Radiation Protection of in Vitro Mammalian Cells: Effects of Hydroxyl Radical Scavengers on the Slopes and Shoulders of Survival Curves

We have tested several chemical compounds, characterized and widely used as hydroxyl radical (^{\bullet}{\rm OH}$) scavengers, for their effects on the radiation sensitivity of Chinese hamster V79 cells irradiated in air or nitrogen. Our purpose is to reexamine the proposed relationship between the level of protection and the rates at which the scavengers react with ^{\bullet}{\rm OH}$. We found that the additives can have two apparently independent effects on the shape of survival curves: a reduction in sensitivity (i.e., "protection," a decrease in the value of k) and an increase in the size of the shoulder of the survival curve (an increase in the value of $D_{{\rm q}}$). We measured intracellular scavenger concentrations, and, using these values in our analysis, we found that neither of the two effects is correlated with the rates at which the scanvengers react with ^{\bullet}{\rm OH}$. Although these results could mean that ^{\bullet}{\rm OH}$ do not cause lethal damage, the interpretation we believe most probably correct is that these scavengers protect in multiple ways. The protection would occur in addition to or instead of simple ^{\bullet}{\rm OH}$ removal.