Antimutagenic activity of gigantol from Dendrobium nobile

A methanol extract from Dendrobium nobile showed a suppressive effect on umu gene expression of the SOS response in Salmonella typhimurium TA1535/pSK1002 against the mutagen 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide (furylfuramide). The methanol extract from D. nobile was re-extracted with n-hexane, dichloromethane, 1-butanol, and water, respectively. A suppressive compound in the n-hexane extract fraction was isolated by SiO2 column chromatography and chemical fractionation and was identified as gigantol by EI-MS and H-1 and C-13 NMR spectroscopy. Gigantol suppressed the SOS-inducing activity of furylfuramide in the umu test. Gene expression was suppressed 90% at <0.73 mu mol/mL, and the ID50 value was 0.35 mu mol/mL. Gigantol was also assayed with the mutagen 3-amino-1,4-dimethyl-5H-pyrido[4,3b]indole (Trp-P-1), which requires liver metabolizing enzymes, and it suppressed the SOS-inducing activity of Trp-P-1 in the umu test. Gene expression was suppressed 91% at <0.73 mu mol/mL, and the ID50 value was 0.32 mu mol/mL. In addition, gigantol was assayed for suppressive effect on UV irradiation in the umu test, where it showed suppression of the SOS-inducing activity caused by UV irradiation. Gene expression was suppressed 84% at <0.36 mu mol/mL, and the ID50 value was 0.17 mu mol/mL. The antimutagenic activities of gigantol against furylfuramide and Trp-P-1 were assayed by an Ames test using S. typhimurium TA100, which indicated that gigantol suppressed each of the mutagens.