N-Nitroso compounds are suspected to be causative agents for human cancer. N-Methyl-N-nitrosourea (MNU) is a typical direct acting mutagen with alkylation activity of DNA, and has been reported to be formed in vivo. Therefore, it is important for cancer chemoprevention to find some compounds to inhibit mutagenicity induced by MNU. The inhibitory effect of plant extracts against the mutagenicity of MNU was evaluated using the Ames assay with Salmonella typhimurium TA1535. Among 43 extracts derived from medicinal and edible plant assayed, Glycyrrhiza aspera ethanolic extract, Glycine max extract with 40% isoflavone aglycone (ISOMAX AG40) and Zingiber officinale ethanolic extract at the range 0.01-1.0 mg/plate inhibited MNU-induced mutagenicity in S. typhimurium TA1535. No cytotoxicity of the three extracts were observed in Salmonella typhimuirum TA1535, indicating that inhibition of MNU-induced mutagenicity was apparently due to the antimutagenic potency of Glycyrrhiza aspera ethanolic extract, ISOMAX AG40 and Zingiber officinale ethanolic extract. Therefore, the results of relative mutagenicity showed that Glycyrrhiza aspera ethanolic extract and ISOMAX AG40 decreased the mutagenic effects to 5.4% and 2.6%, respectively, whereas Zingiber officinale ethanolic extract decreased it to 45%.
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