potassium-bromate and Cell-Transformation--Neoplastic

Topics: Animals; Bromates; Cell Transformation, Neoplastic; DNA Damage; DNA Glycosylases; DNA Mutational Analysis; DNA Repair; Genetic Predisposition to Disease; Intestine, Small; Mice; Neoplasms, Radiation-Induced; Oxidative Stress

To clarify the role of 8-OHdG formation as a starting point for carcinogenesis, we examined the dose-dependence and time-course of changes of OGG1 mRNA expression, 8-OHdG levels and in vivo mutations in the kidneys of gpt delta rats given KBrO3 in their drinking water for 13 weeks. There were no remarkable changes in OGG1 mRNA in spite of some increments being statistically significant. Increases of 8-OHdG occurred after 1 week at 500 p.p.m. and after 13 weeks at 250 p.p.m. Elevation of Spi- mutant frequency, suggestive of deletion mutations, occurred after 9 weeks at 500 p.p.m. In a two-stage experiment, F344 rats were given KBrO3 for 13 weeks then, after a 2-week recovery, treated with 1% NTA in the diet for 39 weeks. The incidence and multiplicity of renal preneoplastic lesions in rats given KBrO3 at 500 p.p.m. followed by NTA treatment were significantly higher than in rats treated with NTA alone. Results suggest that a certain period of time might be required for 8-OHdG to cause permanent mutations. The two-step experiment shows that cells exposed to the alteration of the intranuclear status by oxidative stress including 8-OHdG formation might be able to form tumors with appropriate promotion.

Topics: 8-Hydroxy-2'-Deoxyguanosine; Animals; Animals, Genetically Modified; Bromates; Carcinogens; Cell Transformation, Neoplastic; Deoxyguanosine; DNA Damage; DNA Glycosylases; Dose-Response Relationship, Drug; Kidney; Kidney Neoplasms; Male; Mutation; Nitrilotriacetic Acid; Oxidative Stress; Precancerous Conditions; Rats; Rats, Inbred F344; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Time Factors

Potassium bromate (KBrO3), a food additive, induces renal-cell tumors in rats. KBrO3 induced 8-oxo-7, 8-dihydro-2'-deoxyguanosine (8-oxodG) formation in human leukemia cell line HL-60 as well as in its H2O2-resistant clone, HP100, suggesting no involvement of H2O2. Depletion of GSH by buthionine sulfoximine (BSO) had a little inhibitory effect on KBrO3-induced 8-oxodG formation. However, the amount of 8-oxodG was still significantly higher than that in control, suggesting that intracellular Cys can affect KBrO3 to oxidize DNA, when GSH decreased. KBrO3 caused 8-oxodG in isolated DNA in the presence of GSH (tripeptide; gamma-GluCysGly), gamma-GluCys, CysGly, or Cys. Methional completely inhibited 8-oxodG formation induced by KBrO3 plus GSH, but typical hydroxyl radical scavengers, SOD and catalase, had little or no inhibitory effects. When bromine solution (BrO(-)) was used instead of BrO3(-), similar scavenger effects were observed. Experiments with 32P-labeled DNA fragments obtained from the human p53 tumor suppressor gene and the c-Ha-ras-1 protooncogene suggested that KBrO3 induced 8-oxodG formation at 5'-site guanine of GG and GGG sequences of double-stranded DNA in the presence of GSH and that treatment of formamidopyrimidine-DNA glycosylase led to chain cleavages at the guanine residues. ESR spin-trapping studies showed that 1:2:2:1 quartet DMPO (5,5-dimethyl-1-pyrroline N-oxide) spectrum similar to DMPO/hydroxy radical (*OH) adduct, but the signals were not inhibited by ethanol. Therefore, the signal seemed not to be due to *OH but byproduct due to oxidation of DMPO by the reactive species. The signals were suppressed by the addition of dGMP, but not by other mononucleotides, suggesting the specific reactivity with guanine. On the basis of our results and previous literature, it is speculated that reduction of KBrO3 by SH compounds in renal proximal tubular cells yields bromine oxides and bromine radicals, which are the reactive species that cause guanine oxidation, leading to renal carcinogenesis of KBrO3.

Topics: Animals; Antineoplastic Agents; Bromates; Carcinogens; Cell Transformation, Neoplastic; Cysteine; Deuterium; DNA Damage; Food Additives; Free Radicals; Genes, p53; Genes, ras; Glutathione; Guanine; HL-60 Cells; Humans; Kidney Neoplasms; Rats; Spin Trapping