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At least 685 records · Page 38Linked to original sources
PubMed1998

Survival and DNA damage in Chinese hamster V79 cells exposed to alpha particles emitted by DNA-incorporated astatine-211.

Asynchronous Chinese hamster V79 lung fibroblasts were incubated at 37 degrees C for 30 min with the thymidine analog 5-[211At]astato-2'-deoxyuridine (211AtdU, exposure from DNA-incorporated activity) or with [211At]astatide (211At-, exposure from extracellular activity), and DNA-incorporated activity was determined. The 211AtdU content in cellular DNA increased as a function of extracellular concentration. Incorporation of 211At- was less than 1% of that of 211AtdU. After exposure, cells were frozen in the presence of 10% DMSO. One month later, survival was determined by the colony-forming assay, and DNA double-strand breaks (DSBs) were measured by the neutral elution method (pH 9.6). The survival curve for 211AtdU was biphasic (D37 = 2.8 decays per cell), reflecting killing of 211At-DNA-labeled cells and of unlabeled cells irradiated by 211At in neighboring labeled cells. The toxicity of 211At- decaying outside the cell (30-min exposure) was negligible. Analysis of the survival curve produced a D0 of 1.3 decays/cell for 211At-labeled cells. The yield of DSBs from the decay of DNA-incorporated 211At was compared with that from DNA-incorporated 125I. Each decay of 211At produced at least 10 times the number of DSBs as that obtained per 125I decay. The extreme radiotoxicity of DNA-incorporated 211AtdU seems to be associated with considerable damage to the mammalian cell genome.

Animals↗
PubMed1979

The ability of ionizing radiations of different LET to induce chromosomal deletions in Aspergillus nidulans.

Conidia, derived from a strain of Aspergillus nidulans known to carry a specific chromosomal duplication, were irradiated. The duplicated segment had genetic markers, which, when eliminated from the genome, allowed the easy detection of deletion mutants. Survival curves derived following 15 MeV electron and gamma-ray irradiation were characterised by the presence of an appreciable shoulder, whilst 50 kvp X-rays gave a much smaller shoulder. Irradiation with beta-particles and alpha-particles gave rise to exponential survival curves. The RBE values for these radiations, based on the D37 value were for gamma-rays, 1.0, 15 MeV electrons 1.0, 50 kvp X-rays 1.9, beta-particles 2.1 and alpha-particles 3.4. With the exception of gamma-rays the radiations described were compared with respect to their ability to induce chromosomal deletions. When the number of deletants amongst survivors was plotted against dose, a linear relationship was found for electrons, X-rays and beta-particles. The response recorded for alpha-particles was essentially linear but with a biphasic component. The RBE values for the radiations, based on a value of unity for 15 MeV electrons were as follows: X-rays 1.3, beta-particles 0.8, alpha-particles above 7.5 krad 2.3 and below 7.5 krad 3.5. When these same data were re-plotted with number of deletants amongst survivors against log survival, electrons appeared the most efficient radiation at producing deletants amongst survivors, with an "m value" of 283 X 10(-5). Tritiated water was least efficient, the corresponding value being 182 X 10(-5). The number of deletants per 10(4) conidia plated, when plotted against dose yielded a curve which increased to a peak and then decreased linearly for all radiations. The peaks for electrons, X-rays and alpha-particles each had a value of about 14 deletants per 10(4) conidia plated and the peaks roughly corresponded with the point at which the survival curve became exponential and was clearly indicative of the accumulation of sub-lethal damage. However, for beta-particles the peak had a value of 7 deletants per 10(4) conidia plated. A non-DNA target has been implicated for cellular death following beta-particle irradiation.

Americium↗
PubMed1989

Movement of multiple DNA units between Myxococcus xanthus cells.

Myxococcus xanthus YS produces particles (Mx alpha particles) that transmit genetic information between cells. Mx alpha particles might be viruses, although no host able to sustain lytic growth of Mx alpha has been discovered. The particles could be detected by their ability to transduce a Tn5 transposon tag to recipient bacteria. DNA from purified particles hybridized to a limited number of DNA restriction fragments of strain YS, suggesting that Mx alpha particles contain only specific DNA sequences. A set of Tn5 insertions residing in the transducible region provided genetic markers for cloning cellular DNA packaged by Mx alpha. A map of this region showed that transducible DNA comprised multiple units of approximately 80 kilobases each. Individual units share DNA homology but are divergent in the location of restriction sites. Other wild-type isolates of Myxococcus species contained DNA sequences with homology to Mx alpha DNA, indicating that Mx alpha DNA is widespread in nature. Experiments on the transfer of Mx alpha DNA in strain YS suggested that DNA transfer is enhanced during the developmental cycle.

Blotting, Southern↗
PubMedDate not supplied

[Effects of high energy charged particles on conduction of nerve rhythmic excitation].

The effects of heavy charged particles--alpha-particles and deuterons accelerated by cyclotron to the energies of 30.3 and 15.4 MeV accordingly--on nerve's excitability (amplitude of an action potential (AP) and speed of AP propogation has been studied. The local irradiation of a little segments of nerve by particles having high LET has been used. The differences in dose curves of AP parameters were detected both during the influence of particles, and during the influence of particles on a nerve treated with isopropyl alcohol. The results showed the AP amplitude reducing that was more expressed in case of alpha-particles, and the AP speed decreasing that was more expressed in case of deuterons. During irradiation, the AP blocked by isopropyl alcohol was rehabilitated, and then was disappeared irreversible. The injury of nerve during irradiation had local character and did not influence on neighbor non-irradiated regions.

Action Potentials↗
PubMed2003

Domestic radon risks may be dominated by bystander effects--but the risks are unlikely to be greater than we thought.

Radon risks derive from exposure of bronchio-epithelial cells to alpha particles. Alpha-particle exposure can result in bystander effects when irradiated cells emit signals resulting in damage to nearby unirradiated bystander cells. Bystander effects can cause downwardly-curving dose-response relations and inverse dose-rate effects. We have extended a quantitative mechanistic model of bystander effects to include protracted exposure, with inverse dose-rate effects attributed to replenishment, during exposure, of a subpopulation of cells which are hypersensitive to bystander signals. In this approach, bystander effects and the inverse dose-rate effect are manifestations of the same basic phenomenon. The model was fitted to dose- and dose-rate dependent radon-exposed miner data; the results suggest that one directly-hit target cell can send bystander signals to about 50 neighboring cells and that, in the case of domestic radon exposures, the risk could be dominated by bystander effects. The analysis concludes that a naive linear extrapolation of radon miner data to low doses, without accounting for dose rate/bystander effects, would result in an underestimation of domestic radon risks by about a factor of approximately 4. However, recent domestic radon risk estimates (BEIR VI) have already applied a phenomenological correction factor of approximately 4 for inverse dose-rate effects, and have thus already implicitly taken into account corrections which we here suggest are due to bystander effects. Thus current domestic radon risk estimates are unlikely to be underestimates as a result of bystander effects.

Air Pollution, Indoor↗
PubMed1989

Fission fragment RBE for bone sarcoma induction.

Thirty beagles and 277 mice were injected with 249Cf, and 30 beagles and 274 mice were injected with 252Cf. The skeletal dose (in Gy) from 252Cf was about half from fission fragments and half from alpha particles, whereas 249Cf emits alpha particles in 100% of its transformations. Bone sarcomas (mostly osteosarcomas) were the main radiation-induced cancer. The relative biological effectiveness (RBE) of fission fragment dose relative to alpha-particle dose for bone sarcoma induction was calculated from the ratio of 249Cf/252Cf doses at equal times to bone sarcoma in (a) beagles and (b) mice, and (c) from the ratio 252Cf/249Cf risk coefficients in mice. The average RBE +/- standard deviation of the three evaluations was 0.1 +/- 0.1. The very low RBE for bone sarcomas is supported by the data of A. L. Batchelor, T. J. Jenner, and L. M. Cobb [Phys. Med. Biol. 28, 475-483 (1983)] for lung cancer induction in rats and by that of A. L. Brooks, J. A. Mewhinney, and R. O. McClellan [Health Phys. 22, 701-706 (1972)] for producing chromosome aberrations in the liver cells of Chinese hamsters. The low effectiveness of fission fragments relative to alpha particles, per gray of absorbed dose, is ascribed primarily to the much larger number of cells traversed by the alpha particles. Consideration might be given to decreasing the quality factor of fission fragments by an order of magnitude below that for alpha particles.

Alpha Particles↗
PubMed2006

TOF-SIMS evidence of intercalated molecular gases and diffusion-limited reaction kinetics in an alpha particle-irradiated PTFE matrix.

The chemical evolution of poly(tetrafluoroethylene) (PTFE) that is brought about by increasing levels of irradiation with alpha particles is accompanied by the emergence and proliferation of functionalized moieties. Families of reaction products specifically identified in the alpha-irradiated polymer matrix include hydride-, hydroxide-, and oxide-functionalized fluorocarbons. The data also indicate the emergence of hydrogen peroxide (H2O2) and hydrazine (N2H4), but no distinct evidence suggesting the formation of perfluorinated amines, amides, or cyanogens is found. In this article we substantiate the speciation of emergent species and reveal evidence of intercalated molecular gases with which alpha particle-generated radicals may react to form the observed products. Furthermore, we present evidence to suggest that the kinetics of alpha particle-induced reaction is limited by the diffusion of radicals within the polymer matrix. That is to say, chemical additives in the polymer matrix are shown to be scavengers of H*, O*, and F* radicals and limit the rates of reaction that produce functionalized fluorocarbon moieties. Above a threshold dose of alpha particles, the concentration of radicals exceeds that of the scavenger species, and free radical diffusion commences as evidenced by a sudden increase in the yield of reaction products. Samples of PTFE were irradiated to alpha doses in the range of 10(7) to 5 x 10(10) rad with 5.5 MeV 4He2+ ions from a tandem accelerator. Residual gas analysis (RGA) was utilized to monitor the liberation of molecular gases from PTFE during alpha particle irradiation of samples in vacuum. Static time-of-flight SIMS (TOF-SIMS), equipped with a 20 keV C60+ source, was employed to probe chemical changes as a function of alpha particle irradiation. Chemical images and high-resolution mass spectra were collected in both the positive and negative polarities.

Journal Article↗
PubMed1998

[EGF-dependent association of 20S-proteasome and alpha-RNP particles with the epidermal growth factor receptor in A-431 cells].

Here we demonstrate that the epidermal growth factor (EGF) induces association of prosomes (20S-proteasomes) with its receptor in A-431 cells. Additionally, ligand-dependent association of ribonucleoprotein particles (alpha-RNP), containing small ALU-like RNA, with the EGF receptor was demonstrated. A suggestion has been put forward on the involvement of prosomes and alpha-RNP in the EGF signal transmission to different stages of gene expression.

Cysteine Endopeptidases↗
PubMed2002

Do low dose-rate bystander effects influence domestic radon risks?

PURPOSE: Radon risks derive from exposure of bronchio-epithelial cells to high-linear energy transfer (LET) alpha-particles. alpha-particle exposure can result in bystander effects, where irradiated cells emit signals resulting in damage to nearby unirradiated bystander cells. This can result in non-linear dose-response relations, and inverse dose-rate effects. Domestic radon risk estimates are currently extrapolated from miner data, which are at both higher doses and higher dose-rates, so bystander effects on unhit cells could play a large role in the extrapolation of risks from mines to homes. Therefore, we extend an earlier quantitative mechanistic model of bystander effects to include protracted exposure, with the aim of quantifying the significance of the bystander effect for very prolonged exposures. MATERIALS AND METHODS: A model of high-LET bystander effects, originally developed to analyse oncogenic transformation in vitro, is extended to low dose-rates. The model considers radiation response as a superposition of bystander and linear direct e It attributes bystander effects to a small subpopulation of hypersensitive cells, with the bystander contribution dominating the direct contribution at very low acute doses but saturating as the dose increases. Inverse dose-rate effects are attributed to the replenishment of the hypersensitive subpopulation during prolonged irradiation. RESULTS: The model was fitted to dose- and dose-rate-dependent radon-exposed miner data, suggesting that one directly hit target bronchio-epithelial cell can send bystander signals to about 50 neighbouring target cells. The model suggests that a naïve linear extrapolation of radon miner data to low doses, without accounting for dose-rate, would result in an underestimation of domestic radon risks by about a factor of 4, a value comparable with the empirical estimate applied in the recent BEIR-VI report on radon risk estimation. CONCLUSIONS: Bystander effects represent a plausible quantitative and mechanistic explanation of inverse dose-rate effects by high-LET radiation, resulting in non-linear dose-response relations and a complex interplay between the effects of dose and exposure time. The model presented provides a potential mechanistic underpinning for the empirical exposure-time correction factors applied in the recent BEIR-VI for domestic radon risk estimation.

Air Pollution, Indoor↗
PubMed2002

Track counting and the blots.

Track detectors are very useful devices for alpha particle dosimetry. Alpha particle tracks are registered on the detector's surface. The registered track density is proportional to the dose. When the dose is low the greatest effect on the total error of dose assessment has a Poisson distribution (random error). When the dose is high, the greatest contribution to the total error is the effect of track overlapping (systemic error). This paper describes how to solve the problem of overlapping tracks when a computer aided image analyser is used. The formulae presented in this paper were proven in the international calibration programme run by NRPB and EU.

Calibration↗