Chromosome aberrations induced in human lymphocytes by 3.45 MeV alpha particles analyzed by premature chromosome condensation

Premature chromosome condensation (PCC) experiments using human lymphocytes with centromere staining have shown that after exposure to 3.45 MeV alpha- particle radiation, the full number of dicentric chromosomes appears when t he cell fusion protocol is applied immediately after irradiation. In this c ase, the time available for repair and misrepair of DNA damage is only abou t 30 min. The number of dicentrics does not change with a further increase in the time available for chromatin rearrangement. This fast response confi rms the expectation based on our previous experiments using PCC with 150 kV X rays in which the alpha component of the yield of dicentrics was found t o appear when the cell fusion protocol was applied immediately after irradi ation, whereas the beta component was delayed by several hours. The time co nstant for rejoining of the excess acentric chromosome fragments is found t o be donor-specific and not to differ for alpha particles and X rays, but a lpha-particle radiation leaves a larger fraction of the excess acentric fra gments unrejoined. The RBEs of the 3.45 MeV alpha-particle radiation compar ed to 150 kV X rays, evaluated for the alpha component for the yield of dic entrics and for the yield of unrepaired acentric fragments, have almost equ al values of about 4. This is consistent with data in the literature on chr omosome aberrations observed in metaphase that show the equality of the RBE values for production of dicentrics and acentric fragments. Our experiment al results concerning the fast kinetics of the alpha component of the yield of exchange-type chromosome aberrations are not consistent with Lea's pair wise lesion interaction model, and they support the proposed alternative me chanism of lesion-nonlesion interaction between chromatin regions carrying clustered DNA damage and intact chromatin regions. (C) 1999 by Radiation Re search Society.