Suppressive components in rice husk against mutagens-induced SOS response using Salmonella typhimurium TA1535/pSK1002 umu test

The EtOAc extract from rice (Oriza sativa cv. Hinohikari) husk showed a suppressive effect on umu gene expression of the SOS response in Salmonella typhimurium TA1535/pSK1002 against the mutagen, Trp-P-1, which requires liver metabolizing enzyme. To obtain the suppressive compound, the EtOAc extract was fractionated by SiO(2) column chromatography using umu test as a bioassay guide. Suppressive compound was isolated and identified as momilactone A (1) by EIMS, IR, (1)H- and (13)C-NMR spectroscopy. Compound 1 inhibited of the SOS-inducing activity of Trp-P-1 in the umu test. Gene expression was suppressed by 32.6% at less than 0.60 mM. Compound 1 was assayed with activated Trp-P-1. The suppressive effect of Compound 1 was decreased compared with that of Trp-P-1. Furthermore, 1 was assayed with another mutagens, such as MeIQ, activated MeIQ, furylfuramide (AF-2), MNNG, and UV-irradiation. Compound 1 showed greater suppressive effect on AF-2-inducing SOS response than other mutagens.     

Suppression of chemical mutagen-induced SOS response by allylbenzen from Asiasarum heterotropoides in the Salmonella typhimurium TA1535/PSK1002 umu test

A methanol extract from Asiasarum heterotropoides showed a suppressive effect of the SOS-including activity on the mutagen 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) in the Salmonella typhimurium TA1535/pSK1002 umu test. The methanol extract was re-extracted with chloroform, butanol, and water. The chloroform fraction showed a suppressive effect. Suppressive compounds in the chloroform fraction were isolated by silica gel column chromatography and identified as methyleugenol (1), elemicin (2), and gamma-asaron (3) by GC/MS, IR, and 1H- and 13C-NMR spectroscopy. These compounds suppressed the MeIQ-induced SOS response in the umu test. Gene expression was suppressed 52.2, 61.8, and 71.6% at a concentration of 0.1 mM, respectively. The ID50 values (50% inhibition dose) of these compounds were 0.080, 0.028, and 0.013 mM, respectively. On the other hand, Compounds 1-3 showed weak suppressive effect of the SOS-inducing activity on activated MeIQ. These results indicate that the inhibition of the SOS-inducing activity on MeIQ, which was caused by Compound 1-3 was due to the inhibition of metabolic activity by S9.