DNA oxidation by potassium bromate; a direct mechanism or linked to lipid peroxidation?

Following incubation of calf thymus DNA with potassium bromate (KBrO3) and glutathione (GSH), a statistically significant increase in the concentration of 8-oxodeoxyguanosine (8-oxodG) relative to deoxyguanosine was measured. This was GSH-dependent and was associated with loss of GSH during incubation. In contrast, 8-oxodG was not found to be elevated significantly in either total tissue DNA or mitochondrial DNA isolated from Sprague-Dawley rat kidney perfused in situ with KBrO3 (5 mM) for 15 min or 1 h. There was also no associated increase in the level of renal lipid peroxidation or reduced or oxidised GSH. Following intraperitoneal administration of KBrO3 to Sprague-Dawley rats, a dose of 100 mg/kg (maximum tolerated) gave evidence for oxidative stress in the kidney at 24 h as indicated by a significant increase in lipid peroxidation (P < 0.05) and oxidised GSH (P < 0.05). This was associated with a greater than 2-fold, significant (P < 0.01) increase in the level of 8-oxodG in kidney total DNA and a 57% (not statistically significant) increase in kidney mitochondrial 8-oxodG. Pretreatment of rats with diethylmaleate (DEM) to deplete GSH, elevated the toxicity of 100 mg/kg KBrO3. However, at a dose of 20 mg/kg, no change in any of the parameters indicative of kidney oxidative stress (including indicators of oxidative DNA damage; 8-oxodG or etheno-DNA adducts, which can be produced by lipid peroxides) was seen either with or without DEM pretreatment with the exception of a small but statistically significant (P < 0.05) increase in mitochondrial 8-oxodG when KBrO3 was given following DEM pretreatment. DNA oxidation in the kidney is therefore not inhibited by GSH depletion (contrasting with in vitro findings) and requires a sustained exposure at a near-toxic concentration of KBrO3 which is associated with lipid peroxidation and GSH oxidation. The results do not support a role, in rat kidney, of a direct, GSH-mediated mechanism for KBrO3-induced DNA oxidation as seen in vitro.