Potassium bromate treatment predominantly causes large deletions, but not GC>TA transversion in human cells.
Potassium bromate (KBrO(3)) is strongly carcinogenic in rodents and mutagenic in bacteria and mammalian cells in vitro. The proposed genotoxic mechanism for KBrO(3) is oxidative DNA damage. KBrO(3) can generate high yields of 8-hydroxydeoxyguanosine (8OHdG) DNA adducts, which cause GC>TA transversions in cell-free systems. In this study, we investigated the in vitro genotoxicity of KBrO(3) in human lymphoblastoid TK6 cells using the comet (COM) assay, the micronucleus (MN) test, and the thymidine kinase (TK) gene mutation assay. After a 4h treatment, the alkaline and neutral COM assay demonstrated that KBrO(3) directly yielded DNA damages including DNA double strand breaks (DSBs). KBrO(3) also induced MN and TK mutations concentration-dependently. At the highest concentration (5mM), KBrO(3) induced MN and TK mutation frequencies that were over 30 times the background level. Molecular analysis revealed that 90% of the induced mutations were large deletions that involved loss of heterozygosity (LOH) at the TK locus. Ionizing-irradiation exhibited similar mutational spectrum in our system. These results indicate that the major genotoxicity of KBrO(3) may be due to DSBs that lead to large deletions rather than to 8OHdG adducts that lead to GC>TA transversions, as is commonly believed. To better understand the genotoxic mechanism of KBrO(3), we analyzed gene expression profiles of TK6 cells using Affymetrix Genechip. Some genes involved in stress, apoptosis, and DNA repair were up-regulated by the treatment of KBrO(3). However, we could not observe the similarity of gene expression profile in the treatment of KBrO(3) to ionizing-irradiation as well as oxidative damage inducers.
Luan
Yang
Y
Division of Cellular and Gene Therapy Products, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan.
Suzuki
Takayoshi
T
Palanisamy
Rajaguru
R
Takashima
Yoshio
Y
Sakamoto
Hiroko
H
Sakuraba
Mayumi
M
Koizumi
Tomoko
T
Saito
Mika
M
Matsufuji
Hiroshi
H
Yamagata
Kazuo
K
Yamaguchi
Teruhide
T
Hayashi
Makoto
M
Honma
Masamitsu
M
D000080242:8-Hydroxy-2'-Deoxyguanosine; D001959:Bromates / Q000633:toxicity*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D020552:Comet Assay; D018736:DNA Adducts / Q000737:chemistry / Q000187:drug effects; D053903:DNA Breaks, Double-Stranded; D003849:Deoxyguanosine / Q000031:analogs & derivatives / Q000737:chemistry; D020869:Gene Expression Profiling; D006801:Humans; D019656:Loss of Heterozygosity; D015162:Micronucleus Tests; D009153:Mutagens / Q000633:toxicity*; D009154:Mutation; D020411:Oligonucleotide Array Sequence Analysis; D017384:Sequence Deletion; D013937:Thymidine Kinase / Q000235:genetics; D014965:X-Rays
D001959:Bromates; D018736:DNA Adducts; D009153:Mutagens; C019536:potassium bromate; D000080242:8-Hydroxy-2'-Deoxyguanosine; D013937:Thymidine Kinase; D003849:Deoxyguanosine