Assessment of ãH2AX nuclear foci number and size in normal and repair-deficient cells irradiated with low and high linear energy transfer (LET) radiation

C BRACALENTE; IL IBAÑEZ; B MOLINARI; , MA PALMIERI; A MAGLIOCO; L POLICASTRO; A. KREINER; , A BURLÓN; A VALDA; J DAVIDSON; M DAVIDSON; M VÁZQUEZ; M OZAFRÁN; H DURÁN

Río de Janeiro, Brasil

Congreso; 8th LOWRAD International Conference on "The Effects of Low and Very Low Doses of Ionizing Radiation on Human Health and Biotopes; 2009

Purpose: When cells are exposed to radiation, DNA double-strand breaks (DSBs) triggers a signaling cascade that leads to the rapid formation of a repair complex at the break. Within minutes of DNA damage, histone ãH2AX appears at discrete nuclear foci. In this study we investigated the characteristic of radiation induced foci formation in two related cell lines with different radiation sensitivity exposed to low and high LET radiation. For this purpose, the number and size of nuclear foci were evaluated as quantitative indicators of the extent of DSBs complex formation. Materials and Methods: CHO-10B2 cells and irs-20 cells (defective in DNA-PKcs) were exposed to 0.5, 1, 2, 3 Gy of low LET gamma rays (137Cs) and high LET lithium beams (6Li, 14 MeV/n, 135 keV/ µm, TANDAR accelerator, Buenos Aires, Argentina). DSBs were assessed by the detection of phosphorylated histone H2AX (ãH2AX) by immunofluorescence and image analysis measurements. Results: ãH2AX labeling demonstrated that the number of foci (average size 0.5 µm2 ± 0.1) increases as a function of dose 30 min after irradiation with gamma rays for CHO-10B2 as well as for irs-20 cells. However, the latter cells showed a higher number of foci than CHO-10B2 cells for all doses assayed. Regarding cells irradiated with high LET lithium ions, significantly larger foci were observed in the nuclei of both cell strains (1.2-1.6 µm2 for all doses). The increase in the foci size could be attributed to the densely damaged DNA and probably represents clusters of DNA damage. Moreover, the number of lithium-induced larger foci per nuclei increases with dose and fits with the expected number of hits per nucleus, calculated from the fluence for each dose. Conclusion: This work provides quantitative data on the induction of larger ãH2AX foci by high LET irradiation in related cell strains in comparison with those observed after low LET radiation. A close relationship was detected between larger foci number and particle fluence for all dose assayed.