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Taghipour H, Taherparvar P. Development of modified microdosimetric kinetic model for relative biological effectiveness in proton therapy. RADIATION AND ENVIRONMENTAL BIOPHYSICS 2022; 61:375-390. [PMID: 35699753 DOI: 10.1007/s00411-022-00977-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Accepted: 05/22/2022] [Indexed: 06/15/2023]
Abstract
To predict the biological effects of ionising radiation, the quantity of biological dose is introduced instead of the physical absorbed dose. In proton therapy, a constant relative biological effectiveness (RBE) of 1.1 is usually applied clinically as recommended by the International Commission of Radiation Units and Measurements. This study presents a new model, based on the modified microdosimetric kinetic model (MMKM), for calculating variable RBE values based on experimental data on the induction of DNA double-strand breaks (DSBs) within cells. The MMKM was proposed based on experimental data for the yield of DSBs in mammalian cells, which allows modification of the yield of primary lesions in the MKM. In this approach, a unique function named f(LET), which describes the relation between RBE and linear energy transfer (LET), was considered for charged particles. In the presented model (DMMKM), the MMKM approach was developed further by considering different f(LET)s for different relevant ions involved in energy deposition events in proton therapy. Although experimental data represent the dependence of the yield of primary lesions on the ion species, the DSB yield (assumed as the main primary lesion) is assumed independent of the ion species in the MMKM. In the DMMKM, by considering the yield of primary lesions as a function of the ion species, the α and β values are in better agreement with the experimental data as compared to those of the MKM and MMKM approaches. The biological dose in the DMMKM is predicted to be lower than that in the MMKM. Further, in the proposed model, the variation of the β parameter is higher than the constant value assumed in the MKM, at the distal end of the spread-out Bragg peak (SOBP). Moreover, the level of cell death estimated by the MMKM at the SOBP region is higher than that obtained based on the DMMKM. It is concluded that considering modified f(LET)s in the model developed here is more consistent with experimental results than when MMKM and MKM approaches are considered. The DMMKM examines the biological effects with full detail and will, therefore, be effective in improving proton therapy.
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Affiliation(s)
- Hossein Taghipour
- Department of Physics, Faculty of Science, University of Guilan, Namjoo Avenue, P.O. Box 41635-1914, Rasht, 4193833697, Guilan, Iran
| | - Payvand Taherparvar
- Department of Physics, Faculty of Science, University of Guilan, Namjoo Avenue, P.O. Box 41635-1914, Rasht, 4193833697, Guilan, Iran.
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Klomchitcharoen S, Tangwattanasirikun T, Gallup S, Smerwong N, Arunwiriyakit P, Tachavises P, Tangkijngamwong J, Phatthanaanukun P, Jirapanyalerd B, Chattanupakorn S, Rungpongvanich V, Nangsue N, Meemon K, Wongtrakoonkate P, Hongeng S, Wongsawat Y. MINERVA: A CubeSat for demonstrating DNA damage mitigation against space radiation in C. elegans by using genetic modification. Heliyon 2022; 8:e10267. [PMID: 36033287 PMCID: PMC9404340 DOI: 10.1016/j.heliyon.2022.e10267] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2022] [Revised: 05/06/2022] [Accepted: 08/08/2022] [Indexed: 11/17/2022] Open
Abstract
The ideas of deep-space human exploration, interplanetary travel, and space civilizations are becoming a reality. However, numerous hindrances remain standing in the way of accomplishing these feats, one of which is space ionizing radiation. Space ionizing radiation has become the most hazardous health risk for long-term human space exploration, as it can induce chromosomal damage and epigenetic changes. The Minerva mission aims to demonstrate cutting-edge technology to inhibit DNA damage against deep-space radiation exposure by using genetic modification. The concept of the experiment is to transform a creature with radiation intolerance into a transgenic organism that is radiation-tolerant. In this mission, Caenorhabditis elegans (C. elegans) will be genetically engineered with a protein-coding gene associated with DNA damage protection called damage suppressor (Dsup). Dsup is a nucleosome-binding protein from the tardigrade Ramazzottius varieornatus that has a unique ability to prevent DNA damage. This paper describes the feasibility of Minerva CubeSat, which will venture out to cis-lunar orbit with a biosensor payload capable of sustaining and culturing C. elegans under space environment conditions for 4 months. The mission will set in motion a paradigm shift corresponding to future space medicines and how they will be developed in the future, introducing a platform suitable for future experiments in the fields of space biology. Ultimately, the paramount objective of Minerva will be to test the limits of genetic engineering and incorporate it into the arduous journey of human perseverance to overcome the boundaries of space exploration—a vital step in making Mars colonization safe.
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Affiliation(s)
- Sumeth Klomchitcharoen
- Brain-Computer Interface Laboratory, Department of Biomedical Engineering, Faculty of Engineering, Mahidol University, Nakhon Pathom, Thailand
| | - Tanchanok Tangwattanasirikun
- Brain-Computer Interface Laboratory, Department of Biomedical Engineering, Faculty of Engineering, Mahidol University, Nakhon Pathom, Thailand
| | - Sean Gallup
- Brain-Computer Interface Laboratory, Department of Biomedical Engineering, Faculty of Engineering, Mahidol University, Nakhon Pathom, Thailand
| | - Noparin Smerwong
- Brain-Computer Interface Laboratory, Department of Biomedical Engineering, Faculty of Engineering, Mahidol University, Nakhon Pathom, Thailand
| | - Peetimon Arunwiriyakit
- Brain-Computer Interface Laboratory, Department of Biomedical Engineering, Faculty of Engineering, Mahidol University, Nakhon Pathom, Thailand
| | - Pisitchai Tachavises
- Brain-Computer Interface Laboratory, Department of Biomedical Engineering, Faculty of Engineering, Mahidol University, Nakhon Pathom, Thailand
| | - Jin Tangkijngamwong
- Brain-Computer Interface Laboratory, Department of Biomedical Engineering, Faculty of Engineering, Mahidol University, Nakhon Pathom, Thailand
| | - Pichamon Phatthanaanukun
- Brain-Computer Interface Laboratory, Department of Biomedical Engineering, Faculty of Engineering, Mahidol University, Nakhon Pathom, Thailand
| | - Benjamard Jirapanyalerd
- Brain-Computer Interface Laboratory, Department of Biomedical Engineering, Faculty of Engineering, Mahidol University, Nakhon Pathom, Thailand
| | - Siripak Chattanupakorn
- Brain-Computer Interface Laboratory, Department of Biomedical Engineering, Faculty of Engineering, Mahidol University, Nakhon Pathom, Thailand
| | - Visarut Rungpongvanich
- Brain-Computer Interface Laboratory, Department of Biomedical Engineering, Faculty of Engineering, Mahidol University, Nakhon Pathom, Thailand
| | - Norawit Nangsue
- Institute of Field Robotics, King Mongkut's University of Technology Thonburi, Bangkok, Thailand
| | - Krai Meemon
- Department of Anatomy, Faculty of Science, Mahidol University, Bangkok, Thailand
| | | | - Suradej Hongeng
- Section for Translational Medicine, Faculty of Medicine Ramathibodi Hospital, Mahidol University, Bangkok, Thailand
| | - Yodchanan Wongsawat
- Brain-Computer Interface Laboratory, Department of Biomedical Engineering, Faculty of Engineering, Mahidol University, Nakhon Pathom, Thailand
- Corresponding author.
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Hsiao YY, Chen FH, Chan CC, Tsai CC. Monte Carlo Simulation of Double-Strand Break Induction and Conversion after Ultrasoft X-rays Irradiation. Int J Mol Sci 2021; 22:ijms222111713. [PMID: 34769142 PMCID: PMC8583805 DOI: 10.3390/ijms222111713] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Revised: 10/22/2021] [Accepted: 10/25/2021] [Indexed: 12/26/2022] Open
Abstract
This paper estimates the yields of DNA double-strand breaks (DSBs) induced by ultrasoft X-rays and uses the DSB yields and the repair outcomes to evaluate the relative biological effectiveness (RBE) of ultrasoft X-rays. We simulated the yields of DSB induction and predicted them in the presence and absence of oxygen, using a Monte Carlo damage simulation (MCDS) software, to calculate the RBE. Monte Carlo excision repair (MCER) simulations were also performed to calculate the repair outcomes (correct repairs, mutations, and DSB conversions). Compared to 60Co γ-rays, the RBE values for ultrasoft X-rays (titanium K-shell, aluminum K-shell, copper L-shell, and carbon K-shell) for DSB induction were respectively 1.3, 1.9, 2.3, and 2.6 under aerobic conditions and 1.3, 2.1, 2.5, and 2.9 under a hypoxic condition (2% O2). The RBE values for enzymatic DSBs were 1.6, 2.1, 2.3, and 2.4, respectively, indicating that the enzymatic DSB yields are comparable to the yields of DSB induction. The synergistic effects of DSB induction and enzymatic DSB formation further facilitate cell killing and the advantage in cancer treatment.
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Affiliation(s)
- Ya-Yun Hsiao
- Department of Radiology, Chung Shan Medical University Hospital, Taichung 40201, Taiwan;
- Department of Medical Imaging and Radiological Sciences, Chung Shan Medical University, Taichung 40201, Taiwan
| | - Fang-Hsin Chen
- Department of Medical Imaging and Radiological Sciences, Chang Gung University, Taoyuan 33302, Taiwan;
- Radiation Biology Research Center, Institute for Radiological Research, Chang Gung University, Taoyuan 33302, Taiwan
- Department of Radiation Oncology, Chang Gung Memorial Hospital-Linkou Branch, Taoyuan 33305, Taiwan
| | - Chun-Chieh Chan
- Department of Electrical Engineering, National Chung Hsing University, Taichung 40227, Taiwan
- Correspondence: (C.-C.C.); (C.-C.T.); Tel.: +886-4-22851549-222 (C.-C.T.)
| | - Ching-Chih Tsai
- Department of Electrical Engineering, National Chung Hsing University, Taichung 40227, Taiwan
- Correspondence: (C.-C.C.); (C.-C.T.); Tel.: +886-4-22851549-222 (C.-C.T.)
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Farzipour S, Shaghaghi Z, Abbasi S, Albooyeh H, Alvandi M. Recent Achievements about Targeted Alpha Therapy-Based Targeting Vectors and Chelating Agents. Anticancer Agents Med Chem 2021; 22:1496-1510. [PMID: 34315393 DOI: 10.2174/1871520621666210727120308] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Revised: 06/22/2021] [Accepted: 06/28/2021] [Indexed: 11/22/2022]
Abstract
One of the most rapidly growing options in the management of cancer therapy is Targeted Alpha Therapy (TAT) through which lethal α-emitting radionuclides conjugated to tumor-targeting vectors selectively deliver high amount of radiation to cancer cells.225Ac, 212Bi, 211At, 213Bi, and 223Ra have been investigated by plenty of clinical trials and preclinical researches for the treatment of smaller tumor burdens, micro-metastatic disease, and post-surgery residual disease. In order to send maximum radiation to tumor cells while minimizing toxicity in normal cells, a high affinity of targeting vectors to cancer tissue is essential. Besides that, the stable and specific complex between chelating agent and α-emitters was found as a crucial parameter. The present review was planned to highlight recent achievements about TAT-based targeting vectors and chelating agents and provide further insight for future researches.
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Affiliation(s)
- Soghra Farzipour
- Cardiovascular Diseases Research Center, Department of Cardiology, Heshmat Hospital, School of Medicine, Guilan University of Medical Sciences, Rasht, Iran
| | - Zahra Shaghaghi
- Department of Nuclear Medicine and Molecular Imaging, Clinical Development Research Unit of Farshchian Heart Center, Hamadan University of Medical Sciences, Hamadan, Iran
| | - Sahar Abbasi
- Department of Radiology, Loghman Hakim Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Hajar Albooyeh
- Department of Nuclear Medicine, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran
| | - Maryam Alvandi
- Department of Nuclear Medicine and Molecular Imaging, Clinical Development Research Unit of Farshchian Heart Center, Hamadan University of Medical Sciences, Hamadan, Iran
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Fernando C, Byun SH, Shi X, Seymour CB, Mothersill CE. Isolation of the effects of alpha-related components from total effects of radium at low doses. Int J Radiat Biol 2021; 98:1168-1175. [PMID: 33332185 DOI: 10.1080/09553002.2020.1866226] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
PURPOSE Radium is the most common source of alpha radiation exposure to humans and non-human species in the environment but the dosimetry is complicated by the decay chain which involves gamma exposure due to radon daughters. This paper seeks to determine the separate contributions of alpha and gamma doses to the total dose and total direct and non-targeted effect in a fish and a human cell line. MATERIALS AND METHODS This study aimed to isolate the effect of alpha particles following exposure to low doses of radium in cells, and their progeny which received no further exposure. This was initially done by comparing the survival values of a human keratinocyte cell line (HaCaT) and an embryonic Chinook salmon cell line (CHSE-214) exposed to gamma radiation, from survival of the same cell lines exposed to mixed alpha and gamma radiation through exposure to Ra-226 and its decay products. A Monte Carlo simulation was later performed to determine the contributions of radium decay products including radon daughters. RESULTS The human cell line showed increased radioresistance when exposed to low doses of alpha particles. In contrast the fish cell line, which demonstrated radioresistance to low dose gamma radiation, showed increased lethality when exposed to low doses of alpha particles. Significant and complex levels of non-targeted effects were induced in progeny of irradiated cells. The simulation showed that gamma and beta decay products did not contribute significant dose and the highest beta dose was below the threshold for inducing non-targeted effects. CONCLUSIONS The results confirm the need to consider the dose-response relationship when developing radiation weighting factors for low dose exposures, as well as the need to be aware of possible cell line and species differences.
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Affiliation(s)
- Chandula Fernando
- Radiation Sciences Graduate Program, McMaster University, Hamilton, Canada
| | - Soo Hyun Byun
- Department of Physics and Astronomy, McMaster University, Hamilton, Canada
| | - Xiaopei Shi
- Department of Biology, McMaster University, Hamilton, Canada
| | - Colin B Seymour
- Department of Biology, McMaster University, Hamilton, Canada
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Robertson AKH, McNeil BL, Yang H, Gendron D, Perron R, Radchenko V, Zeisler S, Causey P, Schaffer P. 232Th-Spallation-Produced 225Ac with Reduced 227Ac Content. Inorg Chem 2020; 59:12156-12165. [DOI: 10.1021/acs.inorgchem.0c01081] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Andrew K. H. Robertson
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
- Life Sciences Division, TRIUMF, Vancouver, British Columbia, Canada V6T 2A3
| | - Brooke L. McNeil
- Life Sciences Division, TRIUMF, Vancouver, British Columbia, Canada V6T 2A3
- Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1
| | - Hua Yang
- Life Sciences Division, TRIUMF, Vancouver, British Columbia, Canada V6T 2A3
| | - Denise Gendron
- Canadian Nuclear Laboratories, Chalk River, Ontario, Canada K0J 1J0
| | - Randy Perron
- Canadian Nuclear Laboratories, Chalk River, Ontario, Canada K0J 1J0
| | - Valery Radchenko
- Life Sciences Division, TRIUMF, Vancouver, British Columbia, Canada V6T 2A3
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
| | - Stefan Zeisler
- Life Sciences Division, TRIUMF, Vancouver, British Columbia, Canada V6T 2A3
| | - Patrick Causey
- Canadian Nuclear Laboratories, Chalk River, Ontario, Canada K0J 1J0
| | - Paul Schaffer
- Life Sciences Division, TRIUMF, Vancouver, British Columbia, Canada V6T 2A3
- Department of Chemistry, Simon Fraser University, Vancouver, British Columbia, Canada V5A 1S6
- Department of Radiology, University of British Columbia, Vancouver, British Columbia, Canada V5Z 1M9
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Cornforth MN. Occam's broom and the dirty DSB: cytogenetic perspectives on cellular response to changes in track structure and ionization density. Int J Radiat Biol 2020; 97:1099-1108. [PMID: 31971454 DOI: 10.1080/09553002.2019.1704302] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2019] [Revised: 10/30/2019] [Accepted: 11/11/2019] [Indexed: 12/19/2022]
Abstract
Given equal doses, it is well-known that densely ionizing radiations are more potent in causing a number of biological effects compared to sparsely ionizing radiations, such as x- or gamma rays. According to classical models of radiation action, this results from differences in the spatial distribution of lesions along charged particle tracks. In recent years investigators have been barraged with the alternative narrative that this is instead due to 'qualitative' differences in the types of molecular lesions that each type of radiation produces. The present review discusses, mainly from a cytogenetic perspective, the merits and shortcomings of these seemingly contradictory viewpoints. There may be a kernel of truth to the idea that qualitative differences in the types of molecular lesions produced at the nanometer level affect RBE/LET relationships, but to ignore the fact that such differences result from longer-range spatial distributions of lesions produced along charged particle tracks is an unjustifiably narrow stance tantamount to employing Occam's Broom. Not only are such spatial considerations indispensable in explaining the impact of ionization density upon higher-order biological endpoints, particularly chromosome aberrations, the explanations they provide render arguments based principally on the quality of IR damage largely superfluous.
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Affiliation(s)
- Michael N Cornforth
- Department of Radiation Oncology, University of Texas Medical Branch, Galveston, TX, USA
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Luo WR, Chen FH, Huang RJ, Chen YP, Hsiao YY. Effects of indirect actions and oxygen on relative biological effectiveness: estimate of DSB inductions and conversions induced by therapeutic proton beams. Int J Radiat Biol 2019; 96:187-196. [PMID: 31682784 DOI: 10.1080/09553002.2020.1688883] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Purpose: This study evaluated the DNA double strand breaks (DSBs) induced by indirect actions and its misrepairs to estimate the relative biological effectiveness (RBE) of proton beams.Materials and methods: From experimental data, DSB induction was evaluated in cells irradiated by 62 MeV proton beams in the presence of dimethylsulphoxide (DMSO) and under hypoxic conditions. The DNA damage yields for calculating the RBE were estimated using Monte Carlo Damage Simulation (MCDS) software. The repair outcomes (correct repairs, mutations and DSB conversions) were estimated using Monte Carlo Excision Repair (MCER) simulations.Results: The values for RBE of 62 MeV protons (LET = 1.051 keV/μm) for DSB induction and enzymatic DSB under aerobic condition (21% O2) was 1.02 and 0.94, respectively, as comparing to 60Co γ-rays (LET = 2.4 keV/μm). DMSO mitigated the inference of indirect action and reduced DSB induction to a greater extent when damaged by protons rather than γ-rays, resulting in a decreased RBE of 0.86. DMSO also efficiently prevented enzymatic DSB yields triggered by proton irradiation and reduced the RBE to 0.83. However, hypoxia (2% O2) produced a similar level of DSB induction with respect to the protons and γ-rays, with a comparable RBE of 1.02.Conclusions: The RBE values of proton beams estimated from DSB induction and enzymatic DSB decreased by 16% and 12%, respectively, in the presence of DMSO. Our findings indicate that the overall effects of DSB induction and enzymatic DSB could intensify the tumor killing, while alleviate normal tissue damage when indirect actions are effectively interrupted.
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Affiliation(s)
- Wei-Ren Luo
- Department of Radiology, Chung Shan Medical University Hospital, Taichung, Taiwan
| | - Fang-Hsin Chen
- Department of Medical Imaging and Radiological Sciences, Chang Gung University, Kweishan, Taiwan.,Radiation Biology Research Center, Institute for Radiological Research, Chang Gung University/Chang Gung Memorial Hospital, Taoyuan, Taiwan.,Department of Radiation Oncology, Chang Gung Memorial Hospital-Linkou Branch, Taoyuan, Taiwan
| | - Ren-Jing Huang
- Department of Radiology, Chung Shan Medical University Hospital, Taichung, Taiwan.,Department of Medical Imaging and Radiological Sciences, Chung Shan Medical University, Taichung, Taiwan
| | - Yu-Pin Chen
- Department of Radiology, Taipei Manicipal Wan-Fang Hospital, Taipei Medical University, Taipei, Taiwan
| | - Ya-Yun Hsiao
- Department of Radiology, Chung Shan Medical University Hospital, Taichung, Taiwan.,Department of Medical Imaging and Radiological Sciences, Chung Shan Medical University, Taichung, Taiwan
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Evstratova ES, Petin VG. The delayed appearance of haploid and homozygous diploid Saccharomyces cerevisiae yeast cells of wild-type and radiosensitive mutants surviving after exposure to gamma rays and alpha particles. JOURNAL OF RADIATION RESEARCH AND APPLIED SCIENCES 2019. [DOI: 10.1016/j.jrras.2017.11.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Ekaterina S. Evstratova
- A. Tsyb Medical Radiological Research Center, Branch of the National Medical Research Radiological Center of the Ministry of Health of the Russian Federation, Korolev St., 4, Obninsk, 249036, Russia
| | - Vladislav G. Petin
- A. Tsyb Medical Radiological Research Center, Branch of the National Medical Research Radiological Center of the Ministry of Health of the Russian Federation, Korolev St., 4, Obninsk, 249036, Russia
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Liang Y, Fu Q, Wang X, Liu F, Yang G, Luo C, Ouyang Q, Wang Y. Relative biological effectiveness for photons: implication of complex DNA double-strand breaks as critical lesions. Phys Med Biol 2017; 62:2153-2175. [DOI: 10.1088/1361-6560/aa56ed] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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Shi X, Seymour C, Mothersill C. The effects of chronic, low doses of Ra-226 on cultured fish and human cells. ENVIRONMENTAL RESEARCH 2016; 148:303-309. [PMID: 27093471 DOI: 10.1016/j.envres.2016.04.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2016] [Revised: 04/05/2016] [Accepted: 04/07/2016] [Indexed: 06/05/2023]
Abstract
PURPOSE To determine the chronic low-dose radiation effects caused by α-particle radiation from (226)Ra over multiple cell generations in CHSE/F fish cells and HaCaT human cells. METHODS CHSE/F cells and HaCaT cells were cultured in medium containing (226)Ra to deliver the chronic low-dose α-particle radiation. Clonogenic assay was used to test the clonogenic survival fractions of cells with or without being exposed to radiation from (226)Ra. RESULTS The chronic low-dose radiation from (226)Ra does have effects on the clonogenic survival of CHSE/F cells and HaCaT cells. When CHSE/F cells were cultured in (226)Ra-medium over 9 passages for about 134 days, the clonogenic surviving fractions for cells irradiated at dose rates ranging from 0.00066 to 0.66mGy/d were significantly lower than that of cells sham irradiated. For HaCaT cells grown in medium containing the same range of (226)Ra activity, the clonogenic surviving fraction decreased at first and reached the lowest value at about 42 days (8 passages). After that, the clonogenic survival began to increase, and was significantly higher than that of control cells by the end of the experimental period. CONCLUSION The chronic, low-dose high LET radiation from (226)Ra can influence the clonogenic survival of irradiated cells. CHSE/F cells were sensitized by the radiation, and HaCaT cells were initially sensitized but later appeared to be adapted. The results could have implications for determining risk from chronic versus acute exposures to radium.
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Affiliation(s)
- Xiaopei Shi
- Medical Physics and Applied Radiation Sciences, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4L8, Canada
| | - Colin Seymour
- Medical Physics and Applied Radiation Sciences, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4L8, Canada
| | - Carmel Mothersill
- Medical Physics and Applied Radiation Sciences, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4L8, Canada.
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Pang D, Chasovskikh S, Rodgers JE, Dritschilo A. Short DNA Fragments Are a Hallmark of Heavy Charged-Particle Irradiation and May Underlie Their Greater Therapeutic Efficacy. Front Oncol 2016; 6:130. [PMID: 27376024 PMCID: PMC4901041 DOI: 10.3389/fonc.2016.00130] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2016] [Accepted: 05/16/2016] [Indexed: 11/13/2022] Open
Abstract
Growing interest in proton and heavy ion therapy has reinvigorated research into the fundamental biological mechanisms underlying the therapeutic efficacy of charged-particle radiation. To improve our understanding of the greater biological effectiveness of high-LET radiations, we have investigated DNA double-strand breaks (DSBs) following exposure of plasmid DNA to low-LET Co-60 gamma photon and electron irradiation and to high-LET Beryllium and Argon ions with atomic force microscopy. The sizes of DNA fragments following radiation exposure were individually measured to construct fragment size distributions from which the DSB per DNA molecule and DSB spatial distributions were derived. We report that heavy charged particles induce a significantly larger proportion of short DNA fragments in irradiated DNA molecules, reflecting densely and clustered damage patterns of high-LET energy depositions. We attribute the enhanced short DNA fragmentation following high-LET radiations as an important determinant of the observed, enhanced biological effectiveness of high-LET irradiations.
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Affiliation(s)
- Dalong Pang
- Radiation Medicine, Georgetown University Medical Center , Washington, DC , USA
| | - Sergey Chasovskikh
- Radiation Medicine, Georgetown University Medical Center , Washington, DC , USA
| | - James E Rodgers
- Radiation Oncology, Medstar Franklin Square Medical Center , Rosedale, MD , USA
| | - Anatoly Dritschilo
- Radiation Medicine, Georgetown University Medical Center , Washington, DC , USA
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Liang Y, Yang G, Liu F, Wang Y. Monte Carlo simulation of ionizing radiation induced DNA strand breaks utilizing coarse grained high-order chromatin structures. Phys Med Biol 2015; 61:445-60. [DOI: 10.1088/0031-9155/61/1/445] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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Petin VG, Evstratova ES, Kim JK. Radiosensitivity, liquid-holding recovery and relative biological effectiveness of densely-ionizing radiation after repeated irradiation of yeast cells. MUTATION RESEARCH-GENETIC TOXICOLOGY AND ENVIRONMENTAL MUTAGENESIS 2014; 771:37-42. [PMID: 25308440 DOI: 10.1016/j.mrgentox.2014.06.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2013] [Revised: 05/16/2014] [Accepted: 06/08/2014] [Indexed: 10/25/2022]
Abstract
Experimental results described earlier showed significantly larger relative biological effectiveness (RBE) values for wild-type diploid cells in comparison with radiosensitive mutants. This aspect was further studied in this paper. Diploid yeast cells were irradiated with gamma rays from (60)Co and alpha particles from (239)Pu in the stationary phase of cell growth. Survival curves and the kinetics of the liquid-holding recovery were measured. When the irradiated cells had completely recovered from potentially lethal damage, they were again exposed to radiation and allowed post-irradiation recovery. The procedure was repeated three times. By use of a quantitative approach - describing the process of recovery as a decrease in the effective radiation dose -, the probability of recovery per unit time and the proportion of irreversibly damaged cells were quantitatively estimated. It was shown that the irreversible fraction of cell injury was increased after repeated exposures to gamma rays, from 0.4 after the first irradiation to 0.7 after the third exposure. The effect was more clearly expressed after exposure to densely ionizing radiation, the corresponding values being 0.5 and 1.0. In contrast, the recovery constant did not depend on the number of repeated irradiations and only slightly depended on radiation quality. It is suggested that the process of recovery from potentially lethal radiation damage itself is not impaired after repeated exposures to both low- and high-LET radiations, and the decrease in the ability of the cell to recover from radiation damage is mainly explained by the increase in the proportion of irreversibly damaged cells.
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Affiliation(s)
- Vladislav G Petin
- Biophysical Laboratory, Medical Radiological Research Center, Russian Ministry of Health, Kaluga Region, 249036 Obninsk, Russia.
| | - Ekaterina S Evstratova
- Biophysical Laboratory, Medical Radiological Research Center, Russian Ministry of Health, Kaluga Region, 249036 Obninsk, Russia
| | - Jin K Kim
- Advanced Radiation Technology Institute, Jeongeup 580-185, Republic of Korea
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15
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Lyckesvärd MN, Delle U, Kahu H, Lindegren S, Jensen H, Bäck T, Swanpalmer J, Elmroth K. Alpha particle induced DNA damage and repair in normal cultured thyrocytes of different proliferation status. Mutat Res 2014; 765:48-56. [PMID: 24769180 DOI: 10.1016/j.mrfmmm.2014.04.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2013] [Revised: 04/01/2014] [Accepted: 04/10/2014] [Indexed: 10/25/2022]
Abstract
Childhood exposure to ionizing radiation increases the risk of developing thyroid cancer later in life and this is suggested to be due to higher proliferation of the young thyroid. The interest of using high-LET alpha particles from Astatine-211 ((211)At), concentrated in the thyroid by the same mechanism as (131)I [1], in cancer treatment has increased during recent years because of its high efficiency in inducing biological damage and beneficial dose distribution when compared to low-LET radiation. Most knowledge of the DNA damage response in thyroid is from studies using low-LET irradiation and much less is known of high-LET irradiation. In this paper we investigated the DNA damage response and biological consequences to photons from Cobolt-60 ((60)Co) and alpha particles from (211)At in normal primary thyrocytes of different cell cycle status. For both radiation qualities the intensity levels of γH2AX decreased during the first 24h in both cycling and stationary cultures and complete repair was seen in all cultures but cycling cells exposed to (211)At. Compared to stationary cells alpha particles were more harmful for cycling cultures, an effect also seen at the pChk2 levels. Increasing ratios of micronuclei per cell nuclei were seen up to 1Gy (211)At. We found that primary thyrocytes were much more sensitive to alpha particle exposure compared with low-LET photons. Calculations of the relative biological effectiveness yielded higher RBE for cycling cells compared with stationary cultures at a modest level of damage, clearly demonstrating that cell cycle status influences the relative effectiveness of alpha particles.
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Affiliation(s)
| | - Ulla Delle
- Department of Oncology, Sahlgrenska Academy, University of Gothenburg, Sweden
| | - Helena Kahu
- Department of Oncology, Sahlgrenska Academy, University of Gothenburg, Sweden
| | - Sture Lindegren
- Department of Radiation Physics, Sahlgrenska Academy, University of Gothenburg, Sweden
| | - Holger Jensen
- The PET and Cyclotron Unit Copenhagen University Hospital, Rigshospitalet, Denmark
| | - Tom Bäck
- Department of Radiation Physics, Sahlgrenska Academy, University of Gothenburg, Sweden
| | - John Swanpalmer
- Department of Medical Physics and Biomedical Engineering, Sahlgrenska University Hospital, Gothenburg, Sweden
| | - Kecke Elmroth
- Department of Oncology, Sahlgrenska Academy, University of Gothenburg, Sweden
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16
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Kazama Y, Hirano T, Nishihara K, Ohbu S, Shirakawa Y, Abe T. Effect of high-LET Fe-ion beam irradiation on mutation induction in Arabidopsis thaliana. Genes Genet Syst 2014; 88:189-97. [PMID: 24025247 DOI: 10.1266/ggs.88.189] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Heavy-ion beams are powerful mutagens. They cause a broad spectrum of mutation phenotypes with high efficiency even at low irradiation doses and short irradiation times. These mutagenic effects are due to dense ionisation in a localised region along the ion particle path. Linear energy transfer (LET; keV·μm(-1)), which represents the degree of locally deposited energy, is an important parameter in heavy-ion mutagenesis. For high LET radiation above 290 keV∙μm(-1), however, neither the mutation frequency nor the molecular nature of the mutations has been fully characterised. In this study, we investigated the effect of Fe-ion beams with an LET of 640 keV∙μm(-1) on both the mutation frequency and the molecular nature of the mutations. Screening of well-characterised mutants (hy and gl) revealed that the mutation frequency was lower than any other ion species with low LET. We investigated the resulting mutations in the 4 identified mutants. Three mutants were examined by employing PCR-based methods, one of which had 2-bp deletion, another had 178 bp of tandemly duplication, and other one had complicated chromosomal rearrangements with variable deletions in size at breakpoints. We also detected large deletions in the other mutant by using array comparative genomic hybridisation. From the results of the analysis of the breakpoints and junctions of the detected deletions, it was revealed that the mutants harboured chromosomal rearrangements in their genomes. These results indicate that Fe-ion irradiation tends to cause complex mutations with low efficiency. We conclude that Fe-ion irradiation could be useful for inducing chromosomal rearrangements or large deletions.
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17
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Autsavapromporn N, Suzuki M, Plante I, Liu C, Uchihori Y, Hei TK, Azzam EI, Murakami T. Participation of gap junction communication in potentially lethal damage repair and DNA damage in human fibroblasts exposed to low- or high-LET radiation. Mutat Res 2013; 756:78-85. [PMID: 23867854 PMCID: PMC4001089 DOI: 10.1016/j.mrgentox.2013.07.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2013] [Accepted: 07/05/2013] [Indexed: 10/26/2022]
Abstract
Existing research has not fully explained how different types of ionizing radiation (IR) modulate the responses of cell populations or tissues. In our previous work, we showed that gap junction intercellular communication (GJIC) mediates the propagation of stressful effects among irradiated cells exposed to high linear energy transfer (LET) radiations, in which almost every cells is traversed by an IR track. In the present study, we conducted an in-depth study of the role of GJIC in modulating the repair of potentially lethal damage (PLDR) and micronuclei formation in cells exposed to low- or high-LET IR. Confluent human fibroblasts were exposed in the presence or absence of a gap junction inhibitor to 200kV X rays (LET∼1.7keV/μm), carbon ions (LET∼76keV/μm), silicon ions (LET∼113keV/μm) or iron ions (LET∼400keV/μm) that resulted in isosurvival levels. The fibroblasts were incubated for various times at 37°C. As expected, high-LET IR were more effective than were low-LET X rays at killing cells and damaging DNA shortly after irradiation. However, when cells were held in a confluent state for several hours, PLDR associated with a reduction in DNA damage, occurred only in cells exposed to X rays. Interestingly, inhibition of GJIC eliminated the enhancement of toxic effects, which resulted in an increase of cell survival and reduction in the level of micronucleus formation in cells exposed to high, but not in those exposed to low-LET IR. The experiment shows that gap-junction communication plays an important role in the propagation of stressful effects among irradiated cells exposed to high-LET IR while GJIC has only a minimal effect on PLDR and DNA damage following low-LET irradiation. Together, our results show that PLDR and induction of DNA damage clearly depend on gap-junction communication and radiation quality.
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Affiliation(s)
- Narongchai Autsavapromporn
- Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba 263-8555, Japan
| | - Masao Suzuki
- Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba 263-8555, Japan
| | - Ianik Plante
- University Space Research Association, NASA Johnson Space Center, Houston, TX 77058, USA
| | - Cuihua Liu
- Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba 263-8555, Japan
| | - Yukio Uchihori
- Radiation Measurement Research Section, Research, Development and Support Center, National Institute of Radiological Sciences, Chiba 263-8555, Japan
| | - Tom K. Hei
- Center of Radiological Research, Department of Radiation Oncology, College of Physicians and Surgeons, Columbia University Medical Center, New York, NY 10032, USA
| | - Edouard I. Azzam
- Department of Radiology, New Jersey Medical School Cancer Center-University of Medicine and Dentistry of New Jersey, Newark, NJ 07103, USA
| | - Takeshi Murakami
- Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba 263-8555, Japan
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18
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Dysregulation of IRP1-mediated iron metabolism causes gamma ray-specific radioresistance in leukemia cells. PLoS One 2012; 7:e48841. [PMID: 23155415 PMCID: PMC3498264 DOI: 10.1371/journal.pone.0048841] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2012] [Accepted: 10/01/2012] [Indexed: 12/20/2022] Open
Abstract
Iron is required for nearly all organisms, playing important roles in oxygen transport and many enzymatic reactions. Excess iron, however, can be cytotoxic. Emerging evidence suggests that radioresistance can be achieved in lower organisms by the protection of proteins, but not DNA, immediately following ionizing radiation (IR) exposure, allowing for improved DNA repair. One potential mechanism for protein protection is controlling and limiting the amount of free iron in cells, as has been demonstrated in the extremophile Deinococcus Radiodurans, reducing the potential for oxidative damage to proteins during exposure to IR. We found that iron regulatory protein 1 (IRP1) expression was markedly reduced in human myeloid leukemia HL60 cells resistant to low linear energy transfer (LET) gamma rays, but not to high LET alpha particles. Stable knockdown of IRP1 by short-hairpin RNA (shRNA) interference in radiosensitive parental cells led to radioresistance to low LET IR, reduced intracellular Fenton chemistry, reduced protein oxidation, and more rapid DNA double-strand break (DSB) repair. The mechanism of radioresistance appeared to be related to attenuated free radical-mediated cell death. Control of intracellular iron by IRPs may be a novel radioresistance mechanism in mammalian cells.
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Mechanisms of resistance to high and low linear energy transfer radiation in myeloid leukemia cells. Blood 2012; 120:2087-97. [PMID: 22829630 DOI: 10.1182/blood-2012-01-404509] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Low linear energy transfer (LET) ionizing radiation (IR) is an important form of therapy for acute leukemias administered externally or as radioimmunotherapy. IR is also a potential source of DNA damage. High LET IR produces structurally different forms of DNA damage and has emerged as potential treatment of metastatic and hematopoietic malignancies. Therefore, understanding mechanisms of resistance is valuable. We created stable myeloid leukemia HL60 cell clones radioresistant to either γ-rays or α-particles to understand possible mechanisms in radioresistance. Cross-resistance to each type of IR was observed, but resistance to clustered, complex α-particle damage was substantially lower than to equivalent doses of γ-rays. The resistant phenotype was driven by changes in: apoptosis; late G2/M checkpoint accumulation that was indicative of increased genomic instability; stronger dependence on homology-directed repair; and more robust repair of DNA double-strand breaks and sublethal-type damage induced by γ-rays, but not by α-particles. The more potent cytotoxicity of α-particles warrants their continued investigation as therapies for leukemia and other cancers.
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20
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Kazama Y, Hirano T, Saito H, Liu Y, Ohbu S, Hayashi Y, Abe T. Characterization of highly efficient heavy-ion mutagenesis in Arabidopsis thaliana. BMC PLANT BIOLOGY 2011; 11:161. [PMID: 22085561 PMCID: PMC3261129 DOI: 10.1186/1471-2229-11-161] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2011] [Accepted: 11/15/2011] [Indexed: 05/18/2023]
Abstract
BACKGROUND Heavy-ion mutagenesis is recognised as a powerful technology to generate new mutants, especially in higher plants. Heavy-ion beams show high linear energy transfer (LET) and thus more effectively induce DNA double-strand breaks than other mutagenic techniques. Previously, we determined the most effective heavy-ion LET (LETmax: 30.0 keV μm(-1)) for Arabidopsis mutagenesis by analysing the effect of LET on mutation induction. However, the molecular structure of mutated DNA induced by heavy ions with LETmax remains unclear. Knowledge of the structure of mutated DNA will contribute to the effective exploitation of heavy-ion beam mutagenesis. RESULTS Dry Arabidopsis thaliana seeds were irradiated with carbon (C) ions with LETmax at a dose of 400 Gy and with LET of 22.5 keV μm(-1) at doses of 250 Gy or 450 Gy. The effects on mutation frequency and alteration of DNA structure were compared. To characterise the structure of mutated DNA, we screened the well-characterised mutants elongated hypocotyls (hy) and glabrous (gl) and identified mutated DNA among the resulting mutants by high-resolution melting curve, PCR and sequencing analyses. The mutation frequency induced by C ions with LETmax was two-fold higher than that with 22.5 keV μm(-1) and similar to the mutation frequency previously induced by ethyl methane sulfonate. We identified the structure of 22 mutated DNAs. Over 80% of the mutations caused by C ions with both LETs were base substitutions or deletions/insertions of less than 100 bp. The other mutations involved large rearrangements. CONCLUSIONS The C ions with LETmax showed high mutation efficiency and predominantly induced base substitutions or small deletions/insertions, most of which were null mutations. These small alterations can be determined by single-nucleotide polymorphism (SNP) detection systems. Therefore, C ions with LETmax might be useful as a highly efficient reverse genetic system in conjunction with SNP detection systems, and will be beneficial for forward genetics and plant breeding.
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Affiliation(s)
- Yusuke Kazama
- RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Tomonari Hirano
- RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
- RIKEN Innovation Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Hiroyuki Saito
- RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Yang Liu
- RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Sumie Ohbu
- RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Yoriko Hayashi
- RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Tomoko Abe
- RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
- RIKEN Innovation Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
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21
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Autsavapromporn N, de Toledo SM, Little JB, Jay-Gerin JP, Harris AL, Azzam EI. The role of gap junction communication and oxidative stress in the propagation of toxic effects among high-dose α-particle-irradiated human cells. Radiat Res 2011; 175:347-57. [PMID: 21388278 PMCID: PMC3139025 DOI: 10.1667/rr2372.1] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
We investigated the roles of gap junction communication and oxidative stress in modulating potentially lethal damage repair in human fibroblast cultures exposed to doses of α particles or γ rays that targeted all cells in the cultures. As expected, α particles were more effective than γ rays at inducing cell killing; further, holding γ-irradiated cells in the confluent state for several hours after irradiation promoted increased survival and decreased chromosomal damage. However, maintaining α-particle-irradiated cells in the confluent state for various times prior to subculture resulted in increased rather than decreased lethality and was associated with persistent DNA damage and increased protein oxidation and lipid peroxidation. Inhibiting gap junction communication with 18-α-glycyrrhetinic acid or by knockdown of connexin43, a constitutive protein of junctional channels in these cells, protected against the toxic effects in α-particle-irradiated cell cultures during confluent holding. Upregulation of antioxidant defense by ectopic overexpression of glutathione peroxidase protected against cell killing by α particles when cells were analyzed shortly after exposure. However, it did not attenuate the decrease in survival during confluent holding. Together, these findings indicate that the damaging effect of α particles results in oxidative stress, and the toxic effects in the hours after irradiation are amplified by intercellular communication, but the communicated molecule(s) is unlikely to be a substrate of glutathione peroxidase.
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Affiliation(s)
- Narongchai Autsavapromporn
- Department of Radiology, UMDNJ – New Jersey Medical School Cancer Center, Newark, New Jersey 07103
- Département de Médecine Nucléaire et de Radiobiologie, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke (Québec) J1H 5N4, Canada
| | - Sonia M. de Toledo
- Department of Radiology, UMDNJ – New Jersey Medical School Cancer Center, Newark, New Jersey 07103
| | - John B. Little
- Laboratory of Radiobiology, Harvard School of Public Health, Boston, Massachusetts 02115
| | - Jean-Paul Jay-Gerin
- Département de Médecine Nucléaire et de Radiobiologie, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke (Québec) J1H 5N4, Canada
| | - Andrew L. Harris
- Department of Pharmacology and Physiology, UMDNJ – New Jersey Medical School, Newark, New Jersey 07103
| | - Edouard I. Azzam
- Department of Radiology, UMDNJ – New Jersey Medical School Cancer Center, Newark, New Jersey 07103
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22
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Carabe-Fernandez A, Dale RG, Paganetti H. Repair kinetic considerations in particle beam radiotherapy. Br J Radiol 2011; 84:546-55. [PMID: 21266398 DOI: 10.1259/bjr/19934996] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
OBJECTIVES A second-order repair kinetics model is developed to predict damage repair rates following low or high linear energy transfer (LET) irradiations and to assess the amount of unrepairable damage produced by such radiations. The model is a further development of an earlier version designed to test if low-LET radiation repair processes could be quantified in terms of second-order kinetics. The newer version allows calculation of both the repair rate of the proportion of DNA damages that repair according to second-order kinetics and the proportion of DNA damages that do not repair. METHODS The original and present models are intercompared in terms of their goodness-of-fit to a number of data sets obtained from different ion beams. The analysis demonstrates that the present model provides a better fit to the data in all cases studied. RESULTS The proportions of unrepairable damage created by radiations of different LET predicted by the new model correspond well with previous studies on the increased effectiveness of high-LET radiations in inducing reproductive cell death. The results show that the original model may underestimate the proportion of unrepaired damage at any given time after its creation as well as failing to predict very slow or unrepairable damage components, which may result from high-LET irradiation. CONCLUSION It is suggested that the second-order model presented here offers a more realistic view of the patterns of repair in cell lines or tissues exposed to high-LET radiation.
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Affiliation(s)
- A Carabe-Fernandez
- Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, 30 Fruit Street, Boston, MA 02114, USA.
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23
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Beyreuther E, Lessmann E, Pawelke J, Pieck S. DNA double-strand break signalling: X-ray energy dependence of residual co-localised foci of γ-H2AX and 53BP1. Int J Radiat Biol 2009; 85:1042-50. [DOI: 10.3109/09553000903232884] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Abstract
Postirradiation cellular recovery kinetics for delayed plating, araA, hypertonic saline (HS) treatments and their combinations, were analysed in the framework of the previously developed dsb model (Ostashevsky 1989). Two possible types of DNA double-strand break (dsb) repair kinetics were considered: cooperative, where the rate-limiting step is related to a DNA molecule, and non-cooperative, where the rate-limiting step is related to a dsb. The following estimates were made for plateau-phase V79 cells: (1) HS induces a temporary block of dsb repair. The estimates for the dsb repair block duration are about 0.6 h for a 10-min treatment and about 1.2 h for a 20-min treatment. (2) HS creates additional DNA fragments. The number of these fragments calculated for 0.37 M NaCl treatment, in a way independent of the type of dsb repair, was consistent with the number estimated for 0.5 M NaCl treatment for cooperative dsb repair, but not for noncooperative dsb repair. (3) The estimated time constant for the process restricting the formation of DNA fragments was 10-20 min. In the presence of 200-400 microM araA, the rate of this process should decrease 2-5-fold. (4) The time constant for the araA recovery kinetics coincides with that for dsb repair, in agreement with experimental data. (5) For delayed plating recovery the kinetics curve calculated for cooperative dsb repair fits well experimental data, in contrast to the curve calculated for non-cooperative dsb repair.
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Affiliation(s)
- J Y Ostashevsky
- Department of Radiation Oncology, SUNY-Health Science Center, Brooklyn 11203
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25
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Akpa TC, Weber KJ, Schneider E, Kiefer J, Frankenberg-Schwager M, Harbich R, Frankenberg D. Heavy Ion-induced DNA Double-strand Breaks in Yeast. Int J Radiat Biol 2009; 62:279-87. [PMID: 1356130 DOI: 10.1080/09553009214552121] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
DNA double-strand break (dsb) induction in diploid yeast was measured by neutral sucrose sedimentation after exposure to very heavy ions with values of linear energy transfer (LET) ranging from about 300 to 11500 ke V/microns. Linear fluence dependencies were found in all cases from which dsb production cross-sections (sigma dsb) could be calculated. Corresponding cross-sections for cell killing (sigma i) were derived from final slopes of survival curves measured in parallel and for the same fluence range. A close correlation was found between sigma i and sigma dsb. It is calculated that over the entire LET range, including 30 MeV electron irradiation, about 22 dsb are induced per lethal event when high exposures are considered.
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Affiliation(s)
- T C Akpa
- Institut für Biophysikalische Strahenforschung, GSF, Frankfurt-Main, Germany
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26
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Brenner DJ, Ward JF. Constraints on Energy Deposition and Target Size of Multiply Damaged Sites Associated with DNA Double-strand Breaks. Int J Radiat Biol 2009; 61:737-48. [PMID: 1351522 DOI: 10.1080/09553009214551591] [Citation(s) in RCA: 149] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
We suggest that the observed experimental data on relative double-strand break (dsb) yield as a function of radiation quality can act as valuable constraints in defining the type of energy deposition which causes this basic lesion in radiation biology. Both heavy-ion and alpha-particle data show sufficient trends for quantitative comparisons with calculation to be made. We use the technique of track-structure simulation and search for energy-deposition clusters (containing at least a given number of ionizations in a given diameter) whose relative frequencies (compared to sparsely ionizing radiation) correlate with the relative biological effects (RBEs) for dsb induction. We conclude that locally multiply damaged sites (LMDS) which cause dsb are probably energy depositions of at least two to five ionizations localized, respectively, in sites of diameters of 1-4 nm. Although our derived cluster sizes should be viewed in light of the quality of the experimental data and uncertainties in the computer simulations at the nanometre level, it is unlikely that these estimates of cluster sizes would change greatly.
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Affiliation(s)
- D J Brenner
- Center for Radiological Research, Columbia University, New York, NY 10032
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27
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Jenner TJ, Belli M, Goodhead DT, Ianzini F, Simone G, Tabocchini MA. Direct Comparison of Biological Effectiveness of Protons and Alpha-particles of the Same LET. III. Initial Yield of DNA Double-strand Breaks in V79 Cells. Int J Radiat Biol 2009; 61:631-7. [PMID: 1349627 DOI: 10.1080/09553009214551441] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
The results reported form part of a series of experiments to substantiate and extend the findings by Belli et al. (1989) that protons are more biologically effective at cell killing than alpha-particles of the same LET. The irradiations were carried out using the Variable Energy Cyclotron (VEC) at the Harwell Laboratories. V79-4 Chinese hamster cells were exposed to alpha-particles and protons with LETs of 20 and 23 keV microns-1 in the dose range 40-150 Gy. X-rays were also used for comparison. Two methods were used for measurement of initial DNA double-strand breaks: sedimentation and DNA precipitation assays. The dose-response relationships were found to be well fitted by straight lines in all cases. With the sedimentation assay a slightly lower yield of dsb was found from protons than from alpha-particles of the same LET. The yield from X-rays was not significantly different from either. The precipitation assay showed similar yields of DNA damage from both particle types but significantly higher yields from X-rays. This may reflect a difference in the type of lesions scored by the two methods. Since the initial amount of dsb does not account for the observed differences in cellular response to radiations of different qualities, it is likely that these are related to the nature of the dsb (affecting reparability) or to the occurrence of other types of molecular damage.
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Affiliation(s)
- T J Jenner
- Medical Research Council Radiobiology Unit
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28
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Abstract
A theoretical model permitting estimation of yields of various DNA damages induced by radiations of varying qualities is described. It is based on the Monte-Carlo track structure simulation and DNA structure, and links physical, physicochemical and chemical stages of radiation action. Direct and indirect effects are not strictly distinguished but treated cooperatively. Good agreement between calculated and measured initial yields of double-strand breaks was observed. Other multiple and single damages of DNA are studied. When radiation quality is changed there are quantitative and qualitative transitions in the damage spectrum. The proportion of multiple damage in the damage spectrum is about 30% for low-LET radiations and increases considerably with increasing ionization density.
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Affiliation(s)
- V Michalik
- Division of Biophysics, Joint Institute for Nuclear Research, Dubna, USSR
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29
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Frankenberg-Schwager M, Becker M, Garg I, Pralle E, Wolf H, Frankenberg D. The role of nonhomologous DNA end joining, conservative homologous recombination, and single-strand annealing in the cell cycle-dependent repair of DNA double-strand breaks induced by H(2)O(2) in mammalian cells. Radiat Res 2009; 170:784-93. [PMID: 19138034 DOI: 10.1667/rr1375.1] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2008] [Accepted: 07/22/2008] [Indexed: 11/03/2022]
Abstract
The purpose of this study was to investigate the cell cycle-dependent role of nonhomologous DNA end joining (NHEJ), conservative homologous recombination (HR), and single-strand annealing (SSA) for the repair of simple DNA double-strand breaks (DSBs) induced by H(2)O(2)-mediated OH radicals in CHO cells. Cells of the cell lines V3 (NHEJ-deficient), irs1SF (HR-deficient) and UV41 (SSA-deficient) and their parental cell line AA8 were exposed to various concentrations of H(2)O(2) in G(1) or S phase of the cell cycle and their colony-forming ability was assayed. In G(1) phase, NHEJ was the most important-if not the only-mechanism to repair H(2)O(2)-mediated DSBs; this was similar to results obtained in a parallel study of more complex DSBs induced by sparsely or densely ionizing radiation. Unlike HR (irs1SF)- and SSA (UV41)-deficient cells, the sensitivity of NHEJ-deficient V3 cells to H(2)O(2) relative to parental AA8 cells in G(1) phase is about 50 times higher compared to 200 kV X rays. This points to a specific role of the catalytic subunit of DNA-PK for efficient NHEJ of H(2)O(2)-mediated DSBs that are located at sites critical for the maintenance of the higher-order structure of cellular DNA, whereas X-ray-induced DSBs are distributed stochastically. Surprisingly, SSA-deficient cells in G(1) phase showed an increased sensitivity to high concentrations of H(2)O(2) relative to the parental wild-type cells and to HR-deficient cells, which may be interpreted in terms of a specific type of H(2)O(2)-induced damage requiring SSA for repair after its transfer into S phase. In S phase, HR is the most important mechanism to repair H(2)O(2)-mediated DSBs, followed by NHEJ. In contrast, the action of error-prone SSA may not be beneficial, since SSA-deficient cells are three times more resistant to H(2)O(2) than wild-type AA8 cells. This is likely due to channeling of DSBs into the error-free HR repair pathway or into the potentially error-prone NHEJ pathway. Cells with or without a defect in DSB repair are considerably more sensitive to H(2)O(2) in S phase compared to G(1) phase. This effect is likely due to the fact that topoisomerase II, which is expressed only in proliferating cells, is a target of H(2)O(2), resulting in enhanced accumulation of DSBs and killing of cells treated in S phase with H(2)O(2). The relative sensitivities to H(2)O(2) differ by orders of magnitude for the four cell lines. This seems to be caused mainly by H(2)O(2)-mediated poisoning of topoisomerase IIalpha rather than by a defect in DSB repair.
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Lee HJ, Kim JS, Moon C, Kim JC, Jo SK, Kim SH. Relative biological effectiveness of fast neutrons in a multiorgan assay for apoptosis in mouse. ENVIRONMENTAL TOXICOLOGY 2008; 23:233-239. [PMID: 18214905 DOI: 10.1002/tox.20328] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
This study compared the effects of high linear energy transfer (LET) fast neutrons on the induction of apoptosis in several tissue types (hair follicle, intestine crypt, testis) of ICR mouse exposed to low LET 60Co gamma-rays. The changes that occurred from 0 to 24 h after exposing the mice to either 2 Gy of gamma-rays (2 Gy/min) or 0.8 Gy of neutrons (94 mGy/min, 35 MeV) were examined. The maximum frequency of apoptosis was observed at 8 or 12 h after irradiation. The mice that had received 0-8 Gy of gamma-rays or 0-1.6 Gy of neutrons were examined 8 h after irradiation. The best-fitting dose-response curves were linear-quadratic, and there was a significant relationship between the number of apoptotic cells and the dose. The stained products in the TUNEL-positive cells or bodies correlated with the typical morphologic characteristics of apoptosis observed by optical microscopy. In the follicles showing an apoptosis frequency between 2 and 14 per hair follicle, the relative biological effectiveness (RBE) of the neutrons in the small and large follicles was 2.09 +/- 0.31 and 2.15 +/- 0.18, respectively. In the intestine crypts showing an apoptosis frequency between 1 and 3 per crypt, the RBE of the neutrons was 4.03 +/- 0.06 and 3.87 +/- 0.04 in the base and total crypts, respectively. The RBE of the neutrons in the seminiferous tubule showing an apoptosis frequency between 0.5 and 2 per tubule was 5.18 +/- 0.06. The results determined the time-response relations and the RBE for fast neutron-induced apoptosis in several organs at the same time. The differences in RBE observed between the high and low LET radiation and it is believed that the difference in the DSB repair capacity in hair follicle, intestine crypt, and seminiferous tubule cells plays a role in determining the RBE of the high-LET radiation for the induced apoptotic cell formation.
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Affiliation(s)
- Hae-June Lee
- Laboratory of Radiation Effect, Korea Institute of Radiological and Medical Science, Seoul 139-240, South Korea
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31
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Lee HJ, Kim SH. Relative biological effectiveness of fast neutrons for apoptosis in mouse hair follicles. J Vet Sci 2007; 8:335-40. [PMID: 17993746 PMCID: PMC2868148 DOI: 10.4142/jvs.2007.8.4.335] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
This study compared the effects of high linear energy transfer (LET) fast neutrons on the induction of apoptosis in the hair follicles of ICR mice with those of low LET 60Co γ-rays. The changes that occurred from 0 to 24 h after exposing the mice to either 2 Gy of γ-rays (2 Gy/min) or 0.8 Gy of neutrons (94 mGy/min, 35 MeV) were examined. The maximum frequency was found at 12 h (γ-rays) or 8 h (neutrons) after irradiation. The mice that received 0-8 Gy of γ-rays or 0-1.6 Gy of neutrons were examined 8 h after irradiation. The dose-response curves were analyzed using the best-fit curve model. The dose-response curves were linear-quadratic, and a significant relationship was found between the frequency of apoptotic cells and the dose. The morphological findings in the irradiated groups were typical apoptotic fragments in the matrix region of the hair follicle, but the spontaneous existence of apoptotic fragments was rarely observed in the control group. In the presence of an apoptosis frequency between 2 and 14 per follicle, the relative biological effectiveness values of neutrons in small and large follicles were 2.09 ± 0.30 and 2.15 ± 0.18, respectively.
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Affiliation(s)
- Hae-June Lee
- Korea Institute of Radiological & Medical Science, Seoul 139-240, Korea
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32
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Datta K, Jaruga P, Dizdaroglu M, Neumann RD, Winters TA. Molecular analysis of base damage clustering associated with a site-specific radiation-induced DNA double-strand break. Radiat Res 2006; 166:767-81. [PMID: 17067210 PMCID: PMC2901180 DOI: 10.1667/rr0628.1] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2006] [Accepted: 07/26/2006] [Indexed: 11/03/2022]
Abstract
Base damage flanking a radiation-induced DNA double-strand break (DSB) may contribute to DSB complexity and affect break repair. However, to date, an isolated radiation-induced DSB has not been assessed for such structures at the molecular level. In this study, an authentic site-specific radiation-induced DSB was produced in plasmid DNA by triplex forming oligonucleotide-targeted (125)I decay. A restriction fragment terminated by the DSB was isolated and probed for base damage with the E. coli DNA repair enzymes endonuclease III and formamidopyrimidine-DNA glycosylase. Our results demonstrate base damage clustering within 8 bases of the (125)I-targeted base in the DNA duplex. An increased yield of base damage (purine > pyrimidine) was observed for DSBs formed by irradiation in the absence of DMSO. An internal control fragment 1354 bp upstream from the targeted base was insensitive to enzymatic probing, indicating that the damage detected proximal to the DSB was produced by the (125)I decay that formed the DSB. Gas chromatography-mass spectrometry identified three types of damaged bases in the approximately 32-bp region proximal to the DSB. These base lesions were 8-hydroxyguanine, 8-hydroxyadenine and 5-hydroxycytosine. Finally, evidence is presented for base damage >24 bp upstream from the (125)I-decay site that may form via a charge migration mechanism.
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Affiliation(s)
- Kamal Datta
- Department of Nuclear Medicine, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, MD 20892
| | - Pawel Jaruga
- Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899
- Department of Chemical and Biochemical Engineering, University of Maryland Baltimore County, Baltimore, MD 21250
| | - Miral Dizdaroglu
- Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899
| | - Ronald D. Neumann
- Department of Nuclear Medicine, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, MD 20892
| | - Thomas A. Winters
- Department of Nuclear Medicine, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, MD 20892
- Address correspondence to: Nuclear Medicine Department Warren Grant Magnuson Clinical Center National Institutes of Health Bldg. 10, Room 1C401, 9000 Rockville Pike Bethesda, MD 20892 Tel. 301-496-4388 Fax. 301-480-9712
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33
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Yamaguchi H, Ohara H, Waker AJ. A model for the induction of DNA damages and their evolution into cell clonogenic inactivation. JOURNAL OF RADIATION RESEARCH 2006; 47:197-211. [PMID: 16819146 DOI: 10.1269/jrr.47.197] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
The dependence of the initial production of DNA damages on radiation quality was examined by using a proposed new model on the basis of target theory. For the estimation of DNA damage-production by different radiation qualities, five possible modes of radiation action, including both direct and indirect effects, were assumed inside a target the molecular structure of which was defined to consist of 10 base-pairs of DNA surrounded by water molecules. The induction of DNA damage was modeled on the basis of comparisons between the primary ionization mean free path and the distance between pairs of ionized atoms, such distance being characteristic on the mode of radiation action. The OH radicals per average energy to produce an ion pair on the nanosecond time scale was estimated and used for indirect action. Assuming a relation between estimated yields of DNA damages and experimental inactivation cross sections for AT-cells, the present model enabled the quantitative reproduction of experimental results for AT-cell killing under aerobic or hypoxic conditions. The results suggest a higher order organization of DNA in a way that there will be at least two types of water environment, one filling half the space surrounding DNA with a depth of 3.7-4.3 nm and the other filling all space with a depth 4.6-4.9 nm.
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Affiliation(s)
- Hiroshi Yamaguchi
- International Space Radiation Laboratory National Institute of Radiological Sciences, Chiba, Japan.
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34
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Pang D, Rodgers JE, Berman BL, Chasovskikh S, Dritschilo A. Spatial distribution of radiation-induced double-strand breaks in plasmid DNA as resolved by atomic force microscopy. Radiat Res 2006; 164:755-65. [PMID: 16296881 DOI: 10.1667/rr3425.1] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Atomic force microscopy (AFM) has been used to directly visualize, size and compare the DNA fragments resulting from exposure to low- and high-LET radiation. Double-stranded pUC-19 plasmid ("naked") DNA samples were irradiated by electron-beam or reactor neutron fluxes with doses ranging from 0.9 to 10 kGy. AFM scanning in the tapping mode was used to image and measure the DNA fragment lengths (ranging from a few bp up to 2864 bp long). Double-strand break (DSB) distributions resulting from high-LET neutron and lower-LET electron irradiation revealed a distinct difference between the effects of these two types of radiation: Low-LET radiation-induced DSBs are distributed more uniformly along the DNA, whereas a much larger proportion of neutron-induced DSBs are distributed locally and densely. Furthermore, comparisons with predictions of a random DSB model of radiation damage show that neutron-induced DSBs deviate more from the model than do electron-induced DSBs. In summary, our high-resolution AFM measurements of radiation-induced DNA fragment-length distributions reveal an increased number of very short fragments and hence clustering of DSBs induced by the high-LET neutron radiation compared with low-LET electron radiation and a random DSB model prediction.
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Affiliation(s)
- Dalong Pang
- Department of Radiation Medicine, Georgetown University Medical Center, Washington, DC 20007, USA
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35
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Chambers DB, Osborne RV, Garva AL. Choosing an alpha radiation weighting factor for doses to non-human biota. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2006; 87:1-14. [PMID: 16377039 DOI: 10.1016/j.jenvrad.2005.10.009] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2005] [Revised: 10/19/2005] [Accepted: 10/25/2005] [Indexed: 05/05/2023]
Abstract
The risk to non-human biota from exposure to ionizing radiation is of current international interest. In calculating radiation doses to humans, it is common to multiply the absorbed dose by a factor to account for the relative biological effectiveness (RBE) of the radiation type. However, there is no international consensus on the appropriate value of such a factor for weighting doses to non-human biota. This paper summarizes our review of the literature on experimentally determined RBEs for internally deposited alpha-emitting radionuclides. The relevancy of each experimental result in selecting a radiation weighting factor for doses from alpha particles in biota was judged on the basis of criteria established a priori. We recommend a nominal alpha radiation weighting factor of 5 for population-relevant deterministic and stochastic endpoints, but to reflect the limitations in the experimental data, uncertainty ranges of 1-10 and 1-20 were selected for population-relevant deterministic and stochastic endpoints, respectively.
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Affiliation(s)
- Douglas B Chambers
- SENES Consultants Limited, 121 Granton Drive, Unit 12, Richmond Hill, Ontario L4B 3N4, Canada.
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36
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Kühne M, Urban G, Frankenberg D, Löbrich M. DNA Double-Strand Break Misrejoining after Exposure of Primary Human Fibroblasts to CKCharacteristic X Rays, 29 kVp X Rays and60Co γ Rays. Radiat Res 2005; 164:669-76. [PMID: 16238445 DOI: 10.1667/rr3461.1] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The efficiency of ionizing photon radiation for inducing mutations, chromosome aberrations, neoplastic cell transformation, and cell killing depends on the photon energy. We investigated the induction and rejoining of DNA double-strand breaks (DSBs) as possible contributors for the varying efficiencies of different photon energies. A specialized pulsed-field gel electrophoresis assay based on Southern hybridization of single Mbp genomic restriction fragments was employed to assess DSB induction and rejoining by quantifying the restriction fragment band. Unrejoined and misrejoined DSBs were determined in dose fractionation protocols using doses per fraction of 2.2 and 4.4 Gy for CK characteristic X rays, 4 and 8 Gy for 29 kVp X rays, and 5, 10 and 20 Gy for 60Co gamma rays. DSB induction by CK characteristic X rays was about twofold higher than for 60Co gamma rays, whereas 29 kVp X rays showed only marginally elevated levels of induced DSBs compared with 60Co gamma rays (a factor of 1.15). Compared with these modest variations in DSB induction, the variations in the levels of unrejoined and misrejoined DSBs were more significant. Our results suggest that differences in the fidelity of DSB rejoining together with the different efficiencies for induction of DSBs can explain the varying biological effectiveness of different photon energies.
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Affiliation(s)
- Martin Kühne
- Fachrichtung Biophysik, Universität des Saarlandes, D-66421 Homburg/Saar, Germany
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37
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Kagawa N, Shimura M, Takai A, Endo S, Fujikawa K. Relative biological effectiveness of fission neutrons for induction of micronucleus formation in mouse reticulocytes in vivo. Mutat Res 2005; 556:93-9. [PMID: 15491636 DOI: 10.1016/j.mrfmmm.2004.07.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2004] [Revised: 07/02/2004] [Accepted: 07/08/2004] [Indexed: 11/20/2022]
Abstract
Following whole-body irradiation of ICR mice with various doses of fission neutrons or X-rays, the frequency of micronuclei (MNs) in peripheral blood reticulocytes was measured at 12 h intervals beginning immediately after irradiation and ending at 72 h after irradiation. The resulting time-course curve of MN frequency had a clear peak 36 h after irradiation, irrespective of the type of radiation applied and the dose used. The MN frequency, averaged as the unweighted mean over the experimental time course, showed a linear increase with increasing dose of either fission neutrons or X-rays. The linear response to X-rays supports reported conclusion that induction of MN formation in reticulocytes is a dose-rate independent phenomenon. The relative biological effectiveness (RBE) of fission neutrons to X-rays for MN induction was estimated to be 1.9 +/- 0.3. This value is considerably lower than the RBE value of 4.6 +/- 0.5 reported for the same fission neutrons for induction of lymphocyte apoptosis in the thymus of ICR mice that represents dose-rate independent, one-track event. Based on these results, we propose that MNs increased in reticulocytes after irradiation mostly represent acentric fragments caused by single chromosome breaks, and that some confounding factor is operating in erythroblasts for the formation of aberrations from non-rejoining DNA double-strand breaks more severely after high-LET radiation than after low-LET radiation.
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Affiliation(s)
- Nao Kagawa
- Department of Life Science, Faculty of Science and Technology, Kinki University, Higashiosaka 577-8502, Japan
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38
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Petin VG, Kim JK. Liquid holding recovery kinetics in wild-type and radiosensitive mutants of the yeast Saccharomyces exposed to low- and high-LET radiations. Mutat Res 2005; 570:1-8. [PMID: 15680398 DOI: 10.1016/j.mrfmmm.2004.09.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2004] [Revised: 09/07/2004] [Accepted: 09/08/2004] [Indexed: 05/01/2023]
Abstract
Three wild-type diploid yeast strains Saccharomyces ellipsoideus and Saccharomyces cerevisiae and five radiosensitive mutants of S. cerevisiae in the diploid state were irradiated with gamma-rays from 60Co and alpha-particles from 239Pu in the stationary phase of growth. Survival curves and the kinetics of the liquid holding recovery were measured. It was shown that the irreversible component was enhanced for the densely ionizing radiation in comparison to the low-LET radiation while the probability of the recovery was identical for both the low- and high-LET radiations for all the strains investigated. It means that the recovery process itself is not damaged after densely ionizing radiation and the enhanced RBE of the high-LET radiation may be caused by the increased yield of the irreversible damage. A parent diploid strain and all its radiosensitive mutants showed the same probability for recovery from radiation damage. Thus, the mechanism of the enhanced radiosensitivity of the mutant cells might not be related to the damage of the repair systems themselves but with the production of some kind of radiation damage from which cells are incapable to recover.
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Affiliation(s)
- Vladislav G Petin
- Biophysical Laboratory, Medical Radiological Research Center, 249036 Obninsk, Kaluga Region, Russia
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39
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Gulston M, de Lara C, Jenner T, Davis E, O'Neill P. Processing of clustered DNA damage generates additional double-strand breaks in mammalian cells post-irradiation. Nucleic Acids Res 2004; 32:1602-9. [PMID: 15004247 PMCID: PMC390294 DOI: 10.1093/nar/gkh306] [Citation(s) in RCA: 148] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Clustered DNA damage sites, in which two or more lesions are formed within a few helical turns of the DNA after passage of a single radiation track, are signatures of DNA modifications induced by ionizing radiation in mammalian cells. Mutant hamster cells (xrs-5), deficient in non-homologous end joining (NHEJ), were irradiated at 37 degrees C to determine whether any additional double-strand breaks (DSBs) are formed during processing of gamma-radiation-induced DNA clustered damage sites. A class of non-DSB clustered DNA damage, corresponding to approximately 30% of the initial yield of DSBs, is converted into DSBs reflecting an artefact of preparation of genomic DNA for pulsed field gel electrophoresis. These clusters are removed within 4 min in both NHEJ-deficient and wild-type CHO cells. In xrs-5 cells, a proportion of non-DSB clustered DNA damage, representing approximately 10% of the total yield of non-DSB clustered DNA damage sites, are also converted into DSBs within approximately 30 min post-gamma but not post-alpha irradiation through cellular processing at 37 degrees C. That the majority of radiation-induced non-DSB clustered DNA damage sites are resistant to conversion into DSBs may be biologically significant at environmental levels of radiation exposure, as a non-DSB clustered damage site rather than a DSB, which only constitutes a minor proportion, is more likely to be induced in irradiated cells.
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Affiliation(s)
- Melanie Gulston
- DNA Damage Group, MRC Radiation and Genome Stability Unit, Harwell, Didcot OX11 0RD, UK
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40
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Ward JF. Complexity of damage produced by ionizing radiation. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2003; 65:377-82. [PMID: 12760053 DOI: 10.1101/sqb.2000.65.377] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Affiliation(s)
- J F Ward
- Department of Radiology 0610, University of California, San Diego, La Jolla, California 92093, USA
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41
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Belli M, Sapora O, Tabocchini MA. Molecular targets in cellular response to ionizing radiation and implications in space radiation protection. JOURNAL OF RADIATION RESEARCH 2002; 43 Suppl:S13-S19. [PMID: 12793724 DOI: 10.1269/jrr.43.s13] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
DNA repair systems and cell cycle checkpoints closely co-operate in the attempt of maintaining the genomic integrity of cells damaged by ionizing radiation. DNA double-strand breaks (DSB) are considered as the most biologically important radiation-induced damage. Their spatial distribution and association with other types of damage depend on radiation quality. It is believed these features affect damage reparability, thus explaining the higher efficiency for cellular effects of densely ionizing radiation with respect to gamma-rays. DSB repair systems identified in mammalian cells are homologous recombination (HR), single-strand annealing (SSA) and non-homologous end-joining (NHEJ). Some enzymes may participate in more than one of these repair systems. DNA damage also triggers biochemical signals activating checkpoints responsible for delay in cell cycle progression that allows more time for repair. Those at G1/S and S phases prevent replication of damaged DNA and those at G2/M phase prevent segregation of changed chromosomes. Individuals with lack or alterations of genes involved in DNA DSB repair and cell cycle checkpoints exhibit syndromes characterized by genome instability and predisposition to cancer. Information reviewed in this paper on the basic mechanisms of cellular response to ionizing radiation indicates their importance for a number of issues relevant to protection of astronauts from space radiation.
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Affiliation(s)
- Mauro Belli
- Physics Laboratory, Istituto Superiore di Sanità, 00161 Rome, Italy.
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42
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Puck TT, Johnson R, Webb P, Cui H, Valdez JG, Crissman H. Mutagenesis and repair by low doses of alpha radiation in mammalian cells. Proc Natl Acad Sci U S A 2002; 99:12220-3. [PMID: 12198179 PMCID: PMC129425 DOI: 10.1073/pnas.152433699] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/22/2002] [Indexed: 11/18/2022] Open
Abstract
Low doses of alpha radiation in basements have been causally implicated in lung cancer. Previous studies have concentrated on high dose effects, for which no significant repair was found. In the present study, the methodology for measuring mutation by quantitating mitotic breaks and gaps was found to be applicable to G2-phase Chinese hamster ovary cells irradiated with 10-50 cGy of alpha radiation. The mutation yield in such cells closely resembles that of gamma irradiation. Caffeine, which inhibits repair, produces the same straight line increase of alpha and gamma mutation yields plotted against the dose. In the absence of caffeine, the repair of alpha radiation lesions is almost twice as great as for gamma radiation. Mitotic index changes substantiate these interpretations. It is proposed that the higher ion density associated with alpha radiation may result in fewer lesions being missed by the repair processes. The quantitation of chromosomal lesions for G2 cells exposed to low doses of alpha radiation, gamma radiation, or chemical mutagens in the presence and absence of caffeine is a rapid and reproducible methodology. Protection from mutational disease in a fashion similar to the use of sanitation for infectious disease appears practical.
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Affiliation(s)
- Theodore T Puck
- Eleanor Roosevelt Institute, 1899 Gaylord Street, Denver, CO 80206-1210, USA.
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43
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Gulston M, Fulford J, Jenner T, de Lara C, O'Neill P. Clustered DNA damage induced by gamma radiation in human fibroblasts (HF19), hamster (V79-4) cells and plasmid DNA is revealed as Fpg and Nth sensitive sites. Nucleic Acids Res 2002; 30:3464-72. [PMID: 12140332 PMCID: PMC137090 DOI: 10.1093/nar/gkf467] [Citation(s) in RCA: 150] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The signature DNA lesion induced by ionizing radiation is clustered DNA damage. Gamma radiation-induced clustered DNA damage containing base lesions was investigated in plasmid DNA under cell mimetic conditions and in two cell lines, V79-4 (hamster) and HF19 (human), using bacterial endonucleases Nth (endonuclease III) and Fpg (formamidopyrimidine DNA glycosylase). Following irradiation with 60Co gamma-rays, induction of double-strand breaks (DSB) and clustered DNA damage, revealed as DSB by the proteins, was determined in plasmid using the plasmid-nicking assay and in cells by either conventional pulsed field gel electrophoresis or a hybridization assay, in which a 3 Mb restriction fragment of the X chromosome is used as a radioactive labeled probe. Enzyme concentrations (30-60 ng/microg DNA) were optimized to minimize visualization of background levels of endogenous DNA damage and DSB produced by non-specific cutting by Fpg and Nth in cellular DNA. 60Co gamma-radiation produces a 1.8-fold increase in the yields of both types of enzyme sensitive sites, visualized as DSB compared with that of prompt DSB in plasmid DNA. In mammalian cells, the increase in yields of clustered DNA damage containing either Fpg or Nth sensitive sites compared with that of prompt DSB is 1.4-2.0- and 1.8-fold, respectively. Therefore, clustered DNA damage is induced in cells by sparsely ionizing radiation and their yield is significantly greater than that of prompt DSB.
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Affiliation(s)
- Melanie Gulston
- DNA Damage Group, Radiation and Genome Stability Unit, Medical Research Council, Harwell, Didcot, Oxfordshire OX11 0RD, UK.
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44
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Rydberg B, Heilbronn L, Holley WR, Löbrich M, Zeitlin C, Chatterjee A, Cooper PK. Spatial distribution and yield of DNA double-strand breaks induced by 3-7 MeV helium ions in human fibroblasts. Radiat Res 2002; 158:32-42. [PMID: 12071801 DOI: 10.1667/0033-7587(2002)158[0032:sdayod]2.0.co;2] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Accelerated helium ions with mean energies at the target location of 3-7 MeV were used to simulate alpha-particle radiation from radon daughters. The experimental setup and calibration procedure allowed determination of the helium-ion energy distribution and dose in the nuclei of irradiated cells. Using this system, the induction of DNA double-strand breaks and their spatial distributions along DNA were studied in irradiated human fibroblasts. It was found that the apparent number of double-strand breaks as measured by a standard pulsed-field gel assay (FAR assay) decreased with increasing LET in the range 67-120 keV/microm (corresponding to the energy of 7-3 MeV). On the other hand, the generation of small and intermediate-size DNA fragments (0.1-100 kbp) increased with LET, indicating an increased intratrack long-range clustering of breaks. The fragment size distribution was measured in several size classes down to the smallest class of 0.1-2 kbp. When the clustering was taken into account, the actual number of DNA double-strand breaks (separated by at least 0.1 kbp) could be calculated and was found to be in the range 0.010-0.012 breaks/Mbp Gy(-1). This is two- to threefold higher than the apparent yield obtained by the FAR assay. The measured yield of double-strand breaks as a function of LET is compared with theoretical Monte Carlo calculations that simulate the track structure of energy depositions from helium ions as they interact with the 30-nm chromatin fiber. When the calculation is performed to include fragments larger than 0.1 kbp (to correspond to the experimental measurements), there is good agreement between experiment and theory.
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Affiliation(s)
- Björn Rydberg
- Lawrence Berkeley National Laboratory, Life Sciences Division, Department of Radiation Biology and DNA Repair, Berkeley, California 94720, USA
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Gauter B, Zlobinskaya O, Weber KJ. Rejoining of radiation-induced DNA double-strand breaks: pulsed-field electrophoresis analysis of fragment size distributions after incubation for repair. Radiat Res 2002; 157:721-33. [PMID: 12005552 DOI: 10.1667/0033-7587(2002)157[0721:roridd]2.0.co;2] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The repair of radiation-induced DNA double-strand breaks (DSBs) is frequently investigated by measuring the time-dependent decrease in the fraction of fragmented DNA that is able to enter electrophoresis gels. When transformed into equivalent doses without repair, such measurements are thought to reflect the removal of DSBs, and they typically exhibit a fast initial component and a decreasing rate at longer repair intervals. This formalism, however, assumes that the spatial distribution of unrejoined breakage resembles the pattern of induction of DSBs. While the size distributions for initial fragmentation, such as that resolved by conventional pulsed-field gel electrophoresis (PFGE) (between about 10(5) and 10(7) bp), are well known to agree with the prediction of random breakage, no data are available from studies explicitly testing this relationship for residual breakage. Therefore, Chinese hamster V79 cells and MeWo (human melanoma) cells were irradiated with different doses (10-100 Gy) or were incubated for repair for up to 4 h after a single dose of 100 Gy (V79) or 90 Gy (MeWo) before being subjected to PFGE. Fragment size distributions were calculated by convolution of the PFGE profiles with an appropriately generated size calibration function. The results clearly demonstrate an over-representation of smaller fragments (below about 2-3 Mbp) compared to the prediction of randomness for residual breakage. In consequence, the time-dependent decrease of dose-equivalent values calculated from data on the fraction released may not directly reflect DSB rejoining rates. The present findings are compatible with an earlier suggestion of slow rejoining of breaks which have been induced as multiple breaks (two or more) in large chromosomal loops, thus also predicting an increase of the slowly rejoining DSB fraction with increasing dose.
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Affiliation(s)
- Benjamin Gauter
- Radiobiology Section, Department of Radiotherapy, University of Heidelberg, INF 400, 69120 Heidelberg, Germany
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Pouget JP, Frelon S, Ravanat JL, Testard I, Odin F, Cadet J. Formation of modified DNA bases in cells exposed either to gamma radiation or to high-LET particles. Radiat Res 2002; 157:589-95. [PMID: 11966325 DOI: 10.1667/0033-7587(2002)157[0589:fomdbi]2.0.co;2] [Citation(s) in RCA: 146] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The aim of the present study was to measure the formation of eight base modifications in the DNA of cells exposed to either low-LET ((60)Co gamma rays) or high-LET ((12)C(6+) particles) radiation. For this purpose, a recently optimized HPLC-MS/MS method was used subsequent to DNA extraction and hydrolysis. The background level of the measured modified bases and nucleosides was shown to vary between 0.2 and 2 lesions/10(6) bases. Interestingly, thymidine glycols constitute the main radiation-induced base modifications, with an overall yield of 0.097 and 0.062 lesion/10(6) bases per gray for gamma rays and carbon heavy ions, respectively. Both types of radiations generate four other major degradation products, in the following order of decreasing importance: FapyGua > 5-HmdUrd > 5-FordUrd > 8-oxodGuo. The yields of formation of FapyAde and 8-oxoAde are one order of magnitude lower than those of the related guanine modifications, whereas the radiation-induced generation of 5-OHdUrd was below the limit of detection of the assay. The efficiency for both types of radiation to generate base damage in cellular DNA is low because the highest yield per gray was 0.097 thymine glycols per 10(6) DNA bases. As a striking observation, the yield of formation of the measured DNA lesions was found to be, on average, twofold lower after exposure to high-LET radiation ((12)C(6+)) than after exposure to low-LET gamma radiation. These studies show that the HPLC-MS/MS assay provides an accurate, reliable and sensitive method for measuring cellular DNA base damage.
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Affiliation(s)
- J-P Pouget
- Laboratoire Lésions des Acides Nucléiques, Département de Recherche Fondamentale sur la Matière Condensée/SCIB and UMR 5046, CEA/Grenoble, F-38054 Grenoble Cedex 9, France
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Abstract
The ionizing radiation induced bystander effect is initiated by damage to a cellular molecule which then gives rise to a signal exported to other cells. The nature of this damage is considered with the understanding that it may not be the same as that responsible for the traditional cellular effects of radiation. Consideration is give to amounts of endogenous damage and to radiation yields of the various candidate lesions.
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Affiliation(s)
- John F Ward
- Department of Radiology, 0610, University of California, La Jolla, San Diego, CA 92093, USA.
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Abstract
Induction of DSBs in the diploid yeast, Saccharomyces cerevisiae, was measured by pulsed-field gel electrophoresis (PFGE) after the cells had been exposed on membrane filters to a variety of energetic heavy ions with values of linear energy transfer (LET) ranging from about 2 to 11,500 keV/microm, (241)Am alpha particles, and 80 keV X rays. After irradiation, the cells were lysed, and the chromosomes were separated by PFGE. The gels were stained with ethidium bromide, placed on a UV transilluminator, and analyzed using a computer-coupled camera. The fluorescence intensities of the larger bands were found to decrease exponentially with dose or particle fluence. The slope of this line corresponds to the cross section for at least one double-strand break (DSB), but closely spaced multiple breaks cannot be discriminated. Based on the known size of the native DNA molecules, breakage cross sections per base pair were calculated. They increased with LET until they reached a transient plateau value of about 6 x 10(-7) microm(2) at about 300-2000 keV/microm; they then rose for the higher LETs, probably reflecting the influence of delta electrons. The relative biological effectiveness for DNA breakage displays a maximum of about 2.5 around 100-200 keV/microm and falls below unity for LET values above 10(3) keV/microm. For these yeast cells, comparison of the derived breakage cross sections with the corresponding cross section for inactivation derived from the terminal slope of the survival curves shows a strong linear relationship between these cross sections, extending over several orders of magnitude.
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Affiliation(s)
- Jürgen Kiefer
- Strahlenzentrum der Justus-Liebig-Universität, Leihgesterner Weg 217, 35392 Giessen, Germany.
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Prise KM, Pinto M, Newman HC, Michael BD. A review of studies of ionizing radiation-induced double-strand break clustering. Radiat Res 2001; 156:572-6. [PMID: 11604074 DOI: 10.1667/0033-7587(2001)156[0572:arosoi]2.0.co;2] [Citation(s) in RCA: 132] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Underpinning current models of the mechanisms of the action of radiation is a central role for DNA damage and in particular double-strand breaks (DSBs). For radiations of different LET, there is a need to know the exact yields and distributions of DSBs in human cells. Most measurements of DSB yields within cells now rely on pulsed-field gel electrophoresis as the technique of choice. Previous measurements of DSB yields have suggested that the yields are remarkably similar for different types of radiation with RBE values < or = 1.0. More recent studies in mammalian cells, however, have suggested that both the yield and the spatial distribution of DSBs are influenced by radiation quality. RBE values for DSBs induced by high-LET radiations are greater than 1.0, and the distributions are nonrandom. Underlying this is the interaction of particle tracks with the higher-order chromosomal structures within cell nuclei. Further studies are needed to relate nonrandom distributions of DSBs to their rejoining kinetics. At the molecular level, we need to determine the involvement of clustering of damaged bases with strand breakage, and the relationship between higher-order clustering over sizes of kilobase pairs and above to localized clustering at the DNA level. Overall, these studies will allow us to elucidate whether the nonrandom distributions of breaks produced by high-LET particle tracks have any consequences for their repair and biological effectiveness.
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Affiliation(s)
- K M Prise
- Gray Laboratory Cancer Research Trust, P.O. Box 100, Mount Vernon Hospital, Northwood, HA6 2JR, United Kingdom.
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Jenner TJ, Fulford J, O'Neill P. Contribution of base lesions to radiation-induced clustered DNA damage: implication for models of radiation response. Radiat Res 2001; 156:590-3. [PMID: 11604077 DOI: 10.1667/0033-7587(2001)156[0590:cobltr]2.0.co;2] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Biophysical modeling of radiation-induced DNA damage shows that significant yields of clustered DNA damage are formed after energy deposition by a single radiation track. To date, the majority of studies on radiation-induced DNA damage in cells have concentrated on determination of the yields of single- and double-strand breaks (DSBs), the latter representing one type of clustered DNA damage. It was recognized, however, that clustered DNA damage, which does not contain a DSB, might contain a combination of DNA base lesions and single-strand breaks in proximity. This mini-review discusses some of the recent experimental data confirming the induction of non-DSB, clustered DNA damage by radiation.
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Affiliation(s)
- T J Jenner
- MRC Radiation and Genome Stability Unit, Harwell, Didcot, Oxfordshire, OX11 0RD, United Kingdom
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