Effect of renal impairment on the pharmacokinetics of a single oral dose of tibolone 2.5 mg in early postmenopausal women

Bioequivalence studies of tibolone in premenopausal women and effects on expression of the tibolone-metabolizing enzyme AKR1C (aldo-keto reductase) family caused by estradiol

This study aimed to investigate the bioequivalence of a test formulation of tibolone with the marketed reference formulation in 24 young healthy female volunteers. Tibolone is a synthetic steroid hormone for menopausal women. Volunteers were treated with the 2 formulations of tibolone (total dose of active ingredient 2.5 mg) according to a 2 x 2 crossover design with a 1-week washout period. Plasma concentrations of 3alpha- and 3beta-hydroxytibolone, which are major metabolites of tibolone, were assayed in timed samples over a 24-hour period with a validated gas chromatography/mass spectrometry (GC/MS) method that had a lower limit of quantification of 0.5 ng/mL. The reference and test formulations gave a mean 3alpha-hydroxytibolone C(max) of 5.0 and 5.2 ng/mL, respectively, and a mean 3beta-hydroxytibolone C(max) of 16.4 and 16.5 ng/mL, respectively. The mean AUC(t) of 3alpha-hydroxytibolone was 24.7 and 24.3 ng h/mL, whereas the mean AUC(t) of 3beta-hydroxytibolone was 57.6 and 54.8 ng h/mL for the test and reference formulations, respectively. The authors did not find significant differences in pharmacokinetic parameters between the 2 formulations, but metabolite formation was different from reports in postmenopausal women. The authors therefore measured the effects of estradiol on the expression of the tibolone-metabolizing enzymes, from the aldo-keto reductase (AKR1C) family, using HepG2 cell (human hepatoma cells) and MCF-7 cell (human breast cancer cells). Estradiol increased mRNA levels of AKR1C1, AKR1C2, and AKR1C3 and protein levels of total AKR1C in HepG2 cells. Estradiol selectively enhanced levels of AKR1C2 mRNA in MCF-7 cells. Thus, changes in the major metabolites of tibolone might result from changes in AKR1C family expression by patient estrogen status.

7α-Methyl-ethinyl estradiol is not a metabolite of tibolone but a chemical stress artifact

OBJECTIVE

This study was conducted to establish whether 7alpha-methyl-ethinyl estradiol (7alpha-MEE) in plasma from postmenopausal women treated with tibolone is a metabolite or an artifact.

DESIGN

Clinical samples with known levels of tibolone metabolites, plus plasma samples spiked with tibolone and metabolites, were analyzed for levels of 7alpha-MEE using liquid chromatography-mass spectometry (LC-MS/MS) with and without derivatization.

RESULTS

Approximately 20 to 40 pg/mL 7alpha-MEE was detected using LC-MS/MS with derivatization in plasma samples from postmenopausal women treated with tibolone. In plasma samples spiked with 200 ng/mL tibolone or Delta-tibolone, LC-MS/MS with derivatization revealed the generation of around 200 and 36 pg/mL 7alpha-MEE, respectively, whereas LC-MS/MS without derivatization showed no detectable chemical conversion of tibolone to 7alpha-MEE. Generation of 7alpha-MEE is increased by the "stress conditions" used in the derivatization procedure; simply drying the sample also shows this artifactual conversion. The major active and sulfated 3-hydroxy metabolites of tibolone are not converted to 7alpha-MEE. Without derivatization, and avoiding stress conditions, no detectable levels (<20 pg/mL) of 7alpha-MEE were found in plasma samples from postmenopausal women treated with single (eight participants at 13 time points) or multiple (seven participants at 18 time points) doses of tibolone.

CONCLUSIONS

7alpha-MEE is not a metabolite of tibolone but is a chemical artifact generated during analytical procedures with derivatization. Using LC-MS/MS without derivatization, 7alpha-MEE cannot be demonstrated in plasma from postmenopausal women after single or multiple doses of tibolone.

Pharmacokinetic Parameters of Tibolone and Metabolites in Plasma, Urine, Feces, and Bile from Ovariectomized Cynomolgus Monkeys after a Single Dose or Multiple Doses of Tibolone

Levels of nonsulfated and sulfated tibolone metabolites were determined in plasma, urine, and feces from six ovariectomized, mature female cynomolgus monkeys after a single dose and multiple p.o. doses (including bile) of tibolone using validated gas chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry assays. In plasma, the predominant nonsulfated metabolite after single and multiple dosing was the estrogenic 3alpha-hydroxytibolone; levels of the estrogenic 3beta-hydroxytibolone were 10-fold lower and of progestagenic/androgenic Delta(4)-tibolone, 5-fold lower. Tibolone was undetectable. The predominant sulfated metabolite was 3alphaS,17betaS-tibolone; levels of 3betaS,17betaS-tibolone were about 2-fold lower, and monosulfated 3-hydroxymetabolites were about 10-fold lower. After multiple doses, areas under the curve of nonsulfated metabolites were lower (2-fold), and those of sulfated metabolites were 25% higher. In plasma, >95% metabolites were disulfated. In urine, levels of all the metabolites after single and multiple doses were low. After a single dose, high levels of 3beta-hydroxytibolone and the 3-monosulfated metabolites (3betaS,17betaOH-tibolone and 3alphaS,17betaOH-tibolone) were found in feces. After multiple dosing, 3alpha-hydroxytibolone increased, and the ratio of 3alpha/3beta-hydroxytibolone became about 1. The predominant sulfated metabolite was 3alphaS,17betaS-tibolone. Levels of all the metabolites in feces were higher after multiple doses than after a single dose. Levels of nonsulfated and 3-monosulfated metabolites were higher in feces than in plasma. Bile contained very high metabolite levels, except monosulfates. This may contribute to the metabolite content of the feces after multiple doses. 3beta-Hydroxytibolone and 3alphaS,17betaS-tibolone predominated. In conclusion, tibolone had different metabolite patterns in plasma, urine, feces, and bile in monkeys. The bile contributed to the metabolite pattern in feces after multiple doses. The major excretion route was in feces.

Pharmacokinetic Parameters of Sulfated Tibolone Metabolites in Postmenopausal Women after Single and Multiple Doses of Tibolone

The objective of this study was to determine pharmacokinetic parameters of sulfated tibolone metabolites after single dose and their accumulation after multiple doses of tibolone. Blood samples from postmenopausal women in a single-dose (2.5 mg tibolone), open-label study (n=8) and multiple-dose (placebo, 0.3, 0.625, 1.25, or 2.5 mg/day tibolone for twenty-six cycles of 28 days), randomized, double-blind study (n=15) were analyzed for non-sulfated and sulfated tibolone metabolites by validated gas chromatography-mass spectrometry (GC-MS) and liquid chromatography with tanolam mass spectrometry (LC-MS/MS), respectively. The predominant non-sulfated and sulfated metabolites after a single dose were 3alpha-hydroxy-tibolone and 3alpha,17beta-di-sulfated (di-S)-tibolone. At 3 h, >90% of metabolites were sulfated. Tibolone and Delta(4)-tibolone were detectable for about 6 h. After multiple treatment cycles with different doses, metabolite levels at 10 h were dose-related and levels of di-S metabolites were three- to fivefold higher than after a single dose. Tibolone metabolite levels did not differ between cycles. Inactive di-S tibolone metabolites predominated in blood. No accumulation occurred between cycles 7 and 26.

Metabolism of exogenous sex steroids and effect on brain functions with a focus on tibolone

Around the menopause, changes in ovarian secretion of steroids result in changes in brain function: hot flushes and sweating later followed by changes in mood, libido and cognition. The relationship between sex steroids and brain functions are reviewed, with focus on hormonal treatments, in particular tibolone, on the postmenopausal brain and on associations between tissue levels and brain functions. Data on steroid levels in human brain are limited. Exogenous oestrogens alone or combined with progestagens reduce hot flushes and sweating, and may favourably affect anxiety, depression and mood. Testosterone alone or combined with E(2) improves libido and mood. Tibolone reduces hot flushes and sweating, and improves mood and libido, but does not stimulate endometrium or breast, like oestrogens. Tibolone is an ideal compound for studying steroid levels and metabolism in brain in view of its structural differences from endogenous steroids and its extensive metabolism required to express its endocrine effects. Brain levels of tibolone metabolites were measured in ovariectomized cynomolgus monkeys receiving tibolone for 36 days. Compared to serum, higher levels of the oestrogenic 3alpha/beta-hydroxytibolone and the androgenic/progestagenic Delta(4)-tibolone, and lower levels of sulphated metabolites are found in various brain regions. The high levels of oestrogenic metabolites in the hypothalamus explain hot flush reduction. Combined with the presence of Delta(4)-tibolone, the tibolone-induced increase in free testosterone through SHBG reduction explains androgenic effects of tibolone on mood and libido. The levels of tibolone metabolites in the monkey brain support tibolone's effects on brain functions.

Effect of tibolone on markers of cardiovascular disease risk in postmenopausal women undergoing hemodialysis: a pilot study

OBJECTIVE

To assess the effect of tibolone on markers of vascular risk in postmenopausal women who were receiving hemodialysis.

DESIGN

One-year open-label study.

SETTING

"Zvezdara" University Medical Center, Belgrade, Serbia.

PATIENT(S)

Twenty-eight postmenopausal women undergoing chronic hemodialysis.

INTERVENTION(S)

Fifteen women received tibolone 2.5 mg three times per week; 13 other women served as controls.

MAIN OUTCOME MEASURE(S)

Mean arterial pressure and weight were measured at baseline and at 6 and 12 months, and blood was collected for insulin, total cholesterol, low-density lipoprotein, high-density lipoprotein, triglycerides, lipoprotein(a), high-sensitivity C-reactive protein (hs-CRP), endothelin-1 (ET-1), vascular endothelial growth factor (VEGF), and markers of renal function.

RESULT(S)

Mean arterial pressure fell in the tibolone but not in the control group at 6 and 12 months versus baseline (mean [SD]: 93 [15] vs. 105 [11] mmHg and 94 [10] vs. 105 [11] mmHg, respectively). Weight, insulin, lipids, lipoprotein(a), hs-CRP, ET-1, VEGF, and renal function remained unchanged within each group, but high-density lipoprotein concentrations fell in the tibolone group after 12 months (1.2 [0.3] vs. 1.6 [0.6] mmol/L).

CONCLUSION(S)

The effects of tibolone on markers of vascular risk in postmenopausal women who are receiving hemodialysis and healthy women appear to differ. This should be taken into account when tailoring menopausal therapies to the specific requirements of each individual.

Postmenopausal osteoporosis in the dialysis patient

PURPOSE OF REVIEW

Osteoporosis is the most prevalent bone disorder in the general population, particularly in the middle and older age groups. Although more than half of the prevalent dialysis population is within these age groups, little concern has been given to the possible role of estrogen deficiency in the pathogenesis of bone disease in end-stage renal disease. The purpose of this review is to summarize the recent published evidence that supports a potential role of the postmenopausal state in the pathogenesis of bone disease in end-stage renal disease and their implications for treatment.

RECENT FINDINGS

Recent studies have shown that although the risk factors for fracture in end-stage renal disease are similar to the general population, the incidence is three to fourfold higher. The high prevalence of older population, the frequently observed premature amenorrhea and early menopause in dialysis patients may play a role. Similarly, the proportion of end-stage renal disease women receiving hormone replacement therapy is at least three times lower than the general population. Recent evidence on the risk of hormone replacement therapy should caution about its use in end-stage renal disease patients. New evidence suggests that selective estrogen receptor modulators may increase bone mass without significant secondary effects. Other alternatives, such as the use of bisphosphonates, should be considered with caution due to the risk of excessive suppression of bone turnover, worsening or favoring the development of adynamic bone disease.

SUMMARY

Osteoporosis should be recognized as an important entity that may modify the current conception of renal osteodystrophy in postmenopausal patients with end-stage renal disease. Further clinical studies are needed in order to propose strategies that may reduce the impact of postmenopausal osteoporosis in the dialysis population.