Genotoxicity of aminophenylnorharman, formed from norharman and aniline, in the liver of gpt delta transgenic mouse

K Masumura, MD a, Y Totsuka, PhD b, K Wakabayashi, PhD b, T Nohmi, PhD a

a Division of Genetics and Mutagenesis, National Institute of Health Sciences, Tokyo, Japan, b Cancer Prevention Division, National Cancer Center Research Institute, Tokyo, Japan.

AIM: Aminophenylnorharman (APNH) is formed from norharman and aniline, and is mutagenic to Salmonella typhimurium TA98 with S9 mix. Since norharman and aniline are present in cigarette smoke and cooked foods and are detected in human urine samples, APNH might be a human risk factor if it is mutagenic in vivo. To examine the possibility, the genotoxicity of APNH was examined using gpt delta transgenic mice. METHODS: Transgenic mouse gpt delta has two selection methods to efficiently detect different types of mutations; point mutations are detected by 6-thioguanine selection using the E. coli gpt gene and deletions are identified by Spi- selection using the red/gam genes of lambda phage. The mice at 7 weeks old were fed a diet containing APNH for 12 weeks. Genomic DNAs were extracted, and the gpt and Spi- mutation assays were performed. RESULTS: The gpt mutant frequency (MF) in the liver increased 10-fold in 20 ppm APNH-treated mice. This is almost the same level of MF observed in the liver of the mice treated with 300 ppm MeIQx for 12 weeks. The APNH-induced gpt mutations were dominated by G:C to T:A transversions. The Spi- MF in the liver increased 13-fold in 20 ppm APNH-treated mice. Majority of the APNH-induced Spi- mutations were single G:C bp deletions occurred in G:C run sequences. CONCLUSION: These results suggest that APNH has a strong hepatic mutagenicity in the liver of mice. APNH induced G:C to T:A transversions and single G:C base pair deletions.

KEY WORDS: heterocyclic amine, point mutation, deletion, mutation spectrum, 6-thioguanine selection, Spi- selection.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Carcinogenesis.