Suppression of Chemical Mutagens-Induced SOS Response by Phenolic Acids from Black Rice Bran Using Salmonella typhimurium TA1535/pSK1002 umu Test

Abstract

A methanol extract from black rice bran showed a suppressive effect of the SOS-inducing activity on the mutagen 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide (furylfuramide) in the Salmonella typhimurium TA1535/pSK1002 umu test. The methanol extract was re-extracted with hexane, chloroform, ethylacetate, butanol and water. The ethylacetate fraction showed a suppressive effect. Suppressive compounds in an acidic fraction of the ethylacetate fraction were isolated by silica gel column chromatography and identified as vanillic acid (1) and protocatechuic acid (2) by GC, GC/MS, IR and 1H and 13C NMR spectroscopy. Compounds 1 and 2 suppressed the furylfuramide-induced SOS response in the umu test. Compounds 1 and 2 suppressed 37.7 and 44.5% of the SOS-inducing activity on furylfuramide at a concentration of 1.20 μ mol/mL. These compounds were assayed with other mutagens, 4-nitroquinolin 1-oxide (4NQO) and N -methyl-N ′-nitro-N -nitrosoguanidine (MNNG), which do not require liver metabolizing enzymes. In addition, compounds 1 and 2 were assayed with aflatoxin B1 (AfB1) and 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1), which require liver metabolizing enzymes. These compounds showed suppressive effects of the SOS-inducing activity against furylfuramide, 4NQO, MNNG, AfB1 and Trp-P-1. To research the structure-activity relationship, veratric acid (3) as a similar compound of 1 and methyl esters of 1,2 and 3 (1Me, 2Me and 3Me) were also assayed with all chemical mutagens. Compounds 1Me, 2Me and 3Me exhibited stronger suppressive effects of the SOS-inducing activity against all chemical mutagens than 1,2 and 3.