Comparison Between Indirect and Direct Effects for High and Low LET Radiations in SV40 DNA Strand Break Induction

Using the OH radical scavengers Tris[hydroxymethyl] aminomethane (Tris) and ß-mercaptoethanol (MEth), we studied indirect and direct radiation effects of DNA in solution. SV40 DNA was exposed to low LET X rays and to heavy ion beams (11.4 MeV.u-120Ne, 12.5 MeV.u-1131Xe and 16 MeV.u-1238U) varying in LET. Cross sections for strand break induction were calculated from dose-effect curves in the presence and absence of protector. We found MEth was a more efficient OH radical scavenger than Tris. We also showed differences in the ability of each scavenger to protect against single and double strand breaks. The role of Tris radical formation as a possible explanation of these differences is discussed.