Resistance of pelvic arteries and plasma lipids in postmenopausal women: comparative study of tibolone and continuous combined estradiol and norethindrone acetate replacement therapy

Lipoprotein(a) in postmenopausal women: assessment of cardiovascular risk and therapeutic options

INTRODUCTION

Lipoprotein(a) [Lp(a)], a low-density lipoprotein (LDL)-like particle, has been independently associated with increased cardiovascular disease (CVD) risk in various populations, such as postmenopausal women. The purpose of this narrative review is to present current data on the role of Lp(a) in augmenting CVD risk in postmenopausal women and focus on the available therapeutic strategies.

METHODS

PubMed was searched for English language publications until November 2015 under the following terms: "therapy" OR "treatment" AND ["lipoprotein (a)" OR "Lp(a)"] AND ("postmenopausal women" OR "menopausal women" OR "menopause").

RESULTS

Only hormone replacement therapy (mainly oral estrogens) and tibolone have been specifically studied in postmenopausal women and can reduce Lp(a) concentrations by up to 44%, although evidence indicating a concomitant reduction in CVD risk associated with Lp(a) is lacking. As alternative treatments for women who cannot, or will not, take hormonal therapies, niacin and the upcoming proprotein convertase subtilisin / kexin type 9 (PCSK-9) inhibitors are effective in reducing Lp(a) concentrations by up to 30%. Statins have minimal or no effect on Lp(a). However, data for these and other promising Lp(a)-lowering therapies including mipomersen, lomitapide, cholesterol-ester-transfer protein inhibitors and eprotirome are derived from studies in the general, mainly high CVD risk, population, and include only subpopulations of postmenopausal women.

CONCLUSIONS

Past, present and emerging therapies can reduce Lp(a) concentrations to a varying extent. Overall, it remains to be proven whether the aforementioned reductions in Lp(a) by these therapeutic options are translated into CVD risk reduction in postmenopausal women.

Short-term tibolone does not interfere with endothelial function: a double-blinded, randomized, controlled trial

Objective To evaluate the effect of short-term hormone replacement therapy with tibolone 2.5 mg daily on endothelial function of healthy postmenopausal women, using flow-mediated dilation (FMD) of the brachial artery. Methods We performed a randomized, double-blinded, placebo-controlled study. A total of 100 healthy postmenopausal women were randomly allocated to receive tibolone (n = 50) or placebo (n = 50) for 28 days. Measurement of the FMD of the brachial artery was performed before and after the use of tibolone and placebo. Results A total of 31 women completed the study in the tibolone group, and 32 women completed the study in the control group. The results of the FMD measurements obtained from the women in the two groups before treatment were similar (0.018 and 0.091, for tibolone and placebo, p = 0.57). The values of the FMD in women who used tibolone and placebo, before and after the treatment, were similar in both groups. The numbers of women who presented an increase in the values of the FMD in both groups were also similar. Conclusion Our results demonstrate that the administration of 2.5 mg tibolone to healthy postmenopausal women for 28 days does not promote endothelial-dependent vasodilation, measured by FMD of the brachial artery.

Tibolone: the way to beat many a postmenopausal ailments

OBJECTIVE

The effects of tibolone on climacteric symptoms, osteoporosis, cardiovascular disease, breasts and the endometrium are summarised, and its role in clinical practice is reviewed in this article.

BACKGROUND

Tibolone has tissue-specific effects on receptors and enzymes that influence the synthesis and metabolism of endogenous sexual steroid hormones.

METHODS

This evaluation was based on the findings from several randomised studies, which addressed the basic and clinical research on tibolone.

RESULTS/CONCLUSION

Clinical trials prove that tibolone is effective in the treatment of the menopausal symptoms and for the postponement and calming of symptoms accompanying age-related diseases. The findings of basic researchers that tibolone affects the metabolism of every cell, including malignant cells, opened a door to a whole new domain of research that has a promising future.

Long-term effects of tibolone on circulating levels of vascular cell adhesion molecules and E-selectin in postmenopausal women

OBJECTIVE

Adherence of lymphocytes and monocytes to cell adhesion molecules (vascular cell adhesion molecules [VCAMs]) expressed by activated endothelial cells is the first step in the development of atherosclerotic disease. It is known that administration of tibolone for 8 weeks reduces serum levels of VCAMs in postmenopausal women. We evaluated the effects of the administration of tibolone in postmenopausal women for 1 year.

DESIGN

Randomized, placebo-controlled, crossover trial.

SETTING

Healthy volunteers in an academic environment.

PATIENT(S)

Thirty-six healthy women in postmenopause since 1-4 years.

INTERVENTION(S)

Group A received 2.5 mg/d of tibolone and group B received placebo for 12 months; treatment was subsequently crossed over for 1 month.

MAIN OUTCOME MEASURE(S)

Serum concentrations of VCAM-1, intercellular adhesion molecule-1 (ICAM-1), and E-selectin were evaluated at baseline and at 6, 12, and 13 months.

RESULT(S)

Baseline concentration of VCAM-1, ICAM-1, and E-selectin were similar in both groups. At months 6 and 12, mean concentrations of VCAM-1, ICAM-1, and E-selectin decreased significantly in group A but not in group B. At month 13, levels returned to baseline in group A, whereas they decreased significantly in group B.

CONCLUSION(S)

Tibolone causes a rapid and sustained decrease in circulating levels of VCAMs; the effect is lost soon after stopping the treatment. Tibolone induces favorable changes in endothelial function and may exert a direct cardiovascular protective effect in postmenopausal women.

The effect of raloxifene and tibolone on the uterine blood flow and endometrial thickness: A transvaginal Doppler study

OBJECTIVES

To evaluate and compare the effect of different than classical hormone therapy medications, such as raloxifene and tibolone, on the uterine arteries and endometrium of postmenopausal women using transvaginal ultrasonography.

METHODS

The prospective study included 62 healthy, postmenopausal women recruited from the Menopausal Clinic of the 2nd Department of Obstetrics and Gynecology of the University of Athens. Subjects were randomly allocated to receive raloxifene HCl in a daily dose of 60 mg orally (Group A-31 women) or tibolone in a daily dose of 2.5 mg orally (Group B-31 women). The study period was 6 months and all subjects were assessed using transvaginal ultrasonography before treatment initiation as well as after 3 and 6 months for evaluation of the endometrial thickness and the pulsatility (PI) and resistance (RI) indices at the level of the uterine arteries.

RESULTS

No significant differences in RI, PI and endometrial thickness were observed in the raloxifene group during the 6-month treatment. In the tibolone group, PI and RI values decreased linearly from baseline to the end of the study, whereas the endometrial thickness was significantly increased during the first 3 months remaining unaltered thereafter. Comparisons between the two study groups revealed significant percent change of values in the pre-treatment to month-3 period and no difference with regard to pre-treatment, month-3 and month-6 absolute values.

CONCLUSION

Raloxifene and tibolone exert dissimilar effects on uterine blood supply parameters and endometrial thickness.

Effects of tibolone on the risk factors for cardiovascular diseases in postmenopausal women

Background/Aim. Tibolone is a preparation that belongs to the group of steroidal substances. The effects of the use of the use of tibolone are the consequence of the activities of its metabolities, considering that their hormonal activity depends on the type of tissue in which they develop. The aim of this study was to evaluate the influence of the use of tibolone on risk factors for the development of cardiovascular diseases in postmenopausal women. Methods. A prospective observational stady included 94 patients who had the concentration of l7? estradiol < 50 pg/ml, and who was in menopause more than a year. Out of the total number of patients, 63 accepted to receive tibolone 2.5 mg daily (tibolone group), while 31 of the patients refused to take tibolone (control group). We measured the concentration of lipids (cholesterol, LDL cholesterol, HDL cholesterol, triglicerides), antitrombin III, fibrinogen, and C-reactive protein, before and after the treatment within a 6-month period. Then, we compared the difference between the values of concentrations and tested the statistical significance of the difference. We also evaluated the changes of values in the concentrations of the examinated parameters inside a 6-month period in the control group. Results. In 31 patients of the control group, from the control group there were no significant changes in the values of the defined parameters as compared to their initial values after six months. But there were changes of statistical significance (p < 0.001) in values of the concentrations of the exeminated parameters before and after the treatment in the tibolone group. In fact, we recorded decreases in the total cholesterol by 17.8%, HDL cholesterol by 27%, LDL cholesterol by 4% (without statistical significance p > 0.05) and triglicerids by 35%. There were no statistical differences in the concentrations of antitrombin III, fibrionogen, and C-reactive proteine in the tibolone group before and after the treatment. Conclusion. The use of tibolone dose decrease the concentration of the total cholesterol, triglicerides, HDL cholesterol, without a significant decrease of LDL cholesterol. Also, the use of tibolone does not have any significant effect on the concentrations of antitrombin III, fibrinogen and C-reactive proteine. The number of serum parameters measured in this study was limited, thus that was the reason to discuss only about the metabolism of lipids in the patients from the tibolone group. The final conclusion about the risk for cardiovascular diseases in the patients on tibolone, howerer, reqnires were extensive further clinical exeminations.

Long-term treatment with vaginal estradiol tablets—an impact on uterine artery blood flow

OBJECTIVE

We investigated, using color Doppler ultrasound, possible detectable blood changes of prolonged treatment with 17-beta-estradiol tablets on uterine artery blood flow, in a cohort of low risk postmenopausal women.

METHODS

39 postmenopausal women, who were taking local estrogen therapy for at least 6 months, were examined in the study group. Forty-two women who never used hormone replacement therapy consisted a control group. They were examined with color Doppler ultrasound and the pulsatility index of the uterine artery was measured. The groups were divided into three subgroups (the age, the duration of the postmenopause, and the duration of the treatment) and the data were compared among groups and within subgroups.

RESULTS

The overall mean age of the patients was 66 years, the mean duration of the postmenopause was 15 years, the overall mean PI was 1.96 +/- 0.90, and the mean duration of taking vaginal estradiol tablets was 1.97 years for the study group; and 64 years, 13 years and 2.88 +/- 0.96 for the control group, respectively. There was a difference in the mean PI among groups. No significant differences in pulsatility index values in the subgroups were found.

CONCLUSION

Long-term treatments with vaginal estradiol tablets in low risk women causes lowering of the uterine artery PI values compared to the women who are not receiving hormone replacement therapy.

Tibolone activates nitric oxide synthesis in human endothelial cells

After the unexpected findings of the Women's Health Initiative trial, indicating that traditional cardiovascular risk markers fail to predict the effects of hormone replacement therapy, it is of interest to characterize how steroids act on vascular cells. This is particularly important for tissue-specific drugs such as tibolone, whose actions may differ from other preparations. Because nitric oxide (NO) is a key regulator of vascular tone and atherogenesis, we studied its regulation by tibolone and its metabolites on human endothelial cells. Tibolone and its estrogenic metabolites (3alpha- and 3beta-OH tibolone) activate NO synthesis by recruiting functional estrogen receptors, whereas the progestogenic/androgenic metabolite (Delta(4) isomer) has no effect. During prolonged exposures, tibolone and the estrogenic compounds enhance the expression of endothelial NO synthase (eNOS). In addition, tibolone is able to induce rapid activation of eNOS, leading to rapid increases in the release of NO. Relevant for its clinical effects, the sulfated metabolites of tibolone are also effective in activating eNOS. Different from estrogen, rapid activation of eNOS does not rely on recruitment of phosphatidylinositol-3 kinase but rather on MAPK-dependent cascades. These results help to understand the mechanisms of action of tibolone on the cardiovascular system and have relevant clinical implications.

Tibolone, oral or transdermal hormone replacement and colour Doppler analysis

OBJECTIVE

To compare the plasma thromboxane, the plasma viscosity and the Doppler flow modifications induced by tibolone and by oral or transdermal continuous combined hormone replacement therapy.

METHODS

Forty-two post-menopausal patients underwent either on: oral daily treatment with tibolone (2.5 mg) (Group I; n= 14); or continuous oral administration of 0.625 mg conjugated equine estrogens + medroxyprogesterone 5 mg per day (Group II; n = 14 ); or continuous estradiol transdermal supplementation, at a dose of 50 microg per day, + medroxyprogesterone 5 mg per day (Group III; n = 14 ). The duration of the study was 6 months and the patients were submitted to transvaginal ultrasonographic evaluation of pelvic organs; Doppler analysis of the uterine, internal carotid and ophthalmic arteries; thromboxane and plasma viscosity assays in basal condition, and at 1, 3 and 6 months from the beginning of the study.

RESULTS

Although the endometrial thickness increased significantly, there were no cases in which it exceeded the normal range (< or = 5 mm). In all the three groups, the pulsatility index of the uterine, internal carotid and ophthalmic arteries significantly decreased during the therapy showing a reduced impedance since the first month of treatment. Similar variations were observed for the peak systolic blood flow velocity of the internal carotid and ophthalmic arteries. Hormone replacement therapy and tibolone induced a deep, significant and rapid decrease in plasma thromboxane and plasma viscosity levels.

CONCLUSIONS

Hormone replacement therapy and tibolone seem to have beneficial effects on vascular and hemorrheological parameters.

Serum lipids in oophorectomized women during estrogen and testosterone replacement therapy

OBJECTIVE

To evaluate the effects of giving testosterone undecanoate (TU) in addition to estrogen replacement on serum lipids in oophorectomized women.

METHOD

Women with surgically induced menopause (n = 50) were randomly assigned to oral treatment with 2 mg of estradiol valerate in combination with 40 mg of TU or placebo for 24 weeks. The study was double-blind with cross-over to the other regimen for further 24 weeks of treatment. Forty-four women completed the study. Their serum concentrations of total, high density lipoprotein (HDL)- and low density lipoprotein (LDL)-cholesterol, triglycerides, lipoprotein-(a) (Lp-(a)), total testosterone, estradiol and sex hormone-binding globulin (SHBG) were analyzed at baseline and after 24 weeks of each treatment.

RESULTS

Serum levels of total testosterone increased markedly from a baseline mean of 0.8-4.9 nmol/l during testosterone addition. The levels of free testosterone significantly increased during the combined treatment and fell when given estrogen alone. Total and LDL-cholesterol levels were significantly reduced by both treatments as also were those of Lp-(a) although the difference was not significant. We found a 13% reduction in HDL-cholesterol levels when testosterone was added, but no change with estrogen alone. Triglyceride levels were increased by estrogen treatment, but not affected by the combination of estrogen plus testosterone.

CONCLUSIONS

These findings suggest that 40 mg of TU can be given in addition to estrogen replacement with only little side-effects on the pattern of circulating lipids. Although supraphysiological concentrations of testosterone were induced a significant reduction in total and LDL-cholesterol levels occurred.

Tibolone lowers high density lipoprotein cholesterol by increasing hepatic lipase activity but does not impair cholesterol efflux

OBJECTIVE

Androgens and other drugs that reduce plasma concentrations of high density lipoprotein (HDL) cholesterol are often considered to be pro-atherogenic. Tibolone lowers HDL-cholesterol by 20% but the clinical significance of this effect is unknown.

METHODS

In a randomized, double-blind study, 34 women received 2.5 mg tibolone daily and 34 women received placebo. Serum concentrations of lipids, lipoprotein subclasses and apolipoproteins, together with plasma activities of lipid transfer proteins and lipolytic enzymes and the capacity of plasma to induce cholesterol efflux from cultured cells, were measured.

RESULTS

Compared to placebo, tibolone reduced serum concentrations of HDL-cholesterol (-14%), HDL phosphatidylcholine (-14%), apolipoprotein (apo)A-I (-12%), HDL subclasses lipoprotein (Lp)A-I (-20%), HDL-apoE (-16%), pre beta-LpA-I (-10%) and alpha-LpA-I (-12%) and increased hepatic lipase activity (+25%) and HDL sphingomyelin : phosphatidylcholine ratio (10.5%), but did not alter serum concentrations of HDL sphingomyelin, apoA-IV and LpA-I/A-II, lipoprotein lipase, the plasma activities of lecithin : cholesterol acyl transferase, cholesteryl ester transfer protein, phospholipid transfer protein or the plasma capacity to release cholesterol from cultured fibroblasts or Fu5AH hepatocytes.

CONCLUSIONS

Tibolone lowers HDL-cholesterol in part by increasing hepatic lipase activity. Conservation of sphingomyelin and apoA-II in HDL, as well as cholesteryl ester transfer protein activity, preserves the capacity of plasma to release cholesterol, despite the lower concentrations of HDL-cholesterol. This may have important implications for the use of steroid effects on HDL concentrations as surrogates for atherosclerosis.

Effects of tibolone on plasma levels of nitric oxide in postmenopausal women

OBJECTIVE

To determine the effects of tibolone on nitric oxide (NO) plasma levels in postmenopausal women.

DESIGN

Randomized, double-blind, placebo-controlled, cross-over trial.

SETTING

Healthy volunteers in an academic research environment.

PATIENT(S)

Eighteen healthy women who have been in postmenopause for 1-4 years.

INTERVENTION(S)

Women received either tibolone 2.5 mg/day (group A) or placebo (group B) for 1 month; then the treatment was inverted for the second month.

MAIN OUTCOME MEASURE(S)

Plasma concentration of NO stable oxidation products and blood pressure were evaluated at baseline, month 1, and month 2.

RESULT(S)

Baseline concentration of NO metabolites were similar in both groups. At month 1, mean concentration of NO metabolites increased significantly in group A alone. At the end of month 2, NO metabolite levels in group A returned to baseline, whereas in group B they increased significantly.

CONCLUSION(S)

Tibolone induced a sustained increase in plasma levels of NO in postmenopausal women, suggesting that tibolone may exert a direct cardiovascular protective effect in postmenopausal women.

Lowering of HDL cholesterol in post-menopausal women by tibolone is not associated with changes in cholesterol efflux capacity or paraoxonase activity

Low HDL cholesterol increases the risk of coronary heart disease. Treatment of postmenopausal women with tibolone lowers HDL cholesterol. We elucidated the consequences of this unwanted side effect in a randomized, double-blind study, where 12 women received 2.5 mg tibolone per day and 6 women, placebo. Blood samples were collected on days -1 (i.e. baseline), 28, 56, and 84 for the analysis of various parameters of lipid metabolism and HDL function. Compared to placebo, treatment with tibolone led to statistically significant decreases of HDL cholesterol (-22% to -32%), apoA-I (-14% to -22%), and HDL subclass LpA-I (-30% to -40%) but to no significant changes in apoA-II and HDL subclass LpA-I,A-II. These changes were not associated with statistically significant changes in the activity of plasma to release 3H-cholesterol from radiolabeled fibroblasts or in the serum activity of the anti-oxidative enzyme paraoxonase/arylesterase. There were no significant changes in either serum levels of triglycerides, LDL cholesterol, apoB, and leptin, or in LDL size. We conclude that changes in insulin do not contribute to the lowering of HDL cholesterol by tibolone. Despite decreased HDL cholesterol, putatively anti-atherogenic activities of HDL remained unchanged.

Differential effects on the androgen status of postmenopausal women treated with tibolone and continuous combined estradiol and norethindrone acetate replacement therapy

OBJECTIVE

To determine serum parameters reflective of androgen status in postmenopausal women using two types of hormone replacement therapy (HRT).

DESIGN

Randomized, double-blind, prospective 1-year trial of two oral HRT regimens.

SETTING

University hospital, department of obstetrics and gynecology, menopause clinic.

PATIENT(S)

100 postmenopausal women > or = 45 years.

INTERVENTION(S)

Daily use of the progestogen tibolone (2.5 mg; n = 50) or continuous combined 17-beta-estradiol (2 mg) and norethindrone acetate (E+NA, 1 mg; n = 50).

MAIN OUTCOME MEASURE(S)

Measurements of total testosterone (total T), dehydroepiandrosterone sulfate (DHEAS), androstenedione (A), FSH, and sex-hormone-binding globulin (SHBG), and calculations of free testosterone (free T). Assessment of changes from baseline within and between groups after 6 and 12 months.

RESULT(S)

We found significant differences (% changes) in the tibolone group compared to baseline within the groups after both 6 and 12 months, respectively. Levels of free T doubled, total T decreased slightly, and SHBG decreased by half; DHEAS increased by approximately 20%; and FSH decreased. In the E+NA group, levels of free T, total T, androstenedione, and FSH all decreased, and SHBG increased. Pre-trial levels of DHEAS, A, and total T were significantly higher in the E+NA group. Between groups throughout the study, the changes from baseline were significant due to the different extent of FSH reduction, and opposite changes of free T, SHBG, and DHEAS.

CONCLUSION(S)

Both regimens modify plasma androgens, DHEAS, and SHBG differently. Tibolone decreased the levels of SHBG, and substantially increased free T and to a lesser extent increased DHEAS; this may reflect a modification of adrenal androgen production. Continuous combined estradiol and norethindrone acetate HRT suppressed the peripheral plasma androgens mediated by increased levels of SHBG.