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Mechanism of oxidative DNA damage induced by carcinogenic allyl isothiocyanate
M Murata1, N Yamashita, S Inoue
1Department of Hygiene, Mie University School of Medicine, Tsu, Japan.
Abstract:
Several isothiocyanates have been proposed as promising chemopreventive agents for human cancers. However, it has been reported that allyl isothiocyanate exhibit carcinogenic potential, and benzyl isothiocyanate and phenethyl isothiocyanate have tumor-promoting activities. We investigated whether these isothiocyanates could cause DNA damage, using (32)P-labeled DNA fragments obtained from the human p53 tumor suppressor gene and the c-Ha-ras-1 protooncogene. Allyl isothiocyanate caused Cu(II)-mediated DNA damage and formation of 8-oxo-7, 8-dihydro-2'-deoxyguanosine (8-oxodG) more strongly than benzyl and phenethyl isothiocyanates. Catalase and bathocuproine, a Cu(I)-specific chelator, inhibited Cu(II)-mediated DNA damage by these isothiocyanates, suggesting involvement of H(2)O(2) and Cu(I). Isothiocyanates induced DNA damage frequently at thymine and cytosine residues in the presence of Cu(II). A UV-visible spectroscopic study revealed an association between the generation of superoxide and the yield of SH group from isothiocyanates. Furthermore, the yield of 8-oxodG formation was correlated with their superoxide-generating ability. Allyl isothiocyanate significantly induced 8-oxodG formation in HL-60 cells, but not in H(2)O(2)-resistant HP100 cells, suggesting the involvement of H(2)O(2) in cellular DNA damage. We conclude that oxidative DNA damage may play important roles in carcinogenic processes induced by allyl isothiocyanate.
Insights
Allyl isothiocyanate causes DNA damage through oxidative stress, particularly forming 8-oxo-7, 8-dihydro-2'-deoxyguanosine (8-oxodG). This damage mechanism highlights potential carcinogenic risks associated with certain isothiocyanates.
Area of Science:
- Molecular toxicology
- Cancer chemoprevention research
- Oxidative stress mechanisms
Background:
- Isothiocyanates are explored for cancer chemoprevention.
- However, some, like allyl isothiocyanate, may possess carcinogenic or tumor-promoting properties.
- Understanding their genotoxicity is crucial for risk assessment.
Purpose of the Study:
- To investigate the DNA damaging potential of allyl isothiocyanate (AITC), benzyl isothiocyanate (BITC), and phenethyl isothiocyanate (PEITC).
- To elucidate the mechanisms underlying isothiocyanate-induced DNA damage, focusing on oxidative stress pathways.
- To assess the formation of 8-oxo-7, 8-dihydro-2 -deoxyguanosine (8-oxodG) as a marker of oxidative DNA damage.
Main Methods:
- Utilized (32)P-labeled DNA fragments from human p53 and c-Ha-ras-1 genes.
- Assessed Cu(II)-mediated DNA damage and 8-oxodG formation in vitro.
- Employed catalase and bathocuproine to investigate the roles of H(2)O(2) and Cu(I).
- Spectroscopic analysis to detect superoxide generation and SH group yield.
- Evaluated 8-oxodG formation in HL-60 and H(2)O(2)-resistant HP100 cells.
Main Results:
- AITC induced significantly more Cu(II)-mediated DNA damage and 8-oxodG formation than BITC and PEITC.
- H(2)O(2) and Cu(I) were implicated in the DNA damage, as indicated by inhibition with catalase and bathocuproine.
- DNA damage occurred predominantly at thymine and cytosine residues.
- Superoxide generation correlated with SH group yield and 8-oxodG formation.
- AITC induced 8-oxodG in HL-60 cells, but not in HP100 cells, confirming H(2)O(2) involvement.
Conclusions:
- Allyl isothiocyanate induces oxidative DNA damage, evidenced by 8-oxodG formation.
- The mechanism involves copper(II), hydrogen peroxide, and superoxide generation.
- These findings suggest that oxidative DNA damage contributes to the carcinogenic potential of AITC.