Effects of glutathione on Fenton reagent-dependent radical production and DNA oxidation.

The effects of glutathione (GSH) on the generation of radicals and the oxidation of DNA by Fenton reagent were studied. Hydroxyl radicals and thiyl radicals were detected by electron spin resonance spin trapping when GSH-Fe(II) reacted with H2O2; however, the mixture was ineffective at promoting the hydroxylation of 2'-deoxyguanosine in calf thymus DNA. When the concentrations of ferrous iron and hydrogen peroxide were both 100 microM, the concentration of GSH required to inhibit 8-hydroxy-2'-deoxyguanosine (8-OHdG) production by 92% was 1 mM. Other thiol compounds were also effective at inhibiting 8-OHdG formation; however, mannitol and benzoate were ineffective at inhibiting 8-OHdG formation when present at the same concentration. Single strand breaks were detected in phi X174 plasmid DNA treated with 2 microM Fe(II) and 2 microM H2O2; furthermore, the addition of 50 microM GSH to this system inhibited single strand break formation by 95%. In conclusion, GSH protected DNA from oxidation by Fe(II) and H2O2 even though it did not completely inhibit the production of radicals by the Fenton reaction.