The red clover isoflavone irilone is largely resistant to degradation by the human gut microbiota

Abstract

Intestinal bacteria may influence bioavailability and physiological activity of dietary isoflavones. We therefore investigated the ability of human intestinal microbiota to convert irilone and genistein in vitro. In contrast to genistein, irilone was largely resistant to transformation by fecal slurries of ten human subjects. The fecal microbiota converted genistein to dihydrogenistein, 6'-hydroxy-O-desmethylangolensin, and 2-(4-hydroxyphenyl)-propionic acid. However, considerable interindividual differences in the rate of genistein degradation and the pattern of metabolites formed from genistein were observed. Only one metabolite, namely dihydroirilone, was formed from irilone in minor amounts. In further experiments, Eubacterium ramulus, a prevalent flavonoid-degrading species of the human gut, was tested for transformation of irilone. In contrast to genistein, irilone was not converted by E. ramulus. Irilone only differs from genistein by a methylenedioxy group attached to the A-ring of the isoflavone skeleton. This substitution obviously restricts the degradability of irilone by human intestinal bacteria.

Evaluation of inter-individual differences in gut bacterial isoflavone bioactivation in humans by PCR-based targeting of genes involved in equol formation

“…Dihydrodaidzein was formed as an intermediate or a final metabolite by all but one of the tested microbiomes. This is in agreement with previous studies demonstrating the conversion of daidzein to dihydrodaidzein or genistein to dihydrogenistein in 70-90% of the human FS tested (Gardana et al 2009;Braune et al 2010;Gaya et al 2016).…”

“…The study was approved by the ethical committee of the University of Potsdam (Germany). Sample collection and further processing under strict anoxic conditions were done as described previously (Braune et al 2010). The FS were 10-fold diluted (w/v) with anoxic BHI broth and 200-ll aliquots were transferred to Hungate tubes containing 2 ml of BHI broth and a gas phase of N 2 /CO 2 (80 : 20, v/v) supplemented with 22 ll of 20 mmol l À1 daidzein (Roth) in dimethyl sulfoxide (DMSO) or 20 mmol l À1 dihydrodaidzein (Toronto Research Chemicals, Toronto, ON, Canada) in DMSO or DMSO only.…”

Phytoestrogens: Naturally Occurring, Hormonally Active Compounds in Our Diet

“…5 Since research is now showing that irilone is practically resistant to microbial metabolism, further research is required to determine the biological role, if any, of these minor red clover isoflavones. 17 …”

Trifolium pratense

“…New reduced metabolites of formononetin (dihydroformononetin and angolensin) and biochanin A (dihydrobiochanin A and 6′-hydroxyangolensin) were identifi ed in the urine samples. Studies found intestinal bacteria may infl uence bioavailability and physiological activity of dietary red clover isofl avones (Braune et al 2010 ). In contrast to genistein, irilone was largely resistant to transformation by faecal slurries of ten human subjects.…”