The use of flavonoid aglycones in in vitro systems to test biological activities: Based on bioavailability data, is this a valid approach?

The majority of in vitro assays on biological activities of flavonoids have used the aglycone form as the test compound. This form is readily available from commercial sources and comparable approaches have been used for testing efficacy of drugs. This paper presents the hypothesis that aglycones are only transiently present in vivo at significant concentrations at specific sites. The pathway of metabolism of flavonoids in mammals in vivo, focusing on aglycone formation, is examined to facilitate better design in the future of in vitro cell culture experiments. In vitro experiments using flavonoids and cultured cells require careful consideration of absorption and bioavailability for their appropriate interpretation.