Ps. Hodgkins et al., THE SEVERITY OF ALPHA-PARTICLE-INDUCED DNA-DAMAGE IS REVEALED BY EXPOSURE TO CELL-FREE-EXTRACTS, Radiation research, 146(6), 1996, pp. 660-667
The rejoining of single-strand breaks induced by alpha-particle and ga
mma irradiation in plasmid DNA under two scavenging conditions has bee
n compared. At the two scavenger capacities used of 1.5 x 10(7) and 3
x 10(8) s(-1) using Tris-HCl as the scavenger, the ratio of single- to
double-strand breaks for alpha particles is fivefold less than the co
rresponding ratios for gamma irradiation. The repair of such radiation
-induced single-strand breaks has been examined using a cell-free syst
em derived from human whole-cell extracts. We show that the rejoining
of single-strand breaks for both alpha-particle- and gamma-irradiated
plasmid is dependent upon the scavenging capacity and that the efficie
ncy of rejoining of alpha-particle-induced single-strand breaks is sig
nificantly less than that observed for gamma-ray-induced breaks. In ad
dition, for DNA that had been irradiated under conditions that mimic t
he cellular environment with respect to the radical scavenging capacit
y, 50% of alpha-particle-induced single-strand breaks are converted to
double-strand breaks, in contrast with only similar to 12% conversion
of gamma-ray-induced single-strand breaks, indicating that the initia
l damage caused by alpha particles is more severe. These studies provi
de experimental evidence for increased clustering of damage which may
have important implications for the induction of cancer by low-level a
lpha-particle sources such as domestic radon. (C) 1996 by Radiation Re
search Society