Biological effects induced by low-density heavy ions in normal human fibroblasts

We reported in 2007 that X-ray-induced mutation frequency in cells pre-treated with low-fluence (1 mGy/7-8 h) helium and carbon ions before applying irradiation with an X-ray challenge dose (1.5 Gy) was enhanced at 1.9-4.0 times higher than that of low-dose-radiation untreated control cells. In 2008 we focused on possible mechanisms observed in genomic instability of mutation. Also, we have begun to examine genomic instability of chromosomal damage. To identify possible mechanism(s) of the observed genomic instability in mutation induction, cells were treated with a specific inhibitor of gap-junction mediated cell-cell communication from 24 h before the pre-treatment with neutrons to the end of the irradiation of a X-ray challenging dose. The results clearly showed that the observed enhancement of X-ray induced mutation in cells pre-treated with both helium and carbon ions was reduced to the same level as the control. There is evidence that bystander effect mediated with cell-cell communication plays an important role of genomic instability in mutation observed in cells pre-treated with low-fluence helium and carbon ions. (author)