Mut-Test to detect substances suppressing spontaneous mutation due to oxidative damage

Abstract

Since it has been considered that suppression of spontaneous mutation in cells is related to suppression of spontaneous carcinogenesis, it is significant to detect substances which suppress spontaneous mutation in bacterial cells such as Escherichia coli and Salmonella typhimurium in the environment. However, since the frequency of spontaneous mutation in bacteria is usually very low, generally 10 −8–10 −10,it is difficult to determine significant suppressive ability of such substances on spontaneous mutation. A new method, Mut-Test, was developed by us, applying Luria & Delbruck fluctuation test, to detect substances which suppress spontaneous mutation using E. coli mutT mutant in which spontaneous mutation frequency due to oxidative damage is enhanced to approximately 500–1000 times of the wild type strain. Suppressive abilities of two hydroxyl radical scavengers: d(−)-mannitol and thiourea, were examined and clear positive results were obtained, suggesting that the radical scavengers are suitable as the positive control for the test. Using Mut-Test, suppressive abilities of four vitamins: l-ascorbic acid, β-carotene, folic acid and riboflavin; 10 polyphenols: caffeic acid, ellagic acid, (−)-epicatechin, (−)-epicatechin gallate, (−)-epigallocatechin, gallic acid, pyrocatechol, pyrogallol, quercetin and tannic acid which are recognized as antimutagens, were examined. Furthermore, the concentrations for 50% of suppressive abilities of five positive samples, l-ascorbic acid, folic acid, caffeic acid, pyrocatechol and pyrogallol were compared. Negative results were obtained in nine samples, riboflavin, tannic acid, etc. suggesting that their antimutagenic effect on cells may not be related to oxidative damage in cells.