The role of glutathione in DNA damage by potassium bromate in vitro

Abstract

We have investigated the role of reduced glutathione (GSH) in the genetic toxicity of the rodent renal carcinogen potassium bromate (KBrO3). A statistically significant increase in the concentration of 8-oxodeoxyguanosine (8-oxodG) relative to deoxyguanosine was measured following incubation of calf thymus DNA with KBrO3 and GSH or N-acetylcysteine (NACys). This was dependent on these thiols and was associated with the loss of GSH and production of oxidized glutathione. A short-lived (<6 min) intermediate was apparent which did not react with the spin trap dimethylpyrroline N-oxide. DNA oxidation was not evident when potassium chlorate (KCIO3) or potassium iodate (KIO3) were used instead of KBrO3, though GSH depletion also occurred with KIO3, but not with KCIO3. Other reductants and thiols in combination with KBrO3 did not cause a significant increase in DNA oxidation. DNA strand breakage was also induced by KBrO3 in human white blood cells (5 mM) and rat kidney epithelial cells (NRK-52E, 1.5 mM). This was associated with an apparent small depletion of thiols in NRK-52E cells at 15 min and with an elevation of 8-oxodG at a delayed time of 24 h. Depletion of intra-cellular GSH by diethylmaleate in human lymphocytes decreased the amount of strand breakage induced by KBrO3. Extracellular GSH, however, protected against DNA strand breakage by KBrO3, possibly due to the inability of the reactive product to enter the cell. In contrast, membrane-permeant NACys enhanced KBrO3-induced DNA strand breakage in these cells. DNA damage by KBrO3 is therefore largely dependent on access to intracellular GSH.