| Budget Amount *help |
¥2,900,000 (Direct Cost: ¥2,900,000)
Fiscal Year 2005: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 2004: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2003: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Research Abstract |
Thiabendazole (TBZ), a post-harvest fungicide commonly used on imported citrus fruits, exhibited photo-mutagenicity following UVA-irradiation (320-400 nm) in Trp^+ reverse mutation assay using Escherichia coli WP2uvrA/pKM101 strain. The photo-mutagenicity was not observed in the presence of S9mix, a rat liver homogenate microsome fraction with co-factors for metabolic activation. We found that NADH and NADPH used as co-factor in the S9mix efficiently suppressed the photo-mutagenicity of TBZ. This evidence strongly suggested that non-mutagenicity in the presence of S9mix was not due to the metabolic detoxification of TBZ or the scavenging of UVA-activated TBZ by macromolecules in the S9mix. Rather quenching effect of NADH and NADPH may be more responsible for suppression of UVA-activation of TBZ, because oxidized forms of NAD^+ and NADP^+ did not show inhibitory effects.
Potential of DNA-damaging activity, mutagenicity, and clastogenicity were investigated by short pulse treatment for 10 min with TBZ (50-400 μg/ml) and UVA-irradiation (320-400 nm, 250 μW/cm^2) in bacterial and human cells. UVA-irradiated TBZ caused DNA damage in Escherichia coli and human lymphoblastoid WTK1 cells assayed, respectively, by the umu-test and the single cell gel electrophoresis (comet) assay. In a modified Ames test using Salmonella typhimurium and E.coli, strong induction of -1 frameshift mutations as well as base-substitution mutations were detected. TBZ at 50-100 μg/ml with UVA-irradiation significantly induced micronuclei in WTK1 cells in the in vitro cytochalasin-B micronucleus assay. Pulse treatment for 10 min with TBZ alone did not show any genotoxicity. Although TBZ is a spindle poison that induces aneuploidy, we hypothesize that the photogenotoxicity of TBZ in the present study was produced by a different mechanism, probably by DNA adduct formation. We concluded that UVA-activated TBZ is genotoxic in human cells in vitro.
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