Protection of DNA from high LET radiation by two OH radical scavengers, tris (hydroxymethyl) aminomethane and 2-mercaptoethanol.

The effect of high linear energy transfer (LET) radiation on DNA in vitro, both in protective and non-protective environments was investigated. Two hydroxyl radical scavengers, tris(hydroxymethyl) aminomethane and 2-mercaptoethanol, were compared for their ability to protect SV40 DNA from radiation damage over a wide LET range. At comparable OH scavenging capacities, significant differences were found between these protective agents, indicating that other, radical scavenger-dependent processes affected the extent to which the DNA was protected. In general, a decrease in single-strand breaks (SSBs) relative to double-strand breaks (DSBs) was observed as LET increased. This effect was more pronounced when a radioprotector was present. Comparison of the relative biological efficiency (RBE) of radiation damage as LET increased showed a peak of DSB production in the mid-LET range. These data agree with measurements made by Christensen et al. (1972). An explanation for this increase in DSB production efficiency has been proposed based on the particle track structure of high-LET radiation.