MUTAGENICITY OF PLANT FLAVONOLS IN THE SALMONELLA-MAMMALIAN MICROSOME TEST - ACTIVATION OF FLAVONOL GLYCOSIDES BY MIXED GLYCOSIDASES FROM RAT CECAL BACTERIA AND OTHER SOURCES

Over 70 naturally occurring and synthetic flavonoids were screened for mutagenicity with 5 tester strains in the Salmonella/mammalian microsome assay: TA1535, TA100, TA1537, TA1538 and TA98. Frameshift mutagenicity was confined to the flavonols (flavon-3-ols) in strains TA98, TA1537 and TA100. The two most mutagenic flavonols, namely, quercetin (3,3′,4′5,7-pentahydroxyflavone) and kaempferol (3,4′,5,7-tetrahydroxyflavone), exhibiting 12 and 7 revertants/nmol in TA98 respectively, are also the most common flavonols occuring in plants. Other flavonols exhibited less activity (revertants/nmol): galangin (2.0), rhamnetin (0.45), kaempferide (0.24), fisetin (0.14), myricetin (0.12), robinetin (0.06) and morin (0.05). All of these flavonols apparently exhibited significant activation by Aroclor 1254 induced rat-liver microsome preparations (S9). However, subsequent study revealed that only those flavonols either lacking or possessing one B ring hydroxyl group had an absolute requirement for microsomal activation. Alternatively, quercetin with two Bring OH groups is not activated by microsomal enzymes, but by soluble (S100) enzymes from liver which are apparently constitutive and not subject to the usual chemical induction. 3 flavonol glycosides, namely, quercetrin (quercetin-3-O-rhamnoside), rutin (quercetin-3-O-rutinoside) and robinin (kaempferol-3-O-galactosido-rhamnoside-7-O-rhamnoside), were found to be nonmutagenic. They could, however, be activated by a variety of mixed glycosidases incorporated in the usual pour plate procedure. The most effective enzyme mixtures were obtained from rat Cecal bacteria and from the snail Helixpomatia. © 1979.