Regulation of activities of steroid hormone receptors by tibolone and its primary metabolites

Tibolone and Breast Cancer

Tibolone, a selective tissue estrogenic activity regulator, is a synthetic steroid with distinct pharmacological and clinical characteristics in contrast to conventional menopausal hormone therapy. Tibolone induces estrogenic activity in the brain, vagina, and bone but remains inactive in the endometrium and breast. In particular, several studies have investigated whether tibolone usage increases the risk of breast cancer. This study aims to determine the effects of tibolone on the breast by focusing on the relation between tibolone use and breast cancer. Our investigation emphasizes recent studies, particularly those based on Asian populations.

Network pharmacology and topological analysis on tibolone metabolites and their molecular mechanisms in traumatic brain injury

Traumatic brain injury (TBI) is a pathology of great social impact, affecting millions of people worldwide. Despite the scientific advances to improve the management of TBI in recent years, we still do not have a specific treatment that controls the inflammatory process after mechanical trauma. The discovery and implementation of new treatments is a long and expensive process, making the repurpose of approved drugs for other pathologies a clinical interest. Tibolone is a drug in use for the treatment of symptoms associated with menopause and has been shown to have a broad spectrum of actions by regulating estrogen, androgen and progesterone receptors, whose activation exerts potent anti-inflammatory and antioxidant effects. In the present study, we aimed to investigate the therapeutic potential of the tibolone metabolites 3α-Hydroxytibolone, 3β-Hydroxytibolone, and Δ4-Tibolone as a possible therapy in TBI using network pharmacology and network topology analysis. Our results demonstrate that the estrogenic component mediated by the α and β metabolites can regulate synaptic transmission and cell metabolism, while the Δ metabolite may be involved in modulating the post-TBI inflammatory process. We identified several molecular targets, including KDR, ESR2, AR, NR3C1, PPARD, and PPARA, which are known to play critical roles in the pathogenesis of TBI. Tibolone metabolites were predicted to regulate the expression of key genes involved in oxidative stress, inflammation, and apoptosis. Overall, the repurposing of tibolone as a neuroprotective treatment for TBI holds promise for future clinical trials. However, further studies are needed to confirm its efficacy and safety in TBI patients.

Endometrial cancer risk with menopausal hormone therapy: Health Insurance Database in South Korea-based cohort study

OBJECTIVE

To determine the risk of endometrial cancer according to the types of menopausal hormones used.

METHODS

This retrospective cohort study recruited postmenopausal women older than 40 years from 2003 to 2011, utilizing data from the Korean national health insurance system from 2002 to 2019. The menopausal hormone therapy (MHT) group consisted of women who had been prescribed MHT for greater than 6 months between 2003 and 2011. The non-MHT group consisted of women who had never used menopausal hormones between 2003 and 2011.

RESULTS

A non-MHT group of 1 000 550 women and a MHT group of 353 025 women were chosen. In comparison to never-users, the risk of endometrial cancer was not higher in women who reported last using tibolone (adjusted hazard ratio [aHR] 1.08, 95% confidence interval [CI] 0.96-1.2), combined estrogen plus progestin by the manufacturer (aHR 0.83, 0.72-0.96), combined estrogen plus progestin by the physician (aHR 0.88, 0.7-1.12), and transdermal estrogen (aHR 1.13, 0.36-3.52).

CONCLUSIONS

Tibolone, combined estrogen plus progestin by the physician, and transdermal estrogen do not affect the risk of endometrial cancer. The combination of estrogen plus progestin by the manufacturer decreases the risk of endometrial cancer.

Role of Neuroglobin in the Neuroprotective Actions of Estradiol and Estrogenic Compounds

Estradiol exerts neuroprotective actions that are mediated by the regulation of a variety of signaling pathways and homeostatic molecules. Among these is neuroglobin, which is upregulated by estradiol and translocated to the mitochondria to sustain neuronal and glial cell adaptation to injury. In this paper, we will discuss the role of neuroglobin in the neuroprotective mechanisms elicited by estradiol acting on neurons, astrocytes and microglia. We will also consider the role of neuroglobin in the neuroprotective actions of clinically relevant synthetic steroids, such as tibolone. Finally, the possible contribution of the estrogenic regulation of neuroglobin to the generation of sex differences in brain pathology and the potential application of neuroglobin as therapy against neurological diseases will be examined.

Tibolone as Hormonal Therapy and Neuroprotective Agent

Tibolone (TIB), a selective tissue estrogenic activity regulator (STEAR) in clinical use by postmenopausal women, activates hormonal receptors in a tissue-specific manner. Estrogenic activity is present mostly in the brain, vagina, and bone, while the inactive forms predominate in the endometrium and breast. Conflicting literature on TIB's actions has been observed. While it has benefits for vasomotor symptoms, bone demineralization, and sexual health, a higher relative risk of hormone-sensitive cancer has been reported. In the brain, TIB can improve mood and cognition, neuroinflammation, and reactive gliosis. This review aims to discuss the systemic effects of TIB on peri- and post-menopausal women and its role in the brain. We suggest that TIB is a hormonal therapy with promising neuroprotective properties.

Characterisation of progestins used in hormonal contraception and progesterone via the progesterone receptor

Different progestogens are widely used in hormonal therapy and mediate their therapeutic actions via the progesterone receptor (PR). Little published data exist on their relative efficacies and potencies via the PR, while those available may be confounded by off-target receptors, different methodologies and model systems. We performed dose-response analysis to investigate the efficacies and potencies for transcription of progesterone and several progestins widely used in contraception via the B isoform of human PR (PR-B). We compared responses using three different cell lines and two different transient transfection conditions. Results show that in vitro biological responses via PR-B for the select progestogens can vary significantly in biocharacter, rank order and absolute values for efficacies and potencies, depending on the cell line and transfection condition. Progestogen rank orders for published relative binding affinities are mostly different to those for relative efficacies and potencies. These in vitro differences suggest that rank orders and absolute values of the efficacies and potencies of the progestogens are likely to vary in vivo in a cell-specific and progestogen-specific manner, and cannot easily be extrapolated from in vitro data, as is usually the practice. While obtaining such data in vivo is not possible, these in vitro data show proof of concept for likely significant cell- and progestogen-specific PR-B effects.

Human and Zebrafish Nuclear Progesterone Receptors Are Differently Activated by Manifold Progestins

The environmental risk of natural and synthetic ligands of the nuclear progesterone receptor (nPR) has been pointed out, however there is still a lack of mechanistic information regarding their ability to interact with nuclear PR in aquatic species. To identify possible interspecies differences, we assessed in vitro the ability of manifold progestins to transactivate zebrafish (zf) and human (h) PRs, using two established reporter cell lines, U2OS-zfPR and HELN-hPR, respectively. Reference ligands highlighted some differences between the two receptors. The reference human agonist ligands promegestone and progesterone induced luciferase activity in both cell lines in a concentration-dependent manner, whereas the natural zebrafish progestin 17α,20β-dihydroxy-4-pregnen-3-one activated zfPR but not hPR. The potent human PR antagonist mifepristone (RU486) blocked PR-induced luciferase in both cell models but with different potencies. In addition, a set of 22 synthetic progestins were screened on the two cell lines. Interestingly, all of the tested compounds activated hPR in the HELN-hPR cell line, whereas the majority of them acted as zfPR antagonists in U2OS-zfPR. Such zfPR-specific response was further confirmed in zebrafish liver cells. This study provides novel information regarding the activity of a large set of progestins on human and zebrafish PR and highlights major interspecies differences in their activity, which may result in differential effects of progestins between fish and humans.

Tibolone Effects on Human Glioblastoma Cell Lines

BACKGROUND

Ovarian steroid hormones are involved in modulating the growth of glioblastomas (the most common, aggressive, and lethal brain tumor) through the interaction with their intracellular receptors. Activation of sex hormone receptors is involved in glioblastomas progression. Tibolone (TIB) is a selective tissue estrogenic activity regulator widely prescribed to treat menopausal symptoms and to prevent bone lost. The effects of TIB on the growth of glioblastoma are unknown.

AIM OF THE STUDY

To evaluate the effects of TIB on cell number, migration, and invasion of two derived human glioblastoma cell lines (U251 MG and U87), as well as the role of this steroid in estrogen and progesterone receptors activity and content.

METHODS

U251-MG and U87 human glioblastoma cell lines were grown with different doses of TIB. The number of cells was determined and migration and invasion tests were carried out. Protein expression was performed by Western blot.

RESULTS

We observed that TIB (10 nM) increased the number of cells by inducing proliferation with no effects on cell migration or invasion. The increase in cell proliferation induced by TIB was blocked by estrogen (ERs) or progesterone receptor (PRs) antagonists, ICI 182, 780 and RU 486, suggesting that these receptors mediate proliferating actions of TIB; TIB also modified the content of ERs and PRs by increasing ER-α, ER-β, and PR-B, while decreased PR-A.

CONCLUSION

Our results suggest that TIB increases cell number and proliferation of human glioblastoma cells through the regulation of ERs and PRs actions and content.

The Synthetic Steroid Tibolone Decreases Reactive Gliosis and Neuronal Death in the Cerebral Cortex of Female Mice After a Stab Wound Injury

Previous studies have shown that estradiol reduces reactive gliosis after a stab wound injury in the cerebral cortex. Since the therapeutic use of estradiol is limited by its peripheral hormonal effects, it is of interest to determine whether synthetic estrogenic compounds with tissue-specific actions regulate reactive gliosis. Tibolone is a synthetic steroid that is widely used for the treatment of climacteric symptoms and/or the prevention of osteoporosis. In this study, we have assessed the effect of tibolone on reactive gliosis in the cerebral cortex after a stab wound brain injury in ovariectomized adult female mice. By 7 days after brain injury, tibolone reduced the number of glial fibrillary acidic protein (GFAP) immunoreactive astrocytes, the number of ionized calcium binding adaptor molecule 1 (Iba1) immunoreactive microglia, and the number of microglial cells with a reactive phenotype in comparison to vehicle-injected animals. These effects on gliosis were associated with a reduction in neuronal loss in the proximity to the wound, suggesting that tibolone exerts beneficial homeostatic actions in the cerebral cortex after an acute brain injury.

Recent advances in structure of progestins and their binding to progesterone receptors

The role of progesterone in women's cancers as well as the knowledge of the progesterone receptor (PR) structure has prompted the design of different therapies. The aim of this review is to describe the basic structure of PR agonists and antagonists as well as the recent treatments for illness associated with the progesterone receptor. The rational design for potent and effective drugs for the treatment of female cancer must consider the structural changes of the androgen and progestogen skeleton which are an indicator of their activity as progestins or antiprogestins. The presence of a hydroxyl group at C-17 in the progesterone skeleton brings about a loss of progestational activity whereas acetylation induces a progestational effect. The incorporation of an ethynyl functional group to the testosterone framework results in a loss of androgenic activity with a concomitant enhancement of the progestational effect. On the other hand, an ester function at C-3 of dehydroepiandrosterone skeleton induces partial antagonism to the PR.

Molecular and structural basis of androgen receptor responses to dihydrotestosterone, medroxyprogesterone acetate and Δ(4)-tibolone

Medroxyprogesterone acetate (MPA) has widely been used in hormone replacement therapy (HRT), and is associated with an increased risk of breast cancer, possibly due to disruption of androgen receptor (AR) signaling. In contrast, the synthetic HRT Tibolone does not increase breast density, and is rapidly metabolized to estrogenic 3α-OH-tibolone and 3β-OH-tibolone, and a delta-4 isomer (Δ(4)-TIB) that has both androgenic and progestagenic properties. Here, we show that 5α-dihydrotestosterone (DHT) and Δ(4)-TIB, but not MPA, stabilize AR protein levels, initiate specific AR intramolecular interactions critical for AR transcriptional regulation, and increase proliferation of AR positive MDA-MB-453 breast cancer cells. Structural modeling and molecular dynamic simulation indicate that Δ(4)-TIB induces a more stable AR structure than does DHT, and MPA a less stable one. Microarray expression analyses confirms that the molecular actions of Δ(4)-TIB more closely resembles DHT in breast cancer cells than either ligand does to MPA.

Pharmacologically active drug metabolites: impact on drug discovery and pharmacotherapy

Metabolism represents the most prevalent mechanism for drug clearance. Many drugs are converted to metabolites that can retain the intrinsic affinity of the parent drug for the pharmacological target. Drug metabolism redox reactions such as heteroatom dealkylations, hydroxylations, heteroatom oxygenations, reductions, and dehydrogenations can yield active metabolites, and in rare cases even conjugation reactions can yield an active metabolite. To understand the contribution of an active metabolite to efficacy relative to the contribution of the parent drug, the target affinity, functional activity, plasma protein binding, membrane permeability, and pharmacokinetics of the active metabolite and parent drug must be known. Underlying pharmacokinetic principles and clearance concepts are used to describe the dispositional behavior of metabolites in vivo. A method to rapidly identify active metabolites in drug research is described. Finally, over 100 examples of drugs with active metabolites are discussed with regard to the importance of the metabolite(s) in efficacy and safety.

Safety and efficacy of tibolone and menopausal transition: a randomized, double-blind placebo-controlled trial

OBJECTIVE

To evaluate the efficacy, safety and tolerability of Tibolone use during the menopausal transition (MT).

METHODS

Sixty-five healthy women aged 40-55 years (48.5 ± 3.5 years) were recruited for a randomized, double-blind controlled trial. Thirty participants were recruited to receive oral Tibolone 2.5 mg/day - Tibolone Group (TG), and 35 participants were assigned to the Placebo Group (PG), which received one capsule of lactose/day. Both groups were treated for 12 consecutive weeks. The Blatt-Kupperman Menopausal Index (KMI) and the Greene Climacteric Scale (GCS) were used. The glycaemic and lipid profiles, biochemical measures of hepatic function and endometrial thickness were measured for safety. A daily registry of complaints related to the treatment was maintained, and anthropometric measures were obtained to assess tolerability.

RESULTS

A total of 57 women completed the study. After 12 weeks of Tibolone use, the total score and percentage of the KMI and GCS were significantly decreased compared to baseline, which reflected the efficacy of the treatment of climacteric symptoms. The improvement in blood biochemistry, endometrial atrophy and maintenance of the anthropometrical measures reflected the safety of Tibolone use. The absence of serious side effects demonstrated good tolerability for Tibolone use.

CONCLUSIONS

The results showed good efficacy, tolerability and safety of Tibolone use during the MT.

The androgen receptor and its use in biological assays: looking toward effect-based testing and its applications

Steroid abuse is a growing problem among amateur and professional athletes. Because of an inundation of newly and illegally synthesized steroids with minor structural modifications and other designer steroid receptor modulators, there is a need to develop new methods of detection which do not require prior knowledge of the abused steroid structure. The number of designer steroids currently being abused is unknown because detection methods in general are only identifying substances with a known structure. The detection of doping is moving away from merely checking for exposure to prohibited substance toward detecting an effect of prohibited substances, as biological assays can do. Cell-based biological assays are the next generation of assays which should be utilized by antidoping laboratories; they can detect androgenic anabolic steroid and other human androgen receptor (hAR) ligand presence without knowledge of their structure and assess the relative biological activity of these compounds. This review summarizes the hAR and its action and discusses its relevance to sports doping and its use in biological assays.