O-desmethylangolensin: the importance of equol's lesser known cousin to human health.

The objective for this paper was to review human studies of O-desmethylangolensin (O-DMA) concentrations and of O-DMA producers compared with nonproducers in the context of results from in vitro studies. O-DMA is an intestinal bacterial metabolite of daidzein, an isoflavone compound observed to have phytoestrogenic properties. Not all individuals harbor bacteria capable of metabolizing daidzein to O-DMA, and individuals can be classified as O-DMA producers and nonproducers. O-DMA is less structurally similar to 17β-estradiol than its parent compound, daidzein; thus, it may exhibit different biological actions than daidzein. Evidence from in vitro studies suggests that O-DMA has several cancer-related biological actions. However, results from human metabolic studies and observational studies of disease risk suggest that these actions may not be physiologically relevant in vivo due to the amount and form (primarily glucuronide) of circulating O-DMA. Apart from circulating O-DMA concentrations, the underlying bacteria may have a distinct physiological role. Urinary excretion of O-DMA in humans is a marker of harboring intestinal bacteria capable of C-ring cleavage. Bacterial C-ring cleavage reactions are relevant to other phytochemicals that may exert biological actions in vivo that are stronger than the actions of O-DMA; thus, the role of the phenotype may extend beyond daidzein metabolism. There are a limited number of studies that have evaluated disease risk factors in relation to being an O-DMA producer, with mixed results. Further research evaluating disease risk in relation to the O-DMA-producer phenotype from the perspective of intestinal microbial composition is recommended.