Binding of N-acetylbenzidine and N,N''-diacetylbenzidine to hepatic DNA of rat and hamster in vivo and in vitro

Benzidine, a potent hepatocarcinogen in rodents, is readilymetabolised to acetylated derivatives. In this study, the covalentbinding of [³H-acetyl]N-acetylbenzidine and [³H-acetyl]N,N'-diacetylbenzidineto liver DNA in rats and hamsters was investigated. Bindingto liver DNA of rats at 1 or 7 days after i.p. injection ofN-acetylbenzidine was 2-fold higher than that observed in theliver DNA of hamsters which had been similarly treated. Analysisof enzymically hydrolysed DNA from both species indicated thepresence of a single adduct which co-eluted with N-(deoxyguanosin-8-yl)-N'-acetylbenzidine. In vitro treatment of rat or hamster liverslices with N-acetylbenzidine also resulted in covalent bindingto hepatic DNA and the identical DNA adduct was detected atlevels comparable to that observed in vivo. When N,N'-diacetylbenzidinewas injected i.p. into rats, a comparatively low level of bindingto liver DNA was observed. Following enzymic hydrolysis, themajor DNA adduct detected by h.p.l.c. analysis was again N-(deoxyguanosin-8-yl)-N'-acetylbenzidineaccompanied by a small amount of N-(deoxyguanosin-8-yl)-N,N'-diacetylbenzidine.In vitro incubation of N,N'-diacetylbenzidine with rat liverslices resulted in DNA binding levels similar to that observedwith N-acetylbenzidine. In contrast to what was found in vivo,N-(deoxyguanosin-8-yl)-N,N'-diacetylbenzidine was the majoradduct detected in DNA from rat liver slices. These data suggestthat both N-hydroxy-N'-acetylbenzidine and N-hydroxy-N,N'-diacetylbenzidineare proximate carcinogenic species of benzidine, with N-hydroxy-N'-acetylbenzidinethe more important. The low level of N-(deoxyguanosin-8-yl)N,N'-diacetylbenzidineobserved in vivo may be due to its rapid repair. Alternatively,N-sulphonyloxy-N,N'-diacetylbenzidine, which would produce thisadduct on reaction with DNA, may be efficiently detoxified invivo.