No dose-dependence of DNA double-strand break misrejoining following alpha-particle irradiation

TY - JOUR

T1 - No dose-dependence of DNA double-strand break misrejoining following alpha-particle irradiation

AU - Kühne, M

AU - Rothkamm, K

AU - Löbrich, M

PY - 2000/7

Y1 - 2000/7

N2 - PURPOSE: To investigate whether an explanation for the high effectiveness of densely ionizing radiation with regard to complex biological endpoints can be derived from measurements of radiation-induced double-strand break (DSB) misrejoining.MATERIALS AND METHODS: Misrejoining of radiation-induced DSB in normal human fibroblasts was determined by comparing hybridization analysis of large restriction fragments as a measure for correct rejoining, with results from a conventional pulsed-field gel electrophoresis technique (FAR) that measures total DSB rejoining. In order to investigate DSB misrejoining at doses for which chromosome aberration data are available, a dose fractionation protocol was applied so that the number of DSB at any given timepoint was low but the cumulative amount of misrejoined DSB sufficient for detection and precise quantitation.RESULTS AND CONCLUSION: After an acute 80Gy alpha-particle exposure and a repair incubation period of 24 h, 50% of all initially induced DSB were misrejoined, in agreement with data obtained for X-rays. X-irrradiation with 16 x 5 Gy, 8 x 10 Gy, 4 x 20 Gy, or 2 x 40 Gy and repair incubation of 24 h following each individual dose fraction was recently reported to yield misrejoining frequencies that strongly decrease with increasing fractionation (Löbrich et al. 2000; Genes, Chromosomes and Cancer, 27, 59-68). In the present study, constant misrejoining frequencies of 50% were observed after alpha-particle exposure with the same fractionation protocol. This difference between alpha-particles and X-rays is in accordance with the high biological effectiveness of densely ionizing radiation and provides a direct link between misrejoining of DSB and cytologically visible exchange aberrations. Further evidence suggests that if the same dose range is compared, the number of misrejoined DSB exceeds the number of microscopically visible aberrations by an order of magnitude for both radiation types, probably reflecting the high resolution of the hybridization approach compared with cytological techniques.

AB - PURPOSE: To investigate whether an explanation for the high effectiveness of densely ionizing radiation with regard to complex biological endpoints can be derived from measurements of radiation-induced double-strand break (DSB) misrejoining.MATERIALS AND METHODS: Misrejoining of radiation-induced DSB in normal human fibroblasts was determined by comparing hybridization analysis of large restriction fragments as a measure for correct rejoining, with results from a conventional pulsed-field gel electrophoresis technique (FAR) that measures total DSB rejoining. In order to investigate DSB misrejoining at doses for which chromosome aberration data are available, a dose fractionation protocol was applied so that the number of DSB at any given timepoint was low but the cumulative amount of misrejoined DSB sufficient for detection and precise quantitation.RESULTS AND CONCLUSION: After an acute 80Gy alpha-particle exposure and a repair incubation period of 24 h, 50% of all initially induced DSB were misrejoined, in agreement with data obtained for X-rays. X-irrradiation with 16 x 5 Gy, 8 x 10 Gy, 4 x 20 Gy, or 2 x 40 Gy and repair incubation of 24 h following each individual dose fraction was recently reported to yield misrejoining frequencies that strongly decrease with increasing fractionation (Löbrich et al. 2000; Genes, Chromosomes and Cancer, 27, 59-68). In the present study, constant misrejoining frequencies of 50% were observed after alpha-particle exposure with the same fractionation protocol. This difference between alpha-particles and X-rays is in accordance with the high biological effectiveness of densely ionizing radiation and provides a direct link between misrejoining of DSB and cytologically visible exchange aberrations. Further evidence suggests that if the same dose range is compared, the number of misrejoined DSB exceeds the number of microscopically visible aberrations by an order of magnitude for both radiation types, probably reflecting the high resolution of the hybridization approach compared with cytological techniques.

KW - Alpha Particles

KW - Cells, Cultured

KW - DNA/radiation effects

KW - DNA Damage

KW - DNA Repair

KW - Dose-Response Relationship, Radiation

KW - Humans

KW - X-Rays

U2 - 10.1080/09553000050050909

DO - 10.1080/09553000050050909

M3 - SCORING: Journal article

C2 - 10923613

VL - 76

SP - 891

EP - 900

JO - INT J RADIAT BIOL

JF - INT J RADIAT BIOL

SN - 0955-3002

IS - 7

ER -