DNA fragmentation induced by Fe ions in human cell: shielding influence on spatially correlated damage
Abstract
Outside the magnetic field of the Earth, high energy heavy ions (HZE particles) constitute a relevant part of the biologically significant dose to astronauts during the very long travels through the space. For heavy ions the primary ionization sites occur in a correlated manner along the track of the particles and their typical pattern of energy deposition on the microscopic scale is expected to have an important role in their effects on living cells. It has been pointed out that multiple Double Strand Breaks (DSB) can be produced in local proximity by the same particle track, creating a small region of clustered damage. We have investigated the influence of the shielding on the biological effects of heavy ions, studying the initial production of very small DNA fragments in human fibroblasts irradiated with iron ions. Theoretical studies have shown that materials rich in hydrogen, such as polymethylmethacrylate (PMMA), could be more suitable in reducing the radiation risk. This is due mainly to a lower production of secondary neutrons and target fragments in hydrogen-rich materials compared to aluminium, which is the current shield used to protect astronauts. We have measured the size distribution of DNA fragments induced by high-energy Fe ions over a range from 1 kbp to 23 kpb that are produced by DSB occured over distances comparable with the chromatin fiber dimensions. 1 GeV/u Fe ion beams were obtained from the Alternating Gradient Synchrotron at the Brookhaven National Laboratory and irradiations were performed without and with a 190 mm thick PMMA shielding. Plateau phase AG1522 cells were irradiated in agarose plugs with doses up to 600 Gy and DSB induction was determined by DNA fragmentation analysis after Pulsed/Constant Field Gel Electrophoresis. The results until now obtained show that the number of DSB increases linearly either when plotted versus fluence either versus dose. The fragment distribution indicates the occurrence of a spatially correlated damage. When a PMMA shield is used, the dose-rate of the Fe ions beam decreases by a factor around 0.5 and a concomitant marked decrease in the DNA fragments production per unit dose is found.
- Publication:
-
34th COSPAR Scientific Assembly
- Pub Date:
- 2002
- Bibcode:
- 2002cosp...34E.982A