ARE PHYTOESTROGENS OF ANY HELP

Phytoestrogens are a diverse group of polyphenolytic nonsteroidal plant compounds that have the ability to bind to the human estrogen receptors. Phytoestrogens are present in soy, red clover, black cohosh, chaste berry, wild yam, and hops. Well-studied phytoestrogens are coumestrol, genistein, daidzein, equol, and 8-prenylnaringenin (8 PN). The affinity of the different phytoestrogens varies with genistein preferentially binding to the b-estrogen receptor and 8 PN being a much weaker agonist for the b-estrogen receptor than for the a receptor. Soy is the most important source of isoflavones. Large variations in isoflavone content exist since 1 g of soybeans may contain isoflavones of between 0.14 and 1.53 mg. The isoflavones in soy are bound to a glycoside unit. The deconjugation by the b-galactosidase action of intestinal bacteria results in the metabolic active aglycon. Peak concentrations of plasmic isoflavones (in the magnitude of 2 lmol/L after ingestion of 50 mg aglyconic isoflavones) are reached after 5–9 h of ingestion. Bacteria also play an important role in the metabolization of isoflavones. Daidzein may be transformed by bacteria into the metabolic more active equol. Well-conducted studies indicate that phytoestrogens have some effects on vasomotor symptom relief, osteoporosis prevention, and cardiovascular protection. Concerning endometrial safety, it is important to distinguish between molecules such as genistein and 8 PN. The latter is an aestrogen receptor agonist (100 times more potent than genistein) with the same properties of 17b-estradiol. Depending on the specific bioassay and test conditions, its estrogenic potency is between 10- fold and several 100-fold less pronounced than that of estradiol. 8 PN inhibits angiogenesis and stimulates endometrium proliferation and breast cancer cell growth. On the other hand, improvement of cell–cell adhesion is observed due to 8 PN. Hops also contain xanthohumol that can be transformed into 8 PN. So the actual plasmic concentrations may vary substantial after ingestion of hop-derived products. All the studies performed using soy so far have shown no stimulation of the endometrium, even so with high doses (500 mg aglyconic isoflavones). There seems to be a tendency for soy isoflavones to exert a protective effect on the breast similar to the far better studied b-estrogen receptor stimulator raloxifen. Again, it remains important to study the resorption and the equol-producing capability of the patient. In a randomized study, no difference was found in isoflavone content in the breast tissue after ingestion of soy. A large variation was observed between individuals. The combination of soy isoflavones with tamoxifen is beneficial at high (. 10 lmol/L) isoflavone concentrations. At low concentrations (, 10 lmol/L), the isoflavones may interfere with the metabolization of tamoxifen, reducing its activity. During normal ingestion of soy, the plasmic concentrations of isoflavones are much lower than 10 lmol/L. So it is advised not to prescribe soy in patients undergoing adjuvant tamoxifen treatment. Phytoestrogens are active compounds when they are given at sufficient dosage. There is a large variation in absorption. The influence of intestinal bacteria is important and variable. Once the variation of absorption is solved, some beneficial properties (b-estrogen receptor binding) of isoflavones may be useful to study them as chemopreventive agents for breast cancer.