Genistein bioavailability

The mucosa of the GIT represents an interface between the external and internal environments. The expansive surface area is necessary for the efficient hydrolysis of foodstuffs and the absorption of energy and nutrients. The mucosa also influences the systemic availability of non-nutrient compounds in the diet, both beneficial and detrimental. Digestion and absorption of glucosinolates are critical determinants of health benefits (see Chapter 4) Similarly, the bioavailability and health benefits of phytoestrogens, such as genistein (see Chapters 5 and 10) are at least partly dependent on the carrier-mediated processes of absorption associated with the GIT (Oitate et al, 2001). Moreover, the metabolic activities of the mucosa can influence the systemic concentrations and forms of dietary phytochemicals, as exemplified by research with soy isoflavones (Andlauer et al., 2000). 

King, R.A., Daidzein conjugates are more bioavailable than genistein conjugates in rats. Am. 

Fritz, W, Wang, J, Coward L, Lamartiniere CA. Dietary genistein perinatal mammary cancer prevention, bioavailability and toxicity testing in the rat. Carcinogenesis 19, 2151-2158, 1998. 

Intestinal microflora plays a key role in the metabolism and bioavailibility of isoflavones [86]. After ingestion, soybean isoflavones are hydrolyzed by intestinal glucosidases, which release the aglycones, daidzein and genistein, Fig. (16). 

Xu X, Wang H-J, Murphy PA, Cook L, Hendrich S. 1994. Daidzein is a more bioavailable soymilk isoflavone than is genistein in adult women. J Nutr 124 825-832. 

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. 

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