Chromosome aberrations in normal human fibroblasts analyzed in G0/G1 and G2/M phases after exposure in G0 to radiation with different linear energy transfer (LET)

We have studied the induction of chromosome aberrations in human fibroblasts exposed in G0/G1 to X-rays or heavy ions to study the influence of G1 cell cycle arrest. Confluent normal fibroblasts were exposed to X-rays or accelerated particles with different LET values and chromosome aberrations were investigated in the first G0/G1 and G2//M phase. The particles used here were 490 MeV/nucleon Si, 500 MeV/nucleon Fe, and 200 MeV/nucleon Fe ions. Cells were subcultured 24 h after exposure and premature chromosome condensation (PCC) was performed by fusion-induced method for analysis of G0/G1 cells, and chemically-induced method for analysis of G2 and metaphase cells. Chromosome damage was assessed in chromosomes 1 and 3 using whole chromosome fluorescence in situ hybridization (FISH). Cell cycle was analyzed by flow cytometry at different incubation times following subculture. After irradiation with 2 Gy of high-LET particles, the yields of chromosome aberrations and fragments were significantly higher in G0/G1 phase than in G2/M phase, whereas similar yields of damage were measured in both phases after exposure to X-rays. In contrast, the yield of misrepair, assessed by the number of color junctions, was similar in the G0/G1 and G2/M phases after exposure to either X-rays or high-LET particles. The yields of chromosome aberrations, fragments, and color junctions in both the G0/G1 and the G2/M phases, increased with LET up to 200 keV/μm, then decreased for 440 keV/μm Fe particles. A good correlation was found between chromosome aberrations in both G0/G1 and G2/M cells and survival fractions after 2 Gy of different LET radiations, although the slopes were steeper for the G0/G1 cells. Flow cytometry analysis indicated that high-LET particles induce more non cycling G0/G1 cells within 48 h of subculture than X-rays, suggesting that chromosome aberrations scored at the G2/M phase may not accurately describe the true radiation effect.