA, dC, dT, by SO4.-, the apparent redox potentials are in the order dG much greater than dA approximately equal to dC greater than dT. With the exception of deoxyuridine, the deoxynucleoside radicals produced on interaction with SO4.- have been shown to have oxidizing properties based upon the interactions with tetranitromethane and the nitroxyls, TMPN and NPPN. The deoxynucleoside radicals (dG, dA and dC) do not interact with oxygen (k less than 10(6) dm3 mol-1 s-1) in contrast to the interaction observed with the thymidine radical (k = 2.5 X 10(7) dm3 mol-1 s-1). The implications of these findings are presented in terms of the properties of the discussed radicals as relating to those of potential DNA base radicals (positive centres) produced by direct energy deposition within DNA. The use of SO4.- to mimic, to some extent, the effects of direct energy deposition in DNA may assist in our understanding of the resulting molecular processes relevant to radiobiological studies.
TL;DR: The values obtained for the O2 addition to the thiyl radicals from glutathione and cysteine are considerable lower than those previously published, indicating that the RS.
Abstract: SummaryAbsolute rate constants for the addition of oxygen to thiyl radicals, i.e. RS + O2 → RSOO·, have been determined by applying a new competition method based on RS· formation via one-electron reduction of the corresponding disulphides, and the competition between RS· reacting with O2 and an electron donor such as ascorbate. Bimolecular rate constants have been obtained for the thiyl radicals derived from cysteine (6·1 × 107 mol−1 dm3 s−1), penicillamine (2·5 × 107 mol−1 dm3 s−1), homocysteine (8·0 × 107 mol−1 dm3 s−1), cysteamine (2·8 × 107 mol−1 dm3 s−1), 3-thiopropionic acid (2·2 × 108 mol−1 dm3 s−1) and glutathione (3·0 × 107 mol−1 dm3 s−1), respectively. The values obtained for the O2 addition to the thiyl radicals from glutathione and cysteine are considerable lower (by about two orders of magnitude) than those previously published. This indicates that the RS· + O2 reaction may be of complex nature and is generally a process which is not solely controlled by the diffusion of the reactants.
TL;DR: The cytogenetic effects of restriction endonucleases and X-rays were examined in the radiosensitive mutant Chinese hamster cell line xrs 5 and its normal parental line CHO K1 to indicate that RE-induced dsb are handled by cells in a similar way to those arising during X-ray exposure.
Abstract: The cytogenetic effects of restriction endonucleases (RE) and X-rays were examined in the radiosensitive mutant Chinese hamster cell line xrs 5 and its normal parental line CHO K1. Cells were permeabilized with Sendai virus and exposed to Pvu II and Eco RV which induce blunt-ended double-strand breaks (dsb) in the DNA of cells, or Bam H1 and Eco R1 which induce cohesive-ended dsb with a four-base overlap. Treated cells were then assayed for the presence of metaphase chromosomal aberrations by sampling at multiple fixation times and in experiments where cells were exposed to graded series of RE concentrations. Exposure to X-rays or RE causing blunt-ended dsb was found to be between two and three times more effective in xrs 5 than in CHO K1 cells. We interpret this higher chromosomal sensitivity of xrs 5 cells as reflecting the reported defect in dsb repair in xrs 5. Both xrs 5 and CHO K1 cells yielded less aberrations after exposure to Bam H1 or Eco R1 than after exposure to Pvu II or Eco RV, confirming our previous results and demonstrating that cohesive-ended dsb are less damaging than blunt-ended dsb. Multiple fixation time experiments showed that the higher sensitivity of xrs 5 was evident at several different sampling times after treatment. Similarly the low yield of aberrations after exposure of cells to Bam H1 was evident at all sampling times. Overdispersion of chromosomal aberrations was observed in samples exposed to RE. This is thought to be due to a non-uniform permeabilization of the cell population to RE. Our results indicate that RE-induced dsb are handled by cells in a similar way to those arising during X-ray exposure.
TL;DR: It is proposed that 7 reacts with 1,3-DMU by electron transfer, albeit more slowly (k approximately 1.2 X 10(4) dm3 mol-1 s-1) than does SO4(.-).
Abstract: The sulphate radical SO4(.-) reacts with 1,3-dimethyluracil (1,3-DMU) (k = 5 X 10(9) dm3 mol-1 s-1) thereby forming with greater than or equal to 90 per cent yield the 1,3-DMU C(5)-OH adduct radical 4 as evidenced by its absorption spectrum and its reactivity toward tetranitromethane. Pulse-conductometric experiments have shown that a 1,3-DMU-SO4(.-) aduct 3 as well as the 1,3-DMU radical cation 1, if formed, must be very short-lived (t1/2 less than or equal to 1 microsecond). The 1,3-DMU C(5)-OH adduct 4 reacts slowly with peroxodisulphate (k = 2.1 X 10(5) dm3 mol-1 s-1). It is suggested that the observed new species is the 1,3-DMU-5-OH-6-SO4(.-) radical 7. At low dose rates a chain reaction is observed. The product of this chain reaction is the cis-5,6-dihydro-5,6-dihydroxy-1,3-dimethyluracil 2. At a dose rate of 2.8 X 10(-3) Gys-1 a G value of approximately 200 was observed ([1,3-DMU] = 5 X 10(-3) mol dm-3; [S2O8(2-)] = 10(-2) mol dm-3; [t-butanol] = 10(-2) mol dm-3). The peculiarities of this chain reaction (strong effect of [1,3-DMU], smaller effect of [S2O(2-)8]) is explained by 7 being an important chain carrier. It is proposed that 7 reacts with 1,3-DMU by electron transfer, albeit more slowly (k approximately 1.2 X 10(4) dm3 mol-1 s-1) than does SO4(.-). The resulting sulphate 6 is considered to hydrolyse into 2 and sulphuric acid which is formed in amounts equivalent to those of 2. Computer simulations provide support for the proposed mechanism. The results of some SCF calculations on the electron distribution in the radical cations derived from uracil and 1-methyluracil are also presented.
TL;DR: Covalently closed circular double-stranded DNA of native plasmids was used to determine the yield of single strand breaks and double strand breaks as a consequence of X-irradiation, and G-values were calculated by competition plots.
Abstract: SummaryCovalently closed circular double-stranded DNA (CC) of native plasmids was used to determine the yield of single strand breaks (ssb) and double strand breaks (dsb) as a consequence of X-irradiation. One ssb transforms DNA of the CC form to the nicked circular form (NC), whereas one dsb produced either directly or from random coincidence of single strand breaks transforms DNA of the CC as well as of the NC form to linear DNA molecules (LI form). Plasmids with more than one dsb are cleaved to linear fragments.DNA (30–800 μg/ml) was irradiated in air-saturated sodium phosphate buffer. The different forms of DNA were separated by gel electrophoresis and their amounts measured fluorometrically using ethidium bromide. Large linear DNA fragments with the same electrophoretic mobility as the LI form were considered by using a curve-fitting procedure. From the quantitative changes of each conformation D37 values of ssb and dsb were calculated as a function of the DNA concentration. Finally G-values were cal...
TL;DR: The yield of cells with MN exposed to graded doses of 60Co gamma rays and 90KVP X-rays showed a non-linear increase with dose, indicating that terminal deletions arising from the direct ionization of DNA are a major source of the MN induced by low radiation doses.
Abstract: SummaryThe appearance of micronuclei (MN) is delayed with respect to cell division in populations of irradiated human lymphocytes, so that the length of time in culture, as well as the number of divisions, is a factor in MN assays. Using two assays that control for cell kinetics, we measured the yield of cells with MN exposed to graded doses of 60Co gamma rays and 90 KVP X-rays. The yields showed a non-linear increase with dose. They can be represented by two straight lines: the one in the range below 0·15 Gy has a slight slope, the other in the range above 0·15 Gy has a significantly greater slope. The radical scavengers cysteamine and glycerol, which reduced the MN yields sharply at 3 Gy, were less effective at 0·3 Gy, indicating that terminal deletions arising from the direct ionization of DNA are a major source of the MN induced by low radiation doses. It is likely that the non-linear dose response is due to the saturation of a DNA repair process.
TL;DR: Although more myeloid leukaemia was seen in the mice given plutonium in divided amounts than in those given the plutonium in a single injection it could not be shown that multiple injection significantly affected the yield of either late effect.
Abstract: SummaryPlutonium-239 was injected into 12-week-old female CBA/H mice in the range 1·85–18·5 kBq kg−1 either as a single injection or as 16 injections spaced at 3·5 day intervals over eight weeks. There was a highly significant increase in the yield of fully developed osteosarcomas with increased amounts of 239Pu for both modes of injection. Osteosarcomas too small to be diagnosed radiographically were also seen in many bones and small but significant yields of myeloid leukaemia were seen in animals given plutonium. Although more myeloid leukaemia was seen in the mice given plutonium in divided amounts than in those given the plutonium in a single injection it could not be shown that multiple injection significantly affected the yield of either late effect.
TL;DR: Eleven new hypoxic cell sensitizers representative of those developed in Japan between 1980 and 1985 were evaluated in vitro and in vivo in comparison with misonidazole (MISO), SR-2508, Ro 03-8799, and ANT (2-amino-5-nitrothiazole).
Abstract: Eleven new hypoxic cell sensitizers representative of those developed in Japan between 1980 and 1985 were evaluated in vitro and in vivo in comparison with misonidazole (MISO), SR-2508, Ro 03-8799, and ANT (2-amino-5-nitrothiazole). The new compounds included 2-nitroimidazole nucleoside analogues, nitrotriazoles and other nitroaromatics, non-nitro compounds, and electron-affinic compounds that readily intercalate DNA. The sensitizing activity in the EMT6 single cells correlated not only with the reduction potential but, for some compounds, also with the reactivity with non-protein sulphydryls. The sensitizers were also tested using the EMT6 spheroids and solid tumours. The patterns of changes in sensitizer enhancement ratios (SERs) for single cells, spheroids, and solid tumours were classified into two types: (1) SERs for the three testing systems were similar; and (2) SERs decreased in the order of: single cells, spheroids, and solid tumours. Only nitroimidazole and nitrotriazole derivatives belonged to the former type. RK-28 and RK-29, 2-nitroimidazoles with sugar analogue components, had in vivo effects almost equal to those of MISO. Also 3- and 4-nitrotriazole derivatives had definite in vivo effects.
TL;DR: Under the well-characterized conditions of these experiments the event frequency of alpha-particle traversals through cell nuclei is 9.8 Gy-1, from which it follows that, on average, only one in six of the alpha- particle traversal through a cell nucleus is lethal.
Abstract: SummaryConsiderable interest has been aroused in recent years by reports that the transforming and carcinogenic effectiveness of low doses of high LET radiations can be increased by reducing the dose rate, especially for transformation of 10T1/2 cells in vitro by fission-spectrum neutrons. We report on conditions which have been established for irradiation of 10T1/2 cells with high LET monoenergetic α-particles (energy of 3·2 MeV, LET of 124 keV μm−1) from 238Pu. The α-particle irradiator allows convenient irradiation of multiple dishes of cells at selectable high or low dose rates and temperatures. The survival curves of irradiated cells showed that the mean lethal dose of α-particles was 0·6 Gy and corresponded to an RBE, at high dose rates, of 7·9 at 80 per cent survival and 4·6 at 5 per cent survival, relative to 60Co γ-rays. The mean areas of the 10T1/2 nuclei, perpendicular to the incident α-particles, was measured as 201 μm2, from which it follows that, on average, only one in six of the α-particle...
TL;DR: The results indicate very little repair at the cell survival level (repair of PLD), suggesting that DNA dsbs may underlie chromosome fragmentation.
Abstract: The effect of 125I-decay on cell lethality, and induction of chromosome and DNA damage, was studied in synchronous non-cycling, G1-phase CHO-cells. For this purpose a population of mitotic cells was allowed to divide and progress through S-phase in the presence of 125IdUrd. Cells were subsequently transferred to conditioned medium (C-med) obtained from plateau-phase cultures that allowed cells to divide and accumulate in G1-phase in a non-cycling state. To accumulate 125I-induced damage, cells were kept frozen at -80 degrees C. Freezing was carried out using a new method that optimally preserves cell integrity. After various times of cold storage, cells were thawed and assayed for survival, DNA and chromosome damage, either immediately or after various times in C-med. Neutral filter elution was used to assay repair of DNA double-strand breaks (dsbs), and premature chromosome condensation was used to assay repair of chromosome fragments and induction of ring chromosomes. The results indicate very little repair at the cell survival level (repair of PLD). At the DNA level an efficient repair of DNA dsbs was observed, with kinetics similar to those observed after exposure to X-rays. At the chromosome level a fast repair of prematurely condensed chromosome fragment was observed, with a concomitant increase in the number of ring chromosomes induced. The repair kinetics of chromosome fragments and DNA dsbs were very similar, suggesting that DNA dsbs may underlie chromosome fragmentation.
TL;DR: The relative biological effectiveness (RBE) for the induction of DNA strand breaks and the efficiency of repair of these breaks in cultured diploid bovine lens epithelial cells was measured, using accelerated heavy ions in the linear energy transfer (LET)-range up to 16,200 keV/micron.
Abstract: SummaryThe relative biological effectiveness (RBE) for the induction of DNA strand breaks and the efficiency of repair of these breaks in cultured diploid bovine lens epithelial cells was measured, using accelerated heavy ions in the linear energy transfer (LET)-range up to 16 200 keV/µm At LET values above 800 keV/µm, the number of DNA strand breaks induced per particle increases both with the atomic number of the projectile and with its kinetic energy About 90 per cent or more of the strand breaks induced by ions with an LET of less than 10 000 keV/µm are repaired within 24 h Repair kinetics show a dependence on the particle fluence (irradiation dose) At higher particle fluences a higher proportion of non-rejoined breaks is found, even after prolonged periods of incubation At any LET value, repair is much slower after heavy-ion exposure than after X-irradiation This is especially true for low energetic particles with a very high local density of energy deposition within the particle track At the
TL;DR: With exponential cultures of C3H/10T1/2 cells, the effect of X-ray dose protraction on oncogenic cell transformation in the dose range 0.25-2 Gy is investigated and an empirical formula for relating slopes of dose induction curves obtained at high or reduced dose rate condition is developed.
Abstract: With exponential cultures of C3H/10T1/2 cells, we have investigated the effect of X-ray dose protraction on oncogenic cell transformation in the dose range 0.25-2 Gy. Within a particular experiment a constant exposure time was used. In different experiments exposure time varied between 1 and 5h. Cell transformation was analysed using the linear-quadratic relation, gamma (D) = alpha 1D + alpha 2D2, between transformation frequency per surviving cell and X-ray dose. Based on values of the linear coefficients, we developed an empirical formula for relating slopes of dose induction curves obtained at high or reduced dose rate condition. Our estimate of repair half-time for cell transformation with 95 per cent confidence limits is 2.4 (1.8, 3.0) h.
TL;DR: Results implicate alterations in the protein mass of the nuclear matrix in heat-induced inhibition of repair of DNA single-strand breaks in Chinese hamster ovary cells.
Abstract: The total protein mass co-isolating with the nuclear matrix or nucleoid from Chinese hamster ovary (CHO) cells was observed to increase in heated cells as a function of increasing exposure temperature between 43 degrees C and 45 degrees C or of exposure time at any temperature. The sedimentation distance of the CHO cell nucleoid in sucrose gradients increased with increasing exposure time at 45 degrees C. Both these nuclear alterations correlated in a log-linear manner with heat-induced inhibition of DNA strand break repair. A two-fold threshold increase in nuclear matrix protein mass preceded any substantial inhibition of repair of DNA single-strand breaks. When preheated cells (45 degrees C for 15 min) were incubated at 37 degrees C the nuclear matrix protein mass and nucleoid sedimentation recovered with a half-time of about 5 h, while DNA single-strand-break repair recovered with a half-time of about 2 h. When preheated cells were placed at 41 degrees C (step-down heating; SDH) a further increase was observed in the nuclear matrix protein mass and the half-time of DNA strand break repair, while nucleoid sedimentation recovered toward control values. These results implicate alterations in the protein mass of the nuclear matrix in heat-induced inhibition of repair of DNA single-strand breaks.
TL;DR: The RBEs of the KUR thermal neutron beam and the 10B(n, α)7Li reaction relative to 60Co gamma-rays were estimated as 4·62 and 6·01 at 0·1 surviving fraction, respectively.
Abstract: SummaryThe RBE of a thermal neutron beam and the 10B(n, α)7Li reaction were determined in cultured B-16 melanoma cells. The Kyoto University Research Reactor (KUR) was used as a thermal neutron source which had a very low contamination of gamma-rays and fast neutrons. The cells were irradiated with the beam in the presence or absence of 10B-boric acid. The absorbed dose from the neutron capture reaction to the cells was calculated by a method of Kitao (1975). Survival curves in both conditions had no shoulder and D0 values were 0·506 or 0·604 Gy in the presence or absence of 5 µg 10B/ml-medium, respectively. The D0 value of the 10B(n, α)7Li reaction was also estimated at 0·466 Gy, assuming each component of radiation was additive. The RBEs of the KUR thermal neutron beam and the 10B(n, α)7Li reaction relative to 60Co gamma-rays were estimated as 4·62 and 6·01 at 0·1 surviving fraction, respectively.Using these results, we calculated the absorbed dose from the 10B-compound and estimated the specific accumu...
TL;DR: Transfusion procedures could be used to advantage in the radiotherapy of some cancers by developing exchange transfusion methods to alter the hematocrit of tumour-bearing mice.
Abstract: SummaryWe have developed exchange transfusion methods to alter the haematocrit of tumour-bearing mice. The effects of anaemia and its correction by blood transfusion on the radiosensitivity of two mouse tumours (SCCVII/St and RIF-1) were studied using excision, in vivo/in vitro assay. An acute reduction in haematocrit caused a high degree of radioresistance equivalent to an increase in the hypoxic fractions by factors of 10 (SCCVII/St) and 30 (RIF-1). As the duration of the anaemia was prolonged, radioresistance was lost until within about 6 h normal radiosensitivity was observed even though the anaemia persisted. The restoration of the normal haematocrit by red blood cell transfusion after 24 h of anaemia caused increased radiosensitivity equivalent to a reduction in the hypoxic fraction by factors of 5 (SCCVII/St) and 10 (RIF-1), but again the effect was transient and normal radiosensitivity was re-established within 24–48 h of retransfusion. Measurements of 14C misonidazole (MISO) binding to RIF-1 tumo...
TL;DR: The kinetics of DNA double-strand breakage repair in X-irradiated Chinese hamster V79 cells were found to be affected by cell-cycle position and the repair of DNA d.s.b. repair was also shown to be slower in mitotic than in interphase cells.
Abstract: SummaryThe kinetics of DNA double-strand breakage (d.s.b.) repair in X-irradiated Chinese hamster V79 cells were found to be affected by cell-cycle position. In mitotic cells, the repair kinetics were monophasic with a half-time value of about 32 min, whilst in G1, S, or asynchronous cultures, the kinetics were biphasic with half-time values of around 2·7 and 27 min. The repair of DNA single-strand breakage (s.s.b) was also shown to be slower in mitotic than in interphase cells. The DNA d.s.b. repair system, in both mitotic and interphase cells, showed no evidence of saturation within the X-ray dose range covered. The implications of these findings for the mechanism of DNA d.s.b. repair and for models of ionizing radiation action are discussed.
TL;DR: The role of dithiothreitol and tetranitromethane on the yields of radiation-induced strand break formation in polyuridylic acid was studied in anoxic aqueous solutions at neutral pH by low-angle laser light-scattering.
Abstract: SummaryThe role of dithiothreitol (DTT) and tetranitromethane (TNM) on the yields of radiation-induced strand break formation in polyuridylic acid (poly(U)) was studied in anoxic aqueous solutions at neutral pH by low-angle laser light-scattering. From G (single-strand breaks) as a function of DTT concentration it follows that two different processes lead to OH radical-induced single-strand break (ssb) formation. Only one of the two processes, which accounts for 80 per cent of the ssb formation, is inhibited by DTT, the other one, 20 per cent, is not inhibited. The ‘repair’ process is attributed to H-donation to the C-6-yl radical of the uracil moiety. The C-6-yl radical is produced by OH addition to the C-5 position of the uracil moiety. It follows that the sugar radicals, in contrast to earlier suggestions, do not seem to be repaired by DTT at the low concentrations used. The strand break formation not inhibited by DTT is induced by radicals other than the uracil-6-yl radical, e.g. the uracil-5-yl or th...
TL;DR: Transformation frequencies for gamma irradiated C3H 10T1/2 cells have been analysed, taking account of the occurrence of lethal mutations in these cells, and may help to provide an explanation for the dose response plateau which is seen when these cells are irradiated and transformed foci per surviving cell are scored.
Abstract: SummaryTransformation frequencies for gamma irradiated C3H 10T½ cells have been analysed, taking account of the occurrence of lethal mutations in these cells. Lethal mutations already noted by these authors in primary thyroid and established CHO K1 cells occur at high levels in C3H 10T½ cells and lead, therefore, to considerable underestimates of transformation frequency, particularly at high doses where this is expressed on a per surviving cell basis. The results may help to provide an explanation for the dose response plateau which is seen when these cells are irradiated and transformed foci per surviving cell are scored.
TL;DR: The results suggested that the direct effect of ultrasound alone did not influence cell killing, but enhanced the hyperthermic cell killing synergistically, when both agents simultaneously acted on the cells.
Abstract: The present study was performed to elucidate the mechanism of enhanced hyperthermic cell killing by a non-thermal effect (cavitation and direct effect) of ultrasound under various gas conditions. Cavitation, as indicated by formation of DNA double-strand breaks and liberation of potassium iodide, was completely inhibited under N2O-saturated conditions, while it was promoted under O2-, Ar-, and N2-saturated conditions. Mouse L cells were treated with ultrasound (1 MHz continuous wave, spatial peak temporal average intensity; 3.7 W/cm2) and/or 44 degrees C hyperthermia in medium saturated with O2, Ar, N2 (with cavitation) or N2O (with direct effect). The synergism on cell killing by ultrasound and 44 degrees C hyperthermia was observed under N2O-saturated conditions (enhancement ratio = 1.39). On the other hand, additive enhancement was observed under O2-, Ar-, or N2-saturated conditions. In addition, when cells were treated with 44 degrees C hyperthermia before or after sonication under N2O-saturated conditions, synergistic cell killing was not observed. These results suggested that the direct effect of ultrasound alone did not influence cell killing, but enhanced the hyperthermic cell killing synergistically, when both agents simultaneously acted on the cells.