Estrogen phytoestrogens

BELCHER s M and ZSARNOVSZKY A (2001) Estrogenic actions in the brain estrogen, phytoestrogens and rapid intracellular signalling mechanisms. J Pharmacol Exp Then 299 (2) 408-14. 

In assay sytems, many of these phytoestrogens are able to bind more avidly to the estrogen receptor than estrogen itself. Why plant products should possess such avid estrogenic compounds is unclear, but it has been suggested that consumption of phytoestrogens by insects may result in alterations in the sex... 

Mayr U, Butsch A and Schneider S. 1992. Validation of two in vitro test systems for estrogenic activities with zearalenone, phytoestrogens and cereal extracts. Toxicology 74 135-149. 

Ise R, Han D, Takahashi Y, Terasaka S, Inoue A, Tanji M, et al. Expression profiling of the estrogen responsive genes in response to phytoestrogens using a customized DNA microarray. FEBS Lett 2005 579 1732-40. 

Phytoestrogens may elicit their biological effects by binding to estrogen receptors (ERs). Until recently, only a single ER isoform, ERa, had been identified however, a second receptor termed ERp has also been identified (Enmark et al, 1997, 1999 Saunders et al, 2000, 2001). It has been shown that the ERs have different intracellular and tissue distribution patterns and are responsible for different biological effects (see Table 5.1). A number of spliced variants of both ERa and ERp have also been identified (Inoue et al, 2000 Ogawa et al, 1998 Vladusic et al, 1998). 

In addition to direct interaction with ERs, phytoestrogens may also act indirectly to modulate the concentration of endogenous estrogens. 

The enzyme aromatase catalyses the conversion of testosterone to estrogen. A number of in vitro studies have shown that phytoestrogens can inhibit aromatase (Adlercreutz et al, 1993 Kao et al, 1998 Pelissero et al, 1996). However, the high concentrations required to cause this effect in vitro are unlikely to be achieved in vivo following dietary exposure. 

Phytoestrogens can modulate expression of both sub-types of estrogen receptor (Patisaul et al, 1999,2001 Wang et al, 1996). However, the data is limited to measurements of mRNA content and it is unclear whether this differential expression results in any functional change. 

Endogenous estrogens are known to be active in a number of areas of the brain. There are indications that estrogens may play a role in mood, locomotor activity, pain sensitivity, vulnerability to neurodegenerative diseases and cognition (McEwan, 1999). In humans, the blood brain barrier is not fiilly developed at birth and, for this reason, the central nervous system (CNS) may be more sensitive to phytoestrogens in utero or at birth. As ERs are expressed in the CNS, phytoestrogens may also be active in this area. 

There has been some speculation that estrogenic compounds may adversely affect the fertility of men by reducing testosterone levels and sperm counts (Atanassova et al, 2000). To date, however, the limited information available suggests that consumption of phytoestrogens does not affect reproductive hormones or semen quality (Nagata, 2000 Nagata et al., 2001 Mitchell et... 

KUIPER G G, LEMMEN J G, CARLSSON B, CORTON J 0, SAFE S H, VAN DER SAAG P T, VAN DER BURG B, GUSTAFSSON J A (1998) Interaction of estrogenic chemicals and phytoestrogens with estrogen receptor beta. iiwdocrmo/. 139 4252-63. 

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