Indirect Radiation Effects Research Articles

Comparison of mechanisms for DNA strand break formation by the direct and indirect effect of radiation.

Irradiation of cells may lead to mutations, reproductive cell death and the disappearance of some or all cell activities. These effects, especially reproductive cell death, are believed to be the result of damage to DNA. Two kinds of formation of DNA damage are often distinguished, the so called “direct” and the “indirect” effect of irradiation.1,2 The direct effect is due to ionization or electronic excitation of the DNA, and the indirect effect is caused by reactive species, in most cases free radicals, which are produced in the vicinity of the DNA. These radicals may be primary radicals produced by energy absorption in water (the solvated electron, the H-atom and the OH radical) or organic radicals produced from organic material other than DNA either by interaction with radiation or by reaction with the primary radicals generated from water.

On the kinetics of polymer degradation in solution: Part XI—Radiolysis of poly(olefin sulfones)

Poly(butene-1-sulfone) (PBS) and poly(hexene-1-sulfone) (PHS) were irradiated in dilute solutions (1,4-dioxane and other solvents) with single 100 ns pulses of 16 MeV electrons from a linear accelerator. Changes of the light scattering intensity (LSI) and of the optical density (OD) after the pulse were recorded with aerated and deaerated solutions. It turned out that, with both polymers, the rate of LSI decrease (due to main-chain scission) may be correlated with the rate of fragment diffusion. Main-chain scission occurs in less than 10 μs. With poly(styrene sulfone) no change of the LSI was observed. Based on the energy absorbed by the solvent, the 100 eV yield for main-chain scissions was determined in dioxane solution with the aid of GPC as G(S) = 12 (PBS) and G(S) = 4(PHS). These results indicate that an indirect radiation effect becomes operative, mainly via energy transfer from the solvent to the polymer. OD measurements yielded evidence for the existence of a long-lived species (probably a macroradical) with a lifetime exceeding the time of fragment diffusion, which gives rise to the combination of fragments. The capability of poly(olefin sulfones) to serve as probe material for the investigation of the dynamics of macromolecules in solution is discussed.

Water stress as a factor influencing the distribution of the ericoid shrub Philippia evansii in the Natal Drakensberg mountains, South Africa

Xylem pressure potential (Ψ p ) was measured in Philippia evansii plants growing on a cool, south aspect and a warm, valley bottom site. There were no significant differences in the minimum Ψ p values (min Ψ p ) between sites during the day despite differences in the water vapour pressure deficit (VPD). It is deduced that P. evansii plants are sensitive to water loss with Ψ p values stabilizing at ca − 1100 kPa by the control of transpirational flux. In spite of the higher VPD measured at the warmer site, pre-dawn values of Ψ p (base Ψ p ) were more negative at the cool site. Since plants were experiencing water stress on the cool southern slopes at night, it appears that conditions on the northern slopes would be too dry for colonization by P. evansii plants. It is concluded that the indirect effects of radiation on the water balance are important factors controlling the distribution of P. evansii.

Evidence for an indirect effect of radiation on mammalian chromosomes. II. UV-induced isochromosome formation in cell hybrids

Cell fusion has been used to test the hypothesis that chromosomes may be damaged indirectly by UV light, as well as by direct interaction with DNA. Hybrids were found to contain isochromosomes of mouse origin, whose frequency increased as the dose of UV delivered to the hamster cell parent was increased. This unusual type of aberration was shown to be induced also by direct UV irradiation of mouse or hybrid cells. These results suggest that UV light has a hitherto undiscovered indirect effect on chromosome integrity, mediated by some irradiated cell component.

Evidence for an indirect effect of radiation on mammalian chromosomes. III. UV- and x-ray-induced sister chromatid exchanges in heterokaryons

The hypothesis that chromosomes may be damaged indirectly by radiation was examined by assaying sister chromatid exchange, (SCE) frequency in heterokaryons between irradiated and unirradiated mouse and Chinese hamster cells. One cell line was UV or x irradiated, then fused to unirradiated BrdU-labeled cells of the other line; SCEs in the unirradiated set were scored in heterokaryons. A dose-dependent increase was consistently observed; the magnitude of which suggested that 25% of UV-induced and up to 60% of x-ray-induced SCEs are indirectly induced. Medium transfer experiments, cell mixing, and fusion with irradiated chick erythrocyte ghosts suggested that unirradiated chromosomes in heterokaryons are damaged by a stable, nondiffusible cytoplasmic component contributed by the irradiated cell.

Induction of c-mutations in extracellular phage lambda by gamma-rays.

Mutagenic action of 60Co gamma-rays on extracellular phages lambda red1 and lambda red113 after irradiation in 4% nutrient broth in the absence or in the presence of 0.1 M cysteamine or in dried samples was studied. The yield of c mutations was almost independent of the repair genotype of the host cells (uvrA6, polA1, recA13, lexA102, uvrE502, uvrD3 or xthA9), of the phage Red function and of the conditions of gamma-irradiation and was 1 . 10(-12) per base pair and 1 rad. When the SOS-repair system of the host cells was induced by moderate UV irradiation, the yield of c-mutations was drastically enhanced in phage irradiated in broth, but not in phage irradiated in the dried state. These data allow us to suppose that the direct action of gamma-rays induces, in phage DNA, premutational lesions that are fixed into mutations by replication. On the other hand after gamma-irradiation in broth, when indirect radiation effects are only partially suppressed, about 85% of premutational lesions are converted into mutations by means of the inducible, errorprone SOS-repair system.

Radiolytic Pathways in γ-Irradiated DNA: Influence of Chemical and Conformational Factors

Several chemical and conformational factors have been shown to interfere with the radiolytic pathways in ..gamma..-irradiated DNA, producing different radical populations on the macromolecule. These factors include anoxic or oxic conditions, relative hydration degree, denaturation and/or degradation, and base composition. This led to extreme variations in the ESR spectra. Nevertheless, computer-assisted analysis of these spectra revealed the following common composition: a doublet from thymine anions (T/sup -/), a singlet from guanine cations (G/sup +/), an octet from 5-thymly radicals (TH), and an asymmetrical doublet from thymine-located peroxyl radicals (TOO). This formal interpretation of the experimental spectra permitted us to elucidate the following basic features for DNA radiolysis in frozen aqueous solution; Neutral DNA solutions frozen at 77 K are phase-seperated systems. Radiation damage to DNA does not result from the indirect effects of radiation; Primary radicals on DNA are ions of both signs, randomly produced on the constituent bases; Charge migration occurs via the stacked bases. Thymine is the eventual sink of the long-range electron migration. Guanine is the eventual sink of the short-range positive hole migration. Migration phenomena may be partially or totally hindered by various interfering factors; With increase in temperature, ionic radicals enter conversion reactions: G/sup +/more » decays without reacting with the surrounding water molecules, whereas T/sup -/ does react to form the 5-thymyl radical; In the presence of oxygen, peroxyl radicals TOO are formed rather than 5-thyml radicals; No sugar-located free radicals have been detected in the course of the present investigation.« less

Evidence for an indirect effect of radiation on mammalian chromosomes: I. Indirectly-induced chromosome loss from somatic cell hybrids

Mouse cells UV-irradiated with doses of 0–72 J/m 2 were fused with unirradiated Chinese hamster cells, and the chromosome constitutions of cell hybrids were examined. The number of mouse chromosomes retained by hybrids decreased with UV dose, and, unexpectedly, the number of hamster chromosomes also decreased in a dose-dependent manner. It is suggested that some component contributed by the irradiated mouse parent cell has indirectly induced damage and loss of hamster chromosomes.

Indirect effects of radiation on the decomposition of the constituents of noninjection drug formulations during radiation sterilization

Indirect effects of radiation on the decomposition of the constituents of noninjection drug formulations during radiation sterilization

Alterations in the Radiosensitivity of CHO Cells by Anisotonic Treatments: Correlations between Cell Lethality and Chromosomal Aberrations

The frequency of chromosomal aberrations and cell lethality induced in synchronous CHO cells by X irradiation alone or X irradiation combined with a treatment of 0.05) or 1.5 M NaCl has been examined. Treatment with hypotonic 0.05 M NaCl increased the radiosensitivity, i.e., decreased the D/sub 0/ in M (D/sub 0/ from 87 to 61 rad), in G/sub 1/ (D/sub 0/ from 156 to 122 rad) and in S (D/sub 0/ from 165 to 128 rad). Exposure to hypertonic (1.5 M) NaCl decreased the radiosensitivity in G/sub 1/ and S; i.e., increased the D/sub 0/ in G/sub 1/ (D/sub 0/ from 156 to 182 rad) and in S (D/sub 0/ from 165 to 232 rad), while exposure to 1.5 M NaCl increased the radiosensitivity in mitosis (D/sub 0/ from 87 to 78 rad). The 0.05 or 1.5 M salt treatments had no observable effect on the radiation-induced division delay. The appearance of tetraploid cells following treatment of mitotic cells with 1.5 M NaCl indicates that the hypertonic treatment probably had a deleterious effect on the mitotic apparatus. Except for a decrease in the frequency of radiation-induced chromosomal aberrations in mitotic cells treated with 1.5 M NaCl, the changes in themore » frequency of chromosomal aberrations caused by the salt treatments correlated well with the changes in lethality delineated above. These positive correlations can be illustrated best by a plot of the logarithm of survival versus aberration frequency where the data points fell on a straight line havinga D tilde/sub 0/ of 0.8 aberration per cell. The salt-induced changes in cellular radiosensitivity are hypothesized to be caused by changes in the indirect effect of radiation, associated with free radicals produced in water and interacting in chromatin.« less

Radiation-Induced Damage in Escherichia coli B: The Effect of Superoxide Radicals and Molecular Oxygen

The roles of superoxide radicals and of molecular oxygen in the radiodamage of Escherichia coli B suspended in dilute phosphate buffer were studied. The presence of high concentrations of polyethylene glycol in the ..gamma..-irradiated cell suspensions had no effect on bacterial radiosensitivity. This indicated that the damage was primarily endogenous, i.e., originated intracellularly. Saturation of the cell suspensions with N/sub 2/O doubled the radiosensitivity, thus indicating that OH radicals were responsible for the majority of the damage (indirect radiation effect). The presence of oxygen either in the absence or presence of N/sub 2/O brought about roughly a threefold increase in the radiosensitivity. Since in the presence of N/sub 2/O all e/sub aq//sup -/ were scavenged by the nitrous oxide rather than by oxygen, this shows that superoxide radicals played no role in the bacterial radiodamage. Our results substantiate the attribution of the oxygen effect to a direct interaction of O/sub 2/ with the OH-damaged sites on vital biomolecules and exclude any significant contribution of e/sub aq$/sup -/ and O/sub 2//sup -/ to the cellular radiodamage.

The Effects of g Irradiation on the Hydration Characteristics of DNA and Polynucleotides: II. An NMR Study of Mixed H 2 O/D 2 O Frozen Solutions

We have studied the effects of γ irradiation at different temperatures on the hydration water proton resonance spectra from frozen ${\rm H}_{2}{\rm O}/{\rm D}_{2}{\rm O}$ solutions of DNA and polynucleotides. Comparison of results obtained with pure H2 O solutions showed a striking difference in the temperature-dependent variations of $\Delta _{{\textstyle\frac{1}{2}}}$ values in nonirradiated and irradiated DNA solutions. There is evidence that base rehydration with hydration water molecules occurs after an initial damage to the macromolecular chains in DNA caused by the direct or indirect radiation effects.

Sensitization of Bacteriophage T4 to 60 Co-γ Radiation and to Low-Energy X Radiation by Bromouracil

Bacteriophage T4 with essentially complete substitution of 5-bromouracil (BU) for thymine in its DNA was exposed together with control phage to /sup 60/Co-..gamma.. radiation or 16-keV x radiation. As judged by plaque-forming ability, the BU-enhancement ratio for phage lethality was 1.2-1.4 when irradiated in buffered saline, while the enhancement ratio for induction of double-strand breaks in the DNA was about 2.2. In buffered saline, the indirect effects of radiation on phage proteins may account for a portion of the lethality and for the lack of correlation of lethality with double-strand breaks. Moreover, DNA was released into the buffered saline during irradiation; this factor would further confuse any possible correlation between double-strand breaks and lethality under these conditions. The BU-enhancement ratio for phage lethality increased to 1.8 in oxic broth and to 2.3 in anoxic broth plus cysteamine. Under these latter conditions, where indirect effects of radiation should be minimal, most of the lethality in both the control and BU phage could be accounted for by double-strand breaks in the DNA. There was no evidence for any specific interaction of the 16-keV x radiation with BU phage under the experimental conditions used.

Remarks on oxygen effects.

Oxygen concentration will influence the alpha- and beta-effect (two-component theory of radiation effects) independently. The beta-effect is reduced by a dose-modifying factor gamma. Oxygen, in competition with enzyme repair actions fortifies a part of the beta-lesions and this model leads to a simple equation for the factor gamma. The alpha-effect is also enhanced by oxygen. Measurements of OER indicate that the reduction of the effect from aerobic to anoxic condition might be about 70%. The functional dependence of oxygen concentration has not been investigated. For small oxygen concentrations of 0.15 to 0.5 muM/l and doses below 1000 R Révész and Littbrand have found that oxygen can protect the irradiated cells and thus increase survivals with about 10%. This is explained as a scavenger action where radical hydrogen atoms are oxidized and hydrated electrons captured by oxygen moelcules. When the oxygen concentration is increased, or with higher doses, the usual sensitizing effect of oxygen exceeds the protection effect. The influence of oxygen on alpha-effects are mainly connected with indirect radiation effects and thus depend on temperature and milieu.

Cellular repopulation in irradiated mouse thymus and bone marrow

Summary Cellular repopulation of thymus and bone marrow was investigated in mice after X-irradiation. The animals had either one leg shielded during irradiation for varying lengths of time, or were transplanted with syngeneic bone marrow cells in graded numbers immediately after radiation treatment. During the first 12 days after treatment thymic repopulation was largely independent of the number of bone marrow cells available in the organism. Thereafter repopulation proceeded in relation to the number of the bone marrow cells present. In contrast to the thymus, cellular restoration of the bone marrow was directly related to the number of the protected or transplanted marrow cells from the beginning. An indirect effect of radiation on the regeneration pattern of the population of small size bone marrow cells, comprising largely lymphoid elements, was noted.

A study of radiation protection by sulfur compounds

A group of sulfur containing compounds was investigated to determine if any of these compounds possessed antiradiation character as defined by their ability to protect plant tissue ( Lycopersicon esculentum) from the indirect effects of gamma radiation. Those compounds contain the S-H group or that were able to generate this group in solution were found to afford excellent protection. The ability of these compounds to react with OH radicals was then determined by comparison of rate constant for a known reaction involving OH radicals with and without the compounds being present. The order of reactivity with OH radicals match the protecting order found for the radiolysis of plant tissue.

Temperature Dependence and Effect of Glycerol on the Radiation Sensitivity of Bacteriophage-Escherichia coli Complexes Related to Direct and Indirect Radiation Effect

A test system of T2r bacteriophage DNA injected into the Escherichia coli host (1- or 2-minute development at 37°C) permitted experimentation with biologically active DNA in a cellular environment. By irradiation of this system in the liquid and frozen state with cobalt-60 γ-rays at various temperatures, an estimate of the contribution of direct and indirect radiation effect was made. It was concluded that: 1. Not more than 33% and perhaps as low as 15 to 20% of the radiation effect on T2r DNA in a host bacterium is by direct radiation effect; the remainder is by indirect effect. Percentages of the same magnitude were found for irradiations in air and in nitrogen. An oxygen effect of 1.6 was found in the liquid state and the frozen state. 2. The addition of 1 M glycerol (in air) confers radiation protection in the liquid and the frozen state. The protection is threefold at 0°C and about 35% at -160°C. 3. The activation energy derived for frozen phage-bacterial complex in 1 M glycerol is similar to that fo...

Effect of Irradiated Sucrose on Carbohydrate Metabolism of Carrot Cells

FAUST, Mi., CHASE, B. R., AND MASSEY, L. Mi., JR. Effect of Irradiated Sucrose on Carbohydrate Metabolism of Carrot Cells. Radiation Res. 31, 201-205 (1967). The possible indirect effect of radiation through radiolysis of sucrose on carbohydrate metabolism of carrot cells was investigated. This was accomplished by study of the utilization of specifically labeled substrates in the presence of y-irradiated aqueous sucrose. It was found that the presence of irradiated sucrose did not cause abnormality in the utilization of labeled glucose, acetate, or succinate. An apparent effect of irradiated sucrose on utilization of labeled glucose proved to be an artifact, probably due to radiolytic formation of glucose from sucrose. It was concluded that the Embden-Meyerhof-Paranas pathway, the pentose phosphate pathway, and the citric acid cycle of carrot cells were not affected by the presence of irradiated sucrose.

EFFECT OF TEMPERATURE ON RADIATION RESISTANCE OF SPORES OF CLOSTRIDIUM BOTULINUM 33A

Spores of Clostridium botulinum 33A in two suspending media, phosphate buffer and pork pea broth, were gamma irradiated at radiation temperatures from +20 °C to −196 °C. The liquid–solid transition around 0 °C introduced a one-step plateaulike change in radiation sensitivity of spores. The spores were considerably more resistant in the solidly frozen medium than in the liquid medium. The solid state reduced indirect effects of radiation by physical blocking of secondary radicals. The one-step transition was much smaller in pork pea broth than in buffer. This indicated that scavenging of secondary radicals by pork pea broth caused a considerable reduction of indirect effects of radiation, but did not completely eliminate them.Freezing alone did not eliminate all indirect effects. This was evident from the gradual reduction in radiation sensitivity of spores in the solidly frozen phosphate buffer betweeen −25 °C and −196 °C. Furthermore, even at −196 °C indirect effects of radiation remained active since (a) spore survival did not level off with respect to temperature and (b) the lethal efficiency of radiation was still appreciably greater in phosphate buffer than in pork pea broth at −196 °C.In frozen pork pea broth at −25 °C to −196 °C temperature had no effect on radiation sensitivity of spores. This indicated that spores were killed by direct hits; apparently physical blocking by the solidly frozen medium, plus radical scavenging by pork pea broth eliminated all indirect effects of radiation.

Inhibition by Radiation of the Development of Drug-Detoxification Enzymes

A study was conducted to ascertain the influence of X-irradiation on the synthesis of detoxification enzymes. In the young male rat some of the detoxification enzymes located in the microsomal fraction of the liver exhibit two distinct phases of development. One phase occurs from the time of birth to about 21 days of age, and the second phase occurs from 21 to about 45 days of age. When weanling male rats were exposed to 100 R, 200 R, or 400 R of X-irradiation, a dose-dependent, reversible inhibition of the second phase of enzyme development occurred. This effect rendered the animals more susceptible to drugs that are detoxified by microsomal enzymes. Partial-body shielding experiments revealed that shielding the liver and testes areas did not prevent the inhibition of enzyme development. The inhibition occurred when only the head was irradiated, indicating that it is due to an abscopal effect. The nature of this indirect effect of radiation was not elucidated, but it seems possible that it involves an ab...