Flavonoid glycosides are present in numerous plants such as fruits, leafy vegetables, legumes, herbs and spices. Subjects on a """"""""Western diet"""""""" consume about 1 g of flavonoid glycosides daily. Intestinal bacteria catabolize some flavonoid glycosides to a variety of metabolites, some of which are mutagenic.
The aims of this proposal are to (1) examine systematically the metabolism by human fecal flora of specific flavonoid glycosides e.g. quercitrin, rutin, robinin and their corresponding aglycones e.g. quercetin and kaempferol. The inquiry includes the bacterial hydrolysis of flavonoid glycosides, fission of the C-ring, reduction of the 2, 3-double bond and the C4-keto group and C3-dehydroxylation; (2) isolate and identify the bacterial species synthesizing the enzymes responsible for the transformations; (3) determine the kinetics of the bacterial conversion of individual substrates. The significance of the proposed investigation is to (a) obtain a clear understanding of flavonoid metabolism in humans; (b) identify the source of flavonoid metabolizing enzymes, thereby providing a basis for their isolation and purification and (c) provide a basis for the control of particularly undesirable metabolites, e.g. carcinogens. The methodology used previously to unravel the bacterial metabolism of steroid hormones will be adapted to the present investigation. The metabolites formed in incubations of fecal flora or pure cultures and substrates will be extracted and identified by t.l.c., g.l.c., h.p.l.c., spectrophotometery and when needed mass spectroscopy. The metabolites serve as markers and enumerators for flavonoid metabolizing bacteria. They will determine whether the dilution or replica method should be used for the isolation of the specific organisms. Identification will be performed by conventional bacteriological techniques. Metabolic experiments similar to those outlined here have been performed daily for the last decade in our laboratories, appropriate instrumentation is available.
