PubMed Health⌕ Search

Biomedical subjects

Helenius J Kloosterboer

Publications and source records attributed to Helenius J Kloosterboer.

16 recordsLinked to original sources
PubMed2006

Progestagenic effects of tibolone are target gene-specific in human endometrial cells.

OBJECTIVES: Tibolone (Tib) exhibits progestagenic activities in addition to its tissue-specific estrogenic activities. The purpose of the current study was to determine the progestagenic actions of Tib and its metabolites using target genes known to be regulated by progestins in human endometrial glandular and stromal cells. METHODS: Human endometrial glandular and stromal cells were isolated from endometrial tissue fragments and separately incubated with Tib and its metabolites. Real-time polymerase chain reaction (PCR) was used to determine the mRNA content of 17betahydroxy steroid dehydrogenase (17betaHSD, type 2) and sulfotransferase (SULT1E1) in endometrial glandular cells, and prolactin (PRL) and insulin-like growth factor binding protein-1 (IGFBP1) in endometrial stromal cells. RESULTS: In glandular cells, Tib and Delta4-tibolone (Delta4Tib) significantly increased the content of 17betaHSD and SULT1E1 mRNA. In stromal cells, Tib and Delta4Tib increased PRL mRNA ( approximately 30% of the capacity compared to progesterone) and had little effect on IGFBP1 mRNA. Anti-progestin, RU486, reversed the induction of SULT1E1 and PRL by progesterone or Tib. Also, the two 3 hydroxyl tobolone metabolites, especially 3betaOHTib, showed some progestagenic effects. CONCLUSIONS: The data showed that Tib and Delta4Tib exhibited clear progestagenic effects in endometrial glandular cells by inducing 17betaHSD and SULT1E1, while in stromal cells the response was weaker in the induction of PRL and had little effect on IGFBP1. In addition, the 3betaOHTib metabolite expressed progestagenic activity. These disparate effects in two types of cells may be beneficial for maintaining endometrial cells in a quiescent state.

17-Hydroxysteroid Dehydrogenases↗
PubMed2006

Histological and immunohistochemical evaluation of postmenopausal endometrium after 3 weeks of treatment with tibolone, estrogen only, or estrogen plus progestagen.

OBJECTIVE: To evaluate histological and immunohistochemical parameters of short-term (21 days) tibolone, estrogen-only, and estrogen+progestagen treatment in the human postmenopausal endometrium. DESIGN: An observational, open, nonrandomized, controlled study. SETTING: Three collaborating centers: Amphia Hospital in Breda, Albert Schweitzer Hospital in Dordrecht, Erasmus Medical Center in Rotterdam, the Netherlands. PATIENT(S): Thirty healthy, postmenopausal women. INTERVENTION(S): Control group (n = 9), no hormonal treatment; tibolone group (n = 8), patients were treated with 2.5 mg of tibolone (administered orally) every day, starting 21 days before surgery; estrogen group (n = 7), patients were treated with 2 mg of E(2) (Zumenon, administered orally; Zambon, Amerfoort; The Netherlands) every day, starting 21 days before surgery; estrogen+progestagen group (n = 6), patients were treated with 2 mg of E(2) (Zumenon, administered orally) and 5 mg of medroxyprogesterone acetate (administered orally) every day, starting 21 days before surgery. MAIN OUTCOME MEASURE(S): Uterine tissues were collected, and two pathologists independently assessed histology. Immunohistochemical parameters measured were estrogen receptor alpha, progesterone receptor A/B, Hoxa10, Ki67, and Bcl-2. RESULT(S): On the basis of a number of histological and immunohistochemical parameters measured after 21 days of treatment, it was observed that tibolone displays clearly less stimulation (proliferation) of the human postmenopausal endometrium than estrogen at the beginning of a treatment, but the stimulation is higher than with estrogen+progestagen. CONCLUSION(S): Short-term (21 days) tibolone treatment results in a small stimulation of proliferation of the endometrium, and because long-term treatment with tibolone has been demonstrated to lead to an atrophic endometrium, it may be concluded that the stimulatory effect, as observed in this study, is transient in nature. It is hypothesized that tibolone first displays a more estrogenic mode of action, which over time, is counterbalanced by the induction of its progestagenic properties.

Aged↗
PubMed2006

Effects of tibolone on nuclear receptors in human endometrial cells.

OBJECTIVE: 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. STUDY DESIGN: 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). RESULTS: 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. CONCLUSION: 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.

Blotting, Western↗
PubMed2005

Tibolone metabolism in human liver is catalyzed by 3alpha/3beta-hydroxysteroid dehydrogenase activities of the four isoforms of the aldo-keto reductase (AKR)1C subfamily.

Tibolone [[7alpha,17alpha]-17-hydroxy-7-methyl-19-norpregn-5(10)-en-20-yn-3-one] is used to treat climacteric symptoms and prevent osteoporosis. It exerts tissue-selective effects via site-specific metabolism into 3alpha- and 3beta-hydroxymetabolites and a Delta4-isomer. Recombinant human cytosolic aldo-keto reductases 1C1 and 1C2 (AKR1C1 and AKR1C2) produce 3beta-hydroxytibolone, and the liver-specific AKR1C4 produces predominantly 3alpha-hydroxytibolone. These observations may account for the appearance of 3beta-hydroxytibolone in target tissues and 3alpha-hydroxytibolone in the circulation. Using liver autopsy samples (which express AKR1C1-AKR1C4), tibolone was reduced via 3alpha- and 3beta-hydroxysteroid dehydrogenase (HSD) activity. 3beta-Hydroxytibolone was exclusively formed in the cytosol and was inhibited by the AKR1C2-specific inhibitor 5beta-cholanic acid-3alpha, 7alpha-diol. The cytosolic formation of 3alpha-hydroxytibolone was inhibited by an AKR1C4-selective inhibitor, phenolphthalein. The ratio of these stereoisomers was 4:1 in favor of 3beta-hydroxytibolone. In HepG2 cell cytosol and intact cells (which do not express AKR1C4), tibolone was exclusively reduced to 3beta-hydroxytibolone and was blocked by the AKR1C1-AKR1C3 inhibitor flufenamic acid. In primary hepatocytes (which express AKR1C1-AKR1C4), time-dependent reduction of tibolone into 3beta- and 3alpha-hydroxytibolone was observed again in a 4:1 ratio. 3beta-HSD activity was inhibited by both 5beta-cholanic acid-3alpha,7alpha-diol and flufenamic acid, implicating a role for AKR1C2 and AKR1C1. By contrast, the formation of 3alpha-hydroxytibolone was exclusively inhibited by phenolphthalein implicating AKR1C4 in this reaction. 3beta- and 3alpha-Hydroxytibolone were rapidly metabolized into polar metabolites (>85%). The formation of minor amounts of tibolone was also observed followed by AKR1C-catalyzed epimerization. The low hepatic formation of 3alpha-hydroxytibolone suggests that AKR1C4 is not the primary source of this metabolite and instead it maybe formed by an intestinal or enterobacterial 3alpha-HSD.

17-Hydroxysteroid Dehydrogenases↗
PubMed2005

Tibolone and its metabolites enhance tissue factor and PAI-1 expression in human endometrial stromal cells: Evidence of progestogenic effects.

Tibolone is a highly effective postmenopausal hormone treatment that has its biological activity dependent on metabolism to 3alpha- and 3beta-OH tibolone, which bind solely to the estrogen receptor. Despite the high levels of estrogen receptor-binding metabolites in the circulation, the endometrium becomes atrophic, suggesting inactivation of the estrogen response in this tissue which may be due to the progestogenic activity of tibolone and the Delta-4 tibolone metabolite. We evaluated the effects of tibolone and its metabolites on tissue factor (TF) and plasminogen activator inhibitor type 1 (PAI-1) expression in human endometrial stromal cells (HESCs). Since TF and PAI-1 exhibit long-term in vivo and in vitro up-regulation by progestin they serve as endpoints for assessing chronic effects of progestin exposure. Confluent HESCs were primed in serum-containing medium with vehicle control, 10(-8)mol/L estradiol, 10(-7)mol/L medroxyprogesterone acetate, or 10(-8) to 10(-6)mol/L tibolone or its metabolites, then switched to a defined medium with corresponding vehicle or steroids. After 24h, ELISAs indicated that the progestin elevated TF (6.2-fold +/-3.0; p<0.05) and PAI-1 (eight-fold +/-2.1; p<0.05) levels, whereas the cells were refractory to estradiol exposure. Tibolone and Delta-4 tibolone (10(-8) to 10(-6)mol/L) were as effective as 10(-7)mol/L medroxyprogesterone acetate in enhancing TF and PAI-1 output (p<0.05). Unexpectedly, at the higher concentrations 3alpha- and 3beta-OH tibolone also elevated TF and PAI-1 expression (p<0.05). Western blotting confirmed the ELISA results. Our findings suggest that HESCs metabolize 3alpha- and 3beta-OH tibolone to tibolone and subsequently to Delta-4 tibolone, which can both stimulate the progesterone receptor. Since TF and PAI-1 promote hemostasis by complementary mechanisms, our findings account for the reduced occurrence of abnormal uterine bleeding associated with tibolone therapy.

Androgen Antagonists↗
PubMed2004

Tibolone is metabolized by the 3alpha/3beta-hydroxysteroid dehydrogenase activities of the four human isozymes of the aldo-keto reductase 1C subfamily: inversion of stereospecificity with a delta5(10)-3-ketosteroid.

Tibolone is used to treat climacteric complaints and prevent osteoporosis. These beneficial effects are exerted via its 3alpha-and 3beta-hydroxymetabolites. Undesirable stimulation of the breast and endometrium is not apparent. Endometrial stimulation is prevented by the progestogenic activity of its Delta4-ene metabolite. The enzymes responsible for the formation of these active metabolites are unknown. Human aldo-keto reductase (AKR)1C isoforms have been shown to act as 3alpha/3beta-hydroxysteroid dehydrogenases (HSDs) on 5alpha-dihydrotestosterone (5alpha-DHT). We show that AKR1Cs also efficiently catalyze the reduction of the Delta(5(10))-3-ketosteroid tibolone to yield 3alpha- and 3beta-hydroxytibolone. Homogeneous recombinant AKR1C1, AKR1C3, and AKR1C4 gave similar catalytic profiles to those observed with 5alpha-DHT. AKR1C1 catalyzed exclusively the formation of 3beta-hydroxytibolone, AKR1C3 showed weak 3beta/3alpha-HSD activity, and AKR1C4 acted predominantly as a 3alpha-HSD. Whereas AKR1C2 acted as a 3alpha-HSD toward 5alpha-DHT, it functioned exclusively as a 3beta-HSD on tibolone. Furthermore, strong substrate inhibition was observed for the AKR1C2 catalyzed reduction of tibolone. Using NAD+, the 3-hydroxymetabolites were efficiently oxidized by homogeneous recombinant AKR1C2 and AKR1C4. However, because of potent inhibition of this activity by NADPH, AKR1Cs will probably act only as 3-ketosteroid reductases in vivo. Molecular docking simulations using crystal structures of AKR1C1 and AKR1C2 explained why AKR1C2 inverted its stereospecificity from a 3alpha-HSD with 5alpha-DHT to a 3beta-HSD with tibolone. The preference for AKR1C1 and AKR1C2 to form 3beta-hydroxytibolone, and the preference of the liver-specific AKR1C4 to form 3alpha-hydroxytibolone, may explain why 3beta-hydroxytibolone is the major metabolite in human target tissues and why 3alpha-hydroxytibolone is the major circulating metabolite.

20-Hydroxysteroid Dehydrogenases↗
PubMed2004

Tissue-selectivity: the mechanism of action of tibolone.

Tibolone is effective in preventing bone loss and treating climacteric symptoms, without stimulating the endometrium. The effects on bone, brain and vagina can be accurately explained by the oestrogenic activity of tibolone, but oestrogenic activity is not expressed in the endometrium. Tibolone behaves differently from oestrogen plus progestogen combinations on the breast. Therefore, tibolone can be characterised as a selective oestrogen activity regulator. The objective of this review is to characterise the typical properties of tibolone in order to explain its tissue-selective action. Tibolone is rapidly converted into three major metabolites: 3 alpha- and 3 beta-hydroxy-tibolone, which have oestrogenic effects, and the Delta(4)-isomer, which has progestogenic and androgenic effects. The 3-hydroxy metabolites are present in the circulation, predominantly in their inactive sulphated form. The tissue-selective effects of tibolone are the result of metabolism, enzyme regulation and receptor activation that vary in different tissues. The bone preserving effects are the result of oestradiol receptor activation, whilst other steroid receptors, notably the progesterone and androgen receptor, are not involved. Breast tissue of monkeys is not stimulated, as occurs with oestrogen plus progestogen, because tibolone and its metabolites inhibit sulphatase and 17 beta-hydroxysteroid dehydrogenase (HSD) type I and stimulate sulphotransferase and 17 beta-HSD type II, the combined effects of which prevent conversion to active oestrogens. In addition, tibolone affects cellular homeostasis in the breast by inhibiting proliferation and stimulating apoptosis. Tibolone does not stimulate the endometrium because of the action of the highly stable progestogenic metabolite (Delta(4)-isomer) in combination with an effect on the sulphatase (inhibition)-sulphotransferase (stimulation) system. The oestrogenic metabolites of tibolone have direct favourable effects on the cardiovascular system and, in in vivo models, tibolone has shown no adverse consequences. In conclusion, tibolone shows oestrogenic effects in brain, vagina and bone and has direct oestrogenic effects on the cardiovascular system. In the endometrium, the progestogenic activity of the Delta(4)-metabolite and the effect on oestrogen-inactivating enzymes prevent oestrogenic stimulation. The mammary gland is not stimulated in currently used animal models. Tibolone appears to regulate estrogenic activity in the various tissues by influencing the availability of estrogenic compounds for the estradiol receptor in a tissue-selective manner.

Animals↗
PubMed2004

Tibolone and its metabolites induce antimitogenesis in human coronary artery smooth muscle cells: role of estrogen, progesterone, and androgen receptors.

Tibolone, a hormone replacement drug, protects postmenopausal women against osteoporosis and climacteric symptoms without inducing adverse effects on the endometrium and breast. Compared with other estrogens, little is known about the cardiovascular effects of tibolone. Because abnormal growth of smooth muscle cells (SMCs) is a prerequisite for coronary artery disease, here we investigated the effects of tibolone on SMC growth. We examined the effects of tibolone and its metabolites on human arterial SMC growth (DNA synthesis, cellular proliferation, cell migration, collagen synthesis) and MAPK expression. Fetal calf serum-induced SMC growth, phosphorylated MAPK expression, and platelet-derived growth factor-induced SMC-migration were concentration-dependently inhibited by tibolone and its endogenous estrogenic and progestogenic/androgenic metabolites in the following order of potency: Delta 4-tibolone>3 beta-OH-tibolone congruent with 3 alpha-OH-tibolone. The antimitogenic effects of tibolone were partially blocked by ER antagonist (ICI182780), progesterone receptor antagonist (RU486) but not by the androgen receptor antagonist (flutamide); moreover, RU486 was more potent than ICI182780. The antimitogenic effects of tibolone were completely blocked by RU486 plus ICI182780. In addition, the inhibitory effects of equimolar concentrations of the three tibolone metabolites summed up to the inhibitory effects of tibolone. In conclusion, tibolone inhibits SMC growth and MAPK phosphorylation via both its estrogenic and progestogenic metabolites, and these inhibitory effects involve both progesterone and ERs. Hence, tibolone may induce antivasoocclusive actions and protect women against coronary artery disease.

Arteries↗
PubMed2003

Oestradiol and mirtazapine restore the disturbed tail-temperature of oestrogen-deficient rats.

The purpose of the present study was to further evaluate the tail-temperature test as a tool to test potential steroidal and non-steroidal compounds for the treatment of hot flushes. Ovariectomized rats were implanted with a temperature sensitive probe. After a recovery period of 5 weeks, the effect of oestradiol (given via a silastic tube) and the 5-HT(2) receptor antagonist mirtazapine (10 mg/kg i.p.) on the tail-temperature in the active phase of the animals was measured. Oestradiol completely restored the disturbed tail temperature after 3 days. Treatment with mirtazapine also restored the oestrogen withdrawal-induced disturbed tail-temperature. The effect of mirtazapine was already seen on the first day of treatment. These experiments confirm and extend the idea that measuring the oestradiol withdrawal-induced disturbance of tail-temperature may be a useful tool to select compounds that might have beneficial effects in the treatment of hot flushes. Blockade of the 5-HT(2A) receptors prevented or reduced the ovariectomy-induced disturbance of the rat tail-temperature, which may validate this model to evaluate the effect of compounds on hot flushes.

Animals↗
PubMed2003

Receptor profiling and endocrine interactions of tibolone.

The receptor profiles and in vivo activity of tibolone, and its primary metabolites, Delta(4)-isomer, and 3alpha- and 3beta-hydroxytibolone, were studied and compared to those of structurally related compounds. The Delta(4)-isomer was the strongest binder and activator of the progesterone receptor (PR); tibolone was 10 times weaker in binding and half as potent in transactivation of PR; 3alpha- and 3beta-hydroxytibolone did not bind or activate PR. In rabbits oral tibolone produced a minor progestagenic effect in the endometrium, whereas co-administration of tibolone and the anti-estrogen ICI 164,384 unmasked tibolone's progestagenic effect. 3-Hydroxytibolones were the strongest binders and activators of the estrogen receptors (ERs), with greater affinity for ERalpha than for ERbeta. Tibolone showed weaker binding and activation of both ERs and the Delta(4)-isomer has a binding and activation activity of less than 0.1% of E2 for ERalpha or ERbeta. Tamoxifen and 4-hydroxytamoxifen showed partial ERalpha agonistic effects with a maximal response of 12% and raloxifene of 3-5%. Oral administration of 1mg tibolone to ovariectomized rats induced an estrogenic effect on vaginal epithelium. The Delta(4)-isomer was a stronger binder and activator of the androgen receptor (AR) than tibolone; both 3-hydroxytibolones did not bind or activate AR. Introducing a 7alpha-methyl group decreased progestagenic and increased androgenic activity. We conclude that the progestagenic and androgenic activities of tibolone are mediated by the Delta(4)-isomer, and the estrogenic activity, by the 3-hydroxytibolones. The estrogenic activity of the 3-hydroxytibolones masked the progestagenic activity of tibolone in rabbit endometrium. Full estrogenic response was observed in rat vaginal tissue after oral administration of tibolone.

Animals↗
PubMed2003

Tibolone is not converted by human aromatase to 7alpha-methyl-17alpha-ethynylestradiol (7alpha-MEE): analyses with sensitive bioassays for estrogens and androgens and with LC-MSMS.

To exclude that aromatization plays a role in the estrogenic activity of tibolone, we studied the effect tibolone and metabolites on the aromatization of androstenedione and the aromatization of tibolone and its metabolites to 7alpha-methyl-17alpha-ethynylestradiol (7alpha-MEE) by human recombinant aromatase. Testosterone (T), 17alpha-methyltestosterone (MT), 19-nortestosterone (Nan), 7alpha-methyl-19-nortestosterone (MENT) and norethisterone (NET) were used as reference compounds. Sensitive in vitro bioassays with steroid receptors were used to monitor the generation of product and the reduction of substrate. LC-MSMS without derivatization was used for structural confirmation. A 10 times excess of tibolone and its metabolites did not inhibit the conversion of androstenedione to estrone by human recombinant aromatase as determined by estradiol receptor assay whereas T, MT, Nan, and MENT inhibited the conversion for 75, 53, 85 and 67%, respectively. Tibolone, 3alpha- and 3beta-hydroxytibolone were not converted by human aromatase whereas the estrogenic activity formed with the Delta4-isomer suggests a conversion rate of 0.2% after 120 min incubation. In contrast T, MT, Nan, and MENT were completely converted to their A-ring aromates within 15 min while NET could not be aromatized. Aromatization of T, MT, Nan and MENT was confirmed with LC-MSMS. Structure/function analysis indicated that the 17alpha-ethynyl-group prevents aromatization of (19-nor)steroids while 7alpha-methyl substitution had no effect. Our results with the sensitive estradiol receptor assays show that in contrast to reference compounds tibolone and its metabolites are not aromatized.

Androgens↗
PubMed2002

In vitro studies of tibolone in breast cells.

OBJECTIVE: To investigate the effects of tibolone and its main metabolites on breast homeostasis. DESIGN: In vitro studies in primary cultures of normal breast cells and in breast cancer cell lines. SETTING: Hospital-based academic research center. PATIENT(S): Human breast cells were obtained from women undergoing surgery for hypermastia. Breast cancer cell lines (MCF-7, T47-D, and ZR75-1) were routinely obtained from subcultures. INTERVENTION(S): Cells were incubated with tibolone, its various metabolites, the pure pregnane Org 2058, and the androgen dihydrotestosterone. MAIN OUTCOME MEASURE(S): Proliferation was determined by using a morphometric growth index, apoptosis by using morphologic analysis and flow cytometry, and antiapoptotic proteins bcl-2 and bclx(L) by using Western blot assay. Activity of 17beta-hydroxysteroid dehydrogenase was measured as an epithelial differentiation marker. RESULT(S): Tibolone and its delta(4) isomer were antiproliferative in normal breast cells. Tibolone and its delta(4) isomer increased apoptosis in breast cells. These proapoptotic effects were at least partially mediated through decreased expression of the antiapoptotic proteins bcl-2 and bclx(L). An increase in HSD activity was observed after tibolone administration. CONCLUSION(S): Tibolone is antiproliferative and proapoptotic and induces differentiation in normal breast cells. It is also proapoptotic in breast cancer cell lines.

17-Hydroxysteroid Dehydrogenases↗
PubMedDate not supplied

Endothelium-dependent dilatory effects of 3alpha-OH-tibolone in gracilis muscle arterioles of the female Wistar rat.

OBJECTIVE: Tibolone is a synthetic steroid used for the treatment of the symptoms of menopause that, once metabolized, has estrogenic, progestogenic, and androgenic properties. We investigated the direct vasodilatory effects of the major active tibolone metabolite 3alpha-OH-tibolone and its sulfated form on female rat skeletal muscle arterioles, which play an important role in the control of blood pressure. DESIGN: In isolated, pressurized spontaneously constricted arterioles (mean passive diameter 83 +/- 3 microm), we investigated the vasodilatory effect of 3alpha-OH-tibolone and its sulfated form. To study the role of the endothelium and in particular that of nitric oxide, we repeated the experiments with 3alpha-OH-tibolone after removal of the endothelium and on vessels pretreated with the nitric oxide synthesis inhibitor, Nomega-nitro-L-arginine (L-Na). Finally we compared the vasodilatory effect of 3alpha-OH-tibolone with 17beta-estradiol. RESULTS: A dose-dependent dilatation to 3alpha-OH-tibolone was observed starting at a concentration of 10 M. With the sulfated form of 3alpha-OH-tibolone, dilatation was only present at the highest concentration (10 M). In the denuded vessels, the vasodilatory effect was absent at concentrations from 10 to 10 M. The dilatation induced by 3alpha-OH-tibolone was not significantly reduced by L-Na. The vasodilatory effect of 3alpha-OH-tibolone did not differ from that of 17beta-estradiol. CONCLUSIONS: 3alpha-OH-tibolone has a dose-dependent vasodilatory effect on isolated skeletal muscle arterioles from the rat. The sulfated form has no vasodilatory effect in this setup. This finding suggests that during this short incubation time there was no conversion of the sulfated metabolite into its active form by the vascular endothelium. The vasodilatory effect of 3alpha-OH-tibolone is endothelium dependent at physiologic concentrations and comparable to that of 17beta-estradiol.

Animals↗
PubMedDate not supplied

Effect of tibolone administration on central and peripheral levels of allopregnanolone and beta-endorphin in female rats.

OBJECTIVE: We evaluated the effects of tibolone oral administration on neuroendocrine function by investigating the modulation exerted by tibolone administration on allopregnanolone and central and peripheral beta-endorphin (beta-EP) levels in ovariectomized rats. DESIGN: Female Wistar rats (N = 64) were included: 48 rats were ovariectomized, 8 cycling rats were included as controls, and 8 cycling rats were treated with placebo. The ovariectomized animals were divided into six groups: untreated rats and those that received 14-day oral treatment with either placebo, estradiol valerate (E2V) 0.05 mg/kg/d, or tibolone (0.1, 0.5, or 2 mg/kg/d. beta-EP levels were assessed in the frontal lobe, parietal lobe, hippocampus, hypothalamus, anterior pituitary, neurointermediate pituitary, and plasma, whereas allopregnanolone levels were measured in the frontal lobe, parietal lobe, hippocampus, hypothalamus, anterior pituitary, adrenal glands, and serum. RESULTS: The administration of tibolone (0.5 and 2 mg/kg/d) in ovariectomized rats induces a significant increase of allopregnanolone in the frontal lobe, parietal lobe, hippocampus, hypothalamus, whereas in serum a significant increase of allopregnanolone occurs only with the dose of 2 mg/kg/d, a significant decrease in allopregnanolone levels occurs in the adrenal glands. No changes occurred in the anterior pituitary. Tibolone doses of 0.5 and 2 mg/kg/d induced a significant increase in beta-EP content in the frontal lobe, hypothalamus, and neurointermediate lobe; and, at doses of 2 mg/kg/d, in the parietal lobe, anterior pituitary, and plasma, without changes in the hippocampus. Compared with E2V, 0.5 mg/kg/d tibolone showed a similar effect on allopregnanolone and beta-EP in most brain regions. CONCLUSIONS: Tibolone administration affects beta-EP and allopregnanolone levels, playing a role as a neuroendocrine modulator.

Adrenal Glands↗
PubMedDate not supplied

Conversion of tibolone to 7alpha-methyl-ethinyl estradiol using gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry: interpretation and clinical implications.

OBJECTIVE: Tibolone, a hormone therapy drug, is used to treat climacteric symptoms. This drug is rapidly metabolized into three major metabolites (3alpha-hydroxytibolone, 3beta-hydroxytibolone, and Delta4-tibolone). One clinical study provided evidence of conversion of tibolone to another estrogenic metabolite, 7alpha-methyl-ethinyl estradiol (MEE). However, no evidence of MEE formation was found in another study using the human aromatase enzyme. Because MEE was analyzed by gas chromatography-mass spectrometry (GC-MS), which requires derivatization, together with the fact that derivatization of some steroids may lead to aromatization, it is feasible that the MEE detected resulted from an artifact generated during the derivatization process. Hence, our objective was to assess whether tibolone is converted to MEE. DESIGN: We assayed MEE formation in a nonbiological system using GC-MS after derivatization and by analyzing MEE formation using liquid chromatography-mass spectrometry (LC-MS) in nonderivatized samples. RESULTS: MEE formation was evident in tibolone samples derivatized with either pentafluoropropionic anhydride or trimethylsilyl and analyzed by GC-MS. The amount of MEE formed increased with increasing amounts of tibolone (0.5, 1, 2.5, and 5 microg) derivatized; however, relative to tibolone, the percentage of MEE formed remained constant and ranged between 0.22% and 0.29% of tibolone. In contrast to GC-MS, no MEE formation was seen when tibolone was analyzed by liquid chromatography-mass spectrometry without derivatization. CONCLUSIONS: Our findings prove that conversion of tibolone to MEE is an artifact that is generated in a GC-MS system and is largely due to the intense heating step involved in GC-MS. Caution should be exercised to extrapolate clinical implications from existing data on MEE formation using a GC-MS system.

Chromatography, Liquid↗