Protection of DNA Molecules of Cultured Mammalian Cells from Radiation-induced Single-strand Scissions by Various Alcohols and SH Compounds

Summary

The addition of alcohols (methanol, ethanol, t-butanol, ethylene glycol, and glycerol), SH compounds (cysteamine, cysteine and mercaptoethanol) and cystamine protected DNA molecules of mammalian cells from radiation-induced single-strand scissions. The protection afforded with these scavengers increased as their concentrations were increased, but always only up to a certain maximum. The maximum protection was the same for all the alcohols and cystamine, but another maximum was found for all the SH compounds. The extent of radiation-induced single-strand breaks can therefore be grouped into protectable and non-protectable fractions.

In the protectable fraction, there is a linear relationship between the scavenger concentrations for half maximum protection and the reaction rate constants for the OH radical reacting with the scavengers. No such linear relationship was demonstrated with rate constants of H and e_aq⁻. This leads us to the following suggestions: (1) that the protectable fraction is mostly of indirect action; (2) that the OH radical plays a major role in radiation-induced single-strand breaks of DNA in cultured mammalian cells; (3) that a major protection mechanism in indirect action is radical scavenging (or a competitive reaction); and (4) that the protection mechanism by SH compounds may consist of radical scavenging as well as some other type of reaction(s) resulting in radiation protection.