Phytoestrogens Enterolactone

Three cohort studies have been performed, one in European women, and two in oriental women eating a traditional soy-based diet. The study in European women, performed by Kardinaal et al. (1998), failed to show a correlation between change in forearm bone mineral density and urinary excretion of isoflavonoids. Excretion of enterolactone, a marker of intake of grain and berries, was found to correlate positively with bone mineral density. This may be explained with the difficulty of correlating bone mineral density -a multifactorial variable, influenced by diet only on long-term basis - with excretion of phytoestrogens that only quantify the last 24 to 48 hours of phytoestrogen intake. 

Phytoestrogens may modulate the activity of the human sex steroid binding protein and so influence the role of this protein in the delivery of hormonal information to sex steroid-dependent cells, as reported by Martin et al. [93] in research with NDGA, enterolactone and enterodiol. These phytoestrogens had different dose-dependent inhibitory effects on the steroid binding protein. 

Different lignans, including some known phytoestrogens, were evaluated for their effects on DNA synthesis in estrogen-dependent and independent human breast cancer cells. At 0.1-10 pM, enterolactone induced DNA synthesis by 150-235%, and at 20-90 pM it inhibited DNA synthesis by 50%. Inhibition of estrogen-dependent and independent breast cancer cells... 

FIGURE 25.1 Structures of nonsteroidal phytoestrogens. The most prevalent classes of phytoestrogens are (1) flavones apigenin (2) kaempferol (3) isoflavones daidzein (4) genistein (5) formononetin (6) biochanin A (7) lignans enterolactone (8) coumestans coumestrol (9) flavanones 8-prenylnaringenin. 

Flaxseed contains the compound secoisolariciresinol diglycoside (SDG), which is converted by bacteria in the colon to the mammalian lignans enterodiol and enterolactone, compounds that have phytoestrogenic activity (Power and Thompson 2007). 

Wang L. Mammalian phytoestrogens enterodiol and enterolactone. / Chromatogr, B Anal Technol Biomed Life Sci. 2002 777 289-309. 

The lignan phytoestrogen precursors matairesinol and secisolariciresinol are present in foods as glycosides and are converted by gut bacteria to the two main mammalian lignans enterolactone and entero-diol, respectively, which are weakly oestrogenic. Matairesinol undergoes dehydroxylation and demethylation directly to enterolactone, whereas secisolariciresinol is converted to enterodiol, which can then be oxidized to enterolactone. After absorption, enterolactone and enterodiol are converted to their yS-glucuronides and eventually excreted in urine. 

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