Combinatorial effects of the phytoestrogen genistein and of estradiol in uterus and liver of female Wistar rats.

The knowledge about safety of phytoestrogens on proliferative endpoints in the endometrium is rather limited, particularly when low amounts of estrogens are present like in postmenopausal women. Therefore, we now studied how genistein (GEN) exposure affects proliferative endpoints in the endometrium in estrogenized animals. We investigated the effects of GEN (10 mg/(kgday) BW) on uterine proliferation and on general uterine response markers in intact female rats and ovariectomized (OVX) female rats co-treated with different doses of estradiol (E2; 1 or 4 microg/(kgday) BW). In parallel we investigated generalized hepatic effects of GEN in this co-stimulatory protocol. In agreement to our previous results, GEN treatment of OVX animals for 3 days results in a faint stimulation of the uterine wet weight. In intact animals and in OVX animals co-treated with E2 no effects of GEN on uterine wet weight were detectable. GEN treatment did not affect the uterine epithelial height in intact animals but resulted in a decrease of the protein and mRNA expression of the proliferation marker PCNA. In OVX animals co-treated with E2, GEN antagonized the E2 stimulated increase of the uterine epithelial height and epithelial PCNA expression. Besides PCNA, GEN effects on the uterine mRNA expression of IGF-1, IGF-1R, Complement C3, estrogen receptor-alpha (ERalpha) and -beta (ERbeta), as well as progesterone receptor were investigated in intact and OVX co-treated animals. Overall there was a tendency in all combinatorial groups that GEN counteracts E2 function in uterine tissue. Surprisingly, while investigating estrogenic response markers in liver, we observed very strong effects of GEN on hepatic marker gene expression. GEN significantly down-regulated CaBP9K and IGFBP1 mRNA levels in intact animals. In OVX animals hepatic CABP9K and IGFBP1 mRNA levels were not affected by E2 treatment. GEN treatment, even in combination with E2, decreased the hepatic CaBP9K expression below the levels observed in untreated animals. Interestingly co-treatment of OVX rats with low dose E2 and GEN resulted in a significant increase of IGFBP1 mRNA expression. Summarising our results we conclude that (1) GEN treatment in the presence of E2 is safe regarding proliferative responses in the endometrium of adult animals; (2) the observation of differences of the GEN activity in intact and OVX/E2 substituted animals can be taken as a hint that GEN may interact mechanistically with progestins which has to be proven in detail in future investigations and (3) the detection of strong effects of the phytoestrogen GEN on hepatic gene expression may point to the need of future investigations to rule out the possibility of adverse responses in this organ.