Effects of tibolone on nuclear receptors in human endometrial cells.

Abstract

Tibolone regulates estrogenic activity in a tissue-selective manner. The purpose of this study was to evaluate the effects of tibolone on the mRNA content of nuclear receptors, estrogen receptor-alpha and beta (ERalpha and ERbeta), progesterone receptor (PR), and androgen receptor (AR) in human endometrial stromal and glandular cells. Human endometrial stromal and glandular cells were isolated from endometrial tissue fragments and separately incubated with tibolone and its metabolites. Nuclear receptor mRNA was determined using real-time polymerase chain reaction (PCR). In endometrial stromal cells, tibolone, Delta4-tibolone, and 3betaOH-tibolone, but not 3alphaOH-tibolone, significantly reduced ERalpha mRNA by approximately 60% and ERalpha protein by approximately 80%. No reduction of ERalpha was observed in endometrial glandular cells. Tibolone induced PR mRNAs to various extents and reached up to 6-fold in glandular cells, but only a moderate increase (approximately 1.5-fold) in stromal cells. Tibolone increased ERbeta and had little effect on AR mRNA in endometrial cells. The results showed the majority of the nuclear receptors were not significantly altered. However, tibolone significantly reduced ERalpha in stromal cells and increased PR in glandular cells. These biological effects may play essential roles in averting stimulation of the endometrium in tibolone users.