The influence of mutation induction in normal human fibroblasts irradiated with X rays and iron ions

We investigated the influence of mutation induction on the hypoxanthine guanine phosphoribosyltransferase (hprt) locus in normal human fibroblasts irradiated with Xrays or accelerated iron ions with LET ranging from 200 to 400 keV/miceometer. The relative biological effectiveness (RBE) of the mutation frequency per total number of surviving cells for iron ions with comparatively lower LET values (200 and 260 keV/miceometer) in this study was higher than 1, and the RBE for the 300 keV/miceometer, 350 keV/miceometer and 400 keV/miceometer ions was nearly 1. These results indicated that the mutation induction for iron ions decreased with increasing LET, and these of high-LET regions (over 300 keV/miceometer) and X rays were similar. The deletion spectrum of exons in hprt locus for X rays and 260 keV/miceometer-iron ions were analyzed using multiplex polymerase chain reaction (PCR). About 70% of mutant induced by iron ions showed deletion of the entire exons (total deletion), while mutant induced by X rays showed partial deletion, which one or more exons are missing, of about 70%. The results indicated that iron-ion induced mutants sustained severer damage than X-ray induced mutants even if the doseresponse curves for mutation induction were similar between X rays and iron ions