Genistein

Genistein

Genistein is one of several known isoflavones. Isoflavones, such as genistein and daidzein, are found in a number of plants, with soybeans and soy products like tofu and textured vegetable protein being the primary food source. Soy isoflavones are a group of compounds found in and isolated from the soybean. Besides functioning as antioxidants, many isoflavones have been shown to interact with animal and human estrogen receptors, causing effects in the body similar to those caused by the hormone estrogen. Soy isoflavones also produce non-hormonal effects.

Biological effects

Antioxidant

Some isoflavones act as antioxidants to counteract damaging effects of free radicals in tissues. Genistein has a converse effect in this area compared to other isoflavones; It stimulates a step in nitrate synthesis, which is oxidation.

Atherosclerosis

Cancer links

Some isoflavones have been found to have antiangiogenic effects (blocking formation of new blood vessels), and may block the uncontrolled cell growth associated with cancer, most likely by inhibiting the activity of substances in the body that regulate cell division and cell survival (growth factors). If Genistein has this effect, then it still has the net effect of promoting cancer in one study.

Studies show that gastrointestinal cancer occurs less frequently among North Americans who do not learn to eat meat. North Americans who go to other continents without learning to eat vegetables show more digestive tract cancer than neighbours.

Timing of phytoestrogen use is important.

Genistein makes some cells more sensitive to radio-therapy.

Though research is still ongoing, some recent studies have indicated that soy's phytoestrogens could be contributive factors in some forms of breast cancer, penile birth defects, and infantile leukemia.

Some studies have raised the concern that genistein might increase the risk of leukemia, because it inhibits the enzyme topoisomerase which results in double strand DNA breaks, which are, in turn, mutagenic. Some cancer patients whose chemotherapy drugs inhibited topoisomerase later developed leukemia. NCI researchers have completed animal studies on genistein with no adverse effects being seen. [see discussion page]

Regardless, soy's phytoestrogens, or isoflavones, have been definitely shown to depress thyroid function and to cause infertility in every animal species studied so far.

Genistein's chief method of activity is as a tyrosine kinase inhibitor. Tyrosine kinases are less widespread than their ser/thr counterparts but implicated in almost all cell growth and proliferation signal cascades. Genistein has been used to selectively target pre B-cells via conjugation with an antibody. This highly successful study in mice has promising benefits for future chemotherapy

Effects in males

Isoflavones can act like estrogen, stimulating development and maintenance of female characteristics or they can block cells from using cousins of estrogen. In vitro studies have proven genistein to induce apoptosis of testicular cells at certain levels, thus raising concerns about effects it could have on male fertility.

Molecular function

Genistein influences several targets in living cells. One important function is the inhibition of several tyrosine kinases. Genistein also inhibits the mammalian hexose transporter GLUT1 and contraction of several types of smooth muscles. Genistein can bind to the CFTR channel, potentiating its opening at low concentration and inhibiting it a higher doses.

Sources

Concentrations of genistein in Pueraria mirifica (White Kawo Krua) are so close to zero that experimental estimates of error equalled concentration measured.

References

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