Effect of GSH levels, altered by BSO treatment, on the timescale of the oxygen effect in V79 cells

A major aspect of the radiosensitizing effect of oxygen is its ability to react with free-radical damage sites in competition with their chemical repair by sulphydryls. The authors have examined the kinetics of these reactions in V79 379A cells, using a fast mixing and irradiation method, the gas explosion technique. The role of glutathione (GSH) was determined by inhibiting its synthesis with buthionine sulphoximine (BSO) (50 μM, 18 hours), reducing the GSH and NPSH levels to below 10 percent of those in untreated cells. This treatment significantly increased the anoxic and oxic radiosensitivities, as had been found in steady-state experiments. In addition, it slowed down the rate of decay (or chemical repair) of oxygen-dependent lesions by a factor of approximately 3. The damage decays for treated and untreated cells were each measured up to 10 ms after irradiation with single 5 ns electron pulses. The results are consistent with GSH chemically repairing radiation-induced damage by reacting with it directly and this repair being blocked when competing reaction of the damage with oxygen is favoured kinetically