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

The effect of tibolone treatment on apolipoproteins and lipoprotein (a) concentrations in postmenopausal women: A meta-analysis of randomized controlled trials

OBJECTIVE

Tibolone is a synthetic steroid with estrogenic, androgenic and progestogenic properties that is used as hormone replacement therapy (HRT) in postmenopausal women. Treatment with tibolone has been demonstrated to lead to changes of the lipid profile, including alterations in lipoprotein (a) and apolipoprotein levels. Hence, we conducted the present meta-analysis of randomized controlled trials (RCTs) to assess the effect of tibolone treatment on apolipoproteins and lipoprotein (a) values in postmenopausal women.

METHODS

Several databases (Cochrane Library, PubMed/Medline, Scopus, and Google Scholar) were searched for English-language manuscripts published up to September 2023 that scrutinized the effects of tibolone administration on apolipoprotein A-I (ApoA-I), apolipoprotein A-II (ApoA-II), apolipoprotein B (ApoB), and lipoprotein (a) in postmenopausal women. The results were reported as the weighted mean difference (WMD) with a 95% confidence interval (CI), generated using a random-effects model.

RESULTS

Finally, 12 publications with 13 RCT arms were included in the current meta-analysis. The overall results from the random-effects model demonstrated a notable reduction in ApoA-I (n = 9 RCT arms, WMD: -34.96 mg/dL, 95 % CI: -42.44, -27.48, P < 0.001) and lipoprotein (a) (n = 12 RCT arms, WMD: -7.49 mg/dl, 95 % CI: -12.17, -2.81, P = 0.002) after tibolone administration in postmenopausal women. However, treatment with tibolone did not impact ApoA- II (n = 4 RCT arms, WMD: 1.32 mg/dL, 95 % CI: -4.39, 7.05, P = 0.64) and ApoB (n = 9 RCT arms, WMD: -2.68 mg/dL, 95 % CI: -20.98, 15.61, P = 0.77) values. In the subgroup analyses, we noticed a notable decrease in lipoprotein (a) levels when tibolone was prescribed to females aged < 60 years (WMD: -10.78 mg/dl) and when it was prescribed for ≤ 6 months (WMD: -15.69 mg/dl).

CONCLUSION

The present meta-analysis of RCTs highlighted that treatment with tibolone reduces lipoprotein (a) and apolipoprotein A-I levels in postmenopausal women. As the decrease in serum lipids' concentrations is associated with a decrease in the risk of cardiovascular disease (CVD), treatment with tibolone could be a suitable therapy for postmenopausal women with elevated CVD risk.

The effect of tibolone treatment on lipid profile in women: A systematic review and dose-response meta-analysis of randomized controlled trials

Inconsistencies exist with regard to influence of tibolone treatment on the lipid profile. The reasons for these inconsistencies might derive from several factors, i.e., differences in baseline variables, intervention duration, participants' health status or baseline body mass index (BMI). To address these inconsistencies, based on a systematic search in Scopus, PubMed/Medline, Web of Science, and Embase for papers published until 21 December 2020, we conducted the current dose-response meta-analysis of randomized controlled trials (RCTs) to determine the impact of tibolone treatment on the lipid profile. The overall findings were derived from 26 RCTs. Tibolone administration decreased total cholesterol (TC) (weighted mean difference, WMD: -18.55 mg/dL, CI: -25.95 to -11.16, P < 0.001), high-density lipoprotein-cholesterol (HDL-C) (WMD: -9.42 mg/dL, CI: -11.83 to -7.01, P < 0.001) and triglyceride (TG) (WMD: -21.43 mg/dL, CI: -27.15 to -15.70, P < 0.001) levels. A significant reduction in LDL-C occurred when tibolone was prescribed for ≤ 26 weeks (WMD: -7.64 mg/dL, 95% CI: -14.58 to -0.70, P = 0.031) versus > 26 weeks (WMD: -8.84 mg/dL, 95% CI: -29.98, 12.29, P = 0.412). The decrease in TG (WMD: -22.64 mg/dL) and TC (-18.55 mg/dL) concentrations was more pronounced in patients with BMI ≥ 25 kg/m²versus BMI < 25 kg/m². This systematic review and meta-analysis discovered that tibolone decreases TC, HDL-C and TG levels. LDL-C concentrations are significantly reduced when tibolone administration lasts for ≤ 26 weeks.

A Review of Analytical Methods for the Determination of Tibolone: Pharmacokinetics and Pharmaceutical Formulations Analysis and Application in Doping Control

Background:

Tibolone is a synthetic steroid commercialized by Organon under the brand name Livial (Org OD14), which is used in hormone therapy for menopause management and treatment of postmenopausal osteoporosis. Tibolone is defined as a selective tissue estrogenic activity regulator (STEAR) demonstrating tissue-specific effects on several organs such as brain, breast, urogenital tract, endometrium, bone and cardiovascular system.

Aims:

This work aims to (1) present an overview of important published literature on existing methods for the analysis of tibolone and/or its metabolites in pharmaceutical formulations and biological fluids and (2) to conduct a critical comparison of the analytical methods used in doping control, pharmacokinetics and pharmaceutical formulations analysis of tibolone and its metabolites.

Results and conclusions:

The major analytical method described for the analysis of tibolone in pharmaceutical formulations is High Pressure Liquid Chromatography (HPLC) coupled with ultraviolet (UV) detection, while Liquid Chromatography (LC) or Gas Chromatography (GC) used in combination with Mass Spectrometry (MS) or tandem mass spectrometry (MS/MS) is employed for the analysis of tibolone and/or its metabolites in biological fluids.

Effects of tibolone or continuous combined oestradiol and norethisterone acetate on lipids, high-density lipoprotein subfractions and apolipoproteins in postmenopausal women in a two-year, randomized, double-blind, placebo-controlled trial

OBJECTIVE

To compare the effects of (a) tibolone, (b) continuous combined oestrogen plus progestogen and (c) placebo on plasma lipid and lipoprotein markers of cardiovascular risk in healthy postmenopausal women.

STUDY DESIGN

Randomized, single-centre, placebo-controlled, double-blind study.

PATIENTS

One hundred and one postmenopausal women were randomized (1:1:1) into one of three groups taking daily 2.5 mg tibolone, continuous oral oestradiol-17β 2 mg plus norethisterone acetate 1 mg daily (E₂ /NETA) or placebo.

MAIN OUTCOME MEASURES

Fasting serum lipid, lipoprotein and apolipoprotein concentrations measured at baseline and after 6, 12 and 24 months of treatment.

RESULTS

Both tibolone and E₂ /NETA lowered plasma total cholesterol concentrations relative to placebo. With tibolone, high-density lipoprotein cholesterol (HDL-C) was reduced (-27% at 24 months, P < .001), the greatest effect being in the cholesterol-enriched HDL₂ subfraction (-40%, P < .001). Tibolone's effect on HDL concentrations was also apparent in the principal HDL protein component, apolipoprotein AI (-29% at 24 months, P < .001). However, there was no significant effect of tibolone on low-density or very low-density lipoprotein cholesterol (LDL-C and VLDL-C, respectively). By contrast, the greatest reduction in cholesterol with E₂ /NETA was in LDL-C (-22% at 24 months, P = .008). E₂ /NETA reduced HDL-C to a lesser extent than tibolone (-12% at 24 months, P < .001). Effects on HDL apolipoproteins were similarly diminished relative to tibolone. E₂ /NETA had no effect on VLDL-C or on the protein component of LDL, apolipoprotein B.

CONCLUSION

Tibolone reduces serum HDL. E₂ /NETA reduces LDL cholesterol but not apolipoprotein B, suggesting decreased cholesterol loading of LDL. Any impact these changes may have on CVD risk needs further investigation.

Sphingomyelin in high-density lipoproteins: structural role and biological function

High-density lipoprotein (HDL) levels are an inverse risk factor for cardiovascular diseases, and sphingomyelin (SM) is the second most abundant phospholipid component and the major sphingolipid in HDL. Considering the marked presence of SM, the present review has focused on the current knowledge about this phospholipid by addressing its variable distribution among HDL lipoparticles, how they acquire this phospholipid, and the important role that SM plays in regulating their fluidity and cholesterol efflux from different cells. In addition, plasma enzymes involved in HDL metabolism such as lecithin-cholesterol acyltransferase or phospholipid transfer protein are inhibited by HDL SM content. Likewise, HDL SM levels are influenced by dietary maneuvers (source of protein or fat), drugs (statins or diuretics) and modified in diseases such as diabetes, renal failure or Niemann-Pick disease. Furthermore, increased levels of HDL SM have been shown to be an inverse risk factor for coronary heart disease. The complexity of SM species, described using new lipidomic methodologies, and their distribution in different HDL particles under many experimental conditions are promising avenues for further research in the future.

Testosterone replacement in hypogonadal men alters the HDL proteome but not HDL cholesterol efflux capacity

The effects of androgens on cardiovascular disease (CVD) risk in men remain unclear. To better characterize the relationship between androgens and HDL, we investigated the effects of testosterone replacement on HDL protein composition and serum HDL-mediated cholesterol efflux in hypogonadal men. Twenty-three older hypogonadal men (ages 51-83, baseline testosterone < 280 ng/dl) were administered replacement testosterone therapy (1% transdermal gel) with or without the 5α-reductase inhibitor dutasteride. At baseline and after three months of treatment, we determined fasting lipid concentrations, HDL protein composition, and the cholesterol efflux capacity of serum HDL. Testosterone replacement did not affect HDL cholesterol (HDL-C) concentrations but conferred significant increases in HDL-associated paraoxonase 1 (PON1) and fibrinogen α chain (FGA) (P = 0.022 and P = 0.023, respectively) and a decrease in apolipoprotein A-IV (apoA-IV) (P = 0.016). Exogenous testosterone did not affect the cholesterol efflux capacity of serum HDL. No differences were observed between men who received testosterone alone and those who also received dutasteride. Testosterone replacement in older hypogonadal men alters the protein composition of HDL but does not significantly change serum HDL-mediated cholesterol efflux. These effects appear independent of testosterone conversion to dihydrotestosterone. Further research is needed to determine how changes in HDL protein content affect CVD risk in men.

Acute sex steroid withdrawal increases cholesterol efflux capacity and HDL-associated clusterin in men

Exogenous androgens can lower HDL-cholesterol (HDL-C) concentrations, yet men with low serum testosterone have elevated rates of cardiovascular disease (CVD). HDL function may better predict CVD risk than absolute HDL-C quantity. We evaluated the acute effects of medical castration in men on HDL-C, cholesterol efflux capacity and HDL protein composition. Twenty-one healthy men, ages 18-55, received the GnRH antagonist acyline and one of the following for 28days: Group 1: placebo, Group 2: transdermal testosterone gel and placebo, Group 3: transdermal testosterone gel and an aromatase inhibitor. Sex steroids, fasting lipids, and cholesterol efflux to apoB-depleted serum were measured in all subjects. The HDL proteome was assessed in Group 1 subjects only. In Group 1, serum testosterone concentrations were reduced by >95%, and HDL-C and cholesterol efflux capacity increased (p=0.02 and p=0.03 vs. baseline, respectively). HDL-associated clusterin increased significantly with sex steroid withdrawal (p=0.007 vs. baseline). Testosterone withdrawal in young, healthy men increases HDL-C and cholesterol efflux capacity. Moreover, sex steroid deprivation changes HDL protein composition. Further investigation of the effects of sex steroids on HDL composition and function may help resolve the apparently conflicting data regarding testosterone, HDL-C, and CVD risk.

The effects of hormone therapy on metabolic risk factors in postmenopausal Korean women

OBJECTIVE

We sought to assess the prevalence of metabolic syndrome (MetS) among Korean postmenopausal women and to investigate the effect of hormone therapy status and reproductive characteristics on body composition and MetS risk factors.

STUDY DESIGN

We performed a cross-sectional study involving a cohort of 2005 postmenopausal Korean women. We defined MetS using the modified National Cholesterol Education Program (NCEP) criteria proposed by the American Heart Association/National Heart, Lung, and Blood Institute guidelines. The criteria for abdominal obesity were adopted from the cut-offs suggested by the Korean Society for the Study of Obesity. Participants with three or more of the following conditions were classified as having MetS: waist circumference ≥ 85 cm; blood pressure ≥ 130/85 mmHg; fasting plasma triglycerides ≥ 150 mg/dl; high density lipoprotein cholesterol < 50 mg/dl; glucose ≥ 100 mg/dl and/or receiving treatment for their condition.

RESULTS

The prevalence of MetS was 22.1% in the study population and increased with age. After adjusting for age and related reproductive characteristics, it was found that ever-use of hormone therapy (prior or current) was associated with decreased risk of postmenopausal MetS. Among individual risk factors for MetS, current hormone therapy seemed to be associated with decreased prevalence of abdominal obesity and better glucose metabolism and prior use of hormone therapy were associated with lower risk of abdominal obesity and high blood pressure.

CONCLUSION

Postmenopausal hormone therapy is associated with decreased risk of MetS in postmenopausal Korean women.

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.

The effect of tibolone and continuous combined conjugated equine oestrogens plus medroxyprogesterone acetate on progression of carotid intima–media thickness: the Osteoporosis Prevention and Arterial effects of tiboLone (OPAL) study

AIMS

At the time of the design of the Osteoporosis Prevention and Arterial effects of tiboLone (OPAL) study in 1996, oral hormone therapy (HT) was assumed to reduce cardiovascular risk. The evidence mainly came from the effects of combined conjugated equine oestrogens plus medroxyprogesterone acetate (CEE/MPA) therapy. Other HT regimes had not been studied widely. Tibolone, a selective tissue oestrogenic activity regulator, has several effects on cardiovascular risk factors, one of which is HDL lowering. Because the overall effect of tibolone on cardiovascular risk was unknown, the OPAL study was designed.

METHODS AND RESULTS

The OPAL study was a three-arm, randomized, placebo-controlled, double-blind study to determine the effect of tibolone (2.5 mg daily) and of CEE/MPA (0.625/2.5 mg daily) over 3 years on progression of carotid intima-media thickness (CIMT) in 866 healthy post-menopausal women. The women were recruited from six US and five European centres. The primary outcome was change in mean common CIMT. Annual common CIMT progression rates in the tibolone and CEE/MPA groups were higher than in the placebo group: 0.0077 mm [95% confidence interval (CI) 0.0051-0.0103] in the tibolone group, 0.0074 mm (0.0048-0.0099) in the CEE/MPA group, and 0.0035 mm (0.009-0.0061) in the placebo group. The differences with placebo (0.0042 mm/year for tibolone and 0.0039 mm/year for CEE/MPA) were statistically significant. HDL cholesterol increased in CEE/MPA group and was lowered in the tibolone group.

CONCLUSION

Both tibolone and CEE/MPA showed increased progression of common CIMT. Translation of the increased common CIMT progression of the CEE/MPA group into cardiovascular disease risk could not fully explain the observed increased cardiovascular risk as observed in the Women's Health Initiative study. This suggests that the net effect of tibolone and CEE/MPA on cardiovascular events may depend on the combined effects on the arterial wall, clotting factors, and possibly inflammation.

Effects of oestrogen receptor-active compounds on lipid metabolism

Selective estrogen receptor modulators (SERMs) have been used successfully in the treatment of breast cancer and osteoporosis while Tibolone has been used extensively in Europe for the treatment of menopausal symptoms. Limited data is available on the effect of these agents on the cardiovascular system. Traditional and novel lipid markers are valuable in determining patients at increased cardiovascular risk. The purpose of this article is to discuss the mechanism of action of Tamoxifen, Raloxifene and Tibolone and their effects on lipid metabolism.

Effect of different preparations of hormone therapy on lipid and glucose metabolism, coagulation factors, and bone mineral density in overweight and obese postmenopausal women

OBJECTIVE

To determine the effects of different preparations of hormone therapy (HT) on lipid and glucose metabolism, coagulation factors, and bone mineral density (BMD) in overweight and obese postmenopausal women.

DESIGN

A randomized, nonblinded, controlled study.

SETTING

Karadeniz Technical University, Department of Obstetrics and Gynecology.

PATIENT(S)

A total of 352 overweight and obese (body mass index >25 kg/m2) postmenopausal women.

INTERVENTION(S)

Ninety women received 2.5 mg of tibolone; 84 received 2 mg of E2 plus 1 mg of norethisterone acetate (E2/NETA); 90 received 0.625 mg of conjugated equine estrogen plus 2.5 mg of medroxyprogesterone acetate (CEE/MPA); and 88 did not receive any menopausal therapy (control).

MAIN OUTCOME MEASURE(S)

At baseline and after 6 months of treatment, we measured total cholesterol, triglyceride, high-density lipoprotein cholesterol (HDL), low-density lipoprotein cholesterol (LDL), insulin, glucose, factor VII, factor VIII, von Willebrand factor, antithrombin III, protein S, protein C, fibrinogen, and BMD at the lumbar spine L1-L4.

RESULT(S)

There were no statistically significant differences among the groups for any variables at baseline. After 6 months of treatment, the three regimens decreased total cholesterol, triglyceride, LDL, and fibrinogen; E2/NETA and CEE/MPA increased HDL, and tibolone decreased HDL; higher insulin concentrations were found in the control and tibolone groups. Body mass index, HDL, fibrinogen levels, and L1-L4 BMD were independent factors in the prediction of HT use.

CONCLUSION(S)

Body mass index, HDL, fibrinogen levels and L1-L4 BMD were independent factors in the prediction of HT use. Treatment with tibolone, E2/NETA, and CEE/MPA resulted in minimal improvement in lumbar spine BMD but had a beneficial effect on the procoagulation system, with minimal changes in glucose metabolism after 6 months of therapy.

Significant differential effects of lower doses of hormone therapy or tibolone on markers of cardiovascular disease in post-menopausal women: a randomized, double-blind, crossover study

AIMS

We have previously reported that lower doses of hormone therapy (L-HT) and tibolone have different effects on markers of cardiovascular disease when compared with conventional doses of HT. The objective was to compare the effects of L-HT and tibolone on lipid profile, vasodilation, and factors associated with inflammation and haemostasis.

METHODS AND RESULTS

Forty-one women received a combination of micronized progesterone 100 mg with conjugated equine estrogen 0.3 mg vs. tibolone 2.5 mg alone daily in random order during 2 months with 2 months washout period. When compared with L-HT, tibolone significantly reduced total cholesterol (P<0.001), triglyceride (P<0.001), HDL cholesterol (P<0.001) levels, and triglyceride/HDL cholesterol ratios (P=0.004) except total cholesterol/HDL cholesterol ratios. Tibolone improved flow-mediated response to hyperaemia from baseline values (P<0.001) by a similar magnitude to L-HT. L-HT and tibolone did not increase high-sensitivity C-reactive protein relative to baseline values. L-HT reduced antithrombin III from baseline values (P=0.037), compared with tibolone showing no changes. However, there was no difference between either. In contrast, tibolone increased pro-thrombin fragment 1+2 (F1+2) from baseline values (P=0.002), compared with L-HT showing no changes. Tibolone significantly reduced plasma plasminogen activator inhibitor type 1 (PAI-1) antigen levels from baseline values (P=0.004), compared with L-HT showing no changes. The effects of L-HT and tibolone on F1+2 and PAI-1 were significantly different (P=0.045 and P=0.008, respectively).

CONCLUSION

Both tibolone and L-HT improved flow-mediated response by a similar magnitude and did not significantly increase high-sensitivity C-reactive protein. However, tibolone significantly reduced PAI-1, but increased F1+2 more than L-HT.

Increasing High-Density Lipoprotein Cholesterol in Dyslipidemia by Cholesteryl Ester Transfer Protein Inhibition

Reduced HDL cholesterol may be a risk factor comparable in importance to increased LDL cholesterol. Interventions that raise HDL are antiatherosclerotic, presumably through acceleration of reverse cholesterol transport and by antioxidant and antiinflammatory effects. In the hypercholesterolemic rabbit, HDL levels can be increased by >50% by inhibition of cholesteryl ester transfer protein (CETP), a molecule that plays a central role in HDL metabolism. This HDL-raising effect is antiatherosclerotic in moderately severe hyperlipidemia but appears to be ineffective in the presence of severe hypertriglyceridemia. In humans, mutations resulting in CETP inhibition have been associated with both reduced and increased risk of atherosclerosis. Proposed explanations for these apparently disparate observations are that the antiatherosclerotic effect of CETP inhibition varies with either the metabolic milieu or the degree of CETP inhibition. We now have pharmacological inhibitors of CETP that are capable of increasing HDL by as much as 50% to 100% in humans. The importance of this development is that reduced HDL is a risk factor independent of LDL and that these new agents alter HDL by a magnitude comparable to that of statins on LDL. Clinical trials, now beginning, will need to identify the patient subsets in which CETP inhibition may be more or less effective.

Hepatic lipase: friend or foe and under what circumstances?

Hepatic lipase (HL) plays a role in the metabolism of chylomicron and very low-density lipoprotein remnants, low-density lipoproteins (LDL), and high-density lipoproteins (HDL), which are all implicated in atherosclerosis. Considering the effects of HL on these lipoproteins, it appears that HL has pro- as well as antiatherogenic potential. In line with clinical observations, most effects of HL on lipoprotein metabolism during hypertriglyceridemia may be interpreted as promoting atherosclerosis (formation of small, dense LDL, lowering of HDL levels), whereas most effects during hypercholesterolemia seem to be potentially antiatherogenic (stimulation of reverse cholesterol transport, clearing of intermediate-density lipoprotein). The potential modulation of pro- or antiatherogenics effect of HL by other factors, such as LDL receptor, cholesterol ester transfer protein, lipoprotein lipase, and ATP-binding cassette A-1 activity, is discussed.

Modulation of high-density lipoprotein cholesterol metabolism and reverse cholesterol transport

Low high-density lipoprotein (HDL)-cholesterol (C) is an important risk factor for coronary heart disease. In vitro, HDL exerts several potentially anti-atherogenic effects including reverse cholesterol transport (RCT) from peripheral cells to the liver. Hence, raising HDL-C has become an interesting target for anti-atherosclerotic drug therapy. Levels of HDL-C and the composition of HDL subclasses in plasma are regulated by apolipoproteins, lipolytic enzymes, lipid transfer proteins, receptors, and cellular transporters. The interplay of these factors leads to RCT and determines the composition and thereby the anti-atherogenic properties of HDL. Recent findings suggest that the mechanism of HDL modification rather than a sole increase in HDL-C determines the efficacy of anti-atherosclerotic drug therapy. In several controlled and prospective intervention studies, patients with low HDL-C and additional risk factors benefited from treatment with fibrates or statins. However, in only some of the fibrate trials was prevention of coronary events in patients with low HDL-C and hypertriglyceridaemia related to an increase in HDL-C. This may be because currently available drugs increase HDL-C levels only moderately and because HDL levels per se do not necessarily correlate with the functionality of HDL. However, several novel targets to modify RCT have emerged from the recent understanding of HDL synthesis, maturation and catabolism. The four major targets for an anti-atherogenic strategy in HDL metabolism include stimulation of apoA-I synthesis and secretion, the stimulation of ABCA1 expression, the inhibition of cholesterol ester transfer protein, and the up-regulation of scavenger receptor BI. These and other modulations of HDL metabolism are thought to result in improved RCT making them attractive targets for the development of new regimens of anti-atherogenic drug 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.

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.

Low high-density lipoprotein cholesterol: physiological background, clinical importance and drug treatment

Low high-density lipoprotein (HDL) cholesterol is an important risk factor for coronary heart disease (CHD). In vitro, HDL exerts several potentially anti-atherogenic activities. HDLs mediate the reverse cholesterol transport (RCT) from peripheral cells to the liver, inhibit oxidation of low-density lipoprotein (LDL), adhesion of monocytes to the endothelium, apoptosis of vascular endothelial and smooth muscle cells and platelet activation, and stimulate the endothelial secretion of vasoactive substances as well as smooth muscle cell proliferation. Hence, raising HDL-cholesterol levels has become an interesting target for anti-atherosclerotic drug therapy. Levels of HDL cholesterol and the composition of HDL subclasses in plasma are regulated by apolipoproteins, lipolytic enzymes, lipid transfer proteins, receptors and cellular transporters. The interplay of these factors leads to RCT and determines the composition and, thereby, the anti-atherogenic properties of HDL. Several inborn errors of metabolism, as well as genetic animal models, are characterised by both elevated HDL cholesterol and increased rather than decreased cardiovascular risk. These findings suggest that the mechanism of HDL modification rather than simply increasing HDL cholesterol determine the efficacy of anti-atherosclerotic drug therapy. In several controlled and prospective intervention studies, patients with low HDL cholesterol and additional risk factors benefited from treatment with fibric acid derivatives (fibrates) or HMG-CoA reductase inhibitors (statins). However, only in some trials was prevention of coronary events in patients with low HDL cholesterol and hypertriglyceridaemia related to an increase in HDL cholesterol. We discuss the clinical and metabolic effects of fibrates, statins, nicotinic acid and sex steroids, and present novel therapeutic strategies that show promise in modifying HDL metabolism. In conclusion, HDL-cholesterol levels increase only moderately after treatment with currently available drugs and do not necessarily correlate with the functionality of HDL. Therefore, the anti-atherosclerotic therapy of high-risk cardiovascular patients should currently be focused on the correction of other risk factors present besides low HDL cholesterol. However, modification of HDL metabolism and improvement of RCT remain an attractive target for the development of new regimens of anti-atherogenic drug therapy.

Postmenopausal hormone therapy before and after the women's health initiative study: what consequences?

This review focuses on the question of whether the Women's Health Initiative (WHI) was a test of primary versus secondary cardiovascular benefits of postmenopausal hormone therapy. Evidence is presented to support the conclusion that the WHI was a secondary intervention trial and that primary cardiovascular benefits of hormone therapy are rational, likely, but not yet proven. The review makes clear that hormone therapy is not a 'cardiovascular drug' for the treatment of coronary heart disease; but rather that the public health debate is whether hormone therapy, used for the treatment of menopausal symptoms, provides any cardiovascular benefits that might offset its risk.

Calorie restriction in mice does not affect LDL reverse cholesterol transport in vivo

Calorie restriction (CR) prolongs life in animals, but may reduce plasma HDL, important in reverse cholesterol transport (RCT). The effect of CR, 60% of an ad libitum (AL) diet, on cholesterol removal from rectus femoris muscle injected with cationized LDL, was studied in C57BL male mice. RCT in vivo, on CR and AL diet, and cholesterol efflux from macrophages exposed to CR or AL sera, was similar, despite a 22% reduction in plasma HDL-cholesterol (HDL-C). In CR fed mice total cholesterol (TC) and phospholipid (T-PL) decreased by 32% and 38%, while HDL-C and HDL-PL decreased by 22% and 16% only, resulting in increased HDL-PL/T-PL ratio, which enhanced RCT. Partial re-feeding (CR-RF, 70% of AL) induced normalization of plasma lipids (excluding triglycerides), while HDL-PL/T-PL remained elevated. Thus, as CR did not interfere with RCT in vivo, it could possibly be beneficial to patients at risk for coronary heart disease.

Serum lipids and apolipoproteins in Greek postmenopausal women: association with estrogen, estrogen-progestin, tibolone and raloxifene therapy

The aim of this study was to assess lipid and apolipoprotein levels in postmenopausal women taking various regimens of replacement therapy or no therapy. Seven hundred forty-eight postmenopausal women followed in the Menopause Clinic of the 2nd Department of Obstetrics and Gynecology, University of Athens, Aretaieion Hospital, were studied in a cross-sectional design. Women were either non-users of replacement therapy (no. = 511) or users of one of the following regimens: conjugated equine estrogen 0.625 mg (CEE, no. = 34), CEE 0.625 mg plus medroxyprogesterone acetate 5 mg (CEE/MPA, no. = 60), 17beta-estradiol 2 mg plus norethisterone acetate 1 mg (E2/NETA, no. = 44), tibolone 2.5 mg (no. = 84), raloxifene HCI 60 mg (no. = 51). Total cholesterol (TC), LDL-cholesterol (LDL-C) and HDL-cholesterol (HDL-C), triglycerides (TG), apolipoprotein A1 (ApoA1) and apolipoprotein B (ApoB) levels were assessed. Women were grouped according to replacement regimen and mean levels of lipid and apolipoproteins were compared between groups. Women in the raloxifene group were older and longer menopaused. After adjustment for age and duration of menopause, TG levels were significantly lower in the tibolone and E2/NETA groups (75 and 89.9 mg/dl, respectively) compared to non-users. TC was lower in all therapy groups, but the difference acquired significance only in the E2/NETA (207.8 mg/dl), compared to non-users (231.5 mg/dl). LDL-C levels were significantly lower in the CEE (133.8 mg/dl), CEE/MPA (130.4 mg/dl) and raloxifene group (129.9 mg/dl) compared to non-users (151.9 mg/dl). There was no difference in HDL-C levels between users and non-users (58.9 mg/dl) except for the tibolone group where HDL-C was significantly lower (48.6 mg/dl). ApoA1 levels were significantly higher in the CEE/MPA group (194.4 mg/dl) and significantly lower in the tibolone group (141.6 mg/dl) compared to non-users (170.4 mg/dl). No difference was detected between groups concerning ApoB levels. In conclusion, tibolone therapy is associated with lower TG levels as well as lower HDL and ApoA1 levels. ERT, continuous combined estrogen-progestin therapy (HRT) and raloxifene are associated with lower LDL-C levels. Among continuous combined HRT users, CEE/MPA is associated with higher ApoA1 levels, while E2/NETA with lower TG levels. Large prospective randomized studies are required to validate these results.

Pros and cons of existing treatment modalities in osteoporosis: a comparison between tibolone, SERMs and estrogen (+/-progestogen) treatments

Tibolone, selective estrogen receptor modulators (SERMs) like tamoxifen and raloxifene, and estrogen (+/-progestogen) treatments prevent bone loss in postmenopausal women. They exert their effects on bone via the estrogen receptor (ER) and the increase in bone mass is due to resorption inhibition. The effect of SERMs on bone mineral density is less than that with the other treatments, but the SERM raloxifene still has a positive effect on vertebral fractures. In contrast to tibolone and estrogens (+/-progestogen), SERMs do not treat climacteric complaints, whilst estrogen plus progestogen treatments cause a high incidence of bleeding. Estrogen plus progestogen combinations have compromising effects on the breast. Tibolone and SERMs do not stimulate the breast or endometrium. Unlike SERMs, tibolone does not possess antagonistic biological effects via the ER in these tissues. Estrogenic stimulation in these tissues is prevented by local metabolism and inhibition of steroid metabolizing enzymes by tibolone and its metabolites. SERMs and estrogen (+/-progestogen) treatments increase the risk of venous thromboembolism (VTE), whilst estrogen (+/-progestogen) combinations have unwanted effects on cardiovascular events. So far, no detrimental effects of tibolone have been observed with respect to VTE or cardiovascular events. The clinical profile of tibolone therefore has advantages over those of other treatment modalities. It is also clear that tibolone is a unique compound with a specific mode of action and that it belongs to a separate class of compounds that can best be described as selective, tissue estrogenic activity regulators (STEARs).