Oxidative DNA Damage Induced by an N‐Hydroxy Metabolite of Carcinogenic 4‐Dimethylaminoazobenzene

Abstract

Formation of adducts has been considered to be a major causal factor of DNA damage by carcinogenic aminoazo dyes. We investigated whether a metabolite of hepatocarcinogenic 4-dimethylaminoazobenzene (DAB) can cause oxidative DNA damage or not, using There is ample evidence for the carcinogenicity of 4-dimethylaminoazobenzene (DAB) in experimental animals. DAB induced lung tumors and hepatomas in mice and liver tumors in rats. In dogs it produced bladder tumors following oral administration. DAB has also been tested by s.c. injection in mice, and the results are suggestive of local and hepatic carcinogenicity.1) The International Agency for Research on Cancer (IARC) has assessed that DAB is possibly carcinogenic to humans (group 2B). 2)DAB is metabolized to N-methyl-4-aminoazobenzene (MAB) through N-demethylation. MAB is metabolized to 4-aminoazobenzene (AAB) through demethylation or to N-hydroxy-N-methyl-4-aminoazobenzene (N-OH-MAB) through N-hydroxylation, followed by further transformation to N-hydroxy-4-aminoazobenzene (N-OH-AAB). 3-5)N-Hydroxylation is believed to be a step leading aminoazo dyes to proximate carcinogenic or mutagenic metabolites. Watanabe and Hashimoto reported that N-OH-AAB elicited higher levels of unscheduled DNA synthesis (UDS) than AAB, suggesting higher DNA damaging activity of the N-hydroxy derivative than that of the corresponding mother aminoazo dye.6) It was also reported that N-OH-AAB dyes showed greater mutagenicity than the mother AAB dyes, without S-9 treatment.7) It is generally accepted that covalent binding of these metabolites with DNA is a major carcinogenic factor. 8) N-(Deoxyguanosin-8-yl)-4-aminoazobenzene was also obtained from mice or rats given an i.p. dose of AAB.4) It was regarded as an adduct formed by reaction of deoxyguanosine with a metabolite of AAB after N-hydroxylation and esterification. 4)On the other hand, N-OH-AAB and N-OH-MAB are reported to generate H 2 O 2 and O . 9) Administration of 3′-methyl-4-dimethylaminoazobenzene (3′-MeDAB) which is a stronger carcinogenic derivative of DAB, increased the levels of 8-hydroxyguanine and its repair activity in rodent liver DNA.10) These reports suggested that oxidative DNA damage plays a part in carcinogenesis by aminoazo dyes.To clarify the mechanism of carcinogenesis by DAB, we examined oxidative DNA damage induced by N-OH-AAB, using 32 P-5′-end-labeled DNA fragments obtained from the c-Ha-ras-1 protooncogene and the p53 tumor suppressor gene. In addition, we measured the content of 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG) in calf thymus DNA by high-performance liquid chromatography with an electrochemical detector (HPLC-ECD). It has been reported that 8-oxodG is a marker of oxidative DNA damage and that its formation can lead to DNA misreplication, resulting in mutation and cancer.

Effect of a homeopathic drug, Chelidonium, in amelioration of p-DAB induced hepatocarcinogenesis in mice

“…MAB, AAB etc.) with DNA is a major carcinogenic factor [13]. In the present study, the only PB fed mice also did not develop tumors in liver, while those fed with p-DAB + PB developed tumors.…”

“…p-DAB and its metabolites have been reported to cause oxidative DNA damage [13], which could also be attributable to the various types of chromosome aberrations encountered in the present investigation. The formation of adducts, DNA-copper-hydroperoxo complexes, etc as suggested by Ohnishi et al [13], could also play an important role in the carcinogenic processes of p-DAB.…”

The Influence of Immunohistochemistry on mRNA Recovery from Microdissected Frozen and Formalin-Fixed, Paraffin-Embedded Sections

“…DAB, which was used as chromogen in the study, is known to be carcinogenic. It acts by inducing oxidative DNA damage 29 and DNA adduct formation, and this could in theory have a modifying action on nucleic acids. However, we have previously used DAB in the immunohistochemical marking of single cells, which subsequently were microdissected and analyzed by whole genome amplification and DNA PCR, without any detrimental effect on DNA recovery.…”

Oxidative DNA Damage by a Metabolite of Carcinogenic 1-Nitropyrene

“…A standard reaction mixture (in a microtube; 1.5 ml) contained CuCl 2 , NADH, a DMSO solution of 1-NOP, the 32 P-labeled double-stranded DNA fragments and calf thymus DNA in 200 l of 10 mM sodium phosphate buffer (pH 7.8) containing 2.5 M DTPA. After incubation at 37°C for 1 h, the DNA fragments were heated at 90°C in 1 M piperidine for 20 min and treated as described previously (15,16). The treated DNA fragments were electrophoresed on an 8% polyacrylamide/8 M urea gel and an autoradiogram was obtained by exposing X-ray film to the gel.…”