16-alpha-ethyl-21-hydroxy-19-nor-4-pregnene-3-20-dione and tibolone

In human endometrium, cell proliferation is regulated by ovarian steroids through heterotypic interactions between stromal and epithelial cells populating this tissue. The authors test the proliferative effects of tibolone and its metabolites using endometrial co-cultures that mimic the normal proliferative response to hormones. They found that both the Delta(4)-tibolone metabolite and the pure progestin ORG2058 counteract estradiol-driven epithelial cell proliferation. Surprisingly, the estrogen receptor binding 3-hydroxyl-metabolites of tibolone also counteracted estradiol-driven proliferation. Inhibition of proliferation by 3beta-OH-tibolone was abrogated by low doses of the progesterone receptor antagonist mifepristone. This suggests that 3beta-OH-tibolone is converted to a progestagenic metabolite. The authors found that the stromal cells used in the co-cultures express high levels of the ketosteroid dehydrogenase AKR1C2, which is able to oxidize 3beta-OH-tibolone back to tibolone. Thus, the unexpected progestagenic effect of 3beta-OH-tibolone in these co-cultures may be due to metabolic activity present in the stromal cells of the co-cultures.

Topics: 20-Hydroxysteroid Dehydrogenases; Cell Division; Cell Line; Coculture Techniques; Endometrium; Epithelial Cells; Estradiol; Estrogen Receptor Modulators; Female; Humans; Norpregnenes; Pregnenediones; Reverse Transcriptase Polymerase Chain Reaction; Stromal Cells

In this study, we assessed the effects of tibolone and its metabolites on the production of a progesterone sensitive parameter, prolactin, in human endometrium stroma cells in vitro. In addition, the metabolism of the compounds by isolated stromal and epithelial cells was evaluated. The reference compounds, progesterone, Org 2058, and DHT all induced prolactin production. Oestradiol also slightly induced prolactin production and enhanced the response to Org 2058. Tibolone and Delta4-tibolone were similar with regard to potency to induce prolactin levels in the culture supernatant. Their potency was lower than that of Org 2058, similar to that of progesterone and higher than that of DHT. The efficacies of tibolone, Delta4-tibolone and Org 2058 were similar (approximately 200-fold induction). The estrogenic tibolone metabolites 3alpha- and 3beta-OH tibolone also significantly stimulated prolactin production. Their potency, however, was low since significance was reached only at the highest concentrations tested. The PR antagonist Org 31710 inhibited both tibolone- and Delta4-tibolone-induced prolactin production. The responses of tibolone and Delta4-tibolone were not affected by co-incubation with the androgen receptor antagonist OH-flutamide. The effect of tibolone, but not Delta4-tibolone, was antagonized approximately 50% in combination with the highest dose (1 microM) estrogen receptor antagonist, ICI 164384. The induction of prolactin by 3alpha- and 3beta-OH tibolone was antagonized most potently by Org 31710, but also by ICI 164384 and OH-flutamide. Tibolone is metabolized differently in epithelial and stromal cells of the human endometrium. The epithelial cells mostly produce the progestagenic/androgenic Delta4-tibolone. The stromal cells produce predominantly the 3beta-OH tibolone, and some Delta4-tibolone, but the net effect observed with regard to prolactin production is progestagenic. When the metabolites 3alpha-OH, 3beta-OH, and Delta4-tibolone were added to the cultures no conversions were observed. The HPLC analyses showed no evidence for the production of sulfated metabolites. In conclusion, the net effects on endometrial stromal cells are predominantly progestagenic. Tibolone is converted by epithelial cells into Delta4-tibolone which displays progestagenic and androgenic activities, whereas in stromal cells also the estrogenic metabolites 3alpha- and 3beta-OH tibolone are formed.

Topics: Cells, Cultured; Dihydrotestosterone; Dose-Response Relationship, Drug; Endometrium; Epithelial Cells; Estrogen Receptor Modulators; Female; Humans; Norpregnenes; Pregnenediones; Progesterone; Prolactin; Stromal Cells

Nitric oxide (NO) is a mediator of bone metabolism and its production is under the control of gender hormones in several cell types or tissues. Changes in endogenous NO production, measured as plasma nitrate+nitrite levels, may therefore contribute to ovariectomy (OVX)-induced bone loss. We studied plasma nitrate+nitrite levels and trabecular bone mineral density (TBMD) 4 weeks after sham-operation or OVX in rats receiving various hormonal treatments. OVX decreased plasma nitrate+nitrite levels significantly and this was accompanied by a significant decrease in TBMD. Treatment with oral ethinyl oestradiol (EE) and subcutaneous 17beta-oestradiol dose-dependently prevented the decrease in plasma nitrate+nitrite levels after OVX, but treatment with oral 17beta-oestradiol did not. Oestrogen treatment, 17beta-oestradiol (s. c. or orally) or EE (orally), prevented the OVX-induced decrease in TBMD. Treatment of sham-operated rats with the anti-oestrogen ICI164, 384 induced a significant decrease in TBMD that corresponded to 54% of the decrease observed after OVX, but did not affect plasma nitrate+nitrite levels. Treatment of ovariectomized rats with Org 2058, a pure progestagen, did not prevent bone loss, but prevented the decrease in plasma nitrate+nitrite levels dose-dependently. Treatment with tibolone, a synthetic steroid with combined weak oestrogenic, progestagenic, and androgenic properties, or with progestagen in combination with EE completely prevented bone loss after OVX. These treatments, however, only partly prevented the OVX-induced decrease in plasma nitrate+nitrite levels. In conclusion, OVX decreased both TBMD and plasma nitrate+nitrite levels. Although plasma nitrate+nitrite levels were under the control of both oestrogen and progesterone, TBMD was affected by oestrogen only. Decreased systemic production of NO is, therefore, not involved in OVX-induced bone loss in rats.

Topics: Anabolic Agents; Animals; Bone Density; Dose-Response Relationship, Drug; Estradiol; Estrogen Antagonists; Ethinyl Estradiol; Female; Gonadal Steroid Hormones; Nitrates; Nitrites; Norpregnenes; Ovariectomy; Polyunsaturated Alkamides; Pregnenediones; Progesterone Congeners; Rats; Rats, Wistar