Showing papers in "Radiation and Environmental Biophysics in 1992"
TL;DR: In a recent refinement the repair capacity of the cell has been included in a track structure model by using the complete shouldered x-ray survival curve as a template for the local damage produced by the particle tracks.
Abstract: Swift heavy ions when penetrating through matter strip off those electrons having a smaller orbital velocity than the ion velocity. The remaining electrons screen the nuclear charge yielding an effective charge. The effective charge of the ions interacts predominantly with the target electrons causing excitation and ionizations of the target atoms. Using the Bethe Bloch formula for the energy loss combined with the Barkas formula for effective charge, the energy loss values as well as unrestricted and restricted linear transfer can be calculated within a few percent of accuracy. From the primary energy loss only a small fraction of 10% or less is transformed into excitation. The major part of the energy loss is used for the ionization of the target atoms and the emission of the corresponding electrons with a high kinetic energy. These electrons form the track around the trajectory of the primary ion in which two thirds of the primary energy is deposited by collisions of primary, secondary and later generations of electrons with the target molecules. In the electron diffusion process the energy is transported from the center of the track into the halo. The radial dose decreases with the square of the radial distance from the center. The diameter of the track is determined by the maximum range of the emitted electrons, i.e. by the maximum energy electrons. All ions having the same velocity i.e. the same specific energy produce electrons of the same energy and therefore tracks of the same diameters independent of the effective charge. But the dose inside the track increases with the square of the effective charge. Track structure models using this continuous dose distributions produce a better agreement with the experiment than models based on microdosimetry. The critical volume as used in microdosimetry is too large compared to the size of the DNA as critical structure inside the biological objects. Track structure models yield better results because the gross-structure of the track i.e. its lateral extension and the thin down toward the end of the track is included in these calculations. In a recent refinement the repair capacity of the cell has been included in a track structure model by using the complete shouldered x-ray survival curve as a template for the local damage produced by the particle tracks. This improved model yields presently the best agreement with the experiment.
110 citations
TL;DR: The usefulness of the ratio F690/F735 as a suitable non-destructive indicator of the in-vivo chlorophyll content, especially at medium and low chlorophylla content is confirmed.
Abstract: The chlorophyll content and the fluorescence induction kinetics at two wavelengths (690 nm and 735 nm) have been measured in leaves of nine common broadleaf tree species during the autumnal chlorophyll breakdown. The ratio of the chlorophyll fluorescence maxima F690/F735 was determined at fluorescence maximum (fm) and at steady-state conditions (fs) by the laser-induced fluorescence emission using the two-wavelength fluorometer. The ratio F690/F735 increases with the leaf discolouring during the autumnal chlorophyll breakdown. The relationship between the chlorophyll content and the ratio F690/F735 can be expressed by a power function (curvilinear relationship) which is valid for all the species examined. In most cases the ratio F690/F735 measured in the upper leaf side is lower than that in the lower leaf side, but the trend is the same along the decreasing chlorophyll content. The ratio F690/F735 is always higher at maximum fluorescence than at steady-state fluorescence in the upper as well as lower leaf side and these values are well fitted in a linear correlation. This study confirms the usefulness of the ratio F690/F735 as a suitable non-destructive indicator of the in-vivo chlorophyll content, especially at medium and low chlorophyll content.
81 citations
TL;DR: Understanding of the biological effects of heavy ions is important not only for the welfare of astronauts who will undertake extended interplanetary missions in space but also for the facilitation of a rigorous scientific basis for conventional radiation therapy.
Abstract: For several years, it has been evident that cellular radiation biology is in a necessary period of consolidation and transition (Lett 1987, 1990; Lett et al. 1986, 1987). Both changes are moving apace, and have been stimulated by studies with heavy charged particles. From the standpoint of radiation chemistry, there is now a consensus of opinion that the DNA hydration shell must be distinguished from bulk water in the cell nucleus and treated as an integral part of DNA (chromatin) (Lett 1987). Concomitantly, sentiment is strengthening for the abandonment of the classical notions of “direct” and “indirect” action (Fielden and O'Neill 1991; O'Neill 1991; O'Neill et al. 1991; Schulte-Frohlinde and Bothe 1991 and references therein). A layer of water molecules outside, or in the outer edge of, the DNA (chromatin) hydration shell influences cellular radiosensitivity in ways not fully understood. Charge and energy transfer processes facilitated by, or involving, DNA hydration must be considered in rigorous theories of radiation action on cells. The induction and processing of double stand breaks (DSBs) in DNA (chromatin) seem to be the predominant determinants of the radiotoxicity of normally radioresistant mammalian cells, the survival curves of which reflect the patterns of damage induced and the damage present after processing ceases, and can be modelled in formal terms by the use of reaction (enzyme) kinetics. Incongruities such as sublethal damage are neither scientifically sound nor relevant to cellular radiation biology (Calkins 1991; Lett 1990; Lett et al. 1987a). Increases in linear energy transfer (LET∞) up to 100–200 keV µm−1 cause increases in the extents of neighboring chemical and physical damage in DNA denoted by the general term DSB. Those changes are accompanied by decreasing abilities of cells normally radioresistant to sparsely ionizing radiations to process DSBs in DNA and chromatin and to recover from radiation exposure, so they make significant contributions to the relative biological effectiveness (RBE) of a given radiation. As the LET∞ is raised above a few hundred keV µm−1, the damage associated with DSBs continues to increase, but the efficiency of DSB induction declines to low values (∼0.1), as do RBE and the effective processing of DSBs and chromatin breaks, and the decline in RBE seems to mimic the overall decline in suitable processing of DSBs. Hence, the quality factor (Q) for a given radiation cannot be based solely upon the pattern of energy deposition, a fact attested to also by the quite different RBE responses exhibited by repair-deficient mutant (or variant) cells. Understanding of the biological effects of heavy ions is important not only for the welfare of astronauts who will undertake extended interplanetary missions in space but also for the facilitation of a rigorous scientific basis for conventional radiation therapy.
77 citations
TL;DR: Future experimental and theoretical modeling research emphasis should focus on exploring particle-induced inactivation of endpoints assessing functionality and not just lethality, and on analyzing molecular damage and genetic effects arising in damaged but non-inactivated survivors.
Abstract: The inactivation of cells resulting in lethal or aberrant effects by charged particles is of growing interest. Charged particles at extremely high LET are capable of completely eliminating cell-type and cell-line differences in repair capacity. It is still not clear however whether the repair systems are inactivated, or merely that heavy-ion lesions are less repairable. Studies correlating the particle inactivation dose of radioresistant cells with intact DNA analyzed with pulse field gel electrophoresis and other techniques may be useful, but more experiments are also needed to assess the fidelity of repair. For particle irradiations between 40-100 keV/microns there is however evidence for particle-induced activation of specific genes in mammalian cells, and certain repair processes in bacteria. New data are available on the inactivation of developmental processes in several systems including seeds, and cells of the nematode C. elegans. Future experimental and theoretical modeling research emphasis should focus on exploring particle-induced inactivation of endpoints assessing functionality and not just lethality, and on analyzing molecular damage and genetic effects arising in damaged but non-inactivated survivors. The discrete nature of selective types of particle damage as a function of radiation quality indicates the value of accelerated ions as probes of normal and aberrant biological processes. Information obtained from molecular analyses of damage and repair must however be integrated into the context of cellular and tissue functions of the organism.
71 citations
TL;DR: The137Cs content of 118 species of higher fungi collected in the period from August 1984 to October 1989 at three different locations in Styria, Austria, was determined by gamma-spectrometry.
Abstract: The 137Cs content of 118 species (668 samples) of higher fungi collected in the period from August 1984 to October 1989 at three different locations in Styria, Austria, was determined by gamma-spectrometry. The Cs-content of most mushrooms has been increasing since September 1986. In order to find out which factors determine the 137Cs-contamination of mushrooms and the transfer-value soil to mushroom, the concentration of total and plant-available radiocesium in soils as well as the pH-value, the content of humus, clay, silt, sand, exchangeable cations, the composition of the clay minerals, and the particle size distribution of the soils of two different locations were examined. The higher the 137Cs contamination of the soil, the thicker the layer of humus and the higher the content of humus, the lower the pH-value, and the lower the amount of essential cations, especially of K+, the higher the amount of 137Cs plant-available will be. Therefore, the contamination of the mushrooms in the coniferous forest of Koralpenblick (1000 m) is higher than in the mixed forest at the Rosenberg around Graz at approx. 500 m height. Of 26 different species of mushrooms measured at both sites, only 61% show the highest TF-values soil to mushrooms also at the Koralpenblick. In the spruce forest at Koralpenblick there are many species of mushrooms with high 137Cs-contamination which were not found at the Rosenberg. However, the properties of the species to which a mushroom belongs are more important than environmental conditions and soil properties. The transfer values of 40K stay within narrow bounds, whereas those of 137Cs differ widely.
63 citations
TL;DR: A new dose application method, the voxel scanning, is described which permits three-dimensional irradiation of deep seated tumors.
Abstract: A new dose application method, the voxel scanning, is described which permits three-dimensional irradiation of deep seated tumors.
40 citations
TL;DR: An overview of radiation problems in space, with emphasis on aspects of major interest for manned space exploration, is presented in this article, where a classification of the radiation hazards is presented and strategies for their evaluation are discussed.
Abstract: An overview is presented on radiation problems in space, with emphasis on aspects of major interest for manned space exploration. A classification of the radiation hazards is presented and strategies for their evaluation are discussed. Space radiation problems are compared with characteristic aspects of radiation research in other disciplines, in order to provide further insight into those aspects that are unique to space.
38 citations
TL;DR: The most pronounced effect of the stress for both plant types was a decrease inPN due to a closure of the stomata, and the photochemical quenching (qP) and therefore the electron transport via photosystem II remains unaffected by water stress.
Abstract: This article describes the effect of water stress on the room temperature chlorophyll fluorescence lifetime of plants of wheat (C3) and maize (C4). In addition, net CO2 assimilation rate (P
N
), stomatal conductance and the fluorescence quenching coefficientsqP andqNP at steady state conditions were recorded. The overall fluorescence decay of the control plants can be described by an average decay time of 1 ns for both plant types. Water stress did not modify this parameter in the case of wheat, whereas a shortening of the decay was observed for waterstressed maize plants (τ=0.45 ns). This shortening in the chlorophyll fluorescence decay was accompanied by an increase in the nonphotochemical quenching (qNP). The photochemical quenching (qP) and therefore the electron transport via photosystem II remains unaffected by water stress. The most pronounced effect of the stress for both plant types was a decrease inP
N due to a closure of the stomata.
30 citations
TL;DR: The development of the isocentric gantry, the newest beam delivery system, and clearly a consequence of all the experience gained at the earlier facilities has many advantages and offers advantageous physical properties of the particles as well as being equal in the flexibility of dose delivery to the modern photon radiotherapy gantries.
Abstract: Heavy charged particle therapy, started at research institutes three decades ago, is now on the verge of entering a clinical phase. This phase has resulted from the evolution and development of various beam delivery systems and techniques with existing research accelerators and with newly built accelerators. For the first thirty years, heavy charged particle therapy was administered with a fixed horizontal beam line. In 1991, the first treatment with an isocentric gantry was administered. The development of the isocentric gantry, the newest beam delivery system, and clearly a consequence of all the experience gained at the earlier facilities has many advantages. It offers advantageous physical properties of the particles as well as being equal in the flexibility of dose delivery to the modern photon radiotherapy gantries.
27 citations
TL;DR: The hypothesis that many irradiated 9L tumor cells die because of imbalances in sets of competing biochemical and/or metabolic processes is supported.
Abstract: Induction of unrepairable DNA damage, accumulation of misrepaired DNA damage, and generation of imbalances in competing biochemical and/or metabolic processes have been proposed to explain the relationship between radiation-induced DNA damage and cell lethality. Theoretically, the temperature dependence of the critical DNA repair process(es) should be 1) either independent of or identical to the temperature dependence of cell killing if the first two hypotheses are correct, and 2) different if the third hypothesis is correct. To test this, exponentially growing rat 9L brain tumor cells were left at 37 degrees C or equilibrated for 3-14 h at 20 degrees C before irradiation. Cells were irradiated and allowed to repair at either 20 degrees C or 37 degrees C. Alternatively, the cells were irradiated at one of these temperatures and immediately shifted to the other temperature for repair. DNA damage was assessed by the alkaline elution technique; cell kill was assessed by a clonogenic assay. 9L cells maintained at 20 degrees C or 37 degrees C sustained the same amount of DNA damage as measured by alkaline elution. DNA repair instantaneously assumed the rate characteristic of the postirradiation temperature. For 9L cells equilibrated, irradiated, and repaired at 20 degrees C, the half-time of the fast phase of the DNA repair decreased by a factor of approximately 2 and the half-time of the slow phase decreased by a factor of approximately 5 over that measured in cells incubated, irradiated and repaired at 37 degrees C. Although the rate of DNA repair decreased substantially at 20 degrees C, the survival of 9L cells that were equilibrated and irradiated at 20 degrees C was greater (p less than 10(-4)) than those incubated and irradiated at 37 degrees C, when assayed by an immediate plating protocol. In addition, the survival of 9L cells equilibrated and irradiated at 20 degrees C and then shifted to 37 degrees C immediately after irradiation was greater (p less than 10(-2)) than that obtained with any other delayed plating protocol. Thus, the temperature dependence of the DNA repair processes measured by alkaline elution was different from the temperature dependence of cell killing measured either by an immediate or delayed plating protocol. These data support the hypothesis that many irradiated 9L tumor cells die because of imbalances in sets of competing biochemical and/or metabolic processes.
24 citations
TL;DR: The quantification of chromosomal aberrations, mutations and neoplastic transformations induced by heavy charged particles meets with considerable experimental and conceptual difficulties which are related to the specific pattern of energy deposition.
Abstract: The quantification of chromosomal aberrations, mutations and neoplastic transformations induced by heavy charged particles meets with considerable experimental and conceptual difficulties which are related to the specific pattern of energy deposition. These problems are discussed on the background of current ideas on track structure, and some new experimental results are analysed.
TL;DR: A new device for the measurement of complete laser induced fluorescence emission spectra (maxima near 690 and 735 nm) of leaves during the induction of the chlorophyll fluorescence is described and the ratio F690/F735 allows the non-destructive determination of the chlorine content of leaves.
Abstract: A new device for the measurement of complete laser induced fluorescence emission spectra (maxima near 690 and 735 nm) of leaves during the induction of the chlorophyll fluorescence is described. In this the excitation light (cw He/Ne laser, 632.8 nm) is switched on by a fast electro-mechanical shutter which provides an opening time of 1 ms. The emitted fluorescence is imaged onto the entrance slit of a multichannel spectrograph through a red cut-off filter (> 645 nm). A charge coupled device (CCD) sensor with 2048 elements simultaneously detects the complete chlorophyll fluorescence emission spectrum in the 650–800 nm wavelength range. Scanning is accomplished electronically and the integration time for a complete fluorescence emission spectrum can be selected from 10 ms up to 260 ms. Shutter, detector system and data acquisition are controlled by an IBM-PC/AT compatible computer. A maximum of 32 spectra can be measured at selected times during the fluorescence induction kinetics with the shortest time resolution of 10 ms. The instrument permits the determination of various fluorescence parameters:a) the rise-time of the fluorescence to the maximum level fm,b) the changes in the shape of the fluorescence emission spectra during the induction kinetics,c) the induction kinetics in the fluorescence ratio F690/F735 as well asd) the fluorescence decrease ratio Rfd at any wavelength between 650 to 800 nm. These fluorescence parameters provide information about the functioning of photosynthesis. The ratio F690/F735 allows the non-destructive determination of the chlorophyll content of leaves. The application of this instrument in ecophysiological research and stress physiology of plants is outlined.
TL;DR: The feasibility of dynamic conformal heavy charged particle radiotherapy has been investigated at UCLBL, and shows high promise of an improved therapeutic ratio and reduction in the number of treatment portals required for efficient treatment delivery.
Abstract: The feasibility of dynamic conformal heavy charged particle radiotherapy has been investigated at UCLBL, and shows high promise of: 1. an improved therapeutic ratio and 2. reduction in the number of treatment portals required for efficient treatment delivery. Assessment of dose to tumor and critical structures for several anatomical sites have been carried out using a normal tissue complication algorithm developed at LBL. For high-LET charged particle treatment delivery, dynamic conformal therapy using a raster scanned beam with variable modulation and multileaf collimator appears to be the optimal technique for treatment delivery.
TL;DR: The results suggest that the treatment used decreases the radiation damage of the sensitive thymocyte population in whole-body 1 Gy-irradiated mice, and it is proposed that the joint use of AMP, an adenosine prodrug, and dipyridamole, a drug inhibitingAdenosine uptake by cells, leads to an elevation in extracellular adenoine which activates cell surface adenosines receptors.
Abstract: In whole-body 1 Gy-irradiated mice a modification of early cellular damage by means of preirradiation dipyridamole and adenosine monophosphate (AMP) treatment was investigated. Both drugs were given either alone or in combination, AMP being administered i.p. at doses of 5, 10 and 15mg, dipyridamole s.c. at the dose of 2mg, 20min before AMP. The thymidine level in plasma and the amount of free polynucleotides in the thymus and spleen, both estimated at the interval of 4h after irradiation, were used as indices of early cellular damage in vivo. The elevated level of thymidine observed in the plasma of irradiated controls decreased significantly after the administration of AMP (5 mg) alone to 71%, after the combination of dipyridamole and AMP a still deeper significant fall to 60% was observed. Such a protective effect was observed when injecting AMP 15min before irradiaton. Using the interval of 65min between AMP administration and irradiation, no protection was detected. The higher doses of AMP (10, 15mg) enhanced the protective effect manifested in plasma thymidine level only moderately. The amount of free polynucleotides, elevated in the thymus and spleen of irradiated mice, was significantly decreased in the thymus of mice pretreated with the combination of dipyridamole and AMP. The results suggest that the treatment used decreases the radiation damage of the sensitive thymocyte population. It is proposed that the joint use of AMP, an adenosine prodrug, and dipyridamole, a drug inhibiting adenosine uptake by cells, leads to an elevation in extracellular adenosine which activates cell surface adenosine receptors. Both the systemic (vasodilation-hypotension- hypoxia) and cellular (elevation of cyclic AMP in sensitive cells) consequences of adenosine receptor activation may be responsible for the observed radioprotective effects.
TL;DR: A high relative intensity of the long-lived component was found in damaged spruces as well as in trees showing first symptoms of yellowing, needle loss or parasite infection, and fluorescence spectroscopy with subnanosecond time resolution seems to be a valuable attempt for an early detection of forest decline.
Abstract: Needles from spruces at different environmental and physiological conditions were analyzed by picosecond fluorescence spectroscopy using a novel laser diode and single photon counting detection The decay curves of chlorophyll fluorescence showed a superposition of three exponentially decaying components with time constants of T1 = 100-200 ps, T2 = 300-500 ps and T3 = 20-35 ns A high relative intensity of the long-lived component was found in damaged spruces as well as in trees showing first symptoms of yellowing, needle loss or parasite infection, although all measurements were carried out with green needles which appeared visually intact Therefore, fluorescence spectroscopy with subnanosecond time resolution seems to be a valuable attempt for an early detection of forest decline
TL;DR: It is concluded that damage at two levels of DNA folding is measured at pH 6.9 and 9, indicating damage and/or alteration in the DNA superhelical structure.
Abstract: We examined, by the fluorescent halo assay, alterations in the nucleoid structure (structure formed from cells under mild lysis conditions: in non-ionic detergent Triton X-100, 0.0005% and 1.5 mol/l NaCl) of L5178Y (LY) cell sublines which had been untreated, treated with reducing/chelating agents (beta-mercaptoethanol or sodium diethyl dithiocarbamate (DDTC(Na))) or X-irradiated. These sublines differ in radiation sensitivity: LY-R is more resistant (D0 = 1.1 Gy) and LY-S more sensitive (D0 = 0.5 Gy). Halo diameters were measured after cell lysis in the presence of propidium iodide (PI) (0.5 to 50 micrograms/ml) at pH 6.9 or 9. The maximal DNA unwinding in PI was obtained at 7.5 micrograms/ml PI, at both pH 6.9 and 9 in both sublines; the maximal halo diameter was larger in LY-S than in LY-R cells. In nucleoids from both sublines DNA could be rewound at higher (10-50 micrograms/ml) PI concentrations both at pH 6.9 and 9. This ability was impaired by mercaptoethanol or DDTC(Na) (at pH 9) or by X-irradiation, indicating damage and/or alteration in the DNA superhelical structure. The susceptibility to reducing/chelating agents was greater in LY-S than in LY-R nucleoids, pointing to differences in chromatin structure between these sublines. The amount of X-ray-inflicted damage was higher, when measured at pH 9 than at pH 6.9 and was about twice larger in LY-S than in LY-R nucleoids, when the cells were irradiated with the same X-ray dose.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: Cells subjected to the SDH sequence 42 °C/1 h→40 °C→4 h/4 h develop thermotolerance, as indicated by a reduced sensitivity to further hyperthermic challenges.
Abstract: M-14 human tumor cells have been subjected to two regimens of step-down heating (SDH) consisting of a conditioning treatment at 42 degrees C for 1 h or at 44.5 degrees C for 20 min, immediately followed by heating at 40 degrees C. Both conditioning treatments thermosensitize the cells towards the subsequent heating at 40 degrees C; the thermosensitization ratio is 6.4 for cells conditioned at 42 degrees C for 1 h and 32.3 for cells conditioned at 44.5 degrees C for 20 min. The overall protein synthetic activity is reduced to 32.7% or 18.4% of control values following 1 h at 42 degrees C and 20 min at 44.5 degrees C, respectively; this inhibition is followed by a full recovery of the synthetic activity during the subsequent exposure at 40 degrees C. SDH-treated cells synthetize four heat shock proteins, with approximate molecular weights of 28, 64, 70 and 90 kDa. The pattern of HSPs induction observed in SDH-treated cells is similar to that found in cells subjected to single hyperthermic exposures. Cells subjected to the SDH sequence 42 degrees C/1 h-->40 degrees C/4 h develop thermotolerance, as indicated by a reduced sensitivity to further hyperthermic challenges.
TL;DR: In this paper, a set-up with on-line computer and a specially written computer program was used to analyze the long term delayed luminescence in the seconds-range (LDL) of spruces at different environmental and physiological conditions.
Abstract: Needles from spruces at different environmental and physiological conditions were analyzed by long term delayed luminescence in the seconds-range (LDL) using a novel set-up with on-line computer and a specially written computer program. Upon red light induction, the LDL-kinetics showed a super-position of three exponentially decaying components ("fast", "medium" and "slow") with reaction constants of kf = 5-15 s-1, km = 0.8-1.8 s-1 and ks = 0.13-0.23 s-1, ks-values are fairly independent of the individual tree and quite stable throughout the whole year. They are also independent of the status and localization, i.e. the physiological situation of the individual tree. However, km- and kf-values as well as the related amplitudes Am and Af exhibit a general, significant seasonal variation and obviously are correlated with the damage class or the environmental situation of the individual tree. Therefore, the measurement of long term delayed luminescence might offer a valuable piece of information in search of an early detection of forest decline.
TL;DR: The spectrum of nuclear nucleases in control and irradiated (4 Gy) thymocytes has been investigated using the method of SDS electrophoresis of nuclear proteins in3H - DNA-polyacrylamide gels and a number of polypeptides of MW possessing nuclease activity were found.
Abstract: The spectrum of nuclear nucleases in control and irradiated (4 Gy) thymocytes has been investigated. Using the method of SDS electrophoresis of nuclear proteins in3H - DNA-polyacrylamide gels a number of polypeptides of MW. 35, 32, 17.7, 17.2 and 16.4 kDa possessing nuclease activity were found. The 35 kDa enzyme is only active in the presence of Ca2+ and Mg2+ ions. In response to cycloheximide injection (3 mg/100 g body weight) and irradiation, we did not detect the 35 kDa nuclease activity. Nucleases of 32, 17.7, 17.2 and 16.4 kDa are active in the presence of Ca2+ ions. The activities of these nucleases increases 60 min after irradiation. These nucleases were also found in the fraction of polydeoxyribonucleotide (PDN).
TL;DR: This paper concentrates on the accelerator choices for light ion cancer irradiation facilities, as outlined in several proposals over the last 15 years and concludes with the description of a modern synchrotron facility.
Abstract: The paper concentrates on the accelerator choices for light ion cancer irradiation facilities, as outlined in several proposals over the last 15 years and concludes with the description of a modern synchrotron facility. Further summary papers on the same subject are cited in references [14, 19].
TL;DR: Results obtained with radical scavengers indicate that, unlike non-halogenated nucleotides where the hydroxyl radical (· OH) is the principal damaging species, 5-BrUMP is damaged by the hydrated electron (eaq−), hydrogen atom (H·) and · OH, producing a high yield of base damage and Br− and Pi release in anoxia.
Abstract: This study was undertaken to investigate the mechanism of chemical radiosensitization by halogenated bases incorporated into DNA. Radiation-induced base and sugar-phosphate backbone damage to 5-bromouridine-5'-monophosphate (5-BrUMP) was monitored using a flow system connected in series with a recording spectrophotometer, a bromide (Br-)-specific ion analyzer and a Technicon auto-sampler. The system was used to assay loss of UV-absorbing 5,6 double-bond, release of Br- and inorganic phosphate (Pi) release using an automated colorimetric method, as a function of gamma-ray dose. Results obtained with radical scavengers indicate that, unlike non-halogenated nucleotides where the hydroxyl radical (.OH) is the principal damaging species, 5-BrUMP is damaged by the hydrated electron (e-aq), hydrogen atom (H.) and .OH, producing a high yield of base damage and Br- and Pi release in anoxia. Another novel feature of 5-BrUMP radiolysis is that oxygen, by converting e-aq and H. to the unreactive superoxide radical anion (O2-), has a protective effect on both base and phosphate ester damage. Under .OH-scavenging conditions, where the radiation yield of reductive debromination is 3.8, there is some Pi release, suggesting the possibility of intramolecular hydrogen atom transfer from the sugar ring to the 5-uracilyl radical and subsequent sugar-phosphate bond cleavage. This hypothesis is supported by the action of oxygen and thiols in modifying the e-aq-mediated sugar-phosphate damage.
TL;DR: It is demonstrated that ionizing radiation stimulates proteolysis of erythrocyte membrane proteins by membrane-associated proteases.
Abstract: X- and gamma-irradiation of human erythrocyte membranes (250–1000 Gy) was found to decrease the ratio of weakly to strongly immobilized signal height of membrane-bound maleimide spin label (Mal-6). Subsequent incubation of spin-labeled membranes at ambient temperature (21 °C) induced a progressive increase in this ratio, faster for membranes irradiated with low doses which was hampered by protease inhibitors. These results demonstrate that ionizing radiation stimulates proteolysis of erythrocyte membrane proteins by membrane-associated proteases.
TL;DR: Maximum effectiveness to induce SOS-response has been found for deuterium and helium ions in comparison to γ-rays, carbon or krypton ions, leading to greater SOS-induction potency of radiation.
Abstract: s-galactosidase and alkaline phosphatase activities of Escherichia coli strain PQ37 carrying the fusion gene of sulA and lacZ treated with different types of ionizing radiation were examined. The induction factor (ratio ofs-galactosidase to alkaline phosphatase activity), reflecting the SOS-induction potency, increases significantly with radiation dose. Maximum effectiveness to induce SOS-response has been found for deuterium and helium ions in comparison to γ-rays, carbon or krypton ions. Increased energy of helium ions leads to greater SOS-induction potency of radiation.
TL;DR: The magnetic field increases the number of spleen colonies either directly by affecting membrane components responsible for the seeding of the transplanted stem cells to the recipient spleens or indirectly affecting radical/redox-systems that may have a regulatory function in the stem cells.
Abstract: Transplantation of bone marrow cells of magnetic-field-exposed mice led to increased numbers of spleen colonies (CFU-S 7d) in conditioned recipient mice (Peterson et al. 1986). Here we report on the dependence of this phenomenon on body temperature, field strength and exposure time. It was found that the effect can only be seen when the body temperature is 27° C, the field strength not less than 1.4 T and the exposure time at least 15 min. It is suggested that the magnetic field increases the number of spleen colonies either directly by affecting membrane components (receptors) responsible for the seeding of the transplanted stem cells to the recipient spleens or indirectly affecting radical/redox-systems that may have a regulatory function in the stem cells.
TL;DR: It was concluded that WBI decreass LDH, APH and AcPH levels in the lung cells, which secrete them into bronchoalveolar spaces, which triggers an early damage on cytoplasmic membranes of the endothelial cells in lung capillars.
Abstract: The influence of whole-body irradiation (WBI) with 4, 8 and 15 Gyionizing radiation upon some biochemical indices in the brochoalveolar lavage fluid (BALF) of rat lungs was studied. It was established that lactate dehydrogenase (LDH), alkaline phosphatase, (APH) and acid phosphatase (AcPH) activities show a dose-dependent decrease on the day 1 and day 5 after the irradiation. A similar trend was observed in the total protein content on the day 1. Angiotensin converting enzyme (ACE) activity was increased on the day 1 in the groups irradiated with 8 Gy and 15 Gy in comparison with the controls (190,2% and 187,5%, respectively). It was concluded that WBI decreass LDH, APH and AcPH levels in the lung cells, which secrete them into bronchoalveolar spaces. An irradiation with 8 Gy and 15 Gy WBI provokes an early damage on cytoplasmic membranes of the endothelial cells in lung capillars. It was considered that the bronchoalveolar lavage can find a more wide application for evaluation of the biological effect of ionizing radiation in lungs.
TL;DR: There are a number of issues which must be addressed in developing plans for heavy charged particle therapy which are likely to be achieved in the next few years.
Abstract: The comments herein describe, at a necessarily superficial level, a number of issues which must be addressed in developing plans for heavy charged particle therapy. Programs now exist which provide the needed capabilities. The challenge now is to make the planning process easier and faster- and possibly more efective. It seems likely that this will be achieved in the next few years.
TL;DR: The findings support the concept of a need for prolonged iodine prophylaxy after emissions of radioiodine into the environment.
Abstract: A similar pattern of variation with time in observed maxima of daily dose equivalent rates in human thyroids (TD - µSv·d−1) and of daily fallout radioactivities (FR - kBq·m−2) has been found after the Chernobyl accident. An estimate of the time-lag between the maxima in TD lines and the preceding FR peaks was made of about seven days for adult and nine days for juveniles. Applying this time-lag it was possible to estimate transfer factors from the fall-out to thyroid dose equivalent: the highest estimated values were 221 µSv/kBq·m−2 for adult and 641 µSv/kBq·m−2 for juvenile thyroids. These values differ from those published by UNSCEAR (United Nations 1988), which have been calculated for various regions of Czechoslovakia, from ingestion and inhalation intake estimates. A broad variation of transfer factor values could be expected to result from such transfer calculations using ingestion and inhalation estimates. The findings also support the concept of a need for prolonged iodine prophylaxy after emissions of radioiodine into the environment.
TL;DR: The results suggest that the lower radiation sensitivity of chicken embryo cells is attributable to an initial mechanism of DNA repair and/or DNA protection which may be closely connected to minor chromatin compactness and higher intrinsic activities of repair enzymes.
Abstract: Brain cells (b-cells) and liver cells (l-cells) of the chicken embryo and thymic cells (t-cells) of the rat were X-irradiated in vitro at doses of 1.25-50 Gy. When compared to t-cells, b- and l-cells exhibited 1) a lower stimulation of poly (adenosine diphosphate-ribose) transferase and unscheduled DNA synthesis following X-irradiation, 2) an almost fivefold higher inhibition of semiconservative DNA synthesis, 3) a less condensed chromatin, 4) about fourfold higher threshold doses with regard to significant effects on nucleoid sedimentation and viscometry of alkaline cellular lysates, and 5) an apparently two- to threefold lower DNA repair during a 30 min post-exposure repair period. The results suggest that the lower radiation sensitivity of chicken embryo cells is attributable to an initial mechanism of DNA repair and/or DNA protection which may be closely connected to minor chromatin compactness and higher intrinsic activities of repair enzymes.
TL;DR: The inverse dose-rate effect could not be induced from the different exposure periods but from continuous irradiation of different dose-rates, and was observed from inactivation of transforming activity of DNA irradiated with tritiated water.
Abstract: When an aqueous solution of plasmid DNA at a constant low concentration of 5 µg/cm3 was irradiated with60Coγ-rays, D37 dose of single-strand breaks was decreased from 18 Gy at a dose-rate of 6.77 Gy/h of acute irradiation to 2.3 Gy at a dose-rate of 0.00212 Gy/h. OrG value was increased from 0.0010 to 0.0081. Similar dose-rate dependency of D37 dose andG value were also found when the plasmid DNA solution was treated with various concentrations of tritiated water at various dose-rates, ranging from 5.13 Gy/h to 0.000118 Gy/h. RBE of tritiums-rays for single-strand breaks was ranged from 0.3 to 0.5 in a wide range of dose-rates. When the DNA solution was saturated with argon to remove oxygen, the dose-rate dependency ofγ-rays was abolished and that of tritiums-rays was significantly supressed. When the DNA solution in air was kept at 4° C for 50 h or 25 days after acute irradiation, theG value of DNA breaks was the same as that kept at —20° C for the same period, but much lower than that of the solution irradiated for the same period at a lower dose-rate to give the same total doses. This shows that the inverse dose-rate effect could not be induced from the different exposure periods but from continuous irradiation of different dose-rates. The inverse dose-rate effect for inactivation of transforming activity of DNA irradiated with tritiated water was also observed in the range from 0.0588 Gy/h to 0.00118 Gy/h.
TL;DR: X-irradiation of lymphocytes, before their lysis, altered the DNA content of nucleoids and their sedimantation rate in accord with the view that nuclear DNA is attached along its length at distance corresponding to 1.7 × 1010 g/mol.
Abstract: Human quiescent lymphocytes were lysed onto neutral sucrose gradients in order to sediment subsequently the nuclear DNA released within nucleoids The position of nucleoids in the centrifuge tubes was detected fluorometrically by using the dye, ethidium bromide, and the height of the fluorescence peak was taken as a measure of DNA content X-irradiation of lymphocytes, before their lysis, altered the DNA content of nucleoids and their sedimentation rate in accord with the view that (1) nuclear DNA is attached along its length at distances corresponding to 17 x 10(10) g/mol, and that (2) X-ray-induced double-strand breakage releases DNA fragments at random Incubation at 37 degrees C of irradiated lymphocytes restored the amount of attached DNA as it would be expected from an intracellular repair process for DNA double-strand breaks