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Genistein is a phytoestrogen of the ‘isoflavone’ class compounds. These diphenolic compounds resemble the structure of estradiol and have been shown to have weak estrogenic activity. It appears that they have both estrogenic and antiestrogenic effects, depending on the concentrations of circulating endogenous estrogens and estrogen receptor (ER). In cultured cell lines, the effects of different concentrations of genistein, estrogen or in combination with genistein and estradiol on p21, p53, cyclin B1, bax and bcl2 expressions were examined. At the low concentrations, genistein showed estrogen agonist action with p21 and p53 expressions. But at the higher concentrations, genistein had antiestrogenic activity increasing expression of these proteins in the presence of estrogen. The increased expression of cyclin B1 by estrogen was tampered by genistein at the highest concentration. Genistein increased the expression of bax at the three concentrations tested. In the presence of estrogen, genistein showed estrogen agonistic reaction as for bax protein. The expression of bcl2 protein did not appear to be influenced by either genistein or estrogen. In estrogen-deficient female rats the two different concentrations of genistein were employed along with estrogen treatment. The expressions of p21, pp53 and bax were examined. In vivo system, estrogen agonistic activity was shown with the higher concentration of genistein with bax expression. In Cyclooxygenase-2 (COX-2) expression, the lower concentration of genistein showed estrogen agonistic activity. The inhibitory effect of genistein on the proliferation of cultured cells supports the hypothesis that this compound may play a role in the prevention of particular types of cancers.
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