Isoflavone metabolites

The metabolism and bioavailability of isoflavonoids is likely to be of crucial importance to their ability to help protect human health against disease. Many studies have been published on the metabolism and bioavailability of isoflavones in adults. The metabolism of isoflavones is of particular interest because the potency of isoflavone metabolites differs from that of the parent compounds. The daidzein metabolite equol is three times as potent as is daidzein in an endometrial tumor line. Equol is also a more potent antioxidant in vitro (see Sections 7.3.5 and 7.4.2) ° and the clinical significance of the ability to form equol has been considered in depth. ... 

Setchell KD, Clerici C, Lephart ED, Cole SJ, Heenan C, Castellani D, Wolfe BE, Nechemias-Zimmer L, Brown NM, Lund, TD, Handa RJ, Heubi JE. 2005. S-equol, a potent ligand for estrogen receptor beta, is the exclusive enantiomeric form of the soy isoflavone metabolite produced by human intestinal bacterial flora. Am J Clin Nutr 81 1072-1079. 

Chin-Dusting JP, Boak L, Husband A, Nestel PJ. 2004. The isoflavone metabolite dehydroequol produces vasodilatation in human resistance arteries via a nitric oxide dependent mechanism. Atherosclerosis 176 45-48. 

Nestel P, Fujii A, Zhang L. 2006. An isoflavone metabolite reduces arterial stiffness and blood pressure in overweight men and postmenopausal women. Atherosclerosis 192 184-189. 

The bioavailability of active thyroid hormones depends on the activity of deiodinases in thyroid follicular cells and in target tissues. In vitro experiments with purified enzyme revealed that some dietary flavonoids in micromolar concentrations inhibited thyroid type 1 iodothyronine deiodi-nase activity (Ferreira et al, 2002). Among the compounds tested was an isoflavone metabolite, biochanin A. So far, a few reports using various cell cultures (Mori et ai, 1996) or animals (cats) (White et ai, 2004) have confirmed that genistein at least is capable of inhibiting 5 -deiodinases. 

Hosoda K, Furuta T, Yokokawa A, Ogura K, Hiratsuka A, Ishii K. Plasma profiling of intact isoflavone metabolites by high-performance liquid chromatography and mass spectrometric identification of flavone glycosides daidzin and genistin in human plasma after administration of kinako. Drug Metab Dispos 2008 36 1485-1495. 

Isoflavone metabolites are more potent antioxidants than parent compounds in vitro, but sulfation and glucuronidation suppress this effect. 

Rimbach, G., De Pascual-Teresa, S., Ewins, B.A., Matsugo, S., Uchida, Y., Minihane, A.M., Turner, R., VafeiAdou, K., and Weinberg, P.D. 2003. Antioxidant and free radical scavenging activity of isoflavone metabolites. Xenobiotica 33, 913-925. 

Using RP-HPLC interfaced with ESI to an MS, it is possible to obtain a mass/ intensity map of all isoflavone metabolites in a single 20 min analysis. Analysis of isoflavonoid conjugate in serum/plasma samples requires initial extraction, but the conjugates can be measured intact either by capillary RP-HPLC-ESI-MS or on regular RP columns by HPLC-HN-APCI-MS. When it is only necessary to measure the total isoflavonoids and their metabofites in blood, hydrolysis can be performed directly in semm/plasma samples and flavonoids recovered by ether or ethyl acetate solvent extraction (Barnes et al., 1998). 

SETCHELL K D R, BROWN N M, LYDEKING-OLSEN E (2002) The cluucal importance of the metabolite equol - a clue to the effectiveness of soy and its isoflavones. JNutr 132, 3577-3584. 

Root flavonoids that may act as signals for the initiation and development of endomycorrhizal and ectomycorrhizal symbio.ses have been identified (see Chap. 7). Metabolites of the phenylpropanoid pathways apparently act as signaling molecules in endo- and ectomycorrhizal interactions (14). The role of flavonoids is still controversial, but a variety of flavanones, flavones, and isoflavones... 

Gut microflora metabolites may also be important. As discussed above, the mammalian lignan aglycones, enterodiol and enterolactone, are estrogenic, and equol is more estrogenic than its dietary precursor, the isoflavone daidzein. ... 

Hoey, L., Rowland, I.R., Lloyd, A.S., Clarke, D.B., and Wiseman, H., Influence of soya-based infant formula consumption on isoflavone and gut microflora metabolite concentrations in urine and on faecal microflora composition and metabolic activity in infants and children, Br. J. Nutr, 91, 607, 2004. 

The importance of the gut microflora in the metabolism of isoflavones has been demonstrated. Antibiotic administration blocks isoflavone metabolism and germfree animals do not excrete metabolites. Moreover, only germfree rats colonized with microflora from a good equol producer excrete equol when fed soy. ... 

Arora A, Nair NG, Strasburg GM. Antioxidant activities of isoflavones and their biological metabolites in a liposomal system. Arch. Biochem. Biophys. 356, 133-141, 1998. 

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